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Atomic Layer Deposition (ALD) of Bismuth Titanium Oxide Thin Films Using Direct Liquid Injection (DLI) Method
Young Jin Cho; Yo-Sep Min; Jung-Hyun Lee; Bum-Seok Seo; June Key Lee; Young Soo Park; Jin-Hak Choi
We report on atomic layer deposition of bismuth titanium oxide thin films for use in ferroelectric random access memory (FRAM). Bismuth titanium oxide thin films were grown on ruthenium and platinium coated silicon substrates respectively. We used tris(1-methoxy-2-methyl-2-propoxy)bismuth, Bi(mmp)3 and tetrakis(1-methoxy-2-methyl-2-propoxy)titanium, Ti(mmp)4 as metal organic precursors, which were mixed together in organic solvent, ethyl cyclo hexane (ECH), and then put
Thermoelectric Properties of Bismuth and Silicon Nanowires
NASA Astrophysics Data System (ADS)
Boukai, Akram Issam
Thermoelectric materials convert temperature differences into electricity and vice versa. Such materials utilize the Seebeck effect for power generation and the Peltier effect for refrigeration. In the Seebeck effect, a temperature gradient across a material causes the diffusion of charged carriers across that gradient, thus creating a voltage difference between the hot and cold ends of the material. Conversely, the Peltier effect explains the fact that when current flows through a material a temperature gradient arises because the charged carriers exchange thermal energy at the contacts. Thermoelectrics perform these functions without moving parts and they do not pollute. This makes them highly reliable and more importantly attractive as renewable energy sources, especially at a time when global warming is a growing concern. However, thermoelectrics find only limited use because of their poor efficiency. The efficiency of a thermoelectric material is determined by the dimensionless figure of merit, ZT = S2k T, where S is the thermoelectric power, defined as the thermoelectric voltage, V, produced per degree temperature difference S = dVdT , sigma is the electrical conductivity, kappa is the thermal conductivity, and T is the temperature. To maximize ZT, S must be large so that a small temperature difference can create a large voltage, sigma must be large in order to minimize joule heating losses, and kappa must be small to reduce heat leakage and maintain a temperature difference. Maximizing ZT is challenging because optimizing one physical parameter often adversely affects another. The best commercially available thermoelectric devices are alloys of Bi2Te3 and have a ZT of 1 which corresponds to a cannot efficiency of ÿ10%. My research has focused on achieving efficient thermoelectric performance from the single component systems of bismuth and silicon nanowires. Bismuth nanowires are predicted to undergo a semi-metal to semiconductor transition below a size of 50 nm which should increase the thermopower and thus ZT. Limited experimental evidence by other groups has been acquired to support this claim. Through electric field gating measurements and by tuning the nanowire size, we have shown that no such transition occurs. Instead, surface states dominate the electric transport at a size smaller than 50 nm and bismuth remains a semimetal. Bulk silicon is a poor thermoelectric due to its large thermal conductivity. However, silicon nanowires may have a dramatically reduced thermal conductivity. By varying the nanowire size and impurity doping levels, ZT values representing an approximately 100-fold improvement over bulk silicon are achieved over a broad temperature range, including a ZT ÿ 1 at 200K. Independent measurements of S, sigma, and kappa, combined with theory, indicate that the improved efficiency originates from phonon effects. The thermal conductivity is reduced and the thermopower is enhanced. These results are expected to apply to other classes of semiconductor nanomaterials.
Transport study of a single bismuth nanowire fabricated by the silver and silicon nanowire shadow masks
Transport study of a single bismuth nanowire fabricated by the silver and silicon nanowire shadow bismuth nanowires fabricated by the low energy electron beam lithography using the silver/silicon nanowire of the electrical conductivity of a bismuth nanowire, which is strikingly different from that of the bulk bismuth
Revealing bismuth oxide hollow nanoparticle formation by the Kirkendall effect.
Niu, Kai-Yang; Park, Jungwon; Zheng, Haimei; Alivisatos, A Paul
We study the formation of bismuth oxide hollow nanoparticles by the Kirkendall effect using liquid cell transmission electron microscopy (TEM). Rich dynamics of bismuth diffusion through the bismuth oxide shell have been captured in situ. The diffusion coefficient of bismuth through bismuth oxide shell is 3-4 orders of magnitude higher than that of bulk. Observation reveals that defects, temperature, sizes of the particles, and so forth can affect the diffusion of reactive species and modify the kinetics of the hollowing process. PMID:24131312
Bismuth based oxide electrolytesù structure and ionic conductivity
N. M. Sammes; G. A. Tompsett; H. Nõfe; F. Aldinger
Bismuth oxide systems exhibit high oxide ion conductivity and have been proposed as good electrolyte materials for applications such as solid oxide fuel cells and oxygen sensors. However, due to their instability under conditions of low oxygen partial pressures there has been difficulty in developing these materials as alternative electrolyte materials compared to the state-of-the-art cubic stabilised zirconia electrolyte. Bismuth
Barium Titanate and Bismuth Oxide Nanocomposites Barium titanate, BaTiO3, and bismuth oxide Bi2O3 are transparent materials with
Harmon, Julie P.
Barium Titanate and Bismuth Oxide Nanocomposites Barium titanate, BaTiO3, and bismuth oxide Bi2O3 Wall in Tetragonal Barium Titanate", H. Chaib, F. Schlaphof, T. Otto and L. M. Eng, Journal of Physics
Sadana, Devendra Kumar (Pleasantville, NY); Holland, Orin Wayne (Lenoir, TN)
A process for forming Silicon-On-Insulator is described incorporating the steps of ion implantation of oxygen into a silicon substrate at elevated temperature, ion implanting oxygen at a temperature below 200.degree. C. at a lower dose to form an amorphous silicon layer, and annealing steps to form a mixture of defective single crystal silicon and polycrystalline silicon or polycrystalline silicon alone and then silicon oxide from the amorphous silicon layer to form a continuous silicon oxide layer below the surface of the silicon substrate to provide an isolated superficial layer of silicon. The invention overcomes the problem of buried isolated islands of silicon oxide forming a discontinuous buried oxide layer.
Mullite interaction with bismuth oxide from minerals and sol-gel processes F. Gridi-Bennadji *
Paris-Sud XI, Universit├® de
Mullite interaction with bismuth oxide from minerals and sol-gel processes F. Gridi-Bennadji * , J doped by bismuth oxide was studied by TGA and DTA, X ray diffraction, and electron microscopy (SEM muscovite. With addition of bismuth oxide, SEM observations point to the strong accentuation of mullite
Bismuth qubits in silicon: the role of EPR "cancellation resonances"
Mohammady, M H; Monteiro, T S
We investigate theoretically and experimentally the electron paramagnetic resonance (EPR) spectra of bismuth doped silicon (Si:Bi) at intermediate magnetic fields, $B \\approx 0.05 -0.6$ T. We identify a previously unexplored EPR regime of "cancellation-resonances"- where the non-isotropic part of $ AS_zI_z$, the Ising part of the hyperfine coupling, is resonant with the external field-induced splitting. We show this regime has interesting and experimentally accessible consequences for spectroscopy and quantum information applications. These include reduction of decoherence, faster manipulation of the coupled nuclear-electron qubit system and line narrowing in the multi-qubit case. We test our theoretical analysis by comparing with experimental X-band (9.7 GHz) EPR spectra obtained in the intermediate field regime.
Bismuth in silicon qubits: the role of EPR cancellation resonances
M. H. Mohammady; G. W. Morley; T. S. Monteiro
We investigate theoretically and experimentally the electron paramagnetic resonance (EPR) spectra of bismuth doped silicon (Si:Bi) at intermediate magnetic fields, $B \\approx 0.05 -0.6$ T. We identify a previously unexplored EPR regime of "cancellation-resonances"- where part of the hyperfine coupling is resonant with the external field-induced splitting. We show this regime has interesting and experimentally accessible consequences for spectroscopy and quantum information applications. These include reduction of decoherence, fast manipulation of the coupled nuclear-electron qubit system and line narrowing in the multi-qubit case. We test our theoretical analysis by comparing with experimental X-band (9.7 GHz) EPR spectra obtained in the intermediate field regime.
Bismuth Spheres Grown in Self-Nested Cavities in a Silicon Hong Liu, and Zhong Lin Wang*,
Wang, Zhong L.
Bismuth Spheres Grown in Self-Nested Cavities in a Silicon Wafer Hong Liu, and Zhong Lin Wang-step, hydrofluoric acid-free hydrothermal etching method that not only produces bismuth nano/micrometer-sized spheres Bismuth is a semimetal with unusual electronic properties that results from its highly anisotropic Fermi
Transport study of a single bismuth nanowire fabricated by the silver and silicon nanowire shadow masks
NASA Astrophysics Data System (ADS)
Choi, D. S.; Balandin, A. A.; Leung, M. S.; Stupian, G. W.; Presser, N.; Chung, S. W.; Heath, J. R.; Khitun, A.; Wang, K. L.
The authors have carried out measurements of the electrical conductivity of single bismuth nanowires fabricated by the low energy electron beam lithography using the silver/silicon nanowire shadow masks. The examined nanowires had cross-sectional dimensions of 40Î30 and 40Î50nm2. The chosen nanowire sizes had been slightly below the critical diameter D (ÿ50nm) at which a semimetal to semiconductor phase transition was predicted to occur. The results reveal a semiconductorlike temperature dependence of the electrical conductivity of a bismuth nanowire, which is strikingly different from that of the bulk bismuth.
Oxidation resistance of silicon ceramics
NASA Technical Reports Server (NTRS)
Yasutoshi, H.; Hirota, K.
Oxidation resistance, and examples of oxidation of SiC, Si3N4 and sialon are reviewed. A description is given of the oxidation mechanism, including the oxidation product, oxidation reaction and the bubble size. The oxidation reactions are represented graphically. An assessment is made of the oxidation process, and an oxidation example of silicon ceramics is given.
Silicon oxidation in fluoride solutions
NASA Technical Reports Server (NTRS)
Sancier, K. M.; Kapur, V.
Silicon is produced in a NaF, Na2SiF6, and Na matrix when SiF4 is reduced by metallic sodium. Hydrogen is evolved during acid leaching to separate the silicon from the accompanying reaction products, NaF and Na2SiF6. The hydrogen evolution reaction was studied under conditions simulating leaching conditions by making suspensions of the dry silicon powder in aqueous fluoride solutions. The mechanism for the hydrogen evolution is discussed in terms of spontaneous oxidation of silicon resulting from the cooperative effects of (1) elemental sodium in the silicon that reacts with water to remove a protective silica layer, leaving clean reactive silicon, and (2) fluoride in solution that complexes with the oxidized silicon in solution and retards formation of a protective hydrous oxide gel.
Bismuth Oxide Nanoparticles in the Stratosphere
NASA Technical Reports Server (NTRS)
Rietmeijer, Frans J. M.; Mackinnon, Ian D. R.
Platey grains of cubic Bi2O3, alpha-Bi2O3, and Bi2O(2.75), nanograins were associated with chondritic porous interplanetary dust particles W7029C1, W7029E5, and 2011C2 that were collected in the stratosphere at 17-19 km altitude. Similar Bi oxide nanograins were present in the upper stratosphere during May 1985. These grains are linked to the plumes of several major volcanic eruptions during the early 1980s that injected material into the stratosphere. The mass of sulfur from these eruptions is a proxy for the mass of stratospheric Bi from which we derive the particle number densities (p/cu m) for "average Bi2O3 nanograins" due to this volcanic activity and those necessary to contaminate the extraterrestrial chondritic porous interplanetary dust particles via collisional sticking. The match between both values supports the idea that Bi2O3 nanograins of volcanic origin could contaminate interplanetary dust particles in the Earth's stratosphere.
Processing and Characterization of Bismuth Aluminum Oxide
NASA Astrophysics Data System (ADS)
Larose, Sylvain
The electrical properties of polycrystalline rm Bi_2Al_4O_9 were studied using various electrochemical techniques. The conductivity was measured by impedance spectroscopy for oxygen partial pressures in the range from 6times10 ^{-6} to 1 atm, and temperatures in the range from 550^circ to 850^circC. The resulting Nyquist plots consisted of 2 arcs. The left arc is related to electrical conduction occurring within the grains and the right, with grain-boundary impedance. Modeling of the impedance data provided reasonable values of lattice conductivity. Arrhenius plots for lattice conductivity show that the activation energy is a function of both temperature and oxygen partial pressure, and that the conductivity is lowest at high pO_2 (1atm). The activation energy increases as the temperature increases. The low-temperature, high-pO _2 value (1.1 eV) of activation energy is typical of oxygen vacancy conduction. At the lowest pO _2 (6times10^ {-6} atm), on the other hand, the activation energy is almost constant from 600^circ C to 800^circC, pointing to little change in the conduction mechanism. At low temperature (600^circC), the conductivity is not significantly affected by pO_2. But, as the temperature increases, the low pO_2 -conductivity increases more rapidly than the high pO_2-conductivity. This behavior is typical of a mixed ionic/n-type conductor. Least squares fitting of the conductivity data was used to derive an expression for the lattice ionic conductivity:sigma_ {ion}=[ {154over T} ] exp({-1.08eVover kT}) (Omega^{-1}cm^{ -1}) The electronic conductivity was obtained by subtracting the ionic conductivity from the total conductivity:sigma _{e}(-)=[ {5.65times10 ^6over T}] exp({-2.15eV over kT}) (pO_2)^{{ -}1/4}(Omega^{-1}cm^ {{-}1}) The low ionic conductivity indicates that the material is not an "intrinsically defective fast ion conductor". The analysis of the conductivity data and impurity content of the material suggests that the ionic conductivity results almost exclusively from oxygen vacancies compensating impurities. Non-equilibrium resistance measurements were conducted to estimate the activation energies for formation and migration of excess electrons. The estimated energies are: rm E_{form}(e^{ -})= 0.33 eV; E_{mig}(e ^{-}) = 1.82 eVThe standard enthalpy change associated with the formation of oxygen vacancies is estimated as:Delta H^circ = 0.66 eV = 64 KJ/molThis value is consistent with the known typical weakness of Bi-O bonds and the propensity of the Bi-containing oxides to be reduced. The conductivity of rm Bi_2Al _4O_9 is too low for the material to be used as a solid electrolyte in solid oxide fuel cells. The material could be used if the ionic conductivity were increased by four orders of magnitude through doping. However, considering the quantity of impurity-controlled oxygen vacancies present in the current material, doping with 10% divalent cations would increase the conductivity by less than three orders of magnitude. Moreover, doping trials performed at Argonne National Laboratory showed that the solubility of aliovalent cations in rm Bi_2Al_4O_9 is much smaller than 10%. No further study of this material for fuel cell applications is therefore recommended.
In situ transmission electron microscopy observation of the growth of bismuth oxide whiskers.
Mima, T; Takeuchi, Y; Arai, S; Kishita, K; Kuroda, K; Saka, H
Growth of bismuth oxide (most probably Bi2O3) was observed in situ in a transmission electron microscope. Bi liquid particles were dispersed on the substrates of diamond or SiO2. Introduction of oxygen up to 5 x 10-4 Pa resulted in formation of bismuth oxide (most probably Bi2O3) whiskers. The growth mechanism of the whisker was discussed in terms of a vapor-liquid-solid (VLS) mechanism. It is suggested that the liquid droplet of Bi acts as a physical catalyst for growth of bismuth oxide (most probably Bi2O3) whiskers. PMID:18312721
Nanoporous silicon oxide memory.
Wang, Gunuk; Yang, Yang; Lee, Jae-Hwang; Abramova, Vera; Fei, Huilong; Ruan, Gedeng; Thomas, Edwin L; Tour, James M
Oxide-based two-terminal resistive random access memory (RRAM) is considered one of the most promising candidates for next-generation nonvolatile memory. We introduce here a new RRAM memory structure employing a nanoporous (NP) silicon oxide (SiOx) material which enables unipolar switching through its internal vertical nanogap. Through the control of the stochastic filament formation at low voltage, the NP SiOx memory exhibited an extremely low electroforming voltage (? 1.6 V) and outstanding performance metrics. These include multibit storage ability (up to 9-bits), a high ON-OFF ratio (up to 10(7) A), a long high-temperature lifetime (? 10(4) s at 100 ░C), excellent cycling endurance (? 10(5)), sub-50 ns switching speeds, and low power consumption (? 6 Î 10(-5) W/bit). Also provided is the room temperature processability for versatile fabrication without any compliance current being needed during electroforming or switching operations. Taken together, these metrics in NP SiOx RRAM provide a route toward easily accessed nonvolatile memory applications. PMID:24992278
Bismuth oxide aqueous colloidal nanoparticles inhibit Candida albicans growth and biofilm formation
Hernandez-Delgadillo, Rene; Velasco-Arias, Donaji; Martinez-Sanmiguel, Juan Jose; Diaz, David; Zumeta-Dube, Inti; Arevalo-Ni±o, Katiushka; Cabral-Romero, Claudio
Multiresistance among microorganisms to common antimicrobials has become one of the most significant concerns in modern medicine. Nanomaterials are a new alternative to successfully treat the multiresistant microorganisms. Nanostructured materials are used in many fields, including biological sciences and medicine. Recently, it was demonstrated that the bactericidal activity of zero-valent bismuth colloidal nanoparticles inhibited the growth of Streptococcus mutans; however the antimycotic potential of bismuth nanostructured derivatives has not yet been studied. The main objective of this investigation was to analyze the fungicidal activity of bismuth oxide nanoparticles against Candida albicans, and their antibiofilm capabilities. Our results showed that aqueous colloidal bismuth oxide nanoparticles displayed antimicrobial activity against C. albicans growth (reducing colony size by 85%) and a complete inhibition of biofilm formation. These results are better than those obtained with chlorhexidine, nystatin, and terbinafine, the most effective oral antiseptic and commercial antifungal agents. In this work, we also compared the antimycotic activities of bulk bismuth oxide and bismuth nitrate, the precursor metallic salt. These results suggest that bismuth oxide colloidal nanoparticles could be a very interesting candidate as a fungicidal agent to be incorporated into an oral antiseptic. Additionally, we determined the minimum inhibitory concentration for the synthesized aqueous colloidal Bi2O3 nanoparticles. PMID:23637533
Structure and resistivity of bismuth nanobelts in situ synthesized on silicon wafer through an ethanol-thermal method
Gao Zheng; Qin Haiming; Yan Tao [State Key Laboratory of Crystal Materials, Bio-Micro/Nano Functional Materials Center, Shandong University, Jinan 250100 (China); Liu Hong, E-mail: email@example.com [State Key Laboratory of Crystal Materials, Bio-Micro/Nano Functional Materials Center, Shandong University, Jinan 250100 (China); Wang Jiyang [State Key Laboratory of Crystal Materials, Bio-Micro/Nano Functional Materials Center, Shandong University, Jinan 250100 (China)
Bismuth nanobelts in situ grown on a silicon wafer were synthesized through an ethanol-thermal method without any capping agent. The structure of the bismuth belt-silicon composite nanostructure was characterized by scanning electron microscope, energy-dispersive X-ray spectroscopy, and high resolution transmission electron microscope. The nanobelt is a multilayered structure 100-800 nm in width and over 50 {mu}m in length. One layer has a thickness of about 50 nm. A unique sword-like nanostructure is observed as the initial structure of the nanobelts. From these observations, a possible growth mechanism of the nanobelt is proposed. Current-voltage property measurements indicate that the resistivity of the nanobelts is slightly larger than that of the bulk bismuth material. - Graphical Abstract: TEM images, EDS, and electron diffraction pattern of bismuth nanobelts. Highlights: Black-Right-Pointing-Pointer Bismuth nanobelts in situ grown on silicon wafer were achieved. Black-Right-Pointing-Pointer Special bismuth-silicon nanostructure. Black-Right-Pointing-Pointer Potential application in sensitive magnetic sensor and other electronic devices.
Morphology modulated growth of bismuth tungsten oxide nanocrystals
Yao Shushan [State Key Lab of Crystal Materials, Shandong University, Jinan 250100 (China); Wei, Jiyong [State Key Lab of Crystal Materials, Shandong University, Jinan 250100 (China); Chemistry and Chemical Engineering College, Shandong University, Jinan 250100 (China); Huang Baibiao [State Key Lab of Crystal Materials, Shandong University, Jinan 250100 (China)], E-mail: email@example.com; Feng Shengyu [Chemistry and Chemical Engineering College, Shandong University, Jinan 250100 (China); Zhang Xiaoyang; Qin Xiaoyan; Wang Peng; Wang Zeyan; Zhang Qi; Jing Xiangyang; Zhan Jie [State Key Lab of Crystal Materials, Shandong University, Jinan 250100 (China)
Two kinds of bismuth tungsten oxide nanocrystals were prepared by microwave hydrothermal method. The morphology modulation of nanocrystals synthesized with precursor suspension's pH varied from 0.25 (strong acid) to 10.05 (base) was studied. The 3D flower like aggregation of Bi{sub 2}WO{sub 6} nanoflakes was synthesized in acid precursor suspension and the nanooctahedron crystals of Bi{sub 3.84}W{sub 0.16}O{sub 6.24} were synthesized in alkalescent precursor. The dominant crystal is changed from Bi{sub 2}WO{sub 6} to Bi{sub 3.84}W{sub 0.16}O{sub 6.24} when the precursor suspension changes from acid to alkalescence. The growth mechanisms of Bi{sub 2}WO{sub 6} and Bi{sub 3.84}W{sub 0.16}O{sub 6.24} were attributed to the different solubility of WO{sub 4}{sup 2-} and [Bi{sub 2}O{sub 2}]{sup 2+} in precursor suspensions with various pH. For the decomposition of Rhodamine B (RhB) under visible light irradiation ({lambda}>400 nm), different morphology of Bi{sub 2}WO{sub 6} crystal samples obtained by microwavesolvothermal process showed different photocatalytic activity. - Graphical abstract: The morphology modulation of bismuth tungsten oxide nanocrystals synthesized by microwave hydrothermal method with precursor suspension's pH varied from 0.25 (strong acid) to 10.05 (base) was studied. The 3D flower like aggregation of Bi{sub 2}WO{sub 6} nanoflakes and nanooctahedron crystals of Bi{sub 3.84}W{sub 0.16}O{sub 6.24} were prepared. The growth mechanisms of Bi{sub 2}WO{sub 6} and Bi{sub 3.84}W{sub 0.16}O{sub 6.24} were attributed to the different precipitation ability and solubility of H{sub 2}WO{sub 4} and Bi(OH){sub 3} in precursor suspensions with various pH. The photocatalytic evaluation, via the decomposition of Rhodamine B (RhB) under visible light irradiation ({lambda}>420 nm), reveals that nanocrystalline Bi{sub 2}WO{sub 6} samples obtained in different condition exhibit different photocatalytic activities which depend on pH value of the precursor suspensions.
Structure, defects, and strain in silicon-silicon oxide interfaces
Kova?evi?, Goran, E-mail: email@example.com; Pivac, Branko [Department of Materials Physics, Rudjer Boskovic Institute, Bijeni?ka 56, P.O.B. 180, HR-10002 Zagreb (Croatia)
The structure of the interfaces between silicon and silicon-oxide is responsible for proper functioning of MOSFET devices while defects in the interface can deteriorate this function and lead to their failure. In this paper we modeled this interface and characterized its defects and strain. MD simulations were used for reconstructing interfaces into a thermodynamically stable configuration. In all modeled interfaces, defects were found in the form of three-coordinated silicon atom, five coordinated silicon atom, threefold-coordinated oxygen atom, or displaced oxygen atom. Three-coordinated oxygen atom can be created if dangling bonds on silicon are close enough. The structure and stability of three-coordinated silicon atoms (P{sub b} defect) depend on the charge as well as on the electric field across the interface. The negatively charged P{sub b} defect is the most stable one, but the electric field resulting from the interface reduces that stability. Interfaces with large differences in periodic constants of silicon and silicon oxide can be stabilized by buckling of silicon layer. The mechanical stress resulted from the interface between silicon and silicon oxide is greater in the silicon oxide layer. Ab initio modeling of clusters representing silicon and silicon oxide shows about three time larger susceptibility to strain in silicon oxide than in silicon if exposed to the same deformation.
Efficient water-splitting device based on a bismuth vanadate photoanode and thin-film silicon solar cells.
Han, Lihao; Abdi, Fatwa F; van de Krol, Roel; Liu, Rui; Huang, Zhuangqun; Lewerenz, Hans-Joachim; Dam, Bernard; Zeman, Miro; Smets, Arno H M
A hybrid photovoltaic/photoelectrochemical (PV/PEC) water-splitting device with a benchmark solar-to-hydrogen conversion efficiency of 5.2% under simulated air mass (AM) 1.5 illumination is reported. This cell consists of a gradient-doped tungsten-bismuth vanadate (W:BiVO4 ) photoanode and a thin-film silicon solar cell. The improvement with respect to an earlier cell that also used gradient-doped W:BiVO4 has been achieved by simultaneously introducing a textured substrate to enhance light trapping in the BiVO4 photoanode and further optimization of the W gradient doping profile in the photoanode. Various PV cells have been studied in combination with this BiVO4 photoanode, such as an amorphous silicon (a-Si:H) single junction, an a-Si:H/a-Si:H double junction, and an a-Si:H/nanocrystalline silicon (nc-Si:H) micromorph junction. The highest conversion efficiency, which is also the record efficiency for metal oxide based water-splitting devices, is reached for a tandem system consisting of the optimized W:BiVO4 photoanode and the micromorph (a-Si:H/nc-Si:H) cell. This record efficiency is attributed to the increased performance of the BiVO4 photoanode, which is the limiting factor in this hybrid PEC/PV device, as well as better spectral matching between BiVO4 and the nc-Si:H cell. PMID:25138735
Investigation of solution-processed bismuth-niobium-oxide films
Inoue, Satoshi, E-mail: email@example.com [Green Device Research Center, Japan Advanced Institute of Science and Technology (JAIST), 2-13 Asahidai, Nomi, Ishikawa 923-1211 (Japan); School of Material Science, Japan Advanced Institute of Science and Technology (JAIST), 1-1 Asahidai, Nomi, Ishikawa 923-1292 (Japan); Ariga, Tomoki [Green Device Research Center, Japan Advanced Institute of Science and Technology (JAIST), 2-13 Asahidai, Nomi, Ishikawa 923-1211 (Japan); ERATO Shimoda Nano-Liquid Process Project, Japan Science and Technology Agency (JST), 2-13 Asahidai, Nomi, Ishikawa 923-1211 (Japan); Matsumoto, Shin [School of Material Science, Japan Advanced Institute of Science and Technology (JAIST), 1-1 Asahidai, Nomi, Ishikawa 923-1292 (Japan); Onoue, Masatoshi; Miyasako, Takaaki [ERATO Shimoda Nano-Liquid Process Project, Japan Science and Technology Agency (JST), 2-13 Asahidai, Nomi, Ishikawa 923-1211 (Japan); Tokumitsu, Eisuke; Shimoda, Tatsuya [Green Device Research Center, Japan Advanced Institute of Science and Technology (JAIST), 2-13 Asahidai, Nomi, Ishikawa 923-1211 (Japan); School of Material Science, Japan Advanced Institute of Science and Technology (JAIST), 1-1 Asahidai, Nomi, Ishikawa 923-1292 (Japan); ERATO Shimoda Nano-Liquid Process Project, Japan Science and Technology Agency (JST), 2-13 Asahidai, Nomi, Ishikawa 923-1211 (Japan); Chinone, Norimichi; Cho, Yasuo [Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Miyagi 980-8577 (Japan)
The characteristics of bismuth-niobium-oxide (BNO) films prepared using a solution process were investigated. The BNO film annealed at 550?░C involving three phases: an amorphous phase, Bi{sub 3}NbO{sub 7} fluorite microcrystals, and Nb-rich cubic pyrochlore microcrystals. The cubic pyrochlore structure, which was the main phase in this film, has not previously been reported in BNO films. The relative dielectric constant of the BNO film was approximately 140, which is much higher than that of a corresponding film prepared using a conventional vacuum sputtering process. Notably, the cubic pyrochlore microcrystals disappeared with increasing annealing temperature and were replaced with triclinic ?-BiNbO{sub 4} crystals at 590?░C. The relative dielectric constant also decreased with increasing annealing temperature. Therefore, the high relative dielectric constant of the BNO film annealed at 550?░C is thought to result from the BNO cubic pyrochlore structure. In addition, the BNO films annealed at 500?░C contained approximately 6.5?atm.?% carbon, which was lost at approximately 550?░C. This result suggests that the carbon in the BNO film played an important role in the formation of the cubic pyrochlore structure.
First-principles study of CO oxidation on bismuth-promoted Pt(111) surfaces
Neeti Kapur; Bin Shan; Jangsuk Hyun; Ligen Wang; Sang Yang; John B. Nicholas; Kyeongjae Cho
Vehicle emission control regulations necessitate the removal of carbon monoxide (CO) from engine exhausts via CO oxidation. Although bismuth (Bi)-promoted platinum (Pt) catalysts show improvement in CO oxidation performance over pure Pt, it is still not known whether Bi acts simply as a site blocker to reduce CO poisoning or whether it is an active participant in the catalytic reactions.
Characterization of HT-9 Ferritic-Martensitic Steels Oxidized in Lead Bismuth Eutectic , A. T. Motta1
Motta, Arthur T.
Characterization of HT-9 Ferritic-Martensitic Steels Oxidized in Lead Bismuth Eutectic J. Kunkle1 to neutrons, lead bismuth eutectic (LBE) is an considered an ideal candidate for cooling these fast reactors. Using a combination of techniques, the oxide layers formed on three ferritic-martensitic HT-9 steel
Epitaxial oxide heterostructures on silicon
NASA Astrophysics Data System (ADS)
Posadas, Agham; Reiner, J. W.; Walker, F. J.; Ahn, C. H.
Silicon-based MOSFETs will soon be limited by the large off- state leakage current due to tunneling through the 1 nm thick silicon oxynitride gate dielectric layer. One solution is to replace the silicon oxynitride with a high dielectric constant material, such as LaAlO3, which has a relatively large dielectric constant of 2?4 and band gap of 5.6 eV. We have recently grown LaAlO3 epitaxially onto silicon via a transition layer consisting of SrTiO3. The thickness of this SrTiO3 layer is kept between 2 and 5 unit cells because of considerations of epitaxial strain and the atomic-scale interactions between the perovskite structure and the silicon substrate. The oxide heterostructures show atomically abrupt interfaces and dielectric constants close to the bulk value of LaAlO3. Frequency and voltage dependent measurements of the complex impedance of the as-grown oxide heterostructures show a pinned Fermi level and a high density of interface states. Annealing at low temperatures in wet oxygen shows that the Fermi level can be unpinned, with a greatly reduced density of interface states.
Catalytic oxidation of propylene7. Use of temperature programmed reoxidation to characterize. gamma. -bismuth molybdate
T. Uda; T. T. Lin; G. W. Keulks
Temperature-programed reoxidation of propylene-reduced ..gamma..-BiÔMoOÔ revealed a low-temperature peak (LTP) at 158┬░C and a high-temperature peak (HTP) at 340┬░C. Auger spectroscopy and X-ray diffraction of reduced and partially or completely reoxidized bismuth molybdate showed that at the LTP, molybdenum(IV) is oxidized to molybdenum(VI) and bismuth, from the metallic state to an oxidation state between zero and three, and that the
Catalytic oxidation of propylene--7. Use of temperature programmed reoxidation to characterize. gamma. -bismuth molybdate
Uda, T.; Lin, T.T.; Keulks, G.W.
Temperature-programed reoxidation of propylene-reduced ..gamma..-Bi/sub 2/MoO/sub 6/ revealed a low-temperature peak (LTP) at 158/sup 0/C and a high-temperature peak (HTP) at 340/sup 0/C. Auger spectroscopy and X-ray diffraction of reduced and partially or completely reoxidized bismuth molybdate showed that at the LTP, molybdenum(IV) is oxidized to molybdenum(VI) and bismuth, from the metallic state to an oxidation state between zero and three, and that the HTP is associated with the complete oxidation of bismuth to bismuth(III). Activity tests for propylene oxidation showed lower acrolein formation on the catalyst, on which only the LTP was reoxidized than on catalysts on which both peaks were reoxidized. The reoxidation kinetics of the catalyst under conditions corresponding to the LTP showed an activation energy of 22.9 kcal/mole below 170/sup 0/C and near zero above 170/sup 0/C; the break in the Arrhenius plot of reoxidation of the catalyst under conditions corresponding to the HTP was at 400/sup 0/C, with activation energies of 46 kcal/mole at lower and near zero at higher temperatures. Propylene oxidation was apparently rate-limited by the HTP reoxidation process below 400/sup 0/C and by allylic hydrogen abstraction above 400/sup 0/C.
JOURNAL OF MATERIALS SCIENCE 29 (1994) 4135-4151 Bismuth oxide-based solid electrolytes for
Azad, Abdul-Majeed
JOURNAL OF MATERIALS SCIENCE 29 (1994) 4135-4151 Review Bismuth oxide-based solid electrolytes mainly on the yttria-stabil- ized zirconia (YSZ) electrolyte. Because of the problems associated to de- velop alternative electrolytes with ionic conductivity comparable to that of YSZ at relatively
L3 subshell alignment in bismuth induced by swift silicon ions
NASA Astrophysics Data System (ADS)
Kumar, Ajay; Agnihotri, A. N.; Misra, D.; Kasthurirangan, S.; Sarkadi, L.; Tribedi, L. C.
Angular- and impact energy- dependence of L x-rays of bismuth in collisions with silicon ions has been measured. Unlike isotropic emission of the {{L}? }-group and the {{L}? }-group x-rays, the Ll x-ray yield was observed to have impact energy dependent anisotropy emission. The anisotropy parameter for the Ll x-ray line was obtained by using the intensity ratio of the Ll-to-other L x-rays in the same spectrum. The alignment parameter of the L3 subshell was deduced from the measured anisotropy parameter of the Ll x-ray and has been compared with those obtained from the collisional theoretical models based on the plane-wave Born approximation and its extension.
Analysis of quantum coherence in bismuth-doped silicon: a system of strongly coupled spin qubits
M. H. Mohammady; G. W. Morley; A. Nazir; T. S. Monteiro
There is growing interest in bismuth-doped silicon (Si:Bi) as an alternative to the well-studied proposals for silicon based quantum information processing (QIP) using phosphorus-doped silicon (Si:P). We focus here on the implications of its anomalously strong hyperfine coupling. In particular, we analyse in detail the regime where recent pulsed magnetic resonance experiments have demonstrated the potential for orders of magnitude speedup in quantum gates by exploiting transitions that are electron paramagnetic resonance (EPR) forbidden at high fields. We also present calculations using a phenomenological Markovian master equation which models the decoherence of the electron spin due to Gaussian temporal magnetic field perturbations. The model quantifies the advantages of certain "optimal working points" identified as the $df/dB=0$ regions, where $f$ is the transition frequency, which come in the form of frequency minima and maxima. We show that at such regions, dephasing due to the interaction of the electron spin with a fluctuating magnetic field in the $z$ direction (usually adiabatic) is completely removed.
Method of forming buried oxide layers in silicon
Sadana, Devendra Kumar (Pleasantville, NY); Holland, Orin Wayne (Lenoir City, TN)
A process for forming Silicon-On-Insulator is described incorporating the steps of ion implantation of oxygen into a silicon substrate at elevated temperature, ion implanting oxygen at a temperature below 200.degree. C. at a lower dose to form an amorphous silicon layer, and annealing steps to form a mixture of defective single crystal silicon and polycrystalline silicon or polycrystalline silicon alone and then silicon oxide from the amorphous silicon layer to form a continuous silicon oxide layer below the surface of the silicon substrate to provide an isolated superficial layer of silicon. The invention overcomes the problem of buried isolated islands of silicon oxide forming a discontinuous buried oxide layer.
Promotional Effects of Bismuth on the Formation of Platinum-Bismuth Nanowires Network and the Electrocatalytic Activity toward Ethanol Oxidation
X Teng; W Du; D Su; Q Wang; A Frenkel
Electrocatalytic activities of Pt and their alloys toward small organic molecules oxidation are highly dependent on their morphology, chemical composition, and electronic structure. Here, we report the synthesis of dendrite-like Pt{sub 95}Bi{sub 5}, Pt{sub 83}Bi{sub 17}, and Pt{sub 76}Bi{sub 24} nanowires network with a high aspect ratio (up to 68). The electronic structure and heterogeneous crystalline structure have been studied using combined techniques, including aberration-corrected scanning transmission electron microscopy (STEM) and X-ray absorption near-edge structure (XANES) spectroscopy. Bismuth-oriented attachment growth mechanism has been proposed for the anisotropic growth of Pt/Bi. The electrochemical activities of Pt/Bi nanowires network toward ethanol oxidations have been tested. In particular, the as-made Pt{sub 95}Bi{sub 5} appears to have superior activity toward ethanol oxidation in comparison with the commercial Pt/C catalyst. The reported promotional effect of Bi on the formation of Pt/Bi and electrochemical activities will be important to design effective catalysts for ethanol fuel cell application.
Promotional Effects of Bismuth on the Formation of Platinum-Bismuth Nanowires Network and the Electrocatalytic Activity toward Ethanol Oxidation
Du, W.; Su, D.; Wang, Q.; Frenkel, A.I.; Teng, X.
Electrocatalytic activities of Pt and their alloys toward small organic molecules oxidation are highly dependent on their morphology, chemical composition, and electronic structure. Here, we report the synthesis of dendrite-like Pt{sub 95}Bi{sub 5}, Pt{sub 83}Bi{sub 17}, and Pt{sub 76}Bi{sub 24} nanowires network with a high aspect ratio (up to 68). The electronic structure and heterogeneous crystalline structure have been studied using combined techniques, including aberration-corrected scanning transmission electron microscopy (STEM) and X-ray absorption near-edge structure (XANES) spectroscopy. Bismuth-oriented attachment growth mechanism has been proposed for the anisotropic growth of Pt/Bi. The electrochemical activities of Pt/Bi nanowires network toward ethanol oxidations have been tested. In particular, the as-made Pt{sub 95}Bi{sub 5} appears to have superior activity toward ethanol oxidation in comparison with the commercial Pt/C catalyst. The reported promotional effect of Bi on the formation of Pt/Bi and electrochemical activities will be important to design effective catalysts for ethanol fuel cell application.
Two of the basic problems associated with monolithic Metal - Zinc Oxide - Silicon Dioxide - Silicon (MZOS) surface acoustic wave devices involve (1) drifting of device characteristics due to charge injection and trapping associated with the ZnO and (2) radiation damage in the Si-SiO(,2) subsystem. Both of these problems are addressed in this thesis.^ A quantitative comparison of radiation
Efficient solar water splitting by enhanced charge separation in a bismuth vanadate-silicon tandem photoelectrode
NASA Astrophysics Data System (ADS)
Abdi, Fatwa F.; Han, Lihao; Smets, Arno H. M.; Zeman, Miro; Dam, Bernard; van de Krol, Roel
Metal oxides are generally very stable in aqueous solutions and cheap, but their photochemical activity is usually limited by poor charge carrier separation. Here we show that this problem can be solved by introducing a gradient dopant concentration in the metal oxide film, thereby creating a distributed n+-n homojunction. This concept is demonstrated with a low-cost, spray-deposited and non-porous tungsten-doped bismuth vanadate photoanode in which carrier-separation efficiencies of up to 80% are achieved. By combining this state-of-the-art photoanode with an earth-abundant cobalt phosphate water-oxidation catalyst and a double- or single-junction amorphous Si solar cell in a tandem configuration, stable short-circuit water-splitting photocurrents of ~4 and 3?mA?cm-2, respectively, are achieved under 1 sun illumination. The 4?mA?cm-2 photocurrent corresponds to a solar-to-hydrogen efficiency of 4.9%, which is the highest efficiency yet reported for a stand-alone water-splitting device based on a metal oxide photoanode.
Bismuth and aluminum-codoped germanium oxide glasses for super-broadband optical amplification
Mingying Peng; Jianrong Qiu; Danping Chen; Xiangeng Meng; Ivyun Yang; Xiongwei Jiang; Congshan Zhu
Broadband infrared luminescence from bismuth-doped germanium oxide glasses prepared by a conventional melting-quenching technique was discovered. The absorption spectrum of the glasses covered a wide range from the visible to the near-infrared wavelength regions and consisted of five broad peaks below 370, 500, 700, 800, and 1000 nm. The fluorescence spectrum exhibited broadband characteristics (FWHM) greater than 300 nm with
Effect of additions of praseodymium and bismuth oxides on the properties of barium hexaferrites
Kirichok, P.P.; Garmash, V.Y.; Verezhak, O.F.; Voronina, N.B.
Among oxide permanent magnets, of greatest practical interest are those made of barium hexaferrite. Because of its high constant of uniaxial anisotropy, a barium ferrite can be employed for producing permanent magnets of large coercive force. The formation of important technical properties in barium ferrites is strongly affected by their production technology, in particular, the addition of oxides, such as those or bismuth and some rare-earth elements. The goal of this work was to study the effect of bismuth and praseodymium on the parameters of the static hysteresis loop, magnetic microstructure, and electronic configuration of iron ions in the BaO.nFe/sub 2/O/sub 3/ (5.0 less than or equal tonless than or equal to6.0) system. It is determined that the changes induced in the crystallostructural parameters, magnetic microstructure, and electronic spectrum of a barium ferrite by the addition of praseodymium and bismuth oxides to the ferrite powder charge control to a large extent the formation of the magnetic energy level.
Mechanism of Selective Oxidation and Ammoxidation of Propene on Bismuth Molybdates from DFT Calculations on Model Clusters
Goddard III, William A.
of small alkanes (CH4, C2H6, C3H8, and C4H10) by mixed metal oxides, there is little in the wayMechanism of Selective Oxidation and Ammoxidation of Propene on Bismuth Molybdates from DFT) to examine the mechanism of selective oxidation and ammoxidation of propene by BiMoOx catalysts. To do this
Gamma-ray spectroscopy using small, cooled bismuth germanate scintillators and silicon photodiodes
NASA Astrophysics Data System (ADS)
Derenzo, Stephen E.
Gamma-ray scintillation spectra were measured using a 3 Î 3 Î 3 mm 3 bismuth germanate (BGO) crystal and a 4 mm diam. silicon photodiode (SPD) at temperatures from +20░C to -190░C. At +20░C, using an amplifier peaking time ? = 2 ?s, the 662 keV photopeak pulses had 3200 electrons (e -) and a full-width at half-maximum (fwhm) of 27%. For ? = 1 ?s, the minimum fwhm was 20% at -75░C. The narrowest 662 keV photopeak seen in this work had 7.2% fwhm at -150░C using ? = 10 ?s. Cooling from +20░C to -100░C increased the photopeak amplitude by a factor of 2.4 and reduced amplifier noise by a factor of 1.9. Relative to photomultiplier tubes, SPDs can be made smaller, and in a wider variety of shapes; they have higher quantum efficiencies, and are insensitive to magnetic fields. This work describes the factors that enable small BGO crystals and SPDs to detect gamma rays with an unprecedented combination of detection efficiency, spatial resolution, and energy resolution.
Room temperature electrodeposition and characterization of bismuth ferric oxide (BFO) thin films from aqueous nitrate bath
NASA Astrophysics Data System (ADS)
Gujar, T. P.; Shinde, V. R.; Kulkarni, S. S.; Pathan, H. M.; Lokhande, C. D.
Bismuth ferric oxide (BFO) thin films were prepared on fluorine doped tin oxide (FTO) coated glass substrates using electrodeposition method from aqueous nitrate bath at room temperature. The various preparative parameters, such as bath composition, current density, deposition time, etc were optimized to get good quality BFO thin films. The structural, surface morphological, optical and dielectrical properties of the films were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), optical absorption and dielectric measurement techniques. The results show that electrodeposition method allows to synthesis BFO films. The films are free from pinholes and cracks. The magnitudes of dielectric constant and loss tangent showed inverse frequency dependence.
Silicon oxide colloidal/polymer nanocomposite films Haifeng Wanga)
Cao, Wenwu
Silicon oxide colloidal/polymer nanocomposite films Haifeng Wanga) and Wenwu Cao Materials Research to fabricate sol-gel silicon oxide colloidal/polymer composite film on silicon substrate, in which the particle size of silicon oxide colloidal is between 10 and 40 nm. The acoustic impedance of the nanocomposite
Bismuth doped lanthanum ferrite perovskites as novel cathodes for intermediate-temperature solid oxide fuel cells.
Li, Mei; Wang, Yao; Wang, Yunlong; Chen, Fanglin; Xia, Changrong
Bismuth is doped to lanthanum strontium ferrite to produce ferrite-based perovskites with a composition of La(0.8-x)Bi(x)Sr0.2FeO(3-?) (0 ? x ? 0.8) as novel cathode material for intermediate-temperature solid oxide fuel cells. The perovskite properties including oxygen nonstoichiometry coefficient (?), average valence of Fe, sinterability, thermal expansion coefficient, electrical conductivity (?), oxygen chemical surface exchange coefficient (K(chem)), and chemical diffusion coefficient (D(chem)) are explored as a function of bismuth content. While ? decreases with x due to the reduced Fe(4+) content, D(chem) and K(chem) increase since the oxygen vacancy concentration is increased by Bi doping. Consequently, the electrochemical performance is substantially improved and the interfacial polarization resistance is reduced from 1.0 to 0.10 ? cm(2) at 700 ░C with Bi doping. The perovskite with x = 0.4 is suggested as the most promising composition as solid oxide fuel cell cathode material since it has demonstrated high electrical conductivity and low interfacial polarization resistance. PMID:24971668
Effect of Oxygen Capacity and Oxygen Mobility of Pure Bismuth Molybdate and Multicomponent Bismuth Molybdate on their Catalytic Performance in the Oxidative Dehydrogenation of n Butene to 1,3Butadiene
Ji Chul Jung; Howon Lee; Heesoo Kim; Young-Min Chung; Tae Jin Kim; Seong Jun Lee; Seung-Hoon Oh; Yong Seung Kim; In Kyu Song
Pure bismuth molybdate (?-Bi2MoO6) and multicomponent bismuth molybdate (Co9Fe3Bi1Mo12O51) catalysts were prepared by a co-precipitation method, and were applied to the oxidative dehydrogenation of n-butene to 1,3-butadiene. The Co9Fe3Bi1Mo12O51 catalyst showed a better catalytic performance than the ?-Bi2MoO6 catalyst in terms of conversion of n-butene and yield for 1,3-butadiene, indicating that the multicomponent bismuth molybdate was more efficient than the
Comparison of silicon oxide and silicon carbide absorber materials in silicon thin-film solar cells
NASA Astrophysics Data System (ADS)
Walder, Cordula; Kellermann, Martin; Wendler, Elke; Rensberg, Jura; von Maydell, Karsten; Agert, Carsten
Since solar energy conversion by photovoltaics is most efficient for photon energies at the bandgap of the absorbing material the idea of combining absorber layers with different bandgaps in a multijunction cell has become popular. In silicon thin-film photovoltaics a multijunction stack with more than two subcells requires a high bandgap amorphous silicon alloy top cell absorber to achieve an optimal bandgap combination. We address the question whether amorphous silicon carbide (a-SiC:H) or amorphous silicon oxide (a-SiO:H) is more suited for this type of top cell absorber. Our single cell results show a better performance of amorphous silicon carbide with respect to fill factor and especially open circuit voltage at equivalent Tauc bandgaps. The microstructure factor of single layers indicates less void structure in amorphous silicon carbide than in amorphous silicon oxide. Yet photoconductivity of silicon oxide films seems to be higher which could be explained by the material being not truly intrinsic. On the other hand better cell performance of amorphous silicon carbide absorber layers might be connected to better hole transport in the cell.
Charge decay characteristics of silicon-oxide-nitride-oxide-silicon structure at elevated temperatures and extraction of the nitride
Lee, Jong Duk
-oxide-nitride-oxide-silicon type nonvolatile memory at elevated temperatures. Based on the amphoteric trap model and the thermal known attributes of traps in silicon nitride.8 In the amphoteric model, the traps of both charge states
Thermodynamic stability of binary oxides in contact With silicon
K. J. Hubbard; D. G. Schlom
Using tabulated thermodynamic data, a comprehensive investigation of the thermodynamic stability of binary oxides in contact with silicon at 1000 K was conducted. Reactions between silicon and each binary oxide at 1000 K, including those involving ternary phases, were considered. Sufficient data exists to conclude that all binary oxides except the following are thermodynamically unstable in contact with silicon at
Silicon oxide colloidal/polymer nanocomposite films
NASA Astrophysics Data System (ADS)
Wang, Haifeng; Cao, Wenwu; Zhou, Q. F.; Shung, K. Kirk; Huang, Y. H.
The quarter-wavelength (?/4) acoustic matching layer, a vital component in medical ultrasonic transducer, can bridge the large acoustic impedance mismatch between the piezoelectric material and the human body. Composite materials are widely used as matching materials in order to cover the wide acoustic impedance range that cannot be accomplished by using a single-phase material. At high frequencies (>50MHz), the ? /4 matching layers become extremely thin so that the fabrication of homogeneous composite material matching layers becomes very challenging. A method is reported in this letter to fabricate sol-gel silicon oxide colloidal/polymer composite film on silicon substrate, in which the particle size of silicon oxide colloidal is between 10 and 40 nm. The acoustic impedance of the nanocomposite films versus aging temperature has been measured at the desired operating frequency.
Tailoring Silicon Oxycarbide Glasses for Oxidative Stability
NASA Technical Reports Server (NTRS)
Hurwitz, F. I.; Meador, M. A. B.
Blackglas(Trademark) polysiloxane systems produce silicon oxycarbide glasses by pyrolysis in inert atmosphere. The silicon oxycarbides evidence oxidative degradation that limits their lifetime as composite matrices. The present study characterizes bonding rearrangements in the oxycarbide network accompanying increases in pyrolysis temperature. It also addresses the changes in susceptibility to oxidation due to variations in the distribution of Si bonded species obtained under different processing conditions. The study is carried out using Si-29 nuclear magnetic resonance (NMR) spectroscopy and a design of experiments approach to model the oxidation behavior. The NMR results are compared with those obtained by thermogravimetric analysis (TGA). Samples pyrolyzed under inert conditions are compared to those pyrolyzed in reactive ammonia environments.
Microanalytical study of defect formation in thin bismuth strontium calcium copper oxide films
Howell, R.H.; Chaiken, A.; Musket, R.G. [and others
Thin bismuth strontium calcium copper oxide (BSCCO) films and (BSCCO) films and BSCCO/insulator/BSCCO trilayers have been prepared on SiTiO{sub 3} and MgO substrates by evaporation from elemental sources in an ozone atmosphere. Accurate control of the stoichiometry is achieved through monitoring of the atomic fluxes by use of in situ atomic absorption spectroscopy as well as by reflection high-energy electron diffraction (RHEED). Nevertheless, nanometer-scale second-phase precipitates are sometimes observed. These defects and the flat regions around them have been probed by a variety of microanalytical techniques, including Rutherford backscattering spectroscopy (RBS), particle-induced x-ray emission (PIXE), atomic force microscopy (AFM), microscopic secondary ion mass spectroscopy and transmission electron microscopy (TEM).
Silica substrate or portion formed from oxidation of monocrystalline silicon
Matzke, Carolyn M.; Rieger, Dennis J.; Ellis, Robert V.
A method is disclosed for forming an inclusion-free silica substrate using a monocrystalline silicon substrate as the starting material and oxidizing the silicon substrate to convert it entirely to silica. The oxidation process is performed from both major surfaces of the silicon substrate using a conventional high-pressure oxidation system. The resulting product is an amorphous silica substrate which is expected to have superior etching characteristics for microfabrication than conventional fused silica substrates. The present invention can also be used to convert only a portion of a monocrystalline silicon substrate to silica by masking the silicon substrate and locally thinning a portion the silicon substrate prior to converting the silicon portion entirely to silica. In this case, the silica formed by oxidizing the thinned portion of the silicon substrate can be used, for example, as a window to provide optical access through the silicon substrate.
Porous silicon with embedded metal oxides for gas sensing applications
Vyatcheslav A. Moshnikov; Irina Gracheva; Aleksandr S. Lenshin; Yulia M. Spivak; Maxim G. Anchkov; Vladimir V. Kuznetsov; Jan M. Olchowik
This paper presents an analysis of the sol deposition process on porous silicon in order to produce highly sensitive gas detectors. Sol solutions were deposited within the dendrite structural pore regions of n-type silicon. The parameters for the structures, built of metal oxides (Fe, Ni, Sn), were analyzed. A morphological study of porous silicon, with embedded metal oxide nanocomposites, was
Fabrication of planar silicon nanowires on silicon-on-insulator using stress limited oxidation
Bokor, Jeffrey
Fabrication of planar silicon nanowires on silicon-on-insulator using stress limited oxidation for the fabrication of planar single crystal silicon nanowires down to 8 nm in diameter. In this method silicon lines Vacuum Society. S0734-211X 97 04706-9 I. INTRODUCTION There is a strong interest in the fabrication
Photoconduction in silicon rich oxide films
NASA Astrophysics Data System (ADS)
Luna-L¾pez, J. A.; Aceves-Mijares, M.; Carrillo-L¾pez, J.; Morales-Sanchez, A.; Flores-Gracia, F. J.; Garcia-Salgado, G.
Photoconduction of silicon rich oxide (SRO) thin films were studied by current-voltage (I-V) measurements, where ultraviolet (UV) and white (Vis) light illumination were applied. SRO thin films were deposited by low pressure chemical vapour deposition (LPCVD) technique, using SiH4 (silane) and N2O (nitrous oxide) as reactive gases at 700 ░. The gas flow ratio, Ro = [N2O]/[SiH4] was used to control the silicon excess. The thickness and refractive index of the SRO films were 72.0 nm, 75.5 nm, 59.1 nm, 73.4 nm and 1.7, 1.5, 1.46, 1.45, corresponding to Ro = 10, 20, 30 and 50, respectively. These results were obtained by null ellipsometry. Si nanoparticles (Si-nps) and defects within SRO films permit to obtain interesting photoelectric properties as a high photocurrent and photoconduction. These effects strongly depend on the silicon excess, thickness and structure type. Two different structures (Al/SRO/Si and Al/SRO/SRO/Si metal-oxide-semiconductor (MOS)-like structures) were fabricated and used as devices. The photocurrent in these structures is dominated by the generation of carriers due to the incident photon energies (~3.0-1.6 eV and 5 eV). These structures showed large photoconductive response at room temperature. Therefore, these structures have potential applications in optoelectronics devices.
Iron-oxide catalyzed silicon photoanode for water splitting
Jun, Kimin
This thesis presents an integrated study of high efficiency photoanodes for water splitting using silicon and iron-oxide. The fundamental limitations of silicon to water splitting applications were overcome by an ultrathin ...
Development of tellurium oxide and lead-bismuth oxide glasses for mid-wave infra-red transmission optics
NASA Astrophysics Data System (ADS)
Zhou, Beiming; Rapp, Charles F.; Driver, John K.; Myers, Michael J.; Myers, John D.; Goldstein, Jonathan; Utano, Rich; Gupta, Shantanu
Heavy metal oxide glasses exhibiting high transmission in the Mid-Wave Infra-Red (MWIR) spectrum are often difficult to manufacture in large sizes with optimized physical and optical properties. In this work, we researched and developed improved tellurium-zinc-barium and lead-bismuth-gallium heavy metal oxide glasses for use in the manufacture of fiber optics, optical components and laser gain materials. Two glass families were investigated, one based upon tellurium and another based on lead-bismuth. Glass compositions were optimized for stability and high transmission in the MWIR. Targeted glass specifications included low hydroxyl concentration, extended MWIR transmission window, and high resistance against devitrification upon heating. Work included the processing of high purity raw materials, melting under controlled dry Redox balanced atmosphere, finning, casting and annealing. Batch melts as large as 4 kilograms were sprue cast into aluminum and stainless steel molds or temperature controlled bronze tube with mechanical bait. Small (100g) test melts were typically processed in-situ in a 5%Au░/95%Pt░ crucible. Our group manufactured and evaluated over 100 different experimental heavy metal glass compositions during a two year period. A wide range of glass melting, fining, casting techniques and experimental protocols were employed. MWIR glass applications include remote sensing, directional infrared counter measures, detection of explosives and chemical warfare agents, laser detection tracking and ranging, range gated imaging and spectroscopy. Enhanced long range mid-infrared sensor performance is optimized when operating in the atmospheric windows from ~ 2.0 to 2.4?m, ~ 3.5 to 4.3?m and ~ 4.5 to 5.0?m.
Stress evolution and point defect generation during oxidation of silicon
NASA Astrophysics Data System (ADS)
Charitat, G.; Martinez, A.
The oxidation enhanced diffusion and oxidation stacking faults are assumed to be brought about by a self-interstitial supersaturation in the silicon. In such a case, supersaturation is related to the stresses present in the oxide and in the silicon during oxidation. The detailed analysis of the evolution of these stresses is conducted in relation to time, temperature and the nature of the oxidizing atmosphere, taking into account the viscous relaxation in the oxide. The silicon interstitial concentration during oxidation is directly linked with the stress in the silicon. This stress, which is a function of the stress evolution in the oxide enables us to describe qualitatively the experimental behavior of OED and OSF. However, quantitative analysis of stresses in silicon gives values insufficient to lead to a non-negligible self-interstitials concentration.
Influence of bismuth oxide concentration on the pH level and biocompatibility of white Portland cement
MARCIANO, Marina AngÚlica; GARCIA, Roberto BrandÒo; CAVENAGO, Bruno Cavalini; MINOTTI, Paloma Gagliardi; MIDENA, Raquel Zanin; GUIMAR├ES, Bruno Martini; ORDINOLA-ZAPATA, Ronald; DUARTE, Marco Antonio Hungaro
Objectives To investigate if there is a relation between the increase of bismuth oxide and the decrease of pH levels and an intensification of toxicity in the Portland cement. Material and Methods White Portland cement (WPC) was mixed with 0, 15, 20, 30 and 50% bismuth oxide, in weight. For the pH level test, polyethylene tubes were filled with the cements and immersed in Milli-Q water for 15, 30 and 60 days. After each period, the increase of the pH level was assessed. For the biocompatibility, two polyethylene tubes filled with the cements were implanted in ninety albino rats (n=6). The analysis of the intensity of the inflammatory infiltrate was performed after 15, 30 and 60 days. The statistical analysis was performed using the Kruskal-Wallis, Dunn and Friedman tests for the pH level and the Kruskal-Wallis and Dunn tests for the biological analysis (p<0.05). Results The results showed an increase of the pH level after 15 days, followed by a slight increase after 30 days and a decrease after 60 days. There were no significant statistical differences among the groups (p>0.05). For the inflammatory infiltrates, no significant statistical differences were found among the groups in each period (p>0.05). The 15% WPC showed a significant decrease of the inflammatory infiltrate from 15 to 30 and 60 days (p<0.05). Conclusions The addition of bismuth oxide into Portland cement did not affect the pH level and the biological response. The concentration of 15% of bismuth oxide resulted in significant reduction in inflammatory response in comparison with the other concentrations evaluated. PMID:25141197
Transparent conducting oxide films for thin film silicon photovoltaics
W. Beyer; J. Hupkes; H. Stiebig
The requirements for applications of transparent conducting oxide (TCO) films in thin film silicon solar cells are reviewed with a focus on sputtered Al doped zinc oxide and fluorine doped tin oxide films. TCO films are employed as a front contact and as part of a highly reflective back contact so that the silicon absorber layer is embedded by TCO
Suppression of decoherence due to spin diffusion for bismuth qubits in silicon
Balian, S J; Mohammady, M H; Morley, G W; Witzel, W M; Kay, C W M; Monteiro, T S
We present pulsed electron-nuclear double resonance experiments which enable us to quantify and characterize, for the first time, the coupling between bismuth donor spin qubits and the surrounding $^{29}\\text{Si}$ impurities; the latter provide the dominant decoherence mechanism (nuclear spin diffusion) in this system. Cluster expansion simulations show near-complete suppression of spin diffusion at optimal working points. The suppression takes the form of sharply peaked divergences of the spin diffusion time $T_{\\text{SD}}$, in contrast with previously identified broader regions of insensitivity to classical fluctuations.
Pink Bismuth« ... Bismuth subsalicylate is used to treat diarrhea, heartburn, and upset stomach in adults and children 12 years of age and older. Bismuth subsalicylate is in a class of medications called ...
Correlation between matrix structural order and compressive stress exerted on silicon nanocrystals embedded in silicon-rich silicon oxide
Abstract Silicon nanocrystals embedded in a silicon oxide matrix were deposited by radio frequency reactive magnetron sputtering. By means of Raman spectroscopy, we have found that a compressive stress is exerted on the silicon nanocrystal cores. The stress varies as a function of silicon concentration in the silicon-rich silicon oxide layers varies, which can be attributed to changes of nanocrystal environment. By conducting the Fourier transform infrared absorption experiments, we have correlated the stresses exerted on the nanocrystal core to the degree of matrix structural order. PACS 78.67.Bf, 78.67.Pt, 73.63.Bd, 78.47.D, 74.25.Nd PMID:23336352
Fabrication and characteristics of P-channel silicon-oxide-nitride-oxide-silicon flash memory device based on bulk fin shaped field effect
Lee, Jong Duk
means that the proposed device structure can be applicable to NAND and NOR flash memoriesFabrication and characteristics of P-channel silicon-oxide-nitride-oxide- silicon flash memory-channel silicon-oxide-nitride-oxide-silicon SONOS flash memory device based on bulk fin shaped field effect
The Active Oxidation of Silicon Carbide
NASA Technical Reports Server (NTRS)
Jacobson, Nathan S.; Myers, Dwight L.
The high temperature oxidation of silicon carbide occurs in two very different modes. Passive oxidation forms a protective oxide film which limits further attack of the SiC: SiC(s) + 3/2 O2(g) = SiO2(s) + CO(g) Active oxidation forms a volatile oxide and may lead to extensive attack of the SiC: SiC(s) + O2(g) = SiO(g) + CO(g) Generally passive oxidation occurs at higher oxidant pressures and active oxidation occurs at lower oxidant pressures and elevated temperatures. Active oxidation is a concern for reentry, where the flight trajectory involves the latter conditions. Thus the transition points and rates of active oxidation are a major concern. Passive/active transitions have been studied by a number of investigators. An examination of the literature indicates many questions remain regarding the effect of impurity, the hysteresis of the transition (i.e. the difference between active-to-passive and passive-toactive), and the effect of total pressure. In this study we systematically investigate each of these effects. Experiments were done in both an alumina furnace tube and a quartz furnace tube. It is known that alumina tubes release impurities such as sodium and increase the kinetics in the passive region [1]. We have observed that the active-to-passive transition occurs at a lower oxygen pressure when the experiment is conducted in alumina tubes and the resultant passive silica scale contains sodium. Thus the tests in this study are conducted in quartz tubes. The hysteresis of the transition has been discussed in the detail in the original theoretical treatise of this problem for pure silicon by Wagner [2], yet there is little mention of it in subsequent literature. Essentially Wagner points out that the active-to-passive transition is governed by the criterion for a stable Si/SiO2 equilibria and the passive-to-active transition is governed by the decomposition of the SiO2 film. A series of experiments were conducted for active-to-passive and passive-to-active transitions by increasing and decreasing oxygen pressure, respectively. For pure silicon a dramatic difference was found; whereas for SiC the difference was not as great. This may be due to the oxidation of the carbon in SiC which may break down the scale [3]. The third area is the effect of total pressure. In the literature, low oxygen potentials are achieved via either low total pressure or low oxygen pressure in an O2/Ar mixture. Both types of experiments are done in this study and the differences are discussed with regard to the presence or absence of a boundary layer.
Boron-Doped Strontium-Stabilized Bismuth Cobalt Oxide Thermoelectric Nanocrystalline Ceramic Powders Synthesized via Electrospinning
NASA Astrophysics Data System (ADS)
Koþyi?it, Serhat; Aytimur, Arda; Ã?nar, Emre; Uslu, ?brahim; Akdemir, Ahmet
Boron-doped strontium-stabilized bismuth cobalt oxide thermoelectric nanocrystalline ceramic powders were produced by using a polymeric precursor technique. The powders were characterized by using x-ray diffraction (XRD), scanning electron microscopy (SEM), and physical properties measurement system (PPMS) techniques. The XRD results showed that these patterns have a two-phase mixture. The phases are face-centered cubic (fcc) and body-centered cubic (bcc). Values of the crystallite size, dislocation density, and microstrain were calculated by using the Scherrer equation. The lattice parameters were calculated for fcc and bcc phases. The SEM results showed that needle-like grains are formed in boron-undoped composite materials, but the needle-like grains changed to the plate-like grains with the addition of boron. The distribution of the nanofiber diameters was calculated and the average diameter of the boron-doped sample is smaller than the boron-undoped one. PPMS values showed that the electrical resistivity values decreased, but the thermal conductivity values, the Seebeck coefficients, and figure of merit ( ZT) increased with increasing temperature for the two samples.
Easy synthesis of bismuth iron oxide nanoparticles as photocatalyst for solar hydrogen generation from water
NASA Astrophysics Data System (ADS)
Deng, Jinyi
In this study, high purity bismuth iron oxide (BiFeO3/BFO) nanoparticles of size 50-80 nm have been successfully synthesized by a simple sol-gel method using urea and polyvinyl alcohol at low temperature. X-ray diffraction (XRD) measurement is used to optimize the synthetic process to get highly crystalline and pure phase material. Diffuse reflectance ultraviolet-visible (DRUV-Vis) spectrum indicates that the absorption cut-off wavelength of the nanoparticles is about 620 nm, corresponding to an energy band gap of 2.1 eV. Compared to BaTiO3, BFO has a better degradation of methyl orange under light radiation. Also, photocatalytic tests prove this material to be efficient towards water splitting under simulated solar light to generate hydrogen. The simple synthetic methodology adopted in this paper will be useful in developing low-cost semiconductor materials as effective photocatalysts for hydrogen generation. Photocatalytic tests followed by gas chromatography (GC) analyses show that BiFeO3 generates three times more hydrogen than commercial titania P25 catalyst under the same experimental conditions.
Electrically tailored resistance switching in silicon oxide.
Mehonic, Adnan; Cueff, SÚbastien; Wojdak, Maciej; Hudziak, Stephen; LabbÚ, Christophe; Rizk, Richard; Kenyon, Anthony J
Resistive switching in a metal-free silicon-based material offers a compelling alternative to existing metal oxide-based resistive RAM (ReRAM) devices, both in terms of ease of fabrication and of enhanced device performance. We report a study of resistive switching in devices consisting of non-stoichiometric silicon-rich silicon dioxide thin films. Our devices exhibit multi-level switching and analogue modulation of resistance as well as standard two-level switching. We demonstrate different operational modes that make it possible to dynamically adjust device properties, in particular two highly desirable properties: nonlinearity and self-rectification. This can potentially enable high levels of device integration in passive crossbar arrays without causing the problem of leakage currents in common line semi-selected devices. Aspects of conduction and switching mechanisms are discussed, and scanning tunnelling microscopy (STM) measurements provide a more detailed insight into both the location and the dimensions of the conductive filaments. PMID:23064085
Microbridge testing of plasma-enhanced chemical-vapor deposited silicon oxide films on silicon wafers
Microbridge testing of plasma-enhanced chemical-vapor deposited silicon oxide films on silicon-based microbridge testing method is developed to measure both the residual stresses and Young's modulus of PECVD Si. Experimentally, freestanding microbridges made of PECVD SiOx films were fabricated using the silicon undercut
Edge states and topological properties of electrons on the bismuth on silicon surface with giant spin-orbit coupling
NASA Astrophysics Data System (ADS)
Khomitsky, D. V.; Chubanov, A. A.
We derive a model of localized edge states in a finite-width strip for the two-dimensional electron gas formed in the hybrid system of a bismuth monolayer deposited on the silicon interface and described by the nearly free electron model with giant spin-orbit splitting. The edge states have the energy dispersion in the bulk energy gap with a Dirac-like linear dependence on the quasimomentum and the spin polarization coupled to the direction of propagation, demonstrating the properties of a topological insulator. The topological stability of edge states is confirmed by the calculations of the Z 2 invariant taken from the structure of the Pfaffian for the time reversal operator for the filled bulk bands in the surface Brillouin zone, which is shown to have a stable number of zeros with the variations of material parameters. The proposed properties of the edge states may support future advances in experimental and technological applications of this new material in nanoelectronics and spintronics.
Hart, Gus
CHARACTERIZATION OF URANIUM, URANIUM OXIDE AND SILICON MULTILAYER THIN FILMS by David T. Oliphant. Woolley Dean, College of Physical and Mathematical Sciences #12;ABSTRACT CHARACTERIZATION OF URANIUM, URANIUM OXIDE AND SILICON MULTILAYER THIN FILMS David T. Oliphant Department of Physics and Astronomy
Synthesis and characterization of barium iron oxide and bismuth iron oxide epitaxial films
Charlee J. Callender Bennett
Much interest exists in perovskite oxide materials and the potential they have in possessing two or more functional properties. In recent years, research on developing new materials with simultaneous ferromagnetic and ferroelectric behavior is the key to addressing possible challenges of new storage information applications. This work examines the fundamental properties of a perovskite oxide, namely BaFeO3, and the investigation
Silicon radiation detectors with oxide charge state compensation
NASA Technical Reports Server (NTRS)
Walton, J. T.; Goulding, F. S.
This paper discusses the use of boron implantation on high resistivity P type silicon before oxide growth to compensate for the presence of charge states in the oxide and oxide/silicon interface. The presence of these charge states on high resistivity P type silicon produces an inversion layer which causes high leakage currents on N(+)P junctions and high surface conductance. Compensating the surface region by boron implantation is shown to result in oxide passivated N(+)P junctions with very low leakage currents and with low surface conductance.
Extraction of nitride trap density from stress induced leakage current in silicon-oxide-nitride-oxide-silicon flash memory
Shaw-Hung Gu; Tahui Wang; Wen-Pin Lu; Yen-Hui Joseph Ku; Chih-Yuan Lu
The authors propose a technique to extract a silicon nitride trap density from stress induced leakage current in a polycrystalline silicon-oxide-nitride-oxide-silicon flash memory cell. An analytical model based on the Frenkel-Poole emission is developed to correlate a nitride trap density with stress induced leakage current. The extracted nitride trap density is 7.0Î1012 cm-2 eV-1. They find that nitride trapped charges
Optimized amorphous silicon oxide buffer layers for silicon heterojunction solar cells with microcrystalline silicon oxide contact layers
NASA Astrophysics Data System (ADS)
Ding, Kaining; Aeberhard, Urs; Finger, Friedhelm; Rau, Uwe
We report on the systematic optimization of the intrinsic amorphous silicon oxide buffer layer in interplay with doped microcrystalline silicon oxide contact layers for silicon heterojunction solar cells using all silicon oxide based functional layers on flat p-type float-zone wafers. While the surface passivation quality is comparably good within a wide range of low oxygen contents, the optical band gap increases and the dark conductivity decreases with increasing oxygen content, giving rise to an inevitable trade-off between optical transparency and electrical conductivity. On the cell level, fill factor FF and short circuit current density Jsc losses compete with the open circuit voltage Voc gains resulting from a thickness increase of the front buffer layers, whereas Jsc and Voc gains compete with FF losses resulting from increasing thickness of the rear buffer layers. We obtained the highest active area efficiency of ?act = 18.5% with Voc = 664 mV, Jsc = 35.7 mA/cm2, and FF = 78.0% using 4 nm front and 8 nm rear buffer layer with an oxygen content of 5%.
Nitric oxide-releasing porous silicon nanoparticles
In this study, the ability of porous silicon nanoparticles (PSi NPs) to entrap and deliver nitric oxide (NO) as an effective antibacterial agent is tested against different Gram-positive and Gram-negative bacteria. NO was entrapped inside PSi NPs functionalized by means of the thermal hydrocarbonization (THC) process. Subsequent reduction of nitrite in the presence of d-glucose led to the production of large NO payloads without reducing the biocompatibility of the PSi NPs with mammalian cells. The resulting PSi NPs demonstrated sustained release of NO and showed remarkable antibacterial efficiency and anti-biofilm-forming properties. These results will set the stage to develop antimicrobial nanoparticle formulations for applications in chronic wound treatment. PMID:25114633
Nitric oxide-releasing porous silicon nanoparticles
NASA Astrophysics Data System (ADS)
Kafshgari, Morteza Hasanzadeh; Cavallaro, Alex; Delalat, Bahman; Harding, Frances J.; McInnes, Steven JP; Mõkilõ, Ermei; Salonen, Jarno; Vasilev, Krasimir; Voelcker, Nicolas H.
In this study, the ability of porous silicon nanoparticles (PSi NPs) to entrap and deliver nitric oxide (NO) as an effective antibacterial agent is tested against different Gram-positive and Gram-negative bacteria. NO was entrapped inside PSi NPs functionalized by means of the thermal hydrocarbonization (THC) process. Subsequent reduction of nitrite in the presence of d-glucose led to the production of large NO payloads without reducing the biocompatibility of the PSi NPs with mammalian cells. The resulting PSi NPs demonstrated sustained release of NO and showed remarkable antibacterial efficiency and anti-biofilm-forming properties. These results will set the stage to develop antimicrobial nanoparticle formulations for applications in chronic wound treatment.
A new nano bismuth(III) salophen catalyst for green and efficient catalytic oxidation of sulfides into the corresponding sulfoxides
NASA Astrophysics Data System (ADS)
Tajgardoon, Mohammad Ghaem; Jafari, Marzieh; Rafiee, Ezzat; Feyzi, Mostafa; Joshaghani, Mohammad
Bismuth(III) salophen as a new catalyst has been synthesized. Structural properties of this complex have been studied by Fourier transform infrared spectroscopy, X-ray diffraction, differential scanning calorimetry, and thermal gravimetric analyses. The average crystalline size of Bi-salophen particles was 86 nm. Thermal analyses show that the complex is stable over 300░C. Catalytic activity of this catalyst has been investigated in oxidation of sulfides. Different kinds of sulfides have been oxidized to the corresponding sulfoxides efficiently in the presence of sodium periodate as oxidant in glacial acetic acid as solvent at room temperature. These sulfides were selectively and completely converted into their corresponding sulfoxides in very short reaction times. Selectivity of this method was excellent, which is another advantage of this method.
Observation of threshold oxide electric field for trap generation in oxide films on silicon
Charles Ching-Hsiang Hsu; Toshikazu Nishida; Chih-Tang Sah
VerweyÆs bipolar\\/metal-oxide-silicon-field-effect-transistor structure is used to inject hot electrons into thermally grown wet oxide films on crystalline silicon by forward biasing the substrate emitter-base junction. Two components are separated from the threshold voltage shift: the electron charging of existing neutral oxide traps and the generation of new oxide traps. The density of the generated new oxide traps is found to
Analysis of phosphorous autodoping in P-type silicon measured using corona oxide silicon (COS) techniques
NASA Astrophysics Data System (ADS)
Letherer, Brian; Horner, Gregory
Semiconductor fabrication facilities rely on the integrity of the silicon to manufacture sub-micron devices. Cross contamination of P-type silicon to N-type carriers or vice versa in the near surface region of the silicon can be detrimental to device performance. Semiconductor processing typically includes numerous diffusion and pre-clean steps, any one of which might auto-dope P-type silicon substrate with phosphorous. Inline monitoring of these near surface doping effects enhances the ability to diagnose autodoping problems. A non-contact Corona Oxide Silicon (COS) measurement technique has the ability to detect cross-contaminated P-type silicon with phosphorous from wet clean benches and diffusion furnaces. Results show COS flatband (Vfb) and oxide total charge (Qtot) measurements are sensitive to various levels of intentional phosphorous contamination implanted into the silicon at pre-oxidation. Phosphorous at the silicon/oxide interface can pile up and create an electrically active thin 'N' skin. Phosphorous from this thin 'N' skin is shown to change the electrical characteristics of near surface region of the silicon. The detection of unwanted phosphorus with the use of COS inline monitoring can greatly reduce the response time when auto-doping problems occur.
Surface kinetics modeling of silicon oxide etching in fluorocarbon plasmas
Kwon, Ohseung, 1969-
Fluorocarbon plasma for silicon oxide etching is a complicated system involving many ion and neutral species. Depending on the plasma condition, many difficulties arise such as RIE lag, etch stop, and low selectivity to ...
Indium oxide/n-silicon heterojunction solar cells
Feng, Tom (Morris Plains, NJ); Ghosh, Amal K. (New Providence, NJ)
A high photo-conversion efficiency indium oxide/n-silicon heterojunction solar cell is spray deposited from a solution containing indium trichloride. The solar cell exhibits an Air Mass One solar conversion efficiency in excess of about 10%.
Growth of silicon quantum dots by oxidation of the silicon nanocrystals embedded within silicon carbide matrix
Kole, Arindam; Chaudhuri, Partha, E-mail: email@example.com [Indian Association for the Cultivation of Science, 2A and 2B Raja S.C. Mullick Road, Jadavpur, Kolkata-700032 (India)
A moderately low temperature (?800 ░C) thermal processing technique has been described for the growth of the silicon quantum dots (Si-QD) within microcrystalline silicon carbide (?c-SiC:H) dielectric thin films deposited by plasma enhanced chemical vapour deposition (PECVD) process. The nanocrystalline silicon grains (nc-Si) present in the as deposited films were initially enhanced by aluminium induced crystallization (AIC) method in vacuum at a temperature of T{sub v} = 525 ░C. The samples were then stepwise annealed at different temperatures T{sub a} in air ambient. Analysis of the films by FTIR and XPS reveal a rearrangement of the ?c-SiC:H network has taken place with a significant surface oxidation of the nc-Si domains upon annealing in air. The nc-Si grain size (D{sub XRD}) as calculated from the XRD peak widths using Scherrer formula was found to decrease from 7 nm to 4 nm with increase in T{sub a} from 250 ░C to 800 ░C. A core shell like structure with the nc-Si as the core and the surface oxide layer as the shell can clearly describe the situation. The results indicate that with the increase of the annealing temperature in air the oxide shell layer becomes thicker and the nc-Si cores become smaller until their size reduced to the order of the Si-QDs. Quantum confinement effect due to the SiO covered nc-Si grains of size about 4 nm resulted in a photoluminescence peak due to the Si QDs with peak energy at 1.8 eV.
Growth of silicon quantum dots by oxidation of the silicon nanocrystals embedded within silicon carbide matrix
NASA Astrophysics Data System (ADS)
Kole, Arindam; Chaudhuri, Partha
A moderately low temperature (?800 ░C) thermal processing technique has been described for the growth of the silicon quantum dots (Si-QD) within microcrystalline silicon carbide (?c-SiC:H) dielectric thin films deposited by plasma enhanced chemical vapour deposition (PECVD) process. The nanocrystalline silicon grains (nc-Si) present in the as deposited films were initially enhanced by aluminium induced crystallization (AIC) method in vacuum at a temperature of Tv = 525 ░C. The samples were then stepwise annealed at different temperatures Ta in air ambient. Analysis of the films by FTIR and XPS reveal a rearrangement of the ?c-SiC:H network has taken place with a significant surface oxidation of the nc-Si domains upon annealing in air. The nc-Si grain size (DXRD) as calculated from the XRD peak widths using Scherrer formula was found to decrease from 7 nm to 4 nm with increase in Ta from 250 ░C to 800 ░C. A core shell like structure with the nc-Si as the core and the surface oxide layer as the shell can clearly describe the situation. The results indicate that with the increase of the annealing temperature in air the oxide shell layer becomes thicker and the nc-Si cores become smaller until their size reduced to the order of the Si-QDs. Quantum confinement effect due to the SiO covered nc-Si grains of size about 4 nm resulted in a photoluminescence peak due to the Si QDs with peak energy at 1.8 eV.
Fabrication and testing of oxidized porous silicon field emitter strips
Madduri, Vasanta Bhanu
FABRICATION AND TESTING OF OXIDIZED POROUS SILICON FIELD EM11TER STRIPS A Thesis by VASANTA BHANU MADDURI Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of MASTER... OF SCIENCE August 1992 Major Subject: Electrical Engineering TEXAS ASM UNlvERSITY LIBRARY FABRICATION AND TESTING OF OXIDIZED POROUS SILICON FIELD EMITTER STRIPS A Thesis by VASANTA BHANU MADDURI Approved as to style and content by Mark H. Weichold...
Synthesis of cobaltûsilicon oxide thin films
E Barrera; A Avila; J Mena; V. H Lara; M Ruiz; J MÚndez-Vivar
Siliconûcobalt oxide thin films were prepared by the dipping solûgel process. Samples with different number of dippingûannealing cycles were prepared. Some data regarding the precursor sol are given from small angle X-ray scattering characterization. Composition, structure, surface morphology and optical properties are obtained from X-ray diffraction, reflectance, transmittance, FTIR, scanning electron microscopy and EDX spectroscopy measurements. The siliconûcobalt oxide thin
Structural, electrical, and thermoelectric properties of bismuth telluride: Silicon/carbon nanocomposites thin films
Agarwal, Khushboo; Mehta, B. R., E-mail: email@example.com [Thin Film Laboratory, Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016 (India)
In this study, the effect of the presence of secondary phases on the structural, electrical, and thermoelectric properties of nanocomposite Bi{sub 2}Te{sub 3} films prepared by co-sputtering of silicon and carbon with Bi{sub 2}Te{sub 3} has been investigated. Growth temperature and the presence of Si and C phase are observed to have a strong effect on the topography and orientation of crystallites. X-ray diffraction study demonstrates that Bi{sub 2}Te{sub 3} and Bi{sub 2}Te{sub 3}:C samples have preferred (0 0 15) orientation in comparison to Bi{sub 2}Te{sub 3}:Si sample, which have randomly oriented crystallites. Atomic force, conducting atomic force, and scanning thermal microscopy analysis show significant differences in topographical, electrical, and thermal conductivity contrasts in Bi{sub 2}Te{sub 3}:Si and Bi{sub 2}Te{sub 3}:C samples. Due to the randomly oriented crystallites and the presence of Si along the crystallite boundaries, appreciable Seebeck coefficient, higher electrical conductivity, and lower thermal conductivity is achieved resulting in relatively higher value of power factor (3.71 mW K{sup ?2} m{sup ?1}) for Bi{sub 2}Te{sub 3}:Si sample. This study shows that by incorporating a secondary phase along crystallite boundaries, microstructural, electrical, and thermoelectric properties of the composite samples can be modified.
Structural, electrical, and thermoelectric properties of bismuth telluride: Silicon/carbon nanocomposites thin films
NASA Astrophysics Data System (ADS)
Agarwal, Khushboo; Mehta, B. R.
In this study, the effect of the presence of secondary phases on the structural, electrical, and thermoelectric properties of nanocomposite Bi2Te3 films prepared by co-sputtering of silicon and carbon with Bi2Te3 has been investigated. Growth temperature and the presence of Si and C phase are observed to have a strong effect on the topography and orientation of crystallites. X-ray diffraction study demonstrates that Bi2Te3 and Bi2Te3:C samples have preferred (0 0 15) orientation in comparison to Bi2Te3:Si sample, which have randomly oriented crystallites. Atomic force, conducting atomic force, and scanning thermal microscopy analysis show significant differences in topographical, electrical, and thermal conductivity contrasts in Bi2Te3:Si and Bi2Te3:C samples. Due to the randomly oriented crystallites and the presence of Si along the crystallite boundaries, appreciable Seebeck coefficient, higher electrical conductivity, and lower thermal conductivity is achieved resulting in relatively higher value of power factor (3.71 mW K-2 m-1) for Bi2Te3:Si sample. This study shows that by incorporating a secondary phase along crystallite boundaries, microstructural, electrical, and thermoelectric properties of the composite samples can be modified.
Synthesis and characterization of barium iron oxide and bismuth iron oxide epitaxial films
NASA Astrophysics Data System (ADS)
Callender Bennett, Charlee J.
Much interest exists in perovskite oxide materials and the potential they have in possessing two or more functional properties. In recent years, research on developing new materials with simultaneous ferromagnetic and ferroelectric behavior is the key to addressing possible challenges of new storage information applications. This work examines the fundamental properties of a perovskite oxide, namely BaFeO3, and the investigation of properties of a solid solution between BaFeO3 and BiFeO3. The growth and properties of epitaxial BaFeO3 thin films in the metastable cubic perovskite phase are examined. BaFeO3 films were grown on (012) LaAlO3 and (001) SrTiO3 single crystal substrates by pulsed-laser deposition. X-ray diffraction shows that in situ growth at temperatures between 650-850░C yields an oxygen-deficient BaFeO 2.5+x pseudo-cubic perovskite phase that is insulating and paramagnetic. Magnetization measurements on the asdeposited BaFeO3 films indicate non-ferromagnetic behavior. Annealing these films in 1 atm oxygen ambient converts the films into a pseudo-cubic BaFeO3-x phase that is ferromagnetic with a Curie temperature of 235 K. The observation of ferromagnetism with increasing oxygen content is consistent with superexchange coupling of Fe +4-O-Fe+4. The effects of anneal conditions on BaFeO3 are studied. X-ray characterization, such as reciprocal space maps, show more complex structure for as-grown BaFeO3-x epitaxial films. Epitaxial films grown at low laser energies are highly crystalline. However, they decompose after annealing. When grown at high laser energies, films exhibit complex structure which "cleans up" to a single pseudocubic or tetragonal structure upon ex situ anneal in oxygen ambient environment. Superlattices of BaFeO 3/SrTiO3 were synthesized to explore the nature of "cracking" in annealed BaFeO3, which occurs due to large change in lattice parameter. Magnetization of ex situ annealed BaFeO3-x epitaxial films were examined as a function of applied field direction and was not found to have a change in magnetization with direction of field, despite other research claims. Evidence supports that the unusually weak magnetization of BaFeO3-x is attributed to it being structurally and magnetically disordered. Alloys of a solid-solution between BiFeO3 and BaFeO3-x have been successfully created. X-ray characterizations demonstrate alloy epitaxial films via two-target continuous rotation method have been carried all the way to 80% solubility. In addition, alloy films via solid-solution targets method have been successfully fabricated at near both end-member-points and at the half-point showing that the solubility is possible over the entire range of the solid-solution. Bi0.9Ba0.1FeO3 epitaxial films are of high crystalline quality with rocking curves widths of less than 0.22░, are fully strained, and have highly unusual in-plane and out-of-plane lattice parameters. TEM imaging illustrates that, despite extreme c/a ratios up to 1.26, the films are single phase with sharp interfaces with substrates. SQUID magnetometry was utilized, revealing that the samples are weakly ferromagnetic with a magnetization of 0.2microB per Fe, more than an order of magnitude larger than that of pure BiFeO3. Magnetic hysteresis loops show unfamiliar "pinching," signaling a possible breakdown of the helical magnetic ordering in the fully strained samples. BaFeO3-x, though it can be made ferromagnetic, it is a highly complex material. In studying BaFeO3-x's properties, conclusions can be made that its weak magnetization and unusual structure is highly disordered, magnetically and structurally. The creation of a new solid solution (Bi, Ba)FeO3 by two methods shows that a solid solution between BiFeO3 and BaFeO3-x can be synthesized. Specifically the creation of the alloy Bi0.9Ba0.1FeO3-delta , shows that one can improve on BiFeO3's magnetic properties, and more importantly supports the case that BaFeO3-x exhibits magnetic and structural disorder.
Plasma-nitrided silicon-rich oxide as an extension to ultrathin nitrided oxide gate dielectrics
Cubaynes, F.N.; Venezia, V.C.; Marel, C. van der; Snijders, J.H.M.; Everaert, J.L.; Shi, X.; Rothschild, A.; Schaekers, M. [Philips Research Leuven, Kapeldreef 75, 3001 Leuven (Belgium); Philips Research Eindhoven, Prof. Holstlaan 4, 5656 AA, Eindhoven (Netherlands); Imec, Kapeldreef 75, 3001 Leuven (Belgium)
We have investigated the mechanism of N incorporation, during plasma nitridation, in thermally grown ultrathin (<2 nm) SiO{sub 2} films and deposited silicon-rich oxide films. X-ray photoelectron spectroscopy analysis indicates that N atoms exchange mainly with O to bond with Si atoms in ultrathin plasma-nitrided oxides. Based on this understanding, we were able to increase the amount of N that can be incorporated in plasma-nitrided silicon oxides by increasing the silicon content in these films. This was achieved by depositing ultrathin substoichiometric silicon-rich oxide films. We demonstrate an increase of almost twice as much N in these ultrathin plasma-nitrided silicon-rich oxide films yielding lower gate leakage current for a given thickness.
The photorefractive characteristics of bismuth-oxide doped lithium niobate crystals
NASA Astrophysics Data System (ADS)
Zheng, Dahuai; Kong, Yongfa; Liu, Shiguo; Yao, Jiaying; Zhang, Ling; Chen, Shaolin; Xu, Jingjun
Bismuth-doped lithium niobate (LN:Bi) crystals were grown by Czochralski method and their optical damage resistance, photorefraction, absorption spectra, and defect energy levels were investigated. The experimental results indicate that the photorefractive properties of LN:Bi were enhanced as compared with congruent one, the photorefractive response time was greatly shortened, the photorefractive sensitivity was increased, and the diffraction efficiency of near-stoichiometric LN:Bi (SLN:Bi) reached 31.72% and 49.08% at 532 nm and 488 nm laser, respectively (light intensity of 400 mW/cm2). An absorption peak at about 350 nm was observed in the absorption spectrum of LN:Bi. And the defect energy levels simulation indicates new defect levels appear in the forbidden gap of LN:Bi crystals. Therefore bismuth can act as photorefractive centers in LN crystals.
Evaluation of Radiation Dose Reduction during CT Scans Using Oxide Bismuth and Nano-Barium Sulfate Shields
Seoung, Youl-Hun
The purpose of the present study was to evaluate radiation dose reduction and image quality during CT scanning by using a new dose reduction fiber sheet (DRFS) with commercially available bismuth shields. These DRFS were composed of nano-barium sulfate (BaSO4), filling the gaps left by the large oxide bismuth (Bi2O3) particle sizes. The radiation dose was measured five times at directionss of 12 o'clock from the center of the polymethyl methacrylate (PMMA) head phantom to calculate an average value using a CT ionization chamber. The image quality measured CT transverse images of the PMMA head phantom depending on X-ray tube voltages and the type of shielding. Two regions of interest in CT transverse images were chosen from the right and left areas under the surface of the PMMA head phantom and from ion chamber holes located at directions of 12 o'clock from the center of the PMMA head phantom. The results of this study showed that the new DRFS shields could reduce dosages to 15.61%, 23.05%, and 22.71% more in ...
Preparation of Gadolina Stabilized Bismuth Oxide Doped with Boron via Electrospinning Technique
Tuncay Tunþ; ?brahim Uslu; ?enol Durmu?o?lu; Selda Keskin; Arda Aytimur; Ahmet Akdemir
In this study, boron doped and undoped poly (vinyl) alcohol\\/bismuthûgadolina acetate (PVA\\/BiûGd) nanofibers were prepared\\u000a using electrospinning technique then calcinated at 800á░C for 2áh. The originality of this study is the addition of boron\\u000a to metal acetates. The effects of boron doping were investigated in terms of solution properties, morphological changes and\\u000a thermal characteristics. The characteristics of the fibers were
Alternative method for steam generation for thermal oxidation of silicon
Jeffrey J. Spiegelman
Thermal oxidation of silicon is an important process step in MEMS device fabrication. Thicker oxide layers are often used as structural components and can take days or weeks to grow, causing high gas costs, maintenance issues, and a process bottleneck. Pyrolytic steam, which is generated from hydrogen and oxygen combustion, was the default process, but has serious drawbacks: cost, safety,
I. Electroluminescence from Hydrogen Uranyl Phosphate. I. Indium-Substituted Bismuth Copper Oxide Superconductors
NASA Astrophysics Data System (ADS)
Dieckmann, Gunnar Rudolph
Chapter 1. A review of the general aspects of solid electrolytes is presented along with a summary of the electrical and optical properties of hydrogen uranyl phosphate (HUO_2PO_4 bullet4H_2O, HUP). A review of impedance spectroscopy, as it relates to the determination of ionic conductivities and dielectric constants of solid electrolytes is presented. The final section covers some aspects of gas plasma display devices. Chapter 2. Electroluminescence (EL) cells have been constructed with the ionically conducting solid HUP as the emissive medium. With ac excitation, both uranyl emission and molecular nitrogen plasma emission are observed, with the latter appearing to excite the former. Similar results were obtained with fully-substituted sodium (NaUP), magnesium (Mg_{0.5}UP), and pyridinium (pyHUP) derivatives of HUP. For all of these solids, the dependence of the EL intensity on sample thickness, ac frequency, and applied voltage has been determined. Impedance measurements permitted acquisition of dielectric constants and ionic conductivities for these solids, both of which decrease in the order HUP > NaUP > Mg_{0.5}UP > pyHUP. A model describing the dependence of EL intensity on cell parameters is presented. Chapter 3. The copper oxide superconductors can be structurally classified into five major families, represented by the compositions, (La,Sr)_2CuO _4, YBa_2Cu_3O_7, Pb_2Sr_2(Y,Ca)Cu_3O_8, (TIO)_{m}Ca_{n-1}Ba_2Cu _{n}O_{2n+2}, and Bi_2Sr_2(Ln_{1-x}Ce _{x})_2Cu_2O_{10+y }. All families are linked by a CuO _2 layer, which is crucial for superconductivity. The structural and chemical aspects of each family is covered with emphasis on the bismuth and thallium systems. The effects of substitution and oxygen annealing are also briefly considered. Chapter 4. The attempted substitution of indium into the rm Bi_2(Ca,Sr)_2CuO _6 and Bi_2(Ca,Sr) _3Cu_2O _8 systems is reported. Previously unreported side products, (Ca,Sr)In_2O _4 and Bi-Ca-Sr-O, viz., produced in the attempted reactions, hinder the formation of an indium -containing product. The T_{rm c} are within the range expected for the parent materials. A novel synthetic procedure based on nitrate decomposition was developed, which yielded two meta-stable phases, Bi-Ca-O and Bi_{2 -x}In_{x}O_3; the former is related to the Bi-Ca-Sr-O phase and the latter decomposes in a complex manner. Substitution was accomplished in the rm Bi_2Sr_2Sm_{1.7 }Ce_{0.3}Cu_2O_{10 } system, but the products were not superconducting.
Thermal oxidation-induced strain in silicon nanobeams
NASA Astrophysics Data System (ADS)
Pyzyna, Adam Michael
The injection of self-interstitial atoms into bulk silicon during thermal oxidation has long been associated with atomic scale phenomena, such as oxidation-enhanced diffusion (OED) and the growth of oxidation-induced stacking faults (OISF). The current work suggests that interstitial injection may also be implicated in a nanoscale mechanical phenomenon. Previous researchers have found that the use sacrificial oxidation to fabricate suspended silicon nanowires results in an unexplained accumulation of permanent strain, which is manifested as buckling of the wires. We make use of suspended single-crystal silicon beams of sub-micron thickness to quantify this oxidation-induced strain (OIS) and its dependence on oxidation conditions. Dry oxidation followed by removal of the oxide via etching in HF reduces the thickness of the nanobeams, which are fixed at both ends. As a result of the oxidation, the nanobeams undergo an increase in length, which is quantified by measuring the profiles of the buckled beams. The microscale lateral dimensions of these beams facilitate their measurement by optical interferometry, allowing us to take advantage of the innate amplification of displacement that accompanies buckling. This allows us to measure very small strains, in the range of microstrain. A model for the oxidation-induced strain is developed based on the volumetric strain due to injection of Si atoms, and transition state theory is employed to express strain rate in terms of thermally activated processes. The influence of stress on these processes is also explored.
Zinc oxide varistors and/or resistors
Arnold, W.D. Jr.; Bond, W.D.; Lauf, R.J.
Varistors and/or resistors are described that include doped zinc oxide gel microspheres. The doped zinc oxide gel microspheres preferably have from about 60 to about 95% by weight zinc oxide and from about 5 to about 40% by weight dopants based on the weight of the zinc oxide. The dopants are a plurality of dopants selected from silver salts, boron oxide, silicon oxide and hydrons oxides of aluminum, bismuth, cobalt, chromium, manganese, nickel, and antimony.
Effects of ionizing radiation on oxidized silicon surfaces and planar devices
E. H. Snow; A. S. Grove; D. J. Fitzgerald
This paper examines in detail the effects of high and low energy electron, X-ray, and ultraviolet radiation on oxidized silicon surfaces and planar devices. Two permanent effects of ionizing radiation on oxidized silicon surfaces are distinguished: 1) The buildup of a positive space charge within the oxide, and 2) The creation of fast surface states at the oxide-silicon interface resulting
Effect of porous silicon layer on the performance of Si\\/oxide photovoltaic and photoelectrochemical cells
Waheed A. Badawy
Photovoltaic and photoelectrochemical systems were prepared by the formation of a thin porous film on silicon. The porous silicon layer was formed on the top of a clean oxide free silicon wafer surface by anodic etching in HF\\/H2O\\/C2H5OH mixture (2:1:1). The silicon was then covered by an oxide film (tin oxide, ITO or titanium oxide). The oxide films were prepared
Nanoscale two-bit/cell NAND silicon-oxide-nitride-oxide-silicon memory device with different tunneling oxide thicknesses.
Kim, Hyun Joo; You, Joo Hyung; Kim, Sung Ho; Kwack, Kae Dal; Kim, Tae Whan
Nanoscale two-bit/cell NAND-type silicon-oxide-nitride-oxide-silicon (SONOS) flash memory devices with different tunneling oxide thicknesses were designed to reduce the short channel effect and the coupling interference. The process step and the electrical characteristics of the proposed SONOS memory devices were simulated by using SUPREM-4 and MEDICI, respectively. The short channel effect in the nanoscale two-bit/cell SONOS devices was decreased than that of the conventional devices due to a larger effective channel length. The drain current at the on-state of the proposed NAND SONOS memory devices decreased than that of the conventional NAND SONOS devices due to the high channel resistivity. The I on/I off ratio of the proposed NAND SONOS memory devices was larger than that of the conventional memory devices due to the dramatic decrease in the subthreshold current of the proposed devices. The electrical characteristics of the NAND SONOS memory devices with different tunneling oxide thicknesses were better than those of the conventional NAND SONOS devices. PMID:22121667
A review of oxide, silicon nitride, and silicon carbide brazing
Santella, M.L.; Moorhead, A.J.
There is growing interest in using ceramics for structural applications, many of which require the fabrication of components with complicated shapes. Normal ceramic processing methods restrict the shapes into which these materials can be produced, but ceramic joining technology can be used to overcome many of these limitations, and also offers the possibility for improving the reliability of ceramic components. One method of joining ceramics is by brazing. The metallic alloys used for bonding must wet and adhere to the ceramic surfaces without excessive reaction. Alumina, partially stabilized zirconia, and silicon nitride have high ionic character to their chemical bonds and are difficult to wet. Alloys for brazing these materials must be formulated to overcome this problem. Silicon carbide, which has some metallic characteristics, reacts excessively with many alloys, and forms joints of low mechanical strength. The brazing characteristics of these three types of ceramics, and residual stresses in ceramic-to-metal joints are briefly discussed.
Carbon nanotube network-silicon oxide non-volatile switches.
Liao, Albert D; Araujo, Paulo T; Xu, Runjie; Dresselhaus, Mildred S
The integration of carbon nanotubes with silicon is important for their incorporation into next-generation nano-electronics. Here we demonstrate a non-volatile switch that utilizes carbon nanotube networks to electrically contact a conductive nanocrystal silicon filament in silicon dioxide. We form this device by biasing a nanotube network until it physically breaks in vacuum, creating the conductive silicon filament connected across a small nano-gap. From Raman spectroscopy, we observe coalescence of nanotubes during breakdown, which stabilizes the system to form very small gaps in the network~15?nm. We report that carbon nanotubes themselves are involved in switching the device to a high resistive state. Calculations reveal that this switching event occurs at ~600?░C, the temperature associated with the oxidation of nanotubes. Therefore, we propose that, in switching to a resistive state, the nanotube oxidizes by extracting oxygen from the substrate. PMID:25482919
Carbon nanotube network-silicon oxide non-volatile switches
NASA Astrophysics Data System (ADS)
Liao, Albert D.; Araujo, Paulo T.; Xu, Runjie; Dresselhaus, Mildred S.
The integration of carbon nanotubes with silicon is important for their incorporation into next-generation nano-electronics. Here we demonstrate a non-volatile switch that utilizes carbon nanotube networks to electrically contact a conductive nanocrystal silicon filament in silicon dioxide. We form this device by biasing a nanotube network until it physically breaks in vacuum, creating the conductive silicon filament connected across a small nano-gap. From Raman spectroscopy, we observe coalescence of nanotubes during breakdown, which stabilizes the system to form very small gaps in the network~15?nm. We report that carbon nanotubes themselves are involved in switching the device to a high resistive state. Calculations reveal that this switching event occurs at ~600?░C, the temperature associated with the oxidation of nanotubes. Therefore, we propose that, in switching to a resistive state, the nanotube oxidizes by extracting oxygen from the substrate.
Oxygen permeation in bismuth-based materials part I: Sintering and oxygen permeation fluxes
Paris-Sud XI, Universit├® de
1 Oxygen permeation in bismuth-based materials part I: Sintering and oxygen permeation fluxes E;2 Abstract Oxygen permeation measurements were performed on two layered bismuth based oxide ceramics, 81.05M, 84.32F Keywords: bismuth erbium oxide, bismuth calcium oxide, BIMEVOX, oxygen permeation #12
The influence of bottom oxide thickness on the extraction ofátheátrap energy distribution in SONOS (silicon-oxide-nitride-oxide-silicon) structures
K. Bernert; C. Oestreich; J. Bollmann; T. Mikolajick
The charge retention characteristics of SONOS (silicon-oxide-nitride-oxide-silicon) non-volatile memory cells at elevated\\u000a temperatures were investigated. Assuming thermal excitation to be the dominant charge loss mechanism, the trap energy distribution\\u000a in the nitride was determined. We present an improved model which includes the influence of subsequent tunneling of the charge\\u000a carriers through the bottom oxide after being thermally emitted into the
Oxygen depletion of bismuth molybdates
L. K. Yong; R. F. Howe; G. W. Keulks; W. K. Hall
Pure ..cap alpha..-phase bismuth molybdate (BiÔMoÔOÔüÔ), which is known to be weakly active for selective oxidation, and pure ..gamma..-phase bismuth molybdate (BiÔMoOÔ), which has good activity, were subjected to oxidation-reduction cycles with known amounts of hydrogen and oxygen, at 300┬░Ôü╗ÔüÁÔüÀ┬░sup 0\\/C and with evacuation steps between treatments. The volume of oxygen consumed during reoxidation was equal to half the hydrogen
Nanostructured bismuth vanadate-based materials for solar-energy-driven water oxidation: a review on recent progress
NASA Astrophysics Data System (ADS)
Huang, Zhen-Feng; Pan, Lun; Zou, Ji-Jun; Zhang, Xiangwen; Wang, Li
Water oxidation is the key step for both photocatalytic water splitting and CO2 reduction, but its efficiency is very low compared with the photocatalytic reduction of water. Bismuth vanadate (BiVO4) is the most promising photocatalyst for water oxidation and has become a hot topic for current research. However, the efficiency achieved with this material to date is far away from the theoretical solar-to-hydrogen conversion efficiency, mainly due to the poor photo-induced electron transportation and the slow kinetics of oxygen evolution. Fortunately, great breakthroughs have been made in the past five years in both improving the efficiency and understanding the related mechanism. This review is aimed at summarizing the recent experimental and computational breakthroughs in single crystals modified by element doping, facet engineering, and morphology control, as well as macro/mesoporous structure construction, and composites fabricated by homo/hetero-junction construction and co-catalyst loading. We aim to provide guidelines for the rational design and fabrication of highly efficient BiVO4-based materials for water oxidation.
Ion implantation reduces radiation sensitivity of metal oxide silicon /MOS/ devices
NASA Technical Reports Server (NTRS)
Implanting nitrogen ions improves hardening of silicon oxides 30 percent to 60 percent against ionizing radiation effects. Process reduces sensitivity, but retains stability normally shown by interfaces between silicon and thermally grown oxides.
The Oxidation of CVD Silicon Carbide in Carbon Dioxide
NASA Technical Reports Server (NTRS)
Opila, Elizabeth J.; Nguyen, QuynchGiao N.
Chemically-vapor-deposited silicon carbide (CVD SiC) was oxidized in carbon dioxide (CO2) at temperatures of 1200-1400 C for times between 100 and 500 hours at several gas flow rates. Oxidation weight gains were monitored by thermogravimetric analysis (TGA) and were found to be very small and independent of temperature. Possible rate limiting kinetic laws are discussed. Oxidation of SiC by CO2 is negligible compared to the rates measured for other oxidants typically found in combustion environments: oxygen and water vapor.
An atomistic insight into the corrosion of the oxide film in liquid lead-bismuth eutectic.
Li, Dongdong; Song, Chi; He, H Y; Liu, C S; Pan, B C
When used as a protective scale, the Fe3O4 layer covering the stainless steel surface in accelerator driven subcritical systems (ADS) is corroded by liquid lead-bismuth eutectics (LBE). By performing theoretical calculations, we reveal that both Pb and Bi at the interface between the LBE and the Fe3O4 scale, favorably adsorb onto the Fe3O4 surfaces, weakening the strength of Fe-O bonds nearby significantly. This facilitates the movement of iron atoms toward the deposited Pb(Bi) and away from the Fe3O4 surface, thus causing corrosion. Such corrosion behavior becomes severe if oxygen vacancies exist in the surface region. PMID:24626636
Novel lead-free piezoelectric ceramics in the solid solution (1-x) bismuth iron oxide-barium titanate
NASA Astrophysics Data System (ADS)
Leontsev, Serhiy
Piezoelectric materials are widely used in many areas of science and technology due to their electromechanical properties. The transformation of mechanical energy into electrical signals and vice versa based on the piezoelectric effect has led to the development of sensor devices and piezoelectric actuators used in accelerometers, pressure and vibration meters, micropositioning devices, ultrasound generators, motors etc. The most technologically important piezoelectric material is lead zirconate titanate PbZrO3-PbTiO3 (PZT), however, the commercial manufacture and application of PZT as a lead-based material represent serious health hazards. The need to reduce environmental contamination by lead-based substances has created the current drive to develop alternative lead-free piezoelectric materials. The present work describes a detailed investigation of the novel multifunctional ceramic material in a solid solution of bismuth iron oxide and barium titanate (1-x)BiFeO 3-xBaTiO3 (BFBT) with an emphasis on the room temperature piezoelectric properties and structural study. BFBT ceramics were prepared via the metal oxide solid-state preparation route. Addition of manganese oxide MnO2 increased the DC resistance by one to five orders of magnitude allowing high-field poling and piezoelectric strain measurements in Mn-modified BFBT ceramics. Piezoelectric d33 coefficients of 116 pC/N (low-field, Berlincourt) and 326 pC/N (effective, high-field) are reported for the compositions with x=0.25 and 0.33 respectively. Piezoelectric measurements using the Rayleigh law under applied large DC electric field indicated an increased low-field piezoelectric d33 coefficient to 150 pC/N (x=0.33). The DC bias is believed to stabilize the ferroclectric domain structure leading to stronger intrinsic and extrinsic contributions to the piezoelectric response in BFBT. Bright field TEM imaging confirmed formation of macroscopic domains following high field poling from initially frustrated domain state indicating the ability to induce long-range polarization order in BFBT ceramics. It is believed that the results of this work will contribute to the development of a family of lead-free piezoelectric materials based on BiFeO3-BaTiO3 system. KEYWORDS: Bismuth ferrite, Barium titanate, Lead-free, Piezoelectric ceramics, Crystal Structure
Charge-trapping properties of gate oxide grown on nitrogen-implanted silicon substrate
Misra, Durgamadhab "Durga"
oxide grown on a nitrogen-implanted silicon substrate were investigated using high-field Fowler oxides by growing oxides on nitrogen-implanted silicon substrate.1 Besides, there is a high degree of interest in using high-dose nitrogen implant to change the oxidation rate for multiple-oxide- thickness
UNCORRECTEDPROOF 2 Optical properties of bismuth borate glasses
Osnabrück, Universität
UNCORRECTEDPROOF 2 Optical properties of bismuth borate glasses 3 Isabella-Ioana Oprea, Hartmut in the binary system bismuth oxide (Bi2O3)boric oxide (B2O3) are measured for the composition 8 range 2565 mol.70.Ce; 78.20.Ci 13 Keywords: Bismuth borate; Glass; Refractive index; Optical properties 14 1
Silicon wafer direct bonding without hydrophilic native oxides
NASA Astrophysics Data System (ADS)
Himi, Hiroaki; Matsui, Masaki; Fujino, Seiji; Hattori, Tadashi
Silicon wafer direct bonding was accomplished between two surfaces which had no hydrophilic native oxide layers. Prior to bonding, two wafers were dipped in conv-HF solution (approximately = 49% aq.) to remove the native oxide layers and then immersed in deionized water. It is suggested that the OH groups which substitute the F atoms terminated on the small portion of the surface play an important role in this conv-HF-treated bonding.
Efficient Formation of Iron Nanoparticle Catalysts on Silicon Oxide by
Javey, Ali
Efficient Formation of Iron Nanoparticle Catalysts on Silicon Oxide by Hydroxylamine for CarbonO2. The solution phase catalyst deposition approach allows for submicron scale catalyst patterning. Patterned growth of nanotubes with this catalyst retains high degrees of surface cleanliness and leads
Polynuclear bismuth-oxo clusters: insight into the formation process of a metal oxide.
Mehring, Michael; Mansfeld, Dirk; Paalasmaa, Sanna; Sch³rmann, Markus
The reaction of the bismuth silanolates [Bi(OSiR2R')3] (R = R' = Me, Et, iPr; R = Me, R' = tBu) with water has been studied. Partial hydrolysis gave polynuclear bismuth-oxo clusters whereas amorphous bismuth-oxo(hydroxy) silanolates were obtained when an excess of water was used in the hydrolysis reaction. The metathesis reaction of BiCl3 with NaOSiMe3 provided mixtures of heterobimetallic silanolates. The molecular structures of [Bi18Na4O20(OSiMe3)18] (2), [Bi33NaO38(OSiMe3)24].3 C7H8 (3.3 C7H8), [Bi50Na2O64(OH)2(OSiMe3)22].2 C7H8.2H2O (4.2 C7H8.2 H2O), [Bi4O2(OSiEt3)8] (5), [Bi9O7(OSiMe3)13].0.5 C7H8 (6. 0.5C7H8), [Bi18O18(OSiMe3)18)].2C7H8 (7. 2C7H8) and [Bi20O18(OSiMe3)24].3C7H8 (8.3C7H8) are presented and compared with the solid-state structures of [Bi22O26(OSiMe2tBu)14] (9) and beta-Bi2O3. Compound 2 crystallises in the triclinic space group P1 with the lattice constants a = 17.0337(9), b = 19.5750(14), c = 26.6799(16) A, alpha = 72.691(4), beta = 73.113(4) and gamma = 70.985(4) degrees ; compound 3.3C7H8 crystallises in the monoclinic space group P2(1)/n with the lattice constants a = 20.488(4), b = 22.539(5), c = 26.154(5) A and beta = 100.79(3) degrees ; compound 4.2C7H82 H2O crystallises in the monoclinic space group P2(1)/n with the lattice constants a = 20.0518(12), b = 24.1010(15), c = 27.4976(14) A and beta = 103.973(3) degrees ; compound 5 crystallises in the monoclinic space group P2(1)/c with the lattice constants a = 25.256(5), b = 15.372(3), c = 21.306(4) A and beta = 113.96(3) degrees ; compound 6.0.5C7H8 crystallises in the triclinic space group P1 with the lattice constants a = 15.1916(9), b = 15.2439(13), c = 22.487(5) A, alpha = 79.686(3), beta = 74.540(5) and gamma = 66.020(4) degrees ; compound 7.2C7H8 crystallises in the triclinic space group P1 with the lattice constants a = 14.8295(12), b = 16.1523(13), c = 18.4166(17) A, alpha = 75.960(4), beta = 79.112(4) and gamma = 63.789(4) degrees ; and compound 8.3C7H8 crystallises in the triclinic space group P1 with the lattice constants a = 17.2915(14), b = 18.383(2), c = 18.4014(18) A, alpha = 95.120(5), beta = 115.995(5) and gamma = 106.813(5) degrees . The molecular structures of the bismuth-rich compounds are related to the CaF2-type structure. Formally, the hexanuclear [Bi6O8]2+ fragment might be described as the central building unit, which is composed of bismuth atoms placed at the vertices of an octahedron and oxygen atoms capping the trigonal faces. Depending on the reaction conditions and the identity of R, the thermal decomposition of the hydrolysis products [Bi(n)O(l)(OH)(m-)(OSiR3)(3n-(2l-m))] gives alpha-Bi2O3, beta-Bi2O3, Bi12SiO20 or Bi4Si3O12. PMID:16331714
Tribological interaction between polytetrafluoroethylene and silicon oxide surfaces
Uþar, A.; Ãopuro?lu, M.; Suzer, S., E-mail: firstname.lastname@example.com [Department of Chemistry, Bilkent University, 06800 Ankara (Turkey); Baykara, M. Z. [Department of Mechanical Engineering, Bilkent University, 06800 Ankara (Turkey); Ar?kan, O. [Department of Electrical and Electronics Engineering, Bilkent University, 06800 Ankara (Turkey)
We investigated the tribological interaction between polytetrafluoroethylene (PTFE) and silicon oxide surfaces. A simple rig was designed to bring about a friction between the surfaces via sliding a piece of PTFE on a thermally oxidized silicon wafer specimen. A very mild inclination (?0.5░) along the sliding motion was also employed in order to monitor the tribological interaction in a gradual manner as a function of increasing contact force. Additionally, some patterns were sketched on the silicon oxide surface using the PTFE tip to investigate changes produced in the hydrophobicity of the surface, where the approximate water contact angle was 45░ before the transfer. The nature of the transferred materials was characterized by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). XPS results revealed that PTFE was faithfully transferred onto the silicon oxide surface upon even at the slightest contact and SEM images demonstrated that stable morphological changes could be imparted onto the surface. The minimum apparent contact pressure to realize the PTFE transfer is estimated as 5 kPa, much lower than reported previously. Stability of the patterns imparted towards many chemical washing processes lead us to postulate that the interaction is most likely to be chemical. Contact angle measurements, which were carried out to characterize and monitor the hydrophobicity of the silicon oxide surface, showed that upon PTFE transfer the hydrophobicity of the SiO{sub 2} surface could be significantly enhanced, which might also depend upon the pattern sketched onto the surface. Contact angle values above 100░ were obtained.
Silicon nanowire circuits fabricated by AFM oxidation nanolithography.
MartÝnez, Ramses V; MartÝnez, Javier; Garcia, Ricardo
We report a top-down process for the fabrication of single-crystalline silicon nanowire circuits and devices. Local oxidation nanolithography is applied to define very narrow oxide masks on top of a silicon-on-insulator substrate. In a plasma etching, the nano-oxide mask generates a nanowire with a rectangular section. The nanowire width coincides with the lateral size of the mask. In this way, uniform and well-defined transistors with channel widths in the 10-20 nm range have been fabricated. The nanowires can be positioned with sub-100 nm lateral accuracy. The transistors exhibit an on/off current ratio of 10(5). The atomic force microscope nanolithography offers full control of the nanowire's shape from straight to circular or a combination of them. It also enables the integration of several nanowires within the same circuit. The nanowire transistors have been applied to detect immunological processes. PMID:20484797
Chemical vapor deposition of tungsten on silicon and silicon oxide studied with soft x-ray photoemission
J. A. YarmoffÆ; F. R. McFeely
The growth of tungsten films on silicon and oxidized silicon surfaces via the silicon reduction of WF6 was studied with soft x-ray photoemission. The films were grown in ultra-high vacuum and analyzed in situ. It was found that the growth on clean Si proceeds via diffusion of Si atoms through the W film to the surface, so that the silicon
Enhancement of radiation effects by bismuth oxide nanoparticles for kilovoltage x-ray beams: A dosimetric study using a novel multi-compartment 3D radiochromic dosimeter
NASA Astrophysics Data System (ADS)
Alqathami, M.; Blencowe, A.; Yeo, U. J.; Franich, R.; Doran, S.; Qiao, G.; Geso, M.
The aim of this study is to present the first experimental validation and quantification of the dose enhancement capability of bismuth oxide nanoparticles (Bi2O3-Nps). A recently introduced multi-compartment 3D radiochromic dosimeter for measuring radiation dose enhancement produced from the interaction of X-rays with metal nanoparticles was employed to investigate the 3D spatial distribution of ionizing radiation dose deposition. Dose-enhancement factor for the dosimeters doped with Bi2O3-NPs was ~1.9 for both spectrophotometry and optical CT analyses. Our results suggest that bismuth-based nanomaterials are efficient dose enhancing agents and have great potential for application in clinical radiotherapy.
Synthesis, Characterization, and Thermoelectric Properties of Electrospun Boron-Doped Barium-Stabilized Bismuth-Cobalt Oxide Nanoceramics
NASA Astrophysics Data System (ADS)
Ãinar, Emre; Koþyi?it, Serhat; Aytimur, Arda; Uslu, ?brahim; Akdemir, Ahmet
In this study, the boron-doped barium-stabilized bismuth cobalt oxide thermoelectric nanocrystalline ceramic powders were produced by the polymeric precursor technique. The powders were characterized by X-ray diffraction, scanning electron microscopy, and the physical properties measurement system. The X-ray diffraction results showed that these patterns have mixture of two phases as face-centered cubic and body-centered cubic. Values of the crystallite size, the dislocation density, and the microstrain were calculated by the Scherrer equation. According to these values, the crystallite size decreased from 60 to 51 nm with the boron addition in the boron-undoped and boron-doped samples, respectively. The scanning electron microscope results showed that nanograins are rarely seen in the boron-undoped samples, but nanograins turn into needle-like and layered structures with boron addition. The diameters distribution of nanofibers was calculated. The average diameter of the boron-doped sample is smaller than the boron-undoped sample. The physical properties measurement system values showed that the electrical and thermal conductivity, the Seebeck coefficient, and the figure of merit increased with the temperature rise for both samples. The boron-doping effect increased the electrical and thermal conductivity, decreased the Seebeck coefficient, and decreased the figure of merit.
Controlled oxidation, biofunctionalization, and patterning of alkyl monolayers on silicon and silicon nitride surfaces using plasma treatment.
Rosso, Michel; Giesbers, Marcel; SchroÙn, Karin; Zuilhof, Han
A new method is presented for the fast and reproducible functionalization of silicon and silicon nitride surfaces coated with covalently attached alkyl monolayers. After formation of a methyl-terminated 1-hexadecyl monolayer on H-terminated Si(100) and Si(111) surfaces, short plasma treatments (1-3 s) are sufficient to create oxidized functionalities without damaging the underlying oxide-free silicon. The new functional groups can, e.g., be derivatized using the reaction of surface aldehyde groups with primary amines to form imine bonds. In this way, plasma-treated monolayers on silicon or silicon nitride surfaces were successfully coated with nanoparticles, or proteins such as avidin. In addition, we demonstrate the possibility of micropatterning, using a soft contact mask during the plasma treatment. Using water contact angle measurements, ellipsometry, XPS, IRRAS, AFM, and reflectometry, proof of principle is demonstrated of a yet unexplored way to form patterned alkyl monolayers on oxide-free silicon surfaces. PMID:19728734
Structure and lattice dynamics of heterostructures based on bismuth ferrite and barium strontium titanate on magnesium oxide substrates
Yu. I. Golovko; V. M. Mukhortov; O. A. Bunina; I. N. Zakharchenko; A. S. Anokhin; V. B. Shirokov; Yu. I. Yuzyuk
Bismuth ferrite films doped with neodymium on MgO single-crystal substrates with an epitaxial barium strontium titanate thin\\u000a (1û2 nm) sublayer have been prepared by rf sputtering of ceramic targets at an elevated oxygen partial pressure and at temperatures\\u000a below the ferroelectric and magnetic transition temperatures. It has been revealed using X-ray diffraction and Raman scattering\\u000a spectroscopy that, in these bismuth
Structure and lattice dynamics of heterostructures based on bismuth ferrite and barium strontium titanate on magnesium oxide substrates
Yu. I. Golovko; V. M. Mukhortov; O. A. Bunina; I. N. Zakharchenko; A. S. Anokhin; V. B. Shirokov; Yu. I. Yuzyuk
Bismuth ferrite films doped with neodymium on MgO single-crystal substrates with an epitaxial barium strontium titanate thin (1-2 nm) sublayer have been prepared by rf sputtering of ceramic targets at an elevated oxygen partial pressure and at temperatures below the ferroelectric and magnetic transition temperatures. It has been revealed using X-ray diffraction and Raman scattering spectroscopy that, in these bismuth
Deposition and Properties of Bismuth Strontium Calcium Copper Oxide Superconducting Thin Films
NASA Astrophysics Data System (ADS)
Dimeo, Frank, Jr.
The deposition of superconducting Bi-Sr-Ca-Cu -O thin films has been investigated using metalorganic chemical vapor deposition. For this purpose, a low pressure growth system was designed and built. Using the precursors, triphenyl bismuth, copper acetylacetonate, strontium hexafluoroacetylacetonate tetraglyme, and calcium hexafluoroacetylacetonate tetraglyme, superconducting epitaxial rm Bi_2Sr _2CaCu_2O_8 thin films have been deposited in situ. The addition of H_2 O to the oxygen reactant gas was necessary for the formation of the rm Bi_2Sr_2CaCu _2O_8 phase. The measured stability range for the deposition of the 2212 phase was between temperatures of 820 and 860^circC, at oxygen partial pressures greater than 9 Torr. X-ray diffraction (theta/2 theta and phi scan) measurements indicated that the films were epitaxial to the single crystal substrates LaAlO_3, NdGaO_3, and SrTiO _3. The surface morphology was investigated with SEM and AFM, and consisted of a dense platelet morphology. Individual platelets were several microns in size, and had surface roughnesses between 20-100A. There were significant step edges between platelets, however, ranging from 200-1000A. rm Bi_2Sr_2CaCu_2O _8 films on LaAlO_3 had T_{rm c}'s as high as 90 K, and J_{rm c} 's as high as rm1.9times10^7 A/cm^2 at 5 K. Films on NdGaO _3 had degraded superconducting properties due to contamination from the substrate and suffered from microcracking due to the lattice mismatch. A method for tailoring the electronic properties of the films through the substitution of Y for Ca was also developed, using yttrium dipivaloylmethanate as the source. With increasing Y content, the T_{rm c} was depressed. Insulating films were produced for Y = 0.54 formula units. The resistivity and thermopower behavior as a function of temperature and Y content was studied. The low temperature, T < 50 K, resistivity of insulating samples was found to exhibit variable range hopping behavior of the form, rho~ T^{b}exp(BT^ {-alpha}). The high temperature, T > 100, resistive behavior was analyzed using a narrow band model, consisting of a region of delocalized states surrounded by tails of localized states. This model predicted the resistive behavior of both insulating and superconducting films quite well. It was also found to predict the thermopower data for the superconducting films, although there was a discrepancy between the fitting parameters from the resistivity and those from the thermopower.
Influence of substrate geometry on the distribution and stress on Ge nanocrystals in silicon oxide matrix
Zheng, F. [Microelectronics Laboratory, Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 1176576 (Singapore); Choi, W. K. [Microelectronics Laboratory, Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 1176576 (Singapore); Advanced Materials for Micro- and Nano-Systems Programme, Singapore-MIT Alliance, National University of Singapore, 4 Engineering Drive 3, Singapore 1176576 (Singapore); Liew, T. H. [Advanced Materials for Micro- and Nano-Systems Programme, Singapore-MIT Alliance, National University of Singapore, 4 Engineering Drive 3, Singapore 1176576 (Singapore)
Synthesis of germanium (Ge) nanocrystals embedded in silicon oxide matrix was carried out on cosputtered Ge plus silicon oxide films deposited on the surface of silicon (Si) wafer etched with V- or U-grooves. The V- or U-grooves were fabricated via the laser interference lithography technique. We found that the substrate geometry has a significant influence on the distribution of the Ge nanocrystals in the silicon oxide matrix. The variation in the distribution of the nanocrystals in the silicon oxide matrix may be due to defective oxide regions caused by sputter deposited silicon oxide film on the V- or U-grooves or may also be related to the different strain fields in the oxide layer.
New perspectives on thermal and hyperthermal oxidation of silicon surfaces
NASA Astrophysics Data System (ADS)
Khalilov, Umedjon
The growth of (ultra)thin silica (SiO2) layers on crystalline silicon (c-Si) and controlling the thickness of SiO2 is an important issue in the fabrication of microelectronics and photovoltaic devices (e.g., MOSFETs, solar cells, optical fibers etc.). Such ultrathin oxide can be grown and tuned even at low temperature (including room temperature), by hyperthermal oxidation or when performed on non-planar Si surfaces (e.g., Si nanowires or spheres). However, hyperthermal silica growth as well as small Si-NW oxidation in general and the initial stages in particular have not yet been investigated in full detail. This work is therefore devoted to controlling ultrathin silica thickness on planar and non-planar Si surfaces, which can open new perspectives in nanodevice fabrication. The simulation of hyperthermal (1-100 eV) Si oxidation demonstrate that at low impact energy (<10 eV), oxygen does not damage the Si surface and this energy region could thus beneficially be used for Si oxidation. In contrast to thermal oxidation, 10 eV species can directly oxidize Si subsurface layers. A transition temperature of about 700 K was found: below this temperature, the oxide thickness only depends on the impact energy of the impinging species. Above this temperature, the oxide thickness depends on the impact energy, type of oxidant and the surface temperature. The results show that control over the ultrathin oxide (a-SiO2) thickness is possible by hyperthermal oxidation of silicon surfaces at temperatures below the transition temperature. In small Si-NWs, oxidation is a self-limiting process that occurs at low temperature, resulting in small Si core - SiO2 shell (semiconductor + dielectric) or c-Si|SiOx| a-SiO2 nanowire, which has also being envisaged to be used as nanowire field-effect transistors and photovoltaic devices in near-future nanotechnology. Above the transition temperature such core-shell nanowires are completely converted to a-SiO2 nanowires. It can be concluded that an accurate control over the interfacial stress by choosing a suitable oxidation temperature and Si-NW diameter can lead to precise nanoscale control over the Si-core radius. All investigations were carried out by applying molecular dynamics calculations using the ReaxFF potential, allowing a accurately study of the underpinning physical and chemical processes.
Oxidation of silicon surfaces by CO2 lasers
NASA Astrophysics Data System (ADS)
Boyd, I. W.; Wilson, J. I. B.
We report for the first time, the use of a focussed CO2 laser beam and a controlled oxygen atmosphere to induce localized oxidation on the surface of a silicon wafer. These thin oxide films have been compared by infrared spectrometry with thin furnace-grown layers. We conclude that the laser-grown oxides are compositionally similar to conventional layers, and can be described by the formula SiO2. In contrast the half-width of the Si-O stretching vibration at 1070 cm-1 was found to be consistently less than for furnace-grown oxides. By fabricating simple Al-SiO2-Si-Al diodes, the dielectric properties of the films have been studied.
Silver oxide nanostructure prepared on porous silicon for optoelectronic application
NASA Astrophysics Data System (ADS)
Hassan, Marwa Abdul Muhsien; Agool, Ibrahim Ramdan; Raoof, Lamyaa Mohammed
The thermal evaporation system type (Edwards) has been used to evaporate high purity (99.9 %) silver on glass, n- and p-type silicon and porous silicon substrates at room temperature under low pressure (about 10-6 torr) for different thickness (50, 75, 100, 125 and 150 nm). Using a rapid thermal oxidation of Ag film at oxidation temperature 350 ░C and different oxidation times, Ag2O thin film was prepared. The structural properties of Ag2O film were investigated and compared with other published results. The structural investigation showed that the films formed at thickness 100 nm showed (111) strong reflection along with weak reflections of (101) corresponding to the growth of single phase Ag2O with cubic structure. Dark and illuminated I-V of p-Ag2O/ p-Si, p-Ag2O/ n-Si, Al/ p-PSi/Al, Al/ n-PSi/Al, p-Ag2O/ p-PSi/c-Si and p-Ag2O/ n-PSi/c-Si heterojunction were investigated, discussed and prepared at optimum condition (oxidation temperature 350 ░C and 90 s oxidation time with thickness 100 nm). Ohmic contacts were fabricated by evaporating 99.999 purity silver wires for back and aluminum wires for front contact, respectively.
Silver oxide nanostructure prepared on porous silicon for optoelectronic application
NASA Astrophysics Data System (ADS)
Hassan, Marwa Abdul Muhsien; Agool, Ibrahim Ramdan; Raoof, Lamyaa Mohammed
The thermal evaporation system type (Edwards) has been used to evaporate high purity (99.9 %) silver on glass, n- and p-type silicon and porous silicon substrates at room temperature under low pressure (about 10-6 torr) for different thickness (50, 75, 100, 125 and 150 nm). Using a rapid thermal oxidation of Ag film at oxidation temperature 350 ░C and different oxidation times, Ag2O thin film was prepared. The structural properties of Ag2O film were investigated and compared with other published results. The structural investigation showed that the films formed at thickness 100 nm showed (111) strong reflection along with weak reflections of (101) corresponding to the growth of single phase Ag2O with cubic structure. Dark and illuminated I-V of p-Ag2O/p-Si, p-Ag2O/n-Si, Al/p-PSi/Al, Al/n-PSi/Al, p-Ag2O/p-PSi/c-Si and p-Ag2O/n-PSi/c-Si heterojunction were investigated, discussed and prepared at optimum condition (oxidation temperature 350 ░C and 90 s oxidation time with thickness 100 nm). Ohmic contacts were fabricated by evaporating 99.999 purity silver wires for back and aluminum wires for front contact, respectively.
Processing and Properties of Strontium Bismuth Vanadate Niobate Ferroelectric Ceramics
Cao, Guozhong
Processing and Properties of Strontium Bismuth Vanadate Niobate Ferroelectric Ceramics Yun Wu, Chau, microstructure, and dielectric properties of strontium bismuth niobate vanadate ceramics, SrBi2(VxNb1 x)2O9 (SBVN. Introduction RECENTLY, bismuth-oxide-layered perovskite materials, such as SrBi2Nb2O9 (SBN), SrBi2Ta2O9 (SBT
Ferroelectric and dielectric properties of strontium bismuth niobate vanadates
Cao, Guozhong
Ferroelectric and dielectric properties of strontium bismuth niobate vanadates Yun Wu and Guozhong 19 November 1999; accepted 20 April 2000) Strontium bismuth niobate vanadates, SrBi2(VxNb1-x)2O9 qualitatively different nondestructive read op- erations.3 Recently, bismuth oxide layered perovskite materials
Oxidation of silicon surface with atomic oxygen radical anions
NASA Astrophysics Data System (ADS)
Wang, Lian; Song, Chong-Fu; Sun, Jian-Qiu; Hou, Ying; Li, Xiao-Guang; Li, Quan-Xin
The surface oxidation of silicon (Si) wafers by atomic oxygen radical anions (O- anions) and the preparation of metal-oxide-semiconductor (MOS) capacitors on the O- -oxidized Si substrates have been examined for the first time. The O- anions are generated from a recently developed O- storage-emission material of [Ca24Al28O64]4+.4O-(C12A7-O- for short). After it has been irradiated by an O- anion beam (0.5 ?A/cm2) at 300░C for 1-10 hours, the Si wafer achieves an oxide layer with a thickness ranging from 8 to 32 nm. X-ray photoelectron spectroscopy (XPS) results reveal that the oxide layer is of a mixture of SiO2, Si2O3, and Si2O distributed in different oxidation depths. The features of the MOS capacitor of < Al electrode/SiOx/SI > are investigated by measuring capacitance-voltage (C ù V) and current-voltage (I ù V) curves. The oxide charge density is about 6.0 Î 1011 cm-2 derived from the C ù V curves. The leakage current density is in the order of 10-6A/cm2 below 4MV/cm, obtained from the I ù V curves. The O- anions formed by present method would have potential applications to the oxidation and the surface-modification of materials together with the preparation of semiconductor devices.
Study Trapped Charge Distribution in P-Channel Silicon-Oxide-Nitride-Oxide-Silicon Memory Device Using Dynamic Programming Scheme
NASA Astrophysics Data System (ADS)
Li, Fu-Hai; Chiu, Yung-Yueh; Lee, Yen-Hui; Chang, Ru-Wei; Yang, Bo-Jun; Sun, Wein-Town; Lee, Eric; Kuo, Chao-Wei; Shirota, Riichiro
In this study, we precisely investigate the charge distribution in SiN layer by dynamic programming of channel hot hole induced hot electron injection (CHHIHE) in p-channel silicon-oxide-nitride-oxide-silicon (SONOS) memory device. In the dynamic programming scheme, gate voltage is increased as a staircase with fixed step amplitude, which can prohibits the injection of holes in SiN layer. Three-dimensional device simulation is calibrated and is compared with the measured programming characteristics. It is found, for the first time, that the hot electron injection point quickly traverses from drain to source side synchronizing to the expansion of charged area in SiN layer. As a result, the injected charges quickly spread over on the almost whole channel area uniformly during a short programming period, which will afford large tolerance against lateral trapped charge diffusion by baking.
Optimization of amorphous silicon double junction solar cells for an efficient photoelectrochemical water splitting device based on a bismuth vanadate photoanode.
Han, Lihao; Abdi, Fatwa F; Perez Rodriguez, Paula; Dam, Bernard; van de Krol, Roel; Zeman, Miro; Smets, Arno H M
A photoelectrochemical water splitting device (PEC-WSD) was designed and fabricated based on cobalt-phosphate-catalysed and tungsten-gradient-doped bismuth vanadate (W:BiVO4) as the photoanode. A simple and cheap hydrogenated amorphous silicon (a-Si:H) double junction solar cell has been used to provide additional bias. The advantage of using thin film silicon (TF-Si) based solar cells is that this photovoltaic (PV) technology meets the crucial requirements for the PV component in PEC-WSDs based on W:BiVO4 photoanodes. TF-Si PV devices are stable in aqueous solutions, are manufactured by simple and cheap fabrication processes and their spectral response, voltage and current density show an excellent match with the photoanode. This paper is mainly focused on the optimization of the TF-Si solar cell with respect to the remaining solar spectrum transmitted through the W:BiVO4 photoanode. The current matching between the top and bottom cells is studied and optimized by varying the thickness of the a-Si:H top cell. We support the experimental optimization of the current balance between the two sub-cells with simulations of the PV devices. In addition, the impact of the light induced degradation of the a-Si:H double junction, the so-called Staebler-Wronski Effect (SWE), on the performance of the PEC-WSD has been studied. The light soaking experiments on the a-Si:H/a-Si:H double junctions over 1000 hours show that the efficiency of a stand-alone a-Si:H/a-Si:H double junction cell is significantly reduced due to the SWE. Nevertheless, the SWE has a significantly smaller effect on the performance of the PEC-WSD. PMID:24452785
Stripe width dependence of oxidation-enhanced diffusion in submicron local oxidation of silicon structures
NASA Astrophysics Data System (ADS)
Shibata, Yoshiaki; Taniguchi, Kenji; Hamaguchi, Chihiro
Oxidation enhanced diffusion (OED) of phosphorus under very narrow oxidized region is investigated. The OED effect is found to depend on the oxidized region width for below 4-5 ?m, i.e., the enhancement of phosphorus diffusivity decreases with decreasing the oxidized region width. In order to clarify the mechanism, two dimensional numerical simulations are carried out using various models for silicon self-interstitial generation at the Si/SiO2 interface during thermal oxidation. A series of OED observations is well simulated by using the new model in which the self-interstitial concentration at the oxidized interface is determined by the balance of (a) the interstitial generation due to oxidation reaction at the interface, (b) the kinetics of surface regrowth, and (c) the flux of interstitials into previously formed oxide. Effective surface regrowth rate constants for self-interstitials at the nonoxidized interface are then extracted. It is found that the surface regrowth rate constants in local oxidation of silicon structures are considerably large compared with those extracted from back side oxidation experiments.
Electric current generation in photorefractive bismuth silicon oxide without application of external electric field
NASA Astrophysics Data System (ADS)
Buchhave, Preben; Kukhtarev, Nickolai; Kukhtareva, Tatiana; Edwards, Matthew E.; Reagan, Michael A.; Lyuksyutov, Sergei F.
A holographic radial diffraction grating (HRDG) is an efficient optical element for splitting single laser beam on three 0, -1st, and +1st- diffraction order beams. The rotation of the grating at certain velocity allows a window for quality control over the frequency detuning between -1st, and +1st diffracted beams. The running interference fringes produced by the beams and projected on photorefractive crystal induce running holographic gratings in the crystal. This simple configuration is an effective tool for the study of such phenomena as space charge waves [1], domains motion [2], and electric current generation [3]. Specifics of photorefractive mechanism in cubic photorefractive crystals (BSO, BTO) normally require a use of external electric field to produce reasonable degree of refractive index modulation to observe associated with it phenomena. In this work we provide a direct experimental observation of the electric current generated in photorefractive BSO using running grating technique without an applied electric field. Moving interference fringes modulate a photoconductivity and an electric field in photorefractive crystal thus creating the photo electro-motive force (emf) and the current. The magnitude of the current varies between 1 and 10 nA depending on the rotation speed of HRDG. The peculiarities of the current behavior include a backward current flow, and current oscillations. The holographic current generated through this technique can find applications in non-destructive testing for ultra-sensitive vibrometry, materials characterization, and for motion sensors. References [1] S.F. Lyuksyutov, P. Buchhave, and M.V. Vasnetsov, Physical Review Letters, 79, No.1, 67-70 (1997) [2] P. Buchhave, S. Lyuksyutov, M. Vasnetsov, and C. Heyde, Journal Optical Society of America B, 13, No.11 2595-2602 (1996) [3] M. Vasnetsov, P. Buchhave, and S. Lyuksyutov Optics Communications, 137, 181-191 (1997)
Mid-infrared supercontinuum generation using lead-bismuth-gallium-oxide glass-based photonic crystal fibers pumped at 1560 nm
NASA Astrophysics Data System (ADS)
Sobo?, Grzegorz; Klimczak, Mariusz; Sotor, Jaroslaw; Krzempek, Karol; Pysz, Dariusz; Stepie?, Ryszard; Martynkien, Tadeusz; Dudzik, Grzegorz; Abramski, Krzysztof M.; Buczynski, Ryszard
In this work we present our results on supercontinuum (SC) generation using a photonic crystal fiber (PCF) fabricated from lead-bismuth-gallium-oxide glass (PBG-08). Due to high refractive index, high nonlinearity and high transmittance, the PBG-08 glass-based fibers seem to be excellent media for broad supercontinuum generation in the infrared spectral region. In our experiment, a short-length piece of PCF (6 cm) is pumped by a femtosecond fiber laser system, delivering 540 fs pulses at 60 MHz repetition rate and 2.75 W of maximum average power. This compact and cost-effective system allows to generate supercontinuum spanning from 900 to 2400 nm.
Investigation of PEMFC operation above 100 ░C employing perfluorosulfonic acid silicon oxide composite membranes
K. T Adjemian; S Srinivasan; J Benziger; A. B Bocarsly
Various perfluorosulfonic acid membranes (PFSAs) were studied as pure and silicon oxide composite membranes for operation in hydrogen\\/oxygen proton-exchange membrane fuel cells (PEMFCs) from 80 to 140░C. The composite membranes were prepared either by impregnation of pre-formed PFSAs via solûgel processing of a polymeric silicon oxide, recasting a film using solubilized PFSAs and a silicon oxide polymer\\/gel. All composite membranes
Nafion\\/Silicon oxide composite membrane for high temperature proton exchange membrane fuel cell
Jun Yu; Mu Pan; Runzhang Yuan
Nafion\\/Silicon oxide composite membranes were produced via in situ sol-gel reaction of tetraethylorthosilicate (TEOS) in Nafion membranes. The physicochemical properties of the membranes were\\u000a studied by FT-IR,TG-DSC and tensile strength. The results show that the silicon oxide is compatible with the Nafion membrane\\u000a and the thermo stability of Nafion\\/Silicon oxide composite membrane is higher than that of Nafion membrane. Furthermore,
Process to produce silicon carbide fibers using a controlled concentration of boron oxide vapor
NASA Technical Reports Server (NTRS)
Barnard, Thomas Duncan (Inventor); Lipowitz, Jonathan (Inventor); Nguyen, Kimmai Thi (Inventor)
A process for producing polycrystalline silicon carbide includes heating an amorphous ceramic fiber that contains silicon and carbon in an environment containing boron oxide vapor. The boron oxide vapor is produced in situ by the reaction of a boron containing material such as boron carbide and an oxidizing agent such as carbon dioxide, and the amount of boron oxide vapor can be controlled by varying the amount and rate of addition of the oxidizing agent.
Process to produce silicon carbide fibers using a controlled concentration of boron oxide vapor
NASA Technical Reports Server (NTRS)
Barnard, Thomas Duncan (Inventor); Lipowitz, Jonathan (Inventor); Nguyen, Kimmai Thi (Inventor)
A process for producing polycrystalline silicon carbide by heating an amorphous ceramic fiber that contains silicon and carbon in an environment containing boron oxide vapor. The boron oxide vapor is produced in situ by the reaction of a boron containing material such as boron carbide and an oxidizing agent such as carbon dioxide, and the amount of boron oxide vapor can be controlled by varying the amount and rate of addition of the oxidizing agent.
Atomic layer-deposited tunnel oxide stabilizes silicon photoanodes for water oxidation
Yi Wei Chen; Jonathan D. Prange; Simon D³hnen; Yohan Park; Marika Gunji; Christopher E. D. Chidsey; Paul C. McIntyre
A leading approach for large-scale electrochemical energy production with minimal global-warming gas emission is to use a renewable source of electricity, such as solar energy, to oxidize water, providing the abundant source of electrons needed in fuel synthesis. We report corrosion-resistant, nanocomposite anodes for the oxidation of water required to produce renewable fuels. Silicon, an earth-abundant element and an efficient
Enhanced photoelectrochemical water oxidation on bismuth vanadate by electrodeposition of amorphous titanium dioxide.
Eisenberg, David; Ahn, Hyun S; Bard, Allen J
n-BiVO4 is a promising semiconductor material for photoelectrochemical water oxidation. Although most thin-film syntheses yield discontinuous BiVO4 layers, back reduction of photo-oxidized products on the conductive substrate has never been considered as a possible energy loss mechanism in the material. We report that a 15 s electrodeposition of amorphous TiO2 (a-TiO2) on W:BiVO4/F:SnO2 blocks this undesired back reduction and dramatically improves the photoelectrochemical performance of the electrode. Water oxidation photocurrent increases by up to 5.5 times, and its onset potential shifts negatively by ?500 mV. In addition to blocking solution-mediated recombination at the substrate, the a-TiO2 film-which is found to lack any photocatalytic activity in itself-is hypothesized to react with surface defects and deactivate them toward surface recombination. The proposed treatment is simple and effective, and it may easily be extended to a wide variety of thin-film photoelectrodes. PMID:25243345
Method for removing oxide contamination from silicon carbide powders
Brynestad, J.; Bamberger, C.E.
The described invention is directed to a method for removing oxide contamination in the form of oxygen-containing compounds such as SiO/sub 2/ and B/sub 2/O/sub 3/ from a charge of finely divided silicon carbide. The silicon carbide charge is contacted with a stream of hydrogen fluoride mixed with an inert gas carrier such as argon at a temperature in the range of about 200/sup 0/ to 650/sup 0/C. The oxides in the charge react with the heated hydrogen fluoride to form volatile gaseous fluorides such as SiF/sub 4/ and BF/sub 3/ which pass through the charge along with unreacted hydrogen fluoride and the carrier gas. Any residual gaseous reaction products and hydrogen fluoride remaining in the charge are removed by contacting the charge with the stream of inert gas which also cools the powder to room temperature. The removal of the oxygen contamination by practicing the present method provides silicon carbide powders with desirable pressing and sintering characteristics. 1 tab.
Chemical vapor deposition of tungsten on silicon and silicon oxide studied with soft x-ray photoemission
NASA Astrophysics Data System (ADS)
Yarmoff', J. A.; McFeely, F. R.
The growth of tungsten films on silicon and oxidized silicon surfaces via the silicon reduction of WF6 was studied with soft x-ray photoemission. The films were grown in ultra-high vacuum and analyzed in situ. It was found that the growth on clean Si proceeds via diffusion of Si atoms through the W film to the surface, so that the silicon atoms become available for the reduction reaction. Post-fluorination of these films via XeF2 was performed in order to ascertain the structural details and to investigate further the role of fluorine in the growth process. Silicon oxide surfaces were prepared and subsequently exposed to WF6. It was found that a fully formed SiO2 surface is inert with respect to WF6, but that a partially formed oxide will permit partial WF6 dissociation.
Oxidation enhanced and concentration dependent diffusions of dopants in silicon
NASA Astrophysics Data System (ADS)
Matsumoto, Satoru; Ishikawa, Yutaka; Niimi, Tatsuya
Diffusions of impurities in silicon under oxidizing ambient and under extrinsic conditions have been analyzed by developing the Hu's model. The general expression of diffusion coefficient, which includes both the vacancy and interstitialcy mechanisms, is used. The temperature dependences of a fraction of interstitialcy mechanism for arsenic fAs, phosphorus fP, and boron fB are obtained from the data of oxidation enhanced diffusion (OED) and oxidation induced stacking faults. fAs =42 exp(-0.542/kT), fP =156 exp(-0.666/kT), and fB =860 exp(-0.829/kT). Time dependence of OED and the concentration dependence of the diffusion coefficient of arsenic and boron under extrinsic conditions can be explained by this model.
In situ imaging of the conducting filament in a silicon oxide resistive switch
Yao, Jun; Zhong, Lin; Natelson, Douglas; Tour, James M.
The nature of the conducting filaments in many resistive switching systems has been elusive. Through in situ transmission electron microscopy, we image the real-time formation and evolution of the filament in a silicon oxide resistive switch. The electroforming process is revealed to involve the local enrichment of silicon from the silicon oxide matrix. Semi-metallic silicon nanocrystals with structural variations from the conventional diamond cubic form of silicon are observed, which likely accounts for the conduction in the filament. The growth and shrinkage of the silicon nanocrystals in response to different electrical stimuli show energetically viable transition processes in the silicon forms, offering evidence for the switching mechanism. The study here also provides insights into the electrical breakdown process in silicon oxide layers, which are ubiquitous in a host of electronic devices. PMID:22355755
Optical gain in dye-impregnated oxidized porous silicon waveguides
NASA Astrophysics Data System (ADS)
Oton, C. J.; Navarro-Urrios, D.; Capuj, N. E.; Ghulinyan, M.; Pavesi, L.; Gonzßlez-PÚrez, S.; Lahoz, F.; MartÝn, I. R.
Positive optical gain under pulsed excitation in oxidized porous silicon planar waveguides impregnated with Nile blue (LC 6900) is reported. Amplified spontaneous emission measurements show a dramatic line narrowing when the pump energy is increased, together with a strong superlinear behavior. Variable stripe length measurements were performed to characterize quantitatively the amplification, and an unambiguous transition from losses to gain is observed with a threshold of ÿ3mJ/cm2 at 700nm. A maximum gain coefficient of 8.7cm-1 (ÿ40dB/cm) is reported. Shifting excitation spot measurements confirm the reliability of our results. This system is interesting in view of an optically pumped silicon-based pulsed laser.
Thermal oxidation of 3C silicon carbide single-crystal layers on silicon
NASA Technical Reports Server (NTRS)
Fung, C. D.; Kopanski, J. J.
Thermal oxidation of thick single-crystal 3C SiC layers on silicon substrates was studied. The oxidations were conducted in a wet O2 atmosphere at temperatures from 1000 to 1250 C for times from 0.1 to 50 h. Ellipsometry was used to determine the thickness and index of refraction of the oxide films. Auger analysis showed them to be homogeneous with near stoichiometric composition. The oxide growth followed a linear parabolic relationship with time. Activation energy of the parabolic rate constant was found to be 50 kcal/mole, while the linear rate constant was 74 kcal/mole. The latter value corresponds approximately to the energy required to break a Si-C bond. Electrical measurements show an effective density of 4-6 x 10 to the 11th per sq cm for fixed oxide charges at the oxide-carbide interface, and the dielectric strength of the oxide film is aproximately 6 x 10 to the 6th V/cm.
Optical stimulated thermoluminescence in silicon rich oxide nanostructured films
NASA Astrophysics Data System (ADS)
Berman-Mendoza, D.; Aceves-Mijares, M.; Piters, T.; GarcÝa-GutiÚrrez, R.; Ruiz-Valdez, C. F.; Ramos-Carrasco, A.; Berriel-Valdos, L. R.
In this work, it is study thermoluminescent phenomena (TL) optically stimulated with UV radiation in Silicon Rich Oxide (SRO) nanostructured thin films. The experimental samples used were thin films of this composite deposited by Low Pressure Chemical Vapor Deposition (LPCVD) over a n-type silicon substrate, this samples were fabricated using different flow ratios of precursory gases silane and nitrous oxide R0=SiH4/N2O during the deposition and were given posterior thermal treatment which gave place to the formation of different sized nanoparticles, that are attributed to the luminescent activation mechanism in this material. The silicon excess was controlled by the ratio of the gases used in the deposition process and in this way SRO films with 12, 8 and 6% silicon excess were obtained. The glow-curves experimentally obtained were submitted to analysis using different models in order to obtain important thermoluminescent parameters. The luminescence spectra of SRO show two wavelength regions of emission; one in the blue part and one in the red part of the emission spectrum. The emission in the blue part is related to defects in the SiO lattice. About the origin of the red luminescence there is still a controversy. One model assumes that the red luminescence stems from Si nano particles and another model assumes that defects at the interface of SiO bulk with the Si nano particle are responsible for the red luminescence. Finally is intended to provide favorable conditions for the development of a UV dosimeter with this material.
Electrical characteristics of nanoscale NAND silicon-oxide-nitride-oxide-silicon flash memory devices fabricated on SOI substrates.
Ryu, Ju Tae; You, Joo Hyung; Yoo, Keon-Ho; Kim, Tae Whan
NAND silicon-oxide-nitride-oxide-silicon (SONOS) flash memory devices with double gates fabricated on silicon-on-insulator (SOI) substrates were proposed. The current-voltage characteristics related to the programming operation of the designed nanoscale NAND SONOS flash memory devices on a SOI substrate and on the conventional bulk-Si substrate were simulated and compared in order to investigate device characteristics of the scaled-down memory devices. The simulation results showed that the short channel effect and the subthreshod leakage current for the memory device with a large spacer length were lower than that of the memory device with a small spacer length due to increase of the effective channel length. The device performance of the memory device utilizing the SOI substrate exhibited a smaller subthreshold swing and a larger drain current level in comparison with those on the bulk-Si substrate. These improved electrical characteristices for the SOI devices could be explained by comparing the electric field distribution in a channel region for both devices. PMID:22103232
Origin of complex impact craters on native oxide coated silicon surfaces
Samela, Juha; Nordlund, Kai; Popok, Vladimir N.; Campbell, Eleanor E. B. [Department of Physics, University of Helsinki, P.O. Box 43, FI-00014 Espoo (Finland); Department of Physics, Gothenburg University, 41296 Gothenburg (Sweden); Department of Physics, Gothenburg University, 41296 Gothenburg, Sweden and School of Chemistry, Edinburgh University, West Mains Road, Edinburgh EH9 3JJ, Scotland (United Kingdom)
Crater structures induced by impact of keV-energy Ar{sub n}{sup +} cluster ions on silicon surfaces are measured with atomic force microscopy. Complex crater structures consisting of a central hillock and outer rim are observed more often on targets covered with a native silicon oxide layer than on targets without the oxide layer. To explain the formation of these complex crater structures, classical molecular dynamics simulations of Ar cluster impacts on oxide coated silicon surfaces, as well as on bulk amorphous silica, amorphous Si, and crystalline Si substrates, are carried out. The diameter of the simulated hillock structures in the silicon oxide layer is in agreement with the experimental results, but the simulations cannot directly explain the height of hillocks and the outer rim structures when the oxide coated silicon substrate is free of defects. However, in simulations of 5 keV/atom Ar{sub 12} cluster impacts, transient displacements of the amorphous silicon or silicon oxide substrate surfaces are induced in an approximately 50 nm wide area surrounding the impact point. In silicon oxide, the transient displacements induce small topographical changes on the surface in the vicinity of the central hillock. The comparison of cluster stopping mechanisms in the various silicon oxide and silicon structures shows that the largest lateral momentum is induced in the silicon oxide layer during the impact; thus, the transient displacements on the surface are stronger than in the other substrates. This can be a reason for the higher frequency of occurrence of the complex craters on oxide coated silicon.
Understanding the role of silicon oxide shell in oxide-assisted SiNWs growth
Wu, Shunqing [Ames Laboratory; Wang, Cai-Zhuang Z [Ames Laboratory; Zhu, Z Z [Xiamen University; Ho, Kai-Ming [Ames Laboratory
The role of silicon oxide shell in oxide-assisted SiNWs growth is studied by performing ab initio molecular dynamics simulations on the structural and dynamical properties of the interface between crystalline Si(111) surface and disorder SiO thin film. Si atoms in the SiO film tends to aggregate into the vicinity of the Si(111)/SiO interface. In addition, the diffusion of Si atoms at the interface is anisotropic - the diffusion along the interface is several times faster than that perpendicular to the interface. The segregation and anisotropic diffusion of Si atoms at the Si(111)/SiO interface shed interesting light into the mechanism of oxide-assisted silicon nanowire growth.
Assessment of cytotoxicity and oxidative effect of Bismuth Ferrite (BFO) harmonic nanoparticles for localized DNA photo-interaction
NASA Astrophysics Data System (ADS)
Staedler, Davide; Magouroux, Thibaud; Passemard, SolÞne; Ciepielewski, Daniel; Gerber-Lemaire, Sandrine; Wolf, Jean-Pierre; Bonacina, Luigi
Bismuth Ferrite nanoparticles have been recently used to selectively interact with malignant cell DNA via in situ generated second harmonic in a novel theranostics protocol [Nanoscale 6(5), pp. 2929, 2014]. In this report, we extend the screening of biocompatibility of BFO uncoated uncoated nanoparticles and assess the nanoparticle- mediated production of reactive oxygen species as a function of excitation wavelength.
Enhanced room temperature oxidation in silicon and porous silicon under 10 keV x-ray irradiation
NASA Astrophysics Data System (ADS)
Ryckman, Judson D.; Reed, Robert A.; Weller, Robert A.; Fleetwood, D. M.; Weiss, S. M.
We report the observation of enhanced oxidation on silicon and porous silicon samples exposed in air ambient to high-dose-rate 10 keV x-ray radiation at room temperature. The evolution of the radiation-induced oxide growth is monitored by ellipsometry and interferometric reflectance spectroscopy. Fourier transform infrared (FTIR) spectroscopy shows the emergence of Si-O-Si stretching modes and corresponding suppression of SiHx and Si-Si modes in the porous silicon samples. The radiation response depends strongly on initial native oxide thickness and Si-H surface species. The enhanced oxidation mechanism is attributed to photoinduced oxidation processes wherein energetic photons are used to dissociate molecular oxygen and promote the formation of more reactive oxygen species.
Enhanced room temperature oxidation in silicon and porous silicon under 10 keV x-ray irradiation
Ryckman, Judson D.; Reed, Robert A.; Weller, Robert A.; Fleetwood, D. M.; Weiss, S. M. [Department of Electrical Engineering and Computer Science, Vanderbilt University, Nashville, Tennessee 37235 (United States)
We report the observation of enhanced oxidation on silicon and porous silicon samples exposed in air ambient to high-dose-rate 10 keV x-ray radiation at room temperature. The evolution of the radiation-induced oxide growth is monitored by ellipsometry and interferometric reflectance spectroscopy. Fourier transform infrared (FTIR) spectroscopy shows the emergence of Si-O-Si stretching modes and corresponding suppression of SiH{sub x} and Si-Si modes in the porous silicon samples. The radiation response depends strongly on initial native oxide thickness and Si-H surface species. The enhanced oxidation mechanism is attributed to photoinduced oxidation processes wherein energetic photons are used to dissociate molecular oxygen and promote the formation of more reactive oxygen species.
Study of the processes of carbonization and oxidation of porous silicon by Raman and IR spectroscopy
Vasin, A. V.; Okholin, P. N.; Verovsky, I. N.; Nazarov, A. N.; Lysenko, V. S. [National Academy of Sciences of Ukraine, Lashkaryov Institute of Semiconductor Physics (Ukraine); Kholostov, K. I., E-mail: email@example.com; Bondarenko, V. P. [Belarusian State University of Informatics and Radio Electronics (Belarus); Ishikawa, Y. [Japan Fine Ceramics Center (Japan)
Porous silicon layers were produced by electrochemical etching of single-crystal silicon wafers with the resistivity 10 {Omega} cm in the aqueous-alcohol solution of hydrofluoric acid. Raman spectroscopy and infrared absorption spectroscopy are used to study the processes of interaction of porous silicon with undiluted acetylene at low temperatures and the processes of oxidation of carbonized porous silicon by water vapors. It is established that, even at the temperature 550 Degree-Sign C, the silicon-carbon bonds are formed at the pore surface and the graphite-like carbon condensate emerges. It is shown that the carbon condensate inhibits oxidation of porous silicon by water vapors and contributes to quenching of white photoluminescence in the oxidized carbonized porous silicon nanocomposite layer.
Silicon Wafer Direct Bonding without Hydrophilic Native Oxides
NASA Astrophysics Data System (ADS)
Himi, Hiroaki; Matsui, Masaki; Fujino, Seiji; Hattori, Tadashi
Silicon wafer direct bonding was accomplished between two surfaces which had no hydrophilic native oxide layers. Prior to bonding, two wafers were dipped in conc-HF solution ( ÿ49% aq.) to remove the native oxide layers and then immersed in deionized water. The level of bonding was evaluated by X-ray topography, high resolution transmission electron microscopy (HRTEM) and tensile strength measurement. It was found that the bonded wafer pairs were void-free and had good bonding strength. HRTEM observation showed that the crystal lattice was continuous and had only small distortions and precipitates. Spreading resistance (SR) measurement across the interface showed that the electric resistance did not increase at the bonding interface. It is suggested that the OH groups which substitute the F atoms terminated on the small portion of the surface play an important role in this conc-HF-treated bonding.
Oxide impurities in silicon oxide intermetal dielectrics and their potential to elevate via-resistances.
Qin, Wentao; Alldredge, Donavan; Heleotes, Douglas; Elkind, Alexander; Theodore, N David; Fejes, Peter; Vadipour, Mostafa; Godek, Bill; Lerner, Norman
Silicon oxide used as an intermetal dielectric (IMD) incorporates oxide impurities during both its formation and subsequent processing to create vias in the IMD. Without a sufficient degassing of the IMD, oxide impurities released from the IMD during the physical vapor deposition (PVD) of the glue layer of the vias had led to an oxidation of the glue layer and eventual increase of the via resistances, which correlated with the O-to-Si atomic ratio of the IMD being ~10% excessive as verified by transmission electron microscopy (TEM) analysis. A vacuum bake of the IMD was subsequently implemented to enhance outgassing of the oxide impurities in the IMD before the glue layer deposition. The implementation successfully reduced the via resistances to an acceptable level. PMID:24821584
Transparent conductive oxides for thin-film silicon solar cells
NASA Astrophysics Data System (ADS)
L÷ffler, J.
This thesis describes research on thin-film silicon solar cells with focus on the transparent conductive oxide (TCO) for such devices. In addition to the formation of a transparent and electrically conductive front electrode for the solar cell allowing photocurrent collection with low ohmic losses, the front TCO plays an important role for the light enhancement of thin-film silicon pin type solar cells. If the TCO is rough, light scattering at rough interfaces in the solar cell in combination with a highly reflective back contact leads to an increase in optical path length of the light. Multiple (total) internal reflectance leads to virtual 'trapping' of the light in the solar cell structure, allowing a further decrease in absorber thickness and thus thin-film silicon solar cell devices with higher and more stable efficiency. Here, the optical mechanisms involved in the light trapping in thin-film silicon solar cells have been studied, and two types of front TCO materials have been investigated with respect to their suitability as front TCO in thin-film silicon pin type solar cells. Undoped and aluminum doped zinc oxide layers have been fabricated for the first time by the expanding thermal plasma chemical vapour deposition (ETP CVD) technique at substrate temperatures between 150 ║ C and 350 ║ C, and successfully implemented as a front electrode material for amorphous silicon pin superstrate type solar cells. Solar cells with efficiencies comparable to cells on Asahi U-type reference TCO have been reproducibly obtained. A higher haze is needed for the ZnO samples studied here than for Asahi U-type TCO in order to achieve comparable long wavelength response of the solar cells. This is attributed to the different angular distribution of the scattered light, showing higher scattering intensities at large angles for the Asahi U-type TCO. A barrier at the TCO/p interface and minor collection problems may explain the slightly lower fill factors obtained for the cells on ETP ZnO. The solar cells deposited on the first doped ZnO:Al layers suffered from collection problems reducing the fill factor, and from shunting. This is attributed to the steep trenches, sharp features and vertical steps that have been identified at the TCO surface. ZnO:Al layers with granular structure, deposited at higher argon flow through the cascaded arc plasma source, allowed for fill factors of the solar cells up to 0.70, comparable to cells on undoped ZnO. The best solar cell on doped ZnO:Al deposited by ETP CVD achieved an efficiency of 9.3 % which is comparable to the 9.4 % obtained on Asahi U-type SnO2:F. Fluorinated tin oxide has been deposited by Atmospheric Chemical Vapor Deposition (APCVD) on glass from three different tin precursors, tetramethyltin, monobutyltin trichloride, and tin tetrachloride (TTC). TTC is the Sn precursor which resulted in the TCO with the best performance of a-Si:H pin solar cells. In accordance with the conclusions from our experiments with solar cells on undoped and aluminum doped zinc oxide, a high surface roughness and haze do not necessarily lead to a lower diode quality, and vice versa.
Hole-blocking titanium-oxide/silicon heterojunction and its application to photovoltaics
1:100 hydrofluoric acid etch to hydrogen-passivate the sur- face.10 The titanium dioxideHole-blocking titanium-oxide/silicon heterojunction and its application to photovoltaics Sushobhan-bandgap semiconducting heterojunctions on silicon. Here, we present a wide-bandgap heterojunction--between titanium oxide
A room temperature method for the formation of ultrathin silicon oxide films
Richard John Muisener
Growing interest surrounds the use of thin films to impart unique surface properties without adversely affecting those of the bulk. One such example is the formation of a stable high-energy silicon oxide surface on polymers. Thin silicon oxide films have been used to tailor the surface properties of many materials. Conventional methods for SiOx film fabrication such as chemical vapor
Effect of the silicon/oxide interface on interstitials: Di-interstitial recombination
Florida, University of
Effect of the silicon/oxide interface on interstitials: Di-interstitial recombination M. E. Law recombine at an oxide/silicon interface. Previous experimental work produces contradictory results. Transient enhanced diffusion experiments suggest a nearly infinite surface recombination rate, while
Properties of aluminum oxide and aluminum oxide alloys and their interfaces with silicon and silicon dioxide
Robert Shawn Johnson
A remote plasma enhanced chemical vapor deposition method, RPECVD, was utilized to deposit thin films of aluminum oxide, tantalum oxide, tantalum aluminates, and hafnium aluminates. These films were analyzed using auger electron spectroscopy, AES, Fourier transform infrared spectroscopy, FTIR, X-ray diffraction, XRD, nuclear resonance profiling, NRP, capacitance versus voltage, C-V, and current versus voltage, J-V. FTIR indicated the alloys were
A new bismuth potassium nitrate oxide, Bi 1.7K 0.9O 2(NO 3) 2: Synthesis, structure, thermal behavior, and photocatalytic properties
NASA Astrophysics Data System (ADS)
Shenawi-Khalil, S.; Uvarov, V.; Charkin, D. O.; Goaz, A.; Popov, I.; Dolgikh, V. A.; Sasson, Y.
We report here the first observation of a bismuth potassium nitrate Bi 1.7K 0.9O 2(NO 3) 2, obtained via thermal decomposition of bismuth and potassium nitrate mixtures. The new compound is orthorhombic, space group Immm (71), Z = 2, with a = 3.8698(7) ┼, b = 3.8703(7) ┼, and c = 24.1271(4) ┼. Its crystal structure was refined from powder X-ray diffraction data by analogy with the mineral beyerite, Bi 2O 2Ca(CO 3) 2. The morphology and elemental composition of Bi 1.7K 0.9O 2(NO 3) 2 were characterized using scanning electron microscopy (SEM) with energy dispersive X-Ray spectroscopy (EDS). Its phase transformations upon heating and products of its thermal decomposition were studied using XRD, TGA and FTIR. At 440 ░C, Bi 1.7K 0.9O 2(NO 3) 2 transforms to another basic bismuth potassium nitrate with demonstrates a very similar XRD pattern but slightly larger cell parameters. At 520 ░C, the intermediate oxide nitrate decomposes into a mixture of crystalline ?-Bi 2O 3 and KNO 3. The as prepared Bi 1.7K 0.9O 2(NO 3) 2 showed lower than TiO 2 (Degussa P25) photocatalytic activity upon decomposition of a widely used model pollutant, Rhodamine B (RhB) and photooxidation of potassium iodide under UV-vis light irradiation. Interaction with potassium iodide in alkaline media resulted in formation of Bi 5O 7I.
Low temperature sintering of nanosized ceramic powder: YSZ-bismuth oxide system
NASA Astrophysics Data System (ADS)
Kim, Hyungchan
In this study, the mechanism of sintering and kinetics of nanosized YSZ powder in the presence of Bi2O3 were investigated. The sintering mechanism of YSZ-Bi2O3 system has not been understood well. It has been supposed that liquid phase sintering is main mechanism at temperatures 900░C or higher because Bi2O 3 melts at 825░C. However, the results of the present study indicate that this is not true and that the observed sintering enhancement by Bi 2O3 is entirely due to some solid state mechanism (at least for systems with less than about 5 mole% Bi2O3). A new mechanism termed "stress assisted rearrangement sintering" (STARS) is proposed. STARS occurs when several conditions are met simultaneously. The first condition is the dissolution of Bi2O3 in YSZ. The dissolution of Bi2O3 is associated with a large increase in the concentration of oxygen ion vacancies. The concentration of vacancies is especially large on the surface of the crystallites. This highly defective surface has a high surface mobility. The second condition is the precipitation of monoclinic ZrO2. An additional driving force besides high surface energy of starting nanosized YSZ powder for densification comes from the large stresses caused by the inter-granular precipitation of ZrO2. The third condition is the inhibition of YSZ crystallite growth. The inter-crystallite ZrO 2 precipitates also act as Zener barriers preventing further growth of crystallites. Thus the driving force is not dissipated by coarsening and is used exclusively for densification process. STARS does not occur at higher amounts (>about 5 mole%) of Bi2O 3 because the system composition moves out of the two phase region and into a 3-phase region containing a Bi-rich liquid phase at the sintering temperature. In this situation, liquid phase sintering dominates. Bi2O 3-rich liquid phase forms during heating at about 850░C. Significant growths of crystallites and of composite grains are observed in this region. The overall porosity of YSZ-Bi2O3 system after STARS is controlled by the residual macropores formed by the large size of the initial Bi2O3 particles. Bi2O3 dissolves in YSZ leaving behind micronsize pores (macropores). These pores are removed very slowly only in the final stages of sintering. The ionic conductivity of YSZ-4.5 mole% Bi2O3 sample sintered at 900░C for 1 hour is measured to be about two times higher than that of pure YSZ sintered at 1500░C for 1 hour. The reason for the higher conductivity in YSZ-4.5 mole% Bi2O3 is because of increased concentration of oxygen ion vacancies. This indicates that STARS may be an efficient way to sinter the YSZ electrolyte used in solid oxide fuel cells at low temperatures without loss of ionic conductivity.
Atomic layer-deposited tunnel oxide stabilizes silicon photoanodes for water oxidation
NASA Astrophysics Data System (ADS)
Chen, Yi Wei; Prange, Jonathan D.; D³hnen, Simon; Park, Yohan; Gunji, Marika; Chidsey, Christopher E. D.; McIntyre, Paul C.
A leading approach for large-scale electrochemical energy production with minimal global-warming gas emission is to use a renewable source of electricity, such as solar energy, to oxidize water, providing the abundant source of electrons needed in fuel synthesis. We report corrosion-resistant, nanocomposite anodes for the oxidation of water required to produce renewable fuels. Silicon, an earth-abundant element and an efficient photovoltaic material, is protected by atomic layer deposition (ALD) of a highly uniform, 2?nm thick layer of titanium dioxide (TiO2) and then coated with an optically transmitting layer of a known catalyst (3?nm iridium). Photoelectrochemical water oxidation was observed to occur below the reversible potential whereas dark electrochemical water oxidation was found to have low-to-moderate overpotentials at all pH values, resulting in an inferred photovoltage of ~550?mV. Water oxidation is sustained at these anodes for many hours in harsh pH and oxidative environments whereas comparable silicon anodes without the TiO2 coating quickly fail. The desirable electrochemical efficiency and corrosion resistance of these anodes is made possible by the low electron-tunnelling resistance (<0.006???cm2 for p+-Si) and uniform thickness of atomic-layer deposited TiO2.
Oxidation effects on graded porous silicon anti-reflection coatings
Th°gersen, Annett; Marstein, Erik S; 10.1149/2.jes113659
Efficient anti-reflection coatings (ARC) improve the light collection and thereby increase the current output of solar cells. By simple electrochemical etching of the Si wafer, porous silicon (PS) layers with excellent broadband anti-reflection properties can be fabricated. In this work, ageing of graded PS has been studied using Spectroscopic Ellipsometry, Transmission Electron Microscopy and X-ray Photoelectron Spectroscopy. During oxidation of PS elements such as pure Si (Si$^0$), Si$_2$O (Si$^+$), SiO (Si$^{2+}$), Si$_2$O$_3$ (Si$^{3+}$), and SiO$_2$ (Si$^{4+}$) are present. In addition both hydrogen and carbon is introduced to the PS in the form of Si$_3$SiH and CO. The oxide grows almost linearly with time when exposed to oxygen, from an average thickness of 0 - 3.8 nm for the surface PS. The oxidation is then correlated to the optical stability of multi-layered PS ARCs. It is found that even after extensive oxidation, the changes in the optical properties of the PS structures are small.
Nanoscale two-bit/cell NAND silicon-oxide-nitride-oxide-silicon devices with a separated double-gate saddle-type structure.
Park, Sang Su; You, Joo Hyung; Kwack, Kae Dal; Kim, Tae Whan
Nanoscale two-bit/cell NAND silicon-oxide-nitride-oxide-silicon flash memory devices based on a separated double-gate (SDG) saddle structure with a recess channel region had two different doping regions in silicon-fin channel to operate two-bit per cell. A simulation results showed that the short channel effect, the cross-talk problem between cells, and the increase in threshold voltage distribution were minimized, resulting in the enhancement of the scaling-down characteristics and the program/erase speed. PMID:21456183
Novel synthetic methodology for controlling the orientation of zinc oxide nanowires grown on silicon oxide substrates
NASA Astrophysics Data System (ADS)
Cho, Jinhyun; Salleh, Najah; Blanco, Carlos; Yang, Sungwoo; Lee, Chul-Jin; Kim, Young-Woo; Kim, Jungsang; Liu, Jie
This study presents a simple method to reproducibly obtain well-aligned vertical ZnO nanowire arrays on silicon oxide (SiOx) substrates using seed crystals made from a mixture of ammonium hydroxide (NH4OH) and zinc acetate (Zn(O2CCH3)2) solution. In comparison, high levels of OH- concentration obtained using NaOH or KOH solutions lead to incorporation of Na or K atoms into the seed crystals, destroying the c-axis alignment of the seeds and resulting in the growth of misaligned nanowires. The use of NH4OH eliminates the metallic impurities and ensures aligned nanowire growth in a wide range of OH- concentrations in the seed solution. The difference of crystalline orientations between NH4OH- and NaOH-based seeds is directly observed by lattice-resolved images and electron diffraction patterns using a transmission electron microscope (TEM). This study obviously suggests that metallic impurities incorporated into the ZnO nanocrystal seeds are one of the factors that generates the misaligned ZnO nanowires. This method also enables the use of silicon oxide substrates for the growth of vertically aligned nanowires, making ZnO nanostructures compatible with widely used silicon fabrication technology.This study presents a simple method to reproducibly obtain well-aligned vertical ZnO nanowire arrays on silicon oxide (SiOx) substrates using seed crystals made from a mixture of ammonium hydroxide (NH4OH) and zinc acetate (Zn(O2CCH3)2) solution. In comparison, high levels of OH- concentration obtained using NaOH or KOH solutions lead to incorporation of Na or K atoms into the seed crystals, destroying the c-axis alignment of the seeds and resulting in the growth of misaligned nanowires. The use of NH4OH eliminates the metallic impurities and ensures aligned nanowire growth in a wide range of OH- concentrations in the seed solution. The difference of crystalline orientations between NH4OH- and NaOH-based seeds is directly observed by lattice-resolved images and electron diffraction patterns using a transmission electron microscope (TEM). This study obviously suggests that metallic impurities incorporated into the ZnO nanocrystal seeds are one of the factors that generates the misaligned ZnO nanowires. This method also enables the use of silicon oxide substrates for the growth of vertically aligned nanowires, making ZnO nanostructures compatible with widely used silicon fabrication technology. Electronic supplementary information (ESI) available: Additional SEM images, photographs of seed solution and XRD peaks and XPS. See DOI: 10.1039/c3nr03694d
Atomistic modeling of bending properties of oxidized silicon nanowires
Ilinov, Andrey, E-mail: firstname.lastname@example.com; Kuronen, Antti [Department of Physics, University of Helsinki, P.O. Box 43, FIN-00014 Helsinki (Finland)
In this work, we have modeled a three point bending test of monocrystalline Si nanowires using molecular dynamics simulations in order to investigate their elastic properties. Tested nanowires were about 30?nm in length and had diameters from 5 to 9?nm. To study the influence of a native oxide layer, nanowires were covered with a 1?nm thick silica layer. The bending force was applied by a carbon diamond half-sphere with a 5?nm diameter. The Si-O parametrization for the Tersoff potential was used to describe atomic interactions between Si and O atoms. In order to remove the indentation effect of the diamond half-sphere and to obtain a pure bending behavior, we have also performed a set of simulations with fixed bottoms of the nanowires. Our results show that the oxide layer reduces the nanowire stiffness when compared with a pure Si nanowire with the same number of silicon atomsùin spite of the fact that the oxidized nanowires had larger diameters.
Synthesis of Silicon and Zinc Oxide Nanowhiskers and Studies of Their Properties
NASA Astrophysics Data System (ADS)
Gorbyk, P. P.; Dubrovin, I. V.; Dadykin, A. A.; Demchenko, Yu. A.
The conditions and mechanisms for purposeful pattern formation on the surface of single-crystal silicon wafers by building up silicon or zinc oxide by the vapor-liquid-crystal (VLC) mechanism were studied. For the polished silicon surface we developed a procedure for preparation of areas with randomly distributed nanosized gold metal particles - whisker growth initiators. The arrays of randomly distributed silicon and zinc oxide whiskers were grown. The emission cells with a pointed surface pattern were fabricated. The morphology, structure, and field electron emission properties of the fabricated structures were studied.
Endurance and Data Retention Improvement of Silicon-Oxide-Nitride-Oxide-Silicon Nonvolatile Semiconductor Memory Devices with Partially Bottom-Silicon-Rich Nitride Structure
NASA Astrophysics Data System (ADS)
Chien, Hua-Ching; Wu, Kuo-Hong; Chang, Jui-Wen; Kao, Chin-Hsing; Chen, Tung-Sheng
A significant reliability improvement in silicon-oxide-nitride-oxide-silicon (SONOS) flash memory devices by band-gap engineering of the nitride layer has been attained. The gradually varied reaction gas flow rate during deposition has generated special nitride films with non uniform composition profiles and band gaps. As a result, SONOS devices with partially Si-rich nitride structures have exhibited superior cycling endurance, radiation hardness, and data retention compared with devices with a uniform standard nitride. The marked improvement can be attributed to the increased charge-trapping/detrapping efficiency of the nitride layer since a significant number of highly accessible trapping levels have been created in the nitride that has a graded band gap. In addition, the deepened barrier heights between the nitride and its surrounding oxides may also reduce undesirable charge-loss probability and assist in charge storage. Because the dimension of flash memory cells is continuously shrinking, the proposed technique will be valuable for mass storage applications.
Investigation of PEMFC operation above 100 ░C employing perfluorosulfonic acid silicon oxide composite membranes
NASA Astrophysics Data System (ADS)
Adjemian, K. T.; Srinivasan, S.; Benziger, J.; Bocarsly, A. B.
Various perfluorosulfonic acid membranes (PFSAs) were studied as pure and silicon oxide composite membranes for operation in hydrogen/oxygen proton-exchange membrane fuel cells (PEMFCs) from 80 to 140 ░C. The composite membranes were prepared either by impregnation of pre-formed PFSAs via sol-gel processing of a polymeric silicon oxide, recasting a film using solubilized PFSAs and a silicon oxide polymer/gel. All composite membranes had a silicon oxide content of less than or equal to 10% by weight. Decreasing the equivalent weight and thickness of the PFSAs, in addition to the incorporation of silicon oxide helped improve water management in a PEMFC at elevated temperatures. Fourier transform-infrared spectroscopy-attenuated total reflectance (FT-IR-ATR), and scanning electron microscopy (SEM) experiments indicated an evenly distributed siloxane polymer in all of the composite membranes. At a potential of 0.4 V the Aciplex 1004/silicon oxide composite membrane in a humidified H 2/O 2 PEMFC at 130 ░C and a pressure of 3 atm delivered six times higher current density than unmodified Nafion 115 under the same conditions, and 1.73 times the current density when unmodified Nafion 115 was operated with humidified gases at 80 ░C and 1 atm of pressure. Furthermore, the PEMFC performances with the PFSA/silicon oxide composite membranes were physically more robust than the control membranes (unmodified PFSAs), which degraded after high operation temperature and thermal cycling.
Atomic layer deposition of bismuth oxide using Bi(OCMe{sub 2}{sup i}Pr){sub 3} and H{sub 2}O
Austin, Dustin Z., E-mail: firstname.lastname@example.com; Conley, John F., E-mail: email@example.com [Department of Electrical Engineering and Computer Science, Oregon State University, Corvallis, Oregon 97331 (United States); Allman, Derryl; Price, David; Hose, Sallie [ON Semiconductor, Technology Development, Gresham, Oregon 97030 (United States); Saly, Mark [SAFC Hitech, Haverhill, Massachusetts 01832 (United States)
Bismuth oxide thin films were deposited by atomic layer deposition using Bi(OCMe{sub 2}{sup i}Pr){sub 3} and H{sub 2}O at deposition temperatures between 90 and 270?░C on Si{sub 3}N{sub 4}, TaN, and TiN substrates. Films were analyzed using spectroscopic ellipsometry, x-ray diffraction, x-ray reflectivity, high-resolution transmission electron microscopy, and Rutherford backscattering spectrometry. Bi{sub 2}O{sub 3} films deposited at 150?░C have a linear growth per cycle of 0.039?nm/cycle, density of 8.3?g/cm{sup 3}, band gap of approximately 2.9?eV, low carbon content, and show the ? phase structure with a (201) preferred crystal orientation. Deposition temperatures above 210?░C and postdeposition anneals caused uneven volumetric expansion, resulting in a decrease in film density, increased interfacial roughness, and degraded optical properties.
Serum protein layers on parylene-C and silicon oxide: effect on cell adhesion.
Delivopoulos, Evangelos; Ouberai, Myriam M; Coffey, Paul D; Swann, Marcus J; Shakesheff, Kevin M; Welland, Mark E
Among the range of materials used in bioengineering, parylene-C has been used in combination with silicon oxide and in presence of the serum proteins, in cell patterning. However, the structural properties of adsorbed serum proteins on these substrates still remain elusive. In this study, we use an optical biosensing technique to decipher the properties of fibronectin (Fn) and serum albumin adsorbed on parylene-C and silicon oxide substrates. Our results show the formation of layers with distinct structural and adhesive properties. Thin, dense layers are formed on parylene-C, whereas thicker, more diffuse layers are formed on silicon oxide. These results suggest that Fn acquires a compact structure on parylene-C and a more extended structure on silicon oxide. Nonetheless, parylene-C and silicon oxide substrates coated with Fn host cell populations that exhibit focal adhesion complexes and good cell attachment. Albumin adopts a deformed structure on parylene-C and a globular structure on silicon oxide, and does not support significant cell attachment on either surface. Interestingly, the co-incubation of Fn and albumin at the ratio found in serum, results in the preferential adsorption of albumin on parylene-C and Fn on silicon oxide. This finding is supported by the exclusive formation of focal adhesion complexes in differentiated mouse embryonic stem cells (CGR8), cultured on Fn/albumin coated silicon oxide, but not on parylene-C. The detailed information provided in this study on the distinct properties of layers of serum proteins on substrates such as parylene-C and silicon oxide is highly significant in developing methods for cell patterning. PMID:25555155
Serum protein layers on parylene-C and silicon oxide: Effect on cell adhesion
Delivopoulos, Evangelos; Ouberai, Myriam M.; Coffey, Paul D.; Swann, Marcus J.; Shakesheff, Kevin M.; Welland, Mark E.
Among the range of materials used in bioengineering, parylene-C has been used in combination with silicon oxide and in presence of the serum proteins, in cell patterning. However, the structural properties of adsorbed serum proteins on these substrates still remain elusive. In this study, we use an optical biosensing technique to decipher the properties of fibronectin (Fn) and serum albumin adsorbed on parylene-C and silicon oxide substrates. Our results show the formation of layers with distinct structural and adhesive properties. Thin, dense layers are formed on parylene-C, whereas thicker, more diffuse layers are formed on silicon oxide. These results suggest that Fn acquires a compact structure on parylene-C and a more extended structure on silicon oxide. Nonetheless, parylene-C and silicon oxide substrates coated with Fn host cell populations that exhibit focal adhesion complexes and good cell attachment. Albumin adopts a deformed structure on parylene-C and a globular structure on silicon oxide, and does not support significant cell attachment on either surface. Interestingly, the co-incubation of Fn and albumin at the ratio found in serum, results in the preferential adsorption of albumin on parylene-C and Fn on silicon oxide. This finding is supported by the exclusive formation of focal adhesion complexes in differentiated mouse embryonic stem cells (CGR8), cultured on Fn/albumin coated silicon oxide, but not on parylene-C. The detailed information provided in this study on the distinct properties of layers of serum proteins on substrates such as parylene-C and silicon oxide is highly significant in developing methods for cell patterning. PMID:25555155
Characterization of the mechanism of bi-layer oxide growth on austenitic stainless steels 316L and D9 in oxygen-controlled Lead-Bismuth Eutectic (LBE)
NASA Astrophysics Data System (ADS)
Koury, Daniel
Lead Bismuth Eutectic (LBE) has been proposed for use in programs for accelerator-based and reactor-based transmutation of nuclear waste. LBE is a leading candidate material as a spallation target (in accelerator-based transmutation) and an option for the sub-critical blanket coolant. The corrosion by LBE of annealed and cold-rolled 316L stainless steels, and the modified austenitic stainless steel alloy D9, has been studied using Scanning Electron Microscopy (SEM), Electron Probe Micro Analysis (EPMA), and X-ray Photoelectron Spectroscopy (XPS). Exposed and unexposed samples have been compared and the differences studied. Small amounts of surface contamination are present on the samples and have been removed by ion-beam sputtering. The unexposed samples reveal typical stainless steel characteristics: a chromium oxide passivation surface layer and metallic iron and nickel. The exposed samples show protective iron oxide and chromium oxide growths on the surface. Oxygen takes many forms on the exposed samples, including oxides of iron and chromium, carbonates, and organic acids from subsequent handling after exposure to LBE. Different types of surface preparation have lead to considerably different modes of corrosion. The cold-rold samples were resistant to thick oxide growth, having only a thin (< 1 mum), dense chromium-rich oxide. The annealed 316L and D9 samples developed thick, bi-layered oxides, the inner layer consisting of chromium-rich oxides (likely spinel) and the outer layer consisting mostly of iron oxides. The cold-rolled samples were able to maintain a thin chromium oxide layer because of the surface work performed on it, as ample diffusion pathways provided an adequate supply of chromium atoms. The annealed samples grew thick oxides because iron was the primary diffusant, as there are fewer fast-diffusion pathways and therefore an amount of chromium insufficient to maintain a chromium based oxide. Even the thick oxide, however, can prolong the life of a steel in LBE, provided proper oxygen control. The mechanisms responsible for the differences in the oxidation behaviors are discussed.
High-temperature oxidation behavior of reaction-formed silicon carbide ceramics
NASA Technical Reports Server (NTRS)
Ogbuji, Linus U. J. T.; Singh, M.
The oxidation behavior of reaction-formed silicon carbide (RFSC) ceramics was investigated in the temperature range of 1100 to 1400 C. The oxidation weight change was recorded by TGA; the oxidized materials were examined by light and electron microscopy, and the oxidation product by x-ray diffraction analysis (XRD). The materials exhibited initial weight loss, followed by passive weight gain (with enhanced parabolic rates, k(sub p)), and ending with a negative (logarithmic) deviation from the parabolic law. The weight loss arose from the oxidation of residual carbon, and the enhanced k(sub p) values from internal oxidation and the oxidation of residual silicon, while the logarithmic kinetics is thought to have resulted from crystallization of the oxide. The presence of a small amount of MoSi, in the RFSC material caused a further increase in the oxidation rate. The only solid oxidation product for all temperatures studied was silica.
Monolithic integration of rare-earth oxides and semiconductors for on-silicon technology
Dargis, Rytis, E-mail: firstname.lastname@example.com; Clark, Andrew; Erdem Arkun, Fevzi [Translucent, Inc., 952 Commercial St., Palo Alto, California 94303 (United States); Grinys, Tomas; Tomasiunas, Rolandas [Institute of Applied Research, Vilnius University, Sauletekio al. 10, LT-10223 Vilnius (Lithuania); O'Hara, Andy; Demkov, Alexander A. [Department of Physics, The University of Texas at Austin, 2515 Speedway, C1600, Austin, Texas 78712 (United States)
Several concepts of integration of the epitaxial rare-earth oxides into the emerging advanced semiconductor on silicon technology are presented. Germanium grows epitaxially on gadolinium oxide despite lattice mismatch of more than 4%. Additionally, polymorphism of some of the rare-earth oxides allows engineering of their crystal structure from hexagonal to cubic and formation of buffer layers that can be used for growth of germanium on a lattice matched oxide layer. Molecular beam epitaxy and metal organic chemical vapor deposition of gallium nitride on the rare-earth oxide buffer layers on silicon is discussed.
Heteroepitaxy and dry oxidation of silicon-germanium and silicon-germanium-carbon alloy thin films on silicon(100)
NASA Astrophysics Data System (ADS)
Xiang, Jiong
Heteroepitaxial silicon-germanium (Si1-xGex) alloys have found applications in Si-based technology. However, a good quality dielectric on Si1-xGex cannot be obtained by thermal oxidation. The goal of this study is to investigate the effect of carbon incorporation upon epitaxial growth and thermal oxidation of Si1-xGex alloys and its role on strain compensation in Si1-xGex alloys. Both binary silicon-germanium (Si1-xGex) and ternary silicon-germanium-carbon (Si1-x-yGexCy) alloys with similar Si/Ge ratio are grown by Combined Ion and Molecular beam Deposition (CIMD) on P-type Si (100) substrate and compared. Prior to the epitaxial growth, a unique passivation technique is used to provide an ultra-clean and ultra-smooth Si (100) surface at low temperature. It involves a "modified RCA-type" pre-cleaning followed by HF/Methanol passivation and in situ thermal cleaning at a low temperature. As-deposited epitaxial films are then oxidized at three different temperatures by rapid thermal oxidation and furnace dry oxygen. The composition, structure, crystalline quality and surface morphology of binary and ternary alloys before and after oxidation are compared using a combination of Rutherford Backscattering Spectrometry (RBS) and ion channeling at 2.0 MeV, carbon Nuclear Resonance Analysis (NRA) at 4.3 MeV with 4He++ ions, Secondary Ion-Mass Spectrscopy (SIMS), Tapping Mode Atomic Force Microscopy (TMAFM), High-Resolution Transmission Electron Microscopy (HRTEM), and Fourier Transformation Infrared (FTIR) spectroscopy. The study demonstrates that the hydroxide passivated Si (100) surface obtained by our passivation technique yields exceptionally smooth and ordered (1x1) Si (100) surfaces at room temperature, and ultra-smooth (2x1) ordering after in situ low temperature desorption. We show that it is difficult to grow Si1-x-yGexC y films with quality comparable to binary Si1-xGex. Instead our results indicate a lower barrier to defect formation in Si 1-x-yGexCy than in Si1-xGex. We find that a growth temperature lower than 560░C is necessary to avoid the precipitation of a precursor phase to SiC in Si and in Si1-xGe x matrix, akin to Guinier Preston zones in the growth conditions used. The Si1-x-yGexCy films are considerably rougher than the Si1-xGex films of similar Si/Ge fractions. Roughness increases with increasing C fraction, indicating that the introduction of C lowers the barrier for the onset of Stranski-Krastanov type growth. The importance of an independent and accurate measurement of the total and substitutional C fraction within the films is shown. This study also demonstrates the importance of using a combination of different analysis techniques for film characterization. Dry oxidation of (Si1-xGex) and Si1-x-yGe xCy thin films leads to the formation of a conformal SiO 2 layer on the top surface, while Ge segregates towards the top surface and at the SiO2/Si1-xGex and SiO2/Si 1-x-yGexCy interfaces, in agreement with previous findings. However, we report the first time observation that dry oxidation rates in (Si1-xGex) decrease with increasing Ge fraction x for x > 0.20 and with increasing film minimum yield. Ion channeling analysis and strain measurements indicate that the incorporation of C rather than the amount of C itself affects the dry oxidation mechanism. Dry oxidation relaxes the previously strained (Si1-xGex) making the films more defective with a rougher surface. This is in contrast to the oxidation of Si (100) where oxidation always has a planarization effect. For relaxed Si1-xGex and defective Si1-x-yGexC y, dry oxidation does not have significant effect on the film crystalline quality and on the surface morphology.
Ion irradiation of the native oxide/silicon surface increases the thermal boundary conductance across aluminum/silicon interfaces
NASA Astrophysics Data System (ADS)
Gorham, Caroline S.; Hattar, Khalid; Cheaito, Ramez; Duda, John C.; Gaskins, John T.; Beechem, Thomas E.; Ihlefeld, Jon F.; Biedermann, Laura B.; Piekos, Edward S.; Medlin, Douglas L.; Hopkins, Patrick E.
The thermal boundary conductance across solid-solid interfaces can be affected by the physical properties of the solid boundary. Atomic composition, disorder, and bonding between materials can result in large deviations in the phonon scattering mechanisms contributing to thermal boundary conductance. Theoretical and computational studies have suggested that the mixing of atoms around an interface can lead to an increase in thermal boundary conductance by creating a region with an average vibrational spectra of the two materials forming the interface. In this paper, we experimentally demonstrate that ion irradiation and subsequent modification of atoms at solid surfaces can increase the thermal boundary conductance across solid interfaces due to a change in the acoustic impedance of the surface. We measure the thermal boundary conductance between thin aluminum films and silicon substrates with native silicon dioxide layers that have been subjected to proton irradiation and post-irradiation surface cleaning procedures. The thermal boundary conductance across the Al/native oxide/Si interfacial region increases with an increase in proton dose. Supported with statistical simulations, we hypothesize that ion beam mixing of the native oxide and silicon substrate within ÿ2.2nm of the silicon surface results in the observed increase in thermal boundary conductance. This ion mixing leads to the spatial gradation of the silicon native oxide into the silicon substrate, which alters the acoustic impedance and vibrational characteristics at the interface of the aluminum film and native oxide/silicon substrate. We confirm this assertion with picosecond acoustic analyses. Our results demonstrate that under specific conditions, a "more disordered and defected" interfacial region can have a lower resistance than a more "perfect" interface.
The Effect of Thermal Oxidation of Silicon on Boron Diffusion in Extrinsic Conditions
NASA Astrophysics Data System (ADS)
Ishikawa, Yutaka; Nakamichi, Ichiro; Matsumoto, Satoru; Niimi, Tatsuya
Boron diffusion during extrinsic conditions in silicon has been investigated under both oxidizing and inert atmospheres for different temperatures (950-1100░C) and times. Oxidation-enhanced diffusion (OED) was found. This result is opposite to the oxidation-retarded diffusion of arsenic case.
Epitaxial integration of perovskite-based multifunctional oxides on silicon q
Eom, Chang Beom
- tifunctional oxide devices, these multifunctional films should be integrated directly on Si, maintaining high of oxides into a Si-based platform to realize multifunctional devices. In this sense, it is highly desirableEpitaxial integration of perovskite-based multifunctional oxides on silicon q Seung-Hyub Baek
Chemistry of fluorine in the oxidation of silicon S. 8. Kasi,`) M. Liehr, and S. Cohen
Rubloff, Gary W.
Chemistry of fluorine in the oxidation of silicon S. 8. Kasi,`) M. Liehr, and S. Cohen IBM Research November 1990; accepted for publication 19 April 1991) The chemical environment of fluorine in the oxide moieties are formed with a significant accumulation of fluorine throughout the oxide layer. These changes
Microstructure evolution during silicon oxidation at room temperature under composite ion beam irradiation
NASA Astrophysics Data System (ADS)
Prikhodko, K. E.; Gurovich, B. A.; Komarov, D. A.; Goncharova, D. A.; Kutuzov, L. V.
In this work, we studied the silicon microstructure evolution during its oxidation under composite beam ion irradiation at room temperature. It was found that when the composite ion beam was formed by hydrogen and dry oxygen mixture at low doses (?1018 cm-2), a porous silicon layer was formed. During irradiation, the pore size gradually reduced and at a dose of ?1020 cm-2 pores disappear completely, and an uniform layer of silicon oxide was formed. If residual gases and hydrogen are used to generate a composite ion beam, the formation of porous silicon is not found. The final thickness of irradiation-induced silicon oxide corresponded to the projected range of protons at a given energy in both cases.
Fluorine hot atom oxidation of bismuth vapor. A comment on the evaluation of the BiF bond energy
NASA Astrophysics Data System (ADS)
Devore, T. C.; Gole, J. L.
The energetics of the chemiluminescent reaction between bismuth dimers and fluorine atoms (T.C. Devore et al., Chem. Phys. 155 (1991) 423; 156 (1991) 156) has been evaluated to better refine a determination of the bismuth fluoride dissociation energy. By directly examining the spectrum of the SF 6 discharge used to generate the F atoms to establish the significant energy imparted to these dissociation products and by exploring F atom chemiluminescent reactions with known energetics, the F atom beam is established to have contributed a maximum of 0.8-0.9 eV to the chemiluminescent process. Based upon the observed population of the ?'=4 level of the BiF A0 + state resulting from the Bi 2 + F reaction, a BiF bond energy of 3.9 ▒ 0.2 eV is established. This value is slightly higher than a very recent evaluation of the BiF bond energy (Yoo et al., Chem. Phys. 166 (1992) 215) but disagrees with previous determinations in the literature. Many of the previous evaluations of the group 15 halide dissociation energies have been based on BirgeùSponer extrapolations. The data now available for BiF permits an evaluation of the nature of these extrapolations for this molecule. The limitations of these extrapolations and possible corrections for these shortcomings are presented.
Anodic oxidation-induced delamination of the SUMMiT poly 0 to Silicon Nitride Interface
NASA Astrophysics Data System (ADS)
Plass, Richard A.; Walraven, Jeremy A.; Tanner, Danelle M.; Sexton, Frederick W.
Anodic oxidation can be a catastrophic failure mechanism for MEMS devices that operate in high humidity environments. Shea and coworkers have shown that positively charged polysilicon traces can fail through a progressive silicon oxidation reaction whose rate depends critically on the surface conductivity over the silicon nitride. We have found a related anodic oxidation-based failure mechanism: progressive delamination of Poly 0 electrodes from silicon nitride layers, which then mechanically interfere with device function well before the electrode is fully oxidized. To explain this effect, we propose that the silicon oxide which initially forms at the electrode edge has insufficient strength to hold the local Poly 0 / silicon nitride interface together. This low-density silicon oxide also creates a bilayer system, which curls the edge of the 300 nm thick Poly 0 electrode away from the nitride. As delamination progresses more nitride surface is exposed and more of the interface is then attacked. This process continues cyclically until the electrode edge pushes against other device components, catastrophically and irreversibly interfering with normal operation. Additionally, we observe that the delamination only starts at electrode edges directly under cantilevers, suggesting the oxidation rate also depends on the perpendicular electric field strength.
Lateral extent of oxidation-enhanced diffusion of phosphorus in <100> silicon
NASA Astrophysics Data System (ADS)
Taniguchi, K.; Antoniadis, D. A.
The lateral extent of oxidation-enhanced diffusion (OED) of phosphorus in (100) silicon oxidized in dry oxygen has been investigated. OED was observed near the Si/SiO2 interface under an oxidation mask composed of Si3N4/SiO2. It was found that under the mask OED decays nearly exponentially from the edge of the oxidized region. The characteristic decay length increases with square root of oxidation time and is exponentially dependent on temperature with activation energy of 2 eV. It is proposed that the OED observations can be explained on the basis of excess silicon self-interstitials diffusing away from the oxidized regions. Both diffusion and interface capture of self-interstitials play a role in their distribution in the silicon bulk.
Structural and nuclear characterizations of defects created by noble gas implantation in silicon oxide
Paris-Sud XI, Universit├® de
1 Structural and nuclear characterizations of defects created by noble gas implantation in silicon-implantation provided a low-k silicon oxide that has potential use as a dielectric material for interconnects in Si) and Positron Annihilation Spectroscopy (PAS) were used to provide a comprehensive characterization of defects
Process for depositing an oxide epitaxially onto a silicon substrate and structures prepared with the process
R. A. McKee; F. J. Walker
A process is described for growing an epitaxial oxide having a sodium chloride-type lattice structure onto a silicon substrate comprising the steps of: developing an ultra high vacuum, oxygen-free environment about a silicon substrate having a surface which has been cleaned to atomic cleanliness and raised to a high temperature; depositing an amount of a metal from a flux source
Synchrotron x-ray reflectivity study of oxidation/passivation of copper and silicon.
Chu, Y.; Nagy, Z.; Parkhutik, V.; You, H.
Synchrotron x-ray-scattering technique studies of copper and silicon electrochemical interfaces are reported. These two examples illustrate the application of synchrotron x-ray techniques for oxidation, passivation, and dissolution of metals and semiconductors.
Deposition of sacrificial silicon oxide layers by electron cyclotron resonance plasma
Technische Universiteit Delft
by Fourier transform infrared and ellipsometry. Optical emission spectroscopy and Langmuir probe were used applications.3,7 Silicon oxide films can be deposited by low-pressure chemical vapor deposition LPCVD or plasma
Large area nanoscale patterning of silicon surfaces by parallel local oxidation.
Losilla, N S; MartÝnez, J; GarcÝa, R
The homogeneity and the reproducibility of parallel local oxidation have been improved by introducing a thin film of polymethylmethacrylate (PMMA) between the stamp and the silicon surface. The flexibility of the polymer film enables a homogeneous contact of the stamp with the silicon surface to be achieved. The oxides obtained yield better aspect ratios compared with the ones created with no PMMA layer. The pattern is formed when a bias voltage is applied between the stamp and the silicon surface for 1 min. The patterning can be done by a step and repeat technique and is reproducible across a centimetre length scale. Once the oxide nanostructures have been created, the polymer is removed by etching in acetone. Finally, parallel local oxidation is applied to fabricate silicon nanostructures and templates for the growth of organic molecules. PMID:19875876
Method for forming indium oxide/n-silicon heterojunction solar cells
Feng, Tom (Morris Plains, NJ); Ghosh, Amal K. (New Providence, NJ)
A high photo-conversion efficiency indium oxide/n-silicon heterojunction solar cell is spray deposited from a solution containing indium trichloride. The solar cell exhibits an Air Mass One solar conversion efficiency in excess of about 10%.
Integration of functional complex oxides on silicon using molecular beam epitaxy
NASA Astrophysics Data System (ADS)
Posadas, Agham; Choi, Miri; Dargis, Rytis; Demkov, Alex
Complex oxides exhibit a wide range of electronic properties, including high temperature superconductivity, colossal magnetoresistance, metal-insulator transitions, ferromagnetism, and ferroelectricity. Interesting devices and sensors could be envisioned by fabricating these oxides in epitaxial, thin film form on silicon, the most widely used materials platform for electronic devices. However, integrating the functionality of complex oxides onto silicon turns out to be a very difficult problem. One needs to be able to deposit an oxide in crystalline form on top of silicon without forming SiO2, which grows amorphous and destroys the underlying crystalline order of the substrate surface causing subsequently deposited films to be highly defective. In this talk, we will first describe the new oxide molecular beam epitaxy capabilities at the Materials Physics Laboratory in UT Austin, and then briefly discuss a process by which one can smoothly transition from the oxygen-sensitive, covalently bonded silicon substrate to a fully oxidized, ionically bonded perovskite oxide layer (SrTiO3) using a carefully sequenced deposition of various atomic layers. This capability opens up the possibility of depositing these functional oxide materials in epitaxial form onto silicon.
Thromboresistance Characterization of Extruded Nitric Oxide-Releasing Silicone Catheters
Amoako, Kagya A.; Archangeli, Christopher; Handa, Hitesh; Major, Terry; Meyerhoff, Mark E.; Annich, Gail M.; Bartlett, Robert H.
Intravascular catheters used in clinical practice can activate platelets, leading to thrombus formation and stagnation of blood flow. Nitric oxide (NO)-releasing polymers have been shown previously to reduce clot formation on a number of blood contacting devices. In this work, trilaminar NO-releasing silicone catheters were fabricated and tested for their thrombogenicity. All catheters had specifications of L = 6 cm, inner diameter = 21 gauge (0.0723 cm), outer diameter = 12 gauge (0.2052 cm), and NO-releasing layer thickness = 200 ▒ 11 ?m. Control and NO-releasing catheters were characterized in vitro for their NO flux and NO release duration by gas phase chemiluminescence measurements. The catheters were then implanted in the right and left internal jugular veins of (N = 6 and average weight = 3 kg) adult male rabbits for 4 hours thrombogenicity testing. Platelet counts and function, methemoglobin (metHb), hemoglobin (Hb), and white cell counts and functional time (defined as patency time of catheter) were monitored as measured outcomes. Nitric oxide-releasing catheters (N = 6) maintained an average flux above (2 ▒ 0.5) Î 10?10 mol/min/cm2 for more than 24 hours, whereas controls showed no NO release. Methemoglobin, Hb, white cell, and platelet counts and platelet function at 4 hours were not significantly different from baseline (? = 0.05). However, clots on controls were visibly larger and prevented blood draws at a significantly (p < 0.05) earlier time (2.3 ▒ 0.7 hours) into the experiment, whereas all NO-releasing catheters survived the entire 4 hours test period. Results indicate that catheter NO flux levels attenuated thrombus formation in a short-term animal model. PMID:22395119
Alternative method for steam generation for thermal oxidation of silicon
NASA Astrophysics Data System (ADS)
Spiegelman, Jeffrey J.
Thermal oxidation of silicon is an important process step in MEMS device fabrication. Thicker oxide layers are often used as structural components and can take days or weeks to grow, causing high gas costs, maintenance issues, and a process bottleneck. Pyrolytic steam, which is generated from hydrogen and oxygen combustion, was the default process, but has serious drawbacks: cost, safety, particles, permitting, reduced growth rate, rapid hydrogen consumption, component breakdown and limited steam flow rates. Results from data collected over a 24 month period by a MEMS manufacturer supports replacement of pyrolytic torches with RASIRC Steamer technology to reduce process cycle time and enable expansion previously limited by local hydrogen permitting. Data was gathered to determine whether Steamers can meet or exceed pyrolytic torch performance. The RASIRC Steamer uses de-ionized water as its steam source, eliminating dependence on hydrogen and oxygen. A non-porous hydrophilic membrane selectively allows water vapor to pass. All other molecules are greatly restricted, so contaminants in water such as dissolved gases, ions, total organic compounds (TOC), particles, and metals can be removed in the steam phase. The MEMS manufacturer improved growth rate by 7% over the growth range from 1?m to 3.5?m. Over a four month period, wafer uniformity, refractive index, wafer stress, and etch rate were tracked with no significant difference found. The elimination of hydrogen generated a four-month return on investment (ROI). Mean time between failure (MTBF) was increased from 3 weeks to 32 weeks based on three Steamers operating over eight months.
Simulation study of water/silicon oxide interface
NASA Astrophysics Data System (ADS)
Lorenz, Christian; Rempe, Susan; Stevens, Mark; Grest, Gary; Tsige, Mesfin
The interaction of water with solid surfaces plays a crucial role in many phenomena. The water-silica interface is one of the typical systems encountered in technological and natural materials. Numerous technological applications of silica were found to rely on its specific surface properties. Large scale quantum mechanics (QM) and classical molecular dynamics (MD) simulations are used to study the molecular configurations and wetting properties of water at the interface of different silicon oxide surfaces. In order to understand how the surface coverage of silanols (-SiOH) affects the wetting behavior of the silica surfaces, both crystalline ((001) ?-quartz (coverage 9.6 nm-2) and (100) ?-cristobalite (7.8 nm-2)) and amorphous silica (5.0 nm-2) substrates have been studied. The binding energy of the water, the number of water molecules hydrogen-bonded to the surface and the configuration of the hydrogen-bonded water molecules are determined as a function of silanol coverage from QM simulations. The number of water molecules within a monolayer and the orientation of the water molecules within the monolayer and in the bulk are determined from MD simulations. Results from two classical force fields are compared to one another and to the relevant quantities from the QM simulations. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
Silicon oxide permeation barrier coating of PET bottles and foils
NASA Astrophysics Data System (ADS)
Steves, Simon; Deilmann, Michael; Awakowicz, Peter
Modern packaging materials such as polyethylene terephthalate (PET) have displaced established materials in many areas of food and beverage packaging. Plastic packing materials offer are various advantages concerning production and handling. PET bottles for instance are non-breakable and lightweight compared to glass and metal containers. However, PET offers poor barrier properties against gas permeation. Therefore, the shelf live of packaged food is reduced. Permeation of gases can be reduced by depositing transparent plasma polymerized silicon oxide (SiOx) barrier coatings. A microwave (2.45 GHz) driven low pressure plasma reactor is developed based on a modified Plasmaline antenna to treat PET foils or bottles. To increase the barrier properties of the coatings furthermore a RF substrate bias (13.56 MHz) is applied. The composition of the coatings is analyzed by means of Fourier transform infrared (FTIR) spectroscopy regarding carbon and hydrogen content. Influence of gas phase composition and substrate bias on chemical composition of the coatings is discussed. A strong relation between barrier properties and film composition is found: good oxygen barriers are observed as carbon content is reduced and films become quartz-like. Regarding oxygen permeation a barrier improvement factor (BIF) of 70 is achieved.
Structural alloy with a protective coating containing silicon or silicon-oxide
Natesan, K.
This invention is comprised of an iron-based alloy containing chromium and optionally, nickel. The alloy has a surface barrier of silicon or silicon plus oxygen which converts at high temperature to a protective silicon compound. The alloy can be used in oxygen-sulfur mixed gases at temperatures up to about 1100{degrees}C.
Structural alloy with a protective coating containing silicon or silicon-oxide
Natesan, Ken (Naperville, IL)
An iron-based alloy containing chromium and optionally, nickel. The alloy has a surface barrier of silicon or silicon plus oxygen which converts at high temperature to a protective silicon compound. The alloy can be used in oxygen-sulfur mixed gases at temperatures up to about 1100.degree. C.
Structural alloy with a protective coating containing silicon or silicon-oxide
Natesan, K.
An iron-based alloy is described containing chromium and optionally, nickel. The alloy has a surface barrier of silicon or silicon plus oxygen which converts at high temperature to a protective silicon compound. The alloy can be used in oxygen-sulfur mixed gases at temperatures up to about 1100 C. 8 figures.
Ethylene oxide-block-butylene oxide copolymer uptake by silicone hydrogel contact lens materials
NASA Astrophysics Data System (ADS)
Huo, Yuchen; Ketelson, Howard; Perry, Scott S.
Four major types of silicone hydrogel contact lens material have been investigated following treatments in aqueous solutions containing poly(ethylene oxide) and poly(butylenes oxide) block copolymer (EO-BO). The extent of lens surface modification by EO-BO and the degree of bulk uptake were studied using X-ray photoelectron spectroscopy (XPS) and ultra-performance liquid chromatography (UPLC), respectively. The experimental results suggest that different interaction models exist for the lenses, highlighting the influence of both surface and bulk composition, which greatly differs between the lenses examined. Specifically, lenses with hydrophilic surface treatments, i.e., PureVision« (balafilcon A) and O2OPTIX (lotrafilcon B), demonstrated strong evidence of preferential surface adsorption within the near-surface region. In comparison, surface adsorption on ACUVUE« Oasys« (senofilcon A) and Biofinity« (comfilcon A) was limited. As for bulk absorption, the amount of EO-BO uptake was the greatest for balafilcon A and comfilcon A, and least for lotrafilcon B. These findings confirm the presence of molecular concentration gradients within the silicone hydrogel lenses following exposure to EO-BO solutions, with the nature of such concentration gradients found to be lens-specific. Together, the results suggest opportunities for compositional modifications of lenses for improved performance via solution treatments containing surface-active agents.
Ab-initio simulations on initial growth steps of high-K oxides on silicon
NASA Astrophysics Data System (ADS)
Bloechl, Peter E.
One of the most acute challenges of semiconductor industry is the introduction of new so-called high-K gate oxides. Conventional SiO2 based gate oxides need to be replaced in order to avoid quantum mechanical leakage currents through ultrathin oxide layers. State of the art electronic structure calculations and ab-initio molecular dynamics simulations of the deposition of metals onto silicon and the formation of oxides have been performed. Atomic structure, chemical binding and electronic structure have been analyzed for a wide range of different adsorption structures of Zr, Hf, and Sr on silicon. Silicide formation and the step-wise formation of the oxides have been investigated. Particular emphasis will be given to the formation of the interface between SrTiO3 and silicon (001).
Synthesis and postgrowth doping of silicon nanowires
NASA Astrophysics Data System (ADS)
Byon, K.; Tham, D.; Fischer, J. E.; Johnson, A. T.
High-quality silicon nanowires (SiNWs) were synthesized via a thermal evaporation method without the use of catalysts. Scanning electron microscopy and transmission electron microscopy showed that SiNWs were long and straight crystalline silicon with an oxide sheath. Field effect transistors were fabricated to investigate the electrical transport properties. Devices on as-grown material were p-channel with channel mobilities 1-10cm2V-1s-1. Postgrowth vapor doping with bismuth converted these to n-channel behavior.
Single-Longitudinal-Mode Lanthanum-Codoped Bismuth-Based Erbium Doped Fiber Ring Laser
Wai, Ping-kong Alexander
Single-Longitudinal-Mode Lanthanum-Codoped Bismuth-Based Erbium Doped Fiber Ring Laser K. K and demonstrate a stable single-longitudinal-mode lanthanum-codoped bismuth oxide- based erbium doped fiber ring of the experimental setup to demonstrate the proposed SLM La-codoped bismuth based EDF ring laser. The fiber laser
Mechanism of Selective Ammoxidation of Propene to Acrylonitrile on Bismuth Molybdates from Quantum Mechanical Calculations
Goddard III, William A.
Mechanism of Selective Ammoxidation of Propene to Acrylonitrile on Bismuth Molybdates from Quantum ammoxidation of propene to acrylonitrile by bismuth molybdates, we report quantum mechanical studies (using stages of this industry, acrylonitrile was produced by propene on simple bismuth and molybdenum oxide
Electrical characterization of rapid thermal nitrided and re-oxidized low-pressure chemical-vapor-deposited silicon dioxide metal-oxide-silicon structures
NASA Astrophysics Data System (ADS)
Ang, S. S.; Shi, Y. J.; Brown, W. D.
The electrical characteristics of rapid thermal nitrided and re-oxidized low-pressure chemical-vapor-deposited (LPCVD) silicon dioxide metal-oxide-silicon (MOS) structures were investigated. Both nitridation temperature and time affect the properties of the MOS structures as revealed by capacitance-voltage characteristics. Nitridation at 1000 ░C for 15 s followed by re-oxidation for 60 s at 1000 ░C in an oxygen/nitrogen ambient was found to be superior to the same nitridation for 60 s with no re-oxidation. Typical values of fixed charge and interface state densities for devices subjected to nitridation and re-oxidation in a mixture of oxygen and nitrogen were 4Î1010 cm-2 and 7Î1010 eV-1 cm-2, respectively. Avalanche electron injection using electric fields of 3-3.5 MV/cm produced positive shifts in flatband voltage for devices nitrided at 1000 ░C for 15 s followed by re-oxidation, whereas samples nitrided at 1000 ░C for 60 s without the re-oxidation yielded negative shifts in flatband voltage. An electron barrier height of 2.4 eV was found for these nitrided samples. These results strongly suggest that device quality MOS dielectrics for high-voltage power MOS field-effect-transistors can be realized by nitridation/re-oxidation of LPCVD oxide.
Characterization of microparticles and oxide layers generated by laser irradiation of diamond-machined silicon wafers
NASA Astrophysics Data System (ADS)
Yan, Jiwang; Sakai, Shin; Isogai, Hiromichi; Izunome, Koji
Nanosecond-pulsed laser irradiation is a potential method for removing machining-induced subsurface damage from silicon wafers. In this study, the material compositions and microstructures of microparticles and oxide layers generated during laser irradiation were investigated by atomic force microscopy, energy-dispersive x-ray spectroscopy, cross-sectional transmission electron microscopy, electron energy-loss spectroscopy and Auger electron spectroscopy. The oxide layer was found to be approximately 5 nm thick, which is significantly thicker than the native oxide layer of silicon at room temperature in air (~1 nm). The microparticles have a low-density amorphous structure and are mainly composed of silicon oxide, while a few particles contain silicon. The particles are attached to the substrate, but are distinct from it. The results indicate that silicon boiled during the laser pulse and that the particles are recondensed and oxidized liquid silicon boiled away from the wafer surface. The microparticles can be completely removed from the wafer surface by hydrofluoric acid etching.
OXIDE / LPCVD NITRIDE STACKS ON SILICON: THE EFFECTS OF HIGH TEMPERATURE TREATMENTS ON BULK to many favourable properties of the silicon nitride. If the thickness of the oxide and nitride is chosen correctly, an oxide / nitride stack behaves as a near ideal antireflection coating. Nitride layers allow
Dimethyl sulfoxide as a mild oxidizing agent for porous silicon and its effect on photoluminescence
Song, J.H.; Sailor, M.J. [Univ. of California, San Diego, CA (United States). Dept. of Chemistry and Biochemistry] [Univ. of California, San Diego, CA (United States). Dept. of Chemistry and Biochemistry
Dimethyl sulfoxide acts as a mild room-temperature oxidant of luminescent porous silicon. The oxidation reaction is accompanied by a loss in photoluminescence intensity from the silicon nanocrystallites, indicating that the oxide formed under these conditions is electronically defective. The rate of oxidation is reduced if the reaction is carried out in the presence of the radical traps 2,6-di-tert-butyl-4-methylphenol (butylated hydroxytoluene, BHT) or cumene. In addition, photoluminescence intensity is preserved if the DMSO oxidation reaction is carried out in the presence of high concentrations of BHT. The BHT is proposed to form a more electronically passive oxide layer by hydrogenating the surface radicals (dangling bonds) generated during the oxidation reaction.
Characterization of polycrystalline silicon-oxide-nitride-oxide-silicon devices on a SiO2 or Si3N4 buffer layer
NASA Astrophysics Data System (ADS)
Lee, Sang-Youl; Oh, Jae-Sub; Yang, Seung-Dong; Yun, Ho-Jin; Jeong, Kwang-Seok; Kim, Yu-Mi; Lee, Hi-Deok; Lee, Ga-Won
Silicon-oxide-nitride-oxide-silicon (SONOS) memory devices were fabricated from polycrystalline silicon (poly-Si) using the solid phase crystallization (SPC) method for use in a low-power system-on-panel (SOP) display. In these poly-Si SONOS memories, oxide or nitride was used as a buffer layer. The electrical characteristics, such as the threshold voltage ( V T ), subthreshold slope ( SS) and transconductance ( g m ), were determined for each SONOS device. To interpret the characteristics of both poly-Si devices, x-ray diffraction (XRD) measurements and flicker noise analysis were conducted. The results show that the poly-Si SONOS on the oxide layer has better electrical, memory characteristics, such as turn-on speed and g m , program/erase, endurance and data retention than that on the nitride layer. From the XRD measurements, it is shown that the grain size of the poly-Si on the oxide layer is larger than that on the nitride layer. From the flicker noise analysis, the poly-Si device on oxide was shown to have less traps or defects in the channel layer than that on nitride.
Effect of SiO2 surface chemistry on the oxidation of silicon
NASA Astrophysics Data System (ADS)
deLarios, J. M.; Kao, D. B.; Helms, C. R.; Deal, B. E.
We show that the retardation in the silicon oxidation rate associated with an ammonium hydroxide-hydrogen peroxide preclean is due to trace amounts of aluminum in the region of the SiO2 surface. This aluminum and the retarding effect can be eliminated by removing less than 50 ┼ of thermal oxide in a HF:H2O etch. Depositing thin films of aluminum with thicknesses between 0.05 and 1 monolayers (ML) on HF cleaned surfaces produced the same retardation as the NH4OH based cleans. These results indicate the importance of the SiO2 surface in silicon oxidation.
The complex interface chemistry of thin-film silicon/zinc oxide solar cell structures.
Gerlach, D; Wimmer, M; Wilks, R G; FÚlix, R; Kronast, F; Ruske, F; Bõr, M
The interface between solid-phase crystallized phosphorous-doped polycrystalline silicon (poly-Si(n(+))) and aluminum-doped zinc oxide (ZnO:Al) was investigated using spatially resolved photoelectron emission microscopy. We find the accumulation of aluminum in the proximity of the interface. Based on a detailed photoemission line analysis, we also suggest the formation of an interface species. Silicon suboxide and/or dehydrated hemimorphite have been identified as likely candidates. For each scenario a detailed chemical reaction pathway is suggested. The chemical instability of the poly-Si(n(+))/ZnO:Al interface is explained by the fact that SiO2 is more stable than ZnO and/or that H2 is released from the initially deposited a-Si:H during the crystallization process. As a result, Zn (a deep acceptor in silicon) is "liberated" close to the silicon/zinc oxide interface presenting the inherent risk of forming deep defects in the silicon absorber. These could act as recombination centers and thus limit the performance of silicon/zinc oxide based solar cells. Based on this insight some recommendations with respect to solar cell design, material selection, and process parameters are given for further knowledge-based thin-film silicon device optimization. PMID:25363298
The electroluminescence mechanism of Er{sup 3+} in different silicon oxide and silicon nitride environments
Rebohle, L., E-mail: email@example.com; Wutzler, R.; Braun, M.; Helm, M.; Skorupa, W. [Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden - Rossendorf, Bautzner Landstra▀e 400, 01328 Dresden (Germany); BerencÚn, Y.; RamÝrez, J. M.; Garrido, B. [Dept. Electr‗nica, MartÝ i FranquÞs 1, Universitat de Barcelona, 08028 Barcelona (Spain); Hiller, D. [IMTEK, Faculty of Engineering, Albert-Ludwigs-University Freiburg, Georges-K÷hler-Allee 103, 79110 Freiburg (Germany)
Rare earth doped metal-oxide-semiconductor (MOS) structures are of great interest for Si-based light emission. However, several physical limitations make it difficult to achieve the performance of light emitters based on compound semiconductors. To address this point, in this work the electroluminescence (EL) excitation and quenching mechanism of Er-implanted MOS structures with different designs of the dielectric stack are investigated. The devices usually consist of an injection layer made of SiO{sub 2} and an Er-implanted layer made of SiO{sub 2}, Si-rich SiO{sub 2}, silicon nitride, or Si-rich silicon nitride. All structures implanted with Er show intense EL around 1540?nm with EL power efficiencies in the order of 2?Î?10{sup ?3} (for SiO{sub 2}:Er) or 2?Î?10{sup ?4} (all other matrices) for lower current densities. The EL is excited by the impact of hot electrons with an excitation cross section in the range of 0.5û1.5?Î?10{sup ?15?}cm{sup ?2}. Whereas the fraction of potentially excitable Er ions in SiO{sub 2} can reach values up to 50%, five times lower values were observed for other matrices. The decrease of the EL decay time for devices with Si-rich SiO{sub 2} or Si nitride compared to SiO{sub 2} as host matrix implies an increase of the number of defects adding additional non-radiative de-excitation paths for Er{sup 3+}. For all investigated devices, EL quenching cross sections in the 10{sup ?20} cm{sup 2} range and charge-to-breakdown values in the range of 1û10 C cm{sup ?2} were measured. For the present design with a SiO{sub 2} acceleration layer, thickness reduction and the use of different host matrices did not improve the EL power efficiency or the operation lifetime, but strongly lowered the operation voltage needed to achieve intense EL.
Method for one-to-one polishing of silicon nitride and silicon oxide
NASA Technical Reports Server (NTRS)
Babu, Suryadevara V. (Inventor); Natarajan, Anita (Inventor)
The present invention provides a method of removing silicon nitride at about the same removal rate as silicon dioxide by CMP. The method utilizes a polishing slurry that includes colloidal silica abrasive particles dispersed in water and additives that modulate the silicon dioxide and silicon nitride removal rates such that they are about the same. In one embodiment of the invention, the additive is lysine or lysine mono hydrochloride in combination with picolinic acid, which is effective at a pH of about 8. In another embodiment of the invention, the additive is arginine in combination with picolinic acid, which is effective at a pH of about 10.
Gas-phase formation of silicon carbides, oxides, and sulphides from atomic silicon ions
NASA Technical Reports Server (NTRS)
Bohme, Diethard K.; Wlodek, Stanislaw; Fox, Arnold
A systematic experimental study of the kinetics and mechanisms of the chemical reactions in the gas phase between ground-state Si(+)2p and a variety of astrophysical molecules. The aim of this study is to identify the reactions which trigger the formation of chemical bonds between silicon and carbon, oxygen and sulphur, and the chemical pathways which lead to further molecular growth. Such knowledge is valuable in the identification of new extraterrestrial silicon-bearing molecules and for an assessment of the gas-phase transition from atomic silicon to silicon carbide and silicate grain particles in carbon-rich and oxygen-rich astrophysical environments.
Crack healing behavior of hot pressed silicon nitride due to oxidation
NASA Technical Reports Server (NTRS)
Choi, S. R.; Tikare, V.
It is shown that limited oxidation of an MgO-containing, hot-pressed silicon nitride ceramic at 800 deg C and above results in increased strength due to crack healing. Slight oxidation of the surface produces enstatite and cristobalite which fills in cracks. More extensive oxidation leads to strength degradation due to the formation of new flaws by the evolution of N2 gas at the surface. The apparent fracture toughness also increased at 800 deg C and above due to oxidation. Bonds formed between the two surfaces of the crack during oxidation leads to a reduction in stress intensity at the crack tip, suggesting that valid high-temperature toughness values cannot be obtained in an air environment. The increase in strength due to crack healing by oxidation can be achieved without compromising the fatigue properties of the silicon nitride ceramic.
Optimization of contaminated oxide inversion layer solar cell. [considering silicon oxide coating
NASA Technical Reports Server (NTRS)
Call, R. L.
Contaminated oxide cells have been fabricated with efficiencies of 8.6% with values of I sub sc = 120 ma, V sub oc = .54 volts, and curve factor of .73. Attempts to optimize the fabrication step to yield a higher output have not been successful. The fundamental limitation is the inadequate antireflection coating afforded by the silicon dioxide coating used to hold the contaminating ions. Coatings of SiO, therefore, were used to obtain a good antireflection coating, but the thinness of the coatings prevented a large concentration of the contaminating ions, and the cells was weak. Data of the best cell were .52 volts V sub oc, 110 ma I sub sc, .66 CFF and 6.7% efficiency.
Evaluation of silicon oxide cleaning using F2\\/Ar remote plasma processing
S. C. Kang; J. Y. Hwang; N.-E. Lee; K. S. Joo; G. H. Bae
In this study, chamber cleaning experiments using a F2\\/Ar remote plasma generated from a toroidal-type remote plasma source were carried out in a plasma enhanced chemical vapor deposition (PECVD) system. The cleaning processes for the various silicon oxide layers, including PE-oxide (deposited by PECVD using SiH4 and N2O), O3-TEOS oxide (deposited by thermal CVD using ozone and TEOS precursor), and
Bismuth-doped tin oxide-coated carbon nanotube network: improved anode stability and efficiency for flow-through organic electrooxidation.
Liu, Han; Vajpayee, Akshay; Vecitis, Chad D
In this study, a binder-free, porous, and conductive 3D carbon-nanotube (CNT) network uniformly coated with bismuth-doped tin oxide (BTO) nanoparticles was prepared via a simple electrosorption-hydrothermal method and utilized for the electrooxidative filtration of organics. The BTO-CNT nanocomposite was characterized by scanning electron microscopy, thermogravimetric analysis, transmission electron microscopy, X-ray photoelectron spectroscopy, linear sweep voltammetry, and Tafel analysis. The submonolayer BTO coating is composed of 3.9▒1.5 nm diameter nanoparticles (NPs). The oxygen-evolution potential of the BTO-CNT nanocomposite was determined to be 1.71 V (vs Ag/AgCl), which is 440 mV higher than an uncoated CNT anode. Anodic stability, characterized by CNT oxidative corrosion to form dissolved species, indicated that the BTO-CNT incurred negligible corrosion up to Vanode=2.2 V, whereas the uncoated CNT was compromised at Vanode?1.4 V. The effect of metal oxide-nanoparticle coating on anodic performance was initially studied by oxalate oxidation followed by total organic carbon (TOC) and chemical oxygen demand (COD) analysis. The BTO-CNT displayed the best performance, with ?98% oxalate oxidation (1.2 s filter residence time) and current efficiencies in the range of 32 to >99%. The BTO-CNT anode energy consumption was 25.7 kW h kgCOD(-1) at ?93% TOC removal and 8.6 kW h kgCOD(-1) at ?50% TOC removal, comparable to state-of-the-art oxalate oxidation processes (22.5-81.7 kW h kgCOD(-1)). The improved reactivity, current efficiency, and energy consumption are attributed to the increased conductivity, oxygen-evolution potential, and stability of the BTO-CNT anode. The effectiveness and efficiency of the BTO-CNT anode as compared to the uncoated CNT was further investigated by the electrooxidative filtration of ethanol, methanol, formaldehyde, and formate, and it was determined to have TOC removals 2 to 8 times greater, mineralization current efficiencies 1.5 to 3.5 times greater, and energy consumption 4 to 5 times less than the uncoated CNT anode. Electrooxidation and anode passivation mechanisms are discussed. PMID:24040859
Dynamical study of ion-beam oxidation:?Incorporation of hyperthermal oxygen ions into silicon oxide thin films
NASA Astrophysics Data System (ADS)
Tzvetkov, T.; Qin, X.; Jacobs, D. C.
The complex dynamics associated with ion-beam oxidation of Si(001) by 5 100-eV O+ and O+2 is studied in situ. Room-temperature oxidation of silicon under ultrahigh vacuum conditions is accomplished with a mass-selected, monoenergetic, oxygen ion beam. Initially, a thin Si16Ox film is prepared by bombarding clean Si(001) with hyperthermal energy 16O+. Switching the incident ion flux to 18O+ or 36O+2 creates an isotopically labeled tracer for monitoring the rate at which subsequent incident oxygen ions are incorporated into the topmost layer of the growing silicon oxide film. The cross section for oxygen incorporation is found to depend strongly on (i) the conditions under which the underlying oxide layer was grown, (ii) the kinetic energy of the incorporating ion, and (iii) whether the incident ion is atomic or molecular oxygen.
Silicon solar cells with monolithic rare-earth oxide upconversion layer
Richard H. Sewell; Andrew Clark; Robin Smith; Scott Semans; Aleta Jamora; Gary Vosters
A ternary rare-earth oxide (REO) up-conversion layer was deposited on monocrystalline thin film solar cells to demonstrate up-conversion of sub-band-gap solar radiation into the spectral range of silicon. Laser radiation from 1520 nm to 1560 nm was shown to generate an additional photocurrent in the underlying silicon solar cell. Through combinations of rare-earth ions, portions of the sub-band-gap solar spectrum
Interfaces and defects of high- K oxides on silicon
J. Robertson
The properties of oxides with high-dielectric constant are being extensively studied for use as gate oxides. The criteria for choosing such oxides is discussed. The bonding at Siûoxide interfaces is considered in order to obtain an insulating interface. The stabilities of various atomic configurations of interface are compared, and their band offsets are calculated. The energy levels of point defects
Dispersion engineering of high-Q silicon microresonators via thermal oxidation
Jiang, Wei C. [Institute of Optics, University of Rochester, Rochester, New York 14627 (United States); Zhang, Jidong [Department of Electrical and Computer Engineering, University of Rochester, Rochester, New York 14627 (United States); Usechak, Nicholas G. [Air Force Research Laboratory, Wright-Patterson AFB, Ohio 45433 (United States); Lin, Qiang, E-mail: email@example.com [Institute of Optics, University of Rochester, Rochester, New York 14627 (United States); Department of Electrical and Computer Engineering, University of Rochester, Rochester, New York 14627 (United States)
We propose and demonstrate a convenient and sensitive technique for precise engineering of group-velocity dispersion in high-Q silicon microresonators. By accurately controlling the surface-oxidation thickness of silicon microdisk resonators, we are able to precisely manage the zero-dispersion wavelength, while simultaneously further improving the high optical quality of our devices, with the optical Q close to a million. The demonstrated dispersion management allows us to achieve parametric generation with precisely engineerable emission wavelengths, which shows great potential for application in integrated silicon nonlinear and quantum photonics.
Dispersion engineering of high-Q silicon microresonators via thermal oxidation
Jiang, Wei C; Usechak, Nicholas G; Lin, Qiang
We propose and demonstrate a convenient and sensitive technique for precise engineering of group-velocity dispersion in high-Q silicon microresonators. By accurately controlling the surface-oxidation thickness of silicon microdisk resonators, we are able to precisely manage the zero-dispersion wavelength while simultaneously further improving the high optical quality of our devices, with the optical Q close to a million. The demonstrated dispersion management allows us to achieve parametric generation with precisely engineerable emission wavelengths, which shows great potential for application in integrated silicon nonlinear and quantum photonics.
Dispersion engineering of high-Q silicon microresonators via thermal oxidation
NASA Astrophysics Data System (ADS)
Jiang, Wei C.; Zhang, Jidong; Usechak, Nicholas G.; Lin, Qiang
We propose and demonstrate a convenient and sensitive technique for precise engineering of group-velocity dispersion in high-Q silicon microresonators. By accurately controlling the surface-oxidation thickness of silicon microdisk resonators, we are able to precisely manage the zero-dispersion wavelength, while simultaneously further improving the high optical quality of our devices, with the optical Q close to a million. The demonstrated dispersion management allows us to achieve parametric generation with precisely engineerable emission wavelengths, which shows great potential for application in integrated silicon nonlinear and quantum photonics.
Titanium-silicon oxide film structures for polarization-modulated infrared reflection absorption spectroscopy
Dunlop, Iain E.; Zorn, Stefan; Richter, Gunther; Srot, Vesna; Kelsch, Marion; van Aken, Peter A.; Skoda, Maximilian; Gerlach, Alexander; Spatz, Joachim P.; Schreiber, Frank
We present a titanium-silicon oxide film structure that permits polarization modulated infrared reflection absorption spectroscopy on silicon oxide surfaces. The structure consists of a ~6 nm sputtered silicon oxide film on a ~200 nm sputtered titanium film. Characterization using conventional and scanning transmission electron microscopy, electron energy loss spectroscopy, X-ray photoelectron spectroscopy and X-ray reflectometry is presented. We demonstrate the use of this structure to investigate a selectively protein-resistant self-assembled monolayer (SAM) consisting of silane-anchored, biotin-terminated poly(ethylene glycol) (PEG). PEG-associated IR bands were observed. Measurements of protein-characteristic band intensities showed that this SAM adsorbed streptavidin whereas it repelled bovine serum albumin, as had been expected from its structure. PMID:20418963
Titanium-silicon oxide film structures for polarization-modulated infrared reflection absorption spectroscopy.
Dunlop, Iain E; Zorn, Stefan; Richter, Gunther; Srot, Vesna; Kelsch, Marion; van Aken, Peter A; Skoda, Maximilian; Gerlach, Alexander; Spatz, Joachim P; Schreiber, Frank
We present a titanium-silicon oxide film structure that permits polarization modulated infrared reflection absorption spectroscopy on silicon oxide surfaces. The structure consists of a ~6 nm sputtered silicon oxide film on a ~200 nm sputtered titanium film. Characterization using conventional and scanning transmission electron microscopy, electron energy loss spectroscopy, X-ray photoelectron spectroscopy and X-ray reflectometry is presented. We demonstrate the use of this structure to investigate a selectively protein-resistant self-assembled monolayer (SAM) consisting of silane-anchored, biotin-terminated poly(ethylene glycol) (PEG). PEG-associated IR bands were observed. Measurements of protein-characteristic band intensities showed that this SAM adsorbed streptavidin whereas it repelled bovine serum albumin, as had been expected from its structure. PMID:20418963
Solutions of Simultaneous Equations for Oxidation Enhanced and Retarded Diffusions and Oxidation Stacking Fault in Silicon
NASA Astrophysics Data System (ADS)
Yoshida, Masayuki; Matsumoto, Satoru; Ishikawa, Yutaka
Equations for oxidation enhanced and retarded diffusions (OED and ORD) and oxidation stacking faults (OSF) in silicon have been solved simultaneously, using experimental results at 1100░C for 1.0Î 104--2.4Î 105 s. A simple relation between the concentrations of self-interstitials and vacancies was assumed in order to obtain the solutions. It is concluded that the product of the concentrations of the self-interstitials and vacancies, CICV, is nearly equal to the value for thermal equilibrium, CI0CV0, and that the fractional components of the interstitialcy mechanism for self-, Sb and P diffusions are smaller than 0.5, smaller than 0.5 and larger than 0.5, respectively. This shows that the growth of OSF is caused mainly by the undersaturation of a vacancy, and that the ORD of Sb and the OED of P occur. The time dependences of the supersaturation ratios of the self-interstitials and vacancies were also obtained.
Effective surface passivation of p-type crystalline silicon with silicon oxides formed by light-induced anodisation
NASA Astrophysics Data System (ADS)
Cui, Jie; Grant, Nicholas; Lennon, Alison
Electronic surface passivation of p-type crystalline silicon by anodic silicon dioxide (SiO2) was investigated. The anodic SiO2 was grown by light-induced anodisation (LIA) in diluted sulphuric acid at room temperature, a process that is significantly less-expensive than thermal oxidation which is widely-used in silicon solar cell fabrication. After annealing in oxygen and then forming gas at 400 ░C for 30 min, the effective minority carrier lifetime of 3-5 ? cm, boron-doped Czochralski silicon wafers with a phosphorus-doped 80 ?/? emitter and a LIA anodic SiO2 formed on the p-type surface was increased by two orders of magnitude to 150 ?s. Capacitance-voltage measurements demonstrated a very low positive charge density of 3.4 Î 1011 cm-2 and a moderate density of interface states of 6 Î 1011 eV-1 cm-2. This corresponded to a silicon surface recombination velocity of 62 cm s-1, which is comparable with values reported for other anodic SiO2 films, which required higher temperatures and longer growth times, and significantly lower than oxides grown by chemical vapour deposition techniques. Additionally, a very low leakage current density of 3.5 Î 10-10 and 1.6 Î 10-9 A cm-2 at 1 and -1 V, respectively, was measured for LIA SiO2 suggesting its potential application as insulation layer in IBC solar cells and a barrier for potential induced degradation.
Bismuth-doped germanosilicate fibre laser with 20-W output power at 1460 nm
Firstov, Sergei V; Shubin, Aleksei V; Khopin, V F; Mel'kumov, Mikhail A; Bufetov, Igor' A; Medvedkov, O I; Gur'yanov, Aleksei N; Dianov, Evgenii M
We report the first cw bismuth - germanium codoped silica fibre laser with an output power above 20 W at 1460 nm and 50% optical efficiency. The laser operates on a transition between energy levels of bismuth-related active centres associated with silicon. The incorporation of a small amount ({approx}5 mol %) of germanium into the core of bismuth-doped silica fibre has little effect on its luminescence spectrum but reduces optical losses, which limit the laser efficiency. (letters)
A high-speed silicon optical modulator based on a metal-oxide-semiconductor capacitor.
Liu, Ansheng; Jones, Richard; Liao, Ling; Samara-Rubio, Dean; Rubin, Doron; Cohen, Oded; Nicolaescu, Remus; Paniccia, Mario
Silicon has long been the optimal material for electronics, but it is only relatively recently that it has been considered as a material option for photonics. One of the key limitations for using silicon as a photonic material has been the relatively low speed of silicon optical modulators compared to those fabricated from III-V semiconductor compounds and/or electro-optic materials such as lithium niobate. To date, the fastest silicon-waveguide-based optical modulator that has been demonstrated experimentally has a modulation frequency of only approximately 20 MHz (refs 10, 11), although it has been predicted theoretically that a approximately 1-GHz modulation frequency might be achievable in some device structures. Here we describe an approach based on a metal-oxide-semiconductor (MOS) capacitor structure embedded in a silicon waveguide that can produce high-speed optical phase modulation: we demonstrate an all-silicon optical modulator with a modulation bandwidth exceeding 1 GHz. As this technology is compatible with conventional complementary MOS (CMOS) processing, monolithic integration of the silicon modulator with advanced electronics on a single silicon substrate becomes possible. PMID:14961115
Fabrication of OSOS cells by neutral ion beam sputtering. [Oxide Semiconductor On Silicon solar cells
NASA Technical Reports Server (NTRS)
Burk, D. E.; Dubow, J. B.; Sites, J. R.
Oxide semiconductor on silicon (OSOS) solar cells have been fabricated from various indium tin oxide (In2O3)x(SnO2)1-x compositions sputtered onto p-type single crystal silicon substrates with a neutralized argon ion beam. High temperature processing or annealing was not required. The highest efficiency was achieved with x = 0.91 and was 12 percent. The cells are environmentally rugged, chemically stable, and show promise for still higher efficiencies. Moreover, the ion beam sputtering fabrication technique is amenable to low cost, continuous processing.
Highly reliable ultrathin silicon oxide film formation at low temperature by oxygen radical generated in high-density krypton plasma
Katsuyuki Sekine; Yuji Saito; Masaki Hirayama; Tadahiro Ohmi
This paper focuses attention on electrical properties of silicon oxide films grown by oxygen radical generated in Kr\\/O2 mixed high-density microwave-excited plasma at 400░C. They represent high growth rate, low activation energy, high dielectric strength, high charge-to-breakdown, and low interface trap density and bulk charge enough to replace thermally grown silicon oxide
Plasma-Sprayed Refractory Oxide Coatings on Silicon-Base Ceramics
NASA Technical Reports Server (NTRS)
Tewari, Surendra
Silicon-base ceramics are promising candidate materials for high temperature structural applications such as heat exchangers, gas turbines and advanced internal combustion engines. Composites based on these materials are leading candidates for combustor materials for HSCT gas turbine engines. These materials possess a combination of excellent physical and mechanical properties at high temperatures, for example, high strength, high toughness, high thermal shock resistance, high thermal conductivity, light weight and excellent oxidation resistance. However, environmental durability can be significantly reduced in certain conditions such as when molten salts, H2 or water vapor are present. The oxidation resistance of silicon-base materials is provided by SiO2 protective layer. Molten salt reacts with SiO2 and forms a mixture of SiO2 and liquid silicate at temperatures above 800C. Oxygen diffuses more easily through the chemically altered layer, resulting in a catastrophic degradation of the substrate. SiC and Si3N4 are not stable in pure H2 and decompose to silicon and gaseous species such as CH4, SiH, SiH4, N2, and NH3. Water vapor is known to slightly increase the oxidation rate of SiC and Si3N4. Refractory oxides such as alumina, yttria-stabilized zirconia, yttria and mullite (3Al2O3.2SiO2) possess excellent environmental durability in harsh conditions mentioned above. Therefore, refractory oxide coatings on silicon-base ceramics can substantially improve the environmental durability of these materials by acting as a chemical reaction barrier. These oxide coatings can also serve as a thermal barrier. The purpose of this research program has been to develop refractory oxide chemical/thermal barrier coatings on silicon-base ceramics to provide extended temperature range and lifetime to these materials in harsh environments.
Facile preparation of highly-dispersed cobalt-silicon mixed oxide nanosphere and its catalytic application in cyclohexane selective oxidation
Highly dispersed cobalt-silicon mixed oxide [Co-SiO2] nanosphere was successfully prepared with a modified reverse-phase microemulsion method. This material was characterized in detail by X-ray diffraction, transmission electron microscopy, Fourier transform infrared, ultraviolet-visible diffuse reflectance spectra, X-ray absorption spectroscopy near-edge structure, and N2 adsorption-desorption measurements. High valence state cobalt could be easily obtained without calcination, which is fascinating for the catalytic application for its strong oxidation ability. In the selective oxidation of cyclohexane, Co-SiO2 acted as an efficient catalyst, and good activity could be obtained under mild conditions. PMID:22067075
Effect of external gettering with porous silicon on the electrical properties of Metal-Oxide-Silicon devices
NASA Astrophysics Data System (ADS)
Khedher, N.; Ben Jaballah, A.; Boua´cha, M.; Ezzaouia, H.; Bennnaceur, R.
We study in this paper the effect of porous silicon (PS)-based gettering procedure on electronic quality of p-type Czochralski silicon wafers. We analyzed the effect of N2 and O2 atmospheres on the gettering effectiveness. In addition, we give results on using co-gettering procedures based on the combination of PS with Aluminium (Al), and PS with phosphorus (P). Experiments are made in a closed infrared tubular furnace for temperatures ranging between 700á?C and 950á?C. The efficiency of gettering was monitored by Hall mobility of majority charge carriers deduced from Hall Effect measurement at ambient temperature of the fabricated Metal-Oxide-Silicon (MOS) devices. These results are confirmed with Capacitance-Voltage (C-V) spectroscopy technique at high frequency. Hence, in the linear region of C-2-(V) characteristics of the Schottky diode, the slope of curves (in linear regions) decreases, which indicates an improvement of the ionized boron concentration in the p-type silicon. Results are analyzed and compared to those carried out on a reference sample (i.e.; without gettering).
Effects of dielectric barrier discharges on silicon surfaces: Surface roughness, cleaning, and oxidation
NASA Astrophysics Data System (ADS)
Michel, B.; Giza, M.; Krumrey, M.; Eichler, M.; Grundmeier, G.; Klages, C.-P.
Silicon wafers were exposed to a dielectric barrier discharge (DBD) at atmospheric pressure, which was ignited by applying a high voltage (>12 kV peak voltage) to a small gap (dg=300 ?m) above the wafer surface in an oxygen process gas atmosphere. The effect of the DBD on H-terminated silicon and native silicon oxide surfaces was investigated in situ and ex situ by means of Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy (XPS). The influence of the treatment on surface roughness was studied by atomic force microscopy. In order to determine the thickness of the newly formed oxide under DBD influence, the method of calculating the oxide thickness from the Si 2p peak ratio in the XPS spectrum, which has so far been described for thermal oxides only, was adopted with x-ray reflectometry calibration samples. Additionally, infrared spectroscopy and spectroscopic ellipsometry were used to verify the XPS measurements. The calculated thickness values can be fitted with the growth law d =d0 ln[(t /?)+k], with d being the oxide thickness, grown during DBD exposure time t. Oxide thicknesses of more than 3 nm could be achieved within 350 s DBD exposure time. Our analysis of infrared spectra, XPS, and ellipsometry leads us to conclude that the newly formed oxide is porous with a pore fraction of roughly 10%.
Role of gate oxide thickness in controlling short channel effects in polycrystalline silicon thin film transistors
NASA Astrophysics Data System (ADS)
Valletta, A.; Gaucci, P.; Mariucci, L.; Pecora, A.; CuscunÓ, M.; Maiolo, L.; Fortunato, G.; Brotherton, S. D.
The drain bias induced threshold voltage variation in short channel (L =0.4 ?m) polycrystalline silicon thin-film transistors (TFTs), with different gate oxide thicknesses, is investigated with combined experimental measurements and numerical simulations. Drain-induced barrier lowering (DIBL) and floating body effects (FBEs), triggered by impact ionization, are the main causes of such variations. However, the effects are counterbalancing, with a reducing oxide thickness reducing DIBL, while, at the same time, increasing the relative impact of the FBE. Hence, drain bias induced threshold voltage changes, when normalized by oxide thickness, are independent of the gate oxide thickness in these TFTs.
Investigation of Low Temperature, Atomic-Layer-Deposited Oxides on 4Hydrigen-Silicon Carbide and their Effect on the Silicon Carbide/Silicon Dioxide Interface
NASA Astrophysics Data System (ADS)
Haney, Sarah Kay
Silicon carbide has long been considered an excellent substrate for high power, high temperature applications. Fabrication of conventional MOSFETs on silicon carbide (SiC) relies on thermal oxidation of the SiC for formation of the silicon dioxide (SiO2) gate oxide. Historically, direct oxidation was viewed favorably due to ease of fabrication. However, the resulting MOS devices have exhibited significant interface trap densities, Dit , which reduce effective inversion layer mobility by capturing free carriers and enhancing scattering. While nitridation has been shown to reduce Dit, the inversion layer electron mobility of these devices is still limited by the presence of carbon near the interface. Studies have suggested a low mobility transition region between the SiC and SiO2, on the SiC side, attributed to increased carbon concentration resulting from the thermal oxidation of the SiC. In this work, we have investigated the low temperature, atomic layer deposition (ALD) of SiO2 onto SiC compared to thermal oxidation of SiC for the fabrication of MOS devices. Avoiding the carbon out diffusion and subsequent carbon build-up resulting from thermal oxidation is expected to result in a superior, higher mobility MOSFET. A three-step ALD process using 3-aminopropyltriethoxysiliane (3-APTES), ozone and water was evaluated on silicon and SiC substrates. Ellipsometry and XPS were used to characterize blanket films, and showed good results. Capacitors fabricated on SiC showed the need for optimized post deposition anneals. The effect of post oxidation anneals in nitrogen, forming gas and nitric oxide were examined. The standard nitric oxide (NO) anneal that is used to improve Dit after thermal oxidation was also shown to be the best anneal for the low temperature deposited ALD oxides. Materials characterization of the nitrided ALD and nitrided thermal oxide samples was completed using STEM/EELS techniques in addition to the ellipsometry and XPS. STEM/EELS analysis of the samples revealed no significant difference in transition regions on either side of the SiC/SiO2 interface regardless of oxidation technique or anneal temperature or ambient. All samples analyzed exhibited approximately 2-3nm of transition region on either side of the interface with no evidence of carbon or silicon rich regions. XPS was also used to determine a valence band offset of 2.43eV for the ALD oxide on 4H-SiC. Lateral MOSFETs were fabricated on 4H-SiC substrates with the following oxidation treatments: thermal oxidation at 1175░C, thermal oxidation at 1175░C followed by a nitric oxide (NO) anneal at 1175░C, and ALD of SiC at 150░C followed by an NO post oxidation anneal (POA) at 1175░C. ALD of the SiO2 was performed using 3-aminopropyltriethoxysiliane (3-APTES), ozone and water. Field effect mobility values were comparable for these samples, suggesting common thermal oxidation steps were still limiting the mobility. As such additional lateral MOSFETs were fabricated without the incoming sacrificial oxidation steps. This sacrificial-oxidation free experiment showed a 15% improvement in peak field effect mobility for the nitrided ALD oxide samples as compared to the nitrided thermal oxides. SIMS of the interfaces revealed nitrogen concentrations of ÿ6E21 at/cc in the nitrided ALD sample compared to ÿ4-6E20 in the nitrided thermal sample. This extremely high level of nitrogen incorporation, which is unparalleled in NO annealed thermal oxides, is accountable for the increase in field effect mobility. The low deposition temperature of the ALD oxide causes high levels of carbon incorporation and greater number of dangling bonds at the interface. Both the dangling bonds and excess carbon acts as binding sites for the nitrogen, increasing the nitrogen concentration and resulting in higher mobilities. Results presented support the use of SiO2 deposited using low temperature atomic layer deposition for improved gate oxides on 4H-SiC MOSFETs given the opportunity for increased nitrogen incorporation. The elevated levels of nitrogen measured in the NO annealed
Low-index nanopatterned barrier for hybrid oxide-free III-V silicon conductive bonding.
Bougot-Robin, Kristelle; Talneau, Anne; Benisty, Henri
Oxide-free bonding of a III-V active stack emitting at 1300-1600 nm to a silicon-on-insulator wafer offers the capability to electrically inject lasers from the silicon side. However, a typical 500-nm-thick silicon layer notably attracts the fundamental guided mode of the silicon + III-V stack, a detrimental feature compared to established III-V Separate-Confinement Heterostructure (SCH) stacks. We experimentally probe with photoluminescence as an internal light source the guiding behavior for oxide-free bonding to a nanopatterned silicon wafer that acts as a low-index barrier. We use a sub-wavelength square array of small holes as an effective "low-index silicon" medium. It is weakly modulated along one dimension (superperiodic array) to outcouple the resulting guided modes to free space, where we use an angle-resolved spectroscopy study. Analysis of experimental branches confirms the capability to operate with a fundamental mode well localized in the III-V heterostructures. PMID:25321802
Photoluminescence stabilization of anodically-oxidized porous silicon layers by chemical functionalization
NASA Astrophysics Data System (ADS)
Boukherroub, Rabah; Wayner, Danial D. M.; Lockwood, David J.
Electrochemical oxidation of porous silicon (PSi) produces a surface that is covered with native silicon-hydrogen (Si-Hx) bonds and regions with oxidized Si-Si back-bonds (OSi-Hx). Such anodically oxidized PSi layers were chemically modified using 1-decene under thermal conditions. The hydrosilylation reaction consumes mainly the nonoxidized Si-Hx bonds and yields a surface with oxidized and alkylated regions that were characterized using transmission IR and Raman spectroscopies. The brightest photoluminescence (PL) was obtained when the PSi sample was anodized in 1 M sulfuric acid (H2SO4) at 3 mA/cm2 for 5 min. The chemical process preserves the PL and the physical properties of the porous layer. The derivatized PSi surfaces are stable in boiling CCl4 and in water.
Growth of thin silver films on silicon oxide pretreated by low temperature argon plasma
NASA Astrophysics Data System (ADS)
Romanyuk, Andriy; Steiner, Roland; Mack, Iris; Oelhafen, Peter; Mathys, Daniel
In the present study, we investigate the influence of low energy ion bombardment on nucleation and growth of thin silver films on silicon oxide by in situ photoelectron spectroscopy (PES) combined with specific resistivity measurements. Thermally grown thin silicon oxide films were exposed to a low temperature argon plasma for different time intervals resulting in changes in surface chemical composition as monitored by angle-resolved X-ray photoelectron spectroscopy (ARXPS). We demonstrate that irradiation of the oxide surface with low energy ions results in substantially changed nucleation of silver. Furthermore, silver films deposited on plasma treated oxide tend to have lower resistivity which is attributed to the effect of reduced grain boundary and surface roughness.
The generation mechanism of silicon oxideûaluminum oxide compound clusters by laser ablation of siliceous materials
Can Xu; Yingcai Long; Shixiong Qian; Yufen Li
The generation of silicon dioxideûaluminum oxide compound clusters under 308 nm XeCl excimer laser ablation of ZSM-5 zeolites with different SiO2\\/Al2O3 ratios was studied by time-of-flight mass spectrometry. Two Al-containing cluster sequences [(SiO2)n?1(AlO2)]? and [(SiO2)nOAl]? are observed in the negative ion channel. Through the relationship between the abundance distribution of cluster sequences and the silicon aluminum ratio, the growth mechanism
Development of an oxidized porous silicon vacuum microtriode
Smith, Don Deewayne
parameters. We have done the first such study, fabricating diodes from p, p, and n silicon substrates. Anodization current densities from llmAlcm2 to 15lmAlcm2 were used, and Fowler-Nordheim behavior was observed in over 80% of the samples...
S. Yajima; Y. Kamemoto; Y. Takahashi
The outline of the structure of a bismuth loop is given. The loop was ; charged with bismuth by pressurizing the sumptank with nitrogen gas. In ; operation, the bismuth was pumped by means of a mechanical pump to III, II, and I ; vessels and a flowmeter. The temperature of bismuth metal was controlled at 550 ; deg C
A Model for the Oxidation of Carbon Silicon Carbide Composite Structures
NASA Technical Reports Server (NTRS)
Sullivan, Roy M.
A mathematical theory and an accompanying numerical scheme have been developed for predicting the oxidation behavior of carbon silicon carbide (C/SiC) composite structures. The theory is derived from the mechanics of the flow of ideal gases through a porous solid. The result of the theoretical formulation is a set of two coupled nonlinear differential equations written in terms of the oxidant and oxide partial pressures. The differential equations are solved simultaneously to obtain the partial vapor pressures of the oxidant and oxides as a function of the spatial location and time. The local rate of carbon oxidation is determined using the map of the local oxidant partial vapor pressure along with the Arrhenius rate equation. The nonlinear differential equations are cast into matrix equations by applying the Bubnov-Galerkin weighted residual method, allowing for the solution of the differential equations numerically. The numerical method is demonstrated by utilizing the method to model the carbon oxidation and weight loss behavior of C/SiC specimens during thermogravimetric experiments. The numerical method is used to study the physics of carbon oxidation in carbon silicon carbide composites.
Configurational statistical model for the damaged structure of silicon oxide after ion implantation
NASA Astrophysics Data System (ADS)
Garrido, B.; Samitier, J.; Morante, J. R.; Montserrat, J.; DomÝnguez, C.
A configurational model for silicon oxide damaged after a high-dose ion implantation of a nonreactive species is presented. Based on statistics of silicon-centered tetrahedra, the model takes into account not only the closest environment of a given silicon atom, but also the second neighborhood, so it is specified whether the oxygen attached to one given silicon is bridging two tetrahedra or not. The frequencies and intensities of infrared vibrational bands have been calculated by averaging over the distributions and these results are in agreement with the ones obtained from infrared experimental spectra. Likewise, the chemical shifts obtained from x-ray photoelectron spectroscopy (XPS) analysis are similar to the reported values for the charge-transfer model of SiOx compounds.
Characterization of Silicon Oxide Nanowires Directly Grown from NiO/Si
NASA Astrophysics Data System (ADS)
Park, Byoungtae; Yong, Kijung
Amorphous silicon oxide nanowires (a-SiONW's) were synthesized on a NiO-catalyzed silicon substrate through a simple thermal annealing at 1000-1100░C without any additional silicon source materials. The synthesized nanowires were highly pure (no metal catalyst contamination) and very long (hundreds of micrometers). Most nanowires had a diameter in the range of 50-100 nm. The nickel oxide nanoparticles play a peculiar role in the synthesis of a-SiONW's. The growth of a-SiONW's is most likely controlled by the solid-liquid-solid (SLS) mechanism. IR absorption characteristics clearly showed bending (796 cm-1) and asymmetric stretching (1075 cm-1) modes of Si-O-Si bonds in a-SiONW's. An extraordinary UV emission at 370 nm was observed from a-SiONW's, which could be attributed to defect centers of oxygen excess in the nanowires.
Graded refraction index antireflection coatings based on silicon and titanium oxides
Abdelhakim Mahdjoub
Thin films with a graded refraction index constituted from silicon and titanium oxides were deposited by plasma enhanced chemical vapor deposition using electron cyclotron resonance. A plasma of oxygen reacted with two precursors: the tetraethoxysilane (TEOS) and the titanium isopropoxide (TIPT). The automatic regulation of the precursor flows makes it possible to modify the chemical composition, and consequently the optical
Metal Oxide Silicon /MOS/ transistors protected from destructive damage by wire
NASA Technical Reports Server (NTRS)
Deboo, G. J.; Devine, E. J.
Loop of flexible, small diameter, nickel wire protects metal oxide silicon /MOS/ transistors from a damaging electrostatic potential. The wire is attached to a music-wire spring, slipped over the MOS transistor case, and released so the spring tensions the wire loop around all the transistor leads, shorting them together. This allows handling without danger of damage.
Effect of Oxide on Trench Edge Defect Formation in Ion-Implanted Silicon
Florida, University of
that stress from oxide SiO2 trench structures in ion-implanted silicon Si wafers can lead to the formation-edge defects during SPE in Si wafers amorphized by Si+ implantation. For this study, 300 mm 001 wafers were patterned with SiO2-filled trenches 400 nm deep. After patterning, the wafers were implanted with Si
Silicon-on-insulator technology for high temperature metal oxide semiconductor devices and circuits
Denis Flandre
The high temperature characteristics of devices and circuits realized in complementary metal oxide semiconductor (CMOS) technology on silicon-on-insulator (SOI) substrates are compared with other materials, and it is demonstrated that CMOS on SOI is presently the most suitable process for the realization of electronic circuits operating at up to more than 300 ░C.
Active silicon octagonal micropillar resonator modulators using metal-oxide-semiconductor capacitors
Chao Li; Andrew W. Poon
We propose active silicon waveguide-coupled octagonal micropillar resonator modulators using metal-oxide-semiconductor capacitors. Our initial electrical and optical simulations suggest a high-extinction ratio resonance modulation by selectively embedding capacitors along the octagonal micropillar rim region.
Improved reaction sintered silicon nitride. [protective coatings to improve oxidation resistance
NASA Technical Reports Server (NTRS)
Baumgartner, H. R.
Processing treatments were applied to as-nitrided reaction sintered silicon nitride (RSSN) with the purposes of improving strength after processing to above 350 MN/m2 and improving strength after oxidation exposure. The experimental approaches are divided into three broad classifications: sintering of surface-applied powders; impregnation of solution followed by further thermal processing; and infiltration of molten silicon and subsequent carburization or nitridation of the silicon. The impregnation of RSSN with solutions of aluminum nitrate and zirconyl chloride, followed by heating at 1400-1500 C in a nitrogen atmosphere containing silicon monoxide, improved RSSN strength and oxidation resistance. The room temperature bend strength of RSSN was increased nearly fifty percent above the untreated strength with mean absolute strengths up to 420 MN/m2. Strengths of treated samples that were measured after a 12 hour oxidation exposure in air were up to 90 percent of the original as-nitrided strength, as compared to retained strengths in the range of 35 to 60 percent for untreated RSSN after the same oxidation exposure.
Giant isotope effect in hot electron degradation of metal oxide silicon devices
Karl Hess; Isik C. Kizilyalli; Joseph W. Lyding
A giant isotope effect of hot electron degradation was found by annealing and passivating integrated circuits of recent complementary metal oxide silicon (CMOS) technology with deuterium instead of hydrogen. In this paper, we summarize our experience and present new results of secondary ion mass spectroscopy that correlate deuterium accumulation with reduced hot electron degradation. We also present a first account
Uses of corona oxide silicon (COS) measurements for diffusion process monitoring and troubleshooting
Richard G. Cosway; Kelvin B. Catmull; Janie Shray; Robert Naujokaitis; Megan Peters; Don Grant; G. Horner; B. Letherer
The dynamic nature of modern semiconductor fabrication facilities requires metrology tools that can be used to diagnose infrequent problems. However, due to the high cost of clean room floor space, these tools should also provide routine monitoring capability and be able to diagnose numerous issues. For a diffusion area, the corona oxide silicon (COS) measurement technique lends itself well to
Oxidative dehydrogenation of n-butene to 1,3-butadiene over multicomponent bismuth molybdate (M II 9Fe 3Bi 1Mo 12O 51) catalysts: Effect of divalent metal (M II)
Ji Chul Jung; Howon Lee; Jeong Gil Seo; Sunyoung Park; Young-Min Chung; Tae Jin Kim; Seong Jun Lee; Seung-Hoon Oh; Yong Seung Kim; In Kyu Song
Multicomponent bismuth molybdate (MII9Fe3Bi1Mo12O51) catalysts with different divalent metal (MII=Mg, Mn, Co, Ni, and Zn) were prepared by a co-precipitation method, and were applied to the oxidative dehydrogenation of n-butene to 1,3-butadiene. Effect of divalent metal (MII) on the catalytic performance of MII9Fe3Bi1Mo12O51 catalysts was investigated. X-ray photoelectron spectroscopy (XPS) measurements were conducted to determine the oxygen mobility of MII9Fe3Bi1Mo12O51
Low-damage direct patterning of silicon oxide mask by mechanical processing
To realize the nanofabrication of silicon surfaces using atomic force microscopy (AFM), we investigated the etching of mechanically processed oxide masks using potassium hydroxide (KOH) solution. The dependence of the KOH solution etching rate on the load and scanning density of the mechanical pre-processing was evaluated. Particular load ranges were found to increase the etching rate, and the silicon etching rate also increased with removal of the natural oxide layer by diamond tip sliding. In contrast, the local oxide pattern formed (due to mechanochemical reaction of the silicon) by tip sliding at higher load was found to have higher etching resistance than that of unprocessed areas. The profile changes caused by the etching of the mechanically pre-processed areas with the KOH solution were also investigated. First, protuberances were processed by diamond tip sliding at lower and higher stresses than that of the shearing strength. Mechanical processing at low load and scanning density to remove the natural oxide layer was then performed. The KOH solution selectively etched the low load and scanning density processed area first and then etched the unprocessed silicon area. In contrast, the protuberances pre-processed at higher load were hardly etched. The etching resistance of plastic deformed layers was decreased, and their etching rate was increased because of surface damage induced by the pre-processing. These results show that etching depth can be controlled by controlling the etching time through natural oxide layer removal and mechanochemical oxide layer formation. These oxide layer removal and formation processes can be exploited to realize low-damage mask patterns. PMID:24948891
Analyses of silicon dioxide, magnesium oxide, lead fluoride, bismuth as low-pass velocity filters for neutrons
NASA Technical Reports Server (NTRS)
Connor, D.; Holmryd, S.
Transmission measurement of neutrons by filter materials for low energy neutrons is important for the study of structure and dynamics of condensed matter. Since only thermal neutrons are useful for such experiments, filter materials that transmit thermal neutrons while attenuating fast neutrons and gamma rays are of considerable interest.
Oxygen-18 tracer study of the passive thermal oxidation of silicon
NASA Technical Reports Server (NTRS)
Cawley, J. D.; Halloran, J. W.; Cooper, A. R.
This work focuses on the thermal oxidation of silicon near 1273 K using the double-tracer oxidation method. The results confirm that oxidation occurs by the transport of electrically neutral nonnetwork oxygen through the interstitial space of the vitreous silica (v-SiO2) scale. Simultaneously, self- (or isotopic-) diffusion occurs in the network, resulting in characteristic isotopic fraction distributions near the gas-scale interface. The self-diffusion coefficients calculated from these profiles agree with those reported for tracer diffusion in v-SiO2, and the diffusion coefficient calculated from the scale growth is consistent with reported O2 permeation data. An important parameter that describes the double-oxidation behavior is a ratio relating the scale thickness grown during the second oxidation, the network self-diffusion coefficient for oxygen, and the time of the second oxidation.
Oxidation Kinetics of Chemically Vapor-Deposited Silicon Carbide in Wet Oxygen
NASA Technical Reports Server (NTRS)
Opila, Elizabeth J.
The oxidation kinetics of chemically vapor-deposited SiC in dry oxygen and wet oxygen (P(sub H2O) = 0.1 atm) at temperatures between 1200 C and 1400 C were monitored using thermogravimetric analysis. It was found that in a clean environment, 10% water vapor enhanced the oxidation kinetics of SiC only very slightly compared to rates found in dry oxygen. Oxidation kinetics were examined in terms of the Deal and Grove model for oxidation of silicon. It was found that in an environment containing even small amounts of impurities, such as high-purity Al2O3 reaction tubes containing 200 ppm Na, water vapor enhanced the transport of these impurities to the oxidation sample. Oxidation rates increased under these conditions presumably because of the formation of less protective sodium alumino-silicate scales.
The high-temperature oxidation, reduction, and volatilization reactions of silicon and silicon carbide
Earl A. Gulbransen; Sven A. Jansson
A thermochemical analysis was made of the oxidation, reduction, and volatilization reactions which occur in the Si-O-C system. One characteristic feature is the high SiO(g) and SiO(g) + CO(g) pressures at the Si(s)-SiO2 and SiC(s)-SiO2(s) interfaces. Active oxidation with weight losses and passive oxidation with weight gains were found on oxidizing Si(s) and SiC(s) in low oxygen pressures above 1000░C.
Oxidation and sulfidation resistant alloys with silicon additions
Dunning, John S.; Alman, David E.; Poston, J.A., Jr. (NETL); Siriwardane, R. (NETL)
The Albany Research Center (ARC) has considerable experience in developing lean chromium, austenitic stainless steels with improved high temperature oxidation resistance. Using basic alloy design principles, a baseline composition of Fe-16Cr-16Ni-2Mn-1Mo alloys with Si and Al addition at a maximum of 5 weight percent was selected for potential application at temperatures above 700║C for supercritical and ultra-supercritical power plant application. The alloys were fully austenitic. Cyclic oxidation tests in air for 1000 hours were carried out on alloys with Si only or combined Si and Al additions in the temperature range 700║C to 800║C. Oxidation resistances of alloys with Si only additions were outstanding, particularly at 800║C (i.e., these alloys possessed weight gains 4 times less than a standard type-304 alloy). In addition, Si alloys pre-oxidized at 800║C, showed a zero weight gain in subsequent testing for 1000 hours at 700║C. Similar improvements were observed for Si only alloy after H2S exposure at 700║C compared with type 304 stainless steel. SEM and ESCA analysis of the oxide films and base material at the oxide/base metal interface were conducted to study potential rate controlling mechanisms at ARC. Depth profile analysis and element concentration profiles (argon ion etching/x-ray photoelectron spectroscopy) were conducted on oxidized specimens and base material at the National Energy Technology Laboratory.
Correlations between Self-Interstitials and Vacancies during Thermal Oxidation in Silicon
NASA Astrophysics Data System (ADS)
Okino, Takahisa
It is generally accepted that there are four relations between self-interstitials and vacancies during thermal oxidation in silicon; local equilibrium between self-interstitials and vacancies, oxidation-enhanced and -retarded diffusions (OED and ORD) and oxidation stacking faults (OSF). From a mathematical point of view on these relations, a method for their analysis was established. The results of this study clearly indicate some OED, ORD and OSF to be governed by only an interstitialcy or vacancy mechanism. A method for obtaining analytical solutions is also discussed.
Dependence of cryogenic strength of hydroxide catalysis bonded silicon on type of surface oxide
NASA Astrophysics Data System (ADS)
Beveridge, N. L.; van Veggel, A. A.; Cunningham, L.; Hough, J.; Martin, I. W.; Nawrodt, R.; Reid, S.; Rowan, S.
Hydroxide catalysis bonding is a joining technique used in the construction of highly stable opto-mechanical systems including quasi-monolithic silica suspensions for first and second generation gravitational wave detectors. Future generations of detector are likely to operate at cryogenic temperatures necessitating a change in testmass/suspension material. A promising candidate material is silicon, which requires an oxide surface layer for hydroxide catalysis bonding to be reliable. Here, we present first results showing the influence of the type of oxide layer applied on bond strength, measured at room temperature and 77 K, and identify preferred oxide deposition methods.
Modelling of silicon oxynitridation by nitrous oxide using the reaction rate approach
Dominique Krzeminski, Christophe, E-mail: email@example.com [DÚpartment ISEN, IEMN-UMR-8520, 41 Boulevard Vauban, 59046 Lille Cedex (France)
Large technological progress in oxynitridation processing leads to the introduction of silicon oxynitride as ultra-thin gate oxide. On the theoretical side, few studies have been dedicated to the process modelling of oxynitridation. Such an objective is a considerable challenge regarding the various atomistic mechanisms occurring during this fabrication step. In this article, some progress performed to adapt the reaction rate approach for the modelling of oxynitride growth by a nitrous ambient are reported. The Ellis and Buhrman's approach is used for the gas phase decomposition modelling. Taking into account the mass balance of the species at the interface between the oxynitride and silicon, a minimal kinetic model describing the oxide growth has been calibrated and implemented. The influence of nitrogen on the reaction rate has been introduced in an empirical way. The oxidation kinetics predicted with this minimal model compares well with several experiments.
Integration of functional oxide thin film heterostructures with silicon (100) substrates
NASA Astrophysics Data System (ADS)
Aggarwal, Ravi
The novel functionalities of metal oxides provide the opportunity for the development of next generation optoelectronic, spintronic and a host of other multifunctional devices. A critical issue in the development of practical devices based on metal oxides is the integration of high quality epitaxial oxide thin films with the existing silicon technology which is based on silicon (100) substrates. However, silicon is not suitable for epitaxial growth of oxides owing to its tendency to readily form an amorphous oxide layer at the film-substrate interface. The oxide films deposited directly on silicon exhibit poor crystallinity and are not suitable for device applications. To overcome this challenge, appropriate substrate templates must be developed for growth of oxide thin films on silicon substrates. The present work is focused on developing integration methodology of functional oxides with Si (100) substrates using an yttria-stabilized zirconia (YSZ) template layer. If the deposition conditions are controlled properly, YSZ can be grown epitaxially on silicon substrates even if the native oxide is not etched prior to deposition. This is believed to occur by reaction between zirconium and native silicon dioxide. These Si (100) substrates with epitaxial YSZ template layer can be used to grow functional oxide thin films. The above approach has been used to integrate zinc oxide (ZnO) thin films with Si (100) substrates. The wide band gap (ÿ3.4 eV), large exciton binding energy (60 meV) and room temperature ferromagnetism make ZnO a potential candidate for a host of next generation optoelectronic and spintronic devices. A thorough study on growth and properties of ZnO films on YSZ buffered Si (100) substrates was performed. The ZnO and YSZ films were deposited by pulsed laser deposition (PLD) technique. Detailed characterization of the deposited films was done using x-ray diffraction, transmission electron microscopy (TEM), electrical measurements and photoluminescence spectroscopy. Using YSZ buffer layer, we have been able to epitaxially integrate both non-polar (c-plane) and semi-polar (r-plane) ZnO films with Si (100) substrates. It was observed that, depending on the oxygen pressure during the deposition, ZnO can grow in two different crystallographic orientations (c-plane or r-plane) on YSZ buffered silicon. Experiments carried out to elucidate the role of oxygen pressure indicated that the crystallographic orientation of ZnO depends on the nature of atomic termination of YSZ layer. It has been proposed that crystallographic orientation of ZnO is controlled by chemical free energy associated with the ZnO/YSZ interface. In order to form p-n junction with n-type ZnO, another multifunctional oxide La0.67Sr0.33MnO3 (LSMO) was epitaxially integrated with Si (100) substrates. LSMO is a p-type materials and exhibits interesting properties such as semiconductor to metal transition (SMT), room temperature ferromagnetism and colossal magneto resistance (CMR). Junctions based on CMR materials are of special interest, because their electrical and magnetic properties can be modulated by external electric and magnetic fields. It has been demonstrated that epitaxial nonpolar a-plane ZnO films can be grown on LSMO integrated with Si (100) substrates.
Bismuth as a modifier of Au Pd catalyst: Enhancing selectivity in alcohol oxidation by suppressing parallel reaction
Villa, Alberto [Universita di Milano, Italy; Wang, Di [Fritz Haber Institute of the Max Planck Society, Berlin, Germany; Veith, Gabriel M [ORNL; Prati, Laura [Universita di Milano, Italy
Bi has been widely employed as a modifier for Pd and Pt based catalyst mainly in order to improve selectivity. We found that when Bi was added to the bimetallic system AuPd, the effect on activity in alcohol oxidation mainly depends on the amount of Bi regardless its position, being negligible when Bi was 0.1 wt% and detectably negative when the amount was increased to 3 wt%. However, the selectivity of the reactions notably varied only when Bi was deposited on the surface of metal nanoparticles suppressing parallel reaction in both benzyl alcohol and glycerol oxidation. After a careful characterization of all the catalysts and additional catalytic tests, we concluded that the Bi influence on the activity of the catalysts could be ascribed to electronic effect whereas the one on selectivity mainly to a geometric modification. Moreover, the Bi-modified AuPd/AC catalyst showed possible application in the production of tartronic acid, a useful intermediate, from glycerol.
Cathodoluminescence microcharacterization of the radiation-sensitive defect microstructure of in situ buried oxide in silicon
NASA Astrophysics Data System (ADS)
Stevens-Kalceff, Marion A.
Cathodoluminescence (CL) spectroscopy in a scanning electron microscope has been used to investigate the radiation-sensitive defect structure of the buried amorphous oxide layer produced by oxygen ion implantation in silicon (Silang1 0 0rang) in comparison with bulk amorphous silicon dioxide (a-SiO2). CL microanalysis allows the defect structure of the buried oxide (BOX) layer to be investigated without removal of the silicon-on-insulator (SOI) top layer. CL emissions are observed at 1.63, 2.10, 2.31 and 2.66 eV and are associated with silicon clusters and nanoparticles that form in the BOX as a result of the post-implantation, high-temperature anneal. CL emission at ~3 eV may be associated with excess silicon and/or inclusions of high-pressure crystalline SiO2 polymorph (coesite) in the BOX near the SiO2-Si substrate. A partially resolved CL emission may also be observed at 1.88 eV and is possibly associated with a native non-bridging oxygen defect of SiO2. CL emission from the confined strained BOX is dominated by defects associated with large surface-to-volume ratio nanoscale silicon clusters and their interfaces. CL spectra from the in situ BOX are electron radiation sensitive. Electron irradiation results in localized trapped charge-induced electric fields which are enhanced within the strained confined BOX layer at nanoscale silicon cluster defects and interfaces. These enhanced electric fields and residual strain near the interfaces can contribute to breakdown of the BOX.
Crack healing in silicon nitride due to oxidation
NASA Technical Reports Server (NTRS)
Choi, Sung R.; Tikare, Veena; Pawlik, Ralph
The crack healing behavior of a commercial, MgO-containing, hot pressed Si3N4 was studied as a function of temperature in oxidizing and inert annealing environments. Crack healing occurred at a temperature 800 C or higher due to oxidation regardless of crack size, which ranged from 100 microns (indentation crack) to 1.7 mm (SEPB precrack). The resulting strength and apparent fracture toughness increased at crack healing temperature by 100 percent and 300 percent, respectively. The oxide layer present in the crack plane was found to be highly fatigue resistant, indicating that the oxide is not solely silicate glass, but a mixture of glass, enstatite, and/or cristobalite that was insensitive to fatigue in a room temperature water environment.
Photovoltaic properties of indium tin oxide (ITO)/silicon junctions prepared by spray pyrolysis-dependence on oxidation time
NASA Astrophysics Data System (ADS)
Vasu, V.; Subrahmanyam, A.
Indium tin oxide (ITO)/silicon (on both n- and p-type) junctions are prepared at 380 degrees C by spray pyrolysis technique. The ITO/p-Si yielded an ohmic contact. The photovoltaic behaviour of ITO/n-Si junctions as a function of oxidation time tox is reported in the present paper with the view to understanding the role of the interfacial oxide layer in the photovoltaic process. The junctions have been characterized by I-V and C-V measurements. A maximum efficiency of 9.4% is observed (under GE-ELH illumination of 100 mW cm-2) for both small (0.04 cm2) and large (1.0 cm2) areas of ITO/n-Si junctions at an oxidation time of 60 s. The junctions are observed to be quite stable with time.
Laser spectroscopy of nanocrystals of aluminum and silicon oxides
V. S. Gorelik; A. E. Kozhevin; S. N. Mikov; P. P. SverbilÆ; M. M. Stepanov
The specific features of the spectra of secondary radiation (photoluminescence and Raman scattering) in nanocrystalline samples\\u000a of aluminum oxide and fused silica are reported. The photoluminescence (PL) spectrum of nanocrystalline aluminum oxide was\\u000a found to be strongly modified with the wavelength of exciting radiation. Spectra of secondary radiation were excited using\\u000a a xenon lamp, a pulsed nitrogen laser (with a
On the nature of point defects and the effect of oxidation on substitutional dopant diffusion in silicon
NASA Astrophysics Data System (ADS)
Tan, T. Y.; G÷sele, U.; Morehead, F. F.
An extensive analysis of the substitutional dopant diffusion phenomena in silicon during oxidation is presented. The analysis covers qualitative as well as quantitative aspects of the oxidation-enhanced and -retarded diffusion (OED and ORD) phenomena, and examines three different possible assumptions that can be made on the nature of the silicon thermal equilibrium point defect species: silicon self-interstitials (I) only, vacancies (V) only, coexistence of I and V. The only consistent way to interpret all properly documented OED/ORD data is to assume that I and V coexist under oxidation as well as under thermal equilibrium conditions at high temperatures.
The fabrication and preservation of nanostructures on silicon wafers with a native oxide layer.
Huang, Jen-Ching; Wang, Jui-Yang
This study used nano-oxidation lithography to create oxidized circular nanostructures on a silicon wafer with a native oxide layer (NOL). We also investigated the impact of wet etching on the size of circular oxidized nanostructures and examined how the method and duration of preservation affect them. Experimental results show that the height and width of oxidized circular nanostructures increase proportionally with applied voltage. After wet etching, an increase in applied voltage resulted in a marked increase in the width of the circular nanostructures, a decrease in the inner diameter, and little variation in height. We further demonstrated that in a moist environment, the oxidation process continues, resulting in a further increase in height and width. During the initial stages of preservation, these changes occurred rapidly; however, the increase was negligible after 30 days. We propose the concept of reaction area (RA) ratio to explain the above phenomenon and provide evidence to support these claims. Our results led us to a simple and yet effective method of preserving oxidized circular nanostructures, called the electrostatic patch preservation (EPP) method, to overcome problems associated with changes in size occurring during the preservation of silicon nanostructure molds. PMID:22331793
Deposition and characterization of cerium oxide epitaxial films on silicon substrates for electronic applications
NASA Astrophysics Data System (ADS)
Morshed, Ahmed Hisham Eissa A.
Thin films of the rare earth oxide, cerium oxide, were deposited on silicon substrates using the pulsed laser ablation technique in an ultra high vacuum environment. As probed by in-situ reflection high energy electron diffraction (RHEED), and confirmed by x-ray diffraction and high resolution transmission electron microscopy (HRTEM), single crystal films were deposited on Si(111) substrates. The structural and electrical properties of these films were extensively studied in this thesis. It was found that CeOsb2 films annealed in oxygen have electrical properties that compare favorably to some other insulating films on silicon. Since these films have a multilayer CeOsb2/SiOsb2 structure, a double layer model was used to analyze their electrical characteristics and obtain the properties of the cerium oxide layer. A field strength of 1.4 MV/cm, and a relative dielectric constant of about 24 were obtained. As a further study of the optical properties of the films, their photoluminescence spectra upon ultraviolet irradiation were observed and related to the electronic structure of the material. Films treated by rapid thermal annealing in an Argon environment exhibited a relatively sharp emission in the violet/blue wavelength range accompanied by a phase transformation in the films. This newly observed emission can potentially be useful in optical devices fabricated on silicon substrates. Having an epitaxial insulator which is nearly lattice matched to silicon, CeOsb2 films have a potential for application in silicon on insulator (SOI) technology. The deposition of silicon on CeOsb2/Si(111) to form a silicon on insulator structure was explored by two techniques, namely, Chemical Vapor Deposition (CVD) and molecular beam epitaxy (MBE). Preliminary results were obtained that indicate the deposition of epitaxial silicon on CeOsb2 films by CVD. However, the growth mode of the deposited Si overlayer was three dimensional and further investigation and modification of the growth process might lead to desirable layer by layer growth of epitaxial silicon on insulating CeOsb2/Si substrates.
REVIEWS OF TOPICAL PROBLEMS: Atomic structure of the amorphous nonstoichiometric silicon oxides and nitrides
NASA Astrophysics Data System (ADS)
Gritsenko, V. A.
In addition to amorphous SiO2 and Si3N4, the two key dielectric film materials used in modern silicon devices, the fabrication technology of nonstoichiometric SiOxNy, SiNx, and SiOx compounds is currently under development. Varying the chemical composition of these compounds allows a wide range of control over their physical ù specifically, optical and electrical ù properties. The development of technology for synthesizing such films requires a detailed understanding of their atomic structure. Current views on the atomic structure of nonstoichiometric silicon nitrides and oxides are reviewed and summarized.
Optical properties of bismuth-doped silica fibres in the temperature range 300 - 1500 K
Dvoretskii, D A; Bufetov, Igor' A; Vel'miskin, V V; Zlenko, Alexander S; Khopin, V F; Semjonov, S L; Guryanov, Aleksei N; Denisov, L K; Dianov, Evgenii M
The visible and near-IR absorption and luminescence bands of bismuth-doped silica and germanosilicate fibres have been measured for the first time as a function of temperature. The temperature-dependent IR luminescence lifetime of a bismuth-related active centre associated with silicon in the germanosilicate fibre has been determined. The Bi{sup 3+} profile across the silica fibre preform is shown to differ markedly from the distribution of IR-emitting bismuth centres associated with silicon. The present results strongly suggest that the IR-emitting bismuth centre comprises a lowvalence bismuth ion and an oxygen-deficient glass network defect. (optical fibres, lasers and amplifiers. properties and applications)
REVIEWS OF TOPICAL PROBLEMS: Structure of silicon/oxide and nitride/oxide interfaces
NASA Astrophysics Data System (ADS)
Gritsenko, Vladimir A.
We systematize and generalize modern concepts on the atomic structure of silicon/insulator (Si/SiO2, Si/SiOxNy) and insulator/insulator (Si3N4/SiO2) interfaces in the structures underlying the operation of silicon devices.
Molecular dynamics simulation of silicon oxidation enhanced by energetic hydrogen ion irradiation
NASA Astrophysics Data System (ADS)
Mizotani, Kohei; Isobe, Michiro; Fukasawa, Masanaga; Nagahata, Kazunori; Tatsumi, Tetsuya; Hamaguchi, Satoshi
Molecular dynamics numerical simulations have been performed to clarify the mechanism of enhanced oxidation in Si during silicon gate etching by HBr/O2 plasmas. Such enhanced oxidation sometimes manifests itself as Si recess during gate etching processes. When a Si substrate is subject to energetic ion bombardment together with a flux of radical species, our study has identified the cause of such enhanced oxidation in Si as enhanced O diffusion arising from the momentum transfer from energetic H atoms to O atoms on the surface or in the subsurface of the Si substrate. No chemical effect such as hydrogenation of Si plays a role for the enhanced oxidation. Simulation results are found to be in good agreement with earlier experimental observations of ion-irradiation-enhanced oxidation obtained by beam experiments.
Removal of Surface Oxide Layer from Silicon Nanocrystals by Hydrogen Fluoride Vapor Etching
NASA Astrophysics Data System (ADS)
Nakamine, Yoshifumi; Kodera, Tetsuo; Uchida, Ken; Oda, Shunri
We describe the natural oxidation of silicon nanocrystals (SiNCs) and the method of etching the natural oxide layer of SiNC with hydrogen fluoride (HF) vapor. Electrical measurements are conducted in order to investigate the influence of the natural oxidation of SiNCs. The wet HF etching process, which is currently used in the semiconductor industry, results in the removal of all SiNCs from the substrate. Therefore, we use HF vapor etching, which can remove only the natural oxide layer without the removal of SiNCs from the substrate. Consequently, the HF vapor process is suitable for SiNC devices. From electrical measurements, it is observed that current increases by four orders of magnitude after the HF vapor etching treatment. In addition, it is revealed that we can control the thickness of the oxide layer of SiNCs by changing the HF vapor etching time.
Oxidation Behavior of Germanium- and/or Silicon-Bearing Near-? Titanium Alloys in Air
NASA Astrophysics Data System (ADS)
Kitashima, Tomonori; Yamabe-Mitarai, Yoko
The effect of germanium (Ge) and/or silicon (Si) addition on the oxidation behavior of the near-? alloy Ti-5Al-2Sn-4Zr-2Mo was investigated in air at 973 K (700 ░C). Ge addition decreased the oxidation resistance because of the formation of a Ge-rich layer in the substrate at the TiO2/substrate interface, enhancing Sn segregation at the interface. In addition, a small amount of Ge dissolved in the external Al2O3 layer. These results reduced the aluminum activity at the interface, suppressed the formation of Al2O3, and increased the diffusivity of oxygen in the oxide scales. The addition of 0.2 and 0.9 wt pct Si was beneficial for improving oxidation resistance. The effect of germanide and silicide precipitates in the matrix on the oxide growth process was also discussed.
Extracting mechanical properties of copper coatings on oxidized silicon substrates by nanoindentation
NASA Astrophysics Data System (ADS)
Moharrami, N.; Oila, A.; Bull, S. J.
The thickness of the copper coatings that are used for the manufacture of conducting tracks in microelectronic devices are being aggressively scaled down and there is a need to monitor the mechanical response of metallization at a scale comparable to the material microstructure. When using indentation tests to assess the properties of thin films, the plastic zone dimensions are of a similar scale to the grain size. For the purposes of designs based on continuum mechanics approaches it is usually required that the grain size is much smaller than the deforming volume, which is not always observed in practice. Considerable differences between predicted and observed performance can be seen depending on the material tested and its grain size; the extent of oxidation of the copper after deposition is critical, as is that of its underlying silicon substrate. Whereas it is possible to make good measurements of metallization properties on stiff substrates such as silicon there are serious issues with the reliability of Young's modulus and hardness data from coatings on device quality wafers which may have been oxidized prior to use. The effects of grain size, shape and orientation on the mechanical response of metallic thin films used for semiconductor metallization on oxidized silicon are presented in this paper. The appropriate conditions for the successful use of continuum mechanics are discussed and the importance of considering the consequences of crystallographic anisotropy and oxidation on the selection of suitable design data is presented with regards to copper coatings.
Microstructure and oxidation behaviour of HIPed silicon nitride
Plucknett, K.P.; Lewis, M.H.
Dense beta-Si3N4 based ceramics in the Y-Si-O-N have been fabricated using a commercial glass-encapsulated hot-isostatic pressing process. Compositions were tailored to lie within the Si3N4-Si2N2O-Y2Si2O7 compatibility triangle. Crystallization of the intergranular glassy phase, to Y2Si2O7, was found to occur during the cooling segment of the HIP cycle. HIPed ceramics demonstrated excellent resistance to oxidation at temperatures up to 1450 C, although surface contamination during HIPing resulted in a degradation of the oxidation resistance. 11 refs.
Interface defects of ultrathin rapid-thermal oxide on silicon
NASA Astrophysics Data System (ADS)
Stathis, J. H.; Buchanan, D. A.; Quinlan, D. L.; Parsons, A. H.; Kotecki, D. E.
We have used capacitance-voltage and electron paramagnetic resonance to measure interface defects in ultrathin (30 ┼) SiO2 prepared by rapid-thermal oxidation. We observe a very narrow interface state peak in the upper portion of the Si band gap, as well as both Pb0 and Pb1 defects in the as-oxidized film. Forming-gas annealing removes the interface state and most of the Pb centers. However, from the energy level and charge state of the interface state peak, we argue that it cannot be reliably ascribed to either Pb0 or Pb1.
Effect of W and WC on the oxidation resistance of yttria-doped silicon nitride
NASA Technical Reports Server (NTRS)
Schuon, S.
The effect of tungsten and tungsten carbide contamination on the oxidation and cracking in air of yttria-doped silicon nitride ceramics is investigated. Silicon nitride powder containing 8 wt % Y2O3 was doped with 2 wt % W, 4 wt % W, 2 wt % WC or left undoped, and sintered in order to simulate contamination during milling, and specimens were exposed in air to 500, 750 and 1350 C for various lengths of time. Scanning electron and optical microscopy and X-ray diffraction of the specimens in the as-sintered state reveals that the addition of W or WC does not affect the phase relationships in the system, composed of alpha and beta Si3N4, melilite and an amorphous phase. Catastrophic oxidation is observed at 750 C in specimens containing 2 and 4 wt % W, accompanied by the disappearance of alpha Si3N4 and melilite from the structure. At 1350 C, the formation of a protective glassy oxide layer was observed on all specimens without catastrophic oxidation, and it is found that pre-oxidation at 1350 C also improved the oxidation resistance at 750 C of bars doped with 4 wt % W. It is suggested that tungsten contamination from WC grinding balls may be the major cause of the intermediate-temperature cracking and instability frequently observed in Si3N4-8Y2O3.
Biocompatible magnetofluorescent probes: luminescent silicon quantum dots coupled with superparamagnetic iron(III) oxide.
Erogbogbo, Folarin; Yong, Ken-Tye; Hu, Rui; Law, Wing-Cheung; Ding, Hong; Chang, Ching-Wen; Prasad, Paras N; Swihart, Mark T
Luminescent silicon quantum dots (SiQDs) are gaining momentum in bioimaging applications, based on their unique combination of optical properties and biocompatibility. Here, we report the development of a multimodal probe that combines the optical properties of silicon quantum dots with the superparamagnetic properties of iron oxide nanoparticles to create biocompatible magnetofluorescent nanoprobes. Multiple nanoparticles of each type are coencapsulated within the hydrophobic core of biocompatible phospholipid-polyethyleneglycol (DSPE-PEG) micelles. The size distribution and composition of the magnetofluorescent nanoprobes were characterized by transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS). Enhanced cellular uptake of these probes in the presence of a magnetic field was demonstrated in vitro. Their luminescence stability in a prostate cancer tumor model microenvironment was demonstrated in vivo. This paves the way for multimodal silicon quantum-dot-based nanoplatforms for a variety of imaging and delivery applications. PMID:20738120
Oxidation resistant high temperature thermal cycling resistant coatings on silicon-based substrates and process for the production thereof
Sarin, Vinod K. (Lexington, MA)
An oxidation resistant, high temperature thermal cycling resistant coated ceramic article for ceramic heat engine applications. The substrate is a silicon-based material, i.e. a silicon nitride- or silicon carbide-based monolithic or composite material. The coating is a graded coating of at least two layers: an intermediate AlN or Al.sub.x N.sub.y O.sub.z layer and an aluminum oxide or zirconium oxide outer layer. The composition of the coating changes gradually from that of the substrate to that of the AlN or Al.sub.x N.sub.y O.sub.z layer and further to the composition of the aluminum oxide or zirconium oxide outer layer. Other layers may be deposited over the aluminum oxide layer. A CVD process for depositing the graded coating on the substrate is also disclosed.
Size-dependent elastic properties of oxidized silicon nanorods
NASA Astrophysics Data System (ADS)
Ilinov, Andrey; Kuronen, Antti
In this work, we have simulated a three point bending test for Si nanorods of different sizes with an oxide coating of different thicknesses using molecular dynamics simulations and the finite element modeling (FEM). We tested nanorods with diameters from 6 to 16 nm, which had lengths from 31 to 62 nm. Our aim was to estimate how well the elastic properties of Si nanorods can be described using the classical continuum mechanics approach. The agreement between the MD simulations and the FEM calculations was consistent for the pristine Si nanorods of all sizes, whereas the oxidized Si nanorods with small length-to-diameter ratio had much smaller effective bending moduli values than predicted by FEM. Our assumption is that it is due to the significant decrease of the shear modulus in the oxide layer of the smallest nanorods. We had also introduced surface stresses into the FEM models and found that their influence on the bending properties is more important for partially oxidized nanorods.
Quantum Conductance in Silicon Oxide Resistive Memory Devices
Mehonic, A.; Vrajitoarea, A.; Cueff, S.; Hudziak, S.; Howe, H.; LabbÚ, C.; Rizk, R.; Pepper, M.; Kenyon, A. J.
Resistive switching offers a promising route to universal electronic memory, potentially replacing current technologies that are approaching their fundamental limits. In many cases switching originates from the reversible formation and dissolution of nanometre-scale conductive filaments, which constrain the motion of electrons, leading to the quantisation of device conductance into multiples of the fundamental unit of conductance, G0. Such quantum effects appear when the constriction diameter approaches the Fermi wavelength of the electron in the medium û typically several nanometres. Here we find that the conductance of silicon-rich silica (SiOx) resistive switches is quantised in half-integer multiples of G0. In contrast to other resistive switching systems this quantisation is intrinsic to SiOx, and is not due to drift of metallic ions. Half-integer quantisation is explained in terms of the filament structure and formation mechanism, which allows us to distinguish between systems that exhibit integer and half-integer quantisation. PMID:24048282
Excimer laser CVD of silicon oxide on GaAs: a comparison with deposition on c-Si
NASA Astrophysics Data System (ADS)
Gonzßlez, P.; GarcÝa, E.; Pou, J.; Fernßndez, D.; Le¾n, B.; PÚrez-Amor, M.
Conventional low temperature techniques for deposition of silicon oxide on GaAs can encounter problems in achieving adherent films. We have deposited uniform, non-spalling and adherent silicon oxide films on polished GaAs substrates by photo-CVD using an ArF excimer laser (193 nm) in parallel configuration. The source gases were silane and nitrous oxide diluted in argon (purge gas). A study of the growth rate and refractive index, measured by ellipsometry, as well as FTIR spectroscopic analyses of the simultaneously deposited SiO x films on both GaAs and Si substrates is reported. Film properties on GaAs substrates are very similar to those obtained on silicon substrates. The flexibility of this LCVD approach has allowed the growth of silica films on both substrates with properties very close to those of thermal silicon oxide.
Novel Iron-oxide Catalyzed CNT Formation on Semiconductor Silicon Nanowire.
Adam, Tijjani; U, Hashim
An aqueous ferric nitrate nonahydrate (Fe(NO3)3.9H2O) and magnesium oxide (MgO) were mixed and deposited on silicon nanowires (SiNWs), the carbon nanotubes (CNTs) formed by the concentration of Fe3O4/MgO catalysts with the mole ratio set at 0.15:9.85 and 600░C had diameter between 15.23 to 90nm with high-density distribution of CNT while those with the mole ratio set at 0.45:9.55 and 730░C had diameter of 100 to 230nm. The UV/Vis/NIR and FT-IR spectroscopes clearly confirmed the presence of the silicon-CNTs hybrid structure. UV/Vis/NIR, FT-IR spectra and FESEM images confirmed the silicon-CNT structure exists with diameters ranging between 15-230nm. Thus, the study demonstrated cost effective method of silicon-CNT composite nanowire formation via Iron-oxide Catalyze synthesis. PMID:25237290
High-stability transparent amorphous oxide TFT with a silicon-doped back-channel layer
NASA Astrophysics Data System (ADS)
Lee, Hyoung-Rae; Park, Jea-Gun
We significantly reduced various electrical instabilities of amorphous indium gallium zinc oxide thin-film transistors (TFTs) by using the co-deposition of silicon on an a-IGZO back channel. This process showed improved stability of the threshold voltage ( V th ) under high temperature and humidity and negative gate-bias illumination stress (NBIS) without any reduction of IDS. The enhanced stability was achieved with silicon, which has higher metal-oxide bonding strengths than gallium does. Additionally, SiO X distributed on the a-IGZO surface reduced the adsorption and the desorption of H2O and O2. This process is applicable to the TFT manufacturing process with a variable sputtering target.
Production of Silicon Oxide like Thin Films by the Use of Atmospheric Plasma Torch
NASA Astrophysics Data System (ADS)
Ozono, E. M.; Fachini, E. R.; Silva, M. L. P.; Ruchko, L. F.; GalvÒo, R. M. O.
The advantages of HMDS (hexamethyldisilazane) APT-plasma films for sensor applications were explored producing films in a three-turn copper coil APT equipment. HMDS was introduced into the argon plasma at four different conditions. Additional flux of oxygen could modulate the presence of organic components in the film, the composition varying from pure inorganic oxides to organo-silane polymers. Oxygen promoted deposition rates as high as 900 nm/min on silicon, acrylic or piezoelectric quartz crystal substrates. Films with a clustered morphology and refractive index of 1.45 were obtained, mainly due to a silicon oxide structure. Raman spectroscopy and XPS data showed the presence of CHn and amorphous carbon in the inorganic matrix. The films were sensitive to the humidity of the air. The adsorptive capabilities of outstanding films were tested in a Quartz Crystal Microbalance (QCM). The results support that those films can be a useful and simple alternative for the development of sensors.
Aminosilane functionalizations of mesoporous oxidized silicon for oligonucleotide synthesis and detection
De Stefano, Luca; Oliviero, Giorgia; Amato, Jussara; Borbone, Nicola; Piccialli, Gennaro; Mayol, Luciano; Rendina, Ivo; Terracciano, Monica; Rea, Ilaria
Direct solid phase synthesis of peptides and oligonucleotides (ONs) requires high chemical stability of the support material. In this work, we have investigated the passivation ability of porous oxidized silicon multilayered structures by two aminosilane compounds, 3-aminopropyltriethoxysilane and 3-aminopropyldimethylethoxysilane (APDMES), for optical label-free ON biosensor fabrication. We have also studied by spectroscopic reflectometry the hybridization between a 13 bases ON, directly grown on the aminosilane modified porous oxidized silicon by in situ synthesis, and its complementary sequence. Even if the results show that both devices are stable to the chemicals (carbonate/methanol) used, the porous silica structure passivated by APDMES reveals higher functionalization degree due to less steric hindrance of pores. PMID:23536541
Three-dimensional design and replication of silicon oxide nanostructures using an atomic force microscope
NASA Astrophysics Data System (ADS)
Johannes, Matthew S.; Cole, Daniel G.; Clark, Robert L.
Atomic force microscope (AFM) based local anodic oxidation of metallic and semiconducting layers has emerged as a powerful tool for nanoscale fabrication. A unique nanoscale patterning technique has been created that couples computer aided design (CAD) with the lithographic capabilities of the AFM. Target nanostructures to be deposited on a silicon substrate are rendered as a three-dimensional model. Using AFM based local anodic oxidation on a silicon substrate, the features are duplicated at the nanoscale using voltage bias, probe speed, and humidity modulation, as prescribed by the model. The work presented herein highlights the advantages when three-dimensional modeling is linked with nanolithography; nanoscale features can be precisely replicated from a design plan.
The origin of visible photoluminescence from silicon oxide thin films prepared by dual-plasma chemical vapor deposition
M. Zhu; Y. Han; R. B. Wehrspohn; C. Godet; R. Etemadi; D. Ballutaud
In order to understand the radiative recombination mechanisms in silicon oxides, photoluminescence properties (PL) of H-rich amorphous silicon oxide thin films grown in a dual-plasma chemical vapor deposition reactor have been related to a number of stoichiometry and structure characterizations (x-ray photoelectron spectroscopy, vibrational spectroscopy, and gas evolution studies). The visible photoluminescence at room temperature from a-SiOx:H matrixes with different
Complete coverage of reduced graphene oxide on silicon dioxide substrates
NASA Astrophysics Data System (ADS)
Huang, Jingfeng; Melanie, Larisika; Chen, Hu; Steve, Faulkner; Myra, A. Nimmo; Christoph, Nowak; Alfred Tok Iing, Yoong
Reduced graphene oxide (RGO) has the advantage of an aqueous and industrial-scale production route. No other approaches can rival the RGO field effect transistor platform in terms of cost (
Sinterability, strength and oxidation of alpha silicon carbide powders
NASA Technical Reports Server (NTRS)
Dutta, S.
An investigation is made of pressureless sintering of commercially available alpha-SiC powders at temperatures between 1900 and 2150 C for periods of 10 to 240 min under one atmosphere of argon pressure. It is found that alpha-SiC powder containing boron and carbon sintering aids is sinterable at 2150 C for a period of 30 min to a high final density (greater than 96 percent of theoretical). In alpha-SiC powder containing aluminum and carbon sintering aids, the final density achieved is only about 80 percent of theoretical. Determinations are made of room temperature and high temperature (1370 C) flexure strength and oxidation resistance on sintered high density (more than 96 percent of theoretical) alpha-SiC (boron, carbon) material. It is found that both the strength and the resistance to oxidation are equivalent and comparable to those of the sintered alpha-SiC which represents the state of the art.
Silicon-based thin film solid oxide fuel cell array
NASA Astrophysics Data System (ADS)
Su, Pei-Chen; Prinz, Fritz B.
Solid oxide fuel cells (SOFC) have been known for their clean and efficient energy conversion. SOFCs utilize a range of ceramic electrolyte materials, with yttria stabilized zirconia (YSZ) as the most common choice. Traditional SOFCs operate at relatively high temperatures (800-1000░C) due to their low oxide ion conductivity and high activation energy. Reducing the operating temperature is important to expand the field of SOFC applications, such as power sources for portable electronics. Reducing the electrolyte thickness by means of thin film deposition techniques to the submicrometer range is one way to reduce the Ohmic loss in SOFCs at lower temperature. In this paper, a miniature thin film fuel cell array is designed and fabricated targeting at reduced operating temperature as a potential portable power source.
Interface traps and Pb centers in oxidized (100) silicon wafers
Gary J. Gerardi; Edward H. Poindexter; Philip J. Caplan; Noble M. Johnson
The band-gap energy distribution of Pb centers on oxidized (100) Si wafers has been determined and compared with interface electrical trap density Dit. Two different Pb centers are observed on (100) Si: Pb0, which has the structure ?Si?Si3, and is essentially identical to the sole Pb center observed on (111) Si; and Pb1, of presently uncertain identity, but clearly different
Efficient preservation in a silicon oxide matrix of Escherichia coli , producer of recombinant proteins
MartÝn F. Desimone; Mauricio C. De Marzi; Guillermo J. Copello; Marisa M. Fernßndez; Emilio L. Malchiodi; Luis E. Diaz
The aim of this work was to study the use of silicon oxide matrices for the immobilization and preservation of recombinant-protein-producing\\u000a bacteria. We immobilized Escherichia coli BL21 transformants containing different expression plasmids. One contained DNA coding for a T-cell receptor ? chain, which\\u000a was expressed as inclusion bodies in the cytoplasm. The other two encoded bacterial superantigens Staphylococcal Enterotoxin\\u000a G
Nitric oxide releasing silicone rubbers with improved blood compatibility: preparation, characterization, and in vivo evaluation
Huiping Zhang; Gail M. Annich; Judiann Miskulin; Kathryn Osterholzer; Scott I. Merz; Robert H. Bartlett; Mark E. Meyerhoff
Nitric oxide (NO) releasing silicone rubbers (SR) are prepared via a three-step reaction scheme. A diamino\\/triamino-alkyltrimethoxysilane crosslinker is used to vulcanize hydroxyl terminated polydimethylsiloxane (PDMS) in the presence of ambient moisture and a dibutyltin dilaurate catalyst so that the respective diamine\\/triamine groups are covalently linked to the cured SR structure. These amine sites are then diazeniumdiolated, in situ, when the
The charging and discharging of high-voltage stress-generated traps in thin silicon oxide
R. S. Scott; D. J. Dumin
Excess high-voltage stress-generated low-level leakage currents through 10 nm silicon oxides, previously described as DC currents, are shown to decay to the limit of detection given adequate observation time and, thus, have no discernible component. A physical model is presented which describes the majority of the excess low-level leakage currents in terms of the charging and discharging of traps previously
Influence of molybdenum silicide additions on high-temperature oxidation resistance of silicon nitride materials
Hagen Klemm; Katja Tangermann; Christian Schubert; Waldemar Hermel
The influence of additions of molybdenum disilicide (MoSiÔ) on the microstructure and the mechanical properties of a silicon nitride (SiÔNÔ) material, with neodymium oxide (NdÔOÔ) and aluminum nitride (AlN) as sintering aids, was studied. The composites, containing 5, 10, and 17.6 wt% MoSiÔ, were fabricated by hot pressing. All materials exhibited a similar phase composition, detected by X-ray diffractometry. Up
Ultrathin high-K metal oxides on silicon: processing, characterization and integration issues
E. P Gusev; E Cartier; D. A Buchanan; M Gribelyuk; M Copel; H Okorn-Schmidt; C DÆEmic
An overview of our recent work on ultrathin (<100 ┼) films of metal oxides deposited on silicon for advanced gate dielectrics applications will be presented. Data on ultrathin Al2O3, ZrO2, HfO2, and Y2O3 will be shown to illustrate the complex processing, integration and device-related issues for high dielectric constant (æhigh-KÆ) materials. Both physical and electrical properties, as well as the
A Low Power Non-Volatile Memory Element Based on Copper in Deposited Silicon Oxide
Muralikrishnan Balakrishnan; S. C. P. Thermadam; M. Mitkova; M. N. Kozicki
We describe the electrical characteristics of W-(Cu\\/SiO2)-Cu switching elements formed by thermal diffusion of copper into deposited silicon oxide. These devices switch via the electrochemical formation of a conducting filament within the high resistance Cu\\/SiO2 electrolyte film. Unwritten and fully- erased devices of 350 nm to 1 mum in diameter transitioned from a high resistance state in excess of 100
Nafion\\/silicon oxide\\/phosphotungstic acid nanocomposite membrane with enhanced proton conductivity
A. Mahreni; A. B. Mohamad; A. A. H. Kadhum; W. R. W. Daud; S. E. Iyuke
Nafion-silicon oxide (SiO2)-phosphotungstic acid (PWA) composite membrane has been synthesized to improve Nafion based proton exchange membrane fuel cell (PEMFC) performance. The objective of the study is to fabricate Nafion-SiO2-PWA nanocomposite membrane using solûgel reaction. The composite is composed of the mixture of Nafion solution, tetra ethoxy orthosilane (TEOS) and PWA solution. The mixed solution was casted at certain temperature
Performance evaluation of a Nafion\\/silicon oxide hybrid membrane for direct methanol fuel cell
D. H. Jung; S. Y. Cho; D. H. Peck; D. R. Shin; J. S. Kim
Nafion\\/silicon oxide composite membranes were produced via the in situ acid-catalyzed solûgel reaction of tetraethylorthosilicate (TEOS) in Nafion perfluorosulfonic acid films. The TEOS uptake content of a composite membrane was varied according to the solûgel reaction time. The physicochemical properties of the composite membranes were investigated by FT-IR. The water uptake contents and the thermal properties of the composite membrane
Diffusion-limited interaction of dislocation loops and interstitials during dry oxidation in silicon
NASA Astrophysics Data System (ADS)
Park, Heemyong; Robinson, Heyward; Jones, Kevin S.; Law, Mark E.
The interaction of implantation-induced dislocation loops and interstitials in silicon is studied. Experiments under dry oxidation conditions consistently show a significant reduction of OED (oxidation enhanced diffusion) of boron in a buried layer due to very efficient interstitial capturing action of dislocation loops, suggesting diffusion-limited dislocation loop growth. Simple analytic solution of interstitial supersaturation and analysis of the data in terms of time dependence of the OED suppression demonstrate that the interaction of dislocation loops and interstitials is not a reaction-limited but a diffusion-limited process. Simulations incorporating the model for the interaction mechanism agree with both secondary ion mass spectroscopy and transmission electron spectroscopy data.
Patterns of discoloration and oxidation by direct and scattered fluxes, especially oxygen on silicon
NASA Technical Reports Server (NTRS)
Frederickson, A. R.; Filz, R. C.; Rich, F. J.; Sagalyn, Paul L.
A number of interesting discoloration patterns are clearly evident on M0002-1 which resides on three faces of LDEF: front face, rear face, and earth face. Most interesting is the pattern of blue oxidation on polished single crystal silicon apparently produced by once-scattered ram oxygen atoms along the earth face. Most of the other patterns are seen in the Thermal Control Paint. Also, severe oxidation of CR-39 polycarbonate occurred on the front face of LDEF, as expected. A complete explanation for the patterns has not yet been obtained.
Comparison of beryllium oxide and pyrolytic graphite crucibles for boron doped silicon epitaxy
Ali, Dyan; Richardson, Christopher J. K. [Laboratory for Physical Sciences, University of Maryland, College Park, Maryland 20740 (United States)
This article reports on the comparison of beryllium oxide and pyrolytic graphite as crucible liners in a high-temperature effusion cell used for boron doping in silicon grown by molecular beam epitaxy. Secondary ion mass spectroscopy analysis indicates decomposition of the beryllium oxide liner, leading to significant incorporation of beryllium and oxygen in the grown films. The resulting films are of poor crystal quality with rough surfaces and broad x-ray diffraction peaks. Alternatively, the use of pyrolytic graphite crucible liners results in higher quality films.
Optical waveguides in oxygen-implanted buried-oxide silicon-on-insulator structures
NASA Technical Reports Server (NTRS)
Kurdi, B. N.; Hall, D. G.
An analysis is made of the waveguiding properties of the oxygen-implanted, buried-oxide, silicon-on-insulator structures currently being developed for use in microelectronics. It is found that in spite of the fact that the buried-oxide layer is only a few tenths of a micrometer thick, the single-crystal overlayer can support TEo guided-wave propagation, at subbandgap wavelengths, with losses due to substrate radiation leakage at or below the benchmark level of 1 dB/cm.
Yttrium oxide\\/silicon dioxide: a new dielectric structure for VLSI\\/ULSI circuits
L. Manchanda; M. Gurvitch
Electrical characteristics of Al\\/yttrium oxide (~260 ┼)\\/silicon dioxide (~40 ┼)\\/Si and Al\\/yttrium oxide (~260 ┼)\\/Si structures are described. The Al\\/Y2O3\\/SiO2\\/Si (MYOS) and Al\\/Y2 O3\\/Si (MYS) capacitors show very well-behaved I-V characteristics with leakage current density <10-10 A\\/cm2 at 5 V. High-frequency C- V and quasistatic C-V characteristics show very little hysteresis for bias ramp rate ranging from 10 to 100
Copper-induced dielectric breakdown in silicon oxide deposited by plasma-enhanced chemical vapor deposition using trimethoxysilane
Ken-Ichi Takeda; Daisuke Ryuzaki; Toshiyuki Mine; Kenji Hinode; Ryo Yoneyama
The barrier mechanism against copper-ion diffusion in silicon-oxide films deposited by plasma-enhanced chemical vapor deposition (PECVD) using trimethoxysilane (TMS) and nitrous oxide (N2O) chemistry (PE-TMS oxide) was studied. It was found that the flow ratio of TMS gas to N2O gas during deposition strongly affects a time-dependent dielectric-breakdown lifetime of PE-TMS oxide with a copper electrode as well as other
Effect of ion-plated films of germanium and silicon on friction, wear, and oxidation of 52100 bearing steel
NASA Technical Reports Server (NTRS)
Buckley, D. H.; Spalvins, T.
Friction and wear experiments were conducted with ion plated films of germanium and silicon on the surface of 52100 bearing steel both dry and in the presence of mineral oil. Both silicon and germanium were found to reduce wear, with germanium being more effective than silicon. An optimum film thickness of germanium for minimum wear without surface crack formation was found to be approximately 400 nanometers (4000 A). The presence of silicon and germanium on the 52100 bearing steel surface improved resistance to oxidation.
Coherent x-ray diffraction imaging of silicon oxide growth
Robinson, I.K.; Libbert, J.L. [Department of Physics, University of Illinois, Urbana, Illinois 61801 (United States)] [Department of Physics, University of Illinois, Urbana, Illinois 61801 (United States); Vartanyants, I.A. [Department of Physics, University of Illinois, Urbana, Illinois 61801 (United States)] [Department of Physics, University of Illinois, Urbana, Illinois 61801 (United States); [Institute of Crystallography RAS, Leninsky prospect 59, 117333 Moscow (Russia); Pitney, J.A. [Department of Physics, University of Illinois, Urbana, Illinois 61801 (United States)] [Department of Physics, University of Illinois, Urbana, Illinois 61801 (United States); Smilgies, D.M.; Abernathy, D.L.; Gruebel, G. [European Synchrotron Radiation Facility, 38043 Grenoble (France)] [European Synchrotron Radiation Facility, 38043 Grenoble (France)
We have measured the morphology of Si samples as a function of time in air after stripping of the native oxide. For this purpose we examined the reflectivity of a coherent beam of x rays, which produces a structured diffraction pattern. We have made further progress in the development of an inversion algorithm for conversion of these patterns into one-dimensional height images. Nanometer-sized features are found to grow and evolve in waves across the surface on the time scale of minutes to hours. {copyright} {ital 1999} {ital The American Physical Society}
FT IR spectroscopy of silicon oxide layers prepared with perchloric acid
NASA Astrophysics Data System (ADS)
Kopani, M.; Mikula, M.; Takahashi, M.; Rusnßk, J.; Pin?Ýk, E.
Chlorine oxidation is important methods for improvement of many properties such as passivation of mobile oxide charge, breakdown strength or enhancement of the minority-carrier lifetime in the underlying silicon. In this study we consider effects influencing the density of SiO2 layers formed by three different methods: thermal oxidation at 850 ░C, low temperature oxidation method by use of nitric acid - HNO3 (NAOS) and HClO4 afterward passivated with KCN/HCN solutions. Thicknesses of SiO2 layers determined by both capacitance-voltage (C-V) and XPS revealed fast oxidation rate compared with samples prepared by thermal oxidation. FT IR measurement showed that all absorption spectra are almost similar. Higher absorption of the sample prepared in HClO4 was observed. No Sisbnd Cl bonds were visible. Calculated atomic density of the SiO2 layer obtained from IR measurements was lowest for sample formed in HClO4. Chlorine oxidation results in higher oxidation rate (higher thickness) and formation of stoichiometric SiO2 layer with lower density. Following KCN/HCN passivation causes formation of Sisbnd N, Sisbnd O and Sisbnd OH bonds at the expense of Sisbnd Cl bonds.
Magnetometer uses bismuth-selenide
NASA Technical Reports Server (NTRS)
Woollman, J. A.; Spain, I. L.; Beale, H.
Characteristics of bismuth-selenide magnetometer are described. Advantages of bismuth-selenide magnetometer over standard magnetometers are stressed. Thermal stability of bismuth-selenide magnetometer is analyzed. Linearity of output versus magnetic field over wide range of temperatures is reported.
Fabricating nanostructures through a combination of nano-oxidation and wet etching on silicon wafers with different surface conditions.
Huang, Jen-Ching
This study investigates the surface conditions of silicon wafers with native oxide layers (NOL) or hydrogen passivated layers (HPL) and how they influence the processes of nano-oxidation and wet etching. We also explore the combination of nano-oxidation and wet etching processes to produce nanostructures. Experimental results reveal that the surface conditions of silicon wafers have a considerable impact on the results of nano-oxidation when combined with wet etching. The height and width of oxides on NOL samples exceeded the dimensions of oxides on HPL samples, and this difference became increasingly evident with an increase in applied bias voltage. The height of oxidized nanolines on the HPL sample increased after wet etching; however, the width of the lines increased only marginally. After wet etching, the height and width of oxides on the NOL were more than two times greater than those on the HPL. Increasing the applied bias voltage during nano-oxidation on NOL samples increased both the height and width of the oxides. After wet etching however, the increase in bias voltage appeared to have little effect on the height of oxidized nanolines, but the width of oxidized lines increased. This study also discovered that the use of higher applied bias voltages on NOL samples followed by wet etching results in nanostructures with a section profile closely resembling a curved surface. The use of this technique enabled researchers to create molds in the shape of a silicon nanolens array and an elegantly shaped nanoscale complex structures mold. PMID:22331692
Characterization of the mechanism of bi-layer oxide growth on austenitic stainless steels 316L and D9 in oxygen-controlled Lead-Bismuth Eutectic (LBE)
Daniel Koury
Lead Bismuth Eutectic (LBE) has been proposed for use in programs for accelerator-based and reactor-based transmutation of nuclear waste. LBE is a leading candidate material as a spallation target (in accelerator-based transmutation) and an option for the sub-critical blanket coolant. The corrosion by LBE of annealed and cold-rolled 316L stainless steels, and the modified austenitic stainless steel alloy D9, has
Oxidation of chemically-vapor-deposited silicon nitride and single-crystal silicon
NASA Technical Reports Server (NTRS)
Choi, Doo J.; Fischbach, David B.; Scott, William D.
The present 1000 C and 1300 C oxidation tests on 111-oriented single-crystal Si and dense CVD Si3N4 notes the oxidation rates of the latter in wet O2, dry O2, wet inert gas, and steam atmosphere conditions to be several orders of magnitude lower than the rates for the former in identical atmospheric conditions. Although the parabolic rate constant for Si increased linearly as the water vapor pressure increased, the parabolic rate constant for Si3N4 exhibited a nonlinear dependency on water vapor pressure in the presence of O2. NO and NH3 formation at the reaction interface of Si3N4, and the counterpermeation of these reaction products, are noted to dominate reaction kinetics.
Enhanced reduction of silicon oxide thin films on silicon under electron beam annealing
NASA Astrophysics Data System (ADS)
Kennedy, J.; Leveneur, J.; Fang, F.; Markwitz, A.
Electron beam annealing is an interesting alternative to other annealing methods as it can provide high temperature, rapid heating and cooling and low level of impurity as it operates under high vacuum environment. Furthermore swamping the materials with electrons can lead to dramatic changes in the component valence states with the mechanism involving oxido-reduction reactions. This is illustrated in the present case with the enhancement of the reduction of SiO2. Commercial thermally grown 100 and 400 nm SiO2 films on Si were annealed under three different environments: furnace annealing in open atmosphere with O2 flow, high vacuum furnace annealing and electron beam annealing. The reduction and oxidation of SiO2 films on Si are investigated using ion beam analysis. The validity of the measurement method was confirmed by measuring the oxidation rate through successive Rutherford backscattering spectrometry (RBS) measurements. The oxidation kinetics were observed to be in excellent agreement with literature values. At 1000 ░C reduction of the SiO2 film is observed only with electron beam annealing. A model is proposed to explain the effect of the electron beam.
Hydrothermal synthesis map of bismuth titanates
Sardar, Kripasindhu [Department of Chemistry, University of Warwick, Coventry, CV4 7AL (United Kingdom); Walton, Richard I., E-mail: firstname.lastname@example.com [Department of Chemistry, University of Warwick, Coventry, CV4 7AL (United Kingdom)
The hydrothermal synthesis of four bismuth titanate materials from common bismuth and titanium precursors under hydrothermal conditions is described. Reaction of NaBiO{sub 3}{center_dot}2H{sub 2}O and anatase TiO{sub 2} in concentrated NaOH solution at 240 Degree-Sign C is shown to produce perovskite and sillenite phases Na{sub 0.5}Bi{sub 0.5}TiO{sub 3} and Bi{sub 12}TiO{sub 20}, depending on the ratio of metal precursors used. When KOH solution is used and a 1:1 ratio of the same precursors, a pyrochlore Bi{sub 1.43}Ti{sub 2}O{sub 6}(OH){sub 0.29}(H{sub 2}O){sub 0.66} is formed. The use of a mixture of HNO{sub 3} and NaOH is shown to facilitate the formation of the Aurivillius-type bismuth titanate Bi{sub 4}Ti{sub 3}O{sub 12}. The phases have been isolated separately as phase-pure powders and profile refinement of powder X-ray diffraction data allows comparisons with comparable materials reported in the literature. Analysis of Bi L{sub III}-edge X-ray absorption near edge structure (XANES) spectra of the materials shows the oxidation state of bismuth is +3 in all of the hydrothermally derived products. - Graphical abstract: Use of NaBiO{sub 3}{center_dot}2H{sub 2}O and TiO{sub 2} as reagents under hydrothermal conditions allows the phase-pure preparation of four crystalline bismuth titanate materials. Highlights: Black-Right-Pointing-Pointer NaBiO{sub 3} and TiO{sub 2} under hydrothermal conditions allow formation of bismuth titanates. Black-Right-Pointing-Pointer Synthesis of four distint phases has been mapped. Black-Right-Pointing-Pointer Bi LIII-edge XANES shows Bi is reduced to oxidation state +3 in all materials. Black-Right-Pointing-Pointer A new hydrated bismuth titanate pyrochlore has been isolated.
Structural silicon nitride materials containing rare earth oxides
Andersson, Clarence A. (Pittsburgh, PA)
A ceramic composition suitable for use as a high-temperature structural material, particularly for use in apparatus exposed to oxidizing atmospheres at temperatures of 400 to 1600.degree. C., is found within the triangular area ABCA of the Si.sub.3 N.sub.4 --SiO.sub.2 --M.sub.2 O.sub.3 ternary diagram depicted in FIG. 1. M is selected from the group of Yb, Dy, Er, Sc, and alloys having Yb, Y, Er, or Dy as one component and Sc, Al, Cr, Ti, (Mg +Zr) or (Ni+Zr) as a second component, said alloy having an effective ionic radius less than 0.89 A.
Sintering of silicon nitride ceramics with magnesium silicon nitride and yttrium oxide as sintering aids
NASA Astrophysics Data System (ADS)
Jiang, J.; Xu, J. Y.; Peng, G. H.; Zhuang, H. R.; Li, W. L.; Xu, S. Y.; Mao, Y. J.
Silicon nitride (Si3N4) ceramics had been produced through pressureless sintering and hot-pressing sintering with MgSiN2-Y2O3 or only MgSiN2 as sintering aids. The influences of the amount of MgSiN2 and Y2O3 and sintering methods on the properties of Si3N4 ceramics were investigated. The results show that the bend strength of Si3N4 ceramic fabricated through pressureless sintering at 1820 ░C for 4 h with 5.6 wt.% MgSiN2-15.8 wt.% Y2O3 as sintering additive could achieve 839 MPa. However, the bend strength of Si3N4 ceramic produced by hot-pressing sintering at 1750 ░C for 1 h under uniaxial pressure of 20 MPa with 4.76 wt.% MgSiN2 was 1149 MPa. The thermal conductivity of the Si3N4 ceramic 2 3 4 could reach to 129 WÀm-1ÀK1. The present work demonstrated that MgSiN2 aids and hot-pressing sintering were effective to improve the thermal conductivity of Si3N4 ceramic.
Bismuth glass holey fibers with high nonlinearity
Heike Ebendorff-Heidepriem; P. Petropoulos; S. Asimakis; V. Finazzi; R. C. Moore; K. Frampton; F. Koizumi; D. J. Richardson; T. M. Monro
We report on the progress of bismuth oxide glass holey fibers for nonlinear device applications. The use of micron-scale core diameters has resulted in a very high nonlinearity of 1100 W-1 km-1 at 1550 nm. The nonlinear performance of the fibers is evaluated in terms of a newly introduced figure-of-merit for nonlinear device applications. Anomalous dispersion at 1550 nm has
Oxidation of silicon nitride sintered with rare-earth oxide additions
NASA Technical Reports Server (NTRS)
Mieskowski, D. M.; Sanders, W. A.
The effects of rare-earth oxide additions on the oxidation of sintered Si3N4 were examined. Insignificant oxidation occurred at 700 and 1000 C, with no evidence of phase instability. At 1370 C, the oxidation rate was lowest for Y2O3 and increased for additions of La2O3, Sm2O3, and CeO2, in that order. Data obtained from X-ray diffraction, electron microprobe analysis, and scanning electron microscopy indicate that oxidation occurs via diffusion of cationic species from Si3N4 grain boundaries.
The role of oxide interlayers in back reflector configurations for amorphous silicon solar cells
NASA Astrophysics Data System (ADS)
Demontis, V.; Sanna, C.; Melskens, J.; Santbergen, R.; Smets, A. H. M.; Damiano, A.; Zeman, M.
Thin oxide interlayers are commonly added to the back reflector of thin-film silicon solar cells to increase their current. To gain more insight in the enhancement mechanism, we tested different back reflector designs consisting of aluminium-doped zinc oxide (ZnO:Al) and/or hydrogenated silicon oxide (SiOx:H) interlayers with different metals (silver, aluminium, and chromium) in standard p-i-n a-Si:H solar cells. We use a unique inverse modeling approach to show that in most back reflectors the internal metal reflectance is lower than expected theoretically. However, the metal reflectance is increased by the addition of an oxide interlayer. Our experiments demonstrate that SiOx:H forms an interesting alternative interlayer because unlike the more commonly used ZnO:Al it can be deposited by plasma-enhanced chemical vapour deposition and it does not reduce the fill factor. The largest efficiency enhancement is obtained with a double interlayer of SiOx:H and ZnO:Al.
Identification and Control of Gravity Related Defect Formation During Melt Growth of Bismuth-Silicate (Bi12SiO20)
NASA Technical Reports Server (NTRS)
Zheng, Y.; Witt, A. F.
In the light of strong indications that a majority of critical defects formed in bismuth silicon oxide (BSO) during growth from the melt is related directly or indirectly to gravitational interference, it is suggested to use the reduced gravity environment of outer space for experimentation directed at the identification and control of these defects. The results of these experiments are expected to lead to advances in our understanding of crystal growth related defect formation in general and will establish a basis for effective defect engineering, the approach to efficient achievement of defect related, application specific properties in opto-electronic materials
Optical gain in dye-doped polymer waveguides using oxidized porous silicon cladding
NASA Astrophysics Data System (ADS)
Navarro-Urrios, Daniel; Ghulinyan, Mher; Bettotti, Paolo; Capuj, NÚstor; Oton, Claudio J.; Lahoz, Fernando; Martin, Inocencio R.; Pavesi, Lorenzo
We report on a novel organic/inorganic hybrid waveguide approach, which is composed of a cladding of extremely low refractive index oxidized porous silicon formed on a bulk silicon substrate and of it, a polymeric (polymethylmethacrylate) core doped with a visible laser dye (Nile-Blue) was deposited by spin coating. The waveguiding properties of the structures have been characterised by means of the m-line technique, demonstrating that the use of oxidized porous silicon as a cladding can considerably improve the mode confinement factor of single-mode waveguides. The low refractive index achievable in the cladding (n=1.16) allows forming waveguides with a low index polymer cores. Variable stripe length (VSL) measurements have been also performed in order to characterise the amplification properties of the waveguides. We demonstrate a clear transition from losses to gain at 694nm with a pump threshold of 28mJ/cm2. Values of net optical gain up to 104dB/cm have been measured at this wavelength.
Role of interfacial oxide in high-efficiency graphene-silicon schottky barrier solar cells.
Song, Yi; Li, Xinming; Mackin, Charles; Zhang, Xu; Fang, Wenjing; Palacios, Tomßs; Zhu, Hongwei; Kong, Jing
The advent of chemical vapor deposition (CVD) grown graphene has allowed researchers to investigate large area graphene/n-silicon Schottky barrier solar cells. Using chemically doped graphene, efficiencies of nearly 10% can be achieved for devices without antireflective coatings. However, many devices reported in past literature often exhibit a distinctive s-shaped kink in the measured I/V curves under illumination resulting in poor fill factor. This behavior is especially prevalent for devices with pristine (not chemically doped) graphene but can be seen in some cases for doped graphene as well. In this work, we show that the native oxide on the silicon presents a transport barrier for photogenerated holes and causes recombination current, which is responsible for causing the kink. We experimentally verify our hypothesis and propose a simple semiconductor physics model that qualitatively captures the effect. Furthermore, we offer an additional optimization to graphene/n-silicon devices: by choosing the optimal oxide thickness, we can increase the efficiency of our devices to 12.4% after chemical doping and to a new record of 15.6% after applying an antireflective coating. PMID:25685934
Electrorheological properties of polyaniline-vanadium oxide nanostructures suspended in silicone oil
NASA Astrophysics Data System (ADS)
Goswami, Sumita; Brehm, Tiago; Filonovich, Sergej; Cidade, Maria Teresa
In the present work, organic/inorganic hybrid nanostructures comprised of polyaniline and vanadium oxide were synthesized via a simple hydrothermal technique. The polyaniline/vanadium oxide hybrid morphology was tailored from rods to spheres by controlling the relative concentration of the reactants. The synthesized composites were characterized by x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and field emission scanning electron microscopy (FESEM) for structural and morphological analyses. Electrorheological (ER) properties of the as-prepared nanocomposites suspended in silicone oil were investigated by a rotational viscometer under both steady and dynamic shear. The ER activity of the composite material suspensions showed higher ER effects for the product with the rod-like structures than for the product with the sphere-like structures. The typical ER behaviour showed by the polyaniline-vanadium oxide nanocomposites demonstrated their potential application as an ER smart material.
Monte Carlo study of interfacial silicon suboxide layers and oxidation kinetics
NASA Astrophysics Data System (ADS)
da Silva, E. F.; de Vasconcelos, E. A.; StoÜi?, B. D.
A simple simulation scheme that simultaneously describes the growth kinetics of SiO 2 films at the nanometer scale and the SiO x/Si interface dynamics (its extent, and spatial/temporal evolution) is presented. The simulation successfully applies to experimental data in the region above and below 10 nm, reproduces the Deal and Grove linear-parabolic law and the oxide growth rate enhancement in the very thin film regime (the so-called anomalous region). According to the simulation, the oxidation is governed mainly by two processes: (a) the formation of a transition suboxide layer and (b) its subsequent drift towards the silicon bulk. We found that it is the superposition of these two processes that produces the crossover from the anomalous oxidation region behavior to the linear-parabolic law.
Interaction of silicon-based quantum dots with gibel carp liver: oxidative and structural modifications
Quantum dots (QDs) interaction with living organisms is of central interest due to their various biological and medical applications. One of the most important mechanisms proposed for various silicon nanoparticle-mediated toxicity is oxidative stress. We investigated the basic processes of cellular damage by oxidative stress and tissue injury following QD accumulation in the gibel carp liver after intraperitoneal injection of a single dose of 2 mg/kg body weight Si/SiO2 QDs after 1, 3, and 7 days from their administration. QDs gradual accumulation was highlighted by fluorescence microscopy, and subsequent histological changes in the hepatic tissue were noted. After 1 and 3 days, QD-treated fish showed an increased number of macrophage clusters and fibrosis, while hepatocyte basophilia and isolated hepatolytic microlesions were observed only after substantial QDs accumulation in the liver parenchyma, at 7 days after IP injection. Induction of oxidative stress in fish liver was revealed by the formation of malondialdehyde and advanced oxidation protein products, as well as a decrease in protein thiol groups and reduced glutathione levels. The liver enzymatic antioxidant defense was modulated to maintain the redox status in response to the changes initiated by Si/SiO2 QDs. So, catalase and glutathione peroxidase activities were upregulated starting from the first day after injection, while the activity of superoxide dismutase increased only after 7 days. The oxidative damage that still occurred may impair the activity of more sensitive enzymes. A significant inhibition in glucose-6-phosphate dehydrogenase and glutathione-S-transferase activity was noted, while glutathione reductase remained unaltered. Taking into account that the reduced glutathione level had a deep decline and the level of lipid peroxidation products remained highly increased in the time interval we studied, it appears that the liver antioxidant defense of Carassius gibelio does not counteract the oxidative stress induced 7 days after silicon-based QDs exposure in an efficient manner. PMID:23718202
Interaction of silicon-based quantum dots with gibel carp liver: oxidative and structural modifications
NASA Astrophysics Data System (ADS)
Stanca, Loredana; Petrache, Sorina Nicoleta; Serban, Andreea Iren; Staicu, Andrea Cristina; Sima, Cornelia; Munteanu, Maria Cristina; Z?rnescu, Otilia; Dinu, Diana; Dinischiotu, Anca
Quantum dots (QDs) interaction with living organisms is of central interest due to their various biological and medical applications. One of the most important mechanisms proposed for various silicon nanoparticle-mediated toxicity is oxidative stress. We investigated the basic processes of cellular damage by oxidative stress and tissue injury following QD accumulation in the gibel carp liver after intraperitoneal injection of a single dose of 2 mg/kg body weight Si/SiO2 QDs after 1, 3, and 7 days from their administration. QDs gradual accumulation was highlighted by fluorescence microscopy, and subsequent histological changes in the hepatic tissue were noted. After 1 and 3 days, QD-treated fish showed an increased number of macrophage clusters and fibrosis, while hepatocyte basophilia and isolated hepatolytic microlesions were observed only after substantial QDs accumulation in the liver parenchyma, at 7 days after IP injection. Induction of oxidative stress in fish liver was revealed by the formation of malondialdehyde and advanced oxidation protein products, as well as a decrease in protein thiol groups and reduced glutathione levels. The liver enzymatic antioxidant defense was modulated to maintain the redox status in response to the changes initiated by Si/SiO2 QDs. So, catalase and glutathione peroxidase activities were upregulated starting from the first day after injection, while the activity of superoxide dismutase increased only after 7 days. The oxidative damage that still occurred may impair the activity of more sensitive enzymes. A significant inhibition in glucose-6-phosphate dehydrogenase and glutathione-S-transferase activity was noted, while glutathione reductase remained unaltered. Taking into account that the reduced glutathione level had a deep decline and the level of lipid peroxidation products remained highly increased in the time interval we studied, it appears that the liver antioxidant defense of Carassius gibelio does not counteract the oxidative stress induced 7 days after silicon-based QDs exposure in an efficient manner.
Oxidation-enhanced diffusion of ion-implanted boron in heavily phosphorus-doped silicon
NASA Astrophysics Data System (ADS)
Miyake, Masayasu
Oxidation-enhanced diffusion (OED) of ion-implanted boron in heavily phosphorus-doped silicon is studied by measuring boron depth profiles using secondary ion mass spectroscopy for phosphorus concentration from intrinsic conditions to 1.2Î1020 cm-3. OED is observed for the whole phosphorus concentration range investigated in the present work. However, both the diffusion coefficient in N2 ambient DN and that in dry O2 ambient DO decrease with an increase in substrate phosphorus concentration in extrinsic conditions, i.e., for phosphorus concentration larger than the intrinsic carrier concentration. Diffusion coefficient increment due to OED ?D(=DO-DN) decreases with an increase in phosphorus concentration. The decrease in ?D with an increase in phosphorus concentration is attributed to a decrease in excess silicon interstitials due to recombination with acceptor-type vacancies.
Hydrogen passivation of silicon(100) used as templates for low-temperature epitaxy and oxidation
NASA Astrophysics Data System (ADS)
Atluri, Vasudeva Prasad
Epitaxial growth, oxidation and ohmic contacts require surfaces as free as possible of physical defects and chemical contaminants, especially, oxygen and hydrocarbons. Wet chemical cleaning typically involves a RCA clean to remove contaminants by stripping the native oxide and regrowing a chemical oxide with only trace levels of carbon and metallic impurities. Low temperature epitaxy, T<800sp░ C, limits the thermal budget for the desorption of impurities and surface oxides, and can be performed on processed structures. But, silicon dioxide cannot be desorbed at temperatures lower than 800sp░C. Recently, hydrogen passivation of Si(111) has been reported to produce stable and ordered surfaces at low temperatures. Hydrogen can then be desorbed between 200sp░C and 600sp░C prior to deposition. In this work, Si(100) is passivated via a solution of hydrofluoric acid in alcohol (methanol, ethanol, or isopropyl alcohol) with HF concentrations between 0.5 to 10%. A rinse in water or alcohol is performed after etching to remove excess fluorine. This work investigates wet chemical cleaning of Si(100) to produce ordered, hydrogen-terminated, oxygen- and carbon-free surfaces to be used as templates for low temperature epitaxial growth and rapid thermal oxidation. Ion beam analysis, Tapping mode atomic force microscopy, Fourier transform infrared spectroscopy, Secondary ion mass spectroscopy, Chemical etching, Capacitance-voltage measurements and Ellipsometry are used to measure, at the surface and interface, impurities concentration, residual disorder, crystalline order, surface topography, roughness, chemical composition, defects density, electrical characteristics, thickness, and refractive index as a function of cleaning conditions for homoepitaxial silicon growth and oxidation. The wetting characteristics of the Si(100) surfaces are measured with a tilting plate technique. Different materials are analyzed by ion beam analysis for use as hydrogen standards in elastic recoil detection of hydrogen on sample surfaces. The results obtained in this study provide a quantitative optimization of passivation of Si(100) surfaces and their use as templates for low temperature epitaxy and rapid thermal oxidation. Ion beam analysis shows that the total coverage of H increases during passivation of Si(100) via HF in alcohol, while Fourier transform infrared spectroscopy indicates that more complex termination than the formation of simple silicon hydrides occurs.
Band offsets of a ruthenium gate on ultrathin high-{kappa} oxide films on silicon
Rangan, Sylvie; Bersch, Eric; Bartynski, Robert Allen; Garfunkel, Eric; Vescovo, Elio [Department of Physics and Astronomy and Laboratory for Surface Modification, Rutgers University, 136 Frelinghuysen Road, Piscataway, New Jersey 08854 (United States); Department of Chemistry and Chemical Biology and Laboratory for Surface Modification, Rutgers University, 610 Taylor Road, Piscataway, New Jersey 08854 (United States); National Synchrotron Light Source, Brookhaven National Laboratory, Upton, New York 11973 (United States)
Valence-band and conduction-band edges of ultrathin oxides (SiO{sub 2}, HfO{sub 2}, Hf{sub 0.7}Si{sub 0.3}O{sub 2}, and Al{sub 2}O{sub 3} grown on silicon) and their shifts upon sequential metallization with ruthenium have been measured using synchrotron-radiation-excited x-ray, ultraviolet, and inverse photoemissions. From these techniques, the offsets between the valence-band and conduction-band edges of the oxides, and the ruthenium metal gate Fermi edge have been directly measured. In addition the core levels of the oxides and the ruthenium have been characterized. Upon deposition, Ru remains metallic and no chemical alteration of the underlying oxide gates, or interfacial SiO{sub 2} in the case of the high-{kappa} thin films, can be detected. However a clear shift of the band edges is measured for all samples due to the creation of an interface dipole at the ruthenium-oxide interface. Using the energy gap, the electron affinity of the oxides, and the ruthenium work function that have been directly measured on these samples, the experimental band offsets are compared to those predicted by the induced gap states model.
Silicon oxide and silicon nitride etch mechanisms in nitrogen trifluoride/ethylene plasma
NASA Astrophysics Data System (ADS)
Machima, Puthajat
Low-pressure inductive plasma was used to study SiO 2 and Si3N4 etching with the NF3/C 2H4-based gas chemistry. NF3 and C2H 4 were used so that fluorine and carbon could be supplied from parent gases other than strongly global warming fluorocarbons, which are conventionally used in industry. Experiments were performed at low pressure (<10 mTorr) and low flow rates to minimize production of global-warming CFx species. Selective etching of SiO2 to Si3N4 was not achieved. Etch rates of SiO2 over a wide range of conditions are less than 0.8 times the Si3N4 etch rates. Changing ion energy distributions at the oxide or nitride surface by varying the bias frequency significantly changed the etch rates of both materials but did not strongly affect etch mechanisms or the selectivity. Ex-situ X-ray photoelectron spectroscopy was employed to determine the characteristics of a very thin steady-state film, in order to establish likely etch mechanisms. CHx F, CF2, and CF3 were produced but in small concentrations compared to CHx and CN, as supported by mass spectrometry and XPS results. The C 1s spectra from etched oxide samples show a large percentage of HxC-CHx structures compared to other carbon-containing species. On the other hand, Si3N4 appears to react easily with HxC-CHx structures, yielding CN-bearing etch products and SiC. Although nitride can react quickly with saturated hydrocarbon structures, a too large concentration of HxC-CHx decelerates the removal process of CN-containing etch products from the surface and can lower the nitride etch rate. The lack of selectivity is not limited to C2H 4. Etch rate and selectivity results of NF3-based discharges fed with C2H2, C4H10, and CH 3F are similar to those of the NF3/C2H4 plasma. Comparisons of normalized F 1s spectra of nitride and oxide etched under the same conditions show that relative concentrations of CF2 and CF3 on SiO2 are much lower than the concentrations on Si3N4. It appears that SiO2 preferentially reacts with CF2 and CF3 only but not with HxC-CH x or CHxF. Differences in the abilities of SiO2 and Si3N4 to react with HxC-CHx structures contributed to higher etch rates of Si3N4.
Composition, process, and apparatus, for removal of water and silicon mu-oxides from chlorosilanes
Tom, Glenn M. (New Milford, CT); McManus, James V. (Danbury, CT)
A scavenger composition having utility for removal of water and silicon mu-oxide impurities from chlorosilanes, such scavenger composition comprising: (a) a support; and (b) associated with the support, one or more compound(s) selected from the group consisting of compounds of the formula: R.sub.a-x MCl.sub.x wherein: M is a metal selected from the group consisting of the monovalent metals lithium, sodium, and potassium; the divalent metals magnesium, strontium, barium, and calcium; and the trivalent metal aluminum; R is alkyl; a is a number equal to the valency of metal M; and x is a number having a value from 0 to a, inclusive; and wherein said compound(s) of the formula R.sub.a-x MCl.sub.x have been activated for impurity-removal service by a reaction scheme selected from those of the group consisting of: (i) reaction of such compound(s) with hydrogen chloride to form a first reaction product therefrom, followed by reaction of the first reaction product with a chlorosilane of the formula: SiH.sub.4"y Cl.sub.y, wherein y is a number having a value of from 1 to 3, inclusive; and (ii) reaction of such compound(s) with a chlorosilane of the formula: SiH.sub.4-y Cl.sub.y wherein y is a number having a value of 1 to 3, inclusive. A corresponding method of making the scavenger composition, and of purifying a chlorosilane which contains oxygen and silicon mu-oxide impurities, likewise are disclosed, together with a purifier apparatus, in which a bed of the scavenger composition is disposed. The composition, purification process, and purifier apparatus of the invention have utility in purifying gaseous chlorosilanes which are employed in the semiconductor industry as silicon source reagents for forming epitaxial silicon layers.
Process for removal of water and silicon mu-oxides from chlorosilanes
Tom, Glenn M. (New Milford, CT); McManus, James V. (Danbury, CT)
A scavenger composition having utility for removal of water and silicon mu-oxide impurities from chlorosilanes, such scavenger composition comprising: (a) a support; and (b) associated with the support, one or more compound(s) selected from the group consisting of compounds of the formula: R.sub.a-x MCl.sub.x wherein: M is a metal selected from the group consisting of the monovalent metals lithium, sodium, and potassium; the divalent metals magnesium, strontium, barium, and calcium; and the trivalent metal aluminum; R is alkyl; a is a number equal to the valency of metal M; and x is a number having a value of from 0 to a, inclusive; and wherein said compound(s) of the formula R.sub.a-x MCl.sub.x have been activated for impurity-removal service by a reaction scheme selected from those of the group consisting of: (i) reaction of such compound(s) with hydrogen chloride to form a first reaction product therefrom, followed by reaction of the first reaction product with a chlorosilane of the formula: SiH.sub.4-y Cl.sub.y, wherein y is a number having a value of from 1 to 3, inclusive; and (ii) reaction of such compound(s) with a chlorosilane of the formula: SiH.sub.4-y Cl.sub.y wherein y is a number having a value of 1 to 3, inclusive. A corresponding method of making the scavenger composition, and of purifying a chlorosilane which contains oxygen and silicon mu-oxide impurities, likewise are disclosed, together with a purifier apparatus, in which a bed of the scavenger composition is disposed. The composition, purification process, and purifier apparatus of the invention have utility in purifying gaseous chlorosilanes which are employed in the semiconductor industry as silicon source reagents for forming epitaxial silicon layers.
Anti-reflection zinc oxide nanocones for higher efficiency thin-film silicon solar cells
Mailoa, Jonathan P
Thin film silicon solar cells, which are commonly made from microcrystalline silicon ([mu]c-Si) or amorphous silicon (a-Si), have been considered inexpensive alternatives to thick polycrystalline silicon (polysilicon) solar ...
In-Situ Transmission Electron Microscopy Probing of Native Oxide and Artificial Layers on Silicon Nanoparticles for Lithium Ion Batteries
He, Yang; Piper, Daniela M.; Gu, Meng; Travis, Jonathan J.; George, Steven M.; Lee, Se-Hee; Genc, Arda; Pullan, Lee; Liu, Jun; Mao, Scott X.; Zhang, Jiguang; Ban, Chunmei; Wang, Chong M.
Surface modification of silicon nanoparticle via molecular layer deposition (MLD) has been recently proved to be an effective way for dramatically enhancing the cyclic performance in lithium ion batteries. However, the fundamental mechanism as how this thin layer of coating function is not known, which is even complicated by the inevitable presence of native oxide of several nanometers on the silicon nanoparticle. Using in-situ TEM, we probed in detail the structural and chemical evolution of both uncoated and coated silicon particles upon cyclic lithiation/delithation. We discovered that upon initial lithiation, the native oxide layer converts to crystalline Li2O islands, which essentially increases the impedance on the particle, resulting in ineffective lithiation/delithiation, and therefore low coulombic efficiency. In contrast, the alucone MLD coated particles show extremely fast, thorough and highly reversible lithiation behaviors, which are clarified to be associated with the mechanical flexibility and fast Li+/e- conductivity of the alucone coating. Surprisingly, the alucone MLD coating process chemically changes the silicon surface, essentially removing the native oxide layer and therefore mitigates side reaction and detrimental effects of the native oxide. This study provides a vivid picture of how the MLD coating works to enhance the coulombic efficiency and preserve capacity and clarifies the role of the native oxide on silicon nanoparticles during cyclic lithiation and delithiation. More broadly, this work also demonstrated that the effect of the subtle chemical modification of the surface during the coating process may be of equal importance as the coating layer itself.
Evgenii M. Dianov; V. V. Dvoyrin; V. M. Mashinsky; A. A. Umnikov; M. V. Yashkov; A. N. Gur'yanov
A new fibre laser based on a bismuth-doped aluminosilicate glass fibre is proposed and fabricated. CW lasing is obtained in the spectral region between 1150 and 1300 nm. The fibres are fabricated by the method of modified chemical vapour deposition. Bibtex entry for this abstract Preferred format for this abstract (see Preferences) Find Similar Abstracts: Use: Authors Title Abstract Text
Characteristics of electro-refractive modulating based on Graphene-Oxide-Silicon waveguide.
Xu, Chao; Jin, Yichang; Yang, Longzhi; Yang, Jianyi; Jiang, Xiaoqing
Graphene has attracted a high level of research interest because of its outstanding electronic transport properties and optical properties. Based on the Kubo formalism and the Maxwell equations, it's demonstrated that the optical conductivity of graphene can be controlled through the applied voltage. And we find that the graphene-oxide-silicon (GOS) based waveguide can be made into either the electro-absorptive or electron-refractive modulators. Using graphene as the active medium, we present a new electro-refractive Mach-Zender interferometer based on the GOS structure. This new GOS-based electron-refractive modulation mechanism can enable novel architectures for on-chip optical communications. PMID:23037388
Epitaxial ferromagnetic oxide thin films on silicon with atomically sharp interfaces
Coux, P. de [Institut de CiÞncia de Materials de Barcelona (ICMAB-CSIC), Campus de la UAB, 08193 Bellaterra, Barcelona (Spain); CEMES-CNRS, 29 rue Jeanne Marvig, BP 94347, Toulouse Cedex 4 (France); Bachelet, R.; Fontcuberta, J.; Sßnchez, F., E-mail: email@example.com [Institut de CiÞncia de Materials de Barcelona (ICMAB-CSIC), Campus de la UAB, 08193 Bellaterra, Barcelona (Spain); Warot-Fonrose, B. [CEMES-CNRS, 29 rue Jeanne Marvig, BP 94347, Toulouse Cedex 4 (France); Skumryev, V. [Instituci¾ Catalana de Recerca i Estudis Avanþats (ICREA), Barcelona, Spain and Dep. de FÝsica, Univ. Aut‗noma de Barcelona, 08193 Bellaterra (Spain); Lupina, L.; Niu, G.; Schroeder, T. [IHP, Im Technologiepark 25, 15236 Frankfurt (Oder) (Germany)
A bottleneck in the integration of functional oxides with silicon, either directly grown or using a buffer, is the usual formation of an amorphous interfacial layer. Here, we demonstrate that ferromagnetic CoFe{sub 2}O{sub 4} films can be grown epitaxially on Si(111) using a Y{sub 2}O{sub 3} buffer layer, and remarkably the Y{sub 2}O{sub 3}/Si(111) interface is stable and remains atomically sharp. CoFe{sub 2}O{sub 4} films present high crystal quality and high saturation magnetization.
Using nanopillars of silicon oxide as a versatile platform for visualizing a selective immunosorbent
NASA Astrophysics Data System (ADS)
Chen, Jem-Kun; Zhou, Gang-Yan; Huang, Chih-Feng; Ko, Fu-Hsiang
In this study, we fabricated nanopillar arrays of silicon oxide for use as two-dimensional periodic relief gratings (2DPRGs) on Si surfaces. We deposited antibodies onto the pillar surfaces of 2DPRGs modified with protein G to obtain optical detectors that were specific for the targeted antigen; the antigen units that filled the spaces between the nanopillars of the 2DPRG lead to a dramatic change in the pillar scale. The effective refractive index (neff) of the 2DPRGs was related to the pillar scale of the 2DPRG; after coupling of the antigen, a color change from pure green to orange was observable.
Insights into electrical characteristics of silicon doped hafnium oxide ferroelectric thin films
NASA Astrophysics Data System (ADS)
Zhou, Dayu; M³ller, J.; Xu, Jin; Knebel, S.; Brõuhaus, D.; Schr÷der, U.
Silicon doped hafnium oxide thin films were recently discovered to exhibit ferroelectricity. In the present study, metal-ferroelectric-metal capacitors with Si:HfO2 thin films as ferroelectric material and TiN as electrodes have been characterized with respect to capacitance and current density as functions of temperature and applied voltage. Polarity asymmetry of the frequency dependent coercive field was explained by interfacial effects. No ferroelectric-paraelectric phase transition was observed at temperatures up to 478 K. Clear distinctions between current evolutions with or without polarization switching were correlated to the time competition between the measurement and the response of relaxation mechanisms.
Silicon improves seed germination and alleviates oxidative stress of bud seedlings in tomato under water deficit stress.
Shi, Yu; Zhang, Yi; Yao, Hejin; Wu, Jiawen; Sun, Hao; Gong, Haijun
The beneficial effects of silicon on plant growth and development under drought have been widely reported. However, little information is available on the effects of silicon on seed germination under drought. In this work, the effects of exogenous silicon (0.5 mM) on the seed germination and tolerance performance of tomato (Solanum lycopersicum L.) bud seedlings under water deficit stress simulated by 10% (w/v) polyethylene glycol (PEG-6000) were investigated in four cultivars ('Jinpengchaoguan', 'Zhongza No.9', 'Houpi L402' and 'Oubao318'). The results showed that the seed germination percentage was notably decreased in the four cultivars under water stress, and it was significantly improved by added silicon. Compared with the non-silicon treatment, silicon addition increased the activities of superoxide dismutase (SOD) and catalase (CAT), and decreased the production of superoxide anion (O2À) and hydrogen peroxide (H2O2) in the radicles of bud seedlings under water stress. Addition of silicon decreased the total phenol concentrations in radicles under water stress, which might contribute to the decrease of peroxidase (POD) activity, as observed in the in vivo and in vitro experiments. The decrease of POD activity might contribute to a less accumulation of hydroxyl radical (ÀOH) under water stress. Silicon addition also decreased the concentrations of malondialdehyde (MDA) in the radicles under stress, indicating decreased lipid peroxidation. These results suggest that exogenous silicon could improve seed germination and alleviate oxidative stress to bud seedling of tomato by enhancing antioxidant defense. The positive effects of silicon observed in a silicon-excluder also suggest the active involvement of silicon in biochemical processes in plants. PMID:24607576
Aqueous and thermal oxidation of porous silicon microparticles: implications on molecular interactions.
Jarvis, Karyn L; Barnes, Timothy J; Prestidge, Clive A
Links between the mechanisms and kinetics of aqueous and dry thermal oxidation of porous silicon (pSi) microparticles have been investigated and the influence on molecular interaction established. zeta potential measurements have established the interplay between the dry oxidation state of pSi microparticles and their interfacial chemistry in aqueous solution, and Fourier transform infrared spectroscopy has demonstrated the effect of immersion time and oxidation temperature on surface chemistry. The influence of aqueous and thermal oxidation on molecular interactions and loading was investigated using methylene blue as a probe molecule. Aqueous immersion of pSi microparticles results in an initial increase in OySiH (y = 1-3) species with increasing immersion times, reducing O2SiH concentration, while O3SiH concentration remained constant. Thermal oxidation from 473 to 1073 K causes the gradual transition from SiySiHx to OySiH and finally OySiOH species. Both aqueous and thermal oxidations had an effect on the zeta potentials of pSi microparticles. Methylene blue discoloration occurred due to its reduction by the SiSiHx-terminated surface thereby demonstrating the reactivity of such species. Aqueous and thermal oxidations modify pSi microparticle surface chemistry, which has therefore shown to influence molecular interactions. Understanding the aqueous oxidation of pSi is crucial when loading pSi from aqueous solution due to its impact on molecular interactions. These molecular interactions play an important role in the loading of pSi since they dictate the attraction of the molecule toward the surface and therefore ultimately the loading level. PMID:19053643
Evaluation of silicon oxide cleaning using F2/Ar remote plasma processing
NASA Astrophysics Data System (ADS)
Kang, S. C.; Hwang, J. Y.; Lee, N.-E.; Joo, K. S.; Bae, G. H.
In this study, chamber cleaning experiments using a F2/Ar remote plasma generated from a toroidal-type remote plasma source were carried out in a plasma enhanced chemical vapor deposition (PECVD) system. The cleaning processes for the various silicon oxide layers, including PE-oxide (deposited by PECVD using SiH4 and N2O), O3-TEOS oxide (deposited by thermal CVD using ozone and TEOS precursor), and BPSG (borophosphosilicate glass), were investigated by varying the various process parameters, such as the F2 gas flow rate, the F2/(F2+Ar) flow ratio, and the cleaning temperature. The species emitted during cleaning were monitored by Fourier transformed infrared spectroscopy and residual gas analysis. Under the current experimental conditions, the cleaning rate of the BPSG was 4.1-5.0 and 3.9-7.3 times higher than that those of the PE-oxide and O3-TEOS oxide layers, respectively, at room temperature and an F2/(F2+Ar) flow ratio of 28.5%-83%. As the cleaning temperature increased from 100 to 350 ░C, the cleaning rates of the PE-oxide, O3-TEOS oxide, and BPSG layers were increased by factors of 2.0-3.0, 1.5-2.2, and 3.0-3.4, respectively, at an F2/(F2+Ar) flow ratio of 28%-68%. The F2/(F2+Ar) flow ratio and cleaning temperature were found to be the most critical parameters involved in determining the cleaning rate of the various oxide layers.
Development of silicon electrode enhanced by carbon nanotube and gold nanoparticle composites on silicon neural probe fabricated with complementary metal-oxide-semiconductor process
NASA Astrophysics Data System (ADS)
Zhang, Songsong; Tsang, Wei Mong; Srinivas, Merugu; Sun, Tao; Singh, Navab; Kwong, Dim-Lee; Lee, Chengkuo
We present the fabrication of highly P-doped single crystal silicon electrodes on a silicon probe through complementary metal-oxide-semiconductor (CMOS)-compatible processes. The electrode with diameter of 50 ?m and a separation of 200 ?m is designed for recording/stimulating purposes. Electrochemical impedance spectroscopy indicates that the interfacial impedance of silicon electrodes at 1 KHz is 2.5 ▒ 0.4 M?, which is equivalent to the result reported from the gold (Au) electrode. To further enhance the charge storage capacity, composites of multi-wall carbon nanotubes (MWCNTs) and Au nanoparticles are electroplated onto the highly P-doped silicon electrode after surface roughness treatments. With optimized electroplating processes, MWCNTs and Au nanoparticles are selectively coated onto the electrode site with only a minimum enlargement in physical diameter of electrode (<10%). However, the typical impedance is reduced to 21 ▒ 3 k?. Such improvement can be explained by a boost in double-layer capacitance (Cdl) and the reduction in faradic resistances. The measurement of cyclic voltammetry (CV) shows that the cathodal charge storage capacity is up to 35 mC cm-2, which proves the superior performance of composite coatings on silicon electrodes and validates the functionality of reported CMOS-compatible silicon probe.
21 CFR 73.1162 - Bismuth oxychloride.
Code of Federal Regulations, 2013 CFR
...2013-04-01 2013-04-01 false Bismuth oxychloride. 73.1162 Section 73...CERTIFICATION Drugs º 73.1162 Bismuth oxychloride. (a) Identity. (1) The color additive bismuth oxychloride is a synthetically...
21 CFR 73.2162 - Bismuth oxychloride.
Code of Federal Regulations, 2011 CFR
...2011-04-01 2011-04-01 false Bismuth oxychloride. 73.2162 Section 73...CERTIFICATION Cosmetics º 73.2162 Bismuth oxychloride. (a) Identity and specifications. (1) The color additive bismuth oxychloride shall conform in...
21 CFR 73.1162 - Bismuth oxychloride.
Code of Federal Regulations, 2010 CFR
...2010-04-01 2010-04-01 false Bismuth oxychloride. 73.1162 Section 73...CERTIFICATION Drugs º 73.1162 Bismuth oxychloride. (a) Identity. (1) The color additive bismuth oxychloride is a synthetically...
21 CFR 73.2162 - Bismuth oxychloride.
Code of Federal Regulations, 2013 CFR
...2013-04-01 2013-04-01 false Bismuth oxychloride. 73.2162 Section 73...CERTIFICATION Cosmetics º 73.2162 Bismuth oxychloride. (a) Identity and specifications. (1) The color additive bismuth oxychloride shall conform in...
21 CFR 73.1162 - Bismuth oxychloride.
Code of Federal Regulations, 2011 CFR
...2011-04-01 2011-04-01 false Bismuth oxychloride. 73.1162 Section 73...CERTIFICATION Drugs º 73.1162 Bismuth oxychloride. (a) Identity. (1) The color additive bismuth oxychloride is a synthetically...
21 CFR 73.1162 - Bismuth oxychloride.
Code of Federal Regulations, 2014 CFR
...2014-04-01 2014-04-01 false Bismuth oxychloride. 73.1162 Section 73...CERTIFICATION Drugs º 73.1162 Bismuth oxychloride. (a) Identity. (1) The color additive bismuth oxychloride is a synthetically...
21 CFR 73.2162 - Bismuth oxychloride.
Code of Federal Regulations, 2012 CFR
...2012-04-01 2012-04-01 false Bismuth oxychloride. 73.2162 Section 73...CERTIFICATION Cosmetics º 73.2162 Bismuth oxychloride. (a) Identity and specifications. (1) The color additive bismuth oxychloride shall conform in...
21 CFR 73.1162 - Bismuth oxychloride.
Code of Federal Regulations, 2012 CFR
...2012-04-01 2012-04-01 false Bismuth oxychloride. 73.1162 Section 73...CERTIFICATION Drugs º 73.1162 Bismuth oxychloride. (a) Identity. (1) The color additive bismuth oxychloride is a synthetically...
21 CFR 73.2162 - Bismuth oxychloride.
Code of Federal Regulations, 2014 CFR
...2014-04-01 2014-04-01 false Bismuth oxychloride. 73.2162 Section 73...CERTIFICATION Cosmetics º 73.2162 Bismuth oxychloride. (a) Identity and specifications. (1) The color additive bismuth oxychloride shall conform in...
21 CFR 73.2162 - Bismuth oxychloride.
Code of Federal Regulations, 2010 CFR
...2010-04-01 2010-04-01 false Bismuth oxychloride. 73.2162 Section 73...CERTIFICATION Cosmetics º 73.2162 Bismuth oxychloride. (a) Identity and specifications. (1) The color additive bismuth oxychloride shall conform in...
Phase transformation and morphological evolution of ion-beam sputtered tin oxide films on silicon substrate
Choe, Y.S.; Chung, J.H.; Kim, D.S.; Kim, G.H.; Baik, H.K.
Amorphous tin oxide films were deposited on a silicon substrate by ion-beam sputtering (IBS) using a SnO{sub 2} target. Phase transformation and morphological changes of deposited films at different annealing temperatures were studied by X-ray diffraction and scanning electron microscopy. Crystallization of the as-deposited film started at 350 C and SnO and SnO{sub 2} phases formed at 400 C. Disproportionation of SnO into Sn and SnO{sub 2} was observed at 450 C followed by the oxidation of metallic tin at 550 C. Large volume changes accompanying the oxidation of metallic tin at this temperature caused the partial detachment and formation of heavy wrinkles on the film. These results suggest that the oxygen deficiency of tin oxide films should be avoided by optimizing the deposition process, since a drastic morphological change at the phase transformation to SnO{sub 2} during annealing may destroy the integrity of the thin films and degrade the long-term stability of tin oxide films used as gas sensors at high temperatures.
Densification of chemical vapor deposition silicon dioxide film using oxygen radical oxidation
NASA Astrophysics Data System (ADS)
Kawase, Kazumasa; Teramoto, Akinobu; Umeda, Hiroshi; Suwa, Tomoyuki; Uehara, Yasushi; Hattori, Takeo; Ohmi, Tadahiro
Silicon dioxide (SiO2) films formed by chemical vapor deposition (CVD) were treated with oxygen radical oxidation using Ar/O2 plasma excited by microwave. The mass density depth profiles, carrier trap densities, and current-voltage characteristics of the radical-oxidized CVD-SiO2 films were investigated. The mass density depth profiles were estimated with x ray reflectivity measurement using synchrotron radiation of SPring-8. The carrier trap densities were estimated with x ray photoelectron spectroscopy time-dependent measurement. The mass densities of the radical-oxidized CVD-SiO2 films were increased near the SiO2 surface. The densities of the carrier trap centers in these films were decreased. The leakage currents of the metal-oxide-semiconductor capacitors fabricated by using these films were reduced. It is probable that the insulation properties of the CVD-SiO2 film are improved by the increase in the mass density and the decrease in the carrier trap density caused by the restoration of the Si-O network with the radical oxidation.
Densification of chemical vapor deposition silicon dioxide film using oxygen radical oxidation
Kawase, Kazumasa; Uehara, Yasushi [Advanced Technology R and D Center, Mitsubishi Electric Corporation, 8-1-1 Tsukaguchi-honmachi, Amagasaki, Hyogo 661-8661 (Japan); Teramoto, Akinobu; Suwa, Tomoyuki; Hattori, Takeo; Ohmi, Tadahiro [New Industry Creation Hatchery Center, Tohoku University, 6-6-10 Aoba Aramaki, Aoba-ku, Sendai, Miyagi 980-8579 (Japan); Umeda, Hiroshi [Process Technology Div., Production and Technology Unit, RENESAS Electronics Corporation, 751 Horiguchi, Hitachinaka, Ibaraki 312-8504 (Japan)
Silicon dioxide (SiO{sub 2}) films formed by chemical vapor deposition (CVD) were treated with oxygen radical oxidation using Ar/O{sub 2} plasma excited by microwave. The mass density depth profiles, carrier trap densities, and current-voltage characteristics of the radical-oxidized CVD-SiO{sub 2} films were investigated. The mass density depth profiles were estimated with x ray reflectivity measurement using synchrotron radiation of SPring-8. The carrier trap densities were estimated with x ray photoelectron spectroscopy time-dependent measurement. The mass densities of the radical-oxidized CVD-SiO{sub 2} films were increased near the SiO{sub 2} surface. The densities of the carrier trap centers in these films were decreased. The leakage currents of the metal-oxide-semiconductor capacitors fabricated by using these films were reduced. It is probable that the insulation properties of the CVD-SiO{sub 2} film are improved by the increase in the mass density and the decrease in the carrier trap density caused by the restoration of the Si-O network with the radical oxidation.
ZnO transparent conductive oxide for thin film silicon solar cells
NASA Astrophysics Data System (ADS)
S÷derstr÷m, T.; DominÚ, D.; Feltrin, A.; Despeisse, M.; Meillaud, F.; Bugnon, G.; Boccard, M.; Cuony, P.; Haug, F.-J.; Fa , S.; Nicolay, S.; Ballif, C.
There is general agreement that the future production of electric energy has to be renewable and sustainable in the long term. Photovoltaic (PV) is booming with more than 7GW produced in 2008 and will therefore play an important role in the future electricity supply mix. Currently, crystalline silicon (c-Si) dominates the market with a share of about 90%. Reducing the cost per watt peak and energy pay back time of PV was the major concern of the last decade and remains the main challenge today. For that, thin film silicon solar cells has a strong potential because it allies the strength of c-Si (i.e. durability, abundancy, non toxicity) together with reduced material usage, lower temperature processes and monolithic interconnection. One of the technological key points is the transparent conductive oxide (TCO) used for front contact, barrier layer or intermediate reflector. In this paper, we report on the versatility of ZnO grown by low pressure chemical vapor deposition (ZnO LP-CVD) and its application in thin film silicon solar cells. In particular, we focus on the transparency, the morphology of the textured surface and its effects on the light in-coupling for micromorph tandem cells in both the substrate (n-i-p) and superstrate (p-i-n) configurations. The stabilized efficiencies achieved in NeuchÔtel are 11.2% and 9.8% for p-i-n (without ARC) and n-i-p (plastic substrate), respectively.
Indium-tin-oxide nanowhiskers crystalline silicon photovoltaics combining micro- and nano-scale surface textures
NASA Astrophysics Data System (ADS)
Chang, C. H.; Hsu, M. H.; Chang, W. L.; Sun, W. C.; Yu, Peichen
In this work, we present a solution that employs combined micro- and nano-scale surface textures to increase light harvesting in the near infrared for crystalline silicon photovoltaics, and discuss the associated antireflection and scattering mechanisms. The combined surface textures are achieved by uniformly depositing a layer of indium-tin-oxide nanowhiskers on passivated, micro-grooved silicon solar cells using electron-beam evaporation. The nanowhiskers facilitate optical transmission in the near-infrared, which is optically equivalent to a stack of two dielectric thin-films with step- and graded- refractive index profiles. The ITO nanowhiskers provide broadband anti-reflective properties (R<5%) in the wavelength range of 350-1100nm. In comparison with conventional Si solar cell, the combined surface texture solar cell shows higher external quantum efficiency (EQE) in the range of 700-1100nm. Moreover, the ITO nano-whisker coating Si solar cell shows a high total efficiency increase of 1.1% (from 16.08% to17.18%). Furthermore, the nano-whiskers also provide strong forward scattering for ultraviolet and visible light, favorable in thin-wafer silicon photovoltaics to increase the optical absorption path.
Encapsulation of Au Nanoparticles on a Silicon Wafer During Thermal Oxidation
We report the behavior of Au nanoparticles anchored onto a Si(111) substrate and the evolution of the combined structure with annealing and oxidation. Au nanoparticles, formed by annealing a Au film, appear to ôfloatö upon a growing layer of SiO2 during oxidation at high temperature, yet they also tend to become partially encapsulated by the growing silica layers. It is proposed that this occurs largely because of the differential growth rates of the silica layer on the silicon substrate between the particles and below the particles due to limited access of oxygen to the latter. This in turn is due to a combination of blockage of oxygen adsorption by the Au and limited oxygen diffusion under the gold. We think that such behavior is likely to be seen for other metalûsemiconductor systems. PMID:24163715
Oxidatively stable nanoporous silicon photocathodes with enhanced onset voltage for photoelectrochemical proton reduction.
Zhao, Y; Anderson, N C; Zhu, K; Aguiar, J A; Seabold, J A; Lagemaat, J van de; Branz, H M; Neale, N R; Oh, J
Stable and high-performance nanoporous "black silicon" photoelectrodes with electrolessly deposited Pt nanoparticle (NP) catalysts are made with two metal-assisted etching steps. Doubly etched samples exhibit an ?300 mV positive shift in photocurrent onset for photoelectrochemical proton reduction compared to oxide-free planar Si with identical catalysts. We find that the photocurrent onset voltage of black Si photocathodes prepared from single-crystal planar Si wafers by an Ag-assisted etching process increases in oxidative environments (e.g., aqueous electrolyte) owing to a positive flat-band potential shift caused by surface oxidation. However, within 24 h, the surface oxide layer becomes a kinetic barrier to interfacial charge transfer that inhibits proton reduction. To mitigate this issue, we developed a novel second Pt-assisted etch process that buries the Pt NPs deep into the nanoporous Si surface. This second etch shifts the onset voltage positively, from +0.25 V to +0.4 V versus reversible hydrogen electrode, and reduces the charge-transfer resistance with no performance decrease seen for at least two months. PEC performance was stable owing to Pt NP catalysts that were buried deeply in the photoelectrode by the second etch, below a thick surface layer comprised primarily of amorphous SiO2 along with some degree of remaining crystalline Si as observed by scanning and transmission electron micrographs. Electrochemical impedance studies reveal that the second etch leads to a considerably smaller interfacial charge-transfer resistance than samples without the additional etch, suggesting that burying the Pt NPs improves the interfacial contact to the crystalline silicon surface. PMID:25723908
Reactive atomization of silicon to form in situ oxide sintering aids
NASA Astrophysics Data System (ADS)
Wu, Y.; Zeng, X.; Lavernia, E. J.; Schoenung, J. M.
The present investigation demonstrated the feasibility of using reactive atomization to produce Si powder with in situ oxide sintering aids. With further process optimization, this powder may be an alternative starting material to the conventional, mechanically blended, Si-plus-oxide powder used to produce commercial sintered reaction bonded silicon nitride (SRBSN). In the reactive atomization approach, yttrium and aluminum additives were introduced into silicon metal during induction melting. Reactive atomization was accomplished using a N2-5 pct O2 mixture as the atomization gas. During atomization, oxygen in the atomization gas reacted with Y and Al in the Si melt to produce Y2O3 and Al2O3, which act as in situ sintering aids. The reactive atomized powder demonstrated a Gaussian distribution with a mean diameter of 36 ?m. The powder fines (<38 ?m) were used to produce cold isostatically pressed compacts that were subsequently reaction bonded and sintered. The results demonstrate that ?-Si3N4 formed during reaction bonding and sintering. The density of the SRBSN was 77 pct of theoretical. Transmission electron microscopy (TEM) studies indicated the presence of a glassy phase on the grain boundaries, which is typical in SRBSN and indicative of the presence of the in situ sintering aids. A kinetic model was used to study the influence of processing parameters, such as droplet temperature and oxygen partial pressure, on the kinetics of oxide formation during reactive atomization. The results suggest that the volume fraction of oxides increases with increasing droplet temperature and oxygen partial pressure in the atomization gas mixture.
Silicon nanowire arrays-induced graphene oxide reduction under UV irradiation.
Fellahi, Ouarda; Das, Manash R; Coffinier, Yannick; Szunerits, Sabine; Hadjersi, Toufik; Maamache, Mustapha; Boukherroub, Rabah
This paper reports on efficient UV irradiation-induced reduction of exfoliated graphene oxide. Direct illumination of an aqueous solution of graphene oxide at ? = 312 nm for 6 h resulted in the formation of graphene nanosheets dispersible in water. X-Ray photoelectron spectroscopy (XPS), UV-vis spectroscopy, atomic force microscopy (AFM) and electrochemical measurements (cyclic voltammetry and electrochemical impedance spectroscopy) suggest a restoration of the sp(2) carbon network. The results were compared with graphene nanosheets prepared by photochemical irradiation of a GO aqueous solution in the presence of hydrogenated silicon nanowire (SiNW) arrays or silicon nanowire arrays decorated with silver (SiNW/Ag NPs) or copper nanoparticles (SiNW/Cu NPs). Graphene nanosheets obtained by illumination of the GO aqueous solution at 312 nm for 6 h in the presence of SiNW/Cu NPs exhibited superior electrochemical charge transfer characteristics. This is mainly due to the higher amount of sp(2)-hybridized carbon in these graphene sheets found by XPS analysis. The high level of extended conjugated carbon network was also evident by the water insoluble nature of the resulting graphene nanosheets, which precipitated upon photochemical reduction. PMID:21960142
Silicon nanowire arrays-induced graphene oxide reduction under UV irradiation
NASA Astrophysics Data System (ADS)
Fellahi, Ouarda; Das, Manash R.; Coffinier, Yannick; Szunerits, Sabine; Hadjersi, Toufik; Maamache, Mustapha; Boukherroub, Rabah
This paper reports on efficient UV irradiation-induced reduction of exfoliated graphene oxide. Direct illumination of an aqueous solution of graphene oxide at ? = 312 nm for 6 h resulted in the formation of graphene nanosheets dispersible in water. X-Ray photoelectron spectroscopy (XPS), UV-vis spectroscopy, atomic force microscopy (AFM) and electrochemical measurements (cyclic voltammetry and electrochemical impedance spectroscopy) suggest a restoration of the sp2 carbon network. The results were compared with graphene nanosheets prepared by photochemical irradiation of a GO aqueous solution in the presence of hydrogenated silicon nanowire (SiNW) arrays or silicon nanowire arrays decorated with silver (SiNW/Ag NPs) or copper nanoparticles (SiNW/Cu NPs). Graphene nanosheets obtained by illumination of the GO aqueous solution at 312 nm for 6 h in the presence of SiNW/Cu NPs exhibited superior electrochemical charge transfer characteristics. This is mainly due to the higher amount of sp2-hybridized carbon in these graphene sheets found by XPS analysis. The high level of extended conjugated carbon network was also evident by the water insoluble nature of the resulting graphene nanosheets, which precipitated upon photochemical reduction.
Silicon Carbide and Uranium Oxide Based Composite Fuel Preparation Using Polymer Infiltration and Pyrolysis
Singh, Abhishek K.; Zunjarrao, Suraj C.; Singh, Raman P. [Stony Brook University, Stony Brook, NY 11794 (United States)
Ceramic composite pellets consisting of uranium oxide, U{sub 3}O{sub 8}, particles in a silicon carbide matrix are fabricated using a novel processing technique based on polymer infiltration and pyrolysis (PIP). In this process, spherical particles of depleted uranium oxide, in the form of U{sub 3}O{sub 8}, are dispersed in liquid allyl-hydrido-poly-carbo-silane (AHPCS), and subjected to pyrolysis up to 900 deg. C under a continuous flow of ultra high purity (UHP) argon. Pyrolysis of AHPCS produces near-stoichiometric amorphous SiC at 900 deg. C. Multiple polymer infiltration and pyrolysis (PIP) cycles are required to minimize open porosity and densify the silicon carbide matrix, in order to enhance the mechanical strength of the material. Structural characterization is carried out after first pyrolysis to investigate chemical interaction between U{sub 3}O{sub 8} and SiC. The physical and mechanical properties are also quantified, and it is shown that this processing scheme promotes uniform distribution of uranium fuel source along with a high ceramic yield of the parent matrix. Furthermore, the processing technique involves lower energy requirements than conventional sintering processes currently in practice. (authors)
Observation of oxidation-enhanced and oxidation-retarded diffusion of antimony in silicon
NASA Astrophysics Data System (ADS)
Tan, T. Y.; Ginsberg, B. J.
An experiment was carried out to study oxidation-enhanced and oxidation-retarded diffusion (OED and ORD) of Sb in (100) and (111) Si wafers oxidized in dry O2 at 1160 ░C. The ORD data of (100) wafers agree well with those of Mizuo and Higuchi and with the prediction of a model assuming that Si self-interstitials and vacancies coexist in Si in thermal equilibrium at high temperatures. A small adjustment to the interstitial supersaturation values is needed to bring the ORD/OED data of (111) wafers to fit with the model satisfactorily. This indicates the existence of a mechanism which injects vacancies into (111) wafers in addition to the normal mechanism of interstitial injection due to SiO2 growth.
Low-temperature growth of high-integrity silicon oxide films by oxygen radical generated in high-density krypton plasma
Masaki Hirayama; Katsuyuki Sekine; Yuji Saito; Tadahiro Ohmi
This paper focuses attention on the electrical properties of silicon oxide films grown by Kr-O2 mixed high-density and low electron temperature microwave-excited plasma at 400░C. They exhibit high growth rate, high dielectric strength, high charge-to-breakdown, and low interface traps and bulk charge enough to replace thermally grown silicon oxide
Ion-induced electrical breakdown in metal-oxide-silicon capacitors
NASA Astrophysics Data System (ADS)
Milgram, Alvin A.
Physical effects related to radiation-induced intrinsic electrical breakdown in metal-oxide-silicon capacitors used for the detection of Cf-252 fission fragments were investigated, with special attention given to the effect of the oxide annealing temperature between 100 and 400 K, the oxide thickness, the differing metal electrodes, and the material interaction due to the spark discharge breakdown. It was found that the current emission into the SiO2 was significantly enhanced by means of both Si-ion and Cs-ion implants near the metal-SiO2 interface of the capacitors. However, the enhanced emission had no effect on increasing the sensitivity to lower specific ionization radiation as seen by fission-fragment detection, indicating that the radiation-induced breakdown mechanism occurs within the bulk of the SiO2 film and is not influenced by conditions at the dielectric interfaces. It was also found that thin films of HfO2 or ZrO2 placed between the oxide film and a top electrode prevented the Al-SiO2 interaction during the discharge and made it possible to operate the capacitor at higher electric fields.
986 IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 17, NO. 5, MAY 2005 Wavelength-Switchable La-Codoped Bismuth-Based
Wai, Ping-kong Alexander
-Codoped Bismuth-Based Erbium-Doped Fiber Ring Laser H. L. Liu, H. Y. Tam, Senior Member, IEEE, W. H. Chung, P. K. A. Wai, Senior Member, IEEE, and N. Sugimoto Abstract--A wavelength-switchable La-codoped bismuth polarization controller, and a 0.85-m-long La-codoped bis- muth-based Bi-EDF. La-codoped bismuth oxide glass
Design, microstructure, and high-temperature behavior of silicon nitride sintered with rate-earth oxides
Ciniculk, M.K. (California Univ., Berkeley, CA (United States). Dept. of Materials Science and Mineral Engineering)
The processing-microstructure-property relations of silicon nitride ceramics sintered with rare-earth oxide additives have been investigated with the aim of improving their high-temperature behavior. The additions of the oxides of Y, Sm, Gd, Dy, Er, or Yb were compositionally controlled to tailor the intergranular phase. The resulting microstructure consisted of {beta}-Si{sub 3}N{sub 4} grains and a crystalline secondary phase of RE{sub 2}Si{sub 2}O{sub 7}, with a thin residual amorphous phase present at grain boundaries. The lanthanide oxides were found to be as effective as Y{sub 2}O{sub 3} in densifying Si{sub 3}N{sub 4}, resulting in identical microstructures. The crystallization behavior of all six disilicates was similar, characterized by a limited nucleation and rapid growth mechanism resulting in large single crystals. Complete crystallization of the intergranular phase was obtained with the exception of a residual amorphous, observed at interfaces and believed to be rich in impurities, the cause of incomplete devitrification. The low resistance to oxidation of these materials was attributed to the minimization of amorphous phases via devitrification to disilicates, compatible with SiO{sub 2}, the oxidation product of Si{sub 3}N{sub 4}. The strength retention of these materials at 1300{degrees}C was found to be between 80% and 91% of room-temperature strength, due to crystallization of the secondary phase and a residual but refractory amorphous grain-boundary phase. The creep behavior was found to be strongly dependent on residual amorphous phase viscosity as well as on the oxidation behavior, as evidenced by the nonsteady-state creep rates of all materials. 122 refs., 51 figs., 12 tabs.
Trap and Inversion Layer Mobility Characterization Using Hall Effect in Silicon Carbide-Based MOSFETs With Gate Oxides Grown by Sodium Enhanced Oxidation
Vinayak Tilak; Kevin Matocha; Greg Dunne; Fredrik Allerstam; Einar Í. Sveinbjornsson
Low-temperature MOS-gated Hall measurements and gated diode capacitance-voltage (C-V) measurements were performed to characterize both trap density and Hall mobility on 4H-silicon carbide MOSFETs with gate oxides grown by sodium enhanced oxidation (SEO) and thermally grown in N2O. The interface trap density Dit was determined close to the conduction band edge by Hall effect measurements to be 2?1013 cm-2 ?
Fabrication, strength and oxidation of molybdenum-silicon-boron alloys from reaction synthesis
NASA Astrophysics Data System (ADS)
Middlemas, Michael Robert
Mo-Si-B alloys are a leading candidate for the next generation of jet turbine engine blades and have the potential to raise the operating temperatures by 300-400░C, which would dramatically increase power and efficiency. The alloys of interest are a three-phase mixture of the molybdenum solid solution (Moss) and two intermetallic phases, Mo3Si (A15) and Mo5SiB2 (T2). A novel powder metallurgical method was developed which uses the reaction of molybdenum, silicon nitride (Si3N4) and boron nitride (BN) powders to synthesize a fine dispersion of the intermetallic phases in a Moss matrix. The covalent nitrides are stable in oxidizing environments up to 1000║C, allowing for fine particle processing without the formation of silicon and boron oxides. The process developed uses standard powder processing techniques to create Mo-Si-B alloys in a less complex and expensive manner than previously demonstrated. The formation of the intermetallic phases was examined by thermo-gravimetric analysis and x-ray diffraction. The start of the reactions to form the T2 and A15 phases were observed at 1140░C and 1193░C and the reactions have been demonstrated to be complete in as little as two hours at 1300░C. This powder metallurgy approach yields a fine dispersion of intermetallics in the Moss matrix, with average grain sizes of 2-4mum. Densities up to 95% of theoretical were attained from pressureless sintering at 1600░C and full theoretical density was achieved by hot-isostatic pressing (HIP). Low temperature sintering and HIPing was attempted to limit grain growth and to reduce the equilibrium silicon concentration in the Moss matrix. Sintering and HIPing at 1300░C reduced the grain sizes of all three phases by over a factor of two. Powder metallurgy provides an opportunity for microstructure control through changes in raw materials and processing parameters. Microstructure examination by electron back-scatter diffraction (EBSD) imaging was used to precisely define the location of all three phases and to measure the volume fractions and grain size distributions. Microstructural quantification techniques including two-point correlation functions were used to quantify microstructural features and correlate the BN powder size and morphology to the distribution of the intermetallic phases. High-temperature tensile tests were conducted and yield strengths of 580MPa at 1100░C and 480MPa at 1200░C were measured for the Mo-2Si-1B wt.% alloy. The yield strength of the Mo-3Si-1B wt.% alloy was 680MPa at 1100░C and 420MPa at 1300░C. A review of the pertinent literature reveals that these are among the highest yield strengths measured for these compositions. The oxidation resistance in air at 1000 and 1100░C was found to be comparable to the best values reported in the literature. The protective borosilicate surface layer was formed quickly due to the close spacing of intermetallic particles and pre-oxidation treatment was developed to further limit the transient oxidation behavior. An oxidation model was developed which factors in the different stages of oxidation to predict compositions which minimize the total metal recession due to oxidation.
High performance of graphene oxide-doped silicon oxide-based resistance random access memory
In this letter, a double active layer (Zr:SiO x /C:SiO x ) resistive switching memory device with outstanding performance is presented. Through current fitting, hopping conduction mechanism is found in both high-resistance state (HRS) and low-resistance state (LRS) of double active layer RRAM devices. By analyzing Raman and FTIR spectra, we observed that graphene oxide exists in C:SiO x layer. Compared with single Zr:SiO x layer structure, Zr:SiO x /C:SiO x structure has superior performance, including low operating current, improved uniformity in both set and reset processes, and satisfactory endurance characteristics, all of which are attributed to the double-layer structure and the existence of graphene oxide flakes formed by the sputter process. PMID:24261454
Analysis of Oxidation Enhanced and Retarded Diffusions and Growth of Oxidation Stacking Fault in Silicon
NASA Astrophysics Data System (ADS)
Yoshida, Masayuki
In order to determine the fractional components of the interstitialcy mechanism for Sb, P and self-diffusions, dISb, dIP and dIsd, and the supersaturation ratios of vacancies and self-interstitials, sV and sI, from the experimental results of the oxidation-enhanced diffusion (OED) of P, oxidation-retarded diffusion (ORD) of Sb and growth of the interstitial-type stacking fault by oxidation (OSF), the equations of OED, ORD and OSF and of the special relation between sV and sI were solved simultaneously. The effect of the stacking fault energy upon growth of the OSF was taken into account in the OSF equation. As the experimental results of OED, ORD and OSF did not satisfy their equations exactly, nine kinds of solutions were obtained and three of them were shown. The errors caused by the lack of exact satisfaction were shown. A dIsd much smaller than 0.5 was obtained.
Density change and viscous flow during structural relaxation of plasma-enhanced chemical-vapor-deposited silicon oxide films
thermal cycling and annealing has been studied using wafer curvature measurements. These measurements a series of experimental results that are related to thermal cycling as well as annealing of PECVD silicon oxide films including stress hysteresis generation and reduction and coefficient of thermal
ATOMIC-LAYER-DEPOSITED ALUMINUM OXIDE FOR THE SURFACE PASSIVATION OF HIGH-EFFICIENCY SILICON SOLAR to those measured on reference cells passivated by an aluminum-annealed thermal SiO2, while those of the Al of aluminum ox- ide (Al2O3) grown by atomic layer deposition (ALD) pro- vide an excellent level of sur
Plasma-activated direct bonding of diamond-on-insulator wafers to thermal oxide grown silicon wafers
Akin, Tayfun
Plasma-activated direct bonding of diamond-on-insulator wafers to thermal oxide grown silicon microscopy, profilometer and wafer bow measurements. Plasma-activated direct bonding of DOI wafers to thermal September 2010 Keywords: Diamond-on-insulator Plasma activation Ultrananocrystalline diamond Direct bonding
Hot-pressed silicon nitride with various lanthanide oxides as sintering additives
Ueno, K.; Toibana, Y.
The effects of addition of various lanthanide oxides and their mixture with Y2O3 on the sintering of Si3N4 were investigated. The addition of simple and mixed lanthanide oxides promoted the densification of Si3N4 in hot-pressing at 1800 C under 300-400kg/ centimeters squared for 60 min. The crystallization of yttrium and lanthanide-silicon oxynitrides which was observed inn the sintered body containing yttrium-lanthanide mixed oxides as additives led to the formation of a highly refractory Si3N4 ceramic having a bending strength of 82 and 84 kg/millimeters squared at room temperature and 1300 C respectively. In a Y2O3+La2O3 system, a higher molar ratio of La2O3 to Y2O3 gave a higher hardness and strength at high temperatures. It was found that 90 min was an optimum sintering time for the highest strength.
Controllable shrinking of inverted-pyramid silicon nanopore arrays by dry-oxygen oxidation
NASA Astrophysics Data System (ADS)
Deng, Tao; Chen, Jian; Li, Mengwei; Wang, Yifan; Zhao, Chenxu; Zhang, Zhonghui; Liu, Zewen
A novel and simple technique for the controllable shrinkage of inverted-pyramid silicon (Si) nanopore arrays is reported. The Si nanopore arrays with sizes from 60 to 150 nm, made using a combination of dry and wet etching, were shrunk to sub 10 nm, or even closed, using direct dry-oxygen oxidation at 900?░ C. The shrinkage process of the pyramidal nanopore induced by oxidation was carefully modeled and simulated. The simulation was found to be in good agreement with the experimental data within most of the oxidation time range. Using this method, square nanopore arrays with an average size of 30 nm, and rectangular nanopores and nanoslits with feature sizes as small as 8 nm, have been obtained. Furthermore, focused ion beam cutting experiments revealed that the inner structure of the nanopore after the shrinkage kept its typical inverted-pyramid shape, which is of importance in many fields such as biomolecular sensors and ionic analogs of electronic devices, as well as nanostencils for surface nano-patterning.
Hot-pressed silicon nitride with various lanthanide oxides as sintering additives
NASA Technical Reports Server (NTRS)
Ueno, K.; Toibana, Y.
The effects of addition of various lanthanide oxides and their mixture with Y2O3 on the sintering of Si3N4 were investigated. The addition of simple and mixed lanthanide oxides promoted the densification of Si3N4 in hot-pressing at 1800 C under 300-400kg/ centimeters squared for 60 min. The crystallization of yttrium and lanthanide-silicon oxynitrides which was observed inn the sintered body containing yttrium-lanthanide mixed oxides as additives led to the formation of a highly refractory Si3N4 ceramic having a bending strength of 82 and 84 kg/millimeters squared at room temperature and 1300 C respectively. In a Y2O3+La2O3 system, a higher molar ratio of La2O3 to Y2O3 gave a higher hardness and strength at high temperatures. It was found that 90 min was an optimum sintering time for the highest strength.
Demonstration of nitric oxide on asbestos and silicon carbide fibers with a new ultraviolet spectrophotometric assay.
Leanderson, P; Lagesson, V; Tagesson, C
Nitric oxide (NO) has a number of important functions in biological systems and may play a role in the toxicity of mineral fibers. We investigated whether NO might be present on the surface of mineral fibers and if crocidolite could adsorb NO from NO gas or cigarette smoke. NO was determined with a new gas chromatography-ultraviolet spectrophotometric technique after thermal desorption from the fiber surface and injection in a gas flow cell. NO was found in different amounts on chrysotile B, crocidolite, amosite, and silicon carbide whiskers. There was a strong correlation between the amount of NO and the specific surface area of these fibers (r = 0.98). NO could not be demonstrated on rockwool fibers [man-made vitreous fiber(s) (MMVF)21 and MMVF22] or silicon nitride whiskers. NO on crocidolite, amosite, and silicon carbide whiskers was readily desorbed from the fibers at increased temperature, while NO on chrysotile B seemed to be more firmly adsorbed to the fiber and required a longer period of time to be desorbed. The amount of NO bound to crocidolite increased from 34 micrograms/g fiber to 85 and 474 micrograms/g after exposing the fibers to cigarette smoke and NO gas, respectively. These findings indicate that a) NO adsorbs to fiber surfaces, b) some fibers adsorb more NO than others, c) some fibers adsorb NO more strongly than others, and d) the amounts of NO on fibers may be increased after exposure of the fiber to cigarette smoke or other sources of NO. The biological significance of NO on mineral fibers remains to be investigated. Images Figure 3. PMID:9400696
Electronic passivation of silicon surfaces by thin films of atomic layer deposited gallium oxide
Allen, T. G., E-mail: firstname.lastname@example.com; Cuevas, A. [Research School of Engineering, Australian National University, Canberra 0200 (Australia)
This paper proposes the application of gallium oxide (Ga{sub 2}O{sub 3}) thin films to crystalline silicon solar cells. Effective passivation of n- and p-type crystalline silicon surfaces has been achieved by the application of very thin Ga{sub 2}O{sub 3} films prepared by atomic layer deposition using trimethylgallium (TMGa) and ozone (O{sub 3}) as the reactants. Surface recombination velocities as low as 6.1?cm/s have been recorded with films less than 4.5?nm thick. A range of deposition parameters has been explored, with growth rates of approximately 0.2?┼/cycle providing optimum passivation. The thermal activation energy for passivation of the Si-Ga{sub 2}O{sub 3} interface has been found to be approximately 0.5?eV. Depassivation of the interface was observed for prolonged annealing at increased temperatures. The activation energy for depassivation was measured to be 1.9?eV.
Damp and dry heat degradation of thermal oxide passivation of p+ silicon
NASA Astrophysics Data System (ADS)
Thomson, Andrew; Gardner, Matthew; McIntosh, Keith; Shalav, Avi; Bullock, James
Thermal SiO2 passivates both moderately and heavily doped silicon surfaces irrespective of the dopant type, which is advantageous in high-efficiency solar cell designs. Commercial photovoltaic cells are submitted to accelerated ageing tests, such as damp-heat exposure, to ensure they maintain their performance for at least 20 yr. We find damp-heat exposure causes a severe and rapid degradation of thermal SiO2 passivation on p+ silicon surfaces. The reaction is so severe that the diffused-region recombination in the degraded state is limited by the diffusion of minority carriers to the Si-SiO2 interface not the density of interface defects Dit. Certainly, this effect renders the thermal-oxide passivation useless if employed on a solar cell. To study the cause of the degradation, we also test the effects of storage in dry heat and room ambient conditions. Examination of the rate of degradation in the tested storage conditions in comparison with modelled diffusion of moisture in SiO2, we find a significant correlation between the time dependent J0e and moisture supplied to the interface, leading us to the conclusion that moisture ingression and subsequent reaction at the SiO2-Si interface are the cause of both damp-heat and room- ambient degradation.
Plasma surface oxidation of 316L stainless steel for improving adhesion strength of silicone rubber coating to metal substrate
NASA Astrophysics Data System (ADS)
Latifi, Afrooz; Imani, Mohammad; Khorasani, Mohammad Taghi; Daliri Joupari, Morteza
Stainless steel 316L is one of the most widely used materials for fabricating of biomedical devices hence, improving its surface properties is still of great interest and challenging in biomaterial sciences. Plasma oxidation, in comparison to the conventional chemical or mechanical methods, is one of the most efficient methods recently used for surface treatment of biomaterials. Here, stainless steel specimens were surface oxidized by radio-frequency plasma irradiation operating at 34 MHz under pure oxygen atmosphere. Surface chemical composition of the samples was significantly changed after plasma oxidation by appearance of the chromium and iron oxides on the plasma-oxidized surface. A wettable surface, possessing high surface energy (83.19 mN m-1), was observed after plasma oxidation. Upon completion of the surface modification process, silicone rubber was spray coated on the plasma-treated stainless steel surface. Morphology of the silicone rubber coating was investigated by scanning electron microscopy (SEM). A uniform coating was formed on the oxidized surface with no delamination at polymer-metal interface. Pull-off tests showed the lowest adhesion strength of coating to substrate (0.12 MPa) for untreated specimens and the highest (0.89 MPa) for plasma-oxidized ones.
Transmission electron microscope study of the dry oxidation kinetics of WSi2 on (001)Si and polycrystalline silicon
NASA Astrophysics Data System (ADS)
Hung, S. F.; Chen, L. J.
Cross-section transmission electron microscopy has been applied to study the growth kinetics of oxide of WSi2 on (001)Si and polycrystalline silicon (poly Si) in the dry oxidation process. The linear activation energy and the parabolic activation energy of WSi2 on (001)Si were found to be 0.8▒0.2 and 1.0▒0.2 eV for samples dry oxidized at 800-890 ░C for 10-60 min, respectively. On the other hand, the linear activation energy and parabolic activation energy of WSi2 on polycrystalline silicon for samples dry oxidized at 800-890 ░C for 10-60 min were 1.0▒0.2 and 1.8▒0.2 eV. The linear activation energy is attributed to the diffusion of Si atoms from the substrate to the reaction interface. The different parabolic activation energies of 1.0 and 1.8 eV for WSi2 on (001)Si and poly Si, respectively, indicate significant difference in diffusion of O2 through grown SiO2. It is conceivable that stress generated during oxidation and the amount of fluorine atoms, introduced during the low pressure chemical vapor deposition process, present in the silicide layer and grown oxide, can influence the oxide quality and oxidation kinetics.
Electrical properties of the silicon oxide/Si structure formed with perchloric acid at 203░C
NASA Astrophysics Data System (ADS)
Sakurai, Takeaki; Nishiyama, Masayoshi; Nishioka, Yasushiro; Kobayashi, Hikaru
Immersion of Si in perchloric acid (HClO 4) at 203░C forms silicon dioxide (SiO 2) layers with a low interface state density of 1.5Î10 10 cm 2 eV -1 even without hydrogen treatment. The SiO 2 thickness increases linearly with the immersion time, and a 25 nm-thick SiO 2 layer is formed by the immersion for 400 min. The leakage current density for the as-prepared oxide layers is high, while after heat treatment at 900░C in nitrogen, it decreases to less than 10 -9 A cm -2 at the gate bias of ▒1 V. This decrease is attributable to the desorption of chlorine-containing species from the SiO 2 layers.
Paralinear Oxidation of Silicon Nitride in a Water Vapor/Oxygen Environment
NASA Technical Reports Server (NTRS)
Fox, Dennis S.; Opila, Elizabeth J.; Nguyen, QuynhGiao; Humphrey, Donald L.; Lewton, Susan M.; Gray, Hugh R. (Technical Monitor)
Three silicon nitride materials were exposed to dry oxygen flowing at 0.44 cm/s at temperatures between 1200 and 1400 C. Reaction kinetics were measured with a continuously recording microbalance. Parabolic kinetics were observed. When the same materials were exposed to a 50% H2O - 50% O2 gas mixture flowing at 4.4 cm/s, all three types exhibited paralinear kinetics. The material is oxidized by water vapor to form solid silica. The protective silica is in turn volatilized by water vapor to form primarily gaseous Si(OH)4. Nonlinear least squares analysis and a paralinear kinetic model were used to determine both parabolic and linear rate constants from the kinetic data. Volatilization of the protective silica scale can result in accelerated consumption of Si3N4. Recession rates under conditions more representative of actual combustors are compared to the furnace data.
Soft lithographic functionalization and patterning oxide-free silicon and germanium.
Bowers, Carleen M; Toone, Eric J; Clark, Robert L; Shestopalov, Alexander A
The development of hybrid electronic devices relies in large part on the integration of (bio)organic materials and inorganic semiconductors through a stable interface that permits efficient electron transport and protects underlying substrates from oxidative degradation. Group IV semiconductors can be effectively protected with highly-ordered self-assembled monolayers (SAMs) composed of simple alkyl chains that act as impervious barriers to both organic and aqueous solutions. Simple alkyl SAMs, however, are inert and not amenable to traditional patterning techniques. The motivation for immobilizing organic molecular systems on semiconductors is to impart new functionality to the surface that can provide optical, electronic, and mechanical function, as well as chemical and biological activity. Microcontact printing (?CP) is a soft-lithographic technique for patterning SAMs on myriad surfaces. Despite its simplicity and versatility, the approach has been largely limited to noble metal surfaces and has not been well developed for pattern transfer to technologically important substrates such as oxide-free silicon and germanium. Furthermore, because this technique relies on the ink diffusion to transfer pattern from the elastomer to substrate, the resolution of such traditional printing is essentially limited to near 1 ?m. In contrast to traditional printing, inkless ?CP patterning relies on a specific reaction between a surface-immobilized substrate and a stamp-bound catalyst. Because the technique does not rely on diffusive SAM formation, it significantly expands the diversity of patternable surfaces. In addition, the inkless technique obviates the feature size limitations imposed by molecular diffusion, facilitating replication of very small (<200 nm) features. However, up till now, inkless ?CP has been mainly used for patterning relatively disordered molecular systems, which do not protect underlying surfaces from degradation. Here, we report a simple, reliable high-throughput method for patterning passivated silicon and germanium with reactive organic monolayers and demonstrate selective functionalization of the patterned substrates with both small molecules and proteins. The technique utilizes a preformed NHS-reactive bilayered system on oxide-free silicon and germanium. The NHS moiety is hydrolyzed in a pattern-specific manner with a sulfonic acid-modified acrylate stamp to produce chemically distinct patterns of NHS-activated and free carboxylic acids. A significant limitation to the resolution of many ?CP techniques is the use of PDMS material which lacks the mechanical rigidity necessary for high fidelity transfer. To alleviate this limitation we utilized a polyurethane acrylate polymer, a relatively rigid material that can be easily functionalized with different organic moieties. Our patterning approach completely protects both silicon and germanium from chemical oxidation, provides precise control over the shape and size of the patterned features, and gives ready access to chemically discriminated patterns that can be further functionalized with both organic and biological molecules. The approach is general and applicable to other technologically-relevant surfaces. PMID:22214997
Soft Lithographic Functionalization and Patterning Oxide-free Silicon and Germanium
Bowers, Carleen M.; Toone, Eric J.; Clark, Robert L.; Shestopalov, Alexander A.
The development of hybrid electronic devices relies in large part on the integration of (bio)organic materials and inorganic semiconductors through a stable interface that permits efficient electron transport and protects underlying substrates from oxidative degradation. Group IV semiconductors can be effectively protected with highly-ordered self-assembled monolayers (SAMs) composed of simple alkyl chains that act as impervious barriers to both organic and aqueous solutions. Simple alkyl SAMs, however, are inert and not amenable to traditional patterning techniques. The motivation for immobilizing organic molecular systems on semiconductors is to impart new functionality to the surface that can provide optical, electronic, and mechanical function, as well as chemical and biological activity. Microcontact printing (?CP) is a soft-lithographic technique for patterning SAMs on myriad surfaces.1-9 Despite its simplicity and versatility, the approach has been largely limited to noble metal surfaces and has not been well developed for pattern transfer to technologically important substrates such as oxide-free silicon and germanium. Furthermore, because this technique relies on the ink diffusion to transfer pattern from the elastomer to substrate, the resolution of such traditional printing is essentially limited to near 1 ?m.10-16 In contrast to traditional printing, inkless ?CP patterning relies on a specific reaction between a surface-immobilized substrate and a stamp-bound catalyst. Because the technique does not rely on diffusive SAM formation, it significantly expands the diversity of patternable surfaces. In addition, the inkless technique obviates the feature size limitations imposed by molecular diffusion, facilitating replication of very small (<200 nm) features.17-23 However, up till now, inkless ?CP has been mainly used for patterning relatively disordered molecular systems, which do not protect underlying surfaces from degradation. Here, we report a simple, reliable high-throughput method for patterning passivated silicon and germanium with reactive organic monolayers and demonstrate selective functionalization of the patterned substrates with both small molecules and proteins. The technique utilizes a preformed NHS-reactive bilayered system on oxide-free silicon and germanium. The NHS moiety is hydrolyzed in a pattern-specific manner with a sulfonic acid-modified acrylate stamp to produce chemically distinct patterns of NHS-activated and free carboxylic acids. A significant limitation to the resolution of many ?CP techniques is the use of PDMS material which lacks the mechanical rigidity necessary for high fidelity transfer. To alleviate this limitation we utilized a polyurethane acrylate polymer, a relatively rigid material that can be easily functionalized with different organic moieties. Our patterning approach completely protects both silicon and germanium from chemical oxidation, provides precise control over the shape and size of the patterned features, and gives ready access to chemically discriminated patterns that can be further functionalized with both organic and biological molecules. The approach is general and applicable to other technologically-relevant surfaces. PMID:22214997
Light-induced water oxidation at silicon electrodes functionalized with a cobalt oxygen-evolving catalyst
Pijpers, Joep J. H.; Winkler, Mark T.; Surendranath, Yogesh; Buonassisi, Tonio; Nocera, Daniel G.
Integrating a silicon solar cell with a recently developed cobalt-based water-splitting catalyst (Co-Pi) yields a robust, monolithic, photo-assisted anode for the solar fuels process of water splitting to O2 at neutral pH. Deposition of the Co-Pi catalyst on the Indium Tin Oxide (ITO)-passivated p-side of a np-Si junction enables the majority of the voltage generated by the solar cell to be utilized for driving the water-splitting reaction. Operation under neutral pH conditions fosters enhanced stability of the anode as compared to operation under alkaline conditions (pHá14) for which long-term stability is much more problematic. This demonstration of a simple, robust construct for photo-assisted water splitting is an important step towards the development of inexpensive direct solar-to-fuel energy conversion technologies. PMID:21646536
Highly transparent nonvolatile resistive memory devices from silicon oxide and graphene.
Yao, Jun; Lin, Jian; Dai, Yanhua; Ruan, Gedeng; Yan, Zheng; Li, Lei; Zhong, Lin; Natelson, Douglas; Tour, James M
Transparent electronic memory would be useful in integrated transparent electronics. However, achieving such transparency produces limits in material composition, and hence, hinders processing and device performance. Here we present a route to fabricate highly transparent memory using SiO(x) as the active material and indium tin oxide or graphene as the electrodes. The two-terminal, nonvolatile resistive memory can also be configured in crossbar arrays on glass or flexible transparent platforms. The filamentary conduction in silicon channels generated in situ in the SiO(x) maintains the current level as the device size decreases, underscoring their potential for high-density memory applications, and as they are two-terminal based, transitions to three-dimensional memory packages are conceivable. As glass is becoming one of the mainstays of building construction materials, and conductive displays are essential in modern handheld devices, to have increased functionality in form-fitting packages is advantageous. PMID:23033077
Patterns of discoloration and oxidation by direct and scattered fluxes on LDEF, including oxygen on silicon
NASA Technical Reports Server (NTRS)
Frederickson, A. R.; Filz, R. C.; Rich, F. J.; Sagalyn, P. L.
A number of interesting discoloration patterns are clearly evident on MOOO2-1 which resides on the three faces of the Long Duration Exposure Facility (LDEF). Most interesting is the pattern of blue oxidation on polished single crystal silicon apparently produced by scattered or direct ram oxygen atoms along the earth face. A complete explanation for the patterns has not yet been obtained. All honeycomb outgassing holes have a small discoloration ring around them that varies in color. The shadow cast by a suspended wire on the earth face surface is not easily explained by either solar photons or by ram flux. The shadows and the dark/light regions cannot be explained consistently by the process of solar ultraviolet paint-darkening modulated by ram flux oxygen bleaching of the paint.
Synthesis of magnetite-silica core-shell nanoparticles via direct silicon oxidation.
Wang, Shuxian; Tang, Jing; Zhao, Hongfu; Wan, Jiaqi; Chen, Kezheng
Magnetite-silica core-shell nanoparticles (Fe3O4@SiO2 NPs) were prepared from silicon powder by direct oxidation without using any expensive precursors (such as TEOS) and organic solvents. The as-prepared Fe3O4@SiO2 NPs were characterized by TEM, DLS, XRD, FT-IR, zeta potential and NMR Analyzer. The results show that the Fe3O4@SiO2 NPs are monodispersed core-shell nanostructures with single cores that were uniformly coated by silica shells. The relaxation property indicates that Fe3O4@SiO2 NPs have desirable characteristics for T2 MRI contrast agents. This facile and green method is promising for large-scale production, which would open new opportunities for preparing core-shell nanostructures for biomedical applications. PMID:25072518
Fabrication and characterization of copper oxide-silicon nanowire heterojunction photodiodes
NASA Astrophysics Data System (ADS)
Akgul, Guvenc; Aksoy Akgul, Funda; Mulazimoglu, Emre; Emrah Unalan, Husnu; Turan, Rasit
In this study, copper oxide (CuO) thin film/silicon (Si) nanowire heterojunctions have been fabricated and their optoelectronic performances have been investigated. Vertically aligned n-type Si nanowires have been fabricated using metal-assisted etching (MAE) technique. CuO thin films were synthesized by the sol-gel method and deposited onto the nanowires through spin-coating. Fabricated nanowire heterojunction devices exhibited excellent diode behaviour compared to the planar heterojunction control device. The rectification ratios were found to be 105 and 101 for nanowire and planar heterojunctions, respectively. The improved electrical properties and photosensitivity of the nanowire heterojunction diode was observed, which was related to the three-dimensional nature of the interface between the Si nanowires and the CuO film. Results obtained in this work reveal the potential of Si nanowire-based heterojunctions for various optoelectronic devices.
The formation of light emitting cerium silicates in cerium-doped silicon oxides
Li Jing; Zalloum, Othman; Roschuk, Tyler; Heng Chenglin; Wojcik, Jacek; Mascher, Peter [Department of Engineering Physics and Centre for Emerging Device Technologies, McMaster University, Hamilton, Ontario L8S 4K1 (Canada)
Cerium-doped silicon oxides with cerium concentrations of up to 0.9 at. % were deposited by electron cyclotron resonance plasma enhanced chemical vapor deposition. Bright cerium related photoluminescence, easily seen even under room lighting conditions, was observed from the films and found to be sensitive to film composition and annealing temperature. The film containing 0.9 at. % Ce subjected to anneal in N{sub 2} at 1200 deg. C for 3 h showed the most intense cerium-related emission, easily visible under bright room lighting conditions. This is attributed to the formation of cerium silicate [Ce{sub 2}Si{sub 2}O{sub 7} or Ce{sub 4.667} (SiO{sub 4}){sub 3}O], the presence of which was confirmed by high resolution transmission electron microscopy.
Thermodynamics Calculation and Experimental Study on Separation of Bismuth from a Bismuth Glance Concentrate Through a Low-Temperature Molten Salt Smelting Process
NASA Astrophysics Data System (ADS)
Yang, Jian-Guang; He, De-Wen; Tang, Chao-Bo; Chen, Yong-Ming; Sun, Ya-Hui; Tang, Mo-Tang
The main purpose of this study is to characterize and separate bismuth from a bismuth glance concentrate through a low-temperature, sulfur-fixing smelting process. This article reports on a study conducted on the optimization of process parameters, such as Na2CO3 and zinc oxide wt pct in charging, smelting temperature, smelting duration on the bismuth yield, resultant crude bismuth grade, and sulfur-fixing rate. A maximum bismuth recovery of 97.31 pct, crude bismuth grade of 96.93 pct, and 98.23 pct sulfur-fixing rate are obtained when a charge (containing 63.50 wt pct of Na2CO3 and 22.50 wt pct of bismuth glance, as well as 5 pct in excess of the stoichiometric requirement of zinc oxide dosage) is smelted at 1000 K (727 ░C) for 150 minutes. This smelting operation is free from atmospheric pollution because zinc oxide is used as the sulfur-fixing agent, which can capture sulfur from bismuth sulfide and form the more thermodynamic-stable compound, zinc sulfide. The solid residue is subjected to a mineral dressing operation to obtain suspension, which is filtered to produce a cake, representing the solid particles of zinc sulfide. Based on the results of the chemical content analysis of the as-resultant zinc sulfide, more than 93 pct zinc sulfide can be recovered, and the recovered zinc sulfide grade can reach 60.20 pct. This material can be sold as zinc sulfide concentrate or roasted to be regenerated as zinc oxide.
18% efficient silicon photovoltaic devices by rapid thermal diffusion and oxidation
Doshi, P.; Rohatgi, A. [Georgia Inst. of Tech., Atlanta, GA (United States)] [Georgia Inst. of Tech., Atlanta, GA (United States)
For the first time, cells formed by rapid thermal processing (RTP) have resulted in 18%-efficient 1 and 4 cm{sup 2} single-crystal silicon solar cells. Front surface passivation by rapid thermal oxidation (RTO) significantly enhanced the short wavelength response and decreased the effective front surface recombination velocity (including contact effects) from 7.5 {times} 10{sup 5} to about 2 {times} 10{sup 4} cm/s. This improvement resulted in an increase of about 1% (absolute) in energy conversion efficiency, up to 20 mV in V{sub oe}, and about 1 mA/cm{sup 2} in J{sub sc}. These RTO-induced enhancements are shown to be consistent with model calculations. Since only 3 to 4 min are required to simultaneously form the phosphorus emitter and aluminum back-surface-field (BSF) and 5 to 6 min are required for growing the RTO, this RTP/RTO process represents the fastest technology for diffusing and oxidizing {ge} 18%-efficient solar cells. Both cycles incorporate an in situ anneal lasting about 1.5 min to preserve the minority carrier lifetime of lower quality materials such as dendritic-web and multicrystalline silicon. These high-efficiency cells confirmed that RTP results in equivalent performance to cells fabricated by conventional furnace processing (CFP). Detailed characterization and modeling reveals that because of RTO passivation of the front surface (which reduced J{sub oe} by nearly a factor of ten), these RTP/RTO cells have become base dominated (J{sub ob} {much_gt} J{sub o}), and further improvement in cell efficiency is possible by a reduction in back surface recombination velocity (BSRV). Based upon model calculations, decreasing the BSRV to 200 cm/s is expected to give 20%-efficient RTP/RTO cells.
Bismuth ochers from San Diego Co., California
Schaller, W.T.
The chief points brought out in this paper may be briefly summarized as follows: (1) The existence of natural Bi2O3 has not been established. (2) Natural bismite or bismuth ocher, when pure, is more probably a bismuth hydroxide. (3) The bismuth ochers from San Diego County, California, are either a bismuth hydroxide or bismuth vanadate, pucherite, or mixtures of these two. (4) Pucherite has been found noncrystallin and determined for the first time in the United States.
Complete suppression of boron transient-enhanced diffusion and oxidation-enhanced diffusion in silicon using localized substitutional carbon incorporation
NASA Astrophysics Data System (ADS)
Carroll, M. S.; Chang, C.-L.; Sturm, J. C.; B³y³klimanli, T.
In this letter, we show the ability, through introduction of a thin Si1-x-yGexCy layer, to eliminate the enhancement of enhanced boron diffusion in silicon due to an oxidizing surface or ion implant damage. This reduction of diffusion is accomplished through a low-temperature-grown thin epitaxial Si1-x-yGexCy layer which completely filters out excess interstitials introduced by oxidation or ion implant damage. We also quantify the oxidation-enhanced diffusion (OED) and transient-enhanced diffusion (TED) dependence on substitutional carbon level, and further report both the observation of carbon TED and OED, and its dependence on carbon levels.
p-type microcrystalline silicon oxide emitter for silicon heterojunction solar cells allowing current densities above 40 mA/cm2
NASA Astrophysics Data System (ADS)
Mazzarella, L.; Kirner, S.; Stannowski, B.; Korte, L.; Rech, B.; Schlatmann, R.
We have developed a microcrystalline silicon oxide (?c-SiOx:H) p-type emitter layer that significantly improves the light incoupling at the front side of silicon heterojunction solar cells by minimizing reflection losses. The ?c-SiOx:H p-layer with a refractive index of 2.87 at 632 nm wavelength and the transparent conducting oxide form a stack with refractive indexes which consecutively decrease from silicon to the ambient air and thus significantly reduce the reflection. Optical simulations performed for flat wafers reveal that the antireflective effect of the emitter overcompensates the parasitic absorption and suggest an ideal thickness of about 40 nm. On textured wafers, the increase in current density is still more than 1 mA/cm2 for a typical emitter thickness of 10 nm. Thus, we are able to fabricate heterojunction solar cells with current densities significantly over 40 mA/cm2 and power conversion efficiency above 20%, which is yet mainly limited by the cell's fill factor.
Oxidation processes of surface hydrogenated silicon nanocrystallites prepared by pulsed laser ablation and their effects on the photoluminescence wavelength
NASA Astrophysics Data System (ADS)
Umezu, Ikurou; Sugimura, Akira; Makino, Toshiharu; Inada, Mitsuru; Matsumoto, Kimihisa
Natural oxidation processes of surface hydrogenated silicon nanocrystallites prepared by pulsed laser ablation under various hydrogen gas pressures are discussed by measuring the vibrational frequency of Si-Hn units on the surface and intensity of Si-O-Si stretching vibration. The surfaces of nanocrystallites are predominantly composed of Si-H bonds and oxidation starts from backbonds of these bonds. The deposited nanocrystal films have a porous secondary structure which depends on the background gas pressure. The oxidation rate observed by infrared absorption measurements depended on this porous secondary structure. The oxidation process is discussed by the correlation between oxidation rate and porous structure of nanocrystal film. We found that Si-O bond density increases with covering the surface of the nanocrystallites during the diffusion of oxygen-related molecules through the void spaces in the porous structure. The surface oxidation of each nanocrystallite is not homogeneous; after the coverage of easy-to-oxidize sites, oxidation continues to gradually progress at the post-coverage stage. We point out that the oxidation process at coverage and post-coverage stages result in different photoluminescence (PL) wavelengths. Adsorption of the water molecule before oxidation also affects the PL wavelength. Defect PL centers which have light emission around 600 and 400 nm are generated during the coverage and post-coverage oxidation processes, respectively.
Continuous-flow Mass Production of Silicon Nanowires via Substrate-Enhanced Metal-Catalyzed Electroless Etching of Silicon with Dissolved Oxygen as an Oxidant
NASA Astrophysics Data System (ADS)
Hu, Ya; Peng, Kui-Qing; Liu, Lin; Qiao, Zhen; Huang, Xing; Wu, Xiao-Ling; Meng, Xiang-Min; Lee, Shuit-Tong
Silicon nanowires (SiNWs) are attracting growing interest due to their unique properties and promising applications in photovoltaic devices, thermoelectric devices, lithium-ion batteries, and biotechnology. Low-cost mass production of SiNWs is essential for SiNWs-based nanotechnology commercialization. However, economic, controlled large-scale production of SiNWs remains challenging and rarely attainable. Here, we demonstrate a facile strategy capable of low-cost, continuous-flow mass production of SiNWs on an industrial scale. The strategy relies on substrate-enhanced metal-catalyzed electroless etching (MCEE) of silicon using dissolved oxygen in aqueous hydrofluoric acid (HF) solution as an oxidant. The distinct advantages of this novel MCEE approach, such as simplicity, scalability and flexibility, make it an attractive alternative to conventional MCEE methods.
Continuous-flow Mass Production of Silicon Nanowires via Substrate-Enhanced Metal-Catalyzed Electroless Etching of Silicon with Dissolved Oxygen as an Oxidant
Hu, Ya; Peng, Kui-Qing; Liu, Lin; Qiao, Zhen; Huang, Xing; Wu, Xiao-Ling; Meng, Xiang-Min; Lee, Shuit-Tong
Silicon nanowires (SiNWs) are attracting growing interest due to their unique properties and promising applications in photovoltaic devices, thermoelectric devices, lithium-ion batteries, and biotechnology. Low-cost mass production of SiNWs is essential for SiNWs-based nanotechnology commercialization. However, economic, controlled large-scale production of SiNWs remains challenging and rarely attainable. Here, we demonstrate a facile strategy capable of low-cost, continuous-flow mass production of SiNWs on an industrial scale. The strategy relies on substrate-enhanced metal-catalyzed electroless etching (MCEE) of silicon using dissolved oxygen in aqueous hydrofluoric acid (HF) solution as an oxidant. The distinct advantages of this novel MCEE approach, such as simplicity, scalability and flexibility, make it an attractive alternative to conventional MCEE methods. PMID:24413157
Valence band offset in heterojunctions between crystalline silicon and amorphous silicon (sub)oxides (a-SiOx:H, 0 < x < 2)
NASA Astrophysics Data System (ADS)
Liebhaber, M.; Mews, M.; Schulze, T. F.; Korte, L.; Rech, B.; Lips, K.
The heterojunction between amorphous silicon (sub)oxides (a-SiOx:H, 0 < x < 2) and crystalline silicon (c-Si) is investigated. We combine chemical vapor deposition with in-system photoelectron spectroscopy in order to determine the valence band offset ?EV and the interface defect density, being technologically important junction parameters. ?EV increases from ?0.3 eV for the a-Si:H/c-Si interface to >4 eV for the a-SiO2/c-Si interface, while the electronic quality of the heterointerface deteriorates. High-bandgap a-SiOx:H is therefore unsuitable for the hole contact in heterojunction solar cells, due to electronic transport hindrance resulting from the large ?EV. Our method is readily applicable to other heterojunctions.
Boosting the local anodic oxidation of silicon through carbon nanofiber atomic force microscopy probes
Lorenzoni, Matteo; Matsui, Soichiro; Tanemura, Masaki; Perez-Murano, Francesc
Summary Many nanofabrication methods based on scanning probe microscopy have been developed during the last decades. Local anodic oxidation (LAO) is one of such methods: Upon application of an electric field between tip and surface under ambient conditions, oxide patterning with nanometer-scale resolution can be performed with good control of dimensions and placement. LAO through the non-contact mode of atomic force microscopy (AFM) has proven to yield a better resolution and tip preservation than the contact mode and it can be effectively performed in the dynamic mode of AFM. The tip plays a crucial role for the LAO-AFM, because it regulates the minimum feature size and the electric field. For instance, the feasibility of carbon nanotube (CNT)-functionalized tips showed great promise for LAO-AFM, yet, the fabrication of CNT tips presents difficulties. Here, we explore the use of a carbon nanofiber (CNF) as the tip apex of AFM probes for the application of LAO on silicon substrates in the AFM amplitude modulation dynamic mode of operation. We show the good performance of CNF-AFM probes in terms of resolution and reproducibility, as well as demonstration that the CNF apex provides enhanced conditions in terms of field-induced, chemical process efficiency. PMID:25671165
Investigation of the threshold voltage shift effect of lanthanum(III) oxide on tin/hafnium dioxide/lanthanum oxide/silicon dioxide/silicon stacks
NASA Astrophysics Data System (ADS)
di, Ming
The semiconductor industry continues to scale (shrink) transistor dimensions to both increase the number of transistors per integrated circuit and their speed. One important aspect of scaling is the need to decrease the equivalent oxide thickness of the transistor gate dielectric while minimizing leakage current. Traditional thin layer SiO2 or SiOxNy films have been replaced by higher dielectric constant film stacks Here we study one example, the HfO2/La2O3/SiO 2 stack. This dissertation describes an investigation of the use of La2O3 to reduce the threshold voltage of TiN/HfO 2/SiO2/Si stacks (high-kappa/metal gate stacks). A significant aspect of this study is the determination of band alignment for a series of high-kappa/metal gate stacks that explore the effect of placement and thickness of the Lanthanum oxide layer. In order to achieve this goal, a number of film stack properties were determined including film thicknesses, band gap of the high-kappa oxides, the flat band voltages, Si band bending, and the valence band and conduction band offsets. The first part of this work was measurement of individual layer thickness in the multi-layer film stacks using spectroscopic ellipsometry (SE) and other complementary techniques. In order to more completely understand the SE measurements, complementary techniques were used. These techniques include angle resolved X-ray photoelectron spectroscopy (ARXPS), X-ray reflectivity (XRR), transmission electron microscopy (TEM), and Rutherford backscattering spectroscopy (RBS). In this dissertation, we show that SE can simultaneously measure HfO 2 and SiO2 thicknesses in HfO2/SiO2/Si stacks. We discuss the difficulties in simultaneous measurement of all films in the La oxide Hf oxide film stack. The second part of this dissertation is the measurement of the band gap of high-kappa films. The band gap of a high-kappa film is an important parameter because it affects the conduction band offset (CBO) between high-kappa and Si substrate. The CBO affects the gate leakage current of the transistor. The band gap of high-kappa films was determined from the complex refractive index using several different methods. Comparisons of plots of the extinction coefficient (k), absorption coefficient (alpha), and optical models for imaginary part of the dielectric function (epsilon2) show that each method gives slightly different values for the band gap. The Cody Lorentz model for the dielectric function provides a useful model for the defect induced sub-band gap absorption. We show the impact of the subband gap absorption on band gap extrapolation. Because the existence of sub band gap states is well documented in the literature, we use the Cody Lorentz model to determine the band gap. The next step was to determine band alignment of the valence and conduction bands the layers in the film stack. X-Ray photoelectron spectroscopy (XPS) measurements were used to determine the valence band offset (VBO) and silicon band bending. The conduction band levels were determined from the valence band energy levels and the band gap. The CBO we measured (1.77eV) is well above the specified minimum CBO for Hf oxide (1.0eV). We developed a band alignment model to account for the trends that we observed. Our data is consistent with the presence of a dipole at the high-kappa/SiO2 interface. According to this model, the change in VBO is a direct measure of the change in the interface dipole moment. Because the combination of capacitance -- voltage (C-V) and XPS to measure the flat band voltage and Si band bending, respectively, has rarely been used, relationship between these two quantities has not been discussed in the literature. The agreement between an empirical, theoretical relationship between flat band voltage vs. Si band and our data suggests that XPS can be a useful tool for examining VT shift layers in high-kappa gate stacks. We also investigated the effect of the SiO2 thickness and growth method on the flat band voltage of TiN/HfO2/La2O 3/SiO2/Si stacks. We observed no change in flat band voltage for stacks wit
Hexagonal Ag nanoarrays induced enhancement of blue light emission from amorphous oxidized silicon nitride via localized surface plasmon coupling.
Ma, Zhongyuan; Ni, Xiaodong; Zhang, Wenping; Jiang, Xiaofan; Yang, Huafeng; Yu, Jie; Wang, Wen; Xu, Ling; Xu, Jun; Chen, Kunji; Feng, Duan
A significant enhancement of blue light emission from amorphous oxidized silicon nitride (a-SiNx:O) films is achieved by introduction of ordered and size-controllable arrays of Ag nanoparticles between the silicon substrate and a-SiNx:O films. Using hexagonal arrays of Ag nanoparticles fabricated by nanosphere lithography, the localized surface plasmons (LSPs) resonance can effectively increase the internal quantum efficiency from 3.9% to 13.3%. Theoretical calculation confirms that the electromagnetic field-intensity enhancement is through the dipole surface plasma coupling with the excitons of a-SiNx:O films, which demonstrates a-SiNx:O films with enhanced blue emission are promising for silicon-based light-emitting applications by patterned Ag arrays. PMID:25402058
Corrosion by liquid lead and lead-bismuth: experimental results review and analysis
Zhang, Jinsuo [Los Alamos National Laboratory
Liquid metal technologies for liquid lead and lead-bismuth alloy are under wide investigation and development for advanced nuclear energy systems and waste transmutation systems. Material corrosion is one of the main issues studied a lot recently in the development of the liquid metal technology. This study reviews corrosion by liquid lead and lead bismuth, including the corrosion mechanisms, corrosion inhibitor and the formation of the protective oxide layer. The available experimental data are analyzed by using a corrosion model in which the oxidation and scale removal are coupled. Based on the model, long-term behaviors of steels in liquid lead and lead-bismuth are predictable. This report provides information for the selection of structural materials for typical nuclear reactor coolant systems when selecting liquid lead or lead bismuth as heat transfer media.
Encephalopathy associated with bismuth subgallate therapy.
Friedland, R P; Lerner, A J; Hedera, P; Brass, E P
A 74-year-old man developed paranoid ideation, memory impairment, and defective gustatory and olfactory function while on bismuth subgallate therapy for use as a colostomy deodorant. Twenty-four-hour urine bismuth was elevated at 889 micrograms/day, and whole blood bismuth concentration was 67 micrograms/L. The patient improved after discontinuation of bismuth subgallate; there was resolution of paranoid behavior and gustatory and olfactory functions improved. Follow-up whole blood bismuth concentration was 21 micrograms/L 4 weeks after cessation. Altered gustatory and olfactory function have not been previously reported with bismuth intoxication. PMID:8477413
Role of surface oxides in the formation of solid-electrolyte interphases at silicon electrodes for lithium-ion batteries.
Schroder, Kjell W; Dylla, Anthony G; Harris, Stephen J; Webb, Lauren J; Stevenson, Keith J
Nonaqueous solvents in modern battery technologies undergo electroreduction at negative electrodes, leading to the formation of a solid-electrolyte interphase (SEI). The mechanisms and reactions leading to a stable SEI on silicon electrodes in lithium-ion batteries are still poorly understood. This lack of understanding inhibits the rational design of electrolyte additives, active material coatings, and the prediction of Li-ion battery life in general. We prepared SEI with a common nonaqueous solvent (LiPF6 in PC and in EC/DEC 1:1 by wt %) on silicon oxide and etched silicon (001) surfaces in various states of lithiation to understand the role of surface chemistry on the SEI formation mechanism and SEI structure. Anhydrous and anoxic techniques were used to prevent air and moisture contamination of prepared SEI films, allowing for more accurate characterization of SEI chemical stratification and composition by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS) depth profiling. Additionally, multivariate statistical methods were used to better understand TOF-SIMS depth profiling studies. We conclude that the absence of native-oxide layer on silicon has a significant impact on the formation, composition, structure, and thickness of the SEI. PMID:25402271
Mechanisms of photoluminescent quenching of oxidized porous silicon applications to chemical sensing
Michael T. Kelly; Andrew B. Bocarsly
Silicon can be caused to photoluminesce in the visible by rapid anisotropic etching of bulk samples to form a porous material. Both electrochemical and chemical etching procedures based on an HF reagent have been developed for this purpose. Porous silicon is found to contain nanoscopic silicon particles which have been identified as the luminescent species. The observed photoluminescence is very
Electronic devices containing switchably conductive silicon oxides as a switching element and methods for production and use thereof
Tour, James M; Yao, Jun; Natelson, Douglas; Zhong, Lin; He, Tao
In various embodiments, electronic devices containing switchably conductive silicon oxide as a switching element are described herein. The electronic devices are two-terminal devices containing a first electrical contact and a second electrical contact in which at least one of the first electrical contact or the second electrical contact is deposed on a substrate to define a gap region therebetween. A switching layer containing a switchably conductive silicon oxide resides in the the gap region between the first electical contact and the second electrical contact. The electronic devices exhibit hysteretic current versus voltage properties, enabling their use in switching and memory applications. Methods for configuring, operating and constructing the electronic devices are also presented herein.
On the photoluminescence of as-deposited Tb-doped silicon oxides and oxynitrides fabricated by ECR-PECVD
NASA Astrophysics Data System (ADS)
RamÝrez, J. M.; Wojcik, J.; BerencÚn, Y.; Mascher, P.; Garrido, B.
In-situ doping of Tb3+ ions in silicon oxides and oxynitrides deposited by electron-cyclotron-resonance plasma enhanced chemical-vapour (ECR-PECVD) has been performed. Oxygen and nitrogen gas flow rates were changed to produce a gradual substitution of oxygen by nitrogen in the host matrix. Bright green luminescence from as-deposited layers is observed by the naked eye under daylight conditions. Tbdoped nitrogen-rich samples showed a considerable photoluminescence (PL) enhancement compared to Tb-doped silicon oxides. An optimum layer composition for efficient Tb3+ excitation under non-resonant optical pumping is obtained. The combination of a low temperature treatment with bright luminescence could be instrumental for the development of light emitting devices in other platforms with more restrictive temperature requirements.
Improvement of Surface Morphology of Epitaxial Silicon Film for Elevated Source/Drain Ultrathin Silicon-on-Insulator Complementary-Metal-Oxide-Semiconductor Devices
NASA Astrophysics Data System (ADS)
Sugihara, Kohei; Nakahata, Takumi; Matsumoto, Takuji; Maeda, Shigenobu; Maegawa, Shigeto; Ota, Kazunobu; Sayama, Hirokazu; Oda, Hidekazu; Eimori, Takahisa; Abe, Yuji; Ozeki, Tatsuo; Inoue, Yasuo; Nishimura, Tadashi
A novel selective epitaxial growth (SEG) technology which uses ultrahigh-vacuum chemical vapor deposition and low-damage sidewall etching with a Cl2-plasma gas is experimentally demonstrated for elevated source/drain (S/D) ultrathin silicon-on-insulator (SOI) complementary-metal-oxide-semiconductor (CMOS) devices. It is found that the deviation of parasitic S/D series resistance in elevated S/D sub-40-nm-thick SOI metal-oxide-semiconductor field-effect transistors (MOSFETs) can be nearly as low as that in bulk MOSFETs, because the excellent surface morphology of the epitaxial Si layer enables formation of a uniform CoSi2 film. Moreover, neither gate/drain bridging nor any other leakage phenomena are pronounced. These results indicate that this SEG technology is promising for elevated S/D ultrathin SOI CMOS devices for the 90-nm technology node and beyond.
Spectroscopic characterization of stress-induced leakage current in sub 5-nm-thick silicon oxide film
Kenji Komiya; Yasuhisa Omura
This article proposes a spectroscopic characterization technique for examining the stress-induced leakage current in sub 5-nm-thick silicon oxide films. The fluctuation power of stress-induced leakage currents suggests that defects have a single, dominant energy level. Monte Carlo simulations are carried out to verify the defect model and stress-induced leakage current characteristics. It is clearly demonstrated using simulations and spectroscopic analyses
Theoretical investigation of neutron-induced defects in silicon dioxide MOS structures. [MOS (metal-oxide-semiconductor)
A theoretical investigation was made of neutron radiation damage in silicon dioxide layers in metal-oxide-semiconductor structures. The neutron energy spectra used in these calculations mimic those that one could generate using an infinitely thick lithium target and a beam of protons of several MeV in energy. The RECOIL computer code was used to extract the detailed reaction-dependent recoil spectra that
Enhanced Light Emission of Light-Emitting Diodes with Silicon Oxide Nanobowls Photonic Crystal without Electrical Performance Damages
NASA Astrophysics Data System (ADS)
Du, Chengxiao; Geng, Chong; Zheng, Haiyang; Wei, Tongbo; Chen, Yu; Zhang, Yiyun; Wu, Kui; Yan, Qingfeng; Wang, Junxi; Li, Jinmin
Unencapsulated GaN-based light-emitting diodes (LEDs) with two-dimensional (2D) hexagonal closely-packed silicon oxide nanobowls photonic crystal (PhC) on the indium tin oxide (ITO) transparent conductive layer were fabricated by using polystyrene spheres and sol-gel process. Compared to conventional LEDs with planar ITO layers, the light output power of 600-nm-lattice PhC LEDs was improved by 25.6% at an injection current of 20 mA. Furthermore, electrical performance of the PhC LEDs was damage-free via this chemical technique.
Fabrication of silicon nanowire/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)-graphene oxide hybrid solar cells
NASA Astrophysics Data System (ADS)
Uma, Kasimayan; Subramani, Thiyagu; Syu, Hong-Jhang; Lin, Tzu-Ching; Lin, Ching-Fuh
Silicon nanowire (SiNW)/Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) Schottky junctions have shown great promise as high efficiency, cost effective solar cells. Here, hybrid SiNWs/PEDOT:PSS blended graphene oxide (GO) solar cells are prepared and investigated. The SiNWs/PEDOT:PSS blended GO cells show enhanced light trapping and a large junction area when compared to pure PEDOT:PSS structures. SiNWs combined with GO solar cells show energy conversion efficiencies of up to 9.57% under the AM 1.5G condition, opening the possibility of using semiconductor/graphene oxide in photovoltaic applications.
Characterization of hybrid cobalt-porous silicon systems: protective effect of the Matrix in the metal oxidation
NASA Astrophysics Data System (ADS)
Mu±oz-Noval, ┴lvaro; Gallach, DarÝo; GarcÝa, Miguel ┴ngel; Ferro-Llanos, Vicente; Herrero, Pilar; Fukami, Kazuhiro; Ogata, Yukio H.; Torres-Costa, Vicente; MartÝn-Palma, Ra·l J.; Ciment-Font, Aurelio; Manso-Silvßn, Miguel
In the present work, the characterization of cobalt-porous silicon (Co-PSi) hybrid systems is performed by a combination of magnetic, spectroscopic, and structural techniques. The Co-PSi structures are composed by a columnar matrix of PSi with Co nanoparticles embedded inside, as determined by Transmission Electron Microscopy (TEM). The oxidation state, crystalline structure, and magnetic behavior are determined by X-Ray Absorption Spectroscopy (XAS) and Alternating Gradient Field Magnetometry (AGFM). Additionally, the Co concentration profile inside the matrix has been studied by Rutherford Backscattering Spectroscopy (RBS). It is concluded that the PSi matrix can be tailored to provide the Co nanoparticles with extra protection against oxidation.
Characterization of hybrid cobalt-porous silicon systems: protective effect of the Matrix in the metal oxidation.
Mu±oz-Noval, Alvaro; Gallach, DarÝo; GarcÝa, Miguel Angel; Ferro-Llanos, Vicente; Herrero, Pilar; Fukami, Kazuhiro; Ogata, Yukio H; Torres-Costa, Vicente; MartÝn-Palma, Ra·l J; Ciment-Font, Aurelio; Manso-Silvßn, Miguel
In the present work, the characterization of cobalt-porous silicon (Co-PSi) hybrid systems is performed by a combination of magnetic, spectroscopic, and structural techniques. The Co-PSi structures are composed by a columnar matrix of PSi with Co nanoparticles embedded inside, as determined by Transmission Electron Microscopy (TEM). The oxidation state, crystalline structure, and magnetic behavior are determined by X-Ray Absorption Spectroscopy (XAS) and Alternating Gradient Field Magnetometry (AGFM). Additionally, the Co concentration profile inside the matrix has been studied by Rutherford Backscattering Spectroscopy (RBS). It is concluded that the PSi matrix can be tailored to provide the Co nanoparticles with extra protection against oxidation. PMID:22938050
Behaviour of Antimony and Bismuth in Copper Electrorefining Circuits
Beauchemin,S.; Chen, T.; Dutrizac, J.
Antimony- and bismuth-rich copper anodes, anode slimes and decopperized anode slimes from industrial copper electrorefineries were studied mineralogically. Antimony in the anodes occurs mainly as Cu-Pb-As-Sb-Bi oxide inclusions along the copper grain boundaries; bismuth is mainly present as Cu-Pb-As-Sb-Bi oxide, Cu-Bi-As oxide, Cu-Pb-As-Bi oxide and Cu-Bi oxide inclusions. Sb and Bi partly dissolve during electrorefining, but extensively reprecipitate as As-Sb oxide, As-Sb-Bi oxide and SbAsO4. The presence of As results in the precipitation of essentially all the Bi as BiAsO4. The decopperizing process dissolves much of the Sb and Bi, although the majority of the BiAsO4 phase remains unaffected. Subsequently, some of the dissolved Sb and Bi reprecipitates as various oxide, sulphate and arsenate species. X-ray absorption near-edge structure (XANES) analyses suggest about 70% of the antimony in the anode slimes is present in the pentavalent oxidation state. The XANES analyses indicate that most of the Bi in all the slimes samples is present in the trivalent oxidation state.
Homopolyatomic Bismuth Ions, Part 2= Electronic Excitations in Homopolyatomic Bismuth Cations: Spectroscopic
Glaser, Rainer
Homopolyatomic Bismuth Ions, Part 2= Electronic Excitations in Homopolyatomic Bismuth Cations of the low-valence bismuth cluster cations Bi5 3 , Bi8 2 , and Bi9 5 have been studied with experimental and theoretical tech- niques. The UV-visible spectra of the bismuth ions were measured in acidic chloroaluminate
Low power zinc-oxide based charge trapping memory with embedded silicon nanoparticles via poole-frenkel hole emission
El-Atab, Nazek; Nayfeh, Ammar [Department of Electrical Engineering and Computer Science (EECS), Institute Center for MicrosystemsûiMicro, Masdar Institute of Science and Technology, Abu Dhabi (United Arab Emirates)] [Department of Electrical Engineering and Computer Science (EECS), Institute Center for MicrosystemsûiMicro, Masdar Institute of Science and Technology, Abu Dhabi (United Arab Emirates); Ozcan, Ayse; Alkis, Sabri [UNAM-National Nanotechnology Research Center and Institute of Materials Science and Nanotechnology, Bilkent University, 06800 Ankara (Turkey)] [UNAM-National Nanotechnology Research Center and Institute of Materials Science and Nanotechnology, Bilkent University, 06800 Ankara (Turkey); Okyay, Ali K. [UNAM-National Nanotechnology Research Center and Institute of Materials Science and Nanotechnology, Bilkent University, 06800 Ankara (Turkey) [UNAM-National Nanotechnology Research Center and Institute of Materials Science and Nanotechnology, Bilkent University, 06800 Ankara (Turkey); Department of Electrical and Electronics Engineering, Bilkent University, 06800 Ankara (Turkey)
A low power zinc-oxide (ZnO) charge trapping memory with embedded silicon (Si) nanoparticles is demonstrated. The charge trapping layer is formed by spin coating 2?nm silicon nanoparticles between Atomic Layer Deposited ZnO steps. The threshold voltage shift (?V{sub t}) vs. programming voltage is studied with and without the silicon nanoparticles. Applying ?1?V for 5?s at the gate of the memory with nanoparticles results in a ?V{sub t} of 3.4?V, and the memory window can be up to 8?V with an excellent retention characteristic (>10 yr). Without nanoparticles, at ?1?V programming voltage, the ?V{sub t} is negligible. In order to get ?V{sub t} of 3.4?V without nanoparticles, programming voltage in excess of 10?V is required. The negative voltage on the gate programs the memory indicating that holes are being trapped in the charge trapping layer. In addition, at 1?V the electric field across the 3.6?nm tunnel oxide is calculated to be 0.36 MV/cm, which is too small for significant tunneling. Moreover, the ?V{sub t} vs. electric field across the tunnel oxide shows square root dependence at low fields (E?1 MV/cm) and a square dependence at higher fields (E?>?2.7 MV/cm). This indicates that Poole-Frenkel Effect is the main mechanism for holes emission at low fields and Phonon Assisted Tunneling at higher fields.
In-situ infrared spectroscopic analysis of hafnium diethylamide adsorption on hydrogen terminated silicon and oxide surfaces
NASA Astrophysics Data System (ADS)
Kelly, Michael J.; Parsons, Gregory N.
Atomic layer deposition (ALD) proceeds by a binary reaction process, where metal precursor and oxidizing reactants are introduced sequentially into the deposition reactor. A key challenge in ALD is to control the deposition during the first few adsorption/oxidation cycles that form the heterogeneous semiconductor/dielectric interface. The details of the surface preparation is expected to affect precursor adsorption kinetics and subsequent interface structure, but there are few in-situ surface studies that directly characterize metal organic precursors of interest in metal oxide ALD and CVD. We have used in-situ attenuated total reflection infrared spectroscopy to observe the effect of time and temperature on the adsorption of hafnium diethylamide on various prepared silicon surfaces. For a HF-last silicon surface at 175C, exposing the surface to precursor for 200mtorr-min resulted in no observable CH stretching modes consistent with no adsorption. On an oxidized surface (preannealed at 650C), exposure at 175C resulted in adsorption and self-limiting saturation after 200mtorr-min. The CH stretching modes disappeared in less than 1 min after exposing the surface to 10-6torr vacuum, consistent with reversible physisorption at 175C. A significantly higher precursor adsorption rate was observed on in-situ prepared CVD hafnium oxide surfaces, and non self-limiting adsorption was observed at 250C. Effect of substrate temperature and models of elementary adsorption reactions consistent with results will be discussed.
Oxidation of nanopores in a silicon membrane: self-limiting formation of sub-10 nm circular openings
NASA Astrophysics Data System (ADS)
Zhang, Miao; Schmidt, Torsten; Sangghaleh, Fatemeh; Roxhed, Niclas; Sychugov, Ilya; Linnros, Jan
We describe a simple but reliable approach to shrink silicon nanopores with nanometer precision for potential high throughput biomolecular sensing and parallel DNA sequencing. Here, nanopore arrays on silicon membranes were fabricated by a self-limiting shrinkage of inverted pyramidal pores using dry thermal oxidation at 850 ░C. The shrinkage rate of the pores with various initial sizes saturated after 4 h of oxidation. In the saturation regime, the shrinkage rate is within ▒ 2 nm h-1. Oxidized pores with an average diameter of 32 nm were obtained with perfect circular shape. By careful design of the initial pore size, nanopores with diameters as small as 8 nm have been observed. Statistics of the pore width show that the shrinkage process did not broaden the pore size distribution; in most cases the distribution even decreased slightly. The progression of the oxidation and the deformation of the oxide around the pores were characterized by focused ion beam and electron microscopy. Cross-sectional imaging of the pores suggests that the initial inverted pyramidal geometry is most likely the determining factor for the self-limiting shrinkage.
Oxidation of nanopores in a silicon membrane: self-limiting formation of sub-10 nm circular openings.
Zhang, Miao; Schmidt, Torsten; Sangghaleh, Fatemeh; Roxhed, Niclas; Sychugov, Ilya; Linnros, Jan
We describe a simple but reliable approach to shrink silicon nanopores with nanometer precision for potential high throughput biomolecular sensing and parallel DNA sequencing. Here, nanopore arrays on silicon membranes were fabricated by a self-limiting shrinkage of inverted pyramidal pores using dry thermal oxidation at 850 ░C. The shrinkage rate of the pores with various initial sizes saturated after 4 h of oxidation. In the saturation regime, the shrinkage rate is within ▒ 2 nm h(-1). Oxidized pores with an average diameter of 32 nm were obtained with perfect circular shape. By careful design of the initial pore size, nanopores with diameters as small as 8 nm have been observed. Statistics of the pore width show that the shrinkage process did not broaden the pore size distribution; in most cases the distribution even decreased slightly. The progression of the oxidation and the deformation of the oxide around the pores were characterized by focused ion beam and electron microscopy. Cross-sectional imaging of the pores suggests that the initial inverted pyramidal geometry is most likely the determining factor for the self-limiting shrinkage. PMID:25116147
Fluorine-free high-resolution selective plasma etching of silicon-oxide layers on silicon substrates
NASA Astrophysics Data System (ADS)
Abdolahad, M.; Naghsh Nilchi, J.; Mohajerzadeh, S.
Highly selective and vertical dry etching of SiO2 structures on silicon substrates is reported using a mixture of C2H2 and H2 gases in a direct current plasma reactor and at elevated temperatures ranging from 420 to 620 ░C. Good anisotropic etching of SiO2 features can be achieved by this process without a need for fluorocarbon-based gases which are used to increase the selectivity of etching and to avoid the removal of the underlying silicon. The vertically etched patterns of SiO2 have been accomplished with a high selectivity over the Si and Si3N4 layers. The etch rate can be adjusted to obtain values between 2 and 20 nm min-1 depending on the temperature as well as the gas composition and plasma conditions.
Comparison between transient and frequency modulated excitation: application to silicon nitride and aluminum oxide coatings of silicon.
Klein, D; Ohm, W; Fengler, S; Kunst, M
Contactless measurements of the lifetime of charge carriers are presented with varying ways of photo excitation: with and without bias light and pulsed and frequency modulated. These methods are applied to the study of the surface passivation of single crystalline silicon by a-SiN(x):H and Al2O3 coatings. The properties of these coatings are investigated under consideration of the merits of the different methods. PMID:24985850
Analysis of P and Sb Diffusion during Thermal Oxidation in Silicon
NASA Astrophysics Data System (ADS)
Okino, Takahisa; Onishi, Masami
Using experimental results of oxidation-enhanced/retarded diffusions (OED/ORD) for P/Sb in silicon, OED and ORD equations are rewritten into differential equations for self-interstitials and vacancies (I and V). An extended relation of the local equilibrium between I and V, VIm = n, is derived from asymptotic forms of formal solutions of OED and ORD equations. The differential equations are solved using VIm=n, i.e., OED and ORD equations are simultaneously solved without any assumptions. Consequently, OED/ORD were governed by only the interstitialcy/vacancy mechanism. The local equilibrium between I and V did not occur in the present diffusion time range. From the obtained results, diffusivities of I and V, i.e., D I=2.4Î10-9 cm2 s-1 and D V=2.1Î10-10 cm2 s-1, and also their thermal equilibrium concentrations, C I0=3.3Î1016 cm-3 and C V0=2.2Î1017 cm-3, were determined at 1100░C.
Oxidation-enhanced diffusion of ion-implanted boron in silicon in extrinsic conditions
NASA Astrophysics Data System (ADS)
Miyake, Masayasu
Oxidation-enhanced diffusion (OED) of ion-implanted boron has been studied in extrinsic conditions, i.e, in a high boron concentration range by a new isoconcentration method using secondary ion mass spectroscopy (SIMS). In the isoconcentration method, 10B has been used as a tracer and 11B as a base, considering the SIMS measurement sensitivity. For isoconcentration diffusion at 950 and 1000 ░C, diffusion coefficients both in N2 ambient and in dry O2 ambient increase with boron concentration in extrinsic conditions. The diffusion coefficient in dry O2 is larger than that in N2, i.e., OED is observed for boron concentration from intrinsic conditions to 1020 cm-3. The increment in the diffusion coefficient due to OED is constant for the boron concentration range of 2Î1019-1Î1020 cm-3, and is 2-3.5 times larger than that in intrinsic conditions. On the other hand, for boron implantation into intrinsic substrates, i.e., nonisoconcentration diffusion at 950 and 1000 ░C, OED decreases with the dose and disappears at a 1015 cm-2 dose which has a peak boron concentration of about 4Î1019 cm-3. The OED disappearance at the 1015 cm-2 dose is attributed to the loss of silicon interstitials by the residual damage due to implantation.
Silicon Oxide Cluster Formation and Stability in the Laser Ablation of SiO Targets
NASA Astrophysics Data System (ADS)
Jadraque, MarÝa; Santos, Magna; DÝaz, LuÝs; ┴lvarez-Ruiz, Jes·s; MartÝn, Margarita
The formation mechanism and stability of silicon oxide clusters observed in the ablation of SiO targets at 266 nm were investigated by time-of-flight mass spectrometry, laser-induced fluorescence (LIF), and DFT calculations. Neutral and positively charged Sin+/0 and SinOmH0,1+ clusters were identified in the plume, but neutral SinOm could not be observed. The time distribution of SiO in the plume measured by postionization with an ArF laser (?? ? 1 nm, ? ? 14 ns) and mass spectrometric detection was compared with that obtained by LIF with narrowband dye laser selective excitation of one specific rovibronic transition in SiO. Postionization leads to a multicomponent distribution that extends up to times near 100 ?s after ablation, whereas LIF measurements obtain time distributions shorter than 20 ?s. DFT calculations of several SinOm0/+ were performed, showing that one photon absorption of the postionization laser makes available low-energy dissociation channels of the neutrals, whereas two photon absorption is required for ionization. DFT calculations were carried out for stoichiometric H-containing clusters SinOnH+ (n = 1-4). For n = 1,2, the optimized geometries involve bonding of hydrogen to one oxygen atom in the clusters; for n = 3 and 4, the structures containing H-Si bonds are more stable.
Electronic properties of ultrathin films based on pyrrolofullerene molecules on the surface of oxidized silicon
NASA Astrophysics Data System (ADS)
Komolov, A. S.; Lazneva, E. F.; Gerasimova, N. B.; Gavrikov, A. A.; Khlopov, A. E.; Akhremchik, S. N.; Zimina, M. V.; Panina, Yu. A.; Povolotskii, A. V.; Konev, A. S.; Khlebnikov, A. F.
Results of the investigation into the interface formation during the deposition of the films based on aziridinylphenylpyrrolofullerene (APP-C60) up to 8 nm thick on the surface of the oxidized silicon substrate are presented. The procedure of detecting reflection of testing low-energy electron beam from the surface implemented in the total current spectroscopy mode with a change in the incident electron energy from 0 to 25 eV is used. The structure of maxima in the total current spectra induced by the APP-C60 deposited film is established, and the character of interrelation of these maxima with ?* and ?* energy bands in the studied materials is determined. It is revealed due to analyzing the variation in intensities of the total current spectra of the deposited APP-C60 film and the (SiO2) n-Si substrate that the APP-C60 film is formed at the early deposition stage with the coating thickness thinner than one monolayer without the formation of the intermediate modified organic layer. As the APP-C60/(SiO2) n-Si interface is formed, the work function of the surface increases by 0.7 eV, which corresponds to the transfer of the electron density from substrate (SiO2) n-Si toward the film APP-C60. The optical absorption spectra of the APP-C60 films are measured and compared with the spectra of films of unsubstituted C60.
Evaluation of elastic properties of nanoporous silicon oxide thin films by picosecond laser ultrasonics
NASA Astrophysics Data System (ADS)
Mechri, C.; Ruello, P.; Gusev, V.; Breteau, J. M.; Mounier, D.; Henderson, M.; Gibaud, A.; Dourdain, S.
Picosecond laser ultrasonics uses femtosecond laser pulses for the generation and detection of acoustic pulses with a typical duration between few picoseconds and few hundreds of pico seconds. The shorter the duration of the acoustic pulse is, the more precisely could be made the measurements of the film thickness [C. Thomsen et al., Phys. Rev. B 34, 4129 (1986)] and the elastic modulus by pulse-echo method or through Brillouin scattering detection. In this short communication we report the results of the evaluation of the properties of nanoporous silicon oxide thin films which present potential low-k and thermal barrier properties and are also of great interest for the microelectronic industry to replace the traditional silicate glass films in order to decrease the resistance-capacitance transition delay in the VLSI circuits. Most of the studies that have been carried so far have treated the optical properties of such structures. We report the results of the evaluation of acoustic properties of nanoporous thin films.
Size-tunable silicon/iron oxide hybrid nanoparticles with fluorescence, superparamagnetism, and biocompatibility.
Sato, Keisuke; Yokosuka, Shinobu; Takigami, Yasunori; Hirakuri, Kenji; Fujioka, Kouki; Manome, Yoshinobu; Sukegawa, Hiroaki; Iwai, Hideo; Fukata, Naoki
Magnetic/fluorescent composite materials have become one of the most important tools in the imaging modality in vivo using magnetic resonance imaging (MRI) monitoring and fluorescence optical imaging. We report herein on a simplified procedure to synthesize hybrid nanoparticles (HNPs) that combine silicon and magnetic iron oxides consisting of magnetite (Fe(3)O(4)) and maghemite (?-Fe(2)O(3)). Intriguingly, our unique synthetic approach can control magnetic and optical behaviors by reducing the particle size, demonstrating that the HNPs with the mean diameter of 3.0 nm exhibit superparamagnetic behavior and green fluorescence in an aqueous solution, ambient air, and a cellular environment, whereas the HNPs with the mean diameter more than 5.0 nm indicate ferromagnetic behavior without fluorescence. Additionally, both HNPs with different diameters possess excellent magnetic responsivity for external applied magnetic field and good biocompatibility due to the low cytotoxicity. Our biocompatible HNPs with the superparamagnetism can provide an attractive approach for diagnostic imaging system in vivo. PMID:21991945
Performance enhancement of ITO/oxide/semiconductor MOS-structure silicon solar cells with voltage biasing
In this study, we demonstrate the photovoltaic performance enhancement of a p-n junction silicon solar cell using a transparent-antireflective ITO/oxide film deposited on the spacing of the front-side finger electrodes and with a DC voltage applied on the ITO-electrode. The depletion width of the p-n junction under the ITO-electrode was induced and extended while the absorbed volume and built-in electric field were also increased when the biasing voltage was increased. The photocurrent and conversion efficiency were increased because more photo-carriers are generated in a larger absorbed volume and because the carriers transported and collected more effectively due to higher biasing voltage effects. Compared to a reference solar cell (which was biased at 0áV), a conversion efficiency enhancement of 26.57% (from 12.42% to 15.72%) and short-circuit current density enhancement of 42.43% (from 29.51 to 42.03ámA/cm2) were obtained as the proposed MOS-structure solar cell biased at 2.5áV. In addition, the capacitance-volt (C-V) measurement was also used to examine the mechanism of photovoltaic performance enhancement due to the depletion width being enlarged by applying a DC voltage on an ITO-electrode. PMID:25593550
Organic-on-silicon complementary metalûoxideûsemiconductor colour image sensors
Lim, Seon-Jeong; Leem, Dong-Seok; Park, Kyung-Bae; Kim, Kyu-Sik; Sul, Sangchul; Na, Kyoungwon; Lee, Gae Hwang; Heo, Chul-Joon; Lee, Kwang-Hee; Bulliard, Xavier; Satoh, Ryu-Ichi; Yagi, Tadao; Ro, Takkyun; Im, Dongmo; Jung, Jungkyu; Lee, Myungwon; Lee, Tae-Yon; Han, Moon Gyu; Jin, Yong Wan; Lee, Sangyoon
Complementary metalûoxideûsemiconductor (CMOS) colour image sensors are representative examples of light-detection devices. To achieve extremely high resolutions, the pixel sizes of the CMOS image sensors must be reduced to less than a micron, which in turn significantly limits the number of photons that can be captured by each pixel using silicon (Si)-based technology (i.e., this reduction in pixel size results in a loss of sensitivity). Here, we demonstrate a novel and efficient method of increasing the sensitivity and resolution of the CMOS image sensors by superposing an organic photodiode (OPD) onto a CMOS circuit with Si photodiodes, which consequently doubles the light-input surface area of each pixel. To realise this concept, we developed organic semiconductor materials with absorption properties selective to green light and successfully fabricated highly efficient green-light-sensitive OPDs without colour filters. We found that such a top light-receiving OPD, which is selective to specific green wavelengths, demonstrates great potential when combined with a newly designed Si-based CMOS circuit containing only blue and red colour filters. To demonstrate the effectiveness of this state-of-the-art hybrid colour image sensor, we acquired a real full-colour image using a camera that contained the organic-on-Si hybrid CMOS colour image sensor. PMID:25578322
Permeation mechanisms of pulsed microwave plasma deposited silicon oxide films for food packaging applications
NASA Astrophysics Data System (ADS)
Deilmann, Michael; Grabowski, Mirko; Thei▀, Sebastian; Bibinov, Nikita; Awakowicz, Peter
Silicon oxide barrier layers are deposited on polyethylene terephthalate as permeation barriers for food packaging applications by means of a low pressure microwave plasma. Hexamethyldisiloxane (HMDSO) and oxygen are used as process gases to deposit SiOx coatings via pulsed low pressure plasmas. The layer composition of the coating is investigated by Fourier transform infrared spectroscopy and energy dispersive x-ray spectroscopy to show correlations with barrier properties of the films. The oxygen permeation barrier is determined by the carrier gas method using an electrochemical detector. The transition from low to high barrier films is mapped by the transition from organic SiOxCyHz layers to quartz-like SiO1.7 films containing silanol bound hydrogen. A residual permeation as low as J = 1 ▒ 0.3 cm3 m-2 day-1 bar-1 is achieved, which is a good value for food packaging applications. Additionally, the activation energy Ep of oxygen permeation is analysed and a strong increase from Ep = 31.5 kJ mol-1 for SiOx CyHz-like coatings to Ep = 53.7 kJ mol-1 for SiO1.7 films is observed by increasing the oxygen dilution of HMDSO:O2 plasma. The reason for the residual permeation of high barrier films is discussed and coating defects are visualized by capacitively coupled atomic oxygen plasma etching of coated substrates. A defect density of 3000 mm-2 is revealed.
Organic-on-silicon complementary metal-oxide-semiconductor colour image sensors.
Lim, Seon-Jeong; Leem, Dong-Seok; Park, Kyung-Bae; Kim, Kyu-Sik; Sul, Sangchul; Na, Kyoungwon; Lee, Gae Hwang; Heo, Chul-Joon; Lee, Kwang-Hee; Bulliard, Xavier; Satoh, Ryu-Ichi; Yagi, Tadao; Ro, Takkyun; Im, Dongmo; Jung, Jungkyu; Lee, Myungwon; Lee, Tae-Yon; Han, Moon Gyu; Jin, Yong Wan; Lee, Sangyoon
Complementary metal-oxide-semiconductor (CMOS) colour image sensors are representative examples of light-detection devices. To achieve extremely high resolutions, the pixel sizes of the CMOS image sensors must be reduced to less than a micron, which in turn significantly limits the number of photons that can be captured by each pixel using silicon (Si)-based technology (i.e., this reduction in pixel size results in a loss of sensitivity). Here, we demonstrate a novel and efficient method of increasing the sensitivity and resolution of the CMOS image sensors by superposing an organic photodiode (OPD) onto a CMOS circuit with Si photodiodes, which consequently doubles the light-input surface area of each pixel. To realise this concept, we developed organic semiconductor materials with absorption properties selective to green light and successfully fabricated highly efficient green-light-sensitive OPDs without colour filters. We found that such a top light-receiving OPD, which is selective to specific green wavelengths, demonstrates great potential when combined with a newly designed Si-based CMOS circuit containing only blue and red colour filters. To demonstrate the effectiveness of this state-of-the-art hybrid colour image sensor, we acquired a real full-colour image using a camera that contained the organic-on-Si hybrid CMOS colour image sensor. PMID:25578322
Organic-on-silicon complementary metal-oxide-semiconductor colour image sensors
NASA Astrophysics Data System (ADS)
Lim, Seon-Jeong; Leem, Dong-Seok; Park, Kyung-Bae; Kim, Kyu-Sik; Sul, Sangchul; Na, Kyoungwon; Lee, Gae Hwang; Heo, Chul-Joon; Lee, Kwang-Hee; Bulliard, Xavier; Satoh, Ryu-Ichi; Yagi, Tadao; Ro, Takkyun; Im, Dongmo; Jung, Jungkyu; Lee, Myungwon; Lee, Tae-Yon; Han, Moon Gyu; Jin, Yong Wan; Lee, Sangyoon
Complementary metal-oxide-semiconductor (CMOS) colour image sensors are representative examples of light-detection devices. To achieve extremely high resolutions, the pixel sizes of the CMOS image sensors must be reduced to less than a micron, which in turn significantly limits the number of photons that can be captured by each pixel using silicon (Si)-based technology (i.e., this reduction in pixel size results in a loss of sensitivity). Here, we demonstrate a novel and efficient method of increasing the sensitivity and resolution of the CMOS image sensors by superposing an organic photodiode (OPD) onto a CMOS circuit with Si photodiodes, which consequently doubles the light-input surface area of each pixel. To realise this concept, we developed organic semiconductor materials with absorption properties selective to green light and successfully fabricated highly efficient green-light-sensitive OPDs without colour filters. We found that such a top light-receiving OPD, which is selective to specific green wavelengths, demonstrates great potential when combined with a newly designed Si-based CMOS circuit containing only blue and red colour filters. To demonstrate the effectiveness of this state-of-the-art hybrid colour image sensor, we acquired a real full-colour image using a camera that contained the organic-on-Si hybrid CMOS colour image sensor.
Seed-layer-free hydrothermal growth of zinc oxide nanorods on porous silicon
NASA Astrophysics Data System (ADS)
Kim, Soaram; Kim, Min Su; Park, Hyunggil; Nam, Giwoong; Yoon, Hyunsik; Leem, Jae-Young
Zinc oxide (ZnO) nanorods were grown on porous silicon (PS) using hydrothermal synthesis without a metal catalyst or a seed layer. Scanning electron microscopy, x-ray diffraction, and temperature-dependent photoluminescence (PL) were carried out to investigate the structural and optical properties of the ZnO-PS sample. Most of the nanorods had an average diameter about of 120 nm and an average length of 5 Ám, and were assembled into flower-like clusters where several nanorods were joined at a central point. In some cases, ZnO nanorods were merged in parallel bundles. The ZnO nanorods exhibited an overall compressive residual stress. The Zn-O bond length was 1.953 ┼. ZnO-PS exhibited one PL peak in the ultraviolet (UV) range, and two peaks in the visible range. The UV and green emission peak were generated from the ZnO nanorods, while the red emission peak was attributed to the PS. The fitting parameters for Varshni's empirical equation were ? = 8 Î 10-4 eV/K, ? = 186 K, and E g (0) = 3.375 eV, and the thermal activation energy was about 32 meV.
The catalytic effect of Pt nanoparticles supported on silicon oxide nanowire.
Kim, Jung Hoon; Woo, Hee Jin; Kim, Chang Kyung; Yoon, Chong Seung
3.5 nm sized Pt nanocatalysts supported on silicon oxide nanowires (SiO(X)NWs) were fabricated by decorating the SiO(X)NWs with Pt nanoparticles using a simple physical deposition system without any surface pretreatment. High curvature of the nanowire surface together with the weak metal-substrate interaction helped to maintain discrete particle morphology with spherical shapes during deposition. Catalytic efficiency of the SiO(X)NWs coated with Pt nanoparticles was demonstrated through reduction of methylene blue in the presence of sodium borohydride. It was demonstrated that the highly curved nanowire surface allowed the Pt nanoparticles to be loaded with increased particle density, providing a larger surface area for the catalytic reaction. It was also shown that a simple heat treatment in vacuum improves the effectiveness of the Pt nanoparticles as a catalyst without loss of catalytic activity when used repeatedly. We expect that this metal nanoparticle-decorated nanowire can be easily extended to other heterogeneous reactions and can also be used as a template for building three-dimensional hierarchical nanostructures. PMID:19448290
The optical properties of bismuth nanowires
Black, Marcie R. (Marcie Rochelle)
The optical absorption of bismuth nanowires in the energy (wavenumber) range of 600 - 4000cm-1 is studied. Optical reflection and transmission spectra reveal that bismuth nanowires have a large and intense absorption peak ...
Bismuth Passivation Technique for High-Resolution X-Ray Detectors
NASA Technical Reports Server (NTRS)
Chervenak, James; Hess, Larry
The Athena-plus team requires X-ray sensors with energy resolution of better than one part in 3,000 at 6 keV X-rays. While bismuth is an excellent material for high X-ray stopping power and low heat capacity (for large signal when an X-ray is stopped by the absorber), oxidation of the bismuth surface can lead to electron traps and other effects that degrade the energy resolution. Bismuth oxide reduction and nitride passivation techniques analogous to those used in indium passivation are being applied in a new technique. The technique will enable improved energy resolution and resistance to aging in bismuth-absorber-coupled X-ray sensors. Elemental bismuth is lithographically integrated into X-ray detector circuits. It encounters several steps where the Bi oxidizes. The technology discussed here will remove oxide from the surface of the Bi and replace it with nitridized surface. Removal of the native oxide and passivating to prevent the growth of the oxide will improve detector performance and insulate the detector against future degradation from oxide growth. Placing the Bi coated sensor in a vacuum system, a reduction chemistry in a plasma (nitrogen/hydrogen (N2/H2) + argon) is used to remove the oxide and promote nitridization of the cleaned Bi surface. Once passivated, the Bi will perform as a better X-ray thermalizer since energy will not be trapped in the bismuth oxides on the surface. A simple additional step, which can be added at various stages of the current fabrication process, can then be applied to encapsulate the Bi film. After plasma passivation, the Bi can be capped with a non-diffusive layer of metal or dielectric. A non-superconducting layer is required such as tungsten or tungsten nitride (WNx).
Surface segregation and preferential sputtering of bismuth in rf-magnetron-sputtered iron-garnet films
Krumme, J.; Otterloo, A.F.; Zalm, P.C.; Pertruzzello, J.
Auger electron spectroscopy, x-ray photoelectron spectroscopy, and secondary-ion mass spectrometry have been used to elucidate the role of surface segregation and preferential sputtering of bismuth in rf-magnetron-sputtered bismuth--iron-garnet films. It turns out that bismuth is enriched by a factor of up to 2.4, as compared to the bulk content, within the first 1--1.5 nm beneath the advancing film surface during growth. Furthermore, Ar/sup +/-ion bombardment at projectile energies as low as 50 eV gives rise to a rather complete depletion of bismuth in the garnet surface. As neither surface segregation nor preferential sputtering of bismuth can be observed in as-polished single-crystalline Bi/sub 12/SiO/sub 20/ used as our reference, we conclude that the bond strength between bismuth and oxygen is weaker than that of the other garnet constituents. This is confirmed by comparing the calculated sputter yield of the element oxide. Thus, bismuth-rich crystallographically perfect epitaxial iron-garnet films can only be grown by sputtering if the growing film is protected against energetic particle bombardment.
Mineral resource of the month: bismuth
Carlin, James F.
Bismuth compounds are most known for their soothing effects on the stomach, wounds and sores. These properties make the compounds an essential part of many medicinal and cosmetic preparations, which until 1930 accounted for about 90 percent of the bismuth used. The subsequent development of low-melting alloys and chemical catalysts containing bismuth, as well as its use as an additive to casting alloys, has resulted in a wider variety of industrial applications for bismuth.
Nano sized bismuth oxy chloride by metal organic chemical vapour deposition
NASA Astrophysics Data System (ADS)
Jagdale, Pravin; Castellino, Micaela; Marrec, Franþoise; Rodil, Sandra E.; Tagliaferro, Alberto
Metal organic chemical vapour deposition (MOCVD) method was used to prepare thin films of bismuth based nano particles starting from bismuth salts. Nano sized bismuth oxy chloride (BiOCl) crystals were synthesized from solution containing bismuth chloride (BiCl3) in acetone (CH3sbnd COsbnd CH3). Self-assembly of nano sized BiOCl crystals were observed on the surface of silicon, fused silica, copper, carbon nanotubes and aluminium substrates. Various synthesis parameters and their significant impact onto the formation of self-assembled nano-crystalline BiOCl were investigated. BiOCl nano particles were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy and Micro-Raman spectroscopy. These analyses confirm that bismuth nanometer-sized crystal structures showing a single tetragonal phase were indeed bismuth oxy chloride (BiOCl) square platelets 18-250 nm thick and a few micrometres wide.
Detailed statistical contact angle analyses; "slow moving" drops on inclining silicon-oxide surfaces.
Schmitt, M; Gro▀, K; Grub, J; Heib, F
Contact angle determination by sessile drop technique is essential to characterise surface properties in science and in industry. Different specific angles can be observed on every solid which are correlated with the advancing or the receding of the triple line. Different procedures and definitions for the determination of specific angles exist which are often not comprehensible or reproducible. Therefore one of the most important things in this area is to build standard, reproducible and valid methods for determining advancing/receding contact angles. This contribution introduces novel techniques to analyse dynamic contact angle measurements (sessile drop) in detail which are applicable for axisymmetric and non-axisymmetric drops. Not only the recently presented fit solution by sigmoid function and the independent analysis of the different parameters (inclination, contact angle, velocity of the triple point) but also the dependent analysis will be firstly explained in detail. These approaches lead to contact angle data and different access on specific contact angles which are independent from "user-skills" and subjectivity of the operator. As example the motion behaviour of droplets on flat silicon-oxide surfaces after different surface treatments is dynamically measured by sessile drop technique when inclining the sample plate. The triple points, the inclination angles, the downhill (advancing motion) and the uphill angles (receding motion) obtained by high-precision drop shape analysis are independently and dependently statistically analysed. Due to the small covered distance for the dependent analysis (<0.4mm) and the dominance of counted events with small velocity the measurements are less influenced by motion dynamics and the procedure can be called "slow moving" analysis. The presented procedures as performed are especially sensitive to the range which reaches from the static to the "slow moving" dynamic contact angle determination. They are characterised by small deviations of the computed values. Additional to the detailed introduction of this novel analytical approaches plus fit solution special motion relations for the drop on inclined surfaces and detailed relations about the reactivity of the freshly cleaned silicon wafer surface resulting in acceleration behaviour (reactive de-wetting) are presented. PMID:25465200
Effect of excess bismuth on synthesis of bismuth ferrite
NASA Astrophysics Data System (ADS)
Kumar, Pawan; Kar, Manoranjan
BiFeO3 ceramics were prepared by using the sol-gel technique with adding excess amount of bismuth. Different concentrations of excess bismuth were used to study the evolution of crystal structure and physical properties of BiFeO3. The phase purity and crystal structure of all samples have been studied by powder X-ray diffraction. The primary BiFeO3 phase could be indexed to R3C space group and analyzed by Rietveld method to extract different crystallographic parameters. Secondary phases were suppressed with addition of 4% excess bismuth. The leakage current for all the samples for all samples have been studied by ferroelectric hysteresis loop at room temperature in the maximum electric field of ▒100 kV/cm. The leakage current for 4% sample is least (1.86 nA) among all samples due to reduction of extra phases.
Excitation mechanism and thermal emission quenching of Tb ions in silicon rich silicon oxide thin films grown by plasma-enhanced chemical vapour depositionùDo we need silicon nanoclusters?
Podhorodecki, A., E-mail: firstname.lastname@example.com; Golacki, L. W.; Zatryb, G.; Misiewicz, J. [Institute of Physics, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw (Poland); Wang, J.; Jadwisienczak, W. [School of EECS, Ohio University, Stocker Center 363, Athens, Ohio 45701 (United States); Fedus, K. [Institute of Physics, Nicholas Copernicus University, Grudziadzka 5/7, 87-100 Torun (Poland); Wojcik, J.; Wilson, P. R. J.; Mascher, P. [Department of Engineering Physics and Centre for Emerging Device Technologies, McMaster University, 1280 Main St. W, Hamilton, Ontario L8S4L7 (Canada)
In this work, we will discuss the excitation and emission properties of Tb ions in a Silicon Rich Silicon Oxide (SRSO) matrix obtained at different technological conditions. By means of electron cyclotron resonance plasma-enhanced chemical vapour deposition, undoped and doped SRSO films have been obtained with different Si content (33, 35, 39, 50 at.á%) and were annealed at different temperatures (600, 900, 1100?░C). The samples were characterized optically and structurally using photoluminescence (PL), PL excitation, time resolved PL, absorption, cathodoluminescence, temperature dependent PL, Rutherford backscattering spectrometry, Fourier transform infrared spectroscopy and positron annihilation lifetime spectroscopy. Based on the obtained results, we discuss how the matrix modifications influence excitation and emission properties of Tb ions.
A high-speed silicon optical modulator based on a metal-oxide-semiconductor capacitor
Ansheng Liu; Richard Jones; Ling Liao; Dean Samara-Rubio; Doron Rubin; Oded Cohen; Remus Nicolaescu; Mario Paniccia
Silicon has long been the optimal material for electronics, but it is only relatively recently that it has been considered as a material option for photonics. One of the key limitations for using silicon as a photonic material has been the relatively low speed of silicon optical modulators compared to those fabricated from III-V semiconductor compounds and\\/or electro-optic materials such
Third order nonlinear optical properties of bismuth zinc borate glasses
Shanmugavelu, B.; Ravi Kanth Kumar, V. V., E-mail: firstname.lastname@example.com [Department of Physics, Pondicherry University, Puducherry 605 014 (India); Kuladeep, R.; Narayana Rao, D. [School of Physics, University of Hyderabad, Hyderabad 500046, Andhra Pradesh (India)
Third order nonlinear optical characterization of bismuth zinc borate glasses are reported here using different laser pulse durations. Bismuth zinc borate glasses with compositions xBi{sub 2}O{sub 3}-30ZnO-(70-x) B{sub 2}O{sub 3} (where x?=?30, 35, 40, and 45?mol. %) have been prepared by melt quenching method. These glasses were characterized by Raman, UV-Vis absorption, and Z scan measurements. Raman and UV-Vis spectroscopic results indicate that non-bridging oxygens increase with increase of bismuth content in the glass. Nonlinear absorption and refraction behavior in the nanosecond (ns), picosecond (ps), and femtosecond (fs) time domains were studied in detail. Strong reverse saturable absorption due to dominant two-photon absorption (TPA) was observed with both ps and fs excitations. In the case of ns pulse excitations, TPA and free-carrier absorption processes contribute for the nonlinear absorption. Two-photon absorption coefficient (?) and the absorption cross section due to free carriers (?{sub e}) are estimated by theoretical fit of the open aperture Z-scan measurements and found to be dependent on the amount of bismuth oxide in the glass composition. In both ns and fs regimes the sign and magnitude of the third order nonlinearity are evaluated, and the optical limiting characteristics are also reported.
Fabrication of Bismuth Nanowire Devices Using Focused Ion Beam Milling
NASA Astrophysics Data System (ADS)
Cheng, H. H.; Alkaisi, M. M.; Wu, S. E.; Liu, C. P.
In this work, a focused ion beam (FIB) milling process has been developed to fabricate 50 nm Bi nanowire and transistor structures using FEI-200 dual beam FIB system. For the fabrication, 50 nm bismuth film was thermally evaporated through EBL patterned PMMA windows onto SiO2 substrates with pre-defined contact pads. Bi nanowire widths ranging from 30 nm to 100 nm have been successfully fabricated by milling out unwanted areas using 30 KeV Ga+ ion beam. A single-pixel-line ion beam blanking technique has been utilised to fabricate Bi nanowire as small as 30 nm in diameter and few micrometers long. In order to form good ohmic contacts for sub 50 nm bismuth nanowires, a drill-and-fill process has been developed using FIB to sputter away the surface oxide of bismuth after the in-situ platinum nanowire contacts deposition. To our knowledge, this is the first time a focused ion beam process has been used to fabricate bismuth nanowire. The fabricated Bi nanowires were electrically characterised using a semiconductor analyser that showed good ohmic contact to the electrodes. In this paper, the fabrication experiments and the characterisation results for Bi nanowires as small as 50 nm in diameter are presented. Several FIB issues involved in Bi device making and ohmic contacts to Bi nanowires will also be discussed.
Evaluation of Seebeck coefficients in n- and p-type silicon nanowires fabricated by complementary metal-oxide-semiconductor technology.
Hyun, Younghoon; Park, Youngsam; Choi, Wonchul; Kim, Jaehyeon; Zyung, Taehyoung; Jang, Moongyu
Silicon-based thermoelectric nanowires were fabricated by using complementary metal-oxide-semiconductor (CMOS) technology. 50 nm width n- and p-type silicon nanowires (SiNWs) were manufactured using a conventional photolithography method on 8 inch silicon wafer. For the evaluation of the Seebeck coefficients of the silicon nanowires, heater and temperature sensor embedded test patterns were fabricated. Moreover, for the elimination of electrical and thermal contact resistance issues, the SiNWs, heater and temperature sensors were fabricated monolithically using a CMOS process. For validation of the temperature measurement by an electrical method, scanning thermal microscopy analysis was carried out. The highest Seebeck coefficients were - 169.97 ?V K(-1) and 152.82 ?V K(-1) and the highest power factors were 2.77 mW m(-1) K(-2) and 0.65 mW m(-1) K(-2) for n- and p-type SiNWs, respectively, in the temperature range from 200 to 300 K. The larger power factor value for n-type SiNW was due to the higher electrical conductivity. The total Seebeck coefficient and total power factor for the n- and p-leg unit device were 157.66 ?V K(-1) and 9.30 mW m(-1) K(-2) at 300 K, respectively. PMID:22995969
Gettering effect of high-dose arsenic implantation and boron diffusion on gate oxide integrity in trench isolated high voltage silicon-on -insulator process
David H. Lu; Shinichi Jimbo; Naoto Fujishima; Setsuko Wakimoto; Masaaki Ogino
High-dose arsenic implantation was introduced between active silicon-on-insulator and bwied oxide in bonded and etched-back SOT wafers along with surface boron diffiision to improve gate oxide integrity in fully trench-isolation High-Voltage SO1 process. Layout effect on gettering has been investigated and qualitatively interpreted.
Studies of the oxidation states of phosphorus gettered silicon substrates using X-ray photoelectron spectroscopy and transmission electron microscopy
NASA Astrophysics Data System (ADS)
Th°gersen, Annett; Syre, Marie; Retterstol Olaisen, Birger; Diplas, Spyros
Phosphorus diffusion in p-type silicon wafers with Fe or Cr impurities has been investigated using X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy. Silicon wafers doped with phosphorous are heavily used in semiconductor devices. It is, therefore, of crucial importance to determine their compositions profile. The XPS P2p spectra revealed presence of elemental phosphorus (P0), donor ion (P+), and interstitial or substitutional diffused P- from phosphorus oxides P2O5 and P4O10 as residues of the diffusion process. The surface of the Si wafers was oxidized during the deposition of P2O5 and SiO2 (with a subsequent heating). This resulted in the formation of a 1.3-1.4 nm thick SiOx layer. Pile-up of elemental P was found near the surface of the wafer. This pile-up was larger for Fe contaminated samples compared to Cr contaminated ones. The pile-up may have been caused by a decrease in the diffusion length of P+ donor ions, which could only be found in the first few nm near the surface of the silicon wafer. The observed diffusion length was DLP+
Statistical contact angle analyses; "slow moving" drops on a horizontal silicon-oxide surface.
Schmitt, M; Grub, J; Heib, F
Sessile drop experiments on horizontal surfaces are commonly used to characterise surface properties in science and in industry. The advancing angle and the receding angle are measurable on every solid. Specially on horizontal surfaces even the notions themselves are critically questioned by some authors. Building a standard, reproducible and valid method of measuring and defining specific (advancing/receding) contact angles is an important challenge of surface science. Recently we have developed two/three approaches, by sigmoid fitting, by independent and by dependent statistical analyses, which are practicable for the determination of specific angles/slopes if inclining the sample surface. These approaches lead to contact angle data which are independent on "user-skills" and subjectivity of the operator which is also of urgent need to evaluate dynamic measurements of contact angles. We will show in this contribution that the slightly modified procedures are also applicable to find specific angles for experiments on horizontal surfaces. As an example droplets on a flat freshly cleaned silicon-oxide surface (wafer) are dynamically measured by sessile drop technique while the volume of the liquid is increased/decreased. The triple points, the time, the contact angles during the advancing and the receding of the drop obtained by high-precision drop shape analysis are statistically analysed. As stated in the previous contribution the procedure is called "slow movement" analysis due to the small covered distance and the dominance of data points with low velocity. Even smallest variations in velocity such as the minimal advancing motion during the withdrawing of the liquid are identifiable which confirms the flatness and the chemical homogeneity of the sample surface and the high sensitivity of the presented approaches. PMID:25524007
Sponge-like Si-SiO2 nanocompositeùMorphology studies of spinodally decomposed silicon-rich oxide
NASA Astrophysics Data System (ADS)
Friedrich, D.; Schmidt, B.; Heinig, K. H.; Liedke, B.; M³cklich, A.; H³bner, R.; Wolf, D.; K÷lling, S.; Mikolajick, T.
Sponge-like Si nanostructures embedded in SiO2 were fabricated by spinodal decomposition of sputter-deposited silicon-rich oxide with a stoichiometry close to that of silicon monoxide. After thermal treatment a mean feature size of about 3 nm was found in the phase-separated structure. The structure of the Si-SiO2 nanocomposite was investigated by energy-filtered transmission electron microscopy (EFTEM), EFTEM tomography, and atom probe tomography, which revealed a percolated Si morphology. It was shown that the percolation of the Si network in 3D can also be proven on the basis of 2D EFTEM images by comparison with 3D kinetic Monte Carlo simulations.
Zlenko, Aleksandr S; Dvoirin, Vladislav V; Bogatyrev, Vladimir A; Firstov, Sergei V [Fiber Optics Research Center, Russian Academy of Sciences, Moscow (Russian Federation); Akhmetshin, Ural G [Tarusa Department of A.M. Prokhorov General Physics Institute, Russian Academy of Sciences, Tarusa, Kaluga region (Russian Federation)
A new process for bismuth doping of optical fibres is proposed in which the dopant is introduced into a thin layer surrounding the fibre core. This enables bismuth stabilisation in the silica glass, with no limitations on the core composition. In particular, the GeO{sub 2} content of the fibre core in this study is 16 mol %. Spectroscopic characterisation of such fibres and optical gain measurements suggest that the proposed approach has considerable potential for laser applications. (optical fibres and fibreoptic sensors)
Thickness-dependent optimization of Er3+ light emission from silicon-rich silicon oxide thin films
This study investigates the influence of the film thickness on the silicon-excess-mediated sensitization of Erbium ions in Si-rich silica. The Er3+ photoluminescence at 1.5 ?m, normalized to the film thickness, was found five times larger for films 1 ?m-thick than that from 50-nm-thick films intended for electrically driven devices. The origin of this difference is shared by changes in the local density of optical states and depth-dependent interferences, and by limited formation of Si-based sensitizers in "thin" films, probably because of the prevailing high stress. More Si excess has significantly increased the emission from "thin" films, up to ten times. This paves the way to the realization of highly efficient electrically excited devices. PMID:21711930
Strong and reversible modulation of carbon nanotube-silicon heterojunction solar cells by an interfacial oxide layer.
Jia, Yi; Cao, Anyuan; Kang, Feiyu; Li, Peixu; Gui, Xuchun; Zhang, Luhui; Shi, Enzheng; Wei, Jinquan; Wang, Kunlin; Zhu, Hongwei; Wu, Dehai
Deposition of nanostructures such as carbon nanotubes on Si wafers to make heterojunction structures is a promising route toward high efficiency solar cells with reduced cost. Here, we show a significant enhancement in the cell characteristics and power conversion efficiency by growing a silicon oxide layer at the interface between the nanotube film and Si substrate. The cell efficiency increases steadily from 0.5% without interfacial oxide to 8.8% with an optimal oxide thickness of about 1 nm. This systematic study reveals that formation of an oxide layer switches charge transport from thermionic emission to a mixture of thermionic emission and tunneling and improves overall diode properties, which are critical factors for tailoring the cell behavior. By controlled formation and removal of interfacial oxide, we demonstrate oscillation of the cell parameters between two extreme states, where the cell efficiency can be reversibly altered by a factor of 500. Our results suggest that the oxide layer plays an important role in Si-based photovoltaics, and it might be utilized to tune the cell performance in various nanostructure-Si heterojunction structures. PMID:22573091
Heated ion implantation for high-performance and highly reliable silicon-on-insulator complementary metalûoxideûsilicon fin field-effect transistors
NASA Astrophysics Data System (ADS)
Mizubayashi, Wataru; Onoda, Hiroshi; Nakashima, Yoshiki; Ishikawa, Yuki; Matsukawa, Takashi; Endo, Kazuhiko; Liu, Yongxun; OÆuchi, Shinichi; Tsukada, Junichi; Yamauchi, Hiromi; Migita, Shinji; Morita, Yukinori; Ota, Hiroyuki; Masahara, Meishoku
We have investigated the impact of heated ion implantation (I/I) on the performance and reliability of silicon-on-insulator (SOI) complementary metalûoxideûsilicon (CMOS) fin field-effect transistors (FinFETs). An implantation temperature equal to and higher than 400 ░C is needed to maintain the crystallinity of the Si substrate during I/I within the experimental conditions of ion species, implantation energy, and ion dose in this study. By heated I/I at 500 ░C, the 11-nm-thick SOI layer perfectly maintains the crystallinity even after I/I, and a defect-free crystal is obtained by activation annealing. It was clarified that the cap layer is essential for the suppression of the out-diffusion during heated I/I. Heated I/I on the source and drain improves the on-currentûoff-current (IonûIoff), threshold voltage (Vth) variability, and bias temperature instability (BTI) characteristics of nMOS and pMOS FinFETs as compared with those after room-temperature I/I.
Characterization of lead-bismuth eutectic nanowires
NASA Astrophysics Data System (ADS)
Kuo, C. G.; Hsu, Y. Y.; Wu, M. K.; Chao, C. G.
In this work, lead-bismuth eutectic alloy nanowires were fabricated by a novel vacuum melting method and centrifugal process. An anodic aluminum oxide (AAO) template was used to produce an array of ordered, dense, and continuous Pb-Bi nanowires. Scanning electron microscopy and transmission electron microscopy investigations reveal that nanowires with a diameter of 80 nm are composed of Pb7Bi3 and Bi phases, and have a single orientation of growth. Magnetic susceptibility and hysteresis measurements have been used to characterize the superconductive and magnetic properties of the nanowires. The results show that Pb-Bi nanowires have a slightly lower superconducting transition temperature than Pb-Bi eutectic alloy bulk, and only about 1% superconductivity volume fraction in magnetic fields both perpendicular and parallel to the plate. In magnetization curves, a fairly large hysteresis is observed for both field orientations.
Surface morphology of cellulose films prepared by spin coating on silicon oxide substrates pretreated with cationic polyelectrolyte
NASA Astrophysics Data System (ADS)
Yokota, Shingo; Kitaoka, Takuya; Wariishi, Hiroyuki
Flat cellulose films were prepared and morphologically modified by spin coating a cellulose/ N-methylmorpholine- N-oxide/H 2O solution onto silicon oxide substrates pre-coated with a cationic polyelectrolyte. Spin-coated cellulose films were allowed to stably form on the silicon oxide substrates by pretreatment with either polydiallyldimethylammonium chloride (PDADMAC) or polyvinylamine (PVAm). The film surfaces obtained were analyzed by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). AFM topographical images of the cellulose film surfaces showed a different morphology depending on the underlying polymer, where PVAm pretreatment brought about an anisotropic surface topology. These results suggest that the specific attraction acting at the cellulose/polymer interface influences both the film formation and surface morphology of the cellulose layer. Differences in the solvent used to precipitate cellulose caused variations in the surface roughness by affecting the cellulose separation behavior. The morphological features of spin-coated cellulose film surfaces could be altered to some extent by these film preparation techniques.
Study of the atomic models of three donorlike defects in silicon metal-oxide-semiconductor structures from their gate material and process dependencies
Chih-Tang Sah; Jack Yuan-Chen Sun; Joseph Jeng-Tao Tzou
The atomic models of the generation and annealing of three donorlike defects [the bulk compensating donor, the donorlike interface density-of-state (DOS) peak, and the positive turn-around charge] in silicon metal-oxide-semiconductor capacitors (MOSC) are investigated by studying their dependencies on the gate materials and process conditions. Starting thermal oxides used in this study include 1000 C dry oxides on ?100? p-Si
Effects of the amorphous oxide intergranular layer structure and bonding on the fracture toughness of a high purity silicon nitride
Ziegler, A.; Kisielowski, C.; Hoffmann, M.J.; Ritchie, R.O.
The microstructural evolution and structural characteristics and transitions in the thin grain-boundary oxide films in a silicon nitride ceramic, specifically between two adjacent grains and not the triple junctions, are investigated to find their effect on the macroscopic fracture properties. It is found that by heat treating a model Si3N4-2wt percent Y2O3 ceramic for {approx}200 hr at 1400 degrees C in air, the fracture toughness can be increased by {approx}100 percent, coincident with a change in fracture mechanism from transgranular to intergranular.
Study of the use of Metal-Oxide-Silicon (MOS) devices for particulate detection and monitoring in the earth's atmosphere
NASA Technical Reports Server (NTRS)
Brooks, A. D.; Monteith, L. K.; Wortman, J. J.; Mulligan, J. C.
A metal-oxide-silicon (MOS) capacitor-type particulate sensor was evaluated for use in atmospheric measurements. An accelerator system was designed and tested for the purpose of providing the necessary energy to trigger the MOS-type sensor. The accelerator system and the MOS sensor were characterized as a function of particle size and velocity. Diamond particles were used as particulate sources in laboratory tests. Preliminary tests were performed in which the detector was mounted on an aircraft and flown in the vicinity of coal-fired electric generating plants.
Wettability effect of graphene-based surfaces on silicon carbide and their influence on hydrophobicity of nanocrystalline cerium oxide films.
Souza, Jean C; Neckel, Itamar T; Varalda, Jose; Ribeiro, Evaldo; Schreiner, Wido H; Mosca, Dante H; Sierakowski, Maria-Rita; Fernandes, Vilmar; Ouerghi, Abdelkarim
We investigate the water-repellent ability of graphene-based surfaces stabilized on silicon carbide (SiC) and the nanocrystalline cerium oxide (CeO2) films electrodeposited on them. Water contact angle is revealed strongly dependent on the number of graphene monolayers on SiC, indicating partial permeability of graphene on SiC. Fluctuations in the roughness of textured surfaces as well as variations of oxygen vacancy content in CeO2 electrodeposits are determinant for the hydrophobicity of the interaction between water droplets and nanocrystalline CeO2 electrodeposits on monolayers graphene on SiC. PMID:25490565
Novel processing of bioglass ceramics from silicone resins containing micro- and nano-sized oxide particle fillers.
Fiocco, L; Bernardo, E; Colombo, P; Cacciotti, I; Bianco, A; Bellucci, D; Sola, A; Cannillo, V
Highly porous scaffolds with composition similar to those of 45S5 and 58S bioglasses were successfully produced by an innovative processing method based on preceramic polymers containing micro- and nano-sized fillers. Silica from the decomposition of the silicone resins reacted with the oxides deriving from the fillers, yielding glass ceramic components after heating at 1000░C. Despite the limited mechanical strength, the obtained samples possessed suitable porous architecture and promising biocompatibility and bioactivity characteristics, as testified by preliminary in vitro tests. PMID:23946157
Crystallization of amorphous bismuth titanate
Seiji Kojima; Anwar Hushur; Fuming Jiang; Sinichi Hamazaki; Masaaki Takashige; Min-Su Jang; Shiro Shimada
We studied the transformation of amorphous bismuth titanate by heat treatments. After an as-quenched amorphous sample was annealed at 500 ░C, the lowest Raman peak became intense like a boson peak for glass. This fact indicates the formation of intermediate range order. The medium range correlation length of 7 nm calculated from the boson peak frequency is in agreement with
Decrease in Interference Effects between Cells for Metal-Oxide-Nitride-Oxide-Silicon NAND Flash Memory Devices with Metal Spacer Layers
NASA Astrophysics Data System (ADS)
Kim, Sung Ho; You, Joo Hyung; Kim, Tae Whan
Nanoscale metal-oxide-nitride-oxide-silicon (MONOS) NAND flash memory devices with a metal spacer layer were designed to increase the fringing field and the coupling ratio of the control gate and to decrease the interference effects between the cells. The simulation results showed that the drain current and the threshold voltage shift of the MONOS NAND flash memory devices utilizing a metal spacer increased owing to the increase in the fringing field and the coupling ratio. The electric field on the channel surface of the memory devices with a metal spacer layer increased, indicative of the achievement of the maximum fringing field effect, resulting in an increase in the drain current. The simulation results showed that the interference effects for the memory devices utilizing a metal spacer decreased resulting from the shielding of the electric field between neighboring cells.
Judd-Ofelt analysis, frequency upconversion, and infrared photoluminescence of Ho{sup 3+}-doped and Ho{sup 3+}/Yb{sup 3+}-codoped lead bismuth gallate oxide glasses
Zhou Bo; Pun, Edwin Yue-Bun; Yang Dianlai; Huang Lihui [Department of Electronic Engineering, City University of Hong Kong, Tat Chee Avenue, Kowloon (Hong Kong); Lin Hai [Department of Electronic Engineering, City University of Hong Kong, Tat Chee Avenue, Kowloon (Hong Kong); Faculty of Chemical Engineering and Materials, Dalian Polytechnic University, Dalian 116034 (China)
Ho{sup 3+}-doped and Ho{sup 3+}/Yb{sup 3+}-codoped lead bismuth gallate (PBG) oxide glasses were prepared and their spectroscopic properties were investigated. The derived Judd-Ofelt intensity parameters (OMEGA{sub 2}=6.81x10{sup -20} cm{sup 2}, OMEGA{sub 4}=2.31x10{sup -20} cm{sup 2}, and OMEGA{sub 6}=0.67x10{sup -20} cm{sup 2}) indicate a higher asymmetry and stronger covalent environment for Ho{sup 3+} sites in PBG glass compared with those in tellurite, fluoride (ZBLAN), and some other lead-contained glasses. Intense frequency upconversion emissions peaking at 547, 662, and 756 nm as well as infrared emissions at 1.20 and 2.05 mum in Ho{sup 3+}/Yb{sup 3+}-codoped PBG glass were observed, confirming that energy transfer between Yb{sup 3+} and Ho{sup 3+} takes place, and a two-phonon-assisted energy transfer from Yb{sup 3+} to Ho{sup 3+} ions was determined by the calculation using phonon sideband theory. The 1.20 mum emission observed was primarily due to the weak multiphonon deexcitation originated from the small phonon energy of PBG glass (approx535 cm{sup -1}). A large product of emission cross-section and measured lifetime (9.93x10{sup -25} cm{sup 2} s) was obtained for the 1.20 mum emission and the gain coefficient dependence on wavelength with population inversion rate (P) was performed. The peak emission cross-section for 2.05 mum emission was calculated to be 4.75x10{sup -21} cm{sup 2}. The relative mechanism of Ho{sup 3+}-doped and Ho{sup 3+}/Yb{sup 3+}-codoped PBG glasses on their spectroscopic properties was also discussed. Our results suggest that Ho{sup 3+}/Yb{sup 3+}-doped PBG glasses are a good potential candidate for the frequency upconversion devices and infrared amplifiers/lasers.
Preparation of magnetron sputtered thin cerium oxide films with a large surface on silicon substrates using carbonaceous interlayers.
Dubau, Martin; Lavkovß, Jaroslava; Khalakhan, Ivan; Haviar, Stanislav; Potin, Valerie; MatolÝn, VladimÝr; MatolÝnovß, Iva
The study focuses on preparation of thin cerium oxide films with a porous structure prepared by rf magnetron sputtering on a silicon wafer substrate using amorphous carbon (a-C) and nitrogenated amorphous carbon films (CNx) as an interlayer. We show that the structure and morphology of the deposited layers depend on the oxygen concentration in working gas used for cerium oxide deposition. Considerable erosion of the carbonaceous interlayer accompanied by the formation of highly porous carbon/cerium oxide bilayer systems is reported. Etching of the carbon interlayer with oxygen species occurring simultaneously with cerium oxide film growth is considered to be the driving force for this effect resulting in the formation of nanostructured cerium oxide films with large surface. In this regard, results of oxygen plasma treatment of a-C and CNx films are presented. Gradual material erosion with increasing duration of plasma impact accompanied by modification of the surface roughness is reported for both types of films. The CNx films were found to be much less resistant to oxygen etching than the a-C film. PMID:24372305
Surface Area, and Oxidation Effects on Nitridation Kinetics of Silicon Powder Compacts
NASA Technical Reports Server (NTRS)
Bhatt, R. T.; Palczer, A. R.
Commercially available silicon powders were wet-attrition-milled from 2 to 48 hr to achieve surface areas (SA's) ranging from 1.3 to 70 sq m/g. The surface area effects on the nitridation kinetics of silicon powder compacts were determined at 1250 or 1350 C for 4 hr. In addition, the influence of nitridation environment, and preoxidation on nitridation kinetics of a silicon powder of high surface area (approximately equals 63 sq m/g) was investigated. As the surface area increased, so did the percentage nitridation after 4 hr in N2 at 1250 or 1350 C. Silicon powders of high surface area (greater than 40 sq m/g) can be nitrided to greater than 70% at 1250 C in 4 hr. The nitridation kinetics of the high-surface-area powder compacts were significantly delayed by preoxidation treatment. Conversely, the nitridation environment had no significant influence on the nitridation kinetics of the same powder. Impurities present in the starting powder, and those accumulated during attrition milling, appeared to react with the silica layer on the surface of silicon particles to form a molten silicate layer, which provided a path for rapid diffusion of nitrogen and enhanced the nitridation kinetics of high surface area silicon powder.
Exfoliation and Characterization of Bismuth Telluride Atomic Quintuples and
Exfoliation and Characterization of Bismuth Telluride Atomic Quintuples and Quasi, University of CaliforniasRiverside, Riverside, California 92521 ABSTRACT Bismuth telluride (Bi2Te3) and its describe a method for "graphene-inspired" exfoliation of crystalline bismuth telluride films
21 CFR 520.1204 - Kanamycin, bismuth subcarbonate, activated attapulgite.
Code of Federal Regulations, 2014 CFR
... 2014-04-01 false Kanamycin, bismuth subcarbonate, activated attapulgite...ANIMAL DRUGS º 520.1204 Kanamycin, bismuth subcarbonate, activated attapulgite...kanamycin (as the sulfate), 250 mg bismuth subcarbonate, and 500 mg activated...
21 CFR 520.1204 - Kanamycin, bismuth subcarbonate, activated attapulgite.
Code of Federal Regulations, 2010 CFR
... 2010-04-01 false Kanamycin, bismuth subcarbonate, activated attapulgite...ANIMAL DRUGS º 520.1204 Kanamycin, bismuth subcarbonate, activated attapulgite...kanamycin (as the sulfate), 250 mg bismuth subcarbonate, and 500 mg activated...
21 CFR 520.1204 - Kanamycin, bismuth subcarbonate, activated attapulgite.
Code of Federal Regulations, 2011 CFR
... 2011-04-01 false Kanamycin, bismuth subcarbonate, activated attapulgite...ANIMAL DRUGS º 520.1204 Kanamycin, bismuth subcarbonate, activated attapulgite...kanamycin (as the sulfate), 250 mg bismuth subcarbonate, and 500 mg activated...
21 CFR 520.1204 - Kanamycin, bismuth subcarbonate, activated attapulgite.
Code of Federal Regulations, 2013 CFR
... 2013-04-01 false Kanamycin, bismuth subcarbonate, activated attapulgite...ANIMAL DRUGS º 520.1204 Kanamycin, bismuth subcarbonate, activated attapulgite...kanamycin (as the sulfate), 250 mg bismuth subcarbonate, and 500 mg activated...
21 CFR 520.1204 - Kanamycin, bismuth subcarbonate, activated attapulgite.
Code of Federal Regulations, 2012 CFR
... 2012-04-01 false Kanamycin, bismuth subcarbonate, activated attapulgite...ANIMAL DRUGS º 520.1204 Kanamycin, bismuth subcarbonate, activated attapulgite...kanamycin (as the sulfate), 250 mg bismuth subcarbonate, and 500 mg activated...
Formation and characterization of porous silicon-samarium/gadolinium nanocomposites: effect of substrate oxidation and biosynthesis process
NASA Astrophysics Data System (ADS)
Perdigon-Lagunes, P.; Ascencio, J. A.; Agarwal, V.
Samarium and gadolinium nanoparticles synthesized by bioreduction process have been incorporated into nanostructured porous silicon template to form a nanocomposite. The structural and optical properties of PS-Gd and PS-Sm nanocomposites have been studied through TEM, SEM and UV-Vis spectroscopy. Extent of infiltration has been verified through reflectance interference Fourier transform spectroscopy as a function of substrate oxidation conditions. The substrates oxidized at 600 ░C showed the maximum infiltration and the corresponding change of optical thickness due to nanoparticles. Such biodegradable nanocomposites in the form of particles can have potential applications in localized drug delivery and enhancement of the image contrast and optoelectronic devices. The results here reported open an energy-cheap procedure to take advantages of small rare earth nanoparticles and produced nanocomposites with their immersion in SiO2 substrates, with the perspective to be replied in other similar substrates under controlled conditions.
Solution combustion synthesis and characterization of nanosized bismuth ferrite
NASA Astrophysics Data System (ADS)
Sai Kumar, V. Sesha; Rao, K. Venkateswara; Krishnaveni, T.; Kishore Goud, A. Shiva; Reddy, P. Ranjith
The present paper describes a simple method of nanosized BiFeO3 by the solution combustion synthesis using bismuth and iron nitrates as oxidizers and the combination fuel of citric acid and ammonium hydroxide, with fuel to oxidizer ratio (? = 1) one. The X-ray Diffraction results indicated rhombohedral phase (R3m) with JCPDS data card no: 72-2035. The ferroelectric transition of the sample at 8310C was detected by differential thermal analysis. Thermal analysis was done by Thermal gravimetric-Differential thermal analyzer and obtained results were presented in this paper.
Pr doped bismuth ferrite ceramics with enhanced multiferroic properties.
Uniyal, P; Yadav, K L
Pr modified Bi(0.9-x)La(0.1)Pr(x)FeO(3) (BLPFO-x, x = 0, 0.1 and 0.2) ceramics were prepared by the conventional method based on the solid state reaction of mixed oxides and a detailed study of electrical and magnetic properties of Pr modified bismuth ferrite (BLPFO) is reported. X-ray analysis shows the formation of a bismuth ferrite rhombohedral phase. Pr doping significantly increases the resistivity and leads to a successful observation of electrical polarization hysteresis loops. All the samples have been found to possess a spontaneous magnetic moment at room temperature which increases further at low temperatures. The strong dependence of remnant polarization and dielectric constant on the strength of magnetic field is a direct evidence of magnetoelectric coupling in BLPFO-2 ceramics. PMID:21832425
Structural and Oxidative Changes in the Kidney of Crucian Carp Induced by Silicon-Based Quantum Dots
Petrache, Sorina Nicoleta; Stanca, Loredana; Serban, Andreea Iren; Sima, Cornelia; Staicu, Andreia Cristina; Munteanu, Maria Cristina; Costache, Marieta; Burlacu, Radu; Zarnescu, Otilia; Dinischiotu, Anca
Silicon-based quantum dots were intraperitoneally injected in Carassius auratus gibelio specimens and, over one week, the effects on renal tissue were investigated by following their distribution and histological effects, as well as antioxidative system modifications. After three and seven days, detached epithelial cells from the basal lamina, dilated tubules and debris in the lumen of tubules were observed. At day 7, nephrogenesis was noticed. The reduced glutathione (GSH) concentration decreased in the first three days and started to rise later on. The superoxide dismutase (SOD) activity increased only after one week, whereas catalase (CAT) was up-regulated in a time-dependent manner. The activities of glutathione reductase (GR) and glutathione peroxidise (GPX) decreased dramatically by approximately 50% compared to control, whereas the glutathione-S-transferase (GST) and glucose-6-phosphate dehydrogenase (G6PDH) increased significantly after 3 and 7 days of treatment. Oxidative modifications of proteins and the time-dependent increase of Hsp70 expression were also registered. Our data suggest that silicon-based quantum dots induced oxidative stress followed by structural damages. However, renal tissue is capable of restoring its integrity by nephron development. PMID:22949855
Process for the deposition of high temperature stress and oxidation resistant coatings on silicon-based substrates
Sarin, V.K.
A process is disclosed for depositing a high temperature stress and oxidation resistant coating on a silicon nitride- or silicon carbide-based substrate body. A gas mixture is passed over the substrate at about 900--1500 C and about 1 torr to about ambient pressure. The gas mixture includes one or more halide vapors with other suitable reactant gases. The partial pressure ratios, flow rates, and process times are sufficient to deposit a continuous, fully dense, adherent coating. The halide and other reactant gases are gradually varied during deposition so that the coating is a graded coating of at least two layers. Each layer is a graded layer changing in composition from the material over which it is deposited to the material of the layer and further to the material, if any, deposited thereon, so that no clearly defined compositional interfaces exist. The gases and their partial pressures are varied according to a predetermined time schedule and the halide and other reactant gases are selected so that the layers include (a) an adherent, continuous intermediate layer about 0.5-20 microns thick of an aluminum nitride or an aluminum oxynitride material, over and chemically bonded to the substrate body, and (b) an adherent, continuous first outer layer about 0.5-900 microns thick including an oxide of aluminum or zirconium over and chemically bonded to the intermediate layer.
Oxidation-enhanced or retarded diffusion and the growth or shrinkage of oxidation-induced stacking faults in silicon
NASA Astrophysics Data System (ADS)
Tan, T. Y.; G÷sele, U.
An analysis of the conditions for obtaining oxidation-enhanced or retarded dopant diffusions (OED or ORD), in accordance with the stacking fault growth/shrinkage phenomena, is carried out for the oxidation of Si by assuming that vacancy and Si self-interstitials coexist at high temperatures and that during oxidation a local equilibrium of point defects is attained. It is shown that the Sb ORD data can be explained quantitatively. Under most oxidation conditions the SiO2-Si interface acts as a source of Si self-interstitials, but at sufficiently high temperatures and long oxidation times the SiO2-Si interface behaves as a sink for Si self-interstitials (or equivalently as a source of vacancies). We suggest a model for this sink behavior in terms of the formation of SiO molecules at the interface and of their subsequent diffusion into the SiO2 film.
Theory and experiments of electron-hole recombination at silicon/silicon dioxide interface traps and tunneling in thin oxide MOS transistors
NASA Astrophysics Data System (ADS)
Cai, Jin
Surface recombination and channel have dominated the electrical characteristics, performance and reliability of p/n junction diodes and transistors. This dissertation uses a sensitive direct-current current voltage (DCIV) method to measure base terminal currents (IB) modulated by the gate bias (VGB) and forward p/n junction bias (VPN) in a MOS transistor (MOST). Base terminal currents originate from electron-hole recombination at Si/SiO2 interface traps. Fundamental theories which relate DCIV characteristics to device and material parameters are presented. Three theory-based applications are demonstrated on both the unstressed as well as hot-carrier-stressed MOSTs: (1) determination of interface trap density and energy levels, (2) spatial profile of interface traps in the drain/base junction-space-charge region and in the channel region, and (3) determination of gate oxide thickness and impurity doping concentrations. The results show that interface trap energy levels are discrete, which is consistent with those from silicon dangling bonds; in unstressed MOS transistors interface trap density in the channel region rises sharply toward source and drain, and after channel-hot-carrier stress, interface trap density increases mostly in the junction space-charge region. As the gate oxide thins below 3 nm, the gate oxide leakage current via quantum mechanical tunneling becomes significant. A gate oxide tunneling theory which refined the traditional WKB tunneling probability is developed for modeling tunneling currents at low electric fields through a trapezoidal SiO2 barrier. Correlation with experimental data on thin oxide MOSTs reveals two new results: (1) hole tunneling dominates over electron tunneling in p+gate p-channel MOSTs, and (2) the small gate/drain overlap region passes higher tunneling currents than the channel region under depletion to flatband gate voltages. The good theory-experimental correlation enables the extraction of impurity doping concentrations, which complements the DCIV method. Two fundamental theories of interband tunneling are developed to correlate with the VGB dependence of drain/base p/n junction currents: (1) direct tunneling at the drain/base junction perimeter with and without the quantization effects in the base surface accumulation layer, and (2) interface trap assisted tunneling in the gate/drain overlap region. The second theory gives better correlation, which is further supported by the DCIV peaks originated from interface traps in the gate/drain overlap region.
Photoreductive generation of amorphous bismuth nanoparticles using polysaccharides--bismuth-cellulose nanocomposites.
Breitwieser, Doris; Kriechbaum, Margit; Ehmann, Heike M A; Monkowius, Uwe; Coseri, Sergiu; Sacarescu, Liviu; Spirk, Stefan
A simple and highly reproducible synthesis of amorphous bismuth nanoparticles incorporated into a polysaccharide matrix using a photoreduction process is presented. As precursor for the generation of the Bi nanoparticles, organosoluble triphenylbismuth is used. The precursor is dissolved in toluene and mixed with a hydrophobic organosoluble polysaccharide, namely trimethylsilyl cellulose (TMSC) with high DSSi. The solution is subjected to UV exposure, which induces the homolytic cleavage of the bismuth-carbon bond in BiPh3 resulting in the formation of Bi(0) and phenyl radicals. The aggregation of the Bi atoms can be controlled in the TMSC matrix and yields nanoparticles of around 20 nm size as proven by TEM. The phenyl radicals undergo recombination to form small organic molecules like benzene and biphenyl, which can be removed from the nanocomposite after lyophilization and exposure to high vacuum. Finally, the TMSC matrix is converted to cellulose after exposure to HCl vapors, which remove the trimethylsilyl groups from the TMSC derivative. Although TMSC is converted to cellulose, the formed TMS-OH is not leaving the nanocomposite but reacts instead with surface oxide layer of the Bi nanoparticles to form silylated Bi nanoparticles as proven by TEM/EDX. PMID:25458299
Mechanism of ?-FeSi2 precipitates growth-and-dissolution and pyramidal defects' formation during oxidation of Fe-contaminated silicon wafers
NASA Astrophysics Data System (ADS)
De Luca, Anthony; Texier, MichaÙl; Portavoce, Alain; Burle, Nelly; Grosjean, Catherine; Morata, StÚphane; Michel, Fabrice
Fe-implanted Si-wafers have been oxidized at 900 ░C and 1100 ░C in order to investigate the behaviour of Fe atoms at the growing SiO2/Si interface and the impact on the integrity of microelectronic devices of an involuntary Fe contamination before or during the oxidation process. As-implanted and oxidized wafers have been characterized using secondary ion mass spectroscopy, atom probe tomography, and high-resolution transmission electron microscopy. Experimental results were compared to calculated implantation profiles and simulated images. Successive steps of iron disilicide precipitation and oxidation were evidenced during the silicon oxidation process. The formation of characteristic pyramidal-shaped defects, at the SiO2/Si interface, was notably found to correlate with the presence of ?-FeSi2 precipitates. Taking into account the competitive oxidation of these precipitates and of the surrounding silicon matrix, dynamic mechanisms are proposed to model the observed microstructural evolution of the SiO2/Si interface, during the growth of the silicon oxide layer.