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NASA Astrophysics Data System (ADS)
This work demonstrates a real-time visible-light phototransistor comprised of a wide-band-gap amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistor (TFT) and a narrow-band-gap polymeric capping layer. The capping layer and the IGZO layer form a p-n junction diode. The p-n junction absorbs visible light and consequently injects electrons into the IGZO layer, which in turn affects the body voltage as well as the threshold voltage of a-IGZO TFT. The hysteresis behavior due to the charges at IGZO back interface is also discussed.
Zan, Hsiao-Wen; Chen, Wei-Tsung; Hsueh, Hsiu-Wen; Kao, Shih-Chin; Ku, Ming-Che; Tsai, Chuang-Chuang; Meng, Hsin-Fei
Electrical effect of titanium diffusion on amorphous indium gallium zinc oxide
In this work, thermal diffusion phenomenon of Ti into amorphous indium gallium zinc oxide ({alpha}-IGZO) was carefully investigated with secondary ion mass spectroscopy, I-V, and R{sub s} measurement systems and HSC chemistry simulation tool. According to the experimental and simulated results, the diffused Ti atoms were easily oxidized due to its lowest oxidation free energy. Since oxygen atoms were decomposed from the {alpha}-IGZO during the oxidation of Ti, the number of oxygen vacancies working as electron-donating sites in {alpha}-IGZO was dramatically increased, contributing to the decrease of resistivity ({rho}) from 1.96 {Omega} cm (as-deposited {alpha}-IGZO) to 1.33 Multiplication-Sign 10{sup -3}{Omega} cm (350 Degree-Sign C annealed {alpha}-IGZO).
Choi, Seung-Ha [School of Electronic and Electrical Engineering, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of); Development Group of Oxide Semiconductor, Samsung Display, Yongin 446-711 (Korea, Republic of); Jung, Woo-Shik [Department of Electrical Engineering, Stanford University, Stanford, California 94305 (United States); Park, Jin-Hong [School of Electronic and Electrical Engineering, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of)
NASA Astrophysics Data System (ADS)
The electrical instability behaviors of a positive-gate-bias-stressed amorphous indium-gallium-zinc oxide (a-IGZO) thin film transistor (TFT) are studied under monochromatic light illumination. It is found that as the wavelength of incident light reduces from 750 nm to 450 nm, the threshold voltage of the illuminated TFT shows a continuous negative shift, which is caused by photo-excitation of trapped electrons at the channel/dielectric interface. Meanwhile, an increase of the sub-threshold swing (SS) is observed when the illumination wavelength is below 625 nm (�2.0 eV). The SS degradation is accompanied by a simultaneous increase of the field effect mobility (?FE) of the TFT, which then decreases at even shorter wavelength beyond 540 nm (�2.3 eV). The variation of SS and ?FE is explained by a physical model based on generation of singly ionized oxygen vacancies (Vo+) and double ionized oxygen vacancies (Vo2+) within the a-IGZO active layer by high energy photons, which would form trap states near the mid-gap and the conduction band edge, respectively.
Huang, Xiaoming; Wu, Chenfei; Lu, Hai; Ren, Fangfang; Xu, Qingyu; Ou, Huiling; Zhang, Rong; Zheng, Youdou
NASA Astrophysics Data System (ADS)
An organic sensing layer is capped onto an amorphous indium gallium zinc oxide (a-IGZO) thin-film transistor (TFT) to form a hybrid sensor. The organic layer, served as a second gate, forms a p-n junction with the a-IGZO film. Oxidizing or reducing vapor molecules act like electron acceptors or electron donors to change the potential of the organic layer and the current of a-IGZO TFT. A sensitive and reversible response to 100 ppb ammonia and 100 ppb acetone is obtained at room temperature. This letter opens a route to develop low-cost large-area bio/chemical sensor arrays based on the emerging a-IGZO TFT technology.
Zan, Hsiao-Wen; Li, Chang-Hung; Yeh, Chun-Cheng; Dai, Ming-Zhi; Meng, Hsin-Fei; Tsai, Chuang-Chuang
Bipolar ac stress-induced instability of amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistors is comparatively investigated with that under a positive dc gate bias stress. While the positive dc gate bias stress-induced threshold voltage shift ({delta}V{sub T}) is caused by the charge trapping into the interface/gate dielectric as reported in previous works, the dominant mechanism of the ac stress-induced {delta}V{sub T} is observed to be due to the increase in the acceptorlike deep states of the density of states (DOS) in the a-IGZO active layer. Furthermore, it is found that the variation of deep states in the DOS makes a parallel shift in the I{sub DS}-V{sub GS} curve with an insignificant change in the subthreshold slope, as well as the deformation of the C{sub G}-V{sub G} curves.
Lee, Sangwon; Jeon, Kichan; Park, Jun-Hyun; Kim, Sungchul; Kong, Dongsik; Kim, Dong Myong; Kim, Dae Hwan [School of Electrical Engineering, Kookmin University, 861-1 Jeongneung-dong, Seongbuk-gu, Seoul 136-702 (Korea, Republic of); Kim, Sangwook; Kim, Sunil; Hur, Jihyun; Park, Jae Chul; Song, Ihun; Kim, Chang Jung; Park, Youngsoo; Jung, U-In [Semiconductor Laboratory, Samsung Advanced Institute of Technology, Nongseo-Dong, Giheung-Gu, Yongin-Si, Gyeonggi-Do 446-712 (Korea, Republic of)
NASA Astrophysics Data System (ADS)
We report on the generation and characterization of a hump in the transfer characteristics of amorphous indium gallium zinc-oxide thin-film transistors by positive bias temperature stress. The hump depends strongly on the gate bias stress at 100 �C. Due to the hump, the positive shift of the transfer characteristic in deep depletion is always smaller that in accumulation. Since, the latter shift is twice the former, with very good correlation, we conclude that the effect is due to creation of a double acceptor, likely to be a cation vacancy. Our results indicate that these defects are located near the gate insulator/active layer interface, rather than in the bulk. Migration of donor defects from the interface towards the bulk may also occur under PBST at 100 �C.
Um, Jae Gwang; Mativenga, Mallory; Migliorato, Piero; Jang, Jin
NASA Astrophysics Data System (ADS)
The electrical, optical, and structural properties of amorphous indium gallium zinc oxide (a-IGZO) films deposited at room temperature (RT) examined before and after annealing using a radio frequency (RF) magnetron sputtering system with different hydrogen and oxygen gas flow ratios. The carrier concentration and resistivity of the a-IGZO films fabricated under O2/Ar + O2 and O2/Ar-4%H2 + O2 atmospheres were greatly dependent on the addition of hydrogen and heat treatment. Thin-film transistors (TFTs) with an a-IGZO channel layer deposited under O2/Ar-4%H2 + O2 = 1.6% exhibited good subthreshold gate voltage swing (S), on/off ratio, threshold voltage and ?FE of 0.4 V decade-1, 108, 0.3 V and 4.8 cm2 V-1 s-1, respectively. From analysis of the interfacial structure in TFTs before and after annealing, the electrical conductivity of the a-IGZO channel layer was greatly affected in regard to TFT performance due to the amorphous a-IGZO channel layer and SiO2 gate insulator.
Jung, C. H.; Kang, H. I.; Yoon, D. H.
NASA Astrophysics Data System (ADS)
We report thermally stable coplanar amorphous-indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs) with heavily doped n+ a-IGZO source/drain regions. Doping is through He plasma treatment in which the resistivity of the a-IGZO decreases from 2.98 ? cm to 2.79 � 10-3 ? cm after treatment, and then it increases to 7.92 � 10-2 ? cm after annealing at 300 �C. From the analysis of X-ray photoelectron spectroscopy, the concentration of oxygen vacancies in He plasma treated n+a-IGZO does not change much after thermal annealing at 300 �C, indicating thermally stable n+ a-IGZO, even for TFTs with channel length L = 4 ?m. Field-effect mobility of the coplanar a-IGZO TFTs with He plasma treatment changes from 10.7 to 9.2 cm2/V s after annealing at 300 �C, but the performance of the a-IGZO TFT with Ar or H2 plasma treatment degrades significantly after 300 �C annealing.
Jeong, Ho-young; Lee, Bok-young; Lee, Young-jang; Lee, Jung-il; Yang, Myoung-su; Kang, In-byeong; Mativenga, Mallory; Jang, Jin
NASA Astrophysics Data System (ADS)
We report on microscopic structures and electrical and optical properties of sputter-deposited amorphous indium-gallium-zinc oxide (a-IGZO) films. From electron microscopy observations and an x-ray small angle scattering analysis, it has been confirmed that the sputtered a-IGZO films consist of a columnar structure. However, krypton gas adsorption measurement revealed that boundaries of the columnar grains are not open-pores. The conductivity of the sputter-deposited a-IGZO films shows a change as large as seven orders of magnitude depending on post-annealing atmosphere; it is increased by N2-annealing and decreased by O2-annealing reversibly, at a temperature as low as 300�C. This large variation in conductivity is attributed to thermionic emission of carrier electrons through potential barriers at the grain boundaries, because temperature dependences of the carrier density and the Hall mobility exhibit thermal activation behaviours. The optical band-gap energy of the a-IGZO films changes between before and after annealing, but is independent of the annealing atmosphere, in contrast to the noticeable dependence of conductivity described above. For exploring other possibilities of a-IGZO, we formed multilayer films with an artificial periodic lattice structure consisting of amorphous InO, GaO, and ZnO layers, as an imitation of the layer-structured InGaZnO4 homologous phase. The hall mobility of the multilayer films was almost constant for thicknesses of the constituent layer between 1 and 6 �, suggesting rather small contribution of lateral two-dimensional conduction It increased with increasing the thickness in the range from 6 to 15 �, perhaps owing to an enhancement of two-dimensional conduction in InO layers.
Yabuta, H.; Kaji, N.; Shimada, M.; Aiba, T.; Takada, K.; Omura, H.; Mukaide, T.; Hirosawa, I.; Koganezawa, T.; Kumomi, H.
NASA Astrophysics Data System (ADS)
We performed an X-ray photoelectron spectroscopy (XPS) depth-profiling study on the materials used in amorphous indium-gallium-zinc oxide thin-film transistors (a-IGZO TFTs) with Ti and Mo source/drain (S/D) electrodes. The XPS results suggested that there are some differences between the interface regions of Ti/a-IGZO and Mo/a-IGZO for different chemical states of the materials. The chemical states of the back-channel surfaces were also found to be different between the TFTs with Ti and Mo S/D electrodes. In addition, we fabricated indium-gallium-zinc-titanium oxide composite thin films by deposition using multitarget co-sputtering. The electronic structure of these films observed by XPS is similar to that of the Ti/a-IGZO interface region. The fabricated films were found to have a very low resistivity, much lower than that of an a-IGZO film using typical TFT fabrication processes.
Iwamatsu, Shinnosuke; Takechi, Kazushige; Yahagi, Toru; Watanabe, Yoshiyuki; Tanabe, Hiroshi; Kobayashi, Seiya
NASA Astrophysics Data System (ADS)
Amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) with a solution-processed polymeric gate dielectric of cross-linked poly(4-vinylphenol) (c-PVP) film were fabricated on a poly(ethylene terephthalate) (PET) substrate on which an a-IGZO film, as the active channel layer, was deposited by radio frequency (RF) sputtering. The entire TFT fabrication process was carried out at a temperature below 110 �C. The device exhibited an on/off ratio of 1.5�106 and a high field-effect mobility of 10.2 cm2 V-1 s-1, which is, to our knowledge, the best result ever achieved among a-IGZO TFTs with polymeric gate dielectrics on a plastic substrate.
Hyung, Gun Woo; Park, Jaehoon; Wang, Jian-Xun; Lee, Ho Won; Li, Zhao-Hui; Koo, Ja-Ryong; Kwon, Sang Jik; Cho, Eou-Sik; Kim, Woo Young; Kim, Young Kwan
NASA Astrophysics Data System (ADS)
We have analyzed the effect of applying positive bias stress (PBS) to amorphous-indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs) immediately after applying negative bias under illumination stress (NBIS). By monitoring TFT current-voltage and capacitance-voltage characteristics, we found that PBS facilitates the recovery process. NBIS results in positive charge trapping at the active-layer/gate-insulator interface and the formation of shallow donors in the bulk a-IGZO when neutral oxygen vacancies are ionized by hole capture. In addition to the release of trapped positive charges from the active-layer/gate-insulator interface during the PBS-assisted recovery, ionized oxygen vacancies are neutralized by electron capture and relax back to their original deep levels�well below EF.
Um, Jae Gwang; Mativenga, Mallory; Jang, Jin
NASA Astrophysics Data System (ADS)
The electrical characteristics of amorphous indium-gallium-zinc-oxide (a-IGZO) thin film transistors (TFTs) are systematically studied using a double a-IGZO active layer that is composed of a-IGZO x (oxygen-ion-poor region) and a-IGZO y (oxygen-ion-rich-region). An active layer is designed to have a serially-stacked bi-layer matrix with different oxygen contents, providing the formation of different electron conduction channels. Two different oxygen contents in the active layer are obtained by varying the O2 partial pressure during sputtering. The a-IGZO TFT based on a double active layer exhibits a high mobility of 9.1 cm2/Vsec, a threshold voltage (V T ) of 16.5 V, and ?V T shifts of less than 1.5 V under gate voltage stress. A possible electrical sketch for the double active layer channel is also discussed.
Koo, Ja Hyun; Kang, Tae Sung; Hong, Jin Pyo
NASA Astrophysics Data System (ADS)
We report on the impact of source/drain (S/D) metal (molybdenum) etch and the final passivation (SiO2) layer on the bias-stress stability of back-channel-etch (BCE) configuration based amorphous indium�gallium�zinc oxide (a-IGZO) thin-film transistors (TFTs). It is observed that the BCE configurations TFTs suffer poor bias-stability in comparison to etch-stop-layer (ESL) TFTs. By analysis with transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS), as well as by a comparative analysis of contacts formed by other metals, we infer that this poor bias-stability for BCE transistors having Mo S/D contacts is associated with contamination of the back channel interface, which occurs by Mo-containing deposits on the back channel during the final plasma process of the physical vapor deposited SiO2 passivation.
Nag, Manoj; Bhoolokam, Ajay; Steudel, Soeren; Chasin, Adrian; Myny, Kris; Maas, Joris; Groeseneken, Guido; Heremans, Paul
NASA Astrophysics Data System (ADS)
In this study, the Al2O3 nanoparticles were incorporated into polymer as a nono-composite dielectric for used in a flexible amorphous Indium-Gallium-Zinc Oxide (a-IGZO) thin-film transistor (TFT) on a polyethylene naphthalate substrate by solution process. The process temperature was well below 100 �C. The a-IGZO TFT exhibit a mobility of 5.13 cm2/V s on the flexible substrate. After bending at a radius of 4 mm (strain = 1.56%) for more than 100 times, the performance of this a-IGZO TFT was nearly unchanged. In addition, the electrical characteristics are less altered after positive gate bias stress at 10 V for 1500 s. Thus, this technology is suitable for use in flexible displays.
Lai, Hsin-Cheng; Pei, Zingway; Jian, Jyun-Ruri; Tzeng, Bo-Jie
NASA Astrophysics Data System (ADS)
We investigate the border traps in amorphous indium-gallium-zinc oxide thin-film transistors with SiOX and SiNX interfacial gate dielectrics. Border traps have been known as trapping centers of electronic carriers in field-effect transistors, and non-negligible hysteresis is observed in the bidirectional high-frequency capacitance-voltage curve with a slow ramp rate in both dielectric devices. From the gate voltage transient method and 1/f noise analysis, the spatially and energetically uniform trap distribution is obtained, and approximately four to five times higher border trap densities are extracted from SiNX dielectric devices than from the SiOX dielectric ones.
Jeong, Chan-Yong; Lee, Daeun; Song, Sang-Hun; Cho, In-Tak; Lee, Jong-Ho; Cho, Eou-Sik; Kwon, Hyuck-In
NASA Astrophysics Data System (ADS)
We demonstrate back channel improvement of back-channel-etch amorphous-indium-gallium-zinc-oxide (a-IGZO) thin-film transistors by using solution-processed yttrium oxide (Y2O3) passivation. Two different solvents, which are acetonitrile (35%) + ethylene glycol (65%), solvent A and deionized water, solvent B are investigated for the spin-on process of the Y2O3 passivation�performed after patterning source/drain (S/D) Mo electrodes by a conventional HNO3-based wet-etch process. Both solvents yield devices with good performance but those passivated by using solvent B exhibit better light and bias stability. Presence of yttrium at the a-IGZO back interface, where it occupies metal vacancy sites, is confirmed by X-ray photoelectron spectroscopy. The passivation effect of yttrium is more significant when solvent A is used because of the existence of more metal vacancies, given that the alcohol (65% ethylene glycol) in solvent A may dissolve the metal oxide (a-IGZO) through the formation of alkoxides and water.
An, Sungjin; Mativenga, Mallory; Kim, Youngoo; Jang, Jin
An abnormal sub-threshold leakage current is observed at high temperature in amorphous indium-gallium-zinc-oxide thin film transistors (a-IGZO TFTs). This phenomenon occurs due to a reduced number of defects in the device's a-IGZO active layer after the device has undergone N{sub 2}O plasma treatment. Experimental verification shows that the N{sub 2}O plasma treatment enhances the thin film bonding strength, thereby suppressing the formation of temperature-dependent holes, which are generated above 400?K by oxygen atoms leaving their original sites. The N{sub 2}O plasma treatment devices have better stability performance than as-fabricated devices. The results suggest that the density of defects for a-IGZO TFTs with N{sub 2}O plasma treatment is much lower than that in as-fabricated devices. The N{sub 2}O plasma treatment repairs the defects and suppresses temperature-dependent sub-threshold leakage current.
Jhu, Jhe-Ciou; Chang, Ting-Chang, E-mail: email@example.com [Department of Physics and Institute of Electro-Optical Engineering, Center for Nanoscience and Nanotechnology, National Sun Yat-Sen University, Kaohsiung 804, Taiwan (China); Chang, Geng-Wei; Tai, Ya-Hsiang [Department of Photonics and Institute of Electro-Optical Engineering, National Chiao Tung University, Hsin-Chu 300, Taiwan (China); Tsai, Wu-Wei; Chiang, Wen-Jen; Yan, Jing-Yi [Industrial Technology Research Institute, 195, Sec. 4, Chung Hsing Rd., Hsinchu 31040, Taiwan (China)
NASA Astrophysics Data System (ADS)
In this study, indium-gallium-zinc-oxide thin film transistors can be operated either as transistors or resistance random access memory devices. Before the forming process, current-voltage curve transfer characteristics are observed, and resistance switching characteristics are measured after a forming process. These resistance switching characteristics exhibit two behaviors, and are dominated by different mechanisms. The mode 1 resistance switching behavior is due to oxygen vacancies, while mode 2 is dominated by the formation of an oxygen-rich layer. Furthermore, an easy approach is proposed to reduce power consumption when using these resistance random access memory devices with the amorphous indium-gallium-zinc-oxide thin film transistor.
Yang, Jyun-Bao; Chang, Ting-Chang; Huang, Jheng-Jie; Chen, Yu-Chun; Chen, Yu-Ting; Tseng, Hsueh-Chih; Chu, Ann-Kuo; Sze, Simon M.
An effective approach to reduce defects and increase electron mobility in a-IGZO thin-film transistors (a-IGZO TFTs) is introduced. A strong reduction layer, calcium, is capped onto the back interface of a-IGZO TFT. After calcium capping, the effective electron mobility of a-IGZO TFT increases from 12 cm(2) V(-1) s(-1) to 160 cm(2) V(-1) s(-1). This high mobility is a new record, which implies that the proposed defect reduction effect is key to improve electron transport in oxide semiconductor materials. PMID:22678659
Zan, Hsiao-Wen; Yeh, Chun-Cheng; Meng, Hsin-Fei; Tsai, Chuang-Chuang; Chen, Liang-Hao
NASA Astrophysics Data System (ADS)
We have investigated the parylene-groups for the device scaling-down as the protection layer of polyethersulfone (PES) substrate. In general, photolithography process on the PES substrate could not be allowed due to its poor chemical resistance. In this work, parylene-C is used as the protection layer. However, adhesion problem is observed caused by the hydrophobic property of parylene-groups. Thereby we additionally used SiO2 as the adhesion layer. Finally, we demonstrated the scaling-down of amorphous indium gallium zinc oxide thin film transistor on a plastic substrate by using lithography technique. Field-effect mobility, threshold voltage, current on-to-off ratio are measured to be 0.84 cm2/V s, 19.7 V, and 7.62�104, respectively.
Chang, Seongpil; Dong, Ki-Young; Park, Jung-Ho; Oh, Tae-Yeon; Kim, Jong-Woo; Lee, Sang Yeol; Ju, Byeong-Kwon
NASA Astrophysics Data System (ADS)
A low-power scan driver embedded with a level shifter using depletion-mode amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs) is proposed for high-resolution flat-panel displays (FPDs). In order to achieve low power consumption, the scan driver uses clock signals with a reduced voltage swing. Furthermore, the level shifter is implemented without using a diode-connected TFT. This scan driver is simulated at an output voltage swing of 30 V and an operating frequency (fop) of 153.6 kHz, which satisfy the driving conditions for 10-in. wide quadruple extended graphics array (WQXGA, 1600 � 2560) FPDs with a frame frequency of 60 Hz. The simulation results of the proposed scan driver demonstrate the successful operation even at a threshold voltage shift (?Vth) of -2.0 V. The power consumption of the proposed scan driver per ten stages is 0.41 mW, which is 80.75% less than that reported in a previous work.
Lee, Chang-Hee; Kwon, Oh-Kyong
NASA Astrophysics Data System (ADS)
In this paper, an infrared annealing method was proposed for solution-processed indium gallium zinc oxide films. The optimized IGZO thin-film transistors (TFTs) exhibited a field-effect mobility of 2.04 cm2 (Vs)-1, on-off current ratio of 1.52�106 and subthreshold swing of 0.84 V/dec. Spectroscopic analysis confirmed that the infrared irradiation could enhance the removal of organic species and dehydroxylation. The results suggest that infrared annealing method is a potential process for low-temperature preparation of solution-processed oxide semiconductor layers and dielectric layers, and can be applied to the fabrication of TFT devices.
Pu, Haifeng; Zhou, Qianfei; Yue, Lan; Zhang, Qun
NASA Astrophysics Data System (ADS)
The effect of an ambient atmosphere with a positive bias constant current stress (CCS) and a negative bias illumination stress (NBIS) on the stability of amorphous In-Ga-Zn-O thin film transistors (TFTs) is examined by utilizing a glass-hermetic-sealant with a moisture permeability of less than 10-6 g/m2 . day. In the CCS test, the threshold voltage shift (?Vth) was remarkably suppressed in the glass-sealed TFTs. The unsealed and resin-sealed TFTs exhibited large ?Vth values. During the NBIS tests, the glass-sealed TFTs had almost the same negative ?Vth as the unsealed and resin sealed TFTs. Among the different TFTs, no significant differences were observed in the threshold voltage, the subthreshold swing and the saturation mobility as a function of the photon energy. It is concluded that ambient molecules were the primary origin of the instability of the ?Vth, induced by a CCS, but they were not related to the NBIS instability. The major role of the effective passivation layers in the NBIS test was not to simply block out the ambient effects, but to reduce the extra density of states at/near the surface of the back channel.
Yamada, Kazuo; Nomura, Kenji; Abe, Katsumi; Takeda, Satoshi; Hosono, Hideo
Solution-processed amorphous oxide semiconductors (AOSs) are emerging as important electronic materials for displays and transparent electronics. We report here on the fabrication, microstructure, and performance characteristics of inkjet-printed, low-temperature combustion-processed, amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) grown on solution-processed hafnia self-assembled nanodielectrics (Hf-SANDs). TFT performance for devices processed below 300 �C includes >4� enhancement in electron mobility (?FE) on Hf-SAND versus SiO2 or ALD-HfO2 gate dielectrics, while other metrics such as subthreshold swing (SS), current on:off ratio (ION:IOFF), threshold voltage (Vth), and gate leakage current (Ig) are unchanged or enhanced. Thus, low voltage IGZO/SAND TFT operation (<2 V) is possible with ION:IOFF = 10(7), SS = 125 mV/dec, near-zero Vth, and large electron mobility, ?FE(avg) = 20.6 � 4.3 cm(2) V(-1) s(-1), ?FE(max) = 50 cm(2) V(-1) s(-1). Furthermore, X-ray diffraction analysis indicates that the 300 �C IGZO combustion processing leaves the underlying Hf-SAND microstructure and capacitance intact. This work establishes the compatibility and advantages of all-solution, low-temperature fabrication of inkjet-printed, combustion-derived high-mobility IGZO TFTs integrated with self-assembled hybrid organic-inorganic nanodielectrics. PMID:24187917
Everaerts, Ken; Zeng, Li; Hennek, Jonathan W; Camacho, Diana I; Jariwala, Deep; Bedzyk, Michael J; Hersam, Mark C; Marks, Tobin J
NASA Astrophysics Data System (ADS)
The excellent impermeability of graphene was exploited to produce stable ohmic contact at the interface between Al metal and a semiconducting indium gallium zinc oxide (IGZO) layer after high-temperature annealing. Thin film transistors (TFTs) were fabricated with and without a graphene interlayer between the Al metal and the IGZO channel region. Metal contact at the interface prepared without a graphene interlayer showed serious instabilities in the IGZO TFT under thermal annealing; however, the insertion of a graphene interlayer between the IGZO channel and the Al metal offered good stability under repeated high-temperature annealing cycles and maintained ohmic contact.
Eun Lee, Jeong; Sharma, Bhupendra K.; Lee, Seoung-Ki; Jeon, Haseok; Hee Hong, Byung; Lee, Hoo-Jeong; Ahn, Jong-Hyun
In this study, the effects of different annealing conditions (air, O2, N2, vacuum) on the chemical and electrical characteristics of amorphous indium-gallium-zinc oxide (a-IGZO) thin film transistors (TFT) were investigated. The contact resistance and interface properties between the IGZO film and the gate dielectric improved after an annealing treatment. However, the chemical bonds in the IGZO bulk changed under various annealing atmospheres, which, in turn, altered the characteristics of the TFTs. The TFTs annealed in vacuum and N2 ambients exhibited undesired switching properties due to the high carrier concentration (>10(17) cm(-3)) of the IGZO active layer. In contrast, the IGZO TFTs annealed in air and oxygen ambients displayed clear transfer characteristics due to an adequately adjusted carrier concentration in the operating range of the TFT. Such an optimal carrier concentration arose through the stabilization of unstable chemical bonds in the IGZO film. With regard to device performance, the TFTs annealed in O2 and air exhibited saturation mobility values of 8.29 and 7.54 cm2/Vs, on-off ratios of 7.34 x 10(8) and 3.95 x 10(8), and subthreshold swing (SS) values of 0.23 and 0.19 V/decade, respectively. Therefore, proper annealing ambients contributed to internal modifications in the IGZO structure and led to an enhancement in the oxidation state of the metal. As a result, defects such as oxygen vacancies were eliminated. Oxygen annealing is thus effective for controlling the carrier concentration of the active layer, decreasing electron traps, and enhancing TFT performance. PMID:22121652
Park, Soyeon; Bang, Seokhwan; Lee, Seungjun; Park, Joohyun; Ko, Youngbin; Jeon, Hyeongtag
NASA Astrophysics Data System (ADS)
We found out that in an indium gallium zinc oxide (IGZO) transistor, the energy barrier in the channel region, i.e., the conduction band energy relative to the Fermi energy is lowered by electrons flowing from n+ regions under source and drain electrodes. We have named this phenomenon �conduction band lowering (CBL) effect�. Owing to this effect, even when the Fermi energy of an IGZO film gets closer to the mid-gap, a transistor formed using the film in the channel region is always turned on around a gate voltage of 0 V. In other words, by sufficiently reducing the donor concentration of the channel region, such IGZO transistors are turned on at a certain low gate voltage determined by the CBL effect and their characteristics variation can be suppressed.
Matsubayashi, Daisuke; Kobayashi, Yoshiyuki; Matsuda, Shinpei; Obonai, Toshimitsu; Ishihara, Noritaka; Tanaka, Tetsuhiro; Tezuka, Sachiaki; Suzawa, Hideomi; Yamazaki, Shunpei
NASA Astrophysics Data System (ADS)
In this work, fully transparent dual-layer channel amorphous indium gallium zinc oxide thin-film transistors (a-IGZO TFTs) are fabricated on glass substrates at low temperature. Dual-layer channel a-IGZO TFTs are studied by changing the partial pressure of oxygen while sputtering IGZO layers for comparison with single-layer channel TFTs which are fabricated with a constant oxygen content. All four types of dual-layer channel TFT sample demonstrate better performance, on-to-off ratios of �108 and low subthreshold swing (SS) of less than 200 mV/decade, than the single-layer ones. TFTs with two layers, a low-oxygen layer and a high-oxygen layer formed using oxygen partial pressures of 0.01 and 0.05 Pa, respectively demonstrate relatively better performance with a mobility of more than 60 cm2 V-1 s-1. Among them, the TFTs with a channel layer thickness ratio of 3 : 1 show the best transfer characteristics with a high on-to-off current ratio (Ion/off) of 1.8 � 108 and a low SS of 135 mV/decade.
Tian, Yu; Han, Dedong; Zhang, Suoming; Huang, Fuqing; Shan, Dongfang; Cong, Yingying; Cai, Jian; Wang, Liangliang; Zhang, Shengdong; Zhang, Xing; Wang, Yi
We investigated the chemical stability and electrical properties of dual-active-layered zinc-tin-oxide (ZTO)/indium-gallium-zinc-oxide (IGZO) structures (DALZI) with the durability of the chemical damage. The IGZO film was easily corroded or removed by an etchant, but the DALZI film was effectively protected by the high chemical stability of ZTO. Furthermore, the electrical performance of the DALZI thin-film transistor (TFT) was improved by densification compared to the IGZO TFT owing to the passivation of the pin holes or pore sites and the increase in the carrier concentration due to the effect of Sn(4+) doping. PMID:23738534
Kim, Chul Ho; Rim, You Seung; Kim, Hyun Jae
NASA Astrophysics Data System (ADS)
In this study, we propose a floating dual gate (FDG) indium-gallium-zinc-oxide (IGZO) thin film transistor (TFT) with a floating metal back gate that is directly contact with IGZO without a dielectric layer. The floating back gate effect is investigated by changing the work function (?) of the back gate. The FDG IGZO TFT exhibits an improved field-effect mobility (?), unchanged subthreshold swing (SS), high on/off current ratio, and a tunable threshold voltage ranged (Vth) from -5.0 to +7.9 V without an additional back gate power supply.
Zan, Hsiao-Wen; Chen, Wei-Tsung; Yeh, Chung-Cheng; Hsueh, Hsiu-Wen; Tsai, Chuang-Chuang; Meng, Hsin-Fei
NASA Astrophysics Data System (ADS)
The electrical characteristics of bias temperature stress (BTS) induced in amorphous indium-gallium-zinc oxide thin-film transistors (a-IGZO TFTs) were studied. We analyzed the threshold voltage (VTH) shift on the basis of the effects of positive bias temperature stress (PBTS) and negative bias temperature stress (NBTS), and applied it to the stretched-exponential model. Both stress temperature and bias are considered as important factors in the electrical instabilities of a-IGZO TFTs, and the stretched-exponential equation is well fitted to the stress condition. VTH for the drain current-gate voltage (IDS-VGS) curve and flat-band voltage (VFB) for the capacitance-voltage (C-V) curve move in the positive direction when PBTS is induced. However, in the case of NBTS, they move slightly in the negative direction. To clarify the VTH shift phenomenon by electron and hole injection, the average effective energy barrier (E?) is extracted, and the extracted values of E? under PBTS and NBTS are about 1.33 and 2.25 eV, respectively. The oxide trap charges (Not) of PBTS and NBTS calculated by C-V measurement are 4.4 � 1011 and 1.49 � 1011 cm-2, respectively. On the other hand, the border trap charges of PBTS and NBTS are 6.7 � 108 and 1.7 � 109 cm-2, respectively. This indicates that the increased interface trap charge, after PBTS is induced, captures electrons during detrap processing from the border trap to the conduction band, valence band, and interface trap.
Han, Chang-Hoon; Kim, Sang-Sub; Kim, Kwang-Ryul; Baek, Do-Hyun; Kim, Sang-Soo; Choi, Byoung-Deog
NASA Astrophysics Data System (ADS)
The defect chemistry of compounds in the InGaO3(ZnO) k (IGZO) system (k=1, 2, and 3) was investigated via analysis of the dependence of conductivity and thermopower on oxygen partial pressure (pO2) at high temperature (750�C), i.e., Brouwer analysis. Defect mechanisms were deduced based on the resulting Brouwer slopes for all the k-phases, the prevailing point defect species were proposed to be the Ga antisite defect (Ga�Zn ionically compensated by indium vacancies (mathrm{V('''}_{In}) ) donors.The validity of the proposed defect mechanism was supported by density functional theory predictions, which calculated intrinsic defect formation energies in crystalline IGZO and also calculated a theory-based Brouwer slope that was in agreement with experiment. The defect chemistry of IGZO was compared to that of the related In2O3(ZnO)k system in order to infer the role of cation composition in governing electrical properties in crystalline IGZO. There is a change from electronic compensation of antisite defects (in crystalline k=3 In2O3(ZnO) k) to ionic compensation for nearly all compositions in the crystalline IGZO phases. The electrical properties of amorphous IGZO (a-IGZO) were investigated in situ as a function of pO2 at moderate temperature (200�C). A sluggish decay in conductivity was observed and attributed to relaxation within the amorphous structure. Upon abrupt change of pO2, two transients were observed in the electrical property response. The initial response was attributed to a rapid change of surface states. The latter transient, with a time constant approximately an order of magnitude larger than the first, was attributed to bulk diffusion of oxygen. Bulk diffusion was confirmed by 18O tracer diffusion measurements by Isotope Exchange Depth Profiling via Secondary Ion Mass Spectrometry. Through the isolation of the bulk component of the overall conductivity change, it was possible to propose an oxygen vacancy defect mechanism for a-IGZO. To the author's knowledge, this is the first instance where in situ conductivity measurements (Brouwer analysis) has been successfully employed study the point defect chemistry in amorphous oxide (semi)conductor films, providing a complementary technique to ab initio calculations.
Adler, Alexander U.
NASA Astrophysics Data System (ADS)
All oxide thin film transistors (TFT) with indium gallium zinc oxide (IGZO) active layer were fabricated by chemical solution deposition (CSD) using aqueous solutions on glass substrate. Bottom source - drain and top gate electrodes were fabricated by thermal deposition technique. Source - drain channel length was patterned 120?m. (La0.5Y0.5)2O3 was used as gate dielectric. Polycrystalline growth of oxides IGZO was confirmed by grazing incidence X-ray diffraction, where as AFM shows nanostructured growth with smooth surface morphology. Current voltage (I-V) characteristics of all oxide TFT revealed very small leakage currents. It is found that (La0.5Y0.5)2O3 dielectric is a promising gate dielectrics and produce TFTs with improved performance and stability compared to polysilicon, La2O3 and Y2O3 gate insulators.
Mistry, Bhaumik V.; Mistry, Jaydeep; Trivedi, U. N.; Joshi, V. G.; Joshi, U. S.
NASA Astrophysics Data System (ADS)
A write-once-read-many-times (WORM) memory devices based on O2 plasma-treated indium gallium zinc oxide (IGZO) thin films has been demonstrated. The device has a simple Al/IGZO/Al structure. The device has a normally OFF state with a very high resistance (e.g., the resistance at 2 V is �109 ? for a device with the radius of 50 ?m) as a result of the O2 plasma treatment on the IGZO thin films. The device could be switched to an ON state with a low resistance (e.g., the resistance at 2 V is �103 ? for the radius of 50 ?m) by applying a voltage pulse (e.g., 10 V/1 ?s). The WORM device has good data-retention and reading-endurance capabilities.
Liu, P.; Chen, T. P.; Li, X. D.; Liu, Z.; Wong, J. I.; Liu, Y.; Leong, K. C.
NASA Astrophysics Data System (ADS)
Indium-gallium-zinc oxide (IGZO) and zinc-tin oxide (ZTO) are investigated for thin-film transistor (TFT) applications. Negative bias illumination stress (NBIS) is employed for electrical stability assessment. Unpassivated IGZO and ZTO TFTs suffer from severe NBIS instabilities. Zinc-tin-silicon oxide is found to be an effective passivation layer for IGZO and ZTO TFTs, significantly improving the NBIS stability. NBIS instabilities in unpassivated TFTs are attributed to an NBIS-induced desorption of chemisorbed oxygen from the channel layer top surface, exposing surface oxygen vacancies. A ZTSO layer protects the channel layer top surface from adsorbed gas interactions and also appears to reduce the density of oxygen vacancies. The best device architectures investigated with respect to TFT electrical performance are found to be staggered with aluminum electrodes for unpassivated TFTs and coplanar with ITO electrodes for ZTSO-passivated TFTs. Annealing in wet-O2 is not found to be effective for improving the performance of IGZO or ZTO TFTs or for reducing the post-deposition annealing temperature.
Hoshino, Ken
NASA Astrophysics Data System (ADS)
A novel floating-gate oxide semiconductor (FLOTOS) memory using a wide-band-gap indium-gallium-zinc oxide (IGZO) is presented for low-power system-on-panel applications. An IGZO thin-film-transistor (TFT) is used as a memory transistor for controlling read current as well as a switching transistor for storing charges in a storage capacitor (Cs). The FLOTOS memory is fabricated using a standard IGZO TFT process without any additional process or mask steps. The proposed precharge-assisted threshold voltage compensation technique makes it possible to realize an infinite number of write cycles and a low-power write operation with a bit-line voltage of 5 V. Furthermore, excellent data retention longer than 10 h is obtained at 60 �C even under the worst bias-stress condition of read operation with the ultra low off-state leakage (2.8�10-20 A/�m) of the IGZO TFTs, which is estimated to be smaller by more than 7 orders of magnitude than that of polycrystalline silicon TFTs.
Yamauchi, Yoshimitsu; Kamakura, Yoshinari; Isagi, Yousuke; Matsuoka, Toshimasa; Malotaux, Satoshi
NASA Astrophysics Data System (ADS)
We investigated the bias stress stability of solution-processed indium-gallium-zinc-oxide thin-film transistors (IGZO TFTs) using zinc-tin-oxide (ZTO) as the etch-stopper layer, the so-called dual-active-layered ZTO/IGZO TFT (DALZI TFT). The DALZI TFT can use a low-cost back-channel-etch structure because of the high chemical stability of the upper ZTO layer. The DALZI TFT exhibited only a threshold voltage shift of -1.86 V under negative bias illumination stress (NBIS) conditions (stress time = 1000 s), while the unpassivated IGZO TFT suffered from a threshold voltage shift of -19.59 V under NBIS conditions (stress time = 1000 s). The superior bias stress stability of the DALZI TFT is attributed not only to the densification effect by the multi-stacking process but also to the lower sensitivity to ambient gases (e.g., oxygen and water vapour) due to the low oxygen vacancy in the upper ZTO layer.
Kim, Chul Ho; Rim, You Seung; Kim, Hyun Jae
of the display industry as it moves from liquid crystal to organic light emitting diode technology and with requirements for larger areas and higher resolutions. A number of alternative material systems to a-Si:H have emerged, including organic semiconductors...
Flewitt, Andrew J.; Powell, M.J.
For an application to the channel layer in flexible transparent thin-film transistor (TFT), we have prepared the amorphous indium gallium zinc oxide (a-InGaZnO) thin films on unheated polyethylene naphthalate (PEN) substrate by facing target sputtering. Two types of a-InGaZnO TFT design, one top gate configuration and the other bottom gate, have been fabricated for comparison with each other. The experimental
Han Jae Shin; Dong Cheul Han; Young Cheol Choi; Do Kyung Lee
We demonstrated flexible ferroelectric gate thin-film transistors (Fe-TFTs) with ferroelectric polymer poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] and amorphous indium gallium zinc oxide (a-IGZO) channel on the polyethylene-naphthalate (PEN) substrate. First, we confirm basic ferroelectric properties of the P(VDF-TrFE) film on the PEN substrate with various bending radius. Next, we fabricated Fe-TFTs with Al\\/120 nm-P(VDF-TrFE)\\/40 nm-IGZO top gate structure. Excellent electrical characteristics are
Gwang-Geun Lee; Eisuke Tokumitsu; Sung-Min Yoon; Yoshihisa Fujisaki; Joo-Won Yoon; Hiroshi Ishiwara
Visible-light-induced instability in amorphous metal-oxide based TFTs for transparent electronics
NASA Astrophysics Data System (ADS)
We investigate the origin of visible-light-induced instability in amorphous metal-oxide based thin film transistors (oxide-TFTs) for transparent electronics by exploring the shift in threshold voltage (Vth). A large hysteresis window in amorphous indium-gallium-zinc-oxide (a-IGZO) TFTs possessing large optical band-gap (?3 eV) was observed in a visible-light illuminated condition whereas no hysteresis window was shown in a dark measuring condition. We also report the instability caused by photo irradiation and prolonged gate bias stress in oxide-TFTs. Larger Vth shift was observed after photo-induced stress combined with a negative gate bias than the sum of that after only illumination stress and only negative gate bias stress. Such results can be explained by trapped charges at the interface of semiconductor/dielectric and/or in the gate dielectric which play a role in a screen effect on the electric field applied by gate voltage, for which we propose that the localized-states-assisted transitions by visible-light absorption can be responsible.
Ha, Tae-Jun
We have investigated the effect of hydrogen peroxide (H2O2) on negative bias stress (NBS) stability of solution-processed amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistors (TFTs). The instability of solution-processed a-IGZO TFTs under NBS is attributed to intrinsic oxygen vacancy defects (Vo) and organic chemical-induced defects, such as pores, pin holes, and organic residues. In this respect, we added H2O2 into an indium-gallium-zinc oxide solution to reduce the defects without any degradation of electrical performance. The field-effect mobility and sub-threshold slope of the a-IGZO TFTs were improved from 0.37 cm(2) V(-1) s(-1) and 0.86 V/dec to 0.97 cm(2) V(-1) s(-1) and 0.58 V/dec, respectively. Furthermore, the threshold voltage shift under NBS was dramatically decreased from -3.73 to -0.18 V. These results suggest that H2O2 effectively reduces Vo through strong oxidation and minimizes organic chemical-induced defects by eliminating the organic chemicals at lower temperatures compared to a conventional solution process. PMID:24503476
Kwon, Jeong Moo; Jung, Joohye; Rim, You Seung; Kim, Dong Lim; Kim, Hyun Jae
AC Stress-Induced Degradation of Amorphous InGaZnO Thin Film Transistor Inverter
NASA Astrophysics Data System (ADS)
The degradation of amorphous indium-gallium-zinc-oxide (a-IGZO) thin film transistor (TFT) inverter operation is investigated under AC pulse stresses. From the extraction of subgap density of states (DOSs), the dominant mechanism of the pulse stress-induced degradation of driver TFT is considered as the increase of acceptor-like deep states, while that of the load TFT is attributed to the increased number of electrons trapped into the interface and/or a-IGZO thin films. We also observe that the rising and falling time of the induced pulse affects each TFT of the inverter in a different manner, and discuss the related mechanism of this phenomenon.
Kim, Dae-Hwan; Kong, Dongsik; Kim, Sungchul; Jeon, Young Woo; Kim, Yongsik; Kim, Dong Myong; Kwon, Hyuck-In
NASA Astrophysics Data System (ADS)
Amorphous indium-gallium-zinc oxide (IGZO) transparent conductive thin films are prepared on glass substrates by radio frequency (RF) magnetron sputtering. The effects of seven factors, which are substrate temperature, sputtering atmosphere, working pressure, sputtering power, annealing temperature, negative bias voltage and sputtering time, on Hall mobility, transmittance and surface roughness are studied through orthogonal experiments. The results show that the effects of working pressure, substrate temperature and sputtering atmosphere on performance of films are the most prominent. According to the experimental results and discussion, relatively reasonable process parameters are obtained, which are working pressure of 0.35 Pa, substrate temperature of 200 �C, sputtering atmosphere of Ar, sputtering power of 125 W, sputtering time of 30 min, negative bias voltage of 0 V and annealing temperature of 300 �C.
Niu, Jian-wen; Ma, Rui-xin; Wang, Yuan-yuan; Li, Shi-na; Cheng, Shi-yao; Liu, Zi-lin
NASA Astrophysics Data System (ADS)
We investigated the effect of surface roughness on the electrical characteristics in amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistors (TFTs) fabricating high-? Sm2O3 gate dielectrics, prepared under different annealing temperatures. The high-? Sm2O3 a-IGZO TFT device annealed at 200 �C exhibited better electrical characteristics, including a large field effect mobility of 6.25 cm2/V s, small threshold voltage of 0.79 V, low subthreshold swing of 354 mV/decade, and high Ion/Ioff ratio of 3.1�107. These results are attributed to the formation of smooth surface at the oxide/channel interface. Furthermore, the reliability of a Sm2O3 a-IGZO TFT device can be improved by oxygen annealing at low temperature.
Chen, Fa-Hsyang; Hung, Meng-Ning; Yang, Jui-Fu; Kuo, Shou-Yi; Her, Jim-Long; Matsuda, Yasuhiro H.; Pan, Tung-Ming
NASA Astrophysics Data System (ADS)
Thin-film transistors (TFTs) were fabricated using amorphous indium gallium zinc oxide (a-IGZO) channels by rf-magnetron sputtering at room temperature. The conductivity of the a-IGZO films was controlled from �10-3to10-6Scm-1 by varying the mixing ratio of sputtering gases, O2/(O2+Ar), from �3.1% to 3.7%. The top-gate-type TFTs operated in n-type enhancement mode with a field-effect mobility of 12cm2V-1s-1, an on-off current ratio of �108, and a subthreshold gate voltage swing of 0.2Vdecade-1. It is demonstrated that a-IGZO is an appropriate semiconductor material to produce high-mobility TFTs at low temperatures applicable to flexible substrates by a production-compatible means.
Yabuta, Hisato; Sano, Masafumi; Abe, Katsumi; Aiba, Toshiaki; Den, Tohru; Kumomi, Hideya; Nomura, Kenji; Kamiya, Toshio; Hosono, Hideo
NASA Astrophysics Data System (ADS)
We demonstrate a significant improvement in various electrical instabilities of amorphous indium gallium zinc oxide (a-IGZO) thin film transistor (TFT) by implanting Au nanoparticles (NPs) on the a-IGZO back-channel. This TFT showed the enhanced stability of threshold voltage (Vth) under ambient humidity, illumination stress, and a-IGZO thickness variation tests. Application of back-channel Au NPs to a-IGZO TFT is regarded to control the surface potential, to lead reversible carrier trap/injection, and to increase incident UV light absorption by local surface plasmon. Au NPs are formed by e-beam evaporation, and therefore, this technique can be applicable to the TFT manufacturing process.
Cho, Byungsu; Lee, Jaesang; Seo, Hyungtak; Jeon, Hyeongtag
Self-assembled monolayers (SAMs) have been used to improve both the positive and negative bias-stress stability of amorphous indium gallium zinc oxide (IGZO) bottom gate thin film transistors (TFTs). N-hexylphosphonic acid (HPA) and fluorinated hexylphosphonic acid (FPA) SAMs adsorbed on IGZO back channel surfaces were shown to significantly reduce bias stress turn-on voltage shifts compared to IGZO back channel surfaces with no SAMs. FPA was found to have a lower surface energy and lower packing density than HPA, as well as lower bias stress turn-on voltage shifts. The improved stability of IGZO TFTs with SAMs can be primarily attributed to a reduction in molecular adsorption of contaminants on the IGZO back channel surface and minimal trapping states present with phosphonic acid binding to the IGZO surface.
Du, Xiaosong; Motley, Joshua R; Stickle, William F; Bluhm, Hendrik; Herman, Gregory S
Nontraditional Amorphous Oxide Semiconductor Thin-Film Transistor Fabrication
NASA Astrophysics Data System (ADS)
Fabrication techniques and process integration considerations for amorphous oxide semiconductor (AOS) thin-film transistors (TFTs) constitute the central theme of this dissertation. Within this theme three primary areas of focus are pursued. The first focus involves formulating a general framework for assessing passivation. Avoiding formation of an undesirable backside accumulation layer in an AOS bottom-gate TFT is accomplished by (i) choosing a passivation layer in which the charge neutrality level is aligned with (ideal case) or higher in energy than that of the semiconductor channel layer charge neutrality level, and (ii) depositing the passivation layer in such a manner that a negligible density of oxygen vacancies are present at the channel-passivation layer interface. Two AOS TFT passivation schemes are explored. Sputter-deposited zinc tin silicon oxide (ZTSO) appears promising for suppressing the effects of negative bias illumination stress (NBIS) with respect to ZTO and IGZO TFTs. Solution-deposited silicon dioxide is used as a barrier layer to subsequent PECVD silicon dioxide deposition, yielding ZTO TFT transfer curves showing that the dual-layer passivation process does not significantly alter ZTO TFT electrical characteristics. The second focus involves creating an adaptable back-end process compatible with flexible substrates. A detailed list of possible via formation techniques is presented with particular focus on non-traditional and adaptable techniques. Two of the discussed methods, �hydrophobic surface treatment�and �printed local insulator,� are demonstrated and proven effective. The third focus is printing AOS TFT channel layers in order to create an adaptable and additive front-end integrated circuit fabrication scheme. Printed zinc indium aluminum oxide (ZIAO) and indium gallium zinc oxide (IGZO) channel layers are demonstrated using a SonoPlot piezoelectric printing system. Finally, challenges associated with printing electronic materials are discussed. Organic-based solutions are easier to print due to their ability to �stick� to the substrate and form well-defined patterns, but have poor electrical characteristics due to the weakness of organic bonds. Inorganic aqueous-based solutions demonstrate good electrical performance when deposited by spin coating, but are difficult to print because precise control of a substrate's hydrophillic/hydrophobic nature is required. However, precise control is difficult to achieve, since aqueous-based solutions either spread out or ball up on the substrate surface. Thickness control of any printed solution is always problematic due to surface wetting and the elliptical thickness profile of a dispensed solution.
Sundholm, Eric Steven
NASA Astrophysics Data System (ADS)
The present five masks bottom gate and staggered amorphous silicon (a-Si) thin-film transistor (TFT) process flow is not suitable for indium-gallium-zinc-oxide (IGZO) TFT because of its vulnerability to post etching process during the source/drain pattern. Bottom gate and coplanar IGZO TFTs were made feasible through the reverse of second (channel layer) and third (source/drain electrodes) masks process flow to avoid etching damage problem. Besides, the post IGZO nitrous oxygen (N2O) plasma treatment was employed to improve the stress instability. On the basis of secondary ion mass spectrometry (SIMS) and X-ray spectroscopy (XPS) results, it is believed that the post N2O plasma treatment passivates the interface states and converts the inhomogeneous and low quality IGZO to the homogeneous and high quality IGZO. In the end, a 5-in. IGZO active-matrix liquid crystal display was demonstrated via five masks bottom gate and coplanar TFT configuration.
Hung, Ming-Chin; Hsiao, Hsia-Tsai; Lin, Wei-Ting; Tu, Chun-Hao; Chang, Jiun-Jye; Chen, Po-Lun
NASA Astrophysics Data System (ADS)
We demonstrated flexible ferroelectric gate thin-film transistors (Fe-TFTs) with ferroelectric polymer poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] and amorphous indium gallium zinc oxide (a-IGZO) channel on the polyethylene-naphthalate (PEN) substrate. First, we confirm basic ferroelectric properties of the P(VDF-TrFE) film on the PEN substrate with various bending radius. Next, we fabricated Fe-TFTs with Al/120 nm-P(VDF-TrFE)/40 nm-IGZO top gate structure. Excellent electrical characteristics are demonstrated and nonvolatile memory function was confirmed with a memory window of 8.4 V. A subthreshold voltage swing of 400 mV/decade, Ion/Ioff ratio of more than 107 and the field-effect mobility of �1 cm2/Vs were obtained.
Lee, Gwang-Geun; Tokumitsu, Eisuke; Yoon, Sung-Min; Fujisaki, Yoshihisa; Yoon, Joo-Won; Ishiwara, Hiroshi
NASA Astrophysics Data System (ADS)
The quantitative analysis of mechanism on negative bias illumination stress (NBIS)-induced instability of amorphous indium-tin-zinc-oxide thin-film transistor (TFT) was suggested along with the effect of equivalent oxide thickness (EOT) of gate insulator. The analysis was implemented through combining the experimentally extracted density of subgap states and the device simulation. During NBIS, it was observed that the thicker EOT causes increase in both the shift of threshold voltage and the variation of subthreshold swing as well as the hump-like feature in a transfer curve. We found that the EOT-dependence of NBIS instability can be clearly explicated with the donor creation model, in which a larger amount of valence band tail states is transformed into either the ionized oxygen vacancy VO2+ or peroxide O22- with the increase of EOT. It was also found that the VO2+-related extrinsic factor accounts for 80%-92% of the total donor creation taking place in the valence band tail states while the rest is taken by the O22- related intrinsic factor. The ratio of extrinsic factor compared to the total donor creation also increased with the increase of EOT, which could be explained by more prominent oxygen deficiency. The key founding of our work certainly represents that the established model should be considered very effective for analyzing the instability of the post-indium-gallium-zinc-oxide (IGZO) ZnO-based compound semiconductor TFTs with the mobility, which is much higher than those of a-IGZO TFTs.
Jang, Jaeman; Kim, Dae Geun; Kim, Dong Myong; Choi, Sung-Jin; Lim, Jun-Hyung; Lee, Je-Hun; Kim, Yong-Sung; Ahn, Byung Du; Kim, Dae Hwan
NASA Astrophysics Data System (ADS)
The growing field of large-area flexible electronics presents the need for amorphous materials with electrical performances superior to amorphous hydrogenated silicon (a-Si:H). Metal oxide semiconductors show great promise in thin film transistors (TFTs) due to their high electron mobility (micro, 1--100 cm2V-1s-1), mechanical flexibility, and electrical stability. However, most oxide semiconductor fabrication still relies on expensive, inflexible and energy intensive vacuum deposition methods. To overcome these limitations, my thesis work has focused on developing low-temperature solution processing routes to functional metal oxide materials. In Chapter 2, we demonstrate an optimized "ink" and printing process for inkjet patterning of amorphous indium gallium zinc oxide (a-IGZO) and investigate the effects of device structure on derived electron mobility. Bottom-gate top-contact (BGTC) TFTs are fabricated and shown to exhibit electron mobilities comparable to a-Si:H. Furthermore, a record micro of 2.5 cm 2V-1s-1 is demonstrated for bottom-gate bottom-contact (BGBC) TFTs. The mechanism underlying such impressive performance is investigated using transmission line techniques, and it is shown that the semiconductor-source/drain electrode interface contact resistance is nearly an order of magnitude lower for BGBC transistors versus BGTC devices. In Chapter 3, we report the implementation of amorphous indium yttrium oxide (a-IYO) as a TFT semiconductor for the first time. Amorphous and polycrystalline IYO films are grown via a low-temperature solution process utilizing exothermic "combustion" precursors. Precursor transformation and the IYO films are analyzed by DTA, TGA, XRD, AFM, XPS, and optical transmission, revealing efficient conversion to the metal-oxide lattice, and smooth, transparent films. a-IYO TFTs fabricated with a hybrid nanodielectric exhibit impressive electron mobilities of 7.3 cm2V-1s-1 (Tanneal = 300 �C) and 5.0 cm2V-1s -1 (Tanneal = 250 �C) for 2 V operation. Finally, Chapter 4 examines the role of the strong oxygen binding cation, known as the "oxygen getter" in quaternary metal oxide semiconductors. We present a systematic structural and electrical study of the carrier suppression role of gallium, scandium, yttrium, and lanthanum when introduced into IZO. We conclude that metal oxide lattice energy (HL) and metal ionic radius are the best predictors of the efficacy of an oxygen getter in IXZO and only Ga acts effectively in this role.
Hennek, Jonathan W.
High mobility amorphous zinc oxynitride semiconductor material for thin film transistors
Zinc oxynitride semiconductor material is produced through a reactive sputtering process in which competition between reactions responsible for the growth of hexagonal zinc oxide (ZnO) and for the growth of cubic zinc nitride (Zn{sub 3}N{sub 2}) is promoted. In contrast to processes in which the reaction for either the oxide or the nitride is dominant, the multireaction process yields a substantially amorphous or a highly disordered nanocrystalline film with higher Hall mobility, 47 cm{sup 2} V{sup -1} s{sup -1} for the as-deposited film produced at 50 deg. C and 110 cm{sup 2} V{sup -1} s{sup -1} after annealing at 400 deg. C. In addition, it has been observed that the Hall mobility of the material increases as the carrier concentration decreases in a carrier concentration range where a multicomponent metal oxide semiconductor, indium-gallium-zinc oxide, follows the opposite trend. This indicates that the carrier transports in the single-metal compound and the multimetal compound are probably dominated by different mechanisms. Film stability and thin film transistor performance of the material have also been tested, and results are presented herein.
Ye Yan; Lim, Rodney; White, John M. [Display and SunFab Solar Business Group, Applied Materials, Santa Clara, California 95054 (United States)
Deep-level transient spectroscopy on an amorphous InGaZnO4 Schottky diode
NASA Astrophysics Data System (ADS)
The first direct measurement is reported of the bulk density of deep states in amorphous IGZO (indium-gallium-zinc oxide) semiconductor by means of deep-level transient spectroscopy (DLTS). The device under test is a Schottky diode of amorphous IGZO semiconductor on a palladium (Pd) Schottky-barrier electrode and with a molybdenum (Mo) Ohmic contact at the top. The DLTS technique allows to independently measure the energy and spatial distribution of subgap states in the IGZO thin film. The subgap trap concentration has a double exponential distribution as a function energy, with a value of �1019 cm-3 eV-1 at the conduction band edge and a value of �1017 cm-3 eV-1 at an energy of 0.55 eV below the conduction band. Such spectral distribution, however, is not uniform through the semiconductor film. The spatial distribution of subgap states correlates well with the background doping density distribution in the semiconductor, which increases towards the Ohmic Mo contact, suggesting that these two properties share the same physical origin.
Chasin, Adrian; Simoen, Eddy; Bhoolokam, Ajay; Nag, Manoj; Genoe, Jan; Gielen, Georges; Heremans, Paul
deposition (PECVD) [6], hydrogen plasma treatment [7][9], or argon plasma treatment [10]. How- ever. The oxygen vacancies in the S/D regions caused by argon plasma treatment will decrease after thermal for a-IGZO TFTs with S/D regions formed by argon or hydrogen plasma treatments [6]. In this letter, self
of one enhancement-mode TFT using gold Au as floating gate and one depletion-mode TFT using calcium Ca of threshold voltage adjusting by varying thickness. However, the depletion-mode thin film transistor TFT using as the dielectric. A 35-nm- thick active layer of a-IGZO was deposited by radio- frequency sputtering onto Si
Fabrication of amorphous InGaZnO thin-film transistor-driven flexible thermal and pressure sensors
NASA Astrophysics Data System (ADS)
In this work, we present the results concerning the use of amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistor (TFT) as a driving transistor of the flexible thermal and pressure sensors which are applicable to artificial skin systems. Although the a-IGZO TFT has been attracting much attention as a driving transistor of the next-generation flat panel displays, no study has been performed about the application of this new device to the driving transistor of the flexible sensors yet. The proposed thermal sensor pixel is composed of the series-connected a-IGZO TFT and ZnO-based thermistor fabricated on a polished metal foil, and the ZnO-based thermistor is replaced by the pressure sensitive rubber in the pressure sensor pixel. In both sensor pixels, the a-IGZO TFT acts as the driving transistor and the temperature/pressure-dependent resistance of the ZnO-based thermistor/pressure-sensitive rubber mainly determines the magnitude of the output currents. The fabricated a-IGZO TFT-driven flexible thermal sensor shows around a seven times increase in the output current as the temperature increases from 20 �C to 100 �C, and the a-IGZO TFT-driven flexible pressure sensors also exhibit high sensitivity under various pressure environments.
Park, Ick-Joon; Jeong, Chan-Yong; Cho, In-Tak; Lee, Jong-Ho; Cho, Eou-Sik; Kwon, Sang Jik; Kim, Bosul; Cheong, Woo-Seok; Song, Sang-Hun; Kwon, Hyuck-In
NASA Astrophysics Data System (ADS)
The influence of radio frequency (RF) power on the properties of magnetron sputtered amorphous indium gallium zinc oxide (a-IGZO) thin films and the related thin-film transistor (TFT) devices is investigated comprehensively. A series of a-IGZO thin films prepared with magnetron sputtering at various RF powers are examined. The results prove that the deposition rate sensitively depends on RF power. In addition, the carrier concentration increases from 0.91 � 1019 to 2.15 � 1019 cm-3 with the RF power rising from 40 to 80 W, which may account for the corresponding decrease in the resistivity of the a-IGZO thin films. No evident impacts of RF power are observed on the surface roughness, crystalline nature and stoichiometry of the a-IGZO samples. On the other hand, optical transmittance is apparently influenced by RF power where the extracted optical band-gap value increases from 3.48 to 3.56 eV with RF power varying from 40 to 80 W, as is supposed to result from the carrier-induced band-filling effect. The rise in RF power can also affect the performance of a-IGZO TFTs, in particular by increasing the field-effect mobility clearly, which is assumed to be due to the alteration of the extended states in a-IGZO thin films.
Junfei, Shi; Chengyuan, Dong; Wenjun, Dai; Jie, Wu; Yuting, Chen; Runze, Zhan
Amorphous mixed metal oxides are emerging as high performance semiconductors for thin film transistor (TFT) applications, with indium gallium zinc oxide, InGaZnO (IGZO), being one of the most widely studied and best performing systems. Here, we investigate alkaline earth (barium or strontium) doped InBa(Sr)ZnO as alternative, semiconducting channel layers and compare their performance of the electrical stress stability with IGZO. In films fabricated by solution-processing from metal alkoxide precursors and annealed to 450 �C we achieve high field-effect electron mobility up to 26 cm2 V�1 s�1. We show that it is possible to solution-process these materials at low process temperature (225�200 �C yielding mobilities up to 4.4 cm2 V�1 s�1) and demonstrate a facile �ink-on-demand� process for these materials which utilizes the alcoholysis reaction of alkyl metal precursors to negate the need for complex synthesis and purification protocols. Electrical bias stress measurements which can serve as a figure of merit for performance stability for a TFT device reveal Sr- and Ba-doped semiconductors to exhibit enhanced electrical stability and reduced threshold voltage shift compared to IGZO irrespective of the process temperature and preparation method. This enhancement in stability can be attributed to the higher Gibbs energy of oxidation of barium and strontium compared to gallium. PMID:24511184
Agile micro- and nano-fluidic control is critical to numerous life science and chemical science synthesis as well as kinetic and thermodynamic studies. To this end, we have demonstrated the use of thin film transistor arrays as an active matrix addressing method to control an electrofluidic array. Because the active matrix method minimizes the number of control lines necessary (m + n lines for the m�n element array), the active matrix addressing method integrated with an electrofluidic platform can be a significant breakthrough for complex electrofluidic arrays (increased size or resolution) with enhanced function, agility and programmability. An amorphous indium gallium zinc oxide (a-IGZO) semiconductor active layer is used because of its high mobility of 1-15 cm(2) V(-1) s(-1), low-temperature processing and transparency for potential spectroscopy and imaging. Several electrofluidic functionalities are demonstrated using a simple 2 � 5 electrode array connected to a 2 � 5 IGZO thin film transistor array with the semiconductor channel width of 50 ?m and mobility of 6.3 cm(2) V(-1) s(-1). Additionally, using the TFT device characteristics, active matrix addressing schemes are discussed as the geometry of the electrode array can be tailored to act as a storage capacitor element. Finally, requisite material and device parameters are discussed in context with a VGA scale active matrix addressed electrofluidic platform. PMID:22134753
Noh, Joo Hyon; Noh, Jiyong; Kreit, Eric; Heikenfeld, Jason; Rack, Philip D
Agile micro- and nano-fluidic control is critical to numerous life science and chemical science synthesis as well as kinetic and thermodynamic studies. To this end, we have demonstrated the use of thin film transistor arrays as an active matrix addressing method to control an electrofluidic array. Because the active matrix method minimizes the number of control lines necessary (m + n lines for the m x n element array), the active matrix addressing method integrated with an electrofluidic platform can be a significant breakthrough for complex electrofluidic arrays (increased size or resolution) with enhanced function, agility and programmability. An amorphous indium gallium zinc oxide (a-IGZO) semiconductor active layer is used because of its high mobility of 1-15 cm{sup 2} V{sup -1} s{sup -1}, low-temperature processing and transparency for potential spectroscopy and imaging. Several electrofluidic functionalities are demonstrated using a simple 2 x 5 electrode array connected to a 2 x 5 IGZO thin film transistor array with the semiconductor channel width of 50 {mu}m and mobility of 6.3 cm{sup 2} V{sup -1} s{sup -1}. Additionally, using the TFT device characteristics, active matrix addressing schemes are discussed as the geometry of the electrode array can be tailored to act as a storage capacitor element. Finally, requisite material and device parameters are discussed in context with a VGA scale active matrix addressed electrofluidic platform.
Noh, Joo Hyon [University of Tennessee, Knoxville (UTK); Noh, Jiyong [University of Tennessee, Knoxville (UTK); Kreit, Eric [University of Cincinnati; Heikenfeld, Jason [University of Cincinnati; Rack, Philip D [ORNL
Metal-oxide complementary inverters with a vertical geometry fabricated on flexible substrates
NASA Astrophysics Data System (ADS)
We report on the fabrication of p-channel thin film transistors (TFTs) and vertically stacked complementary inverters comprised of a p-channel copper oxide TFT on top of an n-channel indium gallium zinc oxide TFT fabricated on a flexible polyethersulfone substrate. The p- and n-channel TFTs showed saturation mobility values of 0.0022 and 1.58 cm2/Vs, respectively, yielding inverters with a gain of 120 V/V. This level of performance was achieved by reducing the copper oxide channel thickness, allowing oxygen diffusion into the copper oxide layer at medium processing temperature (150 �C).
Dindar, A.; Kim, J. B.; Fuentes-Hernandez, C.; Kippelen, B.
Facile encapsulation of oxide based thin film transistors by atomic layer deposition based on ozone.
A simplified encapsulation strategy for metal-oxide based TFTs, using ozone instead of water as an oxygen source in a low-temperature ALD process is demonstrated. Thereby, the threshold voltage remains unaltered and the hysteresis is permanently reduced. Costly energy- and time-consuming post-treatment processes can be avoided. This concept is widely applicable to various encapsulation materials (e.g., Al2 O3 , TiO2 , ZrO2 ) and metal-oxide channel semiconductors (e.g., zinc-tin-oxide (ZTO), indium-gallium-zinc-oxide (IGZO)). PMID:23592395
Fakhri, Morteza; Babin, Nikolai; Behrendt, Andreas; Jakob, Timo; G�rrn, Patrick; Riedl, Thomas
Amorphous manganese oxide remains amorphous upon lithium intercalation and cycling
Lithium intercalation in amorphous manganese oxide, synthesized by a room temperature aqueous oxidation route, is analyzed. As reported before, the material yields a very high intercalation capacity and also shows promising rate capability as cathode for rechargeable lithium batteries. The present study investigates the structure of the material using X-ray powder diffraction conducted on composite cathode pellets at different stages
Xu Jun John; Ye Hui; Jain Gaurav; Yang Jingsi
NASA Astrophysics Data System (ADS)
Flexible electronics is an emerging next-generation technology that offers many advantages such as light weight, durability, comfort, and flexibility. These unique features enable many new applications such as flexible display, flexible sensors, conformable electronics, and so forth. For decades, a variety of flexible substrates have been demonstrated for the application of flexible electronics. Most of them are plastic films and metal foils so far. For the fundamental device of flexible circuits, thin film transistors (TFTs) using poly silicon, amorphous silicon, metal oxide and organic semiconductor have been successfully demonstrated. Depending on application, low-cost and disposable flexible electronics will be required for convenience. Therefore it is important to study inexpensive substrates and to explore simple processes such as printing technology. In this thesis, paper is introduced as a new possible substrate for flexible electronics due to its low-cost and renewable property, and amorphous indium gallium zinc oxide (a-IGZO) TFTs are realized as the promising device on the paper substrate. The fabrication process and characterization of a-IGZO TFT on the paper substrate are discussed. a-IGZO TFTs using a polymer gate dielectric on the paper substrate demonstrate excellent performances with field effect mobility of �20 cm2 V-1 s-1, on/off current ratio of �106, and low leakage current, which show the enormous potential for flexible electronics application. In order to complement the n-channel a-IGZO TFTs and then enable complementary metal-oxide semiconductor (CMOS) circuit architectures, cuprous oxide is studied as a candidate material of p-channel oxide TFTs. In this thesis, a printing process is investigated as an alternative method for the fabrication of low-cost and disposable electronics. Among several printing methods, a modified offset roll printing that prints high resolution patterns is presented. A new method to fabricate a high resolution printing plate is investigated and the most favorable condition to transfer ink from a blanket to a cliche is studied. Consequently, a high resolution cliche is demonstrated and the printed patterns of 10mum width and 6mum line spacing are presented. In addition, the top gate a-IGZO TFTs with channel width/length of 12/6mum is successfully demonstrated by printing etch-resists. This work validates the compatibility of a-IGZO TFT on paper substrate for the disposable microelectronics application and presents the potential of low-cost and high resolution printing technology.
Choi, Nack-Bong
Trap States of the Oxide Thin Film Transistor
NASA Astrophysics Data System (ADS)
We investigated the temperature dependent recovery of the threshold voltage shift observed in both ZnO and indium gallium zinc oxide (IGZO) thin film transistors (TFTs) after application of gate bias and light illumination. Two types of recovery were observed for both the ZnO and IGZO TFTs; low temperature recovery (below 110 �C) which is attributed to the trapped charge and high temperature recovery (over 110 �C) which is related to the annihilation of trap states generated during stresses. From a comparison study of the recovery rate with the analysis of hydrogen diffusion isochronal annealing, a similar behavior was observed for both TFT recovery and hydrogen diffusion. This result suggests that hydrogen plays an important role in the generation and annihilation of trap states in oxide TFTs under gate bias or light illumination stresses.
Yu, Kyeong Min; Yuh, Jin Tae; Park, Sang Hee Ko; Ryu, Min Ki; Yun, Eui Jung; Bae, Byung Seong
Amorphous indium�gallium�zinc-oxide (a-IGZO) thin films were prepared using the facing targets sputtering (FTS) method as a function of input power at room temperature. The a-IGZO films were used a channel layer for thin film transistors (TFTs). The electrical, optical, and structural properties of a-IGZO thin films were measured by Hall Effect measurement, UV\\/vis spectrometer and X-ray diffractometer. The performance and
Yu Sup Jung; Kyu Ho Lee; Woo-Jae Kim; Won-Jae Lee; Hyung-Wook Choi; Kyung Hwan Kim
Octahedra's packing in bulk amorphous tungsten oxides
The local and medium range order in amorphous tungsten oxides has been investigated by anomalous wide-angle X-ray scattering (AWAXS). Amorphous phases have been prepared for the first time by non-reactive grinding, from both WO3 pyrochlore-type structure which is metastable, and WO3 � 1H2O hydrate. The AWAXS study is based on measurements performed at the L2 W edge. A differential analysis
S. Laruelle; M. Figlarz; B. Bouchet-Fabre
Catalytic oxidation of an amorphous carbon black
The oxidation of an amorphous carbon black in the presence of a potassium-copper-vanadium catalyst supported on [alpha]-alumina has been studied. Burnoff temperatures in the presence of catalyst were lowered by about 300 K with respect to those for uncatalyzed combustion. Cycles of temperature-programmed reduction and oxidation, along with TG-MS analyses demonstrated that a redox mechanism is at the basis of the catalyst strong activity. A differential flow reactor was employed to perform kinetic tests. The progress of the catalytic combustion process was followed measuring the concentrations of carbon oxides in the product stream at the reactor outlet with on-line NDIR analyzers. The dependence of the reaction rate on the relevant variables was investigated. In particular, the apparent activation energy for the catalytic oxidation was found to be less than half that of the corresponding uncatalyzed process, while the carbon reactivity showed a linear dependence upon the amount of catalyst and a square root dependence upon the oxygen partial pressure. The results allowed the formulation of a mechanism for the catalytic oxidation of carbon black and suggest that the limiting step of the overall process is that of catalyst reduction. On the basis of such findings a kinetic equation for catalytic carbon black oxidation is proposed.
Ciambelli, P.; D'Amore, M.; Palma, V.; Vaccaro, S. (Univ. di Salerno (Italy). Dipt. di Ingegneria Chimia e Alimentare Univ. di Napoli (Italy). Dipt. di Chimica)
NASA Astrophysics Data System (ADS)
This dissertation is focused on the development of thin film transistors (TFTs) using oxide materials composed of post-transitional cations with (n-1)d 10ns0 (n?4). The goal is to achieve high performance oxide-based TFTs fabricated at low processing temperature on either glass or flexible substrates for next generation display applications. In addition, etching mechanism and Ohmic contact formation for oxide heterostructure (ZnO/CuCrO 2) system is demonstrated. The deposition and characterization of oxide semiconductors (In 2O3-ZnO, and InGaZnO4) using a RF-magnetron sputtering system are studied. The main influence on the resistivity of the films is found to be the oxygen partial pressure in the sputtering ambient. The films remained amorphous and transparent (> 70%) at all process conditions. These films showed good transmittance at suitable conductivity for transistor fabrication. The electrical characteristics of both top- and bottom-gate type Indium Zinc Oxide (InZnO) and Indium Gallium Zinc Oxide (InGaZnO4)-based TFTs are reported. The InZnO films were favorable for depletion-mode TFTs due to their tendency to form oxygen vacancies, while enhancement-mode devices were realized with InGaZnO4 films. The InGaZnO4-based TFTs fabricated on either glass or plastic substrates at low temperature (<100�C) exhibit good electrical properties: the saturation mobility of 5--12 cm2.V-1.s-1 and threshold voltage of 0.5--2.5V. The devices are also examined as a function of aging time in order to verify long-term stability in air. The effect of gate dielectric materials on electrical properties of InGaZnO 4-based TFTs was investigated. The use of SiNx film as a gate dielectric reduces the trap density and the roughness at the channel/gate dielectric interface compared to SiO2 gate dielectric, resulting in an improvement of device parameters by reducing scattering of trapped charges at the interface. The quality of interface is shown to have large effect on TFT performance. Plasma etching process of ZnO was carried out using a variety of plasma chemistries: CH4/H2-, C2H6/H 2-, Cl2-, IBr-, ICl-, BI3- and BBr3/Ar. High fidelity pattern transfer can be achieved with practical etch rate and very smooth surface in methane-based chemistries, although the sidewall is not completely vertical. Threshold energy as low as 60 +/- 20 eV for all plasma chemistries was achieved, confirming that etching is driven by ion-assisted mechanism over the whole range of ion energy. Ohmic contacts to p-CuCrO2 are examined using borides (CrB2 and W2B5), nitrides (TaN and ZrN) and a high temperature metal (Ir). These materials are used as a diffusion barrier in Ni/Au based contacts, i.e., Ni/Au/X/Ti/Au metallization scheme, where X is the refractory material. A minimum specific contact resistance of � 5x10 -4 O.cm2 was achieved for the Ir-containing contacts after annealing at temperature of 500--800�C for 60s in O2 ambient. The presence of Ir diffusion barrier increase the thermal stability of the contacts by � 200 �C compared to conventional Ni/Au contacts. By sharp contrast, the use of other refractory materials led to the poorer thermal stability, with the contact resistance increasing sharply above 400�C.
Lim, Wantae
Amorphous copper tungsten oxide with tunable band gaps
We report on the synthesis of amorphous copper tungsten oxide thin films with tunable band gaps. The thin films are synthesized by the magnetron cosputtering method. We find that due to the amorphous nature, the Cu-to-W ratio in the films can be varied without the limit of the solubility (or phase separation) under appropriate conditions. As a result, the band
Le Chen; Sudhakar Shet; Houwen Tang; Kwang-Soon Ahn; Heli Wang; Yanfa Yan; John Turner; Mowafak Al-Jassim
Natural realgar and amorphous AsS oxidation kinetics
The oxidation rates of natural realgar and amorphous synthetic AsS by dissolved oxygen were evaluated using mixed flow reactors at pH 7.2 to 8.8 and dissolved oxygen contents of 5.9 to 16.5 ppm over a temperature range of 25 to 40�C. The ratios of As\\/S are stoichiometric for all amorphous AsS oxidation experiments except for two experiments conducted at pH
Maggy F. Lengke; Regina N. Tempel
NASA Astrophysics Data System (ADS)
This study investigates the suppressed negative gate bias illumination stress (NBIS) -induced instability of via-type amorphous indium-gallium-zinc-oxide (a-IGZO) thin film transistors (TFTs) with fringe field (FF) structures. The less negative threshold voltage shifts of devices after NBIS are showed when device has larger FF structures. This finding is attributed to more dispersive distribution of photo-generated holes in the width direction of a-IGZO during NBIS, which reduce the hole trapping phenomenon in the front channel interface. The a-IGZO TFT with FF structure is expected to be an effective method to increase the electrical reliability of devices after NBIS.
Chen, Yu-Chun; Chang, Ting-Chang; Li, Hung-Wei; Hsieh, Tien-Yu; Chen, Te-Chih; Wu, Chang-Pei; Chou, Cheng-Hsu; Chung, Wang-Cheng; Chang, Jung-Fang; Tai, Ya-Hsiang
Comparison of electrochromic amorphous and crystalline tungsten oxide films
A detailed systematic study of the tungsten oxide thin films has been carried out using WO3 films after they were annealed at progressively increasing temperatures ranging from 350�C to 450�C in oxygen environments. The structural properties of the films were characterized using X-ray diffraction and Raman spectroscopy. The amorphous WO3 films remain as an amorphous phase up to 385�C and
Esra Ozkan; Se-Hee Lee; C. Edwin Tracy; J. Roland Pitts; Satyen K. Deb
Reduced graphene oxide/InGaZn mixed oxide nanocomposite photocatalysts for hydrogen production.
A series of reduced graphene oxide and indium-gallium-zinc mixed oxide (RGO/IGZ) nanocomposites were successfully synthesised by a simple one-step hydrothermal method. The as-synthesised nanocomposites were characterised by crystallographic, microscopic, and spectroscopic methods to explore the robust photocatalytic activity of the prepared materials. XRD patterns confirmed the formation of highly pure, single-phase, hexagonal In2 Ga2 ZnO7 with no impurity-related peaks. All the photocatalysts absorbed visible light as observed from the diffuse reflectance UV/Vis spectra. The electron-hole recombination is effectively minimised by the formation of an RGO/metal oxide nanocomposite, which was successfully derived from a photoluminescence (PL) study and photoelectrochemical measurements. The decoration of IGZ nanocrystals onto reduced graphene sheets leads to significant quenching of its luminescent intensity, dramatically improved photocurrent generation (33 times more than neat IGZ) and significantly enhanced photostability. The high photocatalytic activity for H2 production is explained by the strong interaction between the IGZ nanocrystals with RGO sheets, low PL intensity, high photocurrent and large surface area. PMID:24127386
Martha, Satyabadi; Padhi, Deepak Ku; Parida, Kulamani
Amorphous copper tungsten oxide with tunable band gaps
We report on the synthesis of amorphous copper tungsten oxide thin films with tunable band gaps. The thin films are synthesized by the magnetron cosputtering method. We find that due to the amorphous nature, the Cu-to-W ratio in the films can be varied without the limit of the solubility (or phase separation) under appropriate conditions. As a result, the band gap and conductivity type of the films can be tuned by controlling the film composition. Unfortunately, the amorphous copper tungsten oxides are not stable in aqueous solution and are not suitable for the application of photoelectrochemical splitting of water. Nonetheless, it provides an alternative approach to search for transition metal oxides with tunable band gaps.
Chen Le; Shet, Sudhakar; Tang Houwen; Wang Heli; Yan Yanfa; Turner, John; Al-Jassim, Mowafak [National renewable Energy Laboratory, Golden, Colorado 80401 (United States); Ahn, Kwang-soon [School of Display and Chemical Engineering, Yeungnam University, Dae-dong, Kyungsan 712-749 (Korea, Republic of)
Amorphous tin-cadmium oxide films and the production thereof
A tin-cadmium oxide film having an amorphous structure and a ratio of tin atoms to cadmium atoms of between 1:1 and 3:1. The tin-cadmium oxide film may have an optical band gap of between 2.7 eV and 3.35 eV. The film may also have a charge carrier concentration of between 1.times.10.sup.20 cm.sup.-3 and 2.times.10.sup.20 cm.sup.-3. The tin cadmium oxide film may also exhibit a Hall mobility of between 40 cm.sup.2V.sup.-1 s.sup.-1 and 60 cm.sup.2V.sup.-1 s.sup.-1. Also disclosed is a method of producing an amorphous tin-cadmium oxide film as described and devices using same.
Li, Xiaonan; Gessert, Timothy A
Photochemical route for accessing amorphous metal oxide materials for water oxidation catalysis.
Large-scale electrolysis of water for hydrogen generation requires better catalysts to lower the kinetic barriers associated with the oxygen evolution reaction (OER). Although most OER catalysts are based on crystalline mixed-metal oxides, high activities can also be achieved with amorphous phases. Methods for producing amorphous materials, however, are not typically amenable to mixed-metal compositions. We demonstrate that a low-temperature process, photochemical metal-organic deposition, can produce amorphous (mixed) metal oxide films for OER catalysis. The films contain a homogeneous distribution of metals with compositions that can be accurately controlled. The catalytic properties of amorphous iron oxide prepared with this technique are superior to those of hematite, whereas the catalytic properties of a-Fe(100-y-z)Co(y)Ni(z)O(x) are comparable to those of noble metal oxide catalysts currently used in commercial electrolyzers. PMID:23539180
Smith, Rodney D L; Pr�vot, Mathieu S; Fagan, Randal D; Zhang, Zhipan; Sedach, Pavel A; Siu, Man Kit Jack; Trudel, Simon; Berlinguette, Curtis P
Amorphization and Recrystallization of the ABO(3) Oxides
Single crystals of the ABO3 phases CaTiO3, SrTiO3, BaTiO3, LiNbO3, KNbO3, LiTaO3, and KTaO3 were irradiated by 800 keV Kr+, Xe+, or Ne+ ions over the temperature range from 20 to 1100 K. The critical amorphization temperature, Tc, above which radiation-induced amorphization does not occur varied from approximately 450 K for the titanate compositions to more than 850 K for the tantalates. While the absolute ranking of increasing critical amorphization temperatures could not be explained by any simple physical parameter associated with the ABO3 oxides, within each chemical group defined by the B-site cation (i.e., within the titanates, niobates, and tantalates), Tc tends to increase with increasing mass of the A-site cation. Tc was lower for the Ne+ irradiations as compared to Kr+, but it was approximately the same for the irradiations with Kr+ or Xe+. Thermal recrystallization experiments were performed on the ion-beam-amorphized thin sections in situ in the transmission electron microscope (TEM). In the high vacuum environment of the microscope, the titanates recrystallized epitaxially from the thick areas of the TEM specimens at temperatures of 800 to 850 K. The niobates and tantalates did not recrystallize epitaxially, but instead, new crystals nucleated and grew in the amorphous region in the temperature range 825 to 925 K. These new crystallites apparently retain some''memory'' of the original crystal orientation prior to ion-beam amorphization.
Meldrum, Alkiviathes (Alberta, University of) [Alberta, University of; Boatner, Lynn A.(Oak Ridge National Laboratory) [Oak Ridge National Laboratory; Weber, William J.(BATTELLE (PACIFIC NW LAB)) [BATTELLE (PACIFIC NW LAB); Ewing, Rodney C.(Michigan, Univ Of - Ann Arbor) [Michigan, Univ Of - Ann Arbor
Laser direct patterning of indium tin oxide for defining a channel of thin film transistor.
In this work, using a Q-switched diode-pumped neodymium-doped yttrium vanadate (Nd:YVO4, lambda = 1064 nm) laser, a direct patterning of indium tin oxide (ITO) channel was realized on glass substrates and the results were compared and analyzed in terms of the effect of repetition rate, scanning speed on etching characteristics. The results showed that the laser conditions of 40 kHz repetition rate with a scanning speed of 500 mm/s were appropriate for the channeling of ITO electrodes. The length of laser-patterned channel was maintained at about 55 microm. However, residual spikes (about 50 nm in height) of ITO were found to be formed at the edges of the laser ablated area and a few ITO residues remained on the glass substrate after laser scanning. By dipping the laser-ablated ITO film in ITO diluted etchant (ITO etchant/DI water: 1/10) at 50 degrees C for 3 min, the spikes and residual ITO were effectively removed. At last, using the laser direct patterning, a bottom-source-drain indium gallium zinc oxide thin film transistor (IGZO-TFT) was fabricated. It is successfully demonstrated that the laser direct patterning can be utilized instead of photolithography to simplify the fabrication process of TFT channel, resulting in the increase of productivity and reduction of cost. PMID:24245327
Wang, Jian-Xun; Kwon, Sang Jik; Han, Jae-Hee; Cho, Eou Sik
Amorphous hafnium-indium-zinc oxide semiconductor thin film transistors
NASA Astrophysics Data System (ADS)
We developed amorphous hafnium-indium-zinc oxide (HIZO) thin films as oxide semiconductors and investigated the films electrically and physically. Adding of hafnium (Hf) element can suppress growing the columnar structure and drastically decrease the carrier concentration and hall mobility in HIZO films. The thin film transistors (TFTs) with amorphous HIZO active channel exhibit good electrical properties with field effect mobility of around 10 cm2/Vs, S of 0.23 V/decade, and high Ion/off ratio of over 108, enough to operate the next electronic devices. In particular, under bias-temperature stress test, the HIZO TFTs with 0.3 mol % (Hf content) showed only 0.46 V shift in threshold voltage, compared with 3.25 V shift in HIZO TFT (0.1 mol %). The Hf ions may play a key role to improve the instability of TFTs due to high oxygen bonding ability. Therefore, the amorphous HIZO semiconductor will be a prominent candidate as an operation device for large area electronic applications.
Kim, Chang-Jung; Kim, Sangwook; Lee, Je-Hun; Park, Jin-Seong; Kim, Sunil; Park, Jaechul; Lee, Eunha; Lee, Jaechul; Park, Youngsoo; Kim, Joo Han; Shin, Sung Tae; Chung, U.-In
Transparent amorphous zinc oxide thin films for NLO applications
NASA Astrophysics Data System (ADS)
This review focuses on the growth and optical properties of amorphous zinc oxide (ZnO) thin films. A high quality ZnO films fabricated by dip-coating (sol-gel) method were grown on quartz and glass substrates at temperature equal to 350 K. The amorphous nature of the films was verified by X-ray diffraction. Atomic Force Microscopy was used to evaluate the surface morphology of the films. The optical characteristics of amorphous thin films have been investigated in the spectral range 190-1100 nm. Measurement of the polarized optical properties was shows a high transmissivity (80-99%) and low absorptivity (<5%) in the visible and near infrared regions at different angles of incidence. Linear optical properties were investigated by classic and Time-Resolved Photoluminescence (TRPL) measurements. Photoluminescence spectrum exhibits a strong ultraviolet emission while the visible emission is very weak. An innovative TRPL technique has enabled the measurement of the photoluminescence decay time as a function of temperature. TRPL measurements reveal a multiexponential decay behavior typical for amorphous thin films. Second and third harmonic generation measurements were performed by means of the rotational Maker fringe technique using Nd:YAG laser at 1064 nm in picosecond regime for investigations of the nonlinear optical properties. The obtained values of second and third order nonlinear susceptibilities were found to be high enough for the potential applications in the optical switching devices based on refractive index changes. Presented spectra confirm high structural and optical quality of the investigated zinc oxide thin films.
Zawadzka, A.; P?�ciennik, P.; Strzelecki, J.; Sahraoui, B.
Bismuth-modified amorphous manganese oxides were synthesized via a room temperature aqueous route. They were galvanostatically tested as intercalation cathodes for rechargeable lithium batteries at 1mAcm?2 between 1.5 and 4.3V. In sharp contrast to severe capacity fading of unmodified amorphous manganese oxide synthesized by the same route, a stable cycling performance of the bismuth-modified amorphous manganese oxide was observed. After an
Jingsi Yang; Terrill B Atwater; Jun John Xu
Water oxidation in the neutral pH regime catalyzed by amorphous transition-metal oxides is of high interest in energy science. Crucial determinants of electrocatalytic activity were investigated for a cobalt-based oxide film electrodeposited at various thicknesses on inert electrodes. For water oxidation at low current densities, the turnover frequency (TOF) per cobalt ion of the bulk material stayed fully constant for variation of the thickness of the oxide film by a factor of 100 (from about 15?nm to 1.5??m). Thickness variation changed neither the nanostructure of the outer film surface nor the atomic structure of the oxide catalyst significantly. These findings imply catalytic activity of the bulk hydrated oxide material. Nonclassical dependence on pH was observed. For buffered electrolytes with pKa values of the buffer base ranging from 4.7 (acetate) to 10.3 (hydrogen carbonate), the catalytic activity reflected the protonation state of the buffer base in the electrolyte solution directly and not the intrinsic catalytic properties of the oxide itself. It is proposed that catalysis of water oxidation occurs within the bulk hydrated oxide film at the margins of cobalt oxide fragments of molecular dimensions. At high current densities, the availability of a proton-accepting base at the catalyst-electrolyte interface controls the rate of water oxidation. The reported findings may be of general relevance for water oxidation catalyzed at moderate pH by amorphous transition-metal oxides. PMID:24449514
Klingan, Katharina; Ringleb, Franziska; Zaharieva, Ivelina; Heidkamp, Jonathan; Chernev, Petko; Gonzalez-Flores, Diego; Risch, Marcel; Fischer, Anna; Dau, Holger
Ion implantation-induced amorphization of ceramic oxides
A mechanism of amorphization by ion implantation in ceramic oxides is studied using a rate theory approach. It is proposed that the production of highly localized lattice distortions causes lattice destabilization and the ensuing transition to the amorphous state. These distortions can be caused by a large point defect buildup. It is argued that point defect retention occurs because of the impossibility of producing antisite defects. It is proposed that point defects on each sublattice can shield or trap point defects on the other sublattice. Similarly, metallic impurities may shield oxygen vacancies or trap oxygen interstitial ions, preventing anion Frenkel pairs from recombining. These effects are modeled in {alpha}-alumina for low temperature implantations (e.g., around 78 K), where point defects are immobile. It is shown that, at these temperatures, recombination is strongly hindered by the radiation-induced point defects themselves, rather than by the implanted impurities. The high point defect concentration attained by this mechanism is sufficient to raise the free energy of the crystal above the free energy of the amorphous solid. 29 refs., 2 figs.
Pedraza, D.F.
We demonstrate a tunable electron-blocking layer to enhance the performance of an Earth-abundant metal-oxide solar-cell material. A 5 nm thick amorphous ternary metal-oxide buffer layer reduces interface recombination, ...
Heo, Jaeyeong
Low hydrogen diffusivity and solubility of aluminum oxide make a vapor deposited aluminum oxide (Al2O3) film an anticipated hydrogen permeation barrier coating. In this paper, amorphous Al2O3 film was deposited using filtered vacuum arc method. As a substrate, vapor deposited amorphous tungsten oxide (WO3) film was used in order to characterize hydrogen permeation barrier performance of the Al2O3 film utilizing
Y Yamada-Takamura; F Koch; H Maier; H Bolt
Graphitic carbon growth on crystalline and amorphous oxide substrates using molecular beam epitaxy
We report graphitic carbon growth on crystalline and amorphous oxide substrates by using carbon molecular beam epitaxy. The films are characterized by Raman spectroscopy and X-ray photoelectron spectroscopy. The formations of nanocrystalline graphite are observed on silicon dioxide and glass, while mainly sp2 amorphous carbons are formed on strontium titanate and yttria-stabilized zirconia. Interestingly, flat carbon layers with high degree of graphitization are formed even on amorphous oxides. Our results provide a progress toward direct graphene growth on oxide materials. PACS: 81.05.uf; 81.15.Hi; 78.30.Ly. PMID:22029707
Ceramic oxides: Surfaces and amorphous/crystalline interfaces
NASA Astrophysics Data System (ADS)
Model studies have been carried out to further the basic understanding of ceramic oxide surfaces and the interface between ceramic oxides and amorphous films. Boundary-migration studies using model geometries of alumina and rutile bicrystals have been carried out. In the case of the rutile boundary, migration proceeds faster near the surface, while in the alumina bicrystal migration proceeds faster away from the boundary. A solution/reprecipitation mechanism is proposed for the alumina case, while a mechanism similar to diffusion-induced grain boundary migration (DIGM) is proposed for the rutile case. Three distinct faceting behaviors for the m-plane of alumina have been identified. The low-energy configuration was observed within a glass droplet whereas higher-energy configurations were observed outside dewet droplets and within a migrating grain boundary. These high-energy configurations are due to kinetic limitations. A method for monitoring the evolution of faceting over the course of several heat treatments has been developed which uses a combination of visible-light microscopy (VLM) and atomic-force microscopy (AFM) with the aid of fiducial marks (indentations) as reference markers. Grooves at migrating grain boundaries in high-purity alumina have been studied using a combination of VLM, AFM, and transmission electron microscopy (TEM) through a progression of heat treatments at 1650�C. The partial angles of grooves that developed at migrating grain boundaries were found to be asymmetric compared with those that developed at stationary boundaries. The wetting behavior of an amorphous SiO2 film on single-crystal substrates of TiO2 has been extensively studied. A model involving the initiation of an instability due to surface-tension gradients is proposed as the mechanism for the complex patterns observed. It is proposed that the surface-tension gradients are caused by the changing composition of the SiO 2 thin film due to dissolution of the TiO2 substrate into the film. Surfaces of ceria (CeO2) particles have been studied by electron energy-loss spectroscopy. All the ceria particles analyzed contained Ce 3+ at the surface. Cation impurities were enriched at the surface of the particles. Time series investigations indicate that fluorine substitutes on the oxygen sublattice and is charged balanced by some cerium changing from Ce4+ to Ce3+.
Gilliss, Shelley Rae
Stress dependence of paramagnetic point defects in amorphous silicon oxide.
Room-temperature red cathodoluminescence (CL) emission (R band) arising from the paramagnetic point-defect population present in amorphous silicon oxide (SiOx) has been characterized with respect to its shift upon applied stress, according to a piezo-spectroscopic (PS) approach. The R band (found at around 630 nm) originates from nonbridging oxygen hole centers (NBOHC; Si-O*) generated in the presence of oxygen-excess sites. It is shown that reliable stress assessments can be obtained in silica glass with a relatively high spatial resolution, provided that appropriate spectroscopic procedures are developed to precisely extract from the CL spectrum the shift upon stress of the R band, isolated from other partly overlapping bands. Macroscopic and microscopic PS calibration procedures are shown to lead to consistent results on silica materials with different chemical characteristics and, thus, with different intrinsic defect populations. In addition, quantitative calibrations of both electron probe size and luminescence emission distribution within the electron probe are given. As an application of the PS technique, the magnitude of the residual stress piled up (mainly due to a thermal expansion mismatch) at a sharp silica/silicon interface has been characterized by taking into account the gradient in defect population developed as a function of distance from the interface. In the Results and Discussion section, brief comments are offered regarding the possible impact of highly spatially resolved stress assessments in silica glass upon the development of new materials and advanced electronic devices. PMID:18380491
Leto, Andrea; Munisso, M Chiara; Porporati, A Alan; Zhu, Wenliang; Pezzotti, Giuseppe
Probing of 2 dimensional confinement-induced structural transitions in amorphous oxide thin film
NASA Astrophysics Data System (ADS)
Whereas the atomic structure of surface of crystals is known to be distinct from that of bulk, experimental evidence for thickness-induced structural transitions in amorphous oxides is lacking. We report the NMR result for amorphous alumina with varying thickness from bulk up to 5 nm, revealing the nature of structural transitions near amorphous oxide surfaces/interfaces. The coordination environments in the confined amorphous alumina thin film are distinct from those of bulk, highlighted by a decrease in the fractions of high-energy clusters (and thus the degree of disorder) with thickness. The result implies that a wide range of variations in amorphous structures may be identified by controlling its dimensionality.
Lee, Sung Keun; Ahn, Chi Won
NASA Astrophysics Data System (ADS)
Low-voltage-driven amorphous indium-gallium-zinc-oxide (IGZO) thin-film transistors (TFTs) with an Al2O3 dielectric were fabricated on a Si substrate by using pulsed laser deposition. Both Al2O3 and IGZO thin films are amorphous, and the thin films have very smooth surfaces. The Al2O3 gate dielectric exhibits a very low leakage current density of 1.3 � 10-8 A/cm2 at 5 V and a high capacitance density of 60.9 nF/cm2. The IGZO TFT with a structure of Ni/IGZO/Al2O3/Si exhibits high performance with a low threshold voltage of 1.18 V, a high field effect mobility of 20.25 cm2V-1s-1, an ultra small subthreshold swing of 87 mV/decade, and a high on/off current ratio of 3 � 107.
Geng, G. Z.; Liu, G. X.; Zhang, Q.; Shan, F. K.; Lee, W. J.; Shin, B. C.; Cho, C. R.
Mesoporous amorphous rare earth silicates, new catalysts of methane oxidative coupling
253 The catalytic reaction of methane oxidative coupling (MOC) is a direct route to produce ethylene from natural gas. Rare earth oxides are efficient catalysts for this reaction [1?3]. This paper is the first report on the catalytic activity of mesoporous amorphous rare earth materials based on SiO 2 in the MOC reaction; lanthanum and cerium ions or their mixture
A. G. Dedov; A. S. Loktev; N. O. Tel�pukhovskaya; K. V. Parkhomenko; I. I. Moiseev
Selective epitaxial growth of submicron complex oxide structures by amorphous SrTiO3
by amorphous SrTiO3 STO . Using a combination of pulsed laser deposition and electron-beam lithography A chemical-free technique for fabricating submicron complex oxide structures has been developed based on selective epitaxial growth. The crystallinity and hence the conductivity of the complex oxide is inhibited
Wei, John Y.T.
Amorphous aluminium-doped zinc oxide (AZO) thin films are grown by standard RF sputtering at low temperatures on glass substrates. Due to poor thermal conductivity and thermal energy generated by the sputter gun, controlling the substrate surface temperature is the key to controlling the growth of amorphous and nanocrystalline films. The ratio of grains and amorphous part of the films can
H. Chou; M. S. Yang; C. P. Wu; Y. C. Tsao; B. J. Chen; T. F. Liao; S. J. Sun; J. W. Chiou
NASA Astrophysics Data System (ADS)
We investigate the electrical stress-induced instability in amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistors (TFTs) with Sm2O3 gate dielectrics. Tow-step electrical degradation behavior in Sm2O3 a-IGZO TFT devices was found under high gate and drain voltage stress during 1000 s. A typical small positive shift followed by an unusual negative shift of threshold voltage is characterized in our TFT devices. We believe that the positive shift of the threshold voltage is due to charge trapping in the gate dielectric and/or at the channel/dielectric interfaces, while the negative shift of threshold voltage can be attributed to the generation of extra electrons from oxygen vacancies in the a-IGZO channel. We suggested that the amount of oxygen vacancies and the quality of the high-? gate dielectric probably affect the degradation behavior of a-IGZO TFT devices.
Chen, Fa-Hsyang; Her, Jim-Long; Hung, Meng-Ning; Pan, Tung-Ming
NASA Astrophysics Data System (ADS)
We investigated the impact of Ti doping in the Sm2O3 dielectric on the electrical stress-induced instability in amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistors (TFTs). With increasing stress time in a-IGZO TFT devices, a small initial positive shift followed by a negative shift of threshold voltage is characterized in the Sm2O3 dielectric, whereas only positive shift of threshold voltage is observed for Ti-doped Sm2O3 dielectric. The positive shift of the threshold voltage can be explained by charge trapping in the Sm2O3 film and/or the Sm2O3/IGZO interfaces, while the negative shift of threshold voltage is probably due to the extra charges from the IGZO channel by self-heating effect.
Chen, Fa-Hsyang; Her, Jim-Long; Mondal, Somnath; Hung, Meng-Ning; Pan, Tung-Ming
NASA Astrophysics Data System (ADS)
This letter investigates the degradation mechanism of amorphous indium-gallium-zinc oxide thin-film transistors under gate-bias stress. The larger Vt shift under positive AC gate-bias stress when compared to DC operation indicates that an extra electron trapping mechanism occurs during rising/falling time during the AC pulse period. In contrast, the degradation behavior under illuminated negative gate-bias stress exhibits the opposite degradation tendency. Since electron and hole trapping are the dominant degradation mechanisms under positive and illuminated negative gate-bias stress, respectively, the different degradation tendencies under AC/DC operation can be attributed to the different trapping efficiency of electrons and holes.
Chen, Te-Chih; Chang, Ting-Chang; Hsieh, Tien-Yu; Lu, Wei-Siang; Jian, Fu-Yen; Tsai, Chih-Tsung; Huang, Sheng-Yao; Lin, Chia-Sheng
NASA Astrophysics Data System (ADS)
Thin film transistors (TFTs) based flexible displays have optically transparent and m echanically flexible properties that are attractive for next-generation display technologies. In particular, "amorphous indium-gallium-zinc-oxide" (a- IGZO) and graphene have attracted much attention due to the advantages of their excellent unif ormity and compatibility with transparent and flexible substrates. To maintain these characteristics, it is important to confirm the deformation characteristics of TFTs with applied external for ces, such as compressive or tensile stress, distortion effects, and temperature. The mechanical c haracteristics of modeled devices applied to different active layers on TFTs, such as a- IGZO and graphene, were investigated under various external conditions. The distributions of t he stress-strain curve on each active layer and the deformed shapes were assessed graphically.
Kim, H.-J.; Kim, Youn-Jea
Tin-based amorphous oxide: A high-capacity lithium-ion-storage material
A high-capacity lithium-storage material in metal-oxide form has been synthesized that can replace the carbon-based lithium intercalation materials currently in extensive use as the negative electrode (anode) of lithium-ion rechargeable batteries. This tin-based amorphous composite oxide (TCO) contains Sn(II)-O as the active center for lithium insertion and other glass-forming elements, which make up an oxide network. The TCO anode yields
Yoshio Idota; Tadahiko Kubota; Akihiro Matsufuji
Amorphous semiconducting and conducting transparent metal oxide thin films and production thereof
Metal oxide thin films and production thereof are disclosed. An exemplary method of producing a metal oxide thin film may comprise introducing at least two metallic elements and oxygen into a process chamber to form a metal oxide. The method may also comprise depositing the metal oxide on a substrate in the process chamber. The method may also comprise simultaneously controlling a ratio of the at least two metallic elements and a stoichiometry of the oxygen during deposition. Exemplary amorphous metal oxide thin films produced according to the methods herein may exhibit highly transparent properties, highly conductive properties, and/or other opto-electronic properties.
Perkins, John (Boulder, CO); Van Hest, Marinus Franciscus Antonius Maria (Lakewood, CO); Ginley, David (Evergreen, CO); Taylor, Matthew (Golden, CO); Neuman, George A. (Holland, MI); Luten, Henry A. (Holland, MI); Forgette, Jeffrey A. (Hudsonville, MI); Anderson, John S. (Holland, MI)
Observation of the amorphous zinc oxide recrystalline process by molecular dynamics simulation
The detailed structural variations of amorphous zinc oxide (ZnO) as well as wurtzite (B4) and zinc blende (B3) crystal structures during the temperature elevation process were observed by molecular dynamics simulation. The amorphous ZnO structure was first predicted through the simulated-annealing basin-hopping algorithm with the criterion to search for the least stable structure. The density and X-ray diffraction profiles of amorphous ZnO of the structure were in agreement with previous reports. The local structural transformation among different local structures and the recrystalline process of amorphous ZnO at higher temperatures are observed and can explain the structural transformation and recrystalline mechanism in a corresponding experiment [Bruncko et al., Thin Solid Films 520, 866-870 (2011)]. PMID:23509413
Lin, Ken-Huang; Sun, Shih-Jye; Ju, Shin-Pon; Tsai, Jen-Yu; Chen, Hsin-Tsung; Hsieh, Jin-Yuan
Unipolar resistive switching behaviors in amorphous lutetium oxide films
NASA Astrophysics Data System (ADS)
The resistive switching properties in the amorphous Lu2O3 films deposited by pulsed laser deposition have been investigated. Well unipolar switching behaviors of Pt/Lu2O3/Pt stacks were obtained. The memory cells exhibited a high resistance ratio over 1�103, fast programming speed within 30 ns, and no obvious degradation after an endurance of 300 switching cycles and a duration of 3.2�106 s. The first-principles calculation indicates that the oxygen vacancies in cubic Lu2O3 will form defective energy level below the bottom of conduction band, and reduce the band gap. The absence of grain boundaries in the amorphous Lu2O3 films helps us attribute the switching mechanism of such stacks to the possible redistribution of defects related to oxygen vacancies along the filamentary paths during the resistive switching process.
Gao, Xu; Xia, Yidong; Xu, Bo; Kong, Jizhou; Guo, Hongxuan; Li, Kui; Li, Haitao; Xu, Hanni; Chen, Kai; Yin, Jiang; Liu, Zhiguo
NASA Astrophysics Data System (ADS)
Amorphous manganese oxides have received increasing attention in recent years as intercalation cathodes for rechargeable lithium batteries. The sol-gel method is a versatile method for achieving nanostructured amorphous oxides. In this paper, two different sol-gel routes are investigated, where nanostructured amorphous manganese oxide cryogels are obtained via freeze drying Mn(IV) oxide hydrogels formed in situ. In one route the hydrogels are formed by reaction between a solution of sodium permanganate and a solution of disodium fumarate, and in the other route by reaction between a solution of sodium permanganate and solid fumaric acid. Highly homogeneous monolithic manganese oxide hydrogels are obtained from both synthesis routes with precursor concentrations between 0.1 and 0.2 M. The freeze drying method proves to be an efficient method for obtaining nanostructured amorphous manganese oxide cryogels out of the hydrogels. Depending on the synthesis conditions of the hydrogels, the resultant cryogels can yield very high specific capacities for lithium intercalation and excellent rate performance. The cryogel with the best performance exhibits 289 mAh/g at a C/100 rate and 174 mAh/g at a 2 C rate. Strong dependence of electrochemical properties of the cryogels on the synthesis conditions of the parent hydrogels has been observed. The different electrochemical properties are believed to be due to different surface areas and local structures of the cryogels derived from hydrogels synthesized under different conditions. This strong dependence gives rise to the possibility of achieving promising intercalation materials through tailoring the surface area and the local structure of amorphous manganese oxides by adjusting sol-gel synthesis conditions.
Yang, Jingsi; Xu, Jun John
Carbon-Incorporated Amorphous Indium Zinc Oxide Thin-Film Transistors
NASA Astrophysics Data System (ADS)
We propose the use of amorphous-carbon indium zinc oxide (a-CIZO) as a channel material for thin-film transistor (TFT) fabrication. This study chose a carbon dopant as a carrier suppressor and strong oxygen binder in amorphous-indium zinc oxide (a-IZO) channel material. a-CIZO thin films were deposited using radiofrequency (RF) sputtering and postannealed at 150�C. X-ray diffraction and transmission electron microscopy analysis revealed that the film remained amorphous even after postannealing. The a-CIZO TFT postannealed at 150�C exhibited saturation field-effect mobility of 16.5 cm2 V-1 s-1 and on-off current ratio of �4.3 � 107.
Parthiban, S.; Park, K.; Kim, H.-J.; Yang, S.; Kwon, J.-Y.
Nanoporous Ni-Co binary oxide layers were electrochemically fabricated by deposition followed by anodization, which produced an amorphous layered structure that could act as an efficient electrocatalyst for water oxidation. The highly porous morphologies produced higher electrochemically active surface areas, while the amorphous structure supplied abundant defect sites for oxygen evolution. These Ni-rich (10-40 atom % Co) binary oxides have an increased active surface area (roughness factor up to 17), reduced charge transfer resistance, lowered overpotential (?325 mV) that produced a 10 mA cm(-2) current density, and a decreased Tafel slope (?39 mV decade(-1)). The present technique has a wide range of applications for the preparation of other binary or multiple-metals or metal oxides nanoporous films. Fabrication of nanoporous materials using this method could provide products useful for renewable energy production and storage applications. PMID:25134007
Yang, Yang; Fei, Huilong; Ruan, Gedeng; Xiang, Changsheng; Tour, James M
High efficiency luminescent amorphous silicon nitride films grown at room temperature with subsequent plasma oxidation were used as the active layers in the electroluminescent devices. A strong uniform green-yellow light emission from the devices was realized under forward biased conditions. It was found that the turn-on voltage could be reduced to as low as 6 V while the electroluminescence (EL)
Rui Huang; Kunji Chen; Peigao Han; Hengping Dong; Xiang Wang; Deyuan Chen; Wei Li; Jun Xu; Zhongyuan Ma; Xinfan Huang
Oxidation of amorphous Ni Zr alloys studied by XPS, UPS, ISS and XRD
NASA Astrophysics Data System (ADS)
Amorphous Ni 36Zr 64 and Ni 24Zr 76 alloys were treated under conditions close to those used for activating Ni-Zr alloys in catalytic reactions. The composition and the structure of the surface region were investigated by X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), ion scattering spectroscopy (ISS) and X-ray diffraction (XRD). The results show that exposing the amorphous alloys to 500 mbar O 2 at 523 K led to oxidized surfaces consisting of zirconia and different oxidic nickel species. On the oxidized Ni 24Zr 76 surface, only small amounts of NiO and Ni 2O 3 were found, while Ni 2O 3 was detected as the major Ni-containing species on the oxidized Ni 36Zr 64 surface. Oxidation of Ni in the alloys appeared to be inhibited by the presence of metallic Zr and started only after complete oxidation of the surrounding Zr. Annealing the oxidized alloys to 773 K led to a reduction of the surface oxides. The liberated oxygen atoms presumably diffused into the bulk, releasing metallic Ni. At the topmost layer, zirconia was reduced by carbon atoms originating from the bulk to form a ZrC-like surface compound. The exchange of Ni and Zr atoms between the surface and the bulk was enhanced by the oxidation and the annealing. The preferential oxidation of zirconium, which attracts Zr atoms from the bulk to the surface, provides the driving force for such processes.
Song, Z.; Bao, X.; Wild, U.; Muhler, M.; Ertl, G.
NASA Astrophysics Data System (ADS)
A unified physical model for Seebeck coefficient was presented based on the multiple-trapping and release theory for amorphous oxide semiconductor thin-film transistors. According to the proposed model, the Seebeck coefficient is attributed to the Fermi-Dirac statistics combined with the energy dependent trap density of states and the gate-voltage dependence of the quasi-Fermi level. The simulation results show that the gate voltage, energy disorder, and temperature dependent Seebeck coefficient can be well described. The calculation also shows a good agreement with the experimental data in amorphous In-Ga-Zn-O thin-film transistor.
Lu, Nianduan; Li, Ling; Sun, Pengxiao; Banerjee, Writam; Liu, Ming
High-k (k=30) amorphous hafnium oxide films from high rate room temperature deposition
Amorphous hafnium oxide (HfO{sub x}) is deposited by sputtering while achieving a very high k{approx}30. Structural characterization suggests that the high k is a consequence of a previously unreported cubiclike short range order in the amorphous HfO{sub x} (cubic k{approx}30). The films also possess a high electrical resistivity of 10{sup 14} {Omega} cm, a breakdown strength of 3 MV cm{sup -1}, and an optical gap of 6.0 eV. Deposition at room temperature and a high deposition rate ({approx}25 nm min{sup -1}) makes these high-k amorphous HfO{sub x} films highly advantageous for plastic electronics and high throughput manufacturing.
Li, Flora M.; Bayer, Bernhard C.; Hofmann, Stephan; Milne, William I.; Flewitt, Andrew J. [Department of Engineering, Electrical Engineering Division, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0FA (United Kingdom); Dutson, James D.; Wakeham, Steve J.; Thwaites, Mike J. [Plasma Quest Ltd., Unit 1B, Rose Estate, Osborn Way, Hook, Hampshire RG27 9UT (United Kingdom)
Polymer light-emitting diodes with amorphous indium-zinc oxide anodes deposited at room temperature
The authors report on the performance of polymer-based light-emitting diodes, LEDs, using amorphous zinc oxide-doped indium oxide, IZO, as anode. In particular, LEDs with poly[(2-methoxy-5-(2?-ethyl-hexyloxy)-1,4-phenylene vinylene] as electroluminescent layer and aluminium cathodes, show higher efficiency with this IZO anode (0.015cd\\/A) than with indium-tin oxide (ITO) (0.010cd\\/A). Inspite of the higher resistance of this IZO electrode, compared with ITO, the fact
Gabriel Bernardo; Gon�alo Gon�alves; Pedro Barquinha; Quirina Ferreira; Gra�a Brotas; Lu�s Pereira; Ana Charas; Jorge Morgado; Rodrigo Martins; Elvira Fortunato
Model for determination of mid-gap states in amorphous metal oxides from thin film transistors
NASA Astrophysics Data System (ADS)
The electronic density of states in metal oxide semiconductors like amorphous zinc oxide (a-ZnO) and its ternary and quaternary oxide alloys with indium, gallium, tin, or aluminum are different from amorphous silicon, or disordered materials such as pentacene, or P3HT. Many ZnO based semiconductors exhibit a steep decaying density of acceptor tail states (trap DOS) and a Fermi level (EF) close to the conduction band energy (EC). Considering thin film transistor (TFT) operation in accumulation mode, the quasi Fermi level for electrons (Eq) moves even closer to EC. Classic analytic TFT simulations use the simplification EC-EF> `several'kT and cannot reproduce exponential tail states with a characteristic energy smaller than 1/2 kT. We demonstrate an analytic model for tail and deep acceptor states, valid for all amorphous metal oxides and include the effect of trap assisted hopping instead of simpler percolation or mobility edge models, to account for the observed field dependent mobility.
Bubel, S.; Chabinyc, M. L.
High-temperature oxidation of a rapidly solidified amorphous Ta-Ir alloy
The oxidation products formed at 500 and 700�C on an amorphous Ta-44.5 at% Ir alloy in an Ar-0.1% O2 gas mixture were characterized using SEM, XRD, EPMA, TEM, STEM, AES, and XPS. Initially, a thin (3�4 nm) layer of Ta2O5 formed at the surface of the alloy. Continued growth of the Ta2O5, which occurred very rapidly, involved diffusion of oxygen
Catherine M. Cotell; Gregory J. Yurek
Electron-energy-loss measurements for an amorphous chemical-vapor-deposited silicon nitride film and evaporated sapphire in the broad energy range 1-200 eV are investigated. A method, not requiring the zero-loss peak, to remove the multiple scattering is discussed, applied, and the optical constants obtained. An Elliot-type model used with aluminum oxide gives a valence-exciton binding energy of 1.36+\\/-0.2 eV with a band gap
Peteris Livins; T. Aton; S. E. Schnatterly
Evaluation of Subretinal Implants Coated with Amorphous Aluminum Oxide and Diamond-like Carbon
Retinal prostheses may be used to support patients suffering from age-related macular degeneration (AMD) or retinitis pigmentosa (RP). A hermetic encapsulation of the poly(imide) (PI)-based prosthesis is important in order to prevent the leakage of water and ions into the electric circuitry embedded in the poly(imide) matrix. The deposition of amorphous aluminum oxide (by sputtering) and diamond like carbon (by
Robyn Sweitzer; Carmen Scholz; Sandra Montezuma; Joseph F. Rizzo
Arsenic adsorption on amorphous aluminum and iron oxides was investigated as a function of solution pH, solution ionic strength, and redox state. In this study in situ Raman and Fourier transform infrared (FTIR) spectroscopic methods were combined with sorption techniques, electrophoretic mobility measurements, and surface complexation modeling to study the interaction of As(III) and As(V) with amorphous oxide surfaces. The
Sabine Goldberg; Cliff T. Johnstony
NASA Astrophysics Data System (ADS)
Waterside corrosion of the Zircaloy cladding encasing the uranium oxide pellets is one of the primary factors limiting high "burn up" of nuclear fuel in pressurized water reactors (PWRs). High "burn up" can significantly impact plant safety and economics. Amorphous aluminum oxide coatings with aluminum-based compositional gradient layers (CGLs) were fabricated to develop ceramic coating corrosion protection systems for Zircaloy. Aluminum films were deposited on Zircaloy substrates by electron-beam evaporation, and two-step heat treatments were performed at near the melting temperature of aluminum. Amorphous alumina coatings by rf magnetron sputtering were overcoated on the CGL structures. Morphological and compositional studies were completed using field emission scanning electron microscopy (FE SEM), energy dispersive x-ray analysis (EDX), and auger electron spectroscopy (AES). The AES depth profiles of the annealed coatings showed that gradient compositions of Al, Zr, and O were obtained. Glancing angle x-ray diffraction (GAXRD) analysis showed that a variety of intermetallic and oxide phases (such as Al3Zr, Al2Zr3, Al2O3, ZrO2 and Zr3O) were formed in the coatings during processing. The intermetallic layers improved the adhesion property of the alumina overcoating to Zircaloy substrate, and functioned as oxidation resistant layers. In spite of the successful construction of the compositional gradient layer system with a good adhesion and thermal stability, and the report about the stability of pure alumina and amorphous ceramics in hydrothermal conditions, the amorphous alumina coatings in our study were not stable under nuclear reactor conditions of subcritical water at 350�C and 20.1 MPa (3000 psi). We investigated the behavior of amorphous alumina thin films deposited on Zircaloy substrates in the near-supercritical water. When the coatings were exposed to the subcritical conditions, hydrothermally grown well-faceted crystallite formation was observed. Surface morphology and composition were characterized by FE SEM, AES and EDX. The crystallites were identified to be aluminum hydroxide, boehmite (gamma-AlOOH) by XRD spectra, peak shift in x-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) images. We hypothesized the mechanism of the boehmite formation as the dissolution of amorphous alumina and the reprecipitation of boehmite during the cooling process.
Park, Sang Tae
Investigation on the characteristics of stress-induced hump in amorphous oxide thin film transistors
NASA Astrophysics Data System (ADS)
In this study, we investigate the instability of amorphous oxide thin film transistors using hafnium-indium-zinc oxide under simultaneous application of light and gate dc-bias. The hump characteristics are observed after negative gate bias and light stress. Based on the positive bias-induced recovery, it is proved that photo-generated holes are trapped in the gate insulator by the electrical field enhanced by the optical energy. Moreover, from simulated electric field distribution, it is clearly revealed that the hole-trapping is localized at the edge regions of the gate insulator along channel width/length directions by electric field crowding, resulting in the hump occurrence.
Kim, Jang Hyun; Kwon, Dae Woong; Chang, Ji Soo; Kim, Sang Wan; Park, Jae Chul; Kim, Chang Jung; Park, Byung-Gook
This paper describes synthesis of ultrathin pinhole-free insulating aluminum oxide layers for electronic device protection in corrosive liquid environments, such as phosphate buffered saline (PBS) or clinical fluids, to enable emerging biomedical applications such as biomolecular sensors. A pinhole-free 25-nm thick amorphous aluminum oxide layer has been achieved using ultra-high vacuum DC magnetron reactive sputtering of aluminum in oxygen/argon plasma followed by oxygen plasma post-processing. Deposition parameters were optimized to achieve the best corrosion protection of lithographically defined device structures. Electrochemical deposition of copper through the aluminum oxide layers was used to detect the presence (or absence) of pinholes. FTIR, XPS, and spectroscopic ellipsometry were used to characterize the material properties of the protective layers. Electrical resistance of the copper device structures protected by the aluminum oxide layers and exposed to a PBS solution was used as a metric to evaluate the long-term stability of these device structures. PMID:23682201
Litvinov, Julia; Wang, Yi-Ju; George, Jinnie; Chinwangso, Pawilai; Brankovic, Stanko; Willson, Richard C.; Litvinov, Dmitri
Mechanisms of lithium transport in amorphous polyethylene oxide.
We report calculations using a previously reported model of lithium perchlorate in polyethylene oxide in order to understand the mechanism of lithium transport in these systems. Using an algorithm suggested by Voter, we find results for the diffusion rate which are quite close to experimental values. By analysis of the individual events in which large lithium motions occur during short times, we find that no single type of rearrangement of the lithium environment characterizes these events. We estimate the free energies of the lithium ion as a function of position during these events by calculation of potentials of mean force and thus derive an approximate map of the free energy as a function of lithium position during these events. The results are consistent with a Marcus-like picture in which the system slowly climbs a free energy barrier dominated by rearrangement of the polymer around the lithium ions, after which the lithium moves very quickly to a new position. Reducing the torsion forces in the model causes the diffusion rates to increase. PMID:15740341
Duan, Yuhua; Halley, J W; Curtiss, Larry; Redfern, Paul
Inverted polymer solar cells with amorphous indium zinc oxide as the electron-collecting electrode
We report on the fabrication and performance of polymer-based inverted solar cells utilizing amorphous indium zinc oxide (a-IZO) as the electron-collecting electrode. Amorphous IZO films of 200 nm thickness were deposited by room temperature sputtering in a high-purity argon atmosphere. The films possessed a high optical transmittance in the visible region (? 80%), a low resistivity (3.3 � 10{sup ?4} ?cm), a low surface roughness (root mean square = 0.68 nm), and a low work function (4.46 � 0.02 eV). Inverted solar cells with the structure a-IZO/P3HT: PCBM/PEDOT:PSS/Ag exhibited a power conversion efficiency of 3% estimated for AM 1.5G, 100 mW/cm{sup 2} illumination.
Cheun, Hyeunseok; Kim, Jungbae; Zhou, Yinhua; Fang, Yunnan; Dindar, Amir; Shim, Jae Won; Fuentes-Hernandez, Canek; Sandhage, Kenneth H.; Kippelen, Bernard
An inverted polymer solar cell was fabricated on a polyethylene terephthalate (PET) substrate. The cell structure was ITO\\/amorphous titanium oxide (TiOx)\\/[6,6]-phenyl C61 butyric acid methyl ester (PCBM): regioregular poly(3-hexylthiophene) (P3HT)\\/poly(3,4-ethylenedioxylenethiophene):poly(4-styrene sulfonic acid) (PEDOT:PSS)\\/Au (TiOx cell). It was achieved using low boiling point diethyl amine (DEA) as a Ti4+ complexing agent, and high boiling point 1,2,3,4-tetrahydronaphthalene (Tetralin) containing 2 vol.% 1,8-octanedithiol
Ikumi Sasajima; Shogo Uesaka; Takayuki Kuwabara; Takahiro Yamaguchi; Kohshin Takahashi
High stability of amorphous hafnium-indium-zinc-oxide thin film transistor
NASA Astrophysics Data System (ADS)
Time dependence of the threshold voltage (Vth) shift in amorphous hafnium-indium-zinc oxide (a-HIZO) thin film transistor has been reported under on-current bias temperature stress measured at 60 �C. X-ray photoelectron spectroscopy results show the decrease in oxygen vacancies by Hf metal cations in a-HIZO systems after annealing process. High stability of a-HIZO systems has been observed due to low charge injection from the channel layer. Hf metal cations have been effectively incorporated into the IZO thin films as a suppressor against both the oxygen deficiencies and the carrier generation.
Chong, Eugene; Jo, Kyoung Chul; Lee, Sang Yeol
Optical constants of amorphous, transparent titanium-doped tungsten oxide thin films.
We report on the optical constants and their dispersion profiles determined from spectroscopic ellipsometry (SE) analysis of the 20%-titanium (Ti) doped of tungsten oxide (WO3) thin films grown by sputter-deposition. The Ti-doped WO3 films grown in a wide range of temperatures (25-500 �C) are amorphous and optically transparent. SE data indicates that there is no significant interdiffusion at the film-substrate interface for a W-Ti oxide film growth of ~90 nm. The index refraction (n) at ? = 550 nm vary in the range of 2.17-2.31 with a gradual increase in growth temperature. A correlation between the growth conditions and optical constants is discussed. PMID:23682744
Ramana, C V; Baghmar, Gaurav; Rubio, Ernesto J; Hernandez, Manuel J
NASA Astrophysics Data System (ADS)
Improving the conductivity of earth-abundant transparent conductive oxides (TCOs) remains an important challenge that will facilitate the replacement of indium-based TCOs. Here, we show that a hydrogen (H2)-plasma post-deposition treatment improves the conductivity of amorphous aluminum-doped zinc tin oxide while retaining its low optical absorption. We found that the H2-plasma treatment performed at a substrate temperature of 50 �C reduces the resistivity of the films by 57% and increases the absorptance by only 2%. Additionally, the low substrate temperature delays the known formation of tin particles with the plasma and it allows the application of the process to temperature-sensitive substrates.
Morales-Masis, M.; Ding, L.; Dauzou, F.; Jeangros, Q.; Hessler-Wyser, A.; Nicolay, S.; Ballif, C.
NASA Astrophysics Data System (ADS)
With recent advances in flexible electronics, there is a growing need for transparent conductors with optimum conductivity tailored to the application and nearly zero residual stress to ensure mechanical reliability. Within amorphous transparent conducting oxide (TCO) systems, a variety of sputter growth parameters have been shown to separately impact film stress and optoelectronic properties due to the complex nature of the deposition process. We apply a statistical design of experiments (DOE) approach to identify growth parameter-material property relationships in amorphous indium zinc oxide (a-IZO) thin films and observed large, compressive residual stresses in films grown under conditions typically used for the deposition of highly conductive samples. Power, growth pressure, oxygen partial pressure, and RF power ratio (RF/(RF + DC)) were varied according to a full-factorial test matrix and each film was characterized. The resulting regression model and analysis of variance (ANOVA) revealed significant contributions to the residual stress from individual growth parameters as well as interactions of different growth parameters, but no conditions were found within the initial growth space that simultaneously produced low residual stress and high electrical conductivity. Extrapolation of the model results to lower oxygen partial pressures, combined with prior knowledge of conductivity-growth parameter relationships in the IZO system, allowed the selection of two promising growth conditions that were both empirically verified to achieve nearly zero residual stress and electrical conductivities >1480 S/cm. This work shows that a-IZO can be simultaneously optimized for high conductivity and low residual stress.
Kumar, Mukesh; Sigdel, A. K.; Gennett, T.; Berry, J. J.; Perkins, J. D.; Ginley, D. S.; Packard, C. E.
High-temperature oxidation of a rapidly solidified amorphous Ta-Ir alloy
NASA Technical Reports Server (NTRS)
The oxidation products formed at 500 and 700 C on an amorphous Ta-44.5 at. pct Ir alloy in an Ar-0.1 percent O2 gas mixture were characterized using SEM, XRD, EPMA, TEM, STEM, AES, and XPS. Initially, a thin (3-4 nm) layer of Ta2O5 formed at the surface of the alloy. Continued growth of the Ta2O5, which occurred very rapidly, involved diffusion of oxygen anions from the Ta2O5/gas interface to the alloy/Ta2O5 interface, where tantalum was selectively oxidized. Because the oxide grew more quickly than iridium could diffuse back into the alloy, the iridium coalesced into platelets of crystalline iridium-rich alloy that were oriented approximately parallel to the oxide/alloy interface, and which became embedded in a matrix of Ta2O5. The unoxidized core remained in the glassy state. The oxidation process and/or the dissolution of oxygen into the unoxidized alloy caused the alloy to become embrittled.
Cotell, Catherine M.; Yurek, Gregory J.
High-temperature oxidation of a rapidly solidified amorphous Ta-Ir alloy
The oxidation products formed at 500 and 700/sup 0/C on an amorphous Ta44.5 at% Ir alloy in an Ar-0.1% O/sub 2/ gas mixture were characterized using SEM, XRD, EPMA, TEM, STEM, AES, and XPS. Initially, a thin (3-4 nm) layer of Ta/sub 2/O/sub 5/ formed at the surface of the alloy. Continued growth of the Ta/sub 2/O/sub 5/, which occurred very rapidly, involved diffusion of oxygen anions from the Ta/sub 2/O/sub 5//gas interface to the alloy/Ta/sub 2/O/sub 5/ interface, where tantalum was selectively oxidized. Because the oxide grew more quickly than iridium could diffuse back into the alloy, the iridium coalesced into platelets of crystalline iridium-rich alloy that were oriented approximately parallel to the oxide/alloy interface, and which became embedded in a matrix of Ta/sub 2/O/sub 5/. The unoxidized core remained in the glassy state. The oxidation process and/or the dissolution of oxygen into the unoxidized alloy caused the alloy to become embrittled.
Cotell, C.M.; Yorek, G.J.
NASA Astrophysics Data System (ADS)
Nanoporous Cu (NPC) prepared by dealloying CuZn alloy is used as an economic substrate for the fabrication of Ni-B alloy (Ni-B/NPC) by ultrasonic-assisted electroless technique. The results of scanning electron microscopy (SEM) and X-ray diffraction (XRD) demonstrate the NPC has a bicontinuous network structure and the Ni-B/NPC alloy is amorphous structure with highly dispersed nanoparticles. Electrochemical performances are measured by cyclic voltammetry (CV), chronoamperometry (CA) and linear sweep voltammetry (LSV). The results suggest that the Ni-B/NPC electrode prepared for 5�min shows the highest electrochemical activity and its redox species coverage and proton diffusion coefficient are remarkably improved compared with the bulk Ni. Ethanol oxidation at the Ni-B/NPC electrode suggests the onset oxidation potential has a negative shift of 52�mV and the oxidation peak current increases by 19.4 times, and apparent activation energy decreases 4.75-30.60�kJ�mol-1 at the same potential, in comparison with the bulk Ni. Additionally, the reaction rate constant for ethanol oxidation at the Ni-B/NPC electrode is improved by about one order of magnitude relative to the reported value. Finally, the Ni-B/NPC electrode has a stable redox behavior after complete activation and superior catalytic stability for ethanol oxidation.
Zhang, Shu-Jin; Zheng, Yi-Xiong; Yuan, Lin-Shan; Zhao, Li-Hua
NASA Astrophysics Data System (ADS)
We demonstrate an enhanced electrical stability through a Ti oxide (TiOx) layer on the amorphous InGaZnO (a-IGZO) back-channel; this layer acts as a surface polarity modifier. Ultrathin Ti deposited on the a-IGZO existed as a TiOx thin film, resulting in oxygen cross-binding with a-IGZO surface. The electrical properties of a-IGZO thin film transistors (TFTs) with TiOx depend on the surface polarity change and electronic band structure evolution. This result indicates that TiOx on the back-channel serves as not only a passivation layer protecting the channel from ambient molecules or process variables but also a control layer of TFT device parameters.
Cho, Byungsu; Choi, Yonghyuk; Jeon, Heeyoung; Shin, Seokyoon; Seo, Hyungtak; Jeon, Hyeongtag
Reaction of Formic Acid over Amorphous Manganese Oxide Catalytic Systems: An In Situ Study
The interaction of formic acid with amorphous manganese oxide (AMO) is investigated using in situ photoelectron and infrared spectroscopy techniques. Soft X-ray photoelectron spectroscopy (sXPS) and in situ FTIR illustrate two possible modes of formate bound species at the AMO surface. Two peaks in the IR region from 1340-1390 cm{sup -1} are indicative of formate species bound to the surface in a bidentate configuration. However, a 224 cm{sup -1} band gap between v{sub s}OCO and v{sub as}OCO suggests formate is bound in a bridging configuration. Temperature-programmed desorption studies confirm the formate bound species desorbs as carbon dioxide from the surface at multiple binding sites. At temperatures above 700 K, the presence of K{sup +} {hor_ellipsis} OC complex suggests the bound species interacts at vacant sites related to framework oxygen and cation mobility.
J Durand; S Senanayake; S Suib; D Mullins
NASA Astrophysics Data System (ADS)
We describe an approach to reduce the contact resistance at compositional conducting/semiconducting indium-zinc-oxide (IZO) homojunctions used for contacts in thin film transistors (TFTs). By introducing silver nanoparticles (Ag NPs) at the homojunction interface between the conducting IZO electrodes and the amorphous IZO channel, we reduce the specific contact resistance, obtained by transmission line model measurements, down to �10-2 ? cm2, �3 orders of magnitude lower than either NP-free homojunction contacts or solid Ag metal contacts. The resulting back-gated TFTs with Ag NP contacts exhibit good field effect mobility of �27 cm2/V s and an on/off ratio >107. We attribute the improved contact resistance to electric field concentration by the Ag NPs.
Xu, Rui; He, Jian; Song, Yang; Li, Wei; Zaslavsky, A.; Paine, D. C.
Laser-induced breakdown spectroscopy (LIBS) is a recently developed locally destructive elemental analysis technique that can be used to analyze solid, liquid, and gaseous samples. In the system explored here, a neodymium-doped yttrium aluminum garnet laser ablates a small amount of the sample and spectral emission from the plume is analyzed using a set of synchronized spectrometers. We explore the use of LIBS to map the stoichiometry of compositionally graded amorphous indium zinc oxide thin-film libraries. After optimization of the experimental parameters (distance between lens and samples, spot size on the samples, etc.), the LIBS system was calibrated against inductively coupled plasma atomic emission spectroscopy which resulted in a very consistent LIBS-based elemental analysis. Various parameters that need to be watched closely in order to produce consistent results are discussed. We also compare LIBS and x-ray fluorescence as techniques for the compositional mapping of libraries. PMID:20687701
Widjonarko, N Edwin; Perkins, John D; Leisch, Jennifer E; Parilla, Philip A; Curtis, Calvin J; Ginley, David S; Berry, Joseph J
Laser-induced breakdown spectroscopy (LIBS) is a recently developed locally destructive elemental analysis technique that can be used to analyze solid, liquid, and gaseous samples. In the system explored here, a neodymium-doped yttrium aluminum garnet laser ablates a small amount of the sample and spectral emission from the plume is analyzed using a set of synchronized spectrometers. We explore the use of LIBS to map the stoichiometry of compositionally graded amorphous indium zinc oxide thin-film libraries. After optimization of the experimental parameters (distance between lens and samples, spot size on the samples, etc.), the LIBS system was calibrated against inductively coupled plasma atomic emission spectroscopy which resulted in a very consistent LIBS-based elemental analysis. Various parameters that need to be watched closely in order to produce consistent results are discussed. We also compare LIBS and x-ray fluorescence as techniques for the compositional mapping of libraries.
Widjonarko, N. Edwin [Department of Physics, 390 UCB, University of Colorado, Boulder, Colorado 80309-0390 (United States); National Renewable Energy Laboratory, 1617 Cole Blvd., Golden, Colorado 80401 (United States); Perkins, John D.; Leisch, Jennifer E.; Parilla, Philip A.; Curtis, Calvin J.; Ginley, David S.; Berry, Joseph J. [National Renewable Energy Laboratory, 1617 Cole Blvd., Golden, Colorado 80401 (United States)
NASA Astrophysics Data System (ADS)
We report the dependence of the electronic properties on the metal composition and oxygen content of transparent conducting amorphous indium zinc oxide (a-IZO) films deposited by dc magnetron sputtering. a-IZO shows a clear Burstein-Moss shift with an effective optical band gap of 3.1eV independent of the metal composition. A metal-composition-independent dependence of the mobility (?) on carrier concentration (N) is also found for a-IZO with ?max=54cm2/Vs at N=1.3�1020cm-3 . The electron transport, thermally activated at N?1019cm-3 , becomes limited by lattice scattering at N?1020cm-3 and then by ionized impurity scattering at N>5�1020cm-3 .
Leenheer, Andrew J.; Perkins, John D.; van Hest, Maikel F. A. M.; Berry, Joseph J.; O'Hayre, Ryan P.; Ginley, David S.
Electrical, electronic and optical properties of amorphous indium zinc tin oxide thin films
NASA Astrophysics Data System (ADS)
The electrical and optical properties of amorphous indium zinc tin oxide (a-IZTO) thin films were examined as a function of chemical composition. Effects of Sn/Zn composition ratio and In content on the electrical and optical properties of a-IZTO thin films are discussed. The electron mobility of thin film transistors with higher Sn/Zn composition ratio was dramatically improved due to a shorter zinc-zinc separation distance. The thin film transistor with the composition of In:Zn:Sn = 20:48:32 exhibits a high mobility of 30.6 cm2 V-1 s-1 and a high on-off current ratio of 109.
Denny, Yus Rama; Lee, Kangil; Seo, Soonjoo; Oh, Suhk Kun; Kang, Hee Jae; Yang, Dong Seok; Heo, Sung; Chung, Jae Gwan; Lee, Jae Cheol
Improved Stability Of Amorphous Zinc Tin Oxide Thin Film Transistors Using Molecular Passivation
The role of back channel surface chemistry on amorphous zinc tin oxide (ZTO) bottom gate thin film transistors (TFT) have been characterized by positive bias-stress measurements and x-ray photoelectron spectroscopy. Positive bias-stress turn-on voltage shifts for ZTO-TFTs were significantly reduced by passivation of back channel surfaces with self-assembled monolayers of n-hexylphosphonic acid (n-HPA) when compared to ZTO-TFTs with no passivation. These results indicate that adsorption of molecular species on exposed back channel of ZTO-TFTs strongly influence observed turn-on voltage shifts, as opposed to charge injection into the dielectric or trapping due to oxygen vacancies.
Rajachidambaram, Meena Suhanya; Pandey, Archana; Vilayur Ganapathy, Subramanian; Nachimuthu, Ponnusamy; Thevuthasan, Suntharampillai; Herman, Gregory S.
Amorphous silica nanoparticles (SiO?-NPs) have found broad applications in industry and are currently intensively studied for potential uses in medical and biomedical fields. Several studies have reported cytotoxic and inflammatory responses induced by SiO?-NPs in different cell types. The present study was designed to examine the association of oxidative stress markers with SiO?-NP induced cytotoxicity in human endothelial cells. We used pure monodisperse amorphous silica nanoparticles of two sizes (16 and 60 nm; S16 and S60) and a positive control, iron-doped nanosilica (16 nm; SFe), to study the generation of hydroxyl radicals (HO�) in cellular-free conditions and oxidative stress in cellular systems. We investigated whether SiO?-NPs could influence intracellular reduced glutathione (GSH) and oxidized glutathione (GSSG) levels, increase lipid peroxidation (malondialdehyde (MDA) and 4-hydroxyalkenal (HAE) concentrations), and up-regulate heme oxygenase-1 (HO-1) mRNA expression in the studied cells. None of the particles, except SFe, produced ROS in cell-free systems. We found significant modifications for all parameters in cells treated with SFe nanoparticles. At cytotoxic doses of S16 (40-50 ?g/mL), we detected weak alterations of intracellular glutathione (4 h) and a marked induction of HO-1 mRNA (6 h). Cytotoxic doses of S60 elicited similar responses. Preincubation of cells being exposed to SiO?-NPs with an antioxidant (5 mM N-acetylcysteine, NAC) significantly reduced the cytotoxic activity of S16 and SFe (when exposed up to 25 and 50 ?g/mL, respectively) but did not protect cells treated with S60. Preincubation with NAC significantly reduced HO-1 mRNA expression in cells treated with SFe but did not have any effect on HO-1 mRNA level in cell exposed to S16 and S60. Our study demonstrates that the chemical composition of the silica nanoparticles is a dominant factor in inducing oxidative stress. PMID:22263782
Napierska, Dorota; Rabolli, Virginie; Thomassen, Leen C J; Dinsdale, David; Princen, Catherine; Gonzalez, Laetitia; Poels, Katrien L C; Kirsch-Volders, Micheline; Lison, Dominique; Martens, Johan A; Hoet, Peter H
NASA Astrophysics Data System (ADS)
A novel amorphous cobalt potassium phosphate hydrate compound (KCoPO4�H2O) is identified to be active photocatalyst for oxygen evolution reaction (OER) to facilitate hydrogen generation from water photolysis. It has been synthesized through a facile and cost-effective solution-based precipitation method using earth-abundant materials. Its highly porous structure and large surface areas are found to be responsible for the excellent electrochemical performance featuring a low OER onset at �550 mVSCE and high current density in alkaline condition. Unlike traditional cobalt-based spinel oxides (Co3O4, NiCo2O4) and phosphate (Co-Pi, Co(PO3)2) electrocatalysts, with proper energy band alignment for light-assisted water oxidation, cobalt potassium phosphate hydrate also exhibits robust visible-light response, generating a photocurrent density of �200 ?A cm-2 at 0.7 VSCE. This catalyst could thus be considered as a promising candidate to perform photoelectrochemical water splitting.
Zhang, Ye; Zhao, Chunsong; Dai, Xuezeng; Lin, Hong; Cui, Bai; Li, Jianbao
NASA Astrophysics Data System (ADS)
The use of amorphous and transparent oxides is a key for the development of new thin film transistors and displays. Recently, indium zinc oxide (IZO) was shown to exhibit high transparency in the visible range, low resistivity, and high mobility. Since the properties and the cost of these films depend on the In/(In + Zn) values, the measurement of this ratio is paramount for future developments and applications. We report on accurate analysis of the elemental composition of IZO thin films synthesized using a Combinatorial Pulsed Laser Deposition technique. The monitoring of the thin films elemental composition by Laser-Induced Breakdown Spectroscopy was chosen in view of further in situ and real-time technological developments and process control during IZO fabrication. Our analytical approach is based on plasma modeling, the recorded spectra being then compared to the spectral radiance computed for plasmas in local thermal equilibrium. The cation fractions measured were compared to values obtained by complementary measurements using energy dispersive X-ray spectroscopy and Rutherford backscattering spectrometry. Spectroscopic ellipsometry assisted the scientific discussion. A good agreement between methods was found, independently of the relative fraction of indium and zinc that varied from about 65 to 90 and 35 to 10 at%, respectively, and the measurement uncertainties associated to each analytical method.
Axente, E.; Socol, G.; Beldjilali, S. A.; Mercadier, L.; Luculescu, C. R.; Trinca, L. M.; Galca, A. C.; Pantelica, D.; Ionescu, P.; Becherescu, N.; Hermann, J.; Craciun, V.
A planar violet electroabsorption modulator and modeling of electric effects on zinc oxide excitons
NASA Astrophysics Data System (ADS)
First principle electroabsorption calculations based on WTK spectral density theorem and Dow and Redfield theory were performed and used as the basis of a model to fit experimental electroabsorption data. The calculation results were compared to absorption measurements taken from 4.5 K to 300 K on a c-plane ZnO thin film sample to obtain the temperature broadening linewidth. The extracted broadening parameters were then expressed with two material related coefficients: the exciton-acoustic-phonon interaction strength gammaph = 79.6 +/- 3 microeV/K and exciton-LO-phonon interaction strength Gamma LO G = 242 +/- 10 meV. This expression is independent of sample qualities, or is "generalized" to accommodate the exciton band edge. A concept called "effective microfield intensity" was introduced to represent the crystalline quality. The microfield intensities of two ZnO samples with rocking curve FWHMs � 0.25� and � 0.42� are � 1.3x105 and � 2.26x105 kV/cm respectively. Buffer-assisted growth technique was applied to improve the quality of PLD grown ZnO on sapphire. ZnO thin films were deposited on ATO/ITO/glass substrate at 500 to 700 K, with higher temperature producing better films. XRD of these samples show highly c-oriented ZnO growth on the ATO substrate. ZnO electroabsorption modulators were fabricated based on ZnO/ATO/ITO/glass structure. Two types of top electrodes, Ni semi-transparent electrode (TE) and conducting indium gallium zinc oxide (IGZO) were experimented with the IGZO-coated device reducing the insertion loss by �50%. The DC percentage modulation of these devices have two peaks, over 40% near � 370 nm and around 20% near � 385 nm at 140 V bias. AC testing confirms purely field modulation and shows no evident of frequency cut-off up to 100 kHz. A simple device model attributes the threshold voltage of ZnO electroabsorption modulators to the charge screening effects. Applied voltage was obtained both by converting the electric field based on device model and fitting the observed electroabsorption spectra with the first principle calculation and Gaussian broadening. The field strengths obtained from the two approaches is consistent.
Zhang, Xiyao
An aerosol-spray-assisted approach (ASAA) is proposed and confirmed as a precisely controllable and continuous method to fabricate amorphous mixed metal oxides for electrochemical water splitting. The proportion of metal elements can be accurately controlled to within (5�5)?%. The products can be sustainably obtained, which is highly suitable for industrial applications. ASAA was used to show that Fe6Ni10O(x) is the best catalyst among the investigated Fe-Ni-O(x) series with an overpotential of as low as 0.286?V (10?mA?cm(-2)) and a Tafel slope of 48?mV/decade for the electrochemical oxygen evolution reaction. Therefore, this work contributes a versatile, continuous, and reliable way to produce and optimize amorphous metal oxide catalysts. PMID:24899118
Kuai, Long; Geng, Jing; Chen, Changyu; Kan, Erjie; Liu, Yadong; Wang, Qing; Geng, Baoyou
NASA Astrophysics Data System (ADS)
Hydro-oxygenated amorphous titanium oxide (a-TiO x:OH) films were prepared by plasma-enhanced chemical vapor deposition (PECVD) using precursors of titanium tetraisopropoxide (TTIP) and oxygen. The influences of chemical states and crystal quality on the photocatalytic activity were systematically investigated in the as-deposited and post-annealed films. The degree of the photocatalytic activity was deeply correlated with the porosity related to the hydroxyl (OH) groups in the as-deposited amorphous film. The crystallized anatase structures was observed from the 200 �C-deposited a-TiO x:OH film after a post-annealing treatment at 400 �C. The photocatalytic activity related to the film with anatase structure was markedly superior to that of an amorphous film with porous structures. The larger the crystal size of the anatase structure, the higher the photocatalytic activity obtained. At elevated annealed temperatures, the inferior anatase structure due to the crystalline transformation led to a low photocatalytic activity. It was concluded that the photocatalytic activity of an amorphous TiO x film prepared using PECVD was determined by the porosity originating from the functional OH groups in the film, whereas the crystalline quality of anatase phase in the annealed poly-TiO x film was crucial to the photocatalytic activity.
Wu, Cheng-Yang; Chiang, Bo-Sheng; Chang, Springfield; Liu, Day-Shan
We have investigated the effect of the deposition of an HfO{sub 2} thin film as a gate insulator with different O{sub 2}/(Ar + O{sub 2}) gas ratios using RF magnetron sputtering. The HfO{sub 2} thin film affected the device performance of amorphous indium�gallium�zinc oxide transistors. The performance of the fabricated transistors improved monotonously with increasing O{sub 2}/(Ar + O{sub 2}) gas ratio: at a ratio of 0.35, the field effect mobility of the amorphous InGaZnO thin film transistors was improved to 7.54 cm{sup 2}/(V s). Compared to those prepared with an O{sub 2}/(Ar + O{sub 2}) gas ratio of 0.05, the field effect mobility of the amorphous InGaZnO thin film transistors was increased to 1.64 cm{sup 2}/(V s) at a ratio of 0.35. This enhancement in the field effect mobility was attributed to the reduction of the root mean square roughness of the gate insulator layer, which might result from the trap states and surface scattering of the gate insulator layer at the lower O{sub 2}/(Ar + O{sub 2}) gas ratio.
Jo, Young Je [WCU Department of Printed Electronics, Sunchon National University, Chonnam 540-742 (Korea, Republic of)] [WCU Department of Printed Electronics, Sunchon National University, Chonnam 540-742 (Korea, Republic of); Lee, In-Hwan [School of Advanced Materials Engineering, Chonbuk National University, Chonju 561-756 (Korea, Republic of)] [School of Advanced Materials Engineering, Chonbuk National University, Chonju 561-756 (Korea, Republic of); Kwak, Joon Seop, E-mail: firstname.lastname@example.com [WCU Department of Printed Electronics, Sunchon National University, Chonnam 540-742 (Korea, Republic of)
High-performance solution-processed amorphous zinc-indium-tin oxide thin-film transistors.
Films of the high-performance solution-processed amorphous oxide semiconductor a-ZnIn(4)Sn(4)O(15), grown from 2-methoxyethanol/ethanolamine solutions, were used to fabricate thin-film transistors (TFTs) in combination with an organic self-assembled nanodielectric as the gate insulator. This structurally dense-packed semiconductor composition with minimal Zn(2+) incorporation strongly suppresses transistor off-currents without significant mobility degradation, and affords field-effect electron mobilities of approximately 90 cm(2) V(-1) s(-1) (104 cm(2) V(-1) s(-1) maximum obtained for patterned ZITO films), with I(on)/I(off) ratio approximately 10(5), a subthreshhold swing of approximately 0.2 V/dec, and operating voltage <2 V for patterned devices with W/L = 50. The microstructural and electronic properties of ZITO semiconductor film compositions in the range Zn(9-2x)In(x)Sn(x)O(9+1.5x) (x = 1-4) and ZnIn(8-x)Sn(x)O(13+0.5x) (x = 1-7) were systematically investigated to elucidate those factors which yield optimum mobility, I(on)/I(off), and threshold voltage parameters. It is shown that structural relaxation and densification by In(3+) and Sn(4+) mixing is effective in reducing carrier trap sites and in creating carrier-generating oxygen vacancies. In contrast to the above results for TFTs fabricated with the organic self-assembled nanodielectric, ZnIn(4)Sn(4)O(15) TFTs fabricated with SiO(2) gate insulators exhibit electron mobilities of only approximately 11 cm(2) V(-1) s(-1) with I(on)/I(off) ratios approximately 10(5), and a subthreshhold swing of approximately 9.5 V/dec. PMID:20662515
Kim, Myung-Gil; Kim, Hyun Sung; Ha, Young-Geun; He, Jiaqing; Kanatzidis, Mercouri G; Facchetti, Antonio; Marks, Tobin J
NASA Astrophysics Data System (ADS)
Amorphous tantalum oxide thin films were deposited by reactive rf magnetron sputtering onto [001] silicon substrates. Growth temperature, oxygen partial pressure, and total gas pressure have been varied to obtain thin films with different densities. The thin films were analyzed by glancing angle-of-incidence x-ray diffraction, atomic force microscopy, and variable angle-of-incidence spectroscopic ellipsometry in the near infrared to vacuum ultraviolet spectral region for photon energies from E=1 to 8.5 eV, and in the infrared region from E=0.03 to 1 eV. We present the dielectric function of amorphous tantalum oxide obtained by line shape analysis of the experimental ellipsometric data over the range from E=0.03 to 8.5 eV (40 ?m-145 nm). In the infrared spectral region the ellipsometric data were analyzed using Lorentzian line shapes for each absorption mode observed in the spectra. Amorphous tantalum oxide optical properties in the near infrared to vacuum ultraviolet spectral region were extracted by using a Kim and Garland parameter algorithm [C. C. Kim et al., Phys. Rev. B 45, 11 749 (1992)] in order to model the absorption due to the fundamental band gap of the material. We consider thin film porosity, and therefore analyzed the experimental ellipsometric data by an effective medium approach. We obtain information on the tantalum oxide optical properties, a percentage of void fraction, and film thickness. The "optical" percentage of void fractions corresponds to surface roughness measured by atomic force microscopy and depends on deposition parameters.
Franke, Eva; Trimble, C. L.; DeVries, M. J.; Woollam, J. A.; Schubert, M.; Frost, F.
In this paper a few calcium-manganese oxides and calcium-manganese minerals are studied as catalysts for water oxidation. The natural mineral marokite is also studied as a catalyst for water oxidation for the first time. Marokite is made up of edge-sharing Mn(3+) in a distorted octahedral environment and eight-coordinate Ca(2+) centered polyhedral layers. The structure is similar to recent models of the oxygen evolving complex in photosystem II. Thus, the oxygen evolving complex in photosystem II does not have an unusual structure and could be synthesized hydrothermally. Also in this paper, oxygen evolution is studied with marokite (CaMn?O?), pyrolusite (MnO?) and compared with hollandite (Ba(0.2)Ca(0.15)K(0.3)Mn(6.9)Al(0.2)Si(0.3)O(16)), hausmannite (Mn?O?), Mn?O?.H?O, Ca Mn?O?.H?O, CaMn?O?.H?O, CaMn?O?.H?O and synthetic marokite (CaMn?O?). I propose that the origin of the oxygen evolving complex in photosystem II resulted from absorption of calcium and manganese ions that were precipitated together in the archean oceans by protocyanobacteria because of changing pH from ~5 to ~8-10. As reported in this paper, amorphous calcium-manganese oxides with different ratios of manganese and calcium are effective catalysts for water oxidation. The bond types and lengths of the calcium and manganese ions in the calcium-manganese oxides are directly comparable to those in the OEC. This primitive structure of these amorphous calcium-manganese compounds could be changed and modified by environmental groups (amino acids) to form the oxygen evolving complex in photosystem II. PMID:20814743
Najafpour, Mohammad Mahdi
NASA Astrophysics Data System (ADS)
Negative bias-induced instability of amorphous hafnium indium zinc oxide (?-HIZO) thin film transistors (TFTs) was investigated at various temperatures. In order to examine temperature-induced effects, fabricated TFTs with different combinations of gate insulator and gate metal were stressed by a negative gate bias at various temperatures. As a result, it is proved that negative bias-induced hole-trapping in the gate insulators and temperature-enhanced electron injection from the gate metals occurs at the same time at all temperatures, and the instability of HIZO TFT is more affected by the dominant factor out of the two mechanisms.
Kwon, Dae Woong; Kim, Jang Hyun; Chang, Ji Soo; Kim, Sang Wan; Kim, Wandong; Park, Jae Chul; Song, Ihun; Kim, Chang Jung; Jung, U. In; Park, Byung-Gook
Surface sensitive X-ray reflectivity (XR), fluorescence (XF), and grazing incidence X-ray diffraction (GIXD) experiments were conducted to determine the accumulation of ferric iron Fe (III) or ferrous iron Fe (II) under dihexadecyl phosphate (DHDP) or arachidic acid (AA) Langmuir monolayers at liquid/vapor interfaces. Analysis of the X-ray reflectivity and fluorescence data of monolayers on the aqueous subphases containing FeCl3 indicates remarkably high levels of surface-bound Fe (III) in number of Fe3� ions per molecule (DHDP or AA) that exceed the amount necessary to neutralize a hypothetically completely deprotonated monolayer (DHDP or AA). These results suggest that nano-scale iron (hydr) oxide complexes (oxides, hydroxides or oxyhydroxides) bind to the headgroups and effectively overcompensate the maximum possible charges at the interface. The lack of evidence of in-plane ordering in GIXD measurements and strong effects on the surface-pressure versus molecular area isotherms indicate that an amorphous network of iron (hydr) oxide complexes contiguous to the headgroups is formed. Similar experiments with FeCl2 generally resulted with the oxidation of Fe (II)�Fe (III) which consequently leads to ferric Fe (III) complexes binding albeit with less iron at the interface. Controlling the oxidation of Fe (II) changes the nature and amount of binding significantly. The implications to biomineralization of iron (hydr) oxides are briefly discussed.
Wang, W.; Pleasants, J.; Bu, W.; Park, R.Y.; Kuzmenko, I.; Vaknin, D.
Metal-insulator transitions in IZO, IGZO, and ITZO films
NASA Astrophysics Data System (ADS)
In this study, we measured the low-temperature resistivity of amorphous two- and three-dimensional (2D and 3D) indium-zinc oxide, indium-gallium-zinc oxide, and indium-tin-zinc oxide films with a wide range of carrier densities. To determine their critical characteristics at the metal-insulator transition (MIT), we used the Ioffe-Regel criterion. We found that the MIT occurs in a narrow range between k F ? = 0.13 and k F ? = 0.25, where k F and ? are the Fermi wave number and electron mean free path, respectively. For films in the insulating region, we analyzed ? ( T ) using a procedure proposed by Zabrodskii and Zinov'eva. This analysis confirmed the occurrence of Mott and Efros-Shklovskii (ES) variable-range hopping. The materials studied show crossover behavior from exp(TMott/T)1/4 or exp(TMott/T)1/3 for Mott hopping conduction to exp(TES/T)1/2 for ES hopping conduction with decreasing temperature. For both 2D and 3D materials, we found that the relationship between TMott and TES satisfies TES ? TMott2/3.
Makise, Kazumasa; Hidaka, Kazuya; Ezaki, Syohei; Asano, Takayuki; Shinozaki, Bunju; Tomai, Shigekazu; Yano, Koki; Nakamura, Hiroaki
NASA Astrophysics Data System (ADS)
We fabricated and characterized ferroelectric-gate thin-film transistors (FeTFTs) with an amorphous In�Ga�Zn�O (a-IGZO) channel and an oxide ferroelectric (Bi,La)4Ti3O12 (BLT) gate insulator, and examined the fabrication conditions beforehand for realizing ferroelectric hysteresis in their drain current versus gate voltage (ID�VG) characteristics. First, the optimal annealing conditions for BLT-thin-film formation by the sol�gel method were considered in terms of chemical phenomena and crystallization mechanism. As a result, the leakage current density of the film was decreased by more than two orders of magnitude. Second, sputtering deposition conditions and postdeposition annealing temperatures of a-IGZO thin films were investigated to prepare the a-IGZO channel with good electrical properties. A small charge-injection-type hysteresis width of 0.2 V was obsereved in ID�VG characteristics of a-IGZO/SiO2 TFTs. Finally, a-IGZO/BLT FeTFTs were fabricated using the above results, and the ferroelectric hysteresis with a width of 0.4 V was observed.
Haga, Ken-ichi; Tokumitsu, Eisuke
The mechanisms by which the dissimilatory Fe(III)-reducing bacterium Shewanella alga adheres to amorphous Fe(III) oxide were examined through comparative analysis of S. alga BrY and an adhesion-deficient strain of this species, S. alga RAD20. Approximately 100% of S. alga BrY cells typically adhered to amorphous Fe(III) oxide, while less than 50% of S. alga RAD20 cells adhered. Bulk chemical analysis, isoelectric point analysis, and cell surface analysis by time-of-flight secondary-ion mass spectrometry and electron spectroscopy for chemical analysis demonstrated that the surfaces of S. alga BrY cells were predominantly protein but that the surfaces of S. alga RAD20 cells were predominantly exopolysaccharide. Physicochemical analyses and hydrophobic interaction assays demonstrated that S. alga BrY cells were more hydrophobic than S. alga RAD20 cells. This study represents the first quantitative analysis of the adhesion of a dissimilatory Fe(III)-reducing bacterium to amorphous Fe(III) oxide, and the results collectively suggest that hydrophobic interactions are a factor in controlling the adhesion of this bacterium to amorphous Fe(III) oxide. Despite having a reduced ability to adhere, S. alga RAD20 reduced Fe(III) oxide at a rate identical to that of S. alga BrY. This result contrasts with results of previous studies by demonstrating that irreversible cell adhesion is not requisite for microbial reduction of amorphous Fe(III) oxide. These results suggest that the interaction between dissimilatory Fe(III)-reducing bacteria and amorphous Fe(III) oxide is more complex than previously believed. PMID:16535706
Caccavo, F.; Schamberger, P. C.; Keiding, K.; Nielsen, P. H.
NASA Astrophysics Data System (ADS)
Amorphous metal oxide thin-film transistors (TFTs) are fabricated using InOx-based semiconductors doped with TiO2, WO3, or SiO2. Even at low-dopant densities, the electrical properties of the film strongly depend on the dopant used. We found that this dependence could be reasonably explained by differences in the bond-dissociation energy of the dopants. By incorporating a dopant with a higher bond-dissociation energy, the film became less sensitive to the partial pressure of oxygen used during sputtering and remained electrically stable upon thermal annealing. Thus, choosing a dopant with an appropriate bond-dissociation energy is important when fabricating stable metal-oxide TFTs for flat-panel displays.
Aikawa, Shinya; Nabatame, Toshihide; Tsukagoshi, Kazuhito
We demonstrated self-patterned solution-processed amorphous oxide semiconductor thin-film transistors (TFTs) using photosensitive sol-gels. The photosensitive sol-gels were synthesized by adding ?-diketone compounds, i.e., benzoylacetone and acetylacetone, to sol-gels. The chemically modified photosensitive sol-gels showed a high optical absorption at specific wavelengths due to the formation of metal chelate bonds. Photoreactions of the modified solutions enabled a photoresist-free process. Moreover, Zn�Sn�O with a high Sn ratio, which is hard to wet-etch using conventional photolithography due to its chemical durability, was easily patterned via the self-patterning process. Finally, we fabricated a solution-processed oxide TFT that included fully self-patterned electrodes and an active layer. PMID:24686314
Lim, Hyun Soo; Rim, You Seung; Kim, Hyun Jae
We demonstrated self-patterned solution-processed amorphous oxide semiconductor thin-film transistors (TFTs) using photosensitive sol-gels. The photosensitive sol-gels were synthesized by adding ?-diketone compounds, i.e., benzoylacetone and acetylacetone, to sol-gels. The chemically modified photosensitive sol-gels showed a high optical absorption at specific wavelengths due to the formation of metal chelate bonds. Photoreactions of the modified solutions enabled a photoresist-free process. Moreover, Zn-Sn-O with a high Sn ratio, which is hard to wet-etch using conventional photolithography due to its chemical durability, was easily patterned via the self-patterning process. Finally, we fabricated a solution-processed oxide TFT that included fully self-patterned electrodes and an active layer. PMID:24686314
Lim, Hyun Soo; Rim, You Seung; Kim, Hyun Jae
Amorphous Transparent Conducting Oxides (TCOs) Deposited at T 100<= ..deg.. C (Presentation)
The summary of this report is that amorphous InZnO (a-IZO) is a very versatile TCO with: (1) low process temperatures ({approx} 100 C); (2) easy to make by sputtering; (3) excellent optical and electronic properties; (4) very smooth etchable films; and (5) remarkable thermal processing stability.
Perkins, J.; van Hest, M.; Teplin, C.; Alleman, J.; Dabney, M.; Gedvilas, L.; Keyes, B.; To, B.; Ginley D.
Background The purpose of this study was to investigate the mechanism of noxious effects of amorphous silica nanoparticles on human endothelial cells. Methods Nanoparticle uptake was examined by transmission electron microscopy. Electrochemical nanosensors were used to measure the nitric oxide (NO) and peroxynitrite (ONOO?) released by a single cell upon nanoparticle stimulation. The downstream inflammatory effects were measured by an enzyme-linked immunosorbent assay, real-time quantitative polymerase chain reaction, and flow cytometry, and cytotoxicity was measured by lactate dehydrogenase assay. Results We found that the silica nanoparticles penetrated the plasma membrane and rapidly stimulated release of cytoprotective NO and, to a greater extent, production of cytotoxic ONOO?. The low [NO]/[ONOO?] ratio indicated increased nitroxidative/oxidative stress and correlated closely with endothelial inflammation and necrosis. This imbalance was associated with nuclear factor ?B activation, upregulation of key inflammatory factors, and cell death. These effects were observed in a nanoparticle size-dependent and concentration-dependent manner. Conclusion The [NO]/[ONOO?] imbalance induced by amorphous silica nanoparticles indicates a potentially deleterious effect of silica nanoparticles on vascular endothelium. PMID:22131828
Corbalan, J Jose; Medina, Carlos; Jacoby, Adam; Malinski, Tadeusz; Radomski, Marek W
The design of amorphous noble metallic nanoparticle electrocatalysts is an important fundamental and applied research challenge because their surface is rich in low-coordination sites and defects which could act as the active sites in various catalytic processes. Here we describe new findings on the amorphous platinum-nickel-phosphorous nanoparticles supported on carbon black (PtNiP(a)/C) and the comparison between their catalytic activity and that of the nanoscale crystalline and phase-segregated PtNiP nanoparticles. The nanoscale amorphous, crystalline and phase-segregated catalysts were probed as a function of surface composition, particle size, and thermal treatment conditions using X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, selected area electron diffraction and electrochemical characterization. The results provide the experimental evidence in support of nanoscale amorphous, crystalline, and phase-segregated PtNiP nanoparticles evolution dependence on the catalyst synthesis temperature. More importantly, the results of the electrochemical performance investigation showed that the amorphous structure has not only better catalytic activity for methanol oxidation but also stronger tolerance to carbon monoxide poisoning compared to the crystalline and phase-segregated structure. Besides, the thermal control of the formation of nanoscale amorphous, crystalline and phase-segregated structured catalysts provided the opportunity for establishing the correlation between the nanoscale phase structures of the catalysts and their electrocatalytic activity in methanol oxidation reaction, which plays an important role in developing highly active electrocatalysts for direct methanol fuel cells. PMID:24414092
Ma, Yanjiao; Wang, Rongfang; Wang, Hui; Linkov, Vladimir; Ji, Shan
Amorphous Indium-Zinc-Oxide Transparent Conductors for Thin Film PV: Preprint
Amorphous InZnO's (a-IZO) basic PV applicability has now been demonstrated in prototype CIGS, Si Heterojunction (SiHJ) and organic photovoltaics (OPV). However, to move beyond initial demonstration devices, improved TCO properties and processibility of the a-IZO films are needed. Here, RF-superimposed DC sputtering was used to improve the reliable deposition of a-IZO with conductivity > 3000 S/cm.
Perkins, J.; Gennett, T.; Galante, M.; Gillaspie, D.; Ginley, D.
Transparent electronic devices formed on flexible substrates are expected to meet emerging technological demands where silicon-based electronics cannot provide a solution. Examples of active flexible applications include paper displays and wearable computers. So far, mainly flexible devices based on hydrogenated amorphous silicon (a-Si:H) and organic semiconductors have been investigated. However, the performance of these devices has been insufficient for use
Kenji Nomura; Hiromichi Ohta; Akihiro Takagi; Toshio Kamiya; Masahiro Hirano; Hideo Hosono
New phenomena in FMR and EPR studies of amorphous oxide films and their crystallization
NASA Astrophysics Data System (ADS)
(BiDy) 3Fe 5O 12 films were made in the amorphous state by rf magnetron sputtering from a sintered Bi 2Dy 1Fe 5O 12 ceramic target onto quartz substrates and studied by X-ray diffraction. The films were annealed at temperatures ranging from 500 to 700�C for 1 h in air and also at 650�C for different periods of time from 5 to 60 min. X-ray diffraction was used to determined the phase components of the samples. In the X-ray patterns, the amorphous films had two diffuse broad maxima in X-ray diffraction patterns centred at the double diffraction angles 2 ?=31� and 52�, respectively. The films crystallized at 650�C and all the crystallized samples have a single phase of garnet. The FMR linewidth increased with the decreases in annealing temperature and annealing time. No FMR and EPR of Fe 3+ were observed in the amorphous films even though they contained large amounts of Fe 3+ ions, while the EPR of Fe 3+ was observed in slide glass with the same gain.
Zhang, H. Y.; Gu, B. X.; Zhai, H. R.; Miao, Y. Z.; Lu, M.
NASA Astrophysics Data System (ADS)
MnV 2O 6 + ? � nH 2O (0 < ? < 1) amorphous oxides were prepared by a two-step process including the precipitation of a crystallized precursor MnV 2O 6 � 4H 2O and its ozonation at temperatures below 100 �C. Their characterization by spectroscopic techniques (XAS and EELS) shows that V 5+ retains a VO 5 environment and that Mn, which remains in octahedral coordination, is oxidized to Mn 4+ mainly. MnV 2O 6 + ? compounds insert reversibly large amounts of Li per formula unit (e.g. Li 12MnV 2O 6.96) at low voltage. After the first insertion/de-insertion cycle, subsequent cycles correspond to fully reversible lithium insertion between the two compositions: Li ?MnV 2O 6 + ? ( ? ? 2) and Li 12MnV 2O 6 + ? (from 600 to 900 mAh/g). Investigations on the Li derivatives by XAS and EELS show that during the insertion/de-insertion cycles the V oxidation state varies reversibly between +5 and +3. Mn 4+ cations are reduced to Mn 2+ upon the first discharge. During the subsequent cycles the average Mn oxidation state varies reversibly between +2 and about +2.6. It clearly appears that the electron transfer from Li to the host matrix decreases with increasing x in Li xMnV 2O 6 + ?.
Piffard, Y.; Leroux, F.; Guyomard, D.; Mansot, J.-L.; Tournoux, M.
NASA Astrophysics Data System (ADS)
Intrinsic hydrogenated amorphous silicon oxide (i-a-SiO:H) films deposited by very high frequency plasma-enhanced chemical vapor deposition (60 MHz VHF-PECVD) at a low substrate temperature of approximately 200 �C were used as a front buffer layer in p-type hydrogenated microcrystalline silicon oxide/n-type crystalline silicon (p-�c-SiO:H/n-c-Si) heterojunction solar cells. We found that the oxygen concentration in the i-a-SiO:H buffer layer strongly affected the solar cell performance and that the short wavelength response in quantum efficiency (QE) was improved by oxygen addition. Employing a p-�c-SiO:H/i-a-SiO:H/n-Si [Czochralski (CZ), 200 �m, (100)]/i-a-Si:H/n-a-Si:H/Ag/Al configuration, we achieved an efficiency of 17.9% with Voc of 671 mV.
Sritharathikhun, Jaran; Yamamoto, Hiroshi; Miyajima, Shinsuke; Yamada, Akira; Konagai, Makoto
High mobility bottom gate InGaZnO thin film transistors with SiO{sub x} etch stopper
The authors report on the fabrication of thin film transistors (TFTs), which use an amorphous indium gallium zinc oxide (a-IGZO) channel, by rf sputtering at room temperature and for which the channel length and width are patterned by photolithography and dry etching. To prevent plasma damage to the active channel, a 100-nm-thick SiO{sub x} layer deposited by plasma enhanced chemical vapor deposition was adopted as an etch stopper structure. The a-IGZO TFT (W/L=10 {mu}m/50 {mu}m) fabricated on glass exhibited a high field-effect mobility of 35.8 cm{sup 2}/V s, a subthreshold gate swing value of 0.59 V/decade, a thrseshold voltage of 5.9 V, and an I{sub on/off} ratio of 4.9x10{sup 6}, which is acceptable for use as the switching transistor of an active-matrix TFT backplane.
Kim, Minkyu; Jeong, Jong Han; Lee, Hun Jung; Ahn, Tae Kyung; Shin, Hyun Soo; Park, Jin-Seong; Jeong, Jae Kyeong; Mo, Yeon-Gon; Kim, Hye Dong [Corporate R and D Center, Samsung SDI Co., LTD, 428-5, Gongse-Dong, Kiheung-Gu, Yongin-Si, Gyeonggi-Do 449-902 (Korea, Republic of)
In this letter, we investigated the structural and electrical characteristics of high-? Er2O3 and Er2TiO5 gate dielectrics on the amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistor (TFT) devices. Compared with the Er2O3 dielectric, the a-IGZO TFT device incorporating an Er2TiO5 gate dielectric exhibited a low threshold voltage of 0.39 V, a high field-effect mobility of 8.8 cm2/Vs, a small subthreshold swing of 143 mV/decade, and a high Ion/Ioff current ratio of 4.23 � 107, presumably because of the reduction in the oxygen vacancies and the formation of the smooth surface roughness as a result of the incorporation of Ti into the Er2TiO5 film. Furthermore, the reliability of voltage stress can be improved using an Er2TiO5 gate dielectric. PMID:23294730
Chen, Fa-Hsyang; Her, Jim-Long; Shao, Yu-Hsuan; Matsuda, Yasuhiro H; Pan, Tung-Ming
NASA Astrophysics Data System (ADS)
In this letter, we investigated the structural and electrical characteristics of high- ? Er2O3 and Er2TiO5 gate dielectrics on the amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistor (TFT) devices. Compared with the Er2O3 dielectric, the a-IGZO TFT device incorporating an Er2TiO5 gate dielectric exhibited a low threshold voltage of 0.39 V, a high field-effect mobility of 8.8 cm2/Vs, a small subthreshold swing of 143 mV/decade, and a high I on/ I off current ratio of 4.23 � 107, presumably because of the reduction in the oxygen vacancies and the formation of the smooth surface roughness as a result of the incorporation of Ti into the Er2TiO5 film. Furthermore, the reliability of voltage stress can be improved using an Er2TiO5 gate dielectric.
Chen, Fa-Hsyang; Her, Jim-Long; Shao, Yu-Hsuan; Matsuda, Yasuhiro H.; Pan, Tung-Ming
Flexible double gate a-IGZO TFT fabricated on free standing polyimide foil
NASA Astrophysics Data System (ADS)
In this paper, the concept of double gate transistors is applied to mechanically flexible amorphous indium-gallium-zinc-oxide (a-IGZO) thin film transistors (TFTs) fabricated on free standing plastic foil. Due to the temperature sensitivity of the plastic substrate, a-IGZO is a suitable semiconductor because it provides carrier mobilities around 10 cm2/Vs when deposited at room temperature. Double gate TFTs with connected bottom and top gate are compared to bottom gate reference TFTs fabricated on the same substrate. Double gate a-IGZO TFTs exhibit a by 78% increased gate capacitance, a by 700 mV higher threshold voltage, and therefore an up to 92% increased transconductance when characterized at the same gate voltage above threshold (over-bias voltage). The subthreshold swing and the on/off current ratios are improved as well, and reach excellent values of 69 mV/dec and 2 � 109, respectively. The mechanical flexibility of double gate TFTs compared to bottom gate TTFs is investigated, and device operation is shown while the double gate TFT is exposed to tensile strain of 0.55%, induced by bending to a radius of 5 mm.
M�nzenrieder, Niko; Zysset, Christoph; Petti, Luisa; Kinkeldei, Thomas; Salvatore, Giovanni A.; Tr�ster, Gerhard
NASA Astrophysics Data System (ADS)
We discuss the device degradation mechanism of amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistors (TFTs) under simultaneous gate and drain bias stresses based on the electronic trap characterization results. The transfer curve exhibits an apparent negative shift as the stress time increases, and a formation of hump is observed in the transfer curve after stresses. A notable increase of the frequency dispersion is observed after stresses in both gate-to-drain capacitance-voltage (CGD-VG) and gate-to-source capacitance-voltage (CGS-VG) curves, which implies that the subgap states are generated by simultaneous gate and drain bias stresses, and the damaged location is not limited to the drain side of TFTs. The larger frequency dispersion is observed in CGD-VG curves after stresses in a wider channel device, which implies that the heat is an important factor in the generation of the subgap states under simultaneous gate and drain bias stresses in a-IGZO TFTs. Based on the electronic trap characterization results, we conclude that the impact ionization near the drain side of the device is not a dominant mechanism causing the generation of subgap states and device degradation in a-IGZO TFTs under simultaneous gate and drain bias stresses. The generation of oxygen vacancy-related donor-like traps near the conduction band edge is considered as a possible mechanism causing the device degradation under simultaneous gate and drain bias stresses in a-IGZO TFTs.
Jeong, Chan-Yong; Lee, Daeun; Song, Sang-Hun; In Kim, Jong; Lee, Jong-Ho; Kwon, Hyuck-In
In this letter, we investigated the structural and electrical characteristics of high-? Er2O3 and Er2TiO5 gate dielectrics on the amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistor (TFT) devices. Compared with the Er2O3 dielectric, the a-IGZO TFT device incorporating an Er2TiO5 gate dielectric exhibited a low threshold voltage of 0.39 V, a high field-effect mobility of 8.8 cm2/Vs, a small subthreshold swing of 143 mV/decade, and a high Ion/Ioff current ratio of 4.23 � 107, presumably because of the reduction in the oxygen vacancies and the formation of the smooth surface roughness as a result of the incorporation of Ti into the Er2TiO5 film. Furthermore, the reliability of voltage stress can be improved using an Er2TiO5 gate dielectric. PMID:23294730
NASA Astrophysics Data System (ADS)
We investigated the effects of Ar and O2 treatment and of Ar/O2 mixedplasma treatment on the electrical characteristics of solution-processed amorphous indium-gallium-zinc-oxide ( a-IGZO) thin-film transistors (TFTs). The electrical performance and the instability of a-IGZO TFTs were significantly improved by the plasma treatments. The plasma treatments reduced the carbon-based residual contamination that acted as possible trap sites. In particular, the O2-plasma treatment produced a significant improvement in the reliability of a-IGZO TFTs when compared with the Ar-plasma-treated device, owing to the elimination of residual carbon in the active channel of the solution-processed a-IGZO. However, the optimized improvement of the solution-processed a-IGZO TFT under a gate bias stress was obtained for the device treated with an Ar/O2 mixed-gas plasma. The plasma treatment in the Ar/O2-mixed ambience remarkably enhanced not only the reliability but also the electrical performance of the a-IGZO TFT; the on/off-current ratio, the field-effect mobility, and the subthreshold slope were 6.78 � 107, 1.24 cm2/V�s, and 513 mV/dec, respectively.
Kim, Kwan-Soo; Hwang, Yeong-Hyeon; Hwang, Inchan; Cho, Won-Ju
Enhanced photosensitivity of InGaZnO-TFT with a CuPc light absorption layer
NASA Astrophysics Data System (ADS)
A copper phthalocyanine (CuPc) organic semiconductor is capped onto an amorphous indium-gallium-zinc-oxide (InGaZnO) thin film transistor (TFT) to enhance the photosensitivity of InGaZnO-TFT. The CuPc organic semiconductor is served as a light absorption layer and forms a p-n junction with the InGaZnO film. After 60 s white light illumination, light responsivity (R) of InGaZnO-TFT with a CuPc light absorption layer reaches a value of 148.5 A/W at a gate-source voltage (VGS) of 20 V, which is much larger than that (31.2 A/W) of the conventional InGaZnO-TFT. The results are attributed to the following mechanism. First, a CuPc layer is employed as the light absorption layer. Second, CuPc/InGaZnO p-n junction enables the injection of electron into InGaZnO film. Our results indicate that using CuPc as light absorption layer is an effective approach to improve the photosensitivity of InGaZnO-TFT.
Li, Jun; Zhou, Fan; Lin, Hua-Ping; Zhu, Wen-Qing; Zhang, Jian-Hua; Jiang, Xue-Yin; Zhang, Zhi-Lin
Amorphous oxide semiconductor thin-film transis- tors on flexible plastic substrates typically suffer from perfor- mance and stability issues related to the maximum processing temperature limitation of the polymer. A novel device architecture based on a dual active layer enables significant improvements in both performance and stability. Device fabrication occurs below 200 ? C on a polyethylene naphthalate (PEN) substrate using
Michael A. Marrs; Curtis D. Moyer; Edward J. Bawolek; Rita J. Cordova; Jovan Trujillo; Gregory B. Raupp; Bryan D. Vogt
Amorphous-gallium-indium-zinc-oxide (a-GIZO) thin filmtransistors (TFTs) are fabricated without annealing, using processes and equipment for conventional a-Si:H TFTs. It has been very difficult to obtain sound TFT characteristics, because the a-GIZO active layer becomes conductive after dry etching the Mo source/drain electrode and depositing the a-SiO{sub 2} passivation layer. To prevent such damages, N{sub 2}O plasma is applied to the back surface of the a-GIZO channel layer before a-SiO{sub 2} deposition. N{sub 2}O plasma-treated a-GIZO TFTs exhibit excellent electrical properties: a field effect mobility of 37 cm{sup 2}/V s, a threshold voltage of 0.1 V, a subthreshold swing of 0.25 V/decade, and an I{sub on/off} ratio of 7.
Park, Jaechul; Kim, Sangwook; Kim, Changjung; Kim, Sunil; Song, Ihun; Yin, Huaxiang; Kim, Kyoung-Kok; Lee, Sunghoon; Hong, Kiha; Park, Youngsoo [Semiconductor Device Laboratory, Samsung Advanced Institute of Technology, Yongin-Si, Gyeonggi-Do 449-712 (Korea, Republic of); Lee, Jaecheol; Jung, Jaekwan; Lee, Eunha [Analytical Engineering Center, Samsung Advanced Institute of Technology, Yongin-Si, Gyeonggi-Do 449-712 (Korea, Republic of); Kwon, Kee-Won [Department of Semiconductor Systems Engineering, Sungkyunkwan University, Suwon-Si, Gyeonggi-Do 440-746 (Korea, Republic of)
NASA Astrophysics Data System (ADS)
Fabrication of crystalline indium-tin-oxide (c-ITO) nanogratings and smooth line patterns on amorphous ITO (a-ITO) thin films by femtosecond laser-induced structuring and simultaneous crystallization followed by chemical etching is demonstrated. Three types of c-ITO structures are obtained merely by controlling the laser pulse energy of a high-repetition rate femtosecond laser at wavelength 532 nm: nanogratings perpendicular to laser polarization direction with period of 130 � 11 nm, smooth c-ITO line patterns as well as nanogratings parallel to laser polarization direction with period of 390 � 10 nm. Large area c-ITO patterns and nanograting structures are fabricated, which are expected to be used in optoelectronic and micro-electronic devices.
Cheng, C. W.; Lee, I. M.; Chen, J. S.
NASA Astrophysics Data System (ADS)
In this study, the degradation mechanism and location of defect creation (whether the source or the drain side) of amorphous hafnium-indium-zinc-oxide thin film transistors under negative-bias-illumination stress was investigated. Most of the electrical characteristics�such as threshold voltage, subthreshold slope, and mobility�deteriorated remarkably due to defects generated in the deep-level and tail bands of the semiconductor bandgap. (The extent of hysteresis due to damage reflects the amount of defects generated.) As the drain voltage was increased�whilst under stress and with the gate voltage fixed�the electrical properties of thin film transistors got progressively worse. This indicates that the drain region was more seriously affected (compared to the source region), most likely because the drain region was placed under a higher negative field in the active layer.
Chul Park, Jae; Ahn, Seung-Eon; Jung Kim, Chang; Lee, Ho-Nyeon; Im, Seongil
This study unveils a chemical functionalization provoked phase transformation in the naphthalene modified multi-walled carbon nanotubes (MWCNTs) and the associated formation of amorphous carbonaceous particles of various size and morphology. Functionalized nanotubes were prepared by a sulfonation-oxidization and a highly corrosive oxidative sulfation reaction then characterized by means of thermogravimetry\\/mass spectrometry, X-ray photoelectron spectroscopy, scanning and transmission electron microscopy and
Andr�s Gergely; Zolt�n P�szti; Judith Mih�ly; L�szl� Szab�; Erika K�lm�n
Fe(CO)(5) physisorbs onto Corning's code 7930 porous Vycor glass (PVG) and dried (
Sunil, Dehipalawage; Dong, Jinquan; Gafney, Harry D
Developing electrode materials with both high energy and power densities holds the key for satisfying the urgent demand of energy storage worldwide. In order to realize the fast and efficient transport of ions/electrons and the stable structure during the charge/discharge process, hierarchical porous Fe3O4/graphene nanowires supported by amorphous vanadium oxide matrixes have been rationally synthesized through a facile phase separation process. The porous structure is directly in situ constructed from the FeVO4�1.1H2O@graphene nanowires along with the crystallization of Fe3O4 and the amorphization of vanadium oxide without using any hard templates. The hierarchical porous Fe3O4/VOx/graphene nanowires exhibit a high Coulombic efficiency and outstanding reversible specific capacity (1146 mAh g(-1)). Even at the high current density of 5 A g(-1), the porous nanowires maintain a reversible capacity of ?500 mAh g(-1). Moreover, the amorphization and conversion reactions between Fe and Fe3O4 of the hierarchical porous Fe3O4/VOx/graphene nanowires were also investigated by in situ X-ray diffraction and X-ray photoelectron spectroscopy. Our work demonstrates that the amorphous vanadium oxides matrixes supporting hierarchical porous Fe3O4/graphene nanowires are one of the most attractive anodes in energy storage applications. PMID:25314630
An, Qinyou; Lv, Fan; Liu, Qiuqi; Han, Chunhua; Zhao, Kangning; Sheng, Jinzhi; Wei, Qiulong; Yan, Mengyu; Mai, Liqiang
NASA Astrophysics Data System (ADS)
Amorphous palladium nanoparticles functionalized helical carbon nanofibers (ApPd-HCNFs) were synthesized using a phase-transfer method. Palladium nanoparticles (Pd-NP) were first prepared using n-dodecyl sulfide as reducing agent and stabilizing ligands in ethanol. The Pd-NPs were then modified with benzyl mercaptan and transferred into a toluene solution with HCNFs which were decorated with amorphous palladium. The materials were characterized with high-resolution transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy and cyclic voltammetry showing that amorphous palladium nanoparticles were uniformly anchored at the HCNFs surface and that the ApPd-HCNFs exhibit high electrocatalytic activity towards hydrazine oxidation.
Hu, Guangzhi; Sharifi, Tiva; Nitze, Florian; Barzegar, Hamid Reza; Tai, Cheuk-Wai; W�gberg, Thomas
Bioactive amorphous phase/TiO2 nanocrystal (APTN) composite coatings were fabricated by microarc oxidation (MAO) on Ti. The APTN coatings are composed of much amorphous phase with Si, Na, Ca, Ti and O elements and a few TiO2 nanocrystals. With increasing applied voltage, the micropore density of the APTN coating decreases and the micropore size of the APTN coating increases. The results indicate that less MC3T3-E1 cells attach on the APTN coatings as compared to Ti. However, the APTN coatings greatly enhance the cell proliferation ability and the activity of alkaline phosphatase. The amorphous phase and the concentrations of the released Ca and Si from the APTN coatings during cell culture have significant effects on the cell response. PMID:24863215
Zhou, Rui; Wei, Daqing; Yang, Haoyue; Feng, Wei; Cheng, Su; Li, Baoqiang; Wang, Yaming; Jia, Dechang; Zhou, Yu
NASA Astrophysics Data System (ADS)
Amorphous surface oxides of III-V semiconductors are harmful in many contexts of device development. Using low-energy electron diffraction and photoelectron spectroscopy, we demonstrate that surface oxides formed at Sn-capped GaAs(100) and InAs(100) surfaces in air are effectively removed by heating. This Sn-mediated oxide desorption procedure results in the initial well-defined Sn-stabilized (1�2) surface even for samples exposed to air for a prolonged time. Based on ab initio calculations we propose that the phenomenon is due to indirect and direct effects of Sn. The Sn-induced surface composition weakens oxygen adsorption.
Laukkanen, P.; Punkkinen, M. P. J.; L�ng, J.; Tuominen, M.; Kuzmin, M.; Tuominen, V.; Dahl, J.; Adell, J.; Sadowski, J.; Kanski, J.; Poloj�rvi, V.; Pakarinen, J.; Kokko, K.; Guina, M.; Pessa, M.; V�yrynen, I. J.
Ga2O3 thin films were produced by sputter deposition by varying the substrate temperature (Ts) in a wide range (Ts=25-800 oC). The structural characteristics and optical properties of Ga2O3 films were evaluated using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDS), Rutherford backscattering spectrometry (RBS) and spectrophotometric measurements. The effect of growth temperature is significant on the chemistry, crystal structure and morphology of Ga2O3 films. XRD and SEM analyses indicate that the Ga2O3 films grown at lower temperatures were amorphous while those grown at Ts?500 oC were nanocrystalline. RBS measurements indicate the well-maintained stoichiometry of Ga2O3 films at Ts=300-700 oC. The spectral transmission of the films increased with increasing temperature. The band gap of the films varied from 4.96 eV to 5.17 eV for a variation in Ts in the range 25-800 oC. A relationship between microstructure and optical property is discussed.
Kumar, S. Sampath; Rubio, E. J.; Noor-A-Alam, M.; Martinez, G.; Manandhar, Sandeep; Shutthanandan, V.; Thevuthasan, Suntharampillai; Ramana, C.V.
Resistive Switching Behavior in Amorphous Aluminum Oxide Film Grown by Chemical Vapor Deposition
NASA Astrophysics Data System (ADS)
The repeatable bipolar resistive switching phenomenon is observed in amorphous Al2O3 prepared by metal-organic chemical vapor deposition on ITO glass, with ITO as the bottom electrode and Ag as the top electrode. The crystal structure, morphology, composition and optical properties of Al2O3 thin films are investigated by x-ray diffraction, x-ray photoelectron spectroscopy, atomic force microscopy and ultraviolet-visible-infrared spectroscopy, respectively. The electronic character of Ag/Al2O3/ITO structure is tested by an Agilent B1500A. The device shows a typical bipolar resistive switching behavior under the dc voltage sweep mode at room temperature. The variation ratio between HRS and LRS is larger than nearly three orders of magnitude, which indicates the good potential of this structure in future resistive random access memory (ReRAM) applications. Based on the conductive filament model, the high electric field is considered the main reason for the resistive switching according to our measurements.
Quan, Xiao-Tong; Zhu, Hui-Chao; Cai, Hai-Tao; Zhang, Jia-Qi; Wang, Xiao-Jiao
Liquid and glassy oxide materials play a vital role in multiple scientific and technological disciplines, but little is known about the part played by oxygen�oxygen interactions in the structural transformations that change their physical properties. Here we show that the coordination number of network-forming structural motifs, which play a key role in defining the topological ordering, can be rationalized in terms of the oxygen-packing fraction over an extensive pressure and temperature range. The result is a structural map for predicting the likely regimes of topological change for a range of oxide materials. This information can be used to forecast when changes may occur to the transport properties and compressibility of, e.g., fluids in planetary interiors, and is a prerequisite for the preparation of new materials following the principles of rational design. PMID:24982151
Zeidler, Anita; Salmon, Philip Stephen; Skinner, Lawrie Basil
Liquid and glassy oxide materials play a vital role in multiple scientific and technological disciplines, but little is known about the part played by oxygen-oxygen interactions in the structural transformations that change their physical properties. Here we show that the coordination number of network-forming structural motifs, which play a key role in defining the topological ordering, can be rationalized in terms of the oxygen-packing fraction over an extensive pressure and temperature range. The result is a structural map for predicting the likely regimes of topological change for a range of oxide materials. This information can be used to forecast when changes may occur to the transport properties and compressibility of, e.g., fluids in planetary interiors, and is a prerequisite for the preparation of new materials following the principles of rational design. PMID:24982151
Zeidler, Anita; Salmon, Philip Stephen; Skinner, Lawrie Basil
Formation of thin film Tl-based high-Tc? superconducting oxides from amorphous alloy precursors
and satisfying. John Charles Williams TABLE OF CONTENTS ABSTRACT. ACKNOWLEDGMENTS. TABLE OF CONTENTS. LIST OF TABLES. LIST OF FIGURES. I. INTRODUCTION. 1v v vu1 A. Properties of Perovskites and Copper-Oxide Superconductors. . . . . . . . . 2 1.... Fundamental Properties. 2. Perovskite Crystal Structure. 3. Perovskite Crystal Structure Modifications 4, Structure of Thallate Superconductors . . B. Thallium-based Thin Film Superconductors. . . . 1. Tl-based Thin Film Production Methods. . . . 2...
Williams, John Charles
The uncontrolled aggregation of amorphous calcium phosphate (ACP) particulate fillers and their uneven distribution within polymer matrices can have adverse effects on the properties of ACP composites. In this paper we assessed the influence of non-ionic and anionic surfactants and poly(ethylene oxide) (PEO) introduced during the preparation of ACP on the particle size distribution and compositional properties of ACP. In addition, the mechanical strength of polymeric composites utilizing such fillers with a photo-activated binary methacrylate resin was evaluated. Zirconia-hybridized ACP (Zr-ACP) filler and its corresponding composite served as controls for this study. Surfactant- and PEO-ACPs had an average water content of 16.8 % by mass. Introduction of the anionic surfactant reduced the median particle diameter about 45 % (4.1 ?m vs. 7.4 ?m for the Zr-ACP control). In the presence of PEO, however, the dm increased to 14.1 ?m. There was no improvement in the biaxial flexure strength (BFS) in any of the dry composite specimens prepared with the surfactant- and/or PEO-ACPs compared to those formulated with Zr-ACP. The BFS of wet composite specimens decreased by 50 % or more after a month-long exposure to saline solutions. Other types of surfactants and/or polymers as well as alternative surface modification protocols need to be explored for their potential to provide better dispersion of ACP into the matrix resin and better mechanical performance ACP composites. PMID:18714365
Antonucci, J.M.; Liu, D.W.; Skrtic, D.
In this report, we have investigated on the defect state of diborane (B2H6) doped wide bandgap hydrogenated amorphous silicon oxide (p-type a-SiO:H) films prepared using silane (SiH4), hydrogen (H2) and nitrous oxide (N2O) in a radio frequency (RF) plasma enhanced chemical vapor deposition (PECVD) system with different hydrogen dilutions. The films prepared with higher hydrogen dilution show lower Urbach energy (Eu), lower microstructure (R*), lower short and medium range disorder (omegaTO, Gamma(TO), I(TA)/I(TO), I(LA)/I(TO)), higher dark conductivity (sigma d) and higher refractive index (n) with high optical gap (Eg). Eu decreases from 248 meV to 153 meV, and R* decreases from 0.46 to 0.26, Raman peak omegaTO-TO mode position shifts from 480.24 to 483.28, GammaTO-full width half maximum of omegaTO decreases from 78.16 to 63.87, I(TA)/I(TO)-the ratio of integrated area of TA and TO mode decreases from 0.624 to 0.474, I(LA)/I(TO)-the ratio of integrated area of LA and TO mode deceases from 0.272 to 0.151, sigma d increases from 4.6 x 10(-7) S/cm to 1.1 x 10(-6) S/cm, n increases from 3.70 to 3.86. Reduced Nd, Eu and R* at wide Eg indicates that the films are more useful for solar cell window layer. Applying this layer to a single junction solar cell shows open circuit voltage (Voc) = 0.80 V, short circuit current density (Jsc) = 16.3 mA/cm2, fill factor (FF) = 72%, efficiency (eta) = 9.4%. PMID:24266147
Park, Jinjoo; Iftiquar, S M; Lee, Sunwha; Park, Hyeongsik; Shin, Chonghoon; Jung, Junhee; Lee, Youn-Jung; Balaji, Nagarajan; Yi, Junsin
Solution processed zinc tin oxide (ZTO) thin film transistors (TFTs) were fabricated by varying the Zn/Sn composition. The addition of Sn to the zinc oxide (ZnO) films resulted in improved electrical characteristics, with devices of Zn0.7Sn0.3O composition showing the highest mobility of 7.7 cm(2)/(V s). An improvement in subthreshold swings was also observed, indicative of a reduction of the interfacial trap densities. Mobility studies at low temperature have been carried out, which indicated that the activation energy was reduced with Sn incorporation. Kelvin probe force microscopy was performed on the films to evaluate work function and correlated to the metal-semiconductor barrier indicating Zn0.7Sn0.3O films had the smallest barrier for charge injection. Organic-inorganic hybrid complementary inverters with a maximum gain of 10 were fabricated by integrating ZTO TFTs with poly-3-hexylthiophene (P3HT) transistors. PMID:24380364
Chandra, R Devi; Rao, Manohar; Zhang, Keke; Prabhakar, Rajiv Ramanujam; Shi, Chen; Zhang, Jie; Mhaisalkar, Subodh G; Mathews, Nripan
NASA Astrophysics Data System (ADS)
Controlled photo-induced oxidation and amorphization of elemental trigonal tellurium are achieved by laser irradiation at optical wavelengths. These processes are monitored in situ by time-resolved Raman scattering and ex situ by electron microscopies. Ultrathin TeO2 films form on Te surfaces, as a result of irradiation, with an interface layer of amorphous Te intervening between them. It is shown that irradiation, apart from enabling the controllable transformation of bulk Te to one-dimensional nanostructures, such as Te nanotubes and hybrid core-Te/sheath-TeO2 nanowires, causes also a series of light-driven (athermal) phase transitions involving the crystallization of the amorphous TeO2 layers and its transformation to a multiplicity of crystalline phases including the ?-, ?-, and ?-TeO2 crystalline phases. The kinetics of the above photo-induced processes is investigated by Raman scattering at various laser fluences revealing exponential and non-exponential kinetics at low and high fluence, respectively. In addition, the formation of ultrathin (less than 10 nm) layers of amorphous TeO2 offers the possibility to explore structural transitions in 2D glasses by observing changes in the short- and medium-range structural order induced by spatial confinement.
Vasileiadis, Thomas; Yannopoulos, Spyros N.
Organo-inorgano nanocomposites with colloidal dimensions have interesting optical, catalytic, and mechanical properties, particularly when such hybrids are reinforced with transition metal oxide nanoparticles. Nanoparticles with a mean size of 1.0-2.4 nm are obtained through hydrolysis of aluminum isopropoxide in the L(2) phase of amphiphilic (PDMS-POE) polydimethylsiloxane-polyoxyethylene Silwet L-7607-octanol/acetylacetone-water mixtures. The particle sizes are related weakly to the microemulsion composition: 0.8-1.2 nm for 20 wt% Silwet L-7607 and 2.0-2.4 nm for 50 wt% Silwet L-7607. Protection of the particles against aggregation is ensured through their confinement in the intraaggregate colloidal domains. Factors affecting the hydrolysis-condensation process of acetylacetone-complexed aluminum isopropoxide in copolymer-poor and copolymer-rich regions of PDMS-POE W/O microemulsions are studied by Fourier transform infrared spectroscopy, small angle X-ray scattering, and transmission electron microscopy. Prepared nanoparticulate dispersions possess long-term stability and form clear mixtures in different organic polar and nonpolar solvents. PMID:16290335
Berkovich, Yana; Aserin, Abraham; Wachtel, Ellen; Garti, Nissim
NASA Astrophysics Data System (ADS)
Charging/discharging behaviors of de-alloyed and anodic oxidized Ti-Ni-Si amorphous alloy ribbons were measured as a function of current between 10 pA and 100 mA, using galvanostatic charge/discharging method. In sharp contrast to conventional electric double layer capacitor (EDLC), discharging behaviors for voltage under constant currents of 1, 10 and 100 mA after 1.8 ks charging at 100 mA show parabolic decrease, demonstrating direct electric storage without solvents. The supercapacitors, devices that store electric charge on their amorphous TiO2-x surfaces that contain many 70-nm sized cavities, show the Ragone plot which locates at lower energy density region near the 2nd cells, and RC constant of 800 s (at 1 mHz), which is 157,000 times larger than that (5 ms) in EDLC.
Fukuhara, Mikio; Sugawara, Kazuyuki
NASA Astrophysics Data System (ADS)
We investigate the correlation between the atomic structures of amorphous zinc-tin-oxide (a-ZTO) thin films grown by atomic layer deposition (ALD) and their electronic transport properties. We perform synchrotron-based X-ray absorption spectroscopy at the K-edges of Zn and Sn with varying [Zn]/[Sn] compositions in a-ZTO thin films. In extended X-ray absorption fine structure (EXAFS) measurements, signal attenuation from higher-order shells confirms the amorphous structure of a-ZTO thin films. Both quantitative EXAFS modeling and X-ray absorption near edge spectroscopy (XANES) reveal that structural disorder around Zn atoms increases with increasing [Sn]. Field- and Hall-effect mobilities are observed to decrease with increasing structural disorder around Zn atoms, suggesting that the degradation in electron mobility may be correlated with structural changes.
Siah, Sin Cheng; Lee, Sang Woon; Lee, Yun Seog; Heo, Jaeyeong; Shibata, Tomohiro; Segre, Carlo U.; Gordon, Roy G.; Buonassisi, Tonio
Nitrogen plasma treatment was performed on fluorine-doped tin oxide (SnO{sub 2}:F) front electrodes, and its impact on the performance of pin type amorphous Si (a-Si) solar cells was investigated. Nitrogen plasma treatment reverses the surface band bending of SnO{sub 2}:F from accumulation to depletion, thus in turn reversing the band bending of the p type amorphous silicon carbide (p-a-SiC) window layer. The reversal of band bending leads to the collection of carriers generated in p-a-SiC, and quantum efficiency in the short wavelength regime is thereby enhanced. On the other hand, surface depletion of SnO{sub 2}:F causes a reduction of the diode built-in voltage and increased series resistance, which could degrade the open circuit voltage (Voc) and fill factor (FF), the degradation of which is strongly affected by the deposition time of p-a-SiC.
Baik, Seung Jae; Lim, Koeng Su [Department of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 305-701 (Korea, Republic of)
NASA Technical Reports Server (NTRS)
A proposed mobile robot, denoted the amorphous rover, would vary its own size and shape in order to traverse terrain by means of rolling and/or slithering action. The amorphous rover was conceived as a robust, lightweight alternative to the wheeled rover-class robotic vehicle heretofore used in exploration of Mars. Unlike a wheeled rover, the amorphous rover would not have a predefined front, back, top, bottom, or sides. Hence, maneuvering of the amorphous rover would be more robust: the amorphous rover would not be vulnerable to overturning, could move backward or sideways as well as forward, and could even narrow itself to squeeze through small openings.
Curtis, Steven A.
NASA Astrophysics Data System (ADS)
We studied how electrical erasing of indium gallium zinc oxide-thin-film-transistor memory was improved by adding concurrent irradiation with monochromatic light (ML). At fixed gate bias, irradiating at wavelengths of ?500 nm increased the erasing window (?Vth-e) significantly: At a gate bias of -20 V and an erasing time of 5 min, ML irradiation at 400 nm increased ?Vth-e from 0.29 to 3.21 V. ?Vth-e increased incrementally with gate bias, erasing time, and ML power density, particularly at short ML wavelengths. Analyzing our experimental results, we discuss the underlying erasure mechanisms.
Chen, Sun; Zhang, Wen-Peng; Cui, Xing-Mei; Ding, Shi-Jin; Sun, Qing-Qing; Zhang, Wei
NASA Astrophysics Data System (ADS)
Hysteresis and threshold switching characteristics were investigated in the indium-gallium-zinc-oxide (IGZO) thin-film-transistors (TFTs) with inserted Pt-Fe2O3 core–shell nanocrystals (NCs) layer between source/drain and IGZO channel. The output curves showed the hysteresis with threshold drain voltage and the transfer curves showed the hysteresis with the shift of threshold gate voltage. These hysteresis, threshold switching, and shift of threshold voltage in both output and transfer curves are caused by charging of inserted NCs. These unique features demonstrated the memory and on/off switching operation by controlling both threshold gate and drain voltages through charging NCs.
Baek, Yoon-Jae; Noh, Young Jun; Choi, Young Jin; Kang, Chi Jung; Lee, Hyun Ho; Yoon, Tae-Sik
Electron tunnelling into amorphous germanium and silicon.
NASA Technical Reports Server (NTRS)
Measurements of tunnel conductance versus bias, capacitance versus bias, and internal photoemission were made in the systems aluminum-oxide-amorphous germanium and aluminium-oxide-amorphous silicon. A function was extracted which expresses the deviation of these systems from the aluminium-oxide-aluminium system.
Smith, C. W.; Clark, A. H.
NASA Astrophysics Data System (ADS)
In this study, we report high-performance amorphous In2O3/InZnO bilayer metal-oxide (BMO) thin-film transistor (TFT) using an ultra-thin solution-processed amorphous ZrOx dielectric. A thin layer of In2O3 offers a higher carrier concentration, thereby maximizing the charge accumulation and yielding high carrier mobility. A thick amorphous layer of InZnO controls the charge conductance resulting in low off-state current and suitable threshold voltage. As a consequence, the BMO TFT showed higher filed-effect mobility (37.9 cm2/V s) than single-layer InZnO TFT (7.6 cm2/V s). Apart from that we obtain an on/off current ratio of 109, a subthreshold swing voltage of 120 mV/decade, and a voltage shift ? 0.4 V under positive bias stress for 2.5 h, for a gate voltage of 3 V and drain voltage of 1 V. These data demonstrate that the BMO TFT has great potential for a broad range of applications as switching low-power transistors.
Liu, G. X.; Liu, A.; Shan, F. K.; Meng, Y.; Shin, B. C.; Fortunato, E.; Martins, R.
NASA Astrophysics Data System (ADS)
We report a single step technique of synthesizing particle-agglomerated, amorphous 3-D nanostructures of Al and Si oxides on powder-fused aluminosilicate ceramic plates and a simple novel method of wafer-foil ablation to fabricate crystalline nanostructures of Al and Si oxides at ambient conditions. We also propose a particle size prediction mechanism to regulate the size of vapor-condensed agglomerated nanoparticles in these structures. Size characterization studies performed on the agglomerated nanoparticles of fabricated 3-D structures showed that the size distributions vary with the fluence-to-threshold ratio. The variation in laser parameters leads to varying plume temperature, pressure, amount of supersaturation, nucleation rate, and the growth rate of particles in the plume. The novel wafer-foil ablation technique could promote the possibilities of fabricating oxide nanostructures with varying Al/Si ratio, and the crystallinity of these structures enhances possible applications. The fabricated nanostructures of Al and Si oxides could have great potentials to be used in the fabrication of low power-consuming complementary metal-oxide-semiconductor circuits and in Mn catalysts to enhance the efficiency of oxidation on ethylbenzene to acetophenone in the super-critical carbon dioxide.
Sivayoganathan, Mugunthan; Tan, Bo; Venkatakrishnan, Krishnan
We report a single step technique of synthesizing particle-agglomerated, amorphous 3-D nanostructures of Al and Si oxides on powder-fused aluminosilicate ceramic plates and a simple novel method of wafer-foil ablation to fabricate crystalline nanostructures of Al and Si oxides at ambient conditions. We also propose a particle size prediction mechanism to regulate the size of vapor-condensed agglomerated nanoparticles in these structures. Size characterization studies performed on the agglomerated nanoparticles of fabricated 3-D structures showed that the size distributions vary with the fluence-to-threshold ratio. The variation in laser parameters leads to varying plume temperature, pressure, amount of supersaturation, nucleation rate, and the growth rate of particles in the plume. The novel wafer-foil ablation technique could promote the possibilities of fabricating oxide nanostructures with varying Al/Si ratio, and the crystallinity of these structures enhances possible applications. The fabricated nanostructures of Al and Si oxides could have great potentials to be used in the fabrication of low power-consuming complementary metal-oxide-semiconductor circuits and in Mn catalysts to enhance the efficiency of oxidation on ethylbenzene to acetophenone in the super-critical carbon dioxide. PMID:23140103
The goal of amorphous computing is to identify organizationalprinciples and create programming technologies for obtainingintentional, pre-specified behavior from the cooperation of myriadunreliable parts that are arranged ...
Abelson, Hal
NASA Astrophysics Data System (ADS)
Solution-processable materials offer enormous opportunity in designing lightweight, flexible, and low-cost electronic technologies. Dielectric materials and the different classes of semiconductors (derived from organics, inorganics, or nanomaterials) comprise the two most important components in transistors, which are the basic building blocks of all modern electronic devices. New semiconductors such as single-walled carbon nanotubes (SWCNTs) and inorganic amorphous oxide semiconductors (AOSs), including indium gallium zinc oxide (IGZO), are envisioned for high performance applications as a possible replacement for silicon within integrated circuits, display backplane technologies, or high throughput inkjet printing technologies that can be low in cost and waste. These new semiconductors, amongst others, require corresponding advances in gate dielectric materials to support optimum device function. Herein we describe research surrounding the advancement of organic-inorganic hybrid gate dielectric materials for use in thin-film transistor (TFT) architectures. We describe the reasoning, the strategy, and the properties of a new hafnium oxide-based self-assembled nanodielectric (Hf-SAND), and examine in detail the chemical structure/formation, and electronic performance. Record setting capacitance can be achieved by using thin multilayers of Hf-SAND (1.1 ?F/cm2). Application of this new dielectric to the aforementioned SWCNT and IGZO semiconductors in an effort to demonstrate technological feasibility, yield record field-effect mobilities (20-130 cm2V-1s-1) and large ON state transconductances (up to 5 mS) at very low operating voltages (< 3 V), while retaining the ability to be processed completely from solution and in ambient atmosphere. These TFT performance metrics are examined in detail, and placed in perspective in relation to the Hf-SAND dielectric properties. Finally, we present some forward looking statements to help identify further opportunities for research and development of SAND gate dielectrics for unconventional electronics applications.
Everaerts, Ken
Preparation of amorphous Fe powder with different particle sizes
magnetization measurements. The magnetization of pure amorphous Fe 2 O 3 is very low ( on the concentration of Fe(CO) 5 in decalin. The more dilute the solution, the smaller the particle size of the amorphous Fe 2 O 3 product obtained. Amorphous metal oxides have many important applications amorphous Fe 2
Prozorov, Ruslan
NASA Astrophysics Data System (ADS)
A novel method to produce composite sorbent material compromising porous diatomaceous earth (DE) and surface functionalized amorphous MnO2 is reported. Via a simple in situ redox reaction over the carbonized DE powders, a uniform layer of amorphous MnO2 was anchored onto the DE surface. The hybrid adsorbent was characterized by X-ray diffraction, scanning electron microscopy, and infrared spectroscopy. The batch method has been employed to investigate the effects of surface coating on adsorption performance of DE. According to the equilibrium studies, the adsorption capacity of DE for adsorbing lead ions after MnO2 modification increased more than six times. And the adsorption of Pb2+ on the MnO2 surface is based on ion-exchange mechanism. The developed strategy presents a novel opportunity to prepare composite adsorbent materials by integrating nanocrystals with porous matrix.
Li, Song; Li, Duanyang; Su, Fei; Ren, Yuping; Qin, Gaowu
NASA Astrophysics Data System (ADS)
Carbon nanotubes and metal oxide semiconductors have emerged as important materials for p-type and n-type thin-film transistors, respectively; however, realizing sophisticated macroelectronics operating in complementary mode has been challenging due to the difficulty in making n-type carbon nanotube transistors and p-type metal oxide transistors. Here we report a hybrid integration of p-type carbon nanotube and n-type indium-gallium-zinc-oxide thin-film transistors to achieve large-scale (>1,000 transistors for 501-stage ring oscillators) complementary macroelectronic circuits on both rigid and flexible substrates. This approach of hybrid integration allows us to combine the strength of p-type carbon nanotube and n-type indium-gallium-zinc-oxide thin-film transistors, and offers high device yield and low device variation. Based on this approach, we report the successful demonstration of various logic gates (inverter, NAND and NOR gates), ring oscillators (from 51 stages to 501 stages) and dynamic logic circuits (dynamic inverter, NAND and NOR gates).
Chen, Haitian; Cao, Yu; Zhang, Jialu; Zhou, Chongwu
NASA Astrophysics Data System (ADS)
The electronic structure of the interface between the boron-doped oxygenated amorphous silicon "window layer" (a-SiOx:H(B)) and aluminum-doped zinc oxide (ZnO:Al) was investigated using hard x-ray photoelectron spectroscopy and compared to that of the boron-doped microcrystalline silicon (?c-Si:H(B))/ZnO:Al interface. The corresponding valence band offsets have been determined to be (-2.87 � 0.27) eV and (-3.37 � 0.27) eV, respectively. A lower tunnel junction barrier height at the ?c-Si:H(B)/ZnO:Al interface compared to that at the a-SiOx:H(B)/ZnO:Al interface is found and linked to the higher device performances in cells where a ?c-Si:H(B) buffer between the a-Si:H p-i-n absorber stack and the ZnO:Al contact is employed.
Gerlach, D.; Wilks, R. G.; Wippler, D.; Wimmer, M.; Lozac'h, M.; F�lix, R.; M�ck, A.; Meier, M.; Ueda, S.; Yoshikawa, H.; Gorgoi, M.; Lips, K.; Rech, B.; Sumiya, M.; H�pkes, J.; Kobayashi, K.; B�r, M.
Amorphous titanium oxide (a-TiO{sub x}:OH) films prepared by plasma-enhanced chemical-vapor deposition at 200 and 25 deg. C are in turn deposited onto the GaN-based light-emitting diode (LED) to enhance the associated light extraction efficiency. The refractive index, porosity, and photocatalytic effect of the deposited films are correlated strongly with the deposition temperatures. The efficiency is enhanced by a factor of {approx}1.31 over that of the uncoated LEDs and exhibited an excellent photocatalytic property after an external UV light irradiation. The increase in the light extraction is related to the reduction in the Fresnel transmission loss and the enhancement of the light scattering into the escape cone by using the graded-refractive-index a-TiO{sub x}:OH film with porous structures.
Liu, D.-S.; Lin, T.-W.; Huang, B.-W.; Juang, F.-S.; Lei, P.-H. [Institute of Electro-Optical and Materials Science, National Formosa University, Huwei 63201, Taiwan (China); Hu, C.-Z. [Chilin Technology Co. Ltd., Tainan County 71758, Taiwan (China)
NASA Astrophysics Data System (ADS)
A comprehensive study is done regarding stabilities under simultaneous stress of light and dc-bias in amorphous hafnium-indium-zinc-oxide thin film transistors. The positive threshold voltage (Vth) shift is observed after negative gate bias and light stress, and it is completely different from widely accepted phenomenon which explains that negative-bias stress results in Vth shift in the left direction by bias-induced hole-trapping. Gate current measurement is performed to explain the unusual positive Vth shift under simultaneous application of light and negative gate bias. As a result, it is clearly found that the positive Vth shift is derived from electron injection from gate electrode to gate insulator.
Kwon, Dae Woong; Kim, Jang Hyun; Chang, Ji Soo; Kim, Sang Wan; Sun, Min-Chul; Kim, Garam; Kim, Hyun Woo; Park, Jae Chul; Song, Ihun; Kim, Chang Jung; Jung, U. In; Park, Byung-Gook
NASA Astrophysics Data System (ADS)
Amorphous manganese oxides are known to be efficient sorbents in soils and thus useful in remediation technologies. A novel amorphous hydrous manganese oxide (HMO) was prepared by a modified procedure generally used for birnessite synthesis. Its long-term stability in view of possible applications for chemical stabilization of metals/metalloids in polluted soils was evaluated. HMO was sealed in experimental bags prepared from polyamide fabric (pore size 1 um) and placed in the pots containing 200 g of soil. Three contrasting soils were used (two cambisols with pH values of 4.2 and 5.4, respectively, and a chernozem with a pH of 7.3). Each pot was equipped with a rhizon pore water sampler and the water content was maintained at 80% WHC throughout the experiment. HMO and pore waters were sampled after 1, 7, 15, 30, 45, 60, 75 and 90 days of incubation. Up to 113 mg Mn/L was released into pore water at the beginning of the experiment in more acidic soils indicating a slight dissolution of HMO surfaces. Manganese release into the pore water stabilized after 15 days in agreement with mass loss measurements. Mass loss decreased again after 60 days of the incubation for the neutral soil due to the formation of secondary rhodochrosite (MnCO3) detected on the HMO surfaces by X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM). The efficiency of HMO for trace metal retention in soils (e.g., Zn) slightly decreased after 60 days, probably due to the mineralogical transformation of the sorbent leading to decrease of binding surfaces. Nevertheless, only approximately 10% of HMO dissolved after 90 days of experiment showing that this sorbent can be relatively stable in the studied soils. Its binding capacity for metals/metalloids should be further tested in soils with elevated contaminant concentrations.
Ettler, V.; Knytl, V.; Komarek, M.; Della Puppa, L.; Mihaljevic, M.; Sebek, O.
NASA Astrophysics Data System (ADS)
A modified oxide-reduction-diffusion (ORD) method for the synthesis of single-phase SmCo5 is described. Samarium oxide, cobalt and calcium (20% excess) are heated in sealed niobium tubes following an optimized temperature programme. The reaction proceeds via Ca1-xSmxO as an intermediate and yields SmCo5, and CaO, which may be washed off with dilute acetic acid. Single-phase SmCo5 prepared by this route shows an enhanced reactivity towards hydrogen and reacts already at moderate conditions of p(H2)=0.1 MPa and T<770 K. in situ difference scanning calorimetry and X-ray powder diffraction suggest the formation of ternary hydrides SmCo5Hx at temperatures around 473 and 573 K, and disproportionation into cobalt of poor crystallinity and probably an amorphous binary samarium hydride at 700 K, i.e. a hydrogen induced amorphization (HIA) of SmCo5. Neutron powder diffraction was carried out on a 154SmCo5 sample with the high-intensity neutron powder diffractometer D20 at the Institute Laue-Langevin, Grenoble, France. The CaCu5 type crystal structure was confirmed (space group P6/mmm, a=500.60 (2) pm, c=397.01 (2) pm at T=298 (1) K) and the magnetic moments along the crystallographic c axis, ?||c, were refined to be 0.15 (6), 2.02 (6) and 1.75 (5) ?B for Sm, Co1 and Co2 atoms, respectively, in ferromagnetic SmCo5. The HIA process was confirmed by in situ neutron powder diffraction at higher pressures of 8.1 MPa deuterium gas.
Belener, Kevin L. A.; Kohlmann, Holger
Drug nanocarriers with magnetic targeting and pH-responsive drug-release behavior are promising for applications in controlled drug delivery. Magnetic iron oxides show excellent magnetism, but their application in drug delivery is limited by low drug-loading capacity and poor control over drug release. Herein, core-shell hollow microspheres of magnetic iron oxide@amorphous calcium phosphate (MIO@ACP) were prepared and investigated as magnetic, pH-responsive drug nanocarriers. Hollow microspheres of magnetic iron oxide (HMIOs) were prepared by etching solid MIO microspheres in hydrochloric acid/ethanol solution. After loading a drug into the HMIOs, the drug-loaded HMIOs were coated with a protective layer of ACP by using adenosine 5'-triphosphate (ATP) disodium salt (Na2 ATP) as stabilizer, and drug-loaded core-shell hollow microspheres of MIO@ACP (HMIOs/drug/ACP) were obtained. The as-prepared HMIOs/drug/ACP drug-delivery system exhibits superparamagnetism and pH-responsive drug-release behavior. In a medium with pH?7.4, drug release was slow, but it was significantly accelerated at pH?4.5 due to dissolution of the ACP shell. Docetaxel-loaded core-shell hollow microspheres of MIO@ACP exhibited high anticancer activity. PMID:25100227
Lu, Bing-Qiang; Zhu, Ying-Jie; Chen, Feng; Qi, Chao; Zhao, Xin-Yu; Zhao, Jing
Synthesis of crystalline mesoporous K(2-x)Mn8O16 (Meso-OMS-2), and ?-MnO2 (Meso-?-MnO2) is reported. The synthesis is based on the transformation of amorphous mesoporous manganese oxide (Meso-Mn-A) under mild conditions: aqueous acidic solutions (0.5 M H(+) and 0.5 M K(+)), at low temperatures (70 �C), and short times (2 h). Meso-OMS-2 and Meso-?-MnO2 maintain regular mesoporosity (4.8-5.6 nm) and high surface areas (as high as 277 m(2)/g). The synthesized mesoporous manganese oxides demonstrated enhanced redox (H2-TPR) and catalytic performances (CO oxidation) compared to nonporous analogues. The order of reducibility and enhanced catalytic performance of the samples is Commercial-Mn2O3 < nonporous-OMS-2 < Meso-Mn2O3 < Meso-OMS-2 < Meso-?-MnO2 < Meso-Mn-A. PMID:24971574
Poyraz, Altug S; Song, Wenqiao; Kriz, David; Kuo, Chung-Hao; Seraji, Mohammad S; Suib, Steven L
NASA Astrophysics Data System (ADS)
A novel heterojunction white light emitting diode (LED) structure based on an array of vertically aligned surface-passivated p-type porous Si nanowires (PSiNWs) with n-type amorphous In-Ga-Zn-O (a-IGZO) capping is introduced. PSiNWs were initially synthesized by electroless etching of p-type Si (100) wafers assisted by Ag nanoparticle catalysts and then surface-passivated by thermal oxidation. The nanowires synthesized by metal-assisted electroless etching were found to have longitudinally varying nanoporous morphologies due to differences in the duration of exposure to etching environment. These PSiNWs were optically active with orange red photoluminescence consisting of dark red to yellow emissions attributable to quantum confinement effects and to modified band structures. The LED structures emitted visible white light while exhibiting rectifying current-voltage characteristics. The white light emission was found to be the result of the combination of dark red to yellow emissions originating from the quantum confinement effect within the PSiNWs and green to blue emissions due to the oxygen-deficiency-related recombination centers introduced during the surface oxidation.A novel heterojunction white light emitting diode (LED) structure based on an array of vertically aligned surface-passivated p-type porous Si nanowires (PSiNWs) with n-type amorphous In-Ga-Zn-O (a-IGZO) capping is introduced. PSiNWs were initially synthesized by electroless etching of p-type Si (100) wafers assisted by Ag nanoparticle catalysts and then surface-passivated by thermal oxidation. The nanowires synthesized by metal-assisted electroless etching were found to have longitudinally varying nanoporous morphologies due to differences in the duration of exposure to etching environment. These PSiNWs were optically active with orange red photoluminescence consisting of dark red to yellow emissions attributable to quantum confinement effects and to modified band structures. The LED structures emitted visible white light while exhibiting rectifying current-voltage characteristics. The white light emission was found to be the result of the combination of dark red to yellow emissions originating from the quantum confinement effect within the PSiNWs and green to blue emissions due to the oxygen-deficiency-related recombination centers introduced during the surface oxidation. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr05328h
Moon, Kyeong-Ju; Lee, Tae Il; Lee, Woong; Myoung, Jae-Min
NASA Astrophysics Data System (ADS)
Low temperature gallium tin zinc oxide (GSZO) based thin film transistors fabricated on silicon has been investigated as a potential indium free transparent amorphous oxide semiconductor thin film transistor (TAOS TFT) with potential device applications on plastic substrates. A comprehensive and detailed study on the performance of GSZO TFTs has been carried out by studying the effects of processing parameters such as deposition temperature and annealing temperature/duration, as well as the channel thickness with all temperatures held below 150 �C. Variety of characterization techniques, namely Rutherford backscattering (RBS), x-ray photoelectron spectroscopy (XPS) and x-ray reflectivity (XRR) in addition to I-V and C-V measurements were employed to determine the effects of the above parameters on the composition and quality of the channel. Optimized TFT characteristics of ID=3�10-7 A, ION/OFF =2�106, VON ~ -2 V, SS ~ 1 V/dec and ?FE = 0.14 cm2/V� s with a ?VON of 3.3 V under 3 hours electrical stress were produced.
Alston, Robert; Iyer, Shanthi; Bradley, Tanina; Lewis, Jay; Cunningham, Garry; Forsythe, Eric
Chemical mechanical planarization of amorphous Ge2Sb2Te5 using KClO4 as oxidizer in acidic slurry
NASA Astrophysics Data System (ADS)
Amorphous Ge2Sb2Te5 (a-GST) chemical mechanical planarization (CMP) using KClO4 as the oxidizer in an acidicslurry is investigated in the present work. It is shown that the removal rate (RR ) of the a-GST firstly increases and thentends to saturate when the KClO4 concentration is greater than 0.8 wt%, but the static etch rate (SER) linearly increasesfrom low to high KClO4 concentration. To understand the oxidation-reaction capability of Ge, Sb and Te, depth profilesof composition of elements and etch morphology of a-GST immersed in the slurry for some time are measured,respectively. It is found that selective corrosion occurs among Ge, Sb and Te, and an accumulation of Te and loss of Gein a-GST surface region are obvious observed, especially at high KClO4 concentrations. Temperature dependent sheetresistance measurements of all the samples pre- and post-CMP reveal a similar trend, which implies a-GST CMP is ableto keep its characteristic well.
He, Aodong; Song, Zhitang; Bo, Liu; Zhong, Min; Weili, Liu; Wang, Liangyong; Yan, Weixia; Lei, Yu; Wu, Guangping
NASA Astrophysics Data System (ADS)
Highly textured transparent conducting front electrode (TFE) can enhance light trapping; however, we observed an improved performance of a solar cell by nanometer level modification of surface texture. A 40 nm thick aluminum doped zinc oxide was sputter deposited at an oblique flux on the textured fluorine doped tin oxide TFE, and a TFE double layer was used for the front electrode of solar cells. The cells fabricated on these modified TFEs exhibited an increased open circuit voltage, enhancement in short circuit current density and an increase in fill factor that reached up to 74% because of reduced series resistance of the cell. The surface texture of the TFE was modified with various angular fluxes of the zinc oxide sputter particle, which shows lower texture-induced-surface defect, higher work function. These are thought to have helped in improving the performance of the thin-film solar cells. However, at a near normal angular flux of the zinc oxide sputter particle, light trapping was observed to have reduced significantly, leading to a significant reduction in current density of the cell.
Park, Hyeongsik; Iftiquar, S. M.; Kim, Hee Won; Lee, Jaehyeong; Le, Anh Huy Tuan; Yi, Junsin
Resistance switching random access non-volatile memories (ReRAM) could represent the leading alternative to floating gate technology for post 32nm technology nodes. Among the currently investigated materials for ReRAM, transition metal binary oxides, such as NiO, CuxO, ZrOx, TiO2, MgO, and Nb2O5 are receiving increasing interest as they offer high potential scalability, low-energy switching, thermal stability, and easy integration in CMOS
S. Spiga; A. Lamperti; C. Wiemer; M. Perego; E. Cianci; G. Tallarida; H. L. Lu; M. Alia; F. G. Volpe; M. Fanciulli
Amorphous TiO? coatings stabilize Si, GaAs, and GaP photoanodes for efficient water oxidation.
Although semiconductors such as silicon (Si), gallium arsenide (GaAs), and gallium phosphide (GaP) have band gaps that make them efficient photoanodes for solar fuel production, these materials are unstable in aqueous media. We show that TiO2 coatings (4 to 143 nanometers thick) grown by atomic layer deposition prevent corrosion, have electronic defects that promote hole conduction, and are sufficiently transparent to reach the light-limited performance of protected semiconductors. In conjunction with a thin layer or islands of Ni oxide electrocatalysts, Si photoanodes exhibited continuous oxidation of 1.0 molar aqueous KOH to O2 for more than 100 hours at photocurrent densities of >30 milliamperes per square centimeter and ~100% Faradaic efficiency. TiO2-coated GaAs and GaP photoelectrodes exhibited photovoltages of 0.81 and 0.59 V and light-limiting photocurrent densities of 14.3 and 3.4 milliamperes per square centimeter, respectively, for water oxidation. PMID:24876492
Hu, Shu; Shaner, Matthew R; Beardslee, Joseph A; Lichterman, Michael; Brunschwig, Bruce S; Lewis, Nathan S
For the production of nonfossil fuels, water oxidation by inexpensive cobalt-based catalysts is of high interest. Films for the electrocatalysis of water oxidation were obtained by oxidative self-assembly (electrodeposition) from aqueous solutions containing, apart from Co, either K, Li or Ca with either a phosphate, acetate or chloride anion. X-ray absorption spectroscopy (XAS) at the Co K-edge revealed clusters of edge-sharing CoO(6) octahedra in all films, but the size or structural disorder of the Co-oxido clusters differed. Whereas potassium binding is largely unspecific, CaCo(3) O(4) cubanes, which resemble the CaMn(3) O(4) cubane of the biological catalyst in oxygenic photosynthesis, may form, as suggested by XAS at the Ca K-edge. Cyclic voltammograms in a potassium phosphate buffer at pH?7 revealed that no specific combination of anions and redox-inactive cations is required for catalytic water oxidation. However, the anion type modulates not only the size (or order) of the Co-oxido clusters, but also electrodeposition rates, redox potentials, the capacity for oxidative charging, and catalytic currents. On these grounds, structure-activity relations are discussed. PMID:22323319
Risch, Marcel; Klingan, Katharina; Ringleb, Franziska; Chernev, Petko; Zaharieva, Ivelina; Fischer, Anna; Dau, Holger
The effect of B{sub 2}O{sub 3} addition on the crystallization of amorphous TiO{sub 2}-ZrO{sub 2} mixed oxide was investigated by X-ray diffraction (XRD), thermogravimetric and differential thermal analysis (TG/DTA). TiO{sub 2}-ZrO{sub 2} mixed oxide was prepared by co-precipitation method with aqueous ammonia as the precipitation reagent. Boric acid was used as a source of boria, and boria contents varied from 2 to 20 wt%. The results indicate that the addition of small amount of boria (<8 wt%) hinders the crystallization of amorphous TiO{sub 2}-ZrO{sub 2} into a crystalline ZrTiO{sub 4} compound, while a larger amount of boria ({>=}8 wt%) promotes the crystallization process. FT-IR spectroscopy and {sup 11}B MAS NMR results show that tetrahedral borate species predominate at low boria loading, and trigonal borate species increase with increasing boria loading. Thus it is concluded that highly dispersed tetrahedral BO{sub 4} units delay, while a build-up of trigonal BO{sub 3} promote, the crystallization of amorphous TiO{sub 2}-ZrO{sub 2} to form ZrTiO{sub 4} crystals. - Graphical abstract: The addition of small amount of boria (<8 wt%) hinders the crystallization of amorphous TiO{sub 2}-ZrO{sub 2} into a crystalline ZrTiO{sub 4} compound, while the larger amount of boria ({>=}8 wt%) promotes the crystallization process.
Mao Dongsen [Research Institute of Applied Catalysis, Department of Chemical Engineering, Shanghai Institute of Technology, Number 120, Caobaolu, Shanghai 200235 (China)], E-mail: email@example.com; Lu Guanzhong [Research Institute of Applied Catalysis, Department of Chemical Engineering, Shanghai Institute of Technology, Number 120, Caobaolu, Shanghai 200235 (China)
An improved amorphous metal composite and process of making the composite. The amorphous metal composite comprises amorphous metal (e.g. iron) and a low molecular weight thermosetting polymer binder. The process comprises placing an amorphous metal in particulate form and a thermosetting polymer binder powder into a container, mixing these materials, and applying heat and pressure to convert the mixture into an amorphous metal composite.
Byrne, Martin A. (Troy, NY); Lupinski, John H. (Scotia, NY)
NASA Astrophysics Data System (ADS)
Metal-oxide-semiconductor (MOS) diodes with various gate insulators (G/Is) were characterized by capacitance-voltage characteristics and isothermal capacitance transient spectroscopy (ICTS) to evaluate the effect of H and OH desorption and diffusion on the electronic structures in amorphous In-Ga-Zn-O (a-IGZO) thin films. The density and the distribution of the space charge were found to be varied depending on the nature of the G/I. In the case of thermally grown SiO2 (thermal SiO2) G/Is, a high space-charge region was observed near the a-IGZO and G/I interface. After thermal annealing, the space-charge density in the deeper region of the film decreased, whereas remained unchanged near the interface region. The ICTS spectra obtained from the MOS diodes with the thermal SiO2 G/Is consisted of two broad peaks at around 5 � 10-4 and 3 � 10-2 s before annealing, while one broad peak was observed at around 1 � 10-4 s at the interface and at around 1 � 10-3 s in the bulk after annealing. Further, the trap density was considerably high near the interface. In contrast, the space-charge density was high throughout the bulk region of the MOS diode when the G/I was deposited by chemical vapor deposition (CVD). The ICTS spectra from the MOS diodes with the CVD G/Is revealed the existence of continuously distributed trap states, suggesting formations of high-density tail states below the conduction band minimum. According to secondary ion mass spectroscopy analyses, desorption and outdiffusion of H and OH were clearly observed in the CVD G/I sample. These phenomena could introduce structural fluctuations in the a-IGZO films, resulting in the formation of the conduction band tail states. Thin-film transistors (TFTs) with the same gate structure as the MOS diodes were fabricated to correlate the electronic properties with the TFT performance, and it was found that TFTs with the CVD G/I showed a reduced saturation mobility. These results indicate that the electronic structures in the a-IGZO films were strongly influenced by the nature of the G/Is as well as the process conditions. It is concluded that controlling of the natures of the G/I such as film density and hydrogen content in the films is critical to obtain high-performance electronic devices using a-IGZO.
Hino, Aya; Morita, Shinya; Yasuno, Satoshi; Kishi, Tomoya; Hayashi, Kazushi; Kugimiya, Toshihiro
NASA Astrophysics Data System (ADS)
A simple and versatile route of forming sol-gel-derived metal oxide n-type electron transport layers (ETLs) for flexible inverted polymer solar cells (PSCs) is proposed using low-temperature photochemical activation process. The photochemical activation, which is induced by deep ultraviolet irradiation on sol-gel films, allows formation of metal oxide n-type ETLs such as zinc oxide (ZnO) and indium gallium zinc oxide films at a low temperature. Compared to poly(3-hexylthiophene)/phenyl-C61-butyric acid methyl ester inverted PSCs with thermally annealed ZnO ETLs (optimized efficiency of 3.26 � 0.03 %), the inverted PSCs with photo-activated ZnO ETLs showed an improved efficiency of 3.60 � 0.02 %. The enhanced photovoltaic property is attributed to efficient charge collection from low overall series resistance and high surface area-to-geometric area ratio by the photo-activated ZnO ETLs.
Lee, Jung-Wook; Lee, Soo-Hyoung; Kim, Yong-Hoon; Park, Sung Kyu
NASA Astrophysics Data System (ADS)
Digital computers have always been constructed to behave as precise arrangements of reliable parts, and our techniques for organizing computations depend upon this precision and reliability. Two emerging technologies, however, are begnning to undercut these assumptions about constructing and programming computers. These technologies -- microfabrication and bioengineering -- will make it possible to assemble systems composed of myriad information- processing units at almost no cost, provided: 1) that not all the units need to work correctly; and 2) that there is no need to manufacture precise geometrical arrangements or interconnection patterns among them. Microelectronic mechanical components are becoming so inexpensive to manufacture that we can anticipate combining logic circuits, microsensors, actuators, and communications devices integrated on the same chip to produce particles that could be mixed with bulk materials, such as paints, gels, and concrete. Imagine coating bridges or buildings with smart paint that can sense and report on traffic and wind loads and monitor structural integrity of the bridge. A smart paint coating on a wall could sense vibrations, monitor the premises for intruders, or cancel noise. Even more striking, there has been such astounding progress in understanding the biochemical mechanisms in individual cells, that it appears we'll be able to harness these mechanisms to construct digital- logic circuits. Imagine a discipline of cellular engineering that could tailor-make biological cells that function as sensors and actuators, as programmable delivery vehicles for pharmaceuticals, as chemical factories for the assembly of nanoscale structures. Fabricating such systems seem to be within our reach, even if it is not yet within our grasp Fabrication, however, is only part of the story. We can envision producing vast quantities of individual computing elements, whether microfabricated particles, engineered cells, or macromolecular computing agents constructed by engineered cells, but we have few ideas for programming them effectively: How can one engineer prespecified, coherent behavior from the cooperation of immense numbers of unreliable parts that are interconnected in unknown, irregular, and time-varying ways? This is the challenge of Amorphous Computing.
Sussman, Gerald
Light Response of Top Gate InGaZnO Thin Film Transistor
NASA Astrophysics Data System (ADS)
The light stability of top gate indium gallium zinc oxide (IGZO) thin film transistor (TFT) has been investigated under gate bias and constant current stress to explore the possibility of active matrix display applications. While the halogen lamp irradiation onto the device under positive gate bias stress caused just -0.18 V of threshold voltage shift (?Vth), it resulted in -15.1 V shift under negative gate bias stress. When the white light extracted from the halogen lamp of 100 �W/cm2 power illuminated the device under constant current stress, operation voltage shifted just -0.05 V for 21 h. The result shows good promise for the application of highly stable IGZO TFT to active matrix organic light emitting diodes (AMOLEDs).
Park, Sang-Hee Ko; Ryu, Minki; Yoon, Sung Min; Yang, Shinhyuk; Hwang, Chi-Sun; Jeon, Jae-Hong; Kim, Kyounghwan
NASA Astrophysics Data System (ADS)
We investigated the degradation of indium-gallium-zinc-oxide (IGZO) thin-film transistors (TFTs) for various channel widths under high-gate and drain bias stress. The threshold voltage of IGZO TFT with wide-channel width (W > 100 ?m) was significantly shifted. This included stress-induced hump-effect in a negative direction after the stress, whereas IGZO TFT with narrow-channel width (W < 100 ?m) shifted in a positive direction. This phenomenon may be attributed to the hole trapping into the back-interface region. In order to enhance the reliability of IGZO TFTs, we developed and verified that the multiple-channel device showed better bias-temperature stability (?VTH: -0.1 V), whereas the single-channel device exhibited a -0.4 V?VTH shift.
Choi, Sung-Hwan; Han, Min-Koo
IGZO thin film transistor biosensors functionalized with ZnO nanorods and antibodies.
We demonstrate a biosensor structure consisting of an IGZO (Indium-Gallium-Zinc-Oxide) TFT (thin film transistor) and an extended sensing pad. The TFT acts as the sensing and readout device, while the sensing pad ensures the isolation of biological solution from the transistor channel layer, and meanwhile increases the sensing area. The biosensor is functionalized by first applying ZnO nanorods to increase the surface area for attracting electrical charges of EGFR (epidermal growth factor receptor) antibodies. The device is able to selectively detect 36.2 fM of EGFR in the total protein solution of 0.1 ng/ml extracted from squamous cell carcinoma (SCC). Furthermore, the conjugation duration of the functionalized device with EGFR can be limited to 3 min, implying that the biosensor has the advantage for real-time detection. PMID:24291267
Shen, Yi-Chun; Yang, Chun-Hsu; Chen, Shu-Wen; Wu, Shou-Hao; Yang, Tsung-Lin; Huang, Jian-Jang
Nanocrystal dispersed amorphous alloys
NASA Technical Reports Server (NTRS)
Compositions and methods for obtaining nanocrystal dispersed amorphous alloys are described. A composition includes an amorphous matrix forming element (e.g., Al or Fe); at least one transition metal element; and at least one crystallizing agent that is insoluble in the resulting amorphous matrix. During devitrification, the crystallizing agent causes the formation of a high density nanocrystal dispersion. The compositions and methods provide advantages in that materials with superior properties are provided.
Perepezko, John H. (Inventor); Allen, Donald R. (Inventor); Foley, James C. (Inventor)
Trehalose amorphization and recrystallization.
The stability of the amorphous trehalose prepared by using several procedures is presented and discussed. Amorphization is shown to occur by melting (T(m)=215 degrees C) or milling (room temperature) the crystalline anhydrous form TRE-beta. Fast dehydration of the di-hydrate crystalline polymorph, TRE-h, also produces an amorphous phase. Other dehydration procedures of TRE-h, such as microwave treatment, supercritical extraction or gentle heating at low scan rates, give variable fractions of the polymorph TRE-alpha, that undergo amorphization upon melting (at lower temperature, T(m)=130 degrees C). Additional procedures for amorphization, such as freeze-drying, spray-drying or evaporation of trehalose solutions, are discussed. All these procedures are classified depending on the capability of the undercooled liquid phase to undergo cold crystallization upon heating the glassy state at temperatures above the glass transition temperature (T(g)=120 degrees C). The recrystallizable amorphous phase is invariably obtained by the melt of the polymorph TRE-alpha, while other procedures always give an amorphous phase that is unable to crystallize above T(g). The existence of two different categories is analyzed in terms of the transformation paths and the hypothesis that the systems may exhibit different molecular mobilities. PMID:18768170
Sussich, Fabiana; Ces�ro, Attilio
NSDL National Science Digital Library
This site covers the interesting new frontier of molecular computing, which links molecular biology with computer science. It is Massachusetts Institute of Technology's (MIT's) Amorphous Computing homepage. Amorphous computing is defined by the MIT amorphous computer engineers as "methods for instructing myriads of programmable entities to cooperate to achieve particular goals," and sometimes involves the use of organic molecules. In the News, Research, and Demos are among the pages available at the site. The demonstration of "gunk" software is particularly informative and unusual (HSLIM software required).
NASA Astrophysics Data System (ADS)
In a previous work, we examined subgap states in highly doped amorphous In-Ga-Zn-O (a-IGZO) films by hard x-ray photoelectron spectroscopy (HX-PES) and found they had subgap electronic states above the valence band maximum (VBM) with the densities > 5 � 1020 cm-3 and just below the Fermi level with the densities > 5 � 1019 cm-3 [K. Nomura, T. Kamiya, H. Yanagi, E. Ikenaga, K. Yang, K. Kobayashi, M. Hirano, and H. Hosono, Appl. Phys. Lett. 92, 202117 (2008)]; however, their electron densities (Ne > 3 � 1019 cm-3) are rather high and not compatible with rational properties required for active channel layers in thin-film transistors (TFTs). In this work, we report the effects of Ne and thermal annealing on the subgap states in order to provide the data useful for actual TFTs. It was found that the low-Ne a-IGZO films had extra subgap states above VBM similar to the previous report, but their densities were as small as �2.0 � 1020 cm-3 for the highly resistive, wet-annealed a-IGZO films. Angle-dependent HX-PES revealed that the subgap states above VBM concentrate in the surface region. The O 1s peak indicated that the wet annealing suppressed the generation of subgap states by terminating these states with -OH bonds. The subgap states below EF were observed commonly in all the samples including ZnO, crystalline (c-) IGZO and a-IGZO. It is concluded that these states below EF are neither related to the disordered structures of a-IGZO nor to their TFT characteristics. It is considered that these states are related to the metastable states created by the high-energy photons in vacuum.
Nomura, Kenji; Kamiya, Toshio; Ikenaga, Eiji; Yanagi, Hiroshi; Kobayashi, Keisuke; Hosono, Hideo
Amorphous diamond films having a significant reduction in intrinsic stress are prepared by biasing a substrate to be coated and depositing carbon ions thereon under controlled temperature conditions. 1 fig.
Falabella, S.
Programming reliable behavior on a large mesh network composed of unreliable parts is difficult. Amorphous Medium Language addresses this problem by abstracting robustness and networking issues away from the programmer via ...
Beal, Jacob
Amorphous metal alloys of the iron-chromium and nickel-chromium type have excellent corrosion resistance and high temperature stability and are suitable for use as a protective coating on less corrosion resistant substrates. The alloys are stabilized in the amorphous state by one or more elements of titanium, zirconium, hafnium, niobium, tantalum, molybdenum, and tungsten. The alloy is preferably prepared by sputter deposition.
Wang, R.; Merz, M.D.
High-performance, low-cost amorphous gallium-indium-zinc oxide (a-GIZO) thin-film-transistor (TFT) technology is required for the next generation of active-matrix organic light-emitting diodes. A back-channel-etch structure is the most appropriate device structure for high-performance, low-cost a-GIZO TFT technology. However, channel damage due to source/drain etching and passivation-layer deposition has been a critical issue. To solve this problem, the present work focuses on overall back-channel processes, such as back-channel N2O plasma treatment, SiOx passivation deposition, and final thermal annealing. This work has revealed the dependence of a-GIZO TFT characteristics on the N2O plasma radio-frequency (RF) power and frequency, the SiH4 flow rate in the SiOx deposition process, and the final annealing temperature. On the basis of these results, a high-performance a-GIZO TFT with a field-effect mobility of 35.7 cm(2) V(-1) s(-1), a subthreshold swing of 185 mV dec(-1), a switching ratio exceeding 10(7), and a satisfactory reliability was successfully fabricated. The technology developed in this work can be realized using the existing facilities of active-matrix liquid-crystal display industries. PMID:24221957
Park, Jae Chul; Ahn, Seung-Eon; Lee, Ho-Nyeon
Formation of amorphous materials
Metastable amorphous or fine crystalline materials are formed by solid state reactions by diffusion of a metallic component into a solid compound or by diffusion of a gas into an intermetallic compound. The invention can be practiced on layers of metals deposited on an amorphous substrate or by intermixing powders with nucleating seed granules. All that is required is that the diffusion of the first component into the second component be much faster than the self-diffusion of the first component. The method is practiced at a temperature below the temperature at which the amorphous phase transforms into one or more crystalline phases and near or below the temperature at which the ratio of the rate of diffusion of the first component to the rate of self-diffusion is at least 10.sup.4. This anomalous diffusion criteria is found in many binary, tertiary and higher ordered systems of alloys and appears to be found in all alloy systems that form amorphous materials by rapid quenching. The method of the invention can totally convert much larger dimensional materials to amorphous materials in practical periods of several hours or less.
Johnson, William L. (Pasadena, CA); Schwarz, Ricardo B. (Westmont, IL)
NASA Astrophysics Data System (ADS)
Indium tin zinc oxide (ITZO)-based thin-film transistors (TFTs) were fabricated by dc magnetron sputtering in Ar + O2 reactive gas, at room temperature. We present the effect of post-deposition annealing of ITZO thin films on the oxygen vacancies and on the characteristics of TFT devices. When the annealing temperature was increased from room temperature to 350 �C, the resistivity of ITZO film increased from 2.05 � 101 to 2.60 � 103 ? cm and the interface trap density (Nt) of the TFTs reduced from 3.18 � 1013 to 4.83 � 1011 cm-2. The TFT with the ITZO film which was annealed at 350 �C showed a very small shift in turn-on voltage, even after applying positive bias stress of +12 V for 104 s. The current-voltage characteristics of 350 �C annealing temperature sample indicated that these TFTs were in an enhanced mode of transistor operation with a high on-to-off current ratio of �1.26 � 106, high field-effect mobility of 14.17 cm2 V-1 s-1, and low subthreshold slope of 1.23 V/dec. The trapping time reduced from 3720 to 1546 s as the annealing temperature increased from room temperature to 350 �C. These results suggest that thermal annealing played an important role in reducing defects as well as improvement in stability of the TFTs.
Phu Thi Nguyen, Cam; Thuy Trinh, Thanh; Dao, Vinh Ai; Raja, Jayapal; Jang, Kyungsoo; Le, Tuan Anh Huy; Iftiquar, S. M.; Yi, Junsin
Amorphous semiconductor solar cell
A solar cell comprising a back electrical contact, amorphous silicon semiconductor base and junction layers and a top electrical contact includes in its manufacture the step of heat treating the physical junction between the base layer and junction layer to diffuse the dopant species at the physical junction into the base layer.
Dalal, Vikram L. (Newark, DE)
Disorder-induced amorphization
Many crystalline materials undergo a crystalline-to-amorphous (c-a) phase transition when subjected to energetic particle irradiation at low temperatures. By focusing on the mean-square static atomic displacement as a generic measure of chemical and topological disorder, we are led quite naturally to a generalized version of the Lindemann melting criterion as a conceptual framework for a unified thermodynamic approach to solid-state amorphizing transformations. In its simplest form, the generalized Lindemann criterion assumes that the sum of the static and dynamic mean-square atomic displacements is constant along the polymorphous melting curve so that c-a transformations can be understood simply as melting of a critically-disordered crystal at temperatures below the glass transition temperature where the supercooled liquid can persist indefinitely in a configurationally-frozen state. Evidence in support of the generalized Lindemann melting criterion for amorphization is provided by a large variety of experimental observations and by molecular dynamics simulations of heat-induced melting and of defect-induced amorphization of intermetallic compounds.
Lam, N.Q.; Okamoto, P.R.; Li, Mo
Modeling of the Properties and Processing of Amorphous Gate Stacks on High Electron Mobility: Advances in amorphous gate oxides are severely limited by the inability to adequately model the full gate need high quality models that can identify the atomic structures that correspond to the measured
Kummel, Andrew C.
Impact of amorphization on the magnetic properties of EuO-TiO2 system
Recently, we have reported amorphization-induced ferromagnetism in a magnetic oxide; whereas crystalline EuTiO3 is an antiferromagnet, its amorphous counterpart shows a ferromagnetic transition. In this paper, we have investigated the magnetic properties of amorphous EuO-TiO2 system in detail. The present compounds, i.e., amorphous EuTiO3 and Eu2TiO4 , exhibit a paramagnetic-ferromagnetic transition followed by a spin-glass transition upon cooling down, thereby
Hirofumi Akamatsu; Koji Fujita; Yanhua Zong; Naohiro Takemoto; Shunsuke Murai; Katsuhisa Tanaka
Amorphous to amorphous transition in particle rafts
Space-filling assemblies of athermal hydrophobic particles floating at an air-water interface, called particle rafts, are shown to undergo an unusual phase transition between two i.e., a low density `less-rigid and a high density `more-rigid' amorphous states as a function of particulate number density ($\\Phi$). The former is shown to be a capillary-bridged solid and the later a frictionally-coupled one. Simultaneous studies involving direct imaging as well as measuring its mechanical response to longitudinal and shear stresses show that the transition is marked by a subtle structural anomaly and a weakening of the shear response. The structural anomaly is identified from the variation of the mean coordination number, mean area of the Voronoi cells and the spatial profile of the displacement field with $\\Phi$. The weakened shear response is related to local plastic instabilities caused by the depinning of the contact-line of the underlying fluid on the rough surfaces of the particles.
Atul Varshney; A. Sane; Shankar Ghosh; S. Bhattacharya
Amorphous to amorphous transition in particle rafts
NASA Astrophysics Data System (ADS)
Space-filling assemblies of athermal hydrophobic particles floating at an air-water interface, called particle rafts, are shown to undergo an unusual phase transition between two amorphous states, i.e., a low density �less-rigid� state and a high density �more-rigid� state, as a function of particulate number density (?). The former is shown to be a capillary bridged solid and the latter is shown to be a frictionally coupled one. Simultaneous studies involving direct imaging as well as measuring its mechanical response to longitudinal and shear stresses show that the transition is marked by a subtle structural anomaly and a weakening of the shear response. The structural anomaly is identified from the variation of the mean coordination number, mean area of the Voronoi cells, and spatial profile of the displacement field with ?. The weakened shear response is related to local plastic instabilities caused by the depinning of the contact line of the underlying fluid on the rough surfaces of the particles.
Varshney, Atul; Sane, A.; Ghosh, Shankar; Bhattacharya, S.
Glutamate Surface Speciation on Amorphous Titanium Dioxide and
Glutamate Surface Speciation on Amorphous Titanium Dioxide and Hydrous Ferric Oxide D I M I T R I. Using surface complexation modeling, we have integrated published adsorption data for glutamate on HFO over a range of pH and surface coverage with published in situ ATR-FTIR studies of glutamate speciation
Sverjensky, Dimitri A.
Amorphous carbons and extinction curve
NASA Astrophysics Data System (ADS)
All forms of carbonaceous matter are supposed to be originated from amorphous carbon in the interstellar medium (ISM). In a search for the proper kind of amorphous carbon suitable for ISM particles, a theoretical study of wavelength extinction profiles along peculiar sightlines is performed. We consider nanodiamond core with mantle made of various amorphous carbon models. The study concludes that the extinction curves along different sightlines need different amorphous carbons to compare well with the observational data, whereas a same dust-particle formation process is consistent with all the data, whatever the sightline.
Rai, Rakesh K.; Botet, Robert S.
Programming an Amorphous Computational Medium
Amorphous computing considers the problem of controllingmillions of spatially distributed unreliable devices which communicateonly with nearby neighbors. To program such a system, we need a highleveldescription language ...
Beal, Jacob
Molecular dynamics in amorphous ergocalciferol
NASA Astrophysics Data System (ADS)
While developing new pharmaceutical products based on drug substances in their amorphous form, the molecular mobility of amorphous active ingredients have to be characterized in detail. The molecular mobility in the supercooled liquid and glassy states of ergocalciferol is studied using broadband dielectric spectroscopy over wide frequency and temperature ranges. Dielectric studies revealed a number of relaxation process of different molecular origin.
Mohamed, Sahra; Thayyil, M. Shahin; Capaccioli, S.
Adsorption of selenium by amorphous iron oxyhydroxide and manganese dioxide
This work compares and models the adsorption of selenium and other anions on a neutral to alkaline surface (amorphous iron oxyhydroxide) and an acidic surface (manganese dioxide). Selenium adsorption on these oxides is examined as a function of pH, particle concentration, oxidation state, and competing anion concentration in order to assess how these factors might influence the mobility of selenium in the environment. The data indicate that 1. 1) amorphous iron oxyhydroxide has a greater affinity for selenium than manganese dioxide, 2. 2) selenite [Se(IV)] adsorption increases with decreasing pH and increasing particle concentration and is stronger than selenate [Se(VI)] adsorption on both oxides, and 3. 3) selenate does not adsorb on manganese dioxide. The relative affinity of selenate and selenite for the oxides and the lack of adsorption of selenate on a strongly acidic surface suggests that selenate forms outer-sphere complexes while selenite forms inner-sphere complexes with the surfaces. The data also indicate that the competition sequence of other anions with respect to selenite adsorption at pH 7.0 is phosphate > silicate > molybdate > fluoride > sulfate on amorphous iron oxyhydroxide and molybdate ??? phosphate > silicate > fluoride > sulfate on manganese dioxide. The adsorption of phosphate, molybdate, and silicate on these oxides as a function of pH indicates that the competition sequences reflect the relative affinities of these anions for the surfaces. The Triple Layer surface complexation model is used to provide a quantitative description of these observations and to assess the importance of surface site heterogeneity on anion adsorption. The modeling results suggest that selenite forms binuclear, innersphere complexes with amorphous iron oxyhydroxide and monodentate, inner-sphere complexes with manganese dioxide and that selenate forms outer-sphere, monodentate complexes with amorphous iron oxyhydroxide. The heterogeneity of the oxide surface sites is reflected in decreasing equilibrium constants for selenite with increasing adsorption density and both experimental observations and modeling results suggest that manganese dioxide has fewer sites of higher energy for selenite adsorption than amorphous iron oxyhydroxide. Modeling and interpreting the adsorption of phosphate, molybdate, and silicate on the oxides are made difficult by the lack of constraint in choosing surface species and the fact that equally good fits can be obtained with different surface species. Finally, predictions of anion competition using the model results from single adsorbate systems are not very successful because the model does not account for surface site heterogeneity. Selenite adsorption data from a multi-adsorbate system could be fit if the equilibrium constant for selenite is decreased with increasing anion adsorption density. ?? 1990.
Balistrieri, L. S.; Chao, T. T.
This is the final report for a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The objective of this work was to develop the competency for the synthesis of novel bulk amorphous alloys. The authors researched their synthesis methods and alloy properties, including thermal stability, mechanical, and transport properties. The project also addressed the development of vanadium-spinel alloys for structural applications in hostile environments, the measurement of elastic constants and thermal expansion in single-crystal TiAl from 300 to 750 K, the measurement of elastic constants in gallium nitride, and a study of the shock-induced martensitic transformations in NiTi alloys.
Schwarz, R.B.; Archuleta, J.I.; Sickafus, K.E. [and others
Perspective on photovoltaic amorphous silicon
Amorphous silicon is a thin film option that has the potential for a cost-effective product for large-scale utility photovoltaics application. The initial efficiencies for single-junction and multijunction amorphous silicon cells and modules have increased significantly over the past 10 years. The emphasis of research and development has changed to stabilized efficiency, especially that of multijunction modules. NREL has measured 6.3%--7.2% stabilized amorphous silicon module efficiencies for US products, and 8.1% stable efficiencies have been reported by Fuji Electric. This represents a significant increase over the stabilized efficiencies of modules manufactured only a few years ago. An increasing portion of the amorphous silicon US government funding is now for manufacturing technology development to reduce cost. The funding for amorphous silicon for photovoltaics by Japan over the last 5 years has been about 50% greater than that in the United State, and by Germany in the last 2--3 years more than twice that of the US Amorphous silicon is the only thin-film technology that is selling large-area commercial modules. The cost for amorphous silicon modules is now in the $4.50 range; it is a strong function of plant production capacity and is expected to be reduced to $1.00--1.50/W{sub p} for plants with 10 MW/year capacities. 10 refs.
Luft, W.; Stafford, B.; von Roedern, B.
Polycrystalline Yb{sub 6}W{sub 1}O{sub 12} and Y{sub 6}W{sub 1}O{sub 12} samples, which possess rhombohedral symmetry (structure known as the {delta}-phase, closely related to cubic fluorite structure), were irradiated with 280 keV Kr{sup ++} ions to fluences up to 2 x 10{sup 20} ions/m{sup 2} at cryogenic temperature (100 K). Ion irradiation damage effects in these samples were examined using grazing incidence X-ray diffraction (GIXRD) and cross-sectional transmission electron microscopy (TEM). Irradiation-induced amorphization in both compounds has been observed by GIXRD and TEM, while the amorphization dose for Yb{sub 6}W{sub 1}O{sub 12} is lower than that for Yb{sub 6}W{sub 1}O{sub 12}. Experimental results also revealed that both irradiated samples experience an ordered rhombohedral to disordered cubic fluorite (O-D) transformation before amorphization. Factors influencing the irradiation damage response of these two compounds will be discussed in terms of cation radius ratio and cation antisite formation energy calculated by density functional theory (DFT).
Tang, Ming [Los Alamos National Laboratory; Uberuaga, Blas [Los Alamos National Laboratory; Valdez, James [Los Alamos National Laboratory; Sickafus, Kurt [Los Alamos National Laboratory
Processing of amorphous PEEK and amorphous PEEK based composites
An analysis of the crystallization behavior of amorphous PEEK, its carbon fiber composite, and its relationships with dynamic-mechanical properties of the system measured during and after processing is presented. The effect of the processing conditions, time and temperature, on the quality and on the amount of the crystallinity developed during cold crystallization has been investigated in order to evaluate the processability window of amorphous PEEK and amorphous PEEK based composite above the glass transition temperature and below the melting point. Also, the anomalous behavior of the amorphous matrix, crystallized at low temperatures, has been studied. Multiple melting peaks and changes of the glass transition during crystallization are explained in terms of crystalline morphology and molecular mobility. 20 refs.
Kenny, J.; D'amore, A.; Nicolais, L.; Iannone, M.; Scatteia, B. (Napoli Universita, Naples (Italy); Aeritalia, S.p.A., Naples (Italy))
Containerless processing of amorphous ceramics
NASA Technical Reports Server (NTRS)
The absence of gravity allows containerless processing of materials which could not otherwise be processed. High melting point, hard materials such as borides, nitrides, and refractory metals are usually brittle in their crystalline form. The absence of dislocations in amorphous materials frequently endows them with flexibility and toughness. Systematic studies of the properties of many amorphous materials have not been carried out. The requirements for their production is that they can be processed in a controlled way without container interaction. Containerless processing in microgravity could permit the control necessary to produce amorphous forms of hard materials.
Weber, J. K. Richard; Krishnan, Shankar; Schiffman, Robert A.; Nordine, Paul C.
Structure, Properties, and Dynamics of Oxygen Vacancies in Amorphous SiO2 Zhong-Yi Lu,1
crystalline and amorphous forms. Several of its properties are dominated by a single point defect in the oxide can often be neutralized by a high-temperature anneal at large positive bias, but much, and amorphous supercells led to the iden- tification of the defect as the oxygen vacancy. This defect exhibits
Pantelides, Sokrates T.
Fabrication of amorphous diamond films
Amorphous diamond films having a significant reduction in intrinsic stress are prepared by biasing a substrate to be coated and depositing carbon ions thereon under controlled temperature conditions. 1 fig.
Falabella, S.
Inhibitory Effect of Soil Organic Matter on the Crystallization of Amorphous Ferric Hydroxide
SOILS and sediments often contain large quantities of hydrous ferric oxide which, according to X-ray analysis, cannot be accounted for by crystalline forms of iron oxide. This is surprising in view of the fact that crystallization in vitro of freshly prepared amorphous ferric hydroxide to goethite or haematite is virtually complete after a few months or years, even at room
U. Schwertmann
Processing Bi-Pb-Sr-Ca-Cu-O superconductors from amorphous state
NASA Technical Reports Server (NTRS)
The bismuth based high T sub c superconductors can be processed via an amorphous Bi-Pb-Sr-Ca-Cu oxide. The amorphous oxides were prepared by melting the constituent powders in an alumina crucible at 1200 C in air followed by pouring the liquid onto an aluminum plate, and rapidly pressing with a second plate. In the amorphous state, no crystalline phase was identified in the powder x ray diffraction pattern of the quenched materials. After heat treatment at high temperature the amorphous materials crystallized into a glass ceramic containing a large fraction of the Bi2Sr2Ca2Cu3O(x) phase T sub c = 110 K. The processing method, crystallization, and results of dc electrical resistivity and ac magnetic susceptibility measurements are discussed.
Chiang, C. K.; Wong-Ng, W.; Cook, L. P.; Freiman, S. W.; Hwang, N. M.; Vaudin, M.; Hill, M. D.; Shull, R. D.; Shapiro, A. J.; Swartzendruber, L. J.
NASA Astrophysics Data System (ADS)
Phosphate is an essential element for life on Earth, and therefore if life exists or ever existed on Mars it may have required phosphate. Amorphous Al- and Fe-phosphates rapidly precipitate from acidic solutions and amorphous Al-phosphates likely control phosphate concentrations in some natural waters on Earth. Amorphous phases may be even more important on Mars than on Earth, and amorphous phosphates are therefore likely important in the phosphate cycle on Mars. Despite this importance, however, few dissolution rates exist for amorphous Al- and Fe- phosphates. In this study, dissolution rates of amorphous Al- and Fe-phosphates were measured in flow-through reactors from steady state concentrations of Al, Fe and P. A pH--dependent rate law was calculated from the dissolution rates log R = log k -- npH, where R is the dissolution rate, k is intrinsic rate constant and n is the rate dependence on pH. For amorphous Al-phosphate, log k = -6.539 +/- 1.529, and n = 2.391 +/- 0.493. For amorphous Fe-phosphate, log k = -13.031 +/- 0.558, and n = 1.376 +/- 0.221. Amorphous Al-phosphate dissolves stoichiometrically under all conditions, and amorphous Fe-phosphate dissolves non-stoichiometrically, approaching stoichiometric dissolution as pH decreases, due potentially to Fe-oxides precipitating and armoring grain surfaces. Perhaps due to these effects, amorphous Al-phosphate dissolution rates are approximately three orders of magnitude faster than amorphous Fe-phosphate dissolution rates. Amorphous Al-phosphate dissolution rates measured in this study are also faster than published variscite dissolution rates. Dissolution rates of amorphous Al- and Fe-phosphates in this study therefore imply rapid phosphate release into acidic environments, suggesting phosphate mobility under Mars-relevant conditions.
Tu, Valerie M.
Impact of amorphization on the magnetic properties of EuO-TiO2 system
NASA Astrophysics Data System (ADS)
Recently, we have reported amorphization-induced ferromagnetism in a magnetic oxide; whereas crystalline EuTiO3 is an antiferromagnet, its amorphous counterpart shows a ferromagnetic transition. In this paper, we have investigated the magnetic properties of amorphous EuO-TiO2 system in detail. The present compounds, i.e., amorphous EuTiO3 and Eu2TiO4 , exhibit a paramagnetic-ferromagnetic transition followed by a spin-glass transition upon cooling down, thereby being characterized as reentrant ferromagnets. Interestingly, the magnetic ordering temperatures of amorphous EuTiO3 and Eu2TiO4 are comparable to and higher than those of their crystalline counterparts, respectively, indicating the enhancement of ferromagnetic interactions by amorphization. The origin of these features is discussed in terms of both the essential structural difference between amorphous and crystalline oxides and the magnetism unique to the crystalline EuO-TiO2 compounds. We also find a correlation between the magnitude of ferromagnetic interactions and the covalency of Eu-O bonds.
Akamatsu, Hirofumi; Fujita, Koji; Zong, Yanhua; Takemoto, Naohiro; Murai, Shunsuke; Tanaka, Katsuhisa
Random glass structure and electron localisation in amorphous V2O5
ESR experiments performed on crystalline and amorphous WO3-doped V2O5 indicate different behaviours of both spectra with temperature and microwave frequency. A line broadening is observed for the crystalline oxide as the temperature increases while the ESR spectrum of amorphous V2O5 remains well resolved up to 300K. This suggests that the electron hopping frequency between V4+ and V5+ ions is much
M. Henri; C. Sanchez; C. R. Kha; J. Livage
Room temperature fabricated flexible NiO/IGZO pn diode under mechanical strain
NASA Astrophysics Data System (ADS)
Flexible electronic devices fabricated on plastic substrates require semiconductors, which can be deposited at low temperatures. While Indium-Gallium-Zinc-Oxide (IGZO) is a promising n-type oxide semiconductor, a p-type oxide semiconductor with similar performance is currently not available. Here, the room temperature deposition of nickel oxide (NiO) acting as a p-type oxide semiconductor on a flexible plastic foil is described. NiO exhibits a carrier density of +1.6 � 1017 cm-3 and a Hall mobility of 0.45 cm2/Vs. p-type NiO is combined with n-type IGZO to fabricate flexible pn diodes on a free-standing polyimide substrate. The diodes show an ideality factor of ?3.2 and an on-off current-ratio of ?104. The NiO/IGZO diodes stay fully operational when exposed to tensile or compressive mechanical strain of 0.25%, induced by bending to a radius of 10 mm. In addition, a 50 Hz AC signal was rectified using a flexible diode while flat and bent.
M�nzenrieder, Niko; Zysset, Christoph; Petti, Luisa; Kinkeldei, Thomas; Salvatore, Giovanni A.; Tr�ster, Gerhard
Amorphous-diamond electron emitter
An electron emitter comprising a textured silicon wafer overcoated with a thin (200 .ANG.) layer of nitrogen-doped, amorphous-diamond (a:D-N), which lowers the field below 20 volts/micrometer have been demonstrated using this emitter compared to uncoated or diamond coated emitters wherein the emission is at fields of nearly 60 volts/micrometer. The silicon/nitrogen-doped, amorphous-diamond (Si/a:D-N) emitter may be produced by overcoating a textured silicon wafer with amorphous-diamond (a:D) in a nitrogen atmosphere using a filtered cathodic-arc system. The enhanced performance of the Si/a:D-N emitter lowers the voltages required to the point where field-emission displays are practical. Thus, this emitter can be used, for example, in flat-panel emission displays (FEDs), and cold-cathode vacuum electronics.
Falabella, Steven (Livermore, CA)
Annealing studies of amorphous alloys
Amorphous films of the alloys Ni-Nb, Ni-Mo, Mo-Si, and W-Si were sputter deposited on single-crystal semiconductor substrates. One-hour crystallization temperatures of the films were determined to within +-25/sup 0/C by annealing and x-ray diffraction measurements. Interdiffusion between Au or Cu overlayers and the amorphous films were studied by annealing combined with Auger Electron Spectroscopy (AES) profiling, and by Rutherford Backscatter (RBS) analysis. Supplementary measurements used to study structural relaxation and crystallization included resistivity as a function of temperature; DTA and DSC; and electron microscopy.
Wiley, J.D.; Perepezko, J.H.; Nordman, J.E.
Thermal degradation of amorphous glibenclamide.
A glibenclamide polymorph published by Panagopoulou-Kaplani and Malamataris (2000) [1], obtained by sublimation of amorphous glibenclamide, was analysed. A new interpretation of the data is presented and experimentally confirmed by X-ray powder diffractometry, Fourier transformation infrared spectroscopy, differential scanning calorimetry, and mass spectrometry. The crystals formed during sublimation of amorphous glibenclamide do not represent a glibenclamide polymorph, but a thermal degradation product, namely 1,3-dicyclohexylurea. The reaction mechanism is suggested to be an elimination of cyclohexylisocyanate from glibenclamide. Cyclohexylisocyanate may decompose to carbon monoxide and cyclohexylamine, which may react in an addition reaction with another cyclohexylisocyanate molecule forming 1,3-dicyclohexylurea. PMID:21907802
Rehder, S�nke; Sakmann, Albrecht; Rades, Thomas; Leopold, Claudia S
Amorphous Phases on the Surface of Mars
NASA Astrophysics Data System (ADS)
We discuss orbital and in-situ detections of amorphous materials and their implications for geologic processes on the martian surface, questions that still remain about amorphous phases on Mars, and potential paths toward answering those questions.
Rampe, E. B.; Morris, R. V.; Ruff, S. W.; Horgan, B.; Dehouck, E.; Achilles, C. N.; Ming, D. W.; Bish, D. L.; Chipera, S. J.; MSL Science Team
Mechanics of amorphous polymers and polymer gels
Many applications of amorphous polymers require a thermo-mechanically coupled large-deformation elasto-viscoplasticity theory which models the strain rate and temperature dependent response of amorphous polymeric materials ...
Chester, Shawn Alexander
Nanocrystalline Cr 2O 3 and amorphous CrO 3 produced by solution combustion synthesis
The synthesis of chromium oxides by solution combustion synthesis was investigated. Ammonium dichromate, glycine, urea and ammonium nitrate dissolved in aqueous solution were used as the precursors of the oxides. The effect of different reaction parameters, such as fuel richness, stoichiometry and fuel leanness was evaluated; such parameters were modified by changing the reagents and the fuel\\/oxidant ratio. Amorphous CrO3
M. D. Lima; R. Bonadimann; M. J. de Andrade; J. C. Toniolo; C. P. Bergmann
Hydrogen-induced defect generation in amorphous SiO2
Dielectric breakdown of thin silicon oxides (SiO2) of metal-oxide semiconductor field-effect transistors is a long-standing problem. The breakdown is generally recognized to be due to the accumulation of defects in the oxide. An amorphous SiO2 (a-SiO2) has been known to have very few defects, thanks to its strong and flexible network of Si-O bonds. Then, why are defects created in
Masayasu Miyata; Adri C. T. van Duin
AMORPHOUS AND SPIN GLASSES. Random magnetic anisotropy in amorphous alloys containing rare earth
AMORPHOUS AND SPIN GLASSES. Random magnetic anisotropy in amorphous alloys containing rare earth anisotropy in amorphous alloys containing non 5-state rare earth ions is analysed in detail. Magnetisation of amorphous rare-earth-transition metal/noble metal alloys is reasonably described by dense random packing
Paris-Sud XI, Université de
Compton profiles from amorphous allotropes of carbon
Two amorphous allotropes of carbon are investigated. They are distinguished by their plasmon and K-edge spectra as diamond-like carbon and a rather soft form of amorphous carbon, respectively. By computing the difference profile of the normalized valence Compton profiles of amorphous diamond-like carbon and amorphous carbon, differences in the momentum densities of the two media are shown. A simple atomistic
Alfred Exner; Peter Schattschneider; Ian E. McCarthy
Amorphization by ball milling. A review
A new method for the preparation of amorphous alloys is the mechanical alloying process. So far, three amorphization reaction types were observed when this technique is used. Which reaction type occurs depends on the local conditions during the milling, such as impact energy and local temperature just after an impact. Amorphous alloys prepared by milling following different reaction types are
A. W. Weeber; H. Bakker
Tritiated amorphous silicon for micropower applications
The application of tritiated amorphous silicon as an intrinsic energy conversion semiconductor for radioluminescent structures and betavoltaic devices is presented. Theoretical analysis of the betavoltaic application shows an overall efficiency of 18% for tritiated amorphous silicon. This is equivalent to a 330 Ci intrinsic betavoltaic device producing 1 mW of power for 12 years. Photoluminescence studies of hydrogenated amorphous silicon,
N. P. Kherani; T. Kosteski; S. Zukotynski; W. T. Shmayda
Microwave Absorption of Amorphous Superconductors.
National Technical Information Service (NTIS)
The surface resistance of amorphous Ga and Sn layers of varying thickness have been measured with a further developed microwave cryostat. A two-layer model enabled thinner layers to be included in the evaluation. Deviations in the temperature course betwe...
J. Goebbels
Tunneling states in amorphous solids
A linear temperature dependence of the specific heat in amorphous solids at very low temperatures is shown to follow from an ionic tunneling model. Moreover, this model predicts both the observed temperature dependence and the magnitude of the thermal conductivity and also explains the anomalous results obtained for the phonon free path by means of stimulated Brillouin scattering.
W. A. Phillips
Model for amorphous aggregation processes
NASA Astrophysics Data System (ADS)
The amorphous aggregation of proteins is associated with many phenomena, ranging from the formation of protein wine haze to the development of cataract in the eye lens and the precipitation of recombinant proteins during their expression and purification. While much literature exists describing models for linear protein aggregation, such as amyloid fibril formation, there are few reports of models which address amorphous aggregation. Here, we propose a model to describe the amorphous aggregation of proteins which is also more widely applicable to other situations where a similar process occurs, such as in the formation of colloids and nanoclusters. As first applications of the model, we have tested it against experimental turbidimetry data of three proteins relevant to the wine industry and biochemistry, namely, thaumatin, a thaumatinlike protein, and ? -lactalbumin. The model is very robust and describes amorphous experimental data to a high degree of accuracy. Details about the aggregation process, such as shape parameters of the aggregates and rate constants, can also be extracted.
Stranks, Samuel D.; Ecroyd, Heath; van Sluyter, Steven; Waters, Elizabeth J.; Carver, John A.; von Smekal, Lorenz
Physicochemical determinants in the cellular responses to nanostructured amorphous silicas.
Amorphous silicas, opposite to crystalline polymorphs, have been regarded so far as nonpathogenic, but few studies have addressed the toxicity of the wide array of amorphous silica forms. With the advent of nanotoxicology, there has been a rising concern about the safety of silica nanoparticles to be used in nanomedicine. Here, we report a study on the toxicity of amorphous nanostructured silicas obtained with two different preparation procedures (pyrolysis vs. precipitation), the pyrogenic in two very different particle sizes, in order to assess the role of size and origin on surface properties and on the cell damage, oxidative stress, and inflammatory response elicited in murine alveolar macrophages. A quartz dust was employed as positive control and monodispersed silica spheres as negative control. Pyrogenic silicas were remarkably more active than the precipitated one as to cytotoxicity, reactive oxygen species production, lipid peroxidation, nitric oxide synthesis, and production of tumor necrosis factor-?, when compared both per mass and per unit surface. Between the two pyrogenic silicas, the larger one was the more active. Silanols density is the major difference in surface composition among the three silicas, being much larger than the precipitated one as indicated by joint calorimetric and infrared spectroscopy analysis. We assume here that full hydroxylation of a silica surface, with consequent stable coverage by water molecules, reduces/inhibits toxic behavior. The preparation route appears thus determinant in yielding potentially toxic materials, although the smallest size does not always correspond to an increased toxicity. PMID:22491428
Gazzano, Elena; Ghiazza, Mara; Polimeni, Manuela; Bolis, Vera; Fenoglio, Ivana; Attanasio, Angelo; Mazzucco, Gianna; Fubini, Bice; Ghigo, Dario
The oxidation of ferrous ions, in acid solution, by resting suspensions of Thiobacillus ferrooxidans produced sediments consisting of crystalline jarosites, amorphous ferric hydroxysulfates, or both. These products differed conspicuously in chemical composition and infrared spectra from precipitates formed by abiotic oxidation under similar conditions. The amorphous sediments, produced by bacterial oxidation, exhibited a distinctive fibroporous microstructure when examined by scanning
N. Lazaroff; W. Sigal; A. Wasserman
The influence of calcination temperature upon the solid state chemistry of WO� on Al�O� was examined with laser Raman spectroscopy. Laser Raman spectroscopy revealed the amorphous and crystalline structural transformations occurring in the WO� on Al�O� oxide system. Below monolayer coverage of tungsten oxide on alumina, the tungsten oxide phase is present as a highly dispersed and amorphous surface complex
S. S. Chan; I. E. Wachs; L. L. Murrell; N. C. Jr. Dispenziere
FeSiBNb amorphous powder was prepared by gas atomization and subsequently consolidated into bulk amorphous cores by hot pressing after creating an oxide layer on the surface of the powder. FeSiBNb amorphous powders exhibiting a saturation magnetization of 127 emu/g and a coercivity of 0.34 Oe were successfully obtained by gas atomization. Hot pressing enabled consolidation of the FeSiBNb amorphous powder core within the supercooled liquid region. The core prepared from the FeSiBNb amorphous powder covered with an oxide layer of 1 {mu}m thickness showed excellent high-frequency characteristics with a stable permeability over 10 MHz and a core loss of 400 mW/cm{sup 3} at 50 kHz for B{sub m}=0.1 T. The oxide layer formed on the FeSiBNb amorphous powder was effective in improving the frequency dependence of magnetic properties and in reducing the core loss for the FeSiBNb amorphous powder cores.
Kang, E. Y.; Kim, Yoon B.; Kim, K. Y.; Chung, Y. H.; Baik, H. K. [Advanced Metals Research Center, Korea Institute of Science and Technology, Seoul 136-791 (Korea, Republic of); Department of Metallurgical Engineering, Yonsei University, Seoul 120-749 (Korea, Republic of)
Hot carrier relaxation in amorphous germanium
NASA Astrophysics Data System (ADS)
The ultimate expected efficiencies of thin film amorphous solar cells may be raised by using amorphous alloys of germanium and silicon. To date, no single measurement technique has appeared that directly and decisively identifies and characterizes the key photovoltaic related phenomena occuring in solar cell grade amorphous semiconductors. In this presentation, an ultra high speed electrooptical approach to the measurement of the optical and electrical properties of amorphous semiconducting thin films is described. Results of measurements performed to date on amorphous germanium alloys are presented and the implications of the data regarding solar cell applications are discussed.
Defonzo, A. P.
Amorphous molybdenum sulfides as hydrogen evolution catalysts.
Providing energy for a population projected to reach 9 billion people within the middle of this century is one of the most pressing societal issues. Burning fossil fuels at a rate and scale that satisfy our near-term demand will irreversibly damage the living environment. Among the various sources of alternative and CO2-emission-free energies, the sun is the only source that is capable of providing enough energy for the whole world. Sunlight energy, however, is intermittent and requires an efficient storage mechanism. Sunlight-driven water splitting to make hydrogen is widely considered as one of the most attractive methods for solar energy storage. Water splitting needs a hydrogen evolution catalyst to accelerate the rate of hydrogen production and to lower the energy loss in this process. Precious metals such as Pt are superior catalysts, but they are too expensive and scarce for large-scale applications. In this Account, we summarize our recent research on the preparation, characterization, and application of amorphous molybdenum sulfide catalysts for the hydrogen evolution reaction. The catalysts can be synthesized by electrochemical deposition under ambient conditions from readily available and inexpensive precursors. The catalytic activity is among the highest for nonprecious catalysts. For example, at a loading of 0.2 mg/cm(2), the optimal catalyst delivers a current density of 10 mA/cm(2) at an overpotential of 160 mV. The growth mechanism of the electrochemically deposited film catalysts was revealed by an electrochemical quartz microcrystal balance study. While different electrochemical deposition methods produce films with different initial compositions, the active catalysts are the same and are identified as a "MoS(2+x)" species. The activity of the film catalysts can be further promoted by divalent Fe, Co, and Ni ions, and the origins of the promotional effects have been probed. Highly active amorphous molybdenum sulfide particles can also be prepared from simple wet-chemical routes. Electron transport is sometimes slow in the particle catalysts, and an impedance model has been established to identify this slow electron transport. Finally, the amorphous molybdenum sulfide film catalyst has been integrated onto a copper(I) oxide photocathode for photoelectrochemical hydrogen evolution. The conformal catalyst efficiently extracts the excited electrons to give an impressive photocurrent density of -5.7 mA/cm(2) at 0 V vs RHE. The catalyst also confers good stability. PMID:25065612
Morales-Guio, Carlos G; Hu, Xile
Tritiated amorphous silicon betavoltaic devices
The introduction of tritium into hydrogenated amorphous silicon has given rise to a novel material with interesting physical properties and potential applications. Tritium undergoes radioactive decay, transforming into 3 He + and emitting an electron with average energy 5.7 keV, at a rate equivalent to a half-life of 12.3 years. The decay of tritium results in the creation of electron-
T. Kosteski; N. P. Kherani; P. Stradins; F. Gaspari; W. T. Shmayda; L. S. Sidhu; S. Zukotynski
Allotropic composition of amorphous carbon
Using the concept of an inhomogeneous broadening of spectral lines of the basic oscillators responsible for forming the spectrum,\\u000a the experimental dependences of the dispersion of the imaginary part of permittivity are analyzed for amorphous carbon. It\\u000a turned out that four types of oscillators contribute to this dependence. The first three types represent the electron transitions\\u000a from the energy-spectrum ground
S. G. Yastrebov; V. I. Ivanov-Omski?
Negative effect of Au nanoparticles on an IGZO TFT-based nonvolatile memory device
NASA Astrophysics Data System (ADS)
In this letter, the electrical characteristics of nonvolatile memory devices based on back gatetype indium gallium zinc oxide (IGZO) thin-film transistors (TFTs) are investigated in terms of the Au nanoparticles (NPs) employed in the floating gate-stack of the device. The size of the Au NPs is controlled using a by 500 �C annealing process after the Au thin-film deposition. The size and the roughness of the Au NPs were observed by using scanning electron microscopy, atomic force microscopy, and transmission electron microscopy. In order to analyze the electrical properties according to Au NP size, we measured the current-voltage (I D -V G ) characteristics of the nonvolatile memory devices fabricated without Au NPs and with Au NPs of various sizes. The size of the Au NP increased, so did the surface roughness of the gate. This resulted in increased carrier scattering, which subsequently degraded the on-current of the memory device. In addition, inter-diffusion between the Au and the ?-IGZO through the non-uniform Al2O3 tunneling layer seemed to further degrade the device performance.
Lim, Myung-Hoon; Yoo, Gwangwe; Lee, Jongtaek; Jeong, Seok-Won; Roh, Yonghan; Park, Jin-Hong; Kwon, Namyong; Jung, Woo-Shik
NASA Astrophysics Data System (ADS)
In this paper, we report the device characteristics of indium gallium zinc oxide (IGZO) thin film transistors (TFTs) with high- ? lanthanum aluminate (LaAlO3) based gate insulators. The IGZO TFT with single LaAlO3 gate insulator has an operation voltage as low as 1.5 V but suffers a low on-off-state drive current ratio ( I on/ I off) of 1�103, a large subthreshold swing ( SS) of 0.405 V/dec and a small field effect mobility ( ? FE) of 0.84 cm2/V sec. Inserting a SiO2 buffer layer between IGZO active channel layer and LaAlO3 gate insulator results in a reduced effective dielectric constant but with significant improved characteristics including a high I on/ I off of 6.2�104, a small SS of 0.113 V/dec and a large ? FE of 5.2 cm2/V sec. Such good performances can be attributed to the lowered gate leakage and reduced interface trap issue owing to the smooth SiO2 buffer layer insertion.
Zheng, Z. W.; Chen, Y. C.
Chromic mechanism in amorphous WO{sub 3} films
The authors propose a new model for the chromic mechanism in amorphous tungsten oxide films (WO{sub 3{minus}y}{center_dot}nH{sub 2}O). This model not only explains a variety of seemingly conflicting experimental results reported in the literature that cannot be explained by existing models, it also has practical implications with respect to improving the coloring efficiency and durability of electrochromic devices. According to this model, a typical as-deposited tungsten oxide film has tungsten mainly in W{sup 6+} and W{sup 4+} states and can be represented as W{sub 1{minus}y}{sup 6+} W{sub y}{sup 4+}O{sub 3{minus}y}{center_dot}nH{sub 2}O. The proposed chromic mechanism is based on the small polaron transition between the charge-induced W{sup 5+} state and the original W{sup 4+} state instead of the W{sup 5+} and W{sup 6+} states as suggested in previous models. The correlation between the electrochromic and photochromic behavior in amorphous tungsten oxide films is also discussed.
Zhang, J.G.; Benson, D.K.; Tracy, C.E.; Deb, S.K.; Czanderna, A.W. [National Renewable Energy Lab., Golden, CO (United States); Bechinger, C. [Universitaet Konstanz (Germany)
explained by Maxwell thanks to kinetic theory. In oxide melts and glasses, viscosities determine melting interconnecting SiO4 tetrahedra through bridging oxygen atoms of amorphous silica. At absolute zero temperature it will contain no point #12;defects; however at any finite temperature T the net will contain thermally activated
Sheffield, University of
Optimization of Conductivity and Transparency in Amorphous In-Zn-O Transparent Conductors: Preprint
Amorphous mixed metal oxide TCOs are of increasing interest due to the excellent opto-electronic properties and smoothness (RRMS < 0.5 nm) obtained for sputtered films deposited at less than 100 ..deg..C. Here, we have investigated the combined materials phase space of oxygen stoichiometry and metals composition (In:Zn ratio) and made two key discoveries.
Perkins, J.; Berry, J.; van Hest, M.; Alleman, J.; Dabney, M.; Gedvilas, L.; Ginley, D. S.; Leenheer, A.; O'Hayre, R.
Nanoindentation and nanowear tests on amorphous carbon films
To clarify the physical and tribological properties of pure amorphous carbon films, nanoindentation and scanning-scratched wear tests were conducted on pure amorphous carbon films, diamond and graphite, by using an atomic force microscope with a diamond tip. Two types of pure amorphous carbon films (amorphous carbon 1 and amorphous carbon 2) were deposited on silicon substrates. To evaluate the tribological
S. Umemura; Y. Andoh; S. Hirono; T. Miyamoto; R. Kaneko
Selective laser sintering of amorphous metal powder
For the first time, selective sintering of amorphous PtCuNiP powder with a pulsed Nd:YAG laser has been studied. Upon pulsed interaction, the grains melt only superficially to build necks between the grains. Depending on the laser parameters, the sintered material can be crystallized or retained amorphous. By contrast with crystalline powder, laser sintering of amorphous powder is achieved at substantially
P. Fischer; A. Blatter; V. Romano; H. P. Weber
Recent developments in hot wire amorphous silicon
We present measurements of low temperature internal friction (Q?1) of amorphous silicon (a-Si) films designed to probe how their structure and formation affect low temperature vibrational properties. All a-Si films, whether produced by e-beam evaporation, sputtering, Si self-ion implantation, or chemical vapor deposition (CVD) show the well-known temperature-independent plateau (Q0?1) common to all amorphous solids. For hydrogenated amorphous silicon (a-Si:H)
Richard S Crandall; Xiao Liu; Eugene Iwaniczko
XRD Technique: A way to disseminate structural changes in iron-based amorphous materials
Prevention of corrosion is a vital goal for the Department of Defense when billions of dollars are spent every year. Corrosion resistant materials have applications in all sort of military vehicles, and more importantly in naval vessels and submarines which come in contact with the seawater. It is known that corrosion resistance property can be improved by the used of structurally designed materials in the amorphous state where the atoms are arranged in a non-periodic fashion and specific atoms, tailored to the required properties can be interjected into the matrix for specific application. The XRD techniques reported here is to demonstrate the optimal conditions for characterization of these materials. The samples, which normally contain different compositions of Fe, Cr, B, Mo, Y, Mn, Si and W, are in the form of powders, ribbons and coatings. These results will be compared for the different forms of the sample which appears to correlate to the cooling rate during sample processing. In most cases, the materials are amorphous or amorphous with very small amount of crystallinity. In the ribbon samples for different compositions we observed that the materials are essentially amorphous. In most cases, starting from an amorphous powder sample, the coatings are also observed to be amorphous with a small amount of iron oxide on the surface, probably due to exposure to air.
Saw, C K; Lian, T; Day, D; Farmer, J
Structural and optical characteristics of bismuth oxide thin films
The formation of different phases of Bi�O system during oxidizing process of Bi films from the viewpoint of structure characteristics and optical properties, is investigated. As revealed by structure and surface investigations, the thermal oxidation, in air, of Bi films on glass results in polycrystalline and multiphase bismuth oxide films. At substrate�film interface an amorphous oxide layer forms up, to
L. Leontie; M. Caraman; M. Alexe; C. Harnagea
Quantification of amorphous content in mixed systems: amorphous trehalose with lactose
There has been a lot of interest in quantification of the amorphous content of materials, especially when the amorphous content is a small percentage of the total mass. Whilst there has been success in studies on single materials, there has been little work showing how quantification of the amorphous content of one material can be undertaken in the presence of
Dima Al-Hadithi; Graham Buckton; Stephen Brocchini
Deng & Schiff, Amorphous Silicon Based Solar Cells rev. 7/30/2002, Page 1 Amorphous Silicon Based Solar Cells Xunming Deng and Eric A. Schiff Table of Contents 1 Overview 3 1.1 Amorphous Silicon: The First Bipolar Amorphous Semiconductor 3 1.2 Designs for Amorphous Silicon Solar Cells: A Guided Tour 6
Deng, Xunming
Phase diagram of amorphous solid water: Low-density, high-density, and very-high-density amorphous low-density amorphous LDA , high-density amorphous HDA , and very-high density amorphous VHDA ices. The density of these glasses at different pressure P and temperature T agree well with experimental values. We
Sciortino, Francesco
Inelastic scattering from amorphous solids
The potential of inelastic neutron scattering techniques for surveying various aspects of the dynamics of amorphous solids is briefly reviewed. The recent use of the Intense Pulsed Neutron Source to provide detailed information on the optical vibrations of glasses is discussed in more detail. The density of states represents an averaged quantity which gives information about the general characteristics of the structure and bonding. More extensive information can be obtained by studying the detailed wavevector dependence of the dynamic structure factor. 15 refs., 7 figs.
Price, D.L.
AMORPHOUS metallic alloys ('metallic glasses') lack long-range\\u000a crystalline order and have unique electronic, magnetic and\\u000a corrosion-resistant properties 1-3. Their applications include use in\\u000a power-transformer cores, magnetic storage media, cryothermometry and\\u000a corrosion-resistant coatings. The production of metallic glasses is\\u000a made difficult, however, by the extremely rapid cooling from the melt\\u000a that is necessary to prevent crystallization. Cooling rates of about\\u000a 10(5)
Kenneth S. Suslick; Seok-Burm Choe; Andrzej A. Cichowlas; Mark W. Grinstaff
Optimization of transparent and reflecting electrodes for amorphous silicon solar cells
The specific objectives of this research are to: (1) Deposit and characterize textured zinc oxide with improved conductivities (less than 8 ohms/square sheet resistance) and optical transmission (greater than 85% for 450 to 700 nm), for use as front and back contacts in hydrogenated amorphous silicon p-i-n devices. Study the surface morphology of zinc oxide films deposited by chemical vapor deposition at atmospheric pressure (APCVD), their crystallite sizes, shapes and orientations, and their nucleation (early growth) as a function of chemical precursors and reaction conditions. Optimize the growth process to produce structures that provide good light trapping in an amorphous silicon film deposited on the zinc oxide film. The films must have good adhesion to glass substrates. (2) Study the deposition rate of zinc oxide films as a function of temperature, and concentration and types of reactants. Maximize the growth rate, subject to the conditions of maintaining satisfactory film properties, including high transparency (85%), high conductivity (8 ohm/square sheet resistance), and good light trapping. (3) Develop techniques for deposition of fluorinated zinc oxide films by APCVD on amorphous silicon films in the temperature range of 250-280C for use as back contacts. (4) Deposit titanium nitride films at a temperature of about 250C by APCVD on amorphous silicon as diffusion barrier, and then deposit highly reflective metals such as aluminum or silver. Anneal samples and test for metal diffusion through the TiN into the silicon. Optimize the TiN film for minimum diffusion consistent with maintaining desirable TiN film properties. (5) Incorporate the front and back contacts including the TiN barrier layer developed under this research into amorphous silicon p-i-n devices and determine the film parameters that provide the greatest improvement in the device solar energy conversion efficiency. 23 refs., 18 figs., 2 tabs.
Gordon, R.G.; Hu, Jianhua; Musher, J.; Giunta, C. (Harvard Univ., Cambridge, MA (USA). Dept. of Chemistry)
Fluorination of amorphous thin-film materials with xenon fluoride
A method is disclosed for producing fluorine-containing amorphous semiconductor material, preferably comprising amorphous silicon. The method includes depositing amorphous thin-film material onto a substrate while introducing xenon fluoride during the film deposition process.
Weil, Raoul B. (Haifa, IL)
Fluorination of amorphous thin-film materials with xenon fluoride
A method is disclosed for producing fluorine-containing amorphous semiconductor material, preferably comprising amorphous silicon. The method includes depositing amorphous thin-film material onto a substrate while introducing xenon fluoride during the film deposition process.
Weil, R.B.
Studies of hydrogenated amorphous silicon
This report discusses the results of probing the defect structure and bonding of hydrogenated amorphous silicon films using both nuclear magnetic resonance (NMR) and electron spin resonance (ESR). The doping efficiency of boron in a-Si:H was found to be less than 1%, with 90% of the boron in a threefold coordinated state. On the other hand, phosphorus NMR chemical shift measurements yielded a ration of threefold to fourfold P sites of roughly 4 to 1. Various resonance lines were observed in heavily boron- and phosphorus-doped films and a-SiC:H alloys. These lines were attributed to band tail states on twofold coordinated silicon. In a-SiC:H films, a strong resonance was attributed to dangling bonds on carbon atoms. ESR measurements on low-pressure chemical-vapor-deposited (LPCVD) a-Si:H were performed on samples. The defect density in the bulk of the films was 10/sup 17//cc with a factor of 3 increase at the surface of the sample. The ESR spectrum of LPCVD-prepared films was not affected by prolonged exposure to strong light. Microcrystalline silicon samples were also examined. The phosphorus-doped films showed a strong signal from the crystalline material and no resonance from the amorphous matrix. This shows that phosphorus is incorporated in the crystals and is active as a dopant. No signal was recorded from the boron-doped films.
Bishop, S G; Carlos, W E
Glass forming ranges of amorphous alloys
Two main methods of synthesis of amorphous metallic alloys are based on the rapid solidification of molten alloys and on isothermal solid state reactions between pure metals. We discuss recent calculations for the glass forming range for both techniques and we compare the predicted homogeneity ranges of the amorphous phase with experiments. 10 refs., 2 figs.
Schwarz, R.B.
Thermochemical studies on amorphous calcium phosphate
Previous studies have indicated that synthetically-precipitated amorphous calcium phosphate, even though not a periodically regular structure, possesses a chemically definable local unit of structure. The present paper is a report of thermochemical studies performed to more clearly define this local chemical unit. Upon ignition in the absence of water, freezedried amorphous calcium phosphate preparations converted into crystalline ?-and\\/or ?-tricalcium phosphates.
E. D. EAglES
Amorphous Solid without Low Energy Excitations
We have measured the low temperature internal friction (Q{sup -1}) of amorphous silicon (a-Si) films. {ital e}-beam evaporation or {sup 28}Si{sup +} implantation leads to the temperature-independent Q{sup -1}{sub 0} plateau common to all amorphous solids. For hydrogenated amorphous silicon with 1 at. {percent} H produced by hot wire chemical vapor deposition, however, Q{sup -1}{sub 0} is over 200 times smaller than for {ital e}-beam {ital a}-Si. This is the first observation of an amorphous solid without any significant low energy excitations. It offers the opportunity to study amorphous solids containing controlled densities of tunneling defects, and thus to explore their nature. {copyright} {ital 1997} {ital The American Physical Society}
Liu, X.; White, B.E. Jr.; Pohl, R.O. [Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853-2501 (United States)] [Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853-2501 (United States); Iwanizcko, E.; Jones, K.M.; Mahan, A.H.; Nelson, B.N.; Crandall, R.S. [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States)] [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States); Veprek, S. [Institute for Chemistry of Inorganic Materials, Tech.Univ.Munich, D-85747 Garching (Germany)] [Institute for Chemistry of Inorganic Materials, Tech.Univ.Munich, D-85747 Garching (Germany)
Tritiated amorphous silicon for micropower applications
The application of tritiated amorphous silicon as an intrinsic energy conversion semiconductor for radioluminescent structures and betavoltaic devices is presented. Theoretical analysis of the betavoltaic application shows an overall efficiency of 18% for tritiated amorphous silicon. This is equivalent to a 330 Ci intrinsic betavoltaic device producing 1 mW of power for 12 years. Photoluminescence studies of hydrogenated amorphous silicon, a-Si:H, show emission in the infra-red with a maximum quantum efficiency of 7.2% at 50 K; this value drops by 3 orders of magnitude at a temperature of 300 K. Similar studies of hydrogenated amorphous carbon show emission in the visible with an estimated quantum efficiency of 1% at 300 K. These results suggest that tritiated amorphous carbon may be the more promising candidate for room temperature radioluminescence in the visible. 18 refs., 5 figs.
Kherani, N.P. [Ontario Hydro Technologies, Toronto, Ontario (Canada)]|[Univ. of Toronto, Ontario (Canada); Kosteski, T.; Zukotynski, S. [Univ. of Toronto, Ontario (Canada); Shmayda, W.T. [Ontario Hydro Technologies, Toronto, Ontario (Canada)
Bias-Stress-Stable Solution-Processed Oxide Thin Film Transistors
Bias-Stress-Stable Solution-Processed Oxide Thin Film Transistors Youngmin Jeong, Changdeuck Bae We generated a novel amorphous oxide semiconductor thin film transistor (AOS-TFT) that has exellent-solution-processed transparent flexible transistors with air-stable, reproducible device characteristics. KEYWORDS: amorphous
Cao, Guozhong
Formulation of an amorphous solid dispersion (ASD) is one of the methods commonly considered to increase the bioavailability of a poorly water-soluble small-molecule active pharmaceutical ingredient (API). However, many factors have to be considered in designing an API-polymer system, including any potential changes to the physical stability of the API. In this study, the tendency of ASD systems containing a poorly water-soluble API and a polymer to undergo amorphous-amorphous phase separation was evaluated following exposure to moisture at increasing relative humidity. Infrared spectroscopy was used as the primary method to investigate the phase behavior of the systems. In general, it was observed that stronger drug-polymer interactions, low-ASD hygroscopicity, and a less hydrophobic API led to the formation of systems resistant to moisture-induced amorphous-amorphous phase separation. Orthogonal partial least squares analysis provided further insight into the systems, confirming the importance of the aforementioned properties. In order to design a more physically stable ASD that is resistant to moisture-induced amorphous-amorphous phase separation, it is important to consider the interplay between these properties. PMID:21927960
Rumondor, Alfred C F; Wikstr�m, H�kan; Van Eerdenbrugh, Bernard; Taylor, Lynne S
NASA Astrophysics Data System (ADS)
The amorphous interfacial layer (a-IL) between Al electrode and epitaxial NiO films were studied using electron energy-loss spectroscopy (EELS) and energy-dispersive x-ray spectroscopy. Two distinct properties were found in the a-IL, i.e., a lower metallic and an upper insulating layer. EELS results revealed that the metallic Ni atoms were responsible for the conducting nature of the lower oxide amorphous layer. The resistance behavior of Al/a-IL/epi-NiO was changed from a high to a low resistance state after forming process. The resistance change could be explained by the formation of a nanocrystalline metal alloy in the insulating amorphous layer.
Hyuck Jang, Jae; Kwon, Ji-Hwan; Ran Lee, Seung; Char, Kookrin; Kim, Miyoung
Amorphous metal alloys produced by mechanical alloying
Mechanical alloying is a powder metallurgy method used in commercial production of high temperature superalloys. Under specific conditions, mechanical alloying allows the synthesis of amorphous metal alloys from mixtures of pure metal powders or from the powders of intermetallic compounds. Because the amorphizing transformation during mechanical alloying is a solid state reaction, most of the difficulties related to the amorphization by rapid solidification of melts can be avoided. Mechanical alloying allows the synthesis of amorphous alloys from metals with high melting temperatures and the resulting alloys have interesting properties such as high hardness and high crystallization temperatures. We used mechanical alloying for the synthesis of amorphous alloys in the binary alloy systems Nl-Sn, Nb-Si and Al-Hf. The amorphous alloy powders were characterized by x-ray diffraction, differential scanning calorimetry, scanning and transmission electron microscopy and hardness measurements. Produced alloys were compacted by hot pressing and the obtained compacts were characterized by x-ray diffraction, density and hardness measurements and by optical and scanning electron microscopy. The results of the amorphization and compaction studies are presented and discussed together with the characteristics of the mechanical alloying process. 15 refs., 5 figs.
Tiainen, T.J.; Schwarz, R.B.
Crystalline to amorphous transformation in silicon
In the present investigation, an attempt was made to understand the fundamental mechanism of crystalline-to-amorphous transformation in arsenic-implanted silicon using high-resolution electron microscopy. A comparison of the gradual disappearance of simulated lattice fringes with increasing Frenkel pair concentration with the experimental observation of sharp interfaces between crystalline and amorphous regions was carried out leading to the conclusion that when the defect concentration reaches a critical value, the crystal does relax to an amorphous state. Optical diffraction experiments using atomic models also supported this hypothesis. Both crystalline and amorphous zones were found to co-exist with sharp interfaces at the atomic level. Growth of the amorphous fraction depends on the temperature, dose rate and the mass of the implanted ion. Preliminary results of high-energy electron irradiation experiments of 1.2 MeV also suggested that clustering of point defects occurs near room temperature. An observation in a high-resolution image of a small amorphous zone centered at the core of a dislocation is presented as evidence that the nucleation of an amorphous phase is heterogeneous in nature involving clustering or segregation of point defects near existing defects.
Cheruvu, S.M.
Crystalline to amorphous transformation in silicon
In the present investigation, an attempt was made to understand the fundamental mechanism of crystalline-to-amorphous transformation in arsenic implanted silicon using high resolution electron microscopy. A comparison of the gradual disappearance of simulated lattice fringes with increasing Frenkel pair concentration with the experimental observation of sharp interfaces between crystalline and amorphous regions was carried out leading to the conclusion that when the defect concentration reaches a critical value, the crystal does relax to an amorphous state. Optical diffraction experiments using atomic models also supported this hypothesis. Both crystalline and amorphous zones were found to co-exist with sharp interfaces at the atomic level. Growth of the amorphous fraction depends on the temperature, dose rate and the mass of the implanted ion. Preliminary results of high energy electron irradiation experiments at 1.2 MeV also suggested that clustering of point defects occurs near room temperature. An observation in a high resolution image of a small amorphous zone centered at the core of a dislocation is presented as evidence that the nucleation of an amorphous phase is heterogeneous in nature involving clustering or segregation of point defects near existing defects.
Cheruvu, S.M.
Short channel device performance of amorphous InGaZnO thin film transistor
NASA Astrophysics Data System (ADS)
Short channel device performance of deep-submicron gate length oxide thin film transistor (TFT) with amorphous InGaZnO (a-IGZO) active semiconductor is presented. Remarkable electrical properties of short channel oxide TFT were achieved utilizing crucial structure and material optimization such as self aligned gate structure with homo junction, multi-channel with rounded corners, and high-? gate dielectric. It was found that various device performance parameters of short channel-oxide TFTs were significantly influenced by materials, processes, and structural geometry, which should be more carefully designed.
Jeon, Sanghun; Benayad, Anass; Ahn, Seung-Eon; Park, Sungho; Song, Ihun; Kim, Changjung; Chung, U.-In
Latent ion tracks in amorphous silicon
NASA Astrophysics Data System (ADS)
We present experimental evidence for the formation of ion tracks in amorphous Si induced by swift heavy-ion irradiation. An underlying core-shell structure consistent with remnants of a high-density liquid structure was revealed by small-angle x-ray scattering and molecular dynamics simulations. Ion track dimensions differ for as-implanted and relaxed Si as attributed to different microstructures and melting temperatures. The identification and characterization of ion tracks in amorphous Si yields new insight into mechanisms of damage formation due to swift heavy-ion irradiation in amorphous semiconductors.
Bierschenk, T.; Giulian, R.; Afra, B.; Rodriguez, M. D.; Schauries, D.; Mudie, S.; Pakarinen, O. H.; Djurabekova, F.; Nordlund, K.; Osmani, O.; Medvedev, N.; Rethfeld, B.; Ridgway, M. C.; Kluth, P.
Ge2Sb2Te5 (GST) is a technologically very important phase-change material that is used in digital versatile disks-random access memory and is currently studied for the use in phase-change random access memory devices. This type of data storage is achieved by the fast reversible phase transition between amorphous and crystalline GST upon heat pulse. Here we report pressure-induced reversible crystalline-amorphous and polymorphic amorphous transitions in NaCl structured GST by ab initio molecular dynamics calculations. We have showed that the onset amorphization of GST starts at approximately 18�GPa and the system become completely random at approximately 22�GPa. This amorphous state has a cubic framework (c-amorphous) of sixfold coordinations. With further increasing pressure, the c-amorphous transforms to a high-density amorphous structure with trigonal framework (t-amorphous) and an average coordination number of eight. The pressure-induced amorphization is investigated to be due to large displacements of Te atoms for which weak Te�Te bonds exist or vacancies are nearby. Upon decompressing to ambient conditions, the original cubic crystalline structure is restored for c-amorphous, whereas t-amorphous transforms to another amorphous phase that is similar to the melt-quenched amorphous GST. PMID:21670255
Sun, Zhimei; Zhou, Jian; Pan, Yuanchun; Song, Zhitang; Mao, Ho-Kwang; Ahuja, Rajeev
In this article, we demonstrate that the thermal conductivity of nanostructured porous silicon is reduced by amorphization and also that this amorphous phase in porous silicon can be created by swift (high-energy) heavy ion irradiation. Porous silicon samples with 41%-75% porosity are irradiated with 110 MeV uranium ions at six different fluences. Structural characterisation by micro-Raman spectroscopy and SEM imaging show that swift heavy ion irradiation causes the creation of an amorphous phase in porous Si but without suppressing its porous structure. We demonstrate that the amorphization of porous silicon is caused by electronic-regime interactions, which is the first time such an effect is obtained in crystalline silicon with single-ion species. Furthermore, the impact on the thermal conductivity of porous silicon is studied by micro-Raman spectroscopy and scanning thermal microscopy. The creation of an amorphous phase in porous silicon leads to a reduction of its thermal conductivity, up to a factor of 3 compared to the non-irradiated sample. Therefore, this technique could be used to enhance the thermal insulation properties of porous Si. Finally, we show that this treatment can be combined with pre-oxidation at 300 Degree-Sign C, which is known to lower the thermal conductivity of porous Si, in order to obtain an even greater reduction.
Newby, Pascal J. [Institut des Nanotechnologies de Lyon, Universite de Lyon, INL-UMR5270, CNRS, INSA de Lyon, Villeurbanne 69621 (France); Institut Interdisciplinaire d'Innovation Technologique (3IT), Universite de Sherbrooke, CNRS UMI-LN2, Sherbrooke, Quebec J1K0A5 (Canada); Canut, Bruno; Bluet, Jean-Marie; Lysenko, Vladimir [Institut des Nanotechnologies de Lyon, Universite de Lyon, INL-UMR5270, CNRS, INSA de Lyon, Villeurbanne 69621 (France); Gomes, Severine [Centre de Thermique de Lyon, Universite de Lyon, CETHIL-UMR5008, CNRS, INSA de Lyon, Villeurbanne 69621 (France); Isaiev, Mykola; Burbelo, Roman [Faculty of Physics, Taras Shevchenko National University of Kyiv, 64/13, Volodymyrs'ka St., Kyiv 01601 (Ukraine); Termentzidis, Konstantinos [Laboratoire LEMTA, Universite de Lorraine-CNRS UMR 7563, 54506 Vandoeuvre-les-Nancy cedex (France); Chantrenne, Patrice [Universite de Lyon, INSA de Lyon, MATEIS-UMR CNRS 5510, Villeurbanne 69621 (France); Frechette, Luc G. [Institut Interdisciplinaire d'Innovation Technologique (3IT), Universite de Sherbrooke, CNRS UMI-LN2, Sherbrooke, Quebec J1K0A5 (Canada)
NASA Astrophysics Data System (ADS)
In this article, we demonstrate that the thermal conductivity of nanostructured porous silicon is reduced by amorphization and also that this amorphous phase in porous silicon can be created by swift (high-energy) heavy ion irradiation. Porous silicon samples with 41%-75% porosity are irradiated with 110 MeV uranium ions at six different fluences. Structural characterisation by micro-Raman spectroscopy and SEM imaging show that swift heavy ion irradiation causes the creation of an amorphous phase in porous Si but without suppressing its porous structure. We demonstrate that the amorphization of porous silicon is caused by electronic-regime interactions, which is the first time such an effect is obtained in crystalline silicon with single-ion species. Furthermore, the impact on the thermal conductivity of porous silicon is studied by micro-Raman spectroscopy and scanning thermal microscopy. The creation of an amorphous phase in porous silicon leads to a reduction of its thermal conductivity, up to a factor of 3 compared to the non-irradiated sample. Therefore, this technique could be used to enhance the thermal insulation properties of porous Si. Finally, we show that this treatment can be combined with pre-oxidation at 300 �C, which is known to lower the thermal conductivity of porous Si, in order to obtain an even greater reduction.
Newby, Pascal J.; Canut, Bruno; Bluet, Jean-Marie; Gom�s, S�verine; Isaiev, Mykola; Burbelo, Roman; Termentzidis, Konstantinos; Chantrenne, Patrice; Fr�chette, Luc G.; Lysenko, Vladimir
Origin of ferromagnetism enhancement in bi-layer chromium-doped indium zinc oxides
This work demonstrates that by controlling the rapid thermal annealing temperature, amorphous chromium-doped indium zinc oxide films develop an amorphous-crystalline bi-layer structure and show magnetization up to {approx}30 emu/cm{sup 3}. The crystalline layer arises from significant out-diffusion of Zn from surfaces, leading to a large difference in the Zn:In ratio in amorphous and crystalline layers. Doped Cr ions in amorphous and crystalline layers form different valence configurations, creating a charge reservoir which transfers electrons through amorphous-crystalline interfaces and in turn enhances ferromagnetism.
Hsu, C. Y. [Physics Department, National Sun Yat-Sen University, Kaohsiung 804, Taiwan (China)
A thick layer of amorphous silicon (a-Si) was deposited on industrial grade crystalline n-Si <111>substrate by means of electron beam evaporation. On top of a-Si layer, amorphous hydrogenated carbon (a-C:H) film was grown by direct ion beam deposition from acetylene precursor gas. In order to study on atomic level the a-C:H film growth on amorphous silicon, a theoretical model was
A. Ibenskas; A. Galdikas; �. Me�kinis; M. Andrulevi?ius; S. Tamulevi?ius
Electrochemical lithium intercalation in nanosized manganese oxides
X-ray amorphous manganese oxides were prepared by reduction of sodium permanganate by lithium iodide in aqueous medium (MnOx-I) and by decomposition of manganese carbonate at moderate temperature (MnOx-C). TEM showed that these materials are not amorphous, but nanostructured, with a prominent spinel substructure in MnOx-C. These materials intercalate lithium with capacities up to 200mAh\\/g at first cycle (potential window 1.8�4.3V)
Pierre Strobel; C�line Darie; F. Thi�ry; A. Ibarra-Palos; Maria Bacia; Olivier Proux; Jean-Bruno Soupart
Modelling morphogenesis as an amorphous computation
This thesis presents a programming-language viewpoint for morphogenesis, the process of shape formation during embryological development. We model morphogenesis as a self-organizing, self-repairing amorphous computation ...
Bhattacharyya, Arnab
In Situ Laser Synthesis of Fe-Based Amorphous Matrix Composite Coating on Structural Steel
NASA Astrophysics Data System (ADS)
Iron-based amorphous materials, owing to their very high hardness, elastic modulus, wear resistance, and corrosion resistance, can be potential materials for surface modification and engineering of many structural alloys. The current study focuses on a novel functional coating, synthesized via laser cladding of an iron-based (Fe48Cr15Mo14Y2C15B) amorphous precursor powder, on AISI 4130 steel substrate, using a continuous-wave diode-pumped ytterbium laser. The coatings were characterized by different techniques like X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). SEM and TEM studies indicated the presence of Fe-based nanocrystalline dendrites intermixed within an amorphous matrix. A three-dimensional thermal modeling approach based on COMSOL Multiphysics (COMSOL Inc., Burlington, MA) was used to approximately predict the temperature evolution and cooling rates achieved during laser processing. The mechanisms for the formation of crystalline phases and the morphological changes in the microstructure were studied based on the thermal model developed. Although the thermal model predicted substantially high cooling rates as compared to the critical cooling rate required for retaining an amorphous phase, the formation of crystalline phases is attributed to formation of yttrium oxide, reducing the glass-forming ability, and formation of different oxide phases that act as heterogeneous nucleation sites resulting in the composite microstructure.
Katakam, Shravana; Hwang, Jun Y.; Paital, Sameer; Banerjee, Rajarshi; Vora, Hitesh; Dahotre, Narendra B.
Neutron irradiation induced amorphization of silicon carbide
This paper provides the properties of bulk stoichiometric silicon carbide which has been amorphized under neutron irradiation. Both high purity single crystal hcp and high purity, highly faulted (cubic) chemically vapor deposited (CVD) SiC were irradiated at approximately 60�C to a total fast neutron fluence of 2.6�1025 n\\/m2. Amorphization was seen in both materials as evidenced by TEM, electron diffraction
L. L Snead; J. C Hay
Tests Of Amorphous-Silicon Photovoltaic Modules
NASA Technical Reports Server (NTRS)
Progress in identification of strengths and weaknesses of amorphous-silicon technology detailed. Report describes achievements in testing reliability of solar-power modules made of amorphous-silicon photovoltaic cells. Based on investigation of modules made by U.S. manufacturers. Modules subjected to field tests, to accelerated-aging tests in laboratory, and to standard sequence of qualification tests developed for modules of crystalline-silicon cells.
Ross, Ronald G., Jr.
A Magnetic Sensor with Amorphous Wire
Using a FeCoSiB amorphous wire and a coil wrapped around it, we have developed a sensitive magnetic sensor. When a 5 mm long amorphous wire with the diameter of 0.1 mm was used, the magnetic field noise spectrum of the sensor was about 30 pT/?Hz above 30 Hz. To show the sensitivity and the spatial resolution, the magnetic field of a thousand Japanese yen was scanned with the magnetic sensor. PMID:24940865
He, Dongfeng; Shiwa, Mitsuharu
Tritiated amorphous silicon films and devices
The do saddle-field glow discharge deposition technique has been used to bond tritium within an amorphous silicon thin film network using silane and elemental tritium in the glow discharge. The concentration of tritium is approximately 7 at. %. Minimal outgassing of tritium from tritiated hydrogenated amorphous silicon (a-Si:H:T) at room temperature suggests that tritium is bonded stably. Tritium effusion only
Tome Kosteski
Can amorphization take place in nanoscale interconnects?
The trend of miniaturization has highlighted the problems of heat dissipation and electromigration in nanoelectronic device interconnects, but not amorphization. While amorphization is known to be a high pressure and/or temperature phenomenon, we argue that defect density is the key factor, while temperature and pressure are only the means. For nanoscale interconnects carrying modest current density, large vacancy concentrations may be generated without the necessity of high temperature or pressure due to the large fraction of grain boundaries and triple points. To investigate this hypothesis, we performed in situ transmission electron microscope (TEM) experiments on 200 nm thick (80 nm average grain size) aluminum specimens. Electron diffraction patterns indicate partial amorphization at modest current density of about 10(5) A cm(-2), which is too low to trigger electromigration. Since amorphization results in drastic decrease in mechanical ductility as well as electrical and thermal conductivity, further increase in current density to about 7 � 10(5) A cm(-2) resulted in brittle fracture failure. Our molecular dynamics (MD) simulations predict the formation of amorphous regions in response to large mechanical stresses (due to nanoscale grain size) and excess vacancies at the cathode side of the thin films. The findings of this study suggest that amorphization can precede electromigration and thereby play a vital role in the reliability of micro/nanoelectronic devices. PMID:22322399
Kumar, S; Joshi, K L; van Duin, A C T; Haque, M A
Amorphous silica nanoparticles impair vascular homeostasis and induce systemic inflammation
Amorphous silica nanoparticles (SiNPs) are being used in biomedical, pharmaceutical, and many other industrial applications entailing human exposure. However, their potential vascular and systemic pathophysiologic effects are not fully understood. Here, we investigated the acute (24 hours) systemic toxicity of intraperitoneally administered 50 nm and 500 nm SiNPs in mice (0.5 mg/kg). Both sizes of SiNPs induced a platelet proaggregatory effect in pial venules and increased plasma concentration of plasminogen activator inhibitor-1. Elevated plasma levels of von Willebrand factor and fibrinogen and a decrease in the number of circulating platelets were only seen following the administration of 50 nm SiNPs. The direct addition of SiNPs to untreated mouse blood significantly induced in vitro platelet aggregation in a dose-dependent fashion, and these effects were more pronounced with 50 nm SiNPs. Both sizes of SiNPs increased lactate dehydrogenase activity and interleukin 1? concentration. However, tumor necrosis factor ? concentration was only increased after the administration of 50 nm SiNPs. Nevertheless, plasma markers of oxidative stress, including 8-isoprostane, thiobarbituric acid reactive substances, catalase, and glutathione S-transferase, were not affected by SiNPs. The in vitro exposure of human umbilical vein endothelial cells to SiNPs showed a reduced cellular viability, and more potency was seen with 50 nm SiNPs. Both sizes of SiNPs caused a decrease in endothelium-dependent relaxation of isolated small mesenteric arteries. We conclude that amorphous SiNPs cause systemic inflammation and coagulation events, and alter vascular reactivity. Overall, the effects observed with 50 nm SiNPs were more pronounced than those with 500 nm SiNPs. These findings provide new insight into the deleterious effect of amorphous SiNPs on vascular homeostasis. PMID:24936130
Nemmar, Abderrahim; Albarwani, Sulayma; Beegam, Sumaya; Yuvaraju, Priya; Yasin, Javed; Attoub, Samir; Ali, Badreldin H
Oxidation of aluminum nanoclusters
The dynamics of oxidation of aluminum nanoclusters (20 nm diameter) is investigated using a parallel molecular dynamics approach based on variable charge interatomic interactions due to Streitz and Mintmire that include both ionic and covalent effects. Simulations are performed for both canonical ensembles for molecular oxygen (O{sub 2}) environments and microcanonical ensembles for molecular (O{sub 2}) and atomic (O{sub 1}) oxygen environments. Structural and dynamic correlations in the oxide region are calculated, as well as the evolution of charges, surface oxide thickness, diffusivities of atoms, and local stresses. In the microcanonical ensemble, the oxidizing reaction becomes explosive in both molecular and atomic oxygen environments due to the enormous energy release associated with Al-O bonding. Local stresses in the oxide scale cause rapid diffusion of aluminum and oxygen atoms. Analyses of the oxide scale reveal significant charge transfer and a variation of local structures from the metal-oxide interface to the oxide-environment interface. In the canonical ensemble, oxide depth grows linearly in time until {approx}30 ps, followed by saturation of oxide depth as a function of time. An amorphous oxide layer of thickness {approx}40 A is formed after 466 ps, in good agreement with experiments. The average mass density in the oxide scale is 75% of the bulk alumina density. Evolution of structural correlation in the oxide is analyzed through radial distribution and bond angles. Through detailed analyses of the trajectories of O atoms and their formation of OAl{sub n} structures, we propose a three-step process of oxidative percolation that explains deceleration of oxide growth in the canonical ensemble.
Campbell, Timothy J. [Collaboratory for Advanced Computing and Simulations, Department of Materials Science and Engineering, Department of Physics and Astronomy, Department of Computer Science, University of Southern California, Los Angeles, California 90089-0242 (United States); Mississippi State University, Stennis Space Center, Mississippi 39529 (United States); Aral, Gurcan; Kalia, Rajiv K.; Nakano, Aiichiro; Vashishta, Priya [Collaboratory for Advanced Computing and Simulations, Department of Materials Science and Engineering, Department of Physics and Astronomy, Department of Computer Science, University of Southern California, Los Angeles, California 90089-0242 (United States); Ogata, Shuji [Graduate School of Engineering, Nagoya Institute of Technology, Nagoya 466-8555 (Japan)
Characterization of High- k Gate Dielectric with Amorphous Nanostructure
NASA Astrophysics Data System (ADS)
In the present study, Zr x La1- x O y amorphous nanostructures were prepared by the sol-gel method such that the Zr atomic fraction ( x) ranged from 0% to 70%. An analytical model is described for the dielectric constant ( k) of Zr x La1- x O y nanostructures in a metal-oxide-semiconductor (MOS) device. The structure and morphology of Zr x La1- x O y film was studied using x-ray diffraction, scanning electron microscopy, atomic force microscopy, and transmission electron microscopy. Elemental qualitative analysis was performed using energy-dispersive x-ray spectra and a map that confirmed the findings. Preliminary information on the influence of thermal annealing on the morphological control of Zr x La1- x O y amorphous nanostructures is presented. The dielectric constant of the crystalline Zr0.5La0.5O y thin film is about 36. Electrical property characterization was performed using a metal-dielectric-semiconductor structure via capacitance-voltage and current density-voltage measurements.
Bahari, Ali; Gholipur, Reza
Electron-beam-assisted superplastic shaping of nanoscale amorphous silica
Glasses are usually shaped through the viscous flow of a liquid before its solidification, as practiced in glass blowing. At or near room temperature (RT), oxide glasses are known to be brittle and fracture upon any mechanical deformation for shape change. Here, we show that with moderate exposure to a low-intensity (<1.8�10?2 A cm?2) electron beam (e-beam), dramatic shape changes can be achieved for nanoscale amorphous silica, at low temperatures and strain rates >10?4 per second. We show not only large homogeneous plastic strains in compression for nanoparticles but also superplastic elongations >200% in tension for nanowires (NWs). We also report the first quantitative comparison of the load-displacement responses without and with the e-beam, revealing dramatic difference in the flow stress (up to four times). This e-beam-assisted superplastic deformability near RT is useful for processing amorphous silica and other conventionally-brittle materials for their applications in nanotechnology. PMID:20975693
Zheng, Kun; Wang, Chengcai; Cheng, Yong-Qiang; Yue, Yonghai; Han, Xiaodong; Zhang, Ze; Shan, Zhiwei; Mao, Scott X; Ye, Miaomiao; Yin, Yadong; Ma, Evan
R&D issues in scale-up and manufacturing of amorphous silicon tandem modules
R & D on amorphous silicon based tandem junction devices has improved the throughtput, the material utilization, and the performance of devices on commercial tin oxide coated glass. The tandem junction technology has been scaled-up to produce 8.6&hthinsp;Ft{sup 2} monolithically integrated modules in manufacturing at the TF1 plant. Optimization of performance and stability of these modules is ongoing. {copyright} {ital 1999 American Institute of Physics.}
Arya, R.R.; Carlson, D.E.; Chen, L.F.; Ganguly, G.; He, M.; Lin, G.; Middya, R.; Wood, G.; Newton, J.; Bennett, M.; Jackson, F.; Willing, F. [Solarex, a Business Unit of Amoco/Enron Solar, 826 Newtown-Yardley Road, Newtown, Pennsylvania 18940 (United States)
Effect of bismuth nanolayers on the oriented growth of fullerene C 60 on an amorphous substrate
The effect of a bismuth sublayer with an effective thickness of 0.5 to 4 nm on the structure of C60 fullerene films grown on amorphous substrates (silicon covered with a natural oxide layer; glass) using the quasi-closed-volume\\u000a method is studied. An x-ray diffraction study of fullerene films showed that the intensity ratio between the (220) and (111)\\u000a peaks depends nonmonotonically
V. E. Pukha; V. V. Varganov; I. F. Mikhailov; A. N. Drozdov
Characterization of Amorphous High-k Thin Films by EXAFS and GIXS
Silicon and nitrogen incorporated Hf oxide (HfSiON) is considered to be a promising alternative gate insulator for next-generation MOSFETs. EXAFS and GIXS (Grazing Incidence X-ray Scattering) have been applied to the characterization of amorphous HfSiON films at SPring-8. Novel cluster models have been suggested based on the analogy to the ordered states for the Zr-O-N ternary system.
Takemura, Momoko; Yamazaki, Hideyuki; Ohmori, Hirobumi; Yoshiki, Masahiko; Takeno, Shiro; Ino, Tsunehiro; Nishiyama, Akira [Corporate R and D Center, Toshiba Corporation 1, Komukai Toshiba-cho, Saiwai-ku, Kawasaki 212-8582 (Japan); Sato, Nobutaka [Toshiba Nanoanalysis Corporation, 1, Komukai Toshiba-cho, Saiwai-ku, Kawasaki 212-8583 (Japan); Hirosawa, Ichiro; Sato, Masugu [JASRI/SPring-8, 1-1-1, Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198 (Japan)
Template confined synthesis of amorphous carbon nanotubes and its confocal Raman microscopy
NASA Astrophysics Data System (ADS)
Amorphous carbon nanotubes (aCNTs) were synthesized by AAO (anodic aluminum oxide) template at a temperature 500 �C in nitrogen atmosphere using the citric acid as a carbon source without the help of any catalyst particles. Morphological analysis of the as prepared samples was carried out by field emission scanning electron microscopy (FESEM). Confocal Raman imaging has been studied and an attempt has been made to find out the graphitic (sp2) and disordered phase of the CNTs.
Maity, Supratim; Roychowdhury, Tuhin; Chattopadhyay, Kalyan Kumar
Selective leaches revisited, with emphasis on the amorphous Fe oxyhydroxide phase extraction
A sequential extraction scheme for application to soils, tills and surficial sediments is described that elucidates the form in which an element is held and provides information as to its provenance. The phases selected for extraction have been categorised as: adsorbed\\/exchangeable\\/carbonate (using CH3COONa as extradant); amorphous Fe oxyhydroxide (0.25 M NH2OH-HCl); crystalline Fe oxide (l M NH2OH-HCl); sulphides and organics
G. E. M. Hall; J. E. Vaive; R. Beer; M. Hoashi
Periodic light coupler gratings in amorphous thin film solar cells
Efficient light trapping structures for amorphous hydrogenated silicon (a-Si:H) solar cells have been realized using periodically structured aluminum doped zinc oxide (ZnO:Al) with periods between 390 and 980 nm as a transparent front contact. Atomic force microscopy, optical reflection, and diffraction efficiency measurements were applied to characterize solar cells deposited on such gratings. A simple formula for the threshold wavelength of total internal reflection is derived. Periodic light coupler gratings reduce the reflectance to a value below 10% in the wavelength range of 400{endash}800 nm which is comparable to cells with an optimized statistical texture. Diffraction efficiency measurements and theoretical considerations indicate that a combination of transmission and reflection gratings contribute to the observed reduction of the reflectance. {copyright} 2001 American Institute of Physics.
Eisele, C.; Nebel, C. E.; Stutzmann, M.
NASA Technical Reports Server (NTRS)
An investigation was conducted to examine the microstructure and surface chemistry of amorphous alloys, and their effects on tribological behavior. The results indicate that the surface oxide layers present on amorphous alloys are effective in providing low friction and a protective film against wear in air. Clustering and crystallization in amorphous alloys can be enhanced as a result of plastic flow during the sliding process at a low sliding velocity, at room temperature. Clusters or crystallines with sizes to 150 nm and a diffused honeycomb-shaped structure are produced on sizes to 150 nm and a diffused honeycomb-shaped structure are produced on the wear surface. Temperature effects lead to drastic changes in surface chemistry and friction behavior of the alloys at temperatures to 750 C. Contaminants can come from the bulk of the alloys to the surface upon heating and impart to the surface oxides at 350 C and boron nitride above 500 C. The oxides increase friction while the boron nitride reduces friction drastically in vacuum.
Miyoshi, K.; Buckley, D. H.
NASA Technical Reports Server (NTRS)
Friction and wear tests were conducted with 3.2- and 6.4-millimeter-diameter aluminum oxide spheres sliding, in reciprocating motion, on a Fe67Co18B14Si1 metallic foil. Crystallites with a size range of 10 to 150 nanometers were produced on the wear surface of the amorphous alloy. A strong interaction between transition metals and metalloids such as silicon and boron results in strong segregation during repeated sliding, provides preferential transition metal-metalloid clustering in the amorphous alloy, and subsequently produces the diffused honeycomb structure formed by dark grey bands and primary crystals, that is, alpha-Fe in the matrix. Large plastic flow occurs on an amorphous alloy surface with sliding and the flow film of the alloy transfers to the aluminum oxide pin surface. Multiple slip bands due to shear deformation are observed on the side of the wear track. Two distinct types of wear debris were observed as a result of sliding: an alloy wear debris, and/or powdery-whiskery oxide debris.
Miyoshi, K.; Buckley, D. H.
NASA Technical Reports Server (NTRS)
Friction and wear tests were conducted with 3.2- and 6.4-millimeter-diameter aluminum oxide spheres sliding, in reciprocating motion, on a Fe67Co18B14Si1 metallic foil. Crystallites with a size range of 10 to 150 nanometers were produced on the wear surface of the amorphous alloy. A strong interaction between transition metals and metalloids such as silicon and boron results in strong segregation during repeated sliding, provides preferential transition metal-metalloid clustering in the amorphous alloy, and subsequently produces the diffused honeycomb structure formed by dark grey bands and primary crystals, that is, alpha-Fe in the matrix. Large plastic flow occurs on an amorphous alloy surface with sliding and the flow film of the alloy transfers to the aluminum oxide pin surface. Multiple slip bands due to shear deformation are observed on the side of the wear track. Two distinct types of wear debris were observed as a result of sliding: an alloy wear debris, and/or powdery-whiskery oxide debris.
Miyoshi, K.; Buckley, D. H.
Amorphous silicon detectors in positron emission tomography
The physics of the detection process is studied and the performances of different Positron Emission Tomography (PET) system are evaluated by theoretical calculation and/or Monte Carlo Simulation (using the EGS code) in this paper, whose table of contents can be summarized as follows: a brief introduction to amorphous silicon detectors and some useful equation is presented; a Tantalum/Amorphous Silicon PET project is studied and the efficiency of the systems is studied by Monte Carlo Simulation; two similar CsI/Amorphous Silicon PET projects are presented and their efficiency and spatial resolution are studied by Monte Carlo Simulation, light yield and time characteristics of the scintillation light are discussed for different scintillators; some experimental result on light yield measurements are presented; a Xenon/Amorphous Silicon PET is presented, the physical mechanism of scintillation in Xenon is explained, a theoretical estimation of total light yield in Xenon and the resulting efficiency is discussed altogether with some consideration of the time resolution of the system; the amorphous silicon integrated electronics is presented, total noise and time resolution are evaluated in each of our applications; the merit parameters {epsilon}{sup 2}{tau}'s are evaluated and compared with other PET systems and conclusions are drawn; and a complete reference list for Xenon scintillation light physics and its applications is presented altogether with the listing of the developed simulation programs.
Conti, M. (Istituto Nazionale di Fisica Nucleare, Pisa (Italy) Lawrence Berkeley Lab., CA (USA)); Perez-Mendez, V. (Lawrence Berkeley Lab., CA (USA))
Slow dissolution behaviour of amorphous capecitabine.
In this article, we report the anomalous dissolution behaviour of amorphous capecitabine. In contrast to what is expected from thermodynamic theory, amorphous capecitabine dissolves significantly slower compared to its crystalline counterpart. Our experiments show that this is due to the "gelling" properties of amorphous capecitabine in an aqueous environment. The "gel", which is immediately formed upon contact with water, entraps the capecitabine and significantly slows down its dissolution. This "gelling" property is hypothesized to be related to the low glass transition temperature (Tg 19�C) of amorphous capecitabine, resulting in an instant collapse ("gelling") in an aqueous environment. From IR and DSC analysis it is shown that this collapsed capecitabine is remarkably stable and does not recrystallize upon an increased water content or temperature. This highly reproducible dissolution behaviour can be applied in the development of a sustained release dosage form as substantially less sustained release excipient is required in order to attain the desired release profile. As capecitabine is a high-dosed drug, this is highly favourable in view of the size and thus clinical feasibility of the final dosage form. Currently, we are developing and clinically testing a sustained release formulation making use of amorphous capecitabine and its remarkable dissolution behaviour. PMID:23219704
Meulenaar, Jelte; Beijnen, Jos H; Schellens, Jan H M; Nuijen, Bastiaan
Amorphous carbon enhancement of hydrogen penetration into UO2
NASA Astrophysics Data System (ADS)
The interaction of D2 and H2O (humidity) with amorphous carbon covered UO2 vs. clean UO2 was studied using Secondary Ion Mass Spectrometry (SIMS) and X-ray Photoelectron Spectroscopy (XPS). It was found that SIMS depth profiles of the carbon covered side vs. the bare oxide, show significant higher intensities of H- and D- for the first, through the carbon layer and beneath it. The presence of a thin carbon layer on a UO2 surface caused a significant buildup of hydroxyl, probably adsorbed on the carbon, but maybe also beneath the layer, in the presence of atmospheric humidity. Exposure of the carbon covered oxide to D2 on a UHV annealed surface also caused a growth of the hydroxyl. It is concluded that the carbon surface strongly enhances the dissociation of water vapor as well as that of hydrogen and the penetration of the dissociation products to the oxide, as compared to the bare UO2 surface. The contribution of the latter, beneath the carbon, should be verified or ruled out by further experiments.
Zalkind, S.; Shamir, N.; Gouder, T.; Akhvlediani, R.; Hoffman, A.
Amorphous Diamond MEMS and Sensors
This report describes a new microsystems technology for the creation of microsensors and microelectromechanical systems (MEMS) using stress-free amorphous diamond (aD) films. Stress-free aD is a new material that has mechanical properties close to that of crystalline diamond, and the material is particularly promising for the development of high sensitivity microsensors and rugged and reliable MEMS. Some of the unique properties of aD include the ability to easily tailor film stress from compressive to slightly tensile, hardness and stiffness 80-90% that of crystalline diamond, very high wear resistance, a hydrophobic surface, extreme chemical inertness, chemical compatibility with silicon, controllable electrical conductivity from insulating to conducting, and biocompatibility. A variety of MEMS structures were fabricated from this material and evaluated. These structures included electrostatically-actuated comb drives, micro-tensile test structures, singly- and doubly-clamped beams, and friction and wear test structures. It was found that surface micromachined MEMS could be fabricated in this material easily and that the hydrophobic surface of the film enabled the release of structures without the need for special drying procedures or the use of applied hydrophobic coatings. Measurements using these structures revealed that aD has a Young's modulus of {approx}650 GPa, a tensile fracture strength of 8 GPa, and a fracture toughness of 8 MPa{center_dot}m {sup 1/2}. These results suggest that this material may be suitable in applications where stiction or wear is an issue. Flexural plate wave (FPW) microsensors were also fabricated from aD. These devices use membranes of aD as thin as {approx}100 nm. The performance of the aD FPW sensors was evaluated for the detection of volatile organic compounds using ethyl cellulose as the sensor coating. For comparable membrane thicknesses, the aD sensors showed better performance than silicon nitride based sensors. Greater than one order of magnitude increase in chemical sensitivity is expected through the use of ultra-thin aD membranes in the FPW sensor. The discoveries and development of the aD microsystems technology that were made in this project have led to new research projects in the areas of aD bioMEMS and aD radio frequency MEMS.
Amorphous Silicon Based Neutron Detector
Various large-scale neutron sources already build or to be constructed, are important for materials research and life science research. For all these neutron sources, neutron detectors are very important aspect. However, there is a lack of a high-performance and low-cost neutron beam monitor that provides time and temporal resolution. The objective of this SBIR Phase I research, collaboratively performed by Midwest Optoelectronics, LLC (MWOE), the University of Toledo (UT) and Oak Ridge National Laboratory (ORNL), is to demonstrate the feasibility for amorphous silicon based neutron beam monitors that are pixilated, reliable, durable, fully packaged, and fabricated with high yield using low-cost method. During the Phase I effort, work as been focused in the following areas: 1) Deposition of high quality, low-defect-density, low-stress a-Si films using very high frequency plasma enhanced chemical vapor deposition (VHF PECVD) at high deposition rate and with low device shunting; 2) Fabrication of Si/SiO2/metal/p/i/n/metal/n/i/p/metal/SiO2/ device for the detection of alpha particles which are daughter particles of neutrons through appropriate nuclear reactions; and 3) Testing of various devices fabricated for alpha and neutron detection; As the main results: � High quality, low-defect-density, low-stress a-Si films have been successfully deposited using VHF PECVD on various low-cost substrates; � Various single-junction and double junction detector devices have been fabricated; � The detector devices fabricated have been systematically tested and analyzed. � Some of the fabricated devices are found to successfully detect alpha particles. Further research is required to bring this Phase I work beyond the feasibility demonstration toward the final prototype devices. The success of this project will lead to a high-performance, low-cost, X-Y pixilated neutron beam monitor that could be used in all of the neutron facilities worldwide. In addition, the technologies developed here could be used to develop X-ray and neutron monitors that could be used in the future for security checks at the airports and other critical facilities. The project would lead to devices that could significantly enhance the performance of multi-billion dollar neutron source facilities in the US and bring our nation to the forefront of neutron beam sciences and technologies which have enormous impact to materials, life science and military research and applications.
Xu, Liwei
Strain Rate Induced Amorphization in Metallic Nanowires
Using molecular dynamics simulations with a many-body force field, we studied the deformation of single crystal Ni and NiCu random alloy nanowires subjected to uniform strain rates but kept at 300thinspthinspK. For all strain rates, the Ni nanowire is elastic up to 7.5{percent} strain with a yield stress of 5.5thinspthinspGPa, far above that of bulk Ni. At high strain rates, we find that for both systems the crystalline phase transforms continuously to an amorphous phase, exhibiting a dramatic change in atomic short-range order and a near vanishing of the tetragonal shear elastic constant perpendicular to the tensile direction. This amorphization which occurs directly from the homogeneous, elastically deformed system with no chemical or structural inhomogeneities exhibits a new mode of amorphization. {copyright} {ital 1999} {ital The American Physical Society}
Qi, Y.; Cagin, T.; Goddard, W.A. III [Materials and Process Simulation Center, California Institute of Technology, Pasadena, California 91125 (United States); Ikeda, H.; Samwer, K.; Johnson, W.L. [Keck Laboratory of Engineering Materials, California Institute of Technology, Pasadena, California 91125 (United States)
Rigid Amorphous Fraction in PLA Electrospun Fibers
NASA Astrophysics Data System (ADS)
Electrospun fibers of poly(lactic acid) (PLA) were formed by adopting a high-speed rotating wheel as the counter-electrode. The molecular orientation, crystallization mechanism, and phase structure and transitions of the aligned ES fibers were investigated. Using thermal analysis and wide angle X-ray scattering (WAXS), we evaluated the confinement that exists in as-spun amorphous, and heat-treated semicrystalline, fibers. Differential scanning calorimetry confirmed the existence of a constrained amorphous phase in as-spun aligned fibers, without the presence of crystals or fillers to serve as fixed physical constraints. Using WAXS, for the first time the mesophase fraction, consisting of oriented amorphous PLA chains, was quantitatively characterized in nanofibers.
Cebe, Peggy; Ma, Qian; Simona Cozza, Erika; Pyda, Marek; Mao, Bin; Zhu, Yazhe; Monticelli, Orietta
Amorphous metallic films in silicon metallization systems
NASA Technical Reports Server (NTRS)
Diffusion barrier research was focussed on lowering the chemical reactivity of amorphous thin films on silicon. An additional area of concern is the reaction with metal overlays such as aluminum, silver, and gold. Gold was included to allow for technology transfer to gallium arsenide PV cells. Amorphous tungsten nitride films have shown much promise. Stability to annealing temperatures of 700, 800, and 550 C were achieved for overlays of silver, gold, and aluminum, respectively. The lower results for aluminum were not surprising because there is an eutectic that can form at a lower temperature. It seems that titanium and zirconium will remove the nitrogen from a tungsten nitride amorphous film and render it unstable. Other variables of research interest were substrate bias and base pressure during sputtering.
So, F.; Kolawa, E.; Nicolet, M. A.
Synthesis and photocurrent of amorphous boron nanowires
NASA Astrophysics Data System (ADS)
Although theoretically feasible, synthesis of boron nanostructures is challenging due to the highly reactive nature, high melting and boiling points of boron. We have developed a thermal vapor transfer approach to synthesizing amorphous boron nanowire using a solid boron source. The amorphous nature and chemical composition of boron nanowires were characterized by high resolution transmission electron microscopy, selected area electron diffraction, and electron energy loss spectroscopy. Optical properties and photoconduction of boron nanowires have not yet been reported. In our investigation, the amorphous boron nanowire showed much better optical and electrical properties than previously reported photo-response of crystalline boron nanobelts. When excited by a blue LED, the photo/dark current ratio (I/I0) is 1.5 and time constants in the order of tens of seconds. I/I0 is 1.17 using a green light.
Ge, Liehui; Lei, Sidong; Hart, Amelia H. C.; Gao, Guanhui; Jafry, Huma; Vajtai, Robert; Ajayan, Pulickel M.
Modeling amorphous thin films: Kinetically limited minimization
NASA Astrophysics Data System (ADS)
Atomic-scale models of amorphous structures are typically generated using a simulated annealing (SA) quench from a melt simulation protocol. This approach resembles the preparation of bulk glasses, but it may not be suitable for modeling amorphous materials produced using low-energy and low-temperature physical vapor deposition, where a deposited atom induces only local relaxations and no equilibrated melt is formed. To account for such growth conditions, we developed the kinetically limited minimization (KLM) technique, in which an amorphous structure is constructed from a randomly initialized structure in a number of local perturbation-relaxation steps. We compare formation energies as well as short- and medium-range order of KLM- and SA-generated structures of a-In2O3, a-ZnO, and a-Si.
Zawadzki, Pawe? P.; Perkins, John; Lany, Stephan
Amorphous Insulator Films With Controllable Properties
NASA Technical Reports Server (NTRS)
In experiments described in report, amorphous hydrogenated carbon films grown at room temperature by low-frequency plasma deposition, using methane or butane gas. Films have unique array of useful properties; (a) adhere to wide variety of materials; (b) contain only carbon and hydrogen; (c) smooth and free of pinholes; (d) resistant to attack by moisture and chemicals; and (e) have high electric-breakdown strength and electrical resistivity. Two of optical properties and hardness of this film controlled by deposition conditions. Amorphous a-C:H and BN films used for hermetic sealing and protection of optical, electronic, magnetic, or delicate mechanical systems, and for semiconductor field dielectrics.
Alterovitz, Samuel A.; Warner, Joseph D.; Liu, David C.; Pouch, John J.
Fabrication of amorphous metal matrix composites by severe plastic deformation
by equal channel angular extrusion (ECAE) for consolidation of bulk amorphous metals (BAM) and amorphous metal matrix composites (AMMC) is investigated in this dissertation. The objectives of this research are a) to better understand processing parameters...
Mathaudhu, Suveen Nigel
Amorphous layer formation at the TaC/Cu interface in the Si/TaC/Cu metallization system
NASA Astrophysics Data System (ADS)
An amorphous Ta(O,C)x layer was found to form at the TaC/Cu interface in the Si/TaC/Cu metallization system. The formation of the layer was induced by oxygen trapped in the as-deposited films, since on the basis of thermodynamic evaluation of the ternary Ta-C-O system, the dissociation of the TaC layer and the formation of the Ta2O5 and graphite can be expected to occur during subsequent annealings in this case. However, as observed experimentally, the formation of the amorphous Ta(O,C)x preceded the formation of the stable tantalum oxide.
Laurila, Tomi; Zeng, Kejun; Kivilahti, Jorma K.; Molarius, Jyrki; Suni, Ilkka
Remarkable Thermal Stability of Amorphous In-Zn-O Transparent Conductors
Transparent conducting oxides (TCOs) are increasingly critical components in photovoltaic cells, low-e windows, flat panel displays, electrochromic devices, and flexible electronics. The conventional TCOs, such as Sn-doped In{sub 2}O{sub 3}, are crystalline single phase materials. Here, we report on In-Zn-O (IZO), a compositionally tunable amorphous TCO with some significantly improved properties. Compositionally graded thin film samples were deposited by co-sputtering from separate In{sub 2}O{sub 3} and ZnO targets onto glass substrates at 100 C. For the metals composition range of 55-84 cation% indium, the as-deposited IZO thin films are amorphous, smooth (R{sub RMS} < 0.4 nm), conductive ({sigma} {approx} 3000 {Omega}{sup -1} {center_dot} cm{sup -1}), and transparent in the visible (T{sub Vis} > 90%). Furthermore, the amorphous IZO thin films demonstrate remarkable functional and structural stability with respect to heating up to 600 C in either air or argon. Hence, though not completely understood at present, these amorphous materials constitute a new class of fundamentally interesting and technologically important high performance transparent conductors.
Taylor, M. P.; Readey, D. W.; van Hest, M. F. A. M.; Teplin, C. W.; Alleman, J. L.; Dabney, M. S.; Gedvilas, L. M.; Keyes, B. M.; To, B.; Perkins, J. D.; Ginley, D. S.
In this work we develop an ultrathin barium oxide film by Ba adsorption on a pre?oxidized Ni(110) surface, and characterize it by means of Auger electron spectroscopy, low energy electron diffraction and work function measurements. The results show that the Ba adatoms reduce the NiO surface oxide forming an amorphous and incomplete BaO layer. At higher coverages, the Ba adsorbate
D. Vlachos; S. D. Foulias; M. Kamaratos
Pd induced lateral crystallization of amorphous Si thin films
A thin palladium layer (?40 A?) was selectively formed on top of amorphous silicon films before annealing and the effects of palladium layer on the crystallization behavior of the amorphous silicon films were investigated. It was observed that the amorphous silicon right under the Pd layer could be crystallized to grain sizes of several hundred angstroms by annealing at 500
Seok-Woon Lee; Yoo-Chan Jeon; Seung-Ki Joo
Aluminium oxide and tetrahedral amorphous carbon thin films are deposited at room temperature using pulsed laser deposition (PLD) and their mechanical and electrical properties are investigated. As examples, the hardness of aluminium oxide films is found about 6.8 GPa and the Young's modulus 130 GPa, while the hardness of tetrahedral amorphous carbon (ta-C) layers reaches 45 GPa and its Young's
J. C. Orlianges; A. Pothier; D. Mercier; P. Blondy; C. Champeaux; A. Catherinot; M. I. De Barros; S. Pavant
Advances in selective wet oxidation of AlGaAs alloys
We review the chemistry, microstructure, and processing of buried oxides converted from AlGaAs layers using wet oxidation. Hydrogen is shown to have a central role in the oxidation reaction as the oxidizing agent and to reduce the intermediate predict As2O3 to As. The stable oxide is amorphous (AlxGa1-x) 2O3 which has no defects along the oxide\\/semiconductor interfaces but can exhibit
Kent D. Choquette; Kent M. Geib; Carol I. H. Ashby; Ray D. Twesten; Olga Blum; Hong Q. Hou; David M. Follstaedt; B. Eugene Hammons; Dave Mathes; Robert Hull
Vanadium oxide electrode synthesized by electroless deposition for electrochemical capacitors
NASA Astrophysics Data System (ADS)
A thin film vanadium oxide electrode was synthesized by a simple electroless deposition method. Surface and structural analyses revealed that the deposited oxide is a mixture of amorphous V2O5 and VO2. Electrochemical characterizations of the synthesized vanadium oxide showed capacitive behavior with good cycle life. The electroless deposition of vanadium oxide is inexpensive, easy to process, and environmentally benign, offering a promising route for electrode development for electrochemical capacitors.
Wu, Haoran; Lian, Keryn
A simple fluxgate magnetometer using amorphous alloys
A simple fluxgate magnetometer is developed using low magnetostrictive ferromagnetic amorphous alloy acting as a sensing element. It uses the fact that the magnetization of sensing element symmetrically magnetized by a sinusoidal field contains even harmonic components in presence of dc signal field H and the amplitude of the second harmonic component of magnetization is proportional to H. The sensitivity
Sobhendu K. Ghatak; Amitava Mitra
Athermal nonlinear elastic constants of amorphous solids.
We derive expressions for the lowest nonlinear elastic constants of amorphous solids in athermal conditions (up to third order), in terms of the interaction potential between the constituent particles. The effect of these constants cannot be disregarded when amorphous solids undergo instabilities such as plastic flow or fracture in the athermal limit; in such situations the elastic response increases enormously, bringing the system much beyond the linear regime. We demonstrate that the existing theory of thermal nonlinear elastic constants converges to our expressions in the limit of zero temperature. We motivate the calculation by discussing two examples in which these nonlinear elastic constants play a crucial role in the context of elastoplasticity of amorphous solids. The first example is the plasticity-induced memory that is typical to amorphous solids (giving rise to the Bauschinger effect). The second example is how to predict the next plastic event from knowledge of the nonlinear elastic constants. Using the results of our calculations we derive a simple differential equation for the lowest eigenvalue of the Hessian matrix in the external strain near mechanical instabilities; this equation predicts how the eigenvalue vanishes at the mechanical instability and the value of the strain where the mechanical instability takes place. PMID:20866874
Karmakar, Smarajit; Lerner, Edan; Procaccia, Itamar
Phononic Amorphous Silicon: Theory, Material, and Devices
The field of phononic-engineered amorphous silicon is introduced. Specifically the construction of devices and waveguides for information conveyance and manipulation via phonons are considered. Typically the phononic properties of a given material are immutable and the phonons have such a limited diffusion length (nanometers) as to be unsuitable for engineering purposes. Crystalline silicon on the other hand has a reasonably
S. Chawda; J. Mawyin; H. Mahan; C. Fortmann; G. Halada
Metal electrode for amorphous silicon solar cells
An amorphous silicon solar cell having an N-type region wherein the contact to the N-type region is composed of a material having a work function of about 3.7 electron volts or less. Suitable materials include strontium, barium and magnesium and rare earth metals such as gadolinium and yttrium.
Williams, Richard (Princeton, NJ)
High resolution amorphous silicon radiation detectors
A radiation detector employing amorphous Si:H cells in an array with each detector cell having at least three contiguous layers (n-type, intrinsic, p-type), positioned between two electrodes to which a bias voltage is applied. An energy conversion layer atop the silicon cells intercepts incident radiation and converts radiation energy to light energy of a wavelength to which the silicon cells are responsive. A read-out device, positioned proximate to each detector element in an array allows each such element to be interrogated independently to determine whether radiation has been detected in that cell. The energy conversion material may be a layer of luminescent material having a columnar structure. In one embodiment a column of luminescent material detects the passage therethrough of radiation to be detected and directs a light beam signal to an adjacent a-Si:H film so that detection may be confined to one or more such cells in the array. One or both electrodes may have a comb structure, and the teeth of each electrode comb may be interdigitated for capacitance reduction. The amorphous Si:H film may be replaced by an amorphous Si:Ge:H film in which up to 40 percent of the amorphous material is Ge. Two dimensional arrays may be used in X-ray imaging, CT scanning, crystallography, high energy physics beam tracking, nuclear medicine cameras and autoradiography. 18 figs.
Street, R.A.; Kaplan, S.N.; Perez-Mendez, V.
High resolution amorphous silicon radiation detectors
A radiation detector employing amorphous Si:H cells in an array with each detector cell having at least three contiguous layers (n type, intrinsic, p type), positioned between two electrodes to which a bias voltage is applied. An energy conversion layer atop the silicon cells intercepts incident radiation and converts radiation energy to light energy of a wavelength to which the silicon cells are responsive. A read-out device, positioned proximate to each detector element in an array allows each such element to be interrogated independently to determine whether radiation has been detected in that cell. The energy conversion material may be a layer of luminescent material having a columnar structure. In one embodiment a column of luminescent material detects the passage therethrough of radiation to be detected and directs a light beam signal to an adjacent a-Si:H film so that detection may be confined to one or more such cells in the array. One or both electrodes may have a comb structure, and the teeth of each electrode comb may be interdigitated for capacitance reduction. The amorphous Si:H film may be replaced by an amorphous Si:Ge:H film in which up to 40 percent of the amorphous material is Ge. Two dimensional arrays may be used in X-ray imaging, CT scanning, crystallography, high energy physics beam tracking, nuclear medicine cameras and autoradiography.
Street, Robert A. (Palo Alto, CA); Kaplan, Selig N. (El Cerrito, CA); Perez-Mendez, Victor (Berkeley, CA)
High density amorphous ice at room temperature
The phase diagram of water is both unusual and complex, exhibiting a wide range of polymorphs including proton-ordered or disordered forms. In addition, a variety of stable and metastable forms are observed. The richness of H2O phases attests the versatility of hydrogen-bonded network structures that include kinetically stable amorphous ices. Information of the amorphous solids, however, is rarely available especially for the stability field and transformation dynamics�but all reported to exist below the crystallization temperature of approximately 150�170�K below 4�5�GPa. Here, we present the evidence of high density amorphous (HDA) ice formed well above the crystallization temperature at 1�GPa�well inside the so-called �no-man�s land.� It is formed from metastable ice VII in the stability field of ice VI under rapid compression using dynamic-diamond anvil cell (d-DAC) and results from structural similarities between HDA and ice VII. The formation follows an interfacial growth mechanism unlike the melting process. Nevertheless, the occurrence of HDA along the extrapolated melt line of ice VII resembles the ice Ih-to-HDA transition, indicating that structural instabilities of parent ice VII and Ih drive the pressure-induced amorphization. PMID:21518902
Chen, Jing-Yin; Yoo, Choong-Shik
Monolithic solar cell panel of amorphous silicon
A monolithic solar cell panel has been fabricated using hydrogenated amorphous silicon (a-Si:H) as the semiconductor material. This device consists of a plate glass substrate bearing a number of long, narrow, parallel cells electrically connected in series along the lengths of the cells. It features several characteristics which make it uniquely attractive for large area devices (up to several sq
J. J. Hanak
Surface properties of amorphous carbon films
The sessile-drop experiment was conducted to analyze the wetting characteristics of the different amorphous carbon films before and after the plasma treatment. Initially in the carbon film�distilled water system the average contact angles have been measured within the values range from 50� to 70�. The plasma treatment of different allotropic carbon forms by low energetic ions increases very strongly the
O. Kutsay; O. Loginova; A. Gontar; V. Perevertailo; O. Zanevskyy; A. Katrusha; S. Ivakhnenko; V. Gorokhov; S. Starik; V. Tkach; N. Novikov
Distributed Amorphous Ramp Construction in Unstructured
Distributed Amorphous Ramp Construction in Unstructured Environments Nils Napp and Radhika Nagpal. Such con- struction is locally reactive, both on an algorithmic level, i.e. where robots Nils Napp (nnapp was supported by the Wyss Institute for Biologically Inspired Engineering 1 #12;2 Nils Napp and Radhika Nagpal
Napp, Nils
Distributed Amorphous Ramp Construction in Unstructured
Distributed Amorphous Ramp Construction in Unstructured Environments Nils Napp and Radhika Nagpal level, i.e. where robots deposit based on local cues, and a Nils Napp (firstname.lastname@example.com), Radhika was supported by the Wyss Institute for Bioinspired Engineering 1 #12;2 Nils Napp and Radhika Nagpal (a) (b) Fig
Napp, Nils
We compared nanoindentation and nanoscratch testing of 10 and 50nm thick tetrahedral amorphous carbon (ta-C) and hydrogenated amorphous carbon (a-C:H). Raman spectroscopy shows the expected spectral features for the two carbon forms, however, luminescence from the ceramic substrate can alter the spectra. We find that hard ta-C films can blunt the diamond tip and hence use a tip area function
P. Lemoine; J. P. Quinn; P. Maguire; J. A. McLaughlin
A nanotribological study of thin amorphous C and Cr doped amorphous C coatings
A new rapid method of nano-scale wear testing was applied to a matrix of 150nm amorphous C and Cr doped amorphous C coatings in order to investigate a nano-wear process under conditions which are applicable to MEMS and similar devices. The nano-wear test involved adding a method of controlled oscillation to the sample mounting of a nanoindentation system utilising a
G. M. Wilson; J. F. Smith; J. L. Sullivan
NASA Astrophysics Data System (ADS)
Amorphous Eu2TiO4 and EuTiO3 have been studied by a combination of the Faraday effect in the visible region and polarization-dependent x-ray absorption spectroscopy at the Eu M4,5 and L2,3 edges to examine the role of Eu 4f-5d exchange interactions on the ferromagnetic behavior. The bulk-sensitive x-ray absorption spectra (XAS) for Eu L2,3 edges show that most of the europium ions are present as the divalent state in the amorphous Eu2TiO4 and EuTiO3. The Eu M4,5 edge x-ray magnetic circular dichroism (XMCD) signals, measured for the amorphous Eu2TiO4, dramatically increase upon cooling through the Curie temperature (16 K) determined by a superconducting quantum interference device (SQUID) magnetometer. Sum-rule analysis of the XMCD at Eu M4,5 edges measured at 10 K yields a 4f spin magnetic moment of 6.6?B per Eu2+ ion. These results confirm that the ferromagnetic properties exclusively arise from 4f spins of Eu2+. In addition, for both the amorphous Eu2TiO4 and EuTiO3, the temperature and magnetic-field dependence of Eu L2,3 edge XMCD signals can be scaled with the corresponding magnetization measured by SQUID, indicating that the 5d magnetic polarization of Eu2+ is involved in the process to cause the ferromagnetic interaction between Eu2+ ions. We further discuss the origin of ferromagnetism in the amorphous system on the basis of the energy diagram of Eu 4f and 5d levels deduced from the Faraday effect in the visible region. From the wavelength dependence of Faraday rotation angles of the amorphous EuO-TiO2 system in comparison with those of the divalent Eu chalcogenides as reported previously, it is found that the magnitude of crystal-field splitting of Eu 5d levels in the former is on the same order as that in the latter, which explains an enhanced ferromagnetic exchange interaction between Eu 4f and 5d states.
Kawamoto, Takahiro; Fujita, Koji; Akamatsu, Hirofumi; Nakamura, Tetsuya; Kinoshita, Toyohiko; Mizumaki, Masaichiro; Kawamura, Naomi; Suzuki, Motohiro; Kususe, Yoshiro; Murai, Shunsuke; Tanaka, Katsuhisa
Phononic Amorphous Silicon: Theory, Material, and Devices
The field of phononic-engineered amorphous silicon is introduced. Specifically the construction of devices and waveguides for information conveyance and manipulation via phonons are considered. Typically the phononic properties of a given material are immutable and the phonons have such a limited diffusion length (nanometers) as to be unsuitable for engineering purposes. Crystalline silicon on the other hand has a reasonably large thermal conductivity and phonon diffusion length at sufficiently low temperatures. Phonon diffusion lengths can measure up to centimeters (e.g., crystalline SiO2) at temperature less than 10K but drop to sub microns at room temperature. Amorphous silicon, owing to the inherent scattering structures and owing to localization (of at least some phonon bands), has an anomalously large phonon lifetime [1]. This lifetime maybe indicative of a large phonon diffusion length and/or a fast phonon hop rate from one domain to the next and/or an indication that more than the typical three phonons (umklapp process) are involved in phonon scattering. Techniques involving small-scaled devices and phonon bands to control umklapp phonon-phonon scattering are described. The potential to exploit inherent amorphous silicon structure as well as the engineering (post film deposition) of di-hydride distributions to induce phonon forbidden bands for significantly reduced multi-phonon scattering is explored. The indirect optical band gap of small domain (and possibly amorphous) silicon [3] provides the physical basis for the transduction of phonon and optical energies. Experimental methods for the post-deposition introduction of phonon scattering structure, the transduction of phononic information to optical information, and experimental approaches including the use of micro-Raman to probe phonon spectra and transport are described. The prospects of a fully integrated phononic, photonic, electronic amorphous silicon technology have been described.
Chawda, S.; Mawyin, J.; Mahan, H.; Fortmann, C.; Halada, G.
Influence of corrosion on the magnetic properties of amorphous and nanocrystalline FeZrNbBCu alloy
NASA Astrophysics Data System (ADS)
The corrosion resistance of Fe 84.8Zr 3.4Nb 3.4B 7.4Cu 1 amorphous and nanocrystalline alloy and the effects of corrosion on the soft magnetic properties have been investigated. The corrosion resistance of amorphous sample decreased obviously after partial crystallization, which can be explained by the fact that the uniformity of the passive film was affected and decreased the corrosion resistance for the formation of nanocrystalline embedded in the amorphous. A layer of protective oxides was formed on the surface of the ribbons after corrosion, which leads to the degradation of soft magnetic properties, higher threshold field and higher relaxation frequency. When a small magnetic field was applied, the magnetization process was dominated by the domain wall bulging, and when the applied field was over the threshold field, the magnetization process was dominated by the domain wall bulging and displacement.
Peng, Kun; Tang, Yuanhong; Zhou, Lingping; Tang, Jiancheng; Xu, Feng; Du, Youwei
Amorphization of single composition powders by mechanical milling
Of the various methods which have been used for over 30 years to prepare amorphous materials, such as vapor phase deposition and rapid solidification, mechanical grinding or milling has also been noted as another but much less studied technique. The intermetallic compounds which were amorphized by MM were described by Weeber and Bakker in their review published in 1988. Since that time numerous additional intermetallic compounds, inorganic non-metallic compounds, and even several elements have been reportedly amorphized by MM. This paper will describe selected aspects of the phenomenology of amorphization by MM in single composition materials and then discuss some possible mechanisms for such amorphization.
Koch, C.C. [North Carolina State Univ., Raleigh, NC (United States). Dept. of Materials Science and Engineering] [North Carolina State Univ., Raleigh, NC (United States). Dept. of Materials Science and Engineering
NASA Astrophysics Data System (ADS)
The variation of surface magnetization with corrosion in Fe73.5Cu1Nb3Si13.5B9 in the amorphous and nanocrystalline states is investigated. The results show that in the amorphous samples when the oxidized layer increases the surface saturation magnetization decreases. However, in the nanocrystalline samples the surface saturation magnetization does not change significantly with the corrosion process but the approximation to saturation is different in the non-oxidized and oxidized nanocrystalline samples. In the case of non-oxidized samples, the surface saturation magnetization is reached at a low applied magnetic field (1000 Am-1), whereas in the oxidized samples it is reached at a higher applied magnetic field of 7000 and 9000 Am-1 for the samples annealed at 520�C for 60 min and 30 min, respectively.
Tejedor, M.; Garc�a, J. A.; Elbaile, L.; Santos, J. D.; Pierna, A. R.; Vara, G.; Marzo, F. F.
Emerging trends in the stabilization of amorphous drugs.
The number of active pharmaceutical substances having high therapeutic potential but low water solubility is constantly increasing, making it difficult to formulate these compounds as oral dosage forms. The solubility and dissolution rate, and thus potentially the bioavailability, of these poorly water-soluble drugs can be increased by the formation of stabilized amorphous forms. Currently, formulation as solid polymer dispersions is the preferred method to enhance drug dissolution and to stabilize the amorphous form of a drug. The purpose of this review is to highlight emerging alternative methods to amorphous polymer dispersions for stabilizing the amorphous form of drugs. First, an overview of the properties and stabilization mechanisms of amorphous forms is provided. Subsequently, formulation approaches such as the preparation of co-amorphous small-molecule mixtures and the use of mesoporous silicon and silica-based carriers are presented as potential means to increase the stability of amorphous pharmaceuticals. PMID:22569230
Laitinen, Riikka; L�bmann, Korbinian; Strachan, Clare J; Grohganz, Holger; Rades, Thomas
Obtention par PVD de condensateurs � base d'oxyde de germanium amorphe
NASA Astrophysics Data System (ADS)
This paper describes the elaboration of thin amorphous films of germanium dioxide and mixed germanium and lead oxides by RF cathodic sputtering in order to develop low loss capacitors with the highest possible capacity. The composition and the structure of the films are respectively determined by RBS and EXAFS. The best dielectric characteristics in low frequencies are obtained for the GePb{1.40}O{3.40} material. Cet article d�crit l'�laboration par pulv�risation cathodique RF de films minces amorphes de dioxyde de germanium et d'oxydes mixtes de germanium et de plomb dans le but de r�aliser des condensateurs � faibles pertes et de plus grande capacit� possible. La composition et la structure des films sont d�termin�es respectivement par RBS et par EXAFS. Les meilleures caract�ristiques di�lectriques en basses fr�quences sont obtenues pour le mat�riau GePb{1,40}O{3,40}.
Caperaa, C.; Segda, B.; Jacquet, M.; Baud, G.; Besse, J.-P.
Crystallization of amorphous silicon by self-propagation of nanoengineered thermites
NASA Astrophysics Data System (ADS)
Crystallization of amorphous silicon (a-Si) thin film occurred by the self-propagation of copper oxide/aluminum thermite nanocomposites. Amorphous Si films were prepared on glass at a temperature of 250�C by plasma enhanced chemical vapor deposition. The platinum heater was patterned on the edge of the substrate and the CuO /Al nanoengineered thermite was spin coated on the substrate that connects the heater and the a-Si film. A voltage source was used to ignite the thermites followed by a piranha solution (4:1 of H2SO4:H2O2) etch for the removal of residual products of thermite reaction. Raman spectroscopy was used to confirm the crystallization of a-Si.
Hossain, Maruf; Subramanian, Senthil; Bhattacharya, Shantanu; Gao, Yuanfang; Apperson, Steve; Shende, Rajesh; Guha, Suchi; Arif, Mohammad; Bai, Mengjun; Gangopadhyay, Keshab; Gangopadhyay, Shubhra
NASA Astrophysics Data System (ADS)
Amorphous and crystalline tungsten oxide films were RF-sputtered from a metallic target in oxygen/argon atmosphere onto un-heated and heated substrates. Upon cyclic electrochemical treatment in 0.1 M H 2SO 4 aqueous solution, both types of films showed good electrochromic reversibility beyond 1000 cycles. The crystallinity changes of both types of films were studied by XRD. For c-WO 3, the results showed that hydrogen insertion enhance the degree of crystallinity with the clear appearance of tungsten bronze diffraction peaks due to the formation of H 0.1WO 3, with tetragonal crystalline structure. For a-WO 3, coloration weakens the amorphous features and increases the crystallinity properties. The DC electrical conductivity increases, in a reversible way, with four order of magnitudes namely from 10 -7 to 10 -3 (? cm) -1 for bleached and colored films, respectively. Both types of films exhibit remarkable solar transmission modulation, about 51%, which is adequate for smart windows applications. In contrast to amorphous films, crystalline tungsten oxide films show reflection modulation in the NIR reaching 25% upon charge insertion. The Drude reflectance edge arises for colored films suggesting that coloration in c-WO 3 is attributed to a scattering mechanism of Drude-like free electron, while coloration of a-WO 3 is attributed to a hopping mechanism of small polaron. The visible, infrared and solar modulations are given for both types of films. Coloration/bleaching were found to be faster for amorphous films. Self-bleaching process in different oxidative environments involves a redox cycle aided by water polarity. Crystalline WO 3 showed pronounced coloring persistence relative to amorphous films which is attributed to different binding energy related to large and small polarons.
Kamal, H.; Akl, A. A.; Abdel-Hady, K.
Germanium detector passivated with hydrogenated amorphous germanium
Passivation of predominantly crystalline semiconductor devices (12) is provided for by a surface coating (21) of sputtered hydrogenated amorphous semiconductor material. Passivation of a radiation detector germanium diode, for example, is realized by sputtering a coating (21) of amorphous germanium onto the etched and quenched diode surface (11) in a low pressure atmosphere of hydrogen and argon. Unlike prior germanium diode semiconductor devices (12), which must be maintained in vacuum at cryogenic temperatures to avoid deterioration, a diode processed in the described manner may be stored in air at room temperature or otherwise exposed to a variety of environmental conditions. The coating (21) compensates for pre-existing undesirable surface states as well as protecting the semiconductor device (12) against future impregnation with impurities.
Hansen, William L. (Walnut Creek, CA); Haller, Eugene E. (Berkeley, CA)
Disappearance and Creation of Constrained Amorphous Phase
NASA Astrophysics Data System (ADS)
We report observation of the disappearance and recreation of rigid, or constrained, amorphous phase by sequential thermal annealing. Tempera- ture modulated differential scanning calorimetry (MDSC) is used to study the glass transition and lower melting endotherm after annealing. Cold crystallization of poly(phenylene sulfide), PPS, at a temperature just above Tg creates an initial large fraction of rigid amorphous phase (RAP). Brief, rapid annealing to a higher temperature causes RAP almost to disappear completely. Subsequent reannealing at the original lower temperature restores RAP to its original value. At the same time that RAP is being removed, Tg decreases; when RAP is restored, Tg also returns to its initial value. The crystal fraction remains unaffected by the annealing sequence.
Cebe, Peggy; Lu, Sharon X.
Low-temperature relaxations in amorphous polyolefins
NASA Technical Reports Server (NTRS)
The dynamic mechanical relaxation behavior of two series of amorphous polyolefins, was investigated from 4.2 K to the glass transition. Most of the polymers show a damping maximum or plateau in the 40 to 50 K region. Various mechanisms which have been suggested for cryogenic relaxations in amorphous polymers are considered as they might relate to the polyolefins. Two secondary relaxation processes above 80 K are distinguished. A relaxation at about 160 K (beta) in the second and third member of each series is associated with restricted blackbone motion. This process requires a certain degree of chain flexibility since it is not observed in the first member of each series. A lower temperature process (gamma) is observed in each member of the second series and is attributed to motion of the ethyl side group.
Hiltner, A.; Baer, E.; Martin, J. R.; Gillham, J. K.
Insulating behavior of an amorphous graphene membrane
NASA Astrophysics Data System (ADS)
We investigate the charge transport properties of planar amorphous graphene that is fully topologically disordered, in the form of sp2 threefold coordinated networks consisting of hexagonal rings but also including many pentagons and heptagons distributed in a random fashion. Using the Kubo transport methodology and the Lanczos method, the density of states, mean free paths, and semiclassical conductivities of such amorphous graphene membranes are computed. Despite a large increase in the density of states close to the charge neutrality point, all electronic properties are dramatically degraded, evidencing an Anderson insulating state caused by topological disorder alone. These results are supported by Landauer-B�ttiker conductance calculations, which show a localization length as short as 5 nm.
Van Tuan, Dinh; Kumar, Avishek; Roche, Stephan; Ortmann, Frank; Thorpe, M. F.; Ordejon, Pablo
Advances in amorphous silicon photovoltaic technology
With the advent of new multijunction thin film solar cells, amorphous silicon photovoltaic technology is undergoing a commercial revival with about 30 megawatts of annual capacity coming on-line in the next year. These new {ital a}{endash}Si multijunction modules should exhibit stabilized conversion efficiencies on the order of 8{percent}, and efficiencies over 10{percent} may be obtained in the next several years. The improved performance results from the development of amorphous and microcrystalline silicon alloy films with improved optoelectronic properties and from the development of more efficient device structures. Moreover, the manufacturing costs for these multijunction modules using the new large-scale plants should be on the order of {dollar_sign}1 per peak watt. These new modules may find widespread use in solar farms, photovoltaic roofing, as well as in traditional remote applications. {copyright} {ital 1998 Materials Research Society.}
Carlson, D.E.; Rajan, K.; Arya, R.R.; Willing, F.; Yang, L. [Solarex, a Business Unit of Amoco/Enron Solar, 826 Newtown-Yardley Road, Newtown, Pennsylvania 18940 (United States)
Wear Resistant Amorphous and Nanocomposite Coatings
Glass forming materials (critical cooling rate <10{sup 4}K.s{sup -1}) are promising for their high corrosion and wear resistance. During rapid cooling, the materials form an amorphous structure that transforms to nanocrystalline during a process of devitrification. High hardness (HV 1690) can be achieved through a controlled crystallization. Thermal spray process has been used to apply coatings, which preserves the amorphous/nanocomposite structure due to a high cooling rate of the feedstock particles during the impact on a substrate. Wear properties have been studied with respect to process conditions and feedstock material properties. Application specific properties such as sliding wear resistance have been correlated with laboratory tests based on instrumented indentation and scratch tests.
Racek, O
Milling maps and amorphization during mechanical alloying
The effect of various milling parameters such as, milling intensity, ball: powder weight ratio and number of balls on the glass forming ability of an elemental blend of composition Ti{sub 50}Ni{sub 50} has been studied by mechanical alloying. In order to understand the results, all the milling parameters have been converted into two energy parameters, namely, impact energy of the bill and the total energy of milling. In a milling map of these two parameters, the conditions for amorphous phase formation have been isolated. A similar exercise has been carried out for Ti{sub 50}Cu{sub 50} as a function of milling time at two milling intensities. The results, indicate that a minimum impact energy of the ball and a minimum total energy are essential for amorphization by mechanical alloying.
Murty, B.S.; Mohan Rao, M.; Ranganathan, S. [Indian Inst. of Science, Bangalore (India). Dept. of Metallurgy] [Indian Inst. of Science, Bangalore (India). Dept. of Metallurgy
Study of an amorphous alloy core transformer
NASA Astrophysics Data System (ADS)
Amorphous core transformers (ACT) have become a technological and commercial reality and there are an estimated 400,000 units installed worldwide [1]. Their applications reflect changes in buying practices, where the efficiency evaluation is an important factor in the purchasing decision for distribution transformers. Use of the total ownership cost (TOC) concept facilities the selection of a transformer on the basis of its performance. This concept is used in this paper to investigate the feasibility of applying a distribution ACT in Western Australian (WA). A 10 kVA ACT, evaluated by the TOC method, was compared with a traditional silicon iron core transformer of the same rating. The cost of amorphous metal (relative to alternative materials), the distribution load profile, and the values of capitalised loss costs are factors which affect the cost effectiveness of ACTs.
Nafalski, A.; Frost, D. C.
Synthesis and characterization of bulk amorphous steels
Bulk amorphous steels (BASs) are a novel class of advanced materials having very attractive physical, thermal and mechanical properties and have applications as structural materials. Two BASs Fe50Cr14Mo14C14B6M2 (M=Y and Dy) were designed following the Greer�s confusion principle and cylinders of thickness 3�5mm were synthesized by Cu mold casting technique. Characterization was carried out by techniques of X-ray diffraction (XRD),
M. Iqbal; J. I. Akhter; H. F. Zhang; Z. Q. Hu
Voids in hydrogenated amorphous silicon materials
Effusion measurements of hydrogen and of implanted helium are used to characterize the presence of voids in hydrogenated amorphous silicon (a-Si:H) materials as a function of substrate temperature, hydrogen content, etc. For undoped plasma-grown a-Si:H, interconnected voids are found to prevail at hydrogen concentrations exceeding 15�20at.%, while isolated voids which act as helium traps appear at hydrogen concentrations?15at.%. The concentration
W. Beyer; W. Hilgers; P. Prunici; D. Lennartz
Frenkel defect process in amorphous silica
Point defects strongly influence optical properties of synthetic amorphous silica (synthetic a-SiO2) used in excimer laser photolithography and their properties are intensively studied. Decomposition of an Si-O-Si bond into a pair of oxygen vacancy and interstitial oxygen species is an intrinsic defect process in a-SiO2. It is similar to the creation of vacancy-interstitial pairs in crystalline materials and is regarded
Koichi Kajihara; Masahiro Hirano; Linards Skuja; Hideo Hosono
Hydrogenated amorphous silicon-germanium alloys
This report describes the effects of the germanium fraction in hydrogenated amorphous silicon-germanium alloys on various parameters, especially those that are indicators of film quality, and the impact of deposition methods, feedgas mixtures, and other deposition parameters on a SiGe:H and a-SiGe:H:F film characteristics and quality. Literature data show the relationship between germanium content, hydrogen content, deposition method (various glow
Thermal conductivity of amorphous silicon films
NASA Astrophysics Data System (ADS)
We measured the thermal conductivity of an 80 ?m thick amorphous silicon film from 80K to room temperature. The amorphous silicon sample was prepared by hot-wire chemical-vapor deposition with 1 at. % hydrogen, which was found previously to contain almost no atomic tunneling states that is common in amorphous solids. The value of the thermal conductivity is about a factor of two larger than previous results. To explain this unusually large thermal conductivity, we report on a Kubo theory that makes use of a tight binding electronic structure of a 1000 atom model. We include the low frequency modes that the Kubo model does not take into account because of its finite size. By considering Rayleigh and boundary scattering, and scattering of tunneling states, our theory can explain not only our result but also previous ones as well. We conclude that the large thermal conductivity of our film is attributed to the lack of scattering of the low frequency modes by the tunneling states. Therefore, low frequency modes can make significant contribution to heat transport even at near room temperature.
Feldman, Joseph; Liu, Xiao; Crandall, R.; Bernstein, N.; Mehl, M.; Papaconstantopoulos, D.
Amorphous silicon nanocone array solar cell
In the hydrogenated amorphous silicon [a-Si:H]-thin film solar cell, large amounts of traps reduce the carrier's lifetime that limit the photovoltaic performance, especially the power conversion efficiency. The nanowire structure is proposed to solve the low efficiency problem. In this work, we propose an amorphous silicon [a-Si]-solar cell with a nanocone array structure were implemented by reactive-ion etching through a polystyrene nanosphere template. The amorphous-Si nanocone exhibits absorption coefficient around 5 � 105/cm which is similar to the planar a-Si:H layer in our study. The nanostructure could provide the efficient carrier collection. Owing to the better carrier collection efficiency, efficiency of a-Si solar cell was increased from 1.43% to 1.77% by adding the nanocone structure which has 24% enhancement. Further passivation of the a-Si:H surface by hydrogen plasma treatment and an additional 10-nm intrinsic-a-Si:H layer, the efficiency could further increase to 2.2%, which is 54% enhanced as compared to the planar solar cell. The input-photon-to-current conversion efficiency spectrum indicates the efficient carrier collection from 300 to 800 nm of incident light. PMID:22395021
Inhibition of field crystallization of anodic niobium oxide by incorporation of silicon species
The present work demonstrates effective inhibition of field crystallization of amorphous anodic niobium oxide by incorporation of silicon species from substrate. The field crystallization, detrimental for capacitor application of niobium, occurs during anodizing of magnetron sputtered niobium at 100V in 0.1moldm?3 ammonium pentaborate electrolyte at 333K, while amorphous structure of the anodic oxide is totally retained during anodizing of magnetron
H. Habazaki; T. Ogasawara; K. Fushimi; K. Shimizu; S. Nagata; T. Izumi; P. Skeldon; G. E. Thompson
Solution-based synthesis of manganese oxide cathodes for lithium batteries
With an objective to overcome the cyclability problems of manganese oxides, solution-based procedures are pursued to synthesize metastable manganese oxides. Reduction of permanganate with lithium iodide in an acetonitrile medium followed by heating at 250 C in vacuum gives an amorphous lithium sodium manganese oxyiodide that is intimately mixed with crystalline NaIO. On the other hand, oxidation of manganese acetate
A. Manthiram; J. Kim; S. Choi
Nitroxide-Functionalized Graphene Oxide from Graphite Oxide
A facile method for preparing functionalized graphene oxide single layers with nitroxide groups is reported herein. Highly oxidized graphite oxide (GO=90.6%) was obtained, slightly modifying an improved Hummer�s method. Oxoammonium salts (OS) were investigated to introduce nitroxide groups to GO, resulting in a one-step functionalization and exfoliation. The mechanisms of functionalization/exfoliation are proposed, where the oxidation of aromatic alcohols to ketone groups, and the formation of alkoxyamine species are suggested. Two kinds of functionalized graphene oxide layers (GOFT1 and GOFT2) were obtained by controlling the amount of OS added. GOFT1 and GOFT2 exhibited a high interlayer spacing (d0001 = 1.12nm), which was determined by X-ray diffraction. The presence of new chemical bonds C-N (~9.5 %) and O-O (~4.3 %) from nitroxide attached onto graphene layers were observed by X-ray photoelectron spectroscopy. Single-layers of GOFT1 were observed by HRTEM, exhibiting amorphous and crystalline zones at a 50:50 ratio; in contrast, layers of GOFT2 exhibited a fully amorphous surface. Fingerprint of GOFT1 single layers was obtained by electron diffraction at several tilts. Finally, the potential use of these materials within Nylon 6 matrices was investigated, where an unusual simultaneous increase in tensile stress, tensile strain and Young�s modulus was observed. PMID:24347671
Avila-Vega, Yazmin I.; Leyva-Porras, Cesar C.; Mireles, Marcela; Quevedo-L�pez, Manuel; Macossay, Javier; Bonilla-Cruz, Jos�
Process to produce silicon carbide fibers using a controlled concentration of boron oxide vapor
NASA Technical Reports Server (NTRS)
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.
Barnard, Thomas Duncan (Inventor); Lipowitz, Jonathan (Inventor); Nguyen, Kimmai Thi (Inventor)
Process to produce silicon carbide fibers using a controlled concentration of boron oxide vapor
NASA Technical Reports Server (NTRS)
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.
Barnard, Thomas Duncan (Inventor); Lipowitz, Jonathan (Inventor); Nguyen, Kimmai Thi (Inventor)
Formation of amorphous silicon by light ion damage
Amorphization by implantation of boron ions (which is the lightest element generally used in I.C. fabrication processes) has been systematically studied for various temperatures, various voltages and various dose rates. Based on theoretical considerations and experimental results, a new amorphization model for light and intermediate mass ion damage is proposed consisting of two stages. The role of interstitial type point defects or clusters in amorphization is emphasized. Due to the higher mobility of interstitials out-diffusion to the surface particularly during amorphization with low energy can be significant. From a review of the idealized amorphous structure, diinterstitial-divacancy pairs are suggested to be the embryos of amorphous zones formed during room temperature implantation. The stacking fault loops found in specimens implanted with boron at room temperature are considered to be the origin of secondary defects formed during annealing.
Shih, Y.C.
Crystallization inhibition of an amorphous sucrose system using raffinose*
The shelf life of pure amorphous sucrose systems, such as cotton candy, can be very short. Previous studies have shown that amorphous sucrose systems held above the glass transition temperature will collapse and crystallize. One study, however, showed that adding a small percent of another type of sugar, such as trehalose, to sucrose can extend the shelf life of the amorphous system by slowing crystallization. This study explores the hypothesis that raffinose increases the stability of an amorphous sucrose system. Cotton candy at 5 wt% raffinose and 95 wt% sucrose was made and stored at room temperature and three different relative humidities (%RH) 11%RH, 33%RH, and 43%RH. XRD patterns, and glass transition temperatures were obtained to determine the stability as a function of %RH. The data collected showed that raffinose slows sucrose crystallization in a low moisture amorphous state above the glass transition temperature and therefore improves the stability of amorphous sucrose systems. PMID:16421962
Leinen, K.M.; Labuza, T.P.
This thesis explores how nanopatterns can be used to control the growth of single-crystal silicon on amorphous substrates at low temperature, with potential applications on flat panel liquid-crystal display and 3-dimensional (3D) integrated circuits. I first present excimer laser annealing of amorphous silicon (a-Si) nanostructures on thermally oxidized silicon wafer for controlled formation of single-crystal silicon islands. Preferential nucleation at
Jian Gu
Environmental Testing of Iron-Based Amorphous Alloys
Iron (Fe)-based amorphous alloys possess enhanced hardness and are highly resistant to corrosion, which make them desirable for wear applications in corrosive environments. It was of interest to examine the behavior of amorphous alloys during anodic polarization in concentrated salt solutions and in the salt-fog testing. Results from the testing of one amorphous material (SAM2X5) both in ribbon form and
Raul B. Rebak; S. Daniel Day; Tiangan Lian; Phillip D. Hailey; Joseph C. Farmer
Environmental Testing of Iron-Based Amorphous Alloys
Iron (Fe)-based amorphous alloys possess enhanced hardness and are highly resistant to corrosion, which make them desirable\\u000a for wear applications in corrosive environments. It was of interest to examine the behavior of amorphous alloys during anodic\\u000a polarization in concentrated salt solutions and in the salt-fog testing. Results from the testing of one amorphous material\\u000a (SAM2X5) both in ribbon form and
Raul B. Rebak; S. Daniel Day; Tiangan Lian; Phillip D. Hailey; Joseph C. Farmer
Quantum emission efficiency of nanocrystalline and amorphous Si quantum dots
The paper presents the comparison of emission efficiencies for crystalline Si quantum dots (QDs) and amorphous Si nanoclusters (QDs) embedded in hydrogenated amorphous (a-Si:H) films grown by the hot wire-CVD method (HW-CVD) at the variation of technological parameters. The correlations between the intensities of different PL bands and the volumes of Si nanocrystals (nc-Si:H) and\\/or an amorphous (a-Si:H) phase have
T. V. Torchynska
Polyamorphous transition in amorphous fullerites C{sub 70}
Samples of amorphous fullerites C{sub 70} have been obtained by mechanical activation (grinding in a ball mill). The structure of the samples has been investigated by neutron and X-ray diffraction. The high-temperature (up to 1200 Degree-Sign C) annealing of amorphous fullerites revealed a polyamorphous transition from molecular to atomic glass, which is accompanied by the disappearance of fullerene halos at small scattering angles. Possible structural versions of the high-temperature amorphous phase are discussed.
Borisova, P. A. [Moscow State Institute of Steel and Alloys (Russian Federation); Agafonov, S. S.; Glazkov, V. P. [National Research Center Kurchatov Institute (Russian Federation); D'yakonova, N. P. [Moscow State Institute of Steel and Alloys (Russian Federation); Somenkov, V. A., E-mail: firstname.lastname@example.com [National Research Center Kurchatov Institute (Russian Federation)
Microstructure and interface properties of laterally oxidized AlxGa1- xAs
NASA Astrophysics Data System (ADS)
The microstructure and interface properties of AlxGa1- xAs materials that have been laterally oxidized in wet N2 for several compositions (x equals 0.80, 0.82 . . . 1.00) and temperatures (360 degrees Celsius to 450 degrees Celsius) have been studied. The micro-structure is found to be relatively insensitive to composition and oxidation temperature. The oxidation forms an amorphous solid solution (AlxGa1-x)2O3 that transforms to polycrystalline, (gamma) -(AlxGa1-x)2O3 under electron beam exposure in the electron microscope. Evidence suggests a small fraction of crystalline (AlxGa1- x)2O3 is formed via post oxidation annealing of the oxide. The level of hydrogen present in the oxidized layers is 1.1 multiplied by 1021 cm-3, which is too low for the amorphous phase observed to be a hydroxide rather than an oxide. The amount of As in the layer is reduced to less than 2 atm%, and no As precipitates are observed. The (AlxGa1-x)2O3/GaAs interface is abrupt, but prolonged oxidation will cause the GaAs to oxidize at the internal interfaces. The reaction front between the oxidized and the unoxidized AlxGa1-xAs has a 10 to 20 nm-wide amorphous zone that shows a different contrast than the remainder of the amorphous oxide and is stable under electron irradiation.
Twesten, Ray D.; Follstaedt, David M.; Choquette, Kent D.
Oxidation-assisted ductility of aluminium nanowires.
Oxidation can drastically change mechanical properties of nanostructures that typically have large surface-to-volume ratios. However, the underlying mechanisms describing the effect oxidation has on the mechanical properties of nanostructures have yet to be characterized. Here we use reactive molecular dynamics and show that the oxidation enhances the aluminium nanowire ductility, and the oxide shell exhibits superplastic behaviour. The oxide shell decreases the aluminium dislocation nucleation stress by increasing the activation volume and the number of nucleation sites. Superplasticity of the amorphous oxide shell is due to viscous flow as a result of healing of the broken aluminium-oxygen bonds by oxygen diffusion, below a critical strain rate. The interplay between the strain rate and oxidation rate is not only essential for designing nanodevices in ambient environments, but also controls interface properties in large-scale deformation processes. PMID:24887649
Sen, Fatih G; Alpas, Ahmet T; van Duin, Adri C T; Qi, Yue
NASA Technical Reports Server (NTRS)
Amorphous silicon films (a-Si:H) have been routinely deposited on a variety of substrates. Surface and interfacial studies were carried out with a PHI 5600 X-ray photo electron spectrometer. Co-deposition with fluorine yielded films having oxygen present as bulk oxide. The higher the fluorine content, the greater the amount of bulk oxygen observed. The presence of oxygen may be a contributing factor to inconsistent film properties of fluorine doped silicon materials, reported else where. A definite chemical interface between a layer containing fluorine and a layer made from pure silane has been delineated.
McWhinney, Hylton G.; Burton, Dawn; Fogarty, Thomas N.
Improved conversion efficiency of amorphous Si solar cells using a mesoporous ZnO pattern.
To provide a front transparent electrode for use in highly efficient hydrogenated amorphous silicon (a-Si:H) thin-film solar cells, porous flat layer and micro-patterns of zinc oxide (ZnO) nanoparticle (NP) layers were prepared through ultraviolet nanoimprint lithography (UV-NIL) and deposited on Al-doped ZnO (AZO) layers. Through this, it was found that a porous micro-pattern of ZnO NPs dispersed in resin can optimize the light-trapping pattern, with the efficiency of solar cells based on patterned or flat mesoporous ZnO layers increased by 27% and 12%, respectively. PMID:25276101
Go, Bit-Na; Kim, Yang Doo; Suk Oh, Kyoung; Kim, Chaehyun; Choi, Hak-Jong; Lee, Heon
Improved conversion efficiency of amorphous Si solar cells using a mesoporous ZnO pattern
To provide a front transparent electrode for use in highly efficient hydrogenated amorphous silicon (a-Si:H) thin-film solar cells, porous flat layer and micro-patterns of zinc oxide (ZnO) nanoparticle (NP) layers were prepared through ultraviolet nanoimprint lithography (UV-NIL) and deposited on Al-doped ZnO (AZO) layers. Through this, it was found that a porous micro-pattern of ZnO NPs dispersed in resin can optimize the light-trapping pattern, with the efficiency of solar cells based on patterned or flat mesoporous ZnO layers increased by 27% and 12%, respectively.
Improved conversion efficiency of amorphous Si solar cells using a mesoporous ZnO pattern
NASA Astrophysics Data System (ADS)
To provide a front transparent electrode for use in highly efficient hydrogenated amorphous silicon (a-Si:H) thin-film solar cells, porous flat layer and micro-patterns of zinc oxide (ZnO) nanoparticle (NP) layers were prepared through ultraviolet nanoimprint lithography (UV-NIL) and deposited on Al-doped ZnO (AZO) layers. Through this, it was found that a porous micro-pattern of ZnO NPs dispersed in resin can optimize the light-trapping pattern, with the efficiency of solar cells based on patterned or flat mesoporous ZnO layers increased by 27% and 12%, respectively.
Go, Bit-Na; Kim, Yang Doo; suk Oh, Kyoung; Kim, Chaehyun; Choi, Hak-Jong; Lee, Heon
How the nature of the chemical bond governs resistance to amorphization by radiation damage
We discuss what defines a material's resistance to amorphization by radiation damage. We propose that resistance is generally governed by the competition between the short-range covalent and long-range ionic forces, and we quantify this picture using quantum-mechanical calculations. We calculate the Voronoi deformation density charges and Mulliken overlap populations of 36 materials, representative of different families, including complex oxides. We find that the computed numbers generally follow the trends of experimental resistance in several distinct families of materials: the increase (decrease) of the short-range covalent component in material's total force field decreases (increases) its resistance.
Trachenko, Kostya; Artacho, Emilio; Dove, Martin T. [Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ (United Kingdom); Pruneda, J.M. [Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ (United Kingdom); Institut de Ciencia de Materials de Barcelona, Campus de la U.A.B, 08193 Bellaterra, Barcelona (Spain)
Multilevel unipolar resistive memory switching in amorphous SmGdO3 thin film
NASA Astrophysics Data System (ADS)
Multilevel resistive switching was observed in random access memory device using amorphous SmGdO3 (SGO) ternary oxide thin films. Non-volatile and stable 4-level resistance states with sufficient margin of resistance ratios were observed by varying compliance current which was attributed to compliance current dependent variation in size of conducting filaments. As fabricated Pt/SGO/Pt devices exhibited excellent switching parameters such as stable resistance ratios of reset (ON) to set (OFF) states, non-overlapping switching voltages, excellent data retention, and endurance. Temperature dependent variation of resistances of ON and OFF states of the device was studied to elucidate current conduction and resistive switching mechanisms.
Sharma, Yogesh; Misra, Pankaj; Pavunny, Shojan P.; Katiyar, Ram S.
Irreversible Enthalpic Relaxation of Rigid Amorphous Fraction in Isotactic Polystyrene
NASA Astrophysics Data System (ADS)
The crystalline, rigid amorphous, and mobile amorphous fractions in isotactic polystyrene (iPS) were studied using: 1. quasi-isothermal temperature-modulated differential scanning calorimetry (TMDSC) (i.e., with step-wise increase of temperature), and 2. regular TMDSC (i.e., with constant rate of temperature increase). The crystal fraction was determined from wide angle X-ray scattering and endotherm analysis; mobile amorphous fraction was determined from heat capacity measurements at the glass transition. The validity of a three-phase model for iPS (comprising crystals, mobile and rigid amorphous fractions) is confirmed by heat capacity measurements made during quasi-isothermal cold crystallization. At the same time, we prove the rigid amorphous fraction to be established at the crystallization temperature and not during subsequent cooling. The rigid amorphous fraction is thus stable below the crystallization temperature Tc, and relaxes at a temperature Ta, between Tc and the melting point of the lowest melting crystals. Upon relaxing, the rigid amorphous fraction undergoes a phase transition to mobile amorphous fraction. For cold-crystallized iPS the relaxation of the rigid amorphous fraction is found to be an enthalpy involved, non-reversible relaxation occurring before the melting of the crystals.
Xu, Hui; Cebe, Peggy
Investigating the medium range order in amorphous Ta2O5 coatings
NASA Astrophysics Data System (ADS)
Ion-beam sputtered amorphous heavy metal oxides, such as Ta2O5, are widely used as the high refractive index layer of highly reflective dielectric coatings. Such coatings are used in the ground based Laser Interferometer Gravitational-wave Observatory (LIGO), in which mechanical loss, directly related to Brownian thermal noise, from the coatings forms an important limit to the sensitivity of the LIGO detector. It has previously been shown that heat-treatment and TiO2 doping of amorphous Ta2O5 coatings causes significant changes to the levels of mechanical loss measured and is thought to result from changes in the atomic structure. This work aims to find ways to reduce the levels of mechanical loss in the coatings by understanding the atomic structure properties that are responsible for it, and thus helping to increase the LIGO detector sensitivity. Using a combination of Reduced Density Functions (RDFs) from electron diffraction and Fluctuation Electron Microscopy (FEM), we probe the medium range order (in the 2-3 nm range) of these amorphous coatings.
Bassiri, Riccardo; Hart, Martin; Byer, Robert L.; Borisenko, Konstantin B.; Evans, Keith; Fejer, Martin M.; Lin, Angie C.; MacLaren, Ian; Markosyan, Ashot S.; Martin, Iain W.; Route, Roger K.; Rowan, Sheila
NASA Astrophysics Data System (ADS)
We have investigated the structure and ferroelectric properties of vinylidene fluoride-trifluoroethylene (VDF-TrFE) copolymer thin films fabricated on amorphous alloy electrodes. Thin films of amorphous Pd-Cu-Si alloys with various compositions were successfully prepared by sputtering deposition. An atomically flat surface resulting from a fully amorphous structure of Pd-Cu-Si was obtained upon achieving a uniform surface of a spin-coated VDF-TrFE copolymer thin film. X-ray diffraction (XRD) measurements revealed that the crystalline structure of the VDF-TrFE copolymer thin films was of ferroelectric ?-phase, being independent of the composition and crystalline state of the Pd-Cu-Si alloy. The clearly observed D-E hysteresis loops showed a remanent polarization of 0.075 C/m2 and a coercive field of 90 MV/m at a measurement frequency of 10 Hz for a 50-nm-thick film, which is almost consistent with the results obtained with Pt electrode samples. We also observed the thinning-induced reduction of remanent polarization, which was explained by the depolarization field induced by the surface dead layer in VDF-TrFE copolymer rather than the oxidized layer in Pd-Cu-Si alloy electrode.
Nakajima, Takashi; Yamaura, Shin-ichi; Furukawa, Takeo; Okamura, Soichiro
The formation and conversion of cation radicals (CR) in the absorption of the isomers of trimethylbenzene (TMB), pseudocumene and mesitylene on Y zeolites, a high-silica wide-pore mordenite, the UHS zeolite TsVM, which belong to the class of pentasils, and on an amorphous aluminosilicate (AS) have been studied by EPR. It is shown that the formation of CR takes place in the adsorption of TMB on dehydrated specimens of the H-forms of the zeolites and amorphous AS in the presence of O/sub 2/. The possible structure of the CR formed, the paths for their conversion, as well as the structure of the radical-forming center are discussed. A mechanism is suggested for the formation and conversion of CR at an oxidizing-reducing center activated by oxygen. The radical processes which take place on the zeolites and amorphous AS are associated with the selectivity of the catalytic reactions involving the participation of TMB and also with the deactivation of the catalysts.
Surin, S.A.; Fedorova, L.A.; Gullyev, C.; Chukin, G.D.; Nefedov, B.K.; Radchenko, E.D.
NASA Astrophysics Data System (ADS)
The effects of the electrolytic hydrogenation and oxidation and of the interaction of the surface ribbon with water and vapor on the frequency dependence of magnetic losses per magnetization-reversal cycle are studied based on the example of soft magnetic Fe81B13Si4C2 amorphous alloy, which exhibits a positive saturation magnetostriction. It was shown that, after the hydrogenation and oxidation of soft magnetic amorphous alloys, their frequency dependences of magnetic losses per magnetization-reversal cycle, which are reduced to unit induction, exhibit groups of hydrogen- and oxygen-related peaks in the frequency ranges of 35-55 and 55-80 Hz, which can be explained by the formation of O- A and H- A atomic pairs (where A are atoms of alloy components) and their reorientation in a magnetic field in the course of magnetization reversal at certain frequencies. The formation of analogous groups of peaks for samples of soft magnetic Fe-based amorphous alloys was observed after the interaction of the ribbon surface with water and vapor and after heat treatment in air. This fact confirms the possibility of the hydrogenation and oxidation of the alloys during the aforementioned processes.
Skulkina, N. A.; Ivanov, O. A.; Stepanova, E. A.; Pavlova, I. O.
New type of contact coating for amorphous silicon solar cells
NASA Astrophysics Data System (ADS)
The use of metal-antireflection coatings applied to amorphous silicon solar cells is reported. A stainless steel /p(+)/i/n(+)/Al/ZnS structure in which a semitransparent low work function metal, such as aluminum, is contacted to the n(+) layer to form an ohmic contact is used; this is followed by the deposition of a ZnS layer which acts as an antireflective coating to allow most of the visible light to enter the solar cell. When only a layer of aluminum is used, the visible transmission of aluminum on glass is about 40-50 percent, whereas when ZnS is deposited on the aluminum layer, the enhancement in the current exceeds 70 percent. Further improvements in terms of resistance and transmission are made possible by the use of Ag/ZrO2. It is shown that metal-antireflection coatings are a viable alternative to transparent conducting oxide. The technique is simple and the deposition rates are fast and would shorten the time for complete processing of cells.
Madan, A.; McMahon, T. J.
The absolute entropy of Ni0.667Zr0.333 and Ni0.333Zr0.667 amorphous alloys
NASA Astrophysics Data System (ADS)
The heat capacities of amorphous and crystalline Ni0.667Zr0.333 and Ni0.333Zr0.667 alloys were measured in the temperature range from {\\sim }12 K to the crystallization points for the former or to {\\sim }900 K for the latter. The results together with the data on the thermodynamic properties of the Ni-Zr melt were used for the calculation of the absolute entropy of the amorphous alloys on the assumption that the entropies of a substance in undercooled liquid and glassy states coincide at the glass-transition point. The entropy and heat capacity of the amorphous alloys was found to exceed those of the crystalline ones. The residual entropy of Ni0.333Zr0.667 and Ni0.667Zr0.333 amorphous alloys at 0 K is, respectively, 2.7 � 2.1 and 0.2 � 1.7 J mol-1 K-1, which is significantly below the residual entropy values typical for traditional oxide glasses (4-17 J mol-1 K-1). This points to a much higher degree of order in amorphous metallic alloys as compared to glassy oxides.
Gavrichev, K. S.; Golushina, L. N.; Gorbunov, V. E.; Zaitsev, A. I.; Zaitseva, N. E.; Mogutnov, B. M.; Molokanov, V. V.; Khoroshilov, A. V.
Switching in coplanar amorphous hydrogenated silicon devices
NASA Astrophysics Data System (ADS)
Switching has been observed in a wide variety of materials and devices. Hydrogenated amorphous silicon has become one of the most important cases because of interest in neural network applications. Although there are many reports regarding this phenomenon, not all of the physical processes involved are still determined precisely. Therefore, some more experimental information is needed in order to achieve this task. Much of the behavior of the devices has been ascribed to the existence of a filamentary region which is produced after the first switching process, called forming. We observed this filamentary region in its full extension by producing forming in amorphous silicon devices with coplanar metallic contacts placed near each other (�5 ?m). The I-V characteristics, filament optical and atomic force microscopy images and chemical etching led us to correlate changes in resistance to metal inclusion into the amorphous film. There are two stages: the first is related to contact stabilization, the second to metal transport into the film bulk. Optical images show a permanent filamentary region after forming. AFM images of these filaments showed that they are formed essentially by material accumulation between the contacts. This material tends to get some atomic arrangement, becoming a polycrystalline solid. If the device was led to breakdown, such accumulation becomes either a hillock or a thin conducting channel connecting both contacts. In the case of a switching filament, the accumulation tends to be a chain of smaller hillocks along the conduction path. Metal from the contacts remains in the conduction path after forming and chemical etching indicated that it is placed near the path core. Before forming, a tunneling transport process can be ascribed to the non-ohmic behavior of the samples during the first stage of metallic inclusion.
Avila, A.; Asomoza, R.
Water clustering on nanostructured iron oxide films
NASA Astrophysics Data System (ADS)
The adhesion of water to solid surfaces is characterized by the tendency to balance competing molecule-molecule and molecule-surface interactions. Hydroxyl groups form strong hydrogen bonds to water molecules and are known to substantially influence the wetting behaviour of oxide surfaces, but it is not well-understood how these hydroxyl groups and their distribution on a surface affect the molecular-scale structure at the interface. Here we report a study of water clustering on a moir�-structured iron oxide thin film with a controlled density of hydroxyl groups. While large amorphous monolayer islands form on the bare film, the hydroxylated iron oxide film acts as a hydrophilic nanotemplate, causing the formation of a regular array of ice-like hexameric nanoclusters. The formation of this ordered phase is localized at the nanometre scale; with increasing water coverage, ordered and amorphous water are found to coexist at adjacent hydroxylated and hydroxyl-free domains of the moir� structure.
Merte, Lindsay R.; Bechstein, Ralf; Peng, Guowen; Rieboldt, Felix; Farberow, Carrie A.; Zeuthen, Helene; Knudsen, Jan; L�gsgaard, Erik; Wendt, Stefan; Mavrikakis, Manos; Besenbacher, Flemming
NASA Astrophysics Data System (ADS)
Fluctuation electron microscopy (FEM) is explicitly sensitive to 3- and 4-body atomic correlation functions in amorphous materials; this is sufficient to establish the existence of structural order on the nanoscale, even when the radial distribution function extracted from diffraction data appears entirely amorphous. However, it remains a formidable challenge to invert the FEM data into a quantitative model of the structure. Here, we quantify the FEM method for a-Si by forward simulating the FEM data from a family of high quality atomistic models. Using a modified WWW method, we construct computational models that contain 10-40 vol% of topologically crystalline grains, 1-3 nm in diameter, in an amorphous matrix and calculate the FEM signal, which consists of the statistical variance V (k) of the dark-field image as a function of scattering vector k. We show that V (k) is a complex function of the size and volume fraction of the ordered regions present in the amorphous matrix. However, the ratio of the variance peaks as a function of k affords the size of the ordered regions; and the magnitude of the variance affords a semi-quantitative measure of the volume fraction. We have also compared models that contain various amounts of strain in the ordered regions. This analysis shows that the amount of strain in realistic models is sufficient to mute variance peaks at high k. We conclude with a comparison between the model results and experimental data.
Bogle, Stephanie N.; Voyles, Paul M.; Khare, Sanjay V.; Abelson, John R.
Radiation resistance studies of amorphous silicon films
NASA Technical Reports Server (NTRS)
Hydrogenated amorphous silicon thin films were irradiated with 2.00 MeV helium ions using fluences ranging from 1E11 to 1E15 cm(-2). The films were characterized using photothermal deflection spectroscopy and photoconductivity measurements. The investigations show that the radiation introduces sub-band-gap states 1.35 eV below the conduction band and the states increase supralinearly with fluence. Photoconductivity measurements suggest the density of states above the Fermi energy is not changing drastically with fluence.
Woodyard, James R.; Payson, J. Scott
Progress in amorphous silicon based multijunction modules
Advances in amorphous silicon based alloys and device structure have led to the demonstration of 10.5% initial efficiency and 9.1% stabilized efficiency on 1 Ft{sup 2} a-Si/a-SiGe tandem junction module. Scale-up to 4 Ft{sup 2} in pilot production has resulted in the best initial efficiency of 9.75% as measured by NREL, which should result in a stabilized efficiency over 8%. Presently the 4 Ft{sup 2} modules have an average initial efficiency of 8.75% and a stabilized average efficiency of about 7.5%, as measured by Solarex.
Arya, R.R.; Oswald, R.S.; Li, Y.M. [Solarex Corp., Newtown, PA (United States). Thin-Film Div.] [and others
Obstacles using amorphous materials for volume applications
NASA Astrophysics Data System (ADS)
This contribution is especially focussed on the attempt to use amorphous or nanocrystalline metals in position sensor applications and to describe the difficulties and obstacles encountered in coherence with the development of appropriate industrial high volume series products in conjunction with the related quality requirements. The main motivation to do these investigations was to beat the generally known sensors especially silicon based Hall-sensors as well as AMR- and GMR-sensors - well known from mobile phones and electronic storage devices like hard discs and others - in terms of cost-effectiveness and functionality.
Kiessling, Albert; Reininger, Thomas
Encoding of Memory in Sheared Amorphous Solids
NASA Astrophysics Data System (ADS)
We show that memory can be encoded in a model amorphous solid subjected to athermal oscillatory shear deformations, and in an analogous spin model with disordered interactions, sharing the feature of a deformable energy landscape. When these systems are subjected to oscillatory shear deformation, they retain memory of the deformation amplitude imposed in the training phase, when the amplitude is below a "localization" threshold. Remarkably, multiple persistent memories can be stored using such an athermal, noise-free, protocol. The possibility of such memory is shown to be linked to the presence of plastic deformations and associated limit cycles traversed by the system, which exhibit avalanche statistics also seen in related contexts.
Fiocco, Davide; Foffi, Giuseppe; Sastry, Srikanth
Femtosecond laser crystallization of amorphous Ge
Ultrafast crystallization of amorphous germanium (a-Ge) in ambient has been studied. Plasma enhanced chemical vapor deposition grown a-Ge was irradiated with single femtosecond laser pulses of various durations with a range of fluences from below melting to above ablation threshold. Extensive use of Raman scattering has been employed to determine post solidification features aided by scanning electron microscopy and atomic force microscopy measurements. Linewidth of the Ge optic phonon at 300 cm{sup -1} as a function of laser fluence provides a signature for the crystallization of a-Ge. Various crystallization regimes including nanostructures in the form of nanospheres have been identified.
Salihoglu, Omer; Aydinli, Atilla [Physics Department, Bilkent University, Ankara 06800 (Turkey); Kueruem, Ulas; Gul Yaglioglu, H.; Elmali, Ayhan [Department of Engineering Physics, Ankara University, 06100 Ankara (Turkey)
The future of amorphous silicon photovoltaic technology
Amorphous silicon modules are commercially available. They are the first truly commercial thin-film photovoltaic (PV) devices. Well-defined production processes over very large areas (>1 m{sup 2}) have been implemented. There are few environmental issues during manufacturing, deployment in the field, or with the eventual disposal of the modules. Manufacturing safety issues are well characterized and controllable. The highest measured initial efficiency to date is 13.7% for a small triple-stacked cell and the highest stabilized module efficiency is 10%. There is a consensus among researchers, that in order to achieve a 15% stabilized efficiency, a triple-junction amorphous silicon structure is required. Fundamental improvements in alloys are needed for higher efficiencies. This is being pursued through the DOE/NREL Thin-Film Partnership Program. Cost reductions through improved manufacturing processes are being pursued under the National Renewable Energy Laboratory/US Department of Energy (NREL/DOE)-sponsored research in manufacturing technology (PVMaT). Much of the work in designing a-Si devices is a result of trying to compensate for the Staebler-Wronski effect. Some new deposition techniques hold promise because they have produced materials with lower stabilized defect densities. However, none has yet produced a high efficiency device and shown it to be more stable than those from standard glow discharge deposited material.
Crandall, R.; Luft, W.
Structural Characteristics of Synthetic Amorphous Calcium Carbonate
Amorphous calcium carbonate (ACC) is an important phase involved in calcification by a wide variety of invertebrate organisms and is of technological interest in the development of functional materials. Despite widespread scientific interest in this phase a full characterization of structure is lacking. This is mainly due to its metastability and difficulties in evaluating structure using conventional structure determination methods. Here we present new findings from the application of two techniques, pair distribution function analysis and nuclear magnetic resonance spectroscopy, which provide new insight to structural aspects of synthetic ACC. Several important results have emerged from this study of ACC formed in vitro using two common preparation methods: (1) ACC exhibits no structural coherence over distances > 15 {angstrom} and is truly amorphous; (2) most of the hydrogen in ACC is present as structural H{sub 2}O, about half of which undergoes restricted motion on the millisecond time scale near room temperature; (3) the short- and intermediate-range structure of ACC shows no distinct match to any known structure in the calcium carbonate system; and (4) most of the carbonate in ACC is monodentate making it distinctly different from monohydrocalcite. Although the structure of synthetic ACC is still not fully understood, the results presented provide an important baseline for future experiments evaluating biogenic ACC and samples containing certain additives that may play a role in stabilization of ACC, crystallization kinetics, and final polymorph selection.
Michel, F. Marc; MacDonald, Jason; Feng, Jian; Phillips, Brian L.; Ehm, Lars; Tarabrella, Cathy; Parise, John B.; Reeder, Richard J. (SBU)
Hydrogenated amorphous silicon-germanium alloys
This report describes the effects of the germanium fraction in hydrogenated amorphous silicon-germanium alloys on various parameters, especially those that are indicators of film quality, and the impact of deposition methods, feedgas mixtures, and other deposition parameters on a SiGe:H and a-SiGe:H:F film characteristics and quality. Literature data show the relationship between germanium content, hydrogen content, deposition method (various glow discharges and CVD), feedgas lmixture, and other parameters and properties, such as optical band gap, dark and photoconductivities, photosensitivity, activation energy, Urbach parameter, and spin density. Some of these are convenient quality indicators; another is the absence of microstructure. Examining RF glow discharge with both a diode and triode geometry, DC proximity glow discharge, microwave glow discharge, and photo-CVD, using gas mixtures such as hydrogen-diluted and undiluted mixtures of silane/germane, disilane/germane, silane/germaniumtetrafluoride, and others, it was observed that hydrogen dilution (or inert gas dilution) is essential in achieving high photosensitivity in silicon-germanium alloys (in contradistinction to amorphous hydrogenated silicon). Hydrogen dilution results in a higher photosensitivity than do undiluted gas mixtures. 81 refs., 42 figs., 7 tabs.
Luft, W.
Molecular Dynamics Study of Crack Behavior in AN Amorphous Material
The fracture behavior of amorphous solids has received much attention due to the importance of these materials for a variety of applications in construction, transportation, including space vehicles, communications and computers, and under extreme environmental conditions, such as high temperatures, pressures and corrosive atmospheres. In this thesis, we strive to study the basic mechanisms of brittle fracture in amorphous solids
Oscar Romulo Ochoa
Optical conductivity of amorphous Ta and beta-Ta films
NASA Technical Reports Server (NTRS)
Tantalum films evaporated in high vacuum onto liquid-nitrogen-cooled substrates had an amorphous structure that persisted even after warming to room temperature. The optical conductivity (as well as the dc conductivity) of the amorphous films differed significantly from that of the bcc films.
Nestell, J. E., Jr.; Scoles, K. J.; Christy, R. W.
Magnetic properties of glass-coated amorphous and nanocrystalline microwires
The magnetic properties of Fe- and Co-based amorphous and nanocrystalline glass-coated microwires are reviewed. Such wires are composed of a metallic amorphous nucleus (3 to 20 ?m diameter) and an insulating glass cover (2 to 12 ?m thick). Interest is mainly focused on samples exhibiting squared hysteresis loops (magnetically bistable) which exhibit positive magnetostriction (bistability can be observed for 2
M. V�zquez; A. P. Zhukov
13th International Conference on Liquid and Amorphous Metals
The state of the art in the field of liquid and amorphous metals and alloys is regularly updated through two series of complementary international conferences, the LAM (Liquid and Amorphous Metals) and the RQ (Rapidly Quenched Materials). The first series of the conferences started as LM-1 in 1966 at Brookhaven for the basic understanding of liquid metals. The subsequent LM
Pjotr Popel; Boris Gelchinskii; Valeriy Sidorov; Leonid Son; Alexandre Sabirzjanov
Amorphous Silicon TFT Instabilities in OLED Driver Circuit Applications
Amorphous Silicon TFT Instabilities in OLED Driver Circuit Applications Lars Johanson 3 August 2004 #12;OLED Applications image from http://www.universaldisplay.com #12;Amorphous Silicon Thin Film Subthreshold Slope � Further Study Needed � Design constraints: OLED pixel displays #12;Acknowledgements � Dr
Petta, Jason
Endurance Tests Of Amorphous-Silicon Photovoltaic Modules
NASA Technical Reports Server (NTRS)
Failure mechanisms in high-power service studied. Report discusses factors affecting endurance of amorphous-silicon solar cells. Based on field tests and accelerated aging of photovoltaic modules. Concludes that aggressive research needed if amorphous-silicon modules to attain 10-year life - value U.S. Department of Energy established as goal for photovoltaic modules in commercial energy-generating plants.
Ross, Ronald G., Jr.; Sugimura, Russell S.
Quantifying Nanoscale Order in Amorphous Materials via Fluctuation Electron Microscopy
ERIC Educational Resources Information Center
Fluctuation electron microscopy (FEM) has been used to study the nanoscale order in various amorphous materials. The method is explicitly sensitive to 3- and 4-body atomic correlation functions in amorphous materials; this is sufficient to establish the existence of structural order on the nanoscale, even when the radial distribution function�
Bogle, Stephanie Nicole
Electronic configuration of cerium in amorphous alloys (invited; abstract)
We have investigated the effect of structural disorder on the valence of cerium in different families of amorphous alloys prepared by coevaporation on to cryogenic substrates. The Ce electronic configuration was characterized by LIII x-ray absorption spectroscopy and bulk magnetization measurements. Special attention was paid to the amorphous analogs of prototypic Kondo and strongly mixed valent compounds in the crystalline
J. Durand; D. Malterre; G. Marchal; G. Krill; M. F. Ravet; J.-P. Kappler
Superlattice doped layers for amorphous silicon photovoltaic cells
Superlattice doped layers for amorphous silicon photovoltaic cells comprise a plurality of first and second lattices of amorphous silicon alternatingly formed on one another. Each of the first lattices has a first optical bandgap and each of the second lattices has a second optical bandgap different from the first optical bandgap. A method of fabricating the superlattice doped layers also is disclosed.
Arya, Rajeewa R. (Doylestown, PA)
Health hazards due to the inhalation of amorphous silica
Occupational exposure to crystalline silica dust is associated with an increased risk for pulmonary diseases such as silicosis, tuberculosis, chronic bronchitis, chronic obstructive pulmonary disease (COPD) and lung cancer. This review summarizes the current knowledge about the health effects of amorphous (non-crystalline) forms of silica. The major problem in the assessment of health effects of amorphous silica is its contamination
R. Merget; T. Bauer; H. K�pper; S. Philippou; H. Bauer; R. Breitstadt; T. Bruening
Hydrogen plasma enhanced crystallization of hydrogenated amorphous silicon films
Hydrogen plasma enhanced crystallization of hydrogenated amorphous silicon films K. Pangal,a) J. C August 1998; accepted for publication 21 October 1998 We report that a room temperature hydrogen plasma thermal crystallization of amorphous silicon time by a factor of five. Exposure to hydrogen plasma reduces
Oxidation induced softening in Al nanowires
NASA Astrophysics Data System (ADS)
The mechanical properties of metallic nanowires depend dramatically on the atmospheric conditions. Molecular-dynamics simulations with ReaxFF were conducted to study tensile elastic deformation of oxidized Al nanowires. The thin amorphous oxide shell formed around Al nanowires had a very low Young's modulus of 26 GPa, due to its low density and low Al-O coordination. Consequently, for diameters less than 100 nm, the composite Young's modulus of oxide-covered Al nanowires showed a size dependence implying that in this case "smaller is softer." The model developed also explained the discrepancies in the reported modulus values of nanometer-scale Al thin films.
Sen, Fatih G.; Qi, Yue; van Duin, Adri C. T.; Alpas, Ahmet T.
Structural, electronic, and dynamical properties of amorphous gallium arsenide: a comparison of amorphous gallium arsenide. Using the recentlyproposed ``activation relaxation technique'' and empirical
Lewis, Laurent J.
Fabrication and Characterization of Amorphous/Nanocrystalline Thin Film Composite
NASA Astrophysics Data System (ADS)
Combining the absorption abilities of amorphous silicon and the electron transport capabilities of crystalline silicon would be a great advantage to not only solar cells but other semiconductor devices. In this work composite films were created using molecular beam epitaxy and electron beam deposition interchangeably as a method to create metallic precursors. Aluminum induced crystallization techniques were used to convert an amorphous silicon film with a capping layer of aluminum nanodots into a film composed of a mixture of amorphous silicon and nanocrystalline silicon. This layer was grown into the amorphous layer by cannibalizing a portion of the amorphous silicon material during the aluminum induced crystallization. Characterization was performed on films and metallic precursors utilizing SEM, TEM, ellipsometry and spectrophotometer.
Newton, Benjamin S.
Atomic simulations of interfacial sliding in amorphous Carbon nanocomposites
Nano-composites with amorphous carbon matrix reinforced by hard crystalline nano-particles are fast developing as next generation super-tough and wear resistant coatings. The frictional wear and toughness properties of these composites are determined by the properties of the interface between crystalline-and amorphous phases. In this paper we use molecular dynamics and statics simulations to study the interfacial energetics, sliding and friction behavior of diamond - and amorphous carbon interfaces. It is found that the orientation of crystalline phase has minor effect on sliding behavior. Sliding behavior is affected by two mechanisms (a) bond breaking and reattaching at the interface and (b) deformation of amorphous carbon in the region surrounding the interface. It is found that the deformation away from the interface reduces the resistance to sliding. In structures with higher SP3 content, bond breaking at the interface dominates and there is much lesser deformation in the amorphous phase.
Namilae, Sirish [ORNL; Radhakrishnan, Balasubramaniam [ORNL; Gorti, Sarma B [ORNL
Moringa coagulant as a stabilizer for amorphous solids: Part I.
Stabilization of amorphous state is a focal area for formulators to reap benefits related with solubility and consequently bioavailability of poorly soluble drugs. In the present work, an attempt has been made to explore the potential of moringa coagulant as an amorphous state stabilizer by investigating its role in stabilization of spray-dried (amorphous) ibuprofen, meloxicam and felodipine. Thermal studies like glass forming ability, glass transition temperature, hot stage microscopy and DSC were carried out for understanding thermodynamic stabilization of drugs. PXRD and dissolution studies were performed to support contribution of moringa coagulant. Studies showed that hydrogen bonding and electrostatic interactions between drug and moringa coagulant are responsible for amorphous state stabilization as explored by ATR-FTIR and molecular docking. Especially, H-bonding was found to be predominant mechanism for drug stabilization. Therein, arginine (basic amino acid in coagulant) exhibited various interactions and played important role in stabilization of aforesaid amorphous drugs. PMID:22359158
Bhende, Santosh; Jadhav, Namdeo
Salt Fog Testing Iron-Based Amorphous Alloys
Iron-based amorphous alloys are hard and highly corrosion resistant, which make them desirable for salt water and other applications. These alloys can be produced as powder and can be deposited as coatings on any surface that needs to be protected from the environment. It was of interest to examine the behavior of these amorphous alloys in the standard salt-fog testing ASTM B 117. Three different amorphous