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Influence of the surface band structure on electron emission spectra from metal surfaces
NASA Astrophysics Data System (ADS)
Electron distributions produced by grazing impact of fast protons on Mg(0001), Cu(111), Ag(111), and Au(111) surfaces are investigated, focusing on the effects of the electronic band structure. The process is described within the band-structure-based approximation, which is a perturbative method that includes an accurate representation of the electron-surface interaction, incorporating information of the electronic band structure of the solid. For all the studied surfaces, the presence of partially occupied surface electronic states produces noticeable structures in double-differentialŚenergy- and angle-resolvedŚelectron emission probabilities from the valence band. For Mg, Cu, and Ag these structures remain visible in electron emission spectra after adding contributions coming from core electrons, which might make possible their experimental detection, but for Au they are hidden by inner-shell emission.
Archubi, C. D.; Faraggi, M. N.; Silkin, V. M.; Gravielle, M. S.
TOPICAL REVIEW: Structured surfaces of wide band gap insulators as templates for overgrowth of adsorbates
Microsoft Academic Search
Surface structures on wide band gap insulators and their use as templates for the growth of adsorbates are reviewed. Surface structures include evaporation structures, vicinal surfaces, facetted surfaces, epitaxial structures, or structures transferred to or induced by the growth of thin films. Most structures have been realized so far on Al2O3 and on alkali halide crystals. The guided growth of
Roland Bennewitz
Influence of the surface band structure in photoelectron emission by ultra-short laser pulses
Photoelectron emission from the valence band of aluminum and beryllium surfaces by ultra-short laser pulses is studied within the Band-Structure-Based - Volkov (BSB-V) approximation, which takes into account the contribution of the band structure of the solid. We found that band structure effects are extremely important for Be(0001), for which signatures of partially occupied surface states can be observed in the electron emission spectra.
RĒos Rubiano, C. A.; Gravielle, M. S.; Mitnik, D. M.; Silkin, V. M.
The interplay between the surface band structure and possible surface reconstructions of Mo(112)
: ĀĀThe experimental band structure of Mo(112) and the effects by temperature and adsorbate are presented. A surface resonance,\\u000a identified as crossing the Fermi level at about 1\\/3 from to of surface Brillouin zone, was observed to be very sensitive to both contamination and temperature. We find evidence of adsorbate\\u000a and temperature induced reconstruction of the Mo(112) surface. Examination of
T. McAvoy; J. Zhang; C. Waldfried; D. N. McIlroy; P. A. Dowben; O. Zeybek; T. Bertrams; S. D. Barrett
Lattice and electronic band structure changes across the surface ferroelectric transition
The origin of the surface ferroelectric phase transition in crystalline copolymer films of vinylidene fluoride (70%) with trifluoroethylene (30%) is explored. We report a uniaxial doubling of the surface Brillouin zone in the conduction band dispersion across the surface ferroelectric phase transition. The temperature dependent changes in the electronic structure occur primarily in the conduction band and are accompanied by
Jaewu Choi; P. A. Dowben; Stephen Ducharme; V. M. Fridkin; S. P. Palto; N. Petukhova; S. G. Yudin
Surface structures on wide band gap insulators and their use as templates for the growth of adsorbates are reviewed. Surface structures include evaporation structures, vicinal surfaces, facetted surfaces, epitaxial structures, or structures transferred to or induced by the growth of thin films. Most structures have been realized so far on Al2O3 and on alkali halide crystals. The guided growth of adsorbates is discussed, considering the examples of metallic clusters or wires and ordered films of organic molecules.
Bennewitz, Roland
Band Structure
This chapter deals with the ordering of the valence bands - a topic that has controversially been discussed for more than 40 years. The ? 7, ? 9, ? 7 ordering is discussed in the light of very recent ab initio band structure calculations, and the important role is emphasized, which the Zn 3d-band position plays to the sign of the spin-orbit splitting. This topic is touched again from a different point of view in Chap. 6 on free excitons. Then we summarize the experimental findings on the cationic and anionic substitutions in ZnO and random alloy formation essential for quantum hetero-structures. The chapter closes with the data on the valence and conduction band discontinuities in iso- and hetero-valent hetero-structures.
Meyer, B. K.
The Surface Band Structure of Li/Be(10» {1}0)
A photoemision study of the surface states on Be(10» {1}0) after Li adsorption at room temperature is reported. The surface band structure was mapped along four high symmetry directions of the SBZ. Fairly large shifts in the surface band locations were obtained but all surface states observed experimentally after Li adsorption were found to correspond to Be-derived states and no Li-derived surface states could be identified. The surface state bands located close to the Fermi level (EF) were found to be affected the most and it is suggested that one surface state band which on the clean surface is located above EF is pulled down below EF after Li adsorption.
Johansson, L. I.; Balasubramanian, T.; Virojanadara, C.
Selective doping in a surface band and atomic structures of the Ge(111) (?3 ū ?3)R30░-Au surface.
Atomic and electronic structures of the Ge(111) (?3 ū ?3)R30░-Au surface with two metallic bands are studied by scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES). The bias-voltage-dependent periodic structure observed by STM is consistent with the electronic structure calculated for an optimized conjugate honeycomb chained trimer (CHCT) model. Electrons are selectively doped to the electron-like surface metallic band by excess Au atoms, which form triangle structures with the Au trimers of the CHCT model. The discrepancy for the bottom energy of the electron-like band between the ARPES results and those of the calculation is attributed to the doping. The triangle structure is mobile at room temperature, but stable at 80 K. Both Au and Ge atoms deposited at room temperature on the Ge(111) (?3 ū ?3)R30░-Au surface dope electrons to the electron-like surface metallic band. Moreover, the Au atoms increase the spin-orbit interaction at the surface, and thus make the splitting of the spin-polarized band due to the interaction larger than that before the deposition. PMID:23248164
Nakatsuji, Kan; Motomura, Yuya; Niikura, Ryota; Komori, Fumio
Polarization sensitive surface band structure of doped BaTiO3(001).
We present a spatial and wave-vector resolved study of the electronic structure of micron sized ferroelectric domains at the surface of a BaTiO(3)(001) single crystal. The n-type doping of the BaTiO(3) is controlled by in situ vacuum and oxygen annealing, providing experimental evidence of a surface paraelectric-ferroelectric transition below a critical doping level. Real space imaging of photoemission threshold, core level and valence band spectra show contrast due to domain polarization. Reciprocal space imaging of the electronic structure using linearly polarized light provides unambiguous evidence for the presence of both in- and out-of-plane polarization with two- and fourfold symmetry, respectively. The results agree well with first principles calculations. PMID:24093301
Rault, J E; Dionot, J; Mathieu, C; Feyer, V; Schneider, C M; Geneste, G; Barrett, N
Accessing Surface Brillouin Zone and Band Structure of Picene Single Crystals
We have experimentally revealed the band structure and the surface Brillouin zone of insulating picene single crystals (SCs), the mother organic system for a recently discovered aromatic superconductor, with ultraviolet photoelectron spectroscopy (UPS) and low-energy electron diffraction with a laser for photoconduction. A hole effective mass of 2.24m0 and the hole mobility ?h?9.0cm2/Vs (298 K) were deduced in the ?-Y direction. We have further shown that some picene SCs did not show charging during UPS even without the laser, which indicates that pristine UPS works for high-quality organic SCs.
Xin, Qian; Duhm, Steffen; Bussolotti, Fabio; Akaike, Kouki; Kubozono, Yoshihiro; Aoki, Hideo; Kosugi, Taichi; Kera, Satoshi; Ueno, Nobuo
Valence- and conduction-band structure of the sapphire (11»02) surface
X-ray photoelectron (XPS) and electron-energy-loss spectroscopies have been employed to investigate the valence- and conduction-band densities of states of the sapphire (11»02) surface. The photoemission spectrum of the valence-band region has been adjusted to remove cross-section effects and compared to the recent theoretical density of states calculated by Ciraci and Batra. The energy-loss data have been used to determine the bulk-plasmon energy of sapphire, 24.0+/-0.3 eV, as well as the locations of eight regions of high conduction-band-state density within 20 eV above the conduction-band minimum. One of these regions is an empty surface state 4.0 eV below the conduction-band minimum. Several high-binding-energy satellites in the XPS core-level spectra are reported and interpreted in terms of energy losses to plasmons and interband transitions.
Gignac, W. J.; Williams, R. Stanley; Kowalczyk, Steven P.
The Valence- and conduction-band structure of the sapphire (1102) surface
X-ray photoelectron and electron energy loss spectroscopies have been employed to investigate the valence- and conduction-band densities-of-states of the sapphire (1102) surface. The photoemission spectrum of the valence-band region has been adjusted to remove cross-section effects and compared to the recent theoretical density-of-states calculated by Ciraci and Batra. The energy loss data have been used to determine the bulk plasmon energy of sapphire, 24.0 +or- .3 eV, as well as the locations of eight regions of high conduction-band state density within 20 eV above the conduction-band minimum. One of these regions is an empty surface state 4.0 eV below the conduction-band minimum. Several high binding energy satellites in the XPS core level spectra are reported and interpreted in terms of energy losses to plasmons and interband transitions.
Gignac, W. J.; Williams, R. S.; Kowalczyk, S. P.
Surface and bulk electronic structure of the unconventional superconductor Sr2RuO4: unusual splitting of the ? band
We present an angle-resolved photoemission study of the surface and bulk electronic structure of the single layer ruthenate Sr2RuO4. As the early studies by photoemission and scanning tunneling microscopy were confronted with a problem of surface reconstruction, surface ageing was previously proposed as a possible remedy to access the bulk states. Here, we suggest an alternative way by demonstrating that, in the case of Sr2RuO4, circularly polarized light can be used to disentangle the signals from the bulk and surface layers, thus opening the possibility to investigate many-body interactions both in bulk and surface bands. The proposed procedure results in improved momentum resolution, which enabled us to detect an unexpected splitting of the surface ? band. We discuss the origin of the splitting of the ? band and the possible connection with the Rashba effect at the surface.
Zabolotnyy, V. B.; Carleschi, E.; Kim, T. K.; Kordyuk, A. A.; Trinckauf, J.; Geck, J.; Evtushinsky, D.; Doyle, B. P.; Fittipaldi, R.; Cuoco, M.; Vecchione, A.; B³chner, B.; Borisenko, S. V.
Electronic Band Structure and Fermi Surface of Heavy-Fermion Neptunium Superconductor NpPd5Al2
Electronic band structure calculations were carried out for a new neptunium superconductor NpPd5Al2 using a relativistic linear-augmented plane wave method within a local density approximation. The Fermi energy in the band structure is found to be located just on the 5f-bands of the j=5/2 state with the extremely narrow band width and therefore the theoretical electronic specific heat coefficient ?b is extremely large, being ?b = 74.0 mJ/(K2\\cdotmol), which is compared to ? = 390 mJ/(K2\\cdotmol) estimated experimentally. NpPd5Al2 is an uncompensated metal. The main electron Fermi surface corresponds to a doughnut-like flat Fermi surface centered at the ? point which is connected with cylindrical Fermi surfaces elongated along the X-W-P line.
Yamagami, Hiroshi; Aoki, Dai; Haga, Yoshinori; ?nuki, Yoshichika
Influence of GaAs surface termination on GaSb/GaAs quantum dot structure and band offsets
SciTech Connect
We have investigated the influence of GaAs surface termination on the nanoscale structure and band offsets of GaSb/GaAs quantum dots (QDs) grown by molecular-beam epitaxy. Transmission electron microscopy reveals both coherent and semi-coherent clusters, as well as misfit dislocations, independent of surface termination. Cross-sectional scanning tunneling microscopy and spectroscopy reveal clustered GaSb QDs with type I band offsets at the GaSb/GaAs interfaces. We discuss the relative influences of strain and QD clustering on the band offsets at GaSb/GaAs interfaces.
Zech, E. S.; Chang, A. S.; Martin, A. J.; Canniff, J. C.; Millunchick, J. M. [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States)] [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States); Lin, Y. H. [Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States)] [Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States); Goldman, R. S. [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States) [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States); Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States)
Zech, E. S.; Chang, A. S.; Martin, A. J.; Canniff, J. C.; Lin, Y. H.; Millunchick, J. M.; Goldman, R. S.
Band structure effects on the Be(0001) acoustic surface plasmon energy dispersion
We report first-principles calculations of acoustic surface plasmons on the (0001) surface of Be, as obtained in the random-phase approximation of many-body theory. The energy dispersion of these collective excitations has been obtained along two symmetry directions. Our results show a considerable anisotropy of acoustic surface plasmons, and underline the capability of experimental measurements of these plasmons to {\\it map} the electron-hole excitation spectrum of the quasi two-dimensional Shockley surface state band that is present on the Be(0001) surface.
Silkin, V. M.; Pitarke, J. M.; Chulkov, E. V.; Diaconescu, B.; Pohl, K.; Vattuone, L.; Savio, L.; Hofmann, Ph.; Far?'As, D.; Rocca, M.; Echenique, P. M.
Porous-pyramids structured silicon surface with low reflectance over a broad band by electrochemical etching
Porous-pyramids structured silicon surface was prepared and its influence on the reflectance of the silicon surface was studied. The porous-pyramids structured surface was prepared by electrochemical etching in HF/C2H5OH solution after texturization in NaOH/IPA solution. The average reflectance of the surface in the range of 400-800 nm was as low as 1.9%. The optical photographs and SEM images of the surfaces prepared under optimized condition were investigated. The porous-pyramids structured surface has a gradient-index multilayer structure (i.e., the refraction index of the structure increase from the top to the bottom). A formula that describes the relationship between the reflectance and the index of refraction was used to explain the excellent broadband antireflection of the multilayer silicon surface. The technique of this paper may be valuable in the texturization process for high-efficiency silicon solar cells.
Lv, Hongjie; Shen, Honglie; Jiang, Ye; Gao, Chao; Zhao, Han; Yuan, Jiren
FDTD simulation of 3D surface plasmon polariton band gap waveguide structures
Fundamental to progress in integrated optical systems are techniques for controlling light propagation on small spatial scales. The development of photonic band gap (PBG) waveguides (Joannopoulos, J.D. et al., 1982) represents a major step towards achieving such control, as it permits the nearly lossless redirection of light flows through sharp waveguide bends, a feat unachievable using conventional optical waveguide structures.
Meng Lut; Mingyu Lu; P. Scott Camey; Eric Michielssen
Band structure and fermi surface of Electron-Doped C{sub 60} Monolayers
C60 fullerides are challenging systems because both the electron-phonon and electron-electron interactions are large on the energy scale of the expected narrow band width. We report angle-resolved photoemission data on the band dispersion for an alkali doped C60 monolayer and a detailed comparison with theory. Compared to the maximum bare theoretical band width of 170 meV, the observed 100-meV dispersion is within the range of renormalization by electron-phonon coupling. This dispersion is only a fraction of the integrated peak width, revealing the importance of many-body effects. Additionally, measurements on the Fermi surface indicate the robustness of the Luttinger theorem even for materials with strong interactions.
Yang, W.L.; Brouet, V.; Zhou, X.J.; Choi, Hyoung J.; Louie, Steven G.; Cohen, Marvin L.; Kellar, S.A.; Bogdanov, P.V.; Lanzara, A.; Goldoni, A.; Parmigiani, F.; Hussain, Z.; Shen, Z-X.
Band structure and Fermi surface of electron-doped C60 monolayers.
C60 fullerides are challenging systems because both the electron-phonon and electron-electron interactions are large on the energy scale of the expected narrow band width. We report angle-resolved photoemission data on the band dispersion for an alkali-doped C60 monolayer and a detailed comparison with theory. Compared to the maximum bare theoretical band width of 170 meV, the observed 100-meV dispersion is within the range of renormalization by electron-phonon coupling. This dispersion is only a fraction of the integrated peak width, revealing the importance of many-body effects. Additionally, measurements on the Fermi surface indicate the robustness of the Luttinger theorem even for materials with strong interactions. PMID:12690192
Yang, W L; Brouet, V; Zhou, X J; Choi, Hyoung J; Louie, Steven G; Cohen, Marvin L; Kellar, S A; Bogdanov, P V; Lanzara, A; Goldoni, A; Parmigiani, F; Hussain, Z; Shen, Z-X
Nanosecond laser-induced periodic surface structures on wide band-gap semiconductors
In this work we report on fabrication of laser-induced periodic surface structures (LIPSS) on different semiconductors with bandgap energies in the range of 1.3-3.3 eV and melting temperatures from 1100 to 2700 ░C. In particular, InP, GaAs, GaP and SiC were irradiated in air with nanosecond pulses using a linearly polarized laser beam at 266 nm (6 ns pulse width). The nanostructures, inspected by atomic force microscopy, are produced upon multiple pulse irradiation at fluences near the ablation threshold. LIPSS are perpendicular to the laser polarization direction and their period is of the order of the irradiation wavelength. It was observed that the accumulative effect of both fluence and number of pulses needed for LIPSS formation increased with the material bandgap energy. These results, together with estimations of surface temperature increase, are discussed with reference to the semiconductor electrical, optical and thermal properties.
Sanz, Mikel; Rebollar, Esther; Ganeev, Rashid A.; Castillejo, Marta
Electric-field tuning of the surface band structure of topological insulator Sb2Te3 thin films.
We measured the response of the surface state spectrum of epitaxial Sb(2)Te(3) thin films to applied gate electric fields by low temperature scanning tunneling microscopy. The gate dependent shift of the Fermi level and the screening effect from bulk carriers vary as a function of film thickness. We observed a gap opening at the Dirac point for films thinner than four quintuple layers, due to the coupling of the top and bottom surfaces. Moreover, the top surface state band gap of the three quintuple layer films was found to be tunable by a back gate, indicating the possibility of observing a topological phase transition in this system. Our results are well explained by an effective model of 3D topological insulator thin films with structure inversion asymmetry, indicating that three quintuple layer Sb(2)Te(3) films are topologically nontrivial and belong to the quantum spin Hall insulator class. PMID:23952429
Zhang, Tong; Ha, Jeonghoon; Levy, Niv; Kuk, Young; Stroscio, Joseph
We report first-principles calculations of acoustic surface plasmons on the (0001) surface of Be, as obtained in the random-phase approximation of many-body theory. The energy dispersion of these collective excitations has been obtained along two symmetry directions. Our results show a considerable anisotropy of acoustic surface plasmons, and underline the capability of experimental measurements of these plasmons to {\\\\it map}
V. M. Silkin; J. M. Pitarke; E. V. Chulkov; B. Diaconescu; K. Pohl; L. Vattuone; L. Savio; Ph. Hofmann; D. Fari'As; M. Rocca; P. M. Echenique
Evidence in the XPS valence band of the fold structure at the surface of polyethylene lamellae
For the purpose of identifying surface conformations, the valence XPS spectra of mats of polyethylene single crystals as prepared from the solution and after annealing are reported and compared with the spectrum of a pressed pellet of hexatriacontane. The relative intensity of the two "C?C peaks" in the inner-valence region exhibit significant variations that are related to the chain folds occuring at the surface of the lamellae, on the one hand, and to planar zig-zag segments for the annealed and pellet samples, on the other hand.
Delhalle, J.; Riga, J.; Denis, J. P.; Deleuze, M.; DosiĶre, M.
Surface-plasmon-polariton band structure of nanostructured multi-layer systems
We calculate the optical response of multi-layer systems where at least one layer contains arrays of metalic substructures of nanometer size. The dependence on lattice constant and excitation energy is studied systematically. An - at first glance non-intuitive - dependence of the plasmon intensity on the geometry of the metalic substructures is observed numerically. Generalizing the work of Park and Lee [PRL 95, 103902 (2005)], the results are interpreted in terms of plasmon-plasmon and plasmon-radiation couplings of different strength. A rich surface-plasmon-polarition bandstructure with ``gaps'' due to avoided crossings is seen. Super- and subradiant modes are found in the vicinity of those features.
Runge, Erich; Schwieger, Stephan; Vasa, Parinda
Band Structures in 106Pd
The high spin states of 106Pd have been investigated with in-beam ?-ray spectroscopic methods using the 100Mo(11B, 1p4n)106Pd reaction at a beam energy 60 MeV. All earlier known bands were extended considerably and additional bands were identified. On the basis of the experimental aligned angular momenta and the TRS calculations, the configurations of these bands were discussed respectively. Both two-quasineutron and two-quasiproton structures have been found in 106Pd. The non-yrast low-lying positive-parity band was interpreted as ?-vibrational band.
Yu, B. B.; He, C. Y.; Wu, X. G.; Zheng, Y.; Zhang, B.; Yao, S. H.; Wang, L. L.; Li, G. S.; Hao, X.; Zhu, L. H.; Shi, Y.; Xu, C.; Xu, F. R.; Wang, J. G.; Gu, L.; Zhang, M.
Area dependence of femtosecond laser-induced periodic surface structures for varying band gap materials after double pulse excitation
The formation of laser-induced periodic surface structures upon irradiation of titanium, silicon, and fused silica with multiple irradiation sequences consisting of parallel polarized Ti:sapphire femtosecond laser pulse pairs (pulse duration 50-150 fs, central wavelength ś800 nm) is studied experimentally. The temporal delay between the individual near-equal energy fs-laser pulses was varied between 0 and 5 ps with a temporal resolution of better than 0.2 ps. The surface morphology of the irradiated surface areas is characterized by means of scanning electron microscopy (SEM). In all materials a decrease of the rippled surface area is observed for increasing delays. The characteristic delay decay scale is quantified and related to material dependent excitation and energy relaxation processes.
H÷hm, S.; Rosenfeld, A.; Kr³ger, J.; Bonse, J.
Electronic band structure and Fermi surfaces of the quasi-two-dimensional monophosphate tungsten bronze, P4W12O44
The electronic structure of quasi-two-dimensional monophosphate tungsten bronze, P4W12O44, has been investigated by high-resolution angle-resolved photoemission spectroscopy and density functional theoretical calculations. Experimental electron-like bands around \\Gamma point and Fermi surfaces have similar shapes as predicted by calculations. Fermi surface mapping at different temperatures shows a depletion of density of states at low temperature in certain flat portions of the Fermi surfaces. These flat portions of the Fermi surfaces satisfy the partial nesting condition with incommensurate nesting vectors q_1 and q_2 , which leads to the formation of charge density waves in this phosphate tungsten bronzes. The setting up of charge density wave in these bronzes can well explain the anomaly observed in its transport properties.
Paul, S.; Ghosh, A.; Sato, T.; Sarma, D. D.; Takahashi, T.; Wang, E.; Greenblatt, M.; Raj, S.
High-impedance electromagnetic surfaces with a forbidden frequency band
A new type of metallic electromagnetic structure has been developed that is characterized by having high surface impedance. Although it is made of continuous metal, and conducts dc currents, it does not conduct ac currents within a forbidden frequency band. Unlike normal conductors, this new surface does not support propagating surface waves, and its image currents are not phase reversed.
Dan Sievenpiper; Lijun Zhang; Romulo F. Jimenez Broas; Nicolaos G. Alexopoulos; E. Yablonovitch
Multi-Band Frequency Selective Surfaces: Analysis.
National Technical Information Service (NTIS)
Present trends in antenna development go toward the integration on the same antenna aperture of more functions operating in separate frequency bands. In view of this, the necessity to look at new Frequency Selective Surface (FSS) concepts becomes evident....
A. Francavilla A. Neto D. Beckers G. Gerini S. Monni
Surface correlation effects in two-band strongly correlated slabs.
Using an extension of the Gutzwiller approximation for an inhomogeneous system, we study the two-band Hubbard model with unequal band widths for a slab geometry. The aim is to investigate the mutual effect of individual bands on the spatial distribution of quasi-particle weight and charge density, especially near the surface of the slab. The main effect of the difference in band width is the presence of two different length scales corresponding to the quasi-particle profile of each band. This is enhanced in the vicinity of the critical interaction of the narrow band where an orbitally selective Mott transition occurs and a surface dead layer forms for the narrow band. For the doped case, two different regimes of charge transfer between the surface and the bulk of the slab are revealed. The charge transfer from surface/center to center/surface depends on both the doping level and the average relative charge accumulated in each band. Such effects could also be of importance when describing the accumulation of charges at the interface between structures made of multi-band strongly correlated materials. PMID:24627895
Esfahani, D Nasr; Covaci, L; Peeters, F M
New compact and wide-band high-impedance surface
In this paper, we suggest a new high-impedance surface (HIS) for applications in antenna and microwave techniques. The resonant frequency of our structure is comparable with that of the multi-layered mushroom structure, however the resonant band of our structure is much wider. Another advantage is the angular and polarization stability of the resonance. We present an analytical model for the
C. R. Simovski; A. A. Sochava; S. A. Tretyakov
New view of the occupied band structure of Mo(112)
We present a comprehensive examination of the occupied surface-weighted band structure of Mo(112) along the two high-symmetry directions of the surface Brillouin zone, both from theoretical and experimental perspectives. The band structures are found to be significantly different for the states along the two high-symmetry directions and for the states with even and odd reflection parities with respect to the mirror planes. The present study suggests the existence of a number of surface-weighted bands along both high-symmetry directions. The complexity of the band structure near the Fermi level may impose potential difficulties in experimental determination of the electron-phonon coupling parameters based on the effective mass enhancement distortion (or kink) in the energy-band dispersion, in the vicinity of the Fermi level, for several surface resonance bands of Mo(112).
Fukutani, Keisuke; Hayashi, Hirokazu; Yakovkin, Ivan N.; Paudel, Tula R.; Habuchi, Takafumi; Hirayama, Daisuke; Jiang, Jian; Iwasawa, Hideaki; Shimada, Kenya; Wu, Ning; Tsymbal, Evgeny Y.; Losovyj, Ya. B.; Dowben, P. A.
Surface electronic bands of submonolayer Ge on Ag(111)
Germanium deposited on single-crystal Ag(111) substrates at about 1/3-monolayer coverage forms a stable (3ū3)R30? superstructure as seen by reflection high-energy electron diffraction. In situ angle resolved photoelectron spectroscopy reveals a rich band structure consisting of conelike features that cross the Fermi surface at the center (?» points) of the superstructure surface Brillouin zone (SBZ), exhibiting a high dispersion with the surface parallel wave vector. With the help of first-principles calculations, it can be inferred that most of the features are explained in terms of an Ag2Ge-ordered surface alloy corresponding to surface states localized in the first two layers. One of the bands has a saddle point near the M» point of the SBZ with a characteristic split-band behavior distinguishing Ge surface alloy from other similar systems.
Golias, E.; Xenogiannopoulou, E.; Tsoutsou, D.; Tsipas, P.; Giamini, S. A.; Dimoulas, A.
Match Recognition in Chromosome Band Structure.
An application of pattern recognition techniques to the problem of Drosophila chromosome band match detection has yielded a fast semi-automatic method of band structure comparison. The method locates most of the existing matches without excessive false al...
K. R. Castleman A. J. Welch
Susceptibilities for first principles band structures
We present a parallel implementation of a new method for calculating the unenhanced susceptibility proposed by us recently. Our implementation uses the first principles LMTO band structure within the tight binding approach as input to calculate the joint density of states. The susceptibility is then obtained by integrating over the product of the joint density of states and a Lindhard function. Our program, which has a simple friendly user interface, runs on the PC with a quadputer board, a Meiko Surface running CSTools powered either by T800 or i860 compute boards and the Intel iPSC/860 hypercube in Daresbury. Our method incorporates the troublesome matrix elements naturally and our results on Pd and Ni show that the decrease in ?( q) as we go away from the Brillouin zone centre is due mainly to the matrix elements rather than to the band energies.
Crockford, D. J.; Yeung, W.
Band Structures in ^230Th
Experimental evidence for the recently proposed phenomenon of condensation of rotational-aligned octupole phonons [1] has been observed in ^240Pu [2] and ^238U [3]. In order to study this phenomenon in ^230Th, an experiment has been carried out at ATLAS. The octupole band was extended up to spin 29. In addition, three positive-parity bands were observed for the first time. With increasing spin, the octupole band and the ground state band (gsb) start forming a smooth sequence of states with alternating spin and parity. Furthermore, the Routhian of the octupole band becomes lower than that of the gsb at rotational frequencies above 0.24 MeV. A band built on the second 0^+ state at 567 keV was discovered in this experiment, but it decays only to the gsb. [1] S. Frauendorf, Phys. Rev. C 77, 021304(R) (2008), [2] X. Wang et al., Phys. Rev. Lett. 102, 122501 (2009), [3] S. Zhu et al., Phys. Rev. C 81, 041306(R) (2010). This work was supported by DOE, Office of Nuclear Physics, under Contract No. DE-AC02-06CH11357.
Janssens, R. V. F.; Zhu, S.; Carpenter, M. P.; Ahmad, I.; Hoffman, C. R.; Khoo, T. L.; Kay, B. P.; Kondev, F. G.; Lauritsen, T.; Lister, C. J.; Ricard-McCutchan, E. A.; Seweryniak, D.; Toh, Y.; Ayangeakaa, D.; Frauendorf, S.; Garg, U.; Patel, D.; Matta, J.; Reviol, W.; Sarantites, D. G.; Wang, X.; Lalkovski, S.
An Evaluation of the ALOS PALSAR L-Band BackscatterŚAbove Ground Biomass Relationship Queensland, Australia: Impacts of Surface Moisture Condition and Vegetation Structure
Focusing on woody vegetation in Queensland, Australia, the study aimed to establish whether the relationship between Advanced Land Observing Satellite (ALOS) Phased Array L-band SAR (PALSAR) HH and HV backscattering coefficients and above ground biomass (AGB) was consistent within and between structural formations (forests, woodlands and open woodlands, including scrub). Across these formations, 2781 plot-based measurements (from 1139 sites) of
Richard Lucas; John Armston; Russell Fairfax; Rod Fensham; Arnon Accad; Joao Carreiras; Jack Kelley; Peter Bunting; Dan Clewley; Steven Bray; Dan Metcalfe; John Dwyer; M. Bowen; T. Eyre; M. Laidlaw; M. Shimada
A Second-Order Dual X-\\/Ka-Band Frequency Selective Surface
In this letter, a new technique for designing dual-band frequency selective surfaces with arbitrary bands of operation, with second-order band-pass responses at each band of operation, is presented and experimentally verified. The technique is based on utilizing a particular topology of a second-order band-pass microwave filter and synthesizing its constituting elements using periodic structures with inductive, capacitive, or resonant type
Mohsen Salehi; Nader Behdad
Inter-band Tunneling between Doped Topological Insulator Surface States
Thin films of 3D topological insulators (TIs) have been experimentally synthesized recently. Impurity doping of the TI surface has been reported to modify the position of the Fermi level and generate Rashba-like splitting of the surface band structure. Our research uses a Non-Equilibrium Green's Function (NEGF) method to simulate inter-surface transport properties for TI thin films. A tight-binding model is established by discretizing a 4 x 4 k.p Hamiltonian for 3D TIs. Because of confinement, thin TI slabs of several nanometers allows inter-surface tunneling at quantum number matching states. The tunneling intensity can be tuned by surface Coulomb impurity doping or applying an external bias. Unlike regular topologically trivial surface states, inter-band tunneling between TI surfaces presents a conduction minimum when the dispersions of the two surfaces align perfectly over each other. The suppression of transport originates from the momentum coupling with time reversal symmetry, leading to significant non-linear I-V properties for the P-N tunneling at forward bias. This leads to a NDR current minimum when an external bias completely compensates the built-in potential. The study on inter-surface tunneling in TI thin films benefits the understanding of the transport behavior of TI surface states, which calls for further experimental investigations in the future.
Yin, Gen; Wickramaratne, Darshana; Lake, Roger
Structure of rotational bands in 253No
In-beam gamma-ray and conversion electron spectroscopic studies have been performed on the 253 No nucleus. A strongly coupled rotational band has been identified and the improved statistics allows an assignment of the band structure as built on the ensuremath 9/2^-[734]_{?} ground state. The results agree with previously known transition energies but disagree with the tentative structural assignments made in earlier work.
Herzberg, R.-D.; Moon, S.; Eeckhaudt, S.; Greenlees, P. T.; Butler, P. A.; Page, T.; Afanasjev, A. V.; Amzal, N.; Bastin, J. E.; Becker, F.; Bender, M.; Bruyneel, B.; Cocks, J. F. C.; Darby, I. G.; Dorvaux, O.; Eskola, K.; Gerl, J.; Grahn, T.; Gray-Jones, C.; Hammond, N. J.; Hauschild, K.; Heenen, P.-H.; Helariutta, K.; Herzberg, A.; Hessberger, F.; Houry, M.; H³rstel, A.; Humphreys, R. D.; Jones, G. D.; Jones, P. M.; Julin, R.; Juutinen, S.; Kankaanpõõ, H.; Kettunen, H.; Khoo, T. L.; Korten, W.; Kuusiniemi, P.; Lecoz, Y.; Leino, M.; Leppõnen, A.-P.; Lister, C. J.; Lucas, R.; Muikku, M.; Nieminen, P.; Nyman, M.; Page, R. D.; Page, T.; Pakarinen, J.; Pritchard, A.; Rahkila, P.; Reiter, P.; Sandzelius, M.; Saren, J.; Schlegel, Ch.; Scholey, C.; Theisen, Ch.; Trzaska, W. H.; Uusitalo, J.; Wiens, A.; Wollersheim, H. J.
Tunable band structure effects on ballistic transport in graphene nanoribbons
Graphene nanoribbons (GNR) in mutually perpendicular electric and magnetic fields are shown to exhibit dramatic changes in their band structure and electron transport properties. A strong electric field across the ribbon induces multiple chiral Dirac points, closing the semiconducting gap in armchair GNRs. A perpendicular magnetic field induces partially formed Landau levels as well as dispersive surface-bound states. Each of
Oleksiy Roslyak; Godfrey Gumbs; Danhong Huang
Band Structure and Electrical Conductivity in Semiconductors
NSDL National Science Digital Library
In this experiment, we will, 1. understand how conductivity in semiconductors depends on carrier concentration and mobility, and how these depend on temperature, 2. distinguish between intrinsic and extrinsic temperature regimes and identify the applicable temperature range from an examination of measured data, 3. appreciate and utilize the advantages of the four-probe resistance measurement technique, 4. calculate the energy band gap for doped Si and pure Ge, 5. calculate the temperature dependent coefficient of the majority carriers, 6. through experimental realizations, appreciate a physical understanding of the band gap structure of semiconductors.
Khalid, Asma; Anwar, Muhammad S.; Zia, Wasif
Tests on S-Band Superconducting Niobium Prototype Accelerator Structures
The fabrication, processing, and measurement of two S-band niobium prototype electron accelerator structures are discussed. Maximum surface magnetic fields were typically between 250 and 550 Oe, corresponding to average energy gradients between 4.6 and 6.5 MeV\\/m, with Q0 values typically greater than 5 ?? 109. The structures which were electropolished gave more reproducible results than those which were chemically polished.
P. Kneiselt; C. Lyneis; J. P. Turneaure
Band Structure Measurements of Bottom-up Fabricated Graphene Nanoribbons
Along with the growing interest in graphene, other low-dimensional carbon nanostructures are currently in the focus of research since these materials offer a wide variety of properties interesting e.g. for nanotechnology application. Among these carbon systems, quasi-one-dimensional graphene nanoribbons (GNR) introduce a possibility to tune the electronic structure - for example, GNRs exhibit a band gap which is inversely proportional to their width and can thus be adjusted over a wide range. While many theoretical studies have been published on the band structure of GNRs, experiments are usually limited by the quality of the GNRs' fabrication, e.g. using lithography or unzipping of carbon nanotubes. In order to avoid defects and irregular edges that are inevitable in these methods, lately a surface-assisted bottom-up synthesis has been demonstrated which yields quasi-perfect GNR structures. [1] In the present study we employ complementary surface-sensitive spectroscopies to investigate occupied and unoccupied bands and the band gap in an armchair GNR which has been synthesized on the Au(111) surface. DFT calculations were performed to obtain a thorough understanding of the nature of the observed states.[4pt] [1] J. Cai et al., Nature (London) 466, 470-473 (2010)
Bronner, Christopher; Leyssner, Felix; Meyer, Stephan; Utecht, Manuel; Klamroth, Tillmann; Saalfrank, Peter; Tegeder, Petra
X-Band Photonic Band-Gap Accelerator Structure Breakdown Experiment
In order to understand the performance of photonic band-gap (PBG) structures under realistic high gradient, high power, high repetition rate operation, a PBG accelerator structure was designed and tested at X band (11.424 GHz). The structure consisted of a single test cell with matching cells before and after the structure. The design followed principles previously established in testing a series of conventional pillbox structures. The PBG structure was tested at an accelerating gradient of 65 MV/m yielding a breakdown rate of two breakdowns per hour at 60 Hz. An accelerating gradient above 110 MV/m was demonstrated at a higher breakdown rate. Significant pulsed heating occurred on the surface of the inner rods of the PBG structure, with a temperature rise of 85 K estimated when operating in 100 ns pulses at a gradient of 100 MV/m and a surface magnetic field of 890 kA/m. A temperature rise of up to 250 K was estimated for some shots. The iris surfaces, the location of peak electric field, surprisingly had no damage, but the inner rods, the location of the peak magnetic fields and a large temperature rise, had significant damage. Breakdown in accelerator structures is generally understood in terms of electric field effects. These PBG structure results highlight the unexpected role of magnetic fields in breakdown. The hypothesis is presented that the moderate level electric field on the inner rods, about 14 MV/m, is enhanced at small tips and projections caused by pulsed heating, leading to breakdown. Future PBG structures should be built to minimize pulsed surface heating and temperature rise.
Marsh, Roark A.; /MIT /MIT /NIFS, Gifu /JAERI, Kyoto /LLNL, Livermore; Shapiro, Michael A.; Temkin, Richard J.; /MIT; Dolgashev, Valery A.; Laurent, Lisa L.; Lewandowski, James R.; Yeremian, A.Dian; Tantawi, Sami G.; /SLAC
Quantum Interference in Artificial Band Structures
Magnetotransport experiments on two-dimensional electron systems with an atomically precise, one-dimensional potential modulation reveal striking quantum interference oscillations. Within a semiclassical framework, they are recognized either as self-interference along closed orbits, many of them rendered possible by magnetic breakdown between Fermi contour segments of the artificial band structure, or as interference-enhanced backscattering. The known commensurability oscillations appear as a special
R. A. Deutschmann; W. Wegscheider; M. Rother; M. Bichler; G. Abstreiter; C. Albrecht; J. H. Smet
Magnon band structure of periodic composites
innodata J. O. VASSEUR et al. MAGNON BAND STRUCTURE OF PERIODIC COMPOSITES We calculate the spin-wave spectra of two-dimensional composite materials consisting of periodic square arrays of parallel cylinders made of a ferromagnetic material embedded in a ferromagnetic background. Each material is described by its spontaneous magnetization MS and exchange constant A. An external static magnetic field is applied along the direction of the cylinders and both ferromagnetic materials are assumed to be magnetized parallel to this magnetic field. We consider the spin-waves propagation in the plane perpendicular to the cylinders. We reveal the existence of gaps in the magnon band structure of composite systems such as the periodic array of Fe cylinders in an EuO matrix. We investigate the existence of these gaps in relation to the physical parameters of the materials involved. We also study the influence of the lattice parameter (i.e., the square array periodicity) and the effect of the filling fraction of the cylinders on the magnon band structure.
Vasseur, J. O.; Dobrzynski, L.; Djafari-Rouhani, B.; Puszkarski, H.
Quantum Transport with Band-Structure and Schottky Contacts
We describe (i) a parametrized single-band model that mimics the full-band -valley non-parabolicity, (ii) a method for calculating the semi-classical and quantum electron charge with the sp3s* band-structure model, and (iii) a Schottky contact model compatible with any localized orbital band-structure model.
Lake, R.; Klimeck, G.; Bowen, R. C.; Jovanovic, D.; Blanks, D.; Swaminathan, M.
Lamb wave band gaps in a homogenous plate with periodic Gaussian surfaces
The Lamb wave band structure of a one-dimensional thin plate with periodic Gaussian surfaces is calculated based on the eigen-mode matching theory (EMMT) method. The finite element method is also employed to calculate the transmission power spectra and the band structure, which are both in good agreement with the results of the EMMT method. In contrast with the straight stubs, the low-frequency band gap of the system with the Gaussian surfaces is wider, when the Gaussian domain's height and area are equal to those of the stub, and the two systems' main plate size and materials are the same. This can be confirmed by the æspring-mass' model, which can be used to estimate the resonant frequency. We also investigate the effects of the geometrical parameters on band structure, including the height of the Gaussian domain, the plate thickness and the filling fraction. The results suggest that the band gaps have a close relevance to them.
Ming, Chen; Chen, Jiujiu; Han, Xu; Zhang, Hongbo
Band bending and electrical transport at chemically modified silicon surfaces
High resolution electron energy loss spectroscopy (HREELS) and electrical transport measurements have been used to investigate how various chemical modifications give rise to band bending and alter the conductivity of Si(111) surfaces. HREELS is a sensitive probe of band bending through observations of the low frequency free carrier plasmon mode. For hydrogen terminated surfaces, prepared by the standard etch in ammonium flouride, HREELS measurements on both n and n+ substrates are consistent with nearly flat bands. Chlorination of these surfaces results in substantial upward band bending due to the strong electron withdrawing nature of the chlorine, driving the surface into inversion. The presence of this inversion layer on high resistivity n-type samples is observed through a substantial enhancement of the surface conductivity (relative to the H-terminated surface), as well as through broadening of the quasi-elastic peak in the HREELS measurements. We have also begun to examine organically modified silicon surfaces, prepared by various wet chemical reactions with the H-terminated surface. Decyl modified Si(111) surfaces are seen to exhibit a small degree of band bending, attributed to extrinsic defect states cause by a small degree of oxidation accompanying the modification reaction. The prospects of using conductivity as an in-situ monitor of the rate of these reactions will be discussed.
Lopinski, Greg; Ward, Tim; Hul'Ko, Oleksa; Boukherroub, Rabah
Micromechanics of slip bands on a free surface
NASA Technical Reports Server (NTRS)
A micromechanics analysis for the formation and propagation of slip bands on the free surface of a polycrystal under monotonic loading is presented. For the growth of slip bands, the analysis satisfies the conditions of both equilibrium and displacement continuity, as well as the relation between slip and the resolved shear stress throughout the polycrystal. Numerical calculations show how the microstress field causes the concentration of plastic deformation in discrete sliding bands and give results which are in good qualitative agreement with known slip band observations on aluminum single crystals.
Lin, S. R.; Lin, T. H.
Flat photonic surface bands pinned between Dirac points.
We point out that 2D photonic crystals (PhCs) can support surface bands that are pinned to Dirac points. These bands can be made very flat by optimizing the parameters of the system. Surface modes are found at the interface of two different cladding materials: one is a PhC with Dirac linear dispersion for the TE mode, and the other is a PhC that has a broad TE gap at the Dirac frequency. PMID:23258072
Juki?, Dario; Buljan, Hrvoje; Lee, Dung-Hai; Joannopoulos, John D; Solja?i?, Marin
Thermal Infrared Spectral Band Detection Limits for Unidentified Surface Materials
Infrared emission spectra recorded by airborne or satellite spectrometers can be searched for spectral features to determine the composition of rocks on planetary surfaces. Surface materials are identified by detections of characteristic spectral bands. We show how to define whether to accept an observed spectral feature as a detection when the target material is unknown. We also use remotely sensed spectra measured by the Thermal Emission Spectrometer (TES) and the Spatially Enhanced Broadband Array Spectrograph System to illustrate the importance of instrument parameters and surface properties on band detection limits and how the variation in signal-to-noise ratio with wavelength affects the bands that are most detectable for a given instrument. The spectrometer's sampling interval, spectral resolution, signal-to-noise ratio as a function of wavelength, and the sample's surface properties influence whether the instrument can detect a spectral feature exhibited by a material. As an example, in the 6-13 micrometer wavelength region, massive carbonates exhibit two bands: a very strong, broad feature at approximately 6.5 micrometers and a less intense, sharper band at approximately 11.25 micrometers. Although the 6.5-micrometer band is stronger and broader in laboratory-measured spectra, the 11.25-micrometer band will cause a more detectable feature in TES spectra.
Kirkland, Laurel E.; Herr, Kenneth C.; Salisbury, John W.
Strong discontinuities in the complex photonic band structure of transmission metallic gratings
Complex photonic band structures (CPBS) of transmission metallic gratings with rectangular slits are shown to exhibit strong discontinuities that are not evidenced in the usual energetic band structures. These discontinuities are located on Wood-Rayleigh's anomalies and reveal unambiguously two different types of resonances, which are identified as horizontal and vertical surface-plasmon resonances. Spectral position and width of peaks in the
S. Collin; F. Pardo; R. Teissier; J.-L. Pelouard
Segmental structure in banded mongoose calls
PubMed Central
In complex animal vocalizations, such as bird or whale song, a great variety of songs can be produced via rearrangements of a smaller set of 'syllables', known as 'phonological syntax' or 'phonocoding' However, food or alarm calls, which function as referential signals, were previously thought to lack such combinatorial structure. A new study of calls in the banded mongoose Mungos mungo provides the first evidence of phonocoding at the level of single calls. The first portion of the call provides cues to the identity of the caller, and the second part encodes its current activity. This provides the first example known in animals of something akin to the consonants and vowels of human speech. See research article http://www.biomedcentral.com/1741-7007/10/97
Infrared emission spectra recorded by airborne or satellite spectrometers can be searched for spectral features to determine the composition of rocks on planetary surfaces. Surface materials are identified using detections of characteristic spectral bands. Here we show how to define whether to accept an observed spectral feature as a detection when the target material is unknown. We also use remotely
Laurel E. Kirkland; Kenneth C. Herr; John W. Salisbury
The effect of surface stoichiometry on the band gap of the pyrite FeS2(100) surface
Iron pyrite (FeS2) is experiencing a resurgence of interest for use in solar photovoltaic and photoelectrochemical cells. The main hurdle to the use of pyrite is the low open-circuit voltage of pyrite devices, which may result from gap states created by surface and bulk defects. Recently, systematic spin-polarized DFT calculations were performed for a series of pyrite FeS2(100) surfaces to clarify the effect of surface stoichiometry on stability, electronic structure, and band gap. It was found that while stoichiometric and S-poor FeS2(100) surfaces are semiconductors with band gaps of 0.56-0.72 eV, S-rich surfaces are small-gap semiconductors (Eg< 0.3 eV) or metals. The stoichiometric FeS2(100) surface is spin polarized in the topmost layer (2 ?B per Fe) and displays a band of Fe dz^2 gap states centered 0.2 eV above the valence band edge. Our calculations suggest that the low open-circuit voltage of pyrite solar cells may result from a narrowed surface band gap. S-poor surfaces may provide larger photovoltages than S-rich surfaces. The segregation process of sulfur vacancy under different surface conditions are also being studied, so as to provide useful guidelines for the design and fabrication of better pyrite photovoltaic materials and devices.
Zhang, Yanning; Hu, Jun; Law, Matt; Wu, Ruqian
Band Structure Engineering for Electron Tunneling Devices
Negative differential resistance devices based on electron tunneling have potential applications in the frequency range above 200 GHz, where conventional field -effect and bipolar transistors have not yet been able to operate. High-speed performance depends primarily on increasing the peak current density and reducing the parasitic resistance. The room temperature peak-to-valley current ratio also must be maximized and the peak voltage should be reduced to reduce the power dissipated in the device. Two-terminal negative differential resistance devices are also stepping stones in the development of three-terminal devices based on coherent electron transport. In the future, these novel devices may offer the prospect of continued downscaling of integrated circuit components to nanometer dimensions, where conventional device concepts apparently fail. We apply standard techniques of molecular beam epitaxy to the growth of novel semiconductor heterostructures for electron tunneling devices. The samples are characterized by current and conductance values, measured as a function of device bias and temperature. The observed electrical characteristics are interpreted in terms of the energy band alignments of the heterojunctions and the energy levels and elastic tunneling current flows predicted by calculations based on a two-band model of the bulk band structures of the constituent materials. Such experiments have yielded nine new results that bear on the development of quantum-effect devices: observation of intervalley coupling at a GaAs/AlAs heterointerface, the crystallographic orientation dependence of the excess valley current in AlAs tunneling barriers, negative differential resistance at room temperature in single tunneling barriers of AlGaSb, the longest coherence distance (24 nm) of any resonant tunneling device (InAs/AlSb) resonant tunneling of holes in GaSb/AlSb quantum wells, interband tunneling in polytype InAs/AlSb/GaSb heterostructures, resonant interband tunneling in this system with low-temperature peak-to-valley current ratios greater than 60:1, substantial negative differential conductance in polytype quantum wells wider than 100 nm, and resonant interband coupling in a single -barrier InAs/GaSb/InAs structure. The achievement of large peak-to-valley ratios in wide InAs quantum wells suggests the possibility of high-speed three-terminal tunneling devices.
Beresford, John Roderic
Venus banded terrain - Tectonic models for band formation and their relationship to lithospheric thermal structure
Two classes of tectonic models for the formation of band structure on Venus mountain ranges are quantitatively evaluated: folding models and extensional models. The characteristics of banded terrain on Ishtar Terra are reviewed, particularly the evidence for a tectonic origin and such important details of band geometry as the spacing between adjacent bands. The tectonic models are tested against these observed features, and it it shown that both classes of models are possible explanations of banded terrain as long as the outer elastic-brittle layer of the Venus crust is at most a few kilometers thick. A general assessment is given of hypotheses for the origin of banded terrain and of the relationship between mechanical models for band formation and the thermal structure of the Venus lithosphere.
Solomon, S. C.; Head, J. W.
Structure of Oxide Surfaces
Surfaces of metal oxides are of crucial importance for a variety of technological applications such as heterogeneous catalysis, thin film growth, gas sensing, and corrosion prevention. Due to the complexities of oxides in crystal structure and electronic structure, however, the surface science of oxides lags far behind that of metals or semiconductors. Conventional surface-science techniques are usually limited to surfaces of single crystals of conductors. Metal oxides are usually good insulators, making them difficult for conventional surface science techniques. On the other hand, the complex atomic structures of oxides results in too many structural parameters to be determined by spectroscopy or diffraction methods. We will show that the surface structure of oxides can be directly imaged and measured at the sub-angstrom scale using aberration-corrected transmission electron microscopy. The atomic positions of oxide surfaces can be measured to an accuracy of picometers, comparable to that obtained by conventional surface science techniques on single crystals.[4pt] [1] R. Yu, L.H. Hu, Z.Y. Cheng, Y.D. Li, H.Q. Ye, J. Zhu, Phys. Rev. Lett., 105, 226101 (2010).[0pt] [2] M.R. He, R. Yu, J. Zhu, Angew. Chem. Int. Ed., 124, 7864 (2012).
Yu, Rong
Band structure quantization in nanometer sized ZnO clusters
Nanometer sized ZnO clusters are produced in the gas phase and subsequently deposited on clean Au(111) surfaces under ultra-high vacuum conditions. The zinc blende atomic structure of the approximately spherical ZnO clusters is resolved by high resolution scanning transmission electron microscopy. The large band gap and weak n-type conductivity of individual clusters are determined by scanning tunnelling microscopy and spectroscopy at cryogenic temperatures. The conduction band is found to exhibit clear quantization into discrete energy levels, which can be related to finite-size effects reflecting the zero-dimensional confinement. Our findings illustrate that gas phase cluster production may provide unique possibilities for the controlled fabrication of high purity quantum dots and heterostructures that can be size selected prior to deposition on the desired substrate under controlled ultra-high vacuum conditions.Nanometer sized ZnO clusters are produced in the gas phase and subsequently deposited on clean Au(111) surfaces under ultra-high vacuum conditions. The zinc blende atomic structure of the approximately spherical ZnO clusters is resolved by high resolution scanning transmission electron microscopy. The large band gap and weak n-type conductivity of individual clusters are determined by scanning tunnelling microscopy and spectroscopy at cryogenic temperatures. The conduction band is found to exhibit clear quantization into discrete energy levels, which can be related to finite-size effects reflecting the zero-dimensional confinement. Our findings illustrate that gas phase cluster production may provide unique possibilities for the controlled fabrication of high purity quantum dots and heterostructures that can be size selected prior to deposition on the desired substrate under controlled ultra-high vacuum conditions. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr33989k
Schouteden, Koen; Zeng, Yu-Jia; Lauwaet, Koen; Romero, Christian P.; Goris, Bart; Bals, Sara; van Tendeloo, Gustaaf; Lievens, Peter; Van Haesendonck, Chris
Band Structures in Doubly Odd 126I
The high-spin states in 126I have been investigated by using in-beam ?-ray spectroscopy with the 124Sn(7Li, 5n)126I reaction at a beam energy of 48 MeV. The previously known level scheme of 126I has been extended and modified considerably by adding about 60 new ?-transitions and establishing 5 new bands. The backbendings in the yrast band 1 and the yrare band 3 are found both due to a pair of h11/2 neutrons alignment. The configurations for the newly identified bands 2, 4, 5 and 6 have been assigned.
Zheng, Y.; Wu, X. G.; He, C. Y.; Li, G. S.; Hao, X.; Wang, L. L.; Liu, Y.; Li, X. Q.; Pan, B.; Yu, B. B.; Wang, L.; Zhu, L. H.
Polariton-based band gap and generation of surface acoustic waves in acoustic superlattice lithium niobate
We report the presence of surface acoustic wave (SAW) band gap on acoustic superlattice (ASL) in a single-crystal lithium niobate structure. The band gap behavior is determined by calculating the SAW band structure and also by simulating the transmission of an acoustic wave through a finite length section of ASL using finite element analysis. The calculated band gap appears at a frequency twice the value expected from purely acoustic Bragg scattering. We have identified the band gap as originating from a polariton-based mechanism due to the coupling between the electromagnetic wave and the surface vibrations. We have examined the influence of the band gap on SAW generation with the ASL and have shown that the calculated frequency resonance of the SAW lies in the vicinity of the upper stop-band edges. This results in the localization of the SAW in the ASL. Experimental confirmation is achieved through direct measurement of the SAW displacement by laser vibrometry on an actual ASL SAW transducer. The localization of generated SAW to the ASL transducer is observed confirming the prediction of the existence of a band gap.
Yudistira, Didit; Boes, Andreas; Janner, Davide; Pruneri, Valerio; Friend, James; Mitchell, Arnan
Surface electronic structure of silicon dioxide
By using the empirical tight-binding method, we have investigated the surface electronic structure of silicon dioxide. The two-center energy parameters of the tight-binding Hamiltonian are obtained from the first-principles band calculations and the surfaces of silicon dioxide are represented by the ideal (111), (100), and (110) surfaces of ? crystobalite. For Si-terminated SiO2 surfaces we find surface states in the optical gap and conduction band. Depending upon the degree of oxygen coverage the localized state in the optical gap may be half-filled or empty. In the case of the full oxygen coverage (i.e., the O-terminated SiO2 surface) these surface states are removed and new surface states originating from the oxygen atoms attached to the surface silicons are created in the valence band. Recent experimental data related to the SiO2 surface are outlined. We note that the dangling-bond surface states near the conduction-band edge are also observed experimentally. Furthermore, we examine the ultraviolet photoelectron spectroscopy and electron energy-loss spectroscopy (ELS). Our calculations favor the existence of Si - Si bonds near the SiO2 surface which account for the features lying in the lower part of the ELS spectrum.
Ciraci, S.; Ellialtio?lu, S.
Phase structures, transition behavior and surface alignment in polymers containing rigid-rod backbones with flexible side chains Part VI Novel band structures in a combined main-chain\\/side-chain liquid crystalline polyester: From liquid crystal to crystalline states
Physical origins of banded structures appearing on different length scales have been investigated using polarized light and atomic force microscopies (PLM and AFM), polarized Fourier Transform infrared spectroscopy (FT-IR) and wide angle X-ray diffraction (WAXD) in a combined main-chain\\/side-chain liquid crystalline (LC) polyester, PEFBP(n). This series of PEFBP(n) polymers was synthesized from the polycondensation of 2,2'-bis(trifluoromethyl)-4,4'-biphenyldicarbonyl chloride with 2,2'-bis{?-[4-(4-cyanophenyl)-phenyoxy]-n-alkoxycarbonyl]}-4,4'-biphenyl diol.
J. J. Ge; J. Z. Zhang; Wensheng Zhou; C. Y. Li; Shi Jin; B. H. Calhoun; Shy-Yeu Wang; F. W. Harris; S. Z. D. Cheng
Large spin splitting of metallic surface-state bands at adsorbate-modified gold/silicon surfaces
Finding appropriate systems with a large spin splitting of metallic surface-state band which can be fabricated on silicon using routine technique is an essential step in combining Rashba-effect based spintronics with silicon technology. We have found that originally poor structural and electronic properties of the surface can be substantially improved by adsorbing small amounts of suitable species (e.g., Tl, In, Na, Cs). The resultant surfaces exhibit a highly-ordered atomic structure and spin-split metallic surface-state band with a momentum splitting of up to 0.052 ┼?1 and an energy splitting of up to 190?meV at the Fermi level. The family of adsorbate-modified surfaces, on the one hand, is thought to be a fascinating playground for exploring spin-splitting effects in the metal monolayers on a semiconductor and, on the other hand, expands greatly the list of material systems prospective for spintronics applications.
Bondarenko, L. V.; Gruznev, D. V.; Yakovlev, A. A.; Tupchaya, A. Y.; Usachov, D.; Vilkov, O.; Fedorov, A.; Vyalikh, D. V.; Eremeev, S. V.; Chulkov, E. V.; Zotov, A. V.; Saranin, A. A.
For over thirty years research geneticists have been studying the chromosomes of the species Drosophila (fruitfly). These chromosomes, suitably prepared and stained, have an appearance similar to earthworms with light and dark bands around them. They are ...
Engineering the Electronic Band Structure for Multiband Solar Cells
Using the unique features of the electronic band structure of GaNxAs1-x alloys, we have designed, fabricated and tested a multiband photovoltaic device. The device demonstrates an optical activity of three energy bands that absorb, and convert into electrical current, the crucial part of the solar spectrum. The performance of the device and measurements of electroluminescence, quantum efficiency and photomodulated reflectivity are analyzed in terms of the Band Anticrossing model of the electronic structure of highly mismatched alloys. The results demonstrate the feasibility of using highly mismatched alloys to engineer the semiconductor energy band structure for specific device applications.
Lopez, N.; Reichertz, L.A.; Yu, K.M.; Campman, K.; Walukiewicz, W.
Photonic bands in two-dimensional microplasma arrays. I. Theoretical derivation of band structures of electromagnetic waves
Two theoretical approaches appropriate for two-dimensional plasma photonic crystals reveal dispersions of propagating waves including photonic (electromagnetic) band gaps and multiflatbands. A modified plane-wave expansion method yields dispersions of collisional periodical plasmas, and the complex-value solution of a wave equation by a finite difference method enables us to obtain dispersions with structure effects in an individual microplasma. Periodical plasma arrays form band gaps as well as normal photonic crystals, and multiflatbands are present below the electron plasma frequency in the transverse electric field mode. Electron elastic collisions lower the top frequency of the multiflatbands but have little effect on band gap properties. The spatial gradient of the local dielectric constant resulting from an electron density profile widens the frequency region of the multiflatbands, as demonstrated by the change of surface wave distributions. Propagation properties described in dispersions including band gaps and flatbands agree with experimental observations of microplasma arrays.
Sakai, Osamu; Sakaguchi, Takui; Tachibana, Kunihide [Department of Electronic Science and Engineering, Kyoto University, Kyoto-daigaku Katsura, Nishikyo-ku, Kyoto 615-8510 (Japan)
A dual-band flexible frequency selective surface with miniaturized elements and maximally flat (Butterworth) response
A dual-band flexible frequency selective surface (FSS) with miniaturized elements and maximally flat (Butterworth) response is presented in this paper. It is composed of three metallic layers, which are fabricated on thin flexible polyimide substrates and bonded together using thin bonding films. The overall thickness of the proposed structure is only about 0.3 mm, making it an attractive choice for conformal FSS applications. All the three layers can constitute a miniaturized-element FSS (MEFSS) and produce the first pass-band with miniaturization property, while the up and bottom layers can constitute a symmetric biplanar FSS and produce the second pass-band with maximally flat (Butterworth) response. The two pass-bands are independent and there is a wide band spacing up to 30 GHz between them. The principles of operation, the simulated results by using the vector modal matching method, and the experimental values of the fabricated prototype are also presented and discussed.
Wang, Xiu-Zhi; Gao, Jin-Song; Xu, Nian-Xi; Liu, Hai
Wide band gap photonic structures in dichromate gelatin emulsions
The authors report the fabrication of wide band gap photonic crystals with planar structures in dichromate gelatin emulsions using a two-beam holographic method. By exploiting the differential swelling of the gelatin, planar structures with gradient spacing are fabricated. The crystals exhibit high efficiencies and wide band gaps in the visible range. The authors model the planar gelatin system by an
Rui Ma; Jun Xu; Wing Yim Tam
Frequency-selective surfaces to enhance performance of broad-band reconfigurable arrays
We present a novel frequency-selective surface (FSS) design aimed at enhancing the performance of broad-band reconfigurable antenna apertures. In particular, reconfigurable printed dipole arrays are examined in the presence of a multilayer FSS. Of particular interest is the design of FSS structures whose reflection coefficient has prespecified phase response over a broad set of frequencies. Previous FSSs primarily considered designs
Yunus E. Erdemli; Kubilay Sertel; Roland A. Gilbert; Daniel E. Wright; John L. Volakis
Tunable band gap in germanene by surface adsorption
Opening a sizable band gap in the zero-gap germanene without heavy loss of carrier mobility is a key issue for its application in nanoelectronic devices such as high-performance field effect transistors (FETs) operating at room temperature. Using the first-principles calculations, we find a band gap is opened at the Dirac point in germanene by single-side adsorption of alkali metal (AM) atoms. This band gap is tunable by varying the coverage and the species of AM atoms, ranging from 0.02 to 0.31 eV, and the maximum global band gap is 0.26 eV. Since the effective masses of electrons and holes in germanene near the Dirac point after surface adsorption (ranging from 0.005 to 0.106me) are small, the carrier mobility is expected not to degrade much. Therefore germanene is a potential candidate of effective FET channel operating at room temperature upon surface adsorption.
Ye, Meng; Quhe, Ruge; Zheng, Jiaxin; Ni, Zeyuan; Wang, Yangyang; Yuan, Yakun; Tse, Geoffrey; Shi, Junjie; Gao, Zhengxiang; Lu, Jing
Banded surface flow maintained by convection in a model of the rapidly rotating giant planets
In three-dimensional numerical simulations of a rapidly rotating Boussinesq fluid shell, thermally driven convection in the form of columns parallel to the rotation axis generates an alternately directed mean zonal flow with a cylindrical structure. The mean structure at the outer spherical surface consists of a broad eastward flow at the equator and alternating bands of westward and eastward flows at higher latitudes in both hemispheres. The banded structure persists even though the underlying convective motions are time-dependent. These results, although still far from the actual motions seen on Jupiter and Saturn, provide support for theoretical suggestions that thermal convection can account for the remarkable banded flow structures on these planets.
Sun, Z.-P.; Schubert, G.; Glatzmaier, G. A.
Tuning the electronic band structure of PCBM by electron irradiation
Tuning the electronic band structures such as band-edge position and bandgap of organic semiconductors is crucial to maximize the performance of organic photovoltaic devices. We present a simple yet effective electron irradiation approach to tune the band structure of [6, 6]-phenyl-C61-butyric acid methyl ester (PCBM) that is the most widely used organic acceptor material. We have found that the lowest unoccupied molecular orbital (LUMO) level of PCBM up-shifts toward the vacuum energy level, while the highest occupied molecular orbital (HOMO) level down-shifts when PCBM is electron-irradiated. The shift of the HOMO and the LUMO levels increases as the irradiated electron fluence increases. Accordingly, the band-edge position and the bandgap of PCBM can be controlled by adjusting the electron fluence. Characterization of electron-irradiated PCBM reveals that the variation of the band structure is attributed to the molecular structural change of PCBM by electron irradiation.
Multi-band, highly absorbing, microwave metamaterial structures
A further example of multi-band absorption using ultra-thin, polarization-insensitive, wide-angled metamaterial absorbers that operate in multi-frequency bands within the microwave regime is presented in this work. The basic structure geometry is utilised to create multi-band highly absorbing structures by incorporating the scalability property of the metamaterials. Simulation results verify the structure's ability for high absorption. The multi-band absorbers are promising candidates as absorbing elements in scientific and technical applications because of its multi-band absorption, polarization insensitivity, and wide-angle response. Finally, the current distributions for those structures are presented to gain a better insight into the physics behind the multiple absorption mechanism.
Kollatou, T. M.; Dimitriadis, A. I.; Assimonis, S. D.; Kantartzis, N. V.; Antonopoulos, C. S.
Valence band structure of the icosahedral Ag-In-Yb quasicrystal
The valence band structure of the icosahedral (i) Ag-In-Yb quasicrystal, which is isostructural to the binary i-Cd-Yb system, is investigated by ultraviolet photoemission spectroscopy (UPS). Experimental results are compared with electronic-structure calculations of a cubic approximant of the same phase. UPS spectra from the fivefold, threefold, and twofold i-Ag-In-Yb surfaces reveal that the valence band near to the Fermi level is dominated by Yb 4f-derived states, in agreement with calculations. The spectra also exhibit peaks which are surface core level shifted, caused by changes in the electronic structure in surface layers. Calculations yield a pseudogap in the density of states due to a hybridization of the Yb 5d band with the Ag 5p and In 5p bands. Both experimental and calculated band features are very similar to those of Cd-Yb. The modification of the band structure after surface treatment by sputtering and by oxidation is also studied. Additionally, the work function of i-Ag-In-Yb measured from the width of UPS spectrum is found to be almost unaffected by surface orientation, but increases after sputtering or oxidation.
Sharma, H. R.; Simutis, G.; Dhanak, V. R.; Nugent, P. J.; McGrath, R. [Surface Science Research Centre and Department of Physics, University of Liverpool, Liverpool L69 3BX (United Kingdom); Cui, C. [Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577 (Japan); Shimoda, M. [National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan); Tsai, A. P. [Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577 (Japan); National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan); Ishii, Y. [Department of Physics, Chuo University, Kasuga, Tokyo 112-8551 (Japan)
Fractal FSS: a novel dual-band frequency selective surface
The multiband properties of self-similar fractals can be advantageously exploited to design multiband frequency selective surfaces (FSS). A Sierpinski dipole FSS has been analyzed and measured and the results show an interesting dual-band behavior. Furthermore a near-field measurement technique is applied to characterize the FSS response to different angles of incidence. Finally, it is shown that it is possible to
Jordi Romeu; Yahya Rahmat-Samii
Effect of surface stoichiometry on the band gap of the pyrite FeS2(100) surface
Systematic spin-polarized density functional calculations were performed for a series of pyrite FeS2(100) surfaces to clarify the effect of surface stoichiometry on stability, electronic structure, and band gap. While the bulk FeS2 is nonmagnetic, the topmost layer of the stoichiometric and S-deficient FeS2(100) surfaces are spin polarized, with magnetic moments of 2 ?B or 4 ?B per Fe. These surfaces also have sizeable band gaps, 0.56-0.72 eV; they hence can be useful for spintronic and photovoltaic applications. On the contrary, S-rich surfaces have small-gaps, <0.3 eV, which might be responsible to the low open-circuit voltage of pyrite solar cells.
Zhang, Y. N.; Hu, J.; Law, M.; Wu, R. Q.
One structure for efficient narrow-band bandpass FIR filters
This paper presents a narrow-band bandpass FIR filter design with a small number of multipliers per output sample (NMPS). The proposed method is based on the use of the pipelining\\/interleaving (PI) technique within a quadrature modulation structure, where only one narrow-band lowpass filter is required. In order to reduce the NMPS, the narrow-band lowpass filter is designed with an interpolated
G. Jovanovic-Dolecek; J. Diaz-Carmona
Interaction effects on almost flat surface bands in topological insulators
We consider ferromagnetic instabilities of two-dimensional helical Dirac fermions hosted on the surface of three-dimensional topological insulators. We investigate ways to increase the role of interactions by means of modifying the bulk properties which in turn changes both the surface Dirac theory and the screening of interactions. We discuss both the long-ranged part of the Coulomb interactions controlled by the dimensionless coupling constant ?=e2/(??vFsurf) as well as the effects of local interactions parametrized by the ratio Usurf/Dsurf of a local interaction on the surface Usurf and the surface bandwidth Dsurf. If large compared to 1, both mechanisms can induce spontaneously surface ferromagnetism, thereby gapping the surface Dirac metal and inducing an anomalous quantum Hall effect. We investigate two mechanisms which can naturally lead to small Fermi velocities vFsurf and a corresponding small bandwidth Dsurf at the surface when the bulk band gap is reduced. The same mechanisms can, however, also lead to an enhanced screening of surface interactions. While in all considered cases the long-ranged part of the Coulomb interaction is screened efficiently, ??1, we discuss situations where Usurf/Dsurf becomes parametrically large compared to 1, thus inducing surface magnetism.
Sitte, Matthias; Rosch, Achim; Fritz, Lars
Low-Profile, Highly-Selective, Dual-Band Frequency Selective Surfaces With Closely Spaced Bands of Operation
We present a new design of a dual-band frequency selective surface (FSS) with closely spaced bands of operation and a highly-selective frequency response at each band. A multi-stage design procedure is also proposed for the design and synthesis of this class of frequency selective surfaces. The design procedure is based on synthesizing the desired device from its equivalent circuit parameter
Mudar A. Al-Joumayly; Nader Behdad
Structural information from detailed analysis of infrared absorption bands
The OH-stretching band of more than 500 alcohols and phenols have been measured in the apolar solvents CC14 and CS2 under standard conditions and the band parameters have been determined. Based on these data a system is being developed which provides the molecular structure in the surroundings of the hydroxyl group. The scheme of the system is outlined and discussed.
Bert Lutz; John van der Maas
The electronic structure of heavy fermions: Narrow temperature independent bands
The electronic structure of both Ce and U heavy fermions appears to consist of extremely narrow temperature independent bands. There is no evidence from photoemission for a collective phenomenon normally referred to as the Kondo resonance. In uranium compounds a small dispersion of the bands is easily measurable.
Arko, A.J.; Joyce, J.J.; Smith, J.L.; Andrews, A.B. [and others
Shell model description of band structure in 48Cr
The band structure for normal and abnormal parity bands in 48Cr are described using the m-scheme shell model. In addition to full fp-shell, two particles in the 1d3/2 orbital are allowed in order to describe intruder states. The interaction includes fp-, sd- and mixed matrix elements.
Vargas, Carlos E. [Facultad de Fisica e Inteligencia Artificial, Universidad Veracruzana, Sebastian Camacho 5, Centro, CP 91000, Xalapa, Ver. (Mexico); Velazquez, Victor M. [Facultad de Ciencias, Universidad Nacional Autonoma de Mexico (Mexico)
Chaotic band structure of almost-periodic potentials
It has been conjectured that the band structure of an almost-periodic potential is a Cantor set. Numerical calculations are presented which indeed suggest that there can be an infinite number of allowed and forbidden bands, in a finite energy range.
Peres, Asher
Electronic structure and thermoelectric properties of narrow band gap chalcogenides
In recent years there have been a revival of interest in discovering and understanding the physical properties of novel thermoelectric (TE) systems with high figure of merit. These systems are primarily narrow band gap semiconductors. In this thesis, electronic structure calculations were carried out for several narrow band gap chalcogenide TE materials in order to understand their electronic and transport
Daniel Bilc
Monolayer-induced band shifts at Si(100) and Si(111) surfaces
We report our study of the interfacial electronic structure of Si(100) and Si(111) surfaces that have been chemically modified with various organic monolayers, including octadecene and two para-substituted benzene derivatives. X-ray photoelectron spectroscopy reveals an upward band shift, associated with the assembly of these organic monolayers on the Si substrates, that does not correlate with either the dipole moment or the electron withdrawing/donating character of the molecular moieties. This suggests that the nature and quality of the self-assembled monolayer and the intrinsic electronic structure of the semiconductor material define the interfacial electronic structure of the functionalized Si(100) and Si(111) surfaces.
Mõkinen, A. J.; Kim, Chul-Soo; Kushto, G. P.
Optimization of low band gap polymer photovoltaics through structure modification
In BHJ-type solar cells, the ability to control and optimize the active layer morphology is a critical issue to improve device efficiency, and this is usually achieved by optimizing the processing conditions, eg. using varied annealing procedures and choosing the right solvent additive. In this work, we shown that device performance of DPP based low band gap polymers should be optimized both in processing and structural optimization approach. Without the use of chemical additive in blended thin film preparation, large size-scaled phase separation, up to several hundred of nanometers exist. This morphology is due to the surface aggregation of phenyl-C71-butyric acid methyl ester (PCBM), which forms large oval structures and then buried by a polymer-PCBM mixture thin film. In this process, the miscibility of polymer matrix plays an important role. While using chemical additive processing method can tune the general morphology to a more fibril network texture, fine-tuning of fibril dimensions and domain size needs delicate chemical structure modification. Through this modification, a 30% device performance enhancement was observed, which mostly came from an enhancement of short circuit current, thus strongly related to the morphological details. Besides conventional morphology characterizations, an initiative effort of understanding the domain interface structure was also carried out by using polarized soft x-ray scattering, in which we observed polymer crystal orientation plays an important role.
Liu, Feng; Gu, Yu; Briseno, Alejandro; Russell, Thomas; Wang, Cheng
Active Narrow-Band Vibration Isolation of Large Engineering Structures
We present a narrow-band tracking control method using a variant of the Least Mean Squares (LMS) algorithm to isolate slowly changing periodic disturbances from engineering structures. The advantage of the algorithm is that it has a simple architecture and is relatively easy to implement while it can isolate disturbances on the order of 40-50 dB over decades of frequency band. We also present the results of an experiment conducted on a flexible truss structure. The average disturbance rejection achieved is over 40 dB over the frequency band of 5 Hz to 50 Hz.
Rahman, Zahidul; Spanos, John
Mapping polarization induced surface band bending on the Rashba semiconductor BiTeI
Surfaces of semiconductors with strong spin-orbit coupling are of great interest for use in spintronic devices exploiting the Rashba effect. BiTeI features large Rashba-type spin splitting in both valence and conduction bands. Either can be shifted towards the Fermi level by surface band bending induced by the two possible polar terminations, making Rashba spin-split electron or hole bands electronically accessible. Here we demonstrate the first real-space microscopic identification of each termination with a multi-technique experimental approach. Using spatially resolved tunnelling spectroscopy across the lateral boundary between the two terminations, a previously speculated on p-n junction-like discontinuity in electronic structure at the lateral boundary is confirmed experimentally. These findings realize an important step towards the exploitation of the unique behaviour of the Rashba semiconductor BiTeI for new device concepts in spintronics.
Butler, Christopher John; Yang, Hung-Hsiang; Hong, Jhen-Yong; Hsu, Shih-Hao; Sankar, Raman; Lu, Chun-I; Lu, Hsin-Yu; Yang, Kui-Hon Ou; Shiu, Hung-Wei; Chen, Chia-Hao; Kaun, Chao-Cheng; Shu, Guo-Jiun; Chou, Fang-Cheng; Lin, Minn-Tsong
Mapping polarization induced surface band bending on the Rashba semiconductor BiTeI.
Surfaces of semiconductors with strong spin-orbit coupling are of great interest for use in spintronic devices exploiting the Rashba effect. BiTeI features large Rashba-type spin splitting in both valence and conduction bands. Either can be shifted towards the Fermi level by surface band bending induced by the two possible polar terminations, making Rashba spin-split electron or hole bands electronically accessible. Here we demonstrate the first real-space microscopic identification of each termination with a multi-technique experimental approach. Using spatially resolved tunnelling spectroscopy across the lateral boundary between the two terminations, a previously speculated on p-n junction-like discontinuity in electronic structure at the lateral boundary is confirmed experimentally. These findings realize an important step towards the exploitation of the unique behaviour of the Rashba semiconductor BiTeI for new device concepts in spintronics. PMID:24898943
PhET Simulation: Band Structure
This webpage contains an interactive simulation that allows users to explore quantum bound states in multiple potential wells, and to see the formation of bands of energy levels. Users can interactively change features such as the number, width, spacing, and height of the wells, and see the changes to the energy levels and energy eigenstate wave functions continuously. Options also include using square and Coulomb shaped wells. Probability densities and wave functions can be shown using a variety of representations. This simulation is also contained within the Quantum Bound States simulation. Also included is a teacher's guide as well as sample learning goals for use with the simulation. This simulation is part of a large and growing collection. It has been designed using principles from physics education research and refined based on student interviews.
Development of X-band accelerating structures at Fermilab
The RF Technology Development group at Fermilab is working together with the NLC and JLC groups at SLAC and KEK on developing technology for room temperature X-band accelerating structures for a future linear collider. We have built a few 60 cm long, high phase advance, detuned structures (HDS or FXB series). These structures have 150 degrees phase advance per cell,
T. Khabiboulline; T. Arkan; E. Borissov; H. Carter; D. Finley; C. Boffo; I. Gonin; G. Romanov; B. Smith; N. Solyak
Fabrication of x-band accelerating structures at Fermilab
The RF Technology Development group at Fermilab is working together with the NLC and GLC groups at SLAC and KEK on developing technology for room temperature X-band accelerating structures for a future linear collider. We built six 60-cm long, high phase advance, detuned structures (HDS or FXB series). These structures have 150 degrees phase advance per cell, and are intended
Tug T Arkan; C. Boffo; E. Borissov; H. Carter; D. Finley; I. Gonin; T. Khabiboulline; S. Mishra
In recent years there have been a revival of interest in discovering and understanding the physical properties of novel thermoelectric (TE) systems with high figure of merit. These systems are primarily narrow band gap semiconductors. In this thesis, electronic structure calculations were carried out for several narrow band gap chalcogenide TE materials in order to understand their electronic and transport properties governing their TE characteristics. These calculations were performed within ab initio density functional theory (DFT) using full potential linearized augmented plane wave (FLAPW) method. Transport calculations were carried out using Boltzmann transport equations. For the binary chalcogenides Bi2Se3 and Bi 2Te3 I have studied the effect of quantum confinement (QC) created by the surfaces on their bulk electronic structure. In the presence of such confinement, surface states appear, which are a consequence of the strong influence of the interlayer bonding on the bulk electronic structure of these compounds. I find that in contrast to standard belief, there is an important covalent contribution to the interlayer bonding besides the Van der Waals contribution. (Bi2Te3)m(Sb2 Te3)n superlattices (SL) show very good TE properties at room temperature. To see how the electronic structure of Bi2Se3 and Bi2Te3 are affected by the formation of SL, I have investigated the electronic properties of (Bi 2Te3)m(Sb2Te 3)n SL as compared to those of Bi2 Se3 and Bi2Te3 bulk systems. We find that the formation of SL does not deteriorate the electronic transport properties along the cross plane direction. Complex ternary K2Bi8Se13 system shows great potential for superior TE performance. This compound forms in two distinct phases, alpha and beta. The beta-phase, which has two sites with K/Bi disorder, is a better TE. The calculations show that alpha-phase is an indirect band gap semiconductor. For the beta-phase, we find that the atoms at the "mixed sites" are very important in determining the electronic properties. The incorporation of the K/Bi mixed occupancy at the disordered sites is crucial for the semiconductor behavior. We also find a strong anisotropy in the hole and electron effective mass. Complex quaternary AgPbmSbTe2+ m (LAST-m) systems are excellent high temperature TE. These systems form in the rocksalt structure similar to PbTe where Ag and Sb occupy Pb sites. There are clear experimental evidences that LAST-m systems exhibit microscopic inhomogeneities rich in Ag-Sb embedded into a PbTe matrix. Our calculations show that resonant states appear near the PbTe band gap. The common feature of all Ag-Sb arrangements is that they have a more enhanced density of states (DOS) near the gap as compared to PbTe. To see how these features in the DOS affect the transport properties I have carried out transport calculations in PbTe and LAST-m systems. The results for PbTe show that the temperature dependence of the effective mass md is very important in order to have good agreement with experiment. The LAST-m systems show an enhancement of the power factor (S 2sigma) relative to PbTe. But this enhancement is not large enough to explain the experimentally observed ZT. This suggests that the reduction in the thermal conductivity caused by Ag-Sb nanostructures in PbTe matrix may be significant.
Bilc, Daniel
Monolayer-induced band bending in the near-surface region of Ge(111)
Directly grafted organic monolayers on Ge surfaces offer an interesting opportunity to explore aspects of surface passivation and control of electrical properties, namely, molecular gating, of semiconductor surfaces. We report our study of the interfacial electronic structures of n-type, intrinsic, and p-type Ge(111) surfaces that have been chemically modified with various organic monolayers. The monolayers investigated include octadecane, attached via hydrogermylation of 1-octadecene at Ge surfaces, as well as para-substituted phenyl rings, attached by diazonium activation of hydrogenated Ge surfaces. X-ray photoelectron spectroscopy measurements indicate that there is downward band bending, up to 160 meV, associated with assembling these organic monolayers on the Ge substrates. This band bending does not directly correlate with the dipole moment or electron withdrawing or donating character of the molecular moieties, pointing to the critical roles of the nature and quality of the self-assembled monolayer, and the intrinsic electronic structure of the semiconductor material in defining the interfacial electronic structure of the passivated Ge(111) surfaces.
Mõkinen, A. J.; Kushto, G. P.
The Optical Properties and the Band Structure of Magnesium Bromide
The optical properties of MgBr2 have been studied by means of the reflection spectra in the region from VUV to XUV, the absorption spectra in the VUV region, and also by the XPS and UPS. Besides, the band structure of the valence bands is calculated by the tight binding method and the lower conduction bands by use of the empty lattice model. It is found that the top of the valence bands consists of \\varGamma3- and \\varGamma2- bands which are almost degenerate by the crystal field, and that the observed four exciton peaks are tentatively explained as the spin-orbit splitting of these two levels.
Kinno, Shigeo; Onaka, Ryumyo
[Band electronic structures and crystal packing forces
We investigated the electronic and structural properties of low-dimensional materials and explored the structure-property correlations governing their physical properties. Progress was made on how to interpret the scanning tunneling microscopy and atomic force microscopy images of layered materials and on how to account for charge density wave instabilities in 2-D metals. Materials studied included transition metal chalcogenides, transition metal halides, organic conducting salts, Mo bronzes, A[sub 2]PdH[sub 2], fullerenes, squarate tetrahydrate polymers Fe, Cu(C[sub 4]O[sub 4])4[center dot]H[sub 2]O, BEDT salts, etc.
Not Available
Effective band structure of random III-V alloys
Random substitutional alloys have no long range order (LRO) or translational symmetry so rigorously speaking they have no E(k) band structure or manifestations thereof. Yet, many experiments on alloys are interpreted using the language of band theory, e.g. inferring Van Hove singularities, band dispersion and effective masses. Many standard alloy theories (VCA- or CPA-based) have the LRO imposed on the alloy Hamiltonian, assuming only on-site disorder, so they can not be used to judge the extent of LRO that really exists. We adopt the opposite way, by using large (thousand atom) randomly generated supercells in which chemically identical alloy atoms are allowed to have different local environments (a polymorphous representation). This then drives site-dependent atomic relaxation as well as potential fluctuations. The eigenstates from such supercells are then mapped onto the Brillouin zone (BZ) of the primitive cell, producing effective band dispersion. Results for (In,Ga)X show band-like behaviour only near the centre and faces of the BZ but rapidly lose such characteristics away from ? or for higher bands. We further analyse the effects of stoichiometry variation, internal relaxation, and short-range order on the alloy band structure.
Popescu, Voicu; Zunger, Alex
Self-consistent energy bands in aluminum and electronic surface states and resonances on the (001) surface
The band structure of aluminum has been calculated self-consistently with the use of the Kohn-Sham-Gaspar local exchange potential and the linear combination of Gaussian orbitals method. The resulting band structure, using a basis set of 28 contracted Gaussian-type orbitals, is in excellent agreement with the previous work of Singhal and Callaway in which a basis set of 60 uncontracted Gaussian functions was used. After projection of the bulk bands onto the two-dimensional (001) surface Brillouin zone, surface states and resonances have been calculated along the ?» line with the use of the Green's-function formalism. At point ?», the surface state is located 2.92 eV below EF, in excellent agreement with the experimental result, 2.8+/-0.2 eV below EF. In addition, a resonance is found 0.7 eV below EF with a half-width of 0.4 eV, hitherto interpreted only as Fermi edge intensity. From the midpoint of the ?» axis moving onward up to the Fermi energy, the observed main peak is attributed to surface resonances.
Seel, M.
Solving complex band structure problems with the FEAST eigenvalue algorithm
With straightforward extension, the FEAST eigenvalue algorithm [Polizzi, Phys. Rev. B 79, 115112 (2009)] is capable of solving the generalized eigenvalue problems representing traveling-wave problemsŚas exemplified by the complex band-structure problemŚeven though the matrices involved are complex, non-Hermitian, and singular, and hence outside the originally stated range of applicability of the algorithm. The obtained eigenvalues/eigenvectors, however, contain spurious solutions which must be detected and removed. The efficiency and parallel structure of the original algorithm are unaltered. The complex band structures of Si layers of varying thicknesses and InAs nanowires of varying radii are computed as test problems.
Laux, S. E.
X-band travelling wave accelerator structure R&D
A 1.6 MeV X-band traveling wave linear accelerator is being developed in our Lab. in view of X-band linac R&D and industrial purposes. One section of the accelerator structure has been fabricated successfully. In this paper, the RF coupler computer simulation, the constant powerloss collinear load study and the accelerator section development are described in detail. The manufacture technology and
K. Jin; Y. J. Pei; D. M. Jiang; Y. Z. Liu; Q. J. Lai; M. H. Zhao; H. Zhao
Development of X-band accelerating structures for high gradients
Short copper standing wave (SW) structures operating at an X-band frequency have been recently designed and manufactured at the Laboratori Nazionali di Frascati of the Istituto Nazionale di Fisica Nucleare (INFN) using the vacuum brazing technique. High power tests of the structures have been performed at the SLAC National Accelerator Laboratory. In this manuscript we report the results of these
S. Bini; V. Chimenti; A. Marcelli; L. Palumbo; B. Spataro; V. A. Dolgashev; S. Tantawi; A. D. Yeremian; Y. Higashi; M. G. Grimaldi; L. Romano; F. Ruffino; R. Parodi
Complex band structure of nanostructured metal-dielectric metamaterials.
We study complex eigenmodes of layered metal-dielectric metamaterials. Varying losses from weak to realistic, we analyze band structure of the metamaterial and clarify effect of losses on its intrinsic electromagnetic properties. The structure operates in a regime with infinite numbers of eigenmodes, whereas we analyze dominant ones. PMID:23389143
Orlov, Alexey; Iorsh, Ivan; Belov, Pavel; Kivshar, Yuri
Magnetic dichroism study of the valence-band structure of perpendicularly magnetized Co/Cu(111)
The electronic structure of three monolayers (ML) Co on Cu(111), grown with Pb as a surfactant and capped with two ML Cu, was studied using magnetic circular dichroism in valence-band photoemission. The easy axis of magnetization in these films is perpendicular to the surface, allowing an experimental setup of extreme symmetry (photon spin, light incidence, electron emission, and magnetization all aligned and perpendicular to the surface). In such a geometry features observed in magnetic dichroism can be directly related to the symmetry character of the relativistic band structure. Experimental data in the photon energy range of 6-24 eV are presented. The observed magnetic dichroism and its dispersion with photon energy can be explained on the basis of direct transitions in a bulklike band structure of Co.
Kuch, W.; Dittschar, A.; Salvietti, M.; Lin, M.-T.; Zharnikov, M.; Schneider, C. M.; Camarero, J.; de Miguel, J. J.; Miranda, R.; Kirschner, J.
Band structure of phononic crystals with general damping
In this paper, we present theoretical formalisms for the study of wave dispersion in damped elastic periodic materials. We adopt the well known structural dynamics techniques of modal analysis and state-space transformation and formulate them for the Bloch wave propagation problem. First, we consider a one-dimensional lumped parameter model of a phononic crystal consisting of two masses in the unit cell whereby the masses are connected by springs and dashpot viscous dampers. We then extend our analysis to the study of a two-dimensional phononic crystal, modeled as a dissipative elastic continuum, and consisting of a periodic arrangement of square inclusions distributed in a matrix base material. For our damping model, we consider both proportional damping and general damping. Our results demonstrate the effects of damping on the frequency band structure for various types and levels of damping. In particular, we reveal two intriguing phenomena: branch overtaking and branch cut-off. The former may result in an abrupt drop in the relative band gap size, and the latter implies an opening of full or partial wavenumber (wave vector) band gaps. Following our frequency band structure analysis, we illustrate the concept of a damping ratio band structure.
Hussein, Mahmoud I.; Frazier, Michael J.
Banded structures in collagen vitrigels for corneal injury repair.
There is a growing interest in using collagen vitrigels for corneal injury repair. We recently reported the synthesis and thermal denaturation behavior of these gels. In this paper, the banded structure in these vitrified gels is studied by small-angle X-ray scattering (SAXS) one-dimensional (1-D) correlation function analysis and transmission electron microscopy (TEM). Results demonstrate that the collagen vitrigel possess banded structures similar to those of the starting type I collagen, with an average D-spacing of 64nm (by SAXS) or 57nm (by TEM). A combination of SAXS 1-D correlation function analyses and TEM show that overlap and gap distances ranged from 30 to 33nm and from 23 to 25nm, respectively. Changing the vitrification condition does not impact on the banded structure significantly. PMID:24859294
Xia, Zhiyong; Calder¾n-Col¾n, Xiomara; McCally, Russell; Maranchi, Jeffrey; Rong, Lixia; Hsiao, Benjamin; Elisseeff, Jennifer; Trexler, Morgana
Band Structures and Optical Properties of Semiconducting Layer Compounds GaS and GaSe
The band structures of GaS and GaSe near the Fermi levels are derived in a semiempirical way. In view of the anisotropic structures, the pi band structures are mainly studied. The valence band consists of a pi band with the heavy effective masses. The conduction band at the center of the Brillouin zone has the light effective masses for the
H. Kamimura; K. Nakao
Electronic band structure and phonons in V2O5
Among the vanadium oxides, V2O5 presents special interest as a layered material. As for other layered materials, it is of interest to search for changes in its electronic structure and phonon spectrum in the monolayer modification of this material. For example, reduced screening may modify phonon modes affected by long-range Coulomb interactions. As a preliminary we here present a first-principles study of the bulk electronic band structure and the phonons at the ?-point. Density functional calculations in the local density approximation were carried out for the electronic band structure and the density functional perturbation method was used for the phonon calculations. We used LDA and norm-conserving pseudopotentials in the abinit code. A group theoretical analysis is used to label the phonon modes. Non-analyticity is included for the LO modes. The band structures are in good agreement with previous work and yield an indirect band gap. Relaxed structural properties are also in good agreement with experiment. Simulated infrared and Raman spectra will be presented. Our results will be compared with experimental and previous theoretical work.
Bhandari, Churna; Lambrecht, Walter R. L.
Novel structural flexibility identification in narrow frequency bands
A æSub-PolyMAXÆ method is proposed in this paper not only for estimating modal parameters, but also for identifying structural flexibility by processing the impact test data in narrow frequency bands. The traditional PolyMAX method obtains denominator polynomial coefficients by minimizing the least square (LS) errors of frequency response function (FRF) estimates over the whole frequency range, but FRF peaks in different structural modes may have different levels of magnitude, which leads to the modal parameters identified for the modes with small FRF peaks being inaccurate. In contrast, the proposed Sub-PolyMAX method implements the LS solver in each subspace of the whole frequency range separately; thus the results identified from a narrow frequency band are not affected by FRF data in other frequency bands. In performing structural identification in narrow frequency bands, not in the whole frequency space, the proposed method has the following merits: (1) it produces accurate modal parameters, even for the modes with very small FRF peaks; (2) it significantly reduces computation cost by reducing the number of frequency lines and the model order in each LS implementation; (3) it accurately identifies structural flexibility from impact test data, from which structural deflection under any static load can be predicted. Numerical and laboratory examples are investigated to verify the effectiveness of the proposed method.
Zhang, J.; Moon, F. L.
Electronic band structure calculations of bismuth-antimony nanowires
Alloys of bismuth and antimony received initial interest due to their unmatched low-temperature thermoelectric performance, and have drawn more recent attention as the first 3D topological insulators. One-dimensional bismuth-antimony (BiSb) nanowires display interesting quantum confinement effects, and are expected to exhibit even better thermoelectric properties than bulk BiSb. Due to the small, anisotropic carrier effective masses, the electronic properties of BiSb nanowires show great sensitivity to nanowire diameter, crystalline orientation, and alloy composition. We develop a theoretical model for calculating the band structure of BiSb nanowires. For a given crystalline orientation, BiSb nanowires can be in the semimetallic, direct semiconducting, or indirect semiconducting phase, depending on nanowire diameter and alloy composition. These ``phase diagrams'' turn out to be remarkably similar among the different orientations, which is surprising in light of the anisotropy of the bulk BiSb Fermi surface. We predict a novel direct semiconducting phase for nanowires with diameter less than ś15 nm, over a narrow composition range. We also find that, in contrast to the bulk and thin film BiSb cases, a gapless state with Dirac dispersion cannot be realized in BiSb nanowires.
Levin, Andrei; Dresselhaus, Mildred
Band structure effects on the superconductivity in Hubbard models
We study the influence of the band structure on the symmetry and superconducting transition temperature in the (solvable) weak-coupling limit of the repulsive Hubbard model. Among other results we find that (1) as a function of increasing nematicity, starting from the square-lattice (zero nematicity) limit where a nodal d-wave state is strongly preferred, there is a smooth evolution to the quasi-1D limit, where a striking near-degeneracy is found between a p-wave- and a d-wave-type paired states with accidental nodes on the quasi-one-dimensional Fermi surfacesŚa situation that may be relevant to the Bechgaard salts. (2) In a bilayer system, we find a phase transition as a function of increasing bilayer coupling from a d-wave to an s▒-wave state reminiscent of the iron-based superconductors. (3) When an antinodal gap is produced by charge-density-wave order, not only is the pairing scale reduced, but the symmetry of the pairs switches from dx2-y2 to dxy; in the context of the cuprates, this suggests that were the pseudogap entirely due to a competing CDW order, this would likely cause a corresponding symmetry change of the superconducting order (which is not seen in experiment).
Cho, Weejee; Thomale, Ronny; Raghu, Srinivas; Kivelson, Steven A.
Band-edge electronic structure modification in iron oxide and oxyhydroxide nanoparticles
Transition metal oxide and oxyhydroxide nanoparticles are the focus of considerable current interest in geochemistry because of their roles in biogeochemical redox cycles. Much progress has been made in understanding the structure and phase relationships in mineral nanoparticles, but the effects of small size and modified surface structure on reactivity remains an outstanding problem. Common environmental nanoparticles have been shown to exhibit enhanced chemical reactivity relative to bulk mineral surfaces, but the origin of this behavior is not well established. We studied the electronic structure component of mineral reactivity by comparing oxygen K-edge soft x-ray absorption and emission spectra of three phases of iron oxide and oxyhydroxide nanoparticles with spectra obtained from bulk minerals of the equivalent phases. These spectroscopies probe the electronic states in the vicinity of the semiconductor band gap that are important for interfacial (photo)electrochemical processes. Both the conduction and valence band states of goethite (?-FeOOH) nanoparticles exhibit considerable broadening that is likely associated with surface and interior disorder and which leads to an effective reduction in the band gap. By contrast, the band gaps of hematite (?- Fe2O3) and maghemite (?-Fe2O3) nanoparticles are increased as a consequence of shifts in the threshold positions of the valence and conduction band, respectively. The origins of these electronic structure modifications are presently uncertain. Nevertheless, the data directly predict that the reducing potential of conduction band electrons in maghemite nanoparticles and the oxidizing potential of hematite valence band electrons are enhanced relative to the bulk minerals, and that simple photochemical studies can be used to validate these predictions.
Gilbert, B.
Four-band frequency selective surface with double-square-loop patch elements
Design and experimental verifications are presented for a four-band frequency selective surface (FSS) with perfectly conducting double-square-loop (DSL) patch elements. A single screen DSL element FSS is demonstrated for (1) a four-band FSS which reflects the X- and Ka-band signals while passing the Sand Ku-band signals, and (2) a low-pass (or Ka-add-on) FSS that reflects the Ka-band signal while passing
Te-Kao Wu
Interconnectivity in Surface Wicking Structures
Surface wicking structures possessing strong interconnectivity are designed and examined. The designs aim to optimize the structure's ability to transport fluids by exploiting capillary driven flow in interior corners combined with interconnectivity and alignment. `Waffle-like' structures consisting of vertical rectangular vanes at a variety of orientations are employed as the basic repeat unit. Due to this arrangement, such surfaces possess
Yongkang Chen; Donald Bell; Santiago Rodriguez; Ben Semerjian; Lawrence Melvin; Mark Weislogel
Photonic Band Gap structures: A new approach to accelerator cavities
We introduce a new accelerator cavity design based on Photonic Band Gap (PGB) structures. The PGB cavity consists of a two-dimensional periodic array of high dielectric, low loss cylinders with a single removal defect, bounded on top and bottom by conducting sheets. We present the results of both numerical simulations and experimental measurements on the PGB cavity.
Kroll, N. [California Univ., San Diego, La Jolla, CA (United States). Dept. of Physics]|[Stanford Linear Accelerator Center, Menlo Park, CA (United States); Smith, D.R.; Schultz, S. [California Univ., San Diego, La Jolla, CA (United States). Dept. of Physics
Band-structure loops and multistability in cavity QED
We calculate the band structure of ultracold atoms located inside a laser-driven optical cavity. For parameters where the atom-cavity system exhibits bistability, the atomic band structure develops loop structures akin to the ones predicted for Bose-Einstein condensates in ordinary (noncavity) optical lattices. However, in our case the nonlinearity derives from the cavity back-action rather than from direct interatomic interactions. We find both bi- and tristable regimes associated with the lowest band, and show that the multistability we observe can be analyzed in terms of swallowtail catastrophes. Dynamic and energetic stability of the mean-field solutions is also discussed, and we show that the bistable solutions have, as expected, one unstable and two stable branches. The presence of loops in the atomic band structure has important implications for proposals concerning Bloch oscillations of atoms inside optical cavities [Peden et al., Phys. Rev. A 80, 043803 (2009); Prasanna Venkatesh et al., Phys. Rev. A 80, 063834 (2009)].
Prasanna Venkatesh, B.; O'Dell, D. H. J. [Department of Physics and Astronomy, McMaster University, 1280 Main St. W., Hamilton, Ontario, L8S 4M1 (Canada); Larson, J. [Department of Physics, Stockholm University, S-10691, Stockholm (Sweden)
Elasticity, band structure, and piezoelectricity of Be xZn 1- xO alloys
Lattice constants, elasticity, band structure and piezoelectricity of hexagonal wide band gap Be xZn 1- xO ternary alloys are calculated using first-principles methods. The alloys' lattice constants obey Vegard's law well. As Be concentration increases, the bulk modulus and Young's modulus of the alloys increase, whereas the piezoelectricity decreases. We predict that Be xZn 1- xO/GaN/substrate ( x=0.022) multilayer structure can be suitable for high-frequency surface acoustic wave device applications. Our calculated results are in good agreement with experimental data and other theoretical calculations.
Duan, Yifeng; Shi, Hongliang; Qin, Lixia
Structure of Surfaces of Interfaces.
It has been only relatively recently that electron microscopy has demonstrated its potential for the complete (atomic level) determination of surface and interfacial structure. For years, surfaces were studied exclusively with scanning systems and interfa...
R. Gronsky
Novel Banded Structures in a Combined Main-Chain/Side-Chain Crystalline Polyester: from Liquid Crystals to Confined Crystals
Characterization of banded structures obtained from liquid crystals to confined crystallization has been investigated using optical and atomic force microscopy. A combined main-chain/side-chain liquid crystalline (LC) polyester, PEFBP(n = 11), was focused on to illustrate the formation of interesting additional bands on crystallization. On macroscopic scales, both approaches can be applied to visualize the morphological changes in these banded textures. In tapping mode AFM, the 3-D topographic banding images are detected in the height image from āŅ3.5 ?m LC bands to āŅ50 nm confined crystal bands. The sub-surface fine features of edge-on crystal (KO) lamellae are differentiated in an extended chain conformation in the phase image. The formation of complicated banded structures from liquid crystals to confined crystallization is recognized as a new element: self-elongated 1-D crystal growth in the confined LC matrix on crystallization.
Ge, Jason J.; Wensheng; Zhou; Zhang, John Z.; Wang, Shy-Yeu; Harris, Frank W.; Cheng, Stephen Z. D.
A QES band-structure problem in one dimension
I show that the potential V(x,m)=b24?m(1?m)a(a+1)sn2(x,m)dn2(x,m)?ba+12cn(x,m)dn2(x,m) constitutes a QES band-structure problem in one dimension. In particular, I show that for any positive integral or half-integral a, 2a+1 band edge eigenvalues and eigenfunctions can be obtained analytically. In the limit of m going to 0 or 1, I recover the well known results for the QES double sine-Gordon or double sinh-Gordon
Avinash Khare; Sachivalaya Marg
Band structure for a bend-core liquid crystal fiber
We study the propagation of optical fields in a cylindrical fiber of a banana bend-core liquid crystal formed by uniformly tilted coaxial cylindrical smectic layers, surrounded by vacuum. By solving numerically Maxwell's equations, we find the band structure in both uniaxial and biaxial limits. For the biaxial case, we show that the backward propagation is restricted to certain narrow frequency band gaps, whereas for the forward one the fiber behaves similarly to a standard waveguide. We also find that the fiber modes are elliptically polarized slowly leaky modes whose attenuation coefficients are damped oscillating functions of frequency.
Palomares, Laura O.; Castro-Garay, P.; Reyes, J. Adrian
Microbial Communities in the Surface Mucopolysaccharide Layer and the Black Band Microbial Mat of Black Band-Diseased Siderastrea siderea
Microbial community profiles and species composition associated with two black band-diseased colonies of the coral Siderastrea siderea were studied by 16S rRNA-targeted gene cloning, sequencing, and amplicon-length heter- ogeneity PCR (LH-PCR). Bacterial communities associated with the surface mucopolysaccharide layer (SML) of apparently healthy tissues of the infected colonies, together with samples of the black band disease (BBD) infections, were analyzed
Raju Sekar; DeEtta K. Mills; Elizabeth R. Remily; Joshua D. Voss; Laurie L. Richardson
Inter-band optoelectronic properties in quantum dot structure of low band gap III-V semiconductors
A generalized theory is developed to study inter-band optical absorption coefficient (IOAC) and material gain (MG) in quantum dot structures of narrow gap III-V compound semiconductor considering the wave-vector (k?) dependence of the optical transition matrix element. The band structures of these low band gap semiconducting materials with sufficiently separated split-off valance band are frequently described by the three energy band model of Kane. This has been adopted for analysis of the IOAC and MG taking InAs, InSb, Hg1-xCdxTe, and In1-xGaxAsyP1-y lattice matched to InP, as example of III-V compound semiconductors, having varied split-off energy band compared to their bulk band gap energy. It has been found that magnitude of the IOAC for quantum dots increases with increasing incident photon energy and the lines of absorption are more closely spaced in the three band model of Kane than those with parabolic energy band approximations reflecting the direct the influence of energy band parameters. The results show a significant deviation to the MG spectrum of narrow-gap materials having band nonparabolicity compared to the parabolic band model approximations. The results reflect the important role of valence band split-off energies in these narrow gap semiconductors.
Dey, Anup; Maiti, Biswajit; Chanda Sarkar, Debasree
Structure of the four quasiparticle band in 84Sr
The high spin levels in 84Sr have been populated through the 59Co(28Si, 3p) reaction using 98 MeV 28Si beam. A regular band structure was found to develop above the 12+ state with a deformation parameter ?=0.21+/-0.04 and ?=8░+/-6░. The projected Hartree-Fock calculations predict a two proton and two neutron aligned configuration for this band. The predicted quadrupole moment for this configuration is also in good agreement with the experimental values obtained from the lifetime measurements. In addition, a large enhancement in B(M1)/B(E2) transition rates has been observed in the negative parity band above the 11- state.
Chattopadhyay, S.; Jain, H. C.; Jhingan, M. L.; Praharaj, C. R.
Extensive ?-ray spectroscopy of band structures in 3062Zn32
An experimental study of the 62Zn nucleus has been performed by combining the data sets from four fusion-evaporation reaction experiments. Apart from the previously published data, the present results include ten new rotational band structures and two more superdeformed bands. The Gammasphere Ge-detector array in conjunction with the 4? charged-particle detector array Microball allowed for the detection of ? rays in coincidence with evaporated light particles. The deduced level scheme includes some 260 excited states, which are connected with more than 450 ?-ray transitions. Spins and parities of the excited states have been determined via directional correlations of ? rays emitted from oriented states. The experimental characteristics of the rotational bands are analyzed and compared with results from cranked Nilsson-Strutinsky calculations. The present analysis, combined with available experimental results in the Aś60 mass region, can be used to improve the current set of Nilsson parameters in the N=3 and N=4 oscillator shells.
Gellanki, J.; Rudolph, D.; Ragnarsson, I.; Andersson, L.-L.; Andreoiu, C.; Carpenter, M. P.; Ekman, J.; Fahlander, C.; Johansson, E. K.; Kardan, A.; Reviol, W.; Sarantites, D. G.; Seweryniak, D.; Svensson, C. E.; Waddington, J. C.
Band structures of all polycrystalline forms of silicon dioxide
The band structures and density of states of all polycrystalline forms of SiO2 with known crystal structures are calculated using a first-principles orthogonalized linear combination of atomic orbitals method. These include 4:2-coordinated polymorphs of ?-quartz, ?-quartz, ?-tridymite, ?-crystobalite, ?-crystobalite, keatite, coesite, and two idealized forms of ?-crystobalites, as well as the 6:3-coordinated stishovite. Linear relations between the band gaps and the average Si-O bond lengths and the minimum Si-O-Si angles are firmly established. The electronic structure of stishovite is found to be very much different from the 4:2-coordinated oxides and shows more covalency in the bonding character.
Li, Y. P.; Ching, W. Y.
Band structure parameters for quantum wells: Magnetoluminescence determinations
We report on low-temperature magnetoluminescence determinations of bandstructure parameters for an 8.5nm-wide n-type In{sub 0.20}Ga{sub 0.80}As/GaAs strained single-quantum well structure. We find that the conduction-band is almost parabolic, with its mass varying from 0.067m{sub 0} at zone center to 0.069m{sub 0} at a Fermi energy E{sub f} {approx} 50 meV, and that the valence-bands are highly non-parabolic with the valence band masses m, varying from about 0.1 m{sub 0} at zone center to about 0.3m{sub 0} for large k-vectors. A comparison with a k x p calculation for the valence-band mass and dispersion curve show good agreement. An accurate and unambiguous determination for the band-gap energy E{sub gap} is made by extrapolating the magnetic field dependent Landau level transition energies to zero field.
Jones, E.D.
Unfolding of collapsed polymers in shear flow: Effects of colloid banding structures in confining channels
Using hydrodynamic simulations, we demonstrate that confined colloidal suspensions can greatly enhance the unfolding of collapsed single polymers in flow. When colloids come in direct contact with the polymers due to the flow, the collapsed chains become flattened or elongated on the surface of the colloids, increasing the probability of forming large chain protrusions that the flow can pull out to unfold the polymers. This phenomenon may be suppressed if the colloid size is commensurate with the confining channels, where the colloids form well-defined banding structures. Here, we analyze the colloid banding structures in detail and their relation to the chain unfolding. We find that for colloid volume fractions up to 30%, the confined colloids form simple cubic (sc), hexagonal (hex), or a mixture of sc + hex structures. By directly changing the heights of the confining channels, we show that the collapsed polymers unfold the most in the mixed sc + hex structures. The diffuse (not well-defined) bands in the mixed sc + hex structures provide the highest collision probability for the colloids and the polymers, thus enhancing unfolding the most. Without colloidal suspensions, we show that the confining channels alone do not have an observable effect on the unfolding of collapsed polymers. The well-defined colloid bands also suppress the unfolding of noncollapsed polymers. In fact, the average size for noncollapsed chains is even smaller in the well-defined bands than in a channel without any colloids. The appearance of well-defined bands in this case also indicates that lift forces experienced by the polymers in confinement are negligible compared to those exerted by the colloidal band structures. Our results may be important for understanding the dynamics of mixed colloid polymer solutions.
Chen, Hsieh; Alexander-Katz, Alfredo
Evolution of Narrow Band Spectra of Surface Gravity Waves
It is well-known that a uniform train of surface gravity waves is unstable to the so- called Benjamin-Feir (BF) instability. The stability of a narrow band of Gaussian random wavetrains was considered by Alber and Saffman (1978), Alber (1978) and Crawford et al. (1980). For waves on deep water they found that the BF instability persists provided that the relative spectral width, x, of the wavenumber spectrum (in the main direction of wave propagation, x) is less than twice the average steepness, k0a, where k0 is the central wavenumber and a is the rms value of the amplitude. Here we compare these results with numerical simulations on the evolution of narrow band spectra in two and three dimensions. For deep water waves the results of Alber and Saffman (1978) and Alber (1978) are based on the Non-Linear Schr÷dinger equa- tion (NLS) which is the lowest order model equation (in the relative spectral width, and the wave steepness) taking into account both dispersion and nonlinearity. We have done simulations both with the NLS equation and with a modified NLS-type equation (MNLS) taking into account higher order terms in the relative bandwidth (Trulsen and Dysthe (1996), Trulsen et al. (2000)). The results of the simulations can be summarized as follows: The two dimensional simulations. In the NLS simulation the criterion x > 2 for suppression of the BF instability is verified. In the unstable case (x < 2 ) we find that the spectrum broadens symmetrically till it reaches a stable width. In the MNLS simulation the initially symmetric Gaussian shape of the spectrum does not persist, regardless of the initial spectral width. On the timescale ( 0)-1the spec- tral peak moves towards lower wavenumbers, with a steepening on the low- and a tail forming on the high frequency side. The three dimensional simulations. The 3d NLS simulations do not support the the- oretical results of Alber (1978) and Crawford et al. (1980). A considerable widening of the spectrum is seen almost regardless of the initial spectral width x in the main wave direction. The MNLS simulations still show an asymmetric development. There is a steepen- ing on the low frequency side and a tail growing on the high frequency side with a corresponding downshift of the spectral peak. The tail formation shows a power-law behavior |k|-p with p 2.5 corresponding to a -4 law of the frequency spectrum. The research was funded by the BeMatA program of the Research Council of Norway and by Norsk Hydro.
Dysthe, K. B.; Socquet-Juglard, H.; Trulsen, K.; Krogstad, H.
Electronic band structure and carrier effective mass in calcium aluminates
First-principles electronic band structure investigations of five compounds of the CaO-Al2O3 family, 3CaOĢAl2O3 , 12CaOĢ7Al2O3 , CaOĢAl2O3 , CaOĢ2Al2O3 , and CaOĢ6Al2O3 , as well as CaO and ? -, ? -, and ?-Al2O3 are performed. We find that the conduction band in the complex oxides is formed from the oxygen antibonding p states and, although the band gap in Al2O3 is almost twice larger than in CaO, the s states of both cations. Such a hybrid nature of the conduction band leads to isotropic electron effective masses which are nearly the same for all compounds investigated. This insensitivity of the effective mass to variations in the composition and structure suggests that upon a proper degenerate doping, both amorphous and crystalline phases of the materials will possess mobile extra electrons.
Medvedeva, Julia E.; Teasley, Emily N.; Hoffman, Michael D.
Tunable and sizable band gap in silicene by surface adsorption
Opening a sizable band gap without degrading its high carrier mobility is as vital for silicene as for graphene to its application as a high-performance field effect transistor (FET). Our density functional theory calculations predict that a band gap is opened in silicene by single-side adsorption of alkali atom as a result of sublattice or bond symmetry breaking. The band gap size is controllable by changing the adsorption coverage, with an impressive maximum band gap up to 0.50?eV. The ab initio quantum transport simulation of a bottom-gated FET based on a sodium-covered silicene reveals a transport gap, which is consistent with the band gap, and the resulting on/off current ratio is up to 108. Therefore, a way is paved for silicene as the channel of a high-performance FET.
Quhe, Ruge; Fei, Ruixiang; Liu, Qihang; Zheng, Jiaxin; Li, Hong; Xu, Chengyong; Ni, Zeyuan; Wang, Yangyang; Yu, Dapeng; Gao, Zhengxiang; Lu, Jing
Plasmonic band structure controls single-molecule fluorescence.
Plasmonics and photonic crystals are two complementary approaches to tailor single-emitter fluorescence, using strong local field enhancements near metals on one hand and spatially extended photonic band structure effects on the other hand. Here, we explore the emergence of spontaneous emission control by finite-sized hexagonal arrays of nanoapertures milled in gold film. We demonstrate that already small lattices enable highly directional and enhanced emission from single fluorescent molecules in the central aperture. Even for clusters just four unit cells across, the directionality is set by the plasmonic crystal band structure, as confirmed by full-wave numerical simulations. This realization of plasmonic phase array antennas driven by single quantum emitters opens a flexible toolbox to engineer fluorescence and its detection. PMID:24020654
Langguth, Lutz; Punj, Deep; Wenger, Jķr¶me; Koenderink, A Femius
Experimental verification of directional liquid surface wave emission at band edge frequencies
Directional liquid surface wave emission at band edge frequencies is an interesting physical phenomenon and has already been studied in theoretical research. There has been no experimental validation of it to date, however. This paper has as its subject the experimental investigation of the emission effect when a point source is placed inside a finite square array of rigid cylinders standing vertically in liquid. Both the wave patterns and spatial intensities are obtained by experiment and compared with simulated results calculated by using the finite element method. We can see from this comparison that the two results correspond closely both at lower and upper band edge frequency. Obvious directional wave emission along a desired direction is observed in the source structures, confirming previous theoretical predictions. In the future, this method could serve as a directional liquid wave source in applications used in hydraulic and ocean engineering for the concentration of wave energy.
Wang, Zhenyu; Zhang, Pei; Zhang, Yongqiang; Nie, Xiaofei
Structure of adiabatic shear bands in thermo-viscoplastic materials
The shear band structure in a thermo-viscoplastic material has been analyzed under quasi-static conditions during the final stage of the localization process. A closed form expression of the bandwidth, of the size of the heat-affected zone and of the failure time has been obtained for a homogeneous material. The analysis is based on the assumption that the strain-rate distribution is
Florence Dinzart; Alain Molinari
Graphene on Ru(0001): Evidence for two graphene band structures
High-resolution photoemission illustrates that the band structure of graphene on Ru(0001) exhibits a well-defined splitting. This splitting is largest with the graphene directly on the Ru(0001) substrate, whereas with a chemisorbed oxygen spacer layer between the graphene and the metal substrate, this splitting is considerably reduced. This splitting is attributed to a combination of chemical interactions between graphene and Ru(0001) and to screening of the former by the latter, not spin-orbit coupling.
Katsiev K.; Vescovo E.; Losovyj, Y.; Zhou, Z.; Liu, L.; Dowben, P.A.; Goodman, D.W.
Banded structures in directionally solidified Ti-52Al alloys
The authors report their results on the structure and chemistry of ingots and directionally solidified Ti-48Al and Ti-52Al alloys. Through the banding behavior, quantitative analysis of parts of the high temperature phase field in near-equiatomic Ti-Al alloys is obtained. A possible explanation for certain puzzling and unexplained observations by Oliver is presented. Optical microscopy, electron probe microanalysis (EPMA), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used in this investigation.
Ramanujan, R.V. (Univ. of Birmingham (United Kingdom)); Bi, Y.; Xu, Q.; Abell, J.S. (Univ. of Birmingham (United Kingdom). School of Metallurgy and Materials)
Abnormal Grain Growth in Austenite Structure Reversely Transformed from Ferrite/Pearlite-Banded Structure
The grain growth behavior of austenite reversely transformed from ferrite/pearlite (F/P)-banded and non-banded steels has been studied. It was found that the grain-coarsening temperature [the temperature at which abnormal grain growth (AGG) occurs] of the initially banded F/P structure is quite low compared with that of the non-banded sample. In the F/P-banded sample, the abnormal grains always originate from the former ferrite region. The occurrence of AGG is essentially attributable not to the austenite nucleation process during heating but to the grain growth process after the completion of austenizing. It was proposed that the lowered grain-coarsening temperature in the banded structure is due to the non-uniform pinning-effect of AlN precipitates between former ferrite and pearlite regions.
Zhang, Xianguang; Matsuura, Kiyotaka; Ohno, Munekazu
Band-gap nonlinearity in perovskite structured solid solutions
Compositional effects on optical band-gap energy using end members of ABO3 perovskites have been investigated through an optical absorption with a UV-spectroscopy. Three examples are selected, namely, BaTiO3-CaTiO3, BaTiO3-BaZrO3, and SrTiO3-BaZrO3 solid solutions. To understand the role of high temperature phase equilibria on the band-gap compositional trends, structural and microscopy data were determined. In simple systems such as Si-Ge, the nonlinear variations in band gap with composition is usually associated with the effect of the local lattice relaxations and provides a parabolic dependence, often referred to as the ``bowing'' phenomena. In the case of perovskite solutions, the cases are more complex, and a modified Vegard's law is introduced to account for the trends. This has to be considered in relation to high temperature phase formation where incomplete solid solutions and two-phase regions exist. In addition to high temperature phases, low temperature displacive phase transitions and complex nonstoichiometry also perturb the band-gap variation in perovskite oxide materials.
Lee, Soonil; Levi, Roni D.; Qu, Weiguo; Lee, Sung Chan; Randall, Clive A.
Modification of Optical Band Gap and Surface Morphology of NiTsPc Thin Films
We demonstrate the effects of solvent treatment on the optical band gap and surface morphology of nickel (ii) phthalocyanine tetrasulfonic acid tetrasodium salt (NiTsPc) thin films. The optical band gap and surface morphology modifications are carried out by immersing the films in chloroform for different immersion times until the optimized time (60 min) is found. A Tauc plot is used to calculate the optical energy gaps, which are found to be about 2.70-2.85 eV and 1.43-1.50 eV, in the B and Q bands respectively. AFM topography shows that more granular structures have been formed upon the optimized immersion time. Photoluminescence (PL) quenching occurs in the solvent-treated NiTsPc film incorporated with a tris(8-hydroxyquinolinato)aluminium (Alq3) layer. This PL quenching indicates that the charge carrier transport is more efficient at the interface between NiTsPc/Alq3 as a result of the solvent treatment.
Muhamad Saipul, Fakir; Zubair, Ahmad; Khaulah, Sulaiman
Band to band tunneling in III-V semiconductors: Implications of complex band structure, strain, orientation, and off-zone center contribution
In this paper, we use a tight binding Hamiltonian with spin orbit coupling to study the real and complex band structures of relaxed and strained GaAs. A simple d orbital on-site energy shift coupled with appropriate scaling of the off-diagonal terms is found to correctly reproduce the band-edge shifts with strain. Four different ?100? strain combinations, namely, uniaxial compressive, uniaxial tensile, biaxial compressive, and biaxial tensile strain are studied, revealing rich valence band structure and strong relative orientation dependent tunneling. It is found that complex bands are unable to provide unambiguous tunneling paths away from the Brillouin zone center. Tunneling current density distribution over the Brillouin zone is computed using non-equilibrium Green's function approach elucidating a physical picture of band to band tunneling.
Majumdar, Kausik
Passive and Active L-Band Microwave Observations and Modeling of Ocean Surface Winds
L-band microwave backscatter and brightness temperature of sea surfaces acquired using the Passive\\/Active L-band Sensor during the High Ocean Wind campaign are reported in terms of their dependence on ocean surface wind speed and direction. We find that the L-band VV, HH, and HV radar backscatter data increase by 6-7 dB from 5 to 25 m\\/s wind speed at a
Simon H. Yueh; Steve J. Dinardo; Alexander G. Fore; Fuk K. Li
Simultaneous Multi-band Detection of Low Surface Brightness Galaxies with Markovian Modeling
We present to the astronomical community an algorithm for the detection of low surface brightness (LSB) galaxies in images, called MARSIAA (MARkovian Software for Image Analysis in Astronomy), which is based on multi-scale Markovian modeling. MARSIAA can be applied simultaneously to different bands. It segments an image into a user-defined number of classes, according to their surface brightness and surroundingsŚtypically, one or two classes contain the LSB structures. We have developed an algorithm, called DetectLSB, which allows the efficient identification of LSB galaxies from among the candidate sources selected by MARSIAA. The application of the method to two and three bands simultaneously was tested on simulated images. Based on our tests, we are confident that we can detect LSB galaxies down to a central surface brightness level of only 1.5 times the standard deviation from the mean pixel value in the image background. To assess the robustness of our method, the method was applied to a set of 18 B- and I-band images (covering 1.3 deg2 in total) of the Virgo Cluster to which Sabatini et al. previously applied a matched-filter dwarf LSB galaxy search algorithm. We have detected all 20 objects from the Sabatini et al. catalog which we could classify by eye as bona fide LSB galaxies. Our method has also detected four additional Virgo Cluster LSB galaxy candidates undetected by Sabatini et al. To further assess the completeness of the results of our method, both MARSIAA, SExtractor, and DetectLSB were applied to search for (1) mock Virgo LSB galaxies inserted into a set of deep Next Generation Virgo Survey (NGVS) gri-band subimages and (2) Virgo LSB galaxies identified by eye in a full set of NGVS square degree gri images. MARSIAA/DetectLSB recovered ~20% more mock LSB galaxies and ~40% more LSB galaxies identified by eye than SExtractor/DetectLSB. With a 90% fraction of false positives from an entirely unsupervised pipeline, a completeness of 90% is reached for sources with r e > 3'' at a mean surface brightness level of ?g = 27.7 mag arcsec-2 and a central surface brightness of ?0 g = 26.7 mag arcsec-2. About 10% of the false positives are artifacts, the rest being background galaxies. We have found our proposed Markovian LSB galaxy detection method to be complementary to the application of matched filters and an optimized use of SExtractor, and to have the following advantages: it is scale free, can be applied simultaneously to several bands, and is well adapted for crowded regions on the sky. .
Vollmer, B.; Perret, B.; Petremand, M.; Lavigne, F.; Collet, Ch.; van Driel, W.; Bonnarel, F.; Louys, M.; Sabatini, S.; MacArthur, L. A.
Below-band-gap excitation of a terahertz surface plasmon-polariton
We analyze the excitation of a surface plasmon-polariton at terahertz frequencies by an optical pulse with tilted intensity front incident on a semiconductor surface. We show that one can achieve an order of magnitude increase in the generated terahertz power by using an optical pulse with frequencies below the band gap compared to the above-band-gap excitation.
M. I. Bakunov; A. V. Maslov; S. B. Bodrov
Band gaps in the spectra of terahertz surface plasmons on metallic diffraction gratings
The effect of the appearance of band gaps in the energy spectra of terahertz surface plasmons has been experimentally observed and investigated. The band gaps are formed due to the interference interaction of the surface plasmons excited by pulsed terahertz radiation on metallic diffraction gratings. It has been shown that the experimental dispersion curves of terahertz plasmons are in good
A. V. Andreev; M. M. Nazarov; I. R. Prudnikov; A. P. Shkurinov
Microstrip antennas integrated with electromagnetic band-gap (EBG) structures: a low mutual coupling design for array applications
Utilization of electromagnetic band-gap (EBG) structures is becoming attractive in the electromagnetic and antenna community. In this paper, a mushroom-like EBG structure is analyzed using the finite-difference time-domain (FDTD) method. Its band-gap feature of surface-wave suppression is demonstrated by exhibiting the near field distributions of the electromagnetic waves. The mutual coupling of microstrip antennas is parametrically investigated, including both the
Fan Yang; Yahya Rahmat-Samii
Electronic structure of alkane chains. Complete one-dimensional band structures of the valence states
Several ultrathin films of oriented alkane chains were studied by ultraviolet photoelectron spectroscopy using UV photons in the energy range of 20-200 eV. From the experimental data the full valence band structure has been determined for self-assembled films of long-chain n-alkanethiols, Langmuir-Blodgett films of Cd-arachidate and thin films of hexatriacontane. Significant deviations from band structures obtained by ab initio calculations of Karpfen are found at the boundary of the one-dimensional Brillouin zone. Furthermore it is demonstrated that a mapping of the one-dimensional band structure can be used for precisely determining tilt angles of alkane chains.
Zubrõgel, Ch.; Schneider, F.; Neumann, M.; Hõhner, G.; W÷ll, Ch.; Grunze, M.
Large band gaps in phononic crystal slabs with rectangular cylinder inclusions parallel to the slab surfaces
The propagation of Lamb waves in a new phononic crystal slab composed of rectangular cylinder inclusions embedded periodically in a host material is investigated. The band structure of the phononic crystal is calculated and the influences of the geometry parameters of inclusions on the band structure are discussed. Results show that large band gap occurs in the phononic crystal slab and the band gap is significantly dependent on the width, height and rotation of the inclusions. Moreover, the eigenmodes of the Lamb waves are given to explain the relationship between the band gap and the geometry parameters of the inclusions.
Yu, Kunpeng; Chen, Tianning; Wang, Xiaopeng; Zhou, Anan
Dual-band metamaterial with a windmill-like structure
A broadband negative refractive index metamaterial based on a windmill-like structure is proposed, and investigated numerically and experimentally at the microwave frequency range. From the numerical and experimental results, effect media parameters are retrieved, which clearly show that two broad frequency bands exist in which the permittivity and permeability are negative. The two negative bands are from 9.1 GHz to 10.5 GHz and from 12.05 GHz to 14.65 GHz respectively, and the negative bandwidth is 4 GHz. Due to the good bandwidth performance, the metallic cell with double negative property obtained in this paper is suitable for use in the design of multiband or broadband microwave devices.
Xiong, Han; Hong, Jing-Song; Jin, Da-Lin
First direct observation of a nearly ideal graphene band structure
Angle-resolved photoemission and x-ray diffraction experiments show that multilayer epitaxial graphene grown on the SiC(000{bar 1}) surface is a new form of carbon that is composed of effectively isolated graphene sheets. The unique rotational stacking of these films causes adjacent graphene layers to electronically decouple leading to a set of nearly independent linearly dispersing bands (Dirac cones) at the graphene K point. Each cone corresponds to an individual macroscale graphene sheet in a multilayer stack where AB-stacked sheets can be considered as low density faults.
Sprinkle, M.; Siegel, D.; Hu, Y.; Hicks, J.; Tejeda, A.; Taleb-Ibrahimi, A.; Le FĶvre, P.; Bertran, F.; Vizzini, S.; Enriquez, H.; Chiang, S.; Soukiassian, P.; Berger, C.; de Heer, W.A.; Lanzara, A.; Conrad, E.H.; (CNRS-UMR); (UCB); (CEAS); (SOLEIL); (GIT)
The RF Technology Development group at Fermilab is working together with the NLC and GLC groups at SLAC and KEK on developing technology for room temperature X-band accelerating structures for a future linear collider. We built six 60-cm long, high phase advance, detuned structures (HDS or FXB series). These structures have 150 degrees phase advance per cell, and are intended for high gradient tests. The structures were brazed in a vacuum furnace with a partial pressure of argon, rather than in a hydrogen atmosphere. We have also begun to build 60-cm long, damped and detuned structures (HDDS or FXC/FXD series). We have built 5 FXC and 1 FXD structures. Our goal was to build six structures for the 8-pack test at SLAC by the end of March 2004, as part of the GLC/NLC effort to demonstrate the readiness of room temperature RF technology for a linear collider. This paper describes the RF structure factory infrastructure (clean rooms, vacuum furnaces, vacuum equipment, RF equipment etc.), and the fabrication techniques utilized (the machining of copper cells/couplers, quality control, etching, vacuum brazing, cleanliness requirements etc.) for the production of FXB and FXC/FXD structures.
Tug T Arkan et al.
Subwavelength Structured Surfaces: Theory and Applications
Detailed theoretical analysis of subwavelength structured (SWS) surfaces is presented. These surfaces are designed for applications in both the visible and infrared portions of the spectrum. Applications presented include antireflection structured (ARS) surfaces, polarization components, narrow-band filters, and phase plates. Experimental results for 2-D binary ARS surfaces are illustrated. Analysis of SWS surfaces is performed using rigorous coupled-wave analysis (RCWA) and effective medium theory (EMT). EMT is used to derive intuitive analytical formulae that describe a surface's reflection and transmission characteristics. It is shown, by comparing zeroth-order and higher-order EMT, that as the grating period increases, or the substrate index of refraction increases past a certain threshold, zeroth-order EMT results are erroneous and that results derived from higher-order EMT must be used. Comparisons between EMT and RCWA results are made. EMT results, particularly those derived using second-order EMT, are shown to match RCWA. The match between EMT and RCWA is best when the electric field is perpendicular to the grating vector. ARS surfaces with binary and multi-level 1-D and 2-D profiles are analyzed. The 1-D profiles are shown to be form birefringent and thus better suited for applications involving linearly-polarized light. 2-D profiles are shown to exhibit near-isotropic behavior, and thus are advantageous when randomly polarized radiation is an issue. As the number of levels the profiles contain increases, the tolerance of both 1-D and 2-D structures to bias angles, wavelength detunings, and errors in etch depth increases. ARS surfaces with 1-D continuous profiles are investigated. Analysis is performed using RCWA, as well as using a novel EMT approach which incorporates tapered transmission-line theory to obtain closed-form solutions for the reflection coefficients. Performance analysis is presented versus grating depth, incident wavelength, and angle of incidence, for the specific cases of triangular and sinusoidal profiles. As polarization components, SWS surfaces as wire -grid polarizers and wave plates are illustrated. Examples are given for ZnSe quarter-wave plates designed with binary and continuous 1-D profiles. SWS wave plates with continuous profiles have increased throughput due to reflection losses being minimized. For narrow-band filter designs, EMT is used to predict the location of a SWS filter's operating wavelength. As phase plates, the novel use of SWS surfaces to compress laser pulses is presented. Experimental results are presented for 2-D binary ARS surfaces. These gratings are designed for operation at CO_2-laser wavelengths.
Raguin, Daniel Henri
Surface and interior views on origins of two types of banded spherulites in poly(nonamethylene terephthalate).
Top-surface and three-dimensional views of Type-1 and Type-2 of ring-banded spherulites in poly(nonamethylene terephthalate) (PNT) in thicker bulk crystallized on a nucleating potassium bromide (KBr) substrate were examined using various microscopy techniques: scanning electron microscopy (SEM), polarized-optical microscopy (POM), and atomic-force microscopy (AFM). In PNT crystallized at higher crystallization temperature (T(c)) with heterogeneous nucleating substrate, typically two types of ring-banded spherulites are present that differ significantly in patterns and ring spacings: Type-1 Type-2 (single- and double-ring-banded spherulites). Three-dimensional view on fractured spherulites in bulk PNT samples reveals that the single-ring-banded spherulite (Type-1) tends to be well-rounded spheres as they are nucleated homogeneously from bulk; the double-ring-banded spherulite (Type-2) is concentric hemisphere or truncated sphere shells owing to be nucleated from bottom. With confined thickness of films, the 3-D hemispheres in PNT may become truncated into multi-shell annular cones or arcs when thickness or growth is restricted. Based on the top-surface vs. interior views of banded lamellar assembly, origins and inner structures of dual types of ring bands in PNT were examined in greater details. PMID:21909562
Woo, Eamor M; Nurkhamidah, Siti; Chen, Yu-Fan
Probing surface band bending of surface-engineered metal oxide nanowires.
We in situ probed the surface band bending (SBB) by ultraviolet photoelectron spectroscopy (UPS) in conjunction with field-effect transistor measurements on the incompletely depleted ZnO nanowires (NWs). The diameter range of the NWs is ca. 150-350 nm. Several surface treatments (i.e., heat treatments and Au nanoparticle (NP) decoration) were conducted to assess the impact of the oxygen adsorbates on the SBB. A 100 ░C heat treatment leads to the decrease of the SBB to 0.74 ▒ 0.15 eV with 29.9 ▒ 3.0 nm width, which is attributed to the removal of most adsorbed oxygen molecules from the ZnO NW surfaces. The SBB of the oxygen-adsorbed ZnO NWs is measured to be 1.53 ▒ 0.15 eV with 43.2 ▒ 2.0 nm width. The attachment of Au NPs to the NW surface causes unusually high SBB (2.34 ▒ 0.15 eV with the wide width of 53.3 ▒ 1.6 nm) by creating open-circuit nano-Schottky junctions and catalytically enhancing the formation of the charge O(2) adsorbates. These surface-related phenomena should be generic to all metal oxide nanostructures. Our study is greatly beneficial for the NW-based device design of sensor and optoelectronic applications via surface engineering. PMID:23092152
Chen, Cheng-Ying; Retamal, Jose Ramon Duran; Wu, I-Wen; Lien, Der-Hsien; Chen, Ming-Wei; Ding, Yong; Chueh, Yu-Lun; Wu, Chih-I; He, Jr-Hau
Bulk and surface electronic structure of Li2O
We have used photoemission and electron-energy-loss spectroscopies to determine the surface and bulk electronic structure of a single-crystal sample of the alkali-metal oxide Li2O. The predominately O 2p valence band exhibits two main features in the photoemission spectrum, whose relative widths are consistent with results of an ab initio Hartree-Fock calculation of the bulk electronic structure. However, changes in the intensity of the two features as a function of the exciting photon energy are large and not understood. Energy-loss spectra show the presence of a strong surface exciton in the bulk band gap of Li2O; such excitonic surface states do not exist for the alkali halides. Its energy is about 2 eV less than the bulk band gap, similar to the surface excitonic shifts that have been observed in the alkaline-earth oxides.
Liu, Lizhong; Henrich, Victor E.; Ellis, W. P.; Shindo, I.
Electronic band structure, doping, and defects in the semiconducting Half Heusler compound CoTiSb
We report transport and electronic band structure measurements on epitaxial films of the Half Heusler compound CoTiSb. CoTiSb belongs to the family of Half Heuslers with 18 valence electrons per formula unit that are predicted to be semiconducting despite being composed of all metallic components. Here the CoTiSb films were grown by molecular beam epitaxy on a lattice matched InAlAs buffer. The films are epitaxial and single crystalline, as measured by reflection high-energy electron diffraction and X-ray diffraction. Scanning tunnelling spectroscopy and temperature-dependent transport measurements reveal that the films are semiconducting, with unintentionally doped carrier concentrations comparable to that of highly doped conventional compound semiconductors. These carrier concentrations can be modulated by doping with Sn. The band structure of the films was measured by angle resolved photoemission spectroscopy at the MAX-Lab Synchrotron facility. The bulk bands are in general agreement with density functional theory calculations, with a valence band maximum at ? and surface states within the bulk band gap. The effects of defects are explored in order to explain the ARPES results.
Kawasaki, Jason; Johansson, Linda; Hjort, Martin; Timm, Rainer; Schultz, Brian; Balasubramanian, Thiagarajan; Mikkelsen, Anders; Palmstrom, Chris
Lamķ polynomials, hyperelliptic reductions and Lamķ band structure.
The band structure of the Lamķ equation, viewed as a one-dimensional Schr÷dinger equation with a periodic potential, is studied. At integer values of the degree parameter l, the dispersion relation is reduced to the l=1 dispersion relation, and a previously published l=2 dispersion relation is shown to be partly incorrect. The Hermite-Krichever Ansatz, which expresses Lamķ equation solutions in terms of l=1 solutions, is the chief tool. It is based on a projection from a genus-l hyperelliptic curve, which parametrizes solutions, to an elliptic curve. A general formula for this covering is derived, and is used to reduce certain hyperelliptic integrals to elliptic ones. Degeneracies between band edges, which can occur if the Lamķ equation parameters take complex values, are investigated. If the Lamķ equation is viewed as a differential equation on an elliptic curve, a formula is conjectured for the number of points in elliptic moduli space (elliptic curve parameter space) at which degeneracies occur. Tables of spectral polynomials and Lamķ polynomials, i.e. band-edge solutions, are given. A table in the earlier literature is corrected. PMID:17588866
Maier, Robert S
The influence of A-band and B-band lipopolysaccharide on the surface characteristics and adhesion of Pseudomonas aeruginosa to surfaces
Pseudomonas aenrginosa PA01 possesses two distinct lipopolysaccharide (LPS) O-polysaccharide species, A- and B-band LPS, the relative expression of which appears to be under environmental control. In an attempt to identify the influence these LPS types have on surface characteristics and adhesion, we examined the surface hydrophobicity and surface charge of P. aemginosa PA01 (05 serotype) and its isogenic LPS derivatives
Stephen A. Makin; Terrance J. Beveridge
Band Structure Asymmetry of Bilayer Graphene Revealed by Infrared Spectroscopy
We report on infrared spectroscopy of bilayer graphene integrated in gated structures. We observe a significant asymmetry in the optical conductivity upon electrostatic doping of electrons and holes. We show that this finding arises from a marked asymmetry between the valence and conduction bands, which is mainly due to the inequivalence of the two sublattices within the graphene layer and the next-nearest-neighbor interlayer coupling. From the conductivity data, the energy difference of the two sublattices and the interlayer coupling energy are directly determined.
Li, Z.Q.; Henriksen, E.A.; Jiang, Z.; Hao, Zhao; Martin, Michael C.; Kim, P.; Stormer, H.L.; Basov, Dimitri N.
Band structure in the polymer quantization of the harmonic oscillator
We discuss the detailed structure of the spectrum of the Hamiltonian for the polymerized harmonic oscillator and compare it with the spectrum in the standard quantization. As we will see the non-separability of the Hilbert space implies that the point spectrum consists of bands similar to the ones appearing in the treatment of periodic potentials. This feature of the spectrum of the polymeric harmonic oscillator may be relevant for the discussion of the polymer quantization of the scalar field and may have interesting consequences for the statistical mechanics of these models.
Barbero G, J. Fernando; Prieto, Jorge; Villase±or, Eduardo J. S.
Band structure of odd-mass lanthanum nuclei
Negative parity energy states in 121-131La have been studied using Projected Shell Model (PSM). Some nuclear structure properties like yrast spectra, back-bending in moment of inertia, reduced transition probabilities and band diagrams have been described. The experimental feature of the co-existence of prolate-oblate shapes in 125-131La isotopes has been satisfactorily explained by PSM results. Comparison of the theoretical data with their experimental counterparts has also been made. From the calculations, it is found that the yrast states arise because of multi-quasiparticle states.
Sharma, Deepti; Verma, Preeti; Singh, Suram; Bharti, Arun; Khosa, S. K.
Electronic structure of the valence band of GdS x and Gd 3S 4
Electronic structure of clean surfaces of single crystals of magnetic compounds of sulfides of gadolinium GdS x ( x = 0.8-1.25) with NaCl and Th 3P 4 structures has been investigated by ultra-violet and X-ray photoelectron, Auger and electron energy loss spectroscopy. Clean surfaces of GdS x were obtained by cleavage in situ in ultra-high vacuum and by ion bombardment followed by annealing in vacuum. Photoelectron spectra of the valence band of GdS x family have the similar structure with a maxima at 9 eV and 5 eV related to a photoemission from the 4f-states and valence band formed by 3p-states of S anions respectively and features in the region 0-2 eV associated with 6s-5d conduction band of GdS x. An analysis of electron energy loss spectra has shown that the main features in loss spectra at high beam energy are associated with the 4d-4f giant resonance, 5p-5d resonance and plasmon excitation. At low incident energy a prominent multiplet structure is observed and interpreted in terms of the dipole-forbidden 4f ? 4f electron transitions.
Grazhulis, V. A.; Bozhko, S. I.; Bolotin, I. L.; Bulanov, O. R.; Ionov, A. M.
Nutrient loss in leachate and surface runoff from surface-broadcast and subsurface-banded broiler litter.
Subsurface band application of poultry litter has been shown to reduce the transport of nutrients from fields in surface runoff compared with conventional surface broadcast application. Little research has been conducted to determine the effects of surface broadcast application and subsurface banding of litter on nutrients in leachate. Therefore, a field experiment was conducted to determine the effects of subsurface band application and surface broadcast application of poultry litter on nutrient losses in leachate. Zero-tension pan and passive capillary fiberglass wick lysimeters were installed in situ 50 cm beneath the soil surface of an established tall fescue ( Schreb.) pasture on a sandy loam soil. The treatments were surface broadcast and subsurface-banded poultry litter at 5 Mg ha and an unfertilized control. Results of the rainfall simulations showed that the concentrations of PO-P and total phosphorus (TP) in leachate were reduced by 96 and 37%, respectively, in subsurface-banded litter treatment compared with the surface-applied litter treatment. There was no significant difference in PO-P concentration between control and subsurface-banded litter treatment in leachate. The trend in the loading of nutrients in leachate was similar to the trend in concentration. Concentration and loading of the nutrients (TP, PO-P, NH-N, and NO-N) in runoff from the subsurface-banded treatment were significantly less than for the surface-applied treatment and were similar to those from control plots. These results show that, compared with conventional surface broadcast application of litter, subsurface band application of litter can greatly reduce loss of P in surface runoff and leachate. PMID:24216435
Lamba, Jasmeet; Srivastava, Puneet; Way, Thomas R; Sen, Sumit; Wood, C Wesley; Yoo, Kyung H
Domain structures in nematic liquid crystals on a polycarbonate surface.
Alignment of nematic liquid crystals on polycarbonate films obtained with the use of solvents with different solvations is studied. Domain structures occurring during the growth on the polymer surface against the background of the initial thread-like or schlieren texture are demonstrated. It is established by optical methods that the domains are stable formations visualizing the polymer surface structures. In nematic droplets, the temperature-induced transition from the domain structure with two extinction bands to the structure with four bands is observed. This transition is shown to be caused by reorientation of the nematic director in the liquid crystal volume from the planar alignment to the homeotropic state with the pronounced radial configuration of nematic molecules on the surface. The observed textures are compared with different combinations of the volume LC orientations and the radial distribution of the director field and the disclination lines at the polycarbonate surface. PMID:23965955
Parshin, Alexander M; Gunyakov, Vladimir A; Zyryanov, Victor Y; Shabanov, Vasily F
Analysis and Experimental Observations of Two - Photonic Band Gap Structures
The focus of this dissertation has been to analyze in detail two dimensionally periodic or mostly periodic photonic band gap (PBG) systems. We have accomplished this by developing numerical algorithms which can be applied to such systems. In particular, we have developed codes for computing the photonic band structure of arbitrary 2D dielectric and metal photonic lattices, as well as simulations to study such lattices with local perturbations, such as defects. We have also developed a simulation to study the transmission and reflection properties of photonic lattices. We have performed microwave transmission measurements on test dielectric and metal lattices with and without defects, and found excellent agreement with predictions obtained from the simulations. As a result of our numerical investigations, we discovered that a lattice consisting of periodically placed metal cylinders exhibited a number of similar properties to the dielectric PBG systems. Furthermore, removing one cylinder from the array produced a single, highly localized mode, in which the energy density associated with the mode decayed away from the defect site exponentially, at a rate of 30 dB per lattice constant. We designed and built several versions of the metal PBG cavities with fundamental resonances at 3.3 GHz and 9.0 GHz, and confirmed the behaviour predicted from the simulations. Reflection measurements indicated a Q of ~4,000 for the room temperature copper PBG cavities. Finally, examining a frequency span of up to four times the fundamental frequency of the 3.3 GHz metal cavity, we found numerous higher order, low-Q resonances corresponding to marginally localized modes with frequencies occuring in the pass bands. We discuss the resonances and other technical issues which may limit the performance of PBG structures used as cavities.
Smith, David Richard
Band structure of photonic crystal with dispersive and lossy materials using Dirichlet-to-Neumann wave vector eigen equation method
We present the Dirichlet-to-Neumann wave vector eigen equation (DtN-WVEE) method to calculate the band structure of photonic crystal (PhC) with dispersive and lossy materials, and then use finite-difference time-domain method to verify the validity of the results of the DtN-WVEE method. Since the material is lossy with a non-zero imaginary part of epsilon, the wave vector of PhC band structure also has a non-zero imaginary part which results in the reduction of the intensity of the mode. We further present the band structure which gives the relationship among the normalized frequency, the real part of the wave vector, and the imaginary part of the wave vector. To our knowledge, the band structure of lossy PhC has not been well studied yet, and our results can be useful in designing the devices using surface plasmon polariton effect.
Jiang, Bin; Zhang, Yejin; Wang, Yufei; Zheng, Wanhua
Metal-induced gap states in ferroelectric capacitors and its relationship with complex band structures
At metal-isulator interfaces, the metallic wave functions with an energy eigenvalue within the band gap decay exponentially inside the dielectric (metal-induced gap states, MIGS). These MIGS can be actually regarded as Bloch functions with an associated complex wave vector. Usually only real values of the wave vectors are discussed in text books, since infinite periodicity is assumed and, in that situation, wave functions growing exponentially in any direction would not be physically valid. However, localized wave functions with an exponential decay are indeed perfectly valid solution of the Schrodinger equation in the presence of defects, surfaces or interfaces. For this reason, properties of MIGS have been typically discussed in terms of the complex band structure of bulk materials. The probable dependence on the interface particulars has been rarely taken into account explicitly due to the difficulties to include them into the model or simulations. We aim to characterize from first-principles simulations the MIGS in realistic ferroelectric capacitors and their connection with the complex band structure of the ferroelectric material. We emphasize the influence of the real interface beyond the complex band structure of bulk materials.
Junquera, Javier; Aguado-Puente, Pablo
Quasiparticle semiconductor band structures including spin-orbit interactions.
We present first-principles calculations of the quasiparticle band structure of the group IV materials Si and Ge and the group III-V compound semiconductors AlP, AlAs, AlSb, InP, InAs, InSb, GaP, GaAs and GaSb. Calculations are performed using the plane wave pseudopotential method and the 'one-shot' GW method, i.e. G(0)W(0). Quasiparticle band structures, augmented with the effects of spin-orbit, are obtained via a Wannier interpolation of the obtained quasiparticle energies and calculated spin-orbit matrix. Our calculations explicitly treat the shallow semicore states of In and Ga, which are known to be important in the description of the electronic properties, as valence states in the quasiparticle calculation. Our calculated quasiparticle energies, combining both the ab initio evaluation of the electron self-energy and the vector part of the pseudopotential representing the spin-orbit effects, are in generally very good agreement with experimental values. These calculations illustrate the predictive power of the methodology as applied to group IV and III-V semiconductors. PMID:23396813
Malone, Brad D; Cohen, Marvin L
Photonic band structure calculations using nonlinear eigenvalue techniques
This paper considers the numerical computation of the photonic band structure of periodic materials such as photonic crystals. This calculation involves the solution of a Hermitian nonlinear eigenvalue problem. Numerical methods for nonlinear eigenvalue problems are usually based on Newton's method or are extensions of techniques for the standard eigenvalue problem. We present a new variation on existing methods which has its derivation in methods for bifurcation problems, where bordered matrices are used to compute critical points in singular systems. This new approach has several advantages over the current methods. First, in our numerical calculations the new variation is more robust than existing techniques, having a larger domain of convergence. Second, the linear systems remain Hermitian and are nonsingular as the method converges. Third, the approach provides an elegant and efficient way of both thinking about the problem and organising the computer solution so that only one linear system needs to be factorised at each stage in the solution process. Finally, first- and higher-order derivatives are calculated as a natural extension of the basic method, and this has advantages in the electromagnetic problem discussed here, where the band structure is plotted as a set of paths in the ({omega},k) plane.
Spence, Alastair [Department of Mathematical Sciences, University of Bath, Claverton Down, Bath BA2 7AY (United Kingdom); Poulton, Chris [High Frequency and Quantum Electronics Laboratory, University of Karlsruhe, Kaiserstrasse 12, Karlsruhe 76128 (Germany)]. E-mail: email@example.com
Nonparabolic band structure effect on carrier transport in semiconducting graphene nanoribbons
The band energy of graphene nanoribbon is parabolic when reaching the minimum band energy. Otherwise, it is nonparabolic. In the parabolic band structure, Fermi-Dirac integrals are employed to study the carrier statistic whereas for nonparabolic part, numerical solutions are needed. Numerical method shows Fermi energy with respect to the band edge is a function of temperature that independent of the
N. Aziziah Amin; Zaharah Johari; Mohammad Taghi Ahmadi; Razali Ismail; D. C. Y. Chek; E. H. X. Ng
The effect of spin-orbit coupling in band structure of few-layer graphene
Topological insulators are electronic materials that have a bulk band gap like an ordinary insulator but have protected conducting states on their edge or surface. This can be happened due to spin-orbit coupling and time-reversal symmetry. Moreover, the edge current flows through their edge or surface depends on its spin orientation and also it is robust against non-magnetic impurities. Therefore, topological insulators are predicted to be useful ranging from spintronics to quantum computation. Graphene was first predicted to be the precursor of topological insulator by Kane-Mele. They developed a Hamiltonian model to describe the gap opening in graphene. In this work, we investigate the band structure of few-layer graphene by using this model with analytical approach. The results of our calculations show that the gap opening occurs at K and K' point, not only in single layer, but also in bilayer and trilayer graphene.
Sahdan, Muhammad Fauzi; Darma, Yudi
[Terahertz-band study on surface enhanced Raman scattering of nanoparticle].
Study on surface-enhanced Raman scattering in the terahertz-band proved in that the terahertz-band Raman enhancement also exists. By studing principles of electromagnetic enhancement of surface-enhanced Raman scattering, using the finite difference time-domain method, the electromagnetic enhancement of surface enhanced Raman scattering of nano-particles irradiated by terahertz-wave was simulated, and the enhancement effect of terahertz waves was analyzed. Simulation experiments show that using finite-difference time-domain method could obtain effectively accurate simulation result of nano-particle scattering, proving that for terahertz waves, surface-enhanced effects on the surface of the nano-particle also exist. The results for surface enhanced Raman scattering extended from the visible and infrared to terahertz-band, and provide a basis for application of the combination of surface-enhanced Raman scattering and terahertz-wave. PMID:23905325
Wu, Yu-Deng; Ren, Guang-Jun; Hao, Yun; Yao, Jian-Quan
Effects of surface oxide formation on germanium nanowire band-edge photoluminescence
The effect of intentional surface oxide formation on band-edge photoluminescence (PL) of Ge nanowires was investigated. Thermal oxidation in molecular O{sub 2} was used to produce a surface oxide layer on assemblies of single crystal nanowires grown by the vapor-liquid-solid method. With increasing oxidation of the wires, the band-edge PL associated with the indirect gap transition becomes more intense. X-ray photoelectron spectroscopy confirms the formation of an increasingly GeO{sub 2}-like surface oxide under annealing conditions that enhance the indirect-gap PL, consistent with surface oxide passivation of nonradiative recombination centers initially present on the nanowire surface.
Minaye Hashemi, Fatemeh Sadat [Department of Materials Science and Engineering, Stanford University, Stanford, California 94305 (United States) [Department of Materials Science and Engineering, Stanford University, Stanford, California 94305 (United States); Laboratoire des Materiaux Semiconducteurs, Ecole Polytechnique Federale de Lausanne, 1015 Lausanne (Switzerland); Thombare, Shruti; Brongersma, Mark L. [Department of Materials Science and Engineering, Stanford University, Stanford, California 94305 (United States)] [Department of Materials Science and Engineering, Stanford University, Stanford, California 94305 (United States); Morral, Anna Fontcuberta i [Laboratoire des Materiaux Semiconducteurs, Ecole Polytechnique Federale de Lausanne, 1015 Lausanne (Switzerland)] [Laboratoire des Materiaux Semiconducteurs, Ecole Polytechnique Federale de Lausanne, 1015 Lausanne (Switzerland); McIntyre, Paul C. [Department of Materials Science and Engineering, Stanford University, Stanford, California 94305 (United States) [Department of Materials Science and Engineering, Stanford University, Stanford, California 94305 (United States); Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305 (United States)
Soliton lattice structure and mid-gap band in nearly commensurate charge-density-wave states. II. Self-similar band-structure and coupling-constant dependence
We numerically diagonalize the one-dimensional Fr÷hlich Hamiltonian by taking into account all higher harmonics associated with the charge-density-wave (CDW) formation self-consistently within the mean-field approximation. The overall band structures for various CDW states corresponding to a wide variety of the band fillings are derived to yield a self-similar structure, clarifying the interrelation between the mid-gap band and conduction (or valence)
Kazushige Machida; Masahiro Nakano
Energy band of manipulated atomic structures on an insulator substrate
Stimulated by recent progress in atom manipulation technology, the electronic properties of periodic structures artificially created with atoms on a substrate surface are studied, where constituent atoms are isolated from substrate atoms and interact with one another through neighboring?atom interactions. By reducing the lattice constant from infinity, the neighboring?atom interaction is gradually turned on, and discrete atomic states broaden to
Toshishige Yamada; Yoshihisa Yamamoto; W. A. Harrison
Band Structure of Ni(100) vs. Permalloy (100)
The magnetic characteristics of permalloy make this material widely used in data storage technolgy. Sensors for hard disk reading heads have been using anisotropic magnetoresistance (AMR) of permalloy or giant magnetoresistance (GMR) of permalloy/Cu/Co thin films. It also exhibits an unusually short scattering length for minority spins. Yet, only a few electronic structure studies have been published about permalloy and many questions related to the unusual spin scattering remain open, e.g. the nature of the scattering states introduced by the Fe impurity. We have mapped the valence band of clean Ni(100) and epitaxial permalloy(100) by employing an imaging photoemission spectrometer coupled to an undulator synchrotron radiation beamline. Using the appropriate photon energies we are able to probe the high symmetric points in k-space ?(400) and X(300) and to compare the momentum distributions between Ni and permalloy. They differ, both in the 3d band and at the Fermi level. These differences will be discussed in the context of the electronic and magnetic properties, particularly regarding possible minority spin scattering states. N.Franco acknowledges a scholarship from the Spanish Education and Culture Office, C. Bostedt from the German Academic Exchange Service DAAD. The work is supported by the US-DOE, BES Material Sciences under contract W-7405-ENG-48, LLNL.
Franco, N.; Klepeis, J.; van Buuren, T.; Bostedt, C.; Terminello, L. J.; Himpsel, F.
Band structures of helical nanotubes analyzed with the scattering matrix
It has been reported that helical nanotubes, where each pitch has almost common length, can be produced.(V.Ivanov et al., Chem. Phys. Lett. 223), 329 (1994) It is a reasonable assumption that the bends of these helices are formed by pairs of disclinations, pentagon-heptagon carbon rings, arranged periodically in the hexagonal network. We have obtained scattering matrices of the various nanotube junctions formed by a pair of the pentagon and the heptagon. ( R. Tamura and M. Tsukada, Phys. Rev. B 55) 4991 (1997) The helical nanotubes can be considered as the multiple junctions composed of these junctions connected periodically. >From this viewpoint, close relation between their one dimensional band structures and configurations of the disclinations (K. Akagi et al.,Phys. Rev. B 53),2114 (1996)can be deduced from the scattering matrices. For example, we discuss the mechanism determining the presence or absence near the half-filled Fermi energy based on the configuration of the disclinations. The relation between the size of the helical nanotubes and the width of the gap or the band is also discussed.
Ryo, Tamura; Masaru, Tsukada
Semiconductor Nanocrystals: Structure, Properties, and Band Gap Engineering
Semiconductor nanocrystals are tiny light-emitting particles on the nanometer scale. Researchers have studied these particles intensely and have developed them for broad applications in solar energy conversion, optoelectronic devices, molecular and cellular imaging, and ultrasensitive detection. A major feature of semiconductor nanocrystals is the quantum confinement effect, which leads to spatial enclosure of the electronic charge carriers within the nanocrystal. Because of this effect, researchers can use the size and shape of these ōartificial atomsö to widely and precisely tune the energy of discrete electronic energy states and optical transitions. As a result, researchers can tune the light emission from these particles throughout the ultraviolet, visible, near-infrared, and mid-infrared spectral ranges. These particles also span the transition between small molecules and bulk crystals, instilling novel optical properties such as carrier multiplication, single-particle blinking, and spectral diffusion. In addition, semiconductor nanocrystals provide a versatile building block for developing complex nanostructures such as superlattices and multimodal agents for molecular imaging and targeted therapy. In this Account, we discuss recent advances in the understanding of the atomic structure and optical properties of semiconductor nanocrystals. We also discuss new strategies for band gap and electronic wave function engineering to control the location of charge carriers. New methodologies such as alloying, doping, strain-tuning, and band-edge warping will likely play key roles in the further development of these particles for optoelectronic and biomedical applications.
The reflection and transmission properties of a triple band dichroic surface
The development of a triple-band dichroic surface design is detailed that is reflective in the Ka-band from 22.5 to 27.3 GHz and the Ku-band from 13.7 to 15.1 GHz, yet transparent in the S-band from 2.0 to 2.3 GHz, for all planes of incidence, and for all angles of incidence out to eta = 45 deg. The design is comprised of two gangbuster whole-surfaces separated by a distance, d, that is comparable to a fraction of a wavelength in S-band, and enhanced by the addition of a dielectric matching plate. The gangbuster array is comprised of tightly packed straight skewed dipole elements referred to as half-surfaces. Two of these half-surfaces are oriented orthogonal to each other and placed an array separation distance, s, apart to form the gangbuster whole-surface which allows any arbitrary plane of incidence. Results are given for the triple-band design with and without dielectric and conduction losses. The cross polarization properties of the dichroic surface was further investigated. It is shown that the reflection cross polarized component is dominated by the geometry of the front whole surface of the design (particularly the array separation s) and is never more than -22.5 dB in the frequency band 0 to 30 GHz. The transmission cross polarization component is dependent on both whole-surfaces and is never more than -30 dB in the same frequency band.
Schneider, S. W.; Munk, B. A.
Microstructures of surface white layer and internal white adiabatic shear band
After being impacted in an impact wear tester simulating the conditions in a mill, the surface white layer and internal white adiabatic shear band were observed in a low alloy steel (0.40% C?0.85% Cr?1.55% Ni?0.20% Mo). It was found that cracks can easily nucleate and propagate in the surface white layer and internally formed adiabatic shear band during impact wear
Baofa Zhang; Wanci Shen; Yingjie Liu; Xiangyun Tang; Yuanfei Wang
Modeling Sun Glitter at L-Band for Sea Surface Salinity Remote Sensing With SMOS
Since the sun is an extremely strong radiation source at L-band, accounting for sun glint over the ocean, i.e., solar radiation reflected by the sea surface toward downward-looking radiometers, raises a significant challenge for the remote sensing of sea surface salinity. This paper describes a dedicated physical model for sun glint at L-band frequencies and provides quantitative and qualitative estimates
Nicolas Reul; Joseph Tenerelli; Bertrand Chapron; Philippe Waldteufel
Applying liquid manure by surface banding increases short-term yield compared to broadcasting pro- bably by reducing NH3 loss. However, the response to surface-banding slurry manure on grass N after several years of application has not been reported. This study compared the effects of commercial fertili- zer with drag-shoe applied dairy slurry on yield, N uptake and soil parameters of a
S. Bittman; C. G. Kowalenko; D. E. Hunt; F. Bounaix; T. Forge
Simultaneous measurements of ku- and ka-band sea surface cross sections by an airborne Radar
The dual-frequency Airborne Precipitation Radar-2 (APR-2) was deployed during the Wakasa Bay Experiment in 2003, for validation of the Advanced Microwave Scanning Radiometer-EOS. Besides providing extensive observations of diverse precipitating systems, this Ku-(13.4 GHz) and Ka-band (35.6 GHz) cross-track scanning radar measured sea surface backscatter simultaneously. While the characteristics of the normalized sea surface cross section sigma0 at Ku-band are
Simone Tanelli; Stephen L. Durden; E. Im
The effect of the appearance of band gaps in the energy spectra of terahertz surface plasmons has been experimentally observed\\u000a and investigated. The band gaps are formed due to the interference interaction of the surface plasmons excited by pulsed terahertz\\u000a radiation on metallic diffraction gratings. It has been shown that the experimental dispersion curves of terahertz plasmons\\u000a are in good
Photonic Band Structures and Radiation in Two or Three Dimensional Periodic Structures
In this dissertation, dispersion relations of electromagnetic waves and radiation in two- or three-dimensional periodic structures are studied. It is both theoretically and experimentally indicated that various kinds of electromagnetic radiation can be efficiently controlled by periodic structures. In the first chapter, basic concepts of photonic band theory are explained. In addition, the possibility of controlling radiation (i.e. spontaneous emission)
Toshio Suzuki
Wide-Band Transducer for Surface Elastic Waves.
A log-periodic interdigital transducer for surface elastic waves was fabricated and shown to have good agreement with an approximate analytical model. Experiments were performed on a mechanically variable delay line. (Author)
M. E. Motamedi M. Epstein
Band structure of the spectra of Hamiltonians of regular polynucleotide duplexes
We calculate the band structure of the spectra of Hamiltonians of regular DNA duplexes and show that in single-stranded periodic polynucleotides whose period is determined by the number m of nucleotides in an elementary cell, the spectrum consists of m nonintersecting energy bands. In DNA duplexes, the number of energy bands is equal to 2m, and the bands can intersect. Discrete energy levels can be present in forbidden bands in the case of (semi)bounded chains or duplexes.
Lakhno, V. D.; Sultanov, V. B.
Cloud Bands Structure of Hurricane David, 1979 - A Case Study.
The nature of the spiral banding of Hurricane David immediately before, during, and after a period of intensification is examined. The tropical cyclone spiral banding features are analyzed by the Tactical Environmental Display System (TEDS) program on the...
F. H. Nicholson
Surface wicking structures possessing strong interconnectivity are designed and examined. The designs aim to optimize the structure's ability to transport fluids by exploiting capillary driven flow in interior corners combined with interconnectivity and alignment. `Waffle-like' structures consisting of vertical rectangular vanes at a variety of orientations are employed as the basic repeat unit. Due to this arrangement, such surfaces possess interconnectivity that is stronger than that of other existing designs such as those composed of micro posts. This strong interconnectivity provides several advantages. For example, it is found that the transport of fluid by wicking can be controlled by a clever choice of the interconnectivity and vane alignment. As a result, the shape of the moving front during wicking can be circular, elliptical, or rectangular. The observations as well as a study of the dynamics of the wicking flow will be presented.
Chen, Yongkang; Bell, Donald; Rodriguez, Santiago; Semerjian, Ben; Melvin, Lawrence; Weislogel, Mark
Complex layered materials and periodic electromagnetic band-gap structures: Concepts, characterizations, and applications
The main objective of this dissertation is to characterize and create insight into the electromagnetic performances of two classes of composite structures, namely, complex multi-layered media and periodic Electromagnetic Band-Gap (EBG) structures. The advanced and diversified computational techniques are applied to obtain their unique propagation characteristics and integrate the results into some novel applications. In the first part of this dissertation, the vector wave solution of Maxwell's equations is integrated with the Genetic Algorithm (GA) optimization method to provide a powerful technique for characterizing multi-layered materials, and obtaining their optimal designs. The developed method is successfully applied to determine the optimal composite coatings for Radar Cross Section (RCS) reduction of canonical structures. Both monostatic and bistatic scatterings are explored. A GA with hybrid planar/curved surface implementation is also introduced to efficiently obtain the optimal absorbing materials for curved structures. Furthermore, design optimization of the non-uniform Luneburg and 2-shell spherical lens antennas utilizing modal solution/GA-adaptive-cost function is presented. The lens antennas are effectively optimized for both high gain and suppressed grating lobes. The second part demonstrates the development of an advanced computational engine, which accurately computes the broadband characteristics of challenging periodic electromagnetic band-gap structures. This method utilizes the Finite Difference Time Domain (FDTD) technique with Periodic Boundary Condition/Perfectly Matched Layer (PBC/PML), which is efficiently integrated with the Prony scheme. The computational technique is successfully applied to characterize and present the unique propagation performances of different classes of periodic structures such as Frequency Selective Surfaces (FSS), Photonic Band-Gap (PBG) materials, and Left-Handed (LH) composite media. The results are incorporated into some novel applications such as high Q nanocavity lasers, guiding the electromagnetic waves at sharp bends, and miniaturized microstrip patch antennas.
Mosallaei, Hossein
Surface electronic structure and chemisorption on corundum transition-metal oxides: V2O3
The surface electronic structure of single-crystal V2O3 has been studied by using ultraviolet and x-ray photoelectron spectroscopy. Both nearly-perfect surfaces and surfaces containing point defects have been prepared, and the influence of O2 and H2O on both types of surfaces has been investigated. Cation core-level spectra from cleaved surfaces exhibit complex structure. The surface electronic band structure is similar to
Richard L. Kurtz; Victor E. Henrich
Inverse band structure method via genetic algorithm for nanostructures
With the increased efficiency and accuracy of electronic structure methods, the inverse problem of material design has been tackled in e.g. Refs [1,2]. The inverse problems are solved by optimization, repeatedly applying the forward solving method while scanning the configuration space. We have implemented the inverse method for semiconductor alloys (iaga) by optimization using a genetic algorithm and PGAPack [3]. The forward solver employed is the parallel folded spectrum electronic structure method (PESCAN) with LDA-based empirical pseudopotentials, which has been run on up to million atom supercells. Hierarchical parallelism is adopted for using the parallel forward solver and the parallel genetic algorithm. Examples of inverse band structure results on AlGaAs alloys and superlattices will be presented. The approach is adaptable to a wide range of applications when combined with the efficient forward solvers. [1] A. Franceschetti and A. Zunger, Nature 402, 60 (1999). [2] G. H. Johannesson, et al., Phys. Rev. Lett. 88, 255506 (2002). [3] D. Levine, PGAPack: Parallel Genetic Algorithm Library (1998), T. Cwik and G. Klimeck, Proc. of 1st NASA/DoD Workshop on Evolvable Hardware, IEEE (1999).
Kim, Kwiseon; Jones, Wesley B.; Zunger, Alex
U-band CCD surface brightness profiles for candidate collapsed-core globular clusters
We have determined U-band CCD surface brightness profiles for 15 of the 21 globular clusters that have been characterized as having 'collapsed' cores by Djorgovski and King (1986). We have fitted these profiles with two types of seeing-convolved models: single-mass King models and power laws. We find that in many cases the characterization of a profile as being either 'King' or 'cusp' is somewhat subtle. Of the clusters in our sample, 10 appear to have central power-law cusps with either unresolved or marginally resolved cores, three appear to have resolved cores with surrounding power-law structure that is unlike a King model, and two are approximately described by King model fits. The observed power-law cusps are consistent with the predictions of Fokker-Planck models for core-collapse.
Lugger, Phyllis M.; Cohn, Haldan N.; Grindlay, Jonathan E.; Bailyn, Charles D.; Hertz, Paul L.
Electronic structure of SrPt4Ge12 : Combined photoelectron spectroscopy and band structure study
We present a combined study of the electronic structure of the superconducting skutterudite derivative SrPt4Ge12 by means of x-ray photoelectron spectroscopy and full-potential band structure calculations including an analysis of the chemical bonding. We establish that the states at the Fermi level originate predominantly from the Ge4p electrons and that the Pt5d shell is effectively full. We find excellent agreement between the measured and the calculated valence-band spectra, thereby validating that band structure calculations in combination with photoelectron spectroscopy can provide a solid basis for the modeling of superconductivity in the compound series MPt4Ge12 (M=Sr,Ba,La,Pr) .
Rosner, H.; Gegner, J.; Regesch, D.; Schnelle, W.; Gumeniuk, R.; Leithe-Jasper, A.; Fujiwara, H.; Haupricht, T.; Koethe, T. C.; Hsieh, H.-H.; Lin, H.-J.; Chen, C. T.; Ormeci, A.; Grin, Yu.; Tjeng, L. H.
Method of manufacturing flexible metallic photonic band gap structures, and structures resulting therefrom
A method of manufacturing a flexible metallic photonic band gap structure operable in the infrared region, comprises the steps of spinning on a first layer of dielectric on a GaAs substrate, imidizing this first layer of dielectric, forming a first metal pattern on this first layer of dielectric, spinning on and imidizing a second layer of dielectric, and then removing the GaAs substrate. This method results in a flexible metallic photonic band gap structure operable with various filter characteristics in the infrared region. This method may be used to construct multi-layer flexible metallic photonic band gap structures. Metal grid defects and dielectric separation layer thicknesses are adjusted to control filter parameters.
Gupta, Sandhya (Bloomington, MN); Tuttle, Gary L. (Ames, IA); Sigalas, Mihail (Ames, IA); McCalmont, Jonathan S. (Ames, IA); Ho, Kai-Ming (Ames, IA)
Microscopic structure of semiconductor surfaces
To study the initial reaction steps of hydrogen, oxygen, and water, on differently prepared single crystal surfaces of silicon, germanium/silicon alloys, indium phosphide and gallium arsenide, we used high-resolution electron energy-loss spectroscopy (HREELS) in combination with low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). Very recently, we started a program on the hydrogenation of III V compound semiconductors, and on the oxidation of Si and III V compound semiconductors, using alkali metals as a catalyst. This paper summarizes the present stage of our investigations, describing in particular aspects of the microscopic structure of differently prepared semiconductor surfaces.
Schaefer, J. A.
We present to the astronomical community an algorithm for the detection of low surface brightness (LSB) galaxies in images, called MARSIAA (MARkovian Software for Image Analysis in Astronomy), which is based on multi-scale Markovian modeling. MARSIAA can be applied simultaneously to different bands. It segments an image into a user-defined number of classes, according to their surface brightness and surroundings-typically, one or two classes contain the LSB structures. We have developed an algorithm, called DetectLSB, which allows the efficient identification of LSB galaxies from among the candidate sources selected by MARSIAA. The application of the method to two and three bands simultaneously was tested on simulated images. Based on our tests, we are confident that we can detect LSB galaxies down to a central surface brightness level of only 1.5 times the standard deviation from the mean pixel value in the image background. To assess the robustness of our method, the method was applied to a set of 18 B- and I-band images (covering 1.3 deg{sup 2} in total) of the Virgo Cluster to which Sabatini et al. previously applied a matched-filter dwarf LSB galaxy search algorithm. We have detected all 20 objects from the Sabatini et al. catalog which we could classify by eye as bona fide LSB galaxies. Our method has also detected four additional Virgo Cluster LSB galaxy candidates undetected by Sabatini et al. To further assess the completeness of the results of our method, both MARSIAA, SExtractor, and DetectLSB were applied to search for (1) mock Virgo LSB galaxies inserted into a set of deep Next Generation Virgo Survey (NGVS) gri-band subimages and (2) Virgo LSB galaxies identified by eye in a full set of NGVS square degree gri images. MARSIAA/DetectLSB recovered {approx}20% more mock LSB galaxies and {approx}40% more LSB galaxies identified by eye than SExtractor/DetectLSB. With a 90% fraction of false positives from an entirely unsupervised pipeline, a completeness of 90% is reached for sources with r{sub e} > 3'' at a mean surface brightness level of {mu}{sub g} = 27.7 mag arcsec{sup -2} and a central surface brightness of {mu}{sup 0}{sub g} = 26.7 mag arcsec{sup -2}. About 10% of the false positives are artifacts, the rest being background galaxies. We have found our proposed Markovian LSB galaxy detection method to be complementary to the application of matched filters and an optimized use of SExtractor, and to have the following advantages: it is scale free, can be applied simultaneously to several bands, and is well adapted for crowded regions on the sky.
Vollmer, B.; Bonnarel, F.; Louys, M. [CDS, Observatoire Astronomique, UMR 7550, 11 rue de l'universite, F-67000 Strasbourg (France); Perret, B.; Petremand, M.; Lavigne, F.; Collet, Ch. [LSIIT, Universite de Strasbourg, 7, Rue Rene Descartes, F-67084 Strasbourg (France); Van Driel, W. [GEPI, Observatoire de Paris, CNRS, Universite Paris Diderot, 5 place Jules Janssen, F-92190 Meudon (France); Sabatini, S. [INAF/IASF-Roma, via Fosso de Cavaliere 100, I-00133 Roma (Italy); MacArthur, L. A., E-mail: email@example.com [Herzberg Institute of Astrophysics, National Research Council of Canada, Victoria, BC V9E 2E7 (Canada)
Calculation of Band Structures for Perovskite-Type Crystals Using Discrete Variational Xalpha Method
Electronic structures of perovskite-type oxides were calculated using the discrete variational X alpha method. First, band structures and densities of states (DOS) were calculated for SrTiO3 and tetragonal BaTiO3. The calculated band structures agreed well with the previous reports and the DOS explained the XPS spectra measured well. Furthermore, band structures of SrTiO3\\/SrZrO3 superlattices with double period of SrTiO3 along
Toshio Kamiya; Takeshi Tanaka; Takaaki Tsurumi; Masaki Daimon
Band structure of polymer extracted from oligomer calculations by elongation method and its applications to nanosystems
A method developed for building band structure of polymer from elongation oligomer calculations has been applied for studying electronic structures of nanoscaled periodic systems. Band structures of single-walled (4,4) carbon and boron nitrogen nanotubes have been built at different levels of approximations. This method also has been applied for band structure construction of molecular systems where periodicity is disturbed by presence of local defects.
Pomogaeva, Anna; Springborg, Michael; Kirtman, Bernard; Gu, Feng Long; Aoki, Yuriko
Determination of Energy Band and Surface State Locations in GaAs Using the Separated Medium Surface Acoustoelectric Effect.
The wavelength dependence of the peak transverse acoustoelectric voltage and the surface acoustic wave attenuation determien the energy band and the location of the surface states in the energy gap of GaAs. The dependence is explained by direct optical tr...
H. Gilboa M. E. Motamedi P. Das
Electronic band structures and photovoltaic properties of MWO 4 ( M=Zn, Mg, Ca, Sr) compounds
Divalent metal tungstates, MWO 4, with wolframite ( M=Zn and Mg) and scheelite ( M=Ca and Sr) structures were prepared using a conventional solid state reaction method. Their electronic band structures were investigated by a combination of electronic band structure calculations and electrochemical measurements. From these investigations, it was found that the band structures (i.e. band positions and band gaps) of the divalent metal tungstates were significantly influenced by their crystal structural environments, such as the W-O bond length. Their photovoltaic properties were evaluated by applying to the working electrodes for dye-sensitized solar cells. The dye-sensitized solar cells employing the wolframite-structured metal tungstates (ZnWO 4 and MgWO 4) exhibited better performance than those using the scheelite-structured metal tungstates (CaWO 4 and SrWO 4), which was attributed to their enhanced electron transfer resulting from their appropriate band positions.
Kim, Dong Wook; Cho, In-Sun; Shin, Seong Sik; Lee, Sangwook; Noh, Tae Hoon; Kim, Dong Hoe; Jung, Hyun Suk; Hong, Kug Sun
Surface-electronic structure of. alpha. -like Ce compounds
Photoemission studies with varying degrees of surface sensitivity are reported for the Ce 3{ital d} core-level and Ce 4{ital f} valence-band regions of the {alpha}-like Ce compounds CeIr{sub 2}, CePd{sub 3}, and CeRh{sub 3}. In all cases studied, strong changes of the 4{ital f} electronic structure at the surface towards a more localized {gamma}-like behavior are observed, requiring a reanalysis of previously reported photoemission spectra of {alpha}-like Ce compounds. Implications for an improved understanding of the surface-catalytic properties of Ce systems, as well as of the surface-electronic structure of narrow-band materials, are pointed out.
Laubschat, C.; Weschke, E.; Holtz, C.; Domke, M.; Strebel, O.; Kaindl, G. (Institut fuer Experimentalphysik, Freie Universitaet Berlin, Arnimallee 14, D-1000 Berlin (Federal Republic of Germany))
Influence of banded structure on the mechanical properties of a high-strength maraging steel
Chemical inhomogeneity results in the formation of banded structure in high-strength maraging steels. Segregation of titanium and molybdenum was found to be the primary cause of banded structure formation. When the concentrations of these elements increased beyond certain critical levels, bands comprising different grain sizes formed. The inclusions existed preferentially along the interface of the bands. A high-temperature homogenization treatment substantially reduced or eliminated the banded structure. The large grain size resulting from the homogenization treatment was subsequently reduced by a grain refinement treatment. The mechanical properties of the steel substantially improved following homogenization and grain refinement.
Ahmed, M.; Salam, I.; Hashmi, F.H.; Khan, A.Q. [Dr. A.Q. Khan Research Labs., Rawalpindi (Pakistan). Metallurgy Div.
A Study of Higher-Band Dipole Wakefields in X-Band Accelerating Structures for the G\\/NLC
The X-band linacs for the G\\/NLC (Global\\/Next Linear Collider) have evolved from the DDS (Damped Detuned Structure) series. The present accelerating structures are 60 cm in length and incorporate damping and detuning of the dipole modes which comprise the wakefield. In order to adequately damp the wakefield, frequencies of adjacent structures are interleaved. Limited analysis has been done previously on
Band structures and intruder ?i13/2 state in 197Tl
The excited states in the odd-A 197Tl nucleus have been studied by populating them using the 197Au(?, 4n)197Tl reaction at a beam energy of 48 MeV. The ?-? coincidence data were taken using a combination of clover, low-energy photon spectrometer (LEPS), and single-crystal high-purity germanium (HPGe) detectors. Precise spin and parity assignments of the excited states have been done through polarization and directional correlation from oriented states (DCO) measurements. A new band structure has been identified and evidence for a possible intruder ?i13/2 state has been found for the first time. Possible configurations of the observed bands have been discussed. The total Routhian surface calculations have been performed to study the shape of 197Tl for different configurations.
Pai, H.; Mukherjee, G.; Bhattacharya, S.; Bhattacharya, C.; Bhattacharyya, S.; Bhattacharjee, T.; Chanda, S.; Rajbanshi, S.; Goswami, A.; Gohil, M. R.; Kundu, S.; Ghosh, T. K.; Banerjee, K.; Rana, T. K.; Pandey, R.; Prajapati, G. K.; Banerjee, S. R.; Mukhopadhyay, S.; Pandit, D.; Pal, S.; Meena, J. K.; Mukhopadhyay, P.; Choudhury, A.
The band structure of carbonmonoxide on 2-D Au islands on graphene
The dispersion of the occupied molecular orbitals of carbon monoxide adsorbed on Au 2D islands, vapor-deposited on graphene/Ru(0 0 0 1), is seen to be wave vector dependent, as revealed by angle-resolved photoemission. The band dispersion is similar to CO monolayers adsorbed on many single crystal metal surfaces. Thus not only are the adsorbed gold islands on graphene flat and crystalline, as evident in the dispersion of the Au d-states, but the CO molecular adlayer is both molecular and ordered as well. The experimental angle-resolved photoemission combined with model calculations of the occupied CO band structure, suggest that, in spite of being a very weakly bound adsorbate, the CO adlayer on Au 2D islands on graphene is strongly hybridized to the Au layer.
Katsiev, K.; Losovyj, Y.; Lozova, N.; Wang, Lu; Mei, Wai-Ning; Zheng, Jiaxin; Vescovo, E.; Liu, Li; Dowben, P. A.; Goodman, D. W.
Ocean surface determination from X-band radar-image sequences
An empirical inversion method is presented for determination of time series of ocean surface elevation maps from nautical radar-image sequences. The method is based on the determination of the surface tilt angle in antenna look direction at each pixel of the radar images. Thereby in situ sensors are not required. An external calibration is not necessary. A conventional nautical X-band
H. Dankert; W. Rosenthal
An Iterative Convergence Algorithm to Retrieve Sea Surface Salinity from SMOS L-band Radiometric Measurements
The European Space Agency SMOS (Soil Moisture and Ocean Salinity) mission aims at obtaining global maps of soil moisture and sea surface salinity from space for large scale and climatic studies. It uses an L-band (1400-1427 MHz) microwave interferometric radiometer by aperture synthesis (MIRAS) to measure brightness temperature at the Earth surface at horizontal and vertical polarizations (Th and Tv).
J. Boutin; N. Reul; P. Waldteufel; C. Gabarro; S. Zine; J. Tenerelli; F. Petitcolin; J. L. Vergely
Sea Surface Salinity and Wind Retrieval Using Combined Passive and Active L-Band Microwave Observations
This paper describes an algorithm to simultaneously retrieve ocean surface salinity and wind from combined passive\\/active L-band microwave observations of sea surfaces. The algorithm takes advantage of the differing response of brightness temperatures and radar backscatter to salinity, wind speed, and direction. The algorithm minimizes the least square error (LSE) measure, signifying the difference between measurements and model functions of
Simon H. Yueh; Julian Chaubell
Fermi surface topology and the upper critical field in two-band superconductors: application to MgB2.
Recent measurements of the anisotropy of the upper critical field B(c2) on MgB2 single crystals have shown a puzzling strong temperature dependence. Here, we present a calculation of the upper critical field based on a detailed modeling of band structure calculations that takes into account both the unusual Fermi surface topology and the two gap nature of the superconducting order parameter. Our results show that the strong temperature dependence of the B(c2) anisotropy can be understood as an interplay of the dominating gap on the sigma band, which possesses a small c-axis component of the Fermi velocity, with the induced superconductivity on the pi-band possessing a large c-axis component of the Fermi velocity. We provide analytic formulas for the anisotropy ratio at T=0 and T=T(c) and quantitatively predict the distortion of the vortex lattice based on our calculations. PMID:12906565
Dahm, T; Schopohl, N
The majority of medical accelerators for radiation therapy use frequencies in the S-band range. Having a compact accelerator allows for a wide range of treatments. The size and weight of the accelerator are substantially reduced if a higher frequency is used. X-band frequencies are suitable for such applications. X-band accelerator technology has been used in high-energy, as well as, industrial
The Valence Band Structure of Tellurium. III. The Landau Levels
The Landau levels are calculated for two upper valence bands of tellurium. The peak positions and intensities of the cyclotron resonance and of the inter-valence band magneto-absorption are calculated. Effects of the \\\\mbi{k}-linear terms on them are elucidated. For the magnetic field perpendicular to the c-axis, the Landau levels of the uppermost valence band are doubly degenerate at low magnetic
Kenji Nakao; Takao Doi; Hiroshi Kamimura
Crystal Structures and Band Structures of Acene Chalcogenides: Their Application for OFET.
We have systematically studied acene chalcogenides as active channel materials for Organic Field Effect Transistor (OFET). The molecules have a common structural feature which is of great advantage for carrier channel: chalcogen atoms are located at outside of molecule so that larger orbitals of chalcogen atoms would intensify intermolecular interactions not only for the molecular stacking direction but also for the inter-stacking directions. We then expect that the conduction channels would become more isotropic and the effective mass of the carriers would become lighter compared to the case of aromatic hydrocarbons. The materials we have surveyed are as follows: Hexathiopentacene (HTP), Tetrathiotetracene (TTT), Hexathioanthracene (HTA), Tetrathioanthracene (TTA), Benzo[1,2-c;3,4-c';5,6-c'']tris[1,2]dithiole-1,4,7-trithione (abbreviated as C9S9, which is its chemical formula), and some selenium analogues. The first-principle band structure calculations based on the crystal structures determined by x-ray analysis reveal that the materials have an anisotropic 2-D HOMO band with an effective mass of 1.1me for TSeA, 1.3me for HTA, 1.4me for TTT, respectively. HTP is proved to have a 1-D HOMO band with m*=2.5me in spite of 2-D structural feature. It is interesting that C9S9 has an isotropic 3-D HOMO band with m*=0.68me, properties which are suitable for OFET channel.
Ugawa, A.
Influence of polarity and hydroxyl termination on the band bending at ZnO surfaces
Surface sensitive synchrotron x-ray photoelectron spectroscopy (XPS) and real-time in situ XPS were used to study the thermal stability of the hydroxyl termination and downward band bending on the polar surfaces of ZnO single crystals. On the O-polar face, the position of the Fermi level could be reversibly cycled between the conduction band and the band gap over an energetic distance of approximately 0.8 eV (ś1/4 of the band gap) by controlling the surface H coverage using simple ultrahigh vacuum (UHV) heat treatments up to 750 ░C, dosing with H2O/H2 and atmospheric exposure. A metallic to semiconductorlike transition in the electronic nature of the O-polar face was observed at an H coverage of approximately 0.9 monolayers. For H coverage less than this, semiconducting (depleted) O-polar surfaces were created that were reasonably stable in UHV conditions. In contrast, the downward band bending on the Zn-polar face was significantly more resilient, and depleted surfaces could not be prepared by heat treatment alone.
Heinhold, R.; Williams, G. T.; Cooil, S. P.; Evans, D. A.; Allen, M. W.
A vertical W-band surface-micromachined Yagi-Uda antenna
A vertical W-band surface-micromachined Yagi-Uda monopole array is proposed and implemented for the first time. The monopoles stand on a high-k soda-lime glass substrate and are fed by a coplanar waveguide. The geometry functions as a vertically placed Yagi-Uda antenna due to the image theory. The performance of the vertical Yagi-Uda is to be superior to conventional W-band printed antennas
Y. Yoon; Bo Pan; J. Papapolymerou; M. M. Tentzeris; M. G. Allen
Flat Surface Plasmon Polariton Bands in Bragg Grating Waveguide for Slow Light
The formations of the surface plasmon polariton (SPP) bands in metal\\/air\\/metal (MAM) sub-wavelength plasmonic grating waveguide (PGW) are proposed. The band gaps originating from the highly localized resonances inside the grooves can be simply estimated from the round trip phase condition. Due to the overlap of the localized SPPs between the neighboring grooves, a Bloch mode forms in the bandgap
Jing Zhang; Likang Cai; Wenli Bai; Guofeng Song
Global Kinetic Modeling of Banded Electron Structures in the Plasmasphere
Significant fluxes of 10 eV to 30 keV electrons have been detected in the plasmasphere, appearing as banded structures in energy with broad spatial extents and slowly evolving over several days. It is thought that these populations are decaying plasma sheet electrons injected into the corotating region of near-Earth space. This capture can occur when the convective electric field drops rapidly and the Alfven boundary suddenly outward, trapping the inner edge of the plasma sheet along closed drift paths. Our bounce-averaged kinetic model of superthermal electron transport is able to simulate this capture and the subsequent drift, diffusion, and decay of the plasma cloud. Results of this simulation will be shown and discussed, from the initial injection during the elevated convection to the final loss of the particles. It is thought that not only Coulomb collisions but also wave-particle interactions play a significant role in altering the plasma cloud. Quasilinear diffusion is currently being incorporated into the model and the importance of this mechanism will be examined. Also, the high anisotropy of the trapped population could be unstable and generate plasma waves. These and other processes will be investigated to determine the final fate of the cloud and to quantify where, how, and when the energy of the plasma cloud is deposited. Comparisons with CRRES observations of these events are shown to verify the model and explain the data.
Liemohn, M. W.; Khazanov, G. V.
Miniaturization of electromagnetic band gap structures for mobile applications
It is well known that interference of the human body affects the performance of the antennas in mobile phone handsets. In this contribution, we investigate the use of miniaturized metallodielectric electromagnetic band gap (MEBG) structures embedded in the case of a mobile handset as a means of decoupling the antenna from the user's hand. The closely coupled MEBG concept is employed to achieve miniaturization of the order of 15:1. Full wave dispersion relations for planar closely coupled MEBG arrays are presented and are validated experimentally. The performance of a prototype handset with an embedded conformal MEBG is assessed experimentally and is compared to a similar prototype without the MEBG. Reduction in the detuning of the antenna because of the human hand by virtue of the MEBG is demonstrated. Moreover, the efficiency of the handset when loaded with a human hand model is shown to improve when the MEBG is in place. The improvements are attributed to the decoupling of the antenna from the user's hand, which is achieved by means of suppressing the fields in the locality of the hand.
Goussetis, G.; Feresidis, A. P.; Palikaras, G. K.; Kitra, M.; Vardaxoglou, J. C.
Finite element analysis of valence band structures in quantum wires
Valence band structures with spin-orbit (SO) coupling of quantum wires (QWRs), are investigated using the multiband effective-mass theory by a calculation procedure based on a finite-element method (FEM). The results are also compared to those obtained by finite difference method (FDM) and obtained by FEM without SO coupling. We expect FEM and FDM methods to give similar results, but the FDM has a limitation in dealing with various quantum wire shapes. In the case of QWR with small strains, the SO coupling effect does not greatly change subband energies and the trends of the subband dispersions. On the other hand, in the case of QWR with large strains, the subband energies of all states including the first state are considerably affected by the SO coupling. The amplitudes of the heavy-hole and light-hole wave functions have nonzero mixings even at the zone center (ky=0) in contrast to the case of quantum wells. It is found that the matrix elements for the TE polarization greatly increase due to the SO coupling effect.
Park, Seoung-Hwan; Ahn, Doyeol; Lee, Yong-Tak
Level Structures and Double ?-BANDS in 105Mo, 108Mo and 112Ru
The level structures of 105,108Mo and 112Ru have been carefully investigated by measuring prompt ? - ? - ? coincident measurements of neutron-rich nuclei populated in the spontaneous fission of 252Cf. In 105Mo five new collective bands are observed. The three bands are proposed as single-neutron excitation bands built on the 3/2+[411], 1/2+[411] and 5/2+[413] Nilsson orbitals, respectively. The other two bands are candidates for one-phonon K = 9/2 and two-phonon K = 13/2 ?-vibrational bands, respectively. This is the first observation of such ?-vibrational collective band structures in odd-A nuclei. In 108Mo and 112Ru, the one-phonon ?-vibrational bands have been extended and two-phonon ?-vibrational bands have been identified for the first time.
Zhu, S. J.; Ding, H. B.; Hamilton, J. H.; Ramayya, A. V.; Che, X. L.; Hwang, J. K.; Luo, Y. X.; Rasmussen, J. O.; Li, K.; Goodin, C.; Liu, S.; Chen, Y. J.; Li, M. L.; Daniel, A. V.; Ter-Akopian, G. M.
Band gap structure and electron emission property of chemical-vapor-deposited diamond films
The structures of the band gap and defect states of chemical-vapor-deposited diamond films were investigated by photoluminescence spectroscopy, covering wavelength from visible to vacuum ultraviolet (VUV). Band gaps ranging from 5.5 to 3.2 eV were measured for natural, polycrystalline, and amorphous diamond films. Low voltage field emissions were obtained from wide band gap films with band gap states distributed close
J. J Liu; D. Y. T Chiu; D. C Morton; D. H Kang; V. V Zhirnov; J. J Hren; J. J Cuomo
A PPM-focused klystron at X-band with a traveling-wave output structure
We have developed algorithms for designing disk-loaded traveling-wave output structures for X-band klystrons to be used in the SLAC NLC. We use either a four- or five-cell structure in a {pi}/2 mode. The disk radii are tapered to produce an approximately constant gradient. The matching calculation is not performed on the tapered structure, but rather on a coupler whose input and output cells are the same as the final cell of the tapered structure, and whose interior cells are the same as the penultimate cell in the tapered structure. 2-D calculations using CONDOR model the waveguide as a radial transmission line of adjustable impedance. 3-D calculations with MAFIA model the actual rectangular waveguide and coupling slot. A good match is obtained by adjusting the impedance of the final cell. In 3-D, this requires varying both the radius of the cell and the width of the aperture. When the output cell with the best match is inserted in the tapered structure, we obtain excellent cold-test agreement between the 2-D and 3-D models. We use hot-test simulations with CONDOR to design a structure with maximum efficiency and minimum surface fields. We have designed circuits at 11.424 Ghz for different perveances. At 440 kV, microperveance 1.2, we calculated 81 MW, 53 percent efficiency, with peak surface field 76 MV/m. A microperveance 0.6 design was done using a PPM stack for focusing. At 470 kV, 193 amps, we calculated 58.7 MW, 64.7 percent efficiency, peak surface field 62.3 MV/m. At 500 kV, 212 amps, we calculated 67.1 MW, 63.3 percent efficiency, peak surface field 66.0 MV/m. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.
Eppley, K.R. [Stanford Linear Accelerator Center, P.O. Box 4349, Stanford, California 94309 (United States)
Measurement of the mirror reflective spectrum of typical roughness surface in the ultraviolet band
Reflective light of a surface contains many features of a surface. It is usually used as a powerful tool for process in situ or ex suit monitoring because of its non contact and non destructive nature. Scatter measurements of some typical samples in the UV band are performed by using an ellipsometry WVASE 32 made by J. A. Woolam Co. Inc. The mirror-direction reflective measurement results of different sample obtained by ellipsometer are compared. And these kinds of researches about measuring and analyzing of typical roughness samples in the ultraviolet band have significant meanings in a lot of related fields.
Bai, Lu; Wu, Zhen-sen; Li, Yan-hui
Conductive Bands Diminish Electrostatic Discharges
Electrostatic discharges on surfaces covered with electrically insulating paints reduced by connecting edges of painted surfaces to electrical grounds with band of conductive material. Prevents charge build up on paint which eventually arcs to conductive surface, damaging structures and equipment.
Leung, Philip L.; Whittlesey, Albert
Dynamic shear band propagation and micro-structure of adiabatic shear band
Meshfree Galerkin approximations in both two and three dimensions have been used in simulations of dynamic shear band propagation in an asymmetrically impact-loaded prenotched plate. Failure mode switching and failure mode transitions, which have been reported experimentally, are replicated in numerical computations. For intermediate impact speed (25m\\/s
Shaofan Li; Wing-Kam Liu; Dong Qian; Pradeep R. Guduru; Ares J. Rosakis
Shaofan Li; Wing-Kam Liu; Dong Qian; Pradeep R. Guduru; Ares J. Rosakis
FAST TRACK COMMUNICATION: Field modulation in bilayer graphene band structure
Using an external electric field, one can modulate the band gap of Bernal stacked bilayer graphene by breaking the A-\\tilde {\\mathrm {B}} symmetry. We analyze strain effects on the bilayer graphene using the extended H³ckel theory and find that reduced interlayer distance results in higher band gap modulation, as expected. Furthermore, above about 2.5 ┼ interlayer distance, the band gap is direct, follows a convex relation with the electric field and saturates to a value determined by the interlayer distance. However, below about 2.5 ┼, the band gap is indirect, the trend becomes concave and a threshold electric field is observed, which also depends on the stacking distance.
Raza, Hassan; Kan, Edwin C.
Optical Transitions and Electronic Band structure of Cuprous Oxide Thin Films
Cu2O thin films were grown on Si and SiO2/Si substrates via RF sputtering deposition at various temperatures. The Cu2O thin films had a smooth surface when grown at RT, but developed grain boundaries when grown at 300 ^oC. We observed the high-energy photoluminescence (PL) peaks at 3.18 eV (Ep) and 3.27 eV (Eq). The dielectric functions of the Cu2O thin films were measured using spectroscopic ellipsometry. To estimate the critical point (CP) energies, we applied the standard critical point (SCP) model to the second derivative spectra of the dielectric functions (d^2?/dE^2). We also calculated the electronic band structure of bulk Cu2O by using the screened HSE hybrid density functional. Based on the band structure, the CP was estimated as 2.05 eV (E0A(E0B)), 2.77 eV (E0C(E0D)) at the ? point, 4.17 eV (E1A) and 6.10 eV (E2) at the X point, 4.94 eV (E1B) at the R point. The experimental CP energies are consistent with the HSE results, but are systematically smaller than the calculated values by 0.3-0.8 eV due to large electron-hole interaction in CuO2 that was not included in the simulations. The high-energy peaks in the PL spectra at 3.18 eV (Ep) and 3.27 eV (Eq) were attributed to the quasi-direct transitions between the ? valence band and the M and X conduction bands, respectively. The physical origin of the quasi-direct transitions was attributed to the grain boundaries.
Lee, Hosun; Park, Jun-Woo; Jang, Hyungkeun; Kim, Sung; Choi, Suk-Ho; Kang, Joongoo; Wei, Su-Huai
Some electronic structure parameters calculated to a two-band approximation for zirconium carbonitrides
X-ray spectra of the valence band were obtained and an investigation was carried out into transport properties and their temperature dependence in ZrC-ZrN SSs. The results obtained were employed for calculating the principal electronic structure parameters of these materials within the framework of a two-band DENHs model. The valence band structure consists of three partially overlapping subzones of mixed character.
M. I. Lesnaya; E. A. Zhurakovskii; A. Ya. Kuchma
Carrier Multiplication in Semiconductor Nanocrystals: Theoretical Screening of Candidate Materials Based on Band-Structure Effects
Direct carrier multiplication (DCM) occurs when a highly excited electron-hole pair decays by transferring its excess energy to the electrons rather than to the lattice, possibly exciting additional electron-hole pairs. Atomistic electronic structure calculations have shown that DCM can be induced by electron-hole Coulomb interactions, in an impact-ionization-like process whose rate is proportional to the density of biexciton states {rho}{sub XX}. Here we introduce a DCM 'figure of merit' R{sub 2}(E) which is proportional to the ratio between the biexciton density of states {rho}{sub XX} and the single-exciton density of states {rho}{sub x}, restricted to single-exciton and biexciton states that are coupled by Coulomb interactions. Using R{sub 2}(E), we consider GaAs, InAs, InP, GaSb, InSb, CdSe, Ge, Si, and PbSe nanocrystals of different sizes. Although DCM can be affected by both quantum-confinement effects (reflecting the underly electronic structure of the confined dot-interior states) and surface effects, here we are interested to isolate the former. To this end the nanocrystal energy levels are obtained from the corresponding bulk band structure via the truncated crystal approximation. We find that PbSe, Si, GaAs, CdSe, and InP nanocrystals have larger DCM figure of merit than the other nanocrystals. Our calculations suggest that high DCM efficiency requires high degeneracy of the corresponding bulk band-edge states. Interestingly, by considering band structure effects we find that as the dot size increases the DCM critical energy E{sub 0} (the energy at which R{sub 2}(E) becomes {ge}1) is reduced, suggesting improved DCM. However, whether the normalized E{sub 0}/{var_epsilon}{sub g} increases or decreases as the dot size increases depends on dot material.
Luo, J. W.; Franceschetti, A.; Zunger, A.
Estimation of bare surface soil moisture and surface roughness parameter using L-band SAR image data
An algorithm based on a fit of the single-scattering integral equation method (IEM) was developed to provide estimation of soil moisture and surface roughness parameter (a combination of rms roughness height and surface power spectrum) from quad-polarized synthetic aperture radar (SAR) measurements. This algorithm was applied to a series of measurements acquired at L-band (1.25 GHz) from both AIRSAR (Airborne
Jiancheng Shi; James Wang; Ann Y. Hsu; P. E. O'Neill; E. T. Engman
Micro and nano structurization of semiconductor surfaces
The techniques of micro and nano structurization of surfaces of various materials are utilized in electronics and medicine. Such procedure as wet and dry etching allows to fabricate protruded or recessed micro and nanostructures on the surface. In the paper some examples of utilization of a surface structurization, known from literature, are described. Some structurization methods and experimental results for
A. GėRECKA-DRZAZGA
Applications of Split-Ring Resonances on MultiBand Frequency Selective Surfaces
Multi-band frequency selective surfaces (FSSs) are proposed by utilizing the split-ring resonators (SRRs) as the basic unit cells. The magnetic resonance of SRRs, which makes an additional dip in the reflection and transmission spectrums of FSSs, is discussed based on the equivalent circuit method and the simulation models. Because of the electric and the magnetic resonances of the single SRR
D. Li; Y. J. Xie; P. Wang; R. Yang
Thin frequency selective surface (FSS) superstrate with different periodicities for dual-band directivity enhancement
In this paper we present a novel design of a high directivity resonator antenna that utilizes a two-layered frequency selective surface (FSS) superstrate with different periodicities - as an alternative to a conventional FSS superstrate - for dual band directivity enhancement to reduce its height. Two strip dipole arrays with different periodicities are placed above and below a dielectric layer.
Young Ju Lee; Junho Yeo; R. Mittra; Wee Sang Park
Retrieving sea surface salinity with multiangular L-band brightness temperatures: Improvement by spatiotemporal averaging
The Soil Moisture and Ocean Salinity (SMOS) mission was selected in May 1999 by the European Space Agency to provide global and frequent soil moisture and sea surface salinity maps. SMOS' single payload is Microwave Imaging Radiometer by Aperture Synthesis (MIRAS), an L band two-dimensional aperture synthesis interferometric radiometer with multiangular observation capabilities. Most geophysical parameter retrieval errors studies have
A. Camps; M. Vall-llossera; L. Batres; F. Torres; N. Duffo; I. Corbella
Comparison of two methods for extracting surface soil moisture from C-band radar imagery
The integral equation method (IEM) model and a newly defined delta index were used to estimate near surface soil moisture from C-band radar satellite imagery in a semiarid rangeland in southern Arizona, USA. Model results were validated against soil moisture measurements made in the field at the time of satellite overpass. The IEM model performed poorly in this environment possibly
D. Thoma; M. Moran; R. Bryant; C. Holifield Collins; M. Rahman; S. Skirvin
A spaceborne L-band radiometer-radar concept for land and ocean surface monitoring
An L-band radiometer-radar concept has been studied for spaceborne remote sensing of land surface soil moisture, freeze-thaw state, and ocean surface salinity. The integrated design provides simultaneous passive and active measurements with potential for enhanced geophysical retrieval accuracy and spatial resolution. The design takes advantage of cost savings achievable using shared subsystems and hardware. The baseline system concept has been
E. Njoku; Yunjin Kim; M. Spencer; Wu-Yang Tsai; Y. Rahmat-Samii; M. W. Thomson
Synchrotron photoemission studies of the Sb-passivated Si surfaces: Degenerate doping and bulk band dispersions
Synchrotron photoemission of the Sb-covered Si(001), Si(111), and Si(110) surfaces revealed that the Fermi-level position crosses the conduction-band minimum (CBM) of Si for Sb coverages approaching a one-monolayer saturation limit. Momentum-resolved photoemission of the Sb-saturated Si(001) and Si(110) surfaces showed the existence of an occupied initial state located near the CBM. The photoemission intensity of the state has been examined
D. H. Rich; G. E. Franklin; F. M. Leibsle; T. Miller; T.-C. Chiang
Band Structures and Nucleon Alignments in ^173,175W
Spectroscopic study of nuclei in the Aś180 region is essential to better understand regional relationships between Nilsson orbitals. Highly excited rotational states in both nuclei were populated at Argonne National Laboratory via a 230 MeV ^50Ti beam from the ATLAS accelerator incident on a ^128Te target. The Gammasphere array was used to detect ? decays from excited states. Rotational bands built on the level 1/2^-[521], p3/2 in ^173,175W have been extended to spins of 40 and 35 respectively, and bands built on the 7/2^+[633], i13/2 configuration extended to 38 and 27 respectively. New sidebands in ^173W have been observed in all previously-discovered bands. Alignments from i13/2 neutron and h11/2 proton crossings are consistent with predictions of Woods-Saxon cranking calculations. Experimental results and regional systematics will be presented.
Guess, C. J.; Tandel, S. K.; Chowdhury, P.; Shirwadkar, U.; Carpenter, M. P.; Janssens, R. V. F.; Khoo, T. L.; Lauritsen, T.; Lister, C. J.; Seweryniak, D.; Wang, X.; Zhu, S.; Hartley, D. J.
Structure of adiabatic shear bands in metals: A critical review
Shear bands are redefined as being either transformed or deformed according to how the prior shear deformation is partitioned between two discrete zones in metallographic section. Metals are then classified by their general tendency to form these two types of shear zone during adiabatic shear deformation, based on available literature. Metals of low thermal diffusivity and low resistance to adiabatic shear localization tend more readily to form transformed shear bands. These metals are also capable of transforming to other phases at elevated temperature (and pressure) and forming martensite on rapid cooling to room temperature.
Timothy, S.P.
Topological equivalence of crystal and quasicrystal band structures
A number of recent articles have reported the existence of topologically nontrivial states and associated end states in one-dimensional incommensurate lattice models that would usually only be expected in higher dimensions. Using an explicit construction, we here argue that the end states have precisely the same origin as their counterparts in commensurate models and that incommensurability does not in fact provide a meaningful connection to the topological classification of systems in higher dimensions. In particular, we show that it is possible to smoothly interpolate between states with commensurate and incommensurate modulation parameters without closing the band gap and without states crossing the band gap.
Madsen, Kevin A.; Bergholtz, Emil J.; Brouwer, Piet W.
Structure of dipole bands in {sup 106}In
High spin states in neutron-deficient {sup 106}In were investigated using {sup 78}Se({sup 32}S,p3n) reaction at 125 MeV. The level scheme is extended up to 7 MeV of excitation energy for the negative parity states constituting four dipole bands, and the positive parity states which mainly exhibit single-particle excitations are extended up to 5 MeV. Projected deformed Hartree-Fock calculations were carried out to understand the configurations of different bands in this nucleus.
Deo, A. Y.; Palit, R.; Naik, Z.; Joshi, P. K.; Mazumdar, I. [Department of Nuclear and Atomic Physics, Tata Institute of Fundamental Research, Mumbai-400005 (India); Sihotra, S.; Mehta, D. [Department of Physics, Panjab University, Chandigarh-160014 (India); Kumar, S. [Department of Physics, Indian Institute of Technology, Roorkee-247667 (India); Chakrabarti, R. [UGC-DAE Consortium for Scientific Research, Kolkata-700098 (India); Kshetri, R. [Saha Institute of Nuclear Physics, I/AF, Bidhannagar, Kolkata-700064 (India); Jain, H. C. [Department of Nuclear and Atomic Physics, Tata Institute of Fundamental Research, Mumbai-400005 (India); Department of Physics, University of Mumbai, Vidyanagari, Mumbai-400098 (India)
The ?4 fundamental band of tetrafluoromethane: structure and broadening coefficients
Broadening coefficients for the ?4 fundamental band of carbon tetrafluoromethane, CF4, have been measured for the systems with argon, helium and nitrogen. Broadening coefficient behavior is similar to that previously reported for linear molecules: they coincide for P and R branches; the m-dependence in case of argon is sharper than that for helium. The broadening for nitrogen and helium are practically the same but the values for nitrogen are scattered around the general tendency. Q-branch broadening is also discussed. Our experimental data permitted us to evaluate the line intensity distribution and integrated intensity of the band.
Domanskaya, A. V.; Tonkov, Mikhail V.; Boissoles, J.
Band model for the electronic structure of KHgC8
There is both theoretical and experimental evidence that the band structure of graphite intercalation compounds (GIC's) can be considered as a first approximation, as a superposition of graphitic and intercalant bands. Assuming such a rigid-band-type model is valid, we have obtained the band structure of second-stage potassium-mercury amalgam GIC, KHgC8, by superposing K-Hg-K sandwich bands with the two-dimensional graphite bands. The graphite bands have been zone folded into the smaller Brillouin zone of KHgC8. The self-consistent full potential linearized-augmented-plane-wave formalism for thin films has been used to calculate the sandwich band structure and density of states. The K 3p states lead to a dispersionless set of bands at -17.75 eV. Hybridization of K 4s states with Hg 6p states is very strong. From our band calculation we extract the partial density of states (DOS) due to the intercalant at the Fermi level of KHgC8. Comparison with low-temperature specific-heat measurements suggests a very small contribution to the DOS at the Fermi level from carbon layers. We also compare the model predictions with optical experiments.
Senbetu, L.; Ikezi, H.; Umrigar, C.
SMOS satellite L-band radiometer: A new capability for ocean surface remote sensing in hurricanes
The Soil Moisture and Ocean Salinity (SMOS) mission currently provides multiangular L-band (1.4 GHz) brightness temperature images of the Earth. Because upwelling radiation at 1.4 GHz is significantly less affected by rain and atmospheric effects than at higher microwave frequencies, these new SMOS measurements offer unique opportunities to complement existing ocean satellite high wind observations that are often contaminated by heavy rain and clouds. To illustrate this new capability, we present SMOS data over hurricane Igor, a tropical storm that developed to a Saffir-Simpson category 4 hurricane from 11 to 19 September 2010. Thanks to its large spatial swath and frequent revisit time, SMOS observations intercepted the hurricane 9 times during this period. Without correcting for rain effects, L-band wind-induced ocean surface brightness temperatures (TB) were co-located and compared to H*Wind analysis. We find the L-band ocean emissivity dependence with wind speed appears less sensitive to roughness and foam changes than at the higher C-band microwave frequencies. The first Stokes parameter on a ś50 km spatial scale nevertheless increases quasi-linearly with increasing surface wind speed at a rate of 0.3 K/m s-1 and 0.7 K/m s-1 below and above the hurricane-force wind speed threshold (ś32 m s-1), respectively. Surface wind speeds estimated from SMOS brightness temperature images agree well with the observed and modeled surface wind speed features. In particular, the evolution of the maximum surface wind speed and the radii of 34, 50 and 64 knots surface wind speeds are consistent with GFDL hurricane model solutions and H*Wind analyses. The SMOS sensor is thus closer to a true all-weather satellite ocean wind sensor with the capability to provide quantitative and complementary surface wind information of interest for operational Hurricane intensity forecasts.
Reul, Nicolas; Tenerelli, Joseph; Chapron, Bertrand; Vandemark, Doug; Quilfen, Yves; Kerr, Yann
Doping mode, band structure and photocatalytic mechanism of B-N-codoped TiO 2
The photocatalyst B and N codoped TiO 2 (B-N-TiO 2) was prepared via the sol-gel method by using boric acid and ammonia as B and N precursors. The doping mode, band structure and photocatalytic mechanism of B-N-TiO 2 were investigated well and elucidated in detail. B-N-TiO 2 showed the narrowed band gap and thus extended the optical absorption due to interstitial N and [NOB] species in the TiO 2 crystal lattice. The coexistence of interstitial N and [NOB] species in the TiO 2 crystal lattice and surface NO x species allowed the more efficient utilization of visible light. Simultaneously, interstitial [NOB] and N species and surface B 2O 3 and NO x species facilitated the separation of photo generated electrons and holes and suppress their recombination effectively. Hence, B-N-TiO 2 showed a higher photocatalytic activity than pure TiO 2, N-doped TiO 2 (N-TiO 2) and B-doped TiO 2 (B-TiO 2) under both UV and visible light irradiation.
Yuan, Jixiang; Wang, Enjun; Chen, Yongmei; Yang, Wensheng; Yao, Jianghong; Cao, Yaan
Shear bands are redefined as being either transformed or deformed according to how the prior shear deformation is partitioned between two discrete zones in metallographic section. Metals are then classified by their general tendency to form these two types of shear zone during adiabatic shear deformation, based on available literature. Metals of low thermal diffusivity and low resistance to adiabatic
Photonic band-gap structures of core-shell simple cubic crystals from holographic lithography
We report the investigation of photonic band-gap properties of a core-shell simple cubic structure (air core with a dielectric shell) using a two-parameter level-set approach. The proposed structure can be obtained by partially backfilling high refractive index materials into a polymeric template fabricated by multibeam interference lithography. We find that the shell formation in the inverted simple cubic structure increases the complete photonic band-gap width by 10%-20% in comparison to that of a completely filled structure. The band gap between the fifth and sixth bands begins to appear at a refractive index contrast of 2.7. This study suggests the importance to investigate the core-shell formation in three-dimensional photonic crystals through backfilling, which may offer an additional control over their photonic band-gap properties.
Moon, Jun Hyuk; Yang, Shu; Yang, Seung-Man
Band structures of TiO2 doped with N, C and B*
This study on the band structures and charge densities of nitrogen (N)-, carbon (C)- and boron (B)-doped titanium dioxide (TiO2) by first-principles simulation with the CASTEP code (Segall et al., 2002) showed that the three 2p bands of impurity atom are located above the valence-band maximum and below the Ti 3d bands, and that along with the decreasing of impurity atomic number, the fluctuations become more intensive. We cannot observe obvious band-gap narrowing in our result. Therefore, the cause of absorption in visible light might be the isolated impurity atom 2p states in band-gap rather than the band-gap narrowing.
Xu, Tian-Hua; Song, Chen-Lu; Liu, Yong; Han, Gao-Rong
Fermi loop in interface states and surface flat bands in diamond lattice models
Previously we have shown the gapless interface states between two topological insulators with different chiralities by means of the mirror Chern number [1]. In this presentation we use the Fu-Kane-Mele tight-binding model on diamond lattice with the spin-orbit interaction, and calculate their gapless interface states. We find that when the particle-hole symmetry is imposed in the whole system the Fermi surface of the gapless states becomes a loop in the interface Brillouin zone. We show how to characterize the existence of such Fermi loop in terms of topology. Next we report flat band states in the surface of the diamond lattice model with anisotropic hopping integrals without the spin-orbit interaction. When anisotropy is not so strong, the surface flat band exits in some part of the Brillouin zone. Moreover when the anisotropy becomes sufficiently strong, the surface flat bands cover the whole surface Brillouin zone. [1] R. Takahashi, S. Murakami, Phys. Rev. Lett. 107,166805 (2011).
Takahashi, Ryuji; Murakami, Shuichi
Partitioning of Bacterial Communities between Seawater and Healthy, Black Band Diseased, and Dead Coral Surfaces
Distinct partitioning has been observed in the composition and diversity of bacterial communities inhabiting the surface and overlying seawater of three coral species infected with black band disease (BBD) on the southern Caribbean island of Curańao, Netherlands Antilles. PCR amplification and sequencing of bacterial 16S rRNA genes (rDNA) with universally conserved primers have identified over 524 unique bacterial sequences affiliated with 12 bacterial divisions. The molecular sequences exhibited less than 5% similarity in bacterial community composition between seawater and the healthy, black band diseased, and dead coral surfaces. The BBD bacterial mat rapidly migrates across and kills the coral tissue. Clone libraries constructed from the BBD mat were comprised of eight bacterial divisions and 13% unknowns. Several sequences representing bacteria previously found in other marine and terrestrial organisms (including humans) were isolated from the infected coral surfaces, including Clostridium spp., Arcobacter spp., Campylobacter spp., Cytophaga fermentans, Cytophaga columnaris, and Trichodesmium tenue.
Frias-Lopez, Jorge; Zerkle, Aubrey L.; Bonheyo, George T.; Fouke, Bruce W.
A plane-wave-based approach for complex photonic band structure and its applications to semi-infinite and finite system
A plane-wave-based approach for complex photonic band structure is developed and applied to analyse the behaviour of electromagnetic (EM) waves at the surface of semi-infinite and finite photonic crystals (PCs). The complex photonic band structures of two-dimensional and three-dimensional PCs have been calculated by the present approach and verified by conventional plane wave expansion method and plane-wave-based transfer matrix method.
C S Feng; L M Mei; L Z Cai; X L Yang; S S Wei; P Li
Nanostructure growth-induced defect formation and band bending at ZnO surfaces
Morphological, electrostatic, and optical techniques reveal spontaneous growth of nano-"mounds" on ZnO polar surfaces in air creating native point defects at and under the surface that increase work function locally by hundreds of meV. Nanoscale surface photovoltage spectroscopy reveals Zn vacancies with gap states whose density grows with nano-mound proximity over hundreds of nanometers. The low activation energy for ZnO nano-mound growth with oxygen indicates interstitial Zn diffusion that feeds nanostructure growth, generating deep level acceptors that increase n-type band bending and impact Schottky barrier formation.
Merz, T. A.; Doutt, D. R.; Bolton, T.; Dong, Y.; Brillson, L. J.
Microstructure-dependent band structure of HfO 2 thin films
The effects of rapid thermal annealing on band structure of HfO2 have been investigated using combinational characterization techniques including X-ray diffraction, X-ray photoelectron spectroscopy and ultraviolet¢visible spectrophotometer. The results show that the band structure of the thin film is strongly affected by crystalline structure. Different microstructures of HfO2 formed after annealing at a series of temperatures up to 1000 ░C:
Y. B. Zheng; S. J. Wang; C. H. A. Huan
Band structure of ZnO from resonant x-ray emission spectroscopy
Soft x-ray emission and absorption spectroscopy of the OK -edge are employed to investigate the electronic structure of wurtzite ZnO(0001). A quasiparticle band structure calculated within the GW approximation agrees well with the data, most notably with the energetic location of the Zn3d-O2p hybridized state and the anisotropy of the absorption spectra. Dispersion in the band structure is mapped using
A. R. H. Preston; B. J. Ruck; L. F. J. Piper; A. Demasi; K. E. Smith; A. Schleife; F. Fuchs; F. Bechstedt; J. Chai; S. M. Durbin
Electron momentum density, band structure, and structural properties of SrS
The electron momentum density, the electronic band structure, and the structural properties of SrS are presented in this paper. The isotropic Compton profile, anisotropies in the directional Compton profiles, the electronic band structure and density of states are calculated using the ab initio periodic linear combination of atomic orbitals method with the CRYSTAL06 code. Structural parameters of SrS-lattice constants and bulk moduli in the B1 and B2 phases-are computed together with the transition pressure. The computed parameters are well in agreement with earlier investigations. To compare the calculated isotropic Compton profile, measurement on polycrystalline SrS is performed using 5Ci-{sup 241}Am Compton spectrometer. Additionally, charge transfer is studied by means of the Compton profiles computed from the ionic model. The nature of bonding in the isovalent SrS and SrO compounds is compared on the basis of equal-valenceelectron-density profiles and the bonding in SrS is found to be more covalent than in SrO.
Sharma, G., E-mail: email@example.com [University of Kota, Department of Pure and Applied Physics (India); Munjal, N.; Vyas, V. [Banasthali University, Department of Physics (India)] [Banasthali University, Department of Physics (India); Kumar, R.; Sharma, B. K. [University of Rajasthan, Department of Physics (India)] [University of Rajasthan, Department of Physics (India); Joshi, K. B. [MLS University, Department of Physics (India)] [MLS University, Department of Physics (India)
A DFT study on structural, vibrational properties, and quasiparticle band structure of solid nitromethane
We report a detailed theoretical study of the structural and vibrational properties of solid nitromethane using first principles density functional calculations. The ground state properties were calculated using a plane wave pseudopotential code with either the local density approximation, the generalized gradient approximation, or with a correction to include van der Waals interactions. Our calculated equilibrium lattice parameters and volume using a dispersion correction are found to be in reasonable agreement with the experimental results. Also, our calculations reproduce the experimental trends in the structural properties at high pressure. We found a discontinuity in the bond length, bond angles, and also a weakening of hydrogen bond strength in the pressure range from 10 to 12 GPa, picturing the structural transition from phase I to phase II. Moreover, we predict the elastic constants of solid nitromethane and find that the corresponding bulk modulus is in good agreement with experiments. The calculated elastic constants show an order of C11> C22 > C33, indicating that the material is more compressible along the c-axis. We also calculated the zone center vibrational frequencies and discuss the internal and external modes of this material under pressure. From this, we found the softening of lattice modes around 8-11 GPa. We have also attempted the quasiparticle band structure of solid nitromethane with the G0W0 approximation and found that nitromethane is an indirect band gap insulator with a value of the band gap of about 7.8 eV with G0W0 approximation. Finally, the optical properties of this material, namely the absorptive and dispersive part of the dielectric function, and the refractive index and absorption spectra are calculated and the contribution of different transition peaks of the absorption spectra are analyzed. The static dielectric constant and refractive indices along the three inequivalent crystallographic directions indicate that this material has a considerable optical anisotropy.
Appalakondaiah, S.; Vaitheeswaran, G.; LebĶgue, S.
Electronic properties and band structure of IrSe 2
Transport coefficient measurements (DC conductivity and thermoelectric power) were performed on compacted bars of polycrystalline IrSe 2 in the 100-570 K temperature range. The experimental results are interpeted on the basis of an n-type compensated semiconductor model. At low temperatures, a narrow band which originates from non-stoichiometry mainly participates in the conduction by thermally activated hopping of small polarons. The charge balance adopted by anionic groups is discussed. The schematic band model which is retained takes into account all the transport properties and the ion charge balance Ir 3+Se 2-(Se 2) 2-1/ 2. Moreover, IrSe 2 has recently been shown to function as a cathode material in lithium batteries.
Morsli, M.; Bonnet, A.; Tregouet, Y.; Conan, A.; Jobic, S.; Brec, R.
Band structures in 98Ru and 99Ru
The level schemes of 98, 99Ru were studied with the reactions 98Mo(alpha, 3ngamma) and 98Mo(alpha, 4ngamma) at Ealpha = 35 to 55 MeV, using a large variety of in-beam gamma-ray detection techniques and conversion-electron measurements. A search for the 3- state was carried out with the reaction 98Ru(p, p'). The ground-state band of 98Ru was excited up to Jpi =
E. H. Du Marchie van Voorthuysen; M. J. A. Devoigt; N. Blasi; J. F. W. Jansen
The level schemes of 98, 99Ru were studied with the reactions 98Mo(?, 3n?) and 98Mo(?, 4n?) at E? = 35 to 55 MeV, using a large variety of in-beam ?-ray detection techniques and conversion-electron measurements. A search for the 3 - state was carried out with the reaction 98Ru(p, p'). The ground-state band of 98Ru was excited up to J? = (12) + and a negative-parity band up to (15) -. New levels in 98Ru were found at Ex = 2285 ( J? = 4 +), 2435 ( J? = (3 -, 4 +)), 2671, 3540, 4224, 4847, 4915 ( J? = (12) +), 4989 ( J? = (12 +)), 5521 ( J? = (13) -), 5889, 6591 ( J? = (15) -), and 7621 keV. New unambiguous spin and parity assignments were made for the levels at Ex = 2014 and 3852 keV, as J? = 3 + and 9 -, respectively. New levels in 99Ru were found at Ex = 1976, 2021 ( J ? = ( {15}/{2}+) ), 2393, 2401 ( J ? = ( {17}/{2}+) ), 2875 (? = (+)), 3037, 3201 ( J ? = ( {23}/{2}) -), 3460 ( J = ( {17}/{2}) ), 3484 ( J ? = ( {21}/{2}+) ), 3985, 4224 ( J ? = ( {27}/{2}-) ), and 5359 keV. The 1070 keV, J ? = {11}/{2}- level in 99Ru has a half-life of 2.8 ns. A strongly excited negative-parity band is built on this level. A positive-parity band based on the ground state was excited up to J ? = ( {21}/{2}+) . The level schemes are well reproduced by the interacting boson model in the vibrational limit.
Van Voorthuysen, E. H. Du Marchie; Devoigt, M. J. A.; Blasi, N.; Jansen, J. F. W.
Lunar near-surface structure
Seismic refraction data obtained at the Apollo 14, 16, and 17 landing sites permit a compressional wave velocity profile of the lunar near surface to be derived. Beneath the regolith at the Apollo 14 Fra Mauro site and the Apollo 16 Descartes site is material with a seismic velocity of about 300 m/sec, believed to be brecciated material or impact-derived debris. Considerable detail is known about the velocity structure at the Apollo 17 Taurus-Littrow site. Seismic velocities of 100, 327, 495, 960, and 4700 m/sec are observed. The depth to the top of the 4700-m/sec material is 1385 m, compatible with gravity estimates for the thickness of mare basaltic flows, which fill the Taurus-Littrow valley. The observed magnitude of the velocity change with depth and the implied steep velocity-depth gradient of more than 2 km/sec/km are much larger than have been observed on compaction experiments on granular materials and preclude simple cold compaction of a fine-grained rock powder to thicknesses of the order of kilometers.
Cooper, M. R.; Kovach, R. L.; Watkins, J. S.
Band structure and transport properties of CrO2
The local-spin-density approximation is used to calculate the energy bands of both the ferromagnetic and paramagnetic phases of metallic CrO2. The Fermi level lies in a peak in the paramagnetic density of states, and the ferromagnetic phase is more stable. As predicted by Schwarz, the Fermi level lies in an insulating gap in the minority-spin bands between oxygen p and chromium d states (``half-metallic'' behavior). The resulting magnetic moment is 2?B per Cr atom, in agreement with experiment. The A1g Raman frequency is predicted to be 587 cm-1. Drude plasma frequencies are of order 2 eV, as seen experimentally by Chase. The measured resistivity is used to find the electron mean free path l, which is only a few angstroms at 600 K, but, nevertheless, resistivity continues to rise as temperature increases. This puts CrO2 into the category of ``bad metals'' in common with the high-Tc superconductors, the high-T metallic phase of VO2, and the ferromagnet SrRuO3. In common with both SrRuO3 and Sr2RuO4, the measured specific-heat parameter ? is higher than band theory predicts by a renormalization factor close to 4.
Lewis, Steven P.; Allen, Philip B.; Sasaki, Taizo
Comparative studies on photonic band structures of diamond and hexagonal diamond using the multiple scattering method
Photonic band structures are investigated for both diamond and hexagonal diamond crystals composed of dielectric spheres, and absolute photonic band gaps (PBGs) are found in both cases. In agreement with both Karathanos and Moroz's calculations, a large PBG occurs between the eighth and ninth bands in diamond crystal, but a PBG in hexagonal diamond crystal is found to occur between the sixteenth and seventeenth bands because of the doubling of dielectric spheres in the primitive cell. To explore the physical mechanism of how the photonic band gap might be broadened, we have compared the electric field distributions (|E|2) of the 'valence' and 'conduction' band edges. Results show that the field intensity for the 'conduction' band locates in the inner core of the sphere while that of the 'valence' band concentrates in the outer shell. With this motivation, double-layer spheres are designed to enhance the corresponding photonic band gaps; the PBG is increased by 35% for the diamond structure, and 14% for the hexagonal diamond structure.
Chen, Hui; Zhang, Weiyi; Wang, Zhenlin
Controlling surface band-bending of InP with polysulfide treatments
Surface modification of InP by exposure to hydrogen polysulfide vapor at room temperature and by subsequent heating were studied by X-ray photoelectron spectroscopy (XPS). The XPS measured surface Fermi level ( EFs) position of polysulfide treated p-InP changed from 0.5 eV, relative to the valence band maximum (VBM), to 1.2 eV by heating the exposed surface at 300░C for a few minutes in vacuum. Further heating at 400░C for a few hours resulted in EFs moving back to a position 0.5 eV above the VBM. Surface chemistry changes determined by XPS during this rather large movement of EFs suggest a mechanism which involves the following three steps; (a) the exposure of InP to polysulfides reduces surface states in the bandgap; (b) heating of the exposed surface converts weakly adsorbed polysulfides to more strongly adsorbed species which contribute donor states near the conduction band minimum; (c) heating at 400░C slowly desorbs the surface donor species and gradually returns the EFs of a p-substrate to its original 0.5 eV above the VBM.
Lau, W. M.; Kwok, R. W. M.; Ingrey, S.
Surface Impedance and Bulk Band Geometric Phases in One-Dimensional Systems
Surface impedance is an important concept in classical wave systems such as photonic crystals (PCs). For example, the condition of an interface state formation in the interfacial region of two different one-dimensional PCs is simplyZSL+ZSR=0, where ZSL(ZSR)is the surface impedance of the semi-infinite PC on the left-hand (right-hand) side of the interface. Here, we also show a rigorous relation between the surface impedance of a one-dimensional PC and its bulk properties through the geometrical (Zak) phases of the bulk bands, which can be used to determine the existence or nonexistence of interface states at the interface of the two PCs in a particular band gap. Our results hold for any PCs with inversion symmetry, independent of the frequency of the gap and the symmetry point where the gap lies in the Brillouin zone. Our results provide new insights into the relationship between surface scattering properties, the bulk band properties, and the formation of interface states, which in turn can enable the design of systems with interface states in a rational manner.
Xiao, Meng; Zhang, Z. Q.; Chan, C. T.
Effective properties and band structures of lamellar subwavelength crystals: Plane-wave method revisited
The plane-wave method used to compute the band structure of photonic crystals is revisited in light of recent mathematical results about the Fourier factorization of products of discontinuous functions. Highly accurate numerical predictions for the effective index and for the band structure are obtained for two- and three-dimensional dielectric lamellar crystals with high dielectric contrasts. At the same time, we clarify some aspects related to the effective properties of multidimensional crystals by establishing clear links between their band structures and their effective indices.
Lalanne, Philippe
Compact electromagnetic bandgap structures for notch band in ultra-wideband applications.
This paper introduces a novel approach to create notch band filters in the front-end of ultra-wideband (UWB) communication systems based on electromagnetic bandgap (EBG) structures. The concept presented here can be implemented in any structure that has a microstrip in its configuration. The EBG structure is first analyzed using a full wave electromagnetic solver and then optimized to work at WLAN band (5.15-5.825 GHz). Two UWB passband filters are used to demonstrate the applicability and effectiveness of the novel EBG notch band feature. Simulation results are provided for two cases studied. PMID:22163430
Rotaru, Mihai; Sykulski, Jan
Thermal Performance of Surface Wick Structures
Microscale surface wick structures that exploit capillary driven flow in interior corners have been designed. In this study we examine the interplay between capillary flow and evaporative heat transfer that effectively reduces the surface temperature. The tests are performed by raising the surface temperature to various levels before the flow is introduced to the surfaces. Certainly heat transfer weakens the
Yongkang Chen; Noel Tavan; John Baker; Lawrence Melvin; Mark Weislogel
This paper describes the design of inductive frequency selective surfaces to be used in the beam-waveguide feed system of deep space antenna DSA2 of the European Space Agency. In particular, these frequency selective surfaces are needed to upgrade the antenna for operation in K band, a broad band recently allocated to download scientific data from space probes.
M. Bozzi; M. Formaggi; M. Pasian; L. Perregrini; P. Besso
Chemical changes at the surface of RTV silicone rubber coatings on insulators during dry-band arcing
Under wet and contaminated conditions dry band arcing occurs on the surface of HV outdoor insulators coated with room temperature vulcanizing (RTV) silicone rubber. The thermal impact of the arcing on the surface of the RTV causes chemical changes. The gradual loss of hydrophobicity due to dry band arcing is of considerable concern because it results in a reduction of
Seog-Hyeon Kim; Edward A. Cherney; Reuben Hackam; Kenneth G. Rutherford
C-Band Airport Surface Communications System Standards Development, Phase I
This document is being provided as part of ITT's NASA Glenn Research Center Aerospace Communication Systems Technical Support (ACSTS) contract NNC05CA85C, Task 7: "New ATM Requirements--Future Communications, C-Band and L-Band Communications Standard Development." The proposed future C-band (5091- to 5150-MHz) airport surface communication system, referred to as the Aeronautical Mobile Airport Communications System (AeroMACS), is anticipated to increase overall air-to-ground data communications systems capacity by using a new spectrum (i.e., not very high frequency (VHF)). Although some critical services could be supported, AeroMACS will also target noncritical services, such as weather advisory and aeronautical information services as part of an airborne System Wide Information Management (SWIM) program. AeroMACS is to be designed and implemented in a manner that will not disrupt other services operating in the C-band. This report defines the AeroMACS concepts of use, high-level system requirements, and architecture; the performance of supporting system analyses; the development of AeroMACS test and demonstration plans; and the establishment of an operational AeroMACS capability in support of C-band aeronautical data communications standards to be advanced in both international (International Civil Aviation Organization, ICAO) and national (RTCA) forums. This includes the development of system parameter profile recommendations for AeroMACS based on existing Institute of Electrical and Electronics Engineering (IEEE) 802.16e- 2009 standards
Hall, Edward; Isaacs, James; Zelkin, Natalie; Henriksen. Steve
Direct determination of photonic band structure for waveguiding modes in two-dimensional photonic crystals.
We directly determine the experimental photonic band dispersion structure of waveguiding modes under the light line in a two-dimensional photonic crystal (2D PhC) waveguide by using angle-resolved attenuated total reflection spectroscopy. Resonance coupling between the external evanescent wave from total reflection within the prism and the waveguiding modes in the 2D PhC provides clear information on individual band components by resolving the angle (i.e., wave vector k) and photon energy. The experimentally determined photonic band structure, which is essential for understanding the novel light propagation properties of PhC systems with many degrees of freedom, agrees well with the band structure predicted by theory. Furthermore, we demonstrate the accuracy and suitability of this method by analyzing field distribution and eigen-photon-energy calculations for a model structure identical to the experimental arrangement of the prism and sample structure. PMID:18542325
Inoue, Shin-ichiro; Yokoyama, Shiyoshi; Aoyagi, Yoshinobu
Impact of lattice-shape moduli on band structure of photonic crystals
We conduct a comprehensive study of the effect of the Bravais lattice-shape moduli on the band structure and in particular the band gap of photonic crystals. Unlike the conventional comparisons between triangular and rectangular photonic crystals, where the effect of the volume modulus is not separated, we rigorously decouple the volume modulus and determine the differences that can be attributed
Arash Mafi
A FEM domain decomposition method for photonic and electromagnetic band gap structures
This paper introduces an efficient domain decomposition algorithm for the solution of time-harmonic electromagnetic fields arising in three dimensional, finite-size photonic band gap and electromagnetic band gap structures. The method is based on the finite element approximation and a nonoverlapping domain decomposition method. A set of \\
Marinos N. Vouvakis; Zoltan Cendes; Jin-Fa Lee
Collective Motions and Band Structures in A = 60 to 80, Even--Even Nuclei.
Evidence for and the theoretical understanding of the richness of the collective band structures as illustrated by at least seven bands seen in levels of exp 68 Ge, exp 74 Se are reviewed. The experimental data on even-even nuclei in the A = 60 to 80 regi...
J. H. Hamilton R. L. Robinson A. V. Ramayya
First-principles calculations for the electronic band structures of small diametersingle-wall carbon nanotubes
We present first-principles calculations on the band structures of 40 different small diameter (d) single-wall carbon nanotubes (SWCNTs), including 14 chiral ones, employing density functional theory (DFT) within the local density approximation (LDA), using the Vienna ab initio simulation package (VASP). The band gaps are calculated and discussed for all of the tubes. From small to large diameters, the gap
V. Z¾lyomi; J. K³rti
Band structure analysis of (1 ū 2)-H/Pd(110)-pr
A novel method of band structure analysis based on the atomic orbital (AO) coefficients in LCAO-DFT has been applied to the (1 ū 2)-H/Pd(110)-pr system. The analysis has revealed symmetry-dependent Pd 4d band splitting due to H ligand effects; ensemble effects due to the (1 ū 2) Pd reconstruction are shown to be relatively minor.
Shuttleworth, I. G.
Energy band structures for electrons on the triangular lattice with uniform magnetic field
In the present paper the electron on the triangular lattice with uniform perpendicular magnetic field [1,2] is considered. The energy band structure is visualized using numerical computations. The energy bands as a function of the magnetic field display a Hofstadter butterfly [3,4] type diagram. The influence of the hopping parameters on the energy spectra is also taken into account.
Szakßcs, Zs.
Application of coordinate transformation and finite differences method in numerical modeling of quantum dash band structure
In this paper we propose an efficient and simple method for the band structure calculation of semiconductor quantum dashes. The method combines a coordinate transformation (mapping) based on an analytical function and the finite differences method (FDM) for solving the single-band Schr÷dinger equation. We explore suitable coordinate transformations and propose those, which might simultaneously provide a satisfactory fit of the
B. M. Stupovski; J. V. Crnjanski; D. M. Gvozdic
Electronic band structure, stability, structural, and elastic properties of IrTi alloys
The structural properties and mechanical stabilities of B2-IrTi have been investigated using first-principle calculations. The elastic constants calculations indicate that the B2-IrTi is unstable to external strain and the softening of C11-C12 triggers the B2-IrTi (cubic) to L10-IrTi (tetragonal) phase transformation. Detailed electronic structure analysis revealed a Jahn-Teller-type band split that could be responsible for elastic softening and structure phase transition. The cubic-tetragonal transition is accompanied by a reduction in the density of states (DOS) at the Fermi level and the d-DOS of Ti at Fermi level plays a decisive role in destabilizing the B2-IrTi phase.
Chen, Wen-Zhou; Li, Qian; Jiang, Zhen-Yi; Zhang, Xiao-dong; Si, Liang; Li, Li-Sha; Wu, Rui
The effect of perturbating a frequency-selective surface and its relation to the design of a dual-band surface
A single-layer dual-band frequency selective surface (FSS) created by the perturbation of a single-band dipole array is studied. A simple algebraic formulation is derived to analyze both element and spacing perturbations. Guidelines are then proposed to allow dual-band FSSs to be designed with no anomalous behavior occurring in the two desired bandstop responses. Examples of unsuccessful and successful dual-band FSSs
Roger A. Hill; Benedikt A. Munk
Quasiparticle band structure and tight-binding model for single- and bilayer black phosphorus
By performing ab initio calculations for one- to four-layer black phosphorus within the GW approximation, we obtain a significant difference in the band gap (ś1.5 eV), which is in line with recent experimental data. The results are analyzed in terms of the constructed four-band tight-binding model, which gives accurate descriptions of the mono- and bilayer band structure near the band gap, and reveal an important role of the interlayer hoppings, which are largely responsible for the obtained gap difference.
Rudenko, A. N.; Katsnelson, M. I.
Electronic band structure effects in monolayer, bilayer, and hybrid graphene structures
Since its discovery in 2005, graphene has been the focus of intense theoretical and experimental study owing to its unique two-dimensional band structure and related electronic properties. In this thesis, we explore the electronic properties of graphene structures from several perspectives including the magnetoelectrical transport properties of monolayer graphene, gap engineering and measurements in bilayer graphene, and anomalous quantum oscillation in the monolayer-bilayer graphene hybrids. We also explored the device implications of our findings, and the application of some experimental techniques developed for the graphene work to the study of a complex oxide, Ca3Ru2O7, exhibiting properties of strongly correlated electrons. Graphene's high mobility and ballistic transport over device length scales, make it suitable for numerous applications. However, two big challenges remain in the way: maintaining high mobility in fabricated devices, and engineering a band gap to make graphene compatible with logical electronics and various optical devices. We address the first challenge by experimentally evaluating mobilities in scalable monolayer graphene-based field effect transistors (FETs) and dielectric-covered Hall bars. We find that the mobility is limited in these devices, and is roughly inversely proportional to doping. By considering interaction of graphene's Dirac fermions with local charged impurities at the interface between graphene and the top-gate dielectric, we find that Coulomb scattering is responsible for degraded mobility. Even in the cleanest devices, a band gap is still desirable for electronic applications of graphene. We address this challenge by probing the band structure of bilayer graphene, in which a field-tunable energy band gap has been theoretically proposed. We use planar tunneling spectroscopy of exfoliated bilayer graphene flakes demonstrate both measurement and control of the energy band gap. We find that both the Fermi level and electronic structure are highly sensitive to tunnel bias-induced charging in these devices, an effect that is traditionally neglected in other materials. However, careful consideration of both these effects and non-ideal tunneling processes allows extraction of valuable information from the tunneling spectra. We compare the tunable insulating state to our transport studies of bi-layer graphene-based FETs with similar dielectric environments. This work, as well as our work on top-gated monolayer-based devices, identifies the integration of graphene and a gate dielectric as being the next great challenge towards the realization of graphene-based electronics. We also report the discovery of anomalous quantum oscillations in magnetotransport measurements of monolayer and bilayer graphene hybrids. In these graphene hybrid structures, the Fermi levels of either portion lock at their interface, and the greatly different energy scales of emergent Landau levels support strong charge imbalance. The nature the interface states are yet to be clarified. Finally, we extend the techniques of device fabrication and measurement to exfoliated flakes of a layered material, Ca3Ru2O 7. This strongly correlated electronic system hosts a variety of exotic phenomena at low temperatures, which have been suggested to result from complex d-orbital interactions. We compare transport measurements of flakes to previous studies in bulk crystals, and explore the effects of tuning charge carrier density using an ionic liquid gate to induce densities several orders of magnitude greater than is possible with conventional dielectrics.
Puls, Conor
A Novel Band-Reject Frequency Selective Surface With Pseudo-Elliptic Response
A novel frequency selective surface (FSS) exhibiting pseudo-elliptic band-reject response is presented. The proposed FSS consists of a two-dimensional periodic array of microstrip lines. For an incident wave of linear polarization perpendicular to the printed lines, virtual magnetic walls are formed between the microstrip lines. Since a microstrip line shielded with magnetic side walls supports two quasi-TEM modes, the two-dimensional
Amir Khurrum Rashid; Zhongxiang Shen
The L-band PBMR measurements of surface soil moisture in FIFE
The NASA Langley Research Center's L-band pushbroom microwave radiometer (PBMR) aboard the NASA C-130 aircraft was used to map surface soil moisture at and around the Konza Prairie Natural Research Area in Kansas during the four intensive field campaigns of FIFE in May-October 1987. A total of 11 measurements were made when soils were known to be saturated. This measurement
J. R. Wang; J. C. Shiue; T. J. Schmugge; E. T. Engman
Quasi optical circulator X-band scale model utilizing a circular polarization frequency selective surface
A prototype X-band scale model for a quasi optical 3-port circulator utilizing a double-layer circularly polarizing frequency selective surface is proposed. The operating principles and measured characteristics of the device are discussed. A prototype device operating at 9.9 GHz is built and validated experimentally. The port 1 to port 2 insertion loss of the circulator has been measured to be
M. Euler; V. F. Fusco
Surface-Based Polarimetric C-Band Scatterometer for Field Measurements of Sea Ice
A portable surface-based polarimetric C-band scatterometer for field deployment over sea ice is presented. The scatterometer system, its calibration, signal processing, and near-field correction are described. The near-field correction is shown to be effective for both linear polarized and polarimetric backscatter. Field methods for the scatterometer are described. Sample linear polarized and polarimetric backscatter results are presented for snow-covered first-year
Torsten Geldsetzer; James B. Mead; John J. Yackel; Randall K. Scharien; Stephen E. L. Howell
Banded structure and its distribution in friction stir processing of 316L austenitic stainless steel
Banded structures, which vary with welding parameters, were observed in friction stir processing of 316L austenite stainless steel. Sigma phase precipitation was detected in banded structures by transmission electron microscopy. The amount of banded structure had direct ratio relations with heat input. The higher the heat input, the larger the area of banded structures. This is attributable to slower cooling rate at high heat input, which results in longer exposure to the temperature range for precipitation. The formation of sigma phase produced Cr depletion, which resulted in largely degraded corrosion resistance. The present study suggests that low heat input (i.e. low rotation speeds, low working loads and high welding speed) contributes to restrain sigma phase precipitation.
Chen, Y. C.; Fujii, H.; Tsumura, T.; Kitagawa, Y.; Nakata, K.; Ikeuchi, K.; Matsubayashi, K.; Michishita, Y.; Fujiya, Y.; Katoh, J.
Band structure engineering through orbital interaction for enhanced thermoelectric power factor
Band structure engineering for specific electronic or optical properties is essential for the further development of many important technologies including thermoelectrics, optoelectronics, and microelectronics. In this work, we report orbital interaction as a powerful tool to finetune the band structure and the transport properties of charge carriers in bulk crystalline semiconductors. The proposed mechanism of orbital interaction on band structure is demonstrated for IV-VI thermoelectric semiconductors. For IV-VI materials, we find that the convergence of multiple carrier pockets not only displays a strong correlation with the s-p and spin-orbit coupling but also coincides with the enhancement of power factor. Our results suggest a useful path to engineer the band structure and an enticing solid-solution design principle to enhance thermoelectric performance.
Zhu, Hong; Sun, Wenhao; Armiento, Rickard; Lazic, Predrag; Ceder, Gerbrand
Polymorphism, band-structure, band-lineup, and alloy energetics of the group II oxides and sulfides MgO, ZnO, CdO, MgS, ZnS, CdS
The group II chalcogenides are an important class of functional semiconductor materials exhibiting a remarkable diversity in terms of structure and properties. In order to aid the materials design, a consistent set of electronic structure calculations is presented, including data on the polymorphic energy ordering, the band-structures, the band-lineups relative to the vacuum level, surface energies, as well as on the alloy energetics. To this end, current state-of-the-art electronic structure tools are employed, which, besides standard density functional theory (DFT), include totalenergy calculation in the random phase approximation and GW quasiparticle energy calculations. The ionization potentials and electron affinities are obtained by combining the results of bulk GW and surface DFT calculations. Considering both octahedral and tetrahedral coordination symmetries, exemplified by the rock-salt and zinc-blende lattices, respectively, this data reveals both the chemical and structural trends within this materials family.
Lany, Stephan
Dual-band asymmetric electromagnetic wave transmission for dual polarizations in chiral metamaterial structure
In this paper, we propose a chiral metamaterial structure that enables dual-band asymmetric transmission effect for different linearly polarized electromagnetic waves. The metamaterial is composed of metallic spirals with two split-ring resonators sandwiching a dielectric slab and connecting with via hole. Strong one-way transmission of two orthogonally polarized waves at different frequency bands has been confirmed through both full-wave simulation and test on fabricated prototype at the microwave band. Analysis also shows such asymmetric transmission can be attributed to the induced asymmetric current distributions in the spiral that support strong polarization conversion and cross-polarization transmission. By scaling down the metamaterial structure, the concept could also be utilized at other frequency bands, such as submillimeter or even terahertz band and find applications in designing one-way electromagnetic wave devices or polarization spectral filters.
Wu, Linxiao; Zhang, Meng; Zhu, Bo; Zhao, Junming; Jiang, Tian; Feng, Yijun
Tuning the locally resonant phononic band structures of two-dimensional periodic electroactive composites
The band structures of two locally resonant phononic crystals (LRPCs) with periodic multilayered cylindrical inclusions embedded in an elastic matrix are investigated by the finite-element method. The inclusions consist of electroactive polymer layer(s). Tunability of the band gaps of the phononic crystals by applying electric field upon the electroactive layer is demonstrated. A simple analytical expression is presented on the relationship between the stop band boundaries and the electric field. Good agreement between the analytical and numerical predictions is obtained. The effects of initial stress on the band structures are explored. It is found that tensile initial stress shifts up the band gaps while compressive initial stress shifts down or even closes them.
Zhou, Xiaoling; Chen, Changqing
Measurement of passive film growth kinetics on bare surface band microelectrodes
A new method has been developed for the study of bare surface electrochemistry at shorter times and higher current densities than those conventionally achieved. This technique involves in situ fracture of a sputtered metal film between two glass slides to create a band microelectrode. This has the advantage over electrodes of conventional size of an increase in the rate of mass transport to and from the surface and reduction in the ohmic (IR) drop. The bare microelectrode method has been used to study the repassivation kinetics of sputtered niobium films. 9 refs., 5 figs.
Davenport, A.J.; Isaacs, H.S.
A portable X-band on-axis standing wave linac structure
A portable X-band on-axis standing wave electron linear accelerating structure has been developed that is suitable for portable radiation therapy and radiography. The phase-focusing technique is used. The design parameters of a 2 MeV, X-band, on-axis coupled, SW accelerating guide operated in the ?\\/2 mode is described. A prototype 150 mm long structure has been machined, brazed and sealed, and
Xiang Sun; Tong Dechun; Jin Qingxiu; Lin Yuzheng; Sun Jingqing; Hu Shaoguang; Du Taibin; Duan Xiuming; Chen Bingyi; Li Yuezeng; Zou Yang; Hu Wensheng
Electronic structure of poly(tetrafluoroethylene) studied by UPS, VUV absorption, and band calculations
The electronic structure of poly(tetrafluoroethylene) (PTFE) was studied by UPS, VUV absorption, and ab-initio MO calculations. The UPS spectra give a photoemission threshold energy of 10.6eV, with deeper valence band features consistent with the reported XPS and the oligomer vapour UPS spectra. The UPS spectra are also consistent with the density of states derived from the calculated band structure, which
Kazuhiko Seki; Hiroshi Tanaka; Toshiaki Ohta; Yuriko Aoki; Akira Imamura; Hitoshi Fujimoto; Hiromichi Yamamoto; Hiroo Inokuchi
Compaction bands: a structural analog for anti-mode I cracks in aeolian sandstone
We present evidence for the existence of tabular zones of localized deformation in aeolian sandstone, that accommodate pure compaction. In this sense they are analogs for anticracks or closing mode I fractures such as pressure solution surfaces or stylolites. The so called "compaction bands" are exposed in outcrops of the Jurassic Navajo Sandstone in the Kaibab monocline, Utah. They are characterized by lack of shear offset across their plane, volume loss, micro fracturing and very little grain crushing or comminution. Based on their geometry, two kinds of compaction bands are distinguished: the first kind is 0.5-1.5 cm thick and fairly straight over lengths of about 5-10 m. The second kind is 0.1-0.5 cm thick over lengths up to 2 m, and is conspicuously crooked with wavelengths of 1-5 cm and amplitudes of a few mm to a few cm. Compaction bands preferentially developed in the compressive quadrant at the tips of small faults or "deformation band faults" which suggests, together with the direction of shear along the deformation band faults, that compaction bands form perpendicular to the largest compressive stresses induced by motion along the deformation band faults. Also, the compaction bands typically occur in sedimentary layers with large grain sizes (0.3-0.8 mm) and high porosity (20-25%) whereas the deformation band faults occur in the layers with smaller grain sizes (0.05-0.25 mm) and lower (< 20%) porosity.
Mollema, P. N.; Antonellini, M. A.
Conformal coating of highly structured surfaces
Method of applying a conformal coating to a highly structured substrate and devices made by the disclosed methods are disclosed. An example method includes the deposition of a substantially contiguous layer of a material upon a highly structured surface within a deposition process chamber. The highly structured surface may be associated with a substrate or another layer deposited on a substrate. The method includes depositing a material having an amorphous structure on the highly structured surface at a deposition pressure of equal to or less than about 3 mTorr. The method may also include removing a portion of the amorphous material deposited on selected surfaces and depositing additional amorphous material on the highly structured surface.
Ginley, David S.; Perkins, John; Berry, Joseph; Gennett, Thomas
A Local-Density Band Theory for the Fermi Surface of the Heavy-Electron Compound CeRu2Si2
On the basis of the itinerant-electron model for the 4f electrons, the energy band structure and the Fermi surface are calculated for the metamagnetic heavy-electron compound CeRu2Si2 having the low-temperature electronic specific heat coefficient gamma of 350 mJ\\/K2 mol. by a self-consistent symmetrized relativistic APW method with the exchange and correlation potential in a local-density approximation. The main Fermi surface
Hiroshi sc Yamagami; Akira Hasegawa
XPS and UPS study of the valence band structure and chemisorption of Ti(0001)
Photoemission studies of the clean (0001) face of a titanium single crystal using UV and X-ray photoelectron spectroscopy (UPS and XPS) have revealed two maxima in the valence band density of states at ~0.5 and ~1.4 eV below the Fermi level. The 1.4 eV peak exhibits the following unusual characteristics: (i) Its photoionization cross section decreases rapidly as incident photon energy increases, (ii) Its UPS intensity is rapidly quenched by exposure to small doses of CO and N 2 but large doses of O 2 are required for the same effect, (iii) Its UPS intensity decreases rapidly upon heating from ~120 to ~240░C. The 0.5 eV peak does not exhibit this behavior. The temperature dependence of the 1.4 eV peak gives a near linear Arrhenius plot with an activation energy of 9.1 kcal/mole. This observed temperature dependence is that expected for diffusion of hydrogen during the ? ? ? phase transformation of titanium hydride. The characteristics of this peak are consistent with its identification as photoemission from an electronic structure localized at the surface. This structure may be a titanium hydride layer near the surface.
Fukuda, Yasuo; Honda, Fumihiro; Rabalais, J. Wayne
Sorting of droplets by migration on structured surfaces
Summary Background: Controlled transport of microdroplets is a topic of interest for various applications. It is well known that liquid droplets move towards areas of minimum contact angle if placed on a flat solid surface exhibiting a gradient of contact angle. This effect can be utilised for droplet manipulation. In this contribution we describe how controlled droplet movement can be achieved by a surface pattern consisting of cones and funnels whose length scales are comparable to the droplet diameter. Results: The surface energy of a droplet attached to a cone in a symmetry-preserving way can be smaller than the surface energy of a freely floating droplet. If the value of the contact angle is fixed and lies within a certain interval, then droplets sitting initially on a cone can gain energy by moving to adjacent cones. Conclusion: Surfaces covered with cone-shaped protrusions or cavities may be devised for constructing ōband-conveyorsö for droplets. In our approach, it is essentially the surface structure which is varied, not the contact angle. It may be speculated that suitably patterned surfaces are also utilised in biological surfaces where a large variety of ornamentations and surface structuring are often observed.
Roth-Nebelsick, Anita
Electronic structure of Pt based topological Heusler compounds with C1{sub b} structure and 'zero band gap'
Besides of their well-known wide range of properties it was recently shown that many of the heavy Heusler semiconductors with 1:1:1 composition and C1{sub b} structure exhibit a zero band gap behavior and are topological insulators induced by their inverted band structure. In the present study, the electronic structure of the Heusler compounds PtYSb and PtLaBi was investigated by bulk sensitive hard x-ray photoelectron spectroscopy. The measured valence band spectra are clearly resolved and in well agreement to the first-principles calculations of the electronic structure of the compounds. The experimental results give clear evidence for the zero band gap state.
Ouardi, Siham; Shekhar, Chandra; Fecher, Gerhard H.; Kozina, Xeniya; Stryganyuk, Gregory; Felser, Claudia [Institut fuer Anorganische Chemie und Analytische Chemie, Johannes Gutenberg-Universitaet, D-55099 Mainz (Germany); Ueda, Shigenori; Kobayashi, Keisuke [NIMS Beamline Station at SPring-8, National Institute for Materials Science, Hyogo 679-5148 (Japan)
Fine structure of the red luminescence band in undoped GaN
Many point defects in GaN responsible for broad photoluminescence (PL) bands remain unidentified. Their presence in thick GaN layers grown by hydride vapor phase epitaxy (HVPE) detrimentally affects the material quality and may hinder the use of GaN in high-power electronic devices. One of the main PL bands in HVPE-grown GaN is the red luminescence (RL) band with a maximum at 1.8 eV. We observed the fine structure of this band with a zero-phonon line (ZPL) at 2.36 eV, which may help to identify the related defect. The shift of the ZPL with excitation intensity and the temperature-related transformation of the RL band fine structure indicate that the RL band is caused by transitions from a shallow donor (at low temperature) or from the conduction band (above 50 K) to an unknown deep acceptor having an energy level 1.130 eV above the valence band.
Reshchikov, M. A.; Usikov, A.; Helava, H.; Makarov, Yu.
Surface states and electronic structure of polar and nonpolar InN - An in situ photoelectron spectroscopy study
Valence band structure and surface states of InN with (0001), (000-1), (1-100), and (11-20) orientation were investigated in situ after growth using photoelectron spectroscopy. Depending on surface orientation, different occupied surface states are identified and differentiated from bulk contributions. For N-polar, m-plane, and a-plane InN, the surface states are located at the valence band maximum, while In-polar InN features surface states close to the Fermi level. The surface band alignment correlates with the position of surface states. For InN(0001), a much larger surface downward band bending is observed compared to N-polar, m-plane, and a-plane InN, where almost flat band conditions occur.
Eisenhardt, A.; Krischok, S.; Himmerlich, M. [Institut fuer Physik and Institut fuer Mikro- und Nanotechnologien, Technische Universitaet Ilmenau, PF 100565, 98694 Ilmenau (Germany)] [Institut fuer Physik and Institut fuer Mikro- und Nanotechnologien, Technische Universitaet Ilmenau, PF 100565, 98694 Ilmenau (Germany)
Spatially resolved methane band photometry of Jupiter. III - Cloud vertical structures for several axisymmetric bands and the Great Red Spot
The paper presents cloud structure models for Jupiter's Great Red Spot, Equatorial and North Tropical Zones, North and South Temperate Zones, and North and South Polar Regions. The models are based on images of Jupiter in three methane bands and nearby continuum; radiative transfer calculations include multiple scattering and absorption from three aerosol layers. The model results include the transition in the upper-cloud altitude to 3 km lower altitude from the tropical zones to temperate zones and polar regions, a N/S asymmetry in cloud thickness in the tropical and temperature zones, and the presence of aerosols up to about 0.3 bar in the Great Red Spot and Equatorial Zone. It is concluded that polarization data are sensitive to aerosols in and above the upper cloud layer but insensitive to deeper cloud structure.
West, R. A.; Tomasko, M. G.
Band theoretical studies of the electronic structure of oxides
The O2- ion is a useful concept in ionic solids. Its electron density and large polarizability is well described by the Watson sphere model. The large variation in the electronic structure of oxides is illustrated by discussing the ionic MgO, the partly æcovalentÆ Cu2O, and TiO and NbO which have defects with respect to the ideal NaCl structure. The variation
Karlheinz Schwarz
Estimating Sea Surface Salinity and Wind Using Combined Passive and Active L-Band Microwave Observations
Several L-band microwave radiometer and radar missions have been, or will be, operating in space for land and ocean observations. These include the NASA Aquarius mission and the Soil Moisture Active Passive (SMAP) mission, both of which use combined passive/ active L-band instruments. Aquarius s passive/active L-band microwave sensor has been designed to map the salinity field at the surface of the ocean from space. SMAP s primary objectives are for soil moisture and freeze/thaw detection, but it will operate continuously over the ocean, and hence will have significant potential for ocean surface research. In this innovation, an algorithm has been developed to retrieve simultaneously ocean surface salinity and wind from combined passive/active L-band microwave observations of sea surfaces. The algorithm takes advantage of the differing response of brightness temperatures and radar backscatter to salinity, wind speed, and direction, thus minimizing the least squares error (LSE) measure, which signifies the difference between measurements and model functions of brightness temperatures and radar backscatter. The algorithm uses the conjugate gradient method to search for the local minima of the LSE. Three LSE measures with different measurement combinations have been tested. The first LSE measure uses passive microwave data only with retrieval errors reaching 1 to 2 psu (practical salinity units) for salinity, and 1 to 2 m/s for wind speed. The second LSE measure uses both passive and active microwave data for vertical and horizontal polarizations. The addition of active microwave data significantly improves the retrieval accuracy by about a factor of five. To mitigate the impact of Faraday rotation on satellite observations, the third LSE measure uses measurement combinations invariant under the Faraday rotation. For Aquarius, the expected RMS SSS (sea surface salinity) error will be less than about 0.2 psu for low winds, and increases to 0.3 psu at 25 m/s wind speed for warm waters (25 C). To achieve the required 0.2 psu accuracy, the impact of sea surface roughness (e.g. wind-generated ripples) on the observed brightness temperature has to be corrected to better than one tenth of a degree Kelvin. With this algorithm, the accuracy of retrieved wind speed will be high, varying from a few tenths to 0.6 m/s. The expected direction accuracy is also excellent (less than 10 ) for mid to high winds, but degrades for lower speeds (less than 7 m/s).
Yueh, Simon H.; Chaubell, Mario J.
Surface and Bulk Electronic Structure of Wurtzite GaN
The electronic structure of thin film wurtzite GaN and Al_xGa_1-xN has been studied using angle resolved photoemission, inverse photoemission, soft x-ray absorption and soft x-ray emission. These complimentary spectroscopies allow us to measure the partial density of states (PDOS) of the occupied and unoccupied valence states, and the band dispersion of occupied and unoccupied surface and bulk states. The GaN(0001) thin films used in our experiments were grown using molecular beam epitaxy on sapphire substrates, and were Si doped n-type. Soft x-ray absorption (SXA) and soft x-ray emission (SXE) measurements were performed at the HASYLAB synchrotron, Hamburg, and at the National Synchrotron Light Source (NSLS), Brookhaven National Laboratory. Angle resolved photoemission (ARP) and momentum resolved inverse photoemission (IP) spectra were performed at Brookhaven. Clean surfaces were prepared by repeated cycles of sputtering with N2 ions and annealing in ultra-high vacuum at 900 C. Low energy electron diffraction from the clean surface displays a sharp hexagonal pattern with no evidence of surface reconstruction. ARP measurements for GaN show bulk bands that agree well with theoretical predictions,(A. Rubio, J.L. Corkhill, M.L. Cohen, E.L. Shirley, and S.G. Louie, Phys. Rev. B 48, 11810, (1993)) but also show the existence of a well defined surface state.(S.S. Dhesi, C.B. Stagarescu, K.E. Smith, D. Doppalapudi, R. Singh and T.D. Moustakas, Phys. Rev. B 56, 10271 (1997)) This state is occupied, and lies below the valence band maximum in a projected bulk band gap. It has spz character, consistent with a dangling bond state, and is sensitive to contamination of the surface by O2 or H_2. IP spectroscopy was used to measure the dispersion of the unoccupied GaN conduction band states, and no unoccupied surface states were observed. SXE and SXA were used to measure the bulk valence and conduction band partial density of states and band gap behavior for GaN (C. Stagarescu, L.C. Duda, K.E. Smith, J.H. Guo, J. Nordgren, R. Singh and T.D. Moustakas, Phys. Rev. B 54, 17,335 (1996)) and Al_xGa_1-xN. Given the strong dipole selection rules that govern SXE, and the sensitivity of our spectrometer, we are able to directly observe the hybrid states in these nitrides. Specifically, we find a weak feature in the N K-emission at approximately 19.5 eV below the valence band maximum that arises from hybridization between N 2p and Ga 3d states. We also directly observe hybridization between Ga 4s- and N 2p-states extending to the valence band maximum. X-ray absorption spectra show that the bottom of the conduction band is a mixture of Ga 4s and N 2p states.
Smith, Kevin E.
Band gap and structure of single crystal BiI3: Resolving discrepancies in literature
Bismuth tri-iodide (BiI3) is an intermediate band gap semiconductor with potential for room temperature gamma-ray detection applications. Remarkably, very different band gap characteristics and values of BiI3 have been reported in literature, which may be attributed to its complicated layered structure with strongly bound BiI6 octahedra held together by weak van der Waals interactions. Here, to resolve this discrepancy, the band gap of BiI3 was characterized through optical and computational methods and differences among previously reported values are discussed. Unpolarized transmittance and reflectance spectra in the visible to near ultraviolet (UV-Vis) range at room temperature yielded an indirect band gap of 1.67 +/- 0.09 eV, while spectroscopic ellipsometry detected a direct band gap at 1.96 +/- 0.05 eV and higher energy critical point features. The discrepancy between the UV-Vis and ellipsometry results originates from the low optical absorption coefficients (? ~ 102 cm-1) of BiI3 that renders reflection-based ellipsometry insensitive to the indirect gap for this material. Further, electronic-structure calculations of the band structure by density functional theory methods are also consistent with the presence of an indirect band gap of 1.55 eV in BiI3. Based on this, an indirect band gap with a value of 1.67 +/- 0.09 eV is considered to best represent the band gap structure and value for single crystal BiI3.
Podraza, Nikolas J.; Qiu, Wei; Hinojosa, Beverly B.; Xu, Haixuan; Motyka, Michael A.; Phillpot, Simon R.; Baciak, James E.; Trolier-McKinstry, Susan; Nino, Juan C.
UV spectral filtering by surface structured multilayer mirrors.
A surface structured extreme ultraviolet multilayer mirror was developed showing full band suppression of UV (?=100-400??nm) and simultaneously a high reflectance of EUV light (?=13.5??nm). The surface structure consists of Si pyramids, which are substantially transparent for EUV but reflective for UV light. The reflected UV is filtered out by blazed diffraction, interference, and absorption. A first demonstration pyramid structure was fabricated on a multilayer by using a straightforward deposition technique. It shows an average suppression of 14 times over the whole UV range and an EUV reflectance of 56.2% at 13.5 nm. This robust scheme can be used as a spectral purity solution for all XUV sources that emit longer wavelength radiation as well. PMID:24690702
Huang, Qiushi; Paardekooper, Daniel Mathijs; Zoethout, Erwin; Medvedev, V V; van de Kruijs, Robbert; Bosgra, Jeroen; Louis, Eric; Bijkerk, Fred
Potential energy surface and vibrational band origins of the triatomic lithium cation
The 104 point CISD Li +3 potential energy surface and its analytical representation is reported. The calculations predict the minimum energy geometry to be an equilateral triangle of side RLi?Li = 3.0 ┼ and of energy - 22.20506 E h. A fifth-order MorseŚDunham type analytical force field is used in the CarneyŚPorter normal co-ordinate vibrational Hamiltonian, the corresponding eigenvalue problem being solved variationally using a 560 configurational finite-element basis set. The predicted assignment of the vibrational band origins is in accord with that reported for H +3. Moreover, for 6Li +3 and 7Li +3 the lowest i.r. accessible band origin is the overline?0,1,▒1 predicted to be at 243.6 and 226.0 cm -1 respectively.
Searles, Debra J.; Dunne, Simon J.; von Nagy-Felsobuki, Ellak I.
Band Alignment of Atomic Layer Deposited HfO2 on Clean and N Passivated Germanium Surfaces
Hard x-ray photoelectron spectroscopy has been used to study the band alignment between atomic layer deposited HfO{sub 2} on clean Ge (100) and nitrogen treated Ge (100) surfaces. The position of the valence-band maximum was determined by convolving theoretically calculated density of states from first-principles calculations and comparing with experimental valence-band data. Using Kraut's method, the valence-band offsets were found to be 3.2 {+-} 0.1 and 3.3 {+-} 0.1 eV for the samples grown on clean and N passivated Ge, respectively. The oxide charge measured from capacitance-voltage measurements shows a significant increase between the two samples; however, the small change in the band offset between the two systems strongly indicates negligible contribution of the interface to the conduction/valence-band barrier and the band alignment of the heterojunctions.
Rumaiz, A.K.; Woicik, J.C.; Carini, G.A.; Siddons, D.P.; Cockayne, E.; Huey, E.; Lysaght, P.S.; Fisher, D.A.; Genova, V.
The O2- ion is a useful concept in ionic solids. Its electron density and large polarizability is well described by the Watson sphere model. The large variation in the electronic structure of oxides is illustrated by discussing the ionic MgO, the partly æcovalentÆ Cu2O, and TiO and NbO which have defects with respect to the ideal NaCl structure. The variation in physical properties is shown for the oxides in the rutile structure ranging from the insulating TiO2, the metallic RuO2 to the ferromagnetic CrO2. Electron densities, total energies and densities of states are used to study these materials.
Schwarz, Karlheinz
Photonic band gap of superconductor-medium structure: Two-dimensional triangular lattice
Based on London theory a general form of wave equation is formulated for both dielectric medium and superconductor. Using the wave equation and applying plane wave expansion, we have numerically calculated the band structures and density of states of a photonic crystal, whose intersection is constructed by a two-dimensional triangular lattice of superconductor padding in dielectric medium. Results indicate a wider band gap in the superconductor-medium photonic crystal than that in conventional photonic crystals. And part of original energy levels are found to be rearranged upon consideration of the superconductivity. The dependence of band gap on penetration length and filling factor is also discussed. Band gap width decreases monotonically with the penetration length, but not with the filling factor. Band gaps can be partially shut down or opened by adjusting filling factor.
Liu, Wan-guo; Pan, Feng-ming; Cai, Li-wei
Quasiparticle band structures and interface physics of SnS and GeS
We perform first-principles, density-functional-theory calculations of the electronic structure for the layered bulk materials SnS and GeS which are of interest for photovoltaic applications. Band gap corrections are computed within the GW approximation to the electron self-energy. The resulting quasiparticle gaps in both SnS and GeS are in excellent agreement with the majority of existing experimental measurements. In order to better understand the possible use of GeS layers as a carrier-confining barrier within a SnS-based photovoltaic device, we compute the band offsets for different orientations of a SnS/GeS heterojunction. We find the valence band offsets to be almost independent of interfacial direction while the conduction band offsets show a strong anisotropy as a result of the variation in the band gap caused by epitaxial strain along the different directions.
Malone, Brad D.; Kaxiras, Efthimios
The optical band gap and surface free energy of polyethylene modified by electron beam irradiations
In this study, investigations have been carried out on electron beam irradiated ultra high molecular weight polyethylene (UHMWPE). Polyethylene samples were irradiated with 1.5 MeV electron beam at doses ranging from 50 to 500 kGy. Modifications in optical properties and photoluminescence behavior of the polymer were evaluated by UV-vis and photoluminescence techniques. Changes of surface layer composition of UHMWPE produced by electron irradiations were studied by Rutherford back scattering spectrometry (RBS). The change in wettability and surface free energy induced by irradiations was also investigated. The optical absorption studies reveal that both optical band gap and Urbach's energy decreases with increasing electron dose. A correlation between energy gap and the number of carbon atoms in clusters is discussed. Photoluminescence spectra were reveal remarkable decrease in the integrated luminescence intensity with increasing irradiation dose. Contact angle measurements showed that wettability and surface free energy increases with increasing the irradiation dose.
Abdul-Kader, A. M.
Surface structure of Uukuniemi virus.
Uukuniemi virus, grown in chicken embryo fibroblasts, has been studied by electron microscopy using negative staining, thin sectioning, and freeze-etching techniques. The spherical virus particle measures about 95 nm in diameter. Its envelope consists of a 5-nm thick membrane covered by 8- to 10-nm long surface projections. These are composed of two polypeptides species of about the same size. Both of them can be removed by digestion with the proteolytic enzyme thermolysin except for a small fragment. The enzyme-treated particles are smooth surfaced and extremely deformable. The glycopolypeptides are clustered to form hollow cylindrical morphological units, 10 to 12 nm in diameter, with a 5-nm central cavity. Both negative staining and freeze-etching suggest that these units are penton-hexon clusters arranged in a T = 12, P = 3, icosahedral surface lattice. The membrane to which the surface subunits are attached is probably a lipid bilayer as evidenced by its double-track appearance in thin sections and the tendency of the freeze fracturing to occur within it. The strand-like nucleoprotein appears from thin-sectioning results to be to a large part located in a zone underneath the membrane. Images
von Bonsdorff, C H; Pettersson, R
Design of a frequency selective surface (FSS) type superstrate for dual-band directivity enhancement of microstrip patch antennas
A novel design of a high-directivity resonator antenna that utilizes a two-layered frequency selective surface (FSS) superstrate - as an alternative to a dielectric electromagnetic band gap (EBG) superstrate - for dual band directivity enhancement and reduction in height is presented in this paper.
Nonadiabatic dynamics near metal surfaces: Decoupling quantum equations of motion in the wide-band limit
When an electron in a localized orbital approaches a continuum, resonant charge transfer can occur. For instance, when a beam of ions is scattered from a metal surface, neutralization can take place through the transfer of an electron either from ion to metal--in the case of a negative ion--or from metal to ion--in the case of a positive ion. Similarly, a neutral atom may be ionized by removing an electron from the metal surface. In this paper, we introduce the wide-band diabatic dynamics (WBDD) method for simulating the quantum dynamics of such systems by decoupling the equations of motion for the ionic and neutral diabats. We show numerically that our approximation accurately describes the quantum nuclear dynamics near the metal surface. Although we treat the case of ion neutralization, our method is general, and can be applied to any quantum state interacting with a continuum via a position-dependent interaction, provided that the wide-band approximation holds.
Shenvi, Neil [Department of Chemistry, Yale University, New Haven, Connecticut 06520 (United States); Cheng Hongzhi [Department of Physics, Yale University, New Haven, Connecticut 06520 (United States); Tully, John C. [Department of Chemistry, Yale University, New Haven, Connecticut 06520 (United States); Department of Physics, Yale University, New Haven, Connecticut 06520 (United States)
Quasiparticle band structures of ?-HgS, HgSe, and HgTe
The electronic structures of mercury chalcogenides in the zinc-blende strucrure have been calculated by the LDA, GW (one-shot, G0W0) and quasi-particle self-consistent GW (QSGW) approximations including spin-orbit coupling (SO). The slight tendency to overestimation of the band gaps by QSGW is avoided by using a hybrid scheme (20% LDA and 80 % QSGW. The results of G0W0 depend strongly starting wave functions and are thus quite different from those from QSGW. Within QSGW HgS is found to be a semiconductor, with a ?6 s-like conduction-band minimum state above the valence-band top ?7 and ?8 (``negative'' SO splitting). HgSe and HgTe have ``negative'' gaps (inverted band structure). In HgTe the ?7 state is below ?6 due to the large Te SO splitting, in contrast HgSe where ?6 is below ?7.
Christensen, Niels E.; Svane, Axel; Cardona, Manuel; Chantis, Athanasios; van Schilfgaarde, Mark; Kotani, Takao
Electronic- and band-structure evolution in low-doped (Ga,Mn)As
Modulation photoreflectance spectroscopy and Raman spectroscopy have been applied to study the electronic- and band-structure evolution in (Ga,Mn)As epitaxial layers with increasing Mn doping in the range of low Mn content, up to 1.2%. Structural and magnetic properties of the layers were characterized with high-resolution X-ray diffractometry and SQUID magnetometery, respectively. The revealed results of decrease in the band-gap-transition energy with increasing Mn content in very low-doped (Ga,Mn)As layers with n-type conductivity are interpreted as a result of merging the Mn-related impurity band with the host GaAs valence band. On the other hand, an increase in the band-gap-transition energy with increasing Mn content in (Ga,Mn)As layers with higher Mn content and p-type conductivity indicates the Moss-Burstein shift of the absorption edge due to the Fermi level location within the valence band, determined by the free-hole concentration. The experimental results are consistent with the valence-band origin of mobile holes mediating ferromagnetic ordering in the (Ga,Mn)As diluted ferromagnetic semiconductor.
Yastrubchak, O.; Gluba, L.; ?uk, J. [Institute of Physics, UMCS, Pl. Marii Curie-Sk?odowskiej 1, 20-031 Lublin (Poland)] [Institute of Physics, UMCS, Pl. Marii Curie-Sk?odowskiej 1, 20-031 Lublin (Poland); Sadowski, J. [Institute of Physics, Polish Academy of Sciences, 02-668 Warszawa (Poland) [Institute of Physics, Polish Academy of Sciences, 02-668 Warszawa (Poland); MAX-Lab, Lund University, 22100 Lund (Sweden); Krzy?anowska, H. [Institute of Physics, UMCS, Pl. Marii Curie-Sk?odowskiej 1, 20-031 Lublin (Poland) [Institute of Physics, UMCS, Pl. Marii Curie-Sk?odowskiej 1, 20-031 Lublin (Poland); Department of Physics and Astronomy, Vanderbilt University, 6506 Stevenson Center, Nashville, Tennessee 37325 (United States); Domagala, J. Z.; Andrearczyk, T.; Wosinski, T. [Institute of Physics, Polish Academy of Sciences, 02-668 Warszawa (Poland)] [Institute of Physics, Polish Academy of Sciences, 02-668 Warszawa (Poland)
Towards Complete Photonic Band Gap Structures below Infrared Wavelengths
\\u000a Photonic crystals are structures with a periodically modulated dielectric constant. In analogy to the case of an electron\\u000a moving in a periodic potential, certain photon frequencies can become forbidden, independent of photon polarization and the\\u000a direction of propagation Ś a complete photonic bandgap (CPBG) [1, 2]. As early as 1975, photonic crystals with such a gap\\u000a have been shown to
Alexander Moroz
Two-zone heterogeneous structure within shear bands of a bulk metallic glass
Shear bands, the main plastic strain carrier in metallic glasses, are severely deformed regions often considered as disordered and featureless. Here we report the observations of a sandwich-like heterogeneous structure inside shear bands in Pd{sub 40.5}Ni{sub 40.5}P{sub 19} metallic glass sample after plastic deformation by high-resolution transmission electron microscopy. The experimental results suggest a two-step plastic deformation mechanism with corresponding microstructure evolution at atomic scale, which may intimately connected to the stability of the shear band propagation and the overall plastic deformability.
Shao, Yang; Yao, Kefu; Liu, Xue [School of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China)] [School of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China); Li, Mo [School of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China) [School of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China); School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0245 (United States)
Optical Properties and Band Structure of KTaO3
The optical dielectric functions for single-crystal KTaO{sub 3} are determined using spectroscopic ellipsometry and optical transmission techniques. These results show that the lowest band gap is 3.64 eV (341 nm) with very low absorption up to 4.28 eV, indicating an indirect band gap. The ellipsometry results are analyzed using critical point analysis, which shows that there are three direct gaps at 4.35, 4.68, and 5.03 eV. The results are compared with band structure calculations determined using the local density approximation (LDA) and the Engel-Vosko generalized gradient approximation (GGA).
Jellison Jr, Gerald Earle [ORNL; Paulauskas, Irene E [ORNL; Boatner, Lynn A [ORNL; Singh, David J [ORNL
Tuning the band structures of single walled silicon carbide nanotubes with uniaxial strain: A first principles study
Electronic band structures of single-walled silicon carbide nanotubes are studied under uniaxial strain using first principles calculations. The band structure can be tuned by mechanical strain in a wide energy range. The band gap decreases with uniaxial tensile strain, but initially increases with uniaxial compressive strain and then decreases with further increases in compressive strain. These results may provide a
Zhiguo Wang; Xiaotao T. Zu; Haiyan Xiao; Fei Gao; William J. Weber
Structure and mobility on amorphous silicon surfaces
The structure and dynamics of amorphous surfaces are poorly understood. The present work develops methods employing classical molecular dynamics (MD) simulations to elucidate these phenomena on amorphous silicon. Careful relaxation of the initial ensemble and taking account of exchange with the bulk yield surface diffusion coefficients in good agreement with experiment. Randomly oriented dimer pairs dominate the surface structure. Diffusion proceeds by several pathways, which all differ in basic character from those typically observed on crystalline silicon. The primary pathways involve single atoms and dimer pairs, which typically move only one or two atomic diameters before reincorporating into the surface. Frequent vertical migration takes place between the first two atomic layers.
Dalton, A. S.; Seebauer, E. G.
Semiconductor quantum structures for ultraviolet-to-infrared multi-band radiation detection
In this work, multi-band (multi-color) detector structures considering different semiconductor device concepts and architectures are presented. Results on detectors operating in ultraviolet-to-infrared regions (UV-to-IR) are discussed. Multi-band detectors are based on quantum dot (QD) structures; which include quantum-dots-in-a-well (DWELL), tunneling quantum dot infrared photodetectors (T-QDIPs), and bi-layer quantum dot infrared photodetectors (Bi-QDIPs); and homo-\\/heterojunction interfacial workfunction internal photoemission (HIWIP\\/HEIWIP) structures.
Gamini Ariyawansa
Electronic structure and optical band gap of CoFe2O4 thin films
Electronic structure and optical band gap of CoFe2O4 thin films grown on (001) oriented LaAlO3 have been investigated. Surprisingly, these films show additional Raman modes at room temperature as compared to a bulk spinel structure. The splitting of Raman modes is explained by considering the short-range ordering of Co and Fe cations in octahedral site of spinel structure. In addition, an expansion of band-gap is observed with the reduction of film thickness, which is explained by the quantum size effect and misfit dislocation. Such results provide interesting insights for the growth of spinel phases.
Ravindra, A. V.; Padhan, P.; Prellier, W.
Measurement of the surface wavelength distribution of narrow-band radiation by a colorimetric method
A method is suggested for determining the wavelength of narrow-band light from a digital photograph of a radiating surface. The digital camera used should be appropriately calibrated. The accuracy of the wavelength measurement is better than 1 nm. The method was tested on the yellow doublet of mercury spectrum and on the adjacent continuum of the incandescent lamp radiation spectrum. By means of the method suggested the homogeneity of holographic sensor swelling was studied in stationary and transient cases. (laser applications and other topics in quantum electronics)
Kraiskii, A V; Mironova, T V; Sultanov, T T [P N Lebedev Physical Institute, Russian Academy of Sciences, Moscow (Russian Federation)
True photonic band-gap in vertical-cavity surface-emitting lasers
In this work we show the analysis of high contrast vertical-cavity surface-emitting lasers (VCSEL) mirror with etched photonic crystal, which provide the true photonic band-gap (PBG) for TE-like polarized light. We confirm that PBG is the main light confinement mechanism by analyzing a low-index line-defect as well as a low-index cavity mode. In the latter case we are able to obtain very high cavity Q-factor. Such PBG-VCSELs are compatible with the VCSEL technology and do not require a complicated assembly of three-dimensional photonic crystals.┬Ł
Dems, Maciej; Panajotov, Krassimir
Commensurate magnetic excitations induced by band splitting and Fermi surface topology in n-type cuprates.
The antiferromagnetic correlation plays an important role in high-Tc superconductors. Considering this effect, the magnetic excitations in n-type cuprates near the optimal doping are studied within the spin-density-wave description. The magnetic excitations are commensurate in the low-energy regime and further develop into spin-wave-like dispersion at higher energy, consistent with the inelastic neutron scattering measurements. We clearly demonstrate that the commensurability originates from the band splitting and Fermi surface topology. The commensurability is a normal state property and has nothing to do with d-wave superconductivity. Our results strongly suggest the essential role of antiferromagnetic correlations in the cuprates. PMID:23507793
Zhang, H Y; Zhou, Y; Lin, H Q; Gong, C D
Study on band gap structure of Fibonacci quantum superlattices by using the transfer matrix method
The scattering properties of particles in a one-dimensional Fibonacci sequence based potential have been analyzed by means of the Transfer Matrix Method. The electronic band gaps are examined comparatively with those obtained using the corresponding periodic potentials. The reflection coefficient shows self-similar properties for the Fibonacci superlattices. Moreover, by using the generalized Bragg's condition, the band gaps positions are derived from the golden mean involved in the design of the superlattice structure.
Ferrando, V.; Castro-Palacio, J. C.; MarĒ, B.; Monsoriu, J. A.
Design, simulation and analysis of embedded Uniplanar compact electromagnetic band-gap structure
The design, simulation, analysis and application of embedded Uni-planar compact electromagnetic band-gap (E-UCEBG) structure for high speed digital circuit or mixed circuit application are presented in this paper. Shorting vias between shield plane and EBG plane are used to broaden the band-gap of E-UC-EBG. When the distance between the shorting vias is smaller than 1\\/8 wavelength of high stop frequency
Shen Zhen-ning; Wang Wen-jun; Liu Fei; Zhou Zi-chen
Calculation of Band-Structure Effects in Field-Emission Tunneling from Tungsten
A calculation was made to determine whether band-structure effects in field emission, as described in the Stratton theory of tunneling from a metal, could explain the anomalous total energy distribution (TED) for the directions of tungsten obtained by Swanson and Crouser. In applying the Stratton theory, a simple model for the tungsten energy bands based on Loucks's calculated relativistic augmented-plane-wave
Douglas Nagy; P. H. Cutler
An X-band disk-and-washer accelerating structure for electron accelerators
X-band electron linacs are an excellent choice for portable accelerators. In this pager we present an X-band disk-and-washer standing wave structure is studied in this paper for a low energy accelerating tube. The DAW cavities are optimized to obtain the largest shunt impedance and quality for the TM020 mode. A set of differential equations is used to describe the optimizing
Yuan Hu; Chuanxiang Tang; Huaibi Chen; Yuzheng Lin; Dechun Tong
The pressure dependences of TiS2 and TiSe2 band structures
The band structures of the layer compounds 1T-TiS2 and 1T-TiSe2 have been calculated within the local-density approximation using the self-consistent LAPW method. Both compounds are found to be semimetals with Gamma -L overlaps of 0.24 and 0.55 eV, respectively. The positioning and occupation of the bands near the Fermi level are not consistent with the carrier densities determined from Hall
G. A. Benesh; A. M. Woolley; C. Umrigar
Valence band structure of cubic AlGaN\\/GaN superlattices
The influence of different material parameters, spin-orbit interaction, and strain effects on the valence band structure of cubic AlGaN\\/GaN superlattices is investigated. One-particle hole state calculations are carried out within the k.p theory by means of a full six-band Luttinger-Kohn Hamiltonian in a plane-wave representation. It is shown that the use of distinct values for the Luttinger parameters for the
S. C. P. Rodrigues; L. M. R. Scolfaro; J. R. Leite; G. M. Sipahi
The influence of different material parameters, spin-orbit interaction, and strain effects on the valence band structure of cubic AlGaN\\/GaN superlattices is investigated. One-particle hole state calculations are carried out within the k?p theory by means of a full six-band Luttinger-Kohn Hamiltonian in a plane-wave representation. It is shown that the use of distinct values for the Luttinger parameters for the
Photonic band structure of nanoporous anodized aluminum oxide with radius-to-period ratio modulation
Photonic band structure and photonic band gap of nanoporous anodized aluminum oxide (np-AAO) based photonic crystals is numerically investigated in detail based on the plane-wave expansion method, with emphasis on the modulation of radius-to-period ratio of the cylindrical holes. This ratio is extremely convenient to be controlled experimentally, which is a unique feature of np-AAO. Transverse-electric and transverse-magnetic polarizations are
Liang Zhang; Maoqin Xin; Jinghua Teng; Soojin Chua
Band structure and optical spectra of RbNH 4SO 4 crystals
First-principal density functional theory (DFT) calculations of the band structure, density of states and dielectric functions ?(E) of the rubidium ammonium sulfate (RAS) crystal, RbNH4SO4, in the orthorhombic phase Pnma have been carried out using the CASTEP code. Valence electron bands of the crystal are flat in k-space, that responds to the relatively great effective mass, m*?5me. The top valence
B. Andriyevsky; W. Ciepluch-Trojanek; V. Stadnyk; M. Tuzyak; M. Romanyuk; V. Kurlyak
Wide-band underwater acoustic absorption based on locally resonant unit and interpenetrating network structure
The interpenetrating network structure provides an interesting avenue to novel materials. Locally resonant phononic crystal (LRPC) exhibits excellent sound attenuation performance based on the periodical arrangement of sound wave scatters. Combining the LRPC concept and interpenetrating network glassy structure, this paper has developed a new material which can achieve a wide band underwater strong acoustic absorption. Underwater absorption coefficients of
Heng Jiang; Yu-Ren Wang; Mi-Lin Zhang; Yan-Ping Hu; Ding Lan; Qun-Li Wu; Huan-Tong Lu
International X-Band Linear Collider Accelerator Structure R&D
For more than fifteen years before the International Technology Recommendation Panel (ITRP) decision in August, 2004, there were intensive R&D activities and broad international collaboration among the groups at SLAC, KEK, FNAL, LLNL and other labs for the room temperature X-Band accelerator structures. The goal was to provide an optimized design of the main linac structure for the NLC (Next Linear Collider) or GLC (Global Linear Collider). There have been two major challenges in developing X-band accelerator structures for the linear colliders. The first is to demonstrate stable, long-term operation at the high gradient (65 MV/m) that is required to optimize the machine cost. The second is to strongly suppress the beam induced long-range wakefields, which is required to achieve high luminosity. More than thirty X-band accelerator structures with various RF parameters, cavity shapes and coupler types have been fabricated and tested since 1989. A summary of the main achievements and experiences are presented in this talk including the structure design, manufacturing techniques, high power performance, and other structure related issues. Also, the new progress in collaborating with the CLIC, high gradient structures and X-Band structure applications for RF deflectors and others are briefly introduced.
Wang, J.W.; /SLAC
The main objective of this dissertation is to characterize and create insight into the electromagnetic performances of two classes of composite structures, namely, complex multi-layered media and periodic Electromagnetic Band-Gap (EBG) structures. The advanced and diversified computational techniques are applied to obtain their unique propagation characteristics and integrate the results into some novel applications. In the first part of this
Hossein Mosallaei
A Novel Method for Band Structure Analysis of Photonic Crystal Slabs
We propose a new method to extract the modes of photonic crystal slabs and, thus, obtain their band structures. These slabs, which are 2-D periodic structures with finite thickness, can completely confine light and have the important advantage of simple construction for applications in integrated optic devices. In this paper, reflection pole method (RPM) is utilized to analyze photonic crystal
S. A. H. Nekuee; M. Akbari; K. Mehrany
Narrow bands and electronic structure in unconventional high- T C superconductors
Electronic structure details play a marginal role in the superconductive properties of conventional superconductors. Electronic energies are by far the most important in these materials and the only relevant electronic parameter, with respect to superconductivity, is essentially the density of states N(0). Cooper oxides and fullerene compounds are characterized by narrow band dispersions and by electronic structures of hundreds meV.
E. Cappelluti; C. Grimaldi; L. Pietronero; S. Strõssler
For more than fifteen years before the International Technology Recommendation Panel (ITRP) decision in August, 2004, there were intensive R&D activities and broad international collaboration among the groups at SLAC, KEK, FNAL, LLNL and other labs for the room temperature X-Band accelerator structures. The goal was to provide an optimized design of the main linac structure for the NLC (Next
J. W. Wang
The electronic structures of mercury chalcogenides in the zinc-blende structure have been calculated within the LDA, GW (G0W0, ōone-shotö) and quasi-particle self-consistent GW (QSGW) approximations, including spin-orbit (SO) coupling. The slight tendency to overestimation of band gaps by QSGW is avoided by using a hybridscheme (20% LDA and 80% QSGW). The details of the GW bands near the top of the valence bands differ significantly from the predictions obtained by calculations within the LDA. The results obtained by G0W0 depend strongly on the starting wave functions and are thus quite different from those obtained from QSGW. Within QSGW, HgS is found to be a semiconductor, with a ?6 s-like conduction-band minimum state above the valence top ?7 and ?8 (ōnegativeö SO splitting). HgSe and HgTe have negative gaps (inverted band structures), but for HgTe the ?7 state is below ?6 due to the large Te SO splitting, in contrast to HgSe where ?6 is below ?7. There appears to be significant differences, in particular for HgSe and HgS, between the ordering of the band-edge states as obtained from experiments and theory.
Svane, A.; Christensen, N. E.; Cardona, M.; Chantis, A. N.; van Schilfgaarde, M.; Kotani, T.
Estimation of Bare Surface Soil Moisture and Surface Roughness Parameter Using L-Band SAR Image Data
An algorithm based on a fit of the single-scattering Integral Equation Method (IEM) was developed to provide estimation of soil moisture and surface roughness parameter (a combination of rms roughness height and surface power spectrum) from quad-polarized synthetic aperture radar (SAR) measurements. This algorithm was applied to a series of measurements acquired at L-band (1.25 GHz) from both AIRSAR (Airborne Synthetic Aperture Radar operated by the Jet Propulsion Laboratory) and SIR-C (Spaceborne Imaging Radar-C) over a well- managed watershed in southwest Oklahoma. Prior to its application for soil moisture inversion, a good agreement was found between the single-scattering IEM simulations and the L band measurements of SIR-C and AIRSAR over a wide range of soil moisture and surface roughness conditions. The sensitivity of soil moisture variation to the co-polarized signals were then examined under the consideration of the calibration accuracy of various components of SAR measurements. It was found that the two co-polarized backscattering coefficients and their combinations would provide the best input to the algorithm for estimation of soil moisture and roughness parameter. Application of the inversion algorithm to the co-polarized measurements of both AIRSAR and SIR-C resulted in estimated values of soil moisture and roughness parameter for bare and short-vegetated fields that compared favorably with those sampled on the ground. The root-mean-square (rms) errors of the comparison were found to be 3.4% and 1.9 dB for soil moisture and surface roughness parameter, respectively.
Shi, Jian-Cheng; Wang, James; Hsu, Ann Y.; ONeill, Peggy E.; Engman, Edwin T.
Theoretical Analysis of the Structural Instability and Surface Properties of Some Low-Dimensional Compounds
The structural and electronic properties of several low-dimensional metallic compounds were explained by calculating their electronic band structures and analyzing how the calculated electronic structures are related to the crystal structures. Our calculations confirmed that CuS is a pseudo 2D metal, that the 55K structural phase transition does not originate from any electronic instability of the Fermi surfaces, and that
Weigen Liang
Superhydrophobic surfaces from hierarchically structured wrinkled polymers.
This work reports the creation of superhydrophobic wrinkled surfaces with hierarchical structures at both the nanoscale and microscale. A nanoscale structure with 500 nm line gratings was first fabricated on poly(hydroxyethyl methacrylate) films by nanoimprint lithography while a secondary micro-scale structure was created by spontaneous wrinkling. Compared with random wrinkles whose patterns show no specific orientation, the hierarchical wrinkles exhibit interesting orientation due to confinement effects of pre-imprinted line patterns. The hierarchically wrinkled surfaces have significantly higher water contact angles than random wrinkled surfaces, exhibiting superhydrophobicity with water contact angles higher than 160░ and water sliding angle lower than 5░. The hierarchically structured wrinkled surfaces exhibit tunable wettability from hydrophobic to superhydrophobic and there is an observed transition from anisotropic to isotropic wetting behavior achievable by adjusting the initial film thickness. PMID:24131534
Li, Yinyong; Dai, Shuxi; John, Jacob; Carter, Kenneth R
Structural evolution of cometary surfaces
Comets with a high content of organics and light molecules are expected under cosmic radiation to gain a relatively unreactive crust and less volatile material to some 10 m deep. Interstellar dust impacts act to loosen and turn over about 1 cm of the surface. This paper discusses how far this accords with observations of cometary dust halos and new versus old comets. Two key material properties have emerged from recent studies: (1) the source of cometary volatiles is not ice in the sense of material with a single sublimation energy, and (2) the particulates are not simply mineral dust but include much organic material, some of which undergoes chemical processing and exchanges with the gaseous environment.
Wallis, M. K.; Wickramasinghe, N. C.
Geometric and Electronic Structure of Reconstructed Semiconductor Surfaces
The combination of high-resolution photoemission spectroscopy (PES) using synchrotron radiation, and reflection high-energy electron diffraction (RHEED), along with other techniques, have been used to examine the atomic-scale geometric and electronic properties of clean and adsorbate -covered semiconductor surfaces. The surfaces studied have been probed via core-level, valence band, and angle-resolved photoemission spectroscopy, and with the extended photoemission fine structure technique. The surface core-levels and surface states on the Si(111)-(7 x 7) surface have been used to examine submonolayer deposits of Ge onto this surface. Knowledge of the initial stages of interface formation in these systems is important due to their application in heterostructure device physics. The decomposed Si-2p and Ge-3d core levels and angle-integrated valence band spectra have been analyzed as a function of Ge coverage and annealing temperature. The results support the assignment of the lower binding energy component in both the Si-2p and Ge-3d cores to adatom emission. The implications with respect to adatom-to-rest-atom charge transfer are discussed. Lead adlayers on the (111) surfaces of Si and Ge have been examined as well. The surface phase diagram of Pb on these substrates exhibits interesting properties which arise in part due to the differing degrees of lattice matching (~4% for Pb/Si, < 1% for Pb/Ge) and the nature of the clean surface reconstructions ((7 x 7) vs. c(2 x 8)). Atomically abrupt interfaces are insured for these systems since Pb is insoluble in these surfaces even for temperatures well beyond the Pb melting point (340^circC). Thus, they are considered ideal systems to study with regard to metal-semiconductor interface formation and interface -dependent Schottky barrier studies, in contrast to reactive systems where intermixing usually occurs. This lack of interdiffusion has also allowed studies of the 2D melting of the Pb overlayers. The growth, desorption, Schottky -barrier heights, and atomic structure of the Pb-induced phases on Si and Ge are investigated via synchrotron radiation photoemission spectroscopy, along with other techniques such as reflection high-energy electron diffraction and Auger electron spectroscopy (AES). Examining the differences between these closely related systems nicely illustrates the complex interrelationship between the atomic and electronic structure of reconstructed surfaces.
Carlisle, John Arthur
Observation of 'Band' Structures in Spacecraft Observations of Inner Magnetosphere Plasma Electrons
In previous studies, several authors have reported inner magnetosphere observations of proton distributions confined to narrow energy bands in the range of 1-25 keV. These structures have been known as "nose structures", with reference to their appearance in energy-time spectrograms and are known as "bands" if they are observed for extended periods of time. These proton structures have been studied quite extensively with multiple mechanisms proposed for their formation, not all of which apply for electrons. We examine Double-Star TC1 PEACE electron data recorded in the inner magnetosphere (L<15) near the equatorial plane to see if these features are also observed in the electron energy spectra. These "bands" also appear in electron spectrograms, spanning an energy range of 0.2-30 keV, and are shown to occur predominantly towards the dayside and dusk sectors. We also see multiple bands in some instances. We investigate the properties of these multi-banded structures and carry out a statistical survey analysing them as a function of geomagnetic activity, looking at both the Kp and Auroral Indices, in an attempt to explain their presence.
Mohan Narasimhan, Kirthika; Fazakerley, Andrew; Milhaljcic, Branislav; Grimald, Sandrine; Dandouras, Iannis; Owen, Chris
Improved nanobubble immobility induced by surface structures on hydrophobic surfaces.
In fluid flow on hydrophobic surfaces, boundary slip occurs at the solid-liquid interface and nanobubbles on the surfaces are believed to be the reason for it. Boundary slip is of practical importance in micro/nanofluidics to reduce the drag force in fluid flow. However, nanobubbles tend to move under external disturbance. Therefore, the decreased degree of nanobubble movement (nanobubble immobility) is of interest. In this study, nanobubble immobility is studied on both continuously and partially coated polystyrene films. Experimental results show improved immobility on both surfaces. The nanoindents generated by nanobubbles after immersion in a liquid for a period of time on both films and island-like structures on the partially coated film are thought to be the reasons for improved immobility. A model is developed to reveal the role of nanoindents and island structures in the improvement of nanobubble immobility based on contact angle hysteresis and surface tension. Analysis shows that both structures increase the initial force needed to move nanobubbles. Hence, nanobubble immobility is improved on both surfaces as compared with smooth hydrophobic surfaces. PMID:19572534
Wang, Yuliang; Bhushan, Bharat; Zhao, Xuezeng
Laser induced modification of surface structures
The results on surface modification of materials of different structures; morphology, grain sizes, density and porosity by exposure to nanosecond laser light are given. Laser induced changes in their surface characteristics are presented. Surface layers of Si3N4, SiC dense ceramics and BN graphite and turbostratic pressed powders are studied by scanning electron microscopy to reveal the new nanostructures (nanowires or
L. L. Sartinska; S. Barchikovski; N. Wagenda; B. M. RudÆ; I. I. Timofeeva
The elasticity of structured surface liquid layers
The notion of ōelasticity of structured surface liquid layersö has been introduced and considered in detail for the first\\u000a time. It is shown to be reasonably connected with the thermodynamics of condensed matter, allowing the logical derivation\\u000a of the general equations for the surface tension of liquids and solids which had been impossible before.
V. A. Marichev
Electronic Structure and Catalysis on Metal Surfaces
The powerful computational resources available to scientists today, together with recent improvements in electronic structure calculation algorithms, are providing important new tools for researchers in the fields of surface science and catalysis. In this review, we discuss first principles calculations that are now capable of providing qualitative and, in many cases, quantitative insights into surface chemistry. The calculations can aid
Jeff Greeley; Jens K. Norskov; Manos Mavrikakis
Electronic band structure and photoemission spectra of graphene on silicon substrate
Synergizing graphene on silicon based nanostructures is pivotal in advancing nano-electronic device technology. A combination of molecular dynamics and density functional theory has been used to predict the electronic energy band structure and photo-emission spectrum for graphene-Si system with silicon as a substrate for graphene. The equilibrium geometry of the system after energy minimization is obtained from molecular dynamics simulations. For the stable geometry obtained, density functional theory calculations are employed to determine the energy band structure and dielectric constant of the system. Further the work function of the system which is a direct consequence of photoemission spectrum is calculated from the energy band structure using random phase approximations.
Javvaji, Brahmanandam; Ravikumar, Abhilash; Shenoy, B. M.; Roy Mahapatra, D.; Rahman, M. R.; Hegde, G. M.
Spin-polarised band structure for the semimagnetic semiconductor Zn0.5Mn0.5Se
The spin-polarised band structure, density of states (DOS), magnetic moments and exchange interaction coefficients for a layer structure Zn0.5Mn0.5Se in the ferromagnetic phase have been calculated using the self-consistent linear muffin-tin orbital atomic sphere approximation method. Its band structure and DOS distribution are explained through a p-d repulsion model. The band structure in the antiferromagnetic phase is also analysed qualitatively
He Xiaoguang; Huang Meichun
Residual stresses and structural changes generated at different steps of the manufacturing of gears: Effect of banded structures
Banded ferrite¢pearlite structures, and in general chemically inhomogeneous structures, react non uniformly to elevated temperatures during forging and\\/or subsequent heat treatment processes, affecting the final stress state (plastic deformation is required to accommodate dissimilar thermal expansion behavior for each phase) and consequently leading to distortions. These unpredicted distortions are one of the major causes of rejected components and components that
V. GarcĒa Navas; O. Gonzalo; I. Quintana; T. Pirling
Probing the electronic structure at semiconductor surfaces using charge transport in nanomembranes
The electrical properties of nanostructures are extremely sensitive to their surface condition. In very thin two-dimensional crystalline-semiconductor sheets, termed nanomembranes, the influence of the bulk is diminished, and the electrical conductance becomes exquisitely responsive to the structure of the surface and the type and density of defects there. Its understanding therefore requires a precise knowledge of the surface condition. Here we report measurements, using nanomembranes, that demonstrate direct charge transport through the ?* band of the clean reconstructed Si(001) surface. We determine the charge carrier mobility in this band. These measurements, performed in ultra-high vacuum to create a truly clean surface, lay the foundation for a quantitative understanding of the role of extended or localized surface states, created by surface structure, defects or adsorbed atoms/molecules, in modifying charge transport through semiconductor nanostructures.
Peng, Weina; Aksamija, Zlatan; Scott, Shelley A.; Endres, James J.; Savage, Donald E.; Knezevic, Irena; Eriksson, Mark A.; Lagally, Max G.
Electronic structure and scanning-tunneling-microscopy image of molybdenum dichalcogenide surfaces
Electronic structures of MoS2 and MoSe2 surfaces are investigated by first-principles electronic-structure calculations. The ultrasoft pseudopotential by Vanderbilt is used to perform band calculations with a plane-wave basis. Calculated band structures are consistent with recent calculations using other methods. Scanning-tunneling-microscopy (STM) images are calculated from the results of the band calculations, and it is found that bright spots in experimental STM images correspond to chalcogen atoms of the outermost layer. First-principles band calculations by linear combination of atomic orbitals (LCAO) are also performed. It is found that the LCAO method is not so accurate in expressing the electronic properties of conduction bands of molybdenum dichalcogenides. The calculated band structures near the Fermi level show large dispersions along the direction perpendicular to the surface, which explains indirectly the fact that, in spite of the weak van der Waals interlayer interaction, moirķ patterns are observed in the STM images of a MoSe2 surface grown on a MoS2 substrate. The appearance of the moirķ patterns is more directly demonstrated by performing a band calculation of a MoSe2 surface with an irregular structure modeling the MoSe2/MoS2 surface. It is found that the influence of the substrate on the outermost layer propagating through several Se-Mo-Se sandwiches is sufficiently large to reproduce the moirķ patterns. However, the simulated image cannot explain some features of the experimental moirķ patterns, which suggests that relaxation of atomic structures is also necessary to explain the moirķ patterns.
Kobayashi, Katsuyoshi; Yamauchi, Jun
We present evidence for the existence of tabular zones of localized deformation in aeolian sandstone, that accommodate pure compaction. In this sense they are analogs for anticracks or closing mode I fractures such as pressure solution surfaces or stylolites. The so called ōcompaction bandsö are exposed in outcrops of the Jurassic Navajo Sandstone in the Kaibab monocline, Utah. They are
P. N. Mollema; M. A. Antonellini
High-spin structure of {sup 105}Ag: Search for chiral doublet bands
The high-spin structure of the {sup 105}Ag nucleus has been studied by using the {sup 100}Mo({sup 10}B, 5n){sup 105}Ag reaction to search for chiral doublet bands based on the three-quasiparticle {pi}g{sub 9/2}{nu}(h{sub 11/2}){sup 2} configuration. The level scheme of {sup 105}Ag has been extended. New bands were found and the placement of the yrast {pi}g{sub 9/2}{nu}(h{sub 11/2}){sup 2} band was corrected. No side band to the yrast {pi}g{sub 9/2}{nu}(h{sub 11/2}){sup 2} band could be found in the present experiment. This observation indicates that the {gamma}-soft shape in the {sup 106}Ag changed to a more {gamma}-rigid axially symmetric shape in the yrast {sup 105}Ag configuration. However, a new pair of bands was observed to show the expected properties of a chiral doublet structure.
Timar, J.; Sohler, D.; Berek, G. [Institute of Nuclear Research, Pf. 51, H-4001 Debrecen (Hungary); Koike, T. [Department of Physics and Astronomy, SUNY, Stony Brook, New York 11794-3800 (United States); Graduate School of Science, Tohoku University, Sendai 980-8578 (Japan); Pietralla, N.; Ahn, T.; Costin, A. [Department of Physics and Astronomy, SUNY, Stony Brook, New York 11794-3800 (United States); Institut fuer Kernphysik, Technische Universitaet Darmstadt, D-64289 Darmstadt (Germany); Rainovski, G. [Department of Physics and Astronomy, SUNY, Stony Brook, New York 11794-3800 (United States); Faculty of Physics, St. Kliment Ohridski University of Sofia, BG-1164 Sofia (Bulgaria); Dusling, K.; Li, T. C. [Department of Physics and Astronomy, SUNY, Stony Brook, New York 11794-3800 (United States); Paul, E. S. [Oliver Lodge Laboratory, Department of Physics, University of Liverpool, Liverpool L69 7ZE (United Kingdom); Starosta, K. [NSCL, Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824-1321 (United States); Vaman, C. [Department of Physics and Astronomy, SUNY, Stony Brook, New York 11794-3800 (United States); NSCL, Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824-1321 (United States)
Band offsets in heterojunctions formed by oxides with cubic perovskite structure
A number of recent discoveries on heterostructures formed by oxides suggest the emergence of a new direction in microelectronics, the oxide electronics. In the present work, band offsets in nine heterojunctions formed by titanates, zirconates, and niobates with the cubic perovskite structure are calculated from first principles. The effect of strain in contacting oxides on their energy structure; the GW corrections to the band edge positions resulting from many-body effects; and the conduction band edge splitting resulting from spinorbit coupling are consistently taken into account. It is shown that the neglect of the many-body effects can cause errors in the determination of the band offsets, reaching 0.36 eV. The fundamental inapplicability of the transitivity rule often used to determine the band offsets in heterojunctions by comparing the band offsets in a pair of heterojunctions formed by the components of the heterojunction under study with a third common component is demonstrated. The cause of the inapplicability is explained.
Lebedev, A. I.
Band structure of cubic ZrO2 containing oxygen vacancies and calcium ions
The theoretical analysis of the electronic structure of ZrO2 containing oxygen vacancies and calcium ions is carried out. The electronic band-structure calculations for zirconium dioxide in the cubic fluorite structure containing oxygen vacancies and calcium ions are made according to the LMTO method. The values of the total and partial densities of states are calculated. The results are used for
G. A. Ol'khovic; I. I. Naumov; O. I. Velikokhatnyi
Pseudo-atomic-orbital band theory applied to electron-energy-loss near-edge structures
The near-edge structure in inner-shell spectroscopy is a product of the slowly varying matrix element and the appropriate projected density of states. We have made use of the self-consistent pseudo-atomic-orbital band-structure-calculation method to produce accurate projected density of states. Our calculation is in good agreement with the K near-edge structure of diamond, silicon, cubic SiC, and Be2C, and the L
Xudong Weng; Peter Rez; O. F. Sankey
RF Processing of X-Band Accelerator Structures at the NLCTA
During the initial phase of operation, the linacs of the Next Linear Collider (NLC) will contain roughly 5000 X-Band accelerator structures that will accelerate beams of electrons and positrons to 250 GeV. These structures will nominally operate at an unloaded gradient of 72 MV\\/m. As part of the NLC R&D program, several prototype structures have been built and operated at
Chris Adolphsen; K. Jobe; R. Loewen; D. McCormick; M. Ross; T. Smith; J. W. Wang; T. Higo
The effects of band structure on electron-hole Coulomb scattering
The Coulomb mediated transfer of energy from hot electrons to cool holes can play an important role in the dynamics of photo-excited semiconductor plasmas. We demonstrate that in 3-dimensional systems, accurate modeling of the electron-hole scattering process should at least include the effects of valence band structure on the heavy and light hole wavefunctions. In addition to reducing the effectiveness of intra-valence band processes, the p-orbital nature of hole states also enables hot electrons to cool via inter-valence band hole transitions. Even when the split-off band and non-parabolicity effects are ignored, these latter processes contribute significantly to the net energy exchange rate and become increasingly important at high temperatures and densities.
Young, J. F.; Kelly, P. J.; Henry, N. L.
On the origin of a band gap in compounds of diamond-like structures.
Electronic structure calculations were performed to examine the origin of a band gap present in most 18-electron half-Heusler compounds and its absence in NaTl. In these compounds of diamond-like structures, the presence or absence of a band gap is controlled by the sigma antibonding between the valence s orbitals, and the bonding characteristics of the late-main-group elements depend on the extent of their ns/np hybridization. Implications of these observations on the formal oxidation state and the covalent bonding of the transition-metal atoms in 18-electron half-Heusler and related compounds were discussed. PMID:17290986
K÷hler, J³rgen; Deng, Shuiquan; Lee, Changhoon; Whangbo, Myung-Hwan
Band Structure of Carbon Nanotubes in a Perpendicular Electric Field 2.0
The NanoEd Resource Portal, a ├ó┬┬dynamic repository for information dissemination, research and collaborations among the community of nanoscale science and engineering education (NSEE) learners, teachers and researchers,├ó┬┬ provides this interactive simulator. Contributed by Professor Umberto Ravaioli from the University of Illinois at Urbana-Champaign, this simulator performs "band structure calculations for zigzag and armchair type carbon nanotubes (CNT)." This band structure calculator could prove useful for both students and instructors in the field, and could prove valuable in the classroom as well.
Ravaioli, Umberto
Enlarged band gap and electron switch in graphene-based step-barrier structure
We study the transmission through a step-barrier in gapped graphene and propose a method to enlarge the band gap. The step-barrier structure consists of two or more barriers with different strengths. It is found that the band gap could be effectively enlarged and controlled by adjusting the barrier strengths in the light of the mass term. Klein tunneling at oblique incidence is suppressed due to the asymmetry of step-barrier, contrary to the cases in single-barrier and superlattices. Furthermore, a tunable conductance channel could be opened up in the conductance gap, suggesting an application of the structure as an electron switch.
Lu, Wei-Tao, E-mail: email@example.com; Ye, Cheng-Zhi [School of Science, Linyi University, 276005 Linyi (China) [School of Science, Linyi University, 276005 Linyi (China); Institute of Condensed Matter Physics, Linyi University, 276005 Linyi (China); Li, Wen [School of Science, Linyi University, 276005 Linyi (China)] [School of Science, Linyi University, 276005 Linyi (China)
Influence of dissipation on the energy-band structure of semiconducting superlattices in a magnetic field
We study the influence of dissipation in a semiconducting material with the semiconductor-dielectric periodic layered structure on the passband boundaries for eigenwaves. It is shown that allowance for losses in the superconductor leads to appearance of a bend in dispersion curves for the electromagnetic waves propagating in such a structure. In this case, the minimum value of the phase velocity of the wave is limited. It is found that if the collision rate is high, then one of the band boundaries in the region of cyclotron waves degenerates, i.e., the band ōdestructionö takes place.
Bulgakov, A. A.; Kononenko, V. K.; Kostyleva, O. V.
Band structure and broadband compensation of absorption by amplification in layered optical metamaterials
The frequency dependence of the gain required to compensate for absorption is determined for a layered structure consisting of alternating absorbing and amplifying layers. It is shown that the fulfillment of the same conditions is required for the existence of a band structure consisting of alternating bands allowed and forbidden for optical radiation propagation in the frequency-wave vector parametric region. Conditions are found under which the gain required for compensation is smaller than thresholds for absolute (parasitic lasing) and convective (waveguide amplification of radiation) instabilities.
Rozanov, N. N., E-mail: firstname.lastname@example.com; Fedorov, S. V.; Savel'ev, R. S.; Sukhorukov, A. A.; Kivshar, Yu. S. [St. Petersburg State University of Information Technologies, Mechanics and Optics (Russian Federation)
Micro/nano-photonic structures and devices of III-nitride wide band-gap semiconductors
III-nitride photonic devices offer benefits such as UV/blue emission, large band offsets of InN/GaN/AlN heterostructures allowing novel quantum well (QW) device design, and inherently high emission efficiencies. Furthermore, due to their mechanical hardness and larger band gaps, III-nitride based devices may operate at much higher temperatures and voltages/power levels and are expected to provide much lower temperature sensitivities. These are crucial advantages for many applications. New physical phenomena and properties are expected to dominate as the device size scales down. The micro-size light emitters offer benefits over edge-emitters such as the ability to create arrays of individually controllable pixels on a single chip, enhanced quantum efficiency, and greatly reduced lasing threshold. Micro and nano photonic structures and devices based upon III-nitride wide band-gap semiconductors were designed, fabricated and characterized. Individual microdisk blue-light-emitting diodes (mu-LEDs) of varying diameters from 5 to 20 mum have been fabricated from InGaN/GaN quantum wells (QW). Ultraviolet near-field scanning optical microscopy (UV-NSOM) and near-field spectroscopy have been employed to study the optical properties of AlGaN/GaN quantum-well submicron waveguides. Nanofabrication and characterization of photonic crystals (PCs) with diameter/periodicity as small as 70/150 nm on III-nitride materials has been achieved. An unprecedented maximum optical power enhancement factor of 20 was obtained under optical pumping from PCs on InGaN/GaN MQW. Under current injection, optical power enhancement factors of 2.9, 2.5 and 1.63 were obtained for PC-LEDs at 299 nm UV, 333 nm UV and 460 nm blue emission wavelengths, respectively. Transient responses of III-nitride UV PC-LEDs were measured by pico-second time-resolved electroluminescence (EL) spectroscopy. We have achieved 4-fold enhancement in modulation speed of UV LED by PC formation. The carrier recombination lifetime tauQW of the LED and the surface recombination velocities S of nitride materials were measured. Polarization resolved electroluminescence (EL) studies of III-nitride blue and UV LEDs were performed. It was found that transverse electric (TE) polarization dominates in the InGaN/GaN MQW blue LEDs. (lambda = 458 nm), whereas transverse magnetic (TM) polarization is dominant in the AlInGaN QW UV LEDs (lambda = 333 nm). This emission property makes nitride UV emitters unique and has direct consequences for its performance. New device design architectures are suggested for overcoming the problems associated with it.
Shakya, Jagat B.
Ab initio determination of potential energy surfaces for the first two UV absorption bands of SO2
Three-dimensional potential energy surfaces for the two lowest singlet (A~1B1 and B~1A2) and two lowest triplet (a~3B1 and b~3A2) states of SO2 have been determined at the Davidson corrected internally contracted multi-reference configuration interaction level with the augmented correlation-consistent polarized triple-zeta basis set (icMRCI+Q/AVTZ). The non-adiabatically coupled singlet states, which are responsible for the complex Clements bands of the B band, are expressed in a 2 ū 2 quasi-diabatic representation. The triplet state potential energy surfaces, which are responsible for the weak A band, were constructed in the adiabatic representation. The absorption spectrum spanning both the A and B bands, which is calculated with a three-state non-adiabatic coupled Hamiltonian, is in good agreement with experiment, thus validating the potential energy surfaces and their couplings.
Xie, Changjian; Hu, Xixi; Zhou, Linsen; Xie, Daiqian; Guo, Hua
Colloids with high-definition surface structures
Compared with the well equipped arsenal of surface modification methods for flat surfaces, techniques that are applicable to curved, colloidal surfaces are still in their infancy. This technological gap exists because spin-coating techniques used in traditional photolithographic processes are not applicable to the curved surfaces of spherical objects. By replacing spin-coated photoresist with a vapor-deposited, photodefinable polymer coating, we have now fabricated microstructured colloids with a wide range of surface patterns, including asymmetric and chiral surface structures, that so far were typically reserved for flat substrates. This high-throughput method can yield surface-structured colloidal particles at a rate of ?107 to 108 particles per operator per day. Equipped with spatially defined binding pockets, microstructured colloids can engage in programmable interactions, which can lead to directed self-assembly. The ability to create a wide range of colloids with both simple and complex surface patterns may contribute to the genesis of previously unknown colloidal structures and may have important technological implications in a range of different applications, including photonic and phononic materials or chemical sensors.
Chen, Hsien-Yeh; Rouillard, Jean-Marie; Gulari, Erdogan; Lahann, Joerg
Band gap structures in two-dimensional super porous phononic crystals.
As one kind of new linear cellular alloys (LCAs), Kagome honeycombs, which are constituted by triangular and hexagonal cells, attract great attention due to the excellent performance compared to the ordinary ones. Instead of mechanical investigation, the in-plane elastic wave dispersion in Kagome structures are analyzed in this paper aiming to the multi-functional application of the materials. Firstly, the band structures in the common two-dimensional (2D) porous phononic structures (triangular or hexagonal honeycombs) are discussed. Then, based on these results, the wave dispersion in Kagome honeycombs is given. Through the component cell porosity controlling, the effects of component cells on the whole responses of the structures are investigated. The intrinsic relation between the component cell porosity and the critical porosity of Kagome honeycombs is established. These results will provide an important guidance in the band structure design of super porous phononic crystals. PMID:23089223
Liu, Ying; Sun, Xiu-zhan; Chen, Shao-ting
The electronic band structures of iron, sulfur, and oxygen at high pressures and the earth's core
The relationship between the electronic structure of iron and the earth's core properties is examined by calculating the electronic structure for close-packed phases of epsilon iron, gamma iron, sulfur, and oxygen over a wide range of pressure spanning that of the earth's core. The calculations are based on the linear muffin-tin orbital (LMTO) method for band structure computation described by Andersen (1975), Andersen and Jepsen (1977), and Skriver (1984). To approximate more closely the earth-core stoichiometry, the band structure of Fe3S in the close-packed AuCu3 structure was also calculated. From the results of these calculations, the equations of state were derived, and the relative likelihood of either sulfur or oxygen being the predominant light alloying element in the earth's core was determined.
Boness, D. A.; Brown, J. M.
Surface periodic domain structures for waveguide applications.
We report the results of fabrication and investigations of surface periodic domain structures created by a set of quasi-point e-beam irradiations both on the Y- and X-cuts of LiNbO(3), and on Ti:LiNbO(3) and Zn:LiNbO(3) planar waveguides. Domain gratings with spatial periods from 4.75 to 7.25 ?m were formed by a 25-keV e-beam. Doses from 500 to 2000 ?C/cm(2) were used for different structures to estimate optimal fabrication conditions. The investigations allowed the visualization of the formed surface domain structures, estimation of their uniformity, and determination of waveguide generation of the second optical harmonic. The surface structures can be used in optical devices for the realization of quasi-phase-matched frequency conversion, which includes the creation of compact radiation sources based on waveguides. PMID:22711403
Kokhanchik, Lyudmila S; Borodin, Maxim V; Burimov, Nikolay I; Shandarov, Stanislav M; Shcherbina, Vesta V; Volk, Tatyana R
The Development of Layered Photonic Band Gap Structures Using a Micro-Transfer Molding Technique
Photonic band gap (PBG) crystals are periodic dielectric structures that manipulate electromagnetic radiation in a manner similar to semiconductor devices manipulating electrons. Whereas a semiconductor material exhibits an electronic band gap in which electrons cannot exist, similarly, a photonic crystal containing a photonic band gap does not allow the propagation of specific frequencies of electromagnetic radiation. This phenomenon results from the destructive Bragg diffraction interference that a wave propagating at a specific frequency will experience because of the periodic change in dielectric permitivity. This gives rise to a variety of optical applications for improving the efficiency and effectiveness of opto-electronic devices. These applications are reviewed later. Several methods are currently used to fabricate photonic crystals, which are also discussed in detail. This research involves a layer-by-layer micro-transfer molding ({mu}TM) and stacking method to create three-dimensional FCC structures of epoxy or titania. The structures, once reduced significantly in size can be infiltrated with an organic gain media and stacked on a semiconductor to improve the efficiency of an electronically pumped light-emitting diode. Photonic band gap structures have been proven to effectively create a band gap for certain frequencies of electro-magnetic radiation in the microwave and near-infrared ranges. The objective of this research project was originally two-fold: to fabricate a three dimensional (3-D) structure of a size scaled to prohibit electromagnetic propagation within the visible wavelength range, and then to characterize that structure using laser dye emission spectra. As a master mold has not yet been developed for the micro transfer molding technique in the visible range, the research was limited to scaling down the length scale as much as possible with the current available technology and characterizing these structures with other methods.
Kevin Jerome Sutherland
Surface effects on the atomic and electronic structure of unpassivated GaAs nanowires.
On the basis of accurate ab initio calculations, we propose a model for predicting the stability of III-V nanowires (NW) having different side walls and ridge configurations. The model allows us to obtain the NW formation energies by performing calculations only on relatively "small" systems, small diameter NWs and flat surfaces, to extract the contributions to the stability of each structural motif. Despite the idea illustrated here for the case of hexagonally shaped GaAs NWs grown along the [111]/[0001] direction, the method can also be applied generally to other differently shaped and oriented III-V NWs. The model shows that NW surfaces (side walls plus ridges) mainly determine the NW stability, so the changes to the surface structure (e.g., induced by defects or different growth conditions) would modify the final NW structure in a remarkable way. We find that wurtzite and zinc blende nanowires have similar energies over a wide diameter range, thus explaining the observed polytypism. Furthermore, new more stable ridge reconstructions are proposed for zinc blende nanowires. The surface-related structural motifs also have clear fingerprints on the NW electronic structure. We find that the more stable nanowires are all semiconducting. The band gaps are ruled by surface states and do not follow the trend mandated by the quantum confinement effect. Small diameter wurtzite nanowires have an indirect band gap, but for some of them, an indirect to direct transition can be foreseen to occur at larger diameters. Surface states have a larger impact on the zinc blende NW band gaps than on the wurtzite NW ones. Zinc blende nanowire band gaps reduce significantly with increasing nanowire radius, reaching the bulk value at a diameter of about 30 ┼. The surface structure and the high surface related DOS below the conduction band are going to affect the nanowire dopant incorporation and efficiency when doping is carried out during the NW growth. PMID:20853868
Rosini, Marcello; Magri, Rita
Manipulating the extraordinary acoustic transmission through metamaterial-based acoustic band gap structures
We report theoretical predictions and experimental results on the formation of pass bands and stop bands of extraordinary acoustic transmission in multilayer structures based on alternating layers of acoustic metamaterial and air. The metamaterial layers can be made of any acoustically hard material perforated with a two-dimensional array of subwavelength apertures. In this way, it is possible to tailor the density and speed of sound of an otherwise acoustically bulk hard material with fixed properties. The sonic band structure allows transmission passband and stop bandgaps that depend on the layer thicknesses and effective properties of the metamaterials. In addition, we show the existence of resonant tunneling due to the formation of an acoustic passband in a spectral region of low transmission for a single layer. This opens the possibility to engineer different types of phononic materials to manipulate and control acoustic waves.
Ak÷zbek, N.; Mattiucci, N.; Bloemer, M. J.; Sanghadasa, M.; D'Aguanno, G.
The influence of line shape and band structure on temperatures in planetary atmospheres
Numerical experiments are performed to examine the effects of line shape and band structure on the radiative equilibrium temperature profile in planetary atmospheres. In order to accurately determine these effects, a method for calculating radiative terms is developed which avoids the usual approximations. It differs from the more commonly used methods in that it allows arbitrary dependence of the absorption coefficient on wave number, without requiring tedious line by line integration and without the constraints of band models. The present formulation is restricted to homogeneous atmospheres but the concept can be extended to the more general case. The numerical experiments reveal that the line shape and band structure of the absorbing gases have a large effect on temperatures in the higher layers of the atmosphere (corresponding to the stratosphere and mesosphere). The more nongrey the spectrum (that is, the higher the peaks and the deeper the troughs in the spectrum), the lower the temperature.
Arking, A.; Grossman, K.
Tuning the band structures of single walled silicon carbide nanotubes with uniaxial strain: a first principles study
Electronic band structures of single-walled silicon carbide nanotubes are studied under uniaxial strain using first principles calculations. The band structure can be tuned by mechanical strain in a wide energy range. The band gap decreases with uniaxial tensile strain, but initially increases with uniaxial compressive strain and then decreases with further increases in compressive strain. These results may provide a way to tune the electronic structures of silicon carbide nanotubes, which may have promising applications in building nanodevices.
Wang, Zhiguo; Zu, Xiaotao T.; Xiao, H. Y.; Gao, Fei; Weber, William J.
Structural states in the Z band of skeletal muscle correlate with states of active and passive tension
In skeletal muscle Z bands, the ends of the thin contractile filaments interdigitate in a tetragonal array of axial filaments held together by periodically cross-connecting Z filaments. Changes in these two sets of filaments are responsi- ble for two distinct structural states observed in cross section, the small-square and basketweave forms. We have examined Z bands and A bands in
Optical absorption band III of deoxyheme proteins as a probe of their structure and dynamics
Theory of the temperature dependence of a non-Frank-Condon optical absorption band in the case of weak anharmonicity is developed and applied to the interpretation of band III properties of deoxyheme proteins. It is obtained that dependence of the transition dipole moment on the displacement of the iron out of the heme plane, the weak anharmonic coupling between the heme doming and the iron-histidine vibration, and the glass-liquid phase transition cause notable and very specific temperature and pressure dependence of band III. It follows from this study that intensity of band III is sensitive to the iron-porphyrin distance, whereas its position can be affected by both the changes in this distance and protein electric field on the heme. Because the iron-porphyrin distance is affected by the protein, the band intensity and position (and not only width) must be sensitive to the protein structure and dynamics. In particular, intensity of band III can be used as a probe of protein dynamics, its dependence on the solvent viscosity, and protein and heme relaxation in the flash-photolysis experiments.
Stavrov, Solomon S.
CAROLS: a new airborne L-band radiometer for ocean surface and land observations.
The "Cooperative Airborne Radiometer for Ocean and Land Studies" (CAROLS) L-Band radiometer was designed and built as a copy of the EMIRAD II radiometer constructed by the Technical University of Denmark team. It is a fully polarimetric and direct sampling correlation radiometer. It is installed on board a dedicated French ATR42 research aircraft, in conjunction with other airborne instruments (C-Band scatterometer-STORM, the GOLD-RTR GPS system, the infrared CIMEL radiometer and a visible wavelength camera). Following initial laboratory qualifications, three airborne campaigns involving 21 flights were carried out over South West France, the Valencia site and the Bay of Biscay (Atlantic Ocean) in 2007, 2008 and 2009, in coordination with in situ field campaigns. In order to validate the CAROLS data, various aircraft flight patterns and maneuvers were implemented, including straight horizontal flights, circular flights, wing and nose wags over the ocean. Analysis of the first two campaigns in 2007 and 2008 leads us to improve the CAROLS radiometer regarding isolation between channels and filter bandwidth. After implementation of these improvements, results show that the instrument is conforming to specification and is a useful tool for Soil Moisture and Ocean Salinity (SMOS) satellite validation as well as for specific studies on surface soil moisture or ocean salinity. PMID:22346599
Zribi, Mehrez; Pardķ, Mickael; Boutin, Jacquline; Fanise, Pascal; Hauser, Daniele; Dechambre, Monique; Kerr, Yann; Leduc-Leballeur, Marion; Reverdin, Gilles; Skou, Niels; S°bjµrg, Sten; Albergel, Clement; Calvet, Jean Christophe; Wigneron, Jean Pierre; Lopez-Baeza, Ernesto; Rius, Antonio; Tenerelli, Joseph
Evidence of reduced surface electron-phonon scattering in the conduction band of Bi2Se3 by nonequilibrium ARPES
The nature of the Dirac quasiparticles in topological insulators calls for a direct investigation of the electron-phonon scattering at the surface. By comparing time-resolved ARPES measurements of the topological insulator Bi2Se3 with different probing depths, we show that the relaxation dynamics of the electronic temperature of the conduction band is much slower at the surface than in the bulk. This observation suggests that surface phonons are less effective in cooling the electron gas in the conduction band.
Crepaldi, A.; Cilento, F.; Ressel, B.; Cacho, C.; Johannsen, J. C.; Zacchigna, M.; Berger, H.; Bugnon, Ph.; Grazioli, C.; Turcu, I. C. E.; Springate, E.; Kern, K.; Grioni, M.; Parmigiani, F.
Electronic band structures and photovoltaic properties of MWO{sub 4} (M=Zn, Mg, Ca, Sr) compounds
Divalent metal tungstates, MWO{sub 4}, with wolframite (M=Zn and Mg) and scheelite (M=Ca and Sr) structures were prepared using a conventional solid state reaction method. Their electronic band structures were investigated by a combination of electronic band structure calculations and electrochemical measurements. From these investigations, it was found that the band structures (i.e. band positions and band gaps) of the divalent metal tungstates were significantly influenced by their crystal structural environments, such as the W-O bond length. Their photovoltaic properties were evaluated by applying to the working electrodes for dye-sensitized solar cells. The dye-sensitized solar cells employing the wolframite-structured metal tungstates (ZnWO{sub 4} and MgWO{sub 4}) exhibited better performance than those using the scheelite-structured metal tungstates (CaWO{sub 4} and SrWO{sub 4}), which was attributed to their enhanced electron transfer resulting from their appropriate band positions. - Graphical abstract: The electronic band structures of divalent metal tungstates are described from the combination of experimental results and theoretical calculations, and their electronic structure-dependent photovoltaic performances are also studied. Highlights: > MWO{sub 4} compounds with wolframite (M=Zn and Mg) and scheelite structure (M=Ca and Sr) were prepared. > Their electronic band structures were investigated by the calculations and the measurements. > Their photovoltaic properties were determined by the crystal and electronic structures.
Kim, Dong Wook, E-mail: email@example.com [Department of Materials Science and Engineering, Seoul National University, Seoul 151-744 (Korea, Republic of); Research Institute of Advanced Materials (RIAM), Seoul National University, Seoul 151-744 (Korea, Republic of); Cho, In-Sun [Department of Mechanical Engineering, Stanford University, Stanford, California 94305 (United States); Shin, Seong Sik [Department of Materials Science and Engineering, Seoul National University, Seoul 151-744 (Korea, Republic of); Lee, Sangwook [Department of Materials Science and Engineering, Seoul National University, Seoul 151-744 (Korea, Republic of); Research Institute of Advanced Materials (RIAM), Seoul National University, Seoul 151-744 (Korea, Republic of); Noh, Tae Hoon; Kim, Dong Hoe [Department of Materials Science and Engineering, Seoul National University, Seoul 151-744 (Korea, Republic of); Jung, Hyun Suk [School of Advanced Materials Engineering, Kookmin University, Seoul 136-702 (Korea, Republic of); Hong, Kug Sun, E-mail: firstname.lastname@example.com [Department of Materials Science and Engineering, Seoul National University, Seoul 151-744 (Korea, Republic of); Research Institute of Advanced Materials (RIAM), Seoul National University, Seoul 151-744 (Korea, Republic of)
Thermally induced absorption bands with vibronic structure in LiF crystals
Lithium fluoride single crystals obtained from different sources show a series of narrow absorption bands in the ultraviolet when annealed above 250░C in certain vacuum conditions. The ambient pressure and temperature at which annealing rwes place affects the defect production rate, increasing temperature and decreasing total pressure giving larger absorption strengths.The structure of the absorption was similar for all the
G. C. Crittenden; P. D. Townsend
First-principles calculation of diamagnetic band structure. II. Spectrum and wave functions
The diamagnetic band structure is calculated by means of a variational method. This is done for the simplest nontrivial crystal potential which is characterized by two elementary wave vectors in the plane normal to the magnetic field. The numerical calculations are highly accurate and provide an energy spectrum which is simultaneously correct in the high-field (Landau) case, in the magnetic
Hans-Joachim Schellnhuber; Gustav M. Obermair; Alexander Rauh
An Analytical Solution of Equivalent Stress for Structure Fatigue Life Prediction under Broad Band Random Loading
An analytical solution of an equivalent stress-range calculation, based on the power-spectral density of stress in critical points of structures, and a statistical theory for the peak distribution of a stationary Gaussian random process are presented in this paper for fatigue life assessment under broad-band random loading. This model has more advantages than similar existing models.
Xiaoyun Liu; Pengmin L³
Over-Modification Band in Aluminum--Silicon Eutectic Solidified Structure Modified with Sodium.
The nature and origin of so called ''over modification band'' which appears in the microscopic structure of eutectic Al--Si alloy treated with an excessive amount of sodium has been investigated in detail by the method of (1) the optical and scanning elec...
K. Kobayashi H. Shingu R. Ozaki
Ab-initio procedure for effective models of correlated materials with entangled band structure
We present a first-principles method for deriving effective low-energy models\\u000aof electrons in solids having entangled band structure. The procedure starts\\u000awith dividing the Hilbert space into two subspaces, the low-energy part (\\
Takashi Miyake; Ferdi Aryasetiawan; Masatoshi Imada
Quantum confinement effects on the band structure and dielectric properties of nanostructured GaAs
The electronic band structure and dielectric properties of a GaAs quantum well have been investigated using the pseudopotential approach. The effect of quantum confinement on the electronic and dielectric properties of GaAs has been examined. It is found that significant variations in the studied properties occur at quantum well widths below 5 nm. The information may be useful in obtaining
Najah Hamed M. Al Wadiy; Nadir Bouarissa; M. Ajmal Khan
Describing the Flow Curve of Shear-Banding Fluids Through a Structural Minimal Model
Main characteristics of colloidal systems that develop fluid phases with different mechanical properties, namely shear-banding fluids, are briefly reviewed both from experimental and theoretical (modelling) point of view. A non-monotonic shear stress vs. shear rate constitutive relation is presented. This relation derives from a phenomenological model of a shear ratedependent viscosity describing structural changes and involves the possibility of multivalued
Daniel Quemada; Claudio Berli
Sensitivity of C-band Synthetic Aperture RADAR to field-scale soil surface parameters
This thesis investigates the sensitivity of polarimetric variables from C-band Synthetic Aperture RADAR to near-surface soil moisture (6 cm), micro-topographical surface roughness, and biomass cover, during pre/seed and post-harvest over agricultural fields. Variables examined include: the like-polarized and cross-polarized linear intensity channels; polarization ratios; the Total Power signal; the co-polarized phase difference and co-polarized complex correlation coefficient; Pedestal Height; extrema of the completely polarized and unpolarized components; extrema of the received power and scattered intensity; and the polarization coefficient of variation. Classification of scattering mechanisms with the Cloude-Pottier and Freeman-Durden decompositions are also examined. The empirical relationships between RADAR variables and surface parameters are first analyzed using data collected during field-validation campaigns. Secondly, RADAR imagery is integrated over the watershed scale to assess the operational discrimination of tillage practices with these polarimetric variables and decompositions. Overall results provide an enhanced theoretical understanding of these variables and decompositions for agricultural target retrievals and demonstrate promise for use in an agricultural monitoring scheme.
Adams, Justin
A terahertz band-pass resonator based on enhanced reflectivity using spoof surface plasmons
We demonstrate a band-pass resonator in the terahertz (THz) range, based on a frequency-selective designer reflector. The resonator consists of a parallel-plate waveguide, a designed groove pattern cut into the output facet of each plate, and a reflecting mirror. The patterned facet supports a spoof surface plasmon mode, which modifies the reflectivity at the waveguide output facet by interacting with the waveguide mode. By tuning the geometrical parameters of the groove pattern, the reflectivity at the patterned output facet can be increased up to ?100% for a selected frequency. Broadband THz waves are quasi-optically coupled into this resonator and reflected multiple times from the patterned facet. This leads to a narrowing of the spectrum at the selected frequency. The Q value of the resonator increases as the number of reflections on the patterned facet increases, reaching ?25 when the THz wave has experienced 12 reflections.
Liu, Jingbo; Mendis, Rajind; Mittleman, Daniel M.
Frequency band structure of locally resonant periodic flexural beams suspended with force-moment resonators
Since the introduction of locally resonant (LR) phononic meta-materials and structures a decade ago, there has been a quest for wide band-gaps of elastic wave attenuation in a low frequency range of practical importance. We investigate periodic Euler-Bernoulli beams suspended with two degrees of freedom force-moment resonators. Based on mathematical analysis and calculations, we present their dispersive characteristics in flexural wave attenuation and propagation. As a prime focus, we identify the appearance a below-resonance band-gap of Bragg-scattering (BS) typeŚin addition to the normal post-resonance BS band-gapŚand the dependence of their edge frequencies on the resonator parameters. Furthermore, we present a full characterization of four different groups of pass and stop frequency bands and six distinct types of transitions between them, with conditions for all band edge frequencies. Our results indicate potentially richer dispersion properties in LR periodic structures with resonators of multiple degrees of freedom than those with the conventional force-only (or moment-only) resonators.
Wang, Michael Yu; Wang, Xiaoming
Design of UWB monopole antenna with dual notched bands using one modified electromagnetic-bandgap structure.
A modified electromagnetic-bandgap (M-EBG) structure and its application to planar monopole ultra-wideband (UWB) antenna are presented. The proposed M-EBG which comprises two strip patch and an edge-located via can perform dual notched bands. By properly designing and placing strip patch near the feedline, the proposed M-EBG not only possesses a simple structure and compact size but also exhibits good band rejection. Moreover, it is easy to tune the dual notched bands by altering the dimensions of the M-EBG. A demonstration antenna with dual band-notched characteristics is designed and fabricated to validate the proposed method. The results show that the proposed antenna can satisfy the requirements of VSWR < 2 over UWB 3.1-10.6?GHz, except for the rejected bands of the world interoperability for microwave access (WiMAX) and the wireless local area network (WLAN) at 3.5?GHz and 5.5?GHz, respectively. PMID:24170984
Liu, Hao; Xu, Ziqiang
Spatial demultiplexing in the submillimeter wave band using multilayer free-standing frequency selective surfaces
In this paper, we show that a multilayer freestanding slot array can be designed to give an insertion loss which is significantly lower than the value obtainable from a conventional dielectric backed printed frequency selective surface (FSS). This increase in filter efficiency is highlighted by comparing the performance of two structures designed to provide frequency selective beamsplitting in the quasioptical
Raymond Dickie; Robert Cahill; Harold S. Gamble; Vincent F. Fusco; Alexander G. Schuchinsky; Norman Grant
Low-energy band structures of armchair ribbon-graphene hybrid systems
The electronic properties of armchair ribbon-graphene hybrid systems are studied within the 2pz tight-binding model. The geometric structures of graphene nanoribbons, such as the width (Ny) and the period (Ry) of the ribbons, greatly determine the band structures. Furthermore, the stacking arrangement between graphene nanoribbons and monolayer graphene also plays an important role in low-energy states. Energy gaps caused by
C. H. Lee; S. C. Chen; R. B. Chen; M. F. Lin
Water structure in aqueous solutions of alkali halide salts: FTIR spectroscopy of the OD stretching band
Water structure making\\/breaking studies in solutions of five alkali halide salts (KF, KI, NaI, CsF and CsCl) in 4 wt% D2O in H2O mixtures have been performed by FTIR analysis of the OD stretching band in the full solubility range. The proposed method gives a microscopic picture of the water structure making\\/breaking character of the salts in terms of the
Z. S. Nickolov; J. D. Miller
Band gap behaviours of periodic magnetoelectroelastic composite structures with Kagome lattices
In this paper, the elastic wave propagation in periodic cylinder magnetoelectroelastic composite structures is studied using the plane wave expansion method. The band structure characteristics of magnetoelectroelastic rods embedded in polymer matrix and the reverse case are investigated taking the electric, magnetic and mechanical coupling effects into account. The generalised eigenvalue equation is derived to analyse the in-plane and out-of-plane
Yi-Ze Wang; Feng-Ming Li; Kikuo Kishimoto; Yue-Sheng Wang; Wen-Hu Huang
Challenge to a straight structure for X-band linear collider
The structure of the X-band main linac for the linear collider requires a stringent straightness of the order of several microns. Especially the misalignment from cell-to-cell to over twenty cells should be minimized. An one-shot diffusion bonding technology has been developed at KEK aiming at this requirement. Two 1.3 m-long detuned structures have been made with a gentle bow of
K. Asano; Y. Funahashi; Y. Higashi; T. Higo; N. Hitomi; T. Suzuki; K. Takata; T. Takatomi; N. Toge; Y. Watanabe
A simple way to design complex metallic photonic band-gap structures
\\u000a AbstractĀĀIn this paper, a simple method is presented in order to design complex mpbg structures able to have multiple frequency behaviors.\\u000a This functionality is all the more important as it is wildly used in modern communication systems. In a first study, a mixed\\u000a structure composed of a metallic photonic band gap material and a Bragg mirror is designed in order
G. Poilasne; P. Pouliguen; C. Terret; P. Gelin; L. Desclos
Comment on ``Observation of anomalous peaks in the photoelectron spectra of highly oriented pyrolytic graphite: Folding of the band due to the surface charge density wave transition''
In a recent paper by Tanaka, Matsunami, and Kimura [Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.84.121411 84, 121411(R) (2011)], the surface charge density wave transition at low temperature is proposed to explain the superperiodicity observed in the angle-resolved photoelectron spectroscopy measurement of highly oriented pyrolytic graphite. We have performed density-functional theory and density-functional perturbation theory calculations to investigate the electronic structure and lattice dynamics of the graphite (0001) surface. Neither instability nor anomaly is found in the calculated electronic and phonon band structures. Thus, the surface charge density wave in a pristine graphite surface is less likely, and another clue is necessary to explain the observed superperiodicity.
Hamada, Ikutaro; Morikawa, Yoshitada
Receiver function structure beneath a broad-band seismic station in south Sumatra
We estimated the one-dimensional velocity structure beneath a broad-band station in south Sumatra by the forward modeling and inversion of receiver functions. Station PMBI belongs to the GEOFON seismic network maintained by GFZ-Potsdam, and at a longitude of 104.77░ and latitude of -2.93░, sits atop the south Sumatran basin. This station is of interest to researchers at the Earth Observatory of Singapore, as data from it and other stations in Sumatra and Singapore will be incorporated into a regional velocity model for use in seismic hazard analyses. Three-component records from 193 events at teleseismic distances and Mw ? 5.0 were examined for this study and 67 records were deemed to have sufficient signal to noise characteristics to be retained for analysis. Observations are primarily from source zones in the Bougainville trench with back-azimuths to the east-south-east, the Japan and Kurile trenches with back-azimuths to the northeast, and a scattering of observations from other azimuths. Due to the level of noise present in even the higher-quality records, the usual frequency-domain deconvolution method of computing receiver functions was ineffective, and a time-domain iterative deconvolution was employed to obtain usable wave forms. Receiver functions with similar back-azimuths were stacked in order to improve their signal to noise ratios. The resulting wave forms are relatively complex, with significant energy being present in the tangential components, indicating heterogeneity in the underlying structure. A dip analysis was undertaken but no clear pattern was observed. However, it is apparent that polarities of the tangential components were generally reversed for records that sample the Sunda trench. Forward modeling of the receiver functions indicates the presence of a near-surface low-velocity layer (Vp?1.9 km/s) and a Moho depth of ~31 km. Details of the crustal structure were investigated by employing time-domain inversions of the receiver functions. General features of those velocity models providing a good fit to the waveform include an approximately one kilometer thick near-surface low-velocity zone, a high-velocity layer over a velocity inversion at mid-crustal depths, and a crust-mantle transition at depths between 30 km and 34 km.
MacPherson, K. A.; Hidayat, D.; Goh, S.
The unusual band structure properties of dilute nitride GaAsN alloys
The incorporation of low concentrations of N in GaAs leads to qualitatively new alloy phenomena and electronic properties, which have increased the power and scope of band-structure engineering as a tool for the design of a new generation of electronic devices. The large electronegativity of the N atoms combined with the stretching and compression of neighbouring bonds in GaAs strongly perturbs the band structure properties of the host crystal: N-impurities and N-clusters act to ``disrupt'' the extended Bloch states of GaAs at characteristic resonant energies in the conduction band [1-3]. This leads to a strongly modified energy-wavevector dispersion relation of the conduction electrons and to a large red-shift of the band gap. Here we use magneto-tunneling spectroscopy to probe directly the unusual band structure properties of GaAsN. Of particular interest is the strongly non-parabolic conduction band in which an inflection point occurs in the energy-wavevector dispersion relation at relatively modest wavevectors. We demonstrate that this property can be tailored by quantum confinement effects or by an applied hydrostatic pressure. Also it can be exploited to realize a new type of non-linear device in which electrons are accelerated by a large electric field up to and beyond the inflection point, thus leading to a large negative differential drift velocity effect of potential interest for novel emitters and detectors of high-frequency radiation. [1] W. Shan et al., Phys. Rev. Lett. 82, 1221 (1999). [2] J. Endicott et al., Phys. Rev. Lett. 91, 126802 (2003). [3] A. Lindsay and E .P. O'Reilly, Phys. Rev. Lett. 93, 196402 (2004).
Patane, Amalia
Polarization Dependence of L-Band Measurements Over the Ocean on Surface Wind at 23-25 Incidence Angles
Polarization dependence of L-band measurements over the ocean on surface wind is investigated for the incidence angle ranging from 23 to 25 degrees, by using the Phased-Array L-band Synthetic Aperture Radar (PALSAR) onboard the Advanced Land Observing Satellite (ALOS) and MetOp\\/ASCAT wind vectors. Polarization ratio (VV\\/HH) shows clear incidence angle and wind speed dependencies. It increases with increasing incidence angle
Osamu Isoguchi; Masanobu Shimada
Structural models of amorphous silicon surfaces
Using Monte Carlo simulations within the empirical potential approach, we predict and analyze possible models of the surface structure of amorphous silicon. This is a fundamental problem about which knowledge is incomplete. We address the central question regarding the dominant type of nontetrahedral atoms at the surface. Our investigations lead to two markedly different models of the surface structure. One of the models exhibits a surface layer terminated by threefold- and fourfold-coordinated atoms. In general, threefold atoms are on top and form mostly dimers and chainlike structures. The other model requires that the surface is terminated by fourfold atoms and by fivefold atoms assembled in clusters of pyramidal shape, with both types of geometries heavily distorted. We also use the tight-binding method to calculate the electronic density of states of these two possible models. The electronic fingerprints of the nontetrahedral atoms within and near the energy gap region are quite different. This distinguishes clearly the two models and could guide experimental work to infer the microscopic picture of clean amorphous silicon surfaces.
Hadjisavvas, G.; Kopidakis, G.; Kelires, P. C.
Light scattering from cylindrical structures on surfaces.
Light scattering from a dielectric cylindrical structure on a surface by a plane wave with field vector along the cylinder axis is calculated with a modification of the coupled-dipole method. The interaction matrix is calculated with the use of both the direct contribution of a polarization current filament and its reflection from the surface. The reflected cylindrical waves are computed with the use of the Sommerfeld-type integral expression. Light scattering from structures of arbitrary cross section and the size of the order of a wavelength can be quickly determined with this method. PMID:19759774
Taubenblatt, M A
Band structure and lattice vibration properties of III-P ternary alloys
Electronic band structure, optical and vibrational properties of zinc-blende GaP xSb 1-x and GaAs 1-xP x ternary alloys are obtained from pseudo-potential calculations. Comparisons are made with the available experimental values and with data obtained in previous theoretical studies. These comparisons show generally good agreement between the present results and experiment. The direct and indirect band-gap energies, the transverse effective charge, and the longitudinal and transversal optical phonon energies show a non-linear behavior with varying the composition x. The ionicity of the materials of interest is discussed in terms of the antisymmetric gap.
Alahmary, Abdulaziz; Bouarissa, Nadir; Kamli, Ali
Fine-structure-resolved collisional broadening in the Schumann-Runge bands of O2.
Collisional self-broadening and shift coefficients are presented for selected fine structure resolved rotational lines from the B3?-u?X3?g-(?',1) bands of O2. The coefficients were derived from high-resolution photoabsorption cross-sections measured using the tuneable, narrow-bandwidth, vacuum-ultraviolet radiation generated by the two-photon-resonant difference-frequency four-wave mixing of excimer-pumped dye-laser radiation in Xe. The results, obtained at room temperature and at pressures of less than 800 torr, are consistent with previous results derived from medium-resolution measurements of the (?',0) bands at much higher pressures.
Dooley, P. M.; Lewis, B. R.; Waring, K.; Gibson, S. T.; Baldwin, K. G. H.
Surface structure of thermionic-emission cathodes
We have used surface extended x-ray absorption fine structure (SEXAFS) to study the local geometry around barium atoms on thermionic cathodes. On the surfaces of tungsten and tungsten-osmium alloy dispenser cathodes Ba is bonded to oxygen with a well-defined short-range order. The Ba-O distance is similar (2.62+/-0.04 Å) for the two cathodes, with oxygen atoms occupying hollow sites of the substrate. However, the alloy cathode has Ba bonded to two oxygen near neighbors (compared to one for the tungsten cathode), which will enhance the surface dipole, thus explaining the observed lower work function.
Norman, D.; Tuck, R. A.; Skinner, H. B.; Wadsworth, P. J.; Gardiner, T. M.; Owen, I. W.; Richardson, C. H.; Thornton, G.
Stratospheric and lower mesospheric structure sounding using UV-visible band spectral imagery
Atmospheric mesoscale (100's of meters to a few kilometers) temperature structure and the structure associated with thin cirrus and aerosol layers in the upper stratosphere and lower mesosphere are difficult to measure by ground and satellite based techniques. We show in this paper that the altitude range between about 10 and 80 km is amenable to satellite sounding techniques in the UV-visible-near infrared bands (approximately 200 to 900 nm). The rapid change in optical depth vs. line-of-sight (LOS) end point along a downward-viewing LOS in the 200 - 350 nm spectral range allows separation of atmospheric regions according to the LOS optical weighting functions. The UV imager weighting functions (200 - 300 nm) in combination with the satellite- sensor zenith angle effect allows sounding in the approximately 40 to 80 km region, while the visible band imagery allows detection and separation of high altitude cloud structure leakage from the UV images of clear-air density structure. The instrument requirements necessary to detect such structure and to discriminate aerosol-induced Mie scatter from Rayleigh scatter components consists of UV to visible band spectral imagers having sufficient spatial, temporal and spectral resolutions. Only moderate spectral resolution imagery in the 200 to 900 nm region over a range of sensor line of sight nadir angles is required to detect clouds and infer cloud types. However, high signal to noise ratios and high spatial resolution are required to characterize the structure power spectral density of clouds and clear-air scatter components. Middle atmosphere structure sounding capability on the mesoscale level allows connection between turbulent-like small scale atmospheric phenomenology and larger scale cloud-related and weather- driven atmospheric variability. We demonstrate the stratosphere-mesosphere sounding concept by applying a low altitude mesoscale stochastic structure (LAMSS) model. This model was derived from the NSS (non-stationary stochastic structure) model which utilizes multi-dimensional Fourier- space descriptions of wavelike, turbulent-like, and deterministic, large scale structure to simulate the effects of atmospheric earthlimb structure. LAMSS specifically address tropospheric background clutter processes such as clear-air wind shears, turbulence, temperature inversions, and cirrus cloud structure. The empirical models are applied to synthesis of visible, UV, and IR clutter backgrounds as measured by passive spectral imaging sensors such as the UVISI (UV, Visible Imagers and Spectral Imagers) sensors on the Mid-course Space Experiment (MSX). This paper analyzes images from MSX-UVISI to obtain cloud and atmospheric density structure characteristics in the 200 - 230 nm UV and 300 - 900 nm visible bands. These data illustrates the feasibility of the UV structure sounding concept by comparison to the synthesized structured backgrounds.
Sears, Robert D.; Romick, Gerald J.; Morrison, Daniel; Murphy, Patricia K.
A ppM-focused klystron at X-band with a travelling-wave output structure
We have developed algorithms for designing disk-loaded travelling-wave output structures for X-band klystrons to be used in the SLAC NLC. We use either a four- or five-cell structure in a {pi}/2 mode. The disk radii are tapered to produce an approximately constant gradient. The matching calculation is not performed on the tapered structure, but rather on a coupler whose input and output cells are the same as the final cell of the tapered structure, and whose interior cells are the same as the penultimate cell in the tapered structure. 2-D calculations using CONDOR model the waveguide as a radial transmission line of adjustable impedance. 3-D calculations with MAFIA model the actual rectangular waveguide and coupling slot. A good match is obtained by adjusting the impedance of the final cell. In 3D, this requires varying both the radius of the cell and the width of the aperture. When the output cell with the best match is inserted in the tapered structure, we obtain excellent cold-test agreement between the 2-D and 3-D models. We use hot-test simulations with CONDOR to design a structure with maximum efficiency and minimum surface fields. We have designed circuits at 11.424 GHz for different perveances. At 440 kV, microperveance 1.2, we calculated 81 MW, 53 percent efficiency, with peak surface field 76 MV/m. A microperveance 0.6 design was done using a ppM stack for focusing. At 470 kV, 193 amps, we calculated 58.7 MW, 64.7 percent efficiency, peak surface field 62.3 MV/m. At 500 kV, 212 amps, we calculated 67.1 MW, 63.3 percent efficiency, peak surface field 66.0 MV/m.
Eppley, K.R.
Multi-use applications of dual-band infrared (DBIR) thermal imaging for detecting obscured structural defects
Precise dual-band infrared (DBIR) thermal imaging provides a useful diagnostic tool for wide-area detection of defects from corrosion damage in metal airframes, heat damage in composite structures and structural damage in concrete bridge decks. We use DBIR image ratios to enhance surface temperature contrast, remove surface emissivity noise and increase signal-to-clutter ratios. We clarify interpretation of hidden defect sites by distinguishing temperature differences at defect sites from emissivity differences at clutter sites. This reduces the probability of false calls associated with misinterpreted image data. For airframe inspections, we map flash-heated defects in metal structures. The surface temperature rise above ambient at corrosion-thinned sites correlates with the percentage of material loss from corrosion thinning. For flash-heated composite structures, we measure the temperature-time history which relates to the depth and extent of heat damage. In preparation for bridge deck inspections, we map the natural day and night temperature variations at known concrete slab delamination sites which heat and coot at different rates than their surroundings. The above-ambient daytime and below-ambient nightime delamination site temperature differences correlate with the volume of replaced concrete at the delamination sites.
Del Grande, N.K.; Durbin, P.F.
Excitation, Ionization, and Desorption: How Sub-band gap Photons Modify the Structure of Oxide Nanoparticles
Nanoparticles of wide-band-gap materials MgO and CaO, subjected to low-intensity ultraviolet irradiation with 266 nm (4.66 eV) photons, emit hyperthermal oxygen atoms with kinetic energies up to ~ 0.4 eV. We use ab initio embedded cluster methods to study theoretically a variety of elementary photoinduced processes at both ideal and defect-containing surfaces of these nanoparticles and develop a mechanism for the desorption process. The proposed mechanism includes multiple local photoexcitations resulting in sequential formation of localized excitons, their ionization, and further excitations. It is suggested that judicious choice of sub-band-gap photon energies can be used to selectively modify surfaces of nanomaterials.
Trevisanutto, P. E.; Sushko, Petr V.; Beck, Kenneth M.; Joly, Alan G.; Hess, Wayne P.; Shluger, Alexander L.
Microstripline transient photocurrents in a-Se: Structure resolved in shallow band-tail states
The measurement of transient photocurrents in amorphous semiconductors has been shown in recent years to be a powerful probe of carrier thermalization within the manifold of localized states adjacent to the band edges. Here we discuss recent measurements of transient photocurrents in a-Se made using high-speed stripline techniques in order to observe thermalization within shallow band-tail states. The initial photocurrent decay is power-law like however a sharp change in the slope occurs at 11 nsec at 295K and 22 nsec at 270K. These results provide the first direct evidence for prominent structure superimposed upon the disorder-induced band-tail in a-Se.
Orlowski, T. E.; Abrowitz, M.
Quasiparticle band structure of alkali-metal fluorides, oxides, and nitrides
We present a comparative study of one-particle excitation energies of alkali-metal fluorides (MF), oxides (M2O), and nitrides (M3N) with M = Li, Na, and K. To this end, we have calculated quasiparticle band structures within the G0W0 approximation. We arrive at valence and conduction bands that are in good agreement with the scarcely available experimental data. In addition, the quasiparticle bands corroborate our earlier results of density functional calculations including self-interaction corrections for the fluorides and oxides and yield significant improvements for the nitrides. For example, the G0W0 quasiparticle gap of Na3N amounts to 1.5 eV in close agreement with the experimental gap of 1.6 eV. Finally, we consider the effects of iteratively updating the screening in the Coulomb interaction W.
Sommer, Christoph; Kr³ger, Peter; Pollmann, Johannes
Transport and band structure studies of crystalline ZnRh2O4
We report the synthesis and characterization of non-d{sup 10} p-type transparent conducting oxides of the normal spinel ZnRh{sub 2}O{sub 4}. Undoped ZnRh{sub 2}O{sub 4} was successfully prepared by means of bulk solid-state synthesis. The conduction mechanism and bulk defect chemistry of polycrystalline sintered pellets of ZnRh{sub 2}O{sub 4} were studied through electrical conductivity and Seebeck coefficient measurements, in defect equilibrium at elevated temperature under controlled atmospheres. Optical diffuse reflectance measurements were also carried out to evaluate band gap. The data were analyzed in terms of an activated mobility (small polaron conduction), with a hopping energy of 0.25 eV. Results from band structure calculations by LDA+U and optical band-gap measurement by UV-visible spectrometry are in good agreement with literature data.
Mansourian-Hadavi, Negar; Wansom, Supaporn; Perry, Nicola H.; Nagaraja, Arpun R.; Mason, Thomas O.; Ye, Lin-hui; Freeman, Arthur J.
Ab initio electronic band structure study of III-VI layered semiconductors
We present a total energy study of the electronic properties of the rhombohedral ?-InSe, hexagonal ?-GaSe, and monoclinic GaTe layered compounds. The calculations have been done using the full potential linear augmented plane wave method, including spin-orbit interaction. The calculated valence bands of the three compounds compare well with angle resolved photoemission measurements and a discussion of the small discrepancies found has been given. The present calculations are also compared with recent and previous band structure calculations available in the literature for the three compounds. Finally, in order to improve the calculated band gap value we have used the recently proposed modified Becke-Johnson correction for the exchange-correlation potential.
OlguĒn, Daniel; Rubio-Ponce, Alberto; Cantarero, Andrķs
Band structures of two dimensional solid/air hierarchical phononic crystals
The hierarchical phononic crystals to be considered show a two-order ōhierarchicalö feature, which consists of square array arranged macroscopic periodic unit cells with each unit cell itself including four sub-units. Propagation of acoustic wave in such two dimensional solid/air phononic crystals is investigated by the finite element method (FEM) with the Bloch theory. Their band structure, wave filtering property, and the physical mechanism responsible for the broadened band gap are explored. The corresponding ordinary phononic crystal without hierarchical feature is used for comparison. Obtained results show that the solid/air hierarchical phononic crystals possess tunable outstanding band gap features, which are favorable for applications such as sound insulation and vibration attenuation.
Xu, Y. L.; Tian, X. G.; Chen, C. Q.
Quasiparticle excitations in valence-fluctuation materials: effects of band structure and crystal fields
Evidence is now quite strong that the elementary hybridization model is the correct way to understand the lattice-coherent Fermi liquid regime at very low temperatures. Many-body theory leads to significant renormalizations of the input parameters, and many of the band-theoretic channels for hybridization are suppressed by the combined effects of Hund's-rule coupling, crystal-field splitting, and the f-f Coulomb repulsion U. Some exploratory calculations based on this picture are described, and some inferences are drawn about the band structures of several heavy-fermion materials. These inferences can and should be tested by suitably modified band-theoretic calculations. We find evidence for a significant Baber-scattering contribution in the very-low-temperature resistivity. A new mechanism is proposed for crossover from the coherent Fermi-liquid regime to the incoherent dense-Kondo regime. 28 refs.
Brandow, B.H.
G0W0 band structure of CdWO4.
The full quasiparticle band structure of CdWO4 is calculated within the single-shot GW (G0W0) approximation using maximally localized Wannier functions, which allows one to assess the validity of the commonly used scissor operator. Calculations are performed using the Godby-Needs plasmon pole model and the accurate contour deformation technique. It is shown that while the two methods yield identical band gap energies, the low-lying states are given inaccurately by the plasmon pole model. We report a band gap energy of 4.94 eV, including spin-orbit interaction at the DFT-LDA (density functional theory-local density approximation) level. Quasiparticle renormalization in CdWO4 is shown to be correlated with localization distance. Electron and hole effective masses are calculated at the DFT and G0W0 levels. PMID:24599225
Laasner, Raul
Sonic Stop-Bands for Periodic Arrays of Metallic Rods: Honeycomb Structure
Extensive band structures have been computed for periodic arrays (in the honeycomb structure) of rigid metallic rods in air. Multiple complete acoustic stop bands have been obtained within which sound and vibrations are forbidden. These gaps start opening up for a filling fractionf?8% and tend to increase with the filling fraction, exhibiting a maximum at the close-packing. A tandem structure has also been proposed that allows an ultrawideband filter for environmental or industrial noise to be achieved in the desired frequency range. This work is motivated by the recent experimental observation of sound attenuation on the sculpture by Eusebio Sempere, exhibited at the Juian March Foundation in Madrid [21] and complements the corresponding theoretical work [22, 23].
Kushwaha, M. S.; Djafari-Rouhani, B.
Bending vibration band structure of phononic crystal beam by modified transfer matrix method
The bending vibration band structure of phononic crystal (PC) beam is solved by a unified formulation of the modified transfer matrix (MTM) method in this paper. The improvement of MTM method is the introduction of constitutive matrix U and matrix of derivative functions V, which standardizes and simplifies the deduction by the matrix operation. The band structure of an epoxy-aluminum PC Timoshenko beam is calculated by both MTM method and plane wave expansion (PWE) method. The results show that the present MTM method has a great advantage in the precision of the result. In addition, the formulation of transfer matrix derived from Timoshenko beam condition is a general form which is also suitable for other general beam structures just by replacing corresponding matrices.
Ni, Zhi-Qiang; Zhang, Yan; Jiang, Lin-Hua; Han, Lin
Band-structure calculations for the 3d transition metal oxides in GW
Many-body GW calculations have emerged as a standard for the prediction of band gaps, band structures, and optical properties for main-group semiconductors and insulators, but it is not well established how predictive the GW method is in general for transition metal (TM) compounds. Surveying the series of 3d oxides within a typical GW approach using the random-phase approximation reveals mixed results, including cases where the calculated band gap is either too small or too large, depending on the oxidation states of the TM (e.g., FeO/Fe2O3, Cu2O/CuO). The problem appears to originate mostly from a too high average d-orbital energy, whereas the splitting between occupied and unoccupied d symmetries seems to be reasonably accurate. It is shown that augmenting the GW self-energy by an attractive (negative) and occupation-independent on-site potential for the TM d orbitals with a single parameter per TM cation can reconcile the band gaps for different oxide stoichiometries and TM oxidation states. In Cu2O, which is considered here in more detail, standard GW based on wave functions from initial density or hybrid functional calculations yields an unphysical prediction with an incorrect ordering of the conduction bands, even when the magnitude of the band gap is in apparent agreement with experiment. The correct band ordering is restored either by applying the d-state potential or by iterating the wave functions to self-consistency, which both have the effect of lowering the Cu-d orbital energy. While it remains to be determined which improvements over standard GW implementations are needed to achieve an accurate ab initio description for a wide range of transition metal compounds, the application of the empirical on-site potential serves to mitigate the problems specifically related to d states in GW calculations.
Milankovitch-Band Evolution of Tropical Sea Surface Temperatures Over the Plio- Pleistocene
Benthic foraminiferal oxygen isotope records indicate a transition from relatively warm and weakly variable high latitude conditions during the early and middle Pliocene (3-5 Ma) to increasingly cold, more variable, and more intensely glaciated conditions throughout the late Pliocene and Pleistocene (0-3 Ma). Here, we complement this high latitude perspective on Plio-Pleistocene climate evolution through analysis of three long, continuous, and highly resolved records of sea surface temperature (SST) changes in the tropics. We find that the eastern equatorial Pacific, eastern equatorial Atlantic, and Arabian Sea all record very similar SST histories beginning 2.7 Ma, coincident with the intensification of northern hemisphere glaciation. Amplified ice albedo and carbon cycle feedbacks associated with northern hemisphere glaciations were likely responsible for coupling SST responses throughout the tropics from this time forward. Intensification of the 41 kyr band SST response in the eastern equatorial Pacific beginning ~3 Ma may have provided the trigger for northern hemisphere glaciation, through feedbacks involving poleward heat export. Detailed analysis of the tropical surface ocean response across the mid-Pleistocene transition suggests that tropical SSTs evolved largely in tandem with the benthic foraminiferal oxygen isotope record over this interval.
Cleaveland, L. C.; Lawrence, K. T.; Herbert, T. D.
Influence of indium clustering on the band structure of semiconducting ternary and quaternary nitride alloys
The electronic band structures of InxGa1-xN , InxAl1-xN , and InxGayAl1-x-yN alloys are calculated by ab initio methods using a supercell geometry, and the effects of varying the composition and atomic arrangements are examined. Particular attention is paid to the magnitude of and trends in bowing of the band gaps. Indium composition fluctuation (clustering) is simulated by different distributions of In atoms and it is shown that it strongly influences the band gaps. The gaps are considerably smaller when the In atoms are clustered than when they are uniformly distributed. An explanation of this phenomenon is proposed on the basis of an analysis of the density of states and the bond lengths, performed in detail for ternary alloys. Results for the band gaps of InxGayAl1-x-yN quaternary alloys show a similar trend. It is suggested that the large variation in the band gaps determined on samples grown in different laboratories is caused by different degrees of In clustering.
Gorczyca, I.; ?epkowski, S. P.; Suski, T.; Christensen, N. E.; Svane, A.
Structure of InSb(001) surface.
The InSb(001) surface has been studied experimentally, using room temperature scanning tunnelling microscopy (RT STM), and theoretically, using ab initio density functional theory (DFT) calculations. RT experimental STM images show bright lines running along the bulk crystal [110] direction. Resolved features between the bright lines whose appearance depends on the applied bias voltage confirm clearly the c(8ū2) reconstruction of this surface. Our calculations, which are reported for this surface for the first time, include the reconstructed 4ū2 and c(8ū2) surfaces, the latter according to the so-called ?-model proposed previously by Lee et al and Kumpf et al. A 'defective' structure proposed previously by Kumpf et al, which contains an extra In atom within a top bilayer is also considered. In all cases, we obtained stable structures. Calculated STM images for the c(8ū2) reconstruction obtained using the Tersoff-Hamann approximation compare extremely well with the experimental ones. We also find that the defect structure may not be clearly visible in the STM images. Finally, a brief discussion is given on the other, although closely related, phase of the same surface observed previously in low temperature (LT) experimental STM images (Goryl et al 2007 Surf. Sci. 601 3605). PMID:21386467
Toton, Dawid; He, Jiangping; Goryl, Grzegorz; Kolodziej, Jacek J; Godlewski, Szymon; Kantorovich, Lev; Szymonski, Marek
The Interpolation of Object and Surface Structure
ERIC Educational Resources Information Center
One of the main theoretical challenges of vision science is to explain how the visual system interpolates missing structure. Two forms of visual completion have been distinguished on the basis of the phenomenological states that they induce. "Modal" completion refers to the formation of visible surfaces and/or contours in image regions where theseģ
Anderson, Barton L.; Singh, Manish; Fleming, Roland W.
Interface-induced gap states and band-structure lineup at TiO2 heterostructures and Schottky contacts
The band-structure lineup at semiconductor interfaces is explained by the continuum of the intrinsic interface-induced gap states (IFIGS) which derive from the complex band structures of the semiconductors. Hence, the valence-band offsets of semiconductor heterostructures and the barrier heights of metal-semiconductor or Schottky contacts are composed of a zero-charge transfer and an electrostatic-dipole term, which are determined by the IFIGSÆs
The band-structure lineup at semiconductor interfaces is explained by the continuum of the intrinsic interface-induced gap states (IFIGS) which derive from the complex band structures of the semiconductors. Hence, the valence-band offsets of semiconductor heterostructures and the barrier heights of metal-semiconductor or Schottky contacts are composed of a zero-charge transfer and an electrostatic-dipole term, which are determined by the IFIGS's
Winfried M÷nch
Electronic band structures and x-ray photoelectron spectra of ZrC, HfC, and TaC
The band structures and d