Sample records for surface band structure

  1. Surface band structure of Bi1 -xSbx(111 )

    NASA Astrophysics Data System (ADS)

    Benia, Hadj M.; Straßer, Carola; Kern, Klaus; Ast, Christian R.

    2015-04-01

    Theoretical and experimental studies agree that Bi1-xSbx (0.07 ?x ?0.21 ) is a three-dimensional topological insulator. However, there is still a debate on the corresponding Bi1-xSbx(111 ) surface band structure. While three spin polarized bands have been claimed experimentally, theoretically, only two surface bands appear, with the third band being attributed to surface imperfections. Here, we address this controversy using angle-resolved photoemission spectroscopy (ARPES) on Bi1-xSbx films. To minimize surface imperfections, we have optimized the sample growth recipe. We have measured the evolution of the surface band structure of Bi1-xSbx with x increasing gradually from x =0 to x =0.6 . Our ARPES data show better agreement with the theoretical calculations, where the system is topologically nontrivial with two surface bands.

  2. Surface Science Letters Structure, band offsets and photochemistry at

    E-print Network

    Pennycook, Steve

    Surface Science Letters Structure, band offsets and photochemistry at epitaxial a-Cr2O3/a-Fe2O3 that electron­hole pair separation following light absorption enhances photochemistry at oxide- ally been avoided. Thiel et al. [3] investigated the role of surface vibrations on the photochemistry

  3. Mapping the band structure of a surface phononic crystal

    E-print Network

    Maznev, Alexei

    We map the band structure of surface acoustic modes of a periodic array of copper lines embedded in a SiO2 film on a silicon substrate by means of the laser-induced transient grating technique. A detailed map of the lowest ...

  4. Band-structure effects in photoelectron-emission spectra from metal surfaces

    NASA Astrophysics Data System (ADS)

    Rios Rubiano, C. A.; Gravielle, M. S.; Mitnik, D. M.; Silkin, V. M.

    2012-04-01

    Photoelectron emission from the valence band of a metal surface due to the grazing incidence of ultrashort laser pulses is studied in the framework of a distorted-wave formulation. We propose a model, named the band-structure-based-Volkov (BSB-V) approximation, which takes into account the contribution of the band structure of the solid. The BSB-V approach is applied to calculate differential electron-emission probabilities for Al(111) and Be(0001) surfaces. A noticeable influence of the electronic band structure was observed in the case of beryllium, while for aluminum such effects were found to play a minor role.

  5. GaN m -plane: Atomic structure, surface bands, and optical response

    NASA Astrophysics Data System (ADS)

    Landmann, M.; Rauls, E.; Schmidt, W. Â. G.; Neumann, M. Â. D.; Speiser, E.; Esser, N.

    2015-01-01

    Density-functional-theory calculations are combined with many-body perturbation theory in order to elucidate the geometry, electronic, and optical properties of the w z -GaN (1 1 ¯00 ) surface, i.e., the so-called m -plane. The optical absorption and reflection anisotropy related to electronic transitions between surface states are identified by comparison with measured data covering transition energies from 2.4 up to 5.4 eV. Our results show a surface relaxation mechanism consistent with the electron counting rule that causes a moderate buckling of the GaN surface dimers and gives rise to two distinct surface states: The doubly occupied N dangling bonds form a surface band that is resonant with the GaN valence-band edge at the center of the Brillouin zone, whereas the empty Ga dangling bonds occur within the GaN band gap closely following the dispersion of the conduction-band edge. These two states contribute strongly to the formation of surface excitons that redshift the optical absorption with respect to the bulk optical response. The surface optical absorption i.e., the excitonic onset below the bulk band gap followed by a broad absorption band at higher energies related to the dispersion of the surface band structure, is calculated in agreement with the experimental data.

  6. Electronic structure and band alignment of 9,10-phenanthrenequinone passivated silicon surfaces

    NASA Astrophysics Data System (ADS)

    Avasthi, Sushobhan; Qi, Yabing; Vertelov, Grigory K.; Schwartz, Jeffrey; Kahn, Antoine; Sturm, James C.

    2011-07-01

    In this work we demonstrate that the room-temperature deposition of the organic molecule 9,10-phenanthrenequinone (PQ) reduces the surface defect density of the silicon (100) surface by chemically bonding to the surface dangling bonds. Using various spectroscopic measurements we have investigated the electronic structure and band alignment properties of the PQ/Si interface. The band-bending at the PQ-passivated silicon surface is negligible for both n- and p-type substrates, demonstrating a low density of surface defects. Finally we show that PQ forms a semiconducting wide-bandgap type-I heterojunction with silicon.

  7. Waveguiding in Surface Plasmon Polariton Band Gap Structures

    Microsoft Academic Search

    Sergey I. Bozhevolnyi; John Erland; Kristjan Leosson; Peter M. Skovgaard; Jørn M. Hvam

    2001-01-01

    Using near-field optical microscopy, we investigate propagation and scattering of surface plasmon polaritons (SPP's) excited in the wavelength range of 780-820 nm at nanostructured gold-film surfaces with areas of 200-nm-wide scatterers arranged in a 400-nm-period triangular lattice containing line defects. We observe the SPP reflection by such an area and SPP guiding along line defects at 782 nm, as well

  8. Symmetry and spectral statistics of the magnetic band structure of a one-dimensional surface superlattice

    NASA Astrophysics Data System (ADS)

    Xu, H. Q.; Gu, Ben-Yuan

    2001-10-01

    We report a theoretical study of the spectral statistics of a quasi-one-dimensional surface superlattice in perpendicularly applied magnetic fields. The energy-level-spacing distribution and the Dyson-Mehta ?3 statistic of the magnetic band structure of the system are calculated. The calculations show that for the system with inversion symmetry, the magnetic band structure at the wave vector k = 0 is well described by the statistic derived by a superposition of two independent Gaussian orthogonal ensemble (GOE) statistics. This result is consistent with the fact that the system shows a false time-reversal violation and a real-space symmetry. The calculations show also that when the wave vector k is moved away from the k = 0 point, the statistical properties of the magnetic band structure are excellently described by the GOE statistics. The GOE statistics are also found in the magnetic band structure when the inversion symmetry is removed from the system.

  9. Spin-dependent band structure, Fermi surface, and carrier lifetime of permalloy

    E-print Network

    Himpsel, Franz J.

    magnetization and a high density of states, compensated by a low group velocity. The s,p electrons have a large group velocity but low density. A possible solution of this dilemma has been the notionSpin-dependent band structure, Fermi surface, and carrier lifetime of permalloy D. Y. Petrovykh, K

  10. Band-structure-based collisional model for electronic excitations in ion-surface collisions

    SciTech Connect

    Faraggi, M.N. [Instituto de Astronomia y Fisica del Espacio, CONICET, Casilla de Correo 67, Sucursal 28, 1428 Buenos Aires (Argentina); Gravielle, M.S. [Instituto de Astronomia y Fisica del Espacio, CONICET, Casilla de Correo 67, Sucursal 28, 1428 Buenos Aires (Argentina); Departamento de Fisica, FCEN, Universidad de Buenos Aires, Buenos Aires (Argentina); Alducin, M.; Silkin, V.M. [Donostia International Physics Center DIPC, P. Manuel de Lardizabal 4, 20018 San Sebastian (Spain); Juaristi, J.I. [Departamento de Fisica de Materiales Facultad de Quimicas, UPV/EHU, Apartado 1072, 20080 San Sebastian (Spain); Unidad de Fisica de Materiales Centro Mixto CSIC-UPV/EHU, Facultad de Quimicas, UPV/EHU, Apartado 1072, 20080 San Sebastian (Spain)

    2005-07-15

    Energy loss per unit path in grazing collisions with metal surfaces is studied by using the collisional and dielectric formalisms. Within both theories we make use of the band-structure-based (BSB) model to represent the surface interaction. The BSB approach is based on a model potential and provides a precise description of the one-electron states and the surface-induced potential. The method is applied to evaluate the energy lost by 100 keV protons impinging on aluminum surfaces at glancing angles. We found that when the realistic BSB description of the surface is used, the energy loss obtained from the collisional formalism agrees with the dielectric one, which includes not only binary but also plasmon excitations. The distance-dependent stopping power derived from the BSB model is in good agreement with available experimental data. We have also investigated the influence of the surface band structure in collisions with the Al(100) surface. Surface-state contributions to the energy loss and electron emission probability are analyzed.

  11. Influence of GaAs surface termination on GaSb/GaAs quantum dot structure and band offsets

    SciTech Connect

    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)

    2013-08-19

    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.

  12. Porous-pyramids structured silicon surface with low reflectance over a broad band by electrochemical etching

    NASA Astrophysics Data System (ADS)

    Lv, Hongjie; Shen, Honglie; Jiang, Ye; Gao, Chao; Zhao, Han; Yuan, Jiren

    2012-05-01

    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.

  13. Microwave band gap and cavity mode in spoof–insulator–spoof waveguide with multiscale structured surface

    NASA Astrophysics Data System (ADS)

    Zhang, Qiang; Xiao, Jun Jun; Han, Dezhuan; Qin, Fei Fei; Zhang, Xiao Ming; Yao, Yong

    2015-05-01

    We propose a multiscale spoof–insulator–spoof (SIS) waveguide by introducing periodic geometry modulation in the wavelength scale to a SIS waveguide made of a perfect electric conductor. The MSIS consists of multiple SIS subcells. The dispersion relationship of the fundamental guided mode of the spoof surface plasmon polaritons (SSPPs) is studied analytically within the small gap approximation. It is shown that the multiscale SIS possesses microwave band gap (MBG) due to the Bragg scattering. The ‘gap maps’ in the design parameter space are provided. We demonstrate that the geometry of the subcells can efficiently adjust the effective refraction index of the elementary SIS and therefore further control the width and the position of the MBG. The results are in good agreement with numerical calculations by the finite element method (FEM). For finite-sized MSIS of given geometry in the millimeter scale, FEM calculations show that the first-order symmetric SSPP mode has zero transmission in the MBG within frequency range from 4.29 to 5.1?GHz. A cavity mode is observed inside the gap at 4.58?GHz, which comes from a designer ‘point defect’ in the multiscale SIS waveguide. Furthermore, ultrathin MSIS waveguides are shown to have both symmetric and antisymmetric modes with their own MBGs, respectively. The deep-subwavelength confinement and the great degree of control of the propagation of SSPPs in such structures promise potential applications in miniaturized microwave device.

  14. Complex Quasiparticle Band Structure Induced by Electron-Phonon Interaction: Band Splitting in the 1×1H/W(110) Surface

    NASA Astrophysics Data System (ADS)

    Eiguren, Asier; Ambrosch-Draxl, Claudia

    2008-07-01

    We show that the self-consistent solution of the complex Dyson equation for the electron-phonon (EP) problem introduces many body effects which are often observed in photoemission experiments. The formalism is applied to the H covered W(110) surface, using first-principles results for the electronic and vibrational structure. We demonstrate that the measured spin-polarized surface band splitting [Phys. Rev. Lett. 84, 2925 (2000)PRLTAO0031-900710.1103/PhysRevLett.84.2925; 89, 216802 (2002)] can be traced back to different quasiparticle (QP) states induced by EP coupling. Despite the breakdown of the single QP picture, the spectral functions are very well represented by the predicted multiple QP structure.

  15. Microwave band gap and cavity mode in spoof-insulator-spoof waveguide with multiscale structured surface

    E-print Network

    Zhang, Qiang; Han, Dezhuan; Qin, Fei Fei; Zhang, Xiao Ming; Yao, Yong

    2015-01-01

    We propose a multiscale spoof-insulator-spoof (SIS) waveguide by introducing periodic geometry modulation in the wavelength scale to a SIS waveguide made of perfect electric conductor. The MSIS consists of multiple SIS subcells. The dispersion relationship of the fundamental guided mode of the spoof surface plasmon polaritons (SSPPs) is studied analytically within the small gap approximation. It is shown that the multiscale SIS possesses microwave band gap (MBG) due to the Bragg scattering. The "gap maps" in the design parameter space are provided. We demonstrate that the geometry of the subcells can efficiently adjust the effective refraction index of the elementary SIS and therefore further control the width and the position of the MBG. The results are in good agreement with numerical calculations by the finite element method (FEM). For finite-sized MSIS of given geometry in the millimeter scale, FEM calculations show that the first-order symmetric SSPP mode has zero transmission in the MBG within frequency...

  16. Surface analysis of oxygen free electrolytic-copper X-band accelerating structures and possible correlation to radio frequency breakdown events

    NASA Astrophysics Data System (ADS)

    Harvey, S. E.; Le Pimpec, F.; Kirby, R. E.; Marcelja, F.; Adamson, K.; Garwin, E. L.

    2004-07-01

    X-band accelerator structures meeting the next linear collider design requirements have been found to suffer vacuum surface damage caused by rf breakdown, when processed to high electric-field gradients. Improved understanding of these breakdown events is desirable for the development of structure designs, fabrication procedures, and processing techniques that minimize structure damage. rf reflected wave analysis and acoustic sensor pickup have provided breakdowns localization in rf structures. Particle contaminations found following clean autopsy of four rf-processed traveling wave structures have been catalogued and analyzed. Their influence on rf breakdown, as well as that of several other material-based properties, are discussed. .

  17. Core level line shapes and surface band structures of Sn/Ge(111) and Sn/Si(111)

    NASA Astrophysics Data System (ADS)

    Uhrberg, Roger

    2001-03-01

    We have performed a comparative study of Sn/Ge(111) and the closely related Sn/Si(111) system, using photoelectron spectroscopy (PES) and low energy electron diffraction (LEED). In similarity with the results from the Sn/Ge(111) surface, the Sn 4d spectra from Sn/Si(111) exhibit two major components and the valence band spectra show two surface state bands at both room temperature (RT) and 70 K. These features, which have been associated with the low temperature 3x3 phase in the case of Sn/Ge(111), are not expected for the rt3xrt3 RT surfaces. In contrast to Sn/Ge(111), we do not observe any transition to a 3x3 phase in LEED for Sn/Si(111) at temperatures down to 70 K (the lowest temperature in this study). Despite the absence of a 3x3 phase for Sn/Si(111) the core-level and the valence band data are very similar to those of Sn/Ge(111). The Sn 4d spectra show, however, one interesting difference. The intensity ratio of the two Sn 4d components is reversed for the Sn/Si(111) surface compared the Ge counterpart. This and the other PES results will be discussed in terms of the two different types of 3x3 periodicities that have been reported to be induced by substitutional defects on the Sn/Ge(111) surface [1]. [1] A.V. Melechko et al., Phys. Rev. B61, 2235 (2000)

  18. Band Structures of Plasmonic Polarons

    NASA Astrophysics Data System (ADS)

    Caruso, Fabio; Lambert, Henry; Giustino, Feliciano

    2015-04-01

    Using state-of-the-art many-body calculations based on the "G W plus cumulant" approach, we show that electron-plasmon interactions lead to the emergence of plasmonic polaron bands in the band structures of common semiconductors. Using silicon and group IV transition-metal dichalcogenide monolayers (A X2 with A =Mo ,W and X =S , Se) as prototypical examples, we demonstrate that these new bands are a general feature of systems characterized by well-defined plasmon resonances. We find that the energy versus momentum dispersion relations of these plasmonic structures closely follow the standard valence bands, although they appear broadened and blueshifted by the plasmon energy. Based on our results, we identify general criteria for observing plasmonic polaron bands in the angle-resolved photoelectron spectra of solids.

  19. Band structure from random interactions

    PubMed

    Bijker; Frank

    2000-01-17

    The anharmonic vibrator and rotor regions in nuclei are investigated in the framework of the interacting boson model using an ensemble of random one- and two-body interactions. We find a predominance of L(P) = 0(+) ground states, as well as strong evidence for the occurrence of both vibrational and rotational band structures. This remarkable result suggests that such band structures represent a far more general (robust) property of the collective model space than is generally thought. PMID:11015928

  20. Electronic band structure of zinc blende

    NASA Astrophysics Data System (ADS)

    Barman, S. R.; Ding, S.-A.; Neuhold, G.; Horn, K.; Wolfframm, D.; Evans, D. A.

    1998-09-01

    The electronic bulk and surface band structure of cubic zinc sulphide (``zinc blende'') has been studied by angle-resolved photoelectron spectroscopy using synchrotron radiation. The s-p derived bands along the ?-K-X high-symmetry direction have been determined, and the region of the Zn 3d line has been examined. Spectra at fixed photon energy and variation of polar electron emission angle were used to determine the dispersion of the surface states along the ?¯-X¯ within the surface Brillouin zone. The experimental data for bulk and surface bands are compared with results of a recent density-functional calculation, which includes the interaction between the s-p and the cation d-derived states.

  1. High-impedance electromagnetic surfaces with a forbidden frequency band

    Microsoft Academic Search

    Dan Sievenpiper; Lijun Zhang; Romulo F. Jimenez Broas; Nicolaos G. Alexopoulos; E. Yablonovitch

    1999-01-01

    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.

  2. Band Structures of Plasmonic Polarons

    NASA Astrophysics Data System (ADS)

    Caruso, Fabio; Lambert, Henry; Giustino, Feliciano

    2015-03-01

    In angle-resolved photoemission spectroscopy (ARPES), the acceleration of a photo-electron upon photon absorption may trigger shake-up excitations in the sample, leading to the emission of phonons, electron-hole pairs, and plasmons, the latter being collective charge-density fluctuations. Using state-of-the-art many-body calculations based on the `GW plus cumulant' approach, we show that electron-plasmon interactions induce plasmonic polaron bands in group IV transition metal dichalcogenide monolayers (MoS2, MoSe2, WS2, WSe2). We find that the energy vs. momentum dispersion relations of these plasmonic structures closely follow the standard valence bands, although they appear broadened and blueshifted by the plasmon energy. Based on our results we identify general criteria for observing plasmonic polaron bands in the angle-resolved photoelectron spectra of solids.

  3. Electronic Band Structures of Intermetallic Compound Cu2Sb

    Microsoft Academic Search

    Tadaei Ito; Masafumi Shirai; Kazuko Motizuki

    1992-01-01

    Self-consistent APW band calculations are carried out for Cu2Sb intermetallic compound with Cu2Sb-type structure. The energy dispersion, density of states and Fermi surface are shown. Differences and similarities of the electronic band structures between Cu2Sb and other Cu2Sb-type compounds are clarified.

  4. Effect of the band structure of InGaN/GaN quantum well on the surface plasmon enhanced light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Li, Yi; Zhang, Rong; Liu, Bin; Xie, Zili; Zhang, Guogang; Tao, Tao; Zhuang, Zhe; Zhi, Ting; Zheng, Youdou

    2014-07-01

    The spontaneous emission (SE) of InGaN/GaN quantum well (QW) structure with silver(Ag) coated on the n-GaN layer has been investigated by using six-by-six K-P method taking into account the electron-hole band structures, the photon density of states of surface plasmon polariton (SPP), and the evanescent fields of SPP. The SE into SPP mode can be remarkably enhanced due to the increase of electron-hole pairs near the Ag by modulating the InGaN/GaN QW structure or increasing the carrier injection. However, the ratio between the total SE rates into SPP mode and free space will approach to saturation or slightly decrease for the optimized structures with various distances between Ag film and QW layer at a high injection carrier density. Furthermore, the Ga-face QW structure has a higher SE rate than the N-face QW structure due to the overlap region of electron-hole pairs nearer to the Ag film.

  5. Monolithic Phononic Crystals with a Surface Acoustic Band Gap from Surface Phonon-Polariton Coupling

    NASA Astrophysics Data System (ADS)

    Yudistira, D.; Boes, A.; Djafari-Rouhani, B.; Pennec, Y.; Yeo, L. Y.; Mitchell, A.; Friend, J. R.

    2014-11-01

    We theoretically and experimentally demonstrate the existence of complete surface acoustic wave band gaps in surface phonon-polariton phononic crystals, in a completely monolithic structure formed from a two-dimensional honeycomb array of hexagonal shape domain-inverted inclusions in single crystal piezoelectric Z -cut lithium niobate. The band gaps appear at a frequency of about twice the Bragg band gap at the center of the Brillouin zone, formed through phonon-polariton coupling. The structure is mechanically, electromagnetically, and topographically homogeneous, without any physical alteration of the surface, offering an ideal platform for many acoustic wave applications for photonics, phononics, and microfluidics.

  6. Band mapping of surface states vs. adsorbate coverage

    SciTech Connect

    Rotenberg, E. [Univ. of Oregon, Eugene, OR (United States); [Lawrence Berkeley National Lab., CA (United States); Kevan, S.D. [Univ. of Oregon, Eugene, OR (United States); Denlinger, J.D. [Univ. of Wisconsin, Milwaukee, WI (United States); Chung, Jin-Wook [POSTECH, KyungBuk Pohang (Korea, Republic of)

    1997-04-01

    The theory of electron bands, which arises from basic quantum mechanical principles, has been the cornerstone of solid state physics for over 60 years. Simply put, an energy band is an electron state in a solid whose energy varies with its momentum (similar to, but with a more complicated dependence than, how a free electron`s energy is proportional to its momentum squared). Much attention over the last 15 years has been given to the study of band structure of surfaces and interfaces, especially as the applications of these two-dimensional systems have become increasingly important to industry and science. The ultraESCA endstation at beamline 7.01 at the Advanced Light Source was developed for very high-energy - ({approximately}50 meV) and angular - (<1{degrees}) resolution photoemission studies of materials. The high flux (typically 10{sup 12} photons/sec) makes the detailed study of the evolution of bands possible. The authors are interested in learning how, when one forms a chemical bond between a metal and an overlaying atom or molecule, the resulting charge transfer to or from the adsorbate affects the surface bands. In some cases of interest, intermediate coverages lead to different band structure than at the extremes of clean and saturated surfaces. Surfaces of tungsten are particularly interesting, as their atomic geometry has been shown to be exquisitely sensitive to both the surface vibrational and electronic properties. In this study, the authors looked at the surface bands of tungsten ((110) surface), as a function both of coverage and mass of overlaying atoms. The adsorbed atoms were hydrogen and the alkali atoms lithium and cesium.

  7. Near-Surface Vortex Structure in a Tornado and in a Sub-Tornado-Strength Convective-Storm Vortex Observed by a Mobile, W-Band Radar during VORTEX2

    E-print Network

    Xue, Ming

    Near-Surface Vortex Structure in a Tornado and in a Sub-Tornado-Strength Convective-Storm Vortex Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX2) field campaign, a very high-resolution, mobile, W-band Doppler radar collected near-surface (#200 m AGL) observations in an EF-0 tornado near

  8. Analytical approximation of complex band structures for band-to-band tunneling models

    Microsoft Academic Search

    Ximeng Guan; Donghyun Kim; Krishna C. Saraswat; H.-S. Philip Wong

    2011-01-01

    A unified analytical expression is developed to accurately describe the complex band structures in commonly used diamond and zinc-blende semiconductors. Fitting the model to the numerical complex band structures shows a significantly improved accuracy as compared with the effective mass approximation. The model is used to study the band-to-band tunneling in Si, Ge, GaAs and GaSb, with a maximum error

  9. Unfolding First-Principles Band Structures

    Microsoft Academic Search

    Wei Ku; Tom Berlijn; Chi-Cheng Lee

    2010-01-01

    A general method is presented to unfold band structures of first-principles supercell calculations with proper spectral weight, allowing easier visualization of the electronic structure and the degree of broken translational symmetry. The resulting unfolded band structures contain additional rich information from the Kohn-Sham orbitals, and absorb the structure factor that makes them ideal for a direct comparison with angle resolved

  10. Unfolding first-principles band structures

    Microsoft Academic Search

    Wei Ku; T. Berlijn; C.-C. Lee

    2011-01-01

    A general method [1] is presented to unfold band structures of first-principles supercell calculations with proper spectral weight, allowing easier visualization of the electronic structure and the degree of broken translational symmetry. The resulting unfolded band structures contain additional rich information from the Kohn-Sham orbitals, and absorb the structure factor that makes them ideal for a direct comparison with angle

  11. Modeling and application of 2D photonic band gap structures

    Microsoft Academic Search

    Mizan Rahman; Maria A. Stuchly

    2001-01-01

    Photonic band gap (PBG) structures have originally been explored in electro-optics. During the last five years, 2D planar PBG circuits have also been used at microwave frequencies. PBG structures behave as high impedance surfaces and suppress surface waves in one or more frequency ranges. Until now, these circuits have only been reliably modeled by numerical methods. A new equivalent circuit

  12. Electronically controlled microwave band gap filter structures

    Microsoft Academic Search

    Michael J. Hill; Richard W. Ziolkowski; John Papapolymerou

    2001-01-01

    Microwave band gap structures (MBG) utilizing fixed defects have received much interest because of their ability to operate as narrow band filters. With the recent interest in reconfigurable wireless devices, the need for electronically controllable narrow band filters is on the rise. By altering the defects in an MBG crystal, the transmission properties of the crystal can be changed. Using

  13. Self-Assembled Triply Periodic Minimal Surfaces as Molds for Photonic Band Gap Materials

    Microsoft Academic Search

    L. Martín-Moreno; F. J. García-Vidal; A. M. Somoza

    1999-01-01

    We propose systems with structures defined by self-assembled triply periodic minimal surfaces (STPMS) as candidates for photonic band gap materials. To support our proposal we have calculated the photonic bands for different STPMS and we have found that, at least, the double diamond and gyroid structures present full photonic band gaps. Given the great variety of systems which crystallize in

  14. Electronic Band Structure of Niobium Nitride

    Microsoft Academic Search

    L. F. Mattheiss

    1972-01-01

    The augmented-plane-wave method is applied to calculate the electronic band structure of niobium nitride (NbN). The results are qualitatively similar to those obtained from previous energy-band calculations for the 3d transition-metal monoxides which form with the same rocksalt structure. The Fermi level for NbN falls in the lower portion of the t2g manifold of the niobium 4d bands so that

  15. Angle-Resolved Photoemission and Band Structure of Copper

    NASA Astrophysics Data System (ADS)

    Courths, R.; Cord, B.; Wern, H.; Hüfner, S.

    1983-01-01

    The triangulation method, the appearance angle method and for the first time the surface emission method have been used for the determination of the electronic band structure of copper along the [001], [110] and [111] direction from ARPES spectra taken on the (110) and (111) faces. The experimentally derived bands are compared with first-principles calculations. For the bands up to energies of 20 eV above the Fermi energies it is found that Burdick's band calculation is in good agreement with experiment. Together with published normal emission data an almost complete experimental band structure below the Fermi energy is derived which clearly shows the spin-orbit splitting of the d-bands.

  16. Theory of quasiparticle scattering in a two-dimensional system of helical Dirac fermions: Surface band structure of a three-dimensional topological insulator

    E-print Network

    Hu, Jiangping

    band structure of a three-dimensional topological insulator Xiaoting Zhou, Chen Fang, Wei-Feng Tsai of a topological insulator. The unique features associated with hexagonal warping effects are identified in the QPI quantum state of matter, topological insulators in three dimensions 3D , which exhibit bulk in- sulating

  17. Band structures in 123I

    NASA Astrophysics Data System (ADS)

    Wang, S.-Y.; Komatsubara, T.; Ma, Y.-J.; Furuno, K.; Zhang, Y.-H.; Liu, Y.-Z.; Hayakawa, T.; Mukai, J.; Iwata, Y.; Morikawa, T.; Hagemann, G. B.; Sletten, G.; Nyberg, J.; Jerrestam, D.; Jensen, H. J.; Espino, J.; Gascon, J.; Gjørup, N.; Cederwall, B.; Tjøm, P. O.

    2006-03-01

    Excited states of 123I were populated via the 116Cd(14N, ?3n) reaction at 65 MeV. The resultant ?-rays were detected using standard ?-ray spectroscopic techniques with the NORDBALL detector array. Two previously known positive-parity ?I = 2 sequences have been extended up to 31/2+ and 41/2+. In addition, a number of ?I = 1 transitions linking the two ?I = 2 sequences have been observed. It is suggested that both ?I = 2 sequences are based on a common configuration. This ?I = 1 band is proposed to be built predominantly on the g7/2[404]7/2+ oblate configuration, based on the energy-level spectra, B(M1)/B(E2) ratios and the theoretical predictions from the particle-rotor model. The previously identified ?I = 1 rotational band built on the prolate g9/2[404]9/2+ orbital has also been extended to higher spins. Another previously identified but weakly populated ?I = 1 band is confirmed and is proposed to be built on the d5/2[413]5/2+ configuration with the ground state of 123I as the bandhead.

  18. Unfolding first-principles band structures.

    PubMed

    Ku, Wei; Berlijn, Tom; Lee, Chi-Cheng

    2010-05-28

    A general method is presented to unfold band structures of first-principles supercell calculations with proper spectral weight, allowing easier visualization of the electronic structure and the degree of broken translational symmetry. The resulting unfolded band structures contain additional rich information from the Kohn-Sham orbitals, and absorb the structure factor that makes them ideal for a direct comparison with angle resolved photoemission spectroscopy experiments. With negligible computational expense via the use of Wannier functions, this simple method has great practical value in the studies of a wide range of materials containing impurities, vacancies, lattice distortions, or spontaneous long-range orders. PMID:20867120

  19. Band optimization of two-dimensional photonic crystal surface-emitting laser

    Microsoft Academic Search

    Wenjun Zhou; Bin Jiang; Wei Chen; Anjin Liu; Yufei Wang; Chuanlong Ma; Mingxin Xing; Wanhua Zheng

    2011-01-01

    The three-dimensional (3D) plane wave expansion method with supercell approximation has been employed to investigate in detail the band structure of the two-dimensional photonic crystal (PhC) surface-emitting laser with square lattice. The symmetric point band structure has been calculated to obtain the optimized structures of PhC surface-emitting lasers. There exists a range of parameter pairs, including periods and area-filling factors

  20. Effect of Band Structure on the Symmetry of Superconducting States

    Microsoft Academic Search

    Kazuhiro Kuboki

    2001-01-01

    Effects of band structure on the symmetry of superconducting (SC) states are studied. We show that various symmetries of SC states are possible within the same type of interaction when the shape of the Fermi surface is changed. As a simple model we consider a square lattice system with a nearest-neighbor attractive interaction, and find that the spin-triplet ((px +

  1. Multiple band structures of {sup 131}Cs

    SciTech Connect

    Sihotra, S. [Department of Physics, Panjab University, Chandigarh-160014 (India); Department of Nuclear and Atomic Physics, Tata Institute of Fundamental Research, Mumbai-400005 (India); Department of Physics, Guru Nanak Dev University, Amritsar-143005 (India); Palit, R.; Naik, Z.; Joshi, P. K.; Deo, A. Y.; Jain, H. C. [Department of Nuclear and Atomic Physics, Tata Institute of Fundamental Research, Mumbai-400005 (India); Singh, K.; Goswamy, J.; Mehta, D.; Singh, N. [Department of Physics, Panjab University, Chandigarh-160014 (India); Malik, S. S. [Department of Physics, Guru Nanak Dev University, Amritsar-143005 (India); Praharaj, C. R. [Institute of Physics, Bhubaneswar-751005 (India)

    2008-09-15

    Excited states in {sup 131}Cs were investigated through in-beam {gamma}-ray spectroscopic techniques following its population in the {sup 124}Sn({sup 11}B, 4n) fusion-evaporation reaction at a beam energy of 46 MeV. The previously known level scheme has been substantially extended up to {approx}9 MeV excitation energy and 49/2({Dirac_h}/2{pi}) spin with the addition of seven new band structures. The present level scheme consisting of 15 bands exhibits a variety of collective features in this nucleus at intermediate spin. The excitation energies of the observed levels in different bands and the corresponding ratios of transition strengths, i.e., B(M1)/B(E2), have been compared with the results of projected deformed Hartree-Fock calculations based on various quasiparticle configurations. A strongly coupled band has been reassigned a high-K three-quasiparticle {pi}h{sub 11/2} x {nu}(h{sub 11/2}d{sub 3/2}) configuration based on the properties of this band and that of its new coupled side band. The configurations of these bands are also discussed in the framework of tilted-axis cranking model calculations and the systematics of the odd-A Cs isotopes. Additional three energetically closely placed coupled bands have been assigned different unpaired three-quasiparticle configurations. {gamma}-vibrational bands coupled to the {pi}h{sub 11/2} and {pi}g{sub 7/2} single-particle configurations have been reported in this nucleus. Observation of new E1 transitions linking the opposite-parity {pi}h{sub 11/2} and {pi}d{sub 5/2} bands provides fingerprints of possible octupole correlations.

  2. Band bending and surface defects in ?-Ga2O3

    NASA Astrophysics Data System (ADS)

    Lovejoy, T. C.; Chen, Renyu; Zheng, X.; Villora, E. G.; Shimamura, K.; Yoshikawa, H.; Yamashita, Y.; Ueda, S.; Kobayashi, K.; Dunham, S. T.; Ohuchi, F. S.; Olmstead, M. A.

    2012-04-01

    Surface band bending and surface defects on the UV-transparent conducting oxide ?-Ga2O3 (100) are studied with hard x-ray photoemission spectroscopy and scanning tunneling microscopy. Highly doped ?-Ga2O3 shows flat bands near the surface, while the bands on nominally undoped (but still n-type), air-cleaved ?-Ga2O3 are bent upwards by ?0.5 eV. Negatively charged surface defects are observed on vacuum annealed ?-Ga2O3, which also shows upward band bending. Density functional calculations show oxygen vacancies are not likely to be ionized in the bulk, but could be activated by surface band bending. The large band bending may also hinder formation of ohmic contacts.

  3. Valence band structure of Bi2Se3

    NASA Astrophysics Data System (ADS)

    Gao, Yi-Bin; Parker, David; Heremans, Joseph P.

    2013-03-01

    Bi2Se3 is an interesting candidate for thermoelectric application because Se is a more abundant element than Te, which is commercially used in Bi2Te3-based Peltier coolers. However, intrinsic Se vacancies dominate in Bi2Se3 and dope the material n-type. Due to unfavourable conduction band structure, n-type Bi2Se3 does not have a high power factor. Recently, it has been calculated that Bi2Se3 has a favourable valence band structure for thermoelectric application. In this presentation, high-quality p-type Bi2Se3 single crystals are prepared and Shubnikov de Haas measurement are carried out on them to characterize the band structure. Cross-sectional areas of Fermi surface are mapped out and compared with the theoretical calculation. Bi2Se3 is an interesting candidate for thermoelectric application because Se is a more abundant element than Te, which is commercially used in Bi2Te3-based Peltier coolers. However, intrinsic Se vacancies dominate in Bi2Se3 and dope the material n-type. Due to unfavourable conduction band structure, n-type Bi2Se3 does not have a high power factor. Recently, it has been calculated that Bi2Se3 has a favourable valence band structure for thermoelectric application. In this presentation, high-quality p-type Bi2Se3 single crystals are prepared and Shubnikov de Haas measurement are carried out on them to characterize the band structure. Cross-sectional areas of Fermi surface are mapped out and compared with the theoretical calculation. Funded by zt::plus

  4. Flat photonic surface bands pinned between Dirac points

    E-print Network

    Jukic, Dario

    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 ...

  5. Band structure of segmented semiconductor nanowires

    NASA Astrophysics Data System (ADS)

    Pistol, M.-E.; Pryor, C. E.

    2009-07-01

    We have calculated the band structures for strained segmented nanowires involving all combinations of AlN, GaN, InN, AlP, GaP, AlAs, GaAs, InP, InAs, AlSb, GaSb, and InSb, as a function of segment length. This was done for two different growth directions of the wires, [100] and [111]. Both the ? and the X conduction-band minima were included in the calculations as well as the valence bands. Short segments behave like strained quantum wells and our results thus include strained quantum wells as a subset. We find all material combinations that give metallic segments due to a negative band gap and we find all the band alignments that may occur. We identify those structures which show spontaneous charge separation as well as those which are suitable for the optical generation of polarized exciton gases, with their rich phase diagram, theoretically predicted to include superfluids and supersolids. Some device related ideas are presented. Due to the amount of data (several hundreds of diagrams) most of our results are presented as a webpage.

  6. Band structure engineering in topological insulator based heterostructures.

    PubMed

    Menshchikova, T V; Otrokov, M M; Tsirkin, S S; Samorokov, D A; Bebneva, V V; Ernst, A; Kuznetsov, V M; Chulkov, E V

    2013-01-01

    The ability to engineer an electronic band structure of topological insulators would allow the production of topological materials with tailor-made properties. Using ab initio calculations, we show a promising way to control the conducting surface state in topological insulator based heterostructures representing an insulator ultrathin films on the topological insulator substrates. Because of a specific relation between work functions and band gaps of the topological insulator substrate and the insulator ultrathin film overlayer, a sizable shift of the Dirac point occurs resulting in a significant increase in the number of the topological surface state charge carriers as compared to that of the substrate itself. Such an effect can also be realized by applying the external electric field that allows a gradual tuning of the topological surface state. A simultaneous use of both approaches makes it possible to obtain a topological insulator based heterostructure with a highly tunable topological surface state. PMID:24274792

  7. X-Band Photonic Band-Gap Accelerator Structure Breakdown Experiment

    SciTech Connect

    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

    2012-06-11

    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.

  8. Pseudopotential band structure of indium nitride

    Microsoft Academic Search

    C. P. Foley; T. L. Tansley

    1986-01-01

    The band structure, density of states and the imaginary part of the dielectric function have been calculated for indium nitride by a pseudopotential method. Comparison with published reflectance data permits the identification of principal optical transitions at the GAMMA,M,K, and H symmetry points and we have been able to correct previous transition assignments. The calculated long-wavelength refractive index of 2.88

  9. Electronic band structures and charge densities of NbC and NbN

    Microsoft Academic Search

    D. J. Chadi; Marvin L. Cohen

    1974-01-01

    We present nonlocal-pseudopotential calculations of the electronic band structures and charge densities of NbC and NbN. The major contribution to the charge density of the bands near the Fermi energy comes from C or N 4 p states. The charge density for the first partially filled Nb 4 d band and the shape of the Fermi surface for this band

  10. Thermal Infrared Spectral Band Detection Limits for Unidentified Surface Materials

    NASA Technical Reports Server (NTRS)

    Kirkland, Laurel E.; Herr, Kenneth C.; Salisbury, John W.

    2001-01-01

    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.

  11. Complex Band Structures: From Parabolic to Elliptic Approximation

    Microsoft Academic Search

    Ximeng Guan; Donghyun Kim; Krishna C. Saraswat; H.-S. Philip Wong

    2011-01-01

    We show that the conventional nonparabolic approx- imation of real band structures can be modified and generalized to approximate the complex band structures of common semicon- ductors with a significant improvement of accuracy against the parabolic approximation. The improvement is due to the inherent elliptic nature of the complex band structures in the vicinity of the bandgap, which has a

  12. Absence of X-point band overlap in divalent hexaborides and variability of the surface chemical potential

    SciTech Connect

    Denlinger, Jonathan D.; Gweon, Gey-Hong; Mo, Sung-Kwan; Allen, James W.; Sarrao, John L.; Bianchi, Adrian D.; Fisk, Zachary

    2001-11-04

    Angle-resolved photoemission measurements of divalent hexaborides reveals a >1 eV X-point gap between the valence and conduction bands, in contradiction to the band overlap assumed in several models of their novel ferromagnetism. While the global ARPES band structure and gap size observed are consistent with the results of bulk-sensitive soft x-ray absorption and emission boron K-edge spectroscopy, the surface-sensitive photoemission measurements also show a variation with cation, surface and time of the position of the surface chemical potential in the band structure.

  13. Surface photovoltage in semiconductors under sub-band-gap illumination: continuous distribution of surface states

    Microsoft Academic Search

    L. Szaro; J. Rebisz; J. Misiewicz

    1999-01-01

    .   Surface photovoltage spectra in semiconductors are analyzed when the sub-band-gap illumination induces the electron transitions\\u000a from surface states to the conduction band under the assumption that distribution of surface states is continuous. From analysis\\u000a performed it follows that the fictitious densities of surface states can be induced due to the wavelength dependence of the\\u000a photoionization capture cross-section of surface

  14. Achieving Higher Energies via Passively Driven X-band Structures

    NASA Astrophysics Data System (ADS)

    Sipahi, Taylan; Sipahi, Nihan; Milton, Stephen; Biedron, Sandra

    2014-03-01

    Due to their higher intrinsic shunt impedance X-band accelerating structures significant gradients with relatively modest input powers, and this can lead to more compact particle accelerators. At the Colorado State University Accelerator Laboratory (CSUAL) we would like to adapt this technology to our 1.3 GHz L-band accelerator system using a passively driven 11.7 GHz traveling wave X-band configuration that capitalizes on the high shunt impedances achievable in X-band accelerating structures in order to increase our overall beam energy in a manner that does not require investment in an expensive, custom, high-power X-band klystron system. Here we provide the design details of the X-band structures that will allow us to achieve our goal of reaching the maximum practical net potential across the X-band accelerating structure while driven solely by the beam from the L-band system.

  15. Segmental structure in banded mongoose calls

    PubMed Central

    2012-01-01

    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 PMID:23206277

  16. Observation of banded spherulites and lamellar structures by atomic force microscopy

    Microsoft Academic Search

    Jiang Yong; Luo Yanhong; Fan Zefu; Wang Xiayu; Xu Jun; Guo Baohua; Li Lin

    2003-01-01

    Lamellar structures of banded spherulites of poly(?-caprolactone)\\/poly(vinyl chloride) (PCL\\/PVC) blends are observed using\\u000a tapping mode atomic force microscopy (AFM). The surface of the PCL\\/PVC banded spherulites presents to be concentric periodic\\u000a ups and downs. The period of the bands corresponds to the extinction rings under the polarized optical microscopy observation.\\u000a The lamellae with edge-on orientation in the ridges and the

  17. Self-Assembled Triply Periodic Minimal Surfaces as Molds for Photonic Band Gap Materials

    Microsoft Academic Search

    L. Martín-Moreno; F. García-Vidal; A. M. Somoza

    1999-01-01

    We propose systems with structures defined by self-assembled triply periodic\\u000aminimal surfaces (STPMS) as candidates for photonic bandgap materials. To\\u000asupport our proposal we have calculated the photonic bands for different STPMS\\u000aand we have found that, at least, the double diamond and gyroid structures\\u000apresent full photonic bandgaps. Given the great variety of systems which\\u000acrystalize in these structures,

  18. Angle-resolved photoemission and experimental band structure of Cu

    NASA Astrophysics Data System (ADS)

    Courths, R.; Bachelier, V.; Cord, B.; Hüfner, S.

    1981-12-01

    Two methods of angle-resolved photoemission, the energy coincidence (or triangulation) method and the appearance angle method, have been used for the absolute determination of some points in the electronic band structure of the Cu(001) and Cu(1 overline10) mirror planes. It is found that this can be done with high precision. A comparison with available band structure calculations shows that agreement is good with Burdick's non-self-consistent APW band structure, whereas larger deviations occur from more recent self-consistent band structure calculations.

  19. Interfacial effects on the band edges of functionalized si surfaces in liquid water.

    PubMed

    Pham, Tuan Anh; Lee, Donghwa; Schwegler, Eric; Galli, Giulia

    2014-12-10

    By combining ab initio molecular dynamics simulations and many-body perturbation theory calculations of electronic energy levels, we determined the band edge positions of functionalized Si(111) surfaces in the presence of liquid water, with respect to vacuum and to water redox potentials. We considered surface terminations commonly used for Si photoelectrodes in water splitting experiments. We found that, when exposed to water, the semiconductor band edges were shifted by approximately 0.5 eV in the case of hydrophobic surfaces, irrespective of the termination. The effect of the liquid on band edge positions of hydrophilic surfaces was much more significant and determined by a complex combination of structural and electronic effects. These include structural rearrangements of the semiconductor surfaces in the presence of water, changes in the orientation of interfacial water molecules with respect to the bulk liquid, and charge transfer at the interfaces, between the solid and the liquid. Our results showed that the use of many-body perturbation theory is key to obtain results in agreement with experiments; they also showed that the use of simple computational schemes that neglect the detailed microscopic structure of the solid-liquid interface may lead to substantial errors in predicting the alignment between the solid band edges and water redox potentials. PMID:25402590

  20. Banded surface flow maintained by convection in a model of the rapidly rotating giant planets

    NASA Technical Reports Server (NTRS)

    Sun, Zi-Ping; Schubert, Gerald; Glatzmaier, Gary A.

    1993-01-01

    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.

  1. Banded surface flow maintained by convection in a model of the rapidly rotating giant planets.

    PubMed

    Sun, Z P; Schubert, G; Glatzmaier, G A

    1993-04-30

    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. PMID:17812225

  2. Planar electromagnetic band-gap structure based on graphene

    NASA Astrophysics Data System (ADS)

    Dong, Yanfei; Liu, Peiguo; Yin, Wen-Yan; Li, Gaosheng; Yi, Bo

    2015-06-01

    Electromagnetic band-gap structure with slow-wave effect is instrumental in effectively controlling electromagnetic wave propagation. In this paper, we theoretically analyze equivalent circuit model of electromagnetic band-gap structure based on graphene and evaluate its potential applications. Graphene electromagnetic band-gap based on parallel planar waveguide is investigated, which display good characteristics in dynamically adjusting the electromagnetic wave propagation in terahertz range. The same characteristics are retrieved in a spiral shape electromagnetic band-gap based on coplanar waveguide due to tunable conductivity of graphene. Various potential terahertz planar devices are expected to derive from the prototype structures.

  3. Omnidirectional Band Gap Mirror for Surface Acoustic Wave

    Microsoft Academic Search

    Abdelkrim Khelif; Abdelkrim Choujaa; Sarah Benchabane; Vincent Laude

    \\u000a defect We report on the theoretical and experimental evidence for the occurrence of an omnidirectional elastic band gaps in\\u000a one-dimensional phononic crystal structures. The structure is constituted by a periodically layered mirror deposited on a\\u000a specific substrate that exhibits total reflection of waves for all incident angles and polarizations in a given frequency\\u000a range. We study in this paper the

  4. Band Structure of the Effective-Mass Superlattice

    Microsoft Academic Search

    M. V. Klymenko; I. M. Safonov; O. V. Shulika; L. A. Sukhoivanov

    2006-01-01

    The new kind of semiconductor superlattice is proposed. It is based on the new type of semiconductor heterojunctions that have only carrier effective mass discontinuity and no or extremely small band lineups in both conduction and valence bands. Confinement effects in these structures are due to effective mass discontinuity only. It makes this kind of structures to be very sensitive

  5. A numerical method to compute isotropic band models from anisotropic semiconductor band structures

    Microsoft Academic Search

    Antonio Abramo; Franco Venturi; Enrico Sangiorgi; Jack M. Higman; Bruno Riccò

    1993-01-01

    A numerical method for the determination of isotropic band models has been developed and applied to silicon. The resulting model accurately approximates both density of states and group velocity of the corresponding anisotropic band structure, thus providing an excellent agreement with both the collision and nonhomogeneous terms of the Boltzmann transport equation. The model, represented by a simple set of

  6. The investigation of single, dual and tri-band frequency selective surface

    NASA Astrophysics Data System (ADS)

    Aziz, Mohamad Zoinol Abidin Abd.; Shukor, Mahfuzah Md.; Mustafa, Nur Hanim; Fauzi, Noor Azamiah Md; Ahmad, Badrul Hisham; Suaidi, Mohamad Kadim; Johar, Fauzi Mohd; Salleh, Siti Nadzirah; Azmin, Farah Ayuni; Malek, Mohd Fareq Abd.

    2015-05-01

    The single, dual and tri-band Frequency Selective Surface (FSS) design structure is designed and simulated by using CST Microwave Studio software. The reflection (S11) and transmission (S21) of the design FSS structure is analyzed based on the six types of configuration that have been set up. All configurations are simulated with the same size of the FSS design structure. The hybrid material (FR4 and glass) affects the transmission and reflection signals of the FSS which led to the compact structure. The measurement results are agreed for all FSS design structures but the difference is due to the transmission losses.

  7. Tuning the electronic band structure of PCBM by electron irradiation

    PubMed Central

    2011-01-01

    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. PMID:21970617

  8. Structure band-gap correlations in semiconductors: Implications for computational band gap prediction

    NASA Astrophysics Data System (ADS)

    Schneider, Guenter; Foster, David H.

    2014-03-01

    Large scale structure prediction for novel materials requires computationally inexpensive lattice relaxation methods, which are typically based on density functional theory (DFT) using a semi-local approximation for the exchange-correlation functional. These methods provide structural parameters accurate to within a few percent, but cannot predict band-gaps. Band-gap calculations, require much more computationally expensive methods such as hybrid functionals or the GW approximation. Such an accuracy-tiered method fails dramatically for Cu3PSe4. When the generalized gradient approximation (GGA) is used to relax the lattice and ions, band-gaps calculated using both the single shot GGA+GW method and the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional method are a full 0.5 eV lower than the band gaps calculated for the unrelaxed, experimental structure. The GW and HSE methods predict accurate band gaps only when used with the correct experimental structure. We show that in Cu3PSe4, the calculated band-gap depends strongly on the P-Se bondlength, which can be explained by the P-Se* anti-bonding character of the lowest conduction band state. We show this effect for different lattice relaxation methods including recently developed meta-GGAs.

  9. Brain Surface Parameterization Using Riemann Surface Structure

    E-print Network

    Wang, Yalin

    Brain Surface Parameterization Using Riemann Surface Structure Yalin Wang1 , Xianfeng Gu2 , Kiralee of the brain, including the cortex, hippocampus, and lateral ventricles. We found that the resulting on surfaces for PDE-based signal processing. 1 Introduction In brain imaging research, parameterization

  10. Analysis and design of triple-band high-impedance surface absorber with periodic diversified impedance

    NASA Astrophysics Data System (ADS)

    Rui Zhang, Guo; Heng Zhou, Pei; Bin Zhang, Hui; Bo Zhang, Lin; Liang Xie, Jian; Jiang Deng, Long

    2013-10-01

    In this paper, a triple-band planar absorber with high-impedance surface (HIS) is designed and fabricated. The absorber structure is composed of polyurethane foam sandwiched between a lossy sheet of frequency selective surfaces (FSS) and a perfect electric conductor. The lossy FSS possesses different resistances in a periodic composite unit as compared with typical HIS absorber. Losses in the FSS are introduced by printing the periodic composite square ring pattern on blank stickers using various resistive inks. Physical mechanism of the HIS absorbers is analyzed by equivalent circuit model and electric field distribution studies. The proposed absorber with periodic composite units offers superimposed triple-band absorption as compared with that of the single units having single- or dual-band absorption characteristics. The reflection loss measurements show that the 90% absorption bandwidth of the HIS absorber is increased by 42% by the proposed composite periodic units.

  11. Mapping polarization induced surface band bending on the Rashba semiconductor BiTeI

    PubMed Central

    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

    2014-01-01

    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

  12. A novel TEM-waveguide using uniplanar compact photonic band-gap (UC-PBG) structure

    Microsoft Academic Search

    F. R. Yang; K. P. Ma; Y. Qian; T. Itoh

    1999-01-01

    A novel TEM-waveguide using a photonic band-gap (PBG) structure is presented. The uniplanar compact PBG (UC-PBG) structure which realizes a magnetic surface in the stopband is used in the waveguide walls. TEM mode has been observed by measuring the field distribution and phase velocity of the waveguide

  13. Photoemission spectra and band structures of d band metals. IX. Triangulation analysis of angle-resolved data on copper

    NASA Astrophysics Data System (ADS)

    Pessa, M.; Lindroos, M.; Asonen, H.; Smith, N. V.

    1982-01-01

    Copper is used as a test case in the evaluation of the triangulation method for the determination of the electronic band structure over extended regions of k--> space. High-resolution angle-resolved-photoemission spectra were taken systematically on the (100) and (110) faces, and the energy-coincidence criterion was used to identify the same transition on each face and thereby fix absolutely the values of k-->. The pitfalls of the energy-coincidence criterion are pointed out. The experimentally derived bands are compared, through the mediation of a combined interpolation scheme, with the first-principles calculations of Burdick, and are found to be in excellent agreement after inclusion of spin-orbit splitting in the d bands. Other, less systematic, features are interpreted variously as secondary-cone emission, density-of-states features, or surface-state emission.

  14. Structure of the Red Fluorescence Band in Chloroplasts

    E-print Network

    Govindjee

    Structure of the Red Fluorescence Band in Chloroplasts GOVINDJEE and LOUISA YANG From to the emission of a sample, it is shown that the fluorescencet band in spinach chloroplast fragments at room at different concentrations of chloroplast fragments with excitation in chlorophyll a and b and excitation

  15. Electronic Band Structure and Sub-band-gap Absorption of Nitrogen Hyperdoped Silicon

    PubMed Central

    Zhu, Zhen; Shao, Hezhu; Dong, Xiao; Li, Ning; Ning, Bo-Yuan; Ning, Xi-Jing; Zhao, Li; Zhuang, Jun

    2015-01-01

    We investigated the atomic geometry, electronic band structure, and optical absorption of nitrogen hyperdoped silicon based on first-principles calculations. The results show that all the paired nitrogen defects we studied do not introduce intermediate band, while most of single nitrogen defects can introduce intermediate band in the gap. Considering the stability of the single defects and the rapid resolidification following the laser melting process in our sample preparation method, we conclude that the substitutional nitrogen defect, whose fraction was tiny and could be neglected before, should have considerable fraction in the hyperdoped silicon and results in the visible sub-band-gap absorption as observed in the experiment. Furthermore, our calculations show that the substitutional nitrogen defect has good stability, which could be one of the reasons why the sub-band-gap absorptance remains almost unchanged after annealing. PMID:26012369

  16. Electronic Band Structure and Sub-band-gap Absorption of Nitrogen Hyperdoped Silicon.

    PubMed

    Zhu, Zhen; Shao, Hezhu; Dong, Xiao; Li, Ning; Ning, Bo-Yuan; Ning, Xi-Jing; Zhao, Li; Zhuang, Jun

    2015-01-01

    We investigated the atomic geometry, electronic band structure, and optical absorption of nitrogen hyperdoped silicon based on first-principles calculations. The results show that all the paired nitrogen defects we studied do not introduce intermediate band, while most of single nitrogen defects can introduce intermediate band in the gap. Considering the stability of the single defects and the rapid resolidification following the laser melting process in our sample preparation method, we conclude that the substitutional nitrogen defect, whose fraction was tiny and could be neglected before, should have considerable fraction in the hyperdoped silicon and results in the visible sub-band-gap absorption as observed in the experiment. Furthermore, our calculations show that the substitutional nitrogen defect has good stability, which could be one of the reasons why the sub-band-gap absorptance remains almost unchanged after annealing. PMID:26012369

  17. Band gaps from ring resonators and structural periodicity

    NASA Astrophysics Data System (ADS)

    Qi, Yabing; Hou, Bo; Wen, Weijia

    2005-02-01

    The electromagnetic band gap properties through a two-dimensional plate constructed with centimetre-sized spherical foam balls surrounded by aluminium rings are studied in the microwave range of 0.7-18 GHz. We observe from both experiments and finite-difference time-domain simulations that multiple band gaps appear and correspond to different resonant modes localized in the rings. The principal stop band, the lowest mode, appears at low frequencies and is robust to any lattice structure, even disorder. However, the remaining auxiliary stop bands, caused by high-order resonances, are usually located at higher frequencies and are more sensitive to the configuration of the structure formed by the ring resonators. We note that the stop bands would be broadened and strongly attenuated if more layers of the same plates were packed together. In addition, even or odd modes can be excited under different orientations of the rings with respect to the polarization of the illuminating radiation.

  18. Band modulation and in-plane propagation of surface plasmons in composite nanostructures

    NASA Astrophysics Data System (ADS)

    Fan, Ren-Hao; Xu, Di-Hu; Zhang, Kun; Peng, Ru-Wen; Wang, Mu

    2015-03-01

    In this work, we have experimentally and theoretically studied band modulation and in-plane propagation of surface plasmons (SPs) in composite nanostructures with aperture arrays and metallic gratings. It is shown that the plasmonic band structure of the composite system can be significantly modulated because of coupling between the aperture and the grating. By changing the relative positions between these optical components, the resonant modes would shift or split. And the resonant SP modes launched on the structure surface can be effectively modified by the geometric parameters. Further, we provide an experimental observation to directly show the SP in-plane propagation by using far-field measurements. Our study offers a convenient way for observing the SP propagation in far field, and provides unique composite nanostructures for possible applications in subwavelength optodevices, such as optical sensors and detectors.

  19. Automated effective band structures for defective and mismatched supercells.

    PubMed

    Brommer, Peter; Quigley, David

    2014-12-01

    In plane-wave density functional theory codes, defects and incommensurate structures are usually represented in supercells. However, interpretation of E versus k band structures is most effective within the primitive cell, where comparison to ideal structures and spectroscopy experiments are most natural. Popescu and Zunger recently described a method to derive effective band structures (EBS) from supercell calculations in the context of random alloys. In this paper, we present bs_sc2pc, an implementation of this method in the CASTEP code, which generates an EBS using the structural data of the supercell and the underlying primitive cell with symmetry considerations handled automatically. We demonstrate the functionality of our implementation in three test cases illustrating the efficacy of this scheme for capturing the effect of vacancies, substitutions and lattice mismatch on effective primitive cell band structures. PMID:25388668

  20. Band Structure of {sup 85}Sr

    SciTech Connect

    Kumar, Suresh; Mandal, S. K. [Department of Physics and Astrophysics, University of Delhi, Delhi-110007 (India); Jain, A. K. [Department of Physics, Indian Institute of Technology, Roorkee-247667 (India); Chaturvedi, L. [Guru Ghasidas University, Bilaspur, Chhattisgarh-495009 (India); Sinha, Rishi Kumar [Department of Physics, Banaras Hindu University, Varanasi-221005 (India); Negi, Dinesh; Dhal, Ankul; Kumar, R.; Singh, R. P.; Muralithar, S.; Bhowmik, R. K.; Pancholi, S. C. [Inter University Accelerator Centre, Aruna Asaf Ali Marg, Delhi-110067 (India)

    2010-11-24

    High spin states in {sup 85}Sr were populated using the reaction {sup 76}Ge({sup 13}C, 4n) at a beam energy of 52 MeV. Gamma-gamma coincidence measurements along with investigation of directional correlation ratios were utilized to establish the extended level scheme upto I{sup {pi}}= (35/2{sup -}). One of the positive parity states observed at 3383.3 keV ((I{sup {pi}}= 19/2{sup (+)}) may be considered as a magnetic rotational ({Delta}I = 1) band, the negative parity states built on 3028.0 level show an irregular behaviour and does not exhibit magnetic rotation.

  1. Band structure of core-shell semiconductor nanowires

    NASA Astrophysics Data System (ADS)

    Pistol, M.-E.; Pryor, C. E.

    2008-09-01

    We have calculated band structures for strained core-shell nanowires involving all combinations of AlN, GaN, and InN, as well as all combinations of AlP, GaP, AlAs, GaAs, InP, InAs, AlSb, GaSb, and InSb, as functions of core and shell radii. This gives 78 combinations, most of which have not been experimentally realized, and provides a quite complete overview of which interesting structures can be realized in core-shell zinc-blende III-V nanowires. Both the ? - and the X-conduction-band minima were included in the calculations in addition to the valence-band maximum. The calculations were performed using continuum elasticity theory for the strain, eight-band strain-dependent k?p theory for the ? -point energies, and a single-band approximation for the X-point conduction minima. All combinations of materials having type-I, type-II, and type-III (broken gap) band alignments have been identified, as well as all combinations for which one material becomes metallic due to a negative band gap. We identify structures that may support exciton crystals, excitonic superconductivity, and biomolecular detection. We have also computed the effective masses from which the confinement energy may be estimated. While graphical presentation of the results helps identify trends, all the numerical results are also available online.

  2. Band structure properties of (BGa)P semiconductors for lattice matched integration on (001) silicon

    NASA Astrophysics Data System (ADS)

    Hossain, Nadir; Hosea, Jeff; Liebich, Sven; Zimprich, Martin; Volz, Kerstin; Kunert, Bernerdette; Stolz, Wolfgang; Sweeney, Stephen

    2013-12-01

    We report the band structure properties of (BGa)P layers grown on silicon substrate using metal-organic vapour-phase epitaxy. Using surface photo-voltage spectroscopy we find that both the direct and indirect band gaps of (BGa)P alloys (strained and unstrained) decrease with Boron content. Our experimental results suggest that the band gap of (BGa)P layers up to 6% Boron is large and suitable to be used as cladding and contact layers in GaP-based quantum well heterostructures on silicon substrates.

  3. Photoemission study of the surface electronic structure of W(001)

    Microsoft Academic Search

    Greg S. Elliott; Kevin E. Smith; Stephen D. Kevan

    1991-01-01

    We report a high-resolution angle-resolved photoemission study of the surface electronic structure of the high-temperature phase of W(001). We have focused particularly upon the electron states within a few electron volts of the Fermi level in an attempt to characterize the interplay between the electronic and atomic structures of this surface. We relate these measurements of the surface band structure

  4. Transient band structures in the ultrafast demagnetization of ferromagnetic gadolinium and terbium

    NASA Astrophysics Data System (ADS)

    Teichmann, Martin; Frietsch, Björn; Döbrich, Kristian; Carley, Robert; Weinelt, Martin

    2015-01-01

    We compare the laser-driven demagnetization dynamics of the rare earths gadolinium and terbium by mapping their transient valance band structures with time- and angle-resolved photoelectron spectroscopy. In both metals, the minority and majority spin valence bands evolve independently with different time constants after optical excitation. The ultrafast shift of the partially unoccupied minority spin bulk band to higher binding energy and of the majority spin surface state to lower binding energy suggests spin transport between surface and bulk. The slower response of the fully occupied majority spin band follows the lattice temperature and is attributed to Elliott-Yafet type spin-flip scattering. Terbium shows a stronger and faster decay of the exchange splitting, pointing to ultrafast magnon emission via 4 f spin-to-lattice coupling.

  5. Solving complex band structure problems with the FEAST eigenvalue algorithm

    NASA Astrophysics Data System (ADS)

    Laux, S. E.

    2012-08-01

    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 problems—as exemplified by the complex band-structure problem—even 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.

  6. Spatio-temporal structure of migrating chemotactic band of Escherichia coli. I. Traveling band profile.

    PubMed Central

    Holz, M; Chen, S H

    1979-01-01

    We developed a rapid-scanning, light-scattering densitometer by which extensive measurements of band migration speeds and band profiles of chemotactic bands of Escherichia coli in motility buffer both with and without serine have been made. The purpose is to test the applicability of the phenomenological model proposed by Keller and Segel (J. Theor. Biol. 1971. 30:235) and to determine the motility (mu) and chemotactic (delta) coefficients of the bacteria. We extend the previous analytical solution of the simplified Keller-Segel model by taking into account the substrate diffusion which turns out to be significant in the case of oxygen. We demonstrate that unique sets of values of mu and delta can be obtained for various samples at different stages of migration by comparing the numerical solution of the model equation and the experimental data. The rapid-scanning technique also reveals a hitherto unobserved time-dependent fine structure in the bacterial band. We give a qualitative argument to show that the fine structure is an example of the dissipative structure that arises from a nonlinear coupling between the bacterial density and the oxygen concentration gradient. Implications for a further study of the dissipative structure in testing the Keller-Segel model of chemotaxis are briefly discussed. Images FIGURE 2 PMID:400469

  7. FabryPerot effects in THz time-domain spectroscopy of plasmonic band-gap structures

    E-print Network

    Peinke, Joachim

    Fabry­Perot effects in THz time-domain spectroscopy of plasmonic band-gap structures J. W. Lee, M were reported in the tera- hertz THz region.13­16 We however note that Fabry­Perot resonance has never coupled surface plasmons in the optical and THz regions. In this letter, we explicitly show

  8. Electronic band structure and Kondo coupling in YbRh2Si2

    SciTech Connect

    Wigger, G.A.

    2010-04-15

    The electronic band structure of YbRh2Si2 is calculated in a relativistic framework including correlation corrections and magnetization of the Yb ion and compared to detailed angle-resolved photoemission spectra. The photoemission spectra for LuRh2Si2 are used as reference to identify electronic bands with no f symmetry. The calculated band structure manifests a 4f13 spin-polarized configuration leaving the unoccupied state at 1.4eV above the Fermi energy. At the band theory level, the 4f bands are located far below the Fermi level and the anisotropic Coulomb interaction within the 4f shell spreads the multilevel into broader 4f complexes below -2.5eV . The photoemission spectra obtained on YbRh2Si2 show a clear f -multilevel splitting into j=7/2 and 5/2 excitations. The interaction of the 4f7/2 levels close to the Fermi energy with two conduction bands shows visible hybridization gaps of 45 and 80meV, respectively. We discuss the origin of these excitations and provide an analysis according to Anderson's single-impurity model with parameters suggested by the band-structure calculation and the photoemission spectra. Both experiment and theory indicate nearly identical Fermi surfaces for LuRh2Si2 and YbRh2Si2 . The valency of Yb in YbRh2Si2 is estimated to be close to +3.

  9. Imaging the spotty surface of Betelgeuse in the H band

    NASA Astrophysics Data System (ADS)

    Haubois, X.; Perrin, G.; Lacour, S.; Verhoelst, T.; Meimon, S.; Mugnier, L.; Thiébaut, E.; Berger, J. P.; Ridgway, S. T.; Monnier, J. D.; Millan-Gabet, R.; Traub, W.

    2009-12-01

    Aims. This paper reports on H-band interferometric observations of Betelgeuse made at the three-telescope interferometer IOTA. We image Betelgeuse and its asymmetries to understand the spatial variation of the photosphere, including its diameter, limb darkening, effective temperature, surrounding brightness, and bright (or dark) star spots. Methods: We used different theoretical simulations of the photosphere and dusty environment to model the visibility data. We made images with parametric modeling and two image reconstruction algorithms: MIRA and WISARD. Results: We measure an average limb-darkened diameter of 44.28 ± 0.15 mas with linear and quadratic models and a Rosseland diameter of 45.03 ± 0.12 mas with a MARCS model. These measurements lead us to derive an updated effective temperature of 3600 ± 66 K. We detect a fully-resolved environment to which the silicate dust shell is likely to contribute. By using two imaging reconstruction algorithms, we unveiled two bright spots on the surface of Betelgeuse. One spot has a diameter of about 11 mas and accounts for about 8.5% of the total flux. The second one is unresolved (diameter < 9 mas) with 4.5% of the total flux. Conclusions: Resolved images of Betelgeuse in the H band are asymmetric at the level of a few percent. The MOLsphere is not detected in this wavelength range. The amount of measured limb-darkening is in good agreement with model predictions. The two spots imaged at the surface of the star are potential signatures of convective cells.

  10. Dual-band perfect absorption and field enhancement by interaction between localized and propagating surface plasmons in optical metamaterials

    NASA Astrophysics Data System (ADS)

    Ding, Pei; Liang, Erjun; Cai, Genwang; Hu, Weiqin; Fan, Chunzhen; Xue, Qianzhong

    2011-07-01

    Dual-band perfect absorbers involving an array of gold nanoellipsoids or nanoellipsoid dimers near a gold film are designed and their resonance absorptions and field enhancements are numerically investigated. It is shown that the multilayer structures combining gold nanoparticles and gold film enable dual-band higher absorption and larger field enhancement than the structures without the metal film, due to the strong coupling between the localized surface plasmon resonance from the particles or particle dimers and the surface plasmon polaritons from the gold film. A field enhancement factor (|E|/|E0|) of more than 102 is achieved at the positions of 2.5 nm from the particle tip at two distinct wavelengths in the surface-plasmon-coupled nanoellipsoid dimer structure. The results suggest that the coupling of the localized surface plasmon resonance and the surface plasmon polaritons excited in the plasmonic metamaterials may have potential applications for multifrequency absorbers, emitters and SERS substrates as well as sensing.

  11. Plasmonic band structures and optical properties of subwavelength metal/dielectric/metal Bragg waveguides.

    PubMed

    Li, Chao; Zhou, Yun-Song; Wang, Huai-Yu

    2012-03-26

    In this paper, we applied the band structure theory to investigate the plasmonic band (PB) structures and optical properties of subwavelength metal/dielectric/metal Bragg waveguides in the near infrared range with either dielectric or geometric modulation. The Bloch wave vector, density of states, slowdown factor, propagation length and transmittance are calculated and analyzed. Both the modulations are in favor of manipulating surface-plasmon-polariton (SPP) waves. For the dielectric modulation, the PB structure is mainly formed by SPP modes and possesses a "regular pattern" in which the bands and gaps have a relatively even distribution. For the geometric modulation, due to the strong transverse scattering, the contributions of higher modes have to be considered and the gap widths have a significant increase compared to the dielectric modulation. A larger slowdown factor may emerge at the band edge; especially for the geometric modulation, the group velocity can be reduced to 1/100 of light, and negative group velocity is observed as well. While inside the bands, the slowdown factor is smaller and the bands are flat. The contribution of each eigenmode to the PB structure is analyzed. PMID:22453451

  12. Theoretical Study of Tip-Induced Band Bending and Local Tunneling Barrier Height on H-Terminated Si(100) Surface

    Microsoft Academic Search

    Hideomi Totsuka; Satoshi Watanabe

    2008-01-01

    In scanning tunneling microscopy (STM) measurements on semiconductor surfaces, tip-induced band bending (TIBB) occurs due to the applied high bias voltage, and influences the local electronic structures of the surface detected by STM and scanning tunneling spectroscopy (STS). Recently, Yoshida et al. have reported the effect of the TIBB on local tunneling barrier height (LBH) on Si(100) surfaces by light-modulated

  13. Structural Studies of Oxide Surfaces

    NASA Astrophysics Data System (ADS)

    Gustafsson, T.; Garfunkel, E.; Gusev, E. P.; Häberle, P.; Lu, H. C.; Zhou, J. B.

    We review some recent ion scattering experiments on the structure of oxide surfaces. We show that the MgO(100) surface exhibits very small surface distortions, in agreement with recent theoretical work. For the case of the oxidation of Si(100), we show that the oxidation proceeds in three different spatially separate regions, something which disagrees with the conventional model for silicon oxidation.

  14. Switching band-gaps of a phononic crystal slab by surface instability

    NASA Astrophysics Data System (ADS)

    Bayat, Alireza; Gordaninejad, Faramarz

    2015-07-01

    High-amplitude wrinkle formation is employed to propose a one-dimensional phononic crystal slab consists of a thin film bonded to a thick compliant substrate. Buckling induced surface instability generates a wrinkly structure triggered by a compressive strain. It is demonstrated that a surface periodic pattern and corresponding stress can control elastic wave propagation in the low thickness composite slab. Simulation results show that the periodic wrinkly structure can be used as a transformative phononic crystal that can switch the band diagram of the structure in a reversible manner. The results of this study provide opportunities for the smart design of tunable switches and frequency filters at ultrasonic and hypersonic frequency ranges.

  15. Surface conduction in encapsulated topological gated structures

    NASA Astrophysics Data System (ADS)

    Deshko, Yury; Korzhovska, Inna; Zhao, Lukas; Arefe, Ghidewon; Konczykowski, Marcin; Krusin-Elbaum, Lia

    2015-03-01

    In three-dimensional (3D) topological insulators (TIs), the surface Dirac fermions intermix with the conducting bulk, thereby complicating access to the low-energy surface charge transport or magnetic response. The subsurface 2D states of bulk origin are vulnerable to bandbending due to surface adatoms, a band modification thought to be responsible for the `ageing' effect. To minimize this effect, we have developed an inert environment mechanical exfoliation technique to fabricate transistor-like gated structures in which prototypical binary TIs as well as ultra-low bulk carrier density ternaries (such as Bi2Te2Se) were encapsulated by thin h-BN layers, with electrical contacts made using exfoliated graphene. The effects of electrostatic tuning by the gate bias voltage on surface conductivity as a function of thickness of the TI layers and the variation with disorder will be presented. Supported by NSF-DMR-1312483, and DOD-W911NF-13-1-0159.

  16. Linear bands, zero-momentum Weyl semimetal, and topological transition in skutterudite-structure pnictides

    NASA Astrophysics Data System (ADS)

    Pardo, V.; Smith, J. C.; Pickett, W. E.

    2012-06-01

    It was reported earlier [Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.106.056401 106, 056401 (2011)] that the skutterudite structure compound CoSb3 displays a unique band structure with a topological transition versus a symmetry-preserving sublattice (Sb) displacement very near the structural ground state. The transition is through a massless Dirac-Weyl semimetal, point Fermi surface phase which is unique in that (1) it appears in a three-dimensional crystal, (2) the band critical point occurs at k=0, and (3) linear bands are degenerate with conventional (massive) bands at the critical point (before inclusion of spin-orbit coupling). Further interest arises because the critical point separates a conventional (trivial) phase from a topological phase. In the native cubic structure this is a zero-gap topological semimetal; we show how spin-orbit coupling and uniaxial strain converts the system to a topological insulator (TI). We also analyze the origin of the linear band in this class of materials, which is the characteristic that makes them potentially useful in thermoelectric applications or possibly as transparent conductors. We characterize the formal charge as Co+ d8, consistent with the gap, with its 3¯ site symmetry, and with its lack of moment. The Sb states are characterized as px (separately, py) ?-bonded Sb4 ring states occupied and the corresponding antibonding states empty. The remaining (locally) pz orbitals form molecular orbitals with definite parity centered on the empty 2a site in the skutterudite structure. Eight such orbitals must be occupied; the one giving the linear band is an odd orbital singlet A2u at the zone center. We observe that the provocative linearity of the band within the gap is a consequence of the aforementioned near-degeneracy, which is also responsible for the small band gap.

  17. Band-structure loops and multistability in cavity QED

    SciTech Connect

    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)

    2011-06-15

    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)].

  18. Band-structure loops and multistability in cavity QED

    NASA Astrophysics Data System (ADS)

    Prasanna Venkatesh, B.; Larson, J.; O'Dell, D. H. J.

    2011-06-01

    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 , Phys. Rev. APLRAAN1050-294710.1103/PhysRevA.80.043803 80, 043803 (2009); Prasanna Venkatesh , Phys. Rev. APLRAAN1050-294710.1103/PhysRevA.80.063834 80, 063834 (2009)].

  19. Phase Diagrams and Band Structure of Transition Metal Compounds

    Microsoft Academic Search

    Göran Grimvall; Jan Häglund; Armando Fernández Guillermet

    1993-01-01

    Phase diagrams and phase stabilities have in the past been dealt with using different approaches. In the Calphad method one seeks a description of the Gibbs energy function G(T) which is accurate enough to be used in calculations of phase diagrams for complex alloys. Ab initio electron band structure calculations, on the other hand, have been used to predict the

  20. Photonic Band Gap structures: A new approach to accelerator cavities

    SciTech Connect

    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

    1992-12-31

    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.

  1. Synchrotron Methods of the Conduction Band Electronic Structure Analysis

    Microsoft Academic Search

    A. Kisiel

    2008-01-01

    The experimental and theoretical studies of the density of states for unoccupied conduction band are a valid source of knowledge on the electronic structure of condensed matter. Among known analytical methods of density of states for unoccupied states a significant place is occupied by the methods with the use of intensive synchrotron radiation beam. Adequately chosen monochromatic beam excites electrons

  2. Unfolding of collapsed polymers in shear flow: effects of colloid banding structures in confining channels.

    PubMed

    Chen, Hsieh; Alexander-Katz, Alfredo

    2014-03-01

    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. PMID:24730867

  3. Microwave applications of photonic band-gap (PBG) structures

    Microsoft Academic Search

    Yongxi Qian; Tatsuo Itoh

    1999-01-01

    Photonic band-gap (PBG) structures are essentially periodic lattices which can provide effective and flexible control of the propagation of electromagnetic waves along specific or all directions. This paper gives an overview of a novel planar-oriented PBG structure developed recently at the authors group. This uniplanar compact PBG (UC-PBG) lattice is very simple to implement, and its usefulness has been demonstrated

  4. Surface electronic structure of corundum transition-metal oxides: Ti2O3

    Microsoft Academic Search

    Richard L. Kurtz; Victor E. Henrich

    1982-01-01

    The surface electronic structure of Ti2O3 has been studied on single-crystal samples cleaved in ultrahigh vacuum. Ultraviolet photoelectron spectroscopy, electron-energy-loss spectroscopy, etc., have been used to study nearly perfect surfaces, surfaces containing defects, and O2 chemisorption on both types of surfaces. Cleavage surfaces have a band structure essentially the same as the bulk, with a (1.4+\\/-0.1)-eV-wide Ti 3d a1g band

  5. L-band radiometric behaviour of pine forests for a variety of surface moisture conditions

    E-print Network

    Paris-Sud XI, Université de

    n.1 L-band radiometric behaviour of pine forests for a variety of surface moisture conditions J, using a multi-angle L-band (1.4 GHz) radiometer to measure upwelling radiation above the forest in the context of the upcoming SMOS mission in order to improve our understanding of the behaviour of the L-band

  6. Inter-band optoelectronic properties in quantum dot structure of low band gap III-V semiconductors

    SciTech Connect

    Dey, Anup, E-mail: a-dey2002@yahoo.com [Electronics and Communication Engineering Department, Kalyani Government Engineering College, Kalyani 741235 (India); Maiti, Biswajit [Physics Department, Kalyani Government Engineering College, Kalyani 741235 (India); Chanda, Debasree [Department of Engineering and Technological Studies, Kalyani University, Kalyani 741235 (India)

    2014-04-14

    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{sup ?}) 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, Hg{sub 1?x}Cd{sub x}Te, and In{sub 1?x}Ga{sub x}As{sub y}P{sub 1?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.

  7. Electronic band structure of magnetic bilayer graphene superlattices

    SciTech Connect

    Pham, C. Huy; Nguyen, T. Thuong [Theoretical and Computational Physics Department, Institute of Physics, VAST, 10 Dao Tan, Ba Dinh Distr., Hanoi 10000 (Viet Nam); SISSA/International School for Advanced Study, Via Bonomea 265, I-34136 Trieste (Italy); Nguyen, V. Lien, E-mail: nvlien@iop.vast.ac.vn [Theoretical and Computational Physics Department, Institute of Physics, VAST, 10 Dao Tan, Ba Dinh Distr., Hanoi 10000 (Viet Nam); Institute for Bio-Medical Physics, 109A Pasteur, 1st Distr., Hochiminh City (Viet Nam)

    2014-09-28

    Electronic band structure of the bilayer graphene superlattices with ?-function magnetic barriers and zero average magnetic flux is studied within the four-band continuum model, using the transfer matrix method. The periodic magnetic potential effects on the zero-energy touching point between the lowest conduction and the highest valence minibands of pristine bilayer graphene are exactly analyzed. Magnetic potential is shown also to generate the finite-energy touching points between higher minibands at the edges of Brillouin zone. The positions of these points and the related dispersions are determined in the case of symmetric potentials.

  8. Tuning of a hypersonic surface phononic band gap using a nanoscale two-dimensional lattice of pillars

    NASA Astrophysics Data System (ADS)

    Graczykowski, B.; Mielcarek, S.; Trzaskowska, A.; Sarkar, J.; Hakonen, P.; Mroz, B.

    2012-08-01

    We present experimental and theoretical evidence of a phononic band gap in a hypersonic range for thermally activated surface acoustic waves in two-dimensional (2D) phononic crystals. Surface Brillouin light scattering experiments were performed on the (001) surface of silicon, loaded with a 2D square lattice of 100- or 150-nm-high aluminum pillars with a spacing of 500nm. The surface Brillouin light scattering spectra revealed a different type of surface mode, related to the modulation of the lattice structure and the mechanical eigenmodes of the pillars. The experimental data were in excellent agreement with theoretical calculations performed using the finite-element method.

  9. Experimental verification of directional liquid surface wave emission at band edge frequencies

    NASA Astrophysics Data System (ADS)

    Wang, Zhenyu; Zhang, Pei; Zhang, Yongqiang; Nie, Xiaofei

    2013-12-01

    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.

  10. Ultranarrow band absorbers based on surface lattice resonances in nanostructured metal surfaces.

    PubMed

    Li, Zhongyang; Butun, Serkan; Aydin, Koray

    2014-08-26

    Nanostructured metals have received a significant amount of attention in recent years due to their exciting plasmonic and photonic properties enabling strong field localization, light concentration, and strong absorption and scattering at their resonance frequencies. Resonant plasmonic and metamaterial absorbers are of particular interest for applications in a wide variety of technologies including photothermal therapy, thermophotovoltaics, heat-assisted magnetic recording, hot-electron collection, and biosensing. However, it is rather challenging to realize ultranarrow absorption bands using plasmonic materials due to large optical losses in metals that decrease the quality factor of optical resonators. Here, we theoretically and experimentally demonstrate an ultranarrow band absorber based on the surface lattice resonances (SLRs) in periodic nanowire and nanoring arrays on optically thick, reflecting metallic films. In experiments, we observed ultranarrow band resonant absorption peaks with a bandwidth of 12 nm and absorption amplitude exceeding 90% at visible frequencies. We demonstrate that the resonance absorption wavelength, amplitude of the absorption peak, and the bandwidth can be controlled by tuning the periodicity and the thickness of nanoring and nanowire arrays. Unlike conventional plasmonic absorbers utilizing common metal–insulator–metal stacks, our narrow band absorber consists solely of metals, facilitating stronger optical interaction between the SLR of periodic nanostructures and the highly reflective film. Moreover, by introducing asymmetry to the nanoring/nanowire hybrid system, we observe the spectral evolution of resonance splitting enabled by strong coupling between two individual SLRs arising from nanoring and nanowire arrays. Designing such all-metallic nanostructure arrays is a promising route for achieving ultranarrow band absorbers which can be used as absorption filters, narrow band thermal emitters in thermophotovoltaics, and plasmonic biosensors. PMID:25072803

  11. Omnidirectional elastic band gap in finite lamellar structures.

    PubMed

    Bria, D; Djafari-Rouhani, B

    2002-11-01

    This paper presents a comprehensive theoretical analysis of the occurrence of omnidirectional reflection in one-dimensional phononic crystal structures. We discuss the conditions for a one-dimensional layered structure, made of elastic materials, to exhibit total reflection of acoustic incident waves in a given frequency range, for all incident angles and all polarizations. The property of omnidirectional reflection can be fulfilled with a simple finite superlattice if the substrate from which the incident waves are launched is made of a material with high acoustic velocities (this is very similar to the case of omnidirectional optical mirror where the incident light is generated in vacuum). However, if the substrate is made of a material with low acoustic velocities, we propose two solutions to obtain an omnidirectional band gap, namely, the cladding of a superlattice with a layer of high acoustic velocities, which acts like a barrier for the propagation of phonons, or the association in tandem of two different superlattices in such a way that the superposition of their band structures exhibits an absolute acoustic band gap. We discuss the appropriate choices of the material and geometrical properties to realize such structures. The behavior of the transmission coefficients are discussed in relation with the dispersion curves of the finite structure embedded between two substrates. Both transmission coefficients and densities of states (from which we derive the dispersion curves) are calculated in the framework of a Green's function method. PMID:12513625

  12. Omnidirectional elastic band gap in finite lamellar structures

    NASA Astrophysics Data System (ADS)

    Bria, D.; Djafari-Rouhani, B.

    2002-11-01

    This paper presents a comprehensive theoretical analysis of the occurrence of omnidirectional reflection in one-dimensional phononic crystal structures. We discuss the conditions for a one-dimensional layered structure, made of elastic materials, to exhibit total reflection of acoustic incident waves in a given frequency range, for all incident angles and all polarizations. The property of omnidirectional reflection can be fulfilled with a simple finite superlattice if the substrate from which the incident waves are launched is made of a material with high acoustic velocities (this is very similar to the case of omnidirectional optical mirror where the incident light is generated in vacuum). However, if the substrate is made of a material with low acoustic velocities, we propose two solutions to obtain an omnidirectional band gap, namely, the cladding of a superlattice with a layer of high acoustic velocities, which acts like a barrier for the propagation of phonons, or the association in tandem of two different superlattices in such a way that the superposition of their band structures exhibits an absolute acoustic band gap. We discuss the appropriate choices of the material and geometrical properties to realize such structures. The behavior of the transmission coefficients are discussed in relation with the dispersion curves of the finite structure embedded between two substrates. Both transmission coefficients and densities of states (from which we derive the dispersion curves) are calculated in the framework of a Green's function method.

  13. Mid-frequency Band Dynamics of Large Space Structures

    NASA Technical Reports Server (NTRS)

    Coppolino, Robert N.; Adams, Douglas S.

    2004-01-01

    High and low intensity dynamic environments experienced by a spacecraft during launch and on-orbit operations, respectively, induce structural loads and motions, which are difficult to reliably predict. Structural dynamics in low- and mid-frequency bands are sensitive to component interface uncertainty and non-linearity as evidenced in laboratory testing and flight operations. Analytical tools for prediction of linear system response are not necessarily adequate for reliable prediction of mid-frequency band dynamics and analysis of measured laboratory and flight data. A new MATLAB toolbox, designed to address the key challenges of mid-frequency band dynamics, is introduced in this paper. Finite-element models of major subassemblies are defined following rational frequency-wavelength guidelines. For computational efficiency, these subassemblies are described as linear, component mode models. The complete structural system model is composed of component mode subassemblies and linear or non-linear joint descriptions. Computation and display of structural dynamic responses are accomplished employing well-established, stable numerical methods, modern signal processing procedures and descriptive graphical tools. Parametric sensitivity and Monte-Carlo based system identification tools are used to reconcile models with experimental data and investigate the effects of uncertainties. Models and dynamic responses are exported for employment in applications, such as detailed structural integrity and mechanical-optical-control performance analyses.

  14. Photoelectron spectroscopic study of band alignment of polymer/ZnO photovoltaic device structure

    SciTech Connect

    Nagata, T.; Chikyow, T. [International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044 (Japan)] [International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044 (Japan); Oh, S.; Wakayama, Y. [International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044 (Japan) [International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044 (Japan); Department of Chemistry and Biochemistry, Faculty of Engineering, Kyushu University, 1-1 Namiki, Tsukuba 305-0044 (Japan); Yamashita, Y. [International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044 (Japan) [International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044 (Japan); NIMS Beamline Station at SPring-8, National Institute for Materials Science, 1-1-1 Koto, Sayo-cho, Sayo-gun, Hyogo 679-5148 (Japan); Yoshikawa, H.; Kobayashi, K. [NIMS Beamline Station at SPring-8, National Institute for Materials Science, 1-1-1 Koto, Sayo-cho, Sayo-gun, Hyogo 679-5148 (Japan)] [NIMS Beamline Station at SPring-8, National Institute for Materials Science, 1-1-1 Koto, Sayo-cho, Sayo-gun, Hyogo 679-5148 (Japan); Ikeno, N. [International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044 (Japan) [International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044 (Japan); Nanotechnology Laboratory, Meiji University, 1-1-1 Higashimita, Tama-ku, Kawasaki, Kanagawa 214-8571 (Japan)

    2013-01-28

    Using x-ray photoelectron spectroscopy, we investigated the band alignment of a Ag/poly(3-hexylthiophene-2,5-diyl) (P3HT)/ZnO photovoltaic structure. At the P3HT/ZnO interface, a band bending of P3HT and a short surface depletion layer of ZnO were observed. The offset between the highest occupied molecular orbital of P3HT and the conduction band minimum of ZnO at the interface contributed to the open circuit voltage (Voc) was estimated to be approximately 1.5 {+-} 0.1 eV, which was bigger than that of the electrically measured effective Voc of P3HT/ZnO photovoltaic devices, meaning that the P3HT/ZnO photovoltaic structure has the potential to provide improved photovoltaic properties.

  15. Band structure parameters for quantum wells: Magnetoluminescence determinations

    SciTech Connect

    Jones, E.D.

    1997-04-01

    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.

  16. Microstrip antennas integrated with electromagnetic band-gap (EBG) structures: a low mutual coupling design for array applications

    Microsoft Academic Search

    Fan Yang; Yahya Rahmat-Samii

    2003-01-01

    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

  17. Surface electromagnetic wave excitation on one-dimensional photonic band-gap arrays

    Microsoft Academic Search

    W. M. Robertson; M. S. May

    1999-01-01

    Experiments are described on the prism-coupled excitation of surface electromagnetic waves in one-dimensional photonic band-gap arrays. The low loss of photonic band-gap materials leads to narrow angular reflectivity resonances and high surface fields. These attributes, coupled with the ability to engineer the optical properties of photonic band-gap arrays, suggest these materials as powerful replacements for metal films in many applications

  18. Wireless Channel Characterization in the 5 GHz Microwave Landing System Extension Band for Airport Surface Areas

    NASA Technical Reports Server (NTRS)

    Matolak, David W.

    2007-01-01

    In this project final report, entitled "Wireless Channel Characterization in the 5 GHz Microwave Landing System Extension Band for Airport Surface Areas," we provide a detailed description and model representation for the wireless channel in the airport surface environment in this band. In this executive summary, we review report contents, describe the achieved objectives and major findings, and highlight significant conclusions and recommendations.

  19. Tunable and sizable band gap in silicene by surface adsorption

    NASA Astrophysics Data System (ADS)

    Quhe, Ruge; Fei, Ruixiang; Liu, Qihang; Zheng, Jiaxin; Li, Hong; Xu, Chengyong; Ni, Zeyuan; Wang, Yangyang; Yu, Dapeng; Gao, Zhengxiang; Lu, Jing

    2012-11-01

    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.

  20. Conduction-band states and surface core excitons in InSb(110) and other III-V compounds

    NASA Astrophysics Data System (ADS)

    Faul, Jürgen; Neuhold, Georg; Ley, Lothar; Fraxedas, Jordi; Zollner, Stefan; Riley, John D.; Leckey, Robert C. G.

    1994-09-01

    Angle-resolved constant-initial-state spectroscopy from the valence-band maximum (VBM) as the initial state was used to determine the conduction-band energies at the ? point up to 30 eV above the VBM for InSb. Structure in the spectra up to 20 eV could be assigned to particular interband transitions by comparison with empirical pseudopotential calculations. Autoionizing resonances due to surface core excitons have been observed. From their energies a surface-core-exciton binding energy of 0.5 eV for InSb has been determined. Both results are discussed in light of our previous work on the conduction-band states and surface core exditons of several III-V semiconductors.

  1. Domain Structures in Nematic Liquid Crystals on a Polycarbonate Surface

    PubMed Central

    Parshin, Alexander M.; Gunyakov, Vladimir A.; Zyryanov, Victor Y.; Shabanov, Vasily F.

    2013-01-01

    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

  2. Electron band structure of the high pressure cubic phase of AlH3

    NASA Astrophysics Data System (ADS)

    Shi, Hongliang; Zarifi, Niliffar; Yim, Wai-Leung; Tse, J. S.

    2012-07-01

    The electronic band structure of the cubic Pm3n phase of AlH3 stable above 100 GPa is examined with semi-local, Tran-Blaha modified Becke-Johnson local density approximation (TB-mBJLDA), screened hybrid density functionals and GW methods. The shift of the conduction band to higher energy with increasing pressure is predicted by all methods. However, there are significant differences in detail band structure. In the pressure range from 90 to160 GPa, semi-local, hybrid functional and TB-mBJLDA calculations predicted that AlH3 is a poor metal. In comparison, GW calculations show a gap opening at 160 GPa and AlH3 becomes a small gap semi-conductor. From the trends of the calculated band shifts, it can be concluded that the favourable conditions leading to the nesting of Fermi surfaces predicted by semi-local calculation have disappeared if the exchange term is included. The results highlight the importance of the correction to the exchange energy on the band structure of hydrogen dominant dense metal hydrides at high pressure hydrides and may help to rationalize the absence of superconductivity in AlH3 from experimental measurements.

  3. Banded structures in directionally solidified Ti-52Al alloys

    SciTech Connect

    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)

    1994-03-15

    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.

  4. Hybrid density functional theory band structure engineering in hematite

    Microsoft Academic Search

    Zachary D. Pozun; Graeme Henkelman

    2011-01-01

    We present a hybrid density functional theory (DFT) study of doping effects in alpha-Fe2O3, hematite. Standard DFT underestimates the band gap by roughly 75% and incorrectly identifies hematite as a Mott-Hubbard insulator. Hybrid DFT accurately predicts the proper structural, magnetic, and electronic properties of hematite and, unlike the DFT+U method, does not contain d-electron specific empirical parameters. We find that

  5. Determination of band structure dispersion curves by optical techniques

    SciTech Connect

    Jones, E.D.; Lyo, S.K.; Klem, J.F.

    1995-08-01

    Magnetic field effects upon the photoluminescence spectrum which provide unique information about semiconductor quantum well structures are discussed. Data which provide a simultaneous quantitative measure of both the conduction- and valence-band the energy dispersion curves for an InGaAs/GaAs single-strained-quantum well and a GaAs/AlGaAs lattice-matched single quantum well are presented.

  6. Analysis of photonic band-gap structures in stratified medium

    Microsoft Academic Search

    Ming-Sze Tong; Yinchao Chen; Yilong Lu; Viktor Krozer; Kenichi Kagoshima; Hyeong-Seok Kim; Tae-Gyu Chang

    2005-01-01

    Purpose – To demonstrate the flexibility and advantages of a non-uniform pseudo-spectral time domain (nu-PSTD) method through studies of the wave propagation characteristics on photonic band-gap (PBG) structures in stratified medium Design\\/methodology\\/approach – A nu-PSTD method is proposed in solving the Maxwell's equations numerically. It expands the temporal derivatives using the finite differences, while it adopts the Fourier transform (FT)

  7. Periodic Structures and Photonic-Band-Gap Terminology: Historical Perspectives

    Microsoft Academic Search

    Arthur A. Oliner

    1999-01-01

    This talk will summarize some of the major steps in the development of microwave periodic-structure theory, which has become highly developed and sophisticated over the years. The recent contributions made by the users of photonic-band-gap (PBG) terminology are then examined within the historical development in order to assess those contributions and the value to the microwave rield of PBG terminology.

  8. Exploring material flow in friction stir welding: Tool eccentricity and formation of banded structures

    Microsoft Academic Search

    F. Gratecap; M. Girard; S. Marya; G. Racineux

    Surface striations with spacing equal to feed rate per rotation and banded structures in the weld nugget are some of the striking\\u000a features of friction stir welding. However, their formation is still subject to some debate. This study contributes to comprehend\\u000a their formation by evaluating the possible role played by the eccentricity of the tool during the welding of an

  9. Thermodynamic implications of band structure effects for rare gases on graphite

    SciTech Connect

    Carlos, W.E.; Cole, M.W.; Rauber, S.; Vidali, G.; Silva-Moreira, A.F.; Codona, J.L.; Goodstein, D.L.

    1980-01-01

    Recent analyses of atomic beam scattering data have suggested that an anisotropic He-C pair interaction is appropriate to the problem of He on graphite. This results in considerably more corrugated equipotential surfaces than previously assumed, and correspondingly manifest band structure effects. These have been observed for He/graphite in the specific heat for temperature T > 3/sup 0/K. The implications for other gases and temperatures and for the effective adatom-adatom interaction are discussed.

  10. Band to band tunneling in III-V semiconductors: Implications of complex band structure, strain, orientation, and off-zone center contribution

    SciTech Connect

    Majumdar, Kausik, E-mail: kausik.majumdar@sematech.org [SEMATECH, 257 Fuller Road, STE 2200, Albany, New York 12203 (United States)

    2014-05-07

    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.

  11. Electronic Band Structure And Kondo Coupling in YbRh(2)Si(2)

    SciTech Connect

    Wigger, G.A.; Baumberger, F.; Shen, Z.X.; /Stanford U., Appl. Phys. Dept. /SLAC, SSRL; Yin, Z.P.; Pickett, W.E.; Maquilon, S.; Fisk, Z.; /UC, Davis

    2007-09-26

    The electronic band structure of YbRh{sub 2}Si{sub 2} is calculated in a relativistic framework including correlation corrections and magnetization of the Yb ion and compared to detailed angle-resolved photoemission spectra. The photoemission spectra for LuRh{sub 2}Si{sub 2} are used as reference to identify electronic bands with no f symmetry. The calculated band structure manifests a 4f{sup 13} spin-polarized configuration leaving the unoccupied state at 1.4 eV above the Fermi energy. At the band theory level, the 4f bands are located far below the Fermi level and the anisotropic Coulomb interaction within the 4f shell spreads the multilevel into broader 4f complexes below -2.5 eV. The photoemission spectra obtained on YbRh2Si2 show a clear f-multilevel splitting into j=7/2 and 5/2 excitations. The interaction of the 4f{sub 7/2} levels close to the Fermi energy with two conduction bands shows visible hybridization gaps of 45 and 80 meV, respectively. We discuss the origin of these excitations and provide an analysis according to Anderson's single-impurity model with parameters suggested by the band-structure calculation and the photoemission spectra. Both experiment and theory indicate nearly identical Fermi surfaces for LuRh{sub 2}Si{sub 2} and YbRh{sub 2}Si{sub 2}. The valency of Yb in YbRh{sub 2}Si{sub 2} is estimated to be close to +3.

  12. ForPeerReview Wheat canopy structure and surface roughness effects on

    E-print Network

    Boyer, Edmond

    ForPeerReview Wheat canopy structure and surface roughness effects on multi-angle observations at L-band roughness effects2 on multi-angle observations at L-band3 4 Sandy Peischl, Member, IEEE, Jeffrey P. Walker at multiple incidence angles using airborne L-band data from the26 National Airborne Field Experiment (NAFE

  13. Average band structure of smectic C? type random materials

    NASA Astrophysics Data System (ADS)

    Reyes Cervantes, Juan Adrian

    2014-03-01

    We consider a Smectic C? type structure which exhibits alignment fluctuations which can be described by noise associated with both director angles. We take the propagation of axially incident electromagnetic waves, and from Maxwell equations, we establish the stochastic governing set of equations corresponding to optical phenomena. We note that this set of equations can be expressed as a linear vector stochastic system of differential equations with multiplicative noise. We use a procedure to calculate from the stochastic differential set of equations, the governing equations for the expected value of the electromagnetic transverse magnetic and electric fields for a certain autocorrelation function, and calculate explicitly their corresponding band structure for a particular spectral noise density. We have shown that the average resulting electromagnetic fields exhibit a biased decaying exponential dependence which impedes to propagate the waves in one sense while it permits them in the other sense. We have also found a remarkable widening of the band gap and the appearance of new local maxima for the modes without band gap.

  14. Surface band bending and band alignment of plasma enhanced atomic layer deposited dielectrics on Ga- and N-face gallium nitride

    NASA Astrophysics Data System (ADS)

    Yang, Jialing; Eller, Brianna S.; Nemanich, Robert J.

    2014-09-01

    The effects of surface pretreatment, dielectric growth, and post deposition annealing on interface electronic structure and polarization charge compensation of Ga- and N-face bulk GaN were investigated. The cleaning process consisted of an ex-situ wet chemical NH4OH treatment and an in-situ elevated temperature NH3 plasma process to remove carbon contamination, reduce oxygen coverage, and potentially passivate N-vacancy related defects. After the cleaning process, carbon contamination decreased below the x-ray photoemission spectroscopy detection limit, and the oxygen coverage stabilized at ˜1 monolayer on both Ga- and N-face GaN. In addition, Ga- and N-face GaN had an upward band bending of 0.8 ± 0.1 eV and 0.6 ± 0.1 eV, respectively, which suggested the net charge of the surface states and polarization bound charge was similar on Ga- and N-face GaN. Furthermore, three dielectrics (HfO2, Al2O3, and SiO2) were prepared by plasma-enhanced atomic layer deposition on Ga- or N-face GaN and annealed in N2 ambient to investigate the effect of the polarization charge on the interface electronic structure and band offsets. The respective valence band offsets of HfO2, Al2O3, and SiO2 with respect to Ga- and N-face GaN were 1.4 ± 0.1, 2.0 ± 0.1, and 3.2 ± 0.1 eV, regardless of dielectric thickness. The corresponding conduction band offsets were 1.0 ± 0.1, 1.3 ± 0.1, and 2.3 ± 0.1 eV, respectively. Experimental band offset results were consistent with theoretical calculations based on the charge neutrality level model. The trend of band offsets for dielectric/GaN interfaces was related to the band gap and/or the electronic part of the dielectric constant. The effect of polarization charge on band offset was apparently screened by the dielectric-GaN interface states.

  15. Three-dimensional dynamic thermal imaging of structural flaws by dual-band infrared computed tomography

    NASA Astrophysics Data System (ADS)

    DelGrande, Nancy; Dolan, Kenneth W.; Durbin, Philip F.; Gorvad, Michael R.; Kornblum, B. T.; Perkins, Dwight E.; Schneberk, Daniel J.; Shapiro, Arthur B.

    1993-11-01

    We discuss three-dimensional dynamic thermal imaging of structural flaws using dual-band infrared (DBIR) computed tomography. Conventional (single-band) thermal imaging is difficult to interpret. It yields imprecise or qualitative information (e.g., when subsurface flaws produce weak heat flow anomalies masked by surface clutter). We use the DBIR imaging technique to clarify interpretation. We capture the time history of surface temperature difference patterns at the epoxy-glue disbond site of a flash-heated lap joint. This type of flawed structure played a significant role in causing damage to the Aloha Aircraft fuselage on the aged Boeing 737 jetliner. The magnitude of surface-temperature differences versus time for 0.1 mm air layer compared to 0.1 mm glue layer, varies from 0.2 to 1.6 degree(s)C, for simultaneously scanned front and back surfaces. The scans are taken every 42 ms from 0 to 8 s after the heat flash. By ratioing 3 - 5 micrometers and 8 - 12 micrometers DBIR images, we located surface temperature patterns from weak heat flow anomalies at the disbond site and remove the emissivity mask from surface paint of roughness variations. Measurements compare well with calculations based on TOPAX3D, a three-dimensional, finite element computer model. We combine infrared, ultrasound and x-ray imaging methods to study heat transfer, bond quality and material differences associated with the lap joint disbond site.

  16. The Submesoscale from VIIRS Imagery-Band (375 m) Sea Surface Temperature Fields

    NASA Astrophysics Data System (ADS)

    Cornillon, P. C.; Pan, G.; Schloesser, F.

    2014-12-01

    The Visible-Infrared Imager-Radiometer Suite (VIIRS) carried on the Suomi National Polar-orbiting Partnership (Suomi NPP) spacecraft makes measurements in spectral bands in the infrared at a nadir spatial resolution of 750 m, in what are referred to as the Moderate Resolution Bands (M-Bands), and at a nadir spatial resolution of 375 m in "Imagery Bands" (I-Bands). The spectral coverage of M-Bands allows for the high quality retrieval of sea surface temperature (SST) under cloud-free conditions. In particular, the M-Band suite includes a "split window" in the 10 to 12 micrometer range with which correction for atmospheric water vapor can be made while avoiding issues associated with solar reflection, which afflicts observations in some of the shorter wave-length spectral windows during daylight hours. Unfortunately, there is only one I-Band channel in the 10 to 12 micrometer range precluding the same approach used for M-Band retrievals. In this presentation, we discuss an algorithm developed at the University of Rhode Island that makes use of the atmospheric correction available from M-Band retrieval algorithms together with I-Band radiances to produce a high quality 375 m SST product. The M-Band retrievals used are those from NOAA's Advanced Clear Sky Processor for Oceans (ACSPO) program. In comparisons with ship-borne radiometer SST retrievals, we show that the I-Band retrievals are of similar quality to the underlying M-Band retrievals. We then go on to demonstrate the sub-kilometer scale of the features resolved in the I-Band retrievals as well as how these data may be used to infer near-surface currents on a spatial grid of order 10 kilometers.

  17. Surface structure determines dynamic wetting

    PubMed Central

    Wang, Jiayu; Do-Quang, Minh; Cannon, James J.; Yue, Feng; Suzuki, Yuji; Amberg, Gustav; Shiomi, Junichiro

    2015-01-01

    Liquid wetting of a surface is omnipresent in nature and the advance of micro-fabrication and assembly techniques in recent years offers increasing ability to control this phenomenon. Here, we identify how surface roughness influences the initial dynamic spreading of a partially wetting droplet by studying the spreading on a solid substrate patterned with microstructures just a few micrometers in size. We reveal that the roughness influence can be quantified in terms of a line friction coefficient for the energy dissipation rate at the contact line, and that this can be described in a simple formula in terms of the geometrical parameters of the roughness and the line-friction coefficient of the planar surface. We further identify a criterion to predict if the spreading will be controlled by this surface roughness or by liquid inertia. Our results point to the possibility of selectively controlling the wetting behavior by engineering the surface structure. PMID:25683872

  18. Dual-band metamaterial with a windmill-like structure

    NASA Astrophysics Data System (ADS)

    Xiong, Han; Hong, Jing-Song; Jin, Da-Lin

    2013-01-01

    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.

  19. Band structures and octupole correlation effects in 151Sm

    NASA Astrophysics Data System (ADS)

    Khan, M. K.; Vermeer, W. J.; Urban, W.; Fitzgerald, J. B.; Mowbray, A. S.; Varley, B. J.; Durell, J. L.; Phillips, W. R.

    1994-01-01

    Excited states in 151Sm were populated through the 150Nd(?, 3n) reaction at a beam energy of 35 MeV using a 9 mg/cm 2 thick 150Nd target. An array of twenty Compton-suppressed germanium detectors was used to detect ?? and triple-? coincidences. The prime aim of this work was to investigate the effects of octupole correlations in odd- A nuclei in the A ˜ 150, N ˜ 88 region. A total of fifteen bands has been observed in 151Sm and their decay patterns followed up to spins near 20 ?. Four ?I = 2 bands have some characteristics associated with parity-doublet structures. However, the evidence overall suggests that octupole correlations in 151Sm are too weak to produce stable octupole deformation.

  20. The OmniSaw device concept (OmniSAW: Omnidirectional band gap for surface acoustic wave)

    Microsoft Academic Search

    Abdelkrim Khelif; Abdelkrim Choujaa; Jean-yves Rauch; Valérie Pétréni; Hannane Moubchir; Sarah Benchabane; Vincent Laude

    2008-01-01

    We report the theoretical evidence for the occurrence of omnidirectional elastic band gap in one-dimensional phononic crystal structures. The structure is constituted by a periodic layered deposited on a specific substrate that exhibit total reflection of waves for all incident angles and polarizations in a given frequency range the omnidirectional band gap. We present the influence of the nature and

  1. Nutrient loss in leachate and surface runoff from surface-broadcast and subsurface-banded broiler litter

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Subsurface band application of poultry litter has been shown to reduce the transport of nutrients from fields in surface runoff, compared to the conventional surface broadcast application. Little in situ research has been conducted to determine effects of surface broadcast application and subsurfac...

  2. Optical processes in different types of photonic band gap structures

    NASA Astrophysics Data System (ADS)

    Wang, Zhiguo; Gao, Mengqin; Ullah, Zakir; Chen, Haixia; Zhang, Dan; Zhang, Yiqi; Zhang, Yanpeng

    2015-06-01

    For the first time, we investigate the photonic band gap (PBG) structure in the static and moving electromagnetically induced grating (EIG) through scanning the frequency detunings of the probe field, dressing field and coupling field. Especially, the suppression and enhancement of the four wave mixing band gap signal (FWM BGS) and the probe transmission signal (PTS) can be observed when we scan the dressing field frequency detuning in the FWM BGS system. It is worth noting that the PBG structure and FWM BGS appear at the right of the electromagnetically induced transparency (EIT) position in the case of scanning the frequency detuning of the coupling field in the FWM BGS system, while the PBG structure and FWM BGS appears at the left of the EIT position on the condition of scanning the probe field frequency detuning. Moreover, in the moving PBG structure, we can obtain the nonreciprocity of FWM BGS. Furthermore, we can modulate the intensity, width, location of the FWM BGS and PTS through changing the frequency detunings and intensities of the probe field, dressing field and coupling field, sample length and the frequency difference of coupling fields in EIG. Such scheme could have potential applications in optical diodes, amplifiers and quantum information processing.

  3. Collective band structures in the 99Tc nucleus

    NASA Astrophysics Data System (ADS)

    Li, H. J.; Xiao, Z. G.; Zhu, S. J.; Patial, M.; Qi, C.; Cederwall, B.; Zhang, Z.; Wang, R. S.; Yi, H.; Yan, W. H.; Cheng, W. J.; Huang, Y.; Lyu, L. M.; Zhang, Y.; Wu, X. G.; He, C. Y.; Zheng, Y.; Li, G. S.; Li, C. B.; Li, H. W.; Liu, J. J.; Luo, P. W.; Hu, S. P.; Wang, J. L.; Wu, Y. H.

    2015-05-01

    Excited states in 99Tc with energies up to 6 MeV have been populated using the 96Zr(7Li,4 n )99Tc reaction with a laboratory beam energy of 35 MeV. Coincident ? rays from excited nuclei produced in the reactions were detected using an array of coaxial, planar, and clover-type high-purity germanium detectors. A total of 60 new ? -ray transitions and 21 new levels are identified and placed into a new level scheme. Two collective bands assigned to be built on the ? g9 /2 [422 ]5 /2 + and ? p1 /2 [301 ]1 /2 - Nilsson configurations have been extended with spins up to 35/2 and 33 /2 ? , respectively. Backbending and signature inversion have been observed in the yrast band. The large signature splitting of the positive-parity band in 99Tc may be caused by a triaxial deformation, which agrees well with the electromagnetic properties, theoretical calculations based on total Routhian surface, and triaxial particle-rotor model calculations.

  4. Effects of surface oxide formation on germanium nanowire band-edge photoluminescence

    SciTech Connect

    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)

    2013-06-24

    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.

  5. Survival of hydrogen anions near atomically flat metal surfaces: Band gap confinement and image state recapture effects

    NASA Astrophysics Data System (ADS)

    Schmitz, Andrew; Shaw, John; Chakraborty, Himadri; Thumm, Uwe

    2010-03-01

    Resonant charge transfer (RCT) between ions and surfaces is a key intermediate step in surface-chemical processes as well as in micro- and nano-fabrications on the surface. The RCT process in the collision of hydrogen anions with metal surfaces is described within a wave packet propagation methodology using Crank-Nicholson algorithm [1]. The ion-survival probability is found to strongly enhance at two different ion velocities perpendicular to the surface. The low velocity enhancement is induced from a dynamical confinement of the ion level inside the band gap, while the high velocity enhancement emerges owing to the recapture from transiently populated image states [2]. These structures are found to be somewhat sensitive to the ion's distance of closest approach to the surface and the choice of inter-atomic potentials between the ion and the surface atoms. [1] Chakraborty et al., Phys. Rev. A 70, 052903 (2004); [2] Schmitz et al., Phys. Rev. A (submitted).

  6. The effect of spin-orbit coupling in band structure of few-layer graphene

    SciTech Connect

    Sahdan, Muhammad Fauzi, E-mail: sahdan89@yahoo.co.id; Darma, Yudi, E-mail: sahdan89@yahoo.co.id [Department of Physics, Institut Teknologi Bandung, Jalan Ganesa 10, Bandung 40132 (Indonesia)

    2014-03-24

    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.

  7. Complex Band Structure of the Topological Insulator Bi2Se3

    NASA Astrophysics Data System (ADS)

    Li, Shijie; Betancourt, Jesuan; Burton, J. D.; Velev, Julian P.; Tsymbal, Evgeny Y.

    2015-03-01

    Recently there is a surge of interest in using topological insulators for electronic and spintronic applications. For applications it is important to understand the complex band structure (CBS) of the topological insulator, which determines the decay rate of the protected surface states into the bulk of the material. The Bi2Se3 family of three-dimensional topological insulators is the most studied and best understood. In this work we investigate the CBS of Bi2Se3 using first-principles density-functional calculations. We determine the decay rates and the symmetry of the evanescent states and we follow their evolution from those of the band insulator. We complement these results with Bi2Se3 (0001) slab calculations to explore the penetration depth, oscillatory behavior and spin texture of the surface states. The CBS provides a new insight into the topologically protected states and could be used for the search of new topological insulators and device concepts.

  8. A W-band Surface Micromachined Monopole for Low-cost Wireless Communication Systems

    E-print Network

    Papapolymerou, Ioannis "John"

    -wave antennas, monopole, W-band, 3-D transition. I. INTRODUCTION With the growing demand for higher data rate be better candidates for broadband radiation. The major roadblock for their wide application is that the 3DA W-band Surface Micromachined Monopole for Low-cost Wireless Communication Systems Bo Pan, Y

  9. Optimal Frequency Band Design Scheme of Dyadic Wavelet Processor Array Using Surface Acoustic Wave Devices

    Microsoft Academic Search

    Changbao Wen; Changchun Zhu; Yongfeng Ju; Yanzhang Qiu; Hongke Xu; Wenke Lu

    2009-01-01

    In this paper, the relationship between the center frequency and radius of bandwidth and its effect on the frequency band characteristics of dyadic wavelet processor array using surface acoustic wave (SAW) devices are studied, and an optimal frequency band design scheme is proposed. For an arbitrary scale wavelet processor, we proposed that the center frequency is defined to three times

  10. Design of a wide-band metamaterial absorber based on fractal frequency selective surface and resistive films

    NASA Astrophysics Data System (ADS)

    Cheng, Yong-Zhi; Nie, Yan; Gong, Rong-Zhou

    2013-10-01

    We present the design of a wide-band metamaterial absorber, based on fractal frequency selective surface and resistive films. The total thickness is only 0.8 mm and shows a polarization-insensitive and wide-angle strong absorption. Due to the multiband resonance properties of the Minkowski fractal loop structure and Ohmic loss properties of resistive films, a strongly absorptive bandwidth of about 19 GHz is demonstrated numerically in the range 6.51-25.42 GHz. This design provides an effective and feasible way to construct a broad-band absorber in stealth technology.

  11. Band structure engineering of two-dimensional magnonic vortex crystals

    NASA Astrophysics Data System (ADS)

    Behncke, Carolin; Hänze, Max; Adolff, Christian F.; Weigand, Markus; Meier, Guido

    2015-06-01

    Magnonic vortex crystals are studied via scanning transmission x-ray microscopy and ferromagnetic-resonance spectroscopy. We investigate a two-dimensional vortex crystal by imprinting waves with tunable wave vectors. The dispersion relation ? (k ) is determined via ferromagnetic-resonance spectroscopy with a tunable frequency and wave vector for two vortex core polarization patterns that are adjusted by self-organized state formation prior to the measurement. We demonstrate that the band structure of the crystal is reprogrammed by tuning the vortex polarizations.

  12. X-BAND TRAVELING WAVE RF DEFLECTOR STRUCTURES

    SciTech Connect

    Wang, J.W.; Tantawi, S.; /SLAC

    2008-12-18

    Design studies on the X-Band transverse RF deflectors operating at HEM{sub ll} mode have been made for two different applications. One is for beam measurement of time-sliced emittance and slice energy spread for the upgraded LCLS project, its optimization in RF efficiency and system design are carefully considered. Another is to design an ultra-fast RF kicker in order to pick up single bunches from the bunch-train of the B-factory storage ring. The challenges are to obtain very short structure filling time with high RF group velocity and good RF efficiency with reasonable transverse shunt impedance. Its RF system will be discussed.

  13. Nanoscale probing of electronic band gap and topography of VO2 thin film surfaces by scanning tunneling microscopy

    NASA Astrophysics Data System (ADS)

    Yin, W.; Wolf, S.; Ko, C.; Ramanathan, S.; Reinke, P.

    2011-01-01

    The metal-insulator transition (MIT) in vanadium dioxide in the vicinity of room temperature makes it one of the most interesting materials for novel switching device applications. It is therefore essential to have a fundamental understanding of the VO2 surface when it is incorporated into multilayer structures or nanodevices. This study focuses on the surface modification of VO2 in response to the thermal treatment during phase transition. Vacuum annealing at temperatures in the vicinity of the MIT triggers a partial reduction in the surface, and thus initiates a chemical phase transition. Scanning tunneling microscopy and spectroscopy are used to investigate the electronic properties and surface structure of the VO2 thin film on (0001) sapphire substrates. Band gap maps with a high spatial resolution and single point spectroscopy I-V curves are measured as the sample is cycled through the MIT, and thus provide a direct observation of the surface phase transition at the nanoscale. The VO2 surface exhibits a homogeneous insulating behavior with a typical band gap of ˜0.5 eV at room temperature, and the surface becomes more metallic and spatially inhomogeneous in conductivity during MIT, and wide range of surface oxides can be identified. The surface still remains partially metallic after cooling down from a long period anneal, and such irreversible surface electrical change is attributed to the loss of oxygen. The location of metallic islands after thermal cycling is strongly coupled to the topography of the film, and relaxation processes and continued modification of the spatial distribution of the metallic regions are recognized on a longer timescale. The impact of film morphology, strain, surface chemistry, and structural phase transition on the electronic characteristics of VO2 surfaces are discussed.

  14. Nonparabolic band structure effect on carrier transport in semiconducting graphene nanoribbons

    Microsoft Academic Search

    N. Aziziah Amin; Zaharah Johari; Mohammad Taghi Ahmadi; Razali Ismail; D. C. Y. Chek; E. H. X. Ng

    2010-01-01

    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

  15. Unfolding the band structure of disordered solids: From bound states to high-mobility Kane fermions

    NASA Astrophysics Data System (ADS)

    Rubel, O.; Bokhanchuk, A.; Ahmed, S. J.; Assmann, E.

    2014-09-01

    Supercells are often used in ab initio calculations to model compound alloys, surfaces, and defects. One of the main challenges of supercell electronic structure calculations is to recover the Bloch character of electronic eigenstates perturbed by disorder. Here we apply the spectral weight approach to unfolding the electronic structure of group III-V and II-VI semiconductor solid solutions. The illustrative examples include formation of donorlike states in dilute Ga(PN) and associated enhancement of its optical activity, direct observation of the valence band anticrossing in dilute GaAs:Bi, and a topological band crossover in ternary (HgCd)Te alloy accompanied by emergence of high-mobility Kane fermions. The analysis facilitates interpretation of optical and transport characteristics of alloys that are otherwise ambiguous in traditional first-principles supercell calculations.

  16. The reflection and transmission properties of a triple band dichroic surface

    NASA Technical Reports Server (NTRS)

    Schneider, S. W.; Munk, B. A.

    1990-01-01

    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.

  17. Brain Surface Conformal Parameterization Using Riemann Surface Structure

    Microsoft Academic Search

    Yalin Wang; Lok Ming Lui; Xianfeng Gu; Kiralee M. Hayashi; Tony F. Chan; Arthur W. Toga; Paul M. Thompson; Shing-tung Yau

    2007-01-01

    In medical imaging, parameterized 3-D surface models are useful for anatomical modeling and visualization, statistical comparisons of anatomy, and surface-based registration and signal processing. Here we introduce a parameterization method based on Riemann surface structure, which uses a special curvilinear net structure (conformal net) to partition the surface into a set of patches that can each be conformally mapped to

  18. A Generalized Method for Synthesizing Low-Profile, BandPass Frequency Selective Surfaces With Non-Resonant Constituting Elements

    Microsoft Academic Search

    Mudar A. Al-Joumayly; Nader Behdad

    2010-01-01

    We present a comprehensive synthesis procedure for designing low-profile, band-pass frequency selective surfaces composed of non-resonant constituting elements. The proposed FSSs use arrays of sub-wavelength periodic structures with non-resonant constituting unit cells with unit cell dimensions and periodicities in the range of , where is the free space wavelength. The main advantages of this type of FSS, compared to traditional

  19. ELECTRONIC STRUCTURE AND CHEMICAL BONDING IN ALKALINE EARTH METAL SUBNITRIDES: PHOTOEMISSION STUDIES AND BAND STRUCTURE CALCULATIONS

    Microsoft Academic Search

    U. Steinbrenner; P. Adler; W. Hölle; A. Simon

    1998-01-01

    The electronic structure of various alkaline earth metal subnitrides has been studied by X-ray and ultraviolet photoelectron spectroscopy and by LMTO band structure calculations. Improved methods for the synthesis of several of the materials are described. The electronic structure of compounds with discrete clusters (Na22Ba14SrN6) or Ba3N chains (Ba3N, NaBa3N, Na5Ba3N) in the crystal structure is characterized by a narrow

  20. A parameterized surface reflectivity model and estimation of bare-surface soil moisture with L-band radiometer

    Microsoft Academic Search

    Jiancheng Shi; K. S. Chen; Qin Li; Thomas J. Jackson; P. E. O'Neill; Leung Tsang

    2002-01-01

    Soil moisture is an important parameter for hydrological and climatic investigations. Future satellite missions with L-band passive microwave radiometers will significantly increase the capability of monitoring Earth's soil moisture globally. Understanding the effects of surface roughness on microwave emission and developing quantitative bare-surface soil moisture retrieval algorithms is one of the essential components in many applications of geophysical properties in

  1. Three-dimensional dynamic thermal imaging of structural flaws by dual-band infrared computed tomography

    SciTech Connect

    Del Grande, N.K.; Dolan, K.W.; Durbin, P.F.; Gorvad, M.R.; Kornblum, B.T.; Perkins, D.E.; Schneberk, D.J.; Shapiro, A.B.

    1993-04-01

    We discuss three-dimensional (3D) dynamic thermal imaging of structure flaws using dual-band infrared (DBIR) computed tomography. Conventional thermography provides single-band infrared images which are difficult to interpret. Standard procedures yield imprecise (or qualitative) information about subsurface flaw sites which are typically masked by surface clutter. We use a DBIR imaging unique pioneered at LLNL to capture the time history of surface temperature difference for flash-heated targets. We relate these patterns to the location, size, shape and depth of subsurface flaws. We have demonstrated temperature accuracies of 0.2{degree}C, timing synchronizations of 3 ms (after onset of heat flash) and intervals of 42 ms, between images, during an 8 s cooling (and hearing) interval characterizing the front (and back) surface temperature-time history of an epoxy-glue disbond site in a flash-heated aluminum lap joint. This type of disbond played a significant role in causing damage to the Aloha Aircraft fuselage on the aged Boeing 737 jetliner. By ratioing DBIR images (near 5 and 10 micron), we located surface temperature patterns (generated by weak heat flow anomalies at subsurface flaw sites) and removed the emissivity mask (from surface roughness variations). We compared measurements with calculations from the three-dimensional, finite element computer code: TOPAZ3D. We combined infrared, ultrasound and x-ray imaging methods to characterize the lap joint disbond site spatial, bond quality, and material differences.

  2. Photonic Band Structures and Radiation in Two or Three Dimensional Periodic Structures.

    NASA Astrophysics Data System (ADS)

    Suzuki, Toshio

    1995-01-01

    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) by photonic crystals is suggested. In chapter 2, the plane wave expansion method --a numerical computational method to solve full-vector wave equations is developed with the complete matrix representations of Maxwell's equations. Band diagrams for periodic propagating electromagnetic modes (propagating modes) in non-conducting lossless passive dielectric photonic crystals are presented to demonstrate the theoretical existence of photonic band gaps. Chapter 3 discusses tunneling in the photonic band structures (complex photonic band structures). Maxwell's equations are numerically solved by the plane wave method with complex k-vectors. Furthermore, relations between imaginary parts of k-vectors and tunneling modes are examined. A classical theory for the calculation of the emission power from the electric dipole in three-dimensional periodic structures is developed in chapter 4, by incorporating the plane wave method, dyadic Green's function, Poynting theorem and tetrahedron k-space integration. In chapter 5, a computational method for photonic band structures with active and conductive media is developed by transforming Maxwell's equations into high order non -linear polynomial eigensystems based on the plane wave expansion method with complex k-vectors. Furthermore, by assuming an infinitely fast response of the material, the ordinary or quadratic eigensystems approximating the high order polynomial eigensystems are numerically computed. In the last chapter, photonic band structures and emission power of an electric dipole in two-dimensional systems are discussed. For a two-dimensional square lattice structure with dielectric cylinders, numerically computed results are compared with experimental measurements in a microwave frequency region. The theoretically predicted "alteration of emission spectrum in the photonic band structures" was verified with the experimental data in the two-dimensional structures.

  3. Band structure of ABC-trilayer graphene superlattice

    NASA Astrophysics Data System (ADS)

    Uddin, Salah; Chan, K. S.

    2014-11-01

    We investigate the effect of one-dimensional periodic potentials on the low energy band structure of ABC trilayer graphene first by assuming that all the three layers have the same potential. Extra Dirac points having the same electron hole crossing energy as that of the original Dirac point are generated by superlattice potentials with equal well and barrier widths. When the potential height is increased, the numbers of extra Dirac points are increased. The dispersions around the Dirac points are not isotropic. It is noted that the dispersion along the ky direction for kx = 0 oscillates between a non-linear dispersion and a linear dispersion when the potential height is increased. When the well and barrier widths are not identical, the symmetry of the conduction and valence bands is broken. The extra Dirac points are shifted either upward or downward depending on the barrier and well widths from the zero energy, while the position of the central Dirac point oscillates with the superlattice potential height. By considering different potentials for different layers, extra Dirac points are generated not from the original Dirac points but from the valleys formed in the energy spectrum. Two extra Dirac points appear from each pair of touched valleys, so four Dirac points appeared in the spectrum at particular barrier height. By increasing the barrier height of superlattice potential two Dirac points merge into the original Dirac point. This emerging and merging of extra Dirac points is different from the equal potential case.

  4. Semiconductor Nanocrystals: Structure, Properties, and Band Gap Engineering

    PubMed Central

    SMITH, ANDREW M.; NIE, SHUMING

    2010-01-01

    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 “artificial atoms” 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. PMID:19827808

  5. Surface Structure and Surface Electronic States Related to Plasma Cleaning of Silicon and Germanium

    NASA Astrophysics Data System (ADS)

    Cho, Jaewon

    This thesis discusses the surface structure and the surface electronic states of Si and Ge(100) surfaces as well as the effects of oxidation process on the silicon oxide/Si(100) interface structure. The H-plasma exposure was performed in situ at low temperatures. The active species, produced in the H-plasma by the rf-excitation of H_2 gas, not only remove microcontaminants such as oxygen and carbon from the surface, but also passivate the surface with atomic hydrogen by satisfying the dangling bonds of the surface atoms. The surfaces were characterized by Angle Resolved UV-Photoemission Spectroscopy (ARUPS) and Low Energy Electron Diffraction (LEED). In the case of Si(100), H-plasma exposure produced ordered H-terminated crystallographic structures with either a 2 x 1 or 1 x 1 LEED pattern. The hydride phases, found on the surfaces of the cleaned Si(100), were shown to depend on the temperature of the surface during H-plasma cleaning. The electronic states for the monohydride and dihydride phases were identified by ARUPS. When the plasma cleaned surface was annealed, the phase transition from the dihydride to monohydride was observed. The monohydride Si-H surface bond was stable up to 460^circC, and the dangling bond surface states were identified after annealing at 500^circC which was accompanied by the spectral shift. The H-terminated surface were characterized to have a flat band structure. For the Ge(100) surface, an ordered 2 x 1 monohydride phase was obtained from the surface cleaned at 180 ^circC. After plasma exposure at <=170^circC a 1 x 1 surface was observed, but the ARUPS indicated that the surface was predominantly composed of disordered monohydride structures. After annealing above the H-dissociation temperatures, the shift in the spectrum was shown to occur with the dangling bond surface states. The H-terminated surfaces were identified to be unpinned. The interface structure of silicon oxide/Si(100) was studied using ARUPS. Spectral shifts were observed, which were dependent on the processes of surface preparation and oxidation. The shift was characterized in association with the band bending. The origins of the spectral shifts were discussed, including defects at interface and H-passivation in Si. The interface structure is considered to be dependent on the surface preparation and oxidation process.

  6. Band gap in hypersonic surface phononic lattice of nickel pillars

    NASA Astrophysics Data System (ADS)

    Trzaskowska, A.; Mielcarek, S.; Sarkar, J.

    2013-10-01

    Brillouin light scattering was applied for investigation of surface wave propagation in phononic materials made of a silicon surface loaded with a nanostructure of nickel pillars. The results revealed the presence of phononic energy gap in the GHz range. The presence of such an energy gap was theoretically confirmed by the finite element method. The width of the energy gap was found to be related to the height of the pillars and was shown to be limited by the frequencies of the modes localized in the pillars. The modes were thoroughly analysed.

  7. Dislocation structures in the bands of localized cyclic plastic strain in austenitic 316L and austenitic-ferritic duplex stainless steels

    SciTech Connect

    Kruml, T.; Polak, J.; Obrtlik, K. [Academy of Sciences of the Czech Republic, Brno (Czech Republic). Inst. of Physics of Materials] [Academy of Sciences of the Czech Republic, Brno (Czech Republic). Inst. of Physics of Materials; Degallaix, S. [Ecole Centrale de Lille, Villeneuve d`Ascq (France). Lab. de Mecanique de Lille] [Ecole Centrale de Lille, Villeneuve d`Ascq (France). Lab. de Mecanique de Lille

    1997-12-01

    Dislocation structures in bands corresponding to cyclic strain localization have been studied in two types of stainless steels, single phase austenitic 316L steel and two-phase austenitic-ferritic duplex steel. Dislocation structures are documented in thin foils oriented approximately perpendicular to the active slip plane of individual grains and parallel to the primary Burgers vector. Persistent slip bands, with the structure more or less reminiscent of the well-known ladder structure, were found in austenitic grains of both steels. These bands can be correlated with the distinct surface relief consisting of extrusions, intrusions and shallow surface cracks in austenitic grains were found. The distribution of the wall and labyrinth structure embedded in the matrix structure in ferritic grains, which was proposed to be responsible for the localization of the cyclic strain, however, does not correspond to the distribution of the distinct surface slip lines on the surface.

  8. Estimation of Soil Moisture for Vegetated Surfaces Using Multi-Temporal L-Band SAR Measurements

    NASA Technical Reports Server (NTRS)

    Shi, Jian-Cheng; Sun, G.; Hsu, A.; Wang, J.; ONeill, P.; Ranson, J.; Engman, E. T.

    1997-01-01

    This paper demonstrates the technique to estimate ground surface and vegetation scattering components, based on the backscattering model and the radar decomposition theory, under configuration of multi-temporal L-band polarimetric SAR measurement. This technique can be used to estimate soil moisture of vegetated surface.

  9. Exciton band structure of monolayer MoS2

    NASA Astrophysics Data System (ADS)

    Wu, Fengcheng; Qu, Fanyao; MacDonald, Allan

    2015-03-01

    We describe a theory of the momentum-dependent exciton spectrum of monolayer molybdenum disulfide. Low-energy excitons occur both at the Brillouin zone center and at the Brillouin-zone corners. We find that binding energies at the Brillouin-zone center deviate qualitatively from the (n - 1 / 2) - 2 pattern of the two-dimensional hydrogenic model. Moreover, the four 2 p states of A series are lower in energy than the corresponding 2 s states and not degenerate. The two-fold ground-state valley degeneracy is lifted linearly at small momenta by electron-hole exchange processes that establish inter valley coherence. We conclude that atlhough monolayer MoS2 is a direct-gap semiconductor when classified by its quasiparticle band structure it may well be an indirect gap material when classified by its excitation spectra, and speculate on the role of this property in luminescence characteristics.

  10. Invariant expansion for the trigonal band structure of graphene.

    SciTech Connect

    Winkler, R.; Zulicke, U. (Materials Science Division); (Northern Illinois Univ.)

    2010-12-01

    We present a symmetry analysis of the trigonal band structure in graphene, elucidating the transformational properties of the underlying basis functions and the crucial role of time-reversal invariance. Group theory is used to derive an invariant expansion of the Hamiltonian for electron states near the K points of the graphene Brillouin zone. Besides yielding the characteristic k-linear dispersion and higher oder corrections to it, this approach enables the systematic incorporation of all terms arising from external electric and magnetic fields, strain, and spin-orbit coupling up to any desired order. Several new contributions are found, in addition to reproducing results obtained previously within tight-binding calculations. Physical ramifications of these new terms are discussed.

  11. Surface electronic structure of NiMnSb(001)

    NASA Astrophysics Data System (ADS)

    Correa, J. S.; Eibl, Ch.; Rangelov, G.; Braun, J.; Donath, M.

    2006-03-01

    We report on surface band structure measurements for the (001) surface of single crystal NiMnSb by angle-resolved photoelectron spectroscopy. Through comparisons of our data with previous angle-integrated experiments on various samples, polycrystals, and single crystals, we show that the binding energies of the observed photoemission peaks are sensitive to the particular surface condition and/or preparation. Additionally, our k -resolved measurements reveal a clear energy dispersion of the observed spectral features and a surface state candidate. We compare our measurements to fully-relativistic theoretical calculations and find that while they do not agree with the experimentally observed band dispersion they do explain the elemental origin and energy position of the normal emission photoemission results.

  12. Electronic band structure of the two-dimensional metallic electron system Au/Ge(111)

    NASA Astrophysics Data System (ADS)

    Höpfner, P.; Schäfer, J.; Fleszar, A.; Meyer, S.; Blumenstein, C.; Schramm, T.; Heßmann, M.; Cui, X.; Patthey, L.; Hanke, W.; Claessen, R.

    2011-06-01

    The two-dimensional electron system Au/Ge(111)-(3×3)R30° is studied in detail by angle-resolved photoemission and density functional theory calculations. In combining these results, we identify four metallic bands which are either of dominantly Au or Ge character, respectively. The largest Fermi surface sheet, originating from Au orbitals, is suggestive of a nesting condition due to its hexagonal shape. However, a charge density wave transition is not observed between room temperature and 10 K. The electronic structure obtained by density functional theory with inclusion of a self-energy correction is in good agreement with the experiment. These calculations also indicate that there is significant spin-orbit splitting, especially in the Au-related bands, which is partly of Rashba character.

  13. Band structures and intruder $?$$i_{13/2}$ state in $^{197}$Tl

    E-print Network

    H. Pai; G. Mukherjee; S. Bhattacharya; C. Bhattacharya; S. Bhattacharyya; T. Bhattacharjee; S. Chanda; S. Rajbanshi; A. Goswami; M. R. Gohil; S. Kundu; T. K. Ghosh; K. Banerjee; T. K. Rana; R. Pandey; G. K. Prajapati; S. R. Banerjee; S. Mukhopadhyay; D. Pandit; S. Pal; J. K. Meena; P. Mukhopadhyay; A. Chawdhury

    2013-11-08

    The excited states in the odd-$A$ $^{197}$Tl nucleus have been studied by populating them using the $^{197}$Au($\\alpha$, 4$n$)$^{197}$Tl reaction at the beam energy of 48 MeV. The $\\gamma-\\gamma$ coincidence data were taken using a combination of clover, LEPS and single crystal HPGe detectors. Precise spin and parity assignments of the excited states have been done through the polarization and the DCO measurements. A new band structure has been identified and the evidence for a possible intruder $\\pi i_{13/2}$ 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 $^{197}$Tl for different configurations.

  14. One-dimensional electromagnetic band gap structures formed by discharge plasmas in a waveguide

    NASA Astrophysics Data System (ADS)

    Arkhipenko, V. I.; Callegari, Th.; Simonchik, L. V.; Sokoloff, J.; Usachonak, M. S.

    2014-09-01

    We demonstrate the ability to develop one-dimensional electromagnetic band gap structure in X-band waveguide solely by using the positive columns of glow discharges in neon at the middle pressure. Plasma inhomogeneities are distributed uniformly along a typical X-band waveguide with cross section of 23 × 10 mm2. It is shown that electron densities larger than 1014 cm-3 are needed in order to create an effective one-dimensional electromagnetic band gap structure. Some applications for using the one-dimensional electromagnetic band gap structure in waveguide as a control of microwave (broadband filter and device for variation of pulse duration) are demonstrated.

  15. Flat Surface Plasmon Polariton Bands in Bragg Grating Waveguide for Slow Light

    Microsoft Academic Search

    Jing Zhang; Likang Cai; Wenli Bai; Guofeng Song

    2010-01-01

    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

  16. Usefulness of weak bands in midinfrared remote sensing of particulate planetary surfaces.

    USGS Publications Warehouse

    Salisbury, J.W.; Hapke, B.; Eastes, J.W.

    1987-01-01

    Transmittance and reflectance spectra of calcite and quartz are presented for the wavelength range from 4000 to 400 cm-1 (2.5-25 mu m). It is the purpose of this paper to point out that these weak bands are potentially useful for compositional remote sensing of particulate planetary surfaces; this will require completion of supporting laboratory studies to document the occurrence of weak bands. -from Authors

  17. Hybrid density functional calculations of the surface electronic structure of GdN

    NASA Astrophysics Data System (ADS)

    Marsoner Steinkasserer, Lukas Eugen; Paulus, Beate; Gaston, Nicola

    2015-06-01

    Rare-earth nitrides are a promising class of materials for application in spintronics, with GdN a particularly well-studied example. Here we perform band-structure calculations employing a hybrid density functional, which enables the band gap to be more accurately predicted through the inclusion of short-range exact exchange. The sensitivity of the band gap to the exchange term is demonstrated. The surface electronic structure is simulated through the use of slab models of the GdN(111) surface, which provide a consistent description of metallic surface states in the majority-spin channel.

  18. Scanning tunneling microscopy detection of spin polarized resonant surface bands: The example of Fe(001)

    Microsoft Academic Search

    Athanasios N. Chantis; Darryl L. Smith; J. Fransson; A. V. Balatsky

    2009-01-01

    We study theoretically the effect of a spin polarized resonant surface band on the conductance of scanning tunneling spectroscope with a spin polarized tip (SP-STM). Using the example of the Fe(001) surface, we show that a minority-spin surface state can induce a bias dependence of the tunneling differential conductance which depends strongly on the orientation of the magnetization in the

  19. Structure of superdeformed bands in {sup 195}Hg

    SciTech Connect

    Hackman, G.; Kruecken, R.; Janssens, R.V.; Deleplanque, M.A.; Carpenter, M.P.; Ackermann, D.; Ahmad, I.; Amro, H.; Asztalos, S.; Blumenthal, D.J.; Clark, R.M.; Diamond, R.M.; Fallon, P.; Fischer, S.M.; Herskind, B.; Khoo, T.L.; Lauritsen, T.; Lee, I.; MacLeod, R.W.; Macchiavelli, A.O.; Nisius, D.; Schmid, G.J.; Stephens, F.S.; Vetter, K.; Wyss, R. [Argonne National Laboratory, Argonne, Illinois 60439 (United States)] [Argonne National Laboratory, Argonne, Illinois 60439 (United States); [E.O. Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); [Niels Bohr Institute, University of Copenhagen, Copenhagen (Denmark); [Manne Siegbahn Institute, S-104 05 Stockholm (Sweden)

    1997-01-01

    Four new superdeformed bands have been observed with the Gammasphere array and have been assigned to the {sup 195}Hg nucleus. Two of the bands are interpreted as signature partners most likely based on N{sub osc}=6 neutron quasiparticles coupled to a superdeformed core, while the other two appear to be based on a j{sub 15/2} intruder orbital. These four bands do not exhibit a simple, {open_quotes}identical bands{close_quotes} relationship to other superdeformed bands in this mass region. {copyright} {ital 1997} {ital The American Physical Society}

  20. Plasmonic band gaps and trapped plasmons on nanostructured metal surfaces.

    PubMed

    Kelf, T A; Sugawara, Y; Baumberg, J J; Abdelsalam, M; Bartlett, P N

    2005-09-01

    Nanostructured metal surfaces comprised of periodically arranged spherical voids are grown by electrochemical deposition through a self-assembled template. Detailed measurements of the angle- and orientation-dependent reflectivity reveal the spectral dispersion, from which we identify the presence of both delocalized Bragg and localized Mie plasmons. These couple strongly producing bonding and antibonding mixed plasmons with anomalous dispersion properties. Appropriate plasmon engineering of the void morphology selects the plasmon spatial and spectral positions, allowing these plasmonic crystal films to be optimized for a wide range of sensing applications. PMID:16197028

  1. Plasmonic Band Gaps and Trapped Plasmons on Nanostructured Metal Surfaces

    NASA Astrophysics Data System (ADS)

    Kelf, T. A.; Sugawara, Y.; Baumberg, J. J.; Abdelsalam, M.; Bartlett, P. N.

    2005-09-01

    Nanostructured metal surfaces comprised of periodically arranged spherical voids are grown by electrochemical deposition through a self-assembled template. Detailed measurements of the angle- and orientation-dependent reflectivity reveal the spectral dispersion, from which we identify the presence of both delocalized Bragg and localized Mie plasmons. These couple strongly producing bonding and antibonding mixed plasmons with anomalous dispersion properties. Appropriate plasmon engineering of the void morphology selects the plasmon spatial and spectral positions, allowing these plasmonic crystal films to be optimized for a wide range of sensing applications.

  2. Energy Band Structure of the Electron Gas in Periodic Quantum Wells

    NASA Astrophysics Data System (ADS)

    Mao, Sheng-Hong; Ma, Yu-Ting; Xue, Ju-Kui

    2012-08-01

    The energy band structure and current density of electron gas with an exchange-correlation effect in periodic quantum wells are discussed. It is found that the energy band shows a swallowtail structure at the boundary of the first Brillouin zone when the electron exchange-correlation effect is presented and the average electron density is smaller than a critical value. The energy band structure is closely related to the current density of the system.

  3. Realization of an Active Narrow Band Filter with Electronically Controlled Defects in a Microwave Bandgap Structure

    Microsoft Academic Search

    Michael J. Hill; Richard W. Ziolkowski; John Papapolymerou

    2000-01-01

    Microwave band gap structures (MBG) utilizing fixed defects have received much interest because of their ability to operate as narrow band filters. With the recent interest in reconfigurable wireless devices, the need for electronically controllable narrow band filters is on the rise. By altering the defects in a MBG crystal, the transmission properties of the crystal can be changed. Using

  4. Hyperspectral bands prediction based on inter-band spectral correlation structure

    NASA Astrophysics Data System (ADS)

    Ahmed, Ayman M.; Sharkawy, Mohamed El.; Elramly, Salwa H.

    2013-02-01

    Hyperspectral imaging has been widely studied in many applications; notably in climate changes, vegetation, and desert studies. However, such kind of imaging brings a huge amount of data, which requires transmission, processing, and storage resources for both airborne and spaceborne imaging. Compression of hyperspectral data cubes is an effective solution for these problems. Lossless compression of the hyperspectral data usually results in low compression ratio, which may not meet the available resources; on the other hand, lossy compression may give the desired ratio, but with a significant degradation effect on object identification performance of the hyperspectral data. Moreover, most hyperspectral data compression techniques exploits the similarities in spectral dimensions; which requires bands reordering or regrouping, to make use of the spectral redundancy. In this paper, we analyze the spectral cross correlation between bands for AVIRIS and Hyperion hyperspectral data; spectral cross correlation matrix is calculated, assessing the strength of the spectral matrix, we propose new technique to find highly correlated groups of bands in the hyperspectral data cube based on "inter band correlation square", and finally, we propose a new technique of band regrouping based on correlation values weights for different group of bands as network of correlation.

  5. Valence band structure and magnetic properties of Co-doped Fe3O4(100) films

    Microsoft Academic Search

    F. Y. Ran; Y. Tsunemaru; T. Hasegawa; Y. Takeichi; A. Harasawa; K. Yaji; S. Kim; A. Kakizaki

    2011-01-01

    Structural and magnetic properties, and the valence band structure of pure and Co-doped (up to 33%) Fe3O4(100) films were investigated. Reconstruction of the Fe3O4(100) surface is found to be blocked by Co doping. Doped Co ions in Fe3O4 are in a charge state of 2 + and substitute the Fe2+ in the B site of Fe3O4. All the films exhibit

  6. Comparison between ab initio energy band structures of various chlorinated polyethylene derivatives

    NASA Astrophysics Data System (ADS)

    Assad Abdel-Raouf, Mohamed

    1989-09-01

    The band structures of various chlorinated polyethylene derivatives are calculated using an ab initio self-consisten field (SCF) linear combination of atomic orbitals (LCAO) technique. The results illustrate that the conduction band is shifted steadily towards lower energies as the number of chlorine atoms in the unit cell increases, and the gap between valence and conduction bands is decreased monotonically. The possibility of n-doping is explored. The comparison between the band structures of the chlorinated polymers and that of polytrifluorochloroethylene shows that the latter possesses a lower-lying conduction band and is, therefore, more adequate for doping.

  7. Characterization of the B/Si surface electronic structures

    SciTech Connect

    Cao, R.; Yang, X.; Pianetta, P.

    1992-11-01

    High resolution angle resolved core level and valence band photoelectron spectroscopy have been used to characterize the electronic structures of the B/Si(111)-({radical}3 x {radical}3) surfaces. The results have been compared with theoretic calculations and other group III metals and Si terminated Si(111) surfaces that share the same type of surface reconstruction. We have observed a structure evolution from B-T{sub 4} to B-S{sub 5} and finally to Si- T{sub 4} as deposited boron atoms diffuse into the substrate with increasing annealing temperature. The chemically shifted component appearing in the Si 2p core level spectrum is attributed to charge transfer from the top layer Si and Si adatoms to the sublayer B-S{sub 5} atoms. For the Si/Si(111)-({radical}3 {times} {radical}3) surface, a newly discovered chemically shifted component is associated with back bond formation between the Si adatoms and the underneath Si atoms. A new emission feature has been observed in the valence band spectra unique to the B/Si(111)-({radical}3 {times} {radical}3) surface with B-S{sub 5} configuration. Thin Ge layer growth on this structure has also been performed, and we found that no epitaxial growth could be achieved and the underneath structure was little disturbed.

  8. Dual-band bandpass filter based on compound metallic grating waveguide structure

    NASA Astrophysics Data System (ADS)

    Hu, Rui; Liang, Yuzhang; Qian, Siyu; Peng, Wei

    2015-02-01

    In this paper, we proposed a novel dual-band bandpass filter based on subwavelength compound metallic grating deposited on the waveguide structure by using the finite-difference time domain (FDTD) method. The compound metallic grating is constructed by carving a groove on the top surface of every metal strip. The designed structure generates two remarkable transmission peaks with a dip in-between at normal incidence. Two transmission peaks with narrow bandwidth and high transmission depth is attributed to the existence of grooves in the designed structure. We research the implied physical mechanism of two resonance peaks and one dip by investigating the effect of different structure parameters on transmission spectrum and the electromagnetic field distributions at the location of resonance. It is found that the two resonance peaks are determined by different hybrid modes of F-P like resonance, waveguide resonance mode and SPP mode. Besides, angularly resolved spectra are presented to further reveal physical mechanism of two resonance peaks. This work can be used to develop a dual-band bandpass filter in the telecom wavelength range.

  9. Electronic structure of the surfaces of layered copper oxides

    SciTech Connect

    Prosandeyev, S.A.; Tennenboum, I.M. [Department of Physics, Rostov State University, 5 Zorge Street, 344104 Rostov on Don (Russian Federation)] [Department of Physics, Rostov State University, 5 Zorge Street, 344104 Rostov on Don (Russian Federation)

    1995-08-01

    The electronic structure of the surfaces of layered copper oxides has been investigated in the framework of a tight-binding model together with the unrestricted Hartree-Fock method. The main element of the layered copper oxides, namely the CuO{sub 2} layer, was supposed to lie parallel with the surface, as well as to be trimmed at a boundary of crystal. In the former case, the electrons at the surface were considered to be in an additional (surface) potential. A mode of the calculation of this potential has been developed on the basis of a method being similar to Ewald`s transformation. As an example, the surface of La{sub 2}CuO{sub 4} was studied. In the latter case, when the CuO{sub 2} layer is semi-infinite due to its cutting at the surface, the formation of electronic surface bands was carefully investigated. Both the metal and dielectric phases were examined. For the metal phase, we took into account the possible freezing of the spin-density wave at the surface. In all the cases, surface bands were present in the vicinity of the Fermi level. They had inherent, in the one-dimensional systems, peculiarities.

  10. Estimation of bare surface soil moisture and surface roughness parameter using L-band SAR image data

    Microsoft Academic Search

    Jiancheng Shi; James Wang; Ann Y. Hsu; P. E. O'Neill; E. T. Engman

    1997-01-01

    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

  11. Band Structure of Bose-Einstein Condensates in a Cavity-Mediated Triple-Well System

    NASA Astrophysics Data System (ADS)

    Wang, Bin; Chen, Yan

    2013-02-01

    We investigate the band structure and the dynamics of Bose-Einstein condensates in a triple-well trap, which are located in a high-finesse optical cavity. For the noninteracting atoms, the band structure of the eigenenergies are obtained using the numerical methods under the mean-field approximation. It is demonstrated that the energy band structure is strongly dependent on the value of reduced cavity detuning. Under some conditions, the atomic band structure develops loop structures and swallowtail structure, which mean the atom-cavity system exhibits bistability. We attribute the appearance of new states to the nonlinearity of the cavity-field-induced tilt. For the interacting atoms, the structure of the eigenenergy band appears more complicated for the interaction between atoms.

  12. Guided Elastic Waves at Periodically Structured Surfaces and Interfaces

    Microsoft Academic Search

    A. G. Every; A. A. Maznev

    \\u000a A brief overview is provided of guided elastic waves at periodically structured surfaces, with particular attention given\\u000a to their folded dispersion relations,the occurrence of band gaps, their coupling to bulk elastic waves, and their interaction\\u000a with light.Two examples of physical situations and the dynamic behavior they give rise to are used to illustrate these ideas.\\u000a The first pertains to the

  13. Measuring surface deformation of Beijing and surrounding area using X-band InSAR data

    NASA Astrophysics Data System (ADS)

    Lu, Q.; Sun, J.; Shen, Z.

    2014-12-01

    The InSAR technique has been widely used in surface deformation monitoring in recent years. Although the X-band InSAR data have relatively lower coherence in vegetation covering areas than the C-band and L-band data, they have the potential to capture finer deformation signals in cities with less influence from ionosphere disturbance. In this study, we utilize X-band TarraSAR data to investigate the accumulated surface deformation from 2008 to 2012 in Beijing and the surrounding regions including Cangzhou and part of Tianjin. Our preliminary result shows that in our research area, the nontectonic deformation signals, such as deformation caused by groundwater withdrawal and viaduct and subway constructions are considerably larger than that of tectonic deformation caused by active faults located in the Zhangjiakou-Bohai seismic zone. The main deformation signals discovered so far are from surface subsidence distributed in the east and north downtown area of Beijing, conforming our previous discoveries using the L-band SAR data. Our result also shows the phenomenon that spatial extents of some subsidence areas are aligned with local faults, this indicating that the groundwater flow may be manifested by physical barriers of faults. Our result will help assessing hazard potentials associated with land subsidence in Beijing and surrounding areas.

  14. Complex band structure of topologically protected edge states

    NASA Astrophysics Data System (ADS)

    Dang, Xiaoqian; Burton, J. D.; Kalitsov, Alan; Velev, Julian P.; Tsymbal, Evgeny Y.

    2014-10-01

    One of the great successes of modern condensed matter physics is the discovery of topological insulators (TIs). A thorough investigation of their properties could bring such materials from fundamental research to potential applications. Here, we report on theoretical investigations of the complex band structure (CBS) of two-dimensional (2D) TIs. We utilize the tight-binding form of the Bernevig, Hughes, and Zhang model as a prototype for a generic 2D TI. Based on this model, we outline the conditions that the CBS must satisfy in order to guarantee the presence of topologically protected edge states. Furthermore, we use the Green's function technique to show how these edge states are localized, highlighting the fact that the decay of the edge-state wave functions into the bulk of a TI is not necessarily monotonic and, in fact, can exhibit an oscillatory behavior that is consistent with the predicted CBS of the bulk TI. These results may have implications for electronic and spin transport across a TI when it is used as a tunnel barrier.

  15. BandGap Photonic Structures in Dichromate Pullulan

    Microsoft Academic Search

    Svetlana Savi?-Ševi?; Dejan Panteli?; Marko Nikoli?; Branislav Jelenkovi?

    2009-01-01

    One-dimensional photonic crystals are fabricated in a dichromate-sensitized pullulan as volume holograms. A single-frequency, diode pumped Nd-YAG laser, at 532 nm, is used for exposure. Band gaps in the visible range are observed. The spectral measurements show that band-gap position can be tuned by varying the concentration of ammonium dichromate.

  16. Carrier multiplication in semiconductor nanocrystals: theoretical screening of candidate materials based on band-structure effects.

    PubMed

    Luo, Jun-Wei; Franceschetti, Alberto; Zunger, Alex

    2008-10-01

    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 XX. Here we introduce a DCM "figure of merit" R2(E) which is proportional to the ratio between the biexciton density of states rhoXX and the single-exciton density of states rhoX, restricted to single-exciton and biexciton states that are coupled by Coulomb interactions. Using R2(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 E0 (the energy at which R2(E) becomes >or=1) is reduced, suggesting improved DCM. However, whether the normalized E0/epsilong increases or decreases as the dot size increases depends on dot material. PMID:18729418

  17. Resonant charge transfer in ion-metal surface collisions: Effect of a projected band gap in the H--Cu(111) system

    NASA Astrophysics Data System (ADS)

    Borisov, A. G.; Kazansky, A. K.; Gauyacq, J. P.

    1999-04-01

    A wave-packet propagation method is applied to the treatment of the resonant charge transfer (RCT) process in the interaction between an H- ion and a Cu(111) surface. Using a model description of the Cu(111) electronic structure, it is shown that the RCT efficiency is deeply influenced by the presence of the Cu(111) projected band gap, that partially blocks the electron transfer in the direction normal to the surface. The differences between the RCT process on a free electron metal surface and on a Cu(111) surface are discussed. The two cases are associated with very different pictures of the electron transfer. In particular, the importance of the Cu(111) surface state for the decay of the H- ion is demonstrated. The effect of the band gap is also shown to strongly depend on the interaction time. For short interaction times (large collision velocities), the electron wave packet does not have enough time to probe the metal band structure and the RCT on a Cu(111) surface is very similar to that on a free electron surface. For long interaction times (low collision velocities), the RCT efficiency is drastically reduced by the presence of the band gap. The wave-packet propagation method is also used to discuss the validity of the rate equation approach in the case of a free electron metal target.

  18. Development of Thin-Film Liquid-Crystal-Polymer Surface-Mount Packages for Band Applications

    Microsoft Academic Search

    Kunia Aihara; Morgan Jikang Chen; Anh-Vu Pham

    2008-01-01

    In this paper, we present the design and development of thin-film liquid-crystal-polymer (LCP) surface-mount packages for Ka-band applications. The packages are constructed using multilayer LCP films and are surface mounted on a printed circuit board (PCB). Our experimental results demonstrate that the package feed-through transition including a PCB launch and bond wires achieve a return loss of better than -20

  19. Influence of surface and vegetation characteristics on C-band radar measurements for soil moisture content

    Microsoft Academic Search

    Shakil Ahmad Romshoo; Masahiro Koike; Sadayukihir Onaka; Taikan Oki; Katumi Musiake

    2002-01-01

    Soil moisture estimation using microwave remote sensing faces challenges of the segregation of influences mainly from roughness\\u000a and vegetation. Under static surface conditions, it was found that Radarsat C-band SAR shows reasonably good correlation and\\u000a sensitivity with changing soil moisture. Dynamic surface and vegetation conditions are supposed to result in a substantial\\u000a reduction in radar sensitivity to soil moisture. A

  20. Electronic Structure and Valence Band Spectra of Bi4Ti3O12

    Microsoft Academic Search

    A. V. Postnikov; St. Bartkowski; F. Mersch; M. Neumann; E. Z. Kurmaev; V. M. Cherkashenko; S. N. Nemnonov; V. R. Galakhov

    1995-01-01

    The x-ray photoelectron valence band spectrum and x-ray emission valence-band spectra (Ti K _beta_5, Ti L_alpha, O K_alpha) of Bi4Ti3O12 are presented (analyzed in the common energy scale) and interpreted on the basis of a band-structure calculation for an idealized I4\\/mmm structure of this material.

  1. L-Band microwave observations over land surface using a two-dimensional synthetic aperture radiometer

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Antenna size is major factor that has limited realization of the potential capabilities of L-band (1.4 GHz) microwave radiometry to estimate surface soil moisture from space. However, emerging interferometric technology, called aperture synthesis, has been developed to address this limitation. The ...

  2. L-Band Microwave Observations over land Surface using a Two-Dimensional Synthetic Aperture Radiometer

    Technology Transfer Automated Retrieval System (TEKTRAN)

    A number of studies have demonstrated the potential capabilities of passive microwave remote sensing at L-band (1.4 GHz) to measure surface soil moisture. Aperture synthesis is a technology for obtaining high spatial resolution at long wavelengths with a practical radiometer antenna. During the So...

  3. HIGH SPATIAL RESOLUTION SURFACE AND CLOUD TYPE CLASSIFICATION FROM MODIS MULTI-SPECTRAL BAND MEASUREMENTS

    E-print Network

    Li, Jun

    P5.20 HIGH SPATIAL RESOLUTION SURFACE AND CLOUD TYPE CLASSIFICATION FROM MODIS MULTI-SPECTRAL BAND Spectroradiometer (MODIS) radiance measurements. The MODIS cloud mask (Ackerman et al. 1998) is used to define and a final 1 km resolution classification map is generated for a MODIS granules. This classification

  4. Detecting forest structure and biomass with C-band multipolarization radar - Physical model and field tests

    NASA Technical Reports Server (NTRS)

    Westman, Walter E.; Paris, Jack F.

    1987-01-01

    The ability of C-band radar (4.75 GHz) to discriminate features of forest structure, including biomass, is tested using a truck-mounted scatterometer for field tests on a 1.5-3.0 m pygmy forest of cypress (Cupressus pygmaea) and pine (Pinus contorta ssp, Bolanderi) near Mendocino, CA. In all, 31 structural variables of the forest are quantified at seven sites. Also measured was the backscatter from a life-sized physical model of the pygmy forest, composed of nine wooden trees with 'leafy branches' of sponge-wrapped dowels. This model enabled independent testing of the effects of stem, branch, and leafy branch biomass, branch angle, and moisture content on radar backscatter. Field results suggested that surface area of leaves played a greater role in leaf scattering properties than leaf biomass per se. Tree leaf area index was strongly correlated with vertically polarized power backscatter (r = 0.94; P less than 0.01). Field results suggested that the scattering role of leaf water is enhanced as leaf surface area per unit leaf mass increases; i.e., as the moist scattering surfaces become more dispersed. Fog condensate caused a measurable rise in forest backscatter, both from surface and internal rises in water content. Tree branch mass per unit area was highly correlated with cross-polarized backscatter in the field (r = 0.93; P less than 0.01), a result also seen in the physical model.

  5. Influence of surface heterogeneity on L-band (1.4 GHz) measurements at various spatial resolutions; some preliminary

    E-print Network

    Walker, Jeff

    Influence of surface heterogeneity on L-band (1.4 GHz) measurements at various spatial resolutions Fractions, IGARSS 2004 · J-P Wigneron et al. (2006), `L-band Microwave Emission of the Biosphere (L. MATERIALS: L-band dual-polarized radiometers: - EMIRAD: simultaneous measurements at 0°& 40°(~800m

  6. Advances in X-Band TW Accelerator Structures Operating in the 100 MV/M Regime

    SciTech Connect

    Higo, Toshiyasu; /KEK, Tsukuba; Higashi, Yasuo; /KEK, Tsukuba; Matsumoto, Shuji; /KEK, Tsukuba; Yokoyama, Kazue; /KEK, Tsukuba; Adolphsen, Chris; /SLAC; Dolgashev, Valery; /SLAC; Jensen, Aaron; /SLAC; Laurent, Lisa; /SLAC; Tantawi, Sami; /SLAC; Wang, Faya; /SLAC; Wang, Juwen; /SLAC; Dobert, Steffen; /CERN; Grudiev, Alexej; /CERN; Riddone, Germana; /CERN; Wuensch, Walter; /CERN; Zennaro, Riccardo; /CERN

    2012-07-05

    A CERN-SLAC-KEK collaboration on high gradient X-band accelerator structure development for CLIC has been ongoing for three years. The major outcome has been the demonstration of stable 100 MV/m gradient operation of a number of CLIC prototype structures. These structures were fabricated using the technology developed from 1994 to 2004 for the GLC/NLC linear collider initiative. One of the goals has been to refine the essential parameters and fabrication procedures needed to realize such a high gradient routinely. Another goal has been to develop structures with stronger dipole mode damping than those for GLC/NLC. The latter requires that the surface temperature rise during the pulse be higher, which may increase the breakdown rate. One structure with heavy damping has been RF processed and another is nearly finished. The breakdown rates of these structures were found to be higher by two orders of magnitude compared to those with equivalent acceleration mode parameters but without the damping features. This paper presents these results together with some of the earlier results from non-damped structures.

  7. R&D of C-Band Accelerating Structure at SINAP

    NASA Astrophysics Data System (ADS)

    Gu, Qiang; Fang, Wencheng; Zhao, Zhentang; Tong, Dechun

    2015-10-01

    R&D of a C-band (5712 MHz) high gradient traveling-wave accelerating structure has been in progress at Shanghai Institute of Applied Physics (SINAP). The prototype and new C-band accelerating structures have already been fabricated. In this paper, some details of R&D are introduced.

  8. Theoretical study on the band structure of Bi1?-x?Sbx? thin films

    E-print Network

    Tang, Shuang, S.M. Massachusetts Institute of Technology

    2012-01-01

    The study on the electronic band structures of Bi1-xSbx thin films is a very interesting topic. Recall that in bulk Bi1-xSbx, the electronic band structure can be varied as a function of temperature T, pressure P and ...

  9. Acoustic band-gap engineering using finite-size layered structures of multiple periodicity

    E-print Network

    Cao, Wenwu

    Acoustic band-gap engineering using finite-size layered structures of multiple periodicity Mingrong and also measured as a function of frequency. It was found that acoustic band gaps can be created using structure, very sharp passbands and very broad stopbands can be engineered for acoustic waves. Such acoustic

  10. Effective phase matching conditions for parametric interactions in one-dimensional photonic band gap structures

    Microsoft Academic Search

    M. Centini; C. Sibilia; M. Bertolotti; M. Scalora; M. J. Bloemer; C. M. Bowden

    1999-01-01

    Summary form only given. In a recent publication, the theoretical enhancement of second harmonic generation at the band edge of a mixed quarter-half wave PBG structure was discussed. The structure was chosen so that both the pump and second harmonic fields were tuned near the first and second order band edges respectively, such that the pump was tuned at the

  11. Band structure calculation of GeSn and SiSn

    NASA Astrophysics Data System (ADS)

    Amrane, Na.; Ait Abderrahmane, S.; Aourag, H.

    1995-08-01

    The band structure of GeSn and SiSn in zinc-blende structures is predicted using the empirical pseudopotential. Special emphasis is placed on the effects of inversions asymmetry such as ionicity. We found that GeSn exhibits a direct band gap whereas SiSn still remains indirect gap material.

  12. Solar hydrogen generation with wide-band-gap semiconductors: GaP(100) photoelectrodes and surface modification.

    PubMed

    Kaiser, Bernhard; Fertig, Dominic; Ziegler, Jürgen; Klett, Joachim; Hoch, Sascha; Jaegermann, Wolfram

    2012-08-27

    GaP, with its large band gap of 2.26 eV (indirect) and 2.78 eV (direct), is a very promising candidate for direct photoelectrochemical water splitting. Herein, p-GaP(100) is investigated as a photocathode for hydrogen generation. The samples are characterized after each preparation step regarding how their photoelectrochemical behavior is influenced by surface composition and structure using a combination of electrochemical and surface-science preparation and characterization techniques. The formation of an Ohmic back contact employing an annealed gold layer and the removal of the native oxides using various etchants are studied. It turns out that the latter has a pronounced effect on the surface composition and structure and therefore also on the electronic properties of the interface. The formation of a thin Ga(2)O(3) buffer layer on the p-GaP(100) surface does not lead to a clear improvement in the photoelectrochemical efficiency, neither do Pt nanocatalyst particles deposited on top of the buffer layer. This behavior can be understood by the electronic structure of these layers, which is not well suited for an efficient charge transfer from the absorber to the electrolyte. First experiments show that the efficiency can be considerably improved by employing a thin GaN layer as a buffer layer on top of the p-GaP(100) surface. PMID:22893616

  13. Doppler sidebands in the cross-spectral density of narrow-band reverberation from a dynamic sea surface.

    PubMed

    Gragg, Robert F

    2003-09-01

    Analytic methods are used to formulate the impact of a random dynamic sea surface on the space-frequency characteristics of bistatic reverberation. A narrow-band point source is positioned beneath the time-dependent surface of a range-independent ocean. The small-waveheight perturbative approximation is invoked, and attention is focused on the Doppler sideband contributions to the reverberation cross-spectral density for an arbitrarily placed receiver pair. The new expression that results is identified as an active scattering generalization of the van Cittert-Zernike theorem from classical partial coherence theory. This work is the first to explicitly predict the sideband structure in the cross-spectral density of the field scattered from a realistic moving sea surface. A numerical example is presented for a shallow source and shallow receivers in a homogeneous ocean. PMID:14514191

  14. 480 IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 12, NO. 5, MAY 2000 Coupled Structure for Wide-Band EDFA with Gain

    E-print Network

    Park, Namkyoo

    -Band EDFA with Gain and Noise Figure Improvements from C to L-Band ASE Injection Bumki Min, Student Member, IEEE Abstract--We propose a novel structure for C plus L-band silica based wide-band erbium-doped fiber-mediating injection source for the L-band amplifier unit. Experimental results show gain and noise figure improvements

  15. Partitioning of bacterial communities between seawater and healthy, black band diseased, and dead coral surfaces.

    PubMed

    Frias-Lopez, Jorge; Zerkle, Aubrey L; Bonheyo, George T; Fouke, Bruce W

    2002-05-01

    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 Curaçao, 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. PMID:11976091

  16. Electronic Structure Measurements of Colossal Magnetoresistive Manganese-Oxides: Polaronic Effects on the Band Structure

    Microsoft Academic Search

    D. S. Dessau; T. Saitoh; C.-H. Park; Z.-X. Shen; P. Villella; N. Hamada; Y. Moritomo; Y. Tokura

    1999-01-01

    We have used high energy-resolution angle-resolved photoemission spectroscopy(ARPES) to map the k-dependent electronic structure of single-crystallinesamples of the manganese-based perovskites as a function of doping level, temperature,and layer number. The measured near-Fermi energy states display E vs. kand symmetry relationships which agree relatively well with the LSDA band theoryprediction through much of the Brillouin zone, and the locus of lowest

  17. Doping mode, band structure and photocatalytic mechanism of B-N-codoped TiO 2

    NASA Astrophysics Data System (ADS)

    Yuan, Jixiang; Wang, Enjun; Chen, Yongmei; Yang, Wensheng; Yao, Jianghong; Cao, Yaan

    2011-06-01

    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.

  18. Ka-band backscattering from water surface at small incidence: A wind-wave tank study

    NASA Astrophysics Data System (ADS)

    Boisot, Olivier; Pioch, Sébastien; Fatras, Christophe; Caulliez, Guillemette; Bringer, Alexandra; Borderies, Pierre; Lalaurie, Jean-Claude; Guérin, Charles-Antoine

    2015-05-01

    We report on an experiment conducted at the large Pytheas wind-wave facility in Marseille to characterize the Ka-band radar return from water surfaces when observed at small incidence. Simultaneous measurements of capillary-gravity to gravity wave height and slopes and Normalized Radar Cross Section (NRCS) were carried out for various wind speeds and scattering angles. From this data set we construct an empirical two-dimensional wave number spectrum accounting for the surface current to describe water surface motions from decimeter to millimeter scales. Some consistency tests are proposed to validate the surface wave spectrum, which is then incorporated into simple analytical scattering models. The resulting directional NRCS is found in overall good agreement with the experimental values. Comparisons are performed with oceanic models as well as in situ measurements over different types of natural surfaces. The applicability of the present findings to oceanic as well as continental surfaces is discussed.

  19. Microbial Communities in the Surface Mucopolysaccharide Layer and the Black Band Microbial Mat of Black Band-Diseased Siderastrea siderea

    PubMed Central

    Sekar, Raju; Mills, DeEtta K.; Remily, Elizabeth R.; Voss, Joshua D.; Richardson, Laurie L.

    2006-01-01

    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 heterogeneity 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 using the same techniques for comparison. Gene sequences, ranging from 424 to 1,537 bp, were retrieved from all positive clones (n = 43 to 48) in each of the four clone libraries generated and used for comparative sequence analysis. In addition to LH-PCR community profiling, all of the clone sequences were aligned with LH-PCR primer sequences, and the theoretical lengths of the amplicons were determined. Results revealed that the community profiles were significantly different between BBD and SML samples. The SML samples were dominated by ?-proteobacteria (53 to 64%), followed by ?-proteobacteria (18 to 21%) and ?-proteobacteria (5 to 11%). In contrast, both BBD clone libraries were dominated by ?-proteobacteria (58 to 87%), followed by verrucomicrobia (2 to 10%) and 0 to 6% each of ?-proteobacteria, bacteroidetes, firmicutes, and cyanobacteria. Alphaproteobacterial sequence types related to the bacteria associated with toxin-producing dinoflagellates were observed in BBD clone libraries but were not found in the SML libraries. Similarly, sequences affiliated with the family Desulfobacteraceae and toxin-producing cyanobacteria, both believed to be involved in BBD pathogenesis, were found only in BBD libraries. These data provide evidence for an association of numerous toxin-producing heterotrophic microorganisms with BBD of corals. PMID:16957217

  20. Effect of acicular ferrite on banded structures in low-carbon microalloyed steel

    NASA Astrophysics Data System (ADS)

    Shi, Lei; Yan, Ze-sheng; Liu, Yong-chang; Yang, Xu; Zhang, Cheng; Li, Hui-jun

    2014-12-01

    The effect of acicular ferrite (AF) on banded structures in low-carbon microalloyed steel with Mn segregation during both isothermal transformation and continuous cooling processes was studied by dilatometry and microscopic observation. With respect to the isothermal transformation process, the specimen isothermed at 550°C consisted of AF in Mn-poor bands and martensite in Mn-rich bands, whereas the specimen isothermed at 450°C exhibited two different morphologies of AF that appeared as bands. At a continuous cooling rate in the range of 4 to 50°C/s, a mixture of AF and martensite formed in both segregated bands, and the volume fraction of martensite in Mn-rich bands was always higher than that in Mn-poor bands. An increased cooling rate resulted in a decrease in the difference of martensite volume fraction between Mn-rich and Mn-poor bands and thereby leaded to less distinct microstructural banding. The results show that Mn segregation and cooling rate strongly affect the formation of AF-containing banded structures. The formation mechanism of microstructural banding was also discussed.

  1. Protein Structural Perturbation and Aggregation on Homogeneous Surfaces

    PubMed Central

    Sethuraman, Ananthakrishnan; Belfort, Georges

    2005-01-01

    We have demonstrated that globular proteins, such as hen egg lysozyme in phosphate buffered saline at room temperature, lose native structural stability and activity when adsorbed onto well-defined homogeneous solid surfaces. This structural loss is evident by ?-helix to turns/random during the first 30 min and followed by a slow ?-helix to ?-sheet transition. Increase in intramolecular and intermolecular ?-sheet content suggests conformational rearrangement and aggregation between different protein molecules, respectively. Amide I band attenuated total reflection/Fourier transformed infrared (ATR/FTIR) spectroscopy was used to quantify the secondary structure content of lysozyme adsorbed on six different self-assembled alkanethiol monolayer surfaces with –CH3, –OPh, –CF3, –CN, –OCH3, and –OH exposed functional end groups. Activity measurements of adsorbed lysozyme were in good agreement with the structural perturbations. Both surface chemistry (type of functional groups, wettability) and adsorbate concentration (i.e., lateral interactions) are responsible for the observed structural changes during adsorption. A kinetic model is proposed to describe secondary structural changes that occur in two dynamic phases. The results presented in this article demonstrate the utility of the ATR/FTIR spectroscopic technique for in situ characterization of protein secondary structures during adsorption on flat surfaces. PMID:15542559

  2. Conformal coating of highly structured surfaces

    DOEpatents

    Ginley, David S.; Perkins, John; Berry, Joseph; Gennett, Thomas

    2012-12-11

    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.

  3. The electronic band structure of GaBiAs/GaAs layers: Influence of strain and band anti-crossing

    NASA Astrophysics Data System (ADS)

    Batool, Z.; Hild, K.; Hosea, T. J. C.; Lu, X.; Tiedje, T.; Sweeney, S. J.

    2012-06-01

    The GaBixAs1-x bismide III-V semiconductor system remains a relatively underexplored alloy particularly with regards to its detailed electronic band structure. Of particular importance to understanding the physics of this system is how the bandgap energy Eg and spin-orbit splitting energy ?o vary relative to one another as a function of Bi content, since in this alloy it becomes possible for ?o to exceed Eg for higher Bi fractions, which occurrence would have important implications for minimising non-radiative Auger recombination losses in such structures. However, this situation had not so far been realised in this system. Here, we study a set of epitaxial layers of GaBixAs1-x (2.3% ? x ? 10.4%), of thickness 30-40 nm, grown compressively strained onto GaAs (100) substrates. Using room temperature photomodulated reflectance, we observe a reduction in Eg, together with an increase in ?o, with increasing Bi content. In these strained samples, it is found that the transition energy between the conduction and heavy-hole valence band edges is equal with that between the heavy-hole and spin-orbit split-off valence band edges at ˜9.0 ± 0.2% Bi. Furthermore, we observe that the strained valence band heavy-hole/light-hole splitting increases with Bi fraction at a rate of ˜15 (±1) meV/Bi%, from which we are able to deduce the shear deformation potential. By application of an iterative strain theory, we decouple the strain effects from our experimental measurements and deduce Eg and ?o of free standing GaBiAs; we find that ?o indeed does come into resonance with Eg at ˜10.5 ± 0.2% Bi. We also conclude that the conduction/valence band alignment of dilute-Bi GaBiAs on GaAs is most likely to be type-I.

  4. Optical Elements with Subwavelength Structured Surfaces

    Microsoft Academic Search

    Hisao Kikuta; Hiroshi Toyota; Wanji Yu

    2003-01-01

    Various optical elements with subwavelength structured surfaces have been developed. The periods of the subwavelength structures are too short to generate diffracted light waves. But the structures are equivalent to refractive index materials with form birefringence. Many new optical elements are realized using the artificial refractive indices of these subwavelength structures. Some typical elements are described here in the passive

  5. Surface crystallography and electronic structure of potassium yttrium tungstate

    SciTech Connect

    Atuchin, V. V.; Pokrovsky, L. D. [Laboratory of Optical Materials and Structures, Institute of Semiconductor Physics, SB RAS, Novosibirsk 90, 630090 (Russian Federation); Khyzhun, O. Yu.; Sinelnichenko, A. K. [Frantsevych Institute for Problems of Materials Science, NAS of Ukraine, 3 Krzhyzhanivsky Str., UA-03142 Kiev (Ukraine); Ramana, C. V. [Departments of Metallurgical and Materials Engineering and Electrical and Computer Engineering, University of Texas at El Paso, El Paso, Texas 79968 (United States)

    2008-08-01

    Structural and electronic characteristics of KY(WO{sub 4}){sub 2} (KYW) (010) crystal surfaces have been studied using reflection high-energy electron diffraction (RHEED) and x-ray photoelectron spectroscopy (XPS). The results indicate that the crystal structure and chemical composition of the mechanically polished pristine surface is stoichiometrically well maintained as expected for KYW crystals. Combined measurements of RHEED and XPS as a function of 1.5 keV Ar{sup +} ion irradiation of the KYW (010) surfaces indicate amorphization, partial loss of potassium atoms, and partial transformation of chemical valence state of tungsten from W{sup 6+} to a lower valence state, W{sup 0} state predominantly, which induces electronic states at the top of valence band.

  6. Topological equivalence of crystal and quasicrystal band structures

    E-print Network

    Kevin A. Madsen; Emil J. Bergholtz; Piet W. Brouwer

    2013-09-11

    A number of recent articles have reported the existence of topologically non-trivial 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.

  7. Topological equivalence of crystal and quasicrystal band structures

    NASA Astrophysics Data System (ADS)

    Madsen, Kevin A.; Bergholtz, Emil J.; Brouwer, Piet W.

    2013-09-01

    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.

  8. Bistatic scattering from a contaminated sea surface observed in C, X, and Ku bands

    NASA Astrophysics Data System (ADS)

    Ghanmi, H.; Khenchaf, A.; Comblet, F.

    2014-10-01

    The aim of the work presented in this paper focuses on the study and analysis of variations of the bistatic electromagnetic signature of the sea surface contaminated by pollutants. Therefore, we will start the numerical analyses of the pollutant effect on the geometrical and physical characteristics of sea surface. Then, we will evaluate the electromagnetic (EM) scattering coefficients of the clean and polluted sea surface observed in bistatic configuration by using the numerical Forward-Backward Method (FBM). The obtained numerical results of the electromagnetic scattering coefficients are studied and given as a function of various parameters: sea state, wind velocity, type of pollutant (sea surface polluted by oil emulsion, and sea surface covered by oil layer), incidence and scattering angles, frequencies bands (C, X and Ku) and radar polarization.

  9. Europium underneath graphene on Ir(111): Intercalation mechanism, magnetism, and band structure

    NASA Astrophysics Data System (ADS)

    Schumacher, Stefan; Huttmann, Felix; Petrovi?, Marin; Witt, Christian; Förster, Daniel F.; Vo-Van, Chi; Coraux, Johann; Martínez-Galera, Antonio J.; Sessi, Violetta; Vergara, Ignacio; Rückamp, Reinhard; Grüninger, Markus; Schleheck, Nicolas; Meyer zu Heringdorf, Frank; Ohresser, Philippe; Kralj, Marko; Wehling, Tim O.; Michely, Thomas

    2014-12-01

    The intercalation of Eu underneath Gr on Ir(111) is comprehensively investigated by microscopic, magnetic, and spectroscopic measurements, as well as by density functional theory. Depending on the coverage, the intercalated Eu atoms form either a (2 ×2 ) or a (?{3 }×?{3 }) R 30? superstructure with respect to Gr. We investigate the mechanisms of Eu penetration through a nominally closed Gr sheet and measure the electronic structures and magnetic properties of the two intercalation systems. Their electronic structures are rather similar. Compared to Gr on Ir(111), the Gr bands in both systems are essentially rigidly shifted to larger binding energies resulting in n doping. The hybridization of the Ir surface state S1 with Gr states is lifted, and the moiré superperiodic potential is strongly reduced. In contrast, the magnetic behavior of the two intercalation systems differs substantially, as found by x-ray magnetic circular dichroism. The (2 ×2 ) Eu structure displays plain paramagnetic behavior, whereas for the (?{3 }×?{3 }) R 30? structure the large zero-field susceptibility indicates ferromagnetic coupling, despite the absence of hysteresis at 10 K. For the latter structure, a considerable easy-plane magnetic anisotropy is observed and interpreted as shape anisotropy.

  10. Systematics of chemical and structural disorder on band-edge properties of semiconductor alloys

    Microsoft Academic Search

    Srinivasan Krishnamurthy; M. A. Berding; A. Sher; A.-B. Chen

    1988-01-01

    A comparison between the coherent-potential approximation and second-order perturbation theory (SPT) shows that the SPT can be used to calculate the band-edge properties, e.g., band gaps, effective masses, and the low-field alloy scattering of electrons and holes of semiconductor alloys. The SPT is used in a systematic study of the effects of chemical and structural disorder on band-gap bowing and

  11. C-Band Airport Surface Communications System Standards Development, Phase I

    NASA Technical Reports Server (NTRS)

    Hall, Edward; Isaacs, James; Zelkin, Natalie; Henriksen. Steve

    2010-01-01

    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

  12. Evidence for water structuring forces between surfaces

    SciTech Connect

    Stanley, Christopher B [ORNL; Rau, Dr. Donald [National Institutes of Health

    2011-01-01

    Structured water on apposing surfaces can generate significant energies due to reorganization and displacement as the surfaces encounter each other. Force measurements on a multitude of biological structures using the osmotic stress technique have elucidated commonalities that point toward an underlying hydration force. In this review, the forces of two contrasting systems are considered in detail: highly charged DNA and nonpolar, uncharged hydroxypropyl cellulose. Conditions for both net repulsion and attraction, along with the measured exclusion of chemically different solutes from these macromolecular surfaces, are explored and demonstrate features consistent with a hydration force origin. Specifically, the observed interaction forces can be reduced to the effects of perturbing structured surface water.

  13. Band structures of bilayer radial phononic crystal plate with crystal gliding

    NASA Astrophysics Data System (ADS)

    Ma, Ting; Chen, Tianning; Wang, Xiaopeng; Li, Yinggang; Wang, Peng

    2014-09-01

    Lamb wave propagation in bilayer radial phononic crystal plate with crystal gliding is investigated. Axial symmetric model in cylindrical coordinate is applied to the bilayer radial phononic crystal plate for band structure calculation and transmission spectra. Gliding in radial direction and direction vertical to plate thickness is analyzed to modulate band gaps. Physical mechanism of gliding effects on radial phononic crystal plate is also studied with displacement fields of super cells. Numerical results show that crystal gliding both in radial direction and direction vertical to plate thickness can significantly tune omnidirectional band gaps. New lower band gaps occur and attenuation areas in transmission spectra are in good agreement with gaps of band structure calculation. Band structure evolution together with eigenmodes indicate that gliding effect converts lamb wave modes resulting in separations or interactions of adjacent bands to open new gaps or close the original ones. In addition, band gaps' sensitivity to crystal gliding is also investigated. Higher gaps are more sensitive to crystal gliding in thickness direction, and lowest gap extends in the map. Crystal gliding in radial direction can open new lowest order gap and open or close another two higher gaps, while the fourth gap is insensitive to it. The omnidirectional band gaps properties have potential application in acoustic device with isotropic gap characters.

  14. Electronic structure of the Cu 3Au(1 1 1) surface

    Microsoft Academic Search

    Ch. E. Lekka; N. Bernstein; M. J. Mehl; D. A. Papaconstantopoulos

    2003-01-01

    Using the NRL-tight binding method, we investigate the electronic structure of the unrelaxed Cu3Au(111) surface. The tight binding parameters were determined by fitting to LDA calculations and found to reproduce the surface energy, bulk elastic constants and bulk phonon modes. The surface electronic band structure shows electronic states at the center of the Brillouin zone, within ?0.1Ry of the Fermi

  15. Electronic transitions in GdN band structure

    SciTech Connect

    Vidyasagar, R., E-mail: drsagar@sapphire.kobe-u.ac.jp; Kita, T. [Department of Electrical and Electronic Engineering, Graduate School of Engineering, Kobe University, 1-1 Rokkodai, Kobe 657-8501 (Japan); Sakurai, T. [Centre for Support to Research and Education Activities, Kobe University, 1-1 Rokkodai, Kobe 657-8501 (Japan); Ohta, H. [Molecular Photoscience Research Center and Graduate School of Science, Kobe University, 1-1 Rokkodai, Kobe 657-8501 (Japan)

    2014-05-28

    Using the near-infrared (NIR) absorbance spectroscopy, electronic transitions and spin polarization of the GdN epitaxial film have been investigated; and the GdN epitaxial film was grown by a reactive rf sputtering technique. The GdN film exhibited three broad bands in the NIR frequency regimes; and those bands are attributable primarily to the minority and majority spin transitions at the X-point and an indirect transition along the ?-X symmetric direction of GdN Brillouin zone. We experimentally observe a pronounced red-shift of the indirect band gap when cooling down below the Curie temperature which is ascribed to the orbital-dependent coulomb interactions of Gd-5dxy electrons, which tend to push-up the N-2p bands. On the other hand, we have evaluated the spin polarization of 0.17 (±0.005), which indicates that the GdN epitaxial film has almost 100% spin-polarized carriers. Furthermore, the experimental result of GdN electronic transitions are consistent with the previous reports and are thus well-reproduced. The Arrott plots evidenced that the Curie temperature of GdN film is 36?K and the large spin moment is explained by the nitrogen vacancies and the intra-atomic exchange interaction.

  16. Contactless electroreflectance of InGaN layers with indium content <=36%: The surface band bending, band gap bowing, and Stokes shift issues

    NASA Astrophysics Data System (ADS)

    Kudrawiec, R.; Siekacz, M.; Kry?ko, M.; Cywi?ski, G.; Misiewicz, J.; Skierbiszewski, C.

    2009-12-01

    Contactless electroreflectance (CER) supported by photoluminescence (PL) has been applied to study (i) the surface band bending, (ii) the band gap bowing, and (iii) the Stokes shift for InGaN layers grown by molecular beam epitaxy with 0.14?In?0.36. The type of surface band bending has been investigated on the basis of the shape of CER resonance. It has been found that the surface band bending changes from n-type for layers with low indium content (In<27%) to flatband (or weak p-type band) for layers with In˜35%. The band gap bowing has been determined to be 1.4±0.2 and 2.1±0.3 eV for CER data with and without strain corrections, respectively. From this analysis it has been concluded that the reliable value of the bowing parameter for unstrained InGaN should be between 1.4 and 2.1 eV. Comparing CER with PL data it has been found that the Stokes shift rises from 20 to 120 meV when the indium concentration increased from 14% to 36%. In addition, it has been observed that the intensity of PL from InGaN layers decreased exponentially with the increase in the indium content. The last two findings are attributed to an easier formation of native point defects and stronger indium segregation in InGaN alloys with higher indium concentrations.

  17. Electronic band structure of Charge Density Wave Pdx HoTe3

    NASA Astrophysics Data System (ADS)

    Wang, Shancai; Cai, Yipeng; Liu, Zhonghao; Jia, Leilei; Zhao, Yange; Qian, T.; Ding, Hong; He, Junbao; Chen, Genfu

    2015-03-01

    The origin of superconductivity and interplay between superconductivity and different ground states remains challenging. The Pd-intercalated HoT3, suppresses the charge density wave (CDW) order and leads to the superconductivity. Here we report the detailed Angle-resolved photoemission spectroscopy (ARPES) study of the electronic structure on PdxHoT3. In the CDW parent phase (HoT3), we found out the Fermi surface topology, CDW gap symmetry have 2 fold symmetry, with one CDW vector. With further Pd-intercalations, the system evolves from 2-fold symmetry to 4-fold symmetry with two CDW vectors, and eventually into superconducting state. The evolution of the CDW gap symmetry, gap size and CDW caused shadow bands are discussed at different phases.

  18. van der Waals binding and band structure effects in graphene overlayers and graphane multilayers

    NASA Astrophysics Data System (ADS)

    Hyldgaard, Per; Rohrer, Jochen

    2011-03-01

    We study graphene formation (by selective Si evaporation) and adhesion on SiC surfaces as well as stacking and binding of graphane multilayers using a number of versions of the van der Waals Density Functional (vdW-DF) method and plane-wave density functional theory calculations. For the graphene/SiC systems and for the graphane multilayers we document that the bonding is entirely dominated by van der Waals (vdW) forces. At the same time we find that dispersive forces acting on the layers produce significant modifications in the graphene and graphane band structure. We interpret the changes and discuss a competition between wave function hybridization and interaction with the charge enhancement (between the layers) that results from density overlap. Supported by Svenska Vetenskapsrådet VR #621-2008-4346.

  19. Electron momentum density, band structure, and structural properties of SrS

    SciTech Connect

    Sharma, G., E-mail: gsphysics@gmail.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)

    2013-10-15

    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.

  20. Compact Electromagnetic Bandgap Structures for Notch Band in Ultra-Wideband Applications

    PubMed Central

    Rotaru, Mihai; Sykulski, Jan

    2010-01-01

    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

  1. Near-infrared observations of galaxies in Pisces-Perseus. I. vec H-band surface photometry of 174 spiral

    NASA Astrophysics Data System (ADS)

    Moriondo, G.; Baffa, C.; Casertano, S.; Chincarini, G.; Gavazzi, G.; Giovanardi, C.; Hunt, L. K.; Pierini, D.; Sperandio, M.; Trinchieri, G.

    1999-05-01

    We present near-infrared, H-band (1.65 $() ?m), surface photometry of 174 spiral galaxies in the area of the Pisces-Perseus supercluster. The images, acquired with the ARNICA camera mounted on various telescopes, are used to derive radial profiles of surface brightness, ellipticities, and position angles, together with global parameters such as H-band magnitudes and diameters Radial profiles in tabular form and images FITS files are also available upon request from gmorio@arcetri.astro.it.}. The mean relation between H-band isophotal diameter D_{21.5} and the B-band D25 implies a B-H color of the outer disk bluer than 3.5; moreover, D_{21.5}/D25 depends on (global) color and absolute luminosity. The correlations among the various photometric parameters suggest a ratio between isophotal radius D_{21.5}/2 and disk scale length of ~ m3.5 and a mean disk central brightness ~ meq 17.5 H-mag arcsec^{-2}. We confirm the trend of the concentration index C31$ with absolute luminosity and, to a lesser degree, with morphological type. We also assess the influence of non-axisymmetric structures on the radial profiles and on the derived parameters. Based on observations at the TIRGO, NOT, and VATT telescopes. TIRGO (Gornergrat, CH) is operated by CAISMI-CNR, Arcetri, Firenze. NOT (La Palma, Canary Islands) is operated by NOTSA, the Nordic Observatory Scientific Association. VATT (Mt. Graham, Az) is operated by VORG, the Vatican Observatory Research Group Table 3 and Fig. 4 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html.

  2. The L-band PBMR measurements of surface soil moisture in FIFE

    Microsoft Academic Search

    J. R. Wang; J. C. Shiue; T. J. Schmugge; E. T. Engman

    1990-01-01

    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

  3. Estimation of sea surface temperature using the AVHRR mid-wave IR band

    Microsoft Academic Search

    Jennifer C. Davis; J. X. Tull; S. P. Byrne; James J. Lisowski

    2001-01-01

    We describe a method for estimating sea surface temperature (SST) using MWIR band data from the AVHRR polar orbiter. Currently, SST is routinely calculated with a split-window, nonlinear multichannel algorithm incorporating data from AVHRR Channels 4 and 5 (10.3-11.3 and 11.5-12.5 ?m, respectively). The accuracy of these results is dependent to a certain degree upon regional variations and is inherently

  4. Polarimetric measurements of sea surface brightness temperatures using an aircraft K-band radiometer

    Microsoft Academic Search

    Simon H. Yueh; William J. Wilson; Fuk K. Li; Son V. Nghiem; William B. Ricketts

    1995-01-01

    Presents the first experimental evidence that the polarimetric brightness temperatures of sea surfaces are sensitive to ocean wind direction in the incidence angle range of 30 to 50°. The experimental data were collected by a K-band (19.35 GHz) polarimetric wind radiometer (WINDRAD) mounted on the NASA DC-8 aircraft. A set of aircraft radiometer flights was successfully completed in November 1993.

  5. Band gap widening by photonic crystal heterostructures composed of two dimensional holes and diamond structure

    NASA Astrophysics Data System (ADS)

    Chen, Shibin; Li, Dichen; Zhi-Hui, Yuan

    2013-06-01

    A new kind of heterostructures containing 3D diamond and 2D holes structures, and diamond-structure photonic crystals and 2D holes-structure photonic crystals fabricated by stereolithography and gel-casting with alumina were studied at microwave range, respectively. The heterostructures were designed by 2D holes structure embedded in 3D diamond structure, in which the lattice of three kinds of structures was equivalent. It was found that the band gaps of photonic crystal heterostructure were broadened by 124.6% and 150% comparing to that of diamond-structure crystal and 2D aerial holes structure. Experimental results showed the band gap broadened was not connected with a linear superposition of the band gap of 2D and 3D photonic crystals, which was the superposition of partial overlap.

  6. Strain dependence of valence band structure and intersubband transitions in coupled quantum wells

    Microsoft Academic Search

    Bozena Olejn??ková

    1996-01-01

    We have calculated the structure of the valence bands and its dependence on strain in a lattice mismatched quantum well, and in double quantum wells with equal and unequal well thicknesses. We have used the 4×4 Luttinger-Kohn Hamiltonian and the envelope function approximation. Further the character of the strain dependence of optical transitions in valence band was analysed in all

  7. Sensitivity of seismic waves to structure: Wide-angle broad-band sensitivity packets

    E-print Network

    Cerveny, Vlastislav

    Sensitivity of seismic waves to structure: Wide-angle broad-band sensitivity packets Ludek Klimes domain as the sensitivity beams, and in the time domain as the sensitivity packets. The sensitivity packets are mostly represented by narrow­band Gaussian sensitivity packets studied in the previous paper

  8. Absolute three-dimensional photonic band gap in the infrared regime in woven structures

    Microsoft Academic Search

    Ya-Chih Tsai; John B. Pendry; Kenneth W.-K. Shung

    1999-01-01

    We closely study the formation of a three-dimensional (3D) photonic band gap in a system composed of dielectric fibers. The fibers are woven into layers that are then stacked up to form 3D lattices of different structures. The woven systems have the advantage of easy fabrication and, with the cross sections of fibers in microns, the band gap can be

  9. Highly efficient parametric interactions in one-dimensional photonic band gap structures

    Microsoft Academic Search

    M. Centini; Michael Scalora; Concita Sibilia; Mario Bertolotti; Mark J. Bloemer; Charles M. Bowden

    1999-01-01

    Band edge effects such as increased density of modes, large field enhancement, and low group velocity will provide highly efficient parametric amplification if the proper phase matching conditions can be established. We derive the phase matching conditions for 1D-photonic band gap structures. Direct integration of Maxwell's equations in the time domain confirms these conclusions, and show that parametric amplification in

  10. An ultrathin wide-band planar metamaterial absorber based on a fractal frequency selective surface and resistive film

    NASA Astrophysics Data System (ADS)

    Fan, Yue-Nong; Cheng, Yong-Zhi; Nie, Yan; Wang, Xian; Gong, Rong-Zhou

    2013-06-01

    We propose an ultrathin wide-band metamaterial absorber (MA) based on a Minkowski (MIK) fractal frequency selective surface and resistive film. This absorber consists of a periodic arrangement of dielectric substrates sandwiched with an MIK fractal loop structure electric resonator and a resistive film. The finite element method is used to simulate and analyze the absorption of the MA. Compared with the MA-backed copper film, the designed MA-backed resistive film exhibits an absorption of 90% at a frequency region of 2 GHz-20 GHz. The power loss density distribution of the MA is further illustrated to explain the mechanism of the proposed MA. Simulated absorptions at different incidence cases indicate that this absorber is polarization-insensitive and wide-angled. Finally, further simulated results indicate that the surface resistance of the resistive film and the dielectric constant of the substrate can affect the absorbing property of the MA. This absorber may be used in many military fields.

  11. Surface transport of nutrients from surface broadcast and subsurface-banded broiler litter

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Broiler chicken litter is commonly used as a fertilizer on pastures and cropland in major broiler-producing states. However, phosphorus (P) loss from fields fertilized with broiler litter contributes to eutrophication and growth of toxic algae in surface waters. Recently, to reduce surface transpo...

  12. Band structures in 98Ru and 99Ru

    Microsoft Academic Search

    E. H. Du Marchie van Voorthuysen; M. J. A. Devoigt; N. Blasi; J. F. W. Jansen

    1981-01-01

    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 =

  13. Quasiparticle band structure of rocksalt-CdO determined using maximally localized Wannier functions.

    PubMed

    Dixit, H; Lamoen, D; Partoens, B

    2013-01-23

    CdO in the rocksalt structure is an indirect band gap semiconductor. Thus, in order to determine its band gap one needs to calculate the complete band structure. However, in practice, the exact evaluation of the quasiparticle band structure for the large number of k-points which constitute the different symmetry lines in the Brillouin zone can be an extremely demanding task compared to the standard density functional theory (DFT) calculation. In this paper we report the full quasiparticle band structure of CdO using a plane-wave pseudopotential approach. In order to reduce the computational effort and time, we make use of maximally localized Wannier functions (MLWFs). The MLWFs offer a highly accurate method for interpolation of the DFT or GW band structure from a coarse k-point mesh in the irreducible Brillouin zone, resulting in a much reduced computational effort. The present paper discusses the technical details of the scheme along with the results obtained for the quasiparticle band gap and the electron effective mass. PMID:23235114

  14. Space-based detection of wetlands' surface water level changes from L-band SAR interferometry

    USGS Publications Warehouse

    Wdowinski, S.; Kim, S.-W.; Amelung, F.; Dixon, T.H.; Miralles-Wilhelm, F.; Sonenshein, R.

    2008-01-01

    Interferometric processing of JERS-1 L-band Synthetic Aperture Radar (SAR) data acquired over south Florida during 1993-1996 reveals detectable surface changes in the Everglades wetlands. Although our study is limited to south Florida it has implication for other large-scale wetlands, because south Florida wetlands have diverse vegetation types and both managed and natural flow environments. Our analysis reveals that interferometric coherence level is sensitive to wetland vegetation type and to the interferogram time span. Interferograms with time spans less than six months maintain phase observations for all wetland types, allowing characterization of water level changes in different wetland environments. The most noticeable changes occur between the managed and the natural flow wetlands. In the managed wetlands, fringes are organized, follow patterns related to some of the managed water control structures and have high fringe-rate. In the natural flow areas, fringes are irregular and have a low fringe-rate. The high fringe rate in managed areas reflects dynamic water topography caused by high flow rate due to gate operation. Although this organized fringe pattern is not characteristic of most large-scale wetlands, the high level of water level change enables accurate estimation of the wetland InSAR technique, which lies in the range of 5-10??cm. The irregular and low rate fringe pattern in the natural flow area reflects uninterrupted flow that diffuses water efficiently and evenly. Most of the interferograms in the natural flow area show an elongated fringe located along the transitional zone between salt- and fresh-water wetlands, reflecting water level changes due to ocean tides. ?? 2007 Elsevier Inc. All rights reserved.

  15. Electron Transport and Band Structure in Phosphorus-Doped Polycrystalline Silicon Films

    SciTech Connect

    Young, D. L.; Branz, H. M.; Liu, F.; Reedy, R.; To, B.; Wang, Q.

    2009-01-01

    We study transport mechanisms, effective mass, and band structure by measuring the resistivity, Hall, and Seebeck and Nernst coefficients in heavily phosphorus-doped polycrystalline silicon films made by thermal crystallization of amorphous silicon. We observe a change in transport mechanism which results in an increase in electron mobility from 10% to 80% of the single-crystal silicon mobility as the carrier concentration increases from 10{sup 19} to 10{sup 20} cm{sup -3}. Our measurements of effective mass at the Fermi level indicate that as the carrier concentration increases, there is a shift from impurity-band transport to conduction-band transport, and that the electron effective mass is lower in the impurity band than in the conduction band of Si. The shift to conduction-band transport improves electron mobility with carrier density by improving intragrain carrier mean free path lengths and relaxation times.

  16. Band structure engineering through orbital interaction for enhanced thermoelectric power factor

    NASA Astrophysics Data System (ADS)

    Zhu, Hong; Sun, Wenhao; Armiento, Rickard; Lazic, Predrag; Ceder, Gerbrand

    2014-02-01

    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.

  17. Robust topology optimization of three-dimensional photonic-crystal band-gap structures

    E-print Network

    Lee, K. Y. K.

    We perform full 3D topology optimization (in which “every voxel” of the unit cell is a degree of freedom) of photonic-crystal structures in order to find optimal omnidirectional band gaps for various symmetry groups, ...

  18. Calculation of wakefields in a 17 GHz beam-driven photonic band-gap accelerator structure

    E-print Network

    Hu, Min

    We present the theoretical analysis and computer simulation of the wakefields in a 17 GHz photonic band-gap (PBG) structure for accelerator applications. Using the commercial code CST Particle Studio, the fundamental ...

  19. Coupled structure for wide-band EDFA with gain and noise figure improvements from C to L-band ASE injection

    Microsoft Academic Search

    Bumki Min; Hosung Yoon; Won Jae Lee

    2000-01-01

    We propose a novel structure for C plus L-band silica based wide-band erbium-doped fiber amplifiers (W-EDFA's), which use backward amplified spontaneous emission from the C-band EDFA as the pump-mediating injection source for the L-band amplifier unit. Experimental results show gain and noise figure improvements of over 2.6 dB and 0.6 dB, respectively, at -3.5 dBm of L-band input signal power.

  20. Tensile-strain effects in quantum-well and superlattice band structures

    Microsoft Academic Search

    Arvind Baliga; Dhrupad Trivedi; Neal G. Anderson

    1994-01-01

    The effects of tensile strain on the energy-band structures of semiconductor quantum wells and superlattices (SL's) are studied theoretically, with emphasis on structures with unique valence-subband configurations achievable only through the use of tensile strain. Quantum wells are treated using finite-element envelope-function calculations which fully treat interactions between the light-hole, heavy-hole, and split-off valence bands, whereas strained SL's are modeled

  1. Elctronic band structures and charge densities of NbC and NbN

    Microsoft Academic Search

    D. J. Chadi; Marvin L. Cohen

    1974-01-01

    Nonlocal-pseudopotential calculations of the electronic band structures and of the charge densities of NbC and NbN are presented. The band structures of the two systems are found to be very similar to each other and the most important difference appears to be the position of the Fermi energy which determines the occupancy and electronic charge distribution in the partially filled

  2. Energy-band-structure studies of NbN(100) and VN(100)

    Microsoft Academic Search

    A. Callens; L. I. Johansson; A. N. Christensen; K. Schwarz; P. Blaha

    1985-01-01

    Band-structure studies of NbN and VN are reported. The results of angle-resolved photoemission experiments performed on NbN0.93 and VN0.89 are presented. The bulk-band structures calculated for stoichiometric NbN and VN using the linearized augmented-plane-wave method are presented and utilized in the interpretation of the experimental spectra. It is shown that most of the features in the spectra can be accounted

  3. Surface Characterization by Structure Function Analysis

    NASA Astrophysics Data System (ADS)

    Kreis, T.; Burke, J.; Bergmann, R. B.

    2014-08-01

    The structure function is a tool for characterizing technical surfaces which exhibits a number of advantages over Fourier-based analysis methods. So it is optimally suited for analyzing the height distributions of surfaces measured by full-field non-contacting methods. After the definition of line- and area-structure function and offering effective procedures for their calculation this tutorial paper presents examples using simulated and measured data of machined surfaces as well as optical components. Comparisons with the results of Fourier-based evaluations clearly prove the advantages of structure function analysis.

  4. Surface structure of Uukuniemi virus.

    PubMed Central

    von Bonsdorff, C H; Pettersson, R

    1975-01-01

    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 PMID:52726

  5. Modification of Casimir Forces Due to Band Gaps in Periodic Structures

    NASA Astrophysics Data System (ADS)

    Villarreal, C.; Esquivel-Sirvent, R.; Cocoletzi, G. H.

    The Casimir force between inhomogeneous slabs that exhibit a band-like structure is calculated. The slabs are made of basic unit cells each made of two layers of different materials. As the number of unit cells increases the Casimir force between the slabs changes, since the reflectivity develops a band-like structure characterized by frequency regions of high reflectivity. This is also evident in the difference of the local density of states between free and boundary distorted vacuum, that becomes maximum at frequencies corresponding to the band gaps. The calculations are restricted to vacuum modes with wave vectors perpendicular to the slabs.

  6. Tuning of band structures in porous phononic crystals by grading design of cells.

    PubMed

    Wang, Kai; Liu, Ying; Yang, Qin-Shan

    2015-08-01

    As the results of the evolution of species, grading structures widely exist in the nature and display distinguish advantages. In this manuscript, grading concept is introduced to redesign the topological structure of pores with the aim to see the effects of grading on the band structure in porous phononic crystals. Circular pores are considered and the crossing grading is made. The wave dispersion in graded structures is investigated comparatively to the normal ones under the same porosity. The band gaps in grading structures are given, as well as the vibration modes of the unit cell corresponding to the absolute band gap (ABG) edges. The results show that the grading structure greatly decreases the critical porosity for the opening of the ABGs. Wider ABGs could be obtained at lower frequencies along with the increase of the porosity. Through controlling the topological parameters of the grading structure, the band structure could be tuned. These results will provide an important guidance in the band tuning in porous phononic crystals by grading design of cells. PMID:25890636

  7. Sub-$\\mu$ structured Lotus Surfaces Manufacturing

    E-print Network

    Worgull, M; Mappes, T; Matthis, B; Tosello, G; Metz, T; Gavillet, J; Koltay, P; Hansen, H N

    2008-01-01

    Sub-micro structured surfaces allow modifying the behavior of polymer films or components. Especially in micro fluidics a lotus-like characteristic is requested for many applications. Structure details with a high aspect ratio are necessary to decouple the bottom and the top of the functional layer. Unlike to stochastic methods, patterning with a LIGA-mold insert it is possible to structure surfaces very uniformly or even with controlled variations (e.g. with gradients). In this paper we present the process chain to realize polymer sub-micro structures with minimum lateral feature size of 400 nm and up to 4 micrometers high.

  8. Direct Demonstration of Environment-Sensitive Surface Plasmon Resonance Band in Single Gold Nanoparticles

    NASA Astrophysics Data System (ADS)

    Itoh, Tamitake; Asahi, Tsuyoshi; Masuhara, Hiroshi

    2002-01-01

    We investigated single gold nanoparticles embedded in poly(vinyl alcohol) (PVA) films with different thicknesses using Rayleigh light-scattering microspectroscopy. First, gold nanoparticles with a mean radius of 40 nm were dispersed in a thin polymer film. Then, the film was covered with multiple layers of PVA to the desired thickness. As a result, we confirmed that the surface plasmon (SP) resonance band of single particles demonstrated redshift with the film thickness increase. In a thick film, the SP band peak position was well explained in terms of the size of the gold nanoparticles. In contrast, the spectral variance observed in a thin film did not follow the size-dependence trend. Since nanoparticles in a thin film are partially covered with PVA layers and thus are partially exposed to air, our results confirm that SP resonance strongly depends not only on a particle’s size but also on its surrounding dielectric conditions.

  9. The optical band gap and surface free energy of polyethylene modified by electron beam irradiations

    NASA Astrophysics Data System (ADS)

    Abdul-Kader, A. M.

    2013-04-01

    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.

  10. Subwavelength structured surfaces and their applications

    NASA Technical Reports Server (NTRS)

    Raguin, Daniel H.; Morris, G. Michael

    1993-01-01

    The term subwavelength structured (SWS) surface describes any surface that contains a subwavelength-period grating or gratings. The grating may be of any type provided the period is sufficiently fine so that, unlike conventional gratings, no diffraction orders propagate other than the zeroth orders. Because of the fine periods involved, the fabrication of such surfaces for applications in the visible and infrared portions of the spectral regime have only recently been considered. With refinements in holographic procedures and the push of the semiconductor industry for submicron lithography, production of SWS surfaces is becoming increasingly viable. The topics covered include the following: analytic approaches to analyze SWS surfaces, 1D periodic stratification and effective medium theory, design of waveplates using form birefringence, and 2D binary antireflection structured surfaces.

  11. Fine structure of the red luminescence band in undoped GaN

    SciTech Connect

    Reshchikov, M. A., E-mail: mreshchi@vcu.edu [Department of Physics, Virginia Commonwealth University, Richmond, Virginia 23284 (United States); Usikov, A. [Nitride Crystals, Inc., 181E Industry Ct., Ste. B, Deer Park, New York 11729 (United States); Saint-Petersburg National Research University of Information Technologies, Mechanics and Optics, 49 Kronverkskiy Ave., 197101 Saint Petersburg (Russian Federation); Helava, H.; Makarov, Yu. [Nitride Crystals, Inc., 181E Industry Ct., Ste. B, Deer Park, New York 11729 (United States)

    2014-01-20

    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.

  12. Functional topography of band 3: specific structural alteration linked to function aberrations in human erythrocytes

    SciTech Connect

    Kay, M.M.B.; Bosman, G.J.C.G.M.; Lawrence, C.

    1988-01-01

    Band 3 is the major anion transport polypeptide of erythrocytes. It appears to be the binding site of several glycolytic enzymes. Structurally, band 3 is the major protein spanning the erythrocyte membrane and connects the plasma membrane to band 2.1, which binds to the cytoskeleton. In the present study, the authors report an alteration of band 3 molecule that is associated with the following changes: erythrocyte shape change from discoid to thorny cells (acanthocytes), restriction of rotational diffusion of band 3 in the membrane, increase in anion transport, and decrease in the number of high-affinity ankyrin-binding sites. Changes in erythrocyte IgG binding, glyceraldehyde-3-phosphate dehydrogenase, fluorescence polarization (indicative of membrane fluidity), and other membrane proteins as determined by polyacrylamide gel electrophoresis were not detected. Cells containing the altered band 3 polypeptide were obtained from individuals with abnormal erythrocyte morphology. Two-dimensional peptide maps revealed differences in the M/sub r/ 17,000 anion transport segment of band 3 consistent with additions of tyrosines or tyrosine-containing peptides. The data suggest that (i) this alteration of band 3 does not result in accelerated aging as does cleavage and (ii) structural changes in the anion transport region result in alterations in anion transport.

  13. L Band Radar Backscatter Dependence Upon Surface Wind Stress: A Summary of New SEASAT1 and Aircraft Observations

    Microsoft Academic Search

    T. W. Thompson; D. E. Weissman; F. I. Gonzalez

    1983-01-01

    Radar backscatter from the ocean depends on surface wind stress for a wide range of radar wavelengths. Here, we have reviewed the wind-radar relationships for L band radar wavelengths near 25 cm and 20 ø angle of incidence and HH polarization using a number of aircraft and SEASAT-! SAR observations. At this wavelength, the L band backscatter coefficient (o )

  14. Predicting band structure of 3D mechanical metamaterials with complex geometry via XFEM

    NASA Astrophysics Data System (ADS)

    Zhao, Jifeng; Li, Ying; Liu, Wing Kam

    2015-04-01

    Band structure characterizes the most important property of mechanical metamaterials. However, predicting the band structure of 3D metamaterials with complex microstructures through direct numerical simulation (DNS) is computationally inefficient due to the complexity of meshing. To overcome this issue, an extended finite element method (XFEM)-based method is developed to predict 3D metamaterial band structures. Since the microstructure and material interface are implicitly resolved by the level-set function embedded in the XFEM formulation, a non-conforming (such as uniform) mesh is used in the proposed method to avoid the difficulties in meshing complex geometries. The accuracy and mesh convergence of the proposed method have been validated and verified by studying the band structure of a spherical particle embedded in a cube and comparing the results with DNS. The band structures of 3D metamaterials with different microstructures have been studied using the proposed method with the same finite element mesh, indicating the flexibility of this method. This XFEM-based method opens new opportunities in design and optimization of mechanical metamaterials with target functions, e.g. location and width of the band gap, by eliminating the iterative procedure of re-building and re-meshing microstructures that is required by classical DNS type of methods.

  15. Modeling of Laser Induced Periodic Surface Structures

    Microsoft Academic Search

    J. Z. P. Skolski; G. R. B. E. Römer; A. J. Huis in't Veld; V. S. Mitko; J. V. Obona; V. Ocelik; Hosson de J. Th. M

    2010-01-01

    In surfaces irradiated by short laser pulses, Laser Induced Periodic Surface Structures (LIPSS) have\\u000abeen observed on all kind of materials for over forty years. These LIPSS, also referred to as ripples,\\u000aconsist of wavy surfaces with periodicity equal or smaller than the wavelength of the laser radiation.\\u000aUnfortunately, the physical phenomena explaining ripple initiation, growth and transitions toward other

  16. S-band accelerating structures for the PAL-XFEL

    NASA Astrophysics Data System (ADS)

    Lee, Heung-Soo; Park, Young Jung; Joo, Young-Do; Heo, Hoon; Heo, Jinyul; Kim, Sang-Hee; Park, Soung-Soo; Hwang, Woon Ha; Kang, Heung-Sik; Kim, Kwang-woo; Ko, In-Soo; Oh, Kyoung-Min; Noh, Sung-Joo; Bak, Yong Hwan; Matsumoto, Hiroshi

    2015-02-01

    One hundred seventy-two accelerating structures are required for the Pohang Accelerator Laboratory X-ray free-electron laser's (PAL-XFEL's) 10-GeV main linear accelerator. So far, we have purchased 80 structures from Mitsubishi Heavy Industry (MHI), which have quasi-symmetric couplers in the accelerating structure to reduce the quadruple and the sextuple components of the electric field in the coupling cavity. High-power tests have been conducted for the first structure of the MHI structure, and Research Instruments (RI) has developed a 3-m long accelerating structure that has an operating frequency of 2856 MHz and in/out couplers of quasi-symmetric racetrack shape for the PAL-XFEL linear accelerator. This structure also has been tested by PAL and RI in the Pohang accelerator laboratory (PAL) to check the maximum available electric field gradient. We will describe the test results of these structures and the current status for the fabrication of the other accelerating structures in this paper.

  17. Evidence of ion intercalation mediated band structure modification and opto-ionic coupling in lithium niobite

    NASA Astrophysics Data System (ADS)

    Shank, Joshua C.; Tellekamp, M. Brooks; Doolittle, W. Alan

    2015-01-01

    The theoretically suggested band structure of the novel p-type semiconductor lithium niobite (LiNbO2), the direct coupling of photons to ion motion, and optically induced band structure modifications are investigated by temperature dependent photoluminescence. LiNbO2 has previously been used as a memristor material but is shown here to be useful as a sensor owing to the electrical, optical, and chemical ease of lithium removal and insertion. Despite the high concentration of vacancies present in lithium niobite due to the intentional removal of lithium atoms, strong photoluminescence spectra are observed even at room temperature that experimentally confirm the suggested band structure implying transitions from a flat conduction band to a degenerate valence band. Removal of small amounts of lithium significantly modifies the photoluminescence spectra including additional larger than stoichiometric-band gap features. Sufficient removal of lithium results in the elimination of the photoluminescence response supporting the predicted transition from a direct to indirect band gap semiconductor. In addition, non-thermal coupling between the incident laser and lithium ions is observed and results in modulation of the electrical impedance.

  18. Electronic band structure and effective mass parameters of Ge1-xSnx alloys

    NASA Astrophysics Data System (ADS)

    Lu Low, Kain; Yang, Yue; Han, Genquan; Fan, Weijun; Yeo, Yee-Chia

    2012-11-01

    This work investigates the electronic band structures of bulk Ge1-xSnx alloys using the empirical pseudopotential method (EPM) for Sn composition x varying from 0 to 0.2. The adjustable form factors of EPM were tuned in order to reproduce the band features that agree well with the reported experimental data. Based on the adjusted pseudopotential form factors, the band structures of Ge1-xSnx alloys were calculated along high symmetry lines in the Brillouin zone. The effective masses at the band edges were extracted by using a parabolic line fit. The bowing parameters of hole and electron effective masses were then derived by fitting the effective mass at different Sn compositions by a quadratic polynomial. The hole and electron effective mass were examined for bulk Ge1-xSnx alloys along specific directions or orientations on various crystal planes. In addition, employing the effective-mass Hamiltonian for diamond semiconductor, band edge dispersion at the ?-point calculated by 8-band k.p. method was fitted to that obtained from EPM approach. The Luttinger-like parameters were also derived for Ge1-xSnx alloys. They were obtained by adjusting the effective-mass parameters of k.p method to fit the k.p band structure to that of the EPM. These effective masses and derived Luttinger parameters are useful for the design of optical and electronic devices based on Ge1-xSnx alloys.

  19. Electronic structure of the side surface of Bi2 Se 3

    NASA Astrophysics Data System (ADS)

    Moon, Chang-Youn; Han, Jinhee; Lee, Hyungjun; Choi, Hyoung Joon

    2011-03-01

    We investigate the electronic band structure of a side surface geometry, other than the conventional [111] surface, of the topological insulator Bi 2 Se 3 using the first-principles pseudopotential calculations. As Bi 2 Se 3 is known to be a strong topological insulator, it is expected that an arbitrary surface would have the topological surface state characterized by Dirac-cone-like band dispersion and spin-momentum coupling. Here we indeed obtain surface states with linear band dispersion around the Gamma point, but with a strong anisotropy with different group velocities along different k-directions. Low energy effective hamiltonian is proposed, and physical implications of the anisotropic Dirac fermions are also discussed. This work was supported by NRF of Korea (Grant No. 2009-0081204) and KISTI Supercomputing Center (Project No. KSC-2008-S02-0004).

  20. Correlating simulated surface marks with near-surface tornado structure

    NASA Astrophysics Data System (ADS)

    Zimmerman, Michael I.

    Tornadoes often leave behind patterns of debris deposition, or "surface marks", which provide a direct signature of their near surface winds. The intent of this thesis is to investigate what can be learned about near-surface tornado structure and intensity through the properties of surface marks generated by simulated, debris-laden tornadoes. Earlier work showed through numerical simulations that the tornado's structure and intensity is highly sensitive to properties of the near-surface flow and can change rapidly in time for some conditions. The strongest winds often occur within tens of meters of the surface where the threat to human life and property is highest, and factors such as massive debris loadings and asymmetry of the main vortex have proven to be critical complications in some regimes. However, studying this portion of the flow in the field is problematic; while Doppler radar provides the best tornado wind field measurements, it cannot probe below about 20 m, and interpretation of Doppler data requires assumptions about tornado symmetry, steadiness in time, and correlation between scatterer and air velocities that are more uncertain near the surface. As early as 1967, Fujita proposed estimating tornado wind speeds from analysis of aerial photography and ground documentation of surface marks. A handful of studies followed but were limited by difficulties in interpreting physical origins of the marks, and little scientific attention has been paid to them since. Here, Fujita's original idea is revisited in the context of three-dimensional, large-eddy simulations of tornadoes with fully-coupled debris. In this thesis, the origins of the most prominent simulated marks are determined and compared with historical interpretations of real marks. The earlier hypothesis that cycloidal surface marks were directly correlated with the paths of individual vortices (either the main vortex or its secondary vortices, when present) is unsupported by the simulation results. Cycloids in the simulations arise from debris deposited beneath the central annular updraft that has converged from a much larger area and are modulated by turbulent fluctuations in debris amount. Other classes of marks noted in the literature such as "lineation" and "scalloping" are also reinterpreted. Variations in the shapes, sizes, and spacings of surface marks with the most critical dimensionless parameters characterizing near-surface and debris cloud structure are explored. Analysis techniques are presented to capture the geometric properties of marks in some regimes, and possibilities for inferring near-surface vortex flow scales from mark properties are discussed. The prospects are promising enough to warrant documentation of surface marks when available (likely through aerial photography), particularly for cases where useful Doppler measurements have been gathered.

  1. Electronic absorption band broadening and surface roughening of phthalocyanine double layers by saturated solvent vapor treatment

    SciTech Connect

    Kim, Jinhyun [Department of Chemistry, Kookmin University, Seoul 136-702 (Korea, Republic of)] [Department of Chemistry, Kookmin University, Seoul 136-702 (Korea, Republic of); Yim, Sanggyu, E-mail: sgyim@kookmin.ac.kr [Department of Chemistry, Kookmin University, Seoul 136-702 (Korea, Republic of)] [Department of Chemistry, Kookmin University, Seoul 136-702 (Korea, Republic of)

    2012-10-15

    Variations in the electronic absorption (EA) and surface morphology of three types of phthalocyanine (Pc) thin film systems, i.e. copper phthalocyanine (CuPc) single layer, zinc phthalocyanine (ZnPc) single layer, and ZnPc on CuPc (CuPc/ZnPc) double layer film, treated with saturated acetone vapor were investigated. For the treated CuPc single layer film, the surface roughness slightly increased and bundles of nanorods were formed, while the EA varied little. In contrast, for the ZnPc single layer film, the relatively high solubility of ZnPc led to a considerable shift in the absorption bands as well as a large increase in the surface roughness and formation of long and wide nano-beams, indicating a part of the ZnPc molecules dissolved in acetone, which altered their molecular stacking. For the CuPc/ZnPc film, the saturated acetone vapor treatment resulted in morphological changes in mainly the upper ZnPc layer due to the significantly low solubility of the underlying CuPc layer. The treatment also broadened the EA band, which involved a combination of unchanged CuPc and changed ZnPc absorption.

  2. Omnidirectional elastic band gap in finite lamellar structures

    Microsoft Academic Search

    D. Bria; B. Djafari-Rouhani

    2002-01-01

    This paper presents a comprehensive theoretical analysis of the occurrence of omnidirectional reflection in one-dimensional phononic crystal structures. We discuss the conditions for a one-dimensional layered structure, made of elastic materials, to exhibit total reflection of acoustic incident waves in a given frequency range, for all incident angles and all polarizations. The property of omnidirectional reflection can be fulfilled with

  3. Tunable narrow band source via the strong coupling between optical emitter and nanowire surface plasmons

    E-print Network

    J. Yang; G. W. Lin; Y. P. Niu; Y. H. Qi; F. X. Zhou; S. Q. Gong

    2014-12-30

    The spectrum width can be narrowed to a certain degree by decreasing the coupling strength for the two-level emitter coupled to the propagating surface plasmon. But the width can not be narrowed any further because of the loss of the photon out of system by spontaneous emission from the emitter. Here we propose a new scheme to construct a narrow-band source via a one-dimensional waveguide coupling with a three-level emitter. It is shown that the reflective spectrum width can be narrowed avoiding the impact of the loss. This approach opens up the possibility of plasmonic ultranarrow single-photon source.

  4. Measurement of the surface wavelength distribution of narrow-band radiation by a colorimetric method

    SciTech Connect

    Kraiskii, A V; Mironova, T V; Sultanov, T T [P N Lebedev Physical Institute, Russian Academy of Sciences, Moscow (Russian Federation)

    2010-09-10

    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)

  5. Evidence for water structuring forces between surfaces

    PubMed Central

    Stanley, Christopher

    2011-01-01

    Structured water on apposing surfaces can generate significant energies due to reorganization and displacement of water as the surfaces encounter each other. Force measurements on a multitude of biological structures using the osmotic stress technique have elucidated commonalities that point toward an underlying hydration force. In this review, the forces of two contrasting systems are considered in detail: highly charged DNA and nonpolar, uncharged hydroxypropyl cellulose. Conditions for both net repulsion and attraction, along with the measured exclusion of chemically different solutes from these macromolecular surfaces, are explored and demonstrate common features consistent with a hydration force origin. Specifically, the observed interaction forces can be reduced to the effects of perturbing structured surface water. PMID:22125414

  6. Energy band alignment and electronic states of amorphous carbon surfaces in vacuo and in aqueous environment

    NASA Astrophysics Data System (ADS)

    Caro, Miguel A.; Määttä, Jukka; Lopez-Acevedo, Olga; Laurila, Tomi

    2015-01-01

    In this paper, we obtain the energy band positions of amorphous carbon (a-C) surfaces in vacuum and in aqueous environment. The calculations are performed using a combination of (i) classical molecular dynamics (MD), (ii) Kohn-Sham density functional theory with the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional, and (iii) the screened-exchange hybrid functional of Heyd, Scuseria, and Ernzerhof (HSE). PBE allows an accurate generation of a-C and the evaluation of the local electrostatic potential in the a-C/water system, HSE yields an improved description of energetic positions which is critical in this case, and classical MD enables a computationally affordable description of water. Our explicit calculation shows that, both in vacuo and in aqueous environment, the a-C electronic states available in the region comprised between the H2/H2O and O2/H2O levels of water correspond to both occupied and unoccupied states within the a-C pseudogap region. These are localized states associated to sp2 sites in a-C. The band realignment induces a shift of approximately 300 meV of the a-C energy band positions with respect to the redox levels of water.

  7. A novel compact uni-planar electromagnetic band-gap (UC-EBG) structure

    Microsoft Academic Search

    Wei Wang; Xiang-yu Cao; Wan-yin Zhou; Tao Liu

    2008-01-01

    A novel uni-planar electromagnetic Band Gap (EBG) structure incorporated with spiral shape capacitor and meandered line inductor(SC-ML-EBG) is presented. This structure significantly enlarges the equivalent capacitance between neighboring elements, as well as increases the equivalent inductance. So, it becomes even more compact in size. A comparison has been carried out between this new structure and the conventional UC-EBG structure. The

  8. Triple photonic band-gap structure dynamically induced in the presence of spontaneously generated coherence

    SciTech Connect

    Gao Jinwei; Bao Qianqian; Wan Rengang; Cui Cuili; Wu Jinhui [College of Physics, Jilin University, Changchun 130012 (China)

    2011-05-15

    We study a cold atomic sample coherently driven into the five-level triple-{Lambda} configuration for attaining a dynamically controlled triple photonic band-gap structure. Our numerical calculations show that three photonic band gaps with homogeneous reflectivities up to 92% can be induced on demand around the probe resonance by a standing-wave driving field in the presence of spontaneously generated coherence. All these photonic band gaps are severely malformed with probe reflectivities declining rapidly to very low values when spontaneously generated coherence is gradually weakened. The triple photonic band-gap structure can also be attained in a five-level chain-{Lambda} system of cold atoms in the absence of spontaneously generated coherence, which however requires two additional traveling-wave fields to couple relevant levels.

  9. Quasiparticle band structures of ?-HgS, HgSe, and HgTe

    NASA Astrophysics Data System (ADS)

    Christensen, Niels E.; Svane, Axel; Cardona, Manuel; Chantis, Athanasios; van Schilfgaarde, Mark; Kotani, Takao

    2012-02-01

    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.

  10. Enhanced thermoelectric performance of La-doped BiCuSeO by tuning band structure

    NASA Astrophysics Data System (ADS)

    Liu, Yaochun; Ding, Jingxuan; Xu, Ben; Lan, Jinle; Zheng, Yuanhua; Zhan, Bin; Zhang, Boping; Lin, Yuanhua; Nan, Cewen

    2015-06-01

    Bi1-xLaxCuSeO ceramic bulks have been prepared by the spark plasma sintering method. Our results indicate that La-doping can lead to an obvious change of the band structure evidenced by the absorption spectra and electric transportation behaviors (e.g., m* and Seebeck coefficient). The variation of band structure results in a great enhancement of carrier mobility caused by a decreased energy offset between the primary and secondary valence bands. A maximum ZT value of 0.74 can be obtained in 8% La-doped BiCuSeO sample at 923 K, which is 37% higher than that of the pure BiCuSeO bulk. Our results reveal that band engineering is an effective way to enhance the thermoelectric properties of BiCuSeO system.

  11. Electronic structure and band alignment at an epitaxial spinel/perovskite heterojunction.

    PubMed

    Qiao, Liang; Li, Wei; Xiao, Haiyan; Meyer, Harry M; Liang, Xuelei; Nguyen, N V; Weber, William J; Biegalski, Michael D

    2014-08-27

    The electronic properties of solid-solid interfaces play critical roles in a variety of technological applications. Recent advances of film epitaxy and characterization techniques have demonstrated a wealth of exotic phenomena at interfaces of oxide materials, which are critically dependent on the alignment of their energy bands across the interface. Here we report a combined photoemission and electrical investigation of the electronic structures across a prototypical spinel/perovskite heterojunction. Energy-level band alignment at an epitaxial Co3O4/SrTiO3(001) heterointerface indicates a chemically abrupt, type I heterojunction without detectable band bending at both the film and substrate. The unexpected band alignment for this typical p-type semiconductor on SrTiO3 is attributed to its intrinsic d-d interband excitation, which significantly narrows the fundamental band gap between the top of the valence band and the bottom of the conduction band. The formation of the type I heterojunction with a flat-band state results in a simultaneous confinement of both electrons and holes inside the Co3O4 layer, thus rendering the epitaxial Co3O4/SrTiO3(001) heterostructure to be a very promising material for high-efficiency luminescence and optoelectronic device applications. PMID:25075939

  12. APW Band Structure of Cubic BaPb1-xBixO3

    NASA Astrophysics Data System (ADS)

    Takegahara, Katsuhiko; Kasuya, Tadao

    1987-04-01

    The self-consistent APW band calculations for the materials of the ideal perovskite structure, BaPbO3 and BaBiO3, and the NaCl type super-cell structure BaPb0.5Bi0.5O3 have been done using the local density approximation. In both BaPbO3 and BaBiO3, the bonding-antibonding splitting of the (Pb, Bi) 6s and O 2p states makes a pair of wide bands of about 15 eV width. At the center of these s-p bands, there are non-bonding O 2p bands with about 4 eV width. The character of these bands is substantially different from the previously reported results of LAPW method. In BaPb0.5Bi0.5O3, due to the potential difference between Pb and Bi sites, each bonding and antibonding s-p band splits into two subbands but the split antibonding bands overlap each other slightly. This result refuses the possibility of the gap formation in the Bi-rich alloys due to the charge density wave because the ordered BaPb0.5Bi0.5O3 offers the upper limit of the charge density in the present system. Then the origin of the insulator property is considered on the standpoint of the spin density wave formation on Bi sites.

  13. Predicted band structures of III-V semiconductors in the wurtzite phase

    SciTech Connect

    De, A.; Pryor, Craig E. [Department of Physics and Astronomy and Optical Science and Technology Center, University of Iowa, Iowa City, Iowa 52242 (United States)

    2010-04-15

    While non-nitride III-V semiconductors typically have a zinc-blende structure, they may also form wurtzite crystals under pressure or when grown as nanowhiskers. This makes electronic structure calculation difficult since the band structures of wurtzite III-V semiconductors are poorly characterized. We have calculated the electronic band structure for nine III-V semiconductors in the wurtzite phase using transferable empirical pseudopotentials including spin-orbit coupling. We find that all the materials have direct gaps. Our results differ significantly from earlier ab initio calculations, and where experimental results are available (InP, InAs, and GaAs) our calculated band gaps are in good agreement. We tabulate energies, effective masses, and linear and cubic Dresselhaus zero-field spin-splitting coefficients for the zone-center states. The large zero-field spin-splitting coefficients we find may facilitate the development of spin-based devices.

  14. Photonic stop bands in quasi-random nanoporous anodic alumina structures

    E-print Network

    Maksymov, Ivan; Pallares, Josep; Marsal, Lluis F

    2011-01-01

    The existence of photonic stop bands in the self-assembled arrangement of pores in porous anodic alumina structures is investigated by means of rigorous 2D finite- difference time-domain calculations. Self-assembled porous anodic alumina shows a random distribution of domains, each of them with a very definite triangular pattern, constituting a quasi-random structure. The observed stop bands are similar to those of photonic quasicrystals or random structures. As the pores of nanoporous anodic alumina can be infiltrated with noble metals, nonlinear or active media, it makes this material very attractive and cost-effective for applications including inhibition of spontaneous emission, random lasing, LEDs and biosensors.

  15. Acoustic band-gap engineering using finite-size layered structures of multiple periodicity

    NASA Astrophysics Data System (ADS)

    Shen, Mingrong; Cao, Wenwu

    1999-12-01

    The transmission coefficient of a layered structure made of glass and water was calculated using transfer matrix method and also measured as a function of frequency. It was found that acoustic band gaps can be created using only 3-4 cells of a two-phase layered structure. By introducing two or more periods into the layered structure, very sharp passbands and very broad stopbands can be engineered for acoustic waves. Such acoustic band-gap materials could be used for making high-quality acoustic filters, acoustic mirrors and vibration insulation devices in selective frequency range.

  16. Two-zone heterogeneous structure within shear bands of a bulk metallic glass

    SciTech Connect

    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)

    2013-10-21

    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.

  17. Absolute determination of electronic band structure of copper by angle-resolved photoemission

    NASA Astrophysics Data System (ADS)

    Courths, R.

    1981-11-01

    Structures in the angle-resolved photoemission spectra from copper in the (1 overline10) and (001) mirror planes at fixed photon energy h? as a function of emission angle show discontinuities in energy position or slope as function of emission angle. These discontinuities are due to the appearance of specific interband transitions on zone boundaries. The appearance angle allow the absolute determination of momentum k of the transition. E( k) points have been determined for most d-bands and several conductions bands. Experimental data are in good agreement with Burdick's band calculation, as also are the E( k) points which have been determined using the energy coincidence method.

  18. Optical Properties and Band Structure of KTaO3

    SciTech Connect

    Jellison Jr, Gerald Earle [ORNL; Paulauskas, Irene E [ORNL; Boatner, Lynn A [ORNL; Singh, David J [ORNL

    2006-01-01

    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).

  19. Antiferromagnetic structures and electronic energy levels at reconstructed NiO(111) surfaces: A DFT +U study

    NASA Astrophysics Data System (ADS)

    Li, Lesheng; Kanai, Yosuke

    2015-06-01

    We studied how the surface reconstruction and passivation influence the antiferromagnetic and electronic structures of NiO(111) surface using first-principles electronic structure calculations. These features lead to a surprisingly wide variety of different surface electronic structures, and some surfaces are even metallic. Different reconstructions and surface passivation were also found to qualitatively alter the charge-transfer band gap type of bulk NiO. At the same time, the antiferromagnetic character of bulk NiO in the ?111? direction is retained even near the surface, and the magnetic moment quickly converges to the bulk value within a few surface layers.

  20. Study on band gap structure of Fibonacci quantum superlattices by using the transfer matrix method

    NASA Astrophysics Data System (ADS)

    Ferrando, V.; Castro-Palacio, J. C.; Marí, B.; Monsoriu, J. A.

    2014-02-01

    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.

  1. The Study of Band Structure of Graphite Intercalation Compound Containing Sodium Calculated Using Density Functional Theory

    NASA Astrophysics Data System (ADS)

    Nazrul Rosli, Ahmad; Fatimah Wahab, Izzati; Zabidi, Noriza Ahmad; Abu Kassim, Hasan

    2015-06-01

    Sodium intercalation in graphite (GIC-Na) was investigated by the first principle calculation. The structure of GIC-Na was calculated using density functional theory (DFT) with the aid of CASTEP module of Material Studio. The exchange correlation functional has been treat by local density approximation (LDA) and generalized gradient approximation (GGA). It was shown that, unlike potassium GIC and lithium GIC, the band gap of GIC-Na was not induced and has same value of band gap with bulk graphite.

  2. PHYSICAL REVIEW B 83, 245202 (2011) Band structure engineering of multinary chalcogenide topological insulators

    E-print Network

    Gong, Xingao

    2011-01-01

    found in strained binary HgTe and ternary I-III-VI2 chalcopyrite compounds such as CuTlSe2 which have of I-III- VI2 chalcopyrite compounds (such as CuTlSe2) could have topologically nontrivial band structure. This is an important observation because the chalcopyrite structure is derived from the zinc

  3. Two-dimensional Penrose-tiled photonic quasicrystals: from diffraction pattern to band structure

    Microsoft Academic Search

    M. A. Kaliteevski; S. Brand; R. A. Abram; T. F. Krauss; R. DeLa Rue; P. Millar

    2000-01-01

    We report measurements of the diffraction pattern of a two-dimensional photonic quasicrystal structure and use the set of plane waves defined by the diffraction pattern as the basis of a theoretical approach to calculate the photonic band structure of the system. An important feature of the model is that it retains the essence of the rotational and inflational properties of

  4. International X-Band Linear Collider Accelerator Structure R&D

    SciTech Connect

    Wang, J.W.; /SLAC

    2009-03-04

    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.

  5. Electromagnetic polarization converttion by multilayered structure of metal-dielectric films on optical wave band

    Microsoft Academic Search

    Lin Zhao; Ting-ting Zhu; Yu-jun Liang; Hui Xie

    2009-01-01

    Based on the effective medium theory, anisotropic microwave materials have been realized by a multilayered structure of alternating films. The equivalent material constitutive tensors have been calculated with different film orientations. The prevenient analysis shows that the structure can realize electromagnetic polarization splitter by controlling the orientation of the films on optical wave band. In this paper, the futher research

  6. Widely tunable surface-emitted monochromatic terahertz-wave generation beyond the Reststrahlen band

    NASA Astrophysics Data System (ADS)

    Saito, Kyosuke; Tanabe, Tadao; Oyama, Yutaka

    2015-01-01

    We proposed a surface-emitted THz-wave generation on the basis of difference frequency mixing in a GaP planar waveguide. By utilizing modal birefringence of fundamental TE and TM modes at telecom wavelengths in the GaP membrane waveguide, phase matching condition for the surface-emitted difference frequency mixing (SE-DFM) can be achieved. THz output power is enhanced near the phonon polariton resonance frequency owing to the strong coupling between the transverse optical (TO) phonon of GaP and THz radiation. The SE-DFM scheme can generate THz waves beyond the Reststrahlen band located between 11 and 12 THz, resulting in widely tunable THz wave generation. Our proposed broadband THz sources can be applicable for optically isotropic nonlinear optical materials such as GaAs and InP as well as GaP.

  7. Quasiparticle band structures of ?-HgS, HgSe, and HgTe

    NASA Astrophysics Data System (ADS)

    Svane, A.; Christensen, N. E.; Cardona, M.; Chantis, A. N.; van Schilfgaarde, M.; Kotani, T.

    2011-11-01

    The electronic structures of mercury chalcogenides in the zinc-blende structure have been calculated within the LDA, GW (G0W0, “one-shot”) 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 (“negative” 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.

  8. Using Pattern Search Methods for Surface Structure Determination of Nanomaterials

    E-print Network

    Lee, Jason R.

    Using Pattern Search Methods for Surface Structure Determination of Nanomaterials Zhengji Zhao High, especially in the case of nanomaterials. One of the most effective techniques for surface structure

  9. Shielding effectiveness of reinforced concrete structures in cellular communication bands

    Microsoft Academic Search

    H. M. Elkamchouchi; A. T. Abdelkader

    2002-01-01

    The proliferation of cellular communication systems in and around man-made structures has resulted in a growing need to determine the shielding properties of various materials commonly used in buildings. This will be useful in two major branches of applications, namely radio base station planning and the effect of exposure to very near radiation sources inside buildings, especially those carrying radio

  10. Direct probing of band-structure Berry phase in diluted magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Granada, M.; Lucot, D.; Giraud, R.; Lemaître, A.; Ulysse, C.; Waintal, X.; Faini, G.

    2015-06-01

    We report on experimental evidence of the Berry phase accumulated by the charge-carrier wave function in single-domain nanowires made from a (Ga, Mn)(As, P) diluted ferromagnetic semiconductor layer. Its signature on the mesoscopic transport measurements is revealed as unusual patterns in the magnetoconductance that are clearly distinguished from the universal conductance fluctuations. We show that these patterns appear in a magnetic field region where the magnetization rotates coherently and are related to a change in the band-structure Berry phase as the magnetization direction changes. They should thus be considered a band-structure Berry phase fingerprint of the effective magnetic monopoles in the momentum space. We argue that this is an efficient method to vary the band structure in a controlled way and to probe it directly. Hence, (Ga, Mn)As appears to be a very interesting test bench for new concepts based on this geometrical phase.

  11. Laser-micromachined millimeter-wave photonic band-gap cavity structures

    SciTech Connect

    Oezbay, E. [Department of Physics, Bilkent University, Bilkent, Ankara 06533 (Turkey)] [Department of Physics, Bilkent University, Bilkent, Ankara 06533 (Turkey); Tuttle, G.; McCalmont, J.S.; Sigalas, M.; Biswas, R.; Soukoulis, C.M.; Ho, K.M. [Microelectronics Research Center and DOE Ames Laboratory, Iowa State University, Ames, Iowa 50011 (United States)] [Microelectronics Research Center and DOE Ames Laboratory, Iowa State University, Ames, Iowa 50011 (United States)

    1995-10-02

    We have used laser-micromachined alumina substrates to build a three-dimensional photonic band-gap crystal. The rod-based structure has a three-dimensional full photonic band gap between 90 and 100 GHz. The high resistivity of alumina results in a typical attenuation rate of 15 dB per unit cell within the band gap. By removing material, we have built defects which can be used as millimeter-wave cavity structures. The resulting quality ({ital Q}) factors of the millimeter-wave cavity structures were as high as 1000 with a peak transmission of 10 dB below the incident signal. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

  12. Electronic Band Structures and Native Point Defects of Ultrafine ZnO Nanocrystals.

    PubMed

    Zeng, Yu-Jia; Schouteden, Koen; Amini, Mozhgan N; Ruan, Shuang-Chen; Lu, Yang-Fan; Ye, Zhi-Zhen; Partoens, Bart; Lamoen, Dirk; Van Haesendonck, Chris

    2015-05-20

    Ultrafine ZnO nanocrystals with a thickness down to 0.25 nm are grown by a metalorganic chemical vapor deposition method. Electronic band structures and native point defects of ZnO nanocrystals are studied by a combination of scanning tunneling microscopy/spectroscopy and first-principles density functional theory calculations. Below a critical thickness of ?1 nm ZnO adopts a graphitic-like structure and exhibits a wide band gap similar to its wurtzite counterpart. The hexagonal wurtzite structure, with a well-developed band gap evident from scanning tunneling spectroscopy, is established for a thickness starting from ?1.4 nm. With further increase of the thickness to 2 nm, VO-VZn defect pairs are easily produced in ZnO nanocrystals due to the self-compensation effect in highly doped semiconductors. PMID:25923131

  13. Photonic band structure in one-dimensional nonlinear crystal: Analysis of harmonic stability

    NASA Astrophysics Data System (ADS)

    Avendaño, Carlos G.; Reyes, J. Adrián

    2015-01-01

    We consider a one-dimensional nonlinear photonic crystal consisting of an infinite set of concentrated equidistant scatterers inserted in a linear dielectric medium. Each of the scatterers is made by a very thin layer of a nonlinear medium with high refractive index that we model by a delta function. We show that the nonlinear optical exact solutions of this system form an intensity dependent band structure. To analyze the stability of these solutions we consider a modulation harmonic perturbation of these solutions whose amplitudes are slightly above the instability threshold. We demonstrate that the nonlinearity gives rise to an oscillatory instability of the solutions, which is a localized version of the well-known modulational instability of the nonlinear Schrodinger equation. We show that the linear harmonic perturbation forms as well a band structure whose allowed bands coincide for some intervals with those of the nonlinear band structure of the solutions for which case the structures are unstable whereas in the region where both the linear and nonlinear bands do not coincide, the nonlinear waves are indeed stable so that they conform spatial solitons.

  14. Studies of Breakdown in High Gradient X-Band Accelerator Structures Using Acoustic Emission

    SciTech Connect

    Frisch, Josef C

    2002-08-23

    X-band accelerator structures meeting the Next Linear Collider (NLC) design requirements have been found to suffer damage due to RF breakdown when processed to high gradients. Improved understanding of these breakdown events is desirable for the development of structure designs, fabrication procedures, and processing techniques that minimize structure damage [1]. Acoustic emission sensors attached to an accelerator structure can detect both nominal and breakdown RF pulses [2]. Using an array of acoustic sensors, we have been able to pinpoint both the cell and azimuth location of individual breakdown events. This allows studies of breakdown time and position sequences so that underlying causes can be determined. The technique provided a significant advance in studies of breakdown in the structure input coupler. In this paper we present acoustic emission sensor data and analysis from the breakdown studies in several x-band accelerator structures.

  15. Surface and deep structures in graphics comprehension.

    PubMed

    Schnotz, Wolfgang; Baadte, Christiane

    2015-05-01

    Comprehension of graphics can be considered as a process of schema-mediated structure mapping from external graphics on internal mental models. Two experiments were conducted to test the hypothesis that graphics possess a perceptible surface structure as well as a semantic deep structure both of which affect mental model construction. The same content was presented to different groups of learners by graphics from different perspectives with different surface structures but the same deep structure. Deep structures were complementary: major features of the learning content in one experiment became minor features in the other experiment, and vice versa. Text was held constant. Participants were asked to read, understand, and memorize the learning material. Furthermore, they were either instructed to process the material from the perspective supported by the graphic or from an alternative perspective, or they received no further instruction. After learning, they were asked to recall the learning content from different perspectives by completing graphs of different formats as accurately as possible. Learners' recall was more accurate if the format of recall was the same as the learning format which indicates surface structure influences. However, participants also showed more accurate recall when they remembered the content from a perspective emphasizing the deep structure, regardless of the graphics format presented before. This included better recall of what they had not seen than of what they really had seen before. That is, deep structure effects overrode surface effects. Depending on context conditions, stimulation of additional cognitive processing by instruction had partially positive and partially negative effects. PMID:25465898

  16. Wetting of regularly structured gold surfaces.

    PubMed

    Abdelsalam, Mamdouh E; Bartlett, Philip N; Kelf, Timothy; Baumberg, Jeremy

    2005-03-01

    In this study we report results for a systematic study of the wetting of structured gold surfaces formed by electrodeposition through monolayer templates of close-packed uniform submicrometer spheres. Removal of the template after deposition leaves a regular hexagonal array of sphere segment pores where the depth of the pores and, thus, the topography of the surface are controlled by the thickness of gold deposited through the template. We find that, as the thickness of the porous film increases up to the radius of the pores, the apparent contact angle for water on the surface increases from 70 degrees on the flat surface to more that 130 degrees , and then with increasing thickness above the radius of the pores the apparent contact angle decreases back toward 70 degrees . We show that these changes in the apparent contact angle agree with the model of Cassie and Baxter for nonwetted surfaces even though the gold itself is hydrophilic. We also show that the apparent contact angle is independent of the diameter of the pores over the range 400-800 nm. This is the first reported example showing the change of a hydrophilic surface (theta; < 90 degrees ) into a hydrophobic surface (theta; > 90 degrees ) purely by control of the surface topography. The role of the pore shape and size in stabilizing the nonwetting (Cassie-Baxter) droplet on the surface is discussed. PMID:15723469

  17. Nonlinear photonic band-gap structure with extremely high efficiency for third-harmonic generation

    Microsoft Academic Search

    B. Shi; X. Wang

    2002-01-01

    A method of tailoring the electromagnetic states in photonic band-gap structures was used in designing a dielectric structure optimized for third-harmonic generation. The structure we considered was a stack of several kinds of chi(2) nonlinear bilayers approximately 10 mum in length. In the theoretical analysis and numerical experiment, a conversion efficiency enhancement of more than 14 orders of magnitude, as

  18. Band structures of Ni 3 Pt and NiPt 3

    Microsoft Academic Search

    Alejandro Pisanty; Carlos Amador; Yosadara Ruiz; Martha de la Vega

    1990-01-01

    The results of self-consistent, spin-polarized LMTO band structure calculations are shown for the compounds Ni3Pt and NiPt3, ofL12 (Cu3Au) structure. Lattice constants are reported together with bulk moduli, and the electronic structure is studied in relation to magnetism in both cubic compounds. Covalent magnetism is shown to act against the magnetization in Ni3Pt.

  19. Earth-Viewing L-Band Radiometer Sensing of Sea Surface Scattered Celestial Sky Radiation—Part I: General Characteristics

    Microsoft Academic Search

    Joseph E. Tenerelli; Nicolas Reul; Alexis A. Mouche; Bertrand Chapron

    2008-01-01

    The ldquogalactic glitterrdquo phenomenon at L-band, i.e., the scattering of celestial sky radiation by the rough ocean surface, is examined here as a potential source of error for sea surface salinity (SSS) remote sensing. We begin by considering the transformations that must be applied to downwelling celestial noise in order to compute the eventual impact on the antenna temperature. Then,

  20. Dynamical surface structures in multiparticle-correlated surface growths.

    PubMed

    Kim, Yup; Kim, T S; Park, Hyunggyu

    2002-10-01

    We investigate the scaling properties of the interface fluctuation width for the Q-mer and Q-particle-correlated deposition-evaporation models. These models are constrained with a global conservation law that the particle number at each height is conserved modulo Q. In equilibrium, the stationary roughness is anomalous but universal with the roughness exponent alpha=1/3, while the early time evolution shows nonuniversal behavior with the growth exponent beta varying with models and Q. Nonequilibrium surfaces display diverse growing and stationary behaviors. The Q-mer model shows a faceted structure, while the Q-particle-correlated model shows a macroscopically grooved structure. PMID:12443275

  1. Full band structure calculation of two-photon indirect absorption in bulk silicon

    NASA Astrophysics Data System (ADS)

    Cheng, J. L.; Rioux, J.; Sipe, J. E.

    2011-03-01

    Degenerate two-photon indirect absorption in silicon is an important limiting effect on the use of silicon structures for all-optical information processing at telecommunication wavelengths. We perform a full band structure calculation to investigate two-photon indirect absorption in bulk silicon, using a pseudopotential description of the energy bands and an adiabatic bond charge model to describe phonon dispersion and polarization. Our results agree well with some recent experimental results. The transverse acoustic/optical phonon-assisted processes dominate.

  2. Full band structure calculation of two-photon indirect absorption in bulk silicon

    SciTech Connect

    Cheng, J. L. [Department of Physics, Institute for Optical Sciences, University of Toronto, 60 St. George Street, Toronto, Ontario M5S 1A7 (Canada); Hefei National Laboratory for Physical Sciences at Microscale, University of Science and Technology of China, Hefei, Anhui 230026 (China); Rioux, J.; Sipe, J. E. [Department of Physics, Institute for Optical Sciences, University of Toronto, 60 St. George Street, Toronto, Ontario M5S 1A7 (Canada)

    2011-03-28

    Degenerate two-photon indirect absorption in silicon is an important limiting effect on the use of silicon structures for all-optical information processing at telecommunication wavelengths. We perform a full band structure calculation to investigate two-photon indirect absorption in bulk silicon, using a pseudopotential description of the energy bands and an adiabatic bond charge model to describe phonon dispersion and polarization. Our results agree well with some recent experimental results. The transverse acoustic/optical phonon-assisted processes dominate.

  3. Structural studies and band gap tuning of Cr doped ZnO nanoparticles

    SciTech Connect

    Srinet, Gunjan, E-mail: gunjansrinet@gmail.com; Kumar, Ravindra, E-mail: gunjansrinet@gmail.com; Sajal, Vivek, E-mail: gunjansrinet@gmail.com [Department of Physics and Materials Science and Engineering, Jaypee Institute of Information Technology, Noida-201307, Uttar Pradesh (India)

    2014-04-24

    Structural and optical properties of Cr doped ZnO nanoparticles prepared by the thermal decomposition method are presented. X-ray diffraction studies confirmed the substitution of Cr on Zn sites without changing the wurtzite structure of ZnO. Modified form of W-H equations was used to calculate various physical parameters and their variation with Cr doping is discussed. Significant red shift was observed in band gap, i.e., a band gap tuning is achieved by Cr doping which could eventually be useful for optoelectronic applications.

  4. Influence of leaching on surface composition, microstructure, and valence band of single grain icosahedral Al-Cu-Fe quasicrystal.

    PubMed

    Lowe, M; Yadav, T P; Fournée, V; Ledieu, J; McGrath, R; Sharma, H R

    2015-03-01

    The use of quasicrystals as precursors to catalysts for the steam reforming of methanol is potentially one of the most important applications of these new materials. To develop application as a technology requires a detailed understanding of the microscopic behavior of the catalyst. Here, we report the effect of leaching treatments on the surface microstructure, chemical composition, and valence band of the icosahedral (i-) Al-Cu-Fe quasicrystal in an attempt to prepare a model catalyst. The high symmetry fivefold surface of a single grain i-Al-Cu-Fe quasicrystal was leached with NaOH solution for varying times, and the resulting surface was characterized by x-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The leaching treatments preferentially remove Al producing a capping layer consisting of Fe and Cu oxides. The subsurface layer contains elemental Fe and Cu in addition to the oxides. The quasicrystalline bulk structure beneath remains unchanged. The subsurface gradually becomes Fe3O4 rich with increasing leaching time. The surface after leaching exhibits micron sized dodecahedral cavities due to preferential leaching along the fivefold axis. Nanoparticles of the transition metals and their oxides are precipitated on the surface after leaching. The size of the nanoparticles is estimated by high resolution transmission microscopy to be 5-20 nm, which is in agreement with the AFM results. Selected area electron diffraction (SAED) confirms the crystalline nature of the nanoparticles. SAED further reveals the formation of an interface between the high atomic density lattice planes of nanoparticles and the quasicrystal. These results provide an important insight into the preparation of model catalysts of nanoparticles for steam reforming of methanol. PMID:25747095

  5. The Effect of Oxygen on the ZnS Electronic Energy-Band Structure

    SciTech Connect

    Morozova, N.K.; Karetnikov, I.A.; Golub, K.V.; Danilevich, N.D. [Moscow Power Institute (Technical University), ul. Krasnokazarmennaya 17, Moscow, 111250 (Russian Federation); Lisitsyn, V.M.; Oleshko, V.I. [Tomsk Polytechnical University, pr. Lenina 30, Tomsk, 634034 (Russian Federation)

    2005-05-15

    Experimental data indicating that the band gap of Zn-O-S solid solutions decreases appreciably in accordance with the theory of noncrossing energy bands are reported for the first time. It is shown that this effect is mainly characteristic of ZnS with an excess of Zn. The concentration of dissolved oxygen [O{sub S}] has been determined from data taken using precision X-ray structure analysis and chemical phase analysis. The decrease in the band gap determined from the cathodoluminescence spectra is equal to 75 meV for sphalerite ZnS (s) and 90 meV for wurtzite ZnS (w) per 1 mol % and depends virtually linearly on the oxygen concentration [O{sub S}]. An increase in [O{sub S}], in addition to an intensification and shift of the free-exciton (FE) band, is also conducive to the formation of SA oxygen-containing complexes in ZnS. These complexes are responsible for emission in the visible region of the spectrum and for the band I{sub 1} of excitons bound to these complexes. The binding energy is equal to {approx}61 and {approx}104 meV for ZnS (s) and ZnS (w), respectively. The band I{sub 1} shifts as [O{sub S}] varies, similarly to the shift of the FE band. The obtained dependences define the position of the FE band in oxygen-free ZnS and make it possible to assess the oxygen concentration in the compound from the shift of the FE band.

  6. Comparing photonic band structure calculation methods for diamond and pyrochlore crystals.

    PubMed

    Vermolen, E C M; Thijssen, J H J; Moroz, A; Megens, M; van Blaaderen, A

    2009-04-27

    The photonic band diagrams of close-packed colloidal diamond and pyrochlore structures, have been studied using Korringa-Kohn-Rostoker (KKR) and plane-wave calculations. In addition, the occurrence of a band gap has been investigated for the binary Laves structures and their constituent large- and small-sphere substructures. It was recently shown that these Laves structures give the possibility to fabricate the diamond and pyrochlore structures by self-organization. The comparison of the two calculation methods opens the possibility to study the validity and the convergence of the results, which have been an issue for diamond-related structures in the past. The KKR calculations systematically give a lower value for the gap width than the plane-wave calculations. This difference can partly be ascribed to a convergence issue in the plane-wave code when a contact point of two spheres coincides with the grid. PMID:19399068

  7. Investigations on crystalline structure and optical band gap of nearly stoichiometric LiNbO3 nanoparticles

    NASA Astrophysics Data System (ADS)

    Debnath, C.; Kar, S.; Verma, S.; Bartwal, K. S.

    2014-11-01

    The structural and optical characteristics of nearly stoichiometric lithium niobate, LiNbO3 nanoparticles have been studied. The results are very different compared to the bulk LiNbO3 single crystals. The nanoparticles were synthesized by citrate gel method and the phase was confirmed by powder X-ray diffraction. The size and size distribution of the nanoparticles were obtained by XRD, SEM, TEM and DLS experiments. The particles were in the range of 50-200 nm and most of the particles are about 100 nm of size. The lattice parameters obtained from selected area electron diffraction are aH = 5.213 Å and cH = 14.026 Å for hexagonal system which are slightly larger than the other reported values (JCPDS). The optical properties were obtained from optical absorption spectroscopy in UV-vis.-NIR and IR (FTIR) range, the electronic band gap structure were determined from the fundamental absorption edge in the UV region. The indirect band gap was of 4.78 eV where as the direct gap was of 6.0 eV which are much larger than the other experimental values. The absorption features in the UV range indicate the discrete nature of conduction band and the allowed energy levels in the forbidden gap appeared due to surface defects.

  8. CAROLS: a new airborne L-band radiometer for ocean surface and land observations.

    PubMed

    Zribi, Mehrez; Pardé, Mickael; Boutin, Jacquline; Fanise, Pascal; Hauser, Daniele; Dechambre, Monique; Kerr, Yann; Leduc-Leballeur, Marion; Reverdin, Gilles; Skou, Niels; Søbjærg, Sten; Albergel, Clement; Calvet, Jean Christophe; Wigneron, Jean Pierre; Lopez-Baeza, Ernesto; Rius, Antonio; Tenerelli, Joseph

    2011-01-01

    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

  9. CAROLS: A New Airborne L-Band Radiometer for Ocean Surface and Land Observations

    PubMed Central

    Zribi, Mehrez; Pardé, Mickael; Boutin, Jacquline; Fanise, Pascal; Hauser, Daniele; Dechambre, Monique; Kerr, Yann; Leduc-Leballeur, Marion; Reverdin, Gilles; Skou, Niels; Søbjærg, Sten; Albergel, Clement; Calvet, Jean Christophe; Wigneron, Jean Pierre; Lopez-Baeza, Ernesto; Rius, Antonio; Tenerelli, Joseph

    2011-01-01

    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

  10. Correlation between surface chemistry, density and band gap in nanocrystalline WO3 thin films

    SciTech Connect

    Vemuri, Venkata Rama Ses; Engelhard, Mark H.; Ramana, C.V.

    2012-03-01

    Nanocrystalline WO3 thin films were produced by sputter-deposition by varying the ratio of argon to oxygen in the reactive gas mixture during deposition. The surface chemistry, physical characteristics, and optical properties of nanocrystalline WO3 films were evaluated using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray reflectivity (XRR), and spectrophotometric measurements. The effect of ultra-microstructure was significant on the optical properties of WO3 films. The XPS analyses indicate the formation of stoichiometric WO3 with tungsten existing in fully oxidized valence state (W6+). However, WO3 films grown at high oxygen concentration (>60%) in the sputtering gas mixture were over stoichiometric with excess oxygen. XRR simulations, which are based on isotropic WO3 film - SiO2 interface - Si substrate model, indicate that the density of WO3 films is sensitive to the oxygen content in the sputtering gas. The spectral transmission of the films increased with the increasing oxygen. The band gap of these films increases from 2.78 eV to 3.25 eV with increasing oxygen. A direct correlation between the film-density and band gap in nanocrystalline WO3 films is established based on the observed results.

  11. The Development of Layered Photonic Band Gap Structures Using a Micro-Transfer Molding Technique

    SciTech Connect

    Kevin Jerome Sutherland

    2001-05-01

    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.

  12. Surface structure of potassium dichromate (KBC) crystals

    NASA Astrophysics Data System (ADS)

    Reedijk, M. F.; Arsic, J.; Kaminski, D.; van Enckevort, W. J. P.; Vlieg, E.

    2003-02-01

    We present a surface X-ray diffraction study of the {0 0 1} faces of potassium dichromate crystals in a humid environment. An etch-resistant layer develops in such an environment, which prevents the crystal from etching in a low-solubility solution. This layer is shown to be amorphous and is likely to be permeable for water molecules. The interface between the crystal and the amorphous layer is atomically flat. The crystal surface is not reconstructed, showing a potassium termination. The atomic structure of the surface is influenced by the relative humidity (RH), at 40% RH the top layer of molecules is expanded while at 100% RH these molecules are compressed. A first indication is given of a structural difference between the (0 0 1) and ( 0 0 1¯) faces, which is relevant for understanding the hypomorphism exhibited by this system.

  13. C-band measurement of radar backscatter from the ocean surface during SWADE

    NASA Technical Reports Server (NTRS)

    Carson, S. C.; Mcintosh, R. E.; Paylor, A. W.; Li, F.; Neumann, G.; Mclaughlin, D. J.

    1992-01-01

    A preliminary analysis of backscatter measurements collected during the joint NASA/ONR Surface Wave Dynamics Experiment (SWADE) by a C-band scatterometer (C-SCAT) is presented. Data were collected during a total of ten flights on board the NASA/Ames C-130B off the coast of Virginia. These backscatter measurements are vertically polarized, and were obtained over a full 360* in azimuth, at incidence angles ranging from 20 to 50 . The data set is now in a state where it can provide a unique test bed for normalized radar cross section (NRCS) model functions because of the variety of phenomena encountered, and the quantity and quality of the measurements.

  14. Band structure and transport studies on InP nanotube - A first-principles investigation

    NASA Astrophysics Data System (ADS)

    Chandiramouli, R.

    2015-07-01

    The band structure and electronic transport property of InP nanotube molecular device are studied using density functional theory with GGA/PBE exchange correlation functional. The substitution of nitrogen in InP nanotube slightly widens the band gap. The substitution of nitrogen and aluminium in InP nanostructure modifies the density of states across InP nanotube. The electron density is found to be more on phosphorus sites than indium sites. The substitution of aluminium increases the electron density, whereas nitrogen substitution decreases the electron density across phosphorus site. The transmission spectrum provides the insight to transmission along InP nanotube molecular device. The transmission pathways get modified with the substitution impurity along InP nanotube molecular device. The results of the present work will give information on tuning the band structure and transport properties of InP nanotube molecular device.

  15. Swallowtail band structure of the superfluid Fermi Gas in an optical lattice

    NASA Astrophysics Data System (ADS)

    Watanabe, Gentaro; Yoon, Sukjin; Franco, Dalfovo

    2012-06-01

    We investigate the energy band structure of the superfluid flow of ultracold dilute Fermi gases in a one-dimensional optical lattice along the BCS to BEC crossover within a mean-field approach [1]. In each side of the crossover region, a loop structure (swallowtail) appears in the Bloch energy band of the superfluid above a critical value of the interaction strength. The width of the swallowtail is largest near unitarity. Across the critical value of the interaction strength, the profiles of density and pairing field change more drastically in the BCS side than in the BEC side. It is found that along with the appearance of the swallowtail, there exists a narrow band in the quasiparticle energy spectrum close to the chemical potential and the incompressibility of the Fermi gas consequently experiences a profound dip in the BCS side, unlike in the BEC side.[4pt] [1] G. Watanabe, S. Yoon, and F. Dalfovo, Phys. Rev. Lett. 107, 270404 (2011).

  16. Swallowtail Band Structure of the Superfluid Fermi Gas in an Optical Lattice

    E-print Network

    Gentaro Watanabe; Sukjin Yoon; Franco Dalfovo

    2012-01-05

    We investigate the energy band structure of the superfluid flow of ultracold dilute Fermi gases in a one-dimensional optical lattice along the BCS to BEC crossover within a mean-field approach. In each side of the crossover region, a loop structure (swallowtail) appears in the Bloch energy band of the superfluid above a critical value of the interaction strength. The width of the swallowtail is largest near unitarity. Across the critical value of the interaction strength, the profiles of density and pairing field change more drastically in the BCS side than in the BEC side. It is found that along with the appearance of the swallowtail, there exists a narrow band in the quasiparticle energy spectrum close to the chemical potential and the incompressibility of the Fermi gas consequently experiences a profound dip in the BCS side, unlike in the BEC side.

  17. Swallowtail Band Structure of the Superfluid Fermi Gas in an Optical Lattice

    NASA Astrophysics Data System (ADS)

    Watanabe, Gentaro; Yoon, Sukjin; Dalfovo, Franco

    2011-12-01

    We investigate the energy band structure of the superfluid flow of ultracold dilute Fermi gases in a one-dimensional optical lattice along the BCS to Bose-Einstein condensate (BEC) crossover within a mean-field approach. In each side of the crossover region, a loop structure (swallowtail) appears in the Bloch energy band of the superfluid above a critical value of the interaction strength. The width of the swallowtail is largest near unitarity. Across the critical value of the interaction strength, the profiles of density and pairing field change more drastically in the BCS side than in the BEC side. It is found that along with the appearance of the swallowtail, there exists a narrow band in the quasiparticle energy spectrum close to the chemical potential, and the incompressibility of the Fermi gas consequently experiences a profound dip in the BCS side, unlike in the BEC side.

  18. JOURNAL DE PHYSIQUE Colloque C4, supplkment au no 4 , Tome 40, avril 1979, page C4-19 Band structures of NaCl structure uranium compounds

    E-print Network

    Paris-Sud XI, Université de

    structures of NaCl structure uranium compounds R. Allen and M. S. S. Brooks Commission of the European Karlsruhe 1, F.R.G. R6sum6. -Des calculs de structure de bande ont BtC accomplis pour les monopnictures d'uranium been made for the uranium monopnictides and for the monochalcogenide US. The band structures were

  19. VOLUME 82, NUMBER 20 P H Y S I C A L R E V I E W L E T T E R S 17 MAY 1999 Spin-Orbit Coupling Induced Surface Band Splitting in Li W(110) and Li Mo(110)

    E-print Network

    Kevan, Stephen D.

    Induced Surface Band Splitting in Li W(110) and Li Mo(110) Eli Rotenberg Advanced Light Source, Lawrence orbital magnetic structure versus adsorbate coverage in magnetic materials. We propose a spin ordering in the surface sp band is strongest. In this paper, we show that a similar, though substan- tially larger, spin

  20. Fermi Surface Database

    NSDL National Science Digital Library

    Choy, Tat Sang

    This web site presents illustrations of the Fermi surfaces of many of the elements in the periodic table. Interactive 3D illustrations, stereo-3D images, and standard jpeg images are available. Surfaces can be displayed by band so that the relationships between band structure and electronic properties of materials can be explored. The band structures for different solid phases are also available.

  1. Multi-use applications of dual-band infrared (DBIR) thermal imaging for detecting obscured structural defects

    SciTech Connect

    Del Grande, N.K.; Durbin, P.F.

    1994-05-01

    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.

  2. BAND STRUCTURE OPTIMIZATION OF TWO-DIMENSIONAL PHOTONIC CRYSTALS IN H-POLARIZATION

    E-print Network

    Dobson, David C.

    of the medium, u is the out-of- plane component of the magnetic field, and is the frequency. The structure, band gaps, optimal design. 1. Introduction. Consider electromagnetic wave propagation in a periodic, di- electric, non-magnetic medium in IR2 . We are interested in the case where the mag- netic field vector H

  3. Influence of indium clustering on the band structure of semiconducting ternary and quaternary nitride alloys

    E-print Network

    Svane, Axel Torstein

    of indium. Addition of In, even in small amounts, to nitride compounds leads to an enhancement of lightInfluence of indium clustering on the band structure of semiconducting ternary and quaternary nitride alloys I. Gorczyca, S. P. Lepkowski, and T. Suski Institute of High Pressure Physics, Polish

  4. Observation of 'Band' Structures in Spacecraft Observations of Inner Magnetosphere Plasma Ions

    NASA Astrophysics Data System (ADS)

    Mohan, Kirthika; Fazakerley, Andrew; Grimald, Sandrine; Dandouras, Iannis; Owen, Chris

    2014-05-01

    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 (Smith and Hoffman (1974), etc). These structures have been described as "nose structures", with reference to their appearance in energy-time spectrograms and are also known as "bands" if they occur for extended periods of time. Statistical surveys (Buzulukova et al. (2003); Vallat et al. (2007)) of these features in Interball and Cluster data highlight the presence of single nose in nightside sectors and multi-nose strutures in the dayside sectors. We examine Double-Star TC1 HIA data mainly recorded in the equatorial plane of the inner magnetosphere (L<15) to see how observations of "multi-banded structures" compare to the observations from more inclined orbits of Cluster and Interball. We investigate the properties of these multi-banded structures and carry out a statistical survey analysing them as a function of geomagnetic activity. This is a comparison study to a similar study conducted using DoubleStar TC-1 PEACE electron data.

  5. New analytical approach for computation of band structure in one-dimensional periodic media

    Microsoft Academic Search

    Sina Khorasani; Ali Adibi

    2003-01-01

    In this paper, we present a new approach for the exact calculation of band structure in one-dimensional periodic media, such as photonic crystals and superlattices, based on the recently reported differential transfer matrix method (DTMM). The media analyzed in this paper can have arbitrary profile of refractive index. We derive a closed form dispersion equation using differential transfer matrix formalism,

  6. Band Structures of One-Dimensional Crystals with Square-Well Potentials

    Microsoft Academic Search

    G. Allen

    1953-01-01

    The energy band structure for a one-dimensional periodic square-well potential is obtained in terms of the well depth for the whole range of possible ratios of well width to hill width. This model bears a closer resemblance to a real crystal since, as potential depth is varied for a fixed ratio of well width to hill width, the curves bounding

  7. An Analytical Solution of Equivalent Stress for Structure Fatigue Life Prediction under Broad Band Random Loading

    Microsoft Academic Search

    Xiaoyun Liu; Pengmin Lü

    1997-01-01

    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.

  8. Modification of Planck blackbody radiation by photonic band-gap structures

    Microsoft Academic Search

    Christopher M. Cornelius; Jonathan P. Dowling

    1999-01-01

    We discuss a simple one-dimensional (1D) model of the modification of Planck blackbody radiation by photonic band-gap materials (PBG's). The model gives qualitative predictions for the thermal power spectrum of 2D and 3D PBG structures, and quantitative results for 1D, distributed Bragg reflecting PBG thin films.

  9. Generalized Field Propagator for Arbitrary Finite-Size Photonic Band Gap Structures

    Microsoft Academic Search

    Olivier J. F. Martin; Christian Girard; David R. Smith; Sheldon Schultz

    1999-01-01

    We investigate the properties of photonic band gap structures of finite size and arbitrary geometry using the density of states deduced from scattering calculations. We first demonstrate this procedure on a finite 2D array of cylinders and then study at optical frequencies a system formed by a finite array of finite height cylinders positioned on a substrate and illuminated with

  10. Inuence of band 3 protein absence and skeletal structures on amphiphile-and Ca2

    E-print Network

    Iglic, Ales

    In£uence of band 3 protein absence and skeletal structures on amphiphile- and Ca2 -induced shape Amphiphiles which induce either spiculated (echinocytic) or invaginated (stomatocytic) shapes in human. Both qualitative and quantitative differences were found. Amphiphiles induced no gross morphological

  11. The effect of a multivalley energy band structure on the thermoelectric figure of merit

    E-print Network

    Boyer, Edmond

    scattering. At a carrier concentration which optimizes the thermoelectric figure of merit, the ratio (ZT)mv/(ZTL-49 The effect of a multivalley energy band structure on the thermoelectric figure of merit D. M semiconducteurs à vallées multiples (ZT)mv ou à vallée unique (ZT)sv sont ici comparés. La diffusion des phonons

  12. Band structure engineering through orbital interaction for enhanced thermoelectric power factor

    E-print Network

    Ceder, Gerbrand

    The thermoelectric figure of merit, zT, can be increased by minimizing the thermal conductivity (j) and/or maximizingBand structure engineering through orbital interaction for enhanced thermoelectric power factor of many important technologies including thermoelectrics, optoelectronics, and microelectronics

  13. Band Structure, Phonon Scattering, and the Performance Limit of Single-Walled Carbon Nanotube Transistors

    E-print Network

    McEuen, Paul L.

    predictions for acoustic phonon scattering in combination with the unusual band structure of nanotubes velocity in graphene, plays the role of the speed of light. The carrier effective mass is set by the tube conductance are well described by the predictions of acoustic phonon scattering in concert

  14. Shear-band structure in ballistically tested carbide-free bainitic steels

    E-print Network

    Cambridge, University of

    Shear-band structure in ballistically tested carbide-free bainitic steels L. C. D. Fieldinga , H. K generated by ballistic testing is examined in order to reveal the governing mechanisms. We attempt example during machining, or ballistic impact [3, 4]) and has been speculated to be the reason for damage

  15. Ferromagnetism and the electronic band structure in (Ga,Mn)(Bi,As) epitaxial layers

    SciTech Connect

    Yastrubchak, O., E-mail: yastrub@hektor.umcs.lublin.pl [Institute of Physics, Maria Curie-Sklodowska University in Lublin, Pl. M. Curie-Sk?odowskiej 1, 20-031 Lublin (Poland); Institute of Semiconductor Physics, National Academy of Sciences, 41 pr. Nauki, 03028 Kyiv (Ukraine); Sadowski, J. [MAX-IV Laboratory, Lund University, P.O. Box 118, SE-221 00 Lund (Sweden); Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw (Poland); Gluba, L.; ?uk, J.; Kulik, M. [Institute of Physics, Maria Curie-Sklodowska University in Lublin, Pl. M. Curie-Sk?odowskiej 1, 20-031 Lublin (Poland); Domagala, J. Z.; Andrearczyk, T.; Wosinski, T. [Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw (Poland); Rawski, M. [Analytical Laboratory, Maria Curie-Sklodowska University in Lublin, Pl. M. Curie-Sk?odowskiej 3, 20-031 Lublin (Poland)

    2014-08-18

    Impact of Bi incorporation into (Ga,Mn)As layers on their electronic- and band-structures as well as their magnetic and structural properties has been studied. Homogenous (Ga,Mn)(Bi,As) layers of high structural perfection have been grown by the low-temperature molecular-beam epitaxy technique. Post-growth annealing treatment of the layers results in an improvement of their structural and magnetic properties and an increase in the hole concentration in the layers. The modulation photoreflectance spectroscopy results are consistent with the valence-band model of hole-mediated ferromagnetism in the layers. This material combines the properties of (Ga,Mn)As and Ga(Bi,As) ternary compounds and offers the possibility of tuning its electrical and magnetic properties by controlling the alloy composition.

  16. Nonlinear optical response of semiconductor-nanocrystals-embedded photonic band gap structure

    SciTech Connect

    Liao, Chen; Zhang, Huichao; Tang, Luping; Zhou, Zhiqiang; Lv, Changgui; Cui, Yiping; Zhang, Jiayu, E-mail: jyzhang@seu.edu.cn [Advanced Photonic Center, Southeast University, Nanjing 210096 (China)

    2014-04-28

    Colloidal CdSe/ZnS core/shell nanocrystals (NCs), which were dispersed in SiO{sub 2} sol, were utilized to fabricate a SiO{sub 2}:NCs/TiO{sub 2} all-dielectric photonic band gap (PBG) structure. The third-order nonlinear refractive index (n{sub 2}) of the PBG structure was nearly triple of that of the SiO{sub 2}:NCs film due to the local field enhancement in the PBG structure. The photoinduced change in refractive index (?n) could shift the PBG band edge, so the PBG structure would show significant transmission modification, whose transmission change was ?17 folds of that of the SiO{sub 2}:NCs film. Under excitation of a 30?GW/cm{sup 2} femtosecond laser beam, a transmission decrease of 80% was realized.

  17. Effects of strain on the band structure of group-III nitrides

    NASA Astrophysics Data System (ADS)

    Yan, Qimin; Rinke, Patrick; Janotti, Anderson; Scheffler, Matthias; Van de Walle, Chris G.

    2014-09-01

    We present a systematic study of strain effects on the electronic band structure of the group-III-nitrides (AlN, GaN and InN) in the wurtzite phase. The calculations are based on density functional theory with band-gap-corrected approaches including the Heyd-Scuseria-Ernzerhof hybrid functional (HSE) and quasiparticle G0W0 methods. We study strain effects under realistic strain conditions, hydrostatic pressure, and biaxial stress. The strain-induced modification of the band structures is found to be nonlinear; transition energies and crystal-field splittings show a strong nonlinear behavior under biaxial stress. For the linear regime around the experimental lattice parameters, we present a complete set of deformation potentials (acz, act, D1, D2, D3, D4, D5, D6) that allows us to predict the band positions of group-III nitrides and their alloys (InGaN and AlGaN) under realistic strain conditions. The benchmarking G0W0 results for GaN agree well with the HSE data and indicate that HSE provides an appropriate description for the band structures of nitrides. We present a systematic study of strain effects on the electronic band structure of the group-III nitrides (AlN, GaN, and InN). We quantify the nonlinearity of strain effects by introducing a set of bowing parameters. We apply the calculated deformation potentials to the prediction of strain effects on transition energies and valence-band structures of InGaN alloys and quantum wells (QWs) grown on GaN, in various orientations (including c-plane, m-plane, and semipolar). The calculated band gap bowing parameters, including the strain effect for c-plane InGaN, agree well with the results obtained by hybrid functional alloy calculations. For semipolar InGaN QWs grown in (202¯1), (303¯1), and (303¯1¯) orientations, our calculated deformation potentials have provided results for polarization ratios in good agreement with the experimental observations, providing further confidence in the accuracy of our values.

  18. A numerical method for one-dimensional action functionals of photonic band-gap structures

    NASA Astrophysics Data System (ADS)

    Xie, F.; Reid, G.; Valluri, S.

    2004-06-01

    Photonic band gaps (PBG), photonic analogues of electronic semiconductor band gaps, have attracted much attention recently because of numerous potential applications in communications and computing. Akozbek and John (Phys. Rev. E, 57, 2287 (1998).) developed a variational model of such band gaps, using action functionals, where solitary waves are expanded in terms of a finite orthonormal basis. These expansions to finite order N converged to solitary waves. The nonlinear polynomial equations for the coefficients in the expansions, have nonunique solutions. Our paper, makes a study of the multiplicity of the solutions for one-dimensional photonic band-gap structures. It is found that the nonuniqueness grows dramatically with the order of the expansion N. We use homotopy, which continuously deforms the solutions of exactly solvable systems, into the solutions of the systems to be solved with new results in numeric algebraic geometry, such that all solutions are determined. We used Maple 7 to obtain the polynomial equations for the variational coefficients, extending Akozbek and John's approach. A homotopy-based package PHCpack was used to solve the systems for N less than or equal to 4 and a linearization-extrapolation method was developed to find real solutions for N greater than or equal to 5. The results are compared with the exact soliton solutions and their convergence behavior is discussed. The interplay of geometrical, topological and variational methods is seen in these interesting physical band-gap structures.

  19. Fine Structure of a Deep Photoluminescence Band Related to Oxygen in LEC-GaAs

    NASA Astrophysics Data System (ADS)

    Kazuno, Tadao; Sawada, Yuji; Yokoyama, Takeshi

    1986-11-01

    A fine structure is discovered in a 0.63 eV photoluminescence emission band in GaAs at 4.2 K under the excitation of the 5145 A line of an Ar-laser. The fine structure is interpreted to be due to the phonon side-bands of the oxygen-related radiative transition. The emission band is stronger in both Ga2O3 doped LEC-GaAs and undoped LEC-GaAs grown using wet B2O3, as an encapsulant than in conventional undoped GaAs grown by dry B2O3 encapsulant. Nonlinear least squares fitting of the band gives 6.7 for Huang-Rhys coupling constant, 0.0237 eV for the coupled phonon energy and 0.16 eV for the Franck-Condon shift. Thermal energy of oxygen related level is evaluated as 0.74± 0.02 eV below the conduction band.

  20. Doping and strain dependence of the electronic band structure in Ge and GeSn alloys

    NASA Astrophysics Data System (ADS)

    Xu, Chi; Gallagher, James; Senaratne, Charutha; Brown, Christopher; Fernando, Nalin; Zollner, Stefan; Kouvetakis, John; Menendez, Jose

    2015-03-01

    A systematic study of the effect of dopants and strain on the electronic structure of Ge and GeSn alloys is presented. Samples were grown by UHV-CVD on Ge-buffered Si using Ge3H8 and SnD4 as the sources of Ge and Sn, and B2H6/P(GeH3)3 as dopants. High-energy critical points in the joint-density of electronic states were studied using spectroscopic ellipsometry, which yields detailed information on the strain and doping dependence of the so-called E1, E1 +?1 , E0' and E2 transitions. The corresponding dependencies of the lowest direct band gap E0 and the fundamental indirect band gap Eindwere studied via room-T photoluminescence spectroscopy. Of particular interest for this work were the determination of deformation potentials, band gap renormalization effects, Burstein-Moss shifts due to the presence of carriers at band minima, and the dependence of other critical point parameters, such as amplitudes and phase angles, on the doping concentration. The selective blocking of transitions due to high doping makes it possible to investigate the precise k-space location of critical points. These studies are complemented with detailed band-structure calculations within a full-zone k-dot- p approach. Supported by AFOSR under DOD AFOSR FA9550-12-1-0208 and DOD AFOSR FA9550-13-1-0022.

  1. Theoretical study of influencing factors on the dispersion of bulk band-gap edges and the surface states in topological insulators Bi{sub 2}Te{sub 3} and Bi{sub 2}Se{sub 3}

    SciTech Connect

    Rusinov, I. P., E-mail: rusinovip@gmail.com; Nechaev, I. A. [Tomsk State University (Russian Federation); Chulkov, E. V. [Donostia International Physics Center (DIPC) (Spain)

    2013-06-15

    The dispersion of the band-gap edge states in bulk topological insulators Bi{sub 2}Te{sub 3} and Bi{sub 2}Se{sub 3} is considered within density functional theory. The dependences of this dispersion both on the approximation used for an exchange-correlation functional at fixed unit cell parameters and atomic positions and on these parameters and positions that are obtained upon structural relaxation performed using a certain approximated functional are analyzed. The relative position of the Dirac point of topologically protected surface states and the valence band maximum in the surface electronic structure of the topological insulators is discussed.

  2. On One and Two-Dimensional Electromagnetic Band Gap Structures in Rectangular Waveguides at Microwave Frequencies

    Microsoft Academic Search

    Álvaro Gómez; Angel Vegas; Miguel A. Solano; Akhlesh Lakhtakia

    2005-01-01

    Electromagnetic band gap (EBG) structures of two different configurations implemented inside R120 rectangular waveguides (frequency range 10–15 GHz) are examined. The first configuration has a periodic, piecewise uniform variation of permittivity in the propagation direction. Two types of such one-dimensional (1D) EBG structures are analyzed, one with the unit cell comprising two dielectric layers, the other with three dielectric layers

  3. Dispersive properties of finite, one-dimensional photonic band gap structures: Applications to nonlinear quadratic interactions

    Microsoft Academic Search

    M. Centini; C. Sibilia; M. Scalora; G. D'aguanno; M. Bertolotti; M. J. Bloemer; C. M. Bowden; I. Nefedov

    1999-01-01

    We discuss the linear dispersive properties of finite one-dimensional photonic band-gap structures. We introduce the concept of a complex effective index for structures of finite length, derived from a generalized dispersion equation that identically satisfies the Kramers-Kronig relations. We then address the conditions necessary for optimal, phase-matched, resonant second harmonic generation. The combination of enhanced density of modes, field localization,

  4. Broad-band high-efficiency optoacoustic generation using a novel photonic crystal-metallic structure

    NASA Astrophysics Data System (ADS)

    Guo, Yunbo; Baac, Hyoung Won; Chen, Sung-Liang; Norris, Theodore B.; Guo, L. Jay

    2011-03-01

    Various optical structures have been investigated for high-frequency optoacoustic generation via thermoelastic effect, including metal films, mixture of polydimethylsiloxane (PDMS) and carbon black, two-dimensional (2-D) gold nanostructure with PDMS film, etc. However, they suffer from either low light absorption efficiency which affects the amplitude of generated ultrasound, or thick films that attenuate the amplitude and restrict its spectra bandwidth. Here we propose a novel one-dimensional photonic crystal-metallic (PCM) structure, which can be designed to absorb 100% optical energy of specific wavelengths in a total-internal-reflection geometry. The unique configuration enables us to choose suitable polymer films on top of the metallic structure, which can act as an ideal ultrasound transmitter to generate broad-band ultrasound with high conversion efficiency. Experimental results show that the PCM structure generated several times stronger ultrasound pressure than our previously demonstrated 2-D gold nanostructures [Appl. Phys. Lett. 89, 093901 (2006)]. Moreover, the generated ultrasound exhibited almost the same frequency spectrum as the input laser pulse (duration width 6 ns). This shows that the PCM structure has great potential to generate broad-band ultrasound signal. It is also important to mention that the simple PCM structure with the polymer film forms a Fabry-Pérot resonator and can play a role of an ultrasound receiver, which provides a convenient method to construct a broad-band and all-optical ultrasound transducer.

  5. Structural vs electronic origin of renormalized band widths in TTF-TCNQ: An angular dependent NEXAFS study

    SciTech Connect

    Sing, M.; Meyer, J.; Glawion, S.; Claessen, R. [Experimentelle Physik IV, Universitaet Wuerzburg, D-97074 Wuerzburg (Germany); Hoinkis, M. [Experimentelle Physik IV, Universitaet Wuerzburg, D-97074 Wuerzburg (Germany); Experimentalphysik II, Universitaet Augsburg, D-86135 Augsburg (Germany); Blaha, P. [Institute of Materials Chemistry, Vienna University of Technology, A-1060 Vienna (Austria); Gavrila, G. [Institut fuer Physik, Technische Universitaet Chemnitz, D-09107 Chemnitz (Germany); Jacobsen, C. S. [Department of Physics, Technical University of Denmark, DK-2800 Lyngby (Denmark)

    2007-12-15

    We have performed angle-dependent near-edge x-ray absorption fine structure measurements in the Auger electron yield mode on the correlated quasi-one-dimensional organic conductor tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) in order to determine the orientation of the molecules in the topmost surface layer. We find that the tilt angles of the molecules with respect to the one-dimensional axis are essentially the same as in the bulk. Thus, we can rule out surface relaxation as the origin of the renormalized band widths which were inferred from the analysis of photoemission data within the one-dimensional Hubbard model. Thereby, recent theoretical results are corroborated which invoke long-range Coulomb repulsion as alternative explanation to understand the spectral dispersions of TTF-TCNQ quantitatively within an extended Hubbard model.

  6. On the surface structure of sunspots

    NASA Astrophysics Data System (ADS)

    Franz, M.

    2012-12-01

    A precise knowledge of the surface structure of sunspots is essential to construct adequate input models for helioseismic inversion tools. % and to gain information about the subsurface structure of sunspots. We summarize our recent findings about the velocity and magnetic field in and around sunspots using HINODE observation. To this end we quantize the horizontal and vertical component of the penumbral velocity field at different levels of precision and study the moat flow around sunspot. Furthermore, we find that a significant amount of the penumbral magnetic fields return below the surface within the penumbra. Finally, we explain why the related opposite polarity signals remain hidden in magnetograms constructed from measurements with limited spectral resolution.

  7. Resonant coupling of near-infrared radiation to photonic band structure waveguides

    Microsoft Academic Search

    Vasily N. Astratov; J. S. Culshaw; R. Mark Stevenson; David M. Whittaker; Maurice S. Skolnick; Thomas F. Krauss; R. M. de la Rue

    1999-01-01

    Sharp resonance features are observed in the polarized reflectivity spectra of semiconductor photonic crystals fabricated by deep periodic patterning of AlGaAs surface waveguides. Both one- (1-D) and two-dimensional (2-D) lattices are studied by angular dependent reflectivity. By comparison with theory we show that the sharp features in reflectivity arise from resonant coupling of the external radiation to the folded band

  8. Bragg resonances of magnetostatic surface spin waves in a layered structure: Magnonic crystal-dielectric-metal

    NASA Astrophysics Data System (ADS)

    Beginin, E. N.; Filimonov, Yu. A.; Pavlov, E. S.; Vysotskii, S. L.; Nikitov, S. A.

    2012-06-01

    It is experimentally shown that metal cladding of the surface of a one-dimensional magnonic crystal destroys the Bragg band gaps in microwave transmission spectra of propagating magnetostatic surface spin waves in magnonic crystal. This is a consequence of violating a phase synchronism condition of forward and reflected by a magnonic crystal magnetostatic surface wave. When a magnetostatic surface wave propagates in a layered structure, ferromagnetic film with a magnonic crystal-dielectric layer-metal cladding this synchronism condition can also be fulfilled, not depending on the thickness of a dielectric layer.

  9. Infrared filters using metallic photonic band gap structures on flexible substrates

    SciTech Connect

    Gupta, S.; Tuttle, G. [Department of Electrical and Computer Engineering and the Microelectronics Research Center, Iowa State University, Ames, Iowa 50011 (United States)] [Department of Electrical and Computer Engineering and the Microelectronics Research Center, Iowa State University, Ames, Iowa 50011 (United States); Sigalas, M.; Ho, K. [Department of Physics and Astronomy and the Ames Laboratory, U.S. Department of Energy, Iowa State University, Ames, Iowa 50011 (United States)] [Department of Physics and Astronomy and the Ames Laboratory, U.S. Department of Energy, Iowa State University, Ames, Iowa 50011 (United States)

    1997-10-01

    Metallic photonic band gap (MPBG) filter structures operating at far infrared wavelengths have been designed, fabricated, and characterized. The MPBGs are multilayer metallic meshes imbedded in a flexible polyimide dielectric. Depending on the periodic pattern of the metal grids, the filters have either simple high-pass or more complex transmission characteristics. The critical frequencies of the filters depend on the spatial periodicity of the metal grids and the interlayer separation. Optical transmission measurements on a high-pass structure show cutoff frequency of 3 THz and attenuation of more than 35 dB in the cutoff region, in good agreement with predicted results. Band-reject filters show similarly good attenuation and large fractional bandwidths. The filters maintain their optical characteristics after repeated bending, demonstrating mechanical robustness of the MPBG structure. {copyright} {ital 1997 American Institute of Physics.}

  10. Photomodulated rayleigh scattering of single semiconductor nanowires: probing electronic band structure.

    PubMed

    Montazeri, Mohammad; Wade, Aaron; Fickenscher, Melodie; Jackson, Howard E; Smith, Leigh M; Yarrison-Rice, Jan M; Gao, Qian; Tan, H Hoe; Jagadish, Chennupati

    2011-10-12

    The internal electronic structures of single semiconductor nanowires can be resolved using photomodulated Rayleigh scattering spectroscopy. The Rayleigh scattering from semiconductor nanowires is strongly polarization sensitive which allows a nearly background-free method for detecting only the light that is scattered from a single nanowire. While the Rayleigh scattering efficiency from a semiconductor nanowire depends on the dielectric contrast, it is relatively featureless as a function of energy. However, if the nanowire is photomodulated using a second pump laser beam, the internal electronic structure can be resolved with extremely high signal-to-noise and spectral resolution. The photomodulated Rayleigh scattering spectra can be understood theoretically as a first derivative of the scattering efficiency that results from a modulation of the band gap and depends sensitively on the nanowire diameter. Fits to spectral lineshapes provide both the band structure and the diameter of individual GaAs and InP nanowires under investigation. PMID:21894948

  11. Ground-based testing of the dynamics of flexible space structures using band mechanisms

    NASA Technical Reports Server (NTRS)

    Yang, L. F.; Chew, Meng-Sang

    1991-01-01

    A suspension system based on a band mechanism is studied to provide the free-free conditions for ground based validation testing of flexible space structures. The band mechanism consists of a noncircular disk with a convex profile, preloaded by torsional springs at its center of rotation so that static equilibrium of the test structure is maintained at any vertical location; the gravitational force will be directly counteracted during dynamic testing of the space structure. This noncircular disk within the suspension system can be configured to remain unchanged for test articles with the different weights as long as the torsional spring is replaced to maintain the originally designed frequency ratio of W/k sub s. Simulations of test articles which are modeled as lumped parameter as well as continuous parameter systems, are also presented.

  12. High-throughput combinatorial database of electronic band structures for inorganic scintillator materials.

    PubMed

    Setyawan, Wahyu; Gaume, Romain M; Lam, Stephanie; Feigelson, Robert S; Curtarolo, Stefano

    2011-07-11

    For the purpose of creating a database of electronic structures of all the known inorganic compounds, we have developed a computational framework based on high-throughput ab initio calculations (AFLOW) and an online repository (www.aflowlib.org). In this article, we report the first step of this task: the calculation of band structures for 7439 compounds intended for the research of scintillator materials for ?-ray radiation detection. Data-mining is performed to select the candidates from 193,456 compounds compiled in the Inorganic Crystal Structure Database. Light yield and scintillation nonproportionality are predicted based on semiempirical band gaps and effective masses. We present a list of materials, potentially bright and proportional, and focus on those exhibiting small effective masses and effective mass ratios. PMID:21644557

  13. Stable porous crystalline silicon with nanotubular structure: A predicted allotrope with direct band gap

    NASA Astrophysics Data System (ADS)

    Tang, Chi-Pui; Cao, Jie; Xiong, Shi-Jie

    2015-06-01

    On basis of the first principle calculation we show that a crystalline structure of silicon, as a novel allotrope with nanotubular holes along two perpendicular directions, is stable. The calculations on geometrical and electronic properties reveal that this allotrope possesses a direct band gap wider by 0.5 eV than the indirect one of silicon with diamond structure. The crystal belongs to I41/AMD space group, showing anisotropic optical properties and Young modulus. The bulk modulus is 64.4 GPa and the density is 1.9 g/cm3, lower than that of the diamond silicon due to the presence of nanotubular holes. It is hopeful that the allotrope may widely expand applications of silicon in many fields due to its direct band gap and specific nanotubular structure.

  14. Surface passivation of a photonic crystal band-edge laser by atomic layer deposition of SiO2 and its application for biosensing

    NASA Astrophysics Data System (ADS)

    Cha, Hyungrae; Lee, Jeongkug; Jordan, Luke R.; Lee, Si Hoon; Oh, Sang-Hyun; Kim, Hyo Jin; Park, Juhun; Hong, Seunghun; Jeon, Heonsu

    2015-02-01

    We report on the conformal surface passivation of photonic crystal (PC) laser devices with an ultrathin dielectric layer. Air-bridge-type ?-point band-edge lasers (BELs) are fabricated by forming a honeycomb lattice two-dimensional PC structure into an InGaAsP multiple-quantum-well epilayer. Atomic layer deposition (ALD) is employed for conformal deposition of a few-nanometer-thick SiO2 layer over the entire device surface, not only on the top and bottom surfaces of the air-bridge membrane but also on the air-hole sidewalls. Despite its extreme thinness, the ALD passivation layer is found to protect the InGaAsP BEL devices from harsh chemicals. In addition, the ALD-SiO2 is compatible with the silane-based surface chemistry, which allows us to use ALD-passivated BEL devices as label-free biosensors. The standard streptavidin-biotin interaction shifts the BEL lasing wavelength by ~1 nm for the dipole-like ?-point band-edge mode. A sharp lasing line (<0.2 nm, full width at half-maximum) and a large refractive index sensitivity (~163 nm per RIU) produce a figure of merit as high as ~800 for our BEL biosensor, which is at least an order of magnitude higher than those of more common biosensors that rely on a broad resonance peak, showing that our nanolaser structures are suitable for highly sensitive biosensor applications.

  15. Surface passivation of a photonic crystal band-edge laser by atomic layer deposition of SiO2 and its application for biosensing.

    PubMed

    Cha, Hyungrae; Lee, Jeongkug; Jordan, Luke R; Lee, Si Hoon; Oh, Sang-Hyun; Kim, Hyo Jin; Park, Juhun; Hong, Seunghun; Jeon, Heonsu

    2015-02-28

    We report on the conformal surface passivation of photonic crystal (PC) laser devices with an ultrathin dielectric layer. Air-bridge-type ?-point band-edge lasers (BELs) are fabricated by forming a honeycomb lattice two-dimensional PC structure into an InGaAsP multiple-quantum-well epilayer. Atomic layer deposition (ALD) is employed for conformal deposition of a few-nanometer-thick SiO2 layer over the entire device surface, not only on the top and bottom surfaces of the air-bridge membrane but also on the air-hole sidewalls. Despite its extreme thinness, the ALD passivation layer is found to protect the InGaAsP BEL devices from harsh chemicals. In addition, the ALD-SiO2 is compatible with the silane-based surface chemistry, which allows us to use ALD-passivated BEL devices as label-free biosensors. The standard streptavidin-biotin interaction shifts the BEL lasing wavelength by ?1 nm for the dipole-like ?-point band-edge mode. A sharp lasing line (<0.2 nm, full width at half-maximum) and a large refractive index sensitivity (?163 nm per RIU) produce a figure of merit as high as ?800 for our BEL biosensor, which is at least an order of magnitude higher than those of more common biosensors that rely on a broad resonance peak, showing that our nanolaser structures are suitable for highly sensitive biosensor applications. PMID:25631610

  16. Band gap and electronic structure of MgSiN{sub 2}

    SciTech Connect

    Quirk, J. B., E-mail: james.quirk09@imperial.ac.uk; Råsander, M.; McGilvery, C. M.; Moram, M. A. [Department of Materials, Imperial College London, Exhibition Road, London SW7 2AZ (United Kingdom); Palgrave, R. [Department of Chemistry, University College London, Gordon Street WC1H 0AJ (United Kingdom)

    2014-09-15

    Density functional theory calculations and electron energy loss spectroscopy indicate that the electronic structure of ordered orthorhombic MgSiN{sub 2} is similar to that of wurtzite AlN. A band gap of 5.7?eV was calculated for both MgSiN{sub 2} (indirect) and AlN (direct) using the Heyd-Scuseria-Ernzerhof approximation. Correction with respect to the experimental room-temperature band gap of AlN indicates that the true band gap of MgSiN{sub 2} is 6.2?eV. MgSiN{sub 2} has an additional direct gap of 6.3?eV at the ? point.

  17. Quasiparticle excitations in valence-fluctuation materials: effects of band structure and crystal fields

    SciTech Connect

    Brandow, B.H.

    1985-01-01

    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.

  18. Vibronic structure in triatomic molecules: The hydrocarbon flame bands of the formyl radical (HCO). A theoretical study

    NASA Astrophysics Data System (ADS)

    Serrano-Andrés, Luis; Forsberg, Niclas; Malmqvist, Per-A.?Ke

    1998-05-01

    A theoretical study of the vibrational structure of the X˜ 2A' ground and B˜ 2A' excited states of the formyl radical, HCO, and its deuterated form, DCO, has been performed. The potential energy surfaces have been computed by means of a multiconfigurational perturbative method, CASPT2. The computed geometries and the harmonic and anharmonic frequencies are successfully compared to the available experimental information. The vibrational intensities of the transition B˜ 2A'?X˜2A' have been computed both for absorption and emission. The results lead to accurate determinations of several structural parameters and some reassignments of the vibrational transitions of the so-called hydrocarbon flame bands of the formyl radical.

  19. Atomic arrangement and electron band structure of Si(1 1 1)-ß-[Formula: see text]-Bi reconstruction modified by alkali-metal adsorption: ab initio study.

    PubMed

    Eremeev, S V; Chukurov, E N; Gruznev, D V; Zotov, A V; Saranin, A A

    2015-08-01

    Using ab initio calculations, atomic structure and electronic properties of Si(1 1 1)[Formula: see text]-Bi surface modified by adsorption of 1/3 monolayer of alkali metals, Li, Na, K, Rb and Cs, have been explored. Upon adsorption of all metals, a similar atomic structure develops at the surface where twisted chained Bi trimers are arranged into a honeycomb network and alkali metal atoms occupy the [Formula: see text] sites in the center of each honeycomb unit. Among other structural characteristics, the greatest variation concerns the relative heights at which alkali metals reside with respect to Bi-trimer layer. Except for Li, the other metals reside higher than Bi layer and their heights increase with atomic number. All adsorbed surface structures display similar electron band structures of which the most essential feature is metallic surface-state band with a giant spin splitting. This electronic property allows one to consider the Si(1 1 1)[Formula: see text]-Bi surfaces modified by alkali metal adsorption as a set of material systems showing promise for spintronic applications. PMID:26151642

  20. Structure of the doublet bands in doubly odd nuclei: The case of {sup 128}Cs

    SciTech Connect

    Ganev, H. G. [Institute of Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences, Sofia 1784 (Bulgaria); Brant, S. [Department of Physics, Faculty of Science, University of Zagreb, 10000 Zagreb (Croatia)

    2010-09-15

    The structure of the {Delta}J=1 doublet bands in {sup 128}Cs is investigated within the framework of the interacting vector boson-fermion model. A new, purely collective interpretation of these bands is given on the basis of the used boson-fermion dynamical symmetry of the model. The energy levels of the doublet bands as well as the absolute B(E2) and B(M1) transition probabilities between the states of both yrast and yrare bands are described quite well. The observed odd-even staggering of both B(M1) and B(E2) values is reproduced by the introduction of an appropriate interaction term of quadrupole type, which produces such a staggering effect in the transition strengths. The calculations show that the appearance of doublet bands in certain odd-odd nuclei could be a consequence of the realization of a larger dynamical symmetry based on the noncompact supersymmetry group OSp(2{Omega}/12,R).

  1. Identification of surface structures on 3C-SiC nanocrystals with hydrogen and hydroxyl bonding by photoluminescence.

    PubMed

    Wu, X L; Xiong, S J; Zhu, J; Wang, J; Shen, J C; Chu, Paul K

    2009-12-01

    SiC nanocrystals (NCs) exhibit unique surface chemistry and possess special properties. This provides the opportunity to design suitable surface structures by terminating the surface dangling bonds with different atoms thereby boding well for practical applications. In this article, we report the photoluminescence properties of 3C-SiC NCs in water suspensions with different pH values. Besides a blue band stemming from the quantum confinement effect, the 3C-SiC NCs show an additional photoluminescence band at 510 nm when the excitation wavelengths are longer than 350 nm. Its intensity relative to the blue band increases with the excitation wavelength. The 510 nm band appears only in acidic suspensions but not in alkaline ones. Fourier transform infrared, X-ray photoelectron spectroscopy, and X-ray absorption near-edge structure analyses clearly reveal that the 3C-SiC NCs in the water suspension have Si-H and Si-OH bonds on their surface, implying that water molecules only react with a Si-terminated surface. First-principle calculations suggest that the additional 510 nm band arises from structures induced by H(+) and OH(-) dissociated from water and attached to Si dimers on the modified (001) Si-terminated portion of the NCs. The size requirement is consistent with the observation that the 510 nm band can only be observed when the excitation wavelengths are relatively large, that is, excitation of bigger NCs. PMID:19894694

  2. The Glacier and Ice Surface Topography Interferometer: UAVSAR's Single-pass Ka-Band Interferometer

    NASA Astrophysics Data System (ADS)

    Moller, D.; Hensley, S.; Sadowy, G.; Wu, X.; Carswell, J.; Fisher, C.; Michel, T.; Lou, Y.

    2012-12-01

    In May 2009 a new radar technique for mapping ice surface topography was demonstrated in a Greenland campaign as part of the NASA International Polar Year (IPY) activities. This was achieved with the airborne Glacier and Ice Surface Topography Interferometer (GLISTIN-A): a 35.6 GHz single-pass interferometer. Although the technique of using radar interferometry for mapping terrain has been demonstrated before, this is the first such application at millimeter-wave frequencies. The proof-of-concept demonstration was achieved by interfacing Ka-band RF and antenna hardware with the Uninhabited Airborne Vehicle Synthetic Aperture Radar (UAVSAR). The GLISTIN-A was implemented as a custom installation of the NASA Dryden Flight Research Center Gulfstream III. Instrument performance indicates swath widths over the ice between 5-7km, with height precisions ranging from 30cm-3m at a posting of 3m x 3m. Processing challenges were encountered in achieving the accuracy requirements on several fronts including, aircraft motion sensitivity, multipath and systematic drifts. However, through a combination of processor optimization, a modified phase-screen and motion-compensation implementations were able to minimize the impact of these systematic error sources. We will present results from the IPY data collections including system performance evaluations and imagery. This includes a large area digital elevation model (DEM) collected over Jakobshavn glacier as an illustrative science data product. Further, by intercomparison with the NASA Wallops Airborne Topographic Mapper (ATM) and calibration targets we quantify the interferometric penetration bias of the Ka-band returns into the snow cover. Following the success of the IPY campaign, we are funded under the Earth Science Techonology Office (ESTO) Airborne Innovative Technology Transition (AITT) program to transition GLISTIN-A to a permanently-available pod-only system compatible with unpressurized operation. In addition fundamental system upgrades will greatly enhance the performance and make wider-swath and higher altitude operation possible. We will show results from first flights of GLISTIN-A and summarize the plans for the near future including GLISTIN-H: GLISTIN on the NASA Global Hawk Spring 2013.

  3. Photonic band gap structures of obliquely incident electromagnetic wave propagation in a one-dimension absorptive plasma photonic crystal

    SciTech Connect

    Guo Bin [Department of Physical Science and Technology, Wuhan University of Technology, Wuhan 430070 (China)

    2009-04-15

    The photonic band gap structures of obliquely incident electromagnetic waves propagating in a one-dimension plasma photonic crystal with collision have been studied on the basis of electromagnetic theory and transfer matrix approach. The dispersion relations for both the transverse electric wave case and the transverse magnetic wave case are deduced. And the photonic band gap structures, with their function dependence on the microplasma layer density, microplasma width, collision frequency, background material dielectric constant, and incident angle, are computed. The results show that there exist two photonic band gap structures in an adsorptive plasma photonic crystal: one is a normal photonic band gap structure and the other is an absorption photonic band gap structure. Parameter dependence of the effects is calculated and discussed.

  4. Structure and method for controlling band offset and alignment at a crystalline oxide-on-semiconductor interface

    DOEpatents

    McKee, Rodney A.; Walker, Frederick J.

    2003-11-25

    A crystalline oxide-on-semiconductor structure and a process for constructing the structure involves a substrate of silicon, germanium or a silicon-germanium alloy and an epitaxial thin film overlying the surface of the substrate wherein the thin film consists of a first epitaxial stratum of single atomic plane layers of an alkaline earth oxide designated generally as (AO).sub.n and a second stratum of single unit cell layers of an oxide material designated as (A'BO.sub.3).sub.m so that the multilayer film arranged upon the substrate surface is designated (AO).sub.n (A'BO.sub.3).sub.m wherein n is an integer repeat of single atomic plane layers of the alkaline earth oxide AO and m is an integer repeat of single unit cell layers of the A'BO.sub.3 oxide material. Within the multilayer film, the values of n and m have been selected to provide the structure with a desired electrical structure at the substrate/thin film interface that can be optimized to control band offset and alignment.

  5. HIGH RESOLUTION OCEAN SURFACE WIND FIELDS RETRIEVED FROM SPACEBORNE SYNTHETIC APERTURE RADARS OPERATING AT C-BAND

    Microsoft Academic Search

    Jochen Horstmann; Wolfgang Koch

    This paper introduces algorithms designed to re- trieve high-resolution ocean surface wind fields from satellite borne synthetic aperture radars (SARs) op- erating in C-band at either vertical (VV) or horizon- tal (HH) polarization in transmit and receive. Wind directions are extracted from wind induced streaks that are visible in SAR images at scales above 200 m and that are approximately

  6. Structural phase transition in IrTe2: A combined study of optical spectroscopy and band structure calculations

    PubMed Central

    Fang, A. F.; Xu, G.; Dong, T.; Zheng, P.; Wang, N. L.

    2013-01-01

    Ir1?xPtxTe2 is an interesting system showing competing phenomenon between structural instability and superconductivity. Due to the large atomic numbers of Ir and Te, the spin-orbital coupling is expected to be strong in the system which may lead to nonconventional superconductivity. We grew single crystal samples of this system and investigated their electronic properties. In particular, we performed optical spectroscopic measurements, in combination with density function calculations, on the undoped compound IrTe2 in an effort to elucidate the origin of the structural phase transition at 280?K. The measurement revealed a dramatic reconstruction of band structure and a significant reduction of conducting carriers below the phase transition. We elaborate that the transition is not driven by the density wave type instability but caused by the crystal field effect which further splits/separates the energy levels of Te (px, py) and Te pz bands. PMID:23362455

  7. Structural phase transition in IrTe2: A combined study of optical spectroscopy and band structure calculations

    NASA Astrophysics Data System (ADS)

    Fang, A. F.; Xu, G.; Dong, T.; Zheng, P.; Wang, N. L.

    2013-01-01

    Ir1-xPtxTe2 is an interesting system showing competing phenomenon between structural instability and superconductivity. Due to the large atomic numbers of Ir and Te, the spin-orbital coupling is expected to be strong in the system which may lead to nonconventional superconductivity. We grew single crystal samples of this system and investigated their electronic properties. In particular, we performed optical spectroscopic measurements, in combination with density function calculations, on the undoped compound IrTe2 in an effort to elucidate the origin of the structural phase transition at 280 K. The measurement revealed a dramatic reconstruction of band structure and a significant reduction of conducting carriers below the phase transition. We elaborate that the transition is not driven by the density wave type instability but caused by the crystal field effect which further splits/separates the energy levels of Te (px, py) and Te pz bands.

  8. Photonic band structure of one-dimensional metal/dielectric structures calculated by the plane-wave expansion method

    NASA Astrophysics Data System (ADS)

    Zong, YiXin; Xia, JianBai

    2015-07-01

    The plane-wave expansion (PWE) method is employed to calculate the photonic band structures of metal/dielectric (M/D) periodic systems. We consider a one-dimensional (1D)M/D superlattice with ametal layer characterized by a frequency-dependent dielectric function. To calculate the photonic band of such a system, we propose a new method and thus avoid solving the nonlinear eigenvalue equations. We obtained the frequency dispersions and the energy distributions of eigen-modes of 1D superlattices. This general method is applicable to calculate the photonic band of a broad class of physical systems, e.g. 2D and 3D M/D photonic crystals. For comparison, we present a simple introduction of the finite-difference (FD) method to calculate the same system, and the agreement turns out to be good. But the FD method cannot be applied to the TM modes of the M/D superlattice.

  9. IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING, VOL. 40, NO. 10, OCTOBER 2002 2117 Sea Surface Emissivity Observations at L-Band

    E-print Network

    Reising, Steven C.

    Emissivity Observations at L-Band: First Results of the Wind and Salinity Experiment WISE 2000 A. Camps-Neira, Member, IEEE Abstract--Sea surface salinity can be measured by passive mi- crowave remote sensing at L-band in the radiometric measurements at L-band, their comparison with nu- merical models, and the implications

  10. Unpolarized emissivity with shadow and multiple reflections from random rough surfaces with the geometric optics approximation: application to Gaussian sea surfaces in the infrared band.

    PubMed

    Bourlier, Christophe

    2006-08-20

    The emissivity from a stationary random rough surface is derived by taking into account the multiple reflections and the shadowing effect. The model is applied to the ocean surface. The geometric optics approximation is assumed to be valid, which means that the rough surface is modeled as a collection of facets reflecting locally the light in the specular direction. In particular, the emissivity with zero, single, and double reflections are analytically calculated, and each contribution is studied numerically by considering a 1D sea surface observed in the near infrared band. The model is also compared with results computed from a Monte Carlo ray-tracing method. PMID:16892130

  11. Control of Spin Wave Band Structure and Propagation in Two-Dimensional Magnonic Crystals

    NASA Astrophysics Data System (ADS)

    Sietsema, Glade; Flatté, Michael E.

    2015-03-01

    We have studied the properties of spin waves in two-dimensional magnonic crystals consisting of a magnetic material arranged in a lattice of cylinders and embedded in a second magnetic material. Dispersion curves, linewidths, and spin wave propagation patterns were obtained from the Landau-Lifshitz-Gilbert equation using the plane wave expansion method. We have examined how these results are affected by various parameters including the shape of the cylinders, the lattice structure, the material properties, and the spin-orbit interaction. Adjusting these values can open or close band gaps and drastically shift the frequency range of the band structure. The spin wave propagation patterns were found to exhibit high directionality dependent on the excitation frequency and can also be modified with the aforementioned parameters. This work was supported in part by DARPA/MESO and by C-SPIN, one of six centers of STARnet, a Semiconductor Research Corporation program, sponsored by MARCO and DARPA.

  12. Fracture Induced Sub-Band Absorption as a Precursor to Optical Damage on Fused Silica Surfaces

    SciTech Connect

    Miller, P E; Bude, J D; Suratwala, T I; Shen, N; Laurence, T A; Steele, W A; Menapace, J; Feit, M D; Wong, L L

    2010-03-05

    The optical damage threshold of indentation induced flaws on fused silica surfaces was explored. Mechanical flaws were characterized by laser damaged testing, SEM, optical, and photoluminescence microscopy. Localized polishing, chemical etching, and the control of indentation morphology were used to isolate the structural features which limit optical damage. A thin defect layer on fracture surfaces, including those smaller than the wavelength of visible light, was found to be the dominant source of laser damage initiation during illumination with 355nm, 3ns laser pulses. Little evidence was found that either displaced or densified material or fluence intensification plays a significant role in optical damage at fluences >35J/cm{sup 2}. Elimination of the defect layer was shown to increase the overall damage performance of fused silica optics.

  13. The study of band gap engineering for phononic crystals and gap structures in phononic quasicrystals

    Microsoft Academic Search

    Yun Lai

    2005-01-01

    Phononic crystals and quasicrystals are solid-solid, fluid-solid or fluid-fluid composites with periodic or quasiperiodic long-range order, respectively. They are of interest not only because of the profound effects of their periodic or quasiperiodic structure on wave propagation (e.g. the existence of elastic or acoustic band gaps), but also because of potential applications like sound filters, transducer design and acoustic mirrors,

  14. Loop structure of the lowest Bloch band for a Bose-Einstein condensate

    NASA Astrophysics Data System (ADS)

    Diakonov, Dmitri; Jensen, L. M.; Pethick, C. J.; Smith, H.

    2002-07-01

    We investigate analytically and numerically Bloch waves for a Bose-Einstein condensate in a sinusoidal external potential. At low densities the dependence of the energy on the quasimomentum is similar to that for a single particle, but at densities greater than a critical one the lowest band becomes triple valued near the boundary of the first Brillouin zone and develops the structure characteristic of the swallowtail catastrophe. We comment on the experimental consequences of this behavior.

  15. Structure of the Kpi = 4+ bands in 186,188Os

    Microsoft Academic Search

    A. A. Phillips; P. E. Garrett; L. Bettermann; N. Braun; D. G. Burke; G. A. Demand; T. Faestermann; P. Finlay; K. L. Green; R. Hertenberger; R. Krücken; K. G. Leach; M. A. Schumaker; C. E. Svensson; H.-F. Wirth; J. Wong

    2009-01-01

    The structures of 3+ states in Os have been debated over several decades. Based on measured B(E2) values they were interpreted in 186-192Os as Kpi = 4+ two-phonon vibrations, whereas inelastic scattering, and (t,alpha) work imply a hexadecapole phonon description. To clarify the nature of these Kpi = 4+ bands in 186,188Os, we performed a (3He,d) reaction on 185,187Re targets

  16. Anchorage of a Band 3 Population at the Erythrocyte Cytoplasmic Membrane Surface: Protein Rotational Diffusion Measurements

    Microsoft Academic Search

    Erich A. Nigg; Richard J. Cherry

    1980-01-01

    Direct physical evidence for the linkage of a band 3 population to the cytoskeleton in the erythrocyte ghost membrane is presented. The rotational diffusion of band 3 proteins was measured by observing flash-induced transient dichroism of a covalently bound eosin probe. After proteolytic release of a 40,000-dalton cytoplasmic segment of band 3 by trypsin, a considerable enhancement in the decay

  17. Structure and thermodynamics of surface recognition

    SciTech Connect

    Gupta, G.

    1998-11-01

    This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Interactions of the surface glycoprotein, gp120, with the receptors of host cells define the pathogenesis of HIV-1, the virus that causes AIDS. gp120 is made of several disulfide-bridged loops--the amino acid sequences of some of these loops are fairly conserved whereas the rest are variable. The third variable (V3) loop has been the target of vaccine design for quite some time since this loop is involved in various steps of viral pathogenesis. However, this loop also happens to be the most variable one. The authors have carried out structural and immunological studies to determine the sequence-structure-antigenicity correlations of the HIV-1 V3 loops. This resulted in the identification of a secondary structure at the tip of the V3 loop that remains invariant in spite of the sequence variation. The authors designed a multi-valent V3-based antigen that presents multiple copies of the same tip element several times in the same structure. During the course of this project, they realized that the protective epitopes of gp120 should be judged in the context of the native structure. Therefore, the authors developed a method to obtain a model of gp120 that is consistent with all the immunology and virology data. This model is useful in choosing or designing gp120 subdomains for vaccine development.

  18. Structure in the visible absorption bands of jet-cooled phenylperoxy radicals.

    PubMed

    Freel, Keith A; Sullivan, Michael N; Park, J; Lin, M C; Heaven, Michael C

    2013-08-15

    The visible absorption bands of the phenylperoxy radical in the gas phase have been investigated using cavity ring-down spectroscopy. Jet-cooling was used to reduce the spectral congestion. Structured spectra spanning the range from 17,500 to 19,000 cm(-1) are reported for the first time. Analyses of these data have been guided by the results from time-dependent density functional calculations. The observed spectrum was found to be dominated by the bands of the B?(2)A?-X?(2)A? transition. An analysis of the rotational contour for the origin band yielded a homogeneous line width of 2.2 cm(-1), corresponding to a decay rate of 4.1 × 10(11) s(-1). The results provide a rationale for the lack of structure in room temperature spectra that have been previously attributed to phenylperoxy. They also indicate that the lower energy region of the spectrum may show resolvable structure at room temperature. If so, this would provide a more definitive signature for monitoring phenylperoxy in kinetic measurements. PMID:23590572

  19. Electronic structure of bacterial surface protein layers

    SciTech Connect

    Maslyuk, Volodymyr V.; Mertig, Ingrid; Bredow, Thomas; Mertig, Michael; Vyalikh, Denis V.; Molodtsov, Serguei L. [Martin-Luther-Universitaet Halle-Wittenberg, Fachbereich Physik, D-06099 Halle (Germany); Institut fuer Physikalische und Theoretische Chemie, Universitaet Bonn, D-53115 Bonn (Germany); Max-Bergmann-Zentrum fuer Biomaterialien, Technische Universitaet Dresden, D-01062 Dresden (Germany); Institut fuer Festkoerperphysik, Technische Universitaet Dresden, D-01062 Dresden (Germany)

    2008-01-15

    We report an approach for the calculation of the electronic density of states of the dried two-dimensional crystalline surface protein layer (S layer) of the bacterium Bacillus sphaericus NCTC 9602. The proposed model is based on the consideration of individual amino acids in the corresponding conformation of the peptide chain which additively contribute to the electronic structure of the entire protein complex. The derived results agree well with the experimental data obtained by means of photoemission (PE), resonant PE, and near-edge x-ray absorption spectroscopy.

  20. Observation of an electron band above the Fermi level in FeTe?.??Se?.?? from in-situ surface doping

    DOE PAGESBeta

    Zhang, P. [Chinese Academy of Sciences (CAS), Beijing (China); Gu, G. D. [Brookhaven National Lab. (BNL), Upton, NY (United States); Richard, P. [Chinese Academy of Sciences (CAS), Beijing (China); Collaborative Innovation Center of Quantum Matter, Beijing (China); Xu, N. [Chinese Academy of Sciences (CAS), Beijing (China); Paul Scherrer Inst. (PSI), Villigen (Switzerland); Xu, Y. -M. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Ma, J. [Chinese Academy of Sciences (CAS), Beijing (China); Qian, T. [Chinese Academy of Sciences (CAS), Beijing (China); Fedorov, A. V. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Denlinger, J. D. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Ding, H. [Chinese Academy of Sciences (CAS), Beijing (China); Collaborative Innovation Center of Quantum Matter, Beijing (China)

    2014-10-27

    We used in-situ potassium (K) evaporation to dope the surface of the iron-based superconductor FeTe?.??Se?.??. The systematic study of the bands near the Fermi level confirms that electrons are doped into the system, allowing us to tune the Fermi level of this material and to access otherwise unoccupied electronic states. In particular, we observe an electron band located above the Fermi level before doping that shares similarities with a small three-dimensional pocket observed in the cousin, heavily-electron-doped KFe??xSe? compound.

  1. Emittance, surface structure, and electron emission

    NASA Astrophysics Data System (ADS)

    Jensen, Kevin L.; Shiffler, Donald A.; Petillo, John J.; Pan, Zhigang; Luginsland, John W.

    2014-04-01

    The emittance of high brightness electron sources, particularly field emitters and photocathodes but also thermionic sources, is increased by surface roughness on the emitter. Such structure causes local field enhancement and complicates both the prediction of emittance and the underlying emission models on which such predictions depend. In the present work, a method to find the emission trajectories near regions of high field enhancement is given and applied to emittance predictions for field, photo, and thermal emission for an analytically tractable hemispherical model. The dependence of the emittance on current density, spatial variation, and acceleration close to the emission site is identified and the impact of space charge discussed. The methodology is extensible to field emission from close-spaced wirelike structures, in particular, and extensions to that configuration are discussed. The models have application to electron sources for high frequency vacuum electronics, high power microwave devices, and free-electron lasers.

  2. The use of surface segmentation methods to characterise laser zone surface structure on hard disc drives

    Microsoft Academic Search

    Liam Blunt; Shaojun Xiao

    2011-01-01

    All surfaces, be they at the nano-, micro- or even macroscale are made up of a collection of fundamental features at many different scales which constitute the surface topography. The new generation of so called structured surfaces have features which are organised in deterministic patterns; these include MEMS\\/NEMS surfaces, micro-fluidic device surfaces and surfaces with repeating features to improve their

  3. Y-Shaped Amphiphilic Brushes with Switchable Micellar Surface Structures

    E-print Network

    Zubarev, Eugene

    Y-Shaped Amphiphilic Brushes with Switchable Micellar Surface Structures Duangrut Julthongpiput to a functionalized silicon surface. Postgrafting hydrolysis of poly(tert-butyl acrylate) arms imparts amphiphilicity adaptive macroscopic wetting surface properties of the amphiphilic Y-shaped brushes. This surface structure

  4. Quasiparticle band structure for the Hubbard systems: Application to. alpha. -CeAl sub 2

    SciTech Connect

    Costa-Quintana, J.; Lopez-Aguilar, F. (Departamento de Fisica, Grupo de Electromagnetismo, Universidad Autonoma de Barcelona, Bellaterra, E-08193 Barcelona, Spain (ES)); Balle, S. (Departament de Fisica, Universitat de les Illes Balears, E-07071 Palma de Mallorca, Spain (ES)); Salvador, R. (Control Data Corporation, TALLAHASSEE, FL (USA) Supercomputer Computations Research Institute, Florida State University, Tallahassee, Florida 32306-4052 (USA))

    1990-04-01

    A self-energy formalism for determining the quasiparticle band structure of the Hubbard systems is deduced. The self-energy is obtained from the dynamically screened Coulomb interaction whose bare value is the correlation energy {ital U}. A method for integrating the Schroedingerlike equation with the self-energy operator is given. The method is applied to the cubic Laves phase of {alpha}-CeAl{sub 2} because it is a clear Hubbard system with a very complex electronic structure and, moreover, this system provides us with sufficient experimental data for testing our method.

  5. Band Structure and Quantum Conductance of Nanostructures from Maximally Localized Wannier Functions: The Case of Functionalized Carbon Nanotubes

    Microsoft Academic Search

    Young-Su Lee; Marco Buongiorno Nardelli; Nicola Marzari

    2005-01-01

    We have combined large-scale, Gamma-point electronic-structure calculations with the maximally localized Wannier functions approach to calculate efficiently the band structure and the quantum conductance of complex systems containing thousands of atoms while maintaining full first-principles accuracy. We have applied this approach to study covalent functionalizations in metallic single-walled carbon nanotubes. We find that the band structure around the Fermi energy

  6. Quantitative surface structure analysis by low-energy ion scattering

    Microsoft Academic Search

    M. Aono

    1984-01-01

    A review is presented of low-energy ion scattering spectroscopy (ISS) as a tool for surface atomic structure analysis. Especially, quantitative surface atomic structure analysis by ISS is highlighted. An important difference between ISS and Rutherford backscattering spectroscopy (RBS), a specialization of ISS for quantitative surface atomic structure analysis, and a general feature of the shadow cone in the energy range

  7. Band structures and bandgap bowing parameters of wurtzite and zincblende III-nitrides

    NASA Astrophysics Data System (ADS)

    Lin, Wen-Wei; Kuo, Yen-Kuang

    2002-09-01

    The III-nitride semiconductor materials attract much attention in the past few years owing to their important application in light-emitting diodes and semiconductor lasers. Since the III-nitride semiconductor devices are usually grown on the sapphire substrate, they all have wurtzite crystal structures. The energy bandgaps of the wurtzite III-nitrides are usually obtained experimentally. Several researchers have investigated the energy bandgaps and the bandgap bowing parameters of the wurtzite InGaN, AlGaN, and AlInN alloys; however, the results are quite diverging. In this work we investigate the band structures of the wurtzite InGaN, AlGaN, and AlInN alloys with a CASTEP simulation program. The simulation results suggest that the wurtzite InGaN, AlGaN, and AlInN have a bandgap bowing parameter of 1.21 eV, 0.35 eV, and 3.33 eV respectively. Our simulation results also indicate that the widths of the top valance bands of the wurtzite InGaN and AlGaN alloys decrease when the indium and aluminum compositions increase while the width of the AlInN top valence band has a maximum value of about 6.57 eV when the aluminum composition is near 0.53. In this paper, the investigation of the band structures and bandgap bowing parameters for the zincblende InGaN, AlGaN, and AlInN alloys is also reported.

  8. Surface and electronic structure of epitaxial PtLuSb (001) thin films

    SciTech Connect

    Patel, Sahil J.; Kawasaki, Jason K.; Logan, John [Materials Department, University of California-Santa Barbara, Santa Barbara, California 93106 (United States); Schultz, Brian D. [Department of Electrical and Computer Engineering, University of California-Santa Barbara, Santa Barbara, California 93106 (United States); Adell, J.; Thiagarajan, B. [MAX IV Laboratory, Lund University, Lund 221 00 (Sweden); Mikkelsen, A. [Department of Physics, Lund University, Lund 221 00 (Sweden); Palmstrøm, Chris J., E-mail: cpalmstrom@ece.ucsb.edu [Materials Department, University of California-Santa Barbara, Santa Barbara, California 93106 (United States); Department of Electrical and Computer Engineering, University of California-Santa Barbara, Santa Barbara, California 93106 (United States)

    2014-05-19

    The surface and electronic structure of single crystal thin films of PtLuSb (001) grown by molecular beam epitaxy were studied. Scanning tunneling spectroscopy (STS), photoemission spectroscopy, and temperature dependent Hall measurements of PtLuSb thin films are consistent with a zero-gap semiconductor or semi-metal. STS and photoemission measurements show a decrease in density of states approaching the Fermi level for both valence and conduction bands as well as a slight shift of the Fermi level position into the valence band. Temperature dependent Hall measurements also corroborate the Fermi level position by measurement of p-type carriers.

  9. Proposed Laser Driven Photonic Band Gap Accelerator

    Microsoft Academic Search

    J. H. Han; I. S. Ko

    2004-01-01

    Accelerating gradient field can be guided in a waveguide made out of a photonic band gap structure. The electron beam which has the same velocity as the phase velocity of the guided accelerating field can be accelerated during passing the photonic band gap accelerator structure. A ratio of the surface electric field to the central accelerating gradient field can be

  10. Tertiary structure changes in albumin upon surface adsorption observed via fourier transform infrared spectroscopy.

    PubMed

    Smith, Jack R; Cicerone, Marcus T; Meuse, Curtis W

    2009-04-21

    A nondestructive Fourier transform infrared (FTIR) spectroscopy assay, amenable to exploring a wide range of proteins and polymers, is used to measure changes in the tertiary structure of bovine serum albumin (BSA) adsorbed to three surfaces: gold, polystyrene (PS), and poly(D,L-lactic acid) (PDLLA). Tertiary structural analysis is important because typical secondary structural analysis (FTIR and CD) is not always sensitive enough to distinguish between the sometimes subtle protein structural changes caused by adsorption. The polymers are spin-coated onto a gold surface, exposed to protein, and then immersed in a deuterated buffer solution to probe the protein's tertiary structure before the sample is removed from its aqueous environment. Infrared band intensities, related to the exchange of amide hydrogen for deuterium (HDX), as a function of the immersion time in deuterated buffer, are used to determine the extent of amide solvent exposure. Analysis of the results in terms of a single exponential decay shows that enough amides undergo a measurable amount of exchange in 60 min to quantify relative changes in BSA solvent exposure on different surfaces. In addition, substantial fractions undergo HDX at a rate too fast or too slow to be followed with our experimental protocol. The proportions of these quickly and slowly exchanging amide groups also provide information about relative changes in the BSA structure on different surfaces. Adsorption was found to increase the extent of HDX over that observed for BSA in solution, consistent with surface-induced unfolding and a loss of tertiary structure. Changes in HDX were found to be more sensitive to which surface was absorbing the protein than the typical FTIR secondary structural analysis obtained from fitting the amide I band. HDX was greatest for BSA adsorbed to the surface of PDLLA and least in the case of BSA adsorbed to gold, which indicates the greatest and least degree of unfolding, respectively. PMID:19366224

  11. Electronic and structural differences between wurtzite and zinc blende InAs nanowire surfaces: experiment and theory.

    PubMed

    Hjort, Martin; Lehmann, Sebastian; Knutsson, Johan; Zakharov, Alexei A; Du, Yaojun A; Sakong, Sung; Timm, Rainer; Nylund, Gustav; Lundgren, Edvin; Kratzer, Peter; Dick, Kimberly A; Mikkelsen, Anders

    2014-12-23

    We determine the detailed differences in geometry and band structure between wurtzite (Wz) and zinc blende (Zb) InAs nanowire (NW) surfaces using scanning tunneling microscopy/spectroscopy and photoemission electron microscopy. By establishing unreconstructed and defect-free surface facets for both Wz and Zb, we can reliably measure differences between valence and conduction band edges, the local vacuum levels, and geometric relaxations to the few-millielectronvolt and few-picometer levels, respectively. Surface and bulk density functional theory calculations agree well with the experimental findings and are used to interpret the results, allowing us to obtain information on both surface and bulk electronic structure. We can thus exclude several previously proposed explanations for the observed differences in conductivity of Wz-Zb NW devices. Instead, fundamental structural differences at the atomic scale and nanoscale that we observed between NW surface facets can explain the device behavior. PMID:25406069

  12. Stellar Surface Structure, IAU Colloquium No. 176

    NASA Astrophysics Data System (ADS)

    Pustylnik, I.

    The IAU Symposium No. 176 on the topic "Stellar Surface Structure" was held between October 9-13th 1995 in Vienna. Five scientific Sessions - Stellar Surface Mapping Techniques, Direct Mapping: The Last Frontier, Photospheric Phenomena: Results, Outer Atmosphere Structures, Next Generation Model Atmospheres with more than 200 participants presenting 55 talks and 105 poster papers cook place at the premises of the famous Vienna University. The Vienna symposium was carefully prepared and organized by the LOC (the head of the LOC Professor K. G. Strassmeier). The Abstracts of all the scientific contributions as well as the volume of Poster Proceedings have been published by the hosts and were distributed among the participants of the Symposium. The attendees and their accompanying guests could enjoy several sightseeing tours of the Austrian capital and a rich cultural program including a reception by the Mayor of Vienna Dr M. Haupl in the Rathaus. Symposium No. 176 was sponsored by several institutions and businesses including the Austrian Government Department of Science, Research and Culture, European Space Agency, Austrian Academy of Sciences, Austrian Space Agency and many others. A generous support from the IAU in form of travel grants gave the chance to attend IAU Symposium No. 176 to more than 20 astronomers from FSU and East European countries.

  13. The Surface Structure of Ground Metal Crystals

    NASA Technical Reports Server (NTRS)

    Boas, W.; Schmid, E.

    1944-01-01

    The changes produced on metallic surfaces as a result of grinding and polishing are not as yet fully understood. Undoubtedly there is some more or less marked change in the crystal structure, at least, in the top layer. Hereby a diffusion of separated crystal particles may be involved, or, on plastic material, the formation of a layer in greatly deformed state, with possible recrystallization in certain conditions. Czochralski verified the existence of such a layer on tin micro-sections by successive observations of the texture after repeated etching; while Thomassen established, roentgenographically by means of the Debye-Scherrer method, the existence of diffused crystal fractions on the surface of ground and polished tin bars, which he had already observed after turning (on the lathe). (Thickness of this layer - 0.07 mm). Whether this layer borders direct on the undamaged base material or whether deformed intermediate layers form the transition, nothing is known. One observation ty Sachs and Shoji simply states that after the turning of an alpha-brass crystal the disturbance starting from the surface, penetrates fairly deep (approx. 1 mm) into the crystal (proof by recrystallization at 750 C).

  14. Electronic structure of fluorinated self-assembled monolayer investigated by photoelectron spectroscopy in the valence band region

    NASA Astrophysics Data System (ADS)

    Haruyama, Yuichi; Matsui, Shinji

    2015-07-01

    The electronic structure of the fluorinated self-assembled monolayer (F-SAM) was investigated by using the photoelectron spectroscopy in the valence band region. The photon energy dependence of the photoelectron spectra in the valence band region of the F-SAM was measured from 50 to 420 eV and the orbital components of the photoelectron spectra were clarified. By measuring the photoelectron spectra in the valence band region of four types of F-SAM with different chain lengths, we obtained the evolution of the electronic structures in the F-SAM. In addition, the energy level of the F-SAM molecule obtained by ab initio molecular orbital calculation in a previous study was compared with the photoelectron spectrum in the valence band region. On the basis of the results of the photoelectron spectroscopy measurements in the valence band region, the electronic structure of the F-SAMs is discussed.

  15. Dual-band infrared imaging to detect corrosion damage within airframes and concrete structures

    NASA Astrophysics Data System (ADS)

    DelGrande, Nancy; Durbin, Philip F.

    1994-03-01

    We are developing dual-band IR (DBIR) imaging and detection techniques to inspect airframes and concrete bridge decks for hidden corrosion damage. Using selective DBIR image ratios, we enhanced surface temperature contrast and removed surface emissivity noise associated with clutter. Our surface temperature maps depicted defect sites, which heat and cool at different rates than their surroundings. Our emissivity-ratio maps tagged and removed the masking effects of surface clutter. For airframe inspections, we used time-resolved DBIR temperature, emissivity-ratio and composite thermal inertia maps to locate corrosion-thinning effects within a flash-heated Boeing 737 airframe. Emissivity-ratio maps tagged and removed clutter sites from uneven paint, dirt and surface markers. Temperature and thermal inertia maps characterized defect sites, types, sizes, thicknesses, thermal properties and material-loss effects from airframe corrosion. For concrete inspections, we mapped DBIR temperature and emissivity-ratio patterns to better interpret surrogate delamination sites within naturally- heated, concrete slabs and removed the clutter mask from sand pile-up, grease stains, rocks and other surface objects.

  16. Dual-band infrared imaging to detect corrosion damage within airframes and concrete structures

    SciTech Connect

    Del Grande, N.K.; Durbin, P.F.

    1994-01-01

    We are developing dual-band infrared (DBIR) imaging and detection techniques to inspect air frames and concrete bridge decks for hidden corrosion damage. Using selective DBIR image ratios,, we enhanced surface temperature contrast and removed surface emissivity noise associated with clutter. Our surface temperature maps depicted defect sites, which heat and cool at different rates than their surroundings. Our emissivity-ratio maps tagged and removed the masking effects of surface clutter. For airframe inspections, we used time-resolved DBIR temperature, emissivity-ratio and composite thermal inertia maps to locate corrosion-thinning effects within a flash-heated Boeing 737 airframe. Emissivity-ratio maps tagged and removed clutter sites from uneven paint, dirt and surface markers. Temperature and thermal inertia maps characterized defect sites, types, sizes, thicknesses, thermal properties and material-loss effects from air frame corrosion. For concrete inspections, we mapped DBIR temperature and emissivity-ratio patterns to better interpret surrogate delamination sites within naturally-heated, concrete slabs and remove the clutter mask from sand pile-up, grease stains, rocks and other surface objects.

  17. Search for localized Wannier functions of topological band structures via compressed sensing

    NASA Astrophysics Data System (ADS)

    Budich, J. C.; Eisert, J.; Bergholtz, E. J.; Diehl, S.; Zoller, P.

    2014-09-01

    We investigate the interplay of band structure topology and localization properties of Wannier functions. To this end, we extend a recently proposed compressed sensing based paradigm for the search for maximally localized Wannier functions [Ozolins et al., Proc. Natl. Acad. Sci. USA 110, 18368 (2013), 10.1073/pnas.1318679110]. We develop a practical toolbox that enables the search for maximally localized Wannier functions which exactly obey the underlying physical symmetries of a translationally invariant quantum lattice system under investigation. Most saliently, this allows us to systematically identify the most localized representative of a topological equivalence class of band structures, i.e., the most localized set of Wannier functions that is adiabatically connected to a generic initial representative. We also elaborate on the compressed sensing scheme and find a particularly simple and efficient implementation in which each step of the iteration is an O (NlogN) algorithm in the number of lattice sites N. We present benchmark results on one-dimensional topological superconductors demonstrating the power of these tools. Furthermore, we employ our method to address the open question of whether compact Wannier functions can exist for symmetry-protected topological states such as topological insulators in two dimensions. The existence of such functions would imply exact flat-band models with finite range hopping. Here, we find numerical evidence for the absence of such functions. We briefly discuss applications in dissipative-state preparation and in devising variational sets of states for tensor network methods.

  18. Search for localized Wannier functions of topological band structures via compressed sensing

    E-print Network

    J. C. Budich; J. Eisert; E. J. Bergholtz; S. Diehl; P. Zoller

    2014-09-11

    We investigate the interplay of band structure topology and localization properties of Wannier functions. To this end, we extend a recently proposed compressed sensing based paradigm for the search for maximally localized Wannier functions [Ozolins et al., PNAS 110, 18368 (2013)]. We develop a practical toolbox that enables the search for maximally localized Wannier functions which exactly obey the underlying physical symmetries of a translationally invariant quantum lattice system under investigation. Most saliently, this allows us to systematically identify the most localized representative of a topological equivalence class of band structures, i.e., the most localized set of Wannier functions that is adiabatically connected to a generic initial representative. We also elaborate on the compressed sensing scheme and find a particularly simple and efficient implementation in which each step of the iteration is an $O(N \\log N)$ algorithm in the number of lattice sites $N$. We present benchmark results on one-dimensional topological superconductors demonstrating the power of these tools. Furthermore, we employ our method to address the open question whether compact Wannier functions can exist for symmetry protected topological states like topological insulators in two dimensions. The existence of such functions would imply exact flat band models with strictly finite range hopping. Here, we find numerical evidence for the absence of such functions. We briefly discuss applications in dissipative state preparation and in devising variational sets of states for tensor network methods.

  19. Crustal Structure Beneath Taiwan Using Frequency-band Inversion of Receiver Function Waveforms

    NASA Astrophysics Data System (ADS)

    Tomfohrde, D. A.; Nowack, R. L.

    Receiver function analysis is used to determine local crustal structure beneath Taiwan. We have performed preliminary data processing and polarization analysis for the selection of stations and events and to increase overall data quality. Receiver function analysis is then applied to data from the Taiwan Seismic Network to obtain radial and transverse receiver functions. Due to the limited azimuthal coverage, only the radial receiver functions are analyzed in terms of horizontally layered crustal structure for each station. In order to improve convergence of the receiver function inversion, frequency-band inversion (FBI) is implemented, in which an iterative inversion procedure with sequentially higher low-pass corner frequencies is used to stabilize the waveform inversion. Frequency-band inversion is applied to receiver functions at six stations of the Taiwan Seismic Network. Initial 20-layer crustal models are inverted for using prior tomographic results for the initial models. The resulting 20-1ayer models are then simplified to 4 to 5 layer models and input into an alternating depth and velocity frequency-band inversion. For the six stations investigated, the resulting simplified models provide an average estimate of 38 km for the Moho thickness surrounding the Central Range of Taiwan. Also, the individual station estimates compare well with the recent tomographic model of and the refraction results of Rau and Wu (1995) and the refraction results of Ma and Song (1997).

  20. Crystal structure, conformation, vibration and optical band gap analysis of bis[ rac-propranolol nitrate

    NASA Astrophysics Data System (ADS)

    Franklin, S.; Balasubramanian, T.; Nehru, K.; Kim, Youngmee

    2009-06-01

    The crystal structure of the title rac-propranolol salt, CHNO2+·NO3-, consists of two protonated propranolol residues and nitrate anions. Three virtually flat fragments, characteristics of most of the ?-adrenolytics with oxy-methylene bridge are present in both the cations (A and B). The plane of the propranolol chain is twisted with respect to the plane of the aromatic ring in both the cations. Present study investigates the conformation and hydrogen bonding interactions, which play an important role in biological functions. A gauche conformation is observed for the oxo-methylene bridge of cation A, while a trans conformation prevails in cation B. These conformations are found in majority of ?-blockers. Presence of twenty intermolecular hydrogen bonds mediating through the anions stabilizes the crystal packing. Vibration analysis and earlier theoretical predictions complement the structure analysed. From the UV-Vis spectral analysis for the crystal, the optical band gap is found to be Eg = 5.12 eV, where as the chloride salt has Eg = 3.81 eV. The increase in the band gap may be attributed by the increase in the number of intermolecular hydrogen bonds. Good optical transmittance in the entire visible region and the direct band gap property suggest that it is a suitable candidate for optical applications in UV region.

  1. Optical properties of planar photonic band gap structures measured with femtosecond pulses

    Microsoft Academic Search

    J. Boyd; Peng Liang; K. Huang; J. Bertone; V. Colvin; D. Mittleman

    1999-01-01

    We propose a method for measuring the dielectric function of a periodic structure consisting of an ordered crystalline array of highly monodisperse silica spheres. We fabricate the photonic structure directly on the reflecting surface of a conventional mirror. We then use this mirror as one end of a Michelson interferometer, constructed for the purpose of performing interferometric autocorrelations of femtosecond

  2. Effects of the Antenna Aperture on Remote Sensing of Sea Surface Salinity at L-Band

    NASA Technical Reports Server (NTRS)

    Dinnat, Emmanuel P.; LeVine, David M.

    2006-01-01

    Remote sensing of sea surface salinity with sufficient accuracy to meet the needs of global oceanography is a challenging task. The global variability of the salinity signal in the open ocean is only a few Kelvin even at L-band and an accuracy on the order of 0.1K is desired to study the influence of salinity on ocean circulation and energy exchange with the atmosphere. On the other hand, resolution is not an issue for understanding the dynamics of the open ocean where scales of hundreds of km are not uncommon. This permits remote sensing with large antenna footprints and spatial averaging to reduce noise. However, antennas with large footprints introduce other problems. For example, the angle of incidence and hence the brightness temperature varies over the footprint. Similarly, the polarization of brightness temperature relative to the antenna ports changes. Studies have been conducted using antenna patterns representative of the antenna that will be flown on the Aquarius mission to examine these effects. Aquarius is a pushbroom style radiometer with three beams looking across track away from the sun. The beams are at incidences angles (at the spacecraft) of about 26.5, 34 and 40 degrees each with a half-power beam width of about 5.8 degrees. It is shown that the measured brightness temperature is biased relative to the value at boresight because of changes across the field of view. The bias can be as much as 4K and positive or negative depending on polarization. Polarization mixing because of the variations of the local plane of incidence across the footprint also occur and can result in biased polarimetric measurements. A bias in the third Stokes parameter of as much as 0.4K is possible. Such effects may affect algorithms that use the third Stokes parameter to correct for Faraday rotation. Another issue associated with the antenna is sun glint. This is an issue determined by surface roughness and antenna sidelobes. Examples will be given for the random component (glint) for the case of the Aquarius antenna beams. Fortunately, the Aquarius beams mostly look to the dark side of the day-night termination, but during some portions of the year they will see sun-lighted ocean. In this case, glint could be an issue for the inner-most beam.

  3. Impact of size-dependent non-local elastic strain on the electronic band structure of embedded quantum dots

    E-print Network

    Sharma, Pradeep

    -grained multiband envelope function method to compute the band structure of both strained and unstrained quantum and a subsequent link to the aforementioned eight-band envelope function model. The mechanical strain predicted of other optoe- lectronic properties in quantum dots or wires/wells. For example (while somewhat crude

  4. PHYSICAL REVIEW B 84, 205205 (2011) Quasiparticle band structures of -HgS, HgSe, and HgTe

    E-print Network

    Svane, Axel Torstein

    2011-01-01

    PHYSICAL REVIEW B 84, 205205 (2011) Quasiparticle band structures of -HgS, HgSe, and HgTe A. Svane functions and are thus quite different from those obtained from QSGW. Within QSGW, HgS is found to be significant differences, in particular for HgSe and HgS, between the ordering of the band-edge states

  5. Design of a lunar surface structure

    NASA Astrophysics Data System (ADS)

    Mottaghi, Sohrob

    The next step for manned exploration and settlement is a return to the Moon. In such a return, the most challenging task is the construction of structures for habitation, considering the Moon's hostile environment. Therefore the question is: What is the best way to erect habitable structures on the lunar surface? Given the cost associated with bringing material to the Moon, In-Situ Resource Utilization (ISRU) is viewed by most as the basis for a successful manned exploration and settlement of the Solar system. Along these lines, we propose an advanced concept where the use of freeform fabrication technologies by autonomous mini-robots can form the basis for habitable lunar structures. Also, locally-available magnesium is proposed as the structural material. While it is one of the most pervasive metals in the regolith, magnesium has been only suggested only briefly as a viable option in the past. Therefore, a study has been conducted on magnesium and its alloys, taking into account the availability of the alloying elements on the Moon. An igloo-shaped magnesium structure, covered by sandbags of regolith shielding and supported on a sintered regolith foundation, is considered as a potential design of a lunar base, as well as the test bed for the proposed vision. Three studies are carried out: First a static analysis is conducted which proves the feasibility of the proposed material and method. Second, a thermal analysis is carried out to study the effect of the regolith shielding as well as the sensitivity of such designs to measurement uncertainties of regolith and sintered thermal properties. The lunar thermal environment is modeled for a potential site at 88º latitude in the lunar South Pole Region. Our analysis shows that the uncertainties are in an acceptable range where a three-meter thick shield is considered. Also, the required capacity of a thermal rejection system is estimated, choosing the thermal loads to be those of the Space Station modules. In the third study, a seismic model based on best available data has been developed and applied to our typical structure to assess the vulnerability of designs that ignore seismicity. Using random vibration and modal superposition methods, the structural response to a lunar seismic event of 7 Richter magnitude indicates that the seismic risk is very low. However, it must be considered for certain types of structural designs.

  6. Strain-tunable band parameters of ZnO monolayer in graphene-like honeycomb structure

    NASA Astrophysics Data System (ADS)

    Behera, Harihar; Mukhopadhyay, Gautam

    2012-10-01

    We present ab initio calculations which show that the direct-band-gap, effective masses and Fermi velocities of charge carriers in ZnO monolayer (ML-ZnO) in graphene-like honeycomb structure are all tunable by application of in-plane homogeneous biaxial strain. Within our simulated strain limit of ±10%, the band gap remains direct and shows a strong non-linear variation with strain. Moreover, the average Fermi velocity of electrons in unstrained ML-ZnO is of the same order of magnitude as that in graphene. The results promise potential applications of ML-ZnO in mechatronics/straintronics and other nano-devices such as the nano-electromechanical systems (NEMS) and nano-optomechanical systems (NOMS).

  7. Towards direct-gap silicon phases by the inverse band structure design approach.

    PubMed

    Xiang, H J; Huang, Bing; Kan, Erjun; Wei, Su-Huai; Gong, X G

    2013-03-15

    Diamond silicon (Si) is the leading material in the current solar cell market. However, diamond Si is an indirect band gap semiconductor with a large energy difference (2.3 eV) between the direct gap and the indirect gap, which makes it an inefficient absorber of light. In this work, we develop a novel inverse band structure design approach based on the particle swarming optimization algorithm to predict the metastable Si phases with better optical properties than diamond Si. Using our new method, we predict a cubic Si(20) phase with quasidirect gaps of 1.55 eV, which is a promising candidate for making thin-film solar cells. PMID:25166584

  8. Energy band structure and Frenkel excitons in PbGa2S4

    NASA Astrophysics Data System (ADS)

    Stamov, I. G.; Syrbu, N. N.; Ursaki, V. V.; Parvan, V. I.; Zalamai, V. V.

    2012-11-01

    Optical reflection spectra are measured and calculated in PbGa2S4 crystals in the region of resonances related to excitons with large oscillator strength and binding energy (Frenkel excitons). The splitting of the upper valence band in the center of the Brillouin zone due to crystal field (?cf) and spin orbit (?so) interaction are determined. Optical reflection spectra are measured and calculated according to Kramers-Kronig relations in the region of 3-6 eV in ??? and ??? polarizations, and the optical constants n, k, ?1 and ?2 are determined. The observed electronic transitions in PbGa2S4 crystals are discussed in the frame of theoretical energy band structure calculation for thiogallate crystals.

  9. Periodic dielectric structure for production of photonic band gap and method for fabricating the same

    DOEpatents

    Ozbay, E.; Tuttle, G.; Michel, E.; Ho, K.M.; Biswas, R.; Chan, C.T.; Soukoulis, C.

    1995-04-11

    A method is disclosed for fabricating a periodic dielectric structure which exhibits a photonic band gap. Alignment holes are formed in a wafer of dielectric material having a given crystal orientation. A planar layer of elongate rods is then formed in a section of the wafer. The formation of the rods includes the step of selectively removing the dielectric material of the wafer between the rods. The formation of alignment holes and layers of elongate rods and wafers is then repeated to form a plurality of patterned wafers. A stack of patterned wafers is then formed by rotating each successive wafer with respect to the next-previous wafer, and then placing the successive wafer on the stack. This stacking results in a stack of patterned wafers having a four-layer periodicity exhibiting a photonic band gap. 42 figures.

  10. Periodic dielectric structure for production of photonic band gap and method for fabricating the same

    DOEpatents

    Ozbay, Ekmel (Ames, IA); Tuttle, Gary (Ames, IA); Michel, Erick (Ames, IA); Ho, Kai-Ming (Ames, IA); Biswas, Rana (Ames, IA); Chan, Che-Ting (Ames, IA); Soukoulis, Costas (Ames, IA)

    1995-01-01

    A method for fabricating a periodic dielectric structure which exhibits a photonic band gap. Alignment holes are formed in a wafer of dielectric material having a given crystal orientation. A planar layer of elongate rods is then formed in a section of the wafer. The formation of the rods includes the step of selectively removing the dielectric material of the wafer between the rods. The formation of alignment holes and layers of elongate rods and wafers is then repeated to form a plurality of patterned wafers. A stack of patterned wafers is then formed by rotating each successive wafer with respect to the next-previous wafer, and then placing the successive wafer on the stack. This stacking results in a stack of patterned wafers having a four-layer periodicity exhibiting a photonic band gap.

  11. Enhanced modeling of band nonparabolicity with application to a mid-IR quantum cascade laser structure

    NASA Astrophysics Data System (ADS)

    Vukovic, N.; Radovanovic, J.; Milanovic, V.

    2014-09-01

    We analyze the influence of conduction-band nonparabolicity on bound electronic states in the active region of a quantum cascade laser (QCL). Our model assumes expansion of the conduction-band dispersion relation up to a fourth order in wavevector and use of a suitable second boundary condition at the interface of two III-V semiconductor layers. Numerical results, obtained by the transfer matrix method, are presented for two mid-infrared GaAs/Al0.33Ga0.67As QCL active regions, and they are in very good agreement with experimental data found in the literature. Comparison with a different nonparabolicity model is presented for the example of a GaAs/Al0.38Ga0.62As-based mid-IR QCL. Calculations have also been carried out for one THz QCL structure to illustrate the possible application of the model in the terahertz part of the spectrum.

  12. Surface deformation associated with the March 1996 earthquake swarm at Akutan Island, Alaska, revealed by C-band ERS and L-band JERS radar interferometry

    USGS Publications Warehouse

    Lu, Zhiming; Wicks, C., Jr.; Kwoun, O.; Power, J.A.; Dzurisin, D.

    2005-01-01

    In March 1996, an intense earthquake swarm beneath Akutan Island, Alaska, was accompanied by extensive ground cracking but no eruption of Akutan volcano. Radar interferograms produced from L-band JERS-1 and C-band ERS-1/2 images show uplift associated with the swarm by as much as 60 cm on the western part of the island. The JERS-1 interferogram has greater coherence, especially in areas with loose surface material or thick vegetation. It also shows subsidence of similar magnitude on the eastern part of the island and displacements along faults reactivated during the swarm. The axis of uplift and subsidence strikes about N70??W, which is roughly parallel to a zone of fresh cracks on the northwest flank of the volcano, to normal faults that cut the island and to the inferred maximum compressive stress direction. A common feature of models that fit the deformation is the emplacement of a shallow dike along this trend beneath the northwest flank of the volcano. Both before and after the swarm, the northwest flank was uplifted 5-20 mm/year relative to the southwest flank, probably by magma intrusion. The zone of fresh cracks subsided about 20 mm during 1996-1997 and at lesser rates thereafter, possibly because of cooling and degassing of the intrusion. ?? 2005 CASI.

  13. Cohesive band structure of carbon nanotubes for applications in quantum transport.

    PubMed

    Arora, Vijay K; Bhattacharyya, Arkaprava

    2013-11-21

    An integrated cohesive band structure of carbon nanotubes (CNTs) applicable to all chirality directions (n, m), starting from the Dirac cone of a graphene nanolayer in k-space, is demarcated, in direct contrast to dissimilar chiral and achiral versions in the published literature. The electron wave state of a CNT is quantized into one-dimensional (1-D) nanostructure with a wrapping mode, satisfying the boundary conditions from one Dirac K-point to an equivalent neighboring one with an identical phase and returning to the same K point. The repetitive rotation for an identical configuration with added band index (n-m)mod3, yields one metallic (M) with zero bandgap corresponding to (n-m)mod3 = 0, semiconducting state SC1 with (n-m)mod3 = 1 and SC2 with (n-m)mod3 = 2. The band gap and effective mass of SC2 state are twice as large as those of SC1 state. A broad-spectrum expression signifying the linear dependence of the effective mass on the bandgap is obtained. Both the Fermi energy and the intrinsic velocity limiting the current to the saturation level is calculated as a function of the carrier concentration. Limitations of the parabolic approximation are pointed out. Several new features of the band structure are acquired in a seamlessly unified mode for all CNTs, making it suitable for all-encompassing applications. Applications of the theory to high-field transport are advocated with an example of a metallic CNT, in agreement with experimental observations. The mechanism behind the breakdown of the linear current-voltage relation of Ohm's law and the associated surge in resistance are explained on the basis of the nonequilibrium Arora's distribution function (NEADF). These results are important for the performance evaluation and characterization of a variety of applications on CNT in modern nanoscale circuits and devices. PMID:24061093

  14. Atomic-scale structure and band-gap bowing in Cu(In,Ga)Se2

    NASA Astrophysics Data System (ADS)

    Schnohr, C. S.; Kämmer, H.; Stephan, C.; Schorr, S.; Steinbach, T.; Rensberg, J.

    2012-06-01

    Mixed systems such as the Cu(In,Ga)Se2 chalcopyrite semiconductor consist of different local atomic arrangements, that is, of different combinations of first-nearest-neighbor cations surrounding the Se anions. The anion position of Cu-III-VI2 compounds is predicted to strongly influence the material band gap. We therefore used extended x-ray absorption fine structure spectroscopy to study the atomic-scale structure of Cu(In,Ga)Se2 as a function of composition. Based on these results, the anion position was modeled for all first-nearest-neighbor configurations using a valence force-field approach. We show that the atomic-scale structure strongly depends on the kind of first-nearest-neighbor atoms. Structural relaxation of the anion occurs with respect to both (i) Cu and group III atoms and (ii) In and Ga atoms. In both cases, the average anion displacement exhibits a nonlinear behavior with changing composition and thus results in two separate but significant contributions to the band gap bowing observed in Cu(In,Ga)Se2.

  15. Angle-resolved photoemission study of the Li-induced structures of the Si(001) surface

    NASA Astrophysics Data System (ADS)

    Shin, K. S.; Kim, C. Y.; Chung, J. W.

    1995-01-01

    We have investigated dispersion relations of surface bands induced by Li adsorption on the Si(001) surface at room temperature by Angle-Resolved PhotoE-mission Spectroscopy (ARPES). The characteristic spectral changes in the Energy Distribution Curves (EDCs) with increasing Li coverage implicate that Li adatoms occupy on-top sites of the dimer-forming silicon atoms resulting in 0.5 and 1.0 monolayers for the completion of the first two Li-induced ordered (2×2): Li and (2×1): Li phase, respectively. The unique upward dispersions of the surface bands for these Li-induced structures are ascribed to the size effect of a Li adatom. We further discuss a mechanism which might account for the metallie peak found at the early stage of Li adsorption.

  16. Spectroscopic studies of CdTe ( 111 ) bulk and surface electronic structure

    NASA Astrophysics Data System (ADS)

    Ren, Jie; Fu, Li; Bian, Guang; Wong, Manhong; Wang, Tao; Zha, Gangqiang; Jie, Wanqi; Miller, T.; Hasan, M. Z.; Chiang, T.-C.

    2015-06-01

    Cadmium telluride (CdTe) is a direct band-gap semiconducting material with broad applications in optoelectronic devices. Here we report on a high-resolution angle-resolved photoemission (ARPES) study of CdTe ( 111 ) surfaces prepared by sputtering and annealing that show a (2 ×2 ) reconstruction as observed by electron diffraction. The ARPES maps along high-symmetry directions show prominent features with their intensities modulated by varying the incident photon energy, thus suggesting important matrix element effects associated with photoemission. The results are in excellent agreement with first-principles calculations of the bulk band structure and one-dimensional density of states. A prominent surface state is observed that exhibits a (2 ×2 ) periodicity in agreement with the symmetry of the surface reconstruction.

  17. Terahertz photonic band gap for the transverse-magnetic modes formed by using a planar waveguide structure with a photonic crystal electrode

    NASA Astrophysics Data System (ADS)

    Sakasegawa, Y.; Ihara, T.; Hirakawa, K.

    2010-08-01

    We have investigated the terahertz (THz) emission from a semiconductor superlattice placed in a waveguide structure with a photonic crystal surface electrode of a honeycomb lattice pattern. For uniformly applying bias voltages, we inserted a semitransparent Ti film between the superlattice layer and the photonic crystal electrode. It is found that optimization of the sheet resistivity of the Ti layer is crucial to suppress the coupling between the waveguide mode and the surface leaky mode and obtain a clear photonic band gap. When the Ti layer was 40 nm, a large extinction ratio of ˜120 in the THz emission intensity was obtained at the midgap frequency around 1.7 THz.

  18. Low Wind Speed Radar Backscatter Measurements at C- and Ku-Band Obtained During the Surface Wave Dynamics Experiment

    NASA Technical Reports Server (NTRS)

    Carson, S. C.; Carswell, J. C.; McIntosh, R. E.; Li, F. K.; Nghiem, S. V.; Lou, S. H.; Neumann, G.; McLaughlin, D. J.

    1993-01-01

    Radar backscatter measurements collected at both C- and Ku-Band during the recent SurfaceWaves Dynamics Experiment (SWADE) on 1 March 1991 show dramatic variabilities of thenormalized radar cross section (sigma degree) of the ocean surface at low wind speed. Additionally,measurements of the sigma degree in the cross wind direction fluctuated much more than the sigmadegree in the upwind direction. The C- and Ku-band data are quite similar, both exhibiting a morepronounced roll off of sigma degree with decreasing neutral stability wind than indicated bypreviously published empirical model functions. The data show extremely large azimuthalmodulations, in some cases greater than 20 dB, and show good qualitative agreement with theazimuthal modulation predicted.

  19. Kinetics of band bending and electron affinity at GaAs(001) surface with nonequilibrium cesium overlayers

    SciTech Connect

    Zhuravlev, A. G.; Savchenko, M. L.; Paulish, A. G.; Alperovich, V. L. [Rzhanov Institute of Semiconductor Physics, Lavrentieva, 13, 630090 Novosibirsk, Russia and Novosibirsk State University, Pirogova, 2, 630090 Novosibirsk (Russian Federation); Scheibler, H. E.; Jaroshevich, A. S. [Rzhanov Institute of Semiconductor Physics, Lavrentieva, 13, 630090 Novosibirsk (Russian Federation)

    2013-12-04

    The dosage dependences of surface band bending and effective electron affinity under cesium deposition on the Ga-rich GaAs(001) surface, along with the relaxation of these electronic properties after switching off the Cs source are experimentally studied by means of modified photoreflectance spectroscopy and photoemission quantum yield spectroscopy. At small Cs coverages, below half of a monolayer, additional features in the dosage dependence and subsequent downward relaxation of the photoemission current are determined by the variations of band bending. At coverages above half of a monolayer the upward relaxation of the photocurrent is caused supposedly by the decrease of the electron affinity due to restructuring in the nonequilibrium cesium overlayer.

  20. Sea surface mean square slope from Ku-band backscatter data

    NASA Technical Reports Server (NTRS)

    Jackson, F. C.; Walton, W. T.; Hines, D. E.; Walter, B. A.; Peng, C. Y.

    1992-01-01

    A surface mean-square-slope parameter analysis is conducted for 14-GHz airborne radar altimeter near-nadir, quasi-specular backscatter data, which in raw form obtained by least-squares fitting of an optical scattering model to the return waveform show an approximately linear dependence over the 7-15 m/sec wind speed range. Slope data are used to draw inferences on the structure of the high-wavenumber portion of the spectrum. A directionally-integrated model height spectrum that encompasses wind speed-dependent k exp -5/2 and classical Phillips k exp -3 power laws subranges in the range of gravity waves is supported by the data.

  1. van der Waals epitaxy of monolayer hexagonal boron nitride on copper foil: growth, crystallography and electronic band structure

    NASA Astrophysics Data System (ADS)

    Wood, Grace E.; Marsden, Alexander J.; Mudd, James J.; Walker, Marc; Asensio, Maria; Avila, Jose; Chen, Kai; Bell, Gavin R.; Wilson, Neil R.

    2015-06-01

    We investigate the growth of hexagonal boron nitride (h-BN) on copper foil by low pressure chemical vapour deposition (LP-CVD). At low pressure, h-BN growth proceeds through the nucleation and growth of triangular islands. Comparison between the orientation of the islands and the local crystallographic orientation of the polycrystalline copper foil reveals an epitaxial relation between the copper and h-BN, even on Cu(100) and Cu(110) regions whose symmetry is not matched to the h-BN. However, the growth rate is faster and the islands more uniformly oriented on Cu(111) grains. Angle resolved photoemission spectroscopy measurements reveal a well-defined band structure for the h-BN, consistent with a band gap of 6 eV, that is decoupled from the copper surface beneath. These results indicate that, despite a weak interaction between h-BN and copper, van der Waals epitaxy defines the long range ordering of h-BN even on polycrystalline copper foils and suggest that large area, single crystal, monolayer h-BN could be readily and cheaply produced.

  2. Effects of strain, d-band filling, and oxidation state on the bulk electronic structure of cubic 3d perovskites.

    PubMed

    Akhade, Sneha A; Kitchin, John R

    2011-09-14

    The properties of the d-band structure of the transition metal atom in cubic LaBO(3) and SrBO(3) perovskites (where B = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) and their dependence on strain, d-band filling, and oxidation state were investigated using density functional theory calculations and atom-projected density of states. The strain dependence of the d-band width is shown to depend systematically on the size of the B atom. We show that the transition metal d-band width and center are linearly correlated with each other in agreement with a rectangular band model. A simple matrix element formalism based on the solid state table can readily predict the strain dependence of the d-band width. PMID:21932913

  3. The effect of the ionosphere on remote sensing of sea surface salinity from space: absorption and emission at L band

    Microsoft Academic Search

    David M. Le Vine; Saji Abraham

    2002-01-01

    The purpose of this work is to examine the effects of Faraday rotation and attenuation\\/emission in the ionosphere in the context of a future remote sensing system in space to measure salinity. Sea surface salinity is important for understanding ocean circulation and for modeling energy exchange with the atmosphere. A passive microwave sensor in space operating near 1.4 GHz (L-band)

  4. Ocean surface salinity remote sensing with the JPL Passive\\/Active L-\\/S-band (PALS) microwave instrument

    Microsoft Academic Search

    William J. Wilson; Simon H. Yueh; Fuk K. Li; Steve Dinardo; Yi Chao; Chet Koblinsky; Gary Lagerloef; Stephan Howden

    2001-01-01

    Describes the measurements acquired by the aircraft Passive\\/Active L-\\/S-band (PALS) instrument from two field campaigns in 1999 and 2000. These measurements were in support of the development of ocean surface salinity remote sensing techniques for the future Aquarius space mission. The 2000 measurements demonstrated the aircraft radiometer stability of ±0.3 K over time periods of 30 minutes with a salinity

  5. Ground Wave Propagation Along an Inhomogeneous Rough Surface in the HF Band: Millington Effect for a Flat Earth

    Microsoft Academic Search

    Christophe Bourlier; Gildas Kubicke

    2011-01-01

    In this paper, for a vertically polarized line source in the high-frequency band (3-30 MHz), a detailed analysis of the ground wave propagation over 1-D highly conducting inhomoge- neous (presence of island) smooth and rough surfaces is addressed from two methods: 1) the analytical solution of Bremmer (see also Wait), which assumes that the receiver, emitter, and island heights are

  6. Structural evaluation of Marman V-band coupling and flange with conoseal gasket

    NASA Technical Reports Server (NTRS)

    Oates, J. H.

    1972-01-01

    Results are described of a development test program directed at evaluating the structural capabilities of the Marman V-band coupling and flange with conoseal gasket. The intended end use was for the 75K NERVA flight engine propellant lines. Of major importance in the structural evaluation was the ability to predict stresses throughout the assembly for a variety of loading conditions. Computer finite element analysis was used to predict these stresses but, for the subject configuration, large uncertainties were introduced in modeling the complex geometry and boundary conditions. The purpose of the structural tests was to obtain actual stresses and deflections for correlation with, and updating of the finite element model. Results of the incomplete test program are inconclusive with respect to determining suitability for use on the NERVA engine.

  7. Theoretical Investigation of Positive Parity Band Structure of Y and nb Isotopes

    NASA Astrophysics Data System (ADS)

    Sharma, Chetan; Verma, Preeti; Singh, Suram; Bharti, Arun; Khosa, S. K.

    2012-10-01

    The positive parity band structure of odd mass neutron-rich 97-103Y and 99-105Nb nuclei has been studied using microscopic technique known as the projected shell model (PSM) with the deformed single-particle states generated by the standard Nilsson potential. The nuclear structure properties like yrast spectra, energy splitting, moment of inertia, rotational frequencies and reduced transition probabilities B(M1) and B(E2) have been calculated and their comparison with the available experimental data has been made. A shape evolution has also been predicted in these isotopes as one moves from 97Y to 99Y and 99Nb to 101Nb. The PSM calculations also demonstrate the multi-quasiparticle structure in these nuclei.

  8. Bulk and surface electronic structure of Li{sub 2}O

    SciTech Connect

    Liu, L.; Henrich, V.E. [Department of Applied Physics, Yale University, New Haven, Connecticut 06520 (United States)] [Department of Applied Physics, Yale University, New Haven, Connecticut 06520 (United States); Ellis, W.P. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)] [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Shindo, I. [ASGAL Company Ltd., Yokota 523-2, Sambu-machi, Chiba, 289-12 (Japan)] [ASGAL Company Ltd., Yokota 523-2, Sambu-machi, Chiba, 289-12 (Japan)

    1996-07-01

    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 Li{sub 2}O. The predominately O 2{ital p} valence band exhibits two main features in the photoemission spectrum, whose relative widths are consistent with results of an {ital ab} {ital 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 Li{sub 2}O; 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. {copyright} {ital 1996 The American Physical Society.}

  9. The band-gap structures and recovery rules of generalized n-component Fibonacci piezoelectric superlattices

    NASA Astrophysics Data System (ADS)

    Liu, Da; Zhang, Weiyi

    2011-04-01

    In this communication, the band-gap structures of n-CF piezoelectric superlattices have been calculated using the transfer-matrix-method, the self-similarity behavior and recovery rule have been systematically analyzed. Consistent with the rigorous mathematical proof by Hu et al. [A. Hu, Z.X. Wen, S.S. Jiang, W.T. Tong, R.W. Peng, D. Feng, Phys. Rev. B 48 (1993) 829], we find that the n-CF sequences with 2?n?4 are identified as quasiperiodic. The imaginary wave numbers are characterized by the self-similar spectrum, their major peaks can all be properly indexed. In addition, we find that the n=5 sequence belongs to a critical case which lies at the border between quasiperiodic and non-quasiperiodic structures. The frequency range of the self-similarity pattern approaches zero and a unique indexing of imaginary wave numbers becomes impossible. Our study offers the information on the critical 5-CF superlattice which was not available before. The classification of band-gap structures and the scaling laws around fixed points are also given.

  10. Periodic dielectric structure for production of photonic band gap and devices incorporating the same

    DOEpatents

    Ho, Kai-Ming (Ames, IA); Chan, Che-Ting (Ames, IA); Soukoulis, Costas (Ames, IA)

    1994-08-02

    A periodic dielectric structure which is capable of producing a photonic band gap and which is capable of practical construction. The periodic structure is formed of a plurality of layers, each layer being formed of a plurality of rods separated by a given spacing. The material of the rods contrasts with the material between the rods to have a refractive index contrast of at least two. The rods in each layer are arranged with their axes parallel and at a given spacing. Adjacent layers are rotated by 90.degree., such that the axes of the rods in any given layer are perpendicular to the axes in its neighbor. Alternating layers (that is, successive layers of rods having their axes parallel such as the first and third layers) are offset such that the rods of one are about at the midpoint between the rods of the other. A four-layer periocity is thus produced, and successive layers are stacked to form a three-dimensional structure which exhibits a photonic band gap. By virtue of forming the device in layers of elongate members, it is found that the device is susceptible of practical construction.

  11. Wavefunction Properties and Electronic Band Structures of High-Mobility Semiconductor Nanosheet MoS2

    NASA Astrophysics Data System (ADS)

    Baik, Seung Su; Lee, Hee Sung; Im, Seongil; Choi, Hyoung Joon; Ccsaemp Team; Edl Team

    2014-03-01

    Molybdenum disulfide (MoS2) nanosheet is regarded as one of the most promising alternatives to the current semiconductors due to its significant band-gap and electron-mobility enhancement upon exfoliating. To elucidate such thickness-dependent properties, we have studied the electronic band structures of bulk and monolayer MoS2 by using the first-principles density-functional method as implemented in the SIESTA code. Based on the wavefunction analyses at the conduction band minimum (CBM) points, we have investigated possible origins of mobility difference between bulk and monolayer MoS2. We provide formation energies of substitutional impurities at the Mo and S sites, and discuss feasible electron sources which may induce a significant difference in the carrier lifetime. This work was supported by NRF of Korea (Grant Nos. 2009-0079462 and 2011-0018306), Nano-Material Technology Development Program (2012M3a7B4034985), and KISTI supercomputing center (Project No. KSC-2013-C3-008). Center for Computational Studies of Advanced Electronic Material Properties.

  12. Band structure properties of novel BxGa1-xP alloys for silicon integration

    NASA Astrophysics Data System (ADS)

    Hossain, Nadir; Hosea, T. J. C.; Sweeney, Stephen J.; Liebich, Sven; Zimprich, Martin; Volz, Kerstin; Kunert, Bernardette; Stolz, Wolfgang

    2011-09-01

    We have grown and investigated the band-structure properties of novel III-V alloys based upon BxGa1-xP. These layers are utilized as strain-compensating layers for the lattice-matched integration of novel direct bandgap Ga(NAsP) quantum well lasers on silicon. Experimental and theoretical studies reveal the dependence of the direct and indirect band gaps for strained BxGa1-xP layers grown on silicon as a function of Boron composition from which we derive the properties of free-standing BxGa1-xP. For Boron fractions up to 6%, we find that the bowing parameter for the lowest (indirect) band gap is - 6.2 ± 0.2 eV. High crystalline quality and promising optical material properties are demonstrated and applied to monolithically integrated Ga(NAsP)/(BGa)P multi-quantum well heterostructures on (001) silicon substrates. Our results show that novel (BGa)P layers are suitable for strain compensation purposes, which pave the way towards a commercial solution for the monolithic integration of long term stable laser diodes on silicon substrates.

  13. Measuring large-scale structure with quasars in narrow-band filter surveys

    NASA Astrophysics Data System (ADS)

    Abramo, L. Raul; Strauss, Michael A.; Lima, Marcos; Hernández-Monteagudo, Carlos; Lazkoz, Ruth; Moles, Mariano; de Oliveira, Claudia Mendes; Sendra, Irene; Sodré, Laerte; Storchi-Bergmann, Thaisa

    2012-07-01

    We show that a large-area imaging survey using narrow-band filters could detect quasars in sufficiently high number densities, and with more than sufficient accuracy in their photometric redshifts, to turn them into suitable tracers of large-scale structure. If a narrow-band optical survey can detect objects as faint as i= 23, it could reach volumetric number densities as high as 10-4 h3 Mpc-3 (comoving) at z˜ 1.5. Such a catalogue would lead to precision measurements of the power spectrum up to z˜ 3-4. We also show that it is possible to employ quasars to measure baryon acoustic oscillations at high redshifts, where the uncertainties from redshift distortions and non-linearities are much smaller than at z? 1. As a concrete example we study the future impact of the Javalambre Physics of the Accelerating Universe Astrophysical Survey (J-PAS), which is a narrow-band imaging survey in the optical over 1/5 of the unobscured sky with 42 filters of ˜100-Å full width at half-maximum. We show that J-PAS will be able to take advantage of the broad emission lines of quasars to deliver excellent photometric redshifts, ?z? 0.002 (1 +z), for millions of objects.

  14. The Development of Layered Photonic Band Gap Structures Using a Micro-Transfer Molding Technique

    SciTech Connect

    Kevin Jerome Sutherland

    2001-06-27

    Over the last ten years, photonic band gap (PBG) theory and technology have become an important area of research because of the numerous possible applications ranging from high-efficiency laser diodes to optical circuitry. This research concentrates on reducing the length scale in the fabrication of layered photonic band gap structures and developing procedures to improve processing consistency. Various procedures and materials have been used in the fabrication of layered PBG structures. This research focused on an economical micro transfer molding approach to create the final PBG structure. A poly dimethylsiloxane (PDMS) rubber mold was created from a silicon substrate. It was filled with epoxy and built layer-by-layer to create a 3-D epoxy structure. This structure was infiltrated with nanoparticle titania or a titania sol-gel, then fired to remove the polymer mold, leaving a monolithic ceramic inverse of the epoxy structure. The final result was a lattice of titania rolds that resembles a face-centered tetragonal structure. The original intent of this research was to miniaturize this process to a bar size small enough to create a photonic band gap for wavelengths of visible electro-magnetic radiation. The factor limiting progress was the absence of a silicon master mold of small enough dimensions. The Iowa State Microelectronics Research Center fabricated samples with periodicities of 2.5 and 1.0 microns with the existing technology, but a sample was needed on the order of 0.3 microns or less. A 0.4 micron sample was received from Sandia National Laboratory, which was made through an electron beam lithography process, but it contained several defects. The results of the work are primarily from the 2.5 and 1.0 micron samples. Most of the work focused on changing processing variables in order to optimize the infiltration procedure for the best results. Several critical parameters were identified, ranging from the ambient conditions to the specifics of the procedure. It is believed that most critical for fabrication of high quality samples is control of the temperature of the sample during and after infiltration, and the rate and amount of time spent applying epoxy to the PDMS.

  15. Mechanically robust superhydrophobicity on hierarchically structured Si surfaces.

    PubMed

    Xiu, Yonghao; Liu, Yan; Hess, Dennis W; Wong, C P

    2010-04-16

    Improvement of the robustness of superhydrophobic surfaces is critical in order to achieve commercial applications of these surfaces in such diverse areas as self-cleaning, water repellency and corrosion resistance. In this study, the mechanical robustness of superhydrophobic surfaces was evaluated on hierarchically structured silicon surfaces. The effect of two-scale hierarchical structures on robustness was investigated using an abrasion test and the results compared to those of superhydrophobic surfaces fabricated from polymeric materials and from silicon that contains only nanostructures. Unlike the polymeric and nanostructure-only surfaces, the hierarchical structures retained superhydrophobic behavior after mechanical abrasion. PMID:20332558

  16. Optical Band Edge of Layer Structured Germanium (II) Di-iodide

    NASA Astrophysics Data System (ADS)

    Magness, B.; Kuang, W.; Coleman, C. C.

    1998-03-01

    Thin hexagonal crystals of layer structured Germanium II di-iodide up to 1.5 cm^2 in area were grown by vapor reaction followed by vapor transport. Thin films of this water sensitive crystal were prepared in an evaporator located in a neutral atmosphere glove box. New optical absorption data from both thin films and single crystals indicate that Germanium (II) di-iodide has a direct optical band gap at 2.3 eV. The similarities between germanium II di-iodide and lead (II) diiodide indicate that Germanium (II) di-iodide is a good candidate for intercalation.

  17. First principles electronic band structure and phonon dispersion curves for zinc blend beryllium chalcogenide

    SciTech Connect

    Dabhi, Shweta, E-mail: venu.mankad@gmail.com; Mankad, Venu, E-mail: venu.mankad@gmail.com; Jha, Prafulla K., E-mail: venu.mankad@gmail.com [Department of Physics, Maharaja Krishnakumasinhji Bhavnagar University, Bhavnagar-364001 (India)

    2014-04-24

    A detailed theoretical study of structural, electronic and Vibrational properties of BeX compound is presented by performing ab-initio calculations based on density-functional theory using the Espresso package. The calculated value of lattice constant and bulk modulus are compared with the available experimental and other theoretical data and agree reasonably well. BeX (X = S,Se,Te) compounds in the ZB phase are indirect wide band gap semiconductors with an ionic contribution. The phonon dispersion curves are represented which shows that these compounds are dynamically stable in ZB phase.

  18. Band structure and transport studies of copper selenide: An efficient thermoelectric material

    NASA Astrophysics Data System (ADS)

    Tyagi, Kriti; Gahtori, Bhasker; Bathula, Sivaiah; Auluck, S.; Dhar, Ajay

    2014-10-01

    We report the band structure calculations for high temperature cubic phase of copper selenide (Cu2Se) employing Hartree-Fock approximation using density functional theory within the generalized gradient approximation. These calculations were further extended to theoretically estimate the electrical transport coefficients of Cu2Se employing Boltzmann transport theory, which show a reasonable agreement with the corresponding experimentally measured values. The calculated transport coefficients are discussed in terms of the thermoelectric (TE) performance of this material, which suggests that Cu2Se can be a potential p-type TE material with an optimum TE performance at a carrier concentration of ˜ 4 - 6 × 10 21 cm - 3 .

  19. Electronic band structure imaging of three layer twisted graphene on single crystal Cu(111)

    SciTech Connect

    Marquez Velasco, J. [National Center for Scientific Research “Demokritos,” 15310 Athens (Greece) [National Center for Scientific Research “Demokritos,” 15310 Athens (Greece); Department of Physics, National Technical University of Athens, Athens (Greece); Kelaidis, N.; Xenogiannopoulou, E.; Tsoutsou, D.; Tsipas, P.; Speliotis, Th.; Pilatos, G.; Likodimos, V.; Falaras, P.; Dimoulas, A., E-mail: dimoulas@ims.demokritos.gr [National Center for Scientific Research “Demokritos,” 15310 Athens (Greece); Raptis, Y. S. [Department of Physics, National Technical University of Athens, Athens (Greece)] [Department of Physics, National Technical University of Athens, Athens (Greece)

    2013-11-18

    Few layer graphene (FLG) is grown on single crystal Cu(111) by Chemical Vapor Deposition, and the electronic valence band structure is imaged by Angle-Resolved Photo-Emission Spectroscopy. It is found that graphene essentially grows polycrystalline. Three nearly ideal Dirac cones are observed along the Cu ?{sup ¯}K{sup ¯} direction in k-space, attributed to the presence of ?4° twisted three layer graphene with negligible interlayer coupling. The number of layers and the stacking order are compatible with Raman data analysis demonstrating the complementarity of the two techniques for a more accurate characterization of FLG.

  20. Complex band structure under plane-wave nonlocal pseudopotential Hamiltonian of metallic wires and electrodes

    SciTech Connect

    Yang, Chao

    2009-07-17

    We present a practical approach to calculate the complex band structure of an electrode for quantum transport calculations. This method is designed for plane wave based Hamiltonian with nonlocal pseudopotentials and the auxiliary periodic boundary condition transport calculation approach. Currently there is no direct method to calculate all the evanescent states for a given energy for systems with nonlocal pseudopotentials. On the other hand, in the auxiliary periodic boundary condition transport calculation, there is no need for all the evanescent states at a given energy. The current method fills this niche. The method has been used to study copper and gold nanowires and bulk electrodes.

  1. Photo field-emission spectroscopy of optical transitions in the band structure of rhenium

    NASA Astrophysics Data System (ADS)

    Rado?, T.; Kleint, Ch.

    1984-09-01

    Photo field-emission (PFE) current-voltage curves of clean and barium covered rhenium have been determined with an argon ion laser and phase sensitive detection. Field strength and work function were obtained from Fowler-Nordheim plots of the field emission currents. According to a two-step PFE model the knees of the PFE characteristics are ascribed to optical transitions in the Brillouin zone near the Fermi level. Most of the observed excitations could be correlated to direct transitions in the rhenium band structure as calculated by Mattheiss including spin-orbit coupling.

  2. Photonic Band Gaps in 3D Network Structures with Short-range Order

    E-print Network

    Liew, Seng Fatt; Noh, Heeso; Schreck, Carl F; Dufresne, Eric R; O'Hern, Corey S; Cao, Hui

    2011-01-01

    We present a systematic study of photonic band gaps (PBGs) in three-dimensional (3D) photonic amorphous structures (PAS) with short-range order. From calculations of the density of optical states (DOS) for PAS with different topologies, we find that tetrahedrally connected dielectric networks produce the largest isotropic PBGs. Local uniformity and tetrahedral order are essential to the formation of PBGs in PAS, in addition to short-range geometric order. This work demonstrates that it is possible to create broad, isotropic PBGs for vector light fields in 3D PAS without long-range order.

  3. Tuning surface wettability by designing hairy structures

    NASA Astrophysics Data System (ADS)

    Pei, Han-Wen; Liu, Hong; Lu, Zhong-Yuan; Zhu, You-Liang

    2015-02-01

    We present a molecular dynamics simulation study on the controlling factors that influence the wettability of a hairy surface. By adopting the hairs with appropriate grafting density, hair length, and hair rigidity, the hairy surface shows good performance on droplet repellency. When the droplet sits on the hairy surface, the flexible hairs can spontaneously bundle with the appropriate amount of neighboring hairs to enhance the surface hydrophobicity, thus providing a new possibility to control the surface wettability. The hairy surface with tunable grafting density and hair rigidity, bridges the gap between surfaces with soft polymer brushes and surfaces that are completely hard but porous.

  4. Valence-band structure of the ferromagnetic semiconductor GaMnAs investigated by resonant tunneling spectroscopy

    NASA Astrophysics Data System (ADS)

    Ohya, Shinobu

    2011-03-01

    The origin of ferromagnetism in the prototype ferromagnetic semiconductor GaMnAs is still controversial due to the insufficient understanding of its band structure and Fermi level position. Here, we investigate the valence-band (VB) structure of GaMnAs by analyzing the resonant tunneling levels of the GaMnAs quantum well (QW) in double-barrier heterostructures. The resonant levels including the heavy-hole first state (HH1) are clearly observed in the metallic GaMnAs QW with the Curie temperature (TC) of 60 K, which indicates that no holes reside in the VB of GaMnAs in the equilibrium condition. Clear enhancement of tunnel magnetoresistance induced by resonant tunneling is demonstrated. We find that the resonant levels formed in the GaMnAs QW are well explained by using the transfer matrix method with the 6x6 kp Hamiltonian and small p - d exchange Hamiltonian. The VB structure of GaMnAs is well reproduced by that of GaAs with a small exchange splitting energy of 3-5 meV and with the Fermi level lying at ~ 30 meV higher than HH1 in the bandgap. Furthermore, we show our more recent results of resonant tunneling spectroscopy on various surface GaMnAs films (Mn concentration: 6-15%, TC : 71-154 K) grown on an AlAs layer, where the resonant levels are formed by confinement of the VB holes by the surface Schottky barrier and the AlAs barrier. We systematically investigate the thickness dependence of the resonant levels in GaMnAs by precisely etching the surface of GaMnAs. We find that the p-d exchange interaction is negligibly small (3-5 meV) and that the Fermi level exists in the bandgap. This work was performed in collaboration with I. Muneta, P. N. Hai, K. Takata, and M. Tanaka, and partly supported by Grant-in-Aids for Scientific Research, the Special Coordination Programs for Promoting Science and Technology, and FIRST Program by JSPS.

  5. AVHRR Surface Temperature and Narrow-Band Albedo Comparison with Ground Measurements for the Greenland Ice Sheet

    NASA Technical Reports Server (NTRS)

    Haefliger, M.; Steffen, K.; Fowler, C.

    1993-01-01

    An ice-surface temperature retrieval algorithm for the Greenland ice sheet was developed using NOAA 11 thermal radiances from channels 4 and 5. Temperature, pressure and humidity profiles, cloud observations and skin temperatures from the Swiss Federal Institute of Technology (ETH) camp, located at the equilibrium line altitude at 49 deg17 min W, 69 deg 34 min N, were used in the LOWTRAN 7 model. Through a statistical analysis of daily clear sky profiles, the coefficients that correct for the atmospheric effects were determined for the ETH-Camp field season (May to August). Surface temperatures retrieved by this method were then compared against the in situ observations with a maximum difference of 0.6 K. The NOAA 11 narrow-band planetary albedo values for channels 1 and 2 were calculated using pre-launch calibration coefficients. Scattering and absorption by the atmosphere were modelled with LOWTRAN 7. Then, narrow-band albedo values for the AVHRR visible and near infrared channels were compared with in situ high resolution spectral reflectance measurements. In the visible band (580-680 nm), AVHRR-derived narrow-band albedo and the in situ measurements corrected with radiative transfer model LOWTRAN 7 showed a difference of less than 2%. For the near infrared channel (725-1100 nm) the difference between the measured and modelled narrow-band albedo was 14%. These discrepancies could be either the result of inaccurate aerosol scattering modelling (lack of the in situ observation), or the result of sensor drift due to degradation.

  6. Computer simulation of the structure and stability of forsterite surfaces

    Microsoft Academic Search

    G. W. Watson; P. M. Oliver; S. C. Parker

    1997-01-01

    The aim of this paper is to demonstrate that atomistic simulations can be used to evaluate the structure of mineral surfaces and to provide reliable data for forsterite surfaces up to a plane index of 2 using the code METADISE. The methods used to calculate the surface structure and energy which have more commonly been used to study ceramics are

  7. Observation of strong electron pairing on band without Fermi surfaces in LiFe1- xCox As

    NASA Astrophysics Data System (ADS)

    Miao, Hu; Qian, Tian; Shi, Xun; Richard, Pierre; Kim, T.; Hoesch, M.; Xing, Lingyi; Wang, Xiangcheng; Jin, Changqing; Hu, Jinagping; Ding, Hong

    2015-03-01

    In conventional BCS superconductors, the quantum condensation of superconducting electron pairs is understood as a Fermi surface instability, in which the low-energy electrons are paired by attractive interactions. Whether this explanation is still valid in high-Tc superconductors such as cuprates and iron-based superconductors remains an open question. In particular, a fundamentally different picture of the electron pairs, which are believed to be formed locally by repulsive interactions, may prevail. Here we report a high-resolution angle-resolved photoemission spectroscopy study on LiFe1-xCoxAs. We reveal a large and robust superconducting gap on a band sinking below the Fermi energy upon Co substitution. The observed Fermi surface free superconducting order is also the largest over the momentum space, which rules out a proximity effect origin and indicates that the superconducting order parameter is not tied to the Fermi surface as a result of a Fermi surface instability.

  8. Observation of strong electron pairing on bands without Fermi surfaces in LiFe(1-x)CoxAs.

    PubMed

    Miao, H; Qian, T; Shi, X; Richard, P; Kim, T K; Hoesch, M; Xing, L Y; Wang, X-C; Jin, C-Q; Hu, J-P; Ding, H

    2015-01-01

    In conventional BCS superconductors, the quantum condensation of superconducting electron pairs is understood as a Fermi surface instability, in which the low-energy electrons are paired by attractive interactions. Whether this explanation is still valid in high-Tc superconductors such as cuprates and iron-based superconductors remains an open question. In particular, a fundamentally different picture of the electron pairs, which are believed to be formed locally by repulsive interactions, may prevail. Here we report a high-resolution angle-resolved photoemission spectroscopy study on LiFe(1-x)CoxAs. We reveal a large and robust superconducting gap on a band sinking below the Fermi level on Co substitution. The observed Fermi-surface-free superconducting order is also the largest over the momentum space, which rules out a proximity effect origin and indicates that the order parameter is not tied to the Fermi surface as a result of a surface instability. PMID:25583450

  9. Fabrication of a GHz band surface acoustic wave filter by UV-nanoimprint with an HSQ stamp

    NASA Astrophysics Data System (ADS)

    Chen, Nian-Huei; Huang, Ju-Chun; Wang, Chiu-Yen; Huang, Fon-Shan

    2011-04-01

    A GHz band surface acoustic wave (SAW) filter was fabricated by UV-nanoimprint lithography (UV-NIL). The key techniques to produce a SAW filter include stamp and interdigital transducer (IDT) fabrication. For the stamp, high-aspect-ratio (AR) hydrogen silsesquioxane (HSQ)/ITO/glass stamps were first exposed by low e-beam dose. Adequate post-exposure bake, tetramethylammoniumhydroxide concentration, and etch time were utilized to pattern the HSQ stamps with a perfect vertical sidewall. HSQ/ITO/glass IDT stamps with widths in the range 46-168 nm were fabricated. The stamps were then cured with a novel step-like heating cycle as hard-bake. The modified HSQ stamps have a high hardness of 19 GPa. The HSQ/ITO/glass layered structure shows 80% transmittance at 365 nm UV light. Afterward, the IDT patterns were transferred on UV-curable resist/lithium niobate (LiNbO3) by UV-NIL at room temperature and low pressure. After removing the residual layer, Al/Ti films were deposited on UV-curable resist/LiNbO3. IDTs with widths in the range 62-219 nm and thickness of 20 nm could be obtained by following a lift-off process. The center frequency of 4.3-8.6 GHz and insertion loss of -14.1 to -61.7 dB of the SAW filters were measured by a network analyzer HP 8510C. The reactive ion etching step for residual layer elimination has significant implication for the electrical characterization of a SAW filter. The thorough removal of the residual layer not only ensures a clean interface between IDTs and LiNbO3 for SAW filters with minimum insertion loss, but also keeps intact IDT patterns for small center frequency shift.

  10. Electronic structures of the SrTiO{sub 3}(110) surface in different reconstructions

    SciTech Connect

    Cao Yanwei; Wang Shuai; Liu Shuming; Guo Qinlin; Guo Jiandong [Beijing National Laboratory for Condensed-Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China)

    2012-07-28

    The surface of SrTiO{sub 3}(110) single crystal is prepared in monophase with different reconstructions. The increase of surface Ti concentration is responsible for the evolution of the reconstruction from (4 Multiplication-Sign 1) to (2 Multiplication-Sign 8), and to a new (1 Multiplication-Sign 10) structure. It also induces the enhancement of the surface metallicity, characterized by the appearance of the in-gap states and the increasing Drude weight as measured by the electron and photoelectron spectroscopies. We attribute the metallicity to the reduced Ti ions, which is consistent with the observed band structures and the shift of the phonon energy. It is indicated that a heterointerface between a reduced titanate layer and SrTiO{sub 3} crystal with unique electronic structure can be obtained by the simple treatment.

  11. Slip Flow Over Structured Surfaces with Entrapped Microbubbles

    Microsoft Academic Search

    Jari Hyväluoma; Jens Harting

    2008-01-01

    On hydrophobic surfaces, roughness may lead to a transition to a superhydrophobic state, where gas bubbles at the surface can have a strong impact on a detected slip. We present two-phase lattice Boltzmann simulations of a Couette flow over structured surfaces with attached gas bubbles. Even though the bubbles add slippery surfaces to the channel, they can cause negative slip

  12. Core-shell photonic band gap structures fabricated using laser-assisted chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Wang, H.; Lu, Y. F.

    2008-01-01

    Laser-assisted chemical vapor deposition (LCVD), in combination with three-dimensional (3D) self-assembly of colloidal silica particles, was used to fabricate 3D core-shell photonic band gap (PBG) structures. Self-assembled multilayer silica particles were formed on silicon substrates using the isothermal heating evaporation approach. A continuous-wave CO2 laser (10.6 ?m wavelength) was used as the energy source in the LCVD to fabricate a silica-core-silicon-shell PBG structure. This technique is capable of fabricating structures with various PBGs by adjusting the silica particle size and Si-shell thickness using different LCVD parameters. This capability enables us to engineer positions and widths of PBGs by flexibly controlling the particle size and shell thicknesses. In the fabricated PBG structures, face-centered cubic structures consist of silica-core-silicon-shell "effective atoms." A series of PBG structures with designed PBGs was obtained under different experimental conditions. Incidence-angle-resolved spectroscopic ellipsometry was used to identify specific PBGs. The refractive indices of the effective atoms with different Si-shell thicknesses were calculated using the Bruggeman composite model. The plain-wave expansion method was used to simulate the photonic dispersion diagrams, which supported the experimental results.

  13. Composite isogrid structures for parabolic surfaces

    NASA Technical Reports Server (NTRS)

    Silverman, Edward M. (Inventor); Boyd, Jr., William E. (Inventor); Rhodes, Marvin D. (Inventor); Dyer, Jack E. (Inventor)

    2000-01-01

    The invention relates to high stiffness parabolic structures utilizing integral reinforced grids. The parabolic structures implement the use of isogrid structures which incorporate unique and efficient orthotropic patterns for efficient stiffness and structural stability.

  14. Investigation of band structures for 2D non-diagonal anisotropic photonic crystals using a finite element method based eigenvalue algorithm.

    PubMed

    Hsu, Sen-Ming; Chen, Ming-Mung; Chang, Hung-Chun

    2007-04-30

    A finite element method based eigenvalue algorithm is developed for the analysis of band structures of two-dimensional non-diagonal anisotropic photonic crystals under the in-plane wave propagation. The characteristics of band structures for the square and triangular lattices consisting of anisotropic materials are examined in detail and the intrinsic effect of anisotropy on the construction of band structures is investigated. We discover some interesting relationships of band structures for certain directions of the wave vector in the first Brillouin zone and present a theoretical explanation for this phenomenon. The complete band structures can be conveniently constructed by means of this concept. PMID:19532796

  15. Microscopic surface structure of liquid alkali metals H. Tostmann

    E-print Network

    Pershan, Peter S.

    Microscopic surface structure of liquid alkali metals H. Tostmann Division of Applied Sciences study of the microscopic structure of the surface of a liquid alkali metal. The bulk liquid structure of an elemental liquid alkali metal. Analysis of off-specular diffuse scattering and specular x-ray reflectivity

  16. Finite-difference complex-wavevector band structure solver for analysis and design of periodic radiative microphotonic structures.

    PubMed

    Notaros, Jelena; Popovi?, Miloš A

    2015-03-15

    We demonstrate a finite-difference approach to complex-wavevector band structure simulation and its use as a tool for the analysis and design of periodic leaky-wave photonic devices. With the (usually real) operating frequency and unit-cell refractive index distribution as inputs, the eigenvalue problem yields the complex-wavevector eigenvalues and Bloch modes of the simulated structure. In a two-dimensional implementation for transverse-electric fields with radiation accounted for by perfectly matched layer boundaries, we validate the method and demonstrate its use in simulating the complex-wavevector band structures and modal properties of a silicon photonic crystal waveguide, an array-antenna-inspired grating coupler with unidirectional radiation, and a recently demonstrated low-loss Bloch-mode-based waveguide crossing array. Additionally, we show the first direct solution of the recently proposed open-system low-loss Bloch modes. We expect this method to be a valuable tool in photonics design, enabling the rigorous analysis and synthesis of advanced periodic and quasi-periodic photonic devices. PMID:25768180

  17. Strain Engineering of the Band Structure and Picosecond Carrier Dynamics of Single Semiconductor Nanowires Probed by Modulated Rayleigh Scattering Microscopy

    NASA Astrophysics Data System (ADS)

    Montazeri, Mohammad

    The band structure and carrier dynamics of GaAs, GaAs/GaP and InP semiconductor nanowires is explored using a variety of optical spectroscopy techniques including two newly developed techniques called Photomodulated and Transient Rayleigh scattering spectroscopy. The stress and electronic band structure of as-grown highly strained GaAs/GaP core/shell nanowire is studied via room temperature Raman scattering by phonons and low temperature photoluminescence spectroscopy. Raman measurements reveal the uniaxial nature of the shell-induced stress in the core GaAs nanowire with a significantly different degree of compression in the radial plane and axial direction of the nanowire. The uniaxial stress dramatically modifies the electronic band structure of the nanowire. Raman measurements predict that the shell-induced stress should shift the band gap of GaAs to higher energies by ~260 meV which is experimentally confirmed by low temperature photoluminescence spectroscopy. Furthermore, it is predicted that the uniaxial stress in the nanowire removes the degeneracy of the heavy and light hole valence bands at the zone center by ~100 meV. In order to probe the electronic band structure of single nanowires with high spatial and spectral resolution, the new technique of Photomodulated Rayleigh Scattering spectroscopy (PMRS) is introduced. We show that by photomodulating the dielectric function of the nanowire, the background-free and robust differential Rayleigh spectrum measures the band structure of the nanowire with exceptionally high energy resolution. PMRS measurements are performed on zincblende GaAs and zincblende and wurtzite InP nanowires at both room and low temperature. Furthermore, we show that the diameters of the nanowires can be extracted from the PMRS spectra with an uncertainty of only a few nanometers. By extending the PMRS spectroscopy into time domain, we introduce Transient Rayleigh Scattering spectroscopy (TRS) to study the ultrafast carrier dynamics and cooling within the band structure of single nanowires with picosecond time resolution. Due to many body effects, the Rayleigh cross-section is sensitive to the occupation of the electronic band structure by photo injected carriers which allows one to simultaneously measure the density and temperature of the photo injected electron-hole plasma as a function of time after excitation. The time dependent density and temperature of the plasma provide direct insight into the various mechanisms dominating the dynamics and cooling of carriers within the electronic band structure including ambipolar diffusion, recombination processes and emission of optical and acoustic phonons. Specifically, TRS of a single GaAs/AlGaAs core-shell nanowire is presented which quantifies various fundamental properties of nanowire including carrier mobility, recombination rates and the energy-loss rate of plasma due to optical and acoustic phonon emission. Similar measurements on a single InP nanowire with hexagonal wurtzite symmetry reveals the dynamics associated with various energy bands including the coupling of A, B and C valence bands to the lowest conduction band as well as the theoretically predicted second conduction band. The second conduction band is experimentally measured at 236-240 meV higher than the first conduction band. The second conduction band is theoretically calculated at 238 meV above the first conduction band.

  18. Spectral element method for band structures of three-dimensional anisotropic photonic crystals

    NASA Astrophysics Data System (ADS)

    Luo, Ma; Liu, Qing Huo

    2009-11-01

    A spectral element method (SEM) is introduced for accurate calculation of band structures of three-dimensional anisotropic photonic crystals. The method is based on the finite-element framework with curvilinear hexahedral elements. Gauss-Lobatto-Legendre polynomials are used to construct the basis functions. In order to suppress spurious modes, mixed-order vector basis functions are employed and the Bloch periodic boundary condition is imposed into the basis functions with tangential components at the boundary by multiplying a Bloch phase factor. The fields and coordinates in the curvilinear hexahedral elements are mapped to the reference domain by covariant mapping, which preserves the continuity of tangential components of the field. Numerical results show that the SEM has exponential convergence for both square-lattice and triangular-lattice photonic crystals. The sampling density as small as 3.4 points per wavelength can achieve accuracy as high as 99.9%. The band structures of several modified woodpile photonic crystals are calculated by using the SEM.

  19. Silicon carbide embedded in carbon nanofibres: structure and band gap determination.

    PubMed

    Minella, Anja Bonatto; Pohl, Darius; Täschner, Christine; Erni, Rolf; Ummethala, Raghu; Rümmeli, Mark H; Schultz, Ludwig; Rellinghaus, Bernd

    2014-11-28

    Materials drastically alter their electronic properties when being reduced to the nanoscale due to quantum effects. Concerning semiconductors, the band gap is expected to broaden as a result of the quantum confinement. In this study we report on the successful synthesis of wide bandgap SiC nanowires (with great potential for applications) and the local determination of their band gap. Their value was found to be higher with respect to bulk SiC. The nanowires are grown as a heterostructure, i.e. encapsulated in carbon nanofibres via dc hot-filament Plasma-Enhanced Chemical Vapour Deposition on the Si/SiO2 substrate. The structure of the as-produced carbon nanofibres was characterized by means of aberration-corrected high-resolution transmission electron microscopy. Two different pure SiC polytypes, namely the 3C (cubic) and the 6H (hexagonal) as well as distorted structures are observed. The SiC nanowires have diameters in the range of 10-15 nm and lengths of several hundred nanometers. The formation of the SiC is a result of the substrate etching during the growth of the CNFs and a subsequent simultaneous diffusion of not only carbon, but also silicon through the catalyst particle. PMID:25307877

  20. Band-structure predictions for A2BX4 discovery compounds

    NASA Astrophysics Data System (ADS)

    Lany, Stephan; Stevanovic, V.; Zunger, A.

    2012-02-01

    The inverse design of materials requires to predict the existence and the properties of previously unknown materials. We have performed a computational search for thermodynamically stable materials within the family of A2BX4 compounds (A, B = main group and 3d cations; X = O, S, Se, Te) resulting in the theoretical discovery of about 100 previously unreported compounds. The challenge for the prediction of band-structures and optical spectra is to obtain accurate results for a wide range of materials within a single computational scheme, so that unknown materials can be predicted with confidence. Whereas the main group chalcogenides are rather accurately predicted by many-body GW calculations, large deviations from experiment are observed for many 3d oxides. In particular, we find that the 3d orbitals consistently occur at too high energies, independent on whether they are occupied (e.g., Cu2O) or unoccupied (e.g., TiO2). While the exact nature of these issues are under investigation, we pursue here a pragmatic approach, using attractive on-site potentials with a single parameter for each 3d element, which leads to good agreement with experiment for binary and ternary 3d oxides. We use this approach to predict the band-structures of the discovery compounds.

  1. Band structure in autolocalization and bipolaron models of high-temperature superconductivity

    SciTech Connect

    Myasnikova, A.E. [Rostov State Pedagogical University, 344082 Rostov on Don (Russian Federation)] [Rostov State Pedagogical University, 344082 Rostov on Don (Russian Federation)

    1995-10-01

    We develop the polaron theory taking into account the spatial dispersion of lattice polarizability caused by several phonon branches. This allows us to describe new effects which cannot be obtained in the classical polaron theory because of the limitations of its model medium that has only one dispersionless phonon branch interacting with the carrier. It is demonstrated that if the spatial dispersion is allowed, the carrier spectrum in a medium with many-component polarization proves to have an autolocalization band structure. It occurs due to limitation on the polaron velocity in accordance with Landau`s theory of the quantum liquid. This results in several effects. One of them is ``Cherenkov`` radiation by a sufficiently rapid polaron of the coherent medium vibrations. Owing to this radiation there exists a possibility that two polarons can couple under resonance conditions with the medium vibrations. It leads to the formation of a two-center bipolaron coupled due to the exchange of real phonons. The influence of the autolocalization band structure on the properties of a system with high carrier concentration is also studied. This is of interest as far as the properties of high-temperature superconductors are concerned. Like any complex oxides they are characterized by many-component polarization. The obtained limitation on the velocity of any autolocalized state causes both the existence of maximum polaron concentration (of the order of 10{sup 20} cm{sup {minus}1}) and modification of the Bose-condensation condition for bipolarons.

  2. Fratricide-preventing friend identification tag based on photonic band structure coding

    NASA Astrophysics Data System (ADS)

    Eliyahu, Danny; Sadovnik, Lev S.; Manasson, Vladimir A.

    2000-07-01

    A new friend foe identification tag based on photonic band structure (PBS) is presented. The tag utilizes frequency-coded radar signal return. Targets that include the passive tag responds selectively to slightly different frequencies generated by interrogating MMW radar. It is possible to use in- and out-of-band gap frequencies or defect modes of the PBS in order to obtain frequency dependent radar waves reflections. This tag can be made in the form of patch attachable such as plate or corner reflectors, to be worn by an individual marine, or to be integrated into the platform camouflage. Ultimately, it can be incorporated as smart skin or a ground or airborne vehicle. The proposed tag takes full advantage of existing sensors for interrogation (minimal chances required), it is lightweight and small in dimensions, it operates in degraded environments, it has no impact on platform vulnerability, it has low susceptibility to spoofing and mimicking (code of the day) and it has low susceptibility to active jamming. We demonstrated the operation of the tag using multi-layer dielectric (Duroid) having periodic structure of metal on top of each of the layers (metal strips in this case). The experimental results are consistent with numerical simulation. The device can be combined with temporal coding to increase target detection and identification resolution.

  3. Numerical demonstration of compound structure broad pass-band optical metamaterial filter

    NASA Astrophysics Data System (ADS)

    Zhong, M.; Ye, Y. H.

    2015-01-01

    We have presented a systematic numerical study about a compound structure to obtain a broad pass-band optical metamaterial filter at terahertz frequency. The designed structure consists of periodic composite metallic arrays and dielectric layer. In order to increase the pass-bandwidth of such metamaterial filter, the sidewall length of square hole is increased. The availability of bandwidth enhancement is verified by our simulation in this paper, which is performed through full-wave method by using the commercial software Ansoft HFSS 13.0. Based on analysis of this rich optical response, we found that the effective impedance matched to free space leads to the pass-bandwidth increased. We hope these results are useful to modulate the electromagnetic wave in optoelectronics, such as sensor and spectroscopy in the future.

  4. The valence band structure of Ag{sub x}Rh{sub 1–x} alloy nanoparticles

    SciTech Connect

    Yang, Anli [Synchrotron X-ray Station at SPring-8, National Institute for Materials Science (NIMS), 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148 (Japan); Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency (JST), 7 Goban-cho, Chiyoda-ku, Tokyo 102-0076 (Japan); Sakata, Osami, E-mail: SAKATA.Osami@nims.go.jp [Synchrotron X-ray Station at SPring-8, National Institute for Materials Science (NIMS), 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148 (Japan); Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency (JST), 7 Goban-cho, Chiyoda-ku, Tokyo 102-0076 (Japan); Synchrotron X-ray Group, Quantum Beam Unit, NIMS, 1-1-1 Kouto, Sayo-cho, Hyogo 679-5148 (Japan); Kusada, Kohei; Kobayashi, Hirokazu [Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency (JST), 7 Goban-cho, Chiyoda-ku, Tokyo 102-0076 (Japan); Division of Chemistry, Graduate School of Science, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto 606-8502 (Japan); Yayama, Tomoe; Ishimoto, Takayoshi [Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency (JST), 7 Goban-cho, Chiyoda-ku, Tokyo 102-0076 (Japan); INAMORI Frontier Research Center, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395 (Japan); Yoshikawa, Hideki [Surface Chemical Analysis Group, Nano Characterization Unit, NIMS, 1-2-1 Sengen, Tsukuba 305-0047 (Japan); Koyama, Michihisa [Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency (JST), 7 Goban-cho, Chiyoda-ku, Tokyo 102-0076 (Japan); INAMORI Frontier Research Center, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395 (Japan); International Institute for Carbon-Neutral Energy Research, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395 (Japan); and others

    2014-10-13

    The valence band (VB) structures of face-centered-cubic Ag-Rh alloy nanoparticles (NPs), which are known to have excellent hydrogen-storage properties, were investigated using bulk-sensitive hard x-ray photoelectron spectroscopy. The observed VB spectra profiles of the Ag-Rh alloy NPs do not resemble simple linear combinations of the VB spectra of Ag and Rh NPs. The observed VB hybridization was qualitatively reproduced via a first-principles calculation. The electronic structure of the Ag{sub 0.5}Rh{sub 0.5} alloy NPs near the Fermi edge was strikingly similar to that of Pd NPs, whose superior hydrogen-storage properties are well known.

  5. Structure of the K{sup {pi}} = 4{sup +} bands in {sup 186,188}Os

    SciTech Connect

    Phillips, A. A.; Garrett, P. E.; Demand, G. A.; Finlay, P.; Green, K. L.; Leach, K. G.; Schumaker, M. A.; Svensson, C. E.; Wong, J. [Dept. of Physics, University of Guelph, Guelph, ON (Canada); Bettermann, L.; Braun, N. [Institut fuer Kernphysik, Universitaet zu Koeln (Germany); Burke, D. G. [Dept. of Physics and Astronomy, McMaster University, Hamilton, ON (Canada); Faestermann, T.; Kruecken, R.; Wirth, H.-F. [Physik Dept., Technische Universitaet Muenchen, Garching (Germany); Hertenberger, R. [Fakultaet fuer Physik, Ludwig-Maximillians-Universitaet Muenchen, Garching (Germany)

    2009-01-28

    The structures of {sub 3}{sup +} states in Os have been debated over several decades. Based on measured B(E2) values they were interpreted in {sup 186-192}Os as K{sup {pi}} = 4{sup +} two-phonon vibrations, whereas inelastic scattering, and (t,{alpha}) work imply a hexadecapole phonon description. To clarify the nature of these K{sup {pi}} = 4{sup +} bands in {sup 186,188}Os, we performed a ({sup 3}He,d) reaction on {sup 185,187}Re targets using 30 MeV {sup 3}He beams and a Q3D spectrograph. Absolute cross sections were obtained for excited states up to 3 MeV at 9 angles from 5 deg. to 50 deg. Results indicate a significant (5/2){sup +}[402]{sub {pi}}+(3/2){sup +}[402]{sub {pi}} component in agreement with quasiparticle phonon model predictions for a single hexadecapole phonon structure.

  6. A combined representation method for use in band structure calculations. 1: Method

    NASA Technical Reports Server (NTRS)

    Friedli, C.; Ashcroft, N. W.

    1975-01-01

    A representation was described whose basis levels combine the important physical aspects of a finite set of plane waves with those of a set of Bloch tight-binding levels. The chosen combination has a particularly simple dependence on the wave vector within the Brillouin Zone, and its use in reducing the standard one-electron band structure problem to the usual secular equation has the advantage that the lattice sums involved in the calculation of the matrix elements are actually independent of the wave vector. For systems with complicated crystal structures, for which the Korringa-Kohn-Rostoker (KKR), Augmented-Plane Wave (APW) and Orthogonalized-Plane Wave (OPW) methods are difficult to apply, the present method leads to results with satisfactory accuracy and convergence.

  7. Numerical demonstration of compound structure broad pass-band optical metamaterial filter

    NASA Astrophysics Data System (ADS)

    Zhong, M.; Ye, Y. H.

    2015-05-01

    We have presented a systematic numerical study about a compound structure to obtain a broad pass-band optical metamaterial filter at terahertz frequency. The designed structure consists of periodic composite metallic arrays and dielectric layer. In order to increase the pass-bandwidth of such metamaterial filter, the sidewall length of square hole is increased. The availability of bandwidth enhancement is verified by our simulation in this paper, which is performed through full-wave method by using the commercial software Ansoft HFSS 13.0. Based on analysis of this rich optical response, we found that the effective impedance matched to free space leads to the pass-bandwidth increased. We hope these results are useful to modulate the electromagnetic wave in optoelectronics, such as sensor and spectroscopy in the future.

  8. Accessing quadratic nonlinearities of metals through metallodielectric photonic-band-gap structures.

    PubMed

    D'Aguanno, Giuseppe; Mattiucci, Nadia; Bloemer, Mark J; Scalora, Michael

    2006-09-01

    We study second harmonic generation in a metallodielectric photonic-band-gap structure made of alternating layers of silver and a generic, dispersive, linear, dielectric material. We find that under ideal conditions the conversion efficiency can be more than two orders of magnitude greater than the maximum conversion efficiency achievable in a single layer of silver. We interpret this enhancement in terms of the simultaneous availability of phase matching conditions over the structure and good field penetration into the metal layers. We also give a realistic example of a nine-period, Si3/N4Ag stack, where the backward conversion efficiency is enhanced by a factor of 50 compared to a single layer of silver. PMID:17025762

  9. New muffin tin orbital band calculations of equilibrium properties and electronic structure of actinide metals

    NASA Astrophysics Data System (ADS)

    Penicaud, M.

    1994-10-01

    We test the fully relativistic muffin tin orbital (MTO) method of band calculations by obtaining at the experimental equilibrium densities of actinide metals (Ra-Cf) the pressure, which should be zero. We also compare with experiment the calculated equilibrium atomic radii and bulk moduli. An face centered cubic (f.c.c.) structure is used, with an atomic volume in some cases equivalent to that of a more complex structure. Our calculations are in agreement with previous studies if we expand the wavefunctions in angular momenta up to l(sub max) = 3 (f-states), but we show that we do not have converged results and that it is necessary to make the expansion up to l(sub max) = 8. The character of f-electrons in the actinide series is well shown by examination of the f-electron partial densities of states (DOSs) relative to the total DOS.

  10. Band selection and disentanglement using maximally localized Wannier functions: the cases of Co impurities in bulk copper and the Cu(111) surface.

    PubMed

    Korytár, Richard; Pruneda, Miguel; Junquera, Javier; Ordejón, Pablo; Lorente, Nicolás

    2010-09-29

    We have adapted the maximally localized Wannier function approach of Souza et al (2002 Phys. Rev. B 65 035109) to the density functional theory based SIESTA code (Soler et al 2002 J. Phys.: Condens. Mater. 14 2745) and applied it to the study of Co substitutional impurities in bulk copper as well as to the Cu(111) surface. In the Co impurity case, we have reduced the problem to the Co d-electrons and the Cu sp-band, permitting us to obtain an Anderson-like Hamiltonian from well defined density functional parameters in a fully orthonormal basis set. In order to test the quality of the Wannier approach to surfaces, we have studied the electronic structure of the Cu(111) surface by again transforming the density functional problem into the Wannier representation. An excellent description of the Shockley surface state is attained, permitting us to be confident in the application of this method to future studies of magnetic adsorbates in the presence of an extended surface state. PMID:21386554

  11. Distribution of Phosphorus and Potassium Following Surface Banding of Fertilizer in Conservation Tillage Systems

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Band application of liquid or granular fertilizers is a common practice in maize (Zea mays L.) production systems in some areas of the USA. Our objective in this field study was to determine the relative soil profile distribution of phosphorus (P) and potassium (K) applied as a liquid fertilizer in ...

  12. Numerical simulation of dry-band arcing on the surface of ADSS fiber optic cable

    Microsoft Academic Search

    Qi Huang; George G. Karady; Baozhuang Shi; Monty Tuominen

    2005-01-01

    Deregulation of telecommunication networks and utility companies has led to a worldwide increase in the use of fiber optic cables on long-span overhead power transmission lines. The cable jacket is subject to the deterioration caused by dry-band arcing, which is believed to be the major cause of failure of cable in service. This paper establishes an arc model based on

  13. SpaceBorne Ku-Band Radar Observations of Extreme Surface Water Conditions

    Microsoft Academic Search

    S. V. Nghiem

    2005-01-01

    Acceleration of the global water cycle may lead to an exacerbation of hydrologic extremes. A multitude of extreme events has occurred in the last decade over the world including droughts, floods, record snow accumulation, and minimal ice cover with severe environmental and socioeconomic impacts. This paper presents an overview of the capabilities of space-borne Ku-band radar to measure extreme conditions

  14. The role of beryllium in the band structure of MgZnO: Lifting the valence band maximum

    NASA Astrophysics Data System (ADS)

    Chen, S. S.; Pan, X. H.; Chen, W.; Zhang, H. H.; Dai, W.; Ding, P.; Huang, J. Y.; Lu, B.; Ye, Z. Z.

    2014-09-01

    We investigate the effect of Be on the valence band maximum (VBM) of MgZnO by measuring the band offsets of MgxZn1-xO/BexMgyZn1-x-yO heterojunctions using X-ray photoelectron spectroscopy measurements. MgxZn1-xO and BexMgyZn1-x-yO films have been grown on c-plane sapphire substrates by plasma-assisted molecular beam epitaxy. The valence band offset ( ? E V) of Mg0.15Zn0.85O ( E g = 3.62 eV)/Be0.005Mg0.19Zn0.805O ( E g = 3.73 eV) heterojunction is 0.01 eV and Be0.005Mg0.19Zn0.805O has a lower VBM. The increased Mg composition is the main factor for the reduction of VBM. The VBM of MgxZn1-xO is lower by 0.03 eV with the enlargement of E g from 3.62 eV to 3.73 eV by increasing Mg composition. Considering the effect of increased Mg composition, it is concluded that the little amount of Be makes the VBM go up by 0.02 eV when the E g of the alloy is 3.73 eV. The ? E V of Mg0.11Zn0.89O ( E g = 3.56 eV)/Be0.007Mg0.12Zn0.873O ( E g = 3.56 eV) heterojunction is calculated to be 0.03 eV and Be0.007Mg0.12Zn0.873O has a higher VBM than Mg0.11Zn0.89O, which means that a little amount Be lifts the VBM by 0.03 eV when the E g of the alloy is 3.56 eV. The experimental measurements have offered a strong support for the theoretical research that alloying Be in MgxZn1-xO alloys is hopeful to form a higher VBM and to enhance the p-type dopability of MgZnO.

  15. Structured Surface Grid Generation on Boundary Represented Geometry

    SciTech Connect

    Chou, J J

    2002-01-18

    Generation of surface meshes is the first step in many grid generation processes. For the generation of block-structured meshes, structured surface meshes have to be generated first. This paper investigates the problem of generating a structured surface mesh across multiple surface patches on an object with the boundary representation and relates the problem to other commonly encountered issues in CAD/CAM. It describes a method for solving the problem. This method is based on initial surface construction, point projection and a mixed model-space and parameter-space based elliptic smoothing.

  16. A distinctive feature of the surface structure of quasicrystals

    SciTech Connect

    Thiel, Patricia; Unal, Baris; Jenks, Cynthia; Goldman, Alan; Lograsso, Thomas; Canfield, Paul; Evans, James; Quiquandon, Marianne; Gratias, Denis; Van Hove, Michel

    2011-12-23

    This paper reviews a feature of atomically-clean quasicrystal surfaces that distinguishes them from surfaces of crystalline materials. That feature is a high degree of heterogeneity among different terraces, and among structurally-identical adsorption sites. The heterogeneity can be both structural and chemical in origin. A large variability is expected even for a surface which is perfectly bulk-terminated, and we call this intrinsic heterogeneity. Additional variability can derive from the surface preparation process, which can yield metastable structures. We call this extrinsic heterogeneity. Experimental evidence is given for both cases. This heterogeneity can be an important factor in understanding and predicting surface phenomena such as chemisorption.

  17. Wetting states on structured immiscible liquid coated surfaces

    NASA Astrophysics Data System (ADS)

    Jenner, Elliot; D'Urso, Brian

    2013-12-01

    Water on structured hydrophobic surfaces can be supported in a Wenzel or Cassie state, depending on surface chemistry and structure geometry. The Cassie state is often desirable for superhydrophobic materials as it features high contact angles and low contact angle hysteresis due to an air layer which separates most of the liquid from contact with the solid. We present evidence that multiple wetting states for water can also exist on multiscale structured surfaces with a layer of an immiscible liquid coating the surface and that a Cassie-like state can be achieved which results in enhancement of the surface properties.

  18. Growth and properties of AIIIBV QD structures for intermediate band solar cells

    NASA Astrophysics Data System (ADS)

    Vysko?il, J.; Gladkov, P.; Pet?í?ek, O.; Hospodková, A.; Pangrác, J.

    2015-03-01

    Intermediate band solar cells theoretically offer a promising way to significantly increase cell efficiency compared to a single-junction solar cell. We focused on the preparation of antimony containing materials as a covering of QD layers. In this article we discuss how the concentration gradient of GaAsSb strain reducing layers can influence the resulting optical properties of the solar cell structures. The main principle of the structure is that the absorption of light is achieved at QD excited states with a better overlap of electron and hole wave functions. With fast relaxation of carriers to the ground state, the electrons and holes are quickly spatially separated. Two different composition gradients of GaAsSb SRL were used for the solar cell structure. One or five quantum dot stacks were compared. The maximal PC increased approximately 17 times with increasing number of QD layers from 1 to 5. The highest PC was achieved for sample I5A with increasing concentration of Sb in the SRL, especially in the QD absorption region. The possible explanation is a better carrier separation in this type of structure suppressing the radiative recombination rate in QDs. These results suggest a high application potential of this structure for photovoltaics.

  19. Electronic structures of HgTe and CdTe surfaces and HgTe/CdTe interfaces

    NASA Technical Reports Server (NTRS)

    Schick, J. T.; Bose, S. M.; Chen, A.-B.

    1989-01-01

    A Green's-function method has been used to study the surface and interface electronic structures of the II-VI compounds HgTe and CdTe. Localized surface and resonance states near the cation-terminated (100) surface of CdTe and the anion-terminated surface of HgTe have been found for the ideal surfaces. The energies and strengths of these surface states are altered by surface perturbations. The bulk states near the surface are drastically modified by the creation of the surface, but the band gaps remain unchanged. Numerical evaluation of the local densities of states at the Gamma and J points shows that, at the (100) interface of HgTe/CdTe, the previously observed surface states are no longer present. However, in the interface region, bulk states of one material penetrate some distance into the other material.

  20. Wide Angle, Single Screen, Gridded Square-Loop Frequency Selective Surface for Diplexing Two Closely Separated Frequency Bands

    NASA Technical Reports Server (NTRS)

    Wu, Te-Kao (Inventor)

    1996-01-01

    The design and performance of a wide angle, single screen, frequency selective surface (FSS) with gridded square-loop path elements are described for diplexing closely separated signal bands, for example, X- and Ku-band signals in an Orbiting Very Long Baseline Interferometer (OVLBI) earth station reflector antenna system, as well as other applications such as military and commercial communications via satellites. Excellent agreement is obtained between the predicted and measured results of this FSS design using the gridded square-loop patch elements sandwiched between 0.0889 cm thick tetrafluoroethylene fluorocarbon polymer (PTFE) slabs. Resonant frequency drift is reduced by 1 GHz with an incidence angle from 0 deg normal to 40 deg from normal.