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Sample records for surface band structure

  1. Investigations of the Band Structure and Morphology of Nanostructured Surfaces

    NASA Astrophysics Data System (ADS)

    Knox, Kevin R.

    2011-12-01

    In this dissertation, I examine the electronic structure of two very different types of two-dimensional systems: valence band electrons in single layer graphene and electronic states created at the vacuum interface of single crystal copper surfaces. The characteristics of both electronic systems depend intimately on the morphology of the surfaces they inhabit. Thus, in addition to discussing the respective band structures of these systems, a significant portion of this dissertation will be devoted to measurements of the surface morphology of these systems. Free-standing exfoliated monolayer graphene is an ultra-thin flexible membrane and, as such, is known to exhibit large out-of-plane deformation due to substrate and adsorbate interaction as well as thermal vibrations and, possibly, intrinsic buckling. Such crystal deformation is known to limit mobility and increase local chemical reactivity. Additionally, deformations present a measurement challenge to researchers wishing to determine the band structure by angle-resolved photoemission since they limit electron coherence in such measurements. In this dissertation, I present low energy electron microscopy and micro probe diffraction measurements, which are used to image and characterize corrugation in SiO2-supported and suspended exfoliated graphene at nanometer length scales. Diffraction line-shape analysis reveals quantitative differences in surface roughness on length scales below 20 nm which depend on film thickness and interaction with the substrate. Corrugation decreases with increasing film thickness, reflecting the increased stiffness of multilayer films. Specifically, single-layer graphene shows a markedly larger short range roughness than multilayer graphene. Due to the absence of interactions with the substrate, suspended graphene displays a smoother morphology and texture than supported graphene. A specific feature of suspended single-layer films is the dependence of corrugation on both adsorbate load and temperature, which is manifested by variations in the diffraction lineshape. The effects of both intrinsic and extrinsic corrugation factors will be discussed. Through a carefully coordinated study I show how these surface morphology measurements can be combined with angle resolved photoemission measurements to understand the role of surface corrugation in the ARPES measurement process. The measurements described here rely on the development of an analytical formulation for relating the crystal corrugation to the photoemission linewidth. I present ARPES measurements that show that, despite significant deviation from planarity of the crystal, the electronic structure of exfoliated suspended graphene is nearly that of ideal, undoped graphene; the Dirac point is measured to be within 25 meV of EF. Further, I show that suspended graphene behaves as a marginal Fermi-liquid, with a quasiparticle lifetime which scales as (E -- EF)--1 ; comparison with other graphene and graphite data is discussed. In contrast to graphene, which must be treated as a flexible membrane with continuous height variation, roughness in clean single crystal surfaces arises from lattice dislocations, which introduce discrete height variations. Such height variations can be exploited to generate a self assembled nano-structured surface. In particular, by making a vicinal cut on a single crystal surface, a nanoscale step array can be formed. A model system for such nanoscale self assembly is Cu(111). Cu(775) is formed by making an 8.5 viscinal cut of Cu(111) along the [112] axis. The electronic states formed on the surface of this system, with a nanoscale step array of 14 A terraces, shows markedly different behavior those formed on Cu(111). In this dissertation, I show that the tunability of a femtosecond optical parametric oscillator, combined with its high-repetition rate and short pulse length, provides a powerful tool for resonant band mapping of the sp surface and image states on flat and vicinal Cu(111)-Cu (775) surfaces, over the photon energy range from 3.9 to 5 eV. Since the tim

  2. Effect of tool eccentricity on surface periodic banded structures in friction stir welding

    NASA Astrophysics Data System (ADS)

    Guo, N.; Wang, M. R.; Meng, Q.; Zhou, L.; Tang, D. Y.

    2015-12-01

    This paper describes the relationship between tool eccentricity and surface formation of periodic banded structures in friction stir welding. Motion characteristics of welding tool are calculated to explore the forming mechanism of banded structures. The results reveal that the welding tool motion differences on advancing side and retreating side caused by eccentricity are crucial for the formation of banded structures. The crests and troughs of banded structures form during tool motion on retreating side and advancing side, respectively.

  3. Energy loss of ions at metal surfaces: Band-structure effects

    SciTech Connect

    Alducin, M.; Silkin, V.M.; Juaristi, J.I.; Chulkov, E.V.

    2003-03-01

    We study band-structure effects on the energy loss of protons scattered off the Cu (111) surface. The distance dependent stopping power for a projectile traveling parallel to the surface is calculated within the linear response theory. The self-consistent electronic response of the system is evaluated within the random-phase approximation. In order to characterize the surface band structure, the electronic single-particle wave functions and energies are obtained by solving the Schroedinger equation with a realistic one-dimensional model potential. This potential reproduces the main features of the Cu (111) surface: the energy band gap for electron motion along the surface normal, as well as the binding energy of the occupied surface state and the first image state. Comparison of our results with those obtained within the jellium model allows us to characterize the band-structure effects in the energy loss of protons interacting with the Cu (111) surface.

  4. Electronic structure of reconstructed InAs(001) surfaces - identification of bulk and surface bands based on their symmetries

    NASA Astrophysics Data System (ADS)

    Olszowska, Natalia; Kolodziej, Jacek J.

    2016-02-01

    Using angle-resolved photoelectron spectroscopy (ARPES) band structures of indium- and arsenic-terminated InAs(001) surfaces are investigated. These surfaces are highly reconstructed, elementary cells of their lattices contain many atoms in different chemical configurations, and moreover, they are composed of domains having related but different reconstructions. These domain-type surface reconstructions result in the reciprocal spaces containing regions with well-defined k→∥-vector and regions with not-well-defined one. In the ARPES spectra most of the surface related features appear as straight lines in the indeterminate k→∥-vector space. It is shown that, thanks to differences in crystal and surface symmetries, the single photon energy ARPES may be successfully used for classification of surface and bulk bands of electronic states on complex, highly reconstructed surfaces instead of the most often used variable photon energy studies.

  5. Spectromicroscopy measurements of surface morphology and band structure of exfoliated graphene

    NASA Astrophysics Data System (ADS)

    Knox, Kevin; Locatelli, Andrea; Cvetko, Dean; Mentes, Tevfik; Nino, Miguel; Wang, Shancai; Yilmaz, Mehmet; Kim, Philip; Osgood, Richard; Morgante, Alberto

    2011-03-01

    Monolayer-thick crystals, such as graphene, are an area of intense interest in condensed matter research. ~However, crystal deformations in these 2D systems are known to adversely affect conductivity and increase local chemical reactivity. Additionally, surface roughness in graphene complicates band-mapping and limits resolution in techniques such as angle resolved photoemission spectroscopy (ARPES), the theory of which was developed for atomically flat surfaces. Thus, an understanding of the surface morphology of graphene is essential to making high quality devices and important for interpreting ARPES results. In this talk, we will describe a non-invasive approach to examining the corrugation in exfoliated graphene using a combination of low energy electron microscopy (LEEM) and micro-spot low energy electron diffraction (LEED). We will also describe how such knowledge of surface roughness can be used in the analysis of ARPES data to improve resolution and extract useful information about the band-structure.

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

    SciTech Connect

    Faraggi, M.N.; Gravielle, M.S.; Alducin, M.; Silkin, V.M.; Juaristi, J.I.

    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.

  7. Band structure, Fermi surface, superconductivity, and resistivity of actinium under high pressure

    SciTech Connect

    Dakshinamoorthy, M.; Iyakutti, K.

    1984-12-15

    The electronic band structures of fcc actinium (Ac) have been calculated for a wide range of pressures by reducing the unit-cell volume from 1.0V/sub 0/ to 0.5V/sub 0/ with use of the relativistic augmented-plane-wave method. The density of states and Fermi-surface cross sections corresponding to various volumes are obtained. Calculations for the band-structure-related quantities such as electron-phonon mass enhancement factor lambda, superconducting transition temperature T/sub c/, and resistivity rho corresponding to different volumes are performed. It is seen that T/sub c/ increases with pressure, i.e., with decreasing volume. A new empirical relation for the volume dependence of T/sub c/ is proposed and its validity is checked using the T/sub c/ values obtained from the above band-structure results. The resistivity rho first increases with increasing pressure (i.e., with decreasing volume) and then decreases for higher pressures (i.e., for smaller volumes).

  8. Accessing Surface Brillouin Zone and Band Structure of Picene Single Crystals

    NASA Astrophysics Data System (ADS)

    Xin, Qian; Duhm, Steffen; Bussolotti, Fabio; Akaike, Kouki; Kubozono, Yoshihiro; Aoki, Hideo; Kosugi, Taichi; Kera, Satoshi; Ueno, Nobuo

    2012-06-01

    We have experimentally revealed the band structure and the surface Brillouin zone of insulating picene single crystals (SCs), the mother organic system for a recently discovered aromatic superconductor, with ultraviolet photoelectron spectroscopy (UPS) and low-energy electron diffraction with a laser for photoconduction. A hole effective mass of 2.24m0 and the hole mobility μh≥9.0cm2/Vs (298 K) were deduced in the Γ-Y direction. We have further shown that some picene SCs did not show charging during UPS even without the laser, which indicates that pristine UPS works for high-quality organic SCs.

  9. Unconventional band structure for a periodically gated surface of a three-dimensional topological insulator

    NASA Astrophysics Data System (ADS)

    Mondal, Puja; Ghosh, Sankalpa

    2015-12-01

    The surface states of the three-dimensional (3D) topological insulators are described by a two-dimensional (2D) massless dirac equation. A gate-voltage-induced one-dimensional potential barrier on such surfaces creates a discrete bound state in the forbidden region outside the dirac cone. Even for a single barrier it is shown that such a bound state can create an electrostatic analogue of Shubnikov de Haas oscillation which can be experimentally observed for relatively smaller size samples. However, when these surface states are exposed to a periodic arrangement of such gate-voltage-induced potential barriers, the band structure of the same was significantly modified. This is expected to significantly alter the properties of the macroscopic system. We also suggest that, within suitable limits, the system may offer ways to control electron spin electrostatically, which may be practically useful.

  10. 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.; Lin, Y. H.; Goldman, R. S.; Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-2136

    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.

  11. Band structures in 106Pd

    NASA Astrophysics Data System (ADS)

    He, C. Y.; Yu, B. B.; Zhu, L. H.; Wu, X. G.; Zheng, Y.; Zhang, B.; Yao, S. H.; Wang, L. L.; Li, G. S.; Hao, X.; Shi, Y.; Xu, C.; Xu, F. R.; Wang, J. G.; Gu, L.; Zhang, M.

    2012-10-01

    The high spin states of 106Pd have been investigated with in-beam ?-ray spectroscopic methods using the 100Mo(11B,1p4n)106Pd reaction at a beam energy of 60 MeV. All earlier known bands were extended considerably and additional bands were identified. The configurations of these bands are discussed on the basis of the experimental aligned angular momenta and total Routhian surface calculations. Both two-quasineutron and two-quasiproton structures have been found in 106Pd. The nonyrast low-lying positive-parity band was interpreted as a ?-vibrational band.

  12. Surface transport and band gap structure of exfoliated 2H-MoTe2 crystals

    NASA Astrophysics Data System (ADS)

    Gutirrez Lezama, Ignacio; Ubaldini, Alberto; Longobardi, Maria; Giannini, Enrico; Renner, Christoph; Kuzmenko, Alexey B.; Morpurgo, Alberto F.

    2014-09-01

    Semiconducting transition metal dichalcogenides (TMDs) have emerged as materials that can be used to realize two-dimensional (2D) crystals possessing rather unique transport and optical properties. Most research has so far focused on sulfur and selenium compounds, while tellurium-based materials have attracted little attention so far. As a first step in the investigation of Te-based semiconducting TMDs in this context, we have studied MoTe2 crystals with thicknesses above 4 nm, focusing on surface transport and a quantitative determination of the gap structure. Using ionic-liquid gated transistors, we show that ambipolar transport at the surface of the material is reproducibly achieved, with hole and electron mobility values between 10 and 30 cm2 V-1s-1 at room temperature. The gap structure is determined through three different techniques: ionic-liquid gated transistors and scanning tunneling spectroscopy, which allow the measurement of the indirect gap (Eind), and optical transmission spectroscopy on crystals of different thickness, which enables the determination of both the direct (Edir) and the indirect gap. We find that at room temperature Eind = 0.88 eV and Edir = 1.02 eV. Our results suggest that thin MoTe2 layers may exhibit a transition to a direct gap before mono-layer thickness. They should also drastically extend the range of direct gaps accessible in 2D semiconducting TMDs.

  13. Seismic structure of Precambrian lithosphere: New constraints from broad-band surface-wave dispersion

    NASA Astrophysics Data System (ADS)

    Lebedev, Sergei; Boonen, Jan; Trampert, Jeannot

    2009-04-01

    Depth distributions of seismic velocities and their directional dependence (anisotropy) in the crust and mantle beneath cratons yield essential constraints on processes of their formation and evolution. Despite recent progress in mapping the lateral extent of cratonic roots around the globe, profiles of seismic velocities within them remain uncertain. In this study we employ a novel combination of waveform-analysis techniques and measure inter-station Rayleigh- and Love-wave phase velocities in broad period ranges that enable resolution from the upper crust to deep upper mantle. Sampling a selection of 10 Archean and Proterozoic locations, we derive new constraints on the isotropic and radially anisotropic seismic structure of Precambrian lithosphere. Shear-wave speed VS is consistently higher in the lithosphere of cratons than in the lithosphere of Proterozoic foldbelts. Because known effects of compositional variations in the lithosphere on VS are too small to account for the difference, this implies that temperature in cratonic lithosphere is consistently lower, in spite of sub-lithospheric mantle beneath continents being thermally heterogeneous, with some cratons underlain, as we observe, by a substantially hotter asthenosphere compared to others. Lithospheric geotherms being nearly conductive, this confirms that the stable, buoyant lithosphere beneath cratons must be substantially thicker than beneath younger continental blocks. An increase in VS between the Moho and a 100-150 km depth is consistently preferred by the data in this study and is present in seismic models of continents published previously. We argue that this is largely due to the transition from spinel peridotite to garnet peridotite, proposed previously to give rise to the "Hales discontinuity" within this depth interval. The depth and the width of the phase transformation depend on mantle composition; it is likely to occur deeper and over a broader depth interval beneath cratons than elsewhere because of the high Cr content in the depleted cratonic lithosphere, as evidenced by a number of xenolith studies. Seismic data available at present would be consistent with both a sharp and a gradual increase in VS in the upper lithosphere (a Hales discontinuity or a "Hales gradient"). The VS profile in the upper mantle lithosphere is not shaped by the temperature distribution only; this needs to be considered when relating seismic velocities to lithospheric temperatures. Radial anisotropy in the upper crust is observed repeatedly and indicates vertically oriented anisotropic fabric ( VSH < VSV); this may yield a clue on how cratons grew, lending support to the view that distributed crustal shortening with sub-vertical flow patterns occurred over large scales in hot ancient orogens. In the lower crust and upper lithospheric mantle, radial anisotropy consistently reveals horizontal fabric ( VSH > VSV); the fabric can be interpreted as a record of (sub-)horizontal ductile flow in the lower crust and lithospheric mantle at the time of the formation and stabilisation of the cratons. We also find indications for radial anisotropy below 200 km depth, corroborating recent evidence for anisotropy in the asthenosphere beneath cratons due to current and recent asthenospheric flow.

  14. Band structures in 99Rh

    NASA Astrophysics Data System (ADS)

    Kumar, S.; Singh, V.; Singh, K.; Sihotra, S.; Singh, N.; Goswamy, J.; Malik, S. S.; Ragnarsson, I.; Trivedi, T.; Singh, R. P.; Muralithar, S.; Kumar, R.; Bhowmik, R. K.; Palit, R.; Bharti, A.; Mehta, D.

    2014-10-01

    Excited states in the 99Rh nucleus were populated using the fusion-evaporation reaction 75As(28Si,2p2n) at {{E}_{lab}}=120\\;MeV and the de-excitations were investigated through in-beam ?-ray spectroscopic techniques using the INGA spectrometer consisting of 18 clover detectors. The observed band structures are discussed in the framework of tilted axis cranking shell-model calculations. Level structures at low energies are identified as resulting from the rotational bands based on the \\pi {{p}_{1/2}} and \\pi {{g}_{9/2}} configurations. The \\Delta I = 1 coupled bands are observed at higher excitation energies and have been interpreted as based on the \\pi {{g}_{9/2}}\\otimes \

  15. Electronic bands, Fermi surface, and elastic properties of new 4.2 K superconductor SrPtAs with a honeycomb structure from first principles calculations

    NASA Astrophysics Data System (ADS)

    Shein, I. R.; Ivanovskii, A. L.

    2011-10-01

    The hexagonal phase SrPtAs (s.g. P6/ mmm; #194) with a honeycomb lattice structure was recently declared as a new low-temperature ( T C ? 4.2 K) superconductor. Here, by means of first-principles calculations the optimized structural parameters, electronic bands, Fermi surface, total and partial densities of states, inter-atomic bonding picture, independent elastic constants, bulk and shear moduli for SrPtAs were obtained for the first time and analyzed in comparison with the related layered superconductor SrPt 2As 2.

  16. A study of photoemission using CW and pulsed UV light sources to probe surface slip band structure evolution of single crystal aluminium

    NASA Astrophysics Data System (ADS)

    Cai, Mingdong; Langford, Stephen; Dickinson, J. Thomas

    2008-03-01

    We report measurements of photoelectron emission from high-purity single crystal aluminum during uniaxial tensile deformation. A 248 nm pulsed excimer laser was used as a light source and the generated photoemission data was compared with that using a filtered mercury lamp. Time-of-flight curves of photoelectrons generated by pulsed excimer laser irradiation were observed showing a two peaked structure. These two peaks correspond to photoelectrons of two energy levels. It was also found that real time total photoelectron charge increases linearly with strain; and the increment is heterogeneous. Photoemission using low-energy photons is sensitive to changes in surface morphology accompanying deformation, including slip line and band formation. The discontinuity in photoelectron intensity and the heterogeneous surface slip band structure prove the production of fresh surface area is not continuous, which is predicted by a recent dislocation dynamics theory based on percolation process. Except for differences in instrumentation and data analysis, the photoemission data from a filtered mercury lamp and from the excimer laser are comparable. Current studies extend the application of the excimer laser into surface dynamics analysis.

  17. Formation of the conduction band electronic structure during deposition of ultrathin dicarboximide-substituted perylene films on the oxidized silicon surface

    NASA Astrophysics Data System (ADS)

    Komolov, A. S.; Lazneva, E. F.; Gerasimova, N. B.; Panina, Yu. A.; Baramygin, A. V.; Ovsyannikov, A. D.

    2015-07-01

    The results of the investigation of the conduction band electronic structure and the interfacial potential barrier during deposition of ultrathin dicarboximide-substituted perylene films (PTCBI-C8) on the oxidized silicon surface have been presented. The measurements have been performed using the very low energy electron diffraction (VLEED) technique implemented in the total current spectroscopy (TCS) mode with a variation in the incident electron energy from 0 to 25 eV. Changes in the intensities of the maxima from the deposited PTCBI-C8 film and from the substrate with an increase in the organic coating thickness to 7 nm have been analyzed using TCS measurements. A comparison of the structure of the maxima of PTCBI-C8 and perylene-tetracarboxylic-dianhydride (PTCDA) films has made it possible to distinguish the energy range (8-13 eV above E F) in which distinct differences in the structures of maxima for PTCDA and PTCBI-C8 films are observed. This energy range corresponds to low-lying ?*-states of the conduction band of the films studied. The formation of the interfacial region of the PTCBI-C8 film and (SiO2) n-Si substrate is accompanied by an increase in the surface work function by 0.6 eV, which corresponds to the electron density charge transfer from the (SiO2) n-Si substrate to the PTCBI-C8 film.

  18. Banded structures in stratospheric aerosol distributions

    NASA Technical Reports Server (NTRS)

    Trepte, Charles R.; Thomason, Larry W.; Kent, Geoffrey S.

    1994-01-01

    Zonal bands of stratospheric aerosol optical depth are observed by various sensors under both volcanic and non-volcanic conditions. Maximum optical depths occur within the tropics and at high latitudes, while minima are found between latitudes of approximately 15 deg and 45 deg. This structure is shown to result from a reservoir of aerosol over the tropics, poleward transport, and the departure of the tropopause from isentropic surfaces.

  19. Photonic band gap structure simulator

    DOEpatents

    Chen, Chiping; Shapiro, Michael A.; Smirnova, Evgenya I.; Temkin, Richard J.; Sirigiri, Jagadishwar R.

    2006-10-03

    A system and method for designing photonic band gap structures. The system and method provide a user with the capability to produce a model of a two-dimensional array of conductors corresponding to a unit cell. The model involves a linear equation. Boundary conditions representative of conditions at the boundary of the unit cell are applied to a solution of the Helmholtz equation defined for the unit cell. The linear equation can be approximated by a Hermitian matrix. An eigenvalue of the Helmholtz equation is calculated. One computation approach involves calculating finite differences. The model can include a symmetry element, such as a center of inversion, a rotation axis, and a mirror plane. A graphical user interface is provided for the user's convenience. A display is provided to display to a user the calculated eigenvalue, corresponding to a photonic energy level in the Brilloin zone of the unit cell.

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

    SciTech Connect

    Li, Yi; Zhang, Rong E-mail: bliu@nju.edu.cn; Liu, Bin E-mail: bliu@nju.edu.cn; Xie, Zili; Zhang, Guogang; Tao, Tao; Zhuang, Zhe; Zhi, Ting; Zheng, Youdou

    2014-07-07

    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.

  1. Susceptibilities for first principles band structures

    NASA Astrophysics Data System (ADS)

    Crockford, D. J.; Yeung, W.

    1993-04-01

    We present a parallel implementation of a new method for calculating the unenhanced susceptibility proposed by us recently. Our implementation uses the first principles LMTO band structure within the tight binding approach as input to calculate the joint density of states. The susceptibility is then obtained by integrating over the product of the joint density of states and a Lindhard function. Our program, which has a simple friendly user interface, runs on the PC with a quadputer board, a Meiko Surface running CSTools powered either by T800 or i860 compute boards and the Intel iPSC/860 hypercube in Daresbury. Our method incorporates the troublesome matrix elements naturally and our results on Pd and Ni show that the decrease in ?( q) as we go away from the Brillouin zone centre is due mainly to the matrix elements rather than to the band energies.

  2. Monolithic phononic crystals with a surface acoustic band gap from surface phonon-polariton coupling.

    PubMed

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

    2014-11-21

    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. PMID:25479504

  3. 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.

  4. Evidence for hybrid surface metallic band in (4??4) silicene on Ag(111)

    SciTech Connect

    Tsoutsou, D. Xenogiannopoulou, E.; Golias, E.; Tsipas, P.; Dimoulas, A.

    2013-12-02

    The electronic band structure of monolayer (4??4) silicene on Ag(111) is imaged by angle resolved photoelectron spectroscopy. A dominant hybrid surface metallic band is observed to be located near the bulk Ag sp-band which is also faintly visible. The two-dimensional character of the hybrid band has been distinguished against the bulk character of the Ag(111) sp-band by means of photon energy dependence experiments. The surface band exhibits a steep linear dispersion around the K{sup }{sub Ag} point and has a saddle point near the M{sup }{sub Ag} point of Ag(111) resembling the ?-band dispersion in graphene.

  5. Band structure of W and Mo by empirical pseudopotential method

    NASA Technical Reports Server (NTRS)

    Sridhar, C. G.; Whiting, E. E.

    1977-01-01

    The empirical pseudopotential method (EPM) is used to calculate the band structure of tungsten and molybdenum. Agreement between the calculated reflectivity, density of states, density of states at the Fermi surface and location of the Fermi surface from this study and experimental measurements and previous calculations is good. Also the charge distribution shows the proper topological distribution of charge for a bcc crystal.

  6. Photonic Band Gap Structures for Accelerator Applications

    SciTech Connect

    Smirnova, E.I.

    2004-12-07

    A photonic band gap (PBG) structure is a one-, two- or three-dimensional periodic metallic and/or dielectric system, which acts like a filter, reflecting rf fields in some frequency range and allowing rf fields at other frequencies to transmit through. PBG structures have many promising applications in active and passive devices at millimeter wave and higher frequencies. Metal PBG structures can be employed at X and Ku-band accelerators to suppress wakefields. Dielectric PBG structures are attractive at terahertz frequencies for construction of high gradient laser-driven accelerators. For both applications two-dimensional (2D) PBG structures are of main interest, although planar and three-dimensional (3D) structures are also used. In this paper a review of theoretical studies and computer modeling of 2D metal and dielectric structures is presented, and current experimental efforts on constructing and testing metal and dielectric PBG accelerators are discussed.

  7. Multiple band structures of {sup 131}Cs

    SciTech Connect

    Sihotra, S.; Palit, R.; Naik, Z.; Joshi, P. K.; Deo, A. Y.; Jain, H. C.; Singh, K.; Goswamy, J.; Mehta, D.; Singh, N.; Malik, S. S.; Praharaj, C. R.

    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.

  8. Unfolding the band structure of non-crystalline photonic band gap materials

    NASA Astrophysics Data System (ADS)

    Tsitrin, Samuel; Williamson, Eric Paul; Amoah, Timothy; Nahal, Geev; Chan, Ho Leung; Florescu, Marian; Man, Weining

    2015-08-01

    Non-crystalline photonic band gap (PBG) materials have received increasing attention, and sizeable PBGs have been reported in quasi-crystalline structures and, more recently, in disordered structures. Band structure calculations for periodic structures produce accurate dispersion relations, which determine group velocities, dispersion, density of states and iso-frequency surfaces, and are used to predict a wide-range of optical phenomena including light propagation, excited-state decay rates, temporal broadening or compression of ultrashort pulses and complex refraction phenomena. However, band calculations for non-periodic structures employ large super-cells of hundreds to thousands building blocks, and provide little useful information other than the PBG central frequency and width. Using stereolithography, we construct cm-scale disordered PBG materials and perform microwave transmission measurements, as well as finite-difference time-domain (FDTD) simulations. The photonic dispersion relations are reconstructed from the measured and simulated phase data. Our results demonstrate the existence of sizeable PBGs in these disordered structures and provide detailed information of the effective band diagrams, dispersion relation, iso-frequency contours, and their angular dependence. Slow light phenomena are also observed in these structures near gap frequencies. This study introduces a powerful tool to investigate photonic properties of non-crystalline structures and provides important effective dispersion information, otherwise difficult to obtain.

  9. Unfolding the band structure of non-crystalline photonic band gap materials

    PubMed Central

    Tsitrin, Samuel; Williamson, Eric Paul; Amoah, Timothy; Nahal, Geev; Chan, Ho Leung; Florescu, Marian; Man, Weining

    2015-01-01

    Non-crystalline photonic band gap (PBG) materials have received increasing attention, and sizeable PBGs have been reported in quasi-crystalline structures and, more recently, in disordered structures. Band structure calculations for periodic structures produce accurate dispersion relations, which determine group velocities, dispersion, density of states and iso-frequency surfaces, and are used to predict a wide-range of optical phenomena including light propagation, excited-state decay rates, temporal broadening or compression of ultrashort pulses and complex refraction phenomena. However, band calculations for non-periodic structures employ large super-cells of hundreds to thousands building blocks, and provide little useful information other than the PBG central frequency and width. Using stereolithography, we construct cm-scale disordered PBG materials and perform microwave transmission measurements, as well as finite-difference time-domain (FDTD) simulations. The photonic dispersion relations are reconstructed from the measured and simulated phase data. Our results demonstrate the existence of sizeable PBGs in these disordered structures and provide detailed information of the effective band diagrams, dispersion relation, iso-frequency contours, and their angular dependence. Slow light phenomena are also observed in these structures near gap frequencies. This study introduces a powerful tool to investigate photonic properties of non-crystalline structures and provides important effective dispersion information, otherwise difficult to obtain. PMID:26289434

  10. Unfolding the band structure of non-crystalline photonic band gap materials.

    PubMed

    Tsitrin, Samuel; Williamson, Eric Paul; Amoah, Timothy; Nahal, Geev; Chan, Ho Leung; Florescu, Marian; Man, Weining

    2015-01-01

    Non-crystalline photonic band gap (PBG) materials have received increasing attention, and sizeable PBGs have been reported in quasi-crystalline structures and, more recently, in disordered structures. Band structure calculations for periodic structures produce accurate dispersion relations, which determine group velocities, dispersion, density of states and iso-frequency surfaces, and are used to predict a wide-range of optical phenomena including light propagation, excited-state decay rates, temporal broadening or compression of ultrashort pulses and complex refraction phenomena. However, band calculations for non-periodic structures employ large super-cells of hundreds to thousands building blocks, and provide little useful information other than the PBG central frequency and width. Using stereolithography, we construct cm-scale disordered PBG materials and perform microwave transmission measurements, as well as finite-difference time-domain (FDTD) simulations. The photonic dispersion relations are reconstructed from the measured and simulated phase data. Our results demonstrate the existence of sizeable PBGs in these disordered structures and provide detailed information of the effective band diagrams, dispersion relation, iso-frequency contours, and their angular dependence. Slow light phenomena are also observed in these structures near gap frequencies. This study introduces a powerful tool to investigate photonic properties of non-crystalline structures and provides important effective dispersion information, otherwise difficult to obtain. PMID:26289434

  11. Ionization of Rydberg H atoms at band-gap metal surfaces via surface and image states

    NASA Astrophysics Data System (ADS)

    So, E.; Gibbard, J. A.; Softley, T. P.

    2015-09-01

    Wavepacket propagation calculations are reported for the interaction of a Rydberg hydrogen atom (n=2-8) with Cu(111) and Cu(100) surfaces (represented by a Chulkov potential), in comparison with a Jellium surface. Both copper surfaces have a projected band gap at the surface in the energy range degenerate with some or all of the Rydberg energies. The charge transfer of the Rydberg electron to the surface is found to be enhanced for n values at which there is a near-degeneracy between the Rydberg energy level and an image state or a surface state of the surface. The enhancement is facilitated by the strong overlap of the surface image-state orbital lying outside the surface and the orbital of the incoming Rydberg atom. These calculations point to the possibility of using Rydberg-surface collisions as a probe of surface electronic structure.

  12. Detangling Flat Bands via Fano Structures

    NASA Astrophysics Data System (ADS)

    Bodyfelt, Joshua; Flach, Sergej; Leykam, Daniel; Desyatnikov, Anton; Matthies, Peter

    2014-03-01

    Translationally invariant lattices with flat bands (FB) in the band structure possess irreducible compact localized flat band states (FBS). The number of unit cells involved in one irreducible FBS defines the FB class of the model. For class 1, we transform and detangle the FBS and dispersive states into a Fano lattice. Inverting the scheme, we end up with a continuum of FB models for any FB class. In the case of an on-site disorder potential, the symmetric part lifts the FB degeneracy, keeping compact localization of FBS. The antisymmetric part yields Fano-induced Cauchy tails for the potential felt by the dispersive states. As a result, weak disorder enforces different energy dependent localization length scales, and highly nontrivial mode profiles at the FB energy. Scattering by perturbed FBS can then be understood as Fano resonance.

  13. X-Band Structure Development at KEK

    NASA Astrophysics Data System (ADS)

    Higo, Toshiyasu

    2015-10-01

    X-band accelerator structure development at KEK has been driven targeting the linear colliders in worldwide collaborations. It is based on the technologies developed with high-precision machining, precise assembly and bonding method to preserve the precision. With maximally utilizing the merits of such technologies, the long-range wakefield was suppressed in parallel to realize the high gradient. The latter needs more study and development to actually realize the stable operation at a gradient of 100 MV/m or higher in the view point of the present paper. The worldwide collaboration studies are extensively on-going and the understanding of the vacuum breakdown has been advancing. By describing the development at KEK toward the X-band wakefield suppressed high-gradient accelerator structure, this paper shows how such structures have been evolved and may serve to show a room for the future studies.

  14. Band structure of ABC -stacked graphene trilayers

    NASA Astrophysics Data System (ADS)

    Zhang, Fan; Sahu, Bhagawan; Min, Hongki; MacDonald, A. H.

    2010-07-01

    The ABC -stacked N -layer-graphene family of two-dimensional electron systems is described at low energies by two remarkably flat bands with Bloch states that have strongly momentum-dependent phase differences between carbon π -orbital amplitudes on different layers and large associated momentum-space Berry phases. These properties are most easily understood using a simplified model with only nearest-neighbor interlayer hopping which leads to gapless semiconductor electronic structure and pN dispersion in both conduction and valence bands. We report on a study of the electronic band structures of trilayers which uses ab initio density-functional theory and kṡp theory to fit the parameters of a π -band tight-binding model. We find that when remote interlayer hopping is retained, the triple Dirac point of the simplified model is split into three single Dirac points located along the three KM directions. External potential differences between top and bottom layers are strongly screened by charge transfer within the trilayer but still open an energy gap at overall neutrality.

  15. Photonic Band Gap Structures for Accelerator Applications

    NASA Astrophysics Data System (ADS)

    Smirnova, E. I.; Shapiro, M. A.; Chen, C.; Temkin, R. J.

    2002-12-01

    We report the results of our theoretical investigation and cold test of a two-dimensional (2D) metal photonic band gap (PBG) accelerator cell and propose to construct a 2?/3 linear accelerator structure with reduced wakefields as a stack of PBG cells set between disks with irises. We developed a computer code, called Photonic Band Gap Structure Simulator (PBGSS), to calculate the complete dispersion curves for square and triangular arrays of metal rods [1]. Using the PBGSS code, the global photonic band gaps of the arrays were determined and employed to design the PBG cavities. The modes of the 2D PBG cavity formed by a defect (missing rod) in the triangular array of metal rods were studied numerically using the HFSS [2] code. The cavity was designed with only the fundamental TM01 mode confined and higher order modes suppressed. The cold test was performed and the results proved the suppression of the wakefields. Dielectric PBG structures were also studied as applied to microwave devices. A dielectric PBG resonator with the TM02 mode confined and TM01 and TM11 modes absent was designed. The construction of such a resonator overcomes the problem of mode competition in overmoded structures and thus will allow the extension of the operating frequency of the devices to higher frequencies at higher order modes.

  16. Complex banded structures in directional solidification processes

    NASA Astrophysics Data System (ADS)

    Korzhenevskii, A. L.; Rozas, R. E.; Horbach, J.

    2016-01-01

    A combination of theory and numerical simulation is used to investigate impurity superstructures that form in rapid directional solidification (RDS) processes in the presence of a temperature gradient and a pulling velocity with an oscillatory component. Based on a capillary wave model, we show that the RDS processes are associated with a rich morphology of banded structures, including frequency locking and the transition to chaos.

  17. Complex banded structures in directional solidification processes.

    PubMed

    Korzhenevskii, A L; Rozas, R E; Horbach, J

    2016-01-27

    A combination of theory and numerical simulation is used to investigate impurity superstructures that form in rapid directional solidification (RDS) processes in the presence of a temperature gradient and a pulling velocity with an oscillatory component. Based on a capillary wave model, we show that the RDS processes are associated with a rich morphology of banded structures, including frequency locking and the transition to chaos. PMID:26704726

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

    SciTech Connect

    Marsh, Roark A.; Shapiro, Michael A.; Temkin, Richard J.; 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.

  19. Band structure engineering of topological insulator heterojunctions

    NASA Astrophysics Data System (ADS)

    Jin, Kyung-Hwan; Yeom, Han Woong; Jhi, Seung-Hoon

    2016-02-01

    We investigate the topological surface states in heterostructures formed from a three-dimensional topological insulator (TI) and a two-dimensional insulating thin film, using first-principles calculations and the tight-binding method. Utilizing a single Bi or Sb bilayer on top of the topological insulators B i2S e3 , B i2T e3 , B i2T e2Se , and S b2T e3 , we find that the surface states evolve in very peculiar but predictable ways. We show that strong hybridization between the bilayer and TI substrates causes the topological surface states to migrate to the top bilayer. It is found that the difference in the work function of constituent layers, which determines the band alignment and the strength of hybridization, governs the character of newly emerged Dirac states.

  20. Band Engineering of Dirac Surface States in Topological-Insulator-Based van der Waals Heterostructures

    NASA Astrophysics Data System (ADS)

    Chang, Cui-Zu; Tang, Peizhe; Feng, Xiao; Li, Kang; Ma, Xu-Cun; Duan, Wenhui; He, Ke; Xue, Qi-Kun

    2015-09-01

    The existence of a gapless Dirac surface band of a three dimensional (3D) topological insulator (TI) is guaranteed by the nontrivial topological character of the bulk band, yet the surface band dispersion is mainly determined by the environment near the surface. In this Letter, through in situ angle-resolved photoemission spectroscopy and first-principles calculation on 3D TI-based van der Waals heterostructures, we demonstrate that one can engineer the surface band structures of 3D TIs by surface modifications without destroying their topological nontrivial property. The result provides an accessible method to independently control the surface and bulk electronic structures of 3D TIs, and sheds light on designing artificial topological materials for electronic and spintronic purposes.

  1. Band Engineering of Dirac Surface States in Topological-Insulator-Based van der Waals Heterostructures.

    PubMed

    Chang, Cui-Zu; Tang, Peizhe; Feng, Xiao; Li, Kang; Ma, Xu-Cun; Duan, Wenhui; He, Ke; Xue, Qi-Kun

    2015-09-25

    The existence of a gapless Dirac surface band of a three dimensional (3D) topological insulator (TI) is guaranteed by the nontrivial topological character of the bulk band, yet the surface band dispersion is mainly determined by the environment near the surface. In this Letter, through in situ angle-resolved photoemission spectroscopy and first-principles calculation on 3D TI-based van der Waals heterostructures, we demonstrate that one can engineer the surface band structures of 3D TIs by surface modifications without destroying their topological nontrivial property. The result provides an accessible method to independently control the surface and bulk electronic structures of 3D TIs, and sheds light on designing artificial topological materials for electronic and spintronic purposes. PMID:26451573

  2. Band structure of doubly-odd nuclei around mass 130

    SciTech Connect

    Higashiyama, Koji; Yoshinaga, Naotaka

    2011-05-06

    Nuclear structure of the doublet bands in the doubly-odd nuclei with mass A{approx}130 is studied in terms of a pair-truncated shell model. The model reproduces quite well the energy levels of the doublet bands and the electromagnetic transitions. The analysis of the electromagnetic transitions reveals new band structure of the doublet bands.

  3. Band bending and electrical transport at chemically modified silicon surfaces

    NASA Astrophysics Data System (ADS)

    Lopinski, Greg; Ward, Tim; Hul'Ko, Oleksa; Boukherroub, Rabah

    2002-03-01

    High resolution electron energy loss spectroscopy (HREELS) and electrical transport measurements have been used to investigate how various chemical modifications give rise to band bending and alter the conductivity of Si(111) surfaces. HREELS is a sensitive probe of band bending through observations of the low frequency free carrier plasmon mode. For hydrogen terminated surfaces, prepared by the standard etch in ammonium flouride, HREELS measurements on both n and n+ substrates are consistent with nearly flat bands. Chlorination of these surfaces results in substantial upward band bending due to the strong electron withdrawing nature of the chlorine, driving the surface into inversion. The presence of this inversion layer on high resistivity n-type samples is observed through a substantial enhancement of the surface conductivity (relative to the H-terminated surface), as well as through broadening of the quasi-elastic peak in the HREELS measurements. We have also begun to examine organically modified silicon surfaces, prepared by various wet chemical reactions with the H-terminated surface. Decyl modified Si(111) surfaces are seen to exhibit a small degree of band bending, attributed to extrinsic defect states cause by a small degree of oxidation accompanying the modification reaction. The prospects of using conductivity as an in-situ monitor of the rate of these reactions will be discussed.

  4. Band-gap structures for matter waves

    NASA Astrophysics Data System (ADS)

    Damon, F.; Condon, G.; Cheiney, P.; Fortun, A.; Georgeot, B.; Billy, J.; Guéry-Odelin, D.

    2015-09-01

    Spatial gaps correspond to the projection in position space of the gaps of a periodic structure whose envelope varies spatially. They can be easily generated in cold atomic physics using finite-size optical lattice, and provide a new kind of tunnel barrier which can be used as a versatile tool for quantum devices. We present in detail different theoretical methods to quantitatively describe these systems, and show how they can be used in one dimension to realize matter wave Fabry-Perot cavities. We also provide experimental and numerical results that demonstrate the interest of spatial gap structures for phase space engineering. We then generalize the concept of spatial gaps in two dimensions and show that this enables one to design multiply connected cavities which generate a quantum dot structure for atoms or allow one to construct curved wave guides for matter waves. At last, we demonstrate that modulating in time the amplitude of the periodic structure offers a wide variety of possible atom manipulations including the control of the scattering of an incoming wave packet, the loading of cavities delimited by spatial gaps, their coupling by multiphonon processes or the realization of a tunable source of atoms. This large range of possibilities offered by space and time engineering of optical lattices demonstrates the flexibility of such band-gap structures for matter wave control, quantum simulators, and atomtronics.

  5. 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.

  6. Band structures in doubly odd Rh98

    NASA Astrophysics Data System (ADS)

    Kumar, S.; Sihotra, S.; Singh, K.; Singh, V.; Sandeep, Goswamy, J.; Singh, N.; Mehta, D.; Malik, S. S.; Palit, R.; Kumar, R.; Singh, R. P.; Muralithar, S.; Bhowmik, R. K.

    2014-03-01

    Excited states in the transitional doubly odd Rh98 nucleus were populated in the As75(Si28,2p3n) fusion-evaporation reaction using the 120-MeV incident Si28 beam. The subsequent de-excitations were investigated through in-beam ?-ray spectroscopic techniques using an early implementation phase of the Indian National Gamma Array (INGA) spectrometer equipped with 18 clover Ge detectors. The level structures in Rh98 have been established up to excitation energy ?10 MeV and angular momentum 23?. The previously reported level schemes are considerably modified and extended substantially. Significant expansion of the level scheme at low excitation energies stipulates that the previously reported 842-726-994-980-265 keV ?-transition cascade in Rh98 is not directly based on the ground state (T1/2 = 8.7 min). Tilted-axis cranking (TAC) shell-model calculations have been used to put the present level scheme of Rh98 in perspective. Level structures have been interpreted in terms of the rotational bands based on the ?p1/2??h11/2 [triaxiality parameter (?) = 25?], and ?f5/2??h11/2 proton-neutron configurations having moderate quadrupole deformation (?2 ? 0.13) and the admixtures. Excited band structures are based on the ?p1/2/f5/2??(g9/2)2??h11/2 configuration and the fully stretched [?p1/2??(h11/2)2??d5/2]13- configuration.

  7. Elucidating the stop bands of structurally colored systems through recursion

    NASA Astrophysics Data System (ADS)

    Amir, Ariel; Vukusic, Peter

    2013-04-01

    Interference is the source of some of the spectacular colors of animals and plants in nature. In some of these systems, the physical structure consists of an ordered array of layers with alternating high and low refractive indices. This periodicity leads to an optical band structure that is analogous to the electronic band structure encountered in semiconductor physics: specific bands of wavelengths (the stop bands) are perfectly reflected. Here, we present a minimal model for optical band structure in a periodic multilayer structure and solve it using recursion relations. The stop bands emerge in the limit of an infinite number of layers by finding the fixed point of the recursion. We compare to experimental data for various beetles, whose optical structure resembles the proposed model. Thus, using only the phenomenon of interference and the idea of recursion, we are able to elucidate the concept of band structure in the context of the experimentally observed high reflectance and iridescent appearance of structurally colored beetles.

  8. Measurement of valence band structure in arbitrary dielectric films

    SciTech Connect

    Uhm, Han S.; Choi, Eun H.

    2012-10-15

    A new way of measuring the band structure of various dielectric materials using the secondary electron emission from Auger neutralization of ions is introduced. The first example of this measurement scheme is the magnesium oxide (MgO) films with respect to the application of the films in the display industries. The density of state in the valence bands of MgO film and MgO film with a functional layer (FL) deposited over a dielectric surface reveals that the density peak of film with a FL is considerably less than that of film, thereby indicating a better performance of MgO film with functional layer in display devices. The second example of the measurement is the boron-zinc oxide (BZO) films with respect to the application of the films to the development of solar cells. The measurement of density of state in BZO film suggests that a high concentration of boron impurity in BZO films may enhance the transition of electrons and holes through the band gap from the valence to the conduction band in zinc oxide crystals; thereby improving the conductivity of the film. Secondary electron emission by the Auger neutralization of ions is highly instrumental for the determination of the density of states in the valence band of dielectric materials.

  9. Band structure mapping of photonic crystal intersubband detectors

    NASA Astrophysics Data System (ADS)

    Schartner, S.; Golka, S.; Pflgl, C.; Schrenk, W.; Andrews, A. M.; Roch, T.; Strasser, G.

    2006-10-01

    The authors report on a quantum well infrared detector embedded in a surface-plasmon waveguide and processed into a deeply etched photonic crystal structure. The device was characterized by collecting the polarization dependent response spectra at different angles of incidence. With this method it is possible to map the photonic band structure by directly detecting the modes of the photonic crystal. It therefore represents a new and direct characterization procedure for photonic crystals. The device shows a strong mixing between TE and TM polarized modes, which is caused by the asymmetric vertical waveguide design.

  10. Observation of a nonradiative flat band for spoof surface plasmons in a metallic Lieb lattice

    NASA Astrophysics Data System (ADS)

    Kajiwara, Sho; Urade, Yoshiro; Nakata, Yosuke; Nakanishi, Toshihiro; Kitano, Masao

    2016-02-01

    We demonstrate a nonradiative flat band for spoof surface plasmon polaritons bounded on a structured surface with Lieb lattice symmetry in the terahertz regime. First, we theoretically derive the dispersion relation of spoof plasmons in a metallic Lieb lattice based on the electrical circuit model. We obtain three bands, one of which is independent of wave vector. To confirm the theoretical result, we numerically and experimentally observe the flat band in transmission and attenuated total reflection configurations. We reveal that the quality factor of the nonradiative flat-band mode decoupled from the propagating wave is higher than that of the radiative flat-band mode. This indicates that the nonradiative flat-band mode is three-dimensionally confined in the lattice.

  11. Segmental structure in banded mongoose calls.

    PubMed

    Fitch, W Tecumseh

    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. PMID:23206277

  12. A Theoretical Structure of High School Concert Band Performance

    ERIC Educational Resources Information Center

    Bergee, Martin J.

    2015-01-01

    This study used exploratory (EFA) and confirmatory factor analysis (CFA) to verify a theoretical structure for high school concert band performance and to test that structure for viability, generality, and invariance. A total of 101 university students enrolled in two different bands rated two high school band performances (a "first"…

  13. A Theoretical Structure of High School Concert Band Performance

    ERIC Educational Resources Information Center

    Bergee, Martin J.

    2015-01-01

    This study used exploratory (EFA) and confirmatory factor analysis (CFA) to verify a theoretical structure for high school concert band performance and to test that structure for viability, generality, and invariance. A total of 101 university students enrolled in two different bands rated two high school band performances (a "first"

  14. Localized surface plasmon resonnance induced terahertz broad absorption band

    NASA Astrophysics Data System (ADS)

    Zhong, Min

    2015-12-01

    A broad band metamaterial absorber is designed and simulated, which constitutes by double circular-patterned metal-dielectric stacks. A absorption band is obtained from 14.1 to 16.4 THz. Electric field distributions reveal that the absorption band is obtained from localized surface plasmon (LSP) modes which are excited both on outside and inside edges of each stack, while the high-frequency absorption peak is excited by LSP modes which are excited only on outside edges. The absorption band width can be tuned by increasing the radius (R) of circular-patterned layers and reducing the thickness of dielectric layers (Hd). Moreover, the designed broad band metamaterial absorber is independent of circular-patterned dielectric layer combination.

  15. 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.

  16. The effect of surface stoichiometry on the band gap of the pyrite FeS2(100) surface

    NASA Astrophysics Data System (ADS)

    Zhang, Yanning; Hu, Jun; Law, Matt; Wu, Ruqian

    2012-02-01

    Iron pyrite (FeS2) is experiencing a resurgence of interest for use in solar photovoltaic and photoelectrochemical cells. The main hurdle to the use of pyrite is the low open-circuit voltage of pyrite devices, which may result from gap states created by surface and bulk defects. Recently, systematic spin-polarized DFT calculations were performed for a series of pyrite FeS2(100) surfaces to clarify the effect of surface stoichiometry on stability, electronic structure, and band gap. It was found that while stoichiometric and S-poor FeS2(100) surfaces are semiconductors with band gaps of 0.56-0.72 eV, S-rich surfaces are small-gap semiconductors (Eg< 0.3 eV) or metals. The stoichiometric FeS2(100) surface is spin polarized in the topmost layer (2 ?B per Fe) and displays a band of Fe dz^2 gap states centered 0.2 eV above the valence band edge. Our calculations suggest that the low open-circuit voltage of pyrite solar cells may result from a narrowed surface band gap. S-poor surfaces may provide larger photovoltages than S-rich surfaces. The segregation process of sulfur vacancy under different surface conditions are also being studied, so as to provide useful guidelines for the design and fabrication of better pyrite photovoltaic materials and devices.

  17. Large Rashba spin splitting of a metallic surface-state band on a semiconductor surface

    PubMed Central

    Yaji, Koichiro; Ohtsubo, Yoshiyuki; Hatta, Shinichiro; Okuyama, Hiroshi; Miyamoto, Koji; Okuda, Taichi; Kimura, Akio; Namatame, Hirofumi; Taniguchi, Masaki; Aruga, Tetsuya

    2010-01-01

    The generation of spin-polarized electrons at room temperature is an essential step in developing semiconductor spintronic applications. To this end, we studied the electronic states of a Ge(111) surface, covered with a lead monolayer at a fractional coverage of 4/3, by angle-resolved photoelectron spectroscopy (ARPES), spin-resolved ARPES and first-principles electronic structure calculation. We demonstrate that a metallic surface-state band with a dominant Pb 6p character exhibits a large Rashba spin splitting of 200?meV and an effective mass of 0.028 me at the Fermi level. This finding provides a material basis for the novel field of spin transport/accumulation on semiconductor surfaces. Charge density analysis of the surface state indicated that large spin splitting was induced by asymmetric charge distribution in close proximity to the nuclei of Pb atoms. PMID:20975678

  18. Structural Evolution of a Warm Frontal Precipitation Band During GCPEx

    NASA Technical Reports Server (NTRS)

    Colle, Brian A.; Naeger, Aaron; Molthan, Andrew; Nesbitt, Stephen

    2015-01-01

    A warm frontal precipitation band developed over a few hours 50-100 km to the north of a surface warm front. The 3-km WRF was able to realistically simulate band development, although the model is somewhat too weak. Band genesis was associated with weak frontogenesis (deformation) in the presence of weak potential and conditional instability feeding into the band region, while it was closer to moist neutral within the band. As the band matured, frontogenesis increased, while the stability gradually increased in the banding region. Cloud top generating cells were prevalent, but not in WRF (too stable). The band decayed as the stability increased upstream and the frontogenesis (deformation) with the warm front weakened. The WRF may have been too weak and short-lived with the band because too stable and forcing too weak (some micro issues as well).

  19. Band structure quantization in nanometer sized ZnO clusters.

    PubMed

    Schouteden, Koen; Zeng, Yu-Jia; Lauwaet, Koen; Romero, Christian P; Goris, Bart; Bals, Sara; Van Tendeloo, Gustaaf; Lievens, Peter; Van Haesendonck, Chris

    2013-05-01

    Nanometer sized ZnO clusters are produced in the gas phase and subsequently deposited on clean Au(111) surfaces under ultra-high vacuum conditions. The zinc blende atomic structure of the approximately spherical ZnO clusters is resolved by high resolution scanning transmission electron microscopy. The large band gap and weak n-type conductivity of individual clusters are determined by scanning tunnelling microscopy and spectroscopy at cryogenic temperatures. The conduction band is found to exhibit clear quantization into discrete energy levels, which can be related to finite-size effects reflecting the zero-dimensional confinement. Our findings illustrate that gas phase cluster production may provide unique possibilities for the controlled fabrication of high purity quantum dots and heterostructures that can be size selected prior to deposition on the desired substrate under controlled ultra-high vacuum conditions. PMID:23515535

  20. 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.

  1. 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.

  2. Engineering the Electronic Band Structure for Multiband Solar Cells

    SciTech Connect

    Lopez, N.; Reichertz, L.A.; Yu, K.M.; Campman, K.; Walukiewicz, W.

    2010-07-12

    Using the unique features of the electronic band structure of GaNxAs1-x alloys, we have designed, fabricated and tested a multiband photovoltaic device. The device demonstrates an optical activity of three energy bands that absorb, and convert into electrical current, the crucial part of the solar spectrum. The performance of the device and measurements of electroluminescence, quantum efficiency and photomodulated reflectivity are analyzed in terms of the Band Anticrossing model of the electronic structure of highly mismatched alloys. The results demonstrate the feasibility of using highly mismatched alloys to engineer the semiconductor energy band structure for specific device applications.

  3. Broken symmetry induced band splitting in the Ag2Ge surface alloy on Ag(111)

    NASA Astrophysics Data System (ADS)

    Wang, W.; Sohail, Hafiz M.; Osiecki, Jacek R.; Uhrberg, R. I. G.

    2014-03-01

    We report a study of the atomic and electronic structures of the ordered Ag2Ge surface alloy containing ? monolayer of Ge. Low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), and angle-resolved photoelectron spectroscopy (ARPES) data reveal a symmetry breaking of the expected ?3 ?3 periodicity, which is established for other Ag2M alloys (M = Bi, Sb, Pb, and Sn). The deviation from a simple ?3 ?3 structure manifests itself as a splitting of diffraction spots in LEED, as a striped structure with a 6 periodicity including a distortion of the local hexagonal structure in STM, and as a complex surface band structure in ARPES that is quite different from those of the other Ag2M alloys. These results are interesting in view of the differences in the atomic and electronic structures exhibited by different group IV elements interacting with Ag(111). Pb and Sn form ?3 ?3 surface alloys on Ag(111), of which Ag2Pb shows a surface band structure with a clear spin-orbit split. Si and C form silicene and graphene structures, respectively, with linear band dispersions and the formation of Dirac cones as reported for graphene. The finding that Ag2Ge deviates from the ideal (?3 ?3) Ag2Sn and Ag2Pb surface alloys makes Ge an interesting "link" between the heavy group IV elements (Sn, Pb) and the light group IV elements (Si, C).

  4. Band gap determination of semiconductor powders via surface photovoltage spectroscopy

    NASA Astrophysics Data System (ADS)

    Gal, D.; Mastai, Y.; Hodes, G.; Kronik, L.

    1999-11-01

    Surface photovoltage spectroscopy (SPS) is introduced as a powerful tool for band gap determination of semiconductor powders. The main advantage of SPS is that scattering and reflection do not interfere with the spectra. Therefore, it does not suffer from the inherent limitations of transmission/reflection based spectroscopies, most notably diffuse reflectance spectroscopy (DRS). The principles of the approach are presented and its usefulness is demonstrated by comparing it with DRS for band gap determination of GaAs, InP, CdTe, CdSe, and CdS semiconductor powders.

  5. Bi-directional evolutionary optimization for photonic band gap structures

    NASA Astrophysics Data System (ADS)

    Meng, Fei; Huang, Xiaodong; Jia, Baohua

    2015-12-01

    Toward an efficient and easy-implement optimization for photonic band gap structures, this paper extends the bi-directional evolutionary structural optimization (BESO) method for maximizing photonic band gaps. Photonic crystals are assumed to be periodically composed of two dielectric materials with the different permittivity. Based on the finite element analysis and sensitivity analysis, BESO starts from a simple initial design without any band gap and gradually re-distributes dielectric materials within the unit cell so that the resulting photonic crystal possesses a maximum band gap between two specified adjacent bands. Numerical examples demonstrated the proposed optimization algorithm can successfully obtain the band gaps from the first to the tenth band for both transverse magnetic and electric polarizations. Some optimized photonic crystals exhibit novel patterns markedly different from traditional designs of photonic crystals.

  6. Surface Material Characterization from Multi-band Optical Observations

    NASA Astrophysics Data System (ADS)

    Hall, D.

    2010-09-01

    Ground-based optical and radar sites routinely acquire resolved images of satellites. These resolved images provide the means to construct accurate wire-frame models of the observed body, as well as an understanding of its orientation as a function of time. Unfortunately, because such images are typically acquired in a single spectral band, they provide little information on the types of materials covering the satellite's various surfaces. Detailed surface material characterization generally requires spectrometric and/or multi-band photometric measurements. Fortunately, many instruments provide such multi-band information (e.g., spectrographs and multi-channel photometers). However, these sensors often measure the brightness of the entire satellite, with no spatial resolution at all. Because such whole-body measurements represent a summation of contributions from many reflecting surfaces, an ―un-mixing‖ or inversion process must be employed to determine the materials covering each of the satellite's individual sub-components. The first section of this paper describes the inversion theory required to retrieve satellite surface material properties from temporal sequences of whole-body multi-band brightness measurements. The inversion requires the following as input: 1) a set of multi-band measurements of a satellite's reflected-sunlight brightness, 2) the satellite's wire-frame model, including each major component capable of reflecting sunlight, 3) the satellite's attitude, specifying the body’s orientation at the time of each multi-band measurement, and 4) a database of bi-directional reflection distribution functions for a set of candidate surface materials. As output, the inversion process yields estimates of the fraction of each major satellite component covered by each candidate material. The second section of the paper describes several tests of the method by applying it to simulated multi-band observations of a cubical satellite with different materials on each of its six faces. The tests indicate that the inversion method successfully retrieves the six known materials when provided a complete noise-free scan of the cube as input. The method also performs reasonably well when confronted with the adverse effects of measurement noise, superfluous or unknown candidate materials, and incomplete observations.

  7. All-Optical Reconstruction of Crystal Band Structure.

    PubMed

    Vampa, G; Hammond, T J; Thir, N; Schmidt, B E; Lgar, F; McDonald, C R; Brabec, T; Klug, D D; Corkum, P B

    2015-11-01

    The band structure of matter determines its properties. In solids, it is typically mapped with angle-resolved photoemission spectroscopy, in which the momentum and the energy of incoherent electrons are independently measured. Sometimes, however, photoelectrons are difficult or impossible to detect. Here we demonstrate an all-optical technique to reconstruct momentum-dependent band gaps by exploiting the coherent motion of electron-hole pairs driven by intense midinfrared femtosecond laser pulses. Applying the method to experimental data for a semiconductor ZnO crystal, we identify the split-off valence band as making the greatest contribution to tunneling to the conduction band. Our new band structure measurement technique is intrinsically bulk sensitive, does not require a vacuum, and has high temporal resolution, making it suitable to study reactions at ambient conditions, matter under extreme pressures, and ultrafast transient modifications to band structures. PMID:26588381

  8. All-Optical Reconstruction of Crystal Band Structure

    NASA Astrophysics Data System (ADS)

    Vampa, G.; Hammond, T. J.; Thir, N.; Schmidt, B. E.; Lgar, F.; McDonald, C. R.; Brabec, T.; Klug, D. D.; Corkum, P. B.

    2015-11-01

    The band structure of matter determines its properties. In solids, it is typically mapped with angle-resolved photoemission spectroscopy, in which the momentum and the energy of incoherent electrons are independently measured. Sometimes, however, photoelectrons are difficult or impossible to detect. Here we demonstrate an all-optical technique to reconstruct momentum-dependent band gaps by exploiting the coherent motion of electron-hole pairs driven by intense midinfrared femtosecond laser pulses. Applying the method to experimental data for a semiconductor ZnO crystal, we identify the split-off valence band as making the greatest contribution to tunneling to the conduction band. Our new band structure measurement technique is intrinsically bulk sensitive, does not require a vacuum, and has high temporal resolution, making it suitable to study reactions at ambient conditions, matter under extreme pressures, and ultrafast transient modifications to band structures.

  9. Tunable band gap in germanene by surface adsorption

    NASA Astrophysics Data System (ADS)

    Ye, Meng; Quhe, Ruge; Zheng, Jiaxin; Ni, Zeyuan; Wang, Yangyang; Yuan, Yakun; Tse, Geoffrey; Shi, Junjie; Gao, Zhengxiang; Lu, Jing

    2014-05-01

    Opening a sizable band gap in the zero-gap germanene without heavy loss of carrier mobility is a key issue for its application in nanoelectronic devices such as high-performance field effect transistors (FETs) operating at room temperature. Using the first-principles calculations, we find a band gap is opened at the Dirac point in germanene by single-side adsorption of alkali metal (AM) atoms. This band gap is tunable by varying the coverage and the species of AM atoms, ranging from 0.02 to 0.31 eV, and the maximum global band gap is 0.26 eV. Since the effective masses of electrons and holes in germanene near the Dirac point after surface adsorption (ranging from 0.005 to 0.106me) are small, the carrier mobility is expected not to degrade much. Therefore germanene is a potential candidate of effective FET channel operating at room temperature upon surface adsorption.

  10. Broadening of effective photonic band gaps in biological chiral structures: From intrinsic narrow band gaps to broad band reflection spectra

    NASA Astrophysics Data System (ADS)

    Vargas, W. E.; Hernández-Jiménez, M.; Libby, E.; Azofeifa, D. E.; Solis, Á.; Barboza-Aguilar, C.

    2015-09-01

    Under normal illumination with non-polarized light, reflection spectra of the cuticle of golden-like and red Chrysina aurigans scarabs show a structured broad band of left-handed circularly polarized light. The polarization of the reflected light is attributed to a Bouligand-type left-handed chiral structure found through the scarab's cuticle. By considering these twisted structures as one-dimensional photonic crystals, a novel approach is developed from the dispersion relation of circularly polarized electromagnetic waves traveling through chiral media, to show how the broad band characterizing these spectra arises from an intrinsic narrow photonic band gap whose spectral position moves through visible and near-infrared wavelengths.

  11. Cluster structure and deformed bands in the 38Ar nucleus

    NASA Astrophysics Data System (ADS)

    Sakuda, T.; Ohkubo, S.

    2013-06-01

    The structure of the 38Ar nucleus is investigated by the S34+? orthogonality condition model (OCM). The energy spectra, electromagnetic transitions and ? spectroscopic factors are calculated. The excited states can be grouped into several bands according to the leading configurations of their wave functions, and the structures of the bands are discussed. The first excited K?=0+ band is found to be predominantly S34+? cluster states. It is also shown that the observed energies and E2 transitions of the band are well reproduced by the model. The existence of a negative-parity doublet band of the band is also predicted. The strength of the ?-cluster states is shown to be spread over several levels due to mixing of shell-model states and various ?-cluster states.

  12. 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

  13. Valence band structure of the icosahedral Ag-In-Yb quasicrystal

    SciTech Connect

    Sharma, H. R.; Simutis, G.; Dhanak, V. R.; Nugent, P. J.; McGrath, R.; Cui, C.; Shimoda, M.; Tsai, A. P.; Ishii, Y.

    2010-03-01

    The valence band structure of the icosahedral (i) Ag-In-Yb quasicrystal, which is isostructural to the binary i-Cd-Yb system, is investigated by ultraviolet photoemission spectroscopy (UPS). Experimental results are compared with electronic-structure calculations of a cubic approximant of the same phase. UPS spectra from the fivefold, threefold, and twofold i-Ag-In-Yb surfaces reveal that the valence band near to the Fermi level is dominated by Yb 4f-derived states, in agreement with calculations. The spectra also exhibit peaks which are surface core level shifted, caused by changes in the electronic structure in surface layers. Calculations yield a pseudogap in the density of states due to a hybridization of the Yb 5d band with the Ag 5p and In 5p bands. Both experimental and calculated band features are very similar to those of Cd-Yb. The modification of the band structure after surface treatment by sputtering and by oxidation is also studied. Additionally, the work function of i-Ag-In-Yb measured from the width of UPS spectrum is found to be almost unaffected by surface orientation, but increases after sputtering or oxidation.

  14. Rotational structure in the XECL laser bands at 308 nm

    SciTech Connect

    Singh, M.; Suri, B.M.; Kapoor, R.; Saksena, G.D.; Rao, P.R.K.

    1986-03-01

    The spectrum of XeCl laser emission around 308 nm, photographed and photoelectrically recorded on a 1.5 m monochromator, is presented. The spectrum, recorded at the highest resolution so far, shows partially resolved structure of the violet degraded 0--1 and 0--2 bands of XeCl. The rotational structure of these bands is simulated using estimated rotational constants of XeCl available in literature. Observed and simulated rotational structures are compared. Intracavity absorption is conspicuous in the 0--2 band.

  15. Electronic band structure study of colossal magnetoresistance in Tl 2Mn 2O 7

    NASA Astrophysics Data System (ADS)

    Seo, D.-K.; Whangbo, M.-H.; Subramanian, M. A.

    1997-02-01

    The electronic structure of Tl 2Mn 2O 7 was examined by performing tight binding band calculations. The overlap between the Mn t 2g- and Tl 6 s-block bands results in a partial filling of the Tl 6 s-block bands. The associated Fermi surface consists of 12 cigar-shape electron pockets with each electron pocket about {1}/{1000} of the first Brillouin zone in size. The Tl 6 s-block bands have orbital contributions from the Mn atoms, and the carrier density is very low. These are important for the occurrence of a colossal magnetoresistance in Tl 2Mn 2O 7.

  16. Experimental studies of band-structure properties in Bloch transistors

    NASA Astrophysics Data System (ADS)

    Flees, Daniel John

    A Bloch transistor consists of two small Josephson tunnel junctions connected in series, forming an isolated superconducting island between the source and drain. In the absence of coherence the system has a set of well-defined discrete energy states. The separation between these states corresponds to the electrostatic energy associated with the addition of one excess Cooper-pair on the island. When the system is placed in a particular state, fluctuations in the number of Cooper-pairs on the island are suppressed if the temperature is reduced well below the charging energy of the island. An electrostatically coupled gate electrode can thus be used to control the total charge on the island at the level of a single Cooper-pair. Since the tunneling of Cooper-pairs through the junctions is elastic, all states of the circuit corresponding to an exchange of Cooper-pairs between source and drain are coherently coupled. The degeneracy associated with this property leads to an energy-band structure analogous to the Bloch bands found in crystalline solids. In the Bloch transistor, each band can support a zero-voltage supercurrent. The maximum such current for each energy-band is determined by the band structure. A small applied voltage on the gate electrode can be used to modulate the supercurrents of the bands and the band gaps. The first direct observation of this energy-band structure has been obtained using microwave-induced interband transistions to probe the band gap. The measured band gap agrees well with the theoretical predictions both in the case where the transistor has symmetric junctions and in the asymmetric case where a coherence-induced gap splitting appears at the point of electrostatic degeneracy. The latter result, taken together with the quantitative agreement between the observed supercurrrent modulation and the predictions of the energy-band model, indicates that the Bloch transistor is well described by coherent mixing of discrete charge states on the island.

  17. Monolayer-induced band shifts at Si(100) and Si(111) surfaces

    SciTech Connect

    Mkinen, A. J. Kim, Chul-Soo; Kushto, G. P.

    2014-01-27

    We report our study of the interfacial electronic structure of Si(100) and Si(111) surfaces that have been chemically modified with various organic monolayers, including octadecene and two para-substituted benzene derivatives. X-ray photoelectron spectroscopy reveals an upward band shift, associated with the assembly of these organic monolayers on the Si substrates, that does not correlate with either the dipole moment or the electron withdrawing/donating character of the molecular moieties. This suggests that the nature and quality of the self-assembled monolayer and the intrinsic electronic structure of the semiconductor material define the interfacial electronic structure of the functionalized Si(100) and Si(111) surfaces.

  18. 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.

  19. Banded Electron Structure Formation in the Inner Magnetosphere

    NASA Technical Reports Server (NTRS)

    Liemohn, M. W.; Khazanov, G. V.

    1997-01-01

    Banded electron structures in energy-time spectrograms have been observed in the inner magnetosphere concurrent with a sudden relaxation of geomagnetic activity. In this study, the formation of these banded structures is considered with a global, bounce-averaged model of electron transport, and it is concluded that this structure is a natural occurrence when plasma sheet electrons are captured on closed drift paths near the Earth. These bands do not appear unless there is capture of plasma sheet electrons; convection along open drift paths making open pass around the Earth do not have time to develop this feature. The separation of high-energy bands from the injection population due to the preferential advection of the gradient-curvature drift creates spikes in the energy distribution, which overlap to form a series of bands in the energy spectrograms. The lowest band is the bulk of the injected population in the sub-key energy range. Using the Kp history for an observed banded structure event, a cloud of plasma sheet electrons is captured and the development of their distribution function is examined and discussed.

  20. 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

  1. Quasi one-dimensional band dispersion and surface metallization in long-range ordered polymeric wires

    DOE PAGESBeta

    Vasseur, Guillaume; Fagot-Revurat, Yannick; Sicot, Muriel; Kierren, Bertrand; Moreau, Luc; Malterre, Daniel; Cardenas, Luis; Galeotti, Gianluca; Lipton-Duffin, Josh; Rosei, Frederico; et al

    2016-01-04

    We study the electronic structure of an ordered array of poly(para-phenylene) chains produced by surface-catalyzed dehalogenative polymerization of 1,4-dibromobenzene on copper (110). The quantization of unoccupied molecular states is measured as a function of oligomer length by scanning tunnelling spectroscopy, with Fermi level crossings observed for chains longer than ten phenyl rings. Angle-resolved photoelectron spectroscopy reveals a quasi-one-dimensional valence band as well as a direct gap of 1.15 eV, as the conduction band is partially filled through adsorption on the surface. Tight-binding modelling and ab initio density functional theory calculations lead to a full description of the organic band-structure, includingmore » the k-dispersion, the gap size and electron charge transfer mechanisms, highlighting a strong substrate-molecule interaction that drives the system into a metallic behaviour. In summary, we have fully characterized the band structure of a carbon-based conducting wire. This model system may be considered as a fingerprint of -conjugation of surface organic frameworks.« less

  2. Quasi one-Dimensional Band Dispersion and Surface Metallization in Long Range Ordered Polymeric Wires

    SciTech Connect

    Vasseur, Guillaume; Fagot-Revurat, Yannick; Sicot, Muriel; Kierren, Bertrand; Moreau, Luc; Malterre, Daniel; Cardenas, Luis; Galeotti, Gianluca; Lipton-Duffin, Josh; Rosei, Frederico; Giovannantonio, Marco; Giorgio, Contini; Fèvre, Patrick; Bertran, François; Liang, Liangbo; Meunier, Vincent; Perepichka, Dmytro

    2016-01-01

    We study the electronic structure of an ordered array of poly(para-phenylene) chains produced by surface-catalyzed dehalogenative polymerization of 1,4-dibromobenzene on copper (110). The quantization of unoccupied molecular states is measured as a function of oligomer length by scanning tunnelling spectroscopy, with Fermi level crossings observed for chains longer than ten phenyl rings. Angle-resolved photoelectron spectroscopy reveals a quasi-one-dimensional valence band as well as a direct gap of 1.15 eV, as the conduction band is partially filled through adsorption on the surface. Tight-binding modelling and ab initio density functional theory calculations lead to a full description of the organic band-structure, including the k-dispersion, the gap size and electron charge transfer mechanisms, highlighting a strong substrate-molecule interaction that drives the system into a metallic behaviour. In summary, we have fully characterized the band structure of a carbon-based conducting wire. This model system may be considered as a fingerprint of -conjugation of surface organic frameworks.

  3. 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.

  4. 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

  5. Development of X-Band Dielectric-Loaded Accelerating Structures

    SciTech Connect

    Gold, S. H.; Jing, C.; Kanareykin, A.; Gai, W.; Konecny, R.; Power, J. G.; Kinkead, A. K.

    2010-11-04

    This paper presents a progress report on the development and testing of X-band dielectric-loaded accelerating structures. Recent tests on several quartz DLA structures with different inner diameters are reported. Designs for gap-free DLA structures are presented. Also, planned new experiments are discussed, including higher gradient traveling-wave and standing-wave structures and special grooved structures for multipactor suppression.

  6. Brain surface parameterization using Riemann surface structure.

    PubMed

    Wang, Yalin; Gu, Xianfeng; Hayashi, Kiralee M; Chan, Tony F; Thompson, Paul M; Yau, Shing-Tung

    2005-01-01

    We develop a general approach that uses holomorphic 1-forms to parameterize anatomical surfaces with complex (possibly branching) topology. Rather than evolve the surface geometry to a plane or sphere, we instead use the fact that all orientable surfaces are Riemann surfaces and admit conformal structures, which induce special curvilinear coordinate systems on the surfaces. Based on Riemann surface structure, we can then canonically partition the surface into patches. Each of these patches can be conformally mapped to a parallelogram. The resulting surface subdivision and the parameterizations of the components are intrinsic and stable. To illustrate the technique, we computed conformal structures for several types of anatomical surfaces in MRI scans of the brain, including the cortex, hippocampus, and lateral ventricles. We found that the resulting parameterizations were consistent across subjects, even for branching structures such as the ventricles, which are otherwise difficult to parameterize. Compared with other variational approaches based on surface inflation, our technique works on surfaces with arbitrary complexity while guaranteeing minimal distortion in the parameterization. It also offers a way to explicitly match landmark curves in anatomical surfaces such as the cortex, providing a surface-based framework to compare anatomy statistically and to generate grids on surfaces for PDE-based signal processing. PMID:16686016

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

    PubMed

    Holz, M; Chen, S H

    1979-05-01

    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. PMID:400469

  8. 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

  9. Complex band structure of nanostructured metal-dielectric metamaterials.

    PubMed

    Orlov, Alexey; Iorsh, Ivan; Belov, Pavel; Kivshar, Yuri

    2013-01-28

    We study complex eigenmodes of layered metal-dielectric metamaterials. Varying losses from weak to realistic, we analyze band structure of the metamaterial and clarify effect of losses on its intrinsic electromagnetic properties. The structure operates in a regime with infinite numbers of eigenmodes, whereas we analyze dominant ones. PMID:23389143

  10. Tunable surface band gap in MgxZn1-xO thin films

    NASA Astrophysics Data System (ADS)

    Xue, Mingshan; Guo, Qinlin; Wu, Kehui; Guo, Jiandong

    2008-12-01

    MgxZn1-xO thin films epitaxially grown on Mo(110) substrate under ultrahigh vacuum condition were studied in situ by various surface analysis techniques including x-ray photoelectron spectroscopy, Auger electron spectroscopy, low-energy electron diffraction, and high resolution electron energy loss spectroscopy. The results indicate that as-grown MgxZn1-xO films are soluble phase, and a phase transition from wurtzite to cubic structure occurs in the region of x =0.55-0.67. The surface band gap can be tuned continuously with altering the content of Mg in MgxZn1-xO films, and its tunable window width is about 1.9 eV. Based on heterojunction and quantum well structure, this kind of materials can be applied in wide-band-gap semiconductor devices, such as short-wavelength light-emitting devices.

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

    SciTech Connect

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

    2013-12-04

    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.

  12. Band structure of hydrogenated silicene on Ag(111): Evidence for half-silicane

    NASA Astrophysics Data System (ADS)

    Wang, W.; Olovsson, W.; Uhrberg, R. I. G.

    2016-02-01

    In the case of graphene, hydrogenation removes the conductivity due to the bands forming the Dirac cone by opening up a band gap. This type of chemical functionalization is of the utmost importance for electronic applications. As predicted by theoretical studies, a similar change in the band structure is expected for silicene, the closest analog to graphene. We here report a study of the atomic and electronic structures of hydrogenated silicene with hydrogen on one side, the so-called half-silicane. The ("2 √{3 }×2 √{3 } ") phase of silicene on Ag(111) was used in this Rapid Communication since it can be formed homogeneously across the entire surface of the Ag substrate. Low-energy electron diffraction and scanning tunneling microscopy data clearly show that hydrogenation changes the structure of silicene on Ag(111) resulting in a (1 × 1) periodicity with respect to the silicene lattice. The hydrogenated silicene also exhibits a quasiregular (2 √{3 }×2 √{3 } )-like arrangement of vacancies. Angle-resolved photoelectron spectroscopy revealed two dispersive bands which can be unambiguously assigned to half-silicane. The common top of these bands is located at ˜0.9 eV below the Fermi level. We find that the experimental bands are closely reproduced by the theoretical band structure of free-standing silicene with H adsorbed on the upper hexagonal sublattice.

  13. Quasi one-dimensional band dispersion and surface metallization in long-range ordered polymeric wires

    NASA Astrophysics Data System (ADS)

    Vasseur, Guillaume; Fagot-Revurat, Yannick; Sicot, Muriel; Kierren, Bertrand; Moreau, Luc; Malterre, Daniel; Cardenas, Luis; Galeotti, Gianluca; Lipton-Duffin, Josh; Rosei, Federico; di Giovannantonio, Marco; Contini, Giorgio; Le Fèvre, Patrick; Bertran, François; Liang, Liangbo; Meunier, Vincent; Perepichka, Dmitrii F.

    2016-01-01

    On-surface covalent self-assembly of organic molecules is a very promising bottom-up approach for producing atomically controlled nanostructures. Due to their highly tuneable properties, these structures may be used as building blocks in electronic carbon-based molecular devices. Following this idea, here we report on the electronic structure of an ordered array of poly(para-phenylene) nanowires produced by surface-catalysed dehalogenative reaction. By scanning tunnelling spectroscopy we follow the quantization of unoccupied molecular states as a function of oligomer length, with Fermi level crossing observed for long chains. Angle-resolved photoelectron spectroscopy reveals a quasi-1D valence band as well as a direct gap of 1.15 eV, as the conduction band is partially filled through adsorption on the surface. Tight-binding modelling and ab initio density functional theory calculations lead to a full description of the band structure, including the gap size and charge transfer mechanisms, highlighting a strong substrate-molecule interaction that drives the system into a metallic behaviour.

  14. Quasi one-dimensional band dispersion and surface metallization in long-range ordered polymeric wires.

    PubMed

    Vasseur, Guillaume; Fagot-Revurat, Yannick; Sicot, Muriel; Kierren, Bertrand; Moreau, Luc; Malterre, Daniel; Cardenas, Luis; Galeotti, Gianluca; Lipton-Duffin, Josh; Rosei, Federico; Di Giovannantonio, Marco; Contini, Giorgio; Le Fèvre, Patrick; Bertran, François; Liang, Liangbo; Meunier, Vincent; Perepichka, Dmitrii F

    2016-01-01

    On-surface covalent self-assembly of organic molecules is a very promising bottom-up approach for producing atomically controlled nanostructures. Due to their highly tuneable properties, these structures may be used as building blocks in electronic carbon-based molecular devices. Following this idea, here we report on the electronic structure of an ordered array of poly(para-phenylene) nanowires produced by surface-catalysed dehalogenative reaction. By scanning tunnelling spectroscopy we follow the quantization of unoccupied molecular states as a function of oligomer length, with Fermi level crossing observed for long chains. Angle-resolved photoelectron spectroscopy reveals a quasi-1D valence band as well as a direct gap of 1.15 eV, as the conduction band is partially filled through adsorption on the surface. Tight-binding modelling and ab initio density functional theory calculations lead to a full description of the band structure, including the gap size and charge transfer mechanisms, highlighting a strong substrate-molecule interaction that drives the system into a metallic behaviour. PMID:26725974

  15. GW quasiparticle band structures of stibnite, antimonselite, bismuthinite, and guanajuatite

    NASA Astrophysics Data System (ADS)

    Filip, Marina R.; Patrick, Christopher E.; Giustino, Feliciano

    2013-05-01

    We present first-principles calculations of the quasiparticle band structures of four isostructural semiconducting metal chalcogenides A2B3 (with A = Sb, Bi and B = S, Se) of the stibnite family within the G0W0 approach. We perform extensive convergence tests and identify a sensitivity of the quasiparticle corrections to the structural parameters and to the semicore d electrons. Our calculations indicate that all four chalcogenides exhibit direct band gaps, if we exclude some indirect transitions marginally below the direct gap. Relativistic spin-orbit effects are evaluated for the Kohn-Sham band structures, and included as scissor corrections in the quasiparticle band gaps. Our calculated band gaps are 1.5 eV (Sb2S3), 1.3 eV (Sb2Se3), 1.4 eV (Bi2S3), and 0.9 eV (Bi2Se3). By comparing our calculated gaps with the ideal Shockley-Queisser value we find that all four chalcogenides are promising as light sensitizers for nanostructured photovoltaics.

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

    NASA Astrophysics Data System (ADS)

    Teichmann, Martin; Frietsch, Bjrn; Dbrich, 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.

  17. Band structure engineering at heterojunction interfaces via the piezotronic effect.

    PubMed

    Shi, Jian; Starr, Matthew B; Wang, Xudong

    2012-09-01

    Engineering the electronic band structure using the piezopotential is an important aspect of piezotronics, which describes the coupling between the piezoelectric property and semiconducting behavior and functionalities. The time-independent band structure change under short-circuit condition is believed to be due to the remnant piezopotential present at the interface, a result of the finite charge-screening depth at the interface. A series of materials, including metals, semiconductors and electrolytes, are selected to investigate the interfacial band structure engineered by remnant piezopotential when they are in contact with a strained piezoelectric semiconductor. The remnant piezopotential at the interface can switch the junction between Ohmic and Schottky characters, enhance charge combination/separation, regulate barrier height, and modulate reaction kinetics. The difference between the regular time-dependent, pulse-type piezopotential and constant remnant piezopotential is also discussed in detail using a ZnO-based photoelectrochemical anode as an example. The piezotronic effect offers a new pathway for engineering the interface band structure without altering the interface structure or chemical composition, which is promising for improving the performance of many electronics, optoelectronics, and photovoltaic devices. PMID:22549965

  18. Band-structure loops and multistability in cavity QED

    SciTech Connect

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

    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)].

  19. 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)].

  20. Interfacial chemistry and energy band line-up of pentacene with the GaN (0 0 0 1) surface

    NASA Astrophysics Data System (ADS)

    Uhlrich, J.; Garcia, M.; Wolter, S.; Brown, A. S.; Kuech, T. F.

    2007-03-01

    The chemical nature of the GaN surface combined with the bulk and surface electronic structure opens new potential application areas for this material. The nature of specific organic-GaN was developed for two cases in which the surface electronic structure of such interfaces was developed and utilized. The band alignment between n-GaN and pentacene was determined for surfaces prepared through reaction with HCl. The energy band offset was estimated through combined X-ray photoelectron spectroscopy and ultraviolet photoemission measurements. XPS measurements indicated that there was no interfacial chemical reaction. The measured valence band offset between the n-GaN and the vapor-deposited pentacene was estimated to be greater than 2 eV providing a favorable band-offset for hole-injection from the GaN layer into pentacene. The surface of a AlGaN/GaN heterojunction field effect transistor (HFET) structures was also functionalized by an adsorbed hemin layer and was shown to be sensitive to the presence of reactive species such as NO. The HFET structure provides enhanced sensitivity to changes in the surface electric field, altered through the adsorption of chemically active species either directly on the surface or through the interactions with surface functionalization.

  1. Band energy control of molybdenum oxide by surface hydration

    NASA Astrophysics Data System (ADS)

    Butler, Keith T.; Crespo-Otero, Rachel; Buckeridge, John; Scanlon, David O.; Bovill, Edward; Lidzey, David; Walsh, Aron

    2015-12-01

    The application of oxide buffer layers for improved carrier extraction is ubiquitous in organic electronics. However, the performance is highly susceptible to processing conditions. Notably, the interface stability and electronic structure is extremely sensitive to the uptake of ambient water. In this study we use density functional theory calculations to asses the effects of adsorbed water on the electronic structure of MoOx, in the context of polymer-fullerene solar cells based on PCDTBT. We obtain excellent agreement with experimental values of the ionization potential for pristine MoO3 (010). We find that IP and EA values can vary by as much as 2.5 eV depending on the oxidation state of the surface and that adsorbed water can either increase or decrease the IP and EA depending on the concentration of surface water.

  2. Electronic band structure of magnetic bilayer graphene superlattices

    SciTech Connect

    Pham, C. Huy; Nguyen, T. Thuong

    2014-09-28

    Electronic band structure of the bilayer graphene superlattices with δ-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.

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

    SciTech Connect

    Dey, Anup; Maiti, Biswajit; Chanda, Debasree

    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 IIIV 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.

  4. Tailoring band gaps of insulators by adsorption at surface defects: Benzoic acids on NaCl surfaces

    NASA Astrophysics Data System (ADS)

    Chen, Wei; Tegenkamp, Christoph; Pfnr, Herbert; Bredow, Thomas

    2009-06-01

    The adsorption of benzoic acid and its OH-substituted derivatives, namely, salicylic acid (SA) and parasalicylic acid on various NaCl surfaces has been investigated by density-functional theory with hybrid exchange-correlation functional. The ideal NaCl(100) surface is chemically inert as evidenced by the low binding energies. The molecular adsorption can be enhanced by both an anion vacancy and a surface step site. The bonding between the surface Na and the carboxylic O atom is of covalent character for all adsorption geometries. Our calculations show that the adsorption of SA has the largest binding energy of all three acids due to the additional interaction between Na and the phenolic O atom. Charge transfer between the molecule and the surface is generally very small, except in the presence of an anion vacancy where the unpaired electron is mostly transferred to the adsorbate. Surface defects generally have a strong influence on the electronic structure of the adsorbed molecules. Specifically, the adsorption of SA at [011]-oriented steps can significantly reduce the effective band gap to 1.6 eV due to the up shift of the Cl3p levels at the undercoordinated step edge. Implications of these results to the contact charging effect between wide-band-gap insulators will be discussed.

  5. Coupling effect of quantum wells on band structure

    NASA Astrophysics Data System (ADS)

    Jie, Chen; Weiyou, Zeng

    2015-10-01

    The coupling effects of quantum wells on band structure are numerically investigated by using the Matlab programming language. In a one dimensional finite quantum well with the potential barrier V0, the calculation is performed by increasing the number of inserted barriers with the same height Vb, and by, respectively, varying the thickness ratio of separated wells to inserted barriers and the height ratio of Vb to V0. Our calculations show that coupling is strongly influenced by the above parameters of the inserted barriers and wells. When these variables change, the width of the energy bands and gaps can be tuned. Our investigation shows that it is possible for quantum wells to achieve the desired width of the bands and gaps.

  6. 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

  7. 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.

  8. Development of X-band accelerating structures for high gradients

    NASA Astrophysics Data System (ADS)

    Bini, S.; Chimenti, V.; Marcelli, A.; Palumbo, L.; Spataro, B.; A. Dolgashev, V.; Tantawi, S.; D. Yeremian, A.; Higashi, Y.; G. Grimaldi, M.; Romano, L.; Ruffino, F.; Parodi, R.

    2012-07-01

    Short copper standing wave (SW) structures operating at an X-band frequency have been recently designed and manufactured at the Laboratori Nazionali di Frascati of the Istituto Nazionale di Fisica Nucleare (INFN) using the vacuum brazing technique. High power tests of the structures have been performed at the SLAC National Accelerator Laboratory. In this manuscript we report the results of these tests and the activity in progress to enhance the high gradient performance of the next generation of structures, particularly the technological characterization of high performance coatings obtained via molybdenum sputtering.

  9. Band structure of the quasi two-dimensional purple molybdenum bronze

    NASA Astrophysics Data System (ADS)

    Guyot, H.; Balaska, H.; Perrier, P.; Marcus, J.

    2006-09-01

    The molybdenum purple bronze KMo 6O 17 is quasi two-dimensional (2D) metallic oxide that shows a Peierls transition towards a metallic charge density wave state. Since this specific transition is directly related to the electron properties of the normal state, we have investigated the electronic structure of this bronze at room temperature. The shape of the Mo K1s absorption edge reveals the presence of distorted MoO 6 octahedra in the crystallographic structure. Photoemission experiments evidence a large conduction band, with a bandwidth of 800 meV and confirm the metallic character of this bronze. A wide depleted zone separates the conduction band from the valence band that exhibits a fourfold structure, directly connected to the octahedral symmetry of the Mo sites. The band structure is determined by ARUPS in two main directions of the (0 0 1) Brillouin zone. It exhibits some unpredicted features but corroborates the earlier theoretical band structure and Fermi surface. It confirms the hidden one-dimensionality of KMo 6O 17 that has been proposed to explain the origin of the Peierls transition in this 2D compound.

  10. 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.

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

    PubMed Central

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

    2012-01-01

    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. PMID:23152944

  12. 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 metalinsulatormetal 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

  13. 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.

  14. Gold bands as a suitable surface for enzyme immunoassays.

    PubMed

    Abad-Villar, Eva M; Fernndez-Abedul, M Teresa; Costa-Garca, Agustn

    2002-09-01

    Gold bands sputtered over a polymeric material, Kapton, are employed for the development of enzyme immunoassays. The immunological interaction takes place between human IgM and alkaline phosphatase (AP) conjugated anti-IgM. The model analyte (IgM) could be determined following a non-competitive design in the range of 0.05-5 ppm, with a limit of detection of 50 ppb. After the interaction, gold bands are sequentially inserted in a flow system and the extension of the reaction is followed through the enzymatic hydrolysis of naphthylphosphate, AP substrate. The product, naphthol, is oxidised to naphtoquinone in the gold band of the flow cell that constitutes the detector. Parameters affecting the interaction are studied and calibration curves are performed. The reproducibility between different bands (RSD=4%, n=5) and possibilities of regeneration are also detailed. PMID:12191928

  15. Two-Phase Shear Band Structures at Uniform Stress

    NASA Astrophysics Data System (ADS)

    Britton, Melanie M.; Callaghan, Paul T.

    1997-06-01

    Using NMR microscopy we measure the velocity distribution for a wormlike surfactant solution in the gap of a small angle cone-and-plate rheometer. This system, cetylpyridinium chloride/sodium salicylate 100 mM/60 mM, exhibits biphasic shear band structure when the applied shear rate exceeds the critical rate of strain beyond which a plateau is observed in the shear stress. The structure is characterized by two low/high shear interfaces and the region of high shear evolves by increasing width as the average gap shear is increased.

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

    SciTech Connect

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

    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.

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

    SciTech Connect

    Majumdar, Kausik

    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.

  18. 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.

  19. Coupler Design for the LCLS Injector S-Band Structures

    SciTech Connect

    Li, Z.; Bentson, L.D.; Chan, J.; Dowell, D.H.; Limborg-Deprey, C.; Schmerge, J.F.; Schultz, D.C.; Xiao, L.; /SLAC

    2006-03-03

    The LCLS injector is required to provide a 1-nC, 10-ps bunch with a normalized rms transverse projected emittance of less than 1 micron. The LCLS beam is generated and accelerated in a 1.6-cell S-band RF gun at 120 MV/m up to 6 MeV. The gun is followed by two SLAC 3-m S-band accelerator structures to further accelerate the beam to 135 MeV which moves the beam out of the space-charge dominated regime. In the SLAC S-band structures, the RF power feed is through a single coupling-hole (single-feed coupler) which results in a field asymmetry. The time dependent multipole fields in the coupler induce a transverse kick along the bunch and cause the emittance to increase above the LCLS specification. To meet the stringent emittance requirements for the injector, the single-feed couplers will be replaced by a dual-feed racetrack design to minimize the multipole field effects. We will present detailed studies of the multipole fields in the SLAC linac RF coupler and the improvements with the dual-feed ractrack design using the parallel finite element S-parameter solver S3P.

  20. Simple metamaterial structure enabling triple-band perfect absorber

    NASA Astrophysics Data System (ADS)

    Van Dung, Nguyen; Son Tung, Bui; Khuyen, Bui Xuan; Yoo, Young Joon; Kim, Young Ju; Rhee, Joo Yull; Dinh Lam, Vu; Pak Lee, Young

    2015-09-01

    Two resonators in metamaterial usually correspond only to two absorption peaks. In this report, by breaking the symmetry, we could create multi-fundamental resonances at GHz frequencies in both simulation and experiment. First, a dual-band metamaterial absorber (MA) was achieved for 4.6 and 10.6 GHz. Next, by modifying the relative position of inner square, the triple-band MA was obtained with enhanced absorption properties. In addition, dependence on the polarization of the incident electromagnetic (EM) wave was clarified. The mechanism is elucidated to be an alteration of the coupling strength, which is made by changing the geometrical configuration of the inner square and the outer ring. It is shown that our structural configuration can be applied to the fields where the interaction with a wide range of EM waves exists or is needed.

  1. 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.

  2. 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.

  3. Simultaneous Multi-band Detection of Low Surface Brightness Galaxies with Markovian Modeling

    NASA Astrophysics Data System (ADS)

    Vollmer, B.; Perret, B.; Petremand, M.; Lavigne, F.; Collet, Ch.; van Driel, W.; Bonnarel, F.; Louys, M.; Sabatini, S.; MacArthur, L. A.

    2013-02-01

    We present to the astronomical community an algorithm for the detection of low surface brightness (LSB) galaxies in images, called MARSIAA (MARkovian Software for Image Analysis in Astronomy), which is based on multi-scale Markovian modeling. MARSIAA can be applied simultaneously to different bands. It segments an image into a user-defined number of classes, according to their surface brightness and surroundingstypically, one or two classes contain the LSB structures. We have developed an algorithm, called DetectLSB, which allows the efficient identification of LSB galaxies from among the candidate sources selected by MARSIAA. The application of the method to two and three bands simultaneously was tested on simulated images. Based on our tests, we are confident that we can detect LSB galaxies down to a central surface brightness level of only 1.5 times the standard deviation from the mean pixel value in the image background. To assess the robustness of our method, the method was applied to a set of 18 B- and I-band images (covering 1.3 deg2 in total) of the Virgo Cluster to which Sabatini et al. previously applied a matched-filter dwarf LSB galaxy search algorithm. We have detected all 20 objects from the Sabatini et al. catalog which we could classify by eye as bona fide LSB galaxies. Our method has also detected four additional Virgo Cluster LSB galaxy candidates undetected by Sabatini et al. To further assess the completeness of the results of our method, both MARSIAA, SExtractor, and DetectLSB were applied to search for (1) mock Virgo LSB galaxies inserted into a set of deep Next Generation Virgo Survey (NGVS) gri-band subimages and (2) Virgo LSB galaxies identified by eye in a full set of NGVS square degree gri images. MARSIAA/DetectLSB recovered ~20% more mock LSB galaxies and ~40% more LSB galaxies identified by eye than SExtractor/DetectLSB. With a 90% fraction of false positives from an entirely unsupervised pipeline, a completeness of 90% is reached for sources with r e > 3'' at a mean surface brightness level of ?g = 27.7 mag arcsec-2 and a central surface brightness of ?0 g = 26.7 mag arcsec-2. About 10% of the false positives are artifacts, the rest being background galaxies. We have found our proposed Markovian LSB galaxy detection method to be complementary to the application of matched filters and an optimized use of SExtractor, and to have the following advantages: it is scale free, can be applied simultaneously to several bands, and is well adapted for crowded regions on the sky. .

  4. 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.

  5. Band mixing and ambipolar transport by surface acoustic waves in GaAs quantum wells

    NASA Astrophysics Data System (ADS)

    Santos, P. V.; Alsina, F.; Stotz, J. A.; Hey, R.; Eshlaghi, S.; Wieck, A. D.

    2004-04-01

    The interaction of strong surface acoustic wave (SAW) fields with the electronic band structure of GaAs quantum wells (QWs) is investigated using spatially resolved photoluminescence (PL) spectroscopy. The optical studies are accompanied by k?p and tight-binding (TB) calculations of the SAW effects on the electronic band structure. The SAW induces a time-dependent coupling between the heavy- (hh) and light-hole (lh) states in the valence band of the QWs, which leads to an anticrossing of their energy levels for high SAW intensities. The coupling alters the strength and polarization of the optical transitions and can be reproduced by calculations of the optical transition matrix elements. Spatially resolved PL measurements of the SAW-induced ambipolar transport of electrons and holes provide evidence of a reduction of the transport efficiency for high SAW fields, which is attributed to a decrease of the hole mobility as the hh and lh levels approach each other. This conclusion is supported by TB calculations that show a significant enhancement of the heavy-hole effective mass under these conditions. In addition, the mobility may also be reduced by the squeezing of the wave functions towards the QW interfaces induced by strong piezoelectric fields, which makes the transport more sensitive to potential fluctuations induced by interface roughness and defects in the barrier layers.

  6. Birefringence and band structure of CdP2 crystals

    NASA Astrophysics Data System (ADS)

    Beril, S. I.; Stamov, I. G.; Syrbu, N. N.; Zalamai, V. V.

    2013-08-01

    The spatial dispersion in CdP2 crystals was investigated. The dispersion is positive (nk||?>nk||?) at ?>?0 and negative (nk||?bands. Minimal direct energy intervals correspond to transitions ?1??1 for ?||? and ?2??1 for ???. The temperature coefficient of energy gap sifting in the case of temperature changing between 2 and 4.2 K equals to 10.6 meV/K and 3.2 mev/K for ?1??1 and ?2??1 band gap correspondingly. Reflectivity spectra were measured for energy interval 1.5-10 eV and optical functions (n, k, ?1, ?2,d2?1/dE2 and d2?2/dE2) were calculated by using Kramers-Kronig analyses. All features were interpreted as optical transitions on the basis of both theoretical calculations of band structure.

  7. Band Structure Asymmetry of Bilayer Graphene Revealed by Infrared Spectroscopy

    SciTech Connect

    Li, Z.Q.; Henriksen, E.A.; Jiang, Z.; Hao, Zhao; Martin, Michael C.; Kim, P.; Stormer, H.L.; Basov, Dimitri N.

    2008-12-10

    We report on infrared spectroscopy of bilayer graphene integrated in gated structures. We observe a significant asymmetry in the optical conductivity upon electrostatic doping of electrons and holes. We show that this finding arises from a marked asymmetry between the valence and conduction bands, which is mainly due to the inequivalence of the two sublattices within the graphene layer and the next-nearest-neighbor interlayer coupling. From the conductivity data, the energy difference of the two sublattices and the interlayer coupling energy are directly determined.

  8. 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.

  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. Evidence for a diamondlike electronic band structure of Si multilayers on Ag(111)

    NASA Astrophysics Data System (ADS)

    Mahatha, S. K.; Moras, P.; Sheverdyaeva, P. M.; Flammini, R.; Horn, K.; Carbone, C.

    2015-12-01

    Silicon multilayers on Ag(111) have been suggested to exhibit the structure of silicene, a material that has been heralded as a novel basis for microelectronic applications. However, our angle-resolved photoemission spectra (ARPES) from silicon multilayers on Ag(111) and of the silver-induced reconstruction of Si(111) demonstrate, from the close match in the valence level band structures, that the films exhibit a s p3 diamondlike structure. This refutes the interpretation of silicon multilayers on Ag(111) as silicene, a conclusion that is strengthened by the observation from core level photoemission that significant silver segregation occurs to the surface of these layers.

  11. Probing the band-structures and carrier dynamics of single GaAsSb nanowire heterostructures

    NASA Astrophysics Data System (ADS)

    Wang, Yuda; Badada, Bekele; Jackson, Howard; Smith, Leigh; Yuan, Xiaoming; Caroff, Philippe; Fu, Lan; Tan, Hoe; Jagadish, Chennupati

    2015-03-01

    We present the band structure and carrier relaxation of MOVCD grown single GaAs1-xSbx using photocurrent (PC) spectroscopy and transient Rayleigh Scattering (TRS) spectroscopy techniques. The PC spectroscopy was performed on nanowire devices fabricated using e-beam lithography and deposition of Ti/Au as contacts. The devices show nearly Ohmic behavior and are photosensitive. PC spectra shows an onset of absorption at room temperature in agreement with reported values of bulk GaAs0.6Sb0.4. We also used low temperature (10K) transient Rayleigh scattering (TRS) spectroscopy to measure the band structure as well as carrier relaxation dynamics of individual GaAsSb (x=30% and 40%) nanowires with and without InP passivation layers. The band gaps extracted from the TRS experiments are consistent with both photoluminescence (PL) measurements and theoretical predictions. The InP passivated GaAsSb shows smaller Eg due to the tensile strain from InP on GaAsSb as well as longer lifetimes due to the surface passivation. The carrier density and temperature are extracted by a phenomenological fitting model based on band to band transition theory. We acknowledge the NSF through DMR-1105362, 1105121 and ECCS-1100489, and the Australian Research Council.

  12. Spin-dependent band structure of the ferromagnetic semimetal EuB6

    NASA Astrophysics Data System (ADS)

    Xiong, Peng; Zhang, X.; von Molnar, S.; Fisk, Z.

    2008-03-01

    The spin polarization of EuB6 crystals has been measured using Andreev reflection spectroscopy. The conductance spectra of the EuB6/Pb junctions are well-described by the spin-polarized BTK model, which yields a spin polarization of about 56%. The results demonstrate that ferromagnetic EuB6 is not half-metallic. Further analyses of the Hall effect and magnetoresistivity indicate a semi-metallic band structure with complete spin polarization for the hole band only. The values and the spread of the measured spin polarization are quantitatively consistent with Fermi surface determined by quantum oscillation measurements^1 and carrier densities obtained from standard two-band model fits to the low temperature magnetoresistivity and Hall resistivity. This work was supported by a FSU Research Foundation PEG, NSF DMR 0710492 and 0503360 grants. ^1R. Goodrich et al., PRB 58, 14896 (1998); M. Aronson et al., PRB 59, 4720 (1999).

  13. Multi-band polarization insensitive metamaterial absorber with dual cross-wires structure

    NASA Astrophysics Data System (ADS)

    Yao, Li-fang; Li, Min-hua; Zhai, Xiao-min; Wang, Hui-bo; Dong, Jian-feng

    2015-11-01

    A five-band metamaterial absorber (MMA) based on a simple planar structure is proposed. It utilizes different areas of a single unit cell to match impedance, and produces different absorptive frequencies. Numerical calculation shows that the MMA has five different absorption peaks at 3.78 GHz, 7.66 GHz, 10.9 GHz, 14.5 GHz and 16.7 GHz, and their absorption rates reach 95.5%, 98.6%, 95.7%, 96.6% and 99.8%, respectively. The proposed structure is polarization insensitive for transverse electric (TE) and transverse magnetic (TM) incident waves. Also, the absorptive characteristics over large incident angles are examined. In addition, we analyze the absorption mechanism by the surface current density and power flow density distributions. This simple structure provides a way to design multi-band MMA, and also saves the cost of fabrication.

  14. 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.

  15. Exciton Band Structure in Two-Dimensional Materials

    NASA Astrophysics Data System (ADS)

    Cudazzo, Pierluigi; Sponza, Lorenzo; Giorgetti, Christine; Reining, Lucia; Sottile, Francesco; Gatti, Matteo

    2016-02-01

    Low-dimensional materials differ from their bulk counterparts in many respects. In particular, the screening of the Coulomb interaction is strongly reduced, which can have important consequences such as the significant increase of exciton binding energies. In bulk materials the binding energy is used as an indicator in optical spectra to distinguish different kinds of excitons, but this is not possible in low-dimensional materials, where the binding energy is large and comparable in size for excitons of very different localization. Here we demonstrate that the exciton band structure, which can be accessed experimentally, instead provides a powerful way to identify the exciton character. By comparing the ab initio solution of the many-body Bethe-Salpeter equation for graphane and single-layer hexagonal boron nitride, we draw a general picture of the exciton dispersion in two-dimensional materials, highlighting the different role played by the exchange electron-hole interaction and by the electronic band structure. Our interpretation is substantiated by a prediction for phosphorene.

  16. Photonic band structure calculations using nonlinear eigenvalue techniques

    SciTech Connect

    Spence, Alastair; Poulton, Chris . E-mail: c.poulton@ihq.uni-karlsruhe.de

    2005-03-20

    This paper considers the numerical computation of the photonic band structure of periodic materials such as photonic crystals. This calculation involves the solution of a Hermitian nonlinear eigenvalue problem. Numerical methods for nonlinear eigenvalue problems are usually based on Newton's method or are extensions of techniques for the standard eigenvalue problem. We present a new variation on existing methods which has its derivation in methods for bifurcation problems, where bordered matrices are used to compute critical points in singular systems. This new approach has several advantages over the current methods. First, in our numerical calculations the new variation is more robust than existing techniques, having a larger domain of convergence. Second, the linear systems remain Hermitian and are nonsingular as the method converges. Third, the approach provides an elegant and efficient way of both thinking about the problem and organising the computer solution so that only one linear system needs to be factorised at each stage in the solution process. Finally, first- and higher-order derivatives are calculated as a natural extension of the basic method, and this has advantages in the electromagnetic problem discussed here, where the band structure is plotted as a set of paths in the ({omega},k) plane.

  17. Exciton Band Structure in Two-Dimensional Materials.

    PubMed

    Cudazzo, Pierluigi; Sponza, Lorenzo; Giorgetti, Christine; Reining, Lucia; Sottile, Francesco; Gatti, Matteo

    2016-02-12

    Low-dimensional materials differ from their bulk counterparts in many respects. In particular, the screening of the Coulomb interaction is strongly reduced, which can have important consequences such as the significant increase of exciton binding energies. In bulk materials the binding energy is used as an indicator in optical spectra to distinguish different kinds of excitons, but this is not possible in low-dimensional materials, where the binding energy is large and comparable in size for excitons of very different localization. Here we demonstrate that the exciton band structure, which can be accessed experimentally, instead provides a powerful way to identify the exciton character. By comparing the ab initio solution of the many-body Bethe-Salpeter equation for graphane and single-layer hexagonal boron nitride, we draw a general picture of the exciton dispersion in two-dimensional materials, highlighting the different role played by the exchange electron-hole interaction and by the electronic band structure. Our interpretation is substantiated by a prediction for phosphorene. PMID:26919006

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

    PubMed

    Lamba, Jasmeet; Srivastava, Puneet; Way, Thomas R; Sen, Sumit; Wood, C Wesley; Yoo, Kyung H

    2013-09-01

    Subsurface band application of poultry litter has been shown to reduce the transport of nutrients from fields in surface runoff compared with conventional surface broadcast application. Little research has been conducted to determine the effects of surface broadcast application and subsurface banding of litter on nutrients in leachate. Therefore, a field experiment was conducted to determine the effects of subsurface band application and surface broadcast application of poultry litter on nutrient losses in leachate. Zero-tension pan and passive capillary fiberglass wick lysimeters were installed in situ 50 cm beneath the soil surface of an established tall fescue ( Schreb.) pasture on a sandy loam soil. The treatments were surface broadcast and subsurface-banded poultry litter at 5 Mg ha and an unfertilized control. Results of the rainfall simulations showed that the concentrations of PO-P and total phosphorus (TP) in leachate were reduced by 96 and 37%, respectively, in subsurface-banded litter treatment compared with the surface-applied litter treatment. There was no significant difference in PO-P concentration between control and subsurface-banded litter treatment in leachate. The trend in the loading of nutrients in leachate was similar to the trend in concentration. Concentration and loading of the nutrients (TP, PO-P, NH-N, and NO-N) in runoff from the subsurface-banded treatment were significantly less than for the surface-applied treatment and were similar to those from control plots. These results show that, compared with conventional surface broadcast application of litter, subsurface band application of litter can greatly reduce loss of P in surface runoff and leachate. PMID:24216435

  19. InGaAs inversion layers band structure, electrostatics, and mobility modeling based on 8 band k → · p → theory

    NASA Astrophysics Data System (ADS)

    Pham, Anh-Tuan; Jin, Seonghoon; Choi, Woosung; Lee, Myoung-Jae; Cho, Seong-Ho; Kim, Young-Tae; Lee, Keun-Ho; Park, Youngkwan

    2015-11-01

    8 band k → · p → method is used to calculate subband structures of InGaAs inversion layers accounting for strong coupling between conduction and valence bands around Γ point as well as quantum confinement. Inversion layer mobility is computed employing Kubo-Greenwood formalism. Scatterings due to acoustic phonons, polar optical phonons, ionized impurities, interface fixed charges, surface roughness, and alloy disorder are included. The simulated low-field electron mobility results are in good agreement with experimental data with and without an InP capping layer.

  20. 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...

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

    SciTech Connect

    Sahdan, Muhammad Fauzi Darma, Yudi

    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.

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

    SciTech Connect

    Minaye Hashemi, Fatemeh Sadat; Laboratoire des Materiaux Semiconducteurs, Ecole Polytechnique Federale de Lausanne, 1015 Lausanne ; Thombare, Shruti; Brongersma, Mark L.; Morral, Anna Fontcuberta i; McIntyre, Paul C.; Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305

    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.

  3. Band structure of ABC-trilayer graphene superlattice

    SciTech Connect

    Uddin, Salah Chan, K. S.

    2014-11-28

    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 k{sub y} direction for k{sub x}?=?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

    Smith, Andrew M; Nie, Shuming

    2010-02-16

    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. Manifestation of a Second Dirac Surface State and Bulk Bands in THz Radiation from Topological Insulators.

    PubMed

    Tu, Chien-Ming; Yeh, Tien-Tien; Tzeng, Wen-Yen; Chen, Yi-Ru; Chen, Hsueh-Ju; Ku, Shin-An; Luo, Chih-Wei; Lin, Jiunn-Yuan; Wu, Kaung-Hsiung; Juang, Jenh-Yih; Kobayashi, Takayoshi; Cheng, Cheng-Maw; Tsuei, Ku-Ding; Berger, Helmuth; Sankar, Raman; Chou, Fang-Cheng

    2015-01-01

    Topological insulators (TIs) are interesting quantum matters that have a narrow bandgap for bulk and a Dirac-cone-like conducting surface state (SS). The recent discovered second Dirac surface state (SS) and bulk bands (BBs) located ~1.5?eV above the first SS are important for optical coupling in TIs. Here, we report on the time-domain measurements of THz radiation generated from TIs n-type Cu(0.02)Bi2Se3 and p-type Bi2Te3 single crystals by ultrafast optical pulse excitation. The observed polarity-reversal of the THz pulse originated from transient current is unusual, and cannot be reconciled with the photo-Dember effect. The second SS and BBs are found to be indispensable for the explanation of the unusual phenomenon. Thanks to the existence of the second SS and BBs, TIs manifest an effective wide band gap in THz generation. The present study demonstrates that time-domain THz spectroscopy provide rich information of the optical coupling and the electronic structure of TIs. PMID:26370337

  6. Manifestation of a Second Dirac Surface State and Bulk Bands in THz Radiation from Topological Insulators

    PubMed Central

    Tu, Chien-Ming; Yeh, Tien-Tien; Tzeng, Wen-Yen; Chen, Yi-Ru; Chen, Hsueh-Ju; Ku, Shin-An; Luo, Chih-Wei; Lin, Jiunn-Yuan; Wu, Kaung-Hsiung; Juang, Jenh-Yih; Kobayashi, Takayoshi; Cheng, Cheng-Maw; Tsuei, Ku-Ding; Berger, Helmuth; Sankar, Raman; Chou, Fang-Cheng

    2015-01-01

    Topological insulators (TIs) are interesting quantum matters that have a narrow bandgap for bulk and a Dirac-cone-like conducting surface state (SS). The recent discovered second Dirac surface state (SS) and bulk bands (BBs) located ~1.5?eV above the first SS are important for optical coupling in TIs. Here, we report on the time-domain measurements of THz radiation generated from TIs n-type Cu0.02Bi2Se3 and p-type Bi2Te3 single crystals by ultrafast optical pulse excitation. The observed polarity-reversal of the THz pulse originated from transient current is unusual, and cannot be reconciled with the photo-Dember effect. The second SS and BBs are found to be indispensable for the explanation of the unusual phenomenon. Thanks to the existence of the second SS and BBs, TIs manifest an effective wide band gap in THz generation. The present study demonstrates that time-domain THz spectroscopy provide rich information of the optical coupling and the electronic structure of TIs. PMID:26370337

  7. Manifestation of a Second Dirac Surface State and Bulk Bands in THz Radiation from Topological Insulators

    NASA Astrophysics Data System (ADS)

    Tu, Chien-Ming; Yeh, Tien-Tien; Tzeng, Wen-Yen; Chen, Yi-Ru; Chen, Hsueh-Ju; Ku, Shin-An; Luo, Chih-Wei; Lin, Jiunn-Yuan; Wu, Kaung-Hsiung; Juang, Jenh-Yih; Kobayashi, Takayoshi; Cheng, Cheng-Maw; Tsuei, Ku-Ding; Berger, Helmuth; Sankar, Raman; Chou, Fang-Cheng

    2015-09-01

    Topological insulators (TIs) are interesting quantum matters that have a narrow bandgap for bulk and a Dirac-cone-like conducting surface state (SS). The recent discovered second Dirac surface state (SS) and bulk bands (BBs) located ~1.5?eV above the first SS are important for optical coupling in TIs. Here, we report on the time-domain measurements of THz radiation generated from TIs n-type Cu0.02Bi2Se3 and p-type Bi2Te3 single crystals by ultrafast optical pulse excitation. The observed polarity-reversal of the THz pulse originated from transient current is unusual, and cannot be reconciled with the photo-Dember effect. The second SS and BBs are found to be indispensable for the explanation of the unusual phenomenon. Thanks to the existence of the second SS and BBs, TIs manifest an effective wide band gap in THz generation. The present study demonstrates that time-domain THz spectroscopy provide rich information of the optical coupling and the electronic structure of TIs.

  8. 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

  9. Domain structures in nematic liquid crystals on a polycarbonate surface.

    PubMed

    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

  10. Coherent structures on fault surfaces

    NASA Astrophysics Data System (ADS)

    Kirkpatrick, J. D.; Brodsky, E. E.

    2012-12-01

    Fault zones often contain structures such as corrugations, bumps or lenses that appear to have a regular spacing and/or preferred length or size. The existence of preferred scales is important for frictional processes and earthquake nucleation. However, the power spectral density of fault surface roughness is anisotropic self-affine over a wide range of length scales. No break in scaling is observed in the power spectrum, suggesting that the surfaces do not contain any preferred length scales. To reconcile these paradoxical observations, we calculate the power spectral density of the strike-slip Corona Heights fault surface (San Francisco) from ground-based LiDAR data, and examine the phases calculated from the Fourier transform. In comparison to synthetic faults, the phases defining the Corona Heights fault are non-random, consistent with the sense of curvature of large (5-10 m) bumps or mullions on the fault surface. Bumps are bounded by anastomosing fault surfaces, and are defined by branch lines. Furthermore, corrugations regularly spaced at ~0.1-0.3 m in the slip-perpendicular direction are also defined by the fault curvature. We suggest the phases provide information regarding structure in the fault surface topography that is not captured by the power spectrum alone. The non-random phase distribution reflects the coherence of these structures over the extent of the fault.

  11. 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

  12. 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.

  13. Band structure of topological insulators from noise measurements in tunnel junctions

    NASA Astrophysics Data System (ADS)

    Cascales, Juan Pedro; Martínez, Isidoro; Katmis, Ferhat; Chang, Cui-Zu; Guerrero, Rubén; Moodera, Jagadeesh S.; Aliev, Farkhad G.

    2015-12-01

    The unique properties of spin-polarized surface or edge states in topological insulators (TIs) make these quantum coherent systems interesting from the point of view of both fundamental physics and their implementation in low power spintronic devices. Here we present such a study in TIs, through tunneling and noise spectroscopy utilizing TI/Al2O3/Co tunnel junctions with bottom TI electrodes of either Bi2Te3 or Bi2Se3. We demonstrate that features related to the band structure of the TI materials show up in the tunneling conductance and even more clearly through low frequency noise measurements. The bias dependence of 1/f noise reveals peaks at specific energies corresponding to band structure features of the TI. TI tunnel junctions could thus simplify the study of the properties of such quantum coherent systems that can further lead to the manipulation of their spin-polarized properties for technological purposes.

  14. Effects of non-lasing band in two-dimensional photonic-crystal lasers clarified using omnidirectional band structure.

    PubMed

    Kurosaka, Yoshitaka; Hirose, Kazuyoshi; Watanabe, Akiyoshi; Sugiyama, Takahiro; Liang, Yong; Noda, Susumu

    2012-09-10

    We investigated the effects of non-lasing bands on the beam patterns in photonic-crystal lasers by evaluating the omnidirectional band structure both experimentally and theoretically. We found that a new, weak dual-streak pattern is occasionally generated around the main lobe of the output beam because of scattering of the lasing beam in the non-lasing bands despite a wavenumber mismatch. This result indicates that we can design the high-quality devices without such a noise pattern. In addition, this evaluation method is expected to be useful for developing various high-functionality PC lasers. PMID:23037297

  15. Structured surfaces on metal optics

    NASA Astrophysics Data System (ADS)

    Steinkopf, Ralf; Hartung, Johannes; Kinast, Jan; Gebhardt, Andreas; Risse, Stefan; Eberhardt, Ramona

    2015-09-01

    Diamond machining of metal optics is a flexible way to manufacture structured elements on different surface geometries. Especially curved substrates such as spheres, aspheres, or freeforms in combination with structured elements enable innovative products like headlights of automobiles or spectrometers in life science or space applications. Using diamond turning, servo turning, milling, and shaping, different technologies for arbitrary geometries are available. The addressed wavelengths are typically in the near- infrared (NIR) and infrared (IR) spectral range. Applying additional finishing processes, diamond machining is also used for optics applicable down to the EUV spectral range. This wide range of applications is represented in the used materials, too. However, one important material group for diamond machining is metal substrates. For diamond machining of structured surfaces, it is important to consider the microstructure of the utilized materials thoroughly. Especially amorphous materials as nickel-phosphorus alloys or fine-grained copper allow the fine structuring of refractive and diffractive structures. The paper analyzes the influence variables for diamond machining of structured surfaces and shows the use of this research for applications in the spectral range from IR to EUV.

  16. Band bending at ferroelectric surfaces and interfaces investigated by x-ray photoelectron spectroscopy

    SciTech Connect

    Apostol, Nicoleta Georgiana

    2014-11-24

    This work reports on the use of X-ray photoelectron spectroscopy to quantify band bending at ferroelectric free surfaces and at their interfaces with metals. Surfaces exhibiting out-of-plane ferroelectric polarization are characterized by a band bending, due to the formation of a dipole layer at the surface, composed by the uncompensated polarization charges (due to ionic displacement) and to the depolarization charge sheet of opposite sign, composed by mobile charge carriers, which migrate near surface, owing to the depolarization electric field. To this surface band bending due to out-of-plane polarization states, metal-semiconductor Schottky barriers must be considered additionally when ferroelectrics are covered by metal layers. It is found that the net band bending is not always an algebraic sum of the two effects discussed above, since sometimes the metal is able to provide additional charge carriers, which are able to fully compensate the surface charge of the ferroelectric, up to the vanishing of the ferroelectric band bending. The two cases which will be discussed in more detail are Au and Cu deposited by molecular beam epitaxy on PbZr{sub 0.2}Ti{sub 0.8}O{sub 3}(001) single crystal thin layers, prepared by pulsed laser deposition. Gold forms unconnected nanoparticles, and their effect on the band bending is the apparition of a Schottky band bending additional to the band bending due to the out-of-plane polarization. Copper, starting with a given thickness, forms continuous metal layers connected to the ground of the system, and provide electrons in sufficient quantity to compensate the band bending due to the out-of-plane polarization.

  17. Deriving surface albedo measurements from narrow band satellite data

    NASA Technical Reports Server (NTRS)

    Brest, Christopher L.; Goward, Samuel N.

    1987-01-01

    A target calibration procedure for obtaining surface albedo from satellite data is presented. The methodology addresses two key issues, the calibration of remotely-sensed, discrete wavelength, digital data and the derivation of an albedo measurement (defined over the solar short wave spectrum) from spectrally limited observations. Twenty-seven Landsat observations, calibrated with urban targets (building roof-tops and parking lots), are used to derive spatial and seasonal patterns of surface reflectance and albedo for four land cover types: city, suburb, farm and forest.

  18. Method of manufacturing flexible metallic photonic band gap structures, and structures resulting therefrom

    DOEpatents

    Gupta, Sandhya (Bloomington, MN); Tuttle, Gary L. (Ames, IA); Sigalas, Mihail (Ames, IA); McCalmont, Jonathan S. (Ames, IA); Ho, Kai-Ming (Ames, IA)

    2001-08-14

    A method of manufacturing a flexible metallic photonic band gap structure operable in the infrared region, comprises the steps of spinning on a first layer of dielectric on a GaAs substrate, imidizing this first layer of dielectric, forming a first metal pattern on this first layer of dielectric, spinning on and imidizing a second layer of dielectric, and then removing the GaAs substrate. This method results in a flexible metallic photonic band gap structure operable with various filter characteristics in the infrared region. This method may be used to construct multi-layer flexible metallic photonic band gap structures. Metal grid defects and dielectric separation layer thicknesses are adjusted to control filter parameters.

  19. Complex layered materials and periodic electromagnetic band-gap structures: Concepts, characterizations, and applications

    NASA Astrophysics Data System (ADS)

    Mosallaei, Hossein

    The main objective of this dissertation is to characterize and create insight into the electromagnetic performances of two classes of composite structures, namely, complex multi-layered media and periodic Electromagnetic Band-Gap (EBG) structures. The advanced and diversified computational techniques are applied to obtain their unique propagation characteristics and integrate the results into some novel applications. In the first part of this dissertation, the vector wave solution of Maxwell's equations is integrated with the Genetic Algorithm (GA) optimization method to provide a powerful technique for characterizing multi-layered materials, and obtaining their optimal designs. The developed method is successfully applied to determine the optimal composite coatings for Radar Cross Section (RCS) reduction of canonical structures. Both monostatic and bistatic scatterings are explored. A GA with hybrid planar/curved surface implementation is also introduced to efficiently obtain the optimal absorbing materials for curved structures. Furthermore, design optimization of the non-uniform Luneburg and 2-shell spherical lens antennas utilizing modal solution/GA-adaptive-cost function is presented. The lens antennas are effectively optimized for both high gain and suppressed grating lobes. The second part demonstrates the development of an advanced computational engine, which accurately computes the broadband characteristics of challenging periodic electromagnetic band-gap structures. This method utilizes the Finite Difference Time Domain (FDTD) technique with Periodic Boundary Condition/Perfectly Matched Layer (PBC/PML), which is efficiently integrated with the Prony scheme. The computational technique is successfully applied to characterize and present the unique propagation performances of different classes of periodic structures such as Frequency Selective Surfaces (FSS), Photonic Band-Gap (PBG) materials, and Left-Handed (LH) composite media. The results are incorporated into some novel applications such as high Q nanocavity lasers, guiding the electromagnetic waves at sharp bends, and miniaturized microstrip patch antennas.

  20. Band-structure analysis from photoreflectance spectroscopy in (Ga,Mn)As

    SciTech Connect

    Yastrubchak, Oksana; Gluba, Lukasz; Zuk, Jerzy; Wosinski, Tadeusz; Andrearczyk, Tomasz; Domagala, Jaroslaw Z.; Sadowski, Janusz

    2013-12-04

    Modulation photoreflectance spectroscopy has been applied to study the band-structure evolution in (Ga,Mn)As epitaxial layers with increasing Mn content. Structural and magnetic properties of the layers were characterized with high-resolution X-ray diffractometry and SQUID magnetometery, respectively. The revealed results of decrease in the band-gap-transition energy in the (Ga,Mn)As layers with increasing Mn content are interpreted in terms of a disordered valence band, extended within the band gap, formed, in highly Mn-doped (Ga,Mn)As, as a result of merging the Mn-related impurity band with the host GaAs valence band.

  1. Potassium Postdeposition Treatment-Induced Band Gap Widening at Cu(In,Ga)Se2 Surfaces - Reason for Performance Leap?

    PubMed

    Handick, Evelyn; Reinhard, Patrick; Alsmeier, Jan-Hendrik; Khler, Leonard; Pianezzi, Fabian; Krause, Stefan; Gorgoi, Mihaela; Ikenaga, Eiji; Koch, Norbert; Wilks, Regan G; Buecheler, Stephan; Tiwari, Ayodhya N; Br, Marcus

    2015-12-16

    Direct and inverse photoemission were used to study the impact of alkali fluoride postdeposition treatments on the chemical and electronic surface structure of Cu(In,Ga)Se2 (CIGSe) thin films used for high-efficiency flexible solar cells. We find a large surface band gap (Eg(Surf), up to 2.52 eV) for a NaF/KF-postdeposition treated (PDT) absorber significantly increases compared to the CIGSe bulk band gap and to the Eg(Surf) of 1.61 eV found for an absorber treated with NaF only. Both the valence band maximum (VBM) and the conduction band minimum shift away from the Fermi level. Depth-dependent photoemission measurements reveal that the VBM decreases with increasing surface sensitivity for both samples; this effect is more pronounced for the NaF/KF-PDT CIGSe sample. The observed electronic structure changes can be linked to the recent breakthroughs in CIGSe device efficiencies. PMID:26633568

  2. Fragile surface zero-energy flat bands in three-dimensional chiral superconductors

    NASA Astrophysics Data System (ADS)

    Kobayashi, Shingo; Tanaka, Yukio; Sato, Masatoshi

    2015-12-01

    We study surface zero-energy flat bands in three-dimensional chiral superconductors with pz(px+i py) ν -wave pairing symmetry (ν is a nonzero integer), based on topological arguments and tunneling conductance. It is shown that the surface flat bands are fragile against (i) the surface misorientation and (ii) the surface Rashba spin-orbit interaction. The fragility of (i) is specific to chiral SCs, whereas that of (ii) happens for general odd-parity SCs. We demonstrate that these flat-band instabilities vanish or suppress a zero-bias conductance peak in a normal/insulator/superconductor junction, which behavior is clearly different from high-Tc cuprates and noncentrosymmetric superconductors. By calculating the angle-resolved conductance, we also discuss a topological surface state associated with the coexistence of line and point nodes.

  3. Flexible metamaterial narrow-band-pass filter based on magnetic resonance coupling between ultra-thin bilayer frequency selective surfaces

    NASA Astrophysics Data System (ADS)

    Bai, Zhengyuan; Zhang, Qing; Ju, Yongfeng; Tao, Guiju; Jiang, Xiongwei; Kang, Ning; Liu, Chengpu; Zhang, Long

    2016-02-01

    A novel flexible metamaterial narrow-band-pass filter is designed and proved to be reliable by both numerical simulations and experimental measurements. The unit cell of the designed structure consists of circle ring resonators on top of a thin dielectric layer backed by a metallic mesh. The investigations on the distribution of the surface current and magnetic field as well as the analysis of the equivalent circuit model reveal that the magnetic resonance response between layers induced by the reverse surface current contributes to the high quality factor band-pass property. Importantly, it is a flexible design with a tunable resonance frequency by just changing the radius of the circle rings and can also be easily extended to have the multi-band-pass property. Moreover, this simplified structure with low duty cycle and ultra-thin thickness is also a symmetric design which is insensitive to the polarization and incident angles. Therefore, such a metamaterial narrow-band-pass filter is of great importance in the practical applications such as filtering and radar stealth, and especially for the conformal structure applications in the infrared and optical window area.

  4. SIMULTANEOUS MULTI-BAND DETECTION OF LOW SURFACE BRIGHTNESS GALAXIES WITH MARKOVIAN MODELING

    SciTech Connect

    Vollmer, B.; Bonnarel, F.; Louys, M.; Perret, B.; Petremand, M.; Lavigne, F.; Collet, Ch.; Van Driel, W.; Sabatini, S.

    2013-02-01

    We present to the astronomical community an algorithm for the detection of low surface brightness (LSB) galaxies in images, called MARSIAA (MARkovian Software for Image Analysis in Astronomy), which is based on multi-scale Markovian modeling. MARSIAA can be applied simultaneously to different bands. It segments an image into a user-defined number of classes, according to their surface brightness and surroundings-typically, one or two classes contain the LSB structures. We have developed an algorithm, called DetectLSB, which allows the efficient identification of LSB galaxies from among the candidate sources selected by MARSIAA. The application of the method to two and three bands simultaneously was tested on simulated images. Based on our tests, we are confident that we can detect LSB galaxies down to a central surface brightness level of only 1.5 times the standard deviation from the mean pixel value in the image background. To assess the robustness of our method, the method was applied to a set of 18 B- and I-band images (covering 1.3 deg{sup 2} in total) of the Virgo Cluster to which Sabatini et al. previously applied a matched-filter dwarf LSB galaxy search algorithm. We have detected all 20 objects from the Sabatini et al. catalog which we could classify by eye as bona fide LSB galaxies. Our method has also detected four additional Virgo Cluster LSB galaxy candidates undetected by Sabatini et al. To further assess the completeness of the results of our method, both MARSIAA, SExtractor, and DetectLSB were applied to search for (1) mock Virgo LSB galaxies inserted into a set of deep Next Generation Virgo Survey (NGVS) gri-band subimages and (2) Virgo LSB galaxies identified by eye in a full set of NGVS square degree gri images. MARSIAA/DetectLSB recovered {approx}20% more mock LSB galaxies and {approx}40% more LSB galaxies identified by eye than SExtractor/DetectLSB. With a 90% fraction of false positives from an entirely unsupervised pipeline, a completeness of 90% is reached for sources with r{sub e} > 3'' at a mean surface brightness level of {mu}{sub g} = 27.7 mag arcsec{sup -2} and a central surface brightness of {mu}{sup 0}{sub g} = 26.7 mag arcsec{sup -2}. About 10% of the false positives are artifacts, the rest being background galaxies. We have found our proposed Markovian LSB galaxy detection method to be complementary to the application of matched filters and an optimized use of SExtractor, and to have the following advantages: it is scale free, can be applied simultaneously to several bands, and is well adapted for crowded regions on the sky.

  5. Relativistic effects on the surface electronic structure of Mo(011)

    NASA Astrophysics Data System (ADS)

    Jeong, K.; Gaylord, R. H.; Kevan, S. D.

    1988-11-01

    High-resolution photoemission studies of the Mo(011) surface have allowed us to isolate and to study the effects of the spin-orbit interaction on the surface electronic structure of Mo(011). We have observed and characterized three distinct phenomena, all related to the breaking of symmetry by the spin-orbit interaction. The first is a zone-center surface resonance which exists in a pseudogap between the bulk ?8+ and the ?7+ points, and is similar to one observed previously on W(011). We also have observed a surface state in a projected band gap opened by spin-orbit-induced hybridization between bulk bands at N. Finally, we have observed avoided crossings of surface bands along the symmetry azimuths. These bands would be of opposite mirror-plane symmetry in the absence of the spin-orbit interaction, but hybridize under its influence. The transfer of both the polarization behavior and contamination sensitivity from one band to another is observed and characterized. We speculate on the relevance of these results to other surface properties, including reconstruction and work-function change.

  6. 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.

  7. Micro-metric electronic patterning of a topological band structure using a photon beam

    NASA Astrophysics Data System (ADS)

    Frantzeskakis, E.; de Jong, N.; Zwartsenberg, B.; Huang, Y. K.; Bay, T. V.; Pronk, P.; van Heumen, E.; Wu, D.; Pan, Y.; Radovic, M.; Plumb, N. C.; Xu, N.; Shi, M.; de Visser, A.; Golden, M. S.

    2015-11-01

    In an ideal 3D topological insulator (TI), the bulk is insulating and the surface conducting due to the existence of metallic states that are localized on the surface; these are the topological surface states. Quaternary Bi-based compounds of Bi2‑xSbxTe3‑ySey with finely-tuned bulk stoichiometries are good candidates for realizing ideal 3D TI behavior due to their bulk insulating character. However, despite its insulating bulk in transport experiments, the surface region of Bi2‑xSbxTe3‑ySey crystals cleaved in ultrahigh vacuum also exhibits occupied states originating from the bulk conduction band. This is due to adsorbate-induced downward band-bending, a phenomenon known from other Bi-based 3D TIs. Here we show, using angle-resolved photoemission, how an EUV light beam of moderate flux can be used to exclude these topologically trivial states from the Fermi level of Bi1.46Sb0.54Te1.7Se1.3 single crystals, thereby re-establishing the purely topological character of the low lying electronic states of the system. We furthermore prove that this process is highly local in nature in this bulk-insulating TI, and are thus able to imprint structures in the spatial energy landscape at the surface. We illustrate this by ‘writing’ micron-sized letters in the Dirac point energy of the system.

  8. Micro-metric electronic patterning of a topological band structure using a photon beam.

    PubMed

    Frantzeskakis, E; De Jong, N; Zwartsenberg, B; Huang, Y K; Bay, T V; Pronk, P; Van Heumen, E; Wu, D; Pan, Y; Radovic, M; Plumb, N C; Xu, N; Shi, M; De Visser, A; Golden, M S

    2015-01-01

    In an ideal 3D topological insulator (TI), the bulk is insulating and the surface conducting due to the existence of metallic states that are localized on the surface; these are the topological surface states. Quaternary Bi-based compounds of Bi(2-x)Sb(x)Te(3-y)Se(y) with finely-tuned bulk stoichiometries are good candidates for realizing ideal 3D TI behavior due to their bulk insulating character. However, despite its insulating bulk in transport experiments, the surface region of Bi(2-x)Sb(x)Te(3-y)Se(y) crystals cleaved in ultrahigh vacuum also exhibits occupied states originating from the bulk conduction band. This is due to adsorbate-induced downward band-bending, a phenomenon known from other Bi-based 3D TIs. Here we show, using angle-resolved photoemission, how an EUV light beam of moderate flux can be used to exclude these topologically trivial states from the Fermi level of Bi1.46Sb0.54Te1.7Se1.3 single crystals, thereby re-establishing the purely topological character of the low lying electronic states of the system. We furthermore prove that this process is highly local in nature in this bulk-insulating TI, and are thus able to imprint structures in the spatial energy landscape at the surface. We illustrate this by 'writing' micron-sized letters in the Dirac point energy of the system. PMID:26543011

  9. Micro-metric electronic patterning of a topological band structure using a photon beam

    PubMed Central

    Frantzeskakis, E.; De Jong, N.; Zwartsenberg, B.; Huang, Y. K.; Bay, T. V.; Pronk, P.; Van Heumen, E.; Wu, D.; Pan, Y.; Radovic, M.; Plumb, N. C.; Xu, N.; Shi, M.; De Visser, A.; Golden, M. S.

    2015-01-01

    In an ideal 3D topological insulator (TI), the bulk is insulating and the surface conducting due to the existence of metallic states that are localized on the surface; these are the topological surface states. Quaternary Bi-based compounds of Bi2−xSbxTe3−ySey with finely-tuned bulk stoichiometries are good candidates for realizing ideal 3D TI behavior due to their bulk insulating character. However, despite its insulating bulk in transport experiments, the surface region of Bi2−xSbxTe3−ySey crystals cleaved in ultrahigh vacuum also exhibits occupied states originating from the bulk conduction band. This is due to adsorbate-induced downward band-bending, a phenomenon known from other Bi-based 3D TIs. Here we show, using angle-resolved photoemission, how an EUV light beam of moderate flux can be used to exclude these topologically trivial states from the Fermi level of Bi1.46Sb0.54Te1.7Se1.3 single crystals, thereby re-establishing the purely topological character of the low lying electronic states of the system. We furthermore prove that this process is highly local in nature in this bulk-insulating TI, and are thus able to imprint structures in the spatial energy landscape at the surface. We illustrate this by ‘writing’ micron-sized letters in the Dirac point energy of the system. PMID:26543011

  10. 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.

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

    SciTech Connect

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

    2014-09-28

    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 2310 mm. It is shown that electron densities larger than 10? cm ? 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.

  12. Influence of banded structure on the mechanical properties of a high-strength maraging steel

    SciTech Connect

    Ahmed, M.; Salam, I.; Hashmi, F.H.; Khan, A.Q.

    1997-04-01

    Chemical inhomogeneity results in the formation of banded structure in high-strength maraging steels. Segregation of titanium and molybdenum was found to be the primary cause of banded structure formation. When the concentrations of these elements increased beyond certain critical levels, bands comprising different grain sizes formed. The inclusions existed preferentially along the interface of the bands. A high-temperature homogenization treatment substantially reduced or eliminated the banded structure. The large grain size resulting from the homogenization treatment was subsequently reduced by a grain refinement treatment. The mechanical properties of the steel substantially improved following homogenization and grain refinement.

  13. 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.

  14. Cotton response to poultry litter applied by subsurface banding relative to surface broadcasting

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Dry poultry litter is typically land-applied by surface broadcasting, a practice that exposes certain litter nutrients to volatilization loss. Applying litter with a new, experimental implement that places the litter in narrow bands below the soil surface may reduce or eliminate such losses but has...

  15. Improvement of Bare Surface Soil Moisture Estimation with L-Band Dual-Polarization Radar

    Technology Transfer Automated Retrieval System (TEKTRAN)

    This study demonstrates a new algorithm development for estimating bare surface soil moisture using dual-polarization L-band backscattering measurements. Through our analyses on the numerically simulated surface backscattering database by Advanced Integral Equation Model (AIEM) with a wide range of ...

  16. Surface Structures of Hawaiian Lavas

    NASA Technical Reports Server (NTRS)

    Rowland, S. K.; Walker, G. P. L.

    1985-01-01

    Surface and internal lava structures can be valid indicators of lava viscosity and rheology, provided that care is taken to identify and eliminate structures which are strain-rate-dependent. Here, a spectrum of types among Hawaiian basaltic flows is found ranging from pahoehoe to a'a, that are interpreted as marking a progression in lava viscosity and a change in rheology. The most fluid type in this spectrum is normal pahoehoe that has a smooth but commonly wrinkled or folded (ropy) surface. The next type, distinctly more viscous and probably non-Newtonian in rheology, is spiny pahoehoe which is characterized by a spinose surface and an absence of ropy structures. Preliminary studies on the long lavas of Mauna Loa indicated, perhaps surprisingly, that there is no clear-cut correlation of lava length with type in this spectrum of lavas, indicating that viscosity/yield strength of the basaltic lavas per se are not the primary controls determining flow length. Flowage of the lava through lava tubes, while it may help to account for the long flow distance of some lavas, is not a generally applicable explanation for long flow length.

  17. Global Kinetic Modeling of Banded Electron Structures in the Plasmasphere

    NASA Technical Reports Server (NTRS)

    Liemohn, M. W.; Khazanov, G. V.

    1997-01-01

    Significant fluxes of 10 eV to 30 keV electrons have been detected in the plasmasphere, appearing as banded structures in energy with broad spatial extents and slowly evolving over several days. It is thought that these populations are decaying plasma sheet electrons injected into the corotating region of near-Earth space. This capture can occur when the convective electric field drops rapidly and the Alfven boundary suddenly outward, trapping the inner edge of the plasma sheet along closed drift paths. Our bounce-averaged kinetic model of superthermal electron transport is able to simulate this capture and the subsequent drift, diffusion, and decay of the plasma cloud. Results of this simulation will be shown and discussed, from the initial injection during the elevated convection to the final loss of the particles. It is thought that not only Coulomb collisions but also wave-particle interactions play a significant role in altering the plasma cloud. Quasilinear diffusion is currently being incorporated into the model and the importance of this mechanism will be examined. Also, the high anisotropy of the trapped population could be unstable and generate plasma waves. These and other processes will be investigated to determine the final fate of the cloud and to quantify where, how, and when the energy of the plasma cloud is deposited. Comparisons with CRRES observations of these events are shown to verify the model and explain the data.

  18. Determination of the surface band bending in InxGa1-xN films by hard x-ray photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Lozac'h, Mickael; Ueda, Shigenori; Liu, Shitao; Yoshikawa, Hideki; Liwen, Sang; Wang, Xinqiang; Shen, Bo; Sakoda, Kazuaki; Kobayashi, Keisuke; Sumiya, Masatomo

    2013-02-01

    Core-level and valence band spectra of InxGa1-xN films were measured using hard x-ray photoemission spectroscopy (HX-PES). Fine structure, caused by the coupling of the localized Ga 3d and In 4d with N 2s states, was experimentally observed in the films. Because of the large detection depth of HX-PES (˜20 nm), the spectra contain both surface and bulk information due to the surface band bending. The InxGa1-xN films (x = 0-0.21) exhibited upward surface band bending, and the valence band maximum was shifted to lower binding energy when the mole fraction of InN was increased. On the other hand, downward surface band bending was confirmed for an InN film with low carrier density despite its n-type conduction. Although the Fermi level (EF) near the surface of the InN film was detected inside the conduction band as reported previously, it can be concluded that EF in the bulk of the film must be located in the band gap below the conduction band minimum.

  19. Surface-electronic structure of. alpha. -like Ce compounds

    SciTech Connect

    Laubschat, C.; Weschke, E.; Holtz, C.; Domke, M.; Strebel, O.; Kaindl, G. )

    1990-09-24

    Photoemission studies with varying degrees of surface sensitivity are reported for the Ce 3{ital d} core-level and Ce 4{ital f} valence-band regions of the {alpha}-like Ce compounds CeIr{sub 2}, CePd{sub 3}, and CeRh{sub 3}. In all cases studied, strong changes of the 4{ital f} electronic structure at the surface towards a more localized {gamma}-like behavior are observed, requiring a reanalysis of previously reported photoemission spectra of {alpha}-like Ce compounds. Implications for an improved understanding of the surface-catalytic properties of Ce systems, as well as of the surface-electronic structure of narrow-band materials, are pointed out.

  20. Anomalies in the surface electronic structure of Cr

    NASA Astrophysics Data System (ADS)

    Ali, Khadiza; Varier, Shyama R.; Biswas, Deepnarayan; Kandukuri, Srinivas C.; Maiti, Kalobaran

    2015-11-01

    We studied the electronic structure of high quality Cr(110) films grown on the W(110) surface employing angle resolved photoemission spectroscopy (ARPES). Experimental spectra from differently aged samples exhibit distinct signatures of the surface and bulk character of the features in the electronic structure. We observe that oxygen content on the surface gradually increases with aging and the hybridization of the adsorbed oxygens with the surface Cr atoms is significantly strong at temperature around room temperature or higher. The energy bands exhibit signature of band folding due to the spin density wave transition. In addition, a weakly dispersive sharp feature is found to emerge near the Fermi level at low temperatures presumably due to the correlation induced effects.

  1. Loss of Linear Band Dispersion and Trigonal Structure in Silicene on Ir(111).

    PubMed

    Wei, Wei; Dai, Ying; Huang, Baibiao; Whangbo, Myung-Hwan; Jacob, Timo

    2015-03-19

    The structure of silicene/Ir(111) was examined on the basis of density functional theory. We have found that Ir(111) preserves the 2D character of silicene but significantly distorts its structure from the trigonal one expected for an isolated silicene. The electronic structure of silicene is strongly hybridized with that of Ir(111) so that silicene on Ir(111) loses its linear band dispersion around the Fermi level, giving rise to a metallic band structure; however, silicene/Ir(111) exhibits a hidden linear-dispersive band, which is related to the linear-dispersive conduction band of an isolated silicene. PMID:26262871

  2. Experimental valence-band structure of tin disulfide SnS2

    NASA Astrophysics Data System (ADS)

    Bertrand, Yves; Barski, A.; Pinchaux, R.

    1985-04-01

    Synchrotron radiation has been used to investigate the valance-band photoemission of tin disulfide. From angle-resolved measurements the dispersion E(k-->) of the six uppermost valence bands is obtained. The SnS2 experimental band structure is compared with the pseudopotential predictions. The great similarity of the experimental band schemes of the two dichalcogenides (SnS2 and SnSe2) is found to be fully consistent with the likeness of their optical properties.

  3. Electron capture from occupied surface states within the band gap of LiF(100)

    SciTech Connect

    Yan, Q.; Meyer, F.W.

    1996-09-01

    Measurements of scattered neutral fractions for Na, K, and Cs multicharged ions grazingly incident on Li(100) as function of projectile velocity suggest that near resonant processes are active in the final neutral formation, involving occupied surface states within the band gap of the alkali halide target. Observed scattered negative fractions for incident 0, F. and B projectiles are consistent with such a scenario as well. A model treatment of the projectile charge fraction velocity dependence is utilized to deduce from the experimental data a work function and Fermi energy of 3.8 eV and 0.8 eV, respectively, for this surface band. Measurement of the parallel velocity dependence of the image charge acceleration of Ne{sup 6+} grazingly incident on LiF(100) in the range 0.1 - 0.52 a.u. are shown to provide further support for the presence of a band of surface states having the above parameters.

  4. Ultra-low reflectivity polycrystalline silicon surfaces formed by surface structure chemical transfer method

    NASA Astrophysics Data System (ADS)

    Imamura, Kentaro; Franco, Francisco C.; Matsumoto, Taketoshi; Kobayashi, Hikaru

    2013-07-01

    A nanocrystalline Si layer can be formed by the surface structure chemical transfer (SSCT) method in which a platinum mesh is instantaneously contacted with polycrystalline Si wafers immersed in hydrogen peroxide plus hydrofluoric acid solutions. The polycrystalline Si surface after the SSCT method possesses an ultra-low reflectivity. The nanocrystalline Si layer possesses a 100-150 nm thickness, and gives a photoluminescence with a peak maximum at 670 nm, indicating band-gap widening. The minority carrier lifetime of as-sliced Si wafers greatly increases after the SSCT method most probably due to the enlargement of the nanocrystalline Si band-gap.

  5. Tunable bandwidth of pass-band metamaterial filter based on coupling of localized surface plasmon resonance

    NASA Astrophysics Data System (ADS)

    Han, Bing; Dong, Beibei; Nan, Jingyu; Zhong, Min

    2015-12-01

    A broad pass-band compound structure metamaterial is designed which consists of periodic two metallic particles and hole arrays. The operating bandwidth of the designed structure reaches to ?f ? 33.8 THz. Physical mechanisms are analyzed and validated based on calculated electric field distribution that the interaction and coupled of LSP modes between two metallic particles leads to the bandwidth increased and resonance frequency blue-shifted, while the interaction and coupled between metallic particle and metallic arrays results in the reduced of the pass-band. The pass-band can be expanded through reducing the permittivity of dielectric layer or reducing the width of the metallic particle (a). The effect of the angles of incidence on the pass-band is also analyzed for normal, 15, 30 and 45.

  6. 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.; Degallaix, S.

    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.

  7. Vibrational dynamics and band structure of methyl-terminated Ge(111).

    PubMed

    Hund, Zachary M; Nihill, Kevin J; Campi, Davide; Wong, Keith T; Lewis, Nathan S; Bernasconi, M; Benedek, G; Sibener, S J

    2015-09-28

    A combined synthesis, experiment, and theory approach, using elastic and inelastic helium atom scattering along with ab initio density functional perturbation theory, has been used to investigate the vibrational dynamics and band structure of a recently synthesized organic-functionalized semiconductor interface. Specifically, the thermal properties and lattice dynamics of the underlying Ge(111) semiconductor crystal in the presence of a commensurate (1 1) methyl adlayer were defined for atomically flat methylated Ge(111) surfaces. The mean-square atomic displacements were evaluated by analysis of the thermal attenuation of the elastic He diffraction intensities using the Debye-Waller model, revealing an interface with hybrid characteristics. The methyl adlayer vibrational modes are coupled with the Ge(111) substrate, resulting in significantly softer in-plane motion relative to rigid motion in the surface normal. Inelastic helium time-of-flight measurements revealed the excitations of the Rayleigh wave across the surface Brillouin zone, and such measurements were in agreement with the dispersion curves that were produced using density functional perturbation theory. The dispersion relations for H-Ge(111) indicated that a deviation in energy and lineshape for the Rayleigh wave was present along the nearest-neighbor direction. The effects of mass loading, as determined by calculations for CD3-Ge(111), as well as by force constants, were less significant than the hybridization between the Rayleigh wave and methyl adlayer librations. The presence of mutually similar hybridization effects for CH3-Ge(111) and CH3-Si(111) surfaces extends the understanding of the relationship between the vibrational dynamics and the band structure of various semiconductor surfaces that have been functionalized with organic overlayers. PMID:26429030

  8. Vibrational dynamics and band structure of methyl-terminated Ge(111)

    NASA Astrophysics Data System (ADS)

    Hund, Zachary M.; Nihill, Kevin J.; Campi, Davide; Wong, Keith T.; Lewis, Nathan S.; Bernasconi, M.; Benedek, G.; Sibener, S. J.

    2015-09-01

    A combined synthesis, experiment, and theory approach, using elastic and inelastic helium atom scattering along with ab initio density functional perturbation theory, has been used to investigate the vibrational dynamics and band structure of a recently synthesized organic-functionalized semiconductor interface. Specifically, the thermal properties and lattice dynamics of the underlying Ge(111) semiconductor crystal in the presence of a commensurate (1 1) methyl adlayer were defined for atomically flat methylated Ge(111) surfaces. The mean-square atomic displacements were evaluated by analysis of the thermal attenuation of the elastic He diffraction intensities using the Debye-Waller model, revealing an interface with hybrid characteristics. The methyl adlayer vibrational modes are coupled with the Ge(111) substrate, resulting in significantly softer in-plane motion relative to rigid motion in the surface normal. Inelastic helium time-of-flight measurements revealed the excitations of the Rayleigh wave across the surface Brillouin zone, and such measurements were in agreement with the dispersion curves that were produced using density functional perturbation theory. The dispersion relations for H-Ge(111) indicated that a deviation in energy and lineshape for the Rayleigh wave was present along the nearest-neighbor direction. The effects of mass loading, as determined by calculations for CD3-Ge(111), as well as by force constants, were less significant than the hybridization between the Rayleigh wave and methyl adlayer librations. The presence of mutually similar hybridization effects for CH3-Ge(111) and CH3-Si(111) surfaces extends the understanding of the relationship between the vibrational dynamics and the band structure of various semiconductor surfaces that have been functionalized with organic overlayers.

  9. Metal-to-Insulator Transition in Au Chains on Si(111)-5×2-Au by Band Filling: Infrared Plasmonic Signal and Ab Initio Band Structure Calculation.

    PubMed

    Hötzel, Fabian; Seino, Kaori; Chandola, Sandhya; Speiser, Eugen; Esser, Norbert; Bechstedt, Friedhelm; Pucci, Annemarie

    2015-09-17

    The Si(111)-5×2-Au surface is increasingly of interest because it is one of the rare atomic chain systems with quasi-one-dimensional properties. For the deposition of 0.7 monolayers of Au, these chains are metallic. Upon the evaporation of an additional submonolayer amount of gold, the surface becomes insulating but keeps the 5×2 symmetry. This metal-to-insulator transition was in situ monitored based on the infrared plasmonic signal change with coverage. The phase transition is theoretically explained by total-energy and band-structure calculations. Accordingly, it can be understood in terms of the occupation of the originally half-filled one-dimensional band at the Fermi level. By annealing the system, the additional gold is removed from the surface and the plasmonic signal is recovered, which underlines the stability of the metallic structure. So, recent results on the infrared plasmonic signals of the Si(111)-5 × 2-Au surface are supported. The understanding of potential one-dimensional electrical interconnects is improved. PMID:26722731

  10. A PPM-focused klystron at X-band with a traveling-wave output structure

    SciTech Connect

    Eppley, K.R.

    1995-07-05

    We have developed algorithms for designing disk-loaded traveling-wave output structures for X-band klystrons to be used in the SLAC NLC. We use either a four- or five-cell structure in a {pi}/2 mode. The disk radii are tapered to produce an approximately constant gradient. The matching calculation is not performed on the tapered structure, but rather on a coupler whose input and output cells are the same as the final cell of the tapered structure, and whose interior cells are the same as the penultimate cell in the tapered structure. 2-D calculations using CONDOR model the waveguide as a radial transmission line of adjustable impedance. 3-D calculations with MAFIA model the actual rectangular waveguide and coupling slot. A good match is obtained by adjusting the impedance of the final cell. In 3-D, this requires varying both the radius of the cell and the width of the aperture. When the output cell with the best match is inserted in the tapered structure, we obtain excellent cold-test agreement between the 2-D and 3-D models. We use hot-test simulations with CONDOR to design a structure with maximum efficiency and minimum surface fields. We have designed circuits at 11.424 Ghz for different perveances. At 440 kV, microperveance 1.2, we calculated 81 MW, 53 percent efficiency, with peak surface field 76 MV/m. A microperveance 0.6 design was done using a PPM stack for focusing. At 470 kV, 193 amps, we calculated 58.7 MW, 64.7 percent efficiency, peak surface field 62.3 MV/m. At 500 kV, 212 amps, we calculated 67.1 MW, 63.3 percent efficiency, peak surface field 66.0 MV/m. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

  11. Momentum-Space Imaging of the Dirac Band Structure in Molecular Graphene via Quasiparticle Interference

    NASA Astrophysics Data System (ADS)

    Stephenson, Anna; Gomes, Kenjiro K.; Ko, Wonhee; Mar, Warren; Manoharan, Hari C.

    2014-03-01

    Molecular graphene is a nanoscale artificial lattice composed of carbon monoxide molecules arranged one by one, realizing a dream of exploring exotic quantum materials by design. This assembly is done by atomic manipulation with a scanning tunneling microscope (STM) on a Cu(111) surface. To directly probe the transformation of normal surface state electrons into massless Dirac fermions, we map the momentum space dispersion through the Fourier analysis of quasiparticle scattering maps acquired at different energies with the STM. The Fourier analysis not only bridges the real-space and momentum-space data but also reveals the chiral nature of those quasiparticles, through a set of selection rules of allowed scattering involving the pseudospin and valley degrees of freedom. The graphene-like band structure can be reshaped with simple alterations to the lattice, such as the addition of a strain. We analyze the effect on the momentum space band structure of multiple types of strain on our system. Supported by DOE, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under contract DE-AC02-76SF00515.

  12. Fine structure in the profiles of strong diffuse interstellar bands

    NASA Astrophysics Data System (ADS)

    Galazutdinov, G. A.; Lo Curto, G.; Kre?owski, J.

    2008-06-01

    High-resolution echelle spectra of five reddened OB stars are used to analyse details of the profiles of diffuse interstellar bands (DIBs) at 4726, 4735, 5418, 5850, 6196, 6376, 6379 together with the well studied 5797, 5780 and 6614 ones. All targets do not show Doppler splitting in the interstellar CH 4300 band with the applied resolving power R = 115000. The profiles of DIBs differ from object to object except 5418 which looks invariant in our sample: the DIB is a good candidate for further study of possible isotopic effect. We also found that the width of bands at 5797 and 6614 probably is more sensitive to the temperature (and density) effects than that of other DIBs in the sample, though almost all diffuse bands are narrowest in most ?-type object (HD179406) of the sample. On the other hand, it can be just peculiar effect as in a case of unusual line of sight HD147889 which demonstrates very broad 5780 and 6614 diffuse bands what hardly can be explained by temperature effects. Based on data collected at the European Southern Observatory (ESO) 3.6-m telescope and the HARPS spectrograph (R = 115000). E-mail: gala@kasi.re.kr (GAG); glocurto@eso.org (GLC); jacek@astri.uni.torun.pl (JK)

  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. Carrier Multiplication in Semiconductor Nanocrystals: Theoretical Screening of Candidate Materials Based on Band-Structure Effects

    SciTech Connect

    Luo, J. W.; Franceschetti, A.; Zunger, A.

    2008-01-01

    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}{sub XX}. Here we introduce a DCM 'figure of merit' R{sub 2}(E) which is proportional to the ratio between the biexciton density of states {rho}{sub XX} and the single-exciton density of states {rho}{sub x}, restricted to single-exciton and biexciton states that are coupled by Coulomb interactions. Using R{sub 2}(E), we consider GaAs, InAs, InP, GaSb, InSb, CdSe, Ge, Si, and PbSe nanocrystals of different sizes. Although DCM can be affected by both quantum-confinement effects (reflecting the underly electronic structure of the confined dot-interior states) and surface effects, here we are interested to isolate the former. To this end the nanocrystal energy levels are obtained from the corresponding bulk band structure via the truncated crystal approximation. We find that PbSe, Si, GaAs, CdSe, and InP nanocrystals have larger DCM figure of merit than the other nanocrystals. Our calculations suggest that high DCM efficiency requires high degeneracy of the corresponding bulk band-edge states. Interestingly, by considering band structure effects we find that as the dot size increases the DCM critical energy E{sub 0} (the energy at which R{sub 2}(E) becomes {ge}1) is reduced, suggesting improved DCM. However, whether the normalized E{sub 0}/{var_epsilon}{sub g} increases or decreases as the dot size increases depends on dot material.

  15. Self-consistent band structure of the rutile dioxides NbO2, RuO2, and IrO2

    NASA Astrophysics Data System (ADS)

    Xu, J. H.; Jarlborg, T.; Freeman, A. J.

    1989-10-01

    The electronic structures of the rutile dioxides NbO2, RuO2, and IrO2 have been determined from self-consistent semirelativistic linear muffin-tin-orbital band calculations. The basis set is completed with s and p functions from ``empty spheres'' inserted in the open parts of the structure. The band results are analyzed in terms of Fermi-surface features, band positions, x-ray photoemission spectra, and joint density-of-state functions. Comparisons with available experimental data are, in general, favorable. In particular, the effects from self-consistency are pointed out by comparison with earlier non-self-consistent band results.

  16. Geometrical and Structural Asperities on Fault Surfaces

    NASA Astrophysics Data System (ADS)

    Sagy, A.; Brodsky, E. E.; van der Elst, N.; Agosta, F.; di Toro, G.; Collettini, C.

    2007-12-01

    Earthquake dynamics are strongly affected by fault zone structure and geometry. Fault surface irregularities and the nearby structure control the rupture nucleation and propagation, the fault strength, the near-field stress orientations and the hydraulic properties. New field observations demonstrate the existence of asperities in faults as displayed by topographical bumps on the fault surface and hardening of the internal structure near them. Ground-based LIDAR measurements on more than 30 normal and strike slip faults in different lithologies demonstrate that faults are not planar surfaces and roughness is strongly dependent on fault displacement. In addition to the well-understood roughness exemplified by abrasive striations and fracture segmentation, we found semi-elliptical topographical bumps with wavelengths of a few meters. In many faults the bumps are not spread equally on the surface and zones can be bumpier than others. The bumps are most easily identified on faults with total displacement of dozens to hundreds of meters. Smaller scale roughness on these faults is smoothed by abrasive processes. A key site in southern Oregon shows that the topographic bumps are closely tied to the internal structure of the fault zone. At this location, we combine LiDAR data with detailed structural analysis of the fault zone embedded in volcanic rocks. Here the bumps correlate with an abrupt change in the width of the cohesive cataclasite layer that is exposed under a thin ultracataclasite zone. In most of the exposures the cohesive layer thickness is 10-20 cm. However, under protruding bumps the layer is always thickened and the width can locally exceed one meter. Field and microscopic analyses show that the layer contains grains with dimensions ranging from less than 10 ? up to a few centimeters. There is clear evidence of internal flow, rotation and fracturing of the grains in the layer. X-Ray diffraction measurements of samples from the layer show that the bulk mineralogy is identical to that of the host rock, although thin section analysis suggests that some alteration and secondary mineralization of the grains also occurs. We infer that the cohesiveness of the layer is a consequence of repacking and cementation similar to deformation bands in granular material. By comparing the thickness of the cohesive layer on several secondary faults in this fault area we found that the average thickness of the layer increases with total slip. The correlation is nonlinear and the thickening rate decreases with increasing slip. We conclude that granular flow decreasing with increasing slip and thus the deformation is continually localized.

  17. Structure of dipole bands in {sup 106}In

    SciTech Connect

    Deo, A. Y.; Palit, R.; Naik, Z.; Joshi, P. K.; Mazumdar, I.; Sihotra, S.; Mehta, D.; Kumar, S.; Chakrabarti, R.; Kshetri, R.

    2009-06-15

    High spin states in neutron-deficient {sup 106}In were investigated using {sup 78}Se({sup 32}S,p3n) reaction at 125 MeV. The level scheme is extended up to 7 MeV of excitation energy for the negative parity states constituting four dipole bands, and the positive parity states which mainly exhibit single-particle excitations are extended up to 5 MeV. Projected deformed Hartree-Fock calculations were carried out to understand the configurations of different bands in this nucleus.

  18. The Band Structure of Polymers: Its Calculation and Interpretation. Part 3. Interpretation.

    ERIC Educational Resources Information Center

    Duke, B. J.; O'Leary, Brian

    1988-01-01

    In this article, the third part of a series, the results of ab initio polymer calculations presented in part 2 are discussed. The electronic structure of polymers, symmetry properties of band structure, and generalizations are presented. (CW)

  19. Microbial communities in the surface mucopolysaccharide layer and the black band microbial mat of black band-diseased Siderastrea siderea.

    PubMed

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

    2006-09-01

    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 gamma-proteobacteria (53 to 64%), followed by beta-proteobacteria (18 to 21%) and alpha-proteobacteria (5 to 11%). In contrast, both BBD clone libraries were dominated by alpha-proteobacteria (58 to 87%), followed by verrucomicrobia (2 to 10%) and 0 to 6% each of delta-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. 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 ...

  1. 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...

  2. Grass Forage Response to Broadcast or Surface-Banded Liquid Dairy Manure and Nitrogen Fertilizer

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Manure can provide valuable nutrients, especially N, for grass forage, but N availability is limited because of high NH3 volatilization losses from standard surface-broadcast application. Field experiments were conducted at two sites in NW VT to evaluate effects of broadcast or banded liquid dairy m...

  3. 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 ...

  4. Novel band structures in silicene on monolayer zinc sulfide substrate.

    PubMed

    Li, Sheng-shi; Zhang, Chang-wen; Yan, Shi-shen; Hu, Shu-jun; Ji, Wei-xiao; Wang, Pei-ji; Li, Ping

    2014-10-01

    Opening a sizable band gap in the zero-gap silicene without lowering the carrier mobility is a key issue for its application in nanoelectronics. Based on ?rst-principles calculations, we find that the interaction energies are in the range of -0.09?0.3?eV?per Si atom, indicating a weak interaction between silicene and ZnS monolayer and the ABZn stacking is the most stable pattern. The band gap of silicene can be effectively tuned ranging from 0.025 to 1.05?eV in silicene and ZnS heterobilayer (Si/ZnS HBL). An unexpected indirect-direct band gap crossover is also observed in HBLs, dependent on the stacking pattern, interlayer spacing and external strain effects on silicene. Interestingly, the characteristics of Dirac cone with a nearly linear band dispersion relation of silicene can be preserved in the ABS pattern which is a metastable state, accompanied by a small electron effective mass and thus the carrier mobility is expected not to degrade much. These provide a possible way to design effective FETs out of silicene on a ZnS monolayer. PMID:25158645

  5. Electronic transitions in GdN band structure

    SciTech Connect

    Vidyasagar, R. Kita, T.; Sakurai, T.; Ohta, H.

    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 Γ-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.

  6. Engineering Electronic Band Structure for New Elpasolite Scintillators

    NASA Astrophysics Data System (ADS)

    Du, Mao-Hua; Biswas, Koushik; Singh, David

    2012-02-01

    The utilization of scintillator materials is one of the primary methods for radiation detection. Elpasolites are a large family of quaternary halides that have recently attracted considerable interest for their potential applications as ?-ray and neutron scintillators. A large number (on the order of 10^3) of different chemical compositions exist in the elpasolite family of compounds. This wide range of compositions offers numerous opportunities for fine-tuning the material chemistry to target specific scintillation properties, but they also pose significant challenges in identifying the most promising ones. Many elpasolite scintillator materials currently under development suffer from low light output and long scintillation decay time. The low light output is partially due to a large band gap while the long scintillation decay time is a result of the slow carrier transport to Ce impurities, where carriers recombine to emit photons. We suggest that these problems may be mitigated by optimizing the band gap and carrier mobility by selecting constituent elements of proper electronegativity. For example, cations with lower electronegativity may lower the conduction band and increase the conduction band dispersion simultaneously, resulting in higher light output and faster scintillation. We demonstrate by first-principles calculations that the strategy of manipulating electronegativity can lead to a number of new elpasolite compounds that are potentially brighter and faster scintillators.

  7. Band structure engineering for ultra-low threshold laser diodes

    NASA Astrophysics Data System (ADS)

    Ury, I.; Lau, Kam Y.

    It has been proposed that strained layer superlattice be used to reduce the effective mass of holes, thereby reducing the transparency electron density and subsequently the lasing threshold. In conventional bulk materials, the degeneracy of heavy and light hole bands at zone center means domination of the heavy hold band in hole occupation. It was known that by applying strain to the crystal, the degeneracy can be broken such that under a biaxial compressive stress, the light hole band is lifted above the heavy hole band in the k-vector directions parallel to the applied strain. Since the heavy hole is five times heavier than the light hole, the resultant effective hole mass can be reduced by a factor of 5. The strain can be built in by growing lattice mismatched InGaAs on GaAs substrate. Such lattice-mismatched epitaxial layers cannot be arbitrarily thick for it to be defect free, the maximum thickness being only about 100A.

  8. 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.

  9. 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.

  10. 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 550C consisted of AF in Mn-poor bands and martensite in Mn-rich bands, whereas the specimen isothermed at 450C exhibited two different morphologies of AF that appeared as bands. At a continuous cooling rate in the range of 4 to 50C/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.

  11. Structural properties and quasiparticle band structures of Cu-based quaternary semiconductors for photovoltaic applications

    NASA Astrophysics Data System (ADS)

    Zhang, Yubo; Sun, Xiudong; Zhang, Peihong; Yuan, Xun; Huang, Fuqiang; Zhang, Wenqing

    2012-03-01

    Cu-based quaternary chalcogenide semiconductors (Cu2-II-IV-VI4) are a large group of materials that hold great promises for a variety of applications, especially as thin-film solar cell absorbers. However, despite intensive research activities, a systematic understanding of the evolution of the electronic and structural properties with chemical compositions of these materials is still lacking. In this paper, we present first-principles calculations of the structural and electronic properties of eight such semiconductors (Cu2-II-IV-VI4, with II = Zn and Cd; IV = Ge and Sn; VI = S and Se). The variation of the structural parameters with chemical compositions, investigated using the HSE06 hybrid functional, follows a few interesting trends. The quasiparticle bandgap, calculated using the state-of-the-art GW approximation, also varies systematically with chemical compositions. Effects of cation disordering on the band gaps are also investigated. This systematic understanding of the structural parameters and quasiparticle band gaps would be useful for future structural characterization and material design.

  12. SMOS satellite L-band radiometer: A new capability for ocean surface remote sensing in hurricanes

    NASA Astrophysics Data System (ADS)

    Reul, Nicolas; Tenerelli, Joseph; Chapron, Bertrand; Vandemark, Doug; Quilfen, Yves; Kerr, Yann

    2012-02-01

    The Soil Moisture and Ocean Salinity (SMOS) mission currently provides multiangular L-band (1.4 GHz) brightness temperature images of the Earth. Because upwelling radiation at 1.4 GHz is significantly less affected by rain and atmospheric effects than at higher microwave frequencies, these new SMOS measurements offer unique opportunities to complement existing ocean satellite high wind observations that are often contaminated by heavy rain and clouds. To illustrate this new capability, we present SMOS data over hurricane Igor, a tropical storm that developed to a Saffir-Simpson category 4 hurricane from 11 to 19 September 2010. Thanks to its large spatial swath and frequent revisit time, SMOS observations intercepted the hurricane 9 times during this period. Without correcting for rain effects, L-band wind-induced ocean surface brightness temperatures (TB) were co-located and compared to H*Wind analysis. We find the L-band ocean emissivity dependence with wind speed appears less sensitive to roughness and foam changes than at the higher C-band microwave frequencies. The first Stokes parameter on a 50 km spatial scale nevertheless increases quasi-linearly with increasing surface wind speed at a rate of 0.3 K/m s-1 and 0.7 K/m s-1 below and above the hurricane-force wind speed threshold (32 m s-1), respectively. Surface wind speeds estimated from SMOS brightness temperature images agree well with the observed and modeled surface wind speed features. In particular, the evolution of the maximum surface wind speed and the radii of 34, 50 and 64 knots surface wind speeds are consistent with GFDL hurricane model solutions and H*Wind analyses. The SMOS sensor is thus closer to a true all-weather satellite ocean wind sensor with the capability to provide quantitative and complementary surface wind information of interest for operational Hurricane intensity forecasts.

  13. Homochiral magnetic structures at surfaces

    NASA Astrophysics Data System (ADS)

    Blugel, Stefan

    2008-03-01

    Electrons propagating in the vicinity of inversion asymmetric environments such as surfaces, interfaces, ultrathin films or nanostructures can give rise to an important antisymmetric exchange interaction, known as Dzyaloshinskii-Moriya (DM) interaction. Although this interaction, favoring spatially rotating spin structures, is in principle known for about 50 years, its consequences for the magnetic structure in low-dimensional magnets remained nearly unexplored and has been basically overlooked the past 20 years. Theoretical models considering isotropic exchange, magnetic anisotropy and the DM interaction display a rich phase diagram of complex magnetic phases on different length scales depending on the strength of the different contributions. Today, it is unknown how large is the strength of the DM interaction. Is this just a small perturbation to the collinear uniaxial ferro- or antiferromagnetic state, determined by exchange and magnetic anisotropy or is it strong enough to create new phases which had been overlooked? Surprisingly little first-principles calculations deal with the DM interaction. There might be several reasons for this: The investigation requires the treatment of non-collinear magnetism together with spin-orbit interactions of large magnetic structures in low-symmetry situations. We developed a perturbative strategy implemented into the FLAPW code FLEUR which can cope with this challenge. We show by first- principles calculations based on the vector-spin density formulation of the density- functional theory (DFT) that that there are circumstances whre the DM interaction is indeed sufficiently strong to compete with the interactions that favor collinear spin alignment causing magnetic phases of unique handedness e.g.homochiral magnetic phases such as a left rotation cycloidal spiral in Mn on W(110) [M. Bode et al., Nature 447, 190 (2007)] or favoring magnetic domain-walls with unique turning sense.

  14. Experimental and theoretical investigations of the electronic band structure of metal-organic frameworks of HKUST-1 type

    NASA Astrophysics Data System (ADS)

    Gu, Zhi-Gang; Heinke, Lars; Wll, Christof; Neumann, Tobias; Wenzel, Wolfgang; Li, Qiang; Fink, Karin; Gordan, Ovidiu D.; Zahn, Dietrich R. T.

    2015-11-01

    The electronic properties of metal-organic frameworks (MOFs) are increasingly attracting the attention due to potential applications in sensor techniques and (micro-) electronic engineering, for instance, as low-k-dielectric in semiconductor technology. Here, the band gap and the band structure of MOFs of type HKUST-1 are studied in detail by means of spectroscopic ellipsometry applied to thin surface-mounted MOF films and by means of quantum chemical calculations. The analysis of the density of states, the band structure, and the excitation spectrum reveal the importance of the empty Cu-3d orbitals for the electronic properties of HKUST-1. This study shows that, in contrast to common belief, even in the case of this fairly "simple" MOF, the excitation spectra cannot be explained by a superposition of "intra-unit" excitations within the individual building blocks. Instead, "inter-unit" excitations also have to be considered.

  15. Recent Results from Broad-Band Intensity Mapping Measurements of Cosmic Large Scale Structure

    NASA Astrophysics Data System (ADS)

    Zemcov, Michael B.; CIBER, Herschel-SPIRE

    2016-01-01

    Intensity mapping integrates the total emission in a given spectral band over the universe's history. Tomographic measurements of cosmic structure can be performed using specific line tracers observed in narrow bands, but a wealth of information is also available from broad-band observations performed by instruments capable of capturing high-fidelity, wide-angle images of extragalactic emission. Sensitive to the continuum emission from faint and diffuse sources, these broad-band measurements provide a view on cosmic structure traced by components not readily detected in point source surveys. After accounting for measurement effects and astrophysical foregrounds, the angular power spectra of such data can be compared to predictions from models to yield powerful insights into the history of cosmic structure formation. This talk will highlight some recent measurements of large scale structure performed using broad-band intensity mapping methods that have given new insights on faint, distant, and diffuse components in the extragalactic background light.

  16. Fine structure of the amide i band in acetanilide

    NASA Astrophysics Data System (ADS)

    Careri, G.; Gratton, E.; Shyamsunder, E.

    1988-05-01

    Their absorption spectrum of both single crystals and powdered samples of acetanilide (a model system for proteins) has been studied in the amide i region, where a narrow band has been identified as a highly trapped soliton state. The powder-sample spectra have been decomposed using four Lorentzian bands. A strong temperature dependence has been found for the intensity of two of the subbands, which also show a complementary behavior. Polarization studies performed on thin crystals have shown that the subbands have the same polarization. Low-temperature spectra of partially deuterated samples show the presence of the subbands at the same absorption frequencies found using the fitting procedure in the spectra of nondeuterated samples. The soliton model currently proposed to explain the origin of the anomalous amide i component at 1650 cm-1 still holds, but some modification of the model is required to account for the new features revealed by this study.

  17. Tunable Band Alignment with Unperturbed Carrier Mobility of On-Surface Synthesized Organic Semiconducting Wires.

    PubMed

    Basagni, Andrea; Vasseur, Guillaume; Pignedoli, Carlo A; Vilas-Varela, Manuel; Peña, Diego; Nicolas, Louis; Vitali, Lucia; Lobo-Checa, Jorge; de Oteyza, Dimas G; Sedona, Francesco; Casarin, Maurizio; Ortega, J Enrique; Sambi, Mauro

    2016-02-23

    The tunable properties of molecular materials place them among the favorites for a variety of future generation devices. In addition, to maintain the current trend of miniaturization of those devices, a departure from the present top-down production methods may soon be required and self-assembly appears among the most promising alternatives. On-surface synthesis unites the promises of molecular materials and of self-assembly, with the sturdiness of covalently bonded structures: an ideal scenario for future applications. Following this idea, we report the synthesis of functional extended nanowires by self-assembly. In particular, the products correspond to one-dimensional organic semiconductors. The uniaxial alignment provided by our substrate templates allows us to access with exquisite detail their electronic properties, including the full valence band dispersion, by combining local probes with spatial averaging techniques. We show how, by selectively doping the molecular precursors, the product's energy level alignment can be tuned without compromising the charge carrier's mobility. PMID:26841052

  18. Tunable Band Alignment with Unperturbed Carrier Mobility of On-Surface Synthesized Organic Semiconducting Wires

    PubMed Central

    2016-01-01

    The tunable properties of molecular materials place them among the favorites for a variety of future generation devices. In addition, to maintain the current trend of miniaturization of those devices, a departure from the present top-down production methods may soon be required and self-assembly appears among the most promising alternatives. On-surface synthesis unites the promises of molecular materials and of self-assembly, with the sturdiness of covalently bonded structures: an ideal scenario for future applications. Following this idea, we report the synthesis of functional extended nanowires by self-assembly. In particular, the products correspond to one-dimensional organic semiconductors. The uniaxial alignment provided by our substrate templates allows us to access with exquisite detail their electronic properties, including the full valence band dispersion, by combining local probes with spatial averaging techniques. We show how, by selectively doping the molecular precursors, the product’s energy level alignment can be tuned without compromising the charge carrier’s mobility. PMID:26841052

  19. Effects of surface band bending and scattering on thermoelectric transport in suspended bismuth telluride nanoplates.

    PubMed

    Pettes, Michael Thompson; Maassen, Jesse; Jo, Insun; Lundstrom, Mark S; Shi, Li

    2013-11-13

    A microdevice was used to measure the in-plane thermoelectric properties of suspended bismuth telluride nanoplates from 9 to 25 nm thick. The results reveal a suppressed Seebeck coefficient together with a general trend of decreasing electrical conductivity and thermal conductivity with decreasing thickness. While the electrical conductivity of the nanoplates is still within the range reported for bulk Bi2Te3, the total thermal conductivity for nanoplates less than 20 nm thick is well below the reported bulk range. These results are explained by the presence of surface band bending and diffuse surface scattering of electrons and phonons in the nanoplates, where pronounced n-type surface band bending can yield suppressed and even negative Seebeck coefficient in unintentionally p-type doped nanoplates. PMID:24164564

  20. Partitioning of Bacterial Communities between Seawater and Healthy, Black Band Diseased, and Dead Coral Surfaces

    PubMed Central

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

    2002-01-01

    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

  1. Band bending at the surface of Bi2Se3 studied from first principles

    NASA Astrophysics Data System (ADS)

    Rakyta, P.; Ujfalussy, B.; Szunyogh, L.

    2015-12-01

    The band bending (BB) effect on the surface of the second-generation topological insulators implies a serious challenge to design transport devices. The BB is triggered by the effective electric field generated by charged impurities close to the surface and by the inhomogeneous charge distribution of the occupied surface states (SSs). Our self-consistent calculations in the KorringaKohnRostoker framework showed that in contrast to the bulk bands, the spectrum of the SSs is not bent at the surface. In turn, it is possible to tune the energy level of the Dirac point via the deposited surface dopants. In addition, the electrostatic modifications induced by the charged impurities on the surface induce long range oscillations in the charge density. For dopants located beneath the surface, however, these oscillations become highly suppressed. Our findings are in good agreement with recent experiments, however, our results indicate that the concentration of the surface doping cannot be estimated from the energy shift of the Dirac cone within the scope of the effective continuous model for the protected SSs.

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

    SciTech Connect

    Sharma, G.; Munjal, N.; Vyas, V.; Kumar, R.; Sharma, B. K.; Joshi, K. B.

    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.

  3. Porous silicon multilayer structures: A photonic band gap analysis

    NASA Astrophysics Data System (ADS)

    Lugo, J. E.; Lopez, H. A.; Chan, S.; Fauchet, P. M.

    2002-04-01

    A photonic model for freshly anodized porous silicon multilayer structures is presented. The photonic structures are composed of alternating high and low dielectric function porous silicon layers. The model takes into account the presence of silicon dioxide and its lattice expansion in the porous structure. We work with oxidized structures and our results fit completely the experimentally measured optical shift.

  4. A DFT study on structural, vibrational properties, and quasiparticle band structure of solid nitromethane.

    PubMed

    Appalakondaiah, S; Vaitheeswaran, G; Lebègue, S

    2013-05-14

    We report a detailed theoretical study of the structural and vibrational properties of solid nitromethane using first principles density functional calculations. The ground state properties were calculated using a plane wave pseudopotential code with either the local density approximation, the generalized gradient approximation, or with a correction to include van der Waals interactions. Our calculated equilibrium lattice parameters and volume using a dispersion correction are found to be in reasonable agreement with the experimental results. Also, our calculations reproduce the experimental trends in the structural properties at high pressure. We found a discontinuity in the bond length, bond angles, and also a weakening of hydrogen bond strength in the pressure range from 10 to 12 GPa, picturing the structural transition from phase I to phase II. Moreover, we predict the elastic constants of solid nitromethane and find that the corresponding bulk modulus is in good agreement with experiments. The calculated elastic constants show an order of C11> C22 > C33, indicating that the material is more compressible along the c-axis. We also calculated the zone center vibrational frequencies and discuss the internal and external modes of this material under pressure. From this, we found the softening of lattice modes around 8-11 GPa. We have also attempted the quasiparticle band structure of solid nitromethane with the G0W0 approximation and found that nitromethane is an indirect band gap insulator with a value of the band gap of about 7.8 eV with G0W0 approximation. Finally, the optical properties of this material, namely the absorptive and dispersive part of the dielectric function, and the refractive index and absorption spectra are calculated and the contribution of different transition peaks of the absorption spectra are analyzed. The static dielectric constant and refractive indices along the three inequivalent crystallographic directions indicate that this material has a considerable optical anisotropy. PMID:23676062

  5. 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.

  6. Chaos and band structure in a three-dimensional optical lattice

    NASA Astrophysics Data System (ADS)

    Boretz, Yingyue; Reichl, L. E.

    2015-04-01

    Classical chaos is known to affect wave propagation because it signifies the presence of broken symmetries. The effect of chaos has been observed experimentally for matter waves, electromagnetic waves, and acoustic waves. When these three types of waves propagate through a spatially periodic medium, the allowed propagation energies form bands. For energies in the band gaps, no wave propagation is possible. We show that optical lattices provide a well-defined system that allows a study of the effect of chaos on band structure. We have determined the band structure of a body-centered-cubic optical lattice for all theoretically possible couplings, and we find that the band structure for those lattices realizable in the laboratory differs significantly from that expected for the bands in an "empty" body-centered-cubic crystal. However, as coupling is increased, the lattice becomes increasingly chaotic and it becomes possible to produce band structure that has behavior qualitatively similar to the "empty" body-centered-cubic band structure, although with fewer degeneracies.

  7. Chaos and band structure in a three-dimensional optical lattice.

    PubMed

    Boretz, Yingyue; Reichl, L E

    2015-04-01

    Classical chaos is known to affect wave propagation because it signifies the presence of broken symmetries. The effect of chaos has been observed experimentally for matter waves, electromagnetic waves, and acoustic waves. When these three types of waves propagate through a spatially periodic medium, the allowed propagation energies form bands. For energies in the band gaps, no wave propagation is possible. We show that optical lattices provide a well-defined system that allows a study of the effect of chaos on band structure. We have determined the band structure of a body-centered-cubic optical lattice for all theoretically possible couplings, and we find that the band structure for those lattices realizable in the laboratory differs significantly from that expected for the bands in an "empty" body-centered-cubic crystal. However, as coupling is increased, the lattice becomes increasingly chaotic and it becomes possible to produce band structure that has behavior qualitatively similar to the "empty" body-centered-cubic band structure, although with fewer degeneracies. PMID:25974556

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

    NASA Astrophysics Data System (ADS)

    Boisot, Olivier; Pioch, Sbastien; Fatras, Christophe; Caulliez, Guillemette; Bringer, Alexandra; Borderies, Pierre; Lalaurie, Jean-Claude; Gurin, 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.

  9. Surface-plasmon enhanced photodetection at communication band based on hot electrons

    NASA Astrophysics Data System (ADS)

    Wu, Kai; Zhan, Yaohui; Wu, Shaolong; Deng, Jiajia; Li, Xiaofeng

    2015-08-01

    Surface plasmons can squeeze light into a deep-subwavelength space and generate abundant hot electrons in the nearby metallic regions, enabling a new paradigm of photoconversion by the way of hot electron collection. Unlike the visible spectral range concerned in previous literatures, we focus on the communication band and design the infrared hot-electron photodetectors with plasmonic metal-insulator-metal configuration by using full-wave finite-element method. Titanium dioxide-silver Schottky interface is employed to boost the low-energy infrared photodetection. The photodetection sensitivity is strongly improved by enhancing the plasmonic excitation from a rationally engineered metallic grating, which enables a strong unidirectional photocurrent. With a five-step electrical simulation, the optimized device exhibits an unbiased responsivity of 0.1 mA/W and an ultra-narrow response band (FWHM = 4.66 meV), which promises to be a candidate as the compact photodetector operating in communication band.

  10. 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.

  11. Lunar near-surface structure

    NASA Technical Reports Server (NTRS)

    Cooper, M. R.; Kovach, R. L.; Watkins, J. S.

    1974-01-01

    Seismic refraction data obtained at the Apollo 14, 16, and 17 landing sites permit a compressional wave velocity profile of the lunar near surface to be derived. Beneath the regolith at the Apollo 14 Fra Mauro site and the Apollo 16 Descartes site is material with a seismic velocity of about 300 m/sec, believed to be brecciated material or impact-derived debris. Considerable detail is known about the velocity structure at the Apollo 17 Taurus-Littrow site. Seismic velocities of 100, 327, 495, 960, and 4700 m/sec are observed. The depth to the top of the 4700-m/sec material is 1385 m, compatible with gravity estimates for the thickness of mare basaltic flows, which fill the Taurus-Littrow valley. The observed magnitude of the velocity change with depth and the implied steep velocity-depth gradient of more than 2 km/sec/km are much larger than have been observed on compaction experiments on granular materials and preclude simple cold compaction of a fine-grained rock powder to thicknesses of the order of kilometers.

  12. Calculation of the band structure of polyguanilic acid in the presence of water and Na+ ions

    NASA Astrophysics Data System (ADS)

    Ladik, J.; Bende, A.; Bogar, F.

    2007-08-01

    Using the Hartree-Fock crystal orbital method with a combined symmetry (helix) operation, the band structure of polyguanilic acid was calculated in the presence of water and Na+ ions. The water structure was optimized with the help of molecular mechanics.The obtained band structure shows that both the valence and conduction bands are purely guanine type. The three impurity bands in the 10.66eV large gap are close to the conduction band and therefore cannot play any role in the assumed hole conduction of the system. Namely, according to detailed x-ray diffraction investigations of the nucleosomes in chromatin, there are possibilities of charge transfer from the negative sites of DNA to the positive ones in histones. Therefore most probably there is a hole conduction in DNA and an electronic one in the histone proteins.

  13. Valence band structure of binary chalcogenide vitreous semiconductors by high-resolution XPS

    SciTech Connect

    Kozyukhin, S.; Golovchak, R.; Kovalskiy, A.; Shpotyuk, O.; Jain, H.

    2011-04-15

    High-resolution X-ray photoelectron spectroscopy (XPS) is used to study regularities in the formation of valence band electronic structure in binary As{sub x}Se{sub 100-x}, As{sub x}S{sub 100-x}, Ge{sub x}Se{sub 100-x} and Ge{sub x}S{sub 100-x} chalcogenide vitreous semiconductors. It is shown that the highest occupied energetic states in the valence band of these materials are formed by lone pair electrons of chalcogen atoms, which play dominant role in the formation of valence band electronic structure of chalcogen-rich glasses. A well-expressed contribution from chalcogen bonding p electrons and more deep s orbitals are also recorded in the experimental valence band XPS spectra. Compositional dependences of the observed bands are qualitatively analyzed from structural and compositional points of view.

  14. Structure of Dipole Bands in 112In: Through Lifetime Measurement

    NASA Astrophysics Data System (ADS)

    Trivedi, T.; Palit, R.; Sethi, J.; Saha, S.; Kumar, S.; Naik, Z.; Parkar, V. V.; Naidu, B. S.; Deo, A. Y.; Raghav, A.; Joshi, P. K.; Jain, H. C.; Sihotra, S.; Mehta, D.; Jain, A. K.; Choudhury, D.; Negi, D.; Roy, S.; Chattopadhyay, S.; Singh, A. K.; Singh, P.; Biswas, D. C.; Bhowmik, R. K.; Muralithar, S.; Singh, R. P.; Kumar, R.; Rani, K.

    2012-09-01

    High-spin states of the 112In nucleus have been populated via 100Mo(16O, p3n) reaction at 80 MeV beam energy. Lifetimes of excited states of dipole bands have been measured using Doppler-shift attenuation method. The B(M1) transition rates deduced from the measured lifetimes show a rapid decrease with increasing angular momentum. The decrease in B(M1) values are well accounted by the prediction of tilted axis cranking calculations. These measurements confirm the presence of shears mechanism in this nuclei.

  15. 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

  16. 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 (5.155.825 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

  17. Band Structure and Effective Mass in Monolayer MoS2.

    PubMed

    Wu, Ming-Ting; Fan, Jun-Wei; Chen, Kuan-Ting; Chang, Shu-Tong; Lin, Chung-Yi

    2015-11-01

    Monolayer transition-metal dichalcogenide is a very promising two-dimensional material for future transistor technology. Monolayer molybdenum disulfide (MoS2), owing to the unique electronic properties of its atomically thin two-dimensional layered structure, can be made into a high-performance metal-oxide-semiconductor field-effect transistor, or MOSFET. In this work, we focus on band structure and carrier mobility calculations for MoS2. We use the tight-binding method to calculate the band structure, including a consideration of the linear combination of different atomic orbitals, the interaction of neighboring atoms, and spin-orbit coupling for different tight-binding matrices. With information about the band structure, we can obtain the density of states, the effective mass, and other physical quantities. Carrier mobility using the Kubo-Greenwood formula is calculated based on the tight-binding band structure. PMID:26726660

  18. Optically decomposed near-band-edge structure and excitonic transitions in Ga2S3

    PubMed Central

    Ho, Ching-Hwa; Chen, Hsin-Hung

    2014-01-01

    The band-edge structure and band gap are key parameters for a functional chalcogenide semiconductor to its applications in optoelectronics, nanoelectronics, and photonics devices. Here, we firstly demonstrate the complete study of experimental band-edge structure and excitonic transitions of monoclinic digallium trisulfide (Ga2S3) using photoluminescence (PL), thermoreflectance (TR), and optical absorption measurements at low and room temperatures. According to the experimental results of optical measurements, three band-edge transitions of EA = 3.052?eV, EB = 3.240?eV, and EC = 3.328?eV are respectively determined and they are proven to construct the main band-edge structure of Ga2S3. Distinctly optical-anisotropic behaviors by orientation- and polarization-dependent TR measurements are, respectively, relevant to distinguish the origins of the EA, EB, and EC transitions. The results indicated that the three band-edge transitions are coming from different origins. Low-temperature PL results show defect emissions, bound-exciton and free-exciton luminescences in the radiation spectra of Ga2S3. The below-band-edge transitions are respectively characterized. On the basis of experimental analyses, the optical property of near-band-edge structure and excitonic transitions in the monoclinic Ga2S3 crystal is revealed. PMID:25142550

  19. Tunable band-notched coplanar waveguide based on localized spoof surface plasmons.

    PubMed

    Xu, Bingzheng; Li, Zhuo; Liu, Liangliang; Xu, Jia; Chen, Chen; Ning, Pingping; Chen, Xinlei; Gu, Changqing

    2015-10-15

    This Letter proposes a simple band-notched coplanar waveguide (BNCPW), which consists of a coplanar waveguide (CPW) and an ultra-thin periodic corrugated metallic strip that supports spoof surface plasmon polaritons (SSPPs) with defect units on the back of the substrate. By introducing a defect unit or multiple defect units into the strip, a narrow stopband or multiple narrow stopbands would be generated flexibly and conveniently. The band-notch function is based on the idea that a defect mode, which exists in the bandgap between the fundamental and the first higher mode of the SSPPs, can be introduced to form a stopband. Thus, the SSPPs field is localized around the defect units, which is another form of localized spoof surface plasmons (LSSPs). By properly tuning the dimensions of each defect unit, the absorption level and center frequency of the stopband could be adjusted independently. We offer theoretical analysis and experimental results to validate our idea and design. In this framework, a variety of band-notched devices and antennas in the microwave and terahertz (THz) frequencies can be easily designed without additional band-stop filters. PMID:26469594

  20. Electronic band structure effects in monolayer, bilayer, and hybrid graphene structures

    NASA Astrophysics Data System (ADS)

    Puls, Conor

    Since its discovery in 2005, graphene has been the focus of intense theoretical and experimental study owing to its unique two-dimensional band structure and related electronic properties. In this thesis, we explore the electronic properties of graphene structures from several perspectives including the magnetoelectrical transport properties of monolayer graphene, gap engineering and measurements in bilayer graphene, and anomalous quantum oscillation in the monolayer-bilayer graphene hybrids. We also explored the device implications of our findings, and the application of some experimental techniques developed for the graphene work to the study of a complex oxide, Ca3Ru2O7, exhibiting properties of strongly correlated electrons. Graphene's high mobility and ballistic transport over device length scales, make it suitable for numerous applications. However, two big challenges remain in the way: maintaining high mobility in fabricated devices, and engineering a band gap to make graphene compatible with logical electronics and various optical devices. We address the first challenge by experimentally evaluating mobilities in scalable monolayer graphene-based field effect transistors (FETs) and dielectric-covered Hall bars. We find that the mobility is limited in these devices, and is roughly inversely proportional to doping. By considering interaction of graphene's Dirac fermions with local charged impurities at the interface between graphene and the top-gate dielectric, we find that Coulomb scattering is responsible for degraded mobility. Even in the cleanest devices, a band gap is still desirable for electronic applications of graphene. We address this challenge by probing the band structure of bilayer graphene, in which a field-tunable energy band gap has been theoretically proposed. We use planar tunneling spectroscopy of exfoliated bilayer graphene flakes demonstrate both measurement and control of the energy band gap. We find that both the Fermi level and electronic structure are highly sensitive to tunnel bias-induced charging in these devices, an effect that is traditionally neglected in other materials. However, careful consideration of both these effects and non-ideal tunneling processes allows extraction of valuable information from the tunneling spectra. We compare the tunable insulating state to our transport studies of bi-layer graphene-based FETs with similar dielectric environments. This work, as well as our work on top-gated monolayer-based devices, identifies the integration of graphene and a gate dielectric as being the next great challenge towards the realization of graphene-based electronics. We also report the discovery of anomalous quantum oscillations in magnetotransport measurements of monolayer and bilayer graphene hybrids. In these graphene hybrid structures, the Fermi levels of either portion lock at their interface, and the greatly different energy scales of emergent Landau levels support strong charge imbalance. The nature the interface states are yet to be clarified. Finally, we extend the techniques of device fabrication and measurement to exfoliated flakes of a layered material, Ca3Ru2O 7. This strongly correlated electronic system hosts a variety of exotic phenomena at low temperatures, which have been suggested to result from complex d-orbital interactions. We compare transport measurements of flakes to previous studies in bulk crystals, and explore the effects of tuning charge carrier density using an ionic liquid gate to induce densities several orders of magnitude greater than is possible with conventional dielectrics.

  1. 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.

  2. Features of the band structure for semiconducting iron, ruthenium, and osmium monosilicides

    SciTech Connect

    Shaposhnikov, V. L. Migas, D. B.; Borisenko, V. E.; Dorozhkin, N. N.

    2009-02-15

    The pseudopotential method has been used to optimize the crystal lattice and calculate the energy band spectra for iron, ruthenium and, osmium monosilicides. It is found that all these compounds are indirect-gap semiconductors with band gaps of 0.17, 0.22, and 0.50 eV (FeSi, RuSi, and OsSi, respectively). A distinctive feature of their band structure is the 'loop of extrema' both in the valence and conduction bands near the center of the cubic Brillouin zone.

  3. Quasiparticle band structure and tight-binding model for single- and bilayer black phosphorus

    NASA Astrophysics Data System (ADS)

    Rudenko, A. N.; Katsnelson, M. I.

    2014-05-01

    By performing ab initio calculations for one- to four-layer black phosphorus within the GW approximation, we obtain a significant difference in the band gap (1.5 eV), which is in line with recent experimental data. The results are analyzed in terms of the constructed four-band tight-binding model, which gives accurate descriptions of the mono- and bilayer band structure near the band gap, and reveal an important role of the interlayer hoppings, which are largely responsible for the obtained gap difference.

  4. Band structure and related electronic properties of YxIn1-xN ternary system

    NASA Astrophysics Data System (ADS)

    Benyounes, N.; Boucenna, M.

    2014-11-01

    Based on a pseudopotential formalism under the virtual crystal approximation, a theoretical study is carried out on the electronic band structure and derived properties of YxIn1-xN ternary system for the hypothetical zinc-blende phase. Features such as direct and indirect energy band gaps and electron effective mass have been calculated. Besides, the ionicity of the alloy system under load has been discussed in terms of the antisymmetric band gap. Generally, our results agree well with the available experimental and previously published theoretical data. The alloy composition dependence of the band parameters of interest has been examined.

  5. Surface and guided waves on structured surfaces and inhomogeneous media

    NASA Astrophysics Data System (ADS)

    Polanco, Javier

    Surface and guided waves on structured surfaces and inhomogeneous media studies the propagation of waves in systems with spatially varying parameters. In the rainbow case (chapter 1), the dielectric constant changes with coordinates. In the cylinder case: boundary and the metal (chapter 2), it is a curved surface. Finally, in the last case (chapter 3), the dielectric constant changes in z-direction.

  6. Experimental study of X-band dielectric-loaded accelerating structures

    NASA Astrophysics Data System (ADS)

    Jing, Chunguang

    A joint Argonne National Laboratory (ANL)/Naval Research Laboratory (NRL) program is under way to investigate X-band dielectric-loaded accelerating (DLA) structures, using high-power 11.424GHz radiation from the NRL Magnicon facility. As an advanced accelerator concepts, the dielectric-loaded accelerator offers the potential for a simple, inexpensive alternative to high-gradient RF linear accelerators. In this thesis, a comprehensive account of X-band DLA structure design, including theoretical calculation, numerical simulation, fabrication and testing, is presented in detail. Two types of loading dielectrics, alumina and MgxCa1-xTiO 3 (MCT), are investigated. For alumina (with dielectric constant 9.4), no RF breakdown has been observed up to 5 MW of drive power (equivalent to 8MV/m accelerating gradient) in the high power RF testing at NRL, but multipactor was observed to absorb a large fraction of the incident microwave power. Experimental results on suppression of multipactor using TiN coating on the inner surface of the dielectric are also reported. For MCT (with dielectric constant 20), although we did not observe dielectric breakdown in the structures, breakdown did occur at the ceramic joint, where the electric field is greatly enhanced (estimated to be around 100MV/m) due to the micro-scale vacuum gap. In addition, the MCT structure showed significantly less multipactor for the same level of RF field. The thesis also introduced a new design, a multilayered dielectric-loaded accelerating structure, to improve the performance over the conventional one layer DLA structure. Results of analysis for the case of a four layered DLA structure indicate a large reduction of RF power attenuation and an increase of shunt impedance for the structure. Beyond the main contents, the appendices of the thesis present two individual projects prompted by the experimental study of the dielectric-loaded accelerating structure. Appendix A shows a resonant loop technique that can be used in the bead-pull experiment on any cavity resonator. In appendix B, a direct wakefield measurement of the dielectric-loaded waveguide on the Argonne Wakefield Accelerator beamline is described.

  7. 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...

  8. Early stages of plasma induced nitridation of Si (111) surface and study of interfacial band alignment

    NASA Astrophysics Data System (ADS)

    Shetty, Satish; Shivaprasad, S. M.

    2016-02-01

    We report here a systematic study of the nitridation of the Si (111) surface by nitrogen plasma exposure. The surface and interface chemical composition and surface morphology are investigated by using RHEED, X-ray photoelectron spectroscopy, and atomic force microscopy (AFM). At the initial stage of nitridation two superstructures—"8 × 8" and "8/3 × 8/3"—form, and further nitridation leads to 1 × 1 stoichiometric silicon nitride. The interface is seen to have the Si1+ and Si3+ states of silicon bonding with nitrogen, which suggests an atomically abrupt and defect-free interface. The initial single crystalline silicon nitride layers are seen to become amorphous at higher thicknesses. The AFM image shows that the nitride nucleates at interfacial dislocations that are connected by sub-stoichiometric 2D-nitride layers, which agglomerate to form thick overlayers. The electrical properties of the interface yield a valence band offset that saturates at 1.9 eV and conduction band offset at 2.3 eV due to the evolution of the sub-stoichiometric interface and band bending.

  9. Valence and conduction band structure of the quasi-two-dimensional semiconductor Sn S2

    NASA Astrophysics Data System (ADS)

    Racke, David A.; Neupane, Mahesh R.; Monti, Oliver L. A.

    2016-02-01

    We present the momentum-resolved photoemission spectroscopy of both the valence and the conduction band region in the quasi-two-dimensional van der Waals-layered indirect band gap semiconductor Sn S2 . Using a combination of angle-resolved ultraviolet photoemission and angle-resolved two-photon photoemission (AR-2PPE) spectroscopy, we characterize the band structure of bulk Sn S2 . Comparison with density functional theory calculations shows excellent quantitative agreement in the valence band region and reveals several localized bands that likely originate from defects such as sulfur vacancies. Evidence for a moderate density of defects is also observed by AR-2PPE in the conduction band region, leading to localized bands not present in the computational results. The energetic structure and dispersion of the conduction bands is captured well by the computational treatment, with some quantitative discrepancies remaining. Our results provide a broader understanding of the electronic structure of Sn S2 in particular and van der Waals-layered semiconductors in general.

  10. Banded structure and its distribution in friction stir processing of 316L austenitic stainless steel

    NASA Astrophysics Data System (ADS)

    Chen, Y. C.; Fujii, H.; Tsumura, T.; Kitagawa, Y.; Nakata, K.; Ikeuchi, K.; Matsubayashi, K.; Michishita, Y.; Fujiya, Y.; Katoh, J.

    2012-01-01

    Banded structures, which vary with welding parameters, were observed in friction stir processing of 316L austenite stainless steel. Sigma phase precipitation was detected in banded structures by transmission electron microscopy. The amount of banded structure had direct ratio relations with heat input. The higher the heat input, the larger the area of banded structures. This is attributable to slower cooling rate at high heat input, which results in longer exposure to the temperature range for precipitation. The formation of sigma phase produced Cr depletion, which resulted in largely degraded corrosion resistance. The present study suggests that low heat input (i.e. low rotation speeds, low working loads and high welding speed) contributes to restrain sigma phase precipitation.

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

    SciTech Connect

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

    2014-02-24

    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.

  12. Reinvestigation of the collective band structures in odd-odd 138Pm nucleus

    NASA Astrophysics Data System (ADS)

    Li, H. J.; Xiao, Z. G.; Zhu, S. J.; Qi, C.; Yeoh, E. Y.; Zhang, Z.; Wang, R. S.; Yi, H.; Yan, W. H.; Xu, Q.; Wu, X. G.; He, C. Y.; Zheng, Y.; Li, G. S.; Li, C. B.; Li, H. W.; Liu, J. J.; Hu, S. P.; Wang, J. L.; Yao, S. H.

    2015-05-01

    The high-spin states in the odd-odd 138Pm nucleus have been reinvestigated via the 124Te(19F, 5 n) reaction at the beam energy of 103 MeV. Most of the known transitions and levels are confirmed. A number of bands are revised and one new band has been established. For the yrast ?h 11/2? ?h 11/2 band based on 8+ state, no evidence supporting the occurence of signature inversion is found. The experimental and theoretical B( M1)/ B( E2) ratios have been calculated for band (2), which support the ?g 7/2[413]5/2+ ? ?h 11/2[514]9/2- Nilsson configuration assignment. Four bands with ?I = 2 transitions are tentatively assigned as doubly decoupled bands. The other three bands are proposed as oblate-triaxial bands. The possible configuration assignments for these bands are also discussed under the calculations of total Routhian surface and particle-rotor model.

  13. Valence Band Structure of Highly Efficient p-type Thermoelectric PbTe-PbS Alloys

    SciTech Connect

    Jaworski, C. M.; Nielsen, Mechele; Wang, Hsin; Girard, Steven N.; Cai, Wei; Porter, Wallace D; Kanatzidis, Mercouri G.; Heremans, J. P.

    2013-01-01

    New experimental evidence is given relevant to the temperature-dependence of valence band structure of PbTe and PbTe1-xSx alloys (0.04 x 0.12), and its effect on the thermoelectric figure of merit zT. The x = 0.08 sample has zT ~ 1.55 at 773K. The magnetic field dependence of the high-temperature Hall resistivity of heavily p-type (> 1019 cm-3) Na-doped PbTe1-xSx reveals the presence of high-mobility electrons. This put in question prior analyses of the Hall coefficient and the conclusion that PbTe would be an indirect gap semiconductor at temperatures where its zT is optimal. Possible origins for these electrons are discussed: they can be induced by photoconductivity, or by the topology of the Fermi surface when the L and -bands merge. Negative values for the low-temperature thermopower are also observed. Our data show that PbTe continues to be a direct gap semiconductor at temperatures where the zT and S2 of p-type PbTe are optimal e.g. 700-900K. The previously suggested temperature induced rapid rise in energy of the heavy hole LVB relative to the light hole UVB is not supported by the experimental data.

  14. B3LYP, BLYP and PBE DFT band structures of the nucleotide base stacks

    NASA Astrophysics Data System (ADS)

    Szekeres, Zs; Bogr, F.; Ladik, J.

    DFT crystal orbital (band structure) calculations have been performed for the nucleotide base stacks of cytosine, thymine, adenine, and guanine arranged in DNA B geometry. The band structures obtained with PBE, BLYP, and B3LYP functionals are presented and compared to other related experimental and theoretical results. The influence of the quality of the basis set on the fundamental gap values was also investigated using Clementi's double ?, 6-31G and 6-31G* basis sets.

  15. Observation of interface band structure by ballistic-electron-emission microscopy

    NASA Technical Reports Server (NTRS)

    Bell, L. D.; Kaiser, W. J.

    1988-01-01

    The paper reports an advanced ballistic electron spectroscopy technique that was used to directly measure semiconductor band structure properties at a subsurface interface. Two interface systems having contrasting band structures were investigated by this method: Au-Si and Au-GaAs. It is concluded that the proposed method, based on scanning tunneling microscopy, enables the spatially resolved carrier-transport spectroscopy of interfaces.

  16. Sea Surface Wind Field by X-Band TerraSAR-X and Tandem-X

    NASA Astrophysics Data System (ADS)

    Lehner, Susanne; Li, Xiaoming; Ren, Yongzheng; He, Mingxia

    2013-01-01

    In the present study, we present the newly developed Geophysical Model Function (GMF), denoted XMOD2, to retrieve the sea surface wind field from X-band TerraSAR-X/Tandem-X (TS-X/TD-X) data. In contrary to the previous XMOD1, XMOD2 is based on a nonlinear GMF, and moreover it also depicts the difference between upwind and downwind of the sea surface backscatter. By exploiting 371 collocations, the retrieved TS-X/TD-X sea surface wind speed by XMOD2 agrees well with in situ buoy measurements with a bias of 0.39 m/s, an RMSE of 1.52 m/s and a scatter index (SI) of 16.1%. To evaluate the sea surface wind field retrieved from X-band SAR, we conducted a joint campaign in the South China Sea in August, 2011. Examples of sea surface wind field retrieved from the TS-X/TD-X data acquired in the campaign are shown for demonstration.

  17. Probing the wurtzite conduction band structure using state filling in highly doped InP nanowires.

    PubMed

    Wallentin, Jesper; Mergenthaler, Kilian; Ek, Martin; Wallenberg, L Reine; Samuelson, Lars; Deppert, Knut; Pistol, Mats-Erik; Borgstrm, Magnus T

    2011-06-01

    We have grown InP nanowires doped with hydrogen sulfide, which exhibit sulfur concentrations of up to 1.4%. The highest doped nanowires show a pure wurtzite crystal structure, in contrast to bulk InP which has the zinc blende structure. The nanowires display photoluminescence which is strongly blue shifted compared with the band gap, well into the visible range. We find evidence of a second conduction band minimum at the gamma point about 0.23 eV above the band edge, in excellent agreement with recent theoretical predictions. Electrical measurements show high conductivity and breakdown currents of 10(7) A/cm(2). PMID:21604708

  18. Satellite Surface Characterization from Non-resolved Multi-band Optical Observations

    NASA Astrophysics Data System (ADS)

    Hall, D.; Hamada, K.; Kelecy, T.; Kervin, P.

    2012-09-01

    Ground-based optical and radar sites routinely acquire resolved images of satellites. These resolved images provide the means to construct accurate wire-frame models of the observed body, as well as an understanding of its orientation as a function of time. Unfortunately, because such images are typically acquired at a single wavelength, this kind of analysis provides little or no information on the types of materials covering the satellite's various surfaces. Detailed surface material characterization generally requires multi-band radiometric and/or spectrometric measurements. Fortunately, many widely-available instruments provide such multi-band information (e.g., spectrographs and multi-channel photometers). However, these sensors typically measure the brightness of sunlight reflected from the entire satellite, with no spatial resolution at all. Because such whole-body measurements represent a summation of contributions from many reflecting surfaces, an "un-mixing" analysis process must be employed to characterize the reflectance of the satellite's sub-components. The objective of this presentation is to outline the theory required to retrieve satellite surface properties from temporal sequences of whole-body, multi-band brightness measurements, focusing on two newly-developed analysis methods. Both methods require the following as input: 1) a set of multi-band measurements of a satellite's reflected-sunlight brightness, 2) the satellite's wire-frame model, including each major sub-component capable of reflecting sunlight, 3) the satellite's attitude, specifying the orientation of all of the body's components at the time of each multi-band measurement. In addition, the first method requires laboratory-measured bi-directional reflection distribution functions (BRDFs) for a set of candidate materials covering the satellite's surfaces, and yields estimates of the fraction of each major satellite sub-component covered by each candidate material. The second method does not require any pre-tabulated BRDFs, but instead attempts to retrieve BRDFs for each major satellite sub-component from the non-resolved data using a series expansion approach.

  19. Brain surface conformal parameterization using Riemann surface structure.

    PubMed

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

    2007-06-01

    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 a parallelogram. The resulting surface subdivision and the parameterizations of the components are intrinsic and stable (their solutions tend to be smooth functions and the boundary conditions of the Dirichlet problem can be enforced). Conformal parameterization also helps transform partial differential equations (PDEs) that may be defined on 3-D brain surface manifolds to modified PDEs on a two-dimensional parameter domain. Since the Jacobian matrix of a conformal parameterization is diagonal, the modified PDE on the parameter domain is readily solved. To illustrate our techniques, we computed parameterizations for several types of anatomical surfaces in 3-D magnetic resonance imaging scans of the brain, including the cerebral cortex, hippocampi, and lateral ventricles. For surfaces that are topologically homeomorphic to each other and have similar geometrical structures, we show that the parameterization results are consistent and the subdivided surfaces can be matched to each other. Finally, we present an automatic sulcal landmark location algorithm by solving PDEs on cortical surfaces. The landmark detection results are used as constraints for building conformal maps between surfaces that also match explicitly defined landmarks. PMID:17679336

  20. Brain Surface Conformal Parameterization Using Riemann Surface Structure

    PubMed Central

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

    2011-01-01

    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 a parallelogram. The resulting surface subdivision and the parameterizations of the components are intrinsic and stable (their solutions tend to be smooth functions and the boundary conditions of the Dirichlet problem can be enforced). Conformal parameterization also helps transform partial differential equations (PDEs) that may be defined on 3-D brain surface manifolds to modified PDEs on a two-dimensional parameter domain. Since the Jacobian matrix of a conformal parameterization is diagonal, the modified PDE on the parameter domain is readily solved. To illustrate our techniques, we computed parameterizations for several types of anatomical surfaces in 3-D magnetic resonance imaging scans of the brain, including the cerebral cortex, hippocampi, and lateral ventricles. For surfaces that are topologically homeomorphic to each other and have similar geometrical structures, we show that the parameterization results are consistent and the subdivided surfaces can be matched to each other. Finally, we present an automatic sulcal landmark location algorithm by solving PDEs on cortical surfaces. The landmark detection results are used as constraints for building conformal maps between surfaces that also match explicitly defined landmarks. PMID:17679336

  1. 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.

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

    SciTech Connect

    Reshchikov, M. A.; Usikov, A.; Helava, H.; Makarov, Yu.

    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.

  3. 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

  4. 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.

  5. Micro-metric electronic patterning of a topological band structure using a photon beam

    NASA Astrophysics Data System (ADS)

    Golden, Mark; Frantzeskakis, Emmanouil; de Jong, Nick; Huang, Yingkai; Wu, Dong; Pan, Yu; de Visser, Anne; van Heumen, Erik; van Bay, Tran; Zwartsenberg, Berend; Pronk, Pieter; Varier Ramankutty, Shyama; Tytarenko, Alona; Xu, Nan; Plumb, Nick; Shi, Ming; Radovic, Milan; Varkhalov, Andrei

    2015-03-01

    The only states crossing EF in ideal, 3D TIs are topological surface states. Single crystals of Bi2Se3andBi2Te3 are too defective to exhibit bulk-insulating behaviour, and ARPES shows topologically trivial 2DEGs at EF in the surface region due to downward band bending. Ternary & quaternary alloys of Bi /Te /Se /Sb hold promise for obtaining bulk-insulating crystals. Here we report ARPES data from quaternary, bulk-insulating, Bi-based TIs. Shortly after cleavage in UHV, downward band bending pulls the bulk conduction band below EF, once again frustrating the ``topological only'' ambition for the Fermi surface. However, there is light at the end of the tunnel: we show that a super-band-gap photon beam generates a surface photovoltage sufficient to flatten the bands, thereby recovering the ideal, ``topological only'' situation. In our bulk-insulating quaternary TIs, this effect is local in nature, and permits the writing of arbitrary, micron-sized patterns in the topological energy landscape at the surface. Support from FOM, NWO and the EU is gratefully acknowledged.

  6. 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.

  7. Estimating Sea Surface Salinity and Wind Using Combined Passive and Active L-Band Microwave Observations

    NASA Technical Reports Server (NTRS)

    Yueh, Simon H.; Chaubell, Mario J.

    2012-01-01

    Several L-band microwave radiometer and radar missions have been, or will be, operating in space for land and ocean observations. These include the NASA Aquarius mission and the Soil Moisture Active Passive (SMAP) mission, both of which use combined passive/ active L-band instruments. Aquarius s passive/active L-band microwave sensor has been designed to map the salinity field at the surface of the ocean from space. SMAP s primary objectives are for soil moisture and freeze/thaw detection, but it will operate continuously over the ocean, and hence will have significant potential for ocean surface research. In this innovation, an algorithm has been developed to retrieve simultaneously ocean surface salinity and wind from combined passive/active L-band microwave observations of sea surfaces. The algorithm takes advantage of the differing response of brightness temperatures and radar backscatter to salinity, wind speed, and direction, thus minimizing the least squares error (LSE) measure, which signifies the difference between measurements and model functions of brightness temperatures and radar backscatter. The algorithm uses the conjugate gradient method to search for the local minima of the LSE. Three LSE measures with different measurement combinations have been tested. The first LSE measure uses passive microwave data only with retrieval errors reaching 1 to 2 psu (practical salinity units) for salinity, and 1 to 2 m/s for wind speed. The second LSE measure uses both passive and active microwave data for vertical and horizontal polarizations. The addition of active microwave data significantly improves the retrieval accuracy by about a factor of five. To mitigate the impact of Faraday rotation on satellite observations, the third LSE measure uses measurement combinations invariant under the Faraday rotation. For Aquarius, the expected RMS SSS (sea surface salinity) error will be less than about 0.2 psu for low winds, and increases to 0.3 psu at 25 m/s wind speed for warm waters (25 C). To achieve the required 0.2 psu accuracy, the impact of sea surface roughness (e.g. wind-generated ripples) on the observed brightness temperature has to be corrected to better than one tenth of a degree Kelvin. With this algorithm, the accuracy of retrieved wind speed will be high, varying from a few tenths to 0.6 m/s. The expected direction accuracy is also excellent (less than 10 ) for mid to high winds, but degrades for lower speeds (less than 7 m/s).

  8. Application and comparison of band gap narrowing models for passivated phosphorus doped silicon surfaces

    NASA Astrophysics Data System (ADS)

    Kimmerle, Achim; Greulich, Johannes; Haug, Halvard; Wolf, Andreas

    2016-01-01

    In this work, the recently proposed band-gap narrowing model by Yan and Cuevas [J. Appl. Phys. 114, 044508 (2013)] is evaluated by simulations of the recombination pre-factor J0 of highly phosphorus doped, passivated crystalline silicon surfaces, which are particularly relevant for solar cell applications. The results were fitted to experimental J0 data measured on a large range of samples exhibiting different dopant profiles and passivation coatings, both for planar and textured surfaces. For each sample, the surface recombination velocity parameter Sp was extracted by fitting the simulation results to the experimental data. We show that the Yan and Cuevas' model developed for Fermi-Dirac statistics leads to a smooth and monotonically increasing curve for Sp as a function of the surface dopant concentration Nsurf, for both investigated passivation layers. We provide a parameterization for this relation and compare the findings with those obtained with the widely used model by Schenk [J. Appl. Phys. 84, 3684 (1998)]. On the other hand, we show that the apparent band gap narrowing of Yan and Cuevas developed for use with Boltzmann statistics cannot be used to describe the experimental data, requiring unphysical negative Sp values for high Nsurf.

  9. An open-structure sound insulator against low-frequency and wide-band acoustic waves

    NASA Astrophysics Data System (ADS)

    Chen, Zhe; Fan, Li; Zhang, Shu-yi; Zhang, Hui; Li, Xiao-juan; Ding, Jin

    2015-10-01

    To block sound, i.e., the vibration of air, most insulators are based on sealed structures and prevent the flow of the air. In this research, an acoustic metamaterial adopting side structures, loops, and labyrinths, arranged along a main tube, is presented. By combining the accurately designed side structures, an extremely wide forbidden band with a low cut-off frequency of 80 Hz is produced, which demonstrates a powerful low-frequency and wide-band sound insulation ability. Moreover, by virtue of the bypass arrangement, the metamaterial is based on an open structure, and thus air flow is allowed while acoustic waves can be insulated.

  10. 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.

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

    SciTech Connect

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

    2015-01-21

    The theoretically suggested band structure of the novel p-type semiconductor lithium niobite (LiNbO{sub 2}), the direct coupling of photons to ion motion, and optically induced band structure modifications are investigated by temperature dependent photoluminescence. LiNbO{sub 2} 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.

  12. Electron Microscopy and X-Ray Diffraction Evidence for Two Z-Band Structural States

    PubMed Central

    Perz-Edwards, Robert J.; Reedy, Michael K.

    2011-01-01

    In vertebrate muscles, Z-bands connect adjacent sarcomeres, incorporate several cell signaling proteins, and may act as strain sensors. Previous electron microscopy (EM) showed Z-bands reversibly switch between a relaxed, “small-square” structure, and an active, “basketweave” structure, but the mechanism of this transition is unknown. Here, we found the ratio of small-square to basketweave in relaxed rabbit psoas muscle varied with temperature, osmotic pressure, or ionic strength, independent of activation. By EM, the A-band and both Z-band lattice spacings varied with temperature and pressure, not ionic strength; however, the basketweave spacing was consistently 10% larger than small-square. We next sought evidence for the two Z-band structures in unfixed muscles using x-ray diffraction, which indicated two Z-reflections whose intensity ratios and spacings correspond closely to the EM measurements for small-square and basketweave if the EM spacings are adjusted for 20% shrinkage due to EM processing. We conclude that the two Z-reflections arise from the small-square and basketweave forms of the Z-band as seen by EM. Regarding the mechanism of transition during activation, the effects of Ca2+ in the presence of force inhibitors suggested that the interconversion of Z-band forms was correlated with tropomyosin movement on actin. PMID:21806939

  13. 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.

  14. Effects of chemical pressure on the Fermi surface and band dispersion of the electron-doped high- Tc superconductors

    NASA Astrophysics Data System (ADS)

    Ikeda, M.; Yoshida, T.; Fujimori, A.; Kubota, M.; Ono, K.; Das, Hena; Saha-Dasgupta, T.; Unozawa, K.; Kaga, Y.; Sasagawa, T.; Takagi, H.

    2009-07-01

    We have performed angle-resolved photoemission spectroscopy measurements and first-principles electronic-structure calculations on the electron-doped high- Tc superconductors (HTSCs) Ln1.85Ce0.15CuO4 ( Ln=Nd , Sm, and Eu). The observed Fermi surface and band dispersion show such changes that with decreasing ionic size of Ln3+ (increasing chemical pressure), the curvature of the Fermi surface or -t'/t decreases, where t and t' are transfer integrals between the nearest-neighbor and next-nearest-neighbor Cu sites, respectively, explaining the apparently inconsistent behavior seen in the hole-doped HTSC La2-xSrxCuO4 under epitaxial strain. Around the node, the antiferromagnetic gap is opened with increasing chemical pressure. We propose that the nodal gap opening is possibly due to the decrease in -t'/t through the improved nesting, leading to the decrease in Tc .

  15. Band gap and structure of single crystal BiI3: Resolving discrepancies in literature

    NASA Astrophysics Data System (ADS)

    Podraza, Nikolas J.; Qiu, Wei; Hinojosa, Beverly B.; Xu, Haixuan; Motyka, Michael A.; Phillpot, Simon R.; Baciak, James E.; Trolier-McKinstry, Susan; Nino, Juan C.

    2013-07-01

    Bismuth tri-iodide (BiI3) is an intermediate band gap semiconductor with potential for room temperature gamma-ray detection applications. Remarkably, very different band gap characteristics and values of BiI3 have been reported in literature, which may be attributed to its complicated layered structure with strongly bound BiI6 octahedra held together by weak van der Waals interactions. Here, to resolve this discrepancy, the band gap of BiI3 was characterized through optical and computational methods and differences among previously reported values are discussed. Unpolarized transmittance and reflectance spectra in the visible to near ultraviolet (UV-Vis) range at room temperature yielded an indirect band gap of 1.67 0.09 eV, while spectroscopic ellipsometry detected a direct band gap at 1.96 0.05 eV and higher energy critical point features. The discrepancy between the UV-Vis and ellipsometry results originates from the low optical absorption coefficients (? 102 cm-1) of BiI3 that renders reflection-based ellipsometry insensitive to the indirect gap for this material. Further, electronic-structure calculations of the band structure by density functional theory methods are also consistent with the presence of an indirect band gap of 1.55 eV in BiI3. Based on this, an indirect band gap with a value of 1.67 0.09 eV is considered to best represent the band gap structure and value for single crystal BiI3.

  16. Structure and properties of solid surfaces

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.

    1974-01-01

    Difficulties in experimental studies of crystalline surfaces are related to the fact that surface atoms have an intrinsic tendency to react with their environment. A second problem is connected with the effective thickness of surfaces, which ranges from one to several atom layers. The phenomenology of surface interactions with gases are considered, taking into account physical adsorption, chemisorption, and the oxidation of surfaces. Studies of the surface structure are discussed, giving attention to field emission microscopy, field-ion microscopy, electron diffraction techniques, Auger spectroscopy, scanning electron microscopy, electron probe microanalysis, ion microprobe methods, and low-energy backscattering spectroscopy. Investigations of semiconductor surfaces are also described.

  17. Assessing Surface Textural Variations on the Piton de la Fournaise Volcano Using L-Band Insar and LIDAR Fusion Study

    NASA Astrophysics Data System (ADS)

    Sedze, M.; Heggy, E.; Jacquemoud, S.; Bretar, F.

    2010-12-01

    Interferometric Synthetic Aperture Radar (InSAR) is a powerful tool to monitor deformation in active volcanoes, such as the Piton de La Fournaise (Reunion Island, France). However vegetation and pyrochlast covers could constrain the L-band InSAR coherence and then the reliability for measurement of pre-eruptive surface displacements. To correct this deficiency, we combine normalized airborne LiDAR intensity data with spaceborne InSAR coherence images from ALOS PALSAR L-band acquired over the Piton de la Fournaise in 2008 and 2009, just after the 2007 major eruption. The fusion of the two data sets improves the calculation of coherence and the textural classification of different pyrochlastic and lava flows. For the DESDynI (Deformation, Ecosystem Structure and Dynamics of Ice) mission, such data fusion studies can provide a better analysis of the spatiotemporal variations in InSAR coherence in order to enhance the monitoring of pre-eruptive ground displacements. The LiDAR intensity data are used to improve the accuracy of InSAR-derived estimates of surface elevation and roughness, especially in vegetated areas. The airborne campaigns carried out on overlapping areas of the Piton de la Fournaise cover different types of vegetation and terrain roughness on the central and western part of the volcano. The LiDAR data are first processed to generate an accurate and high-resolution digital terrain model of the volcanic edifice so as to characterize its surface features and to analyze morphological variations during this two-year period. Then normalized LiDAR intensity images are computed and compared to coherence L-band InSAR images for different zones of the volcano to assess the Lidar-inSAR statistical behavior of different lava flows, pyrochlastics, and vegetated surfaces. Empirical models that use normalized LiDAR intensity to correct L-band polarimetric coherence for vegetated surfaces are finally tested. Preliminary results suggest that different A'A and Pahoehoe lava flows have a unique LiDAR-InSAR intensity-coherence function, which remains unchanged even in the case of moderate vegetation cover. Moreover ashes, cinders and spatter cones show a well-distinguished intensity-coherence function for vegetated and bare terrains.

  18. Progress report on new rf breakdown studies in an S-band structure at SLAC

    SciTech Connect

    Wang, J.W.; Loew, G.A.

    1987-02-01

    This paper gives a progress report on RF breakdown studies carried out at SLAC on an S-band standing-wave disk-loaded accelerator structure. The structure is the same as described at two earlier conferences but it has been equipped with eight new radial probes and one output port to observe the emission of light, which has not yet been used. The earlier breakdown limit of 144 MV/m equivalent traveling-wave accelerating gradient and 312 MV/m peak surface field has been reached again and possibly exceeded slightly even though the disk iris edges are severely pitted from earlier tests. Using the new probes it has become possible to monitor field emission as a function of azimuthal direction as well as to record the signals generated at the instant of breakdown. Results are given together with some information on the condition of the structure, chemical cleaning and RF processing. The paper ends with the presentation of some speculations and future plans.

  19. First identification of rotational band structures in 91 75 166Re

    NASA Astrophysics Data System (ADS)

    Li, H. J.; Doncel, M.; Patial, M.; Cederwall, B.; Bäck, T.; Jakobsson, U.; Auranen, K.; Bönig, S.; Drummond, M.; Grahn, T.; Greenlees, P.; HerzáÅ, A.; Joss, D. T.; Julin, R.; Juutinen, S.; Konki, J.; Kröll, T.; Leino, M.; McPeake, C.; O'Donnell, D.; Page, R. D.; Pakarinen, J.; Partanen, J.; Peura, P.; Rahkila, P.; Ruotsalainen, P.; Sandzelius, M.; Sarén, J.; Sayǧı, B.; Scholey, C.; Sorri, J.; Stolze, S.; Taylor, M. J.; Thornthwaite, A.; Uusitalo, J.; Xiao, Z. G.

    2015-07-01

    Excited states in the odd-odd, highly neutron-deficient nucleus 166Re have been investigated via the 92Mo(78Kr,3 p 1 n )166Re reaction. Prompt γ rays were detected by the JUROGAM II γ -ray spectrometer, and the recoiling fusion-evaporation products were separated by the recoil ion transport unit (RITU) gas-filled recoil separator and implanted into the Gamma Recoil Electron Alpha Tagging spectrometer located at the RITU focal plane. The tagging and coincidence techniques were applied to identify the γ -ray transitions in 166Re, revealing two collective, strongly coupled rotational structures, for the first time. The more strongly populated band structure is assigned to the π h11 /2[514 ] 9 /2-⊗ν i13 /2[660 ] 1 /2+ Nilsson configuration, while the weaker structure is assigned to be built on a two-quasiparticle state of mixed π h11 /2[514 ] 9 /2-⊗ν [h9 /2f7 /2] 3 /2- character. The configuration assignments are based on the electromagnetic characteristics and rotational properties, in comparison with predictions from total Routhian surface and particle-rotor model calculations.

  20. Band gap engineering of CdTe nanocrystals through chemical surface modification.

    PubMed

    Akamatsu, Kensuke; Tsuruoka, Takaaki; Nawafune, Hidemi

    2005-02-16

    We demonstrate band gap control of CdTe nanocrystals by selective surface modification using alkanethiol molecules. Both absorption and emission wavelengths can be tuned simply by mixing a dispersion of the nanocrystals with alkanethiol at room temperature, resulting in blue shifts in the optical spectra during reaction. The degree of blue shift depends on both the concentration of alkanethiols and the reaction time, thereby providing kinetic control over the emission peak wavelength of the nanocrystals in mild conditions. The observed spectral changes are suggested to be caused by a decrease in the size of the CdTe core through formation of CdTe1-x(SC10)x shells because of specific exchange of Te with alkanethiolates. The results reported herein provide a new band gap engineering scheme for semiconductor nanocrystals and offer opportunities for the design of ligand-stabilized semiconductor nanocrystals with tunable composition and optical properties. PMID:15700986

  1. Potential energy surface and vibrational band origins of the triatomic lithium cation

    NASA Astrophysics Data System (ADS)

    Searles, Debra J.; Dunne, Simon J.; von Nagy-Felsobuki, Ellak I.

    The 104 point CISD Li +3 potential energy surface and its analytical representation is reported. The calculations predict the minimum energy geometry to be an equilateral triangle of side RLi?Li = 3.0 and of energy - 22.20506 E h. A fifth-order MorseDunham type analytical force field is used in the CarneyPorter normal co-ordinate vibrational Hamiltonian, the corresponding eigenvalue problem being solved variationally using a 560 configurational finite-element basis set. The predicted assignment of the vibrational band origins is in accord with that reported for H +3. Moreover, for 6Li +3 and 7Li +3 the lowest i.r. accessible band origin is the overline?0,1,1 predicted to be at 243.6 and 226.0 cm -1 respectively.

  2. Investigation of the vertical structure of clouds over the Western Ghats, India using X-band and Ka-band Doppler radar observations

    NASA Astrophysics Data System (ADS)

    Das, Subrata Kumar

    Investigation of the vertical structure of clouds over the Western Ghats, India using X-band and Ka-band Doppler radar observations Subrata Kumar Das*, S. M. Deshpande, K. Chakravarty and M. C. R. Kalapureddy Indian Institute of Tropical Meteorology, Pune, India ABSTRACT The Western Ghats (WGs) located parallel to the west coast of India receives a huge amount of rainfall during the Indian summer monsoon (ISM) in which topography plays a huge role in it. To understand the dynamics and microphysics of monsoon precipitating clouds over the WGs, a High Altitude Cloud Physics Laboratory (HACPL) has been setup at Mahabaleshwar (17.92 oN, 73.6 oE, ~1.4 km AMSL) in 2012. As part of this laboratory, a mobile X-band (9.5 GHz) and Ka-band (35.29 GHz) dual-polarization Doppler weather radar system is installed at Mandhardev (18.04 oN, 73.87 oE, ~1.3 km AMSL, at 26 km radial distance from the HACPL). The X-band radar shows the dominant cloud movement is from the western side of the WGs to the eastern side, crossing the HACPL and the radar site. The cloud occurrence statistics show a sudden reduction within a distance of ~30 km on the eastern side of WGs indicates the possibility of a rain shadow area. Further, we investigate the vertical structure of cloud over the HACPL, and identified four cloud modes viz., shallow cumulus mode, congestus mode, deep convective mode, and overshooting convection mode. The frequency distribution of cloud-cell base height (CBH) and cloud-cell top height (CTH) shows most of the clouds with base below 2.5 km and tops usually not exceeding 9 km. This indicates the dominance of warm-rain process in the WGs region. The positive relationships between surface rainfall rates and CTH and 0oC isotherm level have observed. Details will be presented in the upcoming symposium.

  3. Reducing support loss in micromechanical ring resonators using phononic band-gap structures

    NASA Astrophysics Data System (ADS)

    Hsu, Feng-Chia; Hsu, Jin-Chen; Huang, Tsun-Che; Wang, Chin-Hung; Chang, Pin

    2011-09-01

    In micromechanical resonators, energy loss via supports into the substrates may lead to a low quality factor. To eliminate the support loss, in this paper a phononic band-gap structure is employed. We demonstrate a design of phononic-crystal (PC) strips used to support extensional wine-glass mode ring resonators to increase the quality factor. The PC strips are introduced to stop elastic-wave propagation by the band-gap and deaf-band effects. Analyses of resonant characteristics of the ring resonators and the dispersion relations, eigenmodes, and transmission properties of the PC strips are presented. With the proposed resonator architecture, the finite-element simulations show that the leaky power is effectively reduced and the stored energy inside the resonators is enhanced simultaneously as the operating frequencies of the resonators are within the band gap or deaf bands. Realization of a high quality factor micromechanical ring resonator with minimized support loss is expected.

  4. Evidence for water structuring forces between surfaces

    SciTech Connect

    Stanley, Christopher B; Rau, Dr. Donald

    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.

  5. Promoting Photochemical Water Oxidation with Metallic Band Structures.

    PubMed

    Liu, Hongfei; Mor, Ren; Grundmann, Henrik; Cui, Chunhua; Erni, Rolf; Patzke, Greta R

    2016-02-10

    The development of economic water oxidation catalysts is a key step toward large-scale water splitting. However, their current exploration remains empirical to a large extent. Elucidating the correlations between electronic properties and catalytic activity is crucial for deriving general and straightforward catalyst design principles. Herein, strongly correlated electronic systems with abundant and easily tunable electronic properties, namely La1-xSrxBO3 perovskites and La2-xSrxBO4 layered perovskites (B = Fe, Co, Ni, or Mn), were employed as model systems to identify favorable electronic structures for water oxidation. We established a direct correlation between the enhancement of catalytic activity and the insulator to metal transition through tuning the electronic properties of the target perovskite families via the La(3+)/Sr(2+) ratio. Their improved photochemical water oxidation performance was clearly linked to the increasingly metallic character. These electronic structure-activity relations provide a promising guideline for constructing efficient water oxidation catalysts. PMID:26771537

  6. Sorting of droplets by migration on structured surfaces

    PubMed Central

    Roth-Nebelsick, Anita

    2011-01-01

    Summary Background: Controlled transport of microdroplets is a topic of interest for various applications. It is well known that liquid droplets move towards areas of minimum contact angle if placed on a flat solid surface exhibiting a gradient of contact angle. This effect can be utilised for droplet manipulation. In this contribution we describe how controlled droplet movement can be achieved by a surface pattern consisting of cones and funnels whose length scales are comparable to the droplet diameter. Results: The surface energy of a droplet attached to a cone in a symmetry-preserving way can be smaller than the surface energy of a freely floating droplet. If the value of the contact angle is fixed and lies within a certain interval, then droplets sitting initially on a cone can gain energy by moving to adjacent cones. Conclusion: Surfaces covered with cone-shaped protrusions or cavities may be devised for constructing band-conveyors for droplets. In our approach, it is essentially the surface structure which is varied, not the contact angle. It may be speculated that suitably patterned surfaces are also utilised in biological surfaces where a large variety of ornamentations and surface structuring are often observed. PMID:21977433

  7. Density Banding in Coral Skeletons: A Biotic Response to Sea Surface Temperature?

    NASA Astrophysics Data System (ADS)

    Hill, C. A.; Oehlert, A. M.; Piggot, A. M.; Yau, P. M.; Fouke, B. W.

    2008-12-01

    Density bands in the CaCO3 (aragonite) skeleton of scleractinian corals are commonly used as chronometers, where crystalline couplets of high and low density bands represent the span of one year. This provides a sensitive reconstructive tool for paleothermometry, paleoclimatology and paleoecology. However, the detailed mechanisms controlling aragonite nucleation and crystallization events and the rate of skeletal growth remain uncertain. The organic matrix, composed of macromolecules secreted by the calicoblastic ectoderm, is closely associated with skeletal precipitation and is itself incorporated into the skeleton. We postulate that density banding is primarily controlled by changes in the rate of aragonite crystal precipitation mediated by the coral holobiont response to changes in sea surface temperature (SST). To test this hypothesis, data were collected from coral skeleton-tissue biopsies (2.5 cm in diameter) extracted from four species of Montastraea growing on the fringing reef tract of Curacao, Netherlands Antilles (annual mean variation in SST is 29 C in mid-September to 26 C in late February). Samples were collected in the following three contextual modes: 1) at two sites (Water Plant and Playa Kalki) along a lateral 25 km spatial transect; 2) across a vertical bathymetric gradient from 5 to 15 m water depth at each site; and 3) at strategic time periods spanning the 3 C annual variations in SST. Preliminary results indicate that skeletal density banding is also expressed in the organic matrix, permitting biochemical characterization and correlation of the organic matrix banding to the skeletal banding. In addition, both surficial and ectodermal mucins were characterized in terms of total protein content, abundance and location of their anionic, cationic, and neutral macromolecular constituents. Furthermore, the ratio of mucocytes in the oral ectoderm to gastrodermal symbiotic zooxanthellae has permitted estimates of seasonal carbon allocation by the coral holobiont. Our nanometer-scale optical analyses of crystal morphology, arrangement, and densities have revealed consistent changes between high and low skeletal density bands. Mass spectrometry, newly developed immunohistochemical staining, fluorescence and polarized light microscopy are in progress to further quantify and model these observations.

  8. Broad band and absolute measurement of transient dynamic normal velocity of surface

    NASA Astrophysics Data System (ADS)

    Kim, Byoung-Geuk; Enoki, Manabu; Kishi, Teruo

    1998-02-01

    Broad band direct sensing of the transient dynamic normal velocity of an object surface and evaluating its absolute value were realized by using a sensor fabricated with a piezoelectric polyvinylidene fluoride film and a polyvinyl chloride (PVC) back load and a PVC wear plate. The transient output signal from the sensor obtained by a test employing a well-defined steplike force, at the epicenter of a steel plate, showed very good agreement with the dynamic normal velocity calculated by using a Green's function and a simulated source function. The output was proportional to the dynamic normal velocity of the surface, and the frequency-dependent sensitivity for the velocity was flat within a deviation of ±3.8 dB for the average in the frequency range up to 2 MHz. The transient dynamic normal velocity of the surface could be absolutely determined by using a sensor calibrated by theoretical one.

  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. Three-Dimensional Structure of Vertebrate Muscle Z-Band: The Small-Square Lattice Z-Band in Rat Cardiac Muscle.

    PubMed

    Burgoyne, Thomas; Morris, Edward P; Luther, Pradeep K

    2015-11-01

    The Z-band in vertebrate striated muscle crosslinks actin filaments of opposite polarity from adjoining sarcomeres and transmits tension along myofibrils during muscular contraction. It is also the location of a number of proteins involved in signalling and myofibrillogenesis; mutations in these proteins lead to myopathies. Understanding the high-resolution structure of the Z-band will help us understand its role in muscle contraction and the role of these proteins in the function of muscle. The appearance of the Z-band in transverse-section electron micrographs typically resembles a small-square lattice or a basketweave appearance. In longitudinal sections, the Z-band width varies more with muscle type than species: slow skeletal and cardiac muscles have wider Z-bands than fast skeletal muscles. As the Z-band is periodic, Fourier methods have previously been used for three-dimensional structural analysis. To cope with variations in the periodic structure of the Z-band, we have used subtomogram averaging of tomograms of rat cardiac muscle in which subtomograms are extracted and compared and similar ones are averaged. We show that the Z-band comprises four to six layers of links, presumably ?-actinin, linking antiparallel overlapping ends of the actin filaments from the adjoining sarcomeres. The reconstruction shows that the terminal 5-7nm of the actin filaments within the Z-band is devoid of any ?-actinin links and is likely to be the location of capping protein CapZ. PMID:26362007

  11. Relationships between magnetic foot points and G-band bright structures

    NASA Astrophysics Data System (ADS)

    Ishikawa, R.; Tsuneta, S.; Kitakoshi, Y.; Katsukawa, Y.; Bonet, J. A.; Vargas Domnguez, S.; Rouppe van der Voort, L. H. M.; Sakamoto, Y.; Ebisuzaki, T.

    2007-09-01

    Aims:Magnetic elements are thought to be described by flux tube models, and are well reproduced by MHD simulations. However, these simulations are only partially constrained by observations. We observationally investigate the relationship between G-band bright points and magnetic structures to clarify conditions, which make magnetic structures bright in G-band. Methods: The G-band filtergrams together with magnetograms and dopplergrams were taken for a plage region covered by abnormal granules as well as ubiquitous G-band bright points, using the Swedish 1-m Solar Telescope (SST) under very good seeing conditions. Results: High magnetic flux density regions are not necessarily associated with G-band bright points. We refer to the observed extended areas with high magnetic flux density as magnetic islands to separate them from magnetic elements. We discover that G-band bright points tend to be located near the boundary of such magnetic islands. The concentration of G-band bright points decreases with inward distance from the boundary of the magnetic islands. Moreover, G-band bright points are preferentially located where magnetic flux density is higher, given the same distance from the boundary. There are some bright points located far inside the magnetic islands. Such bright points have higher minimum magnetic flux density at the larger inward distance from the boundary. Convective velocity is apparently reduced for such high magnetic flux density regions regardless of whether they are populated by G-band bright points or not. The magnetic islands are surrounded by downflows. Conclusions: These results suggest that high magnetic flux density, as well as efficient heat transport from the sides or beneath, are required to make magnetic elements bright in G-band.

  12. Photonic band gap characteristics of one-dimensional graphene-dielectric periodic structures

    NASA Astrophysics Data System (ADS)

    Al-sheqefi, F. U. Y.; Belhadj, W.

    2015-12-01

    In this paper, we study theoretically, the transmission properties of a one-dimensional graphene-dielectric periodic structure by using the transfer matrix method. Within the framework of this method, we confirm earlier finding that a periodic structure composed of a stack of monolayer graphene sheets separated by dielectric slabs, possesses photonic band-gap (PBG) properties and supports a series of bandpass and band-stop regions at low-terahertz frequencies. Our calculations showed that the suggested structure possesses in addition to the structural Bragg gaps, a new type of band gap that exhibits a rather versatile behavior with varying angle of incidence. We find this type of band gap is omnidirectional (omni-gap) for both transverse electric (TE) and transverse magnetic (TM) polarizations. Our results show that 1D graphene-dielectric periodic structures are very good candidates for band gap engineering. Specifically, we demonstrate the existence of a band gap region for both polarizations which survives for incident angles as high as 80°. Moreover, we show how our proposed structure can also function as a highly efficient polarization splitter. It is also found that the band gaps can be tuned by tuning the properties of the graphene via a gate voltage. In order to investigate difference between the omni-gap and Bragg PBG, we plot the electromagnetic field profiles for some critical frequencies. The proposed structure is promising and can work as a gate tunable perfect stop filter which completely blocks both polarizations, and may have many other potential applications.

  13. Surface crystallography and electronic structure of potassium yttrium tungstate

    SciTech Connect

    Atuchin, V. V.; Pokrovsky, L. D.; Khyzhun, O. Yu.; Sinelnichenko, A. K.; Ramana, C. V.

    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.

  14. Band structure of silicene in the tight binding approximation

    NASA Astrophysics Data System (ADS)

    Gert, A. V.; Nestoklon, M. O.; Yassievich, I. N.

    2015-07-01

    The electronic structure of silicene is simulated by the tight binding method with the basis sp 3 d 5 s*. The results are in good agreement with ab initio calculations. The effective Hamiltonian of silicene in the vicinity of the Dirac point is constructed by the method of invariants. Silicon atoms in silicene are located in two parallel planes displaced perpendicularly to each other by ? z ; the energy spectrum essentially depends on this displacement. Using the tight binding technique, the coefficients of the effective Hamiltonian are determined for various values of ? z .

  15. 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

  16. 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.

  17. Curvature effects in the band structure of carbon nanotubes including spin-orbit coupling

    NASA Astrophysics Data System (ADS)

    Liu, Hong; Heinze, Dirk; Thanh Duc, Huynh; Schumacher, Stefan; Meier, Torsten

    2015-11-01

    The Kane-Mele model was previously used to describe effective spin-orbit couplings (SOCs) in graphene. Here we extend this model and also incorporate curvature effects to analyze the combined influence of SOC and curvature on the band structure of carbon nanotubes (CNTs). The extended model then reproduces the chirality-dependent asymmetric electron-hole splitting for semiconducting CNTs and in the band structure for metallic CNTs shows an opening of the band gap and a change of the Fermi wave vector with spin. For chiral semiconducting CNTs with large chiral angle we show that the spin-splitting configuration of bands near the Fermi energy depends on the value of \\text{mod}(2n+m,3) .

  18. Curvature effects in the band structure of carbon nanotubes including spin-orbit coupling.

    PubMed

    Liu, Hong; Heinze, Dirk; Thanh Duc, Huynh; Schumacher, Stefan; Meier, Torsten

    2015-11-11

    The Kane-Mele model was previously used to describe effective spin-orbit couplings (SOCs) in graphene. Here we extend this model and also incorporate curvature effects to analyze the combined influence of SOC and curvature on the band structure of carbon nanotubes (CNTs). The extended model then reproduces the chirality-dependent asymmetric electron-hole splitting for semiconducting CNTs and in the band structure for metallic CNTs shows an opening of the band gap and a change of the Fermi wave vector with spin. For chiral semiconducting CNTs with large chiral angle we show that the spin-splitting configuration of bands near the Fermi energy depends on the value of [Formula: see text]. PMID:26451898

  19. Electronic- and band-structure evolution in low-doped (Ga,Mn)As

    SciTech Connect

    Yastrubchak, O.; Gluba, L.; Żuk, J.; Sadowski, J.; MAX-Lab, Lund University, 22100 Lund ; Krzyżanowska, H.; Department of Physics and Astronomy, Vanderbilt University, 6506 Stevenson Center, Nashville, Tennessee 37325 ; Domagala, J. Z.; Andrearczyk, T.; Wosinski, T.

    2013-08-07

    Modulation photoreflectance spectroscopy and Raman spectroscopy have been applied to study the electronic- and band-structure evolution in (Ga,Mn)As epitaxial layers with increasing Mn doping in the range of low Mn content, up to 1.2%. Structural and magnetic properties of the layers were characterized with high-resolution X-ray diffractometry and SQUID magnetometery, respectively. The revealed results of decrease in the band-gap-transition energy with increasing Mn content in very low-doped (Ga,Mn)As layers with n-type conductivity are interpreted as a result of merging the Mn-related impurity band with the host GaAs valence band. On the other hand, an increase in the band-gap-transition energy with increasing Mn content in (Ga,Mn)As layers with higher Mn content and p-type conductivity indicates the Moss-Burstein shift of the absorption edge due to the Fermi level location within the valence band, determined by the free-hole concentration. The experimental results are consistent with the valence-band origin of mobile holes mediating ferromagnetic ordering in the (Ga,Mn)As diluted ferromagnetic semiconductor.

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

    SciTech Connect

    Kim, Jinhyun; Yim, Sanggyu

    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.

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

    SciTech Connect

    Shao, Yang; Yao, Kefu; Liu, Xue; Li, Mo; School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0245

    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.

  2. Spin-orbit coupling in the band structure of reconstructed 1T- TaS2

    NASA Astrophysics Data System (ADS)

    Rossnagel, K.; Smith, N. V.

    2006-02-01

    Empirical tight-binding simulations of the band structure of 1T-TaS2 reveal that the combination of spin-orbit coupling and the low-temperature 1313 reconstruction generates a distinct and very narrow band at the Fermi level. Spin-orbit interaction is therefore important in any understanding of the correlation effects in this material. The states within the split-off band are primarily of dx2-y2 , dxy character and reside preferentially on the central atom of the Star-of-David cluster.

  3. SURFACE STRUCTURE OF ISOLATED NEURONS

    PubMed Central

    Hamberger, Anders; Hansson, Hans-Arne; Sjstrand, Johan

    1970-01-01

    Freehand, isolated neuronal perikarya from the hypoglossal nucleus of the rabbit have been examined with light-and electron-microscopy (transmission and scanning). The surface of the cell bodies was largely covered with spherical particles which were 0.52 in diameter. Transmission electron microscopy proved that the spherical particles were synaptic nerve terminals. Crush of the hypoglossal nerve which leads to chromatolysis and swelling of the neuronal cell bodies results in a conspicuous reduction in the number of terminals attached to the surface of hypoglossal neurons. This effect was observed both for isolated neurons and in tissue sections. The effect is considered in relation to earlier reported variations in the adherence of neuropil to isolated neuronal perikarya. The functional importance of nerve ending detachment in connection with nerve injury is discussed. PMID:19866734

  4. Nitrogen δ-doping for band engineering of GaAs-related quantum structures

    NASA Astrophysics Data System (ADS)

    Ishikawa, Fumitaro; Furuse, Shinichiro; Sumiya, Kengo; Kinoshita, Akihiro; Morifuji, Masato

    2012-03-01

    We study energy-band engineering with nitrogen delta (δ)-doping in GaAs-related quantum structures. A tight-binding calculation indicates that the band structure can be engineered by introducing the one-dimensional doping profile of nitrogen into GaAs. Using molecular beam epitaxy, we prepare δ-doped samples of AlGaAs/GaAs quantum wells and GaAs/δ-doped nitrogen superlattice structures at the growth temperature 560 °C. Photoluminescence obtained from the samples shows a clear redshift of the spectral peak positions dependent on the nitrogen coverage. The transition energies of the superlattice structures agree well with those obtained from photoreflectance, indicating the feasibility of band modification with a single or a multiple nitrogen δ-doped layer.

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

    SciTech Connect

    De, A.; Pryor, Craig E.

    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.

  6. Polarization-dependent diffraction in all-dielectric, twisted-band structures

    NASA Astrophysics Data System (ADS)

    Karda?, Tomasz M.; Jagodnicka, Anna; Wasylczyk, Piotr

    2015-11-01

    We propose a concept for light polarization management: polarization-dependent diffraction in all-dielectric microstructures. Numerical simulations of light propagation show that with an appropriately configured array of twisted bands, such structures may exhibit zero birefringence and at the same time diffract two circular polarizations with different efficiencies. Non-birefringent structures as thin as 3 ?m have a significant difference in diffraction efficiency for left- and right-hand circular polarizations. We identify the structural parameters of such twisted-band matrices for optimum performance as circular polarizers.

  7. 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

    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)

  8. Fiber-coupled surface-emitting photonic crystal band edge laser for biochemical sensor applications

    NASA Astrophysics Data System (ADS)

    Kim, Sunghwan; Lee, Jeongkug; Jeon, Heonsu; Kim, Hyo Jin

    2009-03-01

    We report on a refractive index sensor platform based on a surface-emitting photonic crystal (PC) ?-point band edge laser (BEL). A simple butt-end fiber coupling makes the BEL system compact, while the translational symmetry of the PC pattern removes the necessity of fiber alignment. The laser wavelength shifts linearly to longer wavelengths as the refractive index of the environmental medium increases. Our BEL system had an index resolution of 10-3. Taking into account the alignment-free nature, as well as its ultracompactness and high fiber-coupled laser output, the BEL system is well suited to a label-free sensor platform for biochemical applications.

  9. Band structure and dispersion engineering of strongly coupled plasmon-phonon-polaritons in graphene-integrated structures.

    PubMed

    Liu, Feng; Zhan, Tianrong; Zhu, Alexander Y; Yi, Fei; Shi, Wangzhou

    2016-01-25

    We theoretically investigate the polaritonic band structure and dispersion properties of graphene using transfer matrix methods, with strongly coupled graphene plasmons (GPs) and molecular infrared vibrations as a representative example. Two common geometrical configurations are considered: graphene coupled subwavelength dielectric grating (GSWDG) and graphene nanoribbons (GNR). By exploiting the dispersion and the band structure, we show the possibility of tailoring desired polaritonic behavior in each of the two configurations. We compare the strength of coupling occurring in both structures and find that the interaction is stronger in GNR than that of GSWDG structure as a result of the stronger field confinement of the edge modes. The band structure and dispersion analysis not only sheds light on the physics of the hybridized polariton formation but also offers insight into tailoring the optical response of graphene light-matter interactions for numerous applications, such as biomolecular sensing and detection. PMID:26832528

  10. Surface waves in 2D photonic macroporous silicon structures

    NASA Astrophysics Data System (ADS)

    Karachevtseva, Lyudmyla A.; Glushko, Olexandr; Karas, Mikola I.; Onishchenko, Volodimir

    2005-04-01

    Effects of increase in absorption of electromagnetic radiation, enhancement of photoconductivity and surface wave formation in 2D photonic macroporous silicon were investigated. Dependence of photoconductivity on a corner of the falling of the electromagnetic radiation, prevalence of absorption over reflection of light, as well as enhancement of the photoconductivity in comparison with the monocrystalline silicon testify to formation of surface waves (surface polaritons) in illuminated macroporous silicon structures. For wavelengths less than optical period of macropores there is an essential reduction in transmittance of electromagnetic radiation to (2-3)10-2 (in comparison with the homogeneous material) and the polaritonic band formation. Conformity of spectra of photoconductivity of macroporous silicon to spectra of intrinsic photoconductivity of monocrystal silicon testifies the enrichment of a macropore surface by photocarriers and formation of a surface electromagnetic wave of plasmon type. Elecrtroreflectance spectroscopy of macroporous silicon surface showed an intrinsic electric field near 106 V/cm due to positive charge built in oxide layer on the walls of the macropores. Thus, electronic gas is quantified in a surface layer of the macroporous silicon structure. Polariton frequencies in long-wave part of the macroporous silicon optical transmittance are commensurable with experimental values of the surface plasmon frequency in the two dimensional electronic gas on Si-SiO2 boundary.

  11. 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.

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

    SciTech Connect

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

    2015-01-21

    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 H{sub 2}/H{sub 2}O and O{sub 2}/H{sub 2}O levels of water correspond to both occupied and unoccupied states within the a-C pseudogap region. These are localized states associated to sp{sup 2} 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.

  13. WISE 2000 campaign: sea surface salinity and wind retrievals from L-band radiometry

    NASA Astrophysics Data System (ADS)

    Camps, Adriano; Corbella, Ignasi; Font, Jordi; Etchetto, Jacqueline; Duffo, Nuria; Vall-llossera, Merce; Bara, Javier; Torres, Francisco; Wursteisen, Patrick; Martin-Neira, Manuel

    2000-12-01

    Sea surface salinity (SSS) has been recognized as a key parameter in climatological studies. SSS can be measured by passive microwave remote sensing at L band, where the sensitivity of the brightness temperatures shows a maximum and the atmosphere is almost transparent. To provide global coverage of this basic parameter with a 3-day revisit time, the SMOS mission was recently selected by ESA within the frame of the Earth Explorer Opportunity Missions. The SMOS mission will carry the MIRAS instrument, the first 2D L-band aperture synthesis interferometric radiometer. To address new challenges that this mission presents, such as incidence angle variation with pixel, polarization mixing, effect of wind and foam and others, a measurement campaign has been sponsored by ESA under the name of WISE 2000 and it is scheduled for October-November 2000. Two L-band radiometers, a video, a IR and a stereo-camera and four oceanographic and meteorological buoys will be installed in the oil platform 'Casablanca' located at 40 Km off the coast of Tarragona, where the sea conditions are representative of the Mediterranean open sea with periodic influence of the Ebro river fresh water plume.

  14. Band structure calculations for dilute nitride quantum wells under compressive or tensile strain

    NASA Astrophysics Data System (ADS)

    Carrère, H.; Marie, X.; Barrau, J.; Amand, T.; Ben Bouzid, S.; Sallet, V.; Harmand, J.-C.

    2004-08-01

    We have calculated the band structure of InGaAsN/GaAs(N)/GaAs compressively strained quantum wells (QW) emitting at 1.3 µm using the band anticrossing model and an eight-band \\mathbf {k}\\bdot \\mathbf {p} Hamiltonian. The calculated interband optical transition energies have been compared to the experimental ones deduced from photocurrent, photoluminescence and excitation of photoluminescence spectroscopy experiments and measured laser characteristics extracted from the recent literature. Because of the high compressive strain in the QW, strain-compensated structures may be required in order to grow stable multiple QWs; in view of this we have studied the band structure of InGaAsN/GaAsP/GaAs QWs emitting at 1.3 µm. Dilute nitride structures also offer the possibility of growing tensile strained QW lasers on InP substrate emitting in the 1.55 µm emission wavelength range. In order to evaluate the potentialities of such structures we have determined the band characteristics of InGaAsN/InGaAsP/InP heterostructures with a TM polarized fundamental transition.

  15. Structure and functions of fungal cell surfaces

    NASA Technical Reports Server (NTRS)

    Nozawa, Y.

    1984-01-01

    A review with 24 references on the biochemistry, molecular structure, and function of cell surfaces of fungi, especially dermatophytes: the chemistry and structure of the cell wall, the effect of polyene antibiotics on the morphology and function of cytoplasmic membranes, and the chemical structure and function of pigments produced by various fungi are discussed.

  16. Estimation of Bare Surface Soil Moisture and Surface Roughness Parameter Using L-Band SAR Image Data

    NASA Technical Reports Server (NTRS)

    Shi, Jian-Cheng; Wang, James; Hsu, Ann Y.; ONeill, Peggy E.; Engman, Edwin T.

    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 Synthetic Aperture Radar operated by the Jet Propulsion Laboratory) and SIR-C (Spaceborne Imaging Radar-C) over a well- managed watershed in southwest Oklahoma. Prior to its application for soil moisture inversion, a good agreement was found between the single-scattering IEM simulations and the L band measurements of SIR-C and AIRSAR over a wide range of soil moisture and surface roughness conditions. The sensitivity of soil moisture variation to the co-polarized signals were then examined under the consideration of the calibration accuracy of various components of SAR measurements. It was found that the two co-polarized backscattering coefficients and their combinations would provide the best input to the algorithm for estimation of soil moisture and roughness parameter. Application of the inversion algorithm to the co-polarized measurements of both AIRSAR and SIR-C resulted in estimated values of soil moisture and roughness parameter for bare and short-vegetated fields that compared favorably with those sampled on the ground. The root-mean-square (rms) errors of the comparison were found to be 3.4% and 1.9 dB for soil moisture and surface roughness parameter, respectively.

  17. Band structure of charge-ordered doped antiferromagnets

    NASA Astrophysics Data System (ADS)

    Granath, Mats

    2004-06-01

    We study the distribution of electronic spectral weight in a doped antiferromagnet with various types of charge order, and compare to angle resolved photoemission experiments on lightly doped La2-x Srx CuO4 (LSCO) and electron-doped Nd2-x Cex CuO4? . Calculations on in-phase stripe and bubble phases for the electron-doped system are both in good agreement with the experiment, including, in particular, the existence of in-gap spectral weight. In addition we find that for in-phase stripes, in contrast to antiphase stripes, the chemical potential is likely to move with doping. For the hole-doped system we find that staircase stripes, which are globally diagonal but locally vertical or horizontal, can reproduce the photoemission data with the characteristic Fermi arcs, whereas pure diagonal stripes cannot. We also calculate the magnetic structure factors of such staircase stripes and find that as the stripe separation is decreased with increased doping, these evolve from diagonal to vertical, separated by a coexistence region. The results suggest that the transition from horizontal to diagonal stripes seen in neutron scattering on underdoped LSCO may be a crossover between a regime where the typical length of straight stripe segments is longer than the interstripe spacing, to one where it is shorter and that, locally, the stripes are always aligned with the Cu-O bonds.

  18. Turbulence structure over inhomogeneous heated surface

    NASA Astrophysics Data System (ADS)

    Nosov, V. V.; Lukin, V. P.; Nosov, E. V.; Torgaev, A. V.

    2015-11-01

    Structure of air turbulent motion inside closed volume (without exchange of internal and external medium through the borders) over inhomogeneous heated underlying surface had been studied by numerical solving of boundary value problems for hydrodynamics equations (Navier-Stokes). The solitary large vortices (coherent structures, topological solitons) whose decay generates the coherent turbulence are observed over homogeneous heated surface. Inhomogeneous heated surface leads to the appearance of Kolmogorov (incoherent) turbulence. The simulations confirm our previously experimentally (inside the dome rooms of astronomical telescopes) and theoretically stated conclusion that the mixing of coherent structures of different close-by sizes and different frequencies of major vortices results in the non-coherent Kolmogorov turbulence.

  19. Structural evolution of cometary surfaces

    NASA Astrophysics Data System (ADS)

    Wallis, M. K.; Wickramasinghe, N. C.

    1991-04-01

    Comets with a high content of organics and light molecules are expected under cosmic radiation to gain a relatively unreactive crust and less volatile material to some 10 m deep. Interstellar dust impacts act to loosen and turn over about 1 cm of the surface. This paper discusses how far this accords with observations of cometary dust halos and new versus old comets. Two key material properties have emerged from recent studies: (1) the source of cometary volatiles is not ice in the sense of material with a single sublimation energy, and (2) the particulates are not simply mineral dust but include much organic material, some of which undergoes chemical processing and exchanges with the gaseous environment.

  20. H-tailored surface conductivity in narrow band gap In(AsN)

    SciTech Connect

    Velichko, A. V. E-mail: anton.velychko@nottingham.ac.uk; Patanè, A. E-mail: anton.velychko@nottingham.ac.uk; Makarovsky, O.; Capizzi, M.; Polimeni, A.; Sandall, I. C.; Tan, C. H.; Giubertoni, D.; Krier, A.; Zhuang, Q.

    2015-01-12

    We show that the n-type conductivity of the narrow band gap In(AsN) alloy can be increased within a thin (∼100 nm) channel below the surface by the controlled incorporation of H-atoms. This channel has a large electron sheet density of ∼10{sup 18 }m{sup −2} and a high electron mobility (μ > 0.1 m{sup 2}V{sup −1}s{sup −1} at low and room temperature). For a fixed dose of impinging H-atoms, its width decreases with the increase in concentration of N-atoms that act as H-traps thus forming N-H donor complexes near the surface.

  1. Electron emission from conduction band of heavily phosphorus doped diamond negative electron affinity surface

    NASA Astrophysics Data System (ADS)

    Yamada, Takatoshi; Masuzawa, Tomoaki; Mimura, Hidenori; Okano, Ken

    2016-02-01

    Hydrogen (H)-terminated surfaces of diamond have attracted significant attention due to their negative electron affinity (NEA), suggesting high-efficiency electron emitters. Combined with n-type doping technique using phosphorus (P) as donors, the unique NEA surface makes diamond a promising candidate for vacuum cold-cathode applications. However, high-electric fields are needed for the electron emission from the n-type doped diamond with NEA. Here we have clarified the electron emission mechanism of field emission from P-doped diamond having NEA utilizing combined ultraviolet photoelectron spectroscopy/field emission spectroscopy (UPS/FES). An UP spectrum has confirmed the NEA of H-terminated (1 1 1) surface of P-doped diamond. Despite the NEA, electron emission occurs only when electric field at the surface exceeds 4.2  ×  106 V cm‑1. Further analysis by UPS/FES has revealed that the emitted energy level is shifted, indicating that the electron emission mechanism of n-type diamond having NEA surface does not follow a standard field emission theory, but is dominated by potential barrier formed within the diamond due to upward band bending. The reduction of internal barrier is the key to achieve high-efficiency electron emitters using P-doped diamond with NEA, of which application ranges from high-resolution electron spectroscopy to novel vacuum nanoelectronics devices.

  2. Magnifying narrow-band imaging of surface patterns for diagnosing colorectal cancer.

    PubMed

    Misawa, Masashi; Kudo, Shin-Ei; Wada, Yoshiki; Nakamura, Hiroki; Toyoshima, Naoya; Hayashi, Seiko; Mori, Yuichi; Kudo, Toyoki; Hayashi, Takemasa; Wakamura, Kunihiko; Miyachi, Hideyuki; Yamamura, Fuyuhiko; Hamatani, Shigeharu

    2013-07-01

    Narrow-band imaging (NBI) of surface microvessels of colorectal lesions is useful for differentiating neoplasms from non-neoplasms and for predicting histopathological diagnosis. Furthermore, NBI of surface microstructure, or 'surface pattern', is valuable for predicting histopathology in colorectal cancer. The aim of the present study was to investigate whether surface patterns could be used to predict invasion depth in colorectal cancer, and to compare the accuracy of surface pattern diagnosis in each macroscopic type. Between January 2010 and March 2011, a series of 357 consecutive patients with 378 early colorectal cancers were observed by magnifying NBI and the surface pattern was prospectively evaluated. Surface pattern was classified into 3 types: type I, microstructure was clearly recognised with uniform arrangement and form; type II, microstructure was obscured with heterogeneous arrangement and form; and type III, microstructure was invisible. We also classified the macroscopic type into 3 categories: depressed, protruded and flat elevated. Assuming that type III was an index of massively invasive lesions in the submucosal layer (SMm), the sensitivity, specificity and accuracy were 56.9, 91.7 and 85.7%, respectively. The sensitivity, specificity and accuracy of type III for the diagnosis of SMm in each macroscopic type were: depressed, 88.9, 40.0 and 63.2%, respectively; protruded: 34.8, 96.4 and 90.0%, respectively; and flat elevated, 54.2, 92.7 and 85.0%, respectively. These results suggest that the diagnostic accuracy of surface pattern was insufficient and particularly poor for depressed-type lesions. PMID:23673484

  3. Effect of clustering on the surface plasmon band in thin films of metallic nanoparticles

    NASA Astrophysics Data System (ADS)

    Pereira, Rui M. S.; Borges, Joel; Peres, Filipa C. R.; Pereira, Paulo A. S.; Smirnov, Georgi V.; Vaz, Filipe; Cavaleiro, Albano; Vasilevskiy, Mikhail I.

    2015-01-01

    We theoretically investigate the optical response of ensembles of polarizable metallic nanoparticles (NPs) that form (1) submonolayer films of particles adsorbed on a dielectric substrate, considered as two-dimensional (2-D) systems, and (2) thin three-dimensional (3-D) films, where NPs are embedded in a dielectric matrix. For system (1), the effect of NPs' distance to the substrate is taken into account. In both cases, we find that short-range clustering leads to a broadening and a spectral shift of the absorption band related to the surface plasmon resonance (SPR) in individual NPs. We show that the clustering can help in achieving spectrally broad SPR bands, especially if NPs aggregate into fractal clusters, which can be interesting for some applications such as surface-enhanced Raman scattering. In particular, submonolayer films on NPs generated using the diffusion-limited aggregation algorithm produce sizable and spectrally broad absorption, which can be tuned to the visible range by choosing an appropriate capping and/or substrate material. Calculated results for thin 3-D films are compared with experimental data obtained for Au/TiO2 nanocomposite layers produced by reactive cosputtering.

  4. L-Band Brightness Temperature Variations at Dome C and Snow Metamorphism at the Surface

    NASA Technical Reports Server (NTRS)

    Brucker, Ludovic; Dinnat, Emmanuel; Picard, Ghislain; Champollion, Nicolas

    2014-01-01

    The Antarctic Plateau is a promising site to monitor microwave radiometers' drift, and to inter-calibrate microwave radiometers, especially 1.4 GigaHertz (L-band) radiometers on board the Soil Moisture and Ocean Salinity (SMOS), and AquariusSAC-D missions. The Plateau is a thick ice cover, thermally stable in depth, with large dimensions, and relatively low heterogeneities. In addition, its high latitude location in the Southern Hemisphere enables frequent observations by polar-orbiting satellites, and no contaminations by radio frequency interference. At Dome C (75S, 123E), on the Antarctic Plateau, the substantial amount of in-situ snow measurements available allows us to interpret variations in space-borne microwave brightness temperature (TB) (e.g. Macelloni et al., 2007, 2013, Brucker et al., 2011, Champollion et al., 2013). However, to analyze the observations from the Aquarius radiometers, whose sensitivity is 0.15 K, the stability of the snow layers near the surface that are most susceptible to rapidly change needs to be precisely assessed. This study focuses on the spatial and temporal variations of the Aquarius TB over the Antarctic Plateau, and at Dome C in particular, to highlight the impact of snow surface metamorphism on the TB observations at L-band.

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

    NASA Astrophysics Data System (ADS)

    Avendao, Carlos G.; Reyes, J. Adrin

    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.

  6. Graphene Oxide Regulated Tin Oxide Nanostructures: Engineering Composition, Morphology, Band Structure, and Photocatalytic Properties.

    PubMed

    Pan, Xiaoyang; Yi, Zhiguo

    2015-12-16

    A facile, one-step hydrothermal method has been developed to fabricate tin oxide-reduced graphene oxide (Sn-RGO) nanocomposites with tunable composition, morphology, and energy band structure by utilizing graphene oxide (GO) as a multifunctional two-dimensional scaffold. By adjusting the GO concentration during synthesis, a variety of tin oxide nanomaterials with diverse composition and morphology are obtained. Simultaneously, the varying of GO concentration can also narrow the bandgap and tune the band edge positions of the Sn-RGO nanocomposites. As a result, the Sn-RGO nanocomposites with controllable composition, morphology, and energy band structure are obtained, which exhibit efficient photoactivities toward methyl orange (MO) degradation under visible-light irradiation. It is expected that our work would point to the new possibility of using GO for directing synthesis of semiconductor nanomaterials with tailored structure and physicochemical properties. PMID:26581093

  7. 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.

  8. 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

  9. Monte Carlo analysis of band structure influence on impact ionization in InP

    NASA Astrophysics Data System (ADS)

    Chandramouli, V.; Maziar, C. M.

    1993-02-01

    The influence of electronic band structure on the impact ionization phenomena in InP was studied using the Monte Carlo method. Realistic band structures evaluated using the nonlocal pseudopotential method were employed. Threshold energies for impact ionization were calculated throughout the first Brillouin zone. A new impact ionization model which explicitly takes into account the wave-vector dependence of impact ionization threshold energies was used to calculate the ionization rate. The simulation results of drift velocity and ionization coefficient agree very well with experimental data. In spite of significant anisotropy in the threshold energies and complex band structures, no significant orientational dependence was found in the ionization coefficients. An important result of the work presented here is the demonstration that the biaxial elastic strain in InP produced by the lattice mismatch between adjacent layers in a heterostructure can significantly alter the impact ionization thresholds.

  10. Space-Borne Ku-Band Radar Observations of Extreme Surface Water Conditions

    NASA Astrophysics Data System (ADS)

    Nghiem, S. V.

    2005-12-01

    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 of surface water including liquid and solid phases on land, ice, and oceans. Ku-band backscatter data acquired globally by the QuikSCAT satellite scatterometer are used to obtain the results. Hurricane Katrina in 2005 is the deadliest and costliest in U.S. with far-reaching impacts. Radar results of surface water over southern and eastern U.S. reveal the extreme extent of precipitation water deposited on land surface compared to the case of Hurricane Ivan in 2004. Radar monitoring of surface water pattern in California shows the extreme prolonged duration of precipitation-induced water in the 2005 wettest winter season over a century causing widespread flooding and landslide. For drought monitoring, radar maps of precipitation frequency over the U.S. Midwest in summer seasons indicate a sharp change to a severe drought in 2003 from the most frequent rains in 2000. Kenya experienced the worst drought in 45 years affecting more than 3 million people in 2000 when the radar data over Nairobi identified the collapse of the long rain season. Since then, satellite radar time-series up to July 2005 shows the consistency of the annual bimodal precipitation seasons suggesting an improvement in the local drought conditions. In cold land regions, backscatter data map seasonal snowmelt processes showing large variabilities in time and in space over the northern hemisphere. Satellite Ku-band radar measurements of snow accumulation on the Greenland ice sheet identify and map the record snow accumulation in the first quarter of 2005, verified with field observations and measurements from surface station networks, providing an extreme amount of water mass equivalent to more than three times the total glacier discharge by calving over the same duration. In Antarctica, radar results discover extensive ice layer created by anomalous melt in 2005 in coastal areas to regions well inland with local melt detected for the first time ever in the data history. Over the Arctic, sea ice extent has remained in a minimal condition in summers in the past four consecutive years (2002-2005) and multi-year ice areas in winters are reduced as seen in radar mapping results. These Ku-band radar capabilities in observing water states from space lend strong supports to future satellite Ku-band radar systems dedicated to measure crucial hydrologic and cryospheric parameters specifically designed to meet accuracy and resolution requirements by science research and operational applications.

  11. Electronic band structure and optical properties of the cubic, Sc, Y and La hydride systems

    SciTech Connect

    Peterman, D.J.

    1980-01-01

    Electronic band structure calculations are used to interpret the optical spectra of the cubic Sc, Y and La hydride systems. Self-consistent band calculations of ScH/sub 2/ and YH/sub 2/ were carried out. The respective joint densities of states are computed and compared to the dielectric functions determined from the optical measurements. Additional calculations were performed in which the Fermi level or band gap energies are rigidly shifted by a small energy increment. These calculations are then used to simulate the derivative structure in thermomodulation spectra and relate the origin of experimental interband features to the calculated energy bands. While good systematic agreement is obtained for several spectral features, the origin of low-energy interband transitions in YH/sub 2/ cannot be explained by these calculated bands. A lattice-size-dependent premature occupation of octahedral sites by hydrogen atoms in the fcc metal lattice is suggested to account for this discrepancy. Various non-self-consistent calculations are used to examine the effect of such a premature occupation. Measurements of the optical absorptivity of LaH/sub x/ with 1.6 < x < 2.9 are presented which, as expected, indicate a more premature occupation of the octahedral sites in the larger LaH/sub 2/ lattice. These experimental results also suggest that, in contrast to recent calculations, LaH/sub 3/ is a small-band-gap semiconductor.

  12. Surface structure of cubic diamond nanowires

    NASA Astrophysics Data System (ADS)

    Barnard, A. S.; Russo, S. P.; Snook, I. K.

    2003-07-01

    Presented are results of our ab initio study of the surface reconstruction and relaxation of (1 0 0) surfaces on diamond nanowires. We have used a density function theory within the generalized-gradient approximation using the Vienna ab initio simulation package, to consider dehydrogenated and hydrogenated surfaces. Edges of nanowires offer a new challenge in the determination of surface structure. We have applied the methodology for stepped diamond (1 0 0) surfaces to this problem, and consider it useful in describing diamond nanowire edges to first approximation. We have found that dimer lengths and atomic layer depths of the C(1 0 0)(2 1) and C(1 0 0)(2 1):H nanowire surfaces differ slightly from those of bulk diamond and nanodiamond surfaces. The aim of this study is provide a better understanding of the effects of nano-scale surfaces on the stability of diamond nanostructures.

  13. Microscopic structure of deformed and superdeformed collective bands in rotating nuclei

    SciTech Connect

    Kvasil, J.; Knapp, F.; Lo Iudice, N.; Andreozzi, F.; Porrino, A.

    2007-03-15

    We investigate in self-consistent cranked Nilsson plus quasiparticle random-phase approximation the structure of {sup 190,192,194}Hg in their evolution from normal to superdeformation and from low to high rotational frequencies. The analysis of the energy levels suggests a splitting of few normally deformed bands into two or more branches. The investigation of the dynamical moments of inertia supports the octupole character of the low-lying negative parity superdeformed bands, in agreement with previous theoretical predictions and experimental findings. As a more direct confirm of their octupole nature, we obtain strong E1 transitions linking those bands to the yrast superdeformed band, in agreement with experiments. A similar result is shown to hold also for {sup 152}Dy. Like in {sup 152}Dy, the collectivity of the low-lying scissors mode gets enhanced with the onset of superdeformation.

  14. Linguist and Nonlinguist Agreement Concerning Surface Structures

    ERIC Educational Resources Information Center

    Rose, Robert G.

    1973-01-01

    To examine the agreement of linguists and non-linguists concerning the acceptability of surface structure, 48 under-graduates classified each of 66 sentences as acceptable or unacceptable while playing different roles. High agreement was confirmed. (Author/KM)

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

    SciTech Connect

    Srinet, Gunjan Kumar, Ravindra Sajal, Vivek

    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.

  16. Size dependence of band structures in a two-dimensional plasmonic crystal with a square lattice.

    PubMed

    Yamamoto, Naoki; Saito, Hikaru

    2014-12-01

    A scanning transmission electron microscope (STEM) -cathodoluminescence (CL) technique is used to investigate the size dependence of the band structures in two-dimensional plasmonic crystals with a square lattice (SQ-PlCs) composed of cylindrical pillars and holes. The experimentally determined and calculated dependences of the band edge energies of the three SPP modes at the Γ point on the diameter of the cylindrical structure agree well. The photon maps reveal the field strength distributions of the standing SPP waves of the three eigenmodes. Additionally, a mechanism is proposed to explain the dependence of the contrast on the detected light polarization. PMID:25606906

  17. Enlarged band gap and electron switch in graphene-based step-barrier structure

    SciTech Connect

    Lu, Wei-Tao Ye, Cheng-Zhi; Institute of Condensed Matter Physics, Linyi University, 276005 Linyi ; Li, Wen

    2013-11-04

    We study the transmission through a step-barrier in gapped graphene and propose a method to enlarge the band gap. The step-barrier structure consists of two or more barriers with different strengths. It is found that the band gap could be effectively enlarged and controlled by adjusting the barrier strengths in the light of the mass term. Klein tunneling at oblique incidence is suppressed due to the asymmetry of step-barrier, contrary to the cases in single-barrier and superlattices. Furthermore, a tunable conductance channel could be opened up in the conductance gap, suggesting an application of the structure as an electron switch.

  18. 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.

  19. Band structure engineering and thermoelectric properties of charge-compensated filled skutterudites

    DOE PAGESBeta

    Shi, Xiaoya; Yang, Jiong; Wu, Lijun; Salvador, James R.; Zhang, Cheng; Villaire, William L.; Haddad, Daad; Yang, Jihui; Zhu, Yimei; Li, Qiang

    2015-10-12

    Thermoelectric properties of semiconductors are intimately related to their electronic band structure, which can be engineered via chemical doping. Dopant Ga in the cage-structured skutterudite Co4Sb12 substitutes Sb sites while occupying the void sites. Combining quantitative scanning transmission electron microscopy and first-principles calculations, we show that Ga dual-site occupancy breaks the symmetry of the Sb-Sb network, splits the deep triply-degenerate conduction bands, and drives them downward to the band edge. The charge-compensating nature of the dual occupancy Ga increases overall filling fraction limit. By imparting this unique band structure feature, and judiciously doping the materials by increasing the Yb content,more » we promote the Fermi level to a point where carriers are in energetic proximity to these features. Increased participation of these heavier bands in electronic transport leads to increased thermopower and effective mass. Further, the localized distortion from Ga/Sb substitution enhances the phonon scattering to reduce the thermal conductivity effectively.« less

  20. Band Structure and Optical Properties of Dilute Ge:C Alloys

    NASA Astrophysics Data System (ADS)

    Stephenson, Chad; O'Brien, William; Qi, Meng; Penninger, Michael; Schneider, William; Gillett-Kunnath, Miriam; Zajicek, Jaroslav; Wistey, Mark

    2015-03-01

    The last major missing piece to achieving integrated Si photonics is an efficient light emitter. Dilute Ge:C alloys offer a new route to create efficient lasers directly within conventional CMOS electronics. Although neither Ge nor C emits light, Ge:C is a highly mismatched alloy, similar to GaAsN, in which band anticrossing is expected to create a direct bandgap. We have performed ab initio band structure simulations using hybrid functionals and spin-orbit coupling that show a sharp decrease in bandgap at the direct conduction band valley with C incorporation, turning Ge:C into a direct bandgap semiconductor and even a semi-metal. We report on the optical properties, highlighting the strength of free carrier absorption due to the changes in the band structure. Some of its potential applications include integrated light emitters, modulators, and photodetectors. With the three-band system, Ge:C also has potential for use in upconverting structures. We also report successful incorporation of C in Ge using hybrid gas+solid source molecular beam epitaxy (MBE) using a precursor gas, tetra(germyl)methane (4GeMe), that prevents undesirable C-C bonds and interstitial incorporation.

  1. High binding energy band structure of Bi-2212 as measured by ARPES

    NASA Astrophysics Data System (ADS)

    McElroy, K.; Graf, J.; Gweon, G.-H.; Zhou, S. Y.; Sahrakorpi, S.; Lindroos, M.; Markiewicz, R. S.; Bansil, A.; Eisaki, H.; Sasagawa, T.; Takagi, H.; Uchida, S.; Lanzara, A.

    2006-03-01

    The study of the electronic structure of high temperature superconductors by angle resolved photoemission spectroscopy (ARPES) has so far focused on the states near the Fermi level, believed to be fundamental for most of the properties of cuprates. However, it is well known that in doped Mott insulators the low and high energy physics are strongly coupled one to the other. Therefore, to gain insight on the real physics of cuprates a full characterization of the electronic band structure up to energies of the order of the lower Hubbard band and beyond is needed. Here we report a detailed, doping dependent study of the band structure of Bi2212 superconductors at energies of the order of 1-2 eV. The experimental results are interpreted in terms of local density approximation (LDA) based computations, where the presence of the ``spaghetti'' of Cu-O and O-bands is predicted. Comparison between computed and measured bands provides insight into many-body renormalization effects.

  2. Band Structure Engineering and Thermoelectric Properties of Charge-Compensated Filled Skutterudites

    PubMed Central

    Shi, Xiaoya; Yang, Jiong; Wu, Lijun; Salvador, James R.; Zhang, Cheng; Villaire, William L.; Haddad, Daad; Yang, Jihui; Zhu, Yimei; Li, Qiang

    2015-01-01

    Thermoelectric properties of semiconductors are intimately related to their electronic band structure, which can be engineered via chemical doping. Dopant Ga in the cage-structured skutterudite Co4Sb12 substitutes Sb sites while occupying the void sites. Combining quantitative scanning transmission electron microscopy and first-principles calculations, we show that Ga dual-site occupancy breaks the symmetry of the Sb-Sb network, splits the deep triply-degenerate conduction bands, and drives them downward to the band edge. The charge-compensating nature of the dual occupancy Ga increases overall filling fraction limit. By imparting this unique band structure feature, and judiciously doping the materials by increasing the Yb content, we promote the Fermi level to a point where carriers are in energetic proximity to these features. Increased participation of these heavier bands in electronic transport leads to increased thermopower and effective mass. Further, the localized distortion from Ga/Sb substitution enhances the phonon scattering to reduce the thermal conductivity effectively. PMID:26456013

  3. Band Structure Engineering and Thermoelectric Properties of Charge-Compensated Filled Skutterudites

    NASA Astrophysics Data System (ADS)

    Shi, Xiaoya; Yang, Jiong; Wu, Lijun; Salvador, James R.; Zhang, Cheng; Villaire, William L.; Haddad, Daad; Yang, Jihui; Zhu, Yimei; Li, Qiang

    2015-10-01

    Thermoelectric properties of semiconductors are intimately related to their electronic band structure, which can be engineered via chemical doping. Dopant Ga in the cage-structured skutterudite Co4Sb12 substitutes Sb sites while occupying the void sites. Combining quantitative scanning transmission electron microscopy and first-principles calculations, we show that Ga dual-site occupancy breaks the symmetry of the Sb-Sb network, splits the deep triply-degenerate conduction bands, and drives them downward to the band edge. The charge-compensating nature of the dual occupancy Ga increases overall filling fraction limit. By imparting this unique band structure feature, and judiciously doping the materials by increasing the Yb content, we promote the Fermi level to a point where carriers are in energetic proximity to these features. Increased participation of these heavier bands in electronic transport leads to increased thermopower and effective mass. Further, the localized distortion from Ga/Sb substitution enhances the phonon scattering to reduce the thermal conductivity effectively.

  4. Band structure engineering and thermoelectric properties of charge-compensated filled skutterudites

    SciTech Connect

    Shi, Xiaoya; Yang, Jiong; Wu, Lijun; Salvador, James R.; Zhang, Cheng; Villaire, William L.; Haddad, Daad; Yang, Jihui; Zhu, Yimei; Li, Qiang

    2015-10-12

    Thermoelectric properties of semiconductors are intimately related to their electronic band structure, which can be engineered via chemical doping. Dopant Ga in the cage-structured skutterudite Co4Sb12 substitutes Sb sites while occupying the void sites. Combining quantitative scanning transmission electron microscopy and first-principles calculations, we show that Ga dual-site occupancy breaks the symmetry of the Sb-Sb network, splits the deep triply-degenerate conduction bands, and drives them downward to the band edge. The charge-compensating nature of the dual occupancy Ga increases overall filling fraction limit. By imparting this unique band structure feature, and judiciously doping the materials by increasing the Yb content, we promote the Fermi level to a point where carriers are in energetic proximity to these features. Increased participation of these heavier bands in electronic transport leads to increased thermopower and effective mass. Further, the localized distortion from Ga/Sb substitution enhances the phonon scattering to reduce the thermal conductivity effectively.

  5. Band Structure Engineering and Thermoelectric Properties of Charge-Compensated Filled Skutterudites.

    PubMed

    Shi, Xiaoya; Yang, Jiong; Wu, Lijun; Salvador, James R; Zhang, Cheng; Villaire, William L; Haddad, Daad; Yang, Jihui; Zhu, Yimei; Li, Qiang

    2015-01-01

    Thermoelectric properties of semiconductors are intimately related to their electronic band structure, which can be engineered via chemical doping. Dopant Ga in the cage-structured skutterudite Co4Sb12 substitutes Sb sites while occupying the void sites. Combining quantitative scanning transmission electron microscopy and first-principles calculations, we show that Ga dual-site occupancy breaks the symmetry of the Sb-Sb network, splits the deep triply-degenerate conduction bands, and drives them downward to the band edge. The charge-compensating nature of the dual occupancy Ga increases overall filling fraction limit. By imparting this unique band structure feature, and judiciously doping the materials by increasing the Yb content, we promote the Fermi level to a point where carriers are in energetic proximity to these features. Increased participation of these heavier bands in electronic transport leads to increased thermopower and effective mass. Further, the localized distortion from Ga/Sb substitution enhances the phonon scattering to reduce the thermal conductivity effectively. PMID:26456013

  6. The Calculation of the Band Structure in 3D Phononic Crystal with Hexagonal Lattice

    NASA Astrophysics Data System (ADS)

    Aryadoust, Mahrokh; Salehi, H.

    2015-12-01

    In this article, the propagation of acoustic waves in the phononic crystals (PCs) of three dimensions with the hexagonal (HEX) lattice is studied theoretically. The PCs are constituted of nickel (Ni) spheres embedded in epoxy. The calculations of the band structure and the density of states are performed using the plane wave expansion (PWE) method in the irreducible part of the Brillouin zone (BZ). In this study, we analyse the dependence of the band structures inside (the complete band gap width) on c/a and filling fraction in the irreducible part of the first BZ. Also, we have analysed the band structure of the ALHA and MLHKM planes. The results show that the maximum width of absolute elastic band gap (AEBG) (0.045) in the irreducible part of the BZ of HEX lattice is formed for c/a=6 and filling fraction equal to 0.01. In addition, the maximum of the first and second AEBG widths are 0.0884 and 0.0474, respectively, in the MLHKM plane, and the maximum of the first and second AEBG widths are 0.0851 and 0.0431, respectively, in the ALHA plane.

  7. Ab initio determination of potential energy surfaces for the first two UV absorption bands of SO2.

    PubMed

    Xie, Changjian; Hu, Xixi; Zhou, Linsen; Xie, Daiqian; Guo, Hua

    2013-07-01

    Three-dimensional potential energy surfaces for the two lowest singlet (A?(1)B1 and B?(1)A2) and two lowest triplet (a?(3)B1 and b?(3)A2) states of SO2 have been determined at the Davidson corrected internally contracted multi-reference configuration interaction level with the augmented correlation-consistent polarized triple-zeta basis set (icMRCI+Q?AVTZ). The non-adiabatically coupled singlet states, which are responsible for the complex Clements bands of the B band, are expressed in a 2 2 quasi-diabatic representation. The triplet state potential energy surfaces, which are responsible for the weak A band, were constructed in the adiabatic representation. The absorption spectrum spanning both the A and B bands, which is calculated with a three-state non-adiabatic coupled Hamiltonian, is in good agreement with experiment, thus validating the potential energy surfaces and their couplings. PMID:23822301

  8. Ab initio determination of potential energy surfaces for the first two UV absorption bands of SO2

    NASA Astrophysics Data System (ADS)

    Xie, Changjian; Hu, Xixi; Zhou, Linsen; Xie, Daiqian; Guo, Hua

    2013-07-01

    Three-dimensional potential energy surfaces for the two lowest singlet (tilde A{}^1B_1 and tilde B{}^1A_2 ) and two lowest triplet (tilde a^3 B_1 and tilde b^3 A_2 ) states of SO2 have been determined at the Davidson corrected internally contracted multi-reference configuration interaction level with the augmented correlation-consistent polarized triple-zeta basis set (icMRCI+Q/AVTZ). The non-adiabatically coupled singlet states, which are responsible for the complex Clements bands of the B band, are expressed in a 2 × 2 quasi-diabatic representation. The triplet state potential energy surfaces, which are responsible for the weak A band, were constructed in the adiabatic representation. The absorption spectrum spanning both the A and B bands, which is calculated with a three-state non-adiabatic coupled Hamiltonian, is in good agreement with experiment, thus validating the potential energy surfaces and their couplings.

  9. Elimination of surface band bending on N-polar InN with thin GaN capping

    NASA Astrophysics Data System (ADS)

    Kuzmk, J.; Ha?k, .; Ku?era, M.; Kdela, R.; Dobro?ka, E.; Adikimenakis, A.; Mi?uk, M.; Gregor, M.; Plecenik, A.; Georgakilas, A.

    2015-11-01

    0.5-1 ?m thick InN {0001} films grown by molecular-beam epitaxy with N- or In-polarity are investigated for the presence of native oxide, surface energy band bending, and effects introduced by 2 to 4 monolayers of GaN capping. Ex situ angle-resolved x-ray photo-electron spectroscopy is used to construct near-surface (GaN)/InN energy profiles, which is combined with deconvolution of In3d signal to trace the presence of InN native oxide for different types of polarity and capping. Downwards surface energy band bending was observed on bare samples with native oxide, regardless of the polarity. It was found that the In-polar InN surface is most readily oxidized, however, with only slightly less band bending if compared with the N-polar sample. On the other hand, InN surface oxidation was effectively mitigated by GaN capping. Still, as confirmed by ultra-violet photo-electron spectroscopy and by energy band diagram calculations, thin GaN cap layer may provide negative piezoelectric polarization charge at the GaN/InN hetero-interface of the N-polar sample, in addition to the passivation effect. These effects raised the band diagram up by about 0.65 eV, reaching a flat-band profile.

  10. Valence-band density of states and surface electron accumulation in epitaxial SnO2 films

    NASA Astrophysics Data System (ADS)

    Vasheghani Farahani, S. K.; Veal, T. D.; Mudd, J. J.; Scanlon, D. O.; Watson, G. W.; Bierwagen, O.; White, M. E.; Speck, J. S.; McConville, C. F.

    2014-10-01

    The surface band bending and electronic properties of SnO2(101) films grown on r-sapphire by plasma-assisted molecular beam epitaxy have been studied by Fourier-transform infrared spectroscopy (FTIR), x-ray photoemission spectroscopy (XPS), Hall effect, and electrochemical capacitance-voltage measurements. The XPS results were correlated with density functional theory calculation of the partial density of states in the valence-band and semicore levels. Good agreement was found between theory and experiment with a small offset of the Sn 4d levels. Homogeneous Sb-doped SnO2 films allowed for the calculation of the bulk Fermi level with respect to the conduction-band minimum within the k .p carrier statistics model. The band bending and carrier concentration as a function of depth were obtained from the capacitance-voltage characteristics and model space charge calculations of the Mott-Schottky plots at the surface of Sb-doped SnO2 films. It was quantitatively demonstrated that SnO2 films have downward band bending and surface electron accumulation. The surface band bending, unoccupied donor surface-state density, and width of the accumulation region all decrease with increasing Sb concentration.

  11. 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.

  12. Geometric and Electronic Structure of Reconstructed Semiconductor Surfaces

    NASA Astrophysics Data System (ADS)

    Carlisle, John Arthur

    The combination of high-resolution photoemission spectroscopy (PES) using synchrotron radiation, and reflection high-energy electron diffraction (RHEED), along with other techniques, have been used to examine the atomic-scale geometric and electronic properties of clean and adsorbate -covered semiconductor surfaces. The surfaces studied have been probed via core-level, valence band, and angle-resolved photoemission spectroscopy, and with the extended photoemission fine structure technique. The surface core-levels and surface states on the Si(111)-(7 x 7) surface have been used to examine submonolayer deposits of Ge onto this surface. Knowledge of the initial stages of interface formation in these systems is important due to their application in heterostructure device physics. The decomposed Si-2p and Ge-3d core levels and angle-integrated valence band spectra have been analyzed as a function of Ge coverage and annealing temperature. The results support the assignment of the lower binding energy component in both the Si-2p and Ge-3d cores to adatom emission. The implications with respect to adatom-to-rest-atom charge transfer are discussed. Lead adlayers on the (111) surfaces of Si and Ge have been examined as well. The surface phase diagram of Pb on these substrates exhibits interesting properties which arise in part due to the differing degrees of lattice matching (~4% for Pb/Si, < 1% for Pb/Ge) and the nature of the clean surface reconstructions ((7 x 7) vs. c(2 x 8)). Atomically abrupt interfaces are insured for these systems since Pb is insoluble in these surfaces even for temperatures well beyond the Pb melting point (340^circC). Thus, they are considered ideal systems to study with regard to metal-semiconductor interface formation and interface -dependent Schottky barrier studies, in contrast to reactive systems where intermixing usually occurs. This lack of interdiffusion has also allowed studies of the 2D melting of the Pb overlayers. The growth, desorption, Schottky -barrier heights, and atomic structure of the Pb-induced phases on Si and Ge are investigated via synchrotron radiation photoemission spectroscopy, along with other techniques such as reflection high-energy electron diffraction and Auger electron spectroscopy (AES). Examining the differences between these closely related systems nicely illustrates the complex interrelationship between the atomic and electronic structure of reconstructed surfaces.

  13. Band stop vibration suppression using a passive X-shape structured lever-type isolation system

    NASA Astrophysics Data System (ADS)

    Liu, Chunchuan; Jing, Xingjian; Chen, Zhaobo

    2016-02-01

    In the paper, band-stop vibration suppression property using a novel X-shape structured lever-type isolation system is studied. The geometrical nonlinear property of an X-shape supporting structure is used to improve the band-stop characteristics in the low frequency range of the lever-type vibration isolator. With the dynamics modeling of this hybrid structural system, it is shown that the proposed hybrid vibration system has very beneficial nonlinear stiffness and damping properties which are helpful to achieve much wider stop bandwidth. Theoretical results demonstrate that the anti-resonant frequencies, width and magnitude of the stop band can all be flexibly designed with structural parameters, and the parameters of the X-shape supporting structure are very critical for designing the band-stop frequency to achieve excellent low-frequency isolation performance. The results in the study provide a new approach to the design of the passive vibration suppression system in the low frequency region.

  14. Quasiparticle band structure and optical properties of the ?12 Si-Ge superstructure from first principles

    NASA Astrophysics Data System (ADS)

    Ahmadpour Monazam, Mohammad Reza; Hingerl, Kurt; Puschnig, Peter

    2013-08-01

    The quasiparticle band structure and dielectric function for the so-called magic sequence SiGe2Si2Ge2SiGe12 (or ?12) structure [Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.108.027401 108, 027401 (2012)] are calculated by many-body perturbation theory (MBPT) within an ab initio framework. On top of density functional calculations within the local density approximation (LDA) leading to a fundamental band gap of 0.23 eV, we have computed the quasiparticle band structure within the G0W0 approach, opening the gap to 0.61 eV. Moreover, we have calculated the optical properties by solving the Bethe-Salpeter equation (BSE) for the electron-hole two-particle correlation function. When comparing the imaginary part of the dielectric function obtained at various levels of approximation-i.e., the independent particle approximation (or random phase approximation) based on (i) the LDA or (ii) GW band structures, and (iii) the BSE including local field effects and electron-hole correlationswe observe that the important first transition is better explained by taking into account excitonic effects. Moreover, the onset transition originating from the direct transition of the magic sequence structure is also investigated.

  15. Band gap structures in two-dimensional super porous phononic crystals.

    PubMed

    Liu, Ying; Sun, Xiu-zhan; Chen, Shao-ting

    2013-02-01

    As one kind of new linear cellular alloys (LCAs), Kagome honeycombs, which are constituted by triangular and hexagonal cells, attract great attention due to the excellent performance compared to the ordinary ones. Instead of mechanical investigation, the in-plane elastic wave dispersion in Kagome structures are analyzed in this paper aiming to the multi-functional application of the materials. Firstly, the band structures in the common two-dimensional (2D) porous phononic structures (triangular or hexagonal honeycombs) are discussed. Then, based on these results, the wave dispersion in Kagome honeycombs is given. Through the component cell porosity controlling, the effects of component cells on the whole responses of the structures are investigated. The intrinsic relation between the component cell porosity and the critical porosity of Kagome honeycombs is established. These results will provide an important guidance in the band structure design of super porous phononic crystals. PMID:23089223

  16. Observation of lateral band-bending in the edge vicinity of atomically-thin Bi insulating film formed on Si(111) surface

    NASA Astrophysics Data System (ADS)

    Nagaoka, Katsumi; Uchihashi, Takashi; Nakayama, Tomonobu

    2016-02-01

    We investigated the local electronic structure in the vicinity of the domain edge of the atomically-thin Bi insulating film formed on a Si(111) surface using a scanning tunneling microscope (STM). We performed site-dependent differential conductance (dI/dV) measurements and found a clear change in the local electronic structure; the shift in the energy position of the valence-band state showed a parabolic behavior as a function of the distance from the edge. It clearly indicates that the local electronic structure in the edge vicinity was electrostatically modified by the lateral band bending. Understanding the lateral changes of electronic structures in the edge vicinity will be helpful for realizing desirable characteristics for nanoscale devices by means of controlling chemical species for the edge termination.

  17. 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.

  18. Estimation of Bare Surface Soil Moisture and Surface Roughness Parameter Using L-Band SAR Image Data

    NASA Technical Reports Server (NTRS)

    Shi, Jian-Cheng; Wang, James; Hsu, Ann; ONeill, Peggy; Engman, Edwin T.

    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 quasi-polarized synthetic aperture radar (SAR) measurements. This algorithm was applied to a series of measurements acquired at L-band (1.25 GHz) from both AIRSAR (Airborne Synthetic Aperture Radar operated by Jet Propulsion Laboratory) and SIR-C (Spaceborne Imaging Radar-C) over a well-managed watershed in southwest Oklahoma. It was found that the two co-polarized backscattering coefficients and their combinations would provide the best input to the algorithm for estimation of soil moisture and roughness parameter. Application of the inversion algorithm to the co-polarized measurements of both AIRSAR and SIR-C resulted in estimated values of soil moisture and roughness parameter for bare and short-vegetated fields that compared favorably with those sampled on the ground. The root-mean-square (rms) errors of the comparison were found to be 3.4% and 1.9 dB for soil moisture and surface roughness parameter, respectively.

  19. 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).

  20. Damping Effect Studies for X-band Normal Conducting High Gradient Standing Wave Structures

    SciTech Connect

    Pei, S.; Li, Z.; Tantawi, S.G.; Dolgashev, V.A.; Wang, J.; /SLAC

    2009-08-03

    The Multi-TeV colliders should have the capability to accelerate low emittance beam with high rf efficiency, X-band normal conducting high gradient accelerating structure is one of the promising candidate. However, the long range transverse wake field which can cause beam emittance dilution is one of the critical issues. We examined effectiveness of dipole mode damping in three kinds of X-band, {pi}-mode standing wave structures at 11.424GHz with no detuning considered. They represent three damping schemes: damping with cylindrical iris slot, damping with choke cavity and damping with waveguide coupler. We try to reduce external Q factor below 20 in the first two dipole bands, which usually have very high (R{sub T}/Q){sub T}. The effect of damping on the acceleration mode is also discussed.

  1. Reconstruction of band structure induced by electronic nematicity in an FeSe superconductor.

    PubMed

    Nakayama, K; Miyata, Y; Phan, G N; Sato, T; Tanabe, Y; Urata, T; Tanigaki, K; Takahashi, T

    2014-12-01

    We have performed high-resolution angle-resolved photoemission spectroscopy on an FeSe superconductor (T_{c}?8??K), which exhibits a tetragonal-to-orthorhombic structural transition at T_{s}?90??K. At low temperature, we found splitting of the energy bands as large as 50meV at the M point in the Brillouin zone, likely caused by the formation of electronically driven nematic states. This band splitting persists up to T?110??K, slightly above T_{s}, suggesting that the structural transition is triggered by the electronic nematicity. We have also revealed that at low temperature the band splitting gives rise to a van Hove singularity within 5meV of the Fermi energy. The present result strongly suggests that this unusual electronic state is responsible for the unconventional superconductivity in FeSe. PMID:25526150

  2. Effects of electronic and lattice polarization on the band structure of delafossite transparent conductive oxides.

    PubMed

    Vidal, Julien; Trani, Fabio; Bruneval, Fabien; Marques, Miguel A L; Botti, Silvana

    2010-04-01

    We use hybrid functionals and restricted self-consistent GW, state-of-the-art theoretical approaches for quasiparticle band structures, to study the electronic states of delafossite Cu(Al,In)O2, the first p-type and bipolar transparent conductive oxides. We show that a self-consistent GW approximation gives remarkably wider band gaps than all the other approaches used so far. Accounting for polaronic effects in the GW scheme we recover a very nice agreement with experiments. Furthermore, the modifications with respect to the Kohn-Sham bands are strongly k dependent, which makes questionable the common practice of using a scissor operator. Finally, our results support the view that the low energy structures found in optical experiments, and initially attributed to an indirect transition, are due to intrinsic defects in the samples. PMID:20481897

  3. Fully opposite spin polarization of electron and hole bands in DyN and related band structures of GdN and HoN

    NASA Astrophysics Data System (ADS)

    Cheiwchanchamnangij, Tawinan; Lambrecht, Walter R. L.

    2015-07-01

    Using quasiparticle self-consistent G W calculations, we show that DyN has an unusual nearly zero indirect gap semimetallic band structure in which the states near the valence band maximum are fully minority spin polarized at ? while the states near the conduction band minimum (at X ) have fully majority spin character. This arises due to a strong hybridization of one of the minority spin f states of dysprosium with the N-2 p bands. The reason why only one of the f bands hybridizes is explained using symmetry arguments. We show that in HoN, this hybridization is already strongly reduced because of the deeper Ho-4 f minority spin states.

  4. Longitudinal surface structures (flowstripes) on Antarctic glaciers

    NASA Astrophysics Data System (ADS)

    Glasser, N. F.; Gudmundsson, G. H.

    2012-03-01

    Longitudinal surface structures ("flowstripes") are common on many glaciers but their origin and significance are poorly understood. In this paper we present observations of the development of these longitudinal structures from four different Antarctic glacier systems; the Lambert Glacier/Amery Ice Shelf area, the Taylor and Ferrar Glaciers in the Ross Sea sector, Crane and Jorum Glaciers (ice-shelf tributary glaciers) on the Antarctic Peninsula, and the onset zone of a tributary to the Recovery Glacier Ice Stream in the Filchner Ice Shelf area. Mapping from optical satellite images demonstrates that longitudinal surface structures develop in two main situations: (1) as relatively wide flow stripes within glacier flow units and (2) as relatively narrow flow stripes where there is convergent flow around nunataks or at glacier confluence zones. Our observations indicate that the confluence features are narrower, sharper, and more clearly defined features. They are characterised by linear troughs or depressions on the ice surface and are much more common than the former type. Longitudinal surface structures within glacier flow units have previously been explained as the surface expression of localised bed perturbations but a universal explanation for those forming at glacier confluences is lacking. Here we propose that these features are formed at zones of ice acceleration and extensional flow at glacier confluences. We provide a schematic model for the development of longitudinal surface structures based on extensional flow that can explain their ridge and trough morphology as well as their down-ice persistence.

  5. Band gap structure modification of amorphous anodic Al oxide film by Ti-alloying

    SciTech Connect

    Canulescu, S. Schou, J.; Rechendorff, K.; Pleth Nielsen, L.; Borca, C. N.; Jones, N. C.; Hoffmann, S. V.; Bordo, K.; Ambat, R.

    2014-03-24

    The band structure of pure and Ti-alloyed anodic aluminum oxide has been examined as a function of Ti concentration varying from 2 to 20 at. %. The band gap energy of Ti-alloyed anodic Al oxide decreases with increasing Ti concentration. X-ray absorption spectroscopy reveals that Ti atoms are not located in a TiO{sub 2} unit in the oxide layer, but rather in a mixed Ti-Al oxide layer. The optical band gap energy of the anodic oxide layers was determined by vacuum ultraviolet spectroscopy in the energy range from 4.1 to 9.2 eV (300–135 nm). The results indicate that amorphous anodic Al{sub 2}O{sub 3} has a direct band gap of 7.3 eV, which is about ∼1.4 eV lower than its crystalline counterpart (single-crystal Al{sub 2}O{sub 3}). Upon Ti-alloying, extra bands appear within the band gap of amorphous Al{sub 2}O{sub 3}, mainly caused by Ti 3d orbitals localized at the Ti site.

  6. Band structures of 182Os studied by GCM based on 3D-CHFB

    NASA Astrophysics Data System (ADS)

    Horibata, Takatoshi; Oi, Makito; Onishi, Naoki; Ansari, Ahmad

    1999-02-01

    Band structure properties of 182Os are investigated through a particle number and angular momentum constrained generator coordinate (GCM) calculation based on self-consistent threedimensional cranking solutions. From the analysis of the wave function of the lowest GCM solution, we confirm that this nucleus shows a tilted rotational motion in its yrast states, at least with the present set of force parameters of the pairing-plus-quadrupole interaction Hamiltonian. A close examination of the behaviour of the other GCM solutions reveals a sign of a possible occurrence of multi-band crossing in the nucleus. We have also found a new potential curve along the prime meridian on the globe of the J = 18 h? sphere. Along this new solution the characters of proton and neutron gap parameters get interchanged. Namely, ? p almost vanishes while ? n grows to a finite value close to the one corresponding to the principal axis rotation (PAR). A state in the new solution curve at the PAR point turns out to have almost the same characteristic features of an yrare s-band state which is located just above the g-band in our calculation. This fact suggests a new type of seesaw vibrational mode of the proton and the neutron pairing, occurring through a wobbling motion. This mode is considered to bridge the g-band states and the s-band states in the backbending region.

  7. Direct observation of asymmetric band structure of bilayer graphene through quantum capacitance measurements

    NASA Astrophysics Data System (ADS)

    Kanayama, Kaoru; Nagashio, Kosuke; Nishimura, Tomonori; Toriumi, Akira

    2014-03-01

    Although upper conduction and valence sub-bands in bilayer graphene are known to be asymmetric, a detailed analysis based on the electrical measurements is very limited due to the infirm quality of gate insulator. In this study, the electrical quality of the top-gate Y2O3 insulator is drastically improved by the high-pressure O2 post-deposition annealing at 100 atm and the carrier density of ~8*1013 cm-2 is achieved. In quantum capacitance measurements, the drastic increase of the density of states is observed in addition to the van Hove singularity, suggesting that the Fermi energy reaches upper sub-band. At the same carrier density, the sudden reduction of the conductivity is observed, indicating that the inter-band scattering occurs. The estimated carrier density required to fill the upper sub-bands is different between electron and hole sides, i.e., asymmetric band structure between upper conduction and valence bands is revealed by the electrical measurements.

  8. Colloids with high-definition surface structures

    PubMed Central

    Chen, Hsien-Yeh; Rouillard, Jean-Marie; Gulari, Erdogan; Lahann, Joerg

    2007-01-01

    Compared with the well equipped arsenal of surface modification methods for flat surfaces, techniques that are applicable to curved, colloidal surfaces are still in their infancy. This technological gap exists because spin-coating techniques used in traditional photolithographic processes are not applicable to the curved surfaces of spherical objects. By replacing spin-coated photoresist with a vapor-deposited, photodefinable polymer coating, we have now fabricated microstructured colloids with a wide range of surface patterns, including asymmetric and chiral surface structures, that so far were typically reserved for flat substrates. This high-throughput method can yield surface-structured colloidal particles at a rate of ≈107 to 108 particles per operator per day. Equipped with spatially defined binding pockets, microstructured colloids can engage in programmable interactions, which can lead to directed self-assembly. The ability to create a wide range of colloids with both simple and complex surface patterns may contribute to the genesis of previously unknown colloidal structures and may have important technological implications in a range of different applications, including photonic and phononic materials or chemical sensors. PMID:17592149

  9. Colloids with high-definition surface structures.

    PubMed

    Chen, Hsien-Yeh; Rouillard, Jean-Marie; Gulari, Erdogan; Lahann, Joerg

    2007-07-01

    Compared with the well equipped arsenal of surface modification methods for flat surfaces, techniques that are applicable to curved, colloidal surfaces are still in their infancy. This technological gap exists because spin-coating techniques used in traditional photolithographic processes are not applicable to the curved surfaces of spherical objects. By replacing spin-coated photoresist with a vapor-deposited, photodefinable polymer coating, we have now fabricated microstructured colloids with a wide range of surface patterns, including asymmetric and chiral surface structures, that so far were typically reserved for flat substrates. This high-throughput method can yield surface-structured colloidal particles at a rate of approximately 10(7) to 10(8) particles per operator per day. Equipped with spatially defined binding pockets, microstructured colloids can engage in programmable interactions, which can lead to directed self-assembly. The ability to create a wide range of colloids with both simple and complex surface patterns may contribute to the genesis of previously unknown colloidal structures and may have important technological implications in a range of different applications, including photonic and phononic materials or chemical sensors. PMID:17592149

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

    PubMed Central

    Zribi, Mehrez; Pard, Mickael; Boutin, Jacquline; Fanise, Pascal; Hauser, Daniele; Dechambre, Monique; Kerr, Yann; Leduc-Leballeur, Marion; Reverdin, Gilles; Skou, Niels; Sbjrg, 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 scatterometerSTORM, 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

  11. 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.

  12. Surface periodic domain structures for waveguide applications.

    PubMed

    Kokhanchik, Lyudmila S; Borodin, Maxim V; Burimov, Nikolay I; Shandarov, Stanislav M; Shcherbina, Vesta V; Volk, Tatyana R

    2012-06-01

    We report the results of fabrication and investigations of surface periodic domain structures created by a set of quasi-point e-beam irradiations both on the Y- and X-cuts of LiNbO(3), and on Ti:LiNbO(3) and Zn:LiNbO(3) planar waveguides. Domain gratings with spatial periods from 4.75 to 7.25 ?m were formed by a 25-keV e-beam. Doses from 500 to 2000 ?C/cm(2) were used for different structures to estimate optimal fabrication conditions. The investigations allowed the visualization of the formed surface domain structures, estimation of their uniformity, and determination of waveguide generation of the second optical harmonic. The surface structures can be used in optical devices for the realization of quasi-phase-matched frequency conversion, which includes the creation of compact radiation sources based on waveguides. PMID:22711403

  13. Band structure analysis of an analytically solvable Hill equation with continuous potential

    NASA Astrophysics Data System (ADS)

    Morozov, G. V.; Sprung, D. W. L.

    2015-03-01

    This paper concerns analytically solvable cases of Hills equation containing a continuously differentiable periodic potential. We outline a procedure for constructing the Floquet-Bloch fundamental system, and analyze the band structure of the system. The similarities to, and differences from, the cases of a piecewise constant periodic potential and the Mathieu potential, are illuminated.

  14. Design of UWB Monopole Antenna with Dual Notched Bands Using One Modified Electromagnetic-Bandgap Structure

    PubMed Central

    Xu, Ziqiang

    2013-01-01

    A modified electromagnetic-bandgap (M-EBG) structure and its application to planar monopole ultra-wideband (UWB) antenna are presented. The proposed M-EBG which comprises two strip patch and an edge-located via can perform dual notched bands. By properly designing and placing strip patch near the feedline, the proposed M-EBG not only possesses a simple structure and compact size but also exhibits good band rejection. Moreover, it is easy to tune the dual notched bands by altering the dimensions of the M-EBG. A demonstration antenna with dual band-notched characteristics is designed and fabricated to validate the proposed method. The results show that the proposed antenna can satisfy the requirements of VSWR < 2 over UWB 3.110.6?GHz, except for the rejected bands of the world interoperability for microwave access (WiMAX) and the wireless local area network (WLAN) at 3.5?GHz and 5.5?GHz, respectively. PMID:24170984

  15. 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.

  16. Three-Dimensional Structure of Vertebrate Muscle Z-Band: The Small-Square Lattice Z-Band in Rat Cardiac Muscle

    PubMed Central

    Burgoyne, Thomas; Morris, Edward P.; Luther, Pradeep K.

    2015-01-01

    The Z-band in vertebrate striated muscle crosslinks actin filaments of opposite polarity from adjoining sarcomeres and transmits tension along myofibrils during muscular contraction. It is also the location of a number of proteins involved in signalling and myofibrillogenesis; mutations in these proteins lead to myopathies. Understanding the high-resolution structure of the Z-band will help us understand its role in muscle contraction and the role of these proteins in the function of muscle. The appearance of the Z-band in transverse-section electron micrographs typically resembles a small-square lattice or a basketweave appearance. In longitudinal sections, the Z-band width varies more with muscle type than species: slow skeletal and cardiac muscles have wider Z-bands than fast skeletal muscles. As the Z-band is periodic, Fourier methods have previously been used for three-dimensional structural analysis. To cope with variations in the periodic structure of the Z-band, we have used subtomogram averaging of tomograms of rat cardiac muscle in which subtomograms are extracted and compared and similar ones are averaged. We show that the Z-band comprises four to six layers of links, presumably α-actinin, linking antiparallel overlapping ends of the actin filaments from the adjoining sarcomeres. The reconstruction shows that the terminal 5–7 nm of the actin filaments within the Z-band is devoid of any α-actinin links and is likely to be the location of capping protein CapZ. PMID:26362007

  17. 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.

  18. Sensitivity of C-band Synthetic Aperture RADAR to field-scale soil surface parameters

    NASA Astrophysics Data System (ADS)

    Adams, Justin

    This thesis investigates the sensitivity of polarimetric variables from C-band Synthetic Aperture RADAR to near-surface soil moisture (6 cm), micro-topographical surface roughness, and biomass cover, during pre/seed and post-harvest over agricultural fields. Variables examined include: the like-polarized and cross-polarized linear intensity channels; polarization ratios; the Total Power signal; the co-polarized phase difference and co-polarized complex correlation coefficient; Pedestal Height; extrema of the completely polarized and unpolarized components; extrema of the received power and scattered intensity; and the polarization coefficient of variation. Classification of scattering mechanisms with the Cloude-Pottier and Freeman-Durden decompositions are also examined. The empirical relationships between RADAR variables and surface parameters are first analyzed using data collected during field-validation campaigns. Secondly, RADAR imagery is integrated over the watershed scale to assess the operational discrimination of tillage practices with these polarimetric variables and decompositions. Overall results provide an enhanced theoretical understanding of these variables and decompositions for agricultural target retrievals and demonstrate promise for use in an agricultural monitoring scheme.

  19. Band structure of collective modes and effective properties of binary magnonic crystals

    NASA Astrophysics Data System (ADS)

    Zivieri, R.; Malag, P.; Giovannini, L.

    2014-11-01

    In this paper a theoretical study of the band structure of collective modes of binary ferromagnetic systems formed by a submicrometric periodic array of cylindrical cobalt nanodots partially or completely embedded into a permalloy ferromagnetic film is performed. The binary ferromagnetic systems studied are two-dimensional periodic, but they can be regarded as three-dimensional, since the magnetization is non uniform also along the z direction due to the contrast between the saturation magnetizations of the two ferromagnetic materials along the thickness. The dynamical matrix method, a finite-difference micromagnetic approach, formulated for studying the dynamics in one-component periodic ferromagnetic systems is generalized to ferromagnetic systems composed by F ferromagnetic materials. It is then applied to investigate the spin dynamics in four periodic binary ferromagnetic systems differing each other for the volume of cobalt dots and for the relative position of cobalt dots within the primitive cell. The dispersion curves of the most representative frequency modes are calculated for each system for an in-plane applied magnetic field perpendicular to the Bloch wave vector. The dependence of the dispersion curves on the cobalt quantity and position is discussed in terms of distribution of effective "surface magnetic charges" at the interface between the two ferromagnetic materials. The metamaterial properties in the propagative regime are also studied (1) by introducing an effective magnetization and effective "surface magnetic charges" (2) by describing the metamaterial wave dispersion of the most representative mode in each system within an effective medium approximation and in the dipole-exchange regime. It is also shown that the interchange between cobalt and permalloy does not necessarily lead to an interchange of the corresponding mode dispersion. Analogously to the case of electromagnetic waves in two-dimensional photonic crystals, the degree of localization of the localized collective modes is expressed in terms of an energy concentration factor.

  20. Improving Ku-band Scatterometer Ocean Surface Wind Direction Retrievals in Tropical Cyclones

    NASA Astrophysics Data System (ADS)

    Foster, R. C.; Zhang, J.; Black, P. G.

    2014-12-01

    Tropical cyclones are regions of very strong rain and very high winds, both of which present major challenges to surface wind vector retrieval from Ku-band scatterometers. Wind speed and wind direction retrievals can incur severe errors in regions of high rain rates. One particular signature of rain contamination is wind directions in the across-swath direction, which often leads to displaced circulation centers. Recently, Stiles et al. (2014) developed a method for retrieving QuikSCAT tropical cyclone wind speeds using a neural network approach that was tuned using H*WIND surface wind analyses and passive microwave-estimated rain rates from satellites. We are developing a scene-wide methodology by which a set of dynamically-consistent wind directions can be estimated from these wind speeds. The method is based on an iterative use of a tropical cyclone-specific sea-level pressure retrieval technique that we developed. The sea-level pressure analysis uses a boundary layer model that includes the dynamical shallowing of the tropical cyclone boundary layer toward the storm center, a roll-off in surface drag at high wind speeds, and, storm motion-corrected nonlinear mean flow advection effects. Scene-wide consistency is enforced by the integral nature (with respect to the surface wind vector field) of the derived surface pressure pattern and a constraint that the geostrophic contribution to the total flow is non-divergent. We are currently developing methods to evaluate the retrieved wind directions based on HRD aircraft observations and a limited-domain wind vector partitioning of the retrieved wind vectors into irrotational, non-divergent, and, background flow deformation contributions.

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

    SciTech Connect

    Yastrubchak, O.; Sadowski, J.; Domagala, J. Z.; Andrearczyk, T.; Wosinski, T.

    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.

  2. Crystal structure of the anion exchanger domain of human erythrocyte band 3.

    PubMed

    Arakawa, Takatoshi; Kobayashi-Yurugi, Takami; Alguel, Yilmaz; Iwanari, Hiroko; Hatae, Hinako; Iwata, Momi; Abe, Yoshito; Hino, Tomoya; Ikeda-Suno, Chiyo; Kuma, Hiroyuki; Kang, Dongchon; Murata, Takeshi; Hamakubo, Takao; Cameron, Alexander D; Kobayashi, Takuya; Hamasaki, Naotaka; Iwata, So

    2015-11-01

    Anion exchanger 1 (AE1), also known as band 3 or SLC4A1, plays a key role in the removal of carbon dioxide from tissues by facilitating the exchange of chloride and bicarbonate across the plasma membrane of erythrocytes. An isoform of AE1 is also present in the kidney. Specific mutations in human AE1 cause several types of hereditary hemolytic anemias and/or distal renal tubular acidosis. Here we report the crystal structure of the band 3 anion exchanger domain (AE1(CTD)) at 3.5 angstroms. The structure is locked in an outward-facing open conformation by an inhibitor. Comparing this structure with a substrate-bound structure of the uracil transporter UraA in an inward-facing conformation allowed us to identify the anion-binding position in the AE1(CTD), and to propose a possible transport mechanism that could explain why selected mutations lead to disease. PMID:26542571

  3. Electronic band structures and photovoltaic properties of MWO{sub 4} (M=Zn, Mg, Ca, Sr) compounds

    SciTech Connect

    Kim, Dong Wook; Cho, In-Sun; Shin, Seong Sik; Lee, Sangwook; Noh, Tae Hoon; Kim, Dong Hoe; Jung, Hyun Suk; Hong, Kug Sun

    2011-08-15

    Divalent metal tungstates, MWO{sub 4}, with wolframite (M=Zn and Mg) and scheelite (M=Ca and Sr) structures were prepared using a conventional solid state reaction method. Their electronic band structures were investigated by a combination of electronic band structure calculations and electrochemical measurements. From these investigations, it was found that the band structures (i.e. band positions and band gaps) of the divalent metal tungstates were significantly influenced by their crystal structural environments, such as the W-O bond length. Their photovoltaic properties were evaluated by applying to the working electrodes for dye-sensitized solar cells. The dye-sensitized solar cells employing the wolframite-structured metal tungstates (ZnWO{sub 4} and MgWO{sub 4}) exhibited better performance than those using the scheelite-structured metal tungstates (CaWO{sub 4} and SrWO{sub 4}), which was attributed to their enhanced electron transfer resulting from their appropriate band positions. - Graphical abstract: The electronic band structures of divalent metal tungstates are described from the combination of experimental results and theoretical calculations, and their electronic structure-dependent photovoltaic performances are also studied. Highlights: > MWO{sub 4} compounds with wolframite (M=Zn and Mg) and scheelite structure (M=Ca and Sr) were prepared. > Their electronic band structures were investigated by the calculations and the measurements. > Their photovoltaic properties were determined by the crystal and electronic structures.

  4. 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 and cH = 14.026 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.

  5. Effects of thermal and spin fluctuations on the band structure of purple bronze Li2Mo12O34

    NASA Astrophysics Data System (ADS)

    Jarlborg, T.; Chudzinski, P.; Giamarchi, T.

    2012-06-01

    The band structures of ordered and thermally disordered Li2Mo12O34 are calculated by use of the ab initio density-functional-theory-linear-muffin-tin (DFT-LMTO) method. The unusual, very one-dimensional band dispersion obtained in previous band calculations is confirmed for the ordered structure, and the overall band structure agrees reasonably well with existing photoemission data. Dispersion and band structure perpendicular to the main dispersive direction are obtained. A temperature-dependent band broadening is calculated from configurations with thermal disorder of the atomic positions within the unit cell. This leads to band broadening of the two bands at the Fermi energy which can become comparable to their energy separation. The bands are particularly sensitive to in-plane movements of Mo sites far from the Li sites, where the density of states (DOS) is highest. The latter fact makes the effect of Li vacancies on the two bands relatively small. Spin-polarized band results for the ordered structure show a surprisingly large exchange enhancement on the high DOS Mo sites. Consequences for spin fluctuations associated with a cell doubling along the conducting direction are discussed.

  6. Myomesin 3, a novel structural component of the M-band in striated muscle.

    PubMed

    Schoenauer, Roman; Lange, Stephan; Hirschy, Alain; Ehler, Elisabeth; Perriard, Jean-Claude; Agarkova, Irina

    2008-02-15

    The M-band is the cytoskeletal structure that cross-links the myosin and titin filaments in the middle of the sarcomere. Apart from the myosin tails and the C-termini of titin, only two closely related structural proteins had been detected at the M-band so far, myomesin and M-protein. However, electron microscopy studies revealed structural features that do not correlate with the expression of these two proteins, indicating the presence of unknown constituents in the M-band. Using comparative sequence analysis, we have identified a third member of this gene family, myomesin 3, and characterised its biological properties. Myomesin 3 is predicted to consist of a unique head domain followed by a conserved sequence of either fibronectin- or immunoglobulin-like domains, similarly to myomesin 3 and M-protein. While all three members of the myomesin family are localised to the M-band of the sarcomere, each member shows its specific expression pattern. In contrast to myomesin, which is ubiquitously expressed in all striated muscles, and M-protein, whose expression is restricted to adult heart and fast-twitch skeletal muscle, myomesin 3 can be detected mainly in intermediate speed fibers of skeletal muscle. In analogy to myomesin, myomesin 3 targets to the M-band region of the sarcomere via its N-terminal part and forms homodimers via its C-terminal domain. However, despite the high degree of homology, no heterodimer between distinct members of the myomesin gene family can be detected. We propose that each member of the myomesin family is a component of one of the distinct ultrastructures, the M-lines, which modulate the mechanical properties of the M-bands in different muscle types. PMID:18177667

  7. A New Surface-Based Quad-Pol C-band Microwave Scatterometer for Sea Ice Investigations

    NASA Astrophysics Data System (ADS)

    Yackel, J. J.; Barber, D. G.

    2004-05-01

    Quantifying the role of seasonal Arctic sea ice processes in regional coupled ocean-sea ice-atmosphere climate models requires an improvement in our ability to characterize their physical, dynamic and thermodynamic states through a temporal continuum beginning with fall accretion and concluding with summer ablation at a variety of spatial scales. Spaceborne polarimetric microwave remote sensing will shortly evolve as a key tool for measuring, monitoring and modeling such spatio-temporal dependent sea ice states. In this paper we describe a new surface-based quad-pol C-band microwave scatterometer used to collect sea ice backscatter (normalized radar cross section - NRCS) statistics during the Canadian Arctic Shelf Exchange Study (CASES) in the Amundsen Gulf region of the western Canadian Arctic. We present initial backscatter measurements, including polarization ratios, obtained over both marginal and landfast first-year sea ice types. Preliminary results show that the scatterometer is highly sensitive to the physical structure (ie. thickness/age, surface roughness and salinity) of new and marginal ice forms and to ice surface roughness (for cold, winter first-year ice), temperature dependent brine volume near the snow - ice interface (late winter/early spring) and vertical structure of water in liquid phase within the snow cover (spring). Most NRCS measurements were found to be sensitive to the incidence angle of the sensor (15 to 60 degrees). We conclude by demonstrating the utility of the scatterometer to measure and geophysically invert various surface states throughout the winter to summer transition through our ability to upscale our in situ measurements to spaceborne acquired synthetic aperture radar (SAR) data from RADARSAT-1 SAR and EVISAT ASAR.

  8. Anticrossing of Landau levels in HgTe/CdHgTe (013) quantum wells with an inverted band structure

    NASA Astrophysics Data System (ADS)

    Zholudev, M. S.; Teppe, F.; Morozov, S. V.; Orlita, M.; Consejo, C.; Ruffenach, S.; Knap, W.; Gavrilenko, V. I.; Dvoretskii, S. A.; Mikhailov, N. N.

    2015-02-01

    The simultaneous splitting of lines of an interband transition and cyclotron resonance in the conduction band has been detected in the absorption spectra of HgTe/CdHgTe quantum wells with an inverted band structure in quantizing magnetic fields. It has been shown that it is due to the absence of an inversion center in the crystal, which results in the interaction between the lower Landau level of the conduction band and the upper Landau level of the valence band.

  9. Real-space finite-difference calculation method of generalized Bloch wave functions and complex band structures with reduced computational cost

    NASA Astrophysics Data System (ADS)

    Tsukamoto, Shigeru; Hirose, Kikuji; Blgel, Stefan

    2014-07-01

    Generalized Bloch wave functions of bulk structures, which are composed of not only propagating waves but also decaying and growing evanescent waves, are known to be essential for defining the open boundary conditions in the calculations of the electronic surface states and scattering wave functions of surface and junction structures. Electronic complex band structures being derived from the generalized Bloch wave functions are also essential for studying bound states of the surface and junction structures, which do not appear in conventional band structures. We present a novel calculation method to obtain the generalized Bloch wave functions of periodic bulk structures by solving a generalized eigenvalue problem, whose dimension is drastically reduced in comparison with the conventional generalized eigenvalue problem derived by Fujimoto and Hirose [Phys. Rev. B 67, 195315 (2003)], 10.1103/PhysRevB.67.195315. The generalized eigenvalue problem derived in this work is even mathematically equivalent to the conventional one, and, thus, we reduce computational cost for solving the eigenvalue problem considerably without any approximation and losing the strictness of the formulations. To exhibit the performance of the present method, we demonstrate practical calculations of electronic complex band structures and electron transport properties of Al and Cu nanoscale systems. Moreover, employing atom-structured electrodes and jellium-approximated ones for both of the Al and Si monatomic chains, we investigate how much the electron transport properties are unphysically affected by the jellium parts.

  10. Receiver function structure beneath a broad-band seismic station in south Sumatra

    NASA Astrophysics Data System (ADS)

    MacPherson, K. A.; Hidayat, D.; Goh, S.

    2010-12-01

    We estimated the one-dimensional velocity structure beneath a broad-band station in south Sumatra by the forward modeling and inversion of receiver functions. Station PMBI belongs to the GEOFON seismic network maintained by GFZ-Potsdam, and at a longitude of 104.77 and latitude of -2.93, sits atop the south Sumatran basin. This station is of interest to researchers at the Earth Observatory of Singapore, as data from it and other stations in Sumatra and Singapore will be incorporated into a regional velocity model for use in seismic hazard analyses. Three-component records from 193 events at teleseismic distances and Mw ? 5.0 were examined for this study and 67 records were deemed to have sufficient signal to noise characteristics to be retained for analysis. Observations are primarily from source zones in the Bougainville trench with back-azimuths to the east-south-east, the Japan and Kurile trenches with back-azimuths to the northeast, and a scattering of observations from other azimuths. Due to the level of noise present in even the higher-quality records, the usual frequency-domain deconvolution method of computing receiver functions was ineffective, and a time-domain iterative deconvolution was employed to obtain usable wave forms. Receiver functions with similar back-azimuths were stacked in order to improve their signal to noise ratios. The resulting wave forms are relatively complex, with significant energy being present in the tangential components, indicating heterogeneity in the underlying structure. A dip analysis was undertaken but no clear pattern was observed. However, it is apparent that polarities of the tangential components were generally reversed for records that sample the Sunda trench. Forward modeling of the receiver functions indicates the presence of a near-surface low-velocity layer (Vp?1.9 km/s) and a Moho depth of ~31 km. Details of the crustal structure were investigated by employing time-domain inversions of the receiver functions. General features of those velocity models providing a good fit to the waveform include an approximately one kilometer thick near-surface low-velocity zone, a high-velocity layer over a velocity inversion at mid-crustal depths, and a crust-mantle transition at depths between 30 km and 34 km.

  11. Surface chemical reactivity of ultrathin Pd(111) films on Ru(0001): Importance of orbital symmetry in the application of the d-band model

    DOE PAGESBeta

    Yin, Xiangshi; Cooper, Valentino R.; Weitering, Hanno H.; Snijders, Paul C.

    2015-09-22

    The chemical bonding of adsorbate molecules on transition-metal surfaces is strongly influenced by the hybridization between the molecular orbitals and the metal d-band. The strength of this interaction is often correlated with the location of the metal d-band center relative to the Fermi level. Here, we exploit finite size effects in the electronic structure of ultrathin Pd(111) films grown on Ru(0001) to tune their reactivity by changing the film thickness one atom layer at a time, while keeping all other variables unchanged. Interestingly, while bulk Pd(111) is reactive toward oxygen, Pd(111) films below five monolayers are surprisingly inert. This observationmore » is fully in line with the d-band model prediction when applied to the orbitals involved in the bonding. The shift of the d-band center with film thickness is primarily attributed to shifts in the partial density of states associated with the 4dxz and 4dyz orbitals. This study provides an in-depth look into the orbital specific contributions to the surface chemical reactivity, providing new insights that could be useful in surface catalysis.« less

  12. Surface chemical reactivity of ultrathin Pd(111) films on Ru(0001): Importance of orbital symmetry in the application of the d-band model

    SciTech Connect

    Yin, Xiangshi; Cooper, Valentino R.; Weitering, Hanno H.; Snijders, Paul C.

    2015-09-22

    The chemical bonding of adsorbate molecules on transition-metal surfaces is strongly influenced by the hybridization between the molecular orbitals and the metal d-band. The strength of this interaction is often correlated with the location of the metal d-band center relative to the Fermi level. Here, we exploit finite size effects in the electronic structure of ultrathin Pd(111) films grown on Ru(0001) to tune their reactivity by changing the film thickness one atom layer at a time, while keeping all other variables unchanged. Interestingly, while bulk Pd(111) is reactive toward oxygen, Pd(111) films below five monolayers are surprisingly inert. This observation is fully in line with the d-band model prediction when applied to the orbitals involved in the bonding. The shift of the d-band center with film thickness is primarily attributed to shifts in the partial density of states associated with the 4dxz and 4dyz orbitals. This study provides an in-depth look into the orbital specific contributions to the surface chemical reactivity, providing new insights that could be useful in surface catalysis.

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

    SciTech Connect

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

    2015-03-07

    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 Fe{sub 3}O{sub 4} 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.

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

    NASA Astrophysics Data System (ADS)

    Lowe, M.; Yadav, T. P.; Fourne, 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.

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

    PubMed

    Lowe, M; Yadav, T P; Fourne, 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

  16. Influences of surface structures on polarization properties

    NASA Astrophysics Data System (ADS)

    Li, S.; Yu, M.; Wang, Z.

    2015-10-01

    The surface structure is an important factor that affects the polarization properties, which is useful information for object detection. This paper studies the influences of surface structures on polarization properties by the examination of man-made objects and nature objects using a scanning electron microscope (SEM) and white light confocal microscope. In the work, polarization imaging was discussed, and a system was set up to obtain polarization images. Comparing the degree of linear polarization (DOLP) images with traditional spectral images, there are obvious differences between man-made objects and nature objects on the micro- and nano-scales. The experiment results indicate that surface structures have significant influences on polarization properties, and such characteristic can be used to identify the differences between objects or materials.

  17. Spin-polarized surface electronic structure of Ta(110): Similarities and differences to W(110)

    NASA Astrophysics Data System (ADS)

    Engelkamp, B.; Wortelen, H.; Mirhosseini, H.; Schmidt, A. B.; Thonig, D.; Henk, J.; Donath, M.

    2015-08-01

    Tantalum and tungsten, direct neighbors in the periodic table, exhibit a very similar electronic structure. Compared with tungsten, however, the bands of tantalum are less occupied due to the lack of one electron. As a consequence, an exceptional Dirac-cone-like surface state, observed below the Fermi level for W(110), may appear above the Fermi level for Ta(110). To prove this conjecture, we investigate the unoccupied surface electronic structure of Ta(110) by spin- and angle-resolved inverse photoemission and electronic-structure calculations. Surprisingly, our results do not show the expected Dirac-cone-like surface state. Instead, spin-polarized unoccupied surface bands are identified, which have no equivalent in W(110). These findings are explained by the difference in the energetic positions of the surface states relative to the bulk states for Ta(110) and W(110) caused by the different lattice constants.

  18. Structure And Kinetics Of Molecules At Surfaces

    NASA Astrophysics Data System (ADS)

    Chabal, Yves J.

    1989-12-01

    After a brief review of static (i.e. structural) studies of atoms and molecules at surfaces, a time-resolved infrared experiment is presented that measures the diffusion of CO molecules on a platinum surface. The time resolution of this pulsed molecular beam doser/Fourier Transform interferometer system is 5 ms, making it possible to measure molecular hopping rates (diffusion) over 5 orders of magnitude.

  19. Band gap and electronic structure of MgSiN{sub 2}

    SciTech Connect

    Quirk, J. B. Råsander, M.; McGilvery, C. M.; Moram, M. A.; Palgrave, R.

    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 Γ point.

  20. Band structures of a series of alkali metal chlorates and perchlorates

    NASA Astrophysics Data System (ADS)

    Zhuravlev, Yu. N.; Poplavnoi, A. S.

    1996-10-01

    Calculations of the band structures and densities of electronic states have been carried out for cubic NaClO4, CClO4, RbClO4, CsClO4, NaClO3, and rhombohedral RbClO3 with one formula unit per unit cell using the empirical pseudopotential method with a basis of a plane wave expansion of localized Slater orbitals. The valence bands of these compounds are comparatively narrow and are formed by states of anion origin. The conduction bands are separated into two subbands which have predominantly anion and cation character respectively. A qualitatively different character of the anion-cation hybridization of the upper filled and lower free states was established in the chlorates and perchlorates. A comparison of the data found with experimental photoelectic and optical spectra has been carried out.

  1. 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

  2. The energy band structures of the warm dense plasmas with micro-structures inherited from original carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Dong, Q.-L.; Yang, J.; Jiang, Z.-T.; Sheng, Z.-M.; Zhang, J.

    2013-11-01

    The energy band structures of the warm dense plasmas with micro-structures inherited from single-walled carbon nanotubes are studied in detail by using the symmetry-adapted tight-binding model with the electron-ion core Coulomb interactions as the plasma effects. It is found that both the symmetry and the degeneracy of the calculated bands normal for the solid micro-structured targets may be destroyed by the electron-ion core Coulomb interactions. Moreover, the calculated Fermi levels of the micro-structured warm dense plasmas are about 1 eV higher than those of the original carbon nanotubes, while the transition energies of the warm dense plasmas are almost always smaller than those for the original carbon nanotubes.

  3. Band structure, phase transitions, and semiconductor analogs in one-dimensional solid light systems

    SciTech Connect

    Quach, James; Makin, Melissa I.; Su, C.-H.; Hollenberg, Lloyd C. L.; Greentree, Andrew D.

    2009-12-15

    The conjunction of atom-cavity physics and photonic structures ('solid light' systems) offers new opportunities in terms of more device functionality and the probing of designed emulators of condensed-matter systems. By analogy to the canonical one-electron approximation of solid-state physics, we propose a one-polariton approximation to study these systems. Using this approximation, we apply Bloch states to the uniformly tuned Jaynes-Cummings-Hubbard model to analytically determine the energy-band structure. By analyzing the response of the band structure to local atom-cavity control, we explore its application as a quantum simulator and show phase-transition features absent in mean-field theory. Using this approach for solid light systems, we extend the analysis to include detuning impurities to show the solid light analogy of the semiconductor. This investigation also shows features with no semiconductor analog.

  4. 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.

  5. Band structure and itinerant magnetism in quantum critical NbFe2

    SciTech Connect

    Subedi, A. P.; Singh, David J

    2010-01-01

    We report first-principles calculations of the band structure and magnetic ordering in the C14 Laves phase compound NbFe{sub 2}. The magnetism is itinerant in the sense that the moments are highly dependent on ordering. We find an overestimation of the magnetic tendency within the local spin-density approximation, similar to other metals near magnetic quantum critical points. We also find a competition between different magnetic states due to band-structure effects. These lead to competing magnetic tendencies due to competing interlayer interactions, one favoring a ferrimagnetic solution and the other an antiferromagnetic state. While the structure contains Kagome lattice sheets, which could, in principle, lead to strong magnetic frustration, the calculations do not show dominant nearest-neighbor antiferromagnetic interactions within these sheets. These results are discussed in relation to experimental observations.

  6. 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.

  7. Band gap structures in underwater screens of periodically spaced porous plates.

    PubMed

    Trabelsi, W; Franklin, H; Tinel, A; Derible, S

    2014-04-01

    Acoustic properties of different periodic structures composed of alternating fluid and fluid-saturated porous layers obeying Biot's theory are investigated. At first, the network of modes and the transmission coefficients of finite structures of six plates are studied in the frequency-angle of incidence plane. It is shown that the network of modes concentrates in localized domains of the plane where the transmission coefficients will take the greatest values. With this minimum of six plates, the structures exhibit the main features as for structures containing more plates, especially those with an infinite number of plates. Then, considering infinite structures the band gap calculations are led using the Bloch-Floquet theorem. The evanescent and propagative zones in the frequency-angle of incidence plane are determined. What is proposed here is a class of underwater porous screens that exhibits band gaps extending over great angular domains and enlarging in the frequency domain when the pores at the interfaces of the porous plates are sealed. The effect of porosity on the band gaps is also investigated. PMID:24485746

  8. The two-dimensional structure of dynamic boundary layers and shear bands in thermoviscoplastic solids

    NASA Astrophysics Data System (ADS)

    Gioia, G.; Ortiz, M.

    1996-02-01

    A general boundary layer theory for thermoviscoplastic solids which accounts for inertia, rate sensitivity, hardening, thermal coupling, heat convection and conduction, and thermal softening is developed. In many applications of interest, the boundary layer equations can be considerably simplified by recourse to similarity methods, which facilitates the determination of steady-state and transient fully non-linear two-dimensional solutions. A simple analysis of the asymptotic behavior of the steady-state solutions leads to a classification of stable and unstable regimes. Under adiabatic conditions, the resulting material stability criterion coincides with that previously derived by Molinari and Clifton [(1987) Analytical characterization of shear localization in thermoviscoplastic solids. J. Appl, Mech.54, 806-812] by a quasi-static, one-dimensional analysis. The transition from initially stable to unstable behavior can also be conveniently described by similarity methods. This provides a powerful semi-analytical tool for the interpretation of impact tests exhibiting dynamic shear bands, and for the characterization of the two-dimensional structure of such bands. It follows from the theory that, if the velocity of the impactor is held steady, the leading tip of the shear band propagates at a constant speed. This shear band tip speed follows readily from the theory as a function of the impact velocity and material parameters. The two-dimensional velocity, stress, temperature and plastic work fields attendant to the propagating shear band are also determined.

  9. Structure of the doublet bands in doubly odd nuclei: The case of {sup 128}Cs

    SciTech Connect

    Ganev, H. G.; Brant, S.

    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).

  10. Band structure and stability of zinc-blende-based semiconductor polytypes

    SciTech Connect

    Wei, S.; Zhang, S.B.; Zunger, A.

    1999-01-01

    Using a first-principles generalized one-dimensional Ising model we have studied the band structure and stability of two types of zinc-blende-based polytype series: type-a GaInP{sub 2} and type-b CuInSe{sub 2}. The interaction parameters for the formation energy are found to be short range, while the convergence is slower for the band-gap and conduction-band energies of the type-a GaInP{sub 2} polytypes. We predict that the CuAu-like phase can coexist in nominally chalcopyrite CuInSe{sub 2} and CuInS{sub 2}, while such coexistence is less likely in CuGaSe{sub 2}. We also predict that type-II band alignment can exist between different ordered type-a GaInP{sub 2} polytypes, despite that the band alignment between ordered and disordered GaInP{sub 2} are predicted to be type I. {copyright} {ital 1999} {ital The American Physical Society}

  11. A ppM-focused klystron at X-band with a travelling-wave output structure

    SciTech Connect

    Eppley, K.R.

    1994-10-01

    We have developed algorithms for designing disk-loaded travelling-wave output structures for X-band klystrons to be used in the SLAC NLC. We use either a four- or five-cell structure in a {pi}/2 mode. The disk radii are tapered to produce an approximately constant gradient. The matching calculation is not performed on the tapered structure, but rather on a coupler whose input and output cells are the same as the final cell of the tapered structure, and whose interior cells are the same as the penultimate cell in the tapered structure. 2-D calculations using CONDOR model the waveguide as a radial transmission line of adjustable impedance. 3-D calculations with MAFIA model the actual rectangular waveguide and coupling slot. A good match is obtained by adjusting the impedance of the final cell. In 3D, this requires varying both the radius of the cell and the width of the aperture. When the output cell with the best match is inserted in the tapered structure, we obtain excellent cold-test agreement between the 2-D and 3-D models. We use hot-test simulations with CONDOR to design a structure with maximum efficiency and minimum surface fields. We have designed circuits at 11.424 GHz for different perveances. At 440 kV, microperveance 1.2, we calculated 81 MW, 53 percent efficiency, with peak surface field 76 MV/m. A microperveance 0.6 design was done using a ppM stack for focusing. At 470 kV, 193 amps, we calculated 58.7 MW, 64.7 percent efficiency, peak surface field 62.3 MV/m. At 500 kV, 212 amps, we calculated 67.1 MW, 63.3 percent efficiency, peak surface field 66.0 MV/m.

  12. The dependence of S-band sea surface brightness and temperature on wind vector at normal incidence

    SciTech Connect

    Trokhimovski, Y.G.; Etkin, V.S.

    1995-07-01

    Aircraft measurements of the S-band sea surface brightness temperature at nadir as a function of wind speed and wind direction were carried out in various regions in 1985--1989. Data set of 65 circular flights was analyzed. It is shown that for water temperature recovering the wind direction is to be taken into account. This paper considers the relationship between S-band sea surface brightness temperature at nadir view angle and near surface wind speed as well as wind direction. The information of radiometer and scatterometer aircraft data set (RSAD) obtained at Space Research Institute was used. The 1985--1989 aircraft experiments in Pacific Ocean near Kamchatka peninsula and in Barents Sea were analyzed. The S-band radiometer data were used for the investigation due to their potential application of water temperature recovering and in this case the precise knowledge of wind speed dependence is very important.

  13. Surface Relief and Internal Structure in Fatigued Stainless Sanicro 25 Steel

    NASA Astrophysics Data System (ADS)

    Polák, Jaroslav; Mazánová, Veronika; Kuběna, Ivo; Heczko, Milan; Man, Jiří

    2016-02-01

    High-resolution images of persistent slip markings developed on the surface of Sanicro 25 stainless steel during cyclic loading obtained from the FIB-produced surface lamella in TEM simultaneously with the underlying dislocation structure are reported. Extrusions, intrusions, incipient cracks, and the dislocation arrangement corresponding to the bands of intensive cyclic slip are documented and discussed in relation to the models of surface relief formation in cyclic loading.

  14. Interacting quasi-band model for electronic states in compound semiconductor alloys: Zincblende structure

    NASA Astrophysics Data System (ADS)

    Shinozuka, Yuzo; Oda, Masato

    2015-09-01

    The interacting quasi-band model proposed for electronic states in simple alloys is extended for compound semiconductor alloys with general lattice structures containing several atoms per unit cell. Using a tight-binding model, a variational electronic wave function for quasi-Bloch states yields a non-Hermitian Hamiltonian matrix characterized by matrix elements of constituent crystals and concentration of constituents. Solving secular equations for each k-state yields the alloy’s energy spectrum for any type of randomness and arbitrary concentration. The theory is used to address III-V (II-VI) alloys with a zincblende lattice with crystal band structures well represented by the sp3s* model. Using the resulting 15 × 15 matrix, the concentration dependence of valence and conduction bands is calculated in a unified scheme for typical alloys: Al1-xGaxAs, GaAs1-xPx, and GaSb1-xPx. Results agree well with experiments and are discussed with respect to the concentration dependence, direct-indirect gap transition, and band-gap-bowing origin.

  15. Demonstration of molecular beam epitaxy and a semiconducting band structure for I-Mn-V compounds

    SciTech Connect

    Jungwirth, T.; Novak, V.; Cukr, M.; Zemek, J.; Marti, X.; Horodyska, P.; Nemec, P.; Holy, V.; Maca, F.; Shick, A. B.; Masek, J.; Kuzel, P.; Nemec, I.; Gallagher, B. L.; Campion, R. P.; Foxon, C. T.; Wunderlich, J.

    2011-01-15

    Our ab initio theory calculations predict a semiconducting band structure of I-Mn-V compounds. We demonstrate on LiMnAs that high-quality materials with group-I alkali metals in the crystal structure can be grown by molecular beam epitaxy. Optical measurements on the LiMnAs epilayers are consistent with the theoretical electronic structure. Our calculations also reproduce earlier reports of high antiferromagnetic ordering temperature and predict large, spin-orbit-coupling-induced magnetic anisotropy effects. We propose a strategy for employing antiferromagnetic semiconductors in high-temperature semiconductor spintronics.

  16. Spherical silicon-shell photonic band gap structures fabricated by laser-assisted chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Wang, H.; Yang, Z. Y.; Lu, Y. F.

    2007-02-01

    Laser-assisted chemical vapor deposition was applied in fabricating three-dimensional (3D) spherical-shell photonic band gap (PBG) structures by depositing silicon shells covering silica particles, which had been self-assembled into 3D colloidal crystals. The colloidal crystals of self-assembled silica particles were formed on silicon substrates using the isothermal heating evaporation approach. A continuous wave Nd:YAG laser (1064nm wavelength) was used to deposit silicon shells by thermally decomposing disilane gas. Periodic silicon-shell/silica-particle PBG structures were obtained. By removing the silica particles enclosed in the silicon shells using hydrofluoric acid, hollow spherical silicon-shell arrays were produced. This technique is capable of fabricating structures with complete photonic band gaps, which is predicted by simulations with the plane wave method. The techniques developed in this study have the potential to flexibly engineer the positions of the PBGs by varying both the silica particle size and the silicon-shell thickness. Ellipsometry was used to investigate the specific photonic band gaps for both structures.

  17. 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.; Hoinkis, M.; Blaha, P.; Gavrila, G.; Jacobsen, C. S.

    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.

  18. 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.

  19. Role of band 3 in the erythrocyte membrane structural changes under thermal fluctuations -multi scale modeling considerations.

    PubMed

    Pajic-Lijakovic, Ivana

    2015-12-01

    An attempt was made to discuss and connect various modeling approaches on various time and space scales which have been proposed in the literature in order to shed further light on the erythrocyte membrane rearrangement caused by the cortex-lipid bilayer coupling under thermal fluctuations. Roles of the main membrane constituents: (1) the actin-spectrin cortex, (2) the lipid bilayer, and (3) the trans membrane protein band 3 and their course-consequence relations were considered in the context of the cortex non linear stiffening and corresponding anomalous nature of energy dissipation. The fluctuations induce alternating expansion and compression of the membrane parts in order to ensure surface and volume conservation. The membrane structural changes were considered within two time regimes. The results indicate that the cortex non linear stiffening and corresponding anomalous nature of energy dissipation are related to the spectrin flexibility distribution and the rate of its changes. The spectrin flexibility varies from purely flexible to semi flexible. It is influenced by: (1) the number of band 3 molecules attached to single spectrin filaments, and (2) phosphorylation of the actin-junctions. The rate of spectrin flexibility changes depends on the band 3 molecules rearrangement. PMID:26560902

  20. Structural Coloration of Colloidal Fiber by Photonic Band Gap and Resonant Mie Scattering.

    PubMed

    Yuan, Wei; Zhou, Ning; Shi, Lei; Zhang, Ke-Qin

    2015-07-01

    Because structural color is fadeless and dye-free, structurally colored materials have attracted great attention in a wide variety of research fields. In this work, we report the use of a novel structural coloration strategy applied to the fabrication of colorful colloidal fibers. The nanostructured fibers with tunable structural colors were massively produced by colloidal electrospinning. Experimental results and theoretical modeling reveal that the homogeneous and noniridescent structural colors of the electrospun fibers are caused by two phenomena: reflection due to the band gap of photonic structure and Mie scattering of the colloidal spheres. Our unprecedented findings show promise in paving way for the development of revolutionary dye-free technology for the coloration of various fibers. PMID:26066732

  1. Spectral and polarization structure of field-induced photonic bands in cholesteric liquid crystals

    NASA Astrophysics Data System (ADS)

    Palto, S. P.; Barnik, M. I.; Geivandov, A. R.; Kasyanova, I. V.; Palto, V. S.

    2015-09-01

    Transmission of planar layers of cholesteric liquid crystals is studied in pulsed electric fields perpendicular to the helix axis at normal incidence of both linearly polarized and unpolarized light. Spectral and light polarization properties of the primary photonic band and the field-induced bands up to fourth order of Bragg selective reflection are studied in detail. In our experiments we have achieved an electric field strength several times higher than the theoretical values corresponding to the critical field of full helix unwinding. However, the experiments show that despite the high strength of the electric field applied the helix does not unwind, but strongly deforms, keeping its initial spatial period. Strong helix deformation results in distinct spectral band splitting, as well as very high field-induced selective reflectance that can be applied in lasers and other optoelectronic devices. Peculiarities of inducing and splitting the bands are discussed in terms of the scattering coefficient approach. All observed effects are confirmed by numerical simulations. The simulations also show that liquid crystal surface anchoring is not the factor that prevents the helix unwinding. Thus, the currently acknowledged concept of continuous helix unwinding in the electric field should be reconsidered.

  2. Spectral and polarization structure of field-induced photonic bands in cholesteric liquid crystals.

    PubMed

    Palto, S P; Barnik, M I; Geivandov, A R; Kasyanova, I V; Palto, V S

    2015-09-01

    Transmission of planar layers of cholesteric liquid crystals is studied in pulsed electric fields perpendicular to the helix axis at normal incidence of both linearly polarized and unpolarized light. Spectral and light polarization properties of the primary photonic band and the field-induced bands up to fourth order of Bragg selective reflection are studied in detail. In our experiments we have achieved an electric field strength several times higher than the theoretical values corresponding to the critical field of full helix unwinding. However, the experiments show that despite the high strength of the electric field applied the helix does not unwind, but strongly deforms, keeping its initial spatial period. Strong helix deformation results in distinct spectral band splitting, as well as very high field-induced selective reflectance that can be applied in lasers and other optoelectronic devices. Peculiarities of inducing and splitting the bands are discussed in terms of the scattering coefficient approach. All observed effects are confirmed by numerical simulations. The simulations also show that liquid crystal surface anchoring is not the factor that prevents the helix unwinding. Thus, the currently acknowledged concept of continuous helix unwinding in the electric field should be reconsidered. PMID:26465485

  3. Observations of LHR noise with banded structure by the sounding rocket S29 barium-GEOS

    NASA Technical Reports Server (NTRS)

    Koskinen, H. E. J.; Holmgren, G.; Kintner, P. M.

    1983-01-01

    The measurement of electrostatic noise near the lower hybrid frequency made by the sounding rocket S29 barium-GEOS is reported. The noise is related to the spin of the rocket and reaches well below the local lower hybrid resonance frequency. Above the altitude of 300 km the noise shows banded structure roughly organized by the hydrogen cyclotron frequency. Simultaneously with the banded structure a signal near the hydrogen cyclotron frequency is detected. This signal is also spin modulated. The character of the noise strongly suggests that it is locally generated by the rocket payload disturbing the plasma. If this interpretation is correct, plasma wave experiments on other spacecrafts are expected to observe similar phenomena.

  4. Band structure of the four pentacene polymorphs and effect on the hole mobility at low temperature.

    PubMed

    Troisi, Alessandro; Orlandi, Giorgio

    2005-02-10

    The band structure of the four known polymorphs of pentacene is computed from first principles using the accurate molecular orbitals of the isolated molecule as the basis for the calculation of the crystalline orbitals. The computed bands are remarkably different for each polymorph, but their diversity can be easily rationalized using a simple analytical model that employs only three parameters. The effect of the electronic structure on the hole mobility was evaluated using a simple model based on the constant relaxation time approximation. It is found that the mobility tensor is highly anisotropic for three of the four considered polymorphs. The practical implication of this prediction on the technology of thin-film organic transistors is discussed. PMID:16851167

  5. Review and prospects of magnonic crystals and devices with reprogrammable band structure.

    PubMed

    Krawczyk, M; Grundler, D

    2014-03-26

    Research efforts addressing spin waves (magnons) in microand nanostructured ferromagnetic materials have increased tremendously in recent years. Corresponding experimental and theoretical work in magnonics faces significant challenges in that spinwave dispersion relations are highly anisotropic and different magnetic states might be realized via, for example, the magnetic field history. At the same time, these features offer novel opportunities for wave control in solids going beyond photonics and plasmonics. In this topical review we address materials with a periodic modulation of magnetic parameters that give rise to artificially tailored band structures and allow unprecedented control of spin waves. In particular, we discuss recent achievements and perspectives of reconfigurable magnonic devices for which band structures can be reprogrammed during operation. Such characteristics might be useful for multifunctional microwave and logic devices operating over a broad frequency regime on either the macroor nanoscale. PMID:24599025

  6. Observation of wakefields in a beam-driven photonic band gap accelerating structure.

    SciTech Connect

    Conde, M.; Yusof, Z.; Power, J. G.; Jing, C.; Gao, F.; Antipov, S.; Xu, P.; Zheng, S.; Chen, H.; Tang, C.; Gai, W.; High Energy Physics; Euclid Techlabs LLC; Tsinghua Univ.

    2009-12-01

    Wakefield excitation has been experimentally studied in a three-cell X-band standing wave photonic band gap (PBG) accelerating structure. Major monopole (TM{sub 01}- and TM{sub 02}-like) and dipole (TM{sub 11}- and TM{sub 12}-like) modes were identified and characterized by precisely controlling the position of beam injection. The quality factor Q of the dipole modes was measured to be {approx}10 times smaller than that of the accelerating mode. A charge sweep, up to 80 nC, has been performed, equivalent to {approx} 30 MV/m accelerating field on axis. A variable delay low charge witness bunch following a high charge drive bunch was used to calibrate the gradient in the PBG structure by measuring its maximum energy gain and loss. Experimental results agree well with numerical simulations.

  7. Band structure and optical properties of amber studied by first principles

    NASA Astrophysics Data System (ADS)

    Rao, Zhi-Fan; Zhou, Rong-Feng

    2013-03-01

    The band structure and density of states of amber is studied by the first principles calculation based on density of functional theory. The complex structure of amber has 214 atoms and the band gap is 5.0 eV. The covalent bond is combined C/O atoms with H atoms. The O 2p orbital is the biggest effect near the Fermi level. The optical properties' results show that the reflectivity is low, and the refractive index is 1.65 in visible light range. The highest absorption coefficient peak is at 172 nm and another higher peak is at 136 nm. These convince that the amber would have a pretty sheen and that amber is a good and suitable crystal for jewelry and ornaments.

  8. Effective band structure of Ru-doped BaFe2As2

    NASA Astrophysics Data System (ADS)

    Reticcioli, M.; Profeta, G.; Franchini, C.; Continenza, A.

    2016-02-01

    The use of lattice cells in real space that are arbitrarily larger than the primitive one, is nowadays more and more often required by ab initio calculations to study disorder, vacancy or doping effects in real materials. This leads, however, to complex band structures which are hard to interpret. Therefore an unfolding procedure is sought for in order to obtain useful data, directly comparable with experimental results, such as angle-resolved photoemission spectroscopy measurements. Here, we present an extension of the unfolding procedure recently implemented in the VASP code, which includes a projection scheme that leads to a full reconstruction of the primitive space. As a test case, we apply this newly implemented scheme to the Ru-doped BaFe2As2 superconducting compound. The results provide a clear description of the effective electronic band structure in the conventional Brillouin zone, highlighting the crucial role played by doping in this compound.

  9. Control of Spin Wave Band Structure and Propagation in Two-Dimensional Magnonic Crystals

    NASA Astrophysics Data System (ADS)

    Sietsema, Glade; Flatt, 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.

  10. Photonic band structures solved by a plane-wave-based transfer-matrix method.

    PubMed

    Li, Zhi-Yuan; Lin, Lan-Lan

    2003-04-01

    Transfer-matrix methods adopting a plane-wave basis have been routinely used to calculate the scattering of electromagnetic waves by general multilayer gratings and photonic crystal slabs. In this paper we show that this technique, when combined with Bloch's theorem, can be extended to solve the photonic band structure for 2D and 3D photonic crystal structures. Three different eigensolution schemes to solve the traditional band diagrams along high-symmetry lines in the first Brillouin zone of the crystal are discussed. Optimal rules for the Fourier expansion over the dielectric function and electromagnetic fields with discontinuities occurring at the boundary of different material domains have been employed to accelerate the convergence of numerical computation. Application of this method to an important class of 3D layer-by-layer photonic crystals reveals the superior convergency of this different approach over the conventional plane-wave expansion method. PMID:12786509

  11. Infrared photoreflectance investigation of resonant levels and band edge structure in InSb.

    PubMed

    Chen, Xiren; Jung, Jinwook; Qi, Zhen; Zhu, Liangqing; Park, Sehun; Zhu, Liang; Yoon, Euijoon; Shao, Jun

    2015-11-15

    Temperature-dependent infrared photoreflectance (PR) is employed on InSb for clarifying resonant levels (RLs) and band edge structure. Abundant PR features are well resolved around the bandgap and are verified to be of electronic inter-level transitions rather than the Franz-Keldysh oscillations. The evolution of the critical energies with temperature reveals the nature of the PR processes, from which one acceptor RL, two donor RLs, and a shallow acceptor level are quantitatively identified, and a detailed band edge structure is derived. The results show that temperature-dependent infrared PR analysis can serve as an efficient vehicle for clarifying both bound and resonant levels in semiconductors. PMID:26565858

  12. First principles band structure calculations based on self-consistent screened Hartree-Fock exchange potential.

    PubMed

    Shimazaki, Tomomi; Asai, Yoshihiro

    2009-04-28

    A screened Hartree-Fock (HF) exchange potential with the dielectric constant was previously reported by Shimazaki and Asai [Chem. Phys. Lett. 466, 91 (2008)], in which the inverse of the dielectric constant was used to represent a fraction of the HF exchange term. In that report, the experimentally obtained value for the dielectric constant was employed. Herein, we discuss a self-consistent technique, in which the value of the dielectric constant can be automatically determined. This technique enables the energy band structure to be determined without using the experimental value. The band energy structure of diamond is calculated, a self-consistent procedure is determined to give closer bandgaps compared with the local density approximation and the generalized gradient approximation. PMID:19405611

  13. Photonic band gap structures of obliquely incident electromagnetic wave propagation in a one-dimension absorptive plasma photonic crystal

    SciTech Connect

    Guo Bin

    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.

  14. Three-dimensional ordered particulate structures: Method to retrieve characteristics from photonic band gap data

    NASA Astrophysics Data System (ADS)

    Miskevich, Alexander A.; Loiko, Valery A.

    2015-01-01

    A method to retrieve characteristics of ordered particulate structures, such as photonic crystals, is proposed. It is based on the solution of the inverse problem using data on the photonic band gap (PBG). The quasicrystalline approximation (QCA) of the theory of multiple scattering of waves and the transfer matrix method (TMM) are used. Retrieval of the refractive index of particles is demonstrated. Refractive indices of the artificial opal particles are estimated using the published experimental data.

  15. Band-edge engineering of Silicon by Surface Functionalization: a Combined Ab-initio and Photoemission Study

    NASA Astrophysics Data System (ADS)

    Li, Yan; O'Leary, Leslie; Lewis, Nathan; Galli, Giulia

    2012-02-01

    The electrode material choice is limited in solar to fuel formation devices because of the requirement of band-edge matching to the fixed fuel formation potential. This limitation can be relieved via band-edge engineering. The changes of band-edge positions of Si electrodes induced by the adsorption of H-, Cl-, Br- and short-chain alkyl groups were investigated by combining density functional (DFT), many-body perturbation theory (MBPT), and ultraviolet photoelectron spectroscopy. The band edge shifts are related to the formation of surface dipole moments, and determine the barrier height of electrons and holes in doped silicon surfaces. We find that the trends of the sign and magnitude of the computed surface dipoles as a function of the adsorbate may be explained by simple electronegative rules. We show that quasi-particle energies obtained within MBPT are in good agreement with experiment, while DFT values may exhibit substantial errors. However computed band edge differences are in good agreement with spectroscopic and electrical measurements even at the DFT level of theory. [1] Y. Li and G. Galli, Phys. Rev. B 82, 045321 (2010). [2] Y. Li, L. O'Leary, N. Lewis and G. Galli, to be submitted.

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

    NASA Astrophysics Data System (ADS)

    Men, H.; Lee, K. Y. K.; Freund, R. M.; Peraire, J.; Johnson, S. G.

    2014-09-01

    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, including fcc (including diamond), bcc, and simple-cubic lattices. Even without imposing the constraints of any fabrication process, the resulting optimal gaps are only slightly larger than previous hand designs, suggesting that current photonic crystals are nearly optimal in this respect. However, optimization can discover new structures, e.g. a new fcc structure with the same symmetry but slightly larger gap than the well known inverse opal, which may offer new degrees of freedom to future fabrication technologies. Furthermore, our band-gap optimization is an illustration of a computational approach to 3D dispersion engineering which is applicable to many other problems in optics, based on a novel semidefinite-program formulation for nonconvex eigenvalue optimization combined with other techniques such as a simple approach to impose symmetry constraints. We also demonstrate a technique for \\emph{robust} topology optimization, in which some uncertainty is included in each voxel and we optimize the worst-case gap, and we show that the resulting band gaps have increased robustness to systematic fabrication errors.

  17. 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

  18. Shape optimization of phononic band gap structures incorporating inertial amplification mechanisms

    NASA Astrophysics Data System (ADS)

    Yuksel, Osman; Yilmaz, Cetin

    2015-10-01

    The aim of this study is to obtain a wide and deep phononic gap at low frequencies in a two-dimensional periodic solid structure with embedded inertial amplification mechanisms. Size and shape optimizations are performed on the building block mechanism of the periodic structure to maximize phononic gap (stop band) width and depth. It is shown that shape optimization offers a wider and deeper gap, when both size and shape optimized mechanisms have the same mass and stiffness values. Analysis of the shape optimized mechanism is carried out using two different finite element models, one using beam elements and the other using shell elements. Both models produced similar results for the stop band width and depth. A two-dimensional periodic structure is constructed with the shape optimized building block mechanisms. Moreover, experimental and numerical frequency response results of this periodic structure are obtained. The matching frequency response results indicate that the two-dimensional periodic structure has a wide and deep phononic gap for in-plane excitations. Furthermore, due to proper selection of the out-of-plane thickness of the periodic structure, out-of-plane vibration modes do not occur within the phononic gap.

  19. Quasiparticle band structures and thermoelectric transport properties of p-type SnSe

    SciTech Connect

    Shi, Guangsha; Kioupakis, Emmanouil

    2015-02-14

    We used density functional and many-body perturbation theory to calculate the quasiparticle band structures and electronic transport parameters of p-type SnSe both for the low-temperature Pnma and high-temperature Cmcm phases. The Pnma phase has an indirect band gap of 0.829?eV, while the Cmcm has a direct band gap of 0.464?eV. Both phases exhibit multiple local band extrema within an energy range comparable to the thermal energy of carriers from the global extrema. We calculated the electronic transport coefficients as a function of doping concentration and temperature for single-crystal and polycrystalline materials to understand the previous experimental measurements. The electronic transport coefficients are highly anisotropic and are strongly affected by bipolar transport effects at high temperature. Our results indicate that SnSe exhibits optimal thermoelectric performance at high temperature when doped in the 10{sup 19}10{sup 20?}cm{sup ?3} range.

  20. Measurement of valence band structure in boron-zinc-oxide films by making use of ion beams

    SciTech Connect

    Uhm, Han S.; Kwon, Gi C.; Choi, Eun H.

    2011-12-26

    Measurement of valence band structure in the boron-zinc oxide (BZO) films was developed using the secondary electron emission due to the Auger neutralization of ions. The energy distribution profile of the electrons emitted from boron-zinc-oxide films was measured and rescaled so that Auger self-convolution arose; thus, revealing the detailed structure of the valence band and suggesting that a high concentration of boron impurity in BZO films may enhance the transition of electrons and holes through the band gap from the valence to the conduction band in zinc oxide crystals; thereby improving the conductivity of the film.

  1. Structurally tuned iridescent surfaces inspired by nature

    NASA Astrophysics Data System (ADS)

    Deparis, Olivier; Rassart, Marie; Vandenbem, Cdric; Welch, Victoria; Pol Vigneron, Jean; Lucas, Stphane

    2008-01-01

    Iridescent surfaces exhibit vivid colours which change with the angle of incidence or viewing due to optical wave interference in the multilayer structure present at the wavelength scale underneath the surface. In nature, one can find examples of iridescent Coleoptera for which the hue changes either greatly or slightly with the angle. Because these species typically make these structures from a single biological material (usually chitin) and air or water as the low refractive index component, they have evolved by adjusting the layer thicknesses in order to display quite different iridescent aspects. Taking inspiration from this proven strategy, we have designed and fabricated periodic TiO2/SiO2 multilayer films in order to demonstrate the concept of structurally tuned iridescent surfaces. Titanium or silicon oxide layers were deposited on a glass substrate using dc reactive or RF magnetron sputtering techniques, respectively. Two structures were designed for which the period and the TiO2/SiO2 layer thickness ratio were varied in such a way that the films displayed radically different iridescent aspects: a reddish-to-greenish changing hue and a stable bluish hue. The fabricated samples were characterized through specular reflectance/transmittance measurements. Modelling of transmittance spectra using standard multilayer film theory confirmed the high quality of the twelve-period Bragg reflectors. The chromaticity coordinates, which were calculated from measured reflectance spectra taken at different angles, were in accordance with theoretical predictions.

  2. Large band gaps in two-dimensional phononic crystals with self-similarity structure

    NASA Astrophysics Data System (ADS)

    Gao, Nansha; Wu, Jiu Hui; Yu, Lie

    2015-11-01

    In this paper, we study the band gaps (BGs) of two-dimensional (2D) phononic crystals (PCs) composed of self-similarity shape inclusions embedded in the homogenous matrix. The dispersion relations, transmission spectra, and displacement fields of eigenmodes of the proposed structures are calculated by use of finite element method. Due to the simultaneous mechanisms of the Bragg scattering, the structure can exhibit low-frequency BGs, which can be effectively shifted by changing the geometries and degree of the self-similarity structure. The BGs are significantly dependent upon the geometrical parameters and degree of the self-similarity structure. It is concluded that, the PCs with self-similarity structure, can modulate the location and width of BGs. But it must be pointed out, the shape of self-similarity inclusion exercises a great influence on the BGs. The study in this paper is relevant to the design of tuning BGs and isolators in the low-frequency range.

  3. Observation of Wakefield Suppression in a Photonic-Band-Gap Accelerator Structure.

    PubMed

    Simakov, Evgenya I; Arsenyev, Sergey A; Buechler, Cynthia E; Edwards, Randall L; Romero, William P; Conde, Manoel; Ha, Gwanghui; Power, John G; Wisniewski, Eric E; Jing, Chunguang

    2016-02-12

    We report experimental observation of higher order mode (HOM) wakefield suppression in a room-temperature traveling-wave photonic-band-gap (PBG) accelerating structure at 11.700 GHz. It has been long recognized that PBG structures have the potential for reducing long-range wakefields in accelerators. The first ever demonstration of acceleration in a room-temperature PBG structure was conducted in 2005. Since then, the importance of PBG accelerator research has been recognized by many institutions. However, the full experimental characterization of the wakefield spectrum and demonstration of wakefield suppression when the accelerating structure is excited by an electron beam has not been performed to date. We conducted an experiment at the Argonne Wakefield Accelerator test facility and observed wakefields excited by a single high charge electron bunch when it passes through a PBG accelerator structure. Excellent HOM suppression properties of the PBG accelerator were demonstrated in the beam test. PMID:26918995

  4. Buckling and band gap of the Ge(111)21 surface studied by low-temperature scanning tunneling microscopy

    NASA Astrophysics Data System (ADS)

    Feenstra, R. M.; Meyer, G.; Moresco, F.; Rieder, K. H.

    2001-08-01

    Low-temperature scanning tunneling microscopy is used to study the 21 reconstruction of cleaved Ge(111) surfaces. Buckling of the surface atoms is investigated by observations of the corrugation shift between filled and empty states. In the <211> direction, the shift in corrugation maxima from filled to empty states is found to be negative, consistent with expectations for the ``negatively buckled'' model for this surface. A surface band gap of 0.54+/-0.04 eV is measured by tunneling spectroscopy.

  5. Synthesis and band gap of ZnO particles with hexagonal bilayer structure

    NASA Astrophysics Data System (ADS)

    Zhang, Jianhui; Liu, Huaiyong; Wang, Zhenlin; Ming, Naiben

    2007-03-01

    The unique water/PVP (polyvinylpyrrolidone)/n-pentanol interface has been developed to prepare the ZnO particles with hexagonal bilayer structure. By modifying the interface through varying the amount of PVP and water, one can readily tune the particle size and change the particle shape from hexagonal bilayer to capped potlike to hemispherical features. The study of the growth dynamics and extinction spectra suggests that the bilayer structure arises from the selective adsorption of PVP on the ZnO crystallographic planes. Both the photoluminescence and extinction spectra show that the band gap of the hexagonal bilayer ZnO particles shrinks with increasing particle size.

  6. Photonic amorphous diamond structure with a 3D photonic band gap.

    PubMed

    Edagawa, Keiichi; Kanoko, Satoshi; Notomi, Masaya

    2008-01-11

    We report that a full three-dimensional (3D) photonic band gap (PBG) is formed in a photonic amorphous structure in spite of complete lack of lattice periodicity. It is numerically shown that the structure "photonic amorphous diamond" possesses a sizable 3D PBG (18% of the center frequency for Si-air dielectric contrast) and that it can confine light at a defect as strongly as conventional photonic crystals can. These findings present important new insight into the origin of 3D PBG formation and open new possibilities in developing 3D PBG materials. PMID:18232763

  7. Correlation between the surface electronic structure and CO-oxidation activity of Pt alloys.

    PubMed

    Abe, Hideki; Yoshikawa, Hideki; Umezawa, Naoto; Xu, Ya; Saravanan, Govindachetty; Ramesh, Gubbala V; Tanabe, Toyokazu; Kodiyath, Rajesh; Ueda, Shigenori; Sekido, Nobuaki; Yamabe-Mitarai, Yoko; Shimoda, Masahiko; Ohno, Takahisa; Matsumoto, Futoshi; Komatsu, Takayuki

    2015-02-21

    The surface electronic structure and CO-oxidation activity of Pt and Pt alloys, Pt3T (T = Ti, Hf, Ta, Pt), were investigated. At temperatures below 538 K, the CO-oxidation activities of Pt and Pt3T increased in the order Pt < Pt3Ti < Pt3hHf < Pt3Ta. The center-of-gravity of the Pt d-band (the d-band center) of Pt and Pt3T was theoretically calculated to follow the trend Pt3Ti < Pt3Ta < Pt3Hf < Pt. The CO-oxidation activity showed a volcano-type dependence on the d-band center, where Pt3Ta exhibited a maximum in activity. Theoretical calculations demonstrated that the adsorption energy of CO on the catalyst surface monotonically decreases with the lowering of the d-band center because of diminished hybridization of the surface d-band and the lowest-unoccupied molecular orbital (LUMO) of CO. The observed volcano-type correlation between the d-band center and the CO oxidation activity is rationalized in terms of the CO adsorption energy, which counterbalances the surface coverage by CO and the rate of CO oxidation. PMID:25271906

  8. Polarization Effects of GaN and AlGaN: Polarization Bound Charge, Band Bending, and Electronic Surface States

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    GaN-based devices are currently limited by reliability issues such as gate leakage and current collapse, where the mechanisms responsible for degradation are closely related to the electronic surface state configuration. Therefore, understanding the electronic surface state configuration of GaN-based materials will help improve device performance. Since GaN has an inherent polarization, these materials are also subject to a bound polarization charge, which influences the electronic state configuration. In this study, the surface band bending of N-face GaN, Ga-face GaN, and Ga-face AlGaN was measured with x-ray photoemission spectroscopy after various cleaning steps to investigate the effects of the polarization. Despite the different surface bound charge on these materials, similar band bending was observed regardless of the magnitude or direction of the charge. Specifically, the band bending varied from -0.1 eV to 0.9 eV on these samples, which supported the models of a Fermi level pinning state at 0.4 eV to 0.8 eV below the conduction band. Based on available literature, we suggest this pinning state is indirectly evident of a nitrogen vacancy or gallium-dangling bond.

  9. Polarization Effects of GaN and AlGaN: Polarization Bound Charge, Band Bending, and Electronic Surface States

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

    GaN-based devices are currently limited by reliability issues such as gate leakage and current collapse, where the mechanisms responsible for degradation are closely related to the electronic surface state configuration. Therefore, understanding the electronic surface state configuration of GaN-based materials will help improve device performance. Since GaN has an inherent polarization, these materials are also subject to a bound polarization charge, which influences the electronic state configuration. In this study, the surface band bending of N-face GaN, Ga-face GaN, and Ga-face AlGaN was measured with x-ray photoemission spectroscopy after various cleaning steps to investigate the effects of the polarization. Despite the different surface bound charge on these materials, similar band bending was observed regardless of the magnitude or direction of the charge. Specifically, the band bending varied from -0.1 eV to 0.9 eV on these samples, which supported the models of a Fermi level pinning state at 0.4 eV to 0.8 eV below the conduction band. Based on available literature, we suggest this pinning state is indirectly evident of a nitrogen vacancy or gallium-dangling bond.

  10. Superhydrophobic Behavior on Nano-structured Surfaces

    NASA Astrophysics Data System (ADS)

    Schaeffer, Daniel

    2008-05-01

    Superhydrophobic behavior is observed in natural occurrences and has been thoroughly studied over the past few years. Water repellant properties on uniform arrays of vertically aligned nano-cones were investigated to determine the highest achievable contact angle (a measure of water drop repellency), which is measured from the reference plane on which the water drop sits to the tangent line of the point at which the drop makes contact with the reference plane. At low aspect ratios (height vs. width of the nano-cones), surface tension pulls the water into the nano-cone array, resulting in a wetted surface. Higher aspect ratios reverse the effect of the surface tension, resulting in a larger contact angle that causes water drops to roll off the surface. Fiber drawing, bundling, and redrawing are used to produce the structured array glass composite surface. Triple-drawn fibers are fused together, annealed, and sliced into thin wafers. The surface of the composite glass is etched to form nano-cones through a differential etching process and then coated with a fluorinated self-assembled monolayer (SAM). Cone aspect ratios can be varied through changes in the chemistry and concentration of the etching acid solution. Superhydrophobic behavior occurs at contact angles >150 and it is predicted and measured that optimal behavior is achieved when the aspect ratio is 4:1, which displays contact angles >=175 .

  11. 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.

  12. Manifestation of Structure of Electron Bands in Double-Resonant Raman Spectra of Single-Walled Carbon Nanotubes.

    PubMed

    Stubrov, Yurii; Nikolenko, Andrii; Gubanov, Viktor; Strelchuk, Viktor

    2016-12-01

    Micro-Raman spectra of single-walled carbon nanotubes in the range of two-phonon 2D bands are investigated in detail. The fine structure of two-phonon 2D bands in the low-temperature Raman spectra of the mixture and individual single-walled carbon nanotubes is considered as the reflection of structure of their π-electron zones. The dispersion behavior of 2D band fine structure components in the resonant Raman spectra of single-walled carbon nanotube mixture is studied depending on the energy of excitating photons. The role of incoming and outgoing electron-phonon resonances in the formation of 2D band fine structure in Raman spectra of single-walled carbon nanotubes is analyzed. The similarity of dispersion behavior of 2D phonon bands in single-walled carbon nanotubes, one-layer graphene, and bulk graphite is discussed. PMID:26729220

  13. Manifestation of Structure of Electron Bands in Double-Resonant Raman Spectra of Single-Walled Carbon Nanotubes

    NASA Astrophysics Data System (ADS)

    Stubrov, Yurii; Nikolenko, Andrii; Gubanov, Viktor; Strelchuk, Viktor

    2016-01-01

    Micro-Raman spectra of single-walled carbon nanotubes in the range of two-phonon 2D bands are investigated in detail. The fine structure of two-phonon 2D bands in the low-temperature Raman spectra of the mixture and individual single-walled carbon nanotubes is considered as the reflection of structure of their π-electron zones. The dispersion behavior of 2D band fine structure components in the resonant Raman spectra of single-walled carbon nanotube mixture is studied depending on the energy of excitating photons. The role of incoming and outgoing electron-phonon resonances in the formation of 2D band fine structure in Raman spectra of single-walled carbon nanotubes is analyzed. The similarity of dispersion behavior of 2D phonon bands in single-walled carbon nanotubes, one-layer graphene, and bulk graphite is discussed.

  14. Inferring Land Surface Model Parameters for the Assimilation of Satellite-Based L-Band Brightness Temperature Observations into a Soil Moisture Analysis System

    NASA Technical Reports Server (NTRS)

    Reichle, Rolf H.; De Lannoy, Gabrielle J. M.

    2012-01-01

    The Soil Moisture and Ocean Salinity (SMOS) satellite mission provides global measurements of L-band brightness temperatures at horizontal and vertical polarization and a variety of incidence angles that are sensitive to moisture and temperature conditions in the top few centimeters of the soil. These L-band observations can therefore be assimilated into a land surface model to obtain surface and root zone soil moisture estimates. As part of the observation operator, such an assimilation system requires a radiative transfer model (RTM) that converts geophysical fields (including soil moisture and soil temperature) into modeled L-band brightness temperatures. At the global scale, the RTM parameters and the climatological soil moisture conditions are still poorly known. Using look-up tables from the literature to estimate the RTM parameters usually results in modeled L-band brightness temperatures that are strongly biased against the SMOS observations, with biases varying regionally and seasonally. Such biases must be addressed within the land data assimilation system. In this presentation, the estimation of the RTM parameters is discussed for the NASA GEOS-5 land data assimilation system, which is based on the ensemble Kalman filter (EnKF) and the Catchment land surface model. In the GEOS-5 land data assimilation system, soil moisture and brightness temperature biases are addressed in three stages. First, the global soil properties and soil hydraulic parameters that are used in the Catchment model were revised to minimize the bias in the modeled soil moisture, as verified against available in situ soil moisture measurements. Second, key parameters of the "tau-omega" RTM were calibrated prior to data assimilation using an objective function that minimizes the climatological differences between the modeled L-band brightness temperatures and the corresponding SMOS observations. Calibrated parameters include soil roughness parameters, vegetation structure parameters, and the single scattering albedo. After this climatological calibration, the modeling system can provide L-band brightness temperatures with a global mean absolute bias of less than 10K against SMOS observations, across multiple incidence angles and for horizontal and vertical polarization. Third, seasonal and regional variations in the residual biases are addressed by estimating the vegetation optical depth through state augmentation during the assimilation of the L-band brightness temperatures. This strategy, tested here with SMOS data, is part of the baseline approach for the Level 4 Surface and Root Zone Soil Moisture data product from the planned Soil Moisture Active Passive (SMAP) satellite mission.

  15. Surface leakage reduction in narrow band gap type-II antimonide-based superlattice photodiodes

    SciTech Connect

    Huang, Edward Kwei-wei; Hoffman, Darin; Nguyen, Binh-Minh; Delaunay, Pierre-Yves; Razeghi, Manijeh

    2009-02-02

    Inductively coupled plasma (ICP) dry etching rendered structural and electrical enhancements on type-II antimonide-based superlattices compared to those delineated by electron cyclotron resonance (ECR) with a regenerative chemical wet etch. The surface resistivity of 4x10{sup 5} {omega} cm is evidence of the surface quality achieved with ICP etching and polyimide passivation. By only modifying the etching technique in the fabrication steps, the ICP-etched devices with a 9.3 {mu}m cutoff wavelength revealed a diffusion-limited dark current density of 4.1x10{sup -6} A/cm{sup 2} and a maximum differential resistance at zero bias in excess of 5300 {omega} cm{sup 2} at 77 K, which are an order of magnitude better in comparison to the ECR-etched devices.

  16. Broad-band ambient noise surface wave tomography: Technique development and application across the United States

    NASA Astrophysics Data System (ADS)

    Bensen, Gregory David

    2007-05-01

    In recent years, it has been shown that surface wave signals can be extracted from high-quality empirical Green functions (EGF) obtained through cross-correlation of long ambient noise timeseries. Early work showed that Rayleigh wave components of EGFs could be created in a narrow period band under certain background noise characteristics. Such Rayleigh wave signals were used to develop shear wave tomography models of several geographic regions with unprecedented high resolution. However, questions remained regarding the robustness of these signals and their range of applicability. My work focuses on two problems. The first is researching the best method for computing, measuring and selecting high-quality EGFs. The second is to use this new technique to create a three-dimensional (3D) velocity model of the continental United States. Testing a variety of temporal and spectral normalization techniques yields an optimal method of creating EGFs. These signals are evaluated for robustness in a variety of noise environments effectively broadening the bandwidth from 7.5-20 s period to 6-100 s period. An automated dispersion measurement technique is presented as well as a preferred method of measurement selection and certain "best practices" are proposed for future study. Applying this method across the continental United States I develop Rayleigh and Love wave group and phase speed dispersion maps from 8-70 s period. The resulting set of dispersion maps possesses unprecedented high resolution and bandwidth for continental scale surface wave investigations and unites diverse tectonic regions into a coherent model. I invert the dispersion maps for a 3D shear velocity model with resolution from the surface to 150 km depth using a two-step procedure. First is a linearized inversion for the best fitting velocity model. Second is a Monte-Carlo re-sampling to develop an ensemble of models of sufficient quality and to generate uncertainty estimates at all points. The resulting velocity model allows identification of prominent features in the crust and mantle and sheds light on topics such as topographic compensation, crustal heterogeneity and radial anisotropy in the crust.

  17. The Glacier and Ice Surface Topography Interferometer: UAVSAR's Single-pass Ka-Band Interferometer

    NASA Astrophysics Data System (ADS)

    Moller, D.; Hensley, S.; Wu, X.; Michel, T.; Muellerschoen, R.; Carswell, J.; Fisher, C.; Miller, T.; Milligan, L.; Sadowy, G.; Sanchez-Barbetty, M.; Lou, Y.

    2013-12-01

    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. 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 indicated swath widths over the ice between 5-7km, with height precisions ranging from 30cm-3m at a posting of 3m x 3m. Following the success of the IPY campaign, the Earth Science Techonology Office (ESTO) Airborne Innovative Technology Transition (AITT) program funded the upgrade of GLISTIN-A to a permanently-available pod-only system compatible with unpressurized operation. The AITT made three fundamental upgrades to improve system performance: 1. State-of-the-art solid-state power amplifiers (80W peak) were integrated directly on the antenna panel reducing front-end losses; 2. A ping-pong capability was incorporated to effectively double the baseline thereby improving height measurement precision by a factor of two; and 3. A high-fidelity calibration loop was implemented which is critical for routine processing. Upon completion of our engineering flights in February 2013, GLISTIN-A flew a brief campaign to Alaska (4/24-4/27/13). The purpose was to fully demonstrate GLISTIN-A's ability to generate high-precision, high resolution maps of ice surface topography with swaths in excess of 10km. Furthermore, the question of the utility of GLISTIN-A for sea-ice mapping, tracking and inventory has received a great deal of interest. To address this GLISTIN-A collected data over sea-ice in the Beaufort sea including an underflight of CryoSAT II. Note that there are ongoing activities to stage GLISTIN on the Global Hawk (GLISTIN-H) for which sea ice-mapping is a primary driver. Analysis of the data will focus on assessment of performance and interpretation over ice to include: 1. intercomparison of GLISTIN-A glacier height maps with lidar data and heritage SRTM DEM's for performance validation of GLISTIN-A over ice, 2. quantitative evaluation of mass change over the Columbia glacier via repeat observations made by GLISTIN-A with a 3 day separation, 3. assessment of GLISTIN-A's ability map sea ice extent, dynamics and possibly to measure freeboard.

  18. 3D coherent structures of surface turbulence

    NASA Astrophysics Data System (ADS)

    Demekhin, Evgeny

    2004-11-01

    Evolution of unstable natural disturbances in falling films undergoes several changing each other regimes. At sufficiently large Reynolds numbers it reaches the last stage when the surface is randomly covered by three-dimensional nonlinear structures, ``horse-shoe waves'', which are strongly internally coupled and interact with each other as ``quasi-particles.'' Such stage is often called ``surface turbulence'' and it occurs when Reynolds numbers in liquid are small for Tollmien-Schlichting instability and usual turbulence. In this work for the first time such nonlinear waves are found theoretically; the wave has a large curved as a horse-shoe head,two oblique ``legs'' and a well-pronounced dent behind the head. Results of theory are compared with specially made experiments. Taking into account obvious likeness between ``horse-shoe waves'' and localized structures in ordinary turbulence, Lambda-vortisies, we hope that our ``simple'' case will help elucidate also some features of usual turbulence.

  19. Photonic band structure and effective medium properties of doubly-resonant core-shell metallo-dielectric nanowire arrays: low-loss, isotropic optical negative-index behavior

    NASA Astrophysics Data System (ADS)

    Abujetas, D. R.; Paniagua-Domnguez, R.; Nieto-Vesperinas, M.; Snchez-Gil, J. A.

    2015-12-01

    We investigate theoretically and numerically the photonic band structure in the optical domain of an array of coreshell metal-semiconductor nanowires. Corresponding negative-index photonic bands are calculated, showing isotropic equifrequency surfaces. The effective (negative) electric permittivity and magnetic permeability, retrieved from S-parameters, are used to compare the performance of such nanowire arrays with homogeneous media in canonical examples, such as refraction through a prism and flat-lens focusing. Very good agreement is found, confirming the effective medium behavior of the nanowire array as a low-loss, isotropic (2D) and bulk, optical negative index metamaterial. Indeed, disorder is introduced to further stress its robustness.

  20. Electronic structure of Sb monolayers on the Mo(110) surface

    NASA Astrophysics Data System (ADS)

    Proskurin, D.; Nikolaychik, A.; Koval, I. F.; Yakovkin, I. N.

    We compare theory and experimental (LEED and EELS) studies of the atomic and electronic structure of adsorbed Sb layers on Mo(110). At half a monolayer coverage, Sb atoms occupy the ?long-bridge? (hollow) sites forming the (1 2) film structure. At this coverage, a dramatic decrease of surface density of states in vicinity of Fermi level results in a quasi dielectric state of the surface. With increasing coverage, direct lateral interaction between Sb atoms becomes increasingly important and leads to push-out of some Sb atoms in the (2 3/2) surface unit cell from the adsorption sites that are favorable at lower coverages. Substantial overlap of orbitals of neighboring adatoms results in metallic state of adsorbed Sb film, as suggested from significant increase of DOS at Fermi level. In EEL spectra, the nonmetal to metal transition reveals itself also by appearance of the -7.8 eV peak, which may be explained by the interband transition from Sb s band to unoccupied p states above EF.

  1. Photonic band gap structure for a ferroelectric photonic crystal at microwave frequencies.

    PubMed

    King, Tzu-Chyang; Chen, De-Xin; Lin, Wei-Cheng; Wu, Chien-Jang

    2015-10-10

    In this work, the photonic band gap (PBG) structure in a one-dimensional ferroelectric photonic crystal (PC) is theoretically investigated. We consider a PC, air/(AB)N/air, in which layer A is a dielectric of MgO and layer B is taken to be a ferroelectric of Ba0.55Sr0.45TiO3 (BSTO). With an extremely high value in the dielectric constant in BSTO, the calculated photonic band structure at microwave frequencies exhibits some interesting features that are significantly different from those in a usual dielectric-dielectric PC. First, the photonic transmission band consists of multiple and nearly discrete transmission peaks. Second, the calculated bandwidth of the PBG is nearly unchanged as the angle of incidence varies in the TE wave. The bandwidth will slightly reduce for the TM mode. Thus, a wide omnidirectional PBG can be obtained. Additionally, the effect of the thickness of the ferroelectric layer on the PBG is much more pronounced compared to the dielectric layer thickness. That is, the increase of ferroelectric thickness can significantly decrease the PBG bandwidth. PMID:26479812

  2. BoltzTraP. A code for calculating band-structure dependent quantities

    NASA Astrophysics Data System (ADS)

    Madsen, Georg K. H.; Singh, David J.

    2006-07-01

    A program for calculating the semi-classic transport coefficients is described. It is based on a smoothed Fourier interpolation of the bands. From this analytical representation we calculate the derivatives necessary for the transport distributions. The method is compared to earlier calculations, which in principle should be exact within Boltzmann theory, and a very convincing agreement is found. Program summaryTitle of program:BoltzTraP Catalogue identifier:ADXU_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADXU_v1_0 Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Licensing provisions:none Programming language used:Fortran 90 Computer:The program should work on any system with a F90 compiler. The code has been tested with the Intel Fortran compiler Operating system:Unix/Linux RAM:bytes up to 2 GB for low symmetry, small unit cell structures No. of lines in distributed program, including test data, etc.:1 534 213 No. of bytes in distributed program, including test data, etc.:27 473 227 Distribution format:tar.gz External routines:The LaPack and Blas libraries are needed Nature of problem:Analytic expansion of energy-bands. Calculation of semi-classic integrals. Solution method:Smoothed Fourier expansion of bands. Running time:Up to 3 hours for low symmetry, small unit cell structures.

  3. 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).

  4. Model GW band structure of InAs and GaAs in the wurtzite phase

    NASA Astrophysics Data System (ADS)

    Zanolli, Z.; Fuchs, F.; Furthmller, J.; von Barth, U.; Bechstedt, F.

    2007-06-01

    We report quasiparticle calculations of the newly observed wurtzite polymorph of InAs and GaAs . The calculations are performed in the GW approximation (based on a model dielectric function) using plane waves and pseudopotentials. For comparison we also report the study of the zinc-blende phase within the same approximations. In the InAs compound the In4d electrons play a very important role: whether they are frozen in the core or not leads either to a correct or a wrong band ordering (negative gap) within the local-density appproximation (LDA). We have calculated the GW band structure in both cases. In the first approach, we have estimated the correction to the pd repulsion calculated within the LDA and included this effect in the calculation of the GW corrections to the LDA spectrum. In the second case, we circumvent the negative gap problem by first using the screened exchange approximation and then calculating the GW corrections starting from the so obtained eigenvalues and eigenfunctions. This approach, that can be thought of as a step towards self-consistency, leads to a more realistic band structure and was also used for GaAs . For both InAs and GaAs in the wurtzite phase we predict an increase of the quasiparticle gap with respect to the zinc-blende polytype.

  5. 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

  6. 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.

  7. Atomic arrangement and electron band structure of Si(1 1 1)--?3 x ?3-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

  8. Doping effect on electronic band structure and magnetic properties of MFeAs(M = Li, Na)

    NASA Astrophysics Data System (ADS)

    Mahesh, Rajendran; Rajagopalan, M.; Palanivel, Balan

    2015-03-01

    In this paper, detailed examination of the doping effect on electronic band structure, magnetic properties of nonmagnetic (NM) and striped antiferromagnetic (S-AFM) phases of MFeAs(M = Li, Na) compounds were carried out using ab initio method. The crystal structure of these compounds is a well known tetragonal structure. Self-consistent calculations were performed by plane wave pseudo potential, density functional based method using PWSCF-Quantum Espresso code. To study the structural phase stability, the total energies of these compounds were calculated as a function of reduced volumes and fitted with Brich Murnaghan equation. 3d valence elements like Mn, Co induce strong local magnetic moments on doping. However, Cu substitution weakens the average local moments. The 3d elements on doping at Fe site directly affect the electrons correlations in the Fe-As layer.

  9. Giant amplification in degenerate band edge slow-wave structures interacting with an electron beam

    NASA Astrophysics Data System (ADS)

    Othman, Mohamed A. K.; Veysi, Mehdi; Figotin, Alexander; Capolino, Filippo

    2016-03-01

    We propose a new amplification regime based on a synchronous operation of four degenerate electromagnetic (EM) modes in a slow-wave structure and the electron beam, referred to as super synchronization. These four EM modes arise in a Fabry-Pérot cavity when degenerate band edge (DBE) condition is satisfied. The modes interact constructively with the electron beam resulting in superior amplification. In particular, much larger gains are achieved for smaller beam currents compared to conventional structures based on synchronization with only a single EM mode. We demonstrate giant gain scaling with respect to the length of the slow-wave structure compared to conventional Pierce type single mode traveling wave tube amplifiers. We construct a coupled transmission line model for a loaded waveguide slow-wave structure exhibiting a DBE, and investigate the phenomenon of giant gain via super synchronization using the Pierce model generalized to multimode interaction.

  10. Dual-Band Magnetic Loop Antenna with Monopolar Radiation Using Slot-Loaded Composite Right/Left-Handed Structures

    NASA Astrophysics Data System (ADS)

    Pyo, Seongmin; Lee, Min-Jae; Lee, Kyoung-Joo; Kim, Young-Sik

    A novel dual-band magnetic loop antenna is proposed using slot-loaded composite right/left-handed (SL-CRLH) structures. Since each radiating element consists of a symmetrically-array of unit-cells, a dual-band magnetic loop source is obtained with unchanged beam patterns. Simulations and measurements show its good radiation performance with monopole-like radiation patterns in both operating bands.

  11. Electronic band structure and optical absorption of nanotubular zinc oxide doped with Iron, Cobalt, or Copper

    NASA Astrophysics Data System (ADS)

    Zhukov, V. P.; Krasil'nikov, V. N.; Perelyaeva, L. A.; Baklanova, I. V.; Shein, I. R.

    2013-12-01

    The absorption spectra of the precursor-derived solid solutions Zn1 - x M x O ( M = Fe, Co, Cu) with a tubular morphology of aggregates have been investigated in the ultraviolet and visible regions. The maximum metal concentration x in the Zn1 - x M x O solid solutions is 0.075 for iron, 0.2 for cobalt, and 0.1 for copper. It has been found that the optical absorption and the band gap of the Zn1 - x M x O compounds depend on the type of dopant. The obtained experimental data have been interpreted using the results of the performed ab initio calculations of the electronic band structure and optical absorption.

  12. 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.

  13. 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.

  14. Rotational structures in 174Ta and ``identical bands'' in the normal deformation regime

    NASA Astrophysics Data System (ADS)

    Hojman, D.; Kreiner, A. J.; Davidson, M.

    1992-10-01

    174Ta has been studied through the 169Tm(9Be,4n) fusion-evaporation reaction in the energy range E(9Be)=40-65 MeV. γ- and x-ray in-beam and activity singles spectra, γ-γ-t coincidences, and angular-distribution measurements were performed. Four rotational structures have been found and interpreted on the basis of coupling systematics. Mixing ratio signs have been calculated using a semiclassical method and compared with the signs of the angular-distribution coefficients, in order to consolidate configuration assignments. ``Identical bands,'' i.e., bands with similar transition energies, have been found in neighboring odd and doubly-odd 171-174Ta. This similarity is interpreted here as due to fortuitous compensations between different transverse and collective angular momenta and moments of inertia.

  15. Evolution of band structures in MoS2-based homo- and heterobilayers

    NASA Astrophysics Data System (ADS)

    Zhu, H. L.; Zhou, C. J.; Huang, X. J.; Wang, X. L.; Xu, H. Z.; Lin, Yong; Yang, W. H.; Wu, Y. P.; Lin, W.; Guo, F.

    2016-02-01

    Density functional theory calculations have been performed to elucidate the detailed evolution of band structures in MoS2-based homo- and heterobilayers. By constructing the energy-band alignments we observed that biaxial tensile and compressive strain in the constituent transition-metal dichalcogenide (TMD) monolayer shifts the states at the K C, Q C, and K V points down and up, respectively, while the states at the ΓV point are almost unaltered. In contrast, interlayer coupling tends to modify the states at the ΓV and Q C points by splitting the band-edge states of two strained or unstrained constituent TMD monolayers, while it does not affect the states at the K C and K V points. Considering the combined actions of strain and interlayer coupling, the relevant electronic parameters, especially the detailed evolution processes, of the band structures of the investigated bilayer systems can be clearly described. When further applying the extra biaxial strain to the three bilayer systems, it is found that energy differences ΔE(K C  ‑  Q C) and ΔE(K V  ‑  ΓV) decrease linearly as the increasing of the biaxial strain. According to the varying trends of ΔE(K C  ‑  Q C) and ΔE(K V  ‑  ΓV), MoS2 bilayer will maintain the indirect-bandgap character under any compressive or tensile strain. Differently, WS2/MoS2 heterobilayer transforms interestingly to the direct-bandgap material under the strain from  ‑1.6% to  ‑1.2% with the valence band maximum and conduction band minimum located at the K C and K V point respectively. The direct-to-indirect bandgap transition can be obtained for the WSe2/MoS2 heterobilayer when applying much larger extra tensile or compressive strain. The results offer an effective route to verify and tailor the electronic properties of TMD homo- and heterostructures and can be helpful in evaluating the performance of TMD-based electronic devices.

  16. Sound waves induce Volkov-like states, band structure and collimation effect in graphene

    NASA Astrophysics Data System (ADS)

    Oliva-Leyva, M.; Naumis, Gerardo G.

    2016-01-01

    We find exact states of graphene quasiparticles under a time-dependent deformation (sound wave), whose propagation velocity is smaller than the Fermi velocity. To solve the corresponding effective Dirac equation, we adapt the Volkov-like solutions for relativistic fermions in a medium under a plane electromagnetic wave. The corresponding electron-deformation quasiparticle spectrum is determined by the solutions of a Mathieu equation resulting in band tongues warped in the surface of the Dirac cones. This leads to a collimation effect of electron conduction due to strain waves.

  17. Sound waves induce Volkov-like states, band structure and collimation effect in graphene.

    PubMed

    Oliva-Leyva, M; Naumis, Gerardo G

    2016-01-20

    We find exact states of graphene quasiparticles under a time-dependent deformation (sound wave), whose propagation velocity is smaller than the Fermi velocity. To solve the corresponding effective Dirac equation, we adapt the Volkov-like solutions for relativistic fermions in a medium under a plane electromagnetic wave. The corresponding electron-deformation quasiparticle spectrum is determined by the solutions of a Mathieu equation resulting in band tongues warped in the surface of the Dirac cones. This leads to a collimation effect of electron conduction due to strain waves. PMID:26682732

  18. 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

  19. Thermodynamics and surface structure of coals

    SciTech Connect

    Glass, A.S.; Larsen, J.W.; Quay, D.M.; Roberts, J.E.

    1991-01-01

    NMR relaxation and shift reagents are being deposited on the surface of coals. The dipolar coupling of the unpaired electron spin of the relaxation agent and the carbon atom should significantly shorten the carbon T, which should broaden it away. We propose to record the NMR spectrum of a coal before and after deposition and subtract the spectra. The difference spectra will arise from the functionalities within approximately one nanometer of the surface and reveal the surface composition of the coal. In order to determine the surface concentration of the dysprosium in the coal, we are using x-ray photoelectron spectroscopy (XPS) also known as electron spectroscopy for chemical analysis (ESCA). XPS is a surface technique that can be used for the elucidation of chemical structure. The binding energy for each electron in each element is unique. The measurement of the binding energy in XPS allows the identification of the element and its oxidation state. The relative atomic concentrations of each element can also be determined using XPS spectra.

  20. Measurement of surface scratches on aircraft structures

    NASA Astrophysics Data System (ADS)

    Sarr, Dennis P.

    1996-01-01

    In assuring the quality of aircraft, the skin quality must be free of surface imperfections. Surface imperfections such as scratches are unacceptable for cosmetic and structural reasons. Scratches beyond a certain depth are not repairable, resulting in costly replacement of an aircraft's part. Measurements of aircraft exterior surfaces require a ladder or cherry picker for positioning the inspector. Commercially-available computer vision systems are not portable, easy to use, or ergonomic. The machine vision system must be designed with these criteria in mind. The scratch measurement system (SMS) uses computer vision, digital signal processing, and automated inspection methods. The system is portable and battery powered. It is certified for measuring the depth and width of the anomaly. The SMS provides a comprehensive, analytical, and accurate reading. A hardcopy output provides a permanent record of the analysis. The graphical data shows the surface profile and provides substantial information of the surface anomaly. The factory and flight line use the SMS at different stages of aircraft production. Six systems have been built for use within Boeing. A patent was issued for the SMS in February 1994.

  1. Tunable band gap in few-layer graphene by surface adsorption

    PubMed Central

    Quhe, Ruge; Ma, Jianhua; Zeng, Zesheng; Tang, Kechao; Zheng, Jiaxin; Wang, Yangyang; Ni, Zeyuan; Wang, Lu; Gao, Zhengxiang; Shi, Junjie; Lu, Jing

    2013-01-01

    There is a tunable band gap in ABC-stacked few-layer graphene (FLG) via applying a vertical electric field, but the operation of FLG-based field effect transistor (FET) requires two gates to create a band gap and tune channel's conductance individually. Using first principle calculations, we propose an alternative scheme to open a band gap in ABC-stacked FLG namely via single-side adsorption. The band gap is generally proportional to the charge transfer density. The capability to open a band gap of metal adsorption decreases in this order: K/Al > Cu/Ag/Au > Pt. Moreover, we find that even the band gap of ABA-stacked FLG can be opened if the bond symmetry is broken. Finally, a single-gated FET based on Cu-adsorbed ABC-stacked trilayer graphene is simulated. A clear transmission gap is observed, which is comparable with the band gap. This renders metal-adsorbed FLG a promising channel in a single-gated FET device.

  2. Deformable frequency selective surface structure with tuning capability through thermoregulating.

    PubMed

    Chen, Xin; Gao, Jinsong; Fang, Chunyi; Xu, Nianxi; Wang, Yansong; Tang, Yang

    2015-06-15

    We design and fabricate a deformable frequency selective surface (FSS) structure using shape memory alloys (SMA). The unit cell could "remember" two different geometrical shapes and the shapes convert to each other alternately during heating and cooling, that leads to the drift of resonant frequency. Qualitative analysis by equivalent circuit model and accurate numeric calculation are compared to display the character of the transmission. The measurements show that a tuning range of frequency from 13.07GHz to 16.29GHz is achieved when the morphology of the unit cell changes, making the deformable FSS an attractive choice for tunable filter in different frequency bands with the features of wide tuning range and sharp cut-off. PMID:26193605

  3. A new algorithm for sea-surface wind-speed retrieval based on the L-band radiometer onboard Aquarius

    NASA Astrophysics Data System (ADS)

    Wang, Jin; Zhang, Jie; Fan, Chenqing; Wang, Jing

    2015-09-01

    Aquarius is the second satellite mission to focus on the remote sensing of sea-surface salinity from space and it has mapped global sea-surface salinity for nearly 3 years since its launch in 2011. However, benefiting from the high atmospheric transparency and moderate sensitivity to wind speed of the L-band brightness temperature (TB), the Aquarius L-band radiometer can actually provide a new technique for the remote sensing of wind speed. In this article, the sea-surface wind speeds derived from TBs measured by Aquarius' L-band radiometer are presented, the algorithm for which is developed and validated using multisource wind speed data, including WindSat microwave radiometer and National Data Buoy Center buoy data, and the Hurricane Research Division of the Atlantic Oceanographic and Meteorological Laboratory wind field product. The error analysis indicates that the performance of retrieval algorithm is good. The RMSE of the Aquarius wind-speed algorithm is about 1 and 1.5 m/s for global oceans and areas of tropical hurricanes, respectively. Consequently, the applicability of using the Aquarius L-band radiometer as a near all-weather wind-speed measuring method is verified.

  4. 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

  5. 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.

  6. Unified description of rotational-, γ-, and quasiparticle-band structures in neutron-rich mass ∼ 110 region

    NASA Astrophysics Data System (ADS)

    Bhat, G. H.; Sheikh, J. A.; Sun, Y.; Palit, R.

    2016-03-01

    Band structures of the neutron-rich Mo- and Ru-isotopes around A ∼ 110 are investigated using the triaxial projected shell model (TPSM) approach employing multi-quasiparticle configuration space. The mass region under investigation depicts a rich variety of band structures with well developed γ- and γγ-bands, and quasiparticle excitations based on them. It is demonstrated that TPSM provides a reasonable description of most of the observed properties, in particular, detailed structure variations observed in Mo-isotopes are well reproduced in the present work.

  7. 8-band and 14-band kp modeling of electronic band structure and material gain in Ga(In)AsBi quantum wells grown on GaAs and InP substrates

    NASA Astrophysics Data System (ADS)

    Gladysiewicz, M.; Kudrawiec, R.; Wartak, M. S.

    2015-08-01

    The electronic band structure and material gain have been calculated for GaAsBi/GaAs quantum wells (QWs) with various bismuth concentrations (Bi ? 15%) within the 8-band and 14-band kp models. The 14-band kp model was obtained by extending the standard 8-band kp Hamiltonian by the valence band anticrossing (VBAC) Hamiltonian, which is widely used to describe Bi-related changes in the electronic band structure of dilute bismides. It has been shown that in the range of low carrier concentrations n < 5 1018 cm-3, material gain spectra calculated within 8- and 14-band kp Hamiltonians are similar. It means that the 8-band kp model can be used to calculate material gain in dilute bismides QWs. Therefore, it can be applied to analyze QWs containing new dilute bismides for which the VBAC parameters are unknown. Thus, the energy gap and electron effective mass for Bi-containing materials are used instead of VBAC parameters. The electronic band structure and material gain have been calculated for 8 nm wide GaInAsBi QWs on GaAs and InP substrates with various compositions. In these QWs, Bi concentration was varied from 0% to 5% and indium concentration was tuned in order to keep the same compressive strain (? = 2%) in QW region. For GaInAsBi/GaAs QW with 5% Bi, gain peak was determined to be at about 1.5 ?m. It means that it can be possible to achieve emission at telecommunication windows (i.e., 1.3 ?m and 1.55 ?m) for GaAs-based lasers containing GaInAsBi/GaAs QWs. For GaInAsBi/Ga0.47In0.53As/InP QWs with 5% Bi, gain peak is predicted to be at about 4.0 ?m, i.e., at the wavelengths that are not available in current InP-based lasers.

  8. 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.

  9. Prediction of the band structures of Bi2Te3-related binary and Sb/Se-doped ternary thermoelectric materials

    NASA Astrophysics Data System (ADS)

    Ryu, Byungki; Kim, Bong-Seo; Lee, Ji Eun; Joo, Sung-Jae; Min, Bok-Ki; Lee, HeeWoong; Park, Sudong; Oh, Min-Wook

    2016-01-01

    Density functional calculations are performed to study the band structures of Bi2Te3-related binary (Bi2Te3, Sb2Te3, Bi2Se3, and Sb2Se3) and Sb/Se-doped ternary compounds [(Bi1- x Sb x )2Te3 and Bi2(Te1- y Se y )3]. The band gap was found to be increased by Sb doping and to be monotonically increased by Se doping. In ternary compounds, the change in the conduction band structure is more significant as compared to the change in the valence band structure. The band degeneracy of the valence band maximum is maintained at 6 in binaries and ternaries. However, when going from Bi2Te3 to Sb2Te3 (Bi2Se3), the degeneracy of the conduction band minimum is reduced from 6 to 2(1). Based on the results for the band structures, we suggest suitable stoichiometries of ternary compounds for high thermoelectric performance.

  10. Band-gap-confinement and image-state-recapture effects in the survival of anions scattered from metal surfaces

    SciTech Connect

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

    2010-04-15

    The resonant charge transfer process in the collision of hydrogen anions with metal surfaces is described within a single-active-electron wave-packet propagation method. The ion-survival probability is found to be strongly enhanced at two different surface-specific perpendicular velocities of the ion. It is shown that, while the low-velocity enhancement is induced from a dynamical confinement of the ion level inside the band gap, the high-velocity enhancement is due to electron recapture from transiently populated image states. Results are presented for Li(110), Cu(111), and Pd(111) surfaces.

  11. Bioinspired, dynamic, structured surfaces for biofilm prevention

    NASA Astrophysics Data System (ADS)

    Epstein, Alexander K.

    Bacteria primarily exist in robust, surface-associated communities known as biofilms, ubiquitous in both natural and anthropogenic environments. Mature biofilms resist a wide range of biocidal treatments and pose persistent pathogenic threats. Treatment of adherent biofilm is difficult, costly, and, in medical systems such as catheters, frequently impossible. Adding to the challenge, we have discovered that biofilm can be both impenetrable to vapors and extremely nonwetting, repelling even low surface tension commercial antimicrobials. Our study shows multiple contributing factors, including biochemical components and multiscale reentrant topography. Reliant on surface chemistry, conventional strategies for preventing biofilm only transiently affect attachment and/or are environmentally toxic. In this work, we look to Nature's antifouling solutions, such as the dynamic spiny skin of the echinoderm, and we develop a versatile surface nanofabrication platform. Our benchtop approach unites soft lithography, electrodeposition, mold deformation, and material selection to enable many degrees of freedom—material, geometric, mechanical, dynamic—that can be programmed starting from a single master structure. The mechanical properties of the bio-inspired nanostructures, verified by AFM, are precisely and rationally tunable. We examine how synthetic dynamic nanostructured surfaces control the attachment of pathogenic biofilms. The parameters governing long-range patterning of bacteria on high-aspect-ratio (HAR) nanoarrays are combinatorially elucidated, and we discover that sufficiently low effective stiffness of these HAR arrays mechanoselectively inhibits ˜40% of Pseudomonas aeruginosa biofilm attachment. Inspired by the active echinoderm skin, we design and fabricate externally actuated dynamic elastomer surfaces with active surface microtopography. We extract from a large parameter space the critical topographic length scales and actuation time scales for achieving nearly ˜80% attachment reduction. We furthermore investigate an atomically mobile, slippery liquid infused porous surface (SLIPS) inspired by the pitcher plant. We show up to 99.6% reduction of multiple pathogenic biofilms over a 7-day period under both static and physiologically realistic flow conditions—a ˜35x improvement over state-of-the-art surface chemistry, and over a far longer timeframe. Moreover, SLIPS is shown to be nontoxic: bacteria simply cannot attach to the smooth liquid interface. These bio-inspired strategies significantly advance biofilm attachment prevention and promise a tremendous range of industrial, clinical, and consumer applications.

  12. High-order modes of spoof surface plasmonic wave transmission on thin metal film structure.

    PubMed

    Liu, Xiaoyong; Feng, Yijun; Zhu, Bo; Zhao, Junming; Jiang, Tian

    2013-12-16

    Recently, conformal surface plasmon (CSP) structure has been successfully proposed that could support spoof surface plasmon polaritons (SPPs) on corrugated metallic strip with ultrathin thickness [Proc. Natl. Acad. Sci. U.S.A. 110, 40-45 (2013)]. Such concept provides a flexible, conformal, and ultrathin wave-guiding element, very promising for application of plasmonic devices, and circuits in the frequency ranging from microwave to mid-infrared. In this work, we investigated the dispersions and field patterns of high-order modes of spoof SPPs along CSP structure of thin metal film with corrugated edge of periodic array of grooves, and carried out direct measurement on the transmission spectrum of multi-band of surface wave propagation at microwave frequency. It is found that the mode number and mode bands are mainly determined by the depth of the grooves, providing a way to control the multi-band transmission spectrum. We have also experimentally verified the high-order mode spoof SPPs propagation on curved CSP structure with acceptable bending loss. The multi-band propagation of spoof surface wave is believed to be applicable for further design of novel planar devices such as filters, resonators, and couplers, and the concept can be extended to terahertz frequency range. PMID:24514689

  13. [Band electronic structures and crystal packing forces: Progress report, July 1, 1989--December 13, 1991

    SciTech Connect

    Not Available

    1991-12-31

    This report briefly summaries our research accomplishments made during the period of July 1, 1989 to December 13, 1991. A number of significant progresses were achieved in our studies of several different classes of low-dimensional solid state materials. On the basis of tight-binding band electronic structure calculations, we investigated the electronic properties of various organic conducting salts, cuprate superconductors, and transition-metal oxide and chalcogenide metals to find structure-property correlations governing of the physical properties of these low-dimensional materials. By employing a number of different quality basis sets, we also carried out extensive ab initio SCF-MO/MP2 calculations on model molecular systems to accurately describe the weak intermolecular contact interactions governing the structures of organic donor slats and molecular crystals. Our research efforts led to about 80 publications and two important computer programs.

  14. (Band electronic structures and crystal packing forces: Progress report, July 1, 1989--December 13, 1991)

    SciTech Connect

    Not Available

    1991-01-01

    This report briefly summaries our research accomplishments made during the period of July 1, 1989 to December 13, 1991. A number of significant progresses were achieved in our studies of several different classes of low-dimensional solid state materials. On the basis of tight-binding band electronic structure calculations, we investigated the electronic properties of various organic conducting salts, cuprate superconductors, and transition-metal oxide and chalcogenide metals to find structure-property correlations governing of the physical properties of these low-dimensional materials. By employing a number of different quality basis sets, we also carried out extensive ab initio SCF-MO/MP2 calculations on model molecular systems to accurately describe the weak intermolecular contact interactions governing the structures of organic donor slats and molecular crystals. Our research efforts led to about 80 publications and two important computer programs.

  15. 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.

  16. Design of LD in-band direct-pumping side surface polished micro-rod Nd:YVO4 laser

    NASA Astrophysics Data System (ADS)

    Wen-Qi, Zhang; Fei, Wang; Qiang, Liu; Ma-Li, Gong

    2016-02-01

    To diminish the thermal load, two ways, that is, in-band direct pumping and micro-rod crystal, could be adopted at the same time. The efficiency of LD in-band direct-pumping side surface polished micro-rod Nd:YVO4 laser is numerically analyzed. By optimizing parameters such as crystal length, laser mode radius, pump beam radius, doping concentration and crystal cross-section size, the overall efficiency can reach over 50%. It is found that with micro-rod crystal implemented in the laser oscillator, high overall efficiency LD in-band direct-pumping Nd:YVO4 laser could be realized. High efficiency combined with low thermal load makes this laser an outstanding scheme for building high-power Nd:YVO4 lasers.

  17. Viscous-to-viscoelastic transition in phononic crystal and metamaterial band structures.

    PubMed

    Frazier, Michael J; Hussein, Mahmoud I

    2015-11-01

    The dispersive behavior of phononic crystals and locally resonant metamaterials is influenced by the type and degree of damping in the unit cell. Dissipation arising from viscoelastic damping is influenced by the past history of motion because the elastic component of the damping mechanism adds a storage capacity. Following a state-space framework, a Bloch eigenvalue problem incorporating general viscoelastic damping based on the Zener model is constructed. In this approach, the conventional Kelvin-Voigt viscous-damping model is recovered as a special case. In a continuous fashion, the influence of the elastic component of the damping mechanism on the band structure of both a phononic crystal and a metamaterial is examined. While viscous damping generally narrows a band gap, the hereditary nature of the viscoelastic conditions reverses this behavior. In the limit of vanishing heredity, the transition between the two regimes is analyzed. The presented theory also allows increases in modal dissipation enhancement (metadamping) to be quantified as the type of damping transitions from viscoelastic to viscous. In conclusion, it is shown that engineering the dissipation allows one to control the dispersion (large versus small band gaps) and, conversely, engineering the dispersion affects the degree of dissipation (high or low metadamping). PMID:26627790

  18. Collective band structures in the odd-proton nuclei /sup 135,137/Pm

    SciTech Connect

    Beausang, C.W.; Hildingsson, L.; Paul, E.S.; Piel W.F. Jr.; Weng, P.K.; Xu, N.; Fossan, D.B.

    1987-08-01

    Collective bands based on a low-K ..pi..h/sub 11/2/ orbital have been populated to high spins in the odd-proton nuclei /sup 135,137/Pm following the reactions /sup 116/Sn(/sup 24/Mg,p4n)/sup 135/Pm and /sup 114/Cd(/sup 27/Al,4n)/sup 137/Pm, respectively. Both nuclei exhibit a band crossing in the ..pi..h/sub 11/2/ band at a frequency of h-dash-bar..omega..--0.42 MeV. In /sup 135/Pm, an upbend is observed, while a weaker interaction backbend is observed in /sup 137/Pm. Cranked-shell model calculations, including triaxiality, imply that this crossing is due to the alignment of the second and third valence h/sub 11/2/ protons. The systematics of this alignment in the Pm isotopes will be discussed. In addition, positive parity three-quasiproton states were observed in both nuclei. These structures also contain a pair of aligned h/sub 11/2/ protons, in this case the first and second valence protons which align at a much lower frequency of h-dash-bar..omega..--0.28 MeV.

  19. High gain low noise L-band preamplifier with cascade double-pass structure

    NASA Astrophysics Data System (ADS)

    Jia, Dongfang; Wang, Yanyong; Bao, Huanmin; Yang, Tianxin; Li, Shichen

    2005-06-01

    An optimized two-stage-cascade double-pass structure L-band preamplifier was proposed and experimentally studied to overcome the shortcomings of low gain coefficient and high noise figure of L-band erbium-doped fiber amplifier (EDFA). The fiber lengthes of 6.5 and 32.5 m, pump powers of 130 and 119 mW for the first and second stages respectively are used in the experiment. When input signal power is -30 dBm, the amplifier can provide gain above 38.84 dB in a wavelength range of 34 nm (1568---1602 nm), gain ripple less than 2.04 dB (40.88---38.84 dB), and noise figures lower than 5.29 dB with the lowest value of 3.95 dB at 1590 nm. Experimental and simulation results show that this low cost and high pump efficiency amplifier is suitable for the application as an L-band preamplifier in the broadband fiber communication system.

  20. Electronic structure of graphene nanoflakes: band gap evolution with increasing size

    NASA Astrophysics Data System (ADS)

    Martinez-Guerra, E.; Cifuentes-Quintal, M. E.; Rodriguez-Vargas, I.; Vlaev, S.; de Coss, R.

    2009-03-01

    Graphene has unusual electronic properties which make it a promising material for electronic devices. Neverthless, the absence of a band gap sets limitations on its applications. Thus, it is crucial to tune the band gap of systems based on graphene. In this way, we explore to modulate the electronic properties of graphene through the size system. In particular, we studied the evolution of the electronic structure of graphene nanoflakes (C6n2H6n) as a function of size. The calculations were performed using the pseudopotential LCAO method with a Generalized Gradient Approximation for the exchange-correlation functional. We found that the energy gap decreases as the diameter of the nanoflakes increases. From a tight-binding analysis, we show that the energy gap reduction is due to an HOMO-LUMO bands widening. This effect results from the fact that as nanoflakes size increases the ratio between the number of internal and periferical atoms decreases. Thus, we found that controlling the size of graphene nanoflakes is a useful way for the electronic modulation. Supported from CONACyT Grant 83604.