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Sample records for surface band structure

  1. Surface electronic structure with the linear methods of band theory

    NASA Astrophysics Data System (ADS)

    Krasovskii, E. E.; Schattke, W.

    1997-11-01

    We present an ab initio method for calculating electron states in a semi-infinite crystal. The complex band structure is obtained by the extended linear augmented-plane-wave method within the exact k.p formulation of the band-structure problem. We also present a variational scheme of matching the wave functions at the interface. The practical applicability of the method is demonstrated by solving the Schrödinger equation for the (100) surface of Al. We have calculated the normal incidence low-energy electron-diffraction spectra, the occupied surface state at the ? point, and the normal-emission photoelectron spectra within the one-step model. The results are in a good agreement with available measurements. We have developed a simplified procedure to assess the conducting properties of a crystal surface in terms of the k?-projected real band structure. We introduce a new quantity, the conductance index, whose energy dependence is shown to yield gross features of the exact energy dependence of transmitted current.

  2. 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

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

    NASA Astrophysics Data System (ADS)

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

    2001-10-01

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

  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. 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.

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

    PubMed

    Mondal, Puja; Ghosh, Sankalpa

    2015-12-16

    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. PMID:26596345

  10. Band structure and waveguide modelling of epitaxially regrown photonic crystal surface-emitting lasers

    NASA Astrophysics Data System (ADS)

    Taylor, Richard J. E.; Williams, David M.; Orchard, Jon R.; Childs, David T. D.; Khamas, Salam; Hogg, Richard A.

    2013-07-01

    In this paper we describe elements of photonic crystal surface-emitting laser (PCSEL) design and operation, highlighting that epitaxial regrowth may provide advantages over current designs incorporating voids. High coupling coefficients are shown to be possible for all-semiconductor structures. We introduce type I and type II photonic crystals (PCs), and discuss the possible advantages of using each. We discussed band structure and coupling coefficients as a function of atom volume for a circular atom on a square lattice. Additionally we explore the effect PC atom size has on in-plane and out-of-plane coupling. We conclude by discussing designs for a PCSEL combined with a distributed Bragg reflector to maximize external efficiency.

  11. Angle-resolved photoemission studies of the valence-band structure of stepped crystal surfaces: Cu(S)-(3(111) x (100))

    SciTech Connect

    Davis, R.F.; Williams, R.S.; Kevan, S.D.; Wehner, P.S.; Shirley, D.A.

    1985-02-15

    Angle-resolved photoemission spectra are reported for the stepped Cu(211) face in the photon-energy range 9< or =h..nu..< or =34 eV. The valence-band (VB) spectra are interpreted in terms of a direct-transition model for bulk photoemission. Determination of VB dispersion relations and assignment of the bands are aided by use of selection rules involving the transmitted-radiation vector potential and several different experimental geometries. The major results are (1) it is possible to determine experimental VB dispersion relations for a lower-symmetry direction such as Cu(211), and (2) VB dispersion relations for stepped Cu(211) show excellent agreement with bulk valence bands interpolated along the (211) direction, uninterrupted by band-gap photoemission, the effects of which are not observed. It is concluded that the unusual structure of the stepped surface does not significantly perturb the bulk electronic structure near the surface in this case.

  12. Babinet's principle and the band structure of surface waves on patterned metal arrays

    E-print Network

    Exeter, University of

    2010 The microwave response of an array of square metal patches and its complementary structure in the ultraviolet region, yielding a predominantly Drude-type dielectric function dominated by a negative real part typically occurs in the ultraviolet. Since ksw k0 Eq. 1 , these modes are nonradiative but can be coupled

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

    NASA Astrophysics Data System (ADS)

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

    2004-07-01

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

  14. Band structures of plasmonic polarons.

    PubMed

    Caruso, Fabio; Lambert, Henry; Giustino, Feliciano

    2015-04-10

    Using state-of-the-art many-body calculations based on the "GW plus cumulant" approach, we show that electron-plasmon interactions lead to the emergence of plasmonic polaron bands in the band structures of common semiconductors. Using silicon and group IV transition-metal dichalcogenide monolayers (AX_{2} with A=Mo,W and X=S, Se) as prototypical examples, we demonstrate that these new bands are a general feature of systems characterized by well-defined plasmon resonances. We find that the energy versus momentum dispersion relations of these plasmonic structures closely follow the standard valence bands, although they appear broadened and blueshifted by the plasmon energy. Based on our results, we identify general criteria for observing plasmonic polaron bands in the angle-resolved photoelectron spectra of solids. PMID:25910145

  15. 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 \

  16. Structure of Bright 2MASS Galaxies 2D Fits to the Ks-band Surface Brightness Profiles

    E-print Network

    McIntosh, D H; Katz, N; Weinberg, M D; Intosh, Daniel H. Mc; Maller, Ari H.; Katz, Neal; Weinberg, Martin D.

    2002-01-01

    The unprecedented sky coverage and photometric uniformity of the Two Micron All Sky Survey (2MASS) provides a rich resource for obtaining a detailed understanding of the galaxies populating our local (z<0.1) Universe. A full characterization of the physical structure of nearby galaxies is essential for theoretical and observational studies of galaxy evolution and structure formation. We have begun a quantified description of the internal structure and morphology of 10,000 bright (10surface brightness profiles using GIM2D. From our initial Monte Carlo tests on 77 galaxies drawn at random from the RC3, we find that the model derived structural parameter errors due to sky uncertainies are typically less than 10%.

  17. 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.

  18. 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.

  19. Banded structures in stratospheric aerosol distributions

    SciTech Connect

    Trepte, C.R.; Thomason, L.W.; Kent, G.S.

    1994-11-01

    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{degrees} and 45{degrees}. 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. 16 refs., 3 figs.

  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. 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

  2. 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.

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

    E-print Network

    Xue, Ming

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

  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. 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.

  6. 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

  7. 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.

  8. Shear horizontal guided wave band gaps in a homogenous plate with periodic tapered surface

    NASA Astrophysics Data System (ADS)

    Song, Guang-huang; Chen, Jiu-jiu; Han, Xu

    2014-09-01

    The shear horizontal (SH) guided wave band structures and transmission coefficients in a homogenous plate with periodic tapered surface, whose width is gradually decreases from the lower base to the upper base, are calculated based on the eigen-mode matching theory (EMMT) method. The finite element method (FEM) is also employed to calculate the band structures, which is in good agreement with the results by EMMT method. Numerical results show that the SH guided wave band structures in reduced frequency keep unchanged even if the whole homogenous plate with periodic tapered surface is filled with different materials. We also present the numerical investigations of the geometrical factors’ effect on the band structures, including the upper base width, the lower base width, the tapered surface thickness and the plate thickness. These properties of SH guided wave can potentially be utilized to design acoustic sensors, tune band gaps and generate filters.

  9. 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

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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

  15. Electronic Band Structure of TlTe

    SciTech Connect

    Wagner, Frank R.; Stoewe, Klaus

    2001-02-15

    We report about self-consistent ab initio LMTO-ASA calculations of the electronic band structure and the crystal orbital Hamiltonian population function COHP. The calculations support a view of TlTe as an univalent Tl compound with two polyanionic partial structures, linear branched and unbranched chains, characterized by 3c-4e type of bonding, both within the chains and within the branches. The system deviates from classical Peierls-type systems with respect to the lack of energetic separation of the two types of transition-driving {sigma} bands due to the appearance of nonintrachain bands close to E{sub F}. Tl coordination causes the lack of elastic degrees of freedom, which prevents the system from introducing completely alternating chains in one step. The branched Te2 chains are shown to be favored for pairing distortion compared to Te3 chains as a result of the weaker Tl-Te2 interactions. The distortion is interpreted as a dimerization of (Te{sub 3}){sup 3-} units t o form a new type of 42 electron (Te{sub 6}){sup 6-} partial structure not known in polyhalogenide or noble gas halogenide chemistry.

  16. Lamb wave band gaps in a homogenous plate with periodic Gaussian surfaces

    NASA Astrophysics Data System (ADS)

    Ming, Chen; Chen, Jiujiu; Han, Xu; Zhang, Hongbo

    2013-09-01

    The Lamb wave band structure of a one-dimensional thin plate with periodic Gaussian surfaces is calculated based on the eigen-mode matching theory (EMMT) method. The finite element method is also employed to calculate the transmission power spectra and the band structure, which are both in good agreement with the results of the EMMT method. In contrast with the straight stubs, the low-frequency band gap of the system with the Gaussian surfaces is wider, when the Gaussian domain's height and area are equal to those of the stub, and the two systems' main plate size and materials are the same. This can be confirmed by the ‘spring-mass' model, which can be used to estimate the resonant frequency. We also investigate the effects of the geometrical parameters on band structure, including the height of the Gaussian domain, the plate thickness and the filling fraction. The results suggest that the band gaps have a close relevance to them.

  17. Micromechanics of slip bands on a free surface

    NASA Technical Reports Server (NTRS)

    Lin, S. R.; Lin, T. H.

    1976-01-01

    A micromechanics analysis for the formation and propagation of slip bands on the free surface of a polycrystal under monotonic loading is presented. For the growth of slip bands, the analysis satisfies the conditions of both equilibrium and displacement continuity, as well as the relation between slip and the resolved shear stress throughout the polycrystal. Numerical calculations show how the microstress field causes the concentration of plastic deformation in discrete sliding bands and give results which are in good qualitative agreement with known slip band observations on aluminum single crystals.

  18. Banded electron structures in the plasmasphere

    NASA Astrophysics Data System (ADS)

    Burke, William J.; Rubin, Allen G.; Hardy, David A.; Holeman, Ernest G.

    1995-05-01

    The low-energy plasma analyzer on the Combined Release Radiation Effects Satellite (CRRES) has detected significant fluxes of 10-eV to 30-keV electrons trapped on plasmaspheric field lines. On energy-versus-time spectrograms these electrons appear as banded structures that can span the 2 less than L less than 6 range of magnetic shells. We present an example of banded electron structures, encountered in the nightside plasmasphere during the magnetically quiet January 30, 1991. Empirical analysis suggests that two clouds of low-energy electrons were injected from the plasma sheet to L less than 4 on January 26 and 27 while the convective electric field was elevated. The energies of electrons in the first cloud were greater than those in the second. Defence Meteorological Satellite Program Flight 8 (DMSP F8) measurements show that after the second injection, the polar cap potential rapidly decreased from greater than 50 to less than 20 kV. Subsequent encounters with the lower-energy cloud on alternating CRRES orbits over the next 2 days showed a progressive, earthward movement of the electrons' inner boundary. Whistler and electron cyclotron harmonic emissions accompanied the most intense manifestations of cloud electrons. The simplest explanation of these measurements is that after initial injection, the Alfven boundary moved outward, leaving the cloud electrons on closed drift paths. Subsequent fluctuations of the convective electric field penetrated the plasmasphere, transporting cloud elements inward. The magnetic shell distribution of electron temperatures in one of the banded structures suggests that radiative energy losses may be comparable in magnitude to gains due to adiabatic compression.

  19. 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.

  20. Electronic band structure and photoemission: A review and projection

    SciTech Connect

    Falicov, L.M.

    1987-09-01

    A brief review of electronic-structure calculations in solids, as a means of interpreting photoemission spectra, is presented. The calculations are, in general, of three types: ordinary one-electron-like band structures, which apply to bulk solids and are the basis of all other calculations; surface modified calculations, which take into account, self-consistently if at all possible, the presence of a vacuum-solid interface and of the electronic modifications caused thereby; and many-body calculations, which go beyond average-field approximations and consider dynamic rearrangement effects caused by electron-electron correlations during the photoemission process. 44 refs.

  1. Band structure mapping of photonic crystal intersubband detectors

    NASA Astrophysics Data System (ADS)

    Schartner, S.; Golka, S.; Pflügl, 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.

  2. 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.

  3. 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.

  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. Band gap structures for matter waves

    E-print Network

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

    2015-06-08

    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 barriers 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 to realize in one dimension matter wave Fabry-Perot cavities. We also provide experimental and numerical results that demonstrate the interest of spatial gaps structures for phase space engineering. We then generalize the concept of spatial gaps in two dimensions and show that this enables to design multiply connected cavities which generate a quantum dot structure for atoms or allow 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.

  6. 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.

  7. 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"…

  8. 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.

  9. 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.

  10. Shear band structure in ballistically tested bainitic steels

    E-print Network

    Fielding, L. C. D.; Bhadeshia, H. K. D. H.

    Adiabatic shear bands represent intense plastic deformation that is localised because the rate at which the heat generated by deformation is greater than that at which it is dissipated. The structure of such bands generated by ballistic testing...

  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. 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).

  13. 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).

  14. Large spin splitting of metallic surface-state bands at adsorbate-modified gold/silicon surfaces

    PubMed Central

    Bondarenko, L. V.; Gruznev, D. V.; Yakovlev, A. A.; Tupchaya, A. Y.; Usachov, D.; Vilkov, O.; Fedorov, A.; Vyalikh, D. V.; Eremeev, S. V.; Chulkov, E. V.; Zotov, A. V.; Saranin, A. A.

    2013-01-01

    Finding appropriate systems with a large spin splitting of metallic surface-state band which can be fabricated on silicon using routine technique is an essential step in combining Rashba-effect based spintronics with silicon technology. We have found that originally poor structural and electronic properties of the surface can be substantially improved by adsorbing small amounts of suitable species (e.g., Tl, In, Na, Cs). The resultant surfaces exhibit a highly-ordered atomic structure and spin-split metallic surface-state band with a momentum splitting of up to 0.052 Å?1 and an energy splitting of up to 190?meV at the Fermi level. The family of adsorbate-modified surfaces, on the one hand, is thought to be a fascinating playground for exploring spin-splitting effects in the metal monolayers on a semiconductor and, on the other hand, expands greatly the list of material systems prospective for spintronics applications. PMID:23661151

  15. Deep Intermediate-Band Surface Photometry of NGC 5907

    E-print Network

    Zheng, Z Y; Su, H J; Burstein, D; Chen, J S

    1999-01-01

    We obtained very deep exposures of NGC 5907 with a Schmidt telescope, large-format CCD, and intermediate-band filters centered at 6660A and 8020A. These two filters, part of a 15-filter set, are custom-designed to avoid the brightest (and most variable) night sky lines, with the result that our images go deeper, with lower sky noise, than those taken with broad-band filters. Our errors of observation reach 1 mag/arcsec^2 at 29.00 mag/arcsec-2 in the 6660A image (= 28.7 in R-band), and 27.4 mag/arcsec^ in the 8020A image (same zero point as I-band). Fainter than R = 27 mag arcsec^, the surface brightness around NGC 5907 is strongly asymmetric, being mostly brighter the NW side of the galaxy midplane. This asymmetry rules out a halo for the origin of the faint surface brightness we see. Rather, this asymmetry is likely an artifact due to a combination of light from a faint ring around this galaxy (as described in Shang et al. 1998, ApJL 504, 23) and residual surface brightness at faint levels from stars that ou...

  16. Organosilane-functionalized wide band gap semiconductor surfaces

    NASA Astrophysics Data System (ADS)

    Petoral, R. M.; Yazdi, G. R.; Lloyd Spetz, A.; Yakimova, R.; Uvdal, K.

    2007-05-01

    Surface functionalization of wide band gap semiconductors, SiC, ZnO, and GaN, with organosilane is reported. Formation of self-assembled monolayers of mercaptopropyltrimethoxysilane is confirmed by x-ray photoelectron spectroscopy and atomic force microscopy. The molecules are adsorbed on the surfaces through the silane groups with the free thiol groups molecularly oriented away from the surface. Moreover, chemisorption via the thiolate is observed for the ZnO surface. Immobilization of a model biomolecule to the functionalized surface is demonstrated. An amino acid derivative, i.e., phosphotyrosine derived thiol, is linked on the functionalized ZnO and GaN surfaces via formation of disulfide bridges.

  17. 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.

  18. 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.

  19. 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.

  20. All-Optical Reconstruction of Crystal Band Structure.

    PubMed

    Vampa, G; Hammond, T J; Thiré, N; Schmidt, B E; Légaré, 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

  1. All-Optical Reconstruction of Crystal Band Structure

    NASA Astrophysics Data System (ADS)

    Vampa, G.; Hammond, T. J.; Thiré, N.; Schmidt, B. E.; Légaré, 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.

  2. 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 ? 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.

  3. Ultrawide-band Unidirectional Surface Plasmon Polariton Launchers

    E-print Network

    Lu, Cuicui; Yang, Hong; Gong, Qihuang

    2013-01-01

    Plasmonic devices and circuits, bridging the gap between integrated photonic and microelectronic technology, are promising candidates to realize on-chip ultrawide-band and ultrahigh-speed information processing. Unfortunately, the wideband surface plasmon source, one of the most important core components of integrated plasmonic circuits, is still unavailable up to now. This has seriously restricted the practical applications of plasmonic circuits. Here, we report an ultrawide-band unidirectional surface plasmon polariton launcher with high launching efficiency ratio and large extinction ratio, realized by combining plasmonic bandgap engineering and linear interference effect. This device offers excellent performances over an ultrabroad wavelength range from 690 to 900 nm, together with a high average launching efficiency ratio of 1.25, large average extinction ratio of 30 dB, and ultracompact lateral dimension of less than 4 um. Compared with previous reports, the operating bandwidth is enlarged 210 folds, wh...

  4. Surface electrical conduction due to carrier doping into a surface-state band on Si,,111...-3 3-Ag

    E-print Network

    Hasegawa, Shuji

    Surface electrical conduction due to carrier doping into a surface-state band on Si,,111...- 3 3-Ag into an antibonding surface-state band of this substrate, resulting in a steep increase in electrical conductance through the band. The surface space-charge layer makes no contribution to the conductance increase

  5. Deep Intermediate-Band Surface Photometry of NGC 5907

    E-print Network

    BATC Collaboration; Z. Y. Zheng; Z. H. Shang; H. J. Su; D. Burstein; J. S. Chen

    1999-02-19

    We obtained very deep exposures of NGC 5907 with a Schmidt telescope, large-format CCD, and intermediate-band filters centered at 6660A and 8020A. These two filters, part of a 15-filter set, are custom-designed to avoid the brightest (and most variable) night sky lines, with the result that our images go deeper, with lower sky noise, than those taken with broad-band filters. Our errors of observation reach 1 mag/arcsec^2 at 29.00 mag/arcsec-2 in the 6660A image (= 28.7 in R-band), and 27.4 mag/arcsec^ in the 8020A image (same zero point as I-band). Fainter than R = 27 mag arcsec^, the surface brightness around NGC 5907 is strongly asymmetric, being mostly brighter the NW side of the galaxy midplane. This asymmetry rules out a halo for the origin of the faint surface brightness we see. Rather, this asymmetry is likely an artifact due to a combination of light from a faint ring around this galaxy (as described in Shang et al. 1998, ApJL 504, 23) and residual surface brightness at faint levels from stars that our star-masking procedure cannot completely eliminate. Good agreement with the surface photometry of NGC 5907 by Morrison et al. and other workers lead us to conclude that their data are similarly affected at faint levels by ring light and residual effects from their star masking procedures. Inspection of the images published by Morrison et al. and Sackett et al. confirm this to be the case. Thus, we conclude that NGC 5907 does not have a faint, extended halo.

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

    SciTech Connect

    Mäkinen, 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.

  7. New Band Structures in Aapprox110 Neutron-Rich Nuclei

    SciTech Connect

    Zhu, S. J.; Wang, J. G.; Ding, H. B.; Gu, L.; Xu, Q.; Yeoh, E. Y.; Xiao, Z. G.; Hamilton, J. H.; Ramayya, A. V.; Hwang, J. K.; Liu, S. H.; Li, K.; Luo, Y. X.; Rasmussen, J. O.; Lee, I. Y.; Qi, B.; Meng, J.

    2010-05-12

    The high spin states of neutron-rich nuclei in Aapprox110 region have been carefully investigated by measuring prompt gamma-gamma-gamma coincident measurements populated in the spontaneous fission of {sup 252}Cf with the Gammasphere detector array. Many new collective bands have been discovered. In this proceeding paper, we introduce some interesting new band structures recently observed by our cooperative groups, that is, the one-phonon- and two-phonon gamma-vibrational bands in odd-A {sup 103}Nb, {sup 105}Mo and {sup 107}Tc, the chiral doublet bands in even-even {sup 106}Mo, {sup 110}Ru and {sup 112}Ru, and the pseudospin partner bands with in {sup 108}Tc. The characteristics of these band structures have been discussed.

  8. 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.

  9. 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

  10. The electronic structure of heavy fermions: Narrow temperature independent bands

    SciTech Connect

    Arko, A.J.; Joyce, J.J.; Smith, J.L.; Andrews, A.B.

    1996-08-01

    The electronic structure of both Ce and U heavy fermions appears to consist of extremely narrow temperature independent bands. There is no evidence from photoemission for a collective phenomenon normally referred to as the Kondo resonance. In uranium compounds a small dispersion of the bands is easily measurable.

  11. Novel photonic band gap structures for accelerator applications

    E-print Network

    Smirnova, Evgenya I

    2005-01-01

    In this thesis I present the design and experimental demonstration of the first photonic band gap (PBG) accelerator at 17.140 GHz. A photonic band gap structure is a one-, two- or three-dimensional periodic metallic and/or ...

  12. 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

  13. 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.

  14. Band structure engineering in (Bi(1-x)Sb(x))(2)Te(3) ternary topological insulators.

    PubMed

    Zhang, Jinsong; Chang, Cui-Zu; Zhang, Zuocheng; Wen, Jing; Feng, Xiao; Li, Kang; Liu, Minhao; He, Ke; Wang, Lili; Chen, Xi; Xue, Qi-Kun; Ma, Xucun; Wang, Yayu

    2011-01-01

    Topological insulators (TIs) are quantum materials with insulating bulk and topologically protected metallic surfaces with Dirac-like band structure. The most challenging problem faced by current investigations of these materials is to establish the existence of significant bulk conduction. Here we show how the band structure of topological insulators can be engineered by molecular beam epitaxy growth of (Bi(1-x)Sb(x))(2)Te(3) ternary compounds. The topological surface states are shown to exist over the entire composition range of (Bi(1-x)Sb(x))(2)Te(3), indicating the robustness of bulk Z(2) topology. Most remarkably, the band engineering leads to ideal TIs with truly insulating bulk and tunable surface states across the Dirac point that behaves like one-quarter of graphene. This work demonstrates a new route to achieving intrinsic quantum transport of the topological surface states and designing conceptually new topologically insulating devices based on well-established semiconductor technology. PMID:22146393

  15. Surface photometry STRUCTURE OF GALAXIES

    E-print Network

    Kruit, Piet van der

    Outline Surface photometry Dynamics Formation STRUCTURE OF GALAXIES 9. Elliptical galaxies Piet van van der Kruit, Kapteyn Astronomical Institute Elliptical galaxies #12;Outline Surface photometry Dynamics Formation Outline Surface photometry Luminosity distributions Shells and ripples Color gradients

  16. 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.

  17. 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

  18. 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.

  19. Band structure of core-shell semiconductor nanowires

    NASA Astrophysics Data System (ADS)

    Pistol, Mats-Erik; Pryor, Craig

    2009-03-01

    We present band structures of strained core-shell nanowires composed of zincblende III-V (binary) semiconductors. We consider all combinations of AlN, GaN, InN, and all combinations of AlP, GaP, AlAs, GaAs, InP, InAs, AlSb, GaSb, and InSb. We compute the ?- and X-conduction band minima as well as the valence band maximum, all as functions of the core and shell radii. The calculations were performed using continuum elasticity theory for the strain, eight-band strain-dependent k.p theory for the ?-point energies, and single band approximation for the X-point conduction minima. We identify structures with type-I, type-II and type-III band alignment, as well as systems in which one material becomes metallic due to a negative band-gap. We identify structures that may support exciton crystals with and without photoexcitation. We have also computed the effective masses, from which the confinement energy may be estimated. All the results [Pistol and Pryor, Phys. Rev. B 78, 115319] are available in graphical and tabular form at www.semiconductor.physics.uiowa.edu

  20. 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

  1. 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.

  2. [Band electronic structures and crystal packing forces

    SciTech Connect

    Not Available

    1993-01-01

    We investigated the electronic and structural properties of low-dimensional materials and explored the structure-property correlations governing their physical properties. Progress was made on how to interpret the scanning tunneling microscopy and atomic force microscopy images of layered materials and on how to account for charge density wave instabilities in 2-D metals. Materials studied included transition metal chalcogenides, transition metal halides, organic conducting salts, Mo bronzes, A[sub 2]PdH[sub 2], fullerenes, squarate tetrahydrate polymers Fe, Cu(C[sub 4]O[sub 4])4[center dot]H[sub 2]O, BEDT salts, etc.

  3. 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

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

  5. Evidence of surface acoustic wave band gaps in the phononic crystals created on thin plates

    E-print Network

    Deymier, Pierre

    . Though infinite half-space phononic crystals exhibiting for- bidden bands for surface modes13,14 haveEvidence of surface acoustic wave band gaps in the phononic crystals created on thin plates Xinya acoustic wave SAW band gaps. In this letter, we report a new type of phononic crystals manufactured

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

    NASA Astrophysics Data System (ADS)

    Chen, Wei; Tegenkamp, Christoph; Pfnür, 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.

  7. Microscale inverse acoustic band gap structure in aluminum nitride

    NASA Astrophysics Data System (ADS)

    Kuo, Nai-Kuei; Zuo, Chengjie; Piazza, Gianluca

    2009-08-01

    This work presents the design and demonstration of a microscale inverse acoustic band gap (IABG) structure in aluminum nitride (AlN) with a frequency stop band for bulk acoustic waves in the very high frequency range. Conversely to conventional microscale acoustic band gaps, the IABG is formed by a two-dimensional periodic array of unit cells consisting of a high acoustic velocity material cylinder surrounded by a low acoustic velocity medium. The periodic arrangement of the IABG array induces scattering of incident acoustic waves and generates a stop band, whose center frequency is primarily determined by the lattice constant of the unit cell and whose bandwidth depends on the cylinder radius, the film thickness, and the size of the tethers that support the cylinder. A wide band gap (>13% of the center frequency) is formed by the IABG even when thin AlN films are used. The experimental response of an IABG structure having a unit cell of 8.6 ?m and an AlN film thickness of 2 ?m confirms the existence of a frequency band gap between 185 MHz and 240 MHz.

  8. The structure of shear bands in idealized granular materials

    SciTech Connect

    Bardet, J.P.; Proubet, J.

    1992-03-01

    The structure of shear bands in granular materials was investigated by numerically simulating an idealized assembly of two-dimensional particles. Flexible stress-controlled boundaries were used instead of periodic boundaries to avoid constraining the motion of particles within the tested specimen. The particle displacement, particle rotations and rotations of the particle neighborhoods (macro-rotation) were examined within the shear band. The shear band width was found to decrease with axial strain from 18 and 15 times the average particle radius. The particle rotations and macro-rotations were concentrated inside the shear bands. The numerical simulations suggest that the particle rotations are induced by macro-rotations, and support the use of the micropolar theory for examining instable phenomena within granular materials. 18 refs., 6 figs.

  9. Deformation Bands: Strain Localization Structures in Highly Porous Sandstone

    NASA Astrophysics Data System (ADS)

    Fossen, H.; Schultz, R. A.; Shipton, Z. K.; Mair, K.

    2007-12-01

    Deformation bands are the most common strain localization feature found in deformed porous sandstones and sediments, including Quaternary deposits, soft gravity slides and tectonically affected sandstones in hydrocarbon reservoirs and aquifers. They occur as various types of tabular deformation zones where grain reorganization occurs by grain sliding, rotation and/or fracture during overall dilation, shearing, and/or compaction. These structures form in rocks and sediments where porosity exceeds approximately 15 percent, where the pore space allows for a more flexible grain reorganization that that seen in non- and low-porosity rocks. Deformation bands with a significant component of shear are most common and typically accommodate shear offsets of millimeters to centimeters. They can occur as single structures or cluster zones, and are the main deformation element of fault damage zones in porous rocks. Factors such as porosity, mineralogy, grain size and shape, lithification, state of stress and burial depth control the type of deformation band formed. The different types are controlled by deformation mechanisms: cataclasis, rigid grain reorganization (granular flow) and cementation and/or dissolution (wet diffusion). Most bands show a reduction in porosity and permeability, usually between 0 and 3 orders of magnitude. Of the different types, phyllosilicate bands and most notably cataclastic deformation bands show the largest reduction in permeability, and thus have the greatest potential to influence fluid flow. This is particularly so where the bands occur in clusters, and if dissolution accompanies the cataclasis. Disaggregation bands, where non-cataclastic, granular flow is the dominant mechanism, show less influence on fluid flow unless assisted by chemical compaction or cementation.

  10. 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

  11. 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.

  12. Structured surfaces for hemocompatibility

    E-print Network

    Schrauth, Anthony J

    2005-01-01

    The rise of micro- and nano-technologies has brought to light intriguing examples of scale-driven performance in a diverse array of fields. The quest to create highly hydrophobic surfaces is one such field. The application ...

  13. Probing two topological surface bands of Sb2Te3 by spin-polarized photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Pauly, C.; Bihlmayer, G.; Liebmann, M.; Grob, M.; Georgi, A.; Subramaniam, D.; Scholz, M. R.; Sánchez-Barriga, J.; Varykhalov, A.; Blügel, S.; Rader, O.; Morgenstern, M.

    2012-12-01

    Using high-resolution spin- and angle-resolved photoemission spectroscopy, we map the electronic structure and spin texture of the surface states of the topological insulator Sb2Te3. In combination with density functional calculations (DFT), we directly show that Sb2Te3 exhibits a partially occupied, single spin-Dirac cone around the Fermi energy EF, which is topologically protected. DFT obtains a spin polarization of the occupied Dirac cone states of 80-90%, which is in reasonable agreement with the experimental data after careful background subtraction. Furthermore, we observe a strongly spin-orbit split surface band at lower energy. This state is found at E-EF?-0.8 eV at the ?¯ point, disperses upward, and disappears at about E-EF=-0.4 eV into two different bulk bands. Along the ?¯-K¯ direction, the band is located within a spin-orbit gap. According to an argument given by Pendry and Gurman in 1975, such a gap must contain a surface state, if it is located away from the high-symmetry points of the Brillouin zone. Thus, the novel spin-split state is protected by symmetry, too.

  14. 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.

  15. Multi-Quasiparticle Gamma-Band Structure in Neutron-Deficient Ce and Nd Isotopes

    SciTech Connect

    Sheikh, Javid; Bhat, G. H.; Palit, R.; Naik, Z.; Sun, Y.

    2009-01-01

    The newly developed multi-quasiparticle triaxial projected shell-model approach is employed to study the high-spin band structures in neutron-deficient even-even Ce and Nd isotopes. It is observed that gamma bands are built on each intrinsic configuration of the triaxial mean-field deformation. Due to the fact that a triaxial configuration is a superposition of several K states, the projection from these states results in several low-lying bands originating from the same intrinsic configuration. This generalizes the well-known concept of the surface gamma oscillation in deformed nuclei based on the ground state to gamma bands built on multi-quasiparticle configurations. This new feature provides an alternative explanation on the observation of two I=10 aligning states in ^{134}Ce and both exhibiting a neutron character.

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

    NASA Astrophysics Data System (ADS)

    Dey, Anup; Maiti, Biswajit; Chanda Sarkar, Debasree

    2014-04-01

    A generalized theory is developed to study inter-band optical absorption coefficient (IOAC) and material gain (MG) in quantum dot structures of narrow gap III-V compound semiconductor considering the wave-vector (k?) dependence of the optical transition matrix element. The band structures of these low band gap semiconducting materials with sufficiently separated split-off valance band are frequently described by the three energy band model of Kane. This has been adopted for analysis of the IOAC and MG taking InAs, InSb, Hg1-xCdxTe, and In1-xGaxAsyP1-y lattice matched to InP, as example of III-V compound semiconductors, having varied split-off energy band compared to their bulk band gap energy. It has been found that magnitude of the IOAC for quantum dots increases with increasing incident photon energy and the lines of absorption are more closely spaced in the three band model of Kane than those with parabolic energy band approximations reflecting the direct the influence of energy band parameters. The results show a significant deviation to the MG spectrum of narrow-gap materials having band nonparabolicity compared to the parabolic band model approximations. The results reflect the important role of valence band split-off energies in these narrow gap semiconductors.

  17. 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 III–V compound semiconductors, having varied split-off energy band compared to their bulk band gap energy. It has been found that magnitude of the IOAC for quantum dots increases with increasing incident photon energy and the lines of absorption are more closely spaced in the three band model of Kane than those with parabolic energy band approximations reflecting the direct the influence of energy band parameters. The results show a significant deviation to the MG spectrum of narrow-gap materials having band nonparabolicity compared to the parabolic band model approximations. The results reflect the important role of valence band split-off energies in these narrow gap semiconductors.

  18. 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 ?-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.

  19. Band structure of wurtzite quantum dots with cylindrical symmetry

    NASA Astrophysics Data System (ADS)

    Voon, Lok Lew Yan; Galeriu, Calin; Lassen, Benny

    2005-03-01

    A six-band k .p theory for wurtzite semiconductor nanostructures with cylindrical symmetry will be presented. Our work extends the formulation of Vahala and Sercel [Phys. Rev. Lett. 65, 239 (1990)] to the Rashba-Sheka-Pikus Hamiltonian for wurtzite semiconductors, without the need for the axial approximation. Results comparing this new formulation for studying the electronic structure of wurzite GaN and CdS cylindrical quantum dots with the conventional formulation will be shown; our formulation is computationally superior. An application to the search for level crossing in the valence band of cylindrical quantum rods as a function of aspect ratio will be given. Supported by NSF CAREER award.

  20. Structurally tunable resonant absorption bands in ultrathin broadband plasmonic absorbers.

    PubMed

    Butun, Serkan; Aydin, Koray

    2014-08-11

    Light absorption is a fundamental optical process playing significantly important role in wide variety of applications ranging from photovoltaics to photothermal therapy. Semiconductors have well-defined absorption bands with low-energy edge dictated by the band gap energy, therefore it is rather challenging to tune the absorption bandwidth of semiconductors. However, resonant absorbers based on plasmonic nanostructures and optical metamaterials emerged as alternative light absorbers due to spectrally selective absorption bands resulting from optical resonances. Recently, a broadband plasmonic absorber design was introduced by Aydin et al. with a reasonably high broadband absorption. Based on that design, here, structurally tunable, broadband absorbers with improved performance are demonstrated. This broadband absorber has a total thickness of 190 nm with 80% average measured absorption (90% simulated absorption) over the entire visible spectrum (400 - 700 nm). Moreover, the effect of the metal and the oxide thicknesses on the absorption spectra are investigated and results indicate that the shorter and the longer band-edge of broadband absorption can be structurally tuned with the metal and the oxide thicknesses, as well as with the resonator size. Detailed numerical simulations shed light on the type of optical resonances that contribute to the broadband absorption response and provide a design guideline for realizing plasmonic absorbers with structurally tunable bandwidths. PMID:25321029

  1. 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.

  2. Structure of the four quasiparticle band in 84Sr

    NASA Astrophysics Data System (ADS)

    Chattopadhyay, S.; Jain, H. C.; Jhingan, M. L.; Praharaj, C. R.

    1994-07-01

    The high spin levels in 84Sr have been populated through the 59Co(28Si, 3p) reaction using 98 MeV 28Si beam. A regular band structure was found to develop above the 12+ state with a deformation parameter ?=0.21+/-0.04 and ?=8°+/-6°. The projected Hartree-Fock calculations predict a two proton and two neutron aligned configuration for this band. The predicted quadrupole moment for this configuration is also in good agreement with the experimental values obtained from the lifetime measurements. In addition, a large enhancement in B(M1)/B(E2) transition rates has been observed in the negative parity band above the 11- state.

  3. Relationship between hurricane surface winds and L-band radar backscatter from the sea surface

    NASA Technical Reports Server (NTRS)

    Weissman, D. E.; King, D. B.; Thompson, T. W.

    1979-01-01

    High-altitude, airborne, L-band synthetic aperture radar (SAR) data were collected in Hurricane Gloria on 28 and 30 September 1976. The backscattered power levels (proportional to the surface scattering coefficient) averaged over a few square kilometers of surface area were found to vary with surface wind speed and the angle of the wind relative to the radar. Comparisons between the backscatter from the eye and eye-wall regions of the hurricane were made with low-level aircraft wind measurements that were nearly coincident in space and time. The SAR has the potential advantage over other radar types because of its higher spatial resolution. It also appears to have the ability to penetrate rainfall, with a reduction in the echo from the surface. One difference when compared with higher frequency microwave radars is a decrease in the sensitivity of the backscatter to changes in wind speed. This dependence of L-band radar backscatter on surface winds suggests that the winds associated with hurricanes can be measured with airborne or spaceborne radars.

  4. 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.

  5. 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.

  6. Subwavelength Structured Surfaces: Theory and Applications

    NASA Astrophysics Data System (ADS)

    Raguin, Daniel Henri

    1993-01-01

    Detailed theoretical analysis of subwavelength structured (SWS) surfaces is presented. These surfaces are designed for applications in both the visible and infrared portions of the spectrum. Applications presented include antireflection structured (ARS) surfaces, polarization components, narrow-band filters, and phase plates. Experimental results for 2-D binary ARS surfaces are illustrated. Analysis of SWS surfaces is performed using rigorous coupled-wave analysis (RCWA) and effective medium theory (EMT). EMT is used to derive intuitive analytical formulae that describe a surface's reflection and transmission characteristics. It is shown, by comparing zeroth-order and higher-order EMT, that as the grating period increases, or the substrate index of refraction increases past a certain threshold, zeroth-order EMT results are erroneous and that results derived from higher-order EMT must be used. Comparisons between EMT and RCWA results are made. EMT results, particularly those derived using second-order EMT, are shown to match RCWA. The match between EMT and RCWA is best when the electric field is perpendicular to the grating vector. ARS surfaces with binary and multi-level 1-D and 2-D profiles are analyzed. The 1-D profiles are shown to be form birefringent and thus better suited for applications involving linearly-polarized light. 2-D profiles are shown to exhibit near-isotropic behavior, and thus are advantageous when randomly polarized radiation is an issue. As the number of levels the profiles contain increases, the tolerance of both 1-D and 2-D structures to bias angles, wavelength detunings, and errors in etch depth increases. ARS surfaces with 1-D continuous profiles are investigated. Analysis is performed using RCWA, as well as using a novel EMT approach which incorporates tapered transmission-line theory to obtain closed-form solutions for the reflection coefficients. Performance analysis is presented versus grating depth, incident wavelength, and angle of incidence, for the specific cases of triangular and sinusoidal profiles. As polarization components, SWS surfaces as wire -grid polarizers and wave plates are illustrated. Examples are given for ZnSe quarter-wave plates designed with binary and continuous 1-D profiles. SWS wave plates with continuous profiles have increased throughput due to reflection losses being minimized. For narrow-band filter designs, EMT is used to predict the location of a SWS filter's operating wavelength. As phase plates, the novel use of SWS surfaces to compress laser pulses is presented. Experimental results are presented for 2-D binary ARS surfaces. These gratings are designed for operation at CO_2-laser wavelengths.

  7. 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 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 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. .

  8. 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.

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

    SciTech Connect

    Ramanujan, R.V. ); Bi, Y.; Xu, Q.; Abell, J.S. . School of Metallurgy and Materials)

    1994-03-15

    The authors report their results on the structure and chemistry of ingots and directionally solidified Ti-48Al and Ti-52Al alloys. Through the banding behavior, quantitative analysis of parts of the high temperature phase field in near-equiatomic Ti-Al alloys is obtained. A possible explanation for certain puzzling and unexplained observations by Oliver is presented. Optical microscopy, electron probe microanalysis (EPMA), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used in this investigation.

  10. Graphene on Ru(0001): Evidence for two graphene band structures

    SciTech Connect

    Katsiev K.; Vescovo E.; Losovyj, Y.; Zhou, Z.; Liu, L.; Dowben, P.A.; Goodman, D.W.

    2012-05-03

    High-resolution photoemission illustrates that the band structure of graphene on Ru(0001) exhibits a well-defined splitting. This splitting is largest with the graphene directly on the Ru(0001) substrate, whereas with a chemisorbed oxygen spacer layer between the graphene and the metal substrate, this splitting is considerably reduced. This splitting is attributed to a combination of chemical interactions between graphene and Ru(0001) and to screening of the former by the latter, not spin-orbit coupling.

  11. 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 (QW’s) 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 QW’s, 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.

  12. 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.

  13. 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.

  14. 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.

  15. High power breakdown testing of a photonic band-gap accelerator structure with elliptical rods

    NASA Astrophysics Data System (ADS)

    Munroe, Brian J.; Cook, Alan M.; Shapiro, Michael A.; Temkin, Richard J.; Dolgashev, Valery A.; Laurent, Lisa L.; Lewandowski, James R.; Yeremian, A. Dian; Tantawi, Sami G.; Marsh, Roark A.

    2013-01-01

    An improved single-cell photonic band-gap (PBG) structure with an inner row of elliptical rods (PBG-E) was tested with high power at a 60 Hz repetition rate at X-band (11.424 GHz), achieving a gradient of 128MV/m at a breakdown probability of 3.6×10-3 per pulse per meter at a pulse length of 150 ns. The tested standing-wave structure was a single high-gradient cell with an inner row of elliptical rods and an outer row of round rods; the elliptical rods reduce the peak surface magnetic field by 20% and reduce the temperature rise of the rods during the pulse by several tens of degrees, while maintaining good damping and suppression of high order modes. When compared with a single-cell standing-wave undamped disk-loaded waveguide structure with the same iris geometry under test at the same conditions, the PBG-E structure yielded the same breakdown rate within measurement error. The PBG-E structure showed a greatly reduced breakdown rate compared with earlier tests of a PBG structure with round rods, presumably due to the reduced magnetic fields at the elliptical rods vs the fields at the round rods, as well as use of an improved testing methodology. A post-testing autopsy of the PBG-E structure showed some damage on the surfaces exposed to the highest surface magnetic and electric fields. Despite these changes in surface appearance, no significant change in the breakdown rate was observed in testing. These results demonstrate that PBG structures, when designed with reduced surface magnetic fields and operated to avoid extremely high pulsed heating, can operate at breakdown probabilities comparable to undamped disk-loaded waveguide structures and are thus viable for high-gradient accelerator applications.

  16. 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.

  17. 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.

  18. 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.

  19. Fabrication of x-band accelerating structures at Fermilab

    SciTech Connect

    Tug T Arkan et al.

    2004-07-20

    The RF Technology Development group at Fermilab is working together with the NLC and GLC groups at SLAC and KEK on developing technology for room temperature X-band accelerating structures for a future linear collider. We built six 60-cm long, high phase advance, detuned structures (HDS or FXB series). These structures have 150 degrees phase advance per cell, and are intended for high gradient tests. The structures were brazed in a vacuum furnace with a partial pressure of argon, rather than in a hydrogen atmosphere. We have also begun to build 60-cm long, damped and detuned structures (HDDS or FXC/FXD series). We have built 5 FXC and 1 FXD structures. Our goal was to build six structures for the 8-pack test at SLAC by the end of March 2004, as part of the GLC/NLC effort to demonstrate the readiness of room temperature RF technology for a linear collider. This paper describes the RF structure factory infrastructure (clean rooms, vacuum furnaces, vacuum equipment, RF equipment etc.), and the fabrication techniques utilized (the machining of copper cells/couplers, quality control, etching, vacuum brazing, cleanliness requirements etc.) for the production of FXB and FXC/FXD structures.

  20. 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.

  1. 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).

  2. 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.

  3. 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.

  4. Surface structure determines dynamic wetting.

    PubMed

    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

  5. 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

  6. 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.

  7. 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.

  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. 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.

  10. 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.

  11. 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.

  12. 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

  13. 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.

  14. 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

  15. Plasmonic photonic crystal with a complete band gap for surface plasmon polariton waves

    E-print Network

    Fainman, Yeshaiahu

    Plasmonic photonic crystal with a complete band gap for surface plasmon polariton waves Liang Feng crystal for manipulating surface plasmon polariton SPP fields has been designed, fabricated, and tested polaritons SPPs are electromagnetic surface waves formed through strong interaction between op- tical

  16. Suppressing Near-surface Reverse Time Migration Artifacts Using a Band-selecting Imaging Condition

    E-print Network

    Wang, Yao

    2015-05-31

    In this paper, I introduce a frequency band-selecting imaging condition for Reverse Time Migration (RTM) of shallow reflection datasets which effectively eliminates artifacts that are problematic on near-surface reflection sections. Within...

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

    NASA Astrophysics Data System (ADS)

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

    2013-10-01

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

  18. 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.

  19. Quasiparticle semiconductor band structures including spin-orbit interactions.

    PubMed

    Malone, Brad D; Cohen, Marvin L

    2013-03-13

    We present first-principles calculations of the quasiparticle band structure of the group IV materials Si and Ge and the group III-V compound semiconductors AlP, AlAs, AlSb, InP, InAs, InSb, GaP, GaAs and GaSb. Calculations are performed using the plane wave pseudopotential method and the 'one-shot' GW method, i.e. G(0)W(0). Quasiparticle band structures, augmented with the effects of spin-orbit, are obtained via a Wannier interpolation of the obtained quasiparticle energies and calculated spin-orbit matrix. Our calculations explicitly treat the shallow semicore states of In and Ga, which are known to be important in the description of the electronic properties, as valence states in the quasiparticle calculation. Our calculated quasiparticle energies, combining both the ab initio evaluation of the electron self-energy and the vector part of the pseudopotential representing the spin-orbit effects, are in generally very good agreement with experimental values. These calculations illustrate the predictive power of the methodology as applied to group IV and III-V semiconductors. PMID:23396813

  20. 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.

  1. Terahertz surface plasmon polaritons on a semiconductor surface structured with

    E-print Network

    Murphy, Thomas E.

    Terahertz surface plasmon polaritons on a semiconductor surface structured with periodic V-doped silicon surface, using anisotropic wet-etching of crystalline silicon, thereby forming a plasmonic surfaces. © 2013 Optical Society of America OCIS codes: (240.6680) Surface plasmons; (240.6690) Surface

  2. 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; Köhler, Leonard; Pianezzi, Fabian; Krause, Stefan; Gorgoi, Mihaela; Ikenaga, Eiji; Koch, Norbert; Wilks, Regan G; Buecheler, Stephan; Tiwari, Ayodhya N; Bär, 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

  3. 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.

  4. 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.

  5. 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.

  6. Simulation of Band Diagram for Chemical-Vapor-Deposition Diamond Surface Conductivity

    NASA Astrophysics Data System (ADS)

    Kono, Shozo; Koide, Yasuo

    2005-12-01

    One-dimensional energy band simulation has been performed in order to understand chemical-vapor-deposition (CVD) diamond surface conductivity. It was found that the presence of shallow-level acceptors in the subsurface region and defect states at the surface causes a steep rise in the valence band toward the Fermi level, which causes accumulation of holes in the valence band in the subsurface and near-surface regions. An artificial negative charge accumulation (NCA) layer is introduced in the simulation to examine the effect of possible negatively charged adsorbates on surface conductivity. By adjusting the thickness of NCA layers, we have reproduced quantitatively both the surface conductivity change and Fermi-level change found in previous experiments [Kono et al.: Diamond Relat. Mater. 14 (2005) 459; Riedel et al.: ibid. 13 (2004) 746].

  7. 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.

  8. 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.

  9. 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.

  10. 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

  11. 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 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

  12. Anomalous decay of an atom in structured band gap reservoirs

    E-print Network

    Filippo Giraldi; Francesco Petruccione

    2011-04-09

    We analyze the spontaneous emission of a two-level atom interacting with a special class of structured reservoirs of field modes with band gap edge coinciding with the atomic transition frequency. The exact time evolution of the population of the excited level is evaluated analytically through series of Fox-$H$ functions. Over estimated long time scales, inverse power law relaxations emerge, with powers decreasing continuously to 2 according to the choice of the special reservoir. No trapping of the population of the excited level emerges. The same results are recovered in presence of $N-1$ atoms, each one in the ground state, described by the Dicke model. The power of the inverse power law decay results to be independent of $N$. A critical number $N_{\\alpha}^{(\\star)}$ is evaluated, such that, for $N \\gg N_{\\alpha}^{(\\star)}$, the inverse power law decay vanishes.

  13. 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.

  14. Effects of extrinsic and intrinsic perturbations on the electronic structure of graphene: Retaining an effective primitive cell band structure by band unfolding

    NASA Astrophysics Data System (ADS)

    Medeiros, Paulo V. C.; Stafström, Sven; Björk, Jonas

    2014-01-01

    We use a band unfolding technique to recover an effective primitive cell picture of the band structure of graphene under the influence of different types of perturbations. This involves intrinsic perturbations, such as structural defects, and external ones, comprising nitrogen substitutions and the inclusion of graphene in adsorbed systems. In such cases, the band unfolding provides a reliable and efficient tool for quantitatively analyzing the effect of doping and defects on the electronic structure of graphene. We envision that this approach will become a standard method in the computational analysis of graphene's electronic structure in related systems.

  15. 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.

  16. 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 ...

  17. 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.

  18. Landau Damping and Coherent Structures in Narrow-Banded 1+1 Deep Water Gravity Waves

    E-print Network

    M. Onorato; A. Osborne; M. Serio; R. Fedele

    2002-02-12

    We study the nonlinear energy transfer around the peak of the spectrum of surface gravity waves by taking into account nonhomogeneous effects. In the narrow-banded approximation the kinetic equation resulting from a nonhomogeneous wave field is a Vlasov-Poisson type equation which includes at the same time the random version of the Benjamin-Feir instability and the Landau damping phenomenon. We analytically derive the values of the Phillips' constant $\\alpha$ and the enhancement factor $\\gamma$ for which the narrow-banded approximation of the JONSWAP spectrum is unstable. By performing numerical simulations of the nonlinear Schr\\"{o}dinger equation we check the validity of the prediction of the related kinetic equation. We find that the effect of Landau damping is to suppress the formation of coherent structures. The problem of predicting freak waves is briefly discussed.

  19. 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 23×10 mm². It is shown that electron densities larger than 10¹? cm ?³ are needed in order to create an effective one-dimensional electromagnetic band gap structure. Some applications for using the one-dimensional electromagnetic band gap structure in waveguide as a control of microwave (broadband filter and device for variation of pulse duration) are demonstrated.

  20. 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.

  1. Landau damping and coherent structures in narrow-banded 1+1 deep water gravity waves.

    PubMed

    Onorato, Miguel; Osborne, Alfred; Fedele, Renato; Serio, Marina

    2003-04-01

    We study the modulational instability in surface gravity waves with random phase spectra. Starting from the nonlinear Schrödinger equation and using the Wigner-Moyal transform, we study the stability of the narrow-banded approximation of a typical wind-wave spectrum, i.e., the JONSWAP spectrum. By performing numerical simulations of the nonlinear Schrödinger equation we show that in the unstable regime, the nonlinear stage of the modulational instability is responsible for the formation of coherent structures. Furthermore, a Landau-type damping, due to the incoherence of the waves, whose role is to provide a stabilizing effect against the modulational instability, is both analytically and numerically discussed. PMID:12786485

  2. Landau damping and coherent structures in narrow-banded 1+1 deep water gravity waves

    NASA Astrophysics Data System (ADS)

    Onorato, Miguel; Osborne, Alfred; Fedele, Renato; Serio, Marina

    2003-04-01

    We study the modulational instability in surface gravity waves with random phase spectra. Starting from the nonlinear Schrödinger equation and using the Wigner-Moyal transform, we study the stability of the narrow-banded approximation of a typical wind-wave spectrum, i.e., the JONSWAP spectrum. By performing numerical simulations of the nonlinear Schrödinger equation we show that in the unstable regime, the nonlinear stage of the modulational instability is responsible for the formation of coherent structures. Furthermore, a Landau-type damping, due to the incoherence of the waves, whose role is to provide a stabilizing effect against the modulational instability, is both analytically and numerically discussed.

  3. Fractional Band Filling in an Atomic Chain Structure J. N. Crain,1

    E-print Network

    Himpsel, Franz J.

    Fractional Band Filling in an Atomic Chain Structure J. N. Crain,1 A. Kirakosian,1 K. N. Altmann,1 [5­12]. X-ray dif- fraction from the Si(557)-Au structure shows that gold atoms are incorporated by increasing U. We have found a chain structure of gold atoms on silicon, which exhibits a 1=4-filled band. Two

  4. Computation of the band structure of two-dimensional Photonic Crystals with hp Finite Elements

    E-print Network

    Grohs, Philipp

    Computation of the band structure of two-dimensional Photonic Crystals with hp Finite Elements K structure of 2D photonic crystals and their eigenmodes can be efficiently computed with the finite element and phrases: hp-FEM, exponential convergence, corner singularities, photonic crystals, photonic band structure

  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. 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

  7. 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.

  8. Near-infrared observations of galaxies in Pisces-Perseus; 1, H-band surface photometry of 174 spirals

    E-print Network

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

    1999-01-01

    We present near-infrared, H-band (1.65 um), surface photometry of 174 spiral galaxies in the area of the Pisces-Perseus supercluster. The images, acquired with the ARNICA camera mounted on various telescopes, are used to derive radial profiles of surface brightness, ellipticities, and position angles, together with global parameters such as H-band magnitudes and diameters. The mean relation between H-band isophotal diameter D_{21.5} and the B-band D_{25} implies a B-H color of the outer disk bluer than 3.5; moreover, D_{21.5}/D_{25} depends on (global) color and absolute luminosity. The correlations among the various photometric parameters suggest a ratio between isophotal radius D_{21.5}/2 and disk scale length of about 3.5 and a mean disk central brightness of 17.5 H-mag arcsec^{-2}. We confirm the trend of the concentration index C_{31} with absolute luminosity and, to a lesser degree, with morphological type. We also assess the influence of non-axisymmetric structures on the radial profiles and on the der...

  9. Near-infrared observations of galaxies in Pisces-Perseus: I. H-band surface photometry of 174 spirals

    E-print Network

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

    1999-05-06

    We present near-infrared, H-band (1.65 um), surface photometry of 174 spiral galaxies in the area of the Pisces-Perseus supercluster. The images, acquired with the ARNICA camera mounted on various telescopes, are used to derive radial profiles of surface brightness, ellipticities, and position angles, together with global parameters such as H-band magnitudes and diameters. The mean relation between H-band isophotal diameter D_{21.5} and the B-band D_{25} implies a B-H color of the outer disk bluer than 3.5; moreover, D_{21.5}/D_{25} depends on (global) color and absolute luminosity. The correlations among the various photometric parameters suggest a ratio between isophotal radius D_{21.5}/2 and disk scale length of about 3.5 and a mean disk central brightness of 17.5 H-mag arcsec^{-2}. We confirm the trend of the concentration index C_{31} with absolute luminosity and, to a lesser degree, with morphological type. We also assess the influence of non-axisymmetric structures on the radial profiles and on the derived parameters.

  10. Complex band structure of topologically protected edge states

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

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

  11. 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.

  12. 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°.

  13. Effect of projected band gap on neutralization of Cs ions during grazing scattering from a Cu(111) surface

    SciTech Connect

    Borisov, A. G.; Mertens, A.; Wethekam, S.; Winter, H.

    2003-07-01

    Cs ions with energies ranging from 10 keV to 1.8 MeV are scattered under a grazing angle of incidence from a flat and clean Cu(111) surface. The observed fractions of Cs atoms in the scattered beams and their dependence on projectile velocity are well described by a model of kinematically assisted resonant charge transfer between projectile and two-dimensional surface-state continuum of the target surface. A comparison with calculations for a target represented by the electronic structure of a free-electron metal shows neutral fractions which are enhanced for the Cu(111) by more than one order of magnitude. This is the strongest effect of the projected band gap of a metal surface on the charge transfer observed so far.

  14. 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.

  15. 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.

  16. Surface Superconductivity of Dirty Two-Band Superconductors: Applications to MgB2

    NASA Astrophysics Data System (ADS)

    Gorokhov, Denis A.

    2005-02-01

    The minimal magnetic field Hc2 destroying superconductivity in the bulk of a superconductor is smaller than the magnetic field Hc3 needed to destroy surface superconductivity if the surface of a superconductor coincides with one of the crystallographic planes and is parallel to the external magnetic field. While for a dirty single-band superconductor the ratio of Hc3 to Hc2 is a universal temperature-independent constant 1.6946, for dirty two-band superconductors this is not the case. I show that in the latter case the interaction of the two bands leads to a novel scenario with the ratio Hc3/Hc2 varying with temperature and taking values larger and smaller than 1.6946. The results are applied to MgB2 and compared with recent experiments (A. Rydh et al., cond-mat/0307445).

  17. 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.

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

    E-print Network

    Cao, Wenwu

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

  19. 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; Wöll, 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.

  20. Spin-orbit coupling in the band structure WSe2 monolayers

    NASA Astrophysics Data System (ADS)

    Tanabe, Iori; Barinov, Alexei; Le, Duy; Preciado, Edwin; Isarraraz, Miguel; Bartels, Ludwig; Rahman, Talat; Dowben, Peter

    2015-03-01

    We have mapped the occupied band structure of monolayer WSe2 by small spatial spot angle resolved photoemission and have found significant spin-orbit coupling in excess of 500 meV, far larger than for MoS2. The experimental band mapping is consistent with theoretical expectations with the top of the valence band is seen at K, not ?, thus distinct from the band structure for the bilayer and bulk single crystals. This shift of the top of the valence band in monolayer WSe2, from ? to K, is also predicted in density functional theory. In general the wave vector dependent experimental band structure confirms the expectations of density functional theory.

  1. Patterning Nanoscale Structures by Surface Chemistry

    E-print Network

    Lu, Wei

    Patterning Nanoscale Structures by Surface Chemistry Wei Lu* and Dongchoul Kim Department combines spinodal decomposition, surface stress and surface chemistry. The simulation shows that the self-assembly process can be guided by tuning the surface chemistry of a substrate. An epilayer may evolve into various

  2. The Effects Nano-Structuring, Form of Band Structure, Asymmetry of Band-Edges, and Scattering Mechanism for Enhancement on ZT

    NASA Astrophysics Data System (ADS)

    Tang, Shuang; Dresselhaus, Mildred

    2014-03-01

    Since 1993 when Hicks and Dresselhaus proposed that the low dimensional materials have enhanced ZT relative to their bulk counterparts, intensive research attention has been focused on enhancing the ZT in different materials, such as thin films, nanowires, nano-composites, etc. On the other hand, the proposal of bismuth antimony thin films in 2012, has provided a materials system with anisotropic and asymmetrical band edges, where both parabolic and non-parabolic forms of band structure exist. This raises a question on how can we enhance the figure of merit of thermoelectrics by using the special properties of these novel materials. This work will focus on exploring how the dimension, the form of band structure, the asymmetry and anisotropy of the band edges, and the electron scattering mechanism will influence the ZT.

  3. Multicomponent surface materials: subsequent surface structuring and deposition

    NASA Astrophysics Data System (ADS)

    Huovinen, Eero; Suvanto, Mika; Pakkanen, Tapani A.

    2015-05-01

    The surface properties of materials can be modified by tailoring the topography and chemical composition. Functional surfaces with desirable properties have been produced by precisely controlled surface structures and chemical composition at the micro-nanometer scale. Until now, the challenge has been the ability to manipulate surface morphology and chemistry at the micro-millimeter scale. This work presents a new surface modification method capable of permitting subsequent structuring and material deposition. A micro tip patterning technique is based on sharp metal tips that are used for modifying the topography and chemistry of various material surfaces at the micro-millimeter scale. The method is appropriate for characterizing different topographies by probing conductive material surfaces with a needle tip, which permits a precisely controlled surface structuring with continuous 3D profiles. The desired locations of the scanned surface can be chemically modified by delivering materials via the needle tip. The method is appropriate for the multi-object placement of numerous substances such as functional reagents and biological components in a complex microenvironment. The accurate structuring of complex 3D surface topographies and subsequent chemical deposition provides a precisely controlled functionalization of material surface properties suitable for different applications.

  4. 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

  5. Film depth and concentration banding in free-surface Couette flow of a suspension.

    PubMed

    Timberlake, Brian D; Morris, Jeffrey F

    2003-05-15

    The film depth of a free-surface suspension flowing in a partially filled horizontal concentric-cylinder, or Couette, device has been studied in order to assess its role in the axial concentration banding observed in this flow. The flow is driven by rotation of the inner cylinder. The banding phenomenon is characterized by particle-rich bands which under flow appear as elevated regions at the free surface separated axially by regions dilute relative to the mean concentration. The concentric cylinders studied had outer radius R(o) = 2.22 cm and inner radii R(i) = 0.64, 0.95 and 1.27 cm; the suspension, of bulk particle volume fraction phi = 0.2 in all experiments described, was composed of particles of either 250-300 microm diameter or less than 106 microm diameter, with the suspending fluid an equal density liquid of viscosity 160 P. The ratio of the maximum to the minimum particle volume fraction along the axis in the segregated condition varies from O(1) to infinite. The latter case implies complete segregation, with bands of clear fluid separating the concentrated bands. The film depth has been varied through variation of the filled fraction, f, of the annular gap between the cylinders and through the rotation rate. Film depth was analysed by edge detection of video images of the free surface under flow, and the time required for band formation was determined for all conditions at which film depth was studied. The film depth increases roughly as the square root of rotation speed for f = 0.5. Band formation is more rapid for thicker films associated with more rapid rotation rates at f = 0.5, whereas slower formation rates are observed with thicker films caused by large f, f > 0.65. It is observed that the film depth over the inner cylinder grows prior to onset of banding, for as yet unknown reasons. A mechanism for segregation of particles and liquid in film flows based upon 'differential drainage' of the particle and liquid phase in the gravity-driven flow within the film over the inner cylinder is formulated to describe the onset of concentration fluctuations. This model predicts that suspension drainage flows lead to growth of fluctuations in phi under regions of negative surface curvature. PMID:12804220

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

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

  7. 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.

  8. 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.

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

    NASA Astrophysics Data System (ADS)

    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 first-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.

  10. 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 ?-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.

  11. Detailed structure of the outer disk around HD 169142 with polarized light in H-band

    NASA Astrophysics Data System (ADS)

    Momose, Munetake; Morita, Ayaka; Fukagawa, Misato; Muto, Takayuki; Takeuchi, Taku; Hashimoto, Jun; Honda, Mitsuhiko; Kudo, Tomoyuki; Okamoto, Yoshiko K.; Kanagawa, Kazuhiro D.; Tanaka, Hidekazu; Grady, Carol A.; Sitko, Michael L.; Akiyama, Eiji; Currie, Thayne; Follette, Katherine B.; Mayama, Satoshi; Kusakabe, Nobuhiko; Abe, Lyu; Brandner, Wolfgang; Brandt, Timothy D.; Carson, Joseph C.; Egner, Sebastian; Feldt, Markus; Goto, Miwa; Guyon, Olivier; Hayano, Yutaka; Hayashi, Masahiko; Hayashi, Saeko S.; Henning, Thomas; Hodapp, Klaus W.; Ishii, Miki; Iye, Masanori; Janson, Markus; Kandori, Ryo; Knapp, Gillian R.; Kuzuhara, Masayuki; Kwon, Jungmi; Matsuo, Taro; McElwain, Michael W.; Miyama, Shoken; Morino, Jun-Ichi; Moro-Martin, Amaya; Nishimura, Tetsuo; Pyo, Tae-Soo; Serabyn, Eugene; Suenaga, Takuya; Suto, Hiroshi; Suzuki, Ryuji; Takahashi, Yasuhiro H.; Takami, Michihiro; Takato, Naruhisa; Terada, Hiroshi; Thalmann, Christian; Tomono, Daigo; Turner, Edwin L.; Watanabe, Makoto; Wisniewski, John; Yamada, Toru; Takami, Hideki; Usuda, Tomonori; Tamura, Motohide

    2015-10-01

    Coronagraphic imagery of the circumstellar disk around HD 169142 in H-band polarized intensity (PI) with Subaru/HiCIAO is presented. The emission scattered by dust particles at the disk surface in 0{^''.}2 ? r ? 1{^''.}2, or 29 ? r ? 174 au, is successfully detected. The azimuthally averaged radial profile of the PI shows a double power-law distribution, in which the PIs in r = 29-52 au and r = 81.2-145 au respectively show r-3 dependence. These two power-law regions are connected smoothly with a transition zone (TZ), exhibiting an apparent gap in r = 40-70 au. The PI in the inner power-law region shows a deep minimum whose location seems to coincide with the point source at ? = 7 mm. This can be regarded as another sign of a protoplanet in the TZ. The observed radial profile of the PI is reproduced by a minimally flaring disk with an irregular surface density distribution, an irregular temperature distribution, or with a combination of both. The depletion factor of surface density in the inner power-law region (r < 50 au) is derived to be ? 0.16 from a simple model calculation. The obtained PI image also shows small-scale asymmetries in the outer power-law region. Possible origins for these asymmetries include corrugation of the scattering surface in the outer region, and a shadowing effect by a puffed-up structure in the inner power-law region.

  12. 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.

  13. 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

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  15. 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.

  16. 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

  17. 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

  18. 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.

  19. Modulation of L-band signals by the sea surface roughness

    NASA Astrophysics Data System (ADS)

    Guimbard, S.; Gourrion, J.; Joe, T.; Turiel, A.; Font, J.

    2012-12-01

    In the context of the ESA SMOS and Aquarius/SAC-D missions, sea surface thermal emission in L-band is measured from space since almost 3 and 1 years respectively. Using a new instrumental concept for the first one, a Microwave Imaging Radiometer using two dimensional aperture synthesis, sea surface brightness temperatures can be extracted under a large range of incidence and azimuthal angles, and different spatial resolutions. Although using a more classical real aperture radiometer, Aquarius derives its originality from measuring quasi simultaneously active and passive signals for three different incidence and azimuthal angles. A lot of works have been done the last ten years to develop physically based scattering models in order to accurately predict the sea surface roughness impact on brightness temperatures. Recent results have shown that non negligible discrepancies exist between these models and this new data set of L-band measurements. This presentation will provide a review of the last empirical adjustments of radar normalized cross sections and sea surface brightness temperatures modulations by different sea surface roughness characteristics. A discussion regarding possible improvements in electromagnetic scattering modeling and inherent sea surface spectral description will be proposed.

  20. Band Structure of ZnO from Resonant X-ray Emission Spectroscopy

    SciTech Connect

    Preston, A.; Ruck, B; Piper, L; DeMasi, A; Smith, K; Schleife, A; Fuchs, F; Bechstedt, F; Chai, J; Durbin, S

    2008-01-01

    Soft x-ray emission and absorption spectroscopy of the O K-edge are employed to investigate the electronic structure of wurtzite ZnO(0001). A quasiparticle band structure calculated within the GW approximation agrees well with the data, most notably with the energetic location of the Zn 3d-O 2p hybridized state and the anisotropy of the absorption spectra. Dispersion in the band structure is mapped using the coherent k-selective part of the resonant x-ray emission spectra. We show that a more extensive mapping of the bands is possible in the case of crystalline anisotropy such as that found in ZnO.

  1. On a Surface Structure Constraint in Hungarian.

    ERIC Educational Resources Information Center

    Szamosi, Michael

    It is possible to apply the concept of surface-structure constraint to a particular area of Hungarian syntax. A surface-structure constraint, according to David Perlmutter, can be seen as a template which serves as a filter at some level after the transformational component. In the case of Hungarian cooccurrence of noun phrases and verbs in a…

  2. 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.

  3. 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.

  4. A tunable multi-band metamaterial design using micro-split SRR structures

    E-print Network

    Akin, Tayfun

    A tunable multi-band metamaterial design using micro-split SRR structures Evren Ekmekci1, 2 of a feasibility study for the design of multi-band tunable metamaterials based on the use of micro-split SRR which contain columns of different types of metamaterial unit cells. We have shown

  5. Band structure and optical properties of opal photonic crystals E. Pavarini, L. C. Andreani, C. Soci, M. Galli, and F. Marabelli

    E-print Network

    Band structure and optical properties of opal photonic crystals E. Pavarini, L. C. Andreani, C of opal photonic crystals with fcc structure and 111 surface orientation is presented. It is based corresponding to the excitation of photonic modes in the crystal . Reflectance measurements on artificial opals

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

    NASA Astrophysics Data System (ADS)

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

    1999-05-01

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

  7. 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.

  8. 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.

  9. 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...

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. Full band structure calculation of the linear electro-optic susceptibility

    E-print Network

    Sipe,J. E.

    Full band structure calculation of the linear electro-optic susceptibility Ed Ghahramani Phy~im C microscopic quantum mechanical expression for the frequency-dependent (clamped lattice j linear electro-optic

  15. Phase Space Crystals: A New Way to Create a Quasienergy Band Structure

    E-print Network

    Lingzhen Guo; Michael Marthaler; Gerd Schön

    2013-11-04

    A novel way to create a band structure of the quasienergy spectrum for driven systems is proposed based on the discrete symmetry in phase space. The system, e.g., an ion or ultracold atom trapped in a potential, shows no spatial periodicity, but it is driven by a time-dependent field coupling highly nonlinearly to one of its degrees of freedom (e.g., ~ q^n). The band structure in quasienergy arises as a consequence of the n-fold discrete periodicity in phase space induced by this driving field. We propose an explicit model to realize such a phase space crystal and analyze its band structure in the frame of a tight-binding approximation. The phase space crystal opens new ways to engineer energy band structures, with the added advantage that its properties can be changed in situ by tuning the driving field's parameters.

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

    E-print Network

    Lee, K. Y. K.

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

  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. Effect of electric field on the band structure of graphene/boron nitride and boron nitride/boron nitride bilayers

    E-print Network

    Pandey, Ravi

    Effect of electric field on the band structure of graphene/boron nitride and boron nitride/boron of electric field on the band structure of graphene/boron nitride and boron nitride/boron nitride bilayers of electric field on the band structures of graphene/boron nitride (BN) and BN/BN bilayers is investigated

  19. 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.

  20. [Oligoglycine surface structures: molecular dynamics simulation].

    PubMed

    Gus'kova, O A; Khalatur, P G; Khokhlov, A R; Chinarev, A A; Tsygankova, S V; Bovin, N V

    2010-01-01

    The full-atomic molecular dynamics (MD) simulation of adsorption mode for diantennary oligoglycines [H-Gly4-NH(CH2)5]2 onto graphite and mica surface is described. The resulting structure of adsorption layers is analyzed. The peptide second structure motives have been studied by both STRIDE (structural identification) and DSSP (dictionary of secondary structure of proteins) methods. The obtained results confirm the possibility of polyglycine II (PGII) structure formation in diantennary oligoglycine (DAOG) monolayers deposited onto graphite surface, which was earlier estimated based on atomic-force microscopy measurements. PMID:21063448

  1. 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.

  2. 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.

  3. 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.

  4. Surface Science Letters Nano-structures developing at the graphene/silicon carbide interface

    E-print Network

    Chiang, Shirley

    Surface Science Letters Nano-structures developing at the graphene/silicon carbide interface S­semiconductor interfaces Surface defects Silicon carbide Graphene We use scanning tunneling microscopy and spectroscopy­10]. Because silicon carbide (SiC), a IV­IV compound semiconductor, has a wide band gap (ranging from 2.4 to 3

  5. 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).

  6. Tuning Band Gap Energies in Pb3(C6X6) Extended Solid-State Structures

    SciTech Connect

    Stott, Amanda C.; Vaid, Thomas P.; Bylaska, Eric J.; Dixon, David A.

    2012-04-19

    A detailed plane-wave density functional theory investigation of the solid-state properties of the extended organometallic system Pb{sub 3}C{sub 6}X{sub 6} for X = O, S, Se, and Te has been performed. Initial geometry parameters for the Pb-X and C-X bond distances were obtained from optimized calculations on molecular fragment models. The Pb{sub 3}C{sub 6}X{sub 6} extended solid molecular structures were constructed in the space group P6/mmm on the basis of the known structure for X = S. Ground-state geometries, band gap energies, densities of states, and charge densities were calculated with the PBE-generalized gradient exchange-correlation functional and the HSE06 hybrid exchange-correlation functional. The PBE band gap energies were found to be lower than the HSE06 values by >0.7 eV. The band energies at points of high symmetry along the first Brillouin zone in the crystal were larger than the overall band gap of the system. Pb{sub 3}C{sub 6}O{sub 6} was predicted to be a direct semiconductor ({Lambda} point) with a PBE band gap of 0.28 eV and an HSE06 band gap of 1.06 eV. Pb{sub 3}C{sub 6}S{sub 6} and Pb{sub 3}C{sub 6}Se{sub 6} were predicted to have indirect band gaps. The PBE band gap for Pb{sub 3}C{sub 6}S{sub 6} was 0.98 eV, and the HSE06 band gap was 1.91 eV. The HSE06 value is in good agreement with the experimentally observed band gap of 1.7 eV. Pb{sub 3}C{sub 6}Se{sub 6} has a PBE band gap of 0.56 eV and a HSE06 band gap of 1.41 eV. Pb{sub 3}C{sub 6}Te{sub 6} was predicted to be metallic with both of the PBE and HSE06 functionals. A detailed analysis of the PBE band structure and partial density of states at two points before and after the metallic behavior reveals a change in orbital character indicative of band crossing in Pb{sub 3}C{sub 6}Te{sub 6}. These results show that the band gap energies can be fine-tuned by changing the substituent X atom.

  7. 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

  8. 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.

  9. 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.; Say??, 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 ? rays were detected by the JUROGAM II ? -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 ? -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 ? h11 /2[514 ] 9 /2-?? i13 /2[660 ] 1 /2+ Nilsson configuration, while the weaker structure is assigned to be built on a two-quasiparticle state of mixed ? h11 /2[514 ] 9 /2-?? [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.

  10. 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.

  11. Spin-orbit coupling in the band structure of monolayer WSe2

    NASA Astrophysics Data System (ADS)

    Le, Duy; Barinov, Alexei; Preciado, Edwin; Isarraraz, Miguel; Tanabe, Iori; Komesu, Takashi; Troha, Conrad; Bartels, Ludwig; Rahman, Talat S.; Dowben, Peter A.

    2015-05-01

    We used angle-resolved photoemission spectroscopy (ARPES) to map out the band structure of single-layer WSe2. The splitting of the top of the valence band because of spin-orbit coupling is 513 ± 10 meV, in general agreement with theoretical predictions and in the same range as that of bulk WSe2. Overall, our density functional theory (DFT) calculations of the band structure are in excellent agreement with the ARPES results. We have verified that the few discrepancies between theory and experiment are not due to the effect of strain. The differences between the DFT-calculated band structure using local density approximation (LDA) and that using the generalized gradient approximation (GGA), for single-layer WSe2, are caused mainly by differences in the respective charge densities.

  12. Multilayer Stepped-Impedance Resonator Band-Pass Filter Implementing Using Low Temperature Cofired Ceramic Structure

    NASA Astrophysics Data System (ADS)

    Chen, Lih-Shan; Weng, Min-Hung; Huang, Tsung-Hui; Chen, Han-Jan; Su, Sheng-Fu; Houng, Mau-Phon

    2004-10-01

    A tapped-line stepped-impedance resonator band-pass filter was implemented using a low temperature cofired multilayer-ceramic structure. By constructing a multilayer structure, a compact band-pass filter was realized. Moreover, the multilayer structure demonstrated an extra cross-coupling effect that produced extra transmission zeros in the stopband and, hence, realized a highly steep passband skirt. The center frequency of the fabricated band-pass filter was 6.075 GHz and the 3 dB fractional bandwidth was 18%. The measured insertion loss and return loss of the filter were -0.31 dB and -28 dB, respectively. The measured response of the fabricated band-pass filter was in good agreement with simulated results.

  13. 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.

  14. 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

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. Experimental study of photonic band gap accelerator structures

    E-print Network

    Marsh, Roark A

    2009-01-01

    This thesis reports theoretical and experimental research on a novel accelerator concept using a photonic bandgap (PBG) structure. Major advances in higher order mode (HOM) damping are required for the next generation of ...

  1. Effect of oxygen on the electronic band structure in ZnOxSe1-x alloys

    NASA Astrophysics Data System (ADS)

    Shan, W.; Walukiewicz, W.; Ager, J. W.; Yu, K. M.; Wu, J.; Haller, E. E.; Nabetani, Y.; Mukawa, T.; Ito, Y.; Matsumoto, T.

    2003-07-01

    The effect of alloying small amounts of ZnO with ZnSe on the electronic band structure has been studied. Optical transitions in molecular-beam-epitaxy-grown ZnOxSe1-x epitaxial films (0?x?1.35%) were investigated using photoreflectance and photoluminescence spectroscopies. The fundamental band-gap energy of the alloys was found to decrease at a rate of about 0.1 eV per atomic percent of oxygen. The pressure dependence of the band gap was also found to be strongly affected by O incorporation. Both the effects can be quantitatively explained by an anticrossing interaction between the extended states of the conduction band of ZnSe and the highly localized oxygen states located at approximately 0.22 eV above the conduction-band edge.

  2. 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 ?-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 ?-actinin links and is likely to be the location of capping protein CapZ. PMID:26362007

  3. Surface and mineral structure of ferrihydrite

    NASA Astrophysics Data System (ADS)

    Hiemstra, Tjisse

    2013-03-01

    Ferrihydrite (Fh) is an yet enigmatic nano Fe(III)-oxide material, omnipresent in nature that can bind ions in large quantities, regulating bioavailability and ion mobility. Although extensively studied, to date no proper view exists on the surface structure and composition, while it is of vital importance to our understanding of ion complexation in terrestrial and aquatic systems. Here, the surface structure of Fh is elucidated in relation to that of the mineral core, showing a unique surface composition differing from the mineral core. The mineral core is basically defect-free for all Fh particles. Key for understanding Fh is the very large contribution of the surface as an "inter-phase". The surface of Fh is depleted by two specific types of polyhedra (Fe2,Fe3). Surface depletion (SD) explains the observed particle size dependency of the (a) Pair Distribution Function (PDF) derived from High Energy X-ray total Scattering (HEXS), (b) thermogravimetric water content, and (c) mass density. It also explains the isotopic 57Fe exchange ratio. Due to surface groups, two-line Fh particles are water rich but its mineral core is hydrogen poor. The SD model elucidates the surface structure of crystal faces of idealized Fh such as the 1 -1 0 and 1 -1 1 type of faces that may strongly contribute (e.g. ˜75 ± 10%) to the total surface area. These faces are terminated by protruding Fe1 octahedra, creating the singly-coordinated tbnd FeOH(H) groups at the Fh surface. Alternating rows of Fe1 octahedra with singly-coordinated surface groups enable the formation of either double corner (2C) or edge (1E) surface complexes. For Fh, the site densities derived are much higher than for goethite. In combination with the high surface area, it makes Fh to an extremely reactive natural phase.

  4. 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.

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

    E-print Network

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

    2008-02-13

    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. 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. 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.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.

  6. 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 Domínguez, 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.

  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. 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.

  9. 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) .

  10. 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

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

    SciTech Connect

    Yastrubchak, O.; Gluba, L.; ?uk, J.; Sadowski, J.; MAX-Lab, Lund University, 22100 Lund ; Krzy?anowska, 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.

  12. 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.

  13. 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.

  14. 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.

  15. Evidence for water structuring forces between surfaces

    PubMed Central

    Stanley, Christopher

    2011-01-01

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

  16. 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.

  17. Electron Band Structure of MnGaN Dimiter Alexandrov1

    E-print Network

    Dietz, Nikolaus

    Electron Band Structure of MnGaN Dimiter Alexandrov1 , Nikolaus Dietz2 , Ian Ferguson3 , and Hang Yu1 1 Department of Electrical Engineering, Lakehead University, 955 Oliver Road, Thunder Bay, P7B5E1 structure of this semiconductor. The authors model this alloy on the basis of Mn substitutions on Ga sites

  18. Electromagnetic force on structured metallic surfaces

    NASA Astrophysics Data System (ADS)

    Velzen, Andrew H.; Webb, Kevin J.

    2015-09-01

    We present a method by which the relatively weak electromagnetic force exerted on a surface can be dramatically enhanced. By structuring a metal surface at the nanoscale, we show that the force can be substantially increased over that on the planar metallic surface. The basis for this effect is found to be cavity-enhanced fields and the excitation of surface waves, and results are related to theory. In practice, this force enhancement could be expanded to other materials in various frequency regimes. This increased electromagnetic force should facilitate an expansion of applications related to optomechanics.

  19. LIMEX '87 ice surface characteristics - Implications for C-band SAR backscatter signatures

    NASA Technical Reports Server (NTRS)

    Drinkwater, Mark R.

    1989-01-01

    Ice surface characterization data collected in 1987, during the Labrador Sea Ice Margin Experiment, are analyzed to estimate the changes in snow and ice properties at the onset of melt. Surface measurements were made from an ice research vessel on several days (some of which had coincident remote-sensing flights) at a number of locations in the marginal ice zone. These data are used as input parameters in a simple scattering model to simulate the effects of variations in material properties upon C-band scattering signatures. Snow moisture and large-scale surface roughness are demonstrated to have the largest effect upon HH polarization scattering cross-section sigma(HH)(O) and large differences are predicted between undeformed floe surfaces and deformed or undulating rough ice surfaces. Using a parametric approach, an approximate picture of rough and smooth ice signatures and their relative contrast are provided. The models reproduce a trend observed in synthetic aperture radar (SAR) images of increasing backscatter contrast between deformed and underformed ice over an early period of warning: such observations are consistent with the results of analysis of SAR images to date. The model also reproduces a calibrated SAR-derived signature with a reasonable degree of accuracy.

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

    NASA Astrophysics Data System (ADS)

    Saito, Kyosuke; Tanabe, Tadao; Oyama, Yutaka

    2015-01-01

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

  1. 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 (??>?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.

  2. 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.

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

    NASA Astrophysics Data System (ADS)

    Kuzmík, J.; Haš?ík, Š.; Ku?era, M.; Kúdela, R.; Dobro?ka, E.; Adikimenakis, A.; Mi?ušík, 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.

  4. Significant tuning of band structures of magneto-mechanical phononic crystals using extraordinarily small magnetic fields

    NASA Astrophysics Data System (ADS)

    Yang, Aichao; Li, Ping; Wen, Yumei; Lu, Caijiang; Peng, Xiao; Zhang, Jitao; He, Wei; Wang, Decai; Yang, Chao

    2014-07-01

    Tuning band structures of a magneto-mechanical phononic crystal (PnC) (containing elastic plates bonded with magnets) is demonstrated by applying a small static magnetic field (Hdc). Due to magnetic torque effect, the markedly altered coupling between Bragg scattering (related to lattice constants) and local resonances of plates occurs. Consequently, significant tuning of band structures is observed under a greatly small Hdc. Experiments show that an additional passband occurs in band structures when Hdc ? 130 Oe. This threshold (130 Oe) is ˜1/100 as large as that of the conventional PnC using magnetostrictive materials. The adjusted maximum of passband bandwidth is 0.57 kHz under 0-600 Oe.

  5. 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

  6. Impact of [110]/(001) uniaxial stress on valence band structure and hole effective mass of silicon

    NASA Astrophysics Data System (ADS)

    Jianli, Ma; Heming, Zhang; Jianjun, Song; Guanyu, Wang; Xiaoyan, Wang; Xiaobo, Xu

    2011-02-01

    The valence band structure and hole effective mass of silicon under a uniaxial stress in (001) surface along the [110] direction were detailedly investigated in the framework of the k · p theory. The results demonstrated that the splitting energy between the top band and the second band for uniaxial compressive stress is bigger than that of the tensile one at the same stress magnitude, and of all common used crystallographic direction, such as [110], [001], [1¯10] and [100], the effective mass for the top band along [110] crystallographic direction is lower under uniaxial compressive stress compared with other stresses and crystallographic directions configurations. In view of suppressing the scattering and reducing the effective mass, the [110] crystallographic direction is most favorable to be used as transport direction of the charge carrier to enhancement mobility when a uniaxial compressive stress along [110] direction is applied. The obtained results can provide a theory reference for the design and the selective of optimum stress and crystallorgraphic direction configuration of uniaxial strained silicon devices.

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

    PubMed

    Tsukamoto, Shigeru; Hirose, Kikuji; Blügel, 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)]. 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. PMID:25122409

  8. 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.

  9. 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.

  10. 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.

  11. Band structure and broadband compensation of absorption by amplification in layered optical metamaterials

    SciTech Connect

    Rozanov, N. N. Fedorov, S. V.; Savel'ev, R. S.; Sukhorukov, A. A.; Kivshar, Yu. S.

    2012-05-15

    The frequency dependence of the gain required to compensate for absorption is determined for a layered structure consisting of alternating absorbing and amplifying layers. It is shown that the fulfillment of the same conditions is required for the existence of a band structure consisting of alternating bands allowed and forbidden for optical radiation propagation in the frequency-wave vector parametric region. Conditions are found under which the gain required for compensation is smaller than thresholds for absolute (parasitic lasing) and convective (waveguide amplification of radiation) instabilities.

  12. 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.

  13. 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.

  14. 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

  15. The reflection anisotropy spectroscopy of the Au(1?1?0) surface structures in liquid environments.

    PubMed

    Weightman, P; Harrison, P; Lucas, C A; Grunder, Y; Smith, C I

    2015-12-01

    The reflection anisotropy (RAS) profiles of the Au(1?1?0)-(1??×??1), (1??×??2) and (1??×??3) surface structures in electrochemical environments are shown to arise mainly from surface dipole transitions directed along the principal axes of the Au(1?1?0) surface. There are weak contributions to the RAS profiles of the Au(1?1?0)-(1??×??1) and (1??×??3) surfaces in the region of 4.0?eV which probably arise from (1?1?1) facets that are either intrinsic to the surface structures or are associated with steps. A transition involving a surface state just above the Fermi level, E F, contributes to the RAS profiles of the (1??×??2) and (1??×??3) surfaces but not to the RAS profile of the (1??×??1) surface. A strong feature at 2.5?eV in the RAS profiles of the Au(1?1?0)-(1??×??1) and (1??×??2) surfaces is attributed to a transition in the vicinity of the L point of the Brillouin zone between the 5d band and the [Formula: see text] band at E F. It is argued that the applied potential of??-0.6?V, which creates the Au(1?1?0)-(1??×??3) surface, lifts E F above the [Formula: see text] band causing it to become occupied and quenching this contribution to the RAS profile. PMID:26496895

  16. The reflection anisotropy spectroscopy of the Au(1?1?0) surface structures in liquid environments

    NASA Astrophysics Data System (ADS)

    Weightman, P.; Harrison, P.; Lucas, C. A.; Grunder, Y.; Smith, C. I.

    2015-12-01

    The reflection anisotropy (RAS) profiles of the Au(1?1?0)-(1??×??1), (1??×??2) and (1??×??3) surface structures in electrochemical environments are shown to arise mainly from surface dipole transitions directed along the principal axes of the Au(1?1?0) surface. There are weak contributions to the RAS profiles of the Au(1?1?0)-(1??×??1) and (1??×??3) surfaces in the region of 4.0?eV which probably arise from (1?1?1) facets that are either intrinsic to the surface structures or are associated with steps. A transition involving a surface state just above the Fermi level, E F, contributes to the RAS profiles of the (1??×??2) and (1??×??3) surfaces but not to the RAS profile of the (1??×??1) surface. A strong feature at 2.5?eV in the RAS profiles of the Au(1?1?0)-(1??×??1) and (1??×??2) surfaces is attributed to a transition in the vicinity of the L point of the Brillouin zone between the 5d band and the L2\\prime band at E F. It is argued that the applied potential of???0.6?V, which creates the Au(1?1?0)-(1??×??3) surface, lifts E F above the L2\\prime band causing it to become occupied and quenching this contribution to the RAS profile.

  17. 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.

  18. 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.

  19. 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

  20. 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

  1. 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

  2. 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 correlations—we 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.

  3. 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.

  4. Tuning the band structures of single walled silicon carbide nanotubes with uniaxial strain: a first principles study

    SciTech Connect

    Wang, Zhiguo; Zu, Xiaotao T.; Xiao, H. Y.; Gao, Fei; Weber, William J.

    2008-05-09

    Electronic band structures of single-walled silicon carbide nanotubes are studied under uniaxial strain using first principles calculations. The band structure can be tuned by mechanical strain in a wide energy range. The band gap decreases with uniaxial tensile strain, but initially increases with uniaxial compressive strain and then decreases with further increases in compressive strain. These results may provide a way to tune the electronic structures of silicon carbide nanotubes, which may have promising applications in building nanodevices.

  5. 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.; Fournée, V.; Ledieu, J.; McGrath, R.; Sharma, H. R.

    2015-03-01

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

  6. 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.; Fournée, 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

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

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

    PubMed Central

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

    2011-01-01

    The “Cooperative Airborne Radiometer for Ocean and Land Studies” (CAROLS) L-Band radiometer was designed and built as a copy of the EMIRAD II radiometer constructed by the Technical University of Denmark team. It is a fully polarimetric and direct sampling correlation radiometer. It is installed on board a dedicated French ATR42 research aircraft, in conjunction with other airborne instruments (C-Band scatterometer—STORM, the GOLD-RTR GPS system, the infrared CIMEL radiometer and a visible wavelength camera). Following initial laboratory qualifications, three airborne campaigns involving 21 flights were carried out over South West France, the Valencia site and the Bay of Biscay (Atlantic Ocean) in 2007, 2008 and 2009, in coordination with in situ field campaigns. In order to validate the CAROLS data, various aircraft flight patterns and maneuvers were implemented, including straight horizontal flights, circular flights, wing and nose wags over the ocean. Analysis of the first two campaigns in 2007 and 2008 leads us to improve the CAROLS radiometer regarding isolation between channels and filter bandwidth. After implementation of these improvements, results show that the instrument is conforming to specification and is a useful tool for Soil Moisture and Ocean Salinity (SMOS) satellite validation as well as for specific studies on surface soil moisture or ocean salinity. PMID:22346599

  9. 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.

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

    E-print Network

    Gentaro Watanabe; Sukjin Yoon; Franco Dalfovo

    2012-01-05

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

  11. 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 50 meV 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 5 meV of the Fermi energy. The present result strongly suggests that this unusual electronic state is responsible for the unconventional superconductivity in FeSe. PMID:25526150

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. Surface- and point-defect-related Raman scattering in wurtzite semiconductors excited above the band gap

    NASA Astrophysics Data System (ADS)

    Kranert, C.; Schmidt-Grund, R.; Grundmann, M.

    2013-11-01

    We present a model for exciton-mediated first-order Raman scattering by longitudinal optical phonons in the presence of surfaces and point defects. It is consistent with the experimental data for all wurtzite structure materials investigated and reviewed here (GaN, InN, ZnO and CdS) and also explains not yet understood observations in the literature. We distinguish between the involvement of elastic scattering by the surface and by point defects in the scattering process. Surface scattering causes the dependence of the line position on the crystal orientation of the excited surface in pure crystals. Point defect scattering is independent of the crystal orientation and appears as an additional contribution in defect-rich crystals. We postulate the polarization properties of these distinct processes which are in good agreement with the experiments and allow us to identify and separate the contributions of these two effects from the polarized spectra.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. Transmission properties and band structure of a segmented dielectric waveguide for the terahertz range

    E-print Network

    Ku?el, Petr

    ones. The second technique involves a modal analysis approach of diffraction gratings and it is used. More recently, based on a modal analysis, smart filtering proper- ties of such segmented waveguides have been proposed and demonstrated in the THz range [14,15]. The analysis of the band structure

  2. 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 Hill’s 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.

  3. Maximum Theoretical Efficiency Limit of Photovoltaic Devices: Effect of Band Structure on Excited State Entropy

    E-print Network

    Osterloh, Frank

    Maximum Theoretical Efficiency Limit of Photovoltaic Devices: Effect of Band Structure on Excited a theoretical limit for the maximum energy conversion efficiency of single junction photovoltaic cells for the efficiency variations observed for real photovoltaic devices today.4-6 Here, we show that the extractable

  4. Conduction band structure and electron mobility in uniaxially strained Si via externally applied strain in nanomembranes

    E-print Network

    Simons, Jack

    of enhancing charge carrier mobility. Utilizing uniaxial strain in modern low-dimensional electronic OF PHYSICS D: APPLIED PHYSICS J. Phys. D: Appl. Phys. 44 (2011) 325107 (8pp) doi:10 at stacks.iop.org/JPhysD/44/325107 Abstract Strain changes the band structure of semiconductors. We use x

  5. Underlying Spin-Orbit Coupling Structure of Intervalence Charge Transfer Bands in Dinuclear Polypyridyl Complexes of

    E-print Network

    Underlying Spin-Orbit Coupling Structure of Intervalence Charge Transfer Bands in Dinuclear that stereochemical effects lead to fundamental changes in the energy levels of the metal-based d orbitals, which are split by spin-orbit coupling and ligand-field asymmetry. An increase in the separation between the IC

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

    E-print Network

    Cambridge, University of

    alloys developed originally developed for use in gun barrels [14, 15] have been evaluatedShear-band structure in ballistically tested carbide-free bainitic steels L. C. D. Fieldinga , H. K the armour [8]. The mechanisms responsible for shear localisation are well understood, but in steels

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

    E-print Network

    Gong, Xingao

    2011-01-01

    PHYSICAL REVIEW B 83, 245202 (2011) Band structure engineering of multinary chalcogenide importance as representing a novel quantum state and the associated technological applications in spintronics and spintronic devices based on tetrahedral semiconductors, and (iii) ease of synthesis or already synthesized

  8. Electrochemistry at Single-Walled Carbon Nanotubes: The Role of Band Structure and Quantum Capacitance

    E-print Network

    Dekker, Cees

    Electrochemistry at Single-Walled Carbon Nanotubes: The Role of Band Structure and Quantum the electrode kinetics. We model electrochemistry at metallic and semiconducting SWNTs as well as at graphene) as electrodes for electrochemistry.2-4 This interest mostly originates from the prospect of using individual

  9. 2008 IEEE Electrical Performance of Electronic Packaging Suppression of Vertical Coupling using Electromagnetic Band Gap Structures

    E-print Network

    Swaminathan, Madhavan

    2008 IEEE Electrical Performance of Electronic Packaging Suppression of Vertical Coupling using Electromagnetic Band Gap Structures Nithya Sankaran, Suzanne Huh, Madhavan Swaminathan and Rao Tummala Packaging are presented. I. Introduction Multilayer packaging plays a vital role in producing highly miniaturized, low

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

    SciTech Connect

    Liao, Chen; Zhang, Huichao; Tang, Luping; Zhou, Zhiqiang; Lv, Changgui; Cui, Yiping; Zhang, Jiayu

    2014-04-28

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

  11. 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.

  12. 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

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

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

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

  14. Electronic-band structures and optical properties of transition metal doped Zinc oxide

    NASA Astrophysics Data System (ADS)

    Esakki muthuraju, M.; Mahesh, R.; Sreekanth, T.; Venugopal Reddy, P.

    2014-05-01

    Wide band gap Oxide based diluted magnetic semiconductors (ODMS) exhibit unique magnetic, magneto-optical and magneto-electrical effects and can be exploited as spintronic devices. Theoretical studies of transition metal (TM) doped zinc oxide which belongs to these class of materials has been attracting significant research interest in the recent years. In this paper, the electronic band structures, and band gap energies of ZnO doped with transition metal have been analyzed by ab initio calculations based on the density functional theory using quantum espresso PWscf code. For the band gap calculations, we have used both local density approximation (LDA) and generalized gradient approximation (GGA). The magnetic and optical properties of the materials have been studied using the above method. For all the theoretical calculations, the model structures of transition metal-doped ZnO were constructed by using the 16 atom supercell with one Zn atom replaced by a transition metal atom. The results are useful in understanding the band gap variations with doping and other related properties in oxide based diluted magnetic semiconductors such as ZnO.

  15. 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

  16. Specialized cell surface structures in cellulolytic bacteria.

    PubMed Central

    Lamed, R; Naimark, J; Morgenstern, E; Bayer, E A

    1987-01-01

    The cell surface topology of various gram-negative and -positive, anaerobic and aerobic, mesophilic and thermophilic, cellulolytic and noncellulolytic bacteria was investigated by scanning electron microscopic visualization using cationized ferritin. Characteristic protuberant structures were observed on cells of all cellulolytic strains. These structures appeared to be directly related to the previously described exocellular cellulase-containing polycellulosomes of Clostridium thermocellum YS (E. A. Bayer and R. Lamed, J. Bacteriol. 167:828-836, 1986). Immunochemical evidence and lectin-binding studies suggested a further correlation on the molecular level among cellulolytic bacteria. The results indicate that such cell surface cellulase-containing structures may be of general consequence to the bacterial interaction with and degradation of cellulose. Images PMID:3301817

  17. Work function and affinity changes associated with the structure of hydrogen-terminated diamond ,,100... surfaces

    E-print Network

    Mills, Allen P.

    Work function and affinity changes associated with the structure of hydrogen-terminated diamond of diamond 100 surfaces were measured using positron reemission and Kelvin probe techniques to reveal changes in the contact potential of diamond, little band bending is evident at room temperature for variously prepared

  18. Theoretical study of influencing factors on the dispersion of bulk band-gap edges and the surface states in topological insulators Bi{sub 2}Te{sub 3} and Bi{sub 2}Se{sub 3}

    SciTech Connect

    Rusinov, I. P. Nechaev, I. A.; Chulkov, E. V.

    2013-06-15

    The dispersion of the band-gap edge states in bulk topological insulators Bi{sub 2}Te{sub 3} and Bi{sub 2}Se{sub 3} is considered within density functional theory. The dependences of this dispersion both on the approximation used for an exchange-correlation functional at fixed unit cell parameters and atomic positions and on these parameters and positions that are obtained upon structural relaxation performed using a certain approximated functional are analyzed. The relative position of the Dirac point of topologically protected surface states and the valence band maximum in the surface electronic structure of the topological insulators is discussed.

  19. 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.

  20. 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 .

  1. 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 ? point.

  2. Electronic Structure of Regular Bacterial Surface Layers

    NASA Astrophysics Data System (ADS)

    Vyalikh, Denis V.; Danzenbächer, Steffen; Mertig, Michael; Kirchner, Alexander; Pompe, Wolfgang; Dedkov, Yuriy S.; Molodtsov, Serguei L.

    2004-12-01

    We report photoemission and near-edge x-ray absorption fine structure measurements of the occupied and unoccupied valence electronic states of the regular surface layer of Bacillus sphaericus, which is widely used as the protein template for the fabrication of metallic nanostructures. The two-dimensional protein crystal shows a semiconductorlike behavior with a gap value of ˜3.0 eV and the Fermi energy close to the bottom of the lowest unoccupied molecular orbital. We anticipate that these results will open up new possibilities for the electric addressability of biotemplated low-dimensional hybrid structures.

  3. 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

  4. 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.

  5. 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.

  6. 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.

  7. 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

  8. Atomic arrangement and electron band structure of Si(1 1 1)-ß-?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

  9. 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

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. Photonic band structure of one-dimensional metal/dielectric structures calculated by the plane-wave expansion method

    NASA Astrophysics Data System (ADS)

    Zong, YiXin; Xia, JianBai

    2015-07-01

    The plane-wave expansion (PWE) method is employed to calculate the photonic band structures of metal/dielectric (M/D) periodic systems. We consider a one-dimensional (1D)M/D superlattice with ametal layer characterized by a frequency-dependent dielectric function. To calculate the photonic band of such a system, we propose a new method and thus avoid solving the nonlinear eigenvalue equations. We obtained the frequency dispersions and the energy distributions of eigen-modes of 1D superlattices. This general method is applicable to calculate the photonic band of a broad class of physical systems, e.g. 2D and 3D M/D photonic crystals. For comparison, we present a simple introduction of the finite-difference (FD) method to calculate the same system, and the agreement turns out to be good. But the FD method cannot be applied to the TM modes of the M/D superlattice.

  15. Buckling and band gap of the Ge(111)2×1 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 2×1 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 <21¯1¯> 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.

  16. 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.

  17. 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.

  18. 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-Domínguez, R.; Nieto-Vesperinas, M.; Sánchez-Gil, J. A.

    2015-12-01

    We investigate theoretically and numerically the photonic band structure in the optical domain of an array of core–shell 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.

  19. Photonic band structure and effective medium properties of doubly-resonant core-shell metallo-dielectric nanowire arrays: low-loss, isotropic optical negative-index behavior

    E-print Network

    Abujetas, D R; Nieto-Vesperinas, M; Sánchez-Gil, J A

    2015-01-01

    We investigate theoretically and numerically the photonic band structure in the optical domain of an array of core-shell 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, indeed 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. 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. 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.

  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. 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.

  4. Two-dimensional plasmon in a surface-state band Tadaaki Nagao a,b,c,*, Torsten Hildebrandt d

    E-print Network

    Hasegawa, Shuji

    Two-dimensional plasmon in a surface-state band Tadaaki Nagao a,b,c,*, Torsten Hildebrandt d well with the plasmon dispersion calculated from two-dimensional (2D) nearly free-electron theory. As hallmarked from these observations, we identify the measured loss as a longitudinal intraband 2D plasmon

  5. Efficient quasiparticle band-structure calculations for cubic and noncubic crystals

    SciTech Connect

    Wenzien, B.; Cappellini, G.; Bechstedt, F.

    1995-05-15

    An efficient method developed for the calculation of quasiparticle corrections to density-functional-theory--local-density-approximation (DFT-LDA) band structures of diamond and zinc-blende materials is generalized for crystals with other cubic, hexagonal, tetragonal, and orthorhombic Bravais lattices. Local-field effects are considered in the framework of a LDA-like approximation. The dynamical screening is treated by expanding the self-energy linearly in energy. The anisotropy of the inverse dielectric matrix is taken into account. The singularity of the Coulomb potential in the screened-exchange part of the electronic self-energy is treated using auxiliary functions of the appropriate symmetry. An application to the electronic quasiparticle band structure of wurtzite 2{ital H}-SiC is presented within the approach of norm-conserving, nonlocal, fully separable pseudopotentials and a plane-wave expansion of the wave functions for the underlying DFT-LDA.

  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. 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.

  8. 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

  9. Influence of structural parameters on tunable photonic band gaps modulated by liquid crystals

    NASA Astrophysics Data System (ADS)

    Huang, Aiqin; Zheng, Jihong; Jiang, Yanmeng; Zhou, Zengjun; Tang, Pingyu; Zhuang, Songlin

    2011-10-01

    Tunable photonic crystals (PCs), which are infiltrated with nematic liquid crystals (LCs), tune photonic band gap (PBG) by rotating directors of LCs when applied with the external electrical field. Using the plane wave expansion method, we simulated the PBG structure of two-dimensional tunable PCs with a triangular lattice of circular column, square column and hexagon column, respectively. When PCs are composed of LCs and different substrate materials such as germanium (Ge) and silicon (Si), the influence of structural parameters including column shape and packing ration on PBG is discussed separately. Numerical simulations show that absolute PBG can't be found at any conditions, however large tuning range of polarized wave can be achieved by rotating directors of LCs. The simulation results provide theoretical guidance for the fabrication of field-sensitive polarizer with big tunable band range.

  10. 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.

  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. Retrieving sea surface salinity with multiangular L-band brightness temperatures: Improvement by spatiotemporal averaging

    NASA Astrophysics Data System (ADS)

    Camps, A.; Vall-Llossera, M.; Batres, L.; Torres, F.; Duffo, N.; Corbella, I.

    2005-04-01

    The Soil Moisture and Ocean Salinity (SMOS) mission was selected in May 1999 by the European Space Agency to provide global and frequent soil moisture and sea surface salinity maps. SMOS' single payload is Microwave Imaging Radiometer by Aperture Synthesis (MIRAS), an L band two-dimensional aperture synthesis interferometric radiometer with multiangular observation capabilities. Most geophysical parameter retrieval errors studies have assumed the independence of measurements both in time and space so that the standard deviation of the retrieval errors decreases with the inverse of square root of the number of measurements being averaged. This assumption is especially critical in the case of sea surface salinity (SSS), where spatiotemporal averaging is required to achieve the ultimate goal of 0.1 psu error. This work presents a detailed study of the SSS error reduction by spatiotemporal averaging, using the SMOS end-to-end performance simulator (SEPS), including thermal noise, all instrumental error sources, current error correction and image reconstruction algorithms, and correction of atmospheric and sky noises. The most important error sources are the biases that appear in the brightness temperature images. Three different sources of biases have been identified: errors in the noise injection radiometers, Sun contributions to the antenna temperature, and imaging under aliasing conditions. A calibration technique has been devised to correct these biases prior to the SSS retrieval at each satellite overpass. Simulation results show a retrieved salinity error of 0.2 psu in warm open ocean, and up to 0.7 psu at high latitudes and near the coast, where the external calibration method presents more difficulties.

  13. 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.

  14. Analysis of tunable photonic band structure in an extrinsic plasma photonic crystal

    NASA Astrophysics Data System (ADS)

    King, Tzu-Chyang; Yang, Chih-Chiang; Hsieh, Pei-Hung; Chang, Tsung-Wen; Wu, Chien-Jang

    2015-03-01

    In this work, we theoretically investigate the tunable photonic band structure (PBS) for an extrinsic plasma photonic crystal (PPC). The extrinsic PPC is made of a bulk cold plasma layer which is influenced by an externally periodic static magnetic field. The PBS can be tuned by the variation of the magnitude of externally applied magnetic field. In addition, we also show that the PBS can be changed as a function of the electron density as well as the thickness variation.

  15. Fracture Induced Sub-Band Absorption as a Precursor to Optical Damage on Fused Silica Surfaces

    SciTech Connect

    Miller, P E; Bude, J D; Suratwala, T I; Shen, N; Laurence, T A; Steele, W A; Menapace, J; Feit, M D; Wong, L L

    2010-03-05

    The optical damage threshold of indentation induced flaws on fused silica surfaces was explored. Mechanical flaws were characterized by laser damaged testing, SEM, optical, and photoluminescence microscopy. Localized polishing, chemical etching, and the control of indentation morphology were used to isolate the structural features which limit optical damage. A thin defect layer on fracture surfaces, including those smaller than the wavelength of visible light, was found to be the dominant source of laser damage initiation during illumination with 355nm, 3ns laser pulses. Little evidence was found that either displaced or densified material or fluence intensification plays a significant role in optical damage at fluences >35J/cm{sup 2}. Elimination of the defect layer was shown to increase the overall damage performance of fused silica optics.

  16. 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.

  17. 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.

  18. 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.

  19. 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

  20. Iodide surface decoration: a facile and efficacious approach to modulating the band energy level of semiconductors for high-performance visible-light photocatalysis.

    PubMed

    Huang, Hongwei; Xiao, Ke; Yu, Shixin; Dong, Fan; Zhang, Tierui; Zhang, Yihe

    2016-01-01

    We herein report a facile and general approach to modulating the band energy level of semiconductors for visible-light photocatalysis via iodide surface decoration. This strategy enables the wide-band-gap Bi2O2CO3 to possess a continuously tunable band gap and profoundly boosted visible-light photocatalytic performance for dye degradation and NO removal. PMID:26516680

  1. 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.

  2. 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

  3. 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 ?-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

  4. 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.

  5. Structure and thermodynamics of surface recognition

    SciTech Connect

    Gupta, G.

    1998-11-01

    This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Interactions of the surface glycoprotein, gp120, with the receptors of host cells define the pathogenesis of HIV-1, the virus that causes AIDS. gp120 is made of several disulfide-bridged loops--the amino acid sequences of some of these loops are fairly conserved whereas the rest are variable. The third variable (V3) loop has been the target of vaccine design for quite some time since this loop is involved in various steps of viral pathogenesis. However, this loop also happens to be the most variable one. The authors have carried out structural and immunological studies to determine the sequence-structure-antigenicity correlations of the HIV-1 V3 loops. This resulted in the identification of a secondary structure at the tip of the V3 loop that remains invariant in spite of the sequence variation. The authors designed a multi-valent V3-based antigen that presents multiple copies of the same tip element several times in the same structure. During the course of this project, they realized that the protective epitopes of gp120 should be judged in the context of the native structure. Therefore, the authors developed a method to obtain a model of gp120 that is consistent with all the immunology and virology data. This model is useful in choosing or designing gp120 subdomains for vaccine development.

  6. Scattering of alkali atoms and ions from alkali-halide surfaces: No evidence found for electronic surface states within the band gap of the insulator

    SciTech Connect

    Mertens, A.; Auth, C.; Winter, H.; Borisov, A.G.

    1997-02-01

    Fast alkali atoms and ions are scattered with keV energies under grazing incidence from the surface of the alkali halides LiF(100), KCl(100), KI(100), and the scattered beams are analyzed with respect to their charge fractions. From our experiments we find no evidence for occupied or unoccupied electronic surface states within the band gap of the insulator. {copyright} {ital 1997} {ital The American Physical Society}

  7. 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.

  8. Quasiparticle band structures and thermoelectric transport properties of p-type SnSe

    NASA Astrophysics Data System (ADS)

    Shi, Guangsha; Kioupakis, Emmanouil

    2015-03-01

    We used density functional and many-body perturbation theory to calculate the band structure 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 within the constant relaxation time approximation as a function of doping concentration and temperature for single-crystal and polycrystalline materials to understand experimental measurements. The electronic transport coefficients are highly anisotropic and are strongly affected by bipolar transport effects at low doping and high temperature. Our results indicate that SnSe exhibits optimal thermoelectric performance at high temperature when doped in the 1019-1020 cm-3 range. This work was supported in part by the National Science Foundation (DMR-1254314) and in part by CSTEC, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science. Computational resources were provided by the DOE NERSC facility.

  9. 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.

  10. Extracting E Versus K Effective Band Structure from Supercell Calculations on Alloys and Impurities

    SciTech Connect

    Popescu, V.; Zunger, A.

    2012-02-15

    The supercell approach to defects and alloys has circumvented the limitations of those methods that insist on using artificially high symmetry, yet this step usually comes at the cost of abandoning the language of E versus k band dispersion. Here we describe a computational method that maps the energy eigenvalues obtained from large supercell calculations into an effective band structure (EBS) and recovers an approximate E(k) for alloys. Making use of supercells allows one to model a random alloy A{sub 1-x}B{sub x}C by occupying the sites A and B via a coin-toss procedure, affording many different local environments (polymorphic description) to occur. We present the formalism and implementation details of the method and apply it to study the evolution of the impurity band appearing in the dilute GaN:P alloy. We go beyond the perfectly random case, realizing that many alloys may have nonrandom microstructures, and investigate how their formation is reflected in the EBS. It turns out that the EBS is extremely sensitive in determining the critical disorder level for which delocalized states start to appear in the intermediate band. In addition, the EBS allows us to identify the role played by atomic relaxation in the positioning of the impurity levels.

  11. Janus kinases and focal adhesion kinases play in the 4.1 band: a superfamily of band 4.1 domains important for cell structure and signal transduction.

    PubMed Central

    Girault, J. A.; Labesse, G.; Mornon, J. P.; Callebaut, I.

    1998-01-01

    The band 4.1 domain was first identified in the red blood cell protein band 4.1, and subsequently in ezrin, radixin, and moesin (ERM proteins) and other proteins, including tumor suppressor merlin/schwannomin, talin, unconventional myosins VIIa and X, and protein tyrosine phosphatases. Recently, the presence of a structurally related domain has been demonstrated in the N-terminal region of two groups of tyrosine kinases: the focal adhesion kinases (FAK) and the Janus kinases (JAK). Additional proteins containing the 4.1/JEF (JAK, ERM, FAK) domain include plant kinesin-like calmodulin-binding proteins (KCBP) and a number of uncharacterized open reading frames identified by systematic DNA sequencing. Phylogenetic analysis of amino acid sequences suggests that band 4.1/JEF domains can be grouped in several families that have probably diverged early during evolution. Hydrophobic cluster analysis indicates that the band 4.1/JEF domains might consist of a duplicated module of approximately 140 residues and a central hinge region. A conserved property of the domain is its capacity to bind to the membrane-proximal region of the C-terminal cytoplasmic tail of proteins with a single transmembrane segment. Many proteins with band 4.1/JEF domains undergo regulated intra- or intermolecular homotypic interactions. Additional properties common to band 4.1/JEF domains of several proteins are binding of phosphoinositides and regulation by GTPases of the Rho family. Many proteins with band 4. 1/JEF domains are associated with the actin-based cytoskeleton and are enriched at points of contact with other cells or the extracellular matrix, from which they can exert control over cell growth. Thus, proteins with band 4.1/JEF domain are at the crossroads between cytoskeletal organization and signal transduction in multicellular organisms. Their importance is underlined by the variety of diseases that can result from their mutations. Images Fig. 1 Fig. 2 Fig. 4 Fig. 5 PMID:9990861

  12. Structural stability and electronic properties of low-index surfaces of SnS

    SciTech Connect

    Tritsaris, Georgios A.; Malone, Brad D.; Kaxiras, Efthimios

    2014-05-07

    Thin film photovoltaic cells are increasingly important for cost-effective solar energy harvesting. Layered SnS is a promising absorber material due to its high optical absorption in the visible and good doping characteristics. We use first-principles calculations based on density functional theory to study structures of low-index surfaces of SnS using stoichiometric and oxygen-containing structural models, in order to elucidate their possible effect on the efficiency of the photovoltaic device. We find that the surface energy is minimized for the surface with orientation parallel to the layer stacking direction. Compared to stoichiometric surfaces, the oxygen-containing surfaces exhibit fewer electronic states near the band gap. This reduction of near-gap surface states by oxygen should reduce recombination losses at grain boundaries and interfaces of the SnS absorber, and should be beneficial to the efficiency of the solar cell.

  13. 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

  14. ARPES on Na0.6CoO2: Fermi Surface and Unusual Band Dispersion

    SciTech Connect

    Yang, H. B.; Wang, S. -C.; Sekharan, A. K. P.; Matsui, H.; Souma, S.; Sato, T.; Takahashi, T.; Takeuchi, T.; Campuzano, J. C.; Jin, Rongying; Sales, Brian C; Mandrus, David; Wang, Z.; Ding, H.

    2004-01-01

    The electronic structure of single crystals Na{sub 0.6}CoO{sub 2}, which are closely related to the superconducting Na{sub 0.3}CoO{sub 2} {center_dot} yH{sub 2}O (T{sub c}-5 K), is studied by angle-resolved photoelectron spectroscopy. While the measured Fermi surface (FS) is consistent with the large FS enclosing the {Gamma} point from the band theory, the predicted small FS pockets near the K points are absent. In addition, the band dispersion is found to be highly renormalized, and anisotropic along the two principal axes ({Gamma}-K, {Gamma}-M). Our measurements also indicate that an extended flatband is formed slightly above EF along {Gamma}-K.

  15. Electronic structure of bacterial surface protein layers

    SciTech Connect

    Maslyuk, Volodymyr V.; Mertig, Ingrid; Bredow, Thomas; Mertig, Michael; Vyalikh, Denis V.; Molodtsov, Serguei L.

    2008-01-15

    We report an approach for the calculation of the electronic density of states of the dried two-dimensional crystalline surface protein layer (S layer) of the bacterium Bacillus sphaericus NCTC 9602. The proposed model is based on the consideration of individual amino acids in the corresponding conformation of the peptide chain which additively contribute to the electronic structure of the entire protein complex. The derived results agree well with the experimental data obtained by means of photoemission (PE), resonant PE, and near-edge x-ray absorption spectroscopy.

  16. Electronic structure of bacterial surface protein layers

    NASA Astrophysics Data System (ADS)

    Maslyuk, Volodymyr V.; Mertig, Ingrid; Bredow, Thomas; Mertig, Michael; Vyalikh, Denis V.; Molodtsov, Serguei L.

    2008-01-01

    We report an approach for the calculation of the electronic density of states of the dried two-dimensional crystalline surface protein layer ( S layer) of the bacterium Bacillus sphaericus NCTC 9602. The proposed model is based on the consideration of individual amino acids in the corresponding conformation of the peptide chain which additively contribute to the electronic structure of the entire protein complex. The derived results agree well with the experimental data obtained by means of photoemission (PE), resonant PE, and near-edge x-ray absorption spectroscopy.

  17. Constraining Spanish Surface Structure, York Papers in Linguistics 4.

    ERIC Educational Resources Information Center

    Green, John N.

    This article attempts to refute D.M. Perlmutter's claim that the syntactic component in Spanish grammar can generate structures that are grammatical at the deep structure level but not at the surface structure level, and that it is necessary to impose a surface structure constraint (SSC) as a filter to reject the ungrammatical structures. The…

  18. 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.

  19. Surface structures and electronic states of silicon nanotubes stabilized by oxygen atoms

    NASA Astrophysics Data System (ADS)

    Zhao, Mingwen; Zhang, R. Q.; Xia, Yueyuan

    2007-07-01

    The geometric and electronic structures of silicon nanotubes stabilized by incorporating oxygen atoms were studied using first-principles calculations within density functional theory. The predicted tubes present one-dimensional characters stacked with n-side silicon polygons connected by oxygen atoms. The stable configurations considered in this work include the tubes with varied facet number of the silicon polygons (n) from n =4 to 28 and of different surface structures. The configurations with n =5, 12, 15, 18, and 21 were found energetically extremely favorable. All the tubes are narrow-band-gap semiconductors with the band gap varying between 0.17 and 0.84eV, dependent on the surface structure of the tubes. This study provides an interesting route to stabilize silicon nanotubes and tune their electronic properties.

  20. Observation of an electron band above the Fermi level in FeTe?.??Se?.?? from in-situ surface doping

    DOE PAGESBeta

    Zhang, P.; Richard, P.; Xu, N.; Xu, Y. -M.; Ma, J.; Qian, T.; Fedorov, A. V.; Denlinger, J. D.; Gu, G. D.; Ding, H.

    2014-10-27

    We used in-situ potassium (K) evaporation to dope the surface of the iron-based superconductor FeTe?.??Se?.??. The systematic study of the bands near the Fermi level confirms that electrons are doped into the system, allowing us to tune the Fermi level of this material and to access otherwise unoccupied electronic states. In particular, we observe an electron band located above the Fermi level before doping that shares similarities with a small three-dimensional pocket observed in the cousin, heavily-electron-doped KFe??xSe? compound.

  1. 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.

  2. Complementary structure for designer localized surface plasmons

    NASA Astrophysics Data System (ADS)

    Gao, Zhen; Gao, Fei; Zhang, Youming; Zhang, Baile

    2015-11-01

    Magnetic localized surface plasmons (LSPs) supported on metallic structures corrugated by very long and curved grooves have been recently proposed and demonstrated on an extremely thin metallic spiral structure (MSS) in the microwave regime. However, the mode profile for the magnetic LSPs was demonstrated by measuring only the electric field, not the magnetic field. Here, based on Babinet's principle, we propose a Babinet-inverted, or complementary MSS whose electric/magnetic mode profiles match the magnetic/electric mode profiles of MSS. This complementarity of mode profiles allows mapping the magnetic field distribution of magnetic LSP mode profile on MSS by measuring the electric field distribution of the corresponding mode on complementary MSS. Experiment at microwave frequencies also demonstrate the use of complementary MSS in sensing refractive-index change in the environment.

  3. Electronic structure of the Pb/Si(111)-(7×3) surface reconstruction: A first-principles study

    NASA Astrophysics Data System (ADS)

    Hsu, Chia-Hsiu; Chuang, Feng-Chuan; Albao, Marvin A.; Yeh, V.

    2010-01-01

    Electronic structures of the Pb/Si(111)-(7×3) surface reconstruction were reexamined using first-principles calculations. The band structures of the proposed models were analyzed in detail. Our results show that the calculated bands for the H3 model at lead coverage of 1.2 ML are in good agreement with the identified bands in the angle-resolved photoemission study [Phys. Rev. B 75, 075329 (2007)]. Lastly, the work functions of the 7×3 and 3×3 phases were also calculated and compared with experimental measurements.

  4. 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.

  5. GHASP: an H? kinematic survey of spiral galaxies - X. Surface photometry, decompositions and the Tully-Fisher relation in the Rc band

    NASA Astrophysics Data System (ADS)

    Barbosa, C. E.; Mendes de Oliveira, C.; Amram, P.; Ferrari, F.; Russeil, D.; Epinat, B.; Perret, V.; Adami, C.; Marcelin, M.

    2015-11-01

    We present Rc-band surface photometry for 170 of the 203 galaxies in GHASP, the Gassendi H-alpha survey of spirals, a sample of late-type galaxies for which high-resolution Fabry-Perot H? maps have previously been obtained. Our data set is constructed using new Rc-band observations taken at the Observatoire de Haute-Provence, supplemented with Sloan Digital Sky Survey archival data, obtained with the purpose of deriving homogeneous photometric profiles and parameters. Our results include Rc-band surface brightness profiles for 170 galaxies and ugriz profiles for 108 of these objects. We catalogue several parameters of general interest for further reference, such as total magnitude, effective radius and isophotal parameters (magnitude, position angle, ellipticity and inclination). We also perform a structural decomposition of the surface brightness profiles using a multi-component method to separate discs from bulges and bars, and to observe the main scaling relations involving luminosities, sizes and maximum velocities. We determine the Rc-band Tully-Fisher relation using maximum velocities derived solely from H? rotation curves for a sample of 80 galaxies, resulting in a slope of -8.1 ± 0.5, zero-point of -3.0 ± 1.0 and an estimated intrinsic scatter of 0.28 ± 0.07. We note that, unlike the Tully-Fisher relation in the near-infrared derived for the same sample, no change in the slope of the relation is seen at the low-mass end (for galaxies with Vmax < 125 km s-1). We suggest that this different behaviour of the Tully-Fisher relation (with the optical relation being described by a single power law while the near-infrared has two), may be caused by differences in the stellar mass-to-light ratio for galaxies with Vmax < 125 km s-1.

  6. Structural, energetic and electronic properties of (100) surfaces for alkaline earth metal oxides as calculated with hybrid density functional theory

    NASA Astrophysics Data System (ADS)

    Logsdail, Andrew J.; Mora-Fonz, David; Scanlon, David O.; Catlow, C. Richard A.; Sokol, Alexey A.

    2015-12-01

    We perform a systematic investigation of (100) surfaces for rocksalt-structured group 2 metal oxides, namely MgO, CaO, SrO and BaO, using GGA and Hybrid-DFT exchange-correlation functionals. We examine the structural, energetic and electronic properties of the surfaces, with a specific focus on the surface ionisation potential and band bending; the latter of which we quantify by examining the density of states as a function of depth from the system surface. We report structural and energetic results in-line with previous experimental work when we use the Hybrid-DFT method, and for the electronic structure we find inequivalent band bending for the valence and conduction bands, which results in reduced ionisation potentials and the closure of the band gap at the surface when compared to bulk systems. We also report downward bending of the conduction band for MgO that brings it below the vacuum potential, unlike previous theoretical investigations, and thus indicates an origin of the positive electron affinity found in the experiment.

  7. Ionospheric structures correlated with Anatolian surface features

    NASA Astrophysics Data System (ADS)

    Garner, T. W.; Slack, C. M.; Mehta, K.; Scholze, A.; Mahrous, A. M.

    2011-12-01

    A UHF/VHF beacon receiver located in Helwan, Egypt, frequently observes structures in ?TEC/?t measurements (where TEC is total electron count), where the F region (300 km) intercept of the radio rays crosses the steep topographic gradients associated with the Anatolian Plateau. There are three classes of structures: bumps, ripples and waves. A bump is defines as a single spatial ?TEC/?t peak with a peak-to-trough amplitude of at least 0.01 TECU/s (1 TEC unit (TECU) = 1016 electrons/m2) that is at least 1° wide in F region latitude. A ripple is a bump with smaller structures on either side of the central bump. Finally, waves have amplitudes ?0.01 TECU/s with several roughly equal peaks. These features were observed repeatedly in a number passes from 31 August to 30 November 2008. Over half of passes had either a bump (34.6%), a ripple (18.2%) or a wave (6.3%). Most of these structures occur near areas with large orographic gradients. The prevailing surface wind blows across the mountains when bumps and ripples are observed. These correlations suggest that the local ionosphere is affected by the ground topography, most likely through the orographic lifting and the associated gravity waves.

  8. 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).

  9. 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

  10. 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.

  11. Y-Shaped Amphiphilic Brushes with Switchable Micellar Surface Structures

    E-print Network

    Natelson, Douglas

    Y-Shaped Amphiphilic Brushes with Switchable Micellar Surface Structures Duangrut Julthongpiput to a functionalized silicon surface. Postgrafting hydrolysis of poly(tert-butyl acrylate) arms imparts amphiphilicity adaptive macroscopic wetting surface properties of the amphiphilic Y-shaped brushes. This surface structure

  12. AUTOMATING THE DESIGN OF A BAND-PASS SPECTRAL FILTER WITH FREQUENCY SELECTIVE SURFACES ON INHOMOGENEOUS SUBSTRATES

    E-print Network

    Sendur, Gullu Kiziltas

    , emerging applications are low band-gap materials for spectral control filters. An application relates portable generators. A need exists to protect the TPV panels from broadband radiation by employing high flexibility using dielectric periodic structures to deliver a sharper filter response. Although the basic

  13. Photoelectron holography applied to surface structural determination

    SciTech Connect

    Petersen, B.L.

    1995-05-01

    Photoemitted electron waves are used as coherent source waves for angstrom-scale holographic imaging of local atomic geometry at surfaces. Electron angular distribution patterns are collected above a sample surface and serve as a record of the interference between source wave and waves scattered from surrounding ion cores. Using a mathematical imaging integral transformation, the three-dimensional structural information is obtained directly from these collected patterns. Patterns measured with different electron kinetic energies are phase-summed for image improvement. Pt (111) surface is used as a model system. A pattern 9.6{angstrom}{sup {minus}1} (351 eV) is used to generate a full 3-D image of atom locations around an emitter with nearest neighbors within 0.l{angstrom} of the expected bulk positions. Atoms several layers beyond the nearest neighbors are also apparent. Twin-image reduction and artifact suppression is obtained by phase-summing eight patterns measured from 8.8 to 10.2{angstrom}{sup {minus}1} (295 to 396 eV). 32 were measured in 0.2{angstrom}{sup {minus}1} steps from 6.0 to 12.2{angstrom}{sup {minus}1} (137 to 567 eV) are presented here. Simple models of two-slit interference are compared with electron scattering to illuminate understanding of holographic recording of the structural information. This also shows why it sometimes fails due to destructive interferences. Simple theoretical models of electron scattering are compared to experiment to show the origin of the structural information and the differences that result from atomic scattering and from the source wave. Experimental parameters and their relation to imaging is discussed. Comparison is made to the Pt pattern measured at 351 eV using the simple theoretical model. The remaining data set is also modeled, and the eight appropriate theoretical patterns are used to regenerate the multiple-wavenumber experimental result. A clean Cu (001) surface is also measured and imaged.

  14. The Surface Structure of Ground Metal Crystals

    NASA Technical Reports Server (NTRS)

    Boas, W.; Schmid, E.

    1944-01-01

    The changes produced on metallic surfaces as a result of grinding and polishing are not as yet fully understood. Undoubtedly there is some more or less marked change in the crystal structure, at least, in the top layer. Hereby a diffusion of separated crystal particles may be involved, or, on plastic material, the formation of a layer in greatly deformed state, with possible recrystallization in certain conditions. Czochralski verified the existence of such a layer on tin micro-sections by successive observations of the texture after repeated etching; while Thomassen established, roentgenographically by means of the Debye-Scherrer method, the existence of diffused crystal fractions on the surface of ground and polished tin bars, which he had already observed after turning (on the lathe). (Thickness of this layer - 0.07 mm). Whether this layer borders direct on the undamaged base material or whether deformed intermediate layers form the transition, nothing is known. One observation ty Sachs and Shoji simply states that after the turning of an alpha-brass crystal the disturbance starting from the surface, penetrates fairly deep (approx. 1 mm) into the crystal (proof by recrystallization at 750 C).

  15. 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.

  16. 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.

  17. Touching points in the energy band structure of bilayer graphene superlattices.

    PubMed

    Pham, C Huy; Nguyen, V Lien

    2014-10-22

    The energy band structure of the bilayer graphene superlattices with zero-averaged periodic ?-function potentials are studied within the four-band continuum model. Using the transfer matrix method, the study is mainly focused on examining the touching points between adjacent minibands. For the zero-energy touching points the dispersion relation derived shows a Dirac-like double-cone shape with the group velocity which is periodic in the potential strength P with the period of ? and becomes anisotropic at relatively large P. From the finite-energy touching points we have identified those located at zero wave-number. It was shown that for these finite-energy touching points the dispersion is direction-dependent in the sense that it is linear or parabolic in the direction parallel or perpendicular to the superlattice direction, respectively. We have also calculated the density of states and the conductivity which demonstrates a manifestation of the touching points examined. PMID:25274067

  18. 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.

  19. 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.

  20. Atomic-scale structure and band-gap bowing in Cu(In,Ga)Se2

    NASA Astrophysics Data System (ADS)

    Schnohr, C. S.; Kämmer, H.; Stephan, C.; Schorr, S.; Steinbach, T.; Rensberg, J.

    2012-06-01

    Mixed systems such as the Cu(In,Ga)Se2 chalcopyrite semiconductor consist of different local atomic arrangements, that is, of different combinations of first-nearest-neighbor cations surrounding the Se anions. The anion position of Cu-III-VI2 compounds is predicted to strongly influence the material band gap. We therefore used extended x-ray absorption fine structure spectroscopy to study the atomic-scale structure of Cu(In,Ga)Se2 as a function of composition. Based on these results, the anion position was modeled for all first-nearest-neighbor configurations using a valence force-field approach. We show that the atomic-scale structure strongly depends on the kind of first-nearest-neighbor atoms. Structural relaxation of the anion occurs with respect to both (i) Cu and group III atoms and (ii) In and Ga atoms. In both cases, the average anion displacement exhibits a nonlinear behavior with changing composition and thus results in two separate but significant contributions to the band gap bowing observed in Cu(In,Ga)Se2.

  1. Surface and electronic structure of epitaxial PtLuSb (001) thin films

    SciTech Connect

    Patel, Sahil J.; Kawasaki, Jason K.; Logan, John; Schultz, Brian D.; Adell, J.; Thiagarajan, B.; Mikkelsen, A.; Palmstrøm, Chris J.

    2014-05-19

    The surface and electronic structure of single crystal thin films of PtLuSb (001) grown by molecular beam epitaxy were studied. Scanning tunneling spectroscopy (STS), photoemission spectroscopy, and temperature dependent Hall measurements of PtLuSb thin films are consistent with a zero-gap semiconductor or semi-metal. STS and photoemission measurements show a decrease in density of states approaching the Fermi level for both valence and conduction bands as well as a slight shift of the Fermi level position into the valence band. Temperature dependent Hall measurements also corroborate the Fermi level position by measurement of p-type carriers.

  2. 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.

  3. Design of a lunar surface structure

    NASA Astrophysics Data System (ADS)

    Mottaghi, Sohrob

    The next step for manned exploration and settlement is a return to the Moon. In such a return, the most challenging task is the construction of structures for habitation, considering the Moon's hostile environment. Therefore the question is: What is the best way to erect habitable structures on the lunar surface? Given the cost associated with bringing material to the Moon, In-Situ Resource Utilization (ISRU) is viewed by most as the basis for a successful manned exploration and settlement of the Solar system. Along these lines, we propose an advanced concept where the use of freeform fabrication technologies by autonomous mini-robots can form the basis for habitable lunar structures. Also, locally-available magnesium is proposed as the structural material. While it is one of the most pervasive metals in the regolith, magnesium has been only suggested only briefly as a viable option in the past. Therefore, a study has been conducted on magnesium and its alloys, taking into account the availability of the alloying elements on the Moon. An igloo-shaped magnesium structure, covered by sandbags of regolith shielding and supported on a sintered regolith foundation, is considered as a potential design of a lunar base, as well as the test bed for the proposed vision. Three studies are carried out: First a static analysis is conducted which proves the feasibility of the proposed material and method. Second, a thermal analysis is carried out to study the effect of the regolith shielding as well as the sensitivity of such designs to measurement uncertainties of regolith and sintered thermal properties. The lunar thermal environment is modeled for a potential site at 88º latitude in the lunar South Pole Region. Our analysis shows that the uncertainties are in an acceptable range where a three-meter thick shield is considered. Also, the required capacity of a thermal rejection system is estimated, choosing the thermal loads to be those of the Space Station modules. In the third study, a seismic model based on best available data has been developed and applied to our typical structure to assess the vulnerability of designs that ignore seismicity. Using random vibration and modal superposition methods, the structural response to a lunar seismic event of 7 Richter magnitude indicates that the seismic risk is very low. However, it must be considered for certain types of structural designs.

  4. Structure, stability, and electronic properties of the i -AlPdMn quasicrystalline surface

    NASA Astrophysics Data System (ADS)

    Kraj?í, M.; Hafner, J.

    2005-02-01

    The structure, stability, and electronic properties of a fivefold surface of an icosahedral (i) Al-Pd-Mn alloy have been investigated using ab initio density-functional methods. Structural models for a series of rational approximants to the quasicrystalline structure of bulk i -AlPdMn have been constructed using the cut-and-projection technique with triacontahedral acceptance domains in the six-dimensional hyperspace according to the Katz-Gratias-Boudard model. This leads to a real-space structure describable in terms of interpenetrating Mackay and Bergman clusters. A fivefold surface has been prepared by cleaving the bulk structure along a plane perpendicular to a fivefold axis. The position of the cleavage plane has been chosen such as to produce a surface layer with a high atomic density. The atomic structure of these surfaces can be described by a P1 tiling by pentagons, thin rhombi, pentagonal stars, and a “boat”—in terms of a cut-and-projection model the decagonal acceptance domain of the P1 tiling corresponds to the maximal cross section of the triacontahedra defining the three-dimensional quasicrystal. The vertices of the P1 tiling are occupied by Pd atoms surrounded by pentagonal motifs of Al atoms. For the ab initio calculations we have prepared slab models of the surface based on the 3/2 and 2/1 approximants and containing up to 357 atoms in the computational cell. The analysis of the surface charge density shows flat minima at the vertices of the P1 tiling and strong charge depletion in some of the pentagonal tiles (“surface vacancies”). Both observations are in agreement with scanning tunneling microscopy studies of these surfaces. Structural relaxations have been performed only for the 2/1 models with up to 205 atoms/cell. The calculations demonstrate that the skeleton of the P1 tiling fixed by the transition-metal atoms represents a stable surface termination, but considerable rearrangement of the Al atoms and large relaxations of the interlayer distances. The analysis of the surface electronic structure shows that the deep structure-induced pseudogap just above the Fermi level is filled up at the surface as a consequence of the structural disorder in the arrangement of the Al atoms at the surface and of a shift of both the Pd and Mn d band to lower binding energy. The d band shift at the surface is in good agreement with observations based on photoelectron and Auger spectroscopies.

  5. 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.

  6. Electronic and Structural Differences between Wurtzite and Zinc Blende InAs Nanowire Surfaces: Experiment and Theory

    PubMed Central

    2014-01-01

    We determine the detailed differences in geometry and band structure between wurtzite (Wz) and zinc blende (Zb) InAs nanowire (NW) surfaces using scanning tunneling microscopy/spectroscopy and photoemission electron microscopy. By establishing unreconstructed and defect-free surface facets for both Wz and Zb, we can reliably measure differences between valence and conduction band edges, the local vacuum levels, and geometric relaxations to the few-millielectronvolt and few-picometer levels, respectively. Surface and bulk density functional theory calculations agree well with the experimental findings and are used to interpret the results, allowing us to obtain information on both surface and bulk electronic structure. We can thus exclude several previously proposed explanations for the observed differences in conductivity of Wz-Zb NW devices. Instead, fundamental structural differences at the atomic scale and nanoscale that we observed between NW surface facets can explain the device behavior. PMID:25406069

  7. Effect of nanostructuring on the band structure and the galvanomagnetic properties in Bi1-xSbx alloys

    NASA Astrophysics Data System (ADS)

    Will, C. H.; Elm, M. T.; Klar, P. J.; Landschreiber, B.; Güne?, E.; Schlecht, S.

    2013-11-01

    Magnetotransport measurements were performed on a series of nanostructured Bi1-xSbx alloy samples with an Sb content in the range between 0% and 60%. The samples were prepared by cold pressing and annealing of crystalline Bi1-xSbx nanoparticles, which were synthesized by mechanical alloying. The incorporation of Sb changes the band structure of these nanotextured alloys as well as their transport behavior. With increasing Sb content the band gap increases and reaches a maximum band gap of 42 meV at an Sb concentration of about 14% determined from temperature dependent resistivity measurements. For even higher Sb content, the band gap decreases again. The bands and thus the band gaps are shifted with respect to bulk material due to quantum confinement effects in the nanostructures. The change of the band structure with varying Sb content strongly affects the magnetoresistance behavior as well as the magnetic field dependence of the Hall-coefficient. Using a three band model in order to describe both properties, it was possible to determine the main band parameters of the nanostructured material as a function of the Sb content.

  8. Sea Surface Salinity and Wind Retrieval Algorithm Using Combined Passive-Active L-Band Microwave Data

    NASA Technical Reports Server (NTRS)

    Yueh, Simon H.; Chaubell, Mario J.

    2011-01-01

    Aquarius is a combined passive/active L-band microwave instrument developed to map the salinity field at the surface of the ocean from space. The data will support studies of the coupling between ocean circulation, the global water cycle, and climate. The primary science objective of this mission is to monitor the seasonal and interannual variation of the large scale features of the surface salinity field in the open ocean with a spatial resolution of 150 kilometers and a retrieval accuracy of 0.2 practical salinity units globally on a monthly basis. The measurement principle is based on the response of the L-band (1.413 gigahertz) sea surface brightness temperatures (T (sub B)) to sea surface salinity. To achieve the required 0.2 practical salinity units accuracy, the impact of sea surface roughness (e.g. wind-generated ripples and waves) along with several factors on the observed brightness temperature has to be corrected to better than a few tenths of a degree Kelvin. To the end, Aquarius includes a scatterometer to help correct for this surface roughness effect.

  9. Sea surface mean square slope from Ku-band backscatter data

    NASA Technical Reports Server (NTRS)

    Jackson, F. C.; Walton, W. T.; Hines, D. E.; Walter, B. A.; Peng, C. Y.

    1992-01-01

    A surface mean-square-slope parameter analysis is conducted for 14-GHz airborne radar altimeter near-nadir, quasi-specular backscatter data, which in raw form obtained by least-squares fitting of an optical scattering model to the return waveform show an approximately linear dependence over the 7-15 m/sec wind speed range. Slope data are used to draw inferences on the structure of the high-wavenumber portion of the spectrum. A directionally-integrated model height spectrum that encompasses wind speed-dependent k exp -5/2 and classical Phillips k exp -3 power laws subranges in the range of gravity waves is supported by the data.

  10. Bonding and structure of the Si(001)(2 × 1)-Sb surface

    NASA Astrophysics Data System (ADS)

    Jenkins, S. J.; Srivastava, G. P.

    1996-05-01

    A thin layer of Sb adsorbed on to the Si(001) surface is believed to show surfactant behaviour for epitaxial growth of Ge, important for device applications. In this work we describe results of ab initio density functional calculations on the Si(001)(2 × 1)-Sb surface. The surface reconstruction is due to dimerisation of the Sb atoms in the direction perpendicular to the dimer rows of the clean Si(001) surface. Our relaxed geometry is found to be in accord with recent theoretical work and SEXAFS measurement in predicting a structure with symmetric dimers. Furthermore, we investigate the nature of the bonding and band structure of the relaxed Sb-capped surface. We find that the normal energy ordering of ungerade and gerade ? orbitals localised on the Sb dimer is reversed.

  11. Electronic structure of quasicrystalline surfaces: Effects of surface preparation and bulk structure

    SciTech Connect

    Fournee, V.; Pinhero, P. J.; Anderegg, J. W.; Lograsso, T. A.; Ross, A. R.; Canfield, P. C.; Fisher, I. R.; Thiel, P. A.

    2000-12-01

    We elucidate the nature of the surface electronic properties of quasicrystalline Al-Pd-Mn. We do this by using photoelectron and Auger electron spectroscopies, and by making a variety of comparisons -- across types of bulk samples, and across methods of surface preparation. The main conclusions are these: (i) The narrow Mn 2p{sub 3/2} core-level line observed in the icosahedral phase is a fingerprint of a suppression in the density of states (a pseudogap) at the Fermi level and is not unique to the quasicrystalline phase. It is also independent of the symmetry of the quasicrystalline surface. The Auger line shape is also affected and may be used as a fingerprint of a pseudogap. (ii) A similarly narrow Fe 2p{sub 3/2} core-level line characterizes the icosahedral Al-Cu-Fe quasicrystal, consistent with the expectation that the electronic structure is of general importance in the stabilization of icosahedral phases. (iii) In icosahedral Al-Pd-Mn, the pseudogap of the bulk is not retained up to the surface immediately after fracture, but can be restored by annealing, or by sputter annealing to sufficiently high temperatures. Assuming that the pseudogap reflects an electronic stabilization of the atomic structure, these results suggest that the heat-treated surfaces are more stable than the surface obtained by fracturing at room temperature.

  12. Structural-phase states and wear resistance of surface formed on steel by surfacing

    SciTech Connect

    Kapralov, Evgenie V.; Raykov, Sergey V.; Vaschuk, Ekaterina S.; Budovskikh, Evgenie A. Gromov, Victor E.; Ivanov, Yuri F.

    2014-11-14

    Investigations of elementary and phase structure, state of defect structure and tribological characteristics of a surfacing, formed on a low carbon low-alloy steel by a welding method were carried out. It was revealed that a surfacing, formed on a steel surface is accompanied by the multilayer formation, and increases the wear resistance of the layer surfacing as determined.

  13. Kinetics of band bending and electron affinity at GaAs(001) surface with nonequilibrium cesium overlayers

    SciTech Connect

    Zhuravlev, A. G.; Savchenko, M. L.; Paulish, A. G.; Alperovich, V. L.; Scheibler, H. E.; Jaroshevich, A. S.

    2013-12-04

    The dosage dependences of surface band bending and effective electron affinity under cesium deposition on the Ga-rich GaAs(001) surface, along with the relaxation of these electronic properties after switching off the Cs source are experimentally studied by means of modified photoreflectance spectroscopy and photoemission quantum yield spectroscopy. At small Cs coverages, below half of a monolayer, additional features in the dosage dependence and subsequent downward relaxation of the photoemission current are determined by the variations of band bending. At coverages above half of a monolayer the upward relaxation of the photocurrent is caused supposedly by the decrease of the electron affinity due to restructuring in the nonequilibrium cesium overlayer.

  14. Low Wind Speed Radar Backscatter Measurements at C- and Ku-Band Obtained During the Surface Wave Dynamics Experiment

    NASA Technical Reports Server (NTRS)

    Carson, S. C.; Carswell, J. C.; McIntosh, R. E.; Li, F. K.; Nghiem, S. V.; Lou, S. H.; Neumann, G.; McLaughlin, D. J.

    1993-01-01

    Radar backscatter measurements collected at both C- and Ku-Band during the recent SurfaceWaves Dynamics Experiment (SWADE) on 1 March 1991 show dramatic variabilities of thenormalized radar cross section (sigma degree) of the ocean surface at low wind speed. Additionally,measurements of the sigma degree in the cross wind direction fluctuated much more than the sigmadegree in the upwind direction. The C- and Ku-band data are quite similar, both exhibiting a morepronounced roll off of sigma degree with decreasing neutral stability wind than indicated bypreviously published empirical model functions. The data show extremely large azimuthalmodulations, in some cases greater than 20 dB, and show good qualitative agreement with theazimuthal modulation predicted.

  15. Effect of species structure and dielectric constant on C-band forest backscatter

    NASA Technical Reports Server (NTRS)

    Lang, R. H.; Landry, R.; Kilic, O.; Chauhan, N.; Khadr, N.; Leckie, D.

    1993-01-01

    A joint experiment between Canadian and USA research teams was conducted early in Oct. 1992 to determine the effect of species structure and dielectric variations on forest backscatter. Two stands, one red pine and one jack pine, in the Petawawa National Forestry Institute (PNFI) were utilized for the experiment. Extensive tree architecture measurements had been taken by the Canada Centre for Remote Sensing (CCRS) several months earlier by employing a Total Station surveying instrument which provides detailed information on branch structure. A second part of the experiment consisted of cutting down several trees and using dielectric probes to measure branch and needle permittivity values at both sites. The dielectric and the tree geometry data were used in the George Washington University (GWU) Vegetation Model to determine the C band backscattering coefficients of the individual stands for VV polarization. The model results show that backscatter at C band comes mainly from the needles and small branches and the upper portion of the trunks acts only as an attenuator. A discussion of variation of backscatter with specie structure and how dielectric variations in needles for both species may affect the total backscatter returns is provided.

  16. Periodic dielectric structure for production of photonic band gap and devices incorporating the same

    DOEpatents

    Ho, Kai-Ming (Ames, IA); Chan, Che-Ting (Ames, IA); Soukoulis, Costas (Ames, IA)

    1994-08-02

    A periodic dielectric structure which is capable of producing a photonic band gap and which is capable of practical construction. The periodic structure is formed of a plurality of layers, each layer being formed of a plurality of rods separated by a given spacing. The material of the rods contrasts with the material between the rods to have a refractive index contrast of at least two. The rods in each layer are arranged with their axes parallel and at a given spacing. Adjacent layers are rotated by 90.degree., such that the axes of the rods in any given layer are perpendicular to the axes in its neighbor. Alternating layers (that is, successive layers of rods having their axes parallel such as the first and third layers) are offset such that the rods of one are about at the midpoint between the rods of the other. A four-layer periocity is thus produced, and successive layers are stacked to form a three-dimensional structure which exhibits a photonic band gap. By virtue of forming the device in layers of elongate members, it is found that the device is susceptible of practical construction.

  17. Estimating tropical forest structure using LIDAR AND X-BAND INSAR

    NASA Astrophysics Data System (ADS)

    Palace, M. W.; Treuhaft, R. N.; Keller, M. M.; Sullivan, F.; Roberto dos Santos, J.; Goncalves, F. G.; Shimbo, J.; Neumann, M.; Madsen, S. N.; Hensley, S.

    2013-12-01

    Tropical forests are considered the most structurally complex of all forests and are experiencing rapid change due to anthropogenic and climatic factors. The high carbon stocks and fluxes make understanding tropical forests highly important to both regional and global studies involving ecosystems and climate. Large and remote areas in the tropics are prime targets for the use of remotely sensed data. Radar and lidar have previously been used to estimate forest structure, with an emphasis on biomass. These two remote sensing methods have the potential to yield much more information about forest structure, specifically through the use of X-band radar and waveform lidar data. We examined forest structure using both field-based and remotely sensed data in the Tapajos National Forest, Para, Brazil. We measured multiple structural parameters for about 70 plots in the field within a 25 x 15 km area that have TanDEM-X single-pass horizontally and vertically polarized radar interferometric data. High resolution airborne lidar were collected over a 22 sq km portion of the same area, within which 33 plots were co-located. Preliminary analyses suggest that X-band interferometric coherence decreases by about a factor of 2 (from 0.95 to 0.45) with increasing field-measured vertical extent (average heights of 7-25 m) and biomass (10-430 Mg/ha) for a vertical wavelength of 39 m, further suggesting, as has been observed at C-band, that interferometric synthetic aperture radar (InSAR) is substantially more sensitive to forest structure/biomass than SAR. Unlike InSAR coherence versus biomass, SAR power at X-band versus biomass shows no trend. Moreover, airborne lidar coherence at the same vertical wavenumbers as InSAR is also shown to decrease as a function of biomass, as well. Although the lidar coherence decrease is about 15% more than the InSAR, implying that lidar penetrates more than InSAR, these preliminary results suggest that X-band InSAR may be useful for structure and biomass estimation over large spatial scales not attainable with airborne lidar. In this study, we employed a set of less commonly used lidar metrics that we consider analogous to field-based measurements, such as the number of canopy maxima, measures of canopy vegetation distribution diversity and evenness (entropy), and estimates of gap fraction. We incorporated these metrics, as well as lidar coherence metrics pulled from discrete Fourier transforms of pseudowaveforms, and hypothetical stand characteristics of best-fit synthetic vegetation profiles into multiple regression analysis of forest biometric properties. Among simple and complex measures of forest structure, ranging from tree density, diameter at breast height, and various canopy geometry parameters, we found strong relationships with lidar canopy vegetation profile parameters. We suggest that the sole use of lidar height is limited in understanding biomass in a forest with little variation across the landscape and that there are many parameters that may be gleaned by lidar data that inform on forest biometric properties.

  18. 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.

  19. Electronic band structure calculations for biaxially strained Si, Ge, and III-V semiconductors

    NASA Astrophysics Data System (ADS)

    Kim, Jiseok; Fischetti, Massimo V.

    2010-07-01

    Electronic band structure and effective masses for relaxed and biaxially strained Si, Ge, III-V compound semiconductors (GaAs, GaSb, InAs, InSb, InP) and their alloys (InxGa1-xAs, InxGa1-xSb) on different interface orientations, (001), (110), and (111), are calculated using nonlocal empirical pseudopotential with spin-orbit interaction. Local and nonlocal pseudopotential parameters are obtained by fitting transport-relevant quantities, such as band gap and deformation potentials, to available experimental data. A cubic-spline interpolation is used to extend local form factors to arbitrary q and to obtain correct workfunctions. The nonlocal and spin-orbit terms are linearly interpolated between anions and cations for III-V semiconductors. The virtual crystal approximation is employed for the InxGa1-xAs and InxGa1-xSb alloys and deformation potentials are determined using linear deformation-potential theory. Band gap bowing parameters are extracted using least-square fitting for relaxed alloys and for strained InxGa1-xAs on (001), (110), and (111) InP. The dependence on biaxial strain of the electron and hole effective masses at the symmetry points ?, X, and L exhibits a continuous variation at ? and L but sudden changes appear at ? minima caused by the flatness of the dispersion along the ? line near the minimum.

  20. Band structure properties of novel BxGa1-xP alloys for silicon integration

    NASA Astrophysics Data System (ADS)

    Hossain, Nadir; Hosea, T. J. C.; Sweeney, Stephen J.; Liebich, Sven; Zimprich, Martin; Volz, Kerstin; Kunert, Bernardette; Stolz, Wolfgang

    2011-09-01

    We have grown and investigated the band-structure properties of novel III-V alloys based upon BxGa1-xP. These layers are utilized as strain-compensating layers for the lattice-matched integration of novel direct bandgap Ga(NAsP) quantum well lasers on silicon. Experimental and theoretical studies reveal the dependence of the direct and indirect band gaps for strained BxGa1-xP layers grown on silicon as a function of Boron composition from which we derive the properties of free-standing BxGa1-xP. For Boron fractions up to 6%, we find that the bowing parameter for the lowest (indirect) band gap is - 6.2 ± 0.2 eV. High crystalline quality and promising optical material properties are demonstrated and applied to monolithically integrated Ga(NAsP)/(BGa)P multi-quantum well heterostructures on (001) silicon substrates. Our results show that novel (BGa)P layers are suitable for strain compensation purposes, which pave the way towards a commercial solution for the monolithic integration of long term stable laser diodes on silicon substrates.

  1. Theoretical investigation of the band structure of picene single crystals within the GW approximation

    NASA Astrophysics Data System (ADS)

    Yanagisawa, Susumu; Morikawa, Yoshitada; Schindlmayr, Arno

    2014-01-01

    We investigate the band dispersion and related electronic properties of picene single crystals within the GW approximation for the electronic self-energy. The width of the upper highest occupied molecular orbital (HOMOu) band along the ?-Y direction, corresponding to the b crystal axis in real space along which the molecules are stacked, is determined to be 0.60 eV and thus 0.11 eV larger than the value obtained from density-functional theory. As in our recent study of rubrene using the same methodology [S. Yanagisawa, Y. Morikawa, and A. Schindlmayr, Phys. Rev. B 88, 115438 (2013)], this increase in the bandwidth is due to the strong variation of the GW self-energy correction across the Brillouin zone, which in turn reflects the increasing hybridization of the HOMOu states of neighboring picene molecules from ? to Y. In contrast, the width of the lower HOMO (HOMOl) band along ?-Y remains almost unchanged, consistent with the fact that the HOMOl(?) and HOMOl(Y) states exhibit the same degree of hybridization, so that the nodal structure of the wave functions and the matrix elements of the self-energy correction are very similar.

  2. 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.

  3. 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

  4. Maximum Theoretical Efficiency Limit of Photovoltaic Devices: Effect of Band Structure on Excited State Entropy.

    PubMed

    Osterloh, Frank E

    2014-10-01

    The Shockley-Queisser analysis provides a theoretical limit for the maximum energy conversion efficiency of single junction photovoltaic cells. But besides the semiconductor bandgap no other semiconductor properties are considered in the analysis. Here, we show that the maximum conversion efficiency is limited further by the excited state entropy of the semiconductors. The entropy loss can be estimated with the modified Sackur-Tetrode equation as a function of the curvature of the bands, the degeneracy of states near the band edges, the illumination intensity, the temperature, and the band gap. The application of the second law of thermodynamics to semiconductors provides a simple explanation for the observed high performance of group IV, III-V, and II-VI materials with strong covalent bonding and for the lower efficiency of transition metal oxides containing weakly interacting metal d orbitals. The model also predicts efficient energy conversion with quantum confined and molecular structures in the presence of a light harvesting mechanism. PMID:26278444

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

    SciTech Connect

    Kevin Jerome Sutherland

    2001-06-27

    Over the last ten years, photonic band gap (PBG) theory and technology have become an important area of research because of the numerous possible applications ranging from high-efficiency laser diodes to optical circuitry. This research concentrates on reducing the length scale in the fabrication of layered photonic band gap structures and developing procedures to improve processing consistency. Various procedures and materials have been used in the fabrication of layered PBG structures. This research focused on an economical micro transfer molding approach to create the final PBG structure. A poly dimethylsiloxane (PDMS) rubber mold was created from a silicon substrate. It was filled with epoxy and built layer-by-layer to create a 3-D epoxy structure. This structure was infiltrated with nanoparticle titania or a titania sol-gel, then fired to remove the polymer mold, leaving a monolithic ceramic inverse of the epoxy structure. The final result was a lattice of titania rolds that resembles a face-centered tetragonal structure. The original intent of this research was to miniaturize this process to a bar size small enough to create a photonic band gap for wavelengths of visible electro-magnetic radiation. The factor limiting progress was the absence of a silicon master mold of small enough dimensions. The Iowa State Microelectronics Research Center fabricated samples with periodicities of 2.5 and 1.0 microns with the existing technology, but a sample was needed on the order of 0.3 microns or less. A 0.4 micron sample was received from Sandia National Laboratory, which was made through an electron beam lithography process, but it contained several defects. The results of the work are primarily from the 2.5 and 1.0 micron samples. Most of the work focused on changing processing variables in order to optimize the infiltration procedure for the best results. Several critical parameters were identified, ranging from the ambient conditions to the specifics of the procedure. It is believed that most critical for fabrication of high quality samples is control of the temperature of the sample during and after infiltration, and the rate and amount of time spent applying epoxy to the PDMS.

  6. Energy band structure of CuInS2 and optical spectra of CuInS2 nanocrystals

    NASA Astrophysics Data System (ADS)

    Shabaev, A.; Mehl, M. J.; Efros, Al. L.

    2015-07-01

    Using first principles calculations we describe the energy band structure of bulk CuInS2. The energy band parameters for the multiband effective mass approximation that describes the band edges of this semiconductor are obtained by fitting them to the first principles spectra. Within the multiband effective mass approximation we develop a theoretical description for the structure of band-edge levels and optical properties of the CuInS2 nanocrystals. For the nanocrystals of spherical shape, the optical transitions are weakly allowed between the electron and hole ground states due to the tetragonal symmetry of the crystal lattice, resulting in a large Stokes shift of photoluminescence up to 300 meV in the smallest nanocrystals. This theory of the band-edge optical transitions in CuInS2 NCs can be applied to spherical NCs made of other chalcopyrite compounds.

  7. Probing the band structure of LaTe2 using angle resolvedphotoemission spectroscopy

    SciTech Connect

    Garcia, Daniel R.; Zhou, Shuyun Y.; Gweon, Gey-Hong; Jung, M.H.; Kwon, Y.S.; Lanzara, Alessandra

    2006-11-01

    With the current interest in the rare-earth tellurides ashigh temperature charge density wave materials, a greater understandingof the physics of these systems is needed, particularly in the case ofthe ditellurides. We report a detailed study of the band structure ofLaTe_2 in the charge density wave state using high-resolution angleresolved photoemission spectroscopy (ARPES). From thiswork we hope toprovide insights into the successes and weaknesses of past theoreticalstudy as well as helping to clear up prior ambiguities by providing anexperimental basis for future work inthe tellurides.

  8. Complex band structure under plane-wave nonlocal pseudopotential Hamiltonian of metallic wires and electrodes

    SciTech Connect

    Yang, Chao

    2009-07-17

    We present a practical approach to calculate the complex band structure of an electrode for quantum transport calculations. This method is designed for plane wave based Hamiltonian with nonlocal pseudopotentials and the auxiliary periodic boundary condition transport calculation approach. Currently there is no direct method to calculate all the evanescent states for a given energy for systems with nonlocal pseudopotentials. On the other hand, in the auxiliary periodic boundary condition transport calculation, there is no need for all the evanescent states at a given energy. The current method fills this niche. The method has been used to study copper and gold nanowires and bulk electrodes.

  9. Staggering of the B(M1) value as a fingerprint of specific chiral bands structure

    E-print Network

    Ernest Grodner

    2011-01-31

    Nuclear chirality has been intensively studdied for the last several years in the context of experimental as well as theoretical approach. Characteristic gamma selection rules have been predicted for the strong chiral symmetry breaking limit that has been observed in Cs isotopes. The presented analysis shows that the gamma selection rules cannot be attributed only to chiral symmetry breaking. The selection rules relate to structural composition of the chiral rotational bands, i.e. to odd particle configuration and the deformation of the core.

  10. First principles electronic band structure and phonon dispersion curves for zinc blend beryllium chalcogenide

    SciTech Connect

    Dabhi, Shweta Mankad, Venu Jha, Prafulla K.

    2014-04-24

    A detailed theoretical study of structural, electronic and Vibrational properties of BeX compound is presented by performing ab-initio calculations based on density-functional theory using the Espresso package. The calculated value of lattice constant and bulk modulus are compared with the available experimental and other theoretical data and agree reasonably well. BeX (X = S,Se,Te) compounds in the ZB phase are indirect wide band gap semiconductors with an ionic contribution. The phonon dispersion curves are represented which shows that these compounds are dynamically stable in ZB phase.

  11. Structure, electronics, and interaction of hydrogen and oxygen on diamond surfaces

    NASA Astrophysics Data System (ADS)

    Sque, S. J.; Jones, R.; Briddon, P. R.

    2006-02-01

    The atomic geometry and electronic structure of diamond surfaces, both clean and with various hydrogen and oxygen terminations, have been studied using ab initio density-functional-theory calculations. Calculated ionization potentials and estimated electron affinities are presented for the different surfaces, while bulk- and surface-related effects are distinguished. Interaction between hydrogen and oxygen on the technologically important (001) surface is also examined. Structural energies indicate that a hydroxylated (001) surface is favored over an oxygenated surface plus gas-phase hydrogen molecules, although an overestimate in the strength of hydrogen bonding on the ?OH -terminated surface might lend it an artificially high stability. A surface terminated with a combination of ?O? , ?H , and ?OH groups has a structural energy part-way between the extremes of a fully oxygenated and a fully hydroxylated surface. Electronically, while the hydrogenated and oxygenated surfaces respectively show their expected negative and positive (bulk) electron affinities, the ?OH -terminated surface and the surface with the aforementioned combination of groups both show small negative electron affinities. However, all surfaces except the combination surface have introduced unoccupied states into the bandgap, which correspond to positive surface electron affinity and could act as traps for electrons that would otherwise escape the material; the implications for band bending are discussed. As expected, the hydrogenated surfaces show by far the lowest ionization potentials, and are therefore the most suitable for exploiting the transfer doping effect, although ?OH -terminated surfaces might be successfully transfer doped if an adsorbate molecule of very high electron affinity were to be used.

  12. Investigation on wide-band scattering of a 2-D target above 1-D randomly rough surface by FDTD method.

    PubMed

    Li, Juan; Guo, Li-Xin; Jiao, Yong-Chang; Li, Ke

    2011-01-17

    Finite-difference time-domain (FDTD) algorithm with a pulse wave excitation is used to investigate the wide-band composite scattering from a two-dimensional(2-D) infinitely long target with arbitrary cross section located above a one-dimensional(1-D) randomly rough surface. The FDTD calculation is performed with a pulse wave incidence, and the 2-D representative time-domain scattered field in the far zone is obtained directly by extrapolating the currently calculated data on the output boundary. Then the 2-D wide-band scattering result is acquired by transforming the representative time-domain field to the frequency domain with a Fourier transform. Taking the composite scattering of an infinitely long cylinder above rough surface as an example, the wide-band response in the far zone by FDTD with the pulsed excitation is computed and it shows a good agreement with the numerical result by FDTD with the sinusoidal illumination. Finally, the normalized radar cross section (NRCS) from a 2-D target above 1-D rough surface versus the incident frequency, and the representative scattered fields in the far zone versus the time are analyzed in detail. PMID:21263648

  13. Fine-structural aspects of bromodeoxyuridine incorporation in sister chromatid differentiation and replication banding.

    PubMed

    Jack, E M; Harrison, C J; White, G R; Ockey, C H; Allen, T D

    1989-10-01

    The structure of harlequin-stained chromosomes following substitution with low levels of 5-bromodeoxyuridine (BrdUrd) over two cell cycles and high levels over the last part of one cycle (replication banding) was studied in Chinese hamster ovary (CHO) cells. By using correlative light (LM) and scanning electron microscopy (SEM), it was shown that the effects of both the ultraviolet light (u.v.) and hot SSC treatment steps of the harlequin staining procedure were necessary to obtain sister-chromatid differentiation (SCD) or replication banding. u.v. treatment alone resulted in dark Giemsa staining of both chromatids with SEM morphology of short compact protuberances and an overall flattened smooth appearance in both the unsubstituted and BrdUrd-substituted chromatids, a morphology essentially similar to that of untreated chromosomes. SSC alone on the other hand resulted in dark-staining chromatids with an SEM morphology of raised, loosely packed loops of fibres in both types of chromatids. u.v. and SSC treatment together resulted in differentiation, with dark-staining unifilarly (TB) chromatids in the LM corresponding to raised loosely packed loops in the SEM and pale bifilarly (BB) chromatids corresponding to the smooth compact flattened SEM appearance. Where the BrdUrd-substituted strand became the template (BT), or when the nascent strand TB contained high levels of BrdUrd substitution in replication banding, the chromatid stained pale and showed the compact smooth appearance in the SEM. The Giemsa staining ability and ultrastructural morphology of harlequin staining is discussed with respect to putative DNA loss and also in terms of preferential protein-protein, protein-DNA cross-linkage in BrdUrd-containing DNA. These changes are also compared with the ultrastructural morphology observed after other banding methods, where deterioration of protein and DNA-protein interaction resulting in aggregation of chromatin fibres appears to be the major mechanism. PMID:2621225

  14. Effects of polar and nonpolar on band structures in ultrathin ZnO/GaN type-II superlattices

    NASA Astrophysics Data System (ADS)

    Zhang, Heng; Xia, Congxin; Tan, Xiaoming; Wang, Tianxing; Wei, Shuyi

    2015-11-01

    The electronic structures of polar and nonpolar wurtzite (WZ) ZnO/GaN ultrathin superlattices (USLs) are investigated by using first-principles methods. The built-in electric fields and band gap become insensitive to GaN barrier layer in the polar WZ ZnO/GaN USLs when GaN layer is larger than 10 monolayers. However, the band gaps show less dependence on GaN layer in the nonpolar case. Moreover, the polar and nonpolar WZ ZnO/GaN USLs possesses the characteristics of the direct band structures and type-II heterostructures.

  15. AVHRR Surface Temperature and Narrow-Band Albedo Comparison with Ground Measurements for the Greenland Ice Sheet

    NASA Technical Reports Server (NTRS)

    Haefliger, M.; Steffen, K.; Fowler, C.

    1993-01-01

    An ice-surface temperature retrieval algorithm for the Greenland ice sheet was developed using NOAA 11 thermal radiances from channels 4 and 5. Temperature, pressure and humidity profiles, cloud observations and skin temperatures from the Swiss Federal Institute of Technology (ETH) camp, located at the equilibrium line altitude at 49 deg17 min W, 69 deg 34 min N, were used in the LOWTRAN 7 model. Through a statistical analysis of daily clear sky profiles, the coefficients that correct for the atmospheric effects were determined for the ETH-Camp field season (May to August). Surface temperatures retrieved by this method were then compared against the in situ observations with a maximum difference of 0.6 K. The NOAA 11 narrow-band planetary albedo values for channels 1 and 2 were calculated using pre-launch calibration coefficients. Scattering and absorption by the atmosphere were modelled with LOWTRAN 7. Then, narrow-band albedo values for the AVHRR visible and near infrared channels were compared with in situ high resolution spectral reflectance measurements. In the visible band (580-680 nm), AVHRR-derived narrow-band albedo and the in situ measurements corrected with radiative transfer model LOWTRAN 7 showed a difference of less than 2%. For the near infrared channel (725-1100 nm) the difference between the measured and modelled narrow-band albedo was 14%. These discrepancies could be either the result of inaccurate aerosol scattering modelling (lack of the in situ observation), or the result of sensor drift due to degradation.

  16. Revealing the surface origin of green band emission from ZnO nanostructures by plasma immersion ion implantation induced quenching

    SciTech Connect

    Yang, Y.; Sun, X. W.; Tay, B. K.; Cao, Peter H. T.; Wang, J. X.; Zhang, X. H.

    2008-03-15

    Surface defect passivation for ZnO nanocombs (NCBs), random nanowires (RNWs), and aligned nanowires (ANWs) was performed through a metal plasma immersion ion implantation with low bias voltages ranging from 0 to 10 kV, where Ni was used as the modification ion. The depth of surface-originated green band (GB) emission is thus probed, revealing the surface origin of the GB. It is also found that the GB is closely related to oxygen gas content during growth of the nanostructures. The GB origin of NCBs and RNWs grown with higher oxygen content is shallower ({approx}0.5 nm), which can be completely quenched with no bias applied. However, the GB origin of ANWs grown at lower oxygen content is much deeper ({approx}7 nm) with a complete quenching bias of 10 kV. Quenching of the GB can be attributed to passivation of the surface hole or electron trapping sites (oxygen vacancies) by Ni ions.

  17. Fabrication of a flexible UV band-pass filter using surface plasmon metal-polymer nanocomposite films for promising laser applications.

    PubMed

    Kedawat, Garima; Gupta, Bipin Kumar; Kumar, Pawan; Dwivedi, Jaya; Kumar, Arun; Agrawal, Narendra Kumar; Kumar, Sampath Satheesh; Vijay, Yogesh K

    2014-06-11

    We introduce a strategy for the fabrication of silver/polycarbonate (Ag/PC) nanocomposite flexible films of (20 ± 0.01) ?m thickness with different filling factor of surface plasmon metal using customized solution cast-thermal evaporation method. Structural characterizations confirmed the good crystallinity with cubic phase of Ag nanoparticles in PC films. Moreover, the microstructural evolutions of nanocomposite films are investigated by transmission electron microscopy, which indicates that the metal fraction is in the form of fractals. Additionally, the surface plasmonic behavior of nanocomposite films has been explored in detail to examine the distribution of Ag nanoparticles in PC film by spectroscopic technique. Furthermore, the obtained transmittance spectral features of this nanocomposite film are suitable for the applications of band-pass filter at 320 nm UV range, which is highly desirable for a HeCd laser. PMID:24761967

  18. Support loss suppression in micromechanical resonators by the use of phononic band gap structures

    NASA Astrophysics Data System (ADS)

    Mohammadi, Saeed; Eftekhar, Ali A.; Khelif, Abdelkrim; Adibi, Ali

    2010-02-01

    By modifying the supporting structures of a conventional piezoelectric-on-substrate micromechanical (MM) resonator using phononic crystal (PC) slab structures with complete phononic band gaps (PBGs) the support loss in micromechanical resonators is suppressed and the quality factor of the fundamental extensional resonant mode is improved from approximately 1,200 to approximately 6,000. The conventional MM resonator and the PC resonators are both fabricated on the same chip and using the same fabrication process. The PC is made by etching a hexagonal (honeycomb) array of holes in a 15?m-thick slab of silicon. The radii of the holes are approximately 6.4?m and the spacing between the centers of the nearest holes is 15 ?m. The conventional MM resonator is made of a rectangular structure with dimensions of 600 ?m by 60 ?m and the fundamental flexural and extensional modes of the structure in the smaller dimension are excited. In the third dimension, all the structures are made of a 15 ?m silicon (Si) slab, a 100 nm layer of gold, a ~1 ?m layer of zinc oxide, and a patterned 100 nm layer of aluminum electrodes stacked on top of each other to serve as the resonant mass and the transduction medium. The significant improvement obtained using the PC resonator structures makes them excellent candidates for next generation of MM resonators for wireless communication and sensing applications despite some minor remaining challenges.

  19. A study of the band structures of elastic wave propagating in piezoelectric/piezomagnetic layered periodic structures

    NASA Astrophysics Data System (ADS)

    Pang, Yu; Wang, Yue-Sheng; Liu, Jin-Xi; Fang, Dai-Ning

    2010-05-01

    This paper is concerned with wave propagation and localization in piezoelectric (PE) and piezomagnetic (PM) layered periodic structures. Both normal and oblique propagation of waves are considered. The materials are assumed to be transversely isotropic. Wave behaviors are analyzed by calculating the dispersion curves, localization factors and response spectra using the transfer matrix and/or the stiffness matrix methods. The results show that all these quantities can be used to characterize the band structures. Frequency passbands and band gaps exist in PE/PM periodic layered structures. The width of the gaps is determined by the differences between material constants of each constituent in PE/PM composites. The bigger the difference is, the wider the gap is. Most energy is carried by the transmitted waves which are of the same mode as the incident wave. However, the transmission coefficients of the quasi-shear or quasi-pressure waves arising from wave mode conversion may be relatively large at some particular frequencies in some passbands. Compared to coupled transmitted magnetoacoustic and electroacoustic waves, the transmission coefficients of electric potential and magnetic potential waves are a little bigger. This study is useful for the possible applications of PE/PM materials in the fabrication of high frequency acoustic resonance devices.

  20. Fabrication of a GHz band surface acoustic wave filter by UV-nanoimprint with an HSQ stamp

    NASA Astrophysics Data System (ADS)

    Chen, Nian-Huei; Huang, Ju-Chun; Wang, Chiu-Yen; Huang, Fon-Shan

    2011-04-01

    A GHz band surface acoustic wave (SAW) filter was fabricated by UV-nanoimprint lithography (UV-NIL). The key techniques to produce a SAW filter include stamp and interdigital transducer (IDT) fabrication. For the stamp, high-aspect-ratio (AR) hydrogen silsesquioxane (HSQ)/ITO/glass stamps were first exposed by low e-beam dose. Adequate post-exposure bake, tetramethylammoniumhydroxide concentration, and etch time were utilized to pattern the HSQ stamps with a perfect vertical sidewall. HSQ/ITO/glass IDT stamps with widths in the range 46-168 nm were fabricated. The stamps were then cured with a novel step-like heating cycle as hard-bake. The modified HSQ stamps have a high hardness of 19 GPa. The HSQ/ITO/glass layered structure shows 80% transmittance at 365 nm UV light. Afterward, the IDT patterns were transferred on UV-curable resist/lithium niobate (LiNbO3) by UV-NIL at room temperature and low pressure. After removing the residual layer, Al/Ti films were deposited on UV-curable resist/LiNbO3. IDTs with widths in the range 62-219 nm and thickness of 20 nm could be obtained by following a lift-off process. The center frequency of 4.3-8.6 GHz and insertion loss of -14.1 to -61.7 dB of the SAW filters were measured by a network analyzer HP 8510C. The reactive ion etching step for residual layer elimination has significant implication for the electrical characterization of a SAW filter. The thorough removal of the residual layer not only ensures a clean interface between IDTs and LiNbO3 for SAW filters with minimum insertion loss, but also keeps intact IDT patterns for small center frequency shift.

  1. Bulk and surface electronic structure of Li{sub 2}O

    SciTech Connect

    Liu, L.; Henrich, V.E.; Ellis, W.P.; Shindo, I.

    1996-07-01

    We have used photoemission and electron-energy-loss spectroscopies to determine the surface and bulk electronic structure of a single-crystal sample of the alkali-metal oxide Li{sub 2}O. The predominately O 2{ital p} valence band exhibits two main features in the photoemission spectrum, whose relative widths are consistent with results of an {ital ab} {ital initio} Hartree-Fock calculation of the bulk electronic structure. However, changes in the intensity of the two features as a function of the exciting photon energy are large and not understood. Energy-loss spectra show the presence of a strong surface exciton in the bulk band gap of Li{sub 2}O; such excitonic surface states do not exist for the alkali halides. Its energy is about 2 eV less than the bulk band gap, similar to the surface excitonic shifts that have been observed in the alkaline-earth oxides. {copyright} {ital 1996 The American Physical Society.}

  2. Comprehensive comparison and experimental validation of band-structure calculation methods in III-V semiconductor quantum wells

    NASA Astrophysics Data System (ADS)

    Zerveas, George; Caruso, Enrico; Baccarani, Giorgio; Czornomaz, Lukas; Daix, Nicolas; Esseni, David; Gnani, Elena; Gnudi, Antonio; Grassi, Roberto; Luisier, Mathieu; Markussen, Troels; Osgnach, Patrik; Palestri, Pierpaolo; Schenk, Andreas; Selmi, Luca; Sousa, Marilyne; Stokbro, Kurt; Visciarelli, Michele

    2016-01-01

    We present and thoroughly compare band-structures computed with density functional theory, tight-binding, k · p and non-parabolic effective mass models. Parameter sets for the non-parabolic ?, the L and X valleys and intervalley bandgaps are extracted for bulk InAs, GaAs and InGaAs. We then consider quantum-wells with thickness ranging from 3 nm to 10 nm and the bandgap dependence on film thickness is compared with experiments for In0.53Ga0.47 As quantum-wells. The impact of the band-structure on the drain current of nanoscale MOSFETs is simulated with ballistic transport models, the results provide a rigorous assessment of III-V semiconductor band structure calculation methods and calibrated band parameters for device simulations.

  3. Band structure, elementary excitations, and stability of a Bose-Einstein condensate in a periodic potential

    SciTech Connect

    Machholm, M.; Pethick, C.J.; Smith, H.

    2003-05-01

    We investigate the band structure of a Bose-Einstein condensate in a one-dimensional periodic potential by calculating stationary solutions of the Gross-Pitaevskii equation, which have the form of Bloch waves. We demonstrate that loops ('swallow tails') in the band structure occur both at the Brillouin zone boundary and at the center of the zone, and they are therefore a generic feature. A physical interpretation of the swallow tails in terms of periodic solitons is given. The linear stability of the solutions is investigated as a function of the strength of the mean-field interaction, the magnitude of the periodic potential, and the wave vector of the condensate. The regions of energetic and dynamical stability are identified by considering the behavior of the Gross-Pitaevskii energy functional for small deviations of the condensate wave function from a stationary state. It is also shown how for long-wavelength disturbances the stability criteria may be obtained within a hydrodynamic approach.

  4. Band structure and transmission characteristics of complex phononic crystals by multi-level substructure scheme

    NASA Astrophysics Data System (ADS)

    Yin, J.; Zhang, S.; Zhang, H. W.; Chen, B. S.

    2015-10-01

    A fast scheme based on the multi-level substructure technique is proposed for the band structure and transmission characteristics calculation of phononic crystals uniformly. The main idea is that finite element models of phononic crystals are divided into several domains by a special multi-level decomposition. For the band structure calculation, the upscaling calculation is employed to condense the internal stiffness matrix of the unit cell into the Bloch boundary. Due to the internal stiffness matrix does not change along with reduced wave vectors in an iteration process, the scheme can reduce the computational scale and improve the efficiency greatly, meanwhile it does not introduce approximation into the traditional finite element model. For the transmission characteristics calculation, the unit cell of the phononic crystal is periodic which is taken as a substructure with the same coefficient matrix. Moreover, the downscaling calculation of internal displacements can be selected flexibly. Some closely watched examples of the three-dimensional locally resonant, defect state of Lamb wave and Bragg waveguide are analyzed. Numerical results indicate that the proposed scheme is efficient and accurate, which may widely be applicable and suitable for complex phononic crystal problems, and provides a reliable numerical tool to optimize and design crystal devices.

  5. Fratricide-preventing friend identification tag based on photonic band structure coding

    NASA Astrophysics Data System (ADS)

    Eliyahu, Danny; Sadovnik, Lev S.; Manasson, Vladimir A.

    2000-07-01

    A new friend foe identification tag based on photonic band structure (PBS) is presented. The tag utilizes frequency-coded radar signal return. Targets that include the passive tag responds selectively to slightly different frequencies generated by interrogating MMW radar. It is possible to use in- and out-of-band gap frequencies or defect modes of the PBS in order to obtain frequency dependent radar waves reflections. This tag can be made in the form of patch attachable such as plate or corner reflectors, to be worn by an individual marine, or to be integrated into the platform camouflage. Ultimately, it can be incorporated as smart skin or a ground or airborne vehicle. The proposed tag takes full advantage of existing sensors for interrogation (minimal chances required), it is lightweight and small in dimensions, it operates in degraded environments, it has no impact on platform vulnerability, it has low susceptibility to spoofing and mimicking (code of the day) and it has low susceptibility to active jamming. We demonstrated the operation of the tag using multi-layer dielectric (Duroid) having periodic structure of metal on top of each of the layers (metal strips in this case). The experimental results are consistent with numerical simulation. The device can be combined with temporal coding to increase target detection and identification resolution.

  6. Silicon carbide embedded in carbon nanofibres: structure and band gap determination.

    PubMed

    Minella, Anja Bonatto; Pohl, Darius; Täschner, Christine; Erni, Rolf; Ummethala, Raghu; Rümmeli, Mark H; Schultz, Ludwig; Rellinghaus, Bernd

    2014-11-28

    Materials drastically alter their electronic properties when being reduced to the nanoscale due to quantum effects. Concerning semiconductors, the band gap is expected to broaden as a result of the quantum confinement. In this study we report on the successful synthesis of wide bandgap SiC nanowires (with great potential for applications) and the local determination of their band gap. Their value was found to be higher with respect to bulk SiC. The nanowires are grown as a heterostructure, i.e. encapsulated in carbon nanofibres via dc hot-filament Plasma-Enhanced Chemical Vapour Deposition on the Si/SiO2 substrate. The structure of the as-produced carbon nanofibres was characterized by means of aberration-corrected high-resolution transmission electron microscopy. Two different pure SiC polytypes, namely the 3C (cubic) and the 6H (hexagonal) as well as distorted structures are observed. The SiC nanowires have diameters in the range of 10-15 nm and lengths of several hundred nanometers. The formation of the SiC is a result of the substrate etching during the growth of the CNFs and a subsequent simultaneous diffusion of not only carbon, but also silicon through the catalyst particle. PMID:25307877

  7. Effect of point defects on band-gap properties in diamond structure photonic crystals

    NASA Astrophysics Data System (ADS)

    Dai, Wei; Wang, Hong; Chen, Shibin; Li, Dichen; Zhou, Di

    2012-01-01

    Three dimensional diamond structure photonic crystals (PCs) with point defects fabricated by rapid prototyping and gel casting with alumina were studied at microwave frequencies. The sphere, ellipsoid, and cylinder point defects were introduced in the PCs first and it was found that the localization of electromagnetic wave is the strongest in ellipsoid point defect photonic crystals. Then, the size change of the ellipsoid point defect was studied to find out the optimal size. When the size of the ellipsoid point defect is close to one unit cell, the Q factor, which represents the localization intensity of the electromagnetic wave, will be the biggest. Based on the optimal size of ellipsoid point defect, more ellipsoid point defects were introduced into one diamond PC structure. Three point defect resonant modes were found in a photonic crystal with three ellipsoid point defects and the distance between each defect was twice of the lattice constant. A guided band was observed in the forbidden band gap in a photonic crystal with five ellipsoid point defects, in which the distance between each defect was of one lattice constant.

  8. Structure of the K{sup {pi}} = 4{sup +} bands in {sup 186,188}Os

    SciTech Connect

    Phillips, A. A.; Garrett, P. E.; Demand, G. A.; Finlay, P.; Green, K. L.; Leach, K. G.; Schumaker, M. A.; Svensson, C. E.; Wong, J.; Bettermann, L.; Braun, N.; Burke, D. G.; Faestermann, T.; Kruecken, R.; Wirth, H.-F.; Hertenberger, R.

    2009-01-28

    The structures of {sub 3}{sup +} states in Os have been debated over several decades. Based on measured B(E2) values they were interpreted in {sup 186-192}Os as K{sup {pi}} = 4{sup +} two-phonon vibrations, whereas inelastic scattering, and (t,{alpha}) work imply a hexadecapole phonon description. To clarify the nature of these K{sup {pi}} = 4{sup +} bands in {sup 186,188}Os, we performed a ({sup 3}He,d) reaction on {sup 185,187}Re targets using 30 MeV {sup 3}He beams and a Q3D spectrograph. Absolute cross sections were obtained for excited states up to 3 MeV at 9 angles from 5 deg. to 50 deg. Results indicate a significant (5/2){sup +}[402]{sub {pi}}+(3/2){sup +}[402]{sub {pi}} component in agreement with quasiparticle phonon model predictions for a single hexadecapole phonon structure.

  9. The valence band structure of Ag{sub x}Rh{sub 1–x} alloy nanoparticles

    SciTech Connect

    Yang, Anli; Sakata, Osami; Kusada, Kohei; Kobayashi, Hirokazu; Yayama, Tomoe; Ishimoto, Takayoshi; Yoshikawa, Hideki; Koyama, Michihisa; and others

    2014-10-13

    The valence band (VB) structures of face-centered-cubic Ag-Rh alloy nanoparticles (NPs), which are known to have excellent hydrogen-storage properties, were investigated using bulk-sensitive hard x-ray photoelectron spectroscopy. The observed VB spectra profiles of the Ag-Rh alloy NPs do not resemble simple linear combinations of the VB spectra of Ag and Rh NPs. The observed VB hybridization was qualitatively reproduced via a first-principles calculation. The electronic structure of the Ag{sub 0.5}Rh{sub 0.5} alloy NPs near the Fermi edge was strikingly similar to that of Pd NPs, whose superior hydrogen-storage properties are well known.

  10. Femtosecond laser-induced periodic surface structure formation on tungsten

    SciTech Connect

    Vorobyev, A. Y.; Guo Chunlei

    2008-09-15

    In this paper, we demonstrate the generation of periodic surface structures on a technologically important material, tungsten, at both 400 and 800 nm, despite that the table values of dielectric constants for tungsten at these two wavelengths suggest the absence of surface plasmons, a wave necessary for forming periodic structures on metals. Furthermore, we find that the structure periods formed on tungsten are significantly less than the laser wavelengths. We believe that the dielectric constants of tungsten change significantly due to intense laser pulse heating and surface structuring and roughening at nanometer scales, permitting surface plasmon excitation and periodic structure formation.

  11. C-Band Airport Surface Communications System Engineering-Initial High-Level Safety Risk Assessment and Mitigation

    NASA Technical Reports Server (NTRS)

    Zelkin, Natalie; Henriksen, Stephen

    2011-01-01

    This document is being provided as part of ITT's NASA Glenn Research Center Aerospace Communication Systems Technical Support (ACSTS) contract: "New ATM Requirements--Future Communications, C-Band and L-Band Communications Standard Development." ITT has completed a safety hazard analysis providing a preliminary safety assessment for the proposed C-band (5091- to 5150-MHz) airport surface communication system. The assessment was performed following the guidelines outlined in the Federal Aviation Administration Safety Risk Management Guidance for System Acquisitions document. The safety analysis did not identify any hazards with an unacceptable risk, though a number of hazards with a medium risk were documented. This effort represents an initial high-level safety hazard analysis and notes the triggers for risk reassessment. A detailed safety hazards analysis is recommended as a follow-on activity to assess particular components of the C-band communication system after the profile is finalized and system rollout timing is determined. A security risk assessment has been performed by NASA as a parallel activity. While safety analysis is concerned with a prevention of accidental errors and failures, the security threat analysis focuses on deliberate attacks. Both processes identify the events that affect operation of the system; and from a safety perspective the security threats may present safety risks.

  12. Enceladus Jet Orientations: Effects of Surface Structure

    NASA Astrophysics Data System (ADS)

    Helfenstein, P.; Porco, C.; DiNino, D.

    2013-12-01

    Jetting activity across the South Polar Terrain (SPT) of Enceladus is now known to erupt directly from tiger-stripe rifts and associated fracture systems. However, details of the vent conduit geometry are hidden below the icy surface. The three-dimensional orientations of the erupting jets may provide important clues. Porco et al. (2013, Lunar Planet. Sci. Conf. 44th, p.1775) surveyed jet locations and orientations as imaged at high resolution (< 1.3 km/pixel) by Cassini ISS from 2005 through May 2012. Ninety-eight (98) jets were identified either on the main trunks or branches of the 4 tiger-stripes. The azimuth angles of the jets are seen to vary across the SPT. Here, we use histogram analysis of the survey data to test if the jet azimuths are influenced by their placement relative to surface morphology and tectonic structures. Azimuths are measured positive counterclockwise with zero pointing along the fracture in the direction of the sub-Saturn hemisphere, and rosette histograms were binned in 30° increments. Overall, the jet azimuths are not random and only about 11% of them are co-aligned with the tiger stripe valley. There are preferred diagonal orientations between 105°-165° and again between 255°-345°. These trends are dominant along the Damascus and Baghdad tiger-stripes where more than half of the jets are found. Histograms for Cairo and Alexandria show less-distinct trends, fewer jets being measured there, but combining data from both suggests a different pattern of preferred orientations; from 45°-75° and 265°-280°. Many possible factors could affect the orientations of jets, for example, the conduit shape, the presence of obstacles like narrow medial ridges called 'shark-fins' along tiger-stripe valleys, the possibility that jets may breach the surface at some point other than the center of a tiger-stripe, and the presence of structural fabrics or mechanical weaknesses, such as patterns of cross-cutting fractures. The dominance of diagonally crossing azimuths for Damascus and Baghdad suggest that cross-cutting fractures may significantly control jet orientations. At the 100 m/pixel scale of our Enceladus basemap at least 24% of the jets have azimuth orientations that point along or parallel to nearby fractures or fabrics of parallel fractures that approach or intersect the tiger stripe. Structural control of jet orientations by local tectonism is especially suggested by a systematic pattern of jet orientations at the distal end of Damascus Sulcus where it bifurcates into a northern and a southern branch, respectively. The five most distal jets along the northern branch are nearly parallel and point northward while the three most distal jets along the southern branch are also nearly parallel, but they point in the opposite direction. Additional work is needed to show the extent to which jet orientations may be affected at smaller scales by quasi-parallel systems of cross-cutting gossamer fractures or by curving axial discontinuities along the tiger stripes (cf. Helfenstein et al. 2011, http://encfg.ciclops.org/reg/uploads/20110425220109_helfenstein_enceladus_workshop_2011.pdf).

  13. Influence of the sequence on the ab initio band structures of single and double stranded DNA models

    NASA Astrophysics Data System (ADS)

    Bogár, Ferenc; Bende, Attila; Ladik, János

    2014-06-01

    The solid state physical approach is widely used for the characterization of electronic properties of DNA. In the simplest case the helical symmetry is explicitly utilized with a repeat unit containing only a single nucleotide or nucleotide pair. This model provides a band structure that is easily interpretable and reflects the main characteristic features of the single nucleotide or a nucleotide pair chain, respectively. The chemical variability of the different DNA chains is, however, almost completely neglected in this way. In the present work we have investigated the effect of the different sequences on the band structure of periodic DNA models. For this purpose we have applied the Hartree-Fock crystal orbital method for single and double stranded DNA chains with two different subsequent nucleotides in the repeat unit of former and two different nucleotide pairs in the latter case, respectively. These results are compared to simple helical models with uniform sequences. The valence and conduction bands related to the stacked nucleotide bases of single stranded DNA built up only from guanidine as well as of double stranded DNA built up only from guanidine-cytidine pairs showed special properties different from the other cases. Namely, they had higher conduction and lower valence band positions and this way larger band gaps and smaller widths of these bands. With the introduction of non-uniform guanidine containing sequences band structures became more similar to each other and to the band structures of other sequences without guanidine. The maximal bandwidths of the non-uniform sequences are considerably smaller than in the case of uniform sequences implying smaller charge carrier mobilities both in the conduction and valence bands.

  14. Angle Resolved Photoemission Study of Surface States and Orbital Angular Momentum Structure in SrTiO3

    NASA Astrophysics Data System (ADS)

    Soltani, Shoresh; Kim, Beomyoung; Han, Garam; Cho, Soohyun; Denlinger, Jonathan; Leandersson, Mats; Kim, Changyoung

    2015-03-01

    The theoretical understanding of spin orbit coupling (SOC) effects in SrTiO3 (STO) and KTaO3 (KTO) is still in its infancy. To have a better understanding of these effects, we have performed linear and circular dichroism angle resolved photoemission spectroscopy (LD- and CD-ARPES) of surface states of STO and KTO to measure the energy band and local orbital angular momentum (OAM) structure. CD-ARPES measurement revels the OAM chiral structure. Using ARPES results and a new OAM based Hamiltonian we try to explain the origin of band splitting. We believe that OAM has an important role in the surface band splitting and the chiral structure reveled by CD-ARPES.

  15. Breakdown Characteristics Study on an 18 Cell X-band Structure

    SciTech Connect

    Wang, Faya; ,

    2008-11-12

    A CLIC designed 18 cells, low group velocity (2.4% to 1.0% c), X-band (11.4 GHz) accelerator structure (denoted T18) was designed at CERN, its cells were built at KEK, and it was assembled and tested at SLAC. An interesting feature of this structure is that the gradient in the last cell is about 50% higher than that in the first cell. This structure has been RF conditioned at SLAC NLCTA for about 1400 hours where it incurred about 2200 breakdowns. This paper presents the characteristics of these breakdowns, including (1) the breakdown rate dependence on gradient, pulse width and conditioning time, (2) the breakdown distribution along the structure, (3) relation between breakdown and pulsed heating dependence study and (4) electric field decay time for breakdown changing over the whole conditioning time. Overall, this structure performed very well, having a final breakdown rate of less than 1e-6/pulse/m at 106 MV/m with 230 ns pulse width.

  16. Breakdown Characteristics Study on an 18 Cell X-band Structure

    SciTech Connect

    Wang Faya

    2009-01-22

    A CLIC designed 18 cells, low group velocity (2.4% to 1.0% c), X-band (11.4 GHz) accelerator structure (denoted T18) was designed at CERN, its cells were built at KEK, and it was assembled and tested at SLAC. An interesting feature of this structure is that the gradient in the last cell is about 50% higher than that in the first cell. This structure has been RF conditioned at SLAC NLCTA for about 1400 hours where it incurred about 2200 breakdowns. This paper presents the characteristics of these breakdowns, including 1) the breakdown rate dependence on gradient, pulse width and conditioning time, 2) the breakdown distribution along the structure, 3) relation between breakdown and pulsed heating dependence study and 4) electric field decay time for breakdown changing over the whole conditioning time. Overall, this structure performed very well, having a final breakdown rate of less than 1e-6/pulse/m at 106 MV/m with 230 ns pulse width.

  17. Microscopic surface structure of liquid alkali metals H. Tostmann

    E-print Network

    Pershan, Peter S.

    Microscopic surface structure of liquid alkali metals H. Tostmann Division of Applied Sciences study of the microscopic structure of the surface of a liquid alkali metal. The bulk liquid structure of an elemental liquid alkali metal. Analysis of off-specular diffuse scattering and specular x-ray reflectivity

  18. Detailed structure of the outer disk around HD 169142 with polarized light in H-band

    E-print Network

    Momose, Munetake; Fukagawa, Misato; Muto, Takayuki; Takeuchi, Taku; Hashimoto, Jun; Honda, Mitsuhiko; Kudo, Tomoyuki; Okamoto, Yoshiko K; Kanagawa, Kazuhiro D; Tanaka, Hidekazu; Grady, Carol A; Sitko, Michael L; Akiyama, Eiji; Currie, Thayne; Follette, Katherine B; Mayama, Satoshi; Kusakabe, Nobuhiko; Abe, Lyu; Brandner, Wolfgang; Brandt, Timothy D; Carson, Joseph C; Egner, Sebastian; Feldt, Markus; Goto, Miwa; Guyon, Olivier; Hayano, Yutaka; Hayashi, Masahiko; Hayashi, Saeko S; Henning, Thomas; Hodapp, Klaus W; Ishii, Miki; Iye, Masanori; Janson, Markus; Kandori, Ryo; Knapp, Gillian R; Kuzuhara, Masayuki; Kwon, Jungmi; Matsuo, Taro; McElwain, Michael W; Miyama, Shoken; Morino, Jun-Ichi; Moro-Martin, Amaya; Nishimura, Tetsuo; Pyo, Tae-Soo; Serabyn, Eugene; Suenaga, Takuya; Suto, Hiroshi; Suzuki, Ryuji; Takahashi, Yasuhiro H; Takami, Michihiro; Takato, Naruhisa; Terada, Hiroshi; Thalmann, Christian; Tomono, Daigo; Turner, Edwin L; Watanabe, Makoto; Wisniewski, John; Yamada, Toru; Takami, Hideki; Usuda, Tomonori; Tamura, Motohide

    2015-01-01

    Coronagraphic imagery of the circumstellar disk around HD 169142 in H-band polarized intensity (PI) with Subaru/HiCIAO is presented. The emission scattered by dust particles at the disk surface in 0.2" <= r <= 1.2", or 29 <= r <= 174 AU, is successfully detected. The azimuthally-averaged radial profile of the PI shows a double power-law distribution, in which the PIs in r=29-52 AU and r=81.2-145 AU respectively show r^{-3}-dependence. These two power-law regions are connected smoothly with a transition zone (TZ), exhibiting an apparent gap in r=40-70 AU. The PI in the inner power-law region shows a deep minimum whose location seems to coincide with the point source at \\lambda = 7 mm. This can be regarded as another sign of a protoplanet in TZ. The observed radial profile of the PI is reproduced by a minimally flaring disk with an irregular surface density distribution or with an irregular temperature distribution or with the combination of both. The depletion factor of surface density in the inner...

  19. Compositional and structural changes at the anodic surface of thermally poled soda-lime float glass

    SciTech Connect

    Ziemath, E. C.; Araujo, V. D.; Escanhoela, C. A. Jr.

    2008-09-01

    Applying high dc electric fields at elevated temperatures on silicate glasses results in displacement of ions, causing compositional and structural changes in the anodic surface. In this work, the ionic displacement was accompanied by electric current measurements during poling. The thickness of the Na{sup +} depletion layer calculated from the current curves agrees with the thickness measured by EDS only if displacement of Ca{sup 2+} and O{sup -} are also taken into account. A depletion of Ca{sup 2+} in the anodic surface has in fact been observed. Structural changes were confirmed by infrared diffuse and specular reflectance spectroscopies. A narrowing of the band at about 1070 cm{sup -1} can be attributed to an increase in the structural ordering degree. Refractive index measurements confirm compositional changes and contact angle measurements indicate the existence of a negative charge density at the anodic surface.

  20. Pushing the Gradient Limitations of Superconducting Photonic Band Gap Structure Cells

    SciTech Connect

    Simakov, Evgenya I.; Haynes, William B.; Kurennoy, Sergey S.; Shchegolkov, Dmitry; O'Hara, James F.; Olivas, Eric R.

    2012-06-07

    Superconducting photonic band gap resonators present us with unique means to place higher order mode couples in an accelerating cavity and efficiently extract HOMs. An SRF PBG resonator with round rods was successfully tested at LANL demonstrating operation at 15 MV/m. Gradient in the SRF PBG resonator was limited by magnetic quench. To increase the quench threshold in PBG resonators one must design the new geometry with lower surface magnetic fields and preserve the resonator's effectiveness for HOM suppression. The main objective of this research is to push the limits for the high-gradient operation of SRF PBG cavities. A NCRF PBG cavity technology is established. The proof-of-principle operation of SRF PBG cavities is demonstrated. SRF PBG resonators are effective for outcoupling HOMs. PBG technology can significantly reduce the size of SRF accelerators and increase brightness for future FELs.

  1. Product fine-structure resolved photodissociation dynamics: The A band of H{sub 2}O

    SciTech Connect

    Zhou, Linsen; Xie, Daiqian E-mail: hguo@unm.edu; Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026 ; Sun, Zhigang; Guo, Hua E-mail: hguo@unm.edu

    2014-01-14

    The photodissociation dynamics of H{sub 2}O in its first absorption band is investigated on an accurate potential energy surface based on a large number of high-level ab initio points. Several ro-vibrational states of the parent molecule are considered. Different from most previous theoretical studies, the spin-orbit and ?-doublet populations of the open-shell OH fragment are reported from full-dimensional wave packet calculations. The populations of the two spin-orbit manifolds are in most cases close to the statistical limit, but the ?-doublet is dominated by the A{sup ?} component, thanks largely to the fast in-plane dissociation of H{sub 2}O(A{sup ~1}A{sup ??}). Comparisons with experimental data and a Franck-Condon model are generally very good, although some discrepancies exist.

  2. The structure of organic langmuir films on liquid metal surfaces

    E-print Network

    Pershan, Peter S.

    The structure of organic langmuir films on liquid metal surfaces H. Kraack a , M. Deutsch a,*, B Elsevier Science B.V. All rights reserved. Keywords: Langmuir films; Monolayers; Surface; Liquid metals; 2D

  3. Effect of oxygen on the electronic band structure in ZnO{sub x}Se{sub 1-x} alloys

    SciTech Connect

    Shan, W.; Walukiewicz, W.; Ager III, J.W.; Yu, K.M.; Wu, J.; Haller, E.E.; Nabetani, Y.; Mukawa, T.; Ito, Y.; Matsumoto, T.

    2003-03-14

    The effect of alloying small amounts of ZnO with ZnSe on the electronic band structure has been studied. Optical transitions in molecular-beam-epitaxy-grown ZnO{sub x}Se{sub 1-x} epitaxial films (0 {<=} x {<=} 1.35%) were investigated using photoreflectance and photoluminescence spectroscopies. The fundamental band-gap energy of the alloys was found to decrease at a rate of about 0.1 eV per atomic percent of oxygen. The pressure dependence of the band gap was also found to be strongly affected by O incorporation. Both the effects can be quantitatively explained by an anticrossing interaction between the extended states of the conduction band of ZnSe and the highly localized oxygen states located at approximately 0.22 eV above the conduction-band edge.

  4. The roots of coronal structure in the Sun's surface

    NASA Technical Reports Server (NTRS)

    Golub, Leon; Zirin, Harold; Wang, Haimin

    1994-01-01

    We have compared the structures seen on X-ray images obtained by a flight of the NIXT sounding rocket payload on July 11, 1991 with near-simultaneous photospheric and chromospheric structures and magnetic fields observed at Big Bear. The X-ray images reflect emission of both Mg X and Fe XVI, formed at 1 x 10(exp 6) K and 3 x 10(exp 6) K, respectively. The brightest H(alpha) sources correspond to a dying sub-flare and other active region components, all of which reveal coronal enhancements situated spatially well above the H(alpha) emission. The arches appear to lie in a small range of angle in the meridian plane connecting their footpoints. Sunspots are dark on the surface and in the corona. For the first time we see an emerging flux region in X-rays and find the emission extends twice as high as the H(alpha) arches. Many features which we believe to correspond to `X-ray bright points' (XBPs) were observed. Whether by resolution or spectral band, the number detected greatly exceeds that from previous work. All of the brighter XBPs correspond to bipolar H(alpha) features, while unipolar H(alpha) bright points are the base of more diffuse comet-like coronal arches, generally vertical. These diverge from individual features by less than 30 deg, and give a good measure of what the `canopies' must do. The H(alpha) data shows that all the H(alpha) features were present present the entire day, so they are not clearly disappearing or reappearing. We find a new class of XBPs which we call `satellite points', elements of opposite polarity linked to nearby umbrae by invisible field lines. The satellite points change rapidly in X-ray brightness during the flight. An M1.9 flare occurred four hours after the flight; examination of the pre-flare structures reveals nothing unusual.

  5. The role of beryllium in the band structure of MgZnO: Lifting the valence band maximum

    SciTech Connect

    Chen, S. S.; Pan, X. H. E-mail: yezz@zju.edu.cn; Chen, W.; Zhang, H. H.; Dai, W.; Ding, P.; Huang, J. Y.; Lu, B.; Ye, Z. Z. E-mail: yezz@zju.edu.cn

    2014-09-22

    We investigate the effect of Be on the valence band maximum (VBM) of MgZnO by measuring the band offsets of Mg{sub x}Zn{sub 1?x}O/Be{sub x}Mg{sub y}Zn{sub 1?x?y}O heterojunctions using X-ray photoelectron spectroscopy measurements. Mg{sub x}Zn{sub 1?x}O and Be{sub x}Mg{sub y}Zn{sub 1?x?y}O films have been grown on c-plane sapphire substrates by plasma-assisted molecular beam epitaxy. The valence band offset (?E{sub V}) of Mg{sub 0.15}Zn{sub 0.85}O (E{sub g}?=?3.62?eV)/Be{sub 0.005}Mg{sub 0.19}Zn{sub 0.805}O (E{sub g}?=?3.73?eV) heterojunction is 0.01?eV and Be{sub 0.005}Mg{sub 0.19}Zn{sub 0.805}O has a lower VBM. The increased Mg composition is the main factor for the reduction of VBM. The VBM of Mg{sub x}Zn{sub 1?x}O is lower by 0.03?eV with the enlargement of E{sub g} from 3.62?eV to 3.73?eV by increasing Mg composition. Considering the effect of increased Mg composition, it is concluded that the little amount of Be makes the VBM go up by 0.02?eV when the E{sub g} of the alloy is 3.73?eV. The ?E{sub V} of Mg{sub 0.11}Zn{sub 0.89}O (E{sub g}?=?3.56?eV)/Be{sub 0.007}Mg{sub 0.12}Zn{sub 0.873}O (E{sub g}?=?3.56?eV) heterojunction is calculated to be 0.03?eV and Be{sub 0.007}Mg{sub 0.12}Zn{sub 0.873}O has a higher VBM than Mg{sub 0.11}Zn{sub 0.89}O, which means that a little amount Be lifts the VBM by 0.03?eV when the E{sub g} of the alloy is 3.56?eV. The experimental measurements have offered a strong support for the theoretical research that alloying Be in Mg{sub x}Zn{sub 1?x}O alloys is hopeful to form a higher VBM and to enhance the p-type dopability of MgZnO.

  6. Wide Angle, Single Screen, Gridded Square-Loop Frequency Selective Surface for Diplexing Two Closely Separated Frequency Bands

    NASA Technical Reports Server (NTRS)

    Wu, Te-Kao (Inventor)

    1996-01-01

    The design and performance of a wide angle, single screen, frequency selective surface (FSS) with gridded square-loop path elements are described for diplexing closely separated signal bands, for example, X- and Ku-band signals in an Orbiting Very Long Baseline Interferometer (OVLBI) earth station reflector antenna system, as well as other applications such as military and commercial communications via satellites. Excellent agreement is obtained between the predicted and measured results of this FSS design using the gridded square-loop patch elements sandwiched between 0.0889 cm thick tetrafluoroethylene fluorocarbon polymer (PTFE) slabs. Resonant frequency drift is reduced by 1 GHz with an incidence angle from 0 deg normal to 40 deg from normal.

  7. L band radar backscatter dependence upon surface wind stress - A summary of new Seasat-1 and aircraft observations

    NASA Technical Reports Server (NTRS)

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

    1983-01-01

    The wind-scale relationships for L band radar wavelengths near 25 cm and 20 deg angle of incidence and HH polarization are reviewed using a number of aircraft and Seasat-1 SAR observations. The dependence of the L band backscatter coefficient from the ocean upon surface wind speed and direction is stated. The wind speed coefficient is 0.5 + or - 0.1 for a wide range of wind speeds. The wind direction coefficient is near zero for lower winds and stable marine boundary layers, but may be 0.20 + or - 0.05 for moderate wind speeds and an unstable marine boundary layer. These results are interpreted in terms of existing theoretical models for radar scattering from the ocean.

  8. Correlation of Photocatalytic Activity with Band Structure of Low-dimensional Semiconductor Nanostructures

    NASA Astrophysics Data System (ADS)

    Meng, Fanke

    Photocatalytic hydrogen generation by water splitting is a promising technique to produce clean and renewable solar fuel. The development of effective semiconductor photocatalysts to obtain efficient photocatalytic activity is the key objective. However, two critical reasons prevent wide applications of semiconductor photocatalysts: low light usage efficiency and high rates of charge recombination. In this dissertation, several low-dimensional semiconductors were synthesized with hydrothermal, hydrolysis, and chemical impregnation methods. The band structures of the low-dimensional semiconductor materials were engineered to overcome the above mentioned two shortcomings. In addition, the correlation between the photocatalytic activity of the low-dimensional semiconductor materials and their band structures were studied. First, we studied the effect of oxygen vacancies on the photocatalytic activity of one-dimensional anatase TiO2 nanobelts. Given that the oxygen vacancy plays a significant role in band structure and photocatalytic performance of semiconductors, oxygen vacancies were introduced into the anatase TiO2 nanobelts during reduction in H2 at high temperature. The oxygen vacancies of the TiO2 nanobelts boosted visible-light-responsive photocatalytic activity but weakened ultraviolet-light-responsive photocatalytic activity. As oxygen vacancies are commonly introduced by dopants, these results give insight into why doping is not always beneficial to the overall photocatalytic performance despite increases in absorption. Second, we improved the photocatalytic performance of two-dimensional lanthanum titanate (La2Ti2 O7) nanosheets, which are widely studied as an efficient photocatalyst due to the unique layered crystal structure. Nitrogen was doped into the La2Ti2O7 nanosheets and then Pt nanoparticles were loaded onto the La2Ti2O7 nanosheets. Doping nitrogen narrowed the band gap of the La2Ti 2O7 nanosheets by introducing a continuum of states by the valence band edge, unlike the mid-gap states introduced by oxygen vacancies, leading to an improvement in visible and UV photocatalysis. The Pt nanoparticles both enhanced separation of charge carriers and acted as reaction sites for hydrogen evolution. The photocatalytic hydrogen generation rate of the La 2Ti2O7 nanosheets was increased to ˜21 muM g-1 hr-1 from zero in visible light by nitrogen doping and Pt loading, showing the importance of the positioning of dopant energy levels within the band gap. Third, a hematite/reduced graphene oxide (alpha-Fe2 2O3/rGO) nanocomposite was synthesized by a hydrolysis method. The photocatalytic oxygen evolution rate of the hematite was increased from 387 to 752 muM g-1 hr-1 by incorporating rGO. Photoelectrochemical measurements showed that coupling the hematite nanoparticles with the rGO can greatly increase the photocurrent and reduce the charge recombination rate, overcoming the poor charge recombination characteristics of hematite and allowing its small band gap to be taken advantage of. Fourth, a Au/La 2Ti2O7/rGO heterostructure was synthesized to further enhance the photocatalytic hydrogen generation rate of the La 2Ti2O7 nanosheets. The enhanced performance of photocatalytic water splitting was due to plasmonic energy transfer, which resulted from the plasmonic Au nanoparticles on the La2Ti 2O7 nanosheets. This heterostructure showed doping, charge extraction, and plasmonics work synergistically. Fifth, nanoscale p-n junctions on the rGO were formed by depositing the p-type MoS 2 nanoplatelets onto the n-type nitrogen-doped rGO. The p-MoS2/n-rGO heterostructure had significant photocatalytic hydrogen generation activity under solar light irradiation. The enhanced charge generation and suppressed charge recombination due to the p-n junctions led to enhance solar hydrogen generation reaction while allowing replacement of the expensive Pt nanoparticles with an eco-friendly alternative. The research results in this dissertation are contributed to a better understanding of the relationship between the band structure tuning an

  9. Band-gap nonlinear optical generation: The structure of internal optical field and the structural light focusing

    SciTech Connect

    Zaytsev, Kirill I. Katyba, Gleb M.; Yakovlev, Egor V.; Yurchenko, Stanislav O.; Gorelik, Vladimir S.

    2014-06-07

    A novel approach for the enhancement of nonlinear optical effects inside globular photonic crystals (PCs) is proposed and systematically studied via numerical simulations. The enhanced optical harmonic generation is associated with two- and three-dimensional PC pumping with the wavelength corresponding to different PC band-gaps. The interactions between light and the PC are numerically simulated using the finite-difference time-domain technique for solving the Maxwell's equations. Both empty and infiltrated two-dimensional PC structures are considered. A significant enhancement of harmonic generation is predicted owing to the highly efficient PC pumping based on the structural light focusing effect inside the PC structure. It is shown that a highly efficient harmonic generation could be attained for both the empty and infiltrated two- and three-dimensional PCs. We are demonstrating the ability for two times enhancement of the parametric decay efficiency, one order enhancement of the second harmonic generation, and two order enhancement of the third harmonic generation in PC structures in comparison to the nonlinear generations in appropriate homogenous media. Obviously, the nonlinear processes should be allowed by the molecular symmetry. The criteria of the nonlinear process efficiency are specified and calculated as a function of pumping wavelength position towards the PC globule diameter. Obtained criterion curves exhibit oscillating characteristics, which indicates that the highly efficient generation corresponds to the various PC band-gap pumping. The highest efficiency of nonlinear conversions could be reached for PC pumping with femtosecond optical pulses; thus, the local peak intensity would be maximized. Possible applications of the observed phenomenon are also discussed.

  10. Broadband High-Performance Infrared Antireflection Nanowires Facilely Grown on Ultrafast Laser Structured Cu Surface.

    PubMed

    Fan, Peixun; Bai, Benfeng; Long, Jiangyou; Jiang, Dafa; Jin, Guofan; Zhang, Hongjun; Zhong, Minlin

    2015-09-01

    Infrared antireflection is an essential issue in many fields such as thermal imaging, sensors, thermoelectrics, and stealth. However, a limited antireflection capability, narrow effective band, and complexity as well as high cost in implementation represent the main unconquered problems, especially on metal surfaces. By introducing precursor micro/nano structures via ultrafast laser beforehand, we present a novel approach for facile and uniform growth of high-quality oxide semiconductor nanowires on a Cu surface via thermal oxidation. Through the enhanced optical phonon dissipation of the nanowires, assisted by light trapping in the micro structures, ultralow total reflectance of 0.6% is achieved at the infrared wavelength around 17 ?m and keeps steadily below 3% over a broad band of 14-18 ?m. The precursor structures and the nanowires can be flexibly tuned by controlling the laser processing procedure to achieve desired antireflection performance. The presented approach possesses the advantages of material simplicity, structure reconfigurability, and cost-effectiveness for mass production. It opens a new path to realize unique functions by integrating semiconductor nanowires onto metal surface structures. PMID:26280305

  11. Observation of high-spin oblate band structures in {sup 141}Pm

    SciTech Connect

    Gu, L.; Zhu, S. J.; Wang, J. G.; Yeoh, E. Y.; Xiao, Z. G.; Zhang, M.; Liu, Y.; Ding, H. B.; Xu, Q.; Zhang, S. Q.; Meng, J.; Zhu, L. H.; Wu, X. G.; He, C. Y.; Li, G. S.; Wang, L. L.; Zheng, Y.; Zhang, B.

    2011-06-15

    The high-spin states of {sup 141}Pm have been investigated through the reaction {sup 126}Te({sup 19}F,4n) at a beam energy of 90 MeV. A previous level scheme has been updated with spins up to 49/2({h_bar}/2{pi}). Six collective bands at high spins are newly observed. Based on the systematic comparison, one band is proposed as a decoupled band; two bands with strong {Delta}I=1 M1 transitions inside the bands are suggested as the oblate bands with {gamma} {approx}-60 deg.; three other bands with large signature splitting have been proposed with the oblate-triaxial deformation with {gamma}{approx} -90 deg. The triaxial n-particle-n-hole particle rotor model calculations for one of the oblate bands in {sup 141}Pm are in good agreement with the experimental data. The other characteristics for these bands have been discussed.

  12. Band alignment of ultra-thin hetero-structure ZnO/TiO{sub 2} junction

    SciTech Connect

    Shen, Kai; Wu, Kunjie; Wang, Deliang

    2014-03-01

    Graphical abstract: - Highlights: • Band alignment at the ZnO/TiO{sub 2} hetero-structural interface with different ZnO coating thickness was studied. • The valence band offset was decreased with increased ZnO coating layer thickness. • The interface dipole was responsible for the decreased band offset. - Abstract: The band alignment at the ZnO/TiO{sub 2} hetero-structure interface was measured by high resolution X-ray photoelectron spectroscopy. The valence band offset (E{sub ZnO}?E{sub TiO{sub 2}}){sub Valence} was linearly changed from 0.27 to 0.01 eV at the interface with increased ZnO coating thickness from 0.7 to 7 nm. The interface dipole presented at the ZnO/TiO{sub 2} interface was responsible for the decreased band offset. The band alignment of the ZnO/TiO{sub 2} heterojunction is a type II alignment.

  13. Effect of low-temperature annealing on the electronic- and band-structures of (Ga,Mn)As epitaxial layers

    SciTech Connect

    Yastrubchak, O. Gluba, L.; ?uk, J.; Wosinski, T. Andrearczyk, T.; Domagala, J. Z.; Sadowski, J.

    2014-01-07

    The effect of outdiffusion of Mn interstitials from (Ga,Mn)As epitaxial layers, caused by post-growth low-temperature annealing, on their electronic- and band-structure properties has been investigated by modulation photoreflectance (PR) spectroscopy. The annealing-induced changes in structural and magnetic properties of the layers were examined with high-resolution X-ray diffractometry and superconducting quantum interference device magnetometry, respectively. They confirmed an outdiffusion of Mn interstitials from the layers and an enhancement in their hole concentration, which were more efficient for the layer covered with a Sb cap acting as a sink for diffusing Mn interstitials. The PR results demonstrating a decrease in the band-gap-transition energy in the as-grown (Ga,Mn)As layers, with respect to that in the reference GaAs one, are interpreted by assuming a merging of the Mn-related impurity band with the GaAs valence band. Whereas an increase in the band-gap-transition energy caused by the annealing treatment of the (Ga,Mn)As layers is interpreted as a result of annealing-induced enhancement of the free-hole concentration and the Fermi level location within the valence band. The experimental results are consistent with the valence-band origin of itinerant holes mediating ferromagnetic ordering in (Ga,Mn)As, in agreement with the Zener model for ferromagnetic semiconductors.

  14. Structure, energy band, and optical properties of NaLa(PO{sub 3}){sub 4} crystal

    SciTech Connect

    Zhu, J.; Cheng, W.-D. . E-mail: cwd@ms.fjirsm.ac.cn; Wu, D.-S.; Zhang, H.; Gong, Y.-J.; Tong, H.-N.

    2006-02-15

    An alkali metal-rare earth phosphate crystal of NaLa(PO{sub 3}){sub 4} has been synthesized by high temperature solid-state reactions and structurally characterized by single crystal X-ray diffraction analysis, for the first time. It crystallizes in the monoclinic P2{sub 1}/n space group with lattice parameters: a=7.2655(3), b=13.1952(5), c=10.0760(1)A, {beta}=90.382{sup o}(1), V=965.96(5)A{sup 3}, Z=4. It is composed of LaO{sub 8} polyhedra and [(PO{sub 3}){sub 4}]{sup 4-} chains sharing oxygen atoms to form a three-dimensional framework, delimiting intersecting tunnels in which the sodium ions are located. The IR spectrum, absorption spectrum, and emission spectrum of the compound have been investigated. The absorption edge is located at 340nm (3.60eV). The calculated total and partial densities of states indicate that the top of valence bands is mainly built upon O-2p states which interact with P-3p states via {sigma} (P-O) interactions, and the low conduction bands mostly originates from unoccupied La-5d states. The P-O bond is mostly covalent in character, and the ionic character of the Na-O bond is larger than that in the La-O bond.

  15. Measurements of band gap structure in diamond compressed to 370 GPa

    NASA Astrophysics Data System (ADS)

    Gamboa, Eliseo; Fletcher, Luke; Lee, Hae-Ja; Zastrau, Ulf; Gauthier, Maxence; Gericke, Dirk; Vorberger, Jan; Granados, Eduardo; Heimann, Phillip; Hastings, Jerome; Glenzer, Siegfried

    2015-06-01

    We present the first measurements of the electronic structure of dynamically compressed diamond demonstrating a widening of the band gap to pressures of up to 370 +/- 25 GPa. The 8 keV free electron laser x-ray beam from the Linac Coherently Light Source (LCLS) has been focussed onto a diamond foil compressed by two counter-propagating laser pulses to densities of up to 5.3 g/cm3 and temperatures of up to 3000 +/- 400 K. The x-ray pulse excites a collective interband transition of the valence electrons, leading to a plasmon-like loss. We find good agreement with the observed plasmon shift by including the pressure dependence of the band gap as determined from density functional theory simulations. This work was performed at the Matter at Extreme Conditions (MEC) instrument of LCLS, supported by the DOE Office of Science, Fusion Energy Science under Contract No. SF00515. This work was supported by DOE Office of Science, Fusion Energy Science under F.

  16. SMALL-SCALE STRUCTURE OF THE INTERSTELLAR MEDIUM TOWARD {rho} Oph STARS: DIFFUSE BAND OBSERVATIONS

    SciTech Connect

    Cordiner, M. A.; Smith, A. M.; Sarre, P. J.; Fossey, S. J.

    2013-02-10

    We present an investigation of small-scale structure in the distribution of large molecules/dust in the interstellar medium through observations of diffuse interstellar bands (DIBs). High signal-to-noise optical spectra were recorded toward the stars {rho} Oph A, B, C, and DE using the University College London Echelle Spectrograph on the Anglo-Australian Telescope. The strengths of some of the DIBs are found to differ by about 5%-9% between the close binary stars {rho} Oph A and B, which are separated by a projected distance on the sky of only c. 344 AU. This is the first star system in which such small-scale DIB strength variations have been reported. The observed variations are attributed to differences between a combination of carrier abundance and the physical conditions present along each sightline. The sightline toward {rho} Oph C contains relatively dense, molecule-rich material and has the strongest {lambda}{lambda}5850 and 4726 DIBs. The gas toward DE is more diffuse and is found to exhibit weak ''C{sub 2}'' (blue) DIBs and strong yellow/red DIBs. The differences in diffuse band strengths between lines of sight are, in some cases, significantly greater in magnitude than the corresponding variations among atomic and diatomic species, indicating that the DIBs can be sensitive tracers of interstellar cloud conditions.

  17. The band structure of birefractive CdGa2S4 crystals

    NASA Astrophysics Data System (ADS)

    Stamov, I. G.; Syrbu, N. N.; Parvan, V. I.; Zalamai, V. V.; Tiginyanu, I. M.

    2013-11-01

    In this paper, we report on the spectral dependence of ?n=no-ne for CdGa2S4 single crystals for shorter and longer wavelengths than the isotropic wavelength ?0=485.7 nm (300 K). It was established that ?n is positive at ?>?0 and it is negative in the spectral range ?bands splitting, V1-V2, by crystalline field equals 24 meV, and V2-V3 splitting due to the spin-orbital interaction equals to 130 meV. The optical functions n, k, ?1 and ?2 for ??? and ??? polarizations were calculated by means of Kramers-Kronig analyses in the energy interval 3-6 eV. The evidenced features are discussed taking into account the results of new theoretical calculations of CdGa2S4 band structure.

  18. Physical properties and band structure of reactive molecular beam epitaxy grown oxygen engineered HfO{sub 2{+-}x}

    SciTech Connect

    Hildebrandt, Erwin; Kurian, Jose; Alff, Lambert

    2012-12-01

    We have conducted a detailed thin film growth structure of oxygen engineered monoclinic HfO{sub 2{+-}x} grown by reactive molecular beam epitaxy. The oxidation conditions induce a switching between (111) and (002) texture of hafnium oxide. The band gap of oxygen deficient hafnia decreases with increasing amount of oxygen vacancies by more than 1 eV. For high oxygen vacancy concentrations, defect bands form inside the band gap that induce optical transitions and p-type conductivity. The resistivity changes by several orders of magnitude as a function of oxidation conditions. Oxygen vacancies do not give rise to ferromagnetic behavior.

  19. Topology of time-reversal invariant energy bands with adiabatic structure

    E-print Network

    Omri Gat; JM Robbins

    2015-11-29

    We classify the topology of bands defined by the energy states of quantum systems with scale separation between slow and fast degrees of freedom, invariant under fermionic time reversal. Classical phase space transforms differently from momentum space under time reversal, and as a consequence the topology of adiabatic bands is different from that of Bloch bands. We show that bands defined over a two-dimensional phase space are classified by the Chern number, whose parity must be equal to the parity of the band rank. Even-rank bands are equivalently classified by the Kane-Mele index, an integer equal to one half the Chern number.

  20. Elastic and viscoelastic effects in rubber/air acoustic band gap structures: A theoretical and experimental study

    E-print Network

    Deymier, Pierre

    Elastic and viscoelastic effects in rubber/air acoustic band gap structures: A theoretical rubber/air phononic crystal structures is investigated theoretically and experimentally. We introduce in a solid rubber matrix, as well as an array of rubber cylinders in an air matrix, are shown to behave

  1. Experiments on Surface Reconstruction for Partially Submerged Marine Structures

    E-print Network

    Papadopoulos, Georgios

    Over the past 10 years, significant scientific effort has been dedicated to the problem of three-dimensional (3-D) surface reconstruction for structural systems. However, the critical area of marine structures remains ...

  2. ORIGINAL PAPER Analysis of subcellular surface structure, function

    E-print Network

    Bielefeld, Universität

    , the subcellular surface structure of living bacteria (Corynebacterium glutamicum) was investigated with atomic Single cell analysis at the subcellular level gives quantitative information from a structural mechanisms of specific interaction, binding kinetics and the interplay of genomic information and functional

  3. Thermoelectric Properties as a Function of Electronic Band Structure and Microstructure of Textured Materials

    NASA Astrophysics Data System (ADS)

    Jacquot, A.; Farag, N.; Jaegle, M.; Bobeth, M.; Schmidt, J.; Ebling, D.; Böttner, H.

    2010-09-01

    A tool has been developed at Fraunhofer-IPM to calculate the transport properties of thermoelectric material by using its band structure described in terms of effective masses and the location of the ellipsoids in reciprocal space. The calculated transport properties are compared with experimental data measured on bismuth telluride, antimony telluride, and bismuth antimony telluride. Polycrystalline specimens have been prepared by spark plasma sintering (Fraunhofer-IFAM). Electron backscattering diffraction analysis of sample cross-sections yields the frequency distribution of grain orientations. This texture information permits the generation of appropriate finite-element models of the polycrystalline microstructure (TU Dresden). By means of the commercial code COMSOL, which allows anisotropic thermoelectric properties to be taken into account, the effective electrical and thermal conductivities as well as the Seebeck coefficient both parallel and perpendicular to the pressing direction have been calculated.

  4. Calculation and analysis of complex band structure in dispersive and dissipative two-dimensional photonic crystals

    E-print Network

    Brûlé, Yoann; Gralak, Boris

    2015-01-01

    Numerical calculation of modes in dispersive and absorptive systems is performed using the finite element method. The dispersion is tackled in the frame of an extension of Maxwell's equations where auxiliary fields are added to the electromagnetic field. This method is applied to multi-domain cavities and photonic crystals including Drude and Drude-Lorentz metals. Numerical results are compared to analytical solutions for simple cavities and to previous results of the literature for photonic crystals, showing excellent agreement. The advantages of the developed method lie on the versatility of the finite element method regarding geometries, and in sparing the use of tedious complex poles research algorithm. Hence the complex spectrum of resonances of non-hermitian operators and dissipative systems, like two-dimensional photonic crystal made of absorbing Drude metal, can be investigated in detail. The method is used to reveal unexpected features of their complex band structures.

  5. High-power narrow-vertical-divergence photonic band crystal laser diodes with optimized epitaxial structure

    SciTech Connect

    Liu, Lei; Qu, Hongwei; Liu, Yun; Zhang, Yejin; Zheng, Wanhua; Wang, Yufei; Qi, Aiyi

    2014-12-08

    900?nm longitudinal photonic band crystal (PBC) laser diodes with optimized epitaxial structure are fabricated. With a same calculated fundamental-mode divergence, stronger mode discrimination is achieved by a quasi-periodic index modulation in the PBC waveguide than a periodic one. Experiments show that the introduction of over 5.5??m-thick PBC waveguide contributes to only 10% increment of the internal loss for the laser diodes. For broad area PBC lasers, output powers of 5.75?W under continuous wave test and over 10?W under quasi-continuous wave test are reported. The vertical divergence angles are 10.5° at full width at half maximum and 21.3° with 95% power content, in conformity with the simulated angles. Such device shows a prospect for high-power narrow-vertical-divergence laser emission from single diode laser and laser bar.

  6. Electron energy-band structures of some AgCd alloys

    SciTech Connect

    Debnath, N.C.; Roychowdhury, M.; Chatterjee, S.

    1980-09-15

    Complex energy-band structures of AgCd alloys have been determined by the alloy--Koringa-Kohn-Rostoker-Ziman (KKRZ) method for two different concentrations, and the optical properties estimated from these calculations have been compared with experiment. On the low-concentration side agreement with experiment is found to be excellent, whereas on the higher-concentration end a slight deviation is observed. This is probably due to the fact that the average-T-matrix approximation, which is the basis of the alloy--KKRZ method, is more suited for relatively lower concentrations of the alloying material. An effect of the charge transfer on the higher-concentration alloys has also been investigated. The results show that the disagreement with the experiment can also be accounted for by the charge-transfer effect.

  7. The effect of spin-orbit coupling in band structure and edge states of bilayer graphene

    NASA Astrophysics Data System (ADS)

    Sahdan, Muhammad Fauzi; Darma, Yudi

    2015-04-01

    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 bilayer grapheme and also its edge states by using this model with analytical approach. The results of our calculation show that the gap opening occurs at K and K' point in bilayer graphene.In addition, a pair of gapless edge modes occurs both in the zigzag and arm-chair configurations are no longer exist. There are gap created at the edge even though thery are very small.

  8. The effect of spin-orbit coupling in band structure and edge states of bilayer graphene

    SciTech Connect

    Sahdan, Muhammad Fauzi; Darma, Yudi

    2015-04-16

    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 bilayer grapheme and also its edge states by using this model with analytical approach. The results of our calculation show that the gap opening occurs at K and K’ point in bilayer graphene.In addition, a pair of gapless edge modes occurs both in the zigzag and arm-chair configurations are no longer exist. There are gap created at the edge even though thery are very small.

  9. Terahertz dual-band metamaterial absorber based on graphene/MgF(2) multilayer structures.

    PubMed

    Su, Zhaoxian; Yin, Jianbo; Zhao, Xiaopeng

    2015-01-26

    We design an ultra-thin terahertz metamaterial absorber based on graphene/MgF(2) multilayer stacking unit cells arrayed on an Au film plane and theoretically demonstrate a dual-band total absorption effect. Due to strong anisotropic permittivity, the graphene/MgF(2) multilayer unit cells possess a hyperbolic dispersion. The strong electric and magnetic dipole resonances between unit cells make the impedance of the absorber match to that of the free space, which induces two total absorption peaks in terahertz range. These absorption peaks are insensitive to the polarization and nearly omnidirectional for the incident angle. But the absorption intensity and frequency depend on material and geometric parameters of the multilayer structure. The absorbed electromagnetic waves are finally converted into heat and, as a result, the absorber shows a good nanosecond photothermal effect. PMID:25835924

  10. The emission and scattering of L-band microwave radiation from rough ocean surfaces and wind speed measurements from the Aquarius sensor

    NASA Astrophysics Data System (ADS)

    Meissner, Thomas; Wentz, Frank J.; Ricciardulli, Lucrezia

    2014-09-01

    In order to achieve the required accuracy in sea surface salinity (SSS) measurements from L-band radiometers such as the Aquarius/SAC-D or SMOS (Soil Moisture and Ocean Salinity) mission, it is crucial to accurately correct the radiation that is emitted from the ocean surface for roughness effects. We derive a geophysical model function (GMF) for the emission and backscatter of L-band microwave radiation from rough ocean surfaces. The analysis is based on radiometer brightness temperature and scatterometer backscatter observations both taken on board Aquarius. The data are temporally and spatially collocated with wind speeds from WindSat and F17 SSMIS (Special Sensor Microwave Imager Sounder) and wind directions from NCEP (National Center for Environmental Prediction) GDAS (Global Data Assimilation System). This GMF is the basis for retrieval of ocean surface wind speed combining L-band H-pol radiometer and HH-pol scatterometer observations. The accuracy of theses combined passive/active L-band wind speeds matches those of many other satellite microwave sensors. The L-band GMF together with the combined passive/active L-band wind speeds is utilized in the Aquarius SSS retrieval algorithm for the surface roughness correction. We demonstrate that using these L-band wind speeds instead of NCEP wind speeds leads to a significant improvement in the SSS accuracy. Further improvements in the roughness correction algorithm can be obtained by adding VV-pol scatterometer measurements and wave height (WH) data into the GMF.

  11. The Relationship Between Rehearsal Structure and Contest Ratings for High School Bands

    E-print Network

    Love, Justin Willis

    2012-05-31

    The purpose of this study was to determine if the rating received by the band at a state music contest can be predicted by examining the amount of rehearsal time high school band directors allocate to various rehearsal components. Secondly...

  12. Analysis of dispersion and attenuation of surface waves in poroelastic media in the exploration-seismic frequency band

    USGS Publications Warehouse

    Zhang, Y.; Xu, Y.; Xia, J.

    2011-01-01

    We analyse dispersion and attenuation of surface waves at free surfaces of possible vacuum/poroelastic media: permeable-'open pore', impermeable-'closed pore' and partially permeable boundaries, which have not been previously reported in detail by researchers, under different surface-permeable, viscous-damping, elastic and fluid-flowing conditions. Our discussion is focused on their characteristics in the exploration-seismic frequency band (a few through 200 Hz) for near-surface applications. We find two surface-wave modes exist, R1 waves for all conditions, and R2 waves for closed-pore and partially permeable conditions. For R1 waves, velocities disperse most under partially permeable conditions and least under the open-pore condition. High-coupling damping coefficients move the main dispersion frequency range to high frequencies. There is an f1 frequency dependence as a constant-Q model for attenuation at high frequencies. R1 waves for the open pore are most sensitive to elastic modulus variation, but least sensitive to tortuosities variation. R1 waves for partially permeable surface radiate as non-physical waves (Im(k) < 0) at low frequencies. For R2 waves, velocities are slightly lower than the bulk slow P2 waves. At low frequencies, both velocity and attenuation are diffusive of f1/2 frequency dependence, as P2 waves. It is found that for partially permeable surfaces, the attenuation displays -f1 frequency dependence as frequency increasing. High surface permeability, low-coupling damping coefficients, low Poisson's ratios, and low tortuosities increase the slope of the -f1 dependence. When the attenuation coefficients reach 0, R2 waves for partially permeable surface begin to radiate as non-physical waves. ?? 2011 The Authors Geophysical Journal International ?? 2011 RAS.

  13. An Ultra Wide-Band Radar Altimeter for Ice Sheet Surface Elevation and Snow Cover Over Sea Ice Measurement

    NASA Astrophysics Data System (ADS)

    Patel, A. E.; Gogineni, P. S.; Leuschen, C.; Rodriguez-Morales, F.; Panzer, B.

    2010-12-01

    The Ice sheets of Greenland and Antarctica are losing mass at a rapid rate and there has been significant decrease in sea ice volume over the last few years. CryoSat-II with optimized radar altimeter for ice-sheet and sea ice surface elevation measurements is launched. We developed ultra wide-band FM-CW radar that operates over the frequency range from 13-17 GHz for airborne measurements. The radar is designed to provide high-resolution surface-elevation data and also map near surface layers in polar firn with high precision. It is designed to generate an ultra linear transmit chirp using a fast settling PLL with a reference signal from Direct Digital Synthesizer (DDS). The pulse length of the transmit chirp is 240-us and pulse repetition frequency is 2-KHz. The peak transmit power of the system is 100-mW, radiated using horn antennas. The radar was deployed in Greenland and Antarctica in 2009-10 as a part of Operation Ice Bridge campaign to collect data in conjunction with other instruments including Airborne Topographic Mapper (ATM) and Digital Mapping System Camera (DMS). The radar also collected data under the Cryosat-II path. This paper will provide an overview of the Ku-Band radar design along with results from the 2009-2010 field campaigns. The data collected over polar firn shows near surface internal layers down to a depth of about 15-m with a resolution of 15-cm. When flying over sea ice the radar provides snow cover thickness data to a depth of about 0.5-m. Even over highly crevassed areas, such as outlet glaciers, the radar is able to detect large surface elevation changes of a few tens of meters with high resolution.

  14. Structure and Evolution of Band-shaped Convective Rainbands in Typhoon Marokot (2009)

    NASA Astrophysics Data System (ADS)

    Zhang, Y.

    2012-12-01

    Typhoon Morakot struck Taiwan on the night of Friday 7 August 2009 as a Category 1 storm (with sustained winds of 80 knots). Although the center made landfall in Hualien county along the central east coast of Taiwan, it was southern Taiwan that received the heaviest rainfall (2878 mm of rain in three days), resulting in the worst flooding over Taiwan in 50 years. This record-breaking rainfall is produced by the continuous impingement of typhoon rainbands with the steep terrain along the southern Central Mountain Range (CMR). In this study, rainband structures of Typhoon Morakot (2009) are analyzed and compared with the observations using outputs from the cloud-resolving WRF model with high spatial resolution (1-km horizontal grid spacing). The characteristics of the unique band-shaped convective rainband in TC Morakot are explained with respect to the following details: (i) horizontal shape, (ii) structure, and (iii) development and evolution process. The kinematic and precipitation structures of convective-scale elements in the Morakot rainbands are analyzed and compared with those of Hurricanes Katrina and Rita (2005).

  15. Ammonia volatilization from surface-banded and broadcast application of liquid dairy manure on grass forage

    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. Eight field trials were conducted to evaluate the emission of NH3 from liquid dairy manure either surface broadc...

  16. A well-structured metastable ceria surface

    SciTech Connect

    Olbrich, R.; Pieper, H. H.; Oelke, R.; Wilkens, H.; Wollschläger, J.; Reichling, M.; Zoellner, M. H.; Schroeder, T.

    2014-02-24

    By the growth of a 180?nm thick film on Si(111), we produce a metastable ceria surface with a morphology dominated by terraced pyramids with an oriented triangular base. Changes in the nanoscale surface morphology and local surface potential due to annealing at temperatures ranging from 300?K to 1150?K in the ultra-high vacuum are studied with non-contact atomic force microscopy and Kelvin probe force microscopy. As the surface is stable in the temperature range of 300?K to 850?K, it is most interesting for applications requiring regular steps with a height of one O-Ce-O triple layer.

  17. Band-rejection fiber filter and fiber sensor based on a Bragg fiber of transversal resonant structure.

    PubMed

    Chen, Daru; Yang, Tzong-Jer; Wu, Jin-Jei; Shen, Linfang; Liao, Kun-Lin; He, Sailing

    2008-10-13

    We propose a novel band-rejection fiber filter based on a Bragg fiber of transversal resonant structure, which can also be used as a fiber sensor. Defect layers are introduced in the periodic high/low index structure in the cladding of the Bragg fiber. Coupling between the core mode and the defect mode results in large confinement loss for some resonant wavelengths inside the band gap of the Bragg fiber. A segment of the Bragg fiber of transversal resonant structure can be used as a band-rejection fiber filter, whose characteristics are mainly determined by the defect layer. The loss peak wavelength of the Bragg fiber is dependent on the refractive index and the thickness of the defect layer which indicates its applications of refractive index and strain sensing. PMID:18852756

  18. Large-area 2D periodic crystalline silicon nanodome arrays on nanoimprinted glass exhibiting photonic band structure effects.

    PubMed

    Becker, C; Lockau, D; Sontheimer, T; Schubert-Bischoff, P; Rudigier-Voigt, E; Bockmeyer, M; Schmidt, F; Rech, B

    2012-04-01

    Two-dimensional silicon nanodome arrays are prepared on large areas up to 50 cm² exhibiting photonic band structure effects in the near-infrared and visible wavelength region by downscaling a recently developed fabrication method based on nanoimprint-patterned glass, high-rate electron-beam evaporation of silicon, self-organized solid phase crystallization and wet-chemical etching. The silicon nanodomes, arranged in square lattice geometry with 300 nm lattice constant, are optically characterized by angular resolved reflection measurements, allowing the partial determination of the photonic band structure. This experimentally determined band structure agrees well with the outcome of three-dimensional optical finite-element simulations. A 16% photonic bandgap is predicted for an optimized geometry of the silicon nanodome arrays. By variation of the duration of the selective etching step, the geometry as well as the optical properties of the periodic silicon nanodome arrays can be controlled systematically. PMID:22422473

  19. Electronic structure changes during the surface-assisted formation of a graphene nanoribbon

    SciTech Connect

    Bronner, Christopher Tegeder, Petra; Freie Universität Berlin, Fachbereich Physik, Arnimallee 14, 14195 Berlin ; Utecht, Manuel; Saalfrank, Peter; Klamroth, Tillmann; Haase, Anton

    2014-01-14

    High conductivity and a tunability of the band gap make quasi-one-dimensional graphene nanoribbons (GNRs) highly interesting materials for the use in field effect transistors. Especially bottom-up fabricated GNRs possess well-defined edges which is important for the electronic structure and accordingly the band gap. In this study we investigate the formation of a sub-nanometer wide armchair GNR generated on a Au(111) surface. The on-surface synthesis is thermally activated and involves an intermediate non-aromatic polymer in which the molecular precursor forms polyanthrylene chains. Employing angle-resolved two-photon photoemission in combination with density functional theory calculations we find that the polymer exhibits two dispersing states which we attribute to the valence and the conduction band, respectively. While the band gap of the non-aromatic polymer obtained in this way is relatively large, namely 5.25 ± 0.06?eV, the gap of the corresponding aromatic GNR is strongly reduced which we attribute to the different degree of electron delocalization in the two systems.

  20. Electronic structure of the CdTe(111) A-(2 × 2) surface

    NASA Astrophysics Data System (ADS)

    Bekenev, V. L.; Zubkova, S. M.

    2015-09-01

    Based on data of scanning tunneling microscopy, ab initio calculations of the electronic structure were performed for the first time for four variants of Cd-terminated polar CdTe(111) A-(2 × 2) surfaces, namely, ideal, relaxed, reconstructed with a Cd vacancy, and reconstructed with the subsequent relaxation. In the approximation of a layered superlattice, the surfaces were simulated by a film with a thickness of 12 atomic layers and a vacuum gap of ˜16 Å. Dangling bonds of Te atoms were closed by adding, on the opposite side of the film, four fictive hydrogen atoms, each having a charge of 0.5 electrons. Ab initio calculations were performed with the QUANTUM ESPRESSO program based on the density functional theory. In each of the variants, the equilibrium coordinates of 16 (15) atoms of cadmium and tellurium of the upper four freestanding layers were determined. It was shown that the relaxation leads to a splitting of layers of both the unreconstructed and reconstructed surfaces. For four variants of the surfaces, the band structures were calculated and analyzed, as well as the total densities of states of the surfaces and densities of states of individual layers. After the relaxation of the reconstructed surface, the upper two atomic layers 11 and 12 changed their places, which can be responsible for the specific features of the surface structure of these layers.