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1

Surface-wave suppression band gap and plane-wave reflection phase band of mushroomlike photonic band gap structures  

NASA Astrophysics Data System (ADS)

Mushroomlike photonic band gap (PBG) structures exhibit two band gap characteristics: surface-wave suppression and in-phase reflectivity. The fundamental electromagnetic properties and the relationship between the surface-wave suppression band gap and the plane-wave reflection phase band are investigated and clarified by a finite-element full-wave analysis. The results of the plane-wave bistatic reflection experiments on mushroomlike PBG plates in an anechoic chamber are in good agreement with those of numerical simulation, confirming the phenomenon of dual in-phase reflection, i.e., dual-resonant behavior, for a transverse magnetic polarization plane wave at oblique incidence on a mushroomlike PBG surface. A modified local resonance cavity cell model of a PBG structure is presented to provide insight into the physical mechanism of dual-resonant behavior.

Li, Long; Chen, Qiang; Yuan, Qiawei; Liang, Changhong; Sawaya, Kunio

2008-01-01

2

Investigations of the Band Structure and Morphology of Nanostructured Surfaces  

NASA Astrophysics Data System (ADS)

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

Knox, Kevin R.

3

Band Structure  

NASA Astrophysics Data System (ADS)

This chapter deals with the ordering of the valence bands - a topic that has controversially been discussed for more than 40 years. The ? 7, ? 9, ? 7 ordering is discussed in the light of very recent ab initio band structure calculations, and the important role is emphasized, which the Zn 3d-band position plays to the sign of the spin-orbit splitting. This topic is touched again from a different point of view in Chap. 6 on free excitons. Then we summarize the experimental findings on the cationic and anionic substitutions in ZnO and random alloy formation essential for quantum hetero-structures. The chapter closes with the data on the valence and conduction band discontinuities in iso- and hetero-valent hetero-structures.

Meyer, B. K.

4

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

SciTech Connect

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.

Alducin, M.; Silkin, V.M.; Juaristi, J.I.; Chulkov, E.V. [Departamento de Ingenieria Electrica, ETSII, UPV/EHU, Alda. de Urquijo s/n, E-48013 Bilbao (Spain); Donostia International Physics Center (DIPC), P. Manuel de Lardizabal 4, 20018 San Sebastian (Spain); Departamento de Fisica de Materiales and Centro Mixto CSIC-UPV/EHU, Facultad de Quimicas, UPV/EHU, Apartado 1072, 20080 San Sebastian (Spain)

2003-03-01

5

Band structure and Fermi surface of atomically uniform lead films  

Microsoft Academic Search

Atomically uniform lead films are prepared on Si(111)-(7×7) substrates by the molecular beam epitaxy method, and their electronic structures are investigated by high-resolution angle-resolved photoemission spectroscopy and first-principles density functional theory calculations. We have observed the six-fold symmetric Fermi surfaces of Pb\\/Si(111)-(7×7) films. Their topology and size are almost the same regardless of the difference of film thicknesses (17, 21,

Shaolong He; Zhenhua Zeng; Masashi Arita; Masahiro Sawada; Shan Qiao; Guoling Li; Wei-Xue Li; Yan-Feng Zhang; Yi Zhang; Xucun Ma; Jinfeng Jia; Qi-Kun Xue; Hirofumi Namatame; Masaki Taniguchi

2010-01-01

6

Waveguiding in Surface Plasmon Polariton Band Gap Structures  

Microsoft Academic Search

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

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

2001-01-01

7

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

SciTech Connect

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.

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

2005-07-15

8

Electronic band structure of CuInSe2: Bulk and (112) surface  

NASA Astrophysics Data System (ADS)

The nonlinear optical properties and potential technological applications of chalcopyrites have attracted attention in the last few years. The electronic band structure of their surfaces, and of interfaces, quantum wells, and superlattices with chalcopyrites as one of the components, contributes to a deeper understanding of the details underlying their interesting properties. In this paper, we use the Slater-Koster formalism to set a tight-binding Hamiltonian for Cu-based chalcopyrites. We use an sp3 basis for both an atom belonging to the IIIA group (In) and one belonging to the VIA one (Se). For the Cu atom, we use a full sp3d5 basis. With tight-binding parameters (TBP's) obtained from Harrison's formulas, we can reproduce the characteristics of the known ab initio calculated bulk electronic band structures. The gaps are, nevertheless, very badly reproduced. We found a set of more suitable on-site TBP's for Cu by minimizing the deviation from the experimental gap value for the whole series of chalcopyrites considered. Small adjustments with the other on-site TBP's allowed us to fit the experimental optical gap values accurately. Here we present our result for the bulk band structure of CuInSe2, and compare it with the existing ab initio calculations. We also consider the effect of tetragonal deformation. We then proceed to use this Hamiltonian to calculate the (112) surface local density of states making use of the surface Green's-function matching method. This particular direction is the one in which this chalcopyrite is grown to produce an interface with some zinc-blende II-VI semiconductors (CdS, for example) in highly efficient solar cells.

Rodríguez, J. A.; Quiroga, L.; Camacho, A.; Baquero, R.

1999-01-01

9

Polarization Sensitive Surface Band Structure of Doped BaTiO_{3}(001).  

PubMed

We present a spatial and wave-vector resolved study of the electronic structure of micron sized ferroelectric domains at the surface of a BaTiO_{3}(001) single crystal. The n-type doping of the BaTiO_{3} is controlled by in situ vacuum and oxygen annealing, providing experimental evidence of a surface paraelectric-ferroelectric transition below a critical doping level. Real space imaging of photoemission threshold, core level and valence band spectra show contrast due to domain polarization. Reciprocal space imaging of the electronic structure using linearly polarized light provides unambiguous evidence for the presence of both in- and out-of-plane polarization with two- and fourfold symmetry, respectively. The results agree well with first principles calculations. PMID:24093301

Rault, J E; Dionot, J; Mathieu, C; Feyer, V; Schneider, C M; Geneste, G; Barrett, N

2013-09-20

10

Polarization Sensitive Surface Band Structure of Doped BaTiO3(001)  

NASA Astrophysics Data System (ADS)

We present a spatial and wave-vector resolved study of the electronic structure of micron sized ferroelectric domains at the surface of a BaTiO3(001) single crystal. The n-type doping of the BaTiO3 is controlled by in situ vacuum and oxygen annealing, providing experimental evidence of a surface paraelectric-ferroelectric transition below a critical doping level. Real space imaging of photoemission threshold, core level and valence band spectra show contrast due to domain polarization. Reciprocal space imaging of the electronic structure using linearly polarized light provides unambiguous evidence for the presence of both in- and out-of-plane polarization with two- and fourfold symmetry, respectively. The results agree well with first principles calculations.

Rault, J. E.; Dionot, J.; Mathieu, C.; Feyer, V.; Schneider, C. M.; Geneste, G.; Barrett, N.

2013-09-01

11

Accessing Surface Brillouin Zone and Band Structure of Picene Single Crystals  

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

12

Surface and bulk electronic structure of the unconventional superconductor Sr2RuO4: unusual splitting of the ? band  

NASA Astrophysics Data System (ADS)

We present an angle-resolved photoemission study of the surface and bulk electronic structure of the single layer ruthenate Sr2RuO4. As the early studies by photoemission and scanning tunneling microscopy were confronted with a problem of surface reconstruction, surface ageing was previously proposed as a possible remedy to access the bulk states. Here, we suggest an alternative way by demonstrating that, in the case of Sr2RuO4, circularly polarized light can be used to disentangle the signals from the bulk and surface layers, thus opening the possibility to investigate many-body interactions both in bulk and surface bands. The proposed procedure results in improved momentum resolution, which enabled us to detect an unexpected splitting of the surface ? band. We discuss the origin of the splitting of the ? band and the possible connection with the Rashba effect at the surface.

Zabolotnyy, V. B.; Carleschi, E.; Kim, T. K.; Kordyuk, A. A.; Trinckauf, J.; Geck, J.; Evtushinsky, D.; Doyle, B. P.; Fittipaldi, R.; Cuoco, M.; Vecchione, A.; Büchner, B.; Borisenko, S. V.

2012-06-01

13

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

NASA Astrophysics Data System (ADS)

We have investigated the influence of GaAs surface termination on the nanoscale structure and band offsets of GaSb/GaAs quantum dots (QDs) grown by molecular-beam epitaxy. Transmission electron microscopy reveals both coherent and semi-coherent clusters, as well as misfit dislocations, independent of surface termination. Cross-sectional scanning tunneling microscopy and spectroscopy reveal clustered GaSb QDs with type I band offsets at the GaSb/GaAs interfaces. We discuss the relative influences of strain and QD clustering on the band offsets at GaSb/GaAs interfaces.

Zech, E. S.; Chang, A. S.; Martin, A. J.; Canniff, J. C.; Lin, Y. H.; Millunchick, J. M.; Goldman, R. S.

2013-08-01

14

Electronic band structure and fermi surface of CaB6 studied by angle-resolved photoemission spectroscopy  

NASA Astrophysics Data System (ADS)

Electronic band structure and fermi surface of CaB6 studied by angle-resolved photoemission spectroscopy S. SOUMA, T. TAKAHASHI, H. KOMATSU, N. KIMURA, H. AOKI, S. KUNII, Department of Physics, Tohoku Univ., Japan R. KAJI, Y. YOKOO, J. AKIMITSU, Department of Physics, Aoyama-Gakuin Univ., Japan We report high-resolution angle-resolved photoemission spectroscopy (ARPES) on CaB_6. The band structure determined by ultraviolet ARPES shows a 1-eV energy gap at X point between the valence and the conduction band, consistent with the LDA+GW calculation but inconsistent with the LDA calculation. High resolution measurements have revealed a small electron pocket at X point, whose carrier number is estimated to be 4-5×10^19 cm-3, in good agreement with the Hall resistivity measurement with the same crystal. The experimental results are discussed in comparison with band structure calculations and theoretical models for the high-temperature ferromagnetism.

Souma, Seigo; Takahashi, Takashi; Komatsu, Hirotaka; Kimura, Noriaki; Aoki, Haruyoshi; Kunii, Satoru; Kaji, Rina; Yokoo, Tetsuya; Akimitsu, Jun

2003-03-01

15

Electronic structure of graphene on a reconstructed Pt(100) surface: Hydrogen adsorption, doping, and band gaps  

NASA Astrophysics Data System (ADS)

We probe the structure and electronic band structure of graphene grown on a Pt(100) substrate using scanning tunneling microscopy, low energy electron diffraction, and angle-resolved photoemission spectroscopy. It is found that the graphene layer lacks a well-defined azimuthal orientation with respect to the substrate, causing a circular smearing of the ? band instead of a well-defined Dirac cone near the Fermi level. The graphene is found to be electron doped placing the Dirac point ˜0.45 eV below the Fermi level, and a gap of 0.15±0.03 eV is found at the Dirac point. We dose atomic hydrogen and monitor the coverage on the graphene by analyzing the impurity-induced broadening of the ?-band width. Saturation of graphene on Pt(100) with hydrogen does not expand the band gap, but instead hydrogen-mediated broadening and rehybridization of the graphene sp2 bonds into sp3 leads to a complete disruption of the graphene ? band, induces a lifting of the Pt(100) reconstruction, and introduces a dispersing Pt state near the Fermi level. Deposition of rubidium on graphene on Pt(100) leads to further electron doping, pushing the Dirac point to a binding energy of ˜1.35 eV, and increasing the band gap to 0.65±0.04 eV.

Ulstrup, Søren; Nilsson, Louis; Miwa, Jill A.; Balog, Richard; Bianchi, Marco; Hornekær, Liv; Hofmann, Philip

2013-09-01

16

Improved Performance of Amorphous Silicon Photoreceptor by Using a Thick Surface Layer with a Graded-Band-Gap Structure  

NASA Astrophysics Data System (ADS)

A graded-band-gap structure for a thick surface layer was studied to improve the endurance of amorphous silicon (a-Si:H) photoreceptors without deterioration of image quality in high-speed printing. The decay characteristics of the surface potential for the above mentioned photoreceptor after electric charging and subsequent light exposure were compared with those for the ungraded ones. The result shows that the graded-band-gap structure is effective for the restraint of the residual potential in the case of a thick surface layer. The effectiveness was also confirmed by a one-dimensional simulation of the photodecay characteristics, considering the tunnel current through the surface barrier and the neutralization of the surface charges.

Teshima, Akitomo; Miyazaki, Seiichi

2002-11-01

17

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

NASA Astrophysics Data System (ADS)

Porous-pyramids structured silicon surface was prepared and its influence on the reflectance of the silicon surface was studied. The porous-pyramids structured surface was prepared by electrochemical etching in HF/C2H5OH solution after texturization in NaOH/IPA solution. The average reflectance of the surface in the range of 400-800 nm was as low as 1.9%. The optical photographs and SEM images of the surfaces prepared under optimized condition were investigated. The porous-pyramids structured surface has a gradient-index multilayer structure (i.e., the refraction index of the structure increase from the top to the bottom). A formula that describes the relationship between the reflectance and the index of refraction was used to explain the excellent broadband antireflection of the multilayer silicon surface. The technique of this paper may be valuable in the texturization process for high-efficiency silicon solar cells.

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

2012-05-01

18

Selective doping in a surface band and atomic structures of the Ge(111) (\\sqrt{3}\\times \\sqrt{3}){R}3 0^{\\circ}-Au surface  

NASA Astrophysics Data System (ADS)

Atomic and electronic structures of the Ge(111) (\\sqrt{3}\\times \\sqrt{3}){R}3 0^{\\circ}-Au surface with two metallic bands are studied by scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES). The bias-voltage-dependent periodic structure observed by STM is consistent with the electronic structure calculated for an optimized conjugate honeycomb chained trimer (CHCT) model. Electrons are selectively doped to the electron-like surface metallic band by excess Au atoms, which form triangle structures with the Au trimers of the CHCT model. The discrepancy for the bottom energy of the electron-like band between the ARPES results and those of the calculation is attributed to the doping. The triangle structure is mobile at room temperature, but stable at 80 K. Both Au and Ge atoms deposited at room temperature on the Ge(111) (\\sqrt{3}\\times \\sqrt{3}){R}3 0^{\\circ}-Au surface dope electrons to the electron-like surface metallic band. Moreover, the Au atoms increase the spin-orbit interaction at the surface, and thus make the splitting of the spin-polarized band due to the interaction larger than that before the deposition.

Nakatsuji, Kan; Motomura, Yuya; Niikura, Ryota; Komori, Fumio

2013-01-01

19

Electronic Band Structure of Na Adsorbed MoS2(0002) Surface  

NASA Astrophysics Data System (ADS)

Interaction of a MoS_2(0002) surface and surface-deposited Na is investigated by angle-resolved ultraviolet photoemission spectroscopy and a full-potential linearized augmented plane wave density functional theory (FLAPW-DFT). The adsorption of initial sub-monolayer amount of Na onto the basal plane introduces a new density of states at ca 1.2 eV above the valence band maximum of the MoS_2, with FWHM of 0.4 eV. The band dispersion of the new supravalence peak is less than 0.1 eV, indicating highly localized charge. The DFT calculation further reveals the major contribution from the Mo4d orbitals. Thus, the interaction between Na and MoS_2(0002) may be characterized as the ``pure'' electron transfer, as opposed to the chemical reduction observed in Li/MoS_2(0002).

Park, K. T.; Ellis, T. S.; Jayasinghe, A.; Hulbert, S.; Ulrich, M. D.; Rowe, J.

2004-03-01

20

Electronic Band Structure of Na Adsorbed MoS2(0002) Surface  

Microsoft Academic Search

Interaction of a MoS_2(0002) surface and surface-deposited Na is investigated by angle-resolved ultraviolet photoemission spectroscopy and a full-potential linearized augmented plane wave density functional theory (FLAPW-DFT). The adsorption of initial sub-monolayer amount of Na onto the basal plane introduces a new density of states at ca 1.2 eV above the valence band maximum of the MoS_2, with FWHM of 0.4

K. T. Park; T. S. Ellis; A. Jayasinghe; S. Hulbert; M. D. Ulrich; J. Rowe

2004-01-01

21

Electronic structure and Fermi surface of the two-dimensional three-band Hubbard model in doped cuprates  

SciTech Connect

The electronic structure of the high-{ital T}{sub {ital c}} copper oxides is calculated by means of an extended two-dimensional three-band Hubbard model in the unrestricted Hartree-Fock approximation. The influence of the coupling parameters on the obtained bands, as well as their doping dependence are investigated especially at the Fermi surface. Results are discussed in the light of recent experimental data for the cuprate Fermi surfaces. A comparative analysis of these conflicting data on the basis of our results sheds some light on the interpretation of the measured band structures. The direct oxygen-oxygen hopping interaction is found to be essential in fitting experimental results, suggesting that, in the doped regime, the oxygen band plays a key role at least in the near-{ital E}{sub {ital F}} region. Antiferromagnetic correlations among copper atoms turn out as well to be crucial. The results agree remarkably well with previous local-density calculations and with spectroscopic measurements.

Lopez Sancho, M.P.; Rubio, J.; Refolio, M.C.; Lopez Sancho, J.M. [Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Cientificas, Serrano 144, 28006 Madrid (Spain)

1995-09-01

22

Electric-field tuning of the surface band structure of topological insulator Sb2Te3 thin films.  

PubMed

We measured the response of the surface state spectrum of epitaxial Sb(2)Te(3) thin films to applied gate electric fields by low temperature scanning tunneling microscopy. The gate dependent shift of the Fermi level and the screening effect from bulk carriers vary as a function of film thickness. We observed a gap opening at the Dirac point for films thinner than four quintuple layers, due to the coupling of the top and bottom surfaces. Moreover, the top surface state band gap of the three quintuple layer films was found to be tunable by a back gate, indicating the possibility of observing a topological phase transition in this system. Our results are well explained by an effective model of 3D topological insulator thin films with structure inversion asymmetry, indicating that three quintuple layer Sb(2)Te(3) films are topologically nontrivial and belong to the quantum spin Hall insulator class. PMID:23952429

Zhang, Tong; Ha, Jeonghoon; Levy, Niv; Kuk, Young; Stroscio, Joseph

2013-07-30

23

Structure and Anisotropy of Southern Africa's Lithosphere: Constraints From Broad-band Surface-Wave Dispersion  

NASA Astrophysics Data System (ADS)

Southern Africa contains two of the oldest lithospheric blocks on Earth: the Kaapvaal and Zimbabwe Cratons. Understanding the physical properties of southern African lithosphere can help us learn more of the formation, evolution and dynamics of continents. The Kaapvaal Craton and the neighbouring Limpopo Belt are the focus of our study. We measured Rayleigh and Love wave dispersion across southern Africa using data primarily from the SASE broadband experiment and a combination of cross-correlation and waveform inversion approaches. With both methods, we computed dispersion curves of surface waves in period ranges as broad as 5-200 sec between pairs of stations. Combining the dispersion measurements, we then grouped them into four subsets sampling four sub-regions within the Kaapvaal Craton and the Limpopo Belt, each with a relatively homogeneous structure within it. The dispersion data constrains S-velocity profiles between the sub-regions and requires a reduction in S velocities near the bottom of the lithosphere at 150-200 km, although by different amounts in different parts of the region. Radial anisotropy has been observed in both regions with an amplitude of up to 4% near 50 km depth. In the period range 5-130 s, the azimuthal coverage is sufficient to measure azimuthal anisotropy as well. In the period range 5-10 s, sampling the upper crust, azimuthal anisotropy is particularly strong in the Limpopo Belt, with both the “2?” and “4?” terms needed to explain the data. In the lower crust and uppermost mantle, azimuthal anisotropy is weak across the region. At greater depths, near the lithosphere-asthenosphere boundary, anisotropy is stronger and with fast directions aligning uniformly N-NNE, possibly in the direction of the relative motion of the African plate and asthenosphere beneath.

Adam, J.; Lebedev, S.

2009-12-01

24

Band-gap structures of surface-plasmon polaritons in a subwavelength metal slit filled with periodic dielectrics  

SciTech Connect

We propose a combination structure which consists of a subwavelength metal slit filled periodically with two different dielectrics to modulate slit plasmon polaritons (slit-PPs). The transmission spectra are simulated by the finite-difference time-domain method and the photonic band gaps are observed. The theoretical formula to calculate the band-gap structures is deduced and the calculation results agree satisfactorily with simulated results. This structure can be termed as slit-PP crystal.

Zhou Yunsong [Department of Physics, Capital Normal University, Beijing 100048 (China); Gu Benyuan [Institute of Physics, Chinese Academy of Sciences, Post Office Box 603, Beijing 100080 (China); Wang Huaiyu [Department of Physics, Tsinghua University, Beijing 100084 (China)

2010-01-15

25

Band structures in near spherical 138Ce  

NASA Astrophysics Data System (ADS)

The high spin states of N=80138Ce have been populated in the fusion evaporation reaction 130Te(12C, 4n)138Ce at E=65 MeV. The ? transitions belonging to various band structures were detected and characterized using an array of five Clover Germanium detectors. The level scheme has been established up to a maximum spin and excitation energy of 23? and 9511.3 keV, respectively, by including 53 new transitions. The negative parity ?I=1 band, developed on the 6536.3 keV 15 level, has been conjectured to be a magnetic rotation band following a semiclassical analysis and comparing the systematics of similar bands in the neighboring nuclei. The said band is proposed to have a four quasiparticle configuration of [?gh]??. Other band structures are interpreted in terms of multi-quasiparticle configurations, based on Total Routhian Surface (TRS) calculations. For the low and medium spin states, a shell model calculation using a realistic two body interaction has been performed using the code OXBASH.

Bhattacharjee, T.; Chanda, S.; Bhattacharyya, S.; Basu, S. K.; Bhowmik, R. K.; Das, J. J.; Pramanik, U. Datta; Ghugre, S. S.; Madhavan, N.; Mukherjee, A.; Mukherjee, G.; Muralithar, S.; Singh, R. P.

2009-06-01

26

Band structure and Fermi surface of La0.6Sr0.4MnO3 thin films studied by in situ angle-resolved photoemission spectroscopy  

NASA Astrophysics Data System (ADS)

We have performed an in situ angle-resolved photoemission spectroscopy (ARPES) on single-crystal surfaces of La0.6Sr0.4MnO3 (LSMO) thin films grown on SrTiO3 (001) substrates by laser molecular beam epitaxy, and investigated the electronic structure near the Fermi level (EF) . The experimental results were compared with the band-structure calculation based on local density approximation +U . The band structure of LSMO thin films consists of several highly dispersive O2p derived bands in the binding energy range of 2.0-6.0eV and Mn3d derived bands near EF . ARPES spectra around the ? point show a dispersive band near EF indicative of an electron pocket centered at the ? point, although the suppression of spectral weight occurs in the vicinity of EF . Compared with the band-structure calculation, the observed conduction band is assigned to the Mn3deg majority-spin band responsible for the half-metallic nature of LSMO. We have found that the estimated size of the Fermi surface is consistent with the prediction of the band-structure calculation, while the band width becomes significantly narrower than the calculation. Also, the intensity near EF is strongly reduced. The origin of these discrepancies between the experiment and the calculation is discussed based on the strong electron correlation and the strong electron-phonon coupling.

Chikamatsu, A.; Wadati, H.; Kumigashira, H.; Oshima, M.; Fujimori, A.; Hamada, N.; Ohnishi, T.; Lippmaa, M.; Ono, K.; Kawasaki, M.; Koinuma, H.

2006-05-01

27

Banded structures in stratospheric aerosol distributions  

SciTech Connect

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.

Trepte, C.R. [Science Applications International Corp., Hampton, VA (United States); Thomason, L.W. [NASA Langley Research Center, Hampton, VA (United States); Kent, G.S. [Science and Technology Corp., Hampton, VA (United States)

1994-11-01

28

The electronic band structure of cobalt disulfide(100)  

NASA Astrophysics Data System (ADS)

The pyrite-type transition metal compound CoS2 is an itinerant electron ferromagnet and is predicted, in ground state band structure calculations to be close to half-metallic. The Curie temperature is about 120 K. Although some minority spin states are present at the Fermi level in bulk band structure, the system is predicted to be relatively highly spin polarized. The measured saturation magnetization is less than 1.0 microB/Co expected of ideal half-metallic CoS2, which is consistent with these calculations. The measured transport spin polarizations are 56 - 64 %, as determined from point-contact Andreev reflection. An accurate determination of the surface structure is essential for understanding electron spectroscopy studies, as well as providing a starting point for modeling the interface properties, essential for modeling any spintronics device applications. The success of this work was made possible by the cleavage of sufficiently large CoS2 (100) single crystals. LEED I(V) analysis, was used to determine surface structure. 1S-terminated model is favored, in which, the atoms in sublayer S and Co relax outward (toward the vacuum) and inward (toward the bulk), along the surface normal by approximately 0.03 and 0.11 A, respectively. This kind of surface relaxation of best-fit model is also confirmed by surface stability studies. Photon energy dependent and angle dependent photoemission spectra were taken in order to map out the bulk band structure (k?) along surface normal and surface band structure (k//) respectively. The agreement between experimental and theory calculation suggests that the CoS 2 bulk band structure near the Fermi level is sensitive to the S-S separation, and the half-metallic gap may be controlled by antibonding sulfur p states, rather than exchange splitting of Co d states. The calculated surface band structure for the (100) surface includes the corrections for the known surface relaxation. The comparison with the experimental k// indicates that the photoemission spectra are indeed dominated by surface weighted bands. The surface state and surface resonance band dispersions in theoretical and experimental band mappings are in general agreement. The spin polarized band structure calculations indicate a true surface state in the minority spin band structure.

Wu, Ning

29

Photonic Band Structure of fcc Colloidal Crystals  

Microsoft Academic Search

Polystyrene colloidal crystals form three dimensional periodic dielectric structures which can be used for photonic band structure measurements in the visible regime. From transmission measurements the photonic band structure of an fcc crystal has been obtained along the directions between the L point and the W point. Kossel line patterns were used for locating the symmetry points of the lattice

I. Inanç Tarhan; George H. Watson

1996-01-01

30

Tuning Semiconductor Band Edge Energies via Surface Ligand Passivation  

NASA Astrophysics Data System (ADS)

Semiconductor band gaps and band edge energies are key parameters that can dictate the efficiency of photocatalysis in solar energy conversion applications. CdSe is a representative semiconducting system with an ideal band gap for solar photon absorption, but with band edge energies that are not positioned for efficient water splitting. Using first-principles calculations within density functional theory, we present a study of the electronic structure of passivated CdSe surfaces and nanostructures, exploring the ability to tune band edge energies in this system via chemisorbed ligands. We predict substantial shifts in band edge energies that are electrostatic in origin, and due to the induced dipole at the CdSe-ligand interface and the intrinsic dipole of the ligand. We further show that, by changing the size and orientation of the ligand's intrinsic dipole moment via novel functionalization strategies, we can control the magnitude and direction of the shifts of CdSe energy levels. The effect of ligands on energy levels of two-dimensional CdSe surfaces and nanocrystal surfaces are thoroughly discussed.

Yang, Shenyuan; Prendergast, David; Neaton, Jeffrey

2011-03-01

31

Band structure of 78Kr  

Microsoft Academic Search

Lifetimes of fifteen states of the ground-state, octupole and gamma-band in 78Kr have been measured; energies and E2 transition strengths have been interpreted in terms of the neutron-proton boson model.

H. P. Hellmeister; U. Kaup; J. Keinonen; K. P. Lieb; R. Rascher; R. Ballini; J. Delaunay; H. Dumont

1979-01-01

32

Study on Surface Acoustic Wave Characteristics of SiO2/Interdigital-Transducer/ZnO/Diamond Structure and Fabrication of 2.5 GHz Narrow Band Filter  

NASA Astrophysics Data System (ADS)

Surface acoustic wave (SAW) characteristics of the SiO2/interdigital-transducer(IDT)/ZnO/diamond structure were studied theoretically and experimentally. It was found that the 2nd mode in this structure can provide a zero temperature coefficient of frequency (TCF) as well as high velocity of 10,000 m/s and a large electromechanical coupling coefficient of 1.4%. Utilizing this wave, a 2.5 GHz narrow-band SAW filter was successfully fabricated with IDTs of 0.9 µm finger width, which resulted in superior characteristics for a retiming filter with a small insertion loss of 6.7 dB, Q value of 660 and small frequency deviation of 100 ppm in the temperature range from -40 to 85°C. The insertion loss is smaller than any other retiming filters which have ever been reported with quartz, a conventional SAW material, and also the frequency deviation with temperature is smaller than that in the case of ST-cut quartz.

Nakahata, Hideaki; Kitabayashi, Hiroyuki; Uemura, Tomoki; Hachigo, Akihiro; Higaki, Kenjiro; Fujii, Satoshi; Seki, Yuichiro; Yoshida, Kentaro; Shikata, Shin-ichi

1998-05-01

33

Quantum Optical Sources in Photonic Band Structures.  

National Technical Information Service (NTIS)

The advent of 3D periodic dielectric structure possessing photonic band gaps (PBGs) and the ability to incorporate defects in the structure, offer far greater control over the spatial modulation of the field amplitude, and the spectral distribution of its...

G. Kurizki

1995-01-01

34

High spin band structures in104Cd  

NASA Astrophysics Data System (ADS)

High spin states in104Cd have been investigated by means of heavy ion induced reactions using the Nordball detector array. The level scheme constructed from ??-coincidences is dominated by three band structures. The positive parity band shows no rotational like energy spacing. It is thus understood mostly in terms of quasiparticle excitations with vd5/2, vg7/2 and ?g9/2 configurations. The collective properties of the negative parity bands are more pronounced. These bands are most likely due to v(h11/2,d5/2) and v(h11/2,g7/2) structures.

Klamra, W.; Adamides, E.; Atac, A.; Bark, R. A.; Cederwall, B.; Fahlander, C.; Fogelberg, B.; Gizon, A.; Gizon, J.; Grawe, H.; Ideguchi, E.; Jerrestam, D.; Johnson, A.; Julin, R.; Juutinen, S.; Kaczmarczyk, W.; Kerek, A.; Kownacki, J.; Mitarai, S.; Norlin, L. O.; Nyberg, J.; Piiparinen, M.; Schubart, R.; Seweryniak, D.; Sletten, G.; Törmänen, S.; Virtanen, A.; Wyss, R.

1995-06-01

35

Effective Band Structure of Random Alloys  

NASA Astrophysics Data System (ADS)

Random substitutional AxB1-x alloys lack formal translational symmetry and thus cannot be described by the language of band-structure dispersion E(k?). Yet, many alloy experiments are interpreted phenomenologically precisely by constructs derived from wave vector k?, e.g., effective masses or van Hove singularities. Here we use large supercells with randomly distributed A and B atoms, whereby many different local environments are allowed to coexist, and transform the eigenstates into an effective band structure (EBS) in the primitive cell using a spectral decomposition. The resulting EBS reveals the extent to which band characteristics are preserved or lost at different compositions, band indices, and k? points, showing in (In,Ga)N the rapid disintegration of the valence band Bloch character and in Ga(N,P) the appearance of a pinned impurity band.

Popescu, Voicu; Zunger, Alex

2010-06-01

36

Band structure of NiO revisited  

Microsoft Academic Search

The band structure of a strongly correlated semiconductor as NiO has been the\\u000aobject of much debate [PRL 103, 036404 (2009); PRL 102, 226401 (2009)]. Most\\u000aauthors, using computational techniques well beyond the simple density\\u000afunctional theory and the approximations GGA or LDA, claim that the band gap is\\u000aabout 4.0 eV and that the conduction band is of Ni-3d

Luiz G. Ferreira; Lara K. Teles; Marcelo Marques

2009-01-01

37

Band structure of NiO revisited  

Microsoft Academic Search

The band structure of a strongly correlated semiconductor as NiO has been the object of much debate [PRL 103, 036404 (2009); PRL 102, 226401 (2009)]. Most authors, using computational techniques well beyond the simple density functional theory and the approximations GGA or LDA, claim that the band gap is about 4.0 eV and that the conduction band is of Ni-3d

Luiz G. Ferreira; Lara K. Teles; Marcelo Marques

2009-01-01

38

A Second-Order Dual X-\\/Ka-Band Frequency Selective Surface  

Microsoft Academic Search

In this letter, a new technique for designing dual-band frequency selective surfaces with arbitrary bands of operation, with second-order band-pass responses at each band of operation, is presented and experimentally verified. The technique is based on utilizing a particular topology of a second-order band-pass microwave filter and synthesizing its constituting elements using periodic structures with inductive, capacitive, or resonant type

Mohsen Salehi; Nader Behdad

2008-01-01

39

Structural colours in blue-banded bee  

NASA Astrophysics Data System (ADS)

Periodic, micro-textured biological materials are ubiquitous in nature. Electromagnetic waves at different frequencies are selectively reflected by such materials. This phenomenon is the origin of structural colours observed in variety of insects. In this work, we analyze the mechanisms that lead to the bluish-green colour of the blue-banded bee feathers. The reflection spectrum of the blue-banded bee feather was calculated by the transfer matrix method (TMM). The reflection peaks found are compatible within the experimental data. In addition to Bragg scattering, guided resonance has been observed in our theoretical calculation, which leads to a novel understanding of the structural colours in blue-banded bees.

Wan, Jones; Dai, Lixiin; Li, Jensen; Fung, Kwok-Kwong; Chan, Che-Ting

2006-03-01

40

Doping of a surface band on Si (111) &surd;(3)×&surd;(3)Ag  

Microsoft Academic Search

A semiconducting surface-state band on Si (111) &surd;(3)×&surd;(3)-Ag is doped by adsorption of additional Ag and Au atoms. Very high levels of doping can be achieved (0.0015 0.086 electrons per 1×1 unit cell), such that the silicon surface degenerates into a metal. The doping alters the band structure of the surface state and causes the rigid-band model to break down.

J. N. Crain; M. C. Gallagher; J. L. McChesney; M. Bissen; F. J. Himpsel

2005-01-01

41

Design of dual band band-pass filter using defected ground structure  

Microsoft Academic Search

A dual band band-pass filter using ring resonator and defected ground structure is presented in this paper. In design, a ring resonator is used to generate two pass bands, and two defected ground structures help to realize high impedance microstrip lines, which make the control process of the two pass band frequencies convenient. To verify the design, a dual band

Changjiang You; Xiaowei Zhu

2010-01-01

42

Structural colours in blue-banded bee  

Microsoft Academic Search

Periodic, micro-textured biological materials are ubiquitous in nature. Electromagnetic waves at different frequencies are selectively reflected by such materials. This phenomenon is the origin of structural colours observed in variety of insects. In this work, we analyze the mechanisms that lead to the bluish-green colour of the blue-banded bee feathers. The reflection spectrum of the blue-banded bee feather was calculated

Jones Wan; Lixiin Dai; Jensen Li; Kwok-Kwong Fung; Che-Ting Chan

2006-01-01

43

The Band Structure of Bismuth Telluride  

Microsoft Academic Search

Calculations of the band structure of Bi2Te3 are carried out by means of a pseudopotential approach. The pseudopotential used in the calculation is the model potential of Abarenkov, Animalu and Heine. The spin-orbit term is included from the start. The inclusion of the spin-orbit term serves to avoid band overlap throughout the Brillouin zone. The secular equations derived from the

Shin-ichi Katsuki

1969-01-01

44

Engineering band structures in correlated oxides  

NASA Astrophysics Data System (ADS)

The electronic structure of short period digital superlattices of two different phases depends strongly on the superlattice architecture. We have fabricated digital superlattices of super cells consisting of N layers of LaMnO3 and N layers of SrTiO 3, N=1, 2, 3, 8, and measured their optical conductivities to probe the way in which the electronic structure depends on N. We found the valence band structure systematically changes, as N decreases, from bulk like band gaps to interface modified band gaps. The temperature dependence of the derived Mn Jahn-Teller/Mott gap in large period superlattices is completely different from the small period, suggesting different spin ordering states reside in them. The electronic structure of two parent materials are coherently blended at the interface, and the spin ordering is strongly modified. This method of producing meta materials is a promising new way of material engineering.

Zhai, Xiaofang

45

Tunable band structure effects on ballistic transport in graphene nanoribbons  

Microsoft Academic Search

Graphene nanoribbons (GNR) in mutually perpendicular electric and magnetic fields are shown to exhibit dramatic changes in their band structure and electron transport properties. A strong electric field across the ribbon induces multiple chiral Dirac points, closing the semiconducting gap in armchair GNRs. A perpendicular magnetic field induces partially formed Landau levels as well as dispersive surface-bound states. Each of

Oleksiy Roslyak; Godfrey Gumbs; Danhong Huang

2010-01-01

46

Nonreciprocal microwave band-gap structures.  

PubMed

An electrically controlled nonreciprocal electromagnetic band-gap material is proposed and studied. The new material is a periodic three-dimensional regular lattice of small magnetized ferrite spheres. In this paper, we consider plane electromagnetic waves in this medium and design an analytical model for the material parameters. An analytical solution for plane-wave reflection from a planar interface is also presented. In the proposed material, a new electrically controlled stop band appears for one of the two circularly polarized eigenwaves in a frequency band around the ferrimagnetic resonance frequency. This frequency can be well below the usual lattice band gap, which allows the realization of rather compact structures. The main properties of the material are outlined. PMID:12241501

Belov, P A; Tretyakov, S A; Viitanen, A J

2002-07-24

47

Electronic Band Structure of Carbon Nanotubes with Quinoid Structure  

NASA Astrophysics Data System (ADS)

In this paper, we fully describe the geometry of atomic structure of carbon nanotube with quinoid structure. Electronic energy band structure of carbon nanotubes with quinoid structure is studied by tight-binding approximation. In the presence of bond alternation, calculations show that only armchair (n, n) carbon nanotube (without twisting) remains metallic and zigzag (3? - 1, -3? + 1) CNT becomes metallic at the critical elongation. Effect of deformation on the change of band gap is also calculated and discussed.

Hieu, Nguyen Ngoc; Anh, Nguyen Pham Quynh

2013-10-01

48

Band Structure of Polymeric Sulfur Nitride.  

National Technical Information Service (NTIS)

Using the Extended Huckel Method, a band structure calculation of polymeric sulfur nitride based on X-ray crystallographic data has been carried out. The results of the calculation suggest that the metallic properties of (SN)x arise from the accidental ov...

A. A. Bright P. Soven

1975-01-01

49

Multilayer Structures Based on Doped Graded-Band-Gap Semiconductors: Features of Energy Band Diagram  

Microsoft Academic Search

The paper theoretically examines the distinctive features of the energy band gap diagram of symmetric multilayer structures based on uniformly doped graded-band-gap semiconductors with constant gradients of energy band gap and electron affinity. By means of analytical and numerical calculations, it is shown that the energy band diagram of such multilayer structures substantially depends on the layer thickness, with its

B. S. Sokolovskii

1997-01-01

50

Photonic band structure of bcc colloidal crystals  

Microsoft Academic Search

Self-ordering colloidal systems are being recognized as possible candidates for optical photonic crystals. Such structures exhibit three-dimensional periodicity in refractive index, and possess lattice dimensions comparable to optical wavelengths. Recently, fcc colloidal crystals of water-suspended polystyrene microspheres were investigated in the context of photonic band structure. At lower polystyrene volume fractions, these colloidal suspensions crystallize in the bcc crystal lattice.

Ranjit D. Pradhan; John A. Bloodgood; George H. Watson

1997-01-01

51

The use of surface properties for determining semiconductor band gaps  

Microsoft Academic Search

Gallium arsenide surface photovoltage variations with temperature are studied near the band gap, by wavelength modulation spectroscopy. It is thus possible to measure the band gap with the same accuracy as in electroreflectance but with a better signal-to-noise ratio and without making any contact with the surface. The results are compared with similar ones obtained by classical methods.

L. Lassabatere; C. Alibert; J. Bonnet; L. Soonckindt

1976-01-01

52

Direct determination of III-V semiconductor surface band gaps  

Microsoft Academic Search

Applying in situ combination of angle-resolved photoemission and inverse photoemission to cleaved III-V compound semiconductor (110) surfaces, we have determined the surface band gaps between the filled anion-derived dangling-bound state A5 and the empty cation-derived state C3 at the Gamma¯, X¯ ', X¯, and M¯ points of the surface Brillouin zone. The values of the surface band gaps of the

H. Carstensen; R. Claessen; R. Manzke; M. Skibowski

1990-01-01

53

Surface band-gap narrowing in quantized electron accumulation layers.  

PubMed

An energy gap between the valence and the conduction band is the defining property of a semiconductor, and the gap size plays a crucial role in the design of semiconductor devices. We show that the presence of a two-dimensional electron gas near to the surface of a semiconductor can significantly alter the size of its band gap through many-body effects caused by its high electron density, resulting in a surface band gap that is much smaller than that in the bulk. Apart from reconciling a number of disparate previous experimental findings, the results suggest an entirely new route to spatially inhomogeneous band-gap engineering. PMID:20867408

King, P D C; Veal, T D; McConville, C F; Zúñiga-Pérez, J; Muñoz-Sanjosé, V; Hopkinson, M; Rienks, E D L; Jensen, M Fuglsang; Hofmann, Ph

2010-06-24

54

Wakefield Band Partitioning in LINAC Structures  

SciTech Connect

In the NLC project multiple bunches of electrons and positrons will be accelerated initially to a centre of mass of 500 GeV and later to 1 TeV or more. In the process of accelerating 192 bunches within a pulse train, wakefields are excited which kick the trailing bunches off axis and can cause luminosity dilution and BBU (Beam Break Up). Several structures to damp the wakefield have been designed and tested at SLAC and KEK and these have been found to successfully damp the wakefield [1]. However, these 2{pi}/3 structures suffered from electrical breakdown and this has prompted us to explore lower group velocity structures operating at higher fundamental mode phase advances. The wakefield partitioning amongst the bands has been found to change markedly with increased phase advance. Here we report on general trends in the kick factor and associated wakefield band partitioning in dipole bands as a function of phase advance of the synchronous mode in linacs. These results are applicable to both TW (travelling wave) and SW (standing wave) structures.

Jones, Roger M

2003-03-25

55

X-band photonic band-gap accelerator structure breakdown experiment  

NASA Astrophysics Data System (ADS)

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 65MV/m yielding a breakdown rate of two breakdowns per hour at 60 Hz. An accelerating gradient above 110MV/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 100MV/m and a surface magnetic field of 890kA/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 14MV/m, is enhanced at small tips and projections caused by pulsed heating, leading to breakdown. Future PBG structures should be built to minimize pulsed surface heating and temperature rise.

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

2011-02-01

56

A novel compact K band PBG microstrip structure band-pass filter  

Microsoft Academic Search

A novel K band band-pass filter based on photonic band-gap (PBG) is presented. The proposed structures exhibit low insertion loss, compact size, simple fabrication and slow-wave characteristics. Due to slow-wave characteristic, PBG structure minimizes the pass-band filter to one-tenth of conventional filters with spurious-free response and deep attenuation levels. The miniature band-pass filter was simulated, realized and measured. There is

Haili Lin; Junfa Mao; Jianyu Liu

2005-01-01

57

Band structure and related properties of bcc niobium  

SciTech Connect

We report self-consistent, all-electron calculations of the band structure of paramagnetic bcc niobium. Density-functional theory and the linear combination of Gaussian orbitals method were employed. Results are presented and discussed in the light of the existing theoretical and experimental data for the energy bands, density of states, Fermi surface, optical conductivity, x-ray form factors, and Compton profile. In addition, spin-polarized band-structure calculations were carried out to investigate a possible magnetically ordered state for large values of the lattice constant. A composite transition from a nonmagnetic to a low-spin ferromagnetic state and from a low to a high-spin state was found.

Jani, A.R.; Brener, N.E.; Callaway, J.

1988-11-15

58

The electronic band structure of bismuth telluride  

Microsoft Academic Search

Summary  The electronic band structure of Bi2Te3 has been calculated by using the pseudopotential method. A detailed analysis of the sensitivity of the various levels indicated\\u000a the impossibility of using some analytic form of the effective potential. The Fourier coefficients of the pseudopotential\\u000a have been therefore chosen semi-empirically so as to obtain an energy gap throughout the whole Brillouin zone without

F. Borghese; E. Donato

1968-01-01

59

Cu(111) Electron Band Structure and Channeling by VLEED  

NASA Astrophysics Data System (ADS)

Very-low-energy electron diffraction (VLEED) intensities from clean Cu(111) surface have been measured in detail in the energy range 15 to 35 eV by low-energy electron microscope. Corresponding theoretical I - V curves are obtained in good agreement with experimental data when the anisotropy of the electron attenuation is taken into account. The coincidence of the peaks in the I - V curves at normal incidence with two kinds of energy gaps of the electron band structure of the copper crystal (Ek=0) is interpreted. The small width of the resonance peak in the I - V curve at normal incidence is explained in terms of electron surface channeling. VLEED thus provides information about the unoccupied part of the electron band structure of copper which complements that obtained from angular resolved photoemission.

Bartos, I.; Barbieri, A.; van Hove, M. A.; Chung, W. F.; Cai, Q.; Altman, M. S.

1997-10-01

60

Surface hardening of steel ShKh15 by band-type electron beam  

SciTech Connect

It is shown that when a band-type electron beam is used for surface heat treatment, the hardened steels have the same microhardness and structure across the thickness as after treatment with electron or laser beam with circular cross section. The use of a band-type electron beam provides for much more uniform treatment of the surface than an electron or laser beam with circular cross section. Surface hardening of steel products with band-type electron beam may be recommended for use in industry.

Shul'ga, A.A.; Dudko, G.V.; Solov'ev, A.I.

1988-07-01

61

Band bending and electrical transport at chemically modified silicon surfaces  

NASA Astrophysics Data System (ADS)

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

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

2002-03-01

62

Aqueous phase-synthesized small CdSe quantum dots: adsorption layer structure and strong band-edge and surface trap emission  

Microsoft Academic Search

We synthesized, in aqueous solution at room temperature, small water-soluble CdSe quantum dots (QDs) with strong photoluminescence\\u000a (PL) and then correlated the PL with their adsorption layer structure. For synthesizing the QDs, their initial synthesis condition\\u000a was controlled to form small Cd-containing species capable of passivating dangling bonds on the CdSe core surface. Each CdSe\\u000a QD (d ~ 2.5 nm) consisted of a

Yeon-Su Park; Yukihiro Okamoto; Noritada Kaji; Manabu Tokeshi; Yoshinobu Baba

63

Comparison of surface-treated and untreated orthodontic bands: Evaluation of shear force and surface roughness  

Microsoft Academic Search

In an attempt to increase retention of orthodontic bands, orthodontic companies market bands with surfaces prepared to increase roughness. A comparison of six groups of bands, including two with untreated surfaces, revealed a wide range of variation in shear forces. Three classes of retention may be differentiated on the basis of non–statistically significantly different mean shear forces in each category:

Robert A Penna; Francis Mante; Bryan D Huey; Joseph Ghafari

1998-01-01

64

Observation of Band-Bending at the Bare Si(100) Surface Using STM Spectroscopy  

NASA Astrophysics Data System (ADS)

We have investigated the electronic structure of the Si(100) surface by scanning tunneling spectroscopy. We find that the spectral features of the Si(100) surface shift energetically depending on the STM tip height above the surface. In particular, the ?^* band shifts by as much as 1 eV for a tip height change on the order of 1 ÅThis effect also causes apparent phase inversion of dimer row images when the tip is held at different heights above the surface but kept at identical positive sample biases. We explain this behavior through tip-induced band-bending of Si(100) surface states.

Nagaoka, Katsumi; Comstock, Matthew; Hammack, Aaron; Crommie, Michael F.

2003-03-01

65

Dynamical mean field band structure: LDA++ approach.  

NASA Astrophysics Data System (ADS)

We discuss a general approach to the electronic structure of real materials which contains correlated d- or f- electrons. In accordance with the strength of average on-site Coulomb correlations parameter U over the total band width W, it is useful to distinguish three regime of strong, moderate and week correlations. In the case of strong interactions (U/W > 1 - ''rare-earth system``) the Hubbard-I approach is the most suitable. Starting from an exact atomic Green function with the constrained density matrix N_mm^' the band structure problem is formulated as the functional problem on N_mm^' for an f-electrons and the standard LDA-functional for delocalized electrons. In the case of moderate correlations (U/W ~ 1 - ''metal-insulator regime, Kondo systems``) we start from the D_? dynamical mean field ITP-scheme of G. Kotliar et. al. and also make use of our multiband atomic Green function for constrained N_mm^' . Finally for the week interactions (U/W < 1 -''transition metals``) the self-consistent diagrammatic FLEX-approach of N. Bickers and D. Scalapino tested for the multiband case of 3d-metals.

Liechtenstein, A. I.; Katsnelson, M. I.

1997-03-01

66

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

67

Electronic band structure and photoemission: A review and projection  

SciTech Connect

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.

Falicov, L.M.

1987-09-01

68

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

National Technical Information Service (NTIS)

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. K. Yeremin J. R. Lewandowski L. L. Laurent R. A. Marsh S. G. Tantawi V. A. Dolgashev

2012-01-01

69

Transition metal surface electronic structure  

NASA Astrophysics Data System (ADS)

In the automotive industry, solid surface effects are encountered in areas such as exhaust gas catalysis and sensing, corrosion, adhesion, friction and wear. Transition metals are involved in all of these types of interfaces. Our surface and interface physics programs are designed to characterize relevant physical phenomena in the atomistic sense. Transition metals are characterized in large part by their d-electron behavior. The localized nature of the d-orbitals has necessitated the formulation of a self-consistent local orbital method in order to compute surface electronic structure. Results for the (100) surfaces on work functions agree well with experiment. We found a surprisingly large density of surface states, i.e., localized to the surface region, on palladium, copper, and silver. One-fifth to one-fourth of the electrons in the surface layer are in surface states on these metals. A prominent surface state band found theoretically on copper has subsequently have been observed by Heimann et al., and Kevan and Shirley via angular photoemission. It is clear that henceforth surface states will have to be considered in the analysis of physical and chemical processes on transition metal surfaces.

Smith, J. R.; Arlinghaus, F. J.; Gay, J. G.

1981-01-01

70

Band structure and omnidirectional photonic band gap in lamellar structures with left-handed materials  

Microsoft Academic Search

We theoretically investigate the photonic band structure of one-dimensional superlattices composed of alternating layers of right-handed and left-handed materials (RHM and LHM). The dispersion curves are mainly studied by assuming that the dielectric permittivity and magnetic permeability are constant in each layer. It is shown that such structures can exhibit new types of electromagnetic modes and dispersion curves that do

D. Bria; B. Djafari-Rouhani; A. Akjouj; L. Dobrzynski; J. P. Vigneron; E. H. El Boudouti; A. Nougaoui

2004-01-01

71

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

Microsoft Academic Search

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

L. Szaro; J. Rebisz; J. Misiewicz

1999-01-01

72

Segmental structure in banded mongoose calls.  

PubMed

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

Fitch, W Tecumseh

2012-12-03

73

Venus banded terrain - Tectonic models for band formation and their relationship to lithospheric thermal structure  

NASA Astrophysics Data System (ADS)

Two classes of tectonic models for the formation of band structure on Venus mountain ranges are quantitatively evaluated: folding models and extensional models. The characteristics of banded terrain on Ishtar Terra are reviewed, particularly the evidence for a tectonic origin and such important details of band geometry as the spacing between adjacent bands. The tectonic models are tested against these observed features, and it it shown that both classes of models are possible explanations of banded terrain as long as the outer elastic-brittle layer of the Venus crust is at most a few kilometers thick. A general assessment is given of hypotheses for the origin of banded terrain and of the relationship between mechanical models for band formation and the thermal structure of the Venus lithosphere.

Solomon, S. C.; Head, J. W.

1984-08-01

74

Polariton-based band gap and generation of surface acoustic waves in acoustic superlattice lithium niobate  

NASA Astrophysics Data System (ADS)

We report the presence of surface acoustic wave (SAW) band gap on acoustic superlattice (ASL) in a single-crystal lithium niobate structure. The band gap behavior is determined by calculating the SAW band structure and also by simulating the transmission of an acoustic wave through a finite length section of ASL using finite element analysis. The calculated band gap appears at a frequency twice the value expected from purely acoustic Bragg scattering. We have identified the band gap as originating from a polariton-based mechanism due to the coupling between the electromagnetic wave and the surface vibrations. We have examined the influence of the band gap on SAW generation with the ASL and have shown that the calculated frequency resonance of the SAW lies in the vicinity of the upper stop-band edges. This results in the localization of the SAW in the ASL. Experimental confirmation is achieved through direct measurement of the SAW displacement by laser vibrometry on an actual ASL SAW transducer. The localization of generated SAW to the ASL transducer is observed confirming the prediction of the existence of a band gap.

Yudistira, Didit; Boes, Andreas; Janner, Davide; Pruneri, Valerio; Friend, James; Mitchell, Arnan

2013-08-01

75

Band gap analyses for high impedance electromagnetic surfaces using adaptive finite element method in frequency domain  

Microsoft Academic Search

An adaptive finite element method in frequency domain (A-FEM-FD) is presented, which is suitable for the band gap analyses of high impedance electromagnetic surfaces. Three new types of EBG structures are simulated and the regions of their in-plane band gaps for both TE and TM modes are given, which are consistent with the test results by Agilent E8363B VNA.

Wei Hong; Jiasong Wang; Bing Yu; Hehong Fan; Pu Wei; Fujiang Liao; Xiaohan Sun

2009-01-01

76

Band structure quantization in nanometer sized ZnO clusters  

NASA Astrophysics Data System (ADS)

Nanometer sized ZnO clusters are produced in the gas phase and subsequently deposited on clean Au(111) surfaces under ultra-high vacuum conditions. The zinc blende atomic structure of the approximately spherical ZnO clusters is resolved by high resolution scanning transmission electron microscopy. The large band gap and weak n-type conductivity of individual clusters are determined by scanning tunnelling microscopy and spectroscopy at cryogenic temperatures. The conduction band is found to exhibit clear quantization into discrete energy levels, which can be related to finite-size effects reflecting the zero-dimensional confinement. Our findings illustrate that gas phase cluster production may provide unique possibilities for the controlled fabrication of high purity quantum dots and heterostructures that can be size selected prior to deposition on the desired substrate under controlled ultra-high vacuum conditions.Nanometer sized ZnO clusters are produced in the gas phase and subsequently deposited on clean Au(111) surfaces under ultra-high vacuum conditions. The zinc blende atomic structure of the approximately spherical ZnO clusters is resolved by high resolution scanning transmission electron microscopy. The large band gap and weak n-type conductivity of individual clusters are determined by scanning tunnelling microscopy and spectroscopy at cryogenic temperatures. The conduction band is found to exhibit clear quantization into discrete energy levels, which can be related to finite-size effects reflecting the zero-dimensional confinement. Our findings illustrate that gas phase cluster production may provide unique possibilities for the controlled fabrication of high purity quantum dots and heterostructures that can be size selected prior to deposition on the desired substrate under controlled ultra-high vacuum conditions. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr33989k

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

2013-04-01

77

FIBER AND OTHER OPTICAL WAVEGUIDES: Propagation of light in a CdSxSe1-x planar waveguide structure with a variable band gap along the surface  

NASA Astrophysics Data System (ADS)

An investigation was made of the conditions of propagation of light in waveguides having different band gaps Eg formed by two-stage diffusion in the same cadmium sulfide substrate. The efficiency of mode matching at the junction of two waveguides was determined as a function of changes in Eg and the length of the transition zone. Zero-order modes were the most efficiently coupled and as the mode number increased, the matching efficiency decreased. When waveguides having values of Eg differing by 0.12 eV were coupled, the optical energy transfer efficiency was higher than 80%. The overlap integral method used to calculate the efficiency of matching of the waveguide fields ensured a satisfactory agreement with the experimental results.

Buachidze, Z. É.; Morozov, V. N.; Pletnev, V. A.; Pukhta, M.; Semenov, A. S.; ?tyroký, J.

1987-08-01

78

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

NASA Astrophysics Data System (ADS)

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.

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.

2013-05-01

79

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

PubMed Central

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.

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

80

Theoretical studies of electronic band-tail states, Anderson transition and surfaces of amorphous semiconductors  

NASA Astrophysics Data System (ADS)

In this dissertation, we study the Anderson transition within the electronic band tail states, and amorphous surfaces. The disorder induced band tail states is one of the unique character of amorphous semiconductors. Because of the proximity to the Fermi level, the nature of these band tail states is of obvious interest to theory of doping and transport. The study of amorphous solid surface is also an interesting area for theory. It is possible to have some major rearrangements near surfaces of amorphous solids (the amorphous analog of surface reconstruction), and the local bonding environment could be dramatically different from that of bulk. The study of the surfaces can also help people toward understanding the growth mechanism. First, electronic band tail states of amorphous silicon and amorphous diamond were studied based on the large (4096 atom) and realistic structural models. To solve the large tight-binding Hamiltonian matrices, we used two order N methods: the maximum entropy method for computing the total densities of states, and the modified Lanczos techniques for computing the individual energy eigenstates in the band gap regions. The DC conductivity was estimated with the Kubo formula. Next, the structural and electronic properties of the surfaces of tetrahedral amorphous carbon (ta-C) were also studied with a first-principles, local basis LDA technique. We reported two structural models made under different conditions, and examined the transition of the local bonding environment from the bulk to the surface. In the study of band tail states, we observe that Anderson (local-to-extended) transition within the band states proceeds by "cluster proliferation". We interpret the nature of band tail states in terms of a "resonant cluster model" through which one can qualitatively understand the evolution of the states from midgap toward the mobility edges. In the study of ta-C surfaces, we observe that nearly 50% surface atoms are threefold coordinated and planar rings or chains are formed with the spsp2 bonds. This "graphization" character also significantly influences its electronic properties. Electrons are easily de-localized within these surface spsp2 rings/chains and some the surface electronic eigenstates become extended along the surface through such rings/chains.

Dong, Jianjun

81

Algorithm for extraction of quantum oscillation orbits from band structure data  

NASA Astrophysics Data System (ADS)

In determining the Fermi surface of a material, quantum oscillation measurements are often compared to band structure calculations. Each oscillation frequency corresponds to an electron (or hole) orbit on the Fermi surface, perpendicular to the applied magnetic field; only orbits enclosing areas that are locally extremal are detected. To facilitate comparisons between theory and experiment, we have developed an algorithm, ``SKEAF,'' which finds extremal orbits in band structure calculations and determines quantum oscillation frequencies, effective masses and band specific heat contributions. Our code uses a k-space supercell approach, and can successfully locate geometrically-complicated orbits. Example results will be presented for the heavy fermion material UPt3.

Rourke, Patrick; Julian, Stephen

2008-03-01

82

Quasiparticle band structure and optical spectrum of LiBr  

NASA Astrophysics Data System (ADS)

We report the quasiparticle band structure and optical absorption spectrum of bulk LiBr calculated from first-principles approaches. The quasiparticle band structure is calculated within the GW approximation. Taking the electron-hole interaction into consideration, the optical excitation is investigated by solving the Bethe-Salpeter equation for the electron-hole two-particle Green's function. The obtained results for the band gap and optical absorption spectrum are in good agreement with experimental measurements.

Jiang, Yun-Feng; Wang, Neng-Ping; Rohlfing, Michael

2013-10-01

83

Weak morphology dependent valence band structure of boron nitride  

NASA Astrophysics Data System (ADS)

We report a hard X-ray photoelectron spectroscopy (HX-PES) investigation on valence band structure of Boron Nitrides (BN) having different morphologies, including nanosheets, nanotubes, and micro-sized particles. Very weak morphology/valence band structure dependence was observed. For each case, the B-N ?-band overlapping with ?-band between 0 to -12.5 eV and the s-band below -15 eV were identified. No obvious morphology-induced band shifts and intensity variations were observed. First-principles calculations based on density functional theory were performed and the results were compared with the experimental data. This theoretical analysis well explains the weak morphology dependent valence band spectra of BN nanomaterials obtained during HX-PES measurements.

Zhi, Chunyi; Ueda, Shigenori; Zeng, Haibo; Wang, Xuebin; Tian, Wei; Wang, Xi; Bando, Yoshio; Golberg, Dmitri

2013-08-01

84

2 GHz band superconducting band-pass filter with parallel resonators structure  

Microsoft Academic Search

A 2 GHz band 2-pole narrow bandwidth superconducting band-pass filter with the parallel structure of the half-wavelength microstrip line resonator was developed. The novel filter was realized by planar structure for the first time. The novel parallel filter operating at 60 K had center frequency of 1.909 GHz, insertion loss of 0.77 dB, 3 dB bandwidth of 0.49%, and maximally

HIROYUKI KAYANO; HIROYUKI FUKE; FUMIHIKO AIGA; YOSHIAKI TERASHIMA; RIICHI KATO; YASUO SUZUKI

2000-01-01

85

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

SciTech Connect

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

Sharma, H. R.; Simutis, G.; Dhanak, V. R.; Nugent, P. J.; McGrath, R. [Surface Science Research Centre and Department of Physics, University of Liverpool, Liverpool L69 3BX (United Kingdom); Cui, C. [Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577 (Japan); Shimoda, M. [National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan); Tsai, A. P. [Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577 (Japan); National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan); Ishii, Y. [Department of Physics, Chuo University, Kasuga, Tokyo 112-8551 (Japan)

2010-03-01

86

Atomic structure of amorphous shear bands in boron carbide.  

PubMed

Amorphous shear bands are the main deformation and failure mode of super-hard boron carbide subjected to shock loading and high pressures at room temperature. Nevertheless, the formation mechanisms of the amorphous shear bands remain a long-standing scientific curiosity mainly because of the lack of experimental structure information of the disordered shear bands, comprising light elements of carbon and boron only. Here we report the atomic structure of the amorphous shear bands in boron carbide characterized by state-of-the-art aberration-corrected transmission electron microscopy. Distorted icosahedra, displaced from the crystalline matrix, were observed in nano-sized amorphous bands that produce dislocation-like local shear strains. These experimental results provide direct experimental evidence that the formation of amorphous shear bands in boron carbide results from the disassembly of the icosahedra, driven by shear stresses. PMID:24052052

Reddy, K Madhav; Liu, P; Hirata, A; Fujita, T; Chen, M W

2013-09-20

87

New Band Structures in Aapprox110 Neutron-Rich Nuclei  

SciTech Connect

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.

Zhu, S. J.; Wang, J. G.; Ding, H. B.; Gu, L.; Xu, Q.; Yeoh, E. Y.; Xiao, Z. G. [Department of Physics, Tsinghua University, Beijing 100084 (China); Hamilton, J. H.; Ramayya, A. V.; Hwang, J. K.; Liu, S. H.; Li, K. [Department of Physics, Vanderbilt University, Nashville, TN 37235 (United States); Luo, Y. X. [Department of Physics, Vanderbilt University, Nashville, TN 37235 (United States); Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Rasmussen, J. O.; Lee, I. Y. [Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Qi, B.; Meng, J. [School of Physics, Peking University, Beijing 100871 (China)

2010-05-12

88

Cluster structure and deformed bands in the 38Ar nucleus  

NASA Astrophysics Data System (ADS)

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

Sakuda, T.; Ohkubo, S.

2013-06-01

89

Atomic structure of amorphous shear bands in boron carbide  

NASA Astrophysics Data System (ADS)

Amorphous shear bands are the main deformation and failure mode of super-hard boron carbide subjected to shock loading and high pressures at room temperature. Nevertheless, the formation mechanisms of the amorphous shear bands remain a long-standing scientific curiosity mainly because of the lack of experimental structure information of the disordered shear bands, comprising light elements of carbon and boron only. Here we report the atomic structure of the amorphous shear bands in boron carbide characterized by state-of-the-art aberration-corrected transmission electron microscopy. Distorted icosahedra, displaced from the crystalline matrix, were observed in nano-sized amorphous bands that produce dislocation-like local shear strains. These experimental results provide direct experimental evidence that the formation of amorphous shear bands in boron carbide results from the disassembly of the icosahedra, driven by shear stresses.

Reddy, K. Madhav; Liu, P.; Hirata, A.; Fujita, T.; Chen, M. W.

2013-09-01

90

Band Structure Approach to Resonant X-Ray Scattering  

Microsoft Academic Search

We study the resonance behaviour of the forbidden 600 and 222 x-ray Bragg\\u000apeaks in Ge using LDA band structure methods. These Bragg peaks remain\\u000aforbidden in the resonant dipole scattering approximation even taking into\\u000aaccount the non local nature of the band states. However they become allowed at\\u000aresonance if the eigenstates of the unoccupied conduction band involve a

I. S. Elfimov; N. A. Skorikov; V. I. Anisimov; G. A. Sawatzky

2001-01-01

91

One structure for efficient narrow-band bandpass FIR filters  

Microsoft Academic Search

This paper presents a narrow-band bandpass FIR filter design with a small number of multipliers per output sample (NMPS). The proposed method is based on the use of the pipelining\\/interleaving (PI) technique within a quadrature modulation structure, where only one narrow-band lowpass filter is required. In order to reduce the NMPS, the narrow-band lowpass filter is designed with an interpolated

G. Jovanovic-Dolecek; J. Diaz-Carmona

2002-01-01

92

Electronic band structure of graphite-boron nitride alloys  

Microsoft Academic Search

Extended-Hueckel crystal orbital band calculations, frontier crystal orbital analysis, and degenerate-level perturbation theory are used to explore the electronic structure of several graphite-boron nitride alloys: BCâ, CâN, BCâN, and their structural isomers. These materials are treated as two-dimensional solids, and the effect of crystal relaxation on the bandgap is considered. Similarities and differences between the band diagrams of the structurally

John P. LaFemina

1990-01-01

93

Band model for the electronic structure of expanded liquid mercury  

Microsoft Academic Search

The results of a series of band-structure calculations for hypothetical forms of crystalline mercury with the fcc, bcc, sc, and diamond structures are applied to model the variation with density of N(EF), the density of states at the Fermi energy, in expanded liquid mercury. This quasicrystalline model is based on augmented-plane-wave (APW) energy-band calculations for each crystal structure with a

L. F. Mattheiss; W. W. Warren Jr.

1977-01-01

94

Highly increased photonic band gaps in silica\\/air structures  

Microsoft Academic Search

We explore the possibilities of achieving larger out-of-plane band gaps in two-dimensional silica\\/air photonic crystals with hexagonal symmetry. By modification of the basic hexagonal unit-cell, we demonstrate a new photonic crystal structure, for which the size of the band gaps is increased several times compared to those of simple hexagonal structures. The new structure allows design of silica\\/air photonic crystals

Jes Broeng; Stig E Barkou; Anders Bjarklev; Jonathan C Knight; Tim A Birks; Philip St. J Russell

1998-01-01

95

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

Microsoft Academic Search

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

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

2001-01-01

96

The Electronic Band Structure of Bismuth Telluride  

Microsoft Academic Search

The electronic energy levels of Bi2Te3 at symmetry points in the Brillouin zone are classified. An augmented plane waves calculation is carried out to try to determine the possible positions and symmetries of the band edges. The calculation is not self-consistent and several approximations are made in evaluating the potential. It is found that an energy gap arises essentially because

P. M. Lee; L. Pincherle

1963-01-01

97

Uranus in 2003: Zonal winds, banded structure, and discrete features  

Microsoft Academic Search

Imaging of Uranus in 2003 with the Keck 10-m telescope reveals banded zonal structure and dozens of discrete cloud features at J and H bands; several features in the northern hemisphere are also detectable at K?. By tracking features over four days, we extend the zonal wind profile well into the northern hemisphere. We report the first measurements of wind

H. B. Hammel; I. de Pater; S G Gibbard; G. W. Lockwood; K. Rages

2005-01-01

98

Shell model description of band structure in 48Cr  

SciTech Connect

The band structure for normal and abnormal parity bands in 48Cr are described using the m-scheme shell model. In addition to full fp-shell, two particles in the 1d3/2 orbital are allowed in order to describe intruder states. The interaction includes fp-, sd- and mixed matrix elements.

Vargas, Carlos E. [Facultad de Fisica e Inteligencia Artificial, Universidad Veracruzana, Sebastian Camacho 5, Centro, CP 91000, Xalapa, Ver. (Mexico); Velazquez, Victor M. [Facultad de Ciencias, Universidad Nacional Autonoma de Mexico (Mexico)

2007-02-12

99

Locally resonant cavity cell model for electromagnetic band gap structures  

Microsoft Academic Search

Mushroom-like electromagnetic band gap (EBG) structures exhibit unique electromagnetic properties that have found a wide range of electromagnetic device applications. This paper focuses on the local resonance behaviors of EBG structures, and a simply locally resonant cavity cell (LRCC) model for mushroom-like EBG structures is presented to gain insight to the physical mechanism of the EBG structures and the interaction

Long Li; Bin Li; Hai-Xia Liu; Chang-Hong Liang

2006-01-01

100

Photoemission spectra and band structures of simple metals  

NASA Astrophysics Data System (ADS)

We present a detailed calculation of the angle-resolved photoemission spectra of Na. The calculation follows a theory by Mahan, which allows for the inclusion of various bulk and surface effects. We find it important to take into account various broadening effects in order to explain the anomalous structure at EF, which was found by Jensen and Plummer in the spectra of Na. The broadening effects also help to resolve the discrepancy of the conduction-band width. Efforts are made to compare our results with new measurements of Plummer and Lyo. We discuss the ambiguity concerning the sign of the crystal potential and comment on charge-density waves in the systems. We have also generalized our discussions to other simple metals like K.

Shung, Kenneth W.-K.; Mahan, G. D.

1988-08-01

101

Band structure aspects of materials with localizing f-orbitals  

NASA Astrophysics Data System (ADS)

In those materials where the f-states are hybridized, a band structure provides a reasonable description of the ground state. This is amply demonstrated by the successful determination of the Fermi surfaces of CeSn3, URh3, UIr3 and UGe3. But when the f-states become more local, inadequacies of the functionals employed yield incomplete localization. Thus, to obtain a good description of the Fermi surface for high field ferromagnetic CeSb, the local character of the f-orbitals is artificially forced to produce the standard rare earth model. When dealing with excited states, the ground state band structure provides only part of the story. Even thermal excitations can provide significant departures from the ground state as evidenced by the large enhancements found for some materials. The series USi3, UGe3 and USn3 (together with CeSn3) demonstrate the effect very well. NpSn3 provides a useful counter example demonstrating that such enhancements need not be a universal property of localization. In photoemission, the excited state can exhibit a more local character than the ground state as is clearly seen in the analysis of the Ce pnictides. But to emphasize this, it is useful to compare Ce and U compounds where it can be asserted in one limited definition that Ce acts more itinerant than U in the ground state. Yet it is Ce which shows the correlation derived second f-peak. The URh3Bx interstitial alloy system provides a concrete example of the situation in the uranium compounds.

Koelling, D. D.; Norman, M. R.; Arko, A. J.

1987-01-01

102

Band Structure of {sup 85}Sr  

SciTech Connect

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

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

2010-11-24

103

Optimization of low band gap polymer photovoltaics through structure modification  

NASA Astrophysics Data System (ADS)

In BHJ-type solar cells, the ability to control and optimize the active layer morphology is a critical issue to improve device efficiency, and this is usually achieved by optimizing the processing conditions, eg. using varied annealing procedures and choosing the right solvent additive. In this work, we shown that device performance of DPP based low band gap polymers should be optimized both in processing and structural optimization approach. Without the use of chemical additive in blended thin film preparation, large size-scaled phase separation, up to several hundred of nanometers exist. This morphology is due to the surface aggregation of phenyl-C71-butyric acid methyl ester (PCBM), which forms large oval structures and then buried by a polymer-PCBM mixture thin film. In this process, the miscibility of polymer matrix plays an important role. While using chemical additive processing method can tune the general morphology to a more fibril network texture, fine-tuning of fibril dimensions and domain size needs delicate chemical structure modification. Through this modification, a 30% device performance enhancement was observed, which mostly came from an enhancement of short circuit current, thus strongly related to the morphological details. Besides conventional morphology characterizations, an initiative effort of understanding the domain interface structure was also carried out by using polarized soft x-ray scattering, in which we observed polymer crystal orientation plays an important role.

Liu, Feng; Gu, Yu; Briseno, Alejandro; Russell, Thomas; Wang, Cheng

2013-03-01

104

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

PubMed

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

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

2011-12-06

105

Red-cell glycophorin A-band 3 interactions associated with the movement of band 3 to the cell surface.  

PubMed Central

We have examined the mechanism by which glycophorin A (GPA) facilitates the movement of the human red-cell anion exchanger (band 3, AE1) to the cell surface. GPA itself forms stable dimers in membranes and detergent solution. Four mutants of human GPA with impaired dimerization were prepared (L75I, I76A, G79L and G83L). All four GPA mutants enhanced band 3 translocation to the Xenopus oocyte plasma membrane in the same way as wild-type GPA, showing that the GPA monomer is sufficient to mediate this process. Cell-surface expression of the natural band 3 mutant G701D has an absolute requirement for GPA. GPA monomers also rescued the cell-surface expression of this mutant band 3. Taking into account other evidence, we infer that the site of GPA interaction with band 3 is located outside the GPA dimerization interface but within the GPA transmembrane span. The results of examination of the cell-surface expression of GPA and band 3 in different K562 erythroleukaemia cell clones stably transfected with band 3 are consistent with the movement of GPA and band 3 to the cell surface together. We discuss the pathways by which band 3 moves to the cell surface in the presence and the absence of GPA, concluding that GPA has a role in enhancing the folding and maturation of band 3. We propose that GPA functions in erythroid cells to assist with the incorporation of large amounts of properly folded band 3 into the membrane within a limited time span during erythroid maturation.

Young, M T; Beckmann, R; Toye, A M; Tanner, M J

2000-01-01

106

Locally resonant periodic structures with low-frequency band gaps  

NASA Astrophysics Data System (ADS)

Presented in this paper are study results of dispersion relationships of periodic structures composited of concrete and rubber, from which the frequency band gap can be found. Two models with fixed or free boundary conditions are proposed to approximate the bound frequencies of the first band gap. Studies are conducted to investigate the low-frequency and directional frequency band gaps for their application to engineering. The study finds that civil engineering structures can be designed to block harmful waves, such as earthquake disturbance.

Cheng, Zhibao; Shi, Zhifei; Mo, Y. L.; Xiang, Hongjun

2013-07-01

107

Brain surface parameterization using Riemann surface structure.  

PubMed

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

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

2005-01-01

108

PhET Simulation: Band Structure  

NSDL National Science Digital Library

This webpage contains an interactive simulation that allows users to explore quantum bound states in multiple potential wells, and to see the formation of bands of energy levels. Users can interactively change features such as the number, width, spacing, and height of the wells, and see the changes to the energy levels and energy eigenstate wave functions continuously. Options also include using square and Coulomb shaped wells. Probability densities and wave functions can be shown using a variety of representations. This simulation is also contained within the Quantum Bound States simulation. Also included is a teacher's guide as well as sample learning goals for use with the simulation. This simulation is part of a large and growing collection. It has been designed using principles from physics education research and refined based on student interviews.

2006-10-20

109

Band structure engineering in (Bi1-xSbx)2Te3 ternary topological insulators  

Microsoft Academic Search

Three-dimensional (3D) topological insulators (TI) are novel quantum materials with insulating bulk and topologically protected metallic surfaces with Dirac-like band structure. The spin-helical Dirac surface states are expected to host exotic topological quantum effects and find applications in spintronics and quantum computation. The experimental realization of these ideas requires fabrication of versatile devices based on bulk-insulating TIs with tunable surface

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

2011-01-01

110

Band structure and related properties of molybdenum  

SciTech Connect

Self-consistent, all-electron, local-density calculations are reported for bcc molybdenum, using the linear combination of Gaussian orbitals (LCGO) method. We obtain the density of states, the Fermi surface, charge form factors, the Compton profile, and the optical conductivity. Results are compared with other calculations and with experiments where these exist. A possible ferromagnetic state is found for an increased lattice constant, developing at about 8.07 a.u.

Jani, A. R.; Tripathi, G. S.; Brener, N. E.; Callaway, J.

1989-07-15

111

[Band electronic structures and crystal packing forces  

SciTech Connect

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

Not Available

1993-01-01

112

Electronic band structure and carrier effective mass in calcium aluminates  

Microsoft Academic Search

First-principles electronic band structure investigations of five compounds of the CaO-Al2O3 family, 3CaO•Al2O3 , 12CaO•7Al2O3 , CaO•Al2O3 , CaO•2Al2O3 , and CaO•6Al2O3 , as well as CaO and alpha -, theta -, and kappa-Al2O3 are performed. We find that the conduction band in the complex oxides is formed from the oxygen antibonding p states and, although the band gap in

Julia E. Medvedeva; Emily N. Teasley; Michael D. Hoffman

2007-01-01

113

Electronic band structure of graphite-boron nitride alloys  

SciTech Connect

Extended-Hueckel crystal orbital band calculations, frontier crystal orbital analysis, and degenerate-level perturbation theory are used to explore the electronic structure of several graphite-boron nitride alloys: BC{sub 3}, C{sub 3}N, BC{sub 2}N, and their structural isomers. These materials are treated as two-dimensional solids, and the effect of crystal relaxation on the bandgap is considered. Similarities and differences between the band diagrams of the structurally similar materials are discussed and understood in a simple crystal orbital framework.

LaFemina, J.P. (Pacific Northwest Lab., Richland, WA (USA))

1990-05-17

114

Hydrodynamic equations for semiconductors with nonparabolic band structure  

Microsoft Academic Search

A system of generalized hydrodynamic equations is derived from Boltzmann's transport equation for semiconductors without the assumption of a parabolic band structure. After some simplifications these equations can be arranged in such a way that their structure is similar to that of the well-known conventional ones. For this purpose the quantity carrier temperature is redefined and five relaxation times have

Rainer Thoma; Axel Emunds; Bernd Meinerzhagen; Hermann-Josef Peifer; Walter L. Engl

1991-01-01

115

Potential barrier and band structure of closed edge graphene  

NASA Astrophysics Data System (ADS)

The atomic structure, electron distribution, work function, and band structure of closed edge graphene are investigated with density functional theory. Field emission performance of closed edge graphene is compared with that of open edge graphene. We provide a possible explanation for the field emission microscopy image change after high emission current, which appeals to the experimentalists for further investigation.

He, Chunshan; Wang, Weiliang

2013-08-01

116

Identification of band structures and proposed one- and two-phonon {gamma}-vibrational bands in {sup 105}Mo  

SciTech Connect

High-spin band structures in neutron-rich {sup 105}Mo have been investigated by measuring prompt {gamma} rays emitted by the spontaneous fission fragments of {sup 252}Cf with the Gammasphere detector array. The yrast band has been confirmed and five new collective bands are observed. The three bands based on the 246.3-, 332.0-, and 310.0-keV levels are proposed as the single-neutron excitation bands built on the 3/2{sup +}[411], 1/2{sup +}[411], and 5/2{sup +}[413] Nilsson orbitals, respectively. The other two bands with band head levels at 870.5 and 1534.6 keV are candidates for one-phonon K=9/2 and two-phonon K=13/2 {gamma}-vibrational bands, respectively. Systematic comparison of these bands with bands in neighboring nuclei are discussed.

Ding, H. B.; Che, X. L.; Chen, Y. J.; Li, M. L. [Department of Physics, Tsinghua University, Beijing 100084 (China); Zhu, S. J. [Department of Physics, Tsinghua University, Beijing 100084 (China); Department of Physics, Vanderbilt University, Nashville, Tennessee 37235 (United States); Hamilton, J. H.; Ramayya, A. V.; Hwang, J. K.; Li, K.; Goodin, C. T. [Department of Physics, Vanderbilt University, Nashville, Tennessee 37235 (United States); Luo, Y. X. [Department of Physics, Vanderbilt University, Nashville, Tennessee 37235 (United States); Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Rasmussen, J. O.; Lee, I. Y. [Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

2006-11-15

117

Band offsets at zincblende-wurtzite GaAs nanowire sidewall surfaces  

NASA Astrophysics Data System (ADS)

The band structure and the Fermi level pinning at clean and well-ordered sidewall surfaces of zincblende (ZB)-wurtzite (WZ) GaAs nanowires are investigated by scanning tunneling spectroscopy and density functional theory calculations. The WZ-ZB phase transition in GaAs nanowires introduces p-i junctions at the sidewall surfaces. This is caused by the presence of numerous steps, which induce a Fermi level pinning at different energies on the non-polar WZ and ZB sidewall facets.

Capiod, P.; Xu, T.; Nys, J. P.; Berthe, M.; Patriarche, G.; Lymperakis, L.; Neugebauer, J.; Caroff, P.; Dunin-Borkowski, R. E.; Ebert, Ph.; Grandidier, B.

2013-09-01

118

A novel 1D non-periodic photonic band-gap structure  

NASA Astrophysics Data System (ADS)

In this paper, the development and filter characteristic of photonic band-gap (PBG) structure and defected ground structure (DGS) are analyzed. The non-periodic structure has simpler structure, smaller size and smaller ripple compared to the periodic structure. Though the stop band of non-periodic structure is narrower, it can meet the application. What's more, C-shaped structure with two stop bands can realize selection in special frequency band. So it can meet the need of two stop bands.

Li, Yuan; Li, Huancai; Ding, Ronglin

2005-12-01

119

Quantification of electronic band gap and surface states on FeS2(100)  

NASA Astrophysics Data System (ADS)

The interfacial electronic properties and charge transfer characteristics of pyrite, FeS2, are greatly influenced by the presence of electronic states at the crystal free surface. We investigate the surface electronic structure of FeS2 (100) using scanning tunneling spectroscopy (STS) and interpret the results using tunneling current simulations informed by density functional theory. Intrinsic, dangling bond surface states located at the band edges reduce the fundamental band gap Eg from 0.95 eV in bulk FeS2 to 0.4 ± 0.1 eV at the surface. Extrinsic surface states from sulfur and iron defects contribute to Fermi level pinning but, due to their relatively low density of states, no detectable tunneling current was measured at energies within the intrinsic surface Eg. These findings help elucidate the nature of energy alignment for electron transfer processes at pyrite surfaces, which are relevant to evaluation of electrochemical processes including corrosion and solar energy conversion.

Herbert, F. W.; Krishnamoorthy, A.; Van Vliet, K. J.; Yildiz, B.

2013-12-01

120

The structure of shear bands in idealized granular materials  

SciTech Connect

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.

Bardet, J.P.; Proubet, J. [Univ. of Southern California, Los Angeles, CA (United States)

1992-03-01

121

Beyond band gap photoreflectance study on PHEMT device structures  

Microsoft Academic Search

Photoreflectance (PR) studies on device structures have mainly been conducted near the band gap region of the semiconductors of these structures. In this study we have attempted characterization of the important upper epilayers, barrier and channel layers, of pseudomorphic high electron mobility transistor (PHEMT) device structures near the E1 and E1+Delta 1 transition energy range (2.7--3.6 eV). In choosing the

P. L. Stephan Thamban

2005-01-01

122

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

NASA Astrophysics Data System (ADS)

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.

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

2009-06-01

123

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

124

Electronic band structure and phonons in V2O5  

NASA Astrophysics Data System (ADS)

Among the vanadium oxides, V2O5 presents special interest as a layered material. As for other layered materials, it is of interest to search for changes in its electronic structure and phonon spectrum in the monolayer modification of this material. For example, reduced screening may modify phonon modes affected by long-range Coulomb interactions. As a preliminary we here present a first-principles study of the bulk electronic band structure and the phonons at the ?-point. Density functional calculations in the local density approximation were carried out for the electronic band structure and the density functional perturbation method was used for the phonon calculations. We used LDA and norm-conserving pseudopotentials in the abinit code. A group theoretical analysis is used to label the phonon modes. Non-analyticity is included for the LO modes. The band structures are in good agreement with previous work and yield an indirect band gap. Relaxed structural properties are also in good agreement with experiment. Simulated infrared and Raman spectra will be presented. Our results will be compared with experimental and previous theoretical work.

Bhandari, Churna; Lambrecht, Walter R. L.

2013-03-01

125

Band structure effects on the superconductivity in Hubbard models  

NASA Astrophysics Data System (ADS)

We study the influence of the band structure on the symmetry and superconducting transition temperature in the (solvable) weak-coupling limit of the repulsive Hubbard model. Among other results we find that (1) as a function of increasing nematicity, starting from the square-lattice (zero nematicity) limit where a nodal d-wave state is strongly preferred, there is a smooth evolution to the quasi-1D limit, where a striking near-degeneracy is found between a p-wave- and a d-wave-type paired states with accidental nodes on the quasi-one-dimensional Fermi surfaces—a situation that may be relevant to the Bechgaard salts. (2) In a bilayer system, we find a phase transition as a function of increasing bilayer coupling from a d-wave to an s±-wave state reminiscent of the iron-based superconductors. (3) When an antinodal gap is produced by charge-density-wave order, not only is the pairing scale reduced, but the symmetry of the pairs switches from dx2?y2 to dxy; in the context of the cuprates, this suggests that were the pseudogap entirely due to a competing CDW order, this would likely cause a corresponding symmetry change of the superconducting order (which is not seen in experiment).

Cho, Weejee; Thomale, Ronny; Raghu, Srinivas; Kivelson, Steven A.

2013-08-01

126

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

PubMed

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

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

2012-03-26

127

Characterization of the surface structural relaxation behavior of vitreous silica  

Microsoft Academic Search

Fourier transform infrared (FTIR) spectroscopy was used to determine the surface and bulk structural relaxation kinetics of high purity vitreous silica. The fundamental asymmetric stretching vibration located at ˜1120 cm-1 was monitored in reflection mode to determine the surface structural relaxation times, while the first overtone of that band, near 2260 cm-1, was monitored in transmission mode to determine the

Robert William Hepburn

2002-01-01

128

Direct measurement of the band structure of a buried two-dimensional electron gas.  

PubMed

We directly measure the band structure of a buried two dimensional electron gas (2DEG) using angle resolved photoemission spectroscopy. The buried 2DEG forms 2 nm beneath the surface of p-type silicon, because of a dense delta-type layer of phosphorus n-type dopants which have been placed there. The position of the phosphorous layer is beyond the probing depth of the photoemission experiment but the observation of the 2DEG is nevertheless possible at certain photon energies where emission from the states is resonantly enhanced. This permits direct access to the band structure of the 2DEG and its temperature dependence. PMID:23581353

Miwa, Jill A; Hofmann, Philip; Simmons, Michelle Y; Wells, Justin W

2013-03-25

129

The Fermi surface and band folding in La2-xSrxCuO4, probed by angle-resolved photoemission  

NASA Astrophysics Data System (ADS)

A systematic angle-resolved photoemission study of the electronic structure of La2-xSrxCuO4 in a wide doping range is presented in this paper. In addition to the main energy band, we observed a weaker additional band, the (?, ?) folded band, which shows unusual doping dependence. The appearance of the folded band suggests that a Fermi surface reconstruction is doping dependent and could already occur at zero magnetic field.

Razzoli, E.; Sassa, Y.; Drachuck, G.; Månsson, M.; Keren, A.; Shay, M.; Berntsen, M. H.; Tjernberg, O.; Radovic, M.; Chang, J.; Pailhès, S.; Momono, N.; Oda, M.; Ido, M.; Lipscombe, O. J.; Hayden, S. M.; Patthey, L.; Mesot, J.; Shi, M.

2010-12-01

130

Band structure parameters of the nitrides: The origin of the small band gap of InN  

Microsoft Academic Search

Using a band-structure method that includes the correction to the band gap error in the local density approximation (LDA), we study the chemical trends of the band gap variation in III-V semiconductors and predict that the band gap for InN is 0.8 +\\/- 0.1 eV, which is much smaller than previous experimental value of approx. 1.9 eV. The unusually small

Su-Huai Wei; Pierre Carrier

2004-01-01

131

Electronic-Energy-Band Structure of Uranium Hydride.  

National Technical Information Service (NTIS)

We have calculated the electronic energy bands of alpha and beta UH sub 3 . These systems are unique among hydride formers in that a transformation directly to a trihydride occurs without an intervening dihydride phase and in that two trihydride structure...

A. C. Switendick

1982-01-01

132

Complex Band Structure and Tunneling through Ferromagnet \\/Insulator \\/Ferromagnet Junctions  

Microsoft Academic Search

We investigate the importance of metal-induced gap states for the tunneling of metal electrons through epitaxial insulator films. By introducing an imaginary part kappa to the wave vector in order to describe the decay of the wave function in the insulator, we obtain the complex band structure in the gap region. The spectrum of the decay parameters kappa is calculated

Ph. Mavropoulos; N. Papanikolaou; P. H. Dederichs

2000-01-01

133

Electronic energy band structure of MnSi  

Microsoft Academic Search

The electronic energy band structure of the intermetallic compound MnSi, a typical itinerant electron magnet, is calculated by a self-consistent APW method. The density of states at Fermi level is high (148 states\\/Ryd cell). This is consistent with the magnetic properties of MnSi.

O. Nakanishi; A. Yanase; A. Hasegawa

1980-01-01

134

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

NASA Astrophysics Data System (ADS)

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.

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

135

X-band rf structure with integrated alignment monitors  

Microsoft Academic Search

We present the electrical design for an X-band traveling wave accelerator structure with integrated alignment monitors to measure the transverse wake, which will be used as part of the PSI-XFEL project and in the CLIC structure testing program. At PSI, it will compensate nonlinearities in the longitudinal phase space at the injector prototype of the PSI-XFEL. At CLIC it will

M. Dehler; J.-Y. Raguin; A. Citterio; A. Falone; W. Wuensch; G. Riddone; A. Grudiev; R. Zennaro

2009-01-01

136

Surface dependent band alignments for chalcopyrite-ZnO interface  

NASA Astrophysics Data System (ADS)

Chalcopyrites are promising absorber materials for thin film solar cells. A Buffer of CdS is technologically used between Absorber and TCO window layer. To study the junction properties investigations on well defined model systems were performed. CuInSe2 (112) and (001) surfaces were prepared by MBE and investigated by UPS, XPS, LEED and PEEM with respect to junction properties to ZnO. ZnO as TCO is deposited by MOMBE in situ without breaking UHV conditions between preparation, transfer and analysis. Instead of an abrupt CuInSe2-ZnO interface a intermediate ultra thin buffer layer of epitaxial ZnSe is formed on the chalcopyrite substrate despite of the admittance of the oxidizing agent in the MOMBE process. On top of ZnSe a ZnO film growth is observed. ZnO grows in registry with the ZnSe with its own lattice parameters. Annealing to temperatures above the TCO deposition temperature show In diffusion into the ZnO layer forming an oxide as derived from the Auger-parameter. Energy filtered PEEM reveals an inhomogenity of the annealed interface with local In enrichment in the ZnO film. Band alignments determined from our data for the CuInSe2-ZnSe-ZnO junction are beneficial for an application in solar cells.

Pettenkofer, Christian; Hofmann, Andreas

2010-03-01

137

Multi-band and broadband acoustic metamaterial with resonant structures  

NASA Astrophysics Data System (ADS)

We design an acoustic metamaterial (AM) with multi-band of negative modulus composed of different sized split hollow spheres (SHSs). From acoustic transmitted experiment, the AM exhibits simultaneously negative modulus at frequencies 914, 1298 and 1514 Hz. Based on the multi-band designed concept, broadband AM is fabricated by arraying gradually sized SHS. The transmission results indicate that this medium can achieve negative modulus at the frequency range from 900 to 1500 Hz. This kind of broadband AM is very convenient to couple with other structures to gain the double-negative AM.

Ding, Chang-Lin; Zhao, Xiao-Peng

2011-06-01

138

Structural trend analysis by axial surface mapping  

SciTech Connect

We present a new method of structural trend analysis in which axial surfaces (fold hinges) are mapped through grids of seismic reflection profiles and balanced forward models. Axial surface maps (1) define fold trends, lateral terminations, and closure in structure, (2) constrain underlying fault geometry and slip, and (3) highlight and connect regions that can be interpreted by a series of balanced models or cross sections. Maps of folds in southern California and northeastern Pennsylvania are compared with forward model solutions and used to construct balanced three-dimensional structural interpretations using fault-bend fold theory. Axial surface maps generated from balanced fault-bend fold models define theoretical relationships between map patterns and structural geometry and fault slip. Kink-band widths between paired axial surfaces in map view are related to underlying fault slip. Lateral variations in fault slip, which can be identified on axial surface maps, may cause fold plunge and provide lateral closure. Lateral changes in subsurface fault geometry, which include lateral and oblique ramps, are also reflected by terminations, bends, or offsets of axial surfaces in map view. Based on these relationships between folding and faulting, we develop map-view interpretations and balanced cross sections across structures that are consistent with the geology along trend. These maps maybe useful in the exploration and drilling for potential natural gas or petroleum reservoirs. 12 refs., 20 figs.

Shaw, J.H. (Princeton Univ., NJ (United States) Texaco Exploration Production Technology Department, Houston, TX (United States)); Hook, S.C. (Texaco Exploration Production Technology Department, Houston, TX (United States)); Suppe, J. (Princeton Univ., NJ (United States))

1994-05-01

139

Electronic band structure and carrier effective mass in calcium aluminates  

Microsoft Academic Search

First-principles electronic band structure investigations of five compounds\\u000aof the CaO-Al2O3 family, 3CaO.Al2O3, 12CaO.7Al2O3, CaO.Al2O3, CaO.2Al2O3 and\\u000aCaO.6Al2O3, as well as CaO and alpha-, theta- and kappa-Al2O3 are performed. We\\u000afind that the conduction band in the complex oxides is formed from the oxygen\\u000aantibonding p-states and, although the band gap in Al2O3 is almost twice larger\\u000athan in CaO,

Julia E. Medvedeva; Emily N. Teasley; Michael D. Hoffman

2007-01-01

140

Dipole relaxation in dispersive photonic band-gap structures  

NASA Astrophysics Data System (ADS)

Photonic structures are considered with the emphasis on dispersive materials and on one-dimensionally periodic structures. The electromagnetic frequency bands and the corresponding field distributions are determined for a GaAs/AlAs one-dimensional photonic structure and the field quantization is established. The interaction is considered between the electromagnetic fields and an oscillating electric dipole located deep within the layers. This involves coupling to the polariton modes of this inhomogeneous medium, with each type of mode providing a dipole relaxation channel. Relaxation processes due to emission into the polariton channels are analyzed. The results are displayed in terms of the emission rate ? versus the dipole position Z0 for a fixed dipole frequency ?0 and against ?0 for a fixed Z0 . These results strongly indicate the existence of band-edge effects associated with the dispersive response of the materials comprising the layered system.

Kamli, A.; Babiker, M.; Al-Hajry, A.; Enfati, N.

1997-02-01

141

Subwavelength structured narrow-band integrated optical grating filters  

SciTech Connect

A unique type of narrow band integrated optical filter is investigated based on embedding a subwavelength resonant grating structure within a planar waveguide. Current integrated narrow-band optical filters are limited by their size, density of devices that can be produced, overall performance, and ability to be actively altered for tuning and modulation purposes. In contrast, the integrated optical filters described in this work can have extremely narrow bandwidths--on the order of a few angstroms. Also, their compact size enables multiple filters to be integrated in a single high density device for signal routing or wavelength discrimination. Manipulating any of the resonant structure`s parameters will tune the output response of the filter, which can be used for modulation or switching applications.

Grann, E.B.; Holcomb, D.E.; Zuhr, R.A. [Oak Ridge National Lab., TN (United States); Moharam, M.G. [Univ. of Central Florida, Orlando, FL (United States). Center for Research and Education in Optics and Lasers

1998-01-01

142

Band structure of polyethylene from many-body perturbation theory  

NASA Astrophysics Data System (ADS)

The electronic structure of polyethylene is an important benchmark and the infinite chain limit for the electronic properties of many molecules, monolayers, and oligomers. Therefore, the band structure of the ideal, one-dimensional polyethylene chain has been extensively researched, from both the experimental and the theoretical viewpoints. Despite this extensive effort, to the best of our knowledge agreement between theoretical calculations and the electronic structure obtained from photoelectron spectroscopy could only be obtained using artificial shifting and ``stretching'' of the computed data. Here, we present a quantitative quasi-particle band-structure for polyethylene using many-body perturbation theory. The approach is employed within the G0W0 approximation, based on a starting point calculated within the generalized gradient approximation to density functional theory. We compare our calculated band-structure to angle resolved photoemission spectroscopy measurements for various long saturated carbohydrates, demonstrate a much improved agreement with experiment, and discuss remaining discrepancies and their possible origins within both theory and experiment.

Biller, Ariel; Sharifzadeh, Sahar; Segev, Lior; Ismail-Beigi, Sohrab; Neaton, Jeffrey B.; Kronik, Leeor

2013-03-01

143

Landsat thermal band efficiency on characterizing mulched soil surface  

NASA Astrophysics Data System (ADS)

In order to study petroleum mulch effects on soil, and sand dune fixation, thermal, and reflective bands of Landsat thematic mapper TM and ETM data, and other sources of information including topographic maps, aerial photos, and field work were used. The methodology was comprised of: images processing, statistic analysis, and relationship between thermal and reflective data. The results from image processing show that the behaviour of the Landsat thermal data is completely different from reflective data. The results from colour composite images including thermal bands have shown the capability of thermal bands in reparability of mulched and non-mulched areas. It was generally concluded that selection of TM, ETM thermal band is an important step to evaluate the area covered with petroleum mulch. Ratio mulch index was introduced as a best band combination in order to imagine mulch decomposition.

Hashemimanesh, M.; Matinfar, H.; Alavipanah, S.; Zehtabian, G.

2012-07-01

144

Characterising the structure and petrophysical properties of deformation band fault cores in reservoir sandstone  

NASA Astrophysics Data System (ADS)

Deformation band faults in porous sandstone typically have a "core" of intense deformation associated with the localisation of strain onto discrete slip surfaces. In outcrop, the core is recognisable by its glassy appearance and its increased resistance to erosion with respect to the host rock. Samples of fault core have been collected from the San Rafael Swell, Utah, USA (Navajo Sandstone) and the Cheshire Basin, England (Sherwood Sandstone). Outcrop mapping in both localities reveals that the fault core thickness varies from < 3 cm to 30 cm along strike. Thickness variability does not correlate with displacement. The fault core is composed of closely spaced deformation bands and the host rock between these deformation bands is highly crushed. The mean grain size in the fault core is lower than in single deformation bands and there is a greater spread of particle sizes. Quartz grains in the fault core tend to be aligned. Fault core porosity (1-5%) is decreased with respect to the host sandstone (17-22%) and individual deformation bands (7-8%). However, microstructural observations suggest that fluids have moved through these structures during deformation. Cement phases are preferentially located along deformation band boundaries. Clay rims, which are common in the host rock, are absent in the fault core. Additionally preliminary fluid inclusion data show elevated temperatures in healed fault core microfractures. It is essential to characterise the architecture, composition and porosity/permeability of fault core to accurately predict fluid flow parallel and perpendicular to deformation band fault zones.

Bright, A. M.; Shipton, Z. K.

2003-04-01

145

Band gap of the Ge (111) c (2×8) surface by scanning tunneling spectroscopy  

NASA Astrophysics Data System (ADS)

The surface band gap of the Ge(111)c(2×8) surface at low temperature is determined on the basis of scanning tunneling spectroscopy. Electrostatic potential computations permit evaluation of tip-induced band bending, from which a correction to the energy scale of the observed spectra is made. Parameter values in the computations are constrained by comparison of the observed spectrum with known spectral features, including high-lying conduction band features derived from first-principles computations. The surface band gap, lying between the bulk valence band maximum and the minimum of an adatom-induced surface band, is found to have a width of 0.49±0.03eV .

Feenstra, R. M.; Lee, J. Y.; Kang, M. H.; Meyer, G.; Rieder, K. H.

2006-01-01

146

Development of X-band accelerating structures for high gradients  

NASA Astrophysics Data System (ADS)

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.

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

147

Infrared stop-band filter based on a subwavelength structure  

NASA Astrophysics Data System (ADS)

We propose a stop-band filter in infrared region using a periodically chirped subwavelength structure. The structure is made of a stack of metal and dielectric pattern made on a thick metal layer that is deposited a PMMA substrate. It is found that an appropriately designed microstructure of metal-insulator-metal patches can generate a wideband infrared absorption, resulting in an infrared stop-band filter. Different width of metal-insulator-metal resonator arranged in one unit cell generate trough in the reflection spectrum at different wavelengths. The full width at half magnitude (FWHM) of the stop-band filter can thus be adjusted by tuning the width of the resonators. The larger the range of the resonator width, the wider the bandwidth will be. Under the condition of subwavelength dimension of the structure compared with the working wavelength, it is found that a FWHM of 4?m at central wavelength of ~9?m and a high absorption efficiency of up to 80% can be achieved. The proposed structure provides a novel method in the design of wideband efficient plasmonic absorbers in infrared or THz spectral regions with simultaneously wide bandwidth and high efficiency of absorption.

Song, Yanqin; Wang, Chinhua; Lou, Yimin; Cao, Bing; Li, Xiaofeng

2013-08-01

148

Band gaps in the spectra of terahertz surface plasmons on metallic diffraction gratings  

Microsoft Academic Search

The effect of the appearance of band gaps in the energy spectra of terahertz surface plasmons has been experimentally observed and investigated. The band gaps are formed due to the interference interaction of the surface plasmons excited by pulsed terahertz radiation on metallic diffraction gratings. It has been shown that the experimental dispersion curves of terahertz plasmons are in good

A. V. Andreev; M. M. Nazarov; I. R. Prudnikov; A. P. Shkurinov

2009-01-01

149

Below-band-gap excitation of a terahertz surface plasmon-polariton  

Microsoft Academic Search

We analyze the excitation of a surface plasmon-polariton at terahertz frequencies by an optical pulse with tilted intensity front incident on a semiconductor surface. We show that one can achieve an order of magnitude increase in the generated terahertz power by using an optical pulse with frequencies below the band gap compared to the above-band-gap excitation.

M. I. Bakunov; A. V. Maslov; S. B. Bodrov

2006-01-01

150

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

NASA Astrophysics Data System (ADS)

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. .

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

151

Plasmonic band structure controls single-molecule fluorescence.  

PubMed

Plasmonics and photonic crystals are two complementary approaches to tailor single-emitter fluorescence, using strong local field enhancements near metals on one hand and spatially extended photonic band structure effects on the other hand. Here, we explore the emergence of spontaneous emission control by finite-sized hexagonal arrays of nanoapertures milled in gold film. We demonstrate that already small lattices enable highly directional and enhanced emission from single fluorescent molecules in the central aperture. Even for clusters just four unit cells across, the directionality is set by the plasmonic crystal band structure, as confirmed by full-wave numerical simulations. This realization of plasmonic phase array antennas driven by single quantum emitters opens a flexible toolbox to engineer fluorescence and its detection. PMID:24020654

Langguth, Lutz; Punj, Deep; Wenger, Jérôme; Koenderink, A Femius

2013-09-16

152

Calculation of band structure in (101)-biaxially strained Si  

NASA Astrophysics Data System (ADS)

The structure model used for calculation was defined according to Vegard’s rule and Hooke’s law. Calculations were performed on the electronic structures of (101)-biaxially strained Si on relaxed Si1- X Ge X alloy with Ge fraction ranging from X = 0 to 0.4 in steps of 0.1 by CASTEP approach. It was found that [±100] and [00±1] valleys (?4) splitting from the [0±10] valley (?2) constitute the conduction band (CB) edge, that valence band (VB) edge degeneracy is partially lifted and that the electron mass is unaltered under strain while the hole mass decreases in the [100] and [010] directions. In addition, the fitted dependences of CB splitting energy, VB splitting energy and indirect bandgap on X are all linear.

Song, Jianjun; Zhang, Heming; Hu, Huiyong; Fu, Qiang

2009-04-01

153

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

SciTech Connect

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

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

2012-05-03

154

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

SciTech Connect

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

Katsiev, Khabibulakh; Losovyj, Yaroslav; Zhou, Zihao; Vescovo, E; Liu, L.; Dowben, P. A.; Goodman, D. Wayne

2012-01-01

155

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

Microsoft Academic Search

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

Arthur A. Oliner

1999-01-01

156

Broad-band power amplifier using dielectric photonic bandgap structure  

Microsoft Academic Search

Two class AB GaAs field-effect transistor (FET) power amplifiers have been designed and fabricated in the 4.4-4.8 GHz range. In the first case, a dielectric PBG line was incorporated in the design to tune the second harmonic. In the second case, a 50-? line is used with no harmonic tuning. The PBG structure allows broad-band harmonic tuning and is inexpensive

Vesna Radisic; Yongxi Qian; Tatsuo Itoh

1998-01-01

157

Analysis of plasmonic properties of heavily doped semiconductors using full band structure calculations  

NASA Astrophysics Data System (ADS)

Surface plasmon polaritons (SPPs) and localized surface plasmon (LSP) resonances are not limited to noble metals. Any material with a substantial amount of free carriers will support surface plasma oscillations which, when coupled to an electromagnetic field, will result in surface plasmon polaritons and localized surface plasmon resonances in confined systems. Utilizing a full band structure approach, we analyze the plasmonic properties of several heavily doped semiconductors. We present rigorous quantum mechanical calculations of the plasma frequency, and study in detail its dependence on impurity doping concentration. Results are presented for silicon, germanium, gallium arsenide, zinc oxide, and gallium nitride. For silicon and zinc oxide, the surface plasmon resonance frequency is calculated for a large range of doping concentrations and we study the dispersion of surface plasmon polaritons on thin films. The investigated properties of heavily doped semiconductors hold promises for several interesting applications within plasmonics.

Jung, Jesper; Pedersen, Thomas G.

2013-03-01

158

Band Structures of Transition-Metal-Dichalcogenide Layer Compounds  

Microsoft Academic Search

The nonrelativistic augmented-plane-wave (APW) method is applied to calculate the electronic band structures of several transition-metal-dichalcogenide (TX2) layer compounds, including materials with the C 6 (1T-HfS2,1T-TaS2), C 27 (2H-TaS2,2H-NbSe2), and C 7 (2H-MoS2) structure types. These calculations involve crystal potentials that are derived from neutral-atom charge densities. The results of these calculations confirm that the group-IVB (1T-HfS2) and group-VIB (2H-MoS2)

L. F. Mattheiss

1973-01-01

159

Bioinspired structured surfaces.  

PubMed

Nature has evolved objects with desired functionality using commonly found materials. Nature capitalizes on hierarchical structures to achieve functionality. The understanding of the functions provided by objects and processes found in nature can guide us to produce nanomaterials, nanodevices, and processes with desirable functionality. Various natural objects which provide functionality of commercial interest have been characterized to understand how a natural object provides functionality. We have modeled and fabricated structures in the lab using nature's route and developed optimum structures. Once it is understood how nature does it, optimum structures have been fabricated using smart materials and fabrication techniques. This feature article provides an overview of four topics: Lotus effect, rose petal effect, gecko feet, and shark skin. PMID:22233136

Bhushan, Bharat

2012-01-10

160

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

Microsoft Academic Search

We have performed angle-resolved photoemission spectroscopy (ARPES) measurements and first-principles electronic structure calculations on the electron-doped high-Tc superconductors Ln1.85Ce0.15CuO4 (Ln = Nd, Sm, and Eu). The observed Fermi surface and band dispersion show such changes that with decreasing ionic size of Ln3+, the curvature of the Fermi surface or -t'\\/t decreases, where t and t' are transfer integrals between the

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

2008-01-01

161

Coupler Design for the LCLS Injector S-Band Structures  

SciTech Connect

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.

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

162

Thermodynamic implications of band structure effects for rare gases on graphite  

SciTech Connect

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.

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

1980-01-01

163

First direct observation of a nearly ideal graphene band structure  

SciTech Connect

Angle-resolved photoemission and x-ray diffraction experiments show that multilayer epitaxial graphene grown on the SiC(000{bar 1}) surface is a new form of carbon that is composed of effectively isolated graphene sheets. The unique rotational stacking of these films causes adjacent graphene layers to electronically decouple leading to a set of nearly independent linearly dispersing bands (Dirac cones) at the graphene K point. Each cone corresponds to an individual macroscale graphene sheet in a multilayer stack where AB-stacked sheets can be considered as low density faults.

Sprinkle, M.; Siegel, D.; Hu, Y.; Hicks, J.; Tejeda, A.; Taleb-Ibrahimi, A.; Le Fèvre, P.; Bertran, F.; Vizzini, S.; Enriquez, H.; Chiang, S.; Soukiassian, P.; Berger, C.; de Heer, W.A.; Lanzara, A.; Conrad, E.H.; (CNRS-UMR); (UCB); (CEAS); (SOLEIL); (GIT)

2009-12-10

164

Phonon band structures of three-dimensional pentamode metamaterials  

NASA Astrophysics Data System (ADS)

Three-dimensional pentamode metamaterials are artificial solids that approximately behave like liquids, which have vanishing shear modulus. Pentamodes have recently become experimental reality. Here, we calculate their phonon band structures for various parameters. Consistent with static continuum mechanics, we find that compression and shear waves exhibit phase velocities that can realistically be different by more than one order of magnitude. Interestingly, we also find frequency intervals with more than two octaves bandwidth in which pure single-mode behavior is obtained. Herein, exclusively compression waves exist due to a complete three-dimensional band gap for shear waves and, hence, no coupling to shear modes is possible. Such single-mode behavior might, e.g., be interesting for transformation-elastodynamics architectures.

Martin, Aude; Kadic, Muamer; Schittny, Robert; Bückmann, Tiemo; Wegener, Martin

2012-10-01

165

Dual-band metamaterial with a windmill-like structure  

NASA Astrophysics Data System (ADS)

A broadband negative refractive index metamaterial based on a windmill-like structure is proposed, and investigated numerically and experimentally at the microwave frequency range. From the numerical and experimental results, effect media parameters are retrieved, which clearly show that two broad frequency bands exist in which the permittivity and permeability are negative. The two negative bands are from 9.1 GHz to 10.5 GHz and from 12.05 GHz to 14.65 GHz respectively, and the negative bandwidth is 4 GHz. Due to the good bandwidth performance, the metallic cell with double negative property obtained in this paper is suitable for use in the design of multiband or broadband microwave devices.

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

2013-01-01

166

Fabrication of x-band accelerating structures at Fermilab  

SciTech Connect

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

Tug T Arkan et al.

2004-07-20

167

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

NASA Astrophysics Data System (ADS)

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.

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

168

Spin-dependent band structure of the ferromagnetic semimetal EuB6  

NASA Astrophysics Data System (ADS)

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).

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

2008-03-01

169

The Structure and Dynamics of Beryllium Surfaces.  

NASA Astrophysics Data System (ADS)

Beryllium represents a challenging test to our understanding of surface physics because of its unique position in the periodic table. As a group II element, the valence shell is closed. Bonding requires the promotion of an s-electron to an unoccupied p-level. As first-row element, the core is entirely s-like, which leads to strong hybridization of s- and p-levels in the bulk. This mechanism of bonding leads to band structure which cannot be considered "free-electron-like" despite the fact that Be is s-p bonded. We have measured the structure and dynamics of Be surfaces in order to understand the effect of reduced coordination on the bonding of Be atoms. Our low-energy electron diffraction (LEED) measurements indicate that the first interplanar spacing at the Be(0001) surface is expanded outward by nearly 6% from the bulk value. The finding is anomalous because most close-packed metal surfaces exhibit only small relaxations. Our LEED measurements of the Be(1120) surface indicate the existence of a (1 x 3) missing-row (MR) reconstruction, similar to those observed at the (110) surfaces of transition and noble metals. For Be, which possesses no occupied d-bands, the mechanism driving the reconstruction must be different from that of other MR reconstructions. We have measured the dispersion of surface phonons at the Be(0001) surface using Electron-Energy Loss Spectroscopy in order to investigate how the interatomic forces in Be change at the surface. The importance of electronic screening in the lattice dynamics of bulk Be is reflected in large "non-central" forces between ions. While non-central forces are required in order to describe phonon dispersion in bulk Be, our experimental results are consistent with a reduction in the magnitude of non-central forces at the surface. In-plane non-central forces are appreciably reduced in magnitude due to the existence of surface states, which contribute 80% of the density of states at the Fermi level in the surface layer.

Hannon, James Bowler

170

Electronic band structure of a type-II ‘W’ quantum well calculated by an eight-band k · p model  

NASA Astrophysics Data System (ADS)

In this paper, we present an investigation of type-II ‘W’ quantum wells for the InAs/Ga1-xInxSb/AlSb family, where ‘W’ denotes the conduction profile of the material. We focus our attention on using the eight-band k · p model to calculate the band structures within the framework of finite element method. For the sake of clarity, the simulation in this paper is simplified and based on only one period—AlSb/InAs/Ga1-xInxSb/InAs/AlSb. The obtained numerical results include the energy levels and wavefunctions of carriers. We discuss the variations of the electronic properties by changing several important parameters, such as the thickness of either InAs or Ga1-xInxSb layer and the alloy composition in Ga1-xInxSb separately. In the last part, in order to compare the eight-band k · p model, we recalculate the conduction bands of the ‘W’ structure using the one-band k · p model and then discuss the difference between the two results, showing that conduction bands are strongly coupled with valence bands in the narrow band gap structure. The in-plane energy dispersions, which illustrate the suppression of the Auger recombination process, are also obtained. Project supported by the National Natural Science Foundation of China (Grant No. 60636030).

Yu, Xiu; Gu, Yong-Xian; Wang, Qing; Wei, Xin; Chen, Liang-Hui

2011-03-01

171

Simultaneous complete elastic and electromagnetic band gaps in periodic structures  

NASA Astrophysics Data System (ADS)

We study elastic and electromagnetic properties in periodic structures and present “deaf and blind” structures, i.e. materials having simultaneous complete phononic and photonic band gaps, that is, transverse electric (TE) and transverse magnetic (TM) electromagnetic waves, pure shear elastic waves, and mixed shear and dilatation elastic waves, cannot propagate within these structures. These composite materials can control the flow of light and sound at the same time. The existence of complete gaps for electromagnetic and elastic waves can lead to the simultaneous localization of light and sound, a novel phenomena that can have strong influence on photon-phonon interactions. We study the dependence of the simultaneous and complete gaps on material parameters to provide design guidelines on how to create these photonic-phononic crystals.

Maldovan, M.; Thomas, E. L.

2006-06-01

172

X-BAND TRAVELING WAVE RF DEFLECTOR STRUCTURES  

SciTech Connect

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.

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

2008-12-18

173

Band structure effects of transport properties in icosahedral quasicrystals  

NASA Astrophysics Data System (ADS)

Transport properties and optical conductivity are calculated for the crystalline approximant AlMn alloy. The number of electrons at the Fermi energy is very small and, based on the band structure, the anomalously small dc conductivity and temperature dependent thermoelectric power are explained. A model calculation for the two-dimensional Penrose lattice with random phason strain shows that it becomes more conductive than the perfect Penrose lattice. We propose the mechanism of the interband transition by phason randomness and inelastic scattering for the origin of the anomalous conductivity in real quasicrystals.

Fujiwara, Takeo; Yamamoto, Susumu; Trambly de Laissardière, Guy

1993-12-01

174

[Terahertz-band study on surface enhanced Raman scattering of nanoparticle].  

PubMed

Study on surface-enhanced Raman scattering in the terahertz-band proved in that the terahertz-band Raman enhancement also exists. By studing principles of electromagnetic enhancement of surface-enhanced Raman scattering, using the finite difference time-domain method, the electromagnetic enhancement of surface enhanced Raman scattering of nano-particles irradiated by terahertz-wave was simulated, and the enhancement effect of terahertz waves was analyzed. Simulation experiments show that using finite-difference time-domain method could obtain effectively accurate simulation result of nano-particle scattering, proving that for terahertz waves, surface-enhanced effects on the surface of the nano-particle also exist. The results for surface enhanced Raman scattering extended from the visible and infrared to terahertz-band, and provide a basis for application of the combination of surface-enhanced Raman scattering and terahertz-wave. PMID:23905325

Wu, Yu-Deng; Ren, Guang-Jun; Hao, Yun; Yao, Jian-Quan

2013-05-01

175

Band gaps and localization of surface water waves over large-scale sand waves with random fluctuations.  

PubMed

Band structure and wave localization are investigated for sea surface water waves over large-scale sand wave topography. Sand wave height, sand wave width, water depth, and water width between adjacent sand waves have significant impact on band gaps. Random fluctuations of sand wave height, sand wave width, and water depth induce water wave localization. However, random water width produces a perfect transmission tunnel of water waves at a certain frequency so that localization does not occur no matter how large a disorder level is applied. Together with theoretical results, the field experimental observations in the Taiwan Bank suggest band gap and wave localization as the physical mechanism of sea surface water wave propagating over natural large-scale sand waves. PMID:23005218

Zhang, Yu; Li, Yan; Shao, Hao; Zhong, Yaozhao; Zhang, Sai; Zhao, Zongxi

2012-06-25

176

Domain Structures in Nematic Liquid Crystals on a Polycarbonate Surface  

PubMed Central

Alignment of nematic liquid crystals on polycarbonate films obtained with the use of solvents with different solvations is studied. Domain structures occurring during the growth on the polymer surface against the background of the initial thread-like or schlieren texture are demonstrated. It is established by optical methods that the domains are stable formations visualizing the polymer surface structures. In nematic droplets, the temperature-induced transition from the domain structure with two extinction bands to the structure with four bands is observed. This transition is shown to be caused by reorientation of the nematic director in the liquid crystal volume from the planar alignment to the homeotropic state with the pronounced radial configuration of nematic molecules on the surface. The observed textures are compared with different combinations of the volume LC orientations and the radial distribution of the director field and the disclination lines at the polycarbonate surface.

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

2013-01-01

177

Coral Skeleton Density Banding: Biotic Response to Changes in Sea Surface Temperature  

NASA Astrophysics Data System (ADS)

Density bands in the CaCO3 (aragonite) skeleton of scleractinian corals are commonly used as chronometers, where crystalline couplets of high and low density bands represent the span of one year. Isotopic analysis of these density bands provides a sensitive reconstructive tool for paleoclimatology and paleoecology. However, the detailed biotic mechanisms controlling coral skeleton aragonite nucleation and crystallization events and resulting skeletal growth rate remain uncertain. The coral tissue organic matrix, composed of macromolecules secreted by the calicoblastic ectoderm, is closely associated with skeletal precipitation and is itself incorporated into the skeleton. We postulate that density banding is primarily controlled by changes in the rate of aragonite crystal precipitation mediated by the coral holobiont response to changes in sea surface temperature (SST). To test this hypothesis, data were collected from coral skeleton-tissue biopsies (2.5 cm in diameter) extracted from four species of Montastraea growing on the fringing reef tract of Curacao, Netherlands Antilles. Annual mean variation in SST on Curacao range from 29o in mid-September to 26o C in late February. Samples were collected at strategic time periods spanning the 3o C annual variations in SST. Our nanometer-scale optical analyses of skeletal morphology have revealed consistent changes between high- and low-skeletal density bands, resulting in an 11% increase in the volume of aragonite precipitated in high-density skeletal bands. The re-localization and/or change in abundance of mucus, carbonic anhydrase (a molecule that catalyzes the hydration of carbon dioxide), calmodulin (a calcium-binding protein) and the change in density of gastrodermal symbiotic dinoflagellates has permitted estimates of seasonally-fluctuating carbon allocation by the coral holobiont in response to changing environmental conditions. This digital reconstruction of over 2000 images of one-micron-thick histological sections of Montastraea annularis tissue yields a three-dimensional digital elevation map of coral tissue. This technique allows three-dimensional mapping of the cellular and molecular components of coral tissue in the context of the structure of an entire polyp.

Hill, C. A.; Sivaguru, M.; Fried, G. A.; Fouke, B. W.

2010-12-01

178

Modelling of dry-band discharge events on insulation surfaces  

Microsoft Academic Search

Discharges on composite insulator insulation surfaces are one cause of long-term ageing. Consequences of such ageing are further acceleration of damage, and ultimately an increased likelihood of flashover. Normally it is an unacceptable flashover probability that requires maintenance or replacement of aged insulators. In some cases however, the surface discharges can lead to deep erosion which can then lead to

Xin Zhang; Simon M Rowland

2010-01-01

179

Band-structure calculations of specular reflection in spin valves  

SciTech Connect

Band structure calculations are carried out on three types of spin-valve structures: (1) simple spin valves, (2) dual spin valves, and (3) spin valves with a synthetic antiferromagnet. The effect of specular reflection is studied by comparing the transport properties of spin valves with resistive metallic and insulating layers at the outer boundaries. In the spin valve with a synthetic antiferromagnet, an insulating layer needs to be inserted inside the reference layer to achieve similar enhancement to the giant magnetoresistance as the other two types of spin valves with insulating outer boundaries. Results are analyzed in terms of s{endash}d scattering in the different spin channels with different boundary conditions. {copyright} 2001 American Institute of Physics.

Chen, Jian; Fernandez-de-Castro, Juan

2001-06-01

180

Band gaps in the spectra of terahertz surface plasmons on metallic diffraction gratings  

Microsoft Academic Search

The effect of the appearance of band gaps in the energy spectra of terahertz surface plasmons has been experimentally observed\\u000a and investigated. The band gaps are formed due to the interference interaction of the surface plasmons excited by pulsed terahertz\\u000a radiation on metallic diffraction gratings. It has been shown that the experimental dispersion curves of terahertz plasmons\\u000a are in good

A. V. Andreev; M. M. Nazarov; I. R. Prudnikov; A. P. Shkurinov

2009-01-01

181

Numerical simulations of radar surface air pressure measurements at O2 bands  

Microsoft Academic Search

An active microwave method is investigated for measuring surface air pressure by using radar reflections at frequencies around 53-55 GHz O2 bands. The numerical simulation results for homogeneous backgrounds show that with an airborne radar working at these O2 absorption bands, the rms errors of the radar surface pressure estimations with 15-dB signal-to-noise ratio can be as low as 4-7

Bing Lin; Yongxiang Hu

2005-01-01

182

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

NASA Astrophysics Data System (ADS)

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.

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

2013-10-01

183

Surface Structural Model for Ferrihydrite  

Microsoft Academic Search

Abstract--A structural model,for the geometry,of Fe(III) octahe-dra near the surface of finely divided ferrihydrite was elaborated based on the bond-valence,theory and by considering,the interaction of water molecules in the 2 nearest hydration spheres. In contrast to bulk Fe atoms, which are bonded to bridging oxo (O) and hydroxo (OH) ligands, surface Fe atoms are also octahedrally coordinated to HzO ligands

A. Manceau; W. P. Gatest

1997-01-01

184

Human chromosomal bands: nested structure, high-definition map and molecular basis  

Microsoft Academic Search

In this paper, we report investigations on the nested structure, the high-definition mapping, and the molecular basis of the\\u000a classical Giemsa and Reverse bands in human chromosomes. We found the rules according to which the ?3,200 isochores of the\\u000a human genome are assembled in high (850-band) resolution bands, and the latter in low (400-band) resolution bands, so forming\\u000a the nested

Maria Costantini; Oliver Clay; Concetta Federico; Salvatore Saccone; Fabio Auletta; Giorgio Bernardi

2007-01-01

185

Band structure of the spectra of Hamiltonians of regular polynucleotide duplexes  

NASA Astrophysics Data System (ADS)

We calculate the band structure of the spectra of Hamiltonians of regular DNA duplexes and show that in single-stranded periodic polynucleotides whose period is determined by the number m of nucleotides in an elementary cell, the spectrum consists of m nonintersecting energy bands. In DNA duplexes, the number of energy bands is equal to 2m, and the bands can intersect. Discrete energy levels can be present in forbidden bands in the case of (semi)bounded chains or duplexes.

Lakhno, V. D.; Sultanov, V. B.

2013-09-01

186

Modeling the dust bands: Structure in zodiacal clouds  

NASA Astrophysics Data System (ADS)

The solar system dust bands discovered by IRAS are toroidal distributions of dust particles with common proper inclinations. The manner in which dust band profiles change around the sky should allow the determination of the origin of the bands, their radial extent and the size-frequency distribution of the material. The equilibrium model of the dust bands associating the dust bands with the major Hirayama families, suggests Eos as the parent of the 10 degree pair. Comparisons of IRAS observations with two Eos dust band models are presented.

Grogan, K.; Dermott, S. F.; Wyatt, M. C.

1998-04-01

187

Semiconductor nanocrystals: structure, properties, and band gap engineering.  

PubMed

Semiconductor nanocrystals are tiny light-emitting particles on the nanometer scale. Researchers have studied these particles intensely and have developed them for broad applications in solar energy conversion, optoelectronic devices, molecular and cellular imaging, and ultrasensitive detection. A major feature of semiconductor nanocrystals is the quantum confinement effect, which leads to spatial enclosure of the electronic charge carriers within the nanocrystal. Because of this effect, researchers can use the size and shape of these "artificial atoms" to widely and precisely tune the energy of discrete electronic energy states and optical transitions. As a result, researchers can tune the light emission from these particles throughout the ultraviolet, visible, near-infrared, and mid-infrared spectral ranges. These particles also span the transition between small molecules and bulk crystals, instilling novel optical properties such as carrier multiplication, single-particle blinking, and spectral diffusion. In addition, semiconductor nanocrystals provide a versatile building block for developing complex nanostructures such as superlattices and multimodal agents for molecular imaging and targeted therapy. In this Account, we discuss recent advances in the understanding of the atomic structure and optical properties of semiconductor nanocrystals. We also discuss new strategies for band gap and electronic wave function engineering to control the location of charge carriers. New methodologies such as alloying, doping, strain-tuning, and band-edge warping will likely play key roles in the further development of these particles for optoelectronic and biomedical applications. PMID:19827808

Smith, Andrew M; Nie, Shuming

2010-02-16

188

Band gap in hypersonic surface phononic lattice of nickel pillars  

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

189

Electronic structures and transport properties of silicene on Ag surface  

NASA Astrophysics Data System (ADS)

It has been predicted from first-principle that ``silicene'', a two-dimensional buckled honeycomb structure of silicon, is thermally stable and has a graphene-like band structure. In experiments, epitaxial silicene were observed to form at hexagonal Ag(111) and ZrB2(0001) surfaces. However, electronic structure and transport properties related to silicene have not been thoroughly studied. In this work, we have studied band structures of silicene on top of Ag surface using density-functional theory. The effective band structure mapped onto 1x1 unit cell of monolayer silicene on Ag(111) surface could be compared directly with Angle-Resolved Photoemission Spectra (ARPES). We have also studied electronic transport property across monolayer and bilayer silicene sheets using the Non-Equilibrium Green's Function (NEGF) method. The transmission curve shows a maximum at Fermi energy for the monolayer silicene case, but shows a minimum for the bilayer silicene case, which can be explained by their band structures.

Wang, Yun-Peng; Cheng, Hai-Ping

2013-03-01

190

Magnonic and plasmonic band gaps in films with periodically modified surfaces  

NASA Astrophysics Data System (ADS)

It is of current interest to understand the electromagnetic response of different nanostructures. In this study, we focus on the role of geometry, in the so-called static limit. In this limit, the incoming wavelength is much greater than the relevant scales of the object, retardation can be neglected, there are no inductive effects, and the electric and magnetic problems decouple, thus one studies plasmonic and magnonic responses separately. In particular, it is of interest to study enhancements of the fields associated with geometric features of the samples as well as the development of artificial structures that may show desired behaviors. With this in mind, in this work, we study a structure with a periodic geometric perturbation that shows a behavior of interest: plasmons and magnons propagate in it with band gaps associated with the geometry, i.e., they may be controlled by design. The structures in question are dielectric or ferromagnetic thin films whose surfaces are modulated periodically in one direction: we study modes of infinite wavelength along the nonmodulated direction. The results are analogous to those found for electronic wave functions in periodic potentials, i.e., one can introduce a reduced Brillouin zone scheme to describe the modes (its width is 2?/A, with A the period of the geometric perturbations), which are of the Bloch type. Different bands are identified, and they are calculated numerically. For small geometric perturbations, we develop a perturbation theory that agrees well with our numerical results, and we do obtain analytic expressions for the band gaps at the edges of the Brillouin zone (proportional to the amplitudes of the geometric perturbation of the surfaces and very simple in the case of plasmons). The underlying theory used to calculate the modes was previously developed and relies on solving integral equations along the edges of the sample for the electrostatic and magnetostatic potentials, respectively. Interesting features of this method are that it is practical and computationally nonintensive, film perturbations of arbitrary shapes and amplitudes can be addressed, and it merges in one framework the study of magnons and plasmons.

Jarufe, Claudio; Arias, R. E.

2012-05-01

191

Cloud Bands Structure of Hurricane David, 1979 - A Case Study.  

National Technical Information Service (NTIS)

The nature of the spiral banding of Hurricane David immediately before, during, and after a period of intensification is examined. The tropical cyclone spiral banding features are analyzed by the Tactical Environmental Display System (TEDS) program on the...

F. H. Nicholson

1984-01-01

192

Electronic-energy-band structure of uranium hydride  

NASA Astrophysics Data System (ADS)

The electronic energy bands of alpha and beta UH3 were calculated. These systems are unique among hydride formers in that a transformation directly to a trihydride occurs without an intervening dihydride phase and in that two trihydride structures form, both of which are based on the A-15 (V3Si) structure. Evidence was found of fairly large uranium f electron hydrogen s electron bonding interactionn which is allowed and favored by these structures. The beta-UH3 has eight formula units in the unit cell with the hydrogens tetrahedrally coordinated. As usual there is a lowlying set (24) of hydrogen derived states which overlaps the uranium f levels. This leads to the result of two types of f character: localized (magnetic) and itinerant. This latter type may be as large as one electron/U atom with a greater contribution from the linear chain atoms with a greater contribution from the linear chain atoms which form three of the four hydrogen neighbors than from the bcc like uraniums.

Switendick, A. C.

193

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

DOEpatents

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

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

2001-08-14

194

X-band rf structure with integrated alignment monitors  

NASA Astrophysics Data System (ADS)

We present the electrical design for an X-band traveling wave accelerator structure with integrated alignment monitors to measure the transverse wake, which will be used as part of the PSI-XFEL project and in the CLIC structure testing program. At PSI, it will compensate nonlinearities in the longitudinal phase space at the injector prototype of the PSI-XFEL. At CLIC it will be tested for breakdown limits and rates in the high gradient regime. The prolonged operation of such a structure in the PSI-XFEL injector, albeit not for the CLIC parameter regime, will constitute a good quality test of the manufacturing procedures employed. The operation in the PSI-XFEL injector will be at a relatively modest beam energy of 250 MeV, at which transverse wakes can easily destroy the beam emittance. For this reason, the layout chosen employs a large iris, 5?/6 phase advance geometry, which minimizes transverse wakefield effects while still retaining a good efficiency. As a second important feature, the design includes two wakefield monitors coupling to the transverse higher order modes, which allow steering the beam to the structure axis, potentially facilitating a higher precision than mechanical alignment strategies. Of special interest is the time domain envelope of these monitor signals. Local offsets due to bends or tilts have individual signatures in the frequency spectrum, which in turn are correlated with different delays in the signal envelope. By taking advantage of this combined with the single bunch mode at the PSI-XFEL, the use of a relatively simple detector-type rf front end should be possible, which will not only show beam offsets but also higher order misalignments such as tilts in the structure. The resolution of these monitors is determined by the tolerance of the random cell-to-cell misalignment leading to a spurious signal in the monitors.

Dehler, M.; Raguin, J.-Y.; Citterio, A.; Falone, A.; Wuensch, W.; Riddone, G.; Grudiev, A.; Zennaro, R.

2009-06-01

195

Structure of superdeformed bands in {sup 195}Hg  

SciTech Connect

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

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

1997-01-01

196

Band-Gap Design of Quaternary (In,Ga) (As,Sb) Semiconductors via the Inverse-Band-Structure Approach  

SciTech Connect

Quaternary systems illustrated by (Ga,In)(As,Sb) manifest a huge configurational space, offering in principle the possibility of designing structures that are lattice matched to a given substrate and have given electronic properties (e.g., band gap) at more than one composition. Such specific configurations were however, hitherto, unidentified. We show here that using a genetic-algorithm search with a pseudopotential Inverse-band-structure (IBS) approach it is possible to identify those configurations that are naturally lattice matching (to GaSb) and have a specific band gap (310 meV) at more than one composition. This is done by deviating from randomness, allowing the IBS to find a partial atomic ordering. This illustrates multitarget design of the electronic structure of multinary systems.

Piquini, P.; Graf, P. A.; Zunger. A.

2008-01-01

197

Surface properties in West Africa from spaceborne radars in C and Ku bands  

NASA Astrophysics Data System (ADS)

We propose to compare the backscattering responses of land surfaces in West Africa for different radar spaceborne sensors: the nadir-looking radar altimeters and the side-looking radar scatterometers at different frequencies (Ku and C bands). The data used come from Envisat-RA2 measurements in Ku-band over the period 2003-2010 and the Jason-2 measurements in C band over mid-2008-2011 for radar altimetry, and from QuikSCAT - SeaWinds in Ku-band and Metop - ASCAT in C-band for radar scatterometry over the same time-spans. Along-track profiles and their temporal variations are analyzed and their behaviours are related to surfaces properties such as soil types, vegetation cover, and surface hydrology. Temporal variations of backscattering coefficients are extracted for main land covers along the bio-climatic transect (stone and sand deserts, saharo-sahelian, sahelian, and soudano-sahelian savannahs, tropical-seasonal and tropical forests) and compared to both rainfall estimates from TRMM and vegetation activity (NDVI) from MODIS. Range of variations of the backscattering signals are given for different surfaces and ecosystems along with delays between peaks of rainfall, backscattering responses of radar altimetry and scatterometry, and vegetation activity. The stability of the backscattering is also estimated over deserts and during the dry season over Sahelian environments. Finally, the complementarity of the different spaceborne sensors for continental surfaces monitoring is pointed out.

Fatras, Christophe; Frappart, Frédéric; Mougin, Eric; Frison, Pierre-Louis; Faye, Gayane; Jarlan, Lionel

2013-04-01

198

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

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

199

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

PubMed

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

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

2003-04-21

200

Relaxation of GaAs surface band bending by atomic layer passivation  

Microsoft Academic Search

GaAs surface passivation by several atomic layers of InP is presented. The deposition of an atomically thin InP layer on n- and p-type (100) GaAs by chemical vapor deposition shows very strong enhancement in photoluminescence intensity and a remarkable reduction in surface band bending determined by Hall effect measurements. The surface modification effect is very stable, and evidence suggests that

Yoshinori Wada; Kazumi Wada

1993-01-01

201

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

SciTech Connect

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.

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

1997-12-01

202

Surface bound states in n -band systems with the quasiclassical approach  

NASA Astrophysics Data System (ADS)

We discuss the tunneling spectroscopy at a surface in multiband systems such as Fe-based superconductors with the use of the quasiclassical approach. We extend the single-band method by M. Matsumoto and H. Shiba [J. Phys. Soc. Jpn. 64, 1703 (1995)] into n -band systems (n?2) . We show that the appearance condition of the zero-bias conductance peak does not depend on details of the pair-potential anisotropy, but it depends on details of the normal-state properties in the case of fully gapped superconductors. The surface density of states in a two-band superconductor is presented as a simplest application. The quasiclassical approach enables us to calculate readily the surface-angular dependence of the tunneling spectroscopy.

Nagai, Yuki; Hayashi, Nobuhiko

2009-06-01

203

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

SciTech Connect

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

Yan, Q.; Meyer, F.W.

1996-09-01

204

Interferometric investigation of photonic band-structure effects in pure and doped colloidal crystals  

Microsoft Academic Search

A Mach-Zehnder interferometer was developed for accurately measuring relative phase shifts of light propa- gating in photonic colloidal crystals deep into the stop bands. These phase shifts can be used to determine the change in index of refraction and the optical dispersion relation from photonic band structure near the band edges. Phase measurements of colloidal crystals incorporating an impurity peak

Björn T. Rosner; Garrett J. Schneider; George H. Watson

1998-01-01

205

Brain Surface Conformal Parameterization Using Riemann Surface Structure  

Microsoft Academic Search

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

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

2007-01-01

206

Suppression of the parallel-plate noise in high-speed circuits using a metallic electromagnetic band-gap structure  

Microsoft Academic Search

A novel approach for the suppression of the parallel-plate noise in high-speed circuits is proposed by utilizing a metallic electromagnetic band-gap (EBG) structure. The key idea relies on replacing one of the two solid electric conductor plates with a metallic EBG surface of compact texture. To validate the concept, an EBG surface was fabricated and employed in a number of

Ramesh Abhari; George V. Eleftheriades

2002-01-01

207

Effect of RF Parameters on Breakdown Limits in High-Vacuum X-Band Structures  

NASA Astrophysics Data System (ADS)

RF breakdown is one of the major factors determining performance of high power rf components and rf sources. RF breakdown limits working power and produces irreversible surface damage. The breakdown limit depends on the rf circuit, structure geometry, and rf frequency. It is also a function of the input power, pulse width, and surface electric and magnetic fields. In this paper we discuss multi-megawatt operation of X-band rf structures at pulse width on the order of one microsecond. These structures are used in rf systems of high gradient accelerators. Recent experiments at Stanford Linear Accelerator Center (SLAC) have explored the functional dependence of breakdown limit on input power and pulse width. The experimental data covered accelerating structures and waveguides. Another breakdown limit of accelerating structures was associated with high magnetic fields found in waveguide-to-structure couplers. To understand and quantify these limits we simulated 3D structures with the electrodynamics code Ansoft HFSS and the Particle-In-Cell code MAGIC3D. Results of these simulations together with experimental data will be discussed in this paper.

Dolgashev, Valery A.; Tantawi, Sami G.

2003-12-01

208

Remote measurement of surface pressure using absorption in the oxygen A-band  

NASA Astrophysics Data System (ADS)

A simple technique is described that measures the atmospheric absorption in the oxygen A-band near 0.76 microns. A narrow interference filter is tilted so that its passband scans through the two branches of the absorption band. By viewing the direct solar beam a differential absorption measurement of the mass of oxygen in the optical path is obtained which is then compared to surface pressure. A transmittance model is described which gives results that agree well with the measurements. The model is also used to investigate the possible extension of the technique to a satellite-borne instrument for estimating surface pressure.

Barton, I. J.; Scott, J. C.

1986-10-01

209

Design of Miniature Planar Dual-Band Filter Using Dual-Feeding Structures and Embedded Resonators  

Microsoft Academic Search

A new dual-band planar filter has been proposed. It is shown that the two transmission bands can be excited and designed using proposed resonators which combine different sizes of open-loop resonators. The main resonators control the low-band resonant frequency and the sub resonators control the high-band resonant frequency. With dual-feeding structures added, the performances of the filter such as frequency

Chu-Yu Chen; Cheng-Ying Hsu; Huey-Ru Chuang

2006-01-01

210

Band structure of 146Ce studied through ?-? angular correlation measurements  

NASA Astrophysics Data System (ADS)

The ?-decay of 146La was studied using the on-line isotope separator KUR-ISOL. Gamma-gamma angular correlation measurements were performed with a 4-Ge detectors system. Spin assignments of three levels were made: 3+ for the 1576.5 keV level, 4+ for the 1627.1 keV level and 5+ for the 1810.2 keV level. The mixing ratios (E2/M1) were deduced to be ?183.2= 0.25 +/- 0.08, ?638.9= 0.33 +/- 0.05, ?959.0= 1.19+0.16-0.14, ?1015.9= 5.4+3.1-1.5 and ?1318.1= 6.5+1.7-1.1. These were compared to the calculated values obtained in three cases involving different Majorana force parameter values. The band structure of 146Ce is discussed based on the results of calculation using the IBM-2 theory.

Yamada, S.; Taniguchi, A.; Okano, K.; Aoki, K.

211

Infrared detectors and lasers operating in the 3-12 um range using band-gap engineered structures with Type II band-gap alignment  

Microsoft Academic Search

The Type II broken band-gap alignment in semiconductor structures wherein the conduction band minimum is in one semiconductor (e.g., InAs) and the valence band maximum is in another (e.g., GaInSb) offers certain unique advantages which can be utilized to realize band-gap engineered novel quantum electro-optic devices such as lasers and detectors. The advantages of the type II structures include reduced

Venkataraman Swaminathan; John W. Little; Richard L. Tober

212

Infrared detectors and lasers operating in the 3-12 mum range using band-gap engineered structures with type II band-gap alignment  

Microsoft Academic Search

The Type II broken band-gap alignment in semiconductor structures wherein the conduction band minimum is in one semiconductor (e.g., InAs) and the valence band maximum is in another (e.g., GaInSb) offers certain unique advantages which can be utilized to realize band-gap engineered novel quantum electro-optic devices such as lasers and detectors. The advantages of the type II structures include reduced

Venkataraman Swaminathan; John W. Little; Richard L. Tober

2006-01-01

213

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

NASA Astrophysics Data System (ADS)

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.

Cho, Jaewon

214

Band gap engineering at surfaces of insulating films by adsorption of organic molecules  

NASA Astrophysics Data System (ADS)

Adsorption of simple organic molecules on wide band gap insulators is a versatile tool to introduce unoccupied electronic states in the band gap at the surface. Relative energetic positions, varied also by intra-molecular interactions of functional side groups, determine the effective band gap. Specific examples used here are adsorbed molecules of benzoic acid and of its OH-substituted derivates (salicylic acid, etc.) on NaCl, KCl and on MgSO4 · H2O. These acids are mainly physisorbed on NaCl and KCl, whereas on MgSO4 · H2O chemical bond formation is found. Ab initio and semi-empirical calculations are used in order to identify mechanisms of surface-molecule as well as intra-molecular interactions.

Pfnür, H.; Tegenkamp, C.; Maslyuk, V.; Bredow, T.

2006-04-01

215

Lunar banding in the scleractinian coral Montastraea faveolata: Fine-scale structure and influence of temperature  

NASA Astrophysics Data System (ADS)

Lunar cycles play an important role in controlling biological rhythms in many organisms, including hermatypic corals. Coral spawning is correlated with environmental factors, including surface seawater temperature (SST) and lunar phase. Calcium carbonate skeletons of corals possess minute structures that, when viewed via X-radiography, produce high-density (HD) annual banding patterns. Some corals possess dissepiments that serve as the microstructural base for upward corallite growth. Here we report the results of detailed structural analysis of the skeleton of Montastraea faveolata (Scleractinia) (Ellis and Solander, 1786) and quantify the number of dissepiments that occur between HD bands, including interannual and intercorallite variability. Using a 30 year database, spanning from 1961 to 1991, we confirm earlier speculation by several authors that the frequencies of these microbands within a year is tightly linked to the lunar cycle. We also demonstrate that the frequency distribution of the number of these dissepiments per year is skewed to lower numbers. Extensive statistical analyses of long-term daily SST records (University of Puerto Rico, Mayaguez) revealed that precipitation of dissepiments is suppressed in years of cooler-than-average seawater temperature. We propose that dissepiment deposition is driven primarily by lunar cycle and seawater temperature, particularly at lower temperatures, and banding is generally unaffected by normal or high temperatures. These fine-scale banding patterns are also strongly correlated with the number of lunar months between reproductive spawning events in average or warmer-than-average seawater temperature years. This microbanding may represent another proxy for high-resolution estimates of variance in marine palaeo-temperatures, particularly during cooler SST years.

Winter, Amos; Sammarco, Paul W.

2010-10-01

216

New linear accelerator (Linac) design based on C-band accelerating structures for SXFEL facility  

NASA Astrophysics Data System (ADS)

A C-band accelerator structure is one promising technique for a compact XFEL facility. It is also attractive in beam dynamics in maintaining a high quality electron beam, which is an important factor in the performance of a free electron laser. In this paper, a comparison between traditional S-band and C-band accelerating structures is made based on the linac configuration of a Shanghai Soft X-ray Free Electron Laser (SXFEL) facility. Throughout the comprehensive simulation, we conclude that the C-band structure is much more competitive.

Zhang, Meng; Gu, Qiang

2011-11-01

217

Relaxation of GaAs surface band bending by atomic layer passivation  

SciTech Connect

GaAs surface passivation by several atomic layers of InP is presented. The deposition of an atomically thin InP layer on n- and p-type (100) GaAs by chemical vapor deposition shows very strong enhancement in photoluminescence intensity and a remarkable reduction in surface band bending determined by Hall effect measurements. The surface modification effect is very stable, and evidence suggests that the oxidation of InP plays an important role in this passivation mechanism. These results indicates that atomically thin InP layer is very effective for the surface passivation of GaAs. 16 refs., 4 figs.

Wada, Yoshinori; Wada, Kazumi [NTT LSI Labs., Kanagawa (Japan)

1993-07-01

218

The Electronic Structure of Nonpolar Surfaces in Insulating Metal Oxides  

NASA Astrophysics Data System (ADS)

Understanding the electronic and geometric structures of metal oxide surfaces has a key interest in many technological areas. A randomly chosen crystal surface has a high probability of being polar, unstable and containing in-gap states due to surface dangling bonds. As a result, the surface should be stabilized by passivation or reconstruction. However, do the nonpolar surfaces of ionic crystals of insulating metal oxides need the passivation or reconstruction similar to covalent crystals? We address this question by analyzing the nonpolar surfaces and their electronic structure for the common crystal structures of metal oxides. The study using periodic DFT calculations is performed for following representatives: Cu2O, ZnO, Al2O3, TiO2, V2O5, WO3, CaTiO3, Mg2SiO4. It has been shown that the nonpolar surface can be constructed out of dipole-free, charge-neutral and stoichiometric unit cells for each crystal. We demonstrate that all constructed and relaxed nonpolar surfaces of the metal oxides show a clear band gap. It should be emphasized that the constructed surfaces are neither reconstructed nor passivated. Additionally, we show a correlation between the electronic structure of the relaxed surfaces and Ewald energies calculated for the surface ions.

Zherebetskyy, Danylo; Wang, Lin-Wang

2013-03-01

219

Study of Band Structure of Two-Dimensional Anisotropic Honeycomb Photonic Crystals  

NASA Astrophysics Data System (ADS)

Using the plane wave expansion method, we have calculated, for both E and H polarizations, the band structure of 2D anisotropic photonic crystals with honeycomb lattice composed of anisotropic tellurium (Te) rods embedded in air background. The two rods in the unit cell are chosen square and circular in shape. Here, from a practical point of view, in order to obtain maximum band gaps, we have also studied the band structure as a function of size of rods.

Sedghi, A.; Soufiani, A. Rounaghi

2013-10-01

220

Effect of dry band arcing on the surface of RTV silicone rubber coatings  

Microsoft Academic Search

To elucidate the chemical changes due to dry band arcing, under wet and contaminated conditions, of room temperature vulcanized (RTV) silicone rubber used for coating HV outdoor insulators, the thermal impact of the arcing on the rubber surface was investigated. A loss of hydrophobicity, resulting in a reduction of the withstand voltage and subsequent failure of the insulators, was observed.

S. H. Kim; E. A. Cherney; R. Hackam

1992-01-01

221

Design of square-loop frequency selective surfaces utilize C-band radar stations  

Microsoft Academic Search

This research proposes to utilize square-loop frequency selective surface (FSS) in a radar station to increase the efficiency of communication systems and in the same time protect the staff and people against biological effects of C-band microwave radiation. In a radar station, waves propagate in undetermined directions and different frequency ranges which can effect on health of staff and people

M. Hosseinipanah; Qun Wu; Chengwen Zhang; F. A. Mianji; Guohui Yang

2008-01-01

222

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

Technology Transfer Automated Retrieval System (TEKTRAN)

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

223

L-Band Microwave Observations over Land Surface Using a Two-Dimensional Synthetic Aperture Radiometer  

Technology Transfer Automated Retrieval System (TEKTRAN)

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

224

Air-core photonic band-gap fibers: the impact of surface modes  

Microsoft Academic Search

We study the dispersion and leakage properties for the recently reported low-loss photonic band-gap fiber by Smith et al. [Nature 424, 657 (2003)]. We find that surface modes have a significant impact on both the dispersion and leakage properties of the fundamental mode. Our dispersion results are in qualitative agreement with the dispersion profile reported recently by Ouzounov et al.

K. Saitoh; N. A. Mortensen; M. Koshiba

2004-01-01

225

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

Microsoft Academic Search

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

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

2002-01-01

226

Band-Limited Microresonator Reflectors and Mirror Structures  

Microsoft Academic Search

\\u000a An overview of microring resonator architectures, fabricated using both fiber and integrated technologies, whose function\\u000a is to reflect nearly the entire incident signal within a specified band of frequencies, is presented. The signal components\\u000a that lie outside this band, called the stopband, are either transmitted through the device to exit through another port, or\\u000a dissipated. The stopband reflectivity is ideally

Otto Schwelb; Ioannis Chremmos

2010-01-01

227

Spectral analysis of defective photonic band-gap (PBG) structures on coplanar waveguide (CPW)  

Microsoft Academic Search

This paper presents some interesting results in the analysis of some defective photonic band-gap (PBG) structures on a coplanar waveguide. PBG structures have been broadly applied in recent years in communications and microelectronics areas. They are formed by periodic circuit elements and act as a band-stop device in which unwanted signals at certain frequency range are filtered. Frequency characteristics are

Ming-Sze Tong; Yilong Lul; Y. P. Zhangl; Yinchao Chen; Kenichi Kagoshima; Hycong-Seok Kim; Viktor Krozer

2004-01-01

228

Search for Direct Band Gap in Group IV Semiconductor Alloys and Quantum Wire Structures  

Microsoft Academic Search

Interest in creating direct band gap group IV, semiconductor, particularly silicon based structures, has been stimulated with the discovery of the photoluminescence in electrochemically etched porous silicon. This work examines, theoretically, the possibilities of the existence of a direct band gap in group IV alloys and quantum wire structures using empirical pseudopotential method (EPM) for the calculation of the energy

Khalid Mahmood

1994-01-01

229

Effects of hot rolled shear bands on formability and surface ridging of an ultra purified 21%Cr ferritic stainless steel  

Microsoft Academic Search

An ultra purified 21%Cr ferritic stainless steel (FSS) was hot rolled at a low finisher entry temperature (FET) of 750°C to generate shear bands through large shear flow localizations in grain interiors. The effects of shear bands on the formability and surface ridging have been studied as compared to a conventional hot rolled band at the FET of 970°C with

Chi Zhang; Zhenyu Liu; Guodong Wang

2011-01-01

230

Photonic band gap structure containing metamaterial with negative permittivity and permeability.  

PubMed

We have considered theoretically the main properties of layered periodical structures [one-dimensional photonic band gap (PBG) structures] that include layers of so-called backward-wave material (BW), whose both permittivity and permeability are negative. Each period consists of one layer of a usual material and one layer of a BW medium. Eigenwaves in infinite photonic band-gap structures and reflective and transmitting properties of finite-length structures are considered. Our analysis has shown that the usage of the negative material makes it possible to dramatically widen the band gap of one-dimensional layered PBG structures. PMID:12366284

Nefedov, Igor S; Tretyakov, Sergei A

2002-09-23

231

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

232

Two-dimensional band structure and self-energy of Bi(111) near the Gamma¯ point  

Microsoft Academic Search

Angle-resolved photoemission spectroscopy with synchrotron radiation was used to map the Fermi surface and the dispersion of the associated bands of Bi(111) near the Gamma¯ point. Using variable photon energies we prove the two-dimensional nature of these bands. From fits of the spectral function A(omega,k) to momentum distribution curves of the hole band we determined the imaginary part of the

Christian R. Ast; Hartmut Höchst

2002-01-01

233

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

SciTech Connect

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

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

2012-07-05

234

Band structures and proton-neutron interactions in 174Ta  

NASA Astrophysics Data System (ADS)

Six rotational bands in the odd-odd nucleus 174Ta have been populated with the 160Gd(19F,5n) reaction. High-spin states were identified using the NORDBALL array. Both signatures of the doubly decoupled ?1/2-[541]??1/2-[521] band and semi-decoupled ?1/2-[541]??7/2+[633] band are observed, in addition to the high-K couplings of the ?9/2-[514]??7/2+[633], ?9/2-[514]??5/2-[512], ?7/2+[404]??7/2+[633], and ?5/2+[402]??5/2-[512] configurations. The signature splitting of the ?1/2-[541]??7/2+[633] band is inverted from the expected splitting, and this is interpreted as being due to a residual proton-neutron interaction. It is shown empirically that this interaction, together with deformation changes, can account for the increased crossing frequency associated with the alignment of i13/2 neutrons in the ?1/2-[541] bands of odd-Z nuclei.

Bark, R. A.; Carlsson, H.; Freeman, S. J.; Hagemann, G. B.; Ingebretsen, F.; Jensen, H. J.; Lönnroth, T.; Piiparinen, M. J.; Ragnarsson, I.; Ryde, H.; Schnack-Petersen, H.; Semmes, P. B.; Tjøm, P. O.

1998-02-01

235

Fine structure in the profiles of strong diffuse interstellar bands  

NASA Astrophysics Data System (ADS)

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

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

2008-06-01

236

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

PubMed

Distinct partitioning has been observed in the composition and diversity of bacterial communities inhabiting the surface and overlying seawater of three coral species infected with black band disease (BBD) on the southern Caribbean island of Curaçao, Netherlands Antilles. PCR amplification and sequencing of bacterial 16S rRNA genes (rDNA) with universally conserved primers have identified over 524 unique bacterial sequences affiliated with 12 bacterial divisions. The molecular sequences exhibited less than 5% similarity in bacterial community composition between seawater and the healthy, black band diseased, and dead coral surfaces. The BBD bacterial mat rapidly migrates across and kills the coral tissue. Clone libraries constructed from the BBD mat were comprised of eight bacterial divisions and 13% unknowns. Several sequences representing bacteria previously found in other marine and terrestrial organisms (including humans) were isolated from the infected coral surfaces, including Clostridium spp., Arcobacter spp., Campylobacter spp., Cytophaga fermentans, Cytophaga columnaris, and Trichodesmium tenue. PMID:11976091

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

2002-05-01

237

Band Structures and Nucleon Alignments in ^173,175W  

NASA Astrophysics Data System (ADS)

Spectroscopic study of nuclei in the A˜180 region is essential to better understand regional relationships between Nilsson orbitals. Highly excited rotational states in both nuclei were populated at Argonne National Laboratory via a 230 MeV ^50Ti beam from the ATLAS accelerator incident on a ^128Te target. The Gammasphere array was used to detect ? decays from excited states. Rotational bands built on the level 1/2^-[521], p3/2 in ^173,175W have been extended to spins of 40 and 35 respectively, and bands built on the 7/2^+[633], i13/2 configuration extended to 38 and 27 respectively. New sidebands in ^173W have been observed in all previously-discovered bands. Alignments from i13/2 neutron and h11/2 proton crossings are consistent with predictions of Woods-Saxon cranking calculations. Experimental results and regional systematics will be presented.

Guess, C. J.; Tandel, S. K.; Chowdhury, P.; Shirwadkar, U.; Carpenter, M. P.; Janssens, R. V. F.; Khoo, T. L.; Lauritsen, T.; Lister, C. J.; Seweryniak, D.; Wang, X.; Zhu, S.; Hartley, D. J.

2012-10-01

238

Effects of strain on band structure and effective masses in MoS2  

NASA Astrophysics Data System (ADS)

We use hybrid density functional theory to explore the band structure and effective masses of MoS2, and the effects of strain on the electronic properties. Strain allows engineering the magnitude as well as the nature (direct versus indirect) of the band gap. Deformation potentials that quantify these changes are reported. The calculations also allow us to investigate the transition in band structure from bulk to monolayer, and the nature and degeneracy of conduction-band valleys. Investigations of strain effects on effective masses reveal that small uniaxial stresses can lead to large changes in the hole effective mass.

Peelaers, H.; Van de Walle, C. G.

2012-12-01

239

Band structure of two-dimensional square lattice photonic crystals of circular dispersive metamaterial rods  

Microsoft Academic Search

By virtue of the efficiency of the Dirichlet-to-Neumann\\u000a map method, the details of the band structure of a two-dimensional\\u000a square lattice photonic crystal composed of dispersive metamaterial\\u000a circular rods in air background has been studied.\\u000a We show that there are two flat bands at the band structure\\u000a of the system for both H-polarization and E-polarization. These flat bands are created

A. Soltani Vala; S. Roshan Entezar; A. A. Sedghi

2011-01-01

240

Microscopic origin of universal quasilinear band structures of transparent conducting oxides.  

PubMed

A tight-binding-based microscopic theory is developed that accounts for quasilinear conduction bands appearing commonly in transparent conducting oxides. It is found that the interaction between oxygen p and metal s orbtials plays a critical role in determining the band structure around the conduction-band minimum. Under certain types of short-range orders, the tight-binding model universally leads to a dispersion relation which corresponds to that of the massive Dirac particle. The impact of the graphenelike band structure is demonstrated by evaluating the electron mobility of highly doped n-type ZnO. PMID:23003067

Kang, Youngho; Jeon, Sang Ho; Son, Young-Woo; Lee, Young-Su; Ryu, Myungkwan; Lee, Sangyoon; Han, Seungwu

2012-05-11

241

High-spin structure beyond band termination in 157Er.  

PubMed

The angular-momentum induced transition from a deformed state of collective rotation to a noncollective configuration has been studied. In 157Er this transition manifests itself as favored band termination near I=45 Planck's. The feeding of these band terminating states has been investigated for the first time using the Gammasphere spectrometer. Many weakly populated states lying at high excitation energy that decay into these special states have been discovered. Cranked Nilsson-Strutinsky calculations suggest that these states arise from weakly collective "core-breaking" configurations. PMID:15245000

Evans, A O; Paul, E S; Simpson, J; Riley, M A; Appelbe, D E; Campbell, D B; Choy, P T W; Clark, R M; Cromaz, M; Fallon, P; Görgen, A; Joss, D T; Lee, I Y; Macchiavelli, A O; Nolan, P J; Pipidis, A; Ward, D; Ragnarsson, I; Sari?, F

2004-06-25

242

Band structures of TiO2 doped with N, C and B*  

PubMed Central

This study on the band structures and charge densities of nitrogen (N)-, carbon (C)- and boron (B)-doped titanium dioxide (TiO2) by first-principles simulation with the CASTEP code (Segall et al., 2002) showed that the three 2p bands of impurity atom are located above the valence-band maximum and below the Ti 3d bands, and that along with the decreasing of impurity atomic number, the fluctuations become more intensive. We cannot observe obvious band-gap narrowing in our result. Therefore, the cause of absorption in visible light might be the isolated impurity atom 2p states in band-gap rather than the band-gap narrowing.

Xu, Tian-Hua; Song, Chen-Lu; Liu, Yong; Han, Gao-Rong

2006-01-01

243

Rational design of long-wave infrared band for application of the earth surface temperature observation  

NASA Astrophysics Data System (ADS)

For argumentation of feasibility of LST (Land Surface Temperature) retrieval using 8-10 ?m infrared band, this paper focuses on design of long-wave infrared band based on theory research. Basis of thermal infrared radiative transfer and atmospheric simulation, the paper analyses atmospheric effect on different long-wave infrared and obtain a preliminary selection of potential spectral channels. Several configurations of long-wave infrared spectral band were selected to perform in Split-Window algorithm and the relation of LST retrieval precision with error source was analyzed. Results indicate the scheme of LST retrieval using 8.0-9.0?m long-wave infrared is feasibility for needed retrieval precision.

Bao, Yunfei; He, Hongyan; Zhou, Feng

2012-12-01

244

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

PubMed

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

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

2012-08-14

245

Pseudospin flip in doubly decoupled structures and identical bands  

SciTech Connect

Unfavored components of doubly decoupled bands are reported. They can be interpreted as having the pseudospin flipped relative to the orientation in the favored components, i.e., antialigned with respect to the rotation axis. In addition, the differences in consecutive transition energies along the favored and unfavored sequences are strikingly similar among them up to [ital I][sup [pi

Kreiner, A.J.; Cardona, M.A.; Somacal, H.; Debray, M.E.; Hojman, D.; Davidson, J.; Davidson, M.; De Acuna, D.; Napoli, D.R.; Rico, J.; Bazzacco, D.; Burch, R.; Lenzi, S.M.; Rossi Alvarez, C.; Blasi, N.; Lo Bianco, G. (Departamento de Fisica, Comision Nacional de Energia Atomica, 1429 Buenos Aires (Argentina) Departamento de Fisica, Facultad de Ciencias Exactas y Naturales, UBA, Buenos Aires (Argentina) CONICET, 1033 Buenos Aires (Argentina) Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Legnaro, Legnaro (Italy) Dipartimento di Fisica, Sezione di Padova, Padova (Italy) Dipartimento di Fisica and Instituto Nazionale di Fisica Nucleare, Sezione di Milano, Milano (Italy))

1994-08-01

246

Band-structure engineering for ultralow-threshold laser diodes  

SciTech Connect

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

Ury, I.; Lau, K.Y.

1988-01-01

247

Electronic band structures of graphene nanoribbons with self-passivating edge reconstructions.  

PubMed

Using the nearest-neighbor tight-binding approach we study the electronic band structures of graphene nanoribbons with self-passivating edge reconstructions. For zigzag ribbons the edge reconstruction moves both the Fermi energy and the flat band down by several hundred meV, and the flat band is always found to be below the Fermi energy. The states featured by the flat band are shown to be mainly localized at the atoms belonging to several lattice lines closest to the edges. For armchair ribbons the edge reconstruction strongly modifies the band structure in the region close to the Fermi energy, leading to the appearance of a band gap even for ribbons which were predicted to be metallic in the model of standard armchair edges. The gap widths are, however, strongly different in magnitude and behave in different ways regarding the ribbon width. PMID:21737866

Tung Nguyen, L; Huy Pham, C; Lien Nguyen, V

2011-07-08

248

Chemical changes at the surface of RTV silicone rubber coatings on insulators during dry-band arcing  

Microsoft Academic Search

Under wet and contaminated conditions dry band arcing occurs on the surface of HV outdoor insulators coated with room temperature vulcanizing (RTV) silicone rubber. The thermal impact of the arcing on the surface of the RTV causes chemical changes. The gradual loss of hydrophobicity due to dry band arcing is of considerable concern because it results in a reduction of

Seog-Hyeon Kim; Edward A. Cherney; Reuben Hackam; Kenneth G. Rutherford

1994-01-01

249

Heterogeneity of Z-band structure within a single muscle sarcomere: implications for sarcomere assembly.  

PubMed

The vertebrate striated muscle Z-band connects actin filaments of opposite polarity from adjacent sarcomeres and allows tension to be transmitted along a myofibril during contraction. Z-bands in different muscles have a modular structure formed by layers of alpha-actinin molecules cross-linking actin filaments. Successive layers occur at 19 nm intervals and have 90 degrees rotations between them. 3D reconstruction from electron micrographs show a two-layer "simple" Z-band in fish body fast muscle, a three-layer Z-band in fish fin fast muscle, and a six-layer Z-band in mammalian slow muscle. Related to the number of these layers, longitudinal sections of the Z-band show a number of zigzag connections between the oppositely oriented actin filaments. The number of layers also determines the axial width of the Z-band, which is a useful indicator of fibre type; fast fibres have narrow (approximately 30-50 nm) Z-bands; slow and cardiac fibres have wide (approximately 100-140 nm) Z-bands. Here, we report the first observation of two different Z-band widths within a single sarcomere. By comparison with previous studies, the narrower Z-band comprises three layers. Since the increase in width of the wider Z-band is about 19 nm, we conclude that it comprises four layers. This finding is consistent with a Z-band assembly model involving molecular control mechanisms that can add additional layers of 19 nm periodicity. These multiple Z-band structures suggest that different isoforms of nebulin and titin with a variable number of Z-repeats could be present within a single sarcomere. PMID:12946354

Luther, Pradeep K; Padrón, Raúl; Ritter, Stephan; Craig, Roger; Squire, John M

2003-09-01

250

Electronic structure of new multiple band Pt-pnictide superconductors APt3P  

NASA Astrophysics Data System (ADS)

We report LDA calculated band structure, densities of states and Fermi surfaces for recently discovered Pt-pnictide superconductors APt3P (A = Ca, Sr, La), confirming their multiple band nature. Electronic structure is essentially three dimensional, in contrast to Fe pnictides and chalcogenides. LDA calculated Sommerfeld coefficient agrees rather well with experimental data, leaving little space for very strong coupling super-conductivity, suggested by experimental data on specific heat of SrPt3P. Elementary estimates show, that the values of critical temperature can be explained by rather weak or moderately strong coupling, while the decrease in superconducting transition temperature T c from Sr to La compound can be explained by corresponding decrease in total density of states at the Fermi level N( E F). The shape of the density of states near the Fermi level suggests that in SrPt3P electron doping (such as replacement Sr by La) decreases N( E F) and T c , while hole doping (e.g., partial replacement of Sr with K, Rb or Cs, if possible) would increase N( E F) and possibly T c .

Nekrasov, I. A.; Sadovskii, M. V.

2012-10-01

251

Surface electronic structure and chemisorption on corundum transition-metal oxides: V2O3  

NASA Astrophysics Data System (ADS)

The surface electronic structure of single-crystal V2O3 has been studied by using ultraviolet and x-ray photoelectron spectroscopy. Both nearly-perfect surfaces and surfaces containing point defects have been prepared, and the influence of O2 and H2O on both types of surfaces has been investigated. Cation core-level spectra from cleaved surfaces exhibit complex structure. The surface electronic band structure is similar to that of the bulk; at room temperature, V2O3 is metallic with the Fermi level EF lying within the overlapping V(3d) a1g and e?g conduction bands. A minimum in the density of states occurs between the V(3d) and O(2p) bands at 3 eV below EF. The O(2p) valence band has a width of 5.5-6 eV. Surface defects produced by Ar+-ion bombardment are associated with O vacancies and a net charge transfer to V(3d) levels. O2 interacts strongly with both perfect surfaces and surface defects, transferring charge out of the V(3d) levels and bending both valence and conduction bands up at the surface. The work function rises dramatically, indicating the presence of a negatively charged adsorbed species (likely O2-). H2O adsorbs dissociatively on both cleaved and bombarded surfaces, producing adsorbed OH- radicals with a saturation coverage of less than 0.5 monolayer.

Kurtz, Richard L.; Henrich, Victor E.

1983-12-01

252

Surface characterization of Pluto and Charon by L and M band spectra  

NASA Astrophysics Data System (ADS)

Context: One of the main scientific objectives of NASA's New Horizons mission is to map the icy surface compositions of Pluto and its moon Charon. The encounter will be in 2015. Meanwhile remote observations from earth and space are the most suitable means to enhance further our knowledge of the Pluto/Charon system. Aims: We intend to assist the New Horizons mission by improving our knowledge of Pluto's and Charon's surface compositions. Specifically, we extend the wavelength coverage of the surface spectroscopy beyond the K band, with the goal to detect further surface ice absorption bands predicted from the models that are based on the available JHK spectra, and to search for signatures of yet unknown ices. In particular we aim to resolve the binary system Pluto/Charon and to obtain, for the first time, spectra up to 5 ?m of the two objects resolved. Methods: Spectroscopic measurements of Pluto/Charon taken with the adaptive optics instrument NACO at the ESO VLT in the interval 3-7 August 2005 were obtained. The nature and properties of the compounds present on the surface of Pluto and Charon are investigated by applying a Hapke radiative transfer model to the measured spectra. Results: We present Pluto's reflectance spectrum in the wavelength range (1-5) ?m. Apart from known and expected absorption bands of methane ice, our Pluto spectrum reveals a new absorption band centered near 4.6 ?m, not previously detected. This absorption band could be related to the presence of CO and nitriles (compounds of C and N connected with a triple bond). A geographic mixture of pure methane ice with two different grain sizes, methane and CO ice diluted in nitrogen, CH{2}CHCN and titan tholin gives the best fit to Pluto's spectrum, although not in all details. Differences compared to published Pluto spectra from 2001 taken at similar longitude could be due to a different surface coverage in latitude or to a possible resurfacing process on Pluto. Charon's spectrum is measured in the wavelength range (1-4) ?m. The surface of Charon can be modeled by pure water ice darkened by a spectrally neutral continuum absorber.

Protopapa, S.; Boehnhardt, H.; Herbst, T. M.; Cruikshank, D. P.; Grundy, W. M.; Merlin, F.; Olkin, C. B.

2008-10-01

253

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

SciTech Connect

Contactless electroreflectance (CER) supported by photoluminescence (PL) has been applied to study (i) the surface band bending, (ii) the band gap bowing, and (iii) the Stokes shift for InGaN layers grown by molecular beam epitaxy with 0.14<=In<=0.36. The type of surface band bending has been investigated on the basis of the shape of CER resonance. It has been found that the surface band bending changes from n-type for layers with low indium content (In<27%) to flatband (or weak p-type band) for layers with Inapprox35%. The band gap bowing has been determined to be 1.4+-0.2 and 2.1+-0.3 eV for CER data with and without strain corrections, respectively. From this analysis it has been concluded that the reliable value of the bowing parameter for unstrained InGaN should be between 1.4 and 2.1 eV. Comparing CER with PL data it has been found that the Stokes shift rises from 20 to 120 meV when the indium concentration increased from 14% to 36%. In addition, it has been observed that the intensity of PL from InGaN layers decreased exponentially with the increase in the indium content. The last two findings are attributed to an easier formation of native point defects and stronger indium segregation in InGaN alloys with higher indium concentrations.

Kudrawiec, R.; Misiewicz, J. [Institute of Physics, Wroclaw University of Technology, 50-370 Wroclaw (Poland); Siekacz, M.; Krysko, M.; Cywinski, G.; Skierbiszewski, C. [Institute of High Pressure Physics, Polish Academy of Science, Sokolowska 29/37, 01-142 Warsaw (Poland)

2009-12-01

254

Surface photovoltage spectroscopy of semiconductor structures: at the crossroads of physics, chemistry and electrical engineering  

Microsoft Academic Search

The possibility of obtaining a detailed picture of the electronic structure makes surface photovoltage spectroscopy (SPS) eminently suitable for bridging the gap between the chemical, physical, optical and electrical properties of semiconductors. In SPS, changes in band bending (both at the free semiconductor surface and at buried interfaces) are monitored as a function of external illumination. Surface photovoltage spectroscopy can

Leeor Kronik; Yoram Shapira

2001-01-01

255

Dual-band frequency selective surface with quasi-elliptic bandpass response  

NASA Astrophysics Data System (ADS)

Based on the substrate integrated waveguide technology, we present a dual-band frequency selective surface (FSS) with a quasi-elliptic bandpass response. The characteristics of the quasi-elliptic bandpass response are realized by shunting two substrate integrated waveguide cavities of different sizes, with the same slots on both sides of the metal surfaces. Four cavities of different sizes and two slots of different sizes are used to design the novel FSS. Every bandpass response with sharp sidebands is induced by two transmission nulls that are generated by the coupling between the slot aperture resonance and the cavity resonance. The simulation results show that such dual-band FSS has the advantages of high selectivity and stable performance at different oblique incident angles. Moreover, it is easy to fabricate.

Zhou, Hang; Qu, Shao-Bo; Peng, Wei-Dong; Wang, Jia-Fu; Ma, Hua; Zhang, Jie-Qiu; Bai, Peng; Xu, Zhuo

2012-03-01

256

Mapping the band structure of three-dimensional topological insulator Bi2Se3 in two-dimensional limit  

Microsoft Academic Search

In this work, with in situ angle-resolved photoemission spectroscopy, we have investigated the thickness dependent band structure of molecular beam epitaxy grown Bi2Se3, a typical three-dimensional insulator, from 1 quintuple layer (QL) up to 200QL. An energy gap is observed in the topologically protected metallic surface states of bulk Bi2Se3 below the thickness of 6QL, due to the coupling between

Ke He; Yi Zhang; Cui-Zu Chang; Can-Li Song; Li-Li Wang; Xu-Cun Ma; Zhong Fang; Xi Dai; Wen-Yu Shan; Shun-Qing Shen; Qian Niu; Xiao-Liang Qi; Shou-Cheng Zhang; Xi Chen; Jin-Feng Jia; Qi-Kun Xue

2010-01-01

257

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

SciTech Connect

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.

Kozyukhin, S., E-mail: sergkoz@igic.ras.ru [Russian Academy of Science, Institute of General and Inorganic Chemistry (Russian Federation); Golovchak, R. [Lviv Scientific Research Institute of Materials of SRC 'Carat' (Ukraine); Kovalskiy, A. [Lehigh University, Department of Materials Science and Engineering (United States); Shpotyuk, O. [Lviv Scientific Research Institute of Materials of SRC 'Carat' (Ukraine); Jain, H. [Lehigh University, Department of Materials Science and Engineering (United States)

2011-04-15

258

Band structure approach to resonant x-ray scattering.  

PubMed

We study the resonance behavior of the forbidden 600 and 222 x-ray Bragg peaks in Ge. These peaks remain forbidden in the resonant dipole scattering approximation, even taking into account the nonlocal nature of the band states. However, they become allowed at resonance if the eigenstates of the unoccupied conduction band involve a hybridization of p-like and d-like atomic states. We show that the energy dependence of the resonant behavior, including the phase of the scattering, is a direct measure of this p-d hybridization and obtain quantitative agreement with experiment. We discuss the implications of this to other materials like V2O3 in which the resonating atom is not at a center of inversion symmetry. PMID:11800963

Elfimov, I S; Skorikov, N A; Anisimov, V I; Sawatzky, G A

2001-12-17

259

Dependence of oxide surface structure on surface topology and local chemical bonding  

SciTech Connect

The atomic geometries of the charge neutral surfaces of several oxides exhibiting different crystal structures and varying participation of O(2{ital p}) electrons in the chemical bonding have been calculated using tight-binding total energy models. Surface structures have been computed for exemplary cubic (MgO), wurtzite (ZnO), {beta}-tridymite, and ideal {beta}-cristobalite (SiO{sub 2}) oxides. The cubic oxide exhibits a minimum energy structure involving small outward relaxations of the oxygens and inward relaxations of the cations. For the cleavage faces of wurtzite ZnO, large bond-length-conserving relaxations occur because the surface atoms can relax without appreciable distortion of the local bond lengths. The charge neutral faces of {beta}-tridymite and ideal {beta}-cristobalite SiO{sub 2} also undergo bond-length-conserving relaxations. Thus the mechanism for the surface relaxation of tetrahedrally coordinated oxides is significantly different from that of the cubic oxides as is the role of the oxygen {ital p} electrons in the surface chemical bonding. Most importantly, the surface structural chemistry of charge neutral oxide surfaces reflects the interplay of both surface topology (via the ability to undergo bond-length-conserving relaxations) and local coordination chemistry (via the participation of {ital p} electrons in bonding versus nonbonding surface state bands).

LaFemina, J.P. (Molecular Science Research Center, Pacific Northwest Laboratory, P.O. Box 999, Richland, Washington 99352 (USA)); Duke, C.B. (Xerox Webster Research Center, 800 Phillips Road 0114-38D, Webster, New York 14580 (USA))

1991-05-01

260

Band structures extending to very high spin in Xe126  

Microsoft Academic Search

High-spin states in Xe126 have been populated in the Se82(Ca48,4n)Xe126 reaction in two experiments, one at the VIVITRON accelerator in Strasbourg using the Euroball detector array, and a subsequent one with ATLAS at Argonne using the Gammasphere Ge-detector array. Levels and assignments made previously for Xe126 up to I=20 have been confirmed and extended. Four regular bands extending to a

C. Rønn Hansen; G. Sletten; G. B. Hagemann; B. Herskind; D. R. Jensen; P. Bringel; C. Engelhardt; H. Hübel; A. Neußer-Neffgen; A. K. Singh; M. P. Carpenter; R. V. F. Janssens; T. L. Khoo; T. Lauritsen; P. Bednarczyk; T. Byrski; D. Curien; G. Benzoni; A. Bracco; F. Camera; S. Leoni; R. M. Clark; P. Fallon; A. Korichi; J. Roccaz; A. Maj; J. N. Wilson; J. C. Lisle; T. Steinhardt; O. Thelen; S. W. Ødegård

2007-01-01

261

Single layer MoS2 band structure and transport  

Microsoft Academic Search

Ultrathin two dimensional materials have significant potential for application in nano-electronic devices. Graphene is a popular two-dimensional material due to its intrinsic high mobility. However, Graphene does not have any band gap, which makes it hard to be used for field effect transistors (FET)[1]. On the other hand, monolayer Molybdenum Disulfide (MoS2) is a thin two dimensional material with large

Mehdi Salmani-Jelodar; Yaohua Tan; Gerhard Klimeck

2011-01-01

262

Pseudospin flip in doubly decoupled structures and identical bands  

NASA Astrophysics Data System (ADS)

Unfavored components of doubly decoupled bands are reported. They can be interpreted as having the pseudospin flipped relative to the orientation in the favored components, i.e., antialigned with respect to the rotation axis. In addition, the differences in consecutive transition energies along the favored and unfavored sequences are strikingly similar among them up to I?=15+ and 14+, respectively. This feature arises from a cancellation of differences in alignments and moments of inertia.

Kreiner, A. J.; Cardona, M. A.; Somacal, H.; Debray, M. E.; Hojman, D.; Davidson, J.; Davidson, M.; de Acuña, D.; Napoli, D. R.; Rico, J.; Bazzacco, D.; Burch, R.; Lenzi, S. M.; Rossi Alvarez, C.; Blasi, N.; Lo Bianco, G.

1994-08-01

263

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

PubMed Central

This paper introduces a novel approach to create notch band filters in the front-end of ultra-wideband (UWB) communication systems based on electromagnetic bandgap (EBG) structures. The concept presented here can be implemented in any structure that has a microstrip in its configuration. The EBG structure is first analyzed using a full wave electromagnetic solver and then optimized to work at WLAN band (5.15–5.825 GHz). Two UWB passband filters are used to demonstrate the applicability and effectiveness of the novel EBG notch band feature. Simulation results are provided for two cases studied.

Rotaru, Mihai; Sykulski, Jan

2010-01-01

264

CCMR: Steps Toward Direct Comparison of Band Structure Calculations and Photoemission Spectra in 3D Materials  

NSDL National Science Digital Library

Steps are taken to unite theoretical predictions of electronic band structure with direct measurements from high-resolution angle-resolved photoemission spectroscopy (ARPES). A new process of accessing data from self-consistent eld calculations allows for calculations of band structure along any path in momentum space. Using the inner potential model, a primitive model is developed for direct comparison of photoemission measurements and augmented plane-wave + local orbitals (APW+lo) band structure calculations close to the Fermi energy, Ef. This model is then applied to ARPES measurements for URu2Si2.

Hristov, Alexander

2009-08-15

265

Structure of excited bands in 162Tm and residual interactions  

NASA Astrophysics Data System (ADS)

The nucleus 162Tm has been populated by the 130Te(37Cl,5n) reaction, and the ?-cascades detected with the NORDBALL array. Eight coupled rotational bands involving the proton orbitals, g7/2[404]7/2+, d3/2[411]1/2+, d5/2[402]5/2+, h11/2[523]7/2- and h9/2[541]1/2- and neutron orbitals i13/2[642]5/2+, h9/2[523]5/2- and f7/2[521]3/2- have been established in 162Tm, to spins varying from 18 to 47?. Various phenomena which can be related to residual neutron-proton interactions are discussed. In particular, signature inversion in the ?[541]1/2- ??[642]5/2+ bands based on the h9/2 quasiproton and i13/2 quasineutron, respectively, may be explained by a fairly large p-n interaction. In addition, interactions at the crossings of bands with constituent quasiparticles differing both in parity and signature have been extracted with strength of the order of a few (4-12) keV. Such interactions also require terms beyond the standard mean field description.

Espino, J. M.; Hagemann, G. B.; Bearden, I. G.; Bark, R. A.; Bergström, M.; Bracco, A.; Herskind, B.; Jensen, H. J.; Leoni, S.; Martínez-Torre, C.; Million, B.; Tjøm, P. O.

1998-09-01

266

Quasiparticle band structures and optical properties of magnesium fluoride  

NASA Astrophysics Data System (ADS)

The quasiparticle and optical properties of magnesium fluoride (MgF2) are computed within the GW approximation based on many-body perturbation theory (MBPT). The many-body effects appearing in self-energy and electron-hole interactions have an important influence on the electronic and optical properties. The DFT-LDA calculation shows a 6.78 eV band gap. Two methods are employed to evaluate the self-energy within the GW approximation in the present work. The generalized plasmon pole model (GPP) provides a band gap of 12.17 eV, which agrees well with the experimental value of 12.4 eV (Thomas et al 1973 Phys. Status Solidi b 56 163). Another band gap value of 11.30 eV is obtained by using a full frequency-dependent self-energy, which is also not far from the experimental value and is much better than the result from the LDA calculation. The calculated optical spectrum within DFT is significantly different from the experiment. Although the calculated optical absorption threshold within the GW method is close to the experiment, the overall shape of the spectrum is still similar to the case of DFT. However, the overall shape of the spectrum via the Bethe-Salpeter equation (BSE) method agrees well with the experiment.

Yi, Zhijun; Jia, Ran

2012-02-01

267

A Novel Band-Reject Frequency Selective Surface With Pseudo-Elliptic Response  

Microsoft Academic Search

A novel frequency selective surface (FSS) exhibiting pseudo-elliptic band-reject response is presented. The proposed FSS consists of a two-dimensional periodic array of microstrip lines. For an incident wave of linear polarization perpendicular to the printed lines, virtual magnetic walls are formed between the microstrip lines. Since a microstrip line shielded with magnetic side walls supports two quasi-TEM modes, the two-dimensional

Amir Khurrum Rashid; Zhongxiang Shen

2010-01-01

268

TROPICAL SOUTH CHINA SEA SURFACE 14C RECORD IN AN ANNUALLY BANDED CORAL  

Microsoft Academic Search

A surface-water ?14C record of AD 1948-1999 in the tropical South China Sea (SCS) has been reconstructed from accelerator mass spectrometric radiocarbon measurements of annual bands of a Porites coral collected from Con Dao Island, Vietnam. Results gave the following ?14C time series: a steady state of -47.8 ± 2.8‰ (mean ± SD, n = 8) during 1948- 1955 (i.e.

Takehiro Mitsuguchi; Phong X Dang; Hiroyuki Kitagawa; Minoru Yoneda; Yasuyuki Shibata

269

L-band microwave observations over land surface using a two-dimensional synthetic aperture radiometer  

Microsoft Academic Search

Antenna size is a major factor that has limited realization of the potential capabilities of L-band (1.4 GHz) microwave radiometry to estimate surface soil moisture from space. However, emerging interferometric technology, called aperture synthesis, has been developed to address this limitation. The Soil Moisture and Ocean Salinity (SMOS) mission will apply the technique to monitor these parameters at a global-scale

Dongryeol Ryu; Thomas J. Jackson; Rajat Bindlish; David M. Le Vine

2007-01-01

270

Electronic energy bands in the fluorite structure: CaF2 and CdF2  

Microsoft Academic Search

The electronic band structures of calcium and cadmium fluoride are calculated by a combined tight-binding and pseudopotential method. The overall shape of the valence bands is found to be the same in these two compounds and agrees quite well with a \\

J. P. Albert; C. Jouanin; C. Gout

1977-01-01

271

A FEM domain decomposition method for photonic and electromagnetic band gap structures  

Microsoft Academic Search

This paper introduces an efficient domain decomposition algorithm for the solution of time-harmonic electromagnetic fields arising in three dimensional, finite-size photonic band gap and electromagnetic band gap structures. The method is based on the finite element approximation and a nonoverlapping domain decomposition method. A set of \\

Marinos N. Vouvakis; Zoltan Cendes; Jin-Fa Lee

2006-01-01

272

Efficient formulation for band-structure calculations of two-dimensional phononic-crystal plates  

Microsoft Academic Search

Based on Mindlin's plate theory and the plane wave expansion method, a formulation is proposed to study the propagation of Lamb waves in two-dimensional phononic-crystal plates. The method is applied to calculate the frequency band structure of a square array of crystalline gold cylinders in an epoxy matrix with a finite thickness. It is found that complete frequency band gaps

Jin-Chen Hsu; Tsung-Tsong Wu

2006-01-01

273

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

NASA Astrophysics Data System (ADS)

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.

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

2013-06-01

274

Broad energy-bands of continuous-network-structure molybdenum films  

NASA Astrophysics Data System (ADS)

Interband absorption of continuous-network-structure (CNS) molybdenum films with a weight thickness below about 3 nm weakened and shifted to higher energies compared to interband absorption of continuous-thin molybdenum films with bulk energy bands. This weakening and shift agrees qualitatively with that observed in interband absorption of metal particles, which have energy bands broadened by lattice contraction. Based on this agreement, the weakening and shift in the CNS molybdenum films can be qualitatively ascribed to energy-band broadening. Thus, CNS molybdenum films with a weight thickness below about 3 nm have broader energy bands compared to bulk molybdenum.

Anno, Eiji

2010-10-01

275

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

SciTech Connect

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.

Shaposhnikov, V. L., E-mail: shaposhnikov@nano.bsuir.edu.by; Migas, D. B.; Borisenko, V. E. [Belarussian State University of Informatics and Radioelectronics (Belarus); Dorozhkin, N. N. [Belarussian State University (Belarus)

2009-02-15

276

Photonic Band Gaps in Experimentally Realizable Periodic Dielectric Structures  

Microsoft Academic Search

By solving Maxwell's equations for the propagation of electromagnetic waves in periodic dielectric structures (with dielectric constant ?b in a uniform background ?a), we found that several classes of periodic dielectric structures possess full photonic gaps, as in the case of dielectric spheres arranged in the diamond structure. These new structures have the additional advantage that they can be easily

C. T. Chan; K. M. Ho; C. M. Soukoulis

1991-01-01

277

Ultraviolet surface-enhanced Raman scattering at the plasmonic band edge of a metallic grating.  

PubMed

Surface-enhanced Raman Scattering (SERS) is studied in sub-wavelength metallic gratings on a substrate using a rigorous electromagnetic approach. In the ultraviolet SERS is limited by the metallic dampening, yet enhancements as large as 10(5) are predicted. It is shown that these enhancements are directly linked to the spectral position of the plasmonic band edge of the metal/substrate surface plasmon. A simple methodology is presented for selecting the grating pitch to produce optimal enhancement for a given laser frequency. PMID:22274532

Mattiucci, Nadia; D'Aguanno, Giuseppe; Everitt, Henry O; Foreman, John V; Callahan, John M; Buncick, Milan C; Bloemer, Mark J

2012-01-16

278

Dispersion and Damping of a Two-Dimensional Plasmon in a Metallic Surface-State Band  

SciTech Connect

We have studied, for the first time, the energy and the linewidth dispersion of a plasmon in a dense two-dimensional electron system in a metallic surface-state band on a silicon surface. As expected from the considerably high effective density and long Fermi wavelength of the system, the plasmon energy dispersion exhibited an excellent agreement with the nearly free-electron theory. However, in a small wave number region below the Landau edge, we have observed an anomalous linewidth dispersion which nearly free-electron theories do not predict.

Nagao, Tadaaki; Hildebrandt, Torsten; Henzler, Martin; Hasegawa, Shuji

2001-06-18

279

Stability of graphene band structures against an external periodic perturbation: Na on graphene  

NASA Astrophysics Data System (ADS)

The electronic structure of Na-adsorbed graphenes formed on the 6H-SiC(0001) substrate was studied using angle-resolved photoemission spectroscopy with synchrotron photons and ab initio pseudopotential calculations. It was found that the band of the graphenes sensitively changes upon Na adsorption especially at low temperature. With increasing Na dose, the ? band appears to be quickly diffused into the background at 85 K whereas it becomes significantly enhanced with its spectral intensity at room temperature (RT). A new parabolic band centered at ktilde 1.15Å-1 also forms near Fermi energy with Na at 85 K while no such band was observed at RT. Such changes in the band structure are found to be reversible with temperature. The changes in the ? band of graphene are mainly driven by the Na-induced potential especially at low temperature where the potential becomes periodic due to the crystallized Na overlayer. The new parabolic band turns out to be the ? band of the underlying buffer layer partially filled by the charge transfer from Na adatoms. The increase in the hopping rate of Na adatoms at RT by 5 orders of magnitude prevents such a charge transfer, explaining the absence of the new band at RT.

Hwang, C. G.; Shin, S. Y.; Choi, Seon-Myeong; Kim, N. D.; Uhm, S. H.; Kim, H. S.; Hwang, C. C.; Noh, D. Y.; Jhi, Seung-Hoon; Chung, J. W.

2009-03-01

280

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...

281

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

SciTech Connect

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

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

2009-01-01

282

Nanofabrication of broad-band antireflective surfaces using self-assembly of block copolymers.  

PubMed

We present a simple and cost-effective method for the fabrication of antireflective surfaces by self-assembly of block copolymers and subsequent plasma etching. The block copolymers create randomly oriented periodic patterns, which are further transferred into fused silica substrates. The reflection on the patterned fused silica surface is reduced to well below 1% in the ultraviolet, visible, and near-infrared ranges by exploiting subwavelength nanostructures with periodicities down to 48 nm. We show that by choosing the appropriate block copolymers and pattern transfer parameters the optical properties of the antireflective surface can be easily tuned, and the spectral measurements verify a significant reduction of the reflectivity by a factor of 10. The experiments, confirmed with simulations based on rigorous diffraction theory, also show that the tapered shape of the nanostructures gives rise to a graded index surface, resulting in a broad-band antireflective behavior. PMID:21323325

Päivänranta, Birgit; Sahoo, Pratap K; Tocce, Elizabeth; Auzelyte, Vaida; Ekinci, Yasin; Solak, Harun H; Liu, Chi-Chun; Stuen, Karl O; Nealey, Paul F; David, Christian

2011-02-16

283

Rheological characteristics of soft rock structural surface  

Microsoft Academic Search

There are two mechanisms of the coarse surface asperity resistance effect and rubbing resistance effect in the course of the\\u000a soft rock structural surface creep, of which the former plays a dominant role in hindering the deformation in the starting\\u000a creep phase, so that the structural surface creep usually displays the strong surface roughness effect, and so does the latter

Yuan-jiang Chen; Chao Wu; Yi-ming Fu

2008-01-01

284

Structure of Dipole Bands in 112In: Through Lifetime Measurement  

NASA Astrophysics Data System (ADS)

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.

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

285

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

PubMed

Manure can provide valuable nutrients, especially N, for grass forage, but high NH, volatilization losses from standard surface-broadcast application limits N availability and raises environmental concerns. Eight field trials were conducted to evaluate the emission of NH, from liquid dairy manure, either surface broadcast or applied in narrow surface bands with a trailing-foot implement. Manure was applied using both techniques at rates of approximately 25 and 50 m3 ha(-1) on either orchardgrass (Dactylis glomerata L.) on a well-drained silt loam or reed canarygrass (Phalaris arundinacea L.) on a somewhat poorly drained clay soil. Ammonia emission was measured with a dynamic chamber/equilibrium concentration technique. High NH3 emission rates in broadcast treatments, especially at the high rate (2 to 13 kg ha(-1) h(-1)), occurred during the first few hours after spreading, followed by a rapid reduction to low levels (<0.5 kg ha(-1) h(-1) in most cases) by 24 h after spreading and in subsequent days. Band treatments often followed the same pattern but with initial rates substantially lower and with a less dramatic decrease over time. Total estimated NH3 losses from broadcast application, as a percent of total ammoniacal N (TAN) applied, averaged 39% (range of 20 to 59%) from the high manure rate and 25% (range of 9 to 52%) from the low rate. Band spreading reduced total NH3 losses by an average of 52 and 29% for the high and low manure rates, respectively. Results show that the trailing-foot band application method can reduce NH3 losses and conserve N for perennial forage production. PMID:21520744

Pfluke, Paul D; Jokela, William E; Bosworth, Sidney C

286

Detection of Ionospheric Structures with L-Band Synthetic Aperture Radars  

Microsoft Academic Search

Numerical simulations of low-latitude ionospheric instabilities show the formation of plasma density structures can be detected by synthetic aperture radar (SAR) radio signals. At L-band, the phase front distortions produced by propagation through plasma \\

Paul A. Bernhardt; Thomas L. Ainsworth; Keith M. Groves; Ted Beach; Ronald G. Caton; Charles S. Carrano; Christian M. Alcala; Dale D. Sponseller

2008-01-01

287

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

SciTech Connect

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.

Jaworski, C. M. [Ohio State University; Nielsen, Mechele [Ohio State University; Wang, Hsin [ORNL; Girard, Steven N. [Northwestern University, Evanston; Cai, Wei [ORNL; Porter, Wallace D [ORNL; Kanatzidis, Mercouri G. [Northwestern University, Evanston; Heremans, J. P. [Ohio State University

2013-01-01

288

Effect of oxide band structure on the emission process of excited atoms under ion bombardment  

NASA Astrophysics Data System (ADS)

Ion-photon emission (IPE) was investigated under Ar+ ion bombardment of magnesium aluminate spinel crystals of different compositions MgO.nAl2O3 (n=1.0; 2.5) and, for comparison Al-metal target. For all targets the only emission of metal excited particles was observed, which leads to lines of Al I, Al II, Al III, Mg I and Mg II spectra. It was revealed that quantum yield of the IPE of different lines were equal in the range of values 10-4-10-7 photon/ion and increases in 5-7 times of that originated from decay of atomic excited states with Eex<=4.83 eV for oxides to compare with metal. The main criteria, which determines the conservation of excitation in flying-off atoms or ions is relation between the band structure of target and energy level of corresponding exited state of emitting particles. Analysis of obtained data allows us to estimate the width of conduction band (?) in spinel: 0.995eV<=?<=1.16 eV. There was suggested the new approach for description of energy distribution of emission of knocked out excited particles. The best agreement of calculated data with experimental ones was obtained when the contribution of both the cascade collisions and surface recoil processes of primary ions in solids are included to generate flying-off excited particles.

Bobkov, V. V.; Gokov, S. P.; Gritsyna, V. V.; Gritsyna, V. T.; Shevchenko, D. I.

2004-06-01

289

Electronic energy band structure of the double perovskite Ba2MnWO6.  

PubMed

The electronic and magnetic structures of the double perovskite oxide Ba 2MnWO6 (BMW) were determined by employing the density functional theory within the generalized gradient approximation (GGA) + U approach. BMW is considered a prototype double perovskite due to its high degree of B-site ordering and is a good case study for making a comparison between computations and experiments. By adjusting the U-parameter, the electronic energy band structure and magnetic properties, which were consistent with the experimental results, were obtained. These computations revealed that the valence bands are mainly formed from Mn 3d and O 2p states, while the conduction bands are derived from W 5d and O 2p states. The localized bands composed from Mn 3d states are located in the bandgap. The results imply that the formation of polarons in the conduction band initiate the resonance Raman modes observed as a series of equidistant peaks. PMID:18465894

Fujioka, Yukari; Frantti, Johannes; Nieminen, Risto M

2008-05-09

290

Measurement of microwave backscattering signatures of the ocean surface using X band and Ka band airborne scatterometers  

Microsoft Academic Search

An airborne microwave scatterometer-radiometer system operated in X band and Ka band was applied to the observations of microwave backscattering signatures of the ocean. The normalized radar cross sections sigma0 were measured as combined functions of microwave frequency (10.00 GHz and 34.43 GHz), polarization (HH and VV), incident angle (0°-70°), azimuth angle (0°-360°), and wind speed (3.2-17.2 m\\/s). The azimuth

Harunobu Masuko; Ken'ichi Okamoto; Masanobu Shimada; Shuntaro Niwa

1986-01-01

291

Band structure of the superconducting MgB 2 compound and modeling of related ternary systems  

Microsoft Academic Search

Band structure of a novel superconductor—magnesium diboride—is studied by the self-consistent FP-LMTO method. Density of states\\u000a near the Fermi level of MgB2 and its electronic properties are governed by the metal-like boron 2p orbitals in the planar network of boron atoms. The modification of the band structure of MgB2 upon doping the boron (with Be, C, N, and O substitutional

N. I. Medvedeva; J. E. Medvedeva; A. L. Ivanovskii; V. G. Zubkov; A. J. Freeman

2001-01-01

292

Band Structure and Surface Effects in Cadmium Sulfide Photoemission Studies.  

National Technical Information Service (NTIS)

Photoemission measurements have been made on single crystals of cadmium sulfide which were cleaved and tested in high vacuum at photon energies between 7.2 and 11.6 eV. The electron affinity is found to be 4.8 eV. Additional measurements have been made in...

N. B. Kindig

1964-01-01

293

Brain Surface Conformal Parameterization Using Riemann Surface Structure  

PubMed Central

In medical imaging, parameterized 3-D surface models are useful for anatomical modeling and visualization, statistical comparisons of anatomy, and surface-based registration and signal processing. Here we introduce a parameterization method based on Riemann surface structure, which uses a special curvilinear net structure (conformal net) to partition the surface into a set of patches that can each be conformally mapped to a parallelogram. The resulting surface subdivision and the parameterizations of the components are intrinsic and stable (their solutions tend to be smooth functions and the boundary conditions of the Dirichlet problem can be enforced). Conformal parameterization also helps transform partial differential equations (PDEs) that may be defined on 3-D brain surface manifolds to modified PDEs on a two-dimensional parameter domain. Since the Jacobian matrix of a conformal parameterization is diagonal, the modified PDE on the parameter domain is readily solved. To illustrate our techniques, we computed parameterizations for several types of anatomical surfaces in 3-D magnetic resonance imaging scans of the brain, including the cerebral cortex, hippocampi, and lateral ventricles. For surfaces that are topologically homeomorphic to each other and have similar geometrical structures, we show that the parameterization results are consistent and the subdivided surfaces can be matched to each other. Finally, we present an automatic sulcal landmark location algorithm by solving PDEs on cortical surfaces. The landmark detection results are used as constraints for building conformal maps between surfaces that also match explicitly defined landmarks.

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

2011-01-01

294

Low-lying levels and high-spin band structures in 102Rh  

NASA Astrophysics Data System (ADS)

Levels in 102Rh have been populated in the reaction 70Zn+36S at 130 MeV. The level structure of 102Rh has been investigated using the EUROGAM II array. Low-lying states and four high-spin bands have been identified. The configurations of low-lying levels and two-quasiparticle bands are interpreted in the frame of the interacting boson-fermion-fermion model. The four observed band structures are also compared with cranked shell model calculations using a modified oscillator potential.

Gizon, J.; Gizon, A.; Timár, J.; C? Ta-Danil, Gh.; Nyakó, B. M.; Zolnai, L.; Boston, A. J.; Joss, D. T.; Paul, E. S.; Semple, A. T.; O'Brien, N. J.; Parry, C. M.; Bucurescu, D.; Brant, S.; Paar, V.

1999-10-01

295

Constraining the Origin and Structure of the Zodiacal Dust Bands with the MSX Celestial Backgrounds Data  

NASA Astrophysics Data System (ADS)

In recent years much work has been done to establish the provenance of the zodiacal dust bands, near-ecliptic enhancements in the brightness of the zodiacal cloud. The bands represent the debris of collisional activity in the asteroid belt, thought to be occuring within the major asteroid families of Eos, Themis and Koronis. However, recent numerical evidence for relatively fresh collisions in the Karin cluster and the Veritas family, which are located at orbital inclinations matching the observed dust band structures, have provided an alternate theory for the origin of the bands. Here we plan to take advantage of the unique nature of the MSX Celestial Backgrounds data, which in contrast to previous IRAS and COBE measurements include observations over a wide range of solar elongation angle (25 to 180 degrees). This MSX data set therefore represents a powerful resource to reconstruct the full three-dimensional structure of the dust bands, to quantify the size-frequency distribution of the dust band structures as a function of heliocentric distance, and to provide a more concrete genetic relationship between the dust bands and putative parent bodies. Previous work has also demonstrated that the zodiacal cloud is predominantly asteroidal in origin, therefore this investigation also has direct relevance to the nature and structure of asteroidal exozodiacal clouds, which needs to be understood to help ensure the success of future extrasolar planet finding missions such as Terrestrial Planet Finder.

Grogan, K.; Price, S. D.

2003-12-01

296

Surface vibrational structure at alkane liquid/vapor interfaces  

NASA Astrophysics Data System (ADS)

Broadband vibrational sum frequency spectroscopy (VSFS) has been used to examine the surface structure of alkane liquid/vapor interfaces. The alkanes range in length from n-nonane (C9H20) to n-heptadecane (C17H36), and all liquids except heptadecane are studied at temperatures well above their bulk (and surface) freezing temperatures. Intensities of vibrational bands in the CH stretching region acquired under different polarization conditions show systematic, chain length dependent changes. Data provide clear evidence of methyl group segregation at the liquid/vapor interface, but two different models of alkane chain structure can predict chain length dependent changes in band intensities. Each model leads to a different interpretation of the extent to which different chain segments contribute to the anisotropic interfacial region. One model postulates that changes in vibrational band intensities arise solely from a reduced surface coverage of methyl groups as alkane chain length increases. The additional methylene groups at the surface must be randomly distributed and make no net contribution to the observed VSF spectra. The second model considers a simple statistical distribution of methyl and methylene groups populating a three dimensional, interfacial lattice. This statistical picture implies that the VSF signal arises from a region extending several functional groups into the bulk liquid, and that the growing fraction of methylene groups in longer chain alkanes bears responsibility for the observed spectral changes. The data and resulting interpretations provide clear benchmarks for emerging theories of molecular structure and organization at liquid surfaces, especially for liquids lacking strong polar ordering.

Esenturk, Okan; Walker, Robert A.

2006-11-01

297

Structure and Functions of Fungal Cell Surfaces.  

National Technical Information Service (NTIS)

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 cytop...

Y. Nozawa

1984-01-01

298

Sorting of droplets by migration on structured surfaces  

PubMed Central

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.

Roth-Nebelsick, Anita

2011-01-01

299

The retrieval of land surface pressure from MERIS measurements in the oxygen A band  

NASA Astrophysics Data System (ADS)

Measurements of MERIS (Medium Resolution Imaging Spectrometer) on ENVISAT (Environmental Satellite) are used for the retrieval of surface pressure above land and ice surfaces. The algorithm is based on the exploitation of gaseous absorption in the oxygen A band at 762nm. The strength of absorption is directly related to the average photon path length, which in clear sky cases above bright surfaces is mainly determined by the surface pressure with minor influences from scattering at aerosols. Sensitivity studies regarding the influences of aerosol optical thickness and scale height and the temperature profile on the measured radiances are presented. Additionally, the sensitivity of the retrieval to the accuracy of the spectral characterization of MERIS is quantified. The algorithm for the retrieval of surface pressure (SPFUB) is presented and validated against surface pressure maps constructed from ECMWF sea level pressure data in combination with digital elevation models. The accuracy of SPFUB was found to be within 10hPa above ice surfaces at Greenland and 15hPa above desert and mountain scenes in Northern Africa and Southwest Asia. In a case study above Greenland the accuracy of SPFUB could be enhanced to be better than 3hPa ( 0.3%) by spatial averaging over areas of 40 km * 40 km. These results are of interest for the upcoming CO2/CH4 missions OCO and GOSAT, as an accurate determination of air mass using measurements in the oxygen A band is crucial to achieve the accuracy needed to quantify sources and sinks of CO2/CH4.

Lindstrot, R.; Preusker, R.; Fischer, J.

2009-04-01

300

Band Alignment of Atomic Layer Deposited HfO2 on Clean and N Passivated Germanium Surfaces  

SciTech Connect

Hard x-ray photoelectron spectroscopy has been used to study the band alignment between atomic layer deposited HfO{sub 2} on clean Ge (100) and nitrogen treated Ge (100) surfaces. The position of the valence-band maximum was determined by convolving theoretically calculated density of states from first-principles calculations and comparing with experimental valence-band data. Using Kraut's method, the valence-band offsets were found to be 3.2 {+-} 0.1 and 3.3 {+-} 0.1 eV for the samples grown on clean and N passivated Ge, respectively. The oxide charge measured from capacitance-voltage measurements shows a significant increase between the two samples; however, the small change in the band offset between the two systems strongly indicates negligible contribution of the interface to the conduction/valence-band barrier and the band alignment of the heterojunctions.

Rumaiz, A.K.; Woicik, J.C.; Carini, G.A.; Siddons, D.P.; Cockayne, E.; Huey, E.; Lysaght, P.S.; Fisher, D.A.; Genova, V.

2010-12-15

301

Band structures of phononic-crystal plates in the form of a sandwich-layered structure.  

PubMed

This study investigates the propagation of Lamb waves in phononic-crystal plates in the form of a sandwich-layered structure. The composite plates are composed of periodic layers bilaterally deposited on both sides of the homogeneous core layer. Using the analyses of the band structures and the transmission spectra, it is revealed that the core layer may induce significant modulations to the lower-order Lamb modes. The modulations are ascribed to the reshaped particle displacement fields of the eigenmodes. Prominently, the core layer made of soft material (rubber) combines the identical eigenmodes of the periodic layers into a pair of asymmetric and symmetric modes in which case the periodic layers vibrate independently. However, the core layer made of hard material (tungsten) or medium hardness material (silicon) couples the periodic layers tightly, in which case the composites vibrate as a whole. In addition, it is found that the phononic band gaps are very sensitive to the thickness of the core layer; this could be indispensable to practical applications such as bandgap tuning. PMID:22087902

Cheng, Y; Liu, X J; Wu, D J

2011-11-01

302

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

NASA Astrophysics Data System (ADS)

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

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

303

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

SciTech Connect

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

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

1988-01-01

304

Band structure, structural properties and stability of CaxMg1-xS alloys  

NASA Astrophysics Data System (ADS)

An ab initio pseudopotential approach based on the density functional theory within the generalized gradient approximation under the virtual crystal approximation is used in order to investigate the electronic band structure, structural properties and stability of the zinc-blende CaxMg1-xS mixed crystals. Our results and the published experimental and theoretical data for MgS and CaS were compared and they showed generally good agreement. This may provide further support for our data on the alloy CaxMg1-xS (0 < x < 1), where our results are predictions. The information derived from the present study may be useful for optical devices in the blue region.

Ghebouli, M. A.; Choutri, H.; Bouarissa, N.

2013-01-01

305

Electronic band structure and optical properties of silicon nanoporous pillar array  

NASA Astrophysics Data System (ADS)

Silicon nanoporous pillar array (Si-NPA) is fabricated by hydrothermally etching single crystal silicon (c-Si) wafers in hydrofluoric acid containing ferric nitrate. Microstructure studies disclosed that it is a typical micron/nanometer structural composite system with clear hierarchical structures. The optical parameters of Si-NPA were calculated by general light-absorption theory and Kramers-Kronig relations based on the experimental data of reflectance and the variations compared with the counterparts of c-Si were analyzed. The features of the electronic band structure deduced from the optical measurements strongly indicate that Si-NPA material is a direct-band-gap semiconductor and possesses separated conduction sub-bands which accords with conduction band splitting caused by silicon nanocrystallites several nanometers in size. All these electronic and optical results are due to the quantum confinement effect of the carriers in silicon nanocrystallites.

Xu, Hai Jun; Li, De Yao; Li, Xin Jian

2009-10-01

306

Atomic and electronic structures of novel silicon surface structures.  

National Technical Information Service (NTIS)

The modification of silicon surfaces is presently of great interest to the semiconductor device community. Three distinct areas are the subject of inquiry: first, modification of the silicon electronic structure; second, passivation of the silicon surface...

J. H. Terry

1997-01-01

307

Electronic structure of Pt based topological Heusler compounds with C1{sub b} structure and 'zero band gap'  

SciTech Connect

Besides of their well-known wide range of properties it was recently shown that many of the heavy Heusler semiconductors with 1:1:1 composition and C1{sub b} structure exhibit a zero band gap behavior and are topological insulators induced by their inverted band structure. In the present study, the electronic structure of the Heusler compounds PtYSb and PtLaBi was investigated by bulk sensitive hard x-ray photoelectron spectroscopy. The measured valence band spectra are clearly resolved and in well agreement to the first-principles calculations of the electronic structure of the compounds. The experimental results give clear evidence for the zero band gap state.

Ouardi, Siham; Shekhar, Chandra; Fecher, Gerhard H.; Kozina, Xeniya; Stryganyuk, Gregory; Felser, Claudia [Institut fuer Anorganische Chemie und Analytische Chemie, Johannes Gutenberg-Universitaet, D-55099 Mainz (Germany); Ueda, Shigenori; Kobayashi, Keisuke [NIMS Beamline Station at SPring-8, National Institute for Materials Science, Hyogo 679-5148 (Japan)

2011-05-23

308

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

NASA Astrophysics Data System (ADS)

In this study, investigations have been carried out on electron beam irradiated ultra high molecular weight polyethylene (UHMWPE). Polyethylene samples were irradiated with 1.5 MeV electron beam at doses ranging from 50 to 500 kGy. Modifications in optical properties and photoluminescence behavior of the polymer were evaluated by UV-vis and photoluminescence techniques. Changes of surface layer composition of UHMWPE produced by electron irradiations were studied by Rutherford back scattering spectrometry (RBS). The change in wettability and surface free energy induced by irradiations was also investigated. The optical absorption studies reveal that both optical band gap and Urbach's energy decreases with increasing electron dose. A correlation between energy gap and the number of carbon atoms in clusters is discussed. Photoluminescence spectra were reveal remarkable decrease in the integrated luminescence intensity with increasing irradiation dose. Contact angle measurements showed that wettability and surface free energy increases with increasing the irradiation dose.

Abdul-Kader, A. M.

2013-04-01

309

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

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

310

Shape dependence of band-edge exciton fine structure in CdSe nanocrystals.  

PubMed

The band-edge exciton fine structure of wurtzite CdSe nanocrystals is investigated by a plane-wave pseudopotential method that includes spin-orbit coupling, screened electron-hole Coulomb interactions, and exchange interactions. Large-scale, systematic simulations have been carried out on quantum dots, nanorods, nanowires, and nanodisks. The size and shape dependence of the exciton fine structure is explored over the whole diameter-length configuration space and is explained by the interplay of quantum confinement, intrinsic crystal-field splitting, and electron-hole exchange interactions. Our results show that the band-edge exciton fine structure of CdSe nanocrystals is determined by the origin of their valence-band single-particle wave functions. Nanocrystals where the valence-band maximum originates from the bulk A band have a "dark" ground-state exciton. Nanocrystals where the valence-band maximum is derived from the bulk B band have a "quasi-bright" ground-state exciton. Thus, the diameter-length configuration map can be divided into two regions, corresponding to dark and quasi-bright ground-state excitons. We find that the dark/quasi-bright ground-state exciton crossover is not only diameter-dependent but also length-dependent, and it is characterized by a curve in the two-parameter space of diameter and length. PMID:17900160

Zhao, Qingzhong; Graf, Peter A; Jones, Wesley B; Franceschetti, Alberto; Li, Jingbo; Wang, Lin-Wang; Kim, Kwiseon

2007-09-27

311

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

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

312

Electron microscopy and x-ray diffraction evidence for two Z-band structural states.  

PubMed

In vertebrate muscles, Z-bands connect adjacent sarcomeres, incorporate several cell signaling proteins, and may act as strain sensors. Previous electron microscopy (EM) showed Z-bands reversibly switch between a relaxed, "small-square" structure, and an active, "basketweave" structure, but the mechanism of this transition is unknown. Here, we found the ratio of small-square to basketweave in relaxed rabbit psoas muscle varied with temperature, osmotic pressure, or ionic strength, independent of activation. By EM, the A-band and both Z-band lattice spacings varied with temperature and pressure, not ionic strength; however, the basketweave spacing was consistently 10% larger than small-square. We next sought evidence for the two Z-band structures in unfixed muscles using x-ray diffraction, which indicated two Z-reflections whose intensity ratios and spacings correspond closely to the EM measurements for small-square and basketweave if the EM spacings are adjusted for 20% shrinkage due to EM processing. We conclude that the two Z-reflections arise from the small-square and basketweave forms of the Z-band as seen by EM. Regarding the mechanism of transition during activation, the effects of Ca(2+) in the presence of force inhibitors suggested that the interconversion of Z-band forms was correlated with tropomyosin movement on actin. PMID:21806939

Perz-Edwards, Robert J; Reedy, Michael K

2011-08-01

313

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

PubMed Central

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

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

2011-01-01

314

A compact band-stop\\/band-pass filter using a narrow gap capacitive as J-inverter and a new octagonal defected ground structure (DGS)  

Microsoft Academic Search

In this paper, we proposed a new compact DGS band-stop filter with broad passband and low insertion loss in the stop-band. The philosophy of the structure behind this new microstrip band-stop filter is simple as it is composed of a pair of octagonal DGS-slots and an open-stub as compensated microstrip capacitance. The filter will be realized through direct electromagnetic coupling

A. Boutejdar; A. Batmanov; A. Omar; E. Burte

2009-01-01

315

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

NASA Astrophysics Data System (ADS)

In scanning tunneling microscopy (STM) measurements on semiconductor surfaces, tip-induced band bending (TIBB) occurs due to the applied high bias voltage, and influences the local electronic structures of the surface detected by STM and scanning tunneling spectroscopy (STS). Recently, Yoshida et al. have reported the effect of the TIBB on local tunneling barrier height (LBH) on Si(100) surfaces by light-modulated STS [1]. However, theoretical studies on the TIBB and LBH have not been performed yet on semiconductor surfaces. In this study, we have analyzed the TIBB and LBH on an H-terminated Si(100) surface theoretically using the boundary-matching scattering-state density functional method [2], which can calculate the electron states under applied bias voltages self-consistently. In particular, we focus on the bias voltage dependences of the TIBB and LBH, and show that measured LBHs can be basically understood as the sum of TIBB and intrinsic barrier height. [1] S. Yoshida, et al., e-J. Surf. Sci. Nanotech. 4, 192 (2006). [2] Y. Gohda et al., Phys. Rev. Lett. 85, 1750 (2000). [3] M. McEllisterm, et al., Phys. Rev. Lett. 70, 2471 (1993).

Totsuka, Hideomi; Watanabe, Satoshi

2008-03-01

316

Fine-structure enhancement — assessment of a simple method to resolve overlapping bands in spectra  

NASA Astrophysics Data System (ADS)

A simple mathematical procedure — fine-structure enhancement — has been assessed on its ability to resolve overlapping bands in spectra. Its advantages and limitations have been explored using synthetic and experimental spectra. Fine-structure enhancement involves smoothing the original spectrum, multiplying the smoothed spectrum with a weighting factor and subtracting this spectrum from the original spectrum. As a result, the fine-structure of the original spectrum is enhanced in the processed spectrum and bands that overlap in the original spectrum appear as distinct bands in the processed spectrum. To be resolved by fine-structure enhancement, Lorentzian lines have to be separated by more than their quarter width at half maximum, Gaussian lines by more than their half width at half maximum. A comparison of fine-structure enhancement and Fourier self-deconvolution shows that Fourier self-deconvolution has in theory a higher potential to resolve overlapping bands. However, this depends crucially on the correct choice of the parameters. In practice, when parameters commonly used are chosen for Fourier self-deconvolution, fine-structure enhancement leads to similar results. This is demonstrated at the example of the infrared absorbance spectrum of the protein papain, where the amide I band components could be resolved similarly with both methods. Thus, fine-structure enhancement seems to be a simple alternative to Fourier self-deconvolution that does not require specialised software.

Barth, Andreas

2000-05-01

317

The C-Band accelerating structures for SPARC photoinjector energy upgrade  

NASA Astrophysics Data System (ADS)

The use of C-Band structures for electron acceleration and production of high quality beams has been proposed and adopted in several linac projects all over the world. The two main projects that adopted such type of structures are the Japanese Free Electron Laser (FEL) project in Spring-8 and the SwissFEL project at Paul Scherrer Institute (PSI). Also the energy upgrade of the SPARC photo-injector at LNF-INFN (Italy) from 150 to more than 240 MeV will be done by replacing a low gradient S-Band accelerating structure with two C-band structures. The structures are Traveling Wave (TW) and Constant Impedance (CI), have symmetric axial input couplers and have been optimized to work with a SLED RF input pulse. The paper presents the design criteria of the structures, the realization procedure and the low and high power RF test results on a prototype. The high power tests have been carried out by the Frascati INFN Laboratories in close collaboration with the Japanese Laboratory KEK. Experimental results confirmed the feasibility of the operation of the prototype at 50 MV/m with about 10?6 breakdowns per pulse per meter. Such high gradients have not been reached before in C-Band systems and demonstrated the possibility to use C-band accelerators, if needed, at such high field level. The results of the internal inspection of the structure after the high power test are also presented.

Alesini, D.; Boni, R.; Di Pirro, G.; Di Raddo, R.; Ferrario, M.; Gallo, A.; Lollo, V.; Marcellini, F.; Palumbo, L.; Spizzo, V.; Mostacci, A.; Campogiani, G.; Persichelli, S.; Enomoto, A.; Higo, T.; Kakihara, K.; Kamitani, T.; Matsumoto, S.; Sugimura, T.; Yokoyama, K.; Verdú-Andrés, S.

2013-05-01

318

Coherent structures over grooved surfaces  

NASA Astrophysics Data System (ADS)

The effectiveness of riblet surfaces on the coherent motions in the near wall turbulent boundary layer was investigated. The effectiveness of drag reducing flat riblet surfaces during adverse pressure gradient flows was then examined. Some problems which are relevant for applications, like the angle between the flow and the riblets, the partial covering of a flat plate by riblets, and a ship model covered with riblets, were studied.

Schwarz-Vanmanen, Adriana Dymphena

1992-01-01

319

Nonadiabatic dynamics near metal surfaces: Decoupling quantum equations of motion in the wide-band limit  

SciTech Connect

When an electron in a localized orbital approaches a continuum, resonant charge transfer can occur. For instance, when a beam of ions is scattered from a metal surface, neutralization can take place through the transfer of an electron either from ion to metal--in the case of a negative ion--or from metal to ion--in the case of a positive ion. Similarly, a neutral atom may be ionized by removing an electron from the metal surface. In this paper, we introduce the wide-band diabatic dynamics (WBDD) method for simulating the quantum dynamics of such systems by decoupling the equations of motion for the ionic and neutral diabats. We show numerically that our approximation accurately describes the quantum nuclear dynamics near the metal surface. Although we treat the case of ion neutralization, our method is general, and can be applied to any quantum state interacting with a continuum via a position-dependent interaction, provided that the wide-band approximation holds.

Shenvi, Neil [Department of Chemistry, Yale University, New Haven, Connecticut 06520 (United States); Cheng Hongzhi [Department of Physics, Yale University, New Haven, Connecticut 06520 (United States); Tully, John C. [Department of Chemistry, Yale University, New Haven, Connecticut 06520 (United States); Department of Physics, Yale University, New Haven, Connecticut 06520 (United States)

2006-12-15

320

Structure of the doublet bands in doubly odd nuclei: The case of Cs128  

NASA Astrophysics Data System (ADS)

The structure of the ?J=1 doublet bands in Cs128 is investigated within the framework of the interacting vector boson-fermion model. A new, purely collective interpretation of these bands is given on the basis of the used boson-fermion dynamical symmetry of the model. The energy levels of the doublet bands as well as the absolute B(E2) and B(M1) transition probabilities between the states of both yrast and yrare bands are described quite well. The observed odd-even staggering of both B(M1) and B(E2) values is reproduced by the introduction of an appropriate interaction term of quadrupole type, which produces such a staggering effect in the transition strengths. The calculations show that the appearance of doublet bands in certain odd-odd nuclei could be a consequence of the realization of a larger dynamical symmetry based on the noncompact supersymmetry group OSp(2?/12,R).

Ganev, H. G.; Brant, S.

2010-09-01

321

Electron crystallography in surface structure analysis.  

PubMed

Surface structure analysis is an important area of research, and in recent years notable advances have been made in this field, both in improved techniques for studying surfaces and in methods of analyzing them. This review aims to summarize the techniques available, particularly those relating to electron microscopy, and also to outline one of the newest areas of development, the application of direct methods to surface structure analysis. PMID:10420173

Leslie, C; Landree, E; Collazo-Davila, C; Bengu, E; Grozea, D; Marks, L D

1999-08-01

322

Optical bandgap and near surface band bending in degenerate InN films grown by molecular beam epitaxy  

NASA Astrophysics Data System (ADS)

We study the surface charge accumulation on InN thin films that strongly effects mobility of charge carriers. The films are formed by MBE in the temperature range (400-470 °C) yielding films with different morphology, crystallinity, and optical properties. The band-gap values determined by optical absorption and PL studies are found to depend on the Hall carrier concentration as per the Moss-Burstein relation. The magnitude of the near surface band bending is measured on InN thin films by knowing the surface and bulk Fermi level position with respect to the valence band maximum using X-ray photoelectron spectroscopy and optical absorption measurements, respectively. The studies show that the surface charge occurs due to the In adlayer on the film causing band-bending is up to 1 eV for low band gap single crystalline films and nearly a flat band for the highly degenerate polycrystalline films. The absence of the band bending is seen to occur when the bulk carrier concentration related to the crystalline quality of the InN films, tends to equate with the surface charge density.

Tangi, Malleswararao; Kuyyalil, Jithesh; Shivaprasad, S. M.

2013-10-01

323

Analysis of Mars surface hydration through the MEx\\/OMEGA observation of the 3 mum absorption band  

Microsoft Academic Search

The near infrared Mars surface global mapping done by OMEGA gives the first opportunity to study the global and detailed characteristics of the 3µm hydration absorption band on Mars surface. This feature is indistinctly due to bending and stretching vibrations of water bound in minerals or adsorbed at their surface, and of hydroxyl groups (for a review, see e.g. [1

D. Jouglet; F. Poulet; J. P. Bibring; Y. Langevin; B. Gondet; R. E. Milliken; J. F. Mustard

2006-01-01

324

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

SciTech Connect

A method is suggested for determining the wavelength of narrow-band light from a digital photograph of a radiating surface. The digital camera used should be appropriately calibrated. The accuracy of the wavelength measurement is better than 1 nm. The method was tested on the yellow doublet of mercury spectrum and on the adjacent continuum of the incandescent lamp radiation spectrum. By means of the method suggested the homogeneity of holographic sensor swelling was studied in stationary and transient cases. (laser applications and other topics in quantum electronics)

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

2010-09-10

325

The potential energy surface and the highly excited vibrational band origins of the water molecule  

NASA Astrophysics Data System (ADS)

The potential energy surface for the electronic ground state of the water molecule is optimized by means of a variational procedure using the exact vibrational Hamiltonian in the bond length-bond angle coordinates. In the optimization, Jensen's potential energy function (J. Mol. Spectry. 133 (1989) 438) is taken as the starting point andthe recently observed band origins below 22000 cm -1 given by Rothman and co-workers (J. Quantum Spectry. Radiative Transfer 48 (1992) 469) are involved. The standard deviation of this fitting for the 70 vibrational levels is 1.171 cm -1.

Xie, Daiqian; Yan, Guosen

1996-01-01

326

Protection of 6–7GHZ band spaceborne microwave radiometer from interferences to derive sea surface temperature and others  

Microsoft Academic Search

The 6-7GHz band spaceborne microwave radiometer is very important because ocean surface temperature can be observed through cloud with highest sensitivity. Ocean surface temperature is very important in the study of global warming and others. However, 6-7GHz band is not protected in the Radio Regulations (R.R) of ITU-R. In this paper, various interferences to a spaceborne microwave radiometer imagery are

Korehiro Maeda; Akira Shibata; Keiji Imaoka

2011-01-01

327

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

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

328

Electronic band structure of indium tin oxide and criteria for transparent conducting behavior  

NASA Astrophysics Data System (ADS)

Indium-based transparent conductors, notably indium tin oxide (ITO), have a wide range of applications due to a unique combination of visible light transparency and modest conductivity. A fundamental understanding of such an unusual combination of properties is strongly motivated by the great demand for materials with improved transparent conducting properties. Here we formulate conditions for transparent conducting behavior on the basis of the local density full-potential linear muffin-tin orbital electronic band structure calculations for Sn-doped In2O3 and available experimental data. We conclude that the position, dispersion, and character of the lowest conduction band are the key characteristics of the band structure responsible for its electro-optical properties. Further, we find that this lowest band is split with Sn doping due to the strong hybridization with dopant s-type states and this splitting contributes to both the decrease of the plasma frequency and the mobility of the carriers.

Mryasov, O. N.; Freeman, A. J.

2001-12-01

329

Prolate and oblate band structures in odd-odd 186,188Au  

Microsoft Academic Search

High-spin states have been populated in odd-odd 186,188Au via the heavy-ion 171,173Yb(19F,4n) reactions at 93-94 MeV. Rotational bands built on 11- oblate nui-113\\/2?pih-111\\/2 structures have been observed in both nuclei, similar to those reported in 190-194Au. Two new strongly coupled bands in 186Au are interpreted as prolate pih9\\/2?nui132 and pii13\\/2?nui13\\/2 configurations. Based on blocking arguments a band crossing in the

V. P. Janzen; Z.-M. Liu; M. P. Carpenter; L. H. Courtney; H.-Q. Jin; A. J. Larabee; L. L. Riedinger; J. K. Johansson; D. G. Popescu; J. C. Waddington; S. Monaro; S. Pilotte; F. Dönau

1992-01-01

330

Phononic band gaps of elastic periodic structures: A homogenization theory study  

NASA Astrophysics Data System (ADS)

In this study, we investigate the band structures of phononic crystals with particular emphasis on the effects of the mass density ratio and of the contrast of elastic constants. The phononic crystals consist of arrays of different media embedded in a rubber or epoxy. It is shown that the density ratio rather than the contrast of elastic constants is the dominant factor that opens up phononic band gaps. The physical background of this observation is explained by applying the theory of homogenization to investigate the group velocities of the low-frequency bands at the center of symmetry ? .

Liu, Ying-Hong; Chang, Chien C.; Chern, Ruey-Lin; Chang, C. Chung

2007-02-01

331

Band Structure Effects on the Scaling Properties of [111] InAs Nanowire MOSFETs  

Microsoft Academic Search

We have investigated the scaling properties of [111] InAs nanowire MOSFETs in the ballistic limit. The nanowire band structure has been calculated with an sp3d5 s* tight-binding model for nanowire diameters between 2 and 25 nm. Both the effective band gap and the effective masses increase with confinement. Using the atomistic dispersion relations, the ballistic currents and corresponding capacitances have

Erik Lind; Martin P. Persson; Yann-Michel Niquet; Lars-Erik Wernersson

2009-01-01

332

Energy transport model with full band structure for GaAs electronic devices  

Microsoft Academic Search

Electronic band structure is incorporated into a versatile energy transport model that treats heat flow between mobile electron\\u000a ensembles with the thermodynamic identity for ideal gases instead of an electron thermal conductivity. This alleviates the\\u000a closure issue common to thermal conductivity models and is amenable to different forms of charge gas transport. This flexibility\\u000a allows the model to accommodate band

Matt Grupen

333

Periodic and Non-Periodic Band Random Matrices: Structure of Eigenstates  

NASA Astrophysics Data System (ADS)

The structure of eigenstates for the ensembles of standard and periodic Band Random Matrices (BRM) is analysed. The main attention is drawn to the scaling properties of the inverse participation ratio and other measures of localization length. Numerical data are compared with analytical results recently derived for standard BRMs of very large band size. The data for periodic and standard BRM allow us to exhibit the influence of boundary conditions on the properties of eigenstates.

Izrailev, Felix M.; Molinari, Luca; ?yczkowski, Karol

1996-04-01

334

Band Structure, Spin Splitting, and SpinWave Effective Mass in Nickel  

Microsoft Academic Search

We have applied a modified form of the combined interpolation (tight-binding plus pseudopotential) method to the calculation of energy bands in ferromagnetic nickel. A procedure has been developed to enable calculation of the reciprocal spin-wave effective mass in a multiband system in the t-matrix approximation. This has been used in conjunction with the calculated band structure. Matrix elements of the

Joseph Callaway; H. M. Zhang

1970-01-01

335

Valence band structure of cubic AlGaN\\/GaN superlattices  

Microsoft Academic Search

The influence of different material parameters, spin-orbit interaction, and strain effects on the valence band structure of cubic AlGaN\\/GaN superlattices is investigated. One-particle hole state calculations are carried out within the k.p theory by means of a full six-band Luttinger-Kohn Hamiltonian in a plane-wave representation. It is shown that the use of distinct values for the Luttinger parameters for the

S. C. P. Rodrigues; L. M. R. Scolfaro; J. R. Leite; G. M. Sipahi

2000-01-01

336

Valence band structure of cubic AlGaN\\/GaN superlattices  

Microsoft Academic Search

The influence of different material parameters, spin-orbit interaction, and strain effects on the valence band structure of cubic AlGaN\\/GaN superlattices is investigated. One-particle hole state calculations are carried out within the k?p theory by means of a full six-band Luttinger-Kohn Hamiltonian in a plane-wave representation. It is shown that the use of distinct values for the Luttinger parameters for the

S. C. P. Rodrigues; L. M. R. Scolfaro; J. R. Leite; G. M. Sipahi

2000-01-01

337

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

SciTech Connect

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

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

2010-04-15

338

Semiconductor quantum structures for ultraviolet-to-infrared multi-band radiation detection  

Microsoft Academic Search

In this work, multi-band (multi-color) detector structures considering different semiconductor device concepts and architectures are presented. Results on detectors operating in ultraviolet-to-infrared regions (UV-to-IR) are discussed. Multi-band detectors are based on quantum dot (QD) structures; which include quantum-dots-in-a-well (DWELL), tunneling quantum dot infrared photodetectors (T-QDIPs), and bi-layer quantum dot infrared photodetectors (Bi-QDIPs); and homo-\\/heterojunction interfacial workfunction internal photoemission (HIWIP\\/HEIWIP) structures.

Gamini Ariyawansa

2007-01-01

339

[Oligoglycine surface structures: molecular dynamics simulation].  

PubMed

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

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

340

Local surface structure effect on reactivity of molecules confined between metallic surfaces.  

PubMed

Interactions between metallic surfaces separated by nanometer distances create an unusual reactivity environment. Here we evaluate the effect of the geometry given by differences in the structures of the interacting surfaces and by the presence of steps. Adsorption of an oxygen molecule and its dissociation is examined in gaps defined by interacting platinum surfaces that have separations between 5.36 and 4.70 Å, and by comparing the effect of the different gap geometries on the adsorption strength and barriers for dissociation. It is found that specific surface-surface configurations influence the electronic structure of the surface where the molecule is adsorbed, modifying the width of its d-orbital and therefore the adsorption strength due to changes in the overlap of the adsorbate molecular orbitals with the metal d-band. In addition, the degree of the molecule-metal interaction with the other surface may restrict the adsorbate mobility and its dissociation. The presence of defects may decrease the adsorbate-surface interaction strength, but the net result depends on the specific reaction and nature of the intermediates since in some cases weaker adsorptions may result in lower dissociation barriers. PMID:23247727

Martínez de la Hoz, Julibeth M; Balbuena, Perla B

2013-02-01

341

The electronic structures of vanadate salts: Cation substitution as a tool for band gap manipulation  

NASA Astrophysics Data System (ADS)

The electronic structures of six ternary metal oxides containing isolated vanadate ions, Ba3(VO4)2, Pb3(VO4)2, YVO4, BiVO4, CeVO4 and Ag3VO4 were studied using diffuse reflectance spectroscopy and electronic structure calculations. While the electronic structure near the Fermi level originates largely from the molecular orbitals of the vanadate ion, both experiment and theory show that the cation can strongly influence these electronic states. The observation that Ba3(VO4)2 and YVO4 have similar band gaps, both 3.8 eV, shows that cations with a noble gas configuration have little impact on the electronic structure. Band structure calculations support this hypothesis. In Pb3(VO4)2 and BiVO4 the band gap is reduced by 0.9-1.0 eV through interactions of (a) the filled cation 6s orbitals with nonbonding O 2p states at the top of the valence band, and (b) overlap of empty 6p orbitals with antibonding V 3d-O 2p states at the bottom of the conduction band. In Ag3VO4 mixing between filled Ag 4d and O 2p states destabilizes states at the top of the valence band leading to a large decrease in the band gap (Eg=2.2 eV). In CeVO4 excitations from partially filled 4f orbitals into the conduction band lower the effective band gap to 1.8 eV. In the Ce1-xBixVO4 (0?x?0.5) and Ce1-xYxVO4 (x=0.1, 0.2) solid solutions the band gap narrows slightly when Bi3+ or Y3+ are introduced. The nonlinear response of the band gap to changes in composition is a result of the localized nature of the Ce 4f orbitals.

Dolgos, Michelle R.; Paraskos, Alexandra M.; Stoltzfus, Matthew W.; Yarnell, Samantha C.; Woodward, Patrick M.

2009-07-01

342

Configuration-dependent band structures in odd-odd 180Ir  

NASA Astrophysics Data System (ADS)

High-spin states in 180Ir have been investigated by means of in-beam ?-ray spectroscopy techniques with the 154Sm(31P,5n?)180Ir reaction. Excitation functions, x-? and ?-?-t coincidences, DCO (directional correlation of ? rays deexciting oriented states) ratios, and intraband B(M1)/B(E2) ratios were measured. Five rotational bands have been identified and their configurations are proposed on the basis of B(M1)/B(E2) ratios and by comparing the band properties with known bands in neighboring odd-mass and even-mass nuclei. The neutron AB crossing is observed at ??c=0.26(1) MeV for the ?1/2-[541]??1/2-[521] and ?1/2-[541]??5/2-[512] bands, respectively. Staggering of levels as a function of the number of neutron pairs is revealed in the ?1/2-[541]??1/2-[521] doubly decoupled bands of 178-186Ir. The gradual alignment gains at low rotational frequencies are observed in the two strongly coupled bands. Band crossings and alignments in 180Ir are discussed with reference to the total Routhian surface and cranked shell model calculations performed for the neighboring odd-mass nuclei.

Zhang, Y. H.; Hayakawa, T.; Oshima, M.; Katakura, J.; Hatsukawa, Y.; Matsuda, M.; Kusakari, H.; Sugawara, M.; Komatsubara, T.; Furuno, K.

2002-01-01

343

N arrow bands and electronic structure in unconventional high-TC  

Microsoft Academic Search

Electronic structure details play a marginal role in the superconductive properties of conventional superconductors. Electronic energies are by far the most important in these materials and the only relevant electronic parameter, with respect to superconductivity, is essentially the density of states N(0). Cooper oxides and fullerene compounds are characterized by narrow band dispersions and by electronic structures of hundreds meV.

E. Cappelluti; C. Grimaldi; L. Pietronero; S. Strassler

344

A new structure for narrow transition band, lowpass digital filter design  

Microsoft Academic Search

In this paper, a new class of lowpass linear phase FIR filters is introduced. It is shown that lowpass filters with narrow transition bands can be realized efficiently by a structured form composed mainly of a few small FIR filters. The modular structure is suited for an implementation by a fast short convolution algorithm or a few single-chip filter IC's.

Zhongqi Jing; Adly Fam

1984-01-01

345

International X-Band Linear Collider Accelerator Structure R&D  

SciTech Connect

For more than fifteen years before the International Technology Recommendation Panel (ITRP) decision in August, 2004, there were intensive R&D activities and broad international collaboration among the groups at SLAC, KEK, FNAL, LLNL and other labs for the room temperature X-Band accelerator structures. The goal was to provide an optimized design of the main linac structure for the NLC (Next Linear Collider) or GLC (Global Linear Collider). There have been two major challenges in developing X-band accelerator structures for the linear colliders. The first is to demonstrate stable, long-term operation at the high gradient (65 MV/m) that is required to optimize the machine cost. The second is to strongly suppress the beam induced long-range wakefields, which is required to achieve high luminosity. More than thirty X-band accelerator structures with various RF parameters, cavity shapes and coupler types have been fabricated and tested since 1989. A summary of the main achievements and experiences are presented in this talk including the structure design, manufacturing techniques, high power performance, and other structure related issues. Also, the new progress in collaborating with the CLIC, high gradient structures and X-Band structure applications for RF deflectors and others are briefly introduced.

Wang, J.W.; /SLAC

2009-03-04

346

Phononic band gaps and vibrations in one- and two-dimensional mass–spring structures  

Microsoft Academic Search

The vibrational response of finite periodic lattice structures subjected to periodic loading is investigated. Special attention is devoted to the response in frequency ranges with gaps in the band structure for the corresponding infinite periodic lattice. The effects of boundaries, viscous damping, and imperfections are studied by analyzing two examples; a 1-D filter and a 2-D wave guide. In 1-D

J. S. Jensen

2003-01-01

347

Evolution of the higher order band structure in self-assembled photonic crystals  

NASA Astrophysics Data System (ADS)

The existence of the complete photonic band gap (PBG) in self-assembled photonic crystals (inverted opals) remains questionable due to disorder present in real-world crystals. Various defects present in these structures can give rise to significant inhomogeneous broadening of the stop-bands and eventually eliminate the PBG. Here we present quantitative measurements of the higher order photonic band structure in a series of inverted opals with progressively higher refractive index contrast. In order to decrease the concentration of defects, we have used thin, planar opal templates to form inverted opals from various high index materials. To decrease further the influence of remaining defects on the optical response we utilize sub-domain spectroscopy, a technique that optically probes only a few unit cells. Reflection and transmission data reveal a number of spectral features in the region of the higher order photonic bands, where the complete band gap should emerge. Comparison of experimental spectra with rigorous calculations allows all spectral features to be assigned to distinct points in the photonic Brillouin zone. Using this approach the evolution of the photonic band structure towards the opening of the complete PBG can be explored. http://www.neci.nj.nec.com/homepages/vlasov/photonic.html

Vlasov, Yurii; Norris, David

2001-03-01

348

A theoretical study of band structure properties for III-V nitrides quantum wells  

NASA Astrophysics Data System (ADS)

Reliable and precise knowledge about the strain and composition effects on the band structure properties is crucial for the optimization of InGaN based heterostructures for electronic and optoelectronic device applications. AlInGaN as quaternary barrier material permits to control the band gap and the lattice constant independently. Using the model solid theory and the multi-band k.p interaction model, we investigate the composition effects on band offsets and band structure for pseudomorphic Ga1-xInxN/AlzInyGa1-y-zN (0 0 1) heterointerfaces having zinc-blende structure. The results show that both conduction and valence band states are strongly modified while varying In and Al contents in the well and barrier materials. Furthermore, it is found that using AlInGaN as the barrier material allows the design of heterostructures including InGaN wells with tensile, zero or compressive strain. Such results give new insights for III-nitride compounds based applications and especially may guide the design of white-light emission diodes.

Ben Rejeb, S.; Bhouri, A.; Debbichi, M.; Lazzari, J.-L.; Said, M.

2011-10-01

349

Large band gaps in two-dimensional phononic crystals with neck structures  

NASA Astrophysics Data System (ADS)

In this paper, we study the band gap properties of a two-dimensional phononic crystal composed of periodic cylinders embedded in a homogenous matrix. The cylinders are not connected with the matrix directly but linked with it through the neck structures constituted by part of a circle. The dispersion relations, transmission spectra, and displacement fields of the eigenmodes of this phononic crystal are studied using the finite-element method. In contrast to the typical phononic crystals where the cylinders and matrix are in contact completely, the proposed structures with necks display larger band gaps at lower frequencies. The reason for the occurrence of the low-frequency band gaps as well as the effects of the geometrical parameters of the neck structures on the gaps are further explored numerically. Results show that the openings of the band gaps are attributed to the resonance of the cylinders and the interaction between the cylinders and the matrix, resulting from the introduction of the necks. The band gaps are significantly dependent upon the geometrical parameters such as the rotation angle of the necks which is defined as the angle between the centerline of the neck and the x-axis, the arc length of the necks, and also the filling ratio of the inclusions. The study in this paper is relevant to the design of tuning band gaps and isolators in the low-frequency range.

Yu, Kunpeng; Chen, Tianning; Wang, Xiaopeng

2013-04-01

350

Solar spectral fine structure in 18 - 23 GHz band.  

NASA Astrophysics Data System (ADS)

On 30th June 1989 high sensitivity-spectral resolution observations of solar radio bursts were carried out in the frequency range of 18 - 23 GHz. The burst observed at 17:46 UT was different from the 60 bursts observed so far in the sense that it exhibited a frequency fine structure superimposed on the ongoing burst in its rising phase, i.e. an additional enhancement of the flux density of the order of 10 SFU, observed only in the 21 and 22 GHz frequency channels, lasting for about 4 s. Interaction of an emerging loop with an adjacent loop accelerated particles in that loop from which the broadband burst was emitted due to the gyrosynchrotron emission. The observed fine structure is interpreted as due to thermal gyro-emission at the 6th harmonic of the gyrofrequency originated from a hot kernel with short lifetime located at the top of emerging loop.

Cecatto, J. R.; Subramanian, K. R.; Sawant, H. S.

1999-09-01

351

Full-potential band-structure calculation of iron pyrite  

Microsoft Academic Search

Transition metal disulfides of pyrite structure have recently attracted much interest again due to their large variety of electronic, magnetic, and optical properties. The semiconductor iron pyrite (FeS2) shows, for instance, an unusual blueshift of the optical gap under pressure. We present a full-potential total energy calculation of iron pyrite using density functional theory with a nonorthogonal local orbital minimum

I. Opahle; K. Koepernik; H. Eschrig

1999-01-01

352

Band model for the electronic structure of expanded liquid cesium  

Microsoft Academic Search

Self-consistent, scalar-relativistic, linear-augmented-plane-wave calculations have been carried out for four (real and hypothetical) crystalline forms of cesium with the body-centered-cubic, simple-cubic, simple-tetragonal, and diamond structures at a fixed nearest-neighbor bond distance. The results of these calculations are applied to model the variation with density of several one-electron properties of expanded liquid cesium, including the total density of states N(EF), its

W. W. Warren Jr.; L. F. Mattheiss

1984-01-01

353

Spins, Parity, Excitation Energies, and Octupole Structure of an Excited Superdeformed Band in 194Hg and Implications for Identical Bands  

Microsoft Academic Search

An excited superdeformed band in 194Hg, observed to decay directly to both normal-deformed and superdeformed yrast states, is proposed to be a Kpi = 2- octupole vibrational band, based on its excitation energies, spins, and likely parity. The transition energies are identical to those of the yrast superdeformed band in 192Hg, but originate from levels with different spins and parities.

G. Hackman; T. L. Khoo; M. P. Carpenter; T. Lauritsen; A. Lopez-Martens; I. J. Calderin; R. V. Janssens; D. Ackermann; I. Ahmad; S. Agarwala; D. J. Blumenthal; S. M. Fischer; D. Nisius; P. Reiter; J. Young; H. Amro; E. F. Moore; F. Hannachi; A. Korichi; I. Y. Lee; A. O. Macchiavelli; T. Døssing; T. Nakatsukasa

1997-01-01

354

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

NASA Astrophysics Data System (ADS)

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

Nghiem, S. V.

2005-12-01

355

Photonic band structure effects in doped FCC and BCC colloidal crystals  

NASA Astrophysics Data System (ADS)

Photonic band gap crystals are novel periodic dielectric materials, which influence the behavior of photons in much the same manner as crystalline solids affect the behavior of electrons. These materials possess forbidden frequency bands, which overlap for all light propagation directions and polarization resulting in a complete photonic band gap. Several 3-D structures have been numerically shown to possess a complete 3-D photonic band gap. Many of these structures have been realized at microwave wavelength scales. However scaling these structures to yield a complete 3-D photonic band gap at optical wavelengths has yet to be achieved. Self- organizing systems may provide a possible way of producing optical photonic crystals. Our optical photonic crystals consist of uniformly sized charged polystyrene microspheres held apart and in an ordered array owing to their mutual electrostatic interaction. Bragg diffraction of near-IR light produces optical stop bands that are several orders of magnitude deep. Doping these crystals by introducing a few microspheres of a different diameter or a different refractive index constitute defects, which are manifested by the appearance of impurity modes and optical stop band widening. Numerical Transfer Matrix Method computations were used to aid the interpretation of our data. A 1-D periodic system of microwave frequency coaxial cable connectors was constructed to replicate some of these effects. This dissertation also presents a systematic study of the bcc phase of these colloidal crystals, which highlights the role of higher order Brillouin zones in producing deep and wide optical stop bands in this low volume fraction phase.

Pradhan, Ranjit Dinkar

356

Negative Parity Band Structures in ^113,115,117Pd from Fission Studies  

NASA Astrophysics Data System (ADS)

Studies of SF of ^252Cf have yielded band information for odd-A neutron-rich Pd isotopes. These bands were thought to feed negative parity isomeric states above the positive parity ground states. We observe a very similar energy series of transitions in ^113,115,117Pd that appear to be negative parity side bands. However, unexpectedly low energy transitions (85.1, 49.0, 63.7 keV respectively) are found at the bottom of each of these bands. These are previously unreported transitions that are now observable with a lower energy cutoff in our newest fission data. The identification of these bands is difficult because to the isomeric transitions inhibit prompt coincidence studies to the ground band. Examination of systematics indicates they may be 9/2^- or 11/2^- bands. However, the low energy nature of the lowest transition is somewhat unexpected and difficult to explain. We will discuss the possible level structures and the physical consequences.

Fong, D.; Hwang, J. K.; Ramayya, A. V.; Hamilton, J. H.; Beyer, C. J.; Gore, P. M.; Jones, E. F.; Luo, Y. X.; Zhu, S. J.; Rasmussen, J. O.; Wu, S. C.; Lee, I. Y.; Fallon, P.; Ginter, T. N.; Stoyer, M. A.; Asztalos, S. J.; Cole, J. D.; Ter-Akopian, G. M.; Daniel, A.; Donangelo, R.; Walters, W.

2004-11-01

357

Band structure of magnetic excitations in the vortex phase of a ferromagnetic superconductor  

NASA Astrophysics Data System (ADS)

Magnetic excitations in a ferromagnetic superconductor in the presence of an Abrikosov vortex lattice have been studied using the phenomenological London and Landau-Lifshitz equations. Due to the periodicity of the vortex field the magnon spectrum has a band structure, similar to the structure of the electon spectrum in a crystal lattice. The gaps between adjacent bands have been calculated using an analog of the weak-binding approximation. When the applied magnetic field is altered the band structure undergoes a qualitative transformation due to commensurability effects, connected with the nonmonotonicity of the magnon spectrum in the Meissner state. In dirty samples the energy gaps may be smeared out because of the dissipation connected with vortex motion. In sufficiently clean samples the gaps manifest themselves as maxima in the frequency dependence of the microwave reflectivity coefficient.

Bespalov, A. A.; Buzdin, A. I.

2013-03-01

358

Photonic band structures of 1-D plasma photonic crystal with time-variation plasma density  

NASA Astrophysics Data System (ADS)

The photonic band structures of one-dimensional plasma photonic crystal (1-D PPC) with time-variation plasma density are studied by using differential transfer matrix method. Taking an exponential functional form of time as an illustration of the time-varying plasma density, we examine the photonic band structures of the 1-D PPC. The results show that the photonic band structures can be tuned correspondingly by changing the time which modifies the plasma dielectric constant in different frequency regions, especially in the range of 0

Guo, B.; Xie, M. Q.; Qiu, X. M.; Peng, L.

2012-04-01

359

Glucose Transport Protein is Structurally and Immunologically Related to Band 3 and Senescent Cell Antigen  

Microsoft Academic Search

Senescent cell antigen, a polypeptide that appears on the surface of senescent and damaged cells, has been shown to be derived from band 3. In the present study, the relationship between the as yet unidentified glucose transporter and senescent cell antigen is examined. Since cytochalasin B is a specific and potent competitive inhibitor of glucose transport in human erythrocytes, the

Marguerite M. B. Kay

1985-01-01

360

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

SciTech Connect

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.

Peterman, D.J.

1980-01-01

361

Band structure tunability in MoS2 under interlayer compression: A DFT and GW study  

NASA Astrophysics Data System (ADS)

The electronic band structures of MoS2 monolayer and 2H1 bulk polytype are studied within density-functional theory (DFT) and many-body perturbation theory (GW approximation). Interlayer van der Waals (vdW) interactions, responsible for bulk binding, are calculated with the postprocessing Wannier functions method. From both fat bands and Wannier functions analysis, it is shown that the transition from a direct band gap in the monolayer to an indirect band gap in bilayer or bulk systems is triggered by medium- to short-range electronic interactions between adjacent layers, which arise at the equilibrium interlayer distance determined by the balance between vdW attraction and exchange repulsion. The semiconductor-to-semimetal (S-SM) transition is found from both theoretical methods: around c=10.7 Å and c=9.9 Å for DFT and GW, respectively. A metallic transition is also observed for the interlayer distance c=9.7 Å. Dirac conelike band structures and linear bands near Fermi level are found for shorter c lattice parameter values. The VdW correction to total energy was used to estimate the pressure at which S-SM transition takes place from a fitting to a model equation of state.

Espejo, C.; Rangel, T.; Romero, A. H.; Gonze, X.; Rignanese, G.-M.

2013-06-01

362

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

NASA Astrophysics Data System (ADS)

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

Frisch, J.; Nelson, J.; Le Pimpec, F.; Jobe, K.; McCormick, D.

2002-08-01

363

Unravelling the interplay of crystal structure and electronic band structure of tantalum oxide (Ta2O5).  

PubMed

The band structure and bandgap of Ta(2)O(5) are extremely controversial issues. Herein, the use of a hybrid functional reduces the error in bandgap estimation from 95% to 5% resulting in a bandgap of 3.7 eV. This is expected to help controlling the electronic and structural properties of the material. PMID:23243661

Nashed, Ramy; Hassan, Walid M I; Ismail, Yehea; Allam, Nageh K

2013-02-01

364

Effects of strain on band structure and effective masses in MoS2  

NASA Astrophysics Data System (ADS)

Molybdenum disulfide (MoS2) is a layered semiconductor that shows great promise for devices such as field-effect transistors. It has an important advantage compared to graphene, namely that it has a band gap. However, a lot of crucial information about the band structure and electronic properties of this material is still lacking, hampering interpretation of experiments and preventing accurate device modeling. Here we use hybrid density functional theory to calculate key materials parameters such as band gaps and effective masses, as well as to investigate effects of strain. We show how strain allows engineering the nature (direct vs. indirect) and size of the band gap and the magnitude of effective masses. In addition, insight into the fundamental physics is provided by considering the transition between the bulk and the monolayer as a function of tensile uniaxial stress.

Peelaers, Hartwin; van de Walle, Chris G.

2013-03-01

365

Photonic band structures of two-dimensional magnetized plasma photonic crystals  

SciTech Connect

By using modified plane wave method, photonic band structures of the transverse electric polarization for two types of two-dimensional magnetized plasma photonic crystals are obtained, and influences of the external magnetic field, plasma density, and dielectric materials on the dispersion curves are studied, respectively. Results show that two areas of flat bands appear in the dispersion curves due to the role of external magnetic field, and the higher frequencies of the up and down flat bands are corresponding to the right-circled and left-circled cutoff frequencies, respectively. Adjusting external magnetic field and plasma density can not only control positions of the flat bands, but also can control the location and width of the local gap; increasing relative dielectric constant of the dielectric materials makes omni-direction gaps appear.

Qi, L. [College of Physics and Engineering, Qufu Normal University, No. 57, West Jingxuan Road, Qufu 273165 (China)

2012-04-01

366

Electronic Structure and Catalysis on Metal Surfaces  

Microsoft Academic Search

The powerful computational resources available to scientists today, together with recent improvements in electronic structure calculation algorithms, are providing important new tools for researchers in the fields of surface science and catalysis. In this review, we discuss first principles calculations that are now capable of providing qualitative and, in many cases, quantitative insights into surface chemistry. The calculations can aid

Jeff Greeley; Jens K. Norskov; Manos Mavrikakis

2002-01-01

367

Structural evolution of cometary surfaces  

NASA Astrophysics Data System (ADS)

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

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

1991-04-01

368

Pseudo-atomic-orbital band theory applied to electron-energy-loss near-edge structures  

Microsoft Academic Search

The near-edge structure in inner-shell spectroscopy is a product of the slowly varying matrix element and the appropriate projected density of states. We have made use of the self-consistent pseudo-atomic-orbital band-structure-calculation method to produce accurate projected density of states. Our calculation is in good agreement with the K near-edge structure of diamond, silicon, cubic SiC, and Be2C, and the L

Xudong Weng; Peter Rez; O. F. Sankey

1989-01-01

369

High-spin structures in 108Pd: ?-vibrational band and two-quasineutron excitations  

NASA Astrophysics Data System (ADS)

The high-spin structures of the 108Pd nucleus have been studied with the 100Mo(11B,p2n?) reaction at 43 MeV incident energy. ?-?-t,?-?-charged-particle coincidences and directional correlation ratios were measured using the SACI-PERERE ? spectrometer formed by four Compton suppressed HPGe detectors and a 4? charged-particle ancillary detector system. Recent results for the ?-vibrational band and the ?h11/2??(g7/2,d5/2) negative parity structures have been confirmed and complemented. A new band tentatively based on the second lowest (?h11/2) excitation has been observed.

Alcántara-Núñez, J. A.; Oliveira, J. R.; Cybulska, E. W.; Medina, N. H.; Rao, M. N.; Ribas, R. V.; Rizzutto, M. A.; Seale, W. A.; Falla-Sotelo, F.; Wiedemann, K. T.

2005-05-01

370

Electrode band structure effects in thin MgO magnetic tunnel junctions  

NASA Astrophysics Data System (ADS)

In this study, we demonstrate that, beyond the standard magnon excitations, the electronic band structure of the electrodes plays a significant role on the low bias voltage window (0 < |V| < 0.4 V) of the tunnel magnetoresistance (TMR) in thin MgO-CoFeB junctions. The tunneling conductance in the parallel state presents a minimum at about +/-0.35 and +/-0.3 V for the negative and positive bias, respectively. The presence of this minimum indicates a related decrease in the TMR(V). These observations are explained by the electronic band structures of bcc-Fe and Co.

Teixeira, J. M.; Ventura, J.; Fernández-García, M. P.; Araujo, J. P.; Sousa, J. B.; Wisniowski, P.; Freitas, P. P.

2012-02-01

371

Observation of Optical Interferometric Band Structure Representing Plastic Deformation Front under Cyclic Loading  

NASA Astrophysics Data System (ADS)

An interferometric band structure previously observed under monotonic tensile loading has been observed under cyclic loading as well. Like the previous monotonic loading case, the band structure is found to represent the plastic deformation front, indicating that it can be used for visualization of stress concentration. Observed correlation between the motions of the plastic deformation front and the test machine’s crosshead indicates that the plastic deformation front moves in proportion to the strength of the displacement field induced by the test machine. This is consistent with a previous report that the propagation speed of the plastic deformation front varies in proportion to the monotonic loading speed.

Yoshida, Sanichiro; Ishii, Hideyuki; Ichinose, Kensuke; Gomi, Kenji; Taniuchi, Kiyoshi

2004-08-01

372

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

SciTech Connect

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

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

2005-05-15

373

Evidence of reduced surface electron-phonon scattering in the conduction band of Bi2Se3 by nonequilibrium ARPES  

NASA Astrophysics Data System (ADS)

The nature of the Dirac quasiparticles in topological insulators calls for a direct investigation of the electron-phonon scattering at the surface. By comparing time-resolved ARPES measurements of the topological insulator Bi2Se3 with different probing depths, we show that the relaxation dynamics of the electronic temperature of the conduction band is much slower at the surface than in the bulk. This observation suggests that surface phonons are less effective in cooling the electron gas in the conduction band.

Crepaldi, A.; Cilento, F.; Ressel, B.; Cacho, C.; Johannsen, J. C.; Zacchigna, M.; Berger, H.; Bugnon, Ph.; Grazioli, C.; Turcu, I. C. E.; Springate, E.; Kern, K.; Grioni, M.; Parmigiani, F.

2013-09-01

374

Photodissociation of ozone in the Hartley band: Potential energy surfaces, nonadiabatic couplings, and singlet/triplet branching ratio  

NASA Astrophysics Data System (ADS)

The lowest five 1A' states of ozone, involved in the photodissociation with UV light, are analyzed on the basis of multireference configuration interaction electronic structure calculations with emphasis on the various avoided crossings in different regions of coordinate space. Global diabatic potential energy surfaces are constructed for the lowest four states termed X, A, B, and R. In addition, the off-diagonal potentials that couple the initially excited state B with states R and A are constructed to reflect results from additional electronic structure calculations, including the calculation of nonadiabatic coupling matrix elements. The A/X and A/R couplings are also considered, although in a less ambitious manner. The photodissociation dynamics are studied by means of trajectory surface hopping (TSH) calculations with the branching ratio between the singlet, O(1D)+O2(1?g), and triplet, O(3P)+O2(3?g-), channels being the main focus. The semiclassical branching ratio agrees well with quantum mechanical results except for wavelengths close to the threshold of the singlet channel. The calculated O(1D) quantum yield is approximately 0.90-0.95 across the main part of the Hartley band, in good agreement with experimental data. TSH calculations including all four states show that transitions B-->A are relatively unimportant and subsequent transitions A-->X/R to the triplet channel are negligible.

Schinke, R.; McBane, G. C.

2010-01-01

375

Correlation Between Absorption Cross Section and Body Surface Area of Human for Far-Field Exposure at GHz Bands  

Microsoft Academic Search

Our previous study revealed that a dominant factor influencing the electromagnetic absorption in a human body for far field exposure at GHz bands is the body surface area. Based on this finding, we discussed the correlation between absorption cross section and body surface area of human for far-field exposure at 2 GHz. We employed an FDTD algorithm for a large-scale

Akimasa Hirata; Yoshio Nagaya; Fujiwara Osamu; A. T. Nagaoka; Soichi Watanabe

2007-01-01

376

CsSnX3 (X= Cl, Br, I) band structure calculations by the QSGW method  

NASA Astrophysics Data System (ADS)

CsSnX3 (X=Cl,Br,I) perovskite compounds are of interest because of their strong photoluminescence and their potential application to solar cells. We present quasiparticle self-consistent GW (QSGW) calculations for the cubic (?-phase) including spin-orbit coupling and study the changes in band structures from the ?-phase to the ?- and ?-phases in LDA. The QSGW gaps are in good agreement with experiment. An analysis of the orbital character of the bands shows that they have an ``inverted'' band structure: the VBM has a non-degenerate s-like character (Sn-s and X-p antibonding), while the (CBM) has Sn-p character. The strongly intra-atomic dipole allowed nature of the direct gap explains the high photoluminescent intensity. The low hole mass indicates high hole mobility in agreement with experiment. The pressure dependence of the gap is found to be anomalous: the band gap decreases when the lattice constant is decreased. Effective masses and the Kohn-Luttinger type Hamiltonian of the CBM are extracted from the band structures and subsequently used to estimate exciton binding energies using our calculated dielectric constants. These indicate a much lower exciton binding energy for CsSnI3 than recently proposed.

Huang, Ling-Yi; Lambrecht, Walter R. L.

2013-03-01

377

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

SciTech Connect

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

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

2012-03-01

378

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

PubMed

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

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

2012-10-02

379

Band structure parameters of the nitrides: The origin of the small band gap of InN  

Microsoft Academic Search

Using the full-potential linear augmented plane waves (FLAPW) method and adding Christensen's gaussian potential to the standard Kohn-Sham equations that allows to correct the band gap in the local density approximation (LDA), we study the chemical trends of the band gap variation in III-V semiconductors and predict that the band gap for InN is 0.8 (+\\/-0.1 eV), which is much

Pierre Carrier; Su-Huai Wei

2005-01-01

380

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

SciTech Connect

Photonic band gap (PBG) crystals are periodic dielectric structures that manipulate electromagnetic radiation in a manner similar to semiconductor devices manipulating electrons. Whereas a semiconductor material exhibits an electronic band gap in which electrons cannot exist, similarly, a photonic crystal containing a photonic band gap does not allow the propagation of specific frequencies of electromagnetic radiation. This phenomenon results from the destructive Bragg diffraction interference that a wave propagating at a specific frequency will experience because of the periodic change in dielectric permitivity. This gives rise to a variety of optical applications for improving the efficiency and effectiveness of opto-electronic devices. These applications are reviewed later. Several methods are currently used to fabricate photonic crystals, which are also discussed in detail. This research involves a layer-by-layer micro-transfer molding ({mu}TM) and stacking method to create three-dimensional FCC structures of epoxy or titania. The structures, once reduced significantly in size can be infiltrated with an organic gain media and stacked on a semiconductor to improve the efficiency of an electronically pumped light-emitting diode. Photonic band gap structures have been proven to effectively create a band gap for certain frequencies of electro-magnetic radiation in the microwave and near-infrared ranges. The objective of this research project was originally two-fold: to fabricate a three dimensional (3-D) structure of a size scaled to prohibit electromagnetic propagation within the visible wavelength range, and then to characterize that structure using laser dye emission spectra. As a master mold has not yet been developed for the micro transfer molding technique in the visible range, the research was limited to scaling down the length scale as much as possible with the current available technology and characterizing these structures with other methods.

Kevin Jerome Sutherland

2001-05-01

381

Nano-ripple formation on different band-gap semiconductor surfaces using femtosecond pulses  

NASA Astrophysics Data System (ADS)

Nano-ripple formation from ultrashort laser pulse irradiation of semiconductors of different band gaps has been studied using a Ti-sapphire laser with 8 mJ energy, 45 fs pulse duration and 800 nm wavelength (1.5eV) at a fluence in the range of ~100 mJ/cm2 -1J/cm2. The effects of the number of laser shots, angle of incidence, laser polarization, fluence, incident laser wavelength, bandgap, and ambient medium on the ripple period, have been studied. Depending upon the experimental parameters nano-ripple sizes varied in the range of ?-?/9. The studies clearly show that narrower nano-ripples are formed from wide bandgap semiconductors. In addition, the width of the nano-ripples decreases with the laser wavelength and fluence. The observed results are explained considering the transient metallic nature of the semiconductor surface on irradiation with intense femtosecond pulse which excites surface plasmon leading to the nano-ripple formation. The critical role of the surface plasma electron density in deciding ripple period is identified which helps in generation of narrow sub-wavelength nano-ripples.

Chakravarty, U.; Ganeev, R. A.; Naik, P. A.; Chakera, J. A.; Babu, M.; Gupta, P. D.

2011-04-01

382

A terahertz band-pass resonator based on enhanced reflectivity using spoof surface plasmons  

NASA Astrophysics Data System (ADS)

We demonstrate a band-pass resonator in the terahertz (THz) range, based on a frequency-selective designer reflector. The resonator consists of a parallel-plate waveguide, a designed groove pattern cut into the output facet of each plate, and a reflecting mirror. The patterned facet supports a spoof surface plasmon mode, which modifies the reflectivity at the waveguide output facet by interacting with the waveguide mode. By tuning the geometrical parameters of the groove pattern, the reflectivity at the patterned output facet can be increased up to ?100% for a selected frequency. Broadband THz waves are quasi-optically coupled into this resonator and reflected multiple times from the patterned facet. This leads to a narrowing of the spectrum at the selected frequency. The Q value of the resonator increases as the number of reflections on the patterned facet increases, reaching ?25 when the THz wave has experienced 12 reflections.

Liu, Jingbo; Mendis, Rajind; Mittleman, Daniel M.

2013-05-01

383

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

PubMed

We investigate the energy band structure of the superfluid flow of ultracold dilute Fermi gases in a one-dimensional optical lattice along the BCS to Bose-Einstein condensate (BEC) crossover within a mean-field approach. In each side of the crossover region, a loop structure (swallowtail) appears in the Bloch energy band of the superfluid above a critical value of the interaction strength. The width of the swallowtail is largest near unitarity. Across the critical value of the interaction strength, the profiles of density and pairing field change more drastically in the BCS side than in the BEC side. It is found that along with the appearance of the swallowtail, there exists a narrow band in the quasiparticle energy spectrum close to the chemical potential, and the incompressibility of the Fermi gas consequently experiences a profound dip in the BCS side, unlike in the BEC side. PMID:22243294

Watanabe, Gentaro; Yoon, Sukjin; Dalfovo, Franco

2011-12-29

384

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

NASA Astrophysics Data System (ADS)

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

Watanabe, Gentaro; Yoon, Sukjin; Franco, Dalfovo

2012-06-01

385

Complex band structures and evanescent Bloch waves in two-dimensional finite phononic plate  

NASA Astrophysics Data System (ADS)

The complex band structure of a two-dimensional (2D) phononic crystal based on solid or air cylindrical inclusions in solid finite thickness plate is investigated. The plane wave expansion method is developed with a specific extension to calculate the evanescent Bloch modes propagating in the phononic plate. It is shown that, in the opposite of 2D infinite phononic crystals, the complex band structures of Lamb modes exhibits a coupling between in-plane and out-of plane Lamb modes. The polarization and the behavior of the evanescent waves is analyzed and discussed as function of the plate thickness to figure out the physics behind the opening of phononic band gap for the different Lamb modes.

Oudich, Mourad; Badreddine Assouar, M.

2012-11-01

386

Impact of Surface Preparation on RF Breakdown Performance in NLCTA Accelerating Structures(LCC-0081)  

SciTech Connect

In an effort to locate the cause(s) of high electric-field breakdown in X-band accelerating structures, a systematic study was begun on characterizing the effect of etching time on surface roughness, using OFE copper witness coupons made of the same material that was used for structures and machined in identical fashion to those structures. It was found that the minimum surface roughness corresponded to 45 and 5 second etching times on conventional and single-crystal, diamond machined surfaces, respectively. These values are essentially identical, within error, to the times used to obtain the best breakdown results for either type of machined structure.

Kirby, R

2003-10-13

387

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

SciTech Connect

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

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

2008-05-09

388

Quantum well photoemission from atomically uniform Ag films: determination of electronic band structure and quasi-particle lifetime in Ag(100)  

NASA Astrophysics Data System (ADS)

Photoemission from atomically uniform layers of Ag on a Fe(100) substrate is employed for the determination of the bulk electronic band structure of Ag. The high degree of control of the layer thickness allows the interferometric measurement of the electron momentum normal to the sample surface. This leads to an unprecedented precision in the electronic band structure determined from the experiment. The high quality of the layers also allows the discussion of the line shape of the quantum well peaks for the first time and gives access to the intrinsic and extrinsic broadening parameters of the line shape.

Paggel, J. J.; Miller, T.; Luh, D.-A.; Chiang, T.-C.

2000-08-01

389

B4N and Fe3BN nitrides bands structure and theoretical determination of bulk modulus  

Microsoft Academic Search

With the evolution of material science there was some technological evolution as well as the need of finding new links which could be applied to diverse areas of knowledge. Thus, in this article, we study nitrides bands structures which contain boron, in two different stoichiometries Fe3BN and B4N. The choice of these compounds is meant to plan new links and

A. V. Dos Santos

2007-01-01

390

B 4 N and Fe 3 BN nitrides bands structure and theoretical determination of bulk modulus  

Microsoft Academic Search

With the evolution of material science there was some technological evolution as well as the need of finding new links which could be applied to diverse areas of knowledge. Thus, in this article, we study nitrides bands structures which contain boron, in two different stoichiometries Fe3BN and B4N. The choice of these compounds is meant to plan new links and

A. V. dos Santos

2007-01-01

391

Method of projection operators for photonic band structures with perfectly conducting elements  

Microsoft Academic Search

We introduce the method of projection operators based on plane-wave expansion to compute photonic band structures in periodic media containing perfectly conducting elements. Eigenfunctions of a unit configuration potential generate suitable projection operators in the form of a set of eigenvectors in the Fourier domain. By simply applying a projection operator onto a proper subspace, a quadratic or cubic eigensystem

Toshio Suzuki; Paul K. L. Yu

1998-01-01

392

Band structure calculations of Ge-Si core-shell nanowires  

Microsoft Academic Search

We have modeled and calculated the band structure of Ge-Si core-shell nanowire, with both subband interactions between Ge core and Si shell and the inhomogeneous strain effects taken into account. Our results show that the effective masses of subbands, the densities of states and quantum conductance will undergo significant changes and converge to saturated values, as the Si shell turns

Yuhui He; Chun Fan; Yu Ning Zhao; Jinfeng Kang; Xiao Yan Liu; Ruqi Han

2008-01-01

393

Band structures for different kinds of point defect in phononic crystal thin plates  

Microsoft Academic Search

The purpose of this paper is to explore theoretically the band structures for different kinds of point defect in phononic crystal thin plates for square \\/ triangle lattice using the improved plane wave expansion method combining with the supercell technique. The defect is created by several means such as changing the radius, the mass density, the elastic modulus, the geometric

ZongJian Yao; GuiLan Yu; YueSheng Wang

2009-01-01

394

Phononic band gaps of elastic periodic structures: A homogenization theory study  

Microsoft Academic Search

In this study, we investigate the band structures of phononic crystals with particular emphasis on the effects of the mass density ratio and of the contrast of elastic constants. The phononic crystals consist of arrays of different media embedded in a rubber or epoxy. It is shown that the density ratio rather than the contrast of elastic constants is the

Ying-Hong Liu; Chien C. Chang; Ruey-Lin Chern

2007-01-01

395

Lumped-mass method for the study of band structure in two-dimensional phononic crystals  

Microsoft Academic Search

A lumped-mass method is introduced to study the propagation of elastic waves in two-dimensional periodic systems. First, it is used to calculate the band structure of an array of Pb columns in an epoxy background. Second, the method is applied to the same array of Pb columns in a soft rubber background. The results are compared with those calculated with

Gang Wang; Jihong Wen; Yaozong Liu; Xisen Wen

2004-01-01

396

Band-Structure Calculation of the Electron Spin Polarization in Field Emission from Ferromagnetic Nickel.  

National Technical Information Service (NTIS)

A detailed 3d band structure of ferromagnetic Ni is incorporated into a calculation of the electron spin polarization in field emission from the (100) crystal plane. In agreement with a recent experiment of Gleich, Regenfus, and Sizmann, the calculated el...

B. A. Politzer P. H. Cutler

1972-01-01

397

LETTER TO THE EDITOR: An EPM calculation of band structure of zincblende semiconductor alloys  

Microsoft Academic Search

The band structures of several zincblende semiconductor alloys are calculated in the virtual crystal approximation using the empirical pseudopotential method (EPM). The authors propose an interpolation scheme for the pseudopotential form factors that applies universally well to various zincblende semiconductor alloys. The calculated results are in good agreement with experiments, where the lattice mismatch is large. For the case of

Sung Jae Lee; Tae Song Kwon; Hyun Sook Lee; Kyun Nahm; Chul Koo Kim

1989-01-01

398

Simulation and experiment of photonic band-gap structures for microstrip circuits  

Microsoft Academic Search

We report the first comprehensive investigation of synthesized dielectric materials which possess distinctive stopbands for microstrip lines. Four types of these photonic band-gap (PBG) structures have been simulated using FDTD. Experiment with a honeycomb-lattice PBG line shows excellent agreement between theoretical prediction and measurement

Yongxi Qian; Vesna Radisic; Tatsuo Itoh

1997-01-01

399

Photonic band structures of two-dimensional systems containing metallic components  

Microsoft Academic Search

By use of the plane-wave method, we calculate the photonic band structure for electromagnetic waves of E and H polarization propagating in a system consisting of an infinite array of identical, infinitely long, parallel, metal cylinders of circular cross section, embedded in vacuum, whose intersection with a perpendicular plane forms a simple square or triangular lattice. The dielectric function of

V. Kuzmiak; A. A. Maradudin; F. Pincemin

1994-01-01

400

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

PubMed

A modified electromagnetic-bandgap (M-EBG) structure and its application to planar monopole ultra-wideband (UWB) antenna are presented. The proposed M-EBG which comprises two strip patch and an edge-located via can perform dual notched bands. By properly designing and placing strip patch near the feedline, the proposed M-EBG not only possesses a simple structure and compact size but also exhibits good band rejection. Moreover, it is easy to tune the dual notched bands by altering the dimensions of the M-EBG. A demonstration antenna with dual band-notched characteristics is designed and fabricated to validate the proposed method. The results show that the proposed antenna can satisfy the requirements of VSWR < 2 over UWB 3.1-10.6?GHz, except for the rejected bands of the world interoperability for microwave access (WiMAX) and the wireless local area network (WLAN) at 3.5?GHz and 5.5?GHz, respectively. PMID:24170984

Liu, Hao; Xu, Ziqiang

2013-09-19

401

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

PubMed Central

A modified electromagnetic-bandgap (M-EBG) structure and its application to planar monopole ultra-wideband (UWB) antenna are presented. The proposed M-EBG which comprises two strip patch and an edge-located via can perform dual notched bands. By properly designing and placing strip patch near the feedline, the proposed M-EBG not only possesses a simple structure and compact size but also exhibits good band rejection. Moreover, it is easy to tune the dual notched bands by altering the dimensions of the M-EBG. A demonstration antenna with dual band-notched characteristics is designed and fabricated to validate the proposed method. The results show that the proposed antenna can satisfy the requirements of VSWR < 2 over UWB 3.1–10.6?GHz, except for the rejected bands of the world interoperability for microwave access (WiMAX) and the wireless local area network (WLAN) at 3.5?GHz and 5.5?GHz, respectively.

Xu, Ziqiang

2013-01-01

402

Fourier transform profilometry (FTP) using an innovative band-pass filter for accurate 3-D surface reconstruction  

Microsoft Academic Search

This article presents a novel band-pass filter for Fourier transform profilometry (FTP) for accurate 3-D surface reconstruction. FTP can be employed to obtain 3-D surface profiles by one-shot images to achieve high-speed measurement. However, its measurement accuracy has been significantly influenced by the spectrum filtering process required to extract the phase information representing various surface heights. Using the commonly applied

Liang-Chia Chen; Hsuan-Wei Ho; Xuan-Loc Nguyen

2010-01-01

403

Applicability of Photonic Crystal Fiber With Uniform Air-Hole Structure to High-Speed and Wide-Band Transmission Over Conventional Telecommunication Bands  

Microsoft Academic Search

We discuss the applicability of photonic crystal fiber (PCF) with a uniform air-hole structure to high-speed and wide-band transmission over conventional telecommunication bands. We design the PCF to maximize the effective area by utilizing the macro-bending losses of the fundamental and first higher order modes (HOM) and clarify that a single-mode and low bending loss PCF can realize the largest

Takashi Matsui; Kazuhide Nakajima; C. Fukai

2009-01-01

404

Observation of dark-current signals from the S-band structures of the SLAC linac  

SciTech Connect

It is well known that the electro-magnetic fields in high-gradient RF structures can cause electron emission from the metallic structure walls. If the emitted electrons are captured and accelerated by the accelerating fields so-called dark-current is induced. Dark-currents have been measured and studied for various RF-structures. In this paper the authors present measurements of RF induced signals for the SLC S-band structures. For nominal gradients of 17 MV/m it is shown that the dark-current can be strong enough to significantly reduce the signal-to-noise ratio of the SLC beam wire scanners. They also show results from RF measurements in the dipole band. The measurements are compared to more direct observations of dark-current and it is tried to connect the results to possible effects on the accelerated particle beam.

Assmann, R.; Decker, F.J.; Seidel, M.; Siemann, R.H.; Whittum, D.

1997-07-01

405

Results from the CLIC X-Band Structure Test Program at NLCTA  

SciTech Connect

As part of a SLAC-CERN-KEK collaboration on high gradient X-band structure research, several prototype structures for the CLIC linear collider study have been tested using two of the high power (300 MW) X-band rf stations in the NLCTA facility at SLAC. These structures differ in terms of their fabrication (brazed disks and clamped quadrants), gradient profile (amount by which the gradient increases along the structure, which optimizes efficiency and maximizes sustainable gradient) and HOM damping (use of slots or waveguides to rapidly dissipate dipole mode energy). The CLIC goal in the next few years is to demonstrate the feasibility of a CLIC-ready baseline design and to investigate alternatives that could increase efficiency. This paper summarizes the high gradient test results from NLCTA in support of this effort.

Adolphsen, Chris; Bowden, Gordon; Dolgashev, Valery; Laurent, Lisa; Tantawi, Sami; Wang, Faya; Wang, Juwen W.; /SLAC; Doebert, Steffen; Grudiev, Alexej; Riddone, Germana; Wuensch, Walter; Zennaro, Riccardo; /CERN; Higashi, Yasuo; Higo, Toshiyasu; /KEK, Tsukuba

2009-07-06

406

Electronic band structure of zirconia and hafnia polymorphs from the GW perspective  

NASA Astrophysics Data System (ADS)

The electronic structure of crystalline ZrO2 and HfO2 in the cubic, tetragonal, and monoclinic phase has been investigated using many-body perturbation theory in the GW approach based on density-functional theory calculations in the local-density approximation (LDA). ZrO2 and HfO2 are found to have very similar quasiparticle band structures. Small differences between them are already well described at the LDA level indicating that the filled f shell in HfO2 has no significant effect on the GW corrections. A comparison with direct and inverse photoemission data shows that the GW density of states agrees very well with experiment. A systematic investigation into the structural and morphological dependence of the electronic structure reveals that the internal displacement of the oxygen atoms in the tetragonal phase has a significant effect on the band gap.

Jiang, Hong; Gomez-Abal, Ricardo I.; Rinke, Patrick; Scheffler, Matthias

2010-02-01

407

Electronic band structure and Li diffusion paths in (LaLi)TiO 3  

Microsoft Academic Search

The electronic structure and the Li diffusion paths in the lithium doped lanthanum titanate have been studied. The band dispersion and the density of states (DOS) are calculated using the linear-muffin-tin-orbital (LMTO) method. The model structure used contains La-rich and La deficient layers, with the 2ap×2ap×2ap unit cell and base centered C symmetry. The primitive cell contains 20 atoms represented

Shinji Ono; Yusuke Seki; Shoji Kashida; Michisuke Kobayashi

2006-01-01

408

Band Structure Calculations for Two-Dimensional Plasma Photonic Crystals in Honeycomb Lattice Arrangement  

Microsoft Academic Search

We propose an approach originating from plane wave expansion method to calculate band structure for two types of honeycomb lattice two-dimensional plasma photonic crystals. The eigenvalue equations of E-polarization for two types of structures, which depend on the honeycomb lattice realization(plasma rods immersed in dielectric background or vice versa), are derived respectively. A standard linearization technique which solves the general

Xiang-Kun Kong; Shao-Bin Liu; Hai-Feng Zhang; Liang Zhou; Chun-Zao Li

2011-01-01

409

Band structure for a one-dimensional photonic crystal containing left-handed materials  

Microsoft Academic Search

The explicit dispersion equation for a one-dimensional periodic structure with alternative layers of left-handed material (LHM) and right-handed material (RHM) is given and analyzed. Some unusual phenomena such as spurious modes with complex frequencies, discrete modes and photon tunneling modes are observed in the band structure. The existence of spurious modes with complex frequencies is a common problem in the

Liang Wu; Sailing He; Linfang Shen

2003-01-01

410

Carbon K-shell near-edge structure: Multiple scattering and band-theory calculations  

NASA Astrophysics Data System (ADS)

The carbon K-shell near-edge absorption fine structure of both diamond and graphite has been calculated by the multiple-scattering method and by a single-particle self-consistent pseudo-atomic-orbital band-theory method. We compare the results of these two calculations with experiment, and show that they both give agreement with the experimental near-edge structure.

Weng, Xudong; Rez, Peter; Ma, Hong

1989-08-01

411

BAND STRUCTURES AND ABNORMAL BEHAVIOR OF ONE DIMENSIONAL PHOTONIC CRYSTAL CONTAINING NEGATIVE INDEX MATERIALS  

Microsoft Academic Search

Abstract—We have studied the optical properties,band structures and group velocities,of one dimensional photonic crystal (1-D PC) containing negative index materials using translational matrix method (TMM). The 1-D PC containing negative index materials is a periodic arrangement of positive index material (PIM) and negative index material (NIM). The observed group velocity of such structure is larger than the speed of light

Girijesh N. Pandey; Khem B. Thapa; Sanjeev Kumar Srivastava; Sant Prasad Ojha

2008-01-01

412

Miniaturisation of Defected Ground Plane Using Complementary Metallodielectric Electromagnetic Band Gap Structures  

Microsoft Academic Search

The concept of Complementary Electromagnetic Band-Gap Structures employing dipole elements as conductors and apertures is employed for the miniaturisation of Defected Ground Plane (DGS) structures. Conductor and aperture dipoles are placed in close proximity with a rotation of 90 o between them, in order to produce maximum coupling, which proves to yield maximum miniaturisation in the order of 2.3:1. An

George Goussetis; Alexandros P. Feresidis; George Apostolopoulos; John C. Vardaxoglou

2006-01-01

413

Dispersive properties of finite, one-dimensional photonic band gap structures: Applications to nonlinear quadratic interactions  

Microsoft Academic Search

We discuss the linear dispersive properties of finite one-dimensional photonic band-gap structures. We introduce the concept of a complex effective index for structures of finite length, derived from a generalized dispersion equation that identically satisfies the Kramers-Kronig relations. We then address the conditions necessary for optimal, phase-matched, resonant second harmonic generation. The combination of enhanced density of modes, field localization,

M. Centini; C. Sibilia; M. Scalora; G. D'aguanno; M. Bertolotti; M. J. Bloemer; C. M. Bowden; I. Nefedov

1999-01-01

414

Electroluminescence at Si band gap energy based on metal-oxide-silicon structures  

Microsoft Academic Search

Room-temperature electroluminescence corresponding to Si band gap energy from metal-oxide-semiconductor structures on both p-type and n-type Si is observed. With very thin oxide grown by rapid thermal oxidation, the metal-oxide-semiconductor structures behave like light emitting diodes. Luminescence is observed under forward bias even with a current density as low as 0.67 A\\/cm2. The physical reason for the electroluminescence is discussed

Ching-Fuh Lin; C. W. Liu; Miin-Jang Chen; M. H. Lee; I. C. Lin

2000-01-01

415

Using Superlattice Ordering to Reduce the Band Gap of Random (In,Ga)As/InP Alloys to a Target Value Via the Inverse Band Structure Approach  

SciTech Connect

Thermophotovoltaic (TPV) devices are intended to absorb photons from hot blackbody radiating objects, often requiring semiconductor absorbers with band gap of {approx_equal} 0.6 eV. The random In{sub x}Ga{sub 1-x}As alloy lattice matched (x{sub In}=0.53) to a (001) InP substrate has a low-temperature band gap of 0.8 eV, about 0.2 eV too high for a TPV absorber. Bringing the band gap down by raising the In concentration induces strain with the substrate, leading to a two-dimensional (2D) {yields} three-dimensional (3D) morphological transition occurring before band gaps suitable for TPV applications are achieved. We use the inverse band structure approach, based on a genetic algorithm and empirical pseudopotential calculations, to search for lattice-matched InAs/GaAs multiple-repeat unit structures with individual layer thicknesses lower than the critical thickness for a 2D {yields} 3D transition. Despite the fact that quantum confinement usually increases band gaps, we find a quantum superlattice structure with the required reduced gap (and a significant optical transition) that matches all target requirements. This is explained by the predominance of (potential-energy) level anticrossing effects over (kinetic) quantum confinement effects.

Piquini, P.; Zunger, A.

2008-10-01

416

The electronic structures of vanadate salts: Cation substitution as a tool for band gap manipulation  

SciTech Connect

The electronic structures of six ternary metal oxides containing isolated vanadate ions, Ba{sub 3}(VO{sub 4}){sub 2}, Pb{sub 3}(VO{sub 4}){sub 2}, YVO{sub 4}, BiVO{sub 4}, CeVO{sub 4} and Ag{sub 3}VO{sub 4} were studied using diffuse reflectance spectroscopy and electronic structure calculations. While the electronic structure near the Fermi level originates largely from the molecular orbitals of the vanadate ion, both experiment and theory show that the cation can strongly influence these electronic states. The observation that Ba{sub 3}(VO{sub 4}){sub 2} and YVO{sub 4} have similar band gaps, both 3.8 eV, shows that cations with a noble gas configuration have little impact on the electronic structure. Band structure calculations support this hypothesis. In Pb{sub 3}(VO{sub 4}){sub 2} and BiVO{sub 4} the band gap is reduced by 0.9-1.0 eV through interactions of (a) the filled cation 6s orbitals with nonbonding O 2p states at the top of the valence band, and (b) overlap of empty 6p orbitals with antibonding V 3d-O 2p states at the bottom of the conduction band. In Ag{sub 3}VO{sub 4} mixing between filled Ag 4d and O 2p states destabilizes states at the top of the valence band leading to a large decrease in the band gap (E{sub g}=2.2 eV). In CeVO{sub 4} excitations from partially filled 4f orbitals into the conduction band lower the effective band gap to 1.8 eV. In the Ce{sub 1-x}Bi{sub x}VO{sub 4} (0<=x<=0.5) and Ce{sub 1-x}Y{sub x}VO{sub 4} (x=0.1, 0.2) solid solutions the band gap narrows slightly when Bi{sup 3+} or Y{sup 3+} are introduced. The nonlinear response of the band gap to changes in composition is a result of the localized nature of the Ce 4f orbitals. - Graphical abstract: The electronic structures of six vanadate salts, Ba{sub 3}(VO{sub 4}){sub 2}, Pb{sub 3}(VO{sub 4}){sub 2}, YVO{sub 4}, BiVO{sub 4}, Ag{sub 3}VO{sub 4} and CeVO{sub 4}, are studied. The results show that the oxygen to vanadium charge transfer, which is largely responsible for the electronic structure near the Fermi level, can be altered significantly through interactions with the surrounding cations.

Dolgos, Michelle R.; Paraskos, Alexandra M.; Stoltzfus, Matthew W.; Yarnell, Samantha C. [Ohio State University, Department of Chemistry, 100 West 18th Avenue, Columbus, OH 43210 (United States); Woodward, Patrick M., E-mail: woodward@chemistry.ohio-state.ed [Ohio State University, Department of Chemistry, 100 West 18th Avenue, Columbus, OH 43210 (United States)

2009-07-15

417

B4N and Fe3BN nitrides bands structure and theoretical determination of bulk modulus  

NASA Astrophysics Data System (ADS)

With the evolution of material science there was some technological evolution as well as the need of finding new links which could be applied to diverse areas of knowledge. Thus, in this article, we study nitrides bands structures which contain boron, in two different stoichiometries Fe3BN and B4N. The choice of these compounds is meant to plan new links and to understand nitrides fundamental state properties facing these new crystalline structures. In order to resolve the compound band structure we used the method of linear Muffin Tin orbital (LMTO), with atomic sphere approximation (ASA). By using this method we obtained the energy of formation as a function of the lattice parameter as one of the results. We find the equilibrium lattice parameter of 6.9755 a.u., for the Fe3BN nitride, and in B4N, we have 6.8589 a.u. We also discuss in this article the charge transference between sites and the influence of pressure on the compound properties, as well as the Bulk modulus that is 239.82 GPa for Fe3BN and 105.48 GPa for B4N. We show the behaviour of the density of states (DOS) of the new band structure found for the proposed crystalline structure Fe3BN, in which the B atom replace the Fe atom in the corner of the structure ?-Fe4N.

Dos Santos, A. V.

2007-06-01

418

Observations of conduction-band structure of 4H- and 6H-SiC  

NASA Astrophysics Data System (ADS)

Ballistic electron-emission spectroscopy (BEES) and photoluminescence are used to study conduction-band structure related transport properties of the 4H and 6H polytypes of SiC. A secondary energy threshold at 2.7 eV is observed in the BEES spectrum of 4H-SiC, in good agreement with a value of 2.8 eV deduced from reported ab initio calculations. The results from 6H-SiC, are suggested to be influenced by transport properties of other polytype inclusions, also supported by band-edge transitions evident in 6H-SiC photoluminescence spectra.

Shalish, I.; Altfeder, I. B.; Narayanamurti, V.

2002-02-01

419

Comparison Between Experiment and Calculated Band Structures for DyN and SmN  

SciTech Connect

We investigate the electronic band structure of two of the rare-earth nitrides, DyN and SmN. Resistivity measurements imply that both materials have a semiconducting ground state, and both show resistivity anomalies coinciding with the magnetic transition, despite the different magnetic states in DyN and SmN. X-ray absorption and emission measurements are in excellent agreement with densities of states obtained from LSDA+U calculations, although for SmN the calculations predict a zero band gap.

Preston,A.; Granville, S.; Housden, D.; Ludbrook, B.; Ruck, B.; Trodahl, H.; Bittar, A.; Williams, G.; Downes, J.; et al

2007-01-01

420

Band Structure and Oscillatory Electron-Phonon Coupling of Pb Thin Films Determined by Atomic-Layer-Resolved Quantum-Well States  

Microsoft Academic Search

Using a low temperature growth method, we have prepared atomically flat Pb thin films over a wide range of film thickness on a Si-(111)-7×7 surface. The Pb film morphology and electronic structure are investigated in situ by scanning tunneling microscopy and angle-resolved photoemission spectroscopy. Well-defined and atomic-layer-resolved quantum-well states of the Pb films are used to determine the band structure

Yan-Feng Zhang; Jin-Feng Jia; Tie-Zhu Han; Zhe Tang; Quan-Tong Shen; Yang Guo; Z. Q. Qiu; Qi-Kun Xue

2005-01-01

421

Electronic structure of dysprosium silicide films grown on a Si(1 1 1) surface  

NASA Astrophysics Data System (ADS)

The thickness-dependent electronic structures of Dy silicide films grown on a Si(1 1 1) surface have been investigated by angle-resolved photoelectron spectroscopy. Two ( 1×1) periodic bands, both of them cross the Fermi level, have been observed in the silicide films formed by Dy coverages of 1.0 monolayer and below, and more than five ( ?{3}×?{3}) periodic bands have been observed in thicker films. Taking the ( 2?{3}×2?{3}) periodic structure of Dy atoms in the submonolayer silicide film into account, the periodicity of the two metallic bands indicate that they mainly originate from the orbitals of Si atoms, which form a ( 1×1) structure. Of the ( ?{3}×?{3}) periodic bands observed in thick films, four of them are well explained by the folding of the ( 1×1) bands into a ( ?{3}×?{3}) periodicity. Regarding the other band, the three ( ?{3}×?{3}) periodic bands would originate from the electronic states related to the inner Si layers that form a ( ?{3}×?{3}) structure, and the one observed in the 3.0 ML film only might originate from the electron located at the interface between bulk Si and the Dy silicide film.

Imai, Ayako; Kakuta, Haruya; Mawatari, Kenji; Harasawa, Ayumi; Ueno, Nobuo; Okuda, Taichi; Sakamoto, Kazuyuki

2009-11-01

422

Structure, composition and functions of surface structures on oral bacteria  

Microsoft Academic Search

This review describes the surface structures (fibrils and fimbriae), on oral bacteria that can be responsible for adhesion to buccal mucosa, teeth and other bacteria (coaggregation). Fibrils and fimbriae have been found on a number of different species of Streptococcus, Actinomyces and Bacteroides, and are morphologically and biochemically distinct from each other. Either structure can be present on different strains

Pauline S Handley

1990-01-01

423

Electronic band structures and optical properties of type-II superlattice photodetectors with interfacial effect.  

PubMed

The electronic band structures and optical properties of type-II superlattice (T2SL) photodetectors in the mid-infrared (IR) range are investigated. We formulate a rigorous band structure model using the 8-band k · p method to include the conduction and valence band mixing. After solving the 8 × 8 Hamiltonian and deriving explicitly the new momentum matrix elements in terms of envelope functions, optical transition rates are obtained through the Fermi's golden rule under various doping and injection conditions. Optical measurements on T2SL photodetectors are compared with our model and show good agreement. Our modeling results of quantum structures connect directly to the device-level design and simulation. The predicted doping effect is readily applicable to the optimization of photodetectors. We further include interfacial (IF) layers to study the significance of their effect. Optical properties of T2SLs are expected to have a large tunable range by controlling the thickness and material composition of the IF layers. Our model provides an efficient tool for the designs of novel photodetectors. PMID:22330471

Qiao, Peng-Fei; Mou, Shin; Chuang, Shun Lien

2012-01-30

424

Synthesis and structure of nanocrystalline TiO2 with lower band gap showing high photocatalytic activity.  

PubMed

Nanocrystalline TiO2 was synthesized by the solution combustion method using titanyl nitrate and various fuels such as glycine, hexamethylenetetramine, and oxalyldihydrazide. These catalysts are active under visible light, have optical absorption wavelengths below 600 nm, and show superior photocatalytic activity for the degradation of methylene blue and phenol under UV and solar conditions compared to commercial TiO2, Degussa P-25. The higher photocatalytic activity is attributed to the structure of the catalyst. Various studies such as X-ray diffraction, Raman spectroscopy, Brunauer-Emmett-Teller surface area, thermogravimetric-differential thermal analysis, FT-IR spectroscopy, NMR, UV-vis spectroscopy, and surface acidity measurements were conducted. It was concluded that the primary factor for the enhanced activity of combustion-synthesized catalyst is a larger amount of surface hydroxyl groups and a lowered band gap. The lower band gap can be attributed to the carbon inclusion into the TiO2 giving TiO(2-2x)C(x) VO2**. PMID:15835170

Nagaveni, K; Hegde, M S; Ravishankar, N; Subbanna, G N; Madras, Giridhar

2004-03-30

425

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

SciTech Connect

Precise dual-band infrared (DBIR) thermal imaging provides a useful diagnostic tool for wide-area detection of defects from corrosion damage in metal airframes, heat damage in composite structures and structural damage in concrete bridge decks. We use DBIR image ratios to enhance surface temperature contrast, remove surface emissivity noise and increase signal-to-clutter ratios. We clarify interpretation of hidden defect sites by distinguishing temperature differences at defect sites from emissivity differences at clutter sites. This reduces the probability of false calls associated with misinterpreted image data. For airframe inspections, we map flash-heated defects in metal structures. The surface temperature rise above ambient at corrosion-thinned sites correlates with the percentage of material loss from corrosion thinning. For flash-heated composite structures, we measure the temperature-time history which relates to the depth and extent of heat damage. In preparation for bridge deck inspections, we map the natural day and night temperature variations at known concrete slab delamination sites which heat and coot at different rates than their surroundings. The above-ambient daytime and below-ambient nightime delamination site temperature differences correlate with the volume of replaced concrete at the delamination sites.

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

1994-05-01

426

Bimodality of galaxy disc central surface brightness distribution in the Spitzer 3.6 ?m band  

NASA Astrophysics Data System (ADS)

We report on measurements of the disc central surface brightnesses (?0) at 3.6 ?m for 438 galaxies selected by distance and absolute magnitude cutoffs from the 2350 plus galaxies in the Spitzer Survey of Stellar Structure in Galaxies, one of the largest and deepest homogeneous mid-infrared data sets of nearby galaxies. Our sample contains nearly three times more galaxies than the most recent study of the ?0 distribution. We demonstrate that there is a bimodality in the distribution of ?0. Between the low- and high-surface-brightness galaxy regimes there is a lack of intermediate-surface-brightness galaxies. Caveats invoked in the literature from small-number statistics to the knowledge of the environmental influences and possible biases from low-signal-to-noise data or corrections for galaxy inclination are investigated. Analyses show that the bimodal distribution of ?0 cannot be due to any of these biases or statistical fluctuations. It is highly probable that galaxies settle in two stable modes: a dark-matter-dominated mode where the dark matter dominates at all radii - this gives birth to low-surface-brightness galaxies - and a baryonic-matter-dominated mode where the baryons dominate the dark matter in the central parts - this gives rise to the high-surface-brightness discs. The lack of intermediate-surface-brightness objects suggests that galaxies avoid (staying in) a mode where dark matter and baryons are co-dominant in the central parts of galaxies.

Sorce, Jenny G.; Courtois, Hélène M.; Sheth, Kartik; Tully, R. Brent

2013-07-01

427

Obtaining localized orbitals and band structure in self-interaction-corrected density-functional theory  

NASA Astrophysics Data System (ADS)

An efficient minimization method is presented to find the optimal orthogonal localized orbitals within the self-interaction-corrected (SIC) local spin-density (LSD) approximation. By introducing a unified Hamiltonian, both the canonicalvalence bands and conduction bands are obtained by diagonalizing the same matrix. A general criterion for the existence of the self-consistent localized solutions of the SIC-LSD equations is proposed. As an application, we consider the phase diagram and the band structure of the half-filled two-dimensional extended Hubbard model with the next-nearest-neighbor hopping amplitude t'. The phase boundary between the charge-density wave (CDW) and the spin-density wave (SDW) is determined by comparing the ground-state energies. For nonzero t', the CDW and SDW states are unstable over a finite portion of the phase diagram at weak coupling.

Xie, Yuannan; Han, Rushan; Zhang, Xinwei

1999-09-01

428

Quasiparticle excitations in valence-fluctuation materials: effects of band structure and crystal fields  

SciTech Connect

Evidence is now quite strong that the elementary hybridization model is the correct way to understand the lattice-coherent Fermi liquid regime at very low temperatures. Many-body theory leads to significant renormalizations of the input parameters, and many of the band-theoretic channels for hybridization are suppressed by the combined effects of Hund's-rule coupling, crystal-field splitting, and the f-f Coulomb repulsion U. Some exploratory calculations based on this picture are described, and some inferences are drawn about the band structures of several heavy-fermion materials. These inferences can and should be tested by suitably modified band-theoretic calculations. We find evidence for a significant Baber-scattering contribution in the very-low-temperature resistivity. A new mechanism is proposed for crossover from the coherent Fermi-liquid regime to the incoherent dense-Kondo regime. 28 refs.

Brandow, B.H.

1985-01-01

429

Band gap engineering in nano structured graphane by applying elastic strain  

NASA Astrophysics Data System (ADS)

The first principle calculations have been performed to investigate the influence of elastic strain namely: uniaxial compression (-a), symmetrical biaxial compression (-a-b) and asymmetric biaxial (-a+b) stain, on the electronic structure of graphane in chair conformation. It is found that the band gap can be tuned by elastic strain and depends on the type of applied strain. The nature of the graphane has been found to change from wide band gap semiconductor to metal at three types of strain i. e. 19% uniaxial compression, 16% biaxial compression and 16.5% asymmetric biaxial strain. Tunable band gap of graphane with elastic strain can make it suitable for the applications of electromechanical devices and for the fabrication of strain sensors.

Kumar, Naveen; Sharma, Jyoti Dhar; Kumar, Ashok; Ahluwalia, P. K.

2013-02-01

430

Ab initio electronic band structure study of III-VI layered semiconductors  

NASA Astrophysics Data System (ADS)

We present a total energy study of the electronic properties of the rhombohedral ?-InSe, hexagonal ?-GaSe, and monoclinic GaTe layered compounds. The calculations have been done using the full potential linear augmented plane wave method, including spin-orbit interaction. The calculated valence bands of the three compounds compare well with angle resolved photoemission measurements and a discussion of the small discrepancies found has been given. The present calculations are also compared with recent and previous band structure calculations available in the literature for the three compounds. Finally, in order to improve the calculated band gap value we have used the recently proposed modified Becke-Johnson correction for the exchange-correlation potential.

Olguín, Daniel; Rubio-Ponce, Alberto; Cantarero, Andrés

2013-08-01

431

Structure studies of {sup 11}Be and {sup 12}Be: Observation of molecular rotational bands  

SciTech Connect

Excited states of {sup 11}Be have been studied with several transfer reactions. Nine states between 3.96 MeV and 25.0 MeV excitation energy show the characteristic energy dependence of a rotational band. The deduced large moment-of-inertia of this band is consistent with a two-{alpha} structure with large deformation. For {sup 12}Be four high lying states at 7.30 MeV, 10.7 MeV, 14.6 MeV and 21.7 MeV, which were observed in the {sup 9}Be({sup 15}N, {sup 12}N){sup 12}Be reaction, also form a rotational band with almost the same moment-of-inertia as for {sup 11}Be, using the tentative spin assignments of 2{sup +}-8{sup +}.

Bohlen, H. G.; Blazevic, A.; Gebauer, B.; Oertzen, W. von; Thummerer, S.; Wilpert, M. [Hahn-Meitner-Institut, Glienicker Str. 100, D-14109 Berlin (Germany); Grimes, S. M.; Massey, T. N. [Department of Physics and Astronomy, Ohio University, Athens, Ohio 45701-2979 (United States); Kalpakchieva, R. [Flerov Laboratory of Nuclear Reactions, JINR, 141980 Dubna (Russian Federation) Bulgarian Academy of Science, Sofia (Bulgaria)

1999-11-16

432

Structure Studies of {sup 11}Be and {sup 12}Be: Observation of Molecular Rotational Bands  

SciTech Connect

Excited states of {sup 11}Be have been studied with several transfer reactions. Nine states between 3.96 MeV and 25.0 MeV excitation energy show the characteristic energy dependence of a rotational band. The deduced large moment-of-inertia of this band is consistent with a two-{alpha} structure with large deformation. For {sup 12}Be four high lying states at 7.30 MeV, 10.7 MeV, 14.6 MeV and 21.7 MeV, which were observed in the {sup 9}Be({sup 15}N,{sup 12}N){sup 12}Be reaction, also form a rotational band with almost the same moment-of-inertia as for {sup 11}Be, using the tentative spin assignments of 2{sup +} - 8{sup +}.

H.G. Bohlen; A. Blazevic; B. Gebauer; S.M. Grimes; R. Kalpakchieva; T.N. Massey; W. von Oertzen; S. Thummerer; M. Wilpert

1999-12-31

433

Dynamical surface structures in multiparticle-correlated surface growths.  

PubMed

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

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

2002-10-21

434

Photoelectric emission from negative-electron-affinity diamond (111) surfaces: Exciton breakup versus conduction-band emission  

SciTech Connect

We have recently reported that bound electron-hole pairs (Mott-Wannier excitons) are the dominant source of photoelectron emission from specially prepared [``as-polished`` C(111)-(1{times}1):H] negative-electron-affinity diamond surfaces for near-band-gap excitation up to 0.5 eV above threshold [C. Bandis and B. B. Pate, Phys. Rev. Lett. 74, 777 (1995)]. It was found that photoexcited excitons transport to the surface, break up, and emit their electron. In this paper, we extend the study of exciton-derived emission to include partial yield (constant final-state) analysis as well as angular distribution measurements of the photoelectric emission. In addition, we find that exciton-derived emission does not always dominate. Photoelectric emission properties of the {ital in} {ital situ} ``rehydrogenated`` (111)-(1{times}1):H diamond surface are characteristically different than emission observed from the as-polished (111)-(1{times}1):H surface. The rehydrogenated surface has additional downward band bending as compared to the as-polished surface. In confirmation of the assignment of photoelectric yield to exciton breakup emission, we find a significant enhancement of the total electron yield when the downward band bending of the hydrogenated surface is increased. The functional form of the observed total electron yield demonstrates that, in contrast to the as-polished surface, conduction-band electrons are a significant component of the observed photoelectric yield from the {ital in} {ital situ} hydrogenated (111)-(1{times}1):H surface. Furthermore, electron emission characteristics of the rehydrogenated surface confirms our assignment of a Fan phonon-cascade mechanism for thermalization of excitons.

Bandis, C.; Pate, B.B. [Department of Physics, Washington State University, Pullman, Washington 99164-2814 (United States)

1995-10-15

435

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

Microsoft Academic Search

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

Miguel Onorato; Alfred Osborne; Renato Fedele; Marina Serio

2003-01-01

436

Band structure, phase transitions, and semiconductor analogs in one-dimensional solid light systems  

NASA Astrophysics Data System (ADS)

The conjunction of atom-cavity physics and photonic structures (“solid light” systems) offers new opportunities in terms of more device functionality and the probing of designed emulators of condensed-matter systems. By analogy to the canonical one-electron approximation of solid-state physics, we propose a one-polariton approximation to study these systems. Using this approximation, we apply Bloch states to the uniformly tuned Jaynes-Cummings-Hubbard model to analytically determine the energy-band structure. By analyzing the response of the band structure to local atom-cavity control, we explore its application as a quantum simulator and show phase-transition features absent in mean-field theory. Using this approach for solid light systems, we extend the analysis to include detuning impurities to show the solid light analogy of the semiconductor. This investigation also shows features with no semiconductor analog.

Quach, James; Makin, Melissa I.; Su, Chun-Hsu; Greentree, Andrew D.; Hollenberg, Lloyd C. L.

2009-12-01

437

Structure of the doublet bands in doubly odd nuclei: The case of {sup 128}Cs  

SciTech Connect

The structure of the {Delta}J=1 doublet bands in {sup 128}Cs is investigated within the framework of the interacting vector boson-fermion model. A new, purely collective interpretation of these bands is given on the basis of the used boson-fermion dynamical symmetry of the model. The energy levels of the doublet bands as well as the absolute B(E2) and B(M1) transition probabilities between the states of both yrast and yrare bands are described quite well. The observed odd-even staggering of both B(M1) and B(E2) values is reproduced by the introduction of an appropriate interaction term of quadrupole type, which produces such a staggering effect in the transition strengths. The calculations show that the appearance of doublet bands in certain odd-odd nuclei could be a consequence of the realization of a larger dynamical symmetry based on the noncompact supersymmetry group OSp(2{Omega}/12,R).

Ganev, H. G. [Institute of Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences, Sofia 1784 (Bulgaria); Brant, S. [Department of Physics, Faculty of Science, University of Zagreb, 10000 Zagreb (Croatia)

2010-09-15

438

Structural vs electronic origin of renormalized band widths in TTF-TCNQ: An angular dependent NEXAFS study  

SciTech Connect

We have performed angle-dependent near-edge x-ray absorption fine structure measurements in the Auger electron yield mode on the correlated quasi-one-dimensional organic conductor tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) in order to determine the orientation of the molecules in the topmost surface layer. We find that the tilt angles of the molecules with respect to the one-dimensional axis are essentially the same as in the bulk. Thus, we can rule out surface relaxation as the origin of the renormalized band widths which were inferred from the analysis of photoemission data within the one-dimensional Hubbard model. Thereby, recent theoretical results are corroborated which invoke long-range Coulomb repulsion as alternative explanation to understand the spectral dispersions of TTF-TCNQ quantitatively within an extended Hubbard model.

Sing, M.; Meyer, J.; Glawion, S.; Claessen, R. [Experimentelle Physik IV, Universitaet Wuerzburg, D-97074 Wuerzburg (Germany); Hoinkis, M. [Experimentelle Physik IV, Universitaet Wuerzburg, D-97074 Wuerzburg (Germany); Experimentalphysik II, Universitaet Augsburg, D-86135 Augsburg (Germany); Blaha, P. [Institute of Materials Chemistry, Vienna University of Technology, A-1060 Vienna (Austria); Gavrila, G. [Institut fuer Physik, Technische Universitaet Chemnitz, D-09107 Chemnitz (Germany); Jacobsen, C. S. [Department of Physics, Technical University of Denmark, DK-2800 Lyngby (Denmark)

2007-12-15

439

Three-dimensional band structure of layered TiTe{sub 2}: Photoemission final-state effects  

SciTech Connect

Three-dimensional band structure of unoccupied and occupied states of the prototype layered material TiTe{sub 2} is determined focusing on the {gamma}A line of the Brillouin zone. Dispersions and lifetimes of the unoccupied states, acting as the final states in the photoemission process, are determined from a very-low-energy electron diffraction experiment supported by first-principles calculations based on a Bloch waves treatment of multiple scattering. The experimental unoccupied states of TiTe{sub 2} feature dramatic non-free-electron effects such as multiband composition and nonparabolic dispersions. The valence band layer-perpendicular dispersions are then determined from a photoemission experiment consistently interpreted on the basis of the experimental final states to achieve control over the three-dimensional wave vector. The experimental results demonstrate the absence of the Te 4p{sub z}{sup *} Fermi surface pocket at the {gamma} point and significant self-energy renormalization of the valence band dispersions. Photoemission calculations based on a Bloch waves formalism within the one-step theory reveal limitations of understanding photoemission from layered materials such as TiTe{sub 2} in terms of direct transitions.

Strocov, V. N. [Swiss Light Source, Paul Scherrer Institute, CH-5232 Villigen PSI (Switzerland); Krasovskii, E. E. [Institut fuer Theoretische Physik, Christian-Albrechts-Universitaet, D-24098 Kiel (Germany); Schattke, W. [Institut fuer Theoretische Physik, Christian-Albrechts-Universitaet, D-24098 Kiel (Germany); Donostia International Physics Center, 20018 San Sebastian, Basque Country (Spain); Barrett, N. [CEA-DSM/DRECAM-SPCSI, CEA-Saclay, 91191 Gif-sur-Yvette (France); Berger, H. [Institut de Physique de la Matiere Complexe, EPFL, CH-1015 Lausanne (Switzerland); Schrupp, D. [Experimentalphysik II, Universitaet Augsburg, D-86135 Augsburg (Germany); Claessen, R. [Experimentalphysik II, Universitaet Augsburg, D-86135 Augsburg (Germany); Experimentelle Physik 4, Universitaet Wuerzburg, D-97074 Wuerzburg (Germany)

2006-11-15

440

Band structure of Al\\/Si\\/n-type GaAs with a strained Si interfacial layer  

Microsoft Academic Search

The band structure of a coherently strained Si layer (<15 Å) on GaAs has been calculated using the empirical pseudopotential method. The pseudopotential form factor of the strained Si layer is derived by considering that the pseudopotential of the strained layer is slightly modified by a factor which is proportional to the volume change of the unit cell. The band-structure

Z. Chen; S. N. Mohammad; H. Morkoç

1996-01-01