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1

Plasmonic band gap structures for surface-enhanced Raman scattering.  

PubMed

Surface-enhanced Raman Scattering (SERS) of rhodamine 6G (R6G) adsorbed on biharmonic metallic grating structures was studied. Biharmonic metallic gratings include two different grating components, one acting as a coupler to excite surface plasmon polaritons (SPP), and the other forming a plasmonic band gap for the propagating SPPs. In the vicinity of the band edges, localized surface plasmons are formed. These localized plasmons strongly enhance the scattering efficiency of the Raman signal emitted on the metallic grating surfaces. It was shown that reproducible Raman scattering enhancement factors of over 10(5) can be achieved by fabricating biharmonic SERS templates using soft nano-imprint technique. We have shown that the SERS activities from these templates are tunable as a function of plasmonic resonance conditions. Similar enhancement factors were also measured for directional emission of photoluminescence. At the wavelengths of the plasmonic absorption peak, directional enhancement by a factor of 30 was deduced for photoluminescence measurements. PMID:18711483

Kocabas, Askin; Ertas, Gulay; Senlik, S S; Aydinli, Atilla

2008-08-18

2

Band structure of surface states and resonances for clean Cu(1 1 0) surface  

NASA Astrophysics Data System (ADS)

We have used the layer KKR method to calculate the Shockley and Rydberg surface states and resonances for Cu(1 1 0) for a given model of the surface potentials. This method has not been used before to predict all of the surface band structure for the energy range from the bottom of the conduction band to ˜7 eV above the vacuum level. The previous methods that used only local electron interactions in ab initio calculations could not produce the Rydberg surface barrier bands while those relying on nearly-free-electron parameterisation of bands could not deal with d-bands.

Read, M. N.; Qiu, Q. Y.

2007-12-01

3

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.

2011-12-01

4

Influence of the surface band structure in photoelectron emission by ultra-short laser pulses  

NASA Astrophysics Data System (ADS)

Photoelectron emission from the valence band of aluminum and beryllium surfaces by ultra-short laser pulses is studied within the Band-Structure-Based - Volkov (BSB-V) approximation, which takes into account the contribution of the band structure of the solid. We found that band structure effects are extremely important for Be(0001), for which signatures of partially occupied surface states can be observed in the electron emission spectra.

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

2014-04-01

5

Ab initio electronic band structure study of the valence bands of II-VI C(2 × 2) reconstructed surfaces  

NASA Astrophysics Data System (ADS)

The structural and electronic properties of CdTe(001), CdSe(001), and ZnSe(001) C(2 x 2) reconstructed surfaces have been investigated through the use of first-principles calculations. To simulate the surface, we employed the slab model. Using the experimentally determined lattice parameters as inputs, we relaxed the internal atomic positions of the outer atomic layers. We demonstrate that our model appropriately reproduces both the surface structural parameters and the known electronic properties found for these semiconductor compounds in bulk. Finally, we discuss our results of the projected bulk bands and the surface and resonance states found for these surfaces.

Rubio-Ponce, A.; Olguín, D.

2015-01-01

6

Band-Structure Based model for photoelectron emission from metal surfaces  

NASA Astrophysics Data System (ADS)

Photoelectron emission spectra induced by grazing incidence of intense and ultrashort laser pulses on a metal surface are studied within a distorted-wave formalism. The proposed aproximation, named Band-Structure Based-Volkov (BSB-V) approach, includes a precise description of the surface potential, incorporating information of the band structure of the solid. Results are compared with the numerical solution of the time-dependent Schrodinger equation and with values derived from simpler theoretical models.

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

2012-11-01

7

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

8

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

SciTech Connect

The microwave response of an array of square metal patches and its complementary structure, an array of square holes, has been experimentally studied. The resonant phenomena, which yield either enhanced transmission or reflection, are attributed to the excitation of diffractively coupled surface waves. The band structure of these surface modes has been quantified for both p-(transverse magnetic) and s-(transverse electric) polarized radiation and is found to be dependent on the periodicity of the electric and magnetic fields on resonance. The results are in excellent accord with predictions from finite element method modeling and the electromagnetic form of Babinet's principle [Babinet, C. R. Acad. Sci. 4, 638 (1837)].

Edmunds, J. D.; Taylor, M. C.; Hibbins, A. P.; Sambles, J. R. [Electromagnetic Materials Group, School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL (United Kingdom); Youngs, I. J. [DSTL, Salisbury, SP4 0JQ (United Kingdom)

2010-05-15

9

Complexity of band structures: Semi-analytical finite element analysis of one-dimensional surface phononic crystals  

NASA Astrophysics Data System (ADS)

Band structures of surface phononic crystals with one-dimensional periodicity are investigated in this paper. Real and complex dispersion relations of surface acoustic waves are calculated by a semi-analytical finite element method in the frequency domain. The model applies 2D nine-noded elements in the periodic direction to discretize a unit cell with finite depth. Propagation perpendicular to the periodic direction is modeled by analytic functions. Two eigenproblems are obtained from the method which lead to real or to complex dispersion relations of the one-dimensional phononic crystal. The model results in a Lamb wave band structure where the surface modes are identified by their displacement and elastic energy distribution. The complex band structure includes imaginary and complex modes in addition to the real dispersion relation describing also standing and evanescent modes. Such evanescent waves not only include the folded surface waves, but it is also shown that an evanescent mode is present within the stop band.

Veres, Istvan A.; Berer, Thomas

2012-09-01

10

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

SciTech Connect

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

Zech, E. S.; Chang, A. S.; Martin, A. J.; Canniff, J. C.; Millunchick, J. M. [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States)] [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States); Lin, Y. H. [Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States)] [Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States); Goldman, R. S. [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States) [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States); Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States)

2013-08-19

11

Photocatalytic activity of ZnWO?: band structure, morphology and surface modification.  

PubMed

Photocatalytic degradation of organic contaminants is an important application area in solar energy utilization. To improve material photocatalytic properties, understanding their photocatalytic mechanism is indispensable. Here, the photocatalytic performance of ZnWO4 nanocrystals was systematicly investigated by the photodegradation of tetraethylated rhodamine (RhB) under simulated sunlight irradiation, including the influence of morphology, AgO/ZnWO4 heterojunction and comparison with CoWO4 nanowires. The results show that the photocatalytic activity of ZnWO4 is higher than that of CoWO4, and the ZnWO4 nanorods exhibit better photocatalytic activity than that of ZnWO4 nanowires. In addition, the mechanism for the difference of the photocatalytic activity was also investigated by comparison of their photoluminescence and photocurrents. AgO nanoparticles were assembled uniformly on the surface of ZnWO4 nanowires to form a heterojunction that exhibited enhanced photocatalytic activity under irradiation at the initial stage. We found that a good photocatalyst should not only have an active structure for electrons directly to transfer from the valence band to the conduction band without the help of phonons but also a special electronic configuration for the high mobility, to ensure more excited electrons and holes in a catalytic reaction. PMID:25121588

Zhang, Cuiling; Zhang, Hulin; Zhang, Kaiyou; Li, Xiaoyan; Leng, Qiang; Hu, Chenguo

2014-08-27

12

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

NASA Astrophysics Data System (ADS)

The electronic structure of the high-Tc 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-EF 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.

López Sancho, M. P.; Rubio, J.; Refolio, M. C.; López Sancho, J. M.

1995-09-01

13

Microstrip Meander-Line Slow Wave Structure Based on Electromagnetic Band Gap Surface  

Microsoft Academic Search

An electromagnetic band gap structures (EBGS) has been used in the Microstrip meander-line slow wave structures (MML-SWSs) in order to improve their performance. The EBGSs can be used as the substrates to support the MML-SWSs, which replace the ceramic substrates in traditional ones. The simulation results show that the minimum loss of the MML-SWSs used EBGS is half of the

Ningfeng Bai; Ming Xue; Xingqun Zhao; Chao Pan; Fujiang Liao; Xiaohan Sun

2009-01-01

14

Band structure engineering of monolayer MoS? by surface ligand functionalization for enhanced photoelectrochemical hydrogen production activity.  

PubMed

To achieve photoelectrochemical (PEC) activity of MoS2 for hydrogen production through water splitting, the band edges of MoS2 should match with the hydrogen and oxygen production levels. Our first-principles calculations show that the band edges of monolayer MoS2 can be effectively tuned by surface ligand functionalization, resulting from the intrinsic dipole of the ligand itself and the induced dipole at the ligand/MoS2 interface. We further explore the influence of ligand coverage, ligand functionalization and the substrate on the band structure of MoS2. The hybrid C6H5CH2NH2/MoS2/graphene structures may be compelling candidates as they satisfy the stringent requirements of PEC water splitting. PMID:25268589

Pan, Jing; Wang, Zilu; Chen, Qian; Hu, Jingguo; Wang, Jinlan

2014-11-21

15

Band structure engineering of monolayer MoS2 by surface ligand functionalization for enhanced photoelectrochemical hydrogen production activity  

NASA Astrophysics Data System (ADS)

To achieve photoelectrochemical (PEC) activity of MoS2 for hydrogen production through water splitting, the band edges of MoS2 should match with the hydrogen and oxygen production levels. Our first-principles calculations show that the band edges of monolayer MoS2 can be effectively tuned by surface ligand functionalization, resulting from the intrinsic dipole of the ligand itself and the induced dipole at the ligand/MoS2 interface. We further explore the influence of ligand coverage, ligand functionalization and the substrate on the band structure of MoS2. The hybrid C6H5CH2NH2/MoS2/graphene structures may be compelling candidates as they satisfy the stringent requirements of PEC water splitting.To achieve photoelectrochemical (PEC) activity of MoS2 for hydrogen production through water splitting, the band edges of MoS2 should match with the hydrogen and oxygen production levels. Our first-principles calculations show that the band edges of monolayer MoS2 can be effectively tuned by surface ligand functionalization, resulting from the intrinsic dipole of the ligand itself and the induced dipole at the ligand/MoS2 interface. We further explore the influence of ligand coverage, ligand functionalization and the substrate on the band structure of MoS2. The hybrid C6H5CH2NH2/MoS2/graphene structures may be compelling candidates as they satisfy the stringent requirements of PEC water splitting. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr02829e

Pan, Jing; Wang, Zilu; Chen, Qian; Hu, Jingguo; Wang, Jinlan

2014-10-01

16

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

17

Effects of strain, d-band filling, and oxidation state on the surface electronic structure and reactivity of 3d perovskite surfaces.  

PubMed

Trends in the dissociative oxygen adsorption energy and oxygen vacancy formation energy on cubic LaBO(3) and SrBO(3) perovskite (001) surfaces (where B = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) and their dependence on strain, d-band filling, and oxidation state were examined using density functional theory in the generalized gradient approximation. The effects of strain were found to be small compared to the effects of d-band filling and oxidations state. Electronic structure descriptors such as the d-band center of the B-atom were identified for trends in the dissociative oxygen adsorption energy and for the oxygen vacancy formation energy. A chemical correlation between these two reaction energies was also identified showing the trends in these reaction energies are not independent of each other. PMID:22938255

Akhade, Sneha A; Kitchin, John R

2012-08-28

18

Band structure of bcc cobalt  

Microsoft Academic Search

A self-consistent density-functional band-structure calculation using linear combinations of Gaussian orbitals for bcc cobalt has been performed. Also determined were the Fermi surface and x-ray form factors to make possible comparison with measurements on a film of bcc cobalt on chromium recently prepared by Walmsley et al. of Stanford University. The calculation was performed for several lattice parameters, including the

D. Bagayoko; A. Ziegler; J. Callaway

1983-01-01

19

Characteristics of band structure and surface plasmons supported by a one-dimensional graphene-dielectric photonic crystal  

NASA Astrophysics Data System (ADS)

We theoretically investigate characteristics of TM projected band structure and of surface plasmons (SPs) supported by a one-dimensional graphene-dielectric photonic crystal (1D GPC). It is concluded that in addition to supporting structural and graphene absorption bandgaps, both coupled and pure SPs can be supported by the 1D GPC. To be tunable by the electrical gating and having higher localization and larger propagation length are remarkable advantages of pure SPs supported by the 1D GPC, as compared to ones supported by a 1D metallic PC. On one hand, using graphene disks instead of graphene sheets in the 1D GPC, besides supporting SPs in larger frequency range, causes widening bandgaps. Therefore, it increases the far-IR filtering characteristics of the structure. On the other hand, the decrease in width of dielectric layers causes widening graphene absorption bandgaps and also the frequency range of supported SPs. Moreover, this decrease enables the structure to support pure SPs with higher localization and longer length of propagation.

Hajian, H.; Soltani-Vala, A.; Kalafi, M.

2013-04-01

20

Many-body band structure and Fermi surface of the Kondo lattice  

Microsoft Academic Search

We present a theory for the single-particle excitations and Fermi surface of the Kondo lattice. Thereby we construct an effective Hamiltonian describing the creation and propagation of single-particle-like charge fluctuations on a ``resonating-valence-bond background'' of local singlets. The theory may be viewed as a Fermionic version of linear spin-wave theory and is of comparable simplicity so that the calculations for

R. Eder; O. Rogojanu; G. A. Sawatzky

1998-01-01

21

BAND STRUCTURE OF GRAPHITE  

Microsoft Academic Search

Tight-binding calculations, using a two-dimensional model of the ; graphite lattice, lead to a point of contact of of valence and conduction bands ; at the corner of the reduced Brillouin zone. A perturbation calculation which ; starts with wave functions of the two-dimensional lattice and is applied to the ; three-dimensional lattice is described. Some general features of the

J. C. Slonczewski; P. R. Weiss

1958-01-01

22

Area dependence of femtosecond laser-induced periodic surface structures for varying band gap materials after double pulse excitation  

NASA Astrophysics Data System (ADS)

The formation of laser-induced periodic surface structures upon irradiation of titanium, silicon, and fused silica with multiple irradiation sequences consisting of parallel polarized Ti:sapphire femtosecond laser pulse pairs (pulse duration 50-150 fs, central wavelength ˜800 nm) is studied experimentally. The temporal delay between the individual near-equal energy fs-laser pulses was varied between 0 and 5 ps with a temporal resolution of better than 0.2 ps. The surface morphology of the irradiated surface areas is characterized by means of scanning electron microscopy (SEM). In all materials a decrease of the rippled surface area is observed for increasing delays. The characteristic delay decay scale is quantified and related to material dependent excitation and energy relaxation processes.

Höhm, S.; Rosenfeld, A.; Krüger, J.; Bonse, J.

2013-08-01

23

Band structures in 99Rh  

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

24

On the adsorption site of ethylene at the Ni(110) surface: a combined experimental and theoretical study involving the unoccupied band structure  

NASA Astrophysics Data System (ADS)

The adsorption of ethylene on Ni(110) was investigated by angle resolved inverse photoemission (ARIPE) spectroscopy as well as by detailed density functional model cluster and slab model band structure calculations to clarify the preferred adsorption site. Cluster model calculations both at the local density as well as at the gradient corrected level of theory gave a slight preference for the di-? over the ? coordinated geometry on top of the ridges, but no or, at best, a very weak binding over the troughs. A dispersionless band in the ARIPE spectra about 1.8 eV above EF is assigned to the band derived from the lowest unoccupied ethylene orbital, 1b 3g(??). The surface state feature of the clean Ni(110) surface connecting the image state at ¯gG and the d yz state S 2 lowered almost uniformly by 0.8 eV through the interaction with the adsorbate. For adsorption on top of the ridges in the so-called "half-bridge" position intermediate between the short bridge (di-?) and the top site (?), the symmetry requirements imposed by the surface state band are ideally met by the second lowest unoccupied band of the adsorbate monolayer which changes its character from ethylene 4a g at ?' to 2b 3u at Y'. A similarly strong and uniform interaction is not possible when ethylene adsorbs above the troughs. Taking all experimental and theoretical evidence together, the adsorption site in the densely packed c(2×4) C 2H 4Ni(110) adsorption system is identified as the half-bridge position on top of the ridges.

Gutdeutsch, U.; Birkenheuer, U.; Bertel, E.; Cramer, J.; Boettger, J. C.; Rösch, N.

1996-01-01

25

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

E-print Network

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

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

2002-01-01

26

High-impedance electromagnetic surfaces with a forbidden frequency band  

Microsoft Academic Search

A new type of metallic electromagnetic structure has been developed that is characterized by having high surface impedance. Although it is made of continuous metal, and conducts dc currents, it does not conduct ac currents within a forbidden frequency band. Unlike normal conductors, this new surface does not support propagating surface waves, and its image currents are not phase reversed.

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

1999-01-01

27

QM theory of Solids: Band structures, bonding,  

E-print Network

with electron "filling". · The band structure is determined by the lattice and atomic structure. · PrimarilyQM theory of Solids: Part I Band structures, bonding, Fermions Fig 4.1 From Principles now develop a QM theory of solids. · We deal with crystals (otherwise too difficult) · Band structure

Smy, Tom

28

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

PubMed

We theoretically and experimentally demonstrate the existence of complete surface acoustic wave band gaps in surface phonon-polariton phononic crystals, in a completely monolithic structure formed from a two-dimensional honeycomb array of hexagonal shape domain-inverted inclusions in single crystal piezoelectric Z-cut lithium niobate. The band gaps appear at a frequency of about twice the Bragg band gap at the center of the Brillouin zone, formed through phonon-polariton coupling. The structure is mechanically, electromagnetically, and topographically homogeneous, without any physical alteration of the surface, offering an ideal platform for many acoustic wave applications for photonics, phononics, and microfluidics. PMID:25479504

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

2014-11-21

29

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

E-print Network

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

Xue, Ming

30

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

31

Band Structures in ^230Th  

NASA Astrophysics Data System (ADS)

Experimental evidence for the recently proposed phenomenon of condensation of rotational-aligned octupole phonons [1] has been observed in ^240Pu [2] and ^238U [3]. In order to study this phenomenon in ^230Th, an experiment has been carried out at ATLAS. The octupole band was extended up to spin 29. In addition, three positive-parity bands were observed for the first time. With increasing spin, the octupole band and the ground state band (gsb) start forming a smooth sequence of states with alternating spin and parity. Furthermore, the Routhian of the octupole band becomes lower than that of the gsb at rotational frequencies above 0.24 MeV. A band built on the second 0^+ state at 567 keV was discovered in this experiment, but it decays only to the gsb. [1] S. Frauendorf, Phys. Rev. C 77, 021304(R) (2008), [2] X. Wang et al., Phys. Rev. Lett. 102, 122501 (2009), [3] S. Zhu et al., Phys. Rev. C 81, 041306(R) (2010). This work was supported by DOE, Office of Nuclear Physics, under Contract No. DE-AC02-06CH11357.

Janssens, R. V. F.; Zhu, S.; Carpenter, M. P.; Ahmad, I.; Hoffman, C. R.; Khoo, T. L.; Kay, B. P.; Kondev, F. G.; Lauritsen, T.; Lister, C. J.; Ricard-McCutchan, E. A.; Seweryniak, D.; Toh, Y.; Ayangeakaa, D.; Frauendorf, S.; Garg, U.; Patel, D.; Matta, J.; Reviol, W.; Sarantites, D. G.; Wang, X.; Lalkovski, S.

2011-10-01

32

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

SciTech Connect

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

Tsoutsou, D., E-mail: dtsoutsou@ims.demokritos.gr; Xenogiannopoulou, E.; Golias, E.; Tsipas, P.; Dimoulas, A. [National Center for Scientific Research “Demokritos,” 15310 Athens (Greece)] [National Center for Scientific Research “Demokritos,” 15310 Athens (Greece)

2013-12-02

33

Experimental band structure of semimetal bismuth  

Microsoft Academic Search

Angle-resolved photoemission measured from the Bi(111) surface with synchrotron radiation between 7.5 and 100 eV exhibit strong features associated with valence-band states of p and s symmetry and electronic surface states. The valence-band dispersions of p and s states have been measured along the symmetry line GammaLambdaT of the Brillouin zone, which is mapped out by recording normal emission at

G. Jezequel; J. Thomas; I. Pollini

1997-01-01

34

Inter-band Tunneling between Doped Topological Insulator Surface States  

NASA Astrophysics Data System (ADS)

Thin films of 3D topological insulators (TIs) have been experimentally synthesized recently. Impurity doping of the TI surface has been reported to modify the position of the Fermi level and generate Rashba-like splitting of the surface band structure. Our research uses a Non-Equilibrium Green's Function (NEGF) method to simulate inter-surface transport properties for TI thin films. A tight-binding model is established by discretizing a 4 x 4 k.p Hamiltonian for 3D TIs. Because of confinement, thin TI slabs of several nanometers allows inter-surface tunneling at quantum number matching states. The tunneling intensity can be tuned by surface Coulomb impurity doping or applying an external bias. Unlike regular topologically trivial surface states, inter-band tunneling between TI surfaces presents a conduction minimum when the dispersions of the two surfaces align perfectly over each other. The suppression of transport originates from the momentum coupling with time reversal symmetry, leading to significant non-linear I-V properties for the P-N tunneling at forward bias. This leads to a NDR current minimum when an external bias completely compensates the built-in potential. The study on inter-surface tunneling in TI thin films benefits the understanding of the transport behavior of TI surface states, which calls for further experimental investigations in the future.

Yin, Gen; Wickramaratne, Darshana; Lake, Roger

2012-02-01

35

Quasiparticle band structure of HgSe  

SciTech Connect

Motivated by a recent discussion about the existence of a fundamental gap in HgSe [Phys. Rev. Lett. {bold 78}, 3165 (1997)], we calculate the quasiparticle band structure of HgSe within the GW approximation for the electron self-energy. The band-structure results show that HgSe is a semimetal, which is in agreement with most experimental data. We observe a strong wave-vector dependence of the self-energy of the lowest conduction band, leading to an increased dispersion and a small effective mass. This may help to interpret recent photoemission spectroscopy measurements. {copyright} {ital 1998} {ital The American Physical Society}

Rohlfing, M.; Louie, S.G. [Department of Physics, University of California, Berkeley, California94720-7300] [Department of Physics, University of California, Berkeley, California94720-7300; [Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California94720 (United States)

1998-04-01

36

K-band Surface Photometry of the Circinus galaxy  

NASA Astrophysics Data System (ADS)

NIR K-band mosaic and optical B and I-band images of the Circinus galaxy (SA(s)b, 4 Mpc) were taken to study the large-scale structure and the dust opacity. The K-band mosaic image, covering ~ 10.5' x 4.5' , is the first full-coverage K-band image ever taken for this galaxy. 315 image frames were combined to produce the final mosaic with a total integration time of 15 mins/pixel. With very low dust extinction, this astonishing image clearly reveals the large-scale spiral arms at 220" radius, and a nuclear ring or nuclear spiral sturcture at 15" radius. Although not very distinctive, the oval-shaped bar resides at ~ 50" radius. We will present the first K-band surface photometry results for the Circinus galaxy. OKP acknowledges the financial support as scholarships funded by the Australian National University and the Department of Employment, Education, Training and Youth Affairs (DEETYA) of Australia.

Park, O.-K.; Freeman, K. C.

2000-12-01

37

X-Band Structure Development at KEK  

NASA Astrophysics Data System (ADS)

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

Higo, Toshiyasu

2015-10-01

38

Band structure engineering in topological insulator based heterostructures.  

PubMed

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

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

2013-01-01

39

Band structure of indium oxide: Indirect versus direct band gap  

Microsoft Academic Search

The nature of the band gap of indium oxide is still a matter of debate. Based on optical measurements the presence of an indirect band gap has been suggested, which is 0.9 to 1.1eV smaller than the direct band gap at the Gamma point. This could be caused by strong mixing of O2p and In4d orbitals off Gamma . We

Paul Erhart; Andreas Klein; Russell G. Egdell; Karsten Albe

2007-01-01

40

Photocatalytic H2 evolution reaction from aqueous solutions over band structure-controlled (AgIn)xZn2(1-x)S2 solid solution photocatalysts with visible-light response and their surface nanostructures.  

PubMed

(AgIn)(x)Zn(2(1-x))S(2) solid solutions between ZnS photocatalyst with a wide band gap and AgInS(2) with a narrow band gap showed photocatalytic activities for H(2) evolution from aqueous solutions containing sacrificial reagents, SO(3)(2)(-) and S(2)(-), under visible-light irradiation (lambda >or= 420 nm) even without Pt cocatalysts. Loading of the Pt cocatalysts improved the photocatalytic activity. Pt (3 wt %)-loaded (AgIn)(0.22)Zn(1.56)S(2) with a 2.3 eV band gap showed the highest activity for H(2) evolution, and the apparent quantum yield at 420 nm amounted to 20%. H(2) gas evolved at a rate of 3.3 L m(-2) x h(-1) under irradiation using a solar simulator (AM 1.5). The diffuse reflection and the photoluminescence spectra of the solid solutions shifted monotonically to a long wavelength side as the ratio of AgInS(2) to ZnS increased in the solid solutions. The photocatalytic H(2) evolution depended on the compositions as well as the photophysical properties. The dependence of the photophysical and photocatalytic properties upon the composition was mainly due to the change in the band position caused by the contribution of the Ag 4d and In 5s5p orbitals to the valence and conduction bands, respectively. It was found from SEM and TEM observations that the solid solutions partially had nanostep structures on their surfaces. The Pt cocatalysts were selectively photodeposited on the edge of the surface nanosteps. It was suggested that the specific surface nanostructure was effective for the suppression of recombination between photogenerated electrons and holes and for the separation of H(2) evolution sites from oxidation reaction sites. PMID:15479097

Tsuji, Issei; Kato, Hideki; Kobayashi, Hisayoshi; Kudo, Akihiko

2004-10-20

41

Investigation of surface oxides on aluminum alloys by valence band photoemission  

NASA Astrophysics Data System (ADS)

Core level and valence band x-ray photoelectron spectroscopy are used to study the chemical composition of the surface films on aluminum alloys. Certain alloying elements may preferentially migrate to the surface of an alloy, thereby altering the composition and consequently the chemistry of the surface. The behavior of a 6061 aluminum alloy is compared with that of pure aluminum. It is shown that the type of magnesium film formed at the alloy surface can be determined by comparing the valence band spectra of the aluminum alloy surface with that of known magnesium and aluminum compounds. The experimental valence band spectra of these compounds are supported by spectra generated from band structure calculations. The effect of boiling water on the surface film is discussed, with significant differences in surface chemistry being seen for the metal and the alloy. copyright 2002 American Vacuum Society.

Claycomb, Gregory D.; Sherwood, Peter M. A.

2002-07-01

42

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

2010-06-25

43

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

44

Surface effects and band measurements in photonic crystals  

NASA Astrophysics Data System (ADS)

An analytic study of Bloch waves near photonic crystal surfaces has been carried out. This is a generalization of Heine's theory of metal/semiconductor interfaces. The main concern of this study is how the surfaces of a finite system affect band determination-which usually involves transmission measurements on small photonic crystals. An analytic expression for transmission is obtained. The results show that the usual band measurements could lead to considerable errors, especially when they involve narrow band gaps. A possible method to improve band measurements has been suggested. The analytic surface analysis has been demonstrated to be fairly accurate, even for a small system. The theory is expected to be applicable to other surface-related problems of photonic systems.

Shung, Kenneth W.-K.; Tsai, Y. C.

1993-10-01

45

Micromechanics of slip bands on a free surface  

NASA Technical Reports Server (NTRS)

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

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

1976-01-01

46

Elementary energy bands in the band structure of the narrow-band-gap semiconductor CdSb  

NASA Astrophysics Data System (ADS)

Based upon the example of a narrow band gap covalent CdSb crystal (D2h16) , it is shown that a spatial electron density distribution in the unit cell is related to the Zak’s elementary energy bands creating the valence band and to the corresponding Wyckoff positions. A role of particular electronic states in the creation of the elementary energy bands was analyzed by conducting ab initio band structure calculations of CdSb. The investigations of the topology of the elementrary energy bands allows one to predict the nature of chemical bondings in rhombic crystals.

Bercha, D. M.; Slipukhina, I. V.; Sznajder, M.; Rushchanskii, K. Z.

2004-12-01

47

Multiple band structures in {sup 169}Ta  

SciTech Connect

Rotational structures in the {sup 169}Ta nucleus were studied via the {sup 124}Sn({sup 51}V, 6n) reaction. These data were obtained as a side channel of an experiment focusing on {sup 171}Ta, but the sensitivity provided by the Gammasphere spectrometer proved sufficient for a significant extension of the level scheme of this rare-earth nucleus. Over 170 new transitions and four new band structures were placed in {sup 169}Ta, including the intruder {pi}i{sub 13/2} structure. Linking transitions between all of the sequences were identified, and the relative excitation energies between the different configurations were determined for the first time. The rotational sequences were interpreted within the framework of the cranked shell model.

Hartley, D. J.; Mohr, W. H.; Vanhoy, J. R.; Riley, M. A.; Aguilar, A.; Teal, C.; Janssens, R. V. F.; Carpenter, M. P.; Hecht, A. A.; Lauritsen, T.; Moore, E. F.; Zhu, S.; Kondev, F. G.; Djongolov, M. K.; Danchev, M.; Riedinger, L. L.; Hagemann, G. B.; Sletten, G.; Chowdhury, P.; Tandel, S. K. [Department of Physics, U.S. Naval Academy, Annapolis, Maryland 21402 (United States); Department of Physics, Florida State University, Tallahassee, Florida 32306 (United States); Physics Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Nuclear Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996 (United States); Niels Bohr Institute, Blegdamsvej 17, DK-2100 Copenhagen (Denmark); Department of Physics, University of Massachusetts Lowell, Lowell, Massachusetts 01854 (United States); Department of Physics, Mississippi State University, Mississippi State, Mississippi 39762 (United States); Department of Physics, University of Oslo, PB 1048 Blindern, N-0316 Oslo (Norway)] (and others)

2006-11-15

48

Effects of d-band shape on the surface reactivity of transition-metal alloys  

NASA Astrophysics Data System (ADS)

The d-band shape of a metal site, governed by the local geometry and composition of materials, plays an important role in determining trends of the surface reactivity of transition-metal alloys. We discuss this phenomenon using the chemisorption of various adsorbates such as C, N, O, and their hydrogenated species on Pd bimetallic alloys as an example. For many alloys, the d-band center, even with consideration of the d-band width and sp electrons, can not describe variations in reactivity from one surface to another. We investigate the effect of the d-band shape, represented by higher moments of the d band, on the local electronic structure of adsorbates, e.g., energy and filling of adsorbate-metal antibonding states. The upper d-band edge ?u, defined as the highest peak position of the Hilbert transform of the density of states projected onto d orbitals of an active metal site, is identified as an electronic descriptor for the surface reactivity of transition metals and their alloys, regardless of variations in the d-band shape. The utilization of the upper d-band edge with scaling relations enables a considerable reduction of the parameter space in search of improved alloy catalysts and further extends our understanding of the relationship between the electronic structure and chemical reactivity of metal surfaces.

Xin, Hongliang; Vojvodic, Aleksandra; Voss, Johannes; Nørskov, Jens K.; Abild-Pedersen, Frank

2014-03-01

49

Design of Dual-Band Dual-Polarized Antenna with Frequency Selective Surface Cover and Artificial Impedance Surface  

E-print Network

Design of Dual-Band Dual-Polarized Antenna with Frequency Selective Surface Cover and Artificial with dual polarizations in one antenna structure. Moreover, resonant frequency is controllable by changing the antenna performances by preventing surface wave or using as a reflector that acts like magnetic conductor

Nam, Sangwook

50

Robust one-dimensional metallic band structure of silicide nanowires.  

PubMed

Angle-resolved photoemission (ARP) is employed to investigate the electronic structure of an extremely anisotropic form of nanocrystals--GdSi(2-x) nanowires on Si(100). Using a stepped Si(100) surface, a well-ordered and uniformly oriented array of nanowires is formed along the step edges as confirmed by diffraction and microscopy. The ARP measurement discloses two distinct electronic bands near the Fermi level, which disperse one dimensionally along the nanowires. These bands are metallic with the electron filling of 1/4 and 2/5, respectively, and with the effective mass close to that of a free electron along the wires. The metallicity is robust down to 20 K, in contrast to metallic surface atomic chain systems, paving a way to further studies on one-dimensional physics of metallic nanowires. PMID:16384071

Yeom, H W; Kim, Y K; Lee, E Y; Ryang, K-D; Kang, P G

2005-11-11

51

Elucidating the stop bands of structurally colored systems through recursion  

NASA Astrophysics Data System (ADS)

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

Amir, Ariel; Vukusic, Peter

2013-04-01

52

Segmental structure in banded mongoose calls  

PubMed Central

In complex animal vocalizations, such as bird or whale song, a great variety of songs can be produced via rearrangements of a smaller set of 'syllables', known as 'phonological syntax' or 'phonocoding' However, food or alarm calls, which function as referential signals, were previously thought to lack such combinatorial structure. A new study of calls in the banded mongoose Mungos mungo provides the first evidence of phonocoding at the level of single calls. The first portion of the call provides cues to the identity of the caller, and the second part encodes its current activity. This provides the first example known in animals of something akin to the consonants and vowels of human speech. See research article http://www.biomedcentral.com/1741-7007/10/97 PMID:23206277

2012-01-01

53

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

54

The Three-Dimensional Structure of the Zodiacal Dust Bands  

NASA Astrophysics Data System (ADS)

Using observations of the infrared sky brightness by the Cosmic Background Explorer (COBE) 1Diffuse Infrared Background Experiment (DIRBE) and Infrared Astronomical Satellite (IRAS), we have created maps of the surface brightness Fourier-filtered to suppress the smallest (< 1°) structures and the large-scale background (>15°). Dust bands associated with the Themis, Koronis, and Eos families are readily evident. A dust band associated with the Maria family is also present. The parallactic distances to the emitting regions of the Koronis, Eos, and Maria dust bands were found to be 1.4 to 2.5 AU. A weak dust band associated with the Eunomia/Io family is evident, together with another weak and previously unattributed dust band, which may split further into two band pairs, potentially associated with the Hygiea or Vesta family. The brightnesses of the blended Themis/Koronis bands and the Eos dust band vary with ecliptic longitude, such that the northern or southern component of the band pair becomes brighter when its tilt brings it into the ecliptic plane. We attribute the brightness variations to the motion of the Earth within the emitting region, and conclude that at least some dust-band particles are on Earth-crossing orbits. For the Themis and Koronis families, the tilt is sufficient that the Earth may pass to the edges of the emitting region, where the density is highest, leading to "glints" two or four times a year. We compared the observed distributions to theoretically motivated, empirical models for the three-dimensional distribution of asteroid family dust. In the torus model, the dust is distributed among the asteroid family members with the same distributions of proper orbital inclination and semimajor axis but a random ascending node. In the migrating model, particles are presumed to be under the influence of Poynting-Robertson drag, so that they are distributed throughout the inner Solar System. The migrating model is better able to match the parallactic variation of dust-band latitude as well as the 12- to 60-?m spectrum of the dust bands. The annual brightness variations can be explained only by the migrating model. Upper limits are placed on the dust density associated with the Nysa and Flora families—both of the large, inner-belt families with wide inclination dispersions. The association of five (and potentially seven) dust bands with the largest asteroid families suggests that dust bands are an integral part of asteroid families. If nonfamily asteroids produce dust at a rate similar to that of the families with the lowest dust density, then they can account for the brightness of the zodiacal light in the ecliptic. The National Aeronautics and Space Administration/Goddard Space Flight Center (NASA/GSFC) is responsible for the design, development, and operation of the Cosmic Background Explorer (COBE). Scientific guidance is provided by the COBE Science Working Group. GSFC is also responsible for the development of the analysis software and for the production of the mission data sets.

Reach, William T.; Franz, Bryan A.; Weiland, Janet L.

1997-06-01

55

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

PubMed

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

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

2014-12-10

56

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

NASA Astrophysics Data System (ADS)

In three-dimensional numerical simulations of a rapidly rotating Boussinesq fluid shell, thermally driven convection in the form of columns parallel to the rotation axis generates an alternately directed mean zonal flow with a cylindrical structure. The mean structure at the outer spherical surface consists of a broad eastward flow at the equator and alternating bands of westward and eastward flows at higher latitudes in both hemispheres. The banded structure persists even though the underlying convective motions are time-dependent. These results, although still far from the actual motions seen on Jupiter and Saturn, provide support for theoretical suggestions that thermal convection can account for the remarkable banded flow structures on these planets.

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

1993-04-01

57

BAND STRUCTURE AND OPTICAL PROPERTIES OF MAGNESIUM FLUORIDE  

E-print Network

595 BAND STRUCTURE AND OPTICAL PROPERTIES OF MAGNESIUM FLUORIDE C. JOUANIN, J. P. ALBERT and C'autres transitions expéri- mentales. Abstract. 2014 The electronic band structure of magnesium fluoride is calculated, only some qualitative investigations exist for the calcium and magnesium fluorides [1, 2]. This lack

Paris-Sud XI, Université de

58

Multi-band circular polarizer using planar spiral metamaterial structure.  

PubMed

A multi-band circular polarizer is proposed by using multi layered planar spiral metamaterial structure in analogy with classic spiral antenna. At three distinct resonant frequencies, the incident linearly polarized wave with electric field paralleling to one specific direction is transformed into left/right-handed circularly polarized waves through electric field coupling. Measured and simulated results show that right-handed circularly polarized wave is produced at 13.33 GHz and 16.75 GHz while left-handed circularly polarized wave is obtained at 15.56 GHz. The surface current distributions are studied to investigate the transformation behavior for both circular polarizations. The relationship between the resonant positions and the structure parameters is discussed as well. PMID:22772295

Ma, Xiaoliang; Huang, Cheng; Pu, Mingbo; Hu, Chenggang; Feng, Qin; Luo, Xiangang

2012-07-01

59

Three-dimensional simulation of a Ka-band relativistic Cherenkov source with metal photonic-band-gap structures  

NASA Astrophysics Data System (ADS)

This paper presents a three-dimensional particle-in-cell (PIC) simulation of a Ka-band relativistic Cherenkov source with a slow wave structure (SWS) consisting of metal photonic band gap (PBG) structures. In the simulation, a perfect match layer boundary is employed to absorb passing band modes supported by the PBG lattice with an artificial metal boundary. The simulated axial field distributions in the cross section and surface of the SWS demonstrate that the device operates in the vicinity of the ? point of a TM01-like mode. The Fourier transformation spectra of the axial fields as functions of time and space show that only a single frequency appears at 36.27 GHz, which is in good agreement with that of the intersection of the dispersion curve with the slow space charge wave generated on the beam. The simulation results demonstrate that the SWS has good mode selectivity.

Gao, Xi; Yang, Zi-Qiang; Qi, Li-Mei; Lan, Feng; Shi, Zong-Jun; Li, Da-Zhi; Liang, Zheng

2009-06-01

60

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

61

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

NASA Astrophysics Data System (ADS)

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 Yb4f -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 Yb5d band with the Ag5p and In5p 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.; Cui, C.; Shimoda, M.; McGrath, R.; Tsai, A. P.; Ishii, Y.

2010-03-01

62

Elasticity, band structure, and piezoelectricity of Be x Zn 1? x O alloys  

Microsoft Academic Search

Lattice constants, elasticity, band structure and piezoelectricity of hexagonal wide band gap BexZn1?xO ternary alloys are calculated using first-principles methods. The alloys' lattice constants obey Vegard's law well. As Be concentration increases, the bulk modulus and Young's modulus of the alloys increase, whereas the piezoelectricity decreases. We predict that BexZn1?xO\\/GaN\\/substrate (x=0.022) multilayer structure can be suitable for high-frequency surface acoustic

Yifeng Duan; Hongliang Shi; Lixia Qin

2008-01-01

63

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

Microsoft Academic Search

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

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

2010-01-01

64

Formation of Deformation Band Structures Normal to the Shear Plane  

NASA Astrophysics Data System (ADS)

Recent fieldwork has shown that many of the geometric relationships previously observed in cataclastic deformation bands are based on a two dimensional view of a three dimensional structure. When the bands are viewed in the shear direction lenses and inosculating bands are seen, as first noted by Aydin [1978] and later by many others. When viewed normal to the shear direction "ladder structures" (linked mode II echelon stepovers or duplexes) and conjugate structures are seen [Davis, 1999]. Davis [1999] grouped these two geometries as different classes of deformation bands and many have interpreted the duplexes as strain localization in Riedel shear zones. Here we demonstrate an alternative explanation. When viewed normal to the shear direction, deformation bands display either mutually crosscutting ("conjugate") sets or contractional stepovers ("duplexes") between interacting mode-II bands. Our field observations reveal that the principal difference between the two is the relative distance separating the parallel echelon bands. Bands that are sufficiently close interact mechanically to promote linking bands within the stepovers. These linking bands are younger than the bounding echelon bands. Because the orientations of bands within the stepovers are the same as that of "conjugate" bands that are more widely spaced, we infer that the magnitude of stress within the stepovers was increased somewhat over background values, but that stress rotations within the stepovers were negligible. To accomplish this, the echelon deformation bands must be strong relative to the host rock and accommodate only small offsets, leading to only minor perturbations of the local stress state in their vicinity. Ladder structure, "radiator rock" [Davis, 1999], and linked echelon stepovers demonstrate a progression from distributed to more localized strain of the sandstone, with the scale dependent on the size and offset magnitude of individual bands. Occurrence of linked echelon stepovers along both conjugate directions in spaced arrays argues against Riedel shearing as a mechanism for localizing this class of deformation bands. Aydin, A., Small Faults Formed as Deformation Bands in Sandstone, Pure and Applied Geophysics, 116, 913-930, 1978 Davis, G., Structural Geology of the Colorado Plateau Region of Southern Utah: With Special Emphasis on Deformation Bands, GSA Special Paper 342, 157 pp., 1999

Balasko, C. M.; Schultz, R. A.

2001-12-01

65

Interaction effects on almost flat surface bands in topological insulators  

NASA Astrophysics Data System (ADS)

We consider ferromagnetic instabilities of two-dimensional helical Dirac fermions hosted on the surface of three-dimensional topological insulators. We investigate ways to increase the role of interactions by means of modifying the bulk properties which in turn changes both the surface Dirac theory and the screening of interactions. We discuss both the long-ranged part of the Coulomb interactions controlled by the dimensionless coupling constant ?=e2/(??vFsurf) as well as the effects of local interactions parametrized by the ratio Usurf/Dsurf of a local interaction on the surface Usurf and the surface bandwidth Dsurf. If large compared to 1, both mechanisms can induce spontaneously surface ferromagnetism, thereby gapping the surface Dirac metal and inducing an anomalous quantum Hall effect. We investigate two mechanisms which can naturally lead to small Fermi velocities vFsurf and a corresponding small bandwidth Dsurf at the surface when the bulk band gap is reduced. The same mechanisms can, however, also lead to an enhanced screening of surface interactions. While in all considered cases the long-ranged part of the Coulomb interaction is screened efficiently, ??1, we discuss situations where Usurf/Dsurf becomes parametrically large compared to 1, thus inducing surface magnetism.

Sitte, Matthias; Rosch, Achim; Fritz, Lars

2013-11-01

66

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

SciTech Connect

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

Mäkinen, A. J., E-mail: Antti.Makinen@nrl.navy.mil; Kim, Chul-Soo; Kushto, G. P. [Naval Research Laboratory, 4555 Overlook Avenue, Washington, DC 20375 (United States)

2014-01-27

67

A novel double-layer semi-circle fractal multi-band frequency selective surface  

Microsoft Academic Search

In this paper, a novel double-layer frequency selective surface (FSS) is proposed. Each layer consists of two semi-circle fractal elements put into a circular structure on a dielectric substrate. Simulation by CST MICROWAVE STUDIO® is conducted to testify the characteristics of the FSS. The results show that the novel structure has three resonant frequencies in the frequency band 0-30GHz with

Tong Zhang; Guo-hui Yang; Wan-lu Li; Qun Wu

2010-01-01

68

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

69

Elementary energy bands in band structure calculations of some wide-bandgap crystals  

NASA Astrophysics Data System (ADS)

Semiconducting Tl3AsS4 crystal was chosen as an example to show that its valence band is composed of the elementary energy bands. Their topology and symmetry obtained in the empty-lattice approximation is confirmed by ab initio band structure calculations. It was shown that these elementary energy bands correspond to the Wyckoff position c in a unit cell. Earlier predictions that the largest electron density distribution is focused in the vicinity of this position, similarly to the case of YAlO3 and SbSI crystals, is confirmed. A conclusion on the common topology and symmetry of the elementary energy bands in electronic and phonon spectra is presented.

Sznajder, M.; Bercha, D. M.; Rushchanskii, K. Z.

2004-01-01

70

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

71

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

PubMed

Surfaces of semiconductors with strong spin-orbit coupling are of great interest for use in spintronic devices exploiting the Rashba effect. BiTeI features large Rashba-type spin splitting in both valence and conduction bands. Either can be shifted towards the Fermi level by surface band bending induced by the two possible polar terminations, making Rashba spin-split electron or hole bands electronically accessible. Here we demonstrate the first real-space microscopic identification of each termination with a multi-technique experimental approach. Using spatially resolved tunnelling spectroscopy across the lateral boundary between the two terminations, a previously speculated on p-n junction-like discontinuity in electronic structure at the lateral boundary is confirmed experimentally. These findings realize an important step towards the exploitation of the unique behaviour of the Rashba semiconductor BiTeI for new device concepts in spintronics. PMID:24898943

Butler, Christopher John; Yang, Hung-Hsiang; Hong, Jhen-Yong; Hsu, Shih-Hao; Sankar, Raman; Lu, Chun-I; Lu, Hsin-Yu; Yang, Kui-Hon Ou; Shiu, Hung-Wei; Chen, Chia-Hao; Kaun, Chao-Cheng; Shu, Guo-Jiun; Chou, Fang-Cheng; Lin, Minn-Tsong

2014-01-01

72

Structure of nearly degenerate dipole bands in 108Ag  

NASA Astrophysics Data System (ADS)

The high spin negative parity states of 108Ag have been investigated with the 11B + 100Mo reaction at 39 MeV beam energy using the INGA facility at TIFR, Mumbai. From the ?-? coincidence analysis, an excited negative parity band has been established and found to be nearly degenerate with the ground state band. The spin and parity of the levels are assigned using angular correlation and polarization measurements. This pair of degenerate bands in 108Ag is studied using the recently developed microscopic triaxial projected shell model approach. The observed energy levels and the ratio of the electromagnetic transition probabilities of these bands in this isotope are well reproduced by the present model. Further, it is shown that the partner band has a different quasiparticle structure as compared to the yrast band.

Sethi, J.; Palit, R.; Saha, S.; Trivedi, T.; Bhat, G. H.; Sheikh, J. A.; Datta, P.; Carroll, J. J.; Chattopadhyay, S.; Donthi, R.; Garg, U.; Jadhav, S.; Jain, H. C.; Karamian, S.; Kumar, S.; Litz, M. S.; Mehta, D.; Naidu, B. S.; Naik, Z.; Sihotra, S.; Walker, P. M.

2013-08-01

73

Surface photometry STRUCTURE OF GALAXIES  

E-print Network

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

Kruit, Piet van der

74

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

75

Automated effective band structures for defective and mismatched supercells.  

PubMed

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

Brommer, Peter; Quigley, David

2014-12-01

76

Development of X-Band Dielectric-Loaded Accelerating Structures  

SciTech Connect

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

Gold, S. H. [Plasma Physics Division, Naval Research Laboratory, Washington, DC 20375 (United States); Jing, C. [Euclid TechLabs, Rockville, MD 20850 (United States); Argonne National Laboratory, Argonne, IL 60439 (United States); Kanareykin, A. [Euclid TechLabs, Rockville, MD 20850 (United States); Gai, W.; Konecny, R.; Power, J. G. [Argonne National Laboratory, Argonne, IL 60439 (United States); Kinkead, A. K. [Icarus Research, Bethesda, MD 20814 (United States)

2010-11-04

77

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

78

Tunable surface band gap in Mg(x)Zn(1-x)O thin films.  

PubMed

Mg(x)Zn(1-x)O thin films epitaxially grown on Mo(110) substrate under ultrahigh vacuum condition were studied in situ by various surface analysis techniques including x-ray photoelectron spectroscopy, Auger electron spectroscopy, low-energy electron diffraction, and high resolution electron energy loss spectroscopy. The results indicate that as-grown Mg(x)Zn(1-x)O films are soluble phase, and a phase transition from wurtzite to cubic structure occurs in the region of x = 0.55-0.67. The surface band gap can be tuned continuously with altering the content of Mg in Mg(x)Zn(1-x)O films, and its tunable window width is about 1.9 eV. Based on heterojunction and quantum well structure, this kind of materials can be applied in wide-band-gap semiconductor devices, such as short-wavelength light-emitting devices. PMID:19102552

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

2008-12-21

79

Orbital-angular-momentum based origin of Rashba-type surface band splitting.  

PubMed

We propose that the existence of local orbital angular momentum (OAM) on the surfaces of high-Z materials plays a crucial role in the formation of Rashba-type surface band splitting. Local OAM state in a Bloch wave function produces an asymmetric charge distribution (electric dipole). The surface-normal electric field then aligns the electric dipole and results in chiral OAM states and the relevant Rashba-type splitting. Therefore, the band splitting originates from electric dipole interaction, not from the relativistic Zeeman splitting as proposed in the original Rashba picture. The characteristic spin chiral structure of Rashba states is formed through the spin-orbit coupling and thus is a secondary effect to the chiral OAM. Results from first-principles calculations on a single Bi layer under an external electric field verify the key predictions of the new model. PMID:22107313

Park, Seung Ryong; Kim, Choong H; Yu, Jaejun; Han, Jung Hoon; Kim, Changyoung

2011-10-01

80

[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

81

Solving complex band structure problems with the FEAST eigenvalue algorithm  

NASA Astrophysics Data System (ADS)

With straightforward extension, the FEAST eigenvalue algorithm [Polizzi, Phys. Rev. B 79, 115112 (2009)] is capable of solving the generalized eigenvalue problems representing traveling-wave problems—as exemplified by the complex band-structure problem—even though the matrices involved are complex, non-Hermitian, and singular, and hence outside the originally stated range of applicability of the algorithm. The obtained eigenvalues/eigenvectors, however, contain spurious solutions which must be detected and removed. The efficiency and parallel structure of the original algorithm are unaltered. The complex band structures of Si layers of varying thicknesses and InAs nanowires of varying radii are computed as test problems.

Laux, S. E.

2012-08-01

82

Occupied and unoccupied electronic band structure of WSe2  

Microsoft Academic Search

An extensive investigation of the electronic band structure of the layered semiconductor 2H-WSe2 is presented. Angular-resolved photoemission (ARPES) and angular-resolved inverse photoemission spectroscopy (ARIPES) data are compared to a full-potential fully relativistic density-functional calculation, yielding a very gratifying correspondence between the experimental and the theoretical data. The topmost valence band is found to behave differently than previous calculations have predicted,

Th. Finteis; M. Hengsberger; Th. Straub; K. Fauth; R. Claessen; P. Auer; P. Steiner; S. Hüautfner; P. Blaha; M. Vöautgt; M. Lux-Steiner; E. Bucher

1997-01-01

83

X-band travelling wave accelerator structure R&D  

Microsoft Academic Search

A 1.6 MeV X-band traveling wave linear accelerator is being developed in our Lab. in view of X-band linac R&D and industrial purposes. One section of the accelerator structure has been fabricated successfully. In this paper, the RF coupler computer simulation, the constant powerloss collinear load study and the accelerator section development are described in detail. The manufacture technology and

K. Jin; Y. J. Pei; D. M. Jiang; Y. Z. Liu; Q. J. Lai; M. H. Zhao; H. Zhao

2001-01-01

84

Observation of full plasmonic stop bands in fractal structures  

Microsoft Academic Search

In the last year's meeting we reported a novel approach for stabilization of numerical calculation of plasmonic propagation band structure. This method enables us to precisely obtain the propagation modes of periodically patterned two-dimensional conducting sheets, with arbitrarily high order of spatial harmonic content. Following the above contribution, we here present successful construction of a periodic fractal structure based on

Navid Yasrebi; Sina Khorasani; Aryan Hazeghi; Bizhan Rashidian

2011-01-01

85

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

86

Surface Structures and Surface Conductance during Metal Adsorption on Semiconductors  

NASA Astrophysics Data System (ADS)

Epitaxial growth modes for "two-step deposition" processes of metals on a Si(111) surface were investigated. Depth distributions of composition during the growth were analyzed by using RHEED-TRAXS (total reflection angle X-ray spectroscopy). We first made (? {3}× ? {3})-(Ag, Au, Ga), (2? {3}× 2? {3})-Sn and (4×1)-In structures, and then second metals (Ag, Au, Sn, Ga and In) were deposited on these surfaces at room temperature. Growth processes observed are classified into five growth modes: ordinary growth (O), alloying growth (A), substitution atom growth (S), particle formation growth mode (P) and floating atom growth (F). During the growth processes, we measured also surface conductivities which showed interesting behaviors. These results can be partly understood considering the growth modes, atomic arrangement, surface composition, Fermi level pinning and band bending, etc.

Ino, S.

87

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

E-print Network

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

Peinke, Joachim

88

Bulk band structure of Bi2Te3  

NASA Astrophysics Data System (ADS)

The bulk band structure of Bi2Te3 has been determined by angle-resolved photoemission spectroscopy and compared to first-principles calculations. We have performed calculations using the local density approximation (LDA) of density functional theory and the one-shot GW approximation within the all-electron full-potential linearized augmented-plane-wave (FLAPW) formalism, fully taking into account spin-orbit coupling. Quasiparticle effects produce significant changes in the band structure of Bi2Te3 when compared to LDA. Experimental and calculated results are compared in the spectral regions where distinct differences between the LDA and GW results are present. Overall a superior agreement with GW is found, highlighting the importance of many-body effects in the band structure of this family of topological insulators.

Michiardi, Matteo; Aguilera, Irene; Bianchi, Marco; de Carvalho, Vagner Eustáquio; Ladeira, Luiz Orlando; Teixeira, Nayara Gomes; Soares, Edmar Avellar; Friedrich, Christoph; Blügel, Stefan; Hofmann, Philip

2014-08-01

89

Elementary energy bands in ab initio calculations of the YAlO3 and SbSI crystal band structure  

NASA Astrophysics Data System (ADS)

The local density approximation has been implemented to determine the band structure of orthorhombic crystals YAlO3 (YAP) and SbSI. The topology of the valence band structures was analyzed. It has been demonstrated that Zak's elementary energy bands in the band structure are distinguishable on the basis of the empty-lattice approximation. The calculated electron density distribution of YAP and SbSI crystals is related to particular Wyckoff positions. Moreover, there is a direct correspondence between the obtained elementary energy bands and the aforementioned Wyckoff positions characterized by electron density distribution.

Bercha, D. M.; Rushchanskii, K. Z.; Sznajder, M.; Matkovskii, A.; Potera, P.

2002-11-01

90

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

Microsoft Academic Search

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

Hideomi Totsuka; Satoshi Watanabe

2008-01-01

91

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

Microsoft Academic Search

Microbial community profiles and species composition associated with two black band-diseased colonies of the coral Siderastrea siderea were studied by 16S rRNA-targeted gene cloning, sequencing, and amplicon-length heter- ogeneity PCR (LH-PCR). Bacterial communities associated with the surface mucopolysaccharide layer (SML) of apparently healthy tissues of the infected colonies, together with samples of the black band disease (BBD) infections, were analyzed

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

2006-01-01

92

The band structures and photoemission of transition metal dichalcogenides  

Microsoft Academic Search

The yields and energy distributions of electrons photoemitted from MoS2, ?-MoTe2, ?-MoTe2, NbSe2 and ZrS2 have been investigated and the photo-thresholds and work functions established. The results confirm the basic correctness of the Wilson-Yoffe model for the electronic structure of these solids but lead to much wider band gaps for the trigonal prismatic group VIA dichalcogenides. Structure in the photoelectric

R. B. Murray; R. H. Williams

1974-01-01

93

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

94

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

SciTech Connect

A generalized theory is developed to study inter-band optical absorption coefficient (IOAC) and material gain (MG) in quantum dot structures of narrow gap III-V compound semiconductor considering the wave-vector (k{sup ?}) dependence of the optical transition matrix element. The band structures of these low band gap semiconducting materials with sufficiently separated split-off valance band are frequently described by the three energy band model of Kane. This has been adopted for analysis of the IOAC and MG taking InAs, InSb, Hg{sub 1?x}Cd{sub x}Te, and In{sub 1?x}Ga{sub x}As{sub y}P{sub 1?y} lattice matched to InP, as example of III–V compound semiconductors, having varied split-off energy band compared to their bulk band gap energy. It has been found that magnitude of the IOAC for quantum dots increases with increasing incident photon energy and the lines of absorption are more closely spaced in the three band model of Kane than those with parabolic energy band approximations reflecting the direct the influence of energy band parameters. The results show a significant deviation to the MG spectrum of narrow-gap materials having band nonparabolicity compared to the parabolic band model approximations. The results reflect the important role of valence band split-off energies in these narrow gap semiconductors.

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

2014-04-14

95

Electronic band structure of magnetic bilayer graphene superlattices  

NASA Astrophysics Data System (ADS)

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

Pham, C. Huy; Nguyen, T. Thuong; Nguyen, V. Lien

2014-09-01

96

Development of faults as zones of deformation bands and as slip surfaces in sandstone  

Microsoft Academic Search

Three forms of fault are recognized in Entrada and Navajo Sandstones in the San Rafael Desert, southeastern Utah; deformation bands, zones of deformation bands, and slip surfaces. Small faults occur asdeformation bands, about one millimeter thick, in which pores collapse and sand grains fracture, and along which there are shear displacements on the order of a few millimeters or centimeters.

Atilla Aydin; Arvid M. Johnson

1978-01-01

97

Omnidirectional elastic band gap in finite lamellar structures.  

PubMed

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

Bria, D; Djafari-Rouhani, B

2002-11-01

98

Electronic band structure of epitaxial CuInSe2 films  

NASA Astrophysics Data System (ADS)

We report on a synchrotron radiation-based angle-resolved photoelectron spectroscopy study of the chalcopyrite semiconductor CuInSe2. Clean and well-ordered samples with surface orientations (001) and (112) were prepared by molecular beam epitaxy on GaAs (100) and (111)A wafers with a miscut, which allows for the growth of single-domain samples. Band dispersions perpendicular (?-T) and parallel (?-N) to the surface of near-stoichiometric (001) samples show a strikingly good agreement with density functional theory calculation, although a distinct narrowing of the density of states gap around EB = 3 eV is observed. The band structure for the ?-N direction can also be obtained by in-plane measurements of the (112) surface. The results are consistent with the (001) surface and implications of polarization dependency are discussed.

Hofmann, Andreas; Pettenkofer, Christian

2011-09-01

99

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

PubMed

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

Li, Zhongyang; Butun, Serkan; Aydin, Koray

2014-08-26

100

Quasiparticle band structure of Zn-IV-N2 compounds  

NASA Astrophysics Data System (ADS)

Electronic energy-band structures of the Zn-IV-N2 compounds, with IV equal to Si, Ge, and Sn calculated in the quasiparticle self-consistent GW approximation and using the full-potential linearized muffin-tin orbital approach, are presented. A comparison is made with local-density approximation results. The bands near the gap are fitted to an effective Kohn-Luttinger-type Hamiltonian appropriate for the orthorhombic symmetry, and conduction-band effective masses are presented. Exciton binding energies and zero-point motion corrections to the gaps are estimated. While ZnSiN2 is found to be an indirect gap semiconductor, ZnGeN2 and ZnSnN2 are direct gap semiconductors. The gaps range from the orange-red to deep UV. The valence-band maximum is split in three levels of different symmetry, even in the absence of spin-orbit coupling, and should show transitions to the conduction band, each for a separate polarization. Spin-orbit effects are found to be surprisingly small, indicating almost exact compensation of the N-2p and Zn-3d contributions.

Punya, Atchara; Lambrecht, Walter R. L.; van Schilfgaarde, Mark

2011-10-01

101

Tunable and sizable band gap in silicene by surface adsorption  

PubMed Central

Opening a sizable band gap without degrading its high carrier mobility is as vital for silicene as for graphene to its application as a high-performance field effect transistor (FET). Our density functional theory calculations predict that a band gap is opened in silicene by single-side adsorption of alkali atom as a result of sublattice or bond symmetry breaking. The band gap size is controllable by changing the adsorption coverage, with an impressive maximum band gap up to 0.50?eV. The ab initio quantum transport simulation of a bottom-gated FET based on a sodium-covered silicene reveals a transport gap, which is consistent with the band gap, and the resulting on/off current ratio is up to 108. Therefore, a way is paved for silicene as the channel of a high-performance FET. PMID:23152944

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

2012-01-01

102

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

103

Band gap calculation for two layered perfect conductor (PEC) electromagnetic band gap structure in application of microstrip  

Microsoft Academic Search

The object of this paper is to calculate the band gap energy of the newly designed waveguide structure. The structure used was 2 layers of perfect conductor (PEC) sandwiched with an electromagnetic band gap (EBG) or photonic crystals (PC) in the center. The lattice arrangement of the EBG was square lattice. The cylinder rods is made of PEC also and

K. L. Low; M. Z. Mat Jafri; Sohail A. Khan

2008-01-01

104

Global observations of quasi-zonal bands in microwave sea surface temperature  

NASA Astrophysics Data System (ADS)

observations of quasi-zonal jet-like structures have recently been reported in estimates of upper ocean circulation. To date, these observations have come primarily from float-derived and altimeter-derived estimates of zonal velocity. Here, we explore the existence of similar structures in the ocean using satellite-derived estimates of sea surface temperature (SST) from the Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E). Applying an ocean front detection algorithm globally to microwave measurements of SST, we find that repeated ocean fronts occur along quasi-zonal bands in a multiyear (2002-2011) average of detections. Such a pattern is also observed in SST gradient magnitude. Composite analyses of SST, sea surface height (SSH), and upper ocean temperatures from Argo profiling floats suggest repeated fronts in the subtropics occur as a result of neighboring anticyclonic and cyclonic eddies. Horizontal advection in the presence of a background temperature gradient likely plays a role as evidenced by the tilt of temperature anomalies with depth. High gradient events found within the bands are observed to propagate westward with speed comparable to mesoscale eddies and we estimate these events explain 20% of the observed variance in SST gradient magnitude (2002-2011). In a final analysis, we regress the decay of the bands with averaging period and observe mild-to-strong persistence throughout much of the World Ocean. These findings support the view that propagating eddies help give rise to the bands. Whether or not eddies follow preferred paths remain unanswered.

Buckingham, C. E.; Cornillon, P. C.; Schloesser, F.; Obenour, K. M.

2014-08-01

105

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

NASA Astrophysics Data System (ADS)

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

Nagata, T.; Oh, S.; Yamashita, Y.; Yoshikawa, H.; Ikeno, N.; Kobayashi, K.; Chikyow, T.; Wakayama, Y.

2013-01-01

106

Engineering Design of a Multipurpose X-band Accelerating Structure  

E-print Network

Both FEL projects, SwissFEL and Fermi-Elettra each require an X-band RF accelerating structure for optimal bunch compression at the respective injectors. As the CLIC project is pursuing a program for producing and testing the X-band high-gradient RF structures, a collaboration between PSI, Elettra and CERN has been established to build a multipurpose X-band accelerating structure. This paper focuses on its engineering design, which is based on the disked cells jointed together by diffusion bonding. Vacuum brazing and laser beam welding is used for auxiliary components. The accelerating structure consists of two coupler subassemblies, 73 disks and includes a wakefield monitor and diagnostic waveguides. The engineering study includes the external cooling system, consisting of two parallel cooling circuits and an RF tuning system, which allows phase advance tuning of the cell by deforming the outer wall. The engineering solution for the installation and sealing of the wake field monitor feed-through devices that...

Gudkov, Dmitry; Samoshkin, Alexander; Zennaro, Riccardo; Dehler, Micha; Raguin, Jean-Yves

2010-01-01

107

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

108

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

Microsoft Academic Search

Utilization of electromagnetic band-gap (EBG) structures is becoming attractive in the electromagnetic and antenna community. In this paper, a mushroom-like EBG structure is analyzed using the finite-difference time-domain (FDTD) method. Its band-gap feature of surface-wave suppression is demonstrated by exhibiting the near field distributions of the electromagnetic waves. The mutual coupling of microstrip antennas is parametrically investigated, including both the

Fan Yang; Yahya Rahmat-Samii

2003-01-01

109

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

110

Phenomenological band structure model of magnetic coupling in semiconductors  

E-print Network

Phenomenological band structure model of magnetic coupling in semiconductors Gustavo M. Dalpian a,1 the magnetic ordering in Mn-doped semiconductors. This model is based on the p­d and d­d level repulsions doped II­VI and III­V semiconductors such as CdTe, GaAs, ZnO, and GaN. The model can also be used

Gong, Xingao

111

Banded structures in directionally solidified Ti-52Al alloys  

SciTech Connect

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

Ramanujan, R.V. (Univ. of Birmingham (United Kingdom)); Bi, Y.; Xu, Q.; Abell, J.S. (Univ. of Birmingham (United Kingdom). School of Metallurgy and Materials)

1994-03-15

112

A Study of Higher-Band Dipole Wakefields in X-Band Accelerating Structures for the G/NLC  

SciTech Connect

The X-band linacs for the G/NLC (Global/Next Linear Collider) have evolved from the DDS (Damped Detuned Structure) series. The present accelerating structures are 60 cm in length and incorporate damping and detuning of the dipole modes which comprise the wakefield. In order to adequately damp the wakefield, frequencies of adjacent structures are interleaved. Limited analysis has been done previously on the higher order dipole bands. Here, we calculate the contribution of higher order bands of interleaved structures to the wakefield. Beam dynamics issues are also studied.

Jones, R

2004-09-02

113

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

SciTech Connect

In this paper, we use a tight binding Hamiltonian with spin orbit coupling to study the real and complex band structures of relaxed and strained GaAs. A simple d orbital on-site energy shift coupled with appropriate scaling of the off-diagonal terms is found to correctly reproduce the band-edge shifts with strain. Four different ?100? strain combinations, namely, uniaxial compressive, uniaxial tensile, biaxial compressive, and biaxial tensile strain are studied, revealing rich valence band structure and strong relative orientation dependent tunneling. It is found that complex bands are unable to provide unambiguous tunneling paths away from the Brillouin zone center. Tunneling current density distribution over the Brillouin zone is computed using non-equilibrium Green's function approach elucidating a physical picture of band to band tunneling.

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

2014-05-07

114

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

115

Reduced-basis method for band structure calculations George S. H. Pau*  

E-print Network

parameter is the wave vector k and the outputs are the band energies Ei k or functionals of the waveReduced-basis method for band structure calculations George S. H. Pau* Massachusetts Institute of the reduced-basis method in rapid and accurate determination of band energies in band structure calculations

Bell, John B.

116

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. PMID:23965955

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

2013-01-01

117

Shear band structure in ballistically tested bainitic steels  

E-print Network

, as shown in Fig. 3b. The pat- tern formed by the segregation bands shows that in both samples, the extent of plastic deformation of the material beyond the hole increases with depth of penetration, consistent with the expected reduction of the projectile... ’, Acta Metall., 1987, 35, 301–306. 5. W. J. Davies: ‘Surface fatigue in ball bearings, roller bearings, and gears in aircraft engines’, In: Fatigue in Rolling Contact. London, U.K.: Institution of Mechanical Engineers, 1963:23–40. 6. H. Schlicht: ‘About...

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

118

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

119

Electroreflectance and surface photovoltage spectroscopies of semiconductor structures using an indiumtinoxide-coated  

E-print Network

Electroreflectance and surface photovoltage spectroscopies of semiconductor structures using 17 October 2000 Measurements of electroreflectance and surface photovoltage spectroscopy. Photoreflectance1 PR spectroscopy is widely used for nondestructive testing of band gaps, layer composition, etc

Ghosh, Sandip

120

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

121

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

122

Hybrid density functional theory band structure engineering in hematite.  

PubMed

We present a hybrid density functional theory (DFT) study of doping effects in ?-Fe(2)O(3), hematite. Standard DFT underestimates the band gap by roughly 75% and incorrectly identifies hematite as a Mott-Hubbard insulator. Hybrid DFT accurately predicts the proper structural, magnetic, and electronic properties of hematite and, unlike the DFT+U method, does not contain d-electron specific empirical parameters. We find that using a screened functional that smoothly transitions from 12% exact exchange at short ranges to standard DFT at long range accurately reproduces the experimental band gap and other material properties. We then show that the antiferromagnetic symmetry in the pure ?-Fe(2)O(3) crystal is broken by all dopants and that the ligand field theory correctly predicts local magnetic moments on the dopants. We characterize the resulting band gaps for hematite doped by transition metals and the p-block post-transition metals. The specific case of Pd doping is investigated in order to correlate calculated doping energies and optical properties with experimentally observed photocatalytic behavior. PMID:21682532

Pozun, Zachary D; Henkelman, Graeme

2011-06-14

123

Hybrid density functional theory band structure engineering in hematite  

NASA Astrophysics Data System (ADS)

We present a hybrid density functional theory (DFT) study of doping effects in ?-Fe2O3, hematite. Standard DFT underestimates the band gap by roughly 75% and incorrectly identifies hematite as a Mott-Hubbard insulator. Hybrid DFT accurately predicts the proper structural, magnetic, and electronic properties of hematite and, unlike the DFT+U method, does not contain d-electron specific empirical parameters. We find that using a screened functional that smoothly transitions from 12% exact exchange at short ranges to standard DFT at long range accurately reproduces the experimental band gap and other material properties. We then show that the antiferromagnetic symmetry in the pure ?-Fe2O3 crystal is broken by all dopants and that the ligand field theory correctly predicts local magnetic moments on the dopants. We characterize the resulting band gaps for hematite doped by transition metals and the p-block post-transition metals. The specific case of Pd doping is investigated in order to correlate calculated doping energies and optical properties with experimentally observed photocatalytic behavior.

Pozun, Zachary D.; Henkelman, Graeme

2011-06-01

124

Band Structure Asymmetry of Bilayer Graphene Revealed by Infrared Spectroscopy  

SciTech Connect

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

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

2008-12-10

125

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

126

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

SciTech Connect

The effect of intentional surface oxide formation on band-edge photoluminescence (PL) of Ge nanowires was investigated. Thermal oxidation in molecular O{sub 2} was used to produce a surface oxide layer on assemblies of single crystal nanowires grown by the vapor-liquid-solid method. With increasing oxidation of the wires, the band-edge PL associated with the indirect gap transition becomes more intense. X-ray photoelectron spectroscopy confirms the formation of an increasingly GeO{sub 2}-like surface oxide under annealing conditions that enhance the indirect-gap PL, consistent with surface oxide passivation of nonradiative recombination centers initially present on the nanowire surface.

Minaye Hashemi, Fatemeh Sadat [Department of Materials Science and Engineering, Stanford University, Stanford, California 94305 (United States) [Department of Materials Science and Engineering, Stanford University, Stanford, California 94305 (United States); Laboratoire des Materiaux Semiconducteurs, Ecole Polytechnique Federale de Lausanne, 1015 Lausanne (Switzerland); Thombare, Shruti; Brongersma, Mark L. [Department of Materials Science and Engineering, Stanford University, Stanford, California 94305 (United States)] [Department of Materials Science and Engineering, Stanford University, Stanford, California 94305 (United States); Morral, Anna Fontcuberta i [Laboratoire des Materiaux Semiconducteurs, Ecole Polytechnique Federale de Lausanne, 1015 Lausanne (Switzerland)] [Laboratoire des Materiaux Semiconducteurs, Ecole Polytechnique Federale de Lausanne, 1015 Lausanne (Switzerland); McIntyre, Paul C. [Department of Materials Science and Engineering, Stanford University, Stanford, California 94305 (United States) [Department of Materials Science and Engineering, Stanford University, Stanford, California 94305 (United States); Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305 (United States)

2013-06-24

127

Metal-induced gap states in ferroelectric capacitors and its relationship with complex band structures  

NASA Astrophysics Data System (ADS)

At metal-isulator interfaces, the metallic wave functions with an energy eigenvalue within the band gap decay exponentially inside the dielectric (metal-induced gap states, MIGS). These MIGS can be actually regarded as Bloch functions with an associated complex wave vector. Usually only real values of the wave vectors are discussed in text books, since infinite periodicity is assumed and, in that situation, wave functions growing exponentially in any direction would not be physically valid. However, localized wave functions with an exponential decay are indeed perfectly valid solution of the Schrodinger equation in the presence of defects, surfaces or interfaces. For this reason, properties of MIGS have been typically discussed in terms of the complex band structure of bulk materials. The probable dependence on the interface particulars has been rarely taken into account explicitly due to the difficulties to include them into the model or simulations. We aim to characterize from first-principles simulations the MIGS in realistic ferroelectric capacitors and their connection with the complex band structure of the ferroelectric material. We emphasize the influence of the real interface beyond the complex band structure of bulk materials.

Junquera, Javier; Aguado-Puente, Pablo

2013-03-01

128

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

SciTech Connect

Topological insulators are electronic materials that have a bulk band gap like an ordinary insulator but have protected conducting states on their edge or surface. This can be happened due to spin-orbit coupling and time-reversal symmetry. Moreover, the edge current flows through their edge or surface depends on its spin orientation and also it is robust against non-magnetic impurities. Therefore, topological insulators are predicted to be useful ranging from spintronics to quantum computation. Graphene was first predicted to be the precursor of topological insulator by Kane-Mele. They developed a Hamiltonian model to describe the gap opening in graphene. In this work, we investigate the band structure of few-layer graphene by using this model with analytical approach. The results of our calculations show that the gap opening occurs at K and K’ point, not only in single layer, but also in bilayer and trilayer graphene.

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

2014-03-24

129

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

130

Band structure and localization of electronic states of 2DEG in an inhomogeneous magnetic field  

NASA Astrophysics Data System (ADS)

Based on the finite-differences approach, we study the electronic properties of two-dimensional electron gas under an inhomogeneous magnetic field. Such structure can be realized by deposition of ferromagnetic strips on the surface of a semiconductor heterostructure. It is found that the system exhibits rich band structures. Many bound states are twofold degenerate for ? = ?/2, which defines the magnetization direction in the ferromagnetic strips, while few degenerate state exist for ? = 0. Despite of this, there are three kinds of electronic states in our system: the extended, localized and intermediate ones, which is very different from the case of absence of magnetic field.

Zhang, Xiao Wei; Mou, Sun Yu; Liu, Yu Liang; Dai, Bo

2014-10-01

131

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

132

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

133

Photonic band structure calculations using nonlinear eigenvalue techniques  

SciTech Connect

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

Spence, Alastair [Department of Mathematical Sciences, University of Bath, Claverton Down, Bath BA2 7AY (United Kingdom); Poulton, Chris [High Frequency and Quantum Electronics Laboratory, University of Karlsruhe, Kaiserstrasse 12, Karlsruhe 76128 (Germany)]. E-mail: c.poulton@ihq.uni-karlsruhe.de

2005-03-20

134

Quasiparticle semiconductor band structures including spin-orbit interactions.  

PubMed

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

Malone, Brad D; Cohen, Marvin L

2013-03-13

135

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

136

[The study on energy band structure of silicon nanowires with XPS].  

PubMed

Silicon nanowires were obtained via oxide-assisted method, which was operated in a high temperature furnace at 1250 degrees C under 1000 Pa for 5 h using Ar as carrier gas. The silicon nanowires were etched with 5% HF aqueous solution for 5 min, and reacted with 1 X 10(-3) mol X L(-1) AuCL3 solution, and Au-modified silicon nanowires were obtained. The crystal structure of the products was characterized with XRD, and both of the patterns of Si and Au were observed. The morphology checked with SEM and TEM indicated large scale uniform silicon nanowires and Au particles on the surface of silicon nanowires. The average diameter of Au nanoparticls was 8 nm. The energy band structures obtained with XPS showed that gold nanoparticles are in negative charge and exist both at donor and acceptor levels. The Fermi level moved towards the top of valence band due to oxygen. PMID:18051552

Fu, Zhong; Fu, Yan; Hu, Hui; Shao, Ming-Wang; Pan, Shi-Yan

2007-09-01

137

Band offsets of atomic-layer-deposited Al2O3 on GaAs and the effects of surface treatment  

E-print Network

Band offsets of atomic-layer-deposited Al2O3 on GaAs and the effects of surface treatment N. V technologically important parameters. We report the band offsets of the Al/Al2O3/GaAs structure and the effect of GaAs surface treatment. The energy barrier at the Al2O3 and sulfur-passivated GaAs interface is found

Ye, Peide "Peter"

138

Mapping bulk Ge electronic energy bands along ? using ARPES spectra of the (001) 2 × 1 surface  

NASA Astrophysics Data System (ADS)

The E versus k dispersion relations of the second and third bulk valence bands as well as one conduction band of Ge along the ? line of the Brillouin Zone have been experimentally determined from angle-resolved photoelectron spectra collected at the Stanford Synchrotron Radiation Laboratory. The experimentally observed bands show good agreement with those calculated using the empirical pseudopotential parameters of Chelikowsky and Cohen for bulk Ge, even though the Ge(001) surface is reconstructed and ARPES is generally considered to be a surface sensitive technique.

Nelson, Jeffrey G.; Gignac, William J.; Williams, R. Stanley; Robey, Steven W.; Tobin, J. G.; Shirley, D. A.

1983-09-01

139

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

Microsoft Academic Search

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

Mudar A. Al-Joumayly; Nader Behdad

2010-01-01

140

Semiconductor Nanocrystals: Structure, Properties, and Band Gap Engineering  

PubMed Central

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

2010-01-01

141

Band structure of ABC-trilayer graphene superlattice  

NASA Astrophysics Data System (ADS)

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

Uddin, Salah; Chan, K. S.

2014-11-01

142

Mapping surface soil moisture with L-band radiometric measurements  

NASA Technical Reports Server (NTRS)

A NASA C-130 airborne remote sensing aircraft was used to obtain four-beam pushbroom microwave radiometric measurements over two small Kansas tall-grass prairie region watersheds, during a dry-down period after heavy rainfall in May and June, 1987. While one of the watersheds had been burned 2 months before these measurements, the other had not been burned for over a year. Surface soil-moisture data were collected at the time of the aircraft measurements and correlated with the corresponding radiometric measurements, establishing a relationship for surface soil-moisture mapping. Radiometric sensitivity to soil moisture variation is higher in the burned than in the unburned watershed; surface soil moisture loss is also faster in the burned watershed.

Wang, James R.; Shiue, James C.; Schmugge, Thomas J.; Engman, Edwin T.

1989-01-01

143

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

SciTech Connect

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

Vollmer, B.; Bonnarel, F.; Louys, M. [CDS, Observatoire Astronomique, UMR 7550, 11 rue de l'universite, F-67000 Strasbourg (France); Perret, B.; Petremand, M.; Lavigne, F.; Collet, Ch. [LSIIT, Universite de Strasbourg, 7, Rue Rene Descartes, F-67084 Strasbourg (France); Van Driel, W. [GEPI, Observatoire de Paris, CNRS, Universite Paris Diderot, 5 place Jules Janssen, F-92190 Meudon (France); Sabatini, S. [INAF/IASF-Roma, via Fosso de Cavaliere 100, I-00133 Roma (Italy); MacArthur, L. A., E-mail: Bernd.Vollmer@astro.unistra.fr [Herzberg Institute of Astrophysics, National Research Council of Canada, Victoria, BC V9E 2E7 (Canada)

2013-02-01

144

Surface-oxidized carbon fibers: I. Surface structure and chemistry  

Microsoft Academic Search

The surface structure and chemistry of various surface oxidized HT carbon fibers, an IM and a HM carbon fiber were studied by SEM, STM, CAM (contact angle measurement), XPS and TPD with special reference to adsorbed oxidation products and adsorbed water. It is shown that a real image of surface structure and surface chemistry is only obtained after removal of

U. Zielke; K. J. Hüttinger; W. P. Hoffman

1996-01-01

145

Band structures of Ge and InAs: A 20 k.p model  

NASA Astrophysics Data System (ADS)

The band structure of direct-band-gap semiconductor (InAs) and indirect-band-gap semiconductor (Ge) is described theoretically using a 20×20 k.p model and including far-level contribution (essentially the d levels). By using this model, we obtained a quantitatively correct description of the top of the valence band and the lowest two conduction bands both in terms of energetic positions and band curvatures. In particular, the k.p Hamiltonian parameters are adjusted such that the transverse mass of the germanium conduction band is equal to the experimental value of 0.081.

Radhia, S. Ben; Ridene, S.; Boujdaria, K.; Bouchriha, H.; Fishman, G.

2002-10-01

146

Anomalous decay of an atom in structured band gap reservoirs  

E-print Network

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

Filippo Giraldi; Francesco Petruccione

2011-04-09

147

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

148

Band Structure of Transition Metals Studied by ESCA  

Microsoft Academic Search

The position and shape of the energy bands of the following transition metals have been studied by ESCA: Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, Au. The Fermi levels of the metals with unfilled d-bands are found in the high-energy flanks of the valence band spectra. For the noble metals the Fermi level is shifted toward

Y. Baer; P. F. Hedén; J. Hedman; M. Klasson; C. Nordling; K. Siegbahn

1970-01-01

149

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

Technology Transfer Automated Retrieval System (TEKTRAN)

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

150

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

E-print Network

Space-based detection of wetlands' surface water level changes from L-band SAR interferometry­1996 reveals detectable surface changes in the Everglades wetlands. Although our study is limited to south Florida it has implication for other large-scale wetlands, because south Florida wetlands have diverse

Amelung, Falk

151

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

NASA Astrophysics Data System (ADS)

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

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

2011-06-01

152

Influence of polarity and hydroxyl termination on the band bending at ZnO surfaces  

NASA Astrophysics Data System (ADS)

Surface sensitive synchrotron x-ray photoelectron spectroscopy (XPS) and real-time in situ XPS were used to study the thermal stability of the hydroxyl termination and downward band bending on the polar surfaces of ZnO single crystals. On the O-polar face, the position of the Fermi level could be reversibly cycled between the conduction band and the band gap over an energetic distance of approximately 0.8 eV (˜1/4 of the band gap) by controlling the surface H coverage using simple ultrahigh vacuum (UHV) heat treatments up to 750 °C, dosing with H2O/H2 and atmospheric exposure. A metallic to semiconductorlike transition in the electronic nature of the O-polar face was observed at an H coverage of approximately 0.9 monolayers. For H coverage less than this, semiconducting (depleted) O-polar surfaces were created that were reasonably stable in UHV conditions. In contrast, the downward band bending on the Zn-polar face was significantly more resilient, and depleted surfaces could not be prepared by heat treatment alone.

Heinhold, R.; Williams, G. T.; Cooil, S. P.; Evans, D. A.; Allen, M. W.

2013-12-01

153

Bidirectional reflectance distribution function modeling of one-dimensional rough surface in the microwave band  

NASA Astrophysics Data System (ADS)

In this study, the bidirectional reflectance distribution function (BRDF) of a one-dimensional conducting rough surface and a dielectric rough surface are calculated with different frequencies and roughness values in the microwave band by using the method of moments, and the relationship between the bistatic scattering coefficient and the BRDF of a rough surface is expressed. From the theory of the parameters of the rough surface BRDF, the parameters of the BRDF are obtained using a genetic algorithm. The BRDF of a rough surface is calculated using the obtained parameter values. Further, the fitting values and theoretical calculations of the BRDF are compared, and the optimization results are in agreement with the theoretical calculation results. Finally, a reference for BRDF modeling of a Gaussian rough surface in the microwave band is provided by the proposed method.

Guo, Li-Xin; Gou, Xue-Yin; Zhang, Lian-Bo

2014-11-01

154

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

155

Gold Nanoparticles with Externally Controlled, Reversible Shifts of Local Surface Plasmon Resonance Bands  

PubMed Central

We have achieved reversible tunability of local surface plasmon resonance in conjugated polymer functionalized gold nanoparticles. This property was facilitated by the preparation of 3,4-ethylenedioxythiophene (EDOT) containing polynorbornene brushes on gold nanoparticles via surface-initiated ring-opening metathesis polymerization. Reversible tuning of the surface plasmon band was achieved by electrochemically switching the EDOT polymer between its reduced and oxidized states. PMID:19839619

Yavuz, Mustafa S.; Jensen, Gary C.; Penaloza, David P.; Seery, Thomas A. P.; Pendergraph, Samuel A.; Rusling, James F.; Sotzing, Gregory A.

2010-01-01

156

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

Microsoft Academic Search

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

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

2009-01-01

157

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

158

Band electronic structure study of the structural modulation in the Magneli phase Mo sub 8 O sub 23  

SciTech Connect

We examined the cause for the 0.5b{sup *} superlattice modulation in the Magneli phase Mo{sub 8}O{sub 23} by performing tight-binding band electronic structure calculations on Mo{sub 8}O{sub 23}, which consists of perovskite Mo{sub 4}O{sub 15} layers linked by Mo{sub 4}O{sub 14} chains. Our study shows that Mo{sub 8}O{sub 23} is a semimetal and does not possess a half-filled band dispersive along the b{sup *} direction. Thus, the superlattice modulation is not caused by an electronic instability associated with Fermi surface nesting. The most likely cause for the superlattice modulation is a concerted pairwise rotation of MoO{sub 6} octahedra in the perovskite Mo{sub 4}O{sub 15} layers. 18 refs., 5 figs.

Canadell, E. (Universite de Paris-Sud, Orsay (France)); Whangbo, Myunghwan (North Carolina State Univ., Raleigh (USA))

1990-06-13

159

Experimental Evidence for Spin-Split Bands in a One-Dimensional Chain Structure I. Barke, Fan Zheng, T. K. Rugheimer, and F. J. Himpsel  

E-print Network

Experimental Evidence for Spin-Split Bands in a One-Dimensional Chain Structure I. Barke, Fan Zheng, T. K. Ru¨gheimer, and F. J. Himpsel Department of Physics, University of Wisconsin Madison, 1150 chains on vicinal Si(111) surfaces exhibit an unusual doublet of half-filled bands, whose origin has

Himpsel, Franz J.

160

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

E-print Network

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

Himpsel, Franz J.

161

Vector k small middle dotp approach for photonic band structures  

PubMed

We point out that k small middle dotp treatments of photonic band gap materials based on the usual master equation must employ not only the physical photonic band solutions of that equation, but also unphysical solutions, in order to form a complete set. Nonetheless, it is possible to construct correct k small middle dotp expressions for the group velocity and its dispersion in terms of matrix elements involving only the photonic band solutions. PMID:11089125

Sipe

2000-10-01

162

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

SciTech Connect

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

Eppley, K.R. [Stanford Linear Accelerator Center, P.O. Box 4349, Stanford, California 94309 (United States)

1995-07-05

163

Spatially resolved methane band photometry of Jupiter. III - Cloud vertical structures for several axisymmetric bands and the Great Red Spot  

Microsoft Academic Search

The paper presents cloud structure models for Jupiter's Great Red Spot, Equatorial and North Tropical Zones, North and South Temperate Zones, and North and South Polar Regions. The models are based on images of Jupiter in three methane bands and nearby continuum radiative transfer calculations include multiple scattering and absorption from three aerosol layers. The model results include the transition

R. A. West; M. G. Tomasko

1980-01-01

164

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

NASA Astrophysics Data System (ADS)

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

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

2015-02-01

165

Relationship between photonic band structure and emission characteristics of a polymer distributed feedback laser  

NASA Astrophysics Data System (ADS)

We present an experimental study of the emission characteristics and photonic band structure of a distributed feedback polymer laser, based on the material poly[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylene vinylene]. We use measurements of the photonic band dispersion to explain how the substrate microstructure modifies both spontaneous and stimulated emission. The lasing structure exhibits a one-dimensional photonic band gap around 610 nm, with lasing occurring at one of the two associated band edges. The band edge (frequency) selection mechanism is found to be a difference in the level of output coupling of the modes associated with the two band edges. This is a feature of the second-order distributed feedback mechanism we have employed and is clearly evident in the measured photonic band structure.

Turnbull, G. A.; Andrew, P.; Jory, M. J.; Barnes, W. L.; Samuel, I. D. W.

2001-09-01

166

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

Microsoft Academic Search

An algorithm based on a fit of the single-scattering integral equation method (IEM) was developed to provide estimation of soil moisture and surface roughness parameter (a combination of rms roughness height and surface power spectrum) from quad-polarized synthetic aperture radar (SAR) measurements. This algorithm was applied to a series of measurements acquired at L-band (1.25 GHz) from both AIRSAR (Airborne

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

1997-01-01

167

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

SciTech Connect

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

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

2008-01-01

168

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

Microsoft Academic Search

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

Yurii Vlasov; David Norris

2001-01-01

169

Dual-band asymmetric transmission of chiral metamaterial based on complementary U-shaped structure  

NASA Astrophysics Data System (ADS)

In this paper, a chiral metamaterial that consists of two complementary U-shaped structures on both sides of a substrate is proposed, which achieves dual-band asymmetric transmission effect of linearly polarized wave at 0.88 and 1.03 THz bands. The asymmetric transmission effect and resonance frequency can be adjusted through changing structure parameters. The physical mechanisms of dual-band asymmetric transmission are also analyzed based on different couple modes excited at resonant frequency.

Liu, Dejun; Xiao, Zhongyin; Ma, Xiaolong; Wang, Lei; Xu, Kaikai; Tang, Jingyao; Wang, Zihua

2015-01-01

170

Crystal Structure and Calculated Electronic Band Structure of ZrTe 3  

Microsoft Academic Search

Because of inconsistencies in literature data, the crystal structure of ZrTe3was redetermined from single-crystal data and the electronic band structure was calculated using density functional theory in the local density approximation (LDA) and the linear muffin tin orbital method (LMTO). ZrTe3crystallizes in the monoclinic space groupP21\\/mwitha=589.8(1) pm,b=392.69(3) pm,c=1010.3(1) pm, and?=97.81(1)° (Z=2) in the ZrSe3structure type (?data collection,Rw=1.88%). In the layer

Klaus Stöwe; Frank R Wagner

1998-01-01

171

Temperature",dependent composition, ordering, and band bending at GaP(100) surfaces  

E-print Network

prior to removal from the growth chamber. We use core-level and valence-band soft x-ray photoemission to analytical chambers. Surface-sensitive SXPS core-level spectra and more bulk-sensitive AES spectra collected-650 ·e desorption temperature range. Core-level photoemission intensity ratios reveal rapid loss of both

Woodall, Jerry M.

172

Design-charts for grounded, elliptically shaped microstrip periodic surface featuring electromagnetic band-gap  

Microsoft Academic Search

Numerical study of a high impedance surface built in microstrip technology by using periodically arranged elliptical patches, grounded through one to four vias is presented. The effect of the variation of the number of vias manifests in different manner on the electromagnetic band gap aperture and position, as results from the parametric study in function of the patch dimensions and

Aldo De Sabata; Ladislau Matekovits

2010-01-01

173

Reconfigurable dual-band frequency selective surfaces using a new hybrid element  

Microsoft Academic Search

In this paper, a new active frequency selective surface (AFSS) is proposed as an electromagnetic (EM) window for TE- polarized incident waves. A unit cell of this AFSS includes of a strip dipole and an elliptical loop, deliberately combined in a single layer configuration to create a dual-band transmission\\/reflection coefficient response. High frequency PIN- diodes are also integrated into the

Mahmoud Niroo-Jazi; Tayeb A. Denidni

2011-01-01

174

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 ...

175

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

E-print Network

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

Cao, Wenwu

176

Band structure engineering through orbital interaction for enhanced thermoelectric power factor  

E-print Network

interaction on band structure is demonstrated for IV-VI thermoelectric semiconductors. For IV-VI materials, we thermoelectric performance has been demonstrated in the premier thermoelectric material, lead telluride (PbBand structure engineering through orbital interaction for enhanced thermoelectric power factor

Ceder, Gerbrand

177

3D spherical layer photonic band-gap structures in dichromate gelatin.  

E-print Network

??Three-dimensional spherical layer photonic band-gap structures were fabricated in dichromate gelatin (DCG) holographic emulsions by a holographic lithography technique. Five spherical layer structures with different… (more)

Hung, Jenny

2008-01-01

178

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

ERIC Educational Resources Information Center

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

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

1988-01-01

179

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

180

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

181

Lunar near-surface structure  

NASA Technical Reports Server (NTRS)

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

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

1974-01-01

182

Investigation the effect of lattice angle on the band structure in 3D phononic crystals with rhombohedral(II) lattice  

NASA Astrophysics Data System (ADS)

In this paper, the propagation of acoustic waves in the phononic crystals (PC) of 3D with rhombohedral(II) lattice is studied theoretically. The PC are constituted of nickel spheres embedded in epoxy. The calculations of the band structure and density of states are performed with the plane wave expansion method in the irreducible part of the Brillouin zone (BZ). In this study, we analyze the dependence of the band structures inside (the complete band gap width) and outside the complete band gap (negative refraction of acoustic wave) on the lattice angle in the irreducible part of the first BZ. Also the effect of lattice angle has been analyzed on the band structure of the () and (122) planes. Then, the equifrequency surface is calculated for the high symmetry point in the [111] and [100] directions. The results show that the maximum width of AEBG (0.022) in the irreducible part of the BZ of RHL2 is formed for (105?) and no AEBG is found for ? > 150?. Also, the maximum of the first and second AEBG width are 0.1076 and 0.0523 for ? = 133? in the () plane and the maximum of the first and second AEBG width are 0.1446 and 0.0998 for ? = 113? in the (122) plane. In addition, we have found that frequencies in which negative refraction occurs is constant for all lattice angles.

Aryadoust, M.; Salehi, H.

2014-12-01

183

Influence of band structure on the large thermoelectric performance of lanthanum telluride  

SciTech Connect

We investigate the carrier density and temperature dependence of the Seebeck coefficient of La{sub 3-x}Te{sub 4} via density-functional calculations and Boltzmann transport theory. The pertinent band structure has light bands at the band gap and heavy degenerate bands with band minima near energies corresponding to the experimentally determined optimum carrier density. Heavy bands increase the energy dependence of the density of states, which increases the magnitude of the Seebeck coefficient in an itinerant conduction regime, while the light bands provide a conduction channel that works against carrier localization promoted by La vacancies. The net result is thermoelectric performance greater than current n-type materials above 1000 K.

May, Andrew F. [California Institute of Technology, Pasadena; Singh, David J [ORNL; Snyder, G. J. [California Institute of Technology, Pasadena

2009-01-01

184

Journal of ELECTRONIC MATERIALS, Vol. 34, No. 6, 2005 Special Issue Paper Comparison of Normal and Inverted Band Structure  

E-print Network

structures were computed employing an envelope-function-based 14-band K·p method with a 40 K valence band and Inverted Band Structure HgTe/CdTe Superlattices for Very Long Wavelength Infrared Detectors C.H. GREIN,1 band alignment of HgTe/CdTe superlattices leads to the interest- ing possibility of achieving very long

Flatte, Michael E.

185

Electronic transitions in GdN band structure  

SciTech Connect

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

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

2014-05-28

186

High spin band structure of 3885Sr47  

NASA Astrophysics Data System (ADS)

High spin states in the Sr85 nucleus were populated in the reaction Ge76(13C,4n) at a beam energy of 45 MeV. The ?-? and ?-?-? coincidence measurements have been utilized to establish the level scheme of Sr85 up to I?=35/2-. Nearly 50 new ? rays and about 25 new levels were identified and most of the previously known levels confirmed. The spin-parity assignment of the levels was made by using the directional correlations of the oriented nuclei ratios and polarization asymmetry measurements. The shell-model calculations have been performed by using two recent interactions, JUN45 and jj44b, for a detailed comparison between theoretical results and the experimental data obtained in the present work. The shell-model results are in good agreements with the experimental data and are able to explain the various features such as the odd-even staggering well. Tilted axis cranking calculations were also performed to understand the magnetic rotation (MR) phenomenon at higher spins. One of the positive-parity ?I =1 bands has been assigned a three-quasiparticle (3qp) configuration, which appears to behave like a MR band. A negative-parity band populated up to I?=35/2- was also assigned a 3qp configuration at low spin and a five-quasiparticle configuration at high spin; however, it does not exhibit the expected MR features, in contrast to a similar band in the Kr83 nucleus.

Kumar, S.; Kumar, Naveen; Mandal, S.; Pancholi, S. C.; Srivastava, P. C.; Jain, A. K.; Palit, R.; Saha, S.; Sethi, J.; Naidu, B. S.; Donthi, R.; Joshi, P. K.; Trivedi, T.; Muralithar, S.; Singh, R. P.; Kumar, R.; Dhal, A.; Bhowmik, R. K.

2014-08-01

187

Electronic transitions in GdN band structure  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

188

Valence band structure of HgTe/Hg1-xCdxTe single quantum wells  

NASA Astrophysics Data System (ADS)

Properties of the valence-band structure of modulation-doped type-III HgTe/Hg1-xCdxTe(001) quantum wells (QW's) have been studied by means of magneto-transport experiments and self-consistent Hartree calculations using the full 8×8 k.p Hamiltonian in the envelope-function approximation. A metallic top gate was used in order to investigate the band structure by varying the hole concentration or the Fermi energy. This resulted in direct experimental evidence of an indirect band gap in a quantum well with an inverted band structure. The Kramers degeneracy for finite k is removed, and only one spin-orbit split valence subband is occupied due to the indirect band structure. The fourfold symmetry of the H2 valence band at finite values of k|| is also reflected in a QW with a normal band structure, whose H1 valence band has four occupied secondary maxima at finite values of k|| in addition to the central maximum.

Ortner, K.; Zhang, X. C.; Pfeuffer-Jeschke, A.; Becker, C. R.; Landwehr, G.; Molenkamp, L. W.

2002-08-01

189

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. PMID:17679336

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

190

Energy band structure tailoring of vertically aligned InAs/GaAsSb quantum dot structure for intermediate-band solar cell application by thermal annealing process.  

PubMed

This study presents an band-alignment tailoring of a vertically aligned InAs/GaAs(Sb) quantum dot (QD) structure and the extension of the carrier lifetime therein by rapid thermal annealing (RTA). Arrhenius analysis indicates a larger activation energy and thermal stability that results from the suppression of In-Ga intermixing and preservation of the QD heterostructure in an annealed vertically aligned InAs/GaAsSb QD structure. Power-dependent and time-resolved photoluminescence were utilized to demonstrate the extended carrier lifetime from 4.7 to 9.4 ns and elucidate the mechanisms of the antimony aggregation resulting in a band-alignment tailoring from straddling to staggered gap after the RTA process. The significant extension in the carrier lifetime of the columnar InAs/GaAsSb dot structure make the great potential in improving QD intermediate-band solar cell application. PMID:25607045

Liu, Wei-Sheng; Chu, Ting-Fu; Huang, Tien-Hao

2014-12-15

191

Sensitive detection of surface- and size-dependent direct and indirect band gap transitions in ferritin  

NASA Astrophysics Data System (ADS)

Ferritin is a protein nano-cage that encapsulates minerals inside an 8 nm cavity. Previous band gap measurements on the native mineral, ferrihydrite, have reported gaps as low as 1.0 eV and as high as 2.5-3.5 eV. To resolve this discrepancy we have used optical absorption spectroscopy, a well-established technique for measuring both direct and indirect band gaps. Our studies included controls on the protein nano-cage, ferritin with the native ferrihydrite mineral, and ferritin with reconstituted ferrihydrite cores of different sizes. We report measurements of an indirect band gap for native ferritin of 2.140 ± 0.015 eV (579.7 nm), with a direct transition appearing at 3.053 ± 0.005 eV (406.1 nm). We also see evidence of a defect-related state having a binding energy of 0.220 ± 0.010 eV . Reconstituted ferrihydrite minerals of different sizes were also studied and showed band gap energies which increased with decreasing size due to quantum confinement effects. Molecules that interact with the surface of the mineral core also demonstrated a small influence following trends in ligand field theory, altering the native mineral’s band gap up to 0.035 eV.

Colton, J. S.; Erickson, S. D.; Smith, T. J.; Watt, R. K.

2014-04-01

192

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

SciTech Connect

The electron momentum density, the electronic band structure, and the structural properties of SrS are presented in this paper. The isotropic Compton profile, anisotropies in the directional Compton profiles, the electronic band structure and density of states are calculated using the ab initio periodic linear combination of atomic orbitals method with the CRYSTAL06 code. Structural parameters of SrS-lattice constants and bulk moduli in the B1 and B2 phases-are computed together with the transition pressure. The computed parameters are well in agreement with earlier investigations. To compare the calculated isotropic Compton profile, measurement on polycrystalline SrS is performed using 5Ci-{sup 241}Am Compton spectrometer. Additionally, charge transfer is studied by means of the Compton profiles computed from the ionic model. The nature of bonding in the isovalent SrS and SrO compounds is compared on the basis of equal-valenceelectron-density profiles and the bonding in SrS is found to be more covalent than in SrO.

Sharma, G., E-mail: gsphysics@gmail.com [University of Kota, Department of Pure and Applied Physics (India); Munjal, N.; Vyas, V. [Banasthali University, Department of Physics (India)] [Banasthali University, Department of Physics (India); Kumar, R.; Sharma, B. K. [University of Rajasthan, Department of Physics (India)] [University of Rajasthan, Department of Physics (India); Joshi, K. B. [MLS University, Department of Physics (India)] [MLS University, Department of Physics (India)

2013-10-15

193

Conformal coating of highly structured surfaces  

DOEpatents

Method of applying a conformal coating to a highly structured substrate and devices made by the disclosed methods are disclosed. An example method includes the deposition of a substantially contiguous layer of a material upon a highly structured surface within a deposition process chamber. The highly structured surface may be associated with a substrate or another layer deposited on a substrate. The method includes depositing a material having an amorphous structure on the highly structured surface at a deposition pressure of equal to or less than about 3 mTorr. The method may also include removing a portion of the amorphous material deposited on selected surfaces and depositing additional amorphous material on the highly structured surface.

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

2012-12-11

194

Band structures of bilayer radial phononic crystal plate with crystal gliding  

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

195

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

PubMed

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

Appalakondaiah, S; Vaitheeswaran, G; Lebègue, S

2013-05-14

196

Substrate-induced band structure and electronic properties in graphene/Al2O3(0001) interface  

NASA Astrophysics Data System (ADS)

Band structure investigation results of two-dimensional (2D) graphene (SLG) on Al2O3(0001) using the density functional theory (DFT) method as a possible element base for spintronics are presented. Regularities of a band structure change in the order three-dimensional (3D) Al2O3 ? 2D Al2O3(0001) ? 2D SLG/Al2O3(0001) as well as features of a chemical bond between SLG and sapphire on the basis of DFT calculations have been studied. Analysis of the band structure and interatomic spacing in the interface for both models allows speaking about physical SLG adsorption on the (0001)-surface sapphire constrained by aluminum atoms. Energy distribution features of surface states in 2D SLG/Al2O3(0001) interface are discussed. Analysis of effective atomic charge in the interface revealed surface charge fluctuations on the substrate in the presence of SLG, which can be explained by a decrease of the energy of occupied subsurface Al2O3 states relatively to the Fermi level.

Ilyasov, V. V.; Ershov, I. V.; Ilyasov, A. V.; Popova, I. G.; Nguyen, Chuong V.

2015-02-01

197

Protein Structural Perturbation and Aggregation on Homogeneous Surfaces  

PubMed Central

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

Sethuraman, Ananthakrishnan; Belfort, Georges

2005-01-01

198

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

SciTech Connect

We demonstrate the ability to develop one-dimensional electromagnetic band gap structure in X-band waveguide solely by using the positive columns of glow discharges in neon at the middle pressure. Plasma inhomogeneities are distributed uniformly along a typical X-band waveguide with cross section of 23?×?10?mm{sup 2}. It is shown that electron densities larger than 10{sup 14?}cm{sup ?3} are needed in order to create an effective one-dimensional electromagnetic band gap structure. Some applications for using the one-dimensional electromagnetic band gap structure in waveguide as a control of microwave (broadband filter and device for variation of pulse duration) are demonstrated.

Arkhipenko, V. I.; Simonchik, L. V., E-mail: l.simonchik@dragon.bas-net.by; Usachonak, M. S. [B.I. Stepanov Institute of Physics of the NAS of Belarus, Ave. Nezavisimostsi 68, 220072 Minsk (Belarus); Callegari, Th.; Sokoloff, J. [Université de Toulouse, UPS, INPT, LAPLACE, Laboratoire Plasma et Conversion d'Energie, 118 route de Narbonne, F-31062 Toulouse cedex 9 (France)

2014-09-28

199

Optical Elements with Subwavelength Structured Surfaces  

Microsoft Academic Search

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

Hisao Kikuta; Hiroshi Toyota; Wanji Yu

2003-01-01

200

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

201

Dispersion characteristics of a slow wave structure with metal photonic band gap cells  

NASA Astrophysics Data System (ADS)

A slow wave structure consisting of metallic photonic band gap cells for a Ka-band Cherenkov device is proposed in this paper. Attributing to the mode selectivity of the photonic band gap, only the TM 01-like mode among the TM 0n-like modes exists in such a slow wave structure. The dispersion characteristics of the slow wave structure are investigated by simulation and experiment. It is shown that the dispersion curve obtained from the experiment is in agreement with that from simulation.

Gao, Xi; Yang, Ziqiang; Xu, Yong; Qi, Limei; Li, Dazhi; Shi, Zongjun; Lan, Feng; Liang, Zheng

2008-07-01

202

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. PMID:22163430

Rotaru, Mihai; Sykulski, Jan

2010-01-01

203

Electromagnetic Field Properties of Axial Modes in a Finite Length X-Band Slow Wave Structure  

NASA Astrophysics Data System (ADS)

The electromagnetic field properties of axisymmetric transverse magnetic (TM) modes in a specific slow wave structure (SWS) typically used in high power X-band backward wave oscillators are studied numerically. The dispersion relations, electric field distributions, and quality factors of the axial resonant modes are calculated. It is found that some of the axial modes can be switched from the volume modes to the surface ones by changing only the axial boundary of the SWS while the dispersion relations do not alter. This causes a drastic change in quality factors and can be of practical interest for controlling the coupling between beam and TM modes in high-power microwave devices. The calculated dispersion relations are verified experimentally for the TM01 mode.

Amin, Md.; Ogura, Kazuo; Kobayashi, Tadashi; Suzuki, Yasunobu; Watanabe, Tsuguhiro

1996-02-01

204

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

Microsoft Academic Search

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

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

1995-01-01

205

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

NASA Astrophysics Data System (ADS)

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

Ho, Ching-Hwa; Chen, Hsin-Hung

2014-08-01

206

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

E-print Network

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

Akin, Tayfun

207

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

E-print Network

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

Cerveny, Vlastislav

208

Band structure of group IVA transition-metal dichalcogenides  

Microsoft Academic Search

A systematic study of the electronic properties of the layered group IVA transition-metal dichalcogenides TiS2,, TiSe2, ZrS2 ZrSe2 has been performed using the ab initio fully self-consistent symmetrised OPW method according to the local density formalism (Xalpha exchange correlation). Core states, energy bands and valence densities of states are presented. The valence eigenstates are analysed in terms of Slater-Koster LCAO

H. Isomaki; J. von Boehm; P. Krusius

1979-01-01

209

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

E-print Network

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

210

Evidence for water structuring forces between surfaces  

SciTech Connect

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

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

2011-01-01

211

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...

212

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

213

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

214

Band structure engineering through orbital interaction for enhanced thermoelectric power factor  

SciTech Connect

Band structure engineering for specific electronic or optical properties is essential for the further development of many important technologies including thermoelectrics, optoelectronics, and microelectronics. In this work, we report orbital interaction as a powerful tool to finetune the band structure and the transport properties of charge carriers in bulk crystalline semiconductors. The proposed mechanism of orbital interaction on band structure is demonstrated for IV-VI thermoelectric semiconductors. For IV-VI materials, we find that the convergence of multiple carrier pockets not only displays a strong correlation with the s-p and spin-orbit coupling but also coincides with the enhancement of power factor. Our results suggest a useful path to engineer the band structure and an enticing solid-solution design principle to enhance thermoelectric performance.

Zhu, Hong; Sun, Wenhao; Ceder, Gerbrand [Department of Materials Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139 (United States); Armiento, Rickard [Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-58183 Linköping (Sweden); Lazic, Predrag [Theoretical Physics Division, Rudjer Boskovic Institute, Bijenicka Cesta 54, Zagreb (Croatia)

2014-02-24

215

Strong effects of photonic band structures on the diffraction of colloidal crystals Willem L. Vos and Rudolf Sprik  

E-print Network

Strong effects of photonic band structures on the diffraction of colloidal crystals Willem L. Vos The influence of photonic band structures on optical diffraction has been studied with colloidal crystals, and are analogous to electronic band structures in atomic crystals. If the refractive index ratio is larger than 1

Vos, Willem L.

216

Prediction of composition for stable half-Heusler phases from electronic-band-structure analyses  

Microsoft Academic Search

This report describes a procedure to predict the frequently occurring non-stoichiometry of the half-Heusler XYZ alloys (viz. deviations from the equiatomic 1:1:1 composition and the usually accompanied narrow homogeneity regions) from ab initio calculated electronic-band-structure characteristics. The essential feature of this approach is to utilize the valence electron content (VEC) and the calculated electronic band structure to expose factors that

L. Offernes; P. Ravindran; C. W. Seim; A. Kjekshus

2008-01-01

217

Numerical simulation of condensation on structured surfaces.  

PubMed

Condensation of liquid droplets on solid surfaces happens widely in nature and industrial processes. This phase-change phenomenon has great effect on the performance of some microfluidic devices. On the basis of micro- and nanotechnology, superhydrophobic structured surfaces can be well-fabricated. In this work, the nucleating and growth of droplets on different structured surfaces are investigated numerically. The dynamic behavior of droplets during the condensation is simulated by the multiphase lattice Boltzmann method (LBM), which has the ability to incorporate the microscopic interactions, including fluid-fluid interaction and fluid-surface interaction. The results by the LBM show that, besides the chemical properties of surfaces, the topography of structures on solid surfaces influences the condensation process. For superhydrophobic surfaces, the spacing and height of microridges have significant influence on the nucleation sites. This mechanism provides an effective way for prevention of wetting on surfaces in engineering applications. Moreover, it suggests a way to prevent ice formation on surfaces caused by the condensation of subcooled water. For hydrophilic surfaces, however, microstructures may be submerged by the liquid films adhering to the surfaces. In this case, microstructures will fail to control the condensation process. Our research provides an optimized way for designing surfaces for condensation in engineering systems. PMID:25347594

Fu, Xiaowu; Yao, Zhaohui; Hao, Pengfei

2014-11-25

218

Analysis of frequency band structure in one-dimensional sonic crystal using Webster horn equation  

NASA Astrophysics Data System (ADS)

Sound propagation through periodic arrangement of scatterers lead to formation of bands of frequencies, known as band gaps, where sound cannot propagate though the structure. We propose a method based on Webster horn equation, along with Floquet theorem, to predict the band gap of a one-dimensional periodic structure made of hard sound-scatterers. The method is further modified to obtain the complex wave numbers, which give the decay constants. The decay constant is used to predict the sound attenuation of the evanescent wave in the finite sonic crystal. The theoretical prediction is verified with experimental measurements.

Gupta, A.; Lim, K. M.; Chew, C. H.

2011-05-01

219

INFLUENCE OF OPTICAL BAND STRUCTURES ON THE DIFFRACTION OF PHOTONIC COLLOIDAL CRYSTALS  

E-print Network

INFLUENCE OF OPTICAL BAND STRUCTURES ON THE DIFFRACTION OF PHOTONIC COLLOIDAL CRYSTALS WILLEM L crystal structures - e.g. the diamond structure [9]. In this case, no wave with an energy within the gap diffraction studies on colloidal crystals with large re- fractive index mismatches up to 1

Vos, Willem L.

220

Photonic stop bands in nanoporous anodic aluminum oxide-based structures  

Microsoft Academic Search

The photonic band gap properties of nanoporous anodic aluminum oxide structures are numerically investigated. These structures consist of a self-arranged triangular lattice of holes in an aluminum oxide dielectric host and are produced by electrochemical etching under adequate conditions. The triangular order of these structures is however broken into domains of some tens of pores oriented in different lattice directions.

Ivan Maksymov; Josep Ferre´-Borrull; Lluis F. Marsal

2009-01-01

221

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

NASA Technical Reports Server (NTRS)

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

Yueh, Simon H.; Chaubell, Mario J.

2012-01-01

222

Structure and functions of fungal cell surfaces  

NASA Technical Reports Server (NTRS)

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

Nozawa, Y.

1984-01-01

223

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

224

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

E-print Network

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

Chiang, Shirley

225

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

226

Surface Characterization by Structure Function Analysis  

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

227

Lifetimes and band structure of electroluminescence of ZnS:Mn based cells  

NASA Astrophysics Data System (ADS)

Spectral and kinetic properties of the electroluminescent thin film cells containing ZnS:Mn and CuxS layers were investigated. The cells were produced by thermal evaporation and chemical dipping. Kinetic measurements indicate that, for high manganese concentration the decay curve can be expanded in two exponentials. These exponentials are due to two kinds of manganese centers. Mn2+ ions and Mn2+-Mn2+ pairs. For low cells exhibit a reach structure in the blue and green spectral regions. Further investigation disclosed the presence of two types of the spectra. We also obtained a structure of manganese band of the electroluminescence of the cells for high manganese concentration. Similar to the short-wavelength bands, there are two types of the manganese bands. To our knowledge, this is the first observation of such structure of manganese bands at room temperature.

Chimczak, Eugeniusz; Bertrandt-Zytkowiak, Miroslawa

1997-06-01

228

Calculation of the band structure and superconductivity in the hexagonal close-packed phase of silicon  

NASA Astrophysics Data System (ADS)

We report a calculation of the band structure and superconductivity of silicon in the hexagonal close-packed phase under pressure. The effect of pressure on the band structure is obtained by means of the linear muffin-tin orbital method. The superconducting transition temperature T c is calculated using the formulas of Allen and Dynes1 as well as those of McMillan2. It is found that the value of T c increases with pressure up to 74.3 GPa. The increase in T c is attributed to the continuous s ? d electron transfer under pressure. The calculated values of T c are compared with the available experimental data. Further, Heine's fifth power law3 has been tested from the d-band widths obtained from the band-structure results.

Parvathi, A. Azhagu; Natarajan, S.; Palanivel, B.; Rajagopalan, M.

1991-03-01

229

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

230

Shaping topological properties of the band structures in a shaken optical lattice  

NASA Astrophysics Data System (ADS)

The realization of band structures with nontrivial topological properties in an optical lattice is an exciting topic in current studies of ultracold atoms. Here we point out that this lofty goal can be achieved by using a simple scheme of shaking an optical lattice, which is directly applicable in current experiments. The photon-assisted band hybridization leads to the production of an effective spin-orbit coupling, in which the band index represents the pseudospin. When this spin-orbit coupling has finite strengths in multiple directions, nontrivial topological structures emerge in the Brillouin zone, such as topological defects with a winding number of 1 or 2 in a shaken square lattice. The shaken lattice also allows one to study the transition between two band structures with distinct topological properties.

Zhang, Shao-Liang; Zhou, Qi

2014-11-01

231

Fine structure of the red luminescence band in undoped GaN  

SciTech Connect

Many point defects in GaN responsible for broad photoluminescence (PL) bands remain unidentified. Their presence in thick GaN layers grown by hydride vapor phase epitaxy (HVPE) detrimentally affects the material quality and may hinder the use of GaN in high-power electronic devices. One of the main PL bands in HVPE-grown GaN is the red luminescence (RL) band with a maximum at 1.8?eV. We observed the fine structure of this band with a zero-phonon line (ZPL) at 2.36?eV, which may help to identify the related defect. The shift of the ZPL with excitation intensity and the temperature-related transformation of the RL band fine structure indicate that the RL band is caused by transitions from a shallow donor (at low temperature) or from the conduction band (above 50?K) to an unknown deep acceptor having an energy level 1.130?eV above the valence band.

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

2014-01-20

232

Band structure and thermopower of doped YCuO2  

SciTech Connect

First-principles calculations and Boltzmann transport theory are used to analyze the thermopower and related properties of p-type delafossite structure YCuO{sub 2}. We find that the electrical transport properties are only mildly anisotropic in spite of the layered crystal structure and that this compound has high thermopowers indicative of a material that may be a good thermoelectric.

Singh, David J [ORNL

2008-01-01

233

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

234

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

235

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. PMID:21806939

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

2011-01-01

236

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

237

Probing the graphite band structure with resonant soft-x-ray fluorescence  

SciTech Connect

Soft x-ray fluorescence (SXF) spectroscopy using synchrotron radiation offers several advantages over surface sensitive spectroscopies for probing the electronic structure of complex multi-elemental materials. Due to the long mean free path of photons in solids ({approximately}1000 {angstrom}), SXF is a bulk-sensitive probe. Also, since core levels are involved in absorption and emission, SXF is both element- and angular-momentum-selective. SXF measures the local partial density of states (DOS) projected onto each constituent element of the material. The chief limitation of SXF has been the low fluorescence yield for photon emission, particularly for light elements. However, third generation light sources, such as the Advanced Light Source (ALS), offer the high brightness that makes high-resolution SXF experiments practical. In the following the authors utilize this high brightness to demonstrate the capability of SXF to probe the band structure of a polycrystalline sample. In SXF, a valence emission spectrum results from transitions from valence band states to the core hole produced by the incident photons. In the non-resonant energy regime, the excitation energy is far above the core binding energy, and the absorption and emission events are uncoupled. The fluorescence spectrum resembles emission spectra acquired using energetic electrons, and is insensitive to the incident photon`s energy. In the resonant excitation energy regime, core electrons are excited by photons to unoccupied states just above the Fermi level (EF). The absorption and emission events are coupled, and this coupling manifests itself in several ways, depending in part on the localization of the empty electronic states in the material. Here the authors report spectral measurements from highly oriented pyrolytic graphite.

Carlisle, J.A.; Shirley, E.L.; Hudson, E.A. [Lawrence Berkeley National Lab., CA (United States)] [and others

1997-04-01

238

Experimental study of photonic band gap accelerator structures  

E-print Network

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

Marsh, Roark A

2009-01-01

239

Band theoretical studies of the electronic structure of oxides  

Microsoft Academic Search

The O2- ion is a useful concept in ionic solids. Its electron density and large polarizability is well described by the Watson sphere model. The large variation in the electronic structure of oxides is illustrated by discussing the ionic MgO, the partly ‘covalent’ Cu2O, and TiO and NbO which have defects with respect to the ideal NaCl structure. The variation

Karlheinz Schwarz

1987-01-01

240

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

SciTech Connect

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

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

2012-10-15

241

Superhydrophobic surfaces from hierarchically structured wrinkled polymers.  

PubMed

This work reports the creation of superhydrophobic wrinkled surfaces with hierarchical structures at both the nanoscale and microscale. A nanoscale structure with 500 nm line gratings was first fabricated on poly(hydroxyethyl methacrylate) films by nanoimprint lithography while a secondary micro-scale structure was created by spontaneous wrinkling. Compared with random wrinkles whose patterns show no specific orientation, the hierarchical wrinkles exhibit interesting orientation due to confinement effects of pre-imprinted line patterns. The hierarchically wrinkled surfaces have significantly higher water contact angles than random wrinkled surfaces, exhibiting superhydrophobicity with water contact angles higher than 160° and water sliding angle lower than 5°. The hierarchically structured wrinkled surfaces exhibit tunable wettability from hydrophobic to superhydrophobic and there is an observed transition from anisotropic to isotropic wetting behavior achievable by adjusting the initial film thickness. PMID:24131534

Li, Yinyong; Dai, Shuxi; John, Jacob; Carter, Kenneth R

2013-11-13

242

Subwavelength structured surfaces and their applications  

NASA Technical Reports Server (NTRS)

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

Raguin, Daniel H.; Morris, G. Michael

1993-01-01

243

Structure and band gap engineering of Fe-doped SrSnO3 epitaxial films  

NASA Astrophysics Data System (ADS)

\\text{Sr}(\\text{Sn}1-x\\text{Fe}x)\\text{O}3 ( 0? x ? 1) (SSFO) films were epitaxially grown on MgO substrates by pulsed-laser deposition. X-ray diffraction, atomic force microcopy, and optical spectra investigations reveal that the lattice and band structure properties of the SSFO films can be modified significantly by varying the Fe content. With Fe content increasing from 0 to 1 in films, the lattice parameters decrease from 4.0425 to 3.8604 Å gradually, and the optical band gaps Eg decrease from 4.23 to 2.63 eV linearly. The Fe-induced large tuning in band gap was explained by the systematic width increase of the Fe-derived 3d band lying nearly above the O-derived 2p valence band.

Liu, Qinzhuang; Li, Hong; Li, Bing; Wang, Wei; Liu, Qiangchun; Zhang, Yongxing; Dai, Jianming

2014-11-01

244

Surface energy band gap of polycrystalline CuInSe{sub 2} thin-films in tunneling spectroscopy  

SciTech Connect

In this paper the authors demonstrate a tunneling spectroscopic technique to determine energy band gaps of the CuInSe{sub 2} thin-film surfaces. The I-V characteristics are measured with STM in ambient air. Using the well-known theory of tunneling spectroscopy, the normalized differential conductivity corresponding to surface density of states is both evaluates from the measured I-V characteristics and simulated with help of two gap models with and without additional localized state tails in the gap. The poorly defined gap edges are explained by additional localized states near the top of the valence band and the bottom of the conduction band. These additional localized states could be true surface defect states or originate from deep atomic layers underneath the surfaces due to band bending.

Zhang, Z.; Heuell, P.; Kulakov, M.; Bullemer, B. [Federal Armed Forces Univ. Munich, Neubiberg (Germany). Inst. of Physics

1994-12-31

245

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

246

Structure and oxidation at quasicrystal surfaces  

Microsoft Academic Search

We have investigated the atomic and electronic structure, chemical composition, and oxidation characteristics of the surfaces of icosahedral, Al-rich quasicrystals, using a variety of surface-sensitive techniques (LEED, XPS, STM, AES). We have systematically investigated the way that these traits vary with preparation conditions (e.g. sputtering and then annealing to various temperatures, vs. fracture), with surface symmetry (e.g. 2f vs. 3f

Patricia A Thiel

2004-01-01

247

Mechanically triggered transformations of phononic band gaps in periodic elastomeric structures K. Bertoldi and M. C. Boyce  

E-print Network

Mechanically triggered transformations of phononic band gaps in periodic elastomeric structures K a full acoustic band structure calculation for periodic elastomeric solids at different levels of deformation. We demonstrate the ability to use deformation to transform phononic band gaps. Periodic elas

248

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

249

Correlating simulated surface marks with near-surface tornado structure  

NASA Astrophysics Data System (ADS)

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

Zimmerman, Michael I.

250

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

PubMed

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

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

2014-08-27

251

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

SciTech Connect

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

Yastrubchak, O.; Gluba, L.; ?uk, J. [Institute of Physics, UMCS, Pl. Marii Curie-Sk?odowskiej 1, 20-031 Lublin (Poland)] [Institute of Physics, UMCS, Pl. Marii Curie-Sk?odowskiej 1, 20-031 Lublin (Poland); Sadowski, J. [Institute of Physics, Polish Academy of Sciences, 02-668 Warszawa (Poland) [Institute of Physics, Polish Academy of Sciences, 02-668 Warszawa (Poland); MAX-Lab, Lund University, 22100 Lund (Sweden); Krzy?anowska, H. [Institute of Physics, UMCS, Pl. Marii Curie-Sk?odowskiej 1, 20-031 Lublin (Poland) [Institute of Physics, UMCS, Pl. Marii Curie-Sk?odowskiej 1, 20-031 Lublin (Poland); Department of Physics and Astronomy, Vanderbilt University, 6506 Stevenson Center, Nashville, Tennessee 37325 (United States); Domagala, J. Z.; Andrearczyk, T.; Wosinski, T. [Institute of Physics, Polish Academy of Sciences, 02-668 Warszawa (Poland)] [Institute of Physics, Polish Academy of Sciences, 02-668 Warszawa (Poland)

2013-08-07

252

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

253

NUCLEAR AND HEAVY ION PHYSICS: Structural evolution of the intruder band in 118Sn  

NASA Astrophysics Data System (ADS)

Excited states of the positive-parity intruder band in 118Sn have been studied via the 116Cd(7Li, 1p4n) reaction at 7Li energy of 48 MeV using techniques of in-beam ?-ray spectroscopy. This intruder band has been observed up to 7187 keV with spin (16+). The structural evolution of this intruder band with increasing angular momentum has been discussed in terms of the aligned angular momentum and the ratio of the E-Gamma Over Spin (E-GOS) curve.

Wang, Shou-Yu; Duan, Bo-Tao; Zhu, Xin-Xin; Ren, Xiu-Lei; Yang, Xiao-Ling; Xi, Juan; Lü, Feng-Zheng; Sun, Da-Peng; Lü, Ying-Bo; Liu, Xi-Ju; Hua, Hui; Li, Zhong-Yu; Zhang, Shuang-Quan; Qi, Bin; Yao, Jiang-Ming; Zhu, Li-Hua; Wu, Xiao-Guang; Li, Guang-Sheng; Liu, Ying; Li, Xue-Qin; Zheng, Yun; Wang, Lie-Lin; Wang, Lei

2009-10-01

254

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

SciTech Connect

Shear bands, the main plastic strain carrier in metallic glasses, are severely deformed regions often considered as disordered and featureless. Here we report the observations of a sandwich-like heterogeneous structure inside shear bands in Pd{sub 40.5}Ni{sub 40.5}P{sub 19} metallic glass sample after plastic deformation by high-resolution transmission electron microscopy. The experimental results suggest a two-step plastic deformation mechanism with corresponding microstructure evolution at atomic scale, which may intimately connected to the stability of the shear band propagation and the overall plastic deformability.

Shao, Yang; Yao, Kefu; Liu, Xue [School of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China)] [School of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China); Li, Mo [School of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China) [School of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China); School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0245 (United States)

2013-10-21

255

Tunable band structure in diamond–cubic tin–germanium alloys grown on silicon substrates  

Microsoft Academic Search

Novel chemical methods based on deuterium-stabilized Sn hydrides and ultra-high-vacuum chemical vapor deposition were used to grow SnxGe1?x alloys directly on silicon. Device-quality, strain-free films with a Sn-fraction as high as x=0.2 were obtained. The optical properties provide evidence for a well-defined Ge-like band structure. In particular, the direct band gap E0 is reduced to a value as low as

Matthew R. Bauer; John Tolle; Corey Bungay; Andrew V. G. Chizmeshya; David J. Smith; José Menéndez; John Kouvetakis

2003-01-01

256

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

NASA Astrophysics Data System (ADS)

The scattering properties of particles in a one-dimensional Fibonacci sequence based potential have been analyzed by means of the Transfer Matrix Method. The electronic band gaps are examined comparatively with those obtained using the corresponding periodic potentials. The reflection coefficient shows self-similar properties for the Fibonacci superlattices. Moreover, by using the generalized Bragg's condition, the band gaps positions are derived from the golden mean involved in the design of the superlattice structure.

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

2014-02-01

257

Energy band structure of LiNH4SO4 crystals  

NASA Astrophysics Data System (ADS)

The genesis of the LiNH4SO4 crystal has been determined, the energy band structure and the total and partial electron densities of states have been calculated within the electron density functional theory. The coordinates of hydrogen atoms in groups have been determined, and the atomic positions and lattice parameters have been refined. It has been found that the band gap of LiNH4SO4 crystals is 5.32 eV.

Rudysh, M. Ya.; Stadnyk, V. Yo.; Brezvin, R. S.; Shchepanskii, P. A.

2015-01-01

258

Effects of Electronic and Lattice Polarization on the Band Structure of Delafossite Transparent Conductive Oxides  

Microsoft Academic Search

We use hybrid functionals and restricted self-consistent GW, state-of-the-art theoretical approaches for quasiparticle band structures, to study the electronic states of delafossite Cu(Al,In)O2, the first p-type and bipolar transparent conductive oxides. We show that a self-consistent GW approximation gives remarkably wider band gaps than all the other approaches used so far. Accounting for polaronic effects in the GW scheme we

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

2010-01-01

259

Structure and evolution of a convective band MCS  

E-print Network

of 5 May storm system. Cloud-to-ground lightning information during this event (00 UTC on 5 May to 2359 UTC on 6 May 1993) was obtained through the National Lightning Detection Network (NLDN) which is inanaged by Geolvlet Data Services Inc. of Tucson... of ADRAD products during 5 May 1993 MCS . . 4 Summary of NWS sounding sites parameters. . . . . . . 13 . . 14 25 LIST OF FIGURES Figure 1 Networks of radars, CLASS soundings and NWS synoptic (upper- air and surface) stations used in this study...

Valdes-Manzanilla, Arturo

1995-01-01

260

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

NASA Astrophysics Data System (ADS)

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

Saito, Kyosuke; Tanabe, Tadao; Oyama, Yutaka

2015-01-01

261

Superlattice band structure: New and simple energy quantification condition  

NASA Astrophysics Data System (ADS)

Assuming an approximated effective mass and using Bastard's boundary conditions, a simple method is used to calculate the subband structure for periodic semiconducting heterostructures. Our method consists to derive and solve the energy quantification condition (EQC), this is a simple real equation, composed of trigonometric and hyperbolic functions, and does not need any programming effort or sophistic machine to solve it. For less than ten wells heterostructures, we have derived and simplified the energy quantification conditions. The subband is build point by point; each point presents an energy level. Our simple energy quantification condition is used to calculate the subband structure of the GaAs/Ga0.5Al0.5As heterostructures, and build its subband point by point for 4 and 20 wells. Our finding shows a good agreement with previously published results.

Maiz, F.

2014-10-01

262

Evidence for water structuring forces between surfaces  

PubMed Central

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

Stanley, Christopher

2011-01-01

263

Broad-band structured fluorescence from NaI  

Microsoft Academic Search

The emission spectrum of a molecular beam of NaI has been measured following excitation by the 248 nm KrF line of an excimer laser. The fluorescence structure, and the lifetime (17±2 ns), indicate the presence of a bound upper state not previously characterized. We identify this state as correlating with Na(3 2P)+I(5 2P3\\/2) atoms. Through numerical simulation using a Morse

R. D. Bower; P. Chevrier; P. Das; H. J. Foth; J. C. Polanyi; M. G. Prisant; J. P. Visticot

1988-01-01

264

Colloids with high-definition surface structures.  

PubMed

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

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

2007-07-01

265

Colloids with high-definition surface structures  

PubMed Central

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

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

2007-01-01

266

Structure and oxidation at quasicrystal surfaces  

NASA Astrophysics Data System (ADS)

We have investigated the atomic and electronic structure, chemical composition, and oxidation characteristics of the surfaces of icosahedral, Al-rich quasicrystals, using a variety of surface-sensitive techniques (LEED, XPS, STM, AES). We have systematically investigated the way that these traits vary with preparation conditions (e.g. sputtering and then annealing to various temperatures, vs. fracture), with surface symmetry (e.g. 2f vs. 3f vs. 5f surfaces), and with bulk composition (e.g. i-Al-Pd-Mn vs. i-Al-Cu-Fe). We have also compared our results for the quasicrystals with results for crystalline approximants and other related crystalline phases. Our main conclusions are that, under specific conditions of sputter-annealing, the bulk atomic and electronic structures of the clean quasicrystal propagate to the surface. Also, the oxidation chemistry is dominated by that of the primary constituent, aluminum.

Thiel, Patricia A.

2004-08-01

267

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

NASA Technical Reports Server (NTRS)

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

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

2014-01-01

268

Surface periodic domain structures for waveguide applications.  

PubMed

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

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

2012-06-01

269

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

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

270

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

271

X-AND W-BAND EPR SPECTROSCOPY COMBINED WITH MOLECULAR DYNAMICS SIMULATIONS UNRAVEL THE STRUCTURE AND STRUCTURAL  

E-print Network

X- AND W-BAND EPR SPECTROSCOPY COMBINED WITH MOLECULAR DYNAMICS SIMULATIONS UNRAVEL THE STRUCTURE (EPR) spectroscopy is combined with molecular dynamics (MD) simulations to study the structure simulations of EPR spectra of nitroxides on the basis of molecular dynamics simulations of the spin labeled

Steinhoff, Heinz-Jürgen

272

Thermodynamics of copper and nickel: Band-structure effects and their disappearance at high temperatures  

NASA Astrophysics Data System (ADS)

The electronic contribution to the equation of state of copper and nickel is calculated from first principles on the basis of density-functional theory. Two methods are used. The first method is the full quantum statistical model, obtained from an extension of the Thomas-Fermi model; it neglects band-structure effects and yields almost the same results for the two metals. The second method is the finite-temperature linear muffin-tin orbitals band-structure method, based on the local-density approximation. This method yields big differences between the behaviors of the two metals at low temperatures in agreement with experiment. At high temperatures the band-structure effects gradually disappear, and the quantum statistical model results are approached.

Levy, A.; Barak, G.; Ashkenazi, J.

1987-06-01

273

UWB Band-notched Adjustable Antenna Using Concentric Split-ring Slots Structure  

NASA Astrophysics Data System (ADS)

In this paper, a kind of concentric split-ring slots structure is utilized to design a novel triple-band-notched UWB antenna. Firstly, a concentric split-ring slots structure that has a higher VSWR than that of a single slot at notch frequency is presented. What's more, the structure is very simple and feasible to obtain notched-band at different frequency by adjustment of the length of slot. Secondly, a triple-band-notched antenna, whose notched bands are at 3.52-3.81 GHz for WiMAX and 5.03-5.42 GHz and 5.73-56.17 GHz for WLAN, is designed by using this structure. At last, a compact size of 24 × 30 mm2 of the proposed antenna has been fabricated and measured and it is shown that the proposed antenna has a broadband matched impedance (3.05-14 GHz, VSWR < 2), relatively stable gain and good omnidirectional radiation patterns at low bands.

Yin, Y.; Hong, J. S.

2014-09-01

274

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

NASA Astrophysics Data System (ADS)

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

Avendaño, Carlos G.; Reyes, J. Adrián

2015-01-01

275

Compaction bands: a structural analog for anti-mode I cracks in aeolian sandstone  

Microsoft Academic Search

We present evidence for the existence of tabular zones of localized deformation in aeolian sandstone, that accommodate pure compaction. In this sense they are analogs for anticracks or closing mode I fractures such as pressure solution surfaces or stylolites. The so called “compaction bands” are exposed in outcrops of the Jurassic Navajo Sandstone in the Kaibab monocline, Utah. They are

P. N. Mollema; M. A. Antonellini

1996-01-01

276

Optimized 3D structures and energy bands of peanut-shaped C60 polymers  

NASA Astrophysics Data System (ADS)

Optimized three-dimensional (3D) cell structures and energy bands of fused (peanut-shaped) C60 polymers (p55 and p66) have been investigated using the first-principles pseudopotential approach within the local density approximation of the density functional theory. We found that the resulting electronic structure is either metal or semiconductor depending on the shape of the polymer chains and the unit cell structure.

Ohno, K.; Noguchi, Y.; Ueda, S.; Onoe, J.

2007-07-01

277

Cavity resonance suppression in power delivery systems using electromagnetic band gap structures  

Microsoft Academic Search

The utilization of electromagnetic band gap (EBG) structures is a new and promising approach in plane pair noise cavity resonance suppression. In this paper, EBG\\/plane pair structures are studied with full-wave methods and results are experimentally verified. A new equivalent circuit modeling approach of characterizing the frequency behavior of the entire EBG\\/plane pair structure is presented. The equivalent circuit of

Guang Chen; Kathleen L. Melde

2006-01-01

278

Band offsets in heterojunctions formed by oxides with cubic perovskite structure  

NASA Astrophysics Data System (ADS)

A number of recent discoveries on heterostructures formed by oxides suggest the emergence of a new direction in microelectronics, the oxide electronics. In the present work, band offsets in nine heterojunctions formed by titanates, zirconates, and niobates with the cubic perovskite structure are calculated from first principles. The effect of strain in contacting oxides on their energy structure; the GW corrections to the band edge positions resulting from many-body effects; and the conduction band edge splitting resulting from spinorbit coupling are consistently taken into account. It is shown that the neglect of the many-body effects can cause errors in the determination of the band offsets, reaching 0.36 eV. The fundamental inapplicability of the transitivity rule often used to determine the band offsets in heterojunctions by comparing the band offsets in a pair of heterojunctions formed by the components of the heterojunction under study with a third common component is demonstrated. The cause of the inapplicability is explained.

Lebedev, A. I.

2014-05-01

279

Band structures in two-dimensional phononic crystals with periodic Jerusalem cross slot  

NASA Astrophysics Data System (ADS)

In this paper, a novel two-dimensional phononic crystal composed of periodic Jerusalem cross slot in air matrix with a square lattice is presented. The dispersion relations and the transmission coefficient spectra are calculated by using the finite element method based on the Bloch theorem. The formation mechanisms of the band gaps are analyzed based on the acoustic mode analysis. Numerical results show that the proposed phononic crystal structure can yield large band gaps in the low-frequency range. The formation mechanism of opening the acoustic band gaps is mainly attributed to the resonance modes of the cavities inside the Jerusalem cross slot structure. Furthermore, the effects of the geometrical parameters on the band gaps are further explored numerically. Results show that the band gaps can be modulated in an extremely large frequency range by the geometry parameters such as the slot length and width. These properties of acoustic waves in the proposed phononic crystals can potentially be applied to optimize band gaps and generate low-frequency filters and waveguides.

Li, Yinggang; Chen, Tianning; Wang, Xiaopeng; Yu, Kunpeng; Song, Ruifang

2015-01-01

280

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

NASA Astrophysics Data System (ADS)

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

Tsukamoto, Shigeru; Hirose, Kikuji; Blügel, Stefan

2014-07-01

281

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

NASA Astrophysics Data System (ADS)

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

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

2012-05-01

282

Structural studies and band gap tuning of Cr doped ZnO nanoparticles  

SciTech Connect

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

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

2014-04-24

283

Band Structure of Carbon Nanotubes in a Perpendicular Electric Field 2.0  

NSDL National Science Digital Library

The NanoEd Resource Portal, a âÂÂdynamic repository for information dissemination, research and collaborations among the community of nanoscale science and engineering education (NSEE) learners, teachers and researchers,â provides this interactive simulator. Contributed by Professor Umberto Ravaioli from the University of Illinois at Urbana-Champaign, this simulator performs "band structure calculations for zigzag and armchair type carbon nanotubes (CNT)." This band structure calculator could prove useful for both students and instructors in the field, and could prove valuable in the classroom as well.

Ravaioli, Umberto

2012-04-23

284

Alignments and new band structures in the doubly odd nucleus 80Rb  

NASA Astrophysics Data System (ADS)

The high spin structure of 80Rb has been investigated using the reaction 51V( 32S,2pn) at a beam energy 105 MeV. The level scheme was established from ?-? and recoil-?-? coincidence measurements obtained using the Gamma Detector Array consisting of eight Compton suppressed Ge detectors coupled to the recoil mass separator HIRA. Rotational states upto an excitation energy 13 MeV and a spin 25? were studied. Band crossings at ?? = 0.63 and 0.73 MeV in the negative parity band, due to successive g{9}/{2} proton and neutron alignment, were observed for the first time. Evidence has also been found for a hitherto unknown sideband. The yrast positive parity bands in 78Kr and 80Rb have similar transition energies beyond a rotational frequency ?? ? 0.55 MeV. This is the only known example of identical bands in nuclei differing by two quasiparticles, in this mass region.

Tandel, S. K.; Patel, S. B.; Bhowmik, R. K.; Sinha, A. K.; Muralithar, S.; Madhavan, N.

1998-03-01

285

Near-infrared photonic band structure in a semiconductor metamaterial photonic crystal.  

PubMed

In this study, we theoretically investigate the near-infrared (NIR) photonic band structure (PBS) in a one-dimensional semiconductor metamaterial (MM) photonic crystal (PC). The considered PC is (AB)N, where N is the stack number, A is a dielectric, and B is a semiconductor MM composed of Al-doped ZnO and ZnO. It is found that the photonic band gaps (PBGs) can be tunable by the variations in filling factor, and thicknesses of A and B. It is of particular interest to see that the PBG will vanish when the thicknesses of A and B satisfy a certain condition. The results provide fundamental information on a NIR PBS that could be of technical use in photonic applications using such a semiconductor MM. The band gap vanishing makes it possible to design a wider band pass filter at NIR based on the use of such a PC. PMID:25402889

Wu, Meng-Ru; Wu, Chien-Jang; Chang, Shoou-Jinn

2014-11-01

286

Band structure and optical properties of sinusoidal superlattices: ZnSe1-xTex  

NASA Astrophysics Data System (ADS)

This paper examines the band structure and optical selection rules in superlattices with a sinusoidal potential profile. The analysis is motivated by the recent successful fabrication of high quality ZnSe1-xTex superlattices in which the composition x varies sinusoidally along the growth direction. Although the band alignment in the ZnSe1-xTex sinusoidal superlattices is staggered (type II), they exhibit unexpectedly strong photoluminescence, thus suggesting interesting optical behavior. The band structure of such sinusoidal superlattices is formulated in terms of the nearly-free-electron (NFE) approximation, in which the superlattice potential is treated as a perturbation. The resulting band structure is unique, characterized by a single minigap separating two wide, free-electron-like subbands for both electrons and holes. Interband selection rules are derived for optical transitions involving conduction and valence-band states at the superlattice Brillouin-zone center, and at the zone edge. A number of transitions are predicted due to wave-function mixing of different subband states. It should be noted that the zone-center and zone-edge transitions are especially easy to distinguish in these superlattices because of the large width of the respective subbands. The results of the NFE approximation are shown to hold surprisingly well over a wide range of parameters, particularly when the period of the superlattice is short.

Yang, G.; Lee, S.; Furdyna, J. K.

2000-04-01

287

Modification of surface band bending of diamond by low energy argon and carbon ion bombardment  

NASA Astrophysics Data System (ADS)

Argon and carbon ion bombardment of p-diamond at 500-5000 eV in ultrahigh vacuum were studied by in situ x-ray photoelectron spectroscopy (XPS) and low energy electron diffraction analysis. Both argon and carbon ion bombardment at room temperature in the present energy range created a defective surface layer. The radiation damage was manifested by the introduction of a distinct C 1s peak (referred to as the ``defect'' peak later) with a binding energy about 1 eV less than that of the bulklike diamond peak, and by the introduction of some additional filled states (referred to as the ``filled states'') near the valence band edge of diamond. It was found that in comparison to argon bombardment, carbon bombardment was more efficient in producing the filled states but less efficient in raising the C 1s defect peak. While the filled states disappeared by annealing at about 500 °C, the C 1s defect peak did not change much even with a 1000 °C anneal. These results suggest that the C 1s defect peak, which has also been observed on reconstructed diamond surfaces after hydrogen desorption [see, e.g., B. B. Pate, Surf. Sci. 165, 83(1986)], is associated with vacancy formation and aggregation which give some ``internal surfaces'' with a behavior like a reconstructed atomically clean diamond surface. The filled states introduced by ion bombardment are associated with interstitials or interstitial clusters. The amount of residual defects was found to increase with both an increasing bombardment dose and energy. For an argon bombardment at 1000 eV to a dose of 5×1014/cm2, the defective layer was estimated to be about 1.5 nm. Further, it was found that the radiation damage, particularly the ``vacancy defects'', could only be annealed (at 1000 °C) when the dose was below 5×1014/cm2 at a bombardment energy of 500 eV. XPS band bending analyses also showed that room temperature bombardment induced a small reduction (0.2 eV) of the surface Fermi level position (EFs) on the p-diamond. However, subsequent vacuum annealing caused a rather large increase of EFs. But the EFs data from about 20 bombarded and annealed samples were always less than 2.2 eV. Thus the formation of an n-type diamond was not observed.

Lau, W. M.; Huang, L. J.; Bello, I.; Yiu, Y. M.; Lee, S.-T.

1994-04-01

288

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

NASA Astrophysics Data System (ADS)

We study graphene formation (by selective Si evaporation) and adhesion on SiC surfaces as well as stacking and binding of graphane multilayers [1] using a number of versions of the van der Waals Density Functional (vdW-DF) method [2] and plane-wave density functional theory calculations. For the graphene/SiC systems and for the graphane multilayers we document that the bonding is entirely dominated by van der Waals (vdW) forces. At the same time we find that dispersive forces acting on the layers produce significant modifications in the graphene and graphane band structure. We interpret the changes and discuss a competition between wave function hybridization and interaction with the charge enhancement (between the layers) that results from density overlap. [4pt] [1] J. Rohrer and P. Hyldgaard, http://arxiv.org/abs/1010.2925[0pt] [2] Dion et al, PRL 92, 246401 (2004); V.R.Cooper, PRB 81, 161104(R) (2010), K. Lee et al PRB 82, 081101(R) (2010).

Hyldgaard, Per; Rohrer, Jochen

2011-03-01

289

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

290

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

PubMed Central

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

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

2011-01-01

291

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

292

Band structures of cylindrical AlN/GaN quantum dots with fully coupled piezoelectric models  

NASA Astrophysics Data System (ADS)

We study the coupled electro-mechanical effects in the band structure calculations of low dimensional semiconductor nanostructures (LDSNs) such as AlN/GaN quantum dots. Some effects in these systems are essentially nonlinear. Strain, piezoelectric effects, eigenvalues and wave functions of a quantum dot have been used as tuning parameters for the optical response of LDSNs in photonics, band gap engineering and other applications. However, with a few noticeable exceptions, the influence of piezoelectric effects in the electron wave functions in Quantum Dots (QDs) studied with fully coupled models has been largely neglected in the literature. In this paper, by using the fully coupled model of electroelasticity, we analyze the piezoelectric effects into the band structure of cylindrical quantum dots. Results are reported for III-V type semiconductors with a major focus given to AlN/GaN based QD systems.

Prabhakar, Sanjay; Melnik, Roderick

2010-08-01

293

Reconstruction of Band Structure Induced by Electronic Nematicity in an FeSe Superconductor.  

PubMed

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

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

2014-12-01

294

Structural band-gap tuning in g-C3N4.  

PubMed

g-C3N4 is a promising material for hydrogen production from water via photo-catalysis, if we can tune its band gap to desirable levels. Using a combined experimental and ab initio approach, we uncover an almost perfectly linear relationship between the band gap and structural aspects of g-C3N4, which we show to originate in a changing overlap of wave functions associated with the lattice constants. This changing overlap, in turn, causes the unoccupied pz states to experience a significantly larger energy shift than any other occupied state (s, px, or py), resulting in this peculiar relationship. Our results explain and demonstrate the possibility to tune the band gap by structural means, and thus the frequency at which g-C3N4 absorbs light. PMID:25408139

Zuluaga, Sebastian; Liu, Li-Hong; Shafiq, Natis; Rupich, Sara M; Veyan, Jean-François; Chabal, Yves J; Thonhauser, Timo

2015-01-14

295

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

PubMed

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

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

2010-04-01

296

Reconstruction of Band Structure Induced by Electronic Nematicity in an FeSe Superconductor  

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

297

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

SciTech Connect

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

Kim, Dong Wook, E-mail: dong0414@snu.ac.kr [Department of Materials Science and Engineering, Seoul National University, Seoul 151-744 (Korea, Republic of); Research Institute of Advanced Materials (RIAM), Seoul National University, Seoul 151-744 (Korea, Republic of); Cho, In-Sun [Department of Mechanical Engineering, Stanford University, Stanford, California 94305 (United States); Shin, Seong Sik [Department of Materials Science and Engineering, Seoul National University, Seoul 151-744 (Korea, Republic of); Lee, Sangwook [Department of Materials Science and Engineering, Seoul National University, Seoul 151-744 (Korea, Republic of); Research Institute of Advanced Materials (RIAM), Seoul National University, Seoul 151-744 (Korea, Republic of); Noh, Tae Hoon; Kim, Dong Hoe [Department of Materials Science and Engineering, Seoul National University, Seoul 151-744 (Korea, Republic of); Jung, Hyun Suk [School of Advanced Materials Engineering, Kookmin University, Seoul 136-702 (Korea, Republic of); Hong, Kug Sun, E-mail: kshongss@plaza.snu.ac.kr [Department of Materials Science and Engineering, Seoul National University, Seoul 151-744 (Korea, Republic of); Research Institute of Advanced Materials (RIAM), Seoul National University, Seoul 151-744 (Korea, Republic of)

2011-08-15

298

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

299

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

SciTech Connect

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

Canulescu, S., E-mail: stec@fotonik.dtu.dk; Schou, J. [Department of Photonics Engineering, Technical University of Denmark, 4000 Roskilde (Denmark); Rechendorff, K.; Pleth Nielsen, L. [Danish Technological Institute, Kongsvang Alle 29, 8000 Aarhus (Denmark); Borca, C. N. [Paul Scherrer Institute, 5232 Villigen (Switzerland); Jones, N. C.; Hoffmann, S. V. [ISA, Department of Physics and Astronomy, Aarhus University, 8000 Aarhus (Denmark); Bordo, K.; Ambat, R. [Department of Mechanical Engineering, Technical University of Denmark, 2800 Kongens Lyngby (Denmark)

2014-03-24

300

Time-dependent model for diluted magnetic semiconductors including band structure and confinement effects  

E-print Network

Time-dependent model for diluted magnetic semiconductors including band structure and confinement dynamics in confined diluted magnetic semiconductors induced by laser. The hole-spin relaxation process light-induced magnetization dynamics in ferro- magnetic films and in diluted magnetic semiconductors DMS

Boyer, Edmond

301

Band-structure-corrected local density approximation study of semiconductor quantum dots and wires  

Microsoft Academic Search

This paper presents results of ab initio accuracy thousand atom calculations of colloidal quantum dots and wires using the charge patching method. We have used density functional theory under local density approximation (LDA), and we have corrected the LDA bulk band structures by modifying the nonlocal pseudopotentials, so that their effective masses agree with experimental values. We have systematically studied

Jingbo Li; Lin-Wang Wang

2005-01-01

302

PHYSICAL REVIEW B 85, 195405 (2012) Graphene on Ru(0001): Evidence for two graphene band structures  

E-print Network

grown on single-crystal substrates such as Ru(0001) is extremely ordered,1­10 but characterized by two for the "split" valence-band structure of graphene on Ru(0001) (Ref. 25) and SiC.26 The moir´e resulting from

Goodman, Wayne

303

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

E-print Network

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

Swaminathan, Madhavan

304

InN/GaN Superlattices: Band Structures and Their Pressure Dependence Iza Gorczyca1  

E-print Network

InN/GaN Superlattices: Band Structures and Their Pressure Dependence Iza Gorczyca1Ã? , Tadek Suski1; published online May 20, 2013 Creation of short-period InN/GaN superlattices is one of the possible ways with one monolayer of InN and 40 monolayers of GaN. The results are compared with calculations performed

Svane, Axel Torstein

305

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

NASA Astrophysics Data System (ADS)

In previous studies, several authors have reported inner magnetosphere observations of proton distributions confined to narrow energy bands in the range of 1-25 keV (Smith and Hoffman (1974), etc). These structures have been described as "nose structures", with reference to their appearance in energy-time spectrograms and are also known as "bands" if they occur for extended periods of time. Statistical surveys (Buzulukova et al. (2003); Vallat et al. (2007)) of these features in Interball and Cluster data highlight the presence of single nose in nightside sectors and multi-nose strutures in the dayside sectors. We examine Double-Star TC1 HIA data mainly recorded in the equatorial plane of the inner magnetosphere (L<15) to see how observations of "multi-banded structures" compare to the observations from more inclined orbits of Cluster and Interball. We investigate the properties of these multi-banded structures and carry out a statistical survey analysing them as a function of geomagnetic activity. This is a comparison study to a similar study conducted using DoubleStar TC-1 PEACE electron data.

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

2014-05-01

306

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

E-print Network

Electrochemistry at Single-Walled Carbon Nanotubes: The Role of Band Structure and Quantum description of the kinetics of electrochemical charge transfer at single- walled carbon nanotube (SWNT material.1 Recently, there has been a large interest in using single-walled carbon nanotubes (SWNTs

Dekker, Cees

307

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

E-print Network

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

Iglic, Ales

308

Electrochemical studies of the effects of the size, ligand and composition on the band structures of CdSe, CdTe and their alloy nanocrystals.  

PubMed

In this paper, we have elucidated the fundamental principle of employing CV to investigate the band structures of semiconductor nanocrystals (SNCs), and have also built up an optimal protocol for performing such investigation. By utilizing this protocol, we are able to obtain well-defined and characteristic electrochemical redox signals of SNCs, which allows us to intensively explore the influences of the particle size, the surface ligand and particle composition on the band structures of CdSe, CdTe and their alloy nanocrystals. The size-, ligand- and composition-dependent band structures of CdSe and CdTe nanocrystals (NCs) have therefore been mapped out, respectively, which are generally consistent with the previous theoretical and experimental reports. We believe that the optimal protocol and the original results regarding electrochemical characterization of SNCs demonstrated in this paper will definitely benefit the better understanding, modulation and application of the unique electronic and optical properties of SNCs. PMID:24468655

Liu, Jinjin; Yang, Wanting; Li, Yunchao; Fan, Louzhen; Li, Yongfang

2014-03-14

309

Structure of InSb(001) surface.  

PubMed

The InSb(001) surface has been studied experimentally, using room temperature scanning tunnelling microscopy (RT STM), and theoretically, using ab initio density functional theory (DFT) calculations. RT experimental STM images show bright lines running along the bulk crystal [110] direction. Resolved features between the bright lines whose appearance depends on the applied bias voltage confirm clearly the c(8×2) reconstruction of this surface. Our calculations, which are reported for this surface for the first time, include the reconstructed 4×2 and c(8×2) surfaces, the latter according to the so-called ?-model proposed previously by Lee et al and Kumpf et al. A 'defective' structure proposed previously by Kumpf et al, which contains an extra In atom within a top bilayer is also considered. In all cases, we obtained stable structures. Calculated STM images for the c(8×2) reconstruction obtained using the Tersoff-Hamann approximation compare extremely well with the experimental ones. We also find that the defect structure may not be clearly visible in the STM images. Finally, a brief discussion is given on the other, although closely related, phase of the same surface observed previously in low temperature (LT) experimental STM images (Goryl et al 2007 Surf. Sci. 601 3605). PMID:21386467

Toton, Dawid; He, Jiangping; Goryl, Grzegorz; Kolodziej, Jacek J; Godlewski, Szymon; Kantorovich, Lev; Szymonski, Marek

2010-07-01

310

A ppM-focused klystron at X-band with a travelling-wave output structure  

SciTech Connect

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

Eppley, K.R.

1994-10-01

311

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

SciTech Connect

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

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

2014-04-28

312

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

E-print Network

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

Paris-Sud XI, Université de

313

Dielectric functions and electronic band structure of lead zirconate titanate thin films  

NASA Astrophysics Data System (ADS)

We measure pseudodielectric functions in the visible-deep ultraviolet spectral range of Pb(ZrxTi1-x)O3 (x=0.2,0.56,0.82) (PZT), Pb0.98Nb0.04(Zr0.2Ti0.8)0.96O3, Pb0.91La0.09(Zr0.65Ti0.35)0.98O3, and Pb0.85La0.15Ti0.96O3 films grown on platinized silicon substrates using a sol-gel method and on (0001) sapphire using a radio-frequency sputtering method. Using a parametric optical constant model, we estimate the dielectric functions (?) of the perovskite oxide thin films. Taking the second derivative of the fitted layer dielectric functions and using the standard critical-point model, we determine the parameters of the critical points. In the second derivative spectra, the lowest band-gap energy peak near 4 eV is fitted as a double peak for annealed PZTs due to the perovskite phase. As-grown PZTs have mainly pyrochlore phase and the lowest band-gap peak is fitted as a single peak. We also examine the effect of dopants La and Nb, which substitute at Pb and Zr (Ti) sites, respectively. We found three band gaps Ea (~3.9 eV), Eb (~4.5 eV), and Ec (~6.5 eV) in the order of increasing energy. The Ea and Eb band-gap energies were not sensitive to Zr composition. We discuss the change of critical-point parameters for PZTs in comparison to the band-structure calculations based on local-density approximation. The near constancy of the lowest band-gap energy independent of Zr composition is consistent with the band-structure calculations.

Lee, Hosun; Kang, Youn Seon; Cho, Sang-Jun; Xiao, Bo; Morkoç, Hadis; Kang, Tae Dong; Lee, Ghil Soo; Li, Jingbo; Wei, Su-Huai; Snyder, P. G.; Evans, J. T.

2005-11-01

314

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

315

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. PMID:24170984

Xu, Ziqiang

2013-01-01

316

Low-energy band structures of armchair ribbon-graphene hybrid systems  

Microsoft Academic Search

The electronic properties of armchair ribbon-graphene hybrid systems are studied within the 2pz tight-binding model. The geometric structures of graphene nanoribbons, such as the width (Ny) and the period (Ry) of the ribbons, greatly determine the band structures. Furthermore, the stacking arrangement between graphene nanoribbons and monolayer graphene also plays an important role in low-energy states. Energy gaps caused by

C. H. Lee; S. C. Chen; R. B. Chen; M. F. Lin

2011-01-01

317

Surface band-bending and Fermi-level pinning in doped Si observed by Kelvin force microscopy  

NASA Astrophysics Data System (ADS)

The workfunction change in doped Si was examined using Kelvin force microscopy in a wide range of doping concentrations from p-type ˜1019 to n-type ˜1020 cm-3 corresponding to the bulk Fermi-level positions from near the valence-band top to conduction-band minimum. Experimental data can be reproduced by model calculations using an appropriate surface-state density composed of the donor- and acceptor-like gap states. These results indicate that no appreciable surface-band bending occurs for doping concentrations less than ˜1014 cm-3 while the bending becomes prominent and the surface Fermi-level is eventually pinned in the midgap region as the concentration increases to ˜1020 cm-3.

Arita, Makoto; Torigoe, Kazuhisa; Yamauchi, Takashi; Nagaoka, Takashi; Aiso, Toru; Yamashita, Yasuhisa; Motooka, Teruaki

2014-03-01

318

Electron density distribution of bilayer nanographene and band structures of boron-carbon-nitride systems  

E-print Network

Bilayer graphene nanoribbon with zigzag edge is investigated with the tight binding model. Two stacking structures, alpha and beta, are considered. The band splitting is seen in the alpha structure, while the splitting in the wave number direction is found in the beta structure. The local density of states in the beta structure tend to avoid sites where interlayer hopping interactions are present. The calculation is extended to the boron-carbon-nitride systems. The qualitative properties persist when zigzag edge atoms are replaced with borons and nitrogens.

Harigaya, Kikuo

2011-01-01

319

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

320

A compact broadband microstrip patch antenna with defective ground structure for C-Band applications  

NASA Astrophysics Data System (ADS)

A novel design of a circular patch antenna having defected ground structure is presented in this communication. The antenna is designed for C-band applications. A wide bandwidth of 60.3% (4.04-7.28) GHz is obtained in the C-band frequency range 4-8 GHz. It is also found through parametric analysis that shape and dimensions of the finite ground plane and slots in the patch are the key factors in improving the bandwidth of the proposed geometry. The antenna is fabricated using FR-4 substrate and parameters like return loss, VSWR and input impedance are measured experimentally.

Rawat, Sanyog; Sharma, K. K.

2014-09-01

321

The paradox of an insulating contact between a chemisorbed molecule and a wide band gap semiconductor surface.  

PubMed

Controlling the intrinsic optical and electronic properties of a single molecule adsorbed on a surface requires electronic decoupling of some molecular orbitals from the surface states. Scanning tunneling microscopy experiments and density functional theory calculations are used to study a perylene molecule derivative (DHH-PTCDI), adsorbed on the clean 3 × 3 reconstructed wide band gap silicon carbide surface (SiC(0001)-3 × 3). We find that the LUMO of the adsorbed molecule is invisible in I(V) spectra due to the absence of any surface or bulk states and that the HOMO has a very low saturation current in I(z) spectra. These results present a paradox that the molecular orbitals are electronically isolated from the surface of the wide band gap semiconductor even though strong chemical bonds are formed. PMID:22193154

Yang, H; Boudrioua, O; Mayne, A J; Comtet, G; Dujardin, G; Kuk, Y; Sonnet, Ph; Stauffer, L; Nagarajan, S; Gourdon, A

2012-02-01

322

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

323

Determination of the valence band structure of an alkali phosphorus oxynitride glass: A synchrotron XPS study on LiPON  

NASA Astrophysics Data System (ADS)

Lithium phosphorus oxynitride (LiPON) is a solid state electrolyte commonly used in thin film batteries (TFBs). Advanced TFBs face the issue of detrimental electrode-electrolyte interlayer formation, related to the electronic structure of the interface. In this contribution, we study the valence band structure of LiPON using resonant photoemission and synchrotron photoemission with variable excitation energies. The identification of different valence band features is done according to the known valence band features of meta- and orthophosphates. Additionally we compare our results with partial density of states simulations from literature. We find that the valence band structure is similar to the known metaphosphates with an additional contribution of nitrogen states at the top of the valence band. From the results we conclude that synchrotron X-ray photoemission (XPS) is a useful tool to study the valence band structure of nitridated alkali phosphate glasses.

Schwöbel, André; Precht, Ruben; Motzko, Markus; Carrillo Solano, Mercedes A.; Calvet, Wolfram; Hausbrand, René; Jaegermann, Wolfram

2014-12-01

324

Bending vibration band structure of phononic crystal beam by modified transfer matrix method  

NASA Astrophysics Data System (ADS)

The bending vibration band structure of phononic crystal (PC) beam is solved by a unified formulation of the modified transfer matrix (MTM) method in this paper. The improvement of MTM method is the introduction of constitutive matrix U and matrix of derivative functions V, which standardizes and simplifies the deduction by the matrix operation. The band structure of an epoxy-aluminum PC Timoshenko beam is calculated by both MTM method and plane wave expansion (PWE) method. The results show that the present MTM method has a great advantage in the precision of the result. In addition, the formulation of transfer matrix derived from Timoshenko beam condition is a general form which is also suitable for other general beam structures just by replacing corresponding matrices.

Ni, Zhi-Qiang; Zhang, Yan; Jiang, Lin-Hua; Han, Lin

2014-04-01

325

Bloch mode synthesis: Ultrafast methodology for elastic band-structure calculations  

NASA Astrophysics Data System (ADS)

We present a methodology for fast band-structure calculations that is generally applicable to problems of elastic wave propagation in periodic media. The methodology, called Bloch mode synthesis, represents an extension of component mode synthesis, a set of substructuring techniques originally developed for structural dynamics analysis. In Bloch mode synthesis, the unit cell is divided into interior and boundary degrees-of-freedom, which are described, respectively, by a set of normal modes and a set of constraint modes. A combination of these mode sets then forms a reduced basis for the band structure eigenvalue problem. The reduction is demonstrated on a phononic-crystal model and a locally resonant elastic-metamaterial model and is shown to accurately predict the frequencies and Bloch mode shapes with a dramatic decrease in computation time in excess of two orders of magnitude.

Krattiger, Dimitri; Hussein, Mahmoud I.

2014-12-01

326

Structurally tuned iridescent surfaces inspired by nature  

NASA Astrophysics Data System (ADS)

Iridescent surfaces exhibit vivid colours which change with the angle of incidence or viewing due to optical wave interference in the multilayer structure present at the wavelength scale underneath the surface. In nature, one can find examples of iridescent Coleoptera for which the hue changes either greatly or slightly with the angle. Because these species typically make these structures from a single biological material (usually chitin) and air or water as the low refractive index component, they have evolved by adjusting the layer thicknesses in order to display quite different iridescent aspects. Taking inspiration from this proven strategy, we have designed and fabricated periodic TiO2/SiO2 multilayer films in order to demonstrate the concept of structurally tuned iridescent surfaces. Titanium or silicon oxide layers were deposited on a glass substrate using dc reactive or RF magnetron sputtering techniques, respectively. Two structures were designed for which the period and the TiO2/SiO2 layer thickness ratio were varied in such a way that the films displayed radically different iridescent aspects: a reddish-to-greenish changing hue and a stable bluish hue. The fabricated samples were characterized through specular reflectance/transmittance measurements. Modelling of transmittance spectra using standard multilayer film theory confirmed the high quality of the twelve-period Bragg reflectors. The chromaticity coordinates, which were calculated from measured reflectance spectra taken at different angles, were in accordance with theoretical predictions.

Deparis, Olivier; Rassart, Marie; Vandenbem, Cédric; Welch, Victoria; Pol Vigneron, Jean; Lucas, Stéphane

2008-01-01

327

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

SciTech Connect

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

Rusinov, I. P., E-mail: rusinovip@gmail.com; Nechaev, I. A. [Tomsk State University (Russian Federation); Chulkov, E. V. [Donostia International Physics Center (DIPC) (Spain)

2013-06-15

328

Dielectric function and critical points of the band structure for AlGaN alloys  

NASA Astrophysics Data System (ADS)

The ordinary complex dielectric function (DF) of AlxGa1-xN alloys with 0 x 0.53 is determined by fitting spectroscopic ellipsometry data from the infrared to the vacuum ultraviolet spectral region (0.74 eV E 9.8 eV). The dispersion of the real part of the DF below the band gap is found to be in excellent agreement with previously published data. The obtained band gap energies are verified by photoluminescence and photoreflectance spectroscopy. In the high-energy range, three critical points of the band structure are clearly resolved. By applying a third-derivative based DF line shape analysis, the corresponding transition energies are determined. Their compositional dependences can be described on the basis of small bowing parameters.

Buchheim, C.; Goldhahn, R.; Rakel, M.; Cobet, C.; Esser, N.; Rossow, U.; Fuhrmann, D.; Hangleiter, A.

2005-11-01

329

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

330

Semianalytical formulation on the scattering of proximity equilibration cell closed ring photonic band gap structures  

NASA Astrophysics Data System (ADS)

A novel semianalytical methodology is used to analyze a periodic array of printed metallic closed ring elements in a multilayered dielectric structure. This approach is unique in that it is the first methodology capable in modeling structures with resonant implants and interelement dimensions well beyond the effective medium theory. In addition, it yields computational efficiency by 2 orders of magnitude over standard computational methods in computing the scattering parameters for proximity equilibration cell (PEC) closed ring multilayered (electromagnetic band gap and photonic band gap (PBG)) structures. Moreover, it provides physical insight in the implementation of metallic implants for practical applications. This methodology satisfies the Kramers-Kronig relations and causality, and therefore it allows for the development of semianalytical expressions for the composite's wave impedance, index of refraction, as well as the permittivity and permeability parameters accounting for full dispersion. For general artificial multilayered structures (PBG metamaterials) with centrosymmetric scattering matrices, the composite may be replaced by an equivalent homogeneous dispersive magneto-dielectric material and may be used for the design of integrated circuits, filters, and antennas using standard methods. Otherwise, use of the scattering matrix approach to obtain the effective parameters is valid only for semi-infinite structures. The upper band edge is determined by the host material uniquely and the bandwidth is determined by the shunt susceptance for different PEC ring inclusions.

Liu, Yunhong; Alexopoulos, Nicolaos G.

2007-12-01

331

Numerical simulation of evaluation of surface breaking cracks by array-lasers generated narrow-band SAW  

NASA Astrophysics Data System (ADS)

Most of the factors limiting the extensive application of laser-based ultrasonic for nondestructive evaluation of surface breaking crack are its poor sensitivity, low efficiency relative to conventional contact ultrasonic methods and limit on the dimension of the cracks. For this reason, a new technique that multiplepulse narrow-band ultrasound generated by laser arrays has been proposed. It is found that crack detection dependent on spectrum of narrow-band ultrasound generated by laser arrays can be operated with low amplitude requirements. In this paper, the narrow-band ultrasound generated by pulse laser arrays interacting with surface breaking cracks has been simulated in detail by the finite element method (FEM) according to the thermoelastic theory. The pulsed array lasers were assumed to be transient heat source, and the surface acoustic wave (SAW) which propagating on the top of the plate was computed based on thermoelastic theory. Then the frequency spectrums of both reflected waves by crack and transmission ones through crack were compared with the direct waves. Results demonstrate that multiple-frequency components of the narrow-band ultrasound were varied with change of the depth of surface breaking cracks significantly, which provides the possibility for precise evaluation of surface breaking cracks.

Dong, Li-Ming; Ni, Chen-Yin; Shen, Zhong-Hua; Ni, Xiao-Wu

2011-09-01

332

The Glacier and Ice Surface Topography Interferometer: UAVSAR's Single-pass Ka-Band Interferometer  

NASA Astrophysics Data System (ADS)

In May 2009 a new radar technique for mapping ice surface topography was demonstrated in a Greenland campaign as part of the NASA International Polar Year (IPY) activities. This was achieved with the airborne Glacier and Ice Surface Topography Interferometer (GLISTIN-A): a 35.6 GHz single-pass interferometer. Although the technique of using radar interferometry for mapping terrain has been demonstrated before, this is the first such application at millimeter-wave frequencies. The proof-of-concept demonstration was achieved by interfacing Ka-band RF and antenna hardware with the Uninhabited Airborne Vehicle Synthetic Aperture Radar (UAVSAR). The GLISTIN-A was implemented as a custom installation of the NASA Dryden Flight Research Center Gulfstream III. Instrument performance indicates swath widths over the ice between 5-7km, with height precisions ranging from 30cm-3m at a posting of 3m x 3m. Processing challenges were encountered in achieving the accuracy requirements on several fronts including, aircraft motion sensitivity, multipath and systematic drifts. However, through a combination of processor optimization, a modified phase-screen and motion-compensation implementations were able to minimize the impact of these systematic error sources. We will present results from the IPY data collections including system performance evaluations and imagery. This includes a large area digital elevation model (DEM) collected over Jakobshavn glacier as an illustrative science data product. Further, by intercomparison with the NASA Wallops Airborne Topographic Mapper (ATM) and calibration targets we quantify the interferometric penetration bias of the Ka-band returns into the snow cover. Following the success of the IPY campaign, we are funded under the Earth Science Techonology Office (ESTO) Airborne Innovative Technology Transition (AITT) program to transition GLISTIN-A to a permanently-available pod-only system compatible with unpressurized operation. In addition fundamental system upgrades will greatly enhance the performance and make wider-swath and higher altitude operation possible. We will show results from first flights of GLISTIN-A and summarize the plans for the near future including GLISTIN-H: GLISTIN on the NASA Global Hawk Spring 2013.

Moller, D.; Hensley, S.; Sadowy, G.; Wu, X.; Carswell, J.; Fisher, C.; Michel, T.; Lou, Y.

2012-12-01

333

Inferring Land Surface Model Parameters for the Assimilation of Satellite-Based L-Band Brightness Temperature Observations into a Soil Moisture Analysis System  

NASA Technical Reports Server (NTRS)

The Soil Moisture and Ocean Salinity (SMOS) satellite mission provides global measurements of L-band brightness temperatures at horizontal and vertical polarization and a variety of incidence angles that are sensitive to moisture and temperature conditions in the top few centimeters of the soil. These L-band observations can therefore be assimilated into a land surface model to obtain surface and root zone soil moisture estimates. As part of the observation operator, such an assimilation system requires a radiative transfer model (RTM) that converts geophysical fields (including soil moisture and soil temperature) into modeled L-band brightness temperatures. At the global scale, the RTM parameters and the climatological soil moisture conditions are still poorly known. Using look-up tables from the literature to estimate the RTM parameters usually results in modeled L-band brightness temperatures that are strongly biased against the SMOS observations, with biases varying regionally and seasonally. Such biases must be addressed within the land data assimilation system. In this presentation, the estimation of the RTM parameters is discussed for the NASA GEOS-5 land data assimilation system, which is based on the ensemble Kalman filter (EnKF) and the Catchment land surface model. In the GEOS-5 land data assimilation system, soil moisture and brightness temperature biases are addressed in three stages. First, the global soil properties and soil hydraulic parameters that are used in the Catchment model were revised to minimize the bias in the modeled soil moisture, as verified against available in situ soil moisture measurements. Second, key parameters of the "tau-omega" RTM were calibrated prior to data assimilation using an objective function that minimizes the climatological differences between the modeled L-band brightness temperatures and the corresponding SMOS observations. Calibrated parameters include soil roughness parameters, vegetation structure parameters, and the single scattering albedo. After this climatological calibration, the modeling system can provide L-band brightness temperatures with a global mean absolute bias of less than 10K against SMOS observations, across multiple incidence angles and for horizontal and vertical polarization. Third, seasonal and regional variations in the residual biases are addressed by estimating the vegetation optical depth through state augmentation during the assimilation of the L-band brightness temperatures. This strategy, tested here with SMOS data, is part of the baseline approach for the Level 4 Surface and Root Zone Soil Moisture data product from the planned Soil Moisture Active Passive (SMAP) satellite mission.

Reichle, Rolf H.; De Lannoy, Gabrielle J. M.

2012-01-01

334

A Local-Density Band Theory for the Fermi Surface of the Heavy-Electron Compound CeRu2Si2  

NASA Astrophysics Data System (ADS)

On the basis of the itinerant-electron model for the 4f electrons, the energy band structure and the Fermi surface are calculated for the metamagnetic heavy-electron compound CeRu2Si2 having the low-temperature electronic specific heat coefficient ? of 350 mJ/K2 mol. by a self-consistent symmetrized relativistic APW method with the exchange and correlation potential in a local-density approximation. The main Fermi surface consists of a large closed hole sheet and a complicated electron sheet like a jungle gym. The Fermi surface topology is consistent with the experimental result for the high-field magneto-resistance. By comparison with the electronic structure of LaRu2Si2, effects of the 4f bands on the Bloch states on the Fermi surface in CeRu2Si2 are investigated in detail. Strong evidences for existence of the electron sheet are found in available experimental de Haas-van Alphen frequencies. The enhancement factor for ? is estimated as 38.

Yamagami, Hiroshi; Hasegawa, Akira

1993-02-01

335

Surface passivation of a photonic crystal band-edge laser by atomic layer deposition of SiO2 and its application for biosensing.  

PubMed

We report on the conformal surface passivation of photonic crystal (PC) laser devices with an ultrathin dielectric layer. Air-bridge-type ?-point band-edge lasers (BELs) are fabricated by forming a honeycomb lattice two-dimensional PC structure into an InGaAsP multiple-quantum-well epilayer. Atomic layer deposition (ALD) is employed for conformal deposition of a few-nanometer-thick SiO2 layer over the entire device surface, not only on the top and bottom surfaces of the air-bridge membrane but also on the air-hole sidewalls. Despite its extreme thinness, the ALD passivation layer is found to protect the InGaAsP BEL devices from harsh chemicals. In addition, the ALD-SiO2 is compatible with the silane-based surface chemistry, which allows us to use ALD-passivated BEL devices as label-free biosensors. The standard streptavidin-biotin interaction shifts the BEL lasing wavelength by ?1 nm for the dipole-like ?-point band-edge mode. A sharp lasing line (<0.2 nm, full width at half-maximum) and a large refractive index sensitivity (?163 nm per RIU) produce a figure of merit as high as ?800 for our BEL biosensor, which is at least an order of magnitude higher than those of more common biosensors that rely on a broad resonance peak, showing that our nanolaser structures are suitable for highly sensitive biosensor applications. PMID:25631610

Cha, Hyungrae; Lee, Jeongkug; Jordan, Luke R; Lee, Si Hoon; Oh, Sang-Hyun; Kim, Hyo Jin; Park, Juhun; Hong, Seunghun; Jeon, Heonsu

2015-02-12

336

Band structures of phononic crystal composed of lattices with different periodic constants  

NASA Astrophysics Data System (ADS)

With a square lattice mercury and water system being as the model, the band structures of nesting and compound phononic crystals with two different lattice constants were investigated using the method of the supercell plane wave expansion. It was observed that large band gaps can be achieved in low frequency regions by adjusting one of the lattice constants. Meanwhile, effects similar to interstitial impurity defects can be achieved with the increase of lattice constant of the phononic crystal. The corresponding defect modes can be stimulated in band gaps. The larger the lattice constant, the stronger the localization effect of defect modes on the wave. In addition, the change of the filling fraction of impurity exerts great influence on the frequency and localization of defect modes. Furthermore, the change of the position of impurity has notable influence on the frequency of defect modes and their localization. However, the geometry structure and orientation of impurity have little effect on the frequency of defect modes and their localization in the band gap.

Hu, Jia-Guang; Xu, Wen

2014-05-01

337

Energy-band structure in strained silicon: A 20-band k?p and Bir-Pikus Hamiltonian model  

NASA Astrophysics Data System (ADS)

A strain Bir-Pikus Hamiltonian Hst, associated with a 20-band sp3s* k?p Hamiltonian Hkp, is used to describe the valence band and the first two conduction bands all over the Brillouin zone. Because the local (in k space) deformation potentials ?u and ?d used in pseudopotential method are unusable in k?p theory, we show that taking into account the Bir-Pikus parameters (a, b) of the Brillouin zone center in the Hst Hamiltonian allows one to describe the dispersion relation in the whole Brillouin zone. The method is applied to strained Si on a relaxed Si1-xGex alloy. The values of the energy band gap, and of the ?2-4 conduction band splitting between the four equivalent in-plane valleys ?4 and the two valleys along the growth direction ?2 are in very good agreement with those reported in other publications. The small value of the spin-orbit splitting in silicon is taken explicitly into account. We show that the valence band splitting is consequently not proportional to the stress.

Richard, Soline; Aniel, Frédéric; Fishman, Guy; Cavassilas, Nicolas

2003-08-01

338

Structure of the Azotobacter vinelandii surface layer.  

PubMed Central

Electron microscopy of the Azotobacter vinelandii tetragonal surface array, negatively stained with ammonium molybdate in the presence of 1 mM calcium chloride, showed an apparent repeat frequency of 12 to 13 nm. Image processing showed dominant tetrad units alternating with low-contrast cruciform structures formed at the junction of slender linkers extending from corner macromolecules of four adjoining dominant units. The actual unit cell showed p4 symmetry, and a = b = 18.4 nm. Distilled water extraction of the surface array released a multimeric form of the single 60,000 molecular-weight protein (S protein) which constitutes the surface layer. The molecular weight of the multimer was estimated at 255,000 by gel filtration, indicating a tetrameric structure of four identical subunits and suggesting that this multimer was the morphological subunit of the S layer. Tetrameric S protein exhibited low intrinsic stability once released from the outer membrane, dissociating into monomers when incubated in a variety of buffers including those which served as the base for defined media used to cultivate A. vinelandii. The tetramer could not be stabilized in these buffers at any temperature between 4 and 30 degrees C, but the addition of 2 to 5 mM Ca2+ or Mg2+ completely prevented its dissociation into monomers. Circular dichroism measurements indicated that the secondary structure of the tetramer was dominated by aperiodic and beta-sheet conformations, and the addition of Ca2+ did not produce any gross changes in this structure. Only the tetrameric form of S protein was able to reassemble in vitro in the presence of divalent cations onto the surface of cells stripped of their native S layer. Images PMID:3804978

Bingle, W H; Whippey, P W; Doran, J L; Murray, R G; Page, W J

1987-01-01

339

High-order modes of spoof surface plasmonic wave transmission on thin metal film structure.  

PubMed

Recently, conformal surface plasmon (CSP) structure has been successfully proposed that could support spoof surface plasmon polaritons (SPPs) on corrugated metallic strip with ultrathin thickness [Proc. Natl. Acad. Sci. U.S.A. 110, 40-45 (2013)]. Such concept provides a flexible, conformal, and ultrathin wave-guiding element, very promising for application of plasmonic devices, and circuits in the frequency ranging from microwave to mid-infrared. In this work, we investigated the dispersions and field patterns of high-order modes of spoof SPPs along CSP structure of thin metal film with corrugated edge of periodic array of grooves, and carried out direct measurement on the transmission spectrum of multi-band of surface wave propagation at microwave frequency. It is found that the mode number and mode bands are mainly determined by the depth of the grooves, providing a way to control the multi-band transmission spectrum. We have also experimentally verified the high-order mode spoof SPPs propagation on curved CSP structure with acceptable bending loss. The multi-band propagation of spoof surface wave is believed to be applicable for further design of novel planar devices such as filters, resonators, and couplers, and the concept can be extended to terahertz frequency range. PMID:24514689

Liu, Xiaoyong; Feng, Yijun; Zhu, Bo; Zhao, Junming; Jiang, Tian

2013-12-16

340

Photonic band gap structures of obliquely incident electromagnetic wave propagation in a one-dimension absorptive plasma photonic crystal  

SciTech Connect

The photonic band gap structures of obliquely incident electromagnetic waves propagating in a one-dimension plasma photonic crystal with collision have been studied on the basis of electromagnetic theory and transfer matrix approach. The dispersion relations for both the transverse electric wave case and the transverse magnetic wave case are deduced. And the photonic band gap structures, with their function dependence on the microplasma layer density, microplasma width, collision frequency, background material dielectric constant, and incident angle, are computed. The results show that there exist two photonic band gap structures in an adsorptive plasma photonic crystal: one is a normal photonic band gap structure and the other is an absorption photonic band gap structure. Parameter dependence of the effects is calculated and discussed.

Guo Bin [Department of Physical Science and Technology, Wuhan University of Technology, Wuhan 430070 (China)

2009-04-15

341

Structural phase transition in IrTe2: A combined study of optical spectroscopy and band structure calculations  

PubMed Central

Ir1?xPtxTe2 is an interesting system showing competing phenomenon between structural instability and superconductivity. Due to the large atomic numbers of Ir and Te, the spin-orbital coupling is expected to be strong in the system which may lead to nonconventional superconductivity. We grew single crystal samples of this system and investigated their electronic properties. In particular, we performed optical spectroscopic measurements, in combination with density function calculations, on the undoped compound IrTe2 in an effort to elucidate the origin of the structural phase transition at 280?K. The measurement revealed a dramatic reconstruction of band structure and a significant reduction of conducting carriers below the phase transition. We elaborate that the transition is not driven by the density wave type instability but caused by the crystal field effect which further splits/separates the energy levels of Te (px, py) and Te pz bands. PMID:23362455

Fang, A. F.; Xu, G.; Dong, T.; Zheng, P.; Wang, N. L.

2013-01-01

342

Azimuthal anisotropy beneath southern Africa from very broad-band surface-wave dispersion measurements  

NASA Astrophysics Data System (ADS)

Seismic anisotropy within the lithosphere of cratons preserves an important record of their ancient assembly. In southern Africa, anisotropy across the Archean Kaapvaal Craton and Limpopo Belt has been detected previously by observations of SKS-wave splitting. Because SKS-splitting measurements lack vertical resolution, however, the depth distribution of anisotropy has remained uncertain. End-member interpretations invoked the dominance of either anisotropy in the lithosphere (due to the fabric formed by deformation in Archean or Palaeoproterozoic orogenies) or that in the asthenosphere (due to the fabric formed by the recent plate motion), each with significant geodynamic implications. To determine the distribution of anisotropy with depth, we measured phase velocities of seismic surface waves between stations of the Southern African Seismic Experiment. We applied two complementary measurement approaches, very broad-band cross-correlation and multimode waveform inversion. Robust, Rayleigh- and Love-wave dispersion curves were derived for four different subregions of the Archean southern Africa in a period range from 5 s to 250-400 s (Rayleigh) and 5 s to 100-250 s (Love), depending on the region. Rayleigh-wave anisotropy was determined in each region at periods from 5 s to 150-200 s, sampling from the upper crust down to the asthenosphere. The jackknife method was used to estimate uncertainties, and the F-test to verify the statistical significance of anisotropy. We detected strong anisotropy with a N-S fast-propagation azimuth in the upper crust of the Limpopo Belt. We attribute it to aligned cracks, formed by the regional, E-W extensional stress associated with the southward propagation of the East African Rift. Our results show that it is possible to estimate regional stress from short-period, surface wave anisotropy, measured in this study using broad-band array recordings of teleseismic surface waves. Rayleigh-wave anisotropy at 70-120 s periods shows that the fabric within the deep mantle lithosphere of the Limpopo Belt and northern Kaapvaal Craton is aligned parallel to the Archean-Palaeoproterozoic sutures at block boundaries. This confirms that the fabric within the lithosphere created by pervasive ancient deformation is preserved to this day. Suture-parallel fabric is absent, however, in the deep lithosphere of the western Kaapvaal Craton, suggesting that it was not reworked in the collision with the craton's core, either due to its mechanical strength or because the deformation mechanism was different from those that operated in the north. Anisotropy at periods greater than 120-130 s shows fast directions parallel to the plate motion and indicates shear wave anisotropy in the asthenosphere. The depth distribution of anisotropy revealed by surface wave measurements comprises elements of both end-member models proposed previously: anisotropy in the asthenosphere shows fast-propagation directions parallel to the plate motion; anisotropy in the Limpopo and northern Kaapvaal lithosphere shows fast directions parallel to the Archean-Palaeoproterozoic sutures. The distribution of SKS-splitting orientations across southern Africa reflects anisotropic fabric both within the lithosphere (dominating the splitting beneath the Limpopo Belt and northern Kaapvaal Craton) and within the asthenosphere (dominating beneath the western Kaapvaal Craton).

Adam, Joanne M.-C.; Lebedev, Sergei

2012-10-01

343

Polarization Effects of GaN and AlGaN: Polarization Bound Charge, Band Bending, and Electronic Surface States  

NASA Astrophysics Data System (ADS)

GaN-based devices are currently limited by reliability issues such as gate leakage and current collapse, where the mechanisms responsible for degradation are closely related to the electronic surface state configuration. Therefore, understanding the electronic surface state configuration of GaN-based materials will help improve device performance. Since GaN has an inherent polarization, these materials are also subject to a bound polarization charge, which influences the electronic state configuration. In this study, the surface band bending of N-face GaN, Ga-face GaN, and Ga-face AlGaN was measured with x-ray photoemission spectroscopy after various cleaning steps to investigate the effects of the polarization. Despite the different surface bound charge on these materials, similar band bending was observed regardless of the magnitude or direction of the charge. Specifically, the band bending varied from -0.1 eV to 0.9 eV on these samples, which supported the models of a Fermi level pinning state at ˜0.4 eV to 0.8 eV below the conduction band. Based on available literature, we suggest this pinning state is indirectly evident of a nitrogen vacancy or gallium-dangling bond.

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

2014-12-01

344

A Experimental Investigation of Surface Ionized Alkali and Alkaline Earth Plasmas Confined by AN Incandescent X-Band Microwave Cavity  

Microsoft Academic Search

A homogeneous and near thermal equilibrium plasma device with optical and microwave diagnostics has been designed and constructed. The surface ionized plasma is confined by an incandescent x-band microwave cavity. The cylindrical cavity is supported by two refractory metal waveguides, and is heated by radiation from two larger ohmically heated W cylinders concentric with the cylindrical cavity. The microwave resonant

Kwang Seok Kim

1983-01-01

345

Measurement of surface scratches on aircraft structures  

NASA Astrophysics Data System (ADS)

In assuring the quality of aircraft, the skin quality must be free of surface imperfections. Surface imperfections such as scratches are unacceptable for cosmetic and structural reasons. Scratches beyond a certain depth are not repairable, resulting in costly replacement of an aircraft's part. Measurements of aircraft exterior surfaces require a ladder or cherry picker for positioning the inspector. Commercially-available computer vision systems are not portable, easy to use, or ergonomic. The machine vision system must be designed with these criteria in mind. The scratch measurement system (SMS) uses computer vision, digital signal processing, and automated inspection methods. The system is portable and battery powered. It is certified for measuring the depth and width of the anomaly. The SMS provides a comprehensive, analytical, and accurate reading. A hardcopy output provides a permanent record of the analysis. The graphical data shows the surface profile and provides substantial information of the surface anomaly. The factory and flight line use the SMS at different stages of aircraft production. Six systems have been built for use within Boeing. A patent was issued for the SMS in February 1994.

Sarr, Dennis P.

1996-01-01

346

Observations of LHR noise with banded structure by the sounding rocket S29 barium-GEOS  

NASA Technical Reports Server (NTRS)

The measurement of electrostatic noise near the lower hybrid frequency made by the sounding rocket S29 barium-GEOS is reported. The noise is related to the spin of the rocket and reaches well below the local lower hybrid resonance frequency. Above the altitude of 300 km the noise shows banded structure roughly organized by the hydrogen cyclotron frequency. Simultaneously with the banded structure a signal near the hydrogen cyclotron frequency is detected. This signal is also spin modulated. The character of the noise strongly suggests that it is locally generated by the rocket payload disturbing the plasma. If this interpretation is correct, plasma wave experiments on other spacecrafts are expected to observe similar phenomena.

Koskinen, H. E. J.; Holmgren, G.; Kintner, P. M.

1983-01-01

347

Observation of wakefields in a beam-driven photonic band gap accelerating structure.  

SciTech Connect

Wakefield excitation has been experimentally studied in a three-cell X-band standing wave photonic band gap (PBG) accelerating structure. Major monopole (TM{sub 01}- and TM{sub 02}-like) and dipole (TM{sub 11}- and TM{sub 12}-like) modes were identified and characterized by precisely controlling the position of beam injection. The quality factor Q of the dipole modes was measured to be {approx}10 times smaller than that of the accelerating mode. A charge sweep, up to 80 nC, has been performed, equivalent to {approx} 30 MV/m accelerating field on axis. A variable delay low charge witness bunch following a high charge drive bunch was used to calibrate the gradient in the PBG structure by measuring its maximum energy gain and loss. Experimental results agree well with numerical simulations.

Conde, M.; Yusof, Z.; Power, J. G.; Jing, C.; Gao, F.; Antipov, S.; Xu, P.; Zheng, S.; Chen, H.; Tang, C.; Gai, W.; High Energy Physics; Euclid Techlabs LLC; Tsinghua Univ.

2009-12-01

348

Observation of wakefields in a beam-driven photonic band gap accelerating structure  

NASA Astrophysics Data System (ADS)

Wakefield excitation has been experimentally studied in a three-cell X-band standing wave photonic band gap (PBG) accelerating structure. Major monopole (TM01- and TM02-like) and dipole (TM11- and TM12-like) modes were identified and characterized by precisely controlling the position of beam injection. The quality factor Q of the dipole modes was measured to be ˜10times smaller than that of the accelerating mode. A charge sweep, up to 80 nC, has been performed, equivalent to ˜30MV/m accelerating field on axis. A variable delay low charge witness bunch following a high charge drive bunch was used to calibrate the gradient in the PBG structure by measuring its maximum energy gain and loss. Experimental results agree well with numerical simulations.

Jing, C.; Gao, F.; Antipov, S.; Yusof, Z.; Conde, M.; Power, J. G.; Xu, P.; Zheng, S.; Chen, H.; Tang, C.; Gai, W.

2009-12-01

349

Fabrication and cold test of photonic band gap resonators and accelerator structures  

NASA Astrophysics Data System (ADS)

We present the detailed description of the successful design and cold test of photonic band gap (PBG) resonators and traveling-wave accelerator structures. Those tests provided the essential basis for later hot test demonstration of the first PBG accelerator structure at 17.140 GHz [E. I. Smirnova, A. S. Kesar, I. Mastovsky, M. A. Shapiro, and R. J. Temkin, Phys. Rev. Lett., 95, 074801 (2005).PRLTAO0031-900710.1103/PhysRevLett.95.074801]. The advantage of PBG resonators is that they were built to support only the main, TM01-like, accelerator mode while not confining the higher-order modes (HOM) or wakefields. The design of the PBG resonators was based on a triangular lattice of rods, with a missing rod at the center. Following theoretical analysis, the rod radius divided by the rod spacing was held to a value of about 0.15 to avoid supporting HOM. For a single-cell test the PBG structure was fabricated in X-band (11 GHz) and brazed. The mode spectrum and Q factor (Q=5000) agreed well with theory. Excellent HOM suppression was evident from the cold test. A six-cell copper PBG accelerator traveling-wave structure with reduced long-range wakefields was designed and was built by electroforming at Ku-band (17.140 GHz). The structure was tuned by etching the rods. Cold test of the structure yielded excellent agreement with the theoretical design. Successful results of the hot test of the structure demonstrating the acceleration of the electron beam were published in E. I. Smirnova, A. S. Kesar, I. Mastovsky, M. A. Shapiro, and R. J. Temkin, Phys. Rev. Lett., 95, 074801 (2005).PRLTAO0031-900710.1103/PhysRevLett.95.074801

Smirnova, Evgenya I.; Mastovsky, Ivan; Shapiro, Michael A.; Temkin, Richard J.; Earley, Lawrence M.; Edwards, Randall L.

2005-09-01

350

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

NASA Astrophysics Data System (ADS)

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

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

2015-03-01

351

Structure of the Kpi = 4+ bands in 186,188Os  

Microsoft Academic Search

The structures of 3+ states in Os have been debated over several decades. Based on measured B(E2) values they were interpreted in 186-192Os as Kpi = 4+ two-phonon vibrations, whereas inelastic scattering, and (t,alpha) work imply a hexadecapole phonon description. To clarify the nature of these Kpi = 4+ bands in 186,188Os, we performed a (3He,d) reaction on 185,187Re targets

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

2009-01-01

352

Nonlinear effects of energy band structures on optical transitions in quantum dots  

Microsoft Academic Search

The quantum theory of nonlinear effects for optical transitions of electrons in quasi-zero dimensional (Q0D) quantum dots fabricated from n-type III–V compound semiconductor materials such as n-type GaAs has been studied due to the nonparabolicity of energy band structures. We use the effective mass approximation for carriers in the quantum dots. Most realistic quantum dot systems contain the box with

Chhi-Chong Wu; Chau-Jy Lin

2002-01-01

353

Band structures of delafossite transparent conductive oxides from a self-consistent GW approach  

Microsoft Academic Search

We present a comparative study of the electronic band structures of the compounds CuMO2 (M=B,Al,In,Ga) which belong to the family of delafossite transparent conductive oxides. The theoretical approaches we use are the standard local-density approximation (LDA) to density-functional theory, LDA+U , hybrid functionals, and perturbative GW on top of LDA or self-consistent Coulomb hole plus screened exchange calculations. The latter

Fabio Trani; Julien Vidal; Silvana Botti; Miguel A. L. Marques

2010-01-01

354

Three-dimensional ordered particulate structures: Method to retrieve characteristics from photonic band gap data  

NASA Astrophysics Data System (ADS)

A method to retrieve characteristics of ordered particulate structures, such as photonic crystals, is proposed. It is based on the solution of the inverse problem using data on the photonic band gap (PBG). The quasicrystalline approximation (QCA) of the theory of multiple scattering of waves and the transfer matrix method (TMM) are used. Retrieval of the refractive index of particles is demonstrated. Refractive indices of the artificial opal particles are estimated using the published experimental data.

Miskevich, Alexander A.; Loiko, Valery A.

2015-01-01

355

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

PubMed

We perform full 3D topology optimization (in which "every voxel" of the unit cell is a degree of freedom) of photonic-crystal structures in order to find optimal omnidirectional band gaps for various symmetry groups, including fcc (including diamond), bcc, and simple-cubic lattices. Even without imposing the constraints of any fabrication process, the resulting optimal gaps are only slightly larger than previous hand designs, suggesting that current photonic crystals are nearly optimal in this respect. However, optimization can discover new structures, e.g. a new fcc structure with the same symmetry but slightly larger gap than the well known inverse opal, which may offer new degrees of freedom to future fabrication technologies. Furthermore, our band-gap optimization is an illustration of a computational approach to 3D dispersion engineering which is applicable to many other problems in optics, based on a novel semidefinite-program formulation for nonconvex eigenvalue optimization combined with other techniques such as a simple approach to impose symmetry constraints. We also demonstrate a technique for robust topology optimization, in which some uncertainty is included in each voxel and we optimize the worst-case gap, and we show that the resulting band gaps have increased robustness to systematic fabrication errors. PMID:25321732

Men, H; Lee, K Y K; Freund, R M; Peraire, J; Johnson, S G

2014-09-22

356

The Glacier and Ice Surface Topography Interferometer: UAVSAR's Single-pass Ka-Band Interferometer  

NASA Astrophysics Data System (ADS)

In May 2009 a new radar technique for mapping ice surface topography was demonstrated in a Greenland campaign as part of the NASA International Polar Year (IPY) activities. This was achieved with the airborne Glacier and Ice Surface Topography Interferometer (GLISTIN-A): a 35.6 GHz single-pass interferometer. The proof-of-concept demonstration was achieved by interfacing Ka-band RF and antenna hardware with the Uninhabited Airborne Vehicle Synthetic Aperture Radar (UAVSAR). The GLISTIN-A was implemented as a custom installation of the NASA Dryden Flight Research Center Gulfstream III. Instrument performance indicated swath widths over the ice between 5-7km, with height precisions ranging from 30cm-3m at a posting of 3m x 3m. Following the success of the IPY campaign, the Earth Science Techonology Office (ESTO) Airborne Innovative Technology Transition (AITT) program funded the upgrade of GLISTIN-A to a permanently-available pod-only system compatible with unpressurized operation. The AITT made three fundamental upgrades to improve system performance: 1. State-of-the-art solid-state power amplifiers (80W peak) were integrated directly on the antenna panel reducing front-end losses; 2. A ping-pong capability was incorporated to effectively double the baseline thereby improving height measurement precision by a factor of two; and 3. A high-fidelity calibration loop was implemented which is critical for routine processing. Upon completion of our engineering flights in February 2013, GLISTIN-A flew a brief campaign to Alaska (4/24-4/27/13). The purpose was to fully demonstrate GLISTIN-A's ability to generate high-precision, high resolution maps of ice surface topography with swaths in excess of 10km. Furthermore, the question of the utility of GLISTIN-A for sea-ice mapping, tracking and inventory has received a great deal of interest. To address this GLISTIN-A collected data over sea-ice in the Beaufort sea including an underflight of CryoSAT II. Note that there are ongoing activities to stage GLISTIN on the Global Hawk (GLISTIN-H) for which sea ice-mapping is a primary driver. Analysis of the data will focus on assessment of performance and interpretation over ice to include: 1. intercomparison of GLISTIN-A glacier height maps with lidar data and heritage SRTM DEM's for performance validation of GLISTIN-A over ice, 2. quantitative evaluation of mass change over the Columbia glacier via repeat observations made by GLISTIN-A with a 3 day separation, 3. assessment of GLISTIN-A's ability map sea ice extent, dynamics and possibly to measure freeboard.

Moller, D.; Hensley, S.; Wu, X.; Michel, T.; Muellerschoen, R.; Carswell, J.; Fisher, C.; Miller, T.; Milligan, L.; Sadowy, G.; Sanchez-Barbetty, M.; Lou, Y.

2013-12-01

357

Brittle fracture resistance of manganese-silicon low-carbon steels with layered-banded structure  

Microsoft Academic Search

Structural sheet steels 08GNB, 06GNB (F40W), and 09KhMN2D and steel 09G2B imported from Germany are studied. The effect of\\u000a the layered-banded structure on the anisotropy of the resistance of the steels to brittle fracture is determined using the\\u000a results of tests of impact specimens cut in different directions with respect to that of rolling. The critical brittle point\\u000a (CBT) is

V. I. Gorynin

2009-01-01

358

Probing the graphite band structure with resonant soft-x-ray fluorescence  

SciTech Connect

For incident photon energies near the core binding energy, inelastic x-ray scattering theory predicts a coherent absorption-emission process in which crystal momentum is conserved. Momentum conservation should manifest itself as dispersive features in fluorescence spectra. We report the detection of such features for the first time in graphite, and show that there exists a clear relationship between them and the graphite band structure. Our results demonstrate the potential of resonant soft-x-ray fluorescence for examining the momentum-resolved electronic structure of complex materials.

Carlisle, J.A.; Shirley, E.L.; Hudson, E.A.; Terminello, L.J.; Callcott, T.A.; Jia, J.J.; Ederer, D.L.; Perera, R.C.C.; Himpsel, F.J. (Lawrence Livermore National Laboratory, Livermore, California 94551 (United States) University of Tennessee, Knoxville, Tennessee 37996 (United States) Tulane Unviersity, New Orleans, Louisiana 70118 (United States) Lawrence Berkeley Laboratory, Berkeley, California 94720 (United States) IBM Research Division, Thomas J. Watson Research Center, Yorktown Heights, New York 10598 (United States))

1995-02-13

359

Energy-band structure of CdTe and Si: a sp 3(s ?) 2k.p model  

NASA Astrophysics Data System (ADS)

The energy bands of the direct-band-gap semiconductor (CdTe) as well as the indirect-band-gap semiconductor (Si), throughout the entire Brillouin zone, have been obtained by diagonalizing a 24×24 k.p Hamiltonian referred to basis states at k=0. We extend the sp 3s ? basis functions by the inclusion of sV? orbitals. We find that the sp 3'd'(s ?) 2k.p model is fairly sufficient to describe the electronic structure of these systems over a wide energy range, obviating the use of any d orbitals. Finally, the comparison with available theoretical results shows that the present model reproduces known results for bulk CdTe and Si, that is, their band structure, including s and p valence bands and the lowest two conduction bands.

Boujdaria, Kais; Zitouni, Omar

2004-01-01

360

Structure and thermodynamics of surface recognition  

SciTech Connect

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

Gupta, G.

1998-11-01

361

Design optimization of wide-band Tonpilz piezoelectric transducer with a bending piezoelectric disk on the radiation surface.  

PubMed

Wide-band Tonpilz piezoelectric transducer with a bending piezoelectric disk on the radiation surface has been proposed to improve sonar detection performance in shallow water. This transducer is driven by utilizing two vibration modes, i.e., longitudinal and bending. Consequently, to achieve a wide-band signal transmission by this transducer, the phase difference between signals, which drive the ring-stack and the bending-disk piezoelectric resonators has to be optimized. In this paper, optimization approach of this phase difference in the design process is proposed. The effectiveness of this approach was confirmed by water-pool experiments. PMID:21117734

Saijyou, Kenji; Okuyama, Tomonao

2010-05-01

362

Demonstration of a 17-GHz, High-Gradient Accelerator with a Photonic-Band-Gap Structure  

NASA Astrophysics Data System (ADS)

We report the testing of a high gradient electron accelerator with a photonic-band-gap (PBG) structure. The photonic-band-gap structure confines a fundamental TM01-like accelerating mode, but does not support higher-order modes (HOM). The absence of HOM is a major advantage of the PBG accelerator, since it suppresses dangerous beam instabilities caused by wakefields. The PBG structure was designed as a triangular lattice of metal rods with a missing central rod forming a defect confining the TM01-like mode and allowing the electron beam to propagate along the axis. The design frequency of the six-cell structure was 17.14 GHz. The PBG structure was excited by 2 MW, 100 ns pulses. A 16.5 MeV electron beam was transmitted through the PBG accelerator. The observed electron beam energy gain of 1.4 MeV corresponds to an accelerating gradient of 35 MV/m, in excellent agreement with theory.

Smirnova, Evgenya I.; Kesar, Amit S.; Mastovsky, Ivan; Shapiro, Michael A.; Temkin, Richard J.

2005-08-01

363

Band-gap-confinement and image-state-recapture effects in the survival of anions scattered from metal surfaces  

SciTech Connect

The resonant charge transfer process in the collision of hydrogen anions with metal surfaces is described within a single-active-electron wave-packet propagation method. The ion-survival probability is found to be strongly enhanced at two different surface-specific perpendicular velocities of the ion. It is shown that, while the low-velocity enhancement is induced from a dynamical confinement of the ion level inside the band gap, the high-velocity enhancement is due to electron recapture from transiently populated image states. Results are presented for Li(110), Cu(111), and Pd(111) surfaces.

Schmitz, Andrew; Shaw, John; Chakraborty, Himadri S. [Center for Innovation and Entrepreneurship, Department of Chemistry and Physics, Northwest Missouri State University, Maryville, Missouri 64468 (United States); Thumm, Uwe [Department of Physics and Astronomy, Kansas State University, Manhattan, Kansas 66502 (United States)

2010-04-15

364

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

SciTech Connect

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

Tritsaris, Georgios A.; Malone, Brad D. [School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138 (United States); Kaxiras, Efthimios, E-mail: kaxiras@physics.harvard.edu [School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138 (United States); Department of Physics, Harvard University, Cambridge, Massachusetts 02138 (United States)

2014-05-07

365

Band-Structure-Dependent Demagnetization in the Heusler Alloy Co2Mn1xFexSi Daniel Steil,1  

E-print Network

Band-Structure-Dependent Demagnetization in the Heusler Alloy Co2Mn1Ã?xFexSi Daniel Steil,1 Sabine investigate the ultrafast demagnetization for two Heusler alloys (Co2Mn1Ã?xFexSi) with a different lineup-metallic Heusler alloys that possess a band gap in one spin channel at the Fermi level EF. A band gap in one spin

Aeschlimann, Martin

366

Constraining Spanish Surface Structure, York Papers in Linguistics 4.  

ERIC Educational Resources Information Center

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

Green, John N.

367

Femtosecond laser surface structuring technique for making human enamel and dentin surfaces superwetting  

NASA Astrophysics Data System (ADS)

It is known that good wettability of enamel and dentin surfaces is a key factor in enhancing adhesion of restorative materials in dentistry. Here, we report on a femtosecond laser surface texturing approach that makes both the enamel and dentine surfaces superwetting. In contrast to the traditional chemical etching that yields random surface structures, this new approach produces engineered surface structures. The surface structure engineered and tested here is an array of femtosecond laser-produced parallel microgrooves that generates a strong capillary force. Due to the powerful capillary action, water is rapidly sucked into this engineered surface structure and spreads even on a vertical surface.

Vorobyev, A. Y.; Guo, Chunlei

2013-12-01

368

Crustal Structure Beneath Taiwan Using Frequency-band Inversion of Receiver Function Waveforms  

NASA Astrophysics Data System (ADS)

Receiver function analysis is used to determine local crustal structure beneath Taiwan. We have performed preliminary data processing and polarization analysis for the selection of stations and events and to increase overall data quality. Receiver function analysis is then applied to data from the Taiwan Seismic Network to obtain radial and transverse receiver functions. Due to the limited azimuthal coverage, only the radial receiver functions are analyzed in terms of horizontally layered crustal structure for each station. In order to improve convergence of the receiver function inversion, frequency-band inversion (FBI) is implemented, in which an iterative inversion procedure with sequentially higher low-pass corner frequencies is used to stabilize the waveform inversion. Frequency-band inversion is applied to receiver functions at six stations of the Taiwan Seismic Network. Initial 20-layer crustal models are inverted for using prior tomographic results for the initial models. The resulting 20-1ayer models are then simplified to 4 to 5 layer models and input into an alternating depth and velocity frequency-band inversion. For the six stations investigated, the resulting simplified models provide an average estimate of 38 km for the Moho thickness surrounding the Central Range of Taiwan. Also, the individual station estimates compare well with the recent tomographic model of and the refraction results of Rau and Wu (1995) and the refraction results of Ma and Song (1997).

Tomfohrde, D. A.; Nowack, R. L.

369

Search for localized Wannier functions of topological band structures via compressed sensing  

E-print Network

We investigate the interplay of band structure topology and localization properties of Wannier functions. To this end, we extend a recently proposed compressed sensing based paradigm for the search for maximally localized Wannier functions [Ozolins et al., PNAS 110, 18368 (2013)]. We develop a practical toolbox that enables the search for maximally localized Wannier functions which exactly obey the underlying physical symmetries of a translationally invariant quantum lattice system under investigation. Most saliently, this allows us to systematically identify the most localized representative of a topological equivalence class of band structures, i.e., the most localized set of Wannier functions that is adiabatically connected to a generic initial representative. We also elaborate on the compressed sensing scheme and find a particularly simple and efficient implementation in which each step of the iteration is an $O(N \\log N)$ algorithm in the number of lattice sites $N$. We present benchmark results on one-dimensional topological superconductors demonstrating the power of these tools. Furthermore, we employ our method to address the open question whether compact Wannier functions can exist for symmetry protected topological states like topological insulators in two dimensions. The existence of such functions would imply exact flat band models with strictly finite range hopping. Here, we find numerical evidence for the absence of such functions. We briefly discuss applications in dissipative state preparation and in devising variational sets of states for tensor network methods.

J. C. Budich; J. Eisert; E. J. Bergholtz; S. Diehl; P. Zoller

2014-09-11

370

BoltzTraP. A code for calculating band-structure dependent quantities  

NASA Astrophysics Data System (ADS)

A program for calculating the semi-classic transport coefficients is described. It is based on a smoothed Fourier interpolation of the bands. From this analytical representation we calculate the derivatives necessary for the transport distributions. The method is compared to earlier calculations, which in principle should be exact within Boltzmann theory, and a very convincing agreement is found. Program summaryTitle of program:BoltzTraP Catalogue identifier:ADXU_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADXU_v1_0 Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Licensing provisions:none Programming language used:Fortran 90 Computer:The program should work on any system with a F90 compiler. The code has been tested with the Intel Fortran compiler Operating system:Unix/Linux RAM:bytes up to 2 GB for low symmetry, small unit cell structures No. of lines in distributed program, including test data, etc.:1 534 213 No. of bytes in distributed program, including test data, etc.:27 473 227 Distribution format:tar.gz External routines:The LaPack and Blas libraries are needed Nature of problem:Analytic expansion of energy-bands. Calculation of semi-classic integrals. Solution method:Smoothed Fourier expansion of bands. Running time:Up to 3 hours for low symmetry, small unit cell structures.

Madsen, Georg K. H.; Singh, David J.

2006-07-01

371

Emittance, surface structure, and electron emission  

NASA Astrophysics Data System (ADS)

The emittance of high brightness electron sources, particularly field emitters and photocathodes but also thermionic sources, is increased by surface roughness on the emitter. Such structure causes local field enhancement and complicates both the prediction of emittance and the underlying emission models on which such predictions depend. In the present work, a method to find the emission trajectories near regions of high field enhancement is given and applied to emittance predictions for field, photo, and thermal emission for an analytically tractable hemispherical model. The dependence of the emittance on current density, spatial variation, and acceleration close to the emission site is identified and the impact of space charge discussed. The methodology is extensible to field emission from close-spaced wirelike structures, in particular, and extensions to that configuration are discussed. The models have application to electron sources for high frequency vacuum electronics, high power microwave devices, and free-electron lasers.

Jensen, Kevin L.; Shiffler, Donald A.; Petillo, John J.; Pan, Zhigang; Luginsland, John W.

2014-04-01

372

Dual-band infrared imaging to detect corrosion damage within airframes and concrete structures  

SciTech Connect

The authors are developing dual-band infrared (DBIR) imaging and detection techniques to inspect airframes and concrete bridge decks for hidden corrosion damage. Using selective DBIR image ratios, they enhanced surface temperature contrast and removed surface emissivity noise associated with clutter. The surface temperature maps depicted defect sites, which heat and cool at different rates than their surroundings. The emissivity-ratio maps tagged and removed the masking effects of surface clutter. For airframe inspections, the authors used time-resolved DBIR temperature, emissivity-ratio and composite thermal inertia maps to locate corrosion-thinning effects within a flash-heated Boeing 737 airframe. Emissivity-ratio maps tagged and removed clutter sites from uneven paint, dirt and surface markers. Temperature and thermal inertia maps characterized defect sites, types, sizes, thicknesses, thermal properties and material-loss effects from airframe corrosion. For concrete inspections, they mapped DBIR temperature and emissivity-ratio patterns to better interpret surrogate delamination sites within naturally-heated, concrete slabs and removed the clutter mask from sand pile-up, grease stains, rocks and other surface objects.

Del Grande, N.K.; Durbin, P.F. [Lawrence Livermore National Lab., CA (United States)

1994-12-31

373

Dual-band infrared imaging to detect corrosion damage within airframes and concrete structures  

SciTech Connect

We are developing dual-band infrared (DBIR) imaging and detection techniques to inspect air frames and concrete bridge decks for hidden corrosion damage. Using selective DBIR image ratios,, we enhanced surface temperature contrast and removed surface emissivity noise associated with clutter. Our surface temperature maps depicted defect sites, which heat and cool at different rates than their surroundings. Our emissivity-ratio maps tagged and removed the masking effects of surface clutter. For airframe inspections, we used time-resolved DBIR temperature, emissivity-ratio and composite thermal inertia maps to locate corrosion-thinning effects within a flash-heated Boeing 737 airframe. Emissivity-ratio maps tagged and removed clutter sites from uneven paint, dirt and surface markers. Temperature and thermal inertia maps characterized defect sites, types, sizes, thicknesses, thermal properties and material-loss effects from air frame corrosion. For concrete inspections, we mapped DBIR temperature and emissivity-ratio patterns to better interpret surrogate delamination sites within naturally-heated, concrete slabs and remove the clutter mask from sand pile-up, grease stains, rocks and other surface objects.

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

1994-01-01

374

Effects of the Antenna Aperture on Remote Sensing of Sea Surface Salinity at L-Band  

NASA Technical Reports Server (NTRS)

Remote sensing of sea surface salinity with sufficient accuracy to meet the needs of global oceanography is a challenging task. The global variability of the salinity signal in the open ocean is only a few Kelvin even at L-band and an accuracy on the order of 0.1K is desired to study the influence of salinity on ocean circulation and energy exchange with the atmosphere. On the other hand, resolution is not an issue for understanding the dynamics of the open ocean where scales of hundreds of km are not uncommon. This permits remote sensing with large antenna footprints and spatial averaging to reduce noise. However, antennas with large footprints introduce other problems. For example, the angle of incidence and hence the brightness temperature varies over the footprint. Similarly, the polarization of brightness temperature relative to the antenna ports changes. Studies have been conducted using antenna patterns representative of the antenna that will be flown on the Aquarius mission to examine these effects. Aquarius is a pushbroom style radiometer with three beams looking across track away from the sun. The beams are at incidences angles (at the spacecraft) of about 26.5, 34 and 40 degrees each with a half-power beam width of about 5.8 degrees. It is shown that the measured brightness temperature is biased relative to the value at boresight because of changes across the field of view. The bias can be as much as 4K and positive or negative depending on polarization. Polarization mixing because of the variations of the local plane of incidence across the footprint also occur and can result in biased polarimetric measurements. A bias in the third Stokes parameter of as much as 0.4K is possible. Such effects may affect algorithms that use the third Stokes parameter to correct for Faraday rotation. Another issue associated with the antenna is sun glint. This is an issue determined by surface roughness and antenna sidelobes. Examples will be given for the random component (glint) for the case of the Aquarius antenna beams. Fortunately, the Aquarius beams mostly look to the dark side of the day-night termination, but during some portions of the year they will see sun-lighted ocean. In this case, glint could be an issue for the inner-most beam.

Dinnat, Emmanuel P.; LeVine, David M.

2006-01-01

375

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

NASA Technical Reports Server (NTRS)

This paper presents the first experimental evidence that the polarimetric brightness temperatures of sea surfaces are sensitive to ocean wind direction in the incidence angle range of 30 to 50 degrees. Our experimental data were collected by a K-band (19.35 GHz) polarimetric wind radiometer (WINDRAD) mounted on the NASA DC-8 aircraft. A set of aircraft radiometer flights was successfully completed in November 1993. We performed circle flights over National Data Buoy Center (NDBC) moored buoys deployed off the northern California coast, which provided ocean wind measurements. The first WINDRAD flight was made on November 4, 1993. There was clear weather with a wind speed of 12 m/s at 330 degrees around the Pt. Arena buoy. We circled the buoy at three incidence angles, and all data when plotted as functions of azimuth angles show clear modulations of several Kelvin. At 40 degrees incidence angle, there is a 5 Kelvin peak-to-peak signal in the second Stokes parameter Q and the third Stokes parameter U. The Q data maximum is in the upwind direction and U has a 45 degrees phase shift in azimuth as predicted by theory. There is also an up/downwind asymmetry of 2 Kelvin in the Q data, and 1 Kelvin in the U data. At 50 degrees incidence angle, the collected data show very similar wind direction signatures to the SSM/I model function. Additional flights were made on other days under cloudy conditions. Data taken at a wind speed of 8 m/s show that at 40 degrees incidence Q and U have a smaller azimuthal modulation of 3 Kelvin, probably due to the lower wind speed. Additionally, the simultaneously recorded video images of sea surfaces suggested that Q and U data were less sensitive to unpolarized geophysical variations, such as clouds and whitecaps, while the T(v) and T(h) increased by a few Kelvin when the radiometer beam crossed over clouds, or there was a sudden increase of whitecaps in the radiometer footprint. The results of our aircraft flights indicate that passive polarimetric radiometry has a strong potential for global ocean wind speed and direction measurements from space.

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

1995-01-01

376

16O+16O molecular structures of positive- and negative-parity superdeformed bands in 34S  

NASA Astrophysics Data System (ADS)

The structures of excited states in 34S are investigated using the antisymmetrized molecular dynamics and generator coordinate method (GCM). The GCM basis wave functions are calculated via energy variation with a constraint on the quadrupole deformation parameter ? . By applying the GCM after parity and angular momentum projections, the coexistence of two positive- and one negative-parity superdeformed (SD) bands are predicted, and low-lying states and other deformed bands are obtained. The SD bands have structures of 16O+16O + two valence neutrons in molecular orbitals around the two 16O cores in a cluster picture. The configurations of the two valence neutrons are ?2 and ?2 for the positive-parity SD bands and ?1?1 for the negative-parity SD band. The structural changes of the yrast states are also discussed.

Taniguchi, Yasutaka

2014-11-01

377

Ultra-thin quadri-band metamaterial absorber based on spiral structure  

NASA Astrophysics Data System (ADS)

We introduce a design of the metamaterial absorber (MA) consisting of spiral artificial inclusions printed on an ultra-thin dielectric layer backed by a metal plate. Both simulations and experiments show that the MA can achieve absorptions up to 96.49, 94.25, 98.94 and 92.04 % at 6.69, 8.70, 11.90 and 15.14 GHz, respectively. The surface current and power loss density of each absorption frequency were discussed to reveal the physical mechanism. Moreover, the proposed quadri-band MA possesses the advantages of being ultra-thin and polarization-insensitive and thus may find potential applications.

Wang, Wenjie; Yan, Mingbao; Pang, Yongqiang; Wang, Jiafu; Ma, Hua; Qua, Shaobo; Chen, Hongya; Xu, Cuilian; Feng, Mingde

2015-02-01

378

Surface energy bands of p(1 × 1)Cr(1 0 0) and p(1 × 1)O\\/Cr(1 0 0)  

Microsoft Academic Search

Angle resolved photoemission spectra have been measured on clean p(1×1)\\/Cr(100) and p(1×1)O\\/Cr(100) using a He discharge lamp as an excitation source. The dispersion curves of surface energy bands have been obtained. The results are compared with reported results of the energy band calculation. The measured energy band dispersion curves for the surface states of a clean sample agree well with

H. Nakajima; S. Pukird; T. Saitoh; A. Kakizaki; T. Ishii

2005-01-01

379

Periodic dielectric structure for production of photonic band gap and method for fabricating the same  

DOEpatents

A method for fabricating a periodic dielectric structure which exhibits a photonic band gap. Alignment holes are formed in a wafer of dielectric material having a given crystal orientation. A planar layer of elongate rods is then formed in a section of the wafer. The formation of the rods includes the step of selectively removing the dielectric material of the wafer between the rods. The formation of alignment holes and layers of elongate rods and wafers is then repeated to form a plurality of patterned wafers. A stack of patterned wafers is then formed by rotating each successive wafer with respect to the next-previous wafer, and then placing the successive wafer on the stack. This stacking results in a stack of patterned wafers having a four-layer periodicity exhibiting a photonic band gap.

Ozbay, Ekmel (Ames, IA); Tuttle, Gary (Ames, IA); Michel, Erick (Ames, IA); Ho, Kai-Ming (Ames, IA); Biswas, Rana (Ames, IA); Chan, Che-Ting (Ames, IA); Soukoulis, Costas (Ames, IA)

1995-01-01

380

Strain-tunable band parameters of ZnO monolayer in graphene-like honeycomb structure  

NASA Astrophysics Data System (ADS)

We present ab initio calculations which show that the direct-band-gap, effective masses and Fermi velocities of charge carriers in ZnO monolayer (ML-ZnO) in graphene-like honeycomb structure are all tunable by application of in-plane homogeneous biaxial strain. Within our simulated strain limit of ±10%, the band gap remains direct and shows a strong non-linear variation with strain. Moreover, the average Fermi velocity of electrons in unstrained ML-ZnO is of the same order of magnitude as that in graphene. The results promise potential applications of ML-ZnO in mechatronics/straintronics and other nano-devices such as the nano-electromechanical systems (NEMS) and nano-optomechanical systems (NOMS).

Behera, Harihar; Mukhopadhyay, Gautam

2012-10-01

381

Periodic dielectric structure for production of photonic band gap and method for fabricating the same  

DOEpatents

A method is disclosed for fabricating a periodic dielectric structure which exhibits a photonic band gap. Alignment holes are formed in a wafer of dielectric material having a given crystal orientation. A planar layer of elongate rods is then formed in a section of the wafer. The formation of the rods includes the step of selectively removing the dielectric material of the wafer between the rods. The formation of alignment holes and layers of elongate rods and wafers is then repeated to form a plurality of patterned wafers. A stack of patterned wafers is then formed by rotating each successive wafer with respect to the next-previous wafer, and then placing the successive wafer on the stack. This stacking results in a stack of patterned wafers having a four-layer periodicity exhibiting a photonic band gap. 42 figures.

Ozbay, E.; Tuttle, G.; Michel, E.; Ho, K.M.; Biswas, R.; Chan, C.T.; Soukoulis, C.

1995-04-11

382

Fine Structure Analysis of 4702 oA Band of the Molecule  

NASA Astrophysics Data System (ADS)

The emission spectrum of the cobalt monochloride molecule has been excited in a high frequency discharge tube source and the (0,0) band of H-system at 4702 Å was photo-graphed at an inverse dispersion of 0.973 Å/mm in the 5th order of a two meter plane grating spectrograph (Carl-Zeiss). The fine structure analysis of the band has been carried out and the molecular constants are reported for the first time. Rotational isotopic shift due to 37Cl support the analysis. The electronic transition involved is of the type 0---- 0- of case (c) which is equivalent of 3sum+---3sum+ or 5sum+---5sum+.

Sureshkumar, M. B.; Srikant, S. R.

1998-01-01

383

Towards direct-gap silicon phases by the inverse band structure design approach.  

PubMed

Diamond silicon (Si) is the leading material in the current solar cell market. However, diamond Si is an indirect band gap semiconductor with a large energy difference (2.3 eV) between the direct gap and the indirect gap, which makes it an inefficient absorber of light. In this work, we develop a novel inverse band structure design approach based on the particle swarming optimization algorithm to predict the metastable Si phases with better optical properties than diamond Si. Using our new method, we predict a cubic Si(20) phase with quasidirect gaps of 1.55 eV, which is a promising candidate for making thin-film solar cells. PMID:25166584

Xiang, H J; Huang, Bing; Kan, Erjun; Wei, Su-Huai; Gong, X G

2013-03-15

384

Electronic Band Structure of GaNxPyAs1-x -y Highly Mismatched Alloys: Suitability for Intermediate-Band Solar Cells  

NASA Astrophysics Data System (ADS)

Formation of an intermediate band in GaNxP0.4As0.6-x alloys due to the isovalent doping by nitrogen is studied by photoreflectance and absorption spectroscopy. The fundamental energy gap transition (E0) observed for an N-free alloy is replaced by two optical transitions (E- and E+) in GaNPAs layers. The E - and E+ transitions are explained within the band anticrossing model, where the localized level of nitrogen interacts with the conduction band of the GaPAs host, splitting it into two subbands. The valence band (VB) is mostly unaffected by nitrogen incorporation as confirmed by the same spin-orbit splitting for N-free and N-containing alloys. The energy position of the E - subband and a strong optical absorption between the VB and the E- subband indicates the GaNPAs alloys have an electronic structure suitable for intermediate-band solar cells. Such an electronic structure is not observed for other III-V alloys like GaInAs, GaInAsP, etc., for which the virtual crystal approximation can be applied to describe the evolution of the electronic structure with the alloy content. Results obtained in this work clearly show that GaNPAs with a few percent of nitrogen is an unusual material system, for which the electronic structure properties differ very significantly from properties of well-known III-V alloys, and the application of virtual crystal approximation in this case is inappropriate or very limited.

Kudrawiec, R.; Luce, A. V.; Gladysiewicz, M.; Ting, M.; Kuang, Y. J.; Tu, C. W.; Dubon, O. D.; Yu, K. M.; Walukiewicz, W.

2014-04-01

385

Y-Shaped Amphiphilic Brushes with Switchable Micellar Surface Structures  

E-print Network

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

Zubarev, Eugene

386

Comment on ``Band structures and optical spectra of InN polymorphs: Influence of quasiparticle and excitonic effects''  

Microsoft Academic Search

In a recent paper, Furthmüller [Phys. Rev. B 72, 205106 (2005)] reported results of calculations of the band structure and optical spectra of InN polymorphs that included influence of quasiparticle and excitonic effects. We show below calculated results that disagree with their utilization of the pd repulsion to make significant corrections to band gaps obtained with their ab initio density-functional

D. Bagayoko; L. Franklin; H. Jin; G. L. Zhao

2007-01-01

387

The Brillouin zones and band gaps of a two-dimensional phononic crystal with parallelogram lattice structure  

NASA Astrophysics Data System (ADS)

We present a detailed theoretical study on the acoustic band structure of two-dimensional (2D) phononic crystal. The 2D phononic crystal with parallelogram lattice structure is considered to be formed by rigid solid rods embedded in air. For the circular rods, some of the extrema of the acoustic bands appear in the usual high-symmetry points and, in contrast, we find that some of them are located in other specific lines. For the case of elliptic rods, our results indicate that it is necessary to study the whole first Brillouin zone to obtain rightly the band structure and corresponding band gaps. Furthermore, we evaluate the first and second band gaps using the plane wave expansion method and find that these gaps can be tuned by adjusting the side lengths ratio R, inclined angle ? and filling fraction F of the parallelogram lattice with circular rods. The results show that the largest value of the first band gap appears at ?=90° and F=0.7854. In contrast, the largest value of the second band gap is at ?=60° and F=0.9068. Our results indicate that the improvement of matching degree between scatterers and lattice pattern, rather than the reduction of structural symmetry, is mainly responsible for the enhancement of the band gaps in the 2D phononic crystal.

Hu, JiaGuang; Xu, Wen

2014-06-01

388

Staggering in {gamma}-band energies and the transition between different structural symmetries in nuclei  

SciTech Connect

The experimental energy staggering in {gamma} bands of rare earths and actinides exhibits three distinct patterns as a function of angular momentum that are typical of well-deformed structural benchmarks: {gamma}-soft for nuclei situated between a vibrator and a deformed {gamma}-soft structure, axially symmetric for those between a vibrator and a rigid rotor, and triaxial {gamma}-rigid for nuclei between a vibrator and a rigid triaxial rotor. The three patterns are reproduced by appropriate special solutions of the Bohr Hamiltonian, as well as by interacting boson approximation calculations. A particular quantity called S(4), which is proportional to the displacement of the 3{sub {gamma}}{sup +} level relative to the average of the 2{sub {gamma}}{sup +} and 4{sub {gamma}}{sup +} levels, can vary in magnitude and sign for different shapes and is found to give a good indication of structure and the evolution of structure. A sudden change in the {gamma}-band staggering occurring between the vibrator and the axially symmetric rotor limits seems to be connected to the known presence of a first-order phase/shape transition in this region.

McCutchan, E. A.; Casten, R. F. [Wright Nuclear Structure Laboratory, Yale University, New Haven, Connecticut 06520-8124 (United States); Bonatsos, Dennis [Institute of Nuclear Physics, National Center for Scientific Research 'Demokritos', GR-15310 Aghia Paraskevi, Attiki (Greece); Zamfir, N. V. [National Institute of Physics and Nuclear Engineering, Bucharest-Magurele (Romania)

2007-08-15

389

Photoelectron holography applied to surface structural determination  

SciTech Connect

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

Petersen, B.L.

1995-05-01

390

Plasmonic band gap cavities on biharmonic gratings  

Microsoft Academic Search

In this paper, we have experimentally demonstrated the formation of plasmonic band gap cavities in infrared and visible wavelength range. The cavity structure is based on a biharmonic metallic grating with selective high dielectric loading. A uniform metallic grating structure enables strong surface plasmon polariton (SPP) excitation and a superimposed second harmonic component forms a band gap for the propagating

Askin Kocabas; S. Seckin Senlik; Atilla Aydinli

2008-01-01

391

Band mapping of in situ Cs intercalated transition metal dichalcogenides  

Microsoft Academic Search

The valence band structure of in situ Cs intercalated layered transition metal dichalcogenides has been studied with photoemission spectroscopy. The intercalation was achieved by room temperature deposition of Cs onto clean sample surfaces in UHV. The changes in the valence band structure upon intercalation were more extensive than predicted by the rigid band model, with the most profound change being

H. E. Brauer; H. I. Starnberg; H. P. Hughes; L. J. Holleboom

1996-01-01

392

Design of a lunar surface structure  

NASA Astrophysics Data System (ADS)

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

Mottaghi, Sohrob

393

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

SciTech Connect

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

Patel, Sahil J.; Kawasaki, Jason K.; Logan, John [Materials Department, University of California-Santa Barbara, Santa Barbara, California 93106 (United States); Schultz, Brian D. [Department of Electrical and Computer Engineering, University of California-Santa Barbara, Santa Barbara, California 93106 (United States); Adell, J.; Thiagarajan, B. [MAX IV Laboratory, Lund University, Lund 221 00 (Sweden); Mikkelsen, A. [Department of Physics, Lund University, Lund 221 00 (Sweden); Palmstrøm, Chris J., E-mail: cpalmstrom@ece.ucsb.edu [Materials Department, University of California-Santa Barbara, Santa Barbara, California 93106 (United States); Department of Electrical and Computer Engineering, University of California-Santa Barbara, Santa Barbara, California 93106 (United States)

2014-05-19

394

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

395

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

SciTech Connect

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

Zhuravlev, A. G.; Savchenko, M. L.; Paulish, A. G.; Alperovich, V. L. [Rzhanov Institute of Semiconductor Physics, Lavrentieva, 13, 630090 Novosibirsk, Russia and Novosibirsk State University, Pirogova, 2, 630090 Novosibirsk (Russian Federation); Scheibler, H. E.; Jaroshevich, A. S. [Rzhanov Institute of Semiconductor Physics, Lavrentieva, 13, 630090 Novosibirsk (Russian Federation)

2013-12-04

396

Wire Measurement of Impedance of an X-Band Accelerating Structure  

SciTech Connect

Several tens of thousands of accelerator structures will be needed for the next generation of normal conducting linear colliders known as the GLC/NLC (Global Linear Collider/Next Linear Collider). To prevent the beam being driven into a disruptive BBU (Beam Break-Up) mode or at the very least, the emittance being significantly diluted, it is important to damp down the wakefield left by driving bunches to a manageable level. Manufacturing errors and errors in design need to be measured and compared with prediction. In this paper a bench-top method of measuring transverse impedances in X-band accelerating structures is described. Utilizing an off-axis wire the S parameters are measured and converted to impedance. Measurements in a damped and detuned structure built for GLC/NLC are presented and the results are discussed.

Baboi, N

2004-09-02

397

(Band electronic structures and crystal packing forces: Progress report, July 1, 1989--December 13, 1991)  

SciTech Connect

This report briefly summaries our research accomplishments made during the period of July 1, 1989 to December 13, 1991. A number of significant progresses were achieved in our studies of several different classes of low-dimensional solid state materials. On the basis of tight-binding band electronic structure calculations, we investigated the electronic properties of various organic conducting salts, cuprate superconductors, and transition-metal oxide and chalcogenide metals to find structure-property correlations governing of the physical properties of these low-dimensional materials. By employing a number of different quality basis sets, we also carried out extensive ab initio SCF-MO/MP2 calculations on model molecular systems to accurately describe the weak intermolecular contact interactions governing the structures of organic donor slats and molecular crystals. Our research efforts led to about 80 publications and two important computer programs.

Not Available

1991-01-01

398

[Band electronic structures and crystal packing forces: Progress report, July 1, 1989--December 13, 1991  

SciTech Connect

This report briefly summaries our research accomplishments made during the period of July 1, 1989 to December 13, 1991. A number of significant progresses were achieved in our studies of several different classes of low-dimensional solid state materials. On the basis of tight-binding band electronic structure calculations, we investigated the electronic properties of various organic conducting salts, cuprate superconductors, and transition-metal oxide and chalcogenide metals to find structure-property correlations governing of the physical properties of these low-dimensional materials. By employing a number of different quality basis sets, we also carried out extensive ab initio SCF-MO/MP2 calculations on model molecular systems to accurately describe the weak intermolecular contact interactions governing the structures of organic donor slats and molecular crystals. Our research efforts led to about 80 publications and two important computer programs.

Not Available

1991-12-31

399

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

PubMed Central

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

2014-01-01

400

Ground Wave Propagation Along an Inhomogeneous Rough Surface in the HF Band: Millington Effect for a Flat Earth  

Microsoft Academic Search

In this paper, for a vertically polarized line source in the high-frequency band (3-30 MHz), a detailed analysis of the ground wave propagation over 1-D highly conducting inhomoge- neous (presence of island) smooth and rough surfaces is addressed from two methods: 1) the analytical solution of Bremmer (see also Wait), which assumes that the receiver, emitter, and island heights are

Christophe Bourlier; Gildas Kubicke

2011-01-01

401

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

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

402

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

DOEpatents

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

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

1994-08-02

403

Stacking and band structure of van der Waals bonded graphane multilayers  

NASA Astrophysics Data System (ADS)

We use density functional theory and the van der Waals density functional (vdW-DF) method to determine the binding separation in bilayer and bulk graphane and study the changes in electronic band structure that arise with the multilayer formation. The calculated binding separation (distance between center-of-mass planes) and binding energy are 4.5-5.0 Å (4.5-4.8 Å) and 75-102 meV/cell (93-127 meV/cell) in the bilayer (bulk), depending on the choice of vdW-DF version. We obtain the corresponding band diagrams using calculations in the ordinary generalized gradient approximation for the geometries specified by our vdW-DF results, so probing the indirect effect of vdW forces on electron behavior. We find significant band-gap modifications by up to -1.2 eV (+4.0 eV) in various regions of the Brillouin zone, produced by the bilayer (bulk) formation.

Rohrer, Jochen; Hyldgaard, Per

2011-04-01

404

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

SciTech Connect

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

Kevin Jerome Sutherland

2001-06-27

405

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

NASA Astrophysics Data System (ADS)

We present the theoretical analysis and computer simulation of the wakefields in a 17 GHz photonic band-gap (PBG) structure for accelerator applications. Using the commercial code CST Particle Studio, the fundamental accelerating mode and dipole modes are excited by passing an 18 MeV electron beam through a seven-cell traveling-wave PBG structure. The characteristics of the longitudinal and transverse wakefields, wake potential spectrum, dipole mode distribution, and their quality factors are calculated and analyzed theoretically. Unlike in conventional disk-loaded waveguide (DLW) structures, three dipole modes (TM11-like, TM12-like, and TM13-like) are excited in the PBG structure with comparable initial amplitudes. These modes are separated by less than 4 GHz in frequency and are damped quickly due to low radiative Q factors. Simulations verify that a PBG structure provides wakefield damping relative to a DLW structure. Simulations were done with both single-bunch excitation to determine the frequency spectrum of the wakefields and multibunch excitation to compare to wakefield measurements taken at MIT using a 17 GHz bunch train. These simulation results will guide the design of next-generation high-gradient accelerator PBG structures.

Hu, Min; Munroe, Brian J.; Shapiro, Michael A.; Temkin, Richard J.

2013-02-01

406

Electronic band structure imaging of three layer twisted graphene on single crystal Cu(111)  

NASA Astrophysics Data System (ADS)

Few layer graphene (FLG) is grown on single crystal Cu(111) by Chemical Vapor Deposition, and the electronic valence band structure is imaged by Angle-Resolved Photo-Emission Spectroscopy. It is found that graphene essentially grows polycrystalline. Three nearly ideal Dirac cones are observed along the Cu ?¯K¯ direction in k-space, attributed to the presence of ˜4° twisted three layer graphene with negligible interlayer coupling. The number of layers and the stacking order are compatible with Raman data analysis demonstrating the complementarity of the two techniques for a more accurate characterization of FLG.

Marquez Velasco, J.; Kelaidis, N.; Xenogiannopoulou, E.; Raptis, Y. S.; Tsoutsou, D.; Tsipas, P.; Speliotis, Th.; Pilatos, G.; Likodimos, V.; Falaras, P.; Dimoulas, A.

2013-11-01

407

Electronic band structure imaging of three layer twisted graphene on single crystal Cu(111)  

SciTech Connect

Few layer graphene (FLG) is grown on single crystal Cu(111) by Chemical Vapor Deposition, and the electronic valence band structure is imaged by Angle-Resolved Photo-Emission Spectroscopy. It is found that graphene essentially grows polycrystalline. Three nearly ideal Dirac cones are observed along the Cu ?{sup ¯}K{sup ¯} direction in k-space, attributed to the presence of ?4° twisted three layer graphene with negligible interlayer coupling. The number of layers and the stacking order are compatible with Raman data analysis demonstrating the complementarity of the two techniques for a more accurate characterization of FLG.

Marquez Velasco, J. [National Center for Scientific Research “Demokritos,” 15310 Athens (Greece) [National Center for Scientific Research “Demokritos,” 15310 Athens (Greece); Department of Physics, National Technical University of Athens, Athens (Greece); Kelaidis, N.; Xenogiannopoulou, E.; Tsoutsou, D.; Tsipas, P.; Speliotis, Th.; Pilatos, G.; Likodimos, V.; Falaras, P.; Dimoulas, A., E-mail: dimoulas@ims.demokritos.gr [National Center for Scientific Research “Demokritos,” 15310 Athens (Greece); Raptis, Y. S. [Department of Physics, National Technical University of Athens, Athens (Greece)] [Department of Physics, National Technical University of Athens, Athens (Greece)

2013-11-18

408

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

SciTech Connect

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

Dabhi, Shweta, E-mail: venu.mankad@gmail.com; Mankad, Venu, E-mail: venu.mankad@gmail.com; Jha, Prafulla K., E-mail: venu.mankad@gmail.com [Department of Physics, Maharaja Krishnakumasinhji Bhavnagar University, Bhavnagar-364001 (India)

2014-04-24

409

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

E-print Network

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

Ernest Grodner

2011-01-31

410

Dispersion characteristics of a slow wave structure with a modified photonic band gap  

NASA Astrophysics Data System (ADS)

This paper studies the dispersion characteristics of a modified photonic band-gap slow-wave structure with an open boundary by simulation and experiment. A mode launcher with a wheel radiator and a coupling probe is presented to excite a pure TM01-like mode. The cold test and simulation results show that the TM01-like mode is effectively excited and no parasitic modes appear. The dispersion characteristics obtained from the cold test are in good agreement with the calculated results. Project supported by the National Natural Science Foundation of China (Grant Nos. 10975036 and 61071018) and the Guangxi Natural Science Foundation, China (Grant No. 2010GXNSFB013049).

Gao, Xi; Yang, Zi-Qiang; Cao, Wei-Ping; Jiang, Yan-Nan

2011-03-01

411

Band structure and transport studies of copper selenide: An efficient thermoelectric material  

NASA Astrophysics Data System (ADS)

We report the band structure calculations for high temperature cubic phase of copper selenide (Cu2Se) employing Hartree-Fock approximation using density functional theory within the generalized gradient approximation. These calculations were further extended to theoretically estimate the electrical transport coefficients of Cu2Se employing Boltzmann transport theory, which show a reasonable agreement with the corresponding experimentally measured values. The calculated transport coefficients are discussed in terms of the thermoelectric (TE) performance of this material, which suggests that Cu2Se can be a potential p-type TE material with an optimum TE performance at a carrier concentration of ˜ 4 - 6 × 10 21 cm - 3 .

Tyagi, Kriti; Gahtori, Bhasker; Bathula, Sivaiah; Auluck, S.; Dhar, Ajay

2014-10-01

412

Characteristics of terahertz slow-wave system with two-dimensional photonic band-gap structure  

NASA Astrophysics Data System (ADS)

A terahertz slow-wave system model consists of a photonic crystal with two-dimensional band-gap structure and a slow-wave plate as its periodic unit. The electromagnetic field in the slow-wave system has been numerically simulated. The dispersion relation and the coupled impedance of the backward wave mode in the system have been calculated for a variety of geometric settings. The results indicate that this model would be a promising candidate for the slow-wave system with single stable backward wave mode.

Liu, Xiaojie; Lei, Hong; Yu, Tian; Feng, Jinjun; Liao, Fujiang

2008-01-01

413

Antiferromagnetic band structure of La2CuO4: Becke-3Lee-Yang-Parr calculations Jason K. Perry,1,2  

E-print Network

Antiferromagnetic band structure of La2CuO4: Becke-3­Lee-Yang-Parr calculations Jason K. Perry,1 functional, we have performed band-structure calculations on the high-temperature superconductor parent compound, La2CuO4. Under the restricted spin formalism ( ), B3LYP band structure agrees well

Goddard III, William A.

414

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

SciTech Connect

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

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

2000-12-01

415

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

NASA Astrophysics Data System (ADS)

We elucidate the nature of the surface electronic properties of quasicrystalline Al-Pd-Mn. We do this by using photoelectron and Auger electron spectroscopies, and by making a variety of comparisons-across types of bulk samples, and across methods of surface preparation. The main conclusions are these: (i) The narrow Mn 2p3/2 core-level line observed in the icosahedral phase is a fingerprint of a suppression in the density of states (a pseudogap) at the Fermi level and is not unique to the quasicrystalline phase. It is also independent of the symmetry of the quasicrystalline surface. The Auger line shape is also affected and may be used as a fingerprint of a pseudogap. (ii) A similarly narrow Fe 2p3/2 core-level line characterizes the icosahedral Al-Cu-Fe quasicrystal, consistent with the expectation that the electronic structure is of general importance in the stabilization of icosahedral phases. (iii) In icosahedral Al-Pd-Mn, the pseudogap of the bulk is not retained up to the surface immediately after fracture, but can be restored by annealing, or by sputter annealing to sufficiently high temperatures. Assuming that the pseudogap reflects an electronic stabilization of the atomic structure, these results suggest that the heat-treated surfaces are more stable than the surface obtained by fracturing at room temperature.

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

2000-12-01

416

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

PubMed

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

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

2011-01-17

417

Energies of formation and electronic band structure of Zn-IV-N2 semiconductors  

NASA Astrophysics Data System (ADS)

The II-IV-N2 semiconductors are expected to have properties closely related to those of the III-N semiconductors. We focus on Zn-IV-N2 semiconductors with the group IV-element Si, Ge and Sn. The formation energies of the compounds in this series were calculated by the full-potential linearized muffin-tin orbital method with LDA and GGA. Zero point motion corrections were included. Furthermore, the energies of formation of competing Zn3N2, Si3N4, Ge3N4, Sn3N4 compounds were also calculated to determine the allowed ranges of the chemical potentials of the elements where the compounds are stable at zero temperature. For comparison, we also calculated the energy of formation of GaN, which is found to be in good agreement with experimental values. All compounds in the series are found to have a large region of stability. The electronic band structures are calculated using the QSGW method. The band gaps span the region from 1.65 - 5.30 eV, increasing from ZnSnN2 to ZnSiN2, with the bandgap of ZnGeN2 close to that of GaN. While ZnGeN2 and ZnSnN2 are direct band gaps semiconductors, ZnSiN2 is found to have an indirect gap slightly smaller than its lowest direct gap. The states near the valence band maximum at Gamma are symmetry labeled and their splittings analyzed in terms of two crystal field parameters. Spin-orbit coupling is found to have negligible effect on these states.

Punya, Atchara; Lambrecht, Walter R. L.

2011-03-01

418

Lunar surface structural concepts and construction studies  

NASA Technical Reports Server (NTRS)

The topics are presented in viewgraph form and include the following: lunar surface structures construction research areas; lunar crane related disciplines; shortcomings of typical mobile crane in lunar base applications; candidate crane cable suspension systems; NIST six-cable suspension crane; numerical example of natural frequency; the incorporation of two new features for improved performance of the counter-balanced actively-controlled lunar crane; lunar crane pendulum mechanics; simulation results; 1/6 scale lunar crane testbed using GE robot for global manipulation; basic deployable truss approaches; bi-pantograph elevator platform; comparison of elevator platforms; perspective of bi-pantograph beam; bi-pantograph synchronously deployable tower/beam; lunar module off-loading concept; module off-loader concept packaged; starburst deployable precision reflector; 3-ring reflector deployment scheme; cross-section of packaged starburst reflector; and focal point and thickness packaging considerations.

Mikulas, Martin

1991-01-01

419

Valence-band structure of the ferromagnetic semiconductor GaMnAs investigated by resonant tunneling spectroscopy  

NASA Astrophysics Data System (ADS)

The origin of ferromagnetism in the prototype ferromagnetic semiconductor GaMnAs is still controversial due to the insufficient understanding of its band structure and Fermi level position. Here, we investigate the valence-band (VB) structure of GaMnAs by analyzing the resonant tunneling levels of the GaMnAs quantum well (QW) in double-barrier heterostructures. The resonant levels including the heavy-hole first state (HH1) are clearly observed in the metallic GaMnAs QW with the Curie temperature (T/C) of 60 K, which indicates that no holes reside in the VB of GaMnAs in the equilibrium condition. Clear enhancement of tunnel magnetoresistance induced by resonant tunneling is demonstrated. We find that the resonant levels formed in the GaMnAs QW are well explained by using the transfer matrix method with the 6x6 {kp} Hamiltonian and small p-d exchange Hamiltonian. The VB structure of GaMnAs is well reproduced by that of GaAs with a small exchange splitting energy of 3-5 meV and with the Fermi level lying at ˜ 30 meV higher than HH1 in the bandgap. Furthermore, we show our more recent results of resonant tunneling spectroscopy on various surface GaMnAs films (Mn concentration: 6-15/, T/C: 71-154 K) grown on an AlAs layer, where the resonant levels are formed by confinement of the VB holes by the surface Schottky barrier and the AlAs barrier. We systematically investigate the thickness dependence of the resonant levels in GaMnAs by precisely etching the surface of GaMnAs. We find that the p-d exchange interaction is negligibly small (3-5 meV) and that the Fermi level exists in the bandgap. This work was performed in collaboration with I. Muneta, P. N. Hai, K. Takata, and M. Tanaka, and partly supported by Grant-in-Aids for Scientific Research, the Special Coordination Programs for Promoting Science and Technology, and FIRST Program by JSPS.[4pt] [1] S. Ohya et al., Phys. Rev. Lett. 104, 167204 (2010).[0pt] [2] S. Ohya et al., arXiv:1009.2235.

Ohya, Shinobu

2011-03-01

420

Surface electronic structure of periodically ?-doped superlattice  

NASA Astrophysics Data System (ADS)

Surface electronic structure of a semi-infinite superlattice (SL) intentionally ?-doped in each well- or barrier-layer is studied using a terminated Kronig-Penney-type of model interspersed with a periodic array of ?-function potentials representing the deep-center defect sheets. It is shown that SL minibands can be tailored by varying the properties of inserted ?-defects, e.g., the lowest energetic miniband can be shifted below the bottom of SL quantum wells (as a result, the main SL energy gap becomes smaller than those of the host semiconductors) and miniband alignement can occur (as a result, the bandwith is enhanced by an order of magnitude). Special attention is paid to the effect of ?-doping on the properties of surface states (SS's), i.e., the states appearing within energetic minigaps and localized at the SL/substrate interface. It is found that by an appropriate choice of the ?-defect weight and location within the SL period, SS with a required energy position relative to minigap edges and a desired extension into the SL bulk can be achieved. Moreover, in contrast to standard (i.e., undoped) SL's, a possibility of SS existence for the substrate identical to SL barriers is shown in periodically ?-doped SL's.

Brzostowski, B.; Kucharczyk, R.; St??licka, M.

1998-12-01

421

The Electronic Structure and Properties of Different Surface Terminations of Li2B4O6 Single Crystal  

Microsoft Academic Search

The electronic structure of the(100) and (110) surfaces of Li2B4O6 single crystal was investigated by combined angle- resolved photoemission and inverse photoemission spectroscopies. The obtained results are in a qualitative agreement with the available model bulk band structure calculations.Together with some common features, they reveal clear differences between the two surfaces. For both of them the observed dispersion of the

Ihor Ketsman; Yaroslav Losovyj; Volodymyr Adamiv; Yaroslav Burak; David Wooten; James Petrosky; John McClory; Peter Dowben

2011-01-01

422

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

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

423

Observation of strong electron pairing on bands without Fermi surfaces in LiFe1?xCoxAs  

NASA Astrophysics Data System (ADS)

In conventional BCS superconductors, the quantum condensation of superconducting electron pairs is understood as a Fermi surface instability, in which the low-energy electrons are paired by attractive interactions. Whether this explanation is still valid in high-Tc superconductors such as cuprates and iron-based superconductors remains an open question. In particular, a fundamentally different picture of the electron pairs, which are believed to be formed locally by repulsive interactions, may prevail. Here we report a high-resolution angle-resolved photoemission spectroscopy study on LiFe1?xCoxAs. We reveal a large and robust superconducting gap on a band sinking below the Fermi level on Co substitution. The observed Fermi-surface-free superconducting order is also the largest over the momentum space, which rules out a proximity effect origin and indicates that the order parameter is not tied to the Fermi surface as a result of a surface instability.

Miao, H.; Qian, T.; Shi, X.; Richard, P.; Kim, T. K.; Hoesch, M.; Xing, L. Y.; Wang, X.-C.; Jin, C.-Q.; Hu, J.-P.; Ding, H.

2015-01-01

424

Observation of strong electron pairing on bands without Fermi surfaces in LiFe1-xCoxAs.  

PubMed

In conventional BCS superconductors, the quantum condensation of superconducting electron pairs is understood as a Fermi surface instability, in which the low-energy electrons are paired by attractive interactions. Whether this explanation is still valid in high-Tc superconductors such as cuprates and iron-based superconductors remains an open question. In particular, a fundamentally different picture of the electron pairs, which are believed to be formed locally by repulsive interactions, may prevail. Here we report a high-resolution angle-resolved photoemission spectroscopy study on LiFe1-xCoxAs. We reveal a large and robust superconducting gap on a band sinking below the Fermi level on Co substitution. The observed Fermi-surface-free superconducting order is also the largest over the momentum space, which rules out a proximity effect origin and indicates that the order parameter is not tied to the Fermi surface as a result of a surface instability. PMID:25583450

Miao, H; Qian, T; Shi, X; Richard, P; Kim, T K; Hoesch, M; Xing, L Y; Wang, X-C; Jin, C-Q; Hu, J-P; Ding, H

2015-01-01

425

Evaluation of structural change during surface pressure relaxation in Langmuir monolayer of zinc stearate by infrared external reflection spectroscopy  

Microsoft Academic Search

In situ polarized infrared external reflection spectra of the Langmuir monolayer of zinc stearate on a water surface were\\u000a recorded during surface pressure relaxation, and the molecular structure of the monolayer was evaluated. The wavenumber of\\u000a the antisymmetric methylene stretching band decreased during surface pressure relaxation. This result indicated that the shift\\u000a to a highly compact packing of the hydrocarbon

Hiroshi Sakai; Junzo Umemura

2008-01-01

426

Crystal lattice and band structure of the intermediate high-pressure phase of PbSe  

NASA Astrophysics Data System (ADS)

In the present paper the results of fitting synchrotron diffraction data are obtained for the intermediate high-pressure phase (9.5 GPa) of the lead selenide based compound Pb1-xSnxSe (x = 0.125)—an optoelectronic as well as a thermoelectric material—for two types of lattice symmetries Pnma (space group #62) and Cmcm (space group #63). Both lattice parameters and positions of atoms for the above mentioned structures have been used in calculations of the electron structure of high-pressure phases. The main difference between the electronic properties for Cmcm and Pnma structures established in electronic structure calculations is that in the first one the PbSe compound was found to be a metal, while in the second a small semiconductor gap (EG = 0.12 eV) was obtained. Moreover, the forces in the Cmcm structure are an order of magnitude larger than those calculated for the Pnma lattice. In the optimized, Pnma structure within a generalized gradient approximation (GGA), the band gap increases up to EG = 0.27 eV. The result coincides with the data on thermoelectric power and electrical resistance data pointing to a semiconductor gap of ~0.2 eV at ~9.5 GPa. Thus, the Pmna type of lattice seems to be a preferable version for the intermediate phase compared with the Cmcm one.

Streltsov, S. V.; Manakov, A. Yu; Vokhmyanin, A. P.; Ovsyannikov, S. V.; Shchennikov, V. V.

2009-09-01

427

Crystal lattice and band structure of the intermediate high-pressure phase of PbSe.  

PubMed

In the present paper the results of fitting synchrotron diffraction data are obtained for the intermediate high-pressure phase (9.5 GPa) of the lead selenide based compound Pb(1-x)Sn(x)Se (x = 0.125)-an optoelectronic as well as a thermoelectric material-for two types of lattice symmetries Pnma (space group #62) and Cmcm (space group #63). Both lattice parameters and positions of atoms for the above mentioned structures have been used in calculations of the electron structure of high-pressure phases. The main difference between the electronic properties for Cmcm and Pnma structures established in electronic structure calculations is that in the first one the PbSe compound was found to be a metal, while in the second a small semiconductor gap (E(G) = 0.12 eV) was obtained. Moreover, the forces in the Cmcm structure are an order of magnitude larger than those calculated for the Pnma lattice. In the optimized, Pnma structure within a generalized gradient approximation (GGA), the band gap increases up to E(G) = 0.27 eV. The result coincides with the data on thermoelectric power and electrical resistance data pointing to a semiconductor gap of ?0.2 eV at ?9.5 GPa. Thus, the Pmna type of lattice seems to be a preferable version for the intermediate phase compared with the Cmcm one. PMID:21832372

Streltsov, S V; Manakov, A Yu; Vokhmyanin, A P; Ovsyannikov, S V; Shchennikov, V V

2009-09-23

428

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

NASA Astrophysics Data System (ADS)

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

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

2011-04-01

429

Ab-initio study of the structural, electronic and optical properties of BSb (110) and (100) surfaces  

NASA Astrophysics Data System (ADS)

In the present study, the structural, electronic and optical properties of BSb bulk, BSb (110) and (100) surfaces were investigated. The calculations were performed by using Full-Potential Linear Augmented Plane Wave (FP-LAPW) in Density Functional Theory (DFT) framework with various exchange-correlation functionals. Some surface properties such as surface energies, the work functions, surface relaxation, band structures and optical properties of cubic BSb (110) and (100) nano-slabs were studied. The (100) surface of cubic BSb has B- and Sb-terminations while the (110) surface has only one termination. The surface properties of all the terminations were presented and discussed. Moreover, some bulk properties such as structural, electronic, band structure and optical properties of BSb compound were investigated for comparison. The obtained band gap for the BSb (110) nano-slab was 0.38 eV while the BSb (100) nano-slab showed a metallic behavior. Moreover, the surface states of the slabs were identified. The real and imaginary parts of the dielectric function of the BSb (110) nano-slab were also calculated and compared with bulk results.

Badehian, Hojat Allah; Salehi, Hamdollah

2014-10-01

430

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

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

431

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

NASA Astrophysics Data System (ADS)

We investigate the effect of Be on the valence band maximum (VBM) of MgZnO by measuring the band offsets of MgxZn1-xO/BexMgyZn1-x-yO heterojunctions using X-ray photoelectron spectroscopy measurements. MgxZn1-xO and BexMgyZn1-x-yO films have been grown on c-plane sapphire substrates by plasma-assisted molecular beam epitaxy. The valence band offset ( ? E V) of Mg0.15Zn0.85O ( E g = 3.62 eV)/Be0.005Mg0.19Zn0.805O ( E g = 3.73 eV) heterojunction is 0.01 eV and Be0.005Mg0.19Zn0.805O has a lower VBM. The increased Mg composition is the main factor for the reduction of VBM. The VBM of MgxZn1-xO is lower by 0.03 eV with the enlargement of E g from 3.62 eV to 3.73 eV by increasing Mg composition. Considering the effect of increased Mg composition, it is concluded that the little amount of Be makes the VBM go up by 0.02 eV when the E g of the alloy is 3.73 eV. The ? E V of Mg0.11Zn0.89O ( E g = 3.56 eV)/Be0.007Mg0.12Zn0.873O ( E g = 3.56 eV) heterojunction is calculated to be 0.03 eV and Be0.007Mg0.12Zn0.873O has a higher VBM than Mg0.11Zn0.89O, which means that a little amount Be lifts the VBM by 0.03 eV when the E g of the alloy is 3.56 eV. The experimental measurements have offered a strong support for the theoretical research that alloying Be in MgxZn1-xO alloys is hopeful to form a higher VBM and to enhance the p-type dopability of MgZnO.

Chen, S. S.; Pan, X. H.; Chen, W.; Zhang, H. H.; Dai, W.; Ding, P.; Huang, J. Y.; Lu, B.; Ye, Z. Z.

2014-09-01

432

Spurious mid-spatial frequency structure on optical surfaces reconstructed from surface slope measurements  

NASA Astrophysics Data System (ADS)

Mid-spatial frequency structure on an optical surface induces small-angle scatter in the transmitted wavefront. Freeform surfaces are particularly susceptible to mid-spatial frequency errors due to the sub-aperture nature of the fabrication processes. Several surface metrology methods that work for freeform surfaces use an indirect principle, reconstructing the surface shape from measured surface slope data. The integration process in the presence of measurement noise adds a spatial correlation to the dataset, leading to spurious spatial frequency structure. In this paper, we use the autocorrelation function to characterize and evaluate this artificial mid-spatial frequency structure on optical surfaces that are reconstructed by zonal integration methods.

Dong, Yue; Hosseinimakarem, Zahra; Davies, Angela; Evans, Chris J.

2014-07-01

433

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

E-print Network

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