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1

Band Structure and Fermi Surface of Zinc  

Microsoft Academic Search

The band structure of zinc is calculated using a modified orthogonalized-plane-wave method and the Hartree-Fock calculations of neutral zinc by Piper. The band structure is obtained in a form which allows it to be extended readily to slight distortions of the lattice. The calculated structure is compared to an experimental band structure obtained by adjusting the matrix elements to fit

Walter A. Harrison

1962-01-01

2

Surface band structure of Si(111)2×1  

NASA Astrophysics Data System (ADS)

The surface band structures of the three-bond scission (TBS) model and the Pandey-chain (PC) model have been computed using an ab initio Hartree-Fock program crystal 92. In the case of the bulk energy bands, the method gives the correct shapes and structure but overestimates the valence-band dispersion by about 50%. For the TBS model, the calculated valence-band dispersion came out about 50% wider than measured experimentally. This would suggest that the model is consistent with optical data. In the case of the PC model, the valence-band dispersion was qualitatively similar to those of previous calculations, but the width discrepancy was large. The method overestimates the surface band gap for both TBS and PC models. The significance is discussed.

Chen, B.; Haneman, D.

1995-02-01

3

Mapping the band structure of a surface phononic crystal  

E-print Network

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

Maznev, Alexei

4

The surface band structure of ?-Ga2O3  

NASA Astrophysics Data System (ADS)

Ga2O3 belongs to the group of transparent conducting oxides (TCOs) with a wide band gap and electrical conductivity. It exhibits the largest band gap with Eg = 4.8 eV and thus a unique transparency from the visible into the UV region. The information on the electronic structure of ?-Ga2O3 is very scarce. This is in part due to the challenging problem of growing high purity single crystals. Transparent semiconducting ?-Ga2O3 single crystals were grown by the Czochralski method from an iridium crucible under a dynamic protective atmosphere to control partial pressures of volatile species of Ga2O3. The investigated samples were characterized by different techniques (LEED, Laue, and STM). The experimental valence band structure of the of ?-Ga2O3 single crystals along ?-Z and A-M symmetry directions of the (100)-surface of Brillouin zone was determined by high-resolution angle-resolved photoelectron spectroscopy (ARPES) utilizing synchrotron radiation. The experimental band structure is compared and discussed with the theoretical calculations. The effect of changing the temperature from 300K to 20K on the experimental band structure ?-Ga2O3 was studied.

Mohamed, M.; Unger, I.; Janowitz, C.; Manzke, R.; Galazka, Z.; Uecker, R.; Fornari, R.

2011-03-01

5

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

6

Electronic structure and quantized surface electron accumulation of narrow band gap semiconductors  

NASA Astrophysics Data System (ADS)

Narrow band gap semiconductors play a crucial role in thin film photovoltaic cells and optoelectronics devices operating in the infrared region of visible spectrum. The interactions between the valence and conduction bands due to the narrow band gap have a big influence on the electronic structure and the device performance of these materials. The surface and bulk electronic properties of narrow band gap semiconductors were investigated using angle resolved photoelectron spectroscopy (ARPES), x-ray absorption spectroscopy and x-ray emission spectroscopy. Comparisons were made between the experimental results and density functional theory band structure calculations. Intrinsic electron accumulation near the surface of clean InN was directly observed by ARPES. The accumulation layer is discussed in terms of the bulk Fermi level (EF) lying below the pinned surface E F, with a confining potential formed normal to surface due to the downward band bending facilitated by donor type surface states or nitrogen vacancies. Various spectroscopic techniques were used to measure this band bending. The energy of the Fermi level and the size of the Fermi surface for these quantum well states could be controlled by varying the method of surface preparation and by the adsorption of potassium on the surface. Intermixing between the heavy and light hole valence bands in the intrinsic quantum well potential associated with the surface electron accumulation layer results in an inverted band structure, with the valence band maximum lying away from the Brillouin zone center. Similarly, the electronic band structure of CdO was investigated and quantized electron subbands were observed above the valence band maximum. The origin of the accumulation layer is discussed in terms of the bulk band structure of CdO calculated using quasi particle corrected density functional theory. High electron density at the surface of these materials provides new opportunities for potential device structures such as sensors, high frequency transmitters and field effect transistors. Therefore the study of their near surface electron accumulation and electronic structure is of importance in understanding the properties of these materials and discovering new application areas.

Colakerol, Leyla

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

Waveguiding in Surface Plasmon Polariton Band Gap Structures  

Microsoft Academic Search

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

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

2001-01-01

9

Tuning two-dimensional band structure of Cu(111) surface-state electrons that interplay with artificial supramolecular architectures  

NASA Astrophysics Data System (ADS)

We report on the modulation of two-dimensional (2D) bands of Cu(111) surface-state electrons by three isostructural supramolecular honeycomb architectures with different periodicity or constituent molecules. Using Fourier-transformed scanning tunneling spectroscopy and model calculations, we resolved the 2D band structures and found that the intrinsic surface-state band is split into discrete bands. The band characteristics including band gap, band bottom, and bandwidth are controlled by the network unit cell size and the nature of the molecule-surface interaction. In particular, Dirac cones emerge where the second and third bands meet at the K points of the Brillouin zone of the supramolecular lattice.

Wang, Shiyong; Wang, Weihua; Tan, Liang Z.; Li, Xing Guang; Shi, Zilang; Kuang, Guowen; Liu, Pei Nian; Louie, Steven G.; Lin, Nian

2013-12-01

10

Electronic band structure modulated by local surface strain in the (111) facet of the <112> silicon nanowires  

NASA Astrophysics Data System (ADS)

Based on the models built with our "cyclic replacement" method we introduced local strain into the (111) facet of the Si <112> nanowires. With ab initio approach, it is found that the electronic band structures of the nanowires are modulated efficiently by the surface strains: the indirect band gap declines by strong surface compression, while it always decreases and impressively changes to a direct band gap with surface tension. Moreover, the local deformations result in spatial separation of the valence band minimum to the compressed surface and the conduction band minimum to the tensed surface.

Zhang, Lihong; Xin, Xiaojun; Guo, Chunsheng; Gan, Liyong; Zhao, Yong

2015-04-01

11

Band structure and optical parameters of the SnO2(110) surface  

NASA Astrophysics Data System (ADS)

With a first-principles-density-functional method, combined with two different pseudopotentials, ideal oxidized and reduced surfaces of tin oxide are studied. The band structures of bulk and the surface systems are calculated and compared. The nature of the surface Sn2+ ions, their outward relaxation, associated ``dangling bonds'' and band gap states are considered. Also ultraviolet optical constants are determined by using the electric dipole approximation with a scissor correction, and noted to agree with experiments. The presence of the surface, and more significantly, its removed bridging oxygen atoms, becomes apparent in a formation of a new absorption feature. This is predicted to cause about 0.7 eV decrease of the absorption edge.

Mäki-Jaskari, Matti A.; Rantala, Tapio T.

2001-08-01

12

Accessing Surface Brillouin Zone and Band Structure of Picene Single Crystals  

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

13

Theory of nonlinear surface magneto-optics for ferromagnetic nickel: Effects of band structure and matrix elements  

Microsoft Academic Search

The nonlinear magneto-optical Kerr effect has been proposed as an ultrafast spectroscopic probe for the magnetic and electronic properties of ferromagnetic surfaces. We extend our previous calculation of the linear (first-order) and nonlinear (second-order) magneto-optical susceptibilities by the inclusion of the complete nickel band structure and the dipole transition matrix elements within the combined interpolation scheme. As ab initio band-structure

W. Hübner

1990-01-01

14

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

15

Theory of nonlinear surface magneto-optics for ferromagnetic nickel: Effects of band structure and matrix elements  

SciTech Connect

The nonlinear magneto-optical Kerr effect has been proposed as an ultrafast spectroscopic probe for the magnetic and electronic properties of ferromagnetic surfaces. We extend our previous calculation of the linear (first-order) and nonlinear (second-order) magneto-optical susceptibilities by the inclusion of the complete nickel band structure and the dipole transition matrix elements within the combined interpolation scheme. As {ital ab} {ital initio} band-structure calculations usually cannot describe optical and magneto-optical absorption (especially in nickel), the band-structure parameters are taken from a fit to spin-polarized photoemission data and de Haas--van Alphen measurements of the Fermi surface. The detailed shape of the Brillouin zone is included. Comparison to linear magneto-optical Kerr-effect measurements shows that the inclusion of the full anisotropic band structure and of the dipole matrix elements is necessary to remove parameter ambiguities and leads to strongly improved agreement between theory and experiment. This electronic theory confirms the previous assertion that the nonlinear magneto-optical Kerr effect should be observable and clearly shows that this effect contains detailed information about the electronic and magnetic surface properties (band structure, exchange interaction, spin-orbit coupling). Thus, the theory can help to interpret forthcoming nonlinear magneto-optical measurements. We discuss possible geometries for experimental and technological applications.

Huebner, W. (Institute for Theoretical Physics, Freie Universitaet Berlin, Berlin (Germany))

1990-12-15

16

Spectromicroscopy measurements of surface morphology and band structure of exfoliated graphene  

Microsoft Academic Search

Monolayer-thick crystals, such as graphene, are an area of intense interest in condensed matter research. However, crystal deformations in these 2D systems are known to adversely affect conductivity and increase local chemical reactivity. Additionally, surface roughness in graphene complicates band-mapping and limits resolution in techniques such as angle resolved photoemission spectroscopy (ARPES), the theory of which was developed for atomically

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

2011-01-01

17

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

18

Theory of nonlinear surface magneto-optics for ferromagnetic nickel: Effects of band structure and matrix elements  

Microsoft Academic Search

The nonlinear magneto-optical Kerr effect has been proposed as an ultrafast spectroscopic probe for the magnetic and electronic properties of ferromagnetic surfaces. We extend our previous calculation of the linear (first-order) and nonlinear (second-order) magneto-optical susceptibilities by the inclusion of the complete nickel band structure and the dipole transition matrix elements within the combined interpolation scheme. As {ital ab} {ital

Huebner

1990-01-01

19

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

E-print Network

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

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

2015-01-01

20

Surface-oxide stress induced band-structure modulation in two-dimensional Si layers  

NASA Astrophysics Data System (ADS)

We experimentally studied an impact of the surface oxide layer on quantum confinement effects (QCE) in Si quantum well (SQW) structures (surface-oxide/two-dimensional-Si/buried-oxide) with various surface oxide layer thickness TOX on silicon-on-insulator (SOI) substrate, by UV-Raman spectroscopy, photoluminescence (PL) method, and two-dimensional (2D) stress simulator. UV-Raman data show that tensile strain ? of SQW, stressed by a thermal expansion mismatch between surface oxide and Si layers, decreases with decreasing the TOX. According to the strain behavior in the SQW and strained-Si on strained-SOI, PL results show that bandgap EG of the SQW rapidly expands with decreasing TOX. As a result, we can estimate the EG of the fully relaxed SQW. However, QCE in SQW keep thermally stable, in spite of carrying out a high temperature N2 annealing process.

Mizuno, Tomohisa; Suzuki, Yuhya; Nagamine, Yoshiki; Nakahara, Yuhta; Nagata, Yuhsuke; Aoki, Takashi; Maeda, Tatsuro

2015-04-01

21

Characterization of the surface plasmon polariton band gap in an Ag/SiO2/Ag T-shaped periodical structure.  

PubMed

In this study, the localized surface plasmon polariton (LSPP) band gap of an Ag/SiO(2)/Ag asymmetric T-shaped periodical structure is demonstrated and characterized. The Ag/SiO(2)/Ag asymmetric T-shaped periodical structure was designed and fabricated to exhibit the LSPP modes in an infrared wavelength regime, and its band gap can be manipulated through the structural geometry. The LSPP band gap was observed experimentally with the absorbance spectra and its angle dependence characterized with different incident angles. Such a T-shaped structure with a LSPP band gap can be widely exploited in various applications, such as emitters and sensors. PMID:22109396

Cheng, Cheng-Wen; Abbas, Mohammed Nadhim; Shih, Min-Hsiung; Chang, Yia-Chung

2011-11-21

22

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

23

Band structures of defective graphenes  

Microsoft Academic Search

Band structures of defective graphenes are analyzed by crystal orbital method. In laterally slipped faults, there appear ? bands consisting of weakly interacted dangling bonds. The peculiar ? bands cross with frontier ? bands, and the resultant double occupation leads to the disappearance of ferromagnetic interactions. On the other hand, in longitudinally slipped faults, there are no crossings of the

Masashi Hatanaka

2011-01-01

24

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

E-print Network

ta r t i c l e i n f o Article history: Received 20 January 2011 Accepted 14 April 2011 Available an electrical perspective are difficult to integrate. The surface silicon atoms do not chemically react with surface silicon atoms by a cycloaddition "redox" process. Minority carrier lifetime measurements yielded

25

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

26

Extension of the Fenske-Hall Molecular Orbital Approach to Tight-Binding Band Structure Calculations: Bulk and Surface Electronic Structure of MoS(2).  

PubMed

A new tight-binding band structure calculation method is described. This method, which is based on the Fenske-Hall molecular orbital technique, should be extremely useful in the study of the bulk and surface electronic structure of inorganic materials. The approximations used in the Fenske-Hall method are reviewed, and the extension of this approach to periodic band structure calculations is outlined. Results of calculations for bulk MoS(2) are in good agreement with previous experimental and theoretical results. Results of calculations for two-dimensional MoS(2) slabs exposing (100) edge planes provide a description of coordinatively unsaturated Mo and S atoms on these edges. Coordinative unsaturation at the Mo atoms introduces new surface states near the Fermi level. Coordinative unsaturation at the S atoms leads to high-energy occupied bands that can be attributed to S lone pair electrons. Surface bonds between Mo atoms and terminal S atoms are stronger than bulk Mo-S bonds, suggesting that terminal S atoms may be more difficult to remove from the edges of MoS(2) than bridging S atoms. Bonding in a single two-dimensional layer of MoS(2) is found to be more ionic than the bonding in the full three-dimensional structure. This effect is also observed in one-dimensional MoS(2) ribbons that expose (100) edge planes. The simplified one-dimensional ribbons will be used for further studies of the electronic structure of the edge planes of MoS(2). PMID:11670376

Tan, Agnes; Harris, Suzanne

1998-05-01

27

Extension of the Fenske-Hall molecular orbital approach to tight-binding band structure calculations: Bulk and surface electronic structure of MoS{sub 2}  

SciTech Connect

A new tight-binding band structure calculation method is described. This method, which is based on the Fenske-Hall molecular orbital technique, should be extremely useful in the study of the bulk and surface electronic structure of inorganic materials. The approximations used in the Fenske-Hall method are reviewed, and the extension of this approach to periodic band structure calculations is outlined. Results of calculations for bulk MoS{sub 2} are in good agreement with previous experimental and theoretical results. Results of calculations for two-dimensional MoS{sub 2} slabs exposing (100) edge planes provide a description of coordinatively unsaturated Mo and S atoms on these edges. Coordinative unsaturation at the Mo atoms introduces new surface states near the Fermi level. Coordinative unsaturation at the S atoms leads to high-energy occupied bands that can be attributed to S line pair electrons. Surface bonds between Mo atoms and terminal S atoms are strong than bulk Mo-S bonds, suggesting that terminal S atoms may be more difficult to remove from the edges of MoS{sub 2} than bridging S atoms. Bonding in a single two-dimensional layer of MoS{sub 2} is found to be more ionic than the bonding in the full three-dimensional structure. This effect is also observed in one-dimensional MoS{sub 2} ribbons that expose (100) edge planes. The simplified one-dimensional ribbons will be used for further studies of the electronic structure of the edge planes of MoS{sub 2}.

Tan, A.; Harris, S. [Univ. of Wyoming, Laramie, WY (United States). Dept. of Chemistry] [Univ. of Wyoming, Laramie, WY (United States). Dept. of Chemistry

1998-05-04

28

Band structures of porous graphenes  

Microsoft Academic Search

Band structures of porous graphenes are deduced by crystal orbital method. The dispersions suggest ca. 3.7eV of band gaps. Bandwidths of the HOCOs and LUCOs are zero within Hückel approximation due to the nodal character of phenylene units. The graphene ribbons with n porous ladders also have singular electronic states, of which flat HOCOs and LUCOs are n-fold degenerate, respectively.

Masashi Hatanaka

2010-01-01

29

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

30

New compact and wide-band high-impedance surface  

Microsoft Academic Search

In this paper, we suggest a new high-impedance surface (HIS) for applications in antenna and microwave techniques. The resonant frequency of our structure is comparable with that of the multi-layered mushroom structure, however the resonant band of our structure is much wider. Another advantage is the angular and polarization stability of the resonance. We present an analytical model for the

C. R. Simovski; A. A. Sochava; S. A. Tretyakov

2004-01-01

31

Band structure of silicene on zirconium diboride (0001) thin-film surface: Convergence of experiment and calculations in the one-Si-atom Brillouin zone  

NASA Astrophysics Data System (ADS)

So far, it represents a challenging task to reproduce angle-resolved photoelectron (ARPES) spectra of epitaxial silicene by first-principles calculations. Here, we report on the resolution of the previously controversial issue related to the structural configuration of silicene on the ZrB2(0001) surface and its band structure. In particular, by representing the band structure in a large Brillouin zone associated with a single Si atom, it is found that the imaginary part of the one-particle Green's function follows the spectral weight observed in ARPES spectra. By additionally varying the in-plane lattice constant, the results of density functional theory calculations and ARPES data obtained in a wide energy range converge into the "planarlike" phase and provide the orbital character of electronic states in the vicinity of the Fermi level. It is anticipated that the choice of a smaller commensurate unit cell for the representation of the electronic structure will be useful for the study of epitaxial two-dimensional materials on various substrates in general.

Lee, Chi-Cheng; Fleurence, Antoine; Yamada-Takamura, Yukiko; Ozaki, Taisuke; Friedlein, Rainer

2014-08-01

32

Surface electronic bands of submonolayer Ge on Ag(111)  

NASA Astrophysics Data System (ADS)

Germanium deposited on single-crystal Ag(111) substrates at about 1/3-monolayer coverage forms a stable (3×3)R30? superstructure as seen by reflection high-energy electron diffraction. In situ angle resolved photoelectron spectroscopy reveals a rich band structure consisting of conelike features that cross the Fermi surface at the center (?¯ points) of the superstructure surface Brillouin zone (SBZ), exhibiting a high dispersion with the surface parallel wave vector. With the help of first-principles calculations, it can be inferred that most of the features are explained in terms of an Ag2Ge-ordered surface alloy corresponding to surface states localized in the first two layers. One of the bands has a saddle point near the M¯ point of the SBZ with a characteristic split-band behavior distinguishing Ge surface alloy from other similar systems.

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

2013-08-01

33

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

SciTech Connect

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

Li, Yi; Zhang, Rong, E-mail: rzhang@nju.edu.cn, E-mail: bliu@nju.edu.cn; Liu, Bin, E-mail: rzhang@nju.edu.cn, E-mail: bliu@nju.edu.cn; Xie, Zili; Zhang, Guogang; Tao, Tao; Zhuang, Zhe; Zhi, Ting; Zheng, Youdou [Jiangsu Provincial Key Laboratory of Advanced Photonic and Electronic Materials, School of Electronic Science and Engineering, Nanjing University, Nanjing 210093 (China); Nanjing National Laboratory of Microstructures, Nanjing University, Nanjing 210093 (China)

2014-07-07

34

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

NASA Astrophysics Data System (ADS)

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.

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

2014-11-01

35

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

36

Photonic band gap structure simulator  

DOEpatents

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

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

2006-10-03

37

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

NASA Astrophysics Data System (ADS)

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¯Ag point and has a saddle point near the M¯Ag point of Ag(111) resembling the ?-band dispersion in graphene.

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

2013-12-01

38

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

39

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

Microsoft Academic Search

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

Mohsen Salehi; Nader Behdad

2008-01-01

40

Band structure of W and Mo by empirical pseudopotential method  

NASA Technical Reports Server (NTRS)

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

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

1977-01-01

41

Band structures of bilayer graphene superlattices  

Microsoft Academic Search

We have studied the electronic band structures of bilayer graphene (BLG) superlattices. In BLG, there are two distinct types of superlattice modulations - chemical potential modulations and electric field induced gap modulations. We have solved energy bands for one- and two-dimensional superlattices for both kinds of modulations. We found, in particular, for a 2D superlattice with gap modulation, that the

Si Wu; Matthew Killi; Arun Paramekanti

2011-01-01

42

Band structure of 235U  

NASA Astrophysics Data System (ADS)

Over a period of several years we have performed three separate experiments at Lawrence Berkeley National Laboratory's 88-Inch Cyclotron in which 235U (thick target) was Coulomb-excited. The program involved stand-alone experiments with Gammmasphere and with the 8pi Spectrometer using 136Xe beams at 720 MeV, and a CHICO-Gammasphere experiment with a 40Ca beam at 184 MeV. In addition to extending the known negative-parity bands to high spin, we have assigned levels in some seven positive-parity bands which are in some cases (e.g., [631]1/2, [624]7/2, and [622]5/2) strongly populated by E3 excitation. The CHICO data have been analyzed to extract E2 and E3 matrix elements from the observed yields. Additionally, many M1 matrix elements could be extracted from the ?-ray branching ratios. A number of new features have emerged, including the unexpected attenuation of magnetic transitions between states of the same Nilsson multiplet, the breakdown of Coriolis staggering at high spin, and the effect of E3 collectivity on Coriolis interactions.

Ward, D.; Macchiavelli, A. O.; Clark, R. M.; Cline, D.; Cromaz, M.; Deleplanque, M. A.; Diamond, R. M.; Fallon, P.; Görgen, A.; Hayes, A. B.; Lane, G. J.; Lee, I.-Y.; Nakatsukasa, T.; Schmidt, G.; Stephens, F. S.; Svensson, C. E.; Teng, R.; Vetter, K.; Wu, C. Y.

2012-12-01

43

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

44

Tunable band structure effects on ballistic transport in graphene nanoribbons  

Microsoft Academic Search

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

Oleksiy Roslyak; Godfrey Gumbs; Danhong Huang

2010-01-01

45

Effects of band structure and matrix element on RKKY interaction  

Microsoft Academic Search

The effects of band structure and matrix elements on the RKKY interaction J(R) are separately investigated. When the Fermi surface has planes perpendicular to R, effects appear on the period of oscillation, the phase shift and the amplitude of J(R). The applicable region of the asymptotic form for large R and the validity of the free electron approximation are also

A. Narita; T. Kasuya

1984-01-01

46

The complex band structure for armchair graphene nanoribbons  

Microsoft Academic Search

Using a tight binding transfer matrix method, we calculate the complex band structure of armchair graphene nanoribbons. The real part of the complex band structure calculated by the transfer matrix method fits well with the bulk band structure calculated by a Hermitian matrix. The complex band structure gives extra information on carrier's decay behaviour. The imaginary loop connects the conduction

Liu-Jun Zhang; Tong-Sheng Xia

2010-01-01

47

Surface band topology of Ge on Ag(111)  

NASA Astrophysics Data System (ADS)

While compelling evidence for silicene on Ag (111) has been recently published [1], the existence of germanene remains elusive. We have performed MBE growth of (sub) monolayer Ge on single crystal Ag (111) substrates, supported by DFT calculations, with the aim to obtain germanene. RHEED data indicate a ( ?3 x?3 )R30^0 superstructure, while in-situ ARPES reveals a rich surface band structure consisting of linearly, highly dispersive cone-like features with hexagonal and snow-flake warping clearly imaged in the constant energy contour plots kx-ky. Unlike the case of graphene-like 2D crystals where Dirac cones are expected at the K-points, here the cone-like features appear at the center (? points) of the surface Brillouin zone similar to what is observed in topological insulators. This suggests the possibility to witness a non-trivial surface band topology triggered by intrinsic spin-orbit coupling as predicted [2] for 2D honeycomb Ge lattices or by strong Ge and Ag p orbital hybridization in an ordered surface alloy Ag2Ge.[4pt] [1] P. Vogt et al., PRL 108, 155501 (2012);[0pt] [2] C.C-Liu et al., PRL 107, 076802 (2011)

Dimoulas, Athanasios; Golias, Evangelos; Xenogiannopoulou, Evangelia; Tsoutsou, Dimitra; Tsipas, Polixronis; Giamini, Sigiava

2013-03-01

48

Band structure engineering of graphene by strain  

Microsoft Academic Search

We have investigated the electronic structure of graphene under different planar strain distributions using the first principles pseudopotential planewave method and the tight-binding approach. We found that graphene with a symmetrical strain distribution is always a zero band gap semiconductor and its pseudogap decreases linearly with the strain strength in the elastic regime. However, asymmetrical strain distributions in graphene result

Jianxin Zhong; Gui Gui; Jin Li

2008-01-01

49

Flat photonic surface bands pinned between Dirac points  

E-print Network

We point out that 2D photonic crystals (PhCs) can support surface bands that are pinned to Dirac points. These bands can be made very flat by optimizing the parameters of the system. Surface modes are found at the interface ...

Jukic, Dario

50

Subwavelength Structured Surfaces: Theory and Applications  

Microsoft Academic Search

Detailed theoretical analysis of subwavelength structured (SWS) surfaces is presented. These surfaces are designed for applications in both the visible and infrared portions of the spectrum. Applications presented include antireflection structured (ARS) surfaces, polarization components, narrow-band filters, and phase plates. Experimental results for 2-D binary ARS surfaces are illustrated. Analysis of SWS surfaces is performed using rigorous coupled-wave analysis (RCWA)

Daniel Henri Raguin

1993-01-01

51

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

52

X-Band Photonic Band-Gap Accelerator Structure Breakdown Experiment  

SciTech Connect

In order to understand the performance of photonic band-gap (PBG) structures under realistic high gradient, high power, high repetition rate operation, a PBG accelerator structure was designed and tested at X band (11.424 GHz). The structure consisted of a single test cell with matching cells before and after the structure. The design followed principles previously established in testing a series of conventional pillbox structures. The PBG structure was tested at an accelerating gradient of 65 MV/m yielding a breakdown rate of two breakdowns per hour at 60 Hz. An accelerating gradient above 110 MV/m was demonstrated at a higher breakdown rate. Significant pulsed heating occurred on the surface of the inner rods of the PBG structure, with a temperature rise of 85 K estimated when operating in 100 ns pulses at a gradient of 100 MV/m and a surface magnetic field of 890 kA/m. A temperature rise of up to 250 K was estimated for some shots. The iris surfaces, the location of peak electric field, surprisingly had no damage, but the inner rods, the location of the peak magnetic fields and a large temperature rise, had significant damage. Breakdown in accelerator structures is generally understood in terms of electric field effects. These PBG structure results highlight the unexpected role of magnetic fields in breakdown. The hypothesis is presented that the moderate level electric field on the inner rods, about 14 MV/m, is enhanced at small tips and projections caused by pulsed heating, leading to breakdown. Future PBG structures should be built to minimize pulsed surface heating and temperature rise.

Marsh, Roark A.; /MIT /MIT /NIFS, Gifu /JAERI, Kyoto /LLNL, Livermore; Shapiro, Michael A.; Temkin, Richard J.; /MIT; Dolgashev, Valery A.; Laurent, Lisa L.; Lewandowski, James R.; Yeremian, A.Dian; Tantawi, Sami G.; /SLAC

2012-06-11

53

Development of Thin-Film Liquid Crystal Polymer Surface Mount Packages for Ka-band Applications  

E-print Network

956 Development of Thin-Film Liquid Crystal Polymer Surface Mount Packages for Ka-band Applications of thin-film Liquid Crystal Polymer (LCP) surface mount packages for packaging MMIC's in Ka hermetic capabilities in a compact structure. Index Terms - Liquid Crystal Polymer, Surface Mount Packages

Pham, Anh-Vu

54

Banded Structure and Domain Arrangements in PbTiO3 Single Crystals  

NASA Astrophysics Data System (ADS)

In the present work we report the ferroelectric domain arrangements and characteristics of banded structures observed in flux-grown PbTiO3 single crystals. Investigations of etched crystals indicate that most of the specimens show banded structures which may correspond to surface relief characteristics of as-grown crystals. Banded structures, which are different from domain structures, possess structural characteristics similar to those of martensite variants in various alloys and ceramics. The stresses produced during transformation were relieved by the formation of the banded structures and the 90° domain structures, suggesting that the band structures and 90° domains are the products of self-accommodation in as-grown PbTiO3 crystals during the cubic/tetragonal (C/T) transformation. Image characteristics imply that banded-structure-induced domain intersections may store high strain energy in lead titanate crystals and therefore hinder polarization switching of the crystals.

Chou, Chen-Chia; Chen, Cheng-Sao

1998-09-01

55

Band structure of doubly-odd nuclei around mass 130  

SciTech Connect

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

Higashiyama, Koji [Department of Physics, Chiba Institute of Technology, Narashino, Chiba 275-0023 (Japan); Yoshinaga, Naotaka [Department of Physics, Saitama University, Saitama City 338-8570 (Japan)

2011-05-06

56

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

57

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 the antenna performances by preventing surface wave or using as a reflector that acts like magnetic conductor. Nowadays PBG materials are used as the cover of patch antenna or dipole antenna and those structures which

Nam, Sangwook

58

ULTRA-HIGH GRADIENT COMPACT S-BAND ACCELERATING STRUCTURE*  

E-print Network

frequencies is not practical due to the lack of industrially available high peak power RF sources in X-band Accelerator) S- band accelerating structure operating in the pi-mode at 2.856 GHz, where RF power sources successful high gradient operation of X-band (11.4 GHz) and Ku-band (17 GHz) [5,6]. These efforts, without

Brookhaven National Laboratory

59

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

SciTech Connect

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

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

2001-11-04

60

Carbon nanotube conductance model in parabolic band structure  

Microsoft Academic Search

Fermi dirac integral is applied to study the parabolic band structure of Carbon Nanotube (CNT) which is in the range of minimum band energy. In this letter electronic transport property of one dimensional carbon nanotube with parabolic band structures near the charge neutrality point is investigated. The temperature dependent conductance model which shows minimum conductance near the charge neutrality point

M. T. Ahmadi; Z. Johari; N. A. Amin; S. M. Mousavi; R. Ismail

2010-01-01

61

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

62

Segmental structure in banded mongoose calls.  

PubMed

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

Fitch, W Tecumseh

2012-01-01

63

Crossed Surface Flat Bands of Weyl Semimetal Superconductors  

NASA Astrophysics Data System (ADS)

It has been noted that certain surfaces of Weyl semimetals have bound states forming open Fermi arcs, which are never seen in typical metallic states. We show that the Fermi arcs enable them to support an even more exotic surface state with crossed flat bands in the superconducting state. We clarify the topological origin of the crossed flat bands and the relevant symmetry that stabilizes the cross point. Our symmetry analysis is applicable to known candidate materials of time-reversal breaking Weyl semimetals. We also discuss their possible experimental verification by tunneling spectroscopy.

Lu, Bo; Yada, Keiji; Sato, Masatoshi; Tanaka, Yukio

2015-03-01

64

Crossed surface flat bands of weyl semimetal superconductors.  

PubMed

It has been noted that certain surfaces of Weyl semimetals have bound states forming open Fermi arcs, which are never seen in typical metallic states. We show that the Fermi arcs enable them to support an even more exotic surface state with crossed flat bands in the superconducting state. We clarify the topological origin of the crossed flat bands and the relevant symmetry that stabilizes the cross point. Our symmetry analysis is applicable to known candidate materials of time-reversal breaking Weyl semimetals. We also discuss their possible experimental verification by tunneling spectroscopy. PMID:25793841

Lu, Bo; Yada, Keiji; Sato, Masatoshi; Tanaka, Yukio

2015-03-01

65

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

66

Multiple band structure and band termination in 157Ho towards complete high-spin spectroscopy  

NASA Astrophysics Data System (ADS)

Rotational bands of 157Ho have been populated via the 124Sn( 37Cl, 4n) reaction at beam energies of 155 and 165 MeV. Gamma-ray spectroscopy was performed using the 8 ? spectrometer at Chalk River. Many rotational bands have been observed for the first time. A detailed level scheme is presented, containing approximately 380 transitions, and the quasiparticle structure of the various bands is discussed. Band termination has been observed in the yrast states. For strongly coupled bands, B(M1)/ B(E2) transition strength ratios are extracted and compared with previous measurements and theoretical expectations. Branching ratios for out-of-band E2 transitions are analysed to extract band mixing interaction strengths. Implications for rotational damping are considered. The interaction at the first backbend in the ground band is found to be strongly signature dependent; this is evidence for a signature-dependent triaxial shape of the nucleus.

Radford, D. C.; Andrews, H. R.; Ball, G. C.; Horn, D.; Ward, D.; Banville, F.; Flibotte, S.; Monaro, S.; Pilotte, S.; Taras, P.; Johansson, J. K.; Tucker, D.; Waddington, J. C.; Riley, M. A.; Hagemann, G. B.; Hamamoto, I.

1992-08-01

67

Models of bands and Fermi surfaces for electron-doped cuprates  

SciTech Connect

The properties of Fermi surfaces and electron bands in electron-doped cuprates have been studied. The possible origins of a hole pocket in the nodal direction and a pseudogap at hot spots are discussed, including stripe phases and double bands in an antiferromagnetically correlated Fermi liquid. Within the framework of the mean field method, it is shown that both t-t'-t''-U Hubbard model solutions with a homogeneous antifer-romagnetic spin structure and those with a diagonal stripe structure can reproduce the fragmentar character of the Fermi surface. The appearance of hole pockets in various structures is related either to states in the lower Hubbard band or to states localized on domain walls. The behavior of a gap at the leading edge of the energy distribution of photoelectrons and its dependence on oxygen removal in the course of annealing are considered.

Ovchinnikova, M. Ya. [Russian Academy of Sciences, Semenov Institute of Chemical Physics (Russian Federation)], E-mail: movchin@center.chph.ras.ru

2008-06-15

68

Structure of the Red Fluorescence Band in Chloroplasts  

E-print Network

Structure of the Red Fluorescence Band in Chloroplasts GOVINDJEE and LOUISA YANG From known from the analysis of the absorption bands of live cells (11-13). Since the half-band width in Chlorella pyrenoidosa at -196°C by Brody (18). Litvin, Krasnovsky, and Rikhireva (19) discovered another new

Govindjee

69

Band Structure of K(2x2) on graphene  

Microsoft Academic Search

The electronic structure of K(2x2) on graphene, the same stochiometry as bulk KC8, was studied using angle-resolved photoemission spectroscopy (ARPES). In addition to bands derived from the graphene pi states an intercalant induced ``interlayer band'' is observed centered at gamma. Of these two bands, the dominant mass renormalization occurs in the pi-derived bands, as determined by characterization of the ``kinks''

Jessica McChesney; Aaron Bostwick; Taisuke Ohta; Thomas Seyller; K. V. Emtsev; Karsten Horn; Eli Rotenberg

2008-01-01

70

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

71

L-band emission of rough surfaces: Comparison between experimental data and different modeling approaches  

Microsoft Academic Search

In this paper we present a study of a numerical modeling approach based on the Finite Element Method (FEM) for the prediction of rough surface emission at L-band, including a comparison with other modeling approaches and experimental data. The numerical approach relies on the use of ANSYS' numerical computation software HFSS (High Frequency Structure Simulator), which in turn solves Maxwell's

Heather Lawrence; François Demontoux; Jean-Pierre Wigneron; Arnaud Mialon; Tzong-Dar Wu; Valery Mironov; Liang Chen; Jianchen Shi; Yann Kerr

2010-01-01

72

Frequency-selective surfaces to enhance performance of broad-band reconfigurable arrays  

Microsoft Academic Search

We present a novel frequency-selective surface (FSS) design aimed at enhancing the performance of broad-band reconfigurable antenna apertures. In particular, reconfigurable printed dipole arrays are examined in the presence of a multilayer FSS. Of particular interest is the design of FSS structures whose reflection coefficient has prespecified phase response over a broad set of frequencies. Previous FSSs primarily considered designs

Yunus E. Erdemli; Kubilay Sertel; Roland A. Gilbert; Daniel E. Wright; John L. Volakis

2002-01-01

73

Surface doping and band gap tunability in hydrogenated graphene.  

PubMed

We report the first observation of the n-type nature of hydrogenated graphene on SiO(2) and demonstrate the conversion of the majority carrier type from electrons to holes using surface doping. Density functional calculations indicate that the carrier type reversal is directly related to the magnitude of the hydrogenated graphene's work function relative to the substrate, which decreases when adsorbates such as water are present. Additionally, we show by temperature-dependent electronic transport measurements that hydrogenating graphene induces a band gap and that in the moderate temperature regime [220-375 K], the band gap has a maximum value at the charge neutrality point, is tunable with an electric field effect, and is higher for higher hydrogen coverage. The ability to control the majority charge carrier in hydrogenated graphene, in addition to opening a band gap, suggests potential for chemically modified graphene p-n junctions. PMID:22187951

Matis, Bernard R; Burgess, James S; Bulat, Felipe A; Friedman, Adam L; Houston, Brian H; Baldwin, Jeffrey W

2012-01-24

74

Engineering the Electronic Band Structure for Multiband Solar Cells  

SciTech Connect

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

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

2010-07-12

75

Wideband high impedance surface for X-band antenna applications  

Microsoft Academic Search

A novel structure composed of frequency selective surface printed elements implemented on a grounded dielectric slab is proposed for the design of wideband artificial magnetic conductors. In this design, a printed cross with a slot at the center is combined with an L-shaped unclosed rectangular loop, which enables to obtain a wideband high impedance surface. The bandwidth of the surface

Gopinath Gampala; Alexander B. Yakovlev

2007-01-01

76

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

77

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

78

L-Band Acoustic Surface-Wave Tapped Delay Line  

Microsoft Academic Search

Microwave delay lines are of considerable interest because of the large time-bandwidth products that can be realized. Recently it has become possible to extend acoustic surface-wave technology into the microwave frequency range using the sub-micron capability of the scanning electron microscope. This paper reports the design and fabrication of a broadband multi-tapped delay line, centered at L-Band. Emphasis is placed

H. M. Gerard; R. D. Weglein; E. D. Wolf

1970-01-01

79

Fractal FSS: a novel dual-band frequency selective surface  

Microsoft Academic Search

The multiband properties of self-similar fractals can be advantageously exploited to design multiband frequency selective surfaces (FSS). A Sierpinski dipole FSS has been analyzed and measured and the results show an interesting dual-band behavior. Furthermore a near-field measurement technique is applied to characterize the FSS response to different angles of incidence. Finally, it is shown that it is possible to

Jordi Romeu; Yahya Rahmat-Samii

2000-01-01

80

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

81

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

82

Analysis of the sea clutter structure using temporal sequences of X-band marine radar images  

Microsoft Academic Search

This work analyses the spectral structure of the sea clutter obtained from temporal sequences of radar images of the sea surface. The images were acquired by ordinary marine radars, which work in X-band and horizontal polarization. The study analyses the different contributions to the sea clutter spectrum due to those phenomena, such as ocean waves, speckle due to sea surface

Jose C. Nieto-Borge; Ana M. Baquero-Martínez; David de la Mata-Moya; Jose L. Álvarez-Pérez

2008-01-01

83

Band Structures of Bilayer Graphene Superlattices  

Microsoft Academic Search

We formulate a low energy effective Hamiltonian to study superlattices in bilayer graphene (BLG) using a minimal model which supports quadratic band touching points. We show that a one dimensional (1D) periodic modulation of the chemical potential or the electric field perpendicular to the layers leads to the generation of zero-energy anisotropic massless Dirac fermions and finite energy Dirac points

Matthew Killi; Si Wu; Arun Paramekanti

2011-01-01

84

Band-structure determination for finite 3-D photonic crystals  

NASA Astrophysics Data System (ADS)

The partial band structure from a finite photonic crystal is determined using a model based on light diffraction and the transfer-matrix formalism. The predictions from such a model are compared to an experimental measurement of the bands in the LU direction of a face centered cubic colloidal crystal. Then, both the theoretical predictions and the experimental measurements are compared with the usual band-structure calculation based on a plane-wave expansion with perfectly periodic boundary conditions. As in measurements performed in the past, discrepancies between the predictions of this later model and the experimentally determined bands are observed. On the contrary, using the model presented based on light propagation through a finite crystal, where no periodicity is imposed in the direction perpendicular to any of the set of planes considered to determine a specific branch of the band structure, we found a very good agreement between the experimentally determined and the predicted bandwidths.

Botey, M.; Maymó, M.; Martorell, J.

2005-07-01

85

Mapping polarization induced surface band bending on the Rashba semiconductor BiTeI  

PubMed Central

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

86

Asymmetry gap in the electronic band structure of bilayer graphene  

Microsoft Academic Search

A tight-binding model is used to calculate the band structure of bilayer graphene in the presence of a potential difference between the layers that opens a gap Delta between the conduction and valence bands. In particular, a self-consistent Hartree approximation is used to describe imperfect screening of an external gate, employed primarily to control the density n of electrons on

Edward McCann

2006-01-01

87

Band structure asymmetry of bilayer graphene revealed by infrared spectroscopy  

Microsoft Academic Search

We report on infrared spectroscopy of bilayer graphene integrated in gated structures. The dominant feature of the optical conductivity is a resonance peak due to interband transitions between the two conduction bands or two valence bands. Both the frequency and the voltage dependence of the peak show a significant asymmetry upon electrostatic doping of electrons and holes. We show that

Zhiqiang Li; Erik Henriksen; Zhigang Jiang; Zhao Hao; Matt Zhang; Michael Fogler; Michael Martin; Philip Kim; Horst Stormer; Dimitri Basov

2009-01-01

88

Strained bilayer graphene: Band structure topology and Landau level spectrum  

Microsoft Academic Search

We show that topology of the low-energy band structure in bilayer graphene critically depends on mechanical deformations of the crystal which may easily develop in suspended graphene flakes. We describe the Lifshitz transition that takes place in strained bilayers upon splitting the parabolic bands at intermediate energies into several Dirac cones at the energy scale of a few meV. Then,

Marcin Mucha-Kruczynski; Igor L. Aleiner; Vladimir I. Fal'Ko

2011-01-01

89

Band structure calculation of strained graphene on hexagonal boron nitride  

Microsoft Academic Search

The band structure of the graphene on hexagonal boron nitride system are calculated with the ab-initio method, and the dependence on the stress applied to the direction perpendicular to the sheet are investigated. It is shown that there exists an optimal stress condition for widening the band gap of the graphene, which could greatly improve the transistor on\\/off ratio, while

Takeshi Ohmi; Yoshinari Kamakura

2012-01-01

90

The low energy electronic band structure of bilayer graphene  

Microsoft Academic Search

We employ the tight binding model to describe the electronic band structure of bilayer graphene and we explain how the optical absorption coefficient of a bilayer is influenced by the presence and dispersion of the electronic bands, in contrast to the featureless absorption coefficient of monolayer graphene. We show that the effective low energy Hamiltonian is dominated by chiral quasiparticles

E. McCann; D. S. L. Abergel; V. I. Fal'Ko

2007-01-01

91

Experimental study on band dispersion in channels structured with micropillars  

Microsoft Academic Search

The band dispersion in channels with an orderly pillar structure with a pressure-driven liquid flow was determined. Several channels with different geometries were etched in a silicon wafer and enclosed by a glass wafer. The microchannels obtained had the same depth, pillar disposition, and overall porosity, but different pillar diameters and channel widths. The broadening of narrow bands of a

M. De Pra; W. Th. Kok; J. G. E. Gardeniers; G. Desmet; S. Eeltink; Nieuwkasteele van J. W; P. J. Schoenmakers

2006-01-01

92

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

93

Novel photonic band gap structures for accelerator applications  

E-print Network

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

Smirnova, Evgenya I

2005-01-01

94

Band structure of ABC -stacked graphene trilayers  

Microsoft Academic Search

The ABC -stacked N -layer-graphene family of two-dimensional electron systems is described at low energies by two remarkably flat bands with Bloch states that have strongly momentum-dependent phase differences between carbon pi -orbital amplitudes on different layers and large associated momentum-space Berry phases. These properties are most easily understood using a simplified model with only nearest-neighbor interlayer hopping which leads

Fan Zhang; Bhagawan Sahu; Hongki Min; Allan H. MacDonald

2010-01-01

95

Band structure of terahertz metallic photonic crystals with high metal filling factor  

E-print Network

that terahertz transmission through structures composed of metallic objects can be enhanced by surface plasmonBand structure of terahertz metallic photonic crystals with high metal filling factor Benjamin The excitation of resonant eigenmodes in two-dimensional metallic photonic crystals by incident terahertz pulses

96

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

97

Optimization of low band gap polymer photovoltaics through structure modification  

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

98

Multi-band Structure in ^181Hg  

NASA Astrophysics Data System (ADS)

Following our first identification of energy levels in ^181Hg [1], a ?-? coincidence experiment was carried out at ANL using the ^40Ar + ^144Sm reaction. A pair of new bands, connected by interband transitions, were found and proposed to be built on the 7/2^- [514] orbital based on the systematics of mercury isotopes [2] and B(M1)/B(E2) ratio considerations. An 80 keV ?-ray was identified to be the lowest transition in the 1/2^- [521] band indicating a large ground state deformation, which is consistent with results of isotope-shift measurements. DCO ratios were also measured. [1] D.T. Shi et al., Bull. Amer. Phys. Soc. 39 (1994) 1419. [2] D.T. Shi et al., Phys. Rev. C 51 (1995) 1720. * Work at MSU, Vanderbilt, and ANL supported by US DOE under contract Nos. DE-FG05-95ER40939, DE-FG05-88ER40407, and W-31-109-ENG-38.

Varmette, P. G.; Ma, W. C.; Croft, W. L.; Winger, J. A.; Ramayya, A. V.; Hamilton, J. H.; Kormicki, J.; Babu, B. R. S.; Zhu, S. J.; Brown, L. T.; Janssens, R. V. F.; Ahmad, I.; Blumenthal, D. J.; Carpenter, M. P.; Crowell, B.; Khoo, T. L.; Lauritsen, T.; Nisius, D.; Ficher, S. M.; Amro, H.; Ishii, T.

1996-10-01

99

Banded Electron Structure Formation in the Inner Magnetosphere  

NASA Technical Reports Server (NTRS)

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

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

1997-01-01

100

Electromagnetic band-gap structure design using the auxetic unit-structure for easily controllable tunability  

NASA Astrophysics Data System (ADS)

Tunable electromagnetic band-gap structures for matching an intended band-gap range have more potential for various applications than ordinary electromagnetic band-gap structures with a fixed or non-linearly variable band-gap range. However, there has not been much progress on the study of the appropriate shape of the structure. To obtain a controllable and tunable electromagnetic band-gap, we propose a new design concept employing a unit-structure with a negative Poisson's ratio close to -1 to realize an approximately linear band-gap shift according to the variation of the shape of the structure. We used a structural optimization procedure based on the phase field method to obtain the design of the unit-structure. We investigated the relation between the auxetic unit-structure deformation and the change in the band-gap range through numerical simulations and also evaluated the possibility to realize the design experimentally in the radio frequency range.

Lim, Heeseung; Shin, Dongheok; Kim, Kyoungsik; Yoo, Jeonghoon

2014-12-01

101

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

102

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

Microsoft Academic Search

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

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

2011-01-01

103

Surface roughness of orthodontic band cements with different compositions  

PubMed Central

Objectives The present study evaluated comparatively the surface roughness of four orthodontic band cements after storage in various solutions. Material and Methods eight standardized cylinders were made from 4 materials: zinc phosphate cement (ZP), compomer (C), resin-modified glass ionomer cement (RMGIC) and resin cement (RC). Specimens were stored for 24 h in deionized water and immersed in saline (pH 7.0) or 0.1 M lactic acid solution (pH 4.0) for 15 days. Surface roughness readings were taken with a profilometer (Surfcorder SE1200) before and after the storage period. Data were analyzed by two-way ANOVA and Tukey's test (comparison among cements and storage solutions) or paired t-test (comparison before and after the storage period) at 5% significance level. Results The values for average surface roughness were statistically different (p<0.001) among cements at both baseline and after storage. The roughness values of cements in a decreasing order were ZP>RMGIC>C>R (p<0.001). After 15 days, immersion in lactic acid solution resulted in the highest surface roughness for all cements (p<0.05), except for the RC group (p>0.05). Compared to the current threshold (0.2 µm) related to biofilm accumulation, both RC and C remained below the threshold, even after acidic challenge by immersion in lactic acid solution. Conclusions Storage time and immersion in lactic acid solution increased the surface roughness of the majority of the tested cements. RC presented the smoothest surface and it was not influenced by storage conditions. PMID:21625737

van de SANDE, Françoise Hélène; da SILVA, Adriana Fernandes; MICHELON, Douver; PIVA, Evandro; CENCI, Maximiliano Sérgio; DEMARCO, Flávio Fernando

2011-01-01

104

[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

105

Silicene structures on silver surfaces  

Microsoft Academic Search

In this paper we report on several structures of silicene, the analog of graphene for silicon, on the silver surfaces Ag(100), Ag(110) and Ag(111). Deposition of Si produces honeycomb structures on these surfaces. In particular, we present an extensive theoretical study of silicene on Ag(111) for which several recent experimental studies have been published. Different silicene structures were obtained only

Hanna Enriquez; Sébastien Vizzini; Abdelkader Kara; Boubekeur Lalmi; Hamid Oughaddou

2012-01-01

106

Effective band structure of random III-V alloys  

NASA Astrophysics Data System (ADS)

Random substitutional alloys have no long range order (LRO) or translational symmetry so rigorously speaking they have no E(k) band structure or manifestations thereof. Yet, many experiments on alloys are interpreted using the language of band theory, e.g. inferring Van Hove singularities, band dispersion and effective masses. Many standard alloy theories (VCA- or CPA-based) have the LRO imposed on the alloy Hamiltonian, assuming only on-site disorder, so they can not be used to judge the extent of LRO that really exists. We adopt the opposite way, by using large (thousand atom) randomly generated supercells in which chemically identical alloy atoms are allowed to have different local environments (a polymorphous representation). This then drives site-dependent atomic relaxation as well as potential fluctuations. The eigenstates from such supercells are then mapped onto the Brillouin zone (BZ) of the primitive cell, producing effective band dispersion. Results for (In,Ga)X show band-like behaviour only near the centre and faces of the BZ but rapidly lose such characteristics away from ? or for higher bands. We further analyse the effects of stoichiometry variation, internal relaxation, and short-range order on the alloy band structure.

Popescu, Voicu; Zunger, Alex

2010-03-01

107

Shear band structure in ballistically tested bainitic steels  

E-print Network

Shear-band structure in ballistically tested carbide-free bainitic steels L. C. D. Fieldinga, H. K. D. H. Bhadeshiaa aMaterials Science and Metallurgy, University of Cambridge, U.K Abstract Adiabatic shear bands represent intense plastic deformation... . The electrolyte consisted of 15% perchloric acid and 85% ethanol by volume. Samples specifically from the shear bands were extracted using a Helios NanoLab focused ion beam micro- scope, and mounted on a copper grid. For quantitative X-ray analysis, the samples...

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

108

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

PubMed Central

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

Holz, M; Chen, S H

1979-01-01

109

Ab-initio band structure of doped graphene  

Microsoft Academic Search

We present an \\\\emph{ab-initio} study of the graphene quasi-particle band structure as function of the doping in G_0 W_0 approximation. We show that the LDA Fermi velocity is substantially renormalized and this renormalization rapidly decreases as function of the doping. We found, in agreement with previous papers, that close to the Dirac point the linear dispersion of the bands is

C. Attaccalite; A. Grüeneis; T. Pichler; A. Rubio

2008-01-01

110

The low energy electronic band structure of bilayer graphene  

Microsoft Academic Search

.  We employ the tight binding model to describe the electronic band structure of bilayer graphene and we explain how the \\u000a optical absorption coefficient of a bilayer is influenced by the presence and dispersion of the electronic bands, in contrast\\u000a to \\u000a the featureless absorption coefficient of monolayer graphene. We show that the effective low energy Hamiltonian is dominated\\u000a by \\u000a chiral quasiparticles

E. McCann; D. S. L. Abergel; V. I. Fal'ko

2007-01-01

111

Complex layered arrays as photonic band-gap structures  

Microsoft Academic Search

The reflective and transmitting properties of several layers of double-periodic arrays are studied. In the arrays, elements are conducting inclusions of various shapes. It is shown that in these structures all the phenomena recently found in dense wire grids with periodical defects (so called photonic band-gap structures) can be observed and explained in simple terms of interlayer and inclusion resonances.

S. L. Prosvirnin; S. A. Tretyakov; T. D. Vasilyeva; A. Fourrier-Lamer; S. Zouhdi

2000-01-01

112

Band alignment of HfO2 on SiO2/Si structure  

NASA Astrophysics Data System (ADS)

Band alignment of HfO2 with various thicknesses on SiO2/Si structure is investigated by x-ray photoelectron spectroscopy (XPS). Band bending of HfO2/SiO2/Si system is found to vary with HfO2 thickness. Band alignment of entire HfO2/SiO2/Si is demonstrated using concepts of interfacial or surface gap states and charge neutrality level (CNL). The XPS results are interpreted and attributed to lower CNL of HfO2 than SiO2/Si which induces electron transfer from SiO2/Si to HfO2, resulting in band bending upward for SiO2/Si. These further confirm feasibility of gap state based theory in investigating band alignments of oxide/semiconductor and oxide/oxide interfaces.

Wang, Xiaolei; Han, Kai; Wang, Wenwu; Xiang, Jinjuan; Yang, Hong; Zhang, Jing; Ma, Xueli; Zhao, Chao; Chen, Dapeng; Ye, Tianchun

2012-03-01

113

Imaging the spotty surface of Betelgeuse in the H band  

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

114

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

115

Quasiparticle band structure of carbon nanotubes  

Microsoft Academic Search

We study the electronic structure of carbon nanotubes theoretically by first-principles techniques. Geometry is optimized with the local-density approximation (LDA) in density functional theory, and many-body effects between electrons are taken into account within the GW approximation. We find that the (5,0) tube is metallic even at the GW level, being different from the tight-binding result. The (6,0) tube is

Takashi Miyake; Susumu Saito

2003-01-01

116

Structural trend analysis by axial surface mapping  

SciTech Connect

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

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

1994-05-01

117

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

NASA Astrophysics Data System (ADS)

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

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

2009-06-01

118

Four-band frequency selective surface with double-square-loop patch elements  

Microsoft Academic Search

Design and experimental verifications are presented for a four-band frequency selective surface (FSS) with perfectly conducting double-square-loop (DSL) patch elements. A single screen DSL element FSS is demonstrated for (1) a four-band FSS which reflects the X- and Ka-band signals while passing the Sand Ku-band signals, and (2) a low-pass (or Ka-add-on) FSS that reflects the Ka-band signal while passing

Te-Kao Wu

1994-01-01

119

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

SciTech Connect

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

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

2006-11-15

120

Isolated true surface wave in a radiative band on a surface of a stressed auxetic.  

PubMed

We demonstrate that a surface resonance (pseudosurface wave) may transform into a true surface wave, i.e., acquire an infinite lifetime, at a single isolated point within a bulk band (radiative region) in a model of a stressed auxetic material. In contrast with the secluded supersonic elastic surface waves, the one found here does not belong to a dispersion line of true surface waves. Therefore we propose to call it an isolated true surface wave (ITSW). The ITSW manifests itself by a deltalike peak in the local density of states and by anomalies in reflection coefficients. The phenomenon may be useful in redirecting energy and/or information from the bulk to the surface in devices supporting guided acoustic waves. PMID:19792659

Trzupek, D; Zieli?ski, P

2009-08-14

121

Full-Band Tunneling in High-? Oxide MOS Structures  

Microsoft Academic Search

In this paper, we investigate the tunneling properties of ZrO2 and HfO2 high-k oxides, by applying quantum mechanical methods that include the full-band structure of Si and oxide materials. Semiempirical sp3s*d tight-binding parameters have been determined to reproduce ab-initio band dispersions. Transmission coefficients and tunneling currents have been calculated for Si\\/ZrO2\\/Si and Si\\/HfO2\\/Si MOS structures, showing a very low gate

Fabio Sacconi; Jean Marc Jancu; Michael Povolotskyi; Aldo Di Carlo

2007-01-01

122

Simulation of the Band Structure of Graphene and Carbon Nanotube  

NASA Astrophysics Data System (ADS)

Simulation technique has been performed to simulate the band structure of both graphene and carbon nanotube. Accordingly, the dispersion relations for graphene and carbon nanotube are deduced analytically, using the tight binding model & LCAO scheme. The results from the simulation of the dispersion relation of both graphene and carbon nanotube were found to be consistent with those in the literature which indicates the correctness of the process of simulation technique. The present research is very important for tailoring graphene and carbon nanotube with specific band structure, in order to satisfy the required electronic properties of them.

Mina, Aziz N.; Awadallah, Attia A.; Phillips, Adel H.; Ahmed, Riham R.

2012-02-01

123

Duplex Structures in Deformation Bands, how do They Form?  

NASA Astrophysics Data System (ADS)

Recent work has led to the investigation of the growth of deformation band mode II linked duplexes. Here we will demonstrate that growth occurs due to collapse of pore space and accumulation of displacement, rather than by a Reidel shear type mechanism. Instead of Riedel shear [Davis, 2000, Alghren, 2001] the field observations show that deformation bands grow as echelon pairs eventually linking as duplexes. We use boundary element models to predict the failure of these mode II deformation bands. The bands were simulated as seams with normal and shear stopovers. An equivalent plastic modulus, on the order of MPa, was chosen based on the field data. Hoek-Brown failure criterion was used to model these structures but the criterion didn't predict the failure patterns observed in the field. The Hoek-Brown criterion does not work because it predicts a frictional failure as opposed to the deformation band failure, which occurs as grains roll past one another and are crushed. The failure criterion chosen to correctly represent deformation band failure was the maximum distortional strain energy density criterion. Instead of relying on frictional failure this criterion is based on the shearing, or maximum shape change of the element. Mode II deformation bands are not formed in a friction controlled environment and so cannot be represented by the Hoek-Brown failure criterion. Instead they form in a shear-dominated environment as represented by the maximum distortional strain energy density criterion. The plastic modulus of the bands must also be decreased dramatically over the background in order to properly represent the bands.

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

2002-12-01

124

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

PubMed

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

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

2012-03-26

125

Surface mountable liquid crystal polymer package with vertical via transition compensating wire inductance up to V-band  

Microsoft Academic Search

A high performance V-band surface mountable packaging structure has been proposed and demonstrated. We enabled the use of liquid crystal polymer (LCP) as a low-cost SMT millimeter-wave package. This package employed the wire bonding technique as the RF interconnect, and the vertical via as the vertical signal transition, despite it being meant for application up to V-band. The optimized vertical

Hiroshi Kanno; Hiroshi Ogura; Kazuaki Takahashi

2003-01-01

126

Valence band structure of AlN probed by photoluminescence  

NASA Astrophysics Data System (ADS)

Deep ultraviolet photoluminescence (PL) was employed to probe the valence band structure of AlN epilayers grown by metal organic chemical vapor deposition on c-plane sapphire substrates. At 10K, in addition to the dominant emission peak at 6.050eV polarized in the E ?c direction, we observed two additional emission peaks at 6.249 and 6.262eV polarized in the E ?c direction. These two emission lines are assigned to the recombination of free excitons related to the B and C valence bands. A more comprehensive picture of the valence band structure of AlN is thus directly obtained from the PL measurements.

Sedhain, A.; Lin, J. Y.; Jiang, H. X.

2008-01-01

127

Structured surfaces for hemocompatibility  

E-print Network

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

Schrauth, Anthony J

2005-01-01

128

Band structure analysis of crystals with discontinuous metallic wires  

Microsoft Academic Search

The band structure for normal propagation of crystals with finite straight metallic wires is studied for different wire diameters and lengths. The crystal is considered as a set of parallel grids. Dispersion characteristics are obtained by using a transmission line model where the parameters are calculated from the reflection and transmission coefficients of the grids. These coefficients are computed rigorously

Halim Boutayeb; Tayeb A. Denidni; Abdel Razik Sebak; Larbi Talbi

2005-01-01

129

Trigonal Band Structure and Time-Reversal Invariance in Graphene  

Microsoft Academic Search

We present a symmetry analysis of the trigonal band structure in graphene. While the energy spectrum near the Fermi edge equals the spectrum of massless Dirac fermions, the transformational properties of the underlying basis functions are qualitatively different. Using group theory we develop an invariant expansion of the Hamiltonian for the electron states near the K points of the graphene

Roland Winkler; Ulrich Zuelicke

2009-01-01

130

Calculation of band structure using local sampling and Green's functions  

Microsoft Academic Search

A method for calculation of band structure has been proposed based on the Green's function theory and local sampling. Potential energy in the Hamiltonian of Schrödinger's equation is approximated with a series of sampled Dirac delta functions weighted by appropriate factors. These factors are found from multipole expansion of atomic potentials in the crystal lattice, with considering effects such as

Milad Khoshnegar; Sina Khorasani; Amirhossein Hosseinnia

2010-01-01

131

Simulation of the Band Structure of Graphene and Carbon Nanotube  

Microsoft Academic Search

Simulation technique has been performed to simulate the band structure of both graphene and carbon nanotube. Accordingly, the dispersion relations for graphene and carbon nanotube are deduced analytically, using the tight binding model & LCAO scheme. The results from the simulation of the dispersion relation of both graphene and carbon nanotube were found to be consistent with those in the

Aziz N Mina; Attia A Awadallah; Adel H Phillips; Riham R Ahmed

2012-01-01

132

Band Structure Asymmetry of Bilayer Graphene Revealed by Infrared Spectroscopy  

Microsoft Academic Search

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

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

2008-01-01

133

Band structure and optical properties of isolated and bundled nanotubes  

E-print Network

Band structure and optical properties of isolated and bundled nanotubes S. Reich , C. Thomsen , P of isolated and bundled single-walled nanotubes by ab initio calculations. Curvature effects on the electronic states depend on the chirality of the nanotube; the strongest deviations from the zone

Nabben, Reinhard

134

Band structure of charge-ordered doped antiferromagnets Mats Granath*  

E-print Network

the local antiferromagnetism, to- gether with antiphase domain walls of suppressed field strengthBand structure of charge-ordered doped antiferromagnets Mats Granath* Chalmers Technical University June 2004) We study the distribution of electronic spectral weight in a doped antiferromagnet

Johannesson, Henrik

135

Effect of structure, surface passivation, and doping on the electronic properties of Ge nanowires: A first-principles study  

E-print Network

confinement has a substantial effect on the electronic band structure and, hence, the band gap Eg , which The electronic band structure shows a significant response to changes in surface passivation with hydrogen. ivEffect of structure, surface passivation, and doping on the electronic properties of Ge nanowires

Khare, Sanjay V.

136

Photonic-band structure of magnetic photonic crystal slabs  

Microsoft Academic Search

In this paper, we introduce a rigorous computational method for the evaluation of the band structure of magnetic photonic crystal (MPC) slabs. With the help of this method, the full-wave analysis of the structure can be reduced to the analysis of an equivalent multi-conductor transmission line. In this work, we present a semi-analytical characteristic equation for the evaluation of the

Hasan Ajam; Mahmoud Shahabadi

2005-01-01

137

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

138

Electronic band structure of magnetic bilayer graphene superlattices  

SciTech Connect

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

2014-09-28

139

Investigation of phononic band gap structures considering interface effects  

NASA Astrophysics Data System (ADS)

Interface imperfection has a significant effect on the wave's propagation behavior in the phononic crystals. To account for the interface imperfection, a numerical simulation based on the boundary element method has been proposed to investigate the propagation of in-plane waves in the phononic crystals with imperfect interfaces. The effects of interface spring stiffness, volume fractions, density ratio, and the shape of the scatters on the band gaps are analyzed. It can be concluded that slightly interface imperfection would not affect band structures too much. However, when the interface is relatively weak, the effect of interface imperfection cannot be neglected.

Zhu, Xingyi; Zhong, Sheng; Sun, Daquan; Ye, Anke; Deng, Fuwen

2014-10-01

140

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

141

Mid-frequency Band Dynamics of Large Space Structures  

NASA Technical Reports Server (NTRS)

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

Coppolino, Robert N.; Adams, Douglas S.

2004-01-01

142

First Direct Observation of a Nearly Ideal Graphene Band Structure  

Microsoft Academic Search

Angle-resolved photoemission and x-ray diffraction experiments show that multilayer epitaxial graphene grown on the SiC(0001¯) surface is a new form of carbon that is composed of effectively isolated graphene sheets. The unique rotational stacking of these films causes adjacent graphene layers to electronically decouple leading to a set of nearly independent linearly dispersing bands (Dirac cones) at the graphene K

M. Sprinkle; D. Siegel; Y. Hu; J. Hicks; A. Tejeda; A. Taleb-Ibrahimi; P. Le Fèvre; F. Bertran; S. Vizzini; H. Enriquez; S. Chiang; P. Soukiassian; C. Berger; W. A. de Heer; A. Lanzara; E. H. Conrad

2009-01-01

143

First Direct Observation of a Nearly Ideal Graphene Band Structure  

Microsoft Academic Search

Angle-resolved photoemission and x-ray diffraction experiments show that multilayer epitaxial graphene grown on the SiC(0001) surface is a new form of carbon that is composed of effectively isolated graphene sheets. The unique rotational stacking of these films causes adjacent graphene layers to electronically decouple, leading to a set of nearly independent linearly dispersing bands (Dirac cones) at the graphene K-point.

Mike Sprinkle; Y. Hu; J. Hicks; A. Tejeda; A. Taleb-Ibrahimi; P. Le Fèvre; F. Bertran; C. Berger; W. A. de Heer; E. H. Conrad

2010-01-01

144

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

NASA Astrophysics Data System (ADS)

Global 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

145

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

146

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

147

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

NASA Technical Reports Server (NTRS)

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

Matolak, David W.

2007-01-01

148

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

149

Gold bands as a suitable surface for enzyme immunoassays.  

PubMed

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

Abad-Villar, Eva M; Fernández-Abedul, M Teresa; Costa-García, Agustín

2002-09-01

150

Electronic band structure of a Tl/Sn atomic sandwich on Si(111)  

NASA Astrophysics Data System (ADS)

A two-dimensional compound made of one monolayer of Tl and one monolayer of Sn on Si(111) has been found to have a sandwichlike structure in which the Sn layer (having the milk-stool arrangement) resides on the bulklike terminated Si(111) surface and the Tl layer (having the honeycomb-chained-trimer arrangement) is located above the Sn layer. The electronic band structure of the compound contains two spin-split surface-state bands, of which one is nonmetallic and the other is metallic. Near the Fermi level the metallic band is split with the momentum splitting ? k?=0.037 Å-1 and energy splitting ? EF=167 meV. The steep dispersion of the band when crossing the Fermi level corresponds to an electron velocity of ?8.5 ×105 m/s, which is comparable to the value reported for graphene. The 2D Fermi contours have almost circular shape with spin texture typical for hexagonal surfaces.

Gruznev, D. V.; Bondarenko, L. V.; Matetskiy, A. V.; Tupchaya, A. Y.; Alekseev, A. A.; Hsing, C. R.; Wei, C. M.; Eremeev, S. V.; Zotov, A. V.; Saranin, A. A.

2015-01-01

151

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

SciTech Connect

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

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

2012-01-01

152

Invariant expansion for the trigonal band structure of graphene  

Microsoft Academic Search

We present a symmetry analysis of the trigonal band structure in graphene, elucidating the transformational properties of the underlying basis functions and the crucial role of time-reversal invariance. Group theory is used to derive an invariant expansion of the Hamiltonian for electron states near the K points of the graphene Brillouin zone. Besides yielding the characteristic k-linear dispersion and higher-order

R. Winkler; U. Zülicke

2008-01-01

153

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

SciTech Connect

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

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

2012-05-03

154

Orientation and shape effects on nanowire band structure  

Microsoft Academic Search

The impact of wire-axis orientation and cross-sectional shape on the applicability of the Luttinger-Kohn and Burt-Foreman Hamiltonians to modeling the band structure of embedded nanowires is studied. Differences in the two theories at both zero and finite wave vector are derived. The magnitudes of the differences are accessed by carrying out calculations for 3 different wire directions ([001], [110], [111]),

Benny Lassen; Morten Willatzen; Roderick Melnik; Lok Lew Yan Voon

2004-01-01

155

Evidence of nitric-oxide-induced surface band bending of indium tin oxide  

NASA Astrophysics Data System (ADS)

The interaction of indium tin oxide (ITO) film with nitric oxide (NO) has been investigated in situ by a four-point probe and x-ray photoelectron spectroscopy (XPS). The XPS N 1s peak emerged at a high binding energy of 404 eV indicating that NO was molecularly adsorbed on ITO surface. The adsorption of NO on ITO surface also induced a 0.2 eV shift in its valence band maximum to the low binding energy side leading to an upward surface band bending. We have shown that the increase in the ITO sheet resistance was attributed to its surface band bending.

Hu, Jianqiao; Pan, Jisheng; Zhu, Furong; Gong, Hao

2004-06-01

156

Electronic structure and optical properties of Cs2HgI4: Experimental study and band-structure DFT calculations  

NASA Astrophysics Data System (ADS)

High-quality single crystal of cesium mercury tetraiodide, Cs2HgI4, has been synthesized by the vertical Bridgman-Stockbarger method and its crystal structure has been refined. In addition, electronic structure and optical properties of Cs2HgI4 have been studied. For the crystal under study, X-ray photoelectron core-level and valence-band spectra for pristine and Ar+-ion irradiated surfaces have been measured. The present X-ray photoelectron spectroscopy (XPS) results indicate that the Cs2HgI4 single crystal surface is very sensitive with respect to Ar+ ion-irradiation. In particular, Ar+ bombardment of the single crystal surface alters the elemental stoichiometry of the Cs2HgI4 surface. To elucidate peculiarities of the energy distribution of the electronic states within the valence-band and conduction-band regions of the Cs2HgI4 compound, we have performed first-principles band-structure calculations based on density functional theory (DFT) as incorporated in the WIEN2k package. Total and partial densities of states for Cs2HgI4 have been calculated. The DFT calculations reveal that the I p states make the major contributions in the upper portion of the valence band, while the Hg d, Cs p and I s states are the dominant contributors in its lower portion. Temperature dependence of the light absorption coefficient and specific electrical conductivity has been explored for Cs2HgI4 in the temperature range of 77-300 K. Main optical characteristics of the Cs2HgI4 compound have been elucidated by the first-principles calculations.

Lavrentyev, A. A.; Gabrelian, B. V.; Vu, V. T.; Shkumat, P. N.; Myronchuk, G. L.; Khvyshchun, M.; Fedorchuk, A. O.; Parasyuk, O. V.; Khyzhun, O. Y.

2015-04-01

157

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

158

Fermi Energy in the Non-Parabolic Band Structure of a Carbon Nanotube  

Microsoft Academic Search

The band structure of a carbon nanotube is obtained from the graphene band structure. The band energy of CNT near to the minimum band energy is parabolic. However it is not parabolic in other regions. In the non-parabolic regime the density of states is proportional to a numerical integral that is different from Fermi integrals. The carrier statistics to all

Mohammad Taghi Ahmadi; Jeffrey Frank Webb; Razali Ismail

2009-01-01

159

FERMI ENERGY IN THE NON-PARABOLIC BAND STRUCTURE OF A CARBON NANOTUBE  

Microsoft Academic Search

The band structure of a carbon nanotube is obtained from the graphene band structure. The band energy of CNT near to the minimum band energy is parabolic. However it is not parabolic in other regions. In the non-parabolic regime the density of states is proportional to a numerical integral that is different from Fermi integrals. The carrier statistics to all

Mohammad Taghi Ahmadi; Jeffrey Frank Webb; Razali Ismail

2009-01-01

160

Silicene Structures on Silver Surfaces  

E-print Network

In this paper we report on several structures of silicene, the analog of graphene for silicon, on the silver surfaces Ag(100), Ag(110) and Ag(111). Deposition of Si produces honeycomb structures on these surfaces. In particular, we present an extensive theoretical study of silicene on Ag(111) for which several recent experimental studies have been published. Different silicene structures were obtained only by varying the silicon coverage and/or its atomic arrangement. All the structures studied show that silicene is buckled, with a Si-Si nearest neighbor distance varying between 2.28 and 2.5 A{\\deg} . Due to the buckling in the silicene sheet, the apparent (lateral) Si-Si distance can be as low as 1.89 A{\\deg} . We also found that for a given coverage and symmetry, one may observe different scanning tunneling microscopy images corresponding to structures that differ by only a translation.

Enriquez, Hanna; Kara, Abdelkader; Lalmi, Boubekeur; Oughaddou, Hamid

2012-01-01

161

The influence of A-band and B-band lipopolysaccharide on the surface characteristics and adhesion of Pseudomonas aeruginosa to surfaces  

Microsoft Academic Search

Pseudomonas aenrginosa PA01 possesses two distinct lipopolysaccharide (LPS) O-polysaccharide species, A- and B-band LPS, the relative expression of which appears to be under environmental control. In an attempt to identify the influence these LPS types have on surface characteristics and adhesion, we examined the surface hydrophobicity and surface charge of P. aemginosa PA01 (05 serotype) and its isogenic LPS derivatives

Stephen A. Makin; Terrance J. Beveridge

1996-01-01

162

Coupler Design for the LCLS Injector S-Band Structures  

SciTech Connect

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

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

2006-03-03

163

The fcc-bcc structural transition: Band theory and statistical thermodynamics  

NASA Astrophysics Data System (ADS)

Employing a high precision band structure method (FP-LAPW - Full Potential Linearized Augmented Plane Wave) we calculate the total energy variation along the tetragonal-distortion path connecting the body centered cubic (bcc) and the face centered cubic (fcc) structure. The total energy along this Bain-transformation is calculated varying c/a and volume providing a first principles energy surface which has two minima as a function of c/a. These are shallow and occur for the sp-metals at the two cubic structures, while Ti(V) has a minimum at fcc(bcc) but a saddle point at the other cubic structure. The surfaces can be analyzed in terms of an interplay between the Madelung contribution and the band energies. Using these ab initio energy surfaces we formulate a model for temperature induced martensitic phase transitions where the excitations leading to the phase instability are local fluctuations of the respective order parameter which describes the displacement of a single atom or an atomic plane when transforming structure A into structure B. The fluctuations of the order parameter are treated in the framework of a Landau-Ginzburg model and lead to an entropy driven first order phase transition which is caused by strain fluctuations (due to anharmonicities) rather than by phonon softening.

Mohn, P.; Schwarz, K.; Blaha, P.

1996-03-01

164

First direct observation of a nearly ideal graphene band structure  

SciTech Connect

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

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

2009-12-10

165

The CuInSe2-CuIn3Se5 defect compound interface: Electronic structure and band alignment  

NASA Astrophysics Data System (ADS)

The interface formation between stoichiometric chalcopyrite CuInSe2 and the copper-deficient defect phase CuIn3Se5 is investigated by in situ photoelectron spectroscopy. The use of epitaxial samples allows for the preparation of highly defined surfaces and accurate analysis of the electronic structure. Valence band structures measured with synchrotron-based photoelectron spectroscopy are in agreement with density functional theory. We observe a lowering of the top valence band of CuIn3Se5 of 0.29 eV with respect to CuInSe2. The increased optical gap for copper-deficient material leads to aligned conduction bands.

Hofmann, A.; Pettenkofer, C.

2012-08-01

166

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

167

Surface structure determines dynamic wetting  

NASA Astrophysics Data System (ADS)

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

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

2015-02-01

168

Surface structure determines dynamic wetting.  

PubMed

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

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

2015-01-01

169

Electronic structure of the valence band of GdS x and Gd 3S 4  

NASA Astrophysics Data System (ADS)

Electronic structure of clean surfaces of single crystals of magnetic compounds of sulfides of gadolinium GdS x ( x = 0.8-1.25) with NaCl and Th 3P 4 structures has been investigated by ultra-violet and X-ray photoelectron, Auger and electron energy loss spectroscopy. Clean surfaces of GdS x were obtained by cleavage in situ in ultra-high vacuum and by ion bombardment followed by annealing in vacuum. Photoelectron spectra of the valence band of GdS x family have the similar structure with a maxima at 9 eV and 5 eV related to a photoemission from the 4f-states and valence band formed by 3p-states of S anions respectively and features in the region 0-2 eV associated with 6s-5d conduction band of GdS x. An analysis of electron energy loss spectra has shown that the main features in loss spectra at high beam energy are associated with the 4d-4f giant resonance, 5p-5d resonance and plasmon excitation. At low incident energy a prominent multiplet structure is observed and interpreted in terms of the dipole-forbidden 4f ? 4f electron transitions.

Grazhulis, V. A.; Bozhko, S. I.; Bolotin, I. L.; Bulanov, O. R.; Ionov, A. M.

1996-09-01

170

A PARAMETERIZED SURFACE REFLECTIVITY MODEL AND ESTIMATION OF BARE SURFACE SOIL MOISTURE WITH L-BAND RADIOMETER  

Technology Transfer Automated Retrieval System (TEKTRAN)

Soil moisture is an important parameter for hydrological and climatic investigations. Future satellite missions with L-band passive microwave radiometers will significantly increase the capability of monitoring Earth's soil moisture globally. Understanding the effects of surface roughness on microwa...

171

Band structure calculations of Mo2BC under pressure  

NASA Astrophysics Data System (ADS)

Mo2B is a superconductor with a Tc of about 5.8 K and a body centered tetragonal cristalline structure. When carbon is added to the structure it is formed the intermetallic Mo2BC compound, which is a superconductor with a Tc of about 7 K and has a crystalline face centered orthorhombic structure. In this work we make ab initio calculations of the electronics bands for Mo2BC at several pressures up to 5 GPa in order to explain why chemical pressure, generated by decreasing the carbon concentration, decreases TC in a non linear rate. The density of state at the Fermi level is reduced in a non monotonic way suggesting some correlation. We complement the study with high pressure electrical resistivity measurements up to 4.8 GPa which reveal a decreasing of Tc at the rate dTC/dP = - 0.03 K/GPa.

Falconi, R.; Alvarez, F.; Escamilla, R.; Escudero, R.

2010-03-01

172

Band structure of photonic crystal with dispersive and lossy materials using Dirichlet-to-Neumann wave vector eigen equation method  

NASA Astrophysics Data System (ADS)

We present the Dirichlet-to-Neumann wave vector eigen equation (DtN-WVEE) method to calculate the band structure of photonic crystal (PhC) with dispersive and lossy materials, and then use finite-difference time-domain method to verify the validity of the results of the DtN-WVEE method. Since the material is lossy with a non-zero imaginary part of epsilon, the wave vector of PhC band structure also has a non-zero imaginary part which results in the reduction of the intensity of the mode. We further present the band structure which gives the relationship among the normalized frequency, the real part of the wave vector, and the imaginary part of the wave vector. To our knowledge, the band structure of lossy PhC has not been well studied yet, and our results can be useful in designing the devices using surface plasmon polariton effect.

Jiang, Bin; Zhang, Yejin; Wang, Yufei; Zheng, Wanhua

2012-08-01

173

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

174

Birefringence and band structure of CdP2 crystals  

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

175

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

176

L-band doppler radar echoes of the sea surface in coastal zone  

Microsoft Academic Search

A remote sensing experiment using an L-Band radar was conducted in a nearshore environment. The results obtained contribute to identify some aspects of the coherent L- band response of the sea, specified by the Doppler spectrum, in near- grazing conditions. At low winds the radar response is of Bragg type. The asymmetry of Doppler spectra varies with wind direction. Surface

P. Forget; M. Saillard; P. Currier; P. Broche; Y. Barbin

2005-01-01

177

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

178

Distribution of Phosphorus and Potassium Following Surface Banding of Fertilizer in Conservation Tillage Systems  

E-print Network

phosphorus distribution and sorption in starter fertilizerSoil Phosphorus Movement of available fertilizer P into thephosphorus determined via anion exchange resin membranes in six soil layers following surface band application of liquid fertilizer.

Kovar, John L; Bortolon, Leandro; Karlen, Douglas L

2009-01-01

179

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

180

Nonparabolic band structure effect on carrier transport in semiconducting graphene nanoribbons  

Microsoft Academic Search

The band energy of graphene nanoribbon is parabolic when reaching the minimum band energy. Otherwise, it is nonparabolic. In the parabolic band structure, Fermi-Dirac integrals are employed to study the carrier statistic whereas for nonparabolic part, numerical solutions are needed. Numerical method shows Fermi energy with respect to the band edge is a function of temperature that independent of the

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

2010-01-01

181

Photonic band gap structures in 2D tunable magnetic photonic crystals  

Microsoft Academic Search

The photonic band structures in 2D tunable hexagonal magnetic photonic crystals were investigated on the basis of plane wave expansion method. It was found that the photonic band gaps tended to exist in the magnetic photonic crystals, and magnetic permeability affected the photonic band gaps strongly. The width of two absolute band gaps was reduced gradually, then they vanished when

Guan Chunying; Yuan Libo

2006-01-01

182

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

183

Quasiparticle semiconductor band structures including spin-orbit interactions  

NASA Astrophysics Data System (ADS)

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. G0W0. 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.

Malone, Brad D.; Cohen, Marvin L.

2013-03-01

184

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

NASA Astrophysics Data System (ADS)

This work reports on the use of X-ray photoelectron spectroscopy to quantify band bending at ferroelectric free surfaces and at their interfaces with metals. Surfaces exhibiting out-of-plane ferroelectric polarization are characterized by a band bending, due to the formation of a dipole layer at the surface, composed by the uncompensated polarization charges (due to ionic displacement) and to the depolarization charge sheet of opposite sign, composed by mobile charge carriers, which migrate near surface, owing to the depolarization electric field. To this surface band bending due to out-of-plane polarization states, metal-semiconductor Schottky barriers must be considered additionally when ferroelectrics are covered by metal layers. It is found that the net band bending is not always an algebraic sum of the two effects discussed above, since sometimes the metal is able to provide additional charge carriers, which are able to fully compensate the surface charge of the ferroelectric, up to the vanishing of the ferroelectric band bending. The two cases which will be discussed in more detail are Au and Cu deposited by molecular beam epitaxy on PbZr0.2Ti0.8O3(001) single crystal thin layers, prepared by pulsed laser deposition. Gold forms unconnected nanoparticles, and their effect on the band bending is the apparition of a Schottky band bending additional to the band bending due to the out-of-plane polarization. Copper, starting with a given thickness, forms continuous metal layers connected to the ground of the system, and provide electrons in sufficient quantity to compensate the band bending due to the out-of-plane polarization.

Apostol, Nicoleta Georgiana

2014-11-01

185

Plasmon-modulated photoluminescence from gold nanostructures and its dependence on plasmon resonance, excitation energy, and band structure.  

PubMed

Two distinct single-photon plasmon-modulated photo-luminescence processes are generated from nanostructured gold surfaces by tuning the spectral overlap of the incident laser source, localized surface plasmon resonance band, and the interband transitions between the d and sp bands, near the X- and L-symmetry points of the electronic band structure of gold. In the main section of the article, the characteristics of these photoluminescence processes are described and discussed. In the last section, the background continuum accompanying surface-enhanced Raman scattering (SERS) spectra from benzenethiol and 4-mercaptopyridine self-assembled monolayers chemisorbed on nanostructured gold surfaces is shown to originate from plasmon-modulated photoluminescence. PMID:25836787

Ngoc, Loan Le Thi; Wiedemair, Justyna; van den Berg, Albert; Carlen, Edwin T

2015-03-01

186

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

187

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

NASA Astrophysics Data System (ADS)

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

Mosallaei, Hossein

188

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

189

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

190

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

191

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

192

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

PubMed

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

Smith, Andrew M; Nie, Shuming

2010-02-16

193

New high-spin band structures in 184Hg  

NASA Astrophysics Data System (ADS)

The high-spin states in 184Hg have been investigated via the 154Gd (32S,4n) reaction at a beam energy of 160 MeV, with an array of Compton suppressed Ge detectors in the Spin Spectrometer at HHIRF. The ground state oblate band and excited prolate band were extended to 10+ and 26+, respectively, and seven new bands are observed. A new band with odd spins, 13 to 25, has a much larger moment of inertia than the other bands in 184Hg. Two of the new bands feed the prolate excited band and are interpreted as quadrupole vibrational bands. Also, two new signature partner bands are observed for which the configuration of ?i13/2f7/2 is proposed. The similarity of the band with odd spins to the band with intermediate deformation (?2~0.34) in 186Hg, and signature partner bands to the bands observed in 104 isotones 180Os and 182Pt, is discussed.

Deng, J. K.; Ma, W. C.; Hamilton, J. H.; Ramayya, A. V.; Kormicki, J.; Gao, W. B.; Zhao, X.; Shi, D. T.; Lee, I. Y.; Garrett, J. D.; Johnson, N. R.; Winchell, D.; Halbert, M.; Baktash, C.

1995-08-01

194

New high-spin band structures in {sup 184}Hg  

SciTech Connect

The high-spin states in {sup 184}Hg have been investigated via the {sup 154}Gd ({sup 32}S,4{ital n}) reaction at a beam energy of 160 MeV, with an array of Compton suppressed Ge detectors in the Spin Spectrometer at HHIRF. The ground state oblate band and excited prolate band were extended to 10{sup +} and 26{sup +}, respectively, and seven new bands are observed. A new band with odd spins, 13 to 25, has a much larger moment of inertia than the other bands in {sup 184}Hg. Two of the new bands feed the prolate excited band and are interpreted as quadrupole vibrational bands. Also, two new signature partner bands are observed for which the configuration of {nu}{ital i}{sub 13/2}{ital f}{sub 7/2} is proposed. The similarity of the band with odd spins to the band with intermediate deformation ({beta}{sub 2}{similar_to}0.34) in {sup 186}Hg, and signature partner bands to the bands observed in 104 isotones {sup 180}Os and {sup 182}Pt, is discussed.

Deng, J.K.; Ma, W.C.; Hamilton, J.H.; Ramayya, A.V.; Kormicki, J.; Gao, W.B.; Zhao, X.; Shi, D.T. [Physics Department, Vanderbilt University, Nashville, Tennessee 37235 (United States)] [Physics Department, Vanderbilt University, Nashville, Tennessee 37235 (United States); Lee, I.Y.; Garrett, J.D.; Johnson, N.R.; Winchell, D.; Halbert, M.; Baktash, C. [Physics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)] [Physics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)

1995-08-01

195

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

196

Invariant expansion for the trigonal band structure of graphene.  

SciTech Connect

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

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

2010-12-01

197

Exciton band structure of monolayer MoS2  

NASA Astrophysics Data System (ADS)

We address the properties of excitons in monolayer MoS2 from a theoretical point of view, showing that low-energy excitonic states occur both at the Brillouin-zone center and at the Brillouin-zone corners, that binding energies at the Brillouin-zone center deviate strongly from the (n-1 /2 ) -2 pattern of the two-dimensional hydrogenic model, and that the valley-degenerate exciton doublet at the Brillouin-zone center splits at finite momentum into an upper mode with nonanalytic linear dispersion and a lower mode with quadratic dispersion. Although monolayer MoS2 is a direct-gap semiconductor when classified by its quasiparticle band structure, it may well be an indirect gap material when classified by its excitation spectra.

Wu, Fengcheng; Qu, Fanyao; MacDonald, A. H.

2015-02-01

198

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

SciTech Connect

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

Yastrubchak, Oksana; Gluba, Lukasz; Zuk, Jerzy [Institute of Physics, Maria Curie-Sklodowska University, 20-031 Lublin (Poland); Wosinski, Tadeusz; Andrearczyk, Tomasz; Domagala, Jaroslaw Z. [Institute of Physics, Polish Academy of Sciences, 02-668 Warsaw (Poland); Sadowski, Janusz [Institute of Physics, Polish Academy of Sciences, 02-668 Warsaw, Poland and MAX-Lab, Lund University, 22100 Lund (Sweden)

2013-12-04

199

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

DOEpatents

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

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

2001-08-14

200

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

201

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

NASA Technical Reports Server (NTRS)

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

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

1997-01-01

202

New high-spin band structures in 184Hg  

Microsoft Academic Search

The high-spin states in 184Hg have been investigated via the 154Gd (32S,4n) reaction at a beam energy of 160 MeV, with an array of Compton suppressed Ge detectors in the Spin Spectrometer at HHIRF. The ground state oblate band and excited prolate band were extended to 10+ and 26+, respectively, and seven new bands are observed. A new band with

J. K. Deng; W. C. Ma; J. H. Hamilton; A. V. Ramayya; J. Kormicki; W. B. Gao; X. Zhao; D. T. Shi; I. Y. Lee; J. D. Garrett; N. R. Johnson; D. Winchell; M. Halbert; C. Baktash

1995-01-01

203

Band structures of Bernal graphene modulated by electric fields  

Microsoft Academic Search

The tight-binding model is utilized to investigate the influence of modulation electric fields on bilayer Bernal graphene (BBG). The electric potential changes the parabolic bands into oscillatory ones, and induces more band-edge states. As the strength of field is strengthened, it would enhance the oscillation of energy band, affect larger range of energy, induced more band-edge states, and cause more

Sing-Jyun Tsai; Jon-Hsu Ho; Yu-Huang Chiu; Ming-Fa Lin

2010-01-01

204

FAST TRACK COMMUNICATION: Field modulation in bilayer graphene band structure  

Microsoft Academic Search

Using an external electric field, one can modulate the band gap of Bernal stacked bilayer graphene by breaking the A-\\\\tilde {\\\\mathrm {B}} symmetry. We analyze strain effects on the bilayer graphene using the extended Hückel theory and find that reduced interlayer distance results in higher band gap modulation, as expected. Furthermore, above about 2.5 Å interlayer distance, the band gap

Hassan Raza; Edwin C. Kan

2009-01-01

205

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

206

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

207

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

SciTech Connect

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

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

2008-01-01

208

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

209

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

SciTech Connect

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

Ahmed, M.; Salam, I.; Hashmi, F.H.; Khan, A.Q. [Dr. A.Q. Khan Research Labs., Rawalpindi (Pakistan). Metallurgy Div.

1997-04-01

210

Dose banding as an alternative to body surface area-based dosing of chemotherapeutic agents  

PubMed Central

Background: Dose banding is a recently suggested dosing method that uses predefined ranges (bands) of body surface area (BSA) to calculate each patient's dose by using a single BSA-value per band. Thus, drugs with sufficient long-term stability can be prepared in advance. The main advantages of dose banding are to reduce patient waiting time and improve pharmacy capacity planning; additional benefits include reduced medication errors, reduced drug wastage, and prospective quality control. This study compares dose banding with individual BSA dosing and fixed dose according to pharmacokinetic criteria. Methods: Three BSA bands were defined: BSA<1.7?m2, 1.7?m2?BSA<1.9?m2, BSA?1.9?m2 and each patient dose was calculated based on a unique BSA-value per band (1.55, 1.80, and 2.05?m2, respectively). By using individual clearance values of six drugs (cisplatin, docetaxel, paclitaxel, doxorubicin, irinotecan, and topotecan) from 1012 adult cancer patients in total, the AUCs corresponding to three dosing methods (BSA dosing, dose banding, and fixed dose) were compared with a target AUC for each drug. Results: For all six drugs, the per cent variation in individual dose obtained with dose banding compared with BSA dosing ranged between ?14% and +22%, and distribution of AUC values was very similar with both dosing methods. In terms of reaching the target AUC, there was no significant difference in precision between dose banding and BSA dosing, except for paclitaxel (32.0% vs 30.7%, respectively; P<0.05). However, precision was significantly better for BSA dosing compared with fixed dose for four out of six drugs. Conclusion: For the studied drugs, implementation of dose banding should be considered as it entails no significant increase in interindividual plasma exposure. PMID:22929884

Chatelut, E; White-Koning, M L; Mathijssen, R HJ; Puisset, F; Baker, S D; Sparreboom, A

2012-01-01

211

Surface Structure and the Centrality of Syntax.  

ERIC Educational Resources Information Center

This paper examines the status of surface structure in transformational grammar, and the way that surface structure mediates the contacts between the phonological and semantic components of the grammar. Surface structure refers not to a single but to at least four distinct notions that do not necessarily define a homogeneous level of…

Rivero, Maria-Luisa; Walker, Douglas C.

212

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

Microsoft Academic Search

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 TM01-like mode among the TM0n-like modes exists in such a slow wave structure. The dispersion characteristics of the slow wave structure are investigated by simulation and experiment.

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

2008-01-01

213

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.

214

Rotational structures in 106Sn: A new form of band termination\\\\?  

Microsoft Academic Search

Two weakly populated rotational bands have been established in 106Sn from the 54Fe (58Ni,alpha2p) reaction at 243 MeV. One of the bands shows evidence of termination. The result is consistent with cranked Nilsson model calculations, which predict band terminations with a smooth and gradual shape change from a prolate collective to an oblate noncollective structure.

R. Wadsworth; H. R. Andrews; C. W. Beausang; R. M. Clark; J. Degraaf; D. B. Fossan; A. Galindo-Uribarri; I. M. Hibbert; K. Hauschild; J. R. Hughes; V. P. Janzen; D. R. Lafosse; S. M. Mullins; E. S. Paul; L. Persson; S. Pilotte; D. C. Radford; H. Schnare; P. Vaska; D. Ward; J. N. Wilson; I. Ragnarsson

1994-01-01

215

K-band observations of boxy bulges - I. Morphology and surface brightness profiles  

NASA Astrophysics Data System (ADS)

In this first paper of a series on the structure of boxy and peanut-shaped (B/PS) bulges, Kn-band observations of a sample of 30 edge-on spiral galaxies are described and discussed. Kn-band observations best trace the dominant luminous galactic mass and are minimally affected by dust. Images, unsharp-masked images, as well as major-axis and vertically summed surface brightness profiles are presented and discussed. Galaxies with a B/PS bulge tend to have a more complex morphology than galaxies with other bulge types, more often showing centred or off-centred X structures, secondary maxima along the major-axis and spiral-like structures. While probably not uniquely related to bars, those features are observed in three-dimensional N-body simulations of barred discs and may trace the main bar orbit families. The surface brightness profiles of galaxies with a B/PS bulge are also more complex, typically containing three or more clearly separated regions, including a shallow or flat intermediate region (Freeman Type II profiles). The breaks in the profiles offer evidence for bar-driven transfer of angular momentum and radial redistribution of material. The profiles further suggest a rapid variation of the scaleheight of the disc material, contrary to conventional wisdom but again as expected from the vertical resonances and instabilities present in barred discs. Interestingly, the steep inner region of the surface brightness profiles is often shorter than the isophotally thick part of the galaxies, itself always shorter than the flat intermediate region of the profiles. The steep inner region is also much more prominent along the major-axis than in the vertically summed profiles. Similarly to other recent work but contrary to the standard `bulge + disc' model (where the bulge is both thick and steep), we thus propose that galaxies with a B/PS bulge are composed of a thin concentrated disc (a disc-like bulge) contained within a partially thick bar (the B/PS bulge), itself contained within a thin outer disc. The inner disc likely formed secularly through bar-driven processes and is responsible for the steep inner region of the surface brightness profiles, traditionally associated with a classic bulge, while the bar is responsible for the flat intermediate region of the surface brightness profiles and the thick complex morphological structures observed. Those components are strongly coupled dynamically and are formed mostly of the same (disc) material, shaped by the weak but relentless action of the bar resonances. Any competing formation scenario for galaxies with a B/PS bulge, which represent at least 45 per cent of the local disc galaxy population, must explain equally well and self-consistently the above morphological and photometric properties, the complex gas and stellar kinematics observed, and the correlations between them.

Bureau, M.; Aronica, G.; Athanassoula, E.; Dettmar, R.-J.; Bosma, A.; Freeman, K. C.

2006-08-01

216

Calculations of Cleavage Processes, Surface Structures and Electronic Structure of Silicon and Germanium.  

NASA Astrophysics Data System (ADS)

The cleavage processes, surface and step structures, and electronic structure of Si and Ge (111)2 x 1 surfaces were studied. The ab initio quantum chemistry programs KGNMOL-89 and DMol were used to study the cleavage of silicon and germanium clusters in the diamond structure. It was found that the potential energy of stretching and shearing glide planes increases much faster than for shuffle planes. The cleavage process is discussed and it is shown how glide -plane cleavage can occur, with consequences for surface structure models. The Keating strain-energy method has been applied to estimate the energies of surface and step structures on Si(111)2 x 1. Two minimum strain-energy TBS (Three -Bond Scission) model structures were obtained. Since angular strains are involved which go beyond the applicability limits of the Keating formula, a correction factor is used, derived by comparing Keating-type calculations of particular surface models of Si(111) with the results of more extensive calculations. The use of a simple correction factor gives results that agree with a calculation for the Pandey ( pi-bonded chain) model and one for the TBS model. Using this factor, a model for a 3-substep structure of the (322) step on Si is found to be quite stable, while the 2-substep structures are moderately stable. The surface band structure of the TBS and Pandey models have been computed using an ab initio HF LCAO program CRYSTAL-92. In the case of the TBS model, the results showed valence band dispersion that could be compatible with experiments. For the Pandey model, the calculated valence band dispersion seemed large. The surface band gap for both TBS and Pandey models was greatly overestimated. The significance is discussed. The surface electron density of states was calculated for the TBS model and the valence band generally matched experimental results from STM (scanning tunneling microscopy). The electron charge density of various surface regions was calculated. The corrugation amplitude at 5 A from the surface for the TBS model was found to be close to that of the Pandey model and STM measurements. STM would not be able to distinguish between the two models.

Chen, Bo.

217

Electronic structure of the InP(111) semiconductor surface  

NASA Astrophysics Data System (ADS)

We present a first-principles theoretical study of the relative formation energies and the electronic states of the surface. The energetically most favorable reconstruction has a T 4-site P trimer on the surface, which exhibits a metallic band character and does not obey the electron counting rule (ECR). The stability of this structure is attributed to the balance between the ECR and the minimization of local distortion in the surface region. Our results for the simulated scanning tunneling microscopy images confirm the experimental interpretation of bright protrusions on the P trimers.

Yi, Hongsuk

2014-11-01

218

Luminosity and surface brightness distribution of K-band galaxies from the UKIDSS Large Area Survey  

E-print Network

We present luminosity and surface brightness distributions of 40,111 galaxies with K-band photometry from the United Kingdom Infrared Telescope (UKIRT) Infrared Deep Sky Survey (UKIDSS) Large Area Survey (LAS), Data Release 3 and optical photometry from Data Release 5 of the Sloan Digital Sky Survey (SDSS). Various features and limitations of the new UKIDSS data are examined, such as a problem affecting Petrosian magnitudes of extended sources. Selection limits in K- and r-band magnitude, K-band surface brightness and K-band radius are included explicitly in the 1/Vmax estimate of the space density and luminosity function. The bivariate brightness distribution in K-band absolute magnitude and surface brightness is presented and found to display a clear luminosity--surface brightness correlation that flattens at high luminosity and broadens at low luminosity, consistent with similar analyses at optical wavelengths. Best fitting Schechter function parameters for the K-band luminosity function are found to be M*-5 log h=-23.19 +/- 0.04, alpha=-0.81 +/- 0.04 and phi*=(0.0166 +/- 0.0008)h^3 Mpc^{-3}, although the Schechter function provides a poor fit to the data at high and low luminosity, while the luminosity density in the K band is found to be j = (6.305 +/- 0.067) x 10^8 L_sun h Mpc^{-3}. However, we caution that there are various known sources of incompleteness and uncertainty in our results. Using mass-to-light ratios determined from the optical colours we estimate the stellar mass function, finding good agreement with previous results. Possible improvements are discussed that could be implemented when extending this analysis to the full LAS.

Anthony J. Smith; Jon Loveday; Nicholas J. G. Cross

2009-07-06

219

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

220

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

Microsoft Academic Search

Using the nearest-neighbor tight-binding approach we study the electronic band structures of graphene nanoribbons with self-passivating edge reconstructions. For zigzag ribbons the edge reconstruction moves both the Fermi energy and the flat band down by several hundred meV, and the flat band is always found to be below the Fermi energy. The states featured by the flat band are shown

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

2011-01-01

221

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

222

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

223

Graphene band structure and its 2D Raman mode  

NASA Astrophysics Data System (ADS)

High-precision simulations are used to generate the 2D Raman mode of graphene under a range of screening conditions and laser energies EL. We reproduce the decreasing trend of the 2D mode FWHM vs EL and the nearly linearly increasing dispersion ??2D/?EL seen experimentally in freestanding (unscreened) graphene, and propose relations between these experimentally accessible quantities and the local, two-dimensional gradients |? | of the electronic and TO phonon bands. In light of state-of-the-art electronic structure calculations that acutely treat the long-range e-e interactions of isolated graphene and its experimentally observed 2D Raman mode, our calculations determine a 40% greater slope of the TO phonons about K than given by explicit phonon measurements performed in graphite or GW phonon calculations in graphene. We also deduce the variation of the broadening energy ? [EL] for freestanding graphene and find a nominal value ? ˜140 meV, showing a gradually increasing trend for the range of frequencies available experimentally.

Narula, Rohit; Reich, Stephanie

2014-08-01

224

Complex band structure of topologically protected edge states  

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

225

Global Kinetic Modeling of Banded Electron Structures in the Plasmasphere  

NASA Technical Reports Server (NTRS)

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

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

1997-01-01

226

Characterization of the B/Si surface electronic structures  

SciTech Connect

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

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

1992-11-01

227

Band structure calculations of Si Ge Sn alloys: achieving direct band gap materials  

Microsoft Academic Search

Alloys of silicon (Si), germanium (Ge) and tin (Sn) are continuously attracting research attention as possible direct band gap semiconductors with prospective applications in optoelectronics. The direct gap property may be brought about by the alloy composition alone or combined with the influence of strain, when an alloy layer is grown on a virtual substrate of different compositions. In search

Pairot Moontragoon; Zoran Ikonic; Paul Harrison

2007-01-01

228

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

229

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

Microsoft Academic Search

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

Kunia Aihara; Morgan Jikang Chen; Anh-Vu Pham

2008-01-01

230

Development of Thin-Film Liquid Crystal Polymer Surface Mount Packages for Ka-band Applications  

Microsoft Academic Search

We present the development of thin-film liquid crystal polymer (LCP) surface mount packages for packaging MMIC's in Ka-band. The packages are constructed using multilayer LCP films and can be surface mounted on a printed circuit board. Our experimental results demonstrate that the package feed-through transition including bond wires achieve a return loss of -15 dB at 30 GHz and an

K. Aihara; Anh-Vu Pham

2006-01-01

231

Surface-layer band gap widening in Cu(In,Ga)Se2 thin films  

Microsoft Academic Search

Transmission electron microscopy observations, cathodoluminescence spectroscopy and spectrum imaging are combined to investigate the emission spectrum in Cu(In,Ga)Se2 (CIGS) thin films with improved spatial resolution. We report direct evidence for a surface layer of wider band gap, which forms spontaneously in CIGS films. The existence of such a surface layer is critical for attaining high efficiency in solar cells based

M. J. Romero; K. M. Jones; J. Abushama; Y. Yan; M. M. Al-Jassim; R. Noufi

2003-01-01

232

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 ...

233

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 ...

234

Applications of Split-Ring Resonances on MultiBand Frequency Selective Surfaces  

Microsoft Academic Search

Multi-band frequency selective surfaces (FSSs) are proposed by utilizing the split-ring resonators (SRRs) as the basic unit cells. The magnetic resonance of SRRs, which makes an additional dip in the reflection and transmission spectrums of FSSs, is discussed based on the equivalent circuit method and the simulation models. Because of the electric and the magnetic resonances of the single SRR

D. Li; Y. J. Xie; P. Wang; R. Yang

2007-01-01

235

Thin frequency selective surface (FSS) superstrate with different periodicities for dual-band directivity enhancement  

Microsoft Academic Search

In this paper we present a novel design of a high directivity resonator antenna that utilizes a two-layered frequency selective surface (FSS) superstrate with different periodicities - as an alternative to a conventional FSS superstrate - for dual band directivity enhancement to reduce its height. Two strip dipole arrays with different periodicities are placed above and below a dielectric layer.

Young Ju Lee; Junho Yeo; R. Mittra; Wee Sang Park

2005-01-01

236

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

2015-03-01

237

Structurally Complex Surface of Europa  

NASA Technical Reports Server (NTRS)

This is a composite of two images of Jupiter's icy moon Europa obtained from a range of 2119 miles (3410 kilometers) by the Galileo spacecraft during its fourth orbit around Jupiter and its first close pass of Europa. The mosaic spans 11 miles by 30 miles (17 km by 49 km) and shows features as small as 230 feet (70 meters) across. This mosaic is the first very high resolution image data obtained of Europa, and has a resolution more than 50 times better than the best Voyager coverage and 500 times better than Voyager coverage in this area. The mosaic shows the surface of Europa to be structurally complex. The sun illuminates the scene from the right, revealing complex overlapping ridges and fractures in the upper and lower portions of the mosaic, and rugged, more chaotic terrain in the center. Lateral faulting is revealed where ridges show offsets along their lengths (upper left of the picture). Missing ridge segments indicate obliteration of pre-existing materials and emplacement of new terrain (center of the mosaic). Only a small number of impact craters can be seen, indicating the surface is not geologically ancient.

The Jet Propulsion Laboratory, Pasadena, CA manages the mission for NASA's Office of Space Science, Washington, DC.

This image and other images and data received from Galileo are posted on the Galileo mission home page on the World Wide Web at http://galileo.jpl.nasa.gov. Background information and educational context for the images can be found at URL http://www.jpl.nasa.gov/galileo/sepo

1997-01-01

238

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

NASA Technical Reports Server (NTRS)

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

Westman, Walter E.; Paris, Jack F.

1987-01-01

239

5 CFR 9701.321 - Structure of bands.  

Code of Federal Regulations, 2014 CFR

...rates set and adjusted as provided in § 9701.322. Rates must be expressed as annual rates. (b) For each band within an occupational cluster, DHS will establish a common rate range that applies in all...

2014-01-01

240

5 CFR 9701.321 - Structure of bands.  

Code of Federal Regulations, 2012 CFR

...rates set and adjusted as provided in § 9701.322. Rates must be expressed as annual rates. (b) For each band within an occupational cluster, DHS will establish a common rate range that applies in all...

2012-01-01

241

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

PubMed

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

Nefedov, Igor S; Tretyakov, Sergei A

2002-09-01

242

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

E-print Network

Transmission properties and band structure of a segmented dielectric waveguide for the terahertz for the terahertz range. The dis- persion curves are obtained using two different methods. The first approach is based on a close relationship between the band structure and narrow resonances in transmission spectra

Ku?el, Petr

243

Band structure and many body effects in graphene  

Microsoft Academic Search

.  We have determined the electronic bandstructure of clean and potassium-doped single layer graphene, and fitted the\\u000a graphene ?\\u000a bands to a one- and three-near-neighbor tight binding model. We characterized the quasiparticle dynamics using angle resolved\\u000a photoemission spectroscopy. The dynamics reflect the interaction between holes and collective excitations, namely plasmons,\\u000a phonons, and electron-hole pairs. Taking the topology of the bands around

A. Bostwick; T. Ohta; J. L. McChesney; T. Seyller; K. Horn; E. Rotenberg

2007-01-01

244

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

May 2010. In the Tribune case, the tornado's condensation funnel dissipated and then reformed after case, the strongest and longest-lived sub-tornado-strength vortex exhibited similar azimuthal velocity structure to the Tribune tornado, but had weaker azimuthal winds. In both cases, the radius of maximum

Xue, Ming

245

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

246

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

PubMed

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

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

2013-11-13

247

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

PubMed Central

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

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

2002-01-01

248

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

PubMed

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

Timberlake, Brian D; Morris, Jeffrey F

2003-05-15

249

Hepatitis B surface antigen polypeptides: artifactual bands in sodium dodecyl sulfate-polyacrylamide gel electrophoresis caused by aggregation.  

PubMed Central

Hepatitis B surface antigen, subtype ad, was purified and studied by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing conditions. Two major bands with molecular weights of 23,500 and 27,500 and several weaker bands with higher molecular weights were observed. When the low-molecular-weight bands and the group of high-molecular-weight bands were excised from the gel, eluted, and reelectrophoresed, neither the low-molecular-weight bands nor the high-molecular-weight bands ever appeared alone, but both high- and low-molecular-weight bands always appeared. It was concluded that the apparently high-molecular-weight bands represented aggregates of the two small polypeptides whose monomers formed the major bands. The preparation thus contained only two polypeptides. Images PMID:7411691

Koistinen, V U

1980-01-01

250

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

251

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

252

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

Microsoft Academic Search

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

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

1994-01-01

253

Electronic band structure of BaCo2As2: a fully-doped ferropnictide with reduced electronic correlations  

NASA Astrophysics Data System (ADS)

We report an angle-resolved photoemission spectroscopy investigation of the Fermi surface and electronic band structure of BaCo2As2. Although its quasi-nesting-free Fermi surface differs drastically from that of its Fe-pnictide cousins, we show that the BaCo2As2 system can be used as an approximation to the bare unoccupied band structure of the related BaFe2-xCoxAs2 and Ba1-xKxFe2As2 compounds. However, our experimental results, in agreement with dynamical mean field theory calculations, indicate that electronic correlations are much less important in BaCo2As2 than in the ferropnictides. Our findings suggest that this effect is due to the increased filling of the electronic 3d shell in the presence of significant Hund's exchange coupling.

Richard, Pierre; Xu, N.; van Roekeghem, A.; Zhang, P.; Miao, H.; Zhang, W.-L.; Qian, T.; Ferrero, M.; Sefat, A. S.; Biermann, S.; Ding, H.

2013-03-01

254

Electronic Band Structure of BaCo2As2: A Fully Doped Ferropnictide Analog with Reduced Electronic Correlations  

NASA Astrophysics Data System (ADS)

We report an investigation with angle-resolved photoemission spectroscopy of the Fermi surface and electronic band structure of BaCo2As2. Although its quasinesting-free Fermi surface differs drastically from that of its Fe-pnictide cousins, we show that the BaCo2As2 system can be used as an approximation to the bare unoccupied band structure of the related BaFe2-xCoxAs2 and Ba1-xKxFe2As2 compounds. However, our experimental results, in agreement with dynamical-mean-field-theory calculations, indicate that electronic correlations are much less important in BaCo2As2 than in the ferropnictides. Our findings suggest that this effect is due to the increased filling of the electronic 3d shell in the presence of significant Hund’s exchange coupling.

Xu, N.; Richard, P.; van Roekeghem, A.; Zhang, P.; Miao, H.; Zhang, W.-L.; Qian, T.; Ferrero, M.; Sefat, A. S.; Biermann, S.; Ding, H.

2013-01-01

255

The effect of perturbating a frequency-selective surface and its relation to the design of a dual-band surface  

Microsoft Academic Search

A single-layer dual-band frequency selective surface (FSS) created by the perturbation of a single-band dipole array is studied. A simple algebraic formulation is derived to analyze both element and spacing perturbations. Guidelines are then proposed to allow dual-band FSSs to be designed with no anomalous behavior occurring in the two desired bandstop responses. Examples of unsuccessful and successful dual-band FSSs

Roger A. Hill; Benedikt A. Munk

1996-01-01

256

Sorting of droplets by migration on structured surfaces  

PubMed Central

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

Roth-Nebelsick, Anita

2011-01-01

257

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

258

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

259

Study on the Electronic Band Structures of Doped Graphene  

Microsoft Academic Search

Graphene, a carbon sheet self-assembled on a SiC substrate, has been found to undergo changes in an electronic property as a function of doping concentration. Depending on the species of dopants, charge carrier density is gradually modified with increasing dopant coverage. By using angle resolved photoemission spectroscopy, we study how the graphene pi bands are modified by changing doping concentration

C. G. Hwang; Kevin T. Chan; D. Siegel; A. V. Fedorov; Marvin L. Cohen; J. B. Neaton; A. Lanzara

2009-01-01

260

Electronic band structure of isolated and bundled carbon nanotubes  

Microsoft Academic Search

We study the electronic dispersion in chiral and achiral isolated nanotubes as well as in carbon nanotube bundles. The curvature of the nanotube wall is found not only to reduce the band gap of the tubes by hybridization, but also to alter the energies of the electronic states responsible for transitions in the visible energy range. Even for nanotubes with

S. Reich; C. Thomsen; P. Ordejón

2002-01-01

261

Novel band structures in silicene on monolayer zinc sulfide substrate.  

PubMed

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

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

2014-10-01

262

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

263

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

NASA Technical Reports Server (NTRS)

This document is being provided as part of ITT's NASA Glenn Research Center Aerospace Communication Systems Technical Support (ACSTS) contract NNC05CA85C, Task 7: "New ATM Requirements--Future Communications, C-Band and L-Band Communications Standard Development." The proposed future C-band (5091- to 5150-MHz) airport surface communication system, referred to as the Aeronautical Mobile Airport Communications System (AeroMACS), is anticipated to increase overall air-to-ground data communications systems capacity by using a new spectrum (i.e., not very high frequency (VHF)). Although some critical services could be supported, AeroMACS will also target noncritical services, such as weather advisory and aeronautical information services as part of an airborne System Wide Information Management (SWIM) program. AeroMACS is to be designed and implemented in a manner that will not disrupt other services operating in the C-band. This report defines the AeroMACS concepts of use, high-level system requirements, and architecture; the performance of supporting system analyses; the development of AeroMACS test and demonstration plans; and the establishment of an operational AeroMACS capability in support of C-band aeronautical data communications standards to be advanced in both international (International Civil Aviation Organization, ICAO) and national (RTCA) forums. This includes the development of system parameter profile recommendations for AeroMACS based on existing Institute of Electrical and Electronics Engineering (IEEE) 802.16e- 2009 standards

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

2010-01-01

264

Angle and Thickness-Dependent Photonic Band Structure in a Superconducting Photonic Crystal  

Microsoft Academic Search

The angle- and thickness-dependent photonic band structures in a one-dimensional superconducting photonic crystal are theoretically\\u000a investigated based on the transfer matrix method. The band structure is studied near and below the threshold frequency at\\u000a which the superconducting material has a zero permittivity. The gap structure is analyzed as a function of the thicknesses\\u000a of the two constituent superconducting and dielectric

Chien-Jang Wu; Zheng-Hui Wang; Tzong-Jer Yang

2010-01-01

265

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

266

Surface states and electronic structure of polar and nonpolar InN - An in situ photoelectron spectroscopy study  

SciTech Connect

Valence band structure and surface states of InN with (0001), (000-1), (1-100), and (11-20) orientation were investigated in situ after growth using photoelectron spectroscopy. Depending on surface orientation, different occupied surface states are identified and differentiated from bulk contributions. For N-polar, m-plane, and a-plane InN, the surface states are located at the valence band maximum, while In-polar InN features surface states close to the Fermi level. The surface band alignment correlates with the position of surface states. For InN(0001), a much larger surface downward band bending is observed compared to N-polar, m-plane, and a-plane InN, where almost flat band conditions occur.

Eisenhardt, A.; Krischok, S.; Himmerlich, M. [Institut fuer Physik and Institut fuer Mikro- und Nanotechnologien, Technische Universitaet Ilmenau, PF 100565, 98694 Ilmenau (Germany)] [Institut fuer Physik and Institut fuer Mikro- und Nanotechnologien, Technische Universitaet Ilmenau, PF 100565, 98694 Ilmenau (Germany)

2013-06-10

267

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

268

Indirect optical transition due to surface band bending in ZnO nanotubes  

NASA Astrophysics Data System (ADS)

ZnO nanotubes (ZNTs) have been successfully evolved from ZnO nanorods (ZNRs) by a simple chemical etching process. Two peaks located at 382 and 384 nm in the UV emission region has been observed in the room temperature photoluminescence (PL) spectrum of ZNTs since the surface band bending in ZNTs induces the coexistence of indirect and direct transitions in their emission process. In addition, a strong enhancement of total luminescence intensity at room temperature in ZNTs has also be observed in comparison with that of ZNRs. Both temperature-dependent PL and time-resolved PL results not only further testify the coexistence of indirect and direct transitions due to the surface band bending but also reveal that less nonradiative contribution to the emission process in ZNTs finally causes their stronger luminescence intensity.

Yang, L. L.; Zhao, Q. X.; Israr, M. Q.; Sadaf, J. R.; Willander, M.; Pozina, G.; Yang, J. H.

2010-11-01

269

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

270

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

271

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

Microsoft Academic Search

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

Kikuo Harigaya; Hiroshi Imamura

2011-01-01

272

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

273

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

Microsoft Academic Search

The NASA Langley Research Center's L-band pushbroom microwave radiometer (PBMR) aboard the NASA C-130 aircraft was used to map surface soil moisture at and around the Konza Prairie Natural Research Area in Kansas during the four intensive field campaigns of FIFE in May-October 1987. A total of 11 measurements were made when soils were known to be saturated. This measurement

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

1990-01-01

274

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

275

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

Microsoft Academic Search

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

Amir Khurrum Rashid; Zhongxiang Shen

2010-01-01

276

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

277

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

278

Compact electromagnetic bandgap structures for notch band in ultra-wideband applications.  

PubMed

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

279

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

280

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

281

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

NASA Astrophysics Data System (ADS)

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

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

1999-05-01

282

Detecting 1110th Scaled Structures in Dielectric Media Using Monostatic X-Band Radar Scattering Measurements  

E-print Network

Detecting 1110th Scaled Structures in Dielectric Media Using Monostatic X-Band Radar Scattering-GHz. The monostatic X-band measurements were acquired in an anechoic environment, and digital images Modeling, RCS Measurements, Compact Range, Ground Penetrating Radar, Monostatic Measurements

Massachusetts at Lowell, University of

283

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

E-print Network

An improved single-cell photonic band-gap (PBG) structure with an inner row of elliptical rods (PBG-E) was tested with high power at a 60 Hz repetition rate at X-band (11.424 GHz), achieving a gradient of 128??MV/m at a ...

Munroe, Brian James

284

Systematic design of phononic band-gap materials and structures by topology optimization  

Microsoft Academic Search

Phononic band-gap materials prevent elastic waves in certain frequency ranges from propagating, and they may therefore be used to generate frequency filters, as beam splitters, as sound or vibration protection devices, or as waveguides. In this work we show how topology optimization can be used to design and optimize periodic materials and structures exhibiting phononic band gaps. Firstly, we optimize

Ole Sigmund; Jakob Søndergaard Jensen

2003-01-01

285

Evaluation of the electronic band structure of a new semiconductor ternary using Ge, Si, and Sn  

Microsoft Academic Search

Developing new Si based devices whose electronic band structure can be controlled by varying the stoichiometry is crucial for technology advancement in compound semiconductors. The ability to engineer the band gap is essential to obtain the optimal performance of a device, however, it can be affected by lattice mismatch, defects, strain, etc. Therefore, based on the success of previous research

Candi S. Cook; Stefan Zollner; Jose Menendez; A. V. G. Chizmeshya; Pavan Aella; John Tolle; John Kouvetakis

2003-01-01

286

Evaluation of the electronic band structure of a new semiconductor ternary using Ge, Si, and Sn  

Microsoft Academic Search

Developing new Si based devices whose electronic band structure can be controlled by varying the stoichiometry is crucial for technology advancement in compound semiconductors. The ability to engineer the band gap is essential to obtain the optimal performance of a device, however, it can be affected by lattice mismatch, defects, strain, etc. Therefore, based on the success of previous research

Candi S. Cook; Stefan Zollner; Jose Menendez; A. V. G. Chizmeshya; Pavan Aella; John Tolle; John Kouvetakis

2004-01-01

287

1\\/f noise as a probe for investigating band structure in graphene  

Microsoft Academic Search

A distinctive feature of single layer graphene is the linearly dispersive energy bands, which in case of multilayer graphene become parabolic. Other than the quantum Hall effect, this distinction has been hard to capture in electron transport. Carrier mobility of graphene has been scrutinized, but many parallel scattering mechanisms often obscure its sensitivity to band structure. The flicker noise in

Atindra Nath Pal; Subhamoy Ghatak; Vidya Kochat; S. Sneha E; S. Arjun B; Srinivasan Raghavan; Arindam Ghosh

2010-01-01

288

1\\/f noise as a probe to investigate the band structure of graphene  

Microsoft Academic Search

The flicker noise or low frequency resistance fluctuations in graphene depend explicitly on its ability to screen external potential fluctuations and more sensitive compared to the conventional time average transport. Here we show that the flicker noise is a powerful probe to the band structure of graphene that vary differently with the carrier density for the linear and parabolic bands.

Atindra Nath Pal; Arindam Ghosh

2011-01-01

289

HOUSEHOLD AND STRUCTURAL INSECTS Evaluation of an Insecticide Dust Band Treatment Method for  

E-print Network

insecticide dust bands to furniture legs is an effective bed bug control technique. KEY WORDS bed bug, CimexHOUSEHOLD AND STRUCTURAL INSECTS Evaluation of an Insecticide Dust Band Treatment Method bed bug, Cimex lectularius L., control usually involves insecticide applications that pose a high risk

Wang, Changlu

290

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

Microsoft Academic Search

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

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

2006-01-01

291

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

PubMed Central

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

Ho, Ching-Hwa; Chen, Hsin-Hung

2014-01-01

292

Modification of graphene band structure by haptic functionalization  

Microsoft Academic Search

We have employed first-principles density-functional calculations to study the electronic characteristics of covalently functionalized graphene by metal-bis-arene chemistry. It is shown that functionalization with M-bis-arene (M=Ti, V, Cr, Mn, Fe) molecules leads to an opening in the band gap of graphene (up to 0.81eV for the Cr derivative), and as a result, transforms it from a semi-metal to a semiconductor.

Paul Plachinda; David Evans; Raj Solanki

2011-01-01

293

Experimental study of X-band dielectric-loaded accelerating structures  

NASA Astrophysics Data System (ADS)

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

Jing, Chunguang

294

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

295

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

296

Triaxial superdeformed and normal-deformed high-spin band structures in {sup 170}Hf  

SciTech Connect

The high-spin structure of {sup 170}Hf was investigated using the EUROBALL spectrometer. The previously known level scheme was extended in the low-spin region as well as to higher spins, and several new bands were discovered. In particular, two bands were identified which show the characteristics of triaxial superdeformation. One of these bands is strongly populated, and its excitation energy and spins are established. Configuration assignments are made to the normal-deformed bands based on comparisons of their properties with cranked shell model calculations. The results for the very high spin states provide important input for such calculations.

Neusser-Neffgen, A.; Huebel, H.; Bringel, P.; Domscheit, J.; Mergel, E.; Nenoff, N.; Singh, A.K.; Hagemann, G.B.; Jensen, D.R.; Bhattacharya, S.; Curien, D.; Dorvaux, O.; Hannachi, F.; Lopez-Martens, A. [Helmholtz-Institut fuer Strahlen- und Kernphysik, Universitaet Bonn, D-53115 Bonn (Germany); Niels Bohr Institute, Blegdamsvej 17, DK-2100 Copenhagen (Denmark); Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata 700 064 (India); Institut de Recherches Subatomiques, F-67037 Strasbourg (France); Centre d'Etudes Nucleaires de Bordeaux-Gradignan, F-33175 Gradignan (France); Centre de Spectrometrie Nucleaire et de Spectrometrie de Masse, F-91405 Orsay Campus (France)

2006-03-15

297

Triaxial superdeformed and normal-deformed high-spin band structures in Hf170  

NASA Astrophysics Data System (ADS)

The high-spin structure of Hf170 was investigated using the EUROBALL spectrometer. The previously known level scheme was extended in the low-spin region as well as to higher spins, and several new bands were discovered. In particular, two bands were identified which show the characteristics of triaxial superdeformation. One of these bands is strongly populated, and its excitation energy and spins are established. Configuration assignments are made to the normal-deformed bands based on comparisons of their properties with cranked shell model calculations. The results for the very high spin states provide important input for such calculations.

Neußer-Neffgen, A.; Hübel, H.; Bringel, P.; Domscheit, J.; Mergel, E.; Nenoff, N.; Singh, A. K.; Hagemann, G. B.; Jensen, D. R.; Bhattacharya, S.; Curien, D.; Dorvaux, O.; Hannachi, F.; Lopez-Martens, A.

2006-03-01

298

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

USGS Publications Warehouse

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

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

2008-01-01

299

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

300

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

NASA Astrophysics Data System (ADS)

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

Puls, Conor

301

Mercury adsorption on Ni(111). III. Surface electronic structure  

NASA Astrophysics Data System (ADS)

Experimental and theoretical band structures are presented for four mercury adsorption structures on Ni(111): the p(2 × 2)-0.75 ML (1 ML is equivalent to an adatom density equal to the substrate surface atom density), the x = 0.18 "c(2?3 × 2?3)R30°", the p(2 × 2)-0.5 ML and the (?3 × ?3)R30° structures. Calculations are also presented for three free mercury monolayers (unattached to a substrate): square, hexagonal and open hexagon structures. The experimentally observed splitting of the Hg 2D {5}/{2} peak in photoemission is reproduced in the calculations and shown to be due to direct through space d-orbital overlap for compressed Hg layers. The calculations further show that the experimentally observed splitting for the (?3 × ?3) structure must be due to a disordered component with smaller Hg-Hg distances than the ?3 distance. The experimentally observed phase transitions are related to the density of packing/lattice constant and the metallic/non-metallic properties of the mercury phases involved. It is suggested that the pseudo-square "c(2?3 sX 2?3)R30°" structure is more stable than the simple hexagonal p(2 × 2)-0.75 ML structure at coverages of 0.64 ML because the square arrangement leads to better overlap of the empty p-orbitals and hence a lowering of energy and closure of the band-gap.

Singh, Nagindar K.; Dale, P. A. D. M. A.; Bullett, D.; Jones, Robert G.

1993-09-01

302

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

PubMed

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

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

2011-01-01

303

[Oligoglycine surface structures: molecular dynamics simulation].  

PubMed

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

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

2010-01-01

304

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

305

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

E-print Network

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 ...

Hu, Min

306

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

307

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

E-print Network

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, ...

Lee, K. Y. K.

308

Photonic band structure and effect of ? and ? on the reflectivity of one-dimensional magnetic photonic crystal structure  

Microsoft Academic Search

In this paper, we study the photonic band structure and reflection properties in one-dimensional magnetic photonic crystals (MPCs). Investigation of dispersion characteristics shows that in the case of MPCs, photonic band gaps arise due to the contrast in the wave impedance, not due to the contrast in the refractive index, while contrast in the refractive index of the two layers

Sanjeev K. Srivastava; S. P. Ojha

2008-01-01

309

Photonic band structure and effect of [epsilon] and [mu] on the reflectivity of one-dimensional magnetic photonic crystal structure  

Microsoft Academic Search

In this paper, we study the photonic band structure and reflection properties in one-dimensional magnetic photonic crystals (MPCs). Investigation of dispersion characteristics shows that in the case of MPCs, photonic band gaps arise due to the contrast in the wave impedance, not due to the contrast in the refractive index, while contrast in the refractive index of the two layers

Sanjeev K. Srivastava; S. P. Ojha

2008-01-01

310

Lunar near-surface structure  

Microsoft Academic Search

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. Although the regolith is locally variable in thickness, it possesses surprisingly similar seismic characteristics. Beneath the regolith at the Apollo 14 Fra Mauro site and the Apollo 16 Descartes site is material with

Michael R. Cooper; Robert L. Kovach; Joel S. Watkins

1974-01-01

311

Electronic band structure, optical properties, and generalized susceptibility of NbO2  

Microsoft Academic Search

The electronic structure of the high-temperature rutile phase of NbO2 is studied by the linearized-augmented-plane-wave method. Potentials constructed by superposition of neutral-atom and ionic-charge densities are used to explore variability of the electronic band structure. A rigid-band scheme is shown to accurately describe optical absorption of the rutile phase of NbO2 stabilized by the addition of 20 at.% Ti as

M. Posternak; A. J. Freeman; D. E. Ellis

1979-01-01

312

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

313

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

314

Novel structure for magnetic rotation bands in 60Ni  

E-print Network

The self-consistent tilted axis cranking relativistic mean-field theory based on a point-coupling interaction has been established and applied to investigate systematically the newly observed shears bands in 60Ni. The tilted angles, deformation parameters, energy spectra, and reduced M1 and $E2$ transition probabilities have been studied in a fully microscopic and self-consistent way for various configurations and rotational frequencies. It is found the competition between the configurations and the transitions from the magnetic to the electric rotations have to be considered in order to reproduce the energy spectra as well as the band crossing phenomena. The tendency of the experimental electromagnetic transition ratios B(M1)/B(E2) is in a good agreement with the data, in particular, the B(M1) values decrease with increasing spin as expected for the shears mechanism, whose characteristics are discussed in detail by investigating the various contributions to the total angular momentum as well.

P. W. Zhao; S. Q. Zhang; J. Peng; H. Z. Liang; P. Ring; J. Meng

2011-04-22

315

Structural characterization of nanopatterned surfaces  

NASA Astrophysics Data System (ADS)

In this work, chemically and topographically nanopatterned surfaces were produced by a top-down processing approach for biosensing devices. The nanopatterning was the result of the combination of plasma polymerisation (pp) of biofunctional materials and colloidal lithography techniques. The morphological and chemical properties induced by the plasma deposition-etching treatment were characterised by optical method combining ellipsometry and Fourier Transform Infrared spectroscopy studies. This method supported by atomic force microscopy measurements, allowed the full optical characterization of each step of the top-down process. The optical characterization of the end-up nanopatterned samples demonstrated that the chosen process is able to produce well-defined nanostructured surfaces with controlled chemical and morphological properties.

Lejeune, Michaël; Valsesia, Andrea; Kormunda, Martin; Colpo, Pascal; Rossi, François

2005-05-01

316

Butt-end fiber coupling to a surface-emitting ?-point photonic crystal band edge laser  

NASA Astrophysics Data System (ADS)

The authors demonstrate a compact and efficient fiber coupling scheme for a surface-emitting photonic crystal laser by using a cleaved fiber tip connected to a wavelength-division-multiplexing 1×2 fiber coupler. Simultaneous optical excitation and laser light collection are achieved for a 1.55?m InGaAsP graphite-lattice ?-point band edge laser. On comparing with the conventional microphotoluminescence setup based on an objective lens, their direct butt coupling setup is much simpler and yet offers the fiber-coupled output approximately ten times higher. Finite-difference time-domain simulations confirm that the ?-point band edge laser exhibits the desired vertical emission property and that the fiber coupling efficiency can be as high as 30%.

Park, Yeonsang; Kim, Sunghwan; Moon, Chaeyoung; Jeon, Heonsu; Kim, Hyo Jin

2007-04-01

317

Band structure calculations of Mo2BC under pressure  

Microsoft Academic Search

Mo2B is a superconductor with a Tc of about 5.8 K and a body centered tetragonal cristalline structure. When carbon is added to the structure it is formed the intermetallic Mo2BC compound, which is a superconductor with a Tc of about 7 K and has a crystalline face centered orthorhombic structure. In this work we make ab initio calculations of

R. Falconi; F. Alvarez; R. Escamilla; R. Escudero

2010-01-01

318

S-band accelerating structures for the PAL-XFEL  

NASA Astrophysics Data System (ADS)

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

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

2015-02-01

319

Band-edge Bilayer Plasmonic Nanostructure for Surface Enhanced Raman Spectroscopy  

E-print Network

Spectroscopic analysis of large biomolecules is critical in a number of applications, including medical diagnostics and label-free biosensing. Recently, it has been shown that Raman spectroscopy of proteins can be used to diagnose some diseases, including a few types of cancer. These experiments have however been performed using traditional Raman spectroscopy and the development of the Surface enhanced Raman spectroscopy (SERS) assays suitable for large biomolecules could lead to a substantial decrease in the amount of specimen necessary for these experiments. We present a new method to achieve high local field enhancement in surface enhanced Raman spectroscopy through the simultaneous adjustment of the lattice plasmons and localized surface plasmon polaritons, in a periodic bilayer nanoantenna array resulting in a high enhancement factor over the sensing area, with relatively high uniformity. The proposed plasmonic nanostructure is comprised of two interacting nanoantenna layers, providing a sharp band-edge ...

Mousavi, S Hamed Shams; Atabaki, Amir H; Adibi, Ali

2014-01-01

320

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

NASA Astrophysics Data System (ADS)

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

Abdul-Kader, A. M.

2013-04-01

321

Photonic band structure and effect of [epsilon] and [mu] on the reflectivity of one-dimensional magnetic photonic crystal structure  

NASA Astrophysics Data System (ADS)

In this paper, we study the photonic band structure and reflection properties in one-dimensional magnetic photonic crystals (MPCs). Investigation of dispersion characteristics shows that in the case of MPCs, photonic band gaps arise due to the contrast in the wave impedance, not due to the contrast in the refractive index, while contrast in the refractive index of the two layers decides the position and number of the band gaps. We also study the effect of permittivity and permeability on reflection bands, which shows that the structure that has larger values of magnetic permeability ([mu]) than dielectric permittivity ([epsilon]) have wider TM-reflection bands, whereas the structure for which [epsilon] is greater than [mu] has wider TE-reflection bands. But the gap to mid-gap frequency ratio for TM-reflection bands is larger than TE-reflection bands. Thus, magnetic permeability has greater impact on the reflectivity of MPCs than dielectric permittivity. Finally, the analysis of the omni-reflectance in MPCs has also been studied.

Srivastava, Sanjeev K.; Ojha, S. P.

2008-11-01

322

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

323

Band structure engineering and transport properties of aluminium phosphide nanoribbon - A first-principles study  

NASA Astrophysics Data System (ADS)

The band structure and transport properties of pristine, boron, gallium and arsenic substituted AlP nanoribbon are studied using density functional theory. The band structure of pristine, boron, gallium and arsenic substituted AlP nanoribbon exhibits semiconducting behavior. The substitution of boron decreases the band gap of AlP nanoribbon. The substitution of group-III semiconductor has much influence in density of states. The major contribution is observed in p and d orbitals. The electron density increases with boron substitution and there is a slight decrease in electron density for gallium substitution. The transmission of AlP nanoribbon molecular device is analyzed with two probe method. The substitution impurity and bias voltage influence the transmission across AlP nanoribbon. From the results, it is inferred that the band structure and electronic transport properties can be fine-tuned with substitution impurity along AlP nanoribbon.

Chandiramouli, R.; Rubalya Valantina, S.; Nagarajan, V.

2014-12-01

324

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

PubMed Central

Band 3 is the major anion transport polypeptide of erythrocytes. It appears to be the binding site of several glycolytic enzymes. Structurally, band 3 is the major protein spanning the erythrocyte membrane and connects the plasma membrane to band 2.1, which binds to the cytoskeleton. In the present study, we report an alteration of band 3 molecule that is associated with the following changes: erythrocyte shape change from discoid to "thorny cells" (acanthocytes), restriction of rotational diffusion of band 3 in the membrane, increase in anion transport, and decrease in the number of high-affinity ankyrin-binding sites. Changes in erythrocyte IgG binding, glyceraldehyde-3-phosphate dehydrogenase, fluorescence polarization (indicative of membrane fluidity), and other membrane proteins as determined by polyacrylamide gel electrophoresis were not detected. Cells containing the altered band 3 polypeptide were obtained from individuals with abnormal erythrocyte morphology. Two-dimensional peptide maps revealed differences in the Mr 17,000 anion transport segment of band 3 consistent with additions of tyrosines or tyrosine-containing peptides. The data suggest that (i) this alteration of band 3 does not result in accelerated aging as does cleavage and (ii) structural changes in the anion transport region result in alterations in anion transport. Images PMID:2829189

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

1988-01-01

325

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

326

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

327

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

328

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

NASA Astrophysics Data System (ADS)

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

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

2015-02-01

329

Design of a frequency selective surface (FSS) type superstrate for dual-band directivity enhancement of microstrip patch antennas  

Microsoft Academic Search

A novel design of a high-directivity resonator antenna that utilizes a two-layered frequency selective surface (FSS) superstrate - as an alternative to a dielectric electromagnetic band gap (EBG) superstrate - for dual band directivity enhancement and reduction in height is presented in this paper.

Young Ju Lee; Junho Yeo; R. Mittra; Wee Sang Park

2005-01-01

330

Characterizing the surface structure of plastics coatings  

Microsoft Academic Search

Excellent appearance of the coated exterior car parts is one of the aims at the applications of plastics for automotive painting. The painted plastics parts and the metal car body should have comparable surface structures not depending on the different substrate materials (steel or plastics) used. Against this background parameters influencing the surface of plastics parts are becoming recently more

Michael Osterhold; Kornelia Armbruster

2006-01-01

331

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

332

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

E-print Network

AUTOMATING THE DESIGN OF A BAND-PASS SPECTRAL FILTER WITH FREQUENCY SELECTIVE SURFACES of a Frequency Selective Surfaces with cascaded inhomogeneous dielectric substrates. Desired performance finite element-boundary integral (FE-BI) simulators. INTRODUCTION Frequency Selective Surfaces (FSS) find

Sendur, Gullu Kiziltas

333

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

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

334

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.

335

Band structures of graphene hexagonal lattice semiconductor quantum dots  

Microsoft Academic Search

Electronic structures of coupled semiconductor quantum dots (QDs) arranged as graphene hexagonal lattice are studied theoretically using the tight-binding method. In our calculations, the electrons can hop to the third-nearest-neighbors, and the overlap matrix as well as the multicenter integral are taken into account. The novel two-dimensional Dirac-like electronic excitations in graphene are found in these artificial planar QD structures.

Juan Peng; Shu-Shen Li

2010-01-01

336

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

337

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

E-print Network

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

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

2014-12-30

338

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

NASA Astrophysics Data System (ADS)

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

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

2009-03-01

339

Creation of superwetting surfaces with roughness structures.  

PubMed

In this work, we explored the possibility of creating superwetting surfaces, which are defined here as those with apparent contact angles of <5°, using roughness structures for the purpose of eliminating the surface tension effect on a floating small plate, which is denser than the surrounding liquid. The roughness ratio is often thought to play a critical role in generating superwetting surfaces. However, we found that the top surface ratio had more influence on apparent contact angles. When this ratio was <0.013, the resulting apparent contact angle might be less than 5°, when the intrinsic contact angle was ?40°. Accordingly, hybrid micro- and nanostructures, which had such a small ratio, were chosen to create the superwetting surfaces. These surfaces were subsequently applied to eliminate the surface tension effect on a small plate. As a result of this elimination, the small plate sank down to the bottom of the liquid. PMID:25391538

Garg, Varun; Qiao, Lei; Sarwate, Prasha; Luo, Cheng

2014-12-01

340

On the Relation between Perfect Tunneling and Band Gaps for SNG Metamaterial Structures  

E-print Network

In this article we have proposed a compact classification of isotropic and homogenous single negative (SNG) electromagnetic metamaterial based perfect tunneling unit cells. This has been made by means of the band gap theories and properties of the arrays made up of these unit cells. Based on their reported characteristics, we have proposed new structures that simultaneously show perfect tunneling band and complete band gap (CBG - omni directional stop band for both polarizations). Besides, we have identified perfect tunneling which can be considered as "phase shifted perfect tunneling". Several interesting and new phenomena like Complete Perfect Tunneling (CPT - omni-directional perfect tunneling for both polarizations), Band Gap Shifting, CBG in Double Positive (DPS) material range, etc. have been reported with proper physical and mathematical explanations.

Mahdy, M R C; Shawon, Jubayer; Al-Quaderi, Golam Dastegir; Matin, M A

2013-01-01

341

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

NASA Astrophysics Data System (ADS)

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

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

2011-09-01

342

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

343

Relationships between magnetic foot points and G-band bright structures  

E-print Network

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

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

2008-02-13

344

Longitudinal surface structures (flowstripes) on Antarctic glaciers  

NASA Astrophysics Data System (ADS)

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

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

2012-03-01

345

Longitudinal surface structures (flowstripes) on Antarctic glaciers  

NASA Astrophysics Data System (ADS)

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

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

2011-11-01

346

Surface electronic structure of [XMIm]Cl probed by surface-sensitive spectroscopy.  

PubMed

We apply electron spectroscopy methods with different surface sensitivities to elucidate the DOS of the surface and the near-surface region of [XMIm]Cl (X=octyl, hexyl, butyl, and ethyl alkyl chain) ionic liquids. Using metastable induced electron spectroscopy (MIES) we are able to detect the density of states in front of the outermost surface, whereas ultraviolet and X-ray photoelectron spectroscopy (UPS and XPS) measurements provide lower surface sensitivity. The assignment of certain structures in the valence band spectra to particular atoms/functional groups of the ionic liquid based on DFT calculations and the reconstruction of PES spectra enables us to obtain information on the dominating groups at the surface, or in other words, on the molecular/ionic arrangement and orientation at the surface. From angular resolved XPS it is concluded that the alkyl chains dominate at the outermost surface. In agreement with this a decreasing chlorine signal is observed in the UPS spectra for ionic liquids with increasing alkyl chain length. The analysis of the MIES data shows that in case of [OMIm]Cl--in contrast to UPS and XPS--no Cl-induced features are visible in the MIES spectra at all and that the MIES spectra are dominated by the [OMIm](+) alkyl chain. PMID:22517561

Ulbrich, Angela; Reinmöller, Markus; Beenken, Wichard J D; Krischok, Stefan

2012-05-14

347

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

SciTech Connect

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

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

2011-05-15

348

Combined Angle-Resolved Photoemission Spectroscopy and Theoretical Study of the Surface Electronic Structure of SrTiO3  

NASA Astrophysics Data System (ADS)

The surface electronic structure of the O 2p-derived valence band states of (001)-oriented, TiO2-terminated SrTiO3 is measured along various crystallographic directions using angle-resolved photoemission spectroscopy (ARPES). A comparison of ARPES spectra to ab initio, density functional theory (DFT) band structure calculations as well as the theoretical band structure calculated at the tight binding level are in excellent agreement. ARPES measurements also reveal a mid-gap state located roughly 0.5 eV above the valence band which we interpret as a surface state. This interpretation is supported by DFT calculations of an SrTiO3 slab which reveals the existence of a surface state located in the gap roughly 0.5 eV above the projected valence band.

Hatch, Richard C.; Fredrickson, Kurt; Lin, Chungwei; Choi, Miri; Posadas, Agham B.; Seo, Hosung; Demkov, Alexander A.

2013-03-01

349

Strain effects on band structure of wurtzite ZnO: a GGA + U study  

NASA Astrophysics Data System (ADS)

Band structures in wurtzite bulk ZnO/Zn1-xMgxO are calculated using first-principles based on the framework of generalized gradient approximation to density functional theory with the introduction of the on-site Coulomb interaction. Strain effects on band gap, splitting energies of valence bands, electron and hole effective masses in strained bulk ZnO are discussed. According to the results, the band gap increases gradually with increasing stress in strained ZnO as an Mg content of Zn1-xMgxO substrate less than 0.3, which is consistent with the experimental results. It is further demonstrated that electron mass of conduction band (CB) under stress increases slightly. There are almost no changes in effective masses of light hole band (LHB) and heavy hole band (HHB) along [00k] and [k00] directions under stress, and stress leads to an obvious decrease in effective masses of crystal splitting band (CSB) along the same directions.

Liping, Qiao; Changchun, Chai; Yintang, Yang; Xinhai, Yu; Chunlei, Shi

2014-07-01

350

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

351

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

352

Precision photonic band structure calculation of Abrikosov periodic lattice in type-II superconductors  

E-print Network

We have performed a numerical solution for band structure of an Abrikosov vortex lattice in type-II superconductors forming a periodic array in two dimensions for applications of incorporating the photonic crystals concept into superconducting materials with possibilities for optical electronics. The implemented numerical method is based on the extensive numerical solution of the Ginzburg-Landau equation for calculating the parameters of the two-fluid model and obtaining the band structure from the permittivity, which depends on the above parameters and the frequency. This is while the characteristics of such crystals highly vary with an externally applied static normal magnetic field, leading to nonlinear behavior of the band structure, which also has nonlinear dependence on the temperature. The similar analysis for every arbitrary lattice structure is also possible to be developed by this approach as presented in this work. We also present some examples and discuss the results.

Kokabi, Alireza; Khorasani, Sina; Fardmanesh, Mehdi

2011-01-01

353

SbSI Based Photonic Crystal Superlattices: Band Structure and Optics  

NASA Astrophysics Data System (ADS)

In this work, we present an investigation of the optical properties and band structure calculations for the photonic crystal structures (PCs) based on one-dimensional (1D)-photonic crystal. Here we use 1D SbSI based layers in air background. We have theoretically calculated the photonic band structure and optical properties of SbSI based PC superlattices. In our simulation, we employed the finite-difference time domain (FDTD) technique and the plane wave expansion method (PWE), which implies the solution of Maxwell equations with centered finite-difference expressions for the space and time derivatives.

S?msek, Sevket; Koc, Husnu; Palaz, Selam?; Oltulu, Oral; Mamedov, Am?rullah M.; Ozbay, Ekmel

2015-03-01

354

Electronic band structure matching for half- and full-Heusler alloys  

Microsoft Academic Search

We explore the lattice and the electronic band structures matching between the half-metallic Heusler alloys (half-Heusler NiMnSb and full-Heusler Co2MnSi) and several hypothetical non-magnetic Heusler alloys by using first principle calculations. The lattice and band structure matching are almost perfectly satisfied between the two materials of similar crystal structures: (i) NiMnSb and XYSb and (ii) Co2MnSi and X2YSi, where X,

V. Ko; G. Han; Y. P. Feng

2010-01-01

355

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

356

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

357

Study of periodic band gap structure of the magnetized plasma photonic crystals  

NASA Astrophysics Data System (ADS)

The characteristics of the periodic band gaps of the one dimension magnetized plasma photonic crystals are studied with the piecewise linear current density recursive convolution (PLCDRC) finite-differential time-domain (FDTD) method. In frequency-domain, the transmission coefficients of electromagnetic Gaussian pulses are computed, and the effects of the periodic structure constant, plasma layer thickness and parameters of plasma on the properties of periodic band gaps of magnetized photonic crystals are analyzed. The results show that the periodic band gaps depend strongly on the plasma parameters.

Zhang, Hai-Feng; Ma, Li; Liu, Shao-Bin

2009-03-01

358

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

Microsoft Academic Search

The electronic structure of Na-adsorbed graphenes formed on the 6H-SiC(0001) substrate was studied using angle-resolved photoemission spectroscopy with synchrotron photons and ab initio pseudopotential calculations. It was found that the band of the graphenes sensitively changes upon Na adsorption especially at low temperature. With increasing Na dose, the pi band appears to be quickly diffused into the background at 85

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

2009-01-01

359

Comment on ``Band structure engineering of graphene by strain: First-principles calculations''  

Microsoft Academic Search

In their first-principles calculations of the electronic band structure of graphene under uniaxial strain, Gui, Li, and Zhong, [Phys. Rev. B 78, 075435 (2008)] have found opening of band gaps at the Fermi level. This finding is in conflict with the tight-binding description of graphene which is closed gap for small strains. In this Comment, we present first-principles calculations which

M. Farjam; H. Rafii-Tabar

2009-01-01

360

Complex band structures and effective medium descriptions of periodic acoustic composite systems  

NASA Astrophysics Data System (ADS)

We examine the complex band structures and effective medium descriptions of a periodic acoustic composite system. It is shown that if the system exhibits a negative velocity band, the assignment of the system as a phononic crystal or as a “double negative” metamaterial is unambiguous only in some cases. An example is given where the system properties can be tuned gradually and continuously from an acoustic metamaterial to a phononic crystal, and there is no sharp dividing line between these two regimes.

Ao, Xianyu; Chan, C. T.

2009-12-01

361

Energy-Band Structure and Electronic Properties of SnTe  

Microsoft Academic Search

The energy-band structure of SnTe is calculated using the augmented-plane-wave method, taking into account the relativistic corrections. The resulting wave functions at L are used to calculate momentum matrix elements. These matrix elements are then used in a k.p perturbation calculation in the presence of a magnetic field to obtain band parameters at point L in the Brillouin zone. Nonparabolic

Sohrab Rabii

1969-01-01

362

Energy-Level Structure of Zinc in Magnetic Fields Using a Single-Band Effective Hamiltonian  

Microsoft Academic Search

The zero-magnetic-field energy-band structure of the midplane of the second band of zinc is Fourier analyzed and the coefficients E(R-->) are used to construct the magnetic effective Hamiltonian H(pi-->)=RE(R-->)exp(iR-->.pi-->ℏ)(pi-->=p-->+eA-->c). This effective Hamiltonian is cast into the form of a matrix operator, and the eigenvalues are computed by numerical means for a range of magnetic fields. These exact solutions of the

P. S. Kapo; E. Brown

1973-01-01

363

A dual band printed dipole antenna with spiral structure for WLAN application  

Microsoft Academic Search

In this letter, the design procedure and electrical performance of a dual band (2.4\\/5.8GHz) printed dipole antenna using spiral structure are proposed and investigated. For the first time, a dual band printed dipole antenna with spiral configuration is proposed. In addition, a matching method by adjusting the transmission line width, and a new bandwidth broadening method varying the distance between

Mi Jung Kim; Choon Sik Cho; Jaeheung Kim

2005-01-01

364

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

E-print Network

coefficient of a layered structure made of glass and water was calculated using transfer matrix method by using crystals with periodic structures.1,2 The fundamental principle is to use the periodic medium- magnetic waves cannot go through the crystal. In principle, the band-gap phenomena can be produced when

Cao, Wenwu

365

New Reconfigurable Power Divider Based on Radial Waveguide and Cylindrical Electromagnetic Band Gap Structure for Low  

E-print Network

Structure for Low Power and Low Cost Smart Antenna Systems Halim Boutayeb, Paul Watson and Toby Kemp Antenna agile antennas by using a reconfigurable radial waveguide excited by a central probe and feeding by a cylindrical Electromagnetic Band Gap structure with PIN diodes allowing azimuth beam steering and multiple

Paris-Sud XI, Université de

366

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

367

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

368

Calculation of band alignments and quantum confinement effects in zero- and one-dimensional pseudomorphic structures  

NASA Astrophysics Data System (ADS)

The strain field distributions and band lineups of zero-dimensional and one-dimensional strained pseudomorphic semiconductor particles inside a three-dimensional matrix of another semiconductor have been studied. The resulting strain in the particle and the matrix leads to band alignments considerably different from that in the conventional two-dimensional (2D) pseudomorphic growth case. The models are first applied to an ideal spherical and cylindrical Si1-xGex particle in a large Si matrix. In contrast to the 2D case, the band alignments for both structures are predicted to be strongly type II, where the conduction-band edge and the valence-band edge of the Si matrix are both significantly lower than those in the Si1-xGex inclusion, respectively. Band lineups and the lowest electron-heavy-hole transition energies of a pseudomorphic V-groove Si1-xGex quantum wire inside a large Si matrix have been calculated numerically for different size structures. The photoluminescence energies of a large Si1-xGex V-groove structure on Si will be lower than those of conventional 2D strained Si1-xGex for similar Ge contents.

Yang, Min; Sturm, J. C.; Prevost, Jean

1997-07-01

369

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

370

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

371

Towards Complete Photonic Band Gap Structures below Infrared Wavelengths  

Microsoft Academic Search

\\u000a Photonic crystals are structures with a periodically modulated dielectric constant. In analogy to the case of an electron\\u000a moving in a periodic potential, certain photon frequencies can become forbidden, independent of photon polarization and the\\u000a direction of propagation — a complete photonic bandgap (CPBG) [1, 2]. As early as 1975, photonic crystals with such a gap\\u000a have been shown to

Alexander Moroz

372

Spin dimer, electronic band structure and classical spin analyses of spin exchange interactions and ordered magnetic structures of magnetic solids  

Microsoft Academic Search

We reviewed briefly how spin dimer, electronic band structure and classical spin analyses are employed to describe spin exchange interactions and ordered magnetic structures of magnetic solids. It was shown that super-superexchange interactions are crucial in forming strongly interacting spin units of magnetic solids and hence in determining their magnetic properties, and that incommensurate magnetic superstructures are readily described by

M.-H. Whangbo; D. Dai; H.-J. Koo

2005-01-01

373

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

Microsoft Academic Search

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

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

1997-01-01

374

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

375

The coherent structure of atmospheric surface layers  

Microsoft Academic Search

The structure of two-point correlation statistics in the atmospheric surface layer are studied from measurements on the western Utah salt flats at the SLTEST facility. Large-scale features in the stable, neutral and unstable surface layers that adhere to Monin-Obukhov similarity (-10

Kapil Chauhan; Nick Hutchins; Ivan Marusic; Jason Monty

2010-01-01

376

Effect of Nitrogen Doping on the Structure and Optical Band Gap of Fluorinated Diamond-Like Carbon Films  

NASA Astrophysics Data System (ADS)

Radio-frequency plasma-enhanced chemical vapor deposition technology was applied to the manufacture of nitrogen-doped fluorinated diamond-like carbon films under different nitrogen flow ratios. Atomic force microscopy, Fourier transform infrared absorption spectroscopy, X-ray photoelectron spectroscopy, and ultraviolet-visible spectroscopy were performed to determine the surface morphology, microscopic structure, and optical properties of the films. The spectra of the films were analyzed using a Gaussian peak-fitting algorithm. The films manufactured using this technology were compact and even. As the nitrogen flow ratio increased, the surface roughness of the films decreased. Nitrogen doping was favorable for graphite phase formation in the films. Moreover, the number of sp2 structures increases. The optical band gap initially increased and then decreased as the nitrogen flow ratio increased slightly.

Jianrong, Xiao; Aihua, Jiang; Zhiyong, Wang

2013-09-01

377

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

378

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

379

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

PubMed

Generalized Bloch wave functions of bulk structures, which are composed of not only propagating waves but also decaying and growing evanescent waves, are known to be essential for defining the open boundary conditions in the calculations of the electronic surface states and scattering wave functions of surface and junction structures. Electronic complex band structures being derived from the generalized Bloch wave functions are also essential for studying bound states of the surface and junction structures, which do not appear in conventional band structures. We present a novel calculation method to obtain the generalized Bloch wave functions of periodic bulk structures by solving a generalized eigenvalue problem, whose dimension is drastically reduced in comparison with the conventional generalized eigenvalue problem derived by Fujimoto and Hirose [Phys. Rev. B 67, 195315 (2003)]. The generalized eigenvalue problem derived in this work is even mathematically equivalent to the conventional one, and, thus, we reduce computational cost for solving the eigenvalue problem considerably without any approximation and losing the strictness of the formulations. To exhibit the performance of the present method, we demonstrate practical calculations of electronic complex band structures and electron transport properties of Al and Cu nanoscale systems. Moreover, employing atom-structured electrodes and jellium-approximated ones for both of the Al and Si monatomic chains, we investigate how much the electron transport properties are unphysically affected by the jellium parts. PMID:25122409

Tsukamoto, Shigeru; Hirose, Kikuji; Blügel, Stefan

2014-07-01

380

Design of Single-Band and Dual-Band AMC Surfaces by combining a Micro-genetic Algorithm with the Spectral FDTD Method  

Microsoft Academic Search

We present a GA\\/FDTD optimisation technique and its application in the design of single and multi-band artificial magnetic conducting (AMC) surfaces. The technique is a combination of a genetic algorithm (GA) and the finite-difference time-domain (FDTD) method. For the efficiency purpose, a micro-genetic algorithm (MGA) is applied to optimize the geometry of an AMC unit cell, and the fitness functions

Yuehe Ge; Karu P. Esselle

2006-01-01

381

Surface electronic and structural properties of nanostructured titanium oxide grown by pulsed laser deposition  

NASA Astrophysics Data System (ADS)

Titanium oxide nanostructured thin films synthesized by pulsed laser deposition (PLD) were here characterized with a multi-technique approach to investigate the relation between surface electronic, structural and morphological properties. Depending on the growth parameters, these films present characteristic morphologies ranging from compact to columnar and to an extremely open structure. As-deposited films have a disordered structure both in the bulk and on the surface, as shown by Raman spectroscopy and by the fine structure of X-ray absorption spectra near the Ti and O edge (NEXAFS). The surface reactivity towards the atmosphere, with consequent formation of surface hydroxyl terminal groups, turns out to be dependent not only on the effective surface but also on the surface structure. By ultraviolet photoemission spectroscopy, we observed that, depending on the sample structure and morphology, defect states at 1 eV binding energy in the valence band can be induced by exposing the samples to the intense synchrotron photon beam. After annealing in air at 673 K, the structural order increases towards a mainly anatase phase in which the presence of rutile increases in films with a more open morphology. Such structural modifications influence the surface stability since the defect formation in the valence band is strongly reduced in all the annealed films, and it is completely hindered in the most compact films.

Fusi, M.; Maccallini, E.; Caruso, T.; Casari, C. S.; Li Bassi, A.; Bottani, C. E.; Rudolf, P.; Prince, K. C.; Agostino, R. G.

2011-02-01

382

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

SciTech Connect

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

Lu, Wei-Tao, E-mail: luweitao@lyu.edu.cn; Ye, Cheng-Zhi [School of Science, Linyi University, 276005 Linyi (China) [School of Science, Linyi University, 276005 Linyi (China); Institute of Condensed Matter Physics, Linyi University, 276005 Linyi (China); Li, Wen [School of Science, Linyi University, 276005 Linyi (China)] [School of Science, Linyi University, 276005 Linyi (China)

2013-11-04

383

Band Structure of Carbon Nanotubes in a Perpendicular Electric Field 2.0  

NSDL National Science Digital Library

The NanoEd Resource Portal, a â??dynamic 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

384

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

PubMed

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

Yamamoto, Naoki; Saito, Hikaru

2014-12-01

385

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

NASA Astrophysics Data System (ADS)

We used density functional and many-body perturbation theory to calculate the quasiparticle band structures and electronic transport parameters of p-type SnSe both for the low-temperature Pnma and high-temperature Cmcm phases. The Pnma phase has an indirect band gap of 0.829 eV, while the Cmcm has a direct band gap of 0.464 eV. Both phases exhibit multiple local band extrema within an energy range comparable to the thermal energy of carriers from the global extrema. We calculated the electronic transport coefficients as a function of doping concentration and temperature for single-crystal and polycrystalline materials to understand the previous experimental measurements. The electronic transport coefficients are highly anisotropic and are strongly affected by bipolar transport effects at high temperature. Our results indicate that SnSe exhibits optimal thermoelectric performance at high temperature when doped in the 1019-1020 cm-3 range.

Shi, Guangsha; Kioupakis, Emmanouil

2015-02-01

386

Spatial demultiplexing in the submillimeter wave band using multilayer free-standing frequency selective surfaces  

Microsoft Academic Search

In this paper, we show that a multilayer freestanding slot array can be designed to give an insertion loss which is significantly lower than the value obtainable from a conventional dielectric backed printed frequency selective surface (FSS). This increase in filter efficiency is highlighted by comparing the performance of two structures designed to provide frequency selective beamsplitting in the quasioptical

Raymond Dickie; Robert Cahill; Harold S. Gamble; Vincent F. Fusco; Alexander G. Schuchinsky; Norman Grant

2005-01-01

387

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

388

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

PubMed

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

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

2015-03-01

389

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

NASA Astrophysics Data System (ADS)

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

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

2015-03-01

390

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

391

Laser nerve repair by solid protein band technique. I: identification of optimal laser dose, power, and solder surface area.  

PubMed

Thirty-four tibial nerves in 17 adult male wistar rats were repaired by applying protein bands longitudinally across the nerve join. The bands were then irradiated with a fibre-coupled diode laser (lambda = 810 nm). The relations among the laser weld breaking force, the power, and the solder surface area were investigated, while maintaining a consistent ratio between the total mass of protein solder in a band and total laser energy delivered (the laser energy dose). When this laser energy dose was held constant, the average breaking force of the laser welds irradiated by 72 mW laser output power was weaker than that reached after 90 mW laser radiation. There is a linear relation between the solder breaking force and the solder surface area when band thickness, laser power, and laser dose are unvaried. PMID:9635796

Lauto, A; Dawes, J M; Cushway, T; Piper, J A; Owen, E R

1998-01-01

392

STRUCTURE AND SURFACE CHEMISTRY OF THORIUM OXIDE  

Microsoft Academic Search

The structure and surface properties of thorium dioxide were studied ; from the viewpoints of electron microscopy, electron diffraction, x-ray ; diffraction, and water vapor adsorption isotherms in an attempt to obtain a ; better understanding of the caking tendencies exhibited by some aqueous thoria ; slurries when circulated in loop experiments at elevated temperatures. In water ; vapor adsorption

A. L. Draper; W. O. Milligan

1959-01-01

393

Complex band structures and evanescent Bloch waves in two-dimensional finite phononic plate  

NASA Astrophysics Data System (ADS)

The complex band structure of a two-dimensional (2D) phononic crystal based on solid or air cylindrical inclusions in solid finite thickness plate is investigated. The plane wave expansion method is developed with a specific extension to calculate the evanescent Bloch modes propagating in the phononic plate. It is shown that, in the opposite of 2D infinite phononic crystals, the complex band structures of Lamb modes exhibits a coupling between in-plane and out-of plane Lamb modes. The polarization and the behavior of the evanescent waves is analyzed and discussed as function of the plate thickness to figure out the physics behind the opening of phononic band gap for the different Lamb modes.

Oudich, Mourad; Badreddine Assouar, M.

2012-11-01

394

The influence of line shape and band structure on temperatures in planetary atmospheres  

NASA Technical Reports Server (NTRS)

Numerical experiments are performed to examine the effects of line shape and band structure on the radiative equilibrium temperature profile in planetary atmospheres. In order to accurately determine these effects, a method for calculating radiative terms is developed which avoids the usual approximations. It differs from the more commonly used methods in that it allows arbitrary dependence of the absorption coefficient on wave number, without requiring tedious line by line integration and without the constraints of band models. The present formulation is restricted to homogeneous atmospheres but the concept can be extended to the more general case. The numerical experiments reveal that the line shape and band structure of the absorbing gases have a large effect on temperatures in the higher layers of the atmosphere (corresponding to the stratosphere and mesosphere). The more nongrey the spectrum (that is, the higher the peaks and the deeper the troughs in the spectrum), the lower the temperature.

Arking, A.; Grossman, K.

1972-01-01

395

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

396

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

397

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

398

FABRICATION AND INITIAL TESTS OF AN ULTRA-HIGH GRADIENT COMPACT S-BAND (HGS) ACCELERATING STRUCTURE*  

E-print Network

of industrially available high peak power RF sources in X-band and beyond. The development of the HGS structure research was performed under the NLC program to demonstrate successful high gradient operation of X-band of the mature and commercially available S-band high power klystron technology. RF DESIGN The RF design

Brookhaven National Laboratory

399

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

400

Band structure and band offsets in Zn 1 ? x Cd x Se ZnSe quantum wells  

Microsoft Academic Search

The sensitivity of interband and intersubband transition energies to the valence-band offset in Zn1 ? xCdxSeZnSe quantum wells is investigated. Interconduction-band transition energies between the first two conduction subband levels is shown to give the optimum sensitivity. By using the valence-band offset, Qv, as an adjustable parameter we are able to fit calculations to experiment and determine a Qv value

M. Livingstone; I. Galbraith

1996-01-01

401

Specialized cell surface structures in cellulolytic bacteria.  

PubMed Central

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

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

1987-01-01

402

Structurized surface layers of normal alkanes  

NASA Astrophysics Data System (ADS)

The elevated viscosity of micron interlayers of certain normal alkanes compared to their viscosity in the "volume" is determined experimentally in shear flow using a rotational viscometer. The observed difference is considered to be caused by the manifestation, in such interlayers, of structural inhomogeneity due to the presence of structurized polymolecular surface layers on the substrates bounding them. The structural parameters of such layers, i.e., their equilibrium initial thickness and "hydrodynamic strength," are calculated in the model of a constant-viscosity layer. The measured effective viscosity of the interlayers diminishes with growth in the shear-flow velocity, which is attributed to the "cutting" of the structurized layer. Surfactant doping of the liquids leads to an increase in the effective viscosity of the interlayers, which is produced by the strengthening of the layer structure.

Altoiz, B. A.; Kiriyan, S. V.

2010-07-01

403

Selectivity of von Willebrand factor triplet bands towards heparin binding supports structural model.  

PubMed

Human plasma-derived von Willebrand factor (hp-vWF) and recombinant von Willebrand factor (r-vWF) have been fractionated by heparin affinity chromatography followed by multimer analysis using SDS-agarose gel electrophoresis. Because heparin binding sites are contained in each vWF subunit, high molecular weight multimers of r-vWF and hp-vWF, respectively, were eluted with higher salt concentration, in comparison to r-vWF and hp-vWF molecules with a low degree of multimerization. Heparin affinity chromatography did not affect the multimer composition of r-vWF. By contrast, faster migrating satellite bands and slower migrating satellite bands of hp-vWF exhibited reduced and increased heparin affinity, respectively, compared to the intermediate band of the same triplet. Because heparin binding sites are localised in the N-terminal domain of the hp-vWF subunit, this result confirms a structural model of hp-vWF (Fischer et al., Biochem. J. 1998;331:483-488) suggested recently, in which the slower migrating satellite bands have excess of one N-terminal fragment and the faster migrating satellite bands lack one N-terminal fragment, respectively, in comparison with the corresponding intermediate triplet band. PMID:10089894

Fischer, B E; Thomas, K B; Schlokat, U; Dorner, F

1999-03-01

404

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

NASA Astrophysics Data System (ADS)

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

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

2015-03-01

405

Stability analysis of flows of liquid crystal polymers exhibiting a banding structure  

Microsoft Academic Search

A prototype model to describe flows of liquid crystal polymers is analyzed. Under appropriate hypotheses on the constitutive functions, we show existence of steady-state solutions presenting a banding structure parallel to the shear direction, in shear flow geometry. A stability analysis of such solutions is carried out.

Maria-Carme Calderer

1989-01-01

406

Ecosar: A P- band digital beamforming Polarimetric Interferometric SAR instrument to measure ecosystem structure and biomass  

Microsoft Academic Search

1. ABSTRACT In this paper we describe the EcoSAR concept, an airborne Polarimetric and Interferometric P- band SAR instrument that will provide unprecedented two- and three dimensional fine scale measurements of terrestrial ecosystem structure and biomass. These measurements are directly traceable to upcoming international radar missions and the National Research Council’s Decadal Survey ecosystem measurement requirements.

Temilola Fatoyinbo; Rafael F. Rincon; Guoqing Sun; K. Jon Ranson

2011-01-01

407

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

408

Band Structure and Electron Velocity Measurement in Carbon Nanotubes and Graphene  

Microsoft Academic Search

We discuss recent measurements of the interband spectrocopy of carbon nanotubes and studies of cyclotron resonance in graphene, using these to examine the possible dependence of the band structure of graphene on the number of layers present and the role of Coulomb interactions. Cyclotron resonances gives a value for the electron velocity at the Dirac point of 1.093×106 ms-1, which

Robin J. Nicholas; Kai-Chieh Chuang

2009-01-01

409

Two-dimensional electronic and vibrational band structure of uniaxially strained graphene from ab initio calculations  

Microsoft Academic Search

We present an in-depth analysis of the electronic and vibrational band structure of uniaxially strained graphene by ab initio calculations. Depending on the direction and amount of strain, the Fermi crossing moves away from the K point. However, graphene remains semimetallic under small strains. The deformation of the Dirac cone near the K point gives rise to a broadening of

Marcel Mohr; Konstantinos Papagelis; Janina Maultzsch; Christian Thomsen

2009-01-01

410

Localized description of band structure effects on Li atom interaction with graphene  

Microsoft Academic Search

We study theoretically the localized aspects of the interaction between an Li atom and graphene. To this end, we use an ab initio calculation of the Hamiltonian terms within the Anderson model that allows us to take into account the chemical properties of Li and C atoms and the two-dimensional band structure of graphene. In this way, physical magnitudes of

Marcelo A. Romero; A. Iglesias-García; E. C. Goldberg

2011-01-01

411

Simulation and experiment of photonic band-gap structures for microstrip circuits  

Microsoft Academic Search

We report the first comprehensive investigation of synthesized dielectric materials which possess distinctive stopbands for microstrip lines. Four types of these photonic band-gap (PBG) structures have been simulated using FDTD. Experiment with a honeycomb-lattice PBG line shows excellent agreement between theoretical prediction and measurement

Yongxi Qian; Vesna Radisic; Tatsuo Itoh

1997-01-01

412

Photonic-band-gap structures and guide modes in two-dimensional magnetic photonic crystal heterostructures  

Microsoft Academic Search

We first investigate the band gap structures of two-dimensional magnetic photonic crystals (MPC) composed of rectangular (square) magnetic cylinders embedded in a host dielectric material in the rectangular (square) lattice, and we then study guide modes at interface of MPC heterostructures (MPCHs) by use of plane wave expansion method in combination with supercell technique. We find that both the mirror-symmetric

Yun-Song Zhou; Ben-Yuan Gu; Fu-He Wang

2003-01-01

413

Nonreciprocal photonic band structure of low-symmetry magnetic photonic crystals  

Microsoft Academic Search

We propose multicomponent magnetic photonic crystals as a basis component for nonreciprocal optical elements. It is shown that introduction of three or more components may provide violation of mirror reflection symmetry, which is a necessary condition for obtaining nonreciprocity in the dispersion of the structure's eigenmodes. Numerical simulations confirm that nonreciprocity indeed develops in the form of nonreciprocal photonic band

Alexander B. Khanikaev; M. J. Steel

2010-01-01

414

Analyzing symmetry in photonic band structure of gyro-magnetic photonic crystals  

Microsoft Academic Search

In the band structure analysis of photonic crystals it is normally assumed that the full photonic gaps could be found by scanning high-symmetry paths along the edges of Irreducible Brillouin Zones (IBZ). We have recently shown [1] that this assumption is wrong in general for sufficiently symmetry breaking geometries, so that the IBZ is exactly half of the complete BZ.

Ali Najafi; Sina Khorasani; Faezeh Gholami

2011-01-01

415

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

416

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

Microsoft Academic Search

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

Kazuo Ogura; Tadashi Kobayashi; Yasunobu Suzuki; Tsuguhiro Watanabe

1996-01-01

417

C-band traveling-wave maser using a slow-wave structure printed on ruby  

Microsoft Academic Search

The described C-band traveling-wave maser utilizes metallized rubies. The slow-wave structure is directly photo-etched on ruby. Among the advantages of this technology are the reduced size and the easy realization of small pitches, resulting in high slowing factors.

B. Loriou; J. L. Jaouen

1967-01-01

418

Analysis of W-band folded waveguide slow-wave structure  

Microsoft Academic Search

Cold characteristics of W-band folded waveguide slow-wave structure used in micro-TWT are analyzed using the electromagnetic software MAFIA, including dispersion relation and coupling impedance. And the simulation results show good agreement with their theory formula analysis. In this paper the on-axis coupling impedance is directly calculated from its definition equation using MAFIA

Jun Cai; Jinjun Feng; Bingyan Li; Fujiang Liao

2005-01-01

419

Photonic band structures of two-dimensional systems containing metallic components  

Microsoft Academic Search

By use of the plane-wave method, we calculate the photonic band structure for electromagnetic waves of E and H polarization propagating in a system consisting of an infinite array of identical, infinitely long, parallel, metal cylinders of circular cross section, embedded in vacuum, whose intersection with a perpendicular plane forms a simple square or triangular lattice. The dielectric function of

V. Kuzmiak; A. A. Maradudin; F. Pincemin

1994-01-01

420

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

421

Correlation between the surface electronic structure and CO-oxidation activity of Pt alloys.  

PubMed

The surface electronic structure and CO-oxidation activity of Pt and Pt alloys, Pt3T (T = Ti, Hf, Ta, Pt), were investigated. At temperatures below 538 K, the CO-oxidation activities of Pt and Pt3T increased in the order Pt < Pt3Ti < Pt3hHf < Pt3Ta. The center-of-gravity of the Pt d-band (the d-band center) of Pt and Pt3T was theoretically calculated to follow the trend Pt3Ti < Pt3Ta < Pt3Hf < Pt. The CO-oxidation activity showed a volcano-type dependence on the d-band center, where Pt3Ta exhibited a maximum in activity. Theoretical calculations demonstrated that the adsorption energy of CO on the catalyst surface monotonically decreases with the lowering of the d-band center because of diminished hybridization of the surface d-band and the lowest-unoccupied molecular orbital (LUMO) of CO. The observed volcano-type correlation between the d-band center and the CO oxidation activity is rationalized in terms of the CO adsorption energy, which counterbalances the surface coverage by CO and the rate of CO oxidation. PMID:25271906

Abe, Hideki; Yoshikawa, Hideki; Umezawa, Naoto; Xu, Ya; Saravanan, Govindachetty; Ramesh, Gubbala V; Tanabe, Toyokazu; Kodiyath, Rajesh; Ueda, Shigenori; Sekido, Nobuaki; Yamabe-Mitarai, Yoko; Shimoda, Masahiko; Ohno, Takahisa; Matsumoto, Futoshi; Komatsu, Takayuki

2015-02-21

422

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

423

Band Structures and Physical Properties of Magnetic Layered Semiconductors MPS3  

NASA Astrophysics Data System (ADS)

The band structures of manganese chalcogeno-phosphate MnPS3 and iron chalcogeno-phosphate FePS3 are calculated self-consistently. From the calculation of the total energies of two types of magnetic structures of MnPS3, the experimentally observed magnetic structure is proved more stable. Furthermore, by comparing the band structures of MPS3 family (M=Mn, Fe, Ni, Zn), it is found that FePS3 and NiPS3 are more active to the Li intercalation than ZnPS3 and MnPS3, and that NiPS3 is the best cathode material in secondary lithium batteries in the MPS3 family.

Kurita, Noriyuki; Nakao, Kenji

1989-02-01

424

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

SciTech Connect

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

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

2014-08-18

425

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

426

Evaluation of the electronic band structure of a new semiconductor ternary using Ge, Si, and Sn  

NASA Astrophysics Data System (ADS)

Developing new Si based devices whose electronic band structure can be controlled by varying the stoichiometry is crucial for technology advancement in compound semiconductors. The ability to engineer the band gap is essential to obtain the optimal performance of a device, however, it can be affected by lattice mismatch, defects, strain, etc. Therefore, based on the success of previous research on the III-V quaternary semiconductors, the electronic properties of a new ternary, Si_xGe_1-x-ySn_y, are being evaluated as an option to decouple the strain and band structure variables in the group IV compounds. The Si_xGe_1-x-ySny alloys with compositions ranging from x=0.13-0.2, and y=0.02-0.08 were grown by UHV-CVD at low temperatures using novel synthetic chemistry. We used deep ultra violet spectroscopic ellipsometry to determine the optical properties of the new group IV ternary. The optical analysis showed that the dielectric function of the SiGeSn has a similar shape compared to Ge or Ge-Sn and that there is a reduction in the E2 critical point energy value which is related to transitions at and near the X-point of the highest valence band and lowest conduction band.

Cook, Candi S.; Zollner, Stefan; Menendez, Jose; Chizmeshya, A. V. G.; Aella, Pavan; Tolle, John; Kouvetakis, John

2003-10-01

427

Evaluation of the electronic band structure of a new semiconductor ternary using Ge, Si, and Sn  

NASA Astrophysics Data System (ADS)

Developing new Si based devices whose electronic band structure can be controlled by varying the stoichiometry is crucial for technology advancement in compound semiconductors. The ability to engineer the band gap is essential to obtain the optimal performance of a device, however, it can be affected by lattice mismatch, defects, strain, etc. Therefore, based on the success of previous research on the III-V quaternary semiconductors, the electronic properties of a new ternary, Si_xGe_1-x-ySn_y, are being evaluated as an option to decouple the strain and band structure variables in the group IV compounds. The Si_xGe_1-x-ySny alloys with compositions ranging from x=0.13-0.2, and y=0.02-0.08 were grown by UHV-CVD at low temperatures using novel synthetic chemistry. We used deep ultra violet spectroscopic ellipsometry to determine the optical properties of the new group IV ternary. The optical analysis showed that the dielectric function of the SiGeSn has a similar shape compared to Ge or Ge-Sn and that there is a reduction in the E2 critical point energy value which is related to transitions at and near the X-point of the highest valence band and lowest conduction band.

Cook, Candi S.; Zollner, Stefan; Menendez, Jose; Chizmeshya, A. V. G.; Aella, Pavan; Tolle, John; Kouvetakis, John

2004-03-01

428

Narrow band filter using 1D periodic structure with defects for DWDM systems  

NASA Astrophysics Data System (ADS)

A 1D binary periodic structure with defect has been analysed using Transfer Matrix Method. For a particular nine layered structure of SiO2 and InP, a number of full stop bands (in other words, zero passbands or forbidden bands) at different regions of the spectrum under investigation are observed. Introducing a central spatial defect in the system by adjusting the layer width, it is possible to achieve an extremely narrow passband centred on 1554.9 nm in the 7th forbidden band. Moreover by varying the defect width, the number of passbands can be increased. These passbands have flat and 100% stopband and hence can be better candidate to drop single or multiple frequencies in WDM systems. It is further observed that with increase in the number of layers and/or defect width, the number of mini pass bands outside the original forbidden band also increases. Also by FDTD simulation it is seen that the field is localised within the defect for the passband frequency.

Ghosh, R.; Ghosh, K. K.; Chakraborty, R.

2013-02-01

429

Design of UWB monopole antenna with dual notched bands using one modified electromagnetic-bandgap structure.  

PubMed

A modified electromagnetic-bandgap (M-EBG) structure and its application to planar monopole ultra-wideband (UWB) antenna are presented. The proposed M-EBG which comprises two strip patch and an edge-located via can perform dual notched bands. By properly designing and placing strip patch near the feedline, the proposed M-EBG not only possesses a simple structure and compact size but also exhibits good band rejection. Moreover, it is easy to tune the dual notched bands by altering the dimensions of the M-EBG. A demonstration antenna with dual band-notched characteristics is designed and fabricated to validate the proposed method. The results show that the proposed antenna can satisfy the requirements of VSWR < 2 over UWB 3.1-10.6?GHz, except for the rejected bands of the world interoperability for microwave access (WiMAX) and the wireless local area network (WLAN) at 3.5?GHz and 5.5?GHz, respectively. PMID:24170984

Liu, Hao; Xu, Ziqiang

2013-01-01

430

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

431

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

432

How membrane surface affects protein structure.  

PubMed

The immediate environment of the negatively charged membrane surface is characterized by decreased dielectric constant and pH value. These conditions can be modeled by water-alcohol mixtures at moderately low pH. Several globular proteins were investigated under these conditions, and their conformational behavior in the presence of phospholipid membranes was determined, as well as under conditions modeling the immediate environment of the membrane surface. These proteins underwent conformational transitions from the native to a molten globule-like state. Increased flexibility of the protein structure facilitated protein functioning. Our experimental data allow understanding forces that affect the structure of a protein functioning near the membrane surface (in other words, in the membrane field). Similar conformational states are widely reported in the literature. This indicates that the negatively charged membrane surface can serve as a moderately denaturing agent in the cell. We conclude that the effect of the membrane field on the protein structure must be taken into account. PMID:25749161

Bychkova, V E; Basova, L V; Balobanov, V A

2014-12-01

433

M-band structure, M-bridge interactions and contraction speed in vertebrate cardiac muscles  

Microsoft Academic Search

Cardiac muscle M-band structures in several mammals (guinea pig, rabbit, rat and cow) and also from three teleosts (plaice, carp and roach), have been studied using electron microscopy and image processing. Axial structure seen in negatively stained isolated myofibrils or negatively stained cryo-sections shows the presence of five strong M-bridge lines (M6, M4, M1, M4' and M6') except in the

H. T. Pask; K. L. Jones; P. K. Luther; J. M. Squire

1994-01-01

434

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

435

Band Structure Calculations for Two-Dimensional Plasma Photonic Crystals in Honeycomb Lattice Arrangement  

Microsoft Academic Search

We propose an approach originating from plane wave expansion method to calculate band structure for two types of honeycomb lattice two-dimensional plasma photonic crystals. The eigenvalue equations of E-polarization for two types of structures, which depend on the honeycomb lattice realization(plasma rods immersed in dielectric background or vice versa), are derived respectively. A standard linearization technique which solves the general

Xiang-Kun Kong; Shao-Bin Liu; Hai-Feng Zhang; Liang Zhou; Chun-Zao Li

2011-01-01

436

X-band coupled cavity slow wave structure of the traveling wave tube for airborne application  

Microsoft Academic Search

The paper describes the design of the conduction cooling X-band coupled cavity traveling wave tube (CC-TWT) based on the Hughes staggered slots slow wave structure (SWS) which was the first tube of this type made in the Wroclaw Division of PIT. A project of LO-700W traveling wave tube required solving various structural and technological problems e.g. effective termination based on

Waldemar Wiejak

2010-01-01

437

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

438

Semi-empirical dielectric descriptions of the Bethe surface of the valence bands of condensed water  

NASA Astrophysics Data System (ADS)

The Bethe surface of a material is an essential element in the study of inelastic scattering at low impact energies where the optical approximation fails. In this work we examine various semi-empirical models for the dielectric response function of condensed water towards an improved description of the energy-loss function over the whole energy-momentum plane (i.e. Bethe surface). The experimental "optical" data (i.e. at zero momentum transfer) for the valence bands of liquid and solid water are analytically represented by a sum-rule constrained linear combination of Drude-type functions. The dependence on momentum transfer is introduced through various widespread "extension" schemes which are compared against the available Compton scattering data. It is shown that the widely used Lindhard function along with its "single-pole" (or " ?-oscillator") approximation used in the Penn and Ashley models, as well as the Ritchie and Howie extended-Drude scheme with a simple quadratic dispersion, predict a sharp Bethe ridge which compares poorly with the experimental profile. In contrast, the Mermin dielectric function provides a more realistic account of the observed broadening with momentum transfer. An improved fully-extended-Drude model is presented which incorporates the momentum broadening and line-shift of the Bethe ridge and distinguishes between the different dispersion of the discrete and continuum spectra of water.

Emfietzoglou, D.; Abril, I.; Garcia-Molina, R.; Petsalakis, I. D.; Nikjoo, H.; Kyriakou, I.; Pathak, A.

2008-04-01

439

The coherent structure of atmospheric surface layers  

NASA Astrophysics Data System (ADS)

The structure of two-point correlation statistics in the atmospheric surface layer are studied from measurements on the western Utah salt flats at the SLTEST facility. Large-scale features in the stable, neutral and unstable surface layers that adhere to Monin-Obukhov similarity (-10structure inclination angle. Both streamwise and spanwise integral length scales show consistent logarithmic trends that increase with decreasing stability. Further, the structure inclination angle in the wall-normal plane also shows a logarithmic increase with increasing -z/? for the unstable surface layers. The changes in structure of Ruu can be characterized by z/? making it feasible to incorporate the trends in near-wall models of LES of atmospheric flows under stable and unstable conditions.

Chauhan, Kapil; Hutchins, Nick; Marusic, Ivan; Monty, Jason

2010-11-01

440

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

441

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

442

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

443

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

444

Band structure and itinerant magnetism in quantum critical NbFe2  

SciTech Connect

We report first-principles calculations of the band structure and magnetic ordering in the C14 Laves phase compound NbFe{sub 2}. The magnetism is itinerant in the sense that the moments are highly dependent on ordering. We find an overestimation of the magnetic tendency within the local spin-density approximation, similar to other metals near magnetic quantum critical points. We also find a competition between different magnetic states due to band-structure effects. These lead to competing magnetic tendencies due to competing interlayer interactions, one favoring a ferrimagnetic solution and the other an antiferromagnetic state. While the structure contains Kagome lattice sheets, which could, in principle, lead to strong magnetic frustration, the calculations do not show dominant nearest-neighbor antiferromagnetic interactions within these sheets. These results are discussed in relation to experimental observations.

Subedi, A. P. [University of Tennessee, Knoxville (UTK); Singh, David J [ORNL

2010-01-01

445

Transport and band structure studies of crystalline ZnRh2O4  

SciTech Connect

We report the synthesis and characterization of non-d{sup 10} p-type transparent conducting oxides of the normal spinel ZnRh{sub 2}O{sub 4}. Undoped ZnRh{sub 2}O{sub 4} was successfully prepared by means of bulk solid-state synthesis. The conduction mechanism and bulk defect chemistry of polycrystalline sintered pellets of ZnRh{sub 2}O{sub 4} were studied through electrical conductivity and Seebeck coefficient measurements, in defect equilibrium at elevated temperature under controlled atmospheres. Optical diffuse reflectance measurements were also carried out to evaluate band gap. The data were analyzed in terms of an activated mobility (small polaron conduction), with a hopping energy of 0.25 eV. Results from band structure calculations by LDA+U and optical band-gap measurement by UV-visible spectrometry are in good agreement with literature data.

Mansourian-Hadavi, Negar; Wansom, Supaporn; Perry, Nicola H.; Nagaraja, Arpun R.; Mason, Thomas O.; Ye, Lin-hui; Freeman, Arthur J.

2010-01-01

446

Band gap and electronic structure of MgSiN{sub 2}  

SciTech Connect

Density functional theory calculations and electron energy loss spectroscopy indicate that the electronic structure of ordered orthorhombic MgSiN{sub 2} is similar to that of wurtzite AlN. A band gap of 5.7?eV was calculated for both MgSiN{sub 2} (indirect) and AlN (direct) using the Heyd-Scuseria-Ernzerhof approximation. Correction with respect to the experimental room-temperature band gap of AlN indicates that the true band gap of MgSiN{sub 2} is 6.2?eV. MgSiN{sub 2} has an additional direct gap of 6.3?eV at the ? point.

Quirk, J. B., E-mail: james.quirk09@imperial.ac.uk; Råsander, M.; McGilvery, C. M.; Moram, M. A. [Department of Materials, Imperial College London, Exhibition Road, London SW7 2AZ (United Kingdom); Palgrave, R. [Department of Chemistry, University College London, Gordon Street WC1H 0AJ (United Kingdom)

2014-09-15

447

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

448

Band structure and transport properties of carbon nanotubes using a local pseudopotential and a transfer-matrix technique  

Microsoft Academic Search

In order to address the band-structure and transport properties of carbon nanotubes, we build a local pseudopotential from the requirement that results relevant to the ?-bands of simple hexagonal graphite and isolated graphene sheets are reproduced. We then apply a transfer-matrix technique to compute the band structure and conductance of the (10,0), (5,5), (10,10), (15,15) and (10,10)@(15,15) carbon nanotubes. We

A. Mayer

2004-01-01

449

Band-structure calculations for the 3d transition metal oxides in GW  

NASA Astrophysics Data System (ADS)

Many-body GW calculations have emerged as a standard for the prediction of band gaps, band structures, and optical properties for main-group semiconductors and insulators, but it is not well established how predictive the GW method is in general for transition metal (TM) compounds. Surveying the series of 3d oxides within a typical GW approach using the random-phase approximation reveals mixed results, including cases where the calculated band gap is either too small or too large, depending on the oxidation states of the TM (e.g., FeO/Fe2O3, Cu2O/CuO). The problem appears to originate mostly from a too high average d-orbital energy, whereas the splitting between occupied and unoccupied d symmetries seems to be reasonably accurate. It is shown that augmenting the GW self-energy by an attractive (negative) and occupation-independent on-site potential for the TM d orbitals with a single parameter per TM cation can reconcile the band gaps for different oxide stoichiometries and TM oxidation states. In Cu2O, which is considered here in more detail, standard GW based on wave functions from initial density or hybrid functional calculations yields an unphysical prediction with an incorrect ordering of the conduction bands, even when the magnitude of the band gap is in apparent agreement with experiment. The correct band ordering is restored either by applying the d-state potential or by iterating the wave functions to self-consistency, which both have the effect of lowering the Cu-d orbital energy. While it remains to be determined which improvements over standard GW implementations are needed to achieve an accurate ab initio description for a wide range of transition metal compounds, the application of the empirical on-site potential serves to mitigate the problems specifically related to d states in GW calculations.

Lany, Stephan

2013-02-01

450

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

451

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