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1

Magnon band structure and magnon density in one-dimensional magnonic crystals

By using Callen's Green's function method and the Tyablikov and Anderson-Callen decoupling approximations, we systematically study the magnon band structure and magnon density perpendicular to the superlattice plane of one-dimensional magnonic crystals, with a superlattice consisting of two magnetic layers with ferromagnetic (FM) or antiferromagnetic (AFM) interlayer exchange coupling. The effects of temperature, interlayer coupling, anisotropy and external magnetic field on the magnon-energy band and magnon density in the Kx-direction are investigated in three situations: a) the magnon band of magnetic superlattices with FM interlayer coupling, b) separate and c) overlapping magnon bands of magnetic superlattices with AFM interlayer coupling. In the present work, a quantum approach is developed to study the magnon band structure and magnon density of magnonic crystals and the results are beneficial for the design of magnonic-crystal waveguides or gigahertz-range spin-wave filters.

Qiu, Rong-ke; Huang, Te; Zhang, Zhi-dong

2014-11-01

2

The electronic and optical properties of the oligomers of poly(para-phenylene) (PPP) in their crystalline phases are calculated. In particular, the 2-, 3-, 4-, and the technically most important 6-unit oligomer para-hexaphenylene (6P) are considered. The electronic band structures are compared with the corresponding molecular orbitals in isolated molecules and the effect of intermolecular interactions is discussed. Connections between previous studies on the band structure of three-dimensional PPP and the present work are established. From the quasiparticle band structures the dielectric tensors are calculated and discussed also with respect to the corresponding transitions in the isolated molecules.

Puschnig, Peter; Ambrosch-Draxl, Claudia

1999-09-01

3

Energy band structure of osmium

International Nuclear Information System (INIS)

The energy band structure of hexagonal-close-packed osmium metal has been calculated using non-relativistic Augmented Plane Wave (APW) method. The muffin-tin potential is computed using Liberman's atomic charge densities and Kohn-Sham exchange approximation. The density of states and heat capacity are calculated and compared with experimental data. The results are compared with earlier theoretical calculations of Jepson et al and Iyakutti et al. (author)

4

Hybrid density functional theory study of Cu(In1?xGaxSe2 band structure for solar cell application

Directory of Open Access Journals (Sweden)

Full Text Available Cu(In1?xGaxSe2 (CIGS alloy based thin film photovoltaic solar cells have attracted more and more attention due to its large optical absorption coefficient, long term stability, low cost and high efficiency. However, the previous theoretical investigation of this material with first principle calculation cannot fulfill the requirement of experimental development, especially the accurate description of band structure and density of states. In this work, we use first principle calculation based on hybrid density functional theory to investigate the feature of CIGS, with B3LYP applied in the CuIn1?xGaxSe2 stimulation of the band structure and density of states. We report the simulation of the lattice parameter, band gap and chemical composition. The band gaps of CuGaSe2, CuIn0.25Ga0.75Se2, CuIn0.5Ga0.5Se2, CuIn0.75Ga0.25Se2 and CuInSe2 are obtained as 1.568 eV, 1.445 eV, 1.416 eV, 1.275 eV and 1.205 eV according to our calculation, which agree well with the available experimental values. The band structure of CIGS is also in accordance with the current theory.

Xu-Dong Chen

2014-08-01

5

Hybrid density functional theory study of Cu(In1-xGax)Se2 band structure for solar cell application

Cu(In1-xGax)Se2 (CIGS) alloy based thin film photovoltaic solar cells have attracted more and more attention due to its large optical absorption coefficient, long term stability, low cost and high efficiency. However, the previous theoretical investigation of this material with first principle calculation cannot fulfill the requirement of experimental development, especially the accurate description of band structure and density of states. In this work, we use first principle calculation based on hybrid density functional theory to investigate the feature of CIGS, with B3LYP applied in the CuIn1-xGaxSe2 stimulation of the band structure and density of states. We report the simulation of the lattice parameter, band gap and chemical composition. The band gaps of CuGaSe2, CuIn0.25Ga0.75Se2, CuIn0.5Ga0.5Se2, CuIn0.75Ga0.25Se2 and CuInSe2 are obtained as 1.568 eV, 1.445 eV, 1.416 eV, 1.275 eV and 1.205 eV according to our calculation, which agree well with the available experimental values. The band structure of CIGS is also in accordance with the current theory.

Chen, Xu-Dong; Chen, Lin; Sun, Qing-Qing; Zhou, Peng; Zhang, David Wei

2014-08-01

6

Energy Technology Data Exchange (ETDEWEB)

Highlights: ? ZrGa{sub 2} and ZrGa{sub 3} crystals structure was analyzed. ? FP-LAPW method was used to solve the Kohn Sham DFT equations within the framework of the WIEN2K code. ? Electronic band structures are reported. ? The studied crystals exhibit potential optoelectronic applications. -- Abstract: Using FP-LAPW Method we have performed calculations of the band structure of the ZrGa{sub 2} and ZrGa{sub 3} crystals. The all-electron full potential linearized augmented plane wave method was used to solve the Kohn Sham DFT equations. We have explored different approximations using three kinds of exchange-correlation potentials on the electronic structure and we concluded that there is insignificant influence on the band structure and the density of states. It is clear that there exists a difference in the band dispersion with one move from ZrGa{sub 2} to ZrGa{sub 3} that is attributed to the fact that ZrGa{sub 2} has four formula per unit cell (Z = 4) while ZrGa{sub 3} has two formula per unit cell (Z = 2). Despite some similarity in the crystallochemistry of ZrGa{sub 2} to ZrGa{sub 3} some differences are observed in the band structure dispersion. There is a strong hybridization between the states. The interaction of charges between Zr and Ga atoms is due to the strong hybridization, and the covalent bond arises due to the degree of hybridization. Hence, there is a strong covalent bonding between these atoms. We have obtained a space electron charge density distribution in the average unit cell by calculations of the electron charge density distribution. The space electronic charge density contour distribution is illustrated in (1 0 0) and (1 1 0) planes.

Reshak, A.H., E-mail: maalidph@yahoo.co.uk [Institute of Complex systems, FFPW, CENAKVA, University of South Bohemia in CB, Nove Hrady 37333 (Czech Republic); School of Material Engineering, Malaysia University of Perlis, P.O Box 77, d/a Pejabat Pos Besar, 01007 Kangar, Perlis (Malaysia); Lakshminarayana, G., E-mail: glnphysics@rediffmail.com [Materials Science and Technology Division (MST-7), Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Ebothe, J. [Laboratoire de Recherche en Nanosciences, E.A. 4682, Université de Reims, 21, rue Clément Ader, 51685 Reims cedex 02 (France); Fedorchuk, A.O. [Lviv National University of Veterinary Medicine and Biotechnologies, Department of Inorganic and Organic Chemistry, Lviv (Ukraine); Fedyna, M.F. [National University of Forestry and Wood Technology of Ukraine Chuprynky Str., 103, 79057 Lviv (Ukraine); Kamarudin, H. [School of Material Engineering, Malaysia University of Perlis, P.O Box 77, d/a Pejabat Pos Besar, 01007 Kangar, Perlis (Malaysia); Mandracci, P. [Politecnico di Torino, Department of Applied Science and Technology, corso Duca degli Abruzzi 24, 10129, Torino (Italy); Auluck, S. [Council of Scientific and Industrial Research - National Physical Laboratory Dr. K.S. Krishnan Marg, New Delhi 110012 (India)

2013-04-15

7

All-electron first-principles total energy electronic structure calculations were carried out for single chains of four nucleotide base stacks (composed of adenine, thymine, guanine, and cytosine, respectively) in the DNA B conformation (3.36 Å stacking distance and 36° screw angle ?) using the local-density approximation (LDA) within a helical band structure approach. A uracil stack was also computed in the DNA B conformation and compared with the results obtained for the four DNA base stacks. The total energies per unit cell as a function of the stacking distance (at fixed screw angle ?=36°) and of the screw angle (at d=3.36 Å) show in most cases rather good agreement with the experiment. As expected with LDA calculations, the band gaps were underestimated by nearly 50% compared to experimentally suggested values. Finally, some suggestions are given for the improvement of the band structures of the nucleotide base stacks.

Zhang, M.-L.; Miao, M. S.; Van Doren, V. E.; Ladik, J. J.; Mintmire, J. W.

1999-11-01

8

All-electron first-principles total energy electronic structure calculations were carried out for single chains of four nucleotide base stacks (composed of adenine, thymine, guanine, and cytosine, respectively) in the DNA B conformation (3.36Åstacking distance and 36 deg screw angle) using the local-density approximation within a helical band structure approach. A uracil stack was also computed in the DNA B conformation and compared with the results obtained for the four DNA base stacks. The total energies per unit cell as a function of the stacking distance (at fixed screw angle =36 deg) and of the screw angle (at d=3.36Åshow in most cases rather good agreement with the experiment. As expected with LDA calculations, the band gaps were underestimated by nearly 50some suggestions are given for the improvement of the band structures of the nucleotide base stacks.

Zhang, Ming-Liang; Miao, Mao Sheng; van Doren, Victor. E.; J. J. Ladik Collaboration; J. W. Mintmire Collaboration

2000-03-01

9

Using first-principles theoretical techniques within density functional theory and many-body perturbation theory we investigated the structural and electronic properties of two LiInSe2 crystal modifications, orthorhombic (?-NaFeO2-type) and tetragonal (CuFeS2-type), focusing on the interband transitions and band gaps. It is found that the Tran-Blaha (TB09) functional predicts LiInSe2 to be a direct-gap semiconductor with a significantly larger band gap as compared with that from common local-density and gradient-corrected functionals. The most accurate values of the fundamental energy gaps are calculated within quasiparticle GW approximation and found to be 2.95 eV for the orthorhombic phase and 2.85 eV for the tetragonal one, with equal pressure coefficients of 63 meV/GPa. Our theoretical results eliminate the uncertainty in the band gap of LiInSe2. Moreover, the data obtained define the upper limit of the band gap of solid solutions (Cu,Li)InSe2 and (Ag,Li)InSe2, which can be of interest for applications in optoelectronics.

Kosobutsky, A. V.; Basalaev, Yu. M.

2014-12-01

10

Band structure in adaptive curvilinear coordinates

International Nuclear Information System (INIS)

The recently introduced adaptive-coordinate electronic-structure formalism is extended to finite Bloch wave vectors to permit band-structure calculations and more accurate Brillouin-zone sampling in structural energy calculations. Coordinates adapted to minimize the energy of the occupied states are shown to yield an accurate band structure for diamond far up into the conduction bands by comparison with linear augmented plane-wave results. Adaptive coordinate results for the structural properties and charge density of diamond are also reported

11

Energy Technology Data Exchange (ETDEWEB)

High resolution angle-resolved photoemission of quasi-2D KMo{sub 6}O{sub 17} purple bronze has been performed in the range from room temperature to 130 K, slightly above the charge density wave (CDW) transition (T{sub c} = 110 K), and down to 35 K (well below T{sub c}). In this paper we report a detailed study of how electronic band structure is affected by this transition driven by the hidden nesting scenario. The expected spectroscopic fingerprints of the CDW phase transition have been found and discussed according to the hidden one dimension and the development of a quasi-commensurate CDW. The excellent agreement between theory and our experimental results makes of potassium purple bronze a reference system for studying this type of instabilities.

Valbuena, M A [Instituto de Ciencia de Materiales de Madrid, CSIC, 28049 Madrid (Spain); Avila, J; Asensio, M C [Synchrotron SOLEIL, L' Orme des Merisiers, Saint-Aubin, B.P. 48, 91192 Gif-sur-Yvette Cedex (France); Vyalikh, D V; Laubschat, C; Molodtsov, S L [Institut fuer Festkoerperphysik, Technische Universitaet Dresden, D-01062 Dresden (Germany); Guyot, H [LEPES, CNRS, BP 166, 38042 Grenoble Cedex 9 (France)], E-mail: mvbuena@icmm.csic.es

2008-03-15

12

Band structures of zirconium hydrides

International Nuclear Information System (INIS)

The band structures of zirconium hydride compounds are calculated using the APW method. By comparing the bands for a hypothetical f.c.c. compound ZrH0 with f.c.c. ZrH2 (corresponding to the delta-phase), it is shown that the hydrogen atoms give rise to a new 'bonding' band below the Fermi level. The band structures of two interstitial hydrogen h.c.p. compounds ZrHsub(0.5) and ZrH (?-phase) are also calculated. For ZrHsub(0.5)with two Zr atoms and one H atom in the primitive unit cell no new bands are formed. For ZrH with two Zr atoms and two H atoms in the primitive unit cell a new band is formed just below the Fermi level but the band structure is similar to that of ZrHsub(0.5) and ?-Zr with the Fermi level raised. Estimates of the total energies show that the band structure contributions favour formation of f.c.c. ZrH2 (corresponding to the delta-phase) over an interstitial ?-phase, as is observed experimentally. (author)

13

Electronic band structure of beryllium oxide

The energy-momentum resolved valence band structure of beryllium oxide has been measured by electron momentum spectroscopy (EMS). Band dispersions, bandwidths and intervalence bandgap, electron momentum density (EMD) and density of occupied states have been extracted from the EMS data. The experimental results are compared with band structure calculations performed within the full potential linear muffin-tin orbital approximation. Our experimental bandwidths of 2.1 +- 0.2 and 4.8 +- 0.3 eV for the oxygen s and p bands, respectively, are in accord with theoretical predictions, as is the s-band EMD after background subtraction. Contrary to the calculations, however, the measured p-band EMD shows large intensity at the GAMMA point. The measured full valence bandwidth of 19.4 +- 0.3 eV is at least 1.4 eV larger than the theory. The experiment also finds a significantly higher value for the p-to-s-band EMD ratio in a broad momentum range compared to the theory.

Sashin, V A; Kheifets, A S; Ford, M J

2003-01-01

14

International Nuclear Information System (INIS)

Heavily boron-doped p-type diamond is a key material for developing diamond-based applications in various fields. We obtain information about changes in the valence band edge of homoepitaxial boron-doped diamond films around and below Mott's critical density for a metal-non-metal transition. For a boron concentration of about 2-3 x 1020 cm-3, where this transition is expected to occur, a metal-like behaviour is observed at room temperature (RT) with the Fermi-level lying 0.1 eV above the valence band edge. For a boron concentration about 4 x 1019 cm-3, which is well below the critical density, the valence band edge is quite different from that of lightly doped samples. It is proposed as an explanation for these experimental differences that the excited-states of acceptors overlap. (Abstract Copyright [2009], Wiley Periodicals, Inc.)

15

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

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

2014-10-01

16

Electronic band structure and properties of ?-U

International Nuclear Information System (INIS)

We present some results of a detailed study of the electronic band structure and some physical properties of orthorhombic uranium using a relativistic version of the LAPW method. Total and projected (by orbital angular momentum) densities of states are used to discuss the photo-emission data of Veal and Lam. The Fermi surfaces of the dominant 6th and 7th bands are found to have high symmetry (and some nesting features) of interest to dHvA measurements being pursued by Arko and Schirber. The theoretical magnetic field induced neutron form factor is found to be in good agreement with the measurement of Maglic et al

17

Band structure and nuclear dynamics

International Nuclear Information System (INIS)

The relation between the Variable Moment of Inertia model and the Interacting Boson Model are discussed from a phenomenological viewpoint. New results on ground state mean-square radii in nuclei far from stability are reported, and a discussion of band structure extending to high angular momentum states and methods of extracting information on the underlying dynamics is given

18

International Nuclear Information System (INIS)

Nuclei in the A ? 100 mass region exhibit a wide variety of nuclear shapes ranging from spherical to highly deformed. High spin states in deformed odd-odd nuclei in the rare-earth are of utmost important during the recent past because of observation of a number of interesting phenomena. Investigations have revealed diversity in band structures. The present work reports in-beam ?-ray spectroscopic measurements to study level structures in 96Ru nucleus

19

Energy Technology Data Exchange (ETDEWEB)

Heavily boron-doped p-type diamond is a key material for developing diamond-based applications in various fields. We obtain information about changes in the valence band edge of homoepitaxial boron-doped diamond films around and below Mott's critical density for a metal-non-metal transition. For a boron concentration of about 2-3 x 10{sup 20} cm{sup -3}, where this transition is expected to occur, a metal-like behaviour is observed at room temperature (RT) with the Fermi-level lying 0.1 eV above the valence band edge. For a boron concentration about 4 x 10{sup 19} cm{sup -3}, which is well below the critical density, the valence band edge is quite different from that of lightly doped samples. It is proposed as an explanation for these experimental differences that the excited-states of acceptors overlap. (Abstract Copyright [2009], Wiley Periodicals, Inc.)

Takeuchi, D.; Ogura, M.; Tokuda, N.; Okushi, H. [Energy Technology Research Institute (ETRI), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki (Japan); Yamasaki, S. [Energy Technology Research Institute (ETRI), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki (Japan); Graduate School of Pure and Applied Science, University of Tsukuba, Tsukuba, Ibaraki (Japan)

2009-09-15

20

Band Structure of New ReFeAsO Superconductors

Directory of Open Access Journals (Sweden)

Full Text Available We investigate the band structure of Fe-based superconductors using the first-principle method of density-functional theory. We calculated the band structure and the density of states at the Fermi level for ReFeAsO (Re = Sm, Er superconductors. Our calculations indicate that the maximum critical superconducting transition temperature Tc will be observed for compounds with Sm and Er at 55 and 46 K, respectively.

Hyun-Tak Kim

2013-05-01

21

International Nuclear Information System (INIS)

High spin states of 118Xe have been investigated by means of ? ray spectroscopy using the 92Mo(29Si,2pn) at a bombarding energy of 110 MeV. Several new side bands as well as the yrast band were established. A band crossing between the ground state and super bands was observed at ??c = 0.39 MeV. A negative parity band with two quasi particle excitation, and a quasi ? band were also identified. (orig.)

22

Electronic structures of narrow-band materials

International Nuclear Information System (INIS)

This thesis investigates the electronic structures of narrow-band actinide, rare earth, and transition metal materials, using the experimental techniques of photoemission (PES) and inverse photoemission (BIS) spectroscopy. Narrow-band materials exhibit many interesting phenomena such as mixed-valence, heavy-fermion properties, and high temperature superconductivity. This is primarily due to the correlated narrow band electrons and their interaction with conduction or valence band electrons. The theoretical characterization of the electronic structures of a many body system is the spectral weight of the single particle Green's function. The spectral weight of narrow band electrons is determined by measuring the PES/BIS spectrum, the spectrum to remove and add electrons. For Ce compounds, the impurity Anderson Hamiltonian can describe both the ground state properties and the 4f spectrum. In this description, the low-energy properties are determined by a low-energy scale set by the Kondo temperature, which characterizes spin fluctuations. To make a detailed test of this picture, the Ce 3d and 4f spectra are measured and analyzed using this model for Ce(Ru1-xRhx)3B2 and CeCu2Si2. The spectral change during the ?-? phase transition of Ce0.7Th0.3 has been analyzed. The Yb 4f spectrum of YbAl3 is measured and analyzed by applying the impurity Anderson Hamiltonian calculations for Ce to Yb with an electron-hole mapping. The author has studied the 4f spectra of heavy-fermion compounds, YbXCu4, with X = Ag, Au, and Pd. The 5f spectra of uranium materials do not resemble the Ce 4f spectra, in having much more f-weight around EF. However, the measured 5f width of the heavy fermion uranium materials exceeds the 5f width obtained from the local density functional calculations

23

Band structure of W and Mo by empirical pseudopotential method

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

24

Density measurements in air by optically exciting the Cordes bands of I2

We describe an optical method based on laser-induced fluorescence for obtaining instantaneous measurements of density along a line in low-density air seeded with I2 . The Cordes bands of I2 (D 1 icons/Journals/Common/Sigma" ALT="Sigma" ALIGN="TOP"/> u + icons/Journals/Common/leftarrow" ALT="leftarrow" ALIGN="TOP"/> X 1 icons/Journals/Common/Sigma" ALT="Sigma" ALIGN="TOP"/> g + ) are excited with a tunable ArF excimer laser. Air densities in the range (0.1 - 6.5) × 1017 cm-3 are measured over 295 - 583 K using the density-dependent emission ratio of two emission bands of I2 ; the 340 nm bands and the diffuse-structured McLennan bands near 320 nm.

Balla, R. Jeffrey; Exton, Reginald J.

2000-05-01

25

Asymmetry gap in the electronic band structure of bilayer graphene

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 the bilayer, resulting in a potential difference between the layers and a density dependent gap $\\Delta (n)$. We discuss the influence of a finite asymmetry gap $\\Delta (0)$ at zero excess density, caused by the screening of an additional transverse electric field, on observations of the quantum Hall effect.

McCann, E

2006-01-01

26

High spin band structures in 104Cde

International Nuclear Information System (INIS)

High spin states in 104Cd have been investigated by means of heavy ion induced reactions using the Nordball detector array. The level scheme constructed from ??-coincidences is dominated by three band structures. The positive parity band shows no rotational like energy spacing. It is thus understood mostly in terms of quasiparticle excitations with ?d5/2, ?g7/2 and ?g9/2 configurations. The collective properties of the negative parity bands are more pronounced. These bands are most likely due to ?(h11/2,d5/2) and ?(h11/2,g7/2) structures. (orig.)

27

Wilson Fermions at Finite Density as a Band Theory

We analyze the feasibility of using Wilson fermions at finite density to study the physics of conduction electrons in band theory. We only include the interaction of the fermions with an external electromagnetic field. We study properties such as the density of states or the electric conductivity, both by analytical means and with numerical methods based on a path-integral formalism, finding a nice agreement. The numerical methods are generalizable to systems with dynamical interactions.

Alonso, J L; Martín-Mayor, V

2000-01-01

28

Photonic band structures of quadrangular multiconnected networks

International Nuclear Information System (INIS)

By means of the network equation and generalized dimensionless Floquet–Bloch theorem, this paper investigates the properties of the band number and width for quadrangular multiconnected networks (QMNs) with a different number of connected waveguide segments (NCWSs) and various matching ratio of waveguide length (MRWL). It is found that all photonic bands are wide bands when the MRWL is integer. If the integer attribute of MRWL is broken, narrow bands will be created from the wide band near the centre of band structure. For two-segment-connected networks and three-segment-connected networks, it obtains a series of formulae of the band number and width. On the other hand, it proposes a so-called concept of two-segment-connected quantum subsystem and uses it to discuss the complexity of the band structures of QMNs. Based on these formulae, one can dominate the number, width and position of photonic bands within designed frequencies by adjusting the NCWS and MRWL. There would be potential applications for designing optical switches, optical narrow-band filters, dense wavelength-division-multiplexing devices and other correlative waveguide network devices. (classical areas of phenomenology)

29

Band structure of superlattice with ?-like potential

International Nuclear Information System (INIS)

Band structure of superlattice with ?-like potential has been calculated taking into account interaction of carriers of different kinds. Superlattices of semiconductors with degenerated valence band and zero-gap semiconductors have been considered. For the latter semimetal-semiconductor transition has been obtained. (author). 8 refs, 1 fig

30

Electronic energy band structure of osmium metal

International Nuclear Information System (INIS)

The non-relativistic energy band calculation of osmium metal with Kolin-Sham exchange gives fairly well the relative positions of different peaks in the density of states curve. In order to have a good agreement with the electronic specific heat and conduction band peak positions with respect to the Fermi energy, the Fermi energy is to be shifted to the higher energy side. Results are compared with earlier theoretical and experimental data

31

Band structure of boron doped carbon nanotubes

We present {\\it ab initio} and self-consistent tight-binding calculations on the band structure of single wall semiconducting carbon nanotubes with high degrees (up to 25 %) of boron substitution. Besides a lowering of the Fermi energy into the valence band, a regular, periodic distribution of the p-dopants leads to the formation of a dispersive ``acceptor''-like band in the band gap of the undoped tube. This comes from the superposition of acceptor levels at the boron atoms with the delocalized carbon $\\pi$-orbitals. Irregular (random) boron-doping leads to a high concentration of hybrids of acceptor and unoccupied carbon states above the Fermi edge.

Wirtz, L; Wirtz, Ludger; Rubio, Angel

2003-01-01

32

Superconductivity in two-band system with low carrier density

This article is a review of the autor's papers, containing a theory of superconductivity, wich is constructed for systems with two overlapping energy bands at the Fermi surface and with arbitrary charge carrier density.There is taken into account all possible kinds of electron pairing within each band and of electron pairing from different bands. A bell-shape dependence of superconducting-transition temperature $T_c$ on the electron density, and have demonstrated a possible onset of HTSC. The absolute and relative jumps of the electron heat capacity $(C_S - C_N)$ and $(C_S - C_N) / C_N$ at the point $T = T_c$ have been calculated and the density dependence of these quantities have been demonstrated. The theory yields both small values $(C_S - C_N) / C_N 1,43$. Favorable conditions have been manifested for an experimental observation of a bend on the chemical-potential plot $\\mu (T)$ at point $T = T_c$. An application of the path integral method to the two-band model is developed and on this basis, the proces...

Palistrant, M E

2003-01-01

33

Structure of rotational bands in 253No

International Nuclear Information System (INIS)

In-beam gamma-ray and conversion electron spectroscopic studies have been performed on the 253 No nucleus. A strongly coupled rotational band has been identified and the improved statistics allows an assignment of the band structure as built on the 9/2-[734]? ground state. The results agree with previously known transition energies but disagree with the tentative structural assignments made in earlier work. (orig.)

34

Photonic band structure and omnidirectional band gap in anisotropic superlattice

Energy Technology Data Exchange (ETDEWEB)

We investigate theoretically the photonic band structure of one-dimensional superlattices (SL) composed of alternating anisotropic layers with their principal axes oriented at arbitrary directions. The dispersion relation of second order is calculated analytically by using the 4 x 4 matrix method which is based on the boundary conditions of the electric and magnetic fields at each interface. It is shown that such structures can exhibit coupled electromagnetic modes between transverse magnetic TM and transverse electric TE modes, and dispersion curves that do not exist in superlattices composed only of isotropic layers. For a given value of the wave vector k {sub ?} (parallel to the layers), the dispersion curves (frequency ?) versus k {sub B} (where k {sub B} is the Bloch wave vector of the periodic system along the axis of the superlattice) are illustrated. Specific applications of these results are given for the case of the biaxial superlattice. We show that with an appropriate choice of the superlattice parameters an absolute (or omnidirectional) band gap for these coupled electromagnetic waves can be obtained. The band gap width depends on the anisotropic parameters of the media forming the SL. (author)

Ouchani, N.; Bria, D.; Nougaoui, A. [Laboratoire de Dynamique et d' Optique des Materiaux, Departement de Physique, Faculte des Sciences, Universite Mohamed I, B.P. 524, 60000 Oujda (Morocco); Djafari-Rouhani, B. [Laboratoire de Dynamique et Structure des Materiaux Moleculaires, UMR CNRS 8024, UFR de Physique, Universite de Lille 1, 59655 Villeneuve d' Ascq (France)

2006-06-15

35

Electronic band structure and phonons in V2O5

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

Bhandari, Churna; Lambrecht, Walter R. L.

2013-03-01

36

Band-Structure of Thallium by the LMTO Method

DEFF Research Database (Denmark)

The relativistic band structure of thallium has been calculated using the linear muffin-tin orbital (LMTO) method. The positions and extents of the bands were found to follow the Wigner-Seitz rule approximately, and the origin of the dispersion of the bands was established from the canonical s and p bands for the HCP structure. Energy bands have been evaluated both with and without spin-orbit coupling which is particularly large in thallium. Energy bands close to the Fermi level were found to be mainly 6p like in character. The 6s states lay below the 6p bands and were separated from them by an energy gap. The 6d and 7s bands were found to be far above the Fermi level and the 5d states were found to be far below it. Fermi surface properties and the electronic specific heat are computed and compared with experiment. The joint density of states has also been computed and is in reasonable agreement with experimental optical properties.

Skriver, Hans Lomholt

1977-01-01

37

Band structure of chalcogenides under high pressure

The indirect energy gaps of NaCl-,CsCl-, and pyrite-structured chalcogenides are determined at high pressures using absorption spectroscopy. NaCl-structured CdS and CdSe are measured to approximately 55 GPa and 42 GPa, respectively. Band calculations using pseudopotentials and density functional theory are conducted on CdS as a function of pressure. The shift in the energy gap of CdS with pressure (dEsb{gap}/dP), is experimentally determined to be -5.7(6) × 10sp{-3} eV/GPa, in good agreement with the theoretical calculation of -5.6 × 10sp{-3} eV/GPa. The pressure dependence of the gap of CdSe is measured to be -4.0(2) × 10sp{-3} eV/GPa. We estimate the metallization pressures of NaCl-structured CdS and CdSe to be about 250 and 150 GPa, respectively. The energy gaps of CsCl-structured BaS and CaSe are measured from approximately 19 to 41 GPa and 39 GPa and 53 GPa, respectively. Band-structure calculations using density functional theory and quasiparticle correction are conducted on BaS and CaSe as a function of pressure. The measured gaps of BaS and CaSe shift linearly with pressure with a slope (dEsb{gap}/dP) of -1.8(3) × 10sp{-2} and -1.4(6) × 10sp{-3} eV/GPa respectively. These are in good agreement with the theoretical results of -2.2 × 10sp{-2} eV/GPa of BaS and -2.3 × 10sp{-2} eV/GPa for CaSe. We estimate the metallization pressures of CsCl-structured BaS and CaSe to be above 113 and 125 GPa, respectively. Our results are compared with other alkaline earth monochalcogenides. The energy gap and electrical resistivity of FeSsb2 at high pressures have been measured at 300 K using absorption spectroscopy and conductivity measurements, respectively. The highest pressure absorption spectra measured is approximately 28 GPa, while resistivity is determined to 34 GPa. The indirect gap shifts linearly with pressure to about 28 GPa with a slope of -1.13(9) × 10sp{-2} eV/GPa. The pressure dependence of the logarithm of resistivity, drops at a rate of -0.101(1)/GPa to 14 GPa and then decreases to a slope of -0.011(3)/GPa at higher pressure. Therefore, a shift in the pressure dependence of the electronic structure of pyrite occurs near 14 GPa: this is consistent with previous Mossbauer results. We propose a mechanism to help consolidate this phenomenon.

Cervantes, Phillip

1998-11-01

38

Band structure built from oligomer calculations

A method to build accurate band structures of polymers from oligomer calculations has been developed. This method relies on systematic procedures for (i) assigning k values, (2) eliminating strongly localized molecular orbitals, and (iii) connecting bands across the entire Brillouin zone. Illustrative calculations are carried out at the HF/STO-3G level for trans-polyacetylene (PA), poly(para-phenylene) (PPP), and water chains. More stringent tests at several different levels are reported for polydiacetylene/polybutatriene.

Pomogaeva, Anna; Kirtman, Bernard; Gu, Feng Long; Aoki, Yoriko

2008-02-01

39

Photonic band structure and omnidirectional band gap in anisotropic superlattice

International Nuclear Information System (INIS)

We investigate theoretically the photonic band structure of one-dimensional superlattice (SL) composed of alternating anisotropic layers with their principal axis oriented at arbitrary directions. The dispersion relation of order two is calculated analytically by using the 4 x 4 matrix method which is based on boundary conditions of the electric and magnetic fields at each interface. It is shown that such structures can exhibit coupled electromagnetic modes between transverse magnetic TM and transverse electric TE modes, and dispersion curves that do not exist in superlattices composed only of isotropic layers. For a given value of the wave vector kparallel (parallel to the layers), the dispersion curves (frequency ?) versus kB (where kB is the Bloch wave vector of the periodic system along the axis of the superlattice) is illustrated. Specific applications of these results are given for the case of biaxial superlattice. With an appropriate choice of the superlattice parameters, we show that it is possible to realise, for these coupled electromagnetic waves, an absolute (or omnidirectional) band gap of width depending on the anisotropic parameters of the media forming the SL. (author)

40

Photonic Band Gap Structures for Accelerator Applications

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

Smirnova, E. I.

2004-12-01

41

Band Structure Based Analysis of Certain Photonic Crystal Structures

Digital Repository Infrastructure Vision for European Research (DRIVER)

Photonic crystals are periodic dielectric structures that may exhibit a complete photonic band gap. First, I discuss geometric properties of the band structure such as band edges. In a second part, I present work on photonic Wannier functions and their use for solving the wave equation. The third part is devoted to applications of the presented methods: A polarization resolved transmission experiment of opel films and an analogy experiment for spontaneous emission inside a photonic crystal.

Wolff, Christian

2011-01-01

42

Band alignment of semiconductors from density-functional theory and many-body perturbation theory

The band lineup, or alignment, of semiconductors is investigated via first-principles calculations based on density functional theory (DFT) and many-body perturbation theory (MBPT). Twenty-one semiconductors including C, Si, and Ge in the diamond structure, BN, AlP, AlAs, AlSb, GaP, GaAs, GaSb, InP, InAs, InSb, ZnS, ZnSe, ZnTe, CdS, CdSe, and CdTe in the zinc-blende structure, and GaN and ZnO in the wurtzite structure are considered in view of their fundamental and technological importance. Band alignments are determined using the valence and conduction band offsets from heterointerface calculations, the ionization potential (IP) and electron affinity (EA) from surface calculations, and the valence band maximum and conduction band minimum relative to the branch point energy, or charge neutrality level, from bulk calculations. The performance of various approximations to DFT and MBPT, namely the Perdew-Burke-Ernzerhof (PBE) semilocal functional, the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional, and the GW approximation with and without vertex corrections in the screened Coulomb interaction, is assessed using the GW?1 approximation as a reference, where first-order vertex corrections are included in the self-energy. The experimental IPs, EAs, and band offsets are well reproduced by GW?1 for most of the semiconductor surfaces and heterointerfaces considered in this study. The PBE and HSE functionals show sizable errors in the IPs and EAs, in particular for group II-VI semiconductors with wide band gaps, but are much better in the prediction of relative band positions or band offsets due to error cancellation. The performance of the GW approximation is almost on par with GW?1 as far as relative band positions are concerned. The band alignments based on average interfacial band offsets for all pairs of 17 semiconductors and branch point energies agree with explicitly calculated interfacial band offsets with small mean absolute errors of both ˜0.1eV, indicating a good overall transitivity of the band offsets. The alignment based on IPs from selected nonpolar surfaces performs comparably well in the prediction of band offsets at most of the considered interfaces. The maximum errors are, however, as large as 0.3, 0.4, and 0.7 eV for the alignments based on the average band offsets, branch point energies, and IPs, respectively. This margin of error should be taken into account when performing materials screening using these alignments.

Hinuma, Yoyo; Grüneis, Andreas; Kresse, Georg; Oba, Fumiyasu

2014-10-01

43

Detailed band structure of Chevrel phases

International Nuclear Information System (INIS)

We have performed full band-structure calculations for several Chevrel phases. The conduction band is esub(g)-like throughout most of the Brillouin zone, but near the centre we find strong tsub(1u) character. The tsub(1u)(esub(u)) state is a Mo-X intercluster pd? antibond and its occupancy decreases as we proceed from the 24- to the 20-electron compounds. This explains the observed decrease of the intercluster distance, it leads to non rigid-band behaviour, and it may be a source of strong electron-phonon coupling to low-frequency, external modes. Moreover, the esub(g)-tsub(1u) mixing gives rise to critical-field anisotropy. The 22-electron compounds BaMo6S8 and EuMo6S8 with half-filled esub(g)-bands are found to be semimetallic or semiconducting in their low-temperature phase. (orig.)

44

Maximizing band gaps in plate structures

DEFF Research Database (Denmark)

Band gaps, i.e., frequency ranges in which waves cannot propagate, can be found in elastic structures for which there is a certain periodic modulation of the material properties or structure. In this paper, we maximize the band gap size for bending waves in a Mindlin plate. We analyze an infinite periodic plate using Bloch theory, which conveniently reduces the maximization problem to that of a single base cell. Secondly, we construct a finite periodic plate using a number of the optimized base cells in a postprocessed version. The dynamic properties of the finite plate are investigated theoretically and experimentally and the issue of finite size effects is addressed.

Halkjær, SØren; Sigmund, Ole

2006-01-01

45

Investigation of phononic band gap structures considering interface effects

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

46

Band structure mapping of bilayer graphene via quasiparticle scattering

Directory of Open Access Journals (Sweden)

Full Text Available A perpendicular electric field breaks the layer symmetry of Bernal-stacked bilayer graphene, resulting in the opening of a band gap and a modification of the effective mass of the charge carriers. Using scanning tunneling microscopy and spectroscopy, we examine standing waves in the local density of states of bilayer graphene formed by scattering from a bilayer/trilayer boundary. The quasiparticle interference properties are controlled by the bilayer graphene band structure, allowing a direct local probe of the evolution of the band structure of bilayer graphene as a function of electric field. We extract the Slonczewski-Weiss-McClure model tight binding parameters as ?0 = 3.1 eV, ?1 = 0.39 eV, and ?4 = 0.22 eV.

Matthew Yankowitz

2014-07-01

47

Energy Technology Data Exchange (ETDEWEB)

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

48

International Nuclear Information System (INIS)

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

49

Band Structure and Electrical Conductivity in Semiconductors

In this experiment, we will, 1. understand how conductivity in semiconductors depends on carrier concentration and mobility, and how these depend on temperature, 2. distinguish between intrinsic and extrinsic temperature regimes and identify the applicable temperature range from an examination of measured data, 3. appreciate and utilize the advantages of the four-probe resistance measurement technique, 4. calculate the energy band gap for doped Si and pure Ge, 5. calculate the temperature dependent coefficient of the majority carriers, 6. through experimental realizations, appreciate a physical understanding of the band gap structure of semiconductors.

Khalid, Asma; Anwar, Muhammad S.; Zia, Wasif

2012-07-08

50

Band structure and electronic properties of transition metal hydrides

International Nuclear Information System (INIS)

A calculation of band structures, densities of states, and Fermi surfaces for 3d-element hybrides is made. The results of this calculation are compared with the APW calculation by Switendick and the experimental measured values of electronic specific heat, magnetic susceptibility, and optical absorptivity. By using the Gaspari-Gyorffy theory values of the electron-phonon coupling constant and Tsub(c) are calculated. High critical temperatures of superconductivity are predicted for chromium and nickel dihydrides. (author)

51

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

We demonstrate the ability to develop one-dimensional electromagnetic band gap structure in X-band waveguide solely by using the positive columns of glow discharges in neon at the middle pressure. Plasma inhomogeneities are distributed uniformly along a typical X-band waveguide with cross section of 23 × 10 mm2. It is shown that electron densities larger than 1014 cm-3 are needed in order to create an effective one-dimensional electromagnetic band gap structure. Some applications for using the one-dimensional electromagnetic band gap structure in waveguide as a control of microwave (broadband filter and device for variation of pulse duration) are demonstrated.

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

2014-09-01

52

Quantum Interference in Artificial Band Structures

Magnetotransport experiments on two-dimensional electron systems with an atomically precise, one-dimensional potential modulation reveal striking quantum interference oscillations. Within a semiclassical framework, they are recognized either as self-interference along closed orbits, many of them rendered possible by magnetic breakdown between Fermi contour segments of the artificial band structure, or as interference-enhanced backscattering. The known commensurability oscillations appear as a special case of the latter mechanism.

Deutschmann, R. A.; Wegscheider, W.; Rother, M.; Bichler, M.; Abstreiter, G.; Albrecht, C.; Smet, J. H.

2001-02-01

53

Plasmon dispersion and quasiparticle band structures for noble metals

International Nuclear Information System (INIS)

Full text: In density-functional theory the Kohn-Sham eigenvalues cannot be interpreted as excitation energies, but band structures are often qualitatively correct and can be used as a starting point for perturbation-theoretical treatments. The GW approximation for the electronic self-energy is a particularly successful method for accurate quantitative band-structure calculations. The screened interaction W incorporates local field effects from the inversion of the dielectric matrix determined in the Random Phase Approximation. The inverted dielectric matrix combined with non-local empirical pseudopotentials also yields adequately calculated low energy excited state properties of materials. Dielectric calculations based on the pseudo-wavefunctions and energy band structure within a plasmon picture determine mean free path lengths and Fourier components of the inelastic scattering potential. Efficient band structures simulate ballistic transport effects in copper and surface state changes with strain during silver epitaxial film growth on silicon, but care must be taken with convergence, in order to obtain good agreement with first principle calculations and experimental values. Comparisons are made with recent LDA and GW calculations for silver

54

Banded frequency structure from linear mode conversion in inhomogeneous plasmas

International Nuclear Information System (INIS)

Linear mode conversion of unmagnetized Langmuir waves into transverse electromagnetic waves in an inhomogeneous plasma is investigated numerically. It is shown that the presence of a tunneling region and density well near the mode conversion region can significantly influence the mode conversion efficiency. The density cavity acts as a resonator, such that the mode conversion efficiency shifts from zero to a local maximum (up to 100% efficiency) with variation of the cavity width on scales of order the Langmuir wavelength. In this way, Langmuir waves with a smooth (structureless) frequency dependence can be selectively mode converted to produce narrow frequency bands of electromagnetic radiation. Applications are discussed to banded frequency fine structure in electromagnetic emissions at the electron plasma frequency in Earth's foreshock and the solar wind, type III solar radio bursts, and lower ionospheric auroral roar emissions

55

4H-SiC band structure investigated by surface photovoltage spectroscopy

International Nuclear Information System (INIS)

The conduction and valence band structure of high-purity 4H-SiC epilayers have been studied by surface photovoltage spectroscopy (SPS). A comparison between defect-free and single-layer stacking fault affected areas is reported. Electronic transitions, determined by SPS, are in good agreement with ab initio calculations. Electronic transitions and changes in band occupation have been observed in stacking fault rich areas below the band gap. Moreover, stacking faults induce the presence of a split-off band below the conduction band and a modification of the electron density of states in the conduction band always at the M point.

56

Nuclear band structure at very high spin

International Nuclear Information System (INIS)

Complete text of publication follows. The description of nuclear high spin bands in terms of the configuration constrained cranked Nilsson-Strutinsky (CNS) approach will be discussed. Pairing is neglected in these calculations, making it possible to get a simple understanding of the different configurations. Examples from different mass regions show very good agreement between calculations and experiment in many cases making it possible to assign detailed configurations. In this assignment, the fact that the configurations have well-defined maximum spin values is very important, independently of if the bands really terminate or not. Going to lower spin values, the detailed understanding at high spin should be very helpful when trying to understand the structure in the regime where different configurations are more mixed. (author)

57

Electronic structure of periodic curved surfaces -- topological band structure

Electronic band structure for electrons bound on periodic minimal surfaces is differential-geometrically formulated and numerically calculated. We focus on minimal surfaces because they are not only mathematically elegant (with the surface characterized completely in terms of "navels") but represent the topology of real systems such as zeolites and negative-curvature fullerene. The band structure turns out to be primarily determined by the topology of the surface, i.e., how the wavefunction interferes on a multiply-connected surface, so that the bands are little affected by the way in which we confine the electrons on the surface (thin-slab limit or zero thickness from the outset). Another curiosity is that different minimal surfaces connected by the Bonnet transformation (such as Schwarz's P- and D-surfaces) possess one-to-one correspondence in their band energies at Brillouin zone boundaries.

Aoki, H; Takeda, D; Morise, H

2001-01-01

58

Band structure of polyethylene from many-body perturbation theory

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

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

2013-03-01

59

Emission bands of phosphorus and calculation of band structure of rare earth phosphides

International Nuclear Information System (INIS)

The method of x-ray emission spectroscopy has been used to investigate the electronic structure of monophosphides of rare-earth metals (REM). The fluorescence K bands of phosphorus have been obtained in LaP, PrP, SmP, GdP, TbP, DyP, HoP, ErP, TmP, YbP, and LuP and also the Lsub(2,3) bands of phosphorus in ErP, TmP, YbP, and LuP. Using the Green function technique involving the muffin-tin potential, the energy spectrum for ErP has been calculated in the single-electron approximation. The hystogram of electronic state distribution N(E) is compared with the experimental K and Lsub(2,3) bands of phosphorus in ErP. The agreement between the main details of N(E) and that of x-ray spectra allows to state that the model used provides a good description of the electron density distribution in crystals of REM monophosphides. In accordance with the character of the N(E) distribution the compounds under study are classified as semimetals or semiconductors with a very narrow forbidden band

60

Complex Band Structures and Decay Length in Polyethylene Chains

The complex band structure of an isolated polyethylene chain is calculated within Density Functional Theory (DFT). A plane wave basis and ultrasoft pseudopotentials are used. The results are compared with those obtained via a local basis set. We obtain a gap between the highest occupied molecular orbilar (HOMO) and the antibonding unoccupied molecular orbitals of 9.3 eV and a non-resonant tunneling $\\beta$ parameter of 0.9 per monomer, in reasonable agreement with experiment and with results obtained via local basis. Polyethylene is a negative electron affinity material and the actual gap should be the energy of the HOMO with respect to the vacuum level (in DFT approximation only about 5.14 eV). The Bloch states at imaginary k are mainly free-electron-like parabolic bands which are missing in the local basis. We present also the complex bands of the bulk polyethylene in order to estimate the effects of the chain-chain interactions on the complex band structure. The relevance of these results for the tunnellin...

Picaud, F; Corso, A D; Tosatti, E; Picaud, Fabien; Smogunov, Alexander; Corso, Andrea Dal; Tosatti, Erio

2003-01-01

61

Hubbard-*U* band-structure methods

DEFF Research Database (Denmark)

The last decade has seen a large increase in the number of electronic-structure calculations that involve adding a Hubbard term to the local-density approximation band-structure Hamiltonian. The Hubbard term is then determined either at the mean-field level or with sophisticated many-body techniques such as using dynamical mean-field theory. We review the physics underlying these approaches and discuss their strengths and weaknesses in terms of the larger issues of electronic structure that they involve. In particular, we argue that the common assumptions made to justify such calculations are inconsistent with what the calculations actually do. Although many of these calculations are often treated as essentially first-principles calculations, in fact, we argue that they should be viewed from an entirely different point of view, namely, as based on phenomenological many-body corrections to band-structure theory. Alternatively, it may also be considered that they are just based on a Hubbard model that is more complex than the simple one- or few-band models traditionally used in many-body theories of solids.

Albers, R.C.; Christensen, Niels Egede

2009-01-01

62

Electronic structure of Ce 5Rh 4Sn 10 from XPS and band structure calculations

We present a combined experimental and theoretical study of the electronic structure for the heavy-fermion antiferromagnet Ce5Rh4Sn10 based on X-ray photoemission spectroscopy (XPS) data and ab initio band structure calculations. The Ce core-level XPS spectra point to a stable trivalent configuration of Ce atoms in Ce5Rh4Sn10, consistently with both the magnetic susceptibility data and the results of computational structure optimization. The band structure calculations confirm a magnetic ground state with significant magnetic moments only at the Ce atoms. The qualitatively correct description of Ce3+ in Ce5Rh4Sn10 has been achieved using the LSDA+U approach for the Ce 4f states. The comparison of the theoretical results with experimental XPS valence band spectrum supports their validity. The calculated partial densities of states suggest that there is a variation in binding energy of the occupied 4f states between Ce atoms in nonequivalent crystallographic positions, which is related to the hybridization with Sn states. Finally, the band structure and charge density maps point to the formation of zig-zag chains of the strongly bounded Sn(2), Sn(3) and Rh atoms along the tetragonal axis, whereas Sn(1) shows nearly dispersionless 5s bands.

Gam?a, M.; ?lebarski, A.; Rosner, H.

2008-05-01

63

[Band electronic structures and crystal packing forces

Energy Technology Data Exchange (ETDEWEB)

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.

1993-01-01

64

Modeling of graphene nano-ribbon Schottky diodes in the parabolic band structure limit

In this paper we investigate the band structure of graphene nano-ribbons and the current density. A square root approximation shows that the band energy is parabolic in the low energy limit. In this parabolic region charge transport is controlled by the saturation velocity.

Moghaddam, N. S.; Ahmadi, M. T.; Webb, J. F.; Rahmani, M.; Sadegi, H.; Musavi, M.; Ismail, R.

2012-11-01

65

Electron density and carriers of the diffuse interstellar bands

We have used the ionisation equilibrium equation to derive the electron density in interstellar clouds in the direction to 13 stars. A linear relation was found, that allows the determination of the electron density from the Mg I and Mg II column densities in interstellar medium. The comparison of normalised equivalent width of 12 DIBs with the electron density shows that the DIBs equivalent width do not change with varying electron density. Therefore the DIBs carriers (1) can be observed only in one ionisation stage, or (2) the DIBs are arising in cloud regions (cores or cloud coronas) for which we can not determine the electron density.

Gnacinski, P; Galazutdinov, G A

2007-01-01

66

Band Structures in Doubly Odd 126I

The high-spin states in 126I have been investigated by using in-beam ?-ray spectroscopy with the 124Sn(7Li, 5n)126I reaction at a beam energy of 48 MeV. The previously known level scheme of 126I has been extended and modified considerably by adding about 60 new ?-transitions and establishing 5 new bands. The backbendings in the yrast band 1 and the yrare band 3 are found both due to a pair of h11/2 neutrons alignment. The configurations for the newly identified bands 2, 4, 5 and 6 have been assigned.

Zheng, Y.; Wu, X. G.; He, C. Y.; Li, G. S.; Hao, X.; Wang, L. L.; Liu, Y.; Li, X. Q.; Pan, B.; Yu, B. B.; Wang, L.; Zhu, L. H.

2011-08-01

67

Band structures of Al-doped superconductors YBa2Cu3-xAlxO7+?

International Nuclear Information System (INIS)

Based on the EHMO approach, an approximate treatment of electronic energy-band structures is suggested. By employing this treatment, computations of the band structures of the Al-doped superconductors YBa2Cu3-xAlxO7 + ? were carried out. It is shown by analysis of the band structures and the density of states that the 2D Cu-O planes in the Y-Ba-Cu-O superconducting system play a dominant role in superconductivity, whereas the 1D Cu-O ribbons have indirectly an influence on superconductivity through the connection of the O(4) atoms to two Cu-O planes

68

Elucidating the stop bands of structurally colored systems through recursion

Interference phenomena are the source of some of the spectacular colors of animals and plants in nature. In some of these systems, the physical structure consists of an ordered array of layers with alternating high and low refractive indices. This periodicity leads to an optical band structure that is analogous to the electronic band structure encountered in semiconductor physics; namely, specific bands of wavelengths (the stop bands) are perfectly reflected. Here, we present a minimal model for optical band structure in a periodic multilayer and solve it using recursion relations. We present experimental data for various beetles, whose optical structure resembles the proposed model. The stop bands emerge in the limit of an infinite number of layers by finding the fixed point of the recursive relations. In order for these to converge, an infinitesimal amount of absorption needs to be present, reminiscent of the regularization procedures commonly used in physics calculations. Thus, using only the phenomenon of...

Amir, Ariel

2012-01-01

69

?-cluster structure and density waves in oblate nuclei

International Nuclear Information System (INIS)

Pentagon and triangle shapes in 28Si and 12C are discussed in relation to nuclear density waves. In the antisymmetrized molecular dynamics calculations, the K?=5- band in 28Si and the K?=3- band in 12C are described by the pentagon and triangle shapes, respectively. These negative-parity bands can be interpreted as the parity partners of the K?=0+ ground bands and they are constructed from the parity-asymmetric-intrinsic states. The pentagon and the triangle shapes originate in 7?- and 3?-cluster structures, respectively. In a mean-field picture, they are described also by the static one-dimensional density waves at the edge of the oblate states. In analyses with ideal ?-cluster models using Brink-Bloch cluster wave functions and that with a simplified model, we show that the static edge density waves for the pentagon and triangle shapes can be understood by spontaneous breaking of axial symmetry, i.e., the instability of the oblate states with respect to the edge density waves. The density wave is enhanced in the Z=N nuclei due to the proton-neutron coherent density waves, while it is suppressed in Z?N nuclei.

70

International Nuclear Information System (INIS)

The nature of chemical binding for some transition metal compounds (ScN, ScO, TiC, TiN, Tio, VC, VN, VO) with NaCl structure is discussed in terms of energy band structure calculations. The discussion is based on the wave functions and energy eigenvalues, as calculated by the 'Quasi self sonsistent APW method' as well as on the energy eigen values and eigen vectors resulting from the Slater-Koster LCAO-Tight binding interpolation scheme. The LCAO-TB l-like partial density of states can be used to analyse the valence bands. This analysis shows, that the deepest valence band has predominantly s-character. The following bands, which can be derived in essence from the atomic 2p states of the of the non metal are characterized not only by the partial p-like density of states but also by a substantial contribution from the d-like partial density of states, which is decreasing going from a particular Carbide to the corresponding Oxide. For the valence bands, which can be associated with the atomic 3d states of the metal, the density of states exhibits besides the partial d-density of states small contributions from the partial p-like density of states. The decomposition of the d-like partial density of states into an esub(g)-like and a tsub(2g)-like contribution is discussed. By analyzing the APW crystal wave functions the partial l-like charges inside each atomic sphere can be obtained. If the APW total charges within the atomic spheres are compared with the charges of a hyeres are compared with the charges of a hypothetical crystal, which correspond to a superposition of the charge densities of the neutral atoms, a transfer of electrons from the metal to the non-metal sphere is found for all compounds under investigation. (orig.)

71

Engineering the Electronic Band Structure for Multiband Solar Cells

Energy Technology Data Exchange (ETDEWEB)

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

72

Band gap and effective mass of multilayer BN/graphene/BN: van der Waals density functional approach

Using the van der Waals density functional theory method (DFT-D2), we have investigated thickness dependent energy band gaps and effective masses of multilayer BN/graphene/BN structures by changing the stacking order. The band gap is substantially dependent on the stacking order. For instance, the calculated band gap in ABA stacking is about 150 meV, whereas it becomes 31 meV in ABC stacking. No significant thickness dependent band gap is observed in both ABA and ABC stackings although the band gap is gradually increasing with the BN thickness in ABA stacking. In addition, the effective mass is found to be strongly dependent on the stacking order. The effective mass in ABA stacking is much larger than that found in ABC stacking. On the other hand, the effective mass along K-M direction is smaller than that along K-? direction in ABA stacking. However, it is independent on the band direction in ABC stacking. We have found that the inclusion of van der Waals interaction alters thickness dependent band gap and effective mass of BN/graphene/BN multilayer systems compared with those found with standard density functional theory.

Hashmi, Arqum; Hong, Jisang

2014-05-01

73

Band Structure and Quantum Confined Stark Effect in InN/GaN superlattices

DEFF Research Database (Denmark)

InN/GaN superlattices offer an important way of band gap engineering in the blue-green range of the spectrum. This approach represents a more controlled method than the band gap tuning in quantum well systems by application of InGaN alloys. The electronic structures of short-period wurtzite InN/GaN(0001) superlattices are investigated, and the variation of the band gap with the thicknesses of the well and the barrier is discussed. Superlattices of the form mInN/nGaN with n ? m are simulated using band structure calculations in the Local Density Approximation with a semiempirical correction for the gap error. The calculated band gap shows a strong decrease with the thickness (m) of the InN well. In superlattices containing a single layer of InN (m = 1) the band gap increases weakly with the GaN barrier thickness n, reaching a saturation value around 2 eV. In superlattices with n = m and n > 5 the band gap closes and the systems become “metallic”. These effects are related to the existence of the built-in electric fields that strongly influence valence- and conduction-band profiles and thus determine effective band gap and emission energies of the superlattices. Varying the widths of the quantum wells and barriers one may tune band gaps over a wide spectral range, which provides flexibility in band gap engineering.

Gorczyca, I.; Suski, T.

2012-01-01

74

Structural and electronic properties of poly(vinyl alcohol) using density functional theory

Energy Technology Data Exchange (ETDEWEB)

The first principles calculations have been carried out to investigate the structural, electronic band structure density of states along with the projected density of states for poly(vinyl alcohol). Our structural calculation suggests that the poly(vinyl alcohol) exhibits monoclinic structure. The calculated structural lattice parameters are in excellent agreement with available experimental values. The band structure calculations reveal that the direct and indirect band gaps are 5.55 eV and 5.363 eV respectively in accordance with experimental values.

Dabhi, Shweta, E-mail: shwetadabhi1190@gmail.com; Jha, Prafulla K., E-mail: shwetadabhi1190@gmail.com [Department of Physics, Maharaja Krishnakumasinhji Bhavnagar University, Bhavnagar-364001 (India)

2014-04-24

75

Structural and electronic properties of poly(vinyl alcohol) using density functional theory

International Nuclear Information System (INIS)

The first principles calculations have been carried out to investigate the structural, electronic band structure density of states along with the projected density of states for poly(vinyl alcohol). Our structural calculation suggests that the poly(vinyl alcohol) exhibits monoclinic structure. The calculated structural lattice parameters are in excellent agreement with available experimental values. The band structure calculations reveal that the direct and indirect band gaps are 5.55 eV and 5.363 eV respectively in accordance with experimental values

76

Digital Repository Infrastructure Vision for European Research (DRIVER)

Maturation of Trypanosoma brucei mitochondrial mRNA involves massive posttranscriptional insertion and deletion of uridine residues. This RNA editing utilizes an enzymatic complex with seven major proteins, band I through band VII. We here use RNA interference (RNAi) to examine the band II and band V proteins. Band II is found essential for viability; it is needed to maintain the normal structure of the editing complex and to retain the band V ligase protein. Previously, band III was found es...

O Hearn, Sean F.; Huang, Catherine E.; Hemann, Mike; Zhelonkina, Alevtina; Sollner-webb, Barbara

2003-01-01

77

International Nuclear Information System (INIS)

High spin states in 107Ag are studied via the 100Mo(11B, 4n) 107Ag reaction at an incident beam energy of 60 MeV. Prompt ?-? coincidence and DCO ratios are measured by the detector arrays in CIAE. The level scheme has been updated and a new negative band belonging to 107Ag is identified. The new negative side band has been constructed and its configuration is tentatively assigned to ?g9/2 ? Uh11/2 (g7/2/d5/2). (authors)

78

Multi-band, highly absorbing, microwave metamaterial structures

A further example of multi-band absorption using ultra-thin, polarization-insensitive, wide-angled metamaterial absorbers that operate in multi-frequency bands within the microwave regime is presented in this work. The basic structure geometry is utilised to create multi-band highly absorbing structures by incorporating the scalability property of the metamaterials. Simulation results verify the structure's ability for high absorption. The multi-band absorbers are promising candidates as absorbing elements in scientific and technical applications because of its multi-band absorption, polarization insensitivity, and wide-angle response. Finally, the current distributions for those structures are presented to gain a better insight into the physics behind the multiple absorption mechanism.

Kollatou, T. M.; Dimitriadis, A. I.; Assimonis, S. D.; Kantartzis, N. V.; Antonopoulos, C. S.

2014-05-01

79

Tuning the electronic band structure of PCBM by electron irradiation.

Tuning the electronic band structures such as band-edge position and bandgap of organic semiconductors is crucial to maximize the performance of organic photovoltaic devices. We present a simple yet effective electron irradiation approach to tune the band structure of [6, 6]-phenyl-C61-butyric acid methyl ester (PCBM) that is the most widely used organic acceptor material. We have found that the lowest unoccupied molecular orbital (LUMO) level of PCBM up-shifts toward the vacuum energy level, while the highest occupied molecular orbital (HOMO) level down-shifts when PCBM is electron-irradiated. The shift of the HOMO and the LUMO levels increases as the irradiated electron fluence increases. Accordingly, the band-edge position and the bandgap of PCBM can be controlled by adjusting the electron fluence. Characterization of electron-irradiated PCBM reveals that the variation of the band structure is attributed to the molecular structural change of PCBM by electron irradiation. PMID:21970617

Yoo, Seung Hwa; Kum, Jong Min; Cho, Sung Oh

2011-01-01

80

Cluster structure and deformed bands in the 38Ar nucleus

International Nuclear Information System (INIS)

The structure of the 38Ar nucleus is investigated by the 34S+? orthogonality condition model (OCM). The energy spectra, electromagnetic transitions and ? spectroscopic factors are calculated. The excited states can be grouped into several bands according to the leading configurations of their wave functions, and the structures of the bands are discussed. The first excited K?=0+ band is found to be predominantly 34S+? cluster states. It is also shown that the observed energies and E2 transitions of the band are well reproduced by the model. The existence of a negative-parity doublet band of the band is also predicted. The strength of the ?-cluster states is shown to be spread over several levels due to mixing of shell-model states and various ?-cluster states

81

Atomic structure of amorphous shear bands in boron carbide.

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

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

2013-01-01

82

Alpha-cluster structure and density wave in oblate nuclei

Pentagon and triangle shapes in Si-28 and C-12 are discussed in relation with nuclear density wave. In the antisymmetrized molecular dynamics calculations, the $K^\\pi=5^-$ band in Si-28 and the $K^\\pi=3^-$ band in C-12 are described by the pentagon and triangle shapes, respectively. These negative-parity bands can be interpreted as the parity partners of the $K^\\pi=0^+$ ground bands and they are constructed from the parity-asymmetric-intrinsic states. The pentagon and the triangle shapes originate in 7alpha and 3alpha cluster structures, respectively. In a mean-field picture, they are described also by the static one-dimensional density wave at the edge of the oblate states. In analysis with ideal alpha cluster models using Brink-Bloch cluster wave functions and that with a simplified model, we show that the static edge density wave for the pentagon and triangle shapes can be understood by spontaneous breaking of axial symmetry, i.e., the instability of the oblate states with respect to the edge density wave....

Kanada-En'yo, Yoshiko

2011-01-01

83

Shell model description of band structure in 48Cr

International Nuclear Information System (INIS)

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

84

Band-gap and the Electronic structure of BN nanotubes

A verity of BN nanotubes were studied via high resolution electron energy loss spectroscopy. Careful examination of low energy loss spectra (0-50 eV) the band gap of the single tube can be extracted. Moreover the spectral features give insight into the BN nanotube valence band structure.

Okawa, David; Aloni, Shaul; Mickelson, William

2005-03-01

85

Density structures inside the plasmasphere: Cluster observations

DEFF Research Database (Denmark)

The electron density profiles derived from the EFW and WHISPER instruments on board the four Cluster spacecraft reveal density structures inside the plasmasphere and at its outer boundary, the plasmapause. We have conducted a statistical study to characterize these density structures. We focus on the plasmasphere crossing on I I April 2002, during which Cluster observed several density irregularities inside the plasmasphere, as well as a plasmaspheric plume. We derive the density gradient vectors from simultaneous density measurements by the four spacecraft. We also determine the normal velocity of the boundaries of the plume and of the irregularities from the time delays between those boundaries in the four individual density profiles, assuming they are planar. These new observations yield novel insights about the occurrence of density irregularities, their geometry and their dynamics. These in-situ measurements are compared with global images of the plasmasphere from the EUV imager on board the IMAGE satellite.

2004-01-01

86

Quasiparticle band structure of rocksalt-CdO determined using maximally localized Wannier functions.

CdO in the rocksalt structure is an indirect band gap semiconductor. Thus, in order to determine its band gap one needs to calculate the complete band structure. However, in practice, the exact evaluation of the quasiparticle band structure for the large number of k-points which constitute the different symmetry lines in the Brillouin zone can be an extremely demanding task compared to the standard density functional theory (DFT) calculation. In this paper we report the full quasiparticle band structure of CdO using a plane-wave pseudopotential approach. In order to reduce the computational effort and time, we make use of maximally localized Wannier functions (MLWFs). The MLWFs offer a highly accurate method for interpolation of the DFT or GW band structure from a coarse k-point mesh in the irreducible Brillouin zone, resulting in a much reduced computational effort. The present paper discusses the technical details of the scheme along with the results obtained for the quasiparticle band gap and the electron effective mass. PMID:23235114

Dixit, H; Lamoen, D; Partoens, B

2013-01-23

87

We investigate the electronic absorption spectra of several maximally pericondensed polycyclic aromatic hydrocarbon radical cations with time dependent density functional theory calculations. We find interesting trends in the vertical excitation energies and oscillator strengths for this series containing pyrene through circumcoronene, the largest species containing more than 50 carbon atoms. We discuss the implications of these new results for the size and structure distribution of the diffuse interstellar band carriers.

Weisman, Jennifer L.; Lee, Timothy J.; Salama, Farid; Gordon-Head, Martin; Kwak, Dochan (Technical Monitor)

2002-01-01

88

Structure of nearly degenerate dipole bands in 108Ag

International Nuclear Information System (INIS)

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

89

Enhancement of phononic band gaps in ternary/binary structure

International Nuclear Information System (INIS)

Based on the transfer matrix method (TMM) and Bloch theory, the interaction of elastic waves (normal incidence) with 1D phononic crystal had been studied. The transfer matrix method was obtained for both longitudinal and transverse waves by applying the continuity conditions between the consecutive unit cells. Dispersion relations are calculated and plotted for both binary and ternary structures. Also we have investigated the corresponding effects on the band gaps values for the two types of phononic crystals. Furthermore, it can be observed that the complete band gaps are located in the common frequency stop-band regions. Numerical simulations are performed to investigate the effect of different thickness ratios inside each unit cell on the band gap values, as well as unit cells thickness on the central band gap frequency. These phononic band gap materials can be used as a filter for elastic waves at different frequencies values.

90

Configuration structure of superdeformed bands in A?190 mass region

International Nuclear Information System (INIS)

Using the particle-number conservation method for treating the cranked shell model with pairing interaction, the authors systematically investigate the variations of the moments of inertia, the angular moment alignment and the signature splitting with rotational frequencies for superdeformed bands in the A?190 mass region. According to our calculated results, the authors provide a global description of the configuration structure of superdeformed bands in the A?190 mass region. Most superdeformed bands are located at the strong-coupling orbits, such as neutron [512]5/2, [624]9/2. A few superdeformed bands lie on high j orbits, i.e., neutron [761]3/2, [752]5/2. Our calculated configuration assignments give a satisfactorily explanation to the general behavior, the anomalous change and the band crossing of superdeformed bands in the A?190 mass region. (authors)

91

Band structure and optical transitions in atomic layers of hexagonal gallium chalcogenides

Digital Repository Infrastructure Vision for European Research (DRIVER)

We report density-functional-theory calculations of the electronic band structures and optical absorption spectra of two-dimensional crystals of Ga$_2$X$_2$ (X=S, Se, and Te). Our calculations show that all three two-dimensional materials are dynamically stable indirect-band-gap semiconductors with a Mexican-hat dispersion of holes near the top of the valence band. We predict the existence of Lifshitz transitions---changes in the Fermi-surface topology of hole-doped Ga$_2$X$...

Zolyomi, Viktor; Drummond, Neil; Falko, Vladimir

2013-01-01

92

First-principles study of elastic, band structure and optical properties of uranium

International Nuclear Information System (INIS)

We report first principle calculation using plane-wave pseudopotential technique in density-functional theory to investigate the crystal structure, elastic constants, bulk modulus, band structure and optical constants of uranium. Calculated structural properties, bulk modulus and elastic constants compare very favorably with experimental data and other first principle calculations. The calculated optical constants of uranium are compared with experimental data and the contrast is discussed. (authors)

93

Photonic band structures of two-dimensional magnetized plasma photonic crystals

Energy Technology Data Exchange (ETDEWEB)

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

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

2012-04-01

94

Band structure calculations for Ba$_{6}$Ge$_{25}$ and Ba$_{4}$Na$_{2}$Ge$_{25}$ clathrates

Electronic band structures for Ba$_{6}$Ge$_{25}$ and Ba$_{4}$Na$_{2}$Ge$_{25}$ clathrates are calculated using linear muffin-tin orbital method within the local density approximation. It is found that barium states strongly contribute to the density of states at the Fermi level and thus can influence the transport properties of the compounds. A sharp peak of the density of states is found just at the Fermi level. It is also shown that the shifting of barium atoms toward experimentally deduced split positions in Ba$_{6}$Ge$_{25}$ produces a splitting of this peak which may therefore be interpreted as a band Jahn-Teller effect. If the locking of the barium atoms at the observed structural phase transition is assumed, this reduction of the density of states at the Fermi level can qualitatively account for the experimentally observed decrease of the magnetic susceptibility and electrical resistivity at the phase transition.

Zerec, I; Thalmeier, P; Grin, Y; Zerec, Ivica; Yaresko, Alexander; Thalmeier, Peter; Grin, Yuri

2002-01-01

95

Structure of rotational bands in {sup 253}No

Energy Technology Data Exchange (ETDEWEB)

In-beam gamma-ray and conversion electron spectroscopic studies have been performed on the {sup 253} No nucleus. A strongly coupled rotational band has been identified and the improved statistics allows an assignment of the band structure as built on the 9/2{sup -}[734]{sub {nu}} ground state. The results agree with previously known transition energies but disagree with the tentative structural assignments made in earlier work. (orig.)

Herzberg, R.D.; Moon, S.; Butler, P.A.; Page, T.; Amzal, N.; Bastin, J.E.; Cocks, J.F.C.; Darby, I.G.; Gray-Jones, C.; Hammond, N.J.; Herzberg, A.; Humphreys, R.D.; Jones, G.D.; Page, R.D.; Page, T.; Pritchard, A. [University of Liverpool, Oliver Lodge Laboratory, Liverpool (United Kingdom); Eeckhaudt, S.; Greenlees, P.T.; Dorvaux, O.; Jones, P.M.; Julin, R.; Juutinen, S.; Kankaanpaeae, H.; Kettunen, H.; Kuusiniemi, P.; LeCoz, Y.; Leino, M.; Leppaenen, A.P.; Muikku, M.; Nieminen, P.; Nyman, M.; Rahkila, P.; Sandzelius, M.; Saren, J.; Scholey, C.; Trzaska, W.H.; Uusitalo, J. [University of Jyvaeskylae, Department of Physics, Jyvaeskylae (Finland); Afanasjev, A.V. [Mississippi State University, Department of Physics and Astronomy, Mississippi, MS (United States); Becker, F.; Houry, M.; Huerstel, A.; Korten, W.; Lucas, R.; Theisen, C. [DAPNIA/SPhN CEA-Saclay, Saclay (France); Bender, M. [Universite Bordeaux and CNRS/IN2P3, Centre d' Etudes Nucleaires de Bordeaux Gradignan, Bordeaux (France); Bruyneel, B.; Reiter, P.; Wiens, A. [Universitaet zu Koeln, Institut fuer Kernphysik, Koeln (Germany); Eskola, K. [University of Helsinki, Department of Physics, Helsinki (Finland); Gerl, J.; Hessberger, F.; Schlegel, C.; Wollersheim, H.J. [GSI Helmholtzzentrum fuer Schwerionenforschung, Darmstadt (Germany); Grahn, T.; Pakarinen, J. [University of Liverpool, Oliver Lodge Laboratory, Liverpool (United Kingdom); University of Jyvaeskylae, Department of Physics, Jyvaeskylae (Finland); Hauschild, K. [IN2P3-CNRS, CSNSM, Orsay Campus (France); Heenen, P.H. [Universite Libre de Bruxelles, Service de Physique Nucleaire Theorique, Bruxelles (Belgium); Helariutta, K. [University of Jyvaeskylae, Department of Physics, Jyvaeskylae (Finland); University of Helsinki, Department of Physics, Helsinki (Finland); Khoo, T.L.; Lister, C.J. [Argonne National Laboratory, Argonne, IL (United States)

2009-12-15

96

Band structure characteristics of T-square fractal phononic crystals

International Nuclear Information System (INIS)

The T-square fractal two-dimensional phononic crystal model is presented in this article. A comprehensive study is performed for the Bragg scattering and locally resonant fractal phononic crystal. We find that the band structures of the fractal and non-fractal phononic crystals at the same filling ratio are quite different through using the finite element method. The fractal design has an important impact on the band structures of the two-dimensional phononic crystals

97

Correlated band structure of 3d2 vanadates

International Nuclear Information System (INIS)

We study the correlated band structure and the momentum-resolved spectra for 3d2 vanadates, like La O3 and YVO3, using a combination of a first-principles technique and dynamical mean-field theory with a Monte Carlo impurity solver. The self-energy for the effective 3d bands is calculated using maximum-entropy spectral analysis of the Monte Carlo results and a self-consistent procedure. We use this self-energy to calculate the full momentum-resolved spectrum and the correlated band structure, which we compare to available spectroscopy experimental results. We also discuss the effects of the lattice distortions and chemistry

98

Transmission properties of left-handed band-gap structures

We analyze transmission of electromagnetic waves through a periodic band-gap structure consisting of slabs of a left-handed metamaterial and air. Using the effective parameters of the metamaterial derived from its microscopic structure, we study, with the help of the transfer-matrix approach and by means of the finite-difference-time-domain numerical simulations, the transmission properties of such a left-handed photonic crystals in a novel type of band gap associated with the zero averaged refractive index. We demonstrate that the transmission can be made tunable by introducing defects, which allow to access selectively two different types of band gaps.

Shadrivov, I V; Zharov, A A; Kivshar, Yu S; Shadrivov, Ilya V.; Zharova, Nina A.; Zharov, Alexander A.; Kivshar, Yuri S.

2004-01-01

99

The electronic band structure of CoS2

International Nuclear Information System (INIS)

Angle-resolved and energy-dependent photoemission was used to study the band structure of paramagnetic CoS2 from high-quality single-crystal samples. A strongly dispersing hybridized Co-S band is identified along the ?-X line. Fermi level crossings are also analysed along this line, and the results are interpreted using band structure calculations. The Fermi level crossings are very sensitive to the separation in the S-S dimer, and it is suggested that the half-metallic gap in CoS2 may be controlled by the bonding-antibonding splitting in this dimer, rather than by exchange splitting on the Co atoms

100

Banded Electron Structure Formation in the Inner Magnetosphere

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

101

Development of the W-band density profile and fluctuation reflectometer on EAST

Energy Technology Data Exchange (ETDEWEB)

Highlights: • A X-mode W-band reflectometer is designed and installed on Experimental Advanced Superconducting Tokamak (EAST) for the first time. • Both density profile and fluctuations can be measured by the newly developed reflectometer. • The core density profile has been measured in high magnetic field condition together with V-band reflectometer. • Sawtooth precursor has been measured by fluctuation reflectometer in the low magnetic field condition. -- Abstract: A X-mode polarized W-band reflectometer for plasma density profile and fluctuation measurement is designed and installed on EAST. In measuring the density profile, a voltage controlled oscillator (VCO) is used as the source, allowing a high temporal resolution measurement. The density profile in a plasma with high magnetic field (3.0 T) has been measured by combination of V- and W-band reflectometers. For fluctuation measurements, a frequency synthesizer is used instead of the VCO as a microwave source. The core density fluctuations during sawtooth activity are measured and analyzed.

Wang, Y.M.; Gao, X., E-mail: xgao@ipp.ac.cn; Ling, B.L.; Zhang, S.B.; Zhang, T.; Han, X.; Liu, S.C.; Liu, Z.X.; Liu, Y.; Ti, A.

2013-11-15

102

The electron density structure of the Titan ionosphere

Eight vertical profiles of the electron density in Titan's ionosphere were derived from the Cassini radio occultations of March 26, and May28, 2007 (T27 and T31), as well as those of March 19, 2006 (T12), and May 20,2006 (T14) . The 2006 occultations occurred at low Southern latitudes of 14.7S, 36.2S, 19.8S, and 21.9S. The 2007 occultations were nearly polar, at latitudes of 75S and 61N for T27. and 75S and 74N for T31.. The solar zenith angles for all occultations were near the terminator, ranging from 85 to 95 deg. The ionosphere peak was observed to lie close to an altitude of 1200 km, and the observed peak densities ranged from about 1.2 to 2.2 x 103 cm-3, which is in good agreement with other Cassini observations and the previous Voyager radio occultation results. In all measurements, the peak densities are about 30% higher near the dusk terminator, showing the influence of solar EUV. Radio occultation observations of the Titan ionosphere are difficult because of its low density and small size, and it was facilitated by the unprecedented Cassini radio science system, which has three frequencies that can operate simultaneously: S-band (2.3 GHz), X-band (8.4 GHz), and Ka-band (32 GHz). In particular, Ka-band had never been used before to probe Titan's ionosphere, and the signal-to-noise ratios at all frequencies of 42, 54, and 48 dB-Hz., respectively, have never before been achieved. The results indicate a clear dusk-dawn asymmetry in peak electron density, with the average dusk density being about 450% greater than the dawn side. . The dusk profiles also have more structure both above and below the main peak, including a peak at about 500 km. altitude.

Kliore, A. J.; Nagy, A. F.; Flasar, F. M.; Schinder, P. F.; French, R. G.; Marouf, E. A.; Rappaport, N. J.; Anabtawi, A.; McGhee, C. A.

2007-12-01

103

First principles studies of band structure and electronic properties of ZnSe

International Nuclear Information System (INIS)

Highlights: ? In this work, we examined the ground state properties of zincblende (ZnSe). ? The electronic band structure of ZnSe revealed band gap of 2.72 eV and a direct band gap is found. ? The optical and acoustic branches of the phonon dispersion revealed mode splittings in some high symmetry directions in the Brillouin Zone. - Abstract: The structural and electronic properties of semiconductor ZnSe are investigated by performing first principles calculations using density functional theory (DFT). The exchange correlation potentials were treated within the local density approximation (LDA) and the generalized gradient approximation (GGA) with the quantum espresso package. We calculate the density of state (DOS), projected density of state (PDOS), phonon dispersion frequencies and the electron charge density. Also, the bulk modulus and its pressure derivatives are determined. Where available, the calculated quantities are compared with known results. The electronic band structure revealed an occurrence of a 2.72 eV band gap, while the density of state shows split peak at ?2 eV and a minor peak split between 8 and 11 eV. We show that from the gamma points, along the high symmetries ? ? X and ? ? L directions, there are four dispersion (OL, OT, AL and AT) mode curves which later split into six modes along the X ? ? (2OL, OT, 2AT, and AL), L ? X (2OT, OL, 2AT, and AL), X ? W (2OL, OT, 2AT, and AL) and W ? L (2OT, OL, 2AT, and AL) directions. These modes splitting correspond to optical longitudinal mode, optical transverse mode, acoustic longitudinal mode and acoustic transverse mode.

104

First principles studies of band structure and electronic properties of ZnSe

Energy Technology Data Exchange (ETDEWEB)

Highlights: Black-Right-Pointing-Pointer In this work, we examined the ground state properties of zincblende (ZnSe). Black-Right-Pointing-Pointer The electronic band structure of ZnSe revealed band gap of 2.72 eV and a direct band gap is found. Black-Right-Pointing-Pointer The optical and acoustic branches of the phonon dispersion revealed mode splittings in some high symmetry directions in the Brillouin Zone. - Abstract: The structural and electronic properties of semiconductor ZnSe are investigated by performing first principles calculations using density functional theory (DFT). The exchange correlation potentials were treated within the local density approximation (LDA) and the generalized gradient approximation (GGA) with the quantum espresso package. We calculate the density of state (DOS), projected density of state (PDOS), phonon dispersion frequencies and the electron charge density. Also, the bulk modulus and its pressure derivatives are determined. Where available, the calculated quantities are compared with known results. The electronic band structure revealed an occurrence of a 2.72 eV band gap, while the density of state shows split peak at -2 eV and a minor peak split between 8 and 11 eV. We show that from the gamma points, along the high symmetries {Gamma} {yields} X and {Gamma} {yields} L directions, there are four dispersion (OL, OT, AL and AT) mode curves which later split into six modes along the X {yields} {Gamma} (2OL, OT, 2AT, and AL), L {yields} X (2OT, OL, 2AT, and AL), X {yields} W (2OL, OT, 2AT, and AL) and W {yields} L (2OT, OL, 2AT, and AL) directions. These modes splitting correspond to optical longitudinal mode, optical transverse mode, acoustic longitudinal mode and acoustic transverse mode.

Adetunji, B.I.; Adebambo, P.O. [Department of Physics, University of Agriculture, PMB 2240, Abeokuta (Nigeria); Adebayo, G.A., E-mail: gadebayo@ictp.it [Department of Physics, University of Agriculture, PMB 2240, Abeokuta (Nigeria); Abdus Salam International Centre for Theoretical Physics, Strada Costiera 11, I-34014 Trieste (Italy)

2012-02-05

105

Millimeter-wave waveguiding using photonic band structures

Current trends in device miniaturization and integration, especially in the development of microwave monolithic integrated circuits, calls for flexible, arbitrarily shaped and curved interconnects. Standard dielectric waveguides and microstrip lines are subject to prohibitive losses and their functionality is limited because of their unflexible structures. The problem is addressed by confining the wave- guiding path in a substrate with a Photonic Band Gap structure in a manner that will result in the guided mode being localized within the band gap. Two devices implementing Photonic Band Structures for millimeter waves confinement are presented. The first waveguide is a linear defect in triangular lattice created in a silicon slab (TE mode). The structure consists of parallel air holes of circular cross sections. The silicon was laser drilled to create the 2D crystal. The second device consists of alumina rods arranged in a triangular lattice, surrounded by air and sandwiched between two parallel metal plates (TM mode). Electromagnetic wave (W-band) confinement was obtained in both devices for straight and bent waveguides. Three branch waveguides (intersecting line defects) was studied as well. Measurements confirmed the lowloss waveguide confinement property of the utilizing Photonic Band Gap structure. This structure can find applications in power combiner/splitter and other millimeter wave devices.

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

2000-07-01

106

Band structure of fcc-C60 solid state crystal study

Directory of Open Access Journals (Sweden)

Full Text Available We studied the architecture of the C60 cluster to drive its atomic positions which can be seen at room temperature. We then used the obtained carbon positions as a basis set for the fcc structure to construct the fcc-C60 compound. Self consistent calculations were performed based on the density functional theory (DFT utilizing the accurate WIEN2K code to solve the single-particle Kohen-Sham equation within the augmented plane waves plus local orbital (APW+lo method. The cohesive energy has been found to be 1.537 eV for the fcc-C60 . The calculated small cohesive energy that results from the weak Van der Waals-London interactions among a C60 cluster with its nearest neighbors is in good agreement with experiment. The electron densities of states (DOSs were calculated for a C60 macromolecule as well as the fcc-C60 compound and the results were compared with each other. The band gap from DOS calculations has been found to be 0.7 eV. Band structures were also calculated within the generalized gradient approximation (GGA. The band structure calculation results in 1.04 eV for the direct band gap. Two kinds of ? and ? bonds were determined in the band structure. Our results are in good agreement with experiment and pseudopotential calculations.

S Javanbakht

2009-09-01

107

Multi bunch dynamics in detuned x-band structures

International Nuclear Information System (INIS)

The multi bunch dynamics of a 2 x 250 GeV version of the JLC is studied. The rf-properties of detuned x-band tubes are calculated with the Computer codes URMEL and MAFIA. The dispersion curve found with these codes is compared with an equivalent circuit model. The calculation of the dipole mode loss parameters is investigated in detail. Tracking calculations are used to investigate the misalignment tolerances for detuned x-band structures. Also tilted x-band tubes are considered. (author)

108

Design for maximum band-gaps in beam structures

DEFF Research Database (Denmark)

This paper aims to extend earlier optimum design results for transversely vibrating Bernoulli-Euler beams by determining new optimum band-gap beam structures for (i) different combinations of classical boundary conditions, (ii) much larger values of the orders n and n-1 of adjacent upper and lower eigenfrequencies of maximized band-gaps, and (iii) different values of a minimum cross-sectional area constraint. The periodicity of the optimum beams and the attenuation of their band-gaps are also discussed.

Olhoff, Niels; Niu, Bin

2012-01-01

109

International Nuclear Information System (INIS)

A new broad-band microwave reflectometer in the Q-band (33-50 GHz) with only one antenna is presented. The basic principles of density measurements with this device are outlined for a numerical application to the tokamak TJ-1. Experimental results for the electron density profile are given. Some preliminary results of density fluctuation measurements are also presented. (author)

110

Calculation of electronic structure and density of state for BaTiO3

Directory of Open Access Journals (Sweden)

Full Text Available The electronic structure, density of state (DOS and electronic density of state inparaelectric cubic crystal Ba TiO3 are studied using full potential-linearized augmented plane wave (FP-LAPW method in the framework of the density functional theory (DFT with the generalized gradient approximation (GGA by the WIEN2K package. The results show a direct band gap of 1.8 eV at the point in the Brillouin zone. The calculated band structure and density of state of BaTiO3 are in good agreement with theoretical and experimental results.

H. Salehi

2002-12-01

111

Electronic band structure, stability, structural, and elastic properties of IrTi alloys

International Nuclear Information System (INIS)

The structural properties and mechanical stabilities of B2-IrTi have been investigated using first-principle calculations. The elastic constants calculations indicate that the B2-IrTi is unstable to external strain and the softening of C11-C12 triggers the B2-IrTi (cubic) to L10-IrTi (tetragonal) phase transformation. Detailed electronic structure analysis revealed a Jahn-Teller-type band split that could be responsible for elastic softening and structure phase transition. The cubic-tetragonal transition is accompanied by a reduction in the density of states (DOS) at the Fermi level and the d-DOS of Ti at Fermi level plays a decisive role in destabilizing the B2-IrTi phase.

112

Electronic band structure, stability, structural, and elastic properties of IrTi alloys

Energy Technology Data Exchange (ETDEWEB)

The structural properties and mechanical stabilities of B2-IrTi have been investigated using first-principle calculations. The elastic constants calculations indicate that the B2-IrTi is unstable to external strain and the softening of C{sub 11}-C{sub 12} triggers the B2-IrTi (cubic) to L1{sub 0}-IrTi (tetragonal) phase transformation. Detailed electronic structure analysis revealed a Jahn-Teller-type band split that could be responsible for elastic softening and structure phase transition. The cubic-tetragonal transition is accompanied by a reduction in the density of states (DOS) at the Fermi level and the d-DOS of Ti at Fermi level plays a decisive role in destabilizing the B2-IrTi phase.

Chen Wenzhou; Li Qian [Institute of Modern Physics, Northwest University, Xi' an 710069 (China); Jiang Zhenyi, E-mail: jiangzy@nwu.edu.cn [Institute of Modern Physics, Northwest University, Xi' an 710069 (China); Zhang Xiaodong; Si Liang [Institute of Modern Physics, Northwest University, Xi' an 710069 (China); Li Lisha [Department of Physics, Northwest University, Xi' an 710069 (China); Wu Rui [Institute of Modern Physics, Northwest University, Xi' an 710069 (China)

2012-07-15

113

A Hybrid Density Functional Theory Study of Band Gap Tuning in ZnO through Pressure

International Nuclear Information System (INIS)

The structural transformation and electronic structure of ZnO under hydrostatic pressure are investigated using the HSE06 range-separated hybrid functional. We show that wurtzite ZnO under pressure undergoes a structural transition to a graphite-like phase. We also find that the band gap of wurtzite phase is always direct, whereas the new phase can display either direct or indirect band structure. Furthermore, the gap is greatly enhanced by pressure and no semi-metallic phase is observed. This is drastically different from our previous results of AlN and GaN [Appl. Phys. Lett. 100 (2012) 022104

114

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

International Nuclear Information System (INIS)

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

115

Measured energy-momentum densities of the valence band of aluminium

International Nuclear Information System (INIS)

The energy-resolved momentum densities of the valence band of a thin polycrystalline aluminium film have been measured using electron momentum spectroscopy (EMS). The spectrometer used for these measurements has estimated energy and momentum resolutions of 0.9 eV and 0.10 atomic units respectively. The valence band of aluminium was clearly resolved, resembling very closely that of a free-election parabola. The measurement has been compared to linear muffin-tin orbital (LMTO) calculations for spherically averaged crystalline aluminium. Comparison has also been made between the experiment and Monte-Carlo simulations which take into account additional elastic and inelastic scattering events not considered in the LMTO calculations. The final agreement obtained between the measurement and theory for the dispersion and relative intensities of the aluminium valence band is excellent when lifetime broadening of the band is allowed for. 21 refs., 11 figs

116

Two-Dimensional Ferroelectric Photonic Crystals: Optics and Band Structure

In this report we present an investigation of the optical properties and band structure calculations for the photonic structures based on the functional materials- ferroelectrics. A theoretical approach to the optical properties of the 2D and 3D photonic crystals which yields further insight in the phenomenon of the reflection from different families of lattice planes in relation to the presence of photonic gaps or photonic bands. We calculate the photonic bands and optical properties of LiNbO3 based photonic crystals. Calculations of reflection and transmission spectra show the features correspond to the onset of diffraction, as well as to additional reflectance structures at large values of the angle of incidence.

Simsek, Sevket; Ozbay, Ekmel

2013-01-01

117

Banded structures in collagen vitrigels for corneal injury repair.

There is a growing interest in using collagen vitrigels for corneal injury repair. We recently reported the synthesis and thermal denaturation behavior of these gels. In this paper, the banded structure in these vitrified gels is studied by small-angle X-ray scattering (SAXS) one-dimensional (1-D) correlation function analysis and transmission electron microscopy (TEM). Results demonstrate that the collagen vitrigel possess banded structures similar to those of the starting type I collagen, with an average D-spacing of 64nm (by SAXS) or 57nm (by TEM). A combination of SAXS 1-D correlation function analyses and TEM show that overlap and gap distances ranged from 30 to 33nm and from 23 to 25nm, respectively. Changing the vitrification condition does not impact on the banded structure significantly. PMID:24859294

Xia, Zhiyong; Calderón-Colón, Xiomara; McCally, Russell; Maranchi, Jeffrey; Rong, Lixia; Hsiao, Benjamin; Elisseeff, Jennifer; Trexler, Morgana

2014-08-01

118

Tuning the electronic band structure of PCBM by electron irradiation

Directory of Open Access Journals (Sweden)

Full Text Available Abstract Tuning the electronic band structures such as band-edge position and bandgap of organic semiconductors is crucial to maximize the performance of organic photovoltaic devices. We present a simple yet effective electron irradiation approach to tune the band structure of [6, 6]-phenyl-C61-butyric acid methyl ester (PCBM that is the most widely used organic acceptor material. We have found that the lowest unoccupied molecular orbital (LUMO level of PCBM up-shifts toward the vacuum energy level, while the highest occupied molecular orbital (HOMO level down-shifts when PCBM is electron-irradiated. The shift of the HOMO and the LUMO levels increases as the irradiated electron fluence increases. Accordingly, the band-edge position and the bandgap of PCBM can be controlled by adjusting the electron fluence. Characterization of electron-irradiated PCBM reveals that the variation of the band structure is attributed to the molecular structural change of PCBM by electron irradiation.

Yoo Seung

2011-01-01

119

Band structure calculations for Ba$_{6}$Ge$_{25}$ and Ba$_{4}$Na$_{2}$Ge$_{25}$ clathrates

Digital Repository Infrastructure Vision for European Research (DRIVER)

Electronic band structures for Ba$_{6}$Ge$_{25}$ and Ba$_{4}$Na$_{2}$Ge$_{25}$ clathrates are calculated using linear muffin-tin orbital method within the local density approximation. It is found that barium states strongly contribute to the density of states at the Fermi level and thus can influence the transport properties of the compounds. A sharp peak of the density of states is found just at the Fermi level. It is also shown that the shifting of barium atoms toward expe...

Zerec, Ivica; Yaresko, Alexander; Thalmeier, Peter; Grin, Yuri

2002-01-01

120

The full quasiparticle band structure of CdWO4 is calculated within the single-shot GW (G0W0) approximation using maximally localized Wannier functions, which allows one to assess the validity of the commonly used scissor operator. Calculations are performed using the Godby-Needs plasmon pole model and the accurate contour deformation technique. It is shown that while the two methods yield identical band gap energies, the low-lying states are given inaccurately by the plasmon pole model. We report a band gap energy of 4.94 eV, including spin-orbit interaction at the DFT-LDA (density functional theory-local density approximation) level. Quasiparticle renormalization in CdWO4 is shown to be correlated with localization distance. Electron and hole effective masses are calculated at the DFT and G0W0 levels. PMID:24599225

Laasner, Raul

2014-03-26

121

International Nuclear Information System (INIS)

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

122

Modification of band structure in intense laser fields

International Nuclear Information System (INIS)

In the presence of the intense laser field, the Floquet-green's function method has been used for the calculation of the field-modified band structure for a one-dimensional periodic potential. Numerical illustrations show that the energy band structure is strongly modified by the intense laser field (1013-1014 W/cm2 at =780 mn). It is also shown that the laser field creates new laser-induced forbidden gaps, widths of which increase with increasing intensity of radiation. Evaluation of the mean energy spectrum in crystals has been also presented for different intensities of laser field

123

Analytical Study of Band Structure of Material Using Relativistic Concept

Directory of Open Access Journals (Sweden)

Full Text Available In this paper, we present the study of band structure relativistically. Here, Dirac equation is formulated from Hamilto-nian in which the formulation is found to contain a correction term known as spin-orbit coupling given as that modifies the non-relativistic expression for the same formulation. This term leads to double spin-degeneracy within the first Brillioun zone which is a concept that is not found in other method of study of band structure of material.

E. I. Ugwu

2013-08-01

124

Band structure of neutron rich Se and Ge isotopes

International Nuclear Information System (INIS)

The band structure of the neutron-rich Se and Ge isotopes has been studied in terms of the full-fledged shell model. The monopole and quadrupole pairing plus quadrupole-quadrupole interaction is employed as an effective interaction. The model reproduces well the energy levels of high-spin states as well as the low-lying states. In order to investigate the structure of the high-spin states and low-lying collective states, the energy spectra in the shell model are compared with those in the quantum-number-projected generator coordinate method. It is shown that the triaxial components play essential roles in describing the ? bands

125

Let $X_1,...,X_n$ be a random sample from some unknown probability density $f$ defined on a compact homogeneous manifold $\\mathbf M$ of dimension $d \\ge 1$. Consider a 'needlet frame' $\\{\\phi_{j \\eta}\\}$ describing a localised projection onto the space of eigenfunctions of the Laplace operator on $\\mathbf M$ with corresponding eigenvalues less than $2^{2j}$, as constructed in \\cite{GP10}. We prove non-asymptotic concentration inequalities for the uniform deviations of the linear needlet density estimator $f_n(j)$ obtained from an empirical estimate of the needlet projection $\\sum_\\eta \\phi_{j \\eta} \\int f \\phi_{j \\eta}$ of $f$. We apply these results to construct risk-adaptive estimators and nonasymptotic confidence bands for the unknown density $f$. The confidence bands are adaptive over classes of differentiable and H\\"{older}-continuous functions on $\\mathbf M$ that attain their H\\"{o}lder exponents.

Kerkyacharian, Gerard; Picard, Dominique

2011-01-01

126

The energy band structure of AxFe2Se2 (A = K, Rb) superconductors

International Nuclear Information System (INIS)

We study the band structure of antiferromagnetic AxFe2Se2 (A = K, Rb) superconductors by using first-principles electronic structure calculations which is density functional theory. In the vicinity of iron-vacancy, we identify the valence electrons of AxFe2Se2 will be filled up to the Fermi level and no semiconducting gap is observed. Hence, the AxFe2Se2 is a metallic instead of semiconducting which leads to superconductivity in the orbital-selective Mott phase. Similarly, there is non-vanishing density of states at the Fermi level

127

Novel structural flexibility identification in narrow frequency bands

International Nuclear Information System (INIS)

A ‘Sub-PolyMAX’ method is proposed in this paper not only for estimating modal parameters, but also for identifying structural flexibility by processing the impact test data in narrow frequency bands. The traditional PolyMAX method obtains denominator polynomial coefficients by minimizing the least square (LS) errors of frequency response function (FRF) estimates over the whole frequency range, but FRF peaks in different structural modes may have different levels of magnitude, which leads to the modal parameters identified for the modes with small FRF peaks being inaccurate. In contrast, the proposed Sub-PolyMAX method implements the LS solver in each subspace of the whole frequency range separately; thus the results identified from a narrow frequency band are not affected by FRF data in other frequency bands. In performing structural identification in narrow frequency bands, not in the whole frequency space, the proposed method has the following merits: (1) it produces accurate modal parameters, even for the modes with very small FRF peaks; (2) it significantly reduces computation cost by reducing the number of frequency lines and the model order in each LS implementation; (3) it accurately identifies structural flexibility from impact test data, from which structural deflection under any static load can be predicted. Numerical and laboratory examples are investigated to verify the effectiveness of the proposed method. (paper)

128

Self-consistent Green's function method for dilute nitride conduction band structure

We present a self-consistent Green's function (SCGF) approach for the Anderson many-impurity model to calculate the band dispersion and density of states near the conduction band edge in GaNxAs1-x dilute nitride alloys. Two different models of the N states have been studied to investigate the band structure of these materials: (1) the two-band model, which assumes all N states have the same energy, EN; (2) a model which includes a full distribution of N states obtained by allowing for direct interaction between N sites. The density of states, projected onto extended and localised states, calculated by the SCGF two-band model, are in excellent agreement with those previously obtained in supercell calculations and reveal a gap in the density of states just above EN, in contrast with the results of previous non-self-consistent Green's function calculations. However, including the full distribution of N states in a SCGF calculation removes this gap, in agreement with experiment.

Seifikar, Masoud; O'Reilly, Eoin P.; Fahy, Stephen

2014-09-01

129

We present an analysis of K-band stellar distributions for the young stellar clusters GGD 12-15, IRAS 20050+2720, and NGC 7129. We find that the two deeply embedded clusters, GGD 12-15 and IRAS 20050+2720, are not azimuthally symmetric and show a high degree of structure which traces filamentary structure observed in 850 micron emission maps. In contrast, the NGC 7129 cluster is circularly symmetric, less dense, and anti-correlated to 850 micron emission, suggesting recent gas expulsion and dynamical expansion have occured. We estimate stellar volume densities from nearest neighbor distances, and discuss the impact of these densities on the evolution of circumstellar disks and protostellar envelopes in these regions.

Gutermuth, R A; Pipher, J L; Williams, J P; Allen, L E; Myers, P C; Raines, S N

2004-01-01

130

Birefringence and band structure of CdP2 crystals

The spatial dispersion in CdP2 crystals was investigated. The dispersion is positive (nk||?>nk||?) at ?>?0 and negative (nk||?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

131

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english In this paper, single and dual band EBG structures for wider bandwidth are proposed. In each of the discussed EBGs, a metallic patch of regular geometry is chosen for the unit element. The patch is further modified by cutting slots to get extra inductance and capacitance which results into lower cut [...] -off frequency and larger bandwidth. The proposed EBG structures are compared with the standard mushroom type EBG with respect to surface wave attenuation. The -20 dB cut-off frequencies and bandwidths of the various EBGs are compared. The effect of unit element size, gap between unit elements and via diameter on the transmission response is presented. Among the discussed EBGs, the swastika type structure is compact, single band and has wider bandwidth. The square patch with a single disconnected loop type slot EBG and the Fractal EBG are dual band. While square patch is more compact, the fractal EBG has wider bandwidth. All the EBGs can be useful in the design of antenna and other microwave circuits.

Nagendra, Kushwaha; Raj, Kumar.

2014-06-01

132

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english In this paper, single and dual band EBG structures for wider bandwidth are proposed. In each of the discussed EBGs, a metallic patch of regular geometry is chosen for the unit element. The patch is further modified by cutting slots to get extra inductance and capacitance which results into lower cut [...] -off frequency and larger bandwidth. The proposed EBG structures are compared with the standard mushroom type EBG with respect to surface wave attenuation. The -20 dB cut-off frequencies and bandwidths of the various EBGs are compared. The effect of unit element size, gap between unit elements and via diameter on the transmission response is presented. Among the discussed EBGs, the swastika type structure is compact, single band and has wider bandwidth. The square patch with a single disconnected loop type slot EBG and the Fractal EBG are dual band. While square patch is more compact, the fractal EBG has wider bandwidth. All the EBGs can be useful in the design of antenna and other microwave circuits.

Nagendra, Kushwaha; Raj, Kumar.

133

In this letter we address the problem of phase stability in the relatively new element 112, namely Copernicium (Cn). The ground state properties as well as the thermodynamic quantities were computed from a first-principles approach based on the local density approximation with spin orbit (SO) consideration. We found that relativistic effects play a vital role in the phase stability and electronic properties of Cn. The obtained results reveal some unusual energetic competition between the crystallographic forms that Cn may adopt, i.e., sc, bcc, fcc and hcp. Nevertheless, relativistic SO coupling increases the energetic stability of the bcc phase over the other structures; moreover dynamical calculations via phonon dispersion provide strong support for our findings. Band structure results indicate that Copernicium is at least a semiconductor in all possible phases. The valence bands of Cn have strong 6d character, with a significant mixing between the fully occupied 7s and 6d bands.

Zaoui, A.; Ferhat, M.

2012-03-01

134

We report theoretical predictions and experimental results on the formation of pass bands and stop bands of extraordinary acoustic transmission in multilayer structures based on alternating layers of acoustic metamaterial and air. The metamaterial layers can be made of any acoustically hard material perforated with a two-dimensional array of subwavelength apertures. In this way, it is possible to tailor the density and speed of sound of an otherwise acoustically bulk hard material with fixed properties. The sonic band structure allows transmission passband and stop bandgaps that depend on the layer thicknesses and effective properties of the metamaterials. In addition, we show the existence of resonant tunneling due to the formation of an acoustic passband in a spectral region of low transmission for a single layer. This opens the possibility to engineer different types of phononic materials to manipulate and control acoustic waves.

Aközbek, N.; Mattiucci, N.; Bloemer, M. J.; Sanghadasa, M.; D'Aguanno, G.

2014-04-01

135

X-Band Photonic Band-Gap Accelerator Structure Breakdown Experiment

Energy Technology Data Exchange (ETDEWEB)

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

136

X-Band Photonic Band-Gap Accelerator Structure Breakdown Experiment

International Nuclear Information System (INIS)

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 puls 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.

137

Band structure and optical properties of amber studied by first principles

International Nuclear Information System (INIS)

The band structure and density of states of amber is studied by the first principles calculation based on density of functional theory. The complex structure of amber has 214 atoms and the band gap is 5.0 eV. The covalent bond is combined C/O atoms with H atoms. The O 2p orbital is the biggest effect near the Fermi level. The optical properties' results show that the reflectivity is low, and the refractive index is 1.65 in visible light range. The highest absorption coefficient peak is at 172 nm and another higher peak is at 136 nm. These convince that the amber would have a pretty sheen and that amber is a good and suitable crystal for jewelry and ornaments

138

Band structure and optical properties of amber studied by first principles

The band structure and density of states of amber is studied by the first principles calculation based on density of functional theory. The complex structure of amber has 214 atoms and the band gap is 5.0 eV. The covalent bond is combined C/O atoms with H atoms. The O 2p orbital is the biggest effect near the Fermi level. The optical properties' results show that the reflectivity is low, and the refractive index is 1.65 in visible light range. The highest absorption coefficient peak is at 172 nm and another higher peak is at 136 nm. These convince that the amber would have a pretty sheen and that amber is a good and suitable crystal for jewelry and ornaments.

Rao, Zhi-Fan; Zhou, Rong-Feng

2013-03-01

139

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

International Nuclear Information System (INIS)

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

140

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

Energy Technology Data Exchange (ETDEWEB)

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

141

First-Principles Band Calculations on Electronic Structures of Ag-Doped Rutile and Anatase TiO2

International Nuclear Information System (INIS)

The electronic structures of Ag-doped rutile and anatase TiO2 are studied by first-principles band calculations based on density functional theory with the full-potential linearized-augmented-plane-wave method. New occupied bands are found between the band gaps of both Ag-doped rutile and anatase TiO2. The formation of these new bands can be explained mainly by their orbitals of Ag 4d states mixed with Ti 3d states and are supposed to contribute to their visible light absorption. (condensed matter: electronicstructure, electrical, magnetic, and opticalproperties)

142

Multi-band and broadband acoustic metamaterial with resonant structures

International Nuclear Information System (INIS)

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

143

Photonic crystal digital alloys and their band structure properties.

We investigated semi-disordered photonic crystals (PCs), digital alloys, and made thorough comparisons with their counterparts, random alloys. A set of diamond lattice PC digital alloys operating in a microwave regime were prepared by alternately stacking two kinds of sub-PC systems composed of alumina and silica spheres of the same size. Measured transmission spectra as well as calculated band structures revealed that when the digital alloy period is short, band-gaps of the digital alloys are practically the same as those of the random alloys. This study indicates that the concept of digital alloys holds for photons in PCs as well. PMID:21996867

Lee, Jeongkug; Kim, Dong-Uk; Jeon, Heonsu

2011-09-26

144

Electronic band structure of magnetic bilayer graphene superlattices

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

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

2014-09-01

145

Structurally tunable resonant absorption bands in ultrathin broadband plasmonic absorbers.

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

Butun, Serkan; Aydin, Koray

2014-08-11

146

Antiferromagnetic band structure of La2CuO4: Becke- 3-Lee-Yang-Parr calculations

Using the Becke-3-Lee-Yang-Parr (B3LYP) functional, we have performed band-structure calculations on the high-temperature superconductor parent compound, La2CuO4. Under the restricted spin formalism (??=??), B3LYP band structure agrees well with the standard local-density approximation (LDA) band structure. It is metallic with a single Cu x2-y2/O p? band crossing the Fermi level. Under the unrestricted spin formalism (?????), the B3LYP band structure has a spin-polarized antiferromagnetic solution with a band gap of 2.0 eV, agreeing well with experiment. This state is 0.52 eV (per formula unit) lower than that calculated under the restricted spin formalism. The apparent high energy of the spin-restricted state is attributed to an overestimate of on-site Coulomb repulsion, which is corrected in the unrestricted spin calculations. The stabilization of the total energy with spin polarization arises primarily from the stabilization of the x2-y2 band, such that the character of the eigenstates at the top of the valence band in the antiferromagnetic state becomes a strong mixture of Cu x2-y2/O p? and Cu z2/O' pz. Since the Hohenberg-Kohn theorem requires the spin-restricted and spin-unrestricted calculations to give identical ground-state energies and total spatial densities for the exact functionals, this large disparity in energy reflects the inadequacy of current functionals for describing the cuprates. This calls into question the use of band structures based on current restricted spin-density functionals (including LDA) as a basis for single-band theories of superconductivity in these materials.

Perry, Jason K.; Tahir-Kheli, Jamil; Goddard, William A.

2001-04-01

147

As one of the core reservoirs of primary production in the world's oceans, tropical coral reefs support a complex ecosystem that directly impacts over ninety percent of marine organisms at some point in their life cycle. Corals themselves are highly complex organisms and exhibit a range of growth forms that range from branching to massive, foliaceous, columnar, encrusting, free living and laminar coralla. Fierce competition over scarce resources available to each individual coral species creates niche specialization. Throughout the Phanerozic geological record, this has driven speciation events and created distinct skeletal growth morphologies that have differential abilities in feeding strategy. In turn, this has presumably led to the development of niche specialization that can be quantitatively measured through hierarchical morphological differences from the micrometer to the meter scale. Porter (1976) observed significant differences in skeletal morphology between Caribbean coral species that reflects an adaptive geometry based on feeding strategy. Within the Montastraea species complex there are four major morphologies; columnar, bouldering, irregular mounding, and skirted. Each morphotype can be found forming high abundance along the bathymetric gradient of coral reefs that grow along the leeward coast of Curacao, Netherlands Antilles. We have undertaken a study to determine the relative relationships amongst coral morphology, skeletal density and feeding strategy by comparing the morphometric measurements of individual polyps as well as the entire colony along spatial and bathymetric gradients. Polyp diameter, mouth size, interpolyp area, and interpolyp distance were measured from high-resolution images taken on a stereoscope, and evaluated with AxioVision image analysis software. These high-resolution optical analyses have also revealed new observations regarding folded tissue structures of the outer margin of polyps in the Montastrea complex. Skeletal densities were measured in vertical cross-sections of each whole corallum using standard X-ray techniques utilizing a calibrated step wedge to portray banding and overall density. The combination of the stereoscope and X-ray analyses across spatial and temporal gradients provide insight into how coral reef carbonate depositional facies are affected by changes in key environmental parameters, such as increased pollution, or changing photosynthetic activity with depth or sea surface temperature fluctuations.

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

2008-12-01

148

Sieve-based confidence intervals and bands for L\\'{e}vy densities

The estimation of the L\\'{e}vy density, the infinite-dimensional parameter controlling the jump dynamics of a L\\'{e}vy process, is considered here under a discrete-sampling scheme. In this setting, the jumps are latent variables, the statistical properties of which can be assessed when the frequency and time horizon of observations increase to infinity at suitable rates. Nonparametric estimators for the L\\'{e}vy density based on Grenander's method of sieves was proposed in Figueroa-L\\'{o}pez [IMS Lecture Notes 57 (2009) 117--146]. In this paper, central limit theorems for these sieve estimators, both pointwise and uniform on an interval away from the origin, are obtained, leading to pointwise confidence intervals and bands for the L\\'{e}vy density. In the pointwise case, our estimators converge to the L\\'{e}vy density at a rate that is arbitrarily close to the rate of the minimax risk of estimation on smooth L\\'{e}vy densities. In the case of uniform bands and discrete regular sampling, our results are consis...

Figueroa-López, José E

2011-01-01

149

Theoretical Study of Specific Heat and Density of States of MgB2 Superconductor in Two Band Model

Directory of Open Access Journals (Sweden)

Full Text Available MgB2 with Tc ? 40 K, is a record-breaking compound among the s-p metals and alloys. It appears that this material is a rare example of the two band electronic structures, which are weakly connected with each other. Experimental results clearly reveal that boron sub-lattice conduction band is mainly responsible for superconductivity in this simple compound. Experiments such as tunneling spectroscopy, specific heat measurements, and high resolution spectroscopy show that there are two superconducting gaps. Considering a canonical two band BCS Hamiltonian containing a Fermi Surface of ?- and ?-bands and following Green’s function technique and equation of motion method, we have shown that MgB2 possess two superconducting gaps. It is also pointed out that the system admits a precursor phase of Cooper pair droplets that undergoes a phase locking transition at a critical temperature below the mean field solution. Study of specific heat and density of states is also presented. The agreement between theory and experimental results for specific heat is quite convincing. The paper is organized in five sections: Introduction, Model Hamiltonian, Physical properties, Numerical calculations, Discussion and conclusions.

Shyam Lal Kakani

2013-02-01

150

Reduced Bloch mode expansion for periodic media band structure calculations

Reduced Bloch mode expansion is presented for fast periodic media band structure calculations. The expansion employs a natural basis composed of a selected reduced set of Bloch eigenfunctions. The reduced basis is selected within the irreducible Brillouin zone at high symmetry points determined by the medium's crystal structure and group theory (and possibly at additional related points). At each of the reciprocal lattice selection points, a number of Bloch eigenfunctions are selected up to the frequency range of interest for the band structure calculations. Since it is common to initially discretize the periodic unit cell and solution field using some choice of basis, reduced Bloch mode expansion is practically a secondary expansion that uses a selected set of Bloch eigenvectors. Such expansion therefore keeps, and builds on, any favorable attributes a primary expansion approach might exhibit. Being in line with the well known concept of modal analysis, the proposed approach maintains accuracy while reducing...

Hussein, Mahmoud I

2008-01-01

151

QUANTITATIVE ANALYSIS OF BANDED STRUCTURES IN DUAL-PHASE STEELS

Directory of Open Access Journals (Sweden)

Full Text Available Dual-Phase (DP steels are composed of martensite islands dispersed in a ductile ferrite matrix, which provides a good balance between strength and ductility. Current processing conditions (continuous casting followed by hot and cold rolling generate 'banded structures' i.e., irregular, parallel and alternating bands of ferrite and martensite, which are detrimental to mechanical properties and especially for in-use properties. We present an original and simple method to quantify the intensity and wavelength of these bands. This method, based on the analysis of covariance function of binary images, is firstly tested on model images. It is compared with ASTM E-1268 standard and appears to be more robust. Then it is applied on real DP steel microstructures and proves to be sufficiently sensitive to discriminate samples resulting from different thermo-mechanical routes.

Benoit Krebs

2011-05-01

152

Joint density of states of wide-band-gap materials by electron energy loss spectroscopy

International Nuclear Information System (INIS)

Kramers-Kronig analysis for parallel electron energy loss spectroscopy (PEELS) data is developed as a software package. When used with a JEOL 4000EX high-resolution transmission electron microscope (HRTEM) operating at 100 keV this allows us to obtain the dielectric function of relatively wide band gap materials with an energy resolution of approx 1.4 eV. The imaginary part of the dielectric function allows the magnitude of the band gap to be determined as well as the joint-density-of-states function. Routines for obtaining three variations of the joint-density of states function, which may be used to predict the optical and dielectric response for angle-resolved or angle-integration scattering geometries are also described. Applications are presented for diamond, aluminum nitride (AlN), quartz (SiO2) and sapphire (Al2O3). The results are compared with values of the band gap and density of states results for these materials obtained with other techniques. (authors)

153

Local density of optical states in the band gap of a finite photonic crysta

We study the local density of states (LDOS) in a finite photonic crystal, in particular in the frequency range of the band gap. We propose a new point of view on the band gap, which we consider to be the result of vacuum fluctuations in free space that tunnel in the forbidden range in the crystal. As a result, we arrive at a model for the LDOS that is in two major items modified compared to the well-known expression for infinite crystals. Firstly, we modify the Dirac delta functions to become Lorentzians with a width set by the crystal size. Secondly, building on characterization of the fields versus frequency and position we calculated the fields in the band gap. We start from the fields at the band edges, interpolated in space and position, and incorporating the exponential damping in the band gap. We compare our proposed model to exact calculations in one dimension using the transfer matrix method and find very good agreement. Notably, we find that in finite crystals, the LDOS depends on frequency, on posi...

Yeganegi, Elahe; Mosk, Allard P; Vos, Willem L

2014-01-01

154

Polarimetric and Structural Properties of a Boreal Forest at P-Band and L-Band

With this paper we investigate the structural and polarimetric of the boreal forest within the Krycklan river catchment, Northern Sweden, basing on multi-polarimetric and multi-baseline SAR surveys at P-Band and L-Band collected in the framework of the ESA campaign BioSAR 2008. The analysis has been carried out by applying the Algebraic Synthesis (AS) technique, recently introduced in literature, which provides a theoretical framework for the decomposition of the backscattered signal into ground-only and volume-only contributions, basing on both baseline and polarization diversity. The availability of multiple baselines allows the formation of a synthetic aperture not only along the azimuth direction but also in elevation. Accordingly, the backscattered echoes can be focused not only in the slant range, azimuth plane, but in the whole 3D space. This is the rationale of the SAR Tomography (T-SAR) concept, which has been widely considered in the literature of the last years. It follows that, as long as the penetration in the scattering volume is guaranteed, the vertical profile of the vegetation layer is retrieved by separating backscatter contributions along the vertical direction, which is the main reason for the exploitation of Tomographic techniques at longer wavelengths. Still, the capabilities of T-SAR are limited to imaging the global vertical structure of the electromagnetic scattering in a certain polarization. It then becomes important to develop methodologies for the investigation of the vertical structure of different Scattering Mechanisms (SMs), such as ground and volume scattering, in such a way as to derive information that can be delivered also outside the field of Radar processing. This is an issue that may become relevant at longer wavelengths, such as P-Band, where the presence of multiple scattering arising from the interaction with terrain could hinder the correct reconstruction of the forest structure. The availability of multiple polarizations allows to overcome this limitation, thus providing a way to obtain the vertical structures associated with volume-only contributions. Experimental results will be provided showing the following. At P-Band the most relevant scattering contributions are observed at the ground level, not only in the co-polar channels, but also in HV, consistently with he first BioSAR campaign. L-Band data have shown a remarkable difference, resulting in a more uniform distribution of the backscattered power along the vertical direction. Volume top height has been observed to be substantially invariant to the choice of the solution for volume-only scattering. These results underline the validity of modeling a forest scenario as being constituted by volume and ground (or rather ground-locked) scattering, and the importance of forest top height as the most robust indicator of the forest structure as imaged through microwaves measurements. Nevertheless, it has also been shown that different solutions for volume scattering correspond to dramatically different vertical structures. In this framework, tomography represents a powerful tool for investigating the potential solutions, as it allows to see what kind of vertical structure has been retrieved. On this basis, a solution has been proposed as a criterion to emphasize volume contributions at P-Band.

Tebaldini, S.; Rocca, F.

2010-12-01

155

Band structure parameters for quantum wells: Magnetoluminescence determinations

Energy Technology Data Exchange (ETDEWEB)

We report on low-temperature magnetoluminescence determinations of bandstructure parameters for an 8.5nm-wide n-type In{sub 0.20}Ga{sub 0.80}As/GaAs strained single-quantum well structure. We find that the conduction-band is almost parabolic, with its mass varying from 0.067m{sub 0} at zone center to 0.069m{sub 0} at a Fermi energy E{sub f} {approx} 50 meV, and that the valence-bands are highly non-parabolic with the valence band masses m, varying from about 0.1 m{sub 0} at zone center to about 0.3m{sub 0} for large k-vectors. A comparison with a k x p calculation for the valence-band mass and dispersion curve show good agreement. An accurate and unambiguous determination for the band-gap energy E{sub gap} is made by extrapolating the magnetic field dependent Landau level transition energies to zero field.

Jones, E.D.

1997-04-01

156

Band structures of the {sup 123}Cs nucleus

Energy Technology Data Exchange (ETDEWEB)

Band structures of the {sup 123}Cs nucleus have been investigated using the {sup 100}Mo({sup 28}Si,p4n) reaction at a beam energy of 130 MeV. The previously observed rotational bands based on {pi}h{sub 11/2},{pi}g{sub 7/2} and {pi}g{sub 9/2} orbitals have been extended. The excitation energies of these bands have been established with the help of interband transitions and those connecting to the low-energy levels established from the {beta}{sup +}/EC decay of {sup 123}Ba(T{sub 1/2}=2.7 m). The bandhead of the {pi}g{sub 9/2} band at the 328.1 keV (I{sup {pi}}=9/2{sup +}) is proposed to be isomeric following arguments based on the intensity balance of the feeding and de-exciting {gamma} transitions. New multiquasiparticle bands based on {pi}h{sub 11/2} x {nu}h{sub 11/2} x {nu}g{sub 7/2}, {pi}g{sub 7/2} x {pi}(h{sub 11/2}){sup 2} and {pi}g{sub 7/2} x {pi}(h{sub 11/2}){sup 2} x {nu}(h{sub 11/2}){sup 2} configurations have been identified. (orig.)

Singh, Kuljeet; Goswamy, J.; Mehta, D.; Singh, Nirmal; Singh, K.P. [Panjab University, Department of Physics, Chandigarh (India); Singh, R.P.; Muralithar, S.; Madhavan, N.; Das, J.J.; Nath, S.; Jhingan, A.; Sughathan, P.; Bhowmik, R.K. [Nuclear Science Centre, New Delhi (India); Paul, E.S. [University of Liverpool, Oliver Lodge Laboratory (United Kingdom)

2004-09-01

157

Optimum design of band-gap beam structures

DEFF Research Database (Denmark)

The design of band-gap structures receives increasing attention for many applications in mitigation of undesirable vibration and noise emission levels. A band-gap structure usually consists of a periodic distribution of elastic materials or segments, where the propagation of waves is impeded or significantly suppressed for a range of external excitation frequencies. Maximization of the band-gap is therefore an obvious objective for optimum design. This problem is sometimes formulated by optimizing a parameterized design model which assumes multiple periodicity in the design. However, it is shown in the present paper that such an a priori assumption is not necessary since, in general, just the maximization of the gap between two consecutive natural frequencies leads to significant design periodicity. The aim of this paper is to maximize frequency gaps by shape optimization of transversely vibrating Bernoulli–Euler beams subjected to free, standing wave vibration or forced, time-harmonic wave propagation, and to study the associated creation of periodicity of the optimized beam designs. The beams are assumed to have variable cross-sectional area, given total volume and length, and to be made of a single, linearly elastic material without damping. Numerical results are presented for different combinations of classical boundary conditions, prescribed orders of the upper and lower natural frequencies of maximized natural frequency gaps, and a given minimum constraint value for the beam cross-sectional area. To study the band-gap for travelling waves, a repeated inner segment of the optimized beams is analyzed using Floquet theory and the waveguide finite element (WFE) method. Finally, the frequency response is computed for the optimized beams when these are subjected to an external time-harmonic loading with different excitation frequencies, in order to investigate the attenuation levels in prescribed frequency band-gaps. The results demonstrate that there is almost perfect correlation between the band-gap size/location of the emerging band structure and the size/location of the corresponding natural frequency gap in the finite structure.

Olhoff, Niels; Niu, Bin

2012-01-01

158

Engineering Design of a Multipurpose X-band Accelerating Structure

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

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

2010-01-01

159

Charge-Density-Wave Phase of 1T-TiSe2: The Influence of Conduction Band Population

The charge-density-wave phase of TiSe2 was studied by angle-resolved photoelectron spectroscopy and resistivity measurements investigating the influence of the band gap size and of a varying population of the conduction band. A gradual suppression of the charge-density-wave-induced electronic superstructure is observed for a variation of the band gap in the ternary compounds TiCxSe2-x with C=(S,Te) as well as for an occupation of only the conduction band by H2O adsorption-induced band bending. These observations point to an optimum band gap and support an excitonic driving force for the charge-density wave.

May, Matthias M.; Brabetz, Christine; Janowitz, Christoph; Manzke, Recardo

2011-10-01

160

Electronic structure of BaCu$_2$As$_2$ and SrCu$_2$As$_2$: sp-band metals

Digital Repository Infrastructure Vision for European Research (DRIVER)

The electronic structures of ThCr$_2$Si$_2$ structure BaCu$_2$As$_2$ and SrCu$_2$As$_2$ are investigated using density functional calculations. The Cu $d$ orbitals are located at 3 eV and higher binding energy, and are therefore chemically inert with little contribution near the Fermi energy. These materials are moderate density of states, sp-band metals with large Fermi surfaces and low anisotropy.

Singh, D. J.

2009-01-01

161

Structural, elastic, optical properties and quasiparticle band structure of solid cyanuric triazide

In this Letter, we report the structural, elastic, and quasiparticle band structure of cynauric triazide. The structural properties using a dispersion corrected method to treat van der Waals (vdW) forces offers a significant improvement in the description of the ground state properties. The predicted bulk modulus from the equation of state and the elastic constants are consistent and the magnitude lies in the order of secondary explosives. Then, the G0W0 approximation is used to study the band structure and an indirect band gap of 6.33 eV is obtained. Finally, we have calculated the optical and detonation characteristics at ambient pressure.

Appalakondaiah, S.; Vaitheeswaran, G.; Lebègue, S.

2014-06-01

162

First direct observation of a nearly ideal graphene band structure.

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. Each cone corresponds to an individual macroscale graphene sheet in a multilayer stack where AB-stacked sheets can be considered as low density faults. PMID:20366119

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

2009-11-27

163

Novel band structure of odd-A 107Cd

International Nuclear Information System (INIS)

The odd-A 107Cd nucleus is situated in a transitional region between spherical and deformed nuclei. In the 1970s and 1980s, a number of experiments to study the low spin states of 107Cd were carried out by several authors. The high spin states of 107Cd were studied by Jerrestam et al. in 1992. In the present paper, we discuss the spectroscopic features and lifetimes of the negative parity band structure of 107Cd

164

The structure of rotational bands in alpha-cluster nuclei

In this contribution, I discuss an algebraic treatment of alpha-cluster nuclei based on the introduction of a spectrum generating algebra for the relative motion of the alpha-clusters. Particular attention is paid to the discrete symmetry of the geometric arrangement of the alpha-particles, and the consequences for the structure of the rotational bands in the 12C and 16O nuclei.

Bijker, Roelof

2014-01-01

165

The grain growth behavior of austenite reversely transformed from ferrite/pearlite (F/P)-banded and non-banded steels has been studied. It was found that the grain-coarsening temperature [the temperature at which abnormal grain growth (AGG) occurs] of the initially banded F/P structure is quite low compared with that of the non-banded sample. In the F/P-banded sample, the abnormal grains always originate from the former ferrite region. The occurrence of AGG is essentially attributable not to the austenite nucleation process during heating but to the grain growth process after the completion of austenizing. It was proposed that the lowered grain-coarsening temperature in the banded structure is due to the non-uniform pinning-effect of AlN precipitates between former ferrite and pearlite regions.

Zhang, Xianguang; Matsuura, Kiyotaka; Ohno, Munekazu

2014-09-01

166

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

International Nuclear Information System (INIS)

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

167

Phenyl radical (Ph?) adsorption on monolayer graphene sheets is used to investigate the band-gap manipulation of graphene through density functional theory. Adsorption of a single Ph? on graphene breaks the aromatic ?-bond and generates an unpaired electron, which is delocalized to the ortho or para position. Adsorption of a second radical at the ortho or para position saturates the radical by electron pairing and results in semiconducting graphene. Adsorption of a second radical at the ortho position (ortho-ortho pairing) is found to be more favorable than adsorption at the para position (ortho-para pairing), and the ortho-ortho pairing has stronger effects on band-gap opening compared with ortho-para pairing. Adsorption of even numbers of Ph? on graphene by ortho-ortho and ortho-para pairings, in general, increases the band gap. Our study shows promise of band-gap manipulation in monolayer graphene by Ph? adsorption, leading to potential wider applications of graphene. PMID:24925258

Huang, Lin; Sk, Mahasin Alam; Chen, Peng; Lim, Kok Hwa

2014-08-25

168

Detection limit improvement for iodine Cordes-Band based hypersonic density measurements

Measurements in the wake region created by models in supersonic and hypersonic flows are required in order to understand a variety of problems in aerodynamics. In this experiment we investigated the properties of using broadband excitation, as opposed to narrowband excitation, using an ArF laser as a means for increasing the detection limit of density measurements in air. The mechanism for this involves Iodine Cordes-Band spectroscopy. Laser excitation of the Cordes bands of I2 and the resulting emission involve a myriad of rotational, vibrational and electronic energy levels. I2 is optically pumped to the D state where approximately 85% of the emission regardless of buffer gas pressure results from D and D' transitions. In pure I2 McLennan-band emission dominates with the peak signal near 321nm. As the air pressure increases, collisions with air transfer the population from the D to D' state where that emission produces the 340nm band. As the air pressure increases the 321nm emission is rapidly quenched and the D' emission dominates (340nm). This provides a pressure dependent signal contribution. The goal is to improve the current detection limit by an order of magnitude by using a broadband laser beam instead of the narrowband beam. This should increase the detection limit by an order of magnitude.

Mills, Jack; Balla, Robert; Vuskovic, Lephsa

2009-10-01

169

Electronic band structure of the layered compound Td-WTe2

We have studied the electronic structure of the layered compound Td-WTe2 experimentally using high-resolution angle-resolved photoelectron spectroscopy, and theoretically using density-functional based augmented spherical wave calculations. Comparison of the measured and calculated data shows in general good agreement. The theoretical results reveal the semimetallic as well as metallic character of Td-WTe2; the semimetallic character is due to a 0.5 eV overlap of Te 5p- and W 5d-like bands along ?-Y, while the metallic character is due to two classical metallic bands. The rather low conductivity of Td-WTe2 is interpreted as resulting from a low density of states at the Fermi level.

Augustin, J.; Eyert, V.; Böker, Th.; Frentrup, W.; Dwelk, H.; Janowitz, C.; Manzke, R.

2000-10-01

170

Structure of the negative parity bands in Xe125

The high-spin structures of Xe125 were studied by using in-beam ?-ray spectroscopy with the Cd116 (C13, 4n) Xe125 reaction at Elab=62 MeV. The level scheme of Xe125 was constructed through the ?-? coincidences and ?-? angular directional correlation ratios. Several negative parity bands built on the neutron h11/2 orbital were identified. In contrast to the yrast h11/2 band with a large signature splitting, the second (yrare) h11/2 band exhibits a small signature splitting, showing signature inversion below I?=23/2-. In addition, a band built on the 27/2- level at 3619 keV was newly observed and found to be associated with a three quasiparticle alignment based on a neutron in the h11/2 orbital coupled to a pair of protons in the h11/2 orbital, namely, the ?[h11/2]?[(h11/2)2] configuration.

Moon, C.-B.; Lee, C. S.; Komatsubara, T.; Sasaki, Y.; Furuno, K.

2007-12-01

171

In this theoretical study, we employ a codoping strategy to reduce the band gap of NaTaO3 aimed at improving the photocatalytic activity under visible light. The systematic study includes the effects of metal (W) and nonmetal (N) codoping on the electronic structure of NaTaO3 in comparison to the effect of individual dopants. The feasibility of the introduction of N into the NaTaO3 crystal structure is found to be enhanced in the presence of W, as indicated by the calculated formation energy. This codoping leads to formation of a charge compensated system, beneficial for the minimization of vacancy related defect formation. The electronic structure calculations have been carried out using a hybrid density functional for an accurate description of the proposed system. The introduction of W in place of Ta leads to the appearance of donor states below the conduction band, while N doping in place of oxygen introduces isolated acceptor states above the valence band. The codoping of N and W also passivates undesirable discrete midgap states. This feature is not observed in the case of (Cr, N) codoped NaTaO3 in spite of its charge compensated nature. We have also studied charge non-compensated codoping using several dopant pairs, including anion-anion and cation-anion pairs. However, this non-compensated codoping introduces localized states in between the valence band and the conduction band, and hence may not be effective in enhancing the photocatalytic properties of NaTaO3. The optical spectrum shows that the absorption curve for the (W, N)-codoped NaTaO3 is extended to the visible region due to narrowing of the band gap to 2.67 eV. Moreover, its activity for the photo decomposition of water to produce both H2 and O2 remains intact. Hence, based on the present investigation we can propose (W, N) codoped NaTaO3 as a promising photocatalyst for visible light driven water splitting. PMID:25007948

Modak, Brindaban; Srinivasu, K; Ghosh, Swapan K

2014-08-28

172

Ab initio calculations of band structure and thermophysical properties for SnS2 and SnSe2

International Nuclear Information System (INIS)

The electronic band structure and elastic constants of SnS2 and SnSe2 have been calculated by using density-functional theory (DFT). The calculated band structures show that SnS2 and SnSe2 are both indirect band gap semiconductors. The upper valence bands originate mainly from Sp and Snd electrons, while the lowest conduction bands are mainly from (S, Se) p and Sns states. The calculated elastic constants indicate that the bonding strength along the [100] and [010] direction is stronger than that along the [001] direction and the shear elastic properties of the (010) plane are anisotropic for SnS2 and SnSe2. Both compounds exhibit brittle behavior due to their low B/G ratio. Relationships among volumes, the heat capacity, thermal expansion coefficients, entropy, vibrational energy, internal energy, Gibbs energy and temperature at various pressures are also calculated by using the Debye mode in this work.

173

Band structure mapping and calculations of CuInS2(001)

International Nuclear Information System (INIS)

The ternary compound semiconductor CuInS2 is used as an absorber material for thin film solar cells. A better understanding of the detailed electronic structure might lead to an improvement of the junction properties with respect to the still limited photo voltage of the present devices. We report on band structure mapping via ARUPS on thin epitaxial layers of CuInS2(001) prepared on sulfur passivated GaAs(100). To have a better control on the deposition process we introduced a MOMBE type deposition with an organic sulfur precursor. Samples were prepared and precharacterized in a dedicated UHV deposition and analysis system. ARUPS measurements were conducted at the beamline TGM7 at BESSY II. We discuss the experimentally determined band structure in comparison to recent augmented spherical wave (ASW) calculations as based on density functional theory and the local density approximation (LDA). Beside earlier calculations presented by Zunger for some high symmetry directions along ? perpendicular to our calculations include for ? parallel the experimental parameters of an ARUPS experiment thus allowing a direct comparison with our experimentally derived data rather than an idealistic run on the boundary of the Brillouin-zone. Additionally we derive the effective mass from the valence band curvature

174

Cell and band structures in cold rolled polycrystalline copper

DEFF Research Database (Denmark)

The effect of plastic strain on the deformation microstructure has been investigated in polycrystalline copper rolled at room temperature to 5, 10, 20, and 30% reduction in thickness equivalent strain 0.06-0.42). Results from transmission electron microscopy (TEM) observations show that dense dislocation walls (DDWs) and cells develop during the initial stages of cold rolling. Grains having a high density of DDWs are described as high wall density (HWD) structures, and grains having a low density of DDWs are described as low wall density (LWD) structures. These structures are characterised by cell size, misorientation across the cell walls, and the crystallographic orientation of the grains in which they appear. The DDWs in the HWD structures have special characteristics, extending along several cells and having a misorientation across them greater than that across ordinary cell boundaries at the same strain. The DDWs appear to have a macroscopically determined orientation. Analysis of their crystallographic orientation shows that they are not, as frequently reported in the literature, parallel to {111} planes. It is suggested that the DDWs separate regions of the crystal having different operating slip systems. Two generations of microbands are found to develop with increasing deformation. The first generation microbands are related to a continuous development of the structure according to the principle of grain subdivision, whereas the second generation microbands relate to localised shear on {111}. Finally, the evolution of the deformation microstructure in copper is compared with that observed in other face centred cubic metals, especially aluminium.

Leffers, Torben; Hansen, Niels

1991-01-01

175

Collective structures and band termination in {sup 107}Sb

Energy Technology Data Exchange (ETDEWEB)

High-spin states in the near proton-dripline nucleus {sup 107}Sb have been identified, and collectivity in this nucleus has been observed for the first time in the form of two rotational bands. One of the observed rotational structures is a {delta}I=1 band, and is interpreted as based on a {pi}(g{sub 9/2}){sup -1}(multiply-in-circle sign){pi}(g{sub 7/2}d{sub 5/2}){sup 2} proton configuration. A second structure has {delta}I=2 character, and is explained as being based on a {pi}h{sub 11/2}(multiply-in-circle sign)[{pi}(g{sub 9/2}){sup -2}(multiply-in-circle sign){pi}(g{sub 7/2}d{sub 5/2}){sup 2}] proton configuration through comparison with cranked Nilsson-Strutinsky model calculations. The calculations predict that this band terminates at a spin of 79/2 ({Dirac_h}/2{pi}). (c) 2000 The American Physical Society.

LaFosse, D. R. [Department of Physics and Astronomy, State University of New York at Stony Brook, Stony Brook, New York 11794-3800 (United States); Chiara, C. J. [Department of Physics and Astronomy, State University of New York at Stony Brook, Stony Brook, New York 11794-3800 (United States); Fossan, D. B. [Department of Physics and Astronomy, State University of New York at Stony Brook, Stony Brook, New York 11794-3800 (United States); Lane, G. J. [Department of Physics and Astronomy, State University of New York at Stony Brook, Stony Brook, New York 11794-3800 (United States); Sears, J. M. [Department of Physics and Astronomy, State University of New York at Stony Brook, Stony Brook, New York 11794-3800 (United States); Smith, J. F. [Department of Physics and Astronomy, State University of New York at Stony Brook, Stony Brook, New York 11794-3800 (United States); Starosta, K. [Department of Physics and Astronomy, State University of New York at Stony Brook, Stony Brook, New York 11794-3800 (United States); Boston, A. J. [Oliver Lodge Laboratory, University of Liverpool, P.O. Box 147, Liverpool L69 7ZE, (United Kingdom); Paul, E. S. [Oliver Lodge Laboratory, University of Liverpool, P.O. Box 147, Liverpool L69 7ZE, (United Kingdom); Semple, A. T. [Oliver Lodge Laboratory, University of Liverpool, P.O. Box 147, Liverpool L69 7ZE, (United Kingdom)

2000-07-01

176

Band structure of semimagnetic Hg1-yMnyTe quantum wells

The band structure of semimagnetic Hg1-yMnyTe/Hg1-xCdxTe type-III quantum wells (QW’s) has been calculated using an eight-band k•p model in an envelope function approach. Details of the band structure calculations are given for the Mn-free case (y=0) . A mean-field approach is used to take the influence of the sp-d exchange interaction on the band structure of QW’s with low Mn concentrations into account. The calculated Landau level fan diagram and the density of states of a Hg0.98Mn0.02Te/Hg0.3Cd0.7Te QW are in good agreement with recent experimental transport observations. The model can be used to interpret the mutual influence of the two-dimensional confinement and the sp-d exchange interaction on the transport properties of Hg1-yMnyTe/Hg1-xCdxTe QW’s.

Novik, E. G.; Pfeuffer-Jeschke, A.; Jungwirth, T.; Latussek, V.; Becker, C. R.; Landwehr, G.; Buhmann, H.; Molenkamp, L. W.

2005-07-01

177

Air Density Measurements in a Mach 10 Wake Using Iodine Cordes Bands

An exploratory study designed to examine the viability of making air density measurements in a Mach 10 flow using laser-induced fluorescence of the iodine Cordes bands is presented. Experiments are performed in the NASA Langley Research Center 31 in. Mach 10 air wind tunnel in the hypersonic near wake of a multipurpose crew vehicle model. To introduce iodine into the wake, a 0.5% iodine/nitrogen mixture is seeded using a pressure tap at the rear of the model. Air density was measured at 56 points along a 7 mm line and three stagnation pressures of 6.21, 8.62, and 10.0 MPa (900, 1250, and 1450 psi). Average results over time and space show rho(sub wake)/rho(sub freestream) of 0.145 plus or minus 0.010, independent of freestream air density. Average off-body results over time and space agree to better than 7.5% with computed densities from onbody pressure measurements. Densities measured during a single 60 s run at 10.0 MPa are time-dependent and steadily decrease by 15%. This decrease is attributed to model forebody heating by the flow.

Balla, Robert J.; Everhart, Joel L.

2012-01-01

178

Dual-band metamaterial with a windmill-like structure

International Nuclear Information System (INIS)

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

179

Dual-band metamaterial with a windmill-like structure

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

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

2013-01-01

180

A QES band-structure problem in one dimension

I show that the potential V(x,m)= {b 2}/{4}-m(1-m)a(a+1) {sn2(x,m) }/{dn2(x,m) }-b a+ {1}/{2}{cn(x,m) }/{dn2(x,m) } constitutes a QES band-structure problem in one dimension. In particular, I show that for any positive integral or half-integral a, 2 a+1 band edge eigenvalues and eigenfunctions can be obtained analytically. In the limit of m going to 0 or 1, I recover the well known results for the QES double sine-Gordon or double sinh-Gordon equations, respectively. As a by product, I also obtain the bound state eigenvalues and eigenfunctions of the potential V(x)= {? 2}/{4}-a(a+1) sech2x+? a+ {1}/{2}sechx tanhx in case a is any positive integer or half-integer.

Khare, Avinash

2001-09-01

181

Band structures and octupole correlation effects in 151Sm

International Nuclear Information System (INIS)

Excited states in 151Sm were populated through the 150Nd(?,3n) reaction at a beam energy of 35 MeV using a 9 mg/cm2 thick 150Nd target. An array of twenty Compton-suppressed germanium detectors was used to detect ?? and triple-? coincidences. The prime aim of this work was to investigate the effects of octupole correlations in odd-A nuclei in the A?150, N?88 region. A total of fifteen bands has been observed in 151Sm and their decay patterns followed up to spins near 20 h. Four ?I=2 bands have some characteristics associated with parity-doublet structures. However, the evidence overall suggests that octupole correlations in 151Sm are too weak to produce stable octupole deformation. (orig.)

182

The quiet Sun's magnetic flux estimated from CaIIH bright inter-granular G-band structures

We determine the number density and area contribution of small-scale inter-granular Ca II bright G-band structures in images of the quiet Sun as tracers of kilo-Gauss magnetic flux-concentrations. In a 149 arcsec X 117 arcsec G-band image of the disk center at the activity minimum, 7593 small inter-granular structures were segmented with the `multiple-level tracking' pattern recognition algorithm. The scatter-plot of the continuum versus the G-band brightness shows the known magnetic and non-magnetic branches. These branches are largely disentangled by applying an intrinsic Ca II excess criterion. The thus obtained 2995 structures contain 1152 G-band bright points (BP) and 1843 G-band faint points (FP). They show a tendency toward increasing size with decreasing G-band excess, as expected from the `hot wall' picture. Their Ca H and G-band brightness are slightly related, resembling the known relation of Ca II and magnetic field strength. The magnetic flux density of each individual BP and FP is estimated from...

Bovelet, Burkart; 10.1051/0004-6361:200809717

2012-01-01

183

We report here the observation of the enhancement of Europium-tetracycline complex emission in Low Density Lipoprotein (LDL) solutions. Europium emission band of tetracycline solution containing Europium (III) chloride hexahydrate was tested to obtain effective enhancement in the presence of native LDL and oxidized LDL. Europium emission lifetime in the presence of lipoproteins was measured, resulting in a simple method to measure the lipoproteins quantity in an aqueous solution at physiological pH. This method shows that the complex can be used as a sensor to determine the different states of native and oxidized LDL in biological fluids.

Courrol, L. C.; Monteiro, A. M.; Silva, F. R. O.; Gomes, L.; Vieira, N. D., Jr.; Gidlund, M. A.; Figueiredo Neto, A. M.

2007-05-01

184

Crystal structure, electrical properties and electronic band structure of tantalum ditelluride

Motivated by the unexpectedly strong influence of the Te atoms on the structural and bonding properties of the transition metal tellurides, we have performed a detailed study of TaTe sub 2. Experimentally, this comprises a crystal structure determination as well as electrical resistivity measurements. The former analysis leads to an accurate update of the structural data reported in the 1960s, while the latter provides evidence for the mainly electronic character of scattering processes leading to the electrical conductivity. In addition, the electronic properties of TaTe sub 2 have been calculated using the TB-LMTO method. The partial density of states reflects the close connection of the Ta zigzag chains and the Te-Te network. This finding explains the charge transfer in the system in a rather simple way. The orthogonal-orbital character of the bands proved the existence of pi-bonds. The Fermi-surface study supports the interpretation of the experimental resistivity measurements. (author)

Vernes, A; Bensch, W; Heid, W; Naether, C

1998-01-01

185

Crossing points in the electronic band structure of vanadium oxide

Directory of Open Access Journals (Sweden)

Full Text Available The electronic band structures of several models of vanadium oxide are calculated. In the models 1-3, every vanadium atom is connected to 4 oxygen atoms and every oxygen atom is connected to 4 vanadium atoms. In model 1, a=b=c 2.3574 Å; in model 2, a= 4.7148 Å, b= 2.3574 Å and c= 2.3574 Å; and in model 3, a= 4.7148 Å, b= 2.3574 Å and c= 4.7148 Å. In the models 4-6, every vanadium atom is connected to 4 oxygen atoms and every oxygen atom is connected to 2 vanadium atoms. In model 4, a=b= 4.551 Å and c= 2.851 Å; in model 5, a=b=c= 3.468 Å; and in model 6, a=b=c= 3.171 Å. We have searched for a crossing point in the band structure of all the models. In model 1 there is a point at which five bands appear to meet but the gap is 7.3 meV. In model 2 there is a crossing point between G and F points and there is a point between F and Q with the gap ? 3.6608 meV. In model 3, the gap is very small, ~ 10-5 eV. In model 4, the gap is 5.25 meV. In model 5, the gap between Z and G points is 2.035 meV, and in model 6 the gap at Z point is 4.3175 meV. The crossing point in model 2 looks like one line is bent so that the supersymmetry is broken. When pseudopotentials are replaced by a full band calculation, the crossing point changes into a gap of 2.72 x 10-4 eV.

Keshav N. Shrivastava

2010-03-01

186

Electronic band structure of (111) monolayer superlattices of AIVBVI narrow-band semiconductors

International Nuclear Information System (INIS)

The theory of an electron spectrum of monolayer superlattices (MLS) (IVAVIA)1(IVBVIB)1 oriented along axis [111] is developed on the basis of symmetric analysis of p-model of the band spectrum for semiconductors AIVBVI. It is established that superlattices (IVAVIA)m(IVBVIB)m at m+n=3l (m,n,l are whole numbers) have the space group D3d1 and the hexagonal structure, and at m+n ? 3l - group D3d5 and the rhombohedral lattice. It is foreseen that actual band extrema of MLS are inverse, and the spectrum of the second ones - normal. The pattern of retuning the spectrum of superlattices (PbTe)1(SnTe)1 and (PbS)1(PbTe)1 depending on the deformation factor is studied; it is established that in these MLS certain transitions from the semiconductive spectrum to semimetallic one is possible. It is shown that disordering in superlattice (PbTe)1(SnTe)1 leads to decrease of energy gaps in the spectrum, and in (PbS)1(PbTe)1 - to this growth

187

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

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

188

DEFF Research Database (Denmark)

The electronic band structures of InxGa1-xN, InxAl1-xN, and InxGayAl1-x-yN alloys are calculated by ab initio methods using a supercell geometry, and the effects of varying the composition and atomic arrangements methods using a supercell geometry, and the effects of varying the composition and atomic arrangements are examined. Particular attention is paid to the magnitude of and trends in bowing of the band gaps. Indium composition fluctuation (clustering) is simulated by different distributions of In atoms and it is shown that it strongly influences the band gaps. The gaps are considerably smaller when the In atoms are clustered than when they are uniformly distributed. An explanation of this phenomenon is proposed on the basis of an analysis of the density of states and the bond lengths, performed in detail for ternary alloys. Results for the band gaps of InxGayAl1-x-yN quaternary alloys show a similar trend. It is suggested that the large variation in the band gaps determined on samples grown in differentlaboratories is caused by different degrees of In clustering.

Gorczyca,, I.; ?epkowski, S. P.

2009-01-01

189

International Nuclear Information System (INIS)

Background and purpose: We previously determined that the density of a rapidly migrating DNA end-binding complex (termed 'band-A') predicts radiosensitivity of human normal and tumor cells. The goal of this study was first to identify the protein components of band-A and to determine if the protein levels of band-A components would correlate with band-A density and radiosensitivity. Patients and methods: DNA end-binding protein complex (DNA-EBC) protein components were identified by adding antibodies specific for a variety of DNA repair-associated proteins to the DNA-EBC reaction and then noting which antibodies super-shifted various DNA-EBC bands. Band-A levels were correlated with SF2 for a panel of primary human fibroblasts heterozygous for sequence-proven mutations in BRCA1 or BRCA2. The nuclear protein levels of band-A components were determined in each BRCA1 heterozygote by western hybridization. Results: DNA-EBC analysis of human nuclear proteins revealed 10 identifiable bands. The density of the most rapidly migrating DNA-EBC band correlated closely with both BRCA-mutation status and radiosensitivity (r2=0.85). This band was absent in cells with homozygous mutations in their ataxia-telangiectasia-mutated protein (ATM) genes. This band was also completely supershifted by the addition of antibodies to ATM, Ku70, DNA ligase III, Rpa32, Rpa14, DNA ligase IV, XRCC4, WRN, BLM, RAD51 and p53. However, the intranuclear concentrations of these proteins did near concentrations of these proteins did not correlate with either the SF2 or DNA-EBC density. Neither BRCA1 or BRCA2 could be detected in band-A. Conclusions: DNA-EBC analysis of human nuclear extracts resulted in 10 bands, at least six of which contained ATM. The density of one of the DNA-EBCs predicted the radiosensitization caused by BRCA haploinsufficiency, and this band contains Ku70, ATM, DNA ligase III, Rpa32, Rpa14, DNA ligase IV, XRCC4, WRN, BLM, RAD51 and p53 but not BRCA 1 or 2. The density of band-A was independent of the nuclear concentration of any of its known component

190

Directory of Open Access Journals (Sweden)

Full Text Available We have investigated trap density of states (trap DOS in n-channel organic field-effect transistors based on N,N?’-bis(cyclohexylnaphthalene diimide (Cy-NDI and dimethyldicyanoquinonediimine (DMDCNQI. A new method is proposed to extract trap DOS from the Arrhenius plot of the temperature-dependent transconductance. Double exponential trap DOS are observed, in which Cy-NDI has considerable deep states, by contrast, DMDCNQI has substantial tail states. In addition, numerical simulation of the transistor characteristics has been conducted by assuming an exponential trap distribution and the interface approximation. Temperature dependence of transfer characteristics are well reproduced only using several parameters, and the trap DOS obtained from the simulated characteristics are in good agreement with the assumed trap DOS, indicating that our analysis is self-consistent. Although the experimentally obtained Meyer-Neldel temperature is related to the trap distribution width, the simulation satisfies the Meyer-Neldel rule only very phenomenologically. The simulation also reveals that the subthreshold swing is not always a good indicator of the total trap amount, because it also largely depends on the trap distribution width. Finally, band transport is explored from the simulation having a small number of traps. A crossing point of the transfer curves and negative activation energy above a certain gate voltage are observed in the simulated characteristics, where the critical VG above which band transport is realized is determined by the sum of the trapped and free charge states below the conduction band edge.

Joung-min Cho

2013-10-01

191

International Nuclear Information System (INIS)

We have investigated trap density of states (trap DOS) in n-channel organic field-effect transistors based on N,N?’-bis(cyclohexyl)naphthalene diimide (Cy-NDI) and dimethyldicyanoquinonediimine (DMDCNQI). A new method is proposed to extract trap DOS from the Arrhenius plot of the temperature-dependent transconductance. Double exponential trap DOS are observed, in which Cy-NDI has considerable deep states, by contrast, DMDCNQI has substantial tail states. In addition, numerical simulation of the transistor characteristics has been conducted by assuming an exponential trap distribution and the interface approximation. Temperature dependence of transfer characteristics are well reproduced only using several parameters, and the trap DOS obtained from the simulated characteristics are in good agreement with the assumed trap DOS, indicating that our analysis is self-consistent. Although the experimentally obtained Meyer-Neldel temperature is related to the trap distribution width, the simulation satisfies the Meyer-Neldel rule only very phenomenologically. The simulation also reveals that the subthreshold swing is not always a good indicator of the total trap amount, because it also largely depends on the trap distribution width. Finally, band transport is explored from the simulation having a small number of traps. A crossing point of the transfer curves and negative activation energy above a certain gate voltage are observed in the simulated characteristics, where the critical VG above which band transport is realized is determined by the sum of the trapped and free charge states below the conduction band edge

192

Energy Technology Data Exchange (ETDEWEB)

We have investigated trap density of states (trap DOS) in n-channel organic field-effect transistors based on N,N?’-bis(cyclohexyl)naphthalene diimide (Cy-NDI) and dimethyldicyanoquinonediimine (DMDCNQI). A new method is proposed to extract trap DOS from the Arrhenius plot of the temperature-dependent transconductance. Double exponential trap DOS are observed, in which Cy-NDI has considerable deep states, by contrast, DMDCNQI has substantial tail states. In addition, numerical simulation of the transistor characteristics has been conducted by assuming an exponential trap distribution and the interface approximation. Temperature dependence of transfer characteristics are well reproduced only using several parameters, and the trap DOS obtained from the simulated characteristics are in good agreement with the assumed trap DOS, indicating that our analysis is self-consistent. Although the experimentally obtained Meyer-Neldel temperature is related to the trap distribution width, the simulation satisfies the Meyer-Neldel rule only very phenomenologically. The simulation also reveals that the subthreshold swing is not always a good indicator of the total trap amount, because it also largely depends on the trap distribution width. Finally, band transport is explored from the simulation having a small number of traps. A crossing point of the transfer curves and negative activation energy above a certain gate voltage are observed in the simulated characteristics, where the critical V{sub G} above which band transport is realized is determined by the sum of the trapped and free charge states below the conduction band edge.

Cho, Joung-min, E-mail: cho.j.ad@m.titech.ac.jp; Akiyama, Yuto; Kakinuma, Tomoyuki [Department of Organic and Polymeric Materials, Tokyo Institute of Technology, O-okayama, Tokyo 152-8552 (Japan); Mori, Takehiko [Department of Organic and Polymeric Materials, Tokyo Institute of Technology, O-okayama, Tokyo 152-8552 (Japan); ACT-C, JST, Honcho, Kawaguchi, Saitama 332-0012 (Japan)

2013-10-15

193

Energy band structure and its characteristics of a two-dimensional metallic photonic crystal

Energy Technology Data Exchange (ETDEWEB)

The energy band structure and its characteristics of a two-dimensional metallic photonic crystal with square lattice structure have been studied by using the finite-difference time-domain (FDTD) algorithm. In order to determine the band structure accurately, the spatial distribution of the eigenfunction has been analyzed. By comparing the distribution of different wave vectors and of different energy band eigenmodes, an effective method to determine the band structure was found, which has been verified by the simulation results. (orig.)

Bao, Xianfeng [Wuhan Univ. (China). Dept. of Physics; Yao, Duanzheng [Wuhan Univ. (China). Key Lab. of Acoustic and Photonics Material and Devices

2011-05-15

194

Band structure approach to the resonant x-ray scattering

We study the resonance behaviour of the forbidden 600 and 222 x-ray Bragg peaks in Ge using LDA band structure methods. These Bragg peaks remain forbidden in the resonant dipole scattering approximation even taking into account the non local nature of the band states. However they become allowed at resonance if the eigenstates of the unoccupied conduction band involve a hybridization of p like and d like atomic states. We show that the energy dependence of the resonant behaviour, including the phase of the scattering, is a direct measure of this p-d hybridization.and obtain quantitative agreement with experiment. A simple physical picture involving a product of dipole and quadrupolar transition matrix elements explains this behaviour and shows that it should be generally true for cases where the resonating atom is not at an inversion center. This has strong implications for the description of the resonance behavior of x-ray scattering in materials where the resonant atom is not at an inversion center such as ...

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

2002-01-01

195

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2012-03-01

196

Anomalous Quasiparticle Lifetime in Graphite Band Structure Effects

We report ab initio calculation of quasiparticle lifetimes in graphite, as determined from the imaginary part of the self-energy operator within the GW aproximation. The inverse lifetime in the energy range from 0.5 to 3.5 eV above the Fermi level presents significant deviations from the quadratic behavior naively expected from Fermi liquid theory. The deviations are explained in terms of the unique features of the band structure of this material. We also discuss the experimental results from different groups and make some predictions for future experiments.

Spataru, C D; Rubio, A; Benedict, L X; Echenique, P M; Louie, S G; Spataru, Catalin D.; Cazalilla, Miguel A.; Rubio, Angel; Benedict, Lorin X.; Echenique, Pedro M.; Louie, Steven G.

2001-01-01

197

Band structure in the polymer quantization of the harmonic oscillator

International Nuclear Information System (INIS)

We discuss the detailed structure of the spectrum of the Hamiltonian for the polymerized harmonic oscillator and compare it with the spectrum in the standard quantization. As we will see the non-separability of the Hilbert space implies that the point spectrum consists of bands similar to the ones appearing in the treatment of periodic potentials. This feature of the spectrum of the polymeric harmonic oscillator may be relevant for the discussion of the polymer quantization of the scalar field and may have interesting consequences for the statistical mechanics of these models. (paper)

198

Band structure in the polymer quantization of the harmonic oscillator

We discuss the detailed structure of the spectrum of the Hamiltonian for the polymerized harmonic oscillator and compare it with the spectrum in the standard quantization. As we will see the non-separability of the Hilbert space implies that the point spectrum consists of bands similar to the ones appearing in the treatment of periodic potentials. This feature of the spectrum of the polymeric harmonic oscillator may be relevant for the discussion of the polymer quantization of the scalar field and may have interesting consequences for the statistical mechanics of these models.

Barbero G, J. Fernando; Prieto, Jorge; Villaseñor, Eduardo J. S.

2013-08-01

199

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

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

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

2011-03-01

200

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

International Nuclear Information System (INIS)

In this paper, we present an investigation of type-II ‘W’ quantum wells for the InAs/Ga1?xInxSb/AlSb family, where ‘W’ denotes the conduction profile of the material. We focus our attention on using the eight-band k · p model to calculate the band structures within the framework of finite element method. For the sake of clarity, the simulation in this paper is simplified and based on only one period—AlSb/InAs/Ga1?xInxSb/InAs/AlSb. The obtained numerical results include the energy levels and wavefunctions of carriers. We discuss the variations of the electronic properties by changing several important parameters, such as the thickness of either InAs or Ga1?xInxSb layer and the alloy composition in Ga1?xInxSb separately. In the last part, in order to compare the eight-band k · p model, we recalculate the conduction bands of the ‘W’ structure using the one-band k · p model and then discuss the difference between the two results, showing that conduction bands are strongly coupled with valence bands in the narrow band gap structure. The in-plane energy dispersions, which illustrate the suppression of the Auger recombination process, are also obtained. (general)

201

Valence band structure in boron-zinc oxide films characterized by secondary electron emission

Properties of the valence band structure in boron-zinc oxide (BZO) films were investigated using the secondary electron emission due to the Auger neutralization of helium ions, with respect to the application of BZO films to the development of solar cells, in which the conductivity of the BZO films plays a critical role in improving cell performance. The characteristic energy ?0 corresponding to the peak density of states in the valence band showed that BZO film prepared with a 3000 SCCM B2H6 gas flow rate (SCCM denotes cubic centimeters per minute at standard temperature and pressure) had a shallow characteristic energy ?0 = 5 eV, whereas film without boron doping had a deep characteristic energy ?0 = 8.2 eV, suggesting that a high concentration of boron impurity in BZO films might enhance the transition of electrons and holes through the bandgap from the valence to the conduction band in zinc oxide crystals, thereby improving the conductivity of the film. The measurement method developed here demonstrates that the secondary electron emission is very useful in the determination of the band structure in various synthetic films.

Uhm, Han S.; Choi, Joon H.; Yoo, Ha J.; Kwon, Gi C.; Choi, Eun H.

2012-03-01

202

Beyond band gap photoreflectance study on PHEMT device structures

Photoreflectance (PR) studies on device structures have mainly been conducted near the band gap region of the semiconductors of these structures. In this study we have attempted characterization of the important upper epilayers, barrier and channel layers, of pseudomorphic high electron mobility transistor (PHEMT) device structures near the E1 and E1+Delta 1 transition energy range (2.7--3.6 eV). In choosing the higher lying transition for characterization, we were able to minimize PR contributions from the many underlying layers of these device structures. Besides minimizing overlapping PR contributions from various layers, PR signals due to higher lying transitions are low field regime signals that facilitate precise characterization due to a third derivative line shape (TDLS) model, and in the case of highly doped material, one avoids the complexity of interpretation due to greatly distorted contributions from these lower lying transitions. We present the PR signals due to the E1 and E1+ Delta 1 transitions from the strained InxGa1-xAs channel layer and from the AlxGa1-xAs barrier layer of PHEMT device structures. A fitting routine was developed employing the Levenberg Marquardt algorithm to fit the PR signals to a third derivative line shape model through a weighted chi-square minimization procedure. The lifetime broadening parameter of the E1 transition from the channel layer shows significant correlation with the mobility of carriers in that layer. This result, indicating correlation of a PR parameter with an electronic transport parameter, compliments to the advantages of characterization beyond band gap and also has a potential for future research extensions to further exploit the relationship between these two parameters. The mole fractions of aluminum and indium in AlxGa1-x As and InxGa1-xAs ternaries were determined from E1 transition energies. They were found to be in good agreement with the intended composition values during the growth process.

Thamban, P. L. Stephan

203

Structure and density of cometary nuclei

We are still at a very primitive stage in our understanding of the structure and density of cometary nuclei. Much of the evidence at our disposal is fragmentary and often indirect. Nevertheless, a compelling picture is beginning to emerge of cometary nuclei as collisionally processed fractal aggregates, i.e., rubble piles. The evidence comes from observations of split and disrupted comets, in particular Shoemaker-Levy 9, from theories of planetesimal formation in the early solar nebula, from a recognition of the role of collisions in the evolution of cometary nuclei, and from theoretical and experimental studies of the fragmentation and reassembly of asteroids. This paradigm-shift away from nuclei as monolithic bodies parallels that which has occurred for asteroids in the past decade. A related factor that strongly suggests that nuclei contain substantial macroscopic voids is estimates of the nuclear density, which, like asteroids, show comets to be "under-dense" compared with their constituent materials. We find that the bulk density of cometary nuclei lies in the range 0.5-1.2 g cm-3, with a perhaps "best" current value of 0.6 g cm-3.

Weissman, P. R.; Asphaug, E.; Lowry, S. C.

204

We have developed an 8-band Effective Mass Approximation model that describes the zero field spin splitting in the band structure of zincblende heterostructures due to bulk inversion asymmetry (BIA). We have verified that our finite difference Hamiltonian transforms in almost all situations according to the true $D_{2d}$ or $C_{2v}$ symmetry of [001] heterostructures. This makes it a computationally efficient tool for the accurate description of the band structure of heterostructures for spintronics. We first compute the band structure for an AlSb/GaSb/AlSb quantum well (QW), which presents only BIA, and delineate its effects. We then use our model to find the band structure of an AlSb/InAs/GaSb/AlSb QW and the relative contribution of structural and bulk inversion asymmetry to the spin splitting. We clarify statements about the importance of these contributions and conclude that, even for our small gap QW, BIA needs to be taken into account for the proper description of the band structure.

Cartoixa, X; McGill, T C

2002-01-01

205

International Nuclear Information System (INIS)

By utilizing the electrorheological effect, three-dimensional colloidal crystals can be produced, whose lattice structure can be changed from the body-centered-tetragonal lattice to other lattices under the application of electric fields. This paper calculates photonic band structures of such crystals with lattice structure transformation, and demonstrates the existence of complete band gaps for some intermediate lattices. Thus, it becomes possible to use the electrorheological effect to achieve photonic crystals with desired photonic gap properties resulting from tunable structures. (classical areas of phenomenology)

206

Density banding in skeletons of reef-building corals is a valuable source of proxy environmental data. However, skeletal growth strategy has a significant impact on the apparent timing of density-band formation. Some corals employ a strategy where the tissue occupies previously formed skeleton during as the new band forms, which leads to differences between the actual and apparent band timing. To investigate this effect, we collected cores from female and male colonies of Siderastrea siderea and report tissue thicknesses and density-related growth parameters over a 17-yr interval. Correlating these results with monthly sea surface temperature (SST) shows that maximum skeletal density in the female coincides with low winter SSTs, whereas in the male, it coincides with high summer SSTs. Furthermore, maximum skeletal densities in the female coincide with peak Sr/Ca values, whereas in the male, they coincide with low Sr/Ca values. Both results indicate a 6-month difference in the apparent timing of density-band formation between genders. Examination of skeletal extension rates also show that the male has thicker tissue and extends faster, whereas the female has thinner tissue and a denser skeleton—but both calcify at the same rate. The correlation between extension and calcification, combined with the fact that density banding arises from thickening of the skeleton throughout the depth reached by the tissue layer, implies that S. siderea has the same growth strategy as massive Porites, investing its calcification resources into linear extension. In addition, differences in tissue thicknesses suggest that females offset the greater energy requirements of gamete production by generating less tissue, resulting in differences in the apparent timing of density-band formation. Such gender-related offsets may be common in other corals and require that environmental reconstructions be made from sexed colonies and that, in fossil corals where sex cannot be determined, reconstructions must be duplicated in different colonies.

Carricart-Ganivet, J. P.; Vásquez-Bedoya, L. F.; Cabanillas-Terán, N.; Blanchon, P.

2013-09-01

207

International Nuclear Information System (INIS)

The electronic band structures and excited states of III-V semiconductors such as GaP, AlP, AlAs, and AlSb for various polytypes are determined employing the screened-exchange density functional calculations implemented in the full-potential linearized augmented plane-wave methods. We demonstrate that GaP and AlSb in the wurtzite (WZ) structure have direct gap while III-V semiconductors in the zinc blende, 4H, and 6H structures considered in this study exhibit an indirect gap. Furthermore, we find that inclusion of Al atoms less than 17% and 83% in the hexagonal AlxGa1?xP and AlxGa1?xAs alloys, respectively, leads to a direct transition with a gap energy of ?2.3 eV. The feasibility of III-V semiconductors with a direct gap in WZ structure offers a possible crystal structure engineering to tune the optical properties of semiconductor materials

208

Energy Technology Data Exchange (ETDEWEB)

The electronic band structures and excited states of III-V semiconductors such as GaP, AlP, AlAs, and AlSb for various polytypes are determined employing the screened-exchange density functional calculations implemented in the full-potential linearized augmented plane-wave methods. We demonstrate that GaP and AlSb in the wurtzite (WZ) structure have direct gap while III-V semiconductors in the zinc blende, 4H, and 6H structures considered in this study exhibit an indirect gap. Furthermore, we find that inclusion of Al atoms less than 17% and 83% in the hexagonal Al{sub x}Ga{sub 1?x}P and Al{sub x}Ga{sub 1?x}As alloys, respectively, leads to a direct transition with a gap energy of ?2.3 eV. The feasibility of III-V semiconductors with a direct gap in WZ structure offers a possible crystal structure engineering to tune the optical properties of semiconductor materials.

Akiyama, Toru; Nakamura, Kohji; Ito, Tomonori [Department of Physics Engineering, Mie University, 1577 Kurima-Machiya, Tsu 514-8507 (Japan); Freeman, Arthur J. [Department of Physics and Astronomy, Northwestern University, Evanston, Illinois 60208 (United States)

2014-03-31

209

Corals are a key reservoir of biodiversity in coastal, shallow water tropical marine environments, and density banding in their aragonite skeletons is used as a sensitive record of paleoclimate. Therefore, the cellular response of corals to environmental change and its expression in skeletal structure is of significant importance. Chromatophores, pigment-bearing cells within the ectoderm of hermatypic corals, serve to both enhance the photosynthetic activity of zooxanthellae symbionts, as well as protect the coral animal from harmful UV radiation. Yet connections have not previously been drawn between chromatophore tissue density and the development of skeletal density bands. A histological analysis of the coral Montastrea faveolata has therefore been conducted across a bathymetric gradient of 1-20 m on the southern Caribbean island of Curaçao. A combination of field and laboratory photography, serial block face imaging (SBFI), two-photon laser scanning microscopy (TPLSM), and 3D image analysis has been applied to test whether M. faveolata adapts to increasing water depth and decreasing photosynthetically active radiation by shifting toward a more heterotrophic lifestyle (decreasing zooxanthellae tissue density, increasing mucocyte tissue density, and decreasing chromatophores density). This study is among the first to collect and evaluate histological data in the spatial context of an entire unprocessed coral polyp. TPLSM was used to optically thin section unprocessed tissue biopsies with quantitative image analysis to yield a nanometer-scale three-dimensional map of the quantity and distribution of the symbionts (zooxanthellae) and a host fluorescent pigments (chromatophores), which is thought to have photoprotective properties, within the context of an entire coral polyp. Preliminary results have offered new insight regarding the three-dimensional distribution and abundance of chromatophores and have identified: (1) M. faveolata tissue collected from 8M SWD do not contain the abundant chromatophores present in M. faveolata collected from 20M SWD; and (2) a distinct difference in size and distribution of chromatophores between M. faveolata collected from 8-20M SWD. These results suggest that chromatophore cells may have an important photoenhancing function (reflection of light to help facilitate the collection of usable light that reaches the symbiotic algae for effective photosynthesis) rather than a photoinhibitive function (absorbing or refract light that may be harmful to zooxanthellae) which has been previously hypothesized.

Ardisana, R. N.; Miller, C. A.; Sivaguru, M.; Fouke, B. W.

2013-12-01

210

Density functional study of the structure, thermodynamics and electronic properties of CdGeAs2

International Nuclear Information System (INIS)

Structural, thermodynamic and electronic properties of CdGeAs2 with chalcopyrite structure are investigated in the framework of density functional theory. We employ the linear combination of atomic orbitals method with the Gaussian basis sets and present the results for the equation of state, the Grueneisen constant, the electronic band structure and the pressure coefficients of the valence and conduction levels in CdGeAs2. (author)

211

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

Dabhi, Shweta; Mankad, Venu; Jha, Prafulla K.

2014-04-01

212

Energy Technology Data Exchange (ETDEWEB)

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

Dabhi, Shweta, E-mail: venu.mankad@gmail.com; Mankad, Venu, E-mail: venu.mankad@gmail.com; Jha, Prafulla K., E-mail: venu.mankad@gmail.com [Department of Physics, Maharaja Krishnakumasinhji Bhavnagar University, Bhavnagar-364001 (India)

2014-04-24

213

Photonic band structure and symmetry properties of electromagnetic modes in photonic crystals.

Within the Maxwell framework and using a transfer-matrix technique we have determined a general equation which governs the photonic band structure and the density of states of one-dimensional superlattices composed of two alternate layers characterized by different refractive indexes, which may take on positive as well as negative values. Besides the usual well-known results, we have found null-gap points for commensurate values of the optical path lengths of each layer. Furthermore, we have been able to characterize non-Bragg gaps that show up in frequency regions in which the average refractive index is null. PMID:17358436

Cavalcanti, S B; de Dios-Leyva, M; Reyes-Gómez, E; Oliveira, L E

2007-02-01

214

Photonic band gaps in three-dimensional network structures with short-range order

Energy Technology Data Exchange (ETDEWEB)

We present a systematic study of photonic band gaps (PBGs) in three-dimensional (3D) photonic amorphous structures (PASs) with short-range order. From calculations of the density of optical states (DOS) for PASs with different topologies, we find that tetrahedrally connected dielectric networks produce the largest isotropic PBGs. Local uniformity and tetrahedral order are essential to the formation of PBGs in PASs, in addition to short-range geometric order. This work demonstrates that it is possible to create broad, isotropic PBGs for vector light fields in 3D PASs without long-range order.

Liew, Seng Fatt; Noh, Heeso [Department of Applied Physics, Yale University, New Haven, Connecticut 06511 (United States); Yang, Jin-Kyu [Department of Applied Physics, Yale University, New Haven, Connecticut 06511 (United States); Department of Optical Engineering, Kongju National University, Kongju 314-701 (Korea, Republic of); Schreck, Carl F. [Department of Physics, Yale University, New Haven, Connecticut 06511 (United States); Dufresne, Eric R. [Department of Physics, Yale University, New Haven, Connecticut 06511 (United States); Department of Mechanical Engineering and Materials Science, Yale University, New Haven, Connecticut 06511 (United States); Department of Chemical and Environmental Engineering, Yale University, New Haven, Connecticut 06511 (United States); Department of Cell Biology, Yale University, New Haven, Connecticut 06511 (United States); O' Hern, Corey S. [Department of Physics, Yale University, New Haven, Connecticut 06511 (United States); Department of Mechanical Engineering and Materials Science, Yale University, New Haven, Connecticut 06511 (United States); Cao, Hui [Department of Applied Physics, Yale University, New Haven, Connecticut 06511 (United States); Department of Physics, Yale University, New Haven, Connecticut 06511 (United States)

2011-12-15

215

Photonic Band Gaps in 3D Network Structures with Short-range Order

We present a systematic study of photonic band gaps (PBGs) in three-dimensional (3D) photonic amorphous structures (PAS) with short-range order. From calculations of the density of optical states (DOS) for PAS with different topologies, we find that tetrahedrally connected dielectric networks produce the largest isotropic PBGs. Local uniformity and tetrahedral order are essential to the formation of PBGs in PAS, in addition to short-range geometric order. This work demonstrates that it is possible to create broad, isotropic PBGs for vector light fields in 3D PAS without long-range order.

Liew, Seng Fatt; Noh, Heeso; Schreck, Carl F; Dufresne, Eric R; O'Hern, Corey S; Cao, Hui

2011-01-01

216

Photonic band gaps in three-dimensional network structures with short-range order

International Nuclear Information System (INIS)

We present a systematic study of photonic band gaps (PBGs) in three-dimensional (3D) photonic amorphous structures (PASs) with short-range order. From calculations of the density of optical states (DOS) for PASs with different topologies, we find that tetrahedrally connected dielectric networks produce the largest isotropic PBGs. Local uniformity and tetrahedral order are essential to the formation of PBGs in PASs, in addition to short-range geometric order. This work demonstrates that it is possible to create broad, isotropic PBGs for vector light fields in 3D PASs without long-range order.

217

Touching points in the energy band structure of bilayer graphene superlattices

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

Pham, C. Huy; Nguyen, V. Lien

2014-10-01

218

Relativistic Band Structure and Fermi Surface of PdTe2 by the LMTO Method

DEFF Research Database (Denmark)

The energy bands of the trigonal layer compound PdTe2 have been calculated, using the relativistic linear muffin-tin orbitals method. The bandstructure is separated into three distinct regions with low-lying Te 5s bands, conduction bands formed by Pd 4d and Te 5p states, and high-lying bands formed by Pd 5p, Te 6s and Te 5d states. Density of states and joint density of states have been calculated from the bands determined over the appropriate irreducible zone. The Fermi surface consists of two closed sheets in band 11 and band 13, and sheets in band 12 connected to one another by tubes. The results allow an explanation of most of the de Haas-van Alphen frequencies observed previously.

Skriver, Hans Lomholt

1977-01-01

219

Investigations of the Band Structure and Morphology of Nanostructured Surfaces

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.

220

Spin filtering with EuO: Insight from a complex band structure

Spin-filter tunneling is a promising way to create highly-spin-polarized currents. So far the understanding of the spin-filtering effect has been limited to a free-electron description based on the spin-dependent tunneling barrier height. In this work we employ density-functional calculations to explore the complex bands of EuO as a representative ferromagnetic insulator used in spin-filter tunneling experiments and show that the mechanism of spin filtering deviates significantly from the standard free-electron picture and involves effects associated with the symmetry of spin-dependent evanescent states and the dependence of the decay constant on the transverse wave vector. We demonstrate the importance of the multiorbital band structure with an indirect band gap for spin-filter tunneling. By analyzing the symmetry of the complex bands and the decay rates for different wave vectors and energies we draw conclusions about spin-filter efficiency of EuO. Our results provide a new insight into spin-filter tunneling and may help to design tunnel junctions with enhanced spin polarization.

Lukashev, Pavel; Wysocki, Aleksander; Velev, Julian; van Schilfgaarde, Mark; Jaswal, Sitaram; Belashchenko, Kirill; Tsymbal, Evgeny

2013-03-01

221

A Brief Introduction to Band Structure in Three Dimensions

Without our ability to model and manipulate the band structure of semiconducting materials, the modern digital computer would be impractically large, hot, and expensive. In the undergraduate QM curriculum, we studied the effect of spatially periodic potentials on the spectrum of a charged particle in one dimension. We would like to understand how to extend these methods to model actual crystalline materials. Along the way, we will explore the construction of periodic potentials in three dimensions, and we use this framework to relate the single-particle Hamiltonian to the potential contribution from each atom. We then construct a crude model system analogous to the semiconductor silicon, and demonstrate the appearance of level splitting and band gaps as the strength of the potential is varied, in accordance with our intuition from the one-dimensional case. We discuss refinements of the model to include many-particle effects, and finally we show how a careful choice of the potential function leads to good agre...

Iannucci, Peter

2011-01-01

222

Identification of band structures in the 137La nucleus

International Nuclear Information System (INIS)

High-spin states of 137La have been investigated with the reaction 130Te(11B,4n) at a beam energy of 50MeV. The level scheme of 137La has been expanded with spin up to 33/2?. Several new bands have been found in this nucleus. A band crossing in the band based on the 17/2- level has been observed at a rotational frequency of ???0.48 MeV. From systematic comparison, this band crossing probably originates from the alignment of protons. One of the bands with strong M1 transitions is proposed as a collective oblate band (??-60 ). (orig.)

223

Tunable band structure effects on ballistic transport in graphene nanoribbons

International Nuclear Information System (INIS)

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 the applied fields on its own preserves the even symmetry Ek=E-k of the subband dispersion. When applied together, they reverse the dispersion parity to be odd and gives Ee,k=-Eh,-k and mix the electron and hole subbands within the energy range corresponding to the change in potential across the ribbon. This leads to oscillations of the ballistic conductance within this energy range.

224

Tunable band structure effects on ballistic transport in graphene nanoribbons

Energy Technology Data Exchange (ETDEWEB)

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 the applied fields on its own preserves the even symmetry E{sub k}=E{sub -k} of the subband dispersion. When applied together, they reverse the dispersion parity to be odd and gives E{sub e,k}=-E{sub h,-k} and mix the electron and hole subbands within the energy range corresponding to the change in potential across the ribbon. This leads to oscillations of the ballistic conductance within this energy range.

Roslyak, O., E-mail: avroslyak@gmail.co [Department of Physics and Astronomy, Hunter College of City University of New York, 695 Park Avenue, New York, NY 10065-50085 (United States); Gumbs, Godfrey [Department of Physics and Astronomy, Hunter College of City University of New York, 695 Park Avenue, New York, NY 10065-50085 (United States); Donostia International Physics Center (DIPC), P. de Manuel Lardizabal, 4, 20018 San Sebastian, Basque Country (Spain); Huang Danhong [Air Force Research Laboratory (AFRL/RVSS), Kirtland Air Force Base, NM 87117 (United States)

2010-08-30

225

The band structure and carrier dynamics of GaAs, GaAs/GaP and InP semiconductor nanowires is explored using a variety of optical spectroscopy techniques including two newly developed techniques called Photomodulated and Transient Rayleigh scattering spectroscopy. The stress and electronic band structure of as-grown highly strained GaAs/GaP core/shell nanowire is studied via room temperature Raman scattering by phonons and low temperature photoluminescence spectroscopy. Raman measurements reveal the uniaxial nature of the shell-induced stress in the core GaAs nanowire with a significantly different degree of compression in the radial plane and axial direction of the nanowire. The uniaxial stress dramatically modifies the electronic band structure of the nanowire. Raman measurements predict that the shell-induced stress should shift the band gap of GaAs to higher energies by ~260 meV which is experimentally confirmed by low temperature photoluminescence spectroscopy. Furthermore, it is predicted that the uniaxial stress in the nanowire removes the degeneracy of the heavy and light hole valence bands at the zone center by ~100 meV. In order to probe the electronic band structure of single nanowires with high spatial and spectral resolution, the new technique of Photomodulated Rayleigh Scattering spectroscopy (PMRS) is introduced. We show that by photomodulating the dielectric function of the nanowire, the background-free and robust differential Rayleigh spectrum measures the band structure of the nanowire with exceptionally high energy resolution. PMRS measurements are performed on zincblende GaAs and zincblende and wurtzite InP nanowires at both room and low temperature. Furthermore, we show that the diameters of the nanowires can be extracted from the PMRS spectra with an uncertainty of only a few nanometers. By extending the PMRS spectroscopy into time domain, we introduce Transient Rayleigh Scattering spectroscopy (TRS) to study the ultrafast carrier dynamics and cooling within the band structure of single nanowires with picosecond time resolution. Due to many body effects, the Rayleigh cross-section is sensitive to the occupation of the electronic band structure by photo injected carriers which allows one to simultaneously measure the density and temperature of the photo injected electron-hole plasma as a function of time after excitation. The time dependent density and temperature of the plasma provide direct insight into the various mechanisms dominating the dynamics and cooling of carriers within the electronic band structure including ambipolar diffusion, recombination processes and emission of optical and acoustic phonons. Specifically, TRS of a single GaAs/AlGaAs core-shell nanowire is presented which quantifies various fundamental properties of nanowire including carrier mobility, recombination rates and the energy-loss rate of plasma due to optical and acoustic phonon emission. Similar measurements on a single InP nanowire with hexagonal wurtzite symmetry reveals the dynamics associated with various energy bands including the coupling of A, B and C valence bands to the lowest conduction band as well as the theoretically predicted second conduction band. The second conduction band is experimentally measured at 236-240 meV higher than the first conduction band. The second conduction band is theoretically calculated at 238 meV above the first conduction band.

Montazeri, Mohammad

226

Rare-earth based scintillators represent a challenging class of scintillator materials due to pronounced spin-orbit coupling and subtle interactions between d and f states that cannot be reproduced by standard electronic structure methods such as density functional theory. In this contribution we present a detailed investigation of the electronic band structure of LaBr3 using the quasi-particle self-consistent GW (QPscGW) method. This parameter-free approach is shown to yield an excellent description of the electronic structure of LaBr3. Specifically we reproduce the correct level ordering and spacing of the 4f and 5d states, which are inverted with respect to the free La atom, the band gap as well as the spin-orbit splitting of La-derived states. We furthermore present electronic structure calculations using G0W0 for the important scintillator material SrI2. We explicitly take into account spin-orbit coupling at all levels of the theory. Our results demonstrate the applicability and reliability of the GW approach for rare-earth halides and complex halides. They furthermore provide an excellent starting point for investigating the electronic structure of rare-earth dopants such as Ce and Er.

Aberg, Daniel; Ehart, Paul; Sadigh, Babak

2012-02-01

227

International Nuclear Information System (INIS)

We use Hedin's GW framework to compute quasiparticle bands for group-II monoxides in wurtzite (wz) structure. Modern hybrid density functional theory is applied to compute the starting electronic structure for the solution of the quasiparticle equation. We derive band parameters and effective masses for the three uppermost valence bands as well as the lowest conduction band including spin-orbit coupling. Optical transition matrix elements and exciton binding energies are also calculated. In addition to the prediction of parameters for wz-MgO and wz-CdO we discuss the chemical trend. (Abstract Copyright [2009], Wiley Periodicals, Inc.)

228

Density functional calculation of band-parameters for boron nitride at normal and high pressures

International Nuclear Information System (INIS)

The present work employs the total-energy pseudopotential technique within the framework of the density-functional theory with both the local-density approximation (LDA) and the generalized gradient approximation (GGA) for the exchange-correlation functional so as to calculate the structural, electronic, chemical bonding and elastic properties of BN in the zinc-blende structure at normal and high pressures. The results are generally in good agreement with the available experimental data. We found that in many cases (except may be for elastic constants) the GGA improves agreement with experiment. The calculations showed that the transition pressure for BN from the zinc-blende phase to the rocksalt phase is much smaller than previously reported theoretical values

229

Density functional calculation of band-parameters for boron nitride at normal and high pressures

Energy Technology Data Exchange (ETDEWEB)

The present work employs the total-energy pseudopotential technique within the framework of the density-functional theory with both the local-density approximation (LDA) and the generalized gradient approximation (GGA) for the exchange-correlation functional so as to calculate the structural, electronic, chemical bonding and elastic properties of BN in the zinc-blende structure at normal and high pressures. The results are generally in good agreement with the available experimental data. We found that in many cases (except may be for elastic constants) the GGA improves agreement with experiment. The calculations showed that the transition pressure for BN from the zinc-blende phase to the rocksalt phase is much smaller than previously reported theoretical values.

Saib, S. [Physics Department, Faculty of Science and Engineering, University of M' sila, 28000 M' sila (Algeria); Bouarissa, N. [Department of Physics, Faculty of Science, King Khalid University, P.O. Box 9004, Abha (Saudi Arabia)], E-mail: N_Bouarissa@yahoo.fr

2008-01-10

230

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

International Nuclear Information System (INIS)

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

231

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

Energy Technology Data Exchange (ETDEWEB)

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

232

Experimental determination of the band structure of photonic crystals of colloidal silica spheres

International Nuclear Information System (INIS)

A photonic band structure of colloidal crystals of silica spheres is analytically determined by a band model with three fitting parameters: the sphere size, the effective refractive index, and the band-gap. Optical properties of the crystals annealed at various temperatures were characterized by a procedure similar to X-ray diffraction technique, and the width of photonic band-gap measured from the transmission spectra experimentally servers as an additional check on the validation of the model. The photonic band structures defined by the band-gap, the refractive index, and the Brillouin zone are obviously superior to the use of the Bragg's expression involving simple zone folding.

233

Energy Technology Data Exchange (ETDEWEB)

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

234

Band structure calculations of CuAlO2, CuGaO2, CuInO2 and CuCrO2 by screened exchange

Digital Repository Infrastructure Vision for European Research (DRIVER)

We report density functional theory (DFT) band structure calculations on the transparent conducting oxides CuAlO2, CuGaO2, CuInO2 and CuCrO2. The use of the hybrid functional sX-LDA leads to considerably improved electronic properties compared to standard local density approximation (LDA) and generalized gradient approximation (GGA) approaches. We show that the resulting electronic band gaps compare well with experimental values and previous quasiparticle calculations and sh...

Gillen, Roland; Robertson, John

2011-01-01

235

The effects of band structure on recombination processes in narrow gap materials and laser diodes

International Nuclear Information System (INIS)

The work described in this thesis investigates the effects of band structure modifications, brought about by Landau confinement, hydrostatic pressure and uniaxial stress, on recombination processes in narrow-gap materials and laser diodes. The effects of Landau confinement on the characteristics of InSb-based emission devices operating at a wavelength of ?5?m at 77K were studied. The change in performance due to the magnetic field applied along both the cavity and the growth direction and thereby simulating quasi-quantum wire and quasi-quantum dot structures clearly demonstrated the benefits, such as reduced threshold and temperature sensitivity, gained by the reduced dimensionality. On the other hand, suppression of LO-phonon emission due to the discrete nature of the density of states was observed, for the first time, in an interband laser device. Interband recombination dynamics were studied in In1-xGaxSb and PbSe over a range of excited carrier densities and temperatures down to 30K. Detailed analysis of the results found that the Auger-1 mechanism is reduced in In1-xGaxSb as a function of Ga-fraction due to the increased bandgap energy, in good agreement with theoretical predictions. In PbSe, the Auger-1 rate was observed to dominate at low excited carrier concentrations in spite of near-mirror bands, and was found to be approximately constant between 300K and 70K and was seen to be quenched in the low temperature regime. Stimulated emission was seen to be the most efficient recombination mechanism at high excited carrier densities at low temperatures. The Auger coefficient in PbSe was found to be one to two orders of magnitude lower than for materials with a Kane band structure (Hg1-xCdxTe) with comparable bandgap. An experimental technique was developed which enables measurements at high hydrostatic pressures and high magnetic fields at low temperatures. Hydrostatic pressures were applied to a 1.5?m laser diode at different temperatures revealing the effects of pressure on the band structure and hence the laser characteristics. A visible laser diode was measured under the simultaneous application of hydrostatic pressure and uniaxial stress. The change in performance was satisfactorily explained in terms of leakage of carriers into the X-minimum in the cladding region, the process that has been suspected of being one of the major loss mechanisms in visible laser diodes. (author)

236

Quasiparticle band structures of six II-VI compounds: ZnS, ZnSe, ZnTe, CdS, CdSe, and CdTe

International Nuclear Information System (INIS)

Quasiparticle band structures of six II-VI compounds (ZnS, ZnSe, ZnTe, CdS, CdSe, and CdTe in the zinc-blende and wurtzite structures) are calculated using the GW approximation. Results for band structures, calculated using the ab initio pseudopotential method within the local-density approximation (LDA), are given along with the energies of the quasiparticle excitations at symmetry points. Comparisons are made with measured values and trends in the GW corrections to the LDA band structures are examined

237

X-band rf structure with integrated alignment monitors

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

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

2009-06-01

238

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english Previous research using microdensitometric scanning and computer graphic image analysis showed that T-banded segments of human metaphase chromosomes usually exhibit an asymmetrical distribution of high density (HD) chromatin between sister chromatids. Here, we employed the same methods to analyze HD [...] chromatin distribution at opposite ends of T-banded human lymphocyte chromosomes. This study revealed that in most chromosomes with an asymmetrical distribution of HD chromatin at both ends, the highest densities of each arm were located in opposite chromatids. The frequency of this configuration was 0.792 per chromosome, indicating that the highest chromatin densities of the terminal segments of T-banded human chromosomes were non-randomly distributed at opposite chromosome arms. The possible relationship of this observation to the mode of replication of the terminal chromosome region is briefly discussed.

Federico F., Santiñaque; Máximo E., Drets.

1054-10-01

239

International Nuclear Information System (INIS)

The state of bistable defects in crystalline silicon such as iron-boron pairs or the boron-oxygen defect can be changed at room temperature. In this letter, we experimentally demonstrate that the chemical state of a group of defects can be changed to represent a bit of information. The state can then be read without direct contact via the intensity of the emitted band-band photoluminescence signal of the group of defects, via their impact on the carrier lifetime. The theoretical limit of the information density is then computed. The information density is shown to be low for two-dimensional storage but significant for three-dimensional data storage. Finally, we compute the maximum storage capacity as a function of the lower limit of the photoluminescence detector sensitivity

240

Ab initio complex band structure of conjugated polymers: Effects of hydrid DFT and GW schemes

The non-resonant tunneling regime for charge transfer across nanojunctions is critically dependent on the so-called \\beta{} parameter, governing the exponential decay of the current as the length of the junction increases. For periodic materials, this parameter can be theoretically evaluated by computing the complex band structure (CBS) -- or evanescent states -- of the material forming the tunneling junction. In this work we present the calculation of the CBS for organic polymers using a variety of computational schemes, including standard local, semilocal, and hybrid-exchange density functionals, and many-body perturbation theory within the GW approximation. We compare the description of localization and \\beta{} parameters among the adopted methods and with experimental data. We show that local and semilocal density functionals systematically underestimate the \\beta{} parameter, while hybrid-exchange schemes partially correct for this discrepancy, resulting in a much better agreement with GW calculations an...

Ferretti, Andrea; Martin-Samos, Layla; Bussi, Giovanni; Ruini, Alice; Montanari, Barbara; Harrison, Nicholas M

2012-01-01

241

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

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

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

2014-10-01

242

Handbook of the band structure of elemental solids from Z = 1 to Z = 112

This handbook presents electronic structure data and tabulations of Slater-Koster parameters for the whole periodic table. This second edition presents data sets for all elements up to Z = 112, Copernicium, whereas the first edition contained only 53 elements. In this new edition, results are given for the equation of state of the elements together with the parameters of a Birch fit, so that the reader can regenerate the results and derive additional information, such as Pressure-Volume relations and variation of Bulk Modulus with Pressure. For each element, in addition to the equation of state, the energy bands, densities of states, and a set of tight-binding parameters is provided. For a majority of elements, the tight-binding parameters are presented for both a two- and three-center approximation. For the hcp structure, new three-center tight-binding results are given. Other new material in this edition include: energy bands and densities of states of all rare-earth metals, a discussion of the McMillan-Gas...

Papaconstantopoulos, Dimitris A

2015-01-01

243

International Nuclear Information System (INIS)

Strong spatial asymmetries in the spectrum and magnitude of low-frequency (?<density fluctuations have recently been measured in the TEXT tokamak. Large amplitude, narrow-band (as low as ??/?approx. =0.1) modes have been observed on the high-field torus inside in addition to the typical broad-band (??/?approx. =1) microturbulence which is present throughout the plasma cross section. These narrow-band fluctuations are only detected at the plasma interior, being localized towards the midplane, and are not seen at the edge

244

Band structures of ZnTe:O alloys with isolated oxygen and with clustered oxygen impurities

Energy Technology Data Exchange (ETDEWEB)

Highlights: • Band structures of ZnTe:O alloy highly depends on the status of oxygen. • Clustered oxygen lowers the bandgap while isolated oxygen increases the bandgap. • The solar adsorption efficiency of ZnTe:O can be improved by oxygen clustering. -- Abstract: First-principles calculations reveal that band structures of ZnTe:O alloys highly depend on the configuration of oxygen in the alloy. For alloys with isolated oxygen, the calculated band structure shows the formation of intermediate states between valence and conduction band and the shift of conduction band to higher energy level. It expands the gap between valence and conduction band. For alloys with clustered oxygen, the formation of intermediate band is still observed, while the gap between valence and conduction band is decreased. For alloys with oxygen impurities adjacent to Zn vacancy, the band structure only shows the decrease of the gap between valence and conduction band without the formation of any intermediate band. These results suggest the critical role of Zn–O bonding in determining the energy level of the impurity states. On the basis of our results, a possible band engineering approach is suggested in order to improve the performance of ZnTe:O alloy as intermediate band solar adsorbent.

Ling, Chen, E-mail: chen.ling@tema.toyota.com; Zhou, Li Qin; Banerjee, Debasish; Jia, Hongfei

2014-01-25

245

Solar spectral fine structure in 18-23 GHz band

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english On 30th June 1989 high sensitivity-spectral resolution observations of solar radio bursts were carried out in the frequency range of 18 - 23 GHz. The burst observed at 17:46 UT was different from the 60 bursts observed so far in the sense that it exhibited a frequency fine structure superimposed on [...] the ongoing burst in its rising phase, i.e. an additional enhancement of the flux density of the order of 10 SFU, observed only in the 21 and 22 GHz frequency channels, lasting for about 4 s. Interaction of an emerging loop with an adjacent loop accelerated particles in that loop from which the broadband burst was emitted due to the gyrosynchrotron emission. The observed fine structure is interpreted as due to thermal gyro-emission at 6th harmonic of the gyrofrequency originated from a hot kernel with short lifetime located at the top of emerging loop. We derived the hot kernel source parameters, th e temperature as 8 ´10(7) K, the magnetic field as 1250 G and the density as 5 ×10(12) cm-3.

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

1999-09-01

246

On the multi-orbital band structure and itinerant magnetism of iron-based superconductors

Energy Technology Data Exchange (ETDEWEB)

This paper explains the multi-orbital band structures and itinerant magnetism of the iron-pnictide and chalcogenide superconductors. We first describe the generic band structure of a single, isolated FeAs layer. Use of its Abelian glide-mirror group allows us to reduce the primitive cell to one FeAs unit. For the lines and points of high symmetry in the corresponding large, square Brillouin zone, we specify how the one-electron Hamiltonian factorizes. From density-functional theory, and for the observed structure of LaOFeAs, we generate the set of eight Fe d and As p localized Wannier functions and their tight-binding (TB) Hamiltonian, h (k). For comparison, we generate the set of five Fe d Wannier orbitals. The topology of the bands, i. e. allowed and avoided crossings, specifically the origin of the d{sup 6} pseudogap, is discussed, and the role of the As p orbitals and the elongation of the FeAs{sub 4} tetrahedron emphasized. We then couple the layers, mainly via interlayer hopping between As p{sub z} orbitals, and give the formalism for simple tetragonal and body-centered tetragonal (bct) stackings. This allows us to explain the material-specific 3D band structures, in particular the complicated ones of bct BaFe{sub 2}As{sub 2} and CaFe{sub 2}As{sub 2} whose interlayer hoppings are large. Due to the high symmetry, several level inversions take place as functions of k{sub z} or pressure, and linear band dispersions (Dirac cones) are found at many places. The underlying symmetry elements are, however, easily broken by phonons or impurities, for instance, so that the Dirac points are not protected. Nor are they pinned to the Fermi level because the Fermi surface has several sheets. From the paramagnetic TB Hamiltonian, we form the band structures for spin spirals with wavevector q by coupling h (k) and h (k + q). The band structure for stripe order is studied in detail as a function of the exchange potential, {delta}, or moment, m, using Stoner theory. Gapping of the Fermi surface (FS) for small {delta} requires matching of FS dimensions (nesting) and d-orbital characters. The interplay between pd hybridization and magnetism is discussed using simple 4 x 4 Hamiltonians. The origin of the propeller-shaped Fermi surface is explained in detail. Finally, we express the magnetic energy as the sum over band-structure energies and this enables us to understand to what extent the magnetic energies might be described by a Heisenberg Hamiltonian, and to address the much discussed interplay between the magnetic moment and the elongation of the FeAs{sub 4} tetrahedron. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Andersen, O.K.; Boeri, L. [Max-Planck-Institute for Solid State Research, Heisenbergstrasse 1, 70569 Stuttgart (Germany)

2011-01-15

247

Band structures in doubly-odd 120I nucleus

International Nuclear Information System (INIS)

Two new collective bands have been identified in 120I nucleus from the cross-bombardment results of 108Pd(16O,p3n) and 114Cd(11B,5n) reactions. Of these, a strongly coupled band, based on ?g7/2xyh11/2 quasiparticles, exhibits energy staggering in odd even spin states. The other band, based on ?h11/2xyg7/2 configuration, is decoupled in nature and shows a band-crossing at h?=0.39 MeV due to alignment of an h11/2 quasineutron pair. (orig.)

248

High spin structure in a coupled bands model

International Nuclear Information System (INIS)

A coupled bands model proposed earlier is developed. It is a modification of the band crossing models with Coriolis interaction and conserves rotational invariance. It is applied to the phenomenological description of energies and transition rates for crossing rotational bands in even-even nuclei. Information on the strengths of band interactions has been deduced by a fit to experimental energies. The strange clockwise circling dependence of reduced transition probabilities on squared rotational frequencies in the yrast line has been described, and information on interband E2 moment matrix elements has been deduced by a fit to experimental transition rates. (author)

249

Electronic band structures and photovoltaic properties of MWO4 (M=Zn, Mg, Ca, Sr) compounds

International Nuclear Information System (INIS)

Divalent metal tungstates, MWO4, 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 (ZnWO4 and MgWO4) exhibited better performance than those using the scheelite-structured metal tungstates (CaWO4 and SrWO4), 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: ? MWO4 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.

250

Digital Repository Infrastructure Vision for European Research (DRIVER)

The atomic structure of two-dimensional yttrium silicide epitaxially grown on Si(1 1 1) was investigated by means of density functional theory calculations and angle-resolved photoemission experiments. The obtained accuracy of the calculations allowed to discriminate different surface arrangements in a quantitative way via comparing their theoretical band structure to the experimental result. Theoretically we find significant changes in the dispersion of a surface localized band upon varying ...

Koitzsch, Christian; Bovet, M.; Garnier, Michael Bernard Gunnar; Aebi, Philipp; Rogero, C.; Marti?n-gago, J. A.

2009-01-01

251

Microstructure, optical property, and electronic band structure of cuprous oxide thin films

International Nuclear Information System (INIS)

Cuprous oxide (Cu2O) thin films were grown via radio frequency sputtering deposition at various temperatures. The dielectric functions and luminescence properties of the Cu2O thin films were measured using spectroscopic ellipsometry and photoluminescence, respectively. High-energy peaks were observed in the photoluminescence spectra. Several critical points (CPs) were found using second derivative spectra of the dielectric functions and the standard critical point model. The electronic band structure and the dielectric functions were calculated using density functional theory, and the CP energies were estimated to compare with the experimental data. We identified the high-energy photoluminescence peaks to quasi-direct transitions which arose from the granular structures of the Cu2O thin films.

252

SGFM applied to the calculation of surface band structure of V

International Nuclear Information System (INIS)

The surface Green function matching (SGFM) method has been developed recently to deal with a great variety of problems in a unified way. The method was first developed for continuum systems. The recent advances for discrete structures can deal with surfaces, interfaces, quantum wells, superlattices, intercalated layered compounds, and other systems. Several applications of this formalism are being carried out. In the present note we will describe how the formalism applies to the calculation of the electronic surface band structure of vanadium which is a quite interesting transition metal with very active magnetic properties at the surface, in particular at the (100) surface. It is straightforward, on the basis of the calculation presented here, to obtain the magnetic moment on the surface, for example, through the method followed by G. Allan or the surface paramagnon density which should be particularly enhanced at this surface as compared to the bulk

253

Rietveld analysis and electronic bands structure on Tc superconductors systems

International Nuclear Information System (INIS)

A procedure for simultaneous refinement of structural and micro-structural disorder parameters for polycrystalline YBa2Cu3O7-x system is proposed. It is based on Rietveld method combined with Fourier analysis for broadened peaks Another purpose of this paper consists in electronic structure determination studied by using the self-consistent Tight Binding Linear Muffin-Tin Orbital Atomic Spheres Approximation TB-LMTO-ASA methods. The Rietveld method uses an analytical function that describes the profiles, usually pseudo-Voigt (pV) or Pearson VII (PVII). The parameters of the analytical profiles describe its amplitude, position and peak shape. The full width at half maximum (FWHM) is supposed to vary with the diffraction angle in agreement with the Caglioti, Paoletti and Ricci's relationship. The best structural parameters are determined in the least squares sense by the minimisation a classical residual using the Marquardt method. In this case, the peak profiles were modelled by the pseudo-Voigt function corrected by the instrumental asymmetry. The physical information obtained are: scale factor, lattice parameters, atomic position and displacements, atomic occupation numbers, temperature factor (isotropy or anisotropy), preferred orientation parameter, crystalline size and micro-strain along different crystallographic directions, distributions of crystallite size and micro-strain functions. This procedure was implemented on computer cos procedure was implemented on computer code and it has a friendly graphical interface based on pull down menus technique. From the experimental point of view the X-ray diffraction data were collected using a horizontal powder diffractometer in the Bragg-Brentano (BB) geometry with a Ni filtered CuK?, ? = 1.54178 A, at room temperature using a DRON 2 set-up. The diffraction profiles were measured with a proportional gas detector, a single channel pulse-height discrimination and a standard associated counting circuit. The electronic band calculations are based on the TB-LMTO program version 47 under 2.03 LINUX operating system version. The main steps of our calculations are: the generation of the overlapping potentials from the atomic Hartree potentials and the finding of the MT-radii, the calculation and drawing of the sphere overlaps, the finding of the interstitial spheres, the generation of the structure constants and the performing of self-consistent calculations. The LMTO method can be regarded as an LCAO (linear combination atomic orbitals) formalism in which the muffin-tin potential (MT), rather than the atomic potential, defines the set of basis functions used to construct the trial functions of the variational procedure. (authors)

254

International Nuclear Information System (INIS)

Very-low-energy electron diffraction (VLEED) is used to study the unoccupied electronic states of Ru(001). Experimental and theoretical data are presented for reflection of electrons with energies of the specular beam between 7 and 32 eV and at different angles of incidence between 30 and 280 in both the Gamma-barK-bar and Gamma-barM-bar directions. Two sharp reflection minima at kinetic energies of 11.1 and 12.3 eV (relative to the vacuum level) corresponding to a final-state peak in Ru(001) angle-resolved photoemission and secondary-electron emission are observed near normal incidence. Theoretical VLEED intensity and band-structure calculations are carried out to confirm the origin of the experimental spectral features. An energy-dependent optical potential is shown to be sufficient to explain the observed narrow spectral structures. The observed minima can be reproduced excellently with the imaginary part of the optical potential equal to -0.6 eV at 11 eV above the vacuum level. The minimum at 12.3 eV can clearly be correlated with a high density of states in the volume band structure, whereas the other one is assigned to a Shockley-type surface state. The effects of several other parameters on the theoretical spectra are discussed

255

Ab initio quasiparticle band structure of ABA and ABC-stacked graphene trilayers

We obtain the quasiparticle band structure of ABA and ABC-stacked graphene trilayers through ab initio density-functional theory (DFT) and many-body quasiparticle calculations within the GW approximation. To interpret our results, we fit the DFT and GW ? bands to a low-energy tight-binding model, which is found to reproduce very well the observed features near the K point. The values of the extracted hopping parameters are reported and compared with available theoretical and experimental data. For both stackings, the self-energy corrections lead to a renormalization of the Fermi velocity, an effect also observed in previous calculations on monolayer graphene. They also increase the separation between the higher-energy bands, which is proportional to the nearest-neighbor interlayer hopping parameter ?1. Both features are brought to closer agreement with experiment through the self-energy corrections. Finally, other effects, such as trigonal warping, electron-hole asymmetry, and energy gaps, are discussed in terms of the associated parameters.

Menezes, Marcos G.; Capaz, Rodrigo B.; Louie, Steven G.

2014-01-01

256

Directory of Open Access Journals (Sweden)

Full Text Available Transmission coefficient, eigen states and tunneling current density of a potentially symmetric quantum double barrier structure has been numerically computed using transfer matrix technique for qualitative analysis of resonant tunneling probability when realistic band structure of higher band gap material is taken into account. GaAs/AlxGa1-xAs material composition is taken as an example for calculation, and thickness of the barrier and well regions are varied along with material compositions of AlxGa1-xAs to study the effect on electrical parameters; and also to observe the existence of quasi-bound states. Effective mass mismatch at junctions is considered following envelope function approximation, and conduction band discontinuity is taken into account for computational purpose. Under low biasing condition, negative differential regions (NDR can be obtained which speaks in favor of tunneling current.

Arpan Deyasi and Gourab Kumar Ghosh

2012-12-01

257

Complex band structure of topologically protected edge states

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

258

Global Kinetic Modeling of Banded Electron Structures in the Plasmasphere

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

259

Graphene band structure and its 2D Raman mode

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

260

Miniaturization of electromagnetic band gap structures for mobile applications

It is well known that interference of the human body affects the performance of the antennas in mobile phone handsets. In this contribution, we investigate the use of miniaturized metallodielectric electromagnetic band gap (MEBG) structures embedded in the case of a mobile handset as a means of decoupling the antenna from the user's hand. The closely coupled MEBG concept is employed to achieve miniaturization of the order of 15:1. Full wave dispersion relations for planar closely coupled MEBG arrays are presented and are validated experimentally. The performance of a prototype handset with an embedded conformal MEBG is assessed experimentally and is compared to a similar prototype without the MEBG. Reduction in the detuning of the antenna because of the human hand by virtue of the MEBG is demonstrated. Moreover, the efficiency of the handset when loaded with a human hand model is shown to improve when the MEBG is in place. The improvements are attributed to the decoupling of the antenna from the user's hand, which is achieved by means of suppressing the fields in the locality of the hand.

Goussetis, G.; Feresidis, A. P.; Palikaras, G. K.; Kitra, M.; Vardaxoglou, J. C.

2005-12-01

261

Self-consistent treatment of v-groove quantum wire band structure in no parabolic approximation

Directory of Open Access Journals (Sweden)

Full Text Available The self-consistent no parabolic calculation of a V-groove-quantum-wire (VQWR band structure is presented. A comparison with the parabolic flat-band model of VQWR shows that both, the self-consistency and the nonparabolicity shift sub band edges, in some cases even in the opposite directions. These shifts indicate that for an accurate description of inter sub band absorption, both effects have to be taken into the account.

Crnjanski Jasna V.

2004-01-01

262

Selforganized 3-band structure of the doped fermionic Ising spin glass

Digital Repository Infrastructure Vision for European Research (DRIVER)

The fermionic Ising spin glass is analyzed for arbitrary filling and for all temperatures. A selforganized 3-band structure of the model is obtained in the magnetically ordered phase. Deviation from half filling generates a central nonmagnetic band, which becomes sharply separated at T=0 by (pseudo)gaps from upper and lower magnetic bands. Replica symmetry breaking effects are derived for several observables and correlations. They determine the shape of the 3-band DoS, and, ...

Feldmann, H.; Oppermann, R.

1999-01-01

263

Electronic density of states and the x-ray photoelectron spectra of the valence band of Cu-Pd alloys

International Nuclear Information System (INIS)

We present self-consistent-field Korringa-Kohn-Rostoker coherent-potential-approximation calculations of the electronic density of states of random Cu/sub c/Pd/sub 1-c/ alloys. We find strong hybridization of the palladium d bands with the copper d bands over the entire concentration range. We do not obtain a palladium virtual bound state for the copper-rich alloys and therefore contradict the interpretation generally placed on valence-band x-ray photoelectron spectroscopy (XPS) spectra for Cu-Pd. Nevertheless, our first-principles calculations of the XPS spectra are in excellent agreement with recent measurements, and we discuss why this is so. Furthermore, we compare our density of states at the Fermi energy with specific-heat measurements

264

Electronic structure and band parameters for ZnX (X = O, S, Se, Te)

First-principles density-functional calculations have been performed for zinc monochalcogenides with zinc-blende- and wurtzite-type structures. It is shown that the local-density approximation underestimates the band gap, misplaces the energy levels of the Zn-3d states, and overestimates the crystal-field splitting energy. Without spinorbit coupling, the order of the states at the top of VB is found to be normal for all the ZnX phases considered. Upon inclusion of the spinorbit coupling in calculations, ZnO in zinc-blende- and wurtzite-type phases become anomalous. It is shown that the Zn-3d electrons are responsible for the anomalous order. The effective masses of electrons and holes have been calculated and found that holes are much anisotropic and heavier than the electrons in agreement with experimental findings. The typical errors in calculated band gaps and related parameters originate from strong Coulomb correlations, which are found to be highly significant in ZnO. The LDA+U approach is found to corre...

Karazhanov, S Z; Grossner, U; Kjekhus, A; Fjellvag, H; Svensson, B G

2006-01-01

265

High-spin band structure in 166Yb

International Nuclear Information System (INIS)

High-spin states in 166Yb have been studied via the 154Sm (16O,4n)166Yb reaction with 80 Mev 16O ions from the NBI tandem accelerator. ?-? coincidence data were accumulated with an array of four Ge(Li) and four NaI(Tl) detectors to favour high multiplicity events. Totally about 3 x 108 events were accumulated in the coincidence experiment. Measurements of the angular distribution of the ?-radiation and the conversion coefficients were furthermore performed. Four weakly populated side bands are observed besides the yrast cascade which is followed up to its 24+ member. The ground state band has thus been identified to its 18+ state, while the crossing Stockholm band becomes the yrast band from its 16+ member. The S-band is established from its 12+ state. The observed level energies and transition rates are well reproduced in calculations within the particle rotor model. (author)

266

Band Structure of Bose-Einstein Condensates in a Cavity-Mediated Triple-Well System

International Nuclear Information System (INIS)

We investigate the band structure and the dynamics of Bose-Einstein condensates in a triple-well trap, which are located in a high-finesse optical cavity. For the noninteracting atoms, the band structure of the eigenenergies are obtained using the numerical methods under the mean-field approximation. It is demonstrated that the energy band structure is strongly dependent on the value of reduced cavity detuning. Under some conditions, the atomic band structure develops loop structures and swallowtail structure, which mean the atom-cavity system exhibits bistability. We attribute the appearance of new states to the nonlinearity of the cavity-field-induced tilt. For the interacting atoms, the structure of the eigenenergy band appears more complicated for the interaction between atoms

267

Atomic and electronic structures of novel ternary and quaternary narrow band-gap semiconductors

This thesis concerns mainly with atomic and electronic structures of novel ternary and quaternary chalcogenide narrow band-gap semiconductors which are of great interest for infrared devices, photovoltaics, and high temperature thermoelectrics. More specifically, it presents studies of charge ordering and self-assembled nanostructures in a class of quaternary systems and their phase diagram, defect clustering and nanostructure formation in bulk thermoelectrics, atomic and electronic structures of ternary chalcogenides, and nature of defect states in narrow band-gap semiconductors. Studies are carried out using Monte Carlo (MC) and ab initio methods to understand the nanostructuring phenomenon observed in AgPbmSbTem+2 and similar systems. MC simulations in these quaternaries using an ionic model show a distinct phase diagram and a variety of structural orderings depending on the concentration of the monovalent and trivalent atoms as a result of the long-range nature of the Coulomb interaction. Ab initio density functional theory (DFT) based calculations also show that monovalent and trivalent impurities in PbTe, SnTe, and GeTe-based bulk thermoelectric materials like to come close to each other and form clusters or some sort of embedded nanostructures. Interplay of atomic and electronic structures and band gap formation in I-V-VI2 and TI-based III-V-VII2 tertiary chalcogenides (I=Ag, Cu, Au, Na, K; V=As, Sb, Bi; VII=S, Se, Te) are studied using ab initio electronic structure calculations. These calculations have been able to identify low energy ordered structures which are consistent with experiments. Several intriguing physical properties of these materials can be understood in terms of the calculated electronic structure. This thesis suggests how to modify a certain ternary by replacing its constituting elements) such that the electronic structure shows desired features for different applications. Comprehensive studies of the nature of defect-induced electronic states associated with a large class of substitutional impurities and native point defects in PbTe, SnTe, and GeTe are carried out using DFT and supercell models. Calculations are also carried out in PbTe thin films and nanoclusters to study how the defect states change in going from one geometry to another. This thesis also concerns with energetics of the defects, particularly defect formation energy, which may be able to give some information on the doping mechanism and the distribution of the defects in these systems. Based on the calculated electronic structures, one can explain the peculiar properties of PbTe doped with group III (Ga, In, T1) impurities and the observed transport properties of PbTe, SnTe, and GeTe-based thermoelectrics.

Hoang, Khang

268

Band structure and optical properties of highly anisotropic LiBa2[B10O16(OH)3] decaborate crystal

International Nuclear Information System (INIS)

The band structure (BS), charge density distribution and linear-optical properties of the anisotropic crystal LiBa2[B10O16(OH)3] (LBBOH) are calculated using a self-consistent norm-conserving pseudopotential method within the framework of the local-density approximation theory. A high anisotropy of the band energy gap (4.22 eV for the E parallel b, 4.46 eV for the E parallel c) and giant birefringence (up to 0.20) are found. Comparison of the theoretically calculated and the experimentally measured polarised spectra of the imaginary part of the dielectric susceptibility ?2 shows a good agreement. The anisotropy of the charge density distribution, BS dispersion and of the optical spectra originate from anisotropy between the 2pzB-2pzO and 2py,xB-2py,yO bonding orbitals. The observed anisotropy in the LBBOH is principally different from that of ?-BaB2O4 (BBO) single crystals. In the LBBOH single crystals the anisotropy of optical and charge density distribution is caused by different projection of the orbitals originating from particular borate clusters on the particular crystallographic axes, contrary to the BBO, where the anisotropy is caused prevailingly by a different local site symmetry of oxygen within the borate planes. The observed anisotropy is analysed in terms of the band energy dispersion and space charge density distribution

269

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

DEFF Research Database (Denmark)

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 infinitely periodic band-gap materials by maximizing the relative size of the band gaps. Then, finite structures subjected to periodic loading are optimized in order to either minimize the structural response along boundaries (wave damping) or maximize the response at certain boundary locations (waveguiding).

Sigmund, Ole; Jensen, Jakob SØndergaard

2003-01-01

270

Band structures in doubly-odd {sup 120}I nucleus

Energy Technology Data Exchange (ETDEWEB)

Two new collective bands have been identified in {sup 120}I nucleus from the cross-bombardment results of {sup 108}Pd({sup 16}O,p3n) and {sup 114}Cd({sup 11}B,5n) reactions. Of these, a strongly coupled band, based on {pi}g{sub 7/2}xyh{sub 11/2} quasiparticles, exhibits energy staggering in odd even spin states. The other band, based on {pi}h{sub 11/2}xyg{sub 7/2} configuration, is decoupled in nature and shows a band-crossing at h{omega}=0.39 MeV due to alignment of an h{sub 11/2} quasineutron pair. (orig.)

Kaur, H. [Panjab Univ., Chandigarh (India). Dept. of Physics; Singh, J. [Panjab Univ., Chandigarh (India). Dept. of Physics; Sharma, A. [Panjab Univ., Chandigarh (India). Dept. of Physics; Goswamy, J. [Panjab Univ., Chandigarh (India). Dept. of Physics]|[B.B.S. Engineering Coll., Fatehgarh Sahib, Punjab (India); Mehta, D. [Panjab Univ., Chandigarh (India). Dept. of Physics]|[Delhi Univ. (India). Dept. of Physics

1995-06-01

271

Structural failure of two-density-layer cohesionless biaxial ellipsoids

This paper quantitatively evaluates structural failure of biaxial cohesionless ellipsoids that have a two-density-layer distribution. The internal density layer is modeled as a sphere, while the external density layer is the rest of the part. The density is supposed to be constant in each layer. The present study derives averaged stresses over the whole volume of these bodies and uses limit analysis to determine their global failure. The upper bound of global failure is considered in terms of the size of the internal layer and the aspect ratio of the shape. The result shows that the two-density-layer causes the body to have different strength against structural failure.

Hirabayashi, Masatoshi

2014-07-01

272

Energy Technology Data Exchange (ETDEWEB)

The detailed energy-band structure of hexagonal-close-packed technetium, corresponding to the atomic configuration 4d/sup 5/5s/sup 2/ of its seven outermost valence electrons, has been obtained throughout the Brillouin zone using the composite-wave variational version of the augmented-plane-wave (APW) method in conjunction with the X..cap alpha.. (..cap alpha.. = 0.702 99) exchange approximation for obtaining the potentials. From the band-structure data the electronic density of states (DOS) and the angular-momentum--decomposed DOS were calculated by the accurate Gilat-Raubenheimer method. These quantities were used to calculate the electron-phonon coupling constant and the transition temperature (T/sub c/) using the theories of Gaspari and Gyorffy and of McMillan. Also studied were the Fermi surface and the optical properties of Tc via the imaginary part of the interband dielectric constant for bound electrons, the latter being the first of such a study on Tc to date. The superconducting properties and the Fermi surface which could be compared to experiments show, in general, satisfactory agreement.

Chatterjee, P.

1983-04-15

273

The detailed energy-band structure of hexagonal-close-packed technetium, corresponding to the atomic configuration 4d55s2 of its seven outermost valence electrons, has been obtained throughout the Brillouin zone using the composite-wave variational version of the augmented-plane-wave (APW) method in conjunction with the X? (?=0.702 99) exchange approximation for obtaining the potentials. From the band-structure data the electronic density of states (DOS) and the angular-momentum-decomposed DOS were calculated by the accurate Gilat-Raubenheimer method. These quantities were used to calculate the electron-phonon coupling constant and the transition temperature (Tc) using the theories of Gaspari and Gyorffy and of McMillan. Also studied were the Fermi surface and the optical properties of Tc via the imaginary part of the interband dielectric constant for bound electrons, the latter being the first of such a study on Tc to date. The superconducting properties and the Fermi surface which could be compared to experiments show, in general, satisfactory agreement.

Chatterjee, Parsathi

1983-04-01

274

International Nuclear Information System (INIS)

The detailed energy-band structure of hexagonal-close-packed technetium, corresponding to the atomic configuration 4d55s2 of its seven outermost valence electrons, has been obtained throughout the Brillouin zone using the composite-wave variational version of the augmented-plane-wave (APW) method in conjunction with the X? (? = 0.702 99) exchange approximation for obtaining the potentials. From the band-structure data the electronic density of states (DOS) and the angular-momentum--decomposed DOS were calculated by the accurate Gilat-Raubenheimer method. These quantities were used to calculate the electron-phonon coupling constant and the transition temperature (T/sub c/) using the theories of Gaspari and Gyorffy and of McMillan. Also studied were the Fermi surface and the optical properties of Tc via the imaginary part of the interband dielectric constant for bound electrons, the latter being the first of such a study on Tc to date. The superconducting properties and the Fermi surface which could be compared to experiments show, in general, satisfactory agreement

275

Band structure of sup 7 sup 9 Br

High-spin states of sup 7 sup 9 Br have been studied in the reaction sup 7 sup 6 Ge( sup 7 Li, 4n gamma) at 32 MeV. A gamma-detector array with twelve Compton-suppressed HPGe detectors was used. The positive-parity yrast states, interpreted as a rotationally aligned g sub ( sub 9 sub ( sub 2 sub ) sub ) proton band, and the negative-parity ground state band have been extended to spins of (33(2 sup +)) and (25(2 sup -)), respectively. Lifetime measurements indicate that both bands have a similar quadrupole deformation of beta sub 2 approx 0.2. The positive-parity alpha = -(1(2)) band has been identified. Several new inter-band transitions are observed. A cranked-shell model analysis shows that the nu g sub ( sub 9 sub ( sub 2 sub ) sub ) and pi g sub ( sub 9 sub ( sub 2 sub ) sub ) alignments occur in the positive-parity and the negative-parity bands at rotational frequencies of Planck constant omega approx 0.6 and 0.4 MeV, respectively. The level energies and the electromagnetic properties of the g sub ( sub ...

Ray, I; Bhattacharya, S; Saha-Sarkar, M; Sethi, B; Chatterjee, J M; Chattopadhyay, S; Goswami, A; Muralithar, S; Singh, R P; Bhowmik, R K

1999-01-01

276

Local density of optical states in the band gap of a finite one-dimensional photonic crystal

We study the local density of states (LDOS) in a finite photonic crystal, in particular in the frequency range of the band gap. We propose an original point of view on the band gap, which we consider to be the result of vacuum fluctuations in free space that tunnel in the forbidden range in the crystal. As a result, we arrive at a model for the LDOS that is in two major items modified compared to the well-known expression for infinite crystals. First, we modify the Dirac ? functions to become Lorentzian with a width set by the crystal size. Second, building on characterization of the fields versus frequency and position we calculated the fields in the band gap. We start from the fields at the band edges, interpolated in space and position, and incorporating the exponential damping in the band gap. We compare our proposed model to exact calculations in one dimension using the transfer matrix method and find very good agreement. Notably, we find that in finite crystals, the LDOS inside the band gap depends on frequency, on position, and on crystal size, in contrast to the well-known results for infinite crystals where the LDOS is zero, independent of frequency and position.

Yeganegi, Elahe; Lagendijk, Ad; Mosk, Allard P.; Vos, Willem L.

2014-01-01

277

The Density Functional Theory Study of Structural and Electronical Properties of ZnO Clusters

Directory of Open Access Journals (Sweden)

Full Text Available Density functional theory studies of structural and electronic properties of small clusters were performed. For each cluster an optimization of structure and the basic properties of the band structure were conducted. It was determined that with increasing (n energetically more efficient in the small clusters is stabilization from the ring to fulleren-like structures containing tetragonal and hexagonal faces and all atoms have coordination number equal three. Among the clusters (ZnO12 with doped atoms most stable are clusters where Zn was replaced by Mn, Cu and Co atoms. Band gap in the electronic spectrum of doped clusters decreases due to p-d hybridization orbitals of the impurity atom with the orbitals of the oxygen atom.

O.V. Bovgyra

2013-03-01

278

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

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 interest such as the hybridization function, the adatom spectral density and valence occupation are calculated. We find that the interference between the adatom neighboring sites together with the pronounced energy gap around the ? point lead to negligible hybridization widths in a wide range of energies and are practically not dependent on the adsorption site. Consequently, this very weak coupling regime makes possible a local magnetic moment formation. Moreover, the strong suppression of the atom level broadening allows for an explanation of the unexpected neutralization measured at low energies in experiments of Li+ scattering by a highly oriented pyrolytic graphite surface.

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

2011-03-01

279

De Haas-van Alphen effect and energy band structure in UB2

International Nuclear Information System (INIS)

We grew a single crystal of UB2 with the hexagonal structure and observed the de Haas-van Alphen (dHvA) oscillation. All of the dHvA branches, which are about seven in number, are detected in the limited angle regions. They are well explained by the 5f-itinerant relativistic band theory with an exchange and correlation potential in a local density approximation. Namely, UB2 is a compensated metal with an equal number of electron and hole. The Fermi surface consists of two closed but corrugated Fermi surfaces. The cyclotron masses are moderately heavy, ranging from 1.2 to 7.7 m0. (author)

280

Valence band electronic structure of V2O3: identification of V and O bands

Digital Repository Infrastructure Vision for European Research (DRIVER)

We present a comprehensive study of the photon energy dependence of the valence band photoemission yield in the prototype Mott-Hubbard oxide V2O3. The analysis of our experimental results, covering an extended photon energy range (20-6000 eV) and combined with GW calculations, allow us to identify the nature of the orbitals contributing to the total spectral weight at different binding energies, and in particular to locate the V 4s at about 8 eV binding energy. From this c...

Papalazarou, E.; Gatti, Matteo; Marsi, M.; Brouet, V.; Iori, F.; Reining, Lucia; Annese, E.; Vobornik, I.; Offi, F.; Fondacaro, A.; Huotari, S.; Lacovig, P.; Tjernberg, O.; Brookes, N. B.; Sacchi, M.

2009-01-01

281

Elastic band structures of two-dimensional solid phononic crystal with negative Poisson's ratios

International Nuclear Information System (INIS)

In this paper, the elastic band structures of two-dimensional solid phononic crystals (PCs) with both negative and positive Poisson's ratios are investigated based on the finite difference domain method. Systems with different combinations of mass density ratio and shear modulus ratio, filling fractions and lattices are considered. The numerical results show that for the PCs with both large mass density ratio and shear modulus ratio, the first bandgap becomes narrower with its upper edge becoming lower as Poisson's ratio of the scatterers decreases from -0.1 to -0.9. Generally, introducing the material with a negative Poisson's ratio for scatterers will make this bandgap lower and narrower. For the PCs with large mass density ratio and small shear modulus ratio, the first bandgap becomes wider with Poisson's ratio of the scatterers decreasing and that of the host increasing. It is easy to obtain a wide low-frequency bandgap by embedding scatterers with a negative Poisson's ratio into the host with a positive Poisson's ratio. The PCs with large filling fractions are more sensitive to the variations of Poisson's ratios. Use of negative Poisson's ratio provides us a way of tuning bandgaps.

282

Simulation of EMIC wave excitation in a model magnetosphere including structured high-density plumes

The HOTRAY code is used to evaluate the path integrated gain of electromagnetic ion cyclotron (EMIC) waves as a function of frequency in two propagation bands above the O+ and He+ gyrofrequencies. Calculations are performed over a range of L shell (3 40 dB) is found near the plasmapause, within regions with density structure in the plume, and in the low-density trough at L ? 6.5. As a self-consistent test on whether EMIC waves play an important role in relativistic electron loss from the radiation belts, the minimum cyclotron resonant electron energy is evaluated as a function of wave frequency and L shell for those EMIC waves that exhibit significant gain. The lowest electron resonant energies (approximately a few MeV) are found in structured plumes. The sensitivities of both the wave gain and electron minimum resonant energy to variation in thermal ion compositions, the energetic proton properties, or plume density structure are also investigated.

Chen, Lunjin; Thorne, Richard M.; Horne, Richard B.

2009-07-01

283

The simulated annealing basin-hopping method incorporating the penalty function was used to predict the lowest-energy structures for ultrathin tungsten nanowires and nanotubes of different sizes. These predicted structures indicate that tungsten one-dimensional structures at this small scale do not possess B.C.C. configuration as in bulk tungsten material. In order to analyze the relationship between multi-shell geometries and electronic transfer, the electronic and structural properties of tungsten wires and tubes including partial density of state and band structures which were determined and analyzed by quantum chemistry calculations. In addition, in order to understand the application feasibility of these nanowires and tubes on nano-devices such as field emitters or chemical catalysts, the electronic stability of these ultrathin tungsten nanowires was also investigated by density functional theory calculations.

Sun, Shih-Jye; Lin, Ken-Huang; Ju, Shin-Pon; Li, Jia-Yun

2014-10-01

284

Band structure in 121Xe and 119Xe excited by 12C induced reactions

International Nuclear Information System (INIS)

Band structures in 119Xe, 121Xe produced by 110Cd, 112Cd(12C, 3n) reaction have been investigated using in-beam ? spectroscopic techniques. Details of the structures of the hsub(11/2) and gsub(7/2)bands are presented. A new dsub(3/2) decoupled band has been observed in 121Xe and a possible gsub(9/2) band in 119Xe. These collective features are discussed in the framework of the triaxial-rotor-plus-particle model, and the IBFA model

285

The 22Na band structure: the first Jsup(?)=6+ level

International Nuclear Information System (INIS)

Angular correlation and DSAM (Doppler shift attenuation method) lifetime measurements are reported for the 22Na 3706keV level. This level is shown to be the Jsup(?)=6+ member of the ground state band and decays to the Jsup(?)=4+ and 5+ states through E2 transitions of strengths: 6.9+-0.7 and 12.1+-1.6W.u., respectively. The experimental strengths of transitions between the 22Na ground state band members are reviewed and compared to the predictions of different models

286

Topological equivalence of crystal and quasicrystal band structures

A number of recent articles have reported the existence of topologically nontrivial states and associated end states in one-dimensional incommensurate lattice models that would usually only be expected in higher dimensions. Using an explicit construction, we here argue that the end states have precisely the same origin as their counterparts in commensurate models and that incommensurability does not in fact provide a meaningful connection to the topological classification of systems in higher dimensions. In particular, we show that it is possible to smoothly interpolate between states with commensurate and incommensurate modulation parameters without closing the band gap and without states crossing the band gap.

Madsen, Kevin A.; Bergholtz, Emil J.; Brouwer, Piet W.

2013-09-01

287

Gamma decay and band structures in 46Ti

International Nuclear Information System (INIS)

The states of 46Ti have been studied using the 43Ca(?,n?) reaction. The level and decay scheme of 46Ti was deduced from ?-? coincidence, ?-ray energy and intensity measurements. Spins are suggested on the basis of the ?-ray angular distribution, supported by relative excitation functions. The ground state band has been extended to spin 10+, and about 20 new states are observed. Some of these can be grouped into rotational-like bands based on the 3- state at 3.059 MeV and other excited states

288

Estimating tropical forest structure using LIDAR AND X-BAND INSAR

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

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

2013-12-01

289

Electronic band structure of LaCoO{sub 3}/Y/Mn compounds

Energy Technology Data Exchange (ETDEWEB)

Spin polarization effects on electronic properties of pure LaCoO{sub 3} and doped compounds (La{sub 0.5}Y{sub 0.5}CoO{sub 3}, LaCo{sub 0.5}Mn{sub 0.5}O{sub 3}) in the rhombohedral phase have been studied. We have employed the full potential linearized augmented plane wave (FP-LAPW) method with the generalized gradient approximation (GGA+U) under density functional theory (DFT). The calculated band structures along with total as well as partial densities of states reveal that Y and Mn impurities have a significant effect on the structural and electronic properties of LaCoO{sub 3}. It is found that Mn alters insulating behavior of this compound to the half metallic for spin up state. Obtained results show that the magnetic moment for the Co-3d state is near 3.12{mu}{sub B} in LaCoO{sub 3} compound which increases and decreases with addition of Y and Mn dopants respectively.

Rahnamaye Aliabad, H.A., E-mail: rahnama@sttu.ac.ir [Department of Physics, Hakim Sabzevari University, Sabzevar (Iran, Islamic Republic of); Hesam, V. [Department of Physics, Khayyam Institute of Higher Education, Mashhad (Iran, Islamic Republic of); Ahmad, Iftikhar; Khan, Imad [Department of Physics, University of Malakand, Chakdara (Pakistan)

2013-02-01

290

Band structure effects for dripped neutrons in neutron star crust

Digital Repository Infrastructure Vision for European Research (DRIVER)

The outer layers of a neutron star are supposed to be formed of a solid Coulomb lattice of neutron rich nuclei. At densities above neutron drip density (about one thousandth of nuclear saturation density), this lattice is immersed in a neutron fluid. Bragg scattering of those dripped neutrons by the nuclei which has been usually neglected is investigated, within a simple mean field model with Bloch type boundary conditions. The main purpose of this work is to provide some es...

Chamel, Nicolas

2004-01-01

291

Dual-band tunable negative refractive index metamaterial with F-Shape structure

This paper presents a negative refractive index tunable metamaterial based on F-Shape structure which is capable of achieving dual-band negative permeability and permittivity, thus dual-band negative refractive index. An electromagnetic simulation was performed and effective media parameters were retrieved. Numerical investigations show clear existence of two frequency bands in which permeability and permittivity both are negative. The two negative refractive index bandwidths are from 23.8 GHz to 24.1 GHz and from 28.3 GHz to 34.9 GHz, respectively. The geometry of the structure is simple so it can easily be fabricated. The proposed structure can be used in multiband and broad band devices, as the band range in second negative refractive index region is 7 GHz, for potential applications instead of using complex geometric structures and easily tuned by varying the separation between the horizontal wires.

Rizwan, Muhammad; Jin, Hai-Bo; Rehman, Fida; Hou, Zhi-Ling; Li, Jing-Bo; Butt, Faheem K.; Ali, Zulfiqar

2014-08-01

292

Yrast transition strengths and band structure of 75Br

High spin states in 75Br were investigated in the reactions 62Ni(16O,p2n) and 66Zn(12C,p2n). By means of ??- and ?-neutron multiplicity coincidence measurements, rotational bands of both parities were extended up to 7 MeV excitation energy and spin I=(33/2). The lifetimes of 17 yrast states were determined with the recoil distance and Doppler shift attenuation methods; the spin dependence of the side feeding time was also measured. The data have been analyzed in terms of the Strutinsky-Bogolyubov cranking model with a Woods-Saxon average potential. The first crossing observed in the negative parity bands is attributed to the alignment of a g9/2 proton pair; the next irregularity which is also observed in the positive parity band is interpreted as the alignment of g9/2 neutrons. The coexistence of prolate and oblate configurations at low spin and the change of nonaxial deformation with rotational frequency due to the polarization of the even-even core by the odd particle are discussed. The signature inversion visible in the negative parity bands as well as the changes in the signature splitting and reduction of B(E2) values at high spins may be related to a transition from ?0° triaxial shapes.

Lühmann, L.; Debray, M.; Lieb, K. P.; Nazarewicz, W.; Wörmann, B.; Eberth, J.; Heck, T.

1985-03-01

293

Novel band structures in silicene on monolayer zinc sulfide substrate

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.

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

2014-10-01

294

We have derived the expressions for the transition temperature and the isotope effect exponent within the framework of Bogoliubov-Valatin two-band formalism using a linear-energy-dependent electronic density of states assuming a three-square-well potentials model. Our results show that the approach could be used to account for a wide range of values of the transition temperature and isotope effect exponent. The relevance of the present calculations to MgB 2 is analyzed.

Ogbuu, O. A.; Abah, O. C.; Asomba, G. C.; Okoye, C. M. I.

2011-08-01

295

The isotope shift exponent is derived from the two-band BCS gap equation with a linear-energy-dependent electronic density of states and assuming that both the electron-phonon and free-carrier negative- U centre interacting mechanisms are simultaneously present. The result shows that some of the anomalous features of the isotope shift exponent observed in high- Tc superconductors could be interpreted within this present model.

Okoye, C. M. I.

1999-02-01

296

Digital Repository Infrastructure Vision for European Research (DRIVER)

A study is presented of the electrical properties of a series of nanocomposites based on high density polyethylene (HDPE) as a matrix and either carbon nanofiber (CNF) or multiwall carbon nanotube (MWCNT) as a nanoadditive. The measurements of the electrical conductivity over a broad-band of frequencies (10-2 > F/Hz > 109)allow improvement of the description of the electrical properties of polymer nanocomposites based on either carbon nanofibers or carbon nanotubes. Despite the lack of ...

Linares, A.; Canalda, J. C.; Cagiao, M. E.; Garci?a-gutie?rrez, M. C.; Nogales, A.; Marti?n-gullo?n, I.; Vera, J.; Ezquerra, T. A.

2008-01-01

297

InN/GaN Superlattices: Band Structures and Their Pressure Dependence

DEFF Research Database (Denmark)

Creation of short-period InN/GaN superlattices is one of the possible ways of conducting band gap engineering in the green-blue range of the spectrum. The present paper reports results of photoluminescence experiments, including pressure effects, on a superlattice sample consisting of unit cells with one monolayer of InN and 40 monolayers of GaN. The results are compared with calculations performed for different types of superlattices: InN/GaN, InGaN/GaN, and InN/InGaN/GaN with single monolayers of InN and/or InGaN. The superlattices are simulated by band structure calculations based on the local density approximation (LDA) with a semi-empirical correction for the ‘‘LDA gap error’’. A similarity is observed between the results of calculations for an InGaN/GaN superlattice (with one monolayer of InGaN) and the experimental results. This indicates that the fabricated InN quantum wells may contain some Ga atoms due to interdiffusion

Gorczyca, Iza; Suski, Tadek

2013-01-01

298

The magneto-optical properties of semiconductors and the band structure of gallium nitride

the wells, and observing a resonant phenomenon from an undoped GaN/Al sub x Ga sub 1 sub - sub x N single heterojunction. The oscillating peak intensity was understood in terms of the changing screening efficiency of the two-dimensional electron gas. Finally, many-body effects within an electron-hole plasma in ln sub x Al sub y Ga sub 1 sub - sub x sub - sub y As quantum wells have been explored to study the effects of mass renormalisation at carrier densities typically present in laser devices. A peak in the mass renormalisation confirms the importance of excitonic correlations in the excited plasma. This thesis has applied magneto-optical techniques to enable a better understanding of the band structure of gallium nitride, particularly the complex behaviour expected as a result of strong valence band mixing. Effective hole masses are deduced from free excitonic-like transitions observed in magneto-reflectivity, to give a heavy A hole mass of 1.3 m sub o and the first experimental suggestion of a light B ban...

Shields, P A

2001-01-01

299

Superconducting and optical properties of ?-zirconium from its augmented-plane-wave band structure

International Nuclear Information System (INIS)

The detailed electronic energy band structure of hexagonal close-packed ?-zirconium, corresponding to the atomic configuration of 4d25s2 of its four outermost valence electrons, has been computed by the composite-wave variational version of the augmented-plane-wave(APW) method in conjunction with the X?(? = 0.70424) exchange approximation for obtaining the potentials. From these data the electronic density of states and its angular-momentum-decomposed components have been obtained by the Raubenheimer-Gilat method. These quantities are required in order to calculate the electron-phonon interaction parameter (lambda) and the superconducting transition temperature (Tsub(c)) within the framework of the theories of Gaspari and Gyorffy and McMillan. A study of the variation of Tsub(c) with the Coulomb pseudopotential (?*) revealed that ?* = 0.1 yields the best agreement between theory and experiment for ?-Zr. Also studied from the energy band data are the optical properties of ?-Zr via the variation of the imaginary part of the interband dielectric function for bound electrons and the corresponding optical conductivity (?) as a function of the photon energy (?). The results indicate five peaks in the ?-? curve, the positions of which on the energy scale are in fair agreement with experiment. (author)

300

Energy Technology Data Exchange (ETDEWEB)

The detailed electronic energy band structure of hexagonal close-packed ..cap alpha..-zirconium, corresponding to the atomic configuration of 4d/sup 2/5s/sup 2/ of its four outermost valence electrons, has been computed by the composite-wave variational version of the augmented-plane-wave(APW) method in conjunction with the X..cap alpha..(..cap alpha.. = 0.70424) exchange approximation for obtaining the potentials. From these data the electronic density of states and its angular-momentum-decomposed components have been obtained by the Raubenheimer-Gilat method. These quantities are required in order to calculate the electron-phonon interaction parameter (lambda) and the superconducting transition temperature (Tsub(c)) within the framework of the theories of Gaspari and Gyorffy and McMillan. A study of the variation of Tsub(c) with the Coulomb pseudopotential (..mu..*) revealed that ..mu..* = 0.1 yields the best agreement between theory and experiment for ..cap alpha..-Zr. Also studied from the energy band data are the optical properties of ..cap alpha..-Zr via the variation of the imaginary part of the interband dielectric function for bound electrons and the corresponding optical conductivity (sigma) as a function of the photon energy (..omega..). The results indicate five peaks in the sigma-..omega.. curve, the positions of which on the energy scale are in fair agreement with experiment.

Chatterjee, D. (Indian Association for the Cultivation of Science, Jadavpur. Director' s Research Unit)

1984-09-01

301

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

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

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

2002-08-01

302

Effect of cation substitution on electronic band structure of ZnGeAs2 pnictides: A mBJLDA approach

International Nuclear Information System (INIS)

Highlights: ? These compounds are characterized as narrow band gap semiconductors with a maximum gap (1.27 eV) for ZnGeAs2. ? A good agreement of band gaps with experiments is obtained within mBJLDA formalism. ? The band gap decreases with the substitution of either one or both cations in reference compound, ZnGeAs2. ? The ionic/covalent character for A-As/B-As bond has been described on the basis of electro-negativity difference of the atoms. ? The d-states of transition metal, Zn are localized deeper in valence band (E 2 (A = Zn, Cd; B = Ge, Sn) compounds have been investigated using WIEN2k implementation of full potential linearized augmented plane wave (FPLAPW) method with an aim to study the effect of changing local environment by substituting cation(s) with corresponding next group element in reference compound (ZnGeAs2) on these properties. The exchange and correlation (XC) effects are taken into account by an orbital independent modified Becke–Johnson (mBJ) potential as coupled with Local Density Approximation (LDA) for these calculations. We predict a direct band gap in all these compounds and observe that the band gap decreases with the change of either one or both cations. The calculated band gaps are in better agreement with corresponding experimental ones as compared to other calculations. The electronic band structure is analyzed in terms of contributions from various electrons and the covalency of two bonds, Zn-As and Ge-As has been discussed with respect to substitutions.

303

Energy Technology Data Exchange (ETDEWEB)

The effects of pressure on the structural and vibrational properties of the layered molecular crystal 1,1-diamino-2,2-dinitroethelene (FOX-7) are explored by first principles calculations. We observe significant changes in the calculated structural properties with different corrections for treating van der Waals interactions to Density Functional Theory (DFT), as compared with standard DFT functionals. In particular, the calculated ground state lattice parameters, volume and bulk modulus obtained with Grimme's scheme, are found to agree well with experiments. The calculated vibrational frequencies demonstrate the dependence of the intra and inter-molecular interactions on FOX-7 under pressure. In addition, we also found a significant increment in the N–H...O hydrogen bond strength under compression. This is explained by the change in bond lengths between nitrogen, hydrogen, and oxygen atoms, as well as calculated IR spectra under pressure. Finally, the computed band gap is about 2.3 eV with generalized gradient approximation, and is enhanced to 5.1 eV with the GW approximation, which reveals the importance of performing quasiparticle calculations in high energy density materials.

Appalakondaiah, S.; Vaitheeswaran, G., E-mail: gvaithee@gmail.com [Advanced Centre of Research in High Energy Materials (ACRHEM), University of Hyderabad, Prof. C. R. Rao Road, Gachibowli, Hyderabad 500 046, Andhra Pradesh (India); Lebègue, S. [Laboratoire de Cristallographie, Résonance Magnétique et Modélisations (CRM2, UMR CNRS 7036), Institut Jean Barriol, Université de Lorraine, BP 239, Boulevard des Aiguillettes, 54506 Vandoeuvre-lès-Nancy (France)

2014-01-07

304

International Nuclear Information System (INIS)

The effects of pressure on the structural and vibrational properties of the layered molecular crystal 1,1-diamino-2,2-dinitroethelene (FOX-7) are explored by first principles calculations. We observe significant changes in the calculated structural properties with different corrections for treating van der Waals interactions to Density Functional Theory (DFT), as compared with standard DFT functionals. In particular, the calculated ground state lattice parameters, volume and bulk modulus obtained with Grimme's scheme, are found to agree well with experiments. The calculated vibrational frequencies demonstrate the dependence of the intra and inter-molecular interactions on FOX-7 under pressure. In addition, we also found a significant increment in the N–H...O hydrogen bond strength under compression. This is explained by the change in bond lengths between nitrogen, hydrogen, and oxygen atoms, as well as calculated IR spectra under pressure. Finally, the computed band gap is about 2.3 eV with generalized gradient approximation, and is enhanced to 5.1 eV with the GW approximation, which reveals the importance of performing quasiparticle calculations in high energy density materials

305

The effects of pressure on the structural and vibrational properties of the layered molecular crystal 1,1-diamino-2,2-dinitroethelene (FOX-7) are explored by first principles calculations. We observe significant changes in the calculated structural properties with different corrections for treating van der Waals interactions to Density Functional Theory (DFT), as compared with standard DFT functionals. In particular, the calculated ground state lattice parameters, volume and bulk modulus obtained with Grimme's scheme, are found to agree well with experiments. The calculated vibrational frequencies demonstrate the dependence of the intra and inter-molecular interactions on FOX-7 under pressure. In addition, we also found a significant increment in the N-H...O hydrogen bond strength under compression. This is explained by the change in bond lengths between nitrogen, hydrogen, and oxygen atoms, as well as calculated IR spectra under pressure. Finally, the computed band gap is about 2.3 eV with generalized gradient approximation, and is enhanced to 5.1 eV with the GW approximation, which reveals the importance of performing quasiparticle calculations in high energy density materials. PMID:24410219

Appalakondaiah, S; Vaitheeswaran, G; Lebègue, S

2014-01-01

306

Acoustic band pinning in the phononic crystal plates of anti-symmetric structure

International Nuclear Information System (INIS)

Acoustic bands are studied numerically for a Lamb wave propagating in an anti-symmetric structure of a one-dimensional periodic plate by using the method of supercell plane-wave expansion. The results show that all the bands are pinned in pairs at the Brillouin zone boundary as long as the anti-symmetry remains and acoustic band gaps (ABGs) only appear between certain bands. In order to reveal the relationship between the band pinning and the anti-symmetry, the method of eigenmode analysis is introduced to calculate the displacement fields of different plate structures. Further, the method of harmony response analysis is employed to calculate the reference spectra to verify the accuracy of numerical calculations of acoustic band map, and both the locations and widths of ABGs in the acoustic band map are in good agreement with those of the reference spectra. The investigations show that the pinning effect is very sensitive to the anti-symmetry of periodic plates, and by introducing different types of breakages, more ABGs or narrow pass bands will appear, which is meaningful in band gap engineering. (condensed matter: structural, mechanical, and thermal properties)

307

Finite Element Analysis of Valence Band Structure of Square Quantum Well Under the Electric Field

Valence band structure with spin-orbit (SO) coupling of GaAs/Ga1-xAlxAs square quantum well (SQW) under the electric field by a calculation procedure based on a finite element method (FEM) is investigated using the multiband effective mass theory (?c {k}?ot ?c {p} method). The validity of the method is confirmed with the results of D. Ahn, S. L. Chuang and Y. C. Chang (J. Appl. Phys. 64 (1998) 4056), who calculated valence band structure, using axial approximation for Luttinger-Kohn Hamiltonian and finite difference method. Our results demonstrated that SO coupling and electric field have significant effects on the valence band structure.

Gunes, M.; Kasapoglu, E.; Sari, H.; Akgungor, K.; Sökmen, I.

308

Structural properties of low density liquid selenium

International Nuclear Information System (INIS)

We present extensive results of Reverse Monte Carlo (RMC) simulations of the static structural properties of liquid selenium from 573K to 1773K based on the diffraction data of Inui et al. (Inui M, Tamura K, Oh'ishi Y, Nakaso I, Funakoshi K and Utsumi W 1999 J. Non. - Cryst. Solids 250-252, 519). In all cases, the positions of 5000 atoms in a configuration box were altered until the resulting static structure factor S(q) was in agreement with the experimental one. Rom the simulations, we were able to extract information on the temperature dependence of the pair distribution function g(r), bond angle correlation b(cos ?) and coordination number distribution P(N). From our calculations, we deduce that with an increase in temperature, there is a decrease in the fraction of two fold coordinated atoms indicative of a destruction of the chain like structure of Se. Furthermore, our results indicate that the transition from a semiconducting to a metallic state with increasing temperature is accompanied by structural changes. (author)

309

Band structure approach to resonant x-ray scattering.

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

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

2002-01-01

310

Triple Frequency Fractal Patch Structure Antenna for C Band Applications

Directory of Open Access Journals (Sweden)

Full Text Available In this study, a triple frequency fractal triangular shape microstrip patch antenna is presented for C band applications. The proposed antenna comprises of two triangular shape patches with two triangular slots and excited by a 50 ? microstrip transmission line. The antenna excites three separate resonant modes where lower resonant mode of the antenna has an impedance bandwidth (VSWR<2 of 50 MHz (5.64-5.69 GHz, middle resonant modes impedance bandwidth 140 MHz (6.47-6.61 GHz and the upper resonant mode impedance bandwidth of 140 MHz (7.59-7.73 GHz. It has achieved stable radiation pattern in the operating frequency band. The proposed fractal triangular patch antenna is presented and discussed in details.

M. Samsuzzaman

2014-03-01

311

Influence of the surface band structure on electron emission spectra from metal surfaces

Electron distributions produced by grazing impact of fast protons on Mg(0001), Cu(111), Ag(111) and Au(111) surfaces are investigated, focusing on the effects of the electronic band structure. The process is described within the Band-Structure-Based approximation, which is a perturbative method that includes an accurate representation of the electron-surface interaction, incorporating information of the electronic band structure of the solid. For all the studied surfaces, the presence of partially occupied surface electronic states produces noticeable structures in double differential - energy- and angle- resolved - electron emission probabilities from the valence band. These structures remain visible in electron emission spectra after adding contributions coming from core electrons, which might make it possible their experimental detection.

Archubi, C D; Silkin, V M; Gravielle, M S

2013-01-01

312

Quasiparticle band structures and optical properties of magnesium fluoride.

The quasiparticle and optical properties of magnesium fluoride (MgF(2)) are computed within the GW approximation based on many-body perturbation theory (MBPT). The many-body effects appearing in self-energy and electron-hole interactions have an important influence on the electronic and optical properties. The DFT-LDA calculation shows a 6.78 eV band gap. Two methods are employed to evaluate the self-energy within the GW approximation in the present work. The generalized plasmon pole model (GPP) provides a band gap of 12.17 eV, which agrees well with the experimental value of 12.4 eV (Thomas et al 1973 Phys. Status Solidi b 56 163). Another band gap value of 11.30 eV is obtained by using a full frequency-dependent self-energy, which is also not far from the experimental value and is much better than the result from the LDA calculation. The calculated optical spectrum within DFT is significantly different from the experiment. Although the calculated optical absorption threshold within the GW method is close to the experiment, the overall shape of the spectrum is still similar to the case of DFT. However, the overall shape of the spectrum via the Bethe-Salpeter equation (BSE) method agrees well with the experiment. PMID:22277330

Yi, Zhijun; Jia, Ran

2012-02-29

313

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

314

Formation of longitudinal wave band structures in one-dimensional phononic crystals

Existing research on the mechanism of frequency bands in phononic crystals were without exception concerned with the band gaps (stop-bands). This paper reports, for the first time, the formation mechanism of the band structures, including both the phase constant and the attenuation constant spectra, of longitudinal waves in one-dimensional phononic crystals based on the periodic ternary rod model. Closed-form dispersion relation is obtained by our proposed method of reverberation-ray matrix. The band structures of characteristic longitudinal wave in the infinite one-dimensional phononic crystal are found to be generated from the dispersion curves of equivalent longitudinal wave in the unit cell due to zone folding effect and wave interference phenomenon. The characteristic times of longitudinal wave traversing the individual components of the unit cell as well as traversing the unit cell itself and the contrast of characteristic impedances of components are revealed to be the essential parameters determining the band structures. The deep understanding of band-structure formation provides direct scheme for adjusting frequency bands and propagation characteristics of elastic waves in one-dimensional phononic crystals. It will facilitate the design and optimization of phononic crystals to satisfy specific requirements for wave guiding/filtering and vibration control/isolation applications.

Guo, Y. Q.; Fang, D. N.

2011-04-01

315

QUASIPARTICLE BAND STRUCTURE OF Ce-BASED HEAVY-FERMION COMPOUNDS

Digital Repository Infrastructure Vision for European Research (DRIVER)

We study the influence on the Fermi surface topology of many-body corrections beyond LDA. A Renormalized Band method is used to calculate the quasiparticle band structures of both CeAl3 and Ce3Al compounds. We discuss the conditions under which the LDA is expected to predict the correct Fermi surface.

Parlebas, J.; Christensen, N.; Runge, E.; Zwicknagl, G.

1988-01-01

316

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

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

Ho, Ching-Hwa; Chen, Hsin-Hung

2014-08-01

317

Energy Technology Data Exchange (ETDEWEB)

Highlights: • Electronic structure of TlPb{sub 2}Cl{sub 5} is calculated by the FP-LAPW method. • The valence band is dominated by contributions of Cl 3p states. • Contributions of Pb 6p{sup *} states dominate at the bottom of the conduction band. • The FP-LAPW data allow concluding that TlPb{sub 2}Cl{sub 5} is an indirect-gap material. • XPS core-level and valence-band spectra of polycrystalline TlPb{sub 2}Cl{sub 5} are measured. -- Abstract: We report on first-principles calculations of total and partial densities of states of atoms constituting TlPb{sub 2}Cl{sub 5} using the full potential linearized augmented plane wave (FP-LAPW) method. The calculations reveal that the valence band of TlPb{sub 2}Cl{sub 5} is dominated by contributions of the Cl 3p-like states, which contribute mainly at the top of the valence band with also significant contributions throughout the whole valence-band region. In addition, the bottom of the conduction band of TlPb{sub 2}Cl{sub 5} is composed mainly of contributions of the unoccupied Pb 6p-like states. Our FP-LAPW data indicate that the TlPb{sub 2}Cl{sub 5} compound is an indirect-gap material with band gap of 3.42 eV. The X-ray photoelectron core-level and valence-band spectra for pristine and Ar{sup +} ion-irradiated surfaces of a TlPb{sub 2}Cl{sub 5} polycrystalline sample were measured. The measurements reveal high chemical stability and confirm experimentally the low hygroscopicity of TlPb{sub 2}Cl{sub 5} surface.

Khyzhun, O.Y., E-mail: khyzhun@ipms.kiev.ua [Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, 3 Krzhyzhanivsky Street, Kyiv 03142 (Ukraine); Bekenev, V.L.; Denysyuk, N.M. [Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, 3 Krzhyzhanivsky Street, Kyiv 03142 (Ukraine); Parasyuk, O.V. [Department of Inorganic and Physical Chemistry, Eastern European National University, 13 Voli Avenue, Lutsk 43025 (Ukraine); Fedorchuk, A.O. [Department of Inorganic and Organic Chemistry, Lviv National University of Veterinary Medicine and Biotechnologies, Pekarska St., 50, 79010 Lviv (Ukraine)

2014-01-05

318

Intramesoporous Silica Structure Differentiating Protein Loading Density

Energy Technology Data Exchange (ETDEWEB)

We report that hydrothermal aging temperature had a critical effect on intramesoporous structure of mesoporous silica and thus the intramesoporous structure affected protein loading in the mesoporous silica significantly. For a neutral protein Immunoglobulin G with a Y-like molecular shape, the larger desorption pore size allowed the larger protein loading. For a charged protein glucose oxidase with an elliptical molecular shape, the larger surface area resulted in the larger protein loading. Fluorescence emission spectra from tyrosinyl and tryptophanyl residues of the proteins in mesoporous silicas indicated that the charged protein was electrostatically attached inside the mesopores in a way of monolayer, while the neutral protein IgG could continue to aggregate after the monolayer occupancy.

Wen, Qi; Li, Xiaolin; Chen, Baowei; Yao, Pei; Lei, Chenghong; Liu, Jun

2012-05-15

319

Spatial structure of a vortex in low density neutron matter

We study in a fully selfconsistent approach the structure of a vortex in low density superfluid neutron matter. We determine that the matter density profile of a vortex shows a significant depletion in the region of the core, a feature never reported for a vortex state in a fermi superfluid.

Yu, Y; Yu, Yongle; Bulgac, Aurel

2003-01-01

320

Spatial structure of a vortex in low density neutron matter

International Nuclear Information System (INIS)

We study in a fully self-consistent approach the structure of a vortex in low density superfluid neutron matter. We determine that the matter density profile of a vortex shows a significant depletion in the region of the core, a feature never reported for a vortex state in a Fermi superfluid

321

Crystal structure and density data. 2. Titanium halides and chalcogenides

Energy Technology Data Exchange (ETDEWEB)

The following data are tabulated for titanium binary and complex halides and chalcogenides: compound, structural type, crystal system and space group, unit cell dimensions, number of formula units in the unit cell and density.

Franzen, H.F. (Iowa State Univ., of Science and Technology, Ames (USA). Dept. of Chemistry; Ames Lab., IA (USA))

1983-01-01

322

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

International Nuclear Information System (INIS)

The high-spin structure of 170Hf 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

323

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

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

Benyounes, N.; Boucenna, M.

2014-11-01

324

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

International Nuclear Information System (INIS)

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.

325

Energy Technology Data Exchange (ETDEWEB)

We report here a mean-field study of competing antiferromagnetism, superconductivity and lattice strain phases and their effect on the local density of states of the cuprate system. Our model Hamiltonian incorporating these interactions is reported earlier [G.C. Rout et al., Physica C, 2007]. The analytic expression for superconducting, antiferromagnetism and lattice strain order parameters are calculated and solved self-consistently. The interplay of these order parameters is investigated considering the calculated density of states (DOSs) of the conduction electrons. The DOS displays multiple gap structures with multiple peaks. It is suggested that the tunneling conductance data obtained from the scanning tunneling microscopy (STM) measurements could be interpreted by using the quasi-particle bands calculated from our model Hamiltonian. We have discussed the mechanism to calculate the order parameters from the conductance data.

Pradhan, B. [Department of Physics, Govt. Science College, Malkangiri 764 048 (India); Mohanta, K.L. [Department of Physics, ITER, Siksha ' O' Anusandhan University, Bhubaneswar 751 030 (India); Rout, G.C., E-mail: gcr@iopb.res.in [Condensed Matter Physics Group, Dept. of Applied Physics and Ballistics, F.M. University, Balasore 756 019 (India)

2012-05-15

326

Electronic band structures of AV2 (A = Ta, Ti, Hf and Nb) Laves phase compounds

International Nuclear Information System (INIS)

First-principles density functional calculations, using the all-electron full potential linearized augmented plane wave method, have been performed in order to investigate the structural and electronic properties for Laves phase AV2 (A = Ta, Ti, Hf and Nb) compounds. The generalized gradient approximation and the Engel-Vosko-generalized gradient approximation were used. Our calculations show that these compounds are metallic with more bands cutting the Fermi energy (EF) as we move from Nb to Ta, Hf and Ti, consistent with the increase in the values of the density of states at the Fermi level N(EF). N(EF) is controlled by the overlapping of V-p/d, A-d and A-p states around the Fermi energy. The ground state properties of these compounds, such as equilibrium lattice constant, are calculated and compared with the available literature. There is a strong/weak hybridization between the states, V-s states are strongly hybridized with A-s states below and above EF. Around the Fermi energy we notice that V-p shows strong hybridization with A-p states.

327

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

International Nuclear Information System (INIS)

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

328

Yrast band structure of light 170-182Pt isotopes

International Nuclear Information System (INIS)

The neutron rich Pt isotopes with only 4 proton holes (two proton bosons) have been studied for long. For example, 196Pt is cited as the best example of an O(6) nucleus. Gupta et al., in empirical studies of ground band energies of medium mass shape transitional nuclei, calculated the vibrational content of the low spin I = 2 state in 182-196Pt isotopes and noted a phase transition at N = 110 (A = 188), with lighter isotopes showing significant deformation effects. The deformation for Pt is maximum at N = 104, (A = 182)

329

Photonic band-structure and optical S-matrix analyses of the proposed superconducting nanostructures

Special optical structures composed of superconducting nanostructure based on the elemental type-II and layered high-Tc superconductors are proposed. The photonic band structure and the optical S-matrix are calculated for these proposed structures for different geometrical values. Such structures produce terahertz (THz) photonic band gap, which is controlled by the temperature and geometrical parameters. In addition, the proposed structures show controllable optical reflectance and transmittance in the considered terahertz range. The calculations are performed in a special frequency range in which the refractive index of the layered superconductors has negative value according to the previous analyses.

Khakestar, Ali Sobhani; Mehrany, Khashayar; fardmanesh, Mehdi

2011-01-01

330

Magnetic ordering in the striped nickelate La5/3Sr1/3NiO4: A band structure point of view

Digital Repository Infrastructure Vision for European Research (DRIVER)

We report on a comprehensive study of the electronic and magnetic structure of the striped nickelate La5/3Sr1/3NiO4. The investigation is carried out using band structure calculations based on density functional theory. A magnetic structure compatible with experiment is obtained from spin-polarized calculations within the generalized gradient approximation (GGA), whereas inclusion of a local Coulomb interaction in the LDA+U framework results in a different ground state. The ...

Schwingenschlogl, U.; Schuster, C.; Fresard, R.

2007-01-01

331

Band structure of Heusler compounds studied by photoemission and tunneling spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Heusler compounds are key materials for spintronic applications. They have attracted a lot of interest due to their half-metallic properties predicted by band structure calculations. The aim of this work is to evaluate experimentally the validity of the predictions of half metallicity by band structure calculations for two specific Heusler compounds, Co{sub 2}FeAl{sub 0.3}Si{sub 0.7} and Co{sub 2}MnGa. Two different spectroscopy methods for the analysis of the electronic properties were used: Angular Resolved Ultraviolet Photoemission Spectroscopy (ARUPS) and Tunneling Spectroscopy. Heusler compounds are prepared as thin films by RF-sputtering in an ultra high vacuum system. For the characterization of the samples, bulk and surface crystallographic and magnetic properties of Co{sub 2}FeAl{sub 0.3}Si{sub 0.7} and Co{sub 2}MnGa are studied. X-ray and electron diffraction reveal a bulk and surface crossover between two different types of sublattice order (from B2 to L2{sub 1}) with increasing annealing temperature. X-ray magnetic circular dichroism results show that the magnetic properties in the surface and bulk are identical, although the magnetic moments obtained are 5 % below from the theoretically predicted. By ARUPS evidence for the validity of the predicted total bulk density of states (DOS) was demonstrated for both Heusler compounds. Additional ARUPS intensity contributions close to the Fermi energy indicates the presence of a specific surface DOS. Moreover, it is demonstrated that the crystallographic order, controlled by annealing, plays an important role on broadening effects of DOS features. Improving order resulted in better defined ARUPS features. Tunneling magnetoresistance measurements of Co{sub 2}FeAl{sub 0.3}Si{sub 0.7} and Co{sub 2}MnGa based MTJ's result in a Co{sub 2}FeAl{sub 0.3}Si{sub 0.7} spin polarization of 44 %, which is the highest experimentally obtained value for this compound, although it is lower than the 100 % predicted. For Co{sub 2}MnGa no high TMR was achieved. Unpolarized tunneling spectroscopy reveals contribution of interface states close to the Fermi energy. Additionally magnon excitations due to magnetic impurities at the interface are observed. Such contributions can be the reason of a reduced TMR compared to the theoretical predictions. Nevertheless, for energies close to the Fermi energy and for Co{sub 2}MnGa, the validity of the band structure calculations is demonstrated with this technique as well.

Arbelo Jorge, Elena

2011-07-01

332

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1997-04-01

333

Simple inverted band structure model for cadmium arsenide (Cd3As2)

International Nuclear Information System (INIS)

The development of a simple Hamiltonian yielding the inverted band structure of Cd3As2 in the 4 mm (C4v12) low-temperature phase is proposed. The presented theory takes into account the spin orbit interaction and tetragonal distortion of lattice in the low symmetry. The authors obtain k-linear terms in the band structure and therefore a splitting in k-space of spin degenerate energy bands. The reported band model contains only one new crystal field parameter d = cr|Z> in addition to well known Kildal's set. The first evaluation of this shows that (0.028 < d < 0.072) eV using optical absorption edge data. The finite width of the anisotropic heavy and light hole bands is pointed out. (authors)

334

The band structure of BeTe a combined experimental and theoretical study

Using angle-resolved synchrotron-radiation photoemission spectroscopy we have determined the dispersion of the valence bands of BeTe(100) along $\\Gamma X$, i.e. the [100] direction. The measurements are analyzed with the aid of a first-principles calculation of the BeTe bulk band structure as well as of the photoemission peaks as given by the momentum conserving bulk transitions. Taking the calculated unoccupied bands as final states of the photoemission process, we obtain an excellent agreement between experimental and calculated spectra and a clear interpretation of almost all measured bands. In contrast, the free electron approximation for the final states fails to describe the BeTe bulk band structure along $\\Gamma X$ properly.

Nagelstrasser, M; Fischer, F; Litz, T; Waag, A; Fleszar, A; Hanke, W; Steinrück, H P; Landwehr, Gottfried

1998-01-01

335

Relationship between molecular cloud structure and density PDFs

Volume and column density PDFs in molecular clouds are important diagnostics for understanding their general structure. We developed a novel approach to trace the cloud structure by varying the lower PDF cut-off and exploring a suggested mass-density relationship with a power-law index $x^\\prime$. The correspondence of x' as a function of spatial scale to the slope of the high-density PDF tail is studied. To validate the proposed model, we use results from hydrodynamical simulations of a turbulent self-gravitating cloud and recent data on dust continuum emission from the Planck mission.

Stanchev, Orlin; Veltchev, Todor V; Shetty, Rahul

2013-01-01

336

Electronic structure of BaIrO3: A first principle study using local spin-density approximations

We investigate the electronic structure of BaIrO3, an interesting compound exhibiting charge density wave transition in its insulating phase and ferromagnetic transition at the same temperature, using full potential linearized augmented plane wave method within the local spin density approximations. The ferromagnetic ground state could exactly be described in these calculations and the calculated spin magnetic moment is found to be small as observed in the magnetic measurements. Interestingly, no signature of exchange splitting is observed in the density of states corresponding to Ir 5d and/or any other electronic states. The small spin moment appears essentially due to unequal population of the up- and down-spin Ir 5d bands. Comparison of the valence band density of states with the experimental spectral functions suggests that a rigid shift of the Fermi level towards higher energies in the calculated density of states provides a good description of the experimental spectra. This indicates that the intrinsic ...

Maiti, K

2006-01-01

337

Structural failure of two-density-layer cohesionless biaxial ellipsoids

This paper quantitatively evaluates structural failure of biaxial cohesionless ellipsoids that have a two-density-layer distribution. The internal density layer is modeled as a sphere, while the external density layer is the rest of the part. The density is supposed to be constant in each layer. The present study derives averaged stresses over the whole volume of these bodies and uses limit analysis to determine their global failure. The upper bound condition of global failure is considered in terms of the size of the internal layer and the aspect ratio of the shape. The result shows that the two-density-layer causes the body to have different strength against structural failure.

Hirabayashi, Masatoshi

2014-01-01

338

The group II chalcogenides are an important class of functional semiconductor materials exhibiting a remarkable diversity in terms of structure and properties. In order to aid the materials design, a consistent set of electronic structure calculations is presented, including data on the polymorphic energy ordering, the band-structures, the band-lineups relative to the vacuum level, surface energies, as well as on the alloy energetics. To this end, current state-of-the-art electronic structure tools are employed, which, besides standard density functional theory (DFT), include totalenergy calculation in the random phase approximation and GW quasiparticle energy calculations. The ionization potentials and electron affinities are obtained by combining the results of bulk GW and surface DFT calculations. Considering both octahedral and tetrahedral coordination symmetries, exemplified by the rock-salt and zinc-blende lattices, respectively, this data reveals both the chemical and structural trends within this materials family.

Lany, Stephan

2014-03-01

339

Band Structures of the group I and II oxides: using EMS measurements as a test of theoretical models

International Nuclear Information System (INIS)

Full text: The electronic band structure dictates the physical and chemical properties of solids. Quantum chemical models have now been developed to provide predictions of the electronic band structure of solids, however it is their ability to reproduce many body (correlation) interactions between electrons that determines their success. Comparisons of these models with experimental data has unfortunately been limited as their success has mainly been judged using metallic and semiconducting materials. Experimental data on ionic solids is scarcer and as such it is somewhat unclear as to whether or not these quantum mechanical models have universal application. We present here experimental data for the electronic band structure of simple Group I and II oxides, measured using electron momentum spectroscopy (EMS). Using electron impact ionisation this technique maps the absolute square of the wavefunction in momentum space. This is a fundamental observable of the electronic structure and provides a comprehensive test for theoretical models. We compare our experimental results with predictions made through both Hartree Fock and Density Functional methods. The successes and failures of each of these models is highlighted and in an effort to explain some of the differences, the validity of slab calculations to better represent the thin (<200nm) samples is also investigated

340

Realization of Band-Notch UWB Monopole Antenna Using AMC Structure

Directory of Open Access Journals (Sweden)

Full Text Available This article presents the design, simulation and testing of an Ultra Wide Band (UWB planar monopole antenna with WLAN band-notch characteristic. The proposed antenna consists, the combination of planar monopole antenna with partial ground and a pair of AMC structures. The AMC structure used for the design is mushroom-like. Design equation of EBG parameters is also proposed for FR4 substrate using transmission line model. Using proposed equations, Mushroom-like EBG structure is integrated along the feed line of a monopole antenna for WLAN (5 GHz – 6 GHz band rejection. TheCurrent distribution and equivalent circuit model of antenna is used to explain band-notch characteristic of EBG resonator. The proposed antenna is fabricated on an FR4 substrate with a thickness of 1.6 mmand ?r = 4.4. The measured VSWR characteristic is less than 2 for complete UWB band except for WLAN band i.e. 5 GHz – 6 GHz. The gain of the proposed structure is around 2 dBi – 6.7 dBi for complete UWBband except for WLAN band where it is reduced to -4 dBi. The measured radiation pattern of proposed antenna is omnidirectional along H plane and bidirectional in E plane. A nearly constant group delaywith variations < 2ns, except for the notched bandwidth makes proposed antenna suitable for UWB application.

Pradeep Kumar

2013-06-01

341

Plasma density measurements using chirped pulse broad-band Raman amplification

Stimulated Raman backscattering is used as a non-destructive method to determine the density of plasma media at localized positions in space and time. By colliding two counter-propagating, ultra-short laser pulses with a spectral bandwidth larger than twice the plasma frequency, amplification occurs at the Stokes wavelengths, which results in regions of gain and loss separated by twice the plasma frequency, from which the plasma density can be deduced. By varying the relative delay between the laser pulses, and therefore the position and timing of the interaction, the spatio-temporal distribution of the plasma density can be mapped out.

Vieux, G; Farmer, J P; Hur, M S; Issac, R C; Jaraszynski, D A

2013-01-01

342

Three quaternary mercury bismuth chalcohalides, Hg3Q2Bi2Cl8 (Q = S, Se, Te), are reported along with their syntheses, crystal structures, electronic band structures, and optical properties. The compounds are structurally similar with a layer comprised of a hole perforated sheet network of [Hg3Q2](2+) (Q = S and Te) that forms by fused cyclohexane, chairlike Hg6Q6 rings. The cationic charge in the network is balanced by edge-sharing monocapped trigonal-prismatic anions of [Bi2Cl8](2-) that form a two-dimensional network located between layers. Compound 1, Hg3S2Bi2Cl8, crystallizes in the monoclinic space group C12/m1 with a = 12.9381(9) Å, b = 7.3828(6) Å, c = 9.2606(6) Å, and ? = 116.641(5)°. Compound 2, Hg3Te2Bi2Cl8, crystallizes in the monoclinic space group C12/c1 with a = 17.483(4) Å, b = 7.684(2) Å, c = 13.415(3) Å, and ? = 104.72(3)°. The crystals of the Hg3Se2Bi2Cl8 analogue exhibit complex modulations and structural disorder, which complicated its structural refinement. Compounds 1 and 2 melt incongruently and show band gaps of 3.26 and 2.80 eV, respectively, which are in a good agreement with those from band-structure density functional theory calculations. PMID:23448152

Wibowo, Arief C; Malliakas, Christos D; Chung, Duck Young; Im, Jino; Freeman, Arthur J; Kanatzidis, Mercouri G

2013-03-18

343

Energy Technology Data Exchange (ETDEWEB)

We derived the transition temperature and the isotope exponent of two-band superconductor. We employed Bogoliubov-Valatin formalism assuming a three-square-well potential. The effect of linear-energy-dependent electronic DOS in superconductors is considered. The relevance of the studies to MgB{sub 2} is analyzed. We have derived the expressions for the transition temperature and the isotope effect exponent within the framework of Bogoliubov-Valatin two-band formalism using a linear-energy-dependent electronic density of states assuming a three-square-well potentials model. Our results show that the approach could be used to account for a wide range of values of the transition temperature and isotope effect exponent. The relevance of the present calculations to MgB{sub 2} is analyzed.

Ogbuu, O.A., E-mail: ogbuuokechukwu@gmail.com [Department of Physics and Astronomy, University of Nigeria, Nsukka (Nigeria); Abah, O.C., E-mail: abahobinna@gmail.com [Department of Physics and Astronomy, University of Nigeria, Nsukka (Nigeria); Asomba, G.C.; Okoye, C.M.I. [Department of Physics and Astronomy, University of Nigeria, Nsukka (Nigeria)

2011-08-15

344

International Nuclear Information System (INIS)

We derived the transition temperature and the isotope exponent of two-band superconductor. We employed Bogoliubov-Valatin formalism assuming a three-square-well potential. The effect of linear-energy-dependent electronic DOS in superconductors is considered. The relevance of the studies to MgB2 is analyzed. We have derived the expressions for the transition temperature and the isotope effect exponent within the framework of Bogoliubov-Valatin two-band formalism using a linear-energy-dependent electronic density of states assuming a three-square-well potentials model. Our results show that the approach could be used to account for a wide range of values of the transition temperature and isotope effect exponent. The relevance of the present calculations to MgB2 is analyzed.

345

Structural, electronic and phonon properties of MoTa and MoNb: a density functional investigation

First-principles calculations were performed to investigate the structural, electronic and phonon properties of MoTa and MoNb in the CsCl (B2) phase. The calculated lattice constants, static bulk modulus and first-order pressure derivative of the bulk modulus are in good agreement with available experimental data and previous theoretical predictions. Electronic band structures and partial and total densities of states have been derived for MoTa and MoNb. The band structures show metallic character; the conductivity is mostly governed by Mo-4d and Ta-5d (Nb-4d) states. A linear-response approach to the density functional theory is used to derive phonon dispersion curves and the density of states for MoTa and MoNb. Zone centre optical phonon modes of MoTa and MoNb are found to be at 6.46 and 7.24 THz, respectively.

Bayhan, Ü.; Ar?kan, N.; U?ur, ?.; U?ur, G.; Çivi, M.

2010-07-01

346

Structural, electronic and phonon properties of MoTa and MoNb: a density functional investigation

International Nuclear Information System (INIS)

First-principles calculations were performed to investigate the structural, electronic and phonon properties of MoTa and MoNb in the CsCl (B2) phase. The calculated lattice constants, static bulk modulus and first-order pressure derivative of the bulk modulus are in good agreement with available experimental data and previous theoretical predictions. Electronic band structures and partial and total densities of states have been derived for MoTa and MoNb. The band structures show metallic character; the conductivity is mostly governed by Mo-4d and Ta-5d (Nb-4d) states. A linear-response approach to the density functional theory is used to derive phonon dispersion curves and the density of states for MoTa and MoNb. Zone centre optical phonon modes of MoTa and MoNb are found to be at 6.46 and 7.24 THz, respectively.

347

Plasmon-polariton band structures of asymmetric T-shaped plasmonic gratings.

It is shown that asymmetric T-shaped plasmonic gratings can display plasmon-polariton band structures with wide range of band gaps and tunable group velocities. A structure gap is introduced in the post of Tshaped plasmonic gratings and it is found that the size of this gap plays an important role in controlling the plasmon-polariton band gap and group velocities. We obtained variation of energy band gap ranging from 0.4 eV to 0.0323 eV by changing the size of the structure gap from 0 to 250 nm. The plasmon-polariton band structures were obtained by using Rigorous Coupled Wave Analysis. We studied the difference between symmetric and asymmetric T-shaped gratings and found that the symmetric structure has a momentum gap in the photonic band structure, which can be avoided in the asymmetric structure. Furthermore, by varying the post and spacer (made of SiO2) thicknesses we can tune the energy band gap from 0.1 eV to 0.148 eV and from 0.183 eV to 0.19 eV, respectively. In this device, we obtain tunable group velocities ranging from one to several orders of magnitude smaller than the speed of light in the vacuum. This asymmetric T-shaped plasmonic grating is expected to have applications in surface plasmon polariton (SPP) based optical devices, such as filters, waveguides, splitters and lasers, especially for applications requiring large photonic band gap. PMID:20174078

Abbas, Mohammed Nadhim; Chang, Yia-Chung; Shih, M H

2010-02-01

348

Band structure in 180Ta studied with transfer reactions

International Nuclear Information System (INIS)

The differential cross sections of emitted particles have been measured in the reactions 181Ta(p,d)180Ta at 19 MeV, 179Hf(3He,d)180Ta at 36 MeV, and 179Hf(?,t)180Ta at 62.2 MeV. The energy resolution was 15 to 40 keV depending on the reaction. Differential cross sections were fitted using a distorted wave program and level characteristics of 180Ta were deduced in the framework of the Nilsson model for odd-odd deformed nuclei including Coriolis coupling. Members of rotational bands have been identified up to 1 MeV excitation energy. The short-lived isomer in 180Ta with spin 1+ was found to be the ground state whereas the long-lived isomer at 82 +- 20 keV excitation energy has spin 9-

349

International Nuclear Information System (INIS)

Highlights: ? We performed high resolution ARPES on 1T–ZrSxSe2?x. ? A characteristic splitting of the chalcogen p-derived VB along high symmetry directions was observed. ? The splitting size at the A point of the BZ is found to increase from 0.06 to 0.31 eV from ZrS2 towards ZrSe2. ? Electronic structure calculations based on the DFT were performed using the model of TB–MBJ. ? The calculations show that the splitting is due to SO coupling of the valence bands. -- Abstract: Angle-resolved photoelectron spectroscopy using synchrotron radiation has been performed on 1T–ZrSxSe2?x, where x varies from 0 to 2, in order to study the influence of the spin-orbit interaction in the valence bands. The crystals were grown by chemical vapour transport technique using Iodine as transport agent. A characteristic splitting of the chalcogen p-derived valence bands along high symmetry directions has been observed experimentally. The size of the splitting increases with the increase of the atomic number of the chalcogenide, e.g. at the A point of the Brillouin zone from 0.06 eV to 0.31 eV with an almost linear dependence with x, as progressing from ZrS2 towards ZrSe2, respectively. Electronic structure calculations based on the density functional theory have been performed using the model of Tran–Blaha [1] and the modified version of the exchange potential proposed by Becke and Johnson [2] (TB–MBJ) both with and without spin-orbit (SO) coupling. The calculations show that the splitting is mainly due to spin-orbit coupling and the degeneracy of the valance bands is lifted

350

Thermospheric density structures over the polar regions observed with CHAMP

Directory of Open Access Journals (Sweden)

Full Text Available We report on the unexpected detection of considerable structure in high latitude thermospheric densities, as derived from an accelerometer onboard the CHAMP satellite. The width of the structures, which can either be maxima or minima, varies between a few hundred km and 2000 km. The amplitudes of these density extrema can reach 50% of ambient. Maxima cluster around 75° (N and S, while minima are found closer to the poles. In a magnetic latitude-magnetic local time frame the maxima are found mainly around the cusp region. Overall, the observed structures somewhat resemble so-called density cells previously found in model calculations. However the models generate their cells around 140–300 km altitude and show little, if any remnant at 400 km or above. This has to be contrasted with the fact that the CHAMP observations were obtained near 430 km altitude. We have explored Joule heating as a possible mechanism for the generation of the structures, at least in density enhancement regions, using Hall currents measured on CHAMP and simultaneous incoherent scatter measurements with EISCAT. However, the electric fields were usually quite small during the period of observation, making the quest for an explanation for the structures all the more challenging.

Keywords. Meteorology and atmospheric dynamics (Thermospheric dynamics – Magnetospheric physics (Polar cap phenomena – Atmospheric composition and structure (Pressure, density, and temperature

K. Schlegel

2005-07-01

351

International Nuclear Information System (INIS)

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

352

Photonic band gap of loop structure containing negative-index materials.

We predict the existence of a special photonic band gap in a quasi-one-dimensional loop structure containing negative-index materials in the subwavelength regime. The mechanism of the formation for this special band gap is quite different from the so-called zero-average-index gaps in the one-dimensional structures, due to the parallel action of the loop. The parallel action enhances the impedance contrast between the two parts on either side of the interface in each unit cell, thus resulting in strong reflection which increases the width of the band gap. In addition, we show that even large band gaps could be obtained in multichannel structures. PMID:18352138

Tan, Wei; Wang, Zhi Guo; Chen, Hong

2008-02-01

353

Photonic band structure of ZnO photonic crystal slab laser

We recently reported on the first realization of ultraviolet photonic crystal laser based on zinc oxide [Appl. Phys. Lett. {\\bf 85}, 3657 (2004)]. Here we present the details of structural design and its optimization. We develop a computational super-cell technique, that allows a straightforward calculation of the photonic band structure of ZnO photonic crystal slab on sapphire substrate. We find that despite of small index contrast between the substrate and the photonic layer, the low order eigenmodes have predominantly transverse-electric (TE) or transverse-magnetic (TM) polarization. Because emission from ZnO thin film shows strong TE preference, we are able to limit our consideration to TE bands, spectrum of which can possess a complete photonic band gap with an appropriate choice of structure parameters. We demonstrate that the geometry of the system may be optimized so that a sizable band gap is achieved.

Yamilov, A; Cao, H

2005-01-01

354

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 in the upper-cloud altitude to 3 km lower altitude from the tropical zones to temperate zones and polar regions, a N/S asymmetry in cloud thickness in the tropical and temperature zones, and the presence of aerosols up to about 0.3 bar in the Great Red Spot and Equatorial Zone. It is concluded that polarization data are sensitive to aerosols in and above the upper cloud layer but insensitive to deeper cloud structure.

West, R. A.; Tomasko, M. G.

1980-01-01

355

International Nuclear Information System (INIS)

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 in the upper-cloud altitude to 3 km lower altitude from the tropical zones to temperate zones and polar regions, a N/S asymmetry in cloud thickness in the tropical and temperature zones, and the presence of aerosols up to about 0.3 bar in the Great Red Spot and Equatorial Zone. It is concluded that polarization data are sensitive to aerosols in and above the upper cloud layer but insensitive to deeper cloud structure

356

Electronic band structures and x-ray photoelectron spectra of ZrC, HfC, and TaC

International Nuclear Information System (INIS)

The band structures and densities of states (DOSs) of ZrC, HfC, and TaC were calculated by the augmented-plane-wave method, and the x-ray photoelectron spectra of valence bands of these compounds were observed. The theoretical energy distribution curves (EDCs) were in good agreement with the experimental EDCs. These band structures resemble each other and also those of TiC obtained by our previous work. This fact suggests that the rigid-band model is applicable to the transition-metal carbides with the rock-salt structure. Their DOSs are divided into three parts. Peak I derived from the C 2s state is isolated from the higher valence-band peak II arising from the C 2p and the valence electrons of the metal atom. Peak III derived from the d and s states of the metal atom is separated by the Fermi level from peak II. The Fermi level lies at the minimum point of the DOS for the group IV carbides, but for TaC it lies at a relatively large DOS point. The DOS at the Fermi level of ZrC, HfC, and TaC are 0.18, 0.16, and 0.65 electrons/(eV primitive cell), respectively. The characteristic mutual differences among these compounds are a stronger localization of d electrons in ZrC and HfC compared with TiC and an enhancement of the photoelectron spectrum intensity of TaC around the Fermi level

357

International Nuclear Information System (INIS)

The band edge structure of Pbsub(1-x)Snsub(x)Te is derived in detail using a two band ellipsoidal model and compared with a more rigorous calculation based on six bands. A quantitative comparison is made for two values of the energy gap, corresponding to the cases where x=0 and x=0.17. It was found that, for the occupied states in nondegenerate materials, both models are practically equivalent. Discrepancies may occur only in high degeneracies or deep inversion layers. The agreement between both models was significantly improved by introducing an effective energy gap in the two band model. It is suggested that the use of the effective energy gap may improve the agreement between the two band model and experiment whenever the details of the band edge structure enter the interpretation of the experimental results. (author)

358

Density functional calculations including long-range dispersion effects demonstrate that non-covalent doping with an electron donor acceptor couple of molecules can open an energy gap in a bilayer graphene. The band gap modulation can be controlled not only by the choice of adsorbed molecules (n-dopant versus p-dopant) but also by their concentration. A deep analysis of the charge transfer reveals that charge redistribution in bilayer graphene is the key issue for gap opening, due to the induced inversion symmetry breaking. The dual molecular non-covalent doping mode can achieve the opening of a gap up to 138 meV.

Hu, Tao; Gerber, Iann C.

2014-11-01

359

The C-Band accelerating structures for SPARC photoinjector energy upgrade

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

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

2013-05-01

360

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

DEFF Research Database (Denmark)

The vibrational response of finite periodic lattice structures subjected to periodic loading is investigated. Special attention is devoted to the response in frequency ranges with gaps in the band structure for the corresponding infinite periodic lattice. The effects of boundaries, viscous damping, and imperfections are studied by analyzing two examples; a 1-D filter and a 2-D wave guide. In 1-D the structural response in the band gap is shown to be insensitive to damping and small imperfections. In 2-D the similar effect of damping is noted for one type of periodic structure, whereas for another type the band gap effect is nearly eliminated by damping. In both 1-D and 2-D it is demonstrated how the free structural boundaries affect the response in the band gap due to local resonances. Finally, 2-D wave guides are considered by replacing the periodic structure with a homogeneous structure in a straight and a 90fl bent path, and it is shown how the vibrational response is confined to the paths in the band gap frequency ranges.

Jensen, Jakob SØndergaard

2003-01-01

361

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

International Nuclear Information System (INIS)

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

362

Phonon structure in dispersion curves and density of states of massive Dirac Fermions

Dirac fermions exist in many solid state systems including graphene, silicene and other two dimensional membranes such as are found in group VI dichalcogenides, as well as on the surface of some insulators where such states are protected by topology. Coupling of those fermions to phonons introduces new structures in their dispersion curves and, in the case of massive Dirac fermions, can shift and modify the gap. We show how these changes present in angular-resolved photoemission spectroscopy of the dressed charge carrier dispersion curves and scanning tunneling microscopy measurements of their density of states. In particular we focus on the region around the band gap. In this region the charge carrier spectral density no longer consists of a dominant quasiparticle peak and a smaller incoherent phonon related background. The quasiparticle picture has broken down and this leads to important modification in both dispersion curves and density of states.

Li, Zhou

2013-01-01

363

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

International Nuclear Information System (INIS)

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.

364

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

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

365

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

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

Ganev, H. G.; Brant, S.

2010-09-01

366

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

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

367

On the structure of collective bands in 78Kr

International Nuclear Information System (INIS)

Using 16O, 19F, and 12C induced reactions high spin states in 78Kr were excited. The targets consisted of 65Cu, 69Ni, and 68Zn. On the base of gamma spectroscopic methods as ??-coincidences, angular distributions and excitation functions a level scheme of 78Kr is proposed. Four bands could be identified, which decay mostly by stretched E2-transitions. From recoil distance Doppler shift as well as Doppler shift attenuation measurements lifetimes of about 20 states were measured. The ?-decay of the 103 keV isomeric state and the ground state in 78Rb was observed and the half-lifes determined. Altogether a very good agreement of the level scheme and the E2- and E1-transition strength with predictions of the interacting boson model were found. Using a Monte Carlo code the ?-decay of the continuum of highly excited nuclei is described. Entry states, mean ?-energies, ?-spectra, mean multiplicities, multipolarities, and mean feeding times as well as e.g. their second moments were calculated for the reactions 58Ni(16O,2p)72Se and 68Zn(12C,2n)78Kr. The results are discussed and compared with experimental data. (HSI)

368

International Nuclear Information System (INIS)

The use of localized Gaussian basis functions for large scale first principles density functional calculations with periodic boundary conditions (PBC) in 2 dimensions and 3 dimensions has been made possible by using a dual space approach. This new method is applied to the study of electronic properties of II--VI (II=Zn, Cd, Hg; VI=S, Se, Te, Po) and III--V (III=Al, Ga; V=As, N) semiconductors. Valence band offsets of heterojunctions are calculated including both bulk contributions and interfacial contributions. The results agree very well with available experimental data. The p(2x1) cation terminated surface reconstructions of CdTe and HgTe (100) are calculated using the local density approximation (LDA) with two-dimensional PBC and also using the ab initio Hartree--Fock (HF) method with a finite cluster. The LDA and HF results do not agree very well. copyright 1995 American Vacuum Society

369

A Ku-band high power density AlGaN/GaN HEMT monolithic power amplifier

International Nuclear Information System (INIS)

A high power density monolithic power amplifier operated at Ku band is presented utilizing a 0.3 ?m AlGaN/GaN HEMT production process on a 2-inch diameter semi-insulating (SI) 4H-SiC substrate by MOCVD. Over the 12-14 GHz frequency range, the single chip amplifier demonstrates a maximum power of 38 dBm (6.3 W), a peak power added efficiency (PAE) of 24.2% and linear gain of 6.4 to 7.5 dB under a 10% duty pulse condition when operated at Vds = 25 V and Vgs = -4 V. At these power levels, the amplifier exhibits a power density in excess of 5 W/mm.

370

A Ku-band high power density AlGaN/GaN HEMT monolithic power amplifier

Energy Technology Data Exchange (ETDEWEB)

A high power density monolithic power amplifier operated at Ku band is presented utilizing a 0.3 {mu}m AlGaN/GaN HEMT production process on a 2-inch diameter semi-insulating (SI) 4H-SiC substrate by MOCVD. Over the 12-14 GHz frequency range, the single chip amplifier demonstrates a maximum power of 38 dBm (6.3 W), a peak power added efficiency (PAE) of 24.2% and linear gain of 6.4 to 7.5 dB under a 10% duty pulse condition when operated at V{sub ds} = 25 V and V{sub gs} = -4 V. At these power levels, the amplifier exhibits a power density in excess of 5 W/mm.

Ge Qin; Chen Xiaojuan; Luo Weijun; Yuan Tingting; Pang Lei; Liu Xinyu, E-mail: lixy@ime.ac.cn [Key Laboratory of Microwave Devices and Integrated Circuit, Institute of Microelectronics, Chinese Academy of Sciences, Beijing 100029 (China)

2011-08-15

371

International Nuclear Information System (INIS)

Spontaneous CuPt ordering induces a band-gap reduction ?Eg relative to the random alloy, a crystal field splitting ?CF at valence-band maximum, as well as an increase of spin-orbit splitting ?SO. We calculate these quantities for AlxIn1-xP, AlxIn1-xAs, GaxIn1-xP, and GaxIn1-xAs using the local density approximation (LDA), as well as the more reliable LDA-corrected formalism. We further provide these values and the valence-band splittings ?E12 (between bar ?4,5v and bar ?6v(1)) and ?E13 (between bar ?4,5v and bar ?6v(2)) for these materials as a function of the degree ? of long range order. In the absence of an independent measurement of ?, experiment is currently able to deduce only the ratio ?Eg/?CF. Our LDA-corrected results for this quantity compare favorably with recent experiments for GaxIn1-xP and GaxIn1-xAs, but not for AlxIn1-xP, where our calculation does not support the experimental assignment. The open-quotes optical LRO parameter ?close quotes can be obtained by fitting our calculated ?Eg(?) to the measured ?Eg(?), and by expressing the measured ?E12(?) and ?E13(?) in terms of our calculated ?CF(?) and ?SO(?). We also provide the calculated x-ray structure factors for ordered alloys that can be used experimentally to deduce ? independently. copyright 1998 The American Physical Society

372

Influence of strain on band structure of semiconductor nanostructures

Directory of Open Access Journals (Sweden)

Full Text Available The influence of the mechanical strain on the electronic structure of the asymmetric (In,GaAs/GaAs quantum well is considered. Both the direct influence of strain on the orbital part of the electronic structure and an indirect influence through the strain dependent Rashba and Dresselhaus Hamiltonians are taken into account. The analyzed quantum well is taken to have a triangular shape, and is oriented along the <110> direction. For this direction, there exists both the intrinsic and strain-induced spin-orbit interaction. For all analyzed types of spin-orbit interaction, subband splittings depend linearly on the in-plane wave vector. On the other hand, the electronic structure for the Rashba type of the strain-induced spin-orbit interaction shows isotropic dependence in the k-space, while the electronic structure due to the Dresselhaus type shows anisotropy. Furthermore, the Rashba strain-induced spin-orbit interaction increases subband splitting, while the effect of the Dresselhaus Hamiltonian on the electronic structure is opposite to the intrinsic spin-orbit interaction for certain polar angles.

Rai?evi? Nevena

2009-01-01

373

International Nuclear Information System (INIS)

We have examined the interaction of a blocked slip band and a grain boundary in deformed titanium using high-resolution electron backscatter diffraction and atomic force microscopy. From these observations, we have deduced the active dislocation types and assessed the dislocation reactions involved within a selected grain. Dislocation sources have been activated on a prism slip plane, producing a planar slip band and a pile-up of dislocations in a near screw alignment at the grain boundary. This pile-up has resulted in activation of plasticity in the neighbouring grain and left the boundary with a number of dislocations in a pile-up. Examination of the elastic stress state ahead of the pile-up reveals a characteristic “one over the square root of distance” dependence for the shear stress resolved on the active slip plane. This observation validates a dislocation mechanics model given by Eshelby, Frank and Nabarro in 1951 and not previously directly tested, despite its importance in underpinning our understanding of grain size strengthening, fracture initiation, short fatigue crack propagation, fatigue crack initiation and many more phenomena. The analysis also provides a method to measure the resistance to slip transfer of an individual grain boundary in a polycrystalline material. For the boundary and slip systems analysed here a Hall–Petch coefficient of K = 0.41 MPa m½ was determined.

374

Tunable Reflection Bands and Defect Modes in One-Dimensional Tilted Photonic Crystal Structure

Directory of Open Access Journals (Sweden)

Full Text Available We show theoretically that range of reflection bands and defect modes inside the band gap can be tuned by using a one-dimensional tilted photonic crystal (TPC structure. A TPC structure is similar to the conventional PC structure with the only difference that in this case alternate layers are inclined at certain angle in the direction of periodicity of the structure. In order to obtain the reflectance spectra of the proposed structure transfer matrix method (TMM has been employed. From the analysis of the reflectance curve, it is found that 100% reflectance range can be varied and enhanced by using TPC structure for both (TE- and TM- polarizations. The enhancement in reflection bands increases as the tilt angle increases for both the polarizations and hence the enlarged omni-reflectance bands are obtained. Further, we study the properties of the defect modes in TPC structure by introducing the tilted defect at the different tilt angle. The results show that defect modes (tunneling modes can be tuned at different wavelengths by changing the tilt angle of the structure without changing other parameters. Finally, the effect of variation thickness of defect layers on the tunneling mode has been studied for both TPC and conventional PC structure. The proposed model might be used as a tunable broadband omnidirectional reflector as well as tunable tunneling or transmission mode, which has potential applications in the field of photonics and optoelectronics.

Sanjeev K. Srivastava

2012-09-01

375

Precise fabrication of X-band accelerating structure

International Nuclear Information System (INIS)

An accelerating structure with a/?=0.16 is being fabricated to study a precise fabrication method. A frequency control of each cell better than 10-4 level is required to realize a detuned structure. The present machining level is nearly 1 MHz/11.4 GHz in relative frequency error, which just satisfies the above requirement. To keep this machining precision, the diffusion bonding technique is found preferable to join the cells. Various diffusion conditions were tried. The frequency change can be less than 1 MHz/11.4 GHz and it can be controlled well better than that. (author)

376

Band structure engineering of anatase TiO2 by metal-assisted P-O coupling

International Nuclear Information System (INIS)

In this work, we demonstrate that the metal-assisted P-O coupling is an effective approach to improve the photoelectrochemical properties of TiO2. The (Sc + P) and (In + P) codoping effects on electronic structures and photocatalytic activities of anatase TiO2 are examined by performing hybrid density functional theory calculations. It is found that the coupling of P dopant with the second-nearest neighboring O atom assisted by acceptor metals (Sc/In) leads to the fully occupied and delocalized intermediate bands within the band gap of anatase TiO2, which is driven by the P-O antibonding states (?*). This metal-assisted P-O coupling can prevent the recombination of photogenerated electron-hole pairs and effectively reduce the band gap of TiO2. Moreover, the band edge alignments in (Sc + P) and (In + P) codoped anatase TiO2 are desirable for water-splitting. The calculated optical absorption curves indicate that (Sc + P) and (In + P) codoping in anatase TiO2 can also effectively enhance the visible light absorption

377

Study on electro-optic properties of two-dimensional PLZT photonic crystal band structure

The band characteristics of two-dimensional (2D) lead lanthanum zirconate titanate (PLZT) photonic crystals are analyzed by finite element method. The electro-optic effect of PLZT can cause the refractive index change when it is imposed by the applied electric field, and the band structure of 2D photonic crystals based on PLZT varies accordingly. The effect of the applied electric field on the structural characteristics of the first and second band gaps in 2D PLZT photonic crystals is analyzed in detail. And the results show that for each band gap, the variations of start wavelength, cut-off wavelength and bandwidth are proportional to quadratic of the electric field.

Tong, Kai; Wu, Xiao-Gang; Wang, Mei-Ting

2011-07-01

378

Effect of nitrogen on the electronic band structure of group III-N-V alloys

International Nuclear Information System (INIS)

We have studied optical transitions at the ? and L points of the Brillouin zone of GaNxAs1-x and AlyGa1-yNxAs1-x alloys using photomodulation spectroscopy. For GaNxAs1-x with N contents between 0% and 2%, the N-induced shift of the conduction-band L minima is found to be only a fraction of the conduction-band edge shift at the ? point. The measurements of AlyGa1-yNxAs1-x further show that there is no correlation between the location of the X conduction-band minima and the observed E+ and E- transitions. The results demonstrate that the N-induced interactions between extended ?, L, and X conduction-band states do not play a significant role in modification of the conduction-band structure of III-N-V alloys. The N-induced change of the conduction-band structure is predominantly influenced by the anticrossing interaction between the extended states of the ? conduction band and the localized states of nitrogen. (c) 2000 The American Physical Society

379

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

Energy Technology Data Exchange (ETDEWEB)

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); Sadowski, J. [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); 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)

2013-08-07

380

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

381

Photonic stop bands in quasi-random nanoporous anodic alumina structures

The existence of photonic stop bands in the self-assembled arrangement of pores in porous anodic alumina structures is investigated by means of rigorous 2D finite- difference time-domain calculations. Self-assembled porous anodic alumina shows a random distribution of domains, each of them with a very definite triangular pattern, constituting a quasi-random structure. The observed stop bands are similar to those of photonic quasicrystals or random structures. As the pores of nanoporous anodic alumina can be infiltrated with noble metals, nonlinear or active media, it makes this material very attractive and cost-effective for applications including inhibition of spontaneous emission, random lasing, LEDs and biosensors.

Maksymov, Ivan; Pallares, Josep; Marsal, Lluis F

2011-01-01

382

Photonic band gaps of two-dimensional photonic lattices: the face-centered graphite structures

We describe the calculation of photonic band structures of two-dimensional lattices made of more than one dielectric array. In particular, we study a face-centered graphite (fcg) structure obtained by an arrangement of two sets of cylindrical rods, one located at the vertices of regular hexagons (graphite sublattice) and another in the center of the hexagons (triangle sublattice). Changing the diameter of the centered rods, different patterns are produced including both triangle and graphite structures. We evaluate their relationships in terms of the existence of absolute photonic band gaps common to E and H polarized waves.

Chen, Y.

1997-07-01

383

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

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

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

2009-10-01

384

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

International Nuclear Information System (INIS)

We report the band structure properties of (BGa)P layers grown on silicon substrate using metal-organic vapour-phase epitaxy. Using surface photo-voltage spectroscopy we find that both the direct and indirect band gaps of (BGa)P alloys (strained and unstrained) decrease with Boron content. Our experimental results suggest that the band gap of (BGa)P layers up to 6% Boron is large and suitable to be used as cladding and contact layers in GaP-based quantum well heterostructures on silicon substrates

385

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

International Nuclear Information System (INIS)

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 Pd40.5Ni40.5P19 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

386

Band structure in doubly-odd nuclei with mass around 130

Energy Technology Data Exchange (ETDEWEB)

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 doublet bands turn out to be realized by the chopsticks-like motion of two angular momenta of the unpaired neutron and the unpaired proton, weakly coupled with the quadrupole collective excitations of the even-even part of the nucleus.

Higashiyama, K [Department of Physics, University of Tokyo, Hongo, Tokyo 113-0033 (Japan); Yoshinaga, N [Department of Physics, Saitama University, Saitama City 338-8570 (Japan)

2006-10-10

387

Energy Technology Data Exchange (ETDEWEB)

Single crystals of layered transition metal dichalcogenide compounds of ZrS{sub x}Se{sub 2-x} were grown by the chemical vapour transport technique. The S-concentration parameter x was varied over the entire compositional range (0{<=}x{<=}2). As a result, we were able to obtain compositions that are S-rich (x>1) or Se-rich (x<1). The crystals were characterized with the help of different methods e.g. EDX, LEED, and Laue diffraction. The band gaps were determined by means of optical measurements. The values of the band gaps were determined from the analysis of the energy dependence of the measured optical absorption. The obtained band gaps, varying from 1.18 eV for ZrSe{sub 2} to 1.7 eV for ZrS{sub 2}, showed an almost linear dependence on the composition parameter x. This reveals an interesting band gap engineering character of this series of material. Additionally, the temperature dependence of the band gaps has been studied and discussed taking into consideration both the implicit and explicit contributions. The exponential increasing adsorption edge was observed which is known as the Urbach tail is discussed in detail. The electronic band structure of the whole series of ZrS{sub x}Se{sub 2-x} was studied by means of high resolution angle-resolved photoemission spectroscopy (ARPES) used in conjunction with synchrotron radiation facilities. The experimental valence band structure of the complete series is reported along the normal direction and along the major symmetry directions of the Brillouin zone parallel to the layers. The obtained experimental band structure compares well with recent band structure calculations based on the density functional theory (DET). The results show that the binding energies of the topmost valence band shift almost linearly with the composition parameter x. Further, a characteristic splitting of the chalcogen p-derived valence bands along high symmetry directions is observed. Our band structure calculations based on the DFT prove that the splitting is ascribed to the spin-orbit (SO) coupling. Moreover, the energy gap values are determined from the observed emission near to the conduction band minimum. The band gap values deduced by ARPES are discussed and compared to that from the optical measurements. (orig.)

Moustafa, Mohamed Orabi

2012-11-01

388

Information on the band structure of ferromagnetic Ni from ?SR-Knight shift measurements

International Nuclear Information System (INIS)

The authors present results on the temperature dependence of the Knight shift of the hyperfine field at a positive muon in ferromagnetic Nickel and show that the results allow a determination of the Stoner gap, that is the gap between the top of the majority d-band and the Fermi energy. The consistency of the analysis supports the SWS-model but the obtained value for the Stoner gap is far below the predictions of most ferromagnetic band structure calculations. (Auth.)

389

International X-Band Linear Collider Accelerator Structure R&D

Energy Technology Data Exchange (ETDEWEB)

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

Wang, J.W.; /SLAC

2009-03-04

390

Superlattice band structure: New and simple energy quantification condition

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

391

Area Efficient Interpolator Using Half-Band Symmetric Structure

Digital Repository Infrastructure Vision for European Research (DRIVER)

In this paper a cost effective Interpolator has been designed and simulated. An area efficient method has been presented to implement cost effective interpolator for wireless communication systems. Interpolator is particularly useful for smoothing signals such as sinusoids or baseband I/Q waveforms. For these signals, interpolation filter is used to accurately produce new samples of the waveform without reducing signal quality. In this paper three structures for interpolator has been used nam...

Mr. Rajesh Mehra; Shaily Verma

2013-01-01

392

Double enhancement of spontaneous emission due to increased photon density of states at the emission frequency and the small group velocity of light at the excitation frequency was clearly demonstrated by angle-resolved photoluminescence experiments for dielectric multilayers composed of Ta2O5 and SiO2 with oxygen vacancies as light emitters. Theoretical emission profiles given by the weak modulation approximation agreed well with the experimental observations. PMID:19654722

Kuroda, Keiji; Sawada, Tsutomu; Kuroda, Takashi; Watanabe, Kenji; Sakoda, Kazuaki

2009-07-20

393

The indirect energy gaps of CsCl-structured BaS and CaSe are measured at high pressures using absorption spectroscopy to pressures of 41 and 53 GPa, respectively. Band-structure calculations using density-functional theory and quasiparticle corrections are also conducted on BaS and CaSe as a function of pressure. The measured indirect gaps of BaS and CaSe shift linearly with pressure with a slope, (dEgap/dP), of -1.8(2)×10-2 and -1.5(3)×10-2 eV/GPa, respectively. These values are in reasonable agreement with the theoretical results of -2.2×10-2 eV/GPa for BaS and -2.3×10-2 eV/GPa for CaSe. Our calculations indicate that the energy gap in both compounds is indirect with the valence-band maxima at M and the conduction-band minima at ?. Based on a simple linear extrapolation of our data, we estimate the metallization pressures of CsCl-structured BaS and CaSe to be above 113 and 125 GPa, respectively. Our estimates of metallization pressures are compared with those of other alkaline earth monochalcogenides to determine the degree to which changes in the electronic structures of these compounds under pressure can be described using systematic trends based on ionic radii.

Cervantes, Phillip; Williams, Quentin; Côté, Michel; Rohlfing, Michael; Cohen, Marvin L.; Louie, Steven G.

1998-10-01

394

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

International Nuclear Information System (INIS)

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

395

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

Energy Technology Data Exchange (ETDEWEB)

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

Carrere, H [LNMO-INSA, 135 avenue de Rangueil, 31077 Toulouse cedex 4 (France); Marie, X [LNMO-INSA, 135 avenue de Rangueil, 31077 Toulouse cedex 4 (France); Barrau, J [LNMO-INSA, 135 avenue de Rangueil, 31077 Toulouse cedex 4 (France); Amand, T [LNMO-INSA, 135 avenue de Rangueil, 31077 Toulouse cedex 4 (France); Bouzid, S Ben [LPN, Route de Nozay, 91460 Marcoussis (France); Sallet, V [LPN, Route de Nozay, 91460 Marcoussis (France); Harmand, J-C [LPN, Route de Nozay, 91460 Marcoussis (France)

2004-08-11

396

We report first principles calculations of the electronic structure of monolayer 1H-MX2 (M = Mo, W; X = S, Se, Te), using the pseudopotential and numerical atomic orbital basis sets based methods within the local density approximation. Electronic band structure and density of states calculations found that the states around the Fermi energy are mainly due to metal d states. From partial density of states we find a strong hybridisation between metal d and chalcogen p states below the Fermi energy. All studied compounds in this work have emerged as new direct band gap semiconductors. The electronic band gap is found to decrease as one goes from sulphides to the tellurides of both Mo and W. Reducing the slab thickness systematically from bulk to monolayers causes a blue shift in the band gap energies, resulting in tunability of the electronic band gap. The magnitudes of the blue shift in the band gap energies are found to be 1.14 eV, 1.16 eV, 0.78 eV, 0.64, 0.57 eV and 0.37 eV for MoS2, WS2, MoSe2, WSe2, MoTe2 and WTe2, respectively, as we go from bulk phase (indirect band gap) to monolayer limit (direct band gap). This tunability in the electronic band gap and transitions from indirect to direct band make these materials potential candidates for the fabrication of optoelectronic devices.

Kumar, A.; Ahluwalia, P. K.

2012-06-01

397

International Nuclear Information System (INIS)

Diamond-like Cu-based multinary semiconductors are a rich family of materials that hold promise in a wide range of applications. Unfortunately, accurate theoretical understanding of the electronic properties of these materials is hindered by the involvement of Cu d electrons. Density functional theory (DFT) based calculations using the local density approximation or generalized gradient approximation often give qualitative wrong electronic properties of these materials, especially for narrow-gap systems. The modified Becke-Johnson (mBJ) method has been shown to be a promising alternative to more elaborate theory such as the GW approximation for fast materials screening and predictions. However, straightforward applications of the mBJ method to these materials still encounter significant difficulties because of the insufficient treatment of the localized d electrons. We show that combining the promise of mBJ potential and the spirit of the well-established DFT + U method leads to a much improved description of the electronic structures, including the most challenging narrow-gap systems. A survey of the band gaps of about 20 Cu-based semiconductors calculated using the mBJ + U method shows that the results agree with reliable values to within ±0.2 eV

398

Energy Technology Data Exchange (ETDEWEB)

Diamond-like Cu-based multinary semiconductors are a rich family of materials that hold promise in a wide range of applications. Unfortunately, accurate theoretical understanding of the electronic properties of these materials is hindered by the involvement of Cu d electrons. Density functional theory (DFT) based calculations using the local density approximation or generalized gradient approximation often give qualitative wrong electronic properties of these materials, especially for narrow-gap systems. The modified Becke-Johnson (mBJ) method has been shown to be a promising alternative to more elaborate theory such as the GW approximation for fast materials screening and predictions. However, straightforward applications of the mBJ method to these materials still encounter significant difficulties because of the insufficient treatment of the localized d electrons. We show that combining the promise of mBJ potential and the spirit of the well-established DFT + U method leads to a much improved description of the electronic structures, including the most challenging narrow-gap systems. A survey of the band gaps of about 20 Cu-based semiconductors calculated using the mBJ + U method shows that the results agree with reliable values to within ±0.2 eV.

Zhang, Yubo; Zhang, Jiawei; Wang, Youwei [State Key Laboratory of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050 (China); Gao, Weiwei; Abtew, Tesfaye A. [Department of Physics, University at Buffalo, SUNY, Buffalo, New York 14260 (United States); Zhang, Peihong, E-mail: pzhang3@buffalo.edu, E-mail: wqzhang@mail.sic.ac.cn [Department of Physics, University at Buffalo, SUNY, Buffalo, New York 14260 (United States); Beijing Computational Science Research Center, Beijing 100084 (China); Zhang, Wenqing, E-mail: pzhang3@buffalo.edu, E-mail: wqzhang@mail.sic.ac.cn [State Key Laboratory of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050 (China); School of Chemistry and Chemical Engineering and Sate Key Laboratory of Coordination Chemistry, Nanjing University, Jiangsu 210093 (China)

2013-11-14

399

Effect of Structure on the Electronic Density of States of Doped Lanthanum Cuprate

We present a series of detailed band calculations on the various structural phases of doped lanthanum cuprate: HTT, LTO, and LTT. The LTO distortion is shown to have little effect on the electronic density of states (DOS). A fit to the pressure dependence of the superconducting transition temperature indicates that only 2.5\\% of the DOS is affected by the HTT$\\rightarrow$ LTO transition. The LTT distortion also has little effect on the DOS for the experimental value of the octahedral tilt angle. Larger tilt angles, though, lead to a dramatic change in the DOS.

Norman, M R; Novikov, D L; Freeman, A J

1993-01-01

400

Valence-band spectra and electronic structure of CuFeO2

The delafossite-type CuFeO2 single crystal was studied by means of x-ray emission and x-ray photoelectron spectroscopy. The valence state of Cu ions was found to be 1+, whereas Fe ions were found to be trivalent in the high-spin S=5/2 state. The x-ray emission (Cu L?, Fe L?, and O K?) and photoelectron spectra were compared to the results of the local spin density approximation (LSDA) (full-potential linearized augmented plane wave method and linearized muffin-tin orbitals in atomic sphere approximation method) and LSDA+U calculations. It is found that the maximum of the Cu 3d state distribution is localized closer to the Fermi level than that of the Fe 3d states. The LSDA calculations contradict the experimental results and do not give a correct description of the Cu and Fe 3d positions relative to the Fermi level, and incorrectly predict metallic behaviors (semiconductor observed) and give qualitatively incorrect magnetic properties of CuFeO2. The LSDA+U calculations give a much better agreement with the observed valence-band structure, the measured electrical, and the magnetic properties.

Galakhov, V. R.; Poteryaev, A. I.; Kurmaev, E. Z.; Anisimov, V. I.; Bartkowski, St.; Neumann, M.; Lu, Z. W.; Klein, B. M.; Zhao, Tong-Rong

1997-08-01

401

A new selenidoantimonate (CH3NH4)[Mn(phen)2](SbSe4)·phen (1, phen=1,10-phenanthroline) and an iron polyselenide [Fe(phen)2](Se4) (2) were obtained under hydro(solvo)thermal conditions. Compound 1 represents the first example of a selenidoantimonate anion as a ligand to a transition-metal ?-conjugated ligand complex cation. Compound 2 containing a ?2Se1,Se4 chelating tetraselenide ligand, represents the only example of a tetraselenide ligand to a Fe complex cation. Compounds 1 and 2 exhibit optical gaps of 1.71 and 1.20 eV, respectively and their thermal stabilities have been investigated by thermogravimetric analyses. The electronic band structure along with the density of states calculated by the DFT method indicate that the optical absorptions mainly originate from the charge transitions from the Se 4p and Mn 3d states to the phen p-?* orbital for 1 and the Se 4p and Fe 3d states to the phen p-?* orbital for 2.

Liu, Guang-Ning; Zhu, Wen-Juan; Zhang, Ming-Jian; Xu, Bo; Liu, Qi-Sheng; Zhang, Zhen-Wei; Li, Cuncheng

2014-10-01

402

A New Diagnostic of the Radial Density Structure of Be Disks

We analyze the intrinsic polarization of two classical Be stars in the process of losing their circumstellar disks via a Be to normal B star transition originally reported by Wisniewski et al. During each of five polarimetric outbursts which interrupt these disk-loss events, we find that the ratio of the polarization across the Balmer jump (BJ+/BJ-) versus the V-band polarization traces a distinct loop structure as a function of time. Since the polarization change across the Balmer jump is a tracer of the innermost disk density whereas the V-band polarization is a tracer of the total scattering mass of the disk, we suggest such correlated loop structures in Balmer jump-V band polarization diagrams (BJV diagrams) provide a unique diagnostic of the radial distribution of mass within Be disks. We use the 3-D Monte Carlo radiation transfer code HDUST to reproduce the observed clockwise loops simply by turning "on/off" the mass decretion from the disk. We speculate that counter-clockwise loop structures we observe...

Draper, Zachary H; Bjorkman, Karen S; Haubois, Xavier; Carciofi, Alex C; Bjorkman, Jon E; Meade, Marilyn R; Okazaki, Atsuo

2011-01-01

403

Dynamics versus structure: breaking the density degeneracy in star formation

The initial density of individual star-forming regions (and by extension the birth environment of planetary systems) is difficult to constrain due to the `density degeneracy problem': an initially dense region expands faster than a more quiescent region due to two-body relaxation and so two regions with the same observed present-day density may have had very different initial densities. We constrain the initial densities of seven nearby star-forming regions by folding in information on their spatial structure from the {Q}-parameter and comparing the structure and present-day density to the results of N-body simulations. This in turn places strong constraints on the possible effects of dynamical interactions and radiation fields from massive stars on multiple systems and protoplanetary discs. We apply our method to constrain the initial binary population in each of these seven regions and show that the populations in only three - the Orion Nebula Cluster, ? Oph, and Corona Australis - are consistent with having evolved from the Kroupa universal initial period distribution and a binary fraction of unity.

Parker, Richard J.

2014-12-01

404

Evolution of density-dependent dispersal in a structured metapopulation.

We study the evolution of density-dependent dispersal in a structured metapopulation subject to local catastrophes that eradicate local populations. To this end we use the theory of structured metapopulation dynamics and the theory of adaptive dynamics. The set of evolutionarily possible dispersal functions (i.e., emigration rates as a function of the local population density) is derived mechanistically from an underlying resource-consumer model. The local resource dynamics is of a flow-culture type and consumers leave a local population with a constant probability per unit of time kappa when searching for resources but not when handling resources (i.e., eating and digesting). The time an individual spends searching (as opposed to handling) depends on the local resource density, which in turn depends on the local consumer density, and so the average per capita emigration rate depends on the local consumer density as well. The derived emigration rates are sigmoid functions of local consumer population density. The parameters of the local resource-consumer dynamics are subject to evolution. In particular, we find that there exists a unique evolutionarily stable and attracting dispersal rate kappa( *) for searching consumers. The kappa( *) increases with local resource productivity and decreases with resource decay rate. The kappa( *) also increases with the survival probability during dispersal, but as a function of the catastrophe rate it reaches a maximum before dropping off to zero again. PMID:19361534

Geritz, Stefan A H; Gyllenberg, Mats; Ondrácek, Petr

2009-06-01

405

Full waveform inversion schemes for 3D density structure

We develop full waveform inversion schemes for density, based on numerical wave propagation, adjoint techniques and various non-seismological constraints to enhance resolution. Density variations drive convection in the Earth and serve as a discriminator between thermal and compositional heterogeneities. However, classical seismological observables and gravity provide only weak constraints, with strong trade-offs. To put additional constraints on density structure, we develop full waveform inversion schemes that exploit the complete seismic waveform for the benefit of improved density resolution. Our inversion scheme is intended to incorporate any information that can help to constrain 3D density structure. This includes non-seismological information, such as gravity and mineral physical constraints on maximum density heterogeneities (assuming reasonable variations in temperature and composition). As a trial case, we compare the results of current tomographic models to such constraints. In a series of initial synthetic inversion experiments, we aim to construct efficient optimisation schemes that allow us to assimilate all the available types of information. For this, we use 2D numerical wave propagation combined with adjoint techniques for the computation of sensitivity kernels. With these kernels, we drive gradient-based optimisation schemes that incorporate our non-seismological constraints. Specifically, we assess the usefulness of two different inversion strategies: (i) optimising a single augmented objective functional that incorporates all the constraints we have, and (ii) using an objective functional based on the seismological data only, and using the additional information as hard constraints to project the solution onto an allowed range.

Blom, Nienke; Fichtner, Andreas

2014-05-01

406

Effect of structured packing density on performance of air dehumidifier

Energy Technology Data Exchange (ETDEWEB)

An experimental study has been conducted to investigate the performance of a liquid desiccant air dehumidifier equipped with a structured packing made of wood for three different densities using triethylene glycol (TEG) as the liquid desiccant. The structured packing densities used were 77, 100 and 200 m{sup 2}/m{sup 3}. The performance of the dehumidifier was expressed in terms of the moisture removal rate and the dehumidifier effectiveness under different air and desiccant parameters, i.e. the air and TEG flow rates, air and TEG inlet temperatures, inlet air humidity and inlet TEG concentration. In general, the trend in the dehumidifier performance was similar to that reported by other investigators using random packing. The effect of packing density on moisture removal rate and dehumidifier effectiveness is assessed. The differences in the effectiveness of different packing densities are attributed to the wetting condition. Lower effectiveness of the column is shown with the packing density of 200 m{sup 2}/m{sup 3} compared to the other two packing densities when the air flow rate, inlet concentration and desiccant flow rate are increased. However, higher effectiveness is shown when either the inlet temperature of the air or desiccant is increased.

Abdul-Wahab, S.A. E-mail: sabah1@squ.edu.om; Abu-Arabi, M.K.; Zurigat, Y.H

2004-09-01

407

Dynamics versus structure: breaking the density degeneracy in star formation

The initial density of individual star-forming regions (and by extension the birth environment of planetary systems) is difficult to constrain due to the "density degeneracy problem": an initially dense region expands faster than a more quiescent region due to two-body relaxation and so two regions with the same observed present-day density may have had very different initial densities. We constrain the initial densities of seven nearby star-forming regions by folding in information on their spatial structure from the $\\mathcal{Q}$-parameter and comparing the structure and present-day density to the results of $N$-body simulations. This in turn places strong constraints on the possible effects of dynamical interactions and radiation fields from massive stars on multiple systems and protoplanetary discs. We apply our method to constrain the initial binary population in each of these seven regions and show that the populations in only three - the Orion Nebula Cluster, $\\rho$ Oph and Corona Australis - are consi...

Parker, Richard J

2014-01-01

408

3D Coronal Density Reconstruction and Retrieving the Magnetic Field Structure during Solar Minimum

Measurement of the coronal magnetic field is a crucial ingredient in understanding the nature of solar coronal phenomena at all scales. We employed STEREO/COR1 data obtained during a deep minimum of solar activity in February 2008 (Carrington rotation CR 2066) to retrieve and analyze the three-dimensional (3D) coronal electron density in the range of heights from 1.5 to 4 Rsun using a tomography method. With this, we qualitatively deduced structures of the coronal magnetic field. The 3D electron density analysis is complemented by the 3D STEREO/EUVI emissivity in the 195 A band obtained by tomography for the same CR. A global 3D MHD model of the solar corona was used to relate the reconstructed 3D density and emissivity to open/closed magnetic field structures. We show that the density maximum locations can serve as an indicator of current sheet position, while the locations of the density gradient maximum can be a reliable indicator of coronal hole boundaries. We find that the magnetic field configuration du...

Kramar, M; Miki?, Z; Davila, J

2014-01-01

409

Choosing novel materials and structures is important for enhancing the on-state current in tunnel field-effect transistors (TFETs). In this paper, we reveal that the on-state performance of TFETs is mainly determined by the energy band profile of the channel. According to this interpretation, we present a new concept of energy band profile modulation (BPM) achieved with gate structure engineering. It is believed that this approach can be used to suppress the ambipolar effect. Based on this method, a Si TFET device with a symmetrical tri-material-gate (TMG) structure is proposed. Two-dimensional numerical simulations demonstrated that the special band profile in this device can boost on-state performance, and it also suppresses the off-state current induced by the ambipolar effect. These unique advantages are maintained over a wide range of gate lengths and supply voltages. The BPM concept can serve as a guideline for improving the performance of nanoscale TFET devices.

Cui, Ning; Liang, Renrong; Wang, Jing; Xu, Jun

2012-06-01

410

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

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

2014-07-01

411

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

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

2013-02-01

412

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

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

Yin, Y.; Hong, J. S.

2014-09-01