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1

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2013-10-15

2

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

International Nuclear Information System (INIS)

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

3

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

Harigaya, Kikuo

2011-01-01

4

International Nuclear Information System (INIS)

After constructing a stress and strain model, the valence bands of in-plane biaxial tensile strained Si is calculated by k · p method. In the paper we calculate the accurate anisotropy valance bands and the splitting energy between light and heavy hole bands. The results show that the valance bands are highly distorted, and the anisotropy is more obvious. To obtain the density of states (DOS) effective mass, which is a very important parameter for device modeling, a DOS effective mass model of biaxial tensile strained Si is constructed based on the valance band calculation. This model can be directly used in the device model of metal—oxide semiconductor field effect transistor (MOSFET). It also a provides valuable reference for biaxial tensile strained silicon MOSFET design. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

5

The UHF-(70.5 cm wavelength) and S-band (10 cm wavelength) radar at NASA/Wallops Island Research Facility in Virginia, U.S.A. have been used to relate lightning activity with altitude and with the reflectivity structure of thunderstorms. Two centers of lightning flash density were found; one between 6 and 8 km altitude and another between 11 and 15 km. Previously announced in STAR as N83-31206

Mazur, V.; Gerlach, J. C.; Rust, W. D.

1984-01-01

6

International Nuclear Information System (INIS)

Some aspects of the predictions of energy band theory for both the rare earths and actinides and their comparison with experiment are discussed. Recent developments in assessing eigenfunction behavior are emphasized. 5 figures

7

By use of the structural parameters of the single crystal lithium indium orthoborate obtained by Penin et al. (Solid State Sci. 2001, 3, 461-468), from X- ray diffraction data, we present a first-principle study of the electronic structure and the linear optical properties for the novel lithium indium orthoborate Li3InB2O6. A full-potential linear augmented plane wave method within density functional theory with the Engel-Vosko exchange correlation was used. This compound has a wide direct energy band gap of about 3.8 eV with both the valence band maximum and conduction band minimum located at the center of the Brillouin zone. Our calculations of the partial density of states shows that the upper valence band originates predominantly from the O-p, B- p, and In-p states, and the lower conduction band is dominated by the O-s/p, In-p, and B-p states. Thus the O-p states in the upper valence band and lower conduction band has a significant effect on the energy band gap dispersion. The uniaxial anisotropy [deltaepsilon=(epsilon0zz-epsilon0xx)/epsilon0tot] is about -0.041. PMID:19642661

Reshak, Ali Hussain; Auluck, S; Kityk, I V

2009-08-27

8

International Nuclear Information System (INIS)

The crystal structure, thermodynamic stability, and electronic structure of La-, Y-, and Sc-filled CoP3 are predicted from density-functional band-structure calculations. The size of the cubic voids in the skutterudite structure is changed much less than the difference in size between the different filling atoms, and we expect that the larger rattling amplitude of the smaller Sc and Y atoms may decrease the lattice thermal conductivity of Sc- and Y-filled structures significantly compared to La-filled structures. The solubility of La, Y, and Sc in CoP3 is calculated to be around 5, 3-6 %, and below 1% at 0 K, respectively. Based on similar systems, this is expected to increase considerably if Fe is substituted for Co. Fe substitution is also expected to compensate the increased charge carrier concentration of the filled structures that is seen in the calculated electron density of states. In conclusion, Sc- or Y-filled (FeCo)P3 skutterudite structures are promising materials for thermoelectric applications

9

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)

10

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

11

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

12

International Nuclear Information System (INIS)

The electronic structure of single-crystal WO3 and Na0.67WO3 (a sodium–tungsten bronze) has been measured using soft x-ray absorption and resonant soft x-ray emission oxygen K-edge spectroscopies. The spectral features show clear differences in energy and intensity between WO3 and Na0.67WO3. The x-ray emission spectrum of metallic Na0.67WO3 terminates in a distinct Fermi edge. The rigid-band model fails to explain the electronic structure of Na0.67WO3 in terms of a simple addition of electrons to the conduction band of WO3. Instead, Na bonding and Na 3s–O 2p hybridization need to be considered for the sodium–tungsten bronze, along with occupation of the bottom of the conduction band. Furthermore, the anisotropy in the band structure of monoclinic ?-WO3 revealed by the experimental spectra with orbital-resolved geometry is explained via density functional theory calculations. For ?-WO3 itself, good agreement is found between the experimental O K-edge spectra and the theoretical partial density of states of O 2p orbitals. Indirect and direct bandgaps of insulating WO3 are determined from extrapolating separations between spectral leading edges and accounting for the core–hole energy shift in the absorption process. The O 2p non-bonding states show upward band dispersion as a function of incident photon energynction of incident photon energy for both compounds, which is explained using the calculated band structure and experimental geometry. (paper)

13

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

14

International Nuclear Information System (INIS)

We have calculated the band structure of FeSe, FeSe from which 2 atoms of Se out of 4 per unit cell have been removed and a system in which 2 Te atoms have been substituted for 2 Se atoms in a unit cell in the normal state. In all of the cases the Fermi energies cross multiple bands and there is always at least one conduction band minimum whose energy is lower than the valence band maximum. Hence, on the basis of the calculated band structures, these systems have no semiconducting band gap and should behave as metals. Similarly, there is non-vanishing density of states at the Fermi level. Large effects are found in the density of states. The normal state gap reduces in the composition which becomes superconducting.

15

Energy Technology Data Exchange (ETDEWEB)

We present a detailed ARPES investigation of the RTe{sub 3} family, which sets this system as an ideal 'textbook' example for the formation of a nesting driven Charge Density Wave (CDW). This family indeed exhibits the full range of phenomena that can be associated to CDW instabilities, from the opening of large gaps on the best nested parts of Fermi Surface (FS) (up to 0.4eV), to the existence of residual metallic pockets. ARPES is the best suited technique to characterize these features, thanks to its unique ability to resolve the electronic structure in k-space. An additional advantage of RTe{sub 3} is that the band structure can be very accurately described by a simple 2D tight-binding (TB) model, which allows one to understand and easily reproduce many characteristics of the CDW. In this paper, we first establish the main features of the electronic structure, by comparing our ARPES measurements with Linear Muffin-Tin Orbital band calculations. We use this to define the validity and limits of the TB model. We then present a complete description of the CDW properties and, for the first time, of their strong evolution as a function of R. Using simple models, we are able to reproduce perfectly the evolution of gaps in k-space, the evolution of the CDW wave vector with R and the shape of the residual metallic pockets. Finally, we give an estimation of the CDW interaction parameters and find that the change in the electronic density of states n(Ef), due to lattice expansion when different R ions are inserted, has the correct order of magnitude to explain the evolution of the CDW properties.

Brouet, V.; Yang, W.L.; Zhou, X.J.; Hussain, Z.; Moore, R.G.; He, R.; Lu, D.H.; Shen, Z.X.; Laverock, J.; Dugdale, S.; Ru, N.; Fisher, I.R.

2010-02-15

16

Band structure from random interactions

The anharmonic vibrator and rotor regions in nuclei are investigated in the framework of the interacting boson model using an ensemble of random one- and two-body interactions. We find a predominance of L(P)=0(+) ground states, as well as strong evidence for the occurrence of both vibrational and rotational band structures. This remarkable result suggests that such band structures represent a far more general (robust) property of the collective model space than is generally ...

Bijker, R.; Frank, A.

1999-01-01

17

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

18

Energy Technology Data Exchange (ETDEWEB)

We present a detailed angle-resolved photoemission spectroscopy (ARPES) investigation of the RTe3 family, which sets this system as an ideal"textbook" example for the formation of a nesting driven charge density wave (CDW). This family indeed exhibits the full range of phenomena that can be associated to CDWinstabilities, from the opening of large gaps on the best nested parts of Fermi surface (up to 0.4 eV), to the existence of residual metallic pockets. ARPES is the best suited technique to characterize these features, thanks to its unique ability to resolve the electronic structure in k space. An additional advantage of RTe3 is that theband structure can be very accurately described by a simple two dimensional tight-binding (TB) model, which allows one to understand and easily reproduce many characteristics of the CDW. In this paper, we first establish the main features of the electronic structure by comparing our ARPES measurements with the linear muffin-tinorbital band calculations. We use this to define the validity and limits of the TB model. We then present a complete description of the CDW properties and of their strong evolution as a function of R. Using simple models, we are able to reproduce perfectly the evolution of gaps in k space, the evolution of the CDW wave vector with R, and the shape of the residual metallic pockets. Finally, we give an estimation of the CDWinteraction parameters and find that the change in the electronic density of states n (EF), due to lattice expansion when different R ions are inserted, has the correct order of magnitude to explain the evolution of the CDW properties.

Hussain, Zahid; Brouet, Veronique; Yang, Wanli; Zhou, Xingjiang; Hussain, Zahid; Moore, R.G.; He, R.; Lu, D. H.; Shen, Z.X.; Laverock, J.; Dugdale, S.B.; Ru, N.; Fisher, R.

2008-01-16

19

Band Structure of AlSb Nanoclusters

Directory of Open Access Journals (Sweden)

Full Text Available *Ab initio* restricted Hartree-Fock method within the framework of large unit cell formalism is used to investigate the band structure of AlSb nanoclusters. Large unit cells of 8, 16, 54, 64 and 128 atoms are used to analyze the cohesive energy, energy gap, valence bandwidth, and the density of states of the energy levels for AlSb nanoclusters. The results of the present work revealed that the band structure of AlSb nanoclusters differs significantly from that of the bulk AlSb crystal. Also, it is found that the valence band width and the cohesive energy (absolute value increase as the AlSb crystal size increases, and they tend to stabilize for nanoclusters of more than 50 atoms.

Haider I. Isa

2012-08-01

20

Computing Band Structures in Undergraduate Solid State

Understanding band structures is quite challenging for undergraduate solid state physics students. Calculating the band structures is even more difficult. However, using the techniques developed earlier [1], and which were applied to the simple cubic structures, it is possible to extend them to semiconducting systems in a simple way. The idea is to employ the 8-band model concept of Harrison's Hamiltonian approach [2] to model and parametrize the bands. The method also uses the system's band structure's Green's function and employs the k-space Brillouin-zone ray approach [3] combined with a complex integration method [4] to obtain the density of states. The number of occupied electron states up to a certain energy is obtained using Romberg's method and example results will be shown. [1] Javier Hasbun (J42.00013) http://meetings.aps.org/Meeting/MAR10/Event/119248 [2] S. Froyen, and W. A. Harrison, Phys. Rev. B Vol. 20, 2420 (1979). [3] An-Ban Chen, Phys. Rev. B, Vol. 16, 3291 (1977). [4] Javier Hasbun http://meetings.aps.org/link/BAPS.2009.MAR.L29.12

Hasbun, Javier

2011-03-01

21

Multiple band structure and band termination in 157Ho

International Nuclear Information System (INIS)

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

22

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

23

Electron energy loss studies of the valence band density of states of scandium

International Nuclear Information System (INIS)

Electron energy loss spectroscopy of the scandium (0001) surface has indicated both core level and valence band excitation loss structure. Comparison to theoretically calculated bulk densities of states for scandium shows good agreement with the experimental results. (author)

24

Quasirelativistic band structure of bismuth telluride

International Nuclear Information System (INIS)

The band structure of bismuth telluride belonging to the group of the Asub(2)Ssup(5)BsUb(3)-type crystals with the Dsub(3d)sup(5) symmetry is under consideration. The Bi2Te3 band structure was calculated using the Pauli equation pseudopotential method. Calculation results are presented for the Brillouin zone symmetric points. The energy bands are classified according to their symmetry. The evailable basic parameters of the bismuth telluride band structure are compared with the result of other paper. Analysis of the calculated band structure shows that there is some difference of the band behaviour in the direction perpendicular to quintet (GITAL, KA, XU) layers that of bands lying in the quintet plane (other Brillouin zone directions). In the first case the energy band dispersion is well below than that in the second case. This fact conforms with a lower current carrier mobility in the direction perpendicular to the layers, as compared to other crystal directions

25

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...

Wirtz, Ludger; Rubio Secades, A?ngel

2003-01-01

26

Band structure and chemical bond in alkali metal carbonates

The band structure, state density, optical functions, and distribution of valence and difference density in alkali-metal carbonates are calculated within the local electron-density functional theory using the method of pseudopotential in the basis of numerical pseudoorbitals. When passing from a lithium cation to a potassium one, the character of hybridization between the crystal sublattices changes to result in an increase in the valence-band width, a decrease in the forbidden-band width, a complication of the structure of state-density spectrum, and a shift of the maxima of optical functions to the low-energy range. It is found that the electron overflow between the ?-and ?-orbitals of crystallographically nonequivalent oxygen atoms can occur in different ways, hence their interaction force with the surrounding atoms is different. The role of cations in stabilization of anion chains resulting from the electron-cloud overlapping in lithium and sodium carbonates is shown.

Fedorov, I. A.; Zhuravlev, Yu. N.; Korabel'Nikov, D. V.

2006-10-01

27

Electronic band structure of CdF2

International Nuclear Information System (INIS)

Energy distribution curves (EDC) of electrons photoemitted (h?1 = 21.22 eV and h?2 = 40.8 eV) from the valence band (F-2p) and the Cd 4d band of a CdF2 crystal are measured and the valence and conduction band structures are calculated using the local empirical pseudopotential method (EPM). Comparison of the measured and calculated data show that the three main maxima measured in the valence band correspond well to the maxima in X5, L3, and X5 obtained in the calculated histogram of the valence band density of states. The influence of the final-state structure on the position of peaks in the valence band is not observed on EDCs obtained for both, h?1 and h?2 photoemission exciting energies. For Cd 4d band the wide splitting of 1.46 eV is obtained only for h?1 = 21.22 eV while it is not obtained on EDC for h?2 = 40.8 eV. This Cd 4d band splitting may be caused by the influence of the final density-of-states maximum obtained in conduction band in X1-point. The results obtained are compared with reflectivity data available in the literature. (author)

28

Band structure of SnTe studied by photoemission spectroscopy.

We present an angle-resolved photoemission spectroscopy study of the electronic structure of SnTe and compare the experimental results to ab initio band structure calculations as well as a simplified tight-binding model of the p bands. Our study reveals the conjectured complex Fermi surface structure near the L points showing topological changes in the bands from disconnected pockets, to open tubes, and then to cuboids as the binding energy increases, resolving lingering issues about the electronic structure. The chemical potential at the crystal surface is found to be 0.5 eV below the gap, corresponding to a carrier density of p=1.14 × 10(21)? cm(-3) or 7.2 × 10(-2) holes per unit cell. At a temperature below the cubic-rhombohedral structural transition a small shift in spectral energy of the valance band is found, in agreement with model predictions. PMID:20868120

Littlewood, P B; Mihaila, B; Schulze, R K; Safarik, D J; Gubernatis, J E; Bostwick, A; Rotenberg, E; Opeil, C P; Durakiewicz, T; Smith, J L; Lashley, J C

2010-08-20

29

International Nuclear Information System (INIS)

Excited levels in 84Sr have been populated in the reactions 76Ge (12C, 4n) and 81Br (6Li,3n). Singles and coincidence gamma-ray spectra as well as angular distributions were measured. Lifetimes were measured by the recoil-distance method. The positive parity levels were sorted out into four bands; the existence of at least two negative parity bands was established. The properties of 84Sr were compared to those of neighbouring nuclei

30

Excited levels in 84Sr have been populated in the reactions 76Ge (12C, 4n) and 81Br (6Li,3n). Singles and coincidence gamma-ray spectra as well as angular distributions were measured. Lifetimes were measured by the recoil-distance method. The positive parity levels were sorted out into four bands ; the existence of at least two negative parity bands was established. The properties of 84Sr were compared to those of neighbouring nuclei.

Dewald, A.; Kaup, U.; Gast, W.; Gelberg, A.; Schuh, H. -w; Zell, K.; Brentano, Von

1980-01-01

31

Electronic structure and charge density of zirconium diboride

Self-consistent calculations of the electronic band structure of zirconium diboride, ZrB2, have been performed. The total and individual band charge densities are analyzed in terms of their site (zirconium or boron) symmetry and plotted. The total charge density shows very little charge asymmetry about either site.

Switendick, Alfred C.

1991-07-01

32

Electronic structure and charge density of zirconium diboride

International Nuclear Information System (INIS)

Self-consistent calculations of the electronic band structure of zirconium diboride, ZrB2, have been performed. The total and individual band charge densities are analyzed in terms of their site (zirconium or boron) symmetry and plotted. The total charge density shows very little charge asymmetry about either site

33

Band structure calculations of high pressure phases of selenium

International Nuclear Information System (INIS)

We report a detailed theoretical calculation of the electronic band structure of Se in hexagonal and monoclinic phases under pressure. The first principle tight-binding linear Muffin-Tin orbital method (TBLMTO) within local density approximation (LDA) has been used. The total energy calculations have been carried out within the atomic-sphere approximation (ASA) for both phases in order to study the phase stability. Apart from the electronic band structure and structural stability calculations, the density of states (DOS) and Fermi energies at various pressures are calculated. The calculated lattice parameters, transition pressure, bulk modulus and the pressure-volume relation were found to be in good agreement with recent experimental results. Our calculations show that the ambient pressure hexagonal phase has a band gap of 1.49 eV whereas the high pressure monoclinic phase is found to be metallic. (author)

34

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

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

2014-08-01

35

DEFF Research Database (Denmark)

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

Michiardi, Matteo; Aguilera, Irene

2014-01-01

36

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

37

Modeling charged defects inside density functional theory band gaps

Density functional theory (DFT) has emerged as an important tool to probe microscopic behavior in materials. The fundamental band gap defines the energy scale for charge transition energy levels of point defects in ionic and covalent materials. The eigenvalue gap between occupied and unoccupied states in conventional DFT, the Kohn-Sham gap, is often half or less of the experimental band gap, seemingly precluding quantitative studies of charged defects. Applying explicit and rigorous control of charge boundary conditions in supercells, we find that calculations of defect energy levels derived from total energy differences give accurate predictions of charge transition energy levels in Si and GaAs, unhampered by a band gap problem. The GaAs system provides a good theoretical laboratory for investigating band gap effects in defect level calculations: depending on the functional and pseudopotential, the Kohn-Sham gap can be as large as 1.1 eV or as small as 0.1 eV. We find that the effective defect band gap, the computed range in defect levels, is mostly insensitive to the Kohn-Sham gap, demonstrating it is often possible to use conventional DFT for quantitative studies of defect chemistry governing interesting materials behavior in semiconductors and oxides despite a band gap problem.

Schultz, Peter A.; Edwards, Arthur H.

2014-05-01

38

Modeling charged defects inside density functional theory band gaps

International Nuclear Information System (INIS)

Density functional theory (DFT) has emerged as an important tool to probe microscopic behavior in materials. The fundamental band gap defines the energy scale for charge transition energy levels of point defects in ionic and covalent materials. The eigenvalue gap between occupied and unoccupied states in conventional DFT, the Kohn–Sham gap, is often half or less of the experimental band gap, seemingly precluding quantitative studies of charged defects. Applying explicit and rigorous control of charge boundary conditions in supercells, we find that calculations of defect energy levels derived from total energy differences give accurate predictions of charge transition energy levels in Si and GaAs, unhampered by a band gap problem. The GaAs system provides a good theoretical laboratory for investigating band gap effects in defect level calculations: depending on the functional and pseudopotential, the Kohn–Sham gap can be as large as 1.1 eV or as small as 0.1 eV. We find that the effective defect band gap, the computed range in defect levels, is mostly insensitive to the Kohn–Sham gap, demonstrating it is often possible to use conventional DFT for quantitative studies of defect chemistry governing interesting materials behavior in semiconductors and oxides despite a band gap problem

39

Electronic Structure of Calcium Hexaboride within the Weighted Density Approximation

We report calculations of the electronic structure of CaB$_6$ using the weighted density approximation (WDA) to density functional theory. We find a semiconducting band structure with a sizable gap, in contrast to local density approximation (LDA) results, but in accord with recent experimental data. In particular, we find an $X$-point band gap of 0.8 eV. The WDA correction of the LDA error in describing the electronic structure of CaB$_6$ is discussed in terms of the orbital character of the bands and the better cancelation of self-interactions within the WDA.

Wu, Z; Cohen, R E

2004-01-01

40

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.)

41

Multiple band structures in 191Hg

International Nuclear Information System (INIS)

The level structure of the nucleus 191Hg has been considerably extended from previous studies by using the 160Gd(36S, 5n) reaction in conjunction with an array of Compton-suppressed germanium detectors. A series of 13 different level sequences has been established in addition to three superdeformed bands. A majority of the band structures can be understood in cranked shell model calculations assuming on oblate collective nuclear shape. There is some evidence for the onset of triaxiality. Finally, two bands of single-particle character have been found. They are interpreted as being associated with a prolate non-collective shape (?=-120deg). (orig.)

42

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.

Holtham, P. M.; Jan, J. P.

1977-01-01

43

Electronic Band Structure of Carbon Nanotubes with Kekule Structure

Electronic band structure of carbon nanotubes with the Kekule structure is studied by the tight-binding approximation. We give a complete geometrical approach to structural properties of carbon nanotubes with bond alternation, including chiral and achiral tubes. When the Kekule is introduced, all carbon nanotubes become semiconducting with a small band gap at the Fermi level. The band gap of the carbon nanotubes depends only on the difference between C—C bond lengths or the resonance integrals.

Nguyen, Ngoc Hieu; Le Cong, Nhan

2013-09-01

44

Density-matrix renormalization group is used to study the pairing when both of electron-electron and electron-phonon interactions are strong in the Holstein-Hubbard model at half-filling in a region intermediate between the adiabatic (Migdal's) and antiadiabatic limits. We have found: (i) the pairing correlation obtained for a one-dimensional system is nearly degenerate with the CDW correlation in a region where the phonon-induced attraction is comparable with the electron-e...

Tezuka, Masaki; Arita, Ryotaro; Aoki, Hideo

2005-01-01

45

Measurement of valence band structure in arbitrary dielectric films

International Nuclear Information System (INIS)

A new way of measuring the band structure of various dielectric materials using the secondary electron emission from Auger neutralization of ions is introduced. The first example of this measurement scheme is the magnesium oxide (MgO) films with respect to the application of the films in the display industries. The density of state in the valence bands of MgO film and MgO film with a functional layer (FL) deposited over a dielectric surface reveals that the density peak of film with a FL is considerably less than that of film, thereby indicating a better performance of MgO film with functional layer in display devices. The second example of the measurement is the boron-zinc oxide (BZO) films with respect to the application of the films to the development of solar cells. The measurement of density of state in BZO film suggests that a high concentration of boron impurity in BZO films may enhance the transition of electrons and holes through the band gap from the valence to the conduction band in zinc oxide crystals; thereby improving the conductivity of the film. Secondary electron emission by the Auger neutralization of ions is highly instrumental for the determination of the density of states in the valence band of dielectric materials.

46

Band structure calculations of Cu(In1-xGax)Se2

International Nuclear Information System (INIS)

First principles density calculations of the band structure, and density of states of the Cu(In1-xGax)Se2 in the chalcopyrite type structure have been carried out using the density functional theory. The relationship between the band gap and chemical composition in the structure is discussed. The effective masses of the electrons and holes in the different composition crystals are reported.

47

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)

48

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

49

Band structure of CdTe under high pressure

International Nuclear Information System (INIS)

The band structures and density of states of cadmium telluride (CdTe) under various pressures ranging from normal to 4.5 Mbar are obtained. The electronic band structure at normal pressure of CdTe (ZnS structure) is analyzed and the direct band gap value is found to be 1.654 eV. CdTe becomes metal and superconductor under high pressure but before that it undergoes structural phase transition from ZnS phase to NaCl phase. The equilibrium lattice constant, bulk modulus and the phase transition pressure at which the compounds undergo structural phase transition from ZnS to NaCl are predicted from the total energy calculations. The density of states at the Fermi level (N(EF)) gets enhanced after metallization, which leads to the superconductivity in CdTe. In our calculation, the metallization pressure (PM = 1.935 Mbar) and the corresponding reduced volume ((V/V0)M = 0.458) are estimated. Metallization occurs via direct closing of band gap at ? point. (author)

50

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

51

Electronic band structure of helical iodine chains

Energy Technology Data Exchange (ETDEWEB)

The electronic band structure of helical iodine chains was calculated within the empirical tight binding approach. The screw symmetry of the system was used to reduce the size of the problem to a single atom with four atomic orbitals. The overlap parameters were fitted to reproduce the DFT results for a linear iodine chain. The obtained results for helical chains have shown the energy band splitting due to the overlap between p orbitals introduced by the structure twisting. The splitting magnitude depends on the pitch of the helix. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Rybkovskiy, Dmitry [A.M. Prokhorov General Physics Institute, Russian Academy of Sciences, 38 Vavilov street, 119991 Moscow (Russian Federation); Moscow State Institute of Radio Engineering, Electronics and Automation (Technical University), 78 Vernadskogo Prospect, 119454 Moscow (Russian Federation); Osadchy, Alexander; Obraztsova, Elena [A.M. Prokhorov General Physics Institute, Russian Academy of Sciences, 38 Vavilov street, 119991 Moscow (Russian Federation)

2012-12-15

52

Duplex Structures in Deformation Bands, how do They Form?

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

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

2002-12-01

53

Optical And Thermoelectrical Studies On Band Edge Structure Of SnTe

Optical transmission properties and Seebeck coefficient of SnTe were measured to study the energy band edge structures of the SnTe. Burstein-Moss effect in the optical transmission spectra was very small owing to a bumped band edge structure with a large band-edge density of states. The optical transmission spectra were simulated assuming the bumped band edge structure. Dependence of Seebeck coefficient on the carrier concentration was also calculated theoretically assuming the band edge structure. Experimental Seebeck coefficient of SnTe with relatively small hole concentration increased significantly and agreed well with the theoretical value.

Ishida, A.; Tsuchiya, T.; Takaoka, S.

2011-12-01

54

Production of S-band Accelerating Structures

ACCEL currently produces accelerating structures for several scientific laboratories. Multi-cell cavities at S-band frequencies are required for the projects CLIC-driver-linac, DLS and ASP pre-injector linac and the MAMI-C microtron. Based on those projects differences and similarities in design, production technologies and requirements will be addressed.

Piel, C; Vogel, H; Vom Stein, P

2004-01-01

55

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

56

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

2014-05-01

57

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...

Picaud, Fabien; Smogunov, Alexander; Corso, Andrea Dal; Tosatti, Erio

2003-01-01

58

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)

59

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

International Nuclear Information System (INIS)

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.

60

A Multi Purpose X Band Accelerating Structure

In a collaboration between CERN, PSI and Sincrotrone Trieste (ST), a series of four multipurpose X-band accelerating structures has been designed and fabricated. The structures have 72 cells with a phase advance of 5?/6 and include upstream and downstream wake?eld monitors to measure the beam alignment. We give an overview of the electrical and mechanical design and describe the fabrication of the ?rst units. We show the results of the low level RF tests. Furthermore, we present the?rst experiences running the structures under high power.

Dehler, M; Citterio, A; Serpico, C; d’Auria, G; Gudkov, D; Samoshkin, A; Lebet, S; Shi, J; Riddone, G

2012-01-01

61

Ground state band and quasi ?-band structure in 104Ru

International Nuclear Information System (INIS)

The odd-even staggering effect in quasi ?-band is considered most sensitive phenomenon in nuclear spectroscopy that carries information about the variable symmetry in the transitional region. The authors managed the deviation of model estimates of energy levels in 104Ru from that of respective experimental ones restricted to 13% in 2+ level of quasi ?-band

62

International Nuclear Information System (INIS)

We demonstrate that a Bychkov-Rashba dominated band structure can be stabilized in a nominally undoped In0.75Ga0.25As-In0.75Al0.25As quantum well. The transport properties of this system have been measured at 1.7 and 4.2 K and the Rashba coefficient ? has been determined in enhancement and depletion modes with an insulated front gate. In enhancement mode, ? is 1 x 10-11 eV m with carrier densities ns between 1.4 and 1.9 x 1011 cm-2. In depletion mode, with ns11 cm-2, ? was reduced to 0.7 x 10-11 eV m. The wavefunction penetration into the In0.75Al0.25As barriers, i.e. the interface asymmetry, makes no contribution to ? in this system. We minimize the Zeeman energy spin-splitting in this high g-factor system by analysing only the Shubnikov-de Haas structure below 0.5 T, i.e. for Landau level filling factors >12. The combination of the two spin-split subbands in ?xx can be separated using a magnetic field modulation technique where analogue d?xx/dB or d2?xx/dB2 signals are measured directly. The In0.75Ga0.25As-In0.75Al0.25As quantum well will have applications both in one-dimensional systems and in gate-induced two-dimensional electron gases where a dominant Bychkov-Rashba spin-splitting is required withoua spin-splitting is required without the complications of an embedded strained InAs well and without a significant contribution from the interface asymmetry at the In0.75Al0.25As barriers. (fast track communication)

63

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.

64

Relationship between band populations and band structure in the three-band Hubbard model

International Nuclear Information System (INIS)

We study the two-dimensional three-band Hubbard model by means of a four-pole approximation within the Composite Operator Method framework. The model has been solved by considering as basic composite field a four-component spinor field, which includes the p field, the two Hubbard operators for the d field, and a composite operator describing the p field dressed by the spin excitations of the d field. This solution correctly reproduces many results of numerical simulations. In this manuscript, we investigate the relationship between p-and d- populations and the band structure of the model, by varying the on-site potential, the charge-transfer gap, the doping and the hopping integral between the p orbitals.

65

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

66

Band structure and optical properties of opal photonic crystals

A theoretical approach for the interpretation of reflectance spectra of opal photonic crystals with fcc structure and (111) surface orientation is presented. It is based on the calculation of photonic bands and density of states corresponding to a specified angle of incidence in air. The results yield a clear distinction between diffraction in the direction of light propagation by (111) family planes (leading to the formation of a stop band) and diffraction in other directions by higher-order planes (corresponding to the excitation of photonic modes in the crystal). Reflectance measurements on artificial opals made of self-assembled polystyrene spheres are analyzed according to the theoretical scheme and give evidence of diffraction by higher-order crystalline planes in the photonic structure.

Pavarini, E; Soci, C; Galli, M; Marabelli, F; Comoretto, D

2005-01-01

67

Multiple band structures in 169Ta

International Nuclear Information System (INIS)

Rotational structures in the 169Ta nucleus were studied via the 124Sn(51V, 6n) reaction. These data were obtained as a side channel of an experiment focusing on 171Ta, but the sensitivity provided by the Gammasphere spectrometer proved sufficient for a significant extension of the level scheme of this rare-earth nucleus. Over 170 new transitions and four new band structures were placed in 169Ta, including the intruder ?i13/2 structure. Linking transitions between all of the sequences were identified, and the relative excitation energies between the different configurations were determined for the first time. The rotational sequences were interpreted within the framework of the cranked shell model

68

Multiple band structures in Ta169

Rotational structures in the Ta169 nucleus were studied via the Sn124(V51, 6n) reaction. These data were obtained as a side channel of an experiment focusing on Ta171, but the sensitivity provided by the Gammasphere spectrometer proved sufficient for a significant extension of the level scheme of this rare-earth nucleus. Over 170 new transitions and four new band structures were placed in Ta169, including the intruder ?i13/2 structure. Linking transitions between all of the sequences were identified, and the relative excitation energies between the different configurations were determined for the first time. The rotational sequences were interpreted within the framework of the cranked shell model.

Hartley, D. J.; Mohr, W. H.; Vanhoy, J. R.; Riley, M. A.; Aguilar, A.; Teal, C.; Janssens, R. V. F.; Carpenter, M. P.; Hecht, A. A.; Lauritsen, T.; Moore, E. F.; Zhu, S.; Kondev, F. G.; Djongolov, M. K.; Danchev, M.; Riedinger, L. L.; Hagemann, G. B.; Sletten, G.; Chowdhury, P.; Tandel, S. K.; Ma, W. C.; Ødegärd, S. W.

2006-11-01

69

Multiple band structures in {sup 169}Ta.

Energy Technology Data Exchange (ETDEWEB)

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

Hartley, D. J.; Mohr, W. H.; Vanhoy, J. R.; Riley, M. A.; Aguilar, A.; Teal, C.; Janssens, R. V. F.; Carpenter, M. P.; Hecht, A. A.; Lauritsen, T.; Moore, E. F.; Zhu, S.; Kondev, F. G.; Djongolov, M. K.; Danchev, M.; Riedinger, L. L.; Hagemann, G. B.; Sletten, G.; Chowdhury, P.; Tandel, S. K.; Ma, W. C.; Odegard, S. W.; U.S. Naval Academy; Florida State Univ.; Univ. of Tennessee; Niels Bohr Inst.; Univ. of Massachusetts; Mississippi State Univ.; Univ. of Oslo

2006-01-01

70

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

71

Photoemission and density functional theory study of Ir(111); energy band gap mapping

International Nuclear Information System (INIS)

We have performed combined angle-resolved photoemission spectroscopy (ARPES) experiments and density functional theory (DFT) calculations of the electronic structure of the Ir(111) surface, with the focus on the existence of energy band gaps. The investigation was motivated by the experimental results suggesting Ir(111) as an ideal support for the growth of weakly bonded graphene. Therefore, our prime interest was electronic structure around the K-bar symmetry point. In accordance with DFT calculations, ARPES has shown a wide energy band gap with the shape of a parallelogram centred around the K-bar point. Within the gap three surface states were identified; one just below the Fermi level and two spin-orbit split surface states at the bottom of the gap.

72

Band structure in Platinum nuclei (A ? 182)

International Nuclear Information System (INIS)

In this thesis, the author studies the band structure in Platinum nuclei and has divided his work in 5 parts: in the first, the author makes a general presentation of nucleus physics with a high angular momentum and introduces to the deformed nucleus notion -axial, triaxial or mixing of different deformations. The notion of form co-existence will be used to interpret the experimental results. In the second part, the author describes the detection means which have been used to make measurements. An abstract of theoretical notions, usefull for the understanding of fusion-evaporation reaction is presented. The author explains the details, performances and different modes of using of 'Chateau de cristal' and others used spectrometers. In the third part, the author presents all experimental data. He has effected ? coincidence measurements for Pt, Au and Ir nuclei. In the fourth part, for a classical analysis or an interpretation in the frame of cranking model the author presents theoretical models which are adapted at the study of high spin states and band structures

73

New silicon band in haiweeite structure

International Nuclear Information System (INIS)

Structure of (Enraf-Nonius automatic diffractometer, R = 11.8 %, 1260 I > 3?(I)) of haiweeite mineral from Brazil was determined. The experimental data were obtained from block monocrystal with up to 10 Deg block disorientation. Parameters of rhombic cell are as follows: a 14.263(3), b = 17.988(3), c = 18.395(3) A, V = 4719.5 A3, sp.gr P212121, Z = 8. Chemical formula of Ca(UO2)2[Si5O12(OH)2] x 4.5H2O mineral was defined more exactly and its structure peculiarities were determined in composition with other members of the group including occurrence of the original silicon-oxygen band

74

Photonic Crystal Narrow Band Filters Using Biperiodic Structures

Directory of Open Access Journals (Sweden)

Full Text Available In this study, we propose a new type of photonic crystal band-pass and band-stop filter based on biperiodic structure. Usually two types of photonic crystal band-pass filters are utilized in optical circuit. In the first one Fabry-Perot cavities are used while in the second one cavity-coupled waveguide are used. We optimize the second structure in this study. Then we show that by little changing in the band-pass structure, a band-stop filter is attained. Using Finite-Difference Time-Domain (FDTD method we achieve output efficiency over 98% for band-pass filter and below 3% for band-stop filter. Also we investigate filter tunability parameters which affecting central frequency of these filters. Further analysis shows that the central frequency of transmission band (stop band can be changed by altering the refractive index of bigger rods in biperiodic structure.

M. Djavid

2008-01-01

75

Temperature dependence of the electronic band structure of (111) surface Si

International Nuclear Information System (INIS)

The temperature dependence of the electronic band structure of the (111) surface Si has been investigated.The self-consistent pseudopotential method within bounds of the layered superlattice model was used. The peculiarities of the temperature dependence of direct and indirect band gap and electronic density of states of the (111) surface Si are discussed in details

76

Band structure calculations using the transcorrelated method

We have been developing a new wave-function-based method for calculating the electronic properties of solids. The main feature of this method, called the transcorrelated (TC) method, is a similarity transformation of the Hamiltonian using the Jastrow-Slater trial wave function, which leads to an effective non-hermitian Hamiltonian with three-body interactions. Correlation effects are incorporated in the effective Hamiltonian via the similarity transformation. The wave function is optimized by solving a set of Hartree-Fock-like single particle equations derived by minimizing the variance of the effective Hamiltonian. In this work, the TC method is applied to the band structure calculations of sp semiconductors. In the TC method, Koopmans' theorem holds, in which the eigenenergies of the single particle orbitals are interpreted as the ionization energies and electron affinities. By applying the Jastrow function derived from the random phase approximation (RPA), the screening effect is incorporated in the effective Hamiltonian, which significantly reduces the value of band gaps of semiconductors from their Hartree-Fock values.

Sakuma, Rei; Sodeyama, Keitaro; Tsuneyuki, Shinji

2007-03-01

77

Multiple band structures in ^179Au.

The very proton-rich nucleus ^179Au has recently been studied in recoil-mass and decay tagged ? -ray spectroscopic measurements with the Gammasphere array at the Argonne Fragment Mass Analyzer. The main sequences of the level scheme, established so far, are rotational structures which can be associated with proton h_9/2 and i_13/2 states coupled to prolate cores. The excitation energy and the moments of inertia of the i_13/2 yrast band in ^179Au are of special interest. Together with the recently reported high-spin work on ^181,183Au(W.F. Mueller et al., Phys. Rev. C59, 2009 (1999).) a solid set of experimental information on this proton intruder state is available now, and systematic trends in bandhead energies and deformation near the neutron i_13/2 midshell can be addressed. These trends will be presented and compared with the features of prolate bands in neighboring nuclei, e.g. in the Hg isotopes.

Mueller, W. F.; Balabanski, D.; Bingham, C. R.; Hartley, D.; Reviol, W.; Riedinger, L. L.; Zeidan, O.; Carpenter, M. P.; Janssens, R. V. F.; Khoo, T. L.; Kondev, F.; Seweryniak, D.; Uusitalo, J.; Wiedenhover, I.; Jenkins, D.; Wadsworth, R.

1999-10-01

78

The photonic band dispersion and density of states (DOS) are calculated for the three-dimensional (3D) hexagonal structure corresponding to a distributed Bragg reflector patterned with a 2D triangular lattice of circular holes. Results for the Si/SiO$_2$ and GaAs/AlGaAs systems determine the optimal parameters for which a gap in the 2D plane occurs and overlaps the 1D gap of the multilayer. The DOS is considerably reduced in correspondence with the overlap of 2D and 1D gaps....

Pavarini, E.; Andreani, L. C.

2002-01-01

79

Band structure calculations of Mo2BC under pressure

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

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

2010-03-01

80

Photonic Crystal Narrow Band Filters Using Biperiodic Structures

In this study, we propose a new type of photonic crystal band-pass and band-stop filter based on biperiodic structure. Usually two types of photonic crystal band-pass filters are utilized in optical circuit. In the first one Fabry-Perot cavities are used while in the second one cavity-coupled waveguide are used. We optimize the second structure in this study. Then we show that by little changing in the band-pass structure, a band-stop filter is attained. Using Finite-Difference Time-Domain (F...

Djavid, M.; Ghaffari, A.; Monifi, F.; Abrishamian, M. S.

2008-01-01

81

Electronic structure and electron momentum density in TiSi

Energy Technology Data Exchange (ETDEWEB)

We report the electron momentum density in titanium monosilicide using {sup 241}Am Compton spectrometer. Experimental Compton profile has been compared with the theoretical profiles computed using linear combination of atomic orbitals (LCAO). The energy bands, density of states and Fermi surface structures of TiSi are reported using the LCAO and the full potential linearized augmented plane wave methods. Theoretical anisotropies in directional Compton profiles are interpreted in terms of energy bands. To confirm the conducting behavior, we also report the real space analysis of experimental Compton profile of TiSi.

Ghaleb, A.M. [Department of Physics, College of Science, University of Kirkuk, Kirkuk (Iraq); Mohammad, F.M. [Department of Physics, College of Science, University of Tikreet, Tikreet (Iraq); Sahariya, Jagrati [Department of Physics, University College of Science, M.L. Sukhadia University, Udaipur 313001, Rajasthan (India); Sharma, Mukesh [Physics Division, Forensic Science Laboratory, Jaipur, Rajasthan (India); Ahuja, B.L., E-mail: blahuja@yahoo.com [Department of Physics, University College of Science, M.L. Sukhadia University, Udaipur 313001, Rajasthan (India)

2013-03-01

82

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

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

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

1992-08-01

83

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

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

1984-01-01

84

Band structure of SnTe studied by Photoemission Spectroscopy

We present an angle-resolved photoemission spectroscopy study of the electronic structure of SnTe, and compare the experimental results to ab initio band structure calculations as well as a simplified tight-binding model of the p-bands. Our study reveals the conjectured complex Fermi surface structure near the L-points showing topological changes in the bands from disconnected pockets, to open tubes, and then to cuboids as the binding energy increases, resolving lingering is...

Littlewood, P. B.; Mihaila, B.; Schulze, R. K.; Safarik, D. J.; Gubernatis, J. E.; Bostwick, A.; Rotenberg, E.; Opeil, C. P.; Durakiewicz, T.; Smith, J. L.; Lashley, J. C.

2010-01-01

85

Self energy corrections to the ''ab initio'' band structure: Chromium

International Nuclear Information System (INIS)

We describe the effect of many particle corrections to improve the electronic energy spectrum calculated in the framework of the Density Functional Formalism (DFF). We show that it is possible to consider an n particle diagram like a correction to the DFF results for electronic structure, if we take into account the electron-electron interaction with non-zero transmitted momentum q or energy ?. The model is proposed for calculating the leading term of the self-energy expansion as a power series in interactions, i.e. the second order term under the conditions q=O and ??O. This model is illustrated by calculating the electronic band structure and optical properties of anti ferromagnetic chromium. The self-energy correction leads to a better agreement between the theoretical calculations and experimental measurements of electronic properties. (author). 40 refs, 5 figs, 3 tabs

86

?-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.

87

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

88

Graphene Nano ribbon Conductance Model in Parabolic Band Structure

International Nuclear Information System (INIS)

Many experimental measurements have been done on GNR conductance. In this paper, analytical model of GNR conductance is presented. Moreover, comparison with published data which illustrates good agreement between them is studied. Conductance of GNR as a one-dimensional device channel with parabolic band structures near the charge neutrality point is improved. Based on quantum confinement effect, the conductance of GNR in parabolic part of the band structure, also the temperature-dependent conductance which displays minimum conductance near the charge neutrality point are calculated. Graphene nano ribbon (GNR) with parabolic band structure near the minimum band energy terminates Fermi-Dirac integral base method on band structure study. While band structure is parabola, semiconducting GNRs conductance is a function of Fermi-Dirac integral which is based on Maxwell approximation in nondegenerate limit especially for a long channel

89

Band Structure of Periodically Surface-Scattered Water Waves

Bloch wavefunctions are used to derive dispersion relations for water wave propagation in the presence of an infinite array of periodically arranged surface scatterers. For one dimensional periodicity (stripes), band gaps for wavevectors in the direction of periodicity are found corresponding to multiple Bragg scattering. The dependence of these band gaps as a function of scatterer density, strength, and water depth is analyzed. We find in contrast to band gap behavior in el...

Chou, Tom

1997-01-01

90

High spin band structure in 160Yb

International Nuclear Information System (INIS)

States in 160Yb were populated in the 148Sm(16O,4n) reaction at 90 to 110 MeV. The deduced level scheme is presented. Levels up to 30+ were seen; two side bands were also found. The data for the transitions within the bands are consistent with stretched E2 decay. 1 figure

91

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

92

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

93

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

94

Energy Technology Data Exchange (ETDEWEB)

Density changes between sheared zones and their surrounding amorphous matrix as a result of plastic deformation in a cold-rolled metallic glass (melt-spun Al{sub 88}Y{sub 7}Fe{sub 5}) were determined using high-angle annular dark-field (HAADF) detector intensities supplemented by electron-energy loss spectroscopy (EELS), energy-dispersive X-ray (EDX) and nano-beam diffraction analyses. Sheared zones or shear bands were observed as regions of bright or dark contrast arising from a higher or lower density relative to the matrix. Moreover, abrupt contrast changes from bright to dark and vice versa were found within individual shear bands. We associate the decrease in density mainly with an enhanced free volume in the shear bands and the increase in density with concomitant changes of the mass. This interpretation is further supported by changes in the zero loss and Plasmon signal originating from such sites. The limits of this new approach are discussed. - Highlights: • We describe a novel approach for measuring densities in shear bands of metallic glasses. • The linear relation of the dark-field intensity I/I{sub 0} and the mass thickness ?t was used. • Individual shear bands showed abrupt contrast changes from bright to dark and vice versa. • Density changes ranging from about ?10% to +6% were found for such shear bands. • Mixtures of amorphous/medium range ordered domains were found within the shear bands.

Rösner, Harald, E-mail: rosner@uni-muenster.de [Institut für Materialphysik, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Strasse 10, D-48149 Münster (Germany); Peterlechner, Martin [Institut für Materialphysik, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Strasse 10, D-48149 Münster (Germany); Kübel, Christian [Karlsruhe Institute of Technology (KIT), Institute of Nanotechnology (INT), Hermann-von-Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen (Germany); Karlsruhe Nano Micro Facility (KNMF), Karlsruhe Institute of Technology (KIT), D-76344 Eggenstein-Leopoldshafen (Germany); Schmidt, Vitalij [Institut für Materialphysik, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Strasse 10, D-48149 Münster (Germany); Wilde, Gerhard [Institut für Materialphysik, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Strasse 10, D-48149 Münster (Germany); Institute of Nanochemistry and Nanobiology, School of Environmental and Chemical Engineering, Shanghai University, Shanghai 200444 (China)

2014-07-01

95

International Nuclear Information System (INIS)

Density changes between sheared zones and their surrounding amorphous matrix as a result of plastic deformation in a cold-rolled metallic glass (melt-spun Al88Y7Fe5) were determined using high-angle annular dark-field (HAADF) detector intensities supplemented by electron-energy loss spectroscopy (EELS), energy-dispersive X-ray (EDX) and nano-beam diffraction analyses. Sheared zones or shear bands were observed as regions of bright or dark contrast arising from a higher or lower density relative to the matrix. Moreover, abrupt contrast changes from bright to dark and vice versa were found within individual shear bands. We associate the decrease in density mainly with an enhanced free volume in the shear bands and the increase in density with concomitant changes of the mass. This interpretation is further supported by changes in the zero loss and Plasmon signal originating from such sites. The limits of this new approach are discussed. - Highlights: • We describe a novel approach for measuring densities in shear bands of metallic glasses. • The linear relation of the dark-field intensity I/I0 and the mass thickness ?t was used. • Individual shear bands showed abrupt contrast changes from bright to dark and vice versa. • Density changes ranging from about ?10% to +6% were found for such shear bands. • Mixtures of amorphous/medium range ordered domains were found within the shear bands

96

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

97

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-09-28

98

Band-structure calculation of MBe13 (M = La, Ce, Th and U)

International Nuclear Information System (INIS)

The one-electron energy band structures for LaBe13, CeBe13, ThBe13 and UBe13 were calculated by the self-consistent APW method with the local density approximation. It was found that the Be s(p) bands form wide valence bands below a pseudogap at 0.8 eV below the Fermi energy Esub(F) in UBe13; and the Be p bands extend mostly above a pseudogap at 1.9 eV above Esub(F) in UBe13. Between these bands, there are M d-Be p mixed bands. In CeBe13 and UBe13, the f bands are inserted among the d-p mixed bands. Due to the squeezing effect of the p-f mixings from both above and below the f bands, the f band widths in CeBe13 and UBe13 are very small, only 1 eV in UBe13, much narrower than the experimentally observed PES-BIS peak, indicating the importance of the many-body effect. In LaBe13 and ThBe13, the f band widths are much larger, more than twice that in UBe13, due to the reversed p-f mixing effect. The p-f mixing parameters for these materials were also evaluated from the present band calculation. (author)

99

Hybrid density functional theory study of band gap tuning in AlN and GaN through equibiaxial strains

Structural transformation and the variation in the band gap of (0001) AlN and GaN films as a function of equibiaxial in-plane strain are studied using the HSE06 range-separated hybrid functional. Although AlN and GaN under strain share the same structural transition from wurtzite to a graphitelike phase, their electronic properties are significantly different. Both wurtzite and graphitelike AlN under strain can display either direct or indirect band structures, whereas the band gap of wurtzite GaN is always direct and graphitelike GaN always indirect. Furthermore, it is more difficult for AlN than GaN to obtain the graphitelike semi-metallic phase. Our results for GaN support the conclusions obtained from standard density functional theory [Dong et al., Appl. Phys. Lett. 96, 202106 (2010)

Duan, Yifeng; Qin, Lixia; Shi, Liwei; Tang, Gang; Shi, Hongliang

2012-01-01

100

Topological structure of the inter-band phase difference soliton in two-band superconductivity

Energy Technology Data Exchange (ETDEWEB)

Two-component superconductivity based on the two-band superconductor has a functional topology such as an inter-band phase difference soliton (i-soliton) to realize topological electronics (topolonics). Many gauge field theories are applied to investigate the topology of two-band superconductivity. To ease experimental and electronics applications, these theories should be refined. Weinberg-Salam theory and SU(2) (two-dimensional special unitary symmetry) gauge field theory are proper starting points. An effective extra force field because of the crystal structure and inter-band Josephson interaction, rather than spontaneous symmetry breaking, simplifies the conventional gauge field theory.

Tanaka, Y., E-mail: y.tanaka@aist.go.j [National Institute of Advanced Industrial Science and Technology, Tsukuba (Japan); Iyo, A. [National Institute of Advanced Industrial Science and Technology, Tsukuba (Japan); Tokiwa, K.; Watanabe, T. [Tokyo University of Science, Noda (Japan); Crisan, A. [University of Birmingham, Birmingham (United Kingdom); National Institute of Materials Physics, Bucharest (Romania); Sundaresan, A. [Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore (India); Terada, N. [Kagoshima University, Kagoshima (Japan)

2010-11-01

101

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

102

Electronic structure of the valence band of II--VI wide band gap semiconductor interfaces

In this work we present the electronic band structure for (001)--CdTe interfaces with some other II--VI zinc blende semiconductors. We assume ideal interfaces. We use tight binding Hamiltonians with an orthogonal basis ($s p^3 s^*$). We make use of the well--known Surface Green's Function Matching method to calculate the interface band structure. In our calculation the dominion of the interface is constituted by four atomic layers. We consider here anion--anion interfaces on...

Olguin, D.; Baquero, R.

1996-01-01

103

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

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

Colakerol, Leyla

104

The band energy structure of RbKSO4 crystals

Directory of Open Access Journals (Sweden)

Full Text Available The energy band structure of mechanically free and compressed RbKSO4 single crystals is investigated. It is established that the top of the valence band is located at the D point of the Brillouin zone [k = (0.5, 0.5, 0], the bottom of the conduction band lies at the ? point, and the minimum direct band gap Eg is equal to 5.80 eV. The bottom of the conduction band is predominantly formed by the K s, Li p, Rb s, and Rb p states hybridized with the S p and O p antibonding states. The pressure coefficients of the energy position of the valence and conduction band states and the band gap Eg are determined.

O.V.Bovgyra

2007-01-01

105

New Band Structures in A?110 Neutron-Rich Nuclei

International Nuclear Information System (INIS)

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

106

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

107

Design of a Miniaturized Dual Wide Band Frequency Selective Structure

This paper deals with the frequency selective property of a structure comprising of a two dimensional array of patches. This frequency selective surface (FSS) acts like a dual band reject filter. The proposed design has been investigated theoretically using Ansoft Designer® software in which the reflection and transmission band have been predicted by the method known as Method of Moment which is most complicated but its accuracy is best. Efforts have been given to achieve dual high band reje...

Shwetanki Singh; Partha Pratim Sarkar; Sarkar, D.; Biswas, S.

2013-01-01

108

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.

Darrouzet, F.; Decreau, P.M.E.

2004-01-01

109

Electronic band structure and linear optical properties of paraelectric KIO{sub 3}

Energy Technology Data Exchange (ETDEWEB)

The electronic energy band structure, partial (PDOS) and total density of states (DOS), and linear optical properties of the paraelectric KIO{sub 3} single crystal are calculated using density functional theory (DFT) in its local density approximation (LDA). The calculated band structure for paraelectric KIO{sub 3} indicates that the crystal has a direct bandgap. Using LDA and generalized gradient approximation (GGA), structural optimization has been performed. The optical spectra of the paraelectric KIO{sub 3} in the photon energy range up to 30 eV are investigated under the scissor approximation. The real and imaginary parts of the frequency-dependent linear dielectric function, as well as related quantities such as energy-loss function, refractive index and effective number of valence electrons, are calculated. The calculated structural optimization and bandgap of the paraelectric KIO{sub 3} have been compared with experimental data and have been found to be in good agreement with the experimental results.

Erdinc, Bahattin; Akkus, Harun [Physics Department, Yuzuncu Yil University, 65080 Van (Turkey)], E-mail: bahattinerdinc@yyu.edu.tr

2009-03-25

110

The electronic structure of heavy fermions: Narrow temperature independent bands

International Nuclear Information System (INIS)

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

111

Design of a Miniaturized Dual Wide Band Frequency Selective Structure

Directory of Open Access Journals (Sweden)

Full Text Available This paper deals with the frequency selective property of a structure comprising of a two dimensional array of patches. This frequency selective surface (FSS acts like a dual band reject filter. The proposed design has been investigated theoretically using Ansoft Designer® software in which the reflection and transmission band have been predicted by the method known as Method of Moment which is most complicated but its accuracy is best. Efforts have been given to achieve dual high band reject filtering with high band ratio (approx 3.18.

Shwetanki Singh

2013-01-01

112

Coupled Line Band Pass Filter with Defected Ground Structure for Wide Band Application

In this paper a novel wideband microstrip band pass filter is proposed. The band pass filter is designed with coupling between two L-shaped microstriplines and is terminated with a high impedance line. The three circle shapes are etched out at the ground plane and is called defected ground structure (DGS), which provides better return loss as well as it reduces harmonics. Simulated and measured results both are in true agreement with each other. Results show that the defected m...

Abhiruchi Nagpal,; Singhal, Dr P. K.

2014-01-01

113

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

114

Structure of nearly degenerate dipole bands in {sup 108}Ag

Energy Technology Data Exchange (ETDEWEB)

The high spin negative parity states of {sup 108}Ag have been investigated with the {sup 11}B + {sup 100}Mo 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 {sup 108}Ag is studied using the recently developed microscopic triaxial projected shell model approach. The observed energy levels and the ratio of the electromagnetic transition probabilities of these bands in this isotope are well reproduced by the present model. Further, it is shown that the partner band has a different quasiparticle structure as compared to the yrast band.

Sethi, J. [Tata Institute of Fundamental Research, Colaba, Mumbai 400 005 (India); Palit, R., E-mail: palit@tifr.res.in [Tata Institute of Fundamental Research, Colaba, Mumbai 400 005 (India); Saha, S.; Trivedi, T. [Tata Institute of Fundamental Research, Colaba, Mumbai 400 005 (India); Bhat, G.H.; Sheikh, J.A. [Department of Physics, University of Kashmir, Srinagar 190 006 (India); Datta, P. [Ananda Mohan College, Kolkata 700009 (India); Carroll, J.J. [US Army Research Laboratory, Adelphi, MD 20783 (United States); Chattopadhyay, S. [Saha Institute of Nuclear Physics, Kolkata 700064 (India); Donthi, R. [Tata Institute of Fundamental Research, Colaba, Mumbai 400 005 (India); Garg, U. [University of Notre Dame, Notre Dame, IN 46556 (United States); Jadhav, S.; Jain, H.C. [Tata Institute of Fundamental Research, Colaba, Mumbai 400 005 (India); Karamian, S. [Joint Institute for Nuclear Research, Dubna 141980 (Russian Federation); Kumar, S. [University of Delhi, Delhi 110007 (India); Litz, M.S. [US Army Research Laboratory, Adelphi, MD 20783 (United States); Mehta, D. [Panjab University, Chandigarh 160014 (India); Naidu, B.S. [Tata Institute of Fundamental Research, Colaba, Mumbai 400 005 (India); Naik, Z. [Sambalpur University, Sambalpur 143005 (India); Sihotra, S. [Panjab University, Chandigarh 160014 (India); and others

2013-08-09

115

Enhancement of phononic band gaps in ternary/binary structure

Energy Technology Data Exchange (ETDEWEB)

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.

Aly, Arafa H., E-mail: arafa16@yahoo.com [Physics department, Faculty of sciences, Beni-suef University, Beni Suef 62111 (Egypt); Mehaney, Ahmed [Physics department, Faculty of sciences, Beni-suef University, Beni Suef 62111 (Egypt)

2012-11-01

116

Quantum properties of optical field in photonic band gap structures.

A theoretical analysis of the quantum behaviour of radiation field's propagation in photonic band gaps structures is performed. In these initial calculations we consider linear inhomogeneous and nondispersive media. PMID:19424363

Severini, S; Sibilia, C; Bertolotti, M; Scalora, M; Bowden, C

2001-10-22

117

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

118

Photonic band structures of two-dimensional magnetized plasma photonic crystals

International Nuclear Information System (INIS)

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.

119

Possibility of experimental determination of band structure parameters in many-valley semiconductors

International Nuclear Information System (INIS)

A possibility to determine some parameters (density-of-state effective mass of different valleys, energy difference between energy valleys, impurity ionization energy levels split from different valleys) of the band structure in many-valley semiconductors based on experimental curve of overall concentration of charge carriers versus temperature is shown

120

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

121

Band gap, electronic structure, and surface electron accumulation of cubic and rhombohedral In2O3

The bulk and surface electronic structure of In2 O3 has proved controversial, prompting the current combined experimental and theoretical investigation. The band gap of single-crystalline In2 O3 is determined as 2.93±0.15 and 3.02±0.15 eV for the cubic bixbyite and rhombohedral polymorphs, respectively. The valence-band density of states is investigated from x-ray photoemission spectroscopy measurements and density-functional theory calculations. These show excellent agreement, supporting t...

King, Pdc; Veal, Td; Fuchs, F.; Wang, Cy; Payne, DJ; Bourlange, A.; Zhang, H.; Bell, Gr; Cimalla, V.; Ambacher, O.; Egdell, Rg; Bechstedt, F.; Mcconville, Cf

2009-01-01

122

Loop structure of the lowest Bloch band for a Bose-Einstein condensate

We investigate analytically and numerically Bloch waves for a Bose--Einstein condensate in a sinusoidal external potential. At low densities the dependence of the energy on the quasimomentum is similar to that for a single particle, but at densities greater than a critical one the lowest band becomes triple-valued near the boundary of the first Brillouin zone and develops the structure characteristic of the swallow-tail catastrophe. We comment on the experimental consequence...

Diakonov, Dmitri; Jensen, L. M.; Pethick, C. J.; Smith, H.

2001-01-01

123

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

124

Theoretically the Kohn-Sham band gap differs from the exact quasiparticle energy gap by the derivative discontinuity of the exchange-correlation functional. In practice for semiconductors and insulators the band gap calculated within any local or semilocal density approximations underestimates severely the experimental energy gap. On the other hand, calculations with an >exact> exchange potential derived from many-body perturbation theory via the optimized effective potential suggest that imp...

Gru?ning, Myrta; Marini, Andrea; Rubio Secades, A?ngel

2006-01-01

125

X-band RF structure thermal analysis and tests

Energy Technology Data Exchange (ETDEWEB)

The design of X-band multi-cell RF structures for particle accelerators requires an accurate estimation of the sensitivity to the mechanical deformations induced by the surface power loss on the metallic walls. The prediction of these effects is important for conceiving a tuning strategy that assures the correct structure operation when integrated into the accelerator complex. An experimental technique is proposed for preliminary testing of the mechanical deformations caused by a thermal load that can generate in the RF cavity a temperature gradient profile as close as possible to the real one induced by the electromagnetic power loss. Because we want to find a method that can be easily and cheaply implemented in the laboratory, a thermal radiator with uniform heating power density, placed on the axis of the RF cavity, has been chosen as heating source. A multi-physics finite-element code (ANSYS) has allowed comparing the measured temperature gradients with the computed ones. The good agreement validates the application of the code, which has been extended to the joint solution of the electromagnetic and thermal problem. Thus the sensitivity to deformations can be directly evaluated.

Bini, S. [INFN-Laboratori Nazionali di Frascati, 00044 Frascati (Italy); Chimenti, V. [INFN-Laboratori Nazionali di Frascati, 00044 Frascati (Italy); Palumbo, L. [Dipartimento di Energetica- Facolta di Ingegneria, Universita La Sapienza, 00161 Roma (Italy); Quintieri, L. [INFN-Laboratori Nazionali di Frascati, 00044 Frascati (Italy); Spataro, B. [INFN-Laboratori Nazionali di Frascati, 00044 Frascati (Italy); Tazzioli, F. [INFN-Laboratori Nazionali di Frascati, 00044 Frascati (Italy)]. E-mail: Franco.Tazzioli@lnf.infn.it

2007-07-21

126

X-band RF structure thermal analysis and tests

International Nuclear Information System (INIS)

The design of X-band multi-cell RF structures for particle accelerators requires an accurate estimation of the sensitivity to the mechanical deformations induced by the surface power loss on the metallic walls. The prediction of these effects is important for conceiving a tuning strategy that assures the correct structure operation when integrated into the accelerator complex. An experimental technique is proposed for preliminary testing of the mechanical deformations caused by a thermal load that can generate in the RF cavity a temperature gradient profile as close as possible to the real one induced by the electromagnetic power loss. Because we want to find a method that can be easily and cheaply implemented in the laboratory, a thermal radiator with uniform heating power density, placed on the axis of the RF cavity, has been chosen as heating source. A multi-physics finite-element code (ANSYS) has allowed comparing the measured temperature gradients with the computed ones. The good agreement validates the application of the code, which has been extended to the joint solution of the electromagnetic and thermal problem. Thus the sensitivity to deformations can be directly evaluated

127

Effective three-band structure in Fe-based superconductors

We present self-consistent calculations of the multi-gap structure measured in some Fe-based superconductors. These materials are known to have structural disorder in real space and a multi-gap structure due to the 3d Fe orbitals contributing to a complex Fermi surface topology with hole and electron pockets. Different experiments identify three s-wave–like superconducting gaps with a single critical temperature (T_c) . We investigate the temperature dependence of these gaps by a multi-band Bogoliubov-de Gennes theory at different pockets in the presence of effective hybridizations between some bands and an attractive temperature-dependent intra-band interaction. We show that this approach reproduces the three observed gaps and single Tc in different compounds of Ba1?xKxFe2As2, providing some insights into the inter-band interactions.

Möckli, David; de Mello, E. V. L.

2015-01-01

128

Band Structure and Optical Properties of Ordered AuCu3

DEFF Research Database (Denmark)

The optical spectra of ordered AuCu3 have been measured at low temperatures by a direct ellipsometric technique. We find several structural elements above the absorption edge as well as in the infrared. The measured spectra are interpreted in terms of the interband absorption calculated from an ab initio band structure obtained by the relativistic linear muffin-tin orbitals method. The band calculation reveals that ordered AuCu3 has distinct copper and gold d bands positioned in and hybridizing with an s band common to copper and gold. The calculated state density is found to be in good agreement with experiment. The Fermi surface is presented and is found to originate mainly in copper 4s and 4p states.

Skriver, Hans Lomholt; Lengkeek, H. P.

1979-01-01

129

(100) ideal-surface band structure for the series of Cu-based chalcopyrites

We use the Surface Green Function Matching (SGFM) method and a tight-binding hamiltonian to calculate the (100)-surface electronic band structure and local density of states of the series of Cu-based A^{I}B^{III}C2^{VI} chalcopyrites . We find four surface states in the optical gap energy region of s-p character and three surface states in the conduction band region of p-character. We show the trends of different characteristics within the series by means of figures and tables so that the quantitave behavior can be evaluated as well. We did not find Frontier Induced Semi-Infinite states of non-dispersive character in the studied range of energy within the valence band as we found in the case of the (112) surface electronic band structure for CuInSe2.

Tototzintle-Huitle, H

2005-01-01

130

Photonic band gap of superconductor-medium structure: Two-dimensional triangular lattice

Energy Technology Data Exchange (ETDEWEB)

Highlights: • Plane wave expansion is generalized to superconductor-medium periodic structure. • A wider band gap appears than that in conventional photonic crystals. • Part of original energy levels are rearranged upon consideration of the superconductivity. • Band gap width decreases monotonically with penetration length, but not with the filling factor. • Band gaps can be partially shut down or opened by adjusting filling factor. - Abstract: Based on London theory a general form of wave equation is formulated for both dielectric medium and superconductor. Using the wave equation and applying plane wave expansion, we have numerically calculated the band structures and density of states of a photonic crystal, whose intersection is constructed by a two-dimensional triangular lattice of superconductor padding in dielectric medium. Results indicate a wider band gap in the superconductor-medium photonic crystal than that in conventional photonic crystals. And part of original energy levels are found to be rearranged upon consideration of the superconductivity. The dependence of band gap on penetration length and filling factor is also discussed. Band gap width decreases monotonically with the penetration length, but not with the filling factor. Band gaps can be partially shut down or opened by adjusting filling factor.

Liu, Wan-guo; Pan, Feng-ming, E-mail: fmpan@nuaa.edu.cn; Cai, Li-wei

2014-05-15

131

Photonic band gap of superconductor-medium structure: Two-dimensional triangular lattice

International Nuclear Information System (INIS)

Highlights: • Plane wave expansion is generalized to superconductor-medium periodic structure. • A wider band gap appears than that in conventional photonic crystals. • Part of original energy levels are rearranged upon consideration of the superconductivity. • Band gap width decreases monotonically with penetration length, but not with the filling factor. • Band gaps can be partially shut down or opened by adjusting filling factor. - Abstract: Based on London theory a general form of wave equation is formulated for both dielectric medium and superconductor. Using the wave equation and applying plane wave expansion, we have numerically calculated the band structures and density of states of a photonic crystal, whose intersection is constructed by a two-dimensional triangular lattice of superconductor padding in dielectric medium. Results indicate a wider band gap in the superconductor-medium photonic crystal than that in conventional photonic crystals. And part of original energy levels are found to be rearranged upon consideration of the superconductivity. The dependence of band gap on penetration length and filling factor is also discussed. Band gap width decreases monotonically with the penetration length, but not with the filling factor. Band gaps can be partially shut down or opened by adjusting filling factor

132

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

133

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. Th AL) directions. These modes splitting correspond to optical longitudinal mode, optical transverse mode, acoustic longitudinal mode and acoustic transverse mode.

134

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

135

Rotational band structure in 132La

International Nuclear Information System (INIS)

'3'2La was studied using on-line gamma-spectroscopy through the reactions '124,126Te(11,10B, 3, 4n)132La. The excitation function was obtained with 10B(Elab=41.4; 45.4 and 48 MeV) in order to identify 132La gamma-transitions. Gamma-gamma coincidences and angular distributions were performed for the 126Te(10B, 4n)132La reaction. From the experimental results a rotational band with strongest M1 transitions and less intense 'cross-overs' E2 transitions was constructed. Using the methods of Bengtsson and Frauendorf the alignment (ix) and the Routhian (e') as a function of the angular velocity (?) were also obtained from the experimental data. It was observed a constant alignment up to ??0.4 MeV, and a signature-splitting ?e'=25keV. Preliminary triaxial Cranking-Shell Model calculations indicate that a ?=-8deg deformation is consistent with the signature-splitting value of 25 keV experimentally observed. (Author)

136

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

137

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

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

2014-12-01

138

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

139

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

140

Higher Dipole Bands in the NLC Accelerating Structure

We show that scattering matrix calculations for dipole modes between 23-43 GHz for the 206 cell detuned structure (DS) are consistent with finite element calculations and results of the uncoupled model. In particular, the rms sum wake for these bands is comparable to that of the first dipole band. We also show that for RDDS1 uncoupled wakefield calculations for higher bands are consistent with measurements. In particular, a clear 26 GHz signal in the short range wake is found in both results.

Adolphsen, C E; Dolgashev, V A; Ko, K; Li, Z; Miller, R

2000-01-01

141

Rotational band structure in odd-odd 132La

International Nuclear Information System (INIS)

The level scheme of 132La was obtained with in-beam gamma spectroscopy techniques using fusion evaporation reactions with /sup 10,11/B, 14N beams and isotopic targets of Te and Sn. Two rotational band structures were seen. One band, assigned to the ?h/sub 11/2/ direct product ?h/sub 11/2/, shows a smaller signature splitting as compared to the isotones 134Pr and 136Pm, indicating a slight reduction of triaxiality. The other band has been tentatively assigned the ?[422]3/2+ direct product ?h/sub 11/2/ configuration, and shows no signature splitting indicating a near prolate shape

142

Ab initio Green's function formalism for band structures

Using the Green's function formalism, an ab initio theory for band structures of crystals is derived starting from the Hartree-Fock approximation. It is based on the algebraic diagrammatic construction scheme for the self-energy which is formulated for crystal orbitals (CO-ADC). In this approach, the poles of the Green's function are determined by solving a suitable Hermitian eigenvalue problem. The method is not only applicable to the outer valence and conduction bands, it ...

Buth, Christian; Birkenheuer, Uwe; Albrecht, Martin; Fulde, Peter

2004-01-01

143

Electronic valence band structure of V2O5

International Nuclear Information System (INIS)

We present high-resolution ARPES measurements of V2O5 single crystals carried out with synchrotron radiation and He I resonance lamp. The obtained experimentally band structure in k parallel is compared with calculations, e.g. The aging behavior of different bands with time is studied. The degradation of the surface due to the high reactivity is discussed referring to the previous reported experimental work.

144

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

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

2012-03-26

145

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

146

Rotational band structure of the chiral candidate 134Pr

International Nuclear Information System (INIS)

Compete text of publication follows. Pairs of nearly degenerate dipole rotational bands with the same unique-parity configurations are known in several odd-odd nuclei. Such a structure was first studied in 134Pr, and it was considered as manifestation of chiral rotation of the triaxial nucleus. Later, considerably different quadrupole moments were measured for the two bands in this nucleus. This result strongly questioned the chiral interpretation, and new interpretation emerged emphasising the shape difference in the two bands. On the other hand, TRS calculations predict chiral band structure in this nucleus. In order to collect more information on the structure of this key-nucleus among chiral candidates, we studied the rotational bands of 134Pr by in-beam ?-spectroscopic methods. Excited states of 134Pr were populated using the 116Cd(23Na,5n) reaction at a beam energy of 115 MeV and studied using the GAMMASPHERE array. The level scheme of 134Pr was deduced using E?1-E?2-E?3 triple coincidences, which were sorted into Radware cubes. On the basis of the observed ???- coincidence relations several new bands have been identified. One of them is linked to the previous chiral-candidate structure through many M1 and E2 transitions, has the same parity, and the equal-spin levels are nearly degenerate. According to this observation, there are three nearly degenerate ?here are three nearly degenerate ?h11/2?h11/2 bands in 134Pr, what may express a need for rethinking the interpretation of the previous chiral candidate structure.

147

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

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

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

2014-07-01

148

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

149

The Three-Dimensional Structure of the Zodiacal Dust Bands

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

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

1997-06-01

150

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

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

Shi, Guangsha; Kioupakis, Emmanouil

2015-02-01

151

Electronic band structure and carrier effective mass in calcium aluminates

First-principles electronic band structure investigations of five compounds of the CaO-Al2O3 family, 3CaO.Al2O3, 12CaO.7Al2O3, CaO.Al2O3, CaO.2Al2O3 and CaO.6Al2O3, as well as CaO and alpha-, theta- and kappa-Al2O3 are performed. We find that the conduction band in the complex oxides is formed from the oxygen antibonding p-states and, although the band gap in Al2O3 is almost twice larger than in CaO, the s-states of both cations. Such a hybrid nature of the conduction band l...

Medvedeva, J. E.; Teasley, E. N.; Hoffman, M. D.

2007-01-01

152

International Nuclear Information System (INIS)

Using the technique of electron momentum spectroscopy (EMS) we have measured the oxygen 2p- and 2s-derived valence bands and lithium 1s-derived core level in lithium oxide. All three sets of bands have been measured in a single experiment allowing the energy gap between the bands to be determined. At the ? point the O(2p)-O(2s) band gap is measured to be 16.1±0.2 eV, and the O(2s)-Li(1s) band gap is 34.3±0.2 eV. We can also determine bandwidths since EMS measures the full band structure directly, resolved both in energy and momentum. As expected, the O(2s) and Li(1s) bands are essentially non-dispersing, while the O(2p) has an observed width of 1.6±0.2 eV. The experiment is compared with calculations using the linear combination of atomic orbitals approach. At the Hartree-Fock (HF) level these calculations overestimate the gap between the valence bands and the width of the O(2p) band. The three density functional methods used give a reduced intervalence band gap and bandwidth. The hybrid gradient corrected method, PBE0 (where PBE stands for 'Perdew-Burke-Ernzerhof'), gives the closest agreement for the band gap at 16.7 eV, while the gradient corrected method, PBE, gives the best value for the bandwidth at 2.0 eV. At all levels the O(2s)-Li(1s) gap is underestimated; HF gives the closest agreement at 31.8 eV. (author)

153

Dispersive Elastodynamics of 1D Banded Materials and Structures: Design

Within periodic materials and structures, wave scattering and dispersion occur across constituent material interfaces leading to a banded frequency response. In an earlier paper, the elastodynamics of one-dimensional periodic materials and finite structures comprising these materials were examined with an emphasis on their frequency-dependent characteristics. In this work, a novel design paradigm is presented whereby periodic unit cells are designed for desired frequency band properties, and with appropriate scaling, these cells are used as building blocks for forming fully periodic or partially periodic structures with related dynamical characteristics. Through this multiscale dispersive design methodology, which is hierarchical and integrated, structures can be devised for effective vibration or shock isolation without needing to employ dissipative damping mechanisms. The speed of energy propagation in a designed structure can also be dictated through synthesis of the unit cells. Case studies are presented ...

Hussein, M I; Scott, R A

2006-01-01

154

Valence band structure of AlN probed by photoluminescence

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

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

2008-01-01

155

Fluorescent and skeletal density banding in Porites lutea from Papua New Guinea and Indonesia

Shallow water Porites lutea corals were collected along two transects normal to mainland shorelines, parallel to gradients in water quality: one, 7 km long, near Motupore Island in South Papua New Guinea, the other, 70 km long, from Jakarta Bay along the Pulau Seribu chain in the Java Sea. The corals were slabbed and studies were made of skeletal density bands as revealed by X-ray photography and fluorescent bands as revealed by ultraviolet light. Water quality measurements and rain-fall data were assembled for the two areas and related to skeletal banding patterns. For both areas, with increasing distance form mainland there is a decrease in overall brightness of fluorescence in corals and an increase in the contrast between bright and dull fluorescent bands. Fluorescence is bright, but seasonal banding is obscure in corals within about 2 km of stream mouths at Motopure and about 5 km of the coast in Jakarta Bay; this suggests that, despite low freshwater run-off during dry seasons, there are sufficient organic compounds which cause fluorescence in coral skeletons, to swamp seasonal effects. During the wet seasons, deluges of freshwater consequent on mainland rainfall of greater than about 150 mm/ month extend at least 7 km offshore in the Motupore area and perhaps tens of kilometres into Java Sea, giving distinctive bright and dull fluorescent banding in off-shore corals. The fluorescent banding pattern within corals on the Motupore reefs is similar in most corals along the transect and it correlates well with the Port Moresby monthly rainfall data. This relationship suggests that the same body (or bodies) of freshwater affect all reefs of the area during the wet season. The fluorescent banding in Java Sea corals does not show a precise correlation with either mainland or island monthly rainfall data; indeed the pattern of fluorescent banding on Pulau Seribu can only be matched in corals from reefs less than about 25 km apart. This suggests that in this area discrete water bodies carrying the relevant organic acids for coral fluorescence affect the fringing reefs on the chain of islands. Comparisons of fluorescent and density banding have revealed that for these areas, in general, periods of high freshwater run-off are times of deposition of less dense skeleton in Porites lutea corals.

Scoffin, Terence P.; Tudhope, Alexander W.; Brown, Barbara E.

1989-01-01

156

Photonic band edge effects in finite structures and applications to chi 2 interactions.

Using the concept of an effective medium, we derive coupled mode equations for nonlinear quadratic interactions in photonic band gap structures of finite length. The resulting equations reveal the essential roles played by the density of modes and effective phase matching conditions necessary for the strong enhancement of the nonlinear response. Our predictions find confirmation in an experimental demonstration of significant enhancement of second harmonic generation near the photonic band edge. The measured conversion efficiency is in good agreement with the conversion efficiency predicted by the effective-medium model. PMID:11461430

D'Aguanno, G; Centini, M; Scalora, M; Sibilia, C; Dumeige, Y; Vidakovic, P; Levenson, J A; Bloemer, M J; Bowden, C M; Haus, J W; Bertolotti, M

2001-07-01

157

Density Functional Theory of Structural and Electronic Properties of III-N Semiconductors

International Nuclear Information System (INIS)

In this wok, we present the density functional theory (DFT) calculations of cubic III-N based semiconductors by using the full potential linear augmented plane-wave method plus local orbitals as implemented in the WIEN2k code. Our aim is to predict the pressure effect on structural and electronic properties of III-N binaries and ternaries. Results are given for structural properties (e.g., lattice constant, elastic constants, bulk modulus, and its pressure derivative) and electronic properties (e.g., band structure, density of states, band gaps and band widths) of GaAs, GaN, AlN, and InN binaries and GaAsN ternaries. The proposed model uses GGA exchange-correlation potential to determine band gaps of semiconductors at ?, L and X high symmetry points of Brillouin zone. The results are found in good agreement with available experimental data for structural and electronic properties of these semiconductors.

158

Photonic Band Gap structures: A new approach to accelerator cavities

Energy Technology Data Exchange (ETDEWEB)

We introduce a new accelerator cavity design based on Photonic Band Gap (PGB) structures. The PGB cavity consists of a two-dimensional periodic array of high dielectric, low loss cylinders with a single removal defect, bounded on top and bottom by conducting sheets. We present the results of both numerical simulations and experimental measurements on the PGB cavity.

Kroll, N. [California Univ., San Diego, La Jolla, CA (United States). Dept. of Physics]|[Stanford Linear Accelerator Center, Menlo Park, CA (United States); Smith, D.R.; Schultz, S. [California Univ., San Diego, La Jolla, CA (United States). Dept. of Physics

1992-12-31

159

International Nuclear Information System (INIS)

Photoemission, LEED, and AES measurements were made on the mechanically polished (111) surface of a type IIa diamond. No emission from filled states in the fundamental gap was found over the photon energy range 13.3 eV< or =h?< or =200 eV. This result, coupled with the sharp 1 x 1 LEED patterns which were obtained and the relative cleanliness (of elements which can be detected by AES) of the diamond (< or approx. =1 at.% oxygen, <0.5 at.% Si) suggests hydrogen termination of the lattice. Photoelectric yield measurements demonstrate the photoelectric threshold to be at band gap energy radiation. Investigation of the photoemission electron distribution curves (EDC's) shows that, while the electron affinity at the surface is always positive, band bending is sufficient to result in an effective negative electron affinity under certain conditions. A variable surface dipole on the atomic scale, possibly due to the adsorption--desorption of a background gas, is reported. A study of the relative cross section of the upper (p-like) versus the lower (s-like) portion of the diamond valence band indicates comparable cross sections at a photon energy h?=160 eV

160

DEFF Research Database (Denmark)

The electronic energy-band structure of tungsten has been calculated by means of the relativistic-augmented-plane-wave method. A series of mutually related potentials are constructed by varying the electronic configuration and the amount of Slater exchange included. The best band structure is obtained from an ad hoc potential based on a Dirac-Slater atomic calculation for the ground-state configuration and with full Slater exchange in the atomic as well as in the crystal potential. The selection of this best potential is justified by comparing the calculated band structure to Fermi-surface experiments and to optical-reflectance measurements up to 5-eV photon energy. The temperature and strain responses in the band structure are estimated from band calculations with four different lattice constants. The band structure was determined in the entire Brillouin zone and is applied to a calculation of photoemission spectra from W single crystals. The nondirect as well as the direct models for bulk photoemission processes are investigated. The emission from the three low-index surfaces (100), (110), and (111) exhibits strong dependence on direction and acceptance cone. According to the present band model there should essentially be no emission normal to the (110) face for photon energies between 9.4 and 10.6 eV. Experimental observation of emission in this gap, however, implies effects not included in the simple bulk models. In particular, effects arising from surface emission have been considered, i.e., emission of those electrons which are excited in a single-step process from initial states near the surface to final states outside the crystal. The electrons that are emitted from the surface in directions perpendicular to the crystal planes carry information on the one-dimensional surface density of states. The present work includes a crude estimate of this surface density of states, which is derived from the bulk band structure by narrowing the d bands according to an effective number of neighbors per surface atom. Estimates of surface relaxation effects are also included.

Christensen, N. Egede; Feuerbacher, B.

1974-01-01

161

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

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

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

2015-01-01

162

Dispersive Elastodynamics of 1D Banded Materials and Structures: Design

Within periodic materials and structures, wave scattering and dispersion occur across constituent material interfaces leading to a banded frequency response. In an earlier paper, the elastodynamics of one-dimensional periodic materials and finite structures comprising these materials were examined with an emphasis on their frequency-dependent characteristics. In this work, a novel design paradigm is presented whereby periodic unit cells are designed for desired frequency ban...

Hussein, M. I.; Hulbert, G. M.; Scott, R. A.

2006-01-01

163

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

164

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

165

High Density Excitation Effect of the Indirect Band Luminescence in Thallous Halides*

A broad band luminescence is observed at the indirect gap region in highly purified TlBr and TlCl crystals under high density excitation. From the analysis of the line shape, power dependence, lifetime and some characteristic features of the luminescence, it is discussed the possibility that the luminescence is associated with an LA-phonon assisted indirect recombination (X6+-R6-) of electron-hole liquid (EHL). Equilibrium density, binding energy and other parameters of EHL are estimated and it is presumed that the hole-phonon scattering is dominant in their recombination process.

Takiyama, Ken; Nakahara, Junichiro; Takenaka, Hisashi; Kobayashi, Koichi; Fujita, Toshiaki; Fujii, Atsuhiro

1996-01-01

166

Electronic band structure of magnetic bilayer graphene superlattices

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-09-28

167

Unlimited solid solution Fe1-xCoxGa3 was prepared from Ga flux. Its crystal structure was refined for Fe0.5Co0.5Ga3 (P42/mnm, a=6.2436(9), c=6.4654(13), Z=4) and showed no ordering of the metal atoms. A combination of the electronic band structure calculations within the density functional theory (DFT) approach and 69,71Ga nuclear quadrupole resonance (NQR) spectroscopy clearly shows that the Fe-Fe and Co-Co dumbbells are preferred to the Fe-Co dumbbells in the crystals structure. The band structure features a band gap of about 0.4 eV, with the Fermi level crossing peaks of a substantial density of electronic states above the gap for x>0. The solid solution is metallic for x>0.025. The study of the nuclear spin-lattice relaxation shows that the rate of the relaxation, 1/T1, is very sensitive to the Co concentration and correlates well with the square of the density of states at the Fermi level, N2(EF).

Verchenko, V. Yu.; Likhanov, M. S.; Kirsanova, M. A.; Gippius, A. A.; Tkachev, A. V.; Gervits, N. E.; Galeeva, A. V.; Büttgen, N.; Krätschmer, W.; Lue, C. S.; Okhotnikov, K. S.; Shevelkov, A. V.

2012-10-01

168

We discuss the linear dispersive properties of finite one-dimensional photonic band-gap structures. We introduce the concept of a complex effective index for structures of finite length, derived from a generalized dispersion equation that identically satisfies the Kramers-Kronig relations. We then address the conditions necessary for optimal, phase-matched, resonant second harmonic generation. The combination of enhanced density of modes, field localization, and exact phase matching near the band edge conspire to yield conversion efficiencies orders of magnitude higher than quasi-phase-matched structures of similar lengths. We also discuss an unusual and interesting effect: counterpropagating waves can simultaneously travel with different phase velocities, pointing to the existence of two dispersion relations for structures of finite length. PMID:11970354

Centini, M; Sibilia, C; Scalora, M; D'Aguanno, G; Bertolotti, M; Bloemer, M J; Bowden, C M; Nefedov, I

1999-10-01

169

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

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

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

2015-03-01

170

International Nuclear Information System (INIS)

The band structure of metallic sodium is calculated, using for the first time the self-consistent field variational cellular method. In order to implement the self-consistency in the variational cellular theory, the crystal electronic charge density was calculated within the muffin-tin approximation. The comparison between our results and those derived from other calculations leads to the conclusion that the proposed self-consistent version of the variational cellular method is fast and accurate. (author)

171

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

172

Band gap narrowing in nitrogen-doped La2Ti2O7 predicted by density-functional theory calculations.

In order to reveal the origin of enhanced photocatalytic activity of N-doped La2Ti2O7 in both the visible light and ultraviolet light regions, its electronic structure has been studied using spin-polarized conventional density functional theory (DFT) and the Heyd-Scuseria-Ernzerhof (HSE06) hybrid approach. The results show that the deep localized states are formed in the forbidden band when nitrogen solely substitutes for oxygen. Introducing the interstitial Ti atom into the N-doped La2Ti2O7 photocatalyst still causes the formation of a localized energy state. Two nitrogen substitutions co-exist stably with one oxygen vacancy, creating a continuum energy band just above the valence band maximum. The formation of a continuum band instead of mid-gap states can extend the light absorption to the visible light region without increasing the charge recombination, explaining the enhanced visible light performance without deteriorating the ultraviolet light photocatalytic activity. PMID:25751702

Zhang, Junying; Dang, Wenqiang; Ao, Zhimin; Cushing, Scott K; Wu, Nianqiang

2015-04-14

173

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

174

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)

175

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

176

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

177

Fine structure of bands in vibrational spectra of C60

International Nuclear Information System (INIS)

We investigated the fine structure of low-frequency vibrational bands in the Raman, infrared absorption, and diffuse reflectance spectra of C60 fullerite. It is related to the components of the overlapping Davydov and isotope splittings, as well as to a possible splitting of vibrations due to a reduction of the symmetry. It is shown that the splittings for the Raman Hg(1) and Ag(1) bands and the IR Fu(1,2) bands at room temperature are larger than those in the low-temperature phase. The intensification of the intermolecular interaction at higher temperatures is explained by the nonequilibrium vibrational excitation of the medium due to the nonlinear interaction of vibrational modes and a change of energy states.

178

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 heteros...

Cartoixa, X.; Ting, D. Z. -y; Mcgill, T. C.

2002-01-01

179

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

180

Development of X-band accelerating structures for high gradients

Short copper standing wave (SW) structures operating at an X-band frequency have been recently designed and manufactured at the Laboratori Nazionali di Frascati of the Istituto Nazionale di Fisica Nucleare (INFN) using the vacuum brazing technique. High power tests of the structures have been performed at the SLAC National Accelerator Laboratory. In this manuscript we report the results of these tests and the activity in progress to enhance the high gradient performance of the next generation of structures, particularly the technological characterization of high performance coatings obtained via molybdenum sputtering.

Bini, S.; Chimenti, V.; Marcelli, A.; Palumbo, L.; Spataro, B.; A. Dolgashev, V.; Tantawi, S.; D. Yeremian, A.; Higashi, Y.; G. Grimaldi, M.; Romano, L.; Ruffino, F.; Parodi, R.

2012-07-01

181

A NOVEL TRIPLE-BAND ELECTROMAGNETIC BANDGAP (EBG) STRUCTURE

A novel triple-band uni-planar electromagnetic bandgap (UC-EBG) structure is proposed in this paper. This EBG structure can be considered as distorted uni-planar compact-EBG (DUC-EBG) which is connected together by the meandered line inductor. Split ring resonators (SRR) are embedded in four pad corners and two L-shaped slots are etched at the central pad. The proposed EBG structure is modelled in three equivalent circuits. By using in-house developed computational code based on the FDTD meth...

Tran Minh Tuan; Dao Ngoc Chien; Huynh Nguyen Bao Phuong

2013-01-01

182

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

183

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 calcium-II bright G-band structures in images of the quiet Sun as tracers of kilo-Gauss magnetic flux-concentrations. In a 149" x 117" G-band image of the disk center at the activity minimum, 7593 small inter-granular structures ['IGS']were segmented with the `multiple-level tracking' pattern recognition algorithm ['MLT_4']. The scatter-plot of the continuum versus the G-band brightness sho...

Bovelet, Burkart; Wiehr, Eberhard

2012-01-01

184

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

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

Hofmann, A.; Pettenkofer, C.

2012-08-01

185

Electron density profile measurement using Ka-band microwave impulse radar reflectometer on LHD

International Nuclear Information System (INIS)

We have installed a ten channel Ka-band ultrashort pulsed radar reflectometer system in the Large Helical Device. The main objective of this diagnostic is to provide reliable information about the edge electron density profile. The time-of-flight measurement technique is used for the delay time measurement of the reflected pulses from each cut-off layer in the plasma, in order to avoid a mixture of spurious radiation such as electron cyclotron emission and undesired reflection such as another polarization wave mode. As for the signal detection section, a filter bank system is applied; the reflected pulse shape is affected by the bandwidth of band pass filter; thus, the optimum bandwidth must be found experimentally. The reconstructed electron density profile is obtained using an Abel inversion method from the profile of the delay time as a function of the probing frequency. In density modulation experiments, the static island width can be estimated from the temporal change of the density profile

186

International Nuclear Information System (INIS)

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.

187

Effective band structure of correlated materials: the case of VO2

International Nuclear Information System (INIS)

Vanadium dioxide VO2 and its metal-insulator transition at T = 340 K continue to receive considerable interest. The question whether the physics of the insulating low-temperature phase is dominated by the Mott or the Peierls scenario, i.e. by correlation or band effects, is still under debate. A recent cluster dynamical mean field theory calculation (Biermann et al 2005 Phys. Rev. Lett. 94 026404) suggests a combination of both effects, characterizing the transition as of a correlation-assisted Peierls type. In this paper we present a detailed analysis of the excitation spectrum of the insulating M1 phase of VO2, based on this calculation. We implement a scheme to analytically continue self-energies from Matsubara to real frequencies, and study the physics of the strong interactions, as well as the corresponding changes with respect to the density functional theory band structure within the local density approximation (LDA). We find that in the M1 phase lifetime effects are rather negligible, indeed allowing for an effective band structure description. A frequency-independent but orbital-dependent potential, constructed as an approximation to the full cluster dynamical mean field self-energy, turns out to satisfactorily reproduce the fully interacting one-particle spectrum, acting as a scissors operator which pushes the a1g bonding and eg? bands apart and, thus, opens the gapgap

188

Band structure of V2O3 and Ti2O3

International Nuclear Information System (INIS)

A previous calculation of the band structure of trigonal V2O3 and Ti2O3 by Nebenzahl and Weger (Nebenzahl, I. and Weger, M., 1969, Phys. Rev. vol. 184, 936; 1971, Phil. Mag. vol. 24, 1119) is improved, taking a more rigorous treatment and including the effect of covalency. The agreement obtained with experimental results is good. It is found that the width of the 3d band is about 9eV for V2O3 and 11eV for Ti2O3; this band is composed of a wide esub(sigma) and a narrow tsub(2g) sub-band. The tsub(2g) sub-band is the lower; its width is about 3eV for V2O3 and 4eV for Ti2O3, and the Fermi level lies within it. The density of states at the Fermi level is high for V2O3, and low for Ti2O3. It is shown that the inclusion of electron-electron interactions can bring about a metal-to insulator transition in Ti2O3 in terms of a band-crossing model. (author)

189

Length Dependence of Band Structure in Carbon Nanotubes of Ultra Small Diameter

Directory of Open Access Journals (Sweden)

Full Text Available The paper presents results of a study of the band structure and related parameters and also the bond energy of single-walled carbon nanotubes carried out using semiempirical methods and ab initio density functional theory implemented in Gaussian 2003 framework. Much attention is paid to the dependency of the values mentioned on the length and on the chirality of the tubes. Both the infinite and the finite open-ended nanotubes are considered. It was found that the dependency of the band gap on the diameter has oscillating character for infinite zigzag semiconducting tubes. It was also found that finite armchair nanotubes have non-zero band gap which decreases showing oscillations with the length and decreases monotonically with the diameter.

Ganin A.A.

2013-09-01

190

Band gap and electronic structure of MgSiN{sub 2}

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-09-15

191

International Nuclear Information System (INIS)

For the analysis of observed magnetic neutron factors of transition metals and alloys deffdifferent methods are being used. These methods are i) fitting of theoretical free-ion form factors to the experimental data, ii) Fourier analysis, as introduced by Moon, which does not require any a knowledge of the form factor but, instead, extracts its spin and orbital parts from the data, and iii) a modified version of ii) that properly takes into account the full symmetry of the crystal lattice. Spherical spin form factors appearing in i), ii) and iii) are compared with those based upon band structure calculations for Fe and Ni. It is found that only the results of iii) are in agreement with band theory. Since neither band theory nor method iii) leads to the existence of a uniform negative spin density this concept should be abandoned. (orig.)

192

Band gap and electronic structure of MgSiN2

International Nuclear Information System (INIS)

Density functional theory calculations and electron energy loss spectroscopy indicate that the electronic structure of ordered orthorhombic MgSiN2 is similar to that of wurtzite AlN. A band gap of 5.7?eV was calculated for both MgSiN2 (indirect) and AlN (direct) using the Heyd-Scuseria-Ernzerhof approximation. Correction with respect to the experimental room-temperature band gap of AlN indicates that the true band gap of MgSiN2 is 6.2?eV. MgSiN2 has an additional direct gap of 6.3?eV at the ? point.

193

Plasmonic band structure controls single-molecule fluorescence.

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

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

2013-10-22

194

Band structure of metal diboride ZrB2 under high pressure

International Nuclear Information System (INIS)

The effect of pressure on the band structure, density of states (DOS), electronic charge distribution and superconductivity of Zirconium diboride (ZrB2) is investigated. The normal pressure band structure, DOS and superconducting transition temperature of ZrB2 agree well with the previous calculations. The high pressure band structure exhibits significant deviations from the normal pressure band structure. It is found that, the charge transfer from s state to p and d states will cause superconductivity in ZrB2. The Tc value of ZrB2 at the normal pressure is found to be 3.9 K which is comparable with the previous theoretical observation of 5.5 K. On further increase of pressure, Tc increases considerably and it is 9.4 K at a pressure of 5.6 Mbar. The Tc values for ZrB2 are reported for the first time and this metal diboride ZrB2 is identified as pressure induced superconductor. (author)

195

Group Theory Approach to Band Structure: Scarf and Lame Hamiltonians

The group theoretical treatment of bound and scattering state problems is extended to include band structure. We show that one can realize Hamiltonians with periodic potentials as dynamical symmetries, where representation theory provides analytic solutions, or which can be treated with more general spectrum generating algebraic methods. We find dynamical symmetries for which we derive the transfer matrices and dispersion relations. Both compact and non-compact groups are fo...

Li, Hui; Kusnezov, Dimitri

1999-01-01

196

Group Theory Approach to Band Structure Scarf and Lame Hamiltonians

The group theoretical treatment of bound and scattering state problems is extended to include band structure. We show that one can realize Hamiltonians with periodic potentials as dynamical symmetries, where representation theory provides analytic solutions, or which can be treated with more general spectrum generating algebraic methods. We find dynamical symmetries for which we derive the transfer matrices and dispersion relations. Both compact and non-compact groups are found to play a role.

Li, H; Li, Hui; Kusnezov, Dimitri

1999-01-01

197

Spin current in junctions composed of multi-band superconductors with a spin-density wave

We calculate a nondissipative spin current and show that it can flow with or without a charge current. We consider a two-band model which can be applied to the description of Fe-based pnictides in coexistence regime of superconductivity and spin-density wave. Using quasiclassical Green?s functions approach and tunneling Hamiltonian method we show that there exists a possibility to switch off the Josephson current while leaving the spin current finite. Moreover, it is possible to have the critical Josephson current and the critical spin current being proportional to each other, thus giving a possibility to measure the spin current via the Josephson current. The underlying mechanism is the interfering hopping of electron–hole pairs between different bands of the superconductors composing the junction. This is an intrinsic property of the system and provides a unique and natural way to utilize junctions made solely of pnictides in promising applications in spintronics devices.

Moor, Andreas; Volkov, Anatoly F.; Efetov, Konstantin B.

2015-02-01

198

International Nuclear Information System (INIS)

Unlimited solid solution Fe1?xCoxGa3 was prepared from Ga flux. Its crystal structure was refined for Fe0.5Co0.5Ga3 (P42/mnm, a=6.2436(9), c=6.4654(13), Z=4) and showed no ordering of the metal atoms. A combination of the electronic band structure calculations within the density functional theory (DFT) approach and 69,71Ga nuclear quadrupole resonance (NQR) spectroscopy clearly shows that the Fe–Fe and Co–Co dumbbells are preferred to the Fe–Co dumbbells in the crystals structure. The band structure features a band gap of about 0.4 eV, with the Fermi level crossing peaks of a substantial density of electronic states above the gap for x>0. The solid solution is metallic for x>0.025. The study of the nuclear spin–lattice relaxation shows that the rate of the relaxation, 1/T1, is very sensitive to the Co concentration and correlates well with the square of the density of states at the Fermi level, N2(EF). - Graphical abstract: Rate of the nuclear spin–lattice relaxation, 1/T1, observed in the 69Ga NQR experiments for the intermetallic solid solution Fe1?xCoxGa3 is the highest for x=0.25 with the highest calculated density of electronic states at the Fermi level, N(EF); in general, 1/T1 correlates with N2(EF). Highlights: ? Fe1?x1?xCoxGa3 solid solution is prepared in single crystalline form from Ga flux. ? In the crystal structure Fe–Fe and Co–Co dumbbells are preferred to Fe–Co dumbbells. ? Metal-to-semiconductor transition occurs at 069,71Ga NQR spectra efficiently probe local environment of two independent Ga atoms. ? Rate of nuclear spin–lattice relaxation follows squared DOS at the Fermi level.

199

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.

200

Density banding in corals: barcodes of past and current climate change

The predicted sea surface temperature (SST) rise over the next decades is likely hazardous to coral health because precipitation of the calcareous skeleton depends primarily on SST. Temperature modulates vertical growth and density of the skeleton with seasonal SST changes resulting in an alternation of high-density and low-density bands (HDB and LDB). Notably, growth rates and the timing of the HDBs and LDBs relative to the seasons differ on a global scale within geographic regions. In this contribution, we use combined information of skeletal density and seasonally resolved oxygen isotope SST estimates from massive Porites from a Late Miocene (9 Ma) reef in the eastern Mediterranean Sea (Crete, Greece) to understand reef vulnerability over short and geological periods of time. Three types of HDB-SST relationships have been found: (1) coincidence of HDB with summer, (2) winter or (3) autumn and spring. The latter doubles HDBs in a year and implies maximum calcification is coupled to the taxon-specific optimum SST during the transitional seasons and reduced at its respective critical winter and summer SSTs. Modeling with a nonlinear temperature-calcification relationship reproduces the climate barcode of density bands. The model should be relevant for other poikilothermic carbonate producers in reefs and platforms and has implications for judging geographic distributions and causes of extinctions of corals, benthic carbonate communities and entire carbonate systems. With regard to the causes underlying expansion and demise of carbonate platforms and reefs in geological history, we expect the model predictions to help for a deeper understanding of biotic responses during hyperthermals or coolings and possibly also for identifying regions in the modern ocean where corals are endangered or taking advantage of global warming.

Brachert, T. C.; Reuter, M.; Krüger, S.; Böcker, A.; Lohmann, H.; Mertz-Kraus, R.; Fassoulas, C.

2013-12-01

201

de Haas--van Alphen effect and the band structure of UGe3

International Nuclear Information System (INIS)

de Haas--van Alphen measurements, band-structure calculations, and a model of the Fermi surface are presented for UGe3. This system is representative of the L12 structured UX3 compounds (where X is a group-III or -IV element) and is characterized as a spin-fluctuation system. Excellent agreement (considering the complications) is obtained between data and calculations. A large narrow peak in the density of states is found at the Fermi energy and is believed responsible for the nearly magnetic phenomena. Large mass enhancements are indicated. By studying UGe3, we attempt to provide some insight into the systematics of these UX3 systems

202

Electronic structure of the valence band of the II--VI wide band gap binary/ternary alloy interfaces

We present an electronic structure calculation of the valence band for some II--VI binary/ternary alloy interfaces. We use the empirical tight-binding method and the surface Green's function matching method. For the ternary alloys we use our previously set Hamiltonians they describe well the band gap change with composition obtained experimentally. At the interface domain, we find three non-dispersive and two interface states besides the known bulk bands. The non-dispersive ...

Olguin, D.; Baquero, R.

1996-01-01

203

C-band accelerator structure with smooth shape couplers

International Nuclear Information System (INIS)

A new C-band accelerator structure for the SuperKEKB injector linac is under development. This structure corresponds to an upstream half part in a tandem connection of two structures. In order to suppress an RF breakdown around a coupler iris, a fat and smooth iris is adopted. The coupler dimensions such as an aperture of the iris and a diameter of the coupler cavity are first optimized by computer simulation and then decided by cold model measurements. An amount of coupler offset to retain electromagnetic field symmetry is also decided by simulations. The coupler body is processed by a milling machine. Its rough surface after milling is finished by electro-polishing. This structure will be installed in the beam line of the KEKB injector linac this summer. (author)

204

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

205

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

206

In his renormalization paper of the Kondo effect Wilson replaced the full band of s-electrons by a small number of ''Wilson states''. He started from a rather artificial symmetric band with constant density of states and constant interaction with the impurity. It is shown in the present paper that with a minor modification the Wilson states are optimally suited to treat the interaction of an impurity with an arbitrary s-band. Each Wilson state represents electrons of a whole...

Bergmann, Gerd

2007-01-01

207

International Nuclear Information System (INIS)

The [100], [110], and [111] Compton profiles and reciprocal form factors have been derived from Compton scattering measurements made with 60-keV 241Am ? rays on single-crystal samples of vanadium. The same quantities have also been obtained theoretically on the basis of a self-consistent linear-muffin-tin-orbital band-structure calculation, using the local-density approximation for the exchange-correlation potential. An r-space procedure was adopted to calculate the reciprocal form factor B(r) directly from the wave functions. The experimental and theoretical results are compared with previous 412-keV Compton scattering measurements and other band-structure calculations. All calculations overestimate the Compton profile anisotropies at low momenta

208

A first principle study of band structure of III-nitride compounds

Energy Technology Data Exchange (ETDEWEB)

The band structure of both phases, zinc-blende and wurtzite, of aluminum nitride, indium nitride and gallium nitride has been studied using computational methods. The study has been done using first principle full-potential linearized augmented plane wave (FP-LAPW) method, within the framework of density functional theory (DFT). For the exchange correlation potential, generalized gradient approximation (GGA) and an alternative form of GGA proposed by Engel and Vosko (GGA-EV) have been used. Results obtained for band structure of these compounds have been compared with experimental results as well as other first principle computations. Our results show a significant improvement over other theoretical work and are closer to the experimental data.

Ahmed, Rashid [Centre for High Energy Physics University of the Punjab, Lahore-54590 (Pakistan)]. E-mail: rasofi@hotmail.com; Akbarzadeh, H. [Department of Physics, Isfahan University of Technology, 841546 Isfahan (Iran, Islamic Republic of); Fazal-e-Aleem [Centre for High Energy Physics University of the Punjab, Lahore-54590 (Pakistan)

2005-12-15

209

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

210

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

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

2015-04-01

211

Reduction of Dislocation Density by Producing Novel Structures

HgCdTe, because of its narrow band gap and low dark current, is the infrared detector material of choice for several military and commercial applications. CdZnTe is the substrate of choice for HgCdTe as it can be lattice matched, resulting in low-defect-density epitaxy. Being often small and not circular, layers grown on CdZnTe are difficult to process in standard semiconductor equipment. Furthermore, CdZnTe can often be very expensive. Alternate inexpensive large circular substrates, such as silicon or gallium arsenide, are needed to scale HgCdTe detector production. Growth of HgCdTe on these alternate substrates has its own difficulty, namely large lattice mismatch (19% for Si and 14% for GaAs). This large mismatch results in high defect density and reduced detector performance. In this paper we discuss ways to reduce the effects of dislocations by gettering these defects to the edge of a reticulated structure. These reticulated surfaces enable stress-free regions for dislocations to glide to. In this work, a novel structure was developed that allows for etch pit density of less than 4 × 105/cm2 for HgCdTe-on-Si. This is almost two orders of magnitude less than the as-grown etch pit density of 1.1 × 107/cm2. This value of 3.35 × 105/cm2 is below the <1 × 106/cm2 or even the better <5 × 105/cm2 target for this research, making HgCdTe-on- alternate substrate density much more like that of HgCdTe-on-CdZnTe.

Stoltz, A. J.; Benson, J. D.; Jacobs, R.; Smith, P.; Almeida, L. A.; Carmody, M.; Farrell, S.; Wijewarnasuriya, P. S.; Brill, G.; Chen, Y.

2012-10-01

212

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

213

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

214

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

215

Damped structure for JLC X-band linac

International Nuclear Information System (INIS)

Accelerating structures with damping ports for higher modes have been investigated to apply to the JLC X-band linac. The external Q values were evaluated by Slater's tuning method using the computer code MAFIA. It was found by examining the dependence of the external Q value on the geometry of the iris of the damping ports that the structure with circumferential waveguides 11 mm wide was effective in damping the TM110 mode . The external Q values for some of the other higher modes were evaluated and it was found that TE111 mode is hard to damp in such a structure, though its impedance is expected not to be high. To estimate the degradation of the accelerating mode due to the damping ports, the dependence of the Q value and r/Q value on the geometry of the damping port were calculated. Those were about 16% and 4.2%, respectively. (Author) 7 refs., 7 figs., tab

216

Medium- and high-spin band structure of 134Pr

International Nuclear Information System (INIS)

Complete text of publication follows. Unambiguous identification of intrinsic chirality in rotating triaxial nuclei is one of the most intriguing questions of contemporary high-spin nuclear structure studies. The crossing, strongly linked ?I=1 rotational band structure, found in 134Pr, was the first experimental candidate for chiral rotation. In order to collect more information on the structure of this key-nucleus among chiral candidates, we studied the rotational bands of 134Pr by inbeam ?-spectroscopic methods. Excited states of 134Pr were populated using the 116Cd(23Na,5n) reaction at a beam energy of 115 MeV. The experimental setup consisted of the GAMMASPHERE array of 99 HPGe detectors in 16 rings covering a large fraction of the full solid angle. The experiment consisted of two runs; Run 1 performed with a thiner 1.00 mg/cm2 116Cd target backed with 15 mg/cm2 208Pb was aimed in ??-coincidence measurements, while Run 2 performed with a thicker self-supporting 1.22 mg/cm2 116Cd target was aimed in determination of ?-ray multipolarities in 134Pr. For the off-line analysis, the experimental data obtained were sorted using the BLUE and RADWARE software packages. The level scheme of 134Pr was deduced using E?1-E?2-E?3 triple events, which were sorted into Radware cubes. Typical coincideto Radware cubes. Typical coincidence spectra are presented in Figure 1. On the basis of the observed ???-coincidence relations several new bands were found besides the previously published four ones.

217

Band Structure Asymmetry of Bilayer Graphene Revealed by Infrared Spectroscopy

Energy Technology Data Exchange (ETDEWEB)

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

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

2008-12-10

218

Band structure and superconductivity in Lu at high pressures

International Nuclear Information System (INIS)

We report here the effect of pressure on the band structure and the superconducting behavior of the hcp metal lutetium. The present work shows that the average of the square of the phonon frequency is considerably increased under pressure and this effect is taken into account while calculating T/sub c/. The calculated T/sub c/ values are in fairly good agreement with the experimental trends. The question of s?d valence transfer under pressure as well as Heine's fifth-power law are discussed. We also report the variation of other parameters such as the electronic specific heat and conduction bandwidth with pressure

219

Band structure of odd-mass lanthanum nuclei

International Nuclear Information System (INIS)

Negative parity energy states in 121–131La have been studied using Projected Shell Model (PSM). Some nuclear structure properties like yrast spectra, back-bending in moment of inertia, reduced transition probabilities and band diagrams have been described. The experimental feature of the co-existence of prolate–oblate shapes in 125–131La isotopes has been satisfactorily explained by PSM results. Comparison of the theoretical data with their experimental counterparts has also been made. From the calculations, it is found that the yrast states arise because of multi-quasiparticle states. (author)

220

Electronic band structure of calcium selenide under pressure

Energy Technology Data Exchange (ETDEWEB)

Energy band structures under pressure of calcium selenide (CaSe) were calculated using the plane-wave pseudopotential code CASTEP. The results show a progressive transition from a direct to an indirect gap semiconductor at a pressure of about 2 GPa, in the B1 phase. An insulator-conductor change was also observed at 70 GPa, in the B2 phase. Concerning CaSe, these two results could not be evidenced in previous literature. Hence, our work is a first attempt in this direction.

Louail, L. [Faculty of Sciences, Department of Physics, University of Setif, Setif (Algeria)], E-mail: llouail@yahoo.fr; Haddadi, K.; Maouche, D.; Ali Sahraoui, F.; Hachemi, A. [Faculty of Sciences, Department of Physics, University of Setif, Setif (Algeria)

2008-09-01

221

Tunneling and the band structure of chaotic systems

International Nuclear Information System (INIS)

The dispersion laws of chaotic periodic systems are computed using the semiclassical periodic orbit theory to approximate the trace of the powers of the evolution operator. Aside from the usual real trajectories, complex orbits are also included. These turn out to be fundamental for a proper description of the band structure since they incorporate conduction processes through tunneling mechanisms. The results obtained, illustrated with the kicked-Harper model, are in excellent agreement with numerical simulations, even in the extreme quantum regime. (authors). 14 refs., 1 fig

222

We demonstrated direct band gap (DBG) electroluminescence (EL) at room temperature from n-type bulk germanium (Ge) using a fin type asymmetric lateral metal/Ge/metal structure with TiN/Ge and HfGe/Ge contacts, which was fabricated using a low temperature (peaked at 1.55 ?m was clearly observed even at a small current density of 2.2 ?A/?m. Superlinear increase in EL intensity was also observed with increasing current density, due to superlinear increase in population of elections in direct conduction band. The efficiency of hole injection was also clarified.

Wang, Dong; Maekura, Takayuki; Kamezawa, Sho; Yamamoto, Keisuke; Nakashima, Hiroshi

2015-02-01

223

Band structure effects for dripped neutrons in neutron star crust

International Nuclear Information System (INIS)

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 estimates for the entrainment coefficients, as required for hydrodynamical two fluid simulations of neutron star crust [nucl-th/0402057, astro-ph/0408083], which relate the momentum of one fluid to the particle currents of the other two fluids [Sov. Phys. JETP 42 (1976) 164]. The implications for the equilibrium neutron star crust structure are also briefly discussed

224

Reweighted atomic densities to represent ensembles of NMR structures

International Nuclear Information System (INIS)

A reweighted atomic probability density is introduced as a means of representing ensembles of NMR structures in a simple, concise and informative manner. This density is shown to give a better visual representation of molecular structure information than an unweighted density, and should provide a useful interactive graphics tool during the course of iterative NMR structure refinement. The approach is illustrated using several examples

225

Reweighted atomic densities to represent ensembles of NMR structures

Energy Technology Data Exchange (ETDEWEB)

A reweighted atomic probability density is introduced as a means of representing ensembles of NMR structures in a simple, concise and informative manner. This density is shown to give a better visual representation of molecular structure information than an unweighted density, and should provide a useful interactive graphics tool during the course of iterative NMR structure refinement. The approach is illustrated using several examples.

Schwieters, Charles D. [National Institutes of Health, Computational Bioscience and Engineering Laboratory, Center for Information Technology (United States)], E-mail: Charles.Schwieters@nih.gov; Clore, G. Marius [National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Laboratory of Chemical Physics (United States)], E-mail: mariusc@intra.niddk.nih.gov

2002-07-15

226

Band structure aspects of materials with localizing f-orbitals

International Nuclear Information System (INIS)

In those materials where the f-states are hybridized, a band structure provides a reasonable description of the ground state. This is amply demonstrated by the successful determination of the Fermi surfaces of CeSn3, URh3, Ulr3, and UGe3. But when the f-states become more local, inadequacies of the functionals employed yield incomplete localization. Thus, to obtain a good description of the Fermi surface for high field ferromagnetic CeSb, the local character of the f-orbitals is artifically forced to produce the standard rare earth model. When dealing with excited states, the ground state band structure provides only part of the story. Even thermal excitations can provide significant departures from the ground state as evidenced by the large enhancements found for some materials. The series USi3, UGe3, and USn3 (together with CeSn3) demonstrate the effect very well. NpSn3 provides a useful counter example demonstrating that such enhancements need not be a universal property of localization

227

Multi-band circular polarizer using planar spiral metamaterial structure.

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

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

2012-07-01

228

High gradient experiment for X-band travelling wave structure

International Nuclear Information System (INIS)

High gradient performance of a travelling wave X-band accelerating structure 20 cm long was examined. Various observables were measured such as RF pulse waveform at various positions, dark current versus accelerating field level, energy spectra of emitted electrons downstream and so on. The field level of 80 MV/m at the input coupler cell was obtained after 500 hours' conditioning at a typical repetition rate of 10 pps. This field level is equivalent to 70 MV/m accelerating field in 20 cm long structure. Peak dark current decreased down to 1 ?A level at accelerating field of 50 MV/m at the input coupler cell. (Author) 5 refs., 7 figs., tab

229

Electronic band structure and fermi surface of heavy-fermion neptunium superconductor NpPd5Al2

International Nuclear Information System (INIS)

Electronic band structure calculations were carried out for a new neptunium superconductor NpPd5Al2 using a relativistic linear-augmented plane wave method within a local density approximation. The Fermi energy in the band structure is found to be located just on the 5f-bands of the j=5/2 state with the extremely narrow band width and therefore the theoretical electronic specific heat coefficient ?b is extremely large, being ?b=74.0 mJ/(K2·mol), which is compared to ?=390 mJ/(K2·mol) estimated experimentally. NpPd5Al2 is an uncompensated metal. The main electron Fermi surface corresponds to a doughnut-like flat Fermi surface centered at the ? point which is connected with cylindrical Fermi surfaces elongated along the X-W-P line. (author)

230

Electronic Band Structure and Fermi Surface of Heavy-Fermion Neptunium Superconductor NpPd5Al2

Electronic band structure calculations were carried out for a new neptunium superconductor NpPd5Al2 using a relativistic linear-augmented plane wave method within a local density approximation. The Fermi energy in the band structure is found to be located just on the 5f-bands of the j=5/2 state with the extremely narrow band width and therefore the theoretical electronic specific heat coefficient ?b is extremely large, being ?b = 74.0 mJ/(K2\\cdotmol), which is compared to ? = 390 mJ/(K2\\cdotmol) estimated experimentally. NpPd5Al2 is an uncompensated metal. The main electron Fermi surface corresponds to a doughnut-like flat Fermi surface centered at the ? point which is connected with cylindrical Fermi surfaces elongated along the X-W-P line.

Yamagami, Hiroshi; Aoki, Dai; Haga, Yoshinori; ?nuki, Yoshichika

2007-08-01

231

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

232

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.

233

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

234

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

235

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

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

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

2001-08-01

236

International Nuclear Information System (INIS)

Strain changes the band structure of semiconductors. We use x-ray absorption spectroscopy to study the change in the density of conduction band (CB) states when silicon is uniaxially strained along the [1 0 0] and [1 1 0] directions. High stress can be applied to silicon nanomembranes, because their thinness allows high levels of strain without fracture. Strain-induced changes in both the sixfold degenerate ? valleys and the eightfold degenerate L valleys are determined quantitatively. The uniaxial deformation potentials of both ? and L valleys are directly extracted using a strain tensor appropriate to the boundary conditions, i.e., confinement in the plane in the direction orthogonal to the straining direction, which correspond to those of strained CMOS in commercial applications. The experimentally determined deformation potentials match the theoretical predictions well. We predict electron mobility enhancement created by strain-induced CB modifications.

237

We study the Q/B-band intensity ratio (IQ/B) of zinc tetraphenylporphyrin (ZnTPP) in various solvents from its electronic structure by utilizing the polarizable continuum model and density functional theory (DFT). The selected solvents are benzene, chloroform, dichloromethane, pyridine and methanol. The Q/B-band intensity ratio is simplified by dipole strength of HOMO ? LUMO and HOMO?1 ? LUMO from a two-level system, or fQ/B. The results show the linear correlation between the calculated fQ/B and the experimental IQ/B. This suggests that IQ/B of ZnTPP in solvents can be studied from dipole strength ratio from a two-level system, where the orbitals are determined by DFT. The change of fQ/B is due to the change of frontier molecular orbital shape of ZnTPP which are dominantly constructed by pz-orbital. In the core part of ZnTPP, the change of pz-orbital shape is inversely proportional to the solvent dielectric constant, ?.

Rusydi, Febdian; Gandaryus Saputro, Adhitya; Kasai, Hideaki

2014-08-01

238

Analysis of photonic band-gap structures in stratified medium

DEFF Research Database (Denmark)

Purpose - To demonstrate the flexibility and advantages of a non-uniform pseudo-spectral time domain (nu-PSTD) method through studies of the wave propagation characteristics on photonic band-gap (PBG) structures in stratified medium Design/methodology/approach - A nu-PSTD method is proposed in solving the Maxwell's equations numerically. It expands the temporal derivatives using the finite differences, while it adopts the Fourier transform (FT) properties to expand the spatial derivatives in Maxwell's equations. In addition, the method makes use of the chain-rule property in calculus together with the transformed space technique in order to make the algorithm flexible in terms of non-uniform spatial sampling. Findings - Through the studies of the wave propagation characteristics on PBG structures in stratified medium, it has been found that the proposed method retains excellent accuracy in the occasions where the spatial distributions contain step of up to five times larger than the original size, while simultaneously the flexibility of non-uniform sampling offers further savings on computational storage. Research limitations/implications - Research has been mainly limited to the simple one-dimensional (1D) periodic and defective cases of PBG structures. Nevertheless, the findings reveal strong implications that flexibility of sampling and memory savings can be realized in multi-dimensional structures. Practical implications - The proposed method can be applied to various practical structures in electromagnetic and microwave applications once the Maxwell's equations are appropriately modeled. Originality/value - The method validates its values and properties through extensive studies on regular and defective 1D PBG structures in stratified medium, and it can be further extended to solving more complicated structures. CPY Emerald Group Publishing Limited.

Tong, Ming-Sze; Yinchao, Chen

2005-01-01

239

Three-dimensional structure of low-density nuclear matter

International Nuclear Information System (INIS)

We numerically explore the pasta structures and properties of low-density nuclear matter without any assumption on the geometry. We observe conventional pasta structures, while a mixture of the pasta structures appears as a metastable state at some transient densities. We also discuss the lattice structure of droplets.

240

Three dimensional structure of low-density nuclear matter

We numerically explore the pasta structures and properties of low-density nuclear matter without any assumption on the geometry. We observe conventional pasta structures, while a mixture of the pasta structures appears as a metastable state at some transient densities. We also discuss the lattice structure of droplets.

Okamoto, Minoru; Yabana, Kazuhiro; Tatsumi, Toshitaka

2011-01-01

241

Three-dimensional structure of low-density nuclear matter

Energy Technology Data Exchange (ETDEWEB)

We numerically explore the pasta structures and properties of low-density nuclear matter without any assumption on the geometry. We observe conventional pasta structures, while a mixture of the pasta structures appears as a metastable state at some transient densities. We also discuss the lattice structure of droplets.

Okamoto, Minoru, E-mail: okamoto@nucl.ph.tsukuba.ac.jp [Graduate School of Pure and Applied Science, University of Tsukuba, Tennoudai 1-1-1, Tsukuba, Ibaraki 305-8571 (Japan); Advanced Science Research Center, Japan Atomic Energy Agency, Shirakata Shirane 2-4, Tokai, Ibaraki 319-1195 (Japan); Maruyama, Toshiki, E-mail: maruyama.toshiki@jaea.go.jp [Advanced Science Research Center, Japan Atomic Energy Agency, Shirakata Shirane 2-4, Tokai, Ibaraki 319-1195 (Japan); Graduate School of Pure and Applied Science, University of Tsukuba, Tennoudai 1-1-1, Tsukuba, Ibaraki 305-8571 (Japan); Yabana, Kazuhiro, E-mail: yabana@nucl.ph.tsukuba.ac.jp [Graduate School of Pure and Applied Science, University of Tsukuba, Tennoudai 1-1-1, Tsukuba, Ibaraki 305-8571 (Japan); Center of Computational Sciences, University of Tsukuba, Tennoudai 1-1-1, Tsukuba, Ibaraki 305-8571 (Japan); Tatsumi, Toshitaka, E-mail: tatsumi@ruby.scphys.kyoto-u.ac.jp [Department of Physics, Kyoto University, Kyoto 606-8502 (Japan)

2012-07-09

242

De Haas-van Alphen effect and LMTO band structure of LaSn3

International Nuclear Information System (INIS)

Results of de Haas-van Alphen experiments in the intermetallic compound LaSn3 can be explained by a linear muffin-tin orbital band structure calculation without involving the f bands of lanthanum. (author)

243

Exciton band structure of monolayer MoS2

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

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

2015-02-01

244

Role of interface band structure on hot electron transport

Knowledge of electron transport through materials and interfaces is fundamentally and technologically important. For example, metal interconnects within integrated circuits suffer increasingly from electromigration and signal delay due to an increase in resistance from grain boundary and sidewall scattering since their dimensions are becoming shorter than the electron mean free path. Additionally, all semiconductor based devices require the transport of electrons through materials and interfaces where scattering and parallel momentum conservation are important. In this thesis, the inelastic and elastic scattering of hot electrons are studied in nanometer thick copper, silver and gold films deposited on silicon substrates. Hot electrons are electron with energy greater than kBT above the Fermi level (EF). This work was performed utilizing ballistic electron emission microscopy (BEEM) which is a three terminal scanning tunneling microscopy (STM) technique that measures the percentage of hot electrons transmitted across a Schottky barrier interface. Hot electron attenuation lengths of the metals were extracted by measuring the BEEM current as a function of metal overlayer thickness for both hot electron and hot hole injection at 80 K and under ultra high vacuum. The inelastic and elastic scattering lengths were extracted by fitting the energetic dependence of the measured attenuation lengths to a Fermi liquid based model. A sharp increase in the attenuation length is observed at low injection energies, just above the Schottky barrier height, only for metals on Si(001) substrates. In contrast, the attenuation length measured on Si(111) substrates shows a sharp decrease. These results indicate that interface band structure and parallel momentum conservation have significant impact upon the transport of hot electrons across non epitaxial metal-semiconductor interfaces. In addition, they help to separate effects upon hot electron transport that are inherent to the metal film from those associated with the interface and its band structure.

Garramone, John J.

245

Photonic-band-gap effects in two-dimensional polycrystalline and amorphous structures

International Nuclear Information System (INIS)

We study numerically the density of optical states (DOS) in two-dimensional photonic structures with short-range positional order and observe a transition from polycrystalline to amorphous photonic systems. In polycrystals, photonic band gaps (PBGs) are formed within individual domains, which leads to a depletion of the DOS similar to that in periodic structures. In amorphous photonic media, the domain sizes are too small to form PBGs, thus the depletion of the DOS is weakened significantly. The critical domain size that separates the polycrystalline and amorphous regimes is determined by the attenuation length of Bragg scattering, which depends not only on the degree of positional order but also the refractive-index contrast of the photonic material. Even with relatively low-refractive-index contrast, we find that modest short-range positional order in photonic structures enhances light confinement via collective scattering and interference.

246

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

247

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

248

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

249

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

250

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

251

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

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

Kim, Dong Wook; Cho, In-Sun; Shin, Seong Sik; Lee, Sangwook; Noh, Tae Hoon; Kim, Dong Hoe; Jung, Hyun Suk; Hong, Kug Sun

2011-08-01

252

Band structure and optical electron spectra of (TrMA)CoCl3.2H2O crystal

International Nuclear Information System (INIS)

DFT calculations of the band structure, density of states and optical spectra of trimethylammonium cobalt chloride dihydrate [(CH3)3NH]CoCl3.2H2O single crystal have been performed for the first time within a framework of the density functional theory using the CASTEP code (Cambridge serial total energy package). The valence band energy dispersion E(k) was found to be flat, although the bottom of the conduction band reveals noticeable dispersion along the lines [000]-[0012] and [-12012]-[-1200]-[-12120]. The calculations performed in the generalized gradient spin approximation (GGS) predict nonzero magnetic moment for the TrMA-CoCl3 crystal. The optical spectra calculated agree qualitatively with the experimental absorption spectra of the crystal in the range of Co ions excitation, 1.50-2.75eV

253

Nuclear energy density optimization: Shell structure

Nuclear density functional theory is the only microscopical theory that can be applied throughout the entire nuclear landscape. Its key ingredient is the energy density functional. In this work, we propose a new parameterization UNEDF2 of the local Skyrme energy density functional. The functional optimization is carried out using the POUNDerS optimization algorithm within the framework of the Skyrme Hartree-Fock-Bogoliubov theory. Compared to the previous parameterization UNEDF1, restrictions on the tensor term of the energy density have been lifted, yielding the most general form of the Skyrme energy density functional up to second order in derivatives of the one-body local density. In order to impose constraints on all the parameters of the functional, selected data on single-particle splittings in spherical doubly-magic nuclei have been included into the experimental dataset. The agreement with both bulk and spectroscopic nuclear properties achieved by the resulting UNEDF2 parameterization is comparable wi...

Kortelainen, M; Nazarewicz, W; Olsen, E; Reinhard, P -G; Sarich, J; Schunck, N; Wild, S M; Davesne, D; Erler, J; Pastore, A

2013-01-01

254

Solar spectral fine structure in 18-23 GHz band

Scientific Electronic Library Online (English)

Full Text Available 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

255

Band structure, metallization and superconductivity of GaP and GaN under high pressure

International Nuclear Information System (INIS)

The electronic band structure, metallization, structural phase transition and superconductivity of cubic zinc blende-type GaP and GaN are investigated. The equilibrium lattice constant, bulk modulus and pressure at which the compounds undergo a structural phase transition from ZnS structure to NaCl structure are predicted from the total energy calculations. The density of states at the Fermi level (N(EF)) is enhanced after metallization, which leads to the superconductivity in GaP and GaN. The superconducting transition temperatures (Tc) of GaP and GaN are obtained as a function of pressure for both the ZnS and NaCl structures and GaP and GaN come under the category of pressure-induced superconductors. When pressure is increased Tc increases in both the normal and high-pressure structures. The dependence of Tc on the electron-phonon mass enhancement factor ? shows that GaP and GaN are electron-phonon-mediated superconductors. Also, it is found that GaP and GaN retained in their normal structure under high pressure give appreciably high Tc. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

256

Effect of Bond Alternation on Electronic Energy Band Structure of Armchair Carbon Nanotubes

The influence of the bond alternation on electronic energy band structure of armchair carbon nanotubes is studied by the tight-binding approximation. It is shown that the armchair carbon nanotubes at ground state with Kekule structure open small band gap at the Fermi level. Dependence of energy band gap of armchair carbon nanotubes with Kekule structure on their radius is considered and numerically calculated. The numerical calculations are applied to the (n, n) carbon nanotubes with n = 5, 6, 7, 8.

Phong, Tran Cong; Hieu, Nguyen Ngoc

257

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

Winter, Amos; Sammarco, Paul W.

2010-10-01

258

Band structure of Gd2Ni2Al15 intermetallic compound

International Nuclear Information System (INIS)

The results of band structure calculation of the Gd2Ni2Al15 intermetallic compound by the augmented plane wave method are presented. It was found that the positions of nickel 3d bands and gadolinium 4f bands are the same which explains the magnetic moment value of the nickel atom in this compound about 1.6 ?/sub B/

259

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

260

International Nuclear Information System (INIS)

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

261

Southeast Asian ovalocytosis (SAO) human red cell membranes contain similar proportions of normal band 3 and a mutant band 3 with a nine amino acid deletion (band 3 SAO). We employed specific chemical modification and proteolytic cleavage to probe the structures of band 3 in normal and SAO membranes. When the membranes were modified specifically at lysine residues with N-hydroxysulfosuccinimide-SS-biotin, band 3 Lys-851 was not modified in normal membranes but quantitatively modified in SAO membranes. Normal and SAO membranes showed different patterns of band 3 proteolytic cleavage. Notably, many sites cleaved in normal membranes were not cleaved in SAO membranes, despite the presence of normal band 3 in these membranes. The mutant band 3 changes the structure of essentially all the normal band 3 present in the SAO membranes, and these changes extend throughout the normal band 3 molecules. The results also imply that band 3 in SAO membranes is present as hetero-tetramers or higher hetero-oligomers. The dominant structural effects of band 3 SAO on the other band 3 allele have important consequences on the functional and hematological properties of human red cells heterozygous for band 3 SAO. Analysis of the altered profile of biotinylation and protease cleavage sites suggests the location of exposed surfaces in the band 3 membrane domain and identifies likely interacting regions within the molecule. Our approach provides a sensitive method for studying structural changes in polytopic membrane proteins. PMID:11876639

Kuma, Hiroyuki; Abe, Yoshito; Askin, David; Bruce, Lesley J; Hamasaki, Tomohiro; Tanner, Michael J A; Hamasaki, Naotaka

2002-03-12

262

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)

263

Coulomb (or strong) correlation effects in the band structure of Eu2O3

International Nuclear Information System (INIS)

Two band-structure calculations of Eu2O3 are performed, one of them in the metallic phase and the other in the semiconducting phase; the difference between the corresponding band Hamiltonians is the occupation potential U(r) that includes the Coulomb correlation effects. On both phases, the 4f occupied bands are mixed with the 2p bands; this fact broadens these 4f bands so that its calculation is possible in this complex crystal lattice T/sub h/7. In the semiconducting band structure, the 4f empty bands are localized in the d-zone energy showing (4f, 5d) hybridization that produces a broadening still greater than for the 4f occupied bands. The semiconducting gap is GAMMA1+ - H1-and its value is 3.7 eV. (author)

264

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)

265

First-principles calculation of the three-dimensional band structure of poly(phenylene vinylene)

We have carried out a local-density-functional calculation of the three-dimensional (3D) band structure of the conducting polymer poly(phenylene vinylene) (PPV). The motivation was to investigate the effects of interchain coupling. The major effects are due to coupling of carbons in the rings to their closest neighbors, hydrogens on rings in adjacent chains. Among the effects of this coupling are splitting by up to 0.4 eV at various points of the Brillouin zone of the double degeneracy that would exist if the two chains in the unit cell were uncoupled; loss of electron-hole symmetry; the band edge at a point in the Brillouin zone off the chain direction; and a band gap smaller by 0.2 eV than that obtained from 1D calculations. The calculation results in a ratio of the transfer integral t? perpendicular to the chains to t?, parallel to the chains, ~=0.03. This value is too large to permit the existence of polarons in a perfect PPV crystal. Nevertheless, there is evidence for the existence of polarons in PPV crystals currently available. The large value of t?/t? means that polaron existence must be due to defects, such as inclusions of precursor polymer. This would result in the polarons having a wide range of properties, i.e., extent on the chain and energy levels.

Gomes da Costa, P.; Dandrea, R. G.; Conwell, E. M.

1993-01-01

266

Modeling of realistic cladding structures for air-core photonic band-gap fibers

Cladding structures of photonic band-gap fibers often have air-holes of non-circular shape and, typically, close-to-hexagonal air holes with curved corners are observed. We study photonic band-gaps in such structures by aid of a two-parameter representation of the size and curvature. For the fundamental band-gap we find that the band-gap edges (the intersections with the air line) shift toward shorter wavelengths when the air-filling fraction f is increased. The band-gap als...

Mortensen, Niels Asger; Nielsen, Martin Dybendal

2003-01-01

267

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

268

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

269

Electronic structure and band parameters for Zn X ( 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 spin-orbit coupling, the order of the states at the top of VB is found to be normal for all the Zn X phases considered. Upon inclusion of the spin-orbit 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 correct the strong correlation of the Zn-3d electrons, and thus improves the agreement with the experimentally established location of the Zn-3d levels. Consequently, it increases significantly the parameters underestimated in the pure LDA calculations.

Karazhanov, S. Zh.; Ravindran, P.; Kjekhus, A.; Fjellvåg, H.; Grossner, U.; Svensson, B. G.

2006-01-01

270

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

271

Structural and Electronic Properties of Zincblende AlInN Alloy:. a Hybrid Density Functional Study

Conventional local and semilocal density functionals cannot predict correct bandgap energy for semiconductors especially the indium compounds. By employing the density functional theory calculations with a hybrid functional, we studied the bandgap energy and structure properties of AlN and InN compounds as well as their ternary AlInN alloys. We showed that by adjusting the screening parameter in the hybrid functional, the bandgaps calculated are in good agreement with the experimental data. A 2.54 eV natural valence band offset between AlN and InN is found with the hybrid density functional study. Furthermore, we studied the bandgap and band bowing parameter for AlInN alloys by using the hybrid density functional. The bandgap and band bowing parameters obtained are consistent with experimental and other theoretical results. Our results revealed that, although the PBE functional underestimates the bandgap energy for binary compound and ternary AlInN alloy, their band bowing parameters are still reasonable and valid. Our results should be useful for experiment and optoelectronic device applications.

Wang, Fei; Yuan, Pengfei; Wang, Yucang; Wang, Sanjun; Sun, Qiang; Jia, Yu

272

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

273

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

274

Electronic band structure of GaAs/AlxGa1?xAs superlattice in an intense laser field

International Nuclear Information System (INIS)

We perform theoretical calculations for the band structure of semiconductor superlattice under intense high-frequency laser field. In the frame of the non-perturbative approach, the laser effects are included via laser-dressed potential. Results reveal that an intense laser field creates an additional geometric confinement on the electronic states. Numerical results show that when tuning the strength of the laser field significant changes come in the electronic energy levels and density of states. - Graphical abstract: We have theoretically investigated the influence of an intense, high-frequency, non-resonant laser field on the electronic band structure of GaAs/AlxGa1?xAs semiconductor superlattice. By tuning the strength of the laser field significant changes come in the electronic energy levels and density of states. Highlights: ? Band structure of GaAs/AlxGa1?xAs superlattice under an ILF is investigated. ? Dramatic variation of the confinement potential in the well/barrier region is predicted. ? ILF creates an additional geometric confinement on the electronic states. ? Significant changes come in the electronic energy levels and density of states.

275

Electronic Structure and Valence Band Spectra of Bi4Ti3O12

The x-ray photoelectron valence band spectrum and x-ray emission valence-band spectra (Ti K _beta_5, Ti L_alpha, O K_alpha) of Bi4Ti3O12 are presented (analyzed in the common energy scale) and interpreted on the basis of a band-structure calculation for an idealized I4/mmm structure of this material.

Postnikov, A. V.; Bartkowski, St; Mersch, F.; Neumann, M.; Kurmaev, E. Z.; Cherkashenko, V. M.; Nemnonov, S. N.; Galakhov, V. R.

1995-01-01

276

Application of Hyperspectral Band Elimiation Technique to PVT Images of Composite Structures

A new approach to NDT of composite structures using Band Elimination of the analyzed image index by Hyperspectral image analysis approach is presented and discussed. The matrix Band Elimination technique allows the monitoring and analysis of a components structure based on Filtering of bands and correlation between sequentially pulsed thermal images and their indices. The technique produces several matrices resulting from frame deviation and pixel redistribution calculations for intelligent c...

Mahmoud Zaki Iskandarani

2012-01-01

277

Renormalized band structure of Sr2RuO4: A quasiparticle tight-binding approach

International Nuclear Information System (INIS)

Highlights: •We develop an effective quasiparticle tight-binding to experimentally measured Sr2RuO4 band structure. •The model provides a good agreement with the experimentally measured Sommerfeld coefficient, among other quantities. •The model provides an easy way to obtain momentum and orbital dependent Fermi velocity and effective masses close to the FL. •We observe enhanced electron–phonon coupling for surface bands in Sr2RuO4. -- Abstract: We derive an effective quasiparticle tight-binding model which is able to describe with high accuracy the low-energy electronic structure of Sr2RuO4 obtained by means of low temperature angle resolved photoemission spectroscopy. Such an approach is applied to determine the momentum and orbital dependent effective masses and velocities of the electron quasiparticles close to the Fermi level. We demonstrate that the model can provide, among the various computable physical quantities, a very good agreement with the experimentally measured specific heat coefficient and compares well with the plasma frequency estimated from local density calculations. Its use is underlined as a realistic input in the analysis of the possible electronic mechanisms related to the superconducting state of Sr2RuO4

278

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

279

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$\\to$ LTO transition. The LTT distortion also has little effect on the DOS for the experimental value of the octahedral...

Norman, M. R.; Mcmullan, G. J.; Novikov, D. L.; Freeman, A. J.

1993-01-01

280

Design and analysis of defected ground structure transformer for dual-band antenna

Directory of Open Access Journals (Sweden)

Full Text Available This study presents a novel dual-band antenna design methodology utilising a dual-frequency impedance transformer with defected ground structure (DGS. The proposed dual-frequency DGS impedance transformer generates a second resonant frequency from a conventional single-band antenna, resulting dual-band operation. Simulation studies illustrate that the adopted design achieves versatile configurations for arbitrary operating frequencies and diverse input impedance ranges in planar antenna structures. To experimentally verify the proposed design methodology, a dual-frequency DGS impedance transformer was implemented for a 2.4 GHz monopole antenna to obtain a 900/2400 MHz dual-band antenna. Measurement shows that the 10 dB return loss bandwidth in 900 MHz band is 34.4 MHz, whereas that in 2400 MHz band is wider than 530 MHz. Typical monopole radiation patterns are observed at both operating bands.

Wai-Wa Choi

2014-12-01

281

Band structure calculation of GeSn and SiSn

The band structure of GeSn and SiSn in zinc-blende structures is predicted using the empirical pseudopotential. Special emphasis is placed on the effects of inversions asymmetry such as ionicity. We found that GeSn exhibits a direct band gap whereas SiSn still remains indirect gap material.

Amrane, Na.; Ait Abderrahmane, S.; Aourag, H.

1995-08-01

282

Electronic band structure of ferro-pnictide superconductors from ARPES experiment

ARPES experiments on iron based superconductors show that the differences between the measured and calculated electronic band structures look insignificant but can be crucial for understanding of the mechanism of high temperature superconductivity. Here we focus on those differences for 111 and 122 compounds and discuss the observed correlation of the experimental band structure with the superconductivity.

Kordyuk, A. A.; Zabolotnyy, V. B.; Evtushinsky, D. V.; Yaresko, A. N.; Buechner, B.; Borisenko, S. V.

2011-01-01

283

International Nuclear Information System (INIS)

We report a systematic first principles density functional study on the electronic structure, elastic and optical properties of nitrogen based solid hydrogen storage materials LiNH2, NaNH2, KNH2, and RbNH2. The ground state structural properties are calculated by using standard density functional theory, and also dispersion corrected density functional theory. We find that van der Waals interactions are dominant in LiNH2 whereas they are relatively weak in other alkali metal amides. The calculated elastic constants show that all the compounds are mechanically stable and LiNH2 is found to be a stiffer material among the alkali metal amides. The melting temperatures are calculated and follow the order RbNH2 2 2 2. The electronic band structure is calculated by using the Tran–Blaha modified Becke–Johnson potential and found that all the compounds are insulators, with a considerable band gap. The [NH2]? derived states completely dominate in the entire valence band region while the metal atom states occupy the conduction band. The calculated band structure is used to analyze the different interband optical transitions occurring between valence and conduction bands. Our calculations show that these materials have considerable optical anisotropy. (paper)

284

The nitrogen related defect chemistry and electronic structure of wide band gap oxides are investigated by density functional theory defect calculations of N(O)(q), NH(O)(×), and (NH2)(O)(·) as well as V(O)(··) and OH(O)(·) in MgO, CaO, SrO, Al(2)O(3), In(2)O(3), Sc(2)O(3), Y(2)O(3), La(2)O(3), TiO(2), SnO(2), ZrO(2), BaZrO(3), and SrZrO(3). The N(O)(q) acceptor level is found to be deep and the binding energy of NH(O)(×) with respect to N(O)' and (OH(O)(·) is found to be significantly negative, i.e. binding, in all of the investigated oxides. The defect structure of the oxides was found to be remarkably similar under reducing and nitriding conditions (1 bar N(2), 1 bar H(2) and 1 × 10(-7) bar H(2)O): NH(O)(×) predominates at low temperatures and [N(O)'] = 2[V(O)(··) predominates at higher temperatures (>900 K for most of the oxides). Furthermore, we evaluate how the defect structure is affected by non-equilibrium conditions such as doping and quenching. In terms of electronic structure, N(O)' is found to introduce isolated N-2p states within the band gap, while the N-2p states of NH(O)(×) are shifted towards, or overlap with the VBM. Finally, we assess the effect of nitrogen incorporation on the proton conducting properties of oxides and comment on their corrosion resistance in nitriding atmospheres in light of the calculated defect structures. PMID:22828729

Polfus, Jonathan M; Bjørheim, Tor S; Norby, Truls; Haugsrud, Reidar

2012-09-01

285

Energy Technology Data Exchange (ETDEWEB)

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 [Department of Applied Physics, National University of Kaohsiung, Kaohsiung 811, Taiwan (China); Lin, Ken-Huang; Li, Jia-Yun [Department of Mechanical and Electro-Mechanical Engineering, National Sun Yat-Sen University, Kaohsiung 804, Taiwan (China); Ju, Shin-Pon, E-mail: jushin-pon@mail.nsysu.edu.tw [Department of Mechanical and Electro-Mechanical Engineering, National Sun Yat-Sen University, Kaohsiung 804, Taiwan (China); Department of Medicinal and Applied Chemistry, Kaohsiung Medical University, Kaohsiung 807, Taiwan (China)

2014-10-07

286

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

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

2015-04-01

287

International Nuclear Information System (INIS)

We study the electronic structure of graphene with a single substitutional vacancy using a combination of the density-functional, tight-binding and impurity Green's function approaches. Density-functional studies are performed with the all-electron spin-polarized linear augmented plane wave (LAPW) method. The three sp2? dangling bonds adjacent to the vacancy introduce localized states (V?) in the mid-gap region, which split due to the crystal field and a Jahn–Teller distortion, while the pz? states introduce a sharp resonance state (V?) in the band structure. For a planar structure, symmetry strictly forbids hybridization between the ? and the ? states, so that these bands are clearly identifiable in the calculated band structure. As to the magnetic moment of the vacancy, the Hund's rule coupling aligns the spins of the four localized V?1??, V?2? and V?? electrons, resulting in an S = 1 state, with a magnetic moment of 2?B, which is reduced by about 0.3?B due to the anti-ferromagnetic spin polarization of the ? band itinerant states in the vicinity of the vacancy. This results in the net magnetic moment of 1.7?B. Using the Lippmann–Schwinger equation, we reproduce the well-known ?1/r decay of the localized V? wave function with distance, and in addition, find an interference term coming from the two Dirac points, previously unnoticed in the literature. The long-ran. The long-range nature of the V? wave function is a unique feature of the graphene vacancy and we suggest that this may be one of the reasons for the widely varying relaxed structures and magnetic moments reported from the supercell band calculations in the literature. (paper)

288

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.

289

Monolayer transition-metal dichalcogenides (TMDCs) display valley-selective circular dichroism due to the presence of time-reversal symmetry and the absence of inversion symmetry, making them promising candidates for valleytronics. In contrast, in bilayer TMDCs both symmetries are present and these desirable valley-selective properties are lost. Here, by using density-functional tight-binding electronic structure simulations and revised periodic boundary conditions, we show that bending of bilayer MoS2 sheets breaks band degeneracies and localizes states on separate layers due to bending-induced strain gradients across the sheets. We propose a strategy for employing bending deformations in bilayer TMDCs as a simple yet effective means of dynamically and reversibly tuning their band gaps while simultaneously tuning valley-selective physics. PMID:24856713

Koskinen, Pekka; Fampiou, Ioanna; Ramasubramaniam, Ashwin

2014-05-01

290

A wide-band perfect light absorber at mid-wave infrared using multiplexed metal structures

We experimentally demonstrate a wide band near perfect light absorber in the mid-wave infrared region using multiplexed plasmonic metal structures. The wide band near perfect light absorber is made of two different size gold metal squares multiplexed on a thin dielectric spacing layer on the top of a thick metal layer in each unit cell. We also fabricate regular non-multiplexed structure perfect light absorbers. The multiplexed structure IR absorber absorbs above 98% incident light over a much wider spectral band than the regular non-multiplexed structure perfect light absorbers in the mid-wave IR region.

Hendrickson, Joshua; Zhang, Boyang; Buchwald, Walter; Soref, Richard

2012-01-01

291

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

292

Band Structures and Nucleon Alignments in ^173,175W

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

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

2012-10-01

293

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

294

In their Comment, Bagayoko [Phys. Rev. B 76, 037101 (2007)] criticized the three-step electronic-structure calculations of Furthmüller [Phys. Rev. B 72, 205106 (2005)] to calculate the band structures and hence the fundamental energy gaps of crystalline InN polymorphs of 0.82eV (wurtzite InN) or 0.55eV (zinc-blende InN) [J. Furthmüller , Phys. Rev. B 72, 205106 (2005); F. Bechstedt and J. Furthmüller, J. Cryst. Growth 246, 315 (2002)]. In contrast, in their self-consistent density-functional calculations they compute the fundamental gaps at the theoretical lattice constants to 0.88 or 0.65eV in one step, already on the density-functional theory (DFT) local-density approximation (LDA) level of approximation [D. Bagayoko and L. Franklin, J. Appl. Phys. 97, 123708 (2005); D. Bagayoko , J. Appl. Phys. 96, 4297 (2004)].

Furthmüller, J.; Hahn, P. H.; Fuchs, F.; Bechstedt, F.

2007-07-01

295

Band structure effects for dripped neutrons in neutron star crust

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

296

Calculation of the band structure of GdCo2, GdRh2 e GdIr2 by the APW method

International Nuclear Information System (INIS)

The band structure of GdCo2, GdRh2, GdIr2 has been calculated by the APW method. A histogram of the density of states is presented for each compound. The bands are transition-metal-like, with s-d hybridization near the Fermi level. The 5d character near the Fermi level increases as one goes from Co to Ir

297

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

298

Electronic structure of novel multiple-band superconductor SrPt2As2

The electronic structure of the recently discovered superconductor SrPt2As2 with T c = 5.2 K has been calculated in the local-density approximation. Despite its chemical composition and crystal structure are somehow similar to FeAs-based high-temperature superconductors, the electronic structure of SrPt2As2 is very much different. The crystal structure is orthorhombic (or tetragonal if idealized) and has layered nature with alternating PtAs4 and AsPt4 tetrahedra slabs sandwiched with Sr ions. The Fermi level is crossed by Pt-5 d states with rather strong admixture of As-4 p states. Fermi surface of SrPt2As2 is essentially three-dimensional, with complicated sheets corresponding to multiple bands. We compare SrPt2As2 with 1111 and 122 representatives of FeAs-class of superconductors, as well as with isovalent (Ba,Sr)Ni2As2 superconductors. Brief discussion of superconductivity in SrPt2As2 is also presented.

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

2010-12-01

299

Manifestation of the upper Hubbard band in the 2D Hubbard model at low electron density

International Nuclear Information System (INIS)

We consider the 2D Hubbard model in the strong-coupling case (U >> W) and at low electron density (nd 2 > W and low electron density. Both poles produce nontrivial corrections to Landau Fermi-liquid picture already at low electron density but do not destroy it in 2D.

300

Cluster structure and deformed bands in the {sup 38}Ar nucleus

Energy Technology Data Exchange (ETDEWEB)

The structure of the {sup 38}Ar nucleus is investigated by the {sup 34}S+? 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{sup ?}=0{sup +} band is found to be predominantly {sup 34}S+? cluster states. It is also shown that the observed energies and E2 transitions of the band are well reproduced by the model. The existence of a negative-parity doublet band of the band is also predicted. The strength of the ?-cluster states is shown to be spread over several levels due to mixing of shell-model states and various ?-cluster states.

Sakuda, T., E-mail: sakuda@cc.miyazaki-u.ac.jp [Department of Physics, University of Miyazaki, Miyazaki 889-2192 (Japan); Ohkubo, S., E-mail: shigeo@cc.u-kochi.ac.jp [Department of Applied Science and Environment, University of Kochi, Kochi 780-8515 (Japan); Research Center for Nuclear Physics, Osaka University, Ibaraki, Osaka 567-0047 (Japan)

2013-06-17

301

We present electronic structure and total energy calculations for SiC in a variety of polytype structures using the NRL nonorthogonal tight-binding method. We develop one set of parameters optimized for a combination of electronic and energetic properties using a sp basis, and one optimized for electronic properties using a spd basis. We compute the energies of polytypes with up to 62 atoms per unit cell, and find that the hexagonal wurtzite structure is highest in energy, the 4H structure is lowest in energy, and the cubic zinc-blende structure is in between, in agreement with our linear augmented plane-wave and other calculations. For the sp model we find that the electronic structure of the cubic and hexagonal structures are in good agreement with density-functional theory calculations only for the occupied bands. The spd parametrization optimized for the electronic structure of the zinc-blende and wurtzite structures at the equilibrium volume reproduces nearly perfectly both the valence and conduction bands. The sp tight-binding model also yields elastic constants, phonon frequencies, stacking fault energies, and vacancy formation energies for the cubic structure in good agreement with available experimental and theoretical calculations. Using molecular dynamics simulations we compute the finite-temperature thermal expansion coefficient and atomic mean-square displacements in good agreement with available first-principles calculations.

Bernstein, N.; Gotsis, H. J.; Papaconstantopoulos, D. A.; Mehl, M. J.

2005-02-01

302

Electronic transitions in GdN band structure

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-05-28

303

Electronic transitions in GdN band structure

International Nuclear Information System (INIS)

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

304

Triple Frequency Fractal Patch Structure Antenna for C Band Applications

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

Samsuzzaman, M.; Islam, M. T.; Faruque, M. R. I.

2014-01-01

305

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

306

Surface band structure of GaN(0001)-2 x 2

Energy Technology Data Exchange (ETDEWEB)

The results of an in-situ angle-resolved ultraviolet photoelectron spectroscopy investigation of 2 x 2 reconstructed GaN(0001) surfaces prepared by plasma assisted molecular beam epitaxy are presented. The valence band dispersion was measured by variation of the detection angle with respect to the surface normal along the [1 anti 100] (anti {gamma}- anti K) and the [11 anti 20](anti {gamma}- anti M) direction using He I (h{nu}=21.2 eV) and He II (h{nu}=40.8 eV) radiation. In addition to the bulk states which exhibit strong dispersion, two non-dispersive surface states at 2 eV and 3 eV below the Fermi level are detected in both directions. In order to identify the origin of these states and to validate the experimentally determined k-dependence of the surface and bulk electron states we performed ab-initio calculations within the density functional theory and we calculated the band structures of different 2 x 2 surface reconstructions. Based on these calculations we could identify that the aforementioned states arise from a 2 x 2 N adatom surface reconstruction.

Lorenz, Pierre; Himmerlich, Marcel; Schaefer, Juergen A.; Krischok, Stefan [Institut fuer Physik and Institut fuer Mikro- und Nanotechnologien, TU Ilmenau (Germany); Lymperakis, Liverios; Neugebauer, Joerg [Max-Planck-Institut fuer Eisenforschung GmbH, Duesseldorf (Germany); Gutt, Richard [Fraunhofer-Institut fuer Angewandte Festkoerperphysik, Freiburg (Germany)

2010-07-01

307

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)

308

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

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

Jan Sykulski; Mihai Rotaru

2010-01-01

309

A wide-band perfect light absorber at mid-wave infrared using multiplexed metal structures

We experimentally demonstrate a wide band near perfect light absorber in the mid-wave infrared region using multiplexed plasmonic metal structures. The wide band near perfect light absorber is made of two different size gold metal squares multiplexed on a thin dielectric spacing layer on the top of a thick metal layer in each unit cell. We also fabricate regular non-multiplexed structure perfect light absorbers. The multiplexed structure IR absorber absorbs above 98% inciden...

Hendrickson, Joshua; Guo, Junpeng; Zhang, Boyang; Buchwald, Walter; Soref, Richard

2012-01-01

310

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

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

2014-12-15

311

Band structures extending to very high spin in 126Xe

International Nuclear Information System (INIS)

High-spin states in 126Xe have been populated in the 82Se(48Ca,4n)126Xe reaction in two experiments, one at the VIVITRON accelerator in Strasbourg using the Euroball detector array, and a subsequent one with ATLAS at Argonne using the Gammasphere Ge-detector array. Levels and assignments made previously for 126Xe up to I=20 have been confirmed and extended. Four regular bands extending to a spin of almost I=60, which are interpreted as two pairs of signature partners with opposite parity, are identified for the first time. The ? = 0 partner of each pair is connected to the lower-lying levels, whereas the two ? = 1 partners remain floating. A fractional Doppler shift analysis of transitions in the strongest populated (?,?)=(-,0) band provides a value of 5.20.50.4 b for the transition quadrupole moment, which can be related to a minimum in the potential-energy surface calculated by the ULTIMATE CRANKER cranked shell-model code at ??0.35 and ??5 deg. The four lowest bands calculated for this minimum compare well with the two signature pairs experimentally observed over a wide spin range. A sharp upbend at (?/2?)??1170 keV is interpreted as a crossing with a band involving the j15/2 neutron orbital, for which pairing correlations are expected to be totally quenched. The four long bands extend to within ?5 spin units of a crossing with an yrast line defined by calculatline defined by calculated hyperdeformed transitions and will serve as important stepping stones into the spin region beyond 60h for future experiments

312

Band structure and optical properties of hexagonal In-rich In(x)Al(1-x)N alloys.

Full potential linear augmented plane wave calculations have been performed to study the electronic and optical properties of In-rich In(x)Al(1-x)N alloys in the hexagonal wurtzite structure. Compositions of x = 0.9375, 0.8125 and 0.6875 are considered which follow from replacing one, three and five In atoms by Al in the 32-atom supercell. The new form of exchange correlation, i.e. Engel-Vosko's generalized gradient approximation within density functional theory, is employed. The calculations yield the band structure and total density of states as well as the imaginary part ?(2)(?) of the ordinary and extraordinary dielectric function. The calculated dependence of the bandgap on the composition is in good agreement with recent experimental studies. A reversal of the valence band ordering is found between x = 0.8125 and 0.6875. The absorption features in the high-energy range of ?(2)(?) are related to critical points of the band structure. The transition energies for these van Hove singularities are determined and their bowing parameters are discussed. PMID:22076118

Kumar, S; Pandey, Suman; Gupta, S K; Maurya, Tarun K; Schley, P; Gobsch, G; Goldhahn, R

2011-11-30

313

International Nuclear Information System (INIS)

The [14C]2-deoxyglucose (2DG) technique has been used to map the effects of increasing intensities of wide band noise on 2DG uptake in mongolian gerbil brain auditory structures. Animals were injected with [14C]2DG and exposed to silence or continuous wide band noise at 25 dB, 45 dB, 65 dB, 85 dB or 105dB SPL. Brains were removed, frozen-sectioned, and autoradiographed on X-ray film. The ratio of the optical density of gray matter structures to the optical density of cerebellar peduncles in each animal was used to semiquantitate the results. The dorsal and ventral cochlear nuclei, superior olive/trapezoid body, inferior colliculus, and the dorsal and ventral nuclei of the lateral lemniscus all showed increases in 2DG uptake during exposure to wide band noise (WBN). As noise intensity increased from 0 to 105 dB SPL, 2DG uptake increased regularly to a maximum at 85 or 105 dB SPL. As WBN intensity increased, deeper layers of inferior colliculus were activated. The medial geniculate nucleus and auditory cortex showed a lesser increase in 2DG uptake during noise exposure. Non-auditory structures, including the cerebellar cortex and the medullary reticular nuclei, showed no increase in 2DG uptake during noise exposure at any intensity tested. (Auth.)

314

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 erimental 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.

315

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.; Lebègue, S.

2014-01-01

316

Global study of bright band structure as observed from spaceborne precipitation radar

Bright band is perhaps one of the most widely known radar signatures for a long time. Extensive research has been reported in the literature, documenting various features of bright bands. Nevertheless it has always been a challenge to obtain a clear classification of the underlying structure of the vertical profile of reflectivity from radar observations. Classifying the radar profiles of bright band to a limited set will be helpful to further this goal. In this study the Self Organizing Map (SOM) technique is used to classify bright band observed from the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR). The SOM forms a non-linear mapping of the data to a two-dimensional grid map that can be used as an exploratory analysis tool for generating hypotheses on the shape, and characteristics of the vertical profiles of bright bands. Observation of reflectivity profiles in bright band obtained from the TRMM-PR at 125 m vertical resolution are analyzed and visualized with the SOM. Basic descriptions of the vertical structure are extracted from the TRMM-PR bright band region data, and the corresponding statistics are presented in this paper. Statistics of bright band thickness, peak reflectivity, snow reflectivity, rain reflectivity, and the sharpness of bright bands are studied at a global scale over the tropics. The global classification map provides a unique tool to quantitatively classify bright band region. The methodology and results of the analysis are presented in this paper.

Zafar, Basim; Chandrasekar, V.

2004-12-01

317

In this article, we investigate the spontaneous emission properties of radiating molecules embedded in a chiral nematic liquid crystal, under the assumption that the electronic transition frequency is close to the photonic edge mode of the structure, i.e., at resonance. We take into account the transition broadening and the decay of electromagnetic field modes supported by the so-called "mirrorless"cavity. We employ the Jaynes-Cummings Hamiltonian to describe the electron interaction with the electromagnetic field, focusing on the mode with the diffracting polarization in the chiral nematic layer. As known in these structures, the density of photon states, calculated via the Wigner method, has distinct peaks on either side of the photonic band gap, which manifests itself as a considerable modification of the emission spectrum. We demonstrate that, near resonance, there are notable differences between the behavior of the density of states and the spontaneous emission profile of these structures. In addition, we examine in some detail the case of the logarithmic peak exhibited in the density of states in two-dimensional photonic structures and obtain analytic relations for the Lamb shift and the broadening of the atomic transition in the emission spectrum. The dynamical behavior of the atom-field system is described by a system of two first-order differential equations, solved using the Green's-function method and the Fourier transform. The emission spectra are then calculated and compared with experimental data. PMID:23848702

Mavrogordatos, Th K; Morris, S M; Wood, S M; Coles, H J; Wilkinson, T D

2013-06-01

318

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, Yongle; Bulgac, Aurel

2002-01-01

319

Bonding nature as well as structural, optoelectronic and thermal properties of the cubic XMg2O4(X = Si, Ge) spinel compounds have been calculated using a full-potential augmented plane-wave plus local orbitals (FP-APW+lo) method within the density functional theory. The exchange-correlation potential was treated with the PBE-GGA approximation to calculate the total energy. Moreover, the modified Becke-Johnson potential (TB-mBJ) was also applied to improve the electronic band structure calculations. The computed ground-state parameters (a, B, B? and u) are in excellent agreements with the available theoretical data. Calculations of the electronic band structure and bonding properties show that these compounds have a direct energy band gap (?-?) with a dominated ionic character and the TB-mBJ approximation yields larger fundamental band gaps compared to those obtained using the PBE-GGA. Optical properties such as the complex dielectric function ?(?), reflectivity R(?) and energy loss function L(?), for incident photon energy up to 40 eV, have been predicted. Through the quasi-harmonic Debye model, in which the phononic effects are considered, the effects of pressure P and temperature T on the thermal expansion coefficient, Debye temperature and heat capacity for the considered compounds are investigated for the first time.

Semari, F.; Ouahrani, T.; Khachai, H.; Khenata, R.; Rabah, M.; Bouhemadou, A.; Murtaza, G.; Amin, B.; Rached, D.

2013-07-01

320

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)

321

New Band Structures in Neutron-Rich ^108Mo, and ^108,110,112Ru

New insights into the structures of ^108Mo, and ^108,110,112Ru are identified in the spontaneous fission of ^252Cf. The 5.7 x 10^11 triples and higher fold prompt gamma coincidences opened up the possibility to see new weakly populated band structures in these nuclei. Two phonon ?-bands that decay only to the one phonon ?-band were discovered in ^108Mo and ^110,112Ru. We discovered in ^108Mo^ and^ 108,110,112Ru ?I=1, doublet bands. Our theoretical calculations indicate ^108Ru is ?-soft and ^110,112Ru are more rigid triaxial nuclei. The non-yrast band in ^108Ru shows an energy level staggering not seen in its yrast partner band nor in ^110,112Ru. This staggering is proposed to be related to its ?-soft shape perturbing its chiral structure. The doublet bands in ^108Mo^ and ^110,112Ru will be shown to have all the properties expected for chiral vibrational bands. Tilted axis cranking calculations for ^110,112Ru stronly support the chiral vibrational interpretation of these bands but do not support their being accidentally degenerate energy doublets built on different configurations.

Hamilton, J. H.; Luo, Y. X.; Ramayya, A. V.; Goodin, C.; Li, K.; Hwang, J. K.; Liu, S.; Zhu, S. J.; Ding, H.-B.; Che, X. L.; Rasmussen, J. O.; Lee, I. Y.; Almehed, D.; Frauendorf, S.; Dimitrov, V.; Zhang, J. Y.; Stone, N. J.; Ter-Akopian, G. M.; Daniel, A. V.; Stoyer, M. A.; Donangelo, R.; Cole, J. D.

2008-10-01

322

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

Energy Technology Data Exchange (ETDEWEB)

High-resolution X-ray photoelectron spectroscopy (XPS) is used to study regularities in the formation of valence band electronic structure in binary As{sub x}Se{sub 100-x}, As{sub x}S{sub 100-x}, Ge{sub x}Se{sub 100-x} and Ge{sub x}S{sub 100-x} chalcogenide vitreous semiconductors. It is shown that the highest occupied energetic states in the valence band of these materials are formed by lone pair electrons of chalcogen atoms, which play dominant role in the formation of valence band electronic structure of chalcogen-rich glasses. A well-expressed contribution from chalcogen bonding p electrons and more deep s orbitals are also recorded in the experimental valence band XPS spectra. Compositional dependences of the observed bands are qualitatively analyzed from structural and compositional points of view.

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

2011-04-15

323

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

Hristov, Alexander

2009-08-15

324

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

Directory of Open Access Journals (Sweden)

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

Jan Sykulski

2010-11-01

325

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

This paper introduces a novel approach to create notch band filters in the front-end of ultra-wideband (UWB) communication systems based on electromagnetic bandgap (EBG) structures. The concept presented here can be implemented in any structure that has a microstrip in its configuration. The EBG structure is first analyzed using a full wave electromagnetic solver and then optimized to work at WLAN band (5.15-5.825 GHz). Two UWB passband filters are used to demonstrate the applicability and effectiveness of the novel EBG notch band feature. Simulation results are provided for two cases studied. PMID:22163430

Rotaru, Mihai; Sykulski, Jan

2010-01-01

326

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

International Nuclear Information System (INIS)

A slow wave structure consisting of metallic photonic band gap cells for a Ka-band Cherenkov device is proposed in this paper. Attributing to the mode selectivity of the photonic band gap, only the TM01-like mode among the TM0n-like modes exists in such a slow wave structure. The dispersion characteristics of the slow wave structure are investigated by simulation and experiment. It is shown that the dispersion curve obtained from the experiment is in agreement with that from simulation

327

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

328

International Nuclear Information System (INIS)

Highlights: • Electronic structure of TlPb2Cl5 is calculated by the FP-LAPW method. • The valence band is dominated by contributions of Cl 3p states. • Contributions of Pb 6p* states dominate at the bottom of the conduction band. • The FP-LAPW data allow concluding that TlPb2Cl5 is an indirect-gap material. • XPS core-level and valence-band spectra of polycrystalline TlPb2Cl5 are measured. -- Abstract: We report on first-principles calculations of total and partial densities of states of atoms constituting TlPb2Cl5 using the full potential linearized augmented plane wave (FP-LAPW) method. The calculations reveal that the valence band of TlPb2Cl5 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 TlPb2Cl5 is composed mainly of contributions of the unoccupied Pb 6p-like states. Our FP-LAPW data indicate that the TlPb2Cl5 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+ ion-irradiated surfaces of a TlPb2Cl5 polycrystalline sample were measured. The measurements reveal high chemical stability and confirm experimentally the low hygroscopicity of TlPb2Cl5 surface

329

Regularized Scarf potentials: energy band structure and supersymmetry

International Nuclear Information System (INIS)

The singular one-dimensional periodic Scarf potential is regularized by means of one-parameter square well counter-terms. It is shown that the regularized spectrum converges formally to the conventional Scarf energy bands for specific values of the parameter. The behaviour of the regularizations under supersymmetric transformations is also investigated; this is a key point for the algebraic solvability of the regularized Scarf potential

330

Regularized Scarf potentials: energy band structure and supersymmetry

Energy Technology Data Exchange (ETDEWEB)

The singular one-dimensional periodic Scarf potential is regularized by means of one-parameter square well counter-terms. It is shown that the regularized spectrum converges formally to the conventional Scarf energy bands for specific values of the parameter. The behaviour of the regularizations under supersymmetric transformations is also investigated; this is a key point for the algebraic solvability of the regularized Scarf potential.

Negro, J; Nieto, L M; Rosas-Ortiz, O [Departamento de FIsica Teorica, Universidad de Valladolid, 47005 Valladolid (Spain)

2004-10-29

331

Structure-sensitive resonance Raman bands of capped tetraphenylporphyrinatoiron complexes

Resonance Raman spectra have been determined for the capped tetraphenylporphyrinatoiron complexes and their base adducts. The five-coordinate mono-base complexes of these porphyrin complexes display Raman spectra that are nearly identical to those previously determined for five-coordinate iron(II) tetraphenylporphyrin complexes in the marker regions around 1540, 1345, and 370 cm-1. A similar correspondence is found between Raman bands of iron(II) complexes of the capped complexes and those of...

Linard, Jack E.; Shriver, Duward F.; Basolo, Fred

1980-01-01

332

Band Structures in Fission Fragments of Rhodium and Neighbors

We present level schemes from fission-gamma spectroscopy in the region of triaxiality around 110-113Rh, studied by our Gammasphere collaboration. We will here emphasize features involving one or more unpaired nucleons in high-j orbitals, g9/2 protons and h11/2 neutrons. Backbending and bifurcation is observed between rotational frequencies of 0.32 and 0.39 MeV for the oddeven nuclei but not for the odd-odd. Possible chiral doublets in 3-quasiparticle states above the backbend in 111Rh and in 113Rh are noted. We note that signature-splitting patterns in odd-even, g9/2 bands of the region indicate a shape somewhat on the prolate side of maximum triaxiality for the g9/2 ground bands of 109,111,113Rh. The more deformed K=1/2 intruder bands from proton orbitals above the Z=50 shell are probably prolate spheroidal, a case of shape coexistence.

Rasmussen, J. O.; Gilat, J.; Wu, S. C.; Luo, Y. X.; Hwang, J. K.; Ramayya, A. V.; Hamilton, J. H.; Zhu, S. J.; Xu, R. Q.; Donangelo, R.

2003-10-01

333

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

334

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 sim...

Stanchev, Orlin; Donkov, Sava; Veltchev, Todor V.; Shetty, Rahul

2013-01-01

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

Density functional calculations were performed for a cubic quasicrystalline approximant in the Al–Cu–Ir system. A semimetallic band structure was developed and analyzed on the basis of Wannier functions constructed from the valence and a part of the conduction band manifold. The Wannier functions were s- and p-like orbitals centered on either the centers of conventional clusters or the icosahedron-like vertices of pseudo-Mackay clusters, and d-like orbitals centered on the transition metals. Grouping the orbitals according to their center, we considered a small cluster for each group of the orbitals. Most of the orbitals contribute to the density of states only within the valence bands, i.e., they are valence states. The exceptions are some of p-like orbitals centered on the icosahedron-like vertices of the pseudo-Mackay clusters, and they contribute to both valence and conduction bands. Each of these p-like orbitals forms a covalent bond with one centered on the neighboring small cluster. The resulting bonding and antibonding orbitals are valence and conduction states, respectively. The number of valence bands (173) of our Al39Cu8Ir15 model was then decomposed in terms of the numbers of transition metals (23), clusters (16), and covalent bonds between the clusters (6) as 23 × 5 + 16 × 4 - 6 = 173. The description for the valence-band formation may also be applicable to some of the group 13 element–transition metal intermetallic compounds, such as RuAl2.

Kitahara, Koichi; Takagiwa, Yoshiki; Kimura, Kaoru

2015-01-01

337

The electronic properties of LiCoO2 have been studied by theoretical band-structure calculations (using density functional theory) and experimental methods (photoemission). Synchrotron-induced photoelectron spectroscopy, resonant photoemission spectroscopy (ResPES), and soft x-ray absorption (XAS) have been applied to investigate the electronic structure of both occupied and unoccupied states. High-quality PES spectra were obtained from stoichiometric and highly crystalline LiCoO2 thin films deposited “in situ” by rf magnetron sputtering. An experimental approach of separating oxygen- and cobalt-derived (final) states by ResPES in the valence-band region is presented. The procedure takes advantage of an antiresonant behavior of cobalt-derived states at the 3p-3d excitation threshold. Information about the unoccupied density of states has been obtained by OK XAS. The structure of the CoL absorption edge is compared to semiempirical charge-transfer multiplet calculations. The experimental results are furthermore compared with band-structure calculations considering three different exchange potentials [generalized gradient approximation (GGA), using a nonlocal Hubbard U (GGA+U) and using a hybrid functional (Becke, three-parameter, Lee-Yang-Parr [B3LYP])]. For these different approaches total density of states and partial valence-band density of states have been investigated. The best qualitative agreement with experimental results has been obtained by using a GGA+U functional with U=2.9eV .

Ensling, David; Thissen, Andreas; Laubach, Stefan; Schmidt, Peter C.; Jaegermann, Wolfram

2010-11-01

338

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.

339

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

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

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

2014-05-01

340

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

341

Spin structure of impurity band of semiconductors in two and three-dimensional cases

The exchange interaction between electrons located at different randomly distributed impurities is studied for small density of impurities. The singlet-triplet splitting 2J(R) is calculated for two Coulomb centers at a distance R. Interpolated formulas are found which work for all distances R from zero to infinity. The data from atomic physics are used for the interpolation in three-dimensional case. For two-dimensional case the original calculations are performed to find asymptotic behavior of the splitting at large R, the splitting for the ``two-dimensional helium atom'' (R=0) and the splitting at $R=a_B$, where $a_B$ is the effective Bohr radius. The spin structure of impurity band is described by the Heisenberg Hamiltonian. The ground state of a system consists of localized singlets. The new results are obtained for the distribution of the singlet pairs in the ground state. These results are exact at low density. The problem is reduced to a non-trivial geometric problem which is solved in the mean field a...

Ponomarev, I V; Efros, A L

1999-01-01

342

Electronic band structures of AV(2) (A = Ta, Ti, Hf and Nb) Laves phase compounds.

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 AV(2) (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 (E(F)) 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(E(F)). N(E(F)) 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 E(F). Around the Fermi energy we notice that V-p shows strong hybridization with A-p states. PMID:21813979

Charifi, Z; Reshak, Ali Hussain; Baaziz, H

2009-01-14

343

Probing Small-Scale Interstellar Structure At High Column Densities

We propose to obtain very high resolution (~ 1.7 km s^- 1) observations of interstellar K I absorption toward the components of 5 multiple star systems as part of an ongoing program to more thoroughly understand recent evidence of ubiquitous small-scale structure in the diffuse ISM. Based upon KPNO Coude observations, Watson & Meyer (1996) have found interstellar Na I line profile variations toward 17 out of 17 binaries, indicative of ISM structure on scales of 500 to 29,000 AU. Using KPNO Coude Feed measurements of interstellar K I line profiles, Lauroesch & Meyer (1999) detected significant differences between components of multiple star systems in 3 out of 5 cases. However, Na I cannot be used to trace structure at high column densities, due to line saturation. Given its lower cosmic abundance, K I provides a useful probe of high column density sightlines. These differences suggest that the small- scale structure traced by Na I for low column density sightlines is present at some level in clouds of all column densities. However, the current sample size is too small for statistical analyses of the characteristics of structure and its variations. Our proposed observations are designed to supplement the undersampled high column density regime with systems previously selected, but not observed due to poor weather. Observations of these systems will double the size of the sample, allowing us to refine our conclusions about the presence of variations at various column densities and hence the mass fraction of the interstellar material involved.

Lauroesch, James T.; Meyer, David M.; Cartledge, Stefan I. B.

2000-02-01

344

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

Energy Technology Data Exchange (ETDEWEB)

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, Ue [Mehmet Akif Ersoy Ueniversitesi, Fen-Edebiyat Fakueltesi, Fizik Boeluemue, Burdur (Turkey); Arikan, N [Ahi Evran Ueniversitesi, Egitim Fakueltesi, Ilkgretim Boeluemue, Fen Bilgisi Anabilim Dali, Kirsehir (Turkey); Ugur, S; Ugur, G; Civi, M, E-mail: ubayhan@mehmetakif.edu.t [Gazi Ueniversitesi, Fen-Edebiyat Fakueltesi, Fizik Boeluemue, Teknikokullar, Ankara (Turkey)

2010-07-15

345

Band structure engineering through orbital interaction for enhanced thermoelectric power factor

International Nuclear Information System (INIS)

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

346

Band structure engineering through orbital interaction for enhanced thermoelectric power factor

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-02-24

347

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

348

Quadrant-type X-band single-cell structure for high gradient tests

International Nuclear Information System (INIS)

We are building a new high-gradient X-band (11.424 GHz) testbench, called “Shield-B,” for basic studies to establish a acceleration technology with 100MV/m or higher, where various single-cell structures are to be tested. We focus on quadrant-type structures, on which no surface currents associated with magnetic fields flow across cell-to-cell junctions unlike disk-type structures. In this study, we propose a quadrant-type X-band single-cell structure with a heavy damped structure by waveguides, overcoming its issues. (author)

349

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

350

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

351

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

International Nuclear Information System (INIS)

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 (?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

352

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)

353

In this paper, we propose a chiral metamaterial structure that enables dual-band asymmetric transmission effect for different linearly polarized electromagnetic waves. The metamaterial is composed of metallic spirals with two split-ring resonators sandwiching a dielectric slab and connecting with via hole. Strong one-way transmission of two orthogonally polarized waves at different frequency bands has been confirmed through both full-wave simulation and test on fabricated prototype at the microwave band. Analysis also shows such asymmetric transmission can be attributed to the induced asymmetric current distributions in the spiral that support strong polarization conversion and cross-polarization transmission. By scaling down the metamaterial structure, the concept could also be utilized at other frequency bands, such as submillimeter or even terahertz band and find applications in designing one-way electromagnetic wave devices or polarization spectral filters.

Wu, Linxiao; Zhang, Meng; Zhu, Bo; Zhao, Junming; Jiang, Tian; Feng, Yijun

2014-06-01

354

Anomalous Hall effect and energetic band structure of ferromagnetic nickel and iron

International Nuclear Information System (INIS)

The successive quantitative theory of the anomalous Hall effect (AHE) is constructed on the base of the established bond of AHE with the real energetic band structure of 3d-metals. The problem is solves numerically with regard to the presence of the s-band in the electronic 3d-metal structure (the s-band is two-fold degenerated into a spin and splitted into two s-subbands taking into account exchange interaction) and the d-band, which, in its turn, consists of five subbands with spins in the direction of magnetization and vice versa. Integration is carried out thoughout the Brillouin zone using the full law of s- and d-band electron dispersion. Contributions into AHE from impurity and single-phonon scattering processes are found. Calculation results are in good agreement with the existed experimental data on AHE for ferromagnetic iron and nickel

355

Strong Discontinuities in the Complex Photonic Band Structure of Transmission Metallic Gratings

Complex photonic band structures (CPBS) of transmission metallic gratings with rectangular slits are shown to exhibit strong discontinuities that are not evidenced in the usual energetic band structures. These discontinuities are located on Wood's anomalies and reveal unambiguously two different types of resonances, which are identified as horizontal and vertical surface-plasmon resonances. Spectral position and width of peaks in the transmission spectrum can be directly ext...

Collin, S.; Pardo, F.; Teissier, R.; Pelouard, J. -l

2000-01-01

356

Efficient VLSI Architecture For CSD Basedsub-Band Tree Structure Using 4-Tap Filter

A sub-band tree structure hardware design based on canonic signed digit (CSD) architecture is presented in this paper. We have proposed based on canonic signed digit (CSD) arithmetic for low complexity and efficient implementation of sub-band tree structure. The canonic signed digit (CSD) technique has been applied to reduce the number of full adders required by 2’s complement based deigns. This architecture is suitable for high speed on-line applications. With this architec...

Radhe Kant Mishra,; Dr. Subbaratnam Kumar

2014-01-01

357

Communication applications require wide band and highly directive planner antennas. For such requirement this work deals with the analysis and simulation of a rectangular microstrip patch antenna loaded with “INTERCONNECTED SRR” metamaterial structure at a height of 3.2mm from the ground plane. The work also investigates the potential properties of the proposed metamaterial structure. The proposed Antenna is designed at a operating frequency of 2.75GHz to meet S-Band (2-4GHz) applications...

Pramod Singhal; Bimal Garg

2012-01-01

358

International Nuclear Information System (INIS)

The electron energy band spectra of GaN and InN crystals are calculated within the mixed basis consisting of core Bloch functions and plane waves. The exchange potential is obtained on the basis of a new exchange-energy functional including electron density gradient corrections. The obtained parameters of the energy band structure of crystals are in better agreement with the data calculated using the exact exchange potential than those obtained in the Local Density Approximation. The calculated energies of semicore d-electrons are close to the experimental data.

359

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

360

The structure and function of band 3 (AE1): recent developments (review).

This review discusses recent advances in our understanding of the structure, function and molecular genetics of the membrane domain of red cell anion exchanger, band 3 (AE1), and its role in red cell and kidney disease. A new model for the topology of band 3 has been proposed, which suggests the membrane domain has 12 membrane spans, rather than the 14 membrane spans of earlier models. The major difference between the models is in the topology of the region on the C-terminal side of membrane spans 1-7. Two dimensional crystals of the deglycosylated membrane domain of band 3 have yielded two and three dimensional projection maps of the membrane domain dimer at low resolution. The human band 3 gene has been completely sequenced and this has facilitated the study of natural band 3 mutations and their involvement in disease. About 20% of hereditary spherocytosis cases arise from heterozygosity for band 3 mutations, and result in the absence or decrease of the mutant protein in the red cell membrane. Several other natural band 3 mutations are known that appear to be clinically benign, but alter red cell phenotype or are associated with altered red cell blood group antigens. These include the mutant band 3 present in Southeast Asian ovalocytosis, a condition which provides protection against cerebral malaria in children. Familial distal renal tubular acidosis, a condition associated with kidney stones, has been shown to result from a novel group of band 3 mutations. The total absence of band 3 has been described in animals-occurring naturally in cattle and after targeted disruption in mice. Some of these severely anaemic animals survive, so band 3 is not strictly essential for life. Although the band 3-negative red cells were very unstable, they contained a normally-assembled red cell skeleton, suggesting that the bilayer of the normal red cell membrane is stabilized by band 3 interactions with membrane lipids, rather than by interactions with the spectrin skeleton. PMID:9491367

Tanner, M J

1997-01-01

361

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

362

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.; Ersfeld, B.; Farmer, J. P.; Hur, M. S.; Issac, R. C.; Jaroszynski, D. A.

2013-09-01

363

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.

364

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

365

Application of Hyperspectral Band Elimiation Technique to PVT Images of Composite Structures

Directory of Open Access Journals (Sweden)

Full Text Available A new approach to NDT of composite structures using Band Elimination of the analyzed image index by Hyperspectral image analysis approach is presented and discussed. The matrix Band Elimination technique allows the monitoring and analysis of a components structure based on Filtering of bands and correlation between sequentially pulsed thermal images and their indices. The technique produces several matrices resulting from frame deviation and pixel redistribution calculations for intelligent classification and property prediction. The obtained results proved the technique to be capable of identifying damaged components with ability to model various types of damage under different conditions.

Mahmoud Zaki Iskandarani

2012-10-01

366

Dual-Band Terahertz Left-Handed Metamaterial with Fishnet Structure

International Nuclear Information System (INIS)

We present the design of a dual-band left-handed metamaterial with fishnet structure in the terahertz regime. Its left-handed properties are described by the retrieved effective electromagnetic parameters. We introduce an equivalent circuit which offers a theoretical explanation for the left-handed behavior of the dual-band fishnet metamaterial, and investigate its losses receiving higher figure of merit. The design is beneficial to the development of frequency agile and broadband THz materials and devices. The dual-band fishnet metamaterial can be extended to infrared and optical frequency ranges by regulating the structural parameters. (fundamental areas of phenomenology (including applications))

367

We perform first principles band calculation of electron doped iron-based superconductors adopting the virtual crystal approximation. We find that when electrons are doped by element substitution in the blocking layer, the band structure near the Fermi level is affected due to the increase of the positive charge in the layer. On the other hand, when Fe in the conducting layer is substituted by Co, the band structure is barely affected. This difference should be a key factor in understanding the phase diagram of the heavily doped electron doped systems LnFeAsO1-xHx.

Suzuki, K.; Usui, H.; Iimura, S.; Sato, Y.; Matsuishi, S.; Hosono, H.; Kuroki, K.

368

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

369

Ion band-state fusion: Reactions, power density, and the quantum reality question

International Nuclear Information System (INIS)

The effects that limit deuterium-deuterium (D-D) fusion in bound systems, as opposed to those limiting D-D fusion in free space, are the result of quantum-mechanical particle-particle wave function correlation, which may inhibit wave function overlap. Whether or not this occurs at room temperature is determined by system energy minimization, not Gamow theory. A counterintuitive example, known from atomic physics, that demonstrates how this alternative criterion may alter the relevant quantum mechanics is illustrated by the helium atom. At room temperature, near-complete overlap of the two helium electrons takes place when energy is minimized, while Gamow theory predicts negligible overlap. On the other hand, energy minimization does not predict that no nucleus-nucleus overlap ever occurs in any normal molecule. In D+ ion band-state matter, D+-D+ overlap occurs if the distributed charge view of quantum reality is correct, in which case D+ band-state matter converts to 4He++ band-state matter, releasing heat throughout a crystal lattice. This occurs in the limit x ? 1 in PdDx (in agreement with experiments), provided adequate crystalline order is present. Further deuterium loading requires that additional injected deuterium occupy ionic band-like states in which only a small fraction of each additional deuterium atom occupies a lattice unit cell. Then, in each nuclear reaction, again to minimin each nuclear reaction, again to minimize energy of the entire system, the energy is distributed over many lattice sites, inhibiting production of energetic particles. Theory shows that steady-state power is proportional to the loading current. These points are discussed. An expression for P is derived, and possible cold fusion reactions are summarized. 23 refs., 1 fig

370

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

371

Energy Technology Data Exchange (ETDEWEB)

Highlights: ? We performed high resolution ARPES on 1T–ZrS{sub x}Se{sub 2?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 ZrS{sub 2} towards ZrSe{sub 2}. ? 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–ZrS{sub x}Se{sub 2?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 ZrS{sub 2} towards ZrSe{sub 2}, 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.

Moustafa, Mohamed, E-mail: moustafa@physik.hu-berlin.de [Institut für Physik, Humboldt Universität zu Berlin, Newtonstr. 15, D-12489 Berlin (Germany); Faculty of Engineering, Pharos University in Alexandria, Canal El Mahmoudia Str., Alexandria (Egypt); Ghafari, Aliakbar; Paulheim, Alexander; Janowitz, Christoph; Manzke, Recardo [Institut für Physik, Humboldt Universität zu Berlin, Newtonstr. 15, D-12489 Berlin (Germany)

2013-08-15

372

Energy Technology Data Exchange (ETDEWEB)

Highlights: ? Near Edge X-ray Absorption Fine Structure investigated as tool for probing the conduction band in Cu(In,Ga)S{sub 2}. ? Absorption edge of anion contains most pertinent electronic information. ? Development of Cu(In,Ga){sub 2} band gap with increased Ga content reflected in anion absorption edge positions. ? Correspondence with theory found. -- Abstract: A non-optimized interface band alignment in a heterojunction-based solar cell can have negative effects on the current and voltage characteristics of the resulting device. To evaluate the use of Near Edge X-ray Absorption Fine Structure spectroscopy (NEXAFS) as a means to measure the conduction band position, Cu(In,Ga)S{sub 2} chalcopyrite thin film surfaces were investigated as these form the absorber layer in solar cells with the structure ZnO/buffer/Cu(In,Ga)S{sub 2}/Mo/glass. The composition dependence of the structure of the conduction bands of CuIn{sub x}Ga{sub 1?x}S{sub 2} has been revealed for x = 0, 0.67 and 1 with both hard and soft NEXAFS and the resulting changes in conduction band offset at the junction with the buffer layer discussed. A comprehensive study of the positions of the absorption edges of all elements was carried out and the development of the conduction band with Ga content was observed, also with respect to calculated densities of states.

Johnson, Benjamin, E-mail: benjamin.johnson@alumni.tu-berlin.de [Helmholtz-Zentrum Berlin, Albert-Einstein-Str. 15, 12489 Berlin (Germany); Klaer, Jo; Merdes, Saoussen; Gorgoi, Mihaela; Höpfner, Britta; Vollmer, Antje; Lauermann, Iver [Helmholtz-Zentrum Berlin, Albert-Einstein-Str. 15, 12489 Berlin (Germany)

2013-10-15

373

International Nuclear Information System (INIS)

Highlights: ? Near Edge X-ray Absorption Fine Structure investigated as tool for probing the conduction band in Cu(In,Ga)S2. ? Absorption edge of anion contains most pertinent electronic information. ? Development of Cu(In,Ga)2 band gap with increased Ga content reflected in anion absorption edge positions. ? Correspondence with theory found. -- Abstract: A non-optimized interface band alignment in a heterojunction-based solar cell can have negative effects on the current and voltage characteristics of the resulting device. To evaluate the use of Near Edge X-ray Absorption Fine Structure spectroscopy (NEXAFS) as a means to measure the conduction band position, Cu(In,Ga)S2 chalcopyrite thin film surfaces were investigated as these form the absorber layer in solar cells with the structure ZnO/buffer/Cu(In,Ga)S2/Mo/glass. The composition dependence of the structure of the conduction bands of CuInxGa1?xS2 has been revealed for x = 0, 0.67 and 1 with both hard and soft NEXAFS and the resulting changes in conduction band offset at the junction with the buffer layer discussed. A comprehensive study of the positions of the absorption edges of all elements was carried out and the development of the conduction band with Ga content was observed, also with respect to calculated densities of states

374

International Nuclear Information System (INIS)

Besides of their well-known wide range of properties it was recently shown that many of the heavy Heusler semiconductors with 1:1:1 composition and C1b structure exhibit a zero band gap behavior and are topological insulators induced by their inverted band structure. In the present study, the electronic structure of the Heusler compounds PtYSb and PtLaBi was investigated by bulk sensitive hard x-ray photoelectron spectroscopy. The measured valence band spectra are clearly resolved and in well agreement to the first-principles calculations of the electronic structure of the compounds. The experimental results give clear evidence for the zero band gap state.

375

S-band accelerating structures for the PAL-XFEL

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

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

2015-02-01

376

Ab initio calculations of quasiparticle band structure in correlated systems LDA++ approach

We discuss a general approach to a realistic theory of the electronic structure in materials containing correlated d- or f- electrons. The main feature of this approach is the taking into account the energy dependence of the electron self-energy with the momentum dependence being neglected (local approximation). In the case of strong interactions (U/W>>1 - rare-earth system) the Hubbard-I approach is the most suitable. Starting from an exact atomic Green function with the constrained density matrix the band structure problem is formulated as the functional problem on Nmm' for f-electrons and the standard LDA-functional for delocalized electrons. In the case of moderate correlations (U/W=1 metal-insulator regime) we start from the dynamical mean field iterative perturbation scheme (IPS) of G. Kotliar et. al. and also make use of our multiband atomic Green function. Finally for the weak interactions (U/W<1 -transition metals) the self-consistent diagrammatic fluctuation- exchange (FLEX)-approach of N. Bicker...

Lichtenstein, A I

1997-01-01

377

Photonic band gaps in materials with triply periodic surfaces and related tubular structures

We calculate the photonic band gap of triply periodic bicontinuous cubic structures and of tubular structures constructed from the skeletal graphs of triply periodic minimal surfaces. The effect of the symmetry and topology of the periodic dielectric structures on the existence and the characteristics of the gaps is discussed. We find that the C(I2-Y**) structure with Ia3d symmetry, a symmetry which is often seen in experimentally realized bicontinuous structures, has a phot...

Michielsen, K.; Kole, J. S.

2003-01-01

378

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

379

Fine structure of the red luminescence band in undoped GaN

International Nuclear Information System (INIS)

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

380

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

381

Estimating density dependence from time series of population age structure.

Population fluctuations are caused by demographic and environmental stochasticity, time lags due to life history, and density dependence. We model a general life history allowing density dependence within and among age or stage classes in a population undergoing small or moderate fluctuations around a stable equilibrium. We develop a method for estimating the overall strength of density dependence measured by the rate of return toward equilibrium, and we also consider a simplified population description and forecasting using the density-dependent reproductive value. This generality comes at the cost of requiring a time series of the population age or stage structure instead of a univariate time series of adult or total population size. The method is illustrated by analyzing the dynamics of a fully censused population of red deer (Cervus elaphus) based on annual fluctuations of age structure through 21 years. PMID:16685637

Lande, Russell; Engen, Steinar; Saether, Bernt-Erik; Coulson, Tim

2006-07-01

382

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

383

Measurement of wake-field suppression in a detuned X-band accelerator structure

International Nuclear Information System (INIS)

Research is under way at SLAC to develop accelerator structure for a next generation linear collider. A full-scale prototype X-band structure has been built in which the dipole mode frequencies were detuned to suppress the long-range transverse wake field by about 2 orders of magnitude. To verify that the detuning works as expected, a facility, the Accelerator Structure Setup, was constructed in the SLAC Linear Collider to measure the long-range wake field. This Letter presents the results from the measurement of the prototype X-band structure with this facility

384

Control over band structure and tunneling in bilayer graphene induced by velocity engineering

International Nuclear Information System (INIS)

The band structure and transport properties of massive Dirac fermions in bilayer graphene with velocity modulation in space are investigated in the presence of a previously created band gap. It is pointed out that velocity engineering may be considered as a factor to control the band gap of symmetry-broken bilayer graphene. The band gap is direct and independent of velocity value if the velocity modulated in two layers is set up equally. Otherwise, in the case of interlayer asymmetric velocity, not only is the band gap indirect, but also the electron–hole symmetry fails. This band gap is controllable by the ratio of the velocity modulated in the upper layer to the velocity modulated in the lower layer. In more detail, the shift of momentum from the conduction band edge to the valence band edge can be engineered by the gate bias and velocity ratio. A transfer matrix method is also elaborated to calculate the four-band coherent conductance through a velocity barrier possibly subjected to a gate bias. Electronic transport depends on the ratio of velocity modulated inside the barrier to that for surrounding regions. As a result, a quantum version of total internal reflection is observed for thick enough velocity barriers. Moreover, a transport gap originating from the applied gate bias is engineered by modulating the velocities of the carriers in the upper and lower layers. (paper)

385

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

386

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

387

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

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

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

2015-02-01

388

Structures électromagnétiques à bandes interdites pour des applications de filtre

The increasing development of wireless applications turns out to new requirements for transceiver architectures that have to feature excellent microwave performances (linearity, spurious rejection, noise figure and bandwidth) and enhanced integration density that is achieved through the miniaturization of the modules as well as the introduction of multi standard functionalities. All these requirements translate to the need of filter circuits as miniaturized as possible and featuring the highe...

Badr El Din El Shaarawy, Heba

2009-01-01

389

Effect of Upper Mantle Density Structure on Moho Geometry

A constant value of the Moho density contrast is often assumed in the gravimetric methods used for determination of Moho geometry. This assumption might be sufficient in regional studies with a relatively homogenous lithospheric structure (and, consequently, small lateral variations in Moho density contrast). In global studies, however, this assumption is not reasonable, because not only the Moho depth but also the Moho density contrast vary substantially, and are, thus, likely to result in systematic errors in Moho geometry determined globally from gravity data. In this study we address this issue by investigating the effect of variable Moho density contrast on Moho geometry. We demonstrate that assumption of variable Moho density contrast (instead of a uniform model) substantially improves agreement between the global gravimetric and seismic Moho models by approximately 30 %.

Tenzer, Robert; Chen, Wenjin; Jin, Shuanggen

2014-11-01

390

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

391

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

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

2015-01-01

392

Shape Dependence of Band-Edge Exciton Fine Structure in CdSe Nanocrystals

International Nuclear Information System (INIS)

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

393

Structure and vapor adsorption of low-density silica aerogels

International Nuclear Information System (INIS)

Nano-porous material SiO2 aerogels can not only be used as a low temperature Nuclear Target in ICF but also be used as an adsorbent of HTO vapor. BET, SEM, Pore Size Distribution and TEM techniques were used to characterize the morphology and pore structure of the low-density silica aerogels. Gas adsorption of the low-density silica aerogels was measured for the samples with various densities (18.6?200 kg·m-3). Measurements were done at various pressure drops with water and benzene. The results of the adsorption isotherms were analyzed with BET multilayer adsorption theory

394

Quantum dot density studies for quantum dot intermediate band solar cells

Energy Technology Data Exchange (ETDEWEB)

Quantum dots (QDs) have been an active area of research for many years and have been implemented in several applications, such as lasers and detectors. During the last years, some attempts have been made to increase the absorption and efficiency of solar cells by inserting QDs into the intrinsic region of pin solar cells. So far, these attempts have been successful in increasing the absorption, but not the cell efficiency. There are probably several reasons for this lack of efficiency increase, but we believe that one important reason is the low density of the implemented QDs. In this work, samples of single layer InAs QDs on n-GaAs(001) substrates have been grown by molecular beam epitaxy (MBE) and we have performed a systematic study of how deposition parameters affect the QD density. The aim is to achieve densities > 1011 cm-2. The nominal substrate temperature (360 - 500 deg. C), the InAs growth rate (0.085 - 1 ML/s) and thickness (2.0 - 2.8 ML) have been varied in a systematic way for two different deposition methods of InAs, i.e. continuous deposition or deposition with interruptions. In addition, we have for the continuous growth samples also varied the As-flux (0.5 - 6 centre dot10-6 torr). Scanning electron microscopy (SEM) has been the main characterization method to determine quantum dot sizes and densities, and atomic force microscopy (AFM) has been used for evaluation of the quantum dot heights. We find that the QD density increases with reduced growth temperature and that it is higher for samples grown continuously than for samples grown with growth interruptions. The homogeneity is also strongly affected by temperature, InAs deposition method and the As-flux. We have observed QD densities as high as 2.5 centre dot1011 cm-2 for the samples grown at the lowest growth temperatures. (Author)

Thomassen, Sedsel Fretheim; Zhou, Dayong; Vitelli, Stefano; Mayani, Maryam Gholami; Fimland, Bjoern-Ove; Reenaas, Turid Worren

2010-07-01

395

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

396

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

397

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.

398

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

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

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

2015-02-01

399

Study of the 4f and valence band density of states in rare-earth metals

International Nuclear Information System (INIS)

The 4f and valence states of all metallic rare earths have been studied using x-ray photoelectron spectroscopy (XPS) for the occupied part and bremsstrahlung isochromat spectroscopy (BIS) for the unoccupied part. It is found that the bandwidth increases from Gd to Lu, and that the valence band spectra are in fair agreement with APW calculations. The intensities of the 4f final-state multiplets are well described in terms of the coefficients of fractional parentage. There is a symmetry between the fsup(n) XPS and fsup(14-n) BIS spectra. The observed energies of the 4f excitations correspond to transitions to completely screened final states. These values enable one to predict the elements which are liable to interconfiguration fluctuation when their 4f levels are shifted to Esub(F) by the chemical environment or by compression. The large Coulomb correlation energies, U which prevent the formation of 4f bands in these elements, are directly obtained from the spectra observed and are found to be in good agreement with recent calculations. The linewidths and singularity indices of the XPS and BIS 4f lines are determined and discussed. (author)

400

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.

401

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

402

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.

403

Band alignment of HfO2 on SiO2/Si structure

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

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

2012-03-01

404

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

Energy Technology Data Exchange (ETDEWEB)

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; Huang, Tsun-Che; Wang, Chin-Hung; Chang, Pin [Industrial Technology Research Institute-South, Tainan 709, Taiwan (China); Hsu, Jin-Chen, E-mail: fengchiahsu@itri.org.t, E-mail: hsujc@yuntech.edu.t [Department of Mechanical Engineering, National Yunlin University of Science and Technology, Douliou, Yunlin 64002, Taiwan (China)

2011-09-21

405

It was reported earlier [Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.106.056401 106, 056401 (2011)] that the skutterudite structure compound CoSb3 displays a unique band structure with a topological transition versus a symmetry-preserving sublattice (Sb) displacement very near the structural ground state. The transition is through a massless Dirac-Weyl semimetal, point Fermi surface phase which is unique in that (1) it appears in a three-dimensional crystal, (2) the band critical point occurs at k=0, and (3) linear bands are degenerate with conventional (massive) bands at the critical point (before inclusion of spin-orbit coupling). Further interest arises because the critical point separates a conventional (trivial) phase from a topological phase. In the native cubic structure this is a zero-gap topological semimetal; we show how spin-orbit coupling and uniaxial strain converts the system to a topological insulator (TI). We also analyze the origin of the linear band in this class of materials, which is the characteristic that makes them potentially useful in thermoelectric applications or possibly as transparent conductors. We characterize the formal charge as Co+ d8, consistent with the gap, with its 3¯ site symmetry, and with its lack of moment. The Sb states are characterized as px (separately, py) ?-bonded Sb4 ring states occupied and the corresponding antibonding states empty. The remaining (locally) pz orbitals form molecular orbitals with definite parity centered on the empty 2a site in the skutterudite structure. Eight such orbitals must be occupied; the one giving the linear band is an odd orbital singlet A2u at the zone center. We observe that the provocative linearity of the band within the gap is a consequence of the aforementioned near-degeneracy, which is also responsible for the small band gap.

Pardo, V.; Smith, J. C.; Pickett, W. E.

2012-06-01

406

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

407

Band structure engineering of anatase TiO{sub 2} by metal-assisted P-O coupling

Energy Technology Data Exchange (ETDEWEB)

In this work, we demonstrate that the metal-assisted P-O coupling is an effective approach to improve the photoelectrochemical properties of TiO{sub 2}. The (Sc + P) and (In + P) codoping effects on electronic structures and photocatalytic activities of anatase TiO{sub 2} 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 TiO{sub 2}, 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 TiO{sub 2}. Moreover, the band edge alignments in (Sc + P) and (In + P) codoped anatase TiO{sub 2} are desirable for water-splitting. The calculated optical absorption curves indicate that (Sc + P) and (In + P) codoping in anatase TiO{sub 2} can also effectively enhance the visible light absorption.

Wang, Jiajun; Meng, Qiangqiang [Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026 (China); Huang, Jing [Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026 (China); School of Materials and Chemical Engineering, Anhui Jianzhu University, Hefei, Anhui 230601 (China); Li, Qunxiang, E-mail: liqun@ustc.edu.cn; Yang, Jinlong [Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026 (China); Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China)

2014-05-07

408

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

409

A NEW DIAGNOSTIC OF THE RADIAL DENSITY STRUCTURE OF Be DISKS

International Nuclear Information System (INIS)

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 that 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 three-dimensional 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 counterclockwise loop structures we observe in BJV diagrams might be caused by the mass decretion rate changing between subsequent 'on/off' sequences. Applying this new diagnostic to a larger sample of Be disk systems will provide insight into the time-dependent nature of each system's stellar decretion rate.

410

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

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

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

2014-08-27

411

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

412

SbSI Based Photonic Crystal Superlattices: Band Structure and Optics

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

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

2015-03-01

413

Influence of distortion on the electronic band structure of CuInSe2

We present a tight-binding calculation of the influence of distorsion on the bulk electronic structure of the chalcopyrite CuInSe2. We calculate the ideal case and then the effect of the inclusion of the distortions. We analyze our results in detail and conclude from a comparison with other work that the distortions must be included in the Hamiltonian to get a proper account of the electronic band structure. We use our new Hamiltonian to study the effect that both the tetragonal and the anionic distortion have on the (112) surface electronic band structure. We find this effect non-negligible.

Tototzintle-Huitle, H; Rodríguez, José Alberto; Baquero, R

2005-01-01

414

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

415

Electronic structure and optical band gap of CoFe2O4 thin films

Electronic structure and optical band gap of CoFe2O4 thin films grown on (001) oriented LaAlO3 have been investigated. Surprisingly, these films show additional Raman modes at room temperature as compared to a bulk spinel structure. The splitting of Raman modes is explained by considering the short-range ordering of Co and Fe cations in octahedral site of spinel structure. In addition, an expansion of band-gap is observed with the reduction of film thickness, which is explai...

Ravindra, A. V.; Padhan, P.; Prellier, W.

2012-01-01

416

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

Energy Technology Data Exchange (ETDEWEB)

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.

Hossain, Nadir; Sweeney, Stephen [Advanced Technology Institute and Department of Physics, University of Surrey, Guildford, Surrey GU2 7XH (United Kingdom); Hosea, Jeff [Advanced Technology Institute and Department of Physics, University of Surrey, Guildford, Surrey GU2 7XH, UK and Ibnu Sina Institute for Fundamental Science Studies, Universiti Teknologi Malaysia, Johor Bahru 81310 (Malaysia); Liebich, Sven; Zimprich, Martin; Volz, Kerstin; Stolz, Wolfgang [Material Sciences Center and Faculty of Physics, Philipps-University, 35032 Marburg (Germany); Kunert, Bernerdette [NAsP III/V GmbH, Am Knechtacker 19, 35041 Marburg (Germany)

2013-12-04

417

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

418

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

419

DENSITY CONSCIOUS SUBSPACE CLUSTERING USING ITL DATA STRUCTURE

Directory of Open Access Journals (Sweden)

Full Text Available Most of the subspace clustering algorithms uses monotonicity property to generate higher dimensional subspaces. But this property is not applicable here since different subspace cardinalities have varying densities i.e., if a k-dimensional unit is dense, any (k-1 dimensional projection of this unit may not be dense. So in DENCOS a mechanism to compute upper bounds of region densities to constrain the search of dense regions is devised, where the regions whose density upper bounds are lower than the density thresholds will be pruned away in identifying the dense regions. They compute the region density upper bounds by utilizing a data structure, DFP-tree to store the summarized information of the dense regions. DFP-Tree employs FP-Growth algorithm and builds an FP-Tree based on the prefix tree concept and uses it during the entire subspace identification process. This method performs repeated horizontal traversals of the data to generate relevant subspaces which is time consuming. To reduce the time complexity, we employ ITL data structure to build Density Conscious ITL (DITL tree to be used in the entire subspace identification process. ITL reduces the cost by scanning the database only once, by significantly reducing the horizontal traversals of the database. The algorithm is evaluated through experiments on a collection of benchmark data sets datasets. Experimental results have shown favorable performance compared with other popular clustering algorithms.

C. Palanisamy

2011-01-01

420

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

421

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

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

Izrailev, Felix; Molinari, Luca; Z?yczkowski, Karol

1996-01-01

422

Band-structure trend in cuprates and correlation with $T_{c max}$

By calculation and analysis of the band structures of 15 superconducting cuprates, we have identified the energy of the so-called axial-orbital as the essential material dependent parameter. It controls the range of the intralayer hopping, the perpendicular hopping, the Cu 4s-character of the conduction-band orbital, and correlates with the observed Tc at optimal doping. We discuss how it may be influenced.

Pavarini, E; Saha-Dasgupta, T; Jepsen, O; Andersen, O K

2001-01-01

423

Electronic structure and spin-density distribution in Y2Fe17 (abstract)

International Nuclear Information System (INIS)

We have calculated the spin-polarized band structure of the Y2Fe17 compound in the rhombohedral structure using the first-principles self-consistent orthogonalized linear combination of atomic orbitals method in the local spin-density approximation. Using a real space integration scheme, we have obtained the site-decomposed magnetic moments as follows: -0.28?B on Y-6(c), 2.54?B on Fe-6(c), 2.08?B on Fe-9(d), 2.28?B on Fe-18(f), and 2.10 on Fe-18(h). Similar values are obtained when the more traditional Mulliken scheme is used. The calculated spin magnetic moments are in good agreement with Moessbauer data but are somewhat larger than these obtained by Coehoorn using the linear muffin-tin orbitals (LMTO) method.1 The calculated density of states are similar to that of Coehoorn's. In order to have a better insight on the magnetic structure of Y2Fe17, the real space spin density distributions are plotted and it is shown that the negative spin density on the Y site extends to a fairly large region. We will extend our calculation to Nd2Fe17 crystal and to cases in which the Fe atoms are selectively substituted by Al, Si, and Ga, as well as the effect of the N addition. Previous OLCAO calculations2,3 on Nd2Fe17N systems were nonself-consistent and therefore less reliable

424

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

425

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

426

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

427

We have studied the electronic structure of C and N co-doped TiO2 using hard x-ray photoelectron spectroscopy and first-principles density functional theory calculations. Our results reveal overlap of the 2p states of O, N, and C in the system which shifts the valence band maximum towards the Fermi level. Combined with optical data we show that co-doping is an effective route for band gap reduction in TiO2. Comparison of the measured valence band with theoretical photoemission density of states reveals the possibility of C on Ti and N on O site.

Ruzybayev, Inci; Baik, Seung Su; Rumaiz, Abdul. K.; Sterbinsky, G. E.; Woicik, J. C.; Choi, Hyoung Joon; Ismat Shah, S.

2014-12-01

428

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

429

Efficient VLSI Architecture For CSD Basedsub-Band Tree Structure Using 4-Tap Filter

Directory of Open Access Journals (Sweden)

Full Text Available A sub-band tree structure hardware design based on canonic signed digit (CSD architecture is presented in this paper. We have proposed based on canonic signed digit (CSD arithmetic for low complexity and efficient implementation of sub-band tree structure. The canonic signed digit (CSD technique has been applied to reduce the number of full adders required by 2’s complement based deigns. This architecture is suitable for high speed on-line applications. With this architecture the speed of the sub-band tree structure is increased with a factor two but the occupied area of the circuit is less than double. It has 100% hardware utilization efficiency.

Radhe Kant Mishra,

2014-07-01

430

Infrared absorption, multiphonon processes and time reversal effect on Si and Ge band structure

Energy Technology Data Exchange (ETDEWEB)

We have examined the effect of Time Reversal Symmetry (TRS) on vibrational modes and on the electronic band structure of Si and Ge. Most of the primary non-interacting modes are not affected by TRS. Only phonons originating from high symmetry lines S and A of the Brillouin Zone (BZ) indicate extra degeneracy. Selection rules for some two and three phonons originating from high symmetry lines are determined. The states of electrons and holes described by electronic band structure due to spin-inclusion are assigned by spinor representations of the double space group. Inclusion of the TRS into the band structure results in extra degeneracy of electrons and holes, and therefore optical selection rules suppose to be modified.

Kunert, H.W. [Department of Physics, University of Pretoria, 0002 (South Africa); Machatine, A.G.J. [Department of Physics, University of Pretoria, 0002 (South Africa)], E-mail: augusto.machatine@up.ac.za; Malherbe, J.B. [Department of Physics, University of Pretoria, 0002 (South Africa); Barnas, J. [Department of Physics, Adam Mickiewicz University, ul. Umultowska 85, 61-614 Poznan (Poland); Hoffmann, A.; Wagner, M.R. [Institut fuer Festkoerperphysik, Technische Universitaet Berlin, Hardenbergerstr. 36, 10 623 Berlin (Germany)

2008-11-03

431

Infrared absorption, multiphonon processes and time reversal effect on Si and Ge band structure

International Nuclear Information System (INIS)

We have examined the effect of Time Reversal Symmetry (TRS) on vibrational modes and on the electronic band structure of Si and Ge. Most of the primary non-interacting modes are not affected by TRS. Only phonons originating from high symmetry lines S and A of the Brillouin Zone (BZ) indicate extra degeneracy. Selection rules for some two and three phonons originating from high symmetry lines are determined. The states of electrons and holes described by electronic band structure due to spin-inclusion are assigned by spinor representations of the double space group. Inclusion of the TRS into the