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1

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

CERN Document Server

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

2

From Metal Cluster to Metal Nanowire: A Topological Analysis of Electron Density and Band Structure Calculation  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract:We investigate a theoretical model of molecular metalwire constructed from linear polynuclear metal complexes. In particular we study the linear Crn metal complex and Cr molecular metalwire. The electron density distributions of the model nanowire and the linear Crn metal complexes, with n = 3, 5, and 7, are calculated by employing CRYSTAL98 package with topological analysis. The preliminary results indicate that the bonding types between any two neighboring Cr are all the same, namely the polarized open-shell interaction. The pattern of electron density distribution in metal complexes resembles that of the model Cr nanowire as the number of metal ions increases. The conductivity of the model Cr nanowire is also tested by performing the band structure calculation.

Feng-Yin Li; Likey Chen; Chung-Yuan Mou; Shie-Ming Peng; Yu Wang

2002-01-01

3

Band structure of LaB6 by an algorithm for filtering reconstructed electron-positron momentum densities  

CERN Multimedia

A new method (NM) for filtering three-dimensional reconstructed densities is proposed. The algorithm is tested with simulated spectra and employed to study the electronic structure of the rare-earth compound LaB6. For this system, momentum densities are reconstructed from theoretical and experimental two-dimensional angular correlation of electron-positron annihilation radiation (2D ACAR) spectra. The experimental results are in good agreement with the band structure calculated with the full-potential linearized augmented-plane-wave (FLAPW) method within the local-density approximation (LDA), apart from the detection of small electron pockets in the 15th band. It is also shown that, unlike the electron-positron enhancement, the electron-electron correlations affect noticeably the momentum density.

Kontrym-Sznajd, G; Biasini, M; Kubo, Y

2004-01-01

4

Confidence bands in density estimation  

CERN Multimedia

Given a sample from some unknown continuous density $f:\\mathbb{R}\\to\\mathbb{R}$, we construct adaptive confidence bands that are honest for all densities in a "generic" subset of the union of $t$-H\\"older balls, $0densities for which our results do not hold is shown to be nowhere dense in the relevant H\\"older-norm topologies. In the course of the proofs we also obtain limit theorems for maxima of linear wavelet and kernel density estimators, which are of independent interest.

Giné, Evarist; 10.1214/09-AOS738

2010-01-01

5

Energy band structure, fermi surfaces, magnetization densities, and properties of the rare-earths and actinides  

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.

1977-07-06

6

Magnetoresistance in pulsed fields, band structure calculations and charge-density wave instability in (TSeT){sub 2}Cl  

Energy Technology Data Exchange (ETDEWEB)

Diffuse X-rays measurements assign the 26 K metal-semimetal transition in (TSeT){sub 2}Cl, where TSeT = tetraselenotetracene, to the stabilization of a 2k{sub F}=c{sup *}/4 charge-density wave ground state. Tight-binding extended Hueckel band calculations suggest that 2k{sub F} yields to a partial nesting of the four conduction bands. Transverse magnetoresistance experiments performed up to 37 T confirm the previous observation of SdH oscillations. The 0{sup +} Landau level is evidenced for the first time. (orig.)

Goze, F. [Lab. de Physique des Solides et Service National des Champs Magnetiques Pulses du CNRS, 31 Toulouse (France); Audouard, A. [Lab. de Physique des Solides et Service National des Champs Magnetiques Pulses du CNRS, 31 Toulouse (France); Brossard, L. [Lab. de Physique des Solides et Service National des Champs Magnetiques Pulses du CNRS, 31 Toulouse (France); Laukhin, V.N. [Lab. de Physique des Solides et Service National des Champs Magnetiques Pulses du CNRS, 31 Toulouse (France)]|[Inst. of Chemical Physics, Chernogolovka (Russian Federation); Ulmet, J.P. [Lab. de Physique des Solides et Service National des Champs Magnetiques Pulses du CNRS, 31 Toulouse (France); Doublet, M.L. [Lab. de Chimie Theorique, Univ. Paris-Sud, 91 Orsay (France); Canadell, E. [Lab. de Chimie Theorique, Univ. Paris-Sud, 91 Orsay (France); Pouget, J.P. [Lab. de Physique des Solides, Univ. Paris-Sud, 91 Orsay (France); Zavodnik, V.E. [Karpov`s Physics and Chemistry Inst., Moscow (Russian Federation); Shibaeva, R.P. [Inst. of Solid State Physics, Chernogolovka (Russian Federation); Hilti, B. [Central Research Lab., Basel (Switzerland); Mayer, C.W. [Central Research Lab., Basel (Switzerland)

1995-03-15

7

Effects of side-chain and electron exchange correlation on the band structure of perylene diimide liquid crystals: a density functional study.  

UK PubMed Central (United Kingdom)

The structural and electronic properties of perylene diimide liquid crystal PPEEB are studied using ab initio methods based on the density functional theory (DFT). Using available experimental crystallographic data as a guide, we propose a detailed structural model for the packing of solid PPEEB. We find that due to the localized nature of the band edge wave function, theoretical approaches beyond the standard method, such as hybrid functional (PBE0), are required to correctly characterize the band structure of this material. Moreover, unlike previous assumptions, we observe the formation of hydrogen bonds between the side chains of different molecules, which leads to a dispersion of the energy levels. This result indicates that the side chains of the molecular crystal not only are responsible for its structural conformation but also can be used for tuning the electronic and optical properties of these materials.

Arantes JT; Lima MP; Fazzio A; Xiang H; Wei SH; Dalpian GM

2009-04-01

8

Hybrid density functional based study on the band structure of trioctahedral mica and its dependence on the variation of Fe(2+) content.  

Science.gov (United States)

A hybrid density functional based study of a phyllosilicate (PS) is presented here for the first time. Using all-electron electronic structure calculations with the B3LYP hybrid functional, we have investigated the electronic and structural properties of a series of trioctahedral 1M-polytype K-bearing micas starting from phlogopite (the Mg-end member), ending with the annite (the Fe-end member), and passing through the biotite (a solid solution of the end members). Electronic band gap is calculated for all the compositions and nature of the electronic transition is discussed with the aid of band structure and density of states plots. An excellent agreement with the available experimental data has been observed. An insulator to semiconductor transition is explained on the basis of orbital hybridization. A further comparison is made using the pure GGA functional. For the completeness of the study, the dielectric properties of phlogopite are calculated using the coupled perturbed Kohn-Sham scheme, as implemented within the CRYSTAL09 code. PMID:23810986

Timón, V; Praveen, C S; Escamilla-Roa, E; Valant, M

2013-06-06

9

Hybrid density functional based study on the band structure of trioctahedral mica and its dependence on the variation of Fe(2+) content.  

UK PubMed Central (United Kingdom)

A hybrid density functional based study of a phyllosilicate (PS) is presented here for the first time. Using all-electron electronic structure calculations with the B3LYP hybrid functional, we have investigated the electronic and structural properties of a series of trioctahedral 1M-polytype K-bearing micas starting from phlogopite (the Mg-end member), ending with the annite (the Fe-end member), and passing through the biotite (a solid solution of the end members). Electronic band gap is calculated for all the compositions and nature of the electronic transition is discussed with the aid of band structure and density of states plots. An excellent agreement with the available experimental data has been observed. An insulator to semiconductor transition is explained on the basis of orbital hybridization. A further comparison is made using the pure GGA functional. For the completeness of the study, the dielectric properties of phlogopite are calculated using the coupled perturbed Kohn-Sham scheme, as implemented within the CRYSTAL09 code.

Timón V; Praveen CS; Escamilla-Roa E; Valant M

2013-07-01

10

Angle-resolved photoemission study of the evolution of band structure and charge density wave properties in RTe3 (R= Y, La, Ce, Sm, Gd, Tb and Dy)  

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

11

A phenomenological approach of joint density of states for the determination of band structure in the case of a semi-metal studied by FT-STS  

Energy Technology Data Exchange (ETDEWEB)

The authors show that an accurate determination of the band structure can be achieved by using Fourier transform scanning tunnelling microscopy (FT-STM) techniques in the case of a semi-metallic ErSi{sub 2} layer grown on a Si(111) substrate. This material provides an ideally confined 2D electron and hole gas that is reflected in a complex standing wave pattern at 77 K. The quasi-particles exist over a wide energy range from -800 to +300 meV without mixing with silicon bulk excitations. The Fourier transform of dI/dV maps have been successfully interpreted using the concept of the joint density of states (JDOS), which will be properly introduced. We present here an intuitive interpretation of the quasiparticle interference process based on a geometric construction which also allows us to clearly demonstrate that hole-hole and hole-electron quantum interferences dominate over electron-electron quantum interference.

Simon, L; Vonau, F; Aubel, D [Laboratoire de Physique et de Spectroscopie Electronique, CNRS-UMR7014, 4, rue des Freres Lumiere, 68093 Mulhouse (France)

2007-09-05

12

A phenomenological approach of joint density of states for the determination of band structure in the case of a semi-metal studied by FT-STS  

International Nuclear Information System (INIS)

The authors show that an accurate determination of the band structure can be achieved by using Fourier transform scanning tunnelling microscopy (FT-STM) techniques in the case of a semi-metallic ErSi2 layer grown on a Si(111) substrate. This material provides an ideally confined 2D electron and hole gas that is reflected in a complex standing wave pattern at 77 K. The quasi-particles exist over a wide energy range from -800 to +300 meV without mixing with silicon bulk excitations. The Fourier transform of dI/dV maps have been successfully interpreted using the concept of the joint density of states (JDOS), which will be properly introduced. We present here an intuitive interpretation of the quasiparticle interference process based on a geometric construction which also allows us to clearly demonstrate that hole-hole and hole-electron quantum interferences dominate over electron-electron quantum interference.

2007-09-05

13

Excitation spectra and ground-state properties from density functional theory for the inverted band-structure systems ?-HgS, HgSe and HgTe  

International Nuclear Information System (INIS)

We have performed a systematic density-functional study of the mercury chalcogenide compounds ?-HgS, HgSe, and HgTe using an all-electron full-potential linear muffin-tin orbital (FP-LMTO) method. We find that, in the zinc-blende structure, both HgSe and HgTe are semimetals whereas ?-HgS has a small spin-orbit induced band gap. Our calculated relativistic photoemission and inverse photoemission spectra (PES and IPES, respectively) reproduce very well the most recently measured spectra, as do also our theoretical optical spectra. In contrast to the normal situation, we find that the local density approximation (LDA) to the density functional gives calculated equilibrium volumes in much better agreement with experiment than does the generalized gradient corrected functional (GGA). We also address the problem of treating relativistic p electrons with methods based on a scalar-relativistic basis set, and show that the effect is rather small for the present systems. (author)

2002-01-01

14

Electronic band structure of beryllium oxide  

CERN Multimedia

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

15

Electronic band structure of beryllium oxide  

International Nuclear Information System (INIS)

[en] 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 ? 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

2003-06-04

16

Electronic band structure of beryllium oxide  

Energy Technology Data Exchange (ETDEWEB)

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 [School of Chemistry, Physics and Earth Science, Flinders University of South Australia, GPO Box 2100, Adelaide SA 5001 (Australia); Bolorizadeh, M A [Physics Department, Shahid Bahonar University, Kerman (Iran, Islamic Republic of); Kheifets, A S [Atomic and Molecular Physics Laboratories, Research School of Physical Sciences and Engineering, The Australian National University, Canberra ACT 0200 (Australia); Ford, M J [Institute for Nanoscale Technology, University of Technology Sydney, PO Box 123, Broadway NSW 2007 (Australia)

2003-06-04

17

Doping-induced changes in the valence band edge structure of homoepitaxial B-doped diamond films below Mott's critical density  

International Nuclear Information System (INIS)

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

2009-01-01

18

Band structure and nuclear dynamics  

International Nuclear Information System (INIS)

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

1981-09-11

19

Band structures in 96Ru  

International Nuclear Information System (INIS)

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

2011-01-01

20

Band structure and nuclear dynamics  

International Nuclear Information System (INIS)

This Comment examines some of the developments which were discussed during the international conference on band structure and nuclear dynamics held in early 1980 in New Orleans and considers, in particular, the ideas available for the analysis of data at relatively low excitation energies. Subjects discussed include the Bohr-Mottelson or geometrical model, VMI models, the IBM, microscopic theory, and high-spin phenomena in rotational nuclei. (U.K.).

1981-01-01

 
 
 
 
21

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.

Sergei P. Kruchinin; Arkadiy A. Zolotovsky; Hyun-Tak Kim

2013-01-01

22

Weak morphology dependent valence band structure of boron nitride  

Science.gov (United States)

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

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

2013-08-01

23

Large-scale local-density-approximation band gap-corrected GaAsN calculations  

Energy Technology Data Exchange (ETDEWEB)

The electronic structure of a GaAsN alloy is calculated using a 4096 atom supercell, with a 70 Ry plane wave basis cutoff and Ga atom 3d electrons as valence electrons. The charge density of this supercell is generated by patching the charge density of a small unit cell with the charge density of bulk GaAs. The local-density-approximation band gap error is corrected by modifying the nonlocal pseudopotentials. A localized nitrogen state [a{sub 1}(N)] is obtained,and it plays an important role in the band gap reduction of GaAsN.

Wang, Lin-Wang

2001-03-12

24

Large-scale local-density-approximation band gap-corrected GaAsN calculations  

International Nuclear Information System (INIS)

The electronic structure of a GaAsN alloy is calculated using a 4096 atom supercell, with a 70 Ry plane wave basis cutoff and Ga atom 3d electrons as valence electrons. The charge density of this supercell is generated by patching the charge density of a small unit cell with the charge density of bulk GaAs. The local-density-approximation band gap error is corrected by modifying the nonlocal pseudopotentials. A localized nitrogen state [a1(N)] is obtained,and it plays an important role in the band gap reduction of GaAsN.

2001-03-12

25

High spin band structures in104Cd  

Science.gov (United States)

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

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

1995-06-01

26

Band structure of 68Ge  

Science.gov (United States)

The nucleus 68Ge has been studied by gamma-ray spectroscopy following its population at high spin in the reaction 40Ca(32S,4p)68Ge. The reaction channel was selected with the Microball array and gamma rays were detected with the Gammasphere array. The level scheme is very complex, reflecting the many different, and presumably mixed, excitation modes in this nucleus. Nevertheless, there appear to be some simplifications in the spin range above 18? where we have identified a superdeformed band and several terminating bands. The results are compared with a cranked Nilsson-Strutinsky model without pairing.

Ward, D.; Svensson, C. E.; Ragnarsson, I.; Baktash, C.; Bentley, M. A.; Cameron, J. A.; Carpenter, M. P.; Clark, R. M.; Cromaz, M.; Deleplanque, M. A.; Devlin, M.; Diamond, R. M.; Fallon, P.; Flibotte, S.; Galindo-Uribarri, A.; Haslip, D. S.; Janssens, R. V.; Lampman, T.; Lane, G. J.; Lee, I. Y.; Lerma, F.; Macchiavelli, A. O.; Paul, S. D.; Radford, D.; Rudolph, D.; Sarantites, D. G.; Schaly, B.; Seweryniak, D.; Stephens, F. S.; Thelen, O.; Vetter, K.; Waddington, J. C.; Wilson, J. N.; Yu, C.-H.

2001-01-01

27

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

CERN Multimedia

Using a band-structure method that includes the correction to the band gap error in the local density approximation (LDA), we study the chemical trends of the band gap variation in III-V semiconductors and predict that the band gap for InN is 0.8 +/- 0.1 eV, which is much smaller than previous experimental value of approx. 1.9 eV. The unusually small band gap for InN is explained in terms of the high electronegativity of nitrogen and consequently the small band gap deformation potential of InN. The possible origin of the measured large band gaps is discussed in terms of the non-parabolicity of the bands and the Moss-Burstein shift. Based on the error analysis of our LDA calculation and available experimental data we have compiled the recommended band structure parameters for wurtzite AlN, GaN and InN.

Wei, S H; Wei, Su-Huai; Carrier, Pierre

2004-01-01

28

Large-scale local-density-approximation band gap corrected GaAsN calculations  

Energy Technology Data Exchange (ETDEWEB)

A novel method is used to calculate the electronic structure of GaAsN alloy. The charge density of a thousand atom supercell is generated by patching the charge density of a small unit cell with the charge density of bulk GaAs. The LDA band gap error is corrected by modifying the nonlocal pseudopotentials. A localized nitrogen state [a{sub 1}(N)] is obtained for the first time through an ab initio quality calculation. We found that it plays an important role in the band gap reduction of GaAsN.

Wang, Lin-Wang

2000-03-01

29

Band structure of boron doped carbon nanotubes  

CERN Document Server

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

Wirtz, L; Wirtz, Ludger; Rubio, Angel

2003-01-01

30

Highly deformed band structure in 57Co  

International Nuclear Information System (INIS)

Rotational bands have been found in 57Co using the 28Si(32S,3p) reaction at 130 MeV. The bands, extending the mass 60 region of large deformation down to Z=27, are signature-partner sequences. Their quadrupole moments are similar to those of bands in the neighboring nuclei. The features of the new bands are described by Skyrme Hartree-Fock calculations favoring a configuration assignment with one neutron and one proton excited in the respective 1g9/2 intruder orbital. An attempt to describe the magnetic (M1) properties of the signature-partner structure is also presented.

2002-01-01

31

Electronic structure and charge density of zirconium diboride  

Energy Technology Data Exchange (ETDEWEB)

Self-consistent calculations of the electronic band structure of zirconium diboride, ZrB{sub 2}, have been performed. The total and individual band charge densities are analysed in terms of their site (zirconium or boron) symmetry and plotted. The total charge density shows very little charge asymmetry about either site. 6 refs., 6 figs., 37 tabs.

Switendick, A.C.

1990-01-01

32

Quasiparticle band structures in transitional nuclei  

International Nuclear Information System (INIS)

[en] Major advances in the experimental techniques have made it feasible to perform detailed measurements of atomic nuclei at the extremes of angular-momentum, isospin and stability. Detailed spectroscopic studies have provided new insights in our understanding of nuclear many-body problem. Band structures have been observed up to very high angular momentum and far from the valley of stability. For instance, in the deformed nucleus Dy, sixty bands have been reported. The classification and the interpretation of these rich band structures is a challenge to nuclear theory. The three modes of excitations of rotational, vibrational and quasi-particle constitute the primary origin of the observed bands in nuclei. In spherical nuclei, the energy spectrum is primarily built on the quasi-particle excitations. In well deformed nuclei, rotational bands are observed and are classified using the Nilsson scheme

2012-01-01

33

Structure of rotational bands in 253No  

International Nuclear Information System (INIS)

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

2009-01-01

34

Multiple band structures in sup 191 Hg  

Energy Technology Data Exchange (ETDEWEB)

The level structure of the nucleus {sup 191}Hg has been considerably extended from previous studies by using the {sup 160}Gd({sup 36}S, 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 ({gamma}=-120deg). (orig.).

Ye, D.; Beard, K.B.; Garg, U. (Univ. of Notre Dame, IN (United States)); Janssens, R.V.F.; Carpenter, M.P.; Ahmad, I.; Khoo, T.L.; Moore, E.F.; Wolfs, F.L.H. (Argonne National Lab., IL (United States)); Benet, P.; Grabowski, Z.W. (Purdue Univ., West Lafayette, IN (United States)); Drigert, M.W. (Idaho National Engineering Lab., EG and G Idaho Inc., Idaho Falls, ID (United States))

1992-02-01

35

Multiple band structures in 191Hg  

International Nuclear Information System (INIS)

[en] 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.)

1992-01-01

36

Ab initio electronic band structure calculations for calcium monochalcogenides  

Energy Technology Data Exchange (ETDEWEB)

The first principles tight-binding linear muffin-tin orbital method within the local density approximation was used to calculate the electronic band structures and the total energies of CaS, CaSe and CaTe in NaCl-type and CsCl-type structures. The total energies were used to calculate the ground state properties such as lattice parameter, bulk modulus and the structural phase stability of these compounds. The transition pressure at which these compounds undergo the structural phase transition from NaCl-type to CsCl-type structure was calculated. The ground state properties, the transition pressures and the transition volumes are found to agree with the experimental and other theoretical results. The energy band gap at ambient condition in the NaCl-type structure were calculated and compared with the experimental results available for CaS and CaSe. For CaTe the experimental values of energy gap are not available. The valence-band width and the pressure coefficient of energy gap were also calculated. The closure of band gap at transition in CaCl structure for CaSe, and CaTe were explained by comparing the band structures of BaSe and SrSe in this phase.

Banu, I.B.S.; Kalpana, G.; Palanivel, B.; Shenbagaraman, P. [Crescent Engineering Coll., Vandahur (India). Dept. of Physics; Rajagopalan, M. [Anna Univ., Chenni (India). Dept. of Physics; Yousuf, M. [IGCAR, Kalpakkam (India)

1998-07-10

37

Band theoretical investigation of substituted CrO2 within the local density approximation  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The effects of substitutions at différent concentrations within the lattice of CrO2 are investigated assuming ordered configurations. For this purpose we use self-consistent band structure calculations based on the local spin density approximation. All results show an antiparallel spin alignment bet...

Matar, S.; Eyert, V.; Sticht, J.; Kübler, J.; Dernazeau, G.

38

Excitation spectra and ground-state properties from density functional theory for the inverted band-structure systems $\\beta$-HgS, HgSe, and HgTe  

CERN Document Server

We have performed a systematic density-functional study of the mercury chalcogenide compounds $\\beta$-HgS, HgSe, and HgTe using an all-electron full-potential linear muffin-tin orbital (FP-LMTO) method. We find that, in the zinc-blende structure, both HgSe and HgTe are semimetals whereas $\\beta$-HgS has a small spin-orbit induced band gap. Our calculated relativistic photoemission and inverse photoemission spectra (PES and IPES, respectively) reproduce very well the most recently measured spectra, as do also our theoretical optical spectra. In contrast to the normal situation, we find that the local density approximation (LDA) to the density functional gives calculated equilibrium volumes in much better agreement with experiment than does the generalized gradient corrected functional (GGA). We also address the problem of treating relativistic $p$ electrons with methods based on a scalar-relativistic basis set, and show that the effect is rather small for the present systems.

Delin, A

2002-01-01

39

Band structure in 104Ag  

International Nuclear Information System (INIS)

The level structure of 104Ag has been studied through the 103Rh(?,3n?) reaction at E?=40 and 45 MeV. The principal features of the proposed level scheme are in agreement with those obtained earlier through heavy ion reaction. A two-quasiparticle-plus-rotor model calculation has been performed, and the results are compared with experimental data. (orig.)

1995-01-01

40

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)

2004-01-01

 
 
 
 
41

Orbital Localization, Charge Transfer, and Band Gaps in Semilocal Density-Functional Theory  

Science.gov (United States)

We derive an exchange energy functional of generalized gradient form with a corresponding potential that changes discontinuously at integer particle numbers. The functional is semilocal, yet incorporates key features that are connected to the derivative discontinuity of Kohn-Sham density-functional theory. We validate our construction for several paradigm systems and explain how it addresses central well-known deficiencies of antecedent semilocal methods, i.e., the description of charge transfer, properly localized orbitals, and band gaps. We find, e.g., an improved shell structure for atoms, eigenvalues that more closely correspond to ionization energies, and an improved description of band structure where localized states are lowered in energy.

Armiento, R.; Kümmel, S.

2013-07-01

42

Nonreciprocal microwave band-gap structures.  

Science.gov (United States)

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

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

2002-07-24

43

Nonreciprocal microwave band-gap structures.  

UK PubMed Central (United Kingdom)

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

Belov PA; Tretyakov SA; Viitanen AJ

2002-07-01

44

Subwavelength structured narrow-band integrated optical grating filters  

Energy Technology Data Exchange (ETDEWEB)

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

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

1998-01-01

45

Band structures of 121,123I  

International Nuclear Information System (INIS)

The band structures of 121,123I nuclei have been studied using a version of the particle-rotor-model in which the experimental excitation energies of the neighbouring (A-1) cores can be fed directly as input parameters. The calculations have been carried out with axially symmetric Nilsson potential with both prolate and oblate deformations. The parameters of the model have been chosen from earlier theoretical work and experimental odd-even mass differences. Only the Coriolis attenuation factor has been treated as adjustable parameter. The theoretical band structures are in very good agreement with the available experimental data. (orig.)

1995-01-01

46

Quasiparticle band structure of lanthanum hydride  

Energy Technology Data Exchange (ETDEWEB)

We address the problem of the ground-state character of LaH{sub 3}, a semiconductor compound predicted to be semimetallic within density-functional theory. An ab initio, quasiparticle calculation is peformed whose results indicate a very large 1.1 eV opening of the band gap. Such results are obtained using the GW approximation in the calculation of the self-energy operator. The results are compared to existing experimental data.

Chang, Eric K.; Blase, Xavier; Louie, Steven G.

2001-10-15

47

Band structure of the solar system  

International Nuclear Information System (INIS)

[en] Alfven in his early work on the origin of the solar system (1942-1946) noted a pronounced band structure in the gravitational potential distribution of secondary bodies, and suggested this feature to be directly related to the formation process. When the critical velocity phenomenon was later discovered, a close agreement was found between the planet-satellite bands on one hand, and the critical velocity limits of the major compound elements in the interstellar medium on the other, suggesting a specific emplacement mechanism for the dusty plasma which presumably constituted the solar nebula. Since the originally perceived band structure was outlined in a qualitative fashion, an attempt is made here to analyze the distribution by a statistical technique, testing the significance of clustering of the observational data in the bands. The results show that, with proper scaling of the parameters, such a band structure indeed appears, with features closely similar to those originally conceived. Some deviations are indicated by the cluster analysis, however; their significance is discussed in terms of process involved in the formation of the solar system

1988-01-01

48

Electronic Band Structure of Carbon Nanotubes with Quinoid Structure  

Science.gov (United States)

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

Hieu, Nguyen Ngoc; Anh, Nguyen Pham Quynh

2013-10-01

49

Band structure analysis in SiGe nanowires  

International Nuclear Information System (INIS)

[en] One of the main challenges for Silicon-Germanium nanowires (SiGe NWs) electronics is the possibility to modulate and engine their electronic properties in an easy way, in order to obtain a material with the desired electronic features. Diameter and composition constitute two crucial ways for the modification of the band gap and of the band structure of SiGe NWs. Within the framework of density functional theory we present results of ab initio calculations regarding the band structure dependence of SiGe NWs on diameter and composition. We point out the main differences with respect to the case of pure Si and Ge wires and we discuss the particular features of SiGe NWs that are useful for future technological applications.

2012-06-05

50

Rotational band structure in sup 128 Ce  

Energy Technology Data Exchange (ETDEWEB)

The high spin structure of the nucleus {sup 128}Ce has been investigated via the {sup 94}Mo ({sup 37}Cl, p2n) reaction at 158 MeV. New bands have been found. Alignments of h{sub 11/2} protons and h{sub 11/2} neutrons have been observed. (orig.).

Cata-Danil, G.; Bucurescu, D. (Grenoble-1 Univ., 38 (France). Inst. des Sciences Nucleaires Institutul de Fizica Atomica, Bucharest (Romania)); Nyako, B.M. (Grenoble-1 Univ., 38 (France). Inst. des Sciences Nucleaires Institute of Nuclear Research, Debrecen (Hungary)); Gizon, J.; Barci, V.; Gizon, A.; Andre, S.; Foin, C.; Genevey, J. (Grenoble-1 Univ., 38 (France). Inst. des Sciences Nucleaires); Curien, D.; Merdinger, J.C. (Strasbourg-1 Univ., 67 (France). Centre de Recherches Nucleaires); Hildingsson, L.; Klamra, W. (Manne Siegbahn Inst. of Physics, Stockholm (Sweden)); Zolnai, L. (Institute of Nuclear Research, Debrecen (Hungary))

1991-06-01

51

Rotational band structure in /sup 133/Pr  

Energy Technology Data Exchange (ETDEWEB)

The level structure of the odd proton nucleus /sup 133/Pr has been investigated. Excited states up to spin (45/2) have been observed. The yrast band, built on a decoupled h/sub 11/2/ proton, shows an up-bend at h..omega.. = 0.43 MeV when two additional h/sub 11/2/ protons align. Two positive parity side bands, based on the g/sub 7/2/(5/2)/sup +/(413) proton configuration, are established with opposite signature. Both show a band crossing at h..omega../sub c/ = 0.27 MeV with a gain in alignment roughly-equal8h, when two h/sub 11/2/ protons decouple. This low crossing frequency is partly explained by a reduction in the proton pairing gap caused by the g/sub 7/2/ proton.

Hildingsson, L.; Beausang, C.W.; Fossan, D.B.; Piel, W.F. Jr.

1986-06-01

52

Photonic band gap structures for accelerator applications  

International Nuclear Information System (INIS)

We report the results of our theoretical investigation and cold test of a two-dimensional (2D) metal photonic band gap (PBG) accelerator cell and propose to construct a 2?/3 linear accelerator structure with reduced wakefields as a stack of PBG cells set between disks with irises. We developed a computer code, called Photonic Band Gap Structure Simulator (PBGSS), to calculate the complete dispersion curves for square and triangular arrays of metal rods. Using the PBGSS code, the global photonic band gaps of the arrays were determined and employed to design the PBG cavities. The modes of the 2D PBG cavity formed by a defect (missing rod) in the triangular array of metal rods were studied numerically using the HFSS code. The cavity was designed with only the fundamental TM01 mode confined and higher order modes suppressed. The cold test was performed and the results proved the suppression of the wakefields. Dielectric PBG structures were also studied as applied to microwave devices. A dielectric PBG resonator with the TM02 mode confined and TM01 and TM11 modes absent was designed. The construction of such a resonator overcomes the problem of mode competition in overmoded structures and thus will allow the extension of the operating frequency of the devices to higher frequencies at higher order modes.

2002-12-12

53

Plasmonic Band Structure Controls Single Molecule Fluorescence.  

UK PubMed Central (United Kingdom)

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.

Langguth L; Punj D; Wenger J; Koenderink AF

2013-09-01

54

Plasmon dispersion and quasiparticle band structures for noble metals  

International Nuclear Information System (INIS)

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

2002-01-01

55

Wakefield Band Partitioning In Linac Structures  

CERN Document Server

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

Jones, R M; Bane, Karl Leopold Freitag; Lin, E

2002-01-01

56

Band structure of doubly-odd nuclei around mass 130  

International Nuclear Information System (INIS)

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

2011-05-06

57

Self-consistent band structure calculations and optical properties of the La-H system  

Energy Technology Data Exchange (ETDEWEB)

The results of self-consistent band structure calculations of lanthanum dihydride and trihydride which were performed in the framework of local density functional theory are presented. The calculated density and joint density of states are compared with the results of experimental UV photoelectron spectroscopy and X-ray photoelectron spectroscopy studies and optical experimental measurements. Indirect overlap between the conduction and valence bands of LaH/sub 3/ appears when the approximations for the crystal potential are improved.

Kulikov, N.I.

1982-12-01

58

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

Science.gov (United States)

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

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

2010-12-01

59

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

International Nuclear Information System (INIS)

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

1976-09-16

60

Band structure and optical properties of opal photonic crystals  

CERN Document Server

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

 
 
 
 
61

Electronic structure of periodic curved surfaces -- topological band structure  

CERN Multimedia

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

62

Accurate determination of band gaps within density functional formalism  

Science.gov (United States)

In this paper, we report an adaptation of the Harbola-Sahni (HS) exchange potential to the tight-binding linear muffin-tin orbital (TB-LMTO) method to determine band gaps (BGs) of solids accurately. We show that the electrostatic basis of derivation of the Harbola-Sahni potential allows this nonvariational approach to improve substantially over local-density approximation derived BGs, bringing them very close to experimental values. That the accuracy of the HS potential is directly responsible for the determination of correct BGs is demonstrated by performing similar calculations with an accurate model potential that too leads to BGs close to their experimental values. Moreover, ground-state properties like equilibrium lattice parameters and bulk moduli (BM) for various semiconductors like C, Si, AlN, AlP, BP, and 3C-SiC calculated with the HS approach are in close agreement with the experiments. The clear physical interpretation of HS potential leads us to suggest exploring its use for calculating various properties of solids.

Singh, Prashant; Harbola, Manoj K.; Sanyal, Biplab; Mookerjee, Abhijit

2013-06-01

63

Complex Band Structures and Decay Length in Polyethylene Chains  

CERN Multimedia

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

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

2003-01-01

64

Complex band structures and decay length in polyethylene chains  

International Nuclear Information System (INIS)

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 orbital (HOMO) and the antibonding unoccupied molecular orbitals of 9.3 eV and a non-resonant tunnelling ? parameter of 0.9 per monomer, in reasonable agreement with experiment and with results obtained via local basis. Polyethylene is a negative electron affinity material and the actual gap should be the energy of the HOMO with respect to the vacuum level (in DFT approximation only about 5.14 eV). The Bloch states at imaginary k are mainly free-electron-like parabolic bands which are missing in the local basis. We present also the complex bands of bulk polyethylene in order to estimate the effects of the chain-chain interactions on the complex band structure. The relevance of these results for the tunnelling conduction of n-alkane chains is discussed.

2003-06-11

65

Quasiparticle band structure of bulk hexagonal boron nitride and related systems  

Energy Technology Data Exchange (ETDEWEB)

The quasiparticle band structure of bulk hexagonal boron nitride is studied within the [ital GW] approximation for the self-energy operator. The influence of the interlayer distance on the band structure is investigated both within the local density approximation and the quasiparticle approach, and the importance of an interlayer state in determining the gap is demonstrated. Also, the quasiparticle band structure for an isolated sheet of boron nitride is calculated. We show that the equivalent of the interlayer state in the case of the isolated boron nitride sheet plays the same role as in the bulk case in determing the band gap.

Blase, X.; Rubio, A.; Louie, S.G.; Cohen, M.L. (Department of Physics, University of California at Berkeley, Berkeley, California 94720 (United States) Materials Sciences Division, Lawrence Berkeley Laboratory, Berkeley, California 94720 (United States))

1995-03-15

66

Quasiparticle band structure of bulk hexagonal boron nitride and related systems  

International Nuclear Information System (INIS)

The quasiparticle band structure of bulk hexagonal boron nitride is studied within the GW approximation for the self-energy operator. The influence of the interlayer distance on the band structure is investigated both within the local density approximation and the quasiparticle approach, and the importance of an interlayer state in determining the gap is demonstrated. Also, the quasiparticle band structure for an isolated sheet of boron nitride is calculated. We show that the equivalent of the interlayer state in the case of the isolated boron nitride sheet plays the same role as in the bulk case in determing the band gap.

1995-01-01

67

Measures of residue density in protein structures  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A hierarchy of residue density assessments and packing properties in protein structures are contrasted, including a regular density, a variety of charge densities, a hydrophobic density, a polar density, and an aromatic density. These densities are investigated by alternative distance measures and a...

Baud, Franck; Karlin, Samuel

68

Tuning the electronic band structure of PCBM by electron irradiation  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Tuning the electronic band structures such as band-edge position and bandgap of organic semiconductors is crucial to maximize the performance of organic photovoltaic devices. We present a simple yet effective electron irradiation approach to tune the band structure of [6, 6]-phenyl-C61-butyric acid ...

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

69

Electron density and carriers of the diffuse interstellar bands  

CERN Multimedia

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

Gnacinski, P; Galazutdinov, G A

2007-01-01

70

Band edge singularities and density of states in YTaO4 and YNbO4  

International Nuclear Information System (INIS)

We study the structural and electronic properties of YTaO4 and YNbO4 by means of accurate first-principle total energy calculations. The calculations are based on density functional theory (DFT). The total energy, electronic band structure, and density of states are calculated via the full potential linear-augmented plane wave approach, as implemented in the WIEN2K code, within the framework of DFT. The results show that the valence bands of tantalate and niobate systems are from O 2p states. Conduction bands are divided into two parts. The lower conduction band is mainly composed of Ta 5d or Nb 4d states and the upper conduction bands involve contribution mainly from Y 4d states of YTaO4 or YNbO4. The efficient band gaps in yttrium tantalate and niobate are determined about 4.8 and 4.1 eV, respectively. The agreement between the calculations and the experimental data is excellent. The efficient band gap and a simple model illustrating excitation and emission process in considered host lattices are discussed. (authors)

2011-01-01

71

Band Structures in Doubly Odd 126I  

Science.gov (United States)

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

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

2011-08-01

72

Vibronic structural instability on doping-dependent bands  

International Nuclear Information System (INIS)

[en] Supposing the presence of a doping-induced narrow band besides the valence band, the vibronic dynamic instability caused by interaction of these bands is analysed having in mind the description of the recently observed ? = 0.05 structural transformation in YBa2Cu3O7-?. (orig.)

1998-09-01

73

Electronic structure and electron momentum density in TiSi  

Science.gov (United States)

We report the electron momentum density in titanium monosilicide using 241Am 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.; Mohammad, F. M.; Sahariya, Jagrati; Sharma, Mukesh; Ahuja, B. L.

2013-03-01

74

Band structure in /sup 124/Ba  

Energy Technology Data Exchange (ETDEWEB)

Excited states of /sup 124/Ba have been studied using the /sup 96/Zr (/sup 34/S,6n) reaction at 160 MeV. The yrast band is observed up to a I/sup ..pi../=22/sup +/ state with a band crossing at Planck constant..omega..=0.37 MeV. Negative parity levels are also identified.

Martin, J.P.; Barci, V.; El-Samman, H.; Gizon, A.; Gizon, J.; Nyako, B.; Klamra, W.; Beck, F.A.; Byrski, T.; Merdinger, J.C.

1987-03-01

75

The band structure in 124Ba  

International Nuclear Information System (INIS)

Excited states of 124Ba have been studied using the 96Zr (34S,6n) reaction at 160 MeV. The yrast band is observed up to a I?=22+ state with a band crossing at ??=0.37 MeV. Negative parity levels are also identified. (orig.).

1987-01-01

76

Engineering the Electronic Band Structure for Multiband Solar Cells  

Energy Technology Data Exchange (ETDEWEB)

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

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

2010-07-12

77

Engineering the electronic band structure for multiband solar cells.  

UK PubMed Central (United Kingdom)

Using the unique features of the electronic band structure of GaN(x)As(1-x) alloys, we have designed, fabricated and tested a multiband photovoltaic device. The device demonstrates an optical activity of three energy bands that absorb, and convert into electrical current, the crucial part of the solar spectrum. The performance of the device and measurements of electroluminescence, quantum efficiency and photomodulated reflectivity are analyzed in terms of the band anticrossing model of the electronic structure of highly mismatched alloys. The results demonstrate the feasibility of using highly mismatched alloys to engineer the semiconductor energy band structure for specific device applications.

López N; Reichertz LA; Yu KM; Campman K; Walukiewicz W

2011-01-01

78

Universality of Mallmann correlations for nuclear band structures  

International Nuclear Information System (INIS)

It is shown that the Mallmann's energy ratio correlations, first time proposed 50 years ago for the ground state bands of the even-even nuclei, are universal: all band structures in collective nuclei obey the same systematics. Based on a second order anharmonic vibrator description, parameter-free recurrence relations are proposed for Mallmann-type energy ratios, which can be used to extrapolate band structures to higher spin.

2008-11-11

79

Electronic band structure of PuCoGa sub 5  

CERN Multimedia

The electronic band structure is presented for PuCoGa sub 5 , the recently discovered superconductor with T sub C approx 18 K. The band structure is calculated by the tight-binding linear muffin-tin orbital method in the atomic sphere approximation. (letter to the editor)

Szajek, A

2003-01-01

80

Band structure of 158Gd in DPPQ and IBM  

International Nuclear Information System (INIS)

[en] The band structure of 158Gd has been studied extensively in the decay of 158Eu and in reaction work. The Kumar-Baranger semimicroscopic DPPQ model yields the parameters of the collective Hamiltonian and predicts the band structure. The Interacting Boson Model (IBM-1) was also used for comparison

1999-01-01

 
 
 
 
81

Photoemission spectra and band structures of simple metals  

Energy Technology Data Exchange (ETDEWEB)

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

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

1988-08-15

82

Electronic band structure of lithium, sodium and potassium fluorides  

International Nuclear Information System (INIS)

[en] A mixed tight-binding, pseudopotential method is proposed to calculate the energy band structure of large-gap crystals and is tested here on LiF, NaF and KF. Three-centre terms are included in the determination of the valence bands by the tight-binding method and for the conduction bands we use a pseudopotential model proposed by Bassani and Giuliano, modified for the positive ions. By taking into account the polarization corrections, transitions calculated from the energy band structures are compared with experimental data and the agreement is generally good

1975-08-11

83

Band structure of {sup 68}Ge  

Energy Technology Data Exchange (ETDEWEB)

The nucleus {sup 68}Ge has been studied by gamma-ray spectroscopy following its population at high spin in the reaction {sup 40}Ca({sup 32}S,4p){sup 68}Ge. The reaction channel was selected with the Microball array and gamma rays were detected with the Gammasphere array. The level scheme is very complex, reflecting the many different, and presumably mixed, excitation modes in this nucleus. Nevertheless, there appear to be some simplifications in the spin range above 18{Dirac_h} where we have identified a superdeformed band and several terminating bands. The results are compared with a cranked Nilsson-Strutinsky model without pairing.

Ward, D.; Svensson, C. E.; Ragnarsson, I.; Baktash, C.; Bentley, M. A.; Cameron, J. A.; Carpenter, M. P.; Clark, R. M.; Cromaz, M.; Deleplanque, M. A. (and others)

2001-01-01

84

Density and fluctuation profiles obtained with the D-band reflectometer in Tore-Supra  

Energy Technology Data Exchange (ETDEWEB)

Up to now, density measurements in Tore-Supra using the reflectometry was available in the low field side (LFS). These measurements were achieved by two fast sweeps reflectometers covering the 50-110 GHz bands. In addition, a reflectometer has been set up in order to study density fluctuations in the core and in the high field side (HFS) using the 105-155 GHz band. A recent upgrade on this reflectometer allows it to perform fluctuations measurements at fixed frequency and density profiles in the same shot by switching between frequency steps and fast sweeps. Density profiles covering the whole plasma using the 3 reflectometers are presented. The filtering treatments are described. The better knowledge of the core and HFS density allows a higher reliability in fluctuations measurements: both for the localisation of the cutoff layers and for the evaluation of the local index gradient length. Density fluctuation profiles enhanced by these new density profiles are shown. (authors)

Sirinelli, A.; Sabot, R.; Giacalone, J.C.; Clairet, F

2005-07-01

85

Atomic structure of amorphous shear bands in boron carbide.  

UK PubMed Central (United Kingdom)

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

Reddy KM; Liu P; Hirata A; Fujita T; Chen MW

2013-09-01

86

Atomic structure of amorphous shear bands in boron carbide.  

Science.gov (United States)

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

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

2013-09-20

87

Atomic structure of amorphous shear bands in boron carbide  

Science.gov (United States)

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

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

2013-09-01

88

Electronic energy band structure of the double perovskite Ba2MnWO6.  

Science.gov (United States)

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

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

2008-05-09

89

Electronic energy band structure of the double perovskite Ba2MnWO6.  

UK PubMed Central (United Kingdom)

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

Fujioka Y; Frantti J; Nieminen RM

2008-06-01

90

Band structures and shape coexistence in {sup 187}Pt  

Energy Technology Data Exchange (ETDEWEB)

High-spin states in {sup 187}Pt have been studied by means of {gamma}-ray spectroscopy techniques. Known bands have been significantly extended and new bands have been found. The band structures are discussed in the framework of the cranking model and negative-parity states are compared with calculations performed with a semi-microscopic axial-rotor plus one-quasiparticle coupling model. Shape coexistence is observed from low excitation energy. (orig.)

Hojman, D. [Comision Nacional de Energia Atomica, Departamento de Fisica, Buenos Aires (Argentina); CONICET, Buenos Aires (Argentina); Cardona, M.A. [Comision Nacional de Energia Atomica, Departamento de Fisica, Buenos Aires (Argentina); CONICET, Buenos Aires (Argentina); Universidad Nacional de San Martin, Buenos Aires (Argentina); Roussiere, B.; Sauvage, J. [IN2P3/CNRS/Universite Paris-Sud, Institut de Physique Nucleaire, Orsay (France); Riley, M.A.; Tabor, S.L.; Hoffman, C.R.; Aguilar, A.; Cluff, W.T.; Hinners, T.; Lagergren, K.; Lee, S.; Perry, M.; Pipidis, A.; Tripathi, V. [Florida State University, Department of Physics, Tallahassee, Florida (United States)

2012-06-15

91

Detailed band structures in 189Hg and 190Hg  

International Nuclear Information System (INIS)

The level structures of the 189Hg and 190Hg nuclei have been extended considerably from earlier studies by using the 160Gd(34S, 4n and 5n) reactions in conjunction with an array of twelve Compton suppressed Ge detectors. Eight band structures have been delineated in 189Hg and ten in 190Hg. Most bands can be understood within the framework of cranked shell model calculations assuming an oblate collective shape and specific quasiparticle configurations are proposed. There is also some evidence for the onset of triaxiality. In both nuclei level structures which appear to be non-collective in character are interpreted in a band termination picture. ((orig.)).

1994-01-01

92

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; Partha Pratim Sarkar; D. Sarkar; S. Biswas

2013-01-01

93

Band structure and excitons in CsCdBr3  

International Nuclear Information System (INIS)

CsCdBr3 has a very unique electronic band structure. The conduction band is split up into two parts: a lower isolated and very narrow band (?E?4000 cm-1) and higher lying ones. Just below the lowest conduction band we observe an absorption band of excitons localized at lattice defects. Both of them, the low-lying conduction band as well as the localized excitons, play an important role in the fast and very efficient energy transfer within the crystal. This can be shown by analyzing the decay dynamics of the fluorescence of the dopant RE-ions and of the localized and lattice excitons (excitons of the perfect lattice). Also, excitation into either the excitons or the RE-ion clearly shows an energy transfer back and forth between both of them. We deem this mechanism to be the most important one for the observed upconversion processes in CsCdBr3. (orig.)

2000-04-12

94

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.

2012-04-01

95

Relationships between magnetic foot points and G-band bright structures  

CERN Multimedia

Magnetic elements are thought to be described by flux tube models, and are well reproduced by MHD simulations. However, these simulations are only partially constrained by observations. We observationally investigate the relationship between G-band bright points and magnetic structures to clarify conditions, which make magnetic structures bright in G-band. The G-band filtergrams together with magnetograms and dopplergrams were taken for a plage region covered by abnormal granules as well as ubiquitous G-band bright points, using the Swedish 1-m Solar Telescope (SST) under very good seeing conditions. High magnetic flux density regions are not necessarily associated with G-band bright points. We refer to the observed extended areas with high magnetic flux density as magnetic islands to separate them from magnetic elements. We discover that G-band bright points tend to be located near the boundary of such magnetic islands. The concentration of G-band bright points decreases with inward distance from the boundar...

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

2008-01-01

96

The charge carrier density effect on the superconductor parameters in a two-band model  

International Nuclear Information System (INIS)

The effect of the mobile charge concentration on the electron-phonon coupling constant, the band overlapping parameter and the isotopic coefficient is studied for a two-dimensional superconductor in a two-band model. This model is applied to describe the relation between the superconducting transition and the carrier density in CuO2 layered superconductors, within the BCS framework. The experimental data for doping-induced charge in layered Hg-based cuprates are used to obtain numerical results.

2006-11-01

97

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

98

Locally resonant periodic structures with low-frequency band gaps  

Science.gov (United States)

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

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

2013-07-01

99

Quantum confinement, surface roughness, and the conduction band structure of ultrathin silicon membranes.  

UK PubMed Central (United Kingdom)

We report direct measurements of changes in the conduction-band structure of ultrathin silicon nanomembranes with quantum confinement. Confinement lifts the 6-fold-degeneracy of the bulk-silicon conduction-band minimum (CBM), Delta, and two inequivalent sub-band ladders, Delta(2) and Delta(4), form. We show that even very small surface roughness smears the nominally steplike features in the density of states (DOS) due to these sub-bands. We obtain the energy splitting between Delta(2) and Delta(4) and their shift with respect to the bulk value directly from the 2p(3/2)-->Delta transition in X-ray absorption. The measured dependence of the sub-band splitting and the shift of their weighted average on degree of confinement is in excellent agreement with theory, for both Si(001) and Si(110).

Chen F; Ramayya EB; Euaruksakul C; Himpsel FJ; Celler GK; Ding B; Knezevic I; Lagally MG

2010-04-01

100

Electronic structures and state Densities for faujasite clusters  

Energy Technology Data Exchange (ETDEWEB)

MINDO/3 and CNDO/2 methods have been applied to clusters simulating the structure of faujasite, with the inclusion of from 6 to 12 aluminum-oxygen and silicon-oxygen tetrahedra. A study has been made of how the integral and orbital electron-state densities vary with the dimensions of the zeolite fragment, the boundary conditions, and the calculation method. The fine structure in the cation state density peaks for aluminum in the valency band is only slightly dependent on the boundary conditions and the cluster dimensions, while the differences between the MINDO/3 and CNDO/2 results amount to a systematic shift in the peaks together with slight changes in the fine structure. On the other hand, the boundary conditions have a considerable effect on the orbital state density profiles for the oxygen ions in the upper valency quasiband for the faujasite clusters.

Gun' ko, V.M.

1986-09-01

 
 
 
 
101

Development of X-Band Dielectric-Loaded Accelerating Structures  

International Nuclear Information System (INIS)

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

2010-11-04

102

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

Science.gov (United States)

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

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

2001-12-01

103

Rotational bands and noncollective structures in 85Zr  

International Nuclear Information System (INIS)

The structure of the transitional nucleus 85Zr has been investigated through spectroscopy and lifetime measurements. States up to spins of (45/2)(?/2?) and (39/2)(?/2?) in the positive and negative parity bands, respectively, have been established through ?-? coincidence measurements. The results indicate that there is a competition between collective and noncollective modes of excitation. Two pronounced band crossings have been observed in the positive parity sequence, while none is evident in the negative parity states. The pattern of shape evolution in the positive and negative parity bands is markedly different. The results of the experiments qualitatively corroborate the predictions of total Routhian surface calculations

2002-01-01

104

Multi bunch dynamics in detuned x-band structures  

International Nuclear Information System (INIS)

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

1992-01-01

105

Band structures and localization properties of aperiodic layered phononic crystals  

International Nuclear Information System (INIS)

The band structures and localization properties of in-plane elastic waves with coupling of longitudinal and transverse modes oblique propagating in aperiodic phononic crystals based on Thue-Morse and Rudin-Shapiro sequences are studied. Using transfer matrix method, the concept of the localization factor is introduced and the correctness is testified through the Rytov dispersion relation. For comparison, the perfect periodic structure and the quasi-periodic Fibonacci system are also considered. In addition, the influences of the random disorder, local resonance, translational and/or mirror symmetries on the band structures of the aperiodic phononic crystals are analyzed in this paper.

1000-01-00

106

Band structures and localization properties of aperiodic layered phononic crystals  

Energy Technology Data Exchange (ETDEWEB)

The band structures and localization properties of in-plane elastic waves with coupling of longitudinal and transverse modes oblique propagating in aperiodic phononic crystals based on Thue-Morse and Rudin-Shapiro sequences are studied. Using transfer matrix method, the concept of the localization factor is introduced and the correctness is testified through the Rytov dispersion relation. For comparison, the perfect periodic structure and the quasi-periodic Fibonacci system are also considered. In addition, the influences of the random disorder, local resonance, translational and/or mirror symmetries on the band structures of the aperiodic phononic crystals are analyzed in this paper.

Yan Zhizhong, E-mail: zzyan@bit.edu.cn [Department of Applied Mathematics, Beijing Institute of Technology, Beijing 100081 (China); Zhang Chuanzeng [Department of Civil Engineering, University of Siegen, D-57078 Siegen (Germany)

2012-03-15

107

Band structures and localization properties of aperiodic layered phononic crystals  

Science.gov (United States)

The band structures and localization properties of in-plane elastic waves with coupling of longitudinal and transverse modes oblique propagating in aperiodic phononic crystals based on Thue-Morse and Rudin-Shapiro sequences are studied. Using transfer matrix method, the concept of the localization factor is introduced and the correctness is testified through the Rytov dispersion relation. For comparison, the perfect periodic structure and the quasi-periodic Fibonacci system are also considered. In addition, the influences of the random disorder, local resonance, translational and/or mirror symmetries on the band structures of the aperiodic phononic crystals are analyzed in this paper.

Yan, Zhi-Zhong; Zhang, Chuanzeng

2012-03-01

108

Electronic band structure of graphite-boron nitride alloys  

Energy Technology Data Exchange (ETDEWEB)

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

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

1990-05-17

109

Band structures in light neutron-rich nuclei  

International Nuclear Information System (INIS)

The structure of beryllium isotopes in the mass range A = 8-12 has been investigated using the properties of different bands, which are populated in specific reactions. The different structures are formed in transfer reactions with neutron stripping on 9,10Be or proton pick-up on 12,13,14C. The slope in the linear dependence of the excitation energies on J(J+1), where J is the spin, has been deduced for 13 bands and compared for common systematics. From the measured moments-of-inertia the ? - ? distance has been deduced for molecular structures.

2008-01-01

110

Complex band structure of nanostructured metal-dielectric metamaterials.  

UK PubMed Central (United Kingdom)

We study complex eigenmodes of layered metal-dielectric metamaterials. Varying losses from weak to realistic, we analyze band structure of the metamaterial and clarify effect of losses on its intrinsic electromagnetic properties. The structure operates in a regime with infinite numbers of eigenmodes, whereas we analyze dominant ones.

Orlov A; Iorsh I; Belov P; Kivshar Y

2013-01-01

111

Ab-initio Study of Electronic Band Structures of CdBAs2 (B = Si, Ge and Sn) Chalcopyrite Compounds  

Science.gov (United States)

We present ab-initio study of electronic band structures of CdBAs2 (B = Si Ge and Sn) compounds using full potential linearized augmented plane wave (FPLAPW) method. The exchange effects are taken into account by an orbital independent modified Becke-Johnson (MBJ) potential as coupled with correlation term given by Local Density Approximation (LDA) for all the compounds. The band gaps within MBJLDA are very close to corresponding experimental values. The largest band gap of 1.79 eV is found in CdSiAs2 among these compounds. The band structures are analyzed in terms of contributions from various electrons of these compounds.

Singh, Hardev; Singh, Mukhtiyar; Kashyap, Manish K.

2011-12-01

112

Band structure in {sup 104}Ag  

Energy Technology Data Exchange (ETDEWEB)

The level structure of {sup 104}Ag has been studied through the {sup 103}Rh({alpha},3n{gamma}) reaction at E{sub {alpha}}=40 and 45 MeV. The principal features of the proposed level scheme are in agreement with those obtained earlier through heavy ion reaction. A two-quasiparticle-plus-rotor model calculation has been performed, and the results are compared with experimental data. (orig.)

Goswami, A. [Saha Inst. of Nuclear Physics, Calcutta (India); Saha Sarkar, M. [Saha Inst. of Nuclear Physics, Calcutta (India); Datta Pramanik, U. [Saha Inst. of Nuclear Physics, Calcutta (India); Banerjee, P. [Saha Inst. of Nuclear Physics, Calcutta (India); Basu, P. [Saha Inst. of Nuclear Physics, Calcutta (India); Bhattacharya, P. [Saha Inst. of Nuclear Physics, Calcutta (India); Bhattacharya, S. [Saha Inst. of Nuclear Physics, Calcutta (India); Chatterjee, M.L. [Saha Inst. of Nuclear Physics, Calcutta (India); Sen, S. [Saha Inst. of Nuclear Physics, Calcutta (India); Dasmahapatra, B. [Saha Inst. of Nuclear Physics, Calcutta (India)

1995-12-01

113

Band structure of local pairs Mathematical tools  

CERN Multimedia

A system of strongly interacting fermions in a solid state is discussed. A structure of singlet and triplet coupled 2-particle states and their excitation spectra are investigated. It is shown that an account of intersite fermion interaction leads to new boson modes. A problem of interaction of pairs with external fields are discussed. The same analysis can be performed for another sorts of pairings like d-wave.

Rubin, S G

1999-01-01

114

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; S. M. Hosseini; N. Shahtahmasebi

2002-01-01

115

Surface alloying in the Sn/Ni(111) system studied by synchrotron radiation photoelectron valence band spectroscopy and ab-initio density of states calculations  

International Nuclear Information System (INIS)

Photoelectron spectroscopy using synchrotron radiation and ab-initio electronic structure calculations were used in order to describe the fine structure of the valence band in the Sn/Ni(111) system. The characteristic contributions of each metal in the valence band photoemission spectra obtained with a photon energy of 80 eV and their changes upon the formation of the (?3 x ?3)R30o Sn/Ni(111) surface alloy were also born out in the calculated density-of-states curves in fair agreement with the experiments. The Sn-Ni interaction leads to a considerable broadening of the valence band width at the bimetallic surfaces.

2008-03-31

116

Electron band structure of the high pressure cubic phase of AlH3  

Science.gov (United States)

The electronic band structure of the cubic Pm3n phase of AlH3 stable above 100 GPa is examined with semi-local, Tran-Blaha modified Becke-Johnson local density approximation (TB-mBJLDA), screened hybrid density functionals and GW methods. The shift of the conduction band to higher energy with increasing pressure is predicted by all methods. However, there are significant differences in detail band structure. In the pressure range from 90 to160 GPa, semi-local, hybrid functional and TB-mBJLDA calculations predicted that AlH3 is a poor metal. In comparison, GW calculations show a gap opening at 160 GPa and AlH3 becomes a small gap semi-conductor. From the trends of the calculated band shifts, it can be concluded that the favourable conditions leading to the nesting of Fermi surfaces predicted by semi-local calculation have disappeared if the exchange term is included. The results highlight the importance of the correction to the exchange energy on the band structure of hydrogen dominant dense metal hydrides at high pressure hydrides and may help to rationalize the absence of superconductivity in AlH3 from experimental measurements.

Shi, Hongliang; Zarifi, Niliffar; Yim, Wai-Leung; Tse, J. S.

2012-07-01

117

Concentration Inequalities and Confidence Bands for Needlet Density Estimators on Compact Homogeneous Manifolds  

CERN Document Server

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

Kerkyacharian, Gerard; Picard, Dominique

2011-01-01

118

The surface band structure of ?-Ga2O3  

International Nuclear Information System (INIS)

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

2011-03-01

119

Valence band structure of Bi2Se3  

Science.gov (United States)

Bi2Se3 is an interesting candidate for thermoelectric application because Se is a more abundant element than Te, which is commercially used in Bi2Te3-based Peltier coolers. However, intrinsic Se vacancies dominate in Bi2Se3 and dope the material n-type. Due to unfavourable conduction band structure, n-type Bi2Se3 does not have a high power factor. Recently, it has been calculated [1] that Bi2Se3 has a favourable valence band structure for thermoelectric application. In this presentation, high-quality p-type Bi2Se3 single crystals are prepared and Shubnikov de Haas measurement are carried out on them to characterize the band structure. Cross-sectional areas of Fermi surface are mapped out and compared with the theoretical calculation. Reference: [1] Phys. Rev. X 1, 021005 (2011)

Gao, Yi-Bin; Parker, David; Heremans, Joseph P.

2013-03-01

120

Band structure and superconductivity of BCC tellurium under pressure  

International Nuclear Information System (INIS)

[en] We report a theoretical calculation of the band structure and superconductivity of Te in the BCC phase under pressure. The energy band structure and the effect of pressure on the band structure is obtained by means of the linear muffin-tin orbital method. The superconducting transition temperature (Tc) is calculated using McMillan's formula. The calculated value of Tc of Te in the BCC phase at 27.3 GPa is 7.16 K. Further increase in pressure decreases the Tc values. The calculated value of resistivity at 27.3 GPa is 4.37 ?? cm and further increase in pressure decreases the resistivity, which is a typical behaviour of a number of elemental metals under pressure. (orig.)

1993-01-01

 
 
 
 
121

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

Science.gov (United States)

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

Li, Yuan; Li, Huancai; Ding, Ronglin

2005-12-01

122

The structure of shear bands in idealized granular materials  

Energy Technology Data Exchange (ETDEWEB)

The structure of shear bands in granular materials was investigated by numerically simulating an idealized assembly of two-dimensional particles. Flexible stress-controlled boundaries were used instead of periodic boundaries to avoid constraining the motion of particles within the tested specimen. The particle displacement, particle rotations and rotations of the particle neighborhoods (macro-rotation) were examined within the shear band. The shear band width was found to decrease with axial strain from 18 and 15 times the average particle radius. The particle rotations and macro-rotations were concentrated inside the shear bands. The numerical simulations suggest that the particle rotations are induced by macro-rotations, and support the use of the micropolar theory for examining instable phenomena within granular materials. 18 refs., 6 figs.

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

1992-03-01

123

Band structure in /sup 133,135/Pr  

International Nuclear Information System (INIS)

[en] It is shown that the ''normal'' and ''decoupled'' band-like structures recently observed in the nuclei /sup 133/Pr and /sup 135/Pr can be reproduced within the framework of a standard version of the particle-rotor model. In addition, several positive parity levels in /sup 135/Pr, to which no band assignment could be given earlier, are shown to be the members of two positive parity bands with opposite signatures based on the (3/2+[411] Nilsson orbital. The most interesting observation of the present work is the near total attenuation of the Coriolis interaction in the positive parity bands in /sup 135/Pr. It is suggested that this nucleus can be a very good testing ground for different versions of the particle-rotor models currently used by different workers

1988-01-01

124

Computations of conformations, crystal structures and electronic band gaps of polysilanes  

Energy Technology Data Exchange (ETDEWEB)

An all-atom force field for computer simulation of polysilanes, including their alkyl and phenyl side chain derivatives, was developed based on ab initio calculations and liquid simulations of simple silane molecules. Validation of the force field shows good agreement with experimental data of silanes and polysilanes. Conformational structures and energies of polysilane and poly(dimethylsilane) were studied based on the ab initio calculations and the force field developed. The chain conformations of poly(dimethylsilane) are strongly influenced by the intra and inter molecular nonbonded interactions - the isolated chain has a helical backbone, but the crystal-packed chain is all trans. Electronic structures were calculated for polysilanes with different side-chain lengths and backbone conformations. The band structures and electronic densities of states were calculated using ab initio density functional theory and semiempirical methods. We will discuss the calculated results and compare the theoretical band gaps with experimental observations in this presentation.

Sun, H. [Biosym Technologies, Inc., San Diego, CA (United States)

1995-12-01

125

Band structures of {sup 121,123}I  

Energy Technology Data Exchange (ETDEWEB)

The band structures of {sup 121,123}I nuclei have been studied using a version of the particle-rotor-model in which the experimental excitation energies of the neighbouring (A-1) cores can be fed directly as input parameters. The calculations have been carried out with axially symmetric Nilsson potential with both prolate and oblate deformations. The parameters of the model have been chosen from earlier theoretical work and experimental odd-even mass differences. Only the Coriolis attenuation factor has been treated as adjustable parameter. The theoretical band structures are in very good agreement with the available experimental data. (orig.)

Goswami, R. [Saha Inst. of Nuclear Physics, Calcutta (India); Sethi, B. [Saha Inst. of Nuclear Physics, Calcutta (India); Sarkar, M.S. [Saha Inst. of Nuclear Physics, Calcutta (India); Sen, S. [Saha Inst. of Nuclear Physics, Calcutta (India)

1995-09-01

126

Self-isospectrality, tri-supersymmetry and band structure  

CERN Document Server

We reveal an unexpected hidden supersymmetric structure in a self-isospectral system constructed on the base of the periodic finite-gap associated Lame equation. It admits three different choices of the Z_2-grading, under which three basic nontrivial integrals of motion coherently change their fermionic/bosonic nature, and generate a certain nonlinear supersymmetry. These integrals reflect the band structure, its separability, and characteristic properties of the band-edge states of the system, which can be interpreted as an electron in one-dimensional crystal produced by periodic electric and magnetic fields.

Correa, Francisco; Nieto, Luis-Miguel; Plyushchay, Mikhail S

2008-01-01

127

Simulation of the Band Structure of Graphene and Carbon Nanotube  

International Nuclear Information System (INIS)

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

2012-02-08

128

Effects of band broadening and shape of the density of states on the magnetic phase diagram  

International Nuclear Information System (INIS)

We have revisited metallic ferromagnetism to examine the effects of band broadening due to electron-electron interaction on the magnetic phase diagram. Based on the generalized single band tight-binding Hamiltonian, we have explored the condition when the magnetization jumps discontinuously, by comparing results obtained by the local minima search and the total energy minimization. We have also investigated how the shape of the density of states (DOS) affects the magnetic phase diagram. We have found that a system with the DOS shape of a concave-type could have the discontinuous magnetization jump as the effective Stoner parameter increases.

2006-08-09

129

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

Science.gov (United States)

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

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

2013-05-01

130

Band structure analysis of the conduction-band mass anisotropy in 6H and 4H SiC  

CERN Multimedia

The band structures of 6H and 4H SiC calculated by means of the FP-LMTO method are used to determine the effective mass tensors for their conduction-band minima. The results are shown to be consistent with recent optically detected cyclotron resonance measurements and predict an unusual band filling dependence for 6H-SiC.

Lambrecht, W R L; Lambrecht, Walter R. L.; Segall, Benjamin

1995-01-01

131

Structural phase transition in IrTe?: a combined study of optical spectroscopy and band structure calculations.  

UK PubMed Central (United Kingdom)

Ir(1-x)Pt(x)Te? is an interesting system showing competing phenomenon between structural instability and superconductivity. Due to the large atomic numbers of Ir and Te, the spin-orbital coupling is expected to be strong in the system which may lead to nonconventional superconductivity. We grew single crystal samples of this system and investigated their electronic properties. In particular, we performed optical spectroscopic measurements, in combination with density function calculations, on the undoped compound IrTe? in an effort to elucidate the origin of the structural phase transition at 280?K. The measurement revealed a dramatic reconstruction of band structure and a significant reduction of conducting carriers below the phase transition. We elaborate that the transition is not driven by the density wave type instability but caused by the crystal field effect which further splits/separates the energy levels of Te (p(x), p(y)) and Te p(z) bands.

Fang AF; Xu G; Dong T; Zheng P; Wang NL

2013-01-01

132

New band structures and an unpaired crossing in 78Kr  

International Nuclear Information System (INIS)

High-spin states in 78Kr were studied using the 58Ni(23Na,3p) reaction at 70 MeV and the 58Ni(28Si,?4p) reaction at 130 MeV. Prompt ?-? coincidences were measured using the Pitt-FSU detector array and the GAMMASPHERE-MICROBALL array. Results from these experiments have led to 26 new excitation levels, some of which have been grouped into 3 new bands. Spins were assigned based on directional correlations of oriented nuclei. Two of the new negative-parity bands appear to form a signature-partner pair based on a two-quasineutron structure, in contrast to the previously known two-quasiproton negative-parity bands. A forking has been observed at the 24+ state in the yrast band, which calculations suggest may result from an unpaired crossing. The available evidence suggests oblate shapes in the yrast band coexist with prolate shapes in the negative-parity bands. copyright 1999 The American Physical Society.

1999-01-01

133

High-K band structures in 164Er  

International Nuclear Information System (INIS)

Several of the known rotational bands in 164Er are extended considerably (to around 35?). In addition, a new coupled band is established and found to decay by an isomeric transition with t1/2?170 nsec, to the 11- state of the known K?=7- two-quasi-proton band. The new band is interpreted as a four-quasi-particle structure, with measured values of B(M1)/B(E2) consistent with the configuration [7-] x ?i13/2[642 5/2+] x ?h9/2[523 5/2-], i.e. [7-] x [AE,AF]. This is supported by the observation of a crossing which resembles the second i13/2 neutron crossing, BC, associated with the two-quasi-neutron band built on the configuration, [AE,AF]. The routhian of the new band is close to the sum of the individual routhians of [AE,AF] and [7-]. The cause of a small gain in energy of 130-272 keV is discussed. (orig.). With 3 figs.

1997-01-01

134

MAGNETIC BAND STRUCTURE OF CrO2  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Spin-resolved photoemission of polycrystalline CrO2 films shows 3d states with a nearly + 100 % spin polarization about 2 eV below the Fermi level (EF). Extremely low intensity is observed near EF. Our findings are in contrast to recent band structure calculations, predicting CrO2 to be a half-metal...

Kämper, K.; Schmitt, W.; Güntherodt, G.; Gambino, R.; Ruf, R.

135

Band Structure of Crystals with Periodically Loaded Metallic Wires  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The band structure for the normal propagation of crystal formed by periodically loaded metallic wires was analyzed for different wire diameters and for different values of the load, which are assimilated as diodes. The diodes were simulated by an equivalent R-C circuit, which was chosen in agreement...

Boutayeb, Halim; Denidni, Tayeb

136

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

137

Photonic Band Gap structures: A new approach to accelerator cavities  

International Nuclear Information System (INIS)

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.

1992-01-01

138

Band structure loops and multistability in cavity-QED  

CERN Document Server

We calculate the band structure of ultracold atoms located inside a laser-driven optical cavity. For parameters where the atom-cavity system exhibits bistability, the atomic band structure develops loop structures akin to the ones predicted for Bose-Einstein condensates in ordinary (non-cavity) optical lattices. However, in our case the nonlinearity derives from the cavity back-action rather than from direct interatomic interactions. We find both bi- and tri-stable regimes associated with the lowest band, and show that the multistability we observe can be analyzed in terms of swallowtail catastrophes. Dynamic and energetic stability of the mean-?eld solutions is also discussed, and we show that the bistable solutions have, as expected, one unstable and two stable branches. The presence of loops in the atomic band structure has important implications for proposals concerning Bloch oscillations of atoms inside optical cavities [Peden et al., Phys. Rev. A 80, 043803 (2009), Prasanna Venkatesh et al., Phys. Rev. ...

Venkatesh, B Prasanna; O'Dell, D H J

2011-01-01

139

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

International Nuclear Information System (INIS)

Electronic band structure calculations are used to interpret the optical spectra of the cubic Sc, Y and La hydride systems. Self-consistent band calculations of ScH2 and YH2 were carried out. The respective joint densities of states are computed and compared to the dielectric functions determined from the optical measurements. Additional calculations were performed in which the Fermi level or band gap energies are rigidly shifted by a small energy increment. These calculations are then used to simulate the derivative structure in thermomodulation spectra and relate the origin of experimental interband features to the calculated energy bands. While good systematic agreement is obtained for several spectral features, the origin of low-energy interband transitions in YH2 cannot be explained by these calculated bands. A lattice-size-dependent premature occupation of octahedral sites by hydrogen atoms in the fcc metal lattice is suggested to account for this discrepancy. Various non-self-consistent calculations are used to examine the effect of such a premature occupation. Measurements of the optical absorptivity of LaH/sub x/ with 1.6 2 lattice. These experimental results also suggest that, in contrast to recent calculations, LaH3 is a small-band-gap semiconductor.

1980-01-01

140

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

Energy Technology Data Exchange (ETDEWEB)

Electronic band structure calculations are used to interpret the optical spectra of the cubic Sc, Y and La hydride systems. Self-consistent band calculations of ScH/sub 2/ and YH/sub 2/ were carried out. The respective joint densities of states are computed and compared to the dielectric functions determined from the optical measurements. Additional calculations were performed in which the Fermi level or band gap energies are rigidly shifted by a small energy increment. These calculations are then used to simulate the derivative structure in thermomodulation spectra and relate the origin of experimental interband features to the calculated energy bands. While good systematic agreement is obtained for several spectral features, the origin of low-energy interband transitions in YH/sub 2/ cannot be explained by these calculated bands. A lattice-size-dependent premature occupation of octahedral sites by hydrogen atoms in the fcc metal lattice is suggested to account for this discrepancy. Various non-self-consistent calculations are used to examine the effect of such a premature occupation. Measurements of the optical absorptivity of LaH/sub x/ with 1.6 < x < 2.9 are presented which, as expected, indicate a more premature occupation of the octahedral sites in the larger LaH/sub 2/ lattice. These experimental results also suggest that, in contrast to recent calculations, LaH/sub 3/ is a small-band-gap semiconductor.

Peterman, D.J.

1980-01-01

 
 
 
 
141

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

Science.gov (United States)

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

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

2013-06-01

142

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

143

Insights on Coral Adaptation from Polyp and Colony Morphology, Skeletal Density Banding and Carbonate Depositional Facies  

Science.gov (United States)

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

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

2008-12-01

144

Multi-band and broadband acoustic metamaterial with resonant structures  

International Nuclear Information System (INIS)

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

2011-06-01

145

Multi-band and broadband acoustic metamaterial with resonant structures  

Energy Technology Data Exchange (ETDEWEB)

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

Ding Changlin; Zhao Xiaopeng, E-mail: xpzhao@nwpu.edu.cn [Smart Materials Laboratory, Department of Applied Physics, Northwestern Polytechnical University, Xi' an 710129 (China)

2011-06-01

146

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

CERN Multimedia

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

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

2013-01-01

147

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.  

Anuj Nuwal; Shyam Lal Kakani

2013-01-01

148

Band Structure Measurements of Bottom-up Fabricated Graphene Nanoribbons  

Science.gov (United States)

Along with the growing interest in graphene, other low-dimensional carbon nanostructures are currently in the focus of research since these materials offer a wide variety of properties interesting e.g. for nanotechnology application. Among these carbon systems, quasi-one-dimensional graphene nanoribbons (GNR) introduce a possibility to tune the electronic structure - for example, GNRs exhibit a band gap which is inversely proportional to their width and can thus be adjusted over a wide range. While many theoretical studies have been published on the band structure of GNRs, experiments are usually limited by the quality of the GNRs' fabrication, e.g. using lithography or unzipping of carbon nanotubes. In order to avoid defects and irregular edges that are inevitable in these methods, lately a surface-assisted bottom-up synthesis has been demonstrated which yields quasi-perfect GNR structures. [1] In the present study we employ complementary surface-sensitive spectroscopies to investigate occupied and unoccupied bands and the band gap in an armchair GNR which has been synthesized on the Au(111) surface. DFT calculations were performed to obtain a thorough understanding of the nature of the observed states.[4pt] [1] J. Cai et al., Nature (London) 466, 470-473 (2010)

Bronner, Christopher; Leyssner, Felix; Meyer, Stephan; Utecht, Manuel; Klamroth, Tillmann; Saalfrank, Peter; Tegeder, Petra

2012-02-01

149

Effect of metal vacancies on the electronic band structure of hexagonal Nb, Zr and Y diborides  

CERN Multimedia

Energy band structures of metal-deficient hexagonal diborides M$_{0.75}$B$_2$ (M = Nb, Zr and Y) were calculated using the full-potential LMTO method. The metal vacancies change the density of states near the Fermi level and this effect is quite different for III-V group transition metal diborides. Contradictory data on superconductivity in diborides may be supposed to be connected with nonstoichiometry of samples. Vacancy formation energies are estimated and analyzed.

Shein, I R; Medvedeva, N I; Ivanovskii, A L

2002-01-01

150

Extensive ?-ray spectroscopy of band structures in 3062Zn32  

Science.gov (United States)

An experimental study of the 62Zn nucleus has been performed by combining the data sets from four fusion-evaporation reaction experiments. Apart from the previously published data, the present results include ten new rotational band structures and two more superdeformed bands. The Gammasphere Ge-detector array in conjunction with the 4? charged-particle detector array Microball allowed for the detection of ? rays in coincidence with evaporated light particles. The deduced level scheme includes some 260 excited states, which are connected with more than 450 ?-ray transitions. Spins and parities of the excited states have been determined via directional correlations of ? rays emitted from oriented states. The experimental characteristics of the rotational bands are analyzed and compared with results from cranked Nilsson-Strutinsky calculations. The present analysis, combined with available experimental results in the A˜60 mass region, can be used to improve the current set of Nilsson parameters in the N=3 and N=4 oscillator shells.

Gellanki, J.; Rudolph, D.; Ragnarsson, I.; Andersson, L.-L.; Andreoiu, C.; Carpenter, M. P.; Ekman, J.; Fahlander, C.; Johansson, E. K.; Kardan, A.; Reviol, W.; Sarantites, D. G.; Seweryniak, D.; Svensson, C. E.; Waddington, J. C.

2012-09-01

151

Doping dependent quasiparticle band structure in cuprate superconductors  

CERN Multimedia

We present an exact diagonalization study of the single particle spectral function in the so-called t-t'-t''-J model in 2D. As a key result, we find that unlike the `pure' t-J model, hole doping leads to a major reconstruction of the quasiparticle band structure near (pi,0): whereas for the undoped system the quasiparticle states near (pi,0) are deep below the top of the band at (pi/2,pi/2), hole doping shifts these states up to E_F, resulting in extended flat band regions close to E_F and around (pi,0). This strong doping-induced deformation can be directly compared to angle resolved photoemission results on Sr_2 Cu Cl_2 O_2, underdoped Bi2212 and optimally doped Bi2212. We propose the interplay of long range hopping and decreasing spin correlations as the mechanism of this deformation.

Eder, R; Sawatzky, G A

1996-01-01

152

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.

2010-11-01

153

Dipole relaxation in dispersive photonic band-gap structures  

Science.gov (United States)

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

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

1997-02-01

154

Charge-density-wave phase of 1T-TiSe2: the influence of conduction band population.  

UK PubMed Central (United Kingdom)

The charge-density-wave phase of TiSe(2) 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 TiC(x)Se(2-x) with C=(S,Te) as well as for an occupation of only the conduction band by H(2)O adsorption-induced band bending. These observations point to an optimum band gap and support an excitonic driving force for the charge-density wave.

May MM; Brabetz C; Janowitz C; Manzke R

2011-10-01

155

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

Science.gov (United States)

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

156

Development of X-band accelerating structures for high gradients  

Science.gov (United States)

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

157

Probing the band structure of LaTe2 using angle resolved photoemission spectroscopy  

International Nuclear Information System (INIS)

With the current interest in the rare-earth tellurides as 'high temperature' charge density wave materials, a greater understanding of the physics of these systems is needed, particularly in the case of the ditellurides. We report a detailed study of the band structure of LaTe2 in the charge density wave state using high-resolution angle resolved photoemission spectroscopy (ARPES). From this work we hope to provide insights into the successes and weaknesses of past theoretical study as well as helping to clear up prior ambiguities by providing a firm experimental basis for future work in the tellurides.

2006-09-01

158

Probing the band structure of LaTe{sub 2} using angle resolved photoemission spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

With the current interest in the rare-earth tellurides as 'high temperature' charge density wave materials, a greater understanding of the physics of these systems is needed, particularly in the case of the ditellurides. We report a detailed study of the band structure of LaTe{sub 2} in the charge density wave state using high-resolution angle resolved photoemission spectroscopy (ARPES). From this work we hope to provide insights into the successes and weaknesses of past theoretical study as well as helping to clear up prior ambiguities by providing a firm experimental basis for future work in the tellurides.

Garcia, D.R. [Department of Physics, University of California, Berkeley, Berkeley, CA 94720 (United States); Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States)], E-mail: drgarcia@berkeley.edu; Zhou, S.Y. [Department of Physics, University of California, Berkeley, Berkeley, CA 94720 (United States); Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Gweon, G.-H. [Department of Physics, University of California, Berkeley, Berkeley, CA 94720 (United States); Jung, M.H. [National Research Laboratory for Material Science, KBSI, 52 Yeoeun-Dong Yusung-Gu, Daejeon 305-333 (Korea, Republic of); Kwon, Y.S. [Department of Physics, Sung Kyun Kwan University, Suwon 440-746 (Korea, Republic of); Lanzara, A. [Department of Physics, University of California, Berkeley, Berkeley, CA 94720 (United States); Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States)

2007-05-15

159

Probing the band structure of LaTe2 using angle resolvedphotoemission spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

With the current interest in the rare-earth tellurides ashigh temperature charge density wave materials, a greater understandingof the physics of these systems is needed, particularly in the case ofthe ditellurides. We report a detailed study of the band structure ofLaTe_2 in the charge density wave state using high-resolution angleresolved photoemission spectroscopy (ARPES). From thiswork we hope toprovide insights into the successes and weaknesses of past theoreticalstudy as well as helping to clear up prior ambiguities by providing anexperimental basis for future work inthe tellurides.

Garcia, Daniel R.; Zhou, Shuyun Y.; Gweon, Gey-Hong; Jung, M.H.; Kwon, Y.S.; Lanzara, Alessandra

2006-11-01

160

Band Jahn-Teller effect on the density of states of the magnetic high-Tc superconductors: A model study  

International Nuclear Information System (INIS)

[en] 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.

2012-01-01

 
 
 
 
161

Tunneling and the band structure of chaotic systems  

CERN Document Server

We compute the dispersion laws of chaotic periodic systems using the semiclassical periodic orbit theory to approximate the trace of the powers of the evolution operator. Aside from the usual real trajectories, we also include complex orbits. 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.

Leboeuf, P

1994-01-01

162

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2012-05-03

163

Electronic band structure, doping, and defects in the semiconducting Half Heusler compound CoTiSb  

Science.gov (United States)

We report transport and electronic band structure measurements on epitaxial films of the Half Heusler compound CoTiSb. CoTiSb belongs to the family of Half Heuslers with 18 valence electrons per formula unit that are predicted to be semiconducting despite being composed of all metallic components. Here the CoTiSb films were grown by molecular beam epitaxy on a lattice matched InAlAs buffer. The films are epitaxial and single crystalline, as measured by reflection high-energy electron diffraction and X-ray diffraction. Scanning tunnelling spectroscopy and temperature-dependent transport measurements reveal that the films are semiconducting, with unintentionally doped carrier concentrations comparable to that of highly doped conventional compound semiconductors. These carrier concentrations can be modulated by doping with Sn. The band structure of the films was measured by angle resolved photoemission spectroscopy at the MAX-Lab Synchrotron facility. The bulk bands are in general agreement with density functional theory calculations, with a valence band maximum at ? and surface states within the bulk band gap. The effects of defects are explored in order to explain the ARPES results.

Kawasaki, Jason; Johansson, Linda; Hjort, Martin; Timm, Rainer; Schultz, Brian; Balasubramanian, Thiagarajan; Mikkelsen, Anders; Palmstrom, Chris

2013-03-01

164

Nonlocal pseudopotentials in complex band-structure and photoemission calculations  

Energy Technology Data Exchange (ETDEWEB)

Based on a recently proposed localization procedure, a nonlocal pseudopotential scheme is derived to calculate potential coefficients V{sub {rvec G}{rvec G}{sup {prime}}}({rvec k}) which can be decomposed into terms, each being quadratic in {rvec k} and multiplied by a function of ({rvec G}{minus}{rvec G}{sup {prime}}), thus making them applicable to some important cases where local potential coefficients are required. Electronic structure calculations for semiconductors are in agreement with well-known semiempirical local pseudopotential band structures, as shown for GaAs. Nevertheless, the potential may significantly deviate from the semiempirical results. In order to test wave functions and transition probabilities, we prove the success of the procedure in a more troublesome case, i.e., applying it to a transition-metal compound as the experimentally well-investigated layered crystal TiSe{sub 2}, which up to now was not treated with a pseudopotential. Photoemission spectra within the one-step model are presented using Pendry`s method of complex band-structure calculation. The latter formalism had to be slightly generalized for the quasilocal properties of the potential. The agreement of the spectra with experimental data shows this method to be a reliable and practical tool to use nonlocal pseudopotentials for conduction-band wave functions of electron spectroscopies. {copyright} {ital 1997} {ital The American Physical Society}

Boedicker, A.; Schattke, W. [Institut fuer Theoretische Physik, Leibnizstrae 15, D-24118 Kiel (Germany)

1997-02-01

165

Nonlocal pseudopotentials in complex band-structure and photoemission calculations  

International Nuclear Information System (INIS)

Based on a recently proposed localization procedure, a nonlocal pseudopotential scheme is derived to calculate potential coefficients Vrvec Grvec G'(rvec k) which can be decomposed into terms, each being quadratic in rvec k and multiplied by a function of (rvec G-rvec G'), thus making them applicable to some important cases where local potential coefficients are required. Electronic structure calculations for semiconductors are in agreement with well-known semiempirical local pseudopotential band structures, as shown for GaAs. Nevertheless, the potential may significantly deviate from the semiempirical results. In order to test wave functions and transition probabilities, we prove the success of the procedure in a more troublesome case, i.e., applying it to a transition-metal compound as the experimentally well-investigated layered crystal TiSe2, which up to now was not treated with a pseudopotential. Photoemission spectra within the one-step model are presented using Pendry's method of complex band-structure calculation. The latter formalism had to be slightly generalized for the quasilocal properties of the potential. The agreement of the spectra with experimental data shows this method to be a reliable and practical tool to use nonlocal pseudopotentials for conduction-band wave functions of electron spectroscopies. copyright 1997 The American Physical Society.

1997-01-01

166

The crystal and electronic band structure of the diamond-like semiconductor Ag2ZnSiS4  

International Nuclear Information System (INIS)

Highlights: ? The structure of Ag2ZnSiS4 is solved and refined in the space group Pn using single crystal X-ray diffraction. ? Electronic band structure calculations show that Ag2ZnSiS4 is a direct band gap semiconductor with a calculated band gap of 1.88 eV. ? The optical band gap of Ag2ZnSiS4 was experimentally determined as 3.28 eV. - Abstract: Single crystals of the new diamond-like semiconductor Ag2ZnSiS4 have been synthesized using high-temperature, solid state synthesis at 800 °C. The compound crystallizes in the monoclinic, noncentrosymmetric space group Pn with a = 6.4052(1) ?, b = 6.5484(1) ?, c = 7.9340(1) ?, ? = 90.455(1)° and R1 (for all data) = 2.42%. The electronic band structure and density of states were calculated using density functional theory (DFT) and the full potential linearized augmented plane wave (LAPW) method within the Wien2k program suite. The calculated band structure suggests that Ag2ZnSiS4 is a direct band gap semiconductor with a calculated band gap of 1.88 eV at the ?-point. The calculated density of states of Ag2ZnSiS4 is compared with that of AgGaS2. The band gap of Ag2ZnSiS4 was also determined experimentally as 3.28 eV via optical diffuse reflectance spectroscopy.

2012-03-05

167

Electronic band structure and photoemission: A review and projection  

International Nuclear Information System (INIS)

A brief review of electronic-structure calculations in solids, as a means of interpreting photoemission spectra, is presented. The calculations are, in general, of three types: ordinary one-electron-like band structures, which apply to bulk solids and are the basis of all other calculations; surface modified calculations, which take into account, self-consistently if at all possible, the presence of a vacuum-solid interface and of the electronic modifications caused thereby; and many-body calculations, which go beyond average-field approximations and consider dynamic rearrangement effects caused by electron-electron correlations during the photoemission process. 44 refs

1987-01-01

168

Novel fluorescent probe for low density lipoprotein, based on the enhancement of Europium emission band  

Science.gov (United States)

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

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

2007-05-01

169

Band structure of semimagnetic Hg1-yMnyTe quantum wells  

CERN Multimedia

The band structure of semimagnetic Hg_1-yMn_yTe/Hg_1-xCd_xTe type-III quantum wells has been calculated using eight-band kp model in an envelope function approach. Details of the band structure calculations are given for the Mn free case (y=0). A mean field approach is used to take the influence of the sp-d exchange interaction on the band structure of QW's with low Mn concentrations into account. The calculated Landau level fan diagram and the density of states of a Hg_0.98Mn_0.02Te/Hg_0.3Cd_0.7Te QW are in good agreement with recent experimental transport observations. The model can be used to interpret the mutual influence of the two-dimensional confinement and the sp-d exchange interaction on the transport properties of Hg_1-yMn_yTe/Hg_1-xCd_xTe QW's.

Novik, E G; Jungwirth, T; Latussek, V; Becker, C R; Landwehr, G; Buhmann, H; Molenkamp, L W

2004-01-01

170

Band structure quantization in nanometer sized ZnO clusters.  

UK PubMed Central (United Kingdom)

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

Schouteden K; Zeng YJ; Lauwaet K; Romero CP; Goris B; Bals S; Van Tendeloo G; Lievens P; Van Haesendonck C

2013-05-01

171

The incommensurate charge-density-wave instability in the extended three-band Hubbard model  

CERN Document Server

The infinite-U three-band Hubbard model is considered in order to describe the CuO_2 planes of the high temperature superconducting cuprates. The charge instabilities are investigated when the model is extended with a nearest-neighbor repulsion between holes on copper d and oxygen p orbitals and in the presence of a long-range Coulombic repulsion. It is found that a first-order valence instability line ending with a critical point is present like in the previously investigated model without long-range forces. However, the dominant critical instability is the formation of incommensurate charge-density-waves, which always occur before the valence-instability critical point is reached. An effective singular attraction arises in the proximity of the charge-density wave instability, accounting for both a strong pairing mechanism and for the anomalous normal state properties.

Becca, F; Grilli, M

1998-01-01

172

Radiosensitivity is predicted by DNA end-binding complex density, but not by nuclear levels of band components  

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 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.

2004-01-01

173

Fiber felts as low density structural materials  

Energy Technology Data Exchange (ETDEWEB)

Short fiber felts structures can be made which provide improvements in properties over foams. In applications where resistance to compression set or stress relaxation are important, bonded fiber felts excel due to the flexing of individual fibers within their elastic limit. Felts of stainless steel and polyester fibers were prepared by deposition from liquid slurries. Compressive properties were determined as a function of felt parent material, extent of bonding, felt density, and length-to-diameter (L/D) ratio of starting fibers.

Milewski, J.V.; Newfield, S.E.

1981-01-01

174

Effect of pressure on the band structure, Fermi surface, and superconductivity of lanthanum  

International Nuclear Information System (INIS)

[en] The band structures of fcc lanthanum (La) corresponding to ambient pressure, 25 kbar, 50 kbar, 75 kbar, 100 kbar, 150 kbar, and 200 kbar have been calculated by the relativistic augmented plane wave method (RAPW) with the Overhauser prescription for the correlation and exchange. Calculations for the density of states, electron-phonon mass enhancement factor (lambda), superconducting transition temperature (Tsub(c)), and the Fermi surface are performed and the results are compared with available experimental and theoretical results. The superconducting transition temperature increases with pressure. A new empirical relation for the pressure dependence of the superconducting transition temperature is proposed and its validity is checked by use of the Tsub(c) value obtained from the band-structure results. (author)

1983-01-01

175

Protein structure elucidation from NMR proton densities.  

UK PubMed Central (United Kingdom)

The NMR-generated foc proton density affords a template to which the molecule has to be fitted to derive the structure. Here we present a computational protocol that achieves this goal. H(N) atoms are readily recognizable from (1)H/(2)H exchange or (1)H/(15)N heteronuclear single quantum correlation (HSQC) experiments. The primary structure is threaded through the unassigned foc by leapfrogging along peptidyl amide H(N)s and the connected H(alpha)s. Via a Bayesian approach, the probabilities of the sequential connectivity hypotheses are inferred from likelihoods of H(N)/H(N), H(N)/H(alpha), and H(alpha)/H(alpha) interatomic distances as well as (1)H NMR chemical shifts, both derived from public databases. Once the polypeptide sequence is identified, directionality becomes established, and the foc N and C termini are recognized. After a similar procedure, side chain H atoms are found, including discriminated cis/trans proline loci. The folded structure then is derived via a direct molecular dynamics embedding into mirror image-related representations of the foc and selected according to a lowest energy criterion. The method was applied to foc densities calculated for two protein domains, col 2 and kringle 2. The obtained structures are within 1.0-1.5 A (backbone heavy atoms) and 1.5-2.0 A (all heavy atoms) rms deviations from reported x-ray and/or NMR structures.

Grishaev A; Llinas M

2002-05-01

176

Protein structure elucidation from NMR proton densities.  

Science.gov (United States)

The NMR-generated foc proton density affords a template to which the molecule has to be fitted to derive the structure. Here we present a computational protocol that achieves this goal. H(N) atoms are readily recognizable from (1)H/(2)H exchange or (1)H/(15)N heteronuclear single quantum correlation (HSQC) experiments. The primary structure is threaded through the unassigned foc by leapfrogging along peptidyl amide H(N)s and the connected H(alpha)s. Via a Bayesian approach, the probabilities of the sequential connectivity hypotheses are inferred from likelihoods of H(N)/H(N), H(N)/H(alpha), and H(alpha)/H(alpha) interatomic distances as well as (1)H NMR chemical shifts, both derived from public databases. Once the polypeptide sequence is identified, directionality becomes established, and the foc N and C termini are recognized. After a similar procedure, side chain H atoms are found, including discriminated cis/trans proline loci. The folded structure then is derived via a direct molecular dynamics embedding into mirror image-related representations of the foc and selected according to a lowest energy criterion. The method was applied to foc densities calculated for two protein domains, col 2 and kringle 2. The obtained structures are within 1.0-1.5 A (backbone heavy atoms) and 1.5-2.0 A (all heavy atoms) rms deviations from reported x-ray and/or NMR structures. PMID:12011434

Grishaev, Alexander; Llinas, Miguel

2002-05-14

177

Ab initio Green's function formalism for band structures  

CERN Multimedia

Using the Green's function formalism, an ab initio method 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 in terms of 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 is also stable for inner valence bands where strong electron correlations are effective. The key to the proposed scheme is to evaluate the self-energy in terms of Wannier orbitals before transforming it to a crystal momentum representation. Exploiting that electron correlations are mainly local, one can truncate the lattice summations by an appropriate configuration selection scheme. This yields a flat configuration space, i.e., its size scales only linearly with the number of atoms per unit cell for large systems and, under certain conditions, the co...

Buth, C; Albrecht, M; Fulde, P; Buth, Christian; Birkenheuer, Uwe; Albrecht, Martin; Fulde, Peter

2004-01-01

178

Band structure approach to the resonant x-ray scattering  

CERN Document Server

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

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

2002-01-01

179

A NOVEL TRIPLE-BAND ELECTROMAGNETIC BANDGAP (EBG) STRUCTURE  

Directory of Open Access Journals (Sweden)

Full Text Available 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 method, simulated results of dispersion diagrams are presented by complete triple-bandgap. The central frequency of the bandgaps can be reduced to the lower region without increasing the size of the EBG cell. Moreover, an array of 4×5 EBG cells was simulated, fabricated and measured to verify the bandgap characteristic through the transmission coefficient S21. This proposed EBG can be used for multi-band applications, such as dual/triple antennas.

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

2013-01-01

180

The influence of conduction band population on the charge density wave phase of TiSe{sub 2}  

Energy Technology Data Exchange (ETDEWEB)

The origin of the charge density wave (CDW) phase transition of the transition-metal dichalcogenide TiSe{sub 2} has been subject of research for more than 30 years now with a recent tendency towards an excitonic model. This view was probed by investigating the influence of an additional population of the Ti 3d conduction band. The population was realised by means of band bending due to H{sub 2}O adsorption and band gap engineering via ternary compounds, monitored with ARPES at BESSY as well as conductivity measurements. Results indicate the existence of an optimal size for the band gap.

May, Matthias M. [Humboldt-Universitaet zu Berlin (Germany). Institut fuer Physik; Helmholtz-Zentrum Berlin fuer Materialien und Energie, Berlin (Germany); Unger, Isaak; Janowitz, Christoph; Manzke, Recardo [Humboldt-Universitaet zu Berlin (Germany). Institut fuer Physik

2011-07-01

 
 
 
 
181

Engineering band structure in nanoscale quantum-dot supercrystals.  

UK PubMed Central (United Kingdom)

Supercrystals made of periodically arranged semiconductor quantum dots (QDs) are promising structures for nanophotonics applications due to almost unlimited degrees of freedom enabling fine tuning of their optical responses. Here we demonstrate broad engineering opportunities associated with the possibility of tailoring the energy bands of excitons in two-dimensional quantum-dot supercrystals through the alteration in the QD arrangement. These opportunities offer an unprecedented control over the optical properties of the supercrystals, which may be used as a versatile material base for advanced photonics devices on the nanoscale.

Baimuratov AS; Rukhlenko ID; Fedorov AV

2013-07-01

182

Tunneling and the band structure of chaotic systems  

Energy Technology Data Exchange (ETDEWEB)

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.

Leboeuf, P.; Mouchet, A.

1994-04-01

183

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

184

Band structure in the polymer quantization of the harmonic oscillator  

International Nuclear Information System (INIS)

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

2013-08-21

185

X-BAND TRAVELING WAVE RF DEFLECTOR STRUCTURES  

Energy Technology Data Exchange (ETDEWEB)

Design studies on the X-Band transverse RF deflectors operating at HEM{sub ll} mode have been made for two different applications. One is for beam measurement of time-sliced emittance and slice energy spread for the upgraded LCLS project, its optimization in RF efficiency and system design are carefully considered. Another is to design an ultra-fast RF kicker in order to pick up single bunches from the bunch-train of the B-factory storage ring. The challenges are to obtain very short structure filling time with high RF group velocity and good RF efficiency with reasonable transverse shunt impedance. Its RF system will be discussed.

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

2008-12-18

186

Engineering band structure in nanoscale quantum-dot supercrystals.  

Science.gov (United States)

Supercrystals made of periodically arranged semiconductor quantum dots (QDs) are promising structures for nanophotonics applications due to almost unlimited degrees of freedom enabling fine tuning of their optical responses. Here we demonstrate broad engineering opportunities associated with the possibility of tailoring the energy bands of excitons in two-dimensional quantum-dot supercrystals through the alteration in the QD arrangement. These opportunities offer an unprecedented control over the optical properties of the supercrystals, which may be used as a versatile material base for advanced photonics devices on the nanoscale. PMID:23811895

Baimuratov, Anvar S; Rukhlenko, Ivan D; Fedorov, Anatoly V

2013-07-01

187

Gender-related differences in the apparent timing of skeletal density bands in the reef-building coral Siderastrea siderea  

Science.gov (United States)

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

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

2013-09-01

188

Electronic structures and hydrogen bond network of high-density and very high-density amorphous ices.  

UK PubMed Central (United Kingdom)

Electronic structures of hexagonal ice (ice Ih), high-density amorphous ice (HDA), and very high-density amorphous ice (VHDA) are investigated using ab initio density functional theory (DFT) at 77 K under a pressure of 0.1 MPa, focusing on band structure, density of states (DOS), partial density of states (PDOS), and electron density. It is found that the integration intensity of the O-2p bonding band in HDA is 1.53 eV wider than that in the VHDA. Because more 2p electrons in HDA participate the 2p-1s hybridization of O-H. The classical molecular dynamics (MD) method has further been carried out to analyze the hydrogen bond network of HDA and VHDA with larger numbers of water molecules under the same temperature, pressure, and boundary conditions used as those during the DFT calculation. MD results show that there exists some water molecules with five hydrogen bonds in both HDA (4.1 +/- 0.1%) and VHDA (2.8 +/- 0.1%), as compared with the LDA, being consistent with the integration intensity results of PDOS. This result can be used to interpret the physical nature of the similar transition temperature of HDA and VHDA to LDA with different heating rates.

He C; Lian JS; Jiang Q

2005-10-01

189

Bulk Inversion Asymmetry effects on the band structure of zincblende heterostructures in an 8-band Effective Mass Approximation model  

CERN Multimedia

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

Cartoixa, X; McGill, T C

2002-01-01

190

Quasiparticle semiconductor band structures including spin-orbit interactions  

Science.gov (United States)

We present first-principles calculations of the quasiparticle band structure of the group IV materials Si and Ge and the group III-V compound semiconductors AlP, AlAs, AlSb, InP, InAs, InSb, GaP, GaAs and GaSb. Calculations are performed using the plane wave pseudopotential method and the ‘one-shot’ GW method, i.e. G0W0. Quasiparticle band structures, augmented with the effects of spin-orbit, are obtained via a Wannier interpolation of the obtained quasiparticle energies and calculated spin-orbit matrix. Our calculations explicitly treat the shallow semicore states of In and Ga, which are known to be important in the description of the electronic properties, as valence states in the quasiparticle calculation. Our calculated quasiparticle energies, combining both the ab initio evaluation of the electron self-energy and the vector part of the pseudopotential representing the spin-orbit effects, are in generally very good agreement with experimental values. These calculations illustrate the predictive power of the methodology as applied to group IV and III-V semiconductors.

Malone, Brad D.; Cohen, Marvin L.

2013-03-01

191

Surface alloying in the Sn/Ni(111) system studied by synchrotron radiation photoelectron valence band spectroscopy and ab-initio density of states calculations  

Energy Technology Data Exchange (ETDEWEB)

Photoelectron spectroscopy using synchrotron radiation and ab-initio electronic structure calculations were used in order to describe the fine structure of the valence band in the Sn/Ni(111) system. The characteristic contributions of each metal in the valence band photoemission spectra obtained with a photon energy of 80 eV and their changes upon the formation of the ({radical}3 x {radical}3)R30{sup o} Sn/Ni(111) surface alloy were also born out in the calculated density-of-states curves in fair agreement with the experiments. The Sn-Ni interaction leads to a considerable broadening of the valence band width at the bimetallic surfaces.

Karakalos, S.; Ladas, S. [Department of Chemical Engineering, University of Patras and FORTH/ICE-HT, POB 1414, 26504 Rion (Patras) (Greece); Janecek, P.; Sutara, F.; Nehasil, V. [Department of Electronic and Vacuum Physics, Charles University, V.Holesovickach 2, 18000 Prague 8 (Czech Republic); Tsud, N. [Sincrotrone Trieste, Strada Statale 14, km 163.5, 34012 Basovizza-Trieste (Italy); Prince, K. [Sincrotrone Trieste, Strada Statale 14, km 163.5, 34012 Basovizza-Trieste (Italy); INFM, Laboratorio TASC, in Area Science Park, Strada Statale 14, km 163.5, 34012 Basovizza-Trieste (Italy); Matolin, V. [Department of Electronic and Vacuum Physics, Charles University, V.Holesovickach 2, 18000 Prague 8 (Czech Republic); Chab, V. [Institute of Physics, Czech Academy of Sciences, Cucrovarnicka 10, 16200 Prague (Czech Republic); Papanicolaou, N.I. [Department of Physics, University of Ioannina, P.O. Box 1186, 45110 Ioannina (Greece)], E-mail: nikpap@uoi.gr; Dianat, A.; Gross, A. [Institute of Theoretical Chemistry, University of Ulm, D-89069 Ulm (Germany)

2008-03-31

192

Electronic band structure of silver-deficient hexagonal AgB$_2$  

CERN Document Server

Structural, cohesive properties as well as energy band structure of metastable hexagonal AgB$_2$ and silver-deficient borides Ag$_{0.875}$B$_2$ and Ag$_{0.750}$B$_2$ were investigated by means of the projected augmented wave method in the framework of the density functional theory (VASP package). We found that the density of states at the Fermi level for nonstoichiometric diborides is almost constant within a range of vacancy content up to 25%. The formation energy of metal vacancies in silver diboride is the least among all 4d metal diborides, i.e. for AgB$_2$ is possible to expect the wide homogeneity region.

Shein, I R; Ivanovskii, A L

2004-01-01

193

Multi-band circular polarizer using planar spiral metamaterial structure.  

Science.gov (United States)

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

194

Multi-band circular polarizer using planar spiral metamaterial structure.  

UK PubMed Central (United Kingdom)

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.

Ma X; Huang C; Pu M; Hu C; Feng Q; Luo X

2012-07-01

195

Band Structure in N=Z+2 ^80Y  

Science.gov (United States)

Recently, increased attention has been focused on N?Z nuclei as they are now becoming experimentally feasible. The current generation of detector arrays provide detailed spectroscopy of prompt transitions in heavy ion reactions. The use of such arrays has been indensible in the study of unstable nuclei near N=Z as the proton dripline is reached. Two separate experiments have been performed to elucidate the structure of N=Z+2 ^80Y. An in-beam study using the Gammasphere array coupled to Microball provided information of prompt gamma-decays. Seperately, an Isomeric Decay Tagging experiment using the CLARION array was performed to correlate decays both above and below a microsecond isomer. Band structures and possible single-particle configurations will be discussed in relation to neighboring nuclides.

Ressler, Jennifer Jo; Walters, W. B.; Grzywacz, R.; Yu, C.-H.; Baktash, C.; Batchelder, J. C.; Bingham, C.; Gross, C. J.; Lipoglavsek, M.; McConnell, J.; Paul, S. D.; Piechaczek, A.; Radford, D.; Sarantites, D. G.; Shergur, J.

2000-10-01

196

Band-structure calculations of specular reflection in spin valves  

Energy Technology Data Exchange (ETDEWEB)

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

Chen, Jian; Fernandez-de-Castro, Juan

2001-06-01

197

Characterization of band structure for transverse acoustic phonons in Fibonacci superlattices by a bandedge formalism  

International Nuclear Information System (INIS)

We present a divergence-free method to determine the characteristics of band structures and projected band structures of transverse acoustic phonons in Fibonacci superlattices. A set of bandedge equations is formulated to solve the band structures for the phonon instead of using the traditional dispersion relation. Numerical calculations show band structures calculated by the present method for the Fibonacci superlattice without numerical instability, which may occur in traditional methods. Based on the present formalism, the band structure for the acoustic phonons has been characterized by closure points and the projected bandgaps of the forbidden bands. The projected bandgaps are determined by the projected band structure, which is characterized by the cross points of the projected bandedges. We observed that the band structure and projected band structure and their characteristics were quite different for different generation orders and the basic layers for the Fibonacci superlattice. In this study, concise rules to determine these characteristics of the band structure and the projected band structure, including the number and the location of closure points of forbidden bands and those of projected bandgaps, in Fibonacci superlattices with arbitrary generation order and basic layers are proposed.

2008-11-05

198

Band Structure and Transport Properties of $CrO_{2}$  

CERN Multimedia

Local Spin Density Approximation (LSDA) is used to calculate the energy bands of both the ferromagnetic and paramagnetic phases of metallic CrO_2. The Fermi level lies in a peak in the paramagnetic density of states, and the ferromagnetic phase is more stable. As first predicted by Schwarz, the magnetic moment is 2 \\mu_B per Cr atom, with the Fermi level for minority spins lying in an insulating gap between oxygen p and chromium d states ("half-metallic" behavior.) The A_1g Raman frequency is predicted to be 587 cm^{-1}. Drude plasma frequencies are of order 2eV, as seen experimentally by Chase. The measured resistivity is used to find the electron mean-free path l, which is only a few angstroms at 600K, but nevertheless, resistivity continues to rise as temperature increases. This puts CrO_2 into the category of "bad metals" in common with the high T_c superconductors, the high T metallic phase of VO_2, and the ferromagnet SrRuO_3. In common with both SrRuO_3 and Sr_2RuO_4, the measured specific heat \\gamma ...

Lewis, S P; Sasaki, T; Lewis, Steven P.; Allen, Phillip B.; Sasaki, Taizo

1996-01-01

199

Density effects in the experimental structure factor of liquid Kr  

Energy Technology Data Exchange (ETDEWEB)

We report on recent accurate diffraction data on liquid Kr at two different densities along the 130 K isotherm. Significative density effects are present in the isothermal density derivative of the structure factor. (orig.).

Barocchi, F. (Dipt. di Fisica, Univ. di Firenze (Italy)); Chieux, P. (Inst. Laue-Langevin, 38 - Grenoble (France)); Magli, R. (Dipt. di Energetica, Univ. di Firenze (Italy))

1992-06-01

200

Density effects in the experimental structure factor of liquid Kr  

International Nuclear Information System (INIS)

[en] We report on recent accurate diffraction data on liquid Kr at two different densities along the 130 K isotherm. Significative density effects are present in the isothermal density derivative of the structure factor. (orig.)

1992-01-01

 
 
 
 
201

Conduction band structure and electron mobility in uniaxially strained Si via externally applied strain in nanomembranes  

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.

2011-08-17

202

Band structure, Fermi surface, superconductivity, and resistivity of actinium under high pressure  

Energy Technology Data Exchange (ETDEWEB)

The electronic band structures of fcc actinium (Ac) have been calculated for a wide range of pressures by reducing the unit-cell volume from 1.0V/sub 0/ to 0.5V/sub 0/ with use of the relativistic augmented-plane-wave method. The density of states and Fermi-surface cross sections corresponding to various volumes are obtained. Calculations for the band-structure-related quantities such as electron-phonon mass enhancement factor lambda, superconducting transition temperature T/sub c/, and resistivity rho corresponding to different volumes are performed. It is seen that T/sub c/ increases with pressure, i.e., with decreasing volume. A new empirical relation for the volume dependence of T/sub c/ is proposed and its validity is checked using the T/sub c/ values obtained from the above band-structure results. The resistivity rho first increases with increasing pressure (i.e., with decreasing volume) and then decreases for higher pressures (i.e., for smaller volumes).

Dakshinamoorthy, M.; Iyakutti, K.

1984-12-15

203

Band structure, Fermi surface, superconductivity, and resistivity of actinium under high pressure  

International Nuclear Information System (INIS)

[en] The electronic band structures of fcc actinium (Ac) have been calculated for a wide range of pressures by reducing the unit-cell volume from 1.0V0 to 0.5V0 with use of the relativistic augmented-plane-wave method. The density of states and Fermi-surface cross sections corresponding to various volumes are obtained. Calculations for the band-structure-related quantities such as electron-phonon mass enhancement factor lambda, superconducting transition temperature T/sub c/, and resistivity rho corresponding to different volumes are performed. It is seen that T/sub c/ increases with pressure, i.e., with decreasing volume. A new empirical relation for the volume dependence of T/sub c/ is proposed and its validity is checked using the T/sub c/ values obtained from the above band-structure results. The resistivity rho first increases with increasing pressure (i.e., with decreasing volume) and then decreases for higher pressures (i.e., for smaller volumes)

1984-12-15

204

Measuring large-scale structure with quasars in narrow-band filter surveys  

Science.gov (United States)

We show that a large-area imaging survey using narrow-band filters could detect quasars in sufficiently high number densities, and with more than sufficient accuracy in their photometric redshifts, to turn them into suitable tracers of large-scale structure. If a narrow-band optical survey can detect objects as faint as i= 23, it could reach volumetric number densities as high as 10-4 h3 Mpc-3 (comoving) at z˜ 1.5. Such a catalogue would lead to precision measurements of the power spectrum up to z˜ 3-4. We also show that it is possible to employ quasars to measure baryon acoustic oscillations at high redshifts, where the uncertainties from redshift distortions and non-linearities are much smaller than at z? 1. As a concrete example we study the future impact of the Javalambre Physics of the Accelerating Universe Astrophysical Survey (J-PAS), which is a narrow-band imaging survey in the optical over 1/5 of the unobscured sky with 42 filters of ˜100-Å full width at half-maximum. We show that J-PAS will be able to take advantage of the broad emission lines of quasars to deliver excellent photometric redshifts, ?z? 0.002 (1 +z), for millions of objects.

Abramo, L. Raul; Strauss, Michael A.; Lima, Marcos; Hernández-Monteagudo, Carlos; Lazkoz, Ruth; Moles, Mariano; de Oliveira, Claudia Mendes; Sendra, Irene; Sodré, Laerte; Storchi-Bergmann, Thaisa

2012-07-01

205

Measuring large-scale structure with quasars in narrow-band filter surveys  

CERN Multimedia

We show that a large-area imaging survey using narrow-band filters could detect quasars in sufficiently high number densities, and with more than sufficient accuracy in their photometric redshifts, to turn them into suitable tracers of large-scale structure. If a narrow-band optical survey can detect objects as faint as i=23, it could reach volumetric number densities as high as 10^{-4} h^3 Mpc^{-3} (comoving) at z~1.5 . Such a catalog would lead to precision measurements of the power spectrum up to z~3-4. We also show that it is possible to employ quasars to measure baryon acoustic oscillations at high redshifts, where the uncertainties from redshift distortions and nonlinearities are much smaller than at z<1. As a concrete example we study the future impact of J-PAS, which is a narrow-band imaging survey in the optical over 1/5 of the unobscured sky with 42 filters of ~100 A full-width at half-maximum. We show that J-PAS will be able to take advantage of the broad emission lines of quasars to deliver exc...

Abramo, L Raul; Lima, Marcos; Hernández-Monteagudo, Carlos; Lazkoz, Ruth; Moles, Mariano; de Oliveira, Cláudia M; Sendra, Irene; Sodré, Laerte

2011-01-01

206

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 cor...

Mahmoud Zaki Iskandarani

207

Low-density band-gap states in pentacene thin films probed with ultrahigh-sensitivity ultraviolet photoelectron spectroscopy  

Science.gov (United States)

We detected a very low density of electronic states in the band gap of a nondoped pentacene thin film by using ultraviolet photoelectron spectroscopy with ultrahigh sensitivity and ultralow background. The gap states, which may originate from the highest occupied molecular orbital (HOMO) state in imperfect molecular packing regions, are distributed exponentially up to the Fermi level and control the Fermi level relative to the HOMO band.

Sueyoshi, Tomoki; Fukagawa, Hirohiko; Ono, Masaki; Kera, Satoshi; Ueno, Nobuo

2009-11-01

208

Non-random distribution of high density chromatin detected at opposite ends of T-banded human metaphase chromosomes  

Directory of Open Access Journals (Sweden)

Full Text Available 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

2007-01-01

209

Spectral Density Functionals for Electronic Structure Calculations  

CERN Document Server

We introduce a spectral density functional theory which can be used to compute energetics and spectra of real strongly--correlated materials using methods, algorithms and computer programs of the electronic structure theory of solids. The approach considers the total free energy of a system as a functional of a local electronic Green function which is probed in the region of interest. Since we have a variety of notions of locality in our formulation, our method is manifestly basis--set dependent. However, it produces the exact total energy and local excitational spectrum provided that the exact functional is extremized. The self--energy of the theory appears as an auxiliary mass operator similar to the introduction of the ground--state Kohn--Sham potential in density functional theory. It is automatically short--ranged in the same region of Hilbert space which defines the local Green function. We exploit this property to find good approximations to the functional. For example, if electronic self--energy is kn...

Savrasov, S Y

2003-01-01

210

Quasi Normal Modes description of transmission properties for Photonic Band Gap structures  

CERN Multimedia

In this paper, we use the 'Quasi Normal Modes' (QNM) approach for discussing the transmission properties of double-side opened optical cavities: in particular, this approach is specified for one dimensional (1D) 'Photonic Band Gap' (PBG) structures. Moreover, we conjecture that the density of the modes (DOM) is a dynamical variable which has the flexibility of varying with respect to the boundary conditions as well as the initial conditions; in fact, the e.m. field generated by two monochromatic counter-propagating pump waves leads to interference effects inside a quarter-wave (QW) symmetric 1D-PBG structure. Finally, here, for the first time, a large number of theoretical assumptions on QNM metrics for an open cavity, never discussed in literature, are proved, and a simple and direct method to calculate the QNM norm for a 1D-PBG structure is reported.

Settimi, A; Hoenders, B J

2008-01-01

211

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

International Nuclear Information System (INIS)

[en] 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

2005-10-01

212

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

Science.gov (United States)

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 2.75 eV.

Andriyevsky, B.; Kapustianyk, V.; Ciepluch-Trojanek, W.; Batiuk, A.

2005-10-01

213

Band structure and phase stability of the copper oxides Cu2O, CuO, and Cu4O3  

Science.gov (United States)

The p-type semiconductor copper oxide has three distinct phases Cu2O, CuO, and Cu4O3 with different morphologies and oxidation states of the copper ions. We investigate the structural stability and electronic band structure of all three copper oxide compounds using ab initio methods within the framework of density functional theory and consider different exchange correlation functionals. While the local density approximation (LDA) fails to describe the semiconducting states of CuO and Cu4O3, the LDA+U and HSE06 hybrid functional describe both compounds as indirect semiconductors. Using the HSE06 hybrid functional we calculate the electronic band structure in the full Brillouin zone for all three copper oxide compounds.

Heinemann, Markus; Eifert, Bianca; Heiliger, Christian

2013-03-01

214

Solar spectral fine structure in 18-23 GHz band  

Directory of Open Access Journals (Sweden)

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.

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

1999-01-01

215

Solar spectral fine structure in 18-23 GHz band  

Scientific Electronic Library Online (English)

Full Text Available Abstract in english On 30th June 1989 high sensitivity-spectral resolution observations of solar radio bursts were carried out in the frequency range of 18 - 23 GHz. The burst observed at 17:46 UT was different from the 60 bursts observed so far in the sense that it exhibited a frequency fine structure superimposed on the ongoing burst in its rising phase, i.e. an additional enhancement of the flux density of the order of 10 SFU, observed only in the 21 and 22 GHz frequency channels, lasting (more) 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.

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

1999-09-01

216

Vector k small middle dotp approach for photonic band structures  

Science.gov (United States)

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

Sipe

2000-10-01

217

Vector k small middle dotp approach for photonic band structures  

UK PubMed Central (United Kingdom)

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

Sipe JE

2000-10-01

218

Accurate screened exchange band structures for the transition metal monoxides MnO, FeO, CoO and NiO.  

Science.gov (United States)

We report calculations of the band structures and density of states of the four transition metal monoxides MnO, FeO, CoO and NiO using the hybrid density functional sX-LDA ('screened exchange local density approximation'). Late transition metal oxides are prototypical examples of strongly correlated materials, which pose challenges for electronic structure methods. We compare our results with available experimental data and show that our calculations generally yield accurate predictions for the fundamental band gaps and valence bands, in favourable agreement with previously reported theoretical studies. For MnO, the band gaps are still underestimated, suggesting additional many-body effects that are not captured by our screened hybrid functional approach. PMID:23553489

Gillen, Roland; Robertson, John

2013-04-03

219

Accurate screened exchange band structures for the transition metal monoxides MnO, FeO, CoO and NiO.  

UK PubMed Central (United Kingdom)

We report calculations of the band structures and density of states of the four transition metal monoxides MnO, FeO, CoO and NiO using the hybrid density functional sX-LDA ('screened exchange local density approximation'). Late transition metal oxides are prototypical examples of strongly correlated materials, which pose challenges for electronic structure methods. We compare our results with available experimental data and show that our calculations generally yield accurate predictions for the fundamental band gaps and valence bands, in favourable agreement with previously reported theoretical studies. For MnO, the band gaps are still underestimated, suggesting additional many-body effects that are not captured by our screened hybrid functional approach.

Gillen R; Robertson J

2013-04-01

220

Novel semiconductor solar cell structures: The quantum dot intermediate band solar cell  

International Nuclear Information System (INIS)

The Quantum Dot Intermediate Band Solar Cell (QD-IBSC) has been proposed for studying experimentally the operating principles of a generic class of photovoltaic devices, the intermediate band solar cells (IBSC). The performance of an IBSC is based on the properties of a semiconductor-like material which is characterised by the existence of an intermediate band (IB) located within what would otherwise be its conventional bandgap. The improvement in efficiency of the cell arises from its potential (i) to absorb below bandgap energy photons and thus produce additional photocurrent, and (ii) to inject this enhanced photocurrent without degrading its output photo-voltage. The implementation of the IBSC using quantum dots (QDs) takes advantage of the discrete nature of the carrier density of states in a 0-dimensional nano-structure, an essential property for realising the IB concept. In the QD-IBSC, the IB arises from the confined electron states in an array of quantum dots. This paper reviews the operation of the first prototype QD-IBSCs and discusses some of the lessons learnt from their characterisation

2006-07-26

 
 
 
 
221

Theoretical and experimental study of the unoccupied electronic band structure of Ru(001) by electron reflection  

Energy Technology Data Exchange (ETDEWEB)

Very-low-energy electron diffraction (VLEED) is used to study the unoccupied electronic states of Ru(001). Experimental and theoretical data are presented for reflection of electrons with energies of the specular beam between 7 and 32 eV and at different angles of incidence between 3/sup 0/ and 28/sup 0/ in both the Gamma-barK-bar and Gamma-barM-bar directions. Two sharp reflection minima at kinetic energies of 11.1 and 12.3 eV (relative to the vacuum level) corresponding to a final-state peak in Ru(001) angle-resolved photoemission and secondary-electron emission are observed near normal incidence. Theoretical VLEED intensity and band-structure calculations are carried out to confirm the origin of the experimental spectral features. An energy-dependent optical potential is shown to be sufficient to explain the observed narrow spectral structures. The observed minima can be reproduced excellently with the imaginary part of the optical potential equal to -0.6 eV at 11 eV above the vacuum level. The minimum at 12.3 eV can clearly be correlated with a high density of states in the volume band structure, whereas the other one is assigned to a Shockley-type surface state. The effects of several other parameters on the theoretical spectra are discussed.

Lindroos, M.; Pfnuer, H.; Menzel, D.

1986-05-15

222

Theoretical and experimental study of the unoccupied electronic band structure of Ru(001) by electron reflection  

International Nuclear Information System (INIS)

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

1986-05-15

223

Energy and momentum resolved band structure of K2O : electron momentum spectroscopy and linear combination of atomic orbitals calculation  

International Nuclear Information System (INIS)

[en] This paper details an experimental and theoretical investigation into the electronic structure of the highly ionic, alkali oxide, potassium oxide (K2O). The experiments were carried out using the relatively new technique of electron momentum spectroscopy. This is an electron impact technique that is capable of measuring the electron intensity distribution as a function of energy and momentum. Calculations were performed within the linear combination of atomic orbitals approximation using both Hartree-Fock and density functional theory formalisms. We have been able to map the band dispersions and intensities in the oxygen valence bands and potassium 3p and 3s bands for the first time. Overlap of the O 2s and K 3p binding energy peaks makes it difficult to extract the band gaps involving either of these bands. The O 2p and K 3s peaks are resolved, however, and we observe a gap of 30.4 ± 0.2 deg. eV. This value is reproduced by the PBE0 calculation. Intensities within the s bands are reproduced well by all our calculations, whereas the observed p bands show anomalous intensity at the ?-point, which is not present in any of the calculations

2003-10-22

224

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

Science.gov (United States)

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

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

225

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

International Nuclear Information System (INIS)

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

2003-01-01

226

Band-structure calculations and structure-factor estimates of Cu - their complementarity  

International Nuclear Information System (INIS)

Rather than an uncritical comparison of experimental and theoretical values, the various sets of structure-factor values of copper metal derived from experimental diffraction procedures are mutally compared as also are the various sets of theoretical values derived from band-structure calculations. This approach reveals the presence of outlier sets in each group and allows recognition of their condition before any attempt is made to intercompare the groups. Within the experimental group, the ?-ray values do not appear to sustain the absolute status originally claimed from them. Within the theoretical group, an inadequacy in defining the core contribution is indicated. The latter conclusion suggests that it is an inappropriate operation to make direct comparison between diffraction-sourced experimental values of structure factors and theoretical values from band-structure calculations. Instead, the latter should be used on a complementary basis with the full (sin ?)/? range of experimental values to establish the best core contribution. The minor valence-bond contribution to scattering, which is largely restricted to the low (sin ?)/? region, is most sensitively defined by reference to band-structure prediction of photoemission spectral distribution. Attention is drawn to the possible significance of the form-factor curve versus (sin ?)/? being dependent on the unit-cell dimension. (orig.).

1992-01-01

227

Band-structure calculations and structure-factor estimates of Cu - their complementarity  

Energy Technology Data Exchange (ETDEWEB)

Rather than an uncritical comparison of experimental and theoretical values, the various sets of structure-factor values of copper metal derived from experimental diffraction procedures are mutally compared as also are the various sets of theoretical values derived from band-structure calculations. This approach reveals the presence of outlier sets in each group and allows recognition of their condition before any attempt is made to intercompare the groups. Within the experimental group, the {gamma}-ray values do not appear to sustain the absolute status originally claimed from them. Within the theoretical group, an inadequacy in defining the core contribution is indicated. The latter conclusion suggests that it is an inappropriate operation to make direct comparison between diffraction-sourced experimental values of structure factors and theoretical values from band-structure calculations. Instead, the latter should be used on a complementary basis with the full (sin {theta})/{lambda} range of experimental values to establish the best core contribution. The minor valence-bond contribution to scattering, which is largely restricted to the low (sin {theta})/{lambda} region, is most sensitively defined by reference to band-structure prediction of photoemission spectral distribution. Attention is drawn to the possible significance of the form-factor curve versus (sin {theta})/{lambda} being dependent on the unit-cell dimension. (orig.).

Mackenzie, J.K. (Div. of Materials Science and Technology, CSIRO, Clayton, Victoria (Australia)); Mathieson, A.M. (Div. of Materials Science and Technology, CSIRO, Clayton, Victoria (Australia) Chemistry Dept., La Trobe Univ., Bundoora, Victoria (Australia))

1992-03-01

228

Conduction-band edge and Shubnikov–de Haas effect in low-electron-density SrTiO3  

Science.gov (United States)

The Shubnikov–de Haas effect is used to explore the conduction-band edge of high mobility SrTiO3 films doped with La. The results largely confirm the earlier measurements by Uwe [Jpn. J. Appl. Phys.0021-492210.1143/JJAP.24.L335 24 (Suppl. 24-2), 335 (1985)]. The band edge dispersion differs significantly from the predictions of ab initio electronic structure theory.

Allen, S. James; Jalan, Bharat; Lee, SungBin; Ouellette, Daniel G.; Khalsa, Guru; Jaroszynski, Jan; Stemmer, Susanne; MacDonald, Allan H.

2013-07-01

229

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

Science.gov (United States)

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

Sedghi, A.; Soufiani, A. Rounaghi

2013-10-01

230

Density functional theory study of the electronic structure of fluorite Cu2Se.  

UK PubMed Central (United Kingdom)

We have investigated the electronic structure of fluorite Cu2Se using density functional theory calculations within the LDA, PBE and AM05 approximations as well as the non-local hybrid PBE0 and HSE approximations. We find that Cu2Se is a zero gap semiconductor when using either a local or semi-local density functional approximation while the PBE0 functional opens up a gap. For the HSE approximation, we find that the presence of a gap depends on the range separation for the non-local exchange. For the occupied part in the density of states we find that LDA, PBE, AM05, PBE0 and HSE agree with regard to the overall electronic structure. However, the hybrid functionals result in peaks shifted towards lower energy compared to LDA, PBE and AM05. The valence bands obtained using the hybrid functionals are in good agreement with experimental valence band spectra. We also find that the PBE, PBE0 and HSE approximations give similar results regarding bulk properties, such as lattice constants and bulk modulus. In addition, we have investigated the localization of the Cu d-states and its effect on the band gap in the material using the LDA + U approach. We find that a sufficiently high U indeed opens up a gap; however, this U leads to valence bands that disagree with experimental observations.

Råsander M; Bergqvist L; Delin A

2013-03-01

231

Density-functional LCAO calculations for solids: Comparison between Hartree-Fock and Kohn-Sham structural properties  

Energy Technology Data Exchange (ETDEWEB)

The Density-Functional method, with Linear Combination of Atomic Orbitals, has been applied to eight crystals; the lattice equilibrium parameters, and the lattice formation energies have been calculated at the Hartree-Fock level (HF), at the hybrid Hartree-Fock Density-Functional level (DFT/HF), and at the Kohn-Sham Density-Functional level (DFT). The band structures and the electronic charge distributions calculated at the DFT and HF levels are compared.

Causa, M. [Univ. of Torino (Italy); Zupan, A. [Jozef Stefan Institute, Ljublijana (Slovenia)

1994-12-31

232

Density-functional LCAO calculations for solids: Comparison between Hartree-Fock and Kohn-Sham structural properties  

International Nuclear Information System (INIS)

[en] The Density-Functional method, with Linear Combination of Atomic Orbitals, has been applied to eight crystals; the lattice equilibrium parameters, and the lattice formation energies have been calculated at the Hartree-Fock level (HF), at the hybrid Hartree-Fock Density-Functional level (DFT/HF), and at the Kohn-Sham Density-Functional level (DFT). The band structures and the electronic charge distributions calculated at the DFT and HF levels are compared

1994-01-01

233

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

UK PubMed Central (United Kingdom)

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

Nefedov IS; Tretyakov SA

2002-09-01

234

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

Science.gov (United States)

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

Nefedov, Igor S; Tretyakov, Sergei A

2002-09-23

235

Positron band structures of GaAs and CdTe  

International Nuclear Information System (INIS)

The problem of positron and structure in a periodic lattice is similar to its electron counterpart. GaAs and CdTe positron band structures are calculated, a comparison between the electron and positron energies is discussed. (author).

1990-01-01

236

Electronic structure of a subnanometer wide bottom-up fabricated graphene nanoribbon: End states, band gap, and dispersion  

Science.gov (United States)

Angle-resolved two-photon photoemission and high-resolution electron energy loss spectroscopy are employed to derive the electronic structure of a subnanometer atomically precise quasi-one-dimensional graphene nanoribbon (GNR) on Au(111). We resolved occupied and unoccupied electronic bands including their dispersion and determined the band gap, which possesses an unexpectedly large value of 5.1 eV. Supported by density functional theory calculations for the idealized infinite polymer and finite size oligomers, an unoccupied nondispersive electronic state with an energetic position in the middle of the band gap of the GNR could be identified. This state resides at both ends of the ribbon (end state) and is only found in the finite sized systems, i.e., the oligomers.

Bronner, C.; Leyssner, F.; Stremlau, S.; Utecht, M.; Saalfrank, P.; Klamroth, T.; Tegeder, P.

2012-08-01

237

Band Structures and Nucleon Alignments in ^173,175W  

Science.gov (United States)

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

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

2012-10-01

238

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

International Nuclear Information System (INIS)

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

1981-06-13

239

High-spin structure beyond band termination in Er157  

International Nuclear Information System (INIS)

The angular-momentum induced transition from a deformed state of collective rotation to a noncollective configuration has been studied. In Er157 this transition manifests itself as favored band termination near I=45(?/2?). The feeding of these band terminating states has been investigated for the first time using the Gammasphere spectrometer. Many weakly populated states lying at high excitation energy that decay into these special states have been discovered. Cranked Nilsson-Strutinsky calculations suggest that these states arise from weakly collective 'core-breaking' configurations.

2004-06-25

240

Topological equivalence of crystal and quasicrystal band structures  

Science.gov (United States)

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

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

2013-09-01

 
 
 
 
241

On-demand all-optical generation of controlled Rb-vapor densities in photonic-band-gap fibers  

Science.gov (United States)

We investigate the time dynamics of light-induced desorption of Rb atoms in hollow-core photonic-band-gap fibers and demonstrate all-optical generation of precisely controlled Rb-vapor densities. We also compare the performance of the desorption process in an unmodified fiber with one with an organosilane-coated core, and based on the vapor depletion and recovery behavior, we propose a mechanism to describe the desorption processes. We further demonstrate that high densities of Rb vapor can be generated after the desorption beam is switched off and use it to realize ? -scheme electromagnetically induced transparency at control powers as low as 80 nW.

Bhagwat, Amar R.; Slepkov, Aaron D.; Venkataraman, Vivek; Londero, Pablo; Gaeta, Alexander L.

2009-06-01

242

Approximate particle number projection with density dependent forces: superdeformed bands in the A=150 and A=190 regions  

Energy Technology Data Exchange (ETDEWEB)

We derive the equations for approximate particle number projection based on mean field wave functions with finite range density dependent forces. As an application ground bands of even-A superdeformed nuclei in the A=150 and A=190 regions are calculated with the Gogny force. We discuss nuclear properties such as quadrupole moments, moments of inertia and quasiparticle spectra, among others, as a function of the angular momentum. We obtain a good overall description.

Valor, A.; Egido, J.L.; Robledo, L.M

2000-02-14

243

Approximate particle number projection with density dependent forces Superdeformed bands in the A=150 and A=190 regions  

CERN Multimedia

We derive the equations for approximate particle number projection based on mean field wave functions with finite range density dependent forces. As an application ground bands of even-A superdeformed nuclei in the A=150 and A=190 regions are calculated with the Gogny force. We discuss nuclear properties such as quadrupole moments, moments of inertia and quasiparticle spectra, among others, as a function of the angular momentum. We obtain a good overall description.

Valor, A; Robledo, L M

2000-01-01

244

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 (ZnO)12 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; R.V. Bovgyra; M.V. Kovalenko; D.?. Popovych; ?.S. Serednytski

2013-01-01

245

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2013-02-01

246

Electronic band structure of LaCoO3/Y/Mn compounds  

International Nuclear Information System (INIS)

Spin polarization effects on electronic properties of pure LaCoO3 and doped compounds (La0.5Y0.5CoO3, LaCo0.5Mn0.5O3) in the rhombohedral phase have been studied. We have employed the full potential linearized augmented plane wave (FP-LAPW) method with the generalized gradient approximation (GGA+U) under density functional theory (DFT). The calculated band structures along with total as well as partial densities of states reveal that Y and Mn impurities have a significant effect on the structural and electronic properties of LaCoO3. It is found that Mn alters insulating behavior of this compound to the half metallic for spin up state. Obtained results show that the magnetic moment for the Co-3d state is near 3.12?B in LaCoO3 compound which increases and decreases with addition of Y and Mn dopants respectively.

2013-02-01

247

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

International Nuclear Information System (INIS)

[en] 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

1974-01-01

248

Yrast transition strengths and band structure of 75Br  

International Nuclear Information System (INIS)

High spin states in 75Br were investigated in the reactions 62Ni(16O,p2n) and 66Zn(12C,p2n). By means of ??- and ?-neutron multiplicity coincidence measurements, rotational bands of both parities were extended up to 7 MeV excitation energy and spin I = (33/2). The lifetimes of 17 yrast states were determined with the recoil distance and Doppler shift attenuation methods; the spin dependence of the side feeding time was also measured. The data have been analyzed in terms of the Strutinsky-Bogolyubov cranking model with a Woods-Saxon average potential. The first crossing observed in the negative parity bands is attributed to the alignment of a g/sub 9/2/ proton pair; the next irregularity which is also observed in the positive parity band is interpreted as the alignment of g/sub 9/2/ neutrons. The coexistence of prolate and oblate configurations at low spin and the change of nonaxial deformation with rotational frequency due to the polarization of the even-even core by the odd particle are discussed. The signature inversion visible in the negative parity bands as well as the changes in the signature splitting and reduction of B(E2) values at high spins may be related to a transition from ?0 to ?>00 triaxial shapes.

1985-01-01

249

Banded skarns, an example of geochemical dissipative structure  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Banded skarns are metasomatic rocks produced by oscillatory precipitation on a centimetre scale. These rocks result from the transformation of homogeneous carbonate materials by aqueous fluids under metamorphic conditions. After reviewing ordinary, unbanded zoning in skarns and the evolution of this...

Guy, Bernard

250

FP-LAPW study of anhydrous cadmium and silver oxalates: electronic structure and electron density topology  

International Nuclear Information System (INIS)

Results of theoretical studies of electronic structure (full potential linearized augmented plane Wave method within DFT formalism as implemented in Wien2k package), electron density topology and bonding (Bader's quantum theory of atoms in molecules topological analysis of total electron density obtained from FP-LAPW calculations) in anhydrous cadmium and silver oxalates are presented. Detailed analysis of calculated band structures, densities of states (total and projected ones) and bond critical points shows that despite the differences of crystal structure both these compounds reveal important similarities and suggests that one can expect that they should exhibit very similar properties and behavior during e.g. thermal decomposition process (which is in agreement with experiments).

2010-09-01

251

FP-LAPW study of anhydrous cadmium and silver oxalates: electronic structure and electron density topology  

Science.gov (United States)

Results of theoretical studies of electronic structure (full potential linearized augmented plane Wave method within DFT formalism as implemented in Wien2k package), electron density topology and bonding (Bader’s quantum theory of atoms in molecules topological analysis of total electron density obtained from FP-LAPW calculations) in anhydrous cadmium and silver oxalates are presented. Detailed analysis of calculated band structures, densities of states (total and projected ones) and bond critical points shows that despite the differences of crystal structure both these compounds reveal important similarities and suggests that one can expect that they should exhibit very similar properties and behavior during e.g. thermal decomposition process (which is in agreement with experiments).

Kole?y?ski, A.

2010-09-01

252

FP-LAPW study of anhydrous cadmium and silver oxalates: electronic structure and electron density topology  

Energy Technology Data Exchange (ETDEWEB)

Results of theoretical studies of electronic structure (full potential linearized augmented plane Wave method within DFT formalism as implemented in Wien2k package), electron density topology and bonding (Bader's quantum theory of atoms in molecules topological analysis of total electron density obtained from FP-LAPW calculations) in anhydrous cadmium and silver oxalates are presented. Detailed analysis of calculated band structures, densities of states (total and projected ones) and bond critical points shows that despite the differences of crystal structure both these compounds reveal important similarities and suggests that one can expect that they should exhibit very similar properties and behavior during e.g. thermal decomposition process (which is in agreement with experiments).

Kolezynski, A., E-mail: andrzej.kolezynski@agh.edu.p [AGH University of Science and Technology, Faculty of Materials Science and Ceramics, Al. Mickiewicza 30, 30-059 Krakow (Poland)

2010-09-01

253

The crystal and electronic band structure of the diamond-like semiconductor Ag{sub 2}ZnSiS{sub 4}  

Energy Technology Data Exchange (ETDEWEB)

Highlights: Black-Right-Pointing-Pointer The structure of Ag{sub 2}ZnSiS{sub 4} is solved and refined in the space group Pn using single crystal X-ray diffraction. Black-Right-Pointing-Pointer Electronic band structure calculations show that Ag{sub 2}ZnSiS{sub 4} is a direct band gap semiconductor with a calculated band gap of 1.88 eV. Black-Right-Pointing-Pointer The optical band gap of Ag{sub 2}ZnSiS{sub 4} was experimentally determined as 3.28 eV. - Abstract: Single crystals of the new diamond-like semiconductor Ag{sub 2}ZnSiS{sub 4} have been synthesized using high-temperature, solid state synthesis at 800 Degree-Sign C. The compound crystallizes in the monoclinic, noncentrosymmetric space group Pn with a = 6.4052(1) Angstrom-Sign , b = 6.5484(1) Angstrom-Sign , c = 7.9340(1) Angstrom-Sign , {beta} = 90.455(1) Degree-Sign and R1 (for all data) = 2.42%. The electronic band structure and density of states were calculated using density functional theory (DFT) and the full potential linearized augmented plane wave (LAPW) method within the Wien2k program suite. The calculated band structure suggests that Ag{sub 2}ZnSiS{sub 4} is a direct band gap semiconductor with a calculated band gap of 1.88 eV at the {Gamma}-point. The calculated density of states of Ag{sub 2}ZnSiS{sub 4} is compared with that of AgGaS{sub 2}. The band gap of Ag{sub 2}ZnSiS{sub 4} was also determined experimentally as 3.28 eV via optical diffuse reflectance spectroscopy.

Brunetta, Carl D.; Karuppannan, Balamurugan; Rosmus, Kimberly A. [Department of Chemistry and Biochemistry, Duquesne University, 600 Forbes Avenue, Pittsburgh, PA 15282 (United States); Aitken, Jennifer A., E-mail: aitkenj@duq.edu [Department of Chemistry and Biochemistry, Duquesne University, 600 Forbes Avenue, Pittsburgh, PA 15282 (United States)

2012-03-05

254

Structural properties and quasiparticle band structures of Cu-based quaternary semiconductors for photovoltaic applications  

Science.gov (United States)

Cu-based quaternary chalcogenide semiconductors (Cu2-II-IV-VI4) are a large group of materials that hold great promises for a variety of applications, especially as thin-film solar cell absorbers. However, despite intensive research activities, a systematic understanding of the evolution of the electronic and structural properties with chemical compositions of these materials is still lacking. In this paper, we present first-principles calculations of the structural and electronic properties of eight such semiconductors (Cu2-II-IV-VI4, with II = Zn and Cd; IV = Ge and Sn; VI = S and Se). The variation of the structural parameters with chemical compositions, investigated using the HSE06 hybrid functional, follows a few interesting trends. The quasiparticle bandgap, calculated using the state-of-the-art GW approximation, also varies systematically with chemical compositions. Effects of cation disordering on the band gaps are also investigated. This systematic understanding of the structural parameters and quasiparticle band gaps would be useful for future structural characterization and material design.

Zhang, Yubo; Sun, Xiudong; Zhang, Peihong; Yuan, Xun; Huang, Fuqiang; Zhang, Wenqing

2012-03-01

255

GW band structure of InAs and GaAs in the wurtzite phase  

CERN Multimedia

We report the first quasiparticle calculations of a newly observed polymorph of InAs and GaAs, i.e., the wurtzite phase. The calculations are performed in the GW approximation using plane waves and pseudopotentials. For comparison we also report the study of the zinc-blende phase within the same approximations. In the InAs compound the In 4d electrons play a very important role: whether they are frozen in the core or not, leads either to a correct or a wrong band ordering (negative gap) within the Local Density Appproximation (LDA). We have calculated the GW band structure in both cases. In the first approach, we have estimated the correction to the pd repulsion calculated within the LDA and included this effect in the calculation of the GW corrections to the LDA spectrum. In the second case, we circumvent the negative gap problem by first using the screened exchange approximation and then calculating the GW corrections starting from the so obtained eigenvalues and eigenfunctions. This more fundamentally corr...

Zanolli, Z; Furthmueller, J; Von Barth, U; Bechstedt, F

2006-01-01

256

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

International Nuclear Information System (INIS)

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

1361-01-00

257

Tight-binding modelling of the electronic band structure of layered superconducting perovskites  

International Nuclear Information System (INIS)

[en] A detailed tight-binding analysis of the electron band structure of the CuO2 plane of layered cuprates is performed within a ?-band Hamiltonian including four orbitals - Cu 3dx2-y2 and Cu 4s, O 2px and O 2py . Both the experimental and theoretical indications in favour of a Fermi level located in a Cu or O band, respectively, are considered. For these two alternatives, analytical expressions are obtained for the linear combination of atomic orbitals (LCAO) electron wave functions suitable for the treatment of electron superexchange. Simple formulae for the Fermi surface and electron dispersions are derived by applying the Loewdin downfolding procedure to set up the effective copper and oxygen Hamiltonians. They are used to fit the experimental angle-resolved ultraviolet photoelectron spectroscopy (ARUPS) Fermi surface of Pb0.42 Bi1.73 Sr1.94 Ca1.3 Cu1.92 O8+x and both the ARPES and local density approximation (LDA) Fermi surface of Nd2-xCexCuo4-?. The value of presenting the hopping amplitudes as surface integrals of ab initio atomic wave functions is demonstrated as well. The same approach is applied to the RuO2 plane of the ruthenate Sr2 RuO4 . The LCAO Hamiltonians including the three in-plane ?-orbitals Ru 4dxy, Oa 2py , Ob 2px and the four transverse ?-orbitals Ru 4dzx, Ru 4dyz, Oa 2pz , Ob 2pz are considered separately. It is shown that the equation for the constant-energy curves and the Fermi contours has the same canonical form as the one for the layered cuprates. (author)

2000-01-17

258

Exciton spectra and energy band structure of CuGaSe{sub 2} single crystals  

Energy Technology Data Exchange (ETDEWEB)

Photoreflectivity, wavelength modulation spectroscopy and photoluminescence measurements of CuGaSe{sub 2} are used to determine the exciton and band parameters as well as the energy band structure of CuGaSe{sub 2} at photon energies higher than the fundamental band gap. The spectral dependences of the real {epsilon}{sub 1} and imaginary {epsilon}{sub 2} components of the complex dielectric function {epsilon}(E) = {epsilon}{sub 1} (E) + i{epsilon}{sub 2}(E) are calculated using the Kramers-Kronig relations. As a result, the energy band structure of CuGaSe{sub 2} at photon energies higher than the fundamental band gap is derived from the analysis of the structures observed both in the {epsilon} ({omega}) and in the wavelength modulated reflectivity spectra.

Levchenko, S; Tezlevan, V E; Arushanov, E [Institute of Applied Physics, Academy of Sciences of Moldova, Chisinau, MD 2028 (Moldova, Republic of); Syrbu, N N [Laboratory of Optoelectronics, Technical University of Moldova, 168, Bul. Stefan cel Mare, Chisinau, MD-2012 (Moldova, Republic of); Merino, J M; Leon, M [Universidad Autonoma de Madrid, Departamento Fisica Aplicada, C-XII, 28049 Madrid (Spain)], E-mail: maximo.leon@uam.es

2008-03-07

259

Spontaneous emission from radiative chiral nematic liquid crystals at the photonic band-gap edge: an investigation into the role of the density of photon states near resonance.  

UK PubMed Central (United Kingdom)

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.

Mavrogordatos TK; Morris SM; Wood SM; Coles HJ; Wilkinson TD

2013-06-01

260

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.

Mihai Rotaru; Jan Sykulski

2010-01-01

 
 
 
 
261

Band structure in {sup 83}Rb from lifetime measurements  

Energy Technology Data Exchange (ETDEWEB)

Excited states of {sup 83}Rb, populated in the {sup 76}Ge({sup 11}B,-bar 4n{gamma}) reaction at a beam energy of 50 MeV, have been studied. The unfavoured signature partner ({alpha}=-1/2) of the {pi}g{sub 9/2} yrast band is proposed up to an excitation energy of 6669.4 keV and spin (31/2{sup +}). Lifetimes have been estimated for three states belonging to the favoured {alpha}=+1/2 band. The B(E2) values deduced from these lifetimes indicate a moderate quadrupole deformation of {beta}{sub 2}=0.20. Theoretical calculations within the framework of the particle-rotor-model suggest that low energy states before the onset of the {nu}g{sub 9/2} alignment at a rotational frequency of {approx}0.5 MeV are prolate while those above this frequency have an oblate shape. The excited {delta}I=1 band has been extended up to 5422.7 keV and spin 25/2{sup -}. The B(M1) rates derived from the measured lifetimes decrease with spin. The results are in general agreement with an earlier TAC calculation, suggesting the interpretation of these states as arising from magnetic rotation.

Ganguly, S. [Saha Institute of Nuclear Physics, Kolkata 700064 (India); Banerjee, P. [Saha Institute of Nuclear Physics, Kolkata 700064 (India)]. E-mail: polash.banerjee@saha.ac.in; Ray, I. [Saha Institute of Nuclear Physics, Kolkata 700064 (India); Kshetri, R. [Saha Institute of Nuclear Physics, Kolkata 700064 (India); Bhattacharya, S. [Saha Institute of Nuclear Physics, Kolkata 700064 (India); Saha-Sarkar, M. [Saha Institute of Nuclear Physics, Kolkata 700064 (India); Goswami, A. [Saha Institute of Nuclear Physics, Kolkata 700064 (India); Muralithar, S. [Nuclear Science Centre, Post Box 10502, New Delhi 110067 (India); Singh, R.P. [Nuclear Science Centre, Post Box 10502, New Delhi 110067 (India); Kumar, R. [Nuclear Science Centre, Post Box 10502, New Delhi 110067 (India); Bhowmik, R.K. [Nuclear Science Centre, Post Box 10502, New Delhi 110067 (India)

2006-03-20

262

Band structure in odd-odd {sup 86}Nb  

Energy Technology Data Exchange (ETDEWEB)

Odd-odd {sup 86}Nb has been investigated to explore the interaction between single-particle and collective degrees of freedom. High-spin states were populated using the {sup 58}Ni({sup 32}S,3pn){sup 86}Nb reaction at 135 MeV. Cascades of 3 or more {gamma} rays were detected with the early implementation of GAMMA-SPHERE while the evaporated charged particles were observed in the 96-element MICROBALL for channel selection. States have been observed with spins up to 3l{Dirac_h} and rotational frequencies over 1.2 MeV/{Dirac_h}. New bands appear at about 2.5 MeV and eventually become yrast. The level spacings in the yrast positive parity band show a large signature splitting whose phase reverses at the 10+ state, probably due to competition between quasiparticle alignment and rotation. The B(M1) values in this band also exhibit a large alteration, with strengths varying by an order of magnitude depending on the signatures of the states.

Tabor, S.L.; Doering, J.; Johns, G.D.

1995-04-01

263

Band structure in odd-odd 86Nb  

International Nuclear Information System (INIS)

Odd-odd 86Nb has been investigated to explore the interaction between single-particle and collective degrees of freedom. High-spin states were populated using the 58Ni(32S,3pn)86Nb reaction at 135 MeV. Cascades of 3 or more ? rays were detected with the early implementation of GAMMA-SPHERE while the evaporated charged particles were observed in the 96-element MICROBALL for channel selection. States have been observed with spins up to 3l? and rotational frequencies over 1.2 MeV/?. New bands appear at about 2.5 MeV and eventually become yrast. The level spacings in the yrast positive parity band show a large signature splitting whose phase reverses at the 10+ state, probably due to competition between quasiparticle alignment and rotation. The B(M1) values in this band also exhibit a large alteration, with strengths varying by an order of magnitude depending on the signatures of the states.

1995-01-01

264

Band structure of Au monoatomic chains on Si(335) and Si(557) surfaces  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The electronic band structure of the Si(557) and Si(335) surfaces covered with monoatomic Au chains produced in UHV conditions, is investigated in detail by angle-resolved photoelectron spectroscopy (ARPES), especially for the surface state bands near the Fermi energy. The ARPES spectra in the plane...

Marcin KISIEL; Kazimierz SKROBAS; Ryszard ZDYB; Mieczyslaw JALOCHOWSKI

265

Band structure of Au monoatomic chains on Si(335) and Si(557) surfaces  

Directory of Open Access Journals (Sweden)

Full Text Available The electronic band structure of the Si(557) and Si(335) surfaces covered with monoatomic Au chains produced in UHV conditions, is investigated in detail by angle-resolved photoelectron spectroscopy (ARPES), especially for the surface state bands near the Fermi energy. The ARPES spectra in the plane parallel to step edges for Si(557)-Au vicinal surface show strongly dispersive electron energy bands, characteristic of one-dimensional structure. The band dispersion is also calculated within tight-binding model, with two adjustable coupling parameters t1 and t2, for the first and second neighbors along the chains, respectively, and compared with that determined from the photoemission experiment. The scanning tunneling microscopy (STM) imaging and reflection high energy electron diffraction (RHEED) studies enabled us to determine atomic chain separation and its internal structure. The study shows that the structural anisotropy of these surfaces induces highly anisotropic electronic structure.

Marcin KISIEL; Kazimierz SKROBAS; Ryszard ZDYB; Mieczyslaw JALOCHOWSKI

2005-01-01

266

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

Science.gov (United States)

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

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

2013-06-01

267

Spontaneous emission in coupled microcavity-waveguide structures at the band edge.  

Science.gov (United States)

We examine spontaneous emission and photon dynamics in a microcavity coupled to a coupled-resonator optical waveguide (CROW) in a photonic crystal. We present an efficient tight-binding approach to obtain the Green tensor in large, arbitrary systems of coupled microcavities. We use this approach to examine spontaneous emission when the microcavity is strongly coupled to the CROW at the band center and band edge. We confirm the validity of weak-coupling theories for microcavities resonant at band center and obtain strong peak splitting in the previously inaccessible case of band-edge coupled structures. PMID:17546177

Fussell, David P; Dignam, Marc M

2007-06-01

268

Spontaneous emission in coupled microcavity-waveguide structures at the band edge.  

UK PubMed Central (United Kingdom)

We examine spontaneous emission and photon dynamics in a microcavity coupled to a coupled-resonator optical waveguide (CROW) in a photonic crystal. We present an efficient tight-binding approach to obtain the Green tensor in large, arbitrary systems of coupled microcavities. We use this approach to examine spontaneous emission when the microcavity is strongly coupled to the CROW at the band center and band edge. We confirm the validity of weak-coupling theories for microcavities resonant at band center and obtain strong peak splitting in the previously inaccessible case of band-edge coupled structures.

Fussell DP; Dignam MM

2007-06-01

269

Spontaneous emission in coupled microcavity-waveguide structures at the band edge  

Science.gov (United States)

We examine spontaneous emission and photon dynamics in a microcavity coupled to a coupled-resonator optical waveguide (CROW) in a photonic crystal. We present an efficient tight-binding approach to obtain the Green tensor in large, arbitrary systems of coupled microcavities. We use this approach to examine spontaneous emission when the microcavity is strongly coupled to the CROW at the band center and band edge. We confirm the validity of weak-coupling theories for microcavities resonant at band center and obtain strong peak splitting in the previously inaccessible case of band-edge coupled structures.

Fussell, David P.; Dignam, Marc M.

2007-06-01

270

Density functional calculation of electronic surface structure and Fe adsorption on ZnO (0001) and (000 anti 1)  

Energy Technology Data Exchange (ETDEWEB)

The structure and electronic properties of the ZnO(0001) and ZnO(000 anti 1) surfaces as studied by density functional calculations are presented. The stability of the surface has already been investigated by various groups. The electronic surface band structure, however, in particular the existence of surface states and the differences between experimental band dispersion for both terminations, still appears to pose open problems. To address these issues, we compare Kohn Sham band structures and electrostatic potentials close to the surface for the relaxed (1 x 1)-surface, (2 x 2) vacancy reconstructions, and surfaces with pits. In particular the effect of the bending of the electrostatic potential at the surface on the eigenstates is quantified. Comparing the adsorption energies of Fe atoms for various adsorption sites on ZnO(000 anti 1), the fcc hollow position turned out to be energetically favorable. The oxidation state of the Fe atom is derived from the projected density of states.

Pal, Sougata; Jasper-Toennies, Torben; Hack, Michael; Pehlke, Eckhard [Institut fuer Theoretische Physik und Astrophysik, Universitaet Kiel (Germany)

2011-07-01

271

Population and employment densities: structure and change.  

UK PubMed Central (United Kingdom)

"We examine spatial patterns and their changes during the 1970s for the Los Angeles region, by estimating monocentric and polycentric density functions for employment and population. Downtown Los Angeles is clearly identified as the statistical monocentric center of the region, and it is the most consistently strong center in the polycentric patterns. Polycentric models fit statistically better than monocentric models, and there was some shift in employment distribution toward a more polycentric pattern. These findings verify the existence of polycentricity in Los Angeles and demonstrate for the first time that employment and especially population follow a polycentric pattern based on exogenously defined employment centers. The results confirm that both employment and population became more dispersed during the 1970s."

Small KA; Song S

1994-11-01

272

Population and employment densities: structure and change.  

Science.gov (United States)

"We examine spatial patterns and their changes during the 1970s for the Los Angeles region, by estimating monocentric and polycentric density functions for employment and population. Downtown Los Angeles is clearly identified as the statistical monocentric center of the region, and it is the most consistently strong center in the polycentric patterns. Polycentric models fit statistically better than monocentric models, and there was some shift in employment distribution toward a more polycentric pattern. These findings verify the existence of polycentricity in Los Angeles and demonstrate for the first time that employment and especially population follow a polycentric pattern based on exogenously defined employment centers. The results confirm that both employment and population became more dispersed during the 1970s." PMID:12290251

Small, K A; Song, S

1994-11-01

273

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)

2000-01-01

274

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

International Nuclear Information System (INIS)

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

2012-01-01

275

Energy Band Analysis of MQW Structure Based on Kronig-Penny Model  

Directory of Open Access Journals (Sweden)

Full Text Available The effects of different potential well depths, well widths and barrier widths on energy band of multiple quantum well (MQW) structures are discussed in detail based on Kronig-Penny model. The results show that if the well and barrier width stay unchanged, the first and second band gaps increase linearly with the well depth. When the well depth is constant, the first and second band gaps increase exponentially with the barrier width in a wide well. However, in narrow well one, the second band gap saturates when the barrier width is wide enough. On condition that the well and barrier have equal width, the first band gap decreases exponentially with well-barrier width while the second gap still shows an exponential increase with the width. These results are insightful for the design of MQW structure optoelectronic devices.

Yu Zhang; Yi Wang

2013-01-01

276

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

277

Structured surfaces of wide band gap insulators as templates for overgrowth of adsorbates  

International Nuclear Information System (INIS)

Surface structures on wide band gap insulators and their use as templates for the growth of adsorbates are reviewed. Surface structures include evaporation structures, vicinal surfaces, facetted surfaces, epitaxial structures, or structures transferred to or induced by the growth of thin films. Most structures have been realized so far on Al2O3 and on alkali halide crystals. The guided growth of adsorbates is discussed, considering the examples of metallic clusters or wires and ordered films of organic molecules. (topical review)

2006-07-05

278

Complete flexural vibration band gaps in membrane-like lattice structures  

Energy Technology Data Exchange (ETDEWEB)

The propagation of flexural vibration in the periodical membrane-like lattice structure is studied. The band structure calculated with the plane wave expansion method indicates the existence of complete gaps. The frequency response function of a finite periodic structure is simulated with finite element method. Frequency ranges with vibration attenuation are in good agreement with the gaps found in the band structure. Much larger attenuations are found in the complete gaps comparing to those directional ones. The existence of complete flexural vibration gaps in such a lattice structure provides a new idea for vibration control of thin plates.

Yu Dianlong [Institute of Mechatronical Engineering, National University of Defense Technology, Changsha 410073 (China); PBG Research Center, National University of Defense Technology, Changsha 410073 (China); Liu Yaozong [Institute of Mechatronical Engineering, National University of Defense Technology, Changsha 410073 (China) and PBG Research Center, National University of Defense Technology, Changsha 410073 (China)]. E-mail: yzliu@nudt.edu.cn; Qiu Jing [Institute of Mechatronical Engineering, National University of Defense Technology, Changsha 410073 (China); PBG Research Center, National University of Defense Technology, Changsha 410073 (China); Wang Gang [Institute of Mechatronical Engineering, National University of Defense Technology, Changsha 410073 (China); PBG Research Center, National University of Defense Technology, Changsha 410073 (China); Zhao Honggang [Institute of Mechatronical Engineering, National University of Defense Technology, Changsha 410073 (China); PBG Research Center, National University of Defense Technology, Changsha 410073 (China)

2006-09-04

279

Complete flexural vibration band gaps in membrane-like lattice structures  

International Nuclear Information System (INIS)

[en] The propagation of flexural vibration in the periodical membrane-like lattice structure is studied. The band structure calculated with the plane wave expansion method indicates the existence of complete gaps. The frequency response function of a finite periodic structure is simulated with finite element method. Frequency ranges with vibration attenuation are in good agreement with the gaps found in the band structure. Much larger attenuations are found in the complete gaps comparing to those directional ones. The existence of complete flexural vibration gaps in such a lattice structure provides a new idea for vibration control of thin plates

2006-09-04

280

Band-Structure Based model for photoelectron emission from metal surfaces  

Science.gov (United States)

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

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

2012-11-01

 
 
 
 
281

Band structure and occupation for electrons at axial channeling in monocrystals  

Energy Technology Data Exchange (ETDEWEB)

The method of calculating the energy band structure and wave functions for electrons (positrons) in the case of axial channeling in monocrystals is suggested. Different realistic approximations for the chain potential are considered. The band structure for < 111 > channel of silicon and diamond is considered. The population of zones for different electron energies is investigated. The possibility of achieving the inverse zone population is shown.

Ivanov, V.V.; Tulupov, A.V.

1983-05-01

282

Electronic band structure and chemical bonding in the novel antiperovskite ZnCNi3 as compared with 8-K superconductor MgCNi3  

CERN Document Server

Energy band structure of the discovered ternary perovskite-like compound ZnCNi3 reported by Park et al (2004) as a non-superconducting paramagnetic metal was investigated using the FLMTO-GGA method. The electronic bands, density of states, Fermi surface, charge density and electron localization function distributions for ZnCNi3 are obtained and analyzed in comparison with the isoelectronic and isostructural 8K superconductor MgCNi3. The effect of external pressure on the electronic states of ZnCNi3 and MgCNi3 is studied.

Shein, I R; Medvedeva, N I; Ivanovskii, A L

2004-01-01

283

Collective band structures and identification of one-photon and two-phonon ?-vibrational bands in 109Tc  

International Nuclear Information System (INIS)

The high spin states of the neutron-rich 109Tc nucleus are reinvestigated by observing prompt ?-rays from the spontaneous fission of 252Cf. The previously known yrast band based on the 7/2+ state is updated. A side band built on the 11/2+ state is expanded and a new band based on the 15/2+ state is identified. Band crossing in the yrast band occurs around ???0.36 MeV. This band crossing is associated with the alignment of two h11/2 neutrons according to the cranked shell model calculations. The band based on the 11/2+ state is proposed as a candidate for the one-phonon ?-vibrational band, and the band built on the 15/2+ state is proposed as a candidate for the two-phonon ?-vibrational band. Other characteristics for the observed bands are discussed. (authors)

2010-01-01

284

Algorithm for extraction of quantum oscillation orbits from band structure data  

Science.gov (United States)

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

Rourke, Patrick; Julian, Stephen

2008-03-01

285

Negative parity bands of 115Pd and band structures in 113,115,117Pd  

International Nuclear Information System (INIS)

Level structures of 113,115,117Pd have been studied using the Gammasphere and a spontaneous fission source of 252Cf. A new 85.1-keV transition was identified in 113Pd. This indicates that the spin and parity of the isomeric state is 9/2- rather than the previously assigned 11/2-. New low-energy transitions are confirmed in 115,117Pd. In 115Pd, the 39.0.- and 49.0-keV transitions are shown to be in prompt coincidence. This coincidence relationship indicates a spin and parity assignment of 1/2+ for the ground state rather than the previously assigned 3/2+.

2005-01-01

286

Band structure in neutron-deficient 103Cd  

International Nuclear Information System (INIS)

[en] A considerable amount of experimental works has been recently done on the light Cadmium isotopes. The main purpose of these studies was to search for Coriolis decoupling mechanism in a transitional region. Negative and positive parity bands occuring in 105Cd, 107Cd, 109Cd, 111Cd have been correctly reproduced within the rotor-plus-particle model using self-consistent prolate core single-particle states. The aim of the present work is using HI reactions, to search for the high spin states in 103Cd where only two low-lying levels are known so far, from on-line radioactivity studies, and to check whether this theoretical description remains still satisfactory

1979-03-17

287

Band structures in sup(118,120)Te  

International Nuclear Information System (INIS)

The level schemes of sup(118-120)Te were investigated using Sn(?, 2n?)Te reactions and employing standard ?-ray spectroscopic techniques. Definite spin and parity assignments could be made for many newly found levels. The excited states can be classified into two categories. Collective quadrupole excitations on the ground states are compared with results of calculations which are performed with the IBA-2 model. High spin proton and neutron quasi particle excitations are interpreted within the framework of the one-broken-pair model. Although it is apparent that configuration mixing is non-negligible at spins Jsup(?) >= 68, excitation energies of many levels are well accounted for either by the IBA-2 calculations or by the quasiparticle calculation. Several states have been excited belonging to bands based upon the quasiparticle states. Branching and mixing ratios of the depopulating ?-rays agree with this interpretation. (orig.)

1982-05-17

288

Mercury bismuth chalcohalides, Hg3Q2Bi2Cl8 (Q = S, Se, Te): syntheses, crystal structures, band structures, and optical properties.  

Science.gov (United States)

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

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

2013-02-28

289

Mercury bismuth chalcohalides, Hg3Q2Bi2Cl8 (Q = S, Se, Te): syntheses, crystal structures, band structures, and optical properties.  

UK PubMed Central (United Kingdom)

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

Wibowo AC; Malliakas CD; Chung DY; Im J; Freeman AJ; Kanatzidis MG

2013-03-01

290

Relationship between molecular cloud structure and density PDFs  

CERN Document Server

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

291

Electronic structure of Pt based topological Heusler compounds with C1b structure and 'zero band gap'  

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.

2011-05-23

292

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

Energy Technology Data Exchange (ETDEWEB)

The paper presents cloud structure models for Jupiter's Great Red Spot, Equatorial and North Tropical Zones, North and South Temperate Zones, and North and South Polar Regions. The models are based on images of Jupiter in three methane bands and nearby continuum radiative transfer calculations include multiple scattering and absorption from three aerosol layers. The model results include the transition in the upper-cloud altitude to 3 km lower altitude from the tropical zones to temperate zones and polar regions, a N/S asymmetry in cloud thickness in the tropical and temperature zones, and the presence of aerosols up to about 0.3 bar in the Great Red Spot and Equatorial Zone. It is concluded that polarization data are sensitive to aerosols in and above the upper cloud layer but insensitive to deeper cloud structure.

West, R.A. (Colorado, University, Boulder, Colo.); Tomasko, M.G. (Arizona, University, Tucson, Ariz.)

1980-02-01

293

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

International Nuclear Information System (INIS)

[en] 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

1980-01-01

294

CdXO3 (X = C, Si, Ge, Sn, Pb) electronic band structures  

Science.gov (United States)

Electronic properties for a set of CdXO (X = C, Si, Ge, Sn, Pb) crystals were investigated using the density functional theory (DFT) formalism considering both the local density and generalized gradient approximations, LDA and GGA, respectively. Hexagonal CdCO and triclinic CdSiO have indirect main energy band gaps while orthorhombic CdGeO and CdSnO exhibit direct interband transitions. Orthorhombic CdPbO has a very small indirect band gap. The Kohn-Sham minimum electronic band gap oscillates as a function of the X ns level, changing from 2.94 eV (hexagonal CdCO,LDA) to 0.012 eV (orthorhombic CdPbO,LDA).

Barboza, C. A.; Henriques, J. M.; Albuquerque, E. L.; Caetano, E. W. S.; Freire, V. N.; da Costa, J. A. P.

2009-10-01

295

Electronic Band Structure and Magnetic Properties of YCo5  

Science.gov (United States)

We present a first-principles study on the magnetic properties and electronic structure of YCo5 using the two well-known electronic structure packages FPLO and WIEN2k. Our results have been compared with the results of experiments and other ab initio calculations. The comparison shows a fair agreement between the present work and other published investigations.

Aly, Samy H.; Alzahraa Hassan, Fatema; Yehia, Sherif

2011-06-01

296

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

1976-08-15

297

Valence band structure of the Si(331)-(12 x 1) surface reconstruction  

Energy Technology Data Exchange (ETDEWEB)

Using angle-resolved photoelectron spectroscopy we investigate the electronic valence band structure of the Si(331)-(12 x 1) surface reconstruction for which we recently proposed a structural model containing silicon pentamers as elementary structural building blocks. We find that this surface, reported to be metallic in a previous study, shows a clear band gap at the Fermi energy, indicating semiconducting behavior. An occupied surface state, presumably containing several spectral components, is found centered at - 0.6 eV exhibiting a flat energy dispersion. These results are confirmed by scanning tunneling spectroscopy and are consistent with recent first-principles calculations for our structural model.

Battaglia, Corsin [Ecole Polytechnique Federale de Lausanne (EPFL), Institute of Microengineering (IMT), Photovoltaics and Thin Film Electronics Laboratory, Rue A-L Breguet 2, 2000 Neuchatel (Switzerland); Fabian Schwier, Eike; Monney, Claude; Didiot, Clement; Mariotti, Nicolas; Gunnar Garnier, Michael; Aebi, Philipp [Department of Physics and Fribourg Center for Nanomaterials, Universite de Fribourg, Chemin du Musee 3, 1700 Fribourg (Switzerland); Gaal-Nagy, Katalin; Onida, Giovanni, E-mail: corsin.battaglia@epfl.ch [Dipartimento di Fisica and European Theoretical Spectroscopy Facility (ETSF), Universita degli Studi di Milano, Via Celoria 16, 20133 Milano (Italy)

2011-04-06

298

Valence band structure of the Si(331)-(12 x 1) surface reconstruction  

International Nuclear Information System (INIS)

[en] Using angle-resolved photoelectron spectroscopy we investigate the electronic valence band structure of the Si(331)-(12 x 1) surface reconstruction for which we recently proposed a structural model containing silicon pentamers as elementary structural building blocks. We find that this surface, reported to be metallic in a previous study, shows a clear band gap at the Fermi energy, indicating semiconducting behavior. An occupied surface state, presumably containing several spectral components, is found centered at - 0.6 eV exhibiting a flat energy dispersion. These results are confirmed by scanning tunneling spectroscopy and are consistent with recent first-principles calculations for our structural model.

2011-04-06

299

The C-Band accelerating structures for SPARC photoinjector energy upgrade  

Science.gov (United States)

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

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

2013-05-01

300

Stress fields and geometrically necessary dislocation density distributions near the head of a blocked slip band  

International Nuclear Information System (INIS)

[en] 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.

2012-01-01

 
 
 
 
301

Electronic band-structure and X-ray photoemission spectra of ternaries APtGe (A = Th, U)  

International Nuclear Information System (INIS)

UPtGe as a representative of uranium transition metal germanides, UTGe, reveals a unique character of crystal, electronic and magnetic properties. We attempt to elucidate them starting from band-structure calculations of this compound and its non-5f-electron counterpart ThPtGe in the paramagnetic state. The obtained theoretical electron densities of states (DOS) are compared with measured X-ray photoemission spectra (XPS). For both compounds, we achieve good agreement between the theoretical and experimental XPS, particularly concerning positions of peaks in the range of valence band spectra. Thus, in the case of UPtGe some important delocalisation of 5f electrons is well predicted by the LDA theory.

2008-02-28

302

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.

2011-09-21

303

Structure of the doublet bands in doubly odd nuclei: The case of 128Cs  

International Nuclear Information System (INIS)

The structure of the ?J=1 doublet bands in 128Cs is investigated within the framework of the interacting vector boson-fermion model. A new, purely collective interpretation of these bands is given on the basis of the used boson-fermion dynamical symmetry of the model. The energy levels of the doublet bands as well as the absolute B(E2) and B(M1) transition probabilities between the states of both yrast and yrare bands are described quite well. The observed odd-even staggering of both B(M1) and B(E2) values is reproduced by the introduction of an appropriate interaction term of quadrupole type, which produces such a staggering effect in the transition strengths. The calculations show that the appearance of doublet bands in certain odd-odd nuclei could be a consequence of the realization of a larger dynamical symmetry based on the noncompact supersymmetry group OSp(2?/12,R).

2010-01-01

304

Retrieval of stratospheric aerosol density profiles from SCIAMACHY limb radiance measurements in the O2 A-band  

Directory of Open Access Journals (Sweden)

Full Text Available In this paper we present an approach to retrieve stratospheric aerosol number densities in the altitude range 10–40 km from SCIAMACHY limb radiance measurements in the spectral range of the O2 A absorption band, near 760 nm. Here, the characteristic light paths differ for the measured light in the O2 A-band and in the spectral continuum next to the absorption band. This difference is used to distinguish the effect of stratospheric aerosol scattering and ground reflection on the limb measurement. The capability to disentangle both effects is illustrated for SCIAMACHY limb observations over the Libyan desert, where the measurements are not affected by tropospheric clouds. Comparison of the SCIAMACHY retrieval and the SAGE II aerosol extinction product between 75° southern and northern latitude shows the clear need for prior knowledge of the mean size of the stratospheric aerosol for the SCIAMACHY retrieval. We found best agreement between SCIAMACHY and SAGE II aerosol extinction for the period 2003–2005 for a prior choice of the mean aerosol size radius of 0.2 ?m. The overall agreement between both data sets is in the range <50% root mean square difference at 14–30 km with a minimum of 30% at 22 km.

B. Ovigneur; J. Landgraf; R. Snel; I. Aben

2011-01-01

305

Retrieval of stratospheric aerosol density profiles from SCIAMACHY limb radiance measurements in the O2 A-band  

Directory of Open Access Journals (Sweden)

Full Text Available In this paper we present an approach to retrieve stratospheric aerosol number densities in the altitude range 10–40 km from SCIAMACHY limb radiance measurements in the spectral range of the O2 A absorption band, near 760 nm. Here, the characteristic light paths differ for the measured light in the O2 A band and in the spectral continuum next to the absorption band. This difference is used to distinguish the effect of stratospheric aerosol scattering and ground reflection on the limb measurement. The capability to disentangle both effects is illustrated for SCIAMACHY limb observations over the Libyan desert, where the measurements are not affected by tropospheric clouds. Comparison of the SCIAMACHY retrieval and the SAGE II aerosol extinction product between 75 degrees Southern and Northern latitude shows the clear need for prior knowledge of the mean size of the stratospheric aerosol for the SCIAMACHY retrieval. We found best agreement between SCIAMACHY and SAGE II aerosol extinction for the period 2003–2005 for a prior choice of the mean aerosol size radius of 0.2 ?m. The overall agreement between both data sets is in the range <50% root mean square difference at 14–30 km with a minimum of 30% at 22 km.

B. Ovigneur; J. Landgraf; I. Aben

2011-01-01

306

Linear bands, zero-momentum Weyl semimetal, and topological transition in skutterudite-structure pnictides  

Science.gov (United States)

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

307

Influence of strain on band structure of semiconductor nanostructures  

Directory of Open Access Journals (Sweden)

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

Rai?evi? Nevena; Tadi? Milan

2009-01-01

308

Electronic structures of wide band-gap (AlN){sub m}(GaN){sub n} [001] superlattices  

Energy Technology Data Exchange (ETDEWEB)

Wide bandgap III-V nitrides, such as GaN and AlN, have become topical in the near-term technology of blue lasers. The authors report detailed electronic band-structure calculations for (AlN){sub m}(GaN){sub n} [001] zinc-blende superlattices (SL), with m + n {le} 12, using the all-electron full-potential linear-muffin-tin-orbital method. For n {ge} 3, the SL are found to have a direct band gap. For n {le} 2 and m {ge} 3, all the band gaps are indirect. In ultrathin SL, m {le} 3 and n {le} 2, only (m,n) = (3,1) is found to have an indirect gap. The band offsets are estimated by calculating the core-level shifts of nitrogen atoms in the central planes of the GaN and AlN layers. The calculated densities of states, electron- and hole-effective masses (m*), etc., as a function of m and n, are reported; a remarkable dependence of m* on the number of layers is revealed.

Tian, Z.J. [National Research Council, Ottawa, Ontario (Canada). Inst. for Microstructural Sciences]|[Univ. de Montreal, Quebec (Canada); Dharma-Wardana, M.W.C. [National Research Council, Ottawa, Ontario (Canada). Inst. for Microstructural Sciences; Lewis, L.J. [Univ. de Montreal, Quebec (Canada)

1996-11-01

309

High-spin structure of normal-deformed bands in 84Zr  

International Nuclear Information System (INIS)

The reaction 58Ni(32S,?2p) at Elab=135 MeV was used to populate high-spin states in 84Zr. The complete GAMMASPHERE and MICROBALL arrays were used to obtain clean ?-?-? line shapes to be analyzed by the Doppler shift attenuation method and to determine 27 lifetimes in the ground-state band and in two excited bands. Side-feeding times were also measured by comparing the line shapes gated with transitions above and below the state under study. The deduced electric quadrupole moments for the ground-state band are consistent with a very slow reduction with frequency with values ranging between 2.4(3) and 2.0(1)e b. The negative-parity bands feature also an approximate constancy of quadrupole moment with values similar to those in the ground-state band. Cranking calculations agree with this behavior in both parity bands and suggest an interpretation of the upper states in the ground-state band as part of a very slowly terminating band. Shell-dependent cranked Nilsson calculations explain a fourth ? cascade as pertaining to a noncollective structure terminating at I=20+.

2003-01-01

310

High-spin structure of normal-deformed bands in 84Zr  

Science.gov (United States)

The reaction 58Ni(32S,?2p) at Elab=135 MeV was used to populate high-spin states in 84Zr. The complete GAMMASPHERE and MICROBALL arrays were used to obtain clean ?-?-? line shapes to be analyzed by the Doppler shift attenuation method and to determine 27 lifetimes in the ground-state band and in two excited bands. Side-feeding times were also measured by comparing the line shapes gated with transitions above and below the state under study. The deduced electric quadrupole moments for the ground-state band are consistent with a very slow reduction with frequency with values ranging between 2.4(3) and 2.0(1)e b. The negative-parity bands feature also an approximate constancy of quadrupole moment with values similar to those in the ground-state band. Cranking calculations agree with this behavior in both parity bands and suggest an interpretation of the upper states in the ground-state band as part of a very slowly terminating band. Shell-dependent cranked Nilsson calculations explain a fourth ? cascade as pertaining to a noncollective structure terminating at I=20+.

Cardona, R.; Cristancho, F.; Tabor, S. L.; Kaye, R. A.; Solomon, G. Z.; Döring, J.; Johns, G. D.; Devlin, M.; Lerma, F.; Sarantites, D. G.; Lee, I.-Y.; Macchiavelli, A. O.; Ragnarsson, I.

2003-08-01

311

Electronic band structure and specific features of Sm2NiMnO6 compound: DFT calculation  

Science.gov (United States)

The band structure, density of states, electronic charge density, Fermi surface and optical properties of Sm2NiMnO6 compound have been investigated with the support of density functional theory (DFT). The atomic positions of Sm2NiMnO6 compound were optimized by minimizing the forces acting on the atoms, using the full potential linear augmented plane wave method. We employed the local density approximation (LDA), generalized gradient approximation (GGA) and Engel-Vosko GGA (EVGGA) to treat the exchange correlation potential by solving Kohn-Sham equations. The calculation shows that the compound is metallic with strong hybridization near the Fermi energy level (EF). The calculated density of states at the EF is about 21.60, 24.52 and 26.21 states/eV, and the bare linear low-temperature electronic specific heat coefficient (?) is found to be 3.74, 4.25 and 4.54 mJ/mol K2 for EVGGA, GGA and LDA, respectively. The Fermi surface is composed of two sheets. The bonding features of the compounds are analyzed using the electronic charge density in the (011) crystallographic plane. The dispersion of the optical constants was calculated and discussed.

Reshak, A. H.; Azam, Sikander

2013-09-01

312

Precise fabrication of X-band accelerating structure  

Energy Technology Data Exchange (ETDEWEB)

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

Higo, T.; Sakai, H.; Higashi, Y.; Koike, S.; Takatomi, T. [National Lab. for High Energy Physics, Tsukuba, Ibaraki (Japan)

1994-12-31

313

Precise fabrication of X-band accelerating structure  

International Nuclear Information System (INIS)

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

1994-01-01

314

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

International Nuclear Information System (INIS)

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

2000-08-15

315

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

CERN Document Server

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

316

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

Science.gov (United States)

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

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

2009-10-01

317

Local structure dependence of the charge transfer band in nanocrystalline Y2O3:Eu3+  

Science.gov (United States)

Eu doped nanocrystalline Y2O3 with different sizes were prepared by combustion synthesis. Dependences of particle size, crystal status and fluorescence characteristic on ratio of glycine/Y(NO3)3 and annealing temperature were studied. It was observed that the peaks of charge transfer (CT) band do not shift with different size in low-doped concentration. With the increasing of concentration and annealing temperature, the peaks of CT band blue shift distinctly. It can be concluded that the CT band in cubic nanocrystalline Y2O3:Eu3+ has no direct connection with size, but depends on local structure, especially crystal status.

Wang, Ji-Wei; Chang, Yu-Ming; Chang, Huan-Cheng; Lin, Sheng-Hsien; Huang, L.-C. Lora; Kong, Xiang-Lei; Kang, Ming-Wei

2005-04-01

318

Doubly enhanced spontaneous emission due to increased photon density of states at photonic band edge frequencies.  

Science.gov (United States)

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

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

2009-07-20

319

Doubly enhanced spontaneous emission due to increased photon density of states at photonic band edge frequencies.  

UK PubMed Central (United Kingdom)

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

Kuroda K; Sawada T; Kuroda T; Watanabe K; Sakoda K

2009-07-01

320

Self-interaction-free density-functional band theory for magnetic cuprates  

International Nuclear Information System (INIS)

We overview the capability of the pseudo-SIC -a self-interaction-free density-functional approach- to explore the electronic and magnetic properties of cuprates. We consider the relevant test cases of CuO, GeCuO3, and YBa2Cu3O6, and give evidence that this approach provides a description in qualitatively improved agreement with the experiments

2007-01-01

 
 
 
 
321

DAMPING OF ELECTRON DENSITY STRUCTURES AND IMPLICATIONS FOR INTERSTELLAR SCINTILLATION  

International Nuclear Information System (INIS)

The forms of electron density structures in kinetic Alfven wave (KAW) turbulence are studied in connection with scintillation. The focus is on small scales L ? 108-1010 cm where the KAW regime is active in the interstellar medium, principally within turbulent H II regions. Scales at 10 times the ion gyroradius and smaller are inferred to dominate scintillation in the theory of Boldyrev et al. From numerical solutions of a decaying KAW turbulence model, structure morphology reveals two types of localized structures, filaments and sheets, and shows that they arise in different regimes of resistive and diffusive damping. Minimal resistive damping yields localized current filaments that form out of Gaussian-distributed initial conditions. When resistive damping is large relative to diffusive damping, sheet-like structures form. In the filamentary regime, each filament is associated with a non-localized magnetic and density structure, circularly symmetric in cross section. Density and magnetic fields have Gaussian statistics (as inferred from Gaussian-valued kurtosis) while density gradients are strongly non-Gaussian, more so than current. This enhancement of non-Gaussian statistics in a derivative field is expected since gradient operations enhance small-scale fluctuations. The enhancement of density gradient kurtosis over current kurtosis is not obvious, yet it suggests that modest density fluctuations may yield large scintillation events during pulsar signal propagation. In the sheet regime the same statistical observations hold, despite the absence of localized filamentary structures. Probability density functions are constructed from statistical ensembles in both regimes, showing clear formation of long, highly non-Gaussian tails.

2011-04-01

322

Study of nature of light bands in weld metal structure, reinforced with lumpy filler materials  

Energy Technology Data Exchange (ETDEWEB)

A study was made on structure and properties of metal of slightly pickled light band, bordering the reinforcing inclusions in welds, produced by electroslag welding with the use of lumpy filler materials. It is shown that increased level of internal stresses in light band metal is conditioned by the distortion of crystal lattice which is probably caused by plastic deformation of reinforcing inclusion during matrix segregation.

Medovar, B.I.; Tsykulenko, A.K.; Zhuk, N.V.; Kareta, N.L. (AN Ukrainskoj SSR, Kiev. Inst. Ehlektrosvarki)

1984-08-01

323

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

Science.gov (United States)

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

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

1996-04-01

324

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

International Nuclear Information System (INIS)

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.

2007-09-01

325

Influence of distortion on the electronic band structure of CuInSe2  

CERN Document Server

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

326

Photonic stop bands in quasi-random nanoporous anodic alumina structures  

CERN Multimedia

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

327

Analysis of photonic band-gap (PBG) structures using the FDTD method  

DEFF Research Database (Denmark)

In this paper, a number of photonic band-gap (PBG) structures, which are formed by periodic circuit elements printed oil transmission-line circuits, are studied by using a well-known numerical method, the finite-difference time-domain (FDTD) method. The results validate the band-stop filter behavior of these structures, and the computed results generally match well with ones published in the literature. It is also found that the FDTD method is a robust, versatile, and powerful numerical technique to perform such numerical studies. The proposed PBG filter structures may be applied in microwave and communication systems.

Tong, M.S.; Cheng, M.

2004-01-01

328

Theory of composite-band Wannier states and order-N electronic-structure calculations  

CERN Document Server

'Exact' composite-band Wannier states are constructed and analyzed for the diamond-structure solids. The direct relations between the Wannier states and the order-N electronic-structure theory are also discussed as a general theory. The results imply that the locality of Wannier states directly depends on Hamiltonians and can be insensitive to the value of the bandgap.

Hoshi, T; Hoshi, Takeo; Fujiwara, Takeo

1999-01-01

329

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

Science.gov (United States)

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

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

2011-10-01

330

C-band superconducting structure for an e- LINAC  

International Nuclear Information System (INIS)

[en] The authors have built a 5-cell superconducting structure, for the main section (?=1) of an e- linear accelerator, forming half cavities, ''door-bell'' shaped, by deep drawing a 2 mm thick niobium sheet. Running the structure in the ? mode, (the accelerating one) accelerating field in excess of 7 MV/m was achieved at a fairly low Q /SUB o/ value of 3x108. The authors report a comparison between the results obtained in a single cell cavity of the same shape (B /SUB p/ about 50 mT) and that ones previously obtained in the 1 mm thick cavities operating at the same frequency (B /SUB p/ = 105 mT). They introduce a simple model for the heat transfer to He bath which explain the worse behaviour of the low Q /SUB o/ cavities

1983-01-01

331

Longitudinal structure function at intermediate x and the gluon density.  

Energy Technology Data Exchange (ETDEWEB)

Calculations are presented of the longitudinal structure function F{sub L}(x, Q{sup 2}). We use next-to-leading order expressions in QCD (O({alpha}{sup 2}{sub s})) plus parton densities determined previously from global fits to data on deep inelastic lepton scattering, prompt photon production, and bottom quark production. Anticipated data from the DESY ep collider HERA should provide discriminating information on the gluon density, particularly for values of x < 0.05.

Berger, E. L.; Meng, R.; High Energy Physics; CERN

1993-01-01

332

Band structures in neutron-rich odd mass dysprosium nuclei  

International Nuclear Information System (INIS)

[en] The structure of a nucleus is a fingerprint of how neutrons and protons interact in this many particle system to form a bound nucleus. Measuring nuclear properties is of great importance to understand the interactions which bind the protons and neutrons together in an isotope. These basic properties allow us to derive directly or indirectly information on the nuclear structure, as well as, on the strong nuclear force. Comparison of experimental properties of very exotic nuclei to calculations performed with different nuclear models allow testing the predictive power of these models when going to the extremes, or give a hint on how to further improve the nuclear models and their parameters. Neutron-rich nuclei are of particular current interest since they are predicted to reveal new aspects of nuclear structure associated with an excess of neutrons. Hence in the present work, the study of some odd mass Dysprosium isotopes with mass number varying from A = 159 to A = 165 have been undertaken using a framework of calculations known as Projected Shell Model (PSM)

2011-01-01

333

Electronic structure of perovskite-type YBRh3: X-ray photoelectron spectroscopy and ab initio band calculations  

International Nuclear Information System (INIS)

[en] The perovskite structure type YBRh3 was synthesized by the arc melting method. Its electronic structure was studied by XPS and ab initio band calculations. The chemical shifts of the Y and Rh 3d levels from the elements were negative. The experimental and calculated valence band XPS coincided well with each other. The band calculation indicated that the metallic behavior of the compound originates from the Rh 4d electrons. The atomic distance between Y and Rh is 93% of the sum of the radii of the elements. The electron density has a maximum between the Y and Rh atoms, and the distance between the maximum point and center of the Y atom is 77% of its atomic radius. This indicates that charge transfer occurs from Y to Rh. The nearly equal electronegativities of B and Rh result in a covalent bond between them, which is shown as an asymmetric electron distribution in the circumference of the B and Rh atoms. The covalent bond results from hybridization of the B 2p and Rh 4d levels

2003-02-03

334

Damping of Electron Density Structures and Implications for Interstellar Scintillation  

CERN Multimedia

The forms of electron density structures in kinetic Alfven wave turbulence are studied in connection with scintillation. The focus is on small scales $L \\sim 10^8-10^{10}$ cm where the Kinetic Alfv\\'en wave (KAW) regime is active in the interstellar medium. MHD turbulence converts to a KAW cascade, starting at 10 times the ion gyroradius and continuing to smaller scales. These scales are inferred to dominate scintillation in the theory of Boldyrev et al. From numerical solutions of a decaying kinetic Alfv\\'en wave turbulence model, structure morphology reveals two types of localized structures, filaments and sheets, and shows that they arise in different regimes of resistive and diffusive damping. Minimal resistive damping yields localized current filaments that form out of Gaussian-distributed initial conditions. When resistive damping is large relative to diffusive damping, sheet-like structures form. In the filamentary regime, each filament is associated with a non-localized magnetic and density structure,...

Smith, Kurt W

2011-01-01

335

B{sub 4}N and Fe{sub 3}BN nitrides bands structure and theoretical determination of bulk modulus  

Energy Technology Data Exchange (ETDEWEB)

With the evolution of material science there was some technological evolution as well as the need of finding new links which could be applied to diverse areas of knowledge. Thus, in this article, we study nitrides bands structures which contain boron, in two different stoichiometries Fe{sub 3}BN and B{sub 4}N. The choice of these compounds is meant to plan new links and to understand nitrides fundamental state properties facing these new crystalline structures. In order to resolve the compound band structure we used the method of linear Muffin Tin orbital (LMTO), with atomic sphere approximation (ASA). By using this method we obtained the energy of formation as a function of the lattice parameter as one of the results. We find the equilibrium lattice parameter of 6.9755a.u., for the Fe{sub 3}BN nitride, and in B{sub 4}N, we have 6.8589a.u. We also discuss in this article the charge transference between sites and the influence of pressure on the compound properties, as well as the Bulk modulus that is 239.82GPa for Fe{sub 3}BN and 105.48GPa for B{sub 4}N. We show the behaviour of the density of states (DOS) of the new band structure found for the proposed crystalline structure Fe{sub 3}BN, in which the B atom replace the Fe atom in the corner of the structure {gamma}{sup '}-Fe{sub 4}N.

Santos, A.V. dos [Universidade Regional Integrada do Alto Uruguai e das Missoes, URI Campus Santo Angelo, CEP 88040-900, Santo Angelo, RS (Brazil)]. E-mail: vandao@urisan.tche.br

2007-06-15

336

Pyroclastic density current volume estimation after the 2010 Merapi volcano eruption using X-band SAR  

Science.gov (United States)

Pyroclastic density current deposits remobilized by water during periods of heavy rainfall trigger lahars (volcanic mudflows) that affect inhabited areas at considerable distance from volcanoes, even years after an eruption. Here we present an innovative approach to detect and estimate the thickness and volume of pyroclastic density current (PDC) deposits as well as erosional versus depositional environments. We use SAR interferometry to compare an airborne digital surface model (DSM) acquired in 2004 to a post eruption 2010 DSM created using COSMO-SkyMed satellite data to estimate the volume of 2010 Merapi eruption PDC deposits along the Gendol river (Kali Gendol, KG). Results show PDC thicknesses of up to 75 m in canyons and a volume of about 40 × 106 m3, mainly along KG, and at distances of up to 16 km from the volcano summit. This volume estimate corresponds mainly to the 2010 pyroclastic deposits along the KG — material that is potentially available to produce lahars. Our volume estimate is approximately twice that estimated by field studies, a difference we consider acceptable given the uncertainties involved in both satellite- and field-based methods. Our technique can be used to rapidly evaluate volumes of PDC deposits at active volcanoes, in remote settings and where continuous activity may prevent field observations.

Bignami, Christian; Ruch, Joel; Chini, Marco; Neri, Marco; Buongiorno, Maria Fabrizia; Hidayati, Sri; Sayudi, Dewi Sri; Surono

2013-07-01

337

Ta 5d band symmetry of 1T-TaS1.2Se0.8 in the commensurate charge-density-wave phase.  

UK PubMed Central (United Kingdom)

We present a detailed angle-resolved photoemission study on the layered transition-metal dichalcogenide 1T-TaS1.2Se0.8 in the commensurate charge-density-wave (CDW) phase. A drastic reduction in the spectral weight along the high symmetry line GammaM, particularly around the point M, is observed when s-polarized light was used. This implies that the initial state must be symmetric with respect to a mirror plane perpendicular to the line GammaK, which is consistent with conventional band calculations in the absence of the CDW. We conclude that there is only a limited amount of modification of the electronic structure of 1T-TaS1.2Se0.8 in the commensurate CDW phase due to the CDW-related potential.

Aiura Y; Hase I; Bando H; Yagi-Watanabe K; Ozawa K; Iwase T; Nishihara Y; Shiino O; Oshima M; Kubota M; Ono K

2003-12-01

338

Ta 5d band symmetry of 1T-TaS1.2Se0.8 in the commensurate charge-density-wave phase.  

Science.gov (United States)

We present a detailed angle-resolved photoemission study on the layered transition-metal dichalcogenide 1T-TaS1.2Se0.8 in the commensurate charge-density-wave (CDW) phase. A drastic reduction in the spectral weight along the high symmetry line GammaM, particularly around the point M, is observed when s-polarized light was used. This implies that the initial state must be symmetric with respect to a mirror plane perpendicular to the line GammaK, which is consistent with conventional band calculations in the absence of the CDW. We conclude that there is only a limited amount of modification of the electronic structure of 1T-TaS1.2Se0.8 in the commensurate CDW phase due to the CDW-related potential. PMID:14754133

Aiura, Y; Hase, I; Bando, H; Yagi-Watanabe, K; Ozawa, K; Iwase, T; Nishihara, Y; Shiino, O; Oshima, M; Kubota, M; Ono, K

2003-12-18

339

Electronic structure of two-dimensional hexagonal diselenides: Charge density waves and pseudogap behavior  

International Nuclear Information System (INIS)

We theoretically study the electronic structure (spectral functions and Fermi surfaces) of incommensurate pseudogap and charge density wave (CDW) and commensurate CDW phases of quasi-two-dimensional diselenides 2H-TaSe2 and 2H-NbSe2. The incommensurate pseudogap regime is described within the scenario based on short-range-order CDW fluctuations, considered within the static Gaussian random field model. In contrast, e.g., to high-Tc cuprates, layered dichalcogenides have several different CDW scattering vectors and an electronic spectrum with two bands at the Fermi level. For this, we present a theoretical background for the description of multiple scattering processes within a multiple-band electronic spectrum. Theoretical spectral functions and Fermi surfaces thus obtained are compared with recent ARPES experimental data, demonstrating rather good qualitative agreement.

2012-01-01

340

Ab initio density functional theory investigation of structural and electronic properties of silicon carbide nanotube bundles  

Energy Technology Data Exchange (ETDEWEB)

By using ab initio density functional theory the structural and electronic properties of isolated and bundled (8,0) and (6,6) silicon carbide nanotubes (SiCNTs) are investigated. Our results show that for such small diameter nanotubes the inter-tube interaction causes a very small radial deformation, while band splitting and reduction of the semiconducting energy band gap are significant. We compared the equilibrium interaction energy and inter-tube separation distance of (8,0) SiCNT bundle with (10,0) carbon nanotube (CNT) bundle where they have the same radius. We found that there is a larger inter-tube separation and weaker inter-tube interaction in the (8,0) SiCNT bundle with respect to (10,0) CNT bundle, although they have the same radius.

Moradian, Rostam [Physics Department, Faculty of Science, Razi University, Kermanshah (Iran, Islamic Republic of); Nano Science and Technology Research Center, Razi University, Kermanshah (Iran, Islamic Republic of); Department of Nano Science, Computational Physical Science Research Laboratory, Institute for Studies in Theoretical Physics and Mathematics (IPM), P.O. Box 19395-5531, Tehran (Iran, Islamic Republic of)], E-mail: moradian.rostam@gmail.com; Behzad, Somayeh; Chegel, Raad [Physics Department, Faculty of Science, Razi University, Kermanshah (Iran, Islamic Republic of)

2008-10-01

 
 
 
 
341

Effect of energy-band structures on the propagation of ultrasound in degenerate semiconductors  

Energy Technology Data Exchange (ETDEWEB)

The effect of parabolic and nonparabolic band structures on the propagation of ultrasound at an angle theta relative to the direction of a dc magnetic field B in a degenerate semiconductor such as n-type InSb is investigated by using a quantum treatment which is valid at high frequencies and in strong magnetic fields. Numerical results show that the absorption coefficient and change in sound velocity depend strongly on the direction of the propagation of ultrasound relative to the magnetic field for both parabolic and nonparabolic band structures. However, the absorption coefficient and change in sound velocity for the nonparabolic band structure will diminish and become small in the intermediate-magnetic-field region when the angle theta is larger than 30/sup 0/.

Wu, C.; Tsai, J.

1982-06-01

342

Transition rate for impact ionization in the approximation of a parabolic band structure  

Energy Technology Data Exchange (ETDEWEB)

Recently, Alig, Bloom, and Struck have reported a simple model of ionization scattering in semiconductors and insulators. Their model is based upon the random-k approximation to the transition rate for impact ionization, and upon a generic band structure with only two free parameters to describe all materials. The present paper describes the first step in an attempt to understand in detail why such a simple model works so well. The random-k approximation to the transition rate for impact ionization is tested on a highly symmetric band-structure model for which most of the dimensions of the twelve-dimensional transition-rate integral can be treated analytically. The difference near threshold between the random-k approximation and the rigorous result can be much larger than indicated by Kane's Monte Carlo integration for the silicon band structure, but this difference seems to be unimportant in practical problems where impact ionization competes with phonon emission.

Geist, J.; Gladden, W.K.

1983-04-15

343

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

Science.gov (United States)

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

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

2013-03-01

344

A New Diagnostic of the Radial Density Structure of Be Disks  

CERN Document Server

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

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

2011-01-01

345

Band structure and optical electron spectra of (TrMA)CoCl{sub 3}.2H{sub 2}O crystal  

Energy Technology Data Exchange (ETDEWEB)

DFT calculations of the band structure, density of states and optical spectra of trimethylammonium cobalt chloride dihydrate [(CH{sub 3}){sub 3}NH]CoCl{sub 3}.2H{sub 2}O 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-CoCl{sub 3} 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.

Andriyevsky, B. [Technical University of Koszalin, 2 Sniadeckich Str., PL-75-453 Koszalin (Poland)]. E-mail: bandri@tu.koszalin.pl; Kapustianyk, V. [Scientific-Technical and Educational Center of Low Temperature Studies, Lviv I. Franko National University, Dragomanova Str., 50, UA-79005 Lviv (Ukraine); Ciepluch-Trojanek, W. [Technical University of Koszalin, 2 Sniadeckich Str., PL-75-453 Koszalin (Poland); Batiuk, A. [Scientific-Technical and Educational Center of Low Temperature Studies, Lviv I. Franko National University, Dragomanova Str., 50, UA-79005 Lviv (Ukraine)

2005-10-01

346

An increase in the millimeter and centimeter band flux density of Mrk421  

Science.gov (United States)

We have observed an increase in the 15 GHz and 95 GHz flux density of Mrk421, a high-synchrotron-peaked (HSP) BL Lac object. In April the source underwent extreme flaring in X-rays (seen by NuSTAR, ATel #4974), gamma rays (Fermi-LAT and Swift, ATel #4977) and in the very high energy gamma-rays (MAGIC and VERITAS, ATel #4976). Since the major high-energy flaring, we have been monitoring the source on a daily basis at 15 GHz with the Owens Valley Radio Observatory (OVRO) 40m Telescope and 2-3 times a week with the Combined Array for Research in Millimeter-wave Astronomy (CARMA) at 95 GHz.

Hovatta, Talvikki; Balokovic, Mislav; Richards, Joseph L.; Max-Moerbeck, Walter; Readhead, Anthony C. S.

2013-06-01

347

Dependence of the band structure of C-60 monolayers on molecularorientations and doping observed by angle resolved photoemission  

Energy Technology Data Exchange (ETDEWEB)

We present angle resolved photoemission studies of C60monolayers deposited on Ag surfaces. The electronic structure of thesemonolayers is derived from the partial filling of the narrow, 6-folddegenerated, C60 conduction band. By comparing the band structure in twomonolayers deposited, respectively, on Ag(111) and Ag(100), we show thatthe molecular degree of freedom, in this case the relative orientationsbetween C60 molecules, is essential to describe the band structure. Wefurther show that the evolution of the band as a function of doping doesnot follow a rigid band-filling picture. Phase separation is observedbetween a metallic and an insulating phase, which might be a result ofstrong correlations.

Brouet, V.; Yang, W.L.; Zhou, X.J.; Hussain, Z.; Shen, Z.X.

2008-01-17

348

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

UK PubMed Central (United Kingdom)

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.

Nashed R; Hassan WM; Ismail Y; Allam NK

2013-02-01

349

Collective band structures and particle alignments in 124Ba, 125Ba and 125Cs  

International Nuclear Information System (INIS)

High-spin states of 124Ba, 125Ba and 125Cs have been populated in the reactions 110Cd+18O at 80 MeV and 96Zr+34S at 160 MeV and studied using nuclear spectroscopy techniques. Several bands have been established in 124Ba and previously known band structures in 125Ba and 125Cs extended up to (43/2-) levels. Results concerning crossing frequencies and quasiparticle configurations are deduced from experimental routhians and aligned angular momenta. We propose that the two positive-parity bands in 124Ba are generated by h11/2 proton and h11/2 neutron alignments and the three negative-parity bands by the coupling of h11/2, g7/2 neutrons and h11/2, g7/2 or g9/2 protons. (orig.).

1988-01-01

350

Electronic energy band structure of actinide metals and intermetallics  

International Nuclear Information System (INIS)

[en] The behavior of the 5f electrons as the crucial factor in determining the electronic properties of materials containing actinides is discussed. Whether these electrons will be localized or itinerant depends on the relative size of the Coulomb correlation and the near-neighbor interaction (bandwidth) terms. Evidence from optical reflectivity and de Haas-van Alphen measurements which show that the f-states are itinerant in the light actinide metals is examined. The mechanisms by which this occurs are studied and it is shown that the dominant feature is a direct f-f interaction on neighboring sites. It is as a result of this dominance that correlations with actinide separation are found for the observed superconducting and magnetic properties. Since materials which appear as exceptions to this correlation are significant as systems where the direct f-f interaction is not the dominant term, we discuss, as illustrative examples, the L12 crystal structure materials involving uranium. The materials considered in detail are URh3 and UIr3 for which an experimental determination of the Fermi surface has been made. In these systems, the dominant interaction is found to be the formation of a d-f bond. (auth)

1975-09-10

351

Band structure effects on the interaction of charged particles with solids  

Energy Technology Data Exchange (ETDEWEB)

A survey is presented of current investigations of the impact of band structure effects on various aspects of the interaction of charged particles with real solids. The role that interband transitions play in the decay mechanism of bulk plasmons is addressed, and results for plasmon linewidths in Al and Si are discussed. Ab initio calculations of the electronic energy loss of ions moving in Al and Si are also presented, within linear response theory, from a realistic description of the one-electron band structure and a full treatment of the dynamic electronic response of valence electrons. Both random and position-dependent stopping powers of valence electrons are computed.

Pitarke, J.M. E-mail: wmppitoj@lg.ehu.es; Campillo, I

2000-04-01

352

Direct Measurement of the Band Structure of a Buried Two-Dimensional Electron Gas  

DEFF Research Database (Denmark)

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

Miwa, Jill; Hofmann, Philip

2013-01-01

353

Magnetic-field induced band-structure change in CeBiPt  

CERN Document Server

We report on a field-induced change of the electronic band structure of CeBiPt as evidenced by electrical-transport measurements in pulsed magnetic fields. Above ~25 T, the charge-carrier concentration increases nearly 30% with a concomitant disappearance of the Shubnikov-de Haas signal. These features are intimately related to the Ce 4f electrons since for the non-4f compound LaBiPt the Fermi surface remains unaffected. Electronic band-structure calculations point to a 4f-polarization-induced change of the Fermi-surface topology.

Kozlova, N; Doerr, M; Wosnitza, J; Eckert, D; Müller, K H; Schultz, L; Opahle, I; Elgazzar, S; Richter, M; Goll, G; Zwicknagl, G; Yoshino, T; Takabatake, T; Richter, Manuel

2005-01-01

354

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

UK PubMed Central (United Kingdom)

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

Miwa JA; Hofmann P; Simmons MY; Wells JW

2013-03-01

355

Energy band structure of Cr by the Slater-Koster interpolation scheme  

International Nuclear Information System (INIS)

The matrix elements of the Hamiltonian between nine localized wave-functions in tight-binding formalism are derived. The symmetry adapted wave-functions and the secular equations are formed by the group theory method for high symmetry points in the Brillouin zone. A set of interaction integrals is chosen on physical ground and fitted via the Slater-Koster interpolation scheme to the abinito band structure of chromium calculated by the Green function method. Then the energy band structure of chromium is interpolated and extrapolated in the Brillouin zone. (author)

1986-01-01

356

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

Energy Technology Data Exchange (ETDEWEB)

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

Rozanov, N. N., E-mail: nrosanov@yahoo.com; Fedorov, S. V.; Savel' ev, R. S.; Sukhorukov, A. A.; Kivshar, Yu. S. [St. Petersburg State University of Information Technologies, Mechanics and Optics (Russian Federation)

2012-05-15

357

Electronic structure and optical properties of Ag3PO4 photocatalyst calculated by hybrid density functional method  

International Nuclear Information System (INIS)

The electronic structure and optical properties of Ag3PO4 were studied by hybrid density functional theory. The results indicated that the band gap is 2.43 eV, which agrees well with the experimental value of 2.45 eV. The conduction bands of Ag3PO4 are mainly attributable to Ag 5s and 5p states, while the valence bands are dominated by O 2p and Ag 4d states. The highest valence band edge potential was 2.67 V (vs. normal hydrogen electrode), which has enough driving force for photocatalytic water oxidation and pollutants degradation. The optical absorption spectrum showed that Ag3PO4 is a visible light response photocatalyst.

2011-11-07

358

Founder takes all: density-dependent processes structure biodiversity.  

UK PubMed Central (United Kingdom)

Density-dependent processes play a key role in the spatial structuring of biodiversity. Specifically, interrelated demographic processes, such as gene surfing, high-density blocking, and competitive exclusion, can generate striking geographic contrasts in the distributions of genes and species. Here, we propose that well-studied evolutionary and ecological biogeographic patterns of postglacial recolonization, progressive island colonization, microbial sectoring, and even the 'Out of Africa' pattern of human expansion, are fundamentally similar, underpinned by a 'founder takes all' density-dependent principle. Additionally, we hypothesize that older historic constraints of density-dependent processes are seen today in the dramatic biogeographic shifts that occur in response to human-mediated extinction events, whereby surviving lineages rapidly expand their ranges to replace extinct sister taxa.

Waters JM; Fraser CI; Hewitt GM

2013-02-01

359

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

Science.gov (United States)

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

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

2013-03-01

360

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

UK PubMed Central (United Kingdom)

As one kind of new linear cellular alloys (LCAs), Kagome honeycombs, which are constituted by triangular and hexagonal cells, attract great attention due to the excellent performance compared to the ordinary ones. Instead of mechanical investigation, the in-plane elastic wave dispersion in Kagome structures are analyzed in this paper aiming to the multi-functional application of the materials. Firstly, the band structures in the common two-dimensional (2D) porous phononic structures (triangular or hexagonal honeycombs) are discussed. Then, based on these results, the wave dispersion in Kagome honeycombs is given. Through the component cell porosity controlling, the effects of component cells on the whole responses of the structures are investigated. The intrinsic relation between the component cell porosity and the critical porosity of Kagome honeycombs is established. These results will provide an important guidance in the band structure design of super porous phononic crystals.

Liu Y; Sun XZ; Chen ST

2013-02-01

 
 
 
 
361

The Development of Layered Photonic Band Gap Structures Using a Micro-Transfer Molding Technique  

Energy Technology Data Exchange (ETDEWEB)

Photonic band gap (PBG) crystals are periodic dielectric structures that manipulate electromagnetic radiation in a manner similar to semiconductor devices manipulating electrons. Whereas a semiconductor material exhibits an electronic band gap in which electrons cannot exist, similarly, a photonic crystal containing a photonic band gap does not allow the propagation of specific frequencies of electromagnetic radiation. This phenomenon results from the destructive Bragg diffraction interference that a wave propagating at a specific frequency will experience because of the periodic change in dielectric permitivity. This gives rise to a variety of optical applications for improving the efficiency and effectiveness of opto-electronic devices. These applications are reviewed later. Several methods are currently used to fabricate photonic crystals, which are also discussed in detail. This research involves a layer-by-layer micro-transfer molding ({mu}TM) and stacking method to create three-dimensional FCC structures of epoxy or titania. The structures, once reduced significantly in size can be infiltrated with an organic gain media and stacked on a semiconductor to improve the efficiency of an electronically pumped light-emitting diode. Photonic band gap structures have been proven to effectively create a band gap for certain frequencies of electro-magnetic radiation in the microwave and near-infrared ranges. The objective of this research project was originally two-fold: to fabricate a three dimensional (3-D) structure of a size scaled to prohibit electromagnetic propagation within the visible wavelength range, and then to characterize that structure using laser dye emission spectra. As a master mold has not yet been developed for the micro transfer molding technique in the visible range, the research was limited to scaling down the length scale as much as possible with the current available technology and characterizing these structures with other methods.

Kevin Jerome Sutherland

2001-05-01

362

Dielectric band structure of crystals: General properties, and calculations for silicon  

International Nuclear Information System (INIS)

We shift the dielectric band structure method, orginially proposed by Baldereschi and Tosatti for the description of microscopic electronic screening in crystals. Some general properties are examined first, including the requirements of causality and stability. The specific test case of silicon is then considered. Dielectric bands are calculated, according to several different prescriptions for the construction of the dielectric matrix. It is shown that the results allow a very direct appraisal of the screening properties of the system, as well as of the quality of the dielectric model adopted. The electronic charge displacement induced by ?sub(25') and X3 phonon-like displacements of the atoms is also calculated and compared with the results of existent full self-consistent calculations. Conclusions are drawn on the relative accuracies of the dielectric band structures. (author)

1981-01-01

363

Superconducting transition temperatures of Zr, Os And Th from band structure results  

International Nuclear Information System (INIS)

[en] The superconducting transition tenperatures of Zr, Os and Th are calculated using their band-structure results. Under spherical band approximation, the theory of Gaspari and Gyorffy (1972) is used in conjunction with the McMillan's formula (1968) to calculate Tsub(c). As the band-structure calculations have been done for potentials constructed with and without the correlation part, the superconducting transition temperatures are also calculated for all the potentials. The theoretical values of Tsub(c) are found to be very sensitive to the changes in the electron-phonon enhancement factor lambda and the Coulomb Pseudopotential ?sup(asterisk). The theoretical values are compared with the experimental values. (author)

1980-01-01

364

A possible role of $D^{-}$ band in hopping conductivity and metal-insulator transition in 2D structures  

CERN Document Server

A simple two-band model is suggested explaining recently reported unusual features for hopping magnetoresistance and the metal-insulator transition in 2D structures. The model implies that the conductivity is dominated by the upper Hubbard band (D^- band). Experimental studies of hopping magnetoresistance for Si delta doped GaAs/AlGaAs heterostructure give additional evidences for the model.

Kozub, V I; Khondaker, S I; Shlimak, I S

1999-01-01

365

Inference of upper-mantle density structure from seismic velocities  

Science.gov (United States)

The inverse problem for the determination of density structure from perturbations in the gravity field is highly nonunique. The combination of gravity data and other observables can, however, be used to make inferences about the Earth's density structure in three dimensions. We use the three-dimensional shear-wave velocity model of Nettles and Dziewonski (2005) to make a forward prediction of the Earth's gravity field using simple assumptions about the relationship between perturbations in shear velocity and density. A scaling factor f=0.25 relating perturbations in shear velocity and density (?/?? = f · ?vS/vS) is determined empirically by comparison of observed variations in shear velocity in oceanic regions with density variations predicted from a simple model of conductive cooling. This value agrees well with f=0.27 based on the laboratory results of Jackson et al. (1992). The observed gravity signal in the oceans is explained well by this simple thermal-scaling approach. Behavior in some continental regions, such as the Basin and Range and the East African rift zone, is found to be similar to that in the oceans: the high topography in these regions appears to be supported by hot, low-density mantle underneath, a result also found by Kaban and Mooney (2001) for the Basin and Range. A velocity-to-density scaling relationship based only on thermal considerations is clearly inadequate in regions of continental craton, where such scaling leads to unrealistically large perturbations in the predicted gravity field. This result suggests that non-thermal effects must counteract the high density that would occur due to thermal effects alone, consistent with the suggestion of Jordan (1975) and other workers that density increases due to cool temperatures in the continental roots must be balanced by density decreases due to compositional variations. Using the compositional derivatives for density and shear velocity with respect to Mg# determined by Lee (2003), and an assumption of neutral buoyancy in the continental roots, yields perturbations in temperature in agreement with those obtained by Artemieva and Mooney (2001) based on heat-flow and heat-production data and perturbations in Mg# that are generally consistent with values observed for cratonic mantle xenoliths.

Nettles, M.; Dziewonski, A. M.

2005-12-01

366

Band structure and excitons in CsCdBr{sub 3}  

Energy Technology Data Exchange (ETDEWEB)

CsCdBr{sub 3} has a very unique electronic band structure. The conduction band is split up into two parts: a lower isolated and very narrow band ({delta}E{proportional_to}4000 cm{sup -1}) and higher lying ones. Just below the lowest conduction band we observe an absorption band of excitons localized at lattice defects. Both of them, the low-lying conduction band as well as the localized excitons, play an important role in the fast and very efficient energy transfer within the crystal. This can be shown by analyzing the decay dynamics of the fluorescence of the dopant RE-ions and of the localized and lattice excitons (excitons of the perfect lattice). Also, excitation into either the excitons or the RE-ion clearly shows an energy transfer back and forth between both of them. We deem this mechanism to be the most important one for the observed upconversion processes in CsCdBr{sub 3}. (orig.)

Wenzel, M.; Altwein, M.; Demirbilek, R.; Leu, B.; Heber, J.; Kuebler, J. [Technische Univ. Darmstadt (Germany). Inst. fuer Festkoerperphysik; Bleeker, B.; Meijerink, A. [University of Utrecht, Utrecht (Netherlands)

2000-04-12

367

New band structures and an unpaired crossing in {sup 78}Kr  

Energy Technology Data Exchange (ETDEWEB)

High-spin states in {sup 78}Kr were studied using the {sup 58}Ni({sup 23}Na,3p) reaction at 70 MeV and the {sup 58}Ni({sup 28}Si,{alpha}4p) reaction at 130 MeV. Prompt {gamma}-{gamma} coincidences were measured using the Pitt-FSU detector array and the GAMMASPHERE-MICROBALL array. Results from these experiments have led to 26 new excitation levels, some of which have been grouped into 3 new bands. Spins were assigned based on directional correlations of oriented nuclei. Two of the new negative-parity bands appear to form a signature-partner pair based on a two-quasineutron structure, in contrast to the previously known two-quasiproton negative-parity bands. A forking has been observed at the 24{sup +} state in the yrast band, which calculations suggest may result from an unpaired crossing. The available evidence suggests oblate shapes in the yrast band coexist with prolate shapes in the negative-parity bands. {copyright} {ital 1999} {ital The American Physical Society}

Sun, H.; Doering, J.; Johns, G.D.; Kaye, R.A.; Solomon, G.Z.; Tabor, S.L. [Department of Physics, Florida State University, Tallahassee, Florida 32306 (United States); Doering, J. [Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Devlin, M.; LaFosse, D.R.; Lerma, F.; Sarantites, D.G. [Department of Chemistry, Washington University, St. Louis, Missouri 63130 (United States); Baktash, C.; Rudolph, D.; Yu, C. [Physics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Lee, I.Y.; Macchiavelli, A.O. [Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Birriel, I.; Saladin, J.X.; Winchell, D.F.; Wood, V.Q. [Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States); Ragnarsson, I. [Department of Mathematical Physics, Lund Institute of Technology, S-22100 Lund (Sweden)

1999-02-01

368

New band structures and an unpaired crossing in {sup 78}Kr  

Energy Technology Data Exchange (ETDEWEB)

High-spin states in {sup 78}Kr were studied using the {sup 58}Ni({sup 23}Na,3p) reaction at 70 MeV and the {sup 58}Ni({sup 28}Si,{alpha}4p) reaction at 130 MeV. Prompt {gamma}-{gamma} coincidences were measured using the Pitt-FSU detector array and the GAMMASPHERE-MICROBALL array. Results from these experiments have led to 26 new excitation levels, some of which have been grouped into 3 new bands. Spins were assigned based on directional correlations of oriented nuclei. Two of the new negative-parity bands appear to form a signature-partner pair based on a two-quasineutron structure, in contrast to the previously known two-quasiproton negative-parity bands. A forking has been observed at the 24{sup +} state in the yrast band, which calculations suggest may result from an unpaired crossing. The available evidence suggests oblate shapes in the yrast band coexist with prolate shapes in the negative-parity bands.

Sun, H.; Doring, J.; Johns, R.A.; Solomon, G.; Tabor, S.; Devlin, M.; LaFosse, D.; Lerma, F.; Sarantites, D.; Baktash, C.; Rudolph, D.; Yu, C.H.; Lee, I.Y.; Macchiavelli, A.; Birriel, I.; Saladin, J.; Winchell, D.; Wood, V.Q.; Ragnarsson, I.

1998-07-06

369

Band structure effects in nitrogen K-edge resonant inelastic X ray scattering from GaN  

CERN Multimedia

Systematic experimental data on resonant inelastic X-ray scattering (RIXS) in GaN near the N K-edge are presented for the first time. Excitation energy dependence of the spectral structures manifests the band structure effects originating from momentum selectivity of the RIXS process. This finding allows obtaining k-resolved band structure information for GaN crystals and nanostructures.

Strocov, V N; Rubensson, J E; Blaha, P; Paskova, T; Nilsson, P O

2004-01-01

370

DETERMINATION OF THE STRUCTURAL, ELECTRONIC AND OPTICAL PROPERTIES OF STRONTIUM OXIDE FROM DENSITY FUNCTIONAL THEORY  

Directory of Open Access Journals (Sweden)

Full Text Available It was performed a first-principle study of the structural, electronic, and optical properties of SrO in the crystallization phase Fm-3m by means of density functional theory (DFT), using the full potential linearized augmented plane wave method (FP-LAPW) along with the generalized gradient approximation (GGA) for the exchange-correlation energy. The relaxed structural parameters for the ground state are found to be in a good agreement with the experimental data, lattice constant a = 9,826 Bohr, cohesive energy E0 =-0,764 Ry, bulk modulus B = 83 GPa and B’ = 4,71. The calculated electronic structure yield an indirect band gap of 3, 392 eV between and X points in the Brillouin zone, finally it was obtained the absorption, dielectric constant and the refraction index spectrums as energy functions by means of the random phase approximation (RPA).

Gabriel A. Fonseca; María A. Puerto; Wilmer Y. Córdoba; William O. Sosa; Jose Otálora; Jairo A. Rodríguez

2012-01-01

371

A NEW DESIGN APPROACH FOR BANDWIDTH ENHANCEMENT AND DUAL BAND OPERATION OF MICROSTRIP U-SHAPE PATCH ANTENNA USING PHOTONIC BAND GAP STRUCTURE  

Directory of Open Access Journals (Sweden)

Full Text Available Microstrip patch antennas have a rapid growth of its importance in the field of wireless communication due to ease of fabrication and versatility of possible geometries. It is still being the part of development, to design a suitable antenna of high bandwidth with compact geometry for commercial applications. The purpose of thispaper is to design a compact size high bandwidth microstrip patch antenna with promising efficiency for wireless applications. A U-shape microstrip patch antenna, operating in dual band, with PBG structure is proposed. A U-shape probe feed antenna with photonic band gap structure on ground plane could be able to improvebandwidth about 32.26% in the band of frequency 1.6-2.4 GHz & about 23.75 % in the band of frequency 3.7- 4.7 GHz. The results are simulated & depicted with the help of full wave simulator IE3D V9.0.

PANKAJ KUMAR GOSWAMI; RAJESH NEMA

2012-01-01

372

Energy band-alignment of a multimetal-layer gated metal-oxide-semiconductor structure  

Science.gov (United States)

The energy band-alignment of a multimetal-layer gated metal-oxide-semiconductor structure is investigated. An analytical expression for the Fermi level of the metal stack is derived. It is shown that the thin metal layer contacting the gate dielectric plays a critical role in determining the work function of the whole metal stack, in agreement with experimental results.

Li, Zilan; Houssa, Michel; Schram, Tom; de Gendt, Stefan; de Meryer, Kristin

2009-11-01

373

Spin-dependent electronic band structure of Co/Cu(001) with different film thicknesses  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Spin- and angle-resolved photoemission spectroscopy (SARPES) has been applied to the study of spin-polarized electronic structures of face-centered tetragonal (fct) Co thin films with thicknesses from 2 to 9.5 monolayers (MLs). We have clearly observed two dispersive majority and minority spin band ...

Miyamoto, Koji; Iori, Kazuyuki; Sakamoto, Kazuaki; Kimura, Akio; Qiao, S.; Shimada, Kenya; Namatame, Hirofumi; Taniguchi, Masaki

374

Two-band tariff for domestic use: Italian Electricity Board rate structure  

International Nuclear Information System (INIS)

[en] ENEL (the Italian National Electricity Board) has begun to introduce a new rate structure for households: the 'two-band tariff'. This article is an effort to examine in principle how the new tariff could optimize load management when applied to the whole household sector

1992-01-01

375

Two-band tariff for domestic use: Italian Electricity Board rate structure  

Energy Technology Data Exchange (ETDEWEB)

ENEL (the Italian National Electricity Board) has begun to introduce a new rate structure for households: the 'two-band tariff'. This article is an effort to examine in principle how the new tariff could optimize load management when applied to the whole household sector.

Barteselli, R. (Univ. Cattolica del Sacro Cuore, Milan (Italy))

1992-06-01

376

Two- and three-dimensional band structure of ultrathin Ni on Cu(001)  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The momentum-resolved electronic structure of ultrathin films of Ni on Cu(001) is investigated by angle-resolved photoemission in the thickness range between 2 and 6 monolayers and by first-principles slab calculations. While the sp-band Fermi surface of Ni shows a full three-dimensional bulklike to...

Hoesch, M; Petrovic, V N; Muntwiler, M; Hengsberger, M; Lobo-Checa, J; Greber, T; Osterwalder, J

377

Electron transport and band structure in phosphorus-doped polycrystalline silicon films  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We study transport mechanisms, effective mass, and band structure by measuring the resistivity, Hall, and Seebeck and Nernst coefficients in heavily phosphorus-doped polycrystalline silicon films made by thermal crystallization of amorphous silicon. We observe a change in transport mechanism which r...

Young, DL; Branz, HM; Liu, F; Reedy, R; To, B; Wang, Q

378

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

Science.gov (United States)

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

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

2004-03-01

379

Band structures of periodic carbon nanotube junctions and their symmetries analyzed by the effective mass approximation  

CERN Document Server

The band structures of the periodic nanotube junctions are investigated by the effective mass theory and the tight binding model. The periodic junctions are constructed by introducing pairs of a pentagonal defect and a heptagonal defect periodically in the carbon nanotube. We treat the periodic junctions whose unit cell is composed by two kinds of metallic nanotubes with almost same radii, the ratio of which is between 0.7 and 1 . The discussed energy region is near the undoped Fermi level where the channel number is kept to two, so there are two bands. The energy bands are expressed with closed analytical forms by the effective mass theory with some assumptions, and they coincide well with the numerical results by the tight binding model. Differences between the two methods are also discussed. Origin of correspondence between the band structures and the phason pattern discussed in Phys. Rev. B {\\bf 53}, 2114, is clarified. The width of the gap and the band are in inverse proportion to the length of the unit ...

Tamura, R; Tamura, Ryo; Tsukada, Masaru

1998-01-01

380

Design of UWB Monopole Antenna with Dual Notched Bands Using One Modified Electromagnetic-Bandgap Structure.  

Science.gov (United States)

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

Liu, Hao; Xu, Ziqiang

2013-09-19

 
 
 
 
381

Electronic structure of ZrS{sub x}Se{sub 2-x} by density functional theory  

Energy Technology Data Exchange (ETDEWEB)

The electronic properties of the ZrS{sub x}Se{sub 2-x} (x varies between zero and two) semiconductors have been calculated by density functional theory (using the Wien2K code) employing the full potential Hamiltonian within the Generalized Gradient Approximation (GGA) method. The results obtained for the end members of the series, i.e. ZrS{sub 2} and ZrSe{sub 2} reveal that the valence band maximum and conduction band minimum are located at {gamma} and between {gamma} and K respectively which is in agreement with our photoemission experimental data. Trends in the electronic structure for the whole substitution series are discussed.

Ghafari, Ailakbar; Moustafa, Mohamed; Janowitz, Christoph; Dwelk, Helmut; Manzke, Recardo [Institut fuer Physik, Humboldt-Universitaet zu Berlin, Newtonstr. 15, D-12489 Berlin (Germany); Bouchani, Arash [Physics Department, Islamic Azad University, Kermanshah Branch (Iran, Islamic Republic of)

2011-07-01

382

Electronic Structure of Matter Wave Functions and Density Functionals.  

CERN Multimedia

Since the 1920's Schroedinger wave functions have been the principal theoretical concept for understanding and computing the electronic structure of matter. More recently, Density Functional Theory (DFT), couched in terms of the electronic density distribution, n(r), has provided a new perspective and new computational possibilities, especially for systems consisting of very many (up to ~1000) atoms. In this talk some fundamental limitations of wave function methods for very-many-atom-systems will be discussed. The DFT approach will be explained together with some physical/chemical applications and a discussion of its strenghts and weaknesses.

Kohn, W

1999-01-01

383

Subaortic (Type 6) Muscular Band—Innocent Bystander or Pathologic Structure?  

Directory of Open Access Journals (Sweden)

Full Text Available Intraventricular tendons are structures that was identified more than a hundred years ago. It has been suggested that they represent intracavitary radiations of the bundle of His and that they may be an isolated finding or be associated with structural cardiac abnormalities. Loukas et al divided these structures into five categories and recently a sixth type have been added. Various physiological disturbances have been observed due to the sixth type of tendon, such as ST segment elevation and right bundle branch block. It has been noted that this peculiar structure appears too thick to be called a tendon, thus the term band. This retrospective analysis analyzed the incidence of the thick, subaortic (type 6) muscular band in a cardiovascular clinic.

J Ker

2010-01-01

384

Dyadic Green's function study of band structures of dispersive photonic crystals  

International Nuclear Information System (INIS)

We present here in terms of a dyadic Green's function (DGF) a general description of optical phenomena in photonic crystal (PC) structures, described particularly by frequency-dependent components, assuming that PC structures are decomposed into their relatively simple constituent parts via conductivity tensors. We demonstrate this approach by explicitly calculating the DGFs for electromagnetic waves propagating in the one- and two-dimensional dispersive PCs consisting of a periodic array of identical metallic quantum wells and a periodic square array of identical metallic quantum wires, each embedded in a three-dimensional dispersive medium. By means of the explicit analytic dispersion relations, which result from the frequency poles of the corresponding DGFs, we also calculate the band structures of these dispersive PCs by simple numerical means. Our analysis shows that the band structures calculated from our DGF approach conform well with those calculated from the traditional computational methods.

2011-01-01

385

Surface plasmon polariton band gap structures: implications to integrated plasmonic circuits  

DEFF Research Database (Denmark)

Conventional photonic band gap (PBG) structures are composed of regions with periodic modulation of refractive index that do not allow the propagation of electromagnetic waves in a certain interval of wavelengths, i.e., that exhibit the PBG effect. The PBG effect is essentially an interference phenomenon related to strong multiple scattering of light in periodic media. The interest to the PBG structures has dramatically risen since the possibility of efficient waveguiding around a sharp corner of a line defect in the PBG structure has been pointed out. Given the perspective of integrating various PBG-based components within a few hundred micrometers, we realized that other two-dimensional waves, e.g., surface plasmon polaritons (SPPs), might be employed for the same purpose. The SPP band gap (SPPBG) has been observed for the textured silver surfaces by performing angular measurements of the surface reflectivity. Here we report the results of our experimental and theoretical investigations of waveguiding in the SPPBG structures.

Bozhevolnyi, S. I.; Volkov, V. S.

2001-01-01

386

Omnidirectional photonic band gap enlarged by one-dimensional ternary unmagnetized plasma photonic crystals based on a new Fibonacci quasiperiodic structure  

Energy Technology Data Exchange (ETDEWEB)

In this paper, an omnidirectional photonic band gap realized by one-dimensional ternary unmagnetized plasma photonic crystals based on a new Fibonacci quasiperiodic structure, which is composed of homogeneous unmagnetized plasma and two kinds of isotropic dielectric, is theoretically studied by the transfer matrix method. It has been shown that such an omnidirectional photonic band gap originates from Bragg gap in contrast to zero-n gap or single negative (negative permittivity or negative permeability) gap, and it is insensitive to the incidence angle and the polarization of electromagnetic wave. From the numerical results, the frequency range and central frequency of omnidirectional photonic band gap can be tuned by the thickness and density of the plasma but cease to change with increasing Fibonacci order. The bandwidth of omnidirectional photonic band gap can be notably enlarged. Moreover, the plasma collision frequency has no effect on the bandwidth of omnidirectional photonic band gap. It is shown that such new structure Fibonacci quasiperiodic one-dimensional ternary plasma photonic crystals have a superior feature in the enhancement of frequency range of omnidirectional photonic band gap compared with the conventional ternary and conventional Fibonacci quasiperiodic ternary plasma photonic crystals.

Zhang Haifeng [College of Electronic and Information Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China); Nanjing Artillery Academy, Nanjing 211132 (China); Liu Shaobin [College of Electronic and Information Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China); State Key Laboratory of Millimeter Waves of Southeast University, Nanjing Jiangsu 210096 (China); Kong Xiangkun; Bian Borui; Dai Yi [College of Electronic and Information Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China)

2012-11-15

387

Omnidirectional photonic band gap enlarged by one-dimensional ternary unmagnetized plasma photonic crystals based on a new Fibonacci quasiperiodic structure  

Science.gov (United States)

In this paper, an omnidirectional photonic band gap realized by one-dimensional ternary unmagnetized plasma photonic crystals based on a new Fibonacci quasiperiodic structure, which is composed of homogeneous unmagnetized plasma and two kinds of isotropic dielectric, is theoretically studied by the transfer matrix method. It has been shown that such an omnidirectional photonic band gap originates from Bragg gap in contrast to zero-n gap or single negative (negative permittivity or negative permeability) gap, and it is insensitive to the incidence angle and the polarization of electromagnetic wave. From the numerical results, the frequency range and central frequency of omnidirectional photonic band gap can be tuned by the thickness and density of the plasma but cease to change with increasing Fibonacci order. The bandwidth of omnidirectional photonic band gap can be notably enlarged. Moreover, the plasma collision frequency has no effect on the bandwidth of omnidirectional photonic band gap. It is shown that such new structure Fibonacci quasiperiodic one-dimensional ternary plasma photonic crystals have a superior feature in the enhancement of frequency range of omnidirectional photonic band gap compared with the conventional ternary and conventional Fibonacci quasiperiodic ternary plasma photonic crystals.

Zhang, Hai-Feng; Liu, Shao-Bin; Kong, Xiang-Kun; Bian, Bo-Rui; Dai, Yi

2012-11-01

388

Omnidirectional photonic band gap enlarged by one-dimensional ternary unmagnetized plasma photonic crystals based on a new Fibonacci quasiperiodic structure  

International Nuclear Information System (INIS)

In this paper, an omnidirectional photonic band gap realized by one-dimensional ternary unmagnetized plasma photonic crystals based on a new Fibonacci quasiperiodic structure, which is composed of homogeneous unmagnetized plasma and two kinds of isotropic dielectric, is theoretically studied by the transfer matrix method. It has been shown that such an omnidirectional photonic band gap originates from Bragg gap in contrast to zero-n gap or single negative (negative permittivity or negative permeability) gap, and it is insensitive to the incidence angle and the polarization of electromagnetic wave. From the numerical results, the frequency range and central frequency of omnidirectional photonic band gap can be tuned by the thickness and density of the plasma but cease to change with increasing Fibonacci order. The bandwidth of omnidirectional photonic band gap can be notably enlarged. Moreover, the plasma collision frequency has no effect on the bandwidth of omnidirectional photonic band gap. It is shown that such new structure Fibonacci quasiperiodic one-dimensional ternary plasma photonic crystals have a superior feature in the enhancement of frequency range of omnidirectional photonic band gap compared with the conventional ternary and conventional Fibonacci quasiperiodic ternary plasma photonic crystals.

2012-01-01

389

Trial manufacturing process of x-band accelerating structure and future assignments  

International Nuclear Information System (INIS)

[en] Several X-band accelerating structures have been manufactured and investigated concerning their technical characteristics in High Energy Accelerator Research Organization. Because their manufacturing process is in the stage of trial processing, the there are still many awaited solutions for future mass product processing. The process scheduling of the RDDS (Rounded Damped Detuned Structure) - type disk fabrication and the flow of disks through the processing are discussed. (author)

2001-04-20

390

Trial manufacturing process of x-band accelerating structure and future assignments  

Energy Technology Data Exchange (ETDEWEB)

Several X-band accelerating structures have been manufactured and investigated concerning their technical characteristics in High Energy Accelerator Research Organization. Because their manufacturing process is in the stage of trial processing, the there are still many awaited solutions for future mass product processing. The process scheduling of the RDDS (Rounded Damped Detuned Structure) - type disk fabrication and the flow of disks through the processing are discussed. (author)

Funahashi, Yoshisato; Hitomi, Nobuteru [High Energy Accelerator Research Organization, Tsukuba, Ibaraki (Japan)

2001-06-01

391

Wound treatment item with textile bands with fibres and structural characteristics and fibres with non-structured characteristics  

UK PubMed Central (United Kingdom)

Wound care articles having at least one planar structure, comprises fibers with gel-forming properties, and fibers with non-gel-forming properties, where the fibers are arranged in the form of planar fabric bands (3, 4). Independent claims are included for: (1) a kit for the acute, emergency or military medical or chronic wound management, comprising the wound care article and (2) a method for the production of the wound care article comprising providing planar fabric bands exhibiting fibers with gel-forming properties, and fibers with non-gel-forming properties, and weaving, interweaving, stitch-bonding or knitting the bands to a planar structure. - ACTIVITY : Vulnerary. - MECHANISM OF ACTION : None given.

RIESINGER BIRGIT

392

Influence of fabrication conditions on valent band structure of BeO based ceramics  

International Nuclear Information System (INIS)

The influence of fabrication conditions of beryllium oxide base ceramics on valent band structure due to appearance of different impurities on interface of crystallites, varying BeO near-the-surface region, is studied. Comparison of ceramic samples, fabricated by standard sintering technology, and large ceramic samples, prepared by multiple heating in vacuum up to 2000 deg C is carried out. Analysis of the X-ray electron spectra data permitted to make a conclusion that valent band width and energy gap are independent on fabrication procedure. 10 refs.; 1 fig.

1988-01-01

393

Prompt particle decays of deformed bands and nuclear structure near 56Ni  

International Nuclear Information System (INIS)

Excited states in neutron-deficient mass A?60 nuclei were studied by means of several heavy-ion fusion-evaporation reactions. The GAMMASPHERE array in conjunction with ancillary detector systems such as MICROBALL and neutron detectors allowed for the identification of well deformed rotational structures in the second well of nuclei in the direct vicinity of the doubly-magic isotope 56Ni. Most interestingly, some of these bands were found to decay by prompt particle emission in competition to the expected ? decay-out. Experimental details of this decay mode are presented. The rotational bands are interpreted with mean-field and large-scale shell-model calculations.

1999-09-02

394

Combining GW calculations with exact-exchange density-functional theory: an analysis of valence-band photoemission for compound semiconductors  

International Nuclear Information System (INIS)

We report quasi-particle energy calculations of the electronic bandstructure as measured by valence-band photoemission for selected II-VI compounds and group III nitrides. By applying GW as perturbation to the ground state of the fictitious, non-interacting Kohn-Sham electrons of density-functional theory (DFT), we systematically study the electronic structure of zinc-blende GaN, ZnO, ZnS and CdS. Special emphasis is put on analysing the role played by the cation semicore d-electrons that are explicitly included as valence electrons in our pseudo-potential approach. Unlike in the majority of previous GW studies, which are almost exclusively based on ground state calculations in the local-density approximation (LDA), we combine GW with exact-exchange DFT calculations in the optimized-effective potential approach (OEPx). This is a much more elaborate and computationally expensive approach. However, we show that applying the OEPx approach leads to an improved description of the d-electron hybridization compared to the LDA. Moreover, we find that it is essential to use OEPx pseudo-potentials in order to treat core-valence exchange consistently. Our OEPx-based quasi-particle valence bandstructures are in good agreement with available photoemission data in contrast to the ones based on the LDA. We therefore conclude that for these materials, OEPx constitutes the better starting point for subsequent GW calculations.

2005-01-01

395

Electronic band structures and optical properties of type-II superlattice photodetectors with interfacial effect.  

UK PubMed Central (United Kingdom)

The electronic band structures and optical properties of type-II superlattice (T2SL) photodetectors in the mid-infrared (IR) range are investigated. We formulate a rigorous band structure model using the 8-band k · p method to include the conduction and valence band mixing. After solving the 8 × 8 Hamiltonian and deriving explicitly the new momentum matrix elements in terms of envelope functions, optical transition rates are obtained through the Fermi's golden rule under various doping and injection conditions. Optical measurements on T2SL photodetectors are compared with our model and show good agreement. Our modeling results of quantum structures connect directly to the device-level design and simulation. The predicted doping effect is readily applicable to the optimization of photodetectors. We further include interfacial (IF) layers to study the significance of their effect. Optical properties of T2SLs are expected to have a large tunable range by controlling the thickness and material composition of the IF layers. Our model provides an efficient tool for the designs of novel photodetectors.

Qiao PF; Mou S; Chuang SL

2012-01-01

396

Electronic band structures and optical properties of type-II superlattice photodetectors with interfacial effect.  

Science.gov (United States)

The electronic band structures and optical properties of type-II superlattice (T2SL) photodetectors in the mid-infrared (IR) range are investigated. We formulate a rigorous band structure model using the 8-band k · p method to include the conduction and valence band mixing. After solving the 8 × 8 Hamiltonian and deriving explicitly the new momentum matrix elements in terms of envelope functions, optical transition rates are obtained through the Fermi's golden rule under various doping and injection conditions. Optical measurements on T2SL photodetectors are compared with our model and show good agreement. Our modeling results of quantum structures connect directly to the device-level design and simulation. The predicted doping effect is readily applicable to the optimization of photodetectors. We further include interfacial (IF) layers to study the significance of their effect. Optical properties of T2SLs are expected to have a large tunable range by controlling the thickness and material composition of the IF layers. Our model provides an efficient tool for the designs of novel photodetectors. PMID:22330471

Qiao, Peng-Fei; Mou, Shin; Chuang, Shun Lien

2012-01-30

397

Plant lighting system with five wavelength-band light-emitting diodes providing photon flux density and mixing ratio control.  

UK PubMed Central (United Kingdom)

UNLABELLED: BACKGROUND: Plant growth and development depend on the availability of light. Lighting systems therefore play crucial roles in plant studies. Recent advancements of light-emitting diode (LED) technologies provide abundant opportunities to study various plant light responses. The LED merits include solidity, longevity, small element volume, radiant flux controllability, and monochromaticity. To apply these merits in plant light response studies, a lighting system must provide precisely controlled light spectra that are useful for inducing various plant responses. RESULTS: We have developed a plant lighting system that irradiated a 0.18 m2 area with a highly uniform distribution of photon flux density (PFD). The average photosynthetic PFD (PPFD) in the irradiated area was 438 micro-mol m-2 s-1 (coefficient of variation 9.6%), which is appropriate for growing leafy vegetables. The irradiated light includes violet, blue, orange-red, red, and far-red wavelength bands created by LEDs of five types. The PFD and mixing ratio of the five wavelength-band lights are controllable using a computer and drive circuits. The phototropic response of oat coleoptiles was investigated to evaluate plant sensitivity to the light control quality of the lighting system. Oat coleoptiles irradiated for 23 h with a uniformly distributed spectral PFD (SPFD) of 1 micro-mol m-2 s-1 nm-1 at every peak wavelength (405, 460, 630, 660, and 735 nm) grew almost straight upwards. When they were irradiated with an SPFD gradient of blue light (460 nm peak wavelength), the coleoptiles showed a phototropic curvature in the direction of the greater SPFD of blue light. The greater SPFD gradient induced the greater curvature of coleoptiles. The relation between the phototropic curvature (deg) and the blue-light SPFD gradient (micro-mol m-2 s-1 nm-1 m-1) was 2 deg per 1 micro-mol m-2 s-1 nm-1 m-1. CONCLUSIONS: The plant lighting system, with a computer with a graphical user interface program, can control the PFD and mixing ratios of five wavelength-band lights. A highly uniform PFD distribution was achieved, although an intentionally distorted PFD gradient was also created. Phototropic responses of oat coleoptiles to the blue light gradient demonstrated the merit of fine controllability of this plant lighting system.

Yano A; Fujiwara K

2012-01-01

398

Plant lighting system with five wavelength-band light-emitting diodes providing photon flux density and mixing ratio control  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract Background Plant growth and development depend on the availability of light. Lighting systems therefore play crucial roles in plant studies. Recent advancements of light-emitting diode (LED) technologies provide abundant opportunities to study various plant light responses. The LED merits include solidity, longevity, small element volume, radiant flux controllability, and monochromaticity. To apply these merits in plant light response studies, a lighting system must provide precisely controlled light spectra that are useful for inducing various plant responses. Results We have developed a plant lighting system that irradiated a 0.18 m2 area with a highly uniform distribution of photon flux density (PFD). The average photosynthetic PFD (PPFD) in the irradiated area was 438 micro-mol m–2 s–1 (coefficient of variation 9.6%), which is appropriate for growing leafy vegetables. The irradiated light includes violet, blue, orange-red, red, and far-red wavelength bands created by LEDs of five types. The PFD and mixing ratio of the five wavelength-band lights are controllable using a computer and drive circuits. The phototropic response of oat coleoptiles was investigated to evaluate plant sensitivity to the light control quality of the lighting system. Oat coleoptiles irradiated for 23 h with a uniformly distributed spectral PFD (SPFD) of 1 micro-mol m–2 s–1 nm–1 at every peak wavelength (405, 460, 630, 660, and 735 nm) grew almost straight upwards. When they were irradiated with an SPFD gradient of blue light (460 nm peak wavelength), the coleoptiles showed a phototropic curvature in the direction of the greater SPFD of blue light. The greater SPFD gradient induced the greater curvature of coleoptiles. The relation between the phototropic curvature (deg) and the blue-light SPFD gradient (micro-mol m–2 s–1 nm–1 m–1) was 2 deg per 1 micro-mol m–2 s–1 nm–1 m–1. Conclusions The plant lighting system, with a computer with a graphical user interface program, can control the PFD and mixing ratios of five wavelength-band lights. A highly uniform PFD distribution was achieved, although an intentionally distorted PFD gradient was also created. Phototropic responses of oat coleoptiles to the blue light gradient demonstrated the merit of fine controllability of this plant lighting system.

Yano Akira; Fujiwara Kazuhiro

2012-01-01

399

Probing nuclear structure at finite temperature and spin via decay of superdeformed bands in lead nuclei  

International Nuclear Information System (INIS)

[en] The 174Yb(25Mg,5n)194Pb and 173Yb(24Mg,5n)192Pb reactions were used to probe the decay of superdeformed (SD) bands. The total ?-ray spectra associated with the SD bands in 192,194Pb have been studied to determine the energy and angular momenta associated with each step of the cascade, from entry population to decay to the ground state. In particular, the ?-ray spectra associated with the quasicontinuous, non-discrete decay of their respective yrast SD bands has been extracted. Using various model assumptions, the quasi-continuous decay spectrum is expected to have a rapid rise in intensity at an energy associated with the gap, or backshift parameter, in level density; such a rise is observed in the quasicontinuous decay of the SD bands in 194,192Pb. Values of Egap=0.9(0.1) MeV for 194Pb at ?6? and E?0.4-0.1+0.3 MeV for 192Pb at ?10? have been deduced. (orig.)

2000-01-01

400

A statistical characterization of plasmasphere density structure and boundary locations  

Energy Technology Data Exchange (ETDEWEB)

A statistical study of plasmaspheric density profiles and their boundaries is performed, using measurements of core (<50 eV) ions by the retarding ion mass spectrometer (RIMS) on Dynamics Explorer 1. The plasmasphere density profiles are classified into essentially six different categories, indicative of density structure out to the outer boundary of observable cold, isotropic plasma. The most common profiles observed are those which are relatively featureless out to this outer boundary and those which exhibit multiple plateaus and plasmapauses. the multiple plateau profiles occur predominantly in the afternoon and evening sectors, while the featureless profiles are most common in the midnight through morning sectors. In the multiple plateau profiles, the average MLT (magnetic local time)-L locus of the inner plasmapause gradients is nearly circular at L = 3-4. Profiles with significant density troughs occur most often in the evening sector, and the troughs are widest in this sector as well. The MLT-L local time shape of the outer boundary of RIMS-observed cold ions (termed here low-energy ion transition, or LEIT) is similar to previously reported average plasmapause shapes, though its bulge region occurs in the afternoon sector. This MLT-L shape also tends to become more circular with increasing geomagnetic activity. Using simultaneous plasma density measurements from the plasma wave instrument, it is found that the LEIT typically is located between densities of 10 and 100 cm{sup {minus}3}, with an average plasma density there of about 60 cm{sup {minus}3}.

Horwitz, J.L.; Comfort, R.H. (Univ. of Alabama, Huntsville (USA)); Chappell, C.R. (Marshall Space Flight Center, Huntsville, AL (USA))

1990-06-01

 
 
 
 
401

Quasiparticle excitations in valence-fluctuation materials: effects of band structure and crystal fields  

International Nuclear Information System (INIS)

Evidence is now quite strong that the elementary hybridization model is the correct way to understand the lattice-coherent Fermi liquid regime at very low temperatures. Many-body theory leads to significant renormalizations of the input parameters, and many of the band-theoretic channels for hybridization are suppressed by the combined effects of Hund's-rule coupling, crystal-field splitting, and the f-f Coulomb repulsion U. Some exploratory calculations based on this picture are described, and some inferences are drawn about the band structures of several heavy-fermion materials. These inferences can and should be tested by suitably modified band-theoretic calculations. We find evidence for a significant Baber-scattering contribution in the very-low-temperature resistivity. A new mechanism is proposed for crossover from the coherent Fermi-liquid regime to the incoherent dense-Kondo regime. 28 refs

1985-01-01

402

Quasiparticle excitations in valence-fluctuation materials: effects of band structure and crystal fields  

Energy Technology Data Exchange (ETDEWEB)

Evidence is now quite strong that the elementary hybridization model is the correct way to understand the lattice-coherent Fermi liquid regime at very low temperatures. Many-body theory leads to significant renormalizations of the input parameters, and many of the band-theoretic channels for hybridization are suppressed by the combined effects of Hund's-rule coupling, crystal-field splitting, and the f-f Coulomb repulsion U. Some exploratory calculations based on this picture are described, and some inferences are drawn about the band structures of several heavy-fermion materials. These inferences can and should be tested by suitably modified band-theoretic calculations. We find evidence for a significant Baber-scattering contribution in the very-low-temperature resistivity. A new mechanism is proposed for crossover from the coherent Fermi-liquid regime to the incoherent dense-Kondo regime. 28 refs.

Brandow, B.H.

1985-01-01

403

Structure Studies of {sup 11}Be and {sup 12}Be: Observation of Molecular Rotational Bands  

Energy Technology Data Exchange (ETDEWEB)

Excited states of {sup 11}Be have been studied with several transfer reactions. Nine states between 3.96 MeV and 25.0 MeV excitation energy show the characteristic energy dependence of a rotational band. The deduced large moment-of-inertia of this band is consistent with a two-{alpha} structure with large deformation. For {sup 12}Be four high lying states at 7.30 MeV, 10.7 MeV, 14.6 MeV and 21.7 MeV, which were observed in the {sup 9}Be({sup 15}N,{sup 12}N){sup 12}Be reaction, also form a rotational band with almost the same moment-of-inertia as for {sup 11}Be, using the tentative spin assignments of 2{sup +} - 8{sup +}.

H.G. Bohlen; A. Blazevic; B. Gebauer; S.M. Grimes; R. Kalpakchieva; T.N. Massey; W. von Oertzen; S. Thummerer; M. Wilpert

1999-12-31

404

The electronic structure of liquid water within density functional theory  

CERN Multimedia

In the last decade, computational studies of liquid water have mostly concentrated on ground state properties. However recent spectroscopic measurements have been used to infer the structure of water, and the interpretation of optical and x-ray spectra requires accurate theoretical models of excited electronic states, not only of the ground state. To this end, we investigate the electronic properties of water at ambient conditions using ab initio density functional theory within the generalized gradient approximation (DFT/GGA), focussing on the unoccupied subspace of Kohn-Sham eigenstates. We generate long (250 ps) classical trajectories for large supercells, up to 256 molecules, from which uncorrelated configurations of water molecules are extracted for use in DFT/GGA calculations of the electronic structure. We find that the density of occupied states of this molecular liquid is well described with 32 molecule supercells using a single k-point (k = 0) to approximate integration over the first Brillouin zone...

Prendergast, D; Galli, G; Prendergast, David; Grossman, Jeffrey C.; Galli, Giulia

2005-01-01

405

The Evolution of Density Structure of Starless and Protostellar Cores  

CERN Document Server

We present a near-infrared extinction study of nine dense cores at evolutionary stages between starless to Class I. Our results show that the density structure of all but one observed cores can be modeled with a single power law rho \\propto r^p between ~ 0.2R-R of the cores. The starless cores in our sample show two different types of density structures, one follows p ~ -1.0 and the other follows p ~ -2.5, while the protostellar cores all have p ~ -2.5. The similarity between the prestellar cores with p ~ -2.5 and protostellar cores implies that those prestellar cores could be evolving towards the protostellar stage. The slope of p ~ -2.5 is steeper than that of an singular isothermal sphere, which may be interpreted with the evolutionary model of cores with finite mass.

Hung, Chao-Ling; Yan, Chi-Hung

2009-01-01

406

Calculating the Energy Band Structure Using Sampling and Greens Function Techniques  

CERN Document Server

In this paper, a new method based on Greens function theory and Fourier transform analysis has been proposed for calculating band structure with high accuracy and low processing time. This method utilizes sampling of potential energy in some points of crystals unit cell with Dirac delta functions, then through lattice Fourier transform gives us a simple and applicable formula for most of nanostructures. Sampling of potential in a crystal lattice of any kind contains accurate approximation of actual potential energy of atoms in the crystal. The step forward regarding the method concentrated on two novel ideas, Firstly, the potential was sampled and approximated by delta functions spread over the unit cell. Secondly, the principal equation of lattice is translated into reciprocal lattice and resulted in a huge reduction of calculations. By this method, it is possible to extract the band structure of any one, two or three dimensional crystalline structure.

Khoshnegar, Milad; Arjmandi, Nima; Khorasani, Sina

2012-01-01

407

Experimental Studies Of W-band Accelerator Structures At High Field  

CERN Document Server

A high-gradient electron accelerator is desired for high- energy physics research, where frequency scalings of breakdown and trapping of itinerant beamline particles dictates operation of the accelerator at short wavelengths. The first results of design and test of a high-gradient mm-wave linac with an operating frequency at 91.392 GHz (W-band) are presented. A novel approach to particle acceleration is presented employing a planar, dielectric lined waveguide used for particle acceleration. The traveling wave fields in the planar dielectric accelerator (PDA) are analyzed for an idealized structure, along with a circuit equivalent model used for understanding the structure as a microwave circuit. Along with the W-band accelerator structures, other components designed and tested are high power rf windows, high power attenuators, and a high power squeeze-type phase shifter. The design of the accelerator and its components where eased with the aide of numerical simulations using a finite-difference electromagneti...

Hill, M E

2001-01-01

408

Energy band structure of LaCuOCh (Ch = S, Se and Te) calculated by the full-potential linearized augmented plane-wave method  

International Nuclear Information System (INIS)

Energy band diagrams of LaCuOCh (Ch = S, Se and Te) were calculated by a full-potential linearized augmented plane-wave method. The calculations, based on the local density approximation with/without an on-site Coulomb repulsion parameter, were to examine the energy levels of La 4f states. The results of the calculations showed that the on-site correlation parameter is necessary for evaluating the energy levels of La 4f states appropriately. The calculations for LaCuOCh with the on-site correlation parameter revealed that LaCuOS and LaCuOSe have almost the same energy band structure with a direct allowed-type band gap, while LaCuOTe has significantly different conduction band structure that exhibits an indirect-type band gap. This difference in electronic structure between LaCuOCh (Ch = S, Se and Te) is consistent with the observed optical properties of these materials.

2004-07-21

409

Structure of the doublet bands in doubly odd nuclei: The case of $^{128}Cs$  

CERN Multimedia

The structure of the $\\Delta J = 1$ doublet bands in $^{128}Cs$ is investigated within the framework of the Interacting Vector Boson Fermion Model (IVBFM). A new, purely collective interpretation of these bands is given on the basis of the used boson-fermion dynamical symmetry of the model. The energy levels of the doublet bands as well as the absolute $B(E2)$ and $B(M1)$ transition probabilities between the states of both yrast and yrare bands are described quite well. The observed odd-even staggering of both $B(M1)$ and $B(E2)$ values is reproduced by the introduction of an appropriate interaction term of quadrupole type, which produces such a staggering effect in the transition strengths. The calculations show that the appearance of doublet bands in certain odd-odd nuclei could be a consequence of the realization of a larger dynamical symmetry based on the non-compact supersymmetry group $OSp(2\\Omega /12, R)$.

Ganev, H G; 10.1103/PhysRevC.82.034328

2011-01-01

410

Similar rotational band structures in doubly-odd /sup 136/Pm and /sup 134/Pr  

International Nuclear Information System (INIS)

[en] The level structures of the doubly-odd nuclei /sup 136/Pm and /sup 134/Pr have been studied to high spin following the reactions /sup 114/Cd(27Al,5n)/sup 136/Pm, /sup 116/Sn(24Mg,p3n)/sup 136/Pm, and /sup 114/Cd(27Al,?3n)/sup 134/Pr. The two nuclei show very similar collective features. In both nuclei a rotational band built on the ?h/sub 11/2/x?h/sub 11/2/ configuration has been observed. This band shows a constant signature splitting of ?50 keV with no backbend in both cases. In addition, a sideband built on the ?[413](5/2+x?h/sub 11/2/ configuration has been observed in /sup 136/Pm. This band becomes yrast at high spins and shows a gain in alignment of ?8h at a frequency of h??0.28 MeV due to the decoupling of a pair of h/sub 11/2/ protons. In /sup 134/Pr the sideband was only observed above the band crossing. Experimental ratios of reduced transition probabilities, B(M1)/B(E2), have been extracted from transitions within the bands and compared to theoretical values obtained from a semiclassical model

1179-01-00

411

Density Functional Study of the structural properties in Tamoxifen  

Science.gov (United States)

Using the density functional theory, we have studied the structural properties of Tamoxifen. The calculations were performed with two methodological approaches, which were implemented in SIESTA and Spartan codes. For SIESTA, we considerate a linear combination of atomic orbitals method, using pseudopotentials and the van der Waals approximation for the exchange-correlation potential. Here we analyzed and compared the atomic structure between our results and other theoretical study. We found differences in the bond lengths between the results, that could be attributed to code approaches in each one.

de Coss-Martinez, Romeo; Tapia, Jorge A.; Quijano-Quiñones, Ramiro F.; Canto, Gabriel I.

2013-03-01

412

Explanation of persistent high frequency density structure in coalesced bunches  

International Nuclear Information System (INIS)

It has been observed that after the Main Ring rf manipulation of coalescing (where 5 to 13 primary bunches are transferred into a single rf bucket) the new secondary bunch displays evidence of high frequency density structure superimposed on the approximately Gaussian longitudinal bunch length distribution. This structure is persistent over a period of many seconds (hundreds of synchrotron oscillation periods). With the help of multiparticle simulation programs, an explanation of this phenomenon is given in terms of single particle longitudinal phase space dynamics. No coherent effects need be taken into account. 6 refs., 10 figs.

1988-01-01

413

Band Gap and Electronic Structure of an Epitaxial, Semiconducting Cr0.80Al0.20 Thin Film  

Science.gov (United States)

Cr1-xAlx exhibits semiconducting behavior for x=0.15-0.26. This Letter uses hard x-ray photoemission spectroscopy and density functional theory to further understand the semiconducting behavior. Photoemission measurements of an epitaxial Cr0.80Al0.20 thin film show several features in the valence band region, including a gap at the Fermi energy (EF) for which the valence band edge is 95±14meV below EF. Theory agrees well with the valence band measurements, and shows an incomplete gap at EF due to the hole band at M shifting almost below EF.

Boekelheide, Z.; Gray, A. X.; Papp, C.; Balke, B.; Stewart, D. A.; Ueda, S.; Kobayashi, K.; Hellman, F.; Fadley, C. S.

2010-12-01

414

Structural phase transitions and fundamental band gaps of MgxZn1 xO alloys from first principles  

Energy Technology Data Exchange (ETDEWEB)

The structural phase transitions and the fundamental band gaps of MgxZn1 xO alloys are investigated by detailed first-principles calculations in the entire range of Mg concentrations x, applying a multiple-scattering theoretical approach (Korringa-Kohn-Rostoker method). Disordered alloys are treated within the coherent-potential approximation. The calculations for various crystal phases have given rise to a phase diagram in good agreement with experiments and other theoretical approaches. The phase transition from the wurtzite to the rock-salt structure is predicted at the Mg concentration of x=0.33, which is close to the experimental value of 0.33 0.40. The size of the fundamental band gap, typically underestimated by the local-density approximation, is considerably improved by the self-interaction correction. The increase in the gap upon alloying ZnO with Mg corroborates experimental trends. Our findings are relevant for applications in optical, electrical, and, in particular, in magnetoelectric devices.

Maznichenko, I. V. [Martin-Luther University Halle-Wittenberg; Ernst, Arthur [Max Planck Institute of Microstructure Physics; Bouhassoune, M. [Max Planck Institute of Microstructure Physics; Henk, J. [Max Planck Institute of Microstructure Physics; Daene, Markus W [ORNL; Lueders, Martin [Daresbury Laboratory, UK; Bruno, Patrick [European Synchrotron Radiation Facility (ESRF); Wolfam, Hergert [Martin-Luther University Halle-Wittenberg; Mertig, I. [Martin-Luther University Halle-Wittenberg; Szotek, Zdzislawa [Daresbury Laboratory, UK; Temmerman, Walter M [Daresbury Laboratory, UK

2009-01-01

415

Molecular structure and vibrational spectra of Irinotecan: A density functional theoretical study  

Science.gov (United States)

The solid phase FTIR and FT-Raman spectra of Irinotecan have been recorded in the regions 400-4000 and 50-4000 cm-1, respectively. The spectra were interpreted in terms of fundamentals modes, combination and overtone bands. The structure of the molecule was optimized and the structural characteristics were determined by density functional theory (DFT) using B3LYP method with 6-31G(d) as basis set. The vibrational frequencies were calculated for Irinotecan by DFT method and were compared with the experimental frequencies, which yield good agreement between observed and calculated frequencies. The infrared spectrum was also simulated from the calculated intensities. Besides, molecular electrostatic potential (MEP), frontier molecular orbitals (FMO) analysis were investigated using theoretical calculations.

Chinna Babu, P.; Sundaraganesan, N.; Sudha, S.; Aroulmoji, V.; Murano, E.

2012-12-01

416

Increasing of frequency range of noise spectral density of silicon p-n-structures under gamma irradiation  

CERN Multimedia

One studied possibility of purpose-oriented shifting of high-frequency boundary of noise plateau-spectral density of silicon p-n-structures towards high frequency range under irradiation by gamma-quanta. One observed the maximum increase of frequency range working band up to 2-2.5 times. At further irradiation of the studied structures the plateau width was not increased and its boundary was eroded. One detected correlation between the variation of lifetime of charge secondary carriers and the width of low-frequency plateau of noise spectral density. One introduced a qualitative model to describe variation of noise spectral density with irradiation flow fro silicon p-n-structures governed by distances of p-n-transition

Baranovskij, O K; Kuchinskij, P V; Petrunin, A P; Savenok, E D

2001-01-01

417

Effect of cation substitution on electronic band structure of ZnGeAs{sub 2} pnictides: A mBJLDA approach  

Energy Technology Data Exchange (ETDEWEB)

Highlights: Black-Right-Pointing-Pointer These compounds are characterized as narrow band gap semiconductors with a maximum gap (1.27 eV) for ZnGeAs{sub 2}. Black-Right-Pointing-Pointer A good agreement of band gaps with experiments is obtained within mBJLDA formalism. Black-Right-Pointing-Pointer The band gap decreases with the substitution of either one or both cations in reference compound, ZnGeAs{sub 2}. Black-Right-Pointing-Pointer The ionic/covalent character for A-As/B-As bond has been described on the basis of electro-negativity difference of the atoms. Black-Right-Pointing-Pointer The d-states of transition metal, Zn are localized deeper in valence band (E < 5 eV), showing no effective role to decide the magnitude of semiconducting band gap. - Abstract: The electronic properties of ABAs{sub 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 (ZnGeAs{sub 2}) on these properties. The exchange and correlation (XC) effects are taken into account by an orbital independent modified Becke-Johnson (mBJ) potential as coupled with Local Density Approximation (LDA) for these calculations. We predict a direct band gap in all these compounds and observe that the band gap decreases with the change of either one or both cations. The calculated band gaps are in better agreement with corresponding experimental ones as compared to other calculations. The electronic band structure is analyzed in terms of contributions from various electrons and the covalency of two bonds, Zn-As and Ge-As has been discussed with respect to substitutions.

Saini, Hardev S.; Singh, Mukhtiyar [Department of Physics, Kurukshetra University, Kurukshetra 136119 (Haryana) (India); Reshak, Ali H. [School of Complex Systems, FFWP - South Bohemia University, 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); Kashyap, Manish K., E-mail: manishdft@gmail.com [Department of Physics, Kurukshetra University, Kurukshetra 136119 (Haryana) (India)

2012-03-25

418

IMPLICATIONS OF RELATIVISTIC CONFIGURATIONS AND BAND STRUCTURES IN THE PHYSICS OF BIO-MOLECULES AND SOLIDS  

DEFF Research Database (Denmark)

Beyond the second row of elements in the Mendeleev periodic table, the consideration of the relativistic effect is important in determining proper configurations of atoms and ions, in many cases. Many important quantities of interest in determining physical and chemical properties of matter, such as the effective charge, root mean square radii, and higher moments of radii used in many calculations, e.g. in the determinations of legend stabilization bond energies depend on whether the treatment is relativistic or not. In general, these quantities for a given l-orbital having two different j-values, e.g. d(3/2) and d(5/2), differ from each other, hence, making it necessary to treat them as separate orbitals. This also necessitates characterizing bands with their j-values in many instants and not l-values, particularly for "d" and f-orbitals. For example, in Au, 5d(3/2) and 5d(5/2) are to be dealt with as two distinct bands. The observed enhancement of laser induced field emission in W, which is not understood in terms of non-relativistic band-structures, can be explained in terms of the expected relativistic band structure. Spin-orbit coupling, which is the manifestation of the relativistic effect, is a prime factor in facilitating intersystem crossing in bio-molecules.

Islam, M. Fhokrul; Bohr, Henrik

2008-01-01

419

Microstructure and electronic band structure of pulsed laser deposited iron fluoride thin film for battery electrodes.  

UK PubMed Central (United Kingdom)

Battery electrodes in thin-film form are free of the binders used with traditional powder electrodes and present an ideal platform to obtain basic insight to the evolution of the electrode-electrolyte interface passivation layer, the formation of secondary phases, and the structural underpinnings of reversibility. This is particularly relevant to the not yet fully understood conversion electrode materials, which possess enormous potential for providing transformative capacity improvements in next-generation lithium-ion batteries. However, this necessitates an understanding of the electronic charge transport properties and band structure of the thin films. This work presents an investigation of the electron transport properties of iron fluoride (FeF2) thin-film electrodes for Li-ion batteries. FeF2 thin films were prepared by pulsed-laser deposition, and their phase purity was characterized by electron microscopy and diffraction. The grown materials are polycrystalline FeF2 with a P42/mnm crystallographic symmetry. Room-temperature Hall measurements reveal that as-deposited FeF2 is n-type: the Hall coefficients were negative, electron mobility was 0.33 cm2/(V s) and resistivity was 0.255 ? cm. The electronic band diagram of FeF2 was obtained using a combination of ultraviolet photoelectron spectroscopy, photoluminescence, photoluminescence excitation and optical absorption, which revealed that FeF2 is a direct bandgap, n-type semiconductor whose band structure is characterized by a 3.4 eV bandgap, a workfunction of ?4.51 eV, and an effective Fermi level that resides approximately 0.22 eV below the conduction band edge. We propose that the shallow donor levels at 0.22 eV are responsible for the measured n-type conductivity. The band diagram was used to understand electron transport in FeF2 thin film and FeF2-C composite electrodes.

Santos-Ortiz R; Volkov V; Schmid S; Kuo FL; Kisslinger K; Nag S; Banerjee R; Zhu Y; Shepherd ND

2013-04-01

420

Perturbative and nonperturbative parts of eigenstates and local spectral density of states The Wigner-band random-matrix model  

CERN Multimedia

A generalization of Brillouin-Wigner perturbation theory is applied numerically to the Wigner Band Random Matrix model. The perturbation theory tells that a perturbed energy eigenstate can be divided into a perturbative part and a non-perturbative part with the perturbative part expressed as a perturbation expansion. Numerically it is found that such a division is important in understanding many properties of both eigenstates and the so-called local spectral density of states (LDOS). For the average shape of eigenstates, its central part is found to be composed of its non-perturbative part and a region of its perturbative part, which is close to the non-perturbative part. A relationship between the average shape of eigenstates and that of LDOS can be explained. Numerical results also show that the transition for the average shape of LDOS from the Breit-Wigner form to the semicircle form is related to a qualitative change in some properties of the perturbation expansion of the perturbative parts of eigenstates...

Wang, W

2000-01-01

 
 
 
 
421

Demonstration of molecular beam epitaxy and a semiconducting band structure for I-Mn-V compounds  

International Nuclear Information System (INIS)

Our ab initio theory calculations predict a semiconducting band structure of I-Mn-V compounds. We demonstrate on LiMnAs that high-quality materials with group-I alkali metals in the crystal structure can be grown by molecular beam epitaxy. Optical measurements on the LiMnAs epilayers are consistent with the theoretical electronic structure. Our calculations also reproduce earlier reports of high antiferromagnetic ordering temperature and predict large, spin-orbit-coupling-induced magnetic anisotropy effects. We propose a strategy for employing antiferromagnetic semiconductors in high-temperature semiconductor spintronics.

2011-01-01

422

A quantitative discussion on band-gap energy and carrier density of CdO in terms of temperature and oxygen partial pressure  

International Nuclear Information System (INIS)

Calculations relative to the band-gap energy shift and carrier spatial density in cadmium oxide are performed in terms of the oxygen partial pressure and substrate temperature relative to the deposition process in the crystal growth of the above material, starting from the consideration of the Fermi energy of an exciton gas. In particular, the band-gap shift experienced by cadmium oxide in terms of the corresponding partial pressure of oxygen is considered as well as the electron spatial density as a function of the pressure in question. Influence of temperature is discussed by estimating the average rate of variation of the band-gap shift versus temperature. In addition, the sensitivity of the above-mentioned shift to temperature is studied by means of a suitable parameter.

2008-06-30

423

Analysis of the Band-Structure in (Ga, Mn)As Epitaxial Layers by Optical Methods  

Directory of Open Access Journals (Sweden)

Full Text Available The ternary III-V semiconductor (Ga, Mn)As has recently drawn a lot of attention as the model diluted ferromagnetic semiconductor, combining semiconducting properties with magnetism. (Ga, Mn)As layers are usually gown by the low-temperature molecular-beam epitaxy (LT-MBE) technique. Below a magnetic transition temperature, TC, substitutional Mn2+ ions are ferromagnetically ordered owing to interaction with spin-polarized holes. However, the character of electronic states near the Fermi energy and the electronic structure in ferromagnetic (Ga, Mn)As are still a matter of controversy. The photoreflectance (PR) spectroscopy was applied to study the band-structure evolution in (Ga, Mn)As layers with increasing Mn content. We have investigated thick (800-700 nm and 230-300 nm) (Ga, Mn)As layers with Mn content in the wide range from 0.001 % to 6 % and, as a reference, undoped GaAs layer, grown by LT-MBE on semi-insulating (001) GaAs substrates. Our findings were interpreted in terms of the model, which assumes that the mobile holes residing in the valence band of ferromagnetic (Ga, Mn)As and the Fermi level position determined by the concentration of valence-band holes. The ternary III-V semiconductor (Ga, Mn)As has recently drawn a lot of attention as the model diluted ferromagnetic semiconductor, combining semiconducting properties with magnetism. (Ga, Mn)As layers are usually gown by the low-temperature molecular-beam epitaxy (LT-MBE) technique. Below a magnetic transition temperature, TC, substitutional Mn2+ ions are ferromagnetically ordered owing to interaction with spin-polarized holes. However, the character of electronic states near the Fermi energy and the electronic structure in ferromagnetic (Ga, Mn)As are still a matter of controversy. The photoreflectance (PR) spectroscopy was applied to study the band-structure evolution in (Ga, Mn)As layers with increasing Mn content. We have investigated thick (800-700 nm and 230-300 nm) (Ga, Mn)As layers with Mn content in the wide range from 0.001 % to 6 % and, as a reference, undoped GaAs layer, grown by LT-MBE on semi-insulating (001) GaAs substrates. Our findings were interpreted in terms of the model, which assumes that the mobile holes residing in the valence band of ferromagnetic (Ga, Mn)As and the Fermi level position determined by the concentration of valence-band holes. The ternary III-V semiconductor (Ga, Mn)As has recently drawn a lot of attention as the model diluted ferromagnetic semiconductor, combining semiconducting properties with magnetism. (Ga, Mn)As layers are usually gown by the low-temperature molecular-beam epitaxy (LT-MBE) technique. Below a magnetic transition temperature, TC, substitutional Mn2+ ions are ferromagnetically ordered owing to interaction with spin-polarized holes. However, the character of electronic states near the Fermi energy and the electronic structure in ferromagnetic (Ga, Mn)As are still a matter of controversy. The photoreflectance (PR) spectroscopy was applied to study the band-structure evolution in (Ga, Mn)As layers with increasing Mn content. We have investigated thick (800-700 nm and 230-300 nm) (Ga, Mn)As layers with Mn content in the wide range from 0.001 % to 6 % and, as a reference, undoped GaAs layer, grown by LT-MBE on semi-insulating (001) GaAs substrates. Our findings were interpreted in terms of the model, which assumes that the mobile holes residing in the valence band of ferromagnetic (Ga, Mn)As and the Fermi level position determined by the concentration of valence-band holes.

O. Yastrubchak

2012-01-01

424