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1

Strain effects on valence bands of wurtzite ZnO  

Science.gov (United States)

Based on the k.p theory of Luttinger-Kohn and Bir-Pikus, analytical E-k solutions for the valence band of strained wurtzite ZnO materials are obtained. Strain effects on valence band edges and hole effective masses in strained wurtzite ZnO materials are also discussed. In comparison with unstrained ZnO materials, apparent movement of valence band edges such as "light hole band", "heavy hole band" and "crystal splitting band" at ? point is found in strained wurtzite ZnO materials. Moreover, effective masses of "light hole band", "heavy hole band" and "crystal splitting band" for strained wurtzite ZnO materials as the function of stress are given. The analytical results can provide a theoretical foundation for the understanding of physics of strained ZnO materials and its applications with the framework for an effective mass theory.

Qiao, LiPing; Chai, ChangChun; Jin, Zhao; Yang, YinTang; Ma, ZhenYang

2013-09-01

2

Valence band anticrossing in GaBixAs1-x  

Energy Technology Data Exchange (ETDEWEB)

The optical properties of GaBixAs1-x (0.04< x< 0.08) grown by molecular beam epitaxy have been studied by photomodulated reflectance spectroscopy. The alloys exhibit a strong reduction in the bandgap as well as an increase in the spin-orbit splitting energy with increasing Bi concentration. These observations are explained by a valence band anticrossing model, which shows that a restructuring of the valence band occurs as the result of an anticrossing interaction between the extended states of the GaAs valence band and the resonant T2 states of the Bi atoms.

Alberi, K.; Dubon, O. D.; Walukiewicz, W.; Yu, K. M.; Bertulis, K.; Krotkus, A.

2007-07-11

3

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

4

Quasicrystalline valence bands in decagonal AlNiCo  

Science.gov (United States)

Quasicrystals are metallic alloys that possess perfect long-range structural order, in spite of the fact that their rotational symmetries are incompatible with long-range periodicity. The exotic structural properties of this class of materials are accompanied by physical properties that are unexpected for metallic alloys. Considerable progress in resolving the geometric structures of quasicrystals has been made using X-ray and neutron diffraction, and concepts such as the quasi-unit-cell model have provided theoretical insights. But the basic properties of the valence electronic states-whether they are extended as in periodic crystals or localized as in amorphous materials-are still largely unresolved. Here we investigate the electronic bandstructure of quasicrystals through angle-resolved photoemission experiments on decagonal Al71.8Ni14.8Co13.4. We find that the s-p and d states exhibit band-like behaviour with the symmetry of the quasiperiodic lattice, and that the Fermi level is crossed by dispersing d-bands. The observation of free-electron-like bands, distributed in momentum space according to the surface diffraction pattern, suggests that the electronic states are not dominated by localization.

Rotenberg, Eli; Theis, W.; Horn, K.; Gille, P.

2000-08-01

5

Quasicrystalline valence bands in decagonal AlNiCo  

UK PubMed Central (United Kingdom)

Quasicrystals are metallic alloys that possess perfect long-range structural order, in spite of the fact that their rotational symmetries are incompatible with long-range periodicity. The exotic structural properties of this class of materials are accompanied by physical properties that are unexpected for metallic alloys. Considerable progress in resolving the geometric structures of quasicrystals has been made using X-ray and neutron diffraction, and concepts such as the quasi-unit-cell model have provided theoretical insights. But the basic properties of the valence electronic states--whether they are extended as in periodic crystals or localized as in amorphous materials--are still largely unresolved. Here we investigate the electronic bandstructure of quasicrystals through angle-resolved photoemission experiments on decagonal Al71.8Ni14.8Co13.4. We find that the s-p and d states exhibit band-like behaviour with the symmetry of the quasiperiodic lattice, and that the Fermi level is crossed by dispersing d-bands. The observation of free-electron-like bands, distributed in momentum space according to the surface diffraction pattern, suggests that the electronic states are not dominated by localization.

Rotenberg E; Theis W; Horn K; Gille P

2000-08-01

6

Valence band spectroscopy in V-grooved quantum wires  

CERN Document Server

We present a combined theoretical and experimental study of the anisotropy in the optical absorption of V-shaped quantum wires. By means of realistic band structure calculations for these structures, we show that detailed information on the heavy- and light-hole states can be singled out from the anisotropy spectra {\\em independently of the electron confinement}, thus allowing accurate valence band spectroscopy.

Goldoni, G; Molinari, E; Fasolino, A; Rinaldi, R; Cingolani, R

1996-01-01

7

Photon energy dependent valence band response of metallic nanoparticles.  

UK PubMed Central (United Kingdom)

We show that the valence band response to photon impact in metallic nanoparticles is highly energy dependent. This is seen as drastic variations of cross sections in valence photoionization of free and initially charge-neutral nanosized metal clusters. The effect is demonstrated in a combined experimental and theoretical study of Rb clusters. The experimental findings are interpreted theoretically using a jellium model and superatom description. The variations are attributed to the changing overlap with the photon energy between the wave functions of diffuse delocalized valence electrons and continuum electrons producing a series of minima in the cross section.

Jänkälä K; Tchaplyguine M; Mikkelä MH; Björneholm O; Huttula M

2011-10-01

8

Photon energy dependent valence band response of metallic nanoparticles.  

Science.gov (United States)

We show that the valence band response to photon impact in metallic nanoparticles is highly energy dependent. This is seen as drastic variations of cross sections in valence photoionization of free and initially charge-neutral nanosized metal clusters. The effect is demonstrated in a combined experimental and theoretical study of Rb clusters. The experimental findings are interpreted theoretically using a jellium model and superatom description. The variations are attributed to the changing overlap with the photon energy between the wave functions of diffuse delocalized valence electrons and continuum electrons producing a series of minima in the cross section. PMID:22107629

Jänkälä, K; Tchaplyguine, M; Mikkelä, M-H; Björneholm, O; Huttula, M

2011-10-25

9

Valence-band states of ion-bombarded polystyrene  

International Nuclear Information System (INIS)

[en] Ion-bombarded polystyrene with a 0.5-keV Ar+ beam has been investigated by means of photoelectron spectroscopy performed with synchrotron radiation. After a dose of 1015 ions/cm2 the evolution of the valence band of the bombarded sample towards an amorphous carbonlike configuration is reported. From the analysis of valence-band spectra we estimated the out-diffusion of hydrogen and showed that its electronic states remain well identified and stable until the hydrogen presence is about 35% with respect to the pristine sample. Finally, comparison with mass spectroscopy measurements on deuterated polystyrene has been performed to determine hydrogen evolution during the ion irradiation

1991-08-01

10

Molecular Dispersion of Chains in the Mixed-Valence Complexes  

UK PubMed Central (United Kingdom)

A way to prepare molecular electronic wires in organic media is the solubilization of one-dimensional mixed-valence complexes with varied metal species through the formation of amphiphilic supramolecular assemblies (see picture). Dissociation and reassembly of the complex was detected as thermochromism in the intervalence (M(II)-->M(IV)) absorption bands.

Kimizuka N; Lee SH; Kunitake T

2000-01-01

11

Instanton contributions to the valence band of the double Sine-Gordon potential  

International Nuclear Information System (INIS)

The energy dispersion relation for the valence band of the double sine-Gordon potential is calculated, approximating the tunneling amplitude by a sum of contributions of multi-instantons and anti-instatons trajectories. The interesting feature of this potential is that they have to deal with two types of instantons, as there are two different potential barriers within one period of the potential. The results with the standard WKB approximation are compared. (Author).

1982-01-01

12

Valence-band states of ion-bombarded polystyrene  

Energy Technology Data Exchange (ETDEWEB)

Ion-bombarded polystyrene with a 0.5-keV Ar{sup +} beam has been investigated by means of photoelectron spectroscopy performed with synchrotron radiation. After a dose of 10{sup 15} ions/cm{sup 2} the evolution of the valence band of the bombarded sample towards an amorphous carbonlike configuration is reported. From the analysis of valence-band spectra we estimated the out-diffusion of hydrogen and showed that its electronic states remain well identified and stable until the hydrogen presence is about 35% with respect to the pristine sample. Finally, comparison with mass spectroscopy measurements on deuterated polystyrene has been performed to determine hydrogen evolution during the ion irradiation.

Terrasi, A. (Istituto di Metodologie e Tecnologie per la Microelettronica, CNR, Corso Italia 57, 95129 Catania, Italy (IT)); Foti, G. (Dipartimento di Fisica, Universita di Catania, Corso Italia 57, 95129 Catania, (Italy)); Hwu, Y. (Synchrotron Radiation Center, University of Wisconsin-Madison, 3731 Schneider Drive, Stoughton, Wisconsin 53589-3097 (USA)); Margaritondo, G. (Ecole Polytechnique Federale de Lausanne, Department de Physique, PHB-Ecublens, CH 1015 Lausanne, (Switzerland))

1991-08-01

13

Recoil effects in valence band photoemission of organic solids.  

Science.gov (United States)

Recoil effects in valence band X-ray photoelectron spectroscopy (XPS) are studied for both abb-trifluorostyrene and styrene molecular crystal systems. The gradual changes of XPS spectra excited by several photon energies are theoretically investigated within the tight-binding approximation and harmonic approximation of lattice vibrations and have been explained in terms of not only atomic mass but also atomic orbital (AO) population. The recoil effect of valence band photoemission strongly depends on the population and partial photoionization cross section (PICS) of AOs as well as the masses of composite atoms. In abb-trifluorostyrene F 2p dominant bands show the recoil shift close to free F atom recoil shift, and C 2s dominant bands show that to free C atom recoil shift, whereas the mixed bands of C and F give rise to the peak asymmetries due to their different recoil shifts. For these systems, hydrogen contribution is negligibly small which is in contrast to our previous results for the crystals composed of small organic molecules. We also discuss some potential uses of the recoil shifts for these systems. PMID:23441983

Shang, Ming-Hui; Fujikawa, Takashi; Ueno, Nobuo

2013-03-18

14

Recoil effects in valence band photoemission of organic solids.  

UK PubMed Central (United Kingdom)

Recoil effects in valence band X-ray photoelectron spectroscopy (XPS) are studied for both abb-trifluorostyrene and styrene molecular crystal systems. The gradual changes of XPS spectra excited by several photon energies are theoretically investigated within the tight-binding approximation and harmonic approximation of lattice vibrations and have been explained in terms of not only atomic mass but also atomic orbital (AO) population. The recoil effect of valence band photoemission strongly depends on the population and partial photoionization cross section (PICS) of AOs as well as the masses of composite atoms. In abb-trifluorostyrene F 2p dominant bands show the recoil shift close to free F atom recoil shift, and C 2s dominant bands show that to free C atom recoil shift, whereas the mixed bands of C and F give rise to the peak asymmetries due to their different recoil shifts. For these systems, hydrogen contribution is negligibly small which is in contrast to our previous results for the crystals composed of small organic molecules. We also discuss some potential uses of the recoil shifts for these systems.

Shang MH; Fujikawa T; Ueno N

2013-04-01

15

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

16

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

17

Microscopic analysis of the valence band and impurity band theories of (Ga,Mn)As.  

UK PubMed Central (United Kingdom)

We analyze microscopically the valence and impurity band models of ferromagnetic (Ga,Mn)As. We find that the tight-binding Anderson approach with conventional parametrization and the full potential local-density approximation+U calculations give a very similar band structure whose microscopic spectral character is consistent with the physical premise of the k·p kinetic-exchange model. On the other hand, the various models with a band structure comprising an impurity band detached from the valence band assume mutually incompatible microscopic spectral character. By adapting the tight-binding Anderson calculations individually to each of the impurity band pictures in the single Mn impurity limit and then by exploring the entire doping range, we find that a detached impurity band does not persist in any of these models in ferromagnetic (Ga,Mn)As.

Mašek J; Máca F; Kudrnovský J; Makarovsky O; Eaves L; Campion RP; Edmonds KW; Rushforth AW; Foxon CT; Gallagher BL; Novák V; Sinova J; Jungwirth T

2010-11-01

18

Conduction- and valence-band effective masses in spontaneously ordered GaInP2  

International Nuclear Information System (INIS)

[en] An eight-band k·p model is developed for zinc-blende semiconductor alloys that exhibit spontaneous CuPt ordering. Energy dispersions and effective masses are calculated analytically for the conduction band and valence band as a function of the degree of ordering. All the effective-mass tensors are found to be diagonal and the energy dispersions are ellipsoidal to terms quadratic in the wave vector when the axis of quantization (the z direction) is chosen along the ordering direction. The change of effective masses is found to satisfy a sum rule when ordering is weak. Numerical results are given for the ordered GaInP2 alloy. We find that, as the order parameter increases, along the ordering direction, mparallel is unchanged for the heavy-hole band, increases for the light-hole band, and decreases for the spin-orbit split-off band. In the plane perpendicular to the ordering direction, mperpendicular for the heavy- and light-hole bands decreases, whereas it increases for the split-off band. For the conduction band, both mparallel and mperpendicular decrease

1995-05-15

19

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

20

Separability Between Valence and Conduction Bands in Transition Metal Clusters  

Energy Technology Data Exchange (ETDEWEB)

Simplified theories of transition metal electronic structure have been postulated for many decades. Here we test one such approximation, namely separate treatments of d (valence) and s/p (conduction) electrons in transition metal clusters, within a density functional formalism. Two different basic approaches are considered: (a) an independent-band approximation, in which the d- and s/p-bands interact only via the ?-dependent components of the Kohn-Sham operator; and (b) a more realistic approximation, in which the lowest-energy d- and s/p-orbitals (separately derived) are allowed to interact through explicit off-diagonal coupling matrix elements. Results are presented for the energy differences among three structural forms (icosahedral, cuboctahedral and truncated decahedral) of 13-atom Ni and Pt clusters. We demonstrate that an explicit decoupling of the d- and s/p-bands does not produce accurate results for the clusters considered here, not even for nickel, i.e., the transition metal for which d-s/p mixing should be at its minimum. By contrast, allowing the lowest energy orbitals of the two separate bands to interact improves the results considerably, and assures a fair description of metal-metal bonding. This suggests simplified models that exclude explicit d-s/p coupling should be employed with caution.

Apra, Edoardo; Carter, Emily A.; Fortunelli, Alessandro

2004-07-30

 
 
 
 
21

The Role of Fermi Resonance in Formation of Valence Band of Water Raman Scattering  

Directory of Open Access Journals (Sweden)

Full Text Available The role of Fermi resonance in formation of valence band of water Raman scattering was investigated. Simultaneous measurement of characteristics of bending and valence bands of water in D2O solutions, KBr, and KCl and using genetic algorithms in conjunction with variation methods allowed increasing accuracy of estimation of Fermi resonance coupling constant and of Fermi resonance contribution into formation of water Raman valence band.

Sergey A. Burikov; Tatiana A. Dolenko; Victor V. Fadeev

2008-01-01

22

Valence-band photoemission spectroscopy of a single-crystal FePt{sub 3}  

Energy Technology Data Exchange (ETDEWEB)

The valence-band electronic structure of a single-crystal FePt{sub 3} alloy in a paramagnetic phase has been investigated by photoemission spectroscopy using synchrotron radiation. A well-characterized (1 0 0) surface was carefully prepared in an ultrahigh vacuum chamber. A sharp truncated peak was clearly observed just below the Fermi level at photon energy of 190 eV (Pt Cooper minimum). This peak corresponds to the tail of Fe 3d minority-spin band and enhances its intensity around the X point in the Brillouin zone as is predicted by band calculation. Several broad peaks were also observed and their dispersion were in accord with the Brillouin zone.

Tobita, N. [Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8526 (Japan)]. E-mail: nao-tobita@hiroshima-u.ac.jp; Emi, K. [Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8526 (Japan); Nakajima, N. [Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8526 (Japan); Maruyama, H. [Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8526 (Japan); Miura, Y. [Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8526 (Japan); Higashiguchi, M. [Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8526 (Japan); Shimada, K. [HSRC, Hiroshima University, Higashi-Hiroshima 739-0046 (Japan); Namatame, H. [HSRC, Hiroshima University, Higashi-Hiroshima 739-0046 (Japan); Taniguchi, M. [Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8526 (Japan); HSRC, Hiroshima University, Higashi-Hiroshima 739-0046 (Japan)

2007-03-15

23

Band terminations in the valence space of {sup 86}Zr  

Energy Technology Data Exchange (ETDEWEB)

High-spin states in {sup 86}Zr up to 30{sup +} and 27{sup -} were observed via the {sup 58}Ni({sup 32}S,4p) reaction at 135 MeV beam energy using the combined GAMMASPHERE and MICROBALL systems. Calculations performed with the configuration-dependent shell-correction approach show that these states are built from six g{sub 9/2} neutrons and at most four protons excited from the p{sub 1/2},p{sub 3/2},f{sub 5/2} subshells to the g{sub 9/2} subshell at small deformation. The highest observed states at 27{sup -} and 30{sup +} are interpreted as band-terminating states with the latter having the highest spin available in the valence space for {sup 86}Zr. (c) 2000 The American Physical Society.

Doering, J. [Department of Physics, Florida State University, Tallahassee, Florida 32306 (United States); Gesellschaft fuer Schwerionenforschung mbH, D-64291 Darmstadt, (Germany); Akovali, Y. A. [Physics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Baktash, C. [Physics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Durham, F. E. [Department of Physics, Tulane University, New Orleans, Louisiana 70118 (United States); Gross, C. J. [UNISOR, Oak Ridge Institute of Science and Education, Oak Ridge, Tennessee 37831 (United States); Hua, P. F. [Chemistry Department, Washington University, St. Louis, Missouri 63130 (United States); Johns, G. D. [Department of Physics, Florida State University, Tallahassee, Florida 32306 (United States); Korolija, M. [Chemistry Department, Washington University, St. Louis, Missouri 63130 (United States); LaFosse, D. R. [Chemistry Department, Washington University, St. Louis, Missouri 63130 (United States); Lee, I. Y. [Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)] (and others)

2000-03-01

24

Band terminations in the valence space of 86Zr  

International Nuclear Information System (INIS)

High-spin states in 86Zr up to 30+ and 27- were observed via the 58Ni(32S,4p) reaction at 135 MeV beam energy using the combined GAMMASPHERE and MICROBALL systems. Calculations performed with the configuration-dependent shell-correction approach show that these states are built from six g9/2 neutrons and at most four protons excited from the p1/2,p3/2,f5/2 subshells to the g9/2 subshell at small deformation. The highest observed states at 27- and 30+ are interpreted as band-terminating states with the latter having the highest spin available in the valence space for 86Zr. (c) 2000 The American Physical Society

2000-01-01

25

Interband electronic Raman scattering of polarized light in cubic semiconductors with degenerate valence bands  

International Nuclear Information System (INIS)

[en] The cross-sections are calculated for the Raman scattering processes with polarized light in cubic semiconductors where the valence band top is fourfold degenerate ?8. The exciton effect is taken into account. (author). 17 refs

1987-01-01

26

Determination of a natural valence-band offset: The case of HgTe-CdTe  

Energy Technology Data Exchange (ETDEWEB)

We propose a method to determine a natural valence-band offset (NVBO), i.e., the change in the valence-band maximum energy which is intrinsic to the bulk band structure of semiconductors. We use the Hg-Te-CdTe system as an example in which we find that the valence-band maximum of HgTe lies 0.35 +- 0.06 eV above that of CdTe. The NVBO of 0.35 eV is in good agreement with the x-ray photoemission spectroscopy measurement of the heterojunction offset. The procedure to determine the NVBO between semiconductors, and its implication of the heterojunction band line-up and the electronic structures of semiconductor alloys, are discussed.

Shih, C.K.; Spicer, W.E.

1987-06-15

27

Highly dispersive photonic band-gap prism  

Energy Technology Data Exchange (ETDEWEB)

We propose the concept of a photonic band-gap (PBG) prism based on two-dimensional PBG structures and realize it in the millimeter-wave spectral regime. We recognize the highly nonlinear dispersion of PBG materials near Brillouin zone edges and utilize the dispersion to achieve strong prism action. Such a PBG prism is very compact if operated in the optical regime, {approximately}20{mu}m in size for {lambda}{approximately}700nm, and can serve as a dispersive element for building ultracompact miniature spectrometers. {copyright} {ital 1996 Optical Society of America.}

Lin, S.; Hietala, V.M.; Wang, L.; Jones, E.D. [Sandia National Laboratories, P. O. Box 5800, Albuquerque, New Mexico 87185 (United States)

1996-11-01

28

Theory of two-photon absorption by exciton states in cubic semiconductors with degenerate valence bands  

International Nuclear Information System (INIS)

[en] The coefficient of the absorption of two polarized photons is calculated for direct band gap semiconductors with degenerate valence bands. Wannier-Mott exciton states are included in both the intermediate and final states. Numerical calculations are performed for ZnSe and are compared with Sondergeld's experimental and theoretical results. (author). 11 refs, 2 tabs

1987-01-01

29

Valence band hybridization in N-rich GaN1-xAsx alloys  

Energy Technology Data Exchange (ETDEWEB)

We have used photo-modulated transmission and optical absorption spectroscopies to measure the composition dependence of interband optical transitions in N-rich GaN{sub 1-x}As{sub x} alloys with x up to 0.06. The direct bandgap gradually decreases as x increases. In the dilute x limit, the observed band gap approaches 2.8 eV; this limiting value is attributed to a transition between the As localized level, which has been previously observed in As-doped GaN at 0.6 eV above the valence band maximum in As-doped GaN, and the conduction band minimum. The structure of the valence band of GaN{sub 1-x}As{sub x} is explained by the hybridization of the localized As states with the extended valence band states of GaN matrix. The hybridization is directly confirmed by soft x-ray emission experiments. To describe the electronic structure of the GaN{sub 1-x}As{sub x} alloys in the entire composition range a linear interpolation is used to combine the effects of valence band hybridization in N-rich alloys with conduction band anticrossing in As-rich alloys.

Wu, J.; Walukiewicz, W.; Yu, K.M.; Denlinger, J.D.; Shan, W.; Ager III, J.W.; Kimura, A.; Tang, H.F.; Kuech, T.F.

2004-05-04

30

Angle-dependent oscillations in valence-band photoemission intensity of C{sub 60}  

Energy Technology Data Exchange (ETDEWEB)

High-resolution angle-resolved photoelectron spectroscopy (ARPES) has been performed to investigate valence-band photoemission in C{sub 60} single crystals, which were cleaved in ultra-high-vacuum systems. The results present angle-dependent modulations in intensities of valence-band photoemission of the C{sub 60} single crystal. The observed intensity modulations are caused by polarization influence and photoelectron diffraction (PED) effects, of which the latter is also responsible for the similar oscillations produced by varying incident photon energies. The calculated results indicate that only photoelectrons scattered by the top hemisphere of C{sub 60} molecules dominate the angle-dependent interference modulations.

He, S [Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526 (Japan); Arita, M [Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526 (Japan); Namatame, H [Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526 (Japan); Taniguchi, M [Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526 (Japan); Li, H-N [Department of Physics, Zhejiang University, Hangzhou 310027 (China); Li, H-Y [Department of Physics, Zhejiang University, Hangzhou 310027 (China)

2007-01-17

31

Rotational bands terminating at maximal spin in the valence space  

Energy Technology Data Exchange (ETDEWEB)

For nuclei with mass A {le} 120, the spin available in {open_quotes}normal deformation configurations{close_quotes} is experimentally accessible with present detector systems. Of special interest are the nuclei which show collective features at low or medium-high spin and where the corresponding rotational bands with increasing spin can be followed in a continuous way to or close to a non-collective terminating state. Some specific features in this context are discussed for nuclei in the A = 80 region and for {sup 117,118}Xe.

Ragnarsson, I.; Afanasjev, A.V. [Lund Institute of Technology (Sweden)

1996-12-31

32

Theoretical analysis of optical gain in quantum well lasers including valence band-mixing effect  

International Nuclear Information System (INIS)

[en] The linear optical gain in the AlGaAs/GaAs quantum well lasers is studied theoretically, taking into account the valence-band mixing effect. Our approach is based on the multiband effective-mass theory (k p method) and the density-matrix formalism. In order to obtain the valence band's structure we employ the 4x4 Luttinger-Kohn Hamiltonian, neglecting the coupling to the split-off band. The spectral dependence of the linear optical gain is calculated using the density-matrix method with interband relaxation. Finally, we analyse the spatial distribution of the optical gain in the quantum well region for the photon energy corresponding to the peak value of the linear gain. (author)

1997-01-01

33

Application of factor analysis to XPS valence band of superparamagnetic iron oxide nanoparticles  

Energy Technology Data Exchange (ETDEWEB)

X-Ray photoelectron spectra of nano-sized superparamagnetic iron oxide nanoparticles were examined with the aim to discriminate the different degree of iron oxidation. Careful analysis of the valence band regions reveals the presence of both Fe{sub 3}O{sub 4} and Fe{sub 2}O{sub 3}. The application of factor analysis enabled us to extract the relative molar concentrations of these oxides in the nanoparticles. This is of particular interest in improving the magnetic properties of iron oxide nanoparticles whose superparamagnetic character can be optimized to obtain better contrast in images from nuclear magnetic resonance. As a result, the factor analysis allows tuning the nanoparticle synthesis conditions in order to obtain the optimal magnetic properties for imaging. Results obtained by the XPS valence band analysis were compared to the transmission electron microscopy, X-ray diffraction and Raman measurements.

Minati, L., E-mail: luminati@fbk.eu [FBK, Via Sommarive 18, Povo 38123 Trento (Italy); Micheli, V. [FBK, Via Sommarive 18, Povo 38123 Trento (Italy); Rossi, B. [FBK, Via Sommarive 18, Povo 38123 Trento (Italy); Dept. Physics University of Trento, Via Sommarive 14, Povo 38123 Trento (Italy); Migliaresi, C.; Dalbosco, L. [Dept. Material Engineering and Industrial Technologies University of Trento, via Mesiano 77, 38100 Trento (Italy); Bao, G.; Hou, S. [Dept. of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA 30332-0535 (United States); Speranza, G. [FBK, Via Sommarive 18, Povo 38123 Trento (Italy)

2011-10-01

34

Application of factor analysis to XPS valence band of superparamagnetic iron oxide nanoparticles  

International Nuclear Information System (INIS)

X-Ray photoelectron spectra of nano-sized superparamagnetic iron oxide nanoparticles were examined with the aim to discriminate the different degree of iron oxidation. Careful analysis of the valence band regions reveals the presence of both Fe3O4 and Fe2O3. The application of factor analysis enabled us to extract the relative molar concentrations of these oxides in the nanoparticles. This is of particular interest in improving the magnetic properties of iron oxide nanoparticles whose superparamagnetic character can be optimized to obtain better contrast in images from nuclear magnetic resonance. As a result, the factor analysis allows tuning the nanoparticle synthesis conditions in order to obtain the optimal magnetic properties for imaging. Results obtained by the XPS valence band analysis were compared to the transmission electron microscopy, X-ray diffraction and Raman measurements.

2011-10-01

35

On the theory of phonoriton in cubic semiconductors with a degenerate valence band  

International Nuclear Information System (INIS)

[en] The ''phonoriton'' is an elementary excitation constructed from an exciton polariton and phonon in semiconductors under intense excitation by an electromagnetic wave near the exciton resonance (L.V. Keldysh and A.L. Ivanov, 1982). In this paper we develop a theory of phonoriton in direct band gap cubic semiconductor with a degenerate valence band using the simple model of J.L. Birman and B.S. Wang (1990). In addition to experimental proofs of the existence of phonoriton we propose an experiment to measure its flight time. (author). 33 refs

1992-01-01

36

Band-like valence states in d-AlNiCo Quasicrystals  

Science.gov (United States)

A central question for quasicrystals (QCs) is the nature of the valence electronic states: whether or not they consist of Bloch-like states which are extended as in conventional periodic crystals. In this work we report the existence of extended band-like valence states in d-AlNiCo QCs. These states are measured using momentum (k)-resolved photoemission measurements on samples which were prepared by sputter-annealing and characterized with low energy electron diffraction (LEED). Similar to conventional transition metals and ordered alloys, both parabolic sp bands and flatter d bands are found below and crossing the Fermi level. We will show that for the layered quasicrystals, these bands reflect the nature of the quasicrystal ordering in decagonal QCs: periodic in the direction normal to the decagonal layers, and aperiodic parallel to these layers. Furthermore, in-plane sp-like parabolic bands are seen to emanate from the same points in k-space at which bright LEED spots are found.

Horn, K.; Rotenberg, Eli; Theis, W.

2000-03-01

37

Band width and multiple-angle valence-state mapping of diamond  

Energy Technology Data Exchange (ETDEWEB)

The band width may be considered the single most important parameter characterizing the electronic structure of a solid. The ratio of band width and Coulomb repulsion determines how correlated or delocalized an electron system is. Some of the most interesting solids straddle the boundary between localized and delocalized, e.g. the high-temperature superconductors. The bulk of the band calculations available today is based on local density functional (DF) theory. Even though the Kohn-Sham eigenvalues from that theory do not represent the outcome of a band-mapping experiment, they are remarkably similar to the bands mapped via photoemission. Strictly speaking, one should use an excited state calculation that takes the solid`s many-body screening response to the hole created in photoemission into account. Diamond is a useful prototype semiconductor because of its low atomic number and large band width, which has made it a long-time favorite for testing band theory. Yet, the two experimental values of the band width of diamond have error bars of {+-}1 eV and differ by 3.2 eV. To obtain an accurate valence band width for diamond, the authors use a band-mapping method that collects momentum distributions instead of the usual energy distributions. This method has undergone extensive experimental and theoretical tests in determining the band width of lithium fluoride. An efficient, imaging photoelectron spectrometer is coupled with a state-of-the-art undulator beam line at the Advanced Light Source to allow collection of a large number of data sets. Since it takes only a few seconds to take a picture of the photoelectrons emitted into a 84{degrees} cone, the authors can use photon energies as high as 350 eV where the cross section for photoemission from the valence band is already quite low, but the emitted photoelectrons behave free-electron-like. This make its much easier to locate the origin of the inter-band transitions in momentum space.

Jimenez, I.; Terminello, L.J.; Sutherland, D.G.J. [Lawrence Berkeley National Lab., CA (United States)] [and others

1997-04-01

38

Pressure variation of the valence band width in Ge: A self-consistent GW study  

DEFF Research Database (Denmark)

Analyzing x-ray emission spectra XES of germanium under pressure Struzhkin et al. [Phys. Rev. Lett. 96, 137402 (2006)] found that the valence band width of diamond Ge does not vary with pressure. This contradicts the usual experience and also what is predicted by density-functional calculations. In the present work we report results of quasiparticle self-consistent GW  (QSGW) band calculations for diamond- as well as ?-tin-type Ge under pressure. For both phases we find that the band width increases with pressure. For ?-tin Ge this agrees with experiment and density-functional theory, but for diamond Ge neither the local density approximation nor the QSGW calculations agree with the conclusions drawn from the XES data.

Modak, Paritosh; Svane, Axel

2009-01-01

39

Highly dispersive photonic band-gap-edge optofluidic biosensors  

CERN Multimedia

Highly dispersive photonic band-gap-edge optofluidic biosensors are studied theoretically. We demonstrate that these structures are strongly sensitive to the refractive index of the liquid, which is used to tune dispersion of the photonic crystal. The upper frequency band-gap edge shifts about 1.8 nm for dn=0.002, which is quite sensitive. Results from transmission spectra agree well with those obtained from the band structure theory.

Xiao, S; Xiao, Sanshui; Mortensen, Niels Asger

2006-01-01

40

Evidence for Temperature-Dependent Electron Band Dispersion in Pentacene  

Energy Technology Data Exchange (ETDEWEB)

Evidence for temperature-dependent electron band dispersion in a pentacene thin film polymorph on graphite is provided by angle- and energy-dependent ultraviolet photoelectron spectroscopy. The bands derived from the highest occupied molecular orbital exhibit dispersion of {approx}190 meV at room temperature, and {approx}240 meV at 120 K. Intermolecular electronic coupling in pentacene thin films is thus confirmed to be dependent on temperature and possibly crystal structure, as suggested by additional infrared absorption measurements.

Koch,N.; Vollmer, A.; Salzmann, I.; Nickel, B.; Weiss, H.; Rabe, J.

2006-01-01

 
 
 
 
41

Valence band of catalyst doped sodium alanate by X-ray photoelectron spectroscopy using synchrotron radiation  

Energy Technology Data Exchange (ETDEWEB)

In this work, a study is presented that shows the evolution of the valence band analysis of NaAlH{sub 4} doped with 1 mol% of Ce- and 3 mol% of Ti/Zr-hydride using X-ray photoelectron spectroscopy (XPS). The two NaAlH{sub 4} + metal hydride systems contained ball-milled, dehydrogenated, and rehydrogenated samples. The density of states of NaAlH{sub 4}, Al, and Na{sub 3}AlH{sub 6} were calculated with the generalized gradient approximation (GGA). In both of the two-system samples, during the dehydrogenation and rehydrogenation, most electrons in the p orbital disappeared, and the electrons in the s orbital increased. The catalyst Ce-hydride activated the electrons in the s orbital, whereas Ti/Zr-hydride affected those of the p orbital. Thus, the dehydrogenation and rehydrogenation might activate the more electrons in the Al s and p orbitals. (author)

Wan, Chubin; Ju, Xin; Qi, Ying; Chen, Yi; Shen, Jiang [Department of Physics, University of Science and Technology Beijing, Beijing 100083 (China); Wang, Shumao; Liu, Xiaopeng; Jiang, Lijun [General Research Institute for Nonferrous Metals, Beijing 100088 (China)

2010-02-15

42

Effect of As alloying on the valence band tail states in a-Se  

Energy Technology Data Exchange (ETDEWEB)

Transient photocurrent (TPC) measurements have been carried out on evaporated a-Se doped with either 0.2% or 0.5% of As and compared with analogous measurements on undoped and Cl doped a-Se. These measurements show that As doping of a-Se suppresses the shallow defects linked to the dihedral angle variations in a-Se chains, and makes the valence band tail states distribution steeper. These changes in the a-Se density of states increase the relative importance of the deep defect levels in As-doped a-Se and thus explain the widely reported hole lifetime shortening with As addition. (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Benkhedir, Mohammed L.; Djefaflia, Fahima; Mansour, Mohammed [Laboratoire de Physique Appliquee et Theorique, Universite de Tebessa, Tebessa 12000 (Algeria); Qamhieh, Naser [Physics Department, United Arab Emirates University, P. O. Box 17551, Al Ain Abu Dhabi (United Arab Emirates)

2010-04-15

43

Energy spectra and photoluminescence of fractional quantum Hall systems containing a valence-band hole  

CERN Document Server

The energy spectrum of a two-dimensional electron gas (2DEG) interacting with a valence-band hole is studied in the high magnetic field limit as a function of the filling factor nu and the separation d between the electron and hole layers. For d smaller than the magnetic length lambda, the hole binds one or more electrons to form neutral (X) or charged (X-) excitons. The low-lying states can be understood in terms of Laughlin-like correlations among the constituent charged fermions (electrons and X-). For d comparable to lambda, the electron-hole interaction is not strong enough to bind a full electron, and fractionally charged excitons hQEn (bound states of a hole and one or more Laughlin quasielectrons, QE) are formed. The effect of these excitonic complexes on the photoluminescence spectrum is studied numerically for a wide range of values of nu and d.

Wójs, A; Quinn, J J; Wojs, Arkadiusz; Yi, Kyung-Soo; Quinn, John J.

2001-01-01

44

Resonant photoemission at core-level shake-up thresholds: Valence-band satellites in nickel  

Energy Technology Data Exchange (ETDEWEB)

Three-hole satellites (3{ital d}{sup 7} final-state configuration) in the nickel valence-band photoelectron spectrum have been identified at 13 and 18 eV binding energy with use of synchrotron radiation from the MAX storage ring. The three-hole satellites show resonances at photon energies close to the threshold for excitation of 3{ital p}{sup 5}3{ital d}{sup 9} core-hole shake-up states. The 13-eV satellite also shows a resonance directly at the 3{ital p} threshold. This is interpreted as an interference between the direct three-hole ionization and a shake-up transition in the Auger decay of the 3{ital p} hole. This shake-up process is also identified directly in the {ital M}{sub 2,3}{ital M}{sub 4,5}{ital M}{sub 4,5} Auger spectrum.

Bjoerneholm, O. (Department of Physics, Uppsala University, Box 530, S-75121 Uppsala (Sweden)); Andersen, J.N.; Wigren, C. (MAX-lab, Lund University, P.O. Box 118, S-22100 Lund (Sweden)); Nilsson, A. (Department of Physics, Uppsala University, Box 530, S-75121 Uppsala (Sweden)); Nyholm, R. (MAX-lab, Lund University, P.O. Box 118, S-22100 Lund (Sweden)); Ma; Ortensson, N. (Department of Physics, Uppsala University, Box 530, S-75121 Uppsala (Sweden))

1990-05-15

45

Resonant photoemission at core-level shake-up thresholds: Valence-band satellites in nickel  

International Nuclear Information System (INIS)

Three-hole satellites (3d7 final-state configuration) in the nickel valence-band photoelectron spectrum have been identified at 13 and 18 eV binding energy with use of synchrotron radiation from the MAX storage ring. The three-hole satellites show resonances at photon energies close to the threshold for excitation of 3p53d9 core-hole shake-up states. The 13-eV satellite also shows a resonance directly at the 3p threshold. This is interpreted as an interference between the direct three-hole ionization and a shake-up transition in the Auger decay of the 3p hole. This shake-up process is also identified directly in the M2,3M4,5M4,5 Auger spectrum

1990-05-15

46

Atomic orbitals and photoelectron intensity angular distribution patterns of MoS2 valence band  

International Nuclear Information System (INIS)

[en] The ratio of atomic orbitals contributing to the valence band can be determined from the photoelectron intensity angular distribution (PIAD) by using linearly polarized light and display-type spherical mirror analyzer. The experiment was done for MoS2 using a linearly polarized light at the photon energy of 45 eV perpendicularly incident to the sample surface. Atomic orbitals contributing to the bands near the Fermi level were investigated. The PIAD patterns around the ? point showed splitting of intensity. The intensity at the top and bottom K points was strong, while the intensity was weak at the left and right side K points. The PIAD patterns from various kinds of atomic orbitals were calculated. By comparing the experimental PIAD patterns to the simulated ones, we concluded that at the ? point Mo 4dz2 and S 3pz atomic orbitals are the main components and at the K points the Mo 4dxy atomic orbital is dominant. The atomic orbital Mo 4dx2-y2 also gives contribution to the PIAD pattern. These results were in good agreement with the coefficients of the atomic orbitals derived using ab initio band calculation

2008-09-30

47

Atomic orbitals and photoelectron intensity angular distribution patterns of MoS{sub 2} valence band  

Energy Technology Data Exchange (ETDEWEB)

The ratio of atomic orbitals contributing to the valence band can be determined from the photoelectron intensity angular distribution (PIAD) by using linearly polarized light and display-type spherical mirror analyzer. The experiment was done for MoS{sub 2} using a linearly polarized light at the photon energy of 45 eV perpendicularly incident to the sample surface. Atomic orbitals contributing to the bands near the Fermi level were investigated. The PIAD patterns around the {gamma} point showed splitting of intensity. The intensity at the top and bottom K points was strong, while the intensity was weak at the left and right side K points. The PIAD patterns from various kinds of atomic orbitals were calculated. By comparing the experimental PIAD patterns to the simulated ones, we concluded that at the {gamma} point Mo 4d{sub z2} and S 3p{sub z} atomic orbitals are the main components and at the K points the Mo 4d{sub xy} atomic orbital is dominant. The atomic orbital Mo 4d{sub x2-y2} also gives contribution to the PIAD pattern. These results were in good agreement with the coefficients of the atomic orbitals derived using ab initio band calculation.

Janosfalvi, Zs. [Nara Institute of Science and Technology, Ikoma, Nara 630-0192 (Japan); ATOMKI, H-4026 Debrecen, Bem ter 18/c (Hungary)], E-mail: j-zsuzsa@ms.naist.jp; Matsui, F. [Nara Institute of Science and Technology, Ikoma, Nara 630-0192 (Japan); JST-CREST, Honcho, Kawaguchi, Saitama 332-0012 (Japan); Takahashi, N.; Akasaka, M. [Nara Institute of Science and Technology, Ikoma, Nara 630-0192 (Japan); Namba, H. [Nara Institute of Science and Technology, Ikoma, Nara 630-0192 (Japan); Ritsumeikan University, Kusatsu, Shiga 525-8577 (Japan); Daimon, Hiroshi [Nara Institute of Science and Technology, Ikoma, Nara 630-0192 (Japan); JST-CREST, Honcho, Kawaguchi, Saitama 332-0012 (Japan); Ritsumeikan University, Kusatsu, Shiga 525-8577 (Japan)

2008-09-30

48

Modification of the valence band electronic structure under Ag intercalation underneath graphite monolayer on Ni(111)  

CERN Multimedia

Angle-resolved photoemission spectroscopy and Auger electron spectroscopy have been applied to study the intercalation process of silver underneath a monolayer of graphite (MG) on Ni(111). The room-temperature deposition of silver on top of MG/Ni(111) system leads to the islands-like growth of Ag on top of the MG. Annealing of the "as-deposited" system at temperature of 350-450 C results in the intercalation of about 1-2 ML of Ag underneath MG on Ni(111) independently of the thickness of pre-deposited Ag film (3-100 A). The intercalation of Ag is followed by a shift of the graphite-derived valence band states towards energies which are slightly larger than ones characteristic for pristine graphite. This observation is understood in terms of a weakening of chemical bonding between the MG and the substrate in the MG/Ag/Ni(111) system with a small MG/Ni(111) covalent contribution to this interaction.

Dedkov, Y S; Vyalikh, D; Starodubov, A; Shikin, A M; Adamchuk, V K; Dedkov, Yu. S.

2003-01-01

49

Valence-band photoemission study of single crystalline CeNiSn  

Science.gov (United States)

The electronic structure of single crystalline CeNiSn has been investigated using photoemission spectroscopy. The extracted Ce 4f spectrum exhibits three peak structures; the typical Fermi level and 2 eV peaks, and another between them, ~0.9 eV below the Fermi level EF. The near-EF peak reflects a substantial Ce 4f-Sn sp hybridization, whereas the 0.9 eV peak arises from the Ce 4f-Ni 3d and Ce 5d-Ni 3d hybridization. A Ni 3d satellite feature is observed about 6 eV below the Ni 3d main band, indicating a strong Ni 3d Coulomb correlation in CeNiSn. The high-resolution photoemission study indicates a finite metallic density of states at EF, implying a semimetallic ground state. The electronic states near EF are found to have mixed character from the Sn sp, Ce 5d, Ce 4f, and Ni 3d electrons. Constant-initial-state and constant-final-state yield spectra across the 4d-->4f threshold indicate the Ce valence to be close to 3+.

Kang, J.-S.; Olson, C. G.; Inada, Y.; O¯nuki, Y.; Kwon, S. K.; Min, B. I.

1998-08-01

50

Valence-band photoemission study of single crystalline CeNiSn  

International Nuclear Information System (INIS)

The electronic structure of single crystalline CeNiSn has been investigated using photoemission spectroscopy. The extracted Ce 4f spectrum exhibits three peak structures; the typical Fermi level and 2 eV peaks, and another between them, ?0.9 eV below the Fermi level EF. The near-EF peak reflects a substantial Ce 4f-Sn sp hybridization, whereas the 0.9 eV peak arises from the Ce 4f-Ni 3d and Ce 5d-Ni 3d hybridization. A Ni 3d satellite feature is observed about 6 eV below the Ni 3d main band, indicating a strong Ni 3d Coulomb correlation in CeNiSn. The high-resolution photoemission study indicates a finite metallic density of states at EF, implying a semimetallic ground state. The electronic states near EF are found to have mixed character from the Sn sp, Ce 5d, Ce 4f, and Ni 3d electrons. Constant-initial-state and constant-final-state yield spectra across the 4d?4f threshold indicate the Ce valence to be close to 3+. copyright 1998 The American Physical Society.

1998-01-01

51

Valence-band photoemission study of single crystalline CeNiSn  

Energy Technology Data Exchange (ETDEWEB)

The electronic structure of single crystalline CeNiSn has been investigated using photoemission spectroscopy. The extracted Ce 4f spectrum exhibits three peak structures; the typical Fermi level and 2 eV peaks, and another between them, {approximately}0.9 eV below the Fermi level E{sub F}. The near-E{sub F} peak reflects a substantial Ce 4f-Sn sp hybridization, whereas the 0.9 eV peak arises from the Ce 4f-Ni 3d and Ce 5d-Ni 3d hybridization. A Ni 3d satellite feature is observed about 6 eV below the Ni 3d main band, indicating a strong Ni 3d Coulomb correlation in CeNiSn. The high-resolution photoemission study indicates a finite metallic density of states at E{sub F}, implying a semimetallic ground state. The electronic states near E{sub F} are found to have mixed character from the Sn sp, Ce 5d, Ce 4f, and Ni 3d electrons. Constant-initial-state and constant-final-state yield spectra across the 4d{r_arrow}4f threshold indicate the Ce valence to be close to 3+. {copyright} {ital 1998} {ital The American Physical Society}

Kang, J. [Department of Physics, The Catholic University of Korea, Puchon 422-743 (Korea); Olson, C.G. [Ames Laboratory, Iowa State University, Ames, Iowa 50011 (United States); Inada, Y.; Onuki, Y. [Graduate School of Science, Osaka University, Toyonaka 560 (Japan); Kwon, S.K.; Min, B.I. [Department of Physics, Pohang University of Science and Technology, Pohang 790-784 (Korea)

1998-08-01

52

Crossover from impurity to valence band in diluted magnetic semiconductors: Role of Coulomb attraction by acceptors  

Energy Technology Data Exchange (ETDEWEB)

The crossover between an impurity band (IB) and a valence band (VB) regime as a function of the magnetic impurity concentration in a model for diluted magnetic semiconductors (DMSs) is studied systematically by taking into consideration the Coulomb attraction between the carriers and the magnetic impurities. The density of states and the ferromagnetic transition temperature of a spin-fermion model applied to DMSs are evaluated using dynamical mean-field theory and Monte Carlo (MC) calculations. It is shown that the addition of a square-well-like attractive potential can generate an IB at small enough Mn doping x for values of the p-d exchange J that are not strong enough to generate one by themselves. We observe that the IB merges with the VB when x>=xc where xc is a function of J and the Coulomb strength V. Using MC simulations, we demonstrate that the range of the Coulomb attraction plays an important role. While the on-site attraction, which has been used in previous numerical simulations, effectively renormalizes J for all values of x, an unphysical result, a nearest-neighbor range attraction renormalizes J only at very low dopings, i.e., until the bound holes wave functions start to overlap. Thus, our results indicate that the Coulomb attraction can be neglected to study Mn-doped GaSb, GaAs, and GaP in the relevant doping regimes, but it should be included in the case of Mn-doped GaN, which is expected to be in the IB regime.

Popescu, Florentin [Florida State University; Sen, Cengiz [Florida State University; Dagotto, Elbio R [ORNL; Moreo, Adriana [ORNL

2007-01-01

53

Multiband model of the valence-band electronic structure in cylindrical GaAs nanowires  

Directory of Open Access Journals (Sweden)

Full Text Available We compute the hole states in the GaAs free-standing nanowires, and in the GaAs/(Al,Ga)As core-shell nanowires of type I-s, which are grown along the [100] direction. The hole states are extracted from the 4-band Luttinger-Kohn Hamiltonian, which explicitly takes into account mixing between the light and heavy holes. The axial aproximation is adopted, which allowed classification of states according to the total angular monentum (fz when expressed in units of the Planck constant). The envelope functions are expanded in Bessel functions of the first kind. The dispersion relations of the subbands E(kz) obtained by the devised method do not resemble parabolas, which is otherwise a feature of the dispersion relations of the conduction subbands. Furthermore, the energy levels of holes whose total orbital momentum is fz=1/2 are shown to cross for a free-standing wire. The low energy fz=1/2 states are found to anticross, but these anticrossings turn into crossings when the ratio of the inner and outer radius of the core-shell wire takes a certain value. The influence of the geometric parameters on the dispersion relations is considered for both free standing and core-shell nanowires.

?ukari? Nemanja A.; Tadi? Milan Ž.

2010-01-01

54

Density of valence electrons and dispersion energy in annealed dc glow discharge a-Si:H  

International Nuclear Information System (INIS)

Films of amorphous silicon films are prepared by the deposition of SiH/sub 4 in a dc plasma glow discharge reactor and at a substrate temperature of 140 degrees C. The optical energy gap and refractive index are measured at different annealing temperatures of up to 600 degrees C, in an ambient of nitrogen. The refractive index is found to be between 2.05 and 4.01 while the optical gap ranges from 1.93 and 2.16 eV. Using the model of Freeman and Paul, the density of valence electrons in the a-Si:H is estimated to be less than 5 x 10/sup 22 cm/sup -3. The dispersion energy is calculated and it is found that its value changes irregularly within 4.58 to 20.66 eV with the annealing temperature. These observations are correlated to the mechanisms involved during annealing like the out diffusion-effusion of hydrogen, re-ordering process involving microvoids and strained bonds, and finally the amorphous network undergoing recrystallization. (authors)

1992-01-01

55

PHONONS IN MIXED VALENCE COMPOUNDS  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Several mixed-valence NaCl-structure compounds show strong anomalies in the phonon dispersion curves. These anomalies are related to the interaction of localized f-electrons with delocalized band electrons near the Fermi surface and to the iso-structural phase transitions characterized by a softenin...

Kress, W.; Bilz, H.; Güntherodt, G.; Jayaraman, A.

56

CuPc molecules adsorbed on Au(110)-(1x2) growth morphology and evolution of valence band states  

CERN Document Server

We present the growth morphology, the long range ordering, and the evolution of the valence band electronic states of ultra-thin films of copper phthalocyanine (CuPc) deposited on the Au(110)-(1x2) reconstructed surface, as a function of the organic molecule coverage. The Low Energy Electron Diffraction (LEED) patterns present a (5x3) reconstruction from the early adsorption stages. High-Resolution UV photoelectron spectroscopy (HR-UPS) data show the disappearance of the Au surface states related to the (1x2) reconstruction, and the presence of new electronic features related to the molecule-substrate interaction and to the CuPc molecular states. The CuPc highest occupied molecular orbital (HOMO) gradually emerges in the valence band, while the interface electronic states are quenched, upon increasing the coverage.

Evangelista, F; Corradini, V; Donzello, M P; Mariani, C; Betti, M G

2003-01-01

57

Modeling wave dispersion and band gaps in heterogeneous elastic media  

Directory of Open Access Journals (Sweden)

Full Text Available In this paper we report recent developments and results concerning validation of the homogenization approach applied in modeling waves in strongly heterogeneous elastic media. The homogenization limit model is obtained for stationary waves, but can also be used to estimate dispersion properties for long guided waves propagation. Band gaps distribution depends on the material contrast and on the geometrical arrangements in the microstructure. Similarity between discrete structures and heterogeneous continua is used to demonstrate the dispersion phenomena. The modeling approach has been extended to the piezo-phononic materials, which may be useful in designing smart materials. Also problems of optimal shape design at the microscopic level were pursued.

Rohan E.; Seifrt F.

2007-01-01

58

Identifying the electronic character and role of the mn States in the valence band of (ga,mn)as.  

UK PubMed Central (United Kingdom)

We report high-resolution hard x-ray photoemission spectroscopy results on (Ga,Mn)As films as a function of Mn doping. Supported by theoretical calculations we identify, for both low (1%) and high (13%) Mn doping values, the electronic character of the states near the top of the valence band. Magnetization and temperature-dependent core-level photoemission spectra reveal how the delocalized character of the Mn states enables the bulk ferromagnetic properties of (Ga,Mn)As.

Fujii J; Salles BR; Sperl M; Ueda S; Kobata M; Kobayashi K; Yamashita Y; Torelli P; Utz M; Fadley CS; Gray AX; Braun J; Ebert H; Di Marco I; Eriksson O; Thunström P; Fecher GH; Stryhanyuk H; Ikenaga E; Minár J; Back CH; van der Laan G; Panaccione G

2013-08-01

59

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

60

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

 
 
 
 
61

Valence one-electron and shake-up ionisation bands of polycyclic aromatic hydrocarbons. IV. The dibenzanthracene species  

International Nuclear Information System (INIS)

A comprehensive study of the He (I) ultra-violet photoelectron spectra of the 1.2,3.4; 1.2,5.6 and 1.2,7.8 isomers of dibenzanthracene up to the double ionisation threshold at ?18 eV is presented with the aid of one-particle Green's Function calculations performed using the outer-valence Green's Function (OVGF) approach and the third-order algebraic diagrammatic construction [ADC(3)] scheme, along with basis sets of improving quality. Suited extrapolations of the ADC(3) results for the one-electron energies characterising the ?-band system (? b

2006-10-26

62

Modification of valence-band symmetry and Auger threshold energy in biaxially compressed InAs1-xSbx  

International Nuclear Information System (INIS)

Strained-layer superlattices (SLS's) with biaxially compressed InAs1-xSbx were characterized using magnetophotoluminescence and compared with unstrained InAs1-xSbx alloys. Holes in the SLS exhibited a decrease in effective mass, approaching that of the electrons. In the two-dimensional limit, a large increase in the Auger threshold energy accompanies this strain-induced change in SLS valence-band symmetry. Correspondingly, the activation energy for nonradiative recombination in the SLS's displayed a marked increase compared with that of the unstrained alloys. Strained-layer superlattices and alloy activation energies are in agreement with estimated Auger threshold energies.

1995-01-01

63

Effects of ion aggregation on the intervalence transfer band of the mixed-valence biferrocenium cation in solution  

Energy Technology Data Exchange (ETDEWEB)

The concentration dependence of the energy (E/sup op/) of the intervalence transfer (IT) electronic absorption band of mixed-valence biferrocenium triiodide dissolved in either nitrobenzene or dichloromethane is examined. In nitrobenzene, E/sup op/ increases rapidly from approx. 5.57 to approx. 6.05 x 10/sup 3/ cm/sup -1/ in the 0.24-0.4 mM range, whereupon further increases in the concentration of biferrocenium triiodide lead to E/sup op/ increasing more gradually to a value approx. 6.3 x 10/sup 3/ cm/sup -1/ at 24 mM. On the other hand, the full width at half maximum (..delta.. anti v/sub 1/2) and the transition moment of the IT band decrease with increasing concentration for biferrocenium triiodide in nitrobenzene. E/sup op/ increases, ..delta.. anti v/sub 1/2 remains constant, and the transition moment of the IT band increases with increasing concentration for biferrocenium triiodide in dichloromethane in the more limited range of 0.30-0.95 mM. These concentration dependencies of the IT band for biferrocenium triiodide are attributable to variable degrees of ion aggregation in solution. The concentration dependencies of the electrical conductivity of solutions of biferrocenium triiodide in either nitrobenzene or dichloromethane substantiate this proposal. IT band contours obtained at different concentrations are fit to the PKS vibronic model to yield parameters that characterize the electronic and vibronic coupling within the mixed-valence biferrocenium cation.

Lowery, M.D.; Hammack, W.S.; Drickamer, H.G.; Hendrickson, D.N.

1987-12-23

64

Uniaxial compression influence on valence sub-bands energy spectrum and electroluminescence in n-AlGaAs/GaAsP/p-AlGaAs diode structures  

International Nuclear Information System (INIS)

Numerical calculations of the valence band and conduction band size quantized levels in a strained p-AlxGa1-xAs/GaAs1-yPy/n-AlxGa1-xAs (y = 0.16) double heterostructure were performed for different values of the external uniaxial compression along [110] direction. They indicate that the two upper levels in the valence band merge at pressure about 4 kbar and a strong state mixing develops around the merging point. The results of calculations explain the nonlinear character of the photon energy shift and electroluminescence intensity increase that were experimentally observed in these structures under uniaxial compression up to 5 kbar.

2012-07-30

65

Evaluation of n+a-Si Contact with Indium Tin Oxide by X-Ray Photoelectron Spectroscopy Valence Band Measurement  

Science.gov (United States)

We investigated the cause of the high resistance in a contactstructure of phosphorus-doped amorphous silicon (n+a-Si) withindium tin oxide (ITO) for thin-film transistor liquid crystaldisplays (TFT-LCDs). X-ray photoelectron spectroscopy (XPS) valenceband analysis for this interface was newly developed. TFT-LCDfabrication processes could be simplified by using ITO in pixels asthe drain contact electrode. One problem of this drain structure wasthe increase in electrical resistance associated with annealing. XPSvalence band measurements of the n+a-Si/ITO structure revealedthat the upper edge of the Si valence band shifted to a lower bindingenergy after annealing at 250°C. These results suggest thatthe increase in electrical resistance was mainly caused by theincrease in contact resistance. The above-mentioned result was alsoconfirmed by secondary ion mass spectrometry (SIMS) analysis andresistance measurements.

Yabuhara, Hidehiko; Kataoka, Yoshinori

1999-09-01

66

?-Si3N4(0001)/Si(111) interface: Phosphorus defects, valence band offsets, and their role of passivating the interface states  

Science.gov (United States)

This work investigates the ?-Si3N4(0001)/Si(111) interface based on a model with fully saturated interface bonds. The charge transfer at the interface and band alignment are calculated. The band alignment is corrected by GW0 calculations. Furthermore, we investigate how substitutional phosphorus defects affect the electronic structure of the interface, in particular how they saturate the interface states and modify the valence band offsets.

Flage–Larsen, E.; Løvvik, O. M.; Fang, C. M.; Kresse, G.

2013-10-01

67

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

68

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

69

XPS core level and valence band spectra of LaH/sub 3/  

Energy Technology Data Exchange (ETDEWEB)

XPS analysis of LaH/sub 3/ shows theat the conduction band of the La metal disappears and that a new hydrogen induced band is formed 5.8 eV below Esub(F). The La 3d core levels of LaH/sub 3/ are split into two peaks with about 1/3 of the intensity being in the low binding energy peak. It is proposed to describe the observed 3d structure by the screening of the 3d hole by means of a charge transfer from the new hydrogen band to the empty 4f level, the latter being pulled down below th hydrogen band. This would be a shake down process as in La metal.

Schlapbach, L.; Scherrer, H.R. (Eidgenoessische Technische Hochschule, Zurich (Switzerland). Lab. fuer Festkoerperphysik)

1982-03-01

70

X-ray photoemission valence band spectrum of La{sub 0.6}Sr{sub 0.4}MnO{sub 3} perovskite  

Energy Technology Data Exchange (ETDEWEB)

The XPS spectrum was obtained for radiation with photon energy of 1.4866 keV, AlK{sub {alpha}} source. The photoemission spectrum in the valence band region at room temperature is shown. Comparing earlier and the present studies of the valence band of La{sub 1-x}Sr{sub x}MnO{sub 3} one can say that the peak lying in the higher-binding part of the spectrum does not change ist position as the Sr fraction increases. The second peak moves towards the Fermi level by about 1 eV when changing x between 0.3 and 0.4. (orig.)

Kowalczyk, A.; Szajek, A.; Smardz, L.; Baszynski, J. [Polska Akademia Nauk, Poznan (Poland). Inst. Fizyki Molekularnej

2000-08-01

71

Determination of the valence-band offset of CdS/CIS solar cell devices by target factor analysis  

Energy Technology Data Exchange (ETDEWEB)

X-ray photoemission spectroscopy (XPS) is used to determine and compare the valence-band offsets ({Delta}E{sub v}) for CdS grown by chemical bath deposition on single-crystal and thin-film CuInSe{sub 2} (CIS). The thin-film CIS device was suitable for photovoltaic energy production. By sputtering through the CdS/CIS interface and reducing the depth profile with target factor analysis, the magnitude of {Delta}E{sub v} was determined to be {Delta}E{sub v} = 1.06 {+-} 0.15 eV for both the single-crystal and thin-film interfaces. This determination of {Delta}E{sub v} is about 0.25 eV larger than many previously reported estimations CdS grown by physical vapor deposition on CIS and helps explain the record performance of CdS/CIS photovoltaic devices.

Niles, D.W.; Contreras, M.; Ramanathan, K.; Noufi, R. [National Renewable Energy Lab., Golden, CO (United States)

1996-05-01

72

Anisotropic Confinement, Electronic Coupling and Strain Induced Effects Detected by Valence-Band Anisotropy in Self-Assembled Quantum Dots  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract A method to determine the effects of the geometry and lateral ordering on the electronic properties of an array of one-dimensional self-assembled quantum dots is discussed. A model that takes into account the valence-band anisotropic effective masses and strain effects must be used to describe the behavior of the photoluminescence emission, proposed as a clean tool for the characterization of dot anisotropy and/or inter-dot coupling. Under special growth conditions, such as substrate temperature and Arsenic background, 1D chains of In0.4Ga0.6 As quantum dots were grown by molecular beam epitaxy. Grazing-incidence X-ray diffraction measurements directly evidence the strong strain anisotropy due to the formation of quantum dot chains, probed by polarization-resolved low-temperature photoluminescence. The results are in fair good agreement with the proposed model.

Villegas-Lelovsky L; Teodoro MD; Lopez-Richard V; Calseverino C; Malachias A; Marega E; Liang BL; Mazur Yu; Marques GE; Trallero-Giner C; Salamo GJ

2011-01-01

73

Anisotropic Confinement, Electronic Coupling and Strain Induced Effects Detected by Valence-Band Anisotropy in Self-Assembled Quantum Dots.  

UK PubMed Central (United Kingdom)

A method to determine the effects of the geometry and lateral ordering on the electronic properties of an array of one-dimensional self-assembled quantum dots is discussed. A model that takes into account the valence-band anisotropic effective masses and strain effects must be used to describe the behavior of the photoluminescence emission, proposed as a clean tool for the characterization of dot anisotropy and/or inter-dot coupling. Under special growth conditions, such as substrate temperature and Arsenic background, 1D chains of In0.4Ga0.6 As quantum dots were grown by molecular beam epitaxy. Grazing-incidence X-ray diffraction measurements directly evidence the strong strain anisotropy due to the formation of quantum dot chains, probed by polarization-resolved low-temperature photoluminescence. The results are in fair good agreement with the proposed model.

Villegas-Lelovsky L; Teodoro M; Lopez-Richard V; Calseverino C; Malachias A; Marega E Jr; Liang B; Mazur YI; Marques G; Trallero-Giner C; Salamo G

2010-10-01

74

Determination of the valence-band offset of CdS/CIS solar cell devices by target factor analysis  

Energy Technology Data Exchange (ETDEWEB)

X-ray photoemission spectroscopy (XPS) is used to determine and compare the valence-band offsets ({Delta}E{sub v}) for CdS grown by chemical bath deposition on single-crystal and thin-film CuInSe{sub 2} (CIS). The thin-film CIS device was suitable for photovoltaic energy production. By sputtering through the CdS/CIS interface and reducing the depth profile with target factor analysis, the magnitude of {Delta}E{sub v} was determined to be {Delta}E{sub v} = 1.06 {+-} 0.15 eV for both the single-crystal and thin-film interfaces. This determination of {Delta}E{sub v} is about 0.25 eV larger than many previously reported estimations CdS grown by physical vapor deposition on CIS and helps explain the record performance of CdS/CIS photovoltaic devices.

Niles, D.W.; Contreras, M.; Ramanathan, K.; Noufi, R. [National Renewable Energy Lab., Golden, CO (United States)

1996-09-01

75

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

76

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

77

Electron correlation effects in the UPS valence band spectra of Au and Ag  

International Nuclear Information System (INIS)

[en] Modulations of the relative peak heights of the d band maxima previously observed in UPS spectra of Au and Ag are shown to correspond to the thresholds of excitations from inner levels with equal principal quantum number. Contrary to earlier proposed interpretations the correspondence leads to an explanation of the modulations as an effect of atomic electron correlation interaction. (orig.)

1979-01-01

78

Multiband model of the valence-band electronic structure in cylindrical GaAs nanowires  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We compute the hole states in the GaAs free-standing nanowires, and in the GaAs/(Al,Ga)As core-shell nanowires of type I-s, which are grown along the [100] direction. The hole states are extracted from the 4-band Luttinger-Kohn Hamiltonian, which explicitly takes into account mixing between the ligh...

?ukari? Nemanja A.; Tadi? Milan Ž.

79

Valence one-electron and shake-up ionization bands of fluorene, carbazole and dibenzofuran  

Science.gov (United States)

A comprehensive study of the He (I) ultra-violet photoelectron spectra of fluorene, carbazole and dibenzofuran is presented with the aid of one-particle Green's Function calculations employing the outer-valence Green's Function (OVGF) approach and the third-order algebraic diagrammatic construction [ADC(3)] scheme, along with Dunning's correlation consistent basis sets of double and triple zeta quality (cc-pVDZ, cc-pVTZ). Extrapolations of the ADC(3) results for the outermost one-electron ?-ionization energies to the cc-pVTZ basis set enable theoretical insights into He (I) measurements within ˜0.15 eV accuracy, up to the ?-ionization onset. The lower ionization energy of carbazole is the combined result of mesomeric and electronic relaxation effects. OVGF/cc-pVDZ or OVGF/cc-pVTZ pole strengths smaller than 0.85 systematically corroborate a breakdown of the orbital picture of ionization at the ADC(3) level. Comparison is made with calculations of the lowest doublet–doublet excitation energies of the radical cation of fluorene, by means of time-dependent density functional theory (TDDFT).

Shojaei, S. H. Reza; Morini, Filippo; Deleuze, Michael S.

2013-09-01

80

Valence-Band UPS, 6$p$ Core-Level XPS Photoemission Spectroscopy, and Low-Energy Electron Diffraction of a Uranium (001) Single Crystal  

CERN Document Server

Valence-band ultraviolet photoemission spectroscopy (UPS) at 173K and 6p core-level X-ray photoemission spectroscopy (XPS) at room temperature were performed on a high quality uranium single crystal. Significant agreement is found with first-principles electronic band-structure calculations, using a generalized gradient approximation (GGA). In addition, using Low Energy Electron Diffraction (LEED) for the (001) surface, we find a well-ordered orthorhombic crystallographic structure representative of the bulk material.

Opeil, C P; Manley, M E; Lashley, J C; Hults, W L; Hanrahan, R J; Smith, J L; Mihaila, B; Blagoev, K B; Albers, R C; Littlewood, P B

2006-01-01

 
 
 
 
81

On the interpretation of valence band photoemission spectra at organic-metal interfaces  

CERN Multimedia

Adsorption of organic molecules on well-oriented single crystal coinage metal surfaces fundamentally affects the energy distribution curve of ultra-violet photoelectron spectroscopy spectra. New features not present in the spectrum of the pristine metal can be assigned as "interface states" having some degree of molecule-substrate hybridization. Here it is shown that interface states having molecular orbital character can easily be identified at low binding energy as isolated features above the featureless substrate sp-plateau. On the other hand much care must be taken in assigning adsorbate-induced features when these lie within the d-band spectral region of the substrate. In fact, features often interpreted as characteristic of the molecule-substrate interaction may actually arise from substrate photoelectrons scattered by the adsorbates. This phenomenon is illustrated through a series of examples of noble-metal single-crystal surfaces covered by monolayers of large pi-conjugated organic molecules.

Giovanelli, L; Amsalem, P; Lee, H -L; Abel, M; Clair, S; Koudia, M; Faury, T; Petaccia, L; Topwal, D; Salomon, E; Angot, T; Cafolla, A A; Koch, N; Porte, L; Goldoni, A; Themlin, J -M

2012-01-01

82

Ab-initio valence band spectra of Al, In doped ZnO  

International Nuclear Information System (INIS)

We present the structural and electronic characterization of n-doped (Aluminium or Indium) ZnO and the effect of the doping on the calculated photoelectron spectroscopy (PES) spectra. The fully-relaxed calculations have been made using the density functional theory, including a Hubbard correlation term that increases the Zn-3d states binding energy, and which matches the experimental values. The effect of Oxygen vacancies is also included in our study. Our results show that the new Al or In-donor levels appearing in the conduction band hybridize with the Oxygen-2p states and help decrease the resistivity of these doped systems as was found experimentally. The calculated PES spectra show a small enhancement in the intensity close to the chemical potential as a result of these new Al or In levels.

2009-02-02

83

Magnetic susceptibility in weak magnetic field and valence band structure of tin telluride  

International Nuclear Information System (INIS)

Measurement results of magnetic susceptibility (MS) dependence in Sn1-xTe on hole concentration and temperature within p and T wide range are given. Abalysis of experimental curves shows that in ?(p,T=0) curve there are some peculiarities at p=1.1x1020, 2.3x1020 and 4.9x1020 cm-3 which are identified as Van Hove peculiarities corresponding to ?-extremum, to saddle point in ?L direction and to ?-extremum of valent band. Effect of high nonparabolicity of heavy hole spectrum in ?- and ?-subbonds on contribution of heavy holes into MS is considered and estimations of some characteristics of hole spectrum are obtained.

1990-01-01

84

Orientational order in A3C60: effects on valence bands and infrared optical spectra  

International Nuclear Information System (INIS)

By analysis of the electronic contribution to the binding in A3C60, we show that the problem of orientational ordering can be mapped onto the fcc nearest-neighbor antiferromagnetic Ising model with J of the order of 100K. The ground state crystal structure should be therefore antiferromagnetically ordered in two dimensions and disordered in the third. This is not inconsistent with present X-ray powder data. We find that the low-temperature conduction-band structure closely resembles that of the simplest antiferromagnetically ordered (so-called bi-directional) crystal. Calculated optical conductivity can be fitted by a Drude-like contribution and an ''interband'' Lorenzian peak at 400-500 cm-1. (orig.).

1993-01-01

85

Vertical photoionization of liquid-to-supercritical ammonia: thermal effects on the valence-to-conduction band gap.  

UK PubMed Central (United Kingdom)

We recently reported first femtosecond pump–probe experiments on the geminate recombination dynamics of solvated electrons in fluid ammonia (Urbanek et al., J. Phys. Chem. B 2012, 116, 2223–2233). The electrons were generated through a vertical two-photon ionization at a total energy of 9.3 eV. Here, we present a full Monte Carlo analysis of the time-resolved data to determine the solvated electron’s thermalization distance from the ionization hole, NH(3)(+). The simulations are compared with the experiment over wide thermodynamic conditions to obtain insight into the dependence of the vertical ionization mechanism on the electronic properties of the solvent network. The simulations reveal that the average thermalization distance, , decreases strongly with both increasing temperature, T, and decreasing density, ?, from 3.2 nm in the cryogenic fluid down to roughly 0.5 nm in the dilute supercritical phase with almost gas-like densities. We combine our results with the current understanding of the T,?-dependence of the electronic structure of the liquid phase and discuss in detail the role of thermally induced energy level shifts for the valence-to-conduction band gap. The observed changes of the thermalization distance can be well attributed to a gradual decrease of the excess energy initially imparted on the ejected electron as gas-like conditions are progressively approached.

Urbanek J; Vöhringer P

2013-07-01

86

Theoretical study of influencing factors on the dispersion of bulk band-gap edges and the surface states in topological insulators Bi2Te3 and Bi2Se3  

Science.gov (United States)

The dispersion of the band-gap edge states in bulk topological insulators Bi2Te3 and Bi2Se3 is considered within density functional theory. The dependences of this dispersion both on the approximation used for an exchange-correlation functional at fixed unit cell parameters and atomic positions and on these parameters and positions that are obtained upon structural relaxation performed using a certain approximated functional are analyzed. The relative position of the Dirac point of topologically protected surface states and the valence band maximum in the surface electronic structure of the topological insulators is discussed.

Rusinov, I. P.; Nechaev, I. A.; Chulkov, E. V.

2013-06-01

87

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2013-06-15

88

Theoretical study of influencing factors on the dispersion of bulk band-gap edges and the surface states in topological insulators Bi2Te3 and Bi2Se3  

International Nuclear Information System (INIS)

The dispersion of the band-gap edge states in bulk topological insulators Bi2Te3 and Bi2Se3 is considered within density functional theory. The dependences of this dispersion both on the approximation used for an exchange-correlation functional at fixed unit cell parameters and atomic positions and on these parameters and positions that are obtained upon structural relaxation performed using a certain approximated functional are analyzed. The relative position of the Dirac point of topologically protected surface states and the valence band maximum in the surface electronic structure of the topological insulators is discussed

2013-01-01

89

Valence band offset at GaN/?-Si3N4 and ?-Si3N4/Si(111) heterojunctions formed by plasma-assisted molecular beam epitaxy  

International Nuclear Information System (INIS)

Ultra thin films of pure ?-Si3N4 (0001) were grown on Si (111) surface by exposing the surface to radio- frequency nitrogen plasma with a high content of nitrogen atoms. Using ?-Si3N4 layer as a buffer layer, GaN epilayers were grown on Si (111) substrate by plasma-assisted molecular beam epitaxy. The valence band offset (VBO) of GaN/?-Si3N4/Si heterojunctions is determined by X-ray photoemission spectroscopy. The VBO at the ?-Si3N4 / Si interface was determined by valence-band photoelectron spectra to be 1.84 eV. The valence band of GaN is found to be 0.41 ± 0.05 eV below that of ?-Si3N4 and a type-II heterojunction. The conduction band offset was deduced to be ? 2.36 eV, and a change of the interface dipole of 1.29 eV was observed for GaN/?-Si3N4 interface formation.

2012-05-31

90

Valence band offset, strain and shape effects on confined states in self-assembled InAs/InP and InAs/GaAs quantum dots.  

Science.gov (United States)

I present a systematic study of self-assembled InAs/InP and InAs/GaAs quantum dot single-particle and many-body properties as a function of the quantum dot-surrounding matrix valence band offset. I use an atomistic, empirical tight-binding approach and perform numerically demanding calculations for half-million-atom nanosystems. I demonstrate that the overall confinement in quantum dots is a non-trivial interplay of two key factors: strain effects and the valence band offset. I show that strain effects determine both the peculiar structure of confined hole states of lens type InAs/GaAs quantum dots and the characteristic 'shell-like' structure of confined hole states in the commonly considered 'low-strain' lens type InAs/InP quantum dot. I also demonstrate that strain leads to single-band-like behavior of hole states of disk type ('indium flushed') InAs/GaAs and InAs/InP quantum dots. I show how strain and valence band offset affect quantum dot many-body properties: the excitonic fine structure, an important factor for efficient entangled photon pair generation, and the biexciton and charged exciton binding energies. PMID:24129261

Zieli?ski, M

2013-10-15

91

Valence-band and core-level photoemission study of single-crystal Bi2CaSr2Cu2O8 superconductors  

International Nuclear Information System (INIS)

High-quality single crystals of Bi2CaSr2Cu2O8 superconductors have been prepared and cleaved in ultrahigh vacuum. Low-energy electron diffraction measurements show that the surface structure is consistent with the bulk crystal structure. Ultraviolet photoemission and x-ray photoemission experiments were performed on these well-characterized sample surfaces. The valence-band and the core-level spectra obtained from the single-crystal surfaces are in agreement with spectra recorded from polycrystalline samples, justifying earlier results from polycrystalline samples. Cu satellites are observed both in the valence band and Cu 2p core level, signaling the strong correlation among the Cu 3d electrons. The O 1s core-level data exhibit a sharp, single peak at 529-eV binding energy without any clear satellite structures

1988-12-01

92

Valence one-electron and shake-up ionization bands of carbon clusters. I. The C-n (n=3,5,7,9) chains  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The 1h (one-hole) and 2h-1p (two-hole; one-particle) shake-up bands in the valence ionization spectrum of small carbon chains (C-3,C-5,C-7,C-9) are investigated up to 40 eV, using the one-particle Green's function approach. Calculations have been performed at the second- and third-orders of an algeb...

DELEUZE, Michael; GIUFFREDA, Maria; FRANCOIS, Jean-Pierre; Cederbaum, LS

93

Valence one-electron and shake-up ionization bands of carbon clusters. II. The C-n (n=4,6,8,10) rings  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The 1h (one-hole) and 2h-1p (two-hole; one-particle) shake-up bands in the valence ionization spectrum of small carbon rings (C-4, C-6, C-8, C-10) are investigated up to 40 eV, using the one-particle Green's Function approach. Calculations have been performed using both the third-order algebraic dia...

DELEUZE, Michael; GIUFFREDA, Maria; FRANCOIS, Jean-Pierre; Cederbaum, LS

94

Correlation of conductivity and angle integrated valence band photoemission characteristics in single crystal iron perovskites for 300 K < T < 800 K: Comparison of surface and bulk sensitive methods  

International Nuclear Information System (INIS)

A single crystal monolith of La0.9Sr0.1FeO3 and thin pulsed laser deposited film of La0.8Sr0.2Fe0.8Ni0.2O3 were subject to angle integrated valence band photoemission spectroscopy in ultra high vacuum and conductivity experiments in ambient air at temperatures from 300 K to 800 K. Except for several sputtering and annealing cycles, the specimens were not prepared in situ. Peculiar changes in the temperature dependent, bulk representative conductivity profile as a result of reversible phase transitions, and irreversible chemical changes are semi-quantitatively reflected by the intensity variation in the more surface representative valence band spectra near the Fermi energy. X-ray photoelectron diffraction images reflect the symmetry as expected from bulk iron perovskites. The correlation of spectral details in the valence band photoemission spectra (VB PES) and details of the conductivity during temperature variation suggest that valuable information on electronic structure and transport properties of complex materials may be obtained without in situ preparation.

2010-01-01

95

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

96

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

97

Interfacial chemistry and valence band offset between GaN and Al2O3 studied by X-ray photoelectron spectroscopy  

Science.gov (United States)

The interface region between Ga-face n-type GaN and Al2O3 dielectric (achieved via atomic-layer deposition or ALD) is investigated by X-ray photoelectron spectroscopy (XPS). An increase in the Ga-O to Ga-N bond intensity ratio following Al2O3 deposition implies that the growth of an interfacial gallium sub-oxide (GaOx) layer occurred during the ALD process. This finding may be ascribed to GaN oxidation, which may still happen following the reduction of a thin native GaOx by trimethylaluminum (TMA) in the initial TMA-only cycles. The valence band offset between GaN and Al2O3, obtained using both core-level and valence band spectra, is found to vary with the thickness of the deposited Al2O3. This observation may be explained by an upward energy band bending at the GaN surface (due to the spontaneous polarization induced negative bound charge on the Ga-face GaN) and the intrinsic limitation of the XPS method for band offset determination.

Duan, T. L.; Pan, J. S.; Ang, D. S.

2013-05-01

98

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

99

Single-carrier impact ionization favored by a limited band dispersion  

CERN Document Server

A critical requirement for high gain and low noise avalanche photodiodes is the single-carrier avalanche multiplication. We propose that the single-carrier avalanche multiplication can be achieved in materials with a limited width of the conduction or valence band resulting in a restriction of kinetic energy for one of the charge carriers. This feature is not common to the majority of technologically relevant semiconductors, but it is observed in chalcogenides, such as Selenium and compound I2-II-IV-VI4 alloys.

Darbandi, A

2012-01-01

100

Valence band offset at the CdS/Cu2ZnSnS4 interface probed by x-ray photoelectron spectroscopy  

Science.gov (United States)

The valence band offset (VBO) at the interface CdS/Cu2ZnSnS4 was investigated by x-ray photoelectron spectroscopy (XPS). The VBO was measured by two different procedures: an indirect method involving the measurements of the core levels together with the XPS bulk valence band (VB) spectra and a direct method involving the analysis of XPS VB spectra at the interface. The indirect method resulted in a VBO value of (-1.20 ± 0.14) eV while the direct method returned a similar value of (-1.24 ± 0.06) eV but affected by a lower uncertainty. The conduction band offset (CBO) was calculated from the measured VBO values. These two measured values of the VBO allowed us to calculate the CBO, giving (-0.30 ± 0.14) eV and (-0.34 ± 0.06) eV, respectively. These values show that the CBO has a cliff-like behaviour which could be one of the reasons for the Voc limitation in the CdS/CZTS solar cells.

Santoni, A.; Biccari, F.; Malerba, C.; Valentini, M.; Chierchia, R.; Mittiga, A.

2013-05-01

 
 
 
 
101

Valence band offset at the CdS/Cu2ZnSnS4 interface probed by x-ray photoelectron spectroscopy  

International Nuclear Information System (INIS)

[en] The valence band offset (VBO) at the interface CdS/Cu2ZnSnS4 was investigated by x-ray photoelectron spectroscopy (XPS). The VBO was measured by two different procedures: an indirect method involving the measurements of the core levels together with the XPS bulk valence band (VB) spectra and a direct method involving the analysis of XPS VB spectra at the interface. The indirect method resulted in a VBO value of (?1.20 ± 0.14) eV while the direct method returned a similar value of (?1.24 ± 0.06) eV but affected by a lower uncertainty. The conduction band offset (CBO) was calculated from the measured VBO values. These two measured values of the VBO allowed us to calculate the CBO, giving (?0.30 ± 0.14) eV and (?0.34 ± 0.06) eV, respectively. These values show that the CBO has a cliff-like behaviour which could be one of the reasons for the Voc limitation in the CdS/CZTS solar cells. (paper)

2013-05-01

102

Influence of orbital contributions to the valence band alignment of Bi2O3, Fe2O3, BiFeO3, and Bi0.5Na0.5TiO3  

Science.gov (United States)

The formation of an interface between Bi2O3, Fe2O3, BiFeO3, Bi0.5Na0.5TiO3, and the high work function metallic RuO2 is studied using photoelectron spectroscopy with in situ RuO2 deposition. Schottky barrier heights are derived and the valence band maximum energies of the studied materials are aligned with respect to each other as well as to other functional oxides like SrTiO3 and PbTiO3. The energy band alignment follows systematic trends compared to a large number of oxides, and can be understood in terms of the contribution of Fe 3d and Bi 6s/6p (lone pair) orbitals to electronic states near the valence band maximum. The results indicate that the valence band maxima are largely determined by the local environment of the cations, which allows to estimate valence band maximum energies of oxides with multiple cations from those of their parent binary compounds. The high valence band maximum of BiFeO3 is consistent with reported p-type conduction of acceptor doped material, while the high conduction band minimum makes n-type conduction unlikely.

Li, Shunyi; Morasch, Jan; Klein, Andreas; Chirila, Christina; Pintilie, Lucian; Jia, Lichao; Ellmer, Klaus; Naderer, Michael; Reichmann, Klaus; Gröting, Melanie; Albe, Karsten

2013-07-01

103

Development of wave length-dispersive soft x-ray emission spectrometers for transmission electron microscopes - an introduction of valence electron spectroscopy for transmission electron microscopy  

International Nuclear Information System (INIS)

Two types of wavelength-dispersive soft X-ray spectrometers, a high-dispersion type and a conventional one, for transmission electron microscopes were constructed. Those spectrometers were used to study the electronic states of valence electrons (bonding electrons). Both spectrometers extended the acceptable energy regions to higher than 2000 eV. The best energy resolution of 0.08 eV was obtained for an Al L-emission spectrum by using the high-dispersion type spectrometer. By using the spectrometer, C K-emission of carbon allotropes, Cu L-emission of Cu1-xZnx alloys and Pt M-emission spectra were presented. The FWHM value of 12 eV was obtained for the Pt M?-emission peak. The performance of the conventional one was also presented for ZnS and a section specimen of a multilayer device. W-M and Si-K emissions were clearly resolved. Soft X-ray emission spectroscopy based on transmission electron microscopy (TEM) has an advantage for obtaining spectra from a single crystalline specimen with a defined crystal setting. As an example of anisotropic soft X-ray emission, C K-emission spectra of single crystalline graphite with different crystal settings were presented. From the spectra, density of states of ?- and ?-bondings were separately derived. These results demonstrated a method to analyse the electronic states of valence electrons of materials in the nanometre scale based on TEM. (author)

2010-01-01

104

Determination of the natural valence-band offset in the In/sub x/Ga/sub 1-//sub x/As system  

Energy Technology Data Exchange (ETDEWEB)

The natural valence-band offset (NVBO) between semiconductors in a common anion alloy system can be determined through photoemission core level measurements. In this work, we tested this method in the In/sub x/Ga/sub 1-//sub x/As system. The NVBO between GaAs and InAs is measured to be 0.11 +- 0.05 eV. This result is in approximate agreement with the experimental value of 0.17 +- 0.07 eV determined by x-ray photoemission spectroscopy measurements.

Hwang, J.; Pianetta, P.; Shih, C.K.; Spicer, W.E.; Pao, Y.; Harris J.S. Jr.

1987-11-16

105

Study of the valence bands of FePS/sub 3/ and NiPS/sub 3/ by resonant-photoemission spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

We have investigated the valence bands of the tiophosphates FePS/sub 3/ and NiPS/sub 3/ with the resonant-photoemission technique. Some structures of the energy distribution curves show rapid intensity changes when the photon energy is scanned across the Fe or Ni 3p absorption thresholds. Instead, other structures show smooth excitation spectra. We have related the former to the transition metal ion 3d states (direct photoemission and satellites) and the latter to the (P/sub 2/S/sub 6/)/sup 4 -/ states. These results support also a strongly ionic picture of these compounds.

Piacentini, M.; Grasso, V.; Santangelo, S.; Fanfoni, M.; Modesti, S.; Savoia, A.

1984-11-01

106

Raising the thermoelectric performance of p-type PbS with endotaxial nanostructuring and valence-band offset engineering using CdS and ZnS.  

UK PubMed Central (United Kingdom)

We have investigated in detail the effect of CdS and ZnS as second phases on the thermoelectric properties of p-type PbS. We report a ZT of ~1.3 at 923 K for 2.5 at.% Na-doped p-type PbS with endotaxially nanostructured 3.0 at.% CdS. We attribute the high ZT to the combination of broad-based phonon scattering on multiple length scales to reduce (lattice) thermal conductivity and favorable charge transport through coherent interfaces between the PbS matrix and metal sulfide nanophase precipitates, which maintains the requisite high carrier conductivity and the associated power factor. Similar to large ionically bonded metal sulfides (ZnS, CaS, and SrS), the covalently bonded CdS can also effectively reduce the lattice thermal conductivity in p-type PbS. The presence of ubiquitous nanostructuring was confirmed by transmission electron microscopy. Valence and conduction band energy levels of the NaCl-type metal sulfides, MS (M = Pb, Cd, Zn, Ca, and Sr) were calculated from density functional theory to gain insight into the band alignment between PbS and the second phases in these materials. The hole transport is controlled by band offset minimization through the alignment of valence bands between the host PbS and the embedded second phases, MS (M = Cd, Zn, Ca, and Sr). The smallest valence band offset of about 0.13 eV at 0 K was found between PbS and CdS which is diminished further by thermal band broadening at elevated temperature. This allows carrier transport between the endotaxially aligned components (i.e., matrix and nanostructure), thus minimizing significant deterioration of the hole mobility and power factor. We conclude the thermoelectric performance of the PbS system and, by extension, other systems can be enhanced by means of a closely coupled phonon-blocking/electron-transmitting approach through embedding endotaxially nanostructured second phases.

Zhao LD; He J; Hao S; Wu CI; Hogan TP; Wolverton C; Dravid VP; Kanatzidis MG

2012-10-01

107

Band dispersion of MgB sub 2 , graphite and diamond from resonant inelastic scattering  

CERN Multimedia

The quantitative band mapping for MgB sub 2 , graphite and diamond are realized using resonant inelastic x-ray scattering (RIXS) measurements. RIXS shows distinct dispersive features when the excitation energy is tuned near B 1s and C 1s thresholds, which are assigned to the calculated energy bands using k sup->-momentum conservation. The agreement between experiment and theory suggests that electron-electron interactions are not important for MgB sub 2 , which behaves like a conventional metal and is well described by band theory.

Sokolov, A V; Leitch, S; Moewes, A; Kortus, J; Finkelstein, L D; Skorikov, N A; Xiao, C; Hirose, A

2003-01-01

108

Band dispersion of MgB2, graphite and diamond from resonant inelastic scattering  

International Nuclear Information System (INIS)

The quantitative band mapping for MgB2, graphite and diamond are realized using resonant inelastic x-ray scattering (RIXS) measurements. RIXS shows distinct dispersive features when the excitation energy is tuned near B 1s and C 1s thresholds, which are assigned to the calculated energy bands using k?-momentum conservation. The agreement between experiment and theory suggests that electron-electron interactions are not important for MgB2, which behaves like a conventional metal and is well described by band theory.

2003-04-02

109

HOMO band dispersion of crystalline rubrene: Effects of self-energy corrections within the GW approximation  

Science.gov (United States)

We investigate the band dispersion and relevant electronic properties of rubrene single crystals within the GW approximation. Due to the self-energy correction, the dispersion of the highest occupied molecular orbital (HOMO) band increases by 0.10 eV compared to the dispersion of the Kohn-Sham eigenvalues within the generalized gradient approximation, and the effective hole mass consequently decreases. The resulting value of 0.90 times the electron rest mass along the ?-Y direction in the Brillouin zone is closer to experimental measurements than that obtained from density-functional theory. The enhanced bandwidth is explained in terms of the intermolecular hybridization of the HOMO(Y) wave function along the stacking direction of the molecules. Overall, our results support the bandlike interpretation of charge-carrier transport in rubrene.

Yanagisawa, Susumu; Morikawa, Yoshitada; Schindlmayr, Arno

2013-09-01

110

Valence bands of the Cu-III-VI2 chalcopyrites studied by photoemission spectra, X-ray emission spectra, and electronic structure calculations  

International Nuclear Information System (INIS)

Ultraviolet and X-ray excited photoemission spectra and Cu K?5 X-ray emission spectra are used to measure the valence band density of states in CuGaTe2 and CuInTe2. In both compounds the density of states exhibits five structures which are ascribed to Cu 3d-Te 5p hybridized states, Ga 4s/In 5s-Te 5p bonding states, and Te 5s states. The valence band density of states of all Ga- and In-containing Cu-III-VI2 is calculated in an atomic orbital basis with the noble metal d states explicitly included. The agreement between theory and experiment is good for CuGaTe2 and except the In 5s-VI p bonding states also for the Cu-In-VI2 chalcopyrites. Larger discrepancies between theory and experiment are found for CuGaS2 and CuGaSe2. (author)

1984-02-01

111

Pressure effects on the intervalence-transfer band of salts of mixed-valence 1',1'''-disubstituted biferrocenium cations  

Energy Technology Data Exchange (ETDEWEB)

The pressure dependence of the intervalence-transfer (IT) electronic absorption band has been determined for the mixed-valence biferrocenium and 1',1'''-diethylbiferrocenium cations intercalated into a clay and for the following eight microcrystalline compounds: biferrocenium triiodide (1); biferrocenium hexafluorophosphate (2); 1',1'''-diiodobiferrocenium triiodide (3); 1',1'''-diiodobiferrocenium dibromoiodate (4); 1',1'''-dibromobiferrocenium triiodide (5); 1',1'''-dichlorobiferrocenium triiodide hemiiodine (6); 1',1'''-diethylbiferrocenium triiodide (7); 1',1'''-di-n-butylbiferrocenium triiodide (8). Basically three different types of pressure dependencies of the energy of the IT band are seen. Compounds 3-5, which have a solid-state packing arrangement consisting of alternating stacks of cations and anions, exhibit one type of behavior. For these three compounds the IT band shifts blue initially with pressure, and above approx. 80 kbar there is the onset of a rather abrupt reversal where the IT band shifts red with increasing pressure.

Sinha, U.; Lowery, M.D.; Ley, W.W.; Drickamer, H.G.; Hendrickson, D.N.

1988-04-13

112

First-principles study of valence band offsets at ZnSnP2/CdS, ZnSnP2/ZnS, and related chalcopyrite/zincblende heterointerfaces  

Science.gov (United States)

The valence band offsets of chalcopyrite ZnSnP2 (ZSP), CdSnP2 (CSP), CuInSe2 (CIS), and CuGaSe2 (CGS) against zincblende CdS and ZnS are obtained using first-principles calculations based on hybrid density functional theory. The ZSP-CSP (ZCSP) alloy is isostructural to the CIS-CGS (CIGS) alloy and is known for its potential usage in photovoltaic applications. Therefore, the band offsets with other semiconductors, such as CdS and ZnS, are important. The calculated valence band offsets are ~1.0 eV for ZSP/CdS and CSP/CdS, ~1.2 eV for ZSP/ZnS and CSP/ZnS, ~1.2 eV for CIS/CdS and CGS/CdS, and ~1.3 eV for CIS/ZnS and CGS/ZnS. The CdS/ZnS valence band offset is within 0.1 eV. Transitivity of natural valence band offsets in the investigated semiconductors holds within ~0.1 eV, which is smaller than the error in band alignment of ~0.2 eV when ionization potential differences are used. The ZSP-CSP and CIS-CGS systems have similar valence and conduction band positions, which is an important piece of information for band offset engineering in the development of photovoltaics using ZCSP alloys.

Hinuma, Yoyo; Oba, Fumiyasu; Nose, Yoshitaro; Tanaka, Isao

2013-07-01

113

Giant optical anisotropy in R-plane GaN/AlGaN quantum wells caused by valence band mixing effect  

International Nuclear Information System (INIS)

[en] This study investigates the optical anisotropy spectrum in the R-plane (i.e., the [101-bar2]-oriented layer plane) of GaN/Al0.2Ga0.8N quantum wells of different widths. The optical matrix elements in the wurtzite quantum wells are calculated using the k.p finite difference scheme. The calculations show that the valence band mixing effect produces giant in-plane optical anisotropy in [101-bar2]-oriented GaN/Al0.2Ga0.8N quantum wells with a narrow width. The nature of the in-plane optical anisotropy is found to be dependent on the well width. Specifically, it is found that the anisotropy changes from x'-polarization to y'-polarization as the well width increases

2008-03-03

114

Valence-band-mixing effects on the optical gain of GaAs/AlxGa1-xAs graded single quantum wells  

International Nuclear Information System (INIS)

Full text: In the last few years the semiconductor lasers have been attractive for research because they are both physically very interesting and technologically important. This is especially true for quantum well lasers since, with the current technology of quantum wells, it is possible to control the range, depth, and arrangement of quantum mechanical potential wells, which can be useful to make very good lasers. In the last decade the importance of the quantum well laser has steadily grown until today, where it is preferred for most semiconductor laser applications. This growing popularity is because, in almost every aspect, the quantum well laser is somewhat better than the conventional one with bulk active layers. In this work, we have calculated the optical gain spectra in the unstrained graded GaAs/Al0.2Ga0.8As single quantum well laser as a function of the energy of the radiation and the interface width. The calculation of the electronic structure was done using the parabolic band model. The calculation of the valence band structure was done taking into account the effects of sub-band mixing between the heavy and light holes, as well as by using an effective Hamiltonian approach based on the k-vector · p-vector Luttinger-Kohn method. The optical gain was calculated using the density matrix approach, considering all sub-band transitions in the quantum well. We consider both the transversal electrical and the transversal magnetic light polarization. Our results show that the peak gain is sensitive to the width and the graded profile of the interfaces, and the gain spectrum is blue-shifted as a function of the interface width. (author)

2004-01-01

115

Chemical effects on valence?L emissions of lanthanide compounds  

International Nuclear Information System (INIS)

Ce L? emission spectra of CeF3 and CeO2 have been measured with energy resolution of ? 3 eV by a wave-dispersive spectrometer. The observed Ce L?7 band shows certain difference between the two compounds both in profile and intensity. The chemical effects can be reproduced by a band calculation using WIEN2k, which suggests that the Ce L?7 reflects valence-band structure of compounds, and therefore, is hopeful as a probe of selective X-ray absorption fine structure.

2009-01-01

116

Energy dispersion compensation and beam loading in X-band linacs for the JLC/NLC  

CERN Multimedia

The shape of an RF pulse is distorted upon propagating through an X-band accelerator structure due to dispersive effects. This distortion together with beam loading introduce energy spread between 192 bunches. In order to minimize this energy spread we modify the input RF pulse shape. The pulse propagation, energy gain, and beam loading are modelled with a mode-matching computer code and a circuit model. A 2D model and a circuit model of a complete 60 cm structure, consisting of 55 cells and input and output couplers is analyzed. This structure operates with a 5pi/6 phase advance per cell. Dispersive effects for this structure are more significant than for previously studied 2pi/3 phase advance accelerating structures. Experimental results are compared with the theoretical model and excellent agreement is obtained for the propagation of an RF pulse through the structure.

Dolgashev, Valery A; Tantawi, Sami G; Higashi, Yasuo; Higo, Toshiyasu

2003-01-01

117

Energy Dispersion Compensation and Beam Loading in X-Band Linacs for the JLC/NLC  

Energy Technology Data Exchange (ETDEWEB)

The shape of an RF pulse is distorted upon propagating through an X-band accelerator structure due to dispersive effects. This distortion together with beam loading introduce energy spread between 192 bunches. In order to minimize this energy spread we modify the input RF pulse shape. The pulse propagation, energy gain, and beam loading are modeled with a mode-matching computer code and a circuit model. A 2D model and a circuit model of a complete 60 cm structure, consisting of 55 cells and input and output couplers is analyzed. This structure operates with a 5{pi}/6 phase advance per cell. Dispersive effects for this structure are more significant than for previously studied 2{pi}/3 phase advance accelerating structures. Experimental results are compared with the theoretical model and excellent agreement is obtained for the propagation of an RF pulse through the structure.

Jones, Roger M

2003-06-06

118

High-energy anomaly in the band dispersion of the ruthenate superconductor.  

UK PubMed Central (United Kingdom)

We reveal a "high-energy anomaly" (HEA) in the band dispersion of the unconventional ruthenate superconductor Sr2RuO4, by means of high-resolution angle-resolved photoemission spectroscopy (ARPES) with tunable energy and polarization of incident photons. This observation provides another class of correlated materials exhibiting this anomaly beyond high-T(c) cuprates. We demonstrate that two distinct types of band renormalization associated with and without the HEA occur as a natural consequence of the energetics in the bandwidth and the energy scale of the HEA. Our results are well reproduced by a simple analytical form of the self-energy based on the Fermi-liquid theory, indicating that the HEA exists at a characteristic energy scale of the multielectron excitations. We propose that the HEA universally emerges if the systems have such a characteristic energy scale inside of the bandwidth.

Iwasawa H; Yoshida Y; Hase I; Shimada K; Namatame H; Taniguchi M; Aiura Y

2012-08-01

119

Valence Band Character of NiS2-xSex using 3p-3d Resonant ARPES  

Science.gov (United States)

Understanding the strong correlated system is one of the most challenging tasks in condensed matter physics. Especially, the metal insulator transition (MIT) has been one of the major topics recent few decades. NiS2-xSex is known as one of famous material which has MIT. The cubic pyrite NiS2 is a charge-transfer (CT) insulator. NiS2 attracts particular interest as it easily forms a solid solution with NiSe2 (NiS2-xSex) which, while being isoelectronic and isostructural to NiS2, is nevertheless a good metal. MIT, induced by Se alloying, is observed at low temperature (T) for x=0.45. Perucchi and his collaborators revealed closed relation between MIT and band width through comparison of infrared spectroscopy result and LDA calculation. However, it was only an indirect observation, and is inconsistent with recent proposal that NiS2 is not a CT insulator but an insulator due to the bonding-antibonding splitting in the S -- S (Se -- Se) dimers. To reveal the true mechanism in the MIT in NiS2-xSex, resonant photoemission experiment is essential. According to competing theories (CT insulator and insulator due to bonding-antibonding splitting), it is expected that the character of the main band that is responsible for the MIT should be different. Therefore, we performed 3p-3d resonant ARPES for various Se dopings (x=0.43; insulator, x=0.5, 0.7, 2.0; metal) and observed a significant change between on- and off-resonances near the MIT. Our experimental result supports that the origin of MIT in NiS2-xSex is the CT theory rather than the dimer theory.

Han, Garam; Kim, Yeongkwan; Koh, Yoonyoung; Kim, Beomyoung; Song, Dongjoon; Seo, Jungjin; Kyung, Wonshik; Lee, Kyungdong; Kim, Changyoung

2013-03-01

120

Quantum interference in absorption and dispersion of a four-level atom in a double-band photonic crystal  

International Nuclear Information System (INIS)

The probe absorption-dispersion spectrum of a double V-type four-level atom in a double-band photonic crystal is investigated. In the model used, the double V-type transitions are, respectively, coupled by the free vacuum modes and the photonic band gap modes, leading to the two possible types of quantum interference. Three types of zero absorption (transparency) appear in this model. In the first type, there exist two zeroes at the band edge frequencies in the case of isotropic photonic band gap. In the second type, a zero emerges at the middle frequency of two upper levels in the case that the quantum interference takes place in both V-type transitions. Finally, in the third type, a zero occurs at or around the middle frequency of two upper levels in the case that the quantum interference takes place only in the V-type transitions coupled to the free vacuum modes. Ultimately, the probe absorption-dispersion spectrum in the case of the single-band photonic band gap reservoirs compared to those of the double-band photonic band gap reservoirs. The results show that the dispersion property of the system depends on the two types of the quantum interference and the density of states of the photonic band gap reservoir.

2007-01-01

 
 
 
 
121

Gate-controlled zero-magnetic-field spin splitting in the valence band of asymmetric AlGaAs/GaAs quantum wells  

Energy Technology Data Exchange (ETDEWEB)

Zero-magnetic-field-spin-splitting (ZMFSS) in two-dimensional quantum wells (QW) induced by the structure inversion asymmetry, and its control, are of major importance for both fundamental research and spintronic applications, due to its influence on the dynamics and manipulation of the spin. In hole systems the asymmetry leads to a ZMFSS of the heavy hole (HH) states in third order of the in-plane wave vector k {sub parallel}. In our experiments, we focus on highly p-doped asymmetric 2D AlGaAs/GaAs quantum wells (QW). with different QW widths and spacer thicknesses and the manipulation of the Rashba spin splitting via top gates. We utilize electronic intersubband Raman measurements in backscattering geometry at 4.2 K. Using polarization selection rules, one can distinguish between charge-density excitation (CDE, polarized spectra) and spin-density excitation (SDE, depolarized spectra) in the Raman spectra. In all samples we observe a low-energy SDE with excitation energies in the range of 0-2 meV. Comparing these excitation energies to 8 band k.p calculations of the valence subbands, the SDE can be interpreted as an intersubband excitation of the spin-split HH ground state, reflecting directly the ZMFSS.

Hirmer, Michael; Hirmer, Marika; Schuh, Dieter; Wegscheider, Werner; Korn, Tobias; Schueller, Christian [Institut fuer Experimentelle und Angewandte Physik, Universitaet Regensburg (Germany)

2010-07-01

122

A Direct Measurement of Atmospheric Dispersion in N-band Spectra: Implications for Mid-IR Systems on ELTs  

CERN Multimedia

Adaptive optics will almost completely remove the effects of atmospheric turbulence at 10 microns on the Extremely Large Telescope (ELT) generation of telescopes. In this paper, we observationally confirm that the next most important limitation to image quality is atmospheric dispersion, rather than telescope diffraction. By using the 6.5 meter MMT with its unique mid-IR adaptive optics system, we measure atmospheric dispersion in the N-band with the newly commissioned spectroscopic mode on MIRAC4-BLINC. Our results indicate that atmospheric dispersion is generally linear in the N-band, although there is some residual curvature. We compare our measurements to theory, and make predictions for ELT Strehls and image FHWM with and without an atmospheric dispersion corrector (ADC). We find that for many mid-IR applications, an ADC will be necessary on ELTs.

Skemer, Andrew; Hoffmann, William; Close, Laird; Kendrew, Sarah; Mathar, Richard; Stuik, Remko; Greene, Thomas; Woodward, Charles; Kelley, Michael

2009-01-01

123

Spectral properties of quasi-one-dimensional conductors with a finite transverse band dispersion  

International Nuclear Information System (INIS)

We determine the one-particle spectral function and the corresponding derived quantities for the conducting chain lattice with finite inter-chain hopping tperpendicular and three-dimensional long-range Coulomb electron-electron interaction. The standard G0W0 approximation is used. It is shown that, due to the optical character of the anisotropic plasmon dispersion caused by the finite tperpendicular, a low energy quasi-particle ?-peak appears in the spectral function in addition to the hump present at energies of the order of the plasmon energy. Particular attention is devoted to the continuous crossover from the non-Fermi liquid regime to the Fermi liquid regime with increasing tperpendicular. It is shown that the spectral weight of the hump transfers to the quasi-particle as the optical gap in the plasmon dispersion increases together with tperpendicular, with the quasi-particle residuum Z behaving like -ln tperpendicular)-1 in the limit tperpendicular ?0. Our approach is appropriate for the wide range of energy scales given by the plasmon energy and the width of the conduction band, and is complementary to the Luttinger liquid techniques that are limited to the low energy regime close to the Fermi surface

2008-08-13

124

Spectral properties of quasi-one-dimensional conductors with a finite transverse band dispersion  

Energy Technology Data Exchange (ETDEWEB)

We determine the one-particle spectral function and the corresponding derived quantities for the conducting chain lattice with finite inter-chain hopping t{sub perpendicular} and three-dimensional long-range Coulomb electron-electron interaction. The standard G{sub 0}W{sub 0} approximation is used. It is shown that, due to the optical character of the anisotropic plasmon dispersion caused by the finite t{sub perpendicular}, a low energy quasi-particle {delta}-peak appears in the spectral function in addition to the hump present at energies of the order of the plasmon energy. Particular attention is devoted to the continuous crossover from the non-Fermi liquid regime to the Fermi liquid regime with increasing t{sub perpendicular}. It is shown that the spectral weight of the hump transfers to the quasi-particle as the optical gap in the plasmon dispersion increases together with t{sub perpendicular}, with the quasi-particle residuum Z behaving like -ln t{sub perpendicular}){sup -1} in the limit t{sub perpendicular} {yields}0. Our approach is appropriate for the wide range of energy scales given by the plasmon energy and the width of the conduction band, and is complementary to the Luttinger liquid techniques that are limited to the low energy regime close to the Fermi surface.

Losic, Z Bonacic; Zupanovic, P [Department of Physics, Faculty of Natural Sciences, Mathematics and Kinesiology, University of Split, Teslina 12, 21000 Split (Croatia); Bjelis, A [Department of Physics, Faculty of Science, University of Zagreb, POB 162, 10001 Zagreb (Croatia)], E-mail: agicz@pmfst.hr, E-mail: bjelis@phy.hr

2008-08-13

125

The additional contribution caused by Coulomb interaction to the exciton dispersion in multiple quantum wells and superlattices for direct band gap cubic semiconductors  

International Nuclear Information System (INIS)

[en] The exciton dispersion in multiple quantum wells and superlattices is studied for direct band gap cubic semiconductors in the three-band-model. The Coulomb interaction between the light and heavy exciton states in different wells is calculated. This leads to a direction dependence and split of the exciton dispersion. (author). 21 refs

1992-01-01

126

Electronic structure investigation of MoS2 and MoSe2 using angle-resolved photoemission spectroscopy and ab initio band structure studies.  

UK PubMed Central (United Kingdom)

Angle-resolved photoemission spectroscopy (ARPES) and ab initio band structure calculations have been used to study the detailed valence band structure of molybdenite, MoS(2) and MoSe(2). The experimental band structure obtained from ARPES has been found to be in good agreement with the theoretical calculations performed using the linear augmented plane wave (LAPW) method. In going from MoS(2) to MoSe(2), the dispersion of the valence bands decreases along both k(parallel) and k(perpendicular), revealing the increased two-dimensional character which is attributed to the increasing interlayer distance or c/a ratio in these compounds. The width of the valence band and the band gap are also found to decrease, whereas the valence band maxima shift towards the higher binding energy from MoS(2) to MoSe(2).

Mahatha SK; Patel KD; Menon KS

2012-11-01

127

Electronic structure investigation of MoS2 and MoSe2 using angle-resolved photoemission spectroscopy and ab initio band structure studies.  

Science.gov (United States)

Angle-resolved photoemission spectroscopy (ARPES) and ab initio band structure calculations have been used to study the detailed valence band structure of molybdenite, MoS(2) and MoSe(2). The experimental band structure obtained from ARPES has been found to be in good agreement with the theoretical calculations performed using the linear augmented plane wave (LAPW) method. In going from MoS(2) to MoSe(2), the dispersion of the valence bands decreases along both k(parallel) and k(perpendicular), revealing the increased two-dimensional character which is attributed to the increasing interlayer distance or c/a ratio in these compounds. The width of the valence band and the band gap are also found to decrease, whereas the valence band maxima shift towards the higher binding energy from MoS(2) to MoSe(2). PMID:23110779

Mahatha, S K; Patel, K D; Menon, Krishnakumar S R

2012-10-31

128

Photoluminescence modification by high-order photonic band with abnormal dispersion in ZnO inverse opal  

CERN Document Server

We measured the angle- and polarization-resolved reflection and photoluminescence spectra of ZnO inverse opals. Significant enhancement of spontaneous emission is observed. The enhanced emission not only has good directionality but also can be linearly polarized. A detailed theoretical analysis and numerical simulation reveal that such enhancement is caused by the abnormal dispersion of a high-order photonic band. The frozen mode at a stationary inflection point of a dispersion curve can strongly modify the intensity, directionality and polarization of spontaneous emission.

Noh, Heeso; Anderson, Mark A; Chang, Robert P H; Cao, Hui

2007-01-01

129

Luminescent-kinetic parameters of CsPbCl3 nanocrystals dispersed in wide-band perovskite-like matrices  

Directory of Open Access Journals (Sweden)

Full Text Available CsPbCl3 nanocrystals are obtained in perovskite-like CsBCl3 (B=Sr, Ca, Mg) matrices doped with Pb ions (CPb=0.05 and 1 mol.%). The luminescent-kinetic parameters of the CsPbCl3 nanocrystals dispersed in CsBCl3 (B=Sr, Ca, Mg) matrices are studied under the pulsed UV and X-ray excitation. The conclusion about the formation of CsPbCl3 nanocrystals is confirmed with the data of their luminescence decay kinetics and a short-wavelength shift of the exciton luminescence maximum, when compared to that of an excitonic luminescence in a bulk single CsPbCl3 crystal. Under the pulsed X-ray excitation, re-absorption of core-valence luminescence of CsBCl3 (B=Sr, Ca, Mg) matrices with the CsPbCl3 nanocrystals is registered.

S. Myagkota

2003-01-01

130

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

131

Probe absorption-dispersion spectra of a driven three-level atom in a double-band photonic crystal  

Energy Technology Data Exchange (ETDEWEB)

The probe absorption-dispersion spectra of a driven three-level atom in a double-band photonic crystal have been investigated. We use the model which assumes the upper levels of the atomic transitions coupled via a classical driving field. One of the transitions interacts with the free vacuum modes, and the other transition couples to the modes of the modified reservoir (photonic band gap). The effect of the classical driving field on the absorption-dispersion spectra of an atom is investigated in detail. Most interestingly, it is shown that the atom becomes transparent to a probe laser field coupled to the free space transition, and slow group velocities are obtained near the transparency window.

Entezar, S Roshan; Tajalli, H [Research Institute for Applied Physics and Astronomy, Tabriz University, Tabriz (Iran, Islamic Republic of)

2006-07-28

132

Chemical effects on valence{yields}L emissions of lanthanide compounds  

Energy Technology Data Exchange (ETDEWEB)

Ce L{beta} emission spectra of CeF{sub 3} and CeO{sub 2} have been measured with energy resolution of {approx} 3 eV by a wave-dispersive spectrometer. The observed Ce L{beta}{sub 7} band shows certain difference between the two compounds both in profile and intensity. The chemical effects can be reproduced by a band calculation using WIEN2k, which suggests that the Ce L{beta}{sub 7} reflects valence-band structure of compounds, and therefore, is hopeful as a probe of selective X-ray absorption fine structure.

Hayashi, Hisashi [Department of Chemical and Biological Sciences, Faculty of Science, Japan Women' s University, 2-8-1 Mejirodai, Bunkyo, Tokyo 112-8681 (Japan); PRESTO, Japan Science and Technology Agency, 5 Sanbancho, Chiyoda, Tokyo 102-0075 (Japan)], E-mail: hayashih@fc.jwu.ac.jp; Okada, Kyoko [Department of Chemical and Biological Sciences, Faculty of Science, Japan Women' s University, 2-8-1 Mejirodai, Bunkyo, Tokyo 112-8681 (Japan)

2009-08-15

133

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

134

High-resolution (GaAs) sub 1 minus x (Ge sub 2 ) sub x x-ray photoelectron valence-band spectra: Implications for proposed electronic and structural models  

Energy Technology Data Exchange (ETDEWEB)

Valence-band density of states from sputter-deposited epitaxial metastable (GaAs){sub 1{minus}{ital x}}(Ge{sub 2}){sub {ital x}} alloys have been acquired by high-resolution x-ray photoelectron spectroscopy (XPS). Based upon a comparison of XPS results and previously published models of electronic and atomic structure, we conclude that (1) the virtual-crystal approximation is not valid for this system, (2) there are no significant numbers of Ga-Ga and As-As bonds, and (3) Ge is not incorporated randomly. The electronic and atomic structure of these metastable alloys is determined primarily by the large energy-level differences among Ga, As, and Ge atoms.

Kramer, B.; Tomasch, G.; Greene, J.E. (Department of Physics, University of Illinois, Urbana, Illinois 61801 (United States) Department of Materials Science, University of Illinois, Urbana, Illinois 61801 (United States)); Salvati, L. (Perkin-Elmer, Edison, New Jersey 08820 (United States)); Barr, T.L. (Department of Materials Science, University of Wisconsin, Milwaukee, Wisconsin 53201 (United States)); Ray, M.A. (Microelectronics Center of North Carolina, Research Triangle Park, North Carolina 27709 (United States))

1992-07-15

135

Energy-expending behaviour in frightened caribou when dispersed singly or in small bands  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The behaviour of single, and small bands of caribou (Rangifer tarandus groenlandicus) when confronted by humans was compared with the energy—saving behaviour zoologists have ascribed to caribou in encounters with non-hunting wolves (Canis lupus). When confronted by me, or upon getting my scent...

Otto Blehr

136

Si K, Si L, and Cr K x-ray valence-band studies of bonding in chromium silicides: Experiment and theory  

Science.gov (United States)

We present Si K, Si L, and Cr K x-ray emission bands of Cr3Si, CrSi, and CrSi2 together with Si K and Si L emission bands of Cr5Si3. The measured spectra are compared with ab initio pseudopotential calculations of the emission bands of Cr3Si, CrSi, and CrSi2. The Si L spectra were separated into contributions of Si s-like and Si d-like states. Good agreement between theory and experiment is found. The trends in development of spectral features with sample composition can be qualitatively understood by the bonding behavior of Cr and Si atoms.

Šim?nek, A.; Pol?ík, M.; Wiech, G.

1995-10-01

137

Analysis of photonic band gap in dispersive properties of tunable three-dimensional photonic crystals doped by magnetized plasma  

Science.gov (United States)

In this paper, the magnetooptical effects in dispersive properties for two types of three-dimensional magnetized plasma photonic crystals (MPPCs) containing homogeneous dielectric and magnetized plasma with diamond lattices are theoretically investigated for electromagnetic (EM) wave based on plane wave expansion (PWE) method, as incidence EM wave vector is parallel to the external magnetic field. The equations for two types of MPPCs with diamond lattices (dielectric spheres immersed in magnetized plasma background or vice versa) are theoretically deduced. The influences of dielectric constant, plasma collision frequency, filling factor, the external magnetic field, and plasma frequency on the dispersive properties for both types of structures are studied in detail, respectively, and some corresponding physical explanations are also given. From the numerical results, it has been shown that the photonic band gaps (PBGs) for both types of MPPCs can be manipulated by plasma frequency, filling factor, the external magnetic field, and the relative dielectric constant of dielectric, respectively. Especially, the external magnetic field can enlarge the PBG for type-2 structure (plasma spheres immersed in dielectric background). However, the plasma collision frequency has no effect on the dispersive properties of two types of three-dimensional MPPCs. The locations of flatbands regions for both types of structures cannot be tuned by any parameters except for plasma frequency and the external magnetic field. The analytical results may be informative and of technical use to design the MPPCs devices.

Zhang, Hai-Feng; Liu, Shao-Bin; Yang, Huan; Kong, Xiang-Kun

2013-03-01

138

Analysis of photonic band gap in dispersive properties of tunable three-dimensional photonic crystals doped by magnetized plasma  

Energy Technology Data Exchange (ETDEWEB)

In this paper, the magnetooptical effects in dispersive properties for two types of three-dimensional magnetized plasma photonic crystals (MPPCs) containing homogeneous dielectric and magnetized plasma with diamond lattices are theoretically investigated for electromagnetic (EM) wave based on plane wave expansion (PWE) method, as incidence EM wave vector is parallel to the external magnetic field. The equations for two types of MPPCs with diamond lattices (dielectric spheres immersed in magnetized plasma background or vice versa) are theoretically deduced. The influences of dielectric constant, plasma collision frequency, filling factor, the external magnetic field, and plasma frequency on the dispersive properties for both types of structures are studied in detail, respectively, and some corresponding physical explanations are also given. From the numerical results, it has been shown that the photonic band gaps (PBGs) for both types of MPPCs can be manipulated by plasma frequency, filling factor, the external magnetic field, and the relative dielectric constant of dielectric, respectively. Especially, the external magnetic field can enlarge the PBG for type-2 structure (plasma spheres immersed in dielectric background). However, the plasma collision frequency has no effect on the dispersive properties of two types of three-dimensional MPPCs. The locations of flatbands regions for both types of structures cannot be tuned by any parameters except for plasma frequency and the external magnetic field. The analytical results may be informative and of technical use to design the MPPCs devices.

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; Yang Huan [College of Electronic and Information Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China); Kong Xiangkun [College of Electronic and Information Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China); Jiangsu Key Laboratory of Meteorological Observation and Information Processing, Nanjing University of Information Science and Technology, Nanjing 210044 (China)

2013-03-15

139

Levels of valence.  

UK PubMed Central (United Kingdom)

The distinction between the positive and the negative is fundamental in our emotional life. In appraisal theories, in particular in the component process model of emotion (Scherer, 1984, 2010), qualitatively different types of valence are proposed based on appraisals of (un)pleasantness, goal obstructiveness/conduciveness, low or high power, self-(in)congruence, and moral badness/goodness. This multifaceted conceptualization of valence is highly compatible with the frequent observation of mixed feelings in real life. However, it seems to contradict the one-dimensional conceptualization of valence often encountered in psychological theories, and the notion of valence as a common currency used to explain choice behavior. Here, we propose a framework to integrate the seemingly disparate conceptualizations of multifaceted valence and one-dimensional valence by suggesting that valence should be conceived at different levels, micro and macro. Micro-valences correspond to qualitatively different types of evaluations, potentially resulting in mixed feelings, whereas one-dimensional macro-valence corresponds to an integrative "common currency" to compare alternatives for choices. We propose that conceptualizing levels of valence may focus research attention on the mechanisms that relate valence at one level (micro) to valence at another level (macro), leading to new hypotheses, and addressing various concerns that have been raised about the valence concept, such as the valence-emotion relation.

Shuman V; Sander D; Scherer KR

2013-01-01

140

Levels of Valence  

Science.gov (United States)

The distinction between the positive and the negative is fundamental in our emotional life. In appraisal theories, in particular in the component process model of emotion (Scherer, 1984, 2010), qualitatively different types of valence are proposed based on appraisals of (un)pleasantness, goal obstructiveness/conduciveness, low or high power, self-(in)congruence, and moral badness/goodness. This multifaceted conceptualization of valence is highly compatible with the frequent observation of mixed feelings in real life. However, it seems to contradict the one-dimensional conceptualization of valence often encountered in psychological theories, and the notion of valence as a common currency used to explain choice behavior. Here, we propose a framework to integrate the seemingly disparate conceptualizations of multifaceted valence and one-dimensional valence by suggesting that valence should be conceived at different levels, micro and macro. Micro-valences correspond to qualitatively different types of evaluations, potentially resulting in mixed feelings, whereas one-dimensional macro-valence corresponds to an integrative “common currency” to compare alternatives for choices. We propose that conceptualizing levels of valence may focus research attention on the mechanisms that relate valence at one level (micro) to valence at another level (macro), leading to new hypotheses, and addressing various concerns that have been raised about the valence concept, such as the valence-emotion relation.

Shuman, Vera; Sander, David; Scherer, Klaus R.

2013-01-01

 
 
 
 
141

Energy-expending behaviour in frightened caribou when dispersed singly or in small bands  

Directory of Open Access Journals (Sweden)

Full Text Available The behaviour of single, and small bands of caribou (Rangifer tarandus groenlandicus) when confronted by humans was compared with the energy—saving behaviour zoologists have ascribed to caribou in encounters with non-hunting wolves (Canis lupus). When confronted by me, or upon getting my scent, caribou ran away on all occasions. Their flight was occasionally interrupted by short stops to look back in my direction, but would continue on all occasions until they were out of sight. This behaviour is inconsistent with the one ascribed to caribou by zoologists when the intruder is a wolf instead of a human. In their view, the caribou stop their flight soon after the wolf gives up the chase, and accordingly save energy owing to their ability to distinguish between hunting and non-hunting wolves. However, small bands of caribou, as well as single animals, have never been observed to behave in this manner. On the contrary, the behaviour of caribou in such encounters is known to follow the same pattern as in their encounters with humans. Energy—saving behaviour is, however, sometimes observed when caribou become inquisitive about something in their surroundings. They will then readily approach as well as try to get down-wind of the object. When the object does not induce fear, it may simply be ignored, or charged before the caribou calm down. The effect of this "confirming behaviour" is that energy which would otherwise have been spent in needless flights from non-predators is saved.

Otto Blehr

1997-01-01

142

The valence electronic structure of polycrystalline SiC as observed by (e,2e) spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

The spectral momentum density of the valence electrons of a thin polycrystalline silicon carbide (SiC) film has been measured using an (e,2e) spectrometer employing a non-coplanar asymmetric geometry with estimated energy and momentum resolutions of about 2.0 eV and 0.15 a.u., respectively. Well-defined valence band dispersion has been observed from the measured momentum density which resembles a parabola, but deviates from what is expected for a free electron near the top to the band and at the boundary of the Brillouin zone, where the antisymmetric gap due to the unequal potentials between the Si and C sites in SiC is clearly visible. Based on the assumption that the special momentum density of polycrystalline materials is a spherical average of the spectral momentum density of the corresponding single crystalline phase of the materials, ab initio linear muffin-tin orbital (LMTO) calculations have been performed using the zinc-blende structure of {beta}-SiC. The measured dispersion of the energy band is in excellent agreement with theory. Reasonable agreement is also obtained for the energy-integrated momentum density, although the measured momentum density exceeds considerably the calculated one at high momenta. The theoretical implication of using crystal band structure calculations for studying disordered materials is also discussed. 21 refs., 8 figs.

Cai, Y.; Vos, M.; Storer, P.; Kheifets, A.S.; McCarthy, I.E.; Weigold, E.

1994-08-01

143

A simulation study of the effect of the diverse valence-band offset and the electronic activity at the grain boundaries on the performance of polycrystalline Cu(In,Ga)Se2 solar cells  

International Nuclear Information System (INIS)

The paper presents a two-dimensional simulation study of a polycrystalline Cu(In,Ga)Se2 (CIGS) solar cell with various shapes of grains inside the CIGS absorber layer. The grain boundaries (GBs) with a diverse valence-band offset (VBO) and the density of defect states (NtA) are considered so as to evaluate their effects on the performance of the CIGS cell. The numerical simulations show that a CIGS cell with column-like grains can achieve a high conversion efficiency (?), while the ? of a CIGS cell with diamond-like grains is low if the VBO at the GBs exceeds 0.4 eV. The VBO at which the ? of the CIGS cell with diamond-like grains peaks is found at 0.20-0.27 eV. A favorable VBO mainly depends on the shape of the grains, but it also depends on the NtA. The simulations of the CIGS cells in the substrate and superstrate configurations showed that their performances change if the VBO is varied. This result also implies that the configuration of the CIGS cell is important and the substrate configuration with larger grains in the space-charge region has a considerable advantage if the VBO ranges from 0 eV to 0.2 eV.

2011-08-31

144

Conduction- and Valence-Band Energies in Bulk InAs1- x Sb x and Type II InAs1- x Sb x /InAs Strained-Layer Superlattices  

Science.gov (United States)

The energy gaps were studied in two types of structures: unrelaxed bulk InAs1- x Sb x layers with x = 0.2 to 0.46 grown on metamorphic buffers and type II InAs1- x Sb x /InAs strained-layer superlattices (SLS) with x = 0.225 to 0.296 in the temperature range from T = 13 K to 300 K. All structures were grown on GaSb substrates. The longest wavelength of photoluminescence (PL) at low temperatures was observed from bulk InAs0.56Sb0.44 with a peak at 10.3 ?m and full-width at half-maximum (FWHM) of 11 meV. The PL data for the bulk InAs1- x Sb x materials of various compositions imply an energy gap bowing parameter of 0.87 eV. A low-temperature PL peak at 9.1 ?m with FWHM of 13 meV was observed for InAs0.704Sb0.296/InAs SLS. The PL spectrum of InAs0.775Sb0.225/InAs SLS under pulsed excitation revealed a second peak associated with recombination of electrons in the three-dimensional (3D) continuum with holes in the InAs0.775Sb0.225. This experiment determined the conduction-band offset in the InAs0.775Sb0.225/InAs SLS. The energies of the conduction and valence bands in unstrained InAs1- x Sb x and their bowing with respect to the Sb composition are discussed.

Lin, Youxi; Wang, Ding; Donetsky, Dmitry; Shterengas, Leon; Kipshidze, Gela; Belenky, Gregory; Svensson, Stefan P.; Sarney, Wendy L.; Hier, Harry S.

2013-05-01

145

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

146

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

147

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

148

MANIFESTATION OF DEFORMATION EFFECT IN BAND SPECTRA IN CRYSTALS WITH INHOMOGENEOUS BONDING  

Directory of Open Access Journals (Sweden)

Full Text Available The effect of the shear strains on the energy spectrum of the strongly anisotropic SbSI crystal has been investigated by group-theoretical method in combination with the Pikus method of invariants. The first-principles local density approximation has been implemented to determine the band structure of the crystal. Ab initio calculations of the band structure have shown an exact localization of twofold degenerate maximum of the valence band in the T point. It turned out that the shear strains result in the band topology changes in the vicinity of the T point and the k-linear term appears in the corresponding dispersion law.

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

2003-01-01

149

Strong Energy-momentum Dispersion of Phonon Dressed Carriers in the Lightly Doped Band Insulator SrTiO3  

Energy Technology Data Exchange (ETDEWEB)

Much progress has been made recently in the study of the effects of electron-phonon (el-ph) coupling in doped insulators using angle resolved photoemission (ARPES), yielding evidence for the dominant role of el-ph interactions in underdoped cuprates. As these studies have been limited to doped Mott insulators, the important question arises how this compares with doped band insulators where similar el-ph couplings should be at work. The archetypical case is the perovskite SrTiO{sub 3} (STO), well known for its giant dielectric constant of 10000 at low temperature, exceeding that of La{sub 2}CuO{sub 4} by a factor of 500. Based on this fact, it has been suggested that doped STO should be the archetypical bipolaron superconductor. Here we report an ARPES study from high-quality surfaces of lightly doped SrTiO{sub 3}. Comparing to lightly doped Mott insulators, we find the signatures of only moderate electron-phonon coupling: a dispersion anomaly associated with the low frequency optical phonon with a {lambda}{prime} {approx} 0.3 and an overall bandwidth renormalization suggesting an overall {lambda}{prime} {approx} 0.7 coming from the higher frequency phonons. Further, we find no clear signatures of the large pseudogap or small polaron phenomena. These findings demonstrate that a large dielectric constant itself is not a good indicator of el-ph coupling and highlight the unusually strong effects of the el-ph coupling in doped Mott insulators.

Meevasana, Warawat

2010-05-26

150

Band structure of MoS_2, MoSe_2, and alpha-MoTe_2 Angle-resolved photoelectron spectroscopy and ab-initio calculations  

CERN Multimedia

In this work the complete valence-band structure of the molybdenum dichalcogenides MoS_2, MoSe_2, and alpha-MoTe_2 is presented and discussed in comparison. The valence bands have been studied using both angle-resolved photoelectron spectroscopy (ARPES) with synchrotron radiation, as well as, ab-initio band-structure calculations. The ARPES measurements have been carried out in the constant-final-state (CFS) mode. The results of the calculations show in general very good agreement with the experimentally determined valence-band structures allowing for a clear identification of the observed features. The dispersion of the valence bands as a function of the perpendicular component k_perp of the wave vector reveals a decreasing three-dimensional character from MoS_2 to alpha-MoTe_2 which is attributed to an increasing interlayer distance in the three compounds. The effect of this k_perp dispersion on the determination of the exact dispersion of the individual states as a function of k_parallel is discussed. By p...

Böker, T; Müller, A; Janowitz, C; Manzke, R; Voss, D; Krüger, P; Mazur, A I; Pollmann, J; Boeker, Th.

2001-01-01

151

Derivation and characterization of dispersion of defect modes in photonic band gap from stacks of positive and negative index materials  

International Nuclear Information System (INIS)

[en] An expression is derived to predict the incident angle dependence of the frequency of defect modes inside the zero-n-bar gap of one-dimensional photonic crystals stacking with positive and negative index materials. From this expression, the dependence of the dispersion type of the defect mode on both the refractive index and the wave impedance of the component layers of the photonic crystal are given. For situations with a given value of permeability, it is found that, as the adjacent layers of the defect are low refractive index materials, only positive or negative type of angular dispersion exists; as the adjacent layers of the defect are high refractive index materials, all three types of angular dispersion, including the near-zero dispersion, appear with the refractive index of the defect changes. The dispersion relation diagrams of such photonic crystals are presented, the simulated results agree with the theoretical prediction

2006-03-13

152

Band structure of Si/Ge core-shell nanowires along the [110] direction modulated by external uniaxial strain  

International Nuclear Information System (INIS)

Strain modulated electronic properties of Si/Ge core-shell nanowires along the [110] direction were reported, on the basis of first principles density-functional theory calculations. In particular, the energy dispersion relationship of the conduction/valence band was explored in detail. At the ? point, the energy levels of both bands are significantly altered by applied uniaxial strain, which results in an evident change of the band gap. In contrast, for the K vectors far away from ?, the variation of the conduction/valence band with strain is much reduced. In addition, with a sufficient tensile strain (?1%), the valence band edge shifts away from ?, which indicates that the band gap of the Si/Ge core-shell nanowires experiences a transition from direct to indirect. Our studies further showed that effective masses of charge carriers can also be tuned using the external uniaxial strain. The effective mass of the hole increases dramatically with tensile strain, while strain shows a minimal effect on tuning the effective mass of the electron. Finally, the relation between strain and the conduction/valence band edge is discussed thoroughly in terms of site-projected wavefunction characters.

2011-03-23

153

Corrugated flat band as an origin of large thermopower in hole doped PtSb2  

Directory of Open Access Journals (Sweden)

Full Text Available The origin of the recently discovered large thermopower in hole-doped PtSb2 is theoretically analyzed based on a model constructed from first principles band calculation. It is found that the valence band dispersion has an overall flatness combined with some local ups and downs, which gives small Fermi surfaces scattered over the entire Brillouin zone. The Seebeck coefficient is calculated using this model, which gives good agreement with the experiment. We conclude that the good thermoelectric property originates from this “corrugated flat band”, where the coexistence of large Seebeck coefficient and large electric conductivity is generally expected.

Kouta Mori; Hidetomo Usui; Hirofumi Sakakibara; Kazuhiko Kuroki

2012-01-01

154

High performance broadband absorber in the visible band by engineered dispersion and geometry of a metal-dielectric-metal stack  

Science.gov (United States)

We propose a nanostructured broadband absorber in the visible regime through designing the dispersion and geometry of a Cu/Si3N4/Cu stack. Two examples with nearly perfect absorption at different spectral ranges are designed based on the special dispersion relationship and fabricated using nanoimprint lithography. Experiments confirm an ultra flat average absorption greater than 80% from 400 nm to 700 nm. The robustness of the design with angle insensitive absorption characteristic is desirable for the applications in thin-film thermal emitters and photovoltaic cells.

Zhu, Peng; Jay Guo, L.

2012-12-01

155

Fluctuating valence in SmS  

International Nuclear Information System (INIS)

[en] In the ground state of normal SmS, each rare-earth ion is in a (4f) 67F0 state, with all the other electrons filling valence bands. The symmetry of the ground state is therefore known. From an examination of the observed properties it is reasoned that when the lattice collapses under hydrostatic pressure (preserving the cubic symmetry) the new ground state has the same symmetry as the ground state of the uncollapsed phase. Since the new ground state shows fluctuating valence, the problem is to incorporate this feature into its detailed description. It is shown that this can be done in a variety of ways. It is further shown that a band of low-lying states, each with J = 0 at each site but with k is not equal to 0, can also be constructed, as well as higher bands with some sites having J = 1. The picture which emerges is thought to be helpful in providing a theoretical framework within which to discuss the phenomena associated with fluctuating valence. Experimental tests of the model are suggested, from a theory which can be developed further if substantiated. (author)

1976-04-28

156

Are valence quarks rotating?  

CERN Document Server

We suggest to compare the deep inelastic scattering structure functions measured in the unpolarized charged-lepton scattering off a transversely polarized proton and off a longitudinally polarized proton at larger Bjorken variable $x$, one may get a direct evidence concerning the valence quark orbital angular momentum in the proton. This possible rotating effect is estimated by using a proton-ensemble model.

Zhu, Wei

2012-01-01

157

Study on dispersion-induced phase noise in an optical OFDM radio-over-fiber system at 60-GHz band.  

UK PubMed Central (United Kingdom)

While coherency between an RF-tone and OFDM signals in RoF systems at 60 GHz is de-correlated by fiber dispersion, both phase rotation term (PRT) on each subcarrier and inter-carrier interference (ICI) between subcarriers are induced at a receiver. We analytically calculate the powers of PRT and ICI under different parameters, such as subcarrier number, modulation format, laser linewidth and transmission distance. Moreover, dispersion-induced ICI is shown to be non-Gaussian distributed by its kurtosis, and its distribution depends on system parameters. Therefore, using only the power of ICI cannot predict accurate bit error rate (BER) and corresponding power penalty. We propose to use t-distribution to fit the distribution of ICI, and it can be used to compute BER precisely.

Wei CC; Chen JJ

2010-09-01

158

Study on dispersion-induced phase noise in an optical OFDM radio-over-fiber system at 60-GHz band.  

Science.gov (United States)

While coherency between an RF-tone and OFDM signals in RoF systems at 60 GHz is de-correlated by fiber dispersion, both phase rotation term (PRT) on each subcarrier and inter-carrier interference (ICI) between subcarriers are induced at a receiver. We analytically calculate the powers of PRT and ICI under different parameters, such as subcarrier number, modulation format, laser linewidth and transmission distance. Moreover, dispersion-induced ICI is shown to be non-Gaussian distributed by its kurtosis, and its distribution depends on system parameters. Therefore, using only the power of ICI cannot predict accurate bit error rate (BER) and corresponding power penalty. We propose to use t-distribution to fit the distribution of ICI, and it can be used to compute BER precisely. PMID:20940972

Wei, Chia Chien; Chen, Jason Jyehong

2010-09-27

159

Gaining control over rare earth valence fluctuations  

Energy Technology Data Exchange (ETDEWEB)

This paper briefly deals with the problem of narrow band materials. It addresses a new theoretical approach to the fluctuation of valence electrons in rare earth elements. It is believed that the phenomena of interest arize from an instability of the partially filled d or f shell of certain atoms when they are put into a metallic host. The theoretical models which dominate the scene work with two local d or f states on one hand and a structureless sea of free conduction electrons on the other. This procedure ignores at least half of the essential physics; the other held is kept alive in the term valence fluctuation. Basically, what the prevalent models ignore is that, in all these systems, the entire atoms as the source of the anomalies are being dealt with, not just their f shells. In other words, there is important structure in the sea of conduction electrons.

Wohlleben, D.

1987-05-31

160

Dynamics of few-valence nucleon systems  

International Nuclear Information System (INIS)

The dynamics of 2 to 8 valence nucleon systems is discussed in the framework of the shell model and of a residual delta two-body force. Characteristic behaviors of the solutions are shown to be fairly independent of the nature of the shells or of the number of nucleons. The seniority and aligned schemes are tested by projection upon the exact solutions. The problem of nuclear shapes and band crossing is discussed either from the point of view of projecting particular intrinsic states on the exact solutions or from the quadrupole moment values of excited states. The results demonstrate the importance of angular momentum alignment in the nuclear dynamics of few valence nucleon systems, the failure of determinantal approximations of the yrast line states and the existence of remarquable regularities in the spectroscopic properties

1977-01-01

 
 
 
 
161

Valence structure of alkaline and post-transition metal oxides  

Science.gov (United States)

As a stepping point to predicting band gaps and electronic structure of more complicated materials based on alkaline and post-transition metal oxides, we examine the valence structure of these simple binary oxides using both high resolution X-ray emission spectroscopy and a variety of density functional theory calculations. We confirm that the new modified Becke-Johnson (mBJ) extension of the Perdew-Burke-Ernzerhoff (PBE96) functional provides a good estimate of the band gaps of these materials, but we demonstrate that it does not provide an accurate depiction of the valence structure in post-transition metal oxides. A calculation with an exact Hartree-Fock exchange energy does a better job of calculating the valence structure, but no longer accurately reproduces the band gap. Since we expect that d-p repulsion may play an important role in shaping the band gap, we suggest that combining the valence structure from the latter calculation with the band gap of the former calculation may be the best approach for predicting the electronic structure of more advanced materials based on these post-transition metal oxides precursors.

McLeod, John A.; Green, Robert J.; Skorikov, Nikolay A.; Finkelstein, L. D.; Abu-Samak, Mahmoud; Kurmaev, Ernst Z.; Moewes, Alexander

2011-02-01

162

Measurement of the spectral momentum distribution of valence electrons in amorphous carbon by (e,2e) spectroscopy.  

Science.gov (United States)

The spectral momentum density of the valence band of arc evaporated amorphous carbon has been measured by (e,2e) spectroscopy with significantly improved energy resolution relative to earlier studies. The valence band has been studied over a range of mome...

A. S. Kheifets J. Lower K. J. Nygaard S. Utteridge M. Vos

1993-01-01

163

Ductility Enhancement of Molybdenum Phase by Nano-sizedd Oxide Dispersions  

Energy Technology Data Exchange (ETDEWEB)

The present research is focused on ductility enhancement of molybdenum (Mo) alloys by adding nano-sized oxide particles to the alloy system. The research approach includes: (1) determination of microscopic mechanisms responsible for the macroscopic ductility enhancement effects through atomistic modeling of the metal-ceramic interface; (2) subsequent computer simulation-aided optimization of composition and nanoparticle size of the dispersion for improved performance; (3) synthesis and characterization of nanoparticle dispersion following the guidance from atomistic computational modeling analyses (e.g., by processing a small sample of Mo alloy for evaluation); and (4) experimental testing of the mechanical properties to determine optimal ductility enhancement.Through atomistic modeling and electronic structure analysis using full-potential linearized muffin-tin orbital (FP-LMTO) techniques, research to date has been performed on a number of selected chromium (Cr) systems containing nitrogen (N) and/or magnesium oxide (MgO) impurities. The emphasis has been on determining the properties of the valence electrons and the characteristics of the chemical bonds they formed. It was found that the brittle/ductile behavior of this transitional metal system is controlled by the relative population of valence charges: bonds formed by s valence electrons yield metallic, ductile behavior, whereas bonds formed by d valence electrons lead to covalent, brittle behavior. The presence of valence bands from impurities also affects the metal bonding, thereby explaining the detrimental and beneficial effects induced by the inclusion of N impurities and MgO dispersions. These understandings are useful for optimizing ductility enhancement effects on the dispersion materials.

Bruce Kang

2008-07-31

164

Energy spectra of fractional quantum Hall systems in the presence of a valence hole  

CERN Document Server

The energy spectrum of a two-dimensional electron gas (2DEG) in the fractional quantum Hall regime interacting with an optically injected valence band hole is studied as a function of the filling factor $\

Wójs, A; Wojs, Arkadiusz; Quinn, John J.

2001-01-01

165

??????????? ? ??????????(Valency and isomorphism)  

Directory of Open Access Journals (Sweden)

Full Text Available Valency relations in a paraphrase should match those of the source expres- sion. This kind of isomorphism is investigated in the present article.In the passive sentence The plant was visited by Putin the relation between Putin and plant is the same as in the corresponding active sentence. It is not equally easy to see how isomorphism can be preserved in, for example, Who is the author of these lines?, derived from Who wrote these lines? This is achieved by introducing a new concept of basic semantic unit. Obviously, the predicate write, which is explicit in the source expression, must somehow be introduced in the semantic representation of the para- phrase. There are two ways of accounting for this "missing" predicate. It can either be extracted (computed) from the words author and lines and assume the form of an implicit predicate, or the corresponding meaning can be car- ried by an agreement morpheme attached to the noun author (in the Russian paraphrase this noun is marked with the so-called agreement case). The first actant of write needs to be represented only once - through the word who - and therefore the noun author is assigned syntactic status, which means that it does not occupy a node of its own in the semantic graph.A number of further examples - not only sentences, but also phrases and words - are analysed in order to illustrate different cases of isomor- phism.

Lennart Lönngren

2008-01-01

166

Pressure Induced Valence Transitions in f-Electron Systems  

CERN Multimedia

A review is given of pressure induced valence transitions in f-electron systems calculated with the self-interaction corrected local spin density (SIC-LSD) approximation. These calculations show that the SIC-LSD is able to describe valence changes as a function of pressure or chemical composition. An important finding is the dual character of the f-electrons as either localized or band-like. A finite temperature generalisation is presented and applied to the study of the p-T phase diagram of the alpha to gamma phase transition in Ce.

Temmerman, W M; Petit, L; Lueders, M; Strange, P; Szotek, Z

2006-01-01

167

Valence transversities: the collinear extraction  

CERN Document Server

In these proceedings, we propose an extraction of the valence transversity parton distributions. Based on an analysis of pion-pair production in deep-inelastic scattering off transversely polarized targets, this extraction of transversity is performed in the framework of collinear factorization. The recently released data for proton and deuteron targets at HERMES and COMPASS allow for a flavor separation of the valence transversities, for which we give a complete statistical study.

Courtoy, A; Radici, Marco

2013-01-01

168

Choice of compounds with fast core-valence transitions  

Energy Technology Data Exchange (ETDEWEB)

It is now well established that in a number of wide gap ionic crystals a specific intrinsic luminescence can be observed due to radiative hole transitions between the upper core band and valence band. The progress in knowledge about core-valence (CV) transitions is considered in papers. The CV transitions were first observed and interpreted in BaF{sub 2} crystals. The intrinsic luminescence due to CV transitions has a short decay time ({approximately}1ns), a high thermal stability in all its parameters, and a relatively high yield. Because of these luminescence properties, crystals with radiative CV transitions are promising scintillators. Such scintillators are particularly important in devices with a high counting rate, for instance in emission tomography. The presence of a filled valence band above the core band in which the hole is created presents the possibility of population inversion at high excitation densities. This aspect creates new possibilities for producing optical amplification and generation. This work examines different approaches to the problem of CV transitions. A class of ionic crystals, in which the radiative transitions are most efficient, is identified. It is shown how to obtain the necessary spectral width of emission, and the possibility of controlling the decay time of the emission is discussed.

Rodnyi, P.A. [State Technical Univ., St. Petersburg (Russian Federation). Dept. of Experimental Physics

1994-12-31

169

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

170

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

171

Valency Configuration of Transition Metal Impurities in ZnO  

CERN Multimedia

We use the self-interaction corrected local spin-density approximation to investigate the ground state valency configuration of transition metal (TM = Mn, Co) impurities in n- and p-type ZnO. We find that in pure Zn1-xTMxO, the localized TM2+ configuration is energetically favored over the itinerant d-electron configuration of the local spin density (LSD) picture. Our calculations indicate furthermore that the (+/0) donor level is situated in the ZnO gap. Consequently, for n-type conditions, with the Fermi energy eF close to the conduction band minimum, TM remains in the 2+ charge state, while for p-type conditions, with eF close to the valence band maximum, the 3+ charge state is energetically preferred. In the latter scenario, modeled here by co-doping with N, the additional delocalized d-electron charge transfers into the entire states at the top of the valence band, and hole carriers will only exist, if the N concentration exceeds the TM impurity concentration.

Petit, L; Svane, A; Temmerman, W M; Szotek, Z; Janotti, A

2006-01-01

172

Three-band tight-binding model for monolayers of group-VIB transition metal dichalcogenides  

Science.gov (United States)

We present a three-band tight-binding (TB) model for describing the low-energy physics in monolayers of group-VIB transition metal dichalcogenides MX2 (M=Mo, W; X=S, Se, Te). As the conduction- and valence-band edges are predominantly contributed by the dz2, dxy, and dx2-y2 orbitals of M atoms, the TB model is constructed using these three orbitals based on the symmetries of the monolayers. Parameters of the TB model are fitted from the first-principles energy bands for all MX2 monolayers. The TB model involving only the nearest-neighbor M-M hoppings is sufficient to capture the band-edge properties in the ±K valleys, including the energy dispersions as well as the Berry curvatures. The TB model involving up to the third-nearest-neighbor M-M hoppings can well reproduce the energy bands in the entire Brillouin zone. Spin-orbit coupling in valence bands is well accounted for by including the on-site spin-orbit interactions of M atoms. The conduction band also exhibits a small valley-dependent spin splitting which has an overall sign difference between MoX2 and WX2. We discuss the origins of these corrections to the three-band model. The three-band TB model developed here is efficient to account for low-energy physics in MX2 monolayers, and its simplicity can be particularly useful in the study of many-body physics and physics of edge states.

Liu, Gui-Bin; Shan, Wen-Yu; Yao, Yugui; Yao, Wang; Xiao, Di

2013-08-01

173

XANES Pb LIII spectra of mixed-valence compound: Minium, Pb3O4  

CERN Multimedia

Mixed-valence compound Pb3O4 (minium) has been studied using X-ray absorption near-edge structure (XANES) spectroscopy and DFT calculations. In spite of presence of two valence states of lead [Pb(II) and Pb(IV)], the XANES spectrum of studied system is corresponding to apparently unified, an intermediate valence state of Pb. On the other hand, the 207Pb NMR spectra definitely show two different spectral bands corresponding to different Pb2+ and Pb4+ ions in Pb3O4 crystal structure. The explanation of this contradiction is related to the basics of XANES and NMR spectroscopy.

Gabuda, S P; Erenburg, S B; Bausk, N V

2003-01-01

174

Ab initio many-body effects in TiSe2: A possible excitonic insulator scenario from GW band-shape renormalization  

Science.gov (United States)

We present both theoretical ab-initio results within the Hedin's GW approximation and experimental angle-resolved photoemission and scanning tunneling spectroscopy measurements on TiSe2. With respect to the density-functional Kohn-Sham metallic picture, the many-body GW self-energy leads to a ?0.2-eV band-gap insulator consistent with our STS spectra at 5 K. The highest valence and the lowest conduction bands are strongly renormalized, with a loss of k2 parabolic dispersion toward a k4 shape. In particular, GW moves the top of valence moved toward a circle of points away from ?, arising in a Mexican hat shape commonly associated with an excitonic insulator. Our calculations are in good agreement with experiment.

Cazzaniga, M.; Cercellier, H.; Holzmann, M.; Monney, C.; Aebi, P.; Onida, G.; Olevano, V.

2012-05-01

175

Resonant L?,? X-ray emission and L3,2 X-ray absorption spectra of 3d metals in Co2MnZ (Z=Al, Ga, Sn, Sb) Heusler alloys as an element-selective probe of spin character of valence band  

International Nuclear Information System (INIS)

The 3d metal L?,? resonant X-ray emission spectra (RXES) and L3,2 X-ray absorption spectra (XAS) of the Co2MnZ (Z=Al, Ga, Sn, Sb) alloys were measured using linearly polarized soft X-rays. The Mn L? and Co L? spectra are compared with results of spin-polarized calculations of Mn 3d and Co 3d partial densities of states performed for each alloy. It is found that a satellite observed at the high-energy side of Mn L? spectra is due to the localized Mn 3d states located above the Fermi energy. It is shown that the presence of the same satellite structure indicates a higher degree of spin-polarization of Mn 3d states than Co 3d states. Both the intensity of the satellite structure in Mn L? spectra and the L?/L?, peak ratio are increased and follow the atomic number of Z element. The effect is especially strong when excitating slightly above the L3 and L2 threshold energies as well as at resonance. We observe a correlation between these spectral parameters and the magnitude of local magnetic moment. The changes occurring in the Mn L?,? RXES are in good agreement with a predicted decrease in p-d hybridization (between the atoms of Z element and Mn atoms). The calculated local density of Mn 3d states at the Fermi energy follows the same trend as the hybridization. This suggests that L?,? RXES of 3d metals can be used to monitor the degree of spin-polarization of the valence band states and the local density of states at the Fermi level. Note that neither the Mn L2,3 absorption nor the Co L2,3 and Co L?,? emission spectra of the alloys are affected by the different composition (different Z elements).

2005-01-01

176

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

177

Ohmic Losses in Valence-band Photoemission Experiments  

CERN Multimedia

Photoemission experiments involve the motion of an electron near a conducting surface. This necessarily generates heat by ohmic losses from eddy currents. This inelastic scattering of the electrons will result in a downward shift in observed spectra. This effect is most pronounced in poorly conducting metals: in good metals the electron's field is screened out of the material, while insulators are by definition unable to absorb electromagnetic energy at low frequencies. We give a classification of photoemission processes which shows that the effect is an extrinsic proces distinct from final state effects. The shift is illustrated by a model system with a Drude-like conductivity function and a temperature-dependent relaxation time. We give a brief experimental survey of systems in which the ohmic losses may be significant.

Haslinger, R; Haslinger, Robert; Joynt, Robert

2000-01-01

178

Nodeless valence (pseudo)spinors.  

Science.gov (United States)

Atomic calculations using small-core relativistic effective core potentials (RECPs) explicitly treating outer core electrons are used to define two-component nodeless valence spinors (NVSs) and nodeless valence pseudospinors (NVPSs). Errors attributable to nonlocal electron repulsion interactions that arise from large-core RECPs are shown to result from the inherent arbitrariness in the choice of match points and number of derivatives that define shape-consistent pseudospinors, as well as the positions of radial nodes that reside in the outer core regions of atoms. Self-consistent field calculations in omegaomega-coupling for InH and InCl using RECPs derived from NVSs and NVPSs are reported. Increased bond distances relative to those calculated using very-large-core RECPs for In agree with those due to frozen 4d(3/2) and 4d(5/2) spinors and a small-core RECP. Results for AmCl+2 also reveal that the shortening in the bond length is recovered when the very-large-core RECP is derived using nodeless valence (pseudo)spinors. PMID:11206384

Ermler, W C; Marino, M M

179

Nodeless valence (pseudo)spinors.  

UK PubMed Central (United Kingdom)

Atomic calculations using small-core relativistic effective core potentials (RECPs) explicitly treating outer core electrons are used to define two-component nodeless valence spinors (NVSs) and nodeless valence pseudospinors (NVPSs). Errors attributable to nonlocal electron repulsion interactions that arise from large-core RECPs are shown to result from the inherent arbitrariness in the choice of match points and number of derivatives that define shape-consistent pseudospinors, as well as the positions of radial nodes that reside in the outer core regions of atoms. Self-consistent field calculations in omegaomega-coupling for InH and InCl using RECPs derived from NVSs and NVPSs are reported. Increased bond distances relative to those calculated using very-large-core RECPs for In agree with those due to frozen 4d(3/2) and 4d(5/2) spinors and a small-core RECP. Results for AmCl+2 also reveal that the shortening in the bond length is recovered when the very-large-core RECP is derived using nodeless valence (pseudo)spinors.

Ermler WC; Marino MM

2001-01-01

180

Valence degeneracy in cerium systems  

International Nuclear Information System (INIS)

We have calculated the generalized cohesive energies for Ce-systems, using a full-potential linear muffin-tin orbital method and a generalized gradient-corrected density functional. Together with atomic coupling energies for cerium, the generalized cohesive energies are used to study the valence configuration degeneracy in CeAl2 and CeX (X = N, P, As, Sb, Bi). We find that in all these systems, the f1 and f0 configurations are far from being degenerate. (orig.)

1997-08-01

 
 
 
 
181

Coherent potential approximation treatment of the Sm valence transition in SmS induced by alloying  

International Nuclear Information System (INIS)

The Sm valence transition, similar to the pressure-induced transition in pure SmS, has been observed in a large number of cases by substituting a trivalent rare earth, B, for Sm, thereby forming isostructural alloys with a lattice constant smaller than that of semiconducting SmS. Such substitutions are expected to exert a 'chemical' pressure which simulates the external pressure. However, divalent substitutions (Yb, Eu and Ca), although having a favourable 'size' factor, do not induce any valence transition. Accordingly, band structure effects, essentially due to the relative position of the conduction bands of SmS and BS, should also be taken into consideration. In order to clarify the role which the lattice constant and the electronic structure play in the valence transition, these alloys have been studied using the coherent potential approximation (CPA) including both the crystal field effect and the Coulomb interaction between localised and itinerant states as driving mechanisms. For Sm, the 'homogeneous' picture is considered, each Sm site having the average valence; then the Smsub(1-x)Bsub(x)S system is reduced to a binary alloy. Charge transfer between the f states of Sm and the alloy conduction band (i.e. Sm valence change) is determined self-consistently. The calculations are consistent with the experimental behaviour and allow us to understand qualitatively the variation of the critical concentration xsub(c) for the transition as a function of the difference ?a between the lattice parameters of SmS and BS. (author)

1982-01-01

182

Lattice vibrations in intermediate valence compounds SmS and TmSe  

International Nuclear Information System (INIS)

The lattice vibrations in two intermediate valence compounds SmS and TmSe have been investigated using three-body force rigid ion model, for the first time. The three-body forces influence considerably phonon dispersion along zone boundary. The model fairly produces the gross features of phonon dispersion, except the LA(L) mode softening in TmSe. (author). 19 refs., 4 figs., 4 tabs

1993-01-01

183

Mixed valence model for superconductivity  

Scientific Electronic Library Online (English)

Full Text Available Abstract in english Superconductivity often occurs in crystals with one active electron per site with charge density wave (CDW) or spin density wave (SDW) as 'mother state'. It is proposed that superconductivity is possible when the differences in equilibrium geometry and energy between the diabatic CDW and SDW states are so small that there is interaction between them via the zero point vibrations. Electron pairing in real space is directly related to oxidation states being different in two (more) units. Three valence states in succession have to be stable (ground state or low-energy excited states) and we therefore refer to this mixed valence model as the MV-3 model. Examples are chosen from bismuthates, cuprates, and fullerides. The theory is simple and straightforward and offers solutions to other important problems as well, for example for A3C(6)0(A = K; Rb), that (1) there are no magnetic moments in crystal phase, and (2) that these systems are superconducting metals while A4C(6)0 are insulators.

Larsson, Sven

2003-12-01

184

Mixed valence model for superconductivity  

Energy Technology Data Exchange (ETDEWEB)

Superconductivity often occurs in crystals with one active electron per site with charge density wave (CDW) or spin density wave (SDW) as 'mother state'. It is proposed that superconductivity is possible when the differences in equilibrium geometry and energy between the diabatic CDW and SDW states are so small that there is interaction between them via the zero point vibrations. Electron pairing in real space is directly related to oxidation states being different in two units. Three valence states in succession have to be stable (ground state or low-energy excited states) and we therefore refer to this mixed valence model as the MV-3 model. Examples are chosen from bismuthates, cuprates, and fullerides. The theory is simple and straightforward and offers solutions to other important problems as well, for example for A{sub 3}C{sub 6}0(A = K; Rb), that (1) there are no magnetic moments in crystal phase, and (2) that these systems are superconducting metals while A{sub 4}C{sub 6}0 are insulators. (author)

Larsson, Sven [Chalmers University of Technology, Goeteborg (Sweden). Dept. of Chemistry

2003-12-01

185

Mixed valence model for superconductivity  

Directory of Open Access Journals (Sweden)

Full Text Available Superconductivity often occurs in crystals with one active electron per site with charge density wave (CDW) or spin density wave (SDW) as 'mother state'. It is proposed that superconductivity is possible when the differences in equilibrium geometry and energy between the diabatic CDW and SDW states are so small that there is interaction between them via the zero point vibrations. Electron pairing in real space is directly related to oxidation states being different in two units. Three valence states in succession have to be stable (ground state or low-energy excited states) and we therefore refer to this mixed valence model as the MV-3 model. Examples are chosen from bismuthates, cuprates, and fullerides. The theory is simple and straightforward and offers solutions to other important problems as well, for example for A3C(6)0(A = K; Rb), that (1) there are no magnetic moments in crystal phase, and (2) that these systems are superconducting metals while A4C(6)0 are insulators.

Larsson Sven

2003-01-01

186

Valence configurations in 214Rn  

International Nuclear Information System (INIS)

Excited states of 214Rn, up to spins of ? 24 ? have been studied using ?-ray and electron spectroscopy following the 208Pb(9Be,3n) 214Rn reaction. The level scheme (which differs substantially from earlier work) is compared with the results of a semi-empirical shell model calculation. The availability of high spin orbitals for the four valence protons and two valence neutrons, and the effect of the attractive proton-neutron interaction, leads to the prediction of high-spin states at an unusually low excitation energy. Experimentally, the high level density leads to difficulties in the level scheme assignments at high spin. Nevertheless, configuration assignments, supported by transition strengths deduced from the measured lifetimes (in the nanosecond region) are suggested for the main yrast states. The decay properties also suggest that configuration mixing is important. The possibility of a gradual transition to octupole deformation, implied by the decay properties of the 11- and 10+ yrast states is also discussed.

1987-01-01

187

Electronic polaron effects in mixed valence and heavy fermion materials  

International Nuclear Information System (INIS)

It is shown that the Coulomb interaction between line-integral electrons and broad band electrons has a profound influence on the dynamical properties of an line-integral hole in mixed valence and heavy fermion materials. At zero temperature the dynamics of the screening process contains an infrared divergence. The broadening of this divergence by temperature causes the motion of the line-integral electrons to crossover from wave propagation to diffusion. This mechanisms explains the observed dual nature of the line-integral electrons, namely that at low temperatures they behave like a Fermi liquid, while at high temperatures they evolve into a localized magnetic moments

1992-01-01

188

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

189

Advances in Quantum dot Intermediate band Solar Cells.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Several groups have reported on intermediate band solar cells (IBSC) fabricated with InAs/GaAs quantum dots (QD) which exhibit quantum efficiencies (QE) for sub-bandgap photon energies. However, this QE is produced by the absorption of photons only through valence band (VB) to intermediate band (IB)...

Antolín Fernández, Elisa; Martí Vega, Antonio; García-Linares Fontes, Pablo; Ramiro Gonzalez, Iñigo; Hernández Martín, Estela

190

Anomalies in the Fermi surface and band dispersion of quasi-one-dimensional CuO chains in the high-temperature superconductor YBa2Cu4O8.  

UK PubMed Central (United Kingdom)

We have investigated the electronic states in quasi-one-dimensional CuO chains by microprobe angle resolved photoemission spectroscopy. We find that the quasiparticle Fermi surface consists of six disconnected segments, consistent with recent theoretical calculations that predict the formation of narrow, elongated Fermi surface pockets for coupled CuO chains. In addition, we find a strong renormalization effect with a significant kink structure in the band dispersion. The properties of this latter effect [energy scale (?40 meV), temperature dependence, and behavior with Zn-doping] are identical to those of the bosonic mode observed in CuO2 planes of high-temperature superconductors, indicating they have a common origin.

Kondo T; Khasanov R; Karpinski J; Kazakov SM; Zhigadlo ND; Bukowski Z; Shi M; Bendounan A; Sassa Y; Chang J; Pailhés S; Mesot J; Schmalian J; Keller H; Kaminski A

2010-12-01

191

Valence double photoionization of beryllium  

International Nuclear Information System (INIS)

We have measured the double-to-single photoionization ratio of beryllium (1s22s2) between 32 and 80 eV and compare our data with the electron-impact ionization cross section of Be+. In this energy region only simultaneous but not sequential emission of both 2s electrons can take place. We also compare our data with the double-to-single photoionization ratios of He, H2 and Li and find surprisingly good agreement of the photon-energy dependence if the ratio is scaled appropriately. The double-to-single photoionization ratio is lower for Be than for He due to a weaker electron-electron interaction between the valence electrons. (author). Letter-to-the-editor

2001-11-28

192

Core-valence partitioning and quasiparticle pseudopotentials  

International Nuclear Information System (INIS)

Recent advances in quantum Monte Carlo and quasiparticle methods have made accurate many-body calculations for valence electrons possible. Current work is limited by the way core electrons are treated. We present a many-body core-valence partitioning scheme, based upon quasiparticle methods, which can be used in either frozen-core or pseudopotential calculations.

1991-01-01

193

Unusual temperature dependence of band dispersion in Ba(Fe(1-x)Ru(x))2As2 and its consequences for antiferromagnetic ordering.  

UK PubMed Central (United Kingdom)

We have performed detailed studies of the temperature evolution of the electronic structure in Ba(Fe(1-x)Ru(x))(2)As(2) using angle resolved photoemission spectroscopy. Surprisingly, we find that the binding energy of both hole and electron bands changes significantly with temperature in both pure and Ru substituted samples. The hole and electron pockets are well nested at low temperature in unsubstituted (BaFe(2)As(2)) samples, which likely drives the spin density wave and resulting antiferromagnetic order. Upon warming, this nesting is degraded as the hole pocket shrinks and the electron pocket expands. Our results demonstrate that the temperature dependent nesting may play an important role in driving the antiferromagnetic-paramagnetic phase transition.

Dhaka RS; Hahn SE; Razzoli E; Jiang R; Shi M; Harmon BN; Thaler A; Bud'ko SL; Canfield PC; Kaminski A

2013-02-01

194

Theory of XAS and XMCD for the field-controlled valence mixed state in RE compounds  

Energy Technology Data Exchange (ETDEWEB)

A valence fluctuating phenomenon, which is one of the most interesting subjects in strongly correlated electron systems, has been studied theoretically in EuNi{sub 2}(Si{sub 0.18}Ge{sub 0.82}){sub 2}, in which the field-induced valence transition from a nonmagnetic Eu{sup 3+} state (4f{sup 6}) to a magnetic Eu{sup 2+} state (4f{sup 7}c{sup 1}) was observed at around 40 Tesla by means of X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) at Eu L-edges. Here, c denotes a hole in a conduction band. Both XAS and XMCD in fields exhibit two peaks corresponding to the two valence states, although one of them is nonmagnetic. In this paper, we propose a model to explain the field-induced valence transition, in which the hybridization between the 4f{sup 6} state and the 4f{sup 7}c{sup 1} state plays an essential role. Comparing XAS and XMCD calculated with experimental data, we find that XAS and XMCD provide us with detailed microscopic information on the mixed valence state through the polarized 5d electrons. Finally, we demonstrate how effective XAS and XMCD are for studying such mixed valence phenomena.

Oko, Masataka; Harada, Isao; Okada, Kozo, E-mail: harada@cc.okayama-u.ac.j [Dept. Phys. Okayama Univ., 3-1-1 Tsushima-naka Kita-ku 700-8530 Okayama (Japan)

2009-11-15

195

Valence Instability and Mass Enhancement in an Extended Periodic Anderson Model  

Science.gov (United States)

In CeCu2Si2, CeCu2Ge2 and CeRh1-xIrxIn5, the shape of the superconducting region is asymmetric and the superconducting transtition temperature Tc reaches its maximum far away from the antiferromagnetic quantum critical point. Onishi and Miyake ascribed the asymmetric behavior of Tc to the enhanced valence fluctuations. They introduced the repulsive interaction Ucf between a conduction electron and an f electron, in addition to the Coulomb interaction U between f electrons and studied the periodic Anderson model (PAM) with both U and Ucf (which is the so-called extended PAM). We investigated the valence instability in the extended PAM and two-fold degenerate extended PAM with the dynamical mean field theory. In these models, we found that the valence instability is observed when Ucf is larger than the conduction band width 2W and the f-electron level ?f is deeper than the lower bound of the conduction band, -W. It is also found that the orbital degeneracy suppresses the valence instability. In the parameter region of inducing the valence instability, we investigate the mass enhancement factor Zf-1 which is related to the specific heat.

Sugibayashi, Takashi; Saiga, Yasuhiro; Hirashima, Dai

2008-03-01

196

Superdeformed band in 130Ce  

International Nuclear Information System (INIS)

An open-quotes identicalclose quotes superdeformed (SD) band has been discovered in the nucleus 130Ce. This band has transition energies which are identical to the half-way points between the energies in the yrast SD band of 131Ce to a mean degeneracy of 0.4%. The discovery of this band completes the chain of SD Ce isotopes from 129Ce to 133Ce. However, at 0.5% of the reaction channel, it is populated with an intensity which is an order of magnitude smaller than neighboring SD bands. The valence neutron configuration is assigned as ?61 with a hole in either the [523]7/2- or [411]1/2+ Nilsson orbitals. copyright 1996 The American Physical Society.

197

K Emission Band of Ferromagnetic Ni  

Science.gov (United States)

The K emission band of ferromagnetic nickel has been calculated using a one-electron model and dipole approximation. The nickel K band emission was measured using a two crystal X-ray spectrometer. The FWHM of the calculated K emission band shows only about 0.1 eV broadening as compared to the calculated band of paramagnetic nickel. The experimental band is very sensitive to the correction procedure applied to the measured data but any reasonable realistic correction treatment still yields a considerably broader band than the theoretical one. This is contrary to the case of the L emission and XPS valence band for which the calculated bands are much broader than the measured ones. Consequently, the many-body effects already found in XPS and UPS spectra of nickel may also play a significant role in the Ni K band emission.

Lähdeniemi, M.; Ojala, E.; Suoninen, E.; Terakura, I.; Terakura, K.

1982-06-01

198

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

199

Generalized resonating valence bond description of cyclobutadiene  

Energy Technology Data Exchange (ETDEWEB)

The low-lying electronic states of square and rectangular cyclobutadiene (CBD) are calculated by using the generalized resonating valence bond (GRVB) method and compared with the results from Hartree-Fock and configuration interaction wavefunctions. We find that simple valence bond concepts correctly predict the sequence of excited states (including ground-state singlet) and the distortion to a rectangular geometry for the ground state. Contrary to common expectation, we find that the singlet ground state of square CBD has 22 kcal of resonance energy (relative to a single valence bond structure). Thus, CBD is not antiresonant, though it is much less stable than normal conjugated systems.

Voter, A.F.; Goddard, W.A. III

1986-05-28

200

Fourier-transform scanning tunnelling spectroscopy: the possibility to obtain constant-energy maps and band dispersion using a local measurement  

International Nuclear Information System (INIS)

We present here an overview of the Fourier-transform scanning tunnelling spectroscopy technique (FT-STS). This technique allows one to probe the electronic properties of a two-dimensional system by analysing the standing waves formed in the vicinity of defects. We review both the experimental and theoretical aspects of this approach, basing our analysis on some of our previous results, as well as on other results described in the literature. We explain how the topology of the constant-energy maps can be deduced from the FT of dI/dV map images which exhibit standing waves patterns. We show that not only the position of the features observed in the FT maps but also their shape can be explained using different theoretical models of different levels of approximation. Thus, starting with the classical and well known expression of the Lindhard susceptibility which describes the screening of electron in a free electron gas, we show that from the momentum dependence of the susceptibility we can deduce the topology of the constant-energy maps in a joint-density-of-states approximation (JDOS). We describe how some of the specific features predicted by the JDOS are (or are not) observed experimentally in the FT maps. The role of the phase factors which are neglected in the rough JDOS approximation is described using the stationary-phase conditions. We present also the technique of the T-matrix approximation, which accurately takes into account these phase factors. This technique has been successfully applied to normal metals, as well as to systems with more complicated constant-energy contours. We present results recently obtained on graphene systems which demonstrate the power of this technique, and the usefulness of local measurements for determining the band structure, the map of the Fermi energy and the constant-energy maps.

2011-11-23

 
 
 
 
201

Visible light induced generation of hydrogen from H/sub 2/S in CdS-dispersions, hole transfer catalysis by RuO/sub 2/  

Energy Technology Data Exchange (ETDEWEB)

Illumination of CdS-dispersions by visible light in solutions containing H/sub 2/S or sulfide ions leads to efficient generation of hydrogen and sulfur. Very small quantities of RuO/sub 2/ deposited on the CdS-particles improve markedly the quantum yield of H/sub 2/-formation for which the optimum value obtained so far is diameter=0.35+-0.1. The effect of RuO/sub 2/ is attributed to catalysis of hole transfer from the valence band of CdS to H/sub 2/S or sulfide in solution.

Borgarello, E.; Kalyanasundaram, K.; Graetzel, M.; Pelizzetti, E.

1982-01-01

202

Calculation of valence electron momentum densities using the projector augmented-wave method  

CERN Multimedia

We present valence electron Compton profiles calculated within the density-functional theory using the all-electron full-potential projector augmented-wave method (PAW). Our results for covalent (Si), metallic (Li, Al) and hydrogen-bonded ((H_2O)_2) systems agree well with experiments and computational results obtained with other band-structure and basis set schemes. The PAW basis set describes the high-momentum Fourier components of the valence wave functions accurately when compared with other basis set schemes and previous all-electron calculations.

Makkonen, I; Puska, M J

2004-01-01

203

Low temperature fluorescence, valence state and elastic anomalies of samarium phosphate glasses  

Energy Technology Data Exchange (ETDEWEB)

To examine their valence state, the fluorescence of samarium phosphate glasses between 10 and 300 K has been measured. The spectra do not slow any obvious sign of divalent samarium ions, only trivalent samarium ion fluorescence being observed. Room temperature absorption spectra of these glasses also evidence only the absorption bands of trivalent samarium. Hence the anomalous elastic behaviour under pressure in these glasses would not seem to be due to pressure induced changes in an intermediate valence state of samarium ions, as previously inferred. (orig.).

Farok, H.M.; Saunders, G.A. (School of Physics, Univ. of Bath, Claverton Down (United Kingdom)); Poon, W.; Vass, H. (Dept. of Physics, Univ. of Edinburgh (United Kingdom))

1992-04-01

204

Effective valency of Dy ions in Dy3NatC80 metallofullerenes and peapods  

Science.gov (United States)

We report on the electronic properties of the trimetal-nitride fullerene Dy3NatC80 and its encapsulated form inside SWCNT, the metallofullerene peapod, using high-energy spectroscopic methods as probes. From a comparison of the Dy 4d-4f absorption edges and the valence-band photoemission spectra with atomic multiplet calculations the effective valency of the encapsulated rare-earth ions is evaluated. We observe that the Dy ions inside fullerene cage are essentially trivalent which is not affected by the peapod formation.

Shiozawa, H.; Rauf, H.; Pichler, T.; Knupfer, M.; Kalbac, M.; Yang, S.; Dunsch, L.; Büchner, B.; Batchelor, D.; Kataura, H.

2005-09-01

205

Band offsets in transition-metal oxide heterostructures  

Science.gov (United States)

We measured valence band offsets in Ta2O5-WO3, Ta2O5-Nb2O5 and WO3-Nb2O5 heterostructure couples by in situ x-ray photoelectron spectroscopy, immediately following the bi-layer growth in ultra-high vacuum. Conduction band offsets were estimated using the measured valence band offsets in conjunction with the literature values for the respective band gaps. The offsets between Ta2O5 and WO3 and between Ta2O5 and Nb2O5 layers were strongly asymmetric, with 0.8-1.1 eV (0.1-0.2 eV) barriers for the conduction (valence) bands, depending on the particular couple and the stacking sequence. Such asymmetry can be very useful in switching devices.

Goldfarb, I.; Ohlberg, D. A. A.; Strachan, J. P.; Pickett, M. D.; Yang, J. Joshua; Medeiros-Ribeiro, G.; Williams, R. S.

2013-07-01

206

Optically detecting spin-split bands in semiconductors in magnetic fields  

Science.gov (United States)

We report on combined theoretical and experimental studies of spin-split bands in semiconductors in magnetic fields. We have studied a wide range of systems including: 1) electron and valence band splitting in dilute magnetically doped semiconductors (DMS) systems like InMnAs, 2) electron and valence band splitting in strained InSb/AlInSb heterostructures and 3) valence band splitting in GaAs. The systems have been studied with a variety of experimental techniques including: i) ultra-high magnetic field cyclotron resonance ii) magnetoabsorption and iii) optically pumped NMR (OPNMR). Calculations are based on the 8-band Pidgeon-Brown model generalized to include the effects of the quantum confinement potential as well as pseudomorphic strain at the interfaces and sp-d coupling between magnetic impurities and conduction band electrons and valence band holes. Optical properties are calculated within the golden rule approximation and compared with experiments. Detailed comparison to experiment allows one to accurately determine conduction and valence band parameters including effective masses and g-factors. Results for InMnAs show shifts in the cyclotron resonance peaks with Mn doping. For InSb, we find a sensitive dependence of the elecronic structure on the strain at the pseudomorphic interfaces. For GaAs, we show that OPNMR allows us to spin-resolve the valence bands and that structure in the OPNMR signal is dominated by the weaker light hole to conduction band Landau level transitions.

Pan, X.; Sun, Y.; Saha, D.; Sanders, G. D.; Santos, M. B.; Doezema, R. E.; Hayes, S.; Khodaparast, G.; Munekata, H.; Matsuda, Y. H.; Kono, J.; Stanton, C. J.

2012-10-01

207

Dynamics of valence-fluctuating Tm impurities  

International Nuclear Information System (INIS)

A new formalism is presented for describing valence fluctuating Tm impurities. Starting from the self-consistent perturbation scheme valid at arbitrary temperatures, the present formalism incorporates not only the valence fluctuation between 4f12 and 4f13, but also the coupled 4f13 and a conduction electron scattering channel through T-matrix, the latter yielding a singlet ground state at low temperatures. Contribution of this channel to the f-electron spectral function is also discussed.

1988-01-01

208

Optical and thermal band gap energy of chemically deposited bismuth(III) selenide thin films  

Energy Technology Data Exchange (ETDEWEB)

The band gap energy of bismuth(III) selenide in thin-film form was determined using the optical and thermal methods. The optical band gap energy of 0.35 eV was calculated on the basis of the recorded optical spectra in the near-infrared region, within the framework of a parabolic approximation for the dispersion relation, using the equations which arise from Fermi's golden rule for electronic transitions from valence to conduction band. From the temperature dependence of the dark electrical resistance of the bismuth(III) selenide thin films in the region of intrinsic and extrinsic conduction, a thermal band gap energy of 0.37 eV and an ionization energy of the donor impurity level of 0.13 eV were calculated. The thermal, as well as the optical band gap energy are in excellent agreement with a literature value for bulk bismuth(III) selenide. On the basis of these data, several conclusions on the film microstructure (nanocrystalline versus glassy) are derived and also an estimation of the higher bound to the Bohr's excitonic radius for bulk Bi{sub 2}Se{sub 3} is given.

Pejova, Biljana; Grozdanov, Ivan; Tanusevski, Atanas

2004-02-15

209

Optical and thermal band gap energy of chemically deposited bismuth(III) selenide thin films  

International Nuclear Information System (INIS)

The band gap energy of bismuth(III) selenide in thin-film form was determined using the optical and thermal methods. The optical band gap energy of 0.35 eV was calculated on the basis of the recorded optical spectra in the near-infrared region, within the framework of a parabolic approximation for the dispersion relation, using the equations which arise from Fermi's golden rule for electronic transitions from valence to conduction band. From the temperature dependence of the dark electrical resistance of the bismuth(III) selenide thin films in the region of intrinsic and extrinsic conduction, a thermal band gap energy of 0.37 eV and an ionization energy of the donor impurity level of 0.13 eV were calculated. The thermal, as well as the optical band gap energy are in excellent agreement with a literature value for bulk bismuth(III) selenide. On the basis of these data, several conclusions on the film microstructure (nanocrystalline versus glassy) are derived and also an estimation of the higher bound to the Bohr's excitonic radius for bulk Bi2Se3 is given.

2004-02-15

210

Ab-initio calculations of the internal conversion coefficient for valence electrons of hcp-99Tc and bcc-235U  

International Nuclear Information System (INIS)

Using relativistic band structure calculations applying the relativistic linear muffin-tin orbital (RLMTO) method the internal conversion coefficient (ICC) for valence electrons of hcp-99Tc and bcc-235U are calculated. This coefficient describes the probability for a virtual ? -quantum of energy ? ? (2.17keV for Tc, 77eV for U) emitted by a nucleus to eject an electron from the valence band (photoelectron emission with the photon source inside the solid). The resulting ICCs are very similar to the corresponding density of states. (author).

1991-01-01

211

Physical properties and valence state of cerium in the filled skutterudite CePt?Ge??.  

UK PubMed Central (United Kingdom)

Electronic, magnetic, and transport properties of the filled platinum-germanium skutterudite CePt?Ge?? are investigated. High resolution x-ray absorption spectroscopy measurements at the cerium L(III) edge demonstrate that CePt?Ge?? in this compound has a temperature-independent valence close to three. However, magnetic susceptibility, thermopower, Hall effect, and electronic specific heat reveal a broad maximum at Tmax D 65-80 K, suggesting the presence of valence fluctuations. The Sommerfeld coefficient ? = 105 mJ mol?¹ K?², deduced from specific heat, indicates moderately enhanced band masses for CePt?Ge??. We discuss these findings and conclude that CePt?Ge?? represents a system at the border between intermediate valence (IV) and Kondo lattice behavior. In addition, the lattice specific heat and the thermal conductivity are discussed with respect to the vibrational dynamics of Ce in the [Pt?Ge??] framework.

Gumeniuk R; Kvashnina KO; Schnelle W; Nicklas M; Borrmann H; Rosner H; Skourski Y; Tsirlin AA; Leithe-Jasper A; Grin Y

2011-11-01

212

Oil dispersants  

Energy Technology Data Exchange (ETDEWEB)

This book contains papers presented at a symposium of the American Society for Testing and Materials. The topics covered include: The effect of elastomers on the efficiency of oil spill dispersants; planning for dispersant use; field experience with dispersants for oil spills on land; and measurements on natural dispersion.

Flaherty, L.M.

1989-01-01

213

Coherent potential approximation treatment of the Sm valence transition in SmS induced by alloying  

Energy Technology Data Exchange (ETDEWEB)

The Sm valence transition, similar to the pressure-induced transition in pure SmS, has been observed in a large number of cases by substituting a trivalent rare earth, B, for Sm, thereby forming isostructural alloys with a lattice constant smaller than that of semiconducting SmS. Such substitutions are expected to exert a 'chemical' pressure which simulates the external pressure. However, divalent substitutions (Yb, Eu and Ca), although having a favourable 'size' factor, do not induce any valence transition. Accordingly, band structure effects, essentially due to the relative position of the conduction bands of SmS and BS, should also be taken into consideration. In order to clarify the role which the lattice constant and the electronic structure play in the valence transition, these alloys have been studied using the coherent potential approximation (CPA) including both the crystal field effect and the Coulomb interaction between localised and itinerant states as driving mechanisms. For Sm, the 'homogeneous' picture is considered, each Sm site having the average valence; then the Smsub(1-x)Bsub(x)S system is reduced to a binary alloy. Charge transfer between the f states of Sm and the alloy conduction band (i.e. Sm valence change) is determined self-consistently. The calculations are consistent with the experimental behaviour and allow us to understand qualitatively the variation of the critical concentration xsub(c) for the transition as a function of the difference ..delta..a between the lattice parameters of SmS and BS.

Spronken, G. (Montreal Univ., Quebec (Canada). Dept. of Physics); Avignon, M. (Centre National de la Recherche Scientifique, 38 - Grenoble (France))

1982-11-01

214

Subliminal Affect Valence Words Change Conscious Mood Potency but Not Valence: Is This Evidence for Unconscious Valence Affect?  

Directory of Open Access Journals (Sweden)

Full Text Available Whether or not affect can be unconscious remains controversial. Research claiming to demonstrate unconscious affect fails to establish clearly unconscious stimulus conditions. The few investigations that have established unconscious conditions fail to rule out conscious affect changes. We report two studies in which unconscious stimulus conditions were met and conscious mood changes measured. The subliminal stimuli were positive and negative affect words presented at the objective detection threshold; conscious mood changes were measured with standard manikin valence, potency, and arousal scales. We found and replicated that unconscious emotional stimuli produced conscious mood changes on the potency scale but not on the valence scale. Were positive and negative affects aroused unconsciously, but reflected consciously in potency changes? Or were the valence words unconscious cognitive causes of conscious mood changes being activated without unconscious affect? A thought experiment is offered as a way to resolve this dilemma.

Howard Shevrin; Jaak Panksepp; Linda A. W. Brakel; Michael Snodgrass

2012-01-01

215

Many-body core-valence partitioning  

Energy Technology Data Exchange (ETDEWEB)

We discuss the physics related to partitioning core and valence electrons, a common approach taken so that one need deal only with valence electrons in subsequent work. We present an approach to core-valence partitioning which explicitly includes many-body correlations, unlike traditional single-body approaches (such as Hartree Fock or the local-density approximation). Effects of intracore and core-valence correlations are incorporated in a parametrized core-polarization potential (CPP) derived from quasiparticle calculations in atoms presented in the preceding paper. Numerical parameters for CPP's for most elements with atomic number 3[le][ital Z][le]40 are tabulated. Specifically, the CPP's correct a Hartree-Fock treatment of core-valence interactions. The CPP's may be used in full-atomic, rigid-core applications or may be incorporated into pseudopotentials. We present explicit tests of the CPP's on atomic systems, and we cite molecular and solid-state tests also done using ths CPP approach.

Shirley, E.L.; Martin, R.M. (Department of Physics and Materials Research Laboratory, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, Illinois 61801 (United States))

1993-06-15

216

Unoccupied band structure of Bi2Sr2CaCu2O8 by very-low-energy electron diffraction Origin of the final state effects in photoemission  

CERN Multimedia

We present first data on the energy positions, dispersions and lifetimes of the photoemission final states in Bi2Sr2CaCu2O8 achieved by very-low-energy electron diffraction with a support of full-potential band calculations. Direct connection of the diffracted intensities to the final-state effects can be utilized to focus on certain valence states and Fermi surface replicas in the photoemission experiment. At very low energies the diffracted intensities show c(2x2) modulations due to multiple scattering effects possibly connected with the antiferromagnetic fluctuations.

Strocov, V N; Blaha, P

2002-01-01

217

Valence fluctuations in ternary europium compounds  

Energy Technology Data Exchange (ETDEWEB)

We outline the possibility to study europium valence fluctuations with the {mu}SR method and report on {mu}SR experiments on the intermetallic compounds EuPdAs and NdPdAs. Above a magnetic transition at 15 K the temperature dependence of the relaxation rate in the trivalent neodymium system behaves like a typical localized moment system. In the valence fluctuating europium compound the zero field relaxation rate levels off at 1.0 {mu}s{sup -1} above 40 K. Furthermore, the relaxation enhancement in transverse field experiments is much smaller than expected for a pure dipolar coupling. Therefore an isotropic hyperfine coupling of typical strength is assumed and a valence fluctuation rate of 0.8 {mu}s{sup -1} at 200 K is derived. Below the magnetic transition at 5 K a disordered spin freezing is concluded in EuPdAs.

Klauss, H.-H.; Hillberg, M.; Wagener, W.; Melo, M.A.C. de; Litterst, F.J. [Technische Universitaet Braunschweig, Institut fuer Metallphysik und Nukleare Festkoerperphysik (Germany); Schreier, E. [Technische Universitaet Muenchen, Physik Department (Germany); Schlabitz, W.; Michels, G. [Universitaet zu Koeln, II. Physikalisches Institut (Germany)

1997-04-15

218

Valence fluctuations in ternary europium compounds  

International Nuclear Information System (INIS)

We outline the possibility to study europium valence fluctuations with the ?SR method and report on ?SR experiments on the intermetallic compounds EuPdAs and NdPdAs. Above a magnetic transition at 15 K the temperature dependence of the relaxation rate in the trivalent neodymium system behaves like a typical localized moment system. In the valence fluctuating europium compound the zero field relaxation rate levels off at 1.0 ?s-1 above 40 K. Furthermore, the relaxation enhancement in transverse field experiments is much smaller than expected for a pure dipolar coupling. Therefore an isotropic hyperfine coupling of typical strength is assumed and a valence fluctuation rate of 0.8 ?s-1 at 200 K is derived. Below the magnetic transition at 5 K a disordered spin freezing is concluded in EuPdAs.

1997-01-01

219

Valence fluctuations in ternary europium compounds  

International Nuclear Information System (INIS)

We outline the possibility to study europium valence fluctuations with the ?SR method and report on ?SR experiments on the intermetallic compounds EuPdAs and NdPdAs. Above a magnetic transition at 15 K the temperature dependence of the relaxation rate in the trivalent neodymium system behaves like a typical localized moment system. In the valence fluctuating europium compound the zero field relaxation rate levels off at 1.0 ?s-1 above 40 K. Furthermore, the relaxation enhancement in transverse field experiments is much smaller than expected for a pure dipolar coupling. Therefore an isotropic hyperfine coupling of typical strength is assumed and a valence fluctuation rate of 0.8 ?s-1 at 200 K is derived. Below the magnetic transition at 5 K a disordered spin freezing is concluded in EuPdAs. (orig.).

1997-01-01

220

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

 
 
 
 
221

Inner-valence states of N2+ and the dissociation dynamics studied by threshold photoelectron spectroscopy and configuration interaction calculation  

International Nuclear Information System (INIS)

The N2+ states lying in the ionization region of 26-45 eV and the dissociation dynamics are investigated by high-resolution threshold photoelectron spectroscopy and threshold photoelectron-photoion coincidence spectroscopy. The threshold photoelectron spectrum exhibits several broad bands as well as sharp peaks. The band features are assigned to the N2+ states associated with the removal of an inner-valence electron, by a comparison with a configuration interaction calculation. In contrast, most of the sharp peaks on the threshold photoelectron spectrum are allocated to ionic Rydberg states converging to N22+. Dissociation products formed from the inner-valence N2+ states are determined by threshold photoelectron-photoion coincidence spectroscopy. The dissociation dynamics of the inner-valence ionic states is discussed with reference to the potential energy curves calculated.

2006-06-21

222

Band Gap Engineering of Crystal Materials: Band Gap Estimation of Semiconductors via Electronegativity  

Science.gov (United States)

We have developed empirical equations to quantitatively calculate the band gap values of binary ANB8-N and ternary ABC2 chalcopyrite semiconductors from the general viewpoint of chemical bonding processes upon electronegativity (EN). It is found that the band gap of crystal materials is essentially determined by the binding energy of chemical bonds to the bonding electrons, which can be effectively described by the average attractive abilities of two bonded atoms to their valence electrons and the delocalization degree of the valence electrons. The calculated band gap values of a large number of compounds can agree well with the available experimental data. This work provides us an efficient approach to quantitatively predict the band gap values of inorganic crystal materials on the basis of fundamental atom parameters such as EN, atomic radius, etc.

Li, Keyan; Li, Yanju; Xue, Dongfeng

2012-06-01

223

Energy band picture  

International Nuclear Information System (INIS)

By a refined one-electron band theory, the origins of the major experimental frequency branches of de Haas-van Alphen effect observed in the Ce compounds belonging to the valence-fluctuation regime and the moderately heavy-electron regime have recently been clarified on an itinerant-electron model for the 4f electrons. It means that the energy band picture works fairly well for the 4f electrons in the Ce compounds of these regimes, as far as the Fermi surface shape is concerned. In this review, a newly completed, self-consistent symmetrized relativistic APW approach is outlined, and results of the application to CeSn3, CeNi and CeRu2Si2 are summarized. The same approach has been applied to such U compounds as UC and UB12 on an itinerant-electron model for the 5f electrons, and their Fermi surface has been clarified successfully. Results for these U compounds are summarized also. The large cyclotron effective masses and the large electronic specific heat coefficients which are observed in all these f-electron compounds except UB12 cannot be explained by the band structure alone, and their quantitative analysis remains to be solved by many-body theory. (author).

1993-01-01

224

Simultaneous quantization of bulk conduction and valence states through adsorption of nonmagnetic impurities on Bi2Se3.  

UK PubMed Central (United Kingdom)

Exposing the (111) surface of the topological insulator Bi(2)Se(3) to carbon monoxide results in strong shifts of the features observed in angle-resolved photoemission. The behavior is very similar to an often reported "aging" effect of the surface, and it is concluded that this aging is most likely due to the adsorption of rest gas molecules. The spectral changes are also similar to those recently reported in connection with the adsorption of the magnetic adatom Fe. All spectral changes can be explained by a simultaneous confinement of the conduction band and valence band states. This is possible only because of the unusual bulk electronic structure of Bi(2)Se(3). The valence band quantization leads to spectral features which resemble those of a band gap opening at the Dirac point.

Bianchi M; Hatch RC; Mi J; Iversen BB; Hofmann P

2011-08-01

225

Simultaneous quantization of bulk conduction and valence states through adsorption of nonmagnetic impurities on Bi2Se3.  

Science.gov (United States)

Exposing the (111) surface of the topological insulator Bi(2)Se(3) to carbon monoxide results in strong shifts of the features observed in angle-resolved photoemission. The behavior is very similar to an often reported "aging" effect of the surface, and it is concluded that this aging is most likely due to the adsorption of rest gas molecules. The spectral changes are also similar to those recently reported in connection with the adsorption of the magnetic adatom Fe. All spectral changes can be explained by a simultaneous confinement of the conduction band and valence band states. This is possible only because of the unusual bulk electronic structure of Bi(2)Se(3). The valence band quantization leads to spectral features which resemble those of a band gap opening at the Dirac point. PMID:21929189

Bianchi, Marco; Hatch, Richard C; Mi, Jianli; Iversen, Bo Brummerstedt; Hofmann, Philip

2011-08-16

226

Electronic structure of the diamond (111) 1 x 1 surface: Valence-band structure, band bending, and band gap states  

International Nuclear Information System (INIS)

[en] Photoemission, LEED, and AES measurements were made on the mechanically polished (111) surface of a type IIa diamond. No emission from filled states in the fundamental gap was found over the photon energy range 13.3 eV

1980-01-01

227

Valence electronic state density in thorium dioxide  

Directory of Open Access Journals (Sweden)

Full Text Available This work analyses the fine low energy (0-40 eV) X-ray photoelectron spectra of ThO2, taking into account relativistic X?-discrete variation electronic structure calculations for the ThO8 (D4h) cluster reflecting thorium's close environment in ThO2. As a result, it was theoretically shown and experimentally confirmed that Th5f electrons in ThO2 can participate directly (~0.6 Th5f electrons) in chemical bond formation.Th6p electrons were shown to be a significant part (~0.44 Th6p electrons) not only of inner valence molecular orbitals, but to play a significant role in outer valence molecular orbitals formation, as well. Inner valence molecular orbitals composition and sequent order were established to belong to the binding energy range of 13 eV to 40 eV. The valence electronic state density in the range of 0-40 eV in ThO2 was also calculated. For the first time, these data allowed an interpretation of the fine X-ray photoelectron spectra (0-40 eV) and high resolution O4,5(Th) X-ray emition spectral structure (~60 - ~85 eV) of ThO2.

Teterin Anton Yu.; Ryzhkov Mikhail V.; Teterin Yury A.; Vuk?evi? Labud; Terekhov Vladimir A.; Maslakov Konstantin I.; Ivanov Kirill E.

2008-01-01

228

Valence quark approximation of the rescaling model  

Energy Technology Data Exchange (ETDEWEB)

We perform a QCD analysis of the valence quark approximation of the rescaling model via the moment relationship. The existence of a unique renormalization scale seems to be substantiated, but the ratio of the confinement radius and the nucleon overlap probability can vary greatly. (orig.).

Nakano, K.; O' Donnell, P.J.; Wong, S.S.M.

1985-12-05

229

When does event valence affect unrealistic optimism?  

UK PubMed Central (United Kingdom)

"Unrealistic optimism" (UO) has been found to be greater for negative (i.e. undesirable) than for positive (i.e. desirable) events. In two studies, we tested whether this "valence effect" is explicable in terms of motivational processes. In each case, participants were students (n = 159 in Study 1, n = 90 in Study 2), UO for the same health event was measured, and valence was manipulated by framing the event either negatively or positively. The degree to which the event would be expected to evoke concern was varied by manipulating the ease with which it could be avoided (Study 1) or the severity of its consequences (Study 2). A similar pattern of results was found in each study: the valence effect was exhibited in the condition where the event would have evoked concern, but not in the condition where it would have evoked little concern. The findings are in accord with an explanation of the valence effect in motivational terms. Implications for health education are discussed.

Gold RS; de Sousa PN

2012-01-01

230

Effect of phonons in mixed valence systems  

International Nuclear Information System (INIS)

The effect of electron-phonon coupling on valence fluctuations in rare-earth systems is studied. It is shown that the electron-phonon coupling affects both the important electronic parameters and the phonon-frequencies, in particular the short-wavelength longitudinal optical phonons.

1978-09-07

231

Improved Error Estimate for the Valence Approximation  

CERN Document Server

We construct a systematic mean-field-improved coupling constant and quark loop expansion for corrections to the valence (quenched) approximation to vacuum expectation values in the lattice formulation of QCD. Terms in the expansion are evaluated by a combination of weak coupling perturbation theory and a Monte Carlo algorithm.

Lee, W

1998-01-01

232

Valence ordering in the intermediate-valence magnet YbPd  

Science.gov (United States)

An x-ray diffraction study reveals the valence-ordering structure in an intermediate-valence magnet YbPd with a CsCl structure. The valence of the Yb ions forms an incommensurate structure, characterized by the wave vector (±0.07 ±0.07 1/2) below 130 K. At 105 K, the incommensurate structure turns into a commensurate structure, characterized by the wave vector (0 0 1/2). Based on the resonant x-ray diffraction spectra of the superlattice reflections, the valences of the Yb ions below 105 K are found to be 3+ and 2.6+. The origin of the long-wavelength modulation is discussed with the aid of an Ising model having next-nearest-neighbor interaction.

Takahashi, Ryo; Honda, Takashi; Miyake, Atsushi; Kagayama, Tomoko; Shimizu, Katsuya; Ebihara, Takao; Kimura, Tsuyoshi; Wakabayashi, Yusuke

2013-08-01

233

Measurement of AlP/GaP (001) heterojunction band offsets by x-ray photoemission spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

X-ray photoemission spectroscopy has been used to measure the valence band offset {Delta}E{sub v} for the AlP/GaP (001) heterojunction interface. The heterojunction samples were prepared by molecular-beam epitaxy. A value of {triangle}E{sub v}=0.43 eV is obtained (staggered band alignment, with AlP valence band below that of GaP). 24 refs., 8 figs., 1 tab.

Waldrop, J.R.; Grant, R.W.; Kraut, E.A. [Rockwell International Science Center, Thousand Oaks, CA (United States)

1993-07-01

234

Determination of the uranium valence state in the brannerite structure using EELS, XPS, and EDX  

Science.gov (United States)

In this study, the valence states of uranium in synthetic and natural brannerite samples were studied using a combination of transmission electron microscopy-electron energy loss spectroscopy, scanning electron microscopy-energy dispersive X-ray analysis (SEM-EDX), and X-ray photoelectron spectroscopy (XPS) techniques. We used a set of five (UO2, CaUO4, SrCa2UO6, UTi2O6, and Y0.5U0.5Ti2O6) U standard samples, including two synthetic brannerites, to calibrate the EELS branching ratio, M5/(M4 +M5), against the number of f electrons. The EELS data were collected at liquid nitrogen temperature in order to minimise the effects of electron beam reduction of U6+ and U5+. Test samples consisted of three additional synthetic brannerites (Th0.7U0.3Ti2O6, Ca0.2U0.8Ti2O6, and Th0.55U0.3Ca0.15Ti2O6) and three natural brannerites from different localities. The natural brannerite samples are all completely amorphous, due to cumulative alpha decay events over geological time periods (24 508 Ma). Our U valence calibration results are in reasonable agreement with previous work, suggesting possibly a non-linear relationship between the branching ratio and the number of f electrons (and hence the average valence state) of U in solids. We found excellent agreement between the nominal valence states of U and the average valence states determined directly by EELS and estimated by EDX analysis (with assumptions regarding stoichiometry) in two of the three synthetic brannerite test samples. The average U oxidation states of the five synthetic brannerite samples, as derived from XPS analyses, are also in good agreement with those determined by other techniques. The average valence states of U in three amorphous (metamict) natural brannerite samples with alpha decay doses ranging from 3.6×1016 to 6.9×1017 ?/mg were found to be 4.4, 4.7, and 4.8, consistent with the presence of U5+ and/or U6+ as well as U4+ in these samples. These results are in general agreement with previous wet chemical analyses of natural brannerite. However, the average valence states inferred by SEM-EDX for two of the natural brannerite samples do not show satisfactory agreement with the EELS determined valence. This may be due to the occurrence of OH- groups, cation vacancies, anion vacancies, or excess oxygen in the radiation-damaged structure of natural brannerite.

Colella, M.; Lumpkin, G. R.; Zhang, Z.; Buck, E. C.; Smith, K. L.

2005-05-01

235

Calculations of energy levels for atoms with several valence electrons  

International Nuclear Information System (INIS)

A new ab initio method for the high-accuracy calculations of atoms with more than one valence electron is described. An effective Hamiltonian for the valence electrons is formed using may body perturbation theory for the residual core-valence interaction. Configuration interaction method is used then to find the energy levels of the atom. 15 refs.; 3 figs.

1996-01-01

236

Actinides, the narrowwest bands  

Energy Technology Data Exchange (ETDEWEB)

A table of elements is shown that demonstrates the crossover from superconductivity to magnetism as well as regions of mixed valence. In particular, the actinides must eventually show 4f-electron like mixed valence, after the 5f-electrons become localized. There also seems to be an adiabatic continuation between heavy fermion and mixed valence behavior.

Smith, J.L.; Riseborough, P.S.

1984-01-01

237

The method of thermodynamic perturbation in the intermediate valence problem  

International Nuclear Information System (INIS)

[en] The effect of hybridization on the free energy and the magnetic susceptibility X of intermediate valence compounds is studied employing the method of thermodynamic perturbation in second order. This method is applied to a lattice with a variable concentration c of impurities that are described by the Anderson model. A non-divergent logarithmic correction appears when the chemical potential ? sub(e) is not in the middle of the rectangular conduction band, and it is shown by a different method that this correction is also present in the exactly soluble case of independent electrons with hybridization. When c=1 the logarithmic term is cancelled by a term proportional to (?2? sub(e)/?H2). By thermodynamic arguments it is shown that this concentration dependent contribution coincides with a different expression that was recently obtained by another approach. The contribution of the third state of charge to X is discussed; this state is usually neglected in intermediate valence models. (Author)[pt] Estuda-se o efeito da hibridizacao sobre a energia livre e a susceptibilidade magnetica X de compostos de valencia intermediaria, empregando o metodo da perturbacao termodinamica em segunda ordem. Aplica-se esse metodo a uma rede com uma concentracao variavel c de impurezas que sao descritas pelo modelo de Anderson. Uma correcao logaritmica nao divergente aparece quando o potencial quimico ? sub(e) nao esta no meio da banda retangular de conducao, e e mostrado por um metodo diferente que esta correcao esta presente tambem no caso, exatamente soluvel, de eletrons independentes com hibridizacao. Quando c=1 o termo logaritimico e cancelado por um termo proporcional a (?2? sub(e)/?H2). Por argumentos termodinamicos mostra-se que essa contribuicao dependente da concentracao coincide com uma expressao diferente que foi obtida recentemente por outra abordagem. Discute-se a contribuicao do terceiro estado de carga para X; este estado e usualmente desprezado em modelos de valencia intermediaria. (Autor)

1982-01-01

238

Theoretical investigations on valence vibronic transitions  

Scientific Electronic Library Online (English)

Full Text Available Abstract in english This article reviews previously employed methods to study several valence electronic transitions, optically forbidden or not, enhancing intensity through vibronic coupling. Electronic transition dipole moments were calculated using several ab initio methods including electron correlation. In this method the square of the electronic transition dipole moments are directly calculated along the normal coordinates of vibration and then expanded with a polynomial function. Afte (more) rwards, analytical vibrational integration using harmonic wave functions, of the square of the transition moments function, allows us to obtain partial (i.e. for each vibrational mode) and total optical oscillator strengths (OOS), for the vibronic transition of interest. We illustrate the accuracy of the method through valence transitions of benzene (C6H6), formaldehyde (H2CO), acetone (C3H6O) and formic acid (HCOOH).

Borges Jr., Itamar; Rocha, Alexandre B.; Bielschowsky, Carlos Eduardo

2005-12-01

239

Correlated topological insulators with mixed valence.  

UK PubMed Central (United Kingdom)

We propose the local density approximation+Gutzwiller method incorporating a Green's function scheme to study the topological physics of correlated materials from the first principles. Applying this method to typical mixed valence materials SmB(6), we find its nontrivial Z(2) topology, indicating that SmB(6) is a strongly correlated topological insulator. The unique feature of this compound is that its surface states contain three Dirac cones in contrast to most known topological insulators.

Lu F; Zhao J; Weng H; Fang Z; Dai X

2013-03-01

240

Correlated topological insulators with mixed valence.  

Science.gov (United States)

We propose the local density approximation+Gutzwiller method incorporating a Green's function scheme to study the topological physics of correlated materials from the first principles. Applying this method to typical mixed valence materials SmB(6), we find its nontrivial Z(2) topology, indicating that SmB(6) is a strongly correlated topological insulator. The unique feature of this compound is that its surface states contain three Dirac cones in contrast to most known topological insulators. PMID:23496729

Lu, Feng; Zhao, JianZhou; Weng, Hongming; Fang, Zhong; Dai, Xi

2013-02-25

 
 
 
 
241

Dispersion Basics  

Science.gov (United States)

In this Webcast, Dr. Timothy Spangler (Director of the COMET Program and a former air quality consultant) provides a brief overview of the basics of atmospheric dispersion and how dispersion is modeled, particularly for accidental releases of hazardous materials. The lecture is presented in six sections and covers the effects of stability, turbulence, plume rise, and wind. Basic dispersion models are discussed, along with a brief summary of models used in special situations and factors that complicate their use.

Spangler, Tim

2002-11-01

242

Spinon excitation spectra of the resonating valence bond states in the high temperature superconducting cuprates  

Science.gov (United States)

Magnetic excitations of the resonating valence bond (RVB) states were searched in high temperature superconducting cuprates by Raman scattering. Ho et al. [C.-M. Ho et al., Phys. Rev. Lett. 86 (2001) 1626] disclosed that the spin excitation in the two-dimensional resonating valence bond state has a magnon-like dispersion and a spinon continuum above it. The density of states of the spin excitation has a peak at 1.5 J which is lower than the 2.36 J of the spin wave. We found that the A spectra have a broad peak at 1.5 J in common at the underdoped region of p?0.15 in LSCO, Bi2201, and Bi2212 and p?0.1 in YBCO. The B peak and the B peak in the two-magnon region have a fine structure of the spin wave. The carrier density dependence is discussed.

Sugai, S.; Takayanagi, Y.; Hosokawa, T.; Suzuki, H.; Hayamizu, N.; Muroi, T.; Sone, Y.; Mabuchi, H.

2010-12-01

243

Multidimensional X-Ray Spectroscopy of Valence and Core Excitations in Cysteine  

CERN Multimedia

Several nonlinear spectroscopy experiments which employ broadband x-ray pulses to probe the coupling between localized core and delocalized valence excitation are simulated for the amino acid cysteine at the K-edges of oxygen and nitrogen and the K and L-edges of sulfur. We focus on two dimensional (2D) and 3D signals generated by two- and three-pulse stimulated x-ray Raman spectroscopy (SXRS) with frequency-dispersed probe. We show how the four-pulse x-ray signals $\\boldsymbol{k}_\\mathrm{I}=-\\boldsymbol{k}_1+\\boldsymbol{k}_2+\\boldsymbol{k}_3$ and $\\boldsymbol{k}_\\mathrm{II}=\\boldsymbol{k}_1-\\boldsymbol{k}_2+\\boldsymbol{k}_3$ can give new 3D insight into the SXRS signals. The coupling between valence- and core-excited states can be visualized in three dimensional plots, revealing the origin of the polarizability that controls the simpler pump-probe SXRS signals.

Biggs, Jason D; Healion, Daniel; Mukamel, Shaul

2013-01-01

244

A numerical study into the influence of quantum dot size on the sub-bandgap interband photocurrent in intermediate band solar cells  

Directory of Open Access Journals (Sweden)

Full Text Available A numerical study is presented of the sub-bandgap interband photon absorption in quantum dot intermediate band solar cells. Absorption coefficients and photocurrent densities are calculated for the valence band to intermediate band transitions using a four-band k·p method. It is found that reducing the quantum dot width in the plane perpendicular to the growth direction increases the photocurrent from the valence band to the intermediate-band ground state if the fractional surface coverage of quantum dots is conserved. This provides a path to increase the sub-bandgap photocurrent in intermediate band solar cells.

Alexander Mellor; Antonio Luque; Ignacio Tobías; Antonio Martí

2013-01-01

245

Dispersing Electronic States in d-AlNiCo and i-AlPdMn Quasicrystals  

Science.gov (United States)

A basic question about the nature of the valence electronic states -- whether they are extended as in periodic crystals, or localized as in amorphous materials -- remains largely unanswered for quasicrystals. To address this question, we directly measured the momentum (k-) dependent distribution of the electronic states using high-resolution, k-resolved photoemission measurements of quasicrystals at the Advanced Light Source in Berkeley, CA. We present results for both s-p- and d-bands of decagonal AlNiCo (for 10-fold and two principal 2-fold surfaces), and compare the dispersion of the states in the periodic and aperiodic directions. The electronic states were found to strongly disperse in both these directions, with periodic and aperiodic character, respectively. The effective mass of some of these states approaches m*=1, indicating a high degree of delocalization. Renderings of the constant energy surfaces in 3-dimensional k-space show that the s-p bands have spherical energy surfaces emanating from the locations of the strongest in-plane diffraction spots. This supports a nearly-free electron picture in quasicrystals, whereby the strongest Fourier components of the atomic potential contribute most significantly to the momentum distribution of electronic states, and define a pseudo-Brillouin zone. The d-bands were also found to have a delocalized character within the aperiodic plane. These delocalized d-bands cross the Fermi level and so form a well-defined Fermi surface. Similar states were found for icosahedral AlPdMn 5-fold surfaces as well. Since all relevant properties of metals derive from the detailed topology of the Fermi surface, these results should have immediate bearing on the properties of decagonal AlNiCo and icosahedral AlPdMn in particular, and quasicrystals in general.

Rotenberg, Eli

2001-03-01

246

A study of the valence shell electronic structure of uracil and the methyluracils  

International Nuclear Information System (INIS)

The valence shell photoelectron spectra of uracil, 1-methyluracil and 6-methyluracil have been studied experimentally and theoretically. Synchrotron radiation has been used to record spectra at photon energies of 40 and 80 eV. Photoelectron angular distributions have been determined and these provide an experimental means of distinguishing between ?- and ?-type orbitals. Vertical ionization energies and spectral intensities have been evaluated using the many-body Green's function approach, thereby enabling theoretical photoelectron spectra to be derived. The calculated spectra display a satisfactory agreement with the experimental data and this has allowed most of the photoelectron bands to be assigned. Two of the outer-valence vertical ionization energies are similar to one another and the vibrational progressions associated with these transitions overlap strongly. Vibronic interaction between these states, induced through the excitation of out-of-plane vibrational modes, may lead to nonadiabatic effects. Preliminary theoretical investigation of this interaction has been performed.

2008-11-03

247

Formation of an unconventional Ag valence state in Ag2NiO2  

CERN Multimedia

The Ag ion in the recently synthesized novel material Ag2NiO2 adopts an extremely unusual valency of 1/2, leaving the Ni ion as 3+, rather than the expected 2+. Using first principles calculations, we show that this mysterious subvalent state emerges due to a strong bonding-antibonding interaction between the two Ag layers which drives the lower band beneath the O p complex, eliminating the possibility of a conventional Ag 1+ valence state. The strong renormalization of the specific heat coefficient, gamma, is likely due to strong spin fluctuations that stem from nearly complete compensation of the ferro- (metallic double exchange and the 90 degree superexchange) and antiferromagnetic (conventional superexchange via Ni-O-Ag-O-Ni path) interactions.

Johannes, M D; Mazin, I I; Khomskii, D I

2006-01-01

248

Valence transition behavior of the doped Falicov-Kimball model at nonzero temperatures  

CERN Document Server

The extrapolation of small-cluster exact-diagonalization calculations is used to study the influence of doping on valence transitions in the spinless Falicov-Kimball model at nonzero temperatures. Two types of doping are examined, and namely, the substitution of rare-earth ions by non-magnetic ions that introduce (i) one or (ii) none additional electron (per non-magnetic ion) into the conduction band. It is found that the first type of substitution increases the average $f$-state occupancy of rare-earth ions, whereas the second type of substitution has the opposite effect. The results obtained are used to describe valence transition behavior of samarium in the hexaboride solid solutions $Sm_{1-x}M_xB_6$ ($M=Y^{3+},La^{3+}, Sr^{2+},Yb^{2+}$) and a very good agreement of theoretical and experimental results is found.

Farkasovsky, P

2005-01-01

249

XANES study of rare-earth valency in $LRu_{4}P_{12}$ (L = Ce and Pr)  

CERN Document Server

Valency of Ce and Pr in LRu4P12 (L = Ce and Pr) was studied by L2,3-edge x-ray absorption near-edge structure (XANES) spectroscopy. The Ce-L3 XANES spectrum suggests that Ce is mainly trivalent, but the 4f state strongly hybridizes with ligand orbitals. The band gap of CeRu4P12 seems to be formed by strong hybridization of 4f electrons. Pr-L2 XANES spectra indicate that Pr exists in trivalent state over a wide range in temperature, 20 < T < 300 K. We find that the metal-insulator (MI) transition at TMI = 60 K in PrRu4P12 does not originate from Pr valence fluctuation.

Lee, C H; Sekine, C; Shirotani, I; Ishii, M

1999-01-01

250

Correlation-induced corrections to the band structure of boron nitride: a wave-function-based approach.  

UK PubMed Central (United Kingdom)

We present a systematic study of the correlation-induced corrections to the electronic band structure of zinc-blende BN. Our investigation employs an ab initio wave-function-based local Hamiltonian approach which offers a rigorous theoretical framework for the calculation of the polarization and local charge redistribution effects around an extra electron or hole placed into the conduction or valence bands of semiconducting and insulating materials. Moreover, electron correlations beyond relaxation and polarization can be readily incorporated. The electron correlation treatment is performed on finite clusters. In conducting our study, we make use of localized Wannier functions and embedding potentials derived explicitly from prior periodic Hartree-Fock calculations. The on-site and nearest-neighbor charge relaxations bring corrections of several eV to the Hartree-Fock band gap. Additional corrections are caused by long-range polarization effects. In contrast, the dispersion of the Hartree-Fock bands is marginally affected by electron correlations. Our final result for the fundamental gap of zinc-blende BN compares well with that derived from soft x-ray experiments at the B and N K-edges.

Stoyanova A; Hozoi L; Fulde P; Stoll H

2009-07-01

251

Gastric Banding  

Science.gov (United States)

... and certain drugs should not have gastric banding. Surgical Procedure Before Surgery If you are considering whether to ... risks, including death. There are risks from the surgical procedure and the medications or anesthesia used during surgery. ...

252

Energy correlation among three photoelectrons emitted in core-valence-valence triple photoionization of Ne.  

UK PubMed Central (United Kingdom)

The direct observation of triple photoionization involving one inner shell and two valence electrons is reported. The energy distribution of the three photoelectrons emitted from Ne is obtained using a very efficient multielectron coincidence method using the magnetic bottle electron spectroscopic technique. A predominance of the direct path to triple photoionization for the formation of Ne3+ in the 1s 2s2 2p4 configuration is observed. It is demonstrated that the energy distribution evolves with photon energy and indicates a significant difference with triple photoionization involving only valence electrons.

Hikosaka Y; Lablanquie P; Penent F; Palaudoux J; Andric L; Soejima K; Shigemasa E; Suzuki IH; Nakano M; Ito K

2011-09-01

253

Energy correlation among three photoelectrons emitted in core-valence-valence triple photoionization of Ne.  

Science.gov (United States)

The direct observation of triple photoionization involving one inner shell and two valence electrons is reported. The energy distribution of the three photoelectrons emitted from Ne is obtained using a very efficient multielectron coincidence method using the magnetic bottle electron spectroscopic technique. A predominance of the direct path to triple photoionization for the formation of Ne3+ in the 1s 2s2 2p4 configuration is observed. It is demonstrated that the energy distribution evolves with photon energy and indicates a significant difference with triple photoionization involving only valence electrons. PMID:22026663

Hikosaka, Y; Lablanquie, P; Penent, F; Palaudoux, J; Andric, L; Soejima, K; Shigemasa, E; Suzuki, I H; Nakano, M; Ito, K

2011-09-09

254

Strongly correlated impurity band superconductivity in diamond: X-ray spectroscopic evidence  

Directory of Open Access Journals (Sweden)

Full Text Available In a recent X-ray absorption study in boron doped diamond, Nakamura et al. have seen a well isolated narrow boron impurity band in non-superconducting samples and an additional narrow band at the chemical potential in a superconducting sample. We interpret the beautiful spectra as evidence for upper Hubbard band of a Mott insulating impurity band and an additional metallic 'mid-gap band' of a conducting 'self-doped' Mott insulator. This supports the basic framework of a recent theory of the present author of strongly correlated impurity band superconductivity (impurity band resonating valence bond, IBRVB theory) in a template of a wide-gap insulator, with no direct involvement of valence band states.

G. Baskaran

2006-01-01

255

Entanglement in doped Resonating Valence Bond states  

CERN Multimedia

We investigate the entanglement properties of resonating valence bond states on a two dimensional lattice in the presence of dopants that remove electrons from the lattice creating "holes". The movement of the holes generated by the Hubbard Hamiltonian in the regime of strong Coloumb repulsion in this setting could be responsible for the phenomenon of high temperature superconductivity as hypothesised by Anderson in Science {\\bf 235}, 1196, (1987). We argue that there is a particular density of dopants (holes) where the entanglement contained in the lattice attains its maximal value for the nearest-neighbour RVB liquid state.

Ramanathan, Ravishankar; Wiesniak, Marcin; Vedral, Vlatko

2008-01-01

256

Valence Tautomerism in Co-dioxolene Complexes: Static and Time Resolved Infrared Spectroscopy Study.  

UK PubMed Central (United Kingdom)

In this work we studied the valence tautomerism process on two different Co-dioxolene complexes by means of transient infrared spectroscopy (TRIR). The molecules investigated are ls-CoIII(Cat-N-BQ)(Cat-N-SQ) (DQ2) and [ls-CoIII(tpy)(Cat-N-SQ)]PF6 (tpy) were Cat-NBQ = 2-(2-hydroxy-3,5-di-tert-butylphenyl-imino)-4,6-di-tert-butylcyclohexa-3,5-dienone, Cat- N-SQ is the dianionic radical analogue and tpy = 2,2'-6-2"-terpyridine. DFT calculations of the harmonic frequencies for the two complexes allow us to pinpoint the normal modes to be used as markers of the semiquinonate and benzoquinonate isomers. The photoinduced oneelectron charge transfer process from the radical semiquinonate ligand to the metal center leads to a ls-CoII(x)(Cat-N-BQ) electronic state (were x is the other ligand). Following this irst step an ultrafast ISC process ( < 200 fs) takes places, yielding the benzoquinonate isomer (hs-CoII(x)(Cat-N-BQ)). In the experiments we employed different excitation wavelengths on resonance with different a orption bands of the two samples. Excitation in the ligand-to-metal charge transfer (LMCT) band at ?520 nm and in the semiquinonate band at 1000 nm induces the valence tautomerism (VT) in both samples. From the time evolution of the TRIR spectra we determine the time constants of the vibrational cooling in the tautomeric state (7- 14 ps) and the ground state recovery times (? 350 ps for tpy and ? 450 ps for DQ2). In contrast, when the pump frequency is set at ? 700 nm, on resonance with the benzoquinonate absorption band of the second active ligand of the DQ2, no electron transfer takes place: the TRIR spectra basically show only ground state bleaching bands and no marker band of the tautomeric conversion shows up.

Azzaroli N; Lapini A; Di Donato M; Dei A; Righini R

2013-07-01

257

Lone conduction band in Cu2ZnSnSe4  

Science.gov (United States)

We present experimental proof for a narrow first conduction band in Cu2ZnSnSe4 semiconductor films as it has been predicted by theoretical calculations. The optical absorption characteristics of Cu2ZnSnSe4 thin films are analyzed by optical transmission spectroscopy. The experimental data show strong evidence for three absorption edges, as expected from theory, involving the valence band and two conduction bands, which are separated by a second band gap.

Gütay, Levent; Redinger, Alex; Djemour, Rabie; Siebentritt, Susanne

2012-03-01

258

Physical Dispersion.  

Science.gov (United States)

The constitutive parameters, which are defined according to the approach presented in the recent report series to the TDFV case, are different for both of definitions and used functions. The authors call the physical dispersion this case. The conversion o...

T. Sengor

2001-01-01

259

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

260

Composite Chiral Bands in the A?105 Mass Region  

International Nuclear Information System (INIS)

Composite chiral bands, corresponding to the ?g9/2v(h11/2)2 quasiparticle configuration, have been observed in 103Rh and 105Rh. The behaviour of these bands is compared with that of the chiral bands with a ?g9/2vh11/2 quasiparticle configuration observed in the odd-odd 102Rh and 104Rh nuclei. This comparison shows in a model independent way that the energy separation pattern of the chiral partner bands depends strongly on the properties of the triaxial core whilst the dependence on the valence quasiparticle coupling and on the Fermi level is weaker.

2005-11-21

 
 
 
 
261

Surface band-gap narrowing in quantized electron accumulation layers.  

Science.gov (United States)

An energy gap between the valence and the conduction band is the defining property of a semiconductor, and the gap size plays a crucial role in the design of semiconductor devices. We show that the presence of a two-dimensional electron gas near to the surface of a semiconductor can significantly alter the size of its band gap through many-body effects caused by its high electron density, resulting in a surface band gap that is much smaller than that in the bulk. Apart from reconciling a number of disparate previous experimental findings, the results suggest an entirely new route to spatially inhomogeneous band-gap engineering. PMID:20867408

King, P D C; Veal, T D; McConville, C F; Zúñiga-Pérez, J; Muñoz-Sanjosé, V; Hopkinson, M; Rienks, E D L; Jensen, M Fuglsang; Hofmann, Ph

2010-06-24

262

Surface band-gap narrowing in quantized electron accumulation layers.  

UK PubMed Central (United Kingdom)

An energy gap between the valence and the conduction band is the defining property of a semiconductor, and the gap size plays a crucial role in the design of semiconductor devices. We show that the presence of a two-dimensional electron gas near to the surface of a semiconductor can significantly alter the size of its band gap through many-body effects caused by its high electron density, resulting in a surface band gap that is much smaller than that in the bulk. Apart from reconciling a number of disparate previous experimental findings, the results suggest an entirely new route to spatially inhomogeneous band-gap engineering.

King PD; Veal TD; McConville CF; Zúñiga-Pérez J; Muñoz-Sanjosé V; Hopkinson M; Rienks ED; Jensen MF; Hofmann P

2010-06-01

263

Third order corrections and finite conduction band effects on the indirect exchange interaction in the Bloembergen-Rowland approximation  

International Nuclear Information System (INIS)

Third order corrections and finite conduction band effects are investigated on the indirect exchange interaction assuming a large energy gap compared to the valence band width. An oscillatory expression is regained in which as opposed to the Bloembergen-Rowland formula the energy gap as well as the conduction band modifies both the magnitude and phase of the oscillations. (Author)

1981-01-01

264

Ab initio valence bond calculation of intermolecular forces using a non-orthogonal basis set: HeHe and HeLi systems  

International Nuclear Information System (INIS)

A variational valence bond method of calculating intermolecular forces is presented. Its main feature is the use of a non-orthogonal basis set in order to avoid overextension basis errors. Test calculations of the dispersion energy in HeHe and HeLi systems are shown. (author)

1979-01-01

265

Superconductive mixed valence copper oxide, and method of making it  

International Nuclear Information System (INIS)

In this patent a superconducting mixed valence copper oxide is described. The chemical composition of this superconductive mixture contains lanthanum oxide, yttrium oxide, bismuth oxides, and strontium oxides.

1988-03-10

266

Superconductive mixed valence copper oxide, and method of making it  

Energy Technology Data Exchange (ETDEWEB)

In this patent a superconducting mixed valence copper oxide is described. The chemical composition of this superconductive mixture contains lanthanum oxide, yttrium oxide, bismuth oxides, and strontium oxides.

Deslandes, F.; Michel, C.; Provost, J.; Raveau, B.; Sulpice, A.; Tholence, J.L.; Chevalier, B.

1989-06-27

267

Awaking of ferromagnetism in GaMnN through control of Mn valence  

CERN Document Server

Room temperature ferromagnetism of GaMnN thin films is awaked by a mild hydrogenation treatment of samples synthesized by molecular beam epitaxy. Local environment of Mn atoms is monitored by Mn-L2,3 near edge x-ray absorption fine structure (NEXAFS) technique. Doped Mn ions are present at substitutional sites of Ga both before and after the hydrogenation. No secondary phase can be detected. Major valency of Mn changes from +3 to +2 by the hydrogenation. The present result supports the model that the ferromagnetism occurs when Mn2+ and Mn3+ are coexistent and holes in the mid- gap Mn band mediate the magnetic coupling.

Sonoda, S; Oba, F; Ikeno, H; Hayashi, H; Yamamoto, T; Yuba, Y; Yoshida, K; Aoki, M; Asari, M; Akasaka, Y; Kindo, K; Hori, H; Sonoda, Saki; Tanaka, Isao; Oba, Fumiyasu; Ikeno, Hidekazu; Hayashi, Hiroyuki; Yamamoto, Tomoyuki; Yuba, Yoshihiko; Yoshida, Ken'ichi; Aoki, Masahiko; Asari, Masatoshi; Akasaka, Yoichi; Kindo, Koichi; Hori, Hidenobu

2006-01-01

268

Temperature dependence of photoinduced valence changes in rubidium manganese hexacyanoferrate probed by Raman spectroscopy  

International Nuclear Information System (INIS)

[en] Temperature dependence of the photoinduced charge transfer process in Rb0.94Mn[Fe(CN)6]0.98·0.2H2O was investigated by observing the pair valence states of adjacent metal ions by Raman spectroscopy. After irradiation by 395 nm light in resonance with ligand-to-metal charge transfer band (CN- ? Fe(III)), the photoinduced phase containing low-temperature-like phase was generated as a result of the charge transfer from Mn(II) to Fe(III). Since this process was suppressed upon cooling, it was suggested that the charge transfer process was assisted by a thermal-activated process.

2009-02-01

269

Theoretical Magnon Dispersion Curves for Gd  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The magnon dispersion curve of Gd metal has been determined from first principles by use of augmented-plane-wave energy bands and wave functions. The exchange matrix elements I(k?, k??) between the 4f electrons and the conduction electrons from the first six energy bands were calculated under the as...

Lindgård, Per-Anker; Harmon, B. N.; Freeman, A. J.

270

Physical properties and Ce-valence of the filled skutterudite CePt4Ge12  

Science.gov (United States)

Filled skutterudite compounds MPt4Ge12 with a Pt-Ge framework structure show intriguing physical ground states (conventional (M = Sr, Ba) and unconventional superconductivity (M = Pr), heavy-fermion behavior (M = Sm), magnetic ordering), similar to the well-known transition-metal pnicogen skutterudites. Here, we report on the electronic, magnetic, and transport properties of CePt4Ge12 [1]. High-resolution X-ray absorption spectroscopy (XANES) measurements at the cerium LIII edge demonstrate that Ce in this compound has a temperature-independent valence close to three. However, magnetic susceptibility, thermopower, Hall effect, and electronic specific heat reveal broad maxima at Tmax = 65-80,, suggesting the presence of valence fluctuations. The Sommerfeld coefficient ? = 105 mJ,ol-1,-2 indicates moderately enhanced band masses for CePt4Ge12. We discuss these findings and conclude that CePt4Ge12 represents a system at the border between intermediate valence (IV) and Kondo lattice behavior.[4pt] [1] R.Gumeniuk et al. J. Phys.: Condensed Matter 23 (2011) 456601.

Schnelle, Walter; Gumeniuk, Roman; Nicklas, Michael; Rosner, Helge; Leithe-Jasper, Andreas; Grin, Yuri; Kvashnina, Kristina O.; Skourski, Yuri

2012-02-01

271

Chemical bonding in refractory transition metal compounds with 8, 9, and 10 valence electrons  

Energy Technology Data Exchange (ETDEWEB)

The chemical bonding in the refractory transition metal compounds TiC, TiN, and VN is investigated by experimental and theoretical techniques. High-precision x-ray diffraction is used to determine the electron densities in these three compounds experimentally. The x-ray structure factors and the respective valence electron densities are used twice, once to understand the chemical bonding and once to relate the experimental charge densities to those obtained from band structure calculations. These calculations, which in general are in very good agreement with experimental data, utilize the linearized augmented plane wave (LAPW) method. Theory and experiment lead to a detailed analysis of the chemical bonding in these compounds with 8, 9, and 10 valence electrons. By decomposition of the theoretical charge density into contributions from different states (energy regions), it was possible to show the strong covalent nonmetal p-metal d interaction, which is otherwise apparent only in TiC, but not in TiN or VN. In the latter two compounds the additional electrons occupy mainly metal d states with t/sub 2g/ symmetry, so that in the total valence charge densities the most important bonding feature is covered. In addition to covalent interactions all compounds have a metallic bonding contribution as well as a considerable charge transfer from the metal to the nonmetal site. This mixture in chemical bonding accounts for the unusual combination of properties such as ultrahardness, high melting points, and good conductivity.

Blaha, P.; Schwarz, K.; Kubel, F.; Yvon, K.

1987-10-01

272

Circular Photogalvanic Effect at Inter-Band Excitation in Semiconductor Quantum Wells  

CERN Multimedia

We observed a circular photogalvanic effect (CPGE) in GaAs quantum wells at inter-band excitation. The spectral dependence of the CPGE is measured together with that of the polarization degree of the time resolved photoluminescence. A theoretical model takes into account spin splitting of conduction and valence bands.

Belkov, V V; Schneider, P; Back, C; Oestereich, M; Rudolph, J; Haegele, D; Golub, L E; Wegscheider, W; Prettl, W; Schneider, Petra

2003-01-01

273

Colloids with valence and specific directional bonding.  

Science.gov (United States)

The ability to design and assemble three-dimensional structures from colloidal particles is limited by the absence of specific directional bonds. As a result, complex or low-coordination structures, common in atomic and molecular systems, are rare in the colloidal domain. Here we demonstrate a general method for creating the colloidal analogues of atoms with valence: colloidal particles with chemically distinct surface patches that imitate hybridized atomic orbitals, including sp, sp(2), sp(3), sp(3)d, sp(3)d(2) and sp(3)d(3). Functionalized with DNA with single-stranded sticky ends, patches on different particles can form highly directional bonds through programmable, specific and reversible DNA hybridization. These features allow the particles to self-assemble into 'colloidal molecules' with triangular, tetrahedral and other bonding symmetries, and should also give access to a rich variety of new microstructured colloidal materials. PMID:23128225

Wang, Yufeng; Wang, Yu; Breed, Dana R; Manoharan, Vinothan N; Feng, Lang; Hollingsworth, Andrew D; Weck, Marcus; Pine, David J

2012-11-01

274

Colloids with valence and specific directional bonding.  

UK PubMed Central (United Kingdom)

The ability to design and assemble three-dimensional structures from colloidal particles is limited by the absence of specific directional bonds. As a result, complex or low-coordination structures, common in atomic and molecular systems, are rare in the colloidal domain. Here we demonstrate a general method for creating the colloidal analogues of atoms with valence: colloidal particles with chemically distinct surface patches that imitate hybridized atomic orbitals, including sp, sp(2), sp(3), sp(3)d, sp(3)d(2) and sp(3)d(3). Functionalized with DNA with single-stranded sticky ends, patches on different particles can form highly directional bonds through programmable, specific and reversible DNA hybridization. These features allow the particles to self-assemble into 'colloidal molecules' with triangular, tetrahedral and other bonding symmetries, and should also give access to a rich variety of new microstructured colloidal materials.

Wang Y; Wang Y; Breed DR; Manoharan VN; Feng L; Hollingsworth AD; Weck M; Pine DJ

2012-11-01

275

Modulus of unbounded valence subdivision rules  

CERN Multimedia

Cannon, Floyd and Parry have studied the modulus of finite subdivision rules extensively. We investigate the properties of the modulus of subdivision rules with linear and exponential growth at every vertex, using barycentric subdivision and a subdivision rule for the Borromean rings as examples. We show that the subdivision rule arising from the Borromean rings is conformal, and conjecture that the subdivision rules for all alternating links are conformal. We show that the 1,2,3-tile criterion of Cannon, Floyd, and Parry is sufficient to prove conformality for linear growth, but not exponential growth. We show that the criterion gives a weaker form of conformality for subdivision rules of exponential growth at each vertex. We contrast this with the known, bounded-valence case, and illustrate our results with circle packings using Ken Stephenson's Circlepack.

Rushton, Brian

2011-01-01

276

The planar pyrochlore a Valence Bond Crystal  

CERN Document Server

Exact diagonalizations of the spin-1/2 Heisenberg model on the checkerboard lattice have been performed for sizes up to N=36 in the full Hilbert space and N=40 in the restricted subspace of first neighbor dimers. This antiferromagnet does not break SU(2) symmetry and displays long range order in 4-spin S=0 plaquettes. Both the symmetry properties of the spectrum and various correlations functions are extensively studied. At variance with the kagom{\\'e} antiferromagnet, the Heisenberg quantum model on a checkerboard lattice is a Valence Bond Crystal. Some results concerning the 3-dimensionnal spin-1/2 pyrochlore magnet (for sizes 16 and 32) are also shown: this system could behave differently from its 2-dimensional analog.

Fouet, J B; Sindzingre, P; Lhuillier, C

2001-01-01

277

Role of valence electrons for formation of glassy alloys  

International Nuclear Information System (INIS)

The role of valence electrons for formation of glassy alloys was investigated as a function of their valence electron concentration (VEC). The glass transition temperature Tg of 121 kinds of glassy alloys can be expressed as a linear function of VEC: Tg = 131VEC + 65 (2.3 g = -240VEC + 2408 (6.6

2009-08-26

278

Emotional valence and physical space: limits of interaction.  

UK PubMed Central (United Kingdom)

According to the body-specificity hypothesis, people associate positive things with the side of space that corresponds to their dominant hand and negative things with the side corresponding to their nondominant hand. Our aim was to find out whether this association holds also true for a response time study using linguistic stimuli, and whether such an association is activated automatically. Four experiments explored this association using positive and negative words. In Exp. 1, right-handers made a lexical judgment by pressing a left or right key. Attention was not explicitly drawn to the valence of the stimuli. No valence-by-side interaction emerged. In Exp. 2 and 3, right-handers and left-handers made a valence judgment by pressing a left or a right key. A valence-by-side interaction emerged: For positive words, responses were faster when participants responded with their dominant hand, whereas for negative words, responses were faster for the nondominant hand. Exp. 4 required a valence judgment without stating an explicit mapping of valence and side. No valence-by-side interaction emerged. The experiments provide evidence for an association between response side and valence, which, however, does not seem to be activated automatically but rather requires a task with an explicit response mapping to occur.

de la Vega I; de Filippis M; Lachmair M; Dudschig C; Kaup B

2012-04-01

279

Core Polarization with Variable Length Parameters for Valence Particles  

CERN Document Server

We study quadrupole and monopole core polarization using harmonic oscillator wave funtions but with different length parameters for the valence particle as compared to the core. We use perturbation theory with a delta interaction. The results also hold for a density dependent delta interaction [1]. We study how the amount of core polarization varies with the distance of the valence particle from the core.

Zamick, Larry

2010-01-01

280

Core Polarization with Variable Oscillator Length Parameters for Valence Particles  

CERN Multimedia

We study quadrupole and monopole core polarization using harmonic oscillator wave functions but with different length parameters for the valence particle as compared to the core. We use perturbation theory with a delta interaction. The results also hold for a density dependent delta interaction [1]. We study how the amount of core polarization varies with the distance of the valence particle from the core

Zamick, Larry

2010-01-01

 
 
 
 
281

Role of valence electrons for formation of glassy alloys  

Energy Technology Data Exchange (ETDEWEB)

The role of valence electrons for formation of glassy alloys was investigated as a function of their valence electron concentration (VEC). The glass transition temperature T{sub g} of 121 kinds of glassy alloys can be expressed as a linear function of VEC: T{sub g} = 131VEC + 65 (2.3 < VEC < 5.2) for metal/metal bonding type and T{sub g} = -240VEC + 2408 (6.6 < VEC < 9.1) for metal/metalloid bonding one. The thermal stability of the glassy alloys increases by the unsynchronized resonance of electron-pair bonds, and decreases due to increase in covalency by metalloid elements, with an increasing number of valence electrons, respectively. Ab initio molecular orbital calculations of the optimized structures for the Mg monoanion clusters warranted application of the valence electron rule, which is based on a valence electron contribution associated with spd or spf hybridization for glass formation.

Fukuhara, Mikio, E-mail: fukuhara@imr.tohoku.ac.j [Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan); Takahashi, Masae; Kawazoe, Yoshiyuki; Inoue, Akihisa [Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan)

2009-08-26

282

Charge Fluctuations and the Valence Transition in Yb under Pressure  

Energy Technology Data Exchange (ETDEWEB)

We present a dynamical mean field theory study of the valence transition (f{sup 14} {yields} f{sup 13}) in elemental, metallic Yb under pressure. Our calculations reproduce the observed valence transition as reflected in the volume dependence of the 4f occupation. The transition is accelerated by heating, and suggests quasiparticle or Kondo-like structure in the spectra of the trivalent end state, consistent with the early lanthanides. Results for the local charge fluctuations and susceptibility, however, show novel signatures uniquely associated with the valence transition itself, indicating that Yb is a fluctuating valence material in contrast to the intermediate valence behavior seen in the early trivalent lanthanides Ce, Pr, and Nd.

Ylvisaker, E R; Kunes, J; McMahan, A K; Pickett, W E

2009-04-21

283

Mechanisms of chromosome banding. V. Quinacrine banding.  

UK PubMed Central (United Kingdom)

A series of biochemical investigations were undertaken to determine the mechanism of Q-banding. The results were as follows: 1. In agreement with previous studies, highly AT-rich DNA, such as poly(dA)-poly(dT), markedly enhanced quinacrine fluorescence while GC containing DNA quenched fluorescence. These effects persisted at DNA concentrations comparable to those in the metaphase chromosome. 2. Studies of quinacrine-DNA complexes in regard to the hypochromism of quanacrine, DNA Tm, DNA viscosity, and equilibrium dialysis, indicated the quinacrine was bound be intercalation with relatively little sid binding. 3. Single or double stranded nucleotide polymers, in the form of complete or partial helices, were 1000-fold more effective in quenching than solutions of single nucleotides, suggesting that base stacking is required for quenching. 4. Studies of polymers in the A conformation, such as transfer RNA and DNA-RNA hybrids, indicated that marked base tilting does not affect the ability of nuclei acids to cause quenching or enhancement of quinacrine fluorescence. 5. Salts inhibit the binding of quinacrine to DNA. 6. Spermine, polylysine and polyarginine, which bind in the small groove of DNA, inhibited quinacrine binding and quenching, while histones, which probably bind in the large groove, had little effect. This correlated with the observation that removal of histones with acid has no effect on Q-banding. 7. Mouse liver chromatin was separated into five fractions. At concentrations of quinacrine from 2 times 10-6 to 2 times 10-5 M all fractions inhibited to varying degrees the ability of the chromatin DNA to bind quinacrine and quench quinacrine fluorescence. At saturating levels of quinacrine two fractions, the 400 g pellet (rich in heterochromatin) and a dispersed euchromatin supernatant fraction, showed a decreased number of binding sites for quinacrine. These two fractions were also the richest in non-histone proteins. 8. DNA isolated from the different fractions all showed identical quenching of quinacrine fluorescenc. 9. Mouse GC-rich, mid-band, AT-rich, and satellite DNA, isolated by CsCL AND Cs-2SO-4-Ag+ centrifugation all showed identical quenching of quinacrine fluorescence, indicating that within a given organism, except for very AT or GC-rich satellites, the variation in base composition is not adequate to explain Q-banding. We interpret these results to indicate that: (a) quinacrine binds to chromatin by intercalation of the three planar rings with the large group at position 9 lying in the small groove of DNA, (b) most pale staining regions are due to a decrease binding of quinacrine, and (c) this inhibition of binding is predominately due to non-histone proteins.

Comings OE; Kovacs BW; Avelino E; Harris DC

1975-01-01

284

Measurement of the spectral momentum distribution of valence electrons in amorphous carbon by (e,2e) spectroscopy  

International Nuclear Information System (INIS)

The spectral momentum density of the valence band of arc evaporated amorphous carbon has been measured by (e,2e) spectroscopy with significantly improved energy resolution relative to earlier studies. The valence band has been studied over a range of momenta from 0 to 1.6 a.u. with a resolution of 0.15 a.u. and over a range of binding energies from 9 eV above to 35 eV below the Fermi energy with a resolution of 1.5 eV. As seen in earlier studies, two major peaks are observed in the spectral momentum density which previously have been associated with ?- and ?-bands in graphite. A third feature in the spectra, a weak shoulder approximately 4 eV below the Fermi energy, is observed for the first time. A heuristic model is introduced based on the assumption that the spectral momentum density of evaporated amorphous carbon is an angular average of the spectral momentum density of graphite. The behavior of the strongest feature in the experimental spectra is described well by this model, but the other two features, which are in the energy range of the graphitic ?-, ?-2-, and ?3- bands, are poorly represented by the model. It is suggested that the poor agreement is due to re hybridization of these graphitic bands. 29 refs., 9 figs

1993-01-01

285

Low energy valence photoemission in the Anderson impurity model for Ce compounds  

CERN Multimedia

The valence level photoemission spectra in the Anderson impurity model for Ce compounds at zero temperature are studied as a function of the photon energy approximation, which is valid in high energy region. For the photoemission in the adiabatic limit of low energy region, one should consider the dipole matrix elements and the hole-induced photoelectron scattering potential. We can manage it by combining the time-evolution formalism and the $1/N_f$ scheme in a large $f$-level degeneracy $N_f$. This gives the exact results as $N_f\\to\\infty$. In view of experiments on the valence photoemission, two contributions of $4f$- and band emissions are mixed. We study the separate $4f$ and band contributions (from Ce $5d$) and total emission including the interference between two on an equal footing with varying the photon energy. In the $4f$-emission case, we also explore the effects of hole-induced scattering potential of the photoelectron with respect to $\\omega$. Its effects are found very similar to the core level...

Lee, J D

1999-01-01

286

Valence density of states of group IVA transition-metal dichalcogenides  

International Nuclear Information System (INIS)

The valence densities of states (VDOS) of the IVA transition-metal dichalcogenides ZrS2, ZrSe2, TiSe2 are calculated using the Gilat-Raubenheimer method and analysed in detail VDOS based on quadratic Lagrangian interpolation (QLI) of the energies evaluated in the final self-consistent symmetrised OPW (SCSOPW) potential at 131 symmetry independent k points are found to show close resemblance to XPS measurements and recent LCAO VDOS. Using an analysis based on the division of the SCSOPW QLI VDOS into partial VDOS from individual bands we find that four pairs of valence bands (1-2, 3-4, 5-6 and 7-8) give rise to four main peaks of SCSOPW QLI VDOS. A similar analysis shows that the use of the Slater-Koster interpolation caused some artificial deep valleys into the earlier SCSOPW LCAO VDOS. The methods used to calculate SCSOPW QLI VDOS and SCSOPW LCAO VDOS are also described. (author)

1980-06-20

287

Photodissociation of carbon dioxide in singlet valence electronic states. II. Five state absorption spectrum and vibronic assignment  

CERN Multimedia

The absorption spectrum of CO$_2$ in the wavelength range 120\\,nm --- 160\\,nm is analyzed by means of quantum mechanical calculations performed using vibronically coupled PESs of five singlet valence electronic states and the coordinate dependent transition dipole moment vectors. The thermally averaged spectrum, calculated for T=190\\,K via Boltzmann averaging of optical transitions from many initial rotational states, accurtely reproduces the experimental spectral envelope, consisting of a low and a high energy band, the positions of the absorption maxima, their FWHMs, peak intensities, and frequencies of diffuse structures in each band. Contributions of the vibronic interactions due to Renner-Teller coupling, conical intersections, and the Herzberg-Teller effect are isolated and the calculated bands are assigned in terms of adiabatic electronic states. Finally, diffuse structures in the calculated bands are vibronically assigned using wave functions of the underlying resonance states. It is demonstrated that...

Grebenshchikov, Sergy Yu

2013-01-01

288

Neutron scattering on intermediate valence systems  

International Nuclear Information System (INIS)

[en] The temperature dependence of the magnetic relaxation line widths (quasielastic (QE) line widths) and the crystal field excitations of some novel intermediate valent systems were measured by means of inelastic neutron scattering. Some striking new features of the alloys YbBe13, YbPd and Yb3Pd4 appoint them to belong to a new type of intermediate valent systems. YbAl3 shows several inelastic lines, but no QE-line was measurable. The heavy fermion systems CeCu6 and URu2Si2 show a strongly temperature dependent QE-line width, in course of which CeCu6 tends towards a nonvanishing residual value for T->0, which matches with theoretical predictions. For the first time valence instabilities of Pr (PrPd) and Sm (Smsub(0.51)Ysub(0.49)Al2) could be prooved by neutron scattering. In addition to these experiments, in YbCu2Si2 and TmTe the shifts in valency, caused by external hydrostatic pressure, were studied with a pressure cell for neutron scattering, especially designed and constructed for these special purposes. The corresponding observed changes of the QE-line widths coincide with the expected values, both in sign and absolute value. (orig.)[de] Es wurden die Temperaturabhaengigkeit der magnetischen Relaxationslinienbreiten (quasielastische (QE) Linienbreiten) und die Kristallfeldanregungen von verschiedenen neuen zwischenvalenten Systemen mit inelastischer Neutronenstreuung gemessen. Die Verbindungen YbBe13, YbPd und Yb3Pd4 zeichneten sich dabei durch mehrere andersartige Effekte als eine neue Gruppe zwischenvalenter Verbindungen aus. YbAl3 zeigt viele inelastische Anregungen aber keine messbare QE-Linie. Die Heavy Fermion Systeme CeCu6 und URu2Si2 zeigen eine stark temperaturabhaengige QE-Linienbreite, wobei CeCu6, in Uebereinstimmung mit der Theorie, fuer T->0 eine endliche Restlinienbreite besitzt. Es konnte erstmals eine Valenzinstabilitaet von Pr (PrPd) und Sm (Smsub(0.51)Ysub(0.49)Al2) mit Neutronen nachgewiesen werden. Darueber hinaus wurden die Valenzverschiebungen von YbCu2Si2 und TmTe durch aeusseren hydrostatischen Druck, erzeugt durch eine eigens hierfuer konstruierte Druckzelle fuer Neutronenstreuung, untersucht. Die beobachteten entsprechenden Aenderungen der QE-Linienbreite entsprechen in Richtung und Staerke den erwarteten Werten. (orig.)

1985-01-01

289

Habituation, sensitization, and emotional valence modulation of pain responses.  

UK PubMed Central (United Kingdom)

The Emotional Controls of Nociception (ECON) paradigm involves the presentation of emotionally-charged pictures during which painful stimuli are delivered. Across several ECON studies, unpleasant pictures enhanced pain and nociception, whereas pleasant pictures inhibited pain and nociception. However, at this time it is unknown whether emotional valence (unpleasant, neutral, pleasant) influences the habituation or sensitization of pain responses that occurs within a testing session. Indeed, ECON assumes that emotional valence modulation of pain is consistent throughout testing; otherwise the interpretation of valence modulation (unpleasant>neutral>pleasant) could be threatened. To address this issue, the present study (N=120) presented 108 pictures that varied in emotional valence. During and in between pictures, 52 suprathreshold electrocutaneous stimuli were delivered to evoke pain, the nociceptive flexion reflex [NFR], and pain-evoked skin conductance response [SCR]. Mixed effects ANOVAs verified that within-subject changes in pain responses were influenced by stimulus repetition (NFR and SCR habituated, pain ratings sensitized) and emotional valence (responses were highest during unpleasant pictures, intermediate during neutral pictures, and lowest during pleasant pictures). However, habituation/sensitization slopes were unaffected by emotional valence, thus indicating emotional valence modulation was consistently observed throughout the testing session. These results provide additional validation for the ECON paradigm and suggest that the circuit responsible for emotional modulation of pain and nociception is less susceptible to habituation or sensitization than the circuits responsible for responses to suprathreshold shocks.

Rhudy JL; Bartley EJ; Williams AE

2010-02-01

290

Habituation, sensitization, and emotional valence modulation of pain responses.  

Science.gov (United States)

The Emotional Controls of Nociception (ECON) paradigm involves the presentation of emotionally-charged pictures during which painful stimuli are delivered. Across several ECON studies, unpleasant pictures enhanced pain and nociception, whereas pleasant pictures inhibited pain and nociception. However, at this time it is unknown whether emotional valence (unpleasant, neutral, pleasant) influences the habituation or sensitization of pain responses that occurs within a testing session. Indeed, ECON assumes that emotional valence modulation of pain is consistent throughout testing; otherwise the interpretation of valence modulation (unpleasant>neutral>pleasant) could be threatened. To address this issue, the present study (N=120) presented 108 pictures that varied in emotional valence. During and in between pictures, 52 suprathreshold electrocutaneous stimuli were delivered to evoke pain, the nociceptive flexion reflex [NFR], and pain-evoked skin conductance response [SCR]. Mixed effects ANOVAs verified that within-subject changes in pain responses were influenced by stimulus repetition (NFR and SCR habituated, pain ratings sensitized) and emotional valence (responses were highest during unpleasant pictures, intermediate during neutral pictures, and lowest during pleasant pictures). However, habituation/sensitization slopes were unaffected by emotional valence, thus indicating emotional valence modulation was consistently observed throughout the testing session. These results provide additional validation for the ECON paradigm and suggest that the circuit responsible for emotional modulation of pain and nociception is less susceptible to habituation or sensitization than the circuits responsible for responses to suprathreshold shocks. PMID:20022696

Rhudy, Jamie L; Bartley, Emily J; Williams, Amy E

2009-12-22

291

Weighting positive versus negative: the fundamental nature of valence asymmetry.  

UK PubMed Central (United Kingdom)

OBJECTIVE: The relation between weighting of valence information in attitude generalization and evaluation of novel/hypothetical situations was explored. METHOD: Undergraduate participants played a computer game requiring them to learn which stimuli (beans) would increase/decrease their points. Later, participants classified the valence of game beans and novel ones varying in resemblance to game beans. The weighting bias in attitude generalization was estimated as the average response to novel beans, controlling for game bean learning. We examined whether this bias related to judgments of hypothetical situations concerning interpersonal relationships (Study 1), threat assessment (Study 2), risk propensities (Study 3), and risk behavior (Study 6). We also assessed whether valence weighting is specifically predictive of novel situations (Studies 4 and 5). Finally, we explored participants' ability to self-report their weighting bias (Study 7). RESULTS: Valence weighting in attitude generalization was related to judgments of novel situations and risk behavior. The performance-based measure did not correlate with responses to various questionnaires related to valence weighting. CONCLUSIONS: There is a fundamental individual difference associated with valence weighting, resulting in the relation between two processes unrelated in content, but sharing the essential characteristic of valence weighting-attitude generalization and evaluation of novel situations.

Pietri ES; Fazio RH; Shook NJ

2013-04-01

292

Band termination and signature crossing observation in some rare-earth nuclei  

International Nuclear Information System (INIS)

Predictions are very interesting features of moderately high angular momentum configurations as Band Termination, in nuclei with 10-12 valence particles outside the gadolinium 146Gd core. Which are made by core excitation or by promotion as the valence particles to the next shell. General properties of terminating bands are reviewed and exemplified on the observed high-angular momentum properties of 153Ho, 155Ho, 157Ho holmium nuclei. The very similar features are observed in the non-collective ones with N=88 isotones of dysprosium Dy, Erbium Er and tribium Yb nuclei.The spin contribution from different bands is calculated in terminating bands as well as more collective bands. The relation between the level energy minus rigid-rotor rotational energy versus spin for the yrast states is discussed and the plot serves to indicate that something interesting is happing above a certain value of (I). Above this value the nuclei seem to exhibit dominantly band termination behavior

2005-01-01

293

Oil spill dispersants  

Energy Technology Data Exchange (ETDEWEB)

This review with 24 references examines the chemistry of oil spill dispersants, the physics of the dispersant action, the efficiency and effectiveness of dispersants, the testing of dispersant effectiveness, and the option for using dispersants in oil spill response. The debate on dispersant use is addressed, and the impact of dispersant use, dispersant toxicity, natural dispersion, and the net environmental benefit analysis (NEBA) approach for assessing the entire effect of the use or non-use of dispersants are considered. The planning for dispersant use, the decision making at the time of a spill, and operational use of dispersants are discussed. (UK)

Fiocco, R.J.; Lewis, Alun

1999-01-01

294

Dissociative photoionization of adenine following valence excitation.  

UK PubMed Central (United Kingdom)

We present results on the valence level excitation, ionization and dissociation of adenine, using time-of-flight mass spectrometry and synchrotron radiation, in the vacuum ultraviolet (VUV) range of 12-21 eV. The measurements were performed using a gas-phase (Ne) harmonics filter in order to eliminate contributions from higher-order harmonics. Mass spectra were obtained using the photoelectron-photoion coincidence technique (PEPICO). The relative abundances for each ionic fragment and their mean kinetic energy release have been determined from the analysis of the corresponding peak shapes in the mass spectra. Comparison with the available photoelectron spectra and previous measurements allowed the assignment of the main features in the spectra. A discussion on the dissociative photoionization channels of this molecule has also been included. Due to our harmonics-free incident photon beam we were able to propose new appearance energy (AE) for the most important ionic channels in this energy range. The precursor ion, C(5)H(5)N(5)+, is the most abundant species (40% at 15 eV and 20% at 20 eV), which confirms the high stability of adenine upon absorption of VUV photons. We have observed other intense fragment ions such as: C(4)H(4)N(4)+, C(3)H(3)N(3) (+), C(2)H(2)N(2)+ and HCNH+. The production of the neutral HCN fragment represents up to 40% of the dissociative channels for this molecule as induced by VUV photons.

Pilling S; Lago AF; Coutinho LH; de Castilho RB; de Souza GG; de Brito AN

2007-01-01

295

Association of limited valence patchy particles in two dimensions  

International Nuclear Information System (INIS)

We investigate theoretically the phase behavior of particles with limited valence in two dimensions, by solving the first-order Wertheim theory form. As previously found for three dimensions, in two dimensions also the valence has a strong impact on the phase diagram, controlling the location of the gas-liquid coexistence. On decreasing the valence, the critical density and temperature decrease while the region of gas-liquid instability shrinks and vanishes. At low temperatures, the system reaches its ground state with particles forming a fully bonded network which spans the system.

2010-03-17

296

Observation of excitonic and band-to-band behavior in ordered InGaP{sub 2} alloys  

Energy Technology Data Exchange (ETDEWEB)

Photoluminescence measurements on ordered InGaP{sub 2} were studied as a function of temperature, laser power density, and magnetic field. The temperature varied between 1.4 and 300 K, the laser power densities ranged from 10 nW/cm{sup 2} to 20 W/cm{sup 2}, and the maximum magnetic field was 13.6 T. The data show both excitonic and band-to-band behavior, depending upon the incident laser power density. A consistent interpretation of all data leads to a type-II valence-band offset between the ordered domains.

Jones, E.D.; Follstaedt, D.M.; Lee, H.; Nelson, J.S.; Schneider, R.P. Jr. [Sandia National Labs., Albuquerque, NM (United States); Alonso, R.G.; Horner, G.S.; Machol, J.; Mascarenhas, A. [National Renewable Energy Lab., Golden, CO (United States)

1994-09-01

297

Valence, magnetism and conduction in the intermediate valence compounds: the case SmB6  

International Nuclear Information System (INIS)

[en] In some rare earth based compounds, the 4f level is situated so close to the Fermi level that the valence of the compound can become intermediate between two integer values. The so called 'intermediate valence' compound of Samarium hexaboride (SmB6) is one typical example of the exciting physics which can result from this quantum equilibrium between two valence configurations. The first configuration (Sm2+) corresponds to an insulating and non magnetic state whereas the second one (Sm3+) would theoretically give a magnetic and metallic ground state. This dissertation deals with the influence of pressure on this equilibrium. Specific heat measurements under pressure evidenced a new long range magnetic ordering for pressures higher than pc ? 10 GPa. On another hand, transport measurements measured for the first time in good conditions of hydrostatics found a reliable and reproducible critical pressure for the insulator to metal transition equal to pc. The phase diagram of SmB6 is now well known and the observation for the first time of a magnetic anomaly in the high pressure resistivity curves certifies that the onset of the magnetic phase really coincide with the closure of the gap. This change at the critical pressure pc is discussed in a general frame taking into account the Kondo lattice temperature as a key parameter for the renormalization of the wavefunction from one integer configuration to the other whereas the valence itself is still intermediate. This general idea seems to be valid also for other systems studied in this dissertation like SmS or TmSe and could even be valid for more general cases (Ytterbium, Cerium). In the same time, resistivity measurements under uniaxial stress were undertaken. The result is a strong anisotropy effect observed on the pressure dependence of the residual resistivity in the compound SmB6. The comparison with the transport under hydrostatic conditions enables us to consider a new idea for the nature of the gap, considering only one anisotropic gap which would present anyway two energy scales. (author)

2006-01-01

298

Dipole formation and band alignment at the Si(111)/CuInS2 heterojunction  

Science.gov (United States)

Heterojunctions between Si(111):H faces and molecular beam epitaxy grown CuInS2 thin films were investigated. The interface formation was studied by means of photoelectron spectroscopy and low energy electron diffraction. Initial sulfur exposure of the Si substrate at 750 K leads to a surface dipole of (0.61+/-0.10) eV. Upon subsequent CuInS2 deposition, an interface dipole of (1.0+/-0.2) eV is observed. The valence band offsets between Si and CuInS2 films of different [Cu]/[In] ratios were determined and an average valence band offset of (0.08+/-0.15) eV is obtained. Comparison with model considerations points out that the experimental values of the valence band offset are consistent with the observed interface dipole.

Hunger, R.; Pettenkofer, Chr.; Scheer, R.

2002-05-01

299

Fine structure and energy spectrum of exciton in direct band gap cubic semiconductors with degenerate valence bands  

International Nuclear Information System (INIS)

[en] The influence of the cubic structure on the energy spectrum of direct exciton is investigated, using the new method suggested by Nguyen Van Hieu and co-workers. Explicit expressions of the exciton energy levels 1S, 2S and 2P are derived. A comparison with the experiments and the other theory is done for ZnSe. (author). 10 refs, 1 fig., 2 tabs

1987-01-01

300

Spatial representation of odorant valence in an insect brain.  

UK PubMed Central (United Kingdom)

Brains have to decide whether and how to respond to detected stimuli based on complex sensory input. The vinegar fly Drosophila melanogaster evaluates food sources based on olfactory cues. Here, we performed a behavioral screen using the vinegar fly and established the innate valence of 110 odorants. Our analysis of neuronal activation patterns evoked by attractive and aversive odorants suggests that even though the identity of odorants is coded by the set of activated receptors, the main representation of odorant valence is formed at the output level of the antennal lobe. The topographic clustering within the antennal lobe of valence-specific output neurons resembles a corresponding domain in the olfactory bulb of mice. The basal anatomical structure of the olfactory circuit between insects and vertebrates is known to be similar; our study suggests that the representation of odorant valence is as well.

Knaden M; Strutz A; Ahsan J; Sachse S; Hansson BS

2012-04-01

 
 
 
 
301

Hadron Mass Predictions of the Valence Approximation to Lattice QCD  

CERN Multimedia

We evaluate the infinite volume, continuum limits of eight hadron mass ratios predicted by lattice QCD with Wilson quarks in the valence (quenched) approximation. Each predicted ratio differs from the corresponding observed value by less than 6\\%.

Butler, F; Sexton, J C; Vaccarino, A; Weingarten, D

1993-01-01

302

Electron-Phonon Interaction in Mixed Valence Systems.  

Science.gov (United States)

One considers an Hamiltonian describing mixed valence compounds and including d and f electron-phonon coupling. One shows that the renormalization of the electronic energy parameters induced by the electron-phonon interaction depends strongly on the natur...

F. Brouers O. L. T. de Menezes

1980-01-01

303

Hadron mass predictions of the valence approximation to lattice QCD  

Energy Technology Data Exchange (ETDEWEB)

We evaluate the infinite-volume, continuum limits of eight hadron mass ratios predicted by lattice QCD with Wilson quarks in the valence (quenched) approximation. Each predicted ratio differs from the corresponding observed value by less than 6%.

Butler, F.; Chen, H.; Sexton, J.; Vaccarino, A.; Weingarten, D. (IBM Thomas J. Watson Research Center, P.O. Box 218, Yorktown Heights, New York 10598 (United States))

1993-05-10

304

Some formal results for the valence bond basis  

CERN Multimedia

In a system with an even number of SU(2) spins, there is an overcomplete set of states--consisting of all possible pairings of the spins into valence bonds--that spans the S=0 Hilbert subspace. Operator expectation values in this basis are related to the properties of the closed loops that are formed by the overlap of valence bond states. We construct a generating function for spin correlation functions of arbitrary order and show that all nonvanishing contributions arise from configurations that are topologically irreducible. We derive explicit formulas for the correlation functions at second, fourth, and sixth order. We then extend the valence bond basis to include triplet bonds and discuss how to compute properties that are related to operators acting outside the singlet sector. These results are relevant to analytical calculations and to numerical valence bond simulations using quantum Monte Carlo, variational wavefunctions, or exact diagonalization.

Beach, K S D

2006-01-01

305

Laparoscopic gastric banding - discharge  

Science.gov (United States)

... discharge; Laparoscopic adjustable gastric banding - discharge; Bariatric surgery - laparoscopic gastric banding - discharge ... You had laparoscopic gastric banding surgery to help with weight loss. Your surgeon placed a band around the upper part of your stomach ...

306

Laparoscopic gastric banding  

Science.gov (United States)

... Band; LAGB; Laparoscopic adjustable gastric banding; Bariatric surgery - laparoscopic gastric banding ... able to lose weight through diet and exercise. Laparoscopic gastric banding is not a "quick fix" for obesity . It ...

307

f-band narrowing in uranium intermetallics  

Energy Technology Data Exchange (ETDEWEB)

Although the discovery of heavy fermion behavior in uranium compounds has attracted a great deal of attention, relatively little work has been done which is sufficiently systematic to allow an assessment of the relationship of such behavior to more common phenomena, such as mixed valence, narrow-band effects, etc. In this paper we report bulk property measurements for a number of alloys which form a part of such a systematic study. The approach has been to take relatively simple and well-understood materials and alter their behavior by alloying to produce heavy fermion or Kondo behavior in a controlled way.

Dunlap, B.D.; Litterst, F.J.; Malik, S.K.; Kierstead, H.A.; Crabtree, G.W.; Kwok, W.; Lam, D.J.; Mitchell, A.W.

1987-01-01

308

Stimulus affective valence reverses spatial compatibility effect  

Scientific Electronic Library Online (English)

Full Text Available Abstract in english In spatial compatibility tasks, the Reaction Time to right-side stimuli is shorter for right key responses (compatible condition) than for left key responses (incompatible condition) and vice-versa for left-side stimuli. Similar results have been found when the stimulus location is not relevant for response selection, such as in the Simon task. The Simon effect is the difference between the reaction times for non-corresponding and corresponding conditions. The Simon effec (more) t and its variants may be modulated by using emotional stimuli. However, until now, no work has studied how the affective valence of a stimulus influences spatial compatibility effects along the horizontal dimension. The present study investigated this issue by using small lateralized figures of soccer team players as stimuli. In the experiment, a compatible or incompatible response was chosen according to the team shirt. In one block, for the Favorite team, the volunteers had to press the key on the same side as the stimulus hemifield but the opposite-side key for the Rival team. In the other block, a reverse code had to be used. Fourteen right-handed volunteers were tested. Mean reaction times were subjected to analysis of variance with the following variables: Preference (Favorite/Rival), Hemifield (Left/Right), and Response Key (Left/Right). A three-way interaction was found (F1,13 = 6.60, p = .023), showing that the spatial compatibility effects depended on Preference. The Favorite team player elicited the usual spatial compatibility pattern, but for the Rival team player, the reverse effect was found, with incompatible responses being faster than compatible responses. We propose that this modulation may result from approach/avoidance reactions to the Favorite and Rival teams, respectively. Moreover, we suggest as a corollary that the classic spatial compatibility task is a powerful tool for investigating approach/avoidance effects.

Conde, Erick Francisco Quintas; Jazenko, Fernanda; Fraga Filho, Roberto Sena; Costa, Daniella Harth da; Torro-Alves, Nelson; Cavallet, Mikael; Gawryszewski, Luiz G

2011-06-01

309

Study of valence space excitations in 122Te  

International Nuclear Information System (INIS)

The ? stable 12252Te with two protons outside Z = 50 proton shell closure is a good candidate to study the shape coexistence phenomenon in A ? 120 region. A small number of available valence particles tend to drive the nucleus towards deformation. In the present work the valence-space structure which leads to fully aligned configurations in 122Te has been reported. Moreover, observed results have been compared to the CNS calculations

2011-01-01

310

Cerium valence in ternary d-metal silicides  

International Nuclear Information System (INIS)

RxMySiz (R - rare-earth metal, M-d-metal) ternary compounds with rare-earth ion intermediate valence are investigated. Growth of cerium valence with the increase of d-metal content which is linked with growth of energy-level density of metallic matrix electrons is determined using CeMSi, CeMSi2 and CeM2Si compounds (M=Fe, Co, Ni) as an example.

1989-01-01

311

Valence photoionization of the LiCl monomer and dimer  

International Nuclear Information System (INIS)

This paper reports a study of valence photoionization of the LiCl monomer and dimer. The behavior of the photoionization partial cross section for molecular valence orbitals was measured as a function of photon energy between 15 and 35 eV. A square-integrable-function method was used to model the ionization partial cross section in both the LiCl monomer and dimer.

2010-01-01

312

DISPERSE DYES  

UK PubMed Central (United Kingdom)

The present invention is directed to a disperse dye of formula (1) Wherein, X, Y and Z are, independently, hydrogen, halogen, cyano, nitro or SO2F Wherein at least one of X, Y and Z is SO2F. R1 is hydrogen, methyl, hydroxyl or NHR4 R2 is hydrogen, chloro or methoxy R3 is hydrogen, (C1-C4)-alkyl or -CH2 (CH2)nCOOCH2CN R5 is hydrogen, (C1-C4)-alkyl or -CH2 (CH2)mCOOCH2CN R4 is -COCH3,-CO C2H5, -SO2CH3 or SO2C2H5 n and m are independently 0,1 or 2. with the proviso: - When, Y and Z both are Cl, R1 is other than methyl. - When, R2 is Hydrogen and R3, R4 both are alkyl, R1 is selected from NHSO2CH3 or NHSO2C2H5. Disperse dyes of Formula (I) have excellent washing fastness and light fastness on polyester fiber and polyester blends.

DESAI PANKAJ; HIMENO KIYOSHI; DESAI NIKHIL; PATEL JAY

313

Secondary seed dispersal and its role in landscape organization  

Science.gov (United States)

Mathematical models of banded vegetation patterns predict rapid upslope migration of vegetated patches not realized in field observations, a key point of disagreement between theory and observation. It is shown that the disagreement between model results and field observations can arise from seed dispersal dynamics. Two representations of biomass movement are used to test the hypothesis that secondary seed dispersal in overland flow inhibits band migration. The first is based on coupling down-slope water transport and seed advection. The second uses a kernel-based representation of seed transport where an anisotropic dispersal kernel combines the effects of isotropic primary and downslope secondary seed dispersal, and ensures that conclusions about secondary dispersal are independent of diffusive representations of biomass movement. The analysis demonstrates that secondary seed dispersal can retard upward movement of banded vegetation irrespective of the precise representation of biomass movement as long as the anisotropic effects are accounted for.

Thompson, Sally; Katul, Gabriel

2009-01-01

314

Photocatalytic activity of the RuO2-dispersed composite p-block metal oxide LiInGeO4 with d10-d10 configuration for water decomposition.  

UK PubMed Central (United Kingdom)

The ruthenium oxide-loaded composite p-block metal oxide LiInGeO4 with d10-d10 configuration exhibited high photocatalytic activity for the overall splitting of water to produce H2 and O2 under UV irradiation. Changes in the photocatalytic activity with the calcination temperature of LiInGeO4, the amount of RuO2 loaded, and the states of RuO2 indicated that the combination of highly crystallized LiInGeO4 and a high dispersion of RuO2 particles resulted in high photocatalytic activity. Structurally, LiInGeO4 contained heavily distorted InO6 octahedra and GeO4 tetrahedra, generating a dipole moment inside. The high photocatalytic performance of RuO2-loaded LiInGeO4 supports the existing view that the photocatalytic activity correlates with the dipole moment. The DFT calculation showed that the top of the valence band (HOMO) was composed of the O 2p orbital while the bottom of the conduction band (LUMO) was formed by the hybridized In 5s5p + Ge 4s4p + O 2p orbitals. The highly dispersed conduction band, indicative of a high mobility of photoexcited electrons, was responsible for the high photocatalytic performance.

Kadowaki H; Sato J; Kobayashi H; Saito N; Nishiyama H; Simodaira Y; Inoue Y

2005-12-01

315

Photocatalytic activity of the RuO2-dispersed composite p-block metal oxide LiInGeO4 with d10-d10 configuration for water decomposition.  

Science.gov (United States)

The ruthenium oxide-loaded composite p-block metal oxide LiInGeO4 with d10-d10 configuration exhibited high photocatalytic activity for the overall splitting of water to produce H2 and O2 under UV irradiation. Changes in the photocatalytic activity with the calcination temperature of LiInGeO4, the amount of RuO2 loaded, and the states of RuO2 indicated that the combination of highly crystallized LiInGeO4 and a high dispersion of RuO2 particles resulted in high photocatalytic activity. Structurally, LiInGeO4 contained heavily distorted InO6 octahedra and GeO4 tetrahedra, generating a dipole moment inside. The high photocatalytic performance of RuO2-loaded LiInGeO4 supports the existing view that the photocatalytic activity correlates with the dipole moment. The DFT calculation showed that the top of the valence band (HOMO) was composed of the O 2p orbital while the bottom of the conduction band (LUMO) was formed by the hybridized In 5s5p + Ge 4s4p + O 2p orbitals. The highly dispersed conduction band, indicative of a high mobility of photoexcited electrons, was responsible for the high photocatalytic performance. PMID:16853996

Kadowaki, H; Sato, J; Kobayashi, H; Saito, N; Nishiyama, H; Simodaira, Y; Inoue, Y

2005-12-01

316

Bernauer's bands.  

UK PubMed Central (United Kingdom)

Ferdinand Bernauer proposed in his monograph, "Gedrillte" Kristalle (1929), that a great number of simple, crystalline substances grow from solution or from the melt as polycrystalline spherulites with helically twisting radii that give rise to distinct bull's-eye patterns of concentric optical bands between crossed polarizers. The idea that many common molecular crystals can be induced to grow as mesoscale helices is a remarkable proposition poorly grounded in theories of polycrystalline pattern formation. Recent reinvestigation of one of the systems Bernauer described revealed that rhythmic precipitation in the absence of helical twisting accounted for modulated optical properties [Gunn, E. et al. J. Am. Chem. Soc. 2006, 128, 14234-14235]. Herein, the Bernauer hypothesis is re-examined in detail for three substances described in "Gedrillte" Kristalle, potassium dichromate, hippuric acid, and tetraphenyl lead, using contemporary methods of analysis not available to Bernauer, including micro-focus X-ray diffraction, electron microscopy, and Mueller matrix imaging polarimetry. Potassium dichromate is shown to fall in the class of rhythmic precipitates of undistorted crystallites, while hippuric acid spherulites are well described as helical fibrils. Tetraphenyl lead spherulites grow by twisting and rhythmic precipitation. The behavior of tetraphenyl lead is likely typical of many substances in "Gedrillte" Kristalle. Rhythmic precipitation and helical twisting often coexist, complicating optical analyses and presenting Bernauer with difficulties in the characterization and classification of the objects of his interest.

Shtukenberg A; Gunn E; Gazzano M; Freudenthal J; Camp E; Sours R; Rosseeva E; Kahr B

2011-06-01

317

Absence of superconductivity and valence bond order in the Hubbard-Heisenberg model for organic charge-transfer solids.  

UK PubMed Central (United Kingdom)

A frustrated, effective [Formula: see text]-filled band Hubbard-Heisenberg model has been proposed for describing the strongly dimerized charge-transfer solid families ?-(ET)2X and Z[Pd(dmit)2]2. In addition to showing unconventional superconductivity, these materials also exhibit antiferromagnetism, candidate spin-liquid phases, and, in the case of Z=EtMe3P, a spin-gapped phase that has sometimes been referred to as a valence bond solid. We show that neither superconductivity nor the valence bond order phase occurs within the Hubbard-Heisenberg model. We suggest that a description based on [Formula: see text]-filling, that is reached when the carrier concentration per molecule instead of per dimer is considered, thus may be appropriate.

Gomes N; Clay RT; Mazumdar S

2013-09-01

318

Absence of superconductivity and valence bond order in the Hubbard-Heisenberg model for organic charge-transfer solids.  

Science.gov (United States)

A frustrated, effective [Formula: see text]-filled band Hubbard-Heisenberg model has been proposed for describing the strongly dimerized charge-transfer solid families ?-(ET)2X and Z[Pd(dmit)2]2. In addition to showing unconventional superconductivity, these materials also exhibit antiferromagnetism, candidate spin-liquid phases, and, in the case of Z=EtMe3P, a spin-gapped phase that has sometimes been referred to as a valence bond solid. We show that neither superconductivity nor the valence bond order phase occurs within the Hubbard-Heisenberg model. We suggest that a description based on [Formula: see text]-filling, that is reached when the carrier concentration per molecule instead of per dimer is considered, thus may be appropriate. PMID:23995074

Gomes, N; Clay, R T; Mazumdar, S

2013-08-30

319

Crystal structure and mixed-valence state in 1',1'''-dibutylbiferrocenium triiodide  

International Nuclear Information System (INIS)

In 1',1'''-dibutylbiferrocenium triiodide crystals A show temperature-independent trapped-valence state, while crystals B show a valence-delocalization of the mixed-valence state. The mixed-valence states of both crystals are discussed in relation to their crystal structures. (orig.)

1992-01-01

320

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

 
 
 
 
321

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

322

Photoemission in the molecular frame using the vector correlation approach: from valence to inner-valence shell ionization  

Energy Technology Data Exchange (ETDEWEB)

The (VA+, V{sub e}, e-bar ) vector correlation method, combining imaging and time-of-flight resolved electron-ion coincidence techniques, is used to probe dissociative photoionization (DPI) of simple molecules induced by VUV polarized synchrotron radiation, to obtain the I({theta}{sub e}, {phi}{sub e}) molecular frame photoelectron angular distributions (MFPADs). We focus on examples where DPI is induced by valence shell and inner-valence shell excitation. For valence shell ionisation, we report the results of a complete experiment for DPI of O{sub 2} via the O{sub 2}{sup +}(3{sup 2}{pi}{sub u}) ionic state, performed with a single circular polarization of the light at a photon excitation energy h{nu} = 24.4eV. A significant circular dichroism effect characterizes electron emission in the molecular frame. Inner-valence shell ionization induced by linearly polarized light is reported for the CO{sub 2} and N{sub 2}O isoelectronic molecules selecting two specific satellite lines using light with h{nu} {approx}35-bar eV. For both valence and inner-valence ionization, the measured MFPADs are compared with multichannel configuration interaction calculations, as well as with the prediction of a simple theoretical model of photoionization dynamics that probe the role of the initial state molecular orbital and which is presented in this special issue.

Dowek, D. [Laboratoire des Collisions Atomiques et Moleculaires (L.C.A.M.), UMR Universite Paris Sud et CNRS, No. 8625, Batiment 351, Universite Paris Sud, F-91405 Orsay Cedex (France)]. E-mail: dowek@lcam.u-psud.fr; Lebech, M. [Laboratoire des Collisions Atomiques et Moleculaires (L.C.A.M.), UMR Universite Paris Sud et CNRS, No. 8625, Batiment 351, Universite Paris Sud, F-91405 Orsay Cedex (France); Houver, J.C. [Laboratoire des Collisions Atomiques et Moleculaires (L.C.A.M.), UMR Universite Paris Sud et CNRS, No. 8625, Batiment 351, Universite Paris Sud, F-91405 Orsay Cedex (France); Lucchese, R.R. [Department of Chemistry, Texas A and M University, College Station, TX 77843-3255 (United States)

2004-12-01

323

Vaccine composition comprising at least two valences, one enhanced with adjuvant and not the other  

UK PubMed Central (United Kingdom)

The invention concerns a vaccine composition comprising two valences; (i) a first valence which is adjuvant-enhanced with aluminium hydroxide and (ii) a second valence which contains a polysaccharide of bacterial capsule comprising one or more -O- acetyl groups and which is not adsorbed with aluminium oxide due to the presence of a protecting compound which may be a phosphate, a citrate or a carbonate and which prevents said adsorptiuon. The first valence can be any vaccine valence. In one particular embodiment, the vaccine composition contains (i) the Hepatite A valence, adsorbed on aluminium hydroxide and (ii) the typhoid fever valence formed by the polysaccharide Vi of the Salmonella typhi capsule.

FRANCON ALAIN

324

VACCINE COMPOSITION COMPRISING AT LEAST TWO VALENCES, ONE ENHANCED WITH ADJUVANT AND NOT THE OTHER.  

UK PubMed Central (United Kingdom)

The invention concerns a vaccine composition comprising two valences (i) a first valence which is adjuvant-enhanced with aluminium hydroxide and (ii) a second valence which contains a polysaccharide of bacterial capsule comprising one or more -O- acetyl groups and which is not adsorbed with aluminium oxide due to the presence of a protecting compound which may be a phosphate, a citrate or a carbonate and which prevents said adsorption. The first valence can be any vaccine valence. In one particular embodiment, the vaccine composition contains (i) the Hepatite A valence, adsorbed on aluminium hydroxide and (ii) the typhoid fever valence formed by the polysaccharide Vi of the Salmonella typhi capsule.

ALAIN FRANCON

325

VACCINE COMPOSITION COMPRISING AT LEAST TWO VALENCES, ONE ENHANCED WITH ADJUVANT AND NOT THE OTHER  

UK PubMed Central (United Kingdom)

The invention concerns a vaccine composition comprising two valences; (i) a first valence which is adjuvant-enhanced with aluminium hydroxide and (ii) a second valence which contains a polysaccharide of bacterial capsule comprising one or more -O- acetyl groups and which is not adsorbed with aluminium oxide due to the presence of a protecting compound which may be a phosphate, a citrate or a carbonate and which prevents said adsorption. The first valence can be any vaccine valence. In one particular embodiment, the vaccine composition contains (i) the Hepatite A valence, adsorbed on aluminium hydroxide and (ii) the typhoid fever valence formed by the polysaccharide Vi of the Salmonella typhi capsule.

FRANCON Alain

326

Average replicated T-matrix approximation: valence band of non-crystalline metallic alloys  

Directory of Open Access Journals (Sweden)

Full Text Available Here we present a new approximation for calculation of density of states of multi-component metallic alloys using Lloyd formula. We consider the average square of T-matrix as the pair replication of scattering system. The analytical expressions are probed on TixMn1-x and AlxNi1-x binary alloys. The results are in good agreement with the predicted behavior of density of states for such systems.

P.Yakibchuk; O.Volkov; S.Vakarchuk

2007-01-01

327

Valence band photoemission study of CoxPd100-x alloy films  

International Nuclear Information System (INIS)

[en] Electronic structures of CoxPd100-x alloy films have been investigated using photoemission spectroscopy. The extracted Co 3d partial spectral weight (PSW) distribution exhibits interesting features at x = 25% reflecting large Co 3d/Pd 4d hybridization, and the Pd 4d PSW becomes bro[er as x increases. Calculated partial densities of states of CoxPd100-x compounds are found to be qualitatively consistent with experiment. (orig.)

1997-08-01

328

Valence band photoemission study of Co{sub x}Pd{sub 100-x} alloy films  

Energy Technology Data Exchange (ETDEWEB)

Electronic structures of Co{sub x}Pd{sub 100-x} alloy films have been investigated using photoemission spectroscopy. The extracted Co 3d partial spectral weight (PSW) distribution exhibits interesting features at x = 25% reflecting large Co 3d/Pd 4d hybridization, and the Pd 4d PSW becomes bro[er as x increases. Calculated partial densities of states of Co{sub x}Pd{sub 100-x} compounds are found to be qualitatively consistent with experiment. (orig.) 8 refs.

Kang, J.-S. [Catholic Univ. of Korea, Puchon (Korea, Republic of). Dept. of Physics; Kwon, S.K.; Min, B.I. [Dept. of Physics, Pohang Univ. of Science and Technology, Pohang (Korea, Republic of)

1998-01-01

329

Electronic states in valence and conduction bands of group-III nitrides: Experiment and theory  

Energy Technology Data Exchange (ETDEWEB)

A comprehensive study of the electronic structure of group-III nitrides (AlN, GaN, InN, and BN) crystallizing in the wurtzite, zinc-blende, and graphitelike hexagonal (BN) structures is presented. A large set of the x-ray emission and absorption spectra was collected at the several synchrotron radiation facilities at installations offering the highest possible energy resolution. By taking advantage of the linear polarization of the synchrotron radiation and making careful crystallographic orientation of the samples, the bonds along c axis ({pi}) and ''in plane'' ({sigma}) in the wurtzite structure could be separately examined. Particularly for AlN we found pronounced anisotropy of the studied bonds. The experimental spectra are compared directly with ab initio calculations of the partial density of states projected on the cation and anion atomic sites. For the GaN, AlN, and InN the agreement between structures observed in the calculated density of states (DOS) and structures observed in the experimental spectra is very good. In the case of hexagonal BN we have found an important influence of insufficient core screening in the x-ray spectra that influences the DOS distribution. The ionicity of the considered nitrides is also discussed. (c) 2000 The American Physical Society.

Lawniczak-Jablonska, K. [Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02 668 Warsaw, (Poland); Suski, T. [High Pressure Research Center, Polish Academy of Sciences, ulica Sokolowska 29/37, 01 142 Warsaw, (Poland); Gorczyca, I. [High Pressure Research Center, Polish Academy of Sciences, ulica Sokolowska 29/37, 01 142 Warsaw, (Poland); Christensen, N. E. [Institute of Physics and Astronomy, Aarhus University, C8000 Aarhus, (Denmark); Attenkofer, K. E. [HASYLAB, DESY, Notkestrasse 85, 22603 Hamburg, (Germany); Perera, R. C. C. [Center for X-ray Optics, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Gullikson, E. M. [Center for X-ray Optics, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Underwood, J. H. [Center for X-ray Optics, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Ederer, D. L. [Tulane University, New Orleans, Louisiana 70118 (United States); Liliental Weber, Z. [Lawrence Berkeley National Laboratory, MIS 6212031 Berkeley, California 94720 (United States)

2000-06-15

330

Electronic states in valence and conduction bands of group-III nitrides: Experiment and theory  

International Nuclear Information System (INIS)

A comprehensive study of the electronic structure of group-III nitrides (AlN, GaN, InN, and BN) crystallizing in the wurtzite, zinc-blende, and graphitelike hexagonal (BN) structures is presented. A large set of the x-ray emission and absorption spectra was collected at the several synchrotron radiation facilities at installations offering the highest possible energy resolution. By taking advantage of the linear polarization of the synchrotron radiation and making careful crystallographic orientation of the samples, the bonds along c axis (?) and ''in plane'' (?) in the wurtzite structure could be separately examined. Particularly for AlN we found pronounced anisotropy of the studied bonds. The experimental spectra are compared directly with ab initio calculations of the partial density of states projected on the cation and anion atomic sites. For the GaN, AlN, and InN the agreement between structures observed in the calculated density of states (DOS) and structures observed in the experimental spectra is very good. In the case of hexagonal BN we have found an important influence of insufficient core screening in the x-ray spectra that influences the DOS distribution. The ionicity of the considered nitrides is also discussed. (c) 2000 The American Physical Society

2000-06-15

331

Valence band states in Si-based p-type delta-doped field effect transistors  

Energy Technology Data Exchange (ETDEWEB)

We present tight-binding calculations of the hole level structure of delta-doped Field Effect Transistor in a Si matrix within the first neighbors sp{sup 3}s* semi-empirical tight-binding model including spin. We employ analytical expressions for Schottky barrier potential and the p-type delta-doped well based on a Thomas-Fermi approximation, we consider these potentials as external ones, so in the computations they are added to the diagonal terms of the tight-binding Hamiltonian, by this way we have the possibility to study the energy levels behavior as we vary the backbone parameters in the system: the two-dimensional impurity density (p{sub 2d}) of the p-type delta-doped well and the contact voltage (V{sub c}). The aim of this calculation is to demonstrate that the tight-binding approximation is suitable for device characterization that permits us to propose optimal values for the input parameters involved in the device design.

Martinez-Orozco, J C; Vlaev, Stoyan J, E-mail: jcmover@correo.unam.m [Unidad Academica de Fisica, Universidad Autonoma de Zacatecas, Calzada Solidaridad esquina con Paseo la Bufa S/N, C.P. 98060, Zacatecas, Zac. (Mexico)

2009-05-01

332

Valence band states in Si-based p-type delta-doped field effect transistors  

International Nuclear Information System (INIS)

[en] We present tight-binding calculations of the hole level structure of ?-doped Field Effect Transistor in a Si matrix within the first neighbors sp3s* semi-empirical tight-binding model including spin. We employ analytical expressions for Schottky barrier potential and the p-type ?-doped well based on a Thomas-Fermi approximation, we consider these potentials as external ones, so in the computations they are added to the diagonal terms of the tight-binding Hamiltonian, by this way we have the possibility to study the energy levels behavior as we vary the backbone parameters in the system: the two-dimensional impurity density (p2d) of the p-type ?-doped well and the contact voltage (Vc). The aim of this calculation is to demonstrate that the tight-binding approximation is suitable for device characterization that permits us to propose optimal values for the input parameters involved in the device design.

2009-05-01

333

On the O2 Schumann-Runge band system in sunspots  

International Nuclear Information System (INIS)

The visibility in the umbral ultraviolet spectrum of the O2 Schumann-Runge absorption band system has been explored. It is found that the band system may be visble in high dispersion sunspot spectrum. (Auth.)

1979-01-01

334

Dispersion tool  

UK PubMed Central (United Kingdom)

A device for homogenizing a liquid containing a mixture of single cells and cell clusters is provided. The device includes a shroud for channeling the liquid and suspended particles. The shroud defines an inner bore that is formed to include an axial inlet opening and at least one spaced apart outlet opening. A homogenizing bit is provided that is disposed within the inner bore for dispersing the suspended particles in the liquid to form a homogenized substance. The bit includes a shear blade fixed to the bit at a location near the axial inlet opening, with the shear blade configured to cooperate with adjacent shear ports to shear a portion of the suspended particles. The bit also includes a spiral portion that is configured to draw the liquid and suspended particles axially into and through the inner bore from the inlet opening.

GODFREY OTIS W; RAAS WALTER A; AYRES JAMES R

335

Core-valence correlations for atoms with open shells  

International Nuclear Information System (INIS)

We present an efficient method of inclusion of the core-valence correlations into the configuration interaction (CI) calculations. These correlations take place in the core area where the potential of external electrons is approximately constant. A constant potential does not change the core electron wave functions and Green's functions. Therefore, all operators describing interaction of M valence electrons and N-M core electrons [the core part of the Hartree-Fock Hamiltonian VN-M, the correlation potential ?1(r,r',E), and the screening of interaction between valence electrons by the core electrons ?2] may be calculated with all M valence electrons removed. This allows one to avoid subtraction diagrams which make accurate inclusion of the core-valence correlations for M>2 prohibitively complicated. Then the CI Hamiltonian for M valence electrons is calculated using orbitals in complete VN potential (the mean field produced by all electrons); ?1+?2 are added to the CI Hamiltonian to account for the core-valence correlations. We calculate ?1 and ?2 using many-body perturbation theory in which dominating classes of diagrams are included in all orders. We use neutral Xe I and all positive ions up to Xe VIII as a testing ground. We found that the core electron density for all these systems is practically the same. Therefore, we use the same ?1 and ?2 to build the CI Hamiltonian in all these systems (M=1,2,3,4,5,6,7,8). Good agreement with experiment for energy levels and Lande factors is demonstrated for all cases from Xe I to Xe VIII.

2007-01-01

336

Ion valence controlling method in solution  

Energy Technology Data Exchange (ETDEWEB)

Ions at a less noble standard redox potential compared with aimed ions, and at a more noble standard redox potential than any one of ions of palladium, ruthenium, rhenium, rhodium, iridium, gold, silver and mercury present in the solution and taking place a reversible reaction or a material forming such ions are added to a radioactive solution as a cocatalyst. Since the standard redox potential of the cocatalyst is more noble than that of the elements described above, the ratio of reduction of the elements is lowered, thereby enabling to suppress degradation of the catalyst. Further, since the cocatalyst is dispersed in the solution, the rate that the reduced cocatalyst reduces the aimed ions is increased to greater than the rate of reducing the aimed ions on the catalyst, and the ratio of reducing the aimed ions can be increased. Further, the reduction rate of the aimed ions can be controlled by changing the concentration of the cocatalyst. (N.H.).

Sasahira, Akira; Nakamura, Tomotaka.

1994-01-11

337

Particle-phonon excitations in valence-neutron and valence-proton nuclei around 146Gd  

International Nuclear Information System (INIS)

The present thesis deals with the one-valence-particle nuclei 147Tb and 151Er. The main purpose of the study was, to study characteristic properties of the particle-phonon excitations of these nuclei. In the one-valence-proton nucleus 147Tb from the ?h11/2x3- septet only the 15/2+ and 17/2+ Yrast states were known, which underly a strong diagonal exchange interaction. At mass separators in ? decay experiments of the 1/2+ and the 11/2-147Dy activities and in in-beam experiments layed out on excitation of states above the Yrast line with 6Li beams the nucleus 147Tb was spectroscoped. The combination of these three data sets made the nearly complete covering of the spin range from 1/2 to 27/2 of the low-lying states in 147Tb possible. At the whole in this nucleus more than 100 hitherto unknown states could be placed and farly characterized. The unusually manifold data allowed to identify beside the complete ?h11/2x3- septet also very much further particlexphonon states. Furthermore in the excitation range between 2.5 and 4 MeV numerous three-quasiparticle excitations were observed and in very sufficient way described by parameter-free shell-model calculations. A further important result is the manifestation of a neutron-one-particle-one-hole state with I=27/2, which lies with 3.7 MeV excitation close to the Yrast line. (orig./HSI)

1994-01-01

338

Study of band terminating in the A {approx_equal} 100 by EUROGAM; Recherche de terminaisons de bandes dans la region A {approx_equal} 100 avec EUROGAM  

Energy Technology Data Exchange (ETDEWEB)

Terminating bands in nuclei in the A{approx_equal} 100 region have been investigated using the EUROGAM2 array. Results have been obtained for Pd (Z 46) and Rh (Z = 45) isotopes. In the nucleus {sup 102}Pd, eight terminating configurations are identified. It is the first nucleus where terminating bands built on the valence space configurations and on core excited configurations are observed. Terminating bands have been also found in {sup 103}Pd and {sup 102}Rh. For {sup 102}Rh it is the first case of band terminations identified in a doubly-odd nucleus below the Z = 50 shell closure. (authors) 9 refs., 2 figs.

Gizon, J.; Gizon, A.; Genevey, J.; Santos, D. [Inst. des Sciences Nucleaires, Grenoble-1 Univ., 38 (France); Nyako, B.M.; Timar, J.; Zolnai, L. [Institute of Nuclear Research, Debrecen (Hungary); Boston, A.J.; Zoss, D.T.; Paul, E.S.; Semple, A.T. [Oliver Lodge Laboratory, University of Liverpool, Liverpool (United Kingdom); O`Brien, N.J.; Parry, C.M. [Department of Physics, University of York, Heslington, York (United Kingdom); Cata-Danil, Gh.; Bucurescu, D. [Horia Hulubei Institute of Physics and Nuclear Engineering, Bucharest (Romania); Afanasjev, A.V.; Ragnarsson, I. [Department of Mathematical Physics, University of Lund, Lund (Sweden)

1997-12-31

339

Quantum Criticality and Deconfinement in Phase Transitions Between Valence Bond Solids  

CERN Multimedia

We consider spin-half quantum antiferromagnets in two spatial dimensions on bipartite lattices in the quantum limit, where the spins are in a valence bond solid (VBS) phase which breaks some lattice symmetries. The transitions between two such VBS phases is studied. We show that the transition on the square lattice is generically first order. However, for the honeycomb lattice a continuous quantum phase transition can generically exist between two VBS phases of very different symmetry, in contrast to expectations based on Landau's theory of phase transitions. In fact, a line of such fixed points with continuously varying exponents is found to exist. Furthermore, these critical points are deconfined, in the sense that gapped spin-1/2 spinon excitations emerge right at the transition despite being absent in either phase. The low energy physics of this critical point (upto marginally irrelevant interactions) contains just a free quadratically dispersing `photon'. The phase structure on one side of this continuou...

Vishwanath, A; Senthil, T; Vishwanath, Ashvin

2003-01-01

340

On the valence-bond solid phase of the crossed-chain quantum spin model  

CERN Multimedia

Using a series expansion based on the flow-equation method we study the ground state energy and the elementary triplet excitations of a generalized model of crossed spin-1/2 chains starting from the limit of decoupled quadrumers. The triplet dispersion is shown to be very sensitive to the inter-quadrumer frustration, exhibiting a line of almost complete localization as well as lines of quantum phase transitions limiting the stability of the valence-bond solid phase. In the vicinity of the checkerboard-point a finite window of exchange couplings is found with a non-zero spin-gap, consistent with known results from exact diagonalization. The ground state energy is lower than that of the bare quadrumer case for all exchange couplings investigated. In the limiting situation of the fully frustrated checkerboard magnet our results agree with earlier series expansion studies.

Brenig, W; Brenig, Wolfram; Grzeschik, Matthias

2003-01-01

 
 
 
 
341

Collective magnetic excitations in mixed-valence Sm0.83Y0.17S  

CERN Multimedia

The magnetic spectral response of black-phase mixed-valence Sm0.83Y0.17S has been measured by inelastic neutron scattering on a single crystal. Two magnetic peaks are observed in the energy range of the Sm2+ spin-orbit transition (25-40 meV). Both of them exhibit significant dispersion along the three main symmetry directions, reminiscent of the spin-orbit exciton branch found in pure divalent SmS. The results can be reproduced by a simple phenomenological model accounting for the existence of sizeable Sm-Sm exchange interactions, and a microscopic mechanism is proposed on the basis of the "local-bound-state" theory developed previously for SmB6.

Alekseev, P A; Ochiai, A; Nefeodova, E V; Sadikov, I P; Clementyev, E S; Lazukov, V N; Braden, M; Nemkovski, K S

2001-01-01

342

Dimensionality and its effects upon the valence electronic structure of ordered metallic systems  

Energy Technology Data Exchange (ETDEWEB)

The system c(10x2)Ag/Cu(001) was investigated with Angle-Resolved Photoemission (ARP), Low Energy Electron Diffraction (LEED) and Auger Electron Spectroscopy (AES). LEED and AES provided the calibration of a quartz microbalance used to measure the amount of silver evaporated onto the copper single crystal and also established the monolayer geometrical structure at one monolayer exposure. An off-normal ARP bandmapping study performed with polarized HeI and NeI radiation demonstrated the electronically two-dimensional nature of the silver d-bands at coverages of near one monolayer. The states at the surface Brillouin Zone center were assigned upon the basis of their polarization dependences and a structural model of hexagonal symmetry. A normal emission ARP experiment was performed at the Stanford Synchrotron Radiation Laboratory (SSRL) over the photon energy range of 6 to 32 eV. Data from it documented the evolution of the valence electronic structure of the silver overlayer from a two-dimensional hexagonal valence to a three-dimensional behavior converging towards that of bulk Ag(111). A structural study was attempted using the ARP technique of Normal Emission Photoelectron Diffraction over the photon energy range of 3.4 to 3.7 keV at SSRL, the results of which are inconclusive.

Tobin, J.G.

1983-07-01

343

Universality class of non-Fermi liquid behaviour in mixed valence systems  

International Nuclear Information System (INIS)

A generalized Anderson single-impurity model with off-site Coulomb interactions is derived from the extended three-band Hubbard model, originally proposed to describe the physics of the copper-oxides. Using the abelian bosonization technique and canonical transformations, an effective Hamiltonian is derived in the strong coupling limit, which is essentially analogous to the Toulouse limit of the ordinary Kondo problem. In this limit, the effective Hamiltonian can be exactly solved, with a mixed valence quantum critical point separating two different Fermi liquid phases, i.e. the Kondo phase and the empty orbital phase. In the mixed valence quantum critical regime, the local moment is only partially quenched and X-ray edge singularities are generated. Around the quantum critical point, a new type of non-Fermi liquid behaviour is predicted with an extra specific heat Cimp ? T1/4 and a singular spin-susceptibility ?imp ? T-3/4. At the same time, the effective Hamiltonian under single occupancy is transformed into a resonant-level model, from which the correct Kondo physical properties (specific heat, spin susceptibility, and an enhanced Wilson ratio) are easily rederived. Finally, a brief discussion is given to relate these theoretical results to observations in U PdxCu5-x (x=1, 1.5) alloys, which show single-impurity critical behaviour consistent ons. (author). 30 refs.

1995-01-01

344

Microscopic investigation of magnetic dipole bands in {sup 132}Ba  

Energy Technology Data Exchange (ETDEWEB)

Nuclear structure of {sup 132}Ba is investigated within a framework of the pair-truncated shell model. The model reproduces experimental energy levels of the magnetic dipole band with the {nu}(h{sup 2}{sub 11/2}) x {pi}(h{sub 11/2}g{sub 7/2}) configuration. From the analysis of its structure, it turns out that two angular momenta of valence neutrons and protons gradually close as total spin increases.

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

2005-10-01

345

Space-valence priming with subliminal and supraliminal words.  

UK PubMed Central (United Kingdom)

To date it is unclear whether (1) awareness-independent non-evaluative semantic processes influence affective semantics and whether (2) awareness-independent affective semantics influence non-evaluative semantic processing. In the current study, we investigated these questions with the help of subliminal (masked) primes and visible targets in a space-valence across-category congruence effect. In line with (1), we found that subliminal space prime words influenced valence classification of supraliminal target words (Experiment 1): classifications were faster with a congruent prime (e.g., the prime "up" before the target "happy") than with an incongruent prime (e.g., the prime "up" before the target "sad"). In contrast to (2), no influence of subliminal valence primes on the classification of supraliminal space targets into up- and down-words was found (Experiment 2). Control conditions showed that standard masked response priming effects were found with both subliminal prime types, and that an across-category congruence effect was also found with supraliminal valence primes and spatial target words. The final Experiment 3 confirmed that the across-category congruence effect indeed reflected priming of target categorization of a relevant meaning category. Together, the data jointly confirmed prediction (1) that awareness-independent non-evaluative semantic priming influences valence judgments.

Ansorge U; Khalid S; König P

2013-01-01

346

Correlation effects in the valence ionization spectra of large conjugated molecules: p-Benzoquinone, anthracenequinone and pentacenequinone  

Energy Technology Data Exchange (ETDEWEB)

A review of an extensive series of theoretical studies of the valence one-electron and shake-up ionization spectra of polycyclic aromatic hydrocarbons is presented, along with new results for three planar quinone derivatives, obtained using one-particle Green's function (1p-GF) theory along with the so-called third-order algebraic diagrammatic construction [ADC(3)] scheme and the outer-valence Green's function (OVGF) approximation. These results confirm both for the pi- and sigma-band systems the rapid spreading, upon increasing system size, of many shake-up lines with significant intensities at outer-valence energies. Linear regressions demonstrate that with large conjugated molecules the location of the shake-up onset in the pi-band system is merely determined by the energy of the frontier (HOMO, LUMO) orbitals. Electron pair removal effects are found to almost compensate the electron relaxation effects induced by ionization of pi-levels, whereas the latter effects strongly dominate the ionization of more localized lone-pair (n) levels, and may lead to inversions of the energy order of Hartree-Fock (HF) orbitals. Therefore, although it increases upon a lowering of the HF band gap, and thus upon an increase of system size, the dependence of the one-electron ionization energies onto the quality of the basis set is lesser for pi-levels than for sigma-levels relating to electron lone pairs (n). Basis sets of triple- and quadruple-zeta quality are therefore required for treatments of the outermost pi- and n-ionization energies approaching chemical accuracy [1 kcal/mol, i.e. 0.04 eV]. When 1p-GF theory invalidates Koopmans' theorem and the energy order of HF orbitals, a comparison with Kohn-Sham orbital energies confirms the validity of the meta-Koopmans' theorem for density functional theory.

Knippenberg, S. [Institut fuer Physikalische und Theoretische Chemie, Johann Wolfgang Goethe Universitaet Frankfurt, Max-von-Laue-Str. 7, 60438 Frankfurt am Main (Germany); Research Group Theoretical Chemistry, Department SBG, Hasselt University, Agoralaan, Gebouw D, B-3590 Diepenbeek (Belgium); Deleuze, M.S., E-mail: michael.deleuze@uhasselt.b [Research Group Theoretical Chemistry, Department SBG, Hasselt University, Agoralaan, Gebouw D, B-3590 Diepenbeek (Belgium)

2010-05-15

347

Correlation effects in the valence ionization spectra of large conjugated molecules: p-Benzoquinone, anthracenequinone and pentacenequinone  

International Nuclear Information System (INIS)

A review of an extensive series of theoretical studies of the valence one-electron and shake-up ionization spectra of polycyclic aromatic hydrocarbons is presented, along with new results for three planar quinone derivatives, obtained using one-particle Green's function (1p-GF) theory along with the so-called third-order algebraic diagrammatic construction [ADC(3)] scheme and the outer-valence Green's function (OVGF) approximation. These results confirm both for the ?- and ?-band systems the rapid spreading, upon increasing system size, of many shake-up lines with significant intensities at outer-valence energies. Linear regressions demonstrate that with large conjugated molecules the location of the shake-up onset in the ?-band system is merely determined by the energy of the frontier (HOMO, LUMO) orbitals. Electron pair removal effects are found to almost compensate the electron relaxation effects induced by ionization of ?-levels, whereas the latter effects strongly dominate the ionization of more localized lone-pair (n) levels, and may lead to inversions of the energy order of Hartree-Fock (HF) orbitals. Therefore, although it increases upon a lowering of the HF band gap, and thus upon an increase of system size, the dependence of the one-electron ionization energies onto the quality of the basis set is lesser for ?-levels than for ?-levels relating to electron lone pairs (n). Basis sets of triple- and quadruple-zeta quality are therefore required for treatments of the outermost ?- and n-ionization energies approaching chemical accuracy [1 kcal/mol, i.e. 0.04 eV]. When 1p-GF theory invalidates Koopmans' theorem and the energy order of HF orbitals, a comparison with Kohn-Sham orbital energies confirms the validity of the meta-Koopmans' theorem for density functional theory.

2010-01-01

348

The valence electron photoemission spectrum of semiconductors: ab initio description of multiple satellites  

CERN Document Server

The experimental valence band photoemission spectrum of semiconductors exhibits multiple satellites that cannot be described by the GW approximation for the self-energy in the framework of many-body perturbation theory. Taking silicon as a prototypical example, we compare experimental high energy photoemission spectra with GW calculations and analyze the origin of the GW failure. We then propose an approximation to the functional differential equation that determines the exact one-body Green's function, whose solution has an exponential form. This yields a calculated spectrum, including cross sections, secondary electrons, and an estimate for extrinsic and interference effects, in excellent agreement with experiment. Our result can be recast as a dynamical vertex correction beyond GW, giving hints for further developments.

Guzzo, Matteo; Sottile, Francesco; Romaniello, Pina; Gatti, Matteo; Kas, Joshua J; Rehr, John J; Silly, Mathieu G; Sirotti, Fausto; Reining, Lucia

2011-01-01

349

The Fermi surface and f-valence electron count of UPt3  

Science.gov (United States)

Combining old and new de Haas-van Alphen (dHvA) and magnetoresistance data, we arrive at a detailed picture of the Fermi surface of the heavy fermion superconductor UPt3. Our work was partially motivated by a new proposal that two 5f valence electrons per formula unit in UPt3 are localized by correlation effects—agreement with previous dHvA measurements of the Fermi surface was invoked in its support. Comprehensive comparison with our new observations shows that this 'partially localized' model fails to predict the existence of a major sheet of the Fermi surface, and is therefore less compatible with experiment than the originally proposed 'fully itinerant' model of the electronic structure of UPt3. In support of this conclusion, we offer a more complete analysis of the fully itinerant band structure calculation, where we find a number of previously unrecognized extremal orbits on the Fermi surface.

McMullan, G. J.; Rourke, P. M. C.; Norman, M. R.; Huxley, A. D.; Doiron-Leyraud, N.; Flouquet, J.; Lonzarich, G. G.; McCollam, A.; Julian, S. R.

2008-05-01

350

Compounds with mixed and intermediate sulfur valences in pyrite from the Amelia Mine, Southwest Wisconsin  

Science.gov (United States)

Compounds with mixed and intermediate sulfur valences form cloudy small inclusions in banded pyrite and 2 4 mm large rounded aggregates in pyrite stalactites. Such areas under high magnification of SEM appear to be a mixture of FeS2 with FeS2O3. Some of the microareas of 40 50 ?m are homogeneous and can be identified by reflected light microscopy, microprobe and soft X-ray spectroscopy as Fe-thiosulphate, FeS2O3 or (Fe, Pb)2S3O7 with this compound having one sulfur -2 and two sulfurs +6. The intermediate sulfur compounds are enriched in Pb, Ni, Co and As.

Kucha, H.; Barnes, H. L.

1995-02-01

351

Internal conversion coefficient for valence electrons of metals  

International Nuclear Information System (INIS)

The ab-initio electron theory of the internal conversion coefficient (ICC) is developed for the case of pure crystalline metals, the radioactive nuclei of which emit ?-quanta with relatively small energy (? keV) exciting thus preponderantly valence electrons. In this case the photon wavelength is large in comparison with the radius of the nucleus and the ICC (= energy spectrum of the emitted conversion electrons) becomes independent of the properties of the nucleus. For any electric or magnetic transition and using spherically symmetric muffin-tin potentials the ICC is expressed by the characteristic quantities of the electron making a transition from an occupied valence state to an unoccupied free electron state. The calculations for 110Ag show the ICC to reflect directly the density of states of the valence electrons. (author).

1990-01-01

352

Recognizing the emotional valence of names: an ERP study.  

UK PubMed Central (United Kingdom)

Unlike common nouns, person names refer to unique entities and generally have a referring function. We used event-related potentials to investigate the time course of identifying the emotional meaning of nouns and names. The emotional valence of names and nouns were manipulated separately. The results show early N1 effects in response to emotional valence only for nouns. This might reflect automatic attention directed towards emotional stimuli. The absence of such an effect for names supports the notion that the emotional meaning carried by names is accessed after word recognition and person identification. In addition, both names with negative valence and emotional nouns elicited late positive effects, which have been associated with evaluation of emotional significance. This positive effect started earlier for nouns than for names, but with similar durations. Our results suggest that distinct neural systems are involved in the retrieval of names' and nouns' emotional meaning.

Wang L; Zhu Z; Bastiaansen M; Hagoort P; Yang Y

2013-04-01

353

Optical implementation and entanglement distribution in Gaussian valence bond states  

CERN Multimedia

We study Gaussian valence bond states of continuous variable systems, obtained as the outputs of projection operations from an ancillary space of M infinitely entangled bonds connecting neighboring sites, applied at each of $N$ sites of an harmonic chain. The entanglement distribution in Gaussian valence bond states can be controlled by varying the input amount of entanglement engineered in a (2M+1)-mode Gaussian state known as the building block, which is isomorphic to the projector applied at a given site. We show how this mechanism can be interpreted in terms of multiple entanglement swapping from the chain of ancillary bonds, through the building blocks. We provide optical schemes to produce bisymmetric three-mode Gaussian building blocks (which correspond to a single bond, M=1), and study the entanglement structure in the output Gaussian valence bond states. The usefulness of such states for quantum communication protocols with continuous variables, like telecloning and teleportation networks, is finally...

Adesso, Gerardo

2007-01-01

354

Rational subsets of polycyclic monoids and valence automata  

CERN Multimedia

We study the classes of languages defined by valence automata with rational target sets (or equivalently, regular valence grammars with rational target sets), where the valence monoid is drawn from the important class of polycyclic monoids. We show that for polycyclic monoids of rank 2 or more, such automata accept exactly the context-free languages. For the polycyclic monoid of rank 1 (that is, the bicyclic monoid), they accept a class of languages strictly including the partially blind one-counter languages. Key to the proof is a description of the rational subsets of polycyclic and bicyclic monoids, other consequences of which include the decidability of the rational subset membership problem for these monoids, and the closure of the class of rational subsets under intersection and complement.

Render, Elaine

2007-01-01

355

Effects of emotional valence and arousal on recollective and nonrecollective recall.  

UK PubMed Central (United Kingdom)

The authors investigated the effects of valence and arousal on memory using a dual-process model that quantifies recollective and nonrecollective components of recall without relying on metacognitive judgments to separate them. The results showed that valenced words increased reconstruction (a component of nonrecollective retrieval) relative to neutral words. In addition, the authors found that positive valence increased recollective retrieval in comparison to negative valence, whereas negative valence increased nonrecollective retrieval relative to positive valence. The latter effect, however, depended on arousal: It was reliable only when arousal was high. The present findings supported the notion that emotional valence is a conceptual gist because it affected nonrecollective retrieval and because subjects' recall protocols were clustered by valence. The results challenge the hypothesis that valence affects only recollection, and they clarify previous inconsistent findings about the effects of emotion on memory accuracy and brain activity.

Gomes CF; Brainerd CJ; Stein LM

2013-05-01

356

Bonding and valence in uranium compounds with oxygen: a study by X-ray photoelectron spectroscopy and electron paramagnetic resonance  

International Nuclear Information System (INIS)

[en] Uranium oxides UO2, U2O5, U3O8 and UO3 have been studied by X-ray photoemission (E.S.C.A.) and electron paramagnetic resonance. Binding energy values are reported for the U4f core levels, showing that U2O5 is UO2. UO3 and U3O8 is UO2.2UO3. Valence band structures are discussed in relation with the formation of (UO2)2+ groups. Results from EPR spectroscopy support the view that no U(V) species are presented in these compounds. (Auth.)

1975-09-13

357

Band crossing in isovalent semiconductor alloys with large size mismatch  

Science.gov (United States)

Mixing isovalent compounds AC with BC to form alloys A1-xBxC has been an effective way in band structure engineering to enhance the availability of material properties. In most cases, the mixed isovalent atoms A and B, such as Al and Ga in Al1-xGaxAs or As and Sb in GaAs1-xSbx are similar in their atomic sizes and chemical potentials; therefore, the physical properties of A1-xBxC change smoothly from AC to BC. However, in some cases when the chemical and size differences between the isovalent atoms A and B are large, adding a small amount of B to AC or vice versa can lead to a discontinuous change in the electronic band structure. These large size- and chemicalmismatched (LSCM) systems often show unusual and abrupt changes in the alloys' material properties, which provide great potential in material design for novel device applications. In this report, based on first-principles band-structure calculations we show that for LSCM GaAs1-xNx and GaAs1-xBix alloys at the impurity limit the N (Bi)-induced impurity level is above (below) the conduction-(valence-) band edge of GaAs. These trends reverse at high concentration, i.e., the conduction-band edge of GaAs1-xNx becomes an N-derived state and the valence-band edge of GaAs1-xBix becomes a Bi-derived state, as expected from their band characters. We show that this band crossing phenomenon cannot be described by the popular BAC model but can be naturally explained by a simple band broadening picture.

Deng, Hui-Xiong; Wei, Su-Huai

2012-02-01

358

The pion parton distribution function in the valence region  

CERN Document Server

The parton distribution function of the pion in the valence region is extracted in a next-to-leading order analysis from Fermilab E-615 pionic Drell-Yan data. The effects of the parameterization of the pion's valence distributions are examined. Modern nucleon parton distributions and nuclear corrections were used and possible effects from higher twist contributions were considered in the analysis. In the next-to-leading order analysis, the high-$x$ dependence of the pion structure function differs from that of the leading order analysis, but not enough to agree with the expectations of pQCD and Dyson-Schwinger calculations.

Wijesooriya, K; Holt, R J

2005-01-01

359

Peculiarities of core-valence luminescence of CsBr and Rb1-xCsxBr crystals  

International Nuclear Information System (INIS)

The study of the emission and excitation spectra as well as the decay kinetics for the intrinsic core-valence luminescence of CsBr and the impurity core-valence luminescence of Rb1-xCsxBr solid solution under excitation in the 10-20 eV energy range has been carried out in the temperature range of 10-300 K. The change of coordination number for the Cs+ ion from n=8 to n=6 at the transformation of CsBr to Rb0.9Cs0.1Br solid solution is accompanied by significant modification of the core-valence luminescence spectra shape. The temperature dependence of the excitation efficiency in the threshold region observed for Rb0.9Cs0.1Br could be caused by the decay of the 5d3/2 excited state of the Cs+ ion due to thermostimulated electron transition from this state into the conduction band, which leads to the appearance of unbounded 5p Cs+ core holes. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

2004-01-01

360

Antibonding. beta. * valence MOs in the inner-shell and outer-shell spectra of the fluorobenzenes  

Energy Technology Data Exchange (ETDEWEB)

Electron transmission, inner-shell electron energy loss and magnetic circular dichroism spectra have been analyzed in an effort to trace the positions of the sigma* antibonding valence MOs in benzene and its fluorinated derivatives. The correlation of negative-ion resonances in these systems shows clearly that a sigma* valence level descends with increasing fluorination so as to become the lowest virtual MO in hexafluorobenzene. In addition to the low-lying sigma* negative-ion shape resonances, several negative-ion Feshbach resonances are identified as involving 3s and 3p Rydberg orbitals. The carbon K-shell spectra of benzene and its fluorinated derivatives below the respective C 1s ionization potentials are dominated by excitations to 1..pi..* and 2..pi..* valence levels. A systematic shift of the sigma* levels to lower energy with increasing fluorination is observed which is consistent with the perfluoro effect. Resonances terminating at sigma*(C-C) are found to dominate the C 1s near continuum, with dramatic enhancement of these transitions in the more highly fluorinated species. Investigation of hexafluoro- and 1,2,4,5-tetrafluorobenzene by vacuum-ultraviolet magnetic circular dichroism in the vapor phase confirms the presence of bands which are not ..pi.. ..-->.. ..pi..*. Once again, low-lying sigma* MOs are invoked as terminating orbitals.

Hitchcock, A.P.; Fischer, P.; Gedanken, A.; Robin, M.B.

1987-01-29

 
 
 
 
361

Interface properties and band alignment of Cu2S/CdS thin film solar cells  

International Nuclear Information System (INIS)

The stoichiometry and electronic properties of bulk Cu2S thin films obtained by vacuum evaporation were investigated by optical spectroscopy, X-ray diffraction and photoemission spectroscopy. The Cu2S/CdS heterojunction interface has been prepared in situ and characterized by photoelectron spectroscopy (X-ray photoemission spectroscopy and ultraviolet photoelectron spectroscopy) after each growth step under ultra high vacuum conditions. The XPS core level spectra as well as valence band spectra of the substrate Cu2S and overlayer CdS were acquired after each step. From these measurements, a large overall band bending of 0.9 eV is observed. The valence band offset is determined to be ?EVB=1.2 eV and the conduction band offset is ?ECB=0±0.1 eV.

2003-05-01

362

Low-spin identical bands in the N sub p N n scheme  

Energy Technology Data Exchange (ETDEWEB)

The occurrence of low-spin identical bands in the rare-earth region is shown to be the manifestation of a more general property of nuclear excitation mechanism, i.e., a smooth dependence of the moment of inertia on a very simple function of the valence proton and neutron numbers.

Saha, M.; Sen, S. (Saha Institute of Nuclear Physics, Calcutta 700064 (India))

1992-11-01

363

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

364

Parallel measurements of both heterojunction band discontinuities by synchrotron-radiation photoemission  

Science.gov (United States)

Both the conduction-band discontinuity, ?Ec, and the valence-band discontinuity, ?Ev, at the interface between a cleaved GaP substrate and a Si overlayer were measured in parallel with photoemission techniques. ?Ev was measured in the conventional energy distribution curve mode, while ?Ec was measured in the partial-yield mode. The results open the way to more reliable estimates of the discontinuities for compound-semiconductor heterojunctions.

Perfetti, P.; Patella, F.; Sette, F.; Quaresima, C.; Capasso, C.; Savoia, A.; Margaritondo, G.

1984-05-01

365

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

366

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

367

Real-time observation of valence electron motion  

International Nuclear Information System (INIS)

The superposition of quantum states drives motion on the atomic and subatomic scales, with the energy spacing of the states dictating the speed of the motion. In the case of electrons residing in the outer (valence) shells of atoms and molecules which are separated by electronvolt energies, this means that valence electron motion occurs on a subfemtosecond to few-femtosecond timescale (1 fs = 10-15 s). In the absence of complete measurements, the motion can be characterized in terms of a complex quantity, the density matrix. Here we report an attosecond pump-probe measurement of the density matrix of valence electrons in atomic krypton ions. We generate the ions with a controlled few-cycle laser field and then probe them through the spectrally resolved absorption of an attosecond extreme-ultraviolet pulse, which allows us to observe in real time the subfemtosecond motion of valence electrons over a multifemtosecond time span. We are able to completely characterize the quantum mechanical electron motion and determine its degree of coherence in the specimen of the ensemble. Although the present study uses a simple, prototypical open system, attosecond transient absorption spectroscopy should be applicable to molecules and solid-state materials to reveal the elementary electron motions that control physical, chemical and biological properties and processes.

2010-08-05

368

The problem of fluctuating valence in f-electron metals  

International Nuclear Information System (INIS)

[en] Besides some general semi-philosophical ideas about the phenomenon of mixed-valence, the question of the chemistry of this phenomenon and heavy-electron metals are discussed, especially why it is that cerium and uranium can be so similar. 11 refs.; 2 figs

1987-01-01

369

Evidence of valence fluctuations in ytterbium based amorphous alloys  

International Nuclear Information System (INIS)

In this paper, we present magnetic and LIII edge measurements on two amorphous ytterbium based systems: Yb-Pd and Yb-Si. In the crystalline compounds of both systems, ytterbium ions exhibit valence fluctuations and we show that this anomalous electronic configuration is basically preserved in the corresponding amorphous alloys.

1988-01-01

370

Evidence of valence fluctuations in ytterbium based amorphous alloys  

Energy Technology Data Exchange (ETDEWEB)

In this paper, we present magnetic and L{sub III} edge measurements on two amorphous ytterbium based systems: Yb-Pd and Yb-Si. In the crystalline compounds of both systems, ytterbium ions exhibit valence fluctuations and we show that this anomalous electronic configuration is basically preserved in the corresponding amorphous alloys.

Malterre, D.; Durand, J.; Siari, A.; Menny, A.; Krill, G.; Marchal, G. (Nancy-1 Univ., 54 (FR). Lab. de Physique du Solide)

1988-12-01

371

Valence mixing in YbCuAl: a case study  

International Nuclear Information System (INIS)

Results are presented of a study of the valence state of Yb in the intermetallic compound YbCuAl. Both macroscopic physical properties (magnetic susceptibility, heat capacity, thermal expansion, electric resistivity) and microscopic physical properties (neutron inelastic scattering, nuclear magnetic resonance) are determined. The results are compared with a local Fermi liquid theory. (G.T.H.)

1980-01-01

372

Valence electron momentum spectroscopy of inert gas atoms  

International Nuclear Information System (INIS)

The distorted-wave impulse approximation is shown to describe new electron momentum spectroscopy experiments for helium, argon and xenon. Both angular correlations and relative strengths for s-and p-transitions confirm the assignment of spectroscopic factors using the sum rule for states belonging to the inner-valence s-manifolds

1984-01-01

373

On the valence quark approximation of the rescaling model  

International Nuclear Information System (INIS)

[en] We perform a QCD analysis of the valence quark approximation of the rescaling model via the moment relationship. The existence of a unique renormalization scale seems to be substantiated, but the ratio of the confinement radius and the nucleon overlap probability can vary greatly. (orig.)

1985-12-05

374

Valence atom with bohmian quantum potential: the golden ratio approach  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Abstract Background The alternative quantum mechanical description of total energy given by Bohmian theory was merged with the concept of the golden ratio and its appearance as the Heisenberg imbalance to provide a new density-based description of the valence atomic state and reacti...

Putz Mihai V

375

Intrinsic and extrinsic inhomogeneities in mixed-valence manganites  

CERN Multimedia

It is suggested that extrinsic inhomogeneities in mixed-valence manganites deserve more attention and they should be taking into account on equal footing with hypothetical phase separation while examinating experimental data and developing the theoretical models of influence of stoichiometric and other types of inhomogeneities on properties of these and other transition-metal oxides.

Belevtsev, B I

2004-01-01

376

Glueball Mass Predictions of the Valence Approximation to Lattice QCD  

CERN Multimedia

We evaluate the infinite volume, continuum limit of glueball masses in the valence (quenched) approximation to lattice QCD. For the lightest scalar and tensor states we obtain masses of $1648 \\pm 58$ MeV and $2267 \\pm 104$ MeV, respectively.

Vaccarino, A

1999-01-01

377

On the valence fluctuation phenomena in SmS compounds  

International Nuclear Information System (INIS)

The valence fluctuation phenomena, together with the desciption of the metal insulator transition of SmS are formulated within the alloys analogy picture for correlated d and f electrons. Emphasis is made on the relevance of electron-phonon coupling in these phenomena.

1978-09-07

378

Mixed valence of Sm on metal single-crystal surfaces  

Energy Technology Data Exchange (ETDEWEB)

Results of a photoemission study of Sm on a Cu(100) single crystal surface are reported. From the binding energy of the Sm 4f levels it is concluded that the mixed valence of Sm on Cu(100) is of a heterogeneous nature. It is suggested that this conclusion also applies to Al(111) and Al(100).

Andersen, J.N.; Chorkendorff, I.; Onsgaard, J.; Ghijsen, J.; Johnson, R.L.; Grey, F.

1988-03-15

379

The scalar and tensor glueballs in the valence approximation  

CERN Document Server

We evaluate the infinite volume, continuum limit of $0^{++}$ and $2^{++}$ glueball masses in the valence approximation. We find $m_{0^{++}} = 1740 \\pm 71 $~MeV and $m_{2^{++}} = 2359 \\pm 128 $~MeV, consistent with the interpretation of $f_0 ( 1710 )$ as the lightest scalar glueball.

Chen, H; Vaccarino, A; Weingarten, D

1994-01-01

380

Glueball Mass Predictions of the Valence Approximation to Lattice QCD  

CERN Document Server

We evaluate the infinite volume, continuum limit of glueball masses in the valence (quenched) approximation to lattice QCD. For the lightest states with $J^{PC}$ of $0^{++}$ and $2^{++}$, we obtain $m_0 = 1340 \\pm 160$ MeV and $m_2 = 1900 \\pm 320$ MeV.

Chen, H; Vaccarino, A; Weingarten, D

1993-01-01

 
 
 
 
381

Low energy inner valence ionization of the rare gases  

International Nuclear Information System (INIS)

Recent measurements are presented of the triple differential cross section for electron impact ionization of the inner valence shells of argon and krypton at low to intermediate energies, and both coplanar symmetric and asymmetric geometries. Comparison is made with some of the latest available theoretical calculations performed in the distorted wave Born approximation formalism.

2002-01-11

382

On the valence fluctuation phenomena in SmS compounds  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The valence fluctuation phenomena, together with the description of the metal insulator transition of SmS are formulated within the alloy analogy picture for correlated d and f electrons. Emphasis is made on the relevance of electron-phonon coupling in these phenomena.

Brouers, F.; Bennemann, K.; De Menezes, O.; Troper, A.; Gomes, A.

383

Spectroscopic studies of oxo-centered, carboxylate-bridged, trinuclear mixed-valence iron (???, ???, ??) complexes with aromatic hydroxycarboxylic acids.  

UK PubMed Central (United Kingdom)

New type of oxo-centered, carboxylate-bridged, trinuclear, mixed-valence iron complexes of the general formula [Fe3O(OOCR)3(OOCR*)3L3] (where R=C13H27 or C15H31 and R*=C6H4(OH), (R'); C6H5CH(OH), (R") or (C6H5)2C(OH), (R''') and L=Methanol) were synthesized by the reaction of [Fe3O(OOCCH3)6(H2O)3] with straight chain carboxylic acids and aromatic hydroxycarboxylic acids. These were characterized by elemental analyses, spectral (electronic, infrared, Mössbauer, FAB mass and powder XRD) studies, conductance and magnetic susceptibility measurements. Infrared spectra suggested bidentate and bridging mode of coordination of both the carboxylate and hydroxycarboxylate anions along with Fe3O vibrations in the complexes. Mössbauer parameters indicated the presence of high-spin Fe(??) (S=2) and high-spin Fe(???) (S=5/2) centers in the complexes, confirming the valence-localized type of species. An intervalence-transfer band observed at 13,690-13,850 cm(-1) range in the room-temperature electronic spectra of the complexes also suggested the complexes containing iron in mixed-valence state. Trinuclear nature of the complexes was confirmed by their FAB mass spectra. Magnetic moment values displayed octahedral geometry around each iron in the complexes and a net anti-ferromagnetic exchange coupling via ?-oxo atom related to mixed-valence pairs. A plausible structure for these complexes has been established on the basis of spectra and magnetic moment data.

Singh AK; Singh AK

2013-08-01

384

Pairing mechanisms in superconductors with valence-skipping dopants  

Science.gov (United States)

Recent studies of the degenerate semiconductor, lead telluride, doped with the valence skipping element, thallium, have lead to propositions of negative U superconductivity. In this model, charge 2e fluctuations between the stable +1 and +3 thallium valence states stimulate formation of cooper pairs. Significantly, correlated with superconductivity in this material is a minimum in resistance, similar to that found in metals doped with trace magnetic impurities. This behavior has been attributed to a charge-Kondo effect, where scattering from impurities with valence fluctuations between +1 and +3 charge states mimics the effect of scattering from magnetic impurities, causing a minimum in resistance and an enhancement of the density of states at the Fermi level. In this dissertation, I will describe experiments performed on three different sets of materials designed to illuminate aspects of superconductivity in materials that have been doped with valence-skipping elements. In the first project, I examine the effect of additional indium donors on samples of Pb 1-yTlyTe that would otherwise exhibit superconductivity and charge-Kondo behavior. In this work, I find that, as additional electrons are injected into Pb.99Tl.01Te by increasing the indium counterdopant concentration, the Kondo-like behavior and superconductivity are both suppressed near the same indium concentration. This is interpreted as a suppression of the degeneracy between +1 and +3 valence states by introducing additional electrons, which favor the +1 valence state, resulting in a suppression of charge-Kondo scattering and negative U pairing effects. The second project extends this study to the related material indium-doped tin telluride, where the valence-skipping nature of indium has lead others to propose a similar negative U superconducting state. In contrast to thallium-doped lead telluride, where the host material, PbTe, is nonsuperconducting, SnTe superconducts when doped with high concentrations of vacancies on the tin site. This allows for comparisons between the superconducting state in SnTe without additional dopants, and SnTe that has been doped with the valence-skipping element, indium. By comparing the density of states at the Fermi level and the superconducting critical temperature in Sn.995-xInxTe, grown for this study, and Sn1-deltaTe, collected from the literature, I show that enhanced superconductivity in indium-doped material cannot be explained by changes in the density of states at the Fermi level. Instead, a stronger superconducting pairing strength is inferred, which could arise from negative U pairing effects at the mixed-valence impurities. Additionally, comparing the temperature of a structural phase transition to that of the superconducting transition temperature as a function of indium content rules out softening of phonon modes related to this transition as a source of the Tc enhancement. The third study utilizes the high solubility limit of indium in tin telluride of up to 20%, compared to the limit of 1.4% thallium dopants in lead telluride, to examine the question of how interactions between valence-fluctuating impurities might affect superconductivity and the resistance minimum. In this case, resistivity measurements reveal an anomalously large resistance minimum in Sn988-x InxTe doped with 2.7% 6.1%, where samples are found to superconduct. While a detailed theoretical model with which to compare these data is lacking, some possible explanations relying on interactions between indium sites are proposed.

Erickson, Ann Shaklee

385

All-out band structure and band offset ab initio predictions for AlN/GaN and AlP/GaP interfaces  

Science.gov (United States)

We studied the electronic properties of the AlP/GaP and AlN/GaN interfaces and their cubic constituents. The work is developed using approximate quasiparticle approach LDA-1/2 method. First, we provide a detailed calculation of bulk AlN, AlP, GaN, and GaP. In addition to accurate results for fundamental band gap, we also obtained accurate electronic transition levels along valence and conduction bands profiles, compared to experiments and theoretical results using GW and hybrid functionals methods. For the conduction (valence) band offset we obtained 0.27 eV (0.43 eV) for AlP/GaP and 1.47 eV (0.36 eV) for AlN/GaN interfaces, in good agreement with experimental results.

Filho, O. P. Silva; Ribeiro, M.; Pelá, R. R.; Teles, L. K.; Ferreira, L. G.; Marques, M.

2013-07-01

386

Study on the interaction between different CWS dispersants and coals. XI Interface properties of dispersant-modified coal particles and its effect on the properties of CWS  

Energy Technology Data Exchange (ETDEWEB)

The Zeta potential of dispersion system forming by 10 dispersants with 14 coals was determined. The effect of dispersant on the interface electro-chemical property of coal particles was studied. The higher the coal rank and the more the dissolved high-valence cations from coal, the lower the Zeta potential of dispersant-modified coal particle. The more amount of hydrophilic groups and the charge of the anionic dispersant, the higher the Zeta potential of dispersant-modified coal particle. The non-ionic dispersant leads to a decrease in the Zeta potential of anionic dispersant-modified coal reflects its hydrophilicity. The maximum moisture content for most of dispersant-modified coal particles increases with increasing Zeta potentials. An experimental slurryability model including natural and dispersant-modified hydrophilicity of coal particles, the Zeta potential of dispersant-modified coal particle and the adsorption amount of dispersant on unit surface area of coal has been set up. The calculated value from this formula is approximate to the experimental results. 7 refs., 4 figs., 1 tab.

Zou, L.; Zhu, S.; Wang, X.; Guo, X.; Cui, G. [China University of Mining and Technology, Beijing (China)

2006-04-15

387

Electronic structure of NaxCu1-xIn5S8 compounds: X-ray photoemission spectroscopy study and band structure calculations  

International Nuclear Information System (INIS)

[en] The aim of the present work is to complete a preliminary study concerning the electronic band structure investigations of NaxCu1-xIn5S8 compounds with 0?x?1, which are expected to be formed at the Cu(In,Ga)Se2/In2S3 interface. The band structure calculations demonstrate that for the compounds containing both Na and Cu, as the Cu content increases the band gap tends to decrease, and x-ray photoemission spectroscopy measurements show that this variation is mainly due to valence-band-maximum shift along the solid solution. The band gap strongly depends on the nature of the monovalent cation, and the band structure calculations demonstrate that the d electrons of copper are responsible for the shift of the valence band. In addition, it is worth noting that the Cu-containing compounds have indirect gaps

2008-12-15

388

Reinterpretation of the bond-valence model with bond-order formalism: An improved bond-valence-based interatomic potential for PbTiO3  

Science.gov (United States)

We present a modified bond-valence model of PbTiO3 based on the principles of bond-valence and bond-valence vector conservation. The relationship between the bond-valence model and the bond-order potential is derived analytically in the framework of a tight-binding model. An energy term, bond-valence vector energy, is introduced into the atomistic model and the potential parameters are reoptimized. This model potential can be applied both to canonical-ensemble (NVT) and isobaric-isothermal ensemble (NPT) molecular dynamics (MD) simulations. This model reproduces the experimental phase transition in NVT MD simulations and also exhibits the experimental sequence of temperature-driven and pressure-driven phase transitions in NPT simulations. We expect that this improved bond-valence model can be applied to a broad range of inorganic materials.

Liu, Shi; Grinberg, Ilya; Takenaka, Hiroyuki; Rappe, Andrew M.

2013-09-01

389

Orbital momentum profiles and binding energy spectra for the complete valence shell of molecular fluorine  

Energy Technology Data Exchange (ETDEWEB)

The first electronic structural study of the complete valence shell binding energy spectrum of molecular fluorine, encompassing both the outer and inner valence regions, is reported. These binding energy spectra as well as the individual orbital momentum profiles have been measured using an energy dispersive multichannel electron momentum spectrometer at a total energy of 1500 eV, with an energy resolution of 1.5 eV and a momentum resolution of 0.1 a.u. The measured binding energy spectra in the energy range of 14-60 eV are compared with the results of ADC(4) many-body Green`s function and also direct-Configuration Interaction (CI) and MRSD-CI calculations. The experimental orbital electron momentum profiles are compared with SCF theoretical profiles calculated using the target Hartree-Fock approximation with a range of basis sets and with Density Functional Theory predictions in the target Kohn-Sham approximation with non-local potentials. The truncated (aug-cc-pv5z) Dunning basis sets were used for the Density Functional Theory calculations which also include some treatment of correlation via the exchange and correlation potentials. Comparisons are also made with the full ion-neutral overlap amplitude calculated with MRSD-CI wave functions. Large, saturated basis sets (199-GTO) were employed for both the high level SCF near Hartree-Fock limit and MRSD-CI calculations to investigate the effects of electron correlation and relaxation. 66 refs., 9 tabs., 9 figs.

Zheng, Y.; Brion, C.E. [British Columbia Univ., Vancouver, BC (Canada). Dept. of Chemistry; Brunger, M.J.; Zhao, K.; Grisogono, A.M.; Braidwood, S.; Weigold, E. [Flinders Univ. of South Australia, Adelaide, SA (Australia). Electronic Structure of Materials Centre; Chakravorty, S.J.; Davidson, E.R. [Indiana Univ., Bloomington, IN (United States). Dept. of Chemistry; Sgamellotti, A. [Univ di Perugia (Italy). Dipartimento di Chimica; von Niessen, W. [Technische Univ. Braunschweig (Germany). Inst fuer Physikalische

1996-01-01

390

Robust Dirac-cone band structure in the molecular kagome compound (EDT-TTF-CONH2)6[Re6Se8(CN)6].  

UK PubMed Central (United Kingdom)

(EDT-TTF-CONH2)6[Re6Se8(CN)6] is a molecular solid with R3 space group symmetry and has the remarkable feature of exhibiting hybrid donor layers with a kagome topology which sustain metallic conductivity. We report a detailed study of the structural evolution of the system as a function of temperature and pressure. This rhombohedral phase is maintained on cooling down to 220 K or up to 0.7 GPa pressure, beyond which a symmetry-breaking transition to a triclinic P1 phase drives a metal to insulator transition. Band structures calculated from the structural data lead to a clear description of the effects of temperature and pressure on the structural and electronic properties of this system. Linear energy dispersion is calculated at the zero-gap Fermi level where valence and conduction bands touch for the rhombohedral phase. (EDT-TTF-CONH2)6[Re6Se8(CN)6] thus exhibits a regular (right circular) Dirac-cone like that of graphene at the Fermi level, which has not been reported previously in a molecular solid. The Dirac-cone is robust over the stability region of the rhombohedral phase, and may result in exotic electronic transport and optical properties.

Carlsson S; Zorina L; Allan DR; Attfield JP; Canadell E; Batail P

2013-03-01

391

Multicenter bonds, bond valence and bond charge apportion  

Energy Technology Data Exchange (ETDEWEB)

In the same way that the valence of an atom issues from the definition of bond index, we shoe here that the three-center bond index lends itself to the definition of a bond valence. Within the charge of a bond, we show that its self-charge (i.e., the amount of electron kept by the atoms involved in the bond) is parted in a such a way that the more electronegative atom tends to allot more electronic charge than the other atom. We give examples of these quantities and discuss the results for different kinds of chemical systems. We also show some results for four-center indices and report six-center indices for hexagonal rings. (author). 54 refs., 4 figs., 8 tabs.

Giambiagi, Myriam Segre de; Giambiagi, Mario; Souza Fortes, Marcelo de

1996-04-01

392

Configuration of the valence neutrons of 17B  

International Nuclear Information System (INIS)

[en] The reaction cross section of 17B on 12C target at (43.7±2.4) MeV/u has been measured at the Radioactive Ion Beam Line in Lanzhou (RIBLL). The root-mean-square matter radius (Rrms) was deduced to be (2.92±0.10) fm, while the Rrms of the core and the valence neutron distribution are 2.28 fm and 5.98 fm respectively. Assuming a 'core plus 2n' structure in 17B, the mixed configuration of (2s1/2) and (1d5/2) of the valence neutrons is studied and the s-wave spectroscopic factor is found to be (80±21)%. (authors)

2008-01-01

393

Exploring covalently bonded diamondoid particles with valence photoelectron spectroscopy.  

UK PubMed Central (United Kingdom)

We investigated the valence electronic structure of diamondoid particles in the gas phase, utilizing valence photoelectron spectroscopy. The samples were singly or doubly covalently bonded dimers or trimers of the lower diamondoids. Both the bond type and the combination of bonding partners are shown to affect the overall electronic structure. For singly bonded particles, we observe a small impact of the bond on the electronic structure, whereas for doubly bonded particles, the connecting bond determines the electronic structure of the highest occupied orbitals. In the singly bonded particles a superposition of the bonding partner orbitals determines the overall electronic structure. The experimental findings are supported by density functional theory computations at the M06-2X/cc-pVDZ level of theory.

Zimmermann T; Richter R; Knecht A; Fokin AA; Koso TV; Chernish LV; Gunchenko PA; Schreiner PR; Möller T; Rander T

2013-08-01

394

Exploring covalently bonded diamondoid particles with valence photoelectron spectroscopy  

Science.gov (United States)

We investigated the valence electronic structure of diamondoid particles in the gas phase, utilizing valence photoelectron spectroscopy. The samples were singly or doubly covalently bonded dimers or trimers of the lower diamondoids. Both the bond type and the combination of bonding partners are shown to affect the overall electronic structure. For singly bonded particles, we observe a small impact of the bond on the electronic structure, whereas for doubly bonded particles, the connecting bond determines the electronic structure of the highest occupied orbitals. In the singly bonded particles a superposition of the bonding partner orbitals determines the overall electronic structure. The experimental findings are supported by density functional theory computations at the M06-2X/cc-pVDZ level of theory.

Zimmermann, Tobias; Richter, Robert; Knecht, Andre; Fokin, Andrey A.; Koso, Tetyana V.; Chernish, Lesya V.; Gunchenko, Pavel A.; Schreiner, Peter R.; Möller, Thomas; Rander, Torbjörn

2013-08-01

395

Samarium valence in Ybsub(1-x)Smsub(x)S  

International Nuclear Information System (INIS)

In order to study the Ybsub(1-x)Smsub(x)S solid solution synthesis temperature effect on the samarium valence state samples of Ybsub(0.8)Smsub(0.2)S composition, produced by both low- and high-temperature methods were investigated. Samarium and ytterbium valences were determined by X-ray absorption ?-spectroscopy at indoor temperature. The results obtained show, that the nouniphase character occuring in Ybsub(1-x)Smsub(x)S under cation defect presence, is an additional indication of trivalent samarium absence in solid solutions. Under the high-temperature synthesis sample oxidation and Smsup(+3) content increase take place, which is linked with Smsup(+3) presence in mixed oxysulfide.

1985-01-01

396

Zener Double Exchange from Local Valence Fluctuations in Magnetite  

Energy Technology Data Exchange (ETDEWEB)

Magnetite (Fe3O4) is a mixed valent system where electronic conductivity occurs on the B site (octahedral) iron sublattice of the spinel structure. Below Tv = 123 K, a metal-insulator transition occurs which is argued to arise from the charge ordering of 2+ and 3+ iron valences on the B sites (Verwey transition). Inelastic neutron scattering measurements show that optical spin waves propagating on the B site sublattice (~80 meV) are shifted upwards in energy above TV due to the occurrence of B-B ferromagnetic double exchange in the mixed valent phase. The double exchange interaction affects only spin waves of 5 symmetry, not all modes, indicating that valence fluctuations are slow and the double exchange is constrained by short-range electron correlations above Tv.

McQueeney, Robert John [Iowa State University; Yethiraj, M. [Bragg Institute, ANSTO; Chang, S. [National Institute of Standards and Technology (NIST); Montfrooij, W. [University of Missouri, Columbia; Perring, T. G. [ISIS Facility, Rutherford Appleton Laboratory; Honig, J. M. [University of Purdue; Metcalf, P. [Purdue University

2007-01-01

397

Absence of valence-bond supersolidity on the checkerboard lattice  

Science.gov (United States)

The stability of the supersolid state of bosons reported recently on the checkerboard lattice in the vicinity of a valence-bond crystal phase is assessed. In contrast to previously identified supersolid phases of lattice bosons, this state would—if stable—provide superfluidity atop a solid with inherent quantum dynamics, restricted to the particular filling fraction of one quarter. Using large-scale quantum Monte Carlo simulations based on the stochastic series expansion method constrained to the canonical ensemble, the supersolid state is, however, found to be unstable in the thermodynamic limit. Converging crossing points in both the winding number fluctuations and the Binder ratio related to the order parameter of the valence-bond crystal instead exhibit a direct quantum melting transition of the crystal into the superfluid regime.

Wessel, S.

2012-10-01

398

Valence bond solid phases in a cubic antiferromagnet  

CERN Document Server

We report on a valence bond projector Monte Carlo simulation of the cubic lattice quantum Heisenberg model with additional higher-order exchange interactions in each unit cell. The model supports two different valence bond solid ground states. In one of these states, the dimer pattern is a three-dimensional analogue of the columnar pattern familiar from two dimensions. In the other, the dimers are regularly arranged along the four main diagonals in 1/8 of the unit cells. The phases are separated from one other and from a Neel phase by strongly first order boundaries. Our results strengthen the case for exotic transitions in two dimensions, where no discontinuities have been detected at the Heisenberg Neel-VBS transition driven by four-spin plaquet interactions.

Beach, K S D; Sandvik, Anders W.

2006-01-01

399

Theory of valence transitions in Ytterbium and Europium intermetallics  

CERN Multimedia

The exact solution of the multi-component Falicov-Kimball model in infinite-dimensions is presented and used to discuss a new fixed point of valence fluctuating intermetallics with Yb and Eu ions. In these compounds, temperature, external magnetic field, pressure, or chemical pressure induce a transition between a metallic state with the f-ions in a mixed-valent (non-magnetic) configuration and a semi-metallic state with the f-ions in an integral-valence (paramagnetic) configuration. The zero-field transition occurs at the temperature Tv, while the zero-temperature transition sets in at the critical field Hc. We present the thermodynamic and dynamic properties of the model for an arbitrary concentration of d- and f-electrons. For large U, we find a MI transition, triggered by the temperature or field-induced change in the f-occupancy.

Zlatic, V

2001-01-01

400

Theoretical phonon dispersions in monolayers and multilayers of hexagonal boron-nitride  

Energy Technology Data Exchange (ETDEWEB)

Starting from an empirical force constant model of valence interactions and calculating by Ewald's method the electrostatic force constants, we derive the dynamical matrix for a monolayer and for multilayer systems of hexagonal boron nitride (h-BN). Solution of the secular problem leads to the corresponding phonon dispersion relations. The interplay between valence forces and Coulomb forces is discussed. A comparison with previous results on graphene and graphene multilayers is made. Our spectra on the h-BN monolayer are rather similar to previous ab initio theory results. Comparison is also made with Raman and infrared experimental results. (Abstract Copyright [2009], Wiley Periodicals, Inc.)

Michel, K.H.; Verberck, B. [Departement Fysica, Universiteit Antwerpen (Belgium)

2009-12-15

 
 
 
 
401

Dispersion coalescence: Kinetic stability of creamed dispersions  

Energy Technology Data Exchange (ETDEWEB)

A model is developed to predict the coalescence behavior in liquid-liquid dispersions. Coalescence times are based on the lifetimes of the single films that are formed between adjoining drops in a creamed or sedimented dispersion. The model is developed for smaller drop sized dispersions (< 100[mu]m) in which the drops are not substantially deformed due to gravitational forces. The model predicts that coalescence occurs between the emulsion drops without the gross separation of the dispersed phase (that is, the dispersion does not separate into distinct oil and water phases). As a result of interdrop coalescence, the mean drop size of the dispersed phase increases along with an increase in the polydispersity of the drop size. The model's predictions are used to develop a quantitative relationship between the lifetime of the single film and the rate of increase of the mean drop size of the dispersion. The model also accounts for the effect of surfactant on dispersion stability via the models of single film drainage in the presence of surfactant.

Lobo, L.; Ivanov, I.; Wasan, D. (Illinois Inst. of Tech., Chicago (United States))

1993-02-01

402

Few-valence-particle excitations around doubly magic 132Sn  

International Nuclear Information System (INIS)

Prompt ?-ray cascades in neutron-rich nuclei around doubly-magic 132Sn have been studied using a 248Cm fission source. Yrast states located in the N=82 isotones 134Te and 135I are interpreted as valence proton and neutron particle-hole core excitations with the help of shell model calculations employing empirical nucleon-nucleon interactions from both 132Sn and 208Pb regions. (orig.). With 1 fig.

1996-07-06

403

[Power, status and valency in healthy and ill partners  

UK PubMed Central (United Kingdom)

Using the degree of identification and projection (self concept/concept of self as perceived by others--Giessen-test) it was possible to develop a new approach to power, status and valency in couple relationships by means of deriving theoretical probabilities from those three core variables. The anticipated scores were validated using a number of reference scores of typical clinical samples and putting them in relationship to the standardized marital couples.

Beckmann D

1994-08-01

404

Resonating Valence Bond Wave Functions for Strongly Frustrated Spin Systems  

International Nuclear Information System (INIS)

[en] The resonating-valence-bond (RVB) theory for two-dimensional quantum antiferromagnets is shown to be the correct paradigm for large enough ''quantum frustration.'' This scenario, proposed a long time ago but never confirmed by microscopic calculations, is strongly supported by a new type of variational wave function, which is extremely close to the exact ground state of the J1-J2 Heisenberg model for 0.4?2/J1?

2001-08-27

405

Electron-phonon interaction in mixed valence systems  

International Nuclear Information System (INIS)

One considers an Hamiltonian describing mixed valence compounds and including d and f electron-phonon coupling. One shows that the renormalization of the electronic energy parameters induced by the electron-phonon interaction depends strongly on the nature (static or adiabatic) of the approximation used. One discusses the importance of the d-electron-phonon coupling on the narrowing of the f-level and the softening of the phonon modes. (author).

1980-01-01

406

Meson Decay Constants from the Valence Approximation to Lattice QCD  

CERN Document Server

We evaluate $f_{\\pi}/ m_{\\rho}$, $f_K/ m_{\\rho}$, $1/f_{\\rho}$, and $ m_{\\phi}/(f_{\\phi} m_{\\rho})$, extrapolated to physical quark mass, zero lattice spacing and infinite volume, for lattice QCD with Wilson quarks in the valence (quenched) approximation. The predicted ratios differ from experiment by amounts ranging from 12\\% to 17\\% equivalent to between 0.9 and 2.8 times the corresponding statistical uncertainties.

Butler, F; Sexton, J C; Vaccarino, A; Weingarten, D

1994-01-01

407

Kondo universality, energy scales, and intermediate valence in plutonium  

Science.gov (United States)

On the basis of the concepts of an intermediate-valence (IV) regime, an analysis is carried out of macroscopic properties of the ? and ? phases of plutonium, as well as of several model systems based on rare earth elements. Within a single-site approximation (SSA), the characteristic Kondo interaction energy, the f-electron shell occupation number, the effective degeneracy of the ground-state f multiplet, and the crystal field splitting energy are estimated. The ground state in plutonium is considered as a quantum-mechanical superposition of states with different valences. The temperature dependence of the static magnetic susceptibility of ? plutonium is calculated. It is shown that ? plutonium satisfies the Wilson and Kadowaki-Woods universal relations, whereby it can be classified as a Kondo system. At the same time, the problem of the position of plutonium in the general classification of solids, as well as the problem of the temperature dependence of magnetic susceptibility of ? plutonium, remains open. The concept of multiple intermediate valence (MIV) is put forward as a possible means for solving the above problems. The MIV regime is characterized by fluctuations from the basic configuration 3+ to the states 4+ and 2+, which make a fundamental difference between plutonium and 4 f electron systems based, say, on samarium.

Clementyev, E. S.; Mirmelstein, A. V.

2009-07-01

408

Kondo universality, energy scales, and intermediate valence in plutonium  

International Nuclear Information System (INIS)

[en] On the basis of the concepts of an intermediate-valence (IV) regime, an analysis is carried out of macroscopic properties of the ? and ? phases of plutonium, as well as of several model systems based on rare earth elements. Within a single-site approximation (SSA), the characteristic Kondo interaction energy, the f-electron shell occupation number, the effective degeneracy of the ground-state f multiplet, and the crystal field splitting energy are estimated. The ground state in plutonium is considered as a quantum-mechanical superposition of states with different valences. The temperature dependence of the static magnetic susceptibility of ? plutonium is calculated. It is shown that ? plutonium satisfies the Wilson and Kadowaki-Woods universal relations, whereby it can be classified as a Kondo system. At the same time, the problem of the position of plutonium in the general classification of solids, as well as the problem of the temperature dependence of magnetic susceptibility of ? plutonium, remains open. The concept of multiple intermediate valence (MIV) is put forward as a possible means for solving the above problems. The MIV regime is characterized by fluctuations from the basic configuration 3+ to the states 4+ and 2+, which make a fundamental difference between plutonium and 4f electron systems based, say, on samarium.

2009-01-01

409

Core-valence double photoionization of the CS(2) molecule.  

Science.gov (United States)

Double photoionization spectra of the CS(2) molecule have been recorded using the TOF-PEPECO technique in combination with synchrotron radiation at the photon energies h?=220, 230, 240, 243, and 362.7 eV. The spectra were recorded in the S 2p and C 1s inner-shell ionization regions and reflect dicationic states formed out of one inner-shell vacancy and one vacancy in the valence region. MCSCF calculations were performed to model the energies of the dicationic states. The spectra associated with a S 2p vacancy are well structured and have been interpreted in some detail by comparison to conventional S 2p and valence photoelectron spectra. The lowest inner-shell-valence dicationic state is observed at the vertical double ionization energy 188.45 eV and is associated with a (2p(3/2))(-1)(2?(g))(-1) double vacancy. The spectrum connected to the C 1s vacancy shows a distinct line at 310.8 eV, accompanied by additional broad features at higher double ionization energies. This line is associated with a (C?1s)(-1)(2?(g))(-1) double vacancy. PMID:20831316

Andersson, E; Niskanen, J; Hedin, L; Eland, J H D; Linusson, P; Karlsson, L; Rubensson, J-E; Carravetta, V; Agren, H; Feifel, R

2010-09-01

410

Band offset of SnS solar cell structure measured by X-ray photoelectron spectroscopy  

International Nuclear Information System (INIS)

The energy band offset at the heterointerface is one of the most important properties of semiconductor heterostructures, particularly in solar photovoltaic devices. Band discontinuities of CdS/SnS and SnS/SnO2 heterointerfaces were measured by X-ray photoelectron spectroscopy and capacitance-voltage measurements. The valence band offsets were determined to be approximately 1.5 eV for CdS/SnS and 3.5 eV for SnS/SnO2 interfaces whereas the conduction band discontinuities for these junctions were respectively found to be 0.4 eV and 1.0 eV. Using these values and the energy band gaps of the corresponding layers, the energy band diagram was developed and it was considered to be a TYPE-II heterostructure. The Fermi level was found to be much closer to the valence band maximum for SnS, whereas it appeared in the upper half of the band gap for both CdS and SnO2.

2011-08-31

411

Parametric gain in dispersion engineered photonic crystal waveguides.  

UK PubMed Central (United Kingdom)

We present a numerical simulation of parametric gain properties in GaInP PhC dispersion engineered waveguides in which the group velocity dispersion crosses zero twice and where the pump and the signal are 100 ps pulses. The simulations use the M-SSFT algorithm which incorporates dispersive nonlinear coefficients and losses. We concentrate on narrow band parametric gain which occurs for pump wavelengths in the normal group velocity dispersion regime. The effects of structural details, of pump wavelength and of losses are carefully analyzed.

Willinger A; Roy S; Santagiustina M; Combrié S; De Rossi A; Cestier I; Eisenstein G

2013-02-01

412

Radiological Dispersion Device (RDD)  

Science.gov (United States)

... months during cleanup efforts. Before Before an Radiological Dispersion Device (RDD) Event There is no way of ... off by fallout particles. During During an Radiological Dispersion Device (RDD) Event While the explosive blast will ...

413

Dispersive waves and caustics  

Directory of Open Access Journals (Sweden)

Full Text Available The Lagrange manifold (WKB) formalism enables the determination of the asymptotic series solution of linear, non-dispersive wave equations at turning points. The formalism is adapted to include those equations which model dispersive waves.

Arthur D. Gorman

1985-01-01

414

Polarization dependence of Raman 2D band in bilayer graphene  

Science.gov (United States)

The Raman intensity of the double-resonance 2D band in sigle-layer graphene has a strong polarization dependence(Yoon et al. Nano Lett.). The intensity is maximum when the excitation and detection polarization are parallel and minimum when they are orthogonal, whereas that of G band is isotropic. This strong polariztion dependence is the consequence of inhomogeneous optical absorption and emission mediated by electron-phonon interactions. Here, the polarization dependence of the Raman 2D band in bilayer graphene. The 2D band of bilayer graphene can be decomposed to 4 Lorentzian peaks corresponding to different scattering process involving 2 conduction and 2 valence bands. The 2D band in bialyer graphene shows a similar polarization dependence as that of single layer. Futhermore, the excitation energy dependence was investigated by using 4 different excitation laser wavelenghths. The polarization ratio of each of the 4 Lorentizan peaks seems to reflect the features of the electronic band structure of bilayer graphene in the energy range of the excitation laser.

Lee, Jae-Ung; Mbaye Seck, Ngor; Yoon, Duhee; Cheong, Hyeonsik

2013-03-01

415

Seed Dispersal 101  

Science.gov (United States)

This two-minute radio program introduces listeners to the variety of agents that disperse seeds. The program's guest, a plant biologist, cites examples of nonliving and living dispersal agents that include the wind, water, and such animals as birds and bats. He also explains that a plant's fruits or seeds often offer clues about how they are dispersed. The program, which is available here in audio and text, is the first in a series about seed dispersal. Copyright 2005 Eisenhower National Clearinghouse

Planet, Pulse O.

2007-07-26

416

Dispersion, Controlled Dispersion, and Three Applications  

CERN Multimedia

Over the past 15 years, several groups have engineered media that are both strongly dispersive and roughly transparent for some finite bandwidth. Relationships and intuitive models that are satisfactory when it is reasonable to neglect dispersion may then fail. We analyze three such cases of failure. First, a simple generalization of the Abraham and Minkowski momenta to dispersive media entails multiplying each per-photon momentum by $n/n_g$, where $n$ is the refractive index and $n_g$ is the group index. The resulting forms are experimentally relevant for the case of the Abraham momentum, but not for the Minkowski momentum. We show how dispersion modulates the displacement of a sphere embedded in a dispersive medium by a pulse. Second, pulse transformation in a nonstationary medium is modulated by the presence of dispersion. Using an explicit description of the kinetics of dispersive nonstationary inhomogeneous media, we show how the group velocity can modulate pulse response to a change in the refractive in...

Bradshaw, Douglas H

2010-01-01

417

Theoretical Magnon Dispersion Curves for Gd  

DEFF Research Database (Denmark)

The magnon dispersion curve of Gd metal has been determined from first principles by use of augmented-plane-wave energy bands and wave functions. The exchange matrix elements I(k?, k??) between the 4f electrons and the conduction electrons from the first six energy bands were calculated under the assumption of an unscreened Coulomb interaction. The results are in good overall agreement with experiment provided the I(k?, k??) are diminished by a constant scale factor of about 2 which may be caused by screening.

Lindgård, Per-Anker; Harmon, B. N.

1975-01-01

418

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

International Nuclear Information System (INIS)

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

2004-06-01

419

The use of bulk states to accelerate the band edge statecalculation of a semiconductor quantum dot  

Energy Technology Data Exchange (ETDEWEB)

We present a new technique to accelerate the convergence of the folded spectrum method in empirical pseudopotential band edge state calculations for colloidal quantum dots. We use bulk band states of the materials constituent of the quantum dot to construct initial vectors and a preconditioner. We apply these to accelerate the convergence of the folded spectrum method for the interior states at the top of the valence and the bottom of the conduction band. For large CdSe quantum dots, the number of iteration steps until convergence decreases by about a factor of 4 compared to previous calculations.

Vomel, Christof; Tomov, Stanimire Z.; Wang, Lin-Wang; Marques,Osni A.; Dongarra, Jack J.

2006-05-10

420

Change in optimum genetic algorithm solution with changing band discontinuities and band widths of electrically conducting copolymers  

International Nuclear Information System (INIS)

Graphical abstract: Five chromosomes are generated using bits randomly. The fitness function is then evaluated for each chromosome. Through selection and reproduction new population is generated until convergence to get a chromosome with maximum fitness. - Abstract: The interest in copolymers stems from the fact that they present interesting electronic and optical properties leading to a variety of technological applications. In order to get a suitable copolymer for a specific application, genetic algorithm (GA) along with negative factor counting (NFC) method has recently been used. In this paper, we study the effect of change in the ratio of conduction band discontinuity to valence band discontinuity (?Ec/?Ev) on the optimum solution obtained from GA for model binary copolymers. The effect of varying bandwidths on the optimum GA solution is also investigated. The obtained results show that the optimum solution changes with varying parameters like band discontinuity and band width of constituent homopolymers. As the ratio ?Ec/?Ev increases, band gap of optimum solution decreases. With increasing band widths of constituent homopolymers, the optimum solution tends to be dependent on the component with higher band gap.

2010-04-21

 
 
 
 
421

Effect of the valence electron concentration on the bulk modulus and chemical bonding in Ta2AC and Zr2AC (A=Al, Si, and P)  

International Nuclear Information System (INIS)

We have studied the effect of the valence electron concentration, on the bulk modulus and the chemical bonding in Ta2AC and Zr2AC (A=Al, Si, and P) by means of ab initio calculations. Our equilibrium volume and the hexagonal ratio (c/a) agree well (within 2.7% and 1.2%, respectively) with previously published experimental data for Ta2AlC. The bulk moduli of both Ta2AC and Zr2AC increase as Al is substituted with Si and P by 13.1% and 20.1%, respectively. This can be understood since the substitution is associated with an increased valence electron concentration, resulting in band filling and an extensive increase in cohesion.

2005-03-15

422

IBM-2 calculations of the uranium isotopes and their relationship to superdeformed bands  

International Nuclear Information System (INIS)

Neutron-proton Interacting Boson Model (IBM-2) calculations have been carried out for the uranium isotopes. Because of their large number of valence protons and neutrons, the uranium isotopes should have ground-state bands of the same structure as multiparticle-multihole (mp-nh) excited bands in such nuclei as the mercury isotopes. In particular, the rotational band built on the 4p-6h proton excited state in 192Hg should have the same IBM-2 structure as the ground-state band in 232U, because theoretically both of these bands contain five active proton bosons and seven active neutron bosons. Comparison between the authors theoretical results and the experimental results for the superdeformed band in 192Hg indicates that this is a reasonable assumption.

1993-01-01

423

A theoretical approach to the design of reduced band gap noncorrosive electrodes for photoelectrochemical solar cells  

International Nuclear Information System (INIS)

[en] Preliminary results from our charge self-consistent LCAO band structure (CSCBS) calculations with Bloch sums as the basis reveal that a noncorrosive reduced band gap electrode for photoelectrochemical solar cells may be produced from a (1:1) mixture of ?-PbO2 and TiO2 (both rutile). The band gaps for the constituents (?-PbO2 and TiO2) and the 1:1 mixture are calculated and a detailed characterization of the valence and the conduction bands is undertaken to offer a possible mechanism for the reduction of the band gap of the mixture. The band gap for the perovskite PbTiO3 is also calculated to offer a guideline for selecting from the competing pathways to the fabrication of noncorrosive photoelectrochemical electrodes

1990-01-01

424

IBM-2 calculations of the uranium isotopes and their relationship to superdeformed bands  

Energy Technology Data Exchange (ETDEWEB)

Neutron-proton Interacting Boson Model (IBM-2) calculations have been carried out for the uranium isotopes. Because of their large number of valence protons and neutrons, the uranium isotopes should have ground-state bands of the same structure as multiparticle-multihole (mp-nh) excited bands in such nuclei as the mercury isotopes. In particular, the rotational band built on the 4p-6h proton excited state in {sup 192}Hg should have the same IBM-2 structure as the ground-state band in {sup 232}U, because theoretically both of these bands contain five active proton bosons and seven active neutron bosons. Comparison between the authors theoretical results and the experimental results for the superdeformed band in {sup 192}Hg indicates that this is a reasonable assumption.

Barrett, B.R.; Barfield, A.F.

1993-04-01

425

Seed Dispersal: Animals  

Science.gov (United States)

The guest scientist in this two-minute radio program discusses seed dispersal in plants. He first explains why it is important for seeds to be distributed away from the mother plant. Then he contrasts wind-dispersed seeds with animal-dispersed seeds, pointing out that animals can disperse larger seeds that contain more nutrients for an emerging seedling. The program, which is available here in audio and text, is part of a Pulse of the Planet series on seed dispersal. Copyright 2005 Eisenhower National Clearinghouse

Planet, Pulse O.

2007-08-02

426

Dispersants displace hot oiling  

Energy Technology Data Exchange (ETDEWEB)

Laboratory experiments and field testing of dispersants in producing wells have resulted in development of 2 inexpensive paraffin dispersant packages with a broad application range, potential for significant savings over hot oiling, and that can be applied effectively by both continuous and batch treating techniques. The 2 dispersants are soluble in the carrier solvent (one soluble in oil, one in water); are able to readily disperse the wax during a hot flask test conducted in a laboratory; and leave the producing interval water wet. Field data on the 2 dispersants are tabulated, demonstrating their efficacy.

Wash, R.

1984-02-01

427

Generally Contracted Valence-Core/Valence Basis Sets for Use with Relativistic Effective Core Potentials and Spin-Orbit Coupling Operators  

Energy Technology Data Exchange (ETDEWEB)

A procedure for structuring generally contracted valence-core/valence basis sets of Gaussian-type functions for use with relativistic effective core potentials (gcv-c/v-RECP basis sets) is presented. Large valence basis sets are enhanced using a compact basis set derived for outer core electrons in the presence of small-core RECPs. When core electrons are represented by relativistic effective core potentials (RECPs), and appropriate levels of theory, these basis sets are shown to provide accurate representations of atomic and molecular valence and outer-core electrons. Core/valence polarization and correlation effects can be calculated using these basis sets through standard methods for treating electron correlation. Calculations of energies and spectra for Ru, Os, Ir, In and Cs are reported. Spectroscopic constants for RuO2+, OsO2+, Cs2 and InH are calculated and compared with experiment.

Ermler, Walter V.; Tilson, Jeffrey L.

2012-12-15

428

Interfacial chemical bonding state and band alignment of CaF{sub 2}/hydrogen-terminated diamond heterojunction  

Energy Technology Data Exchange (ETDEWEB)

CaF{sub 2} films are deposited on hydrogen-terminated diamond (H-diamond) by a radio-frequency sputter-deposition technique at room temperature. Interfacial chemical bonding state and band alignment of CaF{sub 2}/H-diamond heterojunction are investigated by X-ray photoelectron spectroscopy. It is confirmed that there are only C-Ca bonds at the CaF{sub 2}/H-diamond heterointerface. Valence and conductance band offsets of the CaF{sub 2}/H-diamond heterojunciton are determined to be 3.7 {+-} 0.2 and 0.3 {+-} 0.2 eV, respectively. It shows a type I straddling band configuration. The large valence band offset suggests advantage of the CaF{sub 2}/H-diamond heterojunciton for the development of high power and high frequency field effect transistors.

Liu, J. W.; Liao, M. Y.; Cheng, S. H.; Imura, M. [Optical and Electronic Materials Unit, National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044 (Japan); Koide, Y. [Optical and Electronic Materials Unit, National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044 (Japan); Nanofabrication Platform, NIMS, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan); Center of Materials Research for Low Carbon Emission (CMRLC), NIMS, 1-1 Namiki, Tsukuba, Ibaraki 305-0044 (Japan)

2013-03-28

429

Interfacial chemical bonding state and band alignment of CaF2/hydrogen-terminated diamond heterojunction  

Science.gov (United States)

CaF2 films are deposited on hydrogen-terminated diamond (H-diamond) by a radio-frequency sputter-deposition technique at room temperature. Interfacial chemical bonding state and band alignment of CaF2/H-diamond heterojunction are investigated by X-ray photoelectron spectroscopy. It is confirmed that there are only C-Ca bonds at the CaF2/H-diamond heterointerface. Valence and conductance band offsets of the CaF2/H-diamond heterojunciton are determined to be 3.7 +/- 0.2 and 0.3 +/- 0.2 eV, respectively. It shows a type I straddling band configuration. The large valence band offset suggests advantage of the CaF2/H-diamond heterojunciton for the development of high power and high frequency field effect transistors.

Liu, J. W.; Liao, M. Y.; Cheng, S. H.; Imura, M.; Koide, Y.

2013-03-01

430

Beaufort Sea dispersant trial  

Energy Technology Data Exchange (ETDEWEB)

In August 1986, an offshore dispersant trial was conducted in the Beaufort Sea. The purpose of this trial was to determine the effectiveness of aerially applied dispersants under arctic conditions, to evaluate the efficacy of multi-hit dispersant application, and to define the logistic and cost considerations for conducting a full-scale dispersant operation in the Beaufort Sea. All of the objectives outlined in the trial protocol were achieved as planned. In general, the results indicated that it is logistically possible to conduct an aerial dispersant operation in the Arctic and that there is some indication (mostly visual and photographic) that dispersants produce the desired effect. In spite of this, there is still no clear evidence that dispersants are as effective as they need to be for environmental protection purposes. The trial showed that some mechanism that creates a phenomenon known as 'emulsion balls' interferes with the dispersion process and results in an overall reduction in dispersant effectiveness. These 'balls' formed on the surface of the water in each of the sprayed slicks and tended to confuse the interpretation of the infrared imagery, which was the prime method used in determining dispersant effectiveness. Until the uncertainties created by the presence of these balls can be resolved, the use of remote sensing as a technique for determining dispersant effectiveness should be supported with an adequate ground truthing program. 21 refs., 35 figs., 6 tabs.

Swiss, J.J.; Vanderkooy, N.

1988-01-01

431

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

432

Band anticrossing in highly mismatched semiconductor alloys  

Energy Technology Data Exchange (ETDEWEB)

The basic theoretical aspects of the band anticrossing effects in highly electronegativity-mismatched semiconductor alloys are reviewed. The many-impurity Anderson model treated in the coherent potential approximation is applied to the semiconductor alloys, in which metallic anion atoms are partially substituted by atoms of a highly electronegative element. Analytical solutions for the Green's function describe dispersion relations and state broadening effects for the restructured conduction band. The solutions are identical to those obtained from the physically intuitive and widely used two-level band anticrossing model. It is shown that the model explains key experimental observations including the unusual composition and pressure dependence of the interband optical transitions and the large enhancement of the electron effective mass.

Walukiewicz, W.

2002-07-26

433

Synchrotron Studies of Narrow Band and Low-Dimensional Materials. Final Report for July 1, 1990 --- December 31, 2002  

International Nuclear Information System (INIS)

[en] This report summarizes a 12-year program of various kinds of synchrotron spectroscopies directed at the electronic structures of narrow band and low-dimensional materials that display correlated electron behaviors such as metal-insulator transitions, mixed valence, superconductivity, Kondo moment quenching, heavy Fermions, and non-Fermi liquid properties

2003-01-01

434

Synchrotron Studies of Narrow Band and Low-Dimensional Materials. Final Report for July 1, 1990---December 31, 2002  

Energy Technology Data Exchange (ETDEWEB)

This report summarizes a 12-year program of various kinds of synchrotron spectroscopies directed at the electronic structures of narrow band and low-dimensional materials that display correlated electron behaviors such as metal-insulator transitions, mixed valence, superconductivity, Kondo moment quenching, heavy Fermions, and non-Fermi liquid properties.

Allen, J. W.

2003-05-13

435

Cation distribution and valence state in Mn-Zn ferrite examined by synchrotron X-rays  

International Nuclear Information System (INIS)

Cation distribution and valence state in manganese zinc ferrite have been investigated with the synchrotron X-rays, where the two-wavelengths anomalous dispersion (TWAD) technique of X-ray diffraction was used at wavelengths of 1.7535 and 1.2934 A for Fe K and Zn K absorption edges, respectively. The result shows that a single crystal of Mn0.80Zn0.18Fe2.02O4 grown at T=1373 K has an inverse-spinel ingredient, where 11% of Mn and 44% of Zn ions occupy the octahedral B sites of spinel ferrite. The cation distribution is quite different from that of manganese zinc ferrite manufactured, which was synthesized at T=1873 K and has a typical normal-spinel structure. The chemical shifts in Mn K, Zn K and Fe K X-ray absorption near-edge structure (XANES) spectra support that only Mn2+, Zn2+ and Fe3+ ions exist in the manganese zinc ferrite. From a combination study of XANES and X-ray magnetic circular dichroism (XMCD) spectroscopy at the Mn K edge, it is suggested that Mn2+ ions occupy both tetrahedral A and octahedral B sites. The chemical formula determined in this study is described as (Mn2+0.71Zn2+0.10Fe3+0.19) [Mn2+0.09Zn2+0.08Fe3+1.83]O4.

2008-10-01