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Sample records for valence band dispersion

  1. Angle-resolved photoemission study of the valence band dispersion along major symmetry directions for CdTe and HgCdTe

    International Nuclear Information System (INIS)

    The valence band E(k) dispersion along the major symmetry directions GAMMA-KAPPA-chi, GAMMA-?-chi, and GAMMA-?-L have been determined for CdTe and Hg/sub 1-x/Cd/sub x/Te using angle-resolved photoemission with synchrotron radiation for 14 6, has been resolved

  2. The graphite Valence Band electronic structure: a combined Core-Valence-Valence Auger and Valence Band photoemission study

    International Nuclear Information System (INIS)

    The Valence Band (VB) electronic structure of graphite is investigated via two VB probes, namely Core-Valence-Valence (CVV) Auger emission and VB photoemission, both induced by X-Ray (h?=1486.6 eV) irradiation. The associated spectral structure is resolved by taking either the spectrum second derivative or the spectrum difference with respect to a smooth curve. Comparison between the two derived curves shows that both probes reproduce the VB Density Of States (DOS) in the upper VB region, while many body effects (Coulomb interaction between two final state holes of s-character) distort the CVV spectrum in the lower VB region

  3. Valence band anticrossing in highly mismatched alloys

    Science.gov (United States)

    Alberi, Kirstin Mclean

    Semiconductor alloys offer the ability to tune certain material parameters such as the band gap or carrier effective mass through precise control of the alloy composition, allowing them to be optimized for specific device requirements. While many alloys demonstrate near linear composition dependencies in these properties, those containing isoelectronic anion species that are significantly mismatched in electronegativity or ionization energy, known as highly mismatched alloys (HMA), exhibit substantial deviation from this trend. Here, the optical and electrical properties of HMAs containing dilute concentrations of large metallic anions are investigated in the context of a valence band anticrossing (VBAC) theory. Minority species with low ionization energies often introduce localized p-states near the valence band edge of the host semiconductor. Hybridization of these localized states with the extended p-states of the host may be described by a 12 x 12 Hamiltonian and produces a splitting of the alloy valence band into E+ and E - states. Photomodulated reflectance studies coupled with the VBAC theory confirm that the band gap bowing observed in GaSbxAs1-x and GaBixAs1-x is caused by an upward movement of the valence band edge as a result of the anticrossing interaction between the E+ and E- states. The valence band restructuring also adversely affects hole transport in these alloys through an increase in the heavy hole effective mass and the addition of an alloy disorder scattering mechanism. Finally, the VBAC theory has been extended to group IV HMAs as well as to the dilute magnetic semiconductor Ga1-x MnxAs, both of which exhibit strong hole localization at the minority species sites.

  4. Valence band anticrossing in GaBixAs1-x

    Energy Technology Data Exchange (ETDEWEB)

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

    2007-07-11

    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.

  5. Quasicrystalline valence bands in decagonal AlNiCo

    Science.gov (United States)

    Rotenberg; Theis; Horn; Gille

    2000-08-10

    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. PMID:10949295

  6. Valence band anticrossing in mismatched III-V semiconductor alloys

    Energy Technology Data Exchange (ETDEWEB)

    Alberi, K.; Walukiewicz, W.; Yu, K.M. [Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Wu, J.; Dubon, O.D. [Department of Materials Science and Engineering, University of California, Berkeley, CA 94720 (United States); Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Watkins, S.P.; Wang, C.X. [Department of Physics, Simon Fraser University, Burnaby, BC, V5A 1S6 (Canada); Liu, X.; Cho, Y.J.; Furdyna, J.K. [Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556 (United States)

    2007-04-15

    The valence band anticrossing model (VBAC) is applied to explain the composition-dependent trends in dilute GaSb{sub x}As{sub 1-x} and GaBi{sub x}As{sub 1-x} alloys. Photomodulated reflectance spectroscopy (PR) of GaSb{sub x}As{sub 1-x} shows a reduction of the fundamental bandgap energy as well as an increase of the spin-orbit splitting energy with increasing x. The VBAC model predicts that these shifts are the result of a hybridization of the extended valence band states of GaAs with the localized states of the impurity atoms, which induce an upward movement of the valence band edge. Extrapolation of the model to other III-(Sb,Bi)-V alloys is also discussed. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  7. Recoil effects in valence band photoemission of organic solids.

    Science.gov (United States)

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

    2013-04-01

    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

  8. Valence-band photoemission spectroscopy of a single-crystal FePt3

    International Nuclear Information System (INIS)

    The valence-band electronic structure of a single-crystal FePt3 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

  9. Determination of energy-band dispersion curves in strained-layer structures

    International Nuclear Information System (INIS)

    Simultaneous measurement of both the conduction- and valence-band dispersion curves in single strained-layer structures is presented. These measurements rely on the application of recent observations regarding breaking of the usual selection rules for interband magnetoluminescence transitions in modulation-doped structures. Low-temperature magneto-luminescence data for three representative InGaAs/GaAs n-type single-strained quantum well structures are presented. For energies approaching 50 meV above the band gap, we find that the conduction band is parabolic with an effective mass of 0.071m0. Over the same energy range, the valence bands are highly nonparabolic

  10. Theory of Auger electron and appearance-potential spectroscopy from solids with partially filled valence bands: Effects of valence-band-core interaction

    Science.gov (United States)

    Potthoff, M.; Braun, J.; Borstel, G.; Nolting, W.

    1993-05-01

    CVV Auger electron and appearance-potential spectra of solids are well known to exhibit strong satellite features depending on the ratio of on-site Coulomb interaction among the valence-band electrons U and the width of the free Bloch band W. We present a theory that additionally includes the effects of the Coulomb interaction between the valence-band electrons and the core electrons Uc. The spectra are influenced by the screening of the core hole in the initial state for Auger electron spectroscopy (AES), the sudden response of the valence-band electrons after the destruction of the core hole and, for appearance-potential spectroscopy (APS), by the scattering at the core hole in the final state. These effects become important especially for systems with partially filled energy bands. For APS, however, the Uc interaction already yields nontrivial effects for the limiting case of a completely empty valence band. The localized core hole implies a breakdown of translational symmetry in the distribution of the valence-band electrons, which renders the calculation more difficult. But, extending the theory to finite temperatures, we will show that the translational symmetry may be reestablished in a formal way. Both the AES and APS intensities are directly related to a proper three-particle spectral density that exactly reflects the crystal periodicity. Within the framework of the single-band Hubbard model, which is extended to include the Uc interaction, we calculate the three-particle spectral density in a generalized ladder approximation. The Uc interaction is treated by means of perturbation theory. We develop the theory for the zeroth- and first-order contributions and look at the interesting limiting cases of a completely filled and empty valence band.

  11. Electronic Band Dispersion of Graphene Nanoribbons via Fourier-Transformed Scanning Tunneling Spectroscopy

    OpenAIRE

    So?de, Hajo; Talirz, Leopold; Gro?ning, Oliver; Pignedoli, Carlo Antonio; Berger, Reinhard; Feng, Xinliang; Mu?llen, Klaus; Fasel, Roman; Ruffieux, Pascal

    2014-01-01

    Atomically precise armchair graphene nanoribbons of width $N=7$ (7-AGNRs) are investigated by scanning tunneling spectroscopy (STS) on Au(111). The analysis of energy-dependent standing wave patterns of finite length ribbons allows, by Fourier transformation, the direct extraction of the dispersion relation of frontier electronic states. Aided by density functional theory calculations, we assign the states to the valence band, the conduction band and the next empty band of 7...

  12. Rare earth 4f hybridization with the GaN valence band

    International Nuclear Information System (INIS)

    The placement of the Gd, Er and Yb 4f states within the GaN valence band has been explored by both experiment and theory. The 4d–4f photoemission resonances for various rare-earth(RE)-doped GaN thin films (RE = Gd, Er, Yb) provide an accurate depiction of the occupied 4f state placement within the GaN. The resonant photoemission show that the major Er and Gd RE 4f weight is at about 5–6 eV below the valence band maximum, similar to the 4f weights in the valence band of many other RE-doped semiconductors. For Yb, there is a very little resonant enhancement of the valence band of Yb-doped GaN, consistent with a large 4f14-? occupancy. The placement of the RE 4f levels is in qualitative agreement with theoretical expectations. (paper)

  13. Weak 3p-3d resonance in the valence band photoemission of manganese phosphide

    International Nuclear Information System (INIS)

    The weak 3p-3d resonance in the photoemission of MnP observed around the threshold of the Mn 3p excitation shows an ''energy-band-type'' aspect, i.e. the coherent decay of the photoproduced electron-3p-hole pair into the ionization of a single valence band electron. The resonance occurs all over the valence-band region but no satellite due to the two-hole bound state is found. An appreciable fraction of the apparent resonant enhancement in the bands arising from the 3s and 3p states of P is ascribed to the superimposed Msub(2,3)Msub(4,5)Msub(4,5) super-Coster-Kronig band. The valence-band spectra show no significant change in the spectral shape as measured above and below the Curie temperature. (author)

  14. Valence band offset at silicon/silicon nitride and silicon nitride/silicon oxide interfaces

    International Nuclear Information System (INIS)

    The valence band electronic structure of silicon nitride (Si3N4) is studied using the first principal quantum chemical calculation, X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). Assuming that the valence band is formed with N 2p and Si 3s, 3p and 3d electrons and based on the XPS and UPS results, the valance band offset at the Si/Si3N4 interface was estimated to be 1.5±0.2 eV. This hole barrier explains the hole dominating conduction in Si/Si3N4 structure when a positive potential is applied to the silicon substrate. In addition, the UPS study reveals that the valence band offset at the Si3N4/silicon oxide interface is 2.5±0.2 eV

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

    International Nuclear Information System (INIS)

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

  16. Valence and conduction bands engineering in halide perovskites for solar cell applica- tions

    OpenAIRE

    Meloni, Simone; Palermo, Giulia; Astani, Negar Ashari; Curchod, Basile F. E.; Graetzel, Michael; Roethlisberger, Ursula

    2014-01-01

    We performed ab initio simulations aimed at identifying the atomistic and electronic structure origin of the high valence and conduction band, and band gap tunability of halide perovskites. We found that the two key ingredients are the overlap between bivalent cation and halide atomic orbitals, and the electronic charge of the bottom of the conduction band (CBM) state on the Sn or Pb atoms. In particular, we found that lower gaps are associated to higher negative antibonding...

  17. Composition dependent valence band order in c-oriented wurtzite AlGaN layers

    International Nuclear Information System (INIS)

    The valence band order of polar wurtzite aluminum gallium nitride (AlGaN) layers is analyzed for a dense series of samples, grown heteroepitaxially on sapphire substrates, covering the complete composition range. The excitonic transition energies, found by temperature dependent photoluminescence (PL) spectroscopy, were corrected to the unstrained state using input from X-ray diffraction. k?p theory yields a critical relative aluminum concentration xc=(0.09±0.05) for the crossing of the uppermost two valence bands for strain free material, shifting to higher values for compressively strained samples, as supported by polarization dependent PL. The analysis of the strain dependent valence band crossing reconciles the findings of other research groups, where sample strain was neglected. We found a bowing for the energy band gap to the valence band with ?9 symmetry of b?9=0.85eV, and propose a possible bowing for the crystal field energy of bcf=?0.12eV. A comparison of the light extraction efficiency perpendicular and parallel to the c axis of AlxGa1-xN/AlyGa1-yN quantum well structures is discussed for different compositions.

  18. Composition dependent valence band order in c-oriented wurtzite AlGaN layers

    Energy Technology Data Exchange (ETDEWEB)

    Neuschl, B., E-mail: benjamin.neuschl@uni-ulm.de; Helbing, J.; Knab, M.; Lauer, H.; Madel, M.; Thonke, K. [Institute of Quantum Matter / Semiconductor Physics Group, University of Ulm, Albert-Einstein-Allee 45, 89069 Ulm (Germany); Meisch, T.; Forghani, K.; Scholz, F. [Institute of Optoelectronics, University of Ulm, Albert-Einstein-Allee 45, 89069 Ulm (Germany); Feneberg, M. [Institut für Experimentelle Physik, Otto-von-Guericke-Universität Magdeburg, Universitätsplatz 2, 39106 Magdeburg (Germany)

    2014-09-21

    The valence band order of polar wurtzite aluminum gallium nitride (AlGaN) layers is analyzed for a dense series of samples, grown heteroepitaxially on sapphire substrates, covering the complete composition range. The excitonic transition energies, found by temperature dependent photoluminescence (PL) spectroscopy, were corrected to the unstrained state using input from X-ray diffraction. k?p theory yields a critical relative aluminum concentration x{sub c}=(0.09±0.05) for the crossing of the uppermost two valence bands for strain free material, shifting to higher values for compressively strained samples, as supported by polarization dependent PL. The analysis of the strain dependent valence band crossing reconciles the findings of other research groups, where sample strain was neglected. We found a bowing for the energy band gap to the valence band with ?{sub 9} symmetry of b{sub ?{sub 9}}=0.85eV, and propose a possible bowing for the crystal field energy of b{sub cf}=?0.12eV. A comparison of the light extraction efficiency perpendicular and parallel to the c axis of Al{sub x}Ga{sub 1-x}N/Al{sub y}Ga{sub 1-y}N quantum well structures is discussed for different compositions.

  19. A method of removing the valence band discontinuity in HgCdTe-based nBn detectors

    Science.gov (United States)

    Akhavan, N. D.; Umana-Membreno, G. A.; Jolley, G.; Antoszewski, J.; Faraone, L.

    2014-09-01

    A method is described where the valence band discontinuity in HgCdTe-based nBn detectors will be eliminated. The method relies on doping modulation technique, where grading the material composition and doping concentration of the barrier layer at the same time will lead to elimination of the valence band discontinuity in HgCdTe-based nBn detectors. The method is not limited to the nBn structure and can be applied to any barrier detector structure with xBx (with x = n, p) to eliminate the energy band discontinuity in the valence band or conduction band.

  20. Theory of valence-band and core-level photoemission from plutonium dioxide

    OpenAIRE

    Kolorenc, Jindrich; Kozub, Agnieszka L.; Shick, Alexander B.

    2014-01-01

    The correlated-band theory implemented as a combination of the local-density approximation with the dynamical mean-field theory is applied to PuO2. An insulating electronic structure, consistent with the experimental valence-band photoemission spectra, is obtained. The calculations yield a nonmagnetic ground state that is characterized by a noninteger filling of the plutonium 5f shell. The noninteger filling as well as the satellites appearing in the 4f core-level photoemiss...

  1. Rotational bands terminating at maximal spin in the valence space

    Energy Technology Data Exchange (ETDEWEB)

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

    1996-12-31

    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.

  2. Electron structure and valence band structure of beryllium orthosilicate and lanthanum beryllate

    International Nuclear Information System (INIS)

    An analysis of the electron structure and energy spectrum of Be2SiO4- and Be2La2O5 valence zone on the basis of original and known experimental data, using semiempirical methods, is performed. Results on simulation of Be2SiO3- and Be2La2O5 electron structure are generalized. Peculiarities of molecular orbitals single-electron scheme formation are revealed. The sequence of formation and structure of Be2SiO4- and Be2La2O5 valence bands has been established

  3. Observation of valence-band structure in the LVV Auger spectra of thin epitaxial sodium layers

    Science.gov (United States)

    Schief, H.; Toennies, J. P.

    1994-09-01

    Electron-impact-induced Auger spectra at energies below 30 eV were measured from epitaxial sodium films on Cu(001) from a submonolayer up to several layers and assigned to sodium LVV transitions. According to well established deconvolution and background-correction techniques, the line shape of the Na L2/3VV transition could be used to determine the sodium valence-band density of states. In agreement with photoemission investigations of the Na density of states, our results also suggest a strong narrowing of the valence band with respect to the calculated density of states for a nearly-free-electron metal. Since CVV Auger transitions cannot occur in isolated alkali-metal atoms due to the lack of a second valence s-shell electron, the onset of the Na LVV signal during the growth of the first monolayer unambiguously marks the first stage of an alkali s-level-derived valence-band-like state. Thus, the present model study of Na/Cu(001) demonstrates that CVV Auger spectroscopy can be used as a powerful method to investigate the intriguing electronic behavior during alkali-metal adsorption.

  4. Energy spectrum of second valence band in PbSnTe solid solutions

    International Nuclear Information System (INIS)

    PbTe, PbSnTe solid solutions have a complex structure of valence band. Energy spectrum of the second valence band was calculated, effective masses and g factor were determined in the paper. P model was used in calculations. Electron spectrum in this model is constructed using metal spectrum of praphase -a hypothetic crystal with a simple cubic lattice and half-filled P bands, appeared from orbitales. It is shown that in Pbsub(1-x)Snsub(x)Te solid solutions energy gap and effective mass depend slightly on composition. P model parameters calculated in the approximation of a virtual crystal for composition x=0.2 give effective masses m2*=0.2 m0, m2*=0.04 m0

  5. Accounting for many-body correlation effects in the calculation of the valence band photoelectron emission spectra of ferromagnets

    International Nuclear Information System (INIS)

    The influence of dynamical correlation effects on the valence band photoelectron emission of ferromagnetic Fe, Co and Ni has been investigated. Angle-resolved as well as angle-integrated valence band photoelectron emission spectra were calculated on the basis of the one-particle Green's function, which was obtained by using the fully relativistic Korringa-Kohn-Rostoker method. The correlation effects have been included in terms of the electronic self-energy which was calculated self-consistently within Dynamical Mean-Field Theory (DMFT). In addition a theoretical approach to calculate high-energy angle-resolved valence band photoelectron emission spectra is presented

  6. Atomic cross-section effects in soft-x-ray photoemission from Ag valence bands

    International Nuclear Information System (INIS)

    The relative photoemission intensity from the Ag 4d valence band (VB) was studied as a function of photon energy using 32--250 eV synchrotron radiation. A sharp decrease in intensity of more than an order of magnitude was observed in the range 100 or = 150 eV range in order to bridge the ultraviolet-photomission to x-ray-photoemission gap

  7. Valence band offsets at Cu(In,Ga)Se{sub 2}/Zn(O,S) interfaces

    Energy Technology Data Exchange (ETDEWEB)

    Adler, Tobias; Klein, Andreas [Surface Science Division, Institute of Materials Science, Technische Universitaet Darmstadt, Petersenstrasse 32, 64287, Darmstadt (Germany); Botros, Miriam [Surface Science Division, Institute of Materials Science, Technische Universitaet Darmstadt, Petersenstrasse 32, 64287, Darmstadt (Germany); Zentrum fuer Sonnenenergie- und Wasserstoff-Forschung Baden-Wuerttemberg (ZSW), Industriestrasse 6, 70565, Stuttgart (Germany); Witte, Wolfram; Hariskos, Dimitrios; Menner, Richard; Powalla, Michael [Zentrum fuer Sonnenenergie- und Wasserstoff-Forschung Baden-Wuerttemberg (ZSW), Industriestrasse 6, 70565, Stuttgart (Germany)

    2014-09-15

    The energy band alignment at interfaces between Cu-chalcopyrites and Zn(O,S) buffer layers, which are important for thin-film solar cells, are considered. Valence band offsets derived from X-ray photoelectron spectroscopy for Cu(In,Ga)Se{sub 2} absorber layers with CdS and Zn(O,S) compounds are compared to theoretical predictions. It is shown that the valence band offsets at Cu(In,Ga)Se{sub 2}/Zn(O,S) interfaces approximately follow the theoretical prediction and vary significantly from sample to sample. The integral sulfide content of chemical bath deposited Zn(O,S) is reproducibly found to be 50-70%, fortuitously resulting in a conduction band offset suitable for solar cell applications with Cu(In,Ga)Se{sub 2} absorber materials. The observed variation in offset can neither be explained by variation of the Cu content in the Cu(In,Ga)Se{sub 2} near the interface nor by local variation of the chemical composition. Fermi level pinning induced by high defect concentrations is a possible origin of the variation of band offset. (copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  8. Formation of shear-bands in drying colloidal dispersions

    OpenAIRE

    Kiatkirakajorn, Pree-Cha; Goehring, Lucas

    2015-01-01

    In directionally-dried colloidal dispersions regular bands can appear behind the drying front, inclined at $\\pm45^\\circ$ to the drying line. These have been described as shear bands, based on similarities to such features in metals. Through microscopy of silica and polystyrene dispersions, dried in Hele-Shaw cells, we confirm that the bands are associated with local shear strains. We further show how the bands form, that they scale with the thickness of the drying layer, and...

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1997-04-01

    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.

  10. Valence band mixing versus higher harmonic generation in electric–dipole spin resonance

    Science.gov (United States)

    Pasek, W. J.; Nowak, M. P.; Szafran, B.

    2015-05-01

    We study resonant transitions between hole states in a cylindrical quantum dot driven by an electric field. We find that the transitions obey selection rules for parities of the components of the Luttinger spinors of the initial and final states involved in the resonant transitions. We show, however, that additional resonances may appear in the spectrum as a result of breaking the transition rules when the initial or final states are close in energy to an another state. We study dots of varied radius-to-length ratios. For the quantum dots of disk-like geometry, the confinement leads to separation of the valence bands, and by proper tuning of the external magnetic field, the transitions between heavy- and light-hole bands can be observed. The increased length of the dot leads to mixing of the valence bands and at the same time results in an appearance of fractional resonances due to strong perturbation of the hole wavefunction by the oscillating field.

  11. Experimental study of the valence band of Bi2Se3

    Science.gov (United States)

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

    2014-09-01

    The valence band of Bi2Se3 is investigated by measuring the Shubnikov-de Haas effect as well as galvanomagnetic and thermoelectric transports. At low hole concentration, the hole Fermi surface is closed and boxlike, but at higher carrier concentrations it develops tubelike extensions that are open, in general agreement with our theoretical calculations. However, the experimentally determined density-of-states effective mass is smaller than density-functional-theory calculations predict; although we cannot give a definitive explanation for this, we suspect that the theory may lack sufficient precision to compute room-temperature transport properties, such as the thermopower, in solids with interlayer van der Waals bonds.

  12. Fine structure of the valence band top of 3C BN crystal with nanopore

    International Nuclear Information System (INIS)

    The electron energy structure of the 3C BN boron nitride with pores (the radius r ? 0.3 nm) statistically distributed on the crystal is calculated by the method of the local coherent potential in approximation of multiple scattering. The crystalline potential is determined in the muffin-tin (MT) approximation. The contributions of the neighboring atoms to the electron density and the Coulomb potential of fifteen coordination spheres are accounted for. Comparison of the valence band tops of the crystalline (stoichiometric) and porous boron nitride with the X-ray photoelectron spectrum (XPS) BN and nitrogen emission spectra (SXES) is carried out. The nature of the short-wave floating in the XPS and also in the nitrogen K?-emission bands XES and SXES in the binary nitride is discussed

  13. Determination of the valence band offset of wurtzite InN/ZnO heterojunction by x-ray photoelectron spectroscopy

    International Nuclear Information System (INIS)

    The valence band offset (VBO) of the wurtzite InN/ZnO heterojunction is directly determined by x-ray photoelectron spectroscopy to be 0.82±0.23 eV. The conduction band offset is deduced from the known VBO value to be 1.85±0.23 eV, which indicates a type-I band alignment for InN/ZnO heterojunction

  14. Local Valence Electronic States and Valence-Band Maximum of Ultrathin Silicon Nitride Films on Si(111) Studied by Auger Photoelectron Coincidence Spectroscopy: Thickness and Interface Structure Dependence

    Science.gov (United States)

    Kakiuchi, Takuhiro; Tahara, Masashi; Mase, Kazuhiko; Nagaoka, Shin-ichi

    2015-04-01

    The local valence electronic states of Si3N4 films grown on Si(111)-7 × 7 [Si3N4/Si(111)] have been investigated by coincidence spectroscopy. The Si L23VV Auger electron spectra (AES) measured in coincidence with the Sin+ 2p photoelectrons of ?-Si3N4(0001)/Si(111)-8 × 8 indicate that the binding energy of the local valence electronic state at Sin+ increases as n increases. Si4+ L23VV AES measured as a function of the ?-Si3N4(0001) thickness show that the binding energy at the valence-band maximum (BEVBM) of ?-Si3N4(0001) decreases by 1.6 ± 0.5 eV as the Si3N4 thickness decreases from 3.6 to 0.7 Å. The large decrease is attributed to the hybridization of the valence electronic state of Si3N4 with those of neighboring subnitrides and to the formation of ?-Si3N4(0001) islands. The BEVBM value of the 3.6-Å-Si3N4/Si(111)-quadruplet decreases by 0.7 ± 0.6 eV from that of 3.6-Å-?-Si3N4(0001)/Si(111)-8 × 8. The decrease in BEVBM is attributed to the different interface structures.

  15. Valence band studies of Ag and Pd codeposited on Ru(0 0 0 1)

    International Nuclear Information System (INIS)

    Codeposition of Ag and Pd on the Ru(0 0 0 1) surface has been studied by photoelectron spectroscopy (PES) by recording of valence band (VB) and 3d5/2 core electron energy distribution curves (EDCs). Two- and three-dimensional total film coverages in the temperature range 300-765 K have been characterized. At submonolayer total coverage, a flat, monolayer (ML) thick film with some degree of mixing is formed. A stable surface alloy, with Ag-Pd hybridization states ?2.5 eV binding energy (BE), is found when Pd is deposited after Ag. A 1 nm thick Ag52Pd48 film formed by deposition of Pd on a Ag-precovered surface at room temperature exhibits a substantial interdiffusion of Pd and Ag. A stable concentration profile is reached between 550 and 660 K

  16. Core-level and valence-band electron states in Zr-based bulk metallic glass

    International Nuclear Information System (INIS)

    A Zr-based bulk metallic glass of Zr70Ni20Al10 has an excellent glass-forming ability (GFA), and can form a massive bulk glass by simple water-quenching. In order to clarify the role of electronic structure in this excellent GFA of Zr70Ni20Al10 glass by comparing to the Zr70Ni30 reference glass, having a worse GFA, valence-band photoemission spectra were measured with changing the incident photon energy using synchrotron radiation at BL7 of HiSOR. We have also measured Ni 3p, Zr 3d and Zr 4p core-level photoemission spectra of the Zr70Ni20Al10 glass, and compared them to those of the Zr70Ni30 reference glass. The shifts of the binding energies in every core-level are observed, indicating changes of the chemical nature by replacing the Ni atoms with Al atoms.

  17. Investigation of valence-band splitting in InN by low-temperature photoreflectance spectroscopy

    Science.gov (United States)

    Lin, Kuang-I.; Chen, Yen-Jen; Cheng, Yung-Chen; Gwo, Shangjr

    2015-03-01

    Temperature-dependent photoluminescence (PL) and photoreflectance (PR) spectroscopy and room-temperature Raman spectroscopy and X-ray diffraction have been utilized to investigate the optical properties, electron concentration, crystalline quality, and electronic band structures, especially valence-band splittings, of InN films grown by plasma-assisted molecular beam epitaxy (PAMBE) and metal–organic chemical vapor deposition (MOCVD). The smaller thermal activation energies imply the PAMBE-grown InN film exhibits low-density localized states from band tail states. PR signals of the InN film are detectable when the temperature is below about 100 K due to the cooling down of free electrons to trap states. For the MOCVD-grown InN film, no PR signal is observed even at 15 K due to the higher free electron concentration. To analyze the energetic positions of the features in the PR spectra without ambiguity, the moduli of individual PR resonances are considered. Based on the PR results and appropriate Hamiltonian, the values of the crystal-field splitting and the spin–orbit splitting in InN are experimentally determined as 26.8 and 14.5 meV, respectively. Theoretical and experimental reports are compared and discussed to verify this result.

  18. Core levels, valence band structure and unoccupied states of clean InN surfaces

    International Nuclear Information System (INIS)

    In this study we used a surface analytics system directly connected to a MBE growth module to study the surface properties of thin InN films. The samples were prepared by plasma assisted molecular beam epitaxy on GaN/Al2O3(0001) templates and exhibited a 2 x 2 reconstruction after growth. The prepared samples were analysed by photoelectron spectroscopy as well as electron energy loss spectroscopy (EELS). For the occupied states, a very good agreement to available theoretical calculations is found. Although, the valence band maximum is located at 1.6 eV, indicating strong downward band bending of ?0.9 eV, photoemission is detected up to EF. This indicates that the Fermi level is pinned above the conduction band minimum, as recently predicted. The spin-orbit splitting of the In 4d level at 17.8 eV could be resolved using He II radiation. Furthermore, from the fine structure of the secondary electron cascade peak we extract the energy of different unoccupied states 0 eV to 9 eV above the vacuum level. These measurements enable us to identify features in the InN EELS spectra, with a loss energy larger than 16 eV, as interband transitions from the In 4d level

  19. Valence band offset of MgO/TiO2 (rutile) heterojunction measured by X-ray photoelectron spectroscopy

    International Nuclear Information System (INIS)

    The valence band offset (VBO) of MgO/TiO2 (rutile) heterojunction has been directly measured by X-ray photoelectron spectroscopy. The VBO of the heterojunction is determined to be 1.6 ± 0.3 eV and the conduction band offset (CBO) is deduced to be 3.2 ± 0.3 eV, indicating that the heterojunction exhibits a type-I band alignment. These large values are sufficient for MgO to act as tunneling barriers in TiO2 based devices. The accurate determination of the valence and conduction band offsets is important for use of MgO as a buffer layer in TiO2 based field-effect transistors and dye-sensitized solar cells.

  20. Valence band offset of MgO/TiO{sub 2} (rutile) heterojunction measured by X-ray photoelectron spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Zheng Gaolin, E-mail: zhenggl@semi.ac.cn [Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083 (China); Wang Jun [Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083 (China); Liu Xianglin, E-mail: xlliu@semi.ac.cn [Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083 (China); Yang Anli; Song Huaping; Guo Yan; Wei Hongyuan; Jiao Chunmei; Yang Shaoyan; Zhu Qinsheng; Wang Zhanguo [Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083 (China)

    2010-09-15

    The valence band offset (VBO) of MgO/TiO{sub 2} (rutile) heterojunction has been directly measured by X-ray photoelectron spectroscopy. The VBO of the heterojunction is determined to be 1.6 {+-} 0.3 eV and the conduction band offset (CBO) is deduced to be 3.2 {+-} 0.3 eV, indicating that the heterojunction exhibits a type-I band alignment. These large values are sufficient for MgO to act as tunneling barriers in TiO{sub 2} based devices. The accurate determination of the valence and conduction band offsets is important for use of MgO as a buffer layer in TiO{sub 2} based field-effect transistors and dye-sensitized solar cells.

  1. All-electron Exact Exchange Treatment of Semiconductors: Effect of Core-valence Interaction on Band-gap and $d$-band Position

    CERN Document Server

    Sharma, S; Ambrosch-Draxl, C

    2005-01-01

    Exact exchange (EXX) Kohn-Sham calculations within an all-electron full-potential method are performed on a range of semiconductors and insulators (Ge, GaAs, CdS, Si, ZnS, C, BN, Ne, Ar, Kr and Xe). We find that the band-gaps are not as close to experiment as those obtained from previous pseudopotential EXX calculations. Full-potential band-gaps are also not significantly better for $sp$ semiconductors than for insulators, as had been found for pseudopotentials. The locations of $d$-band states, determined using the full-potential EXX method, are in excellent agreement with experiment, irrespective of whether these states are core, semi-core or valence. We conclude that the inclusion of the core-valence interaction is necessary for accurate determination of EXX Kohn-Sham band structures, indicating a possible deficiency in pseudopotential calculations.

  2. Valence and conduction band offsets at amorphous hexagonal boron nitride interfaces with silicon network dielectrics

    International Nuclear Information System (INIS)

    To facilitate the design of heterostructure devices employing hexagonal/sp2 boron nitride, x-ray photoelectron spectroscopy has been utilized in conjunction with prior reflection electron energy loss spectroscopy measurements to determine the valence and conduction band offsets (VBOs and CBOs) present at interfaces formed between amorphous hydrogenated sp2 boron nitride (a-BN:H) and various low- and high-dielectric-constant (k) amorphous hydrogenated silicon network dielectric materials (a-SiX:H, X?=?O, N, C). For a-BN:H interfaces formed with wide-band-gap a-SiO2 and low-k a-SiOC:H materials (Eg???8.2?8.8?eV), a type I band alignment was observed where the a-BN:H band gap (Eg?=?5.5?±?0.2?eV) was bracketed by a relatively large VBO and CBO of ?1.9 and 1.2?eV, respectively. Similarly, a type I alignment was observed between a-BN:H and high-k a-SiC:H where the a-SiC:H band gap (Eg?=?2.6?±?0.2?eV) was bracketed by a-BN:H with VBO and CBO of 1.0?±?0.1 and 1.9?±?0.2?eV, respectively. The addition of O or N to a-SiC:H was observed to decrease the VBO and increase the CBO with a-BN:H. For high-k a-SiN:H (Eg?=?3.3?±?0.2?eV) interfaces with a-BN:H, a slightly staggered type II band alignment was observed with VBO and CBO of 0.1?±?0.1 and ?2.3?±?0.2?eV, respectively. The measured a-BN:H VBOs were found to be consistent with those deduced via application of the commutative and transitive rules to VBOs reported for a-BN:H, a-SiC:H, a-SiN:H, and a-SiO2 interfaces with Si (100)

  3. Valence band offset and Schottky barrier at amorphous boron and boron carbide interfaces with silicon and copper

    International Nuclear Information System (INIS)

    In order to understand the fundamental charge transport in a-B:H and a-BX:H (X = C, N, P) compound heterostructure devices, X-ray photoelectron spectroscopy has been utilized to determine the valence band offset and Schottky barrier present at amorphous boron compound interfaces formed with (1 0 0) Si and polished poly-crystalline Cu substrates. For interfaces formed by plasma enhanced chemical vapor deposition of a-B4–5C:H on (1 0 0) Si, relatively small valence band offsets of 0.2 ± 0.2 eV were determined. For a-B:H/Cu interfaces, a more significant Schottky barrier of 0.8 ± 0.16 eV was measured. These results are in contrast to those observed for a-BN:H and BP where more significant band discontinuities (>1–2 eV) were observed for interfaces with Si and Cu.

  4. Attenuation and velocity dispersion in the exploration seismic frequency band

    Science.gov (United States)

    Sun, Langqiu

    In an anelastic medium, seismic waves are distorted by attenuation and velocity dispersion, which depend on petrophysical properties of reservoir rocks. The effective attenuation and velocity dispersion is a combination of intrinsic attenuation and apparent attenuation due to scattering, transmission response, and data acquisition system. Velocity dispersion is usually neglected in seismic data processing partly because of insufficient observations in the exploration seismic frequency band. This thesis investigates the methods of measuring velocity dispersion in the exploration seismic frequency band and interprets the velocity dispersion data in terms of petrophysical properties. Broadband, uncorrelated vibrator data are suitable for measuring velocity dispersion in the exploration seismic frequency band, and a broad bandwidth optimizes the observability of velocity dispersion. Four methods of measuring velocity dispersion in uncorrelated vibrator VSP data are investigated, which are the sliding window crosscorrelation (SWCC) method, the instantaneous phase method, the spectral decomposition method, and the cross spectrum method. Among them, the SWCC method is a new method and has satisfactory robustness, accuracy, and efficiency. Using the SWCC method, velocity dispersion is measured in the uncorrelated vibrator VSP data from three areas with different geological settings, i.e., Mallik gas hydrate zone, McArthur River uranium mines, and Outokumpu crystalline rocks. The observed velocity dispersion is fitted to a straight line with respect to log frequency for a constant (frequency-independent) Q value. This provides an alternative method for calculating Q. A constant Q value does not directly link to petrophysical properties. A modeling study is implemented for the Mallik and McArthur River data to interpret the velocity dispersion observations in terms of petrophysical properties. The detailed multi-parameter petrophysical reservoir models are built according to the well logs; the models' parameters are adjusted by fitting the synthetic data to the observed data. In this way, seismic attenuation and velocity dispersion provide new insight into petrophysics properties at the Mallik and McArthur River sites. Potentially, observations of attenuation and velocity dispersion in the exploration seismic frequency band can improve the deconvolution process for vibrator data, Q-compensation, near-surface analysis, and first break picking for seismic data.

  5. Magnetic dichroism in UV photoemission at off-normal emission: Study of the valence bands

    International Nuclear Information System (INIS)

    Magnetic dichroism of angle-resolved UV photoemission from fcc Co/Cu(001) thin films has been measured using linearly p-polarized light, and a coplanar geometry where the light and photoelectron wave vectors are antiparallel, and both are perpendicular to the in-plane sample magnetization. This geometry emphasizes information about state dispersion due to the crystalline symmetry. An orderly dispersion of the features in the magnetic dichroism over a wide range of off-normal angles of electron emission is related in detail to the bulk band structure of fcc Co. The measurements confirm the practical utility of magnetic dichroism experiments as a relatively simple complement to spin-resolved photoemission. copyright 1997 The American Physical Society

  6. Origin of the band dispersion in a metal phthalocyanine crystal

    Science.gov (United States)

    Yanagisawa, Susumu; Yamauchi, Kunihiko; Inaoka, Takeshi; Oguchi, Tamio; Hamada, Ikutaro

    2014-12-01

    Understanding the crystal structure and electronic states of the organic semiconductor is of fundamental importance for developing the materials for the organic electronics. However, the theoretical treatment of organic semiconductors remains challenging, as the semilocal density functional theory fails to describe the dispersion forces accurately. We use van der Waals inclusive density functionals to study the zinc phthalocyanine polymorphs. It is found that the structure and energetics are well described with the van der Waals density functional, and as a result, the electronic band structure is nicely reproduced. Furthermore, we reveal that the distance between the molecules and the molecule tilt angle are important factors that determine the electronic band dispersion.

  7. Resonant 5f valence-band satellite at the 5d threshold in uranium metal

    International Nuclear Information System (INIS)

    Photoelectron energy distribution curves for polycrystalline ?-uranium show a giant Fano-type resonance for the intensity of the 5f valence-band features at the Fermi energy E/sub F/, when the photon energy is tuned through the 5d core absorption edge at around h?roughly-equal94 to 103 eV. Further, a sharp (full width at half maximum = 2.2 eV) 5f satellite excitation at an initial energy E/sub i/ = -2.3 eV below E/sub F/ has been observed, which has a close analogy to the ''6-eV satellite'' in Ni. This shakeup satellite shows also a strong resonant enhancement (> or = 6 times) at the 5d core-level threshold, but a distinctly different cross-section dependence. The origin of the resonances of the 5f main line and the 2.3-eV satellite is discussed in an atomic framework, taking 5f and 6d screening into account

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

    International Nuclear Information System (INIS)

    Highlights: • The photoelectron spectra of the title compounds are assigned in details. • Shake-up lines are found to severely contaminate both ?- and ?-ionization bands. • ?-ionization onsets are subject to severe vibronic coupling complications. • We compare the results of OVGF, ADC(3) and TDDFT calculations. - Abstract: 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)

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

    Energy Technology Data Exchange (ETDEWEB)

    Reza Shojaei, S.H.; Morini, Filippo; Deleuze, Michael S., E-mail: michael.deleuze@uhasselt.be

    2013-05-16

    Highlights: • The photoelectron spectra of the title compounds are assigned in details. • Shake-up lines are found to severely contaminate both ?- and ?-ionization bands. • ?-ionization onsets are subject to severe vibronic coupling complications. • We compare the results of OVGF, ADC(3) and TDDFT calculations. - Abstract: 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)

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

    Directory of Open Access Journals (Sweden)

    ?ukari? Nemanja A.

    2010-01-01

    Full Text Available We compute the hole states in the GaAs free-standing nanowires, and in the GaAs/(Al,GaAs 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.

  11. Valence band structure and density of states effective mass model of biaxial tensile strained silicon based on k · p theory

    Science.gov (United States)

    Kuang, Qian-Wei; Liu, Hong-Xia; Wang, Shu-Long; Qin, Shan-Shan; Wang, Zhi-Lin

    2011-12-01

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

  12. Dispersive Elastodynamics of 1D Banded Materials and Structures: Design

    CERN Document Server

    Hussein, M I; Scott, R A

    2006-01-01

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

  13. Modeling wave dispersion and band gaps in heterogeneous elastic media

    OpenAIRE

    Rohan E.; Seifrt F.

    2007-01-01

    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 heteroge...

  14. Valence state, hybridization and electronic band structure in the charge ordered AlV2O4

    International Nuclear Information System (INIS)

    The valence state, hybridization and electronic band structure of charge ordered AlV2O4 are investigated by measuring the electron energy loss spectra (EELS) and performing band structure calculations using the WIEN2k code. White line ratio and O K edges of V2O5, VO2, V2O3 and AlV2O4, obtained using electron energy loss spectroscopy, are analysed specifically to probe systematically the VO6 octahedra in all of them. The systematic decrease of the L2 intensity and the O K edge intensity from V5+ in V2O5 to AlV2O4 indicates a progressive increase in the occupancy of the hybridized states, which is corroborated by the absence of a transition from O 1s to hybridized 2t2g. Band structure calculations on the parent charge frustrated cubic phase and the charge ordered rhombohedral phase clearly document a band gap in the charge ordered state. From the structural information obtained after convergence and the spectroscopic information from EELS, it appears that partial orbital occupancy may lead to a deviation from an integral valence state on all the vanadium in this exotic charge ordered spinel system. (paper)

  15. Valence state, hybridization and electronic band structure in the charge ordered AlV2O4.

    Science.gov (United States)

    Kalavathi, S; Amirthapandian, S; Chandra, Sharat; Sahu, P Ch; Sahu, H K

    2014-01-01

    The valence state, hybridization and electronic band structure of charge ordered AlV2O4 are investigated by measuring the electron energy loss spectra (EELS) and performing band structure calculations using the WIEN2k code. White line ratio and O K edges of V2O5, VO2, V2O3 and AlV2O4, obtained using electron energy loss spectroscopy, are analysed specifically to probe systematically the VO6 octahedra in all of them. The systematic decrease of the L2 intensity and the O K edge intensity from V(5+) in V2O5 to AlV2O4 indicates a progressive increase in the occupancy of the hybridized states, which is corroborated by the absence of a transition from O 1s to hybridized 2t(2g). Band structure calculations on the parent charge frustrated cubic phase and the charge ordered rhombohedral phase clearly document a band gap in the charge ordered state. From the structural information obtained after convergence and the spectroscopic information from EELS, it appears that partial orbital occupancy may lead to a deviation from an integral valence state on all the vanadium in this exotic charge ordered spinel system. PMID:24285259

  16. Enhancement in the Figure of Merit of p-type BiSb alloys through multiple valence-band doping

    OpenAIRE

    Jin, Hyungyu; Jaworski, Christopher M.; Heremans, Joseph P.

    2013-01-01

    N-type Bi100-xSbx alloys have the highest thermoelectric figure of merit (zT) of all materials below 200K; here we investigate how filling multiple valence band pockets at T and H-points of the Brillouin zone produces high zT in p-type Sn-doped material. This approach, theoretically predicted to potentially give zT>1 in Bi, was used successfully in PbTe. We report thermopower, electrical and thermal conductivity (2 to 400K) of single crystals with 12

  17. Spectroscopy of neutron-rich 168,170Dy: Yrast band evolution close to the NpNn valence maximum

    International Nuclear Information System (INIS)

    The yrast sequence of the neutron-rich dysprosium isotope 168Dy has been studied using multinucleon transfer reactions following collisions between a 460-MeV 82Se beam and an 170Er target. The reaction products were identified using the PRISMA magnetic spectrometer and the ? rays detected using the CLARA HPGe-detector array. The 2+ and 4+ members of the previously measured ground-state rotational band of 168Dy have been confirmed and the yrast band extended up to 10+. A tentative candidate for the 4+?2+ transition in 170Dy was also identified. The data on these nuclei and on the lighter even-even dysprosium isotopes are interpreted in terms of total Routhian surface calculations and the evolution of collectivity in the vicinity of the proton-neutron valence product maximum is discussed.

  18. Two-Photon Absorption in Size-Quantized Semiconductors with Degenerated Valence Band

    OpenAIRE

    Ismailov, T. G.

    2000-01-01

    Two photon absorption in size-quantized films of semiconductors with degenerated band structures are investigated. The carrier energy spectrum and wavefunctions in the bands are calculated using two-band Kane model with spin taken into accont. Two-photon absorption coefficients for different polarizations of incident radiations are calculated. The strong dependence of two-photon absorption on polarizations are stated.

  19. Improved model for the stress-induced leakage current in thin silicon dioxide based on conduction-band electron and valence-band electron tunneling

    Science.gov (United States)

    Chim, W. K.; Lim, P. S.

    2002-02-01

    This article presents a detailed investigation on the stress-induced leakage current (SILC) conduction mechanism via conduction-band electron (CBE) and valence-band electron (VBE) tunneling in thin oxides. An improved SILC model that is able to reproduce the experimental SILC over a wide range of oxide fields, and yet give a realistic level of extracted neutral trap concentration, is proposed. Calculations performed with the improved SILC model suggest that SILC conduction via neutral traps is accompanied by energy relaxation (i.e., an inelastic mechanism), irrespective of the origin (i.e., whether CBE or VBE) of the tunneling species. For both CBE and VBE tunneling, inelastic tunneling with energy relaxation (Erelax) of 1.5 and 0.8 eV, was found to fit the experimental measurements well. These values of Erelax agree with those reported in the literature.

  20. The quasiparticle band dispersion in epitaxial multilayer silicene

    International Nuclear Information System (INIS)

    The growth of multilayer silicene is an exciting challenge for the future of silicon nano-electronics. Here, we use angle-resolved photoemission spectroscopy to map the entire Brillouin zone (BZ) of (?3 × ?3)R30° reconstructed epitaxial multilayer silicene islands, growing on top of the first (3 × 3) reconstructed silicene wetting layer, on Ag(111) substrates. We found ?- and V-shape linear dispersions, which we relate to the ? and ?* bands of massless quasiparticles in multilayer silicene, at the BZ centre ?-bar 0 and at all the ?-bar centres of the (?3 × ?3)R30° Brillouin zones in the extended scheme, due to folding of the Dirac cones at the K-bar and K-bar ' points of the (1 × 1) silicene BZ. The Fermi velocity of ?0.3 × 106 m s?1 obtained is highly promising for potential silicene-based devices. (fast track communication)

  1. The observation of a surface resonance state in the valence-band structure of the perovskite La sub 0 sub . sub 6 sub 5 Ba sub 0 sub . sub 3 sub 5 MnO sub 3

    CERN Document Server

    Waldfried, C; Liou, S H; Sabiryanov, R; Jaswal, S S; Dowben, P A

    1997-01-01

    The valence-band electronic structure of a crystalline thin film of La sub 0 sub . sub 6 sub 5 Ba sub 0 sub . sub 3 sub 5 MnO sub 3 has been investigated using angle-resolved photoemission. The observed valence-band structure has a substantial surface contribution and is strongly influenced by the surface conditions. Surface contamination and disorder attenuate the emission from a Mn-3d-derived state at a binding energy of 3.3 eV. This state was found to be localized at the surface with dispersion only in the plane of the surface and exhibited a strong intensity dependence on emission angle. On the basis of a simple LMTO-ASA bulk band calculation, it is clear that this state does not fall within a bulk band gap. We have therefore identified this Mn-3d-derived state at 3.3 eV below E sub F as a surface resonance. (author)

  2. Impact of cation-based localized electronic states on the conduction and valence band structure of Al1?xInxN alloys

    International Nuclear Information System (INIS)

    We demonstrate that cation-related localized states strongly perturb the band structure of Al1?xInxN leading to a strong band gap bowing at low In content. Our first-principles calculations show that In-related localized states are formed both in the conduction and the valence band in Al1?xInxN for low In composition, x, and that these localized states dominate the evolution of the band structure with increasing x. Therefore, the commonly used assumption of a single composition-independent bowing parameter breaks down when describing the evolution both of the conduction and of the valence band edge in Al1?xInxN

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1996-05-01

    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.

  4. Spin-dependent surface transmission in 3d metals: Implications for magnetic-dichroism measurements of the valence bands

    International Nuclear Information System (INIS)

    The interpretation of measurements of magnetic dichroism in angle-resolved photoemission from the valence bands of 3d ferromagnetic metals is complicated by the simultaneous presence of spin-dependent surface transmission of the spin-polarized photoelectrons into the vacuum. As a result, two separate mechanisms contribute to the change in the photoemission intensity spectra when the sample magnetization is reversed. The magnitude of the surface transmission effect in the ''light'' 3d metals has been measured using Cu(001) as a sample, and an intensity asymmetry of ±3% has been found. This is smaller than, but approximately the same size as, the magnetic dichroism measured for iron and cobalt, and demonstrates experimentally that neither mechanism can be generally neglected in favor of the other

  5. Theoretical study of optoelectronic properties of GaAs1-xBix alloys using valence band anticrossing model

    Science.gov (United States)

    Habchi, M. M.; Ben Nasr, A.; Rebey, A.; El Jani, B.

    2014-11-01

    The (12 × 12) and (14 × 14) valence band anticrossing (V-BAC) models were applied to calculate the electronic band structure of GaAs1-xBix dilute alloys along ?-, ?- and ?-directions at room temperature. A comparative study based on these models was performed in terms of energy levels, optical transitions, spin-orbit splitting and effective mass. We found a significant reduction of the band-gap energy Eg by roughly 81 meV/%Bi accompanied by an increase in the spin-orbit splitting ?so+ by about 56 meV/%Bi. Furthermore, ?so+ does come into resonance with Eg at ?12%Bi for resonance energy equal to 0.73 eV. An excellent agreement has occurred between the (14 × 14) V-BAC model predictions and experimental results reported in the literature. In addition, we have investigated the Bi composition and k-directions dependence of the effective mass at ? point. A slight increase of the holes effective mass with x can affect the holes transport properties of GaAsBi. The intrinsic carrier density increases with both x and the temperature T, but it remains below 1010 cm-3 for x ? 5% and T ? 300 K.

  6. Conduction band/valence band kinetic modeling of the LiF:Mg,Ti system incorporating creation of defects in the irradiation stage

    Science.gov (United States)

    Eliyahu, I.; Horowitz, Y. S.; Oster, L.

    2012-12-01

    A conduction band/valence band kinetic model is described for the irradiation stage of the thermoluminescent LiF:Mg,Ti system. Unlike previous investigations the model incorporates creation of fluorine vacancies via irradiation and their subsequent partial filling by electrons in the relaxation stage leading to the creation of F centers. The radiation induced vacancies thus operate as additional competitors to the 4 eV electron trapping center (TC) associated with composite glow peak 5 in the glow curve of LiF:Mg,Ti. With the appropriate choice of parameter-values the model successfully predicts the experimentally measured, linear/exponentially saturating dose response of the optical absorption (OA) bands of the 4 eV TC and the 5.45 eV competitive center (CC) which serves as well as the recombination stage competitor. The increased competition due to the creation of negative ion vacancies during irradiation is found to lead to changes in the population dose response characteristics of the various centers taking part in the TL mechanism. The implication of these changes on the relative thermoluminescence (TL) efficiency following heavy charged particle (HCP) irradiation is discussed.

  7. Angle-resolved photoemission determination of ?-line valence bands in Pt and Au using synchrotron radiation

    International Nuclear Information System (INIS)

    Angle-resolved photoemission spectra are reported for Au (111) and Pt (111) in the photon-energy range 6 8=3.55, 5.90, GAMMA7=4.45 eV for Au; GAMMA8=1.40, 4.07, GAMMA7=2.80 eV for Pt. The s band is found to be ca. 1 eV (Pt) and 0.5 eV (Au) less bound than the theoretical prediction. Ligand field parameters at GAMMA are presented for both samples: xi(5d)=0.71 +- 0.05 eV, 10Dq=1.22 +- 0.05 eV for Au; xi(5d)=0.66 +- 0.05 eV, 10Dq=1.78 +- 0.05 eV for Pt. The systematics of 10Dq in the noble metals is discussed. The polarization dependence of the spectra was used to assign initial-state symmetries empirically: bands 3, 5 show ?6 symmetry, bands 2, 4, 6, ?4+?5. Cooling of the Au crystal showed that the ''s-p plateau'' is due to a thermally insensitive indirect process, and that both thermal diffuse scattering and phonon-assisted inelastic processes contribute to the loss of spectral contrast at room temperature. Resonances in intensity with photon energy were investigated and assigned in terms of the final-state band structure

  8. Valence band photoemission from in-situ grown GaAs(100)-c(4 x 4).

    Czech Academy of Sciences Publication Activity Database

    Ji?í?ek, Petr; Cukr, Miroslav; Bartoš, Igor; Adell, M.; Strasser, T.; Schattke, W.

    2006-01-01

    Ro?. 56, ?. 1 (2006), s. 21-26. ISSN 0011-4626. [Symposium on Surface Physics /10./. Praha, 11.07.2005-15.07.2005] R&D Projects: GA ?R(CZ) GA202/04/0994 Institutional research plan: CEZ:AV0Z10100521 Keywords : GaAs(100)-c( 4X4 ) * surface states * band structure * structure plot Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.568, year: 2006

  9. Valence band circular dichroism in non-magnetic Ag/Ru(0001) at normal emission

    International Nuclear Information System (INIS)

    For the non-magnetic system of Ag films on Ru(0001), we have measured the circular dichroism of photoelectrons emitted along the surface normal, the geometry typically used in photoemission electron microscopy. Photoemission spectra were acquired from micrometer-sized regions having uniformly thick Ag films on a single, atomically flat Ru terrace. For a single Ag layer, we find a circular dichroism that exceeds 6% at the d-derived band region around 4.5 eV binding energy. The dichroism decreases as the Ag film thickness increases to three atomic layers. We discuss the origin of the circular dichroism in terms of the symmetry lowering that can occur even in normal emission.

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

    Science.gov (United States)

    Urbanek, Janus; Vöhringer, Peter

    2013-07-25

    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. PMID:23815751

  11. 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 < 10 eV) to Dunning's correlation consistent basis set of triple zeta quality (cc-pVTZ) enable theoretical insights into HeI measurements which approach chemical accuracy (1 kcal/mol or 43.4 meV). In contrast, a confrontation of simulated spectral envelopes with high-resolution He I photoelectron spectra indicates that polycyclic aromatic molecules with sterically overcrowded bay regions are more susceptible to undergo vibronic coupling complications at the ?-ionisation onset. OVGF/cc-pVDZ or OVGF/cc-pVTZ pole strengths smaller than 0.85 systematically corroborate a breakdown of the orbital (or one-electron) picture of ionisation at the ADC(3)/6-31G levels. The extent of shake-up bands is correspondingly related to topological, structural and magnetic criteria of aromaticity. Comparison is made with calculations of the lowest doublet-doublet excitation energies of the related radical cations, by means of time-de radical cations, by means of time-dependent density functional theory (TDDFT)

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

    International Nuclear Information System (INIS)

    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. (paper)

  13. Effect of phase formation on valence band photoemission and photoresonance study of Ti/Ni multilayers using synchrotron radiation

    International Nuclear Information System (INIS)

    This paper presents investigation of Ti-Ni alloy phase formation and its effect on valence band (VB) photoemission and photoresonance study of as-deposited as well as annealed Ti/Ni multilayers (MLs) up to 600 deg. C using synchrotron radiation. For this purpose [Ti (50 A)/Ni (50 A)]X10 ML structures were deposited by using electron-beam evaporation technique under ultra-high vacuum (UHV) conditions. Formation of different phases of Ti-Ni alloy due to annealing treatment has been confirmed by the X-ray diffraction (XRD) technique. The XRD pattern corresponding as-deposited ML sample shows crystalline nature of both Ti and Ni deposited layers, whereas 300 deg. C annealed ML sample show solid-state reaction (SSR) leading to amorphization and subsequent recrystallisation at higher temperatures of annealing (?400 deg. C) with the formation of TiNi, TiNi3 and Ti2Ni alloy phases. The survey scans corresponding to 400, 500 and 600 deg. C annealed ML sample shows interdiffusion and intermixing of Ni atoms into Ti layers leading to chemical Ti-Ni alloys phase formation at interface. The corresponding recorded VB spectra using synchrotron radiation at 134 eV on as-deposited ML sample with successive sputtering shows alternately photoemission bands due to Ti 3d and Ni 3d, respectively, indicating there is no mixing of the consequent layers and any phase formation at the interface during deposition. However, ML samples annealed at higher temperar, ML samples annealed at higher temperatures of annealing, particularly at 400, 500 and 600 deg. C show a clear shift in Ni 3d band and its satellite peak position to higher BE side indicates Ti-Ni alloy phase formation. In addition to this, reduction of satellite peak intensity and Ni 3d density of states (DOS) near Fermi level is also observed due to Ti-Ni phase formation with higher annealing temperatures. The variable photon energy VB measurements on as-deposited and ML samples annealed at 400 deg. C confirms existence and BE position of observed Ni 3d satellite structure. The observed changes and modifications in the VB photoemission are discussed and interpreted in terms of structural changes at the interface due to annealing treatment

  14. Valence band offset at Al2O3/In0.17Al0.83N interface formed by atomic layer deposition

    International Nuclear Information System (INIS)

    The valence band offset, ?EV, at an Al2O3/In0.17Al0.83N interface formed by atomic layer deposition was measured by x-ray photoelectron spectroscopy. The conventional method of using the core level separation, ?ECL, between O 1s and In 4d resulted in ?EV = 1.3 eV, which was apparently consistent with the direct observation of the valence band edge varying the photoelectron exit angle, ?. However, ?ECL and full width at half maximum of core-level spectra were dependent on ?, which indicated significant potential gradients in Al2O3 and InAlN layers. An actual ?EV of 1.2 eV was obtained considering the potential gradients.

  15. Valence-Band Structures of Quasi-One-Dimensional Crystals C5H10NH2PbX3 [X = I, Br

    Science.gov (United States)

    Azuma, Junpei; Tanaka, Koichiro; Kamada, Masao; Kan'no, Ken-ichi

    2002-11-01

    X-ray and ultra-violet photoemission spectra have been measured to study the valence-band structures of piperidinium trihaloplumbates C5H10NH2PbX3 [X = I, Br], which have natural nano-scale one-dimensional structures. The valence-band spectra of lead halides, which have the three-dimensional structures, are also reported for comparison. The partial densities of states related to the constituent ions and molecules were obtained with the comparison between the XPS and UPS. Empirical LCAO calculations were also carried out to analyze the experimental results. The quantum-well-like electronic structure in C5H10NH2PbX3 [X = I, Br] is proposed.

  16. Transport properties and valence band feature of high-performance (GeTe)85(AgSbTe2)15 thermoelectric materials

    International Nuclear Information System (INIS)

    This paper aims at elucidating the origin of the high thermoelectric power factor of p-type (AgxSbTex/2+1.5)15(GeTe)85 (TAGS) thermoelectric materials with 0.4 <= x <= 1.2. All samples exhibit good thermoelectric figures of merit (zT) which reach 1.5 at 700 K for x = 0.6. Thermoelectric and thermomagnetic transport properties (electrical resistivity, Seebeck, Hall and transverse Nernst–Ettinghausen coefficients) are measured and used to calculate the scattering factor, the Fermi energy, the density-of-states (DOS) effective mass and hole mean free path (mfp). The DOS effective mass is very high due to the large band mass of the primary valence band and the high degeneracy of pockets in the Fermi surface from the second valence band. The highly degenerate Fermi surface increased the total DOS without decreasing mobility, which is more desirable than the high DOS that comes from a single carrier pocket. The high-temperature hole mfp approaches the Ioffe–Regel limit for band-type conduction, which validates our discussion based on band transport and is also important for TAGS alloys having high zT with heavy bands. The present results show that multiple degenerate Fermi surface pockets provide an effective way of substantially increasing the power factor of thermoelectric materials with low thermal conductivity. (paper)

  17. Spectroscopic investigations of the valence band electronic structure of Pr0.5Sr0.5MnO3

    International Nuclear Information System (INIS)

    We have studied the Pr0.5Sr0.5MnO3 across its PMM-FMM-AFMI phase transition using resonant photoemission spectroscopy in order to identify the states contributing to the valence band electronic structure. We have also studied the material using O - edge X-ray absorption spectroscopy. The results are discussed from the point of view of Jahn-Teller polarons in the CO-AFMI phase. (author)

  18. Measurement of the low energy spectral contribution in coincidence with valence band (VB) energy levels of Ag(100) using VB-VB coincidence spectroscopy

    Science.gov (United States)

    Joglekar, P. V.; Gladen, R.; Lim, Z. H.; Shastry, K.; Hulbert, S. L.; Weiss, A. H.

    2015-03-01

    A set of coincidence measurements were obtained for the study and measurement of the electron contribution arising from the inter-valence band (VB) transitions along with the inelastically scattered VB electron contribution. These Auger-unrelated contributions arise in the Auger spectrum (Ag 4p NVV) obtained using Auger Photoelectron Coincidence Spectroscopy (APECS). The measured Auger-unrelated contribution can be eliminated from Auger spectrum to obtain the spectrum related to Auger. In our VB-VB coincidence measurement, a photon beam of energy 180eV was used to probe the Ag(100) sample. The coincidence spectrum was obtained using two Cylindrical Mirror Analyzers (CMA's). The scan CMA measured the low energy electron contribution in the energy range 0-70eV in coincidence with VB electrons measured by the fixed CMA. In this talk, we present the data obtained for VB-VB coincidence at the valence band energy of 171eV along with the coincidence measurements in the energy range of 4p core and valence band. NSF DMR 0907679, NSF Award Number: 1213727. Use of the National Synchrotron Light Source, Brookhaven National Laboratory, was supported by the U.S. DOE, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-98CH10886.

  19. Conduction and Valence Band States of Sb-Mediated Ge Quantum Dots in n-type Si Studied by Deep Level Transient Spectroscopy

    International Nuclear Information System (INIS)

    Full text: Deep level transient spectroscopy technique is used on a Ti Schottky diode on n-type silicon with embedded Sb-mediated Ge quantum dots (QDs). We discovered an electron trap and two hole traps within the Si band gap at the plane of Ge QDs. An electron trap has activation energy of 87±7 meV. One hole trap has activation energy of 304±32 meV, while the second hole trap is represented by the energy sub-band between 125 and 250 meV above the top of the Si valence band. The electron level (87±7 meV) and the hole energy sub-band (125-250 meV) are identified as energetic states of Ge QDs array. The deepest trap level for holes (304 meV) has not been identified yet. (author)

  20. X-ray photoelectron spectroscopy and theory of the valence band and semicore Ga 3d states in GaN

    Science.gov (United States)

    Lambrecht, W. R. L.; Segall, B.; Strite, S.; Martin, G.; Agarwal, A.; Morkoç, H.; Rockett, A.

    1994-11-01

    The effects of the Ga 3d semicore levels on the electronic structure of GaN are discussed. While band-structure theory using the local-density approximation predicts these states to overlap with the N 2s band and to have important effects on the total energy, x-ray photoelectron spectroscopy (XPS) shows that they occur ~3 eV below the N 2s band. This apparent discrepancy is resolved by means of a so-called ? SCF or difference of self-consistent-fields calculation, in which the binding energy is calculated as a total-energy difference including solid state screening effects by means of the excited-atom model. The calculated valence-band densities of states are found to be in good agreement with the XPS spectrum. The differences between zinc blende and wurtzite GaN are discussed.

  1. Valence one-electron and shake-up ionization bands of polycyclic aromatic hydrocarbons. I. Benzene, naphthalene, anthracene, naphthacene, and pentacene

    Science.gov (United States)

    Deleuze, Michael S.; Trofimov, Alexander B.; Cederbaum, Lorenz S.

    2001-10-01

    The valence ionization bands of benzene and of polyacenes ranging from naphthalene to pentacene have been entirely assigned by means of one-particle Green's function calculations, performed using the third-order algebraic-diagrammatic construction [ADC(3)] scheme and series of basis sets of improving quality. For the sake of consistency, the computations are based on correlated (DFT/B3LYP) rather than uncorrelated geometries. Ionization bands pertaining to ?-orbitals are subject to a severe shake-up contamination at already quite low binding energies (e.g., down to 8.0 eV in the case of pentacene). In sharp contrast, the orbital picture of ionization holds to a much greater extent within the ?-band system (e.g., for pentacene, up to binding energies of 14.6 eV). Despite the intricacy of ionization bands, and, possibly, vibrational complications, ADC(3) spectra consistently match photoionization measurements up to the inner-valence region, where the orbital picture completely breaks down.

  2. A new circular photonic crystal fiber for effective dispersion compensation over E to L wavelength bands

    Scientific Electronic Library Online (English)

    M. M., Haque; M. S., Rahman; M. Samiul, Habib; M. Selim, Habib; S. M. A., Razzak.

    2013-12-01

    Full Text Available This paper presents a new circular photonic crystal fiber (C-PCF) for effective dispersion compensation covering E to L wavelength bands ranging from 1360-1625 nm. To investigate its guiding properties, finite element method (FEM) with a perfectly matched layer absorbing boundary condition is used. [...] From our numerical simulation, it is found that the designed C-PCF simultaneously shows a large negative dispersion of about -248.65 to -1069 ps/(nm.km) over E to L wavelength bands and a relative dispersion slope (RDS) exactly equal to that of a single mode fiber (SMF) at 1.55 µm wavelength. It is also found that residual dispersion after compesating 40 km long SMF is within ±62 ps/nm which ensures application of C-PCF in high speed WDM system. Besides, dispersion slope, slope compensation ratio, effective area and confinement loss of the proposed C-PCF are also evaluated and discussed.

  3. Spin orbit splitting in the valence bands of ZrS{sub x}Se{sub 2?x}: Angle resolved photoemission and density functional theory

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-08-15

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

  4. Two-band model for halogen-bridged mixed-valence transition-metal complexes. I. Ground state and excitation spectrum

    International Nuclear Information System (INIS)

    We consider a 3/4-filled, two-band discrete tight-binding Peierls-Hubbard model for an isolated chain of a halogen-bridged, mixed-valence, transition-metal linear-chain complex (HMMC or MX chain). We have employed the adiabatic approximation in which the quantum fluctuations associated with phonons are implicitly treated as an external field for the electrons, and treat electron-electron effects in the Hartree-Fock approximation. We investigate ground states as functions of the model parameters and doping-induced and photoinduced excitations---kinks, polarons, bipolarons, and excitons. Results for several experimental observables, including the lattice distortion, the excess charge and spin densities of defects, and the optical absorption, are compiled. For the ground state, we find that the bond-order-wave (BOW) portion of the one-band phase diagram is eliminated from the two-band phase diagram, in agreement with the lack of real materials in the pure BOW phase. The extent of electron-hole asymmetry and of spatial localization or delocalization of defects is explored. Two separate solitons or polarons are compared with corresponding bipolarons. We demonstrate explicitly the need to employ the two-band model for a realistic modeling of the MX systems, focusing on three specific systems: (a) highly distorted, valence-localized (strongly charge-disproportionated) PtCl, (b) moderately distorted PtBr, and (c) weakly distorted, valence-delocalized (weak charge-density waveence-delocalized (weak charge-density wave) PtI. The compilation of results reported here constitutes a reference resource against which the rapidly expanding experimental data can be compared

  5. Single-carrier impact ionization favored by a limited band dispersion

    CERN Document Server

    Darbandi, A

    2012-01-01

    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.

  6. Wide-band Simultaneous Observations of Pulsars: Disentangling Dispersion Measure and Profile Variations

    OpenAIRE

    Hassall, TE; Stappers, BW; Hessels, JWT; Kramer, M.; Alexov, A.; Anderson, K.; Coenen, T (Tom); Karastergiou, A.; Keane, EF; Kondratiev, VI; Lazaridis, K; Leeuwen, JV; Noutsos, A.; Serylak, M.; Sobey, C.

    2012-01-01

    Dispersion in the interstellar medium is a well known phenomenon that follows a simple relationship, which has been used to predict the time delay of dispersed radio pulses since the late 1960s. We performed wide-band simultaneous observations of four pulsars with LOFAR (at 40–190 MHz), the 76-m Lovell Telescope (at 1400 MHz) and the Effelsberg 100-m Telescope (at 8000 MHz) to test the accuracy of the dispersion law over a broad frequency range. In this paper we present the results of these...

  7. Size and alloying induced shift in core and valence bands of Pd-Ag and Pd-Cu nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Sengar, Saurabh K.; Mehta, B. R., E-mail: brmehta@physics.iitd.ac.in [Thin Film Laboratory, Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016 (India); Govind [Surface Physics Group, National Physical Laboratory (CSIR), New Delhi 110012 (India)

    2014-03-28

    In this report, X-ray photoelectron spectroscopy studies have been carried out on Pd, Ag, Cu, Pd-Ag, and Pd-Cu nanoparticles having identical sizes corresponding to mobility equivalent diameters of 60, 40, and 20?nm. The nanoparticles were prepared by the gas phase synthesis method. The effect of size on valence and core levels in metal and alloy nanoparticles has been studied by comparing the values to those with the 60?nm nanoparticles. The effect of alloying has been investigated by comparing the valence and core level binding energies of Pd-Cu and Pd-Ag alloy nanoparticles with the corresponding values for Pd, Ag, and Cu nanoparticles of identical sizes. These effects have been explained in terms of size induced lattice contractions, alloying induced charge transfer, and hybridization effects. The observation of alloying and size induced binding energy shifts in bimetallic nanoparticles is important from the point of view of hydrogen reactivity.

  8. Spectroscopy of Neutron-Rich $^{168,170}$Dy: Yrast Band Evolution Close to the $N_{p}N_{n}$ Valence Maximum

    CERN Document Server

    Söderström, P A; Regan, P H; Algora, A; de Angelis, G; Ashley, S F; Aydin, S; Bazzacco, D; Casperson, R J; Catford, W N; Cederkäll, J; Chapman, R; Corradi, L; Fahlander, C; Farnea, E; Fioretto, E; Freeman, S J; Gadea, A; Gelletly, W; Gottardo, A; Grodner, E; He, C Y; Jones, G A; Keyes, K; Labiche, M; Liang, X; Liu, Z; Lunardi, S; Muarginean, N; Mason, P; Menegazzo, R; Mengoni, D; Montagnoli, G; Napoli, D; Ollier, J; Pietri, S; Podolyák, Z; Pollarolo, G; Recchia, F; ?ahin, E; Scarlassara, F; Silvestri, R; Smith, J F; Spohr, K M; Steer, S J; Stefanini, A M; Szilner, S; Thompson, N J; Tveten, G M; Ur, C A; Valiente-Dobón, J J; Werner, V; Williams, S J; Xu, F R; Zhu, J Y; 10.1103/PhysRevC.81.034310

    2010-01-01

    The yrast sequence of the neutron-rich dysprosium isotope Dy-168 has been studied using multi-nucleon transfer reactions following the collision of a 460-MeV Se-82 beam and a Er-170 target. The reaction products were identified using the PRISMA magnetic spectrometer and the gamma rays detected using the CLARA HPGe-detector array. The 2+ and 4+ members of the previously measured ground state rotational band of Dy-168 was confirmed and the yrast band extended up to 10+. A tentative candidate for the 4+ to 2+ transition in Dy-170 was also identified. The data on this and lighter even-even dysprosium isotopes are interpreted in terms of Total Routhian Surface calculations and the evolution of collectivity approaching the proton-neutron valence product maximum is discussed.

  9. 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)

  10. Measurement of valence-band offsets of InAlN/GaN heterostructures grown by metal-organic vapor phase epitaxy

    International Nuclear Information System (INIS)

    The valence band offsets, ?EV, of In0.17Al0.83N/GaN, In0.25Al0.75N/GaN, and In0.30Al0.70N/GaN heterostructures grown by metal-organic vapor phase epitaxy were evaluated by using x-ray photoelectron spectroscopy (XPS). The dependence of the energy position and the full width at half maximum of the Al 2p spectrum on the exit angle indicated that there was sharp band bending caused by the polarization-induced electric field combined with surface Fermi-level pinning in each ultrathin InAlN layer. The ?EV values evaluated without taking into account band bending indicated large discrepancies from the theoretical estimates for all samples. Erroneous results due to band bending were corrected by applying numerical calculations, which led to acceptable results. The evaluated ?EV values were 0.2±0.2 eV for In0.17Al0.83N/GaN, 0.1±0.2 eV for In0.25Al0.75N/GaN, and 0.0±0.2 eV for In0.30Al0.70N/GaN. Despite the large decrease of around 1.0 eV in the band gap of InAlN layers according to the increase in the In molar fraction, the decrease in ?EV was as small as 0.2 eV. Therefore, the change in band-gap discontinuity was mainly distributed to that in conduction band offset.

  11. Band structure of boron doped carbon nanotubes

    OpenAIRE

    Wirtz, Ludger; Rubio Secades, A?ngel

    2003-01-01

    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...

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

    CERN Document Server

    Rinke, P; Neugebauer, J; Freysoldt, C; Scheffler, M; Rinke, Patrick; Qteish, Abdallah; Neugebauer, Joerg; Freysoldt, Christoph; Scheffler, Matthias

    2005-01-01

    We report quasiparticle-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 pseudopotential approach. Unlike in the majority of previous GW studies, which are almost exlusively based on ground state calculations in the local-density approximation (LDA), we combine GW with exact-exchange DFT calculations in the optimised-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 hybridisation compared to t...

  13. Detection of Fe 3d electronic states in the valence band and magnetic properties of Fe-doped ZnO film

    International Nuclear Information System (INIS)

    Fe-doped ZnO film has been grown by laser molecular beam epitaxy (L-MBE) and structurally characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), all of which reveal the high quality of the film. No secondary phase was detected. Resonant photoemission spectroscopy (RPES) with photon energies around the Fe 2p–3d absorption edge is performed to detect the electronic structure in the valence band. A strong resonant effect at a photon energy of 710 eV is observed. Fe3+ is the only valence state of Fe ions in the film and the Fe 3d electronic states are concentrated at binding energies of about 3.8 eV and 7 eV?8 eV. There are no electronic states related to Fe near the Fermi level. Magnetic measurements reveal a typical superparamagnetic property at room temperature. The absence of electronic states related to Fe near the Fermi level and the high quality of the film, with few defects, provide little support to ferromagnetism. (condensed matter: structural, mechanical, and thermal properties)

  14. Dispersion characteristics of a slow wave structure with a modified photonic band gap

    International Nuclear Information System (INIS)

    This paper studies the dispersion characteristics of a modified photonic band-gap slow-wave structure with an open boundary by simulation and experiment. A mode launcher with a wheel radiator and a coupling probe is presented to excite a pure TM01-like mode. The cold test and simulation results show that the TM01-like mode is effectively excited and no parasitic modes appear. The dispersion characteristics obtained from the cold test are in good agreement with the calculated results. (general)

  15. Dispersion of the valence electron energy loss in thin amorphous carbon films deposited by ion assisted evaporation of graphite

    International Nuclear Information System (INIS)

    The dispersion of electron energy loss with transferred wave vector q has been measured for amorphous, non-hydrogenated carbon films. The peak energies for both the loss peak related to the main plasmon loss and for that brought about by the ? ? ?* interband transitions are found to follow a power law in Q. The films exhibited differences of the exponents which may be related to structural differences. For the material deposited with very small ion flux, which is quite similar to ordinary evaporated carbon, a dispersion of the two low loss peaks with q1.6 and q1.9, respectively, has been found whereas in the case of the other two films, the dispersion appears to be nearly linear in q. (authors). 23 refs., 4 figs., 2 tabs

  16. Thermoelectric properties of GeTe at high hydrostatic pressure up to 8.5 GPa and its valence-band structure

    International Nuclear Information System (INIS)

    The thermopower and the relative electrical resistance of rhombohedral ?-GeTe and orthorhombic #betta#-GeTe polycrystalline samples with hole density between 3.9 x 1020 and 2 x 1021 cm-3 are measured under hydrostatic pressure up to 8.5 GPa at room temperature. The phase transition of ?-GeTe to the cubic rocksalt structure (#betta#-GeTe) reported earlier at 3.5 GPa under nonhydrostatic pressure is not observed up to 8.5 GPa. Orthorhombic #betta#-GeTe also exhibits no phase transition. The pressure dependences of the thermopower provide support for the multiple valence-band model of GeTe. (author)

  17. Valence and conduction band alignment at ScN interfaces with 3C-SiC (111) and 2H-GaN (0001)

    International Nuclear Information System (INIS)

    In order to understand and predict the behavior of future scandium nitride (ScN) semiconductor heterostructure devices, we have utilized in situ x-ray and ultra-violet photoelectron spectroscopy to determine the valence band offset (VBO) present at ScN/3C-SiC (111) and 2H-GaN (0001)/ScN (111) interfaces formed by ammonia gas source molecular beam epitaxy. The ScN/3C-SiC (111) VBO was dependent on the ScN growth temperature and resistivity. VBOs of 0.4?±?0.1 and 0.1?±?0.1?eV were, respectively, determined for ScN grown at 925?°C (low resistivity) and 800?°C (high resistivity). Using the band-gaps of 1.6?±?0.2 and 1.4?±?0.2?eV previously determined by reflection electron energy loss spectroscopy for the 925 and 800?°C ScN films, the respective conduction band offsets (CBO) for these interfaces were 0.4?±?0.2 and 0.9?±?0.2?eV. For a GaN (0001) interface with 925?°C ScN (111), the VBO and CBO were similarly determined to be 0.9?±?0.1 and 0.9?±?0.2?eV, respectively.

  18. Charge transport in gapless electron-hole systems with arbitrary band dispersion

    Science.gov (United States)

    Das Sarma, S.; Hwang, E. H.

    2015-05-01

    Using the semiclassical Boltzmann transport theory, we analytically consider dc charge transport in gapless electron-hole (both chiral and nonchiral) systems in the presence of resistive scattering due to static disorder arising from random quenched impurities in the background. We obtain the dependence of the Boltzmann conductivity on carrier density and temperature for arbitrary band dispersion in arbitrary dimensionality assuming long-range (˜1 /r ) Coulomb disorder and zero-range white-noise disorder [˜? (r ) ]. We establish that the temperature and the density dependence of the Boltzmann conductivity manifests scaling behaviors determining, respectively, the intrinsic semimetallic or the extrinsic metallic property of the gapless system. Our results apply equally well to both chiral and nonchiral gapless systems, and provide a qualitative understanding of the dependence of the Boltzmann conductivity on the band dispersion in arbitrary dimensionality.

  19. 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.

  20. Valence bands and Fermi-surface topology of untwinned single-crystal YBa2Cu3O6.9

    International Nuclear Information System (INIS)

    The cleaved surfaces of untwinned, single-crystal YBa2Cu3O6.9 have been probed with synchrotron-radiation photoemission, utilizing both high energy and angular resolution. Acute spectral structure was observed, both at the Fermi energy and at higher binding energies, particularly near the high-symmetry points of the two-dimensional Brillouin zone, bar ?, bar X, bar Y, and bar S. Many band crossings of the Fermi energy were seen, with obvious and important differences between the bands near bar X and those near bar Y. A large superconducting gap was not observed: The data are consistent with a gap of less than 10 meV. The assignment of bands and Fermi-level crossings to chain and plane states will be discussed, including comparisons to the predictions of theory, particularly local-density-approximation calculations

  1. Wide-band Simultaneous Observations of Pulsars: Disentangling Dispersion Measure and Profile Variations

    CERN Document Server

    Hassall, T E; Hessels, J W T; Kramer, M; Alexov, A; Anderson, K; Coenen, T; Karastergiou, A; Keane, E F; Kondratiev, V I; Lazaridis, K; van Leeuwen, J; Noutsos, A; Serylak, M; Sobey, C; Verbiest, J P W; Weltevrede, P; Zagkouris, K; Fender, R; Wijers, R A M J; Bahren, L; Bell, M E; Broderick, J W; Corbel, S; Daw, E J; Dhillon, V S; Eisloffel, J; Falcke, H; Griessmeier, J -M; Jonker, P; Law, C; Markoff, S; Miller-Jones, J C A; Osten, R; Rol, E; Scaife, A M M; Scheers, B; Schellart, P; Spreeuw, H; Swinbank, J; ter Veen, S; Wise, M W; Wijnands, R; Wucknitz, O; Zarka, P; Asgekar, A; Bell, M R; Bentum, M J; Bernardi, G; Best, P; Bonafede, A; Boonstra, A J; Brentjens, M; Brouw, W N; Bruggen, M; Butcher, H R; Ciardi, B; Garrett, M A; Gerbers, M; Gunst, A W; van Haarlem, M P; Heald, G; Hoeft, M; Holties, H; de Jong, A; Koopmans, L V E; Kuniyoshi, M; Kuper, G; Loose, G M; Maat, P; Masters, J; McKean, J P; Meulman, H; Mevius, M; Munk, H; Noordam, J E; Orru, E; Paas, H; Pandey-Pommier, M; Pandey, V N; Pizzo, R; Polatidis, A; Reich, W; Rottgering, H; Sluman, J; Steinmetz, M; Sterks, C G M; Tagger, M; Tang, Y; Tasse, C; Vermeulen, R; van Weeren, R J; Wijnholds, S J; Yatawatta, S

    2012-01-01

    Dispersion in the interstellar medium is a well known phenomenon that follows a simple relationship, which has been used to predict the time delay of dispersed radio pulses since the late 1960s. We performed wide-band simultaneous observations of four pulsars with LOFAR (at 40-190 MHz), the 76-m Lovell Telescope (at 1400 MHz) and the Effelsberg 100-m Telescope (at 8000 MHz) to test the accuracy of the dispersion law over a broad frequency range. In this paper we present the results of these observations which show that the dispersion law is accurate to better than 1 part in 100000 across our observing band. We use this fact to constrain some of the properties of the ISM along the line-of-sight and use the lack of any aberration or retardation effects to determine upper limits on emission heights in the pulsar magnetosphere. We also discuss the effect of pulse profile evolution on our observations, and the 1 implications that it could have for precision pulsar timing projects such as the detection of gravitati...

  2. Spectroscopy of Neutron-Rich 168,170Dy: Yrast Band Evolution Close to the NpNn Valence Maximum

    OpenAIRE

    Pollarolo, Giovanni

    2009-01-01

    The yrast sequence of the neutron-rich dysprosium isotope 168Dy has been studied using multi-nucleon transfer reactions following collisions between a 460-MeV 82Se beam and a 170Er target. The reaction products were identified using the PRISMA magnetic spectrometer and the gamma rays detected using the CLARA HPGe-detector array. The 2+ and 4+ members of the previously measured ground state rotational band of 168Dy have been confirmed and the yrast band extended up to 10+. A ...

  3. Spectroscopy of neutron-rich Dy-168,Dy-170: Yrast band evolution close to the NpNn valence maximum

    OpenAIRE

    Algora, Alejandro; Gadea, Andre?s; Soderstrom, P. -a; Nyberg, J.; Regan, P. H.; Angelis, G.; Ashley, S. F.; Aydin, S.; Bazzacco, D.; Casperson, R. J.; Catford, W. N.; Cederka?ll, J.; Chapman, R.; Corradi, L.; Fahlander, C.

    2010-01-01

    The yrast sequence of the neutron-rich dysprosium isotope Dy-168 has been studied using multinucleon transfer reactions following collisions between a 460-MeV Se-82 beam and an Er-170 target. The reaction products were identified using the PRISMA magnetic spectrometer and the gamma rays detected using the CLARA HPGe-detector array. The 2(+) and 4(+) members of the previously measured ground-state rotational band of Dy-168 have been confirmed and the yrast band extended up to 10(+). A tentativ...

  4. Angle-resolved x-ray photoemission from the valence bands of tungsten with high angular resolution and temperature variation

    International Nuclear Information System (INIS)

    Angle-resolved valence photoemission spectra have been obtained for W(011) and W(001) using Al K? and Mg K? excitation and with both normal and off-normal emission directions. The angular resolution was approx. 0, and thus the highest to date in this energy regime, and the temperature also was varied from 295 to 1000 K. These spectra exhibit features very strongly dependent on emission direction and temperature that can be more precisely associated with direct-transition emission from different Brillouin-zone points than in prior studies. Data obtained at different temperatures are used to deconvolute direct- and nondirect-transition components. The direct-transition components are found to include residual intensity due to nondirect transitions. The simple direct-transition model applied previously to the analysis of such data is also extended to include the effects of correlated lattice vibrations via a cylindrical broadening in k space. This model is found to describe semiquantitatively the effects of phonon-assisted nondirect transitions on spectra

  5. Degeneracy and effective mass in the valence band of two-dimensional (100)-GaAs quantum well systems

    Energy Technology Data Exchange (ETDEWEB)

    Tarquini, Vinicio, E-mail: vinicio.tarquini@wayne.edu; Knighton, Talbot; Wu, Zhe; Huang, Jian [Department of Physics and Astronomy, Wayne State University, 666 W. Hancock, Detroit, Michigan 48201 (United States); Pfeiffer, Loren; West, Ken [Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544 (United States)

    2014-03-03

    Quantum Hall measurement of two-dimensional high-mobility [??2×10{sup 6}?cm{sup 2}/(V·s)] hole systems confined in a 20?nm wide (100)-GaAs quantum well have been performed for charge densities between 4 and 5?×?10{sup 10}?cm{sup ?2} in a temperature range of 10–160 mK. The Fourier analysis of the Shubnikov-de Haas (SdH) oscillations of the magnetoresistance vs. the inverse of the magnetic field 1/B reveals a single peak, indicating a degenerate heavy hole (HH) band. The hole density p=(e/h)·f agrees with the Hall measurement result within 3%. The HH band degeneracy is understood through the diminishing spin-orbit interaction due to the low charge density and the nearly symmetric confinement. SdH oscillations fitted for 0.08?T???B???0.24?T to the Dingle parameters yield an effective mass between 0.30 and 0.50?m{sub e} in good agreement with previous cyclotron resonance results.

  6. Band structure of two-dimensional square lattice photonic crystals of circular dispersive metamaterial rods

    Science.gov (United States)

    Soltani Vala, A.; Roshan Entezar, S.; Sedghi, A. A.

    2011-06-01

    By virtue of the efficiency of the Dirichlet-to-Neumann map method, the details of the band structure of a two-dimensional square lattice photonic crystal composed of dispersive metamaterial circular rods in air background has been studied. We show that there are two flat bands at the band structure of the system for both H-polarization and E-polarization. These flat bands are created around the magnetic resonance frequency, surface plasmon frequency and magnetic surface plasmon frequency. We realized that the modes with frequencies lying above the resonance frequency behave like resonant cavity modes created in a single metallic cylindrical waveguide. While, due to the relatively large and imaginary refractive index of the metamaterial rods at the frequencies lying below the resonance frequency, the modes are localized modes with negligible penetration into the rods. Moreover, the modes are localized at the interface of the cylindrical metamaterial rods and the air background for the frequencies around the surface plasmon frequency and the magnetic surface plasmon frequency.

  7. Valence band electronic structure of V2O5 as determined by resonant soft X-ray emission spectroscopy

    International Nuclear Information System (INIS)

    Resonant soft X-ray emission (SXE) spectra have been measured for a series of excitation energies at the V L? and O K? bands of divanadium pentoxide, V2O5. In addition, a near-edge X-ray absorption fine structure (NEXAFS) spectrum at the V 2p and O 1s edges has been also recorded to aid the assignment of the features seen in the SXE data. The V L? SXE spectrum of V2O5 consists of two distinct components that can be assigned to the V 3deg-like states strongly hybridized with the O 2p?-like states and to the V 3dt2g-like states weakly hybridized with the O 2p?-like states. The resonant SXE spectra recorded at photon energies close to the position of the V LIII edge revealed Raman-like features with an energy loss of 7 eV similar to charge transfer states previously observed by Schmitt et al. [T. Schmitt, L.-C. Duda, M. Matsubara, M. Mattesini, M. Klemm, A. Augustsson, J.-H. Guo, T. Uozumi, S. Horn, R. Ahuja, A. Kotani, J. Nordgren, Phys. Rev. B 69 (2004) 125103] for the V6O13 oxide

  8. Two-band model for halogen-bridged mixed-valence transition-metal complexes. II. Electron-electron correlations and quantum phonons

    International Nuclear Information System (INIS)

    We study the effects of electron-electron interactions in halogen-bridged mixed-valence transition-metal linear-chain complexes (MX chains) applying a simple 3/4-filled two-band discrete tight-binding (extended) Peierls-Hubbard model with both on-site and intersite electron-phonon couplings. We employ a variety of methods: perturbation theory, Hartree-Fock approximation, and exact diagonalization in the limit of classical adiabatic phonons, and a variational approach allowing for a finite phonon frequency, i.e., quantum phonons and isotope effect. This variety of methods has proved necessary to obtain a complete picture, due to the structural richness of this model. We investigate the competition between the electron-electron and electron-phonon interactions in a wide range of parameter regimes for both ground and excited states. We focus on values relevant to the MX chains, probing the experimental variation as X and M are varied among X=Cl, Br, and I and M=Pt, Pd, and Ni (spanning electron-phonon-interaction-dominated to electron-electron-interaction-dominated materials)

  9. Band dispersion and temperature dependence of the HOMO and LUMO photoemission features of alkali intercalated C60

    International Nuclear Information System (INIS)

    Full text: Here we report on the temperature dependent phonon-broadening of the HOMO and LUMO photoemission features in alkali metal intercalated fullerides, including C60, K6C60, Cs6C60, K4C60 and Cs4C60. Compounds with different alkali metal stoichiometry (different C60 electron filling) show different temperature behaviours that may be related to differences in the electron phonon coupling constant (?). In particular we have estimated a ratio ?(C60+)/ ?(C60-) 1.7 ± 0.3, in agreement with theoretical predictions.We will also show angle resolved photoemission measurements of the band dispersion in bcc K6C60 and fcc K3C60. While the dispersion of the filled LUMO-derived bands near the Fermi level in K3C60, as measured at 30 K, is less than 100 meV along the two main symmetry directions of the (111) surface (i.e. about a factor of 2 less than expected), the band dispersion of both LUMO and HOMO derived bands in K6C60 compares well with calculations. Possible reasons for this difference will be discussed and the band dispersion of these 'bulk' intercalated compounds will be compared with the band dispersion measured for C60 monolayers on Ag surfaces

  10. I-band-like non-dispersive inter-shell interaction induced Raman lines in the D band region of double-walled carbon nanotubes

    OpenAIRE

    Gyimesi, Bálint; Koltai, János; Zólyomi, Viktor; Kürti, Jen?

    2014-01-01

    Non-dispersive, inter-layer interaction induced Raman peaks (I bands) -- in the region of the D band -- have been observed recently for bilayer graphene, when the two layers were rotated with respect to each other. Here, similar observations for double-walled carbon nanotubes (DWCNTs) are theoretically predicted. The prediction is based on double resonance theory, involving non-zone-centered phonons, and the effect of disorder is replaced by interaction between the two tubes.

  11. I-band-like non-dispersive inter-shell interaction induced Raman lines in the D-band region of double-walled carbon nanotubes

    Science.gov (United States)

    Gyimesi, Bálint; Koltai, János; Zólyomi, Viktor; Kürti, Jen?

    2015-02-01

    Non-dispersive, inter-layer interaction induced Raman peaks (I bands)—in the region of the D band—have been observed recently for bilayer graphene, when the two layers were rotated with respect to each other. Here, similar observations for double-walled carbon nanotubes are theoretically predicted. The prediction is based on double resonance theory, involving non-zone-centered phonons, and the effect of disorder is replaced by interaction between the two tubes.

  12. Highly birefringent photonic crystal fiber with ultra-flattened negative dispersion over S + C + L + U bands

    DEFF Research Database (Denmark)

    Habib, Selim; Khandker, Emran

    2015-01-01

    We present a new cladding design for photonic crystal fiber (PCF) on a decagonal structure to simultaneously achieve ultra-flattened large negative dispersion and ultrahigh birefringence. Numerical results confirm that the proposed PCFexhibits ultra-flattened large negative dispersion over the S + C + L + U wavelength bands and average dispersion of about ?558.96 ps?nm?km with absolute dispersion variation of 9.7 ps?nm?km from 1460 to 1675 nm (215 nm bandwidth). Moreover, ultrahigh birefringence of 0.0299 is also achieved at a 1500 nm wavelength. © 2015 Optical Society of America

  13. Highly birefringent photonic crystal fiber with ultra-flattened negative dispersion over S??+??C??+??L??+??U bands.

    Science.gov (United States)

    Selim Habib, Md; Khandker, Emran

    2015-04-01

    We present a new cladding design for photonic crystal fiber (PCF) on a decagonal structure to simultaneously achieve ultra-flattened large negative dispersion and ultrahigh birefringence. Numerical results confirm that the proposed PCF exhibits ultra-flattened large negative dispersion over the S+C+L+U wavelength bands and average dispersion of about -558.96??ps/nm/km with absolute dispersion variation of 9.7??ps/nm/km from 1460 to 1675 nm (215 nm bandwidth). Moreover, ultrahigh birefringence of 0.0299 is also achieved at a 1500 nm wavelength. PMID:25967190

  14. Analysis of the valence band photoemission spectrum of $Sr_{2}CuO_{2}Cl_{2}$ along the high-symmetry directions

    CERN Document Server

    Hayn, R; Yushankhai, V Yu; Haffner, S; Dürr, C; Knupfer, M; Krabbes, G; Golden, M; Fink, J; Eschrig, H; Singh, D J; Hien, N T; Menovsky, A A; Jung, C; Reichardt, G; Jung, Ch.

    1999-01-01

    Band structure calculations have been used to identify the different bands contributing to the polarisation-dependent photoemission spectra of the undoped model cuprate Sr$_2$CuO$_2$Cl$_2$ at the high-symmetry points of the CuO$_2$ plane $\\Gamma$, $(\\pi/a,0)$ and $(\\pi/a,\\pi/a)$ and along the high-symmetry directions $\\Gamma - (\\pi/a,\\pi/a)$ and $\\Gamma - (\\pi/a,0)$. Results from calculations within the local density approximation (LDA) have been compared with calculations taking into account the strong electron correlations by LDA+U, with the result that the experimental order of energy levels at the high-symmetry points is better described by the LDA+U calculation than by the simple LDA. All the main peaks in the photoemission spectra at the high symmetry points could be assigned to different Cu 3$d$ and O 2$p$ orbitals which we have classified according to their point symmetries. The dispersions along the high-symmetry directions were compared with an 11-band tight-binding model which was fitted both to th...

  15. The graphite core valence valence Auger spectrum

    Science.gov (United States)

    Calliari, L.; Speranza, G.; Lascovich, J. C.; Santoni, A.

    2002-04-01

    The graphite core-valence-valence (CVV) Auger spectrum is analysed, within a one-particle approximation, by comparison to the X-ray excited valence band (VB) photoemission spectrum, whose structure is well understood in terms of the graphite density of states (DOS). The aim is to identify the electron states originating the components into which the CVV spectrum is resolved by double differentiation. Contributions assigned to self-folds of VB photoemission features and hence due to transitions coupling electrons from the same DOS feature, dominate the spectrum away from the middle region, while folds between different features are important in the middle region. A single particle approximation proves to be adequate to account for the low binding energy, mostly p-like, part of the spectrum. It brakes down however in the high binding energy, mainly s-like, region where spectral distortion is ascribed to a nonnegligible (?2 eV) Coulomb repulsion between final state holes of s-symmetry.

  16. Tunable stop-band hollow waveguide Bragg reflectors with tapered air core for adaptive dispersion-compensation

    Science.gov (United States)

    Sakurai, Yasuki; Matsutani, Akihiro; Koyama, Fumio

    2006-03-01

    We propose a tunable stop-band hollow waveguide Bragg reflector with a variable tapered air core for an adjustable dispersion-compensation device. The tapered air-core structure gives us chirped Bragg reflection. The precise control of tapered air-core thickness and angle enables us to achieve the dynamic tuning of both stop-band width and center wavelength of Bragg reflection. We demonstrate center-wavelength tuning of 20.1nm corresponding to 1.3% of propagation constant change and stop-band expansion up to 5nm. Also, we demonstrate dispersion tuning operation either in negative or positive dispersion ranges with delay-time difference of about 10ps.

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

    OpenAIRE

    Skemer, A.; P. Hinz; Hoffmann, W; Close, L.; Kendrew, S.; Mathar, R.; Stuik, R; Greene, T; WOODWARD, C; Kelley, M.

    2009-01-01

    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 spect...

  18. Band splitting and Modal Dispersion induced by Symmetry braking in Coupled-Resonator Slow-Light Waveguide Structures

    CERN Document Server

    Scheuer, Jacob

    2009-01-01

    We study the dispersion relations in slow-light waveguide structures consisting of coupled microdisk resonators. A group theoretical analysis of the symmetry properties of the propagating modes reveals an interesting phenomenon: The degeneracy of the CW and CCW rotating modes is removed, giving rise to two distinct transmission bands. This effect induces symmetry-based dispersion which may limit usable bandwidth of such structures. The properties of this band splitting and its impact on CROW performance for optical communications are studied in detail.

  19. 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

  20. Weakly nonlinear dispersion and stop-band effects for periodic structures

    DEFF Research Database (Denmark)

    Sorokin, Vladislav; Thomsen, Jon Juel

    Continua and structures composed of periodically repeated elements (cells) are used in many fields of science and technology. Examples of continua are composite materials, consisting of alternating volumes of substances with different properties, mechanical filters and wave guides. Examples of engineering periodic structures include some building frames, bridge trusses, cranes, railway tracks, and compound pipes. Thus dynamic analysis of spatially periodic structures is relevant for many applications, and attracts much attention. An essential feature of periodic structures is the presence of frequency band-gaps, i.e. frequency ranges in which elastic waves cannot propagate. Most existing analytical methods in the field are based on Floquet theory [1]; e.g. this holds for the classical Hill’s method of infinite determinants [1,2], and themethod of space-harmonics [3]. However, application of these methods for studying nonlinear problems isimpossible or cumbersome, since Floquet theory is applicable only for linear systems. Thus the nonlinear effects for periodic structures are not yet fully uncovered, while at the same time applications may demand effects of nonlinearity on structural response to be accounted for.The paper deals with analytically predicting dynamic response for nonlinear elastic structures with a continuous periodic variation in structural properties. Specifically, for a Bernoulli-Euler beam with aspatially continuous modulation of structural properties in the axial direction, not necessarily small, we consider the effects of weak nonlinearity on the dispersion relation and frequency band-gaps. A novel approach, the Method of Varying Amplitudes [4], is employed. This approach is inspired by the method of direct separation of motions [5], and may be considered a natural continuation of the classical methods of harmonic balance [2] and averaging [6]. It implies representing a solution in the form of a harmonic serieswith varying amplitudes, but, in contrast to averaging methods, the amplitudes are not required to varyslowly. The approach is strongly related also to Hill’s method of infinite determinants [1,2], and to the method of space-harmonics [3]. As a result, a shift of band-gaps to a higher frequency range is revealed,while the width of the band-gaps appears relatively insensitive to (weak) nonlinearity. The results are validated by numerical simulation, and explanations of the effects suggested. The work is carried out with financial support from the Danish Council for Independent Research and COFUND: DFF – 1337-00026

  1. Intermediate valence

    International Nuclear Information System (INIS)

    This chapter is divided in three sections. The first one contains an introduction. Section 2 is devoted to the impurity problem, which is better understood from the theoretical point of view. In section 2.1 the Hamiltonian for an impurity in jellium fluctuating between two realistic valence configurations is derived. In section 2.2 the 'Bethe ansatz' technique is briefly reviewed. Using this technique the main thermodynamic properties of certain impurity problems were calculated exactly. In section 2.3 the ground state of the Hamiltonian in the impurity limit is studied, particularly for those cases for which no exact solution exists, using exact diagonalization and the Lanczos method. In section 3, intermediate valence compounds are studied, with particular emphasis in the peculiar properties of TmSe and its alloys. The periodic Hamiltonian is discussed in section 3.1. In section 3.2 the magnetic order of Tm compounds is studied, and the effects of temperature and the antiferromagnetic density of states are considered in section 3.3. (Author)

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

    Energy Technology Data Exchange (ETDEWEB)

    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

    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.

  3. Deduction of the chemical state and the electronic structure of Nd2Fe14B compound from X-ray photoelectron spectroscopy core-level and valence-band spectra

    International Nuclear Information System (INIS)

    Characterization of chemical state and electronic structure of the technologically important Nd2Fe14B compound is attractive for understanding the physical nature of its excellent magnetic properties. X-ray photoelectron spectroscopy (XPS) study of such rare-earth compound is important and also challenging due to the easy oxidation of surface and small photoelectron cross-sections of rare-earth 4f electrons and B 2p electrons, etc. Here, we reported an investigation based on XPS spectra of Nd2Fe14B compound as a function of Ar ion sputtering time. The chemical state of Fe and that of B in Nd2Fe14B compound can be clearly determined to be 0 and ?3, respectively. The Nd in Nd2Fe14B compound is found to have the chemical state of close to +3 instead of +3 as compared with the Nd in Nd2O3. In addition, by comparing the valence-band spectrum of Nd2Fe14B compound to that of the pure Fe, the contributions from Nd, Fe, and B to the valence-band structure of Nd2Fe14B compound is made more clear. The B 2p states and B 2s states are identified to be at ?11.2 eV and ?24.6 eV, respectively, which is reported for the first time. The contribution from Nd 4f states can be identified both in XPS core-level spectrum and XPS valence-band spectrum. Although Nd 4f states partially hybridize with Fe 3d states, Nd 4f states are mainly localized in Nd2Fe14B compound.

  4. Band structure of boron doped carbon nanotubes

    CERN Document Server

    Wirtz, L; Wirtz, Ludger; Rubio, Angel

    2003-01-01

    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.

  5. Highly birefringent broadband-dispersion-compensating photonic crystal fibre over the E + S + C + L + U wavelength bands

    Science.gov (United States)

    Habib, Md. Selim; Rana, Md. Shohel; Moniruzzaman, Md.; Ali, Md. Sharafat; Ahmed, N.

    2014-10-01

    The key features of this manuscript include a hybrid design of a square-core octagonal-lattice photonic crystal fibre with only circular air holes that exhibits high birefringence and broadband dispersion compensation covering the E, S, C, L, and U communication bands (1360-1675 nm) and a statistical comparison of the proposed design with some other recently proposed designs. A numerical simulation showed a negative dispersion coefficient in the range of approximately -134 to -385 ps/(nm km) over E and U bands with a relative dispersion slope (RDS), which is equal to that of a single-mode fibre (SMF, approximately 0.0036 nm-1) and a birefringence in the order of 2.13 × 10-2 at the operating wavelength of 1.55 ?m. Because sensing applications require a highly birefringent fibre, statistical correlations between the birefringence and different parameters were investigated. Moreover, the effective area, residual dispersion, effective dispersion, and confinement loss associated with the proposed design are also reported.

  6. CALIBRATING STELLAR VELOCITY DISPERSIONS BASED ON SPATIALLY RESOLVED H-BAND SPECTRA FOR IMPROVING THE MBH-?* RELATION

    International Nuclear Information System (INIS)

    To calibrate stellar velocity dispersion measurements from optical and near-IR stellar lines, and to improve the black hole mass (MBH)-stellar velocity dispersion (?*) relation, we measure ?* based on high-quality H-band spectra for a sample of 31 nearby galaxies, for which dynamical MBH is available in the literature. By comparing velocity dispersions measured from stellar lines in the H-band with those measured from optical stellar lines, we find no significant difference, suggesting that optical and near-IR stellar lines represent the same kinematics and that dust effect is negligible for early-type galaxies. Based on the spatially resolved rotation and velocity dispersion measurements along the major axis of each galaxy, we find that a rotating stellar disk is present for 80% of galaxies in the sample. For galaxies with a rotation component, ?* measured from a single aperture spectrum can vary by up to ?20%, depending on the size of the adopted extraction aperture. To correct for the rotational broadening, we derive luminosity-weighted ?* within the effective radius of each galaxy, providing uniformly measured velocity dispersions to improve the MBH-?* relation.

  7. Azimuthal anisotropy beneath southern Africa from very broad-band surface-wave dispersion measurements

    Science.gov (United States)

    Adam, Joanne M.-C.; Lebedev, Sergei

    2012-10-01

    Seismic anisotropy within the lithosphere of cratons preserves an important record of their ancient assembly. In southern Africa, anisotropy across the Archean Kaapvaal Craton and Limpopo Belt has been detected previously by observations of SKS-wave splitting. Because SKS-splitting measurements lack vertical resolution, however, the depth distribution of anisotropy has remained uncertain. End-member interpretations invoked the dominance of either anisotropy in the lithosphere (due to the fabric formed by deformation in Archean or Palaeoproterozoic orogenies) or that in the asthenosphere (due to the fabric formed by the recent plate motion), each with significant geodynamic implications. To determine the distribution of anisotropy with depth, we measured phase velocities of seismic surface waves between stations of the Southern African Seismic Experiment. We applied two complementary measurement approaches, very broad-band cross-correlation and multimode waveform inversion. Robust, Rayleigh- and Love-wave dispersion curves were derived for four different subregions of the Archean southern Africa in a period range from 5 s to 250-400 s (Rayleigh) and 5 s to 100-250 s (Love), depending on the region. Rayleigh-wave anisotropy was determined in each region at periods from 5 s to 150-200 s, sampling from the upper crust down to the asthenosphere. The jackknife method was used to estimate uncertainties, and the F-test to verify the statistical significance of anisotropy. We detected strong anisotropy with a N-S fast-propagation azimuth in the upper crust of the Limpopo Belt. We attribute it to aligned cracks, formed by the regional, E-W extensional stress associated with the southward propagation of the East African Rift. Our results show that it is possible to estimate regional stress from short-period, surface wave anisotropy, measured in this study using broad-band array recordings of teleseismic surface waves. Rayleigh-wave anisotropy at 70-120 s periods shows that the fabric within the deep mantle lithosphere of the Limpopo Belt and northern Kaapvaal Craton is aligned parallel to the Archean-Palaeoproterozoic sutures at block boundaries. This confirms that the fabric within the lithosphere created by pervasive ancient deformation is preserved to this day. Suture-parallel fabric is absent, however, in the deep lithosphere of the western Kaapvaal Craton, suggesting that it was not reworked in the collision with the craton's core, either due to its mechanical strength or because the deformation mechanism was different from those that operated in the north. Anisotropy at periods greater than 120-130 s shows fast directions parallel to the plate motion and indicates shear wave anisotropy in the asthenosphere. The depth distribution of anisotropy revealed by surface wave measurements comprises elements of both end-member models proposed previously: anisotropy in the asthenosphere shows fast-propagation directions parallel to the plate motion; anisotropy in the Limpopo and northern Kaapvaal lithosphere shows fast directions parallel to the Archean-Palaeoproterozoic sutures. The distribution of SKS-splitting orientations across southern Africa reflects anisotropic fabric both within the lithosphere (dominating the splitting beneath the Limpopo Belt and northern Kaapvaal Craton) and within the asthenosphere (dominating beneath the western Kaapvaal Craton).

  8. DISPERSAL AND MORTALITY OF RED-SHOULDERED HAWKS BANDED IN OHIO

    Science.gov (United States)

    We banded nestling red-shouldered hawks (Buteo lineatus) in southwestern Ohio and northern Kentucky (SW OHIO, hereafter) to examine movements and determine causes of mortality in this suburban population. For comparison, we examined band recovery records for nestling red-shoulde...

  9. Wide-band and Air Dispersion Effecting the ABCD Algorithm of Phase-Recovery in Long-baseline Interferometry

    CERN Document Server

    Mathar, R J

    2006-01-01

    Long-baseline interferometry detects fringes created by superposition of two beams of light collected by two telescopes pointing into a common direction. The external path difference generated by pointing away from the zenith is commonly compensated by adding a variable optical path length (delay) through air for one beam such that the optical path difference between the beams remains close to zero near the detector. The ABCD formula assigns a (wrapped) phase to the amplitudes A to D of an interference pattern shifted by multiples of 90 degrees in phase. We study the interplay between a wide band pass of the optics and the dispersion of the air in the compensating delay, which leads to small deviations between the ABCD phase and the reduced, monochromatic group-delay representation of the wave packets. In essence, this adds dispersion to the effects that have been discussed for evacuated interferometers (telescopes in space) before [J. Opt. Soc. Am. A 22 (2005) 2774].

  10. The anomalous dispersion of the disorder-induced and the second-order Raman Bands in Carbon Nanotubes

    Scientific Electronic Library Online (English)

    M. A., Pimenta; E. B., Hanlon; A., Marucci; P., Corio; S. D. M., Brown; S. A., Empedocles; M. G., Bawendi; G., Dresselhaus; M. S., Dresselhaus.

    2000-06-01

    Full Text Available In this work we have studied the dispersion of the disorder-induced (D) and the second-order (G') Raman bands in single wall carbon nanotubes using several laser excitation energies (E laser) in the range 1.5-3.0 eV. An anomalous step-like behavior was observed in the E laser dependence of the G'-ba [...] nd frequency. This result is interpreted as a manifestation of the one-dimensional (1D) behavior of the phonon spectrum in carbon nanotubes.

  11. Properties of bands rolled from nickel- and copper powders containing dispersion oxides

    International Nuclear Information System (INIS)

    The effect of various kinds was studied of treatment on the physicomechanical properties of bands rolled from nickel and copper powders containing oxides, 3% each (by mass): SiO2, ?-Al2O3, ZrO2, HfO2. A combination of cold compression with intermediate sintering produced high-density bands of precipitation-strengthened materials, which showed high mechanical properties over a wide range of test temperatures

  12. Intermolecular band dispersion of quasi-single crystalline organic semiconductor monolayer measured by angle-resolved photoemission spectroscopy

    Science.gov (United States)

    Ohtomo, Manabu; Shimada, Toshihiro; Hasegawa, Tetsuya

    2010-03-01

    Band structure of organic semiconductors is important knowledge to improve the molecular design. Angle-Resolved Photoemission Spectroscopy (ARPES) studies using highly conductive single domain samples grown in-situ is the most direct technique. In this study, we developed a novel method to grow quasi-single crystalline monolayer on conductive substrate and electronic structure was investigated. As a template for orientation control, we used a step-bunched Si(111) substrate with dangling bond termination. In case of pentacene, it was confirmed that the crystal is quasi-single crystal with 2.2^o rotated twins. The band dispersion was identical to that of thin-film phase. The effective mass and transfer integrals are evaluated using two-dimensional tight binding fit and compared with band calculations [1]. We also report the growth of 2,7-Dipheny[1]benzothieno[3,2-b]benzothiophene (DPh-BTBT) [2] on Bi-Si substrate and compare discuss its band structure. [4pt] [1] M.Ohtomo et al., APL 95, 123308 (2009).[0pt] [2] K.Takimiya, JACS 128, 3044 (2006).

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1994-08-01

    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.

  14. A multiple-relaxation-time lattice-boltzmann model for bacterial chemotaxis: effects of initial concentration, diffusion, and hydrodynamic dispersion on traveling bacterial bands.

    Science.gov (United States)

    Yan, Zhifeng; Hilpert, Markus

    2014-10-01

    Bacterial chemotaxis can enhance the bioremediation of contaminants in aqueous and subsurface environments if the contaminant is a chemoattractant that the bacteria degrade. The process can be promoted by traveling bands of chemotactic bacteria that form due to metabolism-generated gradients in chemoattractant concentration. We developed a multiple-relaxation-time (MRT) lattice-Boltzmann method (LBM) to model chemotaxis, because LBMs are well suited to model reactive transport in the complex geometries that are typical for subsurface porous media. This MRT-LBM can attain a better numerical stability than its corresponding single-relaxation-time LBM. We performed simulations to investigate the effects of substrate diffusion, initial bacterial concentration, and hydrodynamic dispersion on the formation, shape, and propagation of bacterial bands. Band formation requires a sufficiently high initial number of bacteria and a small substrate diffusion coefficient. Uniform flow does not affect the bands while shear flow does. Bacterial bands can move both upstream and downstream when the flow velocity is small. However, the bands disappear once the velocity becomes too large due to hydrodynamic dispersion. Generally bands can only be observed if the dimensionless ratio between the chemotactic sensitivity coefficient and the effective diffusion coefficient of the bacteria exceeds a critical value, that is, when the biased movement due to chemotaxis overcomes the diffusion-like movement due to the random motility and hydrodynamic dispersion. PMID:25223537

  15. The higher excited electronic states and spin-orbit splitting of the valence band in three-dimensional assemblies of close-packed ZnSe and CdSe quantum dots in thin film form

    International Nuclear Information System (INIS)

    Optical properties of as-deposited and annealed thin films composed of three-dimensional arrays of sphalerite-type ZnSe and CdSe quantum dots (QDs), synthesized by chemical deposition, were investigated. Neglecting the S-D mixing of hole states, the lowest 'band to band' transitions in very small nanoclusters and in bulk-like clusters may be assigned as 1S?1S and 1S??1S, and are split by spin-orbit (SO) splitting energy of the bulk material-?. The splitting energy between these transitions was found to be insensitive to QD size variations, which could be explained assuming that 1S hole states arising from valence band ?7 and ?8 components do not mix with higher angular momentum states and shift together to higher energies coupled via the isotropic hole mass. This implies significant difference between the SO splitting energies in the two semiconductors. Accounting for S-D mixing of hole states, the observed transitions may be attributed to the fundamental ground state-(1S3/2, 1Se) and the ground state-(1S1/2, 1Se) ones. The observed 'splittings' thus do not correspond exactly to SO splitting energy in both semiconductors, but are complex functions of it, as exact position of each hole energy level depends, besides on ?, also on other material-characteristic parameters. - Graphical abstract: Accounting for S-D mixing of hole states, the observed optical transitions in very small sphall transitions in very small sphalerite-type ZnSe and CdSe nanoclusters are attributed to the ground state-(1S3/2, 1Se) and the ground state-(1S1/2, 1Se). The 'splittings' do not correspond to SO splitting energy, but are complex functions of it

  16. Optical evidence of strong coupling between valence-band holes and d-localized spins in Zn1-xMnxO.

    Czech Academy of Sciences Publication Activity Database

    Sokolov, V.I.; Druzhinin, A.V.; Gruzdev, N.B.; Dejneka, Alexandr; Churpita, Olexandr; Hubi?ka, Zden?k; Jastrabík, Lubomír; Trepakov, Vladimír

    2010-01-01

    Ro?. 81, ?. 15 (2010), 153104/1-153104/4. ISSN 1098-0121 R&D Projects: GA ?R GC202/09/J017; GA AV ?R KJB100100703; GA AV ?R KAN301370701; GA MŠk(CZ) 1M06002 Institutional research plan: CEZ:AV0Z10100522 Keywords : Zn 1-x Mn x O thin films * absorption edge * localized Zhang- Rice -type state into the band gap Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.772, year: 2010

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

    Directory of Open Access Journals (Sweden)

    Otto Blehr

    1997-04-01

    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.

  18. Dispersive effects in the excitation of the ground-state rotational band of deformed nuclei by medium energy protons

    International Nuclear Information System (INIS)

    The effects of long-range correlations on high-energy elastic and inelastic proton-nucleus scattering are investigated using a coupled-channel (CC) formalism where dispersive effects, i.e. virtual excitations and de-excitations of the nucleus during the scattering process, are taken into account. When treated to all orders, this CC approach is completely equivalent to the Glauber multiple scattering model, whereas it reduces to the DWIA when the coupling between channels is neglected. In 12C the results of the CC formalism where only a finite number of collective channels are explicitly treated are compared with those obtained in a full Glauber calculation. This permits one to get a clear appreciation of the importance of the various sequential processes. In addition it sheds light on the influence of those channels which have been omitted. This CC approach is then applied to investigate the excitation of the ground-state rotational band in the deformed samarium isotopes, 152Sm and 154Sm, by 1 GeV protons. It appears that the elastic scattering on deformed nuclei is only weakly affected by dispersive corrections, at lease for momentum transfer less than 2 fm-1. In contrast, inelastic scattering to the 2+, 4+ and 6+ rotational states proceeds not only by direct transitions, but includes also crucial multi-step contributions which strongly affect the differential cross sections. (Auth.)fferential cross sections. (Auth.)

  19. Analysis of dispersion and attenuation of surface waves in poroelastic media in the exploration-seismic frequency band

    Science.gov (United States)

    Zhang, Y.; Xu, Y.; Xia, J.

    2011-01-01

    We analyse dispersion and attenuation of surface waves at free surfaces of possible vacuum/poroelastic media: permeable-'open pore', impermeable-'closed pore' and partially permeable boundaries, which have not been previously reported in detail by researchers, under different surface-permeable, viscous-damping, elastic and fluid-flowing conditions. Our discussion is focused on their characteristics in the exploration-seismic frequency band (a few through 200 Hz) for near-surface applications. We find two surface-wave modes exist, R1 waves for all conditions, and R2 waves for closed-pore and partially permeable conditions. For R1 waves, velocities disperse most under partially permeable conditions and least under the open-pore condition. High-coupling damping coefficients move the main dispersion frequency range to high frequencies. There is an f1 frequency dependence as a constant-Q model for attenuation at high frequencies. R1 waves for the open pore are most sensitive to elastic modulus variation, but least sensitive to tortuosities variation. R1 waves for partially permeable surface radiate as non-physical waves (Im(k) < 0) at low frequencies. For R2 waves, velocities are slightly lower than the bulk slow P2 waves. At low frequencies, both velocity and attenuation are diffusive of f1/2 frequency dependence, as P2 waves. It is found that for partially permeable surfaces, the attenuation displays -f1 frequency dependence as frequency increasing. High surface permeability, low-coupling damping coefficients, low Poisson's ratios, and low tortuosities increase the slope of the -f1 dependence. When the attenuation coefficients reach 0, R2 waves for partially permeable surface begin to radiate as non-physical waves. ?? 2011 The Authors Geophysical Journal International ?? 2011 RAS.

  20. Band Structures of Plasmonic Polarons

    Science.gov (United States)

    Caruso, Fabio; Lambert, Henry; Giustino, Feliciano

    2015-03-01

    In angle-resolved photoemission spectroscopy (ARPES), the acceleration of a photo-electron upon photon absorption may trigger shake-up excitations in the sample, leading to the emission of phonons, electron-hole pairs, and plasmons, the latter being collective charge-density fluctuations. Using state-of-the-art many-body calculations based on the `GW plus cumulant' approach, we show that electron-plasmon interactions induce plasmonic polaron bands in group IV transition metal dichalcogenide monolayers (MoS2, MoSe2, WS2, WSe2). We find that the energy vs. momentum dispersion relations of these plasmonic structures closely follow the standard valence bands, although they appear broadened and blueshifted by the plasmon energy. Based on our results we identify general criteria for observing plasmonic polaron bands in the angle-resolved photoelectron spectra of solids.

  1. Electron Correlation and the c-axis Dispersion of Cu d_z^2: a New Band Structure for High Temperature Superconductors

    OpenAIRE

    Perry, Jason K.; Tahir-Kheli, Jamil

    1999-01-01

    Previously we showed the major effect of electron correlation in the cuprate superconductors is to lower the energy of the Cu d_x^2-y^2/O p_sigma (x^2-y^2) band with respect to the Cu d_z^2/O' p_z (z^2) band. In our 2D Hubbard model for La_1.85Sr_0.15CuO_4 (LaSCO), the z^2 band is narrow and crosses the standard x^2-y^2 band just below the Fermi level. In this work, we introduce c-axis dispersion to the model and find the z^2 band to have considerable anisotropic 3D characte...

  2. Valence Bond Entanglement Entropy

    CERN Document Server

    Alet, F; Laflorencie, N; Mambrini, M; Alet, Fabien; Capponi, Sylvain; Laflorencie, Nicolas; Mambrini, Matthieu

    2007-01-01

    We introduce for SU(2) symmetric quantum spin systems the notion of Valence Bond Entanglement Entropy as a counting of valence bond spin singlets shared by two subsystems. For a large class of antiferromagnetic systems, this quantity can be calculated via Quantum Monte Carlo simulations directly performed in the valence bond basis. We show that the Valence Bond Entanglement Entropy contains all features of the von Neumann entanglement entropy and offers, among others, the advantage of being computable in all dimensions. In one dimension, predictions for pure conformally invariant and infinite randomness fixed points are recovered. For two-dimensional Heisenberg models, we find a strict area law for a Valence Bond Solid state and an area law with multiplicative logarithmic corrections for the N\\'eel phase.

  3. Electrical properties and band structures of Pb1-x Snx Te alloys

    International Nuclear Information System (INIS)

    Both p type alloys Pb0.72Sn0.28Te and Pb0.53Sn0.47Te have been studied in the present work. The main obtained results are the following: the materials have a two-valence band structure, the first band following non-parabolic Cohen's dispersion law; at low temperatures, carriers are scattered by ionized impurities; the Coulomb potentials being screened almost completely, impurities act like neutral centers. At room temperature, scattering by acoustic modes can explain lattice mobility behavior; reversing of the thermo-power, for samples with carrier densities of about 1020 cm-3, is possibly due to inter-band scattering between both valence bands; a very simple picture of the band parameters variations as a function of alloy fraction is suggested. (author)

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

    Directory of Open Access Journals (Sweden)

    D.M.Bercha

    2003-01-01

    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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Meevasana, Warawat

    2010-05-26

    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.

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

    CERN Document Server

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

    2001-01-01

    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...

  7. Electronic band structure of magnetic bilayer graphene superlattices

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-09-28

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

  8. Valency and molecular structure

    CERN Document Server

    Cartmell, E

    1977-01-01

    Valency and Molecular Structure, Fourth Edition provides a comprehensive historical background and experimental foundations of theories and methods relating to valency and molecular structures. In this edition, the chapter on Bohr theory has been removed while some sections, such as structures of crystalline solids, have been expanded. Details of structures have also been revised and extended using the best available values for bond lengths and bond angles. Recent developments are mostly noted in the chapter on complex compounds, while a new chapter has been added to serve as an introduction t

  9. Slow-light in photonic crystal waveguides/fibers: dispersion tailoring schemes for obtaining a high group index with wide band and low GVD

    Science.gov (United States)

    Ren, Liyong; Liang, Jian; Liu, Yu; Ju, Haijuan; Yun, Maojin; Ma, Chengju; Han, Xu; Lin, Xiao; Tomita, Yasuo

    2012-03-01

    Phenomenon of slow light has long been a hot research topic due to its promising and potential applications in communication networks, signal processing, optical sensors and nonlinear interactions. Particularly, photonic crystal devices, being capable of supporting slow-light propagation, are much attractive owing to its room-temperature operation and tunable dispersion features. Among them, photonic crystal waveguides (PCWs) are specially used in compact devices, while photonic band-gap fibers (PBGFs) are usually used in short-distance propagation and high sensitive interferometers. In this paper, dispersion tailoring schemes for obtaining a high group index with the wide band and low group velocity dispersion (GVD) are reviewed in both PCWs and PBGFs. For the same purpose, we propose schemes for the slow-pulse propagation in PCWs based on the air-hole shifting method and in PBGFs based on the microfluid infiltration method, respectively. Simulation results using 2D plane wave expansion method and finite-difference timedomain (FDTD) method are given. Pulse distortion and design optimization are also discussed in some detail with the consideration of the practical fabrication errors. Slow-light pulse propagation in photonic crystal fiber is also demonstrated in the experiment based on stimulated Brillouin scattering.

  10. Biaxial strain-modified valence and conduction band offsets of zinc-blende GaN, GaP, GaAs, InN, InP, and InAs, and optical bowing of strained epitaxial InGaN alloys

    Science.gov (United States)

    Kent, P. R. C.; Hart, Gus L. W.; Zunger, Alex

    2002-12-01

    Using density-functional calculations, we obtain the (001) biaxial strain dependence of the valence and conduction band energies of GaN, GaP, GaAs, InN, InP, and InAs. The results are fit to a convenient-to-use polynomial and the fits provided in tabular form. Using the calculated biaxial deformation potentials in large supercell empirical pseudopotential calculations, we demonstrate that epitaxial strain reduces the InGaN alloy bowing coefficient compared to relaxed bulk alloys.

  11. Understanding core--valence--valence Auger line shapes

    International Nuclear Information System (INIS)

    Core--valence--valence (CVV) Auger spectroscopy can now be used as a local valence probe of molecular, chemisorbed and solid-state species. Analysis of Auger data has led to the discovery of localized multihole valence excitations in covalent systems, and there is evidence that these excitations may play a major role in the dissociation of large molecules and in stimulated desorption from semiconductor surfaces. The basic physics behind the CVV decay is summarized. The relative importance of factors that influence the decay amplitudes (local charge density, initial-state screening, valence nonorthogonality, and configuration mixing) and the Auger energies (independent vs coupled final-state holes) is explored

  12. The effect of temperature and angle of incidence on photonic band gap in a dispersive Si-based one dimensional photonic crystal

    International Nuclear Information System (INIS)

    The effect of temperature and angle of incidence on photonic band gaps (PBGs) in a dispersive Si-based one dimensional photonic crystal consisting of alternate layers of silicon and air has been investigated. More physically realistic situation is considered by taking the refractive index of silicon layers as a function of temperature and wavelength. The effect of temperature and angle of incidence on reflection spectra of proposed structure for TE polarization has also been studied. The PBG can be tuned by varying the temperature of the geometry or by changing the angle of incidence. The propagation characteristics of the proposed structure are analyzed using transfer matrix method

  13. The effect of temperature and angle of incidence on photonic band gap in a dispersive Si-based one dimensional photonic crystal

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Vipin [Department of Physics, Digamber Jain (P.G.) College, Baraut 250611 (India); Suthar, B., E-mail: bhuvneshwer@gmail.com [Department of Physics, Government Engineering College, Bikaner 334004 (India); Kumar, Arun [AITTM, Amity University, Noida (India); Singh, Kh.S. [Department of Physics, Digamber Jain (P.G.) College, Baraut 250611 (India); Bhargava, A. [Nanophysics Laboratory, Department of Physics, Government Dungar College, Bikaner 334001 (India)

    2013-05-01

    The effect of temperature and angle of incidence on photonic band gaps (PBGs) in a dispersive Si-based one dimensional photonic crystal consisting of alternate layers of silicon and air has been investigated. More physically realistic situation is considered by taking the refractive index of silicon layers as a function of temperature and wavelength. The effect of temperature and angle of incidence on reflection spectra of proposed structure for TE polarization has also been studied. The PBG can be tuned by varying the temperature of the geometry or by changing the angle of incidence. The propagation characteristics of the proposed structure are analyzed using transfer matrix method.

  14. Design Of Near Zero Ultra-Flattened Chromatic Dispersion Highly Non Linear Holey Fiber In Tele Communication Band

    OpenAIRE

    Mahbubur Rahman; A.H. Md. Mostazir; Alam, M. A.; Md. Samiul Habib

    2012-01-01

    We propose a four-ring hexagonal holey fiber (HF) which exhibits near zero ultra-flattened chromatic dispersion and nonlinear property simultaneously in a modest number of rings. The finite element method with perfectly matched layers boundary condition is used to investigate the guiding properties. A four ring HF with flattened dispersion of 0.85ps/nm/km from 1.14 to 1.60 µm wavelength range, 21.34W-1km-1 nonlinear coefficient and splice loss 3.82 dB at 1.55µm is numerically demonstrated.

  15. Design Of Near Zero Ultra-Flattened Chromatic Dispersion Highly Non Linear Holey Fiber In Tele Communication Band

    Directory of Open Access Journals (Sweden)

    Mahbubur Rahman

    2012-11-01

    Full Text Available We propose a four-ring hexagonal holey fiber (HF which exhibits near zero ultra-flattened chromatic dispersion and nonlinear property simultaneously in a modest number of rings. The finite element method with perfectly matched layers boundary condition is used to investigate the guiding properties. A four ring HF with flattened dispersion of 0.85ps/nm/km from 1.14 to 1.60 µm wavelength range, 21.34W-1km-1 nonlinear coefficient and splice loss 3.82 dB at 1.55µm is numerically demonstrated.

  16. Thermal stability of the HfO2/SiO2 interface for sub-0.1 ?m complementary metal-oxide-semiconductor gate oxide stacks: A valence band and quantitative core-level study by soft x-ray photoelectron spectroscopy

    Science.gov (United States)

    Barrett, N.; Renault, O.; Damlencourt, J.-F.; Martin, F.

    2004-12-01

    Synchrotron-radiation photoelectron spectroscopy is used to study the valence-band structure and the core-level photoemission spectra of HfO2 ultrathin films grown onto SiO2/Si substrates by atomic layer deposition (ALD). We determine the band offsets (valence and conduction) of HfO2 to Si as a function of postdeposition annealing treatments (under an inert N2 atmosphere or in situ in ultrahigh vacuum) and find a significant evolution, the conduction-band offset remaining larger than 1.5eV. The Si2p and the Hf4f core-level spectra give detailed information on the composition and the spatial extent of the interfacial Hf silicate layer formed between the SiO2 bottom oxide and the HfO2 ALD thin film. By a quantitative treatment of the Si2p core-level intensities, we examine the thermal stability of the interface silicate after postdeposition annealing under N2 and in situ annealing in ultrahigh vacuum (UHV), both at 800°C. The as-deposited layer gives rise to a HfO2/Hf0.35Si0.65O2/SiO2 stack with corresponding thicknesses of 0.74/0.51/0.73nm. After postdeposition annealing at 800°C in a N2 atmosphere, this becomes a HfO2/Hf0.31Si0.69O2/SiO2 stack with corresponding thicknesses of 0.71:0.58:0.91nm. In situ annealing in UHV, on the other hand, gives a HfO2/Hf0.35Si0.65O2/SiO2 stack with corresponding thicknesses of 0.65:0.70:0.76nm. The former favors an extension of both the silicate and the SiO2 interface layers, whereas the latter develops only the silicate layer.

  17. Valence Surface Electronic States on Ge(001)

    Science.gov (United States)

    Radny, M. W.; Shah, G. A.; Schofield, S. R.; Smith, P. V.; Curson, N. J.

    2008-06-01

    The optical, electrical, and chemical properties of semiconductor surfaces are largely determined by their electronic states close to the Fermi level (EF). We use scanning tunneling microscopy and density functional theory to clarify the fundamental nature of the ground state Ge(001) electronic structure near EF, and resolve previously contradictory photoemission and tunneling spectroscopy data. The highest energy occupied surface states were found to be exclusively back bond states, in contrast to the Si(001) surface, where dangling bond states also lie at the top of the valence band.

  18. Parameterization of CuIn1-xGaxSe2 (x = 0, 0.5, and 1) energy bands

    International Nuclear Information System (INIS)

    Parameterization of the electronic band structure of CuIn1-xGaxSe2 (x = 0, 0.5, and 1) demonstrates that the energy dispersions of the three uppermost valence bands [Ej(k); j = v1, v2, and v3] are strongly anisotropic and non-parabolic even very close to the ?-point valence-band maximum Ev1(0). Also the lowest conduction band Ec1(k) is anisotropic and non-parabolic for energies ? 0.05 eV above the band-gap energy. Since the electrical conductivity depends directly on the energy dispersion, future electron and hole transport simulations of CuIn1-xGaxSe2 need to go beyond the parabolic approximation of the bands. We therefore present a parameterization of the energy bands, the k-dependency of the effective electron and hole masses mj(k), and also an average energy-dependent approximation of the masses mj(E).

  19. Pressure Induced Valence Transitions in f-Electron Systems

    CERN Document Server

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

    2006-01-01

    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.

  20. Thermoelectric, band structure, chemical bonding and dispersion of optical constants of new metal chalcogenides Ba4CuGa5Q12 (Q=S, Se)

    International Nuclear Information System (INIS)

    The electronic structure and dispersion of optical constants of the Ba4CuGa5S12 and Ba4CuGa5Se12 compounds were calculated by the first-principles full-potential linearized augmented plane wave (FPLAPW) method. We employed the local density approximation (LDA), generalized gradient approximation (GGA) and Engel–Vosko GGA (EVGGA) to calculate the electronic structures, Fermi surface, thermoelectric, chemical bonding and dispersion of optical constants of these compounds. By investigating the influence of replacing S by Se, it has been found that the charge density around ‘Ga’ is greater in Ba4CuGa5Se12 than Ba4CuGa5S12. Fermi surface of Ba4CuGa5S12 consists of an electronic sheet only because there is no empty region while Ba4CuGa5Se12 contains both holes and electronic sheets because this compound contains both empty and shaded region. As we replace S by Se the heights of the peaks decreases as a results the reflectivity also decreases. It is noticed that the reflectivity is over 68% (60%) for Ba4CuGa5S12 (Ba4CuGa5Se12) compounds within the energy range studied. This implies that the material will serve as a good reflector. By replacing S by Se the figure of merit values increases from 0.97 to 1.0, which shows the good thermoelectric behavior of both compounds. - Highlights: • DFT-FPLAPW method used for calculating the properties. • For predicting the chemical bonding the charge density behavior is studied in 2D. • The optical properties were also calculated and analyzed. • The Fermi surface is composed of two bands crossing along the EF level. • The thermoelectric properties have also been calculated

  1. An experimental and theoretical study of the valence shell photoelectron spectrum of bromochlorofluoromethane

    International Nuclear Information System (INIS)

    The complete valence shell photoelectron spectrum of bromochlorofluoromethane (CHFClBr), covering the binding energy range ?10-50 eV, has been recorded using synchrotron radiation and the observed structure has been interpreted using ionization energies and relative spectral intensities computed using the third-order algebraic-diagrammatic-construction (ADC(3)) scheme for the one-particle Green's function and the outer valence Green's function (OVGF) method. The theoretical results demonstrate that the inner valence region of the photoelectron spectrum is dominated by satellite structure. Angle-resolved photoelectron spectra, recorded at selected excitation energies, have enabled the orbital assignments for the outer valence bands to be confirmed. The four outermost photoelectron bands, ascribed to the two pairs of orbitals associated with the nominally chlorine and bromine lone-pairs, exhibit characteristic angular distributions. The photon energy dependent variations in the relative photoelectron band intensities provide additional support for the orbital assignments.

  2. Effects of Optical-density and Phase Dispersion of an Imperfect Band-limited Occulting Mask on the Broadband Performance of a TPF Coronagraph

    Science.gov (United States)

    Sidiek, Erkin; Balasubramanian, Kunjithapatham

    2007-01-01

    Practical image-plane occulting masks required by high-contrast imaging systems such as the TPF-Coronagraph introduce phase errors into the transmitting beam., or, equivalently, diffracts the residual starlight into the area of the final image plane used for detecting exo-planets. Our group at JPL has recently proposed spatially Profiled metal masks that can be designed to have zero parasitic phase at the center wavelength of the incoming broadband light with small amounts of' 00 and phase dispersions at other wavelengths. Work is currently underway to design. fabricate and characterize such image-plane masks. In order to gain some understanding on the behaviors of these new imperfect band-limited occulting masks and clarify how such masks utilizing different metals or alloys compare with each other, we carried out some modeling and simulations on the contrast performance of the high-contrast imaging testbed (HCIT) at .JPL. In this paper we describe the details of our simulations and present our results.

  3. Optical band gap and refractive index dispersion parameters of As x Se70Te30- x (0? x?30 at.%) amorphous films

    Science.gov (United States)

    Aly, Kamal A.

    2010-06-01

    Amorphous As x Se70Te30- x thin films with (0? x?30 at.%) were deposited onto glass substrates by using thermal evaporation method. The transmission spectra T( ?) of the films at normal incidence were measured in the wavelength range 400-2500 nm. A straightforward analysis proposed by Swanepoel based on the use of the maxima and minima of the interference fringes has been used to drive the film thickness, d, the complex index of refraction, n, and the extinction coefficient, k. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple and DiDomenico model (WDD). Increasing As content is found to affect the refractive index and the extinction coefficient of the As x Se70Te30- x films. With increasing As content the optical band gap increases while the refractive index decreases. The optical absorption is due to allowed indirect transition. The chemical bond approach has been applied successfully to interpret the increase of the optical gap with increasing As content.

  4. Optical band gap and refractive index dispersion parameters of Asx Se70Te30-x (0 ?x ?30 at.%) amorphous films

    International Nuclear Information System (INIS)

    Amorphous Asx Se70Te30-x thin films with (0?x?30 at.%) were deposited onto glass substrates by using thermal evaporation method. The transmission spectra T(?) of the films at normal incidence were measured in the wavelength range 400-2500 nm. A straightforward analysis proposed by Swanepoel based on the use of the maxima and minima of the interference fringes has been used to drive the film thickness, d, the complex index of refraction, n, and the extinction coefficient, k. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple and DiDomenico model (WDD). Increasing As content is found to affect the refractive index and the extinction coefficient of the Asx Se70Te30-x films. With increasing As content the optical band gap increases while the refractive index decreases. The optical absorption is due to allowed indirect transition. The chemical bond approach has been applied successfully to interpret the increase of the optical gap with increasing As content. (orig.)

  5. Valence effects of sorption: laboratory control of valence state

    International Nuclear Information System (INIS)

    Estimation of the rates of migration of nuclides from nuclear waste repositories required knowledge of the interaction of these nuclides with the components of the geological formations in the path of the migration. These interactions will be dependent upon the valence state and speciation of the nuclide. If the valence state is not known, then there can be little confidence in use of the data for safety analysis. An electrochemical method of valence state control was developed which makes use of a porous electrode in a flow system containing a column of the adsorbent. By use of this method and solvent extraction analyses of the valence states, a number of reactions of interest to HLW repositories were investigated. These include the reduction of Np(V) and Tc(VII) by crushed basalt and other minerals. For the reduction of Np(V) by basalt, the experiments indicate that sorption on basalt increases with pH and that most of the Np is reduced to Np(IV). The adsorbed Np(IV) is very difficult to remove from the basalt. For the experiments with Tc(VII), the results are considerably more complicated. The results of these experiments are used to assess some of the techniques and methods currently used in safety analyses of proposed HLW repositories. Perhaps the most important consideration is that predictive modeling of valence change reactions, such as the reduction of Np(V) and Tc(VII), must be used with considerable caution, and the occurrence of such reactions should be verified as best as possible with experiments using valence state control and analyses. 13 references, 3 figures, 1 table

  6. Valency Configuration of Transition Metal Impurities in ZnO

    CERN Document Server

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

    2006-01-01

    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.

  7. Understanding intermediate-band solar cells

    OpenAIRE

    Luque Lo?pez, Antonio; Marti? Vega, Antonio; Stanley, Colin

    2012-01-01

    The intermediate-band solar cell is designed to provide a large photogenerated current while maintaining a high output voltage. To make this possible, these cells incorporate an energy band that is partially filled with electrons within the forbidden bandgap of a semiconductor. Photons with insufficient energy to pump electrons from the valence band to the conduction band can use this intermediate band as a stepping stone to generate an electron-hole pair. Nanostructured materials and certain...

  8. Molecular invariants: atomic group valence

    International Nuclear Information System (INIS)

    Molecular invariants may be deduced in a very compact way through Grassman algebra. In this work, a generalized valence is defined for an atomic group; it reduces to the Known expressions for the case of an atom in a molecule. It is the same of the correlations between the fluctions of the atomic charges qc and qd (C belongs to the group and D does not) around their average values. Numerical results agree with chemical expectation. (author)

  9. Magnetoelastic effects and magnetic anisotropy in the intermediate-valence compound YbInCu4

    International Nuclear Information System (INIS)

    YbInCu4 compound exhibits a first-order valence transition of Yb from a trivalent state to a mixed-valence state with decreasing temperature. Here we provide an overview of our recent high-field and high-pressure measurements of magnetization, thermal expansion and magnetostriction of the valence-fluctuating compound. The results are analyzed using the Kondo single-impurity model. It is shown that the change of the 4f-conduction band electron hybridization is responsible for a large modification of the physical properties of YbInCu4 at the valence transition. The volume magnetostriction is rather large for the low-temperature mixed-valence state, but strongly suppressed in the high-temperature local-moment state. From the magnetization measurements of the oriented YbInCu4 single crystal, an appreciable anisotropy was found in the susceptibility, high-field magnetization, effective moment, paramagnetic Curie temperature and critical field of the valence transition. The type of the magnetic anisotropy and the value of anisotropic magnetoelastic coupling constant do not change significantly on going from the mixed-valence to the local-moment state. The anisotropic magnetostriction and magnetic anisotropy are described well in terms of a single-ion model of the interaction of anisotropic 4f-shell of Yb ion with the crystal electric field

  10. Ohmic Losses in Valence-band Photoemission Experiments

    CERN Document Server

    Haslinger, R; Haslinger, Robert; Joynt, Robert

    2000-01-01

    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.

  11. Band-to-Band Tunneling in Carbon Nanotube Field-Effect Transistors

    Science.gov (United States)

    Appenzeller, J.; Lin, Y.-M.; Knoch, J.; Avouris, Ph.

    2004-11-01

    A detailed study on the mechanism of band-to-band tunneling in carbon nanotube field-effect transistors (CNFETs) is presented. Through a dual-gated CNFET structure tunneling currents from the valence into the conduction band and vice versa can be enabled or disabled by changing the gate potential. Different from a conventional device where the Fermi distribution ultimately limits the gate voltage range for switching the device on or off, current flow is controlled here by the valence and conduction band edges in a bandpass-filter-like arrangement. We discuss how the structure of the nanotube is the key enabler of this particular one-dimensional tunneling effect.

  12. Mixed valence model for superconductivity

    Scientific Electronic Library Online (English)

    Sven, Larsson.

    2003-12-01

    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.

  13. Electronic and thermoelectric properties of Mexican hat bands in van-der-Waals materials

    Science.gov (United States)

    Wickramaratne, Darshana; Zahid, Ferdows; Lake, Roger

    2015-03-01

    Mexican hat dispersions are relatively common in few-layer two-dimensional materials. In one to four monolayers of the group-III chalcogenides (GaS, GaSe, InS, InSe) and Bi2Se3 the valence band undergoes a band inversion from a parabolic to an inverted Mexican hat dispersion as the film thickness is reduced from bulk to a single monolayer. The band inversion is robust against changes in stacking order, omission or inclusion of spin-orbit coupling and the choice of functional. The Mexican hat dispersion results in a 1/?{ E} singularity in the two-dimensional density of states and a step-function turn on in the density of modes. The largest radius of the ring of states occurs for a single monolayer of each material. The dispersion with the largest radius coincides with the maximum power factor and ZT for a material at room temperature. Ab-initio electronic structure calculations are used with a Landauer approach to calculate the thermoelectric transport coefficients. Analytical models of the Mexican hat and the parabolic dispersions are used for comparison and analysis. Vertically biased bilayer graphene could serve as an experimental test-bed for measuring this effect since the radius of the Mexican hat band edge increases linearly with vertical electric field. Mexican hat dispersions are relatively common in few-layer two-dimensional materials. In one to four monolayers of the group-III chalcogenides (GaS, GaSe, InS, InSe) and Bi2Se3 the valence band undergoes a band inversion from a parabolic to an inverted Mexican hat dispersion as the film thickness is reduced from bulk to a single monolayer. The band inversion is robust against changes in stacking order, omission or inclusion of spin-orbit coupling and the choice of functional. The Mexican hat dispersion results in a 1/?{ E} singularity in the two-dimensional density of states and a step-function turn on in the density of modes. The largest radius of the ring of states occurs for a single monolayer of each material. The dispersion with the largest radius coincides with the maximum power factor and ZT for a material at room temperature. Ab-initio electronic structure calculations are used with a Landauer approach to calculate the thermoelectric transport coefficients. Analytical models of the Mexican hat and the parabolic dispersions are used for comparison and analysis. Vertically biased bilayer graphene could serve as an experimental test-bed for measuring this effect since the radius of the Mexican hat band edge increases linearly with vertical electric field. Support by the NSF and SRC-NRI Project 2204.001 (NSF-ECCS-1124733), FAME, one of six centers of STARnet, a SRC program sponsored by MARCO and DARPA and the use of XSEDE NSF Grant # OCI-1053575.

  14. Electronic states of valence-skipping compounds

    Science.gov (United States)

    Hase, I.; Yanagisawa, T.

    2008-03-01

    'Valence skip' means that an element leaps a particular valence state in compounds. For example, Bi forms the compounds in +3 and +5 valence states, and T1 forms in +1 and +3 valence states. In BaBiO3, the average valence of Bi is +4, but the system spontaneously brakes its crystal symmetry and forms the charge density wave (CDW) state like (Bi3+,Bi5+). This means that the effective electron-electron interaction is attractive, contrary to the well-known on-site Coulomb repulsive interaction. In the valence skip compounds, it is expected that some carrier doping can induce superconductivity with high-Tc. For example, (Ba,K) BiO3 shows high-Tc that is not plausible merely from the convectional electron-phonon mechanism. T1-doped PbTe is also considered as the superconducting compound that T1 valence fluctuates and enhances Tc. We estimated the formation energy of the CDW in BaBiO3, T1S and T1Se by evaluating the Madelung energy, in order to show the CDW state is more stable than the uniform charge state, and the valence skip is actually realized.

  15. Electronic states of valence-skipping compounds

    International Nuclear Information System (INIS)

    'Valence skip' means that an element leaps a particular valence state in compounds. For example, Bi forms the compounds in +3 and +5 valence states, and T1 forms in +1 and +3 valence states. In BaBiO3, the average valence of Bi is +4, but the system spontaneously brakes its crystal symmetry and forms the charge density wave (CDW) state like (Bi3+,Bi5+). This means that the effective electron-electron interaction is attractive, contrary to the well-known on-site Coulomb repulsive interaction. In the valence skip compounds, it is expected that some carrier doping can induce superconductivity with high-Tc. For example, (Ba,K) BiO3 shows high-Tc that is not plausible merely from the convectional electron-phonon mechanism. T1-doped PbTe is also considered as the superconducting compound that T1 valence fluctuates and enhances Tc. We estimated the formation energy of the CDW in BaBiO3, T1S and T1Se by evaluating the Madelung energy, in order to show the CDW state is more stable than the uniform charge state, and the valence skip is actually realized

  16. Indirect-direct band gap transition through electric tuning in bilayer MoS2

    International Nuclear Information System (INIS)

    We investigate the electronic properties of bilayer MoS2 exposed to an external electric field by using first-principles calculations. It is found that a larger interlayer distance, referring to that by standard density functional theory (DFT) with respect to that by DFT with empirical dispersion corrections, makes indirect-direct band gap transition possible by electric control. We show that external electric field effectively manipulates the valence band contrast between the K- and ?-valleys by forming built-in electric dipole fields, which realizes an indirect-direct transition before a semiconductor-metal transition happens. Our results provide a novel efficient access to tune the electronic properties of two-dimensional layered materials

  17. Electronic band structure of CdF2

    International Nuclear Information System (INIS)

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

  18. Plasmon excitation in valence shell photoelectron spectroscopy for PAHs

    Science.gov (United States)

    Mishra, P. M.; Avaldi, L.; Bolognesi, P.; Prince, K. C.; Richter, R.; Kadhane, U.

    2015-01-01

    The photon energy dependence of photoelectron spectra (PES) for two members of the polycyclic aromatic hydrocarbon (PAH) family namely pyrene and fluorene is studied in FUV regime (15 - 40 eV) using high-resolution synchrotron photoelectron spectrometer. The difference in outer (? dominated) and inner (? dominated) valence relative photoelectron emission cross sections as a function of photon energy identifies the region of plasmon excitation (~ 15-27 eV). This excitation mode is present in the same region for both the molecule irrespective of the difference in their structure and symmetry. The feature is observed to be independent of the details of the molecular orbital associated with the outgoing electron. The results are in contradiction to the observed in benzene for inner valence bands. With the help of OVGF/cc-pVDZ calculations, the experimental bands are assigned as per their binding energy and symmetry. The first ionization potentials are estimated to be 7.436 ± 0.015 and 7.944 ± 0.055 eV for pyrene and fluorene, respectively.

  19. Avoided valence transition in a plutonium superconductor.

    Science.gov (United States)

    Ramshaw, B J; Shekhter, Arkady; McDonald, Ross D; Betts, Jon B; Mitchell, J N; Tobash, P H; Mielke, C H; Bauer, E D; Migliori, Albert

    2015-03-17

    The d and f electrons in correlated metals are often neither fully localized around their host nuclei nor fully itinerant. This localized/itinerant duality underlies the correlated electronic states of the high-[Formula: see text] cuprate superconductors and the heavy-fermion intermetallics and is nowhere more apparent than in the [Formula: see text] valence electrons of plutonium. Here, we report the full set of symmetry-resolved elastic moduli of PuCoGa5-the highest [Formula: see text] superconductor of the heavy fermions ([Formula: see text] = 18.5 K)-and find that the bulk modulus softens anomalously over a wide range in temperature above [Formula: see text]. The elastic symmetry channel in which this softening occurs is characteristic of a valence instability-therefore, we identify the elastic softening with fluctuations of the plutonium 5f mixed-valence state. These valence fluctuations disappear when the superconducting gap opens at [Formula: see text], suggesting that electrons near the Fermi surface play an essential role in the mixed-valence physics of this system and that PuCoGa5 avoids a valence transition by entering the superconducting state. The lack of magnetism in PuCoGa5 has made it difficult to reconcile with most other heavy-fermion superconductors, where superconductivity is generally believed to be mediated by magnetic fluctuations. Our observations suggest that valence fluctuations play a critical role in the unusually high [Formula: see text] of PuCoGa5. PMID:25737548

  20. Ab initio valence calculations in chemistry

    CERN Document Server

    Cook, D B

    1974-01-01

    Ab Initio Valence Calculations in Chemistry describes the theory and practice of ab initio valence calculations in chemistry and applies the ideas to a specific example, linear BeH2. Topics covered include the Schrödinger equation and the orbital approximation to atomic orbitals; molecular orbital and valence bond methods; practical molecular wave functions; and molecular integrals. Open shell systems, molecular symmetry, and localized descriptions of electronic structure are also discussed. This book is comprised of 13 chapters and begins by introducing the reader to the use of the Schrödinge

  1. Valence instabilities in cerium intermetallics

    International Nuclear Information System (INIS)

    The primary purpose of this investigation was to study the magnetic behaviour of cerium in intermetallic compounds, that show an IV behaviour, e.g. CeSn3. In the progress of the investigations, it became of interest to study the effect of changes in the lattice of the IV compound by substituting La or Y for Ce, thus constituting the Cesub(1-x)Lasub(x)Sn3 and Cesub(1-x)Ysub(x)Sn3 quasibinary systems. A second purpose was to examine the possibility of introducing instabilities in the valency of a trivalent intermetallic cerium compound: CeIn3, also by La and Y-substitutions in the lattice. Measurements on the resulting Cesub(1-x)Lasub(x)In3 and Cesub(1-x)Ysub(x)In3 quasibinaries are described. A third purpose was to study the (gradual) transition from a trivalent cerium compound into an IV cerium compound. This was done by examining the magnetic properties of the CeInsub(x)Snsub(3-x) and CePbsub(x)Snsub(3-x) systems. Finally a new possibility was investigated: that of the occurrence of IV behaviour in CeSi2, CeSi, and in CeGa2. (Auth.)

  2. Valence fluctuation in CeMo2Si2C

    International Nuclear Information System (INIS)

    Highlights: •Evidence for valence fluctuation of Ce ions. •XAS provides average formal LIII valence of Ce. •Kadowaki Woods ratio and Sommerfeld Wilson ratio indicate Fermi-liquid behavior. •DFT calculations reveal strong hybridization between Ce 4f and Mo 4d states. -- Abstract: We report on the valence fluctuation of Ce in CeMo2Si2C as studied by means of magnetic susceptibility ?(T), specific heat C(T), electrical resistivity ?(T) and X-ray absorption spectroscopy. Powder X-ray diffraction revealed that CeMo2Si2C crystallizes in CeCr2Si2C-type layered tetragonal crystal structure (space group P4/mmm). The unit cell volume of CeMo2Si2C deviates from the expected lanthanide contraction, indicating non-trivalent state of Ce ions in this compound. The observed weak temperature dependence of the magnetic susceptibility and its low value indicate that Ce ions are in valence fluctuating state. The formal LIII Ce valence in CeMo2Si2C????=3.14 as determined from X-ray absorption spectroscopy measurement is well below the value ?????3.4 in tetravalent Ce compound CeO2. The temperature dependence of specific heat does not show any anomaly down to 1.8 K which rules out any magnetic ordering in the system. The Sommerfeld coefficient obtained from the specific heat data is ? = 23.4 mJ/mol K2. The electrical resistivity follows the T2 behavior in the low temperature range below 35 K confirming a Fermi liquid behavior. Accordingly both the Kadowaki Woods ratio A/?2 and the Sommerfeld Wilson ratio ?(0)/? are in the range expected for Fermi-liquid systems. In order to get some information on the electronic states, we calculated the band structure within the density functional theory, eventhough this approach is not able to treat 4f electrons accurately. The non-f electron states crossing the Fermi level have mostly Mo 4d character. They provide the states with which the 4f sates are strongly hybridized, leading to the intermediate valent state

  3. Dielectric dispersion and energy band gap of Bi{sub 1.5?x}Sm{sub x}Zn{sub 0.92}Nb{sub 1.5}O{sub 6.92} solid solution

    Energy Technology Data Exchange (ETDEWEB)

    Qasrawi, A.F., E-mail: aqasrawi@atilim.edu.tr [Department of Physics, Arab-American University, Jenin, West Bank, Palestine (Country Unknown); Group of Physics, Faculty of Engineering, Atilim University, 06836 Ankara (Turkey); Mergen, A. [Metallurgical and Materials Engineering Department, Marmara University, 34722 Istanbul (Turkey)

    2014-05-01

    The optical transmittance and reflectance spectra of samarium doped bismuth–zinc–niobium-oxide (BZN) pyrochlore ceramics are investigated in the wavelength range of 200–1050 nm (200–1500 THz). The Sm content in the Bi{sub 1.5?x}Sm{sub x}Zn{sub 0.92}Nb{sub 1.5}O{sub 6.92} solid solution significantly alters the optical properties. Therefore, increasing the Sm doping ratio from x=0.10 to x=0.13 decreased the indirect forbidden energy band gap from 3.60 to 3.05 eV. In addition, above 350 THz, increasing the Sm content decreases the dielectric constant values and alters the dielectric dispersion parameters. The dielectric spectra which were evaluated in the frequency range of 200–1500 THz reflected a sharp decrease in the dielectric constant with increasing frequency down to 358 THz. The spectra reflected a resonance peak at this frequency. Such resonance spectrum is promising for technological applications as it is close to the illumination of 870 nm IR lasers that are used in optical communications. The calculated oscillator (E{sub o}) and dispersion (E{sub d}) energies near that critical range (375–425 THz) reflected an increase in both E{sub o} and E{sub d} with increasing Sm content.

  4. Gastric Banding

    Science.gov (United States)

    ... two FDA approved gastric banding devices on the market designed to treat obesity: Lap-Band Gastric Banding ... moving of the gastric band from its original position, requiring another surgery to reposition it erosion of ...

  5. On the quantum-chemical description of the atomic valence states on the basis of ab initio SCF MO calculations

    International Nuclear Information System (INIS)

    The atomic valence indices VA (doubled charge dispersions) and hybrid AOs have been calculated for molecules Li2, B2, C2, N2, and F2 using the Cade and Wahl ab initio SCF MOs and Clementi and Roetti SCF AO bases. A comparison of alternative definitions of VA has been performed

  6. Advances in Quantum dot Intermediate band Solar Cells.

    OpenAIRE

    Antoli?n Ferna?ndez, Elisa; Marti? Vega, Antonio; Garci?a-linares Fontes, Pablo; Ramiro Gonzalez, In?igo; Herna?ndez Marti?n, Estela; Farmer, C. D.; Stanley, Colin; Luque Lo?pez, Antonio

    2010-01-01

    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) transitions. The absorption of photons of that energy in IB to conduction band (CB) transitions is weak and is usually replaced by carrier escape. This mechanism is incompatible with the preservat...

  7. Composition dependent band gap and band edge bowing in AlInN: A combined theoretical and experimental study

    OpenAIRE

    Schulz, S; Caro, M.A.; Tan, L. -T.; Parbrook, P. J.; Martin, R. W.; O'Reilly, E. P.

    2013-01-01

    A combined experimental and theoretical study is presented of the band gap of AlInN, confirming the breakdown of the virtual crystal approximation (VCA) for the conduction and valence band edges. Composition dependent bowing parameters for these quantities are extracted. Additionally, composition dependent band offsets for GaN/AlInN systems are provided. We show that local strain and built-in fields affect the band edges significantly, leading to optical polarization switchi...

  8. Molybdenum Valence in Basaltic Silicate Melts

    Science.gov (United States)

    Danielson, L. R.; Righter, K.; Newville, M.; Sutton, S.; Pando, K.

    2010-01-01

    The moderately siderophile element molybdenum has been used as an indicator in planetary differentiation processes, and is particularly relevant to core formation [for example, 1-6]. However, models that apply experimental data to an equilibrium differentiation scenario infer the oxidation state of molybdenum from solubility data or from multivariable coefficients from metal-silicate partitioning data [1,3,7]. Partitioning behavior of molybdenum, a multivalent element with a transition near the J02 of interest for core formation (IW-2) will be sensitive to changes in JO2 of the system and silicate melt structure. In a silicate melt, Mo can occur in either 4+ or 6+ valence state, and Mo6+ can be either octahedrally or tetrahedrally coordinated. Here we present first XANES measurements of Mo valence in basaltic run products at a range of P, T, and JO2 and further quantify the valence transition of Mo.

  9. Laser-induced defect centers and valence state change of Mn ions in sodium borate glasses

    International Nuclear Information System (INIS)

    In this report, an ultrafast laser was used to produce persistent change of valence states of Mn ions in sodium borate glasses. Glass composition of sodium borate in this study was 85B2O3-15Na2O. We observed a broad emission at 600 nm of the transition 4T1-6A1 of doped Mn2+ ions with excitation at 325 nm in an unirradiated area. Femtosecond laser irradiation produced additional strong blue emission at 440 nm and reduced the emission intensity from Mn2+ ions. The irradiation produced the absorption band of Mn3+ at 550 nm, resulting in color change of the glass. The blue band was measured as a function of irradiation exposure for samples with various concentrations of Mn ions. The valence state change of Mn2+ to Mn3+ was suppressed in Mn and Cr codoped glasses

  10. Self-trapped exciton and core-valence luminescence in BaF2 nanoparticles

    International Nuclear Information System (INIS)

    The influence of the BaF2 nanoparticle size on the intensity of the self-trapped exciton luminescence and the radiative core-valence transitions is studied by the luminescence spectroscopy methods using synchrotron radiation. The decrease of the self-trapped exciton emission intensity at energies of exciting photons in the range of optical exciton creation (h? ? Eg) is less sensitive to the reduction of the nanoparticle sizes than in the case of band-to-band excitation, where excitons are formed by the recombination way. The intensity of the core-valence luminescence shows considerably weaker dependence on the nanoparticle sizes in comparison with the intensity of self-trapped exciton luminescence. The revealed regularities are explained by considering the relationship between nanoparticle size and photoelectron or photohole thermalization length as well as the size of electronic excitations

  11. Variable valency and yttrium ceramics ESR study

    International Nuclear Information System (INIS)

    Formulae for spin susceptibility, ESR line width and shift of resonance frequency of paramagnetic ions in a state with variable valency are derived. Agreement between temperature dependences of theoretic and experimental parameters of ESR spectra of nonsuperconducting YBa2Cu3O7 ceramic phases is ascertained. An assumption is made thta with the growth of oxygen index in YBa2Cu3Ox from 6.1, copper ion valency drops in Cu1 position and for superconducting phases of this ceramic it acquires 2Cu3Ox samples

  12. Valence electronic state density in thorium dioxide

    Directory of Open Access Journals (Sweden)

    Teterin Anton Yu.

    2008-01-01

    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.

  13. Understanding intermediate-band solar cells

    Science.gov (United States)

    Luque, Antonio; Martí, Antonio; Stanley, Colin

    2012-03-01

    The intermediate-band solar cell is designed to provide a large photogenerated current while maintaining a high output voltage. To make this possible, these cells incorporate an energy band that is partially filled with electrons within the forbidden bandgap of a semiconductor. Photons with insufficient energy to pump electrons from the valence band to the conduction band can use this intermediate band as a stepping stone to generate an electron-hole pair. Nanostructured materials and certain alloys have been employed in the practical implementation of intermediate-band solar cells, although challenges still remain for realizing practical devices. Here we offer our present understanding of intermediate-band solar cells, as well as a review of the different approaches pursed for their practical implementation. We also discuss how best to resolve the remaining technical issues.

  14. Band alignment of ultra-thin hetero-structure ZnO/TiO2 junction

    International Nuclear Information System (INIS)

    Graphical abstract: - Highlights: • Band alignment at the ZnO/TiO2 hetero-structural interface with different ZnO coating thickness was studied. • The valence band offset was decreased with increased ZnO coating layer thickness. • The interface dipole was responsible for the decreased band offset. - Abstract: The band alignment at the ZnO/TiO2 hetero-structure interface was measured by high resolution X-ray photoelectron spectroscopy. The valence band offset (EZnO?ETiO2)Valence was linearly changed from 0.27 to 0.01 eV at the interface with increased ZnO coating thickness from 0.7 to 7 nm. The interface dipole presented at the ZnO/TiO2 interface was responsible for the decreased band offset. The band alignment of the ZnO/TiO2 heterojunction is a type II alignment

  15. Electronic band structure of the layered dichalcogenide MoTe2

    International Nuclear Information System (INIS)

    The transition metal dichalcogenide ?-MoTe2 grown by chemical vapour transport (CVT) at temperatures above 1175 K and cooled to room temperature shows a layered structure that can be described as stacked sandwiches of the tree layers Te-Mo-Te. One molybdenum atom is surrounded by six tellurium atoms forming an octahedron which is slightly distorted because of the molybdenum atom being displaced from the centre. Therefore strong metal-metal bonds are found which form zigzag chains along the crystallographic b-direction. Upon cooling below 250 K the material undergoes a structural phase transition where the ? phase (monoclinic) changes to an orthorhombic Td-structure. In this contribution we present a detailed temperature dependent study of electronic band structure and Fermi-surface of ?-MoTe2 performed by angle-resolved photoemission spectroscopy (ARPES). The measurements were carried out at BESSY II. It results that the dispersion of the valence bands along the different high-symmetric directions of the Brillouin zone are extremely weak. These bands reveal close insight into the low temperature and phase transition behaviour of quasi-two dimensional materials like ?-MoTe2. Fermi level crossings are studied by Fermi-surface maps. The experimental findings will be compared with tight-binding band structure calculations

  16. Valence, arousal and cognitive control: A voluntary task switching study

    OpenAIRE

    JelleDemanet; BaptistLiefooghe; FrederickVerbruggen

    2011-01-01

    The present study focused on the interplay between arousal, valence and cognitive control. To this end, we investigated how arousal and valence associated with affective stimuli influenced cognitive flexibility when switching between tasks voluntarily. Three hypotheses were tested. First, a valence hypothesis that states that the positive valence of affective stimuli will facilitate both global and task-switching performance because of increased cognitive flexibility. Second, an arousal hypot...

  17. The mixed valence phenomenon in compounds of f-electron

    International Nuclear Information System (INIS)

    The classification and identification of the mixed valence state in the rare earth compounds are presented. The methods of the transformation to the collapsed mixed valence phase are described. As examples of the mixed valence compounds the samarium chalcogenides, thulium monoselenide and Cesub(1-x)Thsub(x) alloys are discussed. Also critical review of some properties of actinides which can suggest the existence of the mixed valence state is provided. (author)

  18. Momentum-Transfer-Resolved Electron Energy Loss Spectroscopy of BaBiO3: Anisotropic Dispersion of Threshold Excitation and Optically Forbidden Transition

    Science.gov (United States)

    Wang, Y. Y.; Dravid, V. P.; Bulut, N.; Han, P. D.; Klein, M. V.; Schnatterly, S. E.; Zhang, F. C.

    1995-09-01

    Momentum-transfer-resolved electron energy loss spectroscopy of the valence band transitions in BaBiO3 has revealed for the first time that dispersion of the excitation at the optical gap \\(~2 eV\\) and an optically forbidden transition at 4.5 eV are all anisotropic along [100] and [110]. The anisotropic dispersion of the threshold excitation cannot be described by a simple charge density wave picture but can be explained by a small exciton model proposed in this paper. The optically forbidden transition is found to agree well with a proposed molecular orbital model, where the transition is assigned as the excitation from the O 2p? nonbonding states to the empty Bi 6s state.

  19. Intermediate Band Solar Cell with Extreme Broadband Spectrum Quantum Efficiency

    Science.gov (United States)

    Datas, A.; López, E.; Ramiro, I.; Antolín, E.; Martí, A.; Luque, A.; Tamaki, R.; Shoji, Y.; Sogabe, T.; Okada, Y.

    2015-04-01

    We report, for the first time, about an intermediate band solar cell implemented with InAs/AlGaAs quantum dots whose photoresponse expands from 250 to ˜6000 nm . To our knowledge, this is the broadest quantum efficiency reported to date for a solar cell and demonstrates that the intermediate band solar cell is capable of producing photocurrent when illuminated with photons whose energy equals the energy of the lowest band gap. We show experimental evidences indicating that this result is in agreement with the theory of the intermediate band solar cell, according to which the generation recombination between the intermediate band and the valence band makes this photocurrent detectable.

  20. Intermediate band solar cell with extreme broadband spectrum quantum efficiency.

    Science.gov (United States)

    Datas, A; López, E; Ramiro, I; Antolín, E; Martí, A; Luque, A; Tamaki, R; Shoji, Y; Sogabe, T; Okada, Y

    2015-04-17

    We report, for the first time, about an intermediate band solar cell implemented with InAs/AlGaAs quantum dots whose photoresponse expands from 250 to ?6000??nm. To our knowledge, this is the broadest quantum efficiency reported to date for a solar cell and demonstrates that the intermediate band solar cell is capable of producing photocurrent when illuminated with photons whose energy equals the energy of the lowest band gap. We show experimental evidence indicating that this result is in agreement with the theory of the intermediate band solar cell, according to which the generation recombination between the intermediate band and the valence band makes this photocurrent detectable. PMID:25933339

  1. Dispersion Basics

    Science.gov (United States)

    COMET

    2002-11-12

    A webcast presentation by Dr. Timothy Spangler (Director of the COMET Program and a former air quality consultant). This 25-minute lecture provides an overview of the basics of dispersion, the effects of different atmospheric conditions on dispersion, and how dispersion is commonly modeled after an accidental release of a hazardous material.

  2. Thermoelectric, band structure, chemical bonding and dispersion of optical constants of new metal chalcogenides Ba{sub 4}CuGa{sub 5}Q{sub 12} (Q=S, Se)

    Energy Technology Data Exchange (ETDEWEB)

    Reshak, A.H. [New Technologies – Research Center, University of West Bohemia, Univerzitni 8, 306 14 Pilsen (Czech Republic); Center of Excellence Geopolymer and Green Technology, School of Material Engineering, University Malaysia Perlis, 01007 Kangar, Perlis (Malaysia); Azam, Sikander, E-mail: sikander.physicst@gmail.com [New Technologies – Research Center, University of West Bohemia, Univerzitni 8, 306 14 Pilsen (Czech Republic)

    2014-08-01

    The electronic structure and dispersion of optical constants of the Ba{sub 4}CuGa{sub 5}S{sub 12} and Ba{sub 4}CuGa{sub 5}Se{sub 12} compounds were calculated by the first-principles full-potential linearized augmented plane wave (FPLAPW) method. We employed the local density approximation (LDA), generalized gradient approximation (GGA) and Engel–Vosko GGA (EVGGA) to calculate the electronic structures, Fermi surface, thermoelectric, chemical bonding and dispersion of optical constants of these compounds. By investigating the influence of replacing S by Se, it has been found that the charge density around ‘Ga’ is greater in Ba{sub 4}CuGa{sub 5}Se{sub 12} than Ba{sub 4}CuGa{sub 5}S{sub 12}. Fermi surface of Ba{sub 4}CuGa{sub 5}S{sub 12} consists of an electronic sheet only because there is no empty region while Ba{sub 4}CuGa{sub 5}Se{sub 12} contains both holes and electronic sheets because this compound contains both empty and shaded region. As we replace S by Se the heights of the peaks decreases as a results the reflectivity also decreases. It is noticed that the reflectivity is over 68% (60%) for Ba{sub 4}CuGa{sub 5}S{sub 12} (Ba{sub 4}CuGa{sub 5}Se{sub 12}) compounds within the energy range studied. This implies that the material will serve as a good reflector. By replacing S by Se the figure of merit values increases from 0.97 to 1.0, which shows the good thermoelectric behavior of both compounds. - Highlights: • DFT-FPLAPW method used for calculating the properties. • For predicting the chemical bonding the charge density behavior is studied in 2D. • The optical properties were also calculated and analyzed. • The Fermi surface is composed of two bands crossing along the EF level. • The thermoelectric properties have also been calculated.

  3. A study of the valence shell spectroscopic and thermodynamic properties of trifluoronitrosomethane cations

    Science.gov (United States)

    Graham, D. M.; Powis, I.; Underwood, J. G.; Shaw, D. A.; Holland, D. M. P.

    2012-02-01

    A time-of-flight mass spectrometry study has been carried out to investigate the fragmentation processes occurring in trifluoronitrosomethane (CF3NO) as a result of valence shell photoionisation. Synchrotron radiation has been used to record spectra in the photon energy range ˜10-42 eV, and appearance energies have been determined for 10 fragment ions. At high excitation energies, singly charged atomic fragments have been observed. For the main dissociation channels, leading to the formation of NO+, CF2+ or CF3+, the experimental appearance energies have been compared with thermochemical estimates, and a satisfactory agreement has been found. Structure observed in the total ion yield curve has been interpreted with the aid of excited state transition energies and oscillator strengths obtained in a time-dependent Hartree Fock calculation. The theoretical results show that configuration interaction strongly affects many of the valence states. A HeI excited photoelectron spectrum of CF3NO has been measured and the orbital ionisation energies have been compared with theoretical values computed using the Outer Valence Green's Function approach. A large Franck-Condon gap is observed between the X˜A and the A˜A state bands, in accord with the calculated vertical ionisation energies of 10.87 and 16.32 eV for the 12a' (n-) and the 11a' (n+) orbitals, respectively. In the ion yield curve, the corresponding energy range is strongly influenced by autoionising valence states.

  4. Origin of the unusually large band-gap bowing and the breakdown of the band-edge distribution rule in the SnxGe1-x alloys

    Science.gov (United States)

    Yin, Wan-Jian; Gong, Xin-Gao; Wei, Su-Huai

    2008-10-01

    The unusual nonlinear behaviors of the band gaps in SnxGe1-x alloys are investigated using first-principles calculations. We show that the large bowing of the direct band gap is induced by the disordering effect. Moreover, we calculated individual contribution of the band-edge states and found that the bowing of the conduction band edge is much larger than the bowing of the valence band edge, although the natural valence-band offset between Ge and Sn is larger than the natural conduction-band offset. The breakdown of the band-edge distribution rule is explained by the large lattice mismatch between Ge and Sn and the large deformation potential of the band-edge states.

  5. Investigation of band non-parabolicities in strain-balanced GaInAs/GaAlInAs coupled quantum wells

    Science.gov (United States)

    Martin, R. W.; McGow, F. J.; Hopkinson, M.; David, J. P. R.

    1997-12-01

    Magneto-optical investigations of a series of strain-balanced InGaAs/GaAlInAs coupled quantum wells are described, showing how changes in the strain within the InGaAs wells modify the conduction and valence-band dispersion curves. Large non-parabolicities in both bands are demonstrated by comparison of measured and calculated excitonic Landau levels. Increasing tensile strain within the wells results in the heavy-hole in-plane mass changing from a very high value to less than 0.2m0as the first light-hole confined level shifts to an energy above that of the first heavy-hole state.

  6. Janus Nematic Colloids with Designable Valence

    Directory of Open Access Journals (Sweden)

    Simon ?opar

    2014-05-01

    Full Text Available Generalized Janus nematic colloids based on various morphologies of particle surface patches imposing homeotropic and planar surface anchoring are demonstrated. By using mesoscopic numerical modeling, multiple types of Janus particles are explored, demonstrating a variety of novel complex colloidal structures. We also show binding of Janus particles to a fixed Janus post in the nematic cell, which acts as a seed and a micro-anchor for the colloidal structure. Janus colloidal structures reveal diverse topological defect configurations, which are effectively combinations of surface boojum and bulk defects. Topological analysis is applied to defects, importantly showing that topological charge is not a well determined topological invariant in such patchy nematic Janus colloids. Finally, this work demonstrates colloidal structures with designable valence, which could allow for targeted and valence-conditioned self-assembly at micro- and nano-scale.

  7. Evaluative conditioning induces changes in sound valence

    Directory of Open Access Journals (Sweden)

    AnnaC.Bolders

    2012-04-01

    Full Text Available Evaluative Conditioning (EC has hardly been tested in the auditory domain, but it is a potentially valuable research tool. In Experiment 1 we investigated whether the affective evaluation of short environmental sounds can be changed using affective words as unconditioned stimuli (US. Congruence effects on an affective priming task (APT for conditioned sounds demonstrated successful EC. Subjective ratings for sounds paired with negative words changed accordingly. In Experiment 2 we investigated whether the acquired valence remains stable after repeated presentation of the conditioned sound without the US or whether extinction occurs. The acquired affective value remained present, albeit weaker, even after 40 extinction trials. These results warrant the use of EC to study processing of short environmental sounds with acquired valence, even if this requires repeated stimulus presentations. This paves the way for studying processing of affective environmental sounds while effectively controlling low level-stimulus properties.

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

    CERN Document Server

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

    2013-01-01

    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.

  9. ??????? ?????? ?????? ?????? ???????????Russian cases through the prism of valency

    Directory of Open Access Journals (Sweden)

    Lennart Lönngren

    2013-12-01

    Full Text Available The article is a fairly extensive description of the functions of cases in Russian, based on valency theory. Pervadingly a distinction is made between signs occypying nodes in the corresponding graph, and "node-less" signs. Each Russian case can function in both capacities, except the prepositional case, which is always nodeless. In addition to the traditional six cases, two more are postulated, namely the agreement case and the indeterminate case.

  10. Avoided Valence Transition in a Plutonium Superconductor

    OpenAIRE

    Ramshaw, B.J.; Shekhter, A; McDonald, R. D.; Betts, J. B.; Mitchell, J. N.; Tobash, P.H.; Mielke, C. H; Bauer, E.D.; A. Migliori

    2014-01-01

    Some of the most remarkable phenomena---and greatest theoretical challenges---in condensed matter physics arise when $d$ or $f$ electrons are neither fully localized around their host nuclei, nor fully itinerant. This localized/itinerant "duality" underlies the correlated electronic states of the high-$T_c$ cuprate superconductors and the heavy-fermion intermetallics, and is nowhere more apparent than in the $5f$ valence electrons of plutonium. Here we report the full set of...

  11. Valence bond solid states with symplectic symmetry

    International Nuclear Information System (INIS)

    We introduce a one-dimensional valence bond solid (VBS) state with symplectic symmetry SP(n) and construct the corresponding parent Hamiltonian. We argue that there is a gap in the spectrum. We calculate exactly the static correlation functions, which fall off exponentially. Hence the model introduced here shares all properties of the Haldane scenario for integer-spin quantum antiferromagnets. We further show that the VBS state possesses string order and discuss its generalization to higher dimensions

  12. 5th International Conference on Valence Fluctuations

    CERN Document Server

    Malik, S

    1987-01-01

    During the Koln meeting (August 28-31, 1984), Irdia was chosen as the venue for the next International Conference on Valence Fluctuations. lhis was in recognition ard appreciation of the work done, both experimental ard theoretical, by the Irdian scientists in this area during the last decade. We decided to hold this Conference in the month of January, 1987 at Bangalore. lhe subject of Valence Fluctuations has kept itself alive ard active as it has provided many shocks ard suprises particularly among the Ce- ard U-based intermetallies. lhe richness of many interesting physical phenomena occurring in mixed valent materials, the flexibility of modifying their physical properties (by alloying, for example) ard the possibility of synthesizing a wide variety of new such materials seem to be the key factors in this regard. Barely six months before this Conference, an International Conference on Anomalous Rare Earths and Actinides (ICAREA) had been held at Grenoble (July, 1986) which also focussed on mixed valence a...

  13. Oxygenation mediating the valence density-of-states and work function of Ti(0001) skin.

    Science.gov (United States)

    Li, Lei; Meng, Fanling; Tian, Hongwei; Hu, Xiaoying; Zheng, Weitao; Sun, Chang Q

    2015-04-21

    Consistency between density function theory calculations and photoelectron spectroscopy observations confirmed predictions based on the framework of bond-band-barrier (3B) correlation notation [Sun, Prog. Mater. Sci., 2003, 48, 521-685] that an oxygen adsorbate interacts with Ti(0001) skin atoms to form a tetrahedron with creation of four valence density-of-state features: O-Ti bonding electron pairs, O nonbonding lone pairs, Ti electronic holes, and Ti antibonding dipoles. Formation of the dipoles lowers the work function of the Ti(0001) skin and electron-hole generation turns the metallic Ti(0001) into the semiconductive O-Ti(0001). Findings confirm the universality of the 3B correlation in understanding the dynamics of oxygen chemisorption and the associated valence electrons involved in the process of oxidation. PMID:25777318

  14. Influence of valence nucleon on shape change in 131Ce and 131Pr

    International Nuclear Information System (INIS)

    The 95 MeV 19F beam projects on an enriched 116Sn target with backing. The ?-ray emitted from evaporation-residual nuclei was detected in ?-? coincidence measurement by using 11 BGO Compton suppressed HPGe detectors. Lifetimes of the high spin states for 131Ce and 131Pr were determined through analysis of the Doppler broadened line shapes. The transition quadrupole moments extracted from the measured lifetimes demonstrate that change in nuclear shape occurs in the band crossing region. From a comparison with the neighbouring even-even nucleus 130Ce it follows that influence of the valence neutron is stronger than that of the valence proton on shape change of the core. (authors)

  15. Band Alignment in WSe2-Graphene Heterostructures.

    Science.gov (United States)

    Kim, Kyounghwan; Larentis, Stefano; Fallahazad, Babak; Lee, Kayoung; Xue, Jiamin; Dillen, David C; Corbet, Chris M; Tutuc, Emanuel

    2015-04-28

    Using different types of WSe2 and graphene-based heterostructures, we experimentally determine the offset between the graphene neutrality point and the WSe2 conduction and valence band edges, as well as the WSe2 dielectric constant along the c-axis. In a first heterostructure, consisting of WSe2-on-graphene, we use the WSe2 layer as the top dielectric in dual-gated graphene field-effect transistors to determine the WSe2 capacitance as a function of thickness, and the WSe2 dielectric constant along the c-axis. In a second heterostructure consisting of graphene-on-WSe2, the lateral electron transport shows ambipolar behavior characteristic of graphene combined with a conductivity saturation at sufficiently high positive (negative) gate bias, associated with carrier population of the conduction (valence) band in WSe2. By combining the experimental results from both heterostructures, we determine the band offset between the graphene charge neutrality point, and the WSe2 conduction and valence band edges. PMID:25768037

  16. Verb Valencies and Croatian as a Foreign and Second Language

    Directory of Open Access Journals (Sweden)

    Marica ?ilaš-Mikuli?

    2011-11-01

    Full Text Available The article deals with verb valency and the description and list of verb valencies in Croatian as the first and as the second and foreign language. Since the importance of researching verb valency was observed in linguistics several decades ago, it has been researched in many languages, and many verb valency dictionaries have been written. In Croatia, the valency structure of the Croatian verb system has been the subject of several projects, resulting in the publishing of valency lexicons and dictionaries of Croatian verbs and their supplements. The approach to the description of verb valency differs depending on whether it is intended for native or for non-native speakers. Using the example of the verb ``i?i'', the authors research the approach to the treatment of verb valencies in the existing dictionaries and handbooks, on one hand in those intended for native speakers of Croatian, and on the other hand in the handbooks and textbooks written for non-native speakers of Croatian. The purpose of this article is to demonstrate important differences between those two approaches to the valency of Croatian verbs, and to provide basic guidelines for the approach to verb valency for non-native speakers.

  17. Quest for chiral doublet bands in A?110 mass region

    International Nuclear Information System (INIS)

    High spin states of 106,108Ag were studied by using fusion evaporation reaction on Beijing HI-13 Tandem Accelerator. The negative-parity bands were updated for both nuclei. Doublet bands similar to chiral bands in 104Rh were identified in 106,108Ag respectively. But there is much difference of the moment of inertia and alignment between the yrast and yrare bands in both of them. It may result from the different deformations of the core and angular momentum coupling mode between valence particles and the inner-core for the yrast and yrare bands. (authors)

  18. Collective structures and smooth band termination in 109Sn

    International Nuclear Information System (INIS)

    Six rotational bands up to energies Ex = 24.7 MeV and spins J?=(79/2-) have been identified in 109Sn using the GAMMASPHERE ?-detector array. Four of the bands show smoothly decreasing dynamic moments of inertia at rotational frequencies ??>0.6 MeV. The bands arise at medium spins from a coupling of a valence d5/2, g7/2 or h11/2 neutron to the deformed 2p2h proton excitation of the Z=50 core 108Sn. At very high ?? these bands show the typical behaviour of smoothly terminating bands, i.e. a gradual alignment of the angular momenta of the valence particles and holes corresponding to a transition from high collectivity to noncollective states. (orig.)

  19. Elementary energy bands in ab initio calculations of the YAlO3 and SbSI crystal band structure

    Science.gov (United States)

    Bercha, D. M.; Rushchanskii, K. Z.; Sznajder, M.; Matkovskii, A.; Potera, P.

    2002-11-01

    The local density approximation has been implemented to determine the band structure of orthorhombic crystals YAlO3 (YAP) and SbSI. The topology of the valence band structures was analyzed. It has been demonstrated that Zak's elementary energy bands in the band structure are distinguishable on the basis of the empty-lattice approximation. The calculated electron density distribution of YAP and SbSI crystals is related to particular Wyckoff positions. Moreover, there is a direct correspondence between the obtained elementary energy bands and the aforementioned Wyckoff positions characterized by electron density distribution.

  20. Temporal dispersion

    CERN Document Server

    Boon, J P; Boon, Jean Pierre; Grosfils, Patrick

    2001-01-01

    A {\\em propagation-dispersion equation} is derived for the distribution function of a particle moving on a substrate with time-delays. The equation is obtained as the continuous limit of an exact microscopic finite difference equation describing the motion of a point particle on a D-dimensional (D = 1, 2) lattice whose sites are occupied by scatterers. The propagation-dispersion equation should be contrasted with the convection-diffusion equation (or the classical Fokker-Planck equation) as it describes a dispersion process in {\\em time} (instead of diffusionin space) with a drift expressed by a propagation speed with non-zero bounded values. The {\\em temporal dispersion} coefficient is shown to exhibit a Green-Kubo form with integration over space instead of time. Physical systems where the propagation-dispersion equation applies are discussed.

  1. Non-Fermi liquid phenomena and intermediate valence in Yb-based compounds located close to the quantum critical point

    International Nuclear Information System (INIS)

    In this paper, we focus on the mechanism of non-Fermi liquid phenomena in the vicinity of the magnetic field-tuned quantum critical point in Yb-based heavy fermion compounds YbAuCu4, YbRh2Si2 and YbFe4P12. A comparative study of YbAuCu4 and YbPdCu4 with differently magnetically ordered ground states of antiferromagnetic (AFM) and ferromagnetic (FM) indicates that the competition between the field-destabilized AFM and field-stabilized FM correlations plays an important role on the field-tuned quantum critical behavior. The non-integer valence of these compounds leads to a consideration that the experimental susceptibility is dominated by the weakly broadened 4f hole level above the Fermi sea that extends to the cf hybridized band located at the Fermi level. Whilst, the monotonic increase of T0 (an estimate of Kondo temperature) with field, derived from the transport and spin-fluctuation measurements, is ascribed to the variation of conduction bands from a weakly cf hybridized band toward the originally underlying conduction bands. The important role of the crossover transition upon cooling from the mixed valence localized f hole state to an itinerant electron state with the intermediate valence is also suggested

  2. Reply to Isgur's comments on valence QCD

    International Nuclear Information System (INIS)

    With the goal of understanding the complexity of QCD and the role of symmetry in dynamics, the authors studied a field theory called Valence QCD (VQCD) in which the Z graphs are forbidden so that the Fock space is limited to the valence quarks. The authors calculated nucleon form factors, matrix elements, and hadron masses both with this theory and with quenched QCD on a set of lattices with the same gauge background. Comparing the results of the lattice calculations in these two theories, the authors drew conclusions regarding the SU(6) valence quark model and chiral symmetry. While recognizing the goal of VQCD, Nathan Isgur disagrees on some of the conclusions the authors have drawn. The foremost objection raised in section 2 is to their suggestion that the major part of the hyperfine splittings in baryons is due to Goldstone boson exchange and not one-gluon-exchange (OGE) interactions. The logic of Isgur's objection is that VQCD yields a spectroscopy vastly different from quenched QCD and therefore the structure of the hadrons (to which hyperfine splittings in a quark model are intimately tied) is also suspect so no definite conclusions are possible. To put this into perspective it should be emphasized at the outset that spectroscopy is only one aspect of hadron physics examined in section 1. The authors have studied the axial and scalar couplings of nucleon in terms of FA/DA and FS/DS, the neutron to proton magnetic mome/sub>, the neutron to proton magnetic moment ratio ?n/?p, and various form factors. None of these results reveal any pathologies of hadron structure and turn out to be close to the SU(6) relations, as expected. In fact this is what motivated the study of valence degrees of freedom via VQCD. In section 2 the authors address specific issues related to spectroscopy in VQCD. Isgur also presented more general arguments against the idea of boson exchange as a contributor to hyperfine effects. A cornerstone of his discussion is the unifying aspect of OGE in a quark model picture. The authors believe that it is also natural and economical to identify chiral symmetry as the common origin for much of the physics being discussed here. Therefore in section 3 the authors take the opportunity to sketch out an effective theory that may serve as a framework to interpret the numerical results of VQCD

  3. The variational subspace valence bond method.

    Science.gov (United States)

    Fletcher, Graham D

    2015-04-01

    The variational subspace valence bond (VSVB) method based on overlapping orbitals is introduced. VSVB provides variational support against collapse for the optimization of overlapping linear combinations of atomic orbitals (OLCAOs) using modified orbital expansions, without recourse to orthogonalization. OLCAO have the advantage of being naturally localized, chemically intuitive (to individually model bonds and lone pairs, for example), and transferrable between different molecular systems. Such features are exploited to avoid key computational bottlenecks. Since the OLCAO can be doubly occupied, VSVB can access very large problems, and calculations on systems with several hundred atoms are presented. PMID:25854233

  4. Neutron scattering on intermediate valence systems

    International Nuclear Information System (INIS)

    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.)

  5. A study of core and valence levels in ?-PbO2 by hard X-ray photoemission

    International Nuclear Information System (INIS)

    The core and valence levels of ?-PbO2 have been studied using hard X-ray photoemission spectroscopy (h? = 6000 eV and 7700 eV). The Pb 4f core levels display an asymmetric lineshape which may be fitted with components associated with screened and unscreened final states. It is found that intrinsic final state screening is suppressed in the near-surface region. A shift in the O 1s binding energy due to recoil effects is observed under excitation at 7700 eV. It is shown that conduction band states have substantial 6s character and are selectively enhanced in hard X-ray photoemission spectra. However, the maximum amplitude in the Pb 6s partial density of states is found at the bottom of the valence band and the associated photoemission peak shows the most pronounced enhancement in intensity at high photon energy

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

    Directory of Open Access Journals (Sweden)

    G. Baskaran

    2006-01-01

    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.

  7. Awaking of ferromagnetism in GaMnN through control of Mn valence

    CERN Document Server

    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

    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.

  8. On the electrical conductivity for the mixed-valence model with d-f correlations

    International Nuclear Information System (INIS)

    The static electrical conductivity of mixed-valence systems is calculated in the model of Matlak and Nolting [Solid State Commun., 47, 11 (1983); Z. Phys., B55, 103 (1984)]. The method takes into account the atomic properties more exactly than those connected with bands, and hence emphasizes the ionic aspect of the problem in some way; indeed, the calculations overestimate the atomic properties. Some results are presented in a graph. It is found that the electrical conductivity depends strongly on temperature and the electron-hole attraction constant

  9. BCS theory on a flat band lattice

    International Nuclear Information System (INIS)

    It is important to study the many-body effects of the electrons on the flat band lattice, since the flatness of the dispersion may lead to instabilities in the presence of interactions. To clarify the effects of flat dispersion for superconductivity, we investigate a simple two-band BCS Hamiltonian, where one of the bands has a flat dispersion, in the mean field approximation. A superconducting gap ? and a critical temperature Tc strongly depend on the pairing coupling constant V. Especially, for small coupling constant, ? and Tc are proportional to V, which are quite different from the single band BCS cases. Higher Tc, compared to the normal BCS system, are realized due to the existence of the flat band

  10. Equilibrium gels of low-valence DNA nanostars: a colloidal model for strong glass formers.

    Science.gov (United States)

    Biffi, Silvia; Cerbino, Roberto; Nava, Giovanni; Bomboi, Francesca; Sciortino, Francesco; Bellini, Tommaso

    2015-04-01

    Kinetic arrest in colloidal dispersions with isotropic attractive interactions usually occurs through the destabilization of the homogeneous phase and the formation of a non-equilibrium network of jammed particles. Theory and simulations predict that a different route to gelation should become available when the valence of each colloidal particle is suitably reduced. Under these conditions, gelation should be achievable through a reversible sequence of equilibrium states. Here we report the reversible dynamic arrest of a dispersion of DNA-based nanoparticles with anisotropic interactions and a coordination number equal to four. As the temperature is decreased, the relaxation time for density fluctuations slows down by about five orders of magnitude, following an Arrhenius scaling in the entire experimentally accessible temperature window. The system is in thermodynamic equilibrium at all temperatures. Gelation in our system mimics the dynamic arrest of networking atomic strong glass formers such as silica, for which it could thus provide a suitable colloidal model. PMID:25747102

  11. A study of the valence shell electronic structure and photoionisation dynamics of meta-dichlorobenzene and meta-bromochlorobenzene

    International Nuclear Information System (INIS)

    Highlights: ? Electronic structure and photoionisation dynamics of mDCB and mBCB have been studied. ? Dynamics affected by halogen atom Cooper minimum. ? Many-body effects influence inner valence shell ionisation. - Abstract: A combined experimental and theoretical investigation has been performed to study the valence shell electronic structure and photoionisation dynamics of meta-dichlorobenzene and meta-bromochlorobenzene. Angle resolved photoelectron spectra of meta-dichlorobenzene have been recorded using synchrotron radiation in the photon energy range from close to threshold to 100 eV. These have enabled photoelectron anisotropy parameters and branching ratios to be derived. The continuum multiple scattering approach has been employed to calculate photoionisation partial cross-sections and photoelectron angular distributions of the outer valence orbitals of meta-dichlorobenzene. A comparison between the corresponding experimental and theoretical results has demonstrated that ionisation from some of the orbitals is influenced by the Cooper minimum associated with the chlorine atom. Ionisation energies and spectral intensities evaluated with the third-order algebraic diagrammatic construction approximation for the one-particle Green’s function and the outer valence Green’s function approaches have allowed the features observed in the complete valence shell photoelectron spectra of meta-dichlorobenzene and meta-bromochlorobenzene to be interpreted. Many-body phenomena strongly influence ionisation from the inner valence orbitals and lead to the intensity associated with a particular orbital being redistributed amongst numerous satellites. High resolution photoelectron spectra have been recorded with HeI radiation. Vibrational structure has been observed in some of the photoelectron bands and tentative assignments have been proposed

  12. A study of the valence shell electronic structure and photoionisation dynamics of s-triazine

    Science.gov (United States)

    Coriani, S.; Stener, M.; Decleva, P.; Holland, D. M. P.; Potts, A. W.; Karlsson, L.

    2015-04-01

    A joint experimental and theoretical approach has been used to study the valence shell electronic structure and photoionisation dynamics of s-triazine (1,3,5-triazine). Synchrotron radiation has been employed to record angle resolved photoelectron spectra of the complete valence shell for photon energies between 17.5 and 100 eV, thereby allowing photoelectron anisotropy parameters and branching ratios to be determined. Absolute photoionisation partial cross sections have been estimated as the product of these branching ratios and the absolute photoabsorption cross section. The Kohn-Sham and the time-dependent version of density functional theory methods have been used to calculate photoelectron anisotropy parameters and photoionisation partial cross sections, and these have been compared with the corresponding experimental data. The calculations predict that shape resonances affect the photoionisation dynamics of several of the molecular orbitals. The angle resolved photoelectron spectra suggest that the 1 a2? (?) orbital is more tightly bound than the 5e?(?) orbital, and that the 4 a1? (?) orbital is more tightly bound than the 1 a2? (?) orbital, in agreement with the predicted molecular orbital sequence. For the outer valence orbitals the single-particle picture of ionisation holds but electron correlation becomes increasingly important for the inner valence 4e?, 3e? and 3 a1? orbitals and leads to a redistribution of intensity. Instead of a readily distinguishable main-line, associated with each of these orbitals, the photoelectron intensity is spread over numerous satellite states and the resulting band is broad and featureless.

  13. High Resolution Core Valence Valence Auger Electron Specroscopy on Free Molecules

    Science.gov (United States)

    Svensson, S.; Karlsson, L.

    1992-01-01

    Recent experimental results from Core Valence Valence (CVV) Auger electron spectroscopy on free molecules are discussed. The practical use of calculated potential curves for the dicationic final states is illustrated using the NO molecule as an example. The assignment of the CVV spectra to get experimental potential curves for the dicationic states of diatomic molecules is reviewed. The spin-orbit splitting of the initial core hole state in the Auger process is discussed and is related to the molecular field splitting of the Core levels. The importance of making monochromatized photon-impact experiments in order to study the high energy satellites is underlined. The Auger shake-up satellite spectrum of the N2 molecule is discussed as an example and it is found that the participator transitions dominate this spectrum.

  14. Ab initio Green's function formalism for band structures

    OpenAIRE

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

    2004-01-01

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

  15. Elementary energy bands in band structure calculations of some wide-bandgap crystals

    Science.gov (United States)

    Sznajder, M.; Bercha, D. M.; Rushchanskii, K. Z.

    2004-01-01

    Semiconducting Tl3AsS4 crystal was chosen as an example to show that its valence band is composed of the elementary energy bands. Their topology and symmetry obtained in the empty-lattice approximation is confirmed by ab initio band structure calculations. It was shown that these elementary energy bands correspond to the Wyckoff position c in a unit cell. Earlier predictions that the largest electron density distribution is focused in the vicinity of this position, similarly to the case of YAlO3 and SbSI crystals, is confirmed. A conclusion on the common topology and symmetry of the elementary energy bands in electronic and phonon spectra is presented.

  16. Elementary energy bands in band structure calculations of some wide-bandgap crystals

    Energy Technology Data Exchange (ETDEWEB)

    Sznajder, M. [Institute of Physics, University of Rzeszow, Rejtana 16a, 35-310 Rzeszow (Poland); Bercha, D.M. [Institute of Physics, University of Rzeszow, Rejtana 16a, 35-310 Rzeszow (Poland); Institute of Physics and Chemistry of Solid State, Uzhgorod National University, 54 Voloshin Str. 88000 Uzhgorod (Ukraine); Rushchanskii, K.Z. [Institute of Physics and Chemistry of Solid State, Uzhgorod National University, 54 Voloshin Str. 88000 Uzhgorod (Ukraine)

    2004-01-01

    Semiconducting Tl{sub 3}AsS{sub 4} crystal was chosen as an example to show that its valence band is composed of the elementary energy bands. Their topology and symmetry obtained in the empty-lattice approximation is confirmed by ab initio band structure calculations. It was shown that these elementary energy bands correspond to the Wyckoff position c in a unit cell. Earlier predictions that the largest electron density distribution is focused in the vicinity of this position, similarly to the case of YAlO{sub 3} and SbSI crystals, is confirmed. A conclusion on the common topology and symmetry of the elementary energy bands in electronic and phonon spectra is presented. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  17. Fluctuations near quantum critical points of valence transition and superconductivity

    International Nuclear Information System (INIS)

    Full text: In CeCu2Ge2, CeCu2Si2 and CeCu2(Si{-x}Ge{x})2, it has been observed that the superconducting(SC) transition temperature has maximum in the regime where valence change is prominent under pressure[1], and the relation between valence fluctuation and the mechanism of the superconductivity attracts much attention[2]. To get insight into valence instabilities in the Ce systems, the ground-state properties of the periodic Anderson model with the Coulomb repulsion between f and conduction electrons are studied by using the density matrix renormalization group method and by analytical methods [3]. It is found that the first-order valence transition emerges with the quantum critical point(QCP) and the crossover from the Kondo to the mixed-valence regimes is strongly stabilized by quantum fluctuation and electron correlation. It is found that the SC correlation is developed near the QCP of the valence transition. The origin of the superconductivity is ascribed to the development of the coherent motion of electrons with enhanced valence fluctuation, which results in the enhancement of the charge velocity, but not of the charge compressibility. This is in striking contrast to ordinary mechanisms which exhibit enhanced SC correlations. It is also shown that the charge compressibility does not diverge at the QCP of the valence transition, whereas the valence susceptibility diverges. The underlying mechanism of these results is clarified to be the fact that the order parameter of the valence transition is not a conserving quantity. The relevance of these results to the Ce compounds will be discussed by noting the key control parameter of valence instabilities. It will be also pointed out why Ce compounds are hard to show the first-order valence transition in comparison with Ce metal which shows sharp gamma-alpha transition. Our recent results on the magnetic-field control of the valence instabilities [4] will be also mentioned. This presentation is based on the works done with Kazumasa Miyake (Osaka Univ.) and Masatoshi Imada (Univ. of Tokyo). (authors)

  18. 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

  19. Theoretical studies of inner-valence-shell photoionization cross sections in N2 and CO

    International Nuclear Information System (INIS)

    Theoretical studies in the intensity-borrowing sudden approximation are reported of inner-valence-shell photoionization cross sections in N2 and CO. The required ionic-state energies and spectroscopic amplitudes are obtained from appropriate Green's-function and configuration-interaction calculations, and previously devised Stieltjes-Tchebycheff moment-theory techniques are employed in determinations of corresponding continuum dipole transition moments in the static-exchange approximation. Comparisons are made of the Green's-function calculations in the two-particle-hole Tamm-Dancoff approximation with wavefunction results obtained from single-excitation and polarization configuration-interaction calculations. Detailed descriptions are given of the calculated spectroscopic intensity distributions and of the hole-particle configurational compositions of the corresponding inner-valence-shell ionic states, and comparisons are made with previously reported wavefunction studies in N+2 and CO+. Spectroscopic assignments are suggested on basis of the present calculations for the strong features observed recently in higher-resolution inner-valence-shell photoelectron spectra. The corresponding calculated partial-channel photoionization cross sections for the designated C2 ?+sub(u), F 2?+sub(g), G 2?+sub(g), and (2sigma-1sub(g)) 2?+/sup>sub(g)) 2?+sub(g) bands in N2 and C 2?+, D 2PI, F 2?+, G 2?+, and (3sigma-1) 2?+ bands in CO are found to be in good quantitative accord with dipole (e,2e), (e,e + ion), and synchrotron-radiation studies. (orig.)

  20. A study of the inner-valence ionization region in HCl and DCl

    International Nuclear Information System (INIS)

    An in-depth photoionization study of the inner-valence electrons in HCl and DCl has been performed using synchrotron radiation. A series of photoelectron spectra of HCl were obtained at a resolution of 23 meV over the binding energy range 25-30.5 eV at various excitation energies and at two different electron collection angles relative to the plane of polarization of the undulator radiation. In addition, photoelectron spectra of DCl were recorded at two different excitation energies. These spectra were compared directly with the threshold photoelectron spectra of HCl and DCl that were recorded previously under similar resolution conditions (?30 meV). This comparative study reveals new information on the nature of the numerous band systems observed in this binding energy region. In addition, we present the experimental confirmation of the theoretical prediction given by Andersson et al (2001 Phys. Rev. A 65 012705) that a vibrational progression showing interference structure would appear in the main inner-valence ionization band in the photoelectron spectrum of DCl at a resolution of 10 meV

  1. Emotion and language: valence and arousal affect word recognition.

    Science.gov (United States)

    Kuperman, Victor; Estes, Zachary; Brysbaert, Marc; Warriner, Amy Beth

    2014-06-01

    Emotion influences most aspects of cognition and behavior, but emotional factors are conspicuously absent from current models of word recognition. The influence of emotion on word recognition has mostly been reported in prior studies on the automatic vigilance for negative stimuli, but the precise nature of this relationship is unclear. Various models of automatic vigilance have claimed that the effect of valence on response times is categorical, an inverted U, or interactive with arousal. In the present study, we used a sample of 12,658 words and included many lexical and semantic control factors to determine the precise nature of the effects of arousal and valence on word recognition. Converging empirical patterns observed in word-level and trial-level data from lexical decision and naming indicate that valence and arousal exert independent monotonic effects: Negative words are recognized more slowly than positive words, and arousing words are recognized more slowly than calming words. Valence explained about 2% of the variance in word recognition latencies, whereas the effect of arousal was smaller. Valence and arousal do not interact, but both interact with word frequency, such that valence and arousal exert larger effects among low-frequency words than among high-frequency words. These results necessitate a new model of affective word processing whereby the degree of negativity monotonically and independently predicts the speed of responding. This research also demonstrates that incorporating emotional factors, especially valence, improves the performance of models of word recognition. PMID:24490848

  2. Bosonic condensation in a flat energy band

    CERN Document Server

    Baboux, F; Jacqmin, T; Biondi, M; Lemaître, A; Gratiet, L Le; Sagnes, I; Schmidt, S; Türeci, H E; Amo, A; Bloch, J

    2015-01-01

    Flat bands are non-dispersive energy bands made of fully degenerate quantum states. Such bands are expected to support emergent phenomena with extraordinary spatial and temporal structures, as they strongly enhance the effect of any perturbation induced by disorder, dissipation or interactions. However, flat bands usually appear at energies above the ground state, preventing their study in systems in thermodynamic equilibrium. Here we use cavity polaritons to circumvent this issue. We engineer a flat band in a frustrated lattice of micro-pillar optical cavities. By taking advantage of the non-hermiticity of our system, we achieve for the first time bosonic condensation in a flat band. This allows revealing the peculiar effect of disorder in such band: The condensate fragments into highly localized modes, reflecting the elementary eigenstates produced by geometric frustration. This non-hermitian engineering of a bosonic flat band condensate offers a novel approach to studying coherent phases of light and matte...

  3. Valence Loss Electron Spectroscopy of Ni-Al Mixed Oxides

    Science.gov (United States)

    Aires, F. J. Cadete Santos; Howie, A.; Walsh, C. A.

    1993-09-01

    An outline is given of the extension of the classical theory of dielectric excitation to deal with the spatially localized valence electron spectroscopy of inhomogeneous media. The valence spectroscopy technique has been applied to mixed oxides of Hi and Al. The results have then been interpreted in terms of this extended theory. Significant variations in the position of the main collective loss peak were noted at different points on the samples and are tentatively ascribed to the presence of internal voids or pores rather than to variations in composition. Valence loss spectroscopy may thus provide a means of assessing local pore volume in mixed oxide catalysts.

  4. Positron annihilation with core and valence electrons

    CERN Document Server

    Green, D G

    2015-01-01

    $\\gamma$-ray spectra for positron annihilation with the core and valence electrons of the noble gas atoms Ar, Kr and Xe is calculated within the framework of diagrammatic many-body theory. The effect of positron-atom and short-range positron-electron correlations on the annihilation process is examined in detail. Short-range correlations, which are described through non-local corrections to the vertex of the annihilation amplitude, are found to significantly enhance the spectra for annihilation on the core orbitals. For Ar, Kr and Xe, the core contributions to the annihilation rate are found to be 0.55\\%, 1.5\\% and 2.2\\% respectively, their small values reflecting the difficulty for the positron to probe distances close to the nucleus. Importantly however, the core subshells have a broad momentum distribution and markedly contribute to the annihilation spectra at Doppler energy shifts $\\gtrsim3$\\,keV, and even dominate the spectra of Kr and Xe at shifts $\\gtrsim5$\\,keV. Their inclusion brings the theoretical ...

  5. Band to band tunneling in III-V semiconductors: Implications of complex band structure, strain, orientation, and off-zone center contribution

    International Nuclear Information System (INIS)

    In this paper, we use a tight binding Hamiltonian with spin orbit coupling to study the real and complex band structures of relaxed and strained GaAs. A simple d orbital on-site energy shift coupled with appropriate scaling of the off-diagonal terms is found to correctly reproduce the band-edge shifts with strain. Four different ?100? strain combinations, namely, uniaxial compressive, uniaxial tensile, biaxial compressive, and biaxial tensile strain are studied, revealing rich valence band structure and strong relative orientation dependent tunneling. It is found that complex bands are unable to provide unambiguous tunneling paths away from the Brillouin zone center. Tunneling current density distribution over the Brillouin zone is computed using non-equilibrium Green's function approach elucidating a physical picture of band to band tunneling

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

    International Nuclear Information System (INIS)

    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)

  7. Origin of the unusually large band gap bowing and the breakdown of the band-edge distribution rule in the SnxGe1-x alloys

    Science.gov (United States)

    Yin, Wan-Jian; Gong, Xin-Gao; Wei, Su-Huai

    2009-03-01

    Most semiconductor alloy AxB1-x has a non-linear dependence of its band gap Eg(x) as a function of the alloy composition x, and the variation is usually described by a parabolic function Eg(x) = xEg^A + (1-x)Eg^B - bgx(1-x), where Eg^A and Eg^B are the band gaps of A and B at their respective equilibrium lattice constants and bg is the so-called bowing parameter. The conventional band-edge distribution of bg is usually described by the equation bVBM(CBM) = ?EVBM(CBM)/?Egbg , where ?EVBM(CBM) and ?EVBM(CBM) are VBM and CBM natural band offsets. Using first-principles calculations, we investigate the unusual nonlinear behaviors of the band gaps in SnxGe1-x alloys. We show that the large bowing of the direct band gap is induced by the disordering effect. Moreover, we calculated individual contribution of the band edge states and find that the bowing of the conduction band edge is much larger than the bowing of the valence band edge, although the natural valence band offset between Ge and Sn is larger than the natural conduction band offset. The breakdown of the band-edge distribution rule is explained by the large lattice mismatch between Ge and Sn and the large deformation potential of the band edge states.

  8. Bond valence calculation for several perovskites and the evidences for a valence charge transfer process in these compounds

    OpenAIRE

    Nhat, Hoang Nam

    2003-01-01

    This paper presents the bond valence calculation for several perovskite systems and describes the evidences for a valence charge transfer process in these compounds. The reviewing of the crystal structures of La1-xPbxMnO3 (x=0.1-0.5), La0.6Sr0.4-xTixMnO3 (x=0.0-0.25) and La1-xSrxCoO3 (x=0.1-0.5) is also presented. On the basis of testing samples, the distribution of valence charge has been evaluated which showed the failure of elastic bonding mechanism on all studied systems...

  9. Effect of valence on the electromigration in silver

    International Nuclear Information System (INIS)

    It is shown that the apparent effective valence ZB** of a solute deduced from experiments differs from the true effective valence ZB* defined in the atomic models by a corrective term due to the 'vacancy flow effect'. The experimental results suggest that this corrective term is very important and that it is negative for transition elements; this hypothesis is confirmed for the case of iron in a copper matrix. For the elements to the right of silver in the periodic table, where the correction can be neglected, the effective valence of the solute varies linearly with z (z + 1), z being the difference between the valency of the solute and the solvent; in contrast, the further the solute is from the solvent in the periodic table the more nearly the electronic structure of the ion at the saddle point resembles that of the ion at the equilibrium position. (author)

  10. Origin of the large band-gap bowing in highly mismatched semiconductor alloys

    Science.gov (United States)

    Wu, J.; Walukiewicz, W.; Yu, K. M.; Ager, J. W.; Haller, E. E.; Miotkowski, I.; Ramdas, A. K.; Su, Ching-Hua; Sou, I. K.; Perera, R. C.; Denlinger, J. D.

    2003-01-01

    Photomodulated reflection, optical absorption, and photoluminescence spectroscopies have been used to measure the composition dependence of interband optical transitions in ZnSe1-xTex and ZnS1-xTex alloys. The results reveal entirely different origins of the large band-gap bowing for small and large Te content. On the Te-rich side, the reduction of the band gap is well explained by the band anticrossing interaction between the Se or S localized states and the ZnTe conduction-band states. On the Se- or S-rich side, an interaction between the localized Te states and the degenerate ? valence bands of ZnSe or ZnS is responsible for the band-gap reduction and the rapid increase of the spin-orbit splitting with increasing Te concentration. Results of the soft-x-ray emission experiment provide direct proof of the valence-band anticrossing interaction. The band-gap bowing in the entire composition range is accounted for by a linear interpolation between the conduction-band anticrossing and valence-band anticrossing models.

  11. Probing the visible luminescence mechanism in ZnO nanoparticles by band edge modulation.

    Science.gov (United States)

    Chen, X L; Xu, C S; Liu, Y X; Qiao, H Q; Xu, H T; Ning, Y H; Liu, Y C

    2010-03-01

    The visible luminescence mechanism of ZnO is an important but controversial problem. In this paper, we report the structural and optical properties of Mg-doped ZnO nanoparticles (approximately 3-4 nm) synthesized via the sol-gel method. X-ray diffraction (XRD) analysis and absorption spectra observations revealed that Mg ions replace Zn ions in the lattice. In the room temperature photoluminescence (PL) spectra, three emission bands, ultraviolet (UV), blue, and green, were observed. With increasing concentration of Mg, the near band edge (NBE) emission band progressively shifted to the higher energy side. The green emission in the visible emission band, however, presented an inconspicuous shift. The reason is probably that the bottom of the conduction band in ZnO is determined by the Zn 4s state, and the top of the valence band is determined by the O 2p state. Mg ions in ZnO substitute for zinc ions and enter a slightly distorted tetrahedral site, which causes the bottom of the ZnO conduction band to be shifted to higher energy and leaves the top of the valence band unchanged. This combined with the fact that the deep level position is insensitive to the shift of the band edge led us to conclude that the green emission originates from electronic transition between the deep defect level and the top of the valence band (or very shallow acceptor level). PMID:20355653

  12. Extended Quantum Dimer Model and novel valence-bond phases

    OpenAIRE

    Nakata, Kouki; Totsuka, Keisuke

    2011-01-01

    We extend the quantum dimer model (QDM) introduced by Rokhsar and Kivelson so as to construct a concrete example of the model which exhibits the first-order phase transition between different valence-bond solids suggested recently by Batista and Trugman and look for the possibility of other exotic dimer states. We show that our model contains three exotic valence-bond phases (herringbone, checkerboard and dimer smectic) in the ground-state phase diagram and that it realizes ...

  13. Inelastic collisions of positrons with one-valence-electron targets

    Science.gov (United States)

    Abdel-Raouf, Mohamed Assad

    1990-01-01

    The total elastic and positronium formation cross sections of the inelastic collisions between positrons and various one-valence-electron atoms, (namely hydrogen, lithium, sodium, potassium and rubidium), and one-valence-electron ions, (namely hydrogen-like, lithium-like and alkaline-earth positive ions) are determined using an elaborate modified coupled-static approximation. Special attention is devoted to the behavior of the Ps cross sections at the energy regions lying above the Ps formation thresholds.

  14. Valence bond solid phases in a cubic antiferromagnet

    OpenAIRE

    Beach, K. S. D.; Sandvik, Anders W.

    2006-01-01

    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...

  15. Band alignment of InAs1-xSbx (0.05

    Science.gov (United States)

    Wu, Chen-Jun; Tsai, Gene; Lin, Hao-Hsiung

    2009-05-01

    We determined the unstrained conduction-band and valence-band edge energies of InAs1-xSbx (0.05VBAC) model to explain the bowing of the valence band in InAsSb. Moreover, the spin-orbit splitting energy of InAsSb calculated by our VBAC model fits well with the experimental results reported in previous studies.

  16. Valence, arousal and cognitive control: A voluntary task switching study

    Directory of Open Access Journals (Sweden)

    JelleDemanet

    2011-11-01

    Full Text Available The present study focused on the interplay between arousal, valence and cognitive control. To this end, we investigated how arousal and valence associated with affective stimuli influenced cognitive flexibility when switching between tasks voluntarily. Three hypotheses were tested. First, a valence hypothesis that states that the positive valence of affective stimuli will facilitate both global and task-switching performance because of increased cognitive flexibility. Second, an arousal hypothesis that states that arousal, and not valence, will specifically impair task-switching performance by strengthening the previously executed task-set. Third, an attention hypothesis that states that both cognitive and emotional control ask for limited attentional resources, and predicts that arousal will impair both global and task-switching performance. The results showed that arousal affected task-switching but not global performance, possibly by phasic modulations of the noradrenergic system that reinforces the previously executed task. In addition, positive valence only affected global performance but not task-switching performance, possibly by phasic modulations of dopamine that stimulates the general ability to perform in a multitasking environment.

  17. Stimulus affective valence reverses spatial compatibility effect

    Directory of Open Access Journals (Sweden)

    rick Francisco Quintas Conde

    2011-01-01

    Full Text Available 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 effect and its variants may be modulated by using emotional stimuli. However, until now, no work has studied how the affective valence of a stimulus infuences spatial compatibility effects along the horizontal dimension. The present study investigated this issue by using small lateralized fgures 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 hemifeld 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, Hemifeld (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.

  18. Stimulus affective valence reverses spatial compatibility effect

    Scientific Electronic Library Online (English)

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

    2011-06-01

    Full Text Available 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 effect 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.

  19. Band gap bowing and band offsets in relaxed and strained Si1-xGex alloys by employing a new nonlinear interpolation scheme

    Science.gov (United States)

    Sant, Saurabh; Lodha, Saurabh; Ganguly, Udayan; Mahapatra, Souvik; Heinz, Frederik O.; Smith, Lee; Moroz, Victor; Ganguly, Swaroop

    2013-01-01

    We present nonlocal empirical pseudopotential calculations for SiGe alloys employing a novel nonlinear interpolation scheme. Our interpolation scheme is able to correctly model for the first time the band gap bowing observed in relaxed SiGe alloys. The valence-band-edge and conduction-band-edge energies in relaxed Si1-xGex for arbitrary x, which are difficult to obtain by experimental techniques, have been evaluated using pseudopotential calculations. We have also calculated the band energies of pseudomorphic [100]-strained Si1-xGex alloys grown over unstrained Si1-yGey substrates. The energy gaps, valence and conduction band offsets, effective masses, and strain induced splittings in pseudomorphic SiGe layers are calculated for the whole range of alloy compositions x and y.

  20. Band structures in 99Rh

    International Nuclear Information System (INIS)

    Excited states in the 99Rh nucleus were populated using the fusion-evaporation reaction 75As(28Si,2p2n) at Elab=120 MeV and the de-excitations were investigated through in-beam ?-ray spectroscopic techniques using the INGA spectrometer consisting of 18 clover detectors. The observed band structures are discussed in the framework of tilted axis cranking shell-model calculations. Level structures at low energies are identified as resulting from the rotational bands based on the ?p1/2 and ?g9/2 configurations. The ?I = 1 coupled bands are observed at higher excitation energies and have been interpreted as based on the ?g9/2??g7/2??d5/2, ?p1/2??h11/2??d5/2 and ?g9/2??h11/2??g7/2 configurations. Calculations based on cranked Nilsson–Strutinsky (CNS) formalism have been performed to interpret the favoured states with I? = (41/2?, 43/2?) and (51/2?, 53/2?) as maximal spin aligned states built on the valence space ?(d5/2g7/2)15/2,17/23(h11/2)11/21 configuration combined with the fully-aligned ?(g9/2)25/25 configuration and the ?(g9/2)15/25 configuration with one anti-aligned g9/2 proton, respectively. (paper)

  1. Reaching degeneracy in two-quasiparticle chiral bands

    Energy Technology Data Exchange (ETDEWEB)

    Lawrie, E.A., E-mail: elena@tlabs.ac.z [iThemba LABS, PO Box 722, 7129 Somerset West (South Africa); Shirinda, O., E-mail: obed@tlabs.ac.z [iThemba LABS, PO Box 722, 7129 Somerset West (South Africa); University of the Western Cape, Private Bag X17, 7535 Bellville (South Africa)

    2010-05-24

    The conditions for reaching degeneracy in chiral partner bands built on two-quasiparticle configurations are examined using the two-quasiparticle-plus-triaxial-rotor model. It is shown that in order for degeneracy to occur it is not sufficient to have an aplanar orientation of the total angular momentum, but the angular momenta of the two valence particles need to be completely aligned along the short and long nuclear axes. Such perfect alignment seems impossible to reach with realistic parameters within this model. These results suggest that two-quasiparticle chiral bands may be formed in suitable nuclei, but perfect degeneracy between the partner bands is unlikely to be found.

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

    OpenAIRE

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

    2003-01-01

    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 ...

  3. Nonequilibrium Green's function formulation of intersubband absorption for nonparabolic single-band effective mass Hamiltonian

    Science.gov (United States)

    Kolek, Andrzej

    2015-05-01

    The formulas are derived that enable calculations of intersubband absorption coefficient within nonequilibrium Green's function method applied to a single-band effective-mass Hamiltonian with the energy dependent effective mass. The derivation provides also the formulas for the virtual valence band components of the two-band Green's functions which can be used for more exact estimation of the density of states and electrons and more reliable treatment of electronic transport in unipolar n-type heterostructure semiconductor devices.

  4. Application of the photoreflectance technique to the characterization of quantum dot intermediate band materials for solar cells

    OpenAIRE

    Ca?novas Di?az, Enrique; Marti? Vega, Antonio; Lo?pez Marti?nez, Nair; Antoli?n Ferna?ndez, Elisa; Garci?a-linares Fontes, Pablo; Farmer, C. D.; Stanley, Colin; Luque Lo?pez, Antonio

    2008-01-01

    Intermediate band materials rely on the creation of a new electronic band within the bandgap of a conventional semiconductor that is isolated from the conduction and valence band by a true zero density of states. Due to the presence of the intermediate band, a solar cell manufactured using these materials is capable of producing additional photocurrent, thanks to the absorption of photons with energy lower than the conventional bandgap. In this respect, the characterization of these materials...

  5. Multiplet-Splitting of the Quasi-Atomic-Like Core-Valence-Valence Auger Spectra of Zinc Metal

    Science.gov (United States)

    Yuan, Jian-Min

    2001-10-01

    Multiplet-splitting of the quasi-atomic-like core-valence-valence (CVV) Auger spectra of zinc metal is calculated by explicitly considering the so-called hole-hole interaction in the final valence states of the Auger transition. We assume that before the Auger transition occurs, the occupied valence states relax to screen the core-hole which results in a redistribution of the valence electrons, in particular within the atom that contains a hole in the core. The supercell method is used to calculate the electronic states concerned by the Auger transition, which is accomplished by the self-consistent full-potential linearized augmented plane wave method. In each supercell, one atom is considered to have a core-hole and many others without it. Due to relaxation and screening, the valence states at the site of the Auger transition are more localized compared with those in the ground-state metal. The multiplet peaks of the quasi-atomic-like CVV Auger spectra of zinc metal are obtained by calculating the Auger transition matrix elements between the referred states.

  6. Colloidal Nanoparticles for Intermediate Band Solar Cells

    Science.gov (United States)

    Voros, Marton; Galli, Giulia; Zimanyi, Gergely

    2015-03-01

    The Intermediate Band (IB) solar cell concept is a promising idea to transcend the Shockley-Queisser limit. Using the results of first principles calculations, we proposed that colloidal nanoparticles (CNPs) are a viable and efficient platform for the implementation of the IB solar cell concept. We focused on CdSe and we showed that intragap states present in the isolated dots with reconstructed surfaces combine to form an IB in arrays of NPs, which is well separated from the valence and conduction band edges. We also showed that in solution such IB may be electron doped using, e.g. decamethylcobaltocene, thus activating an IB-induced absorption process. Our results, together with the recent report of a nearly 9% efficient CNP solar cell indicate that colloidal nanoparticle intermediate band solar cells are a promising platform to overcome the Shockley-Queisser limit. The Intermediate Band (IB) solar cell concept is a promising idea to transcend the Shockley-Queisser limit. Using the results of first principles calculations, we proposed that colloidal nanoparticles (CNPs) are a viable and efficient platform for the implementation of the IB solar cell concept. We focused on CdSe and we showed that intragap states present in the isolated dots with reconstructed surfaces combine to form an IB in arrays of NPs, which is well separated from the valence and conduction band edges. We also showed that in solution such IB may be electron doped using, e.g. decamethylcobaltocene, thus activating an IB-induced absorption process. Our results, together with the recent report of a nearly 9% efficient CNP solar cell indicate that colloidal nanoparticle intermediate band solar cells are a promising platform to overcome the Shockley-Queisser limit. Work supported by NSF Solar Collaborative under DMR-1035468 and the Center for Advanced Solar Photophysics, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences.

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

    International Nuclear Information System (INIS)

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

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

    International Nuclear Information System (INIS)

    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

  9. The effect of the electronic and structural environment on the valence of cerium

    International Nuclear Information System (INIS)

    By means of a semiempirical analysis the electrostatic energy Esub(psi) of a charge immersed in the screened Coulomb potential of the total charge distribution of the metal was selected as the most appropriate parameter for correlating different cerium environments. The choice was made by determining the smallest dispersion in plots of various physicochemical parameters versus the rate of depression ? of the superconducting transition temperature Tsub(c) of thorium-based alloys containing cerium impurities. The magnetic moment of cerium, which depends on the environment, was found to have the greatest effect on the depression of Tsub(c). Esub(psi) was found to be proportional to ?sup(-1/2). The analysis was extended to some ABsub(j) compounds (A equivalent to elements of groups II - V including cerium and thorium; Bsub(j) equivalent to N, Sn3, Tl3, Rh3, Co2, Ir2, B6 and Be13). An empirical relationship between Esub(psi) and the volume contraction ?V/V due to the formation of the compound was found. The cerium valence for any CeBsub(j) compound is deduced from the Esub(psi)(Ce) value compatible with the curve of ?V/V versus Esub(psi)(A), taking into account the fact that the valence and atomic radius of cerium are related. (Auth.)

  10. A novel dispersion monitoring technique in W-band radio-over-fiber signals using clustering on asynchronous histograms / Nueva técnica de monitoreo sobre la dispersión en las señales de radio- sobre-fibra en la banda W usando clustering en histogramas asíncronos

    Scientific Electronic Library Online (English)

    J. J, Granada; A. M, Cárdenas; N, Guerrero.

    2014-12-01

    Full Text Available Los sistemas de Radio sobre Fibra (RoF), se proponen como una solución prometedora para transmitir señales de radiofrecuencia a altas tasas de transmisión y sobre largas distancias. Algunos estudios proponen el uso de frecuencias portadoras en la banda W (75 - 110 GHz), para lograr transmisiones en [...] el rango de los Gbps. Sin embargo, en este rango de frecuencias la dispersión cromática, se convierte en uno de los principales factores para el incremento de la tasa de error del bit. Este artículo presenta un nuevo método de monitoreo de la dispersión, basado en histogramas asíncronos para sistemas de RoF. El método planteado cuantifica el nivel de distorsión de la señal de radiofrecuencia, mediante un valor adimensional llamado: factor de dispersión. Dicho factor, se calcula mediante una técnica de agrupamiento, la cual se lleva a cabo usando ajustamiento gaussiano, mediante el algoritmo de máxima esperanza sobre histogramas asíncronos. El monitoreo de la dispersión se realiza sobre una plataforma de simulación, donde se transmiten las señales de radiofrecuencia, empleando modulación No retorno a cero (NRZ) y modulación binaria con desplazamiento de fase (BPSK), sobre 80 km de fibra óptica a 60, 75 y 100 GHz. Así, se estima la tasa de error de bit y se compara con el factor de dispersión; dónde se evidencia que los efectos de la dispersión no son proporcionales al incremento en la frecuencia de la portadora, la velocidad de transmisión y la distancia. El novedoso método de monitoreo, puede ser usado para estimar la viabilidad de los futuros sistemas de telecomunicaciones híbridos, basados en redes de fibra y bajo ciertos parámetros de transmisión tales como: la distancia, el formato de modulación y la frecuencia de la portadora. Abstract in english Radio over Fiber (RoF) systems have been proposed as a promising solution for transmitting radiofrequency signals at high data rates over long distances. To reach data rates in the Gbps range, studies indicate using the W-Band (75 -110 GHz). However, in this frequency band, chromatic dispersion beco [...] mes an issue that increases the bit-error-rate. This paper presents a novel digital dispersion monitoring technique for RoF systems based on asynchronous histogram analysis. This method quantifies the intensity level of the distortion of a radiofrequency demodulated signal by a dispersion factor. This dispersion factor is calculated using an enhanced clustering approach, which carries out a Gaussian fitting technique through the expectation-maximization algorithm. Dispersion monitoring was performed on radiofrequency transmission simulations using non-return-to-zero and binary phase-shift keying modulated signals over 80 km of optical fiber at 60, 75 and 100 GHz. The bit error rate is estimated and compared to the dispersion factor, showing that the behavior of the dispersion effects are not proportional to the increase of carrier frequency, bit rate and distances. This novel monitoring method can be used to estimate the feasibility of RoF systems for future hybrid networks under specific transmission parameters such as fiber length, modulation format, and carrier frequency.

  11. Dispersion-Enhanced Laser Gyroscope

    Science.gov (United States)

    Smith, David D.; Chang, Hongrok; Arissian, L.; Diels, J. C.

    2008-01-01

    We analyze the effect of a highly dispersive element placed inside a modulated optical cavity on the frequency and amplitude of the output modulation to determine the conditions for enhanced gyroscopic sensitivities. The element is treated as both a phase and amplitude filter, and the time-dependence of the cavity field is considered. Both atomic gases (two-level and multi-level) and optical resonators (single and coupled) are considered and compared as dispersive elements. We find that it is possible to simultaneously enhance the gyro scale factor sensitivity and suppress the dead band by using an element with anomalous dispersion that has greater loss at the carrier frequency than at the side-band frequencies, i.e., an element that simultaneously pushes and intensifies the perturbed cavity modes, e.g. a two-level absorber or an under-coupled optical resonator. The sensitivity enhancement is inversely proportional to the effective group index, becoming infinite at a group index of zero. However, the number of round trips required to reach a steady-state also becomes infinite when the group index is zero (or two). For even larger dispersions a steady-state cannot be achieved, and nonlinear dynamic effects such as bistability and periodic oscillations are predicted in the gyro response.

  12. Determination of the Uranium Valence State in the Brannerite Structure using EELS, XPS, and EDX

    International Nuclear Information System (INIS)

    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 (TEM-EELS), 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, 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 minimize the effects of electron beam reduction of U(VI) and U(V)

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

    International Nuclear Information System (INIS)

    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

  14. 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)

  15. IR spectra of mixed-valence vanadium oxides M2V3O8 (M=K, Rb, Cs, NH4)

    International Nuclear Information System (INIS)

    The compounds M2V3O8 (M=K, Rb, Cs, NH4) were prepared from solutions of the MVO3/VOSO4=2 composition at pH 8 and the temperature 80 Deg C. The prepared compounds were identified by means of chemical analysis, X-ray diffraction, IR spectroscopy. Their spectra are single-type in the range of oscillation frequencies of the vanadium-oxygen sublattices (1000 - 300 cm-1) on account of their isostructural states. Four-valence vanadium occupies the position V(1) with the symmetry C4 and it is surrounded by oxygen atoms in the form of the tetragonal pyramid V(1)O5. Five-valence vanadium in the position V(2) forms the diortho-group V(2)O7 of the local symmetry C2v. For the studied mixed-valence vanadium oxides the bands responsible for valence oscillations of the VIVO5 and V2VO7 polyhedrons were scattered. The frequencies of the absorption bands peaks change in the range from 3 to 22 cm-1 in relation to the nature of cation

  16. Valence state studies of CO2+ and CS2+ by photoionization with synchrotron radiation

    International Nuclear Information System (INIS)

    In the present work, we describe several types of photoelectron spectroscopy experiments for elucidating certain valence photoionization mechanisms and the spectroscopy of residual ions in the case of two linear triatomic molecules CO2 and CS2. Using synchrotron radiation, we have measured the partial cross section (?) and angular distribution (?) associated to the ejection of an electron from the 4?g orbital of CO2. These measurements continuously performed between 25 and 55 eV photon energy have shown some evidence of the ?u shape resonance. We have suggested that the bending motion may be responsible of the large disagreement between experiment and various theories. The numerous satellite bands which appear in photoelectron spectra of CO2 and CS2 in the region of inner valence ionization (20-40 eV) have been systematically studied at several photon energies and various angles. The ? and ? variations have allowed to determine the symmetry of some of excited-ionized states of the ion. A comparison between the experimental and calculated spectra of CO2 and CS2 within a configuration interaction method (CIPSI) shows an excellent agreement and demonstrates the important role of 3 hole-two electrons configurations. In the CS2 case we also show the relationship between the double ionization continua and the structures observed at high binding energy. (author)

  17. High pressure study of mixed valence compound CsAuI3

    Science.gov (United States)

    Wang, Shibing; Hirai, Shigeto; Kemper, Alexander; Baldini, Maria; Ma, Hongwei; Riggs, Scott; Shapiro, Maxwell; Devereaux, Tom; Fisher, Ian; Mao, Wendy; Geballe, Ted

    2012-02-01

    CsAuI3, chemically described as Cs2Au^IAu^IIII6, is a mixed valence compound in the family of CsAuX3 (X = Cl, Br, I), resembling the high Tc superconductor parent compound BaBiO3. At ambient conditions it adopts a distorted perovskite structure with compressed Au^IX6 octahedra and elongated Au^IIIX6 octahedra along the crystallographic c-axis. The compound undergoes a pressure-induced transition into a new tetragonal phase comprising nearly equivalent AuX6 octahedra around 5.3 GPa, which agrees with the valence transition previously reported using M"ossbauer spectroscopy between 8-12 GPa. We present a thorough high pressure studies of CsAuI3 through X-ray diffraction and Raman spectroscopy, confirming a pressure-induced band Jahn-Teller effect associated with the 5d^9 Au^II ion. We will also report the reversible amorphization above 15 GPa.

  18. Band-Gap Bowing Parameter of the AlxIn1-xN Derived from Theoretical Simulation

    Science.gov (United States)

    Kuo, Yen-Kuang; Lin, Wen-Wei

    2002-09-01

    The band-gap energy and band-gap bowing parameter of the wurtzite AlInN alloys are investigated numerically with the CASTEP simulation program. The simulation results suggest that the unstrained band-gap bowing parameter of the wurtzite AlInN alloys is b=3.326 ± 0.072 eV. The simulation results also show that the width of the AlxIn1-xN top valence band at the ? point has a maximum value of about 6.57 eV when the aluminum composition is near 0.53. A summary of the band-gap energies, the width of the top valence band at the ? point, and the band-gap energy versus lattice constant relationship of the ternary InxGa1-xN alloys, AlxGa1-xN alloys, and AlxIn1-xN alloys is also provided.

  19. Space-Valence Priming with Subliminal and Supraliminal Words

    Directory of Open Access Journals (Sweden)

    UlrichAnsorge

    2013-02-01

    Full Text Available 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.

  20. Comparison between ab initio energy band structures of various chlorinated polyethylene derivatives

    Science.gov (United States)

    Assad Abdel-Raouf, Mohamed

    1989-09-01

    The band structures of various chlorinated polyethylene derivatives are calculated using an ab initio self-consisten field (SCF) linear combination of atomic orbitals (LCAO) technique. The results illustrate that the conduction band is shifted steadily towards lower energies as the number of chlorine atoms in the unit cell increases, and the gap between valence and conduction bands is decreased monotonically. The possibility of n-doping is explored. The comparison between the band structures of the chlorinated polymers and that of polytrifluorochloroethylene shows that the latter possesses a lower-lying conduction band and is, therefore, more adequate for doping.

  1. Electronic band structure modulated by local surface strain in the (111) facet of the silicon nanowires

    Science.gov (United States)

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

    2015-04-01

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

  2. The electronic band structure of GaBiAs/GaAs layers: Influence of strain and band anti-crossing

    Science.gov (United States)

    Batool, Z.; Hild, K.; Hosea, T. J. C.; Lu, X.; Tiedje, T.; Sweeney, S. J.

    2012-06-01

    The GaBixAs1-x bismide III-V semiconductor system remains a relatively underexplored alloy particularly with regards to its detailed electronic band structure. Of particular importance to understanding the physics of this system is how the bandgap energy Eg and spin-orbit splitting energy ?o vary relative to one another as a function of Bi content, since in this alloy it becomes possible for ?o to exceed Eg for higher Bi fractions, which occurrence would have important implications for minimising non-radiative Auger recombination losses in such structures. However, this situation had not so far been realised in this system. Here, we study a set of epitaxial layers of GaBixAs1-x (2.3% ? x ? 10.4%), of thickness 30-40 nm, grown compressively strained onto GaAs (100) substrates. Using room temperature photomodulated reflectance, we observe a reduction in Eg, together with an increase in ?o, with increasing Bi content. In these strained samples, it is found that the transition energy between the conduction and heavy-hole valence band edges is equal with that between the heavy-hole and spin-orbit split-off valence band edges at ˜9.0 ± 0.2% Bi. Furthermore, we observe that the strained valence band heavy-hole/light-hole splitting increases with Bi fraction at a rate of ˜15 (±1) meV/Bi%, from which we are able to deduce the shear deformation potential. By application of an iterative strain theory, we decouple the strain effects from our experimental measurements and deduce Eg and ?o of free standing GaBiAs; we find that ?o indeed does come into resonance with Eg at ˜10.5 ± 0.2% Bi. We also conclude that the conduction/valence band alignment of dilute-Bi GaBiAs on GaAs is most likely to be type-I.

  3. A study of the valence shell spectroscopic and thermodynamic properties of trifluoronitrosomethane cations

    Energy Technology Data Exchange (ETDEWEB)

    Graham, D.M. [School of Physics and Astronomy, and the Photon Science Institute, University of Manchester, Oxford Road, Manchester M13 9PL (United Kingdom); Powis, I. [School of Chemistry, University of Nottingham, Nottingham NG7 2RD (United Kingdom); Underwood, J.G. [Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT (United Kingdom); Shaw, D.A. [Daresbury Laboratory, Daresbury, Warrington, Cheshire WA4 4AD (United Kingdom); Holland, D.M.P., E-mail: david.holland@stfc.ac.uk [Daresbury Laboratory, Daresbury, Warrington, Cheshire WA4 4AD (United Kingdom)

    2012-02-06

    Highlights: Black-Right-Pointing-Pointer Fragmentation processes in CF{sub 3}NO have been studied using mass spectrometry. Black-Right-Pointing-Pointer Singly charged atomic fragments have been observed. Black-Right-Pointing-Pointer Experimental appearance energies have been compared to thermochemical estimates. Black-Right-Pointing-Pointer Hartree Fock transition energies and oscillator strengths have been calculated. - Abstract: A time-of-flight mass spectrometry study has been carried out to investigate the fragmentation processes occurring in trifluoronitrosomethane (CF{sub 3}NO) as a result of valence shell photoionisation. Synchrotron radiation has been used to record spectra in the photon energy range {approx}10-42 eV, and appearance energies have been determined for 10 fragment ions. At high excitation energies, singly charged atomic fragments have been observed. For the main dissociation channels, leading to the formation of NO{sup +}, CF{sub 2}{sup +} or CF{sub 3}{sup +}, the experimental appearance energies have been compared with thermochemical estimates, and a satisfactory agreement has been found. Structure observed in the total ion yield curve has been interpreted with the aid of excited state transition energies and oscillator strengths obtained in a time-dependent Hartree Fock calculation. The theoretical results show that configuration interaction strongly affects many of the valence states. A HeI excited photoelectron spectrum of CF{sub 3}NO has been measured and the orbital ionisation energies have been compared with theoretical values computed using the Outer Valence Green's Function approach. A large Franck-Condon gap is observed between the 12a Prime (n{sub -}) and the 11a{sup Prime} state bands, in accord with the calculated vertical ionisation energies of 10.87 and 16.32 eV for the 12a Prime (n{sub -}) and the 11a Prime (n{sub +}) orbitals, respectively. In the ion yield curve, the corresponding energy range is strongly influenced by autoionising valence states.

  4. Electron transfer within charge-localized arylhydrazine-centered mixed valence radical cations having larger bridges.

    Science.gov (United States)

    Nelsen, Stephen F; Schultz, Kevin P

    2009-05-14

    Kinetics for intramolecular charge transfer between two diarylhydrazine units, measured by ESR, are reported for six charge-localized mixed valence compounds having 9, 11, 13, and 16 bonds between the nitrogen atoms. A 17-bond bridged compound had too slow electron transfer to measure the rate constant by ESR. The optical spectra of these radical cations are compared with tert-butyl,aryl-substituted hydrazines, and rate constants calculated using parameters derived from the optical spectra are compared with the experimental values where possible. The charge-transfer band overlapped too badly with bridge-centered absorption for the 16-bond bridged compound to allow the comparison to be made. The 13-bond bridged compound gave worse agreement than the other compounds. Its optical rate constant was about 5.4 times the ESR rate constant at a temperature between the ranges in which the data were collected. PMID:19374409

  5. Competing valence-bond states of spin-3/2 fermions on a strongly coupled ladder

    Science.gov (United States)

    Szirmai, E.; Nonne, H.

    2014-12-01

    We study the possible ground-state configurations of two strongly coupled chains of charge neutral spin-3/2 fermionic atoms interacting via short-range van der Waals interaction. The coupling between the two chains is realized by a relatively large hopping amplitude. Exploiting the fact that such a ladder configuration can be mapped to an effective one-band model, we analyze the emerging ground states of the system. We show that various spatially inhomogeneous states, valence-bond states, and plaquette states compete depending on the filling and the ratio of the interaction strengths in the singlet and quintet scattering channel. We find that a Luttinger liquid state is the ground state of the strongly coupled ladder in an extended region of the parameter space, and we also show that a topologically nontrivial charge Haldane state can emerge in the strongly coupled ladder at quarter and three-quarter fillings.

  6. The Fermi surface and f-valence electron count of UPt3

    Science.gov (United States)

    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

    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.

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

    CERN Document Server

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

    2011-01-01

    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.

  8. Valence-band satellite in ferromagnetic nickel: LDA+DMFT study with exact diagonalization.

    Czech Academy of Sciences Publication Activity Database

    Koloren?, Jind?ich; Poteryaev, A.I.; Lichtenstein, A.I.

    2012-01-01

    Ro?. 85, ?. 23 (2012), "235136-1"-"235136-7". ISSN 1098-0121 Institutional research plan: CEZ:AV0Z10100520 Keywords : transition metals * strongly correlated electrons * LDA+DMFT Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.767, year: 2012 http://prb.aps.org/abstract/PRB/v85/i23/e235136

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

    International Nuclear Information System (INIS)

    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.

  10. Optical implementation and entanglement distribution in Gaussian valence bond states

    CERN Document Server

    Adesso, Gerardo

    2007-01-01

    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...

  11. RKKY interaction in mixed valence system and heavy fermion superconductivity

    International Nuclear Information System (INIS)

    The 1-D RKKY interaction of mixed valence system is given by using the thermodynamic perturbation theory. The numerical comparisons of 1-D and 3-D RKKY interaction between systems with localized magnetic moments of mixed valence and non-mixed valence show that the former is much stronger than the latter. From some analyses we propose that the heavy Fermion superconductivity comes from the RKKY interaction between two local f electrons which hop off the impurity site to become two continuum electrons. The source of the two impurity electrons hopping is the Coulomb interaction. It is also emphasized that the RKKY interaction does not disappear for the Kondo lattice, when the temperature is less than the Kondo temperature. (author)

  12. Fermi level stabilization and band edge energies in CdxZn1?xO alloys

    International Nuclear Information System (INIS)

    We have measured the band edge energies of CdxZn1?xO thin films as a function of composition by three independent techniques: we determine the Fermi level stabilization energy by pinning the Fermi level with ion irradiation, measure the binding energy of valence band states and core levels by X-ray photoelectron spectroscopy, and probe shifts in the conduction band and valence band density of states using soft X-ray absorption and emission spectroscopy, respectively. The three techniques find consensus in explaining the origin of compositional trends in the optical-bandgap narrowing upon Cd incorporation in wurtzite ZnO and widening upon Zn incorporation in rocksalt CdO. The conduction band minimum is found to be stationary for both wurtzite and rocksalt alloys, and a significant upward rise of the valence band maximum accounts for the majority of these observed bandgap changes. Given these band alignments, alloy disorder scattering is found to play a negligible role in decreasing the electron mobility for all alloys. These band alignment details, combined with the unique optical and electrical properties of the two phase regimes, make CdZnO alloys attractive candidates for photoelectrochemical water splitting applications.

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

    Energy Technology Data Exchange (ETDEWEB)

    Tsoutsou, D., E-mail: dtsoutsou@ims.demokritos.gr; Xenogiannopoulou, E.; Golias, E.; Tsipas, P.; Dimoulas, A. [National Center for Scientific Research “Demokritos,” 15310 Athens (Greece)

    2013-12-02

    The electronic band structure of monolayer (4?×?4) silicene on Ag(111) is imaged by angle resolved photoelectron spectroscopy. A dominant hybrid surface metallic band is observed to be located near the bulk Ag sp-band which is also faintly visible. The two-dimensional character of the hybrid band has been distinguished against the bulk character of the Ag(111) sp-band by means of photon energy dependence experiments. The surface band exhibits a steep linear dispersion around the K{sup ¯}{sub Ag} point and has a saddle point near the M{sup ¯}{sub Ag} point of Ag(111) resembling the ?-band dispersion in graphene.

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

    International Nuclear Information System (INIS)

    The electronic band structure of monolayer (4?×?4) silicene on Ag(111) is imaged by angle resolved photoelectron spectroscopy. A dominant hybrid surface metallic band is observed to be located near the bulk Ag sp-band which is also faintly visible. The two-dimensional character of the hybrid band has been distinguished against the bulk character of the Ag(111) sp-band by means of photon energy dependence experiments. The surface band exhibits a steep linear dispersion around the K¯Ag point and has a saddle point near the M¯Ag point of Ag(111) resembling the ?-band dispersion in graphene

  15. Solvent dependence of the g-anisotropy in the ESR of cyanide-bridged mixed-valence complexes.

    OpenAIRE

    Laidlaw, WM; Denning, RG; Murphy, DM; Green, JC

    2008-01-01

    The low temperature (approximately 5 K) X-band ESR spectra are reported of the cyanide-bridged mixed-valence complexes [(OC)5Cr(mu-CN)M(NH3)5]X2 (M = Ru, Os; X = PF6(-)) in frozen matrices formed from nitromethane, acetonitrile and dimethylformamide with toluene. The anisotropy (g paralell-g perpendicular) is greater for the ruthenium than for the osmium complex. It is positive in all cases and is strongly dependent on the hydrogen-bonding interaction between the solvent matrix and the metal-...

  16. Protected Fe valence in quasi-two-dimensional ?-FeSi2.

    Science.gov (United States)

    Miiller, W; Tomczak, J M; Simonson, J W; Smith, G; Kotliar, G; Aronson, M C

    2015-05-01

    We report the first comprehensive study of the high temperature form (?-phase) of iron disilicide. Measurements of the magnetic susceptibility, magnetization, heat capacity and resistivity were performed on well characterized single crystals. With a nominal iron d(6) configuration and a quasi-two-dimensional crystal structure that strongly resembles that of LiFeAs, ?-FeSi2 is a potential candidate for unconventional superconductivity. Akin to LiFeAs, ?-FeSi2 does not develop any magnetic order and we confirm its metallic state down to the lowest temperatures (T = 1.8 K). However, our experiments reveal that paramagnetism and electronic correlation effects in ?-FeSi2 are considerably weaker than in the pnictides. Band theory calculations yield small Sommerfeld coefficients of the electronic specific heat ? = Ce/T that are in excellent agreement with experiment. Additionally, realistic many-body calculations further corroborate that quasi-particle mass enhancements are only modest in ?-FeSi2. Remarkably, we find that the natural tendency to vacancy formation in the iron sublattice has little influence on the iron valence and the density of states at the Fermi level. Moreover, Mn doping does not significantly change the electronic state of the Fe ion. This suggests that the iron valence is protected against hole doping and indeed the substitution of Co for Fe causes a rigid-band like response of the electronic properties. As a key difference from the pnictides, we identify the smaller inter-iron layer spacing, which causes the active orbitals near the Fermi level to be of a different symmetry in ?-FeSi2. This change in orbital character might be responsible for the lack of superconductivity in this system, providing constraints on pairing theories in the iron based pnictides and chalcogenides. PMID:25837013

  17. Protected Fe valence in quasi-two-dimensional ?-FeSi2

    Science.gov (United States)

    Miiller, W.; Tomczak, J. M.; Simonson, J. W.; Smith, G.; Kotliar, G.; Aronson, M. C.

    2015-05-01

    We report the first comprehensive study of the high temperature form (?-phase) of iron disilicide. Measurements of the magnetic susceptibility, magnetization, heat capacity and resistivity were performed on well characterized single crystals. With a nominal iron d6 configuration and a quasi-two-dimensional crystal structure that strongly resembles that of LiFeAs, ?-FeSi2 is a potential candidate for unconventional superconductivity. Akin to LiFeAs, ?-FeSi2 does not develop any magnetic order and we confirm its metallic state down to the lowest temperatures (T = 1.8 K). However, our experiments reveal that paramagnetism and electronic correlation effects in ?-FeSi2 are considerably weaker than in the pnictides. Band theory calculations yield small Sommerfeld coefficients of the electronic specific heat ? = Ce/T that are in excellent agreement with experiment. Additionally, realistic many-body calculations further corroborate that quasi-particle mass enhancements are only modest in ?-FeSi2. Remarkably, we find that the natural tendency to vacancy formation in the iron sublattice has little influence on the iron valence and the density of states at the Fermi level. Moreover, Mn doping does not significantly change the electronic state of the Fe ion. This suggests that the iron valence is protected against hole doping and indeed the substitution of Co for Fe causes a rigid-band like response of the electronic properties. As a key difference from the pnictides, we identify the smaller inter-iron layer spacing, which causes the active orbitals near the Fermi level to be of a different symmetry in ?-FeSi2. This change in orbital character might be responsible for the lack of superconductivity in this system, providing constraints on pairing theories in the iron based pnictides and chalcogenides.

  18. Production of photocurrent due to intermediate-to-conduction-band transitions: a demonstration of a key operating principle of the intermediate-band solar cell.

    Science.gov (United States)

    Martí, A; Antolín, E; Stanley, C R; Farmer, C D; López, N; Díaz, P; Cánovas, E; Linares, P G; Luque, A

    2006-12-15

    We present intermediate-band solar cells manufactured using quantum dot technology that show for the first time the production of photocurrent when two sub-band-gap energy photons are absorbed simultaneously. One photon produces an optical transition from the intermediate-band to the conduction band while the second pumps an electron from the valence band to the intermediate-band. The detection of this two-photon absorption process is essential to verify the principles of operation of the intermediate-band solar cell. The phenomenon is the cornerstone physical principle that ultimately allows the production of photocurrent in a solar cell by below band gap photon absorption, without degradation of its output voltage. PMID:17280325

  19. Dispersed Indeterminacy

    CERN Document Server

    Fayngold, Moses

    2013-01-01

    A state of a single particle can be represented by a quantum blob in the corresponding phase space, or a patch (granule) in its 2-D subspace. Its area is frequently stated to be no less than, implying that such a granule is an indivisible quantum of the 2-D phase space. But this is generally not true, as is evident, for instance, from representation of some states in the basis of innately discrete observables like angular momentum. Here we consider some dispersed states involving the evanescent waves different from that in the total internal reflection. Such states are represented by a set of separated granules with individual areas, but with the total indeterminacy . An idealized model has a discrete Wigner function and is described by a superposition of eigenstates with eigenvalues and forming an infinite periodic array of dots on the phase plane. The question about the total indeterminacy in such state is discussed. We argue that the eigenstates corresponding to the considered EW cannot be singled out by a...

  20. Hydrodynamic dispersion

    International Nuclear Information System (INIS)

    A dominant mechanism contributing to hydrodynamic dispersion in fluid flow through rocks is variation of travel speeds within the channels carrying the fluid, whether these be interstices between grains, in granular rocks, or cracks in fractured crystalline rocks. The complex interconnections of the channels ensure a mixing of those parts of the fluid which travel more slowly and those which travel faster. On a macroscopic scale this can be treated statistically in terms of the distribution of times taken by a particle of fluid to move from one surface of constant hydraulic potential to another, lower, potential. The distributions in the individual channels are such that very long travel times make a very important contribution. Indeed, while the mean travel time is related to distance by a well-defined transport speed, the mean square is effectively infinite. This results in an asymmetrical plume which differs markedly from a gaussian shape. The distribution of microscopic travel times is related to the distribution of apertures in the interstices, or in the microcracks, which in turn are affected in a complex way by the stresses acting on the rock matrix

  1. Optical properties of Eu2+/Eu3+ mixed valence, silicon nitride based materials

    International Nuclear Information System (INIS)

    Eu2SiN3, a mixed valence europium nitridosilicate, has been prepared via solid-state reaction synthesis and its oxidation behavior and optical properties have been determined. Furthermore, the stability of several isostructural compounds of the type M2+L3+SiN3 has been predicted by using the density functional theory calculations, and verified by the actual synthesis of CaLaSiN3, CaEuSiN3 and EuLaSiN3. The band gap of CaLaSiN3 was found around 3.2 eV giving the material its yellow color. Eu2SiN3 on the other hand is black due to a combination of the 4f–5d absorption band of Eu2+ and the charge transfer band of Eu3+. Thermogravimetric analysis and Raman spectroscopic study of Eu2SiN3 revealed that oxidation of this compound in dry air takes place via a nitrogen retention complex. - Graphical abstract: Energy level scheme of Eu2SiN3 showing the occupied N3? 2p band (blue rectangle), unoccupied Eu2+ 5d band (white rectangle), occupied Eu2+ 4f ground states (filled red circles) and unoccupied Eu2+ ground states (open red circles). - Highlights: • Density functional theory calculations on the stability of M2+L3+SiN3 compounds. • Solid-state reaction synthesis of Eu2SiN3, CaLaSiN3, EuLaSiN3 and CaEuSiN3. • Determination of the Eu2+ 4f–5d and Eu3+ CT transitions in M2+L3+SiN3 compounds. • Oxidation of Eu2SiN3 in dry air takes place via a nitrogen retention complex

  2. The use and misuse of some positively valenced community concepts.

    Science.gov (United States)

    Cowen, E L

    2001-02-01

    Considers the usage of four somewhat amorphous, but positively valenced, community mental health terms: primary prevention in mental health (and closely related notions such as wellness enhancement and positive psychology); resilience; charter schools; and empowerment. Use of these concepts often reflects a need to align with currently popular, "in"-terminology, rather than an intrinsic connection between what is being written about and a tight definition of the concept in question. Usages built primarily around a concept's positive valence and glitter tend to: (a) break down communication; (b) confuse rather than clarify; and (c) ultimately retard a field's growth and progress. PMID:11300664

  3. Core-valence luminescence in ABX3 crystals

    International Nuclear Information System (INIS)

    The investigation of the new type of intrinsic emission caused by recombination of core holes and valence electrons, i.e., the core valence luminescence (CVL), is made for perovskite-like ABX3 crystals (A = Li, K, Rb, Cs; B = Mg, Ca, Sr, Ba; X = F, Cl, Br). For this crystals the spectra of CVL cover 9 - 2 eV region, time decay constants change in 1 - 3 ns and bound, emission intensity in some crystals exceeds the intensity in AHC in several times. The possibility of growing ABX3 crystals with different lattice parameters allows us to control spectral and kinetics parameters as well as CVL light yield

  4. Coupled-cluster calculations for valence systems around O-16

    OpenAIRE

    Gour, J. R.; Piecuch, P.; Hjorth-Jensen, M.; Wloch, M.; Dean, D. J.

    2005-01-01

    We study the ground and low-lying excited states of O-15, O-17, N-15, and F-17 using modern two-body nucleon-nucleon interactions and the suitably designed variants of the ab initio equation-of-motion coupled-cluster theory aimed at an accurate description of systems with valence particles and holes. A number of properties of O-15, O-17, N-15, and F-17, including ways the energies of ground and excited states of valence systems around O-16 change as functions of the number o...

  5. Isolated flat bands and spin-1 conical bands in two-dimensional lattices

    Science.gov (United States)

    Green, Dmitry; Santos, Luiz; Chamon, Claudio

    2010-08-01

    Dispersionless bands, such as Landau levels, serve as a good starting point for obtaining interesting correlated states when interactions are added. With this motivation in mind, we study a variety of dispersionless (“flat”) band structures that arise in tight-binding Hamiltonians defined on hexagonal and kagome lattices with staggered fluxes. The flat bands and their neighboring dispersing bands have several notable features: (a) flat bands can be isolated from other bands by breaking time-reversal symmetry, allowing for an extensive degeneracy when these bands are partially filled; (b) an isolated flat band corresponds to a critical point between regimes where the band is electron-like or hole-like, with an anomalous Hall conductance that changes sign across the transition; (c) when the gap between a flat band and two neighboring bands closes, the system is described by a single spin-1 conical-like spectrum, extending to higher angular momentum the spin-1/2 Dirac-like spectra in topological insulators and graphene; (d) some configurations of parameters admit two isolated parallel flat bands, raising the possibility of exotic “heavy excitons”; and (e) we find that the Chern number of the flat bands, in all instances that we study here, is zero.

  6. Band Anticrossing in Highly Mismatched Compound Semiconductor Alloys

    Science.gov (United States)

    Yu, Kin Man; Wu, J.; Walukiewicz, W.; Ager, J. W.; Haller, E. E.; Miotkowski, I.; Su, Ching-Hua; Curreri, Peter A. (Technical Monitor)

    2001-01-01

    Compound semiconductor alloys in which metallic anions are partially replaced with more electronegative isoelectronic atoms have recently attracted significant attention. Group IIIN(sub x)V(sub 1-x) alloys with a small amount of the electronegative N substituting more metallic column V elements has been the most extensively studied class of such Highly Mismatched Alloys (HMAs). We have shown that many of the unusual properties of the IIIN(sub x)V(sub 1-x) alloys can be well explained by the Band Anticrossing (BAC) model that describes the electronic structure in terms of an interaction between highly localized levels of substitutional N and the extended states of the host semiconductor matrix. Most recently the BAC model has been also used to explain similar modifications of the electronic band structure observed in Te-rich ZnS(sub x)Te(sub 1-x) and ZnSe(sub y)Te(sub 1-y) alloys. To date studies of HMAs have been limited to materials with relatively small concentrations of highly electronegative atoms. Here we report investigations of the electronic structure of ZnSe(sub y)Te(sub 1-y) alloys in the entire composition range, y between 0 and 1. The samples used in this study are bulk ZnSe(sub y)Te(sub 1-y) crystals grown by either a modified Bridgman method or by physical vapor transport. Photomodulated reflection (PR) spectroscopy was used to measure the composition dependence of optical transitions from the valence band edge and from the spin-orbit split off band to the conduction band. The pressure dependence of the band gap was measured using optical absorption in a diamond anvil cell. We find that the energy of the spin-orbit split off valence band edge does not depend on composition and is located at about 3 eV below the conduction band edge of ZnSe. On the Te-rich side the pressure and the composition dependence of the optical transitions are well explained by the BAC model which describes the downward shift of the conduction band edge in terms of the interaction between localized Se states and the conduction band. On the other hand we show that the large band gap reduction observed on the Se-rich side of the alloy system is a result of an interaction between the localized Te level and the valence bands. This interaction leads to the formation of a Te-like valence band edge that strongly interacts with the light hole valence band. Calculations based on a modified k(sup dot)p model account for the reduction of the band gap and the large increase of the spin-orbit splitting observed in Se-rich ZnSe(sub y)Te(sub 1-y) alloys. We will also discuss the importance of these new results for understanding of the electronic structure and band offsets in other highly mismatched alloy systems.

  7. Composition-Dependent Band Gap and Band-Edge Bowing in AlInN: A Combined Theoretical and Experimental Study

    Science.gov (United States)

    Schulz, Stefan; Caro, Miguel A.; Tan, Lay-Theng; Parbrook, Peter J.; Martin, Robert W.; O'Reilly, Eoin P.

    2013-12-01

    A combined experimental and theoretical study of the band gap of AlInN is presented, which confirms the breakdown of the virtual crystal approximation (VCA) for the conduction and valence band edges. Composition-dependent bowing parameters for these quantities are extracted. Additionally, composition-dependent band offsets for GaN/AlInN systems are provided. We show that local strain and built-in fields affect the band edges significantly, leading to optical polarization switching at a much lower In composition than expected from a VCA approach.

  8. Band-gap bowing, band offsets, and electron affinity for InGaN alloys: A DFT study.

    Science.gov (United States)

    Moses, Poul; van de Walle, Chris

    2009-03-01

    InGaN alloys are successfully being used in optical, electronic, and photovoltaic devices; a novel application is for photochemical water splitting. In order to further improve InGaN-based devices a detailed understanding of the materials properties as a function of alloy composition is needed. To obtain such insight we have investigated the band bowing and absolute band positions of InGaN alloys using density functional theory. The HSE exchange correlation functional has been used in order to accurately calculate the electronic band structure [1]. Detailed surface calculations have been performed that, combined with bulk calculations for alloys, yield information about the positions of valence and conduction bands on an absolute energy scale. We will discuss bowing effects, band offsets, and electron affinities in light of the application of InGaN alloys for photochemical hydrogen production. [1] J. Heyd, G. E. Scuseria, and M. Ernzerhof, J. Chem. Phys. 118, 8207 (2003)

  9. Extended Composite Right/Left-Handed Transmission Line and Dual-Band Reactance Transformation

    OpenAIRE

    Yuming Zhang; Barry Spielman

    2010-01-01

    An extended composite right/left-handed transmission line is introduced, and its dual-band bandpass filter characteristics are explored. Novel reactance transformations, derived from this transmission line, are formulated to transform a low-pass prototype filter into a dual-band bandpass filter with arbitrary dual pass bands, well-defined in-band attenuation ripples, and high out-of-band rejection. The physical insight into such a dual-band bandpass filter is provided with a dispersion analys...

  10. Brillouin scattering, piezobirefringence, and dispersion of photoelastic coefficients of CdS and ZnO

    DEFF Research Database (Denmark)

    Berkowicz, R.; Skettrup, Torben

    1975-01-01

    We have measured the dispersion of the Brillouin scattering from acoustoelectrical domains in CdS and ZnO. These spectra are compared with the birefringence spectra obtained by applying uniaxial stress. The resonant cancellation of the Brillouin scattering occurs at the spectral position of the isotropic point of the stress-induced birefringence. From these spectra it is concluded that the Brillouin scattering in CdS and ZnO is determined by elasto-optic effects alone. The spectra of some of the photoelastic coefficients have been determined. A model dielectric constant is derived where both ground-state excitons and unbound continuum exciton states contribute. From this dielectric constant and the quasicubic model we calculate all the six independent photoelastic coefficents. By comparison with the experimental results the shear deformation potentials of the valence bands are obtained. It is found that the exchange interaction between the excitons may change the values of the photoelastic coefficients in ZnOabout 10%.

  11. 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)

  12. Automatic Dispersion Measurements of Helical Slow- Wave Structure

    Directory of Open Access Journals (Sweden)

    S. J. Rao

    2000-01-01

    Full Text Available An experimental setup for computer-controlled automatic measurement of dispersion characteristi of helical slow-wave structures (SWSs has been described. A non-resonant perturbation technique was employed for this purpose. The dispersion characteristics of a practical X-Ku band helical SWSwere studied using this experimental setup. The experimental results have shown good agreement with analytical results obtained using an equivalent circuit approach for an X-Ku band helix SWS.

  13. Band alignment switching and the interaction between neighboring silicon nanocrystals embedded in a SiC matrix

    Science.gov (United States)

    Kocevski, V.; Eriksson, O.; Rusz, J.

    2015-04-01

    We present results from density functional theory study of the electronic properties of silicon nanocrystals (Si NCs) embedded in a silicon carbide (SiC) matrix, considering different combinations of various NCs and host matrix sizes. We show that the NC and the host matrix form a type-II band alignment, with the states at the top of the valence band being in the Si NC and the states at the bottom of the conduction band in the host matrix. Moreover, this band alignment can be interchanged with introducing oxygen at the interface. This interchange in the band alignment has a rather weak influence on the absorption of the system. We demonstrate that the charge densities of some valence band states can overlap with the charge densities of the neighboring NCs. We also demonstrate that this leakage of states is significant when the distance between the neighboring NCs is less than ˜1.6 nm .

  14. 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

  15. Light absorption and reflection in mixed valence TmSe

    International Nuclear Information System (INIS)

    Theoretical description of an imaginary part of dielectric permittivity (optical density of states) for TmSe compound with intermediate valence of f-electrons is suggested. The results of quantitative calculation which are compared with TmSe experimental reflection spectrum are presented

  16. Vection Modulates Emotional Valence of Autobiographical Episodic Memories

    Science.gov (United States)

    Seno, Takeharu; Kawabe, Takahiro; Ito, Hiroyuki; Sunaga, Shoji

    2013-01-01

    We examined whether illusory self-motion perception ("vection") induced by viewing upward and downward grating motion stimuli can alter the emotional valence of recollected autobiographical episodic memories. We found that participants recollected positive episodes more often while perceiving upward vection. However, when we tested a small moving…

  17. Suppression of valence-quark recombination in ?+ fragmentation into ?+

    International Nuclear Information System (INIS)

    We present inclusive ?±-,0 and ? cross sections in the beam fragmentation region of ?+p interactions at 250 GeV/c. The near equality of the ?+ and ?0 cross sections implies suppression of valence quark recombination in forward vector meson production. (orig.)

  18. An alternative approach of valence advantage in spatial competition

    OpenAIRE

    Hollard, Guillaume; Rossignol, Ste?phane

    2008-01-01

    This paper explores a two-candidate spatial voting model, where one candidate has a valence advantage. Contrary to previous models, we introduce a multiplicative advantage, rather than an additive one. This takes into account the possible interaction between the quality of a candidate and his policy platform. This leads to a strikingly different model, in which all extreme voters support the favored candidate.

  19. Mobile linkers on DNA-coated colloids: valency without patches.

    Science.gov (United States)

    Angioletti-Uberti, Stefano; Varilly, Patrick; Mognetti, Bortolo M; Frenkel, Daan

    2014-09-19

    Colloids coated with single-stranded DNA (ssDNA) can bind selectively to other colloids coated with complementary ssDNA. The fact that DNA-coated colloids (DNACCs) can bind to specific partners opens the prospect of making colloidal "molecules." However, in order to design DNACC-based molecules, we must be able to control the valency of the colloids, i.e., the number of partners to which a given DNACC can bind. One obvious, but not very simple approach is to decorate the colloidal surface with patches of single-stranded DNA that selectively bind those on other colloids. Here we propose a design principle that exploits many-body effects to control the valency of otherwise isotropic colloids. Using a combination of theory and simulation, we show that we can tune the valency of colloids coated with mobile ssDNA, simply by tuning the nonspecific repulsion between the particles. Our simulations show that the resulting effective interactions lead to low-valency colloids self-assembling in peculiar open structures, very different from those observed in DNACCs with immobile DNA linkers. PMID:25279648

  20. Tagging Multiple Emotional Stimuli: Negative Valence Has Little Benefit

    Science.gov (United States)

    Watson, Derrick G.; Blagrove, Elisabeth

    2012-01-01

    Six experiments examined the influence of emotional valence on the tagging and enumeration of multiple targets. Experiments 1, 5 and 6 found that there was no difference in the efficiency of tagging/enumerating multiple negative or positive stimuli. Experiment 2 showed that, when neutral-expression face distractors were present, enumerating…

  1. Opposing influences of affective state valence on visual cortical encoding.

    Science.gov (United States)

    Schmitz, Taylor W; De Rosa, Eve; Anderson, Adam K

    2009-06-01

    Positive and negative emotional states are thought to have originated from fundamentally opposing approach and avoidance behaviors. Furthermore, affective valence has been hypothesized to exert opposing biases in cognitive control. Here we examined with functional magnetic resonance imaging whether the opposing influences of positive and negative states extend to perceptual encoding in the visual cortices. Based on prior behavioral research, we hypothesized that positive states would broaden and negative states would narrow visual field of view (FOV). Positive, neutral, and negative states were induced on alternating blocks. To index FOV, observers then viewed brief presentations (300 ms) of face/place concentric center/surround stimuli on interleaved blocks. Central faces were attended, rendering the place surrounds unattended. As face and place information was presented at different visual eccentricities, our physiological metric of FOV was a valence-dependent modulation of place processing in the parahippocampal place area (PPA). Consistent with our hypotheses, positive affective states increased and negative states decreased PPA response to novel places as well as adaptation to repeated places. Individual differences in self-reported positive and negative affect correlated inversely with PPA encoding of peripheral places, as well as with activation in the mesocortical prefrontal cortex and amygdala. Psychophysiological interaction analyses further demonstrated that valence-dependent responses in the PPA arose from opponent coupling with extrafoveal regions of the primary visual cortex during positive and negative states. These findings collectively suggest that affective valence differentially biases gating of early visual inputs, fundamentally altering the scope of perceptual encoding. PMID:19494142

  2. 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.)

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

    Energy Technology Data Exchange (ETDEWEB)

    Yastrubchak, O.; Gluba, L.; ?uk, J. [Institute of Physics, UMCS, Pl. Marii Curie-Sk?odowskiej 1, 20-031 Lublin (Poland); Sadowski, J. [Institute of Physics, Polish Academy of Sciences, 02-668 Warszawa (Poland); MAX-Lab, Lund University, 22100 Lund (Sweden); Krzy?anowska, H. [Institute of Physics, UMCS, Pl. Marii Curie-Sk?odowskiej 1, 20-031 Lublin (Poland); Department of Physics and Astronomy, Vanderbilt University, 6506 Stevenson Center, Nashville, Tennessee 37325 (United States); Domagala, J. Z.; Andrearczyk, T.; Wosinski, T. [Institute of Physics, Polish Academy of Sciences, 02-668 Warszawa (Poland)

    2013-08-07

    Modulation photoreflectance spectroscopy and Raman spectroscopy have been applied to study the electronic- and band-structure evolution in (Ga,Mn)As epitaxial layers with increasing Mn doping in the range of low Mn content, up to 1.2%. Structural and magnetic properties of the layers were characterized with high-resolution X-ray diffractometry and SQUID magnetometery, respectively. The revealed results of decrease in the band-gap-transition energy with increasing Mn content in very low-doped (Ga,Mn)As layers with n-type conductivity are interpreted as a result of merging the Mn-related impurity band with the host GaAs valence band. On the other hand, an increase in the band-gap-transition energy with increasing Mn content in (Ga,Mn)As layers with higher Mn content and p-type conductivity indicates the Moss-Burstein shift of the absorption edge due to the Fermi level location within the valence band, determined by the free-hole concentration. The experimental results are consistent with the valence-band origin of mobile holes mediating ferromagnetic ordering in the (Ga,Mn)As diluted ferromagnetic semiconductor.

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

    International Nuclear Information System (INIS)

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

  5. Rotational bands terminating at maximal spin in the Rh-Pd region

    International Nuclear Information System (INIS)

    The interplay between collective and non-collective degrees of freedom is well accounted for in configurations evolving from rotational behaviour to terminating sates. These states are characterized by spins built from the angular momentum of the valence holes and valence particles and by oblate (? = +60 degree) or prolate (? = -120 degree) shape. Results obtained with the multidetector EUROGAM2 are presented. The cases of 102Pd, which is the first nucleus in which terminating bands built on valence space and core excited configurations have been observed, and 102Rh, which is the first odd-odd nucleus between the Z = 28 and Z = 50 shell closures in which terminating bands have been found, are discussed. Comments are made on lifetimes and transitions feeding the terminations

  6. Band alignment of n-SnO2/p-GaN hetero-junction studied by x-ray photoelectron spectroscopy

    International Nuclear Information System (INIS)

    X-ray photoelectron spectroscopy has been used to study band offsets at the n-SnO2/p-GaN hetero-junction. The valence-band offset (?EV) and the conduction-band offset (?Ec) are determined to be 0.97 ± 0.2 eV and 0.77 ± 0.2 eV respectively, indicating that the n-SnO2/p-GaN hetero-junction has a type II band alignment. (paper)

  7. Radiative thermal escape in intermediate band solar cells

    OpenAIRE

    Luque, A.; Martí, A.; E. Antolín; P. G. Linares; I. Tobías; Ramiro, I.

    2011-01-01

    To achieve high efficiency, the intermediate band (IB) solar cell must generate photocurrent from sub-bandgap photons at a voltage higher than that of a single contributing sub-bandgap photon. To achieve the latter, it is necessary that the IB levels be properly isolated from the valence and conduction bands. We prove that this is not the case for IB cells formed with the confined levels of InAs quantum dots (QDs) in GaAs grown so far due to the strong density of internal thermal photons at t...

  8. Valence, Arousal, and Cognitive Control: A Voluntary Task-Switching Study

    OpenAIRE

    Demanet, Jelle; Liefooghe, Baptist; Verbruggen, Frederick

    2011-01-01

    The present study focused on the interplay between arousal, valence, and cognitive control. To this end, we investigated how arousal and valence associated with affective stimuli influenced cognitive flexibility when switching between tasks voluntarily. Three hypotheses were tested. First, a valence hypothesis that states that the positive valence of affective stimuli will facilitate both global and task-switching performance because of increased cognitive flexibility. Second, an arousal hypo...

  9. Simulations with different lattice Dirac operators for valence and sea quarks

    OpenAIRE

    Baer, O.; Rupak, G.; Shoresh, N.

    2002-01-01

    We discuss simulations with different lattice Dirac operators for sea and valence quarks. A goal of such a "mixed" action approach is to probe deeper the chiral regime of QCD by enabling simulations with light valence quarks. This is achieved by using chiral fermions as valence quarks while computationally inexpensive fermions are used in the sea sector. Specifically, we consider Wilson sea quarks and Ginsparg-Wilson valence quarks. The local Symanzik action for this mixed t...

  10. Developmental Reversals in False Memory: Effects of Emotional Valence and Arousal

    Science.gov (United States)

    Brainerd, C. J.; Holliday, R. E.; Reyna, V. F.; Yang, Y.; Toglia, M. P.

    2010-01-01

    Do the emotional valence and arousal of events distort children's memories? Do valence and arousal modulate counterintuitive age increases in false memory? We investigated those questions in children, adolescents, and adults using the Cornell/Cortland Emotion Lists, a word list pool that induces false memories and in which valence and arousal can…

  11. Valence-Specific Laterality Effects in Vocal Emotion: Interactions with Stimulus Type, Blocking and Sex

    Science.gov (United States)

    Schepman, Astrid; Rodway, Paul; Geddes, Pauline

    2012-01-01

    Valence-specific laterality effects have been frequently obtained in facial emotion perception but not in vocal emotion perception. We report a dichotic listening study further examining whether valence-specific laterality effects generalise to vocal emotions. Based on previous literature, we tested whether valence-specific laterality effects were…

  12. BROAD-BAND CERAMIC-POLYMER PIEZOELECTRIC COMPOSITES

    OpenAIRE

    Sol Sanchez, M.; Montero Espinosa, F. R.; San Emeterio, J.

    1990-01-01

    Different aproaches have been used to enlarge the frequency of (1-3) ceramic polymer piezoelectric composites. In this paper a new concept of (1-3) composite desing is presented which introduces an additional band- width enlargement due to the resonant frequency dispersion of the composite ceramic bars. This frequency dispersion is obtained by chosing bars with different width to thickness ratios.

  13. Exciton dispersion from first principles

    OpenAIRE

    Matteo Gatti; Francesco Sottile

    2013-01-01

    We present a scheme to calculate exciton dispersions in real materials that is based on the first-principles many-body Bethe-Salpeter equation. We assess its high level of accuracy by comparing our results for LiF with recent inelastic x-ray scattering experimental data on a wide range of energy and momentum transfer. We show its great analysis power by investigating the role of the different electron-hole interactions that determine the exciton band structure and the peculiar “exciton revi...

  14. First-principles band-structure calculations and X-ray photoelectron spectroscopy studies of the electronic structure of TlPb{sub 2}Cl{sub 5}

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-01-05

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

  15. First-principles band-structure calculations and X-ray photoelectron spectroscopy studies of the electronic structure of TlPb2Cl5

    International Nuclear Information System (INIS)

    Highlights: • Electronic structure of TlPb2Cl5 is calculated by the FP-LAPW method. • The valence band is dominated by contributions of Cl 3p states. • Contributions of Pb 6p* states dominate at the bottom of the conduction band. • The FP-LAPW data allow concluding that TlPb2Cl5 is an indirect-gap material. • XPS core-level and valence-band spectra of polycrystalline TlPb2Cl5 are measured. -- Abstract: We report on first-principles calculations of total and partial densities of states of atoms constituting TlPb2Cl5 using the full potential linearized augmented plane wave (FP-LAPW) method. The calculations reveal that the valence band of TlPb2Cl5 is dominated by contributions of the Cl 3p-like states, which contribute mainly at the top of the valence band with also significant contributions throughout the whole valence-band region. In addition, the bottom of the conduction band of TlPb2Cl5 is composed mainly of contributions of the unoccupied Pb 6p-like states. Our FP-LAPW data indicate that the TlPb2Cl5 compound is an indirect-gap material with band gap of 3.42 eV. The X-ray photoelectron core-level and valence-band spectra for pristine and Ar+ ion-irradiated surfaces of a TlPb2Cl5 polycrystalline sample were measured. The measurements reveal high chemical stability and confirm experimentally the low hygroscopicity of TlPb2Cl5 surface

  16. The Band Gap of Graphene Is Efficiently Tuned by Monovalent Ions

    OpenAIRE

    Colherinhas, Guilherme; Fileti, Eudes Eterno; Chaban, Vitaly V.

    2014-01-01

    Following recently published study of Prezhdo and coworkers (JPC Letters, 2014, 5, 4129-4133), we report a systematic investigation of how monovalent and divalent ions influence valence electronic structure of graphene. Pure density functional theory is employed to compute electronic energy levels. We show that LUMO of an alkali ion (Li+, Na+) fits between HOMO and LUMO of graphene, in such a way tuning the bottom of the conduction band (i.e. band gap). In turn, Mg2+ shares ...

  17. Intermediate Valence Model for the Colossal Magnetoresistance in $Tl_{2}Mn_{2}O_{7}$

    CERN Document Server

    Ventura, C I

    1997-01-01

    The colossal magnetoresistance exhibited by Tl_{2}Mn_{2}O_{7} is an interesting phenomenon, as it is very similar to that found in perovskite manganese oxides although the compound differs both in its crystalline structure and electronic properties from the manganites. At the same time, other pyrochlore compounds, though sharing the same structure with Tl_{2}Mn_{2}O_{7}, do not exhibit the strong coupling between magnetism and transport properties found in this material. Mostly due to the absence of evidence for significant doping into the Mn-O sublattice, and the tendency of Tl to form conduction bands, the traditional double exchange mechanism mentioned in connection with manganites does not seem suitable to explain the experimental results in this case. We propose a model for Tl_{2}Mn_{2}O_{7} consisting of a lattice of intermediate valence ions fluctuating between two magnetic configurations, representing Mn-3d orbitals, hybridized with a conduction band, which we associate with Tl. This model had been pr...

  18. Charge density waves and local states in quasi-one-dimensional mixed valence inorganic complexes

    International Nuclear Information System (INIS)

    The ground state structures and local states associated with chemical defects in quasi-one-dimensional halogen (X) bridged transition metal (M) mixed valence solids of MX and MMX type have been studied. An adiabatic Hartree-Fock theoretical framework is presented and representative members are classified. The MX materials provide a class whose strong electron-phonon coupling usually favors a charge-density-wave (CDW) ground state. However, the coupling strength can be chemically tuned (e.g., by extension to MMX systems) or altered by pressure, driving the ground state structures towards, e.g., a bond-order-wave (BOW) phase. Electron-phonon driven self-trapped states are expected in both the CDW or BOW regimes. Resonance Raman spectra of the MMX solid K4(Pt2(P2O5H2)4Cl)·H2O show, in addition to the homogeneous ground state modes, sharp new features with excitation profiles shifted to the red of the intervalence-charge-transfer (IVCT) band. We attribute these new bands to a local polaron state formed by oxidation of the Pt2 Cl chain by a chemical defect. The observed spectral characteristics of this local state are in good agreement with theoretical predictions. (author). 28 refs, 4 figs, 1 tab

  19. Band offsets in c-Si/Si-XII heterojunctions

    Science.gov (United States)

    Mustafa, Jamal I.; Malone, Brad D.; Cohen, Marvin L.; Louie, Steven G.

    2014-08-01

    Silicon has a rich phase diagram with a multitude of phases existing over a wide range of pressures and temperatures, in addition to the common cubic silicon (c-Si) phase. One such phase, Si-XII, was first observed less than 2 decades ago in diamond anvil experiments, and more recently as a product of nanoindentation. In some of these latter experiments, I-V measurements were performed to characterize the c-Si/Si-XII interface that results when Si-XII is formed in cubic silicon substrates. In this paper we describe calculations of the band offsets in c-Si/Si-XII heterojunctions. We find that the heterojunction is of Type I and that the band offsets are estimated to be ?Ev=0.3 eV and ?Ec=0.5 eV for the valence bands and conduction bands, respectively.

  20. Emotional valence differentially affects encoding and retrieval of prospective memory in older adults.

    Science.gov (United States)

    Ballhausen, Nicola; Rendell, Peter G; Henry, Julie D; Joeffry, Sebastian; Kliegel, Matthias

    2015-09-01

    Studies manipulating emotional valence in prospective memory (PM) have so far revealed inconsistent results. In the present study, two experiments were conducted to systematically disentangle the effects of varying emotional valence in the encoding versus retrieval phase of PM in older adults. Results showed that, while cue valence at retrieval had no influence on PM performance, at encoding both positive and negative valence resulted in reduced PM performance. Findings suggest that emotional valence may have an influence on mnemonic processes at encoding rather than modifying cue detection in aging. PMID:25633458

  1. On valence electron density, energy dissipation and plasticity of bulk metallic glasses

    Energy Technology Data Exchange (ETDEWEB)

    Pang, J.J.; Tan, M.J. [School of Mechanical and Aerospace Engineering, Nanyang Technological University, 639798 Singapore (Singapore); Liew, K.M., E-mail: kmliew@cityu.edu.hk [Department of Civil and Architectural Engineering, City University of Hong Kong, Kowloon (Hong Kong)

    2013-11-15

    Highlights: ? Relationship between valence electron density and plasticity of metallic glasses. ? Poisson's ratio increases as electron density decreases. ? Energy dissipation proposed to understand plasticity. ? Low electron density indicates small activation energy. -- Abstract: In conventional crystalline alloys, valence electron density (VED) is one of the most significant factors in determining their phase stability and mechanical properties. Extending the concept to metallic glasses (MGs), it is found, not totally surprisingly, that their mechanical properties are VED-dependent as in crystalline alloys. Interestingly, the whole VED region can be separated into two zones: Zone 1 consists of Mg-, Ca-, and RE-based (RE for rare earth) alloys; Zone 2 consists of the rest of MGs. In either zone, for each type of MGs, Poisson's ratio generally decreases as VED increases. From the energy dissipation viewpoint proposed recently, the amorphous plasticity is closely related to the activation energy for the operation of shear-transformation-zones (STZs). Smaller STZ activation energy suggests higher ductility because STZs with lower activation energy are able to convert deformation work more efficiently into configurational energy rather than heat, which yields mechanical softening and advances the growth of shear bands (SBs). Following this model, it is revealed that the activation energies for STZ operation and crystallization are certainly proportional to VED. Thus, it is understood that, in Zone 2, MGs have a smaller VED and hence lower activation energies which are favorable for ductility and Poisson's ratio. In Zone 1, MGs have the lowest VED but apparent brittleness because either of low glass transition temperature and poor resistance to oxidation or of a large fraction of covalent bonds.

  2. Su(4) mixed valence regime in carbon nanotube quantum dots

    International Nuclear Information System (INIS)

    We study the evolution of conductance regimes in carbon nanotubes with doubly degenerate orbitals ('shells') by controlling the contact transparency within the same sample. For sufficiently open contacts, Kondo behavior is observed for 1, 2, and 3 electrons in the topmost shell. As the contacts are opened more, the sample enters the 'mixed valence' regime, where different charge states are strongly hybridized by electron tunneling. Here, the conductance as a function of gate voltage shows pronounced modulations with a period of four electrons, and all single-electron features are washed away at low temperature. We successfully describe this behavior by a simple formula with no fitting parameters. Finally, we find a surprisingly small energy scale that controls the temperature evolution of conductance and the tunneling density of states in the mixed valence regime

  3. Valence bond entanglement entropy of frustrated spin chains

    CERN Document Server

    Alet, Fabien; Capponi, Sylvain; Mambrini, Matthieu

    2010-01-01

    We extend the definition of the recently introduced valence bond entanglement entropy to arbitrary SU(2) wave functions of S=1/2 spin systems. Thanks to a reformulation of this entanglement measure in terms of a projection, we are able to compute it with various numerical techniques for frustrated spin models. We provide extensive numerical data for the one-dimensional J1-J2 spin chain where we are able to locate the quantum phase transition by using the scaling of this entropy with the block size. We also systematically compare with the scaling of the von Neumann entanglement entropy. We finally underline that the valence-bond entropy definition does depend on the choice of bipartition so that, for frustrated models, a "good" bipartition should be chosen, for instance according to the Marshall sign.

  4. Spin dynamics and magnetic ordering in mixed valence systems

    International Nuclear Information System (INIS)

    Neutron scattering measurements are reported on the mixed valence compounds Ce/sub 1-x/Th/sub x/ and TmSe. The Chi''(Q,?) as derived from the inelastic spectra of Ce0.74Th0.26 shows a peak in the ? phase near 20.0 meV and shifts abruptly to greater than 70.0 meV at the transition to the ? phase. The temperature independence of the susceptibility within the ? phase cannot be simply reconciled with the temperature dependence of the valence within the ? phase. TmSe is shown to order in a type I antiferromagnetic structure below T/sub N/ approx. 3.2 K. The magnetic phase diagram is understood as a successive domain reorientation and a metamagnetic phase transition for T 3+ orders in a type II structure but never achieves long range order

  5. Multicenter bonds, bond valence and bond charge apportion

    International Nuclear Information System (INIS)

    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

  6. Realistic estimate of valence transversity distributions from inclusive dihadron production

    CERN Document Server

    Radici, Marco; Bacchetta, Alessandro; Guagnelli, Marco

    2015-01-01

    We present an updated extraction of the transversity parton distribution based on the analysis of pion-pair production in deep-inelastic scattering off transversely polarized targets in collinear factorization. Data for proton and deuteron targets make it possible to perform a flavor separation of the valence components of the transversity distribution, using di-hadron fragmentation functions taken from the semi-inclusive production of two pion pairs in back-to-back jets in e+e- annihilation. The e+e- data from Belle have been reanalyzed using the replica method and a more realistic estimate of the uncertainties on the chiral-odd interference fragmentation function has been obtained. Then, the transversity distribution has been extracted by using the most recent and more precise COMPASS data for deep-inelastic scattering off proton targets. Our results represent the most accurate estimate of the uncertainties on the valence components of the transversity distribution currently available.

  7. Effects of musical valence on the cognitive processing of lyrics

    OpenAIRE

    Fiveash, Anna

    2014-01-01

    The effects of music on the brain have been extensively researched, and numerous connections have been found between music and language, music and emotion, and music and cognitive processing. Despite this work, these three research areas have never before been drawn together in a single research paradigm. This is significant as their combination could lead to valuable insights into the effects of musical valence on the cognitive processing of lyrics. Based on the feelings-as-information theor...

  8. Electronic coherence in mixed-valence systems: Spectral analysis

    OpenAIRE

    Jung, Y; Silbey, R. J.; Cao, J

    2000-01-01

    The electron transfer kinetics of mixed-valence systems is studied via solving the eigen-structure of the two-state non-adiabatic diffusion operator for a wide range of electronic coupling constants and energy bias constants. The calculated spectral structure consists of three branches in the eigen-diagram, a real branch corresponding to exponential or multi-exponential decay and two symmetric branches corresponding to population oscillations between donor and acceptor state...

  9. Topology of the resonating valence-bond state

    International Nuclear Information System (INIS)

    The authors study the topological order in the resonating valence-bond state. The elementary excitations have reversed charge-statistics relations: There are neutral spin-1/2 fermions and charge ±e spinless bosons, analogous to the solitons in polyacetylene. The charged excitations are very light, and form a degenerate Bose gas even at high temperatures. The authors discuss this model in the context of the recently discovered oxide superconductors

  10. On rational homology disk smoothings of valency 4 surface singularities

    OpenAIRE

    Wahl, Jonathan

    2010-01-01

    Thanks to the recent work of Bhupal, Stipsicz, Szabo, and the author, one has a complete list of resolution graphs of weighted homogeneous complex surface singularities admitting a rational homology disk ("QHD") smoothing, i.e., one with Milnor number 0. They fall into several classes, the most interesting of which are the three classes whose resolution dual graph has central vertex with valency 4. We give a uniform "quotient construction" of the QHD smoothings for these cla...

  11. Dynamic control of the photonic band gap using quantum coherence

    International Nuclear Information System (INIS)

    We propose a scheme of employing quantum interference and coherence in an optical medium with coupled electromagnetic fields to create a photonic band gap. A variable photonic band gap is achieved by the cross-phase-modulation of two counterpropagating coupling fields on a weak probe pulse. The proposed photonic band gap has potential applications for the dynamic control of group velocity dispersion compensation in fiber-optic communications

  12. Sketching the pion's valence-quark generalised parton distribution

    Directory of Open Access Journals (Sweden)

    C. Mezrag

    2015-02-01

    Full Text Available In order to learn effectively from measurements of generalised parton distributions (GPDs, it is desirable to compute them using a framework that can potentially connect empirical information with basic features of the Standard Model. We sketch an approach to such computations, based upon a rainbow-ladder (RL truncation of QCD's Dyson–Schwinger equations and exemplified via the pion's valence dressed-quark GPD, H?v(x,?,t. Our analysis focuses primarily on ?=0, although we also capitalise on the symmetry-preserving nature of the RL truncation by connecting H?v(x,?=±1,t with the pion's valence-quark parton distribution amplitude. We explain that the impulse-approximation used hitherto to define the pion's valence dressed-quark GPD is generally invalid owing to omission of contributions from the gluons which bind dressed-quarks into the pion. A simple correction enables us to identify a practicable improvement to the approximation for H?v(x,0,t, expressed as the Radon transform of a single amplitude. Therewith we obtain results for H?v(x,0,t and the associated impact-parameter dependent distribution, q?v(x,|b??|, which provide a qualitatively sound picture of the pion's dressed-quark structure at a hadronic scale. We evolve the distributions to a scale ?=2 GeV, so as to facilitate comparisons in future with results from experiment or other nonperturbative methods.

  13. Basic features of the pion valence-quark distribution function

    Directory of Open Access Journals (Sweden)

    Lei Chang

    2014-10-01

    Full Text Available The impulse-approximation expression used hitherto to define the pion's valence-quark distribution function is flawed because it omits contributions from the gluons which bind quarks into the pion. A corrected leading-order expression produces the model-independent result that quarks dressed via the rainbow–ladder truncation, or any practical analogue, carry all the pion's light-front momentum at a characteristic hadronic scale. Corrections to the leading contribution may be divided into two classes, responsible for shifting dressed-quark momentum into glue and sea-quarks. Working with available empirical information, we use an algebraic model to express the principal impact of both classes of corrections. This enables a realistic comparison with experiment that allows us to highlight the basic features of the pion's measurable valence-quark distribution, q?(x; namely, at a characteristic hadronic scale, q?(x?(1?x2 for x?0.85; and the valence-quarks carry approximately two-thirds of the pion's light-front momentum.

  14. Coupled-cluster calculations for valence systems around 16O

    International Nuclear Information System (INIS)

    We study the ground and low-lying excited states of 15O, 17O, 15N, and 17F using modern two-body nucleon-nucleon interactions and the suitably designed variants of the ab initio equation-of-motion coupled-cluster theory aimed at an accurate description of systems with valence particles and holes. A number of properties of 15O, 17O, 15N, and 17F, including ways the energies of ground and excited states of valence systems around 16O change as functions of the number of nucleons, are correctly reproduced by the equation-of-motion coupled-cluster calculations performed in up to eight major-oscillator shells. Certain disagreements with experiment are in part because of the degrees of freedom such as three-body interactions not accounted for in our effective two-body Hamiltonians. In particular, the calculated binding energies of 15O/15N and 17O/17F enable us to rationalize the discrepancy between the experimental and recently published [Phys. Rev. Lett. 94, 212501 (2005)] equation-of-motion coupled-cluster excitation energies for the J?=3- state of 16O. Our calculations demonstrate the feasibility of the equation-of-motion coupled-cluster methods to deal with valence systems around closed-shell nuclei and to provide results for systems beyond A=16

  15. Coupled-cluster calculations for valence systems around O16

    Science.gov (United States)

    Gour, J. R.; Piecuch, P.; Hjorth-Jensen, M.; W?och, M.; Dean, D. J.

    2006-08-01

    We study the ground and low-lying excited states of O15, O17, N15, and F17 using modern two-body nucleon-nucleon interactions and the suitably designed variants of the ab initio equation-of-motion coupled-cluster theory aimed at an accurate description of systems with valence particles and holes. A number of properties of O15, O17, N15, and F17, including ways the energies of ground and excited states of valence systems around O16 change as functions of the number of nucleons, are correctly reproduced by the equation-of-motion coupled-cluster calculations performed in up to eight major-oscillator shells. Certain disagreements with experiment are in part because of the degrees of freedom such as three-body interactions not accounted for in our effective two-body Hamiltonians. In particular, the calculated binding energies of O15/N15 and O17/F17 enable us to rationalize the discrepancy between the experimental and recently published [Phys. Rev. Lett. 94, 212501 (2005)] equation-of-motion coupled-cluster excitation energies for the J?=3- state of O16. Our calculations demonstrate the feasibility of the equation-of-motion coupled-cluster methods to deal with valence systems around closed-shell nuclei and to provide results for systems beyond A=16.

  16. Sketching the pion's valence-quark generalised parton distribution

    CERN Document Server

    Mezrag, C; Moutarde, H; Roberts, C D; Rodriguez-Quintero, J; Sabatie, F; Schmidt, S M

    2014-01-01

    In order to learn effectively from measurements of generalised parton distributions (GPDs), it is desirable to compute them using a framework that can potentially connect empirical information with basic features of the Standard Model. We sketch an approach to such computations, based upon a rainbow-ladder (RL) truncation of QCD's Dyson-Schwinger equations and exemplified via the pion's valence dressed-quark GPD, $H_\\pi^{\\rm v}(x,\\xi,t)$. Our analysis focuses primarily on $\\xi=0$, although we also capitalise on the symmetry-preserving nature of the RL truncation by connecting $H_\\pi^{\\rm v}(x,\\xi=\\pm 1,t)$ with the pion's valence-quark parton distribution amplitude. We explain that the impulse-approximation used hitherto to define the pion's valence dressed-quark GPD is generally invalid owing to omission of contributions from the gluons which bind dressed-quarks into the pion. A simple correction enables us to identify a practicable improvement to the approximation for $H_\\pi^{\\rm v}(x,0,t)$, expressed as th...

  17. Effects of valence-valence, core-valence, and core-core correlations on the fine-structure energy levels in Al-like ions

    International Nuclear Information System (INIS)

    This paper reports on multiconfiguration Dirac-Hartree-Fock calculations for both allowed and intercombination transitions and fine structure referring to the levels of a term in highly charged aluminum like ions. Results for fine-structure energy levels, the term splitting, the wavelengths, transition rates, and thereby the branching ratios and lifetimes for the Al-like 3s23p-3s3p2 transitions in the ions Fe XIV-Au LXVII are reported and compared with other theories and experiments, using the codes GRASP2K. Our calculated fine-structure energy levels are in excellent agreement with the experimental results and the experimentally compiled energy values of the National Institute for Standards and Technology wherever available. The calculated values including core-valence correlation are found to be similar and to compare very well with other theoretical and experimental values for medium-Z ions. For higher Z the inclusion of the valence correlation gives results in excellent agreement with those from many-body perturbation theory. We believe that our extensive calculated values can guide experimentalists in identifying the fine-structure levels in their future work. From our radiative decay rates we have also calculated radiative lifetimes of some fine-structure levels. In this calculation we also predict new data for several fine-structure levels where no other theoretical and/or experimental results are available.available.

  18. Effects of valence-valence, core-valence, and core-core correlations on the fine-structure energy levels in Al-like ions

    Science.gov (United States)

    Hao, Liang-Huan; Jiang, Gang; Hou, Hai-Jun

    2010-02-01

    This paper reports on multiconfiguration Dirac-Hartree-Fock calculations for both allowed and intercombination transitions and fine structure referring to the levels of a term in highly charged aluminum like ions. Results for fine-structure energy levels, the term splitting, the wavelengths, transition rates, and thereby the branching ratios and lifetimes for the Al-like 3s23p-3s3p2 transitions in the ions Fe XIV-Au LXVII are reported and compared with other theories and experiments, using the codes GRASP2K. Our calculated fine-structure energy levels are in excellent agreement with the experimental results and the experimentally compiled energy values of the National Institute for Standards and Technology wherever available. The calculated values including core-valence correlation are found to be similar and to compare very well with other theoretical and experimental values for medium-Z ions. For higher Z the inclusion of the valence correlation gives results in excellent agreement with those from many-body perturbation theory. We believe that our extensive calculated values can guide experimentalists in identifying the fine-structure levels in their future work. From our radiative decay rates we have also calculated radiative lifetimes of some fine-structure levels. In this calculation we also predict new data for several fine-structure levels where no other theoretical and/or experimental results are available.

  19. The determination of the acoustical phonon dispersion branches of CePd3 by inelastic neutron diffraction

    International Nuclear Information System (INIS)

    The result of this thesis is, that the phonon dispersion of CePd3, measured by inelastic neutron scattering, does not show any phonon softening effects due to valence fluctuations as it is observed in the phonon dispersion spectra of TmSe, SmS under pressure and SMsub(.75)Ysub(.25)S in dependence of the temperature. Even at low temperature no softening effects could be detected in comparison to the room temperature data. However we see indications for the existence of intermediate valence induced electron-phonon couplings in the linewidth of the longitudinal acoustic phonon in -direction with reduced wavevector xi=0.2. This phonon seems to be broadened at 135 K. If this broadening is a real intermediate valence effect, this effects manifest themselves much weaker in CePd3 than in the substances with NaCl-structure. The question whether such couplings realy exist can only be answered by further measurements. (orig.)

  20. Theoretical performance of solar cell based on mini-bands quantum dots

    International Nuclear Information System (INIS)

    The tremendous amount of research in solar energy is directed toward intermediate band solar cell for its advantages compared with the conventional solar cell. The latter has lower efficiency because the photons have lower energy than the bandgap energy and cannot excite mobile carriers from the valence band to the conduction band. On the other hand, if mini intermediate band is introduced between the valence and conduction bands, then the smaller energy photons can be used to promote charge carriers transfer to the conduction band and thereby the total current increases while maintaining a large open circuit voltage. In this article, the influence of the new band on the power conversion efficiency for structure of quantum dots intermediate band solar cell is theoretically investigated and studied. The time-independent Schrödinger equation is used to determine the optimum width and location of the intermediate band. Accordingly, achievement of a maximum efficiency by changing the width of quantum dots and barrier distances is studied. Theoretical determination of the power conversion efficiency under the two different ranges of QD width is presented. From the obtained results, the maximum power conversion efficiency is about 70.42%. It is carried out for simple cubic quantum dot crystal under fully concentrated light. It is strongly dependent on the width of quantum dots and barrier distances

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

    Science.gov (United States)

    Carlsson, Sandra; Zorina, Leokadiya; Allan, David R; Attfield, J Paul; Canadell, Enric; Batail, Patrick

    2013-03-18

    (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. PMID:23432439

  2. Magnetic oscillations and frequency mixing in a two-band conductor

    OpenAIRE

    Fortin, Jean-yves; Perez, Emmanuel; Audouard, Alain

    2003-01-01

    Exact analytical results of the de Haas-van Alphen (dHvA) effect in an idealized two-band Fermi liquid with parabolic dispersion are presented. We consider a Fermi surface consisting in two electron bands with different band edges and band masses. Magnetic breakthrough (MB) between the bands is negligible. Analytical expressions of the dHvA Fourier amplitudes are derived in the case where the total number of electron is fixed (Canonical Ensemble, CE). As already reported in ...

  3. Optimum estimate of delays and dispersive effects in low-frequency interferometric observations

    OpenAIRE

    Marti-Vidal, I

    2010-01-01

    Modern radio interferometers sensitive to low frequencies will make use of wide-band detectors. For such wide bandwidths, dispersive atmospheric effects introduce variations in the fringe delay which change through the band of the receivers. These undesired dispersive effects must be estimated and calibrated with the highest precision. We studied the achievable precision in the estimate of the ionospheric dispersion and the dynamic range of the correlated fringes for differe...

  4. Investigation of the Band Gap in Co3O4

    Science.gov (United States)

    Sholte, Mark; Lin, Chungwei; Kormondy, Kristy; Nunley, Timothy; Posadas, Agham; Zollner, Stefan; Demkov, Alexander

    2015-03-01

    Co3O4 is a strongly correlated oxide with a spinel structure and G-type antiferromagnetic order at temperatures below 40 K. It is a widely studied material owing to its applications in gas sensing, spintronics, batteries, and catalysis. The strong correlation and magnetism make it a difficult material to model from first principles. Density functional theory calculations require the use of a Hubbard U to correctly model its magnetic behavior. The band gap is sensitive to the choice of U allowing one to tailor the gap to a wide range of values. This often provides a phenomenological approach to determining U, but in the case of Co3O4 there is no experimental consensus on the actual value of the band gap. We utilize an alternate approach by matching the theoretical valence band structure to the actual valence band data obtained via x-ray photoemission spectroscopy. This generated set of U values is used to compute an absorption spectrum, which is in good agreement with ellipsometry results.

  5. Flat bands in the Weaire–Thorpe model and silicene

    Science.gov (United States)

    Hatsugai, Y.; Shiraishi, K.; Aoki, H.

    2015-02-01

    In order to analytically capture and identify peculiarities in the electronic structure of silicene, the Weaire–Thorpe (WT) model, a standard model for treating three-dimensional (3D) silicon, is applied to silicene with a buckled 2D structure. In the original WT model for four hybridized sp3 orbitals on each atom along with inter-atom hopping, the band structure can be systematically examined in 3D, where flat (dispersionless) bands exist as well. For examining silicene, here we re-formulate the WT model in terms of the overlapping molecular-orbital (MO) method which enables us to describe flat bands away from the electron–hole symmetric point. The overlapping MO formalism indeed enables us to reveal an important difference: while in 3D the dipersive bands with cones are sandwiched by doubly-degenerate flat bands, in 2D the dipersive bands with cones are sandwiched by triply-degenerate and non-degenerate (nearly) flat bands, which is consistent with the original band calculation by Takeda and Shiraishi. Thus there emerges a picture for why the whole band structure of silicene comprises a pair of dispersive bands with Dirac cones with each of the bands touching a nearly flat (narrow) band at ?. We can also recognize that, for band engineering, the bonds perpendicular to the atomic plane are crucial, and that ferromagnetism or structural instabilities are expected if we can shift the chemical potential close to the flat bands.

  6. Design of Broadband Dispersion Compensating Photonic Crystal Fiber

    Directory of Open Access Journals (Sweden)

    Md. Selim Habib

    2012-08-01

    Full Text Available This paper presents a triangular-lattice photonic crystal fiber for broadband dispersion compensation. The finite element method with perfectly matched absorbing layers boundary condition is used to investigate the guiding properties. The designed dispersion compensating fiber shows that it is possible to obtain a larger negative dispersion coefficient of ?360 ps/(nm.km at 1.55 ?m, better dispersion slope compensation, better compensation ratio in the entire  telecommunication (1460-1640 nm band by using a modest number of design parameters and very simple cladding design.

  7. Chromatic Dispersion Compensation Using Photonic Crystal Fibers with Hexagonal Distribution

    Directory of Open Access Journals (Sweden)

    Erick E. Reyes-Vera

    2013-11-01

    Full Text Available In this paper we show various configurations of photonic crystal fiber with hexagonal holes distribution for compensation of chromatic dispersion in optical communications links. The vectorial finite element method with scattering boundary condition was used for the analysis of the fibers. From these results it was estimated variation of the dispersion and the dispersion slope with respect to change in the diameter of the holes in the microstructure. With the above was possible to obtain values of dispersion in the C and L bands of telecommunications close to -850 ps / nm * km, with confinement losses 10-3 dB / km

  8. 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 ...

  9. Dispersing powders in liquids

    CERN Document Server

    Nelson, R D

    1988-01-01

    This book provides powder technologists with laboratory procedures for selecting dispersing agents and preparing stable dispersions that can then be used in particle size characterization instruments. Its broader goal is to introduce industrial chemists and engineers to the phenomena, terminology, physical principles, and chemical considerations involved in preparing and handling dispersions on a commercial scale. The book introduces novices to: - industrial problems due to improper degree of dispersion; - the nomenclature used in describing particles; - the basic physica

  10. Dispersion, Controlled Dispersion, and Three Applications

    CERN Document Server

    Bradshaw, Douglas H

    2010-01-01

    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...

  11. Investigation of crystalline and electronic band alignment properties of GaP/Ge(111) heterostructure

    International Nuclear Information System (INIS)

    Gallium phosphide (GaP) epitaxial layer and nanostructures are grown on n-Ge(111) substrates using metal organic vapour phase epitaxy. It is confirmed by high resolution x-ray diffraction measurements that the layer is highly crystalline and oriented with the coexistence of two domains, i.e., GaP(111)A and GaP(111)B, with an angle of 60° between them due to the formation of a wurtzite monolayer at the interface. The valence band offset between GaP and Ge is 0.7?±?0.1?eV as determined from the valence band onsets and from Kraut's method. A band alignment diagram for GaP/Ge/GeOx is also constructed which can be used to design monolithic optoelectronic integrated circuits

  12. Rydberg and valence excited states of dibromomethane in 35,000–95,000 cm?1 region studied using synchrotron radiation

    International Nuclear Information System (INIS)

    The UV–VUV photoabsorption spectrum of dibromomethane (CH2Br2) in the energy region 4.3–11.8 eV (35,000–95,000 cm?1) is investigated using synchrotron radiation. Rydberg series converging to the first four ionization limits at 10.52, 10.74, 11.21 and 11.30 eV corresponding to excitations from the 3b1, 2b2, 1a2, and 4a1 orbitals of CH2Br2 are identified and analyzed. Quantum defect values are observed to be consistent with excitation from the bromine lone pair orbitals. Assignments of the ns Rydberg series are revised and the np and nd Rydberg series are assigned for the first time. Observed vibrational features accompanying the 5p and 4d Rydberg states are assigned exclusively to the totally symmetric (a1) –CBr symmetric stretching mode (?3) in contrast to the earlier assignment to ?3 and –CH2 bending (?2) modes. The Rydberg and valence transitions observed in the present experiment are found to be in good agreement with the vertical excited states calculated using the TDDFT method. The calculations are further used to infer the valence transitions responsible for the broad intensity pedestals underlying the Rydberg transitions. The assignments are confirmed using isotopic substitution studies on CD2Br2 whose UV–VUV photoabsorption spectrum is reported here for the first time. This work presents a consolidated analysis of the UV–VUV photoabsorption spectrum of dibromomethane. - Highlights: • VUV spectroscopy of CH2Br2 using synchrotron radiation and TDDFT calculations. • Assignments of np and nd series for the first time and revised assignments of ns series. • Vibrational bands assigned to ?3 in contrast to earlier assignments of ?2 and ?3. • Valence states identified responsible for underlying intensity in VUV spectrum. • First VUV study of CD2Br2, used to consolidate Rydberg and vibronic assignments

  13. 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.

  14. Mixed Valence Europium Nitridosilicate Eu2SiN3

    OpenAIRE

    Zeuner, Martin; Pagano, Sandro; Matthes, Philipp; Bichler, Daniel; Johrendt, Dirk; Harmening, Thomas; Pöttgen, Rainer; Schnick, Wolfgang

    2009-01-01

    The mixed valence europium nitridosilicate Eu2SiN3 has been synthesized at 900°C in welded tantalum ampules starting from europium and silicon diimide Si(NH)2 in a lithium flux. The structure of the black material has been determined by single-crystal X-ray diffraction analysis (Cmca (no. 64), a=542.3(11) pm, b=1061.0(2) pm, c=1162.9(2) pm, Z=8, 767 independent reflections, 37 parameters, R1=0.017, wR2=0.032). Eu2SiN3 is a chain-type silicate comprising one-dimensional infinite nonbranched zw...

  15. An ecological valence theory of human color preference

    OpenAIRE

    Palmer, Stephen E.; Schloss, Karen B.

    2010-01-01

    Color preference is an important aspect of visual experience, but little is known about why people in general like some colors more than others. Previous research suggested explanations based on biological adaptations [Hurlbert AC, Ling YL (2007) Curr Biol 17:623–625] and color-emotions [Ou L-C, Luo MR, Woodcock A, Wright A (2004) Color Res Appl 29:381–389]. In this article we articulate an ecological valence theory in which color preferences arise from people’s average affective respon...

  16. Les nucleons de valence et la fission nucleaire asymetrique

    International Nuclear Information System (INIS)

    A new interpretation of the asymmetric nuclear fission is proposed as a two-step process. The first is a change in configuration of the valence shell. The second one is a jump of nucleons from the last shells to the new nucleus. There are several arguments sustaining such and interpretation as the linear variation of the average mass of the fission products with the number of the shell nucleons Np + Nn , or the existence of the reverse process - the cold fusion. Thus the systematic formation of a compound nucleus in the neutron capture is questioned. (Author)

  17. Valence Fluctuation in CeMo2Si2C

    OpenAIRE

    Paramanik, U. B.; Anupam; Burkhard, U.; Prasad, R.; Geibel, C.; Hossain, Z.

    2013-01-01

    We report on the valence fluctuation of Ce in CeMo$_{2}$Si$_{2}$C as studied by means of magnetic susceptibility $\\chi(T)$, specific heat $C(T)$, electrical resistivity $\\rho(T)$ and x-ray absorption spectroscopy. Powder x-ray diffraction revealed that CeMo$_{2}$Si$_{2}$C crystallizes in CeCr$_{2}$Si$_{2}$C-type layered tetragonal crystal structure (space group \\textit{P4/mmm}). The unit cell volume of CeMo$_{2}$Si$_{2}$C deviates from the expected lanthanide contraction, in...

  18. Valence Electron Energy Loss Spectroscopy of III-Nitride Semiconductors

    OpenAIRE

    Palis?aitis, Justinas

    2012-01-01

    This doctorate thesis covers both experimental and theoretical investigations of the optical responses of the group III-nitrides (AlN, GaN, InN) and their ternary alloys. The goal of this research has been to explore the usefulness of valence electron energy loss spectroscopy (VEELS) for materials characterization of group III-nitride semiconductors at the nanoscale. The experiments are based on the evaluation of the bulk plasmon characteristics in the low energy loss part of the EEL spectrum...

  19. Accurate ab initio potential energy curve of F2. II. Core-valence correlations, relativistic contributions, and long-range interactions

    Science.gov (United States)

    Bytautas, L.; Matsunaga, N.; Nagata, T.; Gordon, M. S.; Ruedenberg, K.

    2007-11-01

    The nonrelativistic, valence-shell-only-correlated ab initio potential energy curve of the F2 molecule, which was reported in the preceding paper, is complemented by determining the energy contributions that arise from the electron correlations that involve the core electrons as well as the contributions that are due to spin-orbit coupling and scalar relativistic effects. The dissociation curve rises rather steeply toward the energy of the dissociated atoms because, at larger distances, the atomic quadrupole-quadrupole repulsion and spin-orbit coupling counteract the attractive contributions from incipient covalent binding and correlation forces including dispersion.

  20. Study of the dielectric properties near the band gap by VEELS: gap measurement in bulk materials

    International Nuclear Information System (INIS)

    Measuring the band gap of bulk materials by valence electron energy loss spectroscopy (VEELS) is not straightforward. Mathematical procedures used to recover the single scattering distribution from raw data introduce artefacts in the signal, which complicate the gap measurement. In this work, we propose a method to overcome this and measure the direct band gap energy with an accuracy of ±0.1 eV. The method is tested on six crystalline wide-band gap materials: MgO, Ga2O3, SrTiO3, ZnO, BN and GaN

  1. The valence shell electronic states of trimethylene sulphide studied by photoabsorption and ab initio multireference configuration interaction calculations

    International Nuclear Information System (INIS)

    The absolute photoabsorption cross section of trimethylene sulphide has been measured between threshold and 30 eV using monochromated synchrotron radiation. Below the ionization threshold the spectrum exhibits numerous sharp peaks associated with Rydberg states belonging to series converging onto the X-tilde2B limit. At excitation energies above the ionization threshold at 8.655 eV intravalence transitions play a dominant role, resulting in the appearance of prominent broad bands. Ab initio multireference configuration interaction calculations have been performed to obtain excitation energies for valence electron transitions into Rydberg or virtual valence orbitals. These theoretical predictions have enabled assignments to be proposed for most of the structure due to Rydberg series converging onto the X-tilde2B1 limit. The calculations show that configuration interaction is important in the description of many of the excited states. This is particularly evident close to threshold where the theoretical results suggest that the observed, highly irregular, structure may be attributed to two Rydberg transitions and an intravalence transition. The calculations also establish that both of the dipole allowed 4b1 ? nda1 B1 Rydberg series should contribute to the absorption spectrum.

  2. Extended Composite Right/Left-Handed Transmission Line and Dual-Band Reactance Transformation

    Directory of Open Access Journals (Sweden)

    Yuming Zhang

    2010-01-01

    Full Text Available An extended composite right/left-handed transmission line is introduced, and its dual-band bandpass filter characteristics are explored. Novel reactance transformations, derived from this transmission line, are formulated to transform a low-pass prototype filter into a dual-band bandpass filter with arbitrary dual pass bands, well-defined in-band attenuation ripples, and high out-of-band rejection. The physical insight into such a dual-band bandpass filter is provided with a dispersion analysis. The transformations are verified by simulated results for dual-band bandpass filters.

  3. Valence admixture in the Eu/sub x/Rh/sub 1-x/ amorphous alloys

    International Nuclear Information System (INIS)

    Magnetic, Moessbauer, and L/sub III/-edge measurements are reported on the Eu/sub x/Rh/sub 1-x/ amorphous alloys. The experimental results clearly indicate that an inhomogeneous valence admixture occurs in the disordered phase. The fluctuating valence encountered in the crystalline EuRh2 is destroyed by the structural disorder. The average valence is discussed in terms of local environment

  4. Two-candidate competition with endogenous valence: a differential game approach

    OpenAIRE

    Köppl Turyna, Monika

    2014-01-01

    We propose a differential game approach to analyze two--candidate competition in a la Hotelling game with candidates simultaneously choosing locations and investment in valence. We find a Markov perfect equilibrium in which candidates choose divergent locations. Divergence from the median is increasing if the parameter measuring the importance of policy relative to valence is decreasing and if valence depreciates slowly. The results are generalizable to a version of the game with probabilisti...

  5. Core - valence correlation effects in the ground and low - lying excited states of GaN

    OpenAIRE

    Kraus, Michal; Šimová, Lucia; Neogrády, Pavel; Urban, Miroslav

    2010-01-01

    Abstract We present careful analysis of the accuracy of molecular properties of the GaN molecule calculated by the Coupled Cluster CCSD(T) method including the core-valence correlation effects. We demonstrate that calculations of the core-valence correlation effects with basis sets which were optimized considering just valence electrons of the gallium atom lead to unreliable results. Our objective is finding the relation between the accuracy and the oversimplification due to the us...

  6. Dispersion, controlled dispersion, and three applications

    Science.gov (United States)

    Bradshaw, Douglas H.

    Causality dictates that all physical media must be dispersive. (We will call a medium dispersive if its refractive index varies with frequency.) Ordinarily, strong dispersion is accompanied either by strong absorption or strong gain. However, over the past 15 years several groups have demonstrated that it is possible to have media that are both strongly dispersive and roughly transparent for some finite bandwidth. In these media, group and phase velocities may differ from each other by many orders of magnitude and even by sign. Relationships and intuitive models that are satisfactory when it is reasonable to neglect dispersion may then fail dramatically. In this dissertation we analyze three such cases of failure. Before looking at the specific cases, we review some basic ideas relating to dispersion. We review some of the geometric meanings of group velocity, touch on the relationship between group velocity and causality, and give some examples of techniques by which the group velocity may be manipulated. We describe the interplay between group velocity and energy density for non-absorbing dispersive media. We discuss the ideas of temporary absorption and emission as dictated by an instantaneous spectrum. We then apply these concepts in three specific areas. First, non-dispersive formulations for the momentum of light in a medium must be adjusted to account for dispersion. For over 100 years, there has been a gradual discussion of the proper form for the per-photon momentum. Two forms, each of which has experimental relevance in a 'dispersionless' medium, are the Abraham momentum, and the Minkowski momentum. If h is the angular frequency, n is the refractive index, h is Planck's constant, and c is the speed of light, then these reduce in a dispersionless medium to per-photon momenta of ho/(nc), and nho/c respectively. A simple generalization of the two momenta to dispersive media entails multiplying each per-photon momentum by n/ng, where ng is the group refractive 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. Dispersion may enhance or mitigate the frequency response of a pulse to a changing refractive index, and if dispersion changes with time, the pulse bandwidth must change in a compensatory fashion. We introduce an explicit description of the kinetics of dispersive nonstationary inhomogeneous media. Using this description, we show how the group velocity can modulate the frequency response to a change in the refractive index and how Doppler shifts may become large in a dispersive medium as the velocity of the Doppler shifting surface approaches the group velocity. We explain a simple way to use existing technology to either compress or decompress a given pulse, changing its bandwidth and spatial extent by several orders of magnitude while otherwise preserving its envelope shape. We then introduce a dynamic descriptions of two simple media--one dispersive and one nondispersive. We compare the transformation of basic quantities like photon number, momentum density, and frequency by a temporal change in the refractive index in a specific non-dispersive medium to those wrought by a temporal change in the group refractive index in a specific dispersive medium. The differences between to media are fundamental and emphasize the salience of dispersion in the study of nonstationary media. Finally, we note that the nature of a single optical cavity quasimode depends on intracavity dispersion. We show that the quantum field noise associated with a single cavity mode may be modulated by dispersion. For a well-chosen mode in a high-Q cavity, this can amount to either an increase or a decrease in total vacuum field energy by several orders of magnitude. We focus on the "white light cavity," showing that the quantum noise of an ideal white

  7. Plasma Dispersion in Fractional-Dimension Space

    CERN Document Server

    Mohapatra, Krushna Mohan

    2014-01-01

    The dielectric function for electron gas with parabolic energy bands is derived in a fractional dimensional space. The static response function shows a good dimensional dependance. The plasma frequencies are obtained from the roots of the dielectric functions. The plasma dispersion shows strong dimensional dependence. It is found that the plasma frequencies in the low dimensional systems are strongly dependent on the wave vector. It is weakly dependent in the three dimensional system and has a finite value at zero wave vector.

  8. The valence state of uranium in K6Cu12U2S15

    International Nuclear Information System (INIS)

    The paramagnetic behaviour of K6Cu12U2S15 has been analysed, regarding copper as diamagnetic (Cu+), sulfur as mixed-valent S2-/S- with magnetically silent delocalized S- holes in the valence band, and the actinide as either U5+[5f1] or U4+[5f2] in trigonally distorted octahedral surrounding (pseudosymmetry 3-bar) of sulfur. Fitting procedures have been carried out, accounting for spin-orbit coupling, ligand-field potential (parameters Bkq), interelectronic repulsion (for U4+[5f2]), cooperative magnetic effects (molecular field parameter ?), and applied magnetic field. Keeping the ratios B43/B40, B63/B60, B66/B60 on their point charge electrostatic values with respect to the sulfur ligands, the three axial parameters Bk0 (k=2,4,6) and ? were refined. Agreement between measured and calculated susceptibility data was obtained for U5+ with Bk0 values expected for octahedral surrounding and ?4+ model does yield a fit of comparable quality, but gives Bk0 values that are unreasonable with respect to sign and magnitude. To conclude,ect to sign and magnitude. To conclude, on the basis of the magnetic properties the title compound is a 5f1 system corresponding to the elements formal charges (K+)6(Cu+)12(U5+)2(S2-)13(S-)2

  9. Advantages of low beam energies in a TEM for valence EELS

    Science.gov (United States)

    Stöger-Pollach, M.; Pongratz, P.

    2010-02-01

    Since the availability of monochromators in transmission electron microscopes (TEMs), electron energy loss spectrometry (EELS) is widely used to determine band gaps and the dielectric properties of semiconductors on a nano-metre scale. Nevertheless, three physical effects hamper straightforward analysis: (a) relativistic energy losses, (b) the delocalization of the energy loss which is in the 10 nano-metreer range for valence losses, and (c) the presence of interface plasmons. When reducing the operation voltage of the TEM one can kill two birds with one stone: (a) the relativistic losses will disappear as soon as vespeed of the electron, c0 as the vacuum speed of light and n as the refractive index of the investigated sample) and (b) the delocalization will decrease, because it also depends on the energy of the incident electron probe. The determination of the optical properties of quantum structures is discussed in the case of GaP/GaAs interface at 200 keV and 20 keV beam energy, respectively. Further, the influence of the delocalization of the energy loss signal is discussed theoretically and experimentally.

  10. The Fermi surface and f-valence electron count of UPt{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    McMullan, G J [MRC Laboratory of Molecular Biology, Hills Road, Cambridge, CB2 0QH (United Kingdom); Rourke, P M C; McCollam, A; Julian, S R [Department of Physics, University of Toronto, Toronto, ON, M5S 1A7 (Canada); Norman, M R [Materials Science Division, Argonne National Laboratory, Argonne, IL 60439 (United States); Huxley, A D [School of Physics, James Clerk Maxwell Building, King' s Buildings, Mayfield Road, Edinburgh EH9 3JZ (United Kingdom); Doiron-Leyraud, N [Departement de Physique, Universite de Sherbrooke, Sherbrooke, PQ, J1K 2R1 (Canada); Flouquet, J [Departement de Recherche Fondamentale sur la Matiere Condensee, SPSMS, CEA/Grenoble, 17 rue des Martyrs, 38054 Grenoble cedex 9 (France); Lonzarich, G G [Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge, CB3 OHE (United Kingdom)], E-mail: sjulian@physics.utoronto.ca

    2008-05-15

    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 UPt{sub 3}. Our work was partially motivated by a new proposal that two 5f valence electrons per formula unit in UPt{sub 3} 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 UPt{sub 3}. 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.

  11. Dzyaloshinskii-Moriya interactions in valence bond systems I

    Science.gov (United States)

    Shtengel, Kirill; Raman, Kumar; Tovar, Mayra

    2009-03-01

    We investigate the effect of Dzyaloshinskii-Moriya interactions on the low temperature magnetic susceptibility for a system whose low energy physics is dominated by short-range valence bonds (singlets). Our general perturbative approach is applied to specific models expected to be in this class, including the Shastry-Sutherland model of the spin-dimer compound SrCu2(BO3)2 and the antiferromagnetic Heisenberg model of the recently discovered S=1/2 kagome compound ZnCu3(OH)6Cl2. The central result is that a short-ranged valence bond phase, when perturbed with Dzyaloshinskii-Moriya interactions, will remain time-reversal symmetric in the absence of a magnetic field but the susceptibility will be nonzero in the zero temperature limit. Applied to ZnCu3(OH)6Cl2, this model provides an avenue for reconciling experimental results, such as the lack of magnetic order and lack of any sign of a spin gap, with known theoretical facts about the kagome Heisenberg antiferromagnet.

  12. Dzyaloshinskii-Moriya interactions in valence-bond systems

    Science.gov (United States)

    Tovar, Mayra; Raman, Kumar S.; Shtengel, Kirill

    2009-01-01

    We investigate the effect of Dzyaloshinskii-Moriya interactions on the low-temperature magnetic susceptibility for a system whose low energy physics is dominated by short-range valence bonds (singlets). Our general perturbative approach is applied to specific models expected to be in this class, including the Shastry-Sutherland model of the spin-dimer compound SrCu2(BO3)2 and the antiferromagnetic Heisenberg model of the recently discovered S=1/2 kagomé compound ZnCu3(OH)6Cl2 . The central result is that a short-ranged valence-bond phase, when perturbed with Dzyaloshinskii-Moriya interactions, will remain time-reversal symmetric in the absence of a magnetic field but the susceptibility will be nonzero in the T?0 limit. Applied to ZnCu3(OH)6Cl2 , this model provides an avenue for reconciling experimental results, such as the lack of magnetic order and lack of any sign of a spin gap, with known theoretical facts about the kagomé Heisenberg antiferromagnet.

  13. Dzyloshinskii-Moriya interactions in valence bond systems II

    Science.gov (United States)

    Tovar, Mayra; Raman, Kumar; Shtengel, Kirill

    2009-03-01

    We investigate the effect of Dzyaloshinskii-Moriya interactions on the low temperature magnetic susceptibility for a system whose low energy physics is dominated by short-range valence bonds (singlets). Our general perturbative approach is applied to specific models expected to be in this class, including the Shastry-Sutherland model of the spin-dimer compound SrCu2(BO3)2 and the antiferromagnetic Heisenberg model of the recently discovered S=1/2 kagome compound ZnCu3(OH)6Cl2. The central result is that a short-ranged valence bond phase, when perturbed with Dzyaloshinskii-Moriya interactions, will remain time-reversal symmetric in the absence of a magnetic field but the susceptibility will be nonzero in the zero temperature limit. Applied to ZnCu3(OH)6Cl2, this model provides an avenue for reconciling experimental results, such as the lack of magnetic order and lack of any sign of a spin gap, with known theoretical facts about the kagome Heisenberg antiferromagnet.

  14. Coupled-cluster calculations for valence systems around O-16

    CERN Document Server

    Gour, J R; Hjorth-Jensen, M; Wloch, M; Dean, D J

    2006-01-01

    We study the ground and low-lying excited states of O-15, O-17, N-15, and F-17 using modern two-body nucleon-nucleon interactions and the suitably designed variants of the ab initio equation-of-motion coupled-cluster theory aimed at an accurate description of systems with valence particles and holes. A number of properties of O-15, O-17, N-15, and F-17, including ways the energies of ground and excited states of valence systems around O-16 change as functions of the number of nucleons, are correctly reproduced by the equation-of-motion coupled-cluster calculations. Within a harmonic oscillator basis and large effective model spaces, our results are converged for the chosen two-body Hamiltonians. Thus, all disagreements with experiment are, most likely, due to the degrees of freedom such as three-body interactions not accounted for in our effective two-body Hamiltonians. In particular, the calculated binding energies of O-15/N-15 and O-17/F-17 enable us to rationalize the discrepancy between the experimental a...

  15. +2 Valence Metal Concentrations in Lion Creek, Oakland, California

    Science.gov (United States)

    Vazquez, P.; Zedd, T.; Chagolla, R.; Dutton-Starbuck, M.; Negrete, A.; Jinham, M.; Lapota, M.

    2012-12-01

    Seven major creeks exist within the City of Oakland, California. These creeks all flow in the southwest direction from forested hills down through densely populated streets where they become susceptible to urban runoff. Lion Creek has been diverted to engineered channels and underground culverts and runs directly under our school (Roots International) before flowing into the San Leandro Bay. One branch of the creek begins near an abandoned sulfur mine. Previous studies have shown that extremely high levels of lead, arsenic and iron exist in this portion of the creek due to acid mine drainage. In this study +2 valence heavy metals concentration data was obtained from samples collected from a segment of the creek located approximately 2.8 miles downstream from the mine. Concentrations in samples collected at three different sites along this segment ranged between 50 ppb and 100 ppb. We hypothesize that these levels are related to the high concentration of +2 valence heavy metals at the mining site. To test this hypothesis, we have obtained samples from various locations along the roughly 3.75 miles of Lion Creek that are used to assess changes in heavy metals concentration levels from the mining site to the San Leandro Bay.

  16. Competing valence bond crystals in the kagome quantum dimer model

    Science.gov (United States)

    Poilblanc, Didier; Misguich, Grégoire

    2011-12-01

    The singlet dynamics, which plays a major role in the physics of the spin-1/2 quantum Heisenberg antiferromagnet (QHAF) on the kagome lattice, can be approximately described by projecting onto the nearest-neighbor valence bond (NNVB) singlet subspace. We revisit here the effective quantum dimer model, which originates from the latter NNVB-projected Heisenberg model via a nonperturbative Rokhsar-Kivelson-like scheme. By using Lanczos exact diagonalization on a 108-site cluster supplemented by a careful symmetry analysis, it is shown that a previously found 36-site valence bond crystal (VBC) in fact competes with a new type of 12-site “resonating-columnar” VBC. Interestingly, these two VBCs “emerge” in different topological sectors. The exceptionally large degeneracy of the ground-state multiplets (144 on our 108-site cluster) and the proximity of a Z2 dimer liquid have implications for the interpretation of numerical results on the QHAF, which are outlined. The possibility of a chiral VBC (i.e., spontaneously breaking time-reversal symmetry) is also discussed.

  17. Thermomechanical properties of graphene: valence force field model approach

    International Nuclear Information System (INIS)

    Using the valence force field model of Perebeinos and Tersoff (2009 Phys. Rev. B 79 241409(R)), different energy modes of suspended graphene subjected to tensile or compressive strain are studied. By carrying out Monte Carlo simulations it is found that: (i) only for small strains (|?| ? 0.02) is the total energy symmetrical in the strain, while it behaves completely differently beyond this threshold; (ii) the important energy contributions in stretching experiments are stretching, angle bending, an out-of-plane term, and a term that provides repulsion against ?-? misalignment; (iii) in compressing experiments the two latter terms increase rapidly, and beyond the buckling transition stretching and bending energies are found to be constant; (iv) from stretching-compressing simulations we calculated the Young’s modulus at room temperature 350 ± 3.15 N m-1, which is in good agreement with experimental results (340 ± 50 N m-1) and with ab initio results (322-353) N m-1; (v) molar heat capacity is estimated to be 24.64 J mol-1 K-1 which is comparable with the Dulong-Petit value, i.e. 24.94 J mol-1 K-1, and is almost independent of the strain; (vi) nonlinear scaling properties are obtained from height-height correlations at finite temperature; (vii) the used valence force field model results in a temperature independent bending modulus for graphene, and (viii) the Grüneisen parameter is eii) the Grüneisen parameter is estimated to be 0.64. (paper)

  18. Calculation of conduction-to-conduction and valence-to-valence transitions between bound states in (In,Ga)As/GaAs quantum dots

    OpenAIRE

    Narvaez, Gustavo A.; Zunger, Alex

    2006-01-01

    We have calculated the conduction-to-conduction and valence-to-valence absorption spectrum of bound states in (In,Ga)As/GaAs quantum dots charged with up to three electrons or holes. Several features emerge: (i) In pure (non-alloyed) InAs/GaAs dots, the 1S-1P_1 and 1S-1P_2 conduction intraband transitions are fully in-plane polarized along [1\\bar 10] and [110], respectively, while valence transitions are weakly polarized because the hole P states do not show any in-plane pre...

  19. Band alignment and defects of the diamond zinc oxide heterojunction; Bandstruktur und Defekte der Diamant-Zinkoxid-Heterostruktur

    Energy Technology Data Exchange (ETDEWEB)

    Geithner, Peter

    2008-09-12

    Zinc oxide films were grown on diamond single crystals by rf sputtering of zinc oxide. The valence and conduction band offset was determined by photoelectron spectroscopy. A deep defect occurring in the zinc oxide films on diamond was characterized by cathodoluminescence spectroscopy. (orig.)

  20. Synchrotron Studies of Narrow Band and Low-Dimensional Materials. Final Report for July 1, 1990 --- December 31, 2002

    International Nuclear Information System (INIS)

    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

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

    Energy Technology Data Exchange (ETDEWEB)

    Kaur, Avneet [Department of Chemistry, University of Delhi, Delhi 110 007 (India); Bakhshi, A.K., E-mail: akbakhshi2000@yahoo.com [Department of Chemistry, University of Delhi, Delhi 110 007 (India)

    2010-04-21

    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 ({Delta}E{sub c}/{Delta}E{sub v}) 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 {Delta}E{sub c}/{Delta}E{sub v} 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.

  2. In-clustering induced anomalousbehavior of band gap in InAlN and InGaN

    DEFF Research Database (Denmark)

    Gorczyca, I.; Suski, T.

    2010-01-01

    Electronic band structure calculations of In containing ternary nitride alloys are presented showing a strong modification of the band gap, EG and its pressure coefficient, dEG/dp, as a function of In-content. Two different arrangements of In atoms are considered: uniform and clustered. It is shown that Indium clustering is the additional, large factor leading to the unusual bowings of the band gaps and their pressure coefficients. The theoretical results are compared with experimental data on variations of EG with In content. In the analysis of observed phenomena we point out the particular role of the uppermost valence band.

  3. Angle-resolved photoemission and quasiparticle calculation of ZnO: The need for d band shift in oxide semiconductors

    Science.gov (United States)

    Lim, Linda Y.; Lany, Stephan; Chang, Young Jun; Rotenberg, Eli; Zunger, Alex; Toney, Michael F.

    2012-12-01

    ZnO is a prototypical semiconductor with occupied d10 bands that interact with the anion p states and is thus challenging for electronic structure theories. Within the context of these theories, incomplete cancellation of the self-interaction energy results in a Zn d band that is too high in energy, resulting in upwards repulsion of the valence band maximum (VBM) states, and an unphysical reduction of the band gap. Methods such as GW should significantly reduce the self-interaction error, and in order to evaluate such calculations, we measured high-resolution and resonant angle-resolved photoemission spectroscopy (ARPES) and compared these to several electronic structure calculations. We find that, in a standard GW calculation, the d bands remain too high in energy by more than 1 eV irrespective of the Hamiltonian used for generating the input wave functions, causing a slight underestimation of the band gap due to the p-d repulsion. We show that a good agreement with the ARPES data over the full valence band spectrum is obtained, when the Zn-d band energy is shifted down by applying an on-site potential Vd for Zn-d states during the GW calculations to match the measured d band position. The magnitude of the GW quasiparticle energy shift relative to the initial density functional calculation is of importance for the prediction of charged defect formation energies, band-offsets, and ionization potentials.

  4. Multi-center interference effects on generalized oscillator strengths for the valence-shell electronic excitations of CF4

    Science.gov (United States)

    Watanabe, Noboru; Suzuki, Daisuke; Takahashi, Masahiko

    2012-11-01

    We report on multi-center interference effects on valence electronic excitations in CF4 induced by electron impact. Generalized oscillator strength (GOS) profiles for Rydberg transitions have been derived from electron energy loss spectra measured at an impact energy of 3.0 keV. We have also performed a theoretical calculation at the equation-of-motion coupled cluster singles and doubles level. The calculation has demonstrated the existence of interference features in the GOS profiles for 3s Rydberg transitions. Furthermore, a secondary maximum being interpreted as indicative of interference effects has actually been found in the experimental GOS profile for the 13.8 eV transition band.

  5. Cobalt valence states and origins of ferromagnetism in Co doped TiO2 rutile thin films

    International Nuclear Information System (INIS)

    Co doped rutile thin films were fabricated on ?-Al2O3 (10-12) substrates by laser molecular beam epitaxy. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy indicated that the rutile thin films are (101) oriented and have smooth surfaces with no impurity phases. Co K-edge x-ray absorption near-edge structure, extended x-ray absorption fine structure, and x-ray photoelectron spectroscopy revealed the coexistence of different valence states of Co in the film. Magnetic circular dichroism studies suggest that the observed ferromagnetism is uniform and is related to the electron band structure of TiO2 rutile. Contribution of oxidized (Co2+) and metallic (Co0) cobalt to the ferromagnetism is discussed

  6. Optoelectronic properties of InAlN/GaN distributed bragg reflector heterostructure examined by valence electron energy loss spectroscopy.

    Science.gov (United States)

    Eljarrat, A; Estradé, S; Ga?evi?, Z; Fernández-Garrido, S; Calleja, E; Magén, C; Peiró, F

    2012-10-01

    High-resolution monochromated electron energy loss spectroscopy (EELS) at subnanometric spatial resolution and Bragg reflector multilayer heterostructure composed of InAlN lattice matched to GaN. This work thoroughly presents the collection of methods and computational tools put together for this task. Among these are zero-loss-peak subtraction and nonlinear fitting tools, and theoretical modeling of the electron scattering distribution. EELS analysis allows retrieval of a great amount of information: indium concentration in the InAlN layers is monitored through the local plasmon energy position and calculated using a bowing parameter version of Vegard Law. Also a dielectric characterization of the InAlN and GaN layers has been performed through Kramers-Kronig analysis of the Valence-EELS data, allowing band gap energy to be measured and an insight on the polytypism of the GaN layers. PMID:23058502

  7. Multi-center interference effects on generalized oscillator strengths for the valence-shell electronic excitations of CF4

    International Nuclear Information System (INIS)

    We report on multi-center interference effects on valence electronic excitations in CF4 induced by electron impact. Generalized oscillator strength (GOS) profiles for Rydberg transitions have been derived from electron energy loss spectra measured at an impact energy of 3.0 keV. We have also performed a theoretical calculation at the equation-of-motion coupled cluster singles and doubles level. The calculation has demonstrated the existence of interference features in the GOS profiles for 3s Rydberg transitions. Furthermore, a secondary maximum being interpreted as indicative of interference effects has actually been found in the experimental GOS profile for the 13.8 eV transition band.

  8. Photonic band gap materials

    International Nuclear Information System (INIS)

    An overview of the theoretical and experimental efforts in obtaining a photonic band gap, a frequency band in three-dimensional dielectric structures in which electromagnetic waves are forbidden, is presented

  9. Magnetoelastic coupling model for fluctuating-valence Ce(Ni1-xCox)Sn (0.35?x?0.40) compounds at high magnetic fields and temperatures

    International Nuclear Information System (INIS)

    A model of magnetoelastic coupling has been developed which explains the volume and anisotropic magnetostriction thermal dependences of the fluctuating-valence intermetallic compounds Ce(Ni1-xCox)Sn, above their valence transition temperatures and in a strong magnetic field (14 T), in the range 0.35?x?0.40. The model assumes narrow 4f-conduction electron hybridized bands, where only the ground-state vertical bar ± 3/2> bands are populated, and that the magnetoelastic coupling stems from the interaction of the Ce3+ ion with the site crystal electric field. As a result the values of the corresponding microscopic magnetoelastic coupling parameters of volume (Ma:1) and tetragonal (Ma:2) characters have been determined for x=0.38. Their values (about 10-50 K/Ce3+) are unusually large for unstable 4f-shell intermetallics. (author)

  10. Dispersible carbon nanotubes.

    Science.gov (United States)

    Soulié-Ziakovic, Corinne; Nicolaÿ, Renaud; Prevoteau, Alexandre; Leibler, Ludwik

    2014-01-27

    A method is proposed to produce nanoparticles dispersible and recyclable in any class of solvents, and the concept is illustrated with the carbon nanotubes. Classically, dispersions of CNTs can be achieved through steric stabilization induced by adsorbed or grafted polymer chains. Yet, the surface modification of CNTs surfaces is irreversible, and the chemical nature of the polymer chains imposes the range of solvents in which CNTs can be dispersed. To address this limitation, supramolecular bonds can be used to attach and to detach polymer chains from the surface of CNTs. The reversibility of supramolecular bonds offers an easy way to recycle CNTs as well as the possibility to disperse the same functional CNTs in any type of solvent, by simply adapting the chemical nature of the stabilizing chains to the dispersing medium. The concept of supramolecular functionalization can be applied to other particles, for example, silica or metal oxides, as well as to dispersing in polymer melts, films or coatings. PMID:24458908

  11. Rubber Band Racers

    Science.gov (United States)

    IEEE

    2013-08-30

    In this activity, learners explore the design of rubber band powered cars. Learners work in teams of "engineers" to design and build their own rubber band cars out of everyday items. They test their rubber band cars, evaluate their results, and present to the group.

  12. Theoretical and experimental studies of electronic band structure for GaSb1?xBix in the dilute Bi regime

    International Nuclear Information System (INIS)

    Photoreflectance (PR) spectroscopy was applied to study the band gap in GaSb1?xBix alloys with Bi < 5%. Obtained results have been interpreted in the context of ab initio electronic band structure calculations in which the supercell (SC) based calculations are joined with the alchemical mixing (AM) approximation applied to a single atom in the cell. This approach, which we call SC-AM, allows on the one hand to study alloys with a very small Bi content, and on the other hand to avoid limitations characteristic of a pure AM approximation. It has been shown that the pure AM does not reproduce the GaSb1?xBix band gap determined from PR while the agreement between experimental data and the ab initio calculations of the band gap obtained within the SC-AM approach is excellent. These calculations show that the incorporation of Bi atoms into the GaSb host modifies both the conduction and the valence band. The shift rates found in this work are respectively ?26.0 meV per % Bi for the conduction band and 9.6 meV per % Bi for the valence band that consequently leads to a reduction in the band gap by 35.6 meV per % Bi. The shifts found for the conduction and valence band give a ?27% (73%) valence (conduction) band offset between GaSb1?xBix and GaSb. The rate of the Bi-related shift for the split-off band is ?7.0 meV per % Bi and the respective increase in the spin–orbit split-off is 16.6 meV per % Bi. (paper)

  13. Codoping in SnTe: Enhancement of Thermoelectric Performance through Synergy of Resonance Levels and Band Convergence.

    Science.gov (United States)

    Tan, Gangjian; Shi, Fengyuan; Hao, Shiqiang; Chi, Hang; Zhao, Li-Dong; Uher, Ctirad; Wolverton, Chris; Dravid, Vinayak P; Kanatzidis, Mercouri G

    2015-04-22

    We report a significant enhancement of the thermoelectric performance of p-type SnTe over a broad temperature plateau with a peak ZT value of ?1.4 at 923 K through In/Cd codoping and a CdS nanostructuring approach. Indium and cadmium play different but complementary roles in modifying the valence band structure of SnTe. Specifically, In-doping introduces resonant levels inside the valence bands, leading to a considerably improved Seebeck coefficient at low temperature. Cd-doping, however, increases the Seebeck coefficient of SnTe remarkably in the mid- to high-temperature region via a convergence of the light and heavy hole bands and an enlargement of the band gap. Combining the two dopants in SnTe yields enhanced Seebeck coefficient and power factor over a wide temperature range due to the synergy of resonance levels and valence band convergence, as demonstrated by the Pisarenko plot and supported by first-principles band structure calculations. Moreover, these codoped samples can be hierarchically structured on all scales (atomic point defects by doping, nanoscale precipitations by CdS nanostructuring, and mesoscale grains by SPS treatment) to achieve highly effective phonon scattering leading to strongly reduced thermal conductivities. In addition to the high maximum ZT the resultant large average ZT of ?0.8 between 300 and 923 K makes SnTe an attractive p-type material for high-temperature thermoelectric power generation. PMID:25856499

  14. Mesoscale Banded Precipitation

    Science.gov (United States)

    2014-09-14

    Precipitation frequently falls and accumulates in discrete bands with accumulations that vary markedly over short distances. This module examines several mechanisms that result in mesoscale banded precipitation, focusing primarily on processes at work in midlatitude cyclones. The module starts with a review of the Norwegian and conveyor belt cyclone models. Then several banding processes are examined in detail, including deformation/frontogenesis, the Trowal (Trough of Warm Air Aloft), frontal merger, CSI/slantwise convection, and melting/evaporation-induced circulations. The module concludes with discussions of the representation of banded precipitation by NWP models and the detection of banded precipitation with satellite sensors.

  15. Exciton dispersion in molecular solids

    Science.gov (United States)

    Cudazzo, Pierluigi; Sottile, Francesco; Rubio, Angel; Gatti, Matteo

    2015-03-01

    The investigation of the exciton dispersion (i.e. the exciton energy dependence as a function of the momentum carried by the electron–hole pair) is a powerful approach to identify the exciton character, ranging from the strongly localised Frenkel to the delocalised Wannier–Mott limiting cases. We illustrate this possibility at the example of four prototypical molecular solids (picene, pentacene, tetracene and coronene) on the basis of the parameter-free solution of the many-body Bethe–Salpeter equation. We discuss the mixing between Frenkel and charge-transfer excitons and the origin of their Davydov splitting in the framework of many-body perturbation theory and establish a link with model approaches based on molecular states. Finally, we show how the interplay between the electronic band dispersion and the exchange electron–hole interaction plays a fundamental role in setting the nature of the exciton. This analysis has a general validity holding also for other systems in which the electron wavefunctions are strongly localized, as in strongly correlated insulators.

  16. Electronic dispersion anomalies in Fe-pnictide superconductors

    International Nuclear Information System (INIS)

    We investigate anomalies in the electronic band dispersion in Fe-pnictides that result from a coupling of electrons to spin fluctuations. It is known from inelastic neutron scattering experiments that a magnetic resonance feature appears in the dynamical spin susceptibility when entering the superconducting state, both in Fe-pnictides and in cuprates. This raises the question, if similar mechanisms are at work. An important question related to this is to which extend the dispersion of the electronic bands is modified by the interaction between electrons and this resonant spin excitation, similarly as it is the case for cuprate superconductors. We present a theoretical study of this problem.

  17. Electronic pairing mechanism due to band modification in a two-band model: Tc evaluation

    International Nuclear Information System (INIS)

    Following the electronic model developed by us previously (Mizia and Romanowski, Mizia) we estimate the superconducting transition temperature in a simple electronic two-band model for materials characterized by a broad superconducting band and a narrow level within the same energy range. A large electron deformation coupling constant and large electron correlation effects are assumed. It is shown that high-temperature superconductivity is entirely possible within a range of reasonable electronic parameters. This model does not assume any artificial interactions to obtain a negative pairing potential. Instead, the negative part of the electronic interaction potential comes from the modification of the electron dispersion relation with growing number of superconducting pairs. Such a modification is possible in soft electronic systems, i.e. in systems partial to band modification due to large internal stresses, strong electronic correlation effects and broad band narrow level charge transfer during the superconducting transition. (orig.)

  18. The dynamics of a photonic band gap in 2D Si-based photonic crystals

    International Nuclear Information System (INIS)

    The theoretical investigations of the photonic band structure of two-dimensional photonic crystals for the off-plane propagation of electromagnetic waves and the influence of a surface layer on the position and width of photonic band gaps are carried out. The experimentally measured width of a photonic band gap and the dispersion for two-dimensional silicon structures at the off-plane propagation of an electromagnetic wave correlate with the theoretical band gap position and width

  19. Chemistry and band offsets of HfO2 thin films on Si revealed by photoelectron spectroscopy and x-ray absorption spectroscopy

    International Nuclear Information System (INIS)

    High-resolution photoelectron spectroscopy and x-ray absorption spectroscopy (XAS) measurements have been performed on HfO2 films grown on Si(0 0 1) for ULSI ultra-thin gate insulators to elucidate the chemistry and band offsets of interfacial silicate layers. The valence-band discontinuity is determined by subtracting valence-band spectra of H-terminated Si(0 0 1) from those of the HfO2 films on Si which have a HfO2/Hf1-xSixO2/Si double layer structure. On the other hand, the conduction-band discontinuity is clearly deduced by oxygen K-edge absorption spectra and O 1s photoelectron spectra. Consequently, two kinds of energy-band offsets of HfO2/Hf1-xSixO2 and Hf1-xSixO2/Si are determined separately

  20. Band anticrossing in highly mismatched semiconductor alloys

    Energy Technology Data Exchange (ETDEWEB)

    Walukiewicz, W.

    2002-07-26

    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.

  1. Calculation of conduction-to-conduction and valence-to-valence transitions between bound states in (In,Ga)As/GaAs quantum dots

    CERN Document Server

    Narvaez, G A; Narvaez, Gustavo A.; Zunger, Alex

    2006-01-01

    We have calculated the conduction-to-conduction and valence-to-valence absorption spectrum of bound states in (In,Ga)As/GaAs quantum dots charged with up to three electrons or holes. Several features emerge: (i) In pure (non-alloyed) InAs/GaAs dots, the 1S-1P_1 and 1S-1P_2 conduction intraband transitions are fully in-plane polarized along [1\\bar 10] and [110], respectively, while valence transitions are weakly polarized because the hole P states do not show any in-plane preferential orientation. (ii) In alloyed In_{0.6}Ga_{0.4}As/GaAs dots the [110] and [1\\bar 10] polarization of the corresponding 1S-1P conduction intraband transitions is weakened since the two 1P states are mixed by alloy fluctuations. The polarization of valence intraband transitions is insensitive to changes in alloy fluctuations. (iii) For light polarized along [001], we find a strong valence-to-valence transition that involves a weakly confined hole state with predominant light-hole character. (iv) When charging the dots with a few elec...

  2. Effects of Emotional Valence and Arousal on Recollective and Nonrecollective Recall

    Science.gov (United States)

    Gomes, Carlos F. A.; Brainerd, Charles J.; Stein, Lilian M.

    2013-01-01

    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…

  3. Identifying Facial Emotions: Valence Specific Effects and an Exploration of the Effects of Viewer Gender

    Science.gov (United States)

    Jansari, Ashok; Rodway, Paul; Goncalves, Salvador

    2011-01-01

    The valence hypothesis suggests that the right hemisphere is specialised for negative emotions and the left hemisphere is specialised for positive emotions (Silberman & Weingartner, 1986). It is unclear to what extent valence-specific effects in facial emotion perception depend upon the gender of the perceiver. To explore this question 46…

  4. Valence fluctuation of Yb in the superconducting ytterbium-rhodium stannides

    International Nuclear Information System (INIS)

    YB LIII X-ray absorption edge measurements yielded 2.20+ and 2.50+ for the Yb valence in the Yb-Rh-Sn compounds with phase I and II', respectively. The former is superconducting (Tc?8 K), and contains only one crystallographic site for Yb, which suggests that this atom is in a valence fluctuation state. (orig.)

  5. Pressure and irradiation effects on transport properties of samarium compounds with instable valence

    International Nuclear Information System (INIS)

    Electron transport properties in samarium compounds with instable valence are studied in this thesis: from SmS in its integer valence phases at common pressure to SmB6 compound IV at common pressure through SmSsub(1-x)Psub(x) (x6 is presented

  6. Dissociable modulation of overt visual attention in valence and arousal revealed by topology of scan path.

    Science.gov (United States)

    Ni, Jianguang; Jiang, Huihui; Jin, Yixiang; Chen, Nanhui; Wang, Jianhong; Wang, Zhengbo; Luo, Yuejia; Ma, Yuanye; Hu, Xintian

    2011-01-01

    Emotional stimuli have evolutionary significance for the survival of organisms; therefore, they are attention-grabbing and are processed preferentially. The neural underpinnings of two principle emotional dimensions in affective space, valence (degree of pleasantness) and arousal (intensity of evoked emotion), have been shown to be dissociable in the olfactory, gustatory and memory systems. However, the separable roles of valence and arousal in scene perception are poorly understood. In this study, we asked how these two emotional dimensions modulate overt visual attention. Twenty-two healthy volunteers freely viewed images from the International Affective Picture System (IAPS) that were graded for affective levels of valence and arousal (high, medium, and low). Subjects' heads were immobilized and eye movements were recorded by camera to track overt shifts of visual attention. Algebraic graph-based approaches were introduced to model scan paths as weighted undirected path graphs, generating global topology metrics that characterize the algebraic connectivity of scan paths. Our data suggest that human subjects show different scanning patterns to stimuli with different affective ratings. Valence salient stimuli (with neutral arousal) elicited faster and larger shifts of attention, while arousal salient stimuli (with neutral valence) elicited local scanning, dense attention allocation and deep processing. Furthermore, our model revealed that the modulatory effect of valence was linearly related to the valence level, whereas the relation between the modulatory effect and the level of arousal was nonlinear. Hence, visual attention seems to be modulated by mechanisms that are separate for valence and arousal. PMID:21494331

  7. Theoretical valence charge densities for graphite, diamond, and LiC6

    International Nuclear Information System (INIS)

    The valence charge density of graphite was determined from first-principles, self-consistent electronic structure calculations and found to be in excellent agreement with values derived from experimental X-ray form factors. Similar calculations were carried out for the valence charge densities of diamond and of a first stage intercalation compound, LiC6

  8. Valence isomerization of cyclohepta-1,3,5-triene and its heteroelement analogues

    OpenAIRE

    Helen Jansen; J. Chris Slootweg; Koop Lammertsma

    2011-01-01

    The valence isomerization of the all-carbon and heteroelement analogues of cyclohepta-1,3,5-triene into the corresponding bicyclo[4.1.0]hepta-2,4-dienes is reviewed to show the impact of the heteroatom on the stability of both valence isomers. The focus is on the parent systems and their synthetic applications.

  9. Valence isomerization of cyclohepta-1,3,5-triene and its heteroelement analogues.

    Science.gov (United States)

    Jansen, Helen; Slootweg, J Chris; Lammertsma, Koop

    2011-01-01

    The valence isomerization of the all-carbon and heteroelement analogues of cyclohepta-1,3,5-triene into the corresponding bicyclo[4.1.0]hepta-2,4-dienes is reviewed to show the impact of the heteroatom on the stability of both valence isomers. The focus is on the parent systems and their synthetic applications. PMID:22238550

  10. Valence isomerization of cyclohepta-1,3,5-triene and its heteroelement analogues

    Directory of Open Access Journals (Sweden)

    Helen Jansen

    2011-12-01

    Full Text Available The valence isomerization of the all-carbon and heteroelement analogues of cyclohepta-1,3,5-triene into the corresponding bicyclo[4.1.0]hepta-2,4-dienes is reviewed to show the impact of the heteroatom on the stability of both valence isomers. The focus is on the parent systems and their synthetic applications.

  11. Valence quark annihilation effect on charmed meson production in $\\pi N$ collisions

    CERN Document Server

    Tashiro, T; Kinoshita, K; Nakariki, S; Tashiro, Tsutomu; Noda, Hujio; Kinoshita, Kisei; Nakariki, Shin-ichi

    1998-01-01

    We discuss the hadroproduction of charmed mesons in the framework of the constituent cascade model taking into account the valence quark annihilation. It is shown that the small valence quark annihilation process dominates the leading particle production at large Feynman x and explains the recent experimental data on the asymmetry between D^0 and D^0 bar at 350 GeV/c.

  12. Valence quark annihilation effect on charmed meson production in pi N collisions

    OpenAIRE

    Tashiro, Tsutomu; Noda, Hujio; Kinoshita, Kisei; Nakariki, Shin-ichi

    1998-01-01

    We discuss the hadroproduction of charmed mesons in the framework of the constituent cascade model taking into account the valence quark annihilation. It is shown that the small valence quark annihilation process dominates the leading particle production at large Feynman x and explains the recent experimental data on the asymmetry between D^0 and D^0 bar at 350 GeV/c.

  13. Exploring covalently bonded diamondoid particles with valence photoelectron spectroscopy

    CERN Document Server

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

    2013-01-01

    We investigated the electronic structures 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 bond type and the combination of the bonding partners affect the overall electronic structures. For singly bonded particles we observe a small impact of the bond type on the electronic structure, whereas for doubly bonded particles the connecting bond is the deciding factor, determining the electronic structure of the uppermost occupied orbitals. In the singly bonded particles a superposition of the bonding partner orbitals determines the overall electronic structure. The strength of quantum confinement effects, i.e., the localization of electrons, depends on the bonding partner orbital energy difference. The experimental findings correspond well to density functional theory computations.

  14. Transition temperature of a superconductor containing mixed-valence impurities

    International Nuclear Information System (INIS)

    The reduction of the superconductor transition temperature of an alloy containing mixed-valence impurities has been calculated. We considered the U?infinity limit of the Anderson model by keeping only the ground multiplets of the two active ionic configurations, 4f/sup eta/ and 4f/sup eta+1/. If one of the multiplets is a singlet, T/sub c/ is reduced by pair weakening and decreases exponentially with the impurity concentration. On the other hand, if both multiplets are magnetic, the T/sub c/ dependence on c is similar to that of the Abrikosov-Gorkov theory. The superconductivity quenching mechanism in this case is Cooper-pair breaking

  15. Intermediate valence behavior in CeCo9Si4

    CERN Document Server

    El-Hagary, M; Bauer, E; Groessinger, R; Kerschl, P; Eckert, D; Müller, K H; Rogl, P; Giester, G; Hilscher, G

    2004-01-01

    The novel ternary compound CeCo$_9$Si$_4$ has been studied by means of specific heat, magnetisation, and transport measurements. Single crystal X-ray Rietveld refinements reveal a fully ordered distribution of Ce, Co and Si atoms with the tetragonal space group I4/mcm isostructural with other RCo9Si4. The smaller lattice constants of CeCo9Si4 in comparison with the trend established by other RCo9Si4 is indicative for intermediate valence of cerium. While RCo9Si4 with R= Pr, .. Tb, and Y show ferromagnetism and LaCo9Si4 is nearly ferromagnetic, CeCo9Si4 remains paramagnetic even in external fields as large as 40 T, though its electronic specific heat coefficient (g~190 mJ/molK^2) is of similar magnitude as that of metamagnetic LaCo9Si4 and weakly ferromagnetic YCo9Si4.

  16. Neutron scattering on rare earth intermediate valence systems

    International Nuclear Information System (INIS)

    A survey on neutron scattering experiments performed on rare earth compounds and alloys with intermediate valency (IV-systems) is given. The dynamical susceptibility of these systems as deduced from inelastic magnetic neutron scattering experiments is characterized by a very broad, structureless and nearly temperature independent energy spectrum which can be interpreted by a fast (10-13 s) relaxation process of the IV-spins. This simple behaviour is observed for all IV-systems with one magnetic and one nonmagnetic configuration (e.g.,CePd3). The only IV-system with two magnetic configurations (TmSe) behaves similarly at temperatures above 120 K; at lower temperatures, however, the spin fluctuations slow down with decreasing temeprature and an additional inelastic magnetic transition develops around 10 meV energy transfer. At the end of our survey, we will discuss the influence of the IV-phenomenon on the magnetic formfactor, atomic excitations and phonon spectra. (orig.)

  17. Resonating valence bonds states in the PEPS formalism

    CERN Document Server

    Schuch, Norbert; Cirac, J Ignacio; Perez-Garcia, David

    2012-01-01

    We study resonating valence bond (RVB) states in the Projected Entangled Pair States (PEPS) formalism. Based on symmetries in the PEPS description, we establish relations between the toric code state, the orthogonal dimer state, and the SU(2) singlet RVB state on the kagome lattice: We prove the equivalence of toric code and dimer state, and devise an interpolation between the dimer state and the RVB state. This interpolation corresponds to a continuous path in Hamiltonian space, proving that the RVB state is the four-fold degenerate ground state of a local Hamiltonian on the (finite) kagome lattice. Using numerical methods, we study whether this interpolation exhibits a phase transition: We find that all studied correlation functions behave smoothly, whereas the overlap of the wavefunction shows possible signs of a high-order phase transition.

  18. ???????—?????? The Process Mechanism of Anger——From Valence to Motivation

    Directory of Open Access Journals (Sweden)

    ???

    2012-07-01

    Full Text Available ????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????Anger is a kind of emotion caused by provocative stimuli. According to the valence hypothesis and the motivation hypothesis, anger is a negative emotion prone to approach motivation. Recent behavioral and neuroimaging studies, however, challenged these hypotheses. Some researchers explained these new findings in opinions of anger expression or anger specificity. These opinions were efficient but limited. A contextually dependent view of motivation model might be adopted to better understand the mechanism of anger both in general situation and in special situation. It regarded anger as the reaction to provocative stimuli, which was induced by real situation or experience and was in conformity with motivation and behavior.

  19. The itinerant resonating-valence-bond model for superconductivity

    International Nuclear Information System (INIS)

    It has been proposed by Anderson that the pairing interaction in high temperature superconductors La/sub 2-x/ Sr/sub x/ Cuo4 and Yba2Cu3O/sub 7-x/ is magnetic in origin, and the recent discovery of antiferromagnetic ordering in La2CuO4 has been regarded as strong evidence in support of this so-called resonating-valence-bond (RVB) model. Close examination of the ordered state of this material reveals that it is an itinerant antiferromagnet. Accordingly, the superconducting properties must also be studied using the itinerant model approach, rather than the local moment model discussed so far in literature. This paper reports an approximate solution of the itinerant RVB model of superconductivity. It is shown that superconductivity can take place in a narrow region of the parameter space, and that the fluctuating local exchange field causes the superconducting state to be gapless. 19 refs

  20. Mixed-valence copper oxides related to perovskite

    International Nuclear Information System (INIS)

    Among the characteristics which lead to high-temperature superconducting Ba-La-Cu-O systems, the mixed-valence of copper Cu(II)-Cu(III) and the dimensionality of the oxide microstructure are considered to be of foremost importance. It is shown that in copper oxides related to perovskites, in which an ordered elimination of oxygen atoms or of rows of oxygen atoms in the host lattice can lead to very anisotropic structures, the presence of oxygen-deficient ordered structures coincides with superconductivity. Similarly, it is shown that, as the oxygen content of the orthorhombic YBa2Cu3O(7-epsilon) crystals decreases, the superconductivity of the crystals increases. 30 references

  1. Nature of the Frequency Shift of Hydrogen Valence Vibrations

    CERN Document Server

    Zhyganiuk, I V

    2015-01-01

    The physical nature of a frequency shift of hydrogen valence vibrations in a water molecule due to its interaction with neighbor molecules has been studied. Electrostatic forces connected with the multipole moments of molecules are supposed to give a dominating contribution to the intermolecular interaction. The frequency shift was calculated in the case where two neighbor molecules form a dimer. The obtained result is in qualitative agreement with the frequency shifts observed for water vapor, hexagonal ice, and liquid water, as well as for aqueous solutions of alcohols. This fact testifies to the electrostatic nature of H-bonds used to describe both the specific features of the intermolecular interaction in water and the macroscopic properties of the latter.

  2. Valence framing of political preferences and resistance to persuasion

    Directory of Open Access Journals (Sweden)

    Žeželj Iris

    2007-01-01

    Full Text Available This study tested the "valence framing effect": an assumption that negatively conceptualized attitudes (as opposing the non-preferred alternative are more resistant to later persuasion attempts. In the experiment we created choice between two political candidates and experimental subjects were led to conceptualize their political preferences in one of two possible ways: either as supporting the preferred candidate or as opposing the non-preferred candidate. The data indicate that negative preferences show less overall change when exposed to counterarguments. This finding can be incorporated in two theoretical frameworks: dual process theories of attitude change (Elaboration likelihood model and descriptive decision making theories (Prospect theory. Results are discussed for their implications for the efficacy of political communication. .

  3. Isotopic exchange in mixed valence compounds in the solid state

    International Nuclear Information System (INIS)

    This work aims at the determination of isotopic exchange kinetics and mechanism in two mixed valence compounds: Cs10(Sbsup(V)Cl6) (Sbsup(III)Cl6)3 and Tl3sup(I)(Tlsup(III)Cl6). The synthesis of the first compound is very difficult because in most of the cases mixtures of chloroantimoniates are obtained. Exchange in Tl4Cl6 labelled on Tlsup(III) is studied in detail by radiochemical analysis and physical techniques: ionic conductivity and positon annihilation. Cation vacancies are easily created in the lattice with formation enthalpy of 0.35 eV and migration enthalpy of 0.52 eV. Isochronic and isothermal exchange curves are described by a kinetic based on species diffusion. Models are given. Exchange is increased by grinding probably because extrinseque defects are introduced

  4. Error estimate for the valence approximation to lattice QCD

    International Nuclear Information System (INIS)

    A Monte Carlo algorithm is used to calculate msub(N)/msub(rho), msub(?)/msub(rho), msub(q)msub(rho)/msub(?)2, fsub(?)/msub(rho), fsub(rho)/msub(rho) and #betta#sub(mo) for lattice QCD with the number of flavors Nsub(f) of quarks contributing virtual loops given by zero, the valence approximation, and with Nsub(f) chosen, in effect to be -2. The difference between corresponding pairs of quantities with Nsub(f) of zero and Nsub(f) of -2 we take to be an estimate of the difference between the value for a realistic theory with Nsub(f) of +2 and for the approximate theory with Nsub(f) of zero. The changes in mass ratios and #betta#sub(mo) are consistent with zero and typically (20 +- 20)% while decay constant ratios change by as much as (88 +- 24)%. (orig.)

  5. Kaon semileptonic decay form factors with HISQ valence quarks

    CERN Document Server

    Gamiz, E; Bazavov, A; Bernard, C; Bouchard, C; DeTar, C; Du, D; El-Khadra, A X; Foley, J; Freeland, E D; Gottlieb, Steven; Heller, U M; Kim, J; Kronfeld, A S; Laiho, J; Levkova, L; Mackenzie, P B; Neil, E T; Oktay, M B; Qiu, Si-Wei; Simone, J N; Sugar, R; Toussaint, D; Van de Water, R S; Zhou, R

    2012-01-01

    We report on the status of our kaon semileptonic form factor calculations using the highly-improved staggered quark (HISQ) formulation to simulate the valence fermions. We present results for the form factor f_+^{K \\pi}(0) on the asqtad N_f=2+1 MILC configurations, discuss the chiral-continuum extrapolation, and give a preliminary estimate of the total error. We also present a more preliminary set of results for the same form factor but with the sea quarks also simulated with the HISQ action; these results include data at the physical light quark masses. The improvements that we expect to achieve with the use of the HISQ configurations and simulations at the physical quark masses are briefly discussed.

  6. Nanostructured high valence silver oxide produced by pulsed laser deposition

    International Nuclear Information System (INIS)

    Among silver oxides, Ag4O4, i.e. high valence Ag(I)Ag(III) oxide, is interesting for applications in high energy batteries and for the development of antimicrobial coatings. We here show that ns UV pulsed laser deposition (PLD) in an oxygen containing atmosphere allows the synthesis of pure Ag4O4 nanocrystalline thin films, permitting at the same time to control the morphology of the material at the sub-micrometer scale. Ag4O4 films with a crystalline domain size of the order of tens of nm can be deposited provided the deposition pressure is above a threshold (roughly 4 Pa pure O2 or 20 Pa synthetic air). The formation of this particular high valence silver oxide is explained in terms of the reactions occurring during the expansion of the ablated species in the reactive atmosphere. In particular, expansion of the PLD plasma plume is accompanied by formation of low stability Ag-O dimers and atomic oxygen, providing reactive species at the substrate where the film grows. Evidence of reactive collisions in the expanding ablation plume is obtained by analysis of the plume visible shape in inert and reactive atmospheres. In addition, we show how the dimensionless deposition parameter L, relating the target-to-substrate distance to the ablation plume maximum expansion length, can be used to classify different growth regimes. It is thus possible to vary the stoichiometry and the morphology of the fistoichiometry and the morphology of the films, from compact and columnar to foam-like, by controlling both the gas pressure and the target-to-substrate distance

  7. Simulation of the Band Structure of Graphene and Carbon Nanotube

    International Nuclear Information System (INIS)

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

  8. Visualizing Dispersion Interactions

    Science.gov (United States)

    Gottschalk, Elinor; Venkataraman, Bhawani

    2014-01-01

    An animation and accompanying activity has been developed to help students visualize how dispersion interactions arise. The animation uses the gecko's ability to walk on vertical surfaces to illustrate how dispersion interactions play a role in macroscale outcomes. Assessment of student learning reveals that students were able to develop…

  9. Valence bond supersolid in a bilayer extended Bose-Hubbard model

    Science.gov (United States)

    Ng, Kwai-Kong

    2015-02-01

    The hardcore extended Bose Hubbard model on a bilayer square lattice with attractive (repulsive) interplane (intraplane) interactions has been investigated numerically. Focusing on the strong interplane hopping parameter regime, triplet valence bonds of dimers are stabilized to form valence bond checkerboard solid at quarter filling. Increasing the particle number we confirm the presence of the exotic valence bond supersolid phase, where the valence bond solid ordering and the boson superfluidity coexist. Rising further the particle number will lead to a checkerboard solid of dimer pair at half filling for strong intraplane repulsion, or a valence bond Mott insulator for weak repulsive interactions. We analyze the rich ground state phase diagrams of this model, which can be experimentally realized in optical lattices of cold atoms.

  10. Madelung energy of the valence-skipping compound BaBiO3

    Science.gov (United States)

    Hase, Izumi; Yanagisawa, Takashi

    2007-11-01

    Several elements show valence skip fluctuation, for instance, Tl forms the compounds in valence states +1 and +3 and Bi forms in +3 and +5 states. This kind of fluctuation gives rise to a negative effective attractive interaction and the Kondo effect. In the compounds of valence-skipping elements, the carrier doping will induce superconductivity with high critical temperature. For example, Ba1-xKxBiO3 shows high Tc which is unlikely from the conventional electron-phonon mechanism. The reason for missing of some valence states in such valence skip compounds remains a mystery. We have performed the evaluation of the Madelung potential for BaBiO3 and have shown that the charge-ordered state is stabilized if we take into account the polarization of the oxygen charge. We argue that the effective Coulomb interaction energy U may be negative evaluating the local excitation energy.

  11. The dominant contributions of the inner valence electrons to the positron annihilation process in methanol

    International Nuclear Information System (INIS)

    The positron–electron annihilation gamma-ray spectra of methanol have been studied in the present work. The contributions of the bound electrons to the Doppler-shift of gamma-ray spectra have been analysed as well. These bound electrons are divided into three groups: core, inner valence and outer valence rather than the conventional two groups: core and valence in the positron annihilation process in the present work. The results obtained show a dominance of the inner valence electrons of methanol rather than the electrons occupied in the highest occupied molecular orbital (HOMO) in the positron–electron annihilation process. These inner valence electrons occupied in 3a? and 4a? orbitals consist of over 80% outermost atomic 2s electrons in oxygen and carbon atoms. That the positron prefers to annihilate with these outermost s electrons in atoms is suggested.

  12. Negative band gap bowing in epitaxial InAs/GaAs alloys and predicted band offsets of the strained binaries and alloys on various substrates

    Science.gov (United States)

    Kim, Kwiseon; Hart, Gus L. W.; Zunger, Alex

    2002-04-01

    We use pseudopotential theory to provide (1) the band offsets of strained GaAs and InAs on various substrates and (2) the energies Ev(x) and Ec(x) of the valence and conduction bands of InxGa1-xAs alloy, as a function of composition. Results are presented for both the bulk alloy and for the alloy strained on InP or GaAs. We predict that while Ec(x) bows downward for relaxed bulk alloys, it bows upward for strained epitaxial alloys. The calculated alloy offsets are used to discuss electron and hole localization in this system.

  13. Velocity dispersion among galaxies

    International Nuclear Information System (INIS)

    The galaxies in the Revised Shapley-Ames redshift catalog, which is complete to Broughly-equal13, are used to determine the velocity dispersion in the local galaxy field (?-1). By studying the velocity differences of neighboring pairs of galaxies, we find for the one dimensional velocity dispersion per galaxy sigma = 70 +- 10 km s-1. (For the three dimensional dispersion, multiply by 3/sup 1/2/; and for the rms velocity difference between pairs, multiply by 2/sup 1/2/.) This velocity dispersion is found in pairs of galaxies irrespective of how isolated they are, and whether or not they are each other's nearest neighbors. The interpretation of isolated galaxy pairs as binaries, whose dynamics is dominated by the two-body force, is therefore questioned. Various implications of the derived velocity dispersion are discussed, with particular attention given to its significance in the virialization process occurring in the cores of the great clusters of galaxies

  14. First-principles study of Cu2ZnSnS4 and the related band offsets for photovoltaic applications

    International Nuclear Information System (INIS)

    First-principles calculations of the band offsets between Cu2ZnSnS4 (CZTS) and XS (X = Cd, Zn) are performed. While the interface dipole contribution for the band offsets is calculated using the Perdew-Burke-Ernzerhof functional, the Heyd-Scuseria-Ernzerhof hybrid functional is employed to introduce the quasiparticle corrections to the band offsets. The calculated conduction band offset between CZTS and CdS is 0.2 eV, validating CdS for the buffer layer of the CZTS solar cell. The small conduction band offset stems from the band gap narrowing of CdS under the interface strain caused by the lattice misfit with CZTS. A large valence band offset over 0.9 eV between CZTS and ZnS indicates that precipitated ZnS is regarded as an inactive insulator phase in CZTS absorbers.

  15. Chirality-Dependent Properties of Carbon Nanotubes. Electronic Structure: Optical Dispersion Properties, Hamaker Coefficients and van der Waals - London dispersion interactions

    OpenAIRE

    Rajter, Rick F.; French, Roger H.; Ching, W. Y.; Podgornik, Rudolf; Parsegian, V. Adrian

    2012-01-01

    Optical dispersion spectra at energies up to 30 eV play a vital role in understanding the chirality-dependent van der Waals London dispersion interactions of single wall carbon nanotubes (SWCNTs). We use one-electron theory based calculations to obtain the band structures and the frequency dependent dielectric response function from 0-30 eV for 64 SWCNTs differing in radius, electronic structure classification, and geometry. The resulting optical dispersion properties can be...

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

    DEFF Research Database (Denmark)

    Gorczyca, I.; Suski, T.

    2012-01-01

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

  17. Band alignment between GaN and ZrO2 formed by atomic layer deposition

    International Nuclear Information System (INIS)

    The band alignment between Ga-face GaN and atomic-layer-deposited ZrO2 was investigated using X-ray photoelectron spectroscopy (XPS). The dependence of Ga 3d and Zr 3d core-level positions on the take-off angles indicated upward band bending at GaN surface and potential gradient in ZrO2 layer. Based on angle-resolved XPS measurements combined with numerical calculations, valence band discontinuity ?EV of 1?±?0.2?eV and conduction band discontinuity ?EC of 1.2?±?0.2?eV at ZrO2/GaN interface were determined by taking GaN surface band bending and potential gradient in ZrO2 layer into account.

  18. Band alignment between GaN and ZrO2 formed by atomic layer deposition

    Science.gov (United States)

    Ye, Gang; Wang, Hong; Arulkumaran, Subramaniam; Ng, Geok Ing; Li, Yang; Liu, Zhi Hong; Ang, Kian Siong

    2014-07-01

    The band alignment between Ga-face GaN and atomic-layer-deposited ZrO2 was investigated using X-ray photoelectron spectroscopy (XPS). The dependence of Ga 3d and Zr 3d core-level positions on the take-off angles indicated upward band bending at GaN surface and potential gradient in ZrO2 layer. Based on angle-resolved XPS measurements combined with numerical calculations, valence band discontinuity ?EV of 1 ± 0.2 eV and conduction band discontinuity ?EC of 1.2 ± 0.2 eV at ZrO2/GaN interface were determined by taking GaN surface band bending and potential gradient in ZrO2 layer into account.

  19. Particle-hole induced intruder bands in 117Sb and 119Sb

    International Nuclear Information System (INIS)

    Collective structures have been investigated via ?-ray studies in 117,119Sb. Previously observed strongly coupled (?g9/2)-1 bands in both nuclei involving 1p-1h proton excitations across the Z=50 gap have been extended, and an alignment of h11/2 neutrons identified. New negative-parity strongly coupled bands based on this proton configuration have also been observed in both nuclei. Decoupled bands involving 2p-2h excitations across the gap have been observed in 119Sb, similar to those presented earlier for 117Sb. These bands are interpreted as due to the coupling of a low-K valence proton to the (?g7/2d5/2)2 circle-times(?g9/2)-2 deformed state of the respective 50Sn core nuclei. Anomalies in the expected h11/2 neutron crossing of these bands are discussed. copyright 1997 The American Physical Society

  20. Band Alignment for Ambipolar-Doping of SnxZn1-xTe Alloys

    International Nuclear Information System (INIS)

    Using the first-principles band-structure method and a special quasirandom structure (SQS) approach, we have systematically calculated the alloy bowing coefficients and the nature band offsets of SnxZn1-xTe alloys. We show that the bowing coefficients and band gaps of these alloys are sensitively composition dependent. Due to wave functions full overlapping and delocalization of the Sn outermost p orbits and Zn s orbits, the coupling between these states is very strong, resulting in a significant downshift of conduction band edge with the increase of the Sn concentration x, While the valence band edge keeps almost unchanged compared with that of the binary ZnTe, thus improving the possibility for ambipolar-doping. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  1. On the origin of inter band gap radiative emission in crystalline silicon

    Directory of Open Access Journals (Sweden)

    I. Burud

    2012-12-01

    Full Text Available Crystal imperfections degrade the quality of multicrystalline silicon wafers by introducing alternative recombination mechanisms. Here we use non-destructive hyperspectral imaging to detect photoluminescence signals from radiatively active recombination processes over the wafer with a highly resolved spectral third dimension. We demonstrate that band-to-band recombination can be visually separated from recombination through traps across the whole surface of a wafer using hyperspectral imaging. Our samples are studied in the near infrared wavelength region, 900-1700 nm, which includes the region of the so called D-band emission lines. These constitute four resolved emission lines found in the photoluminescence spectrum of silicon, commonly related to recombination through shallow inter-band gap energy levels near the conduction- and valence band edges. The shape and structure of these emissions from our measurements suggest that all the D-lines have different origins.

  2. Band Interaction between Chiral Doublet Bands

    International Nuclear Information System (INIS)

    Band interaction between the chiral doublet bands based on ?h11/2 vh?111/2 configuration is investigated in the particle rotor model with different triaxial deformation ?. The variation of chiral partner states with ? values is understood qualitatively based on the basic picture of two interaction levels, which is confirmed further by the calculated overlap integral of wave functions at different ? values. It is found that the interaction strengths of chiral partner states are obviously different for odd spins and even ones. (nuclear physics)

  3. Smelly and Dirty: Valence, not semantics, of odours prompt cleaning behaviour

    DEFF Research Database (Denmark)

    Dijksterhuis, Garmt Bernard; Zandstra, Elizabeth

    Odours typically associated with cleaning products, such as citrus, have been reported to activate cleaning behaviours. The aim of the present study was to test whether odours in general or pleasant odours specifically, would also do so. Furthermore, the concentration of the odour might be expected to play an important role: it is known that clearly recognisable odours lead to fewer behavioural effects than odours that are barely noticed. Once odours are recognised they may elicit all types of conscious reasoning that can inhibit behavioural effects. We used three odours: clearly unpleasant (Sulphur), clearly pleasant (Orange) and somewhat less familiar but also pleasant (Grass). Naïve subjects were led into special odour-controlled rooms in which each odour was dispersed, for what they believed to be a food product test. They were requested to cut a rusk into several parts, eat the parts, and then answer some questions presented on a computer screen. The behaviour of the subjects was recorded on video, and scored by several independent assessors using a structured observation method for quantitative coding and description of the cleaning behaviours observed (e.g. sweeping the table). The crumbs that remained after testing were also collected and weighted. These results show that different odour qualities appeared to trigger different levels of behavioural effects, and in particular that cleaning behaviour is not activated exclusively by a fragrance prompting associations with cleaning products, like citrus odours. Green grass, not known for its association with cleaning, showed similar effects to Orange. We posit that odour valence plays an important role, as Grass -and Orange- are in general well liked and have positive connotations, and produced more sweeping movements than the unpleasant Sulphur.

  4. Low-Dispersion Fibre Bragg Gratings Written Using the Polarization Control Method

    DEFF Research Database (Denmark)

    Deyerl, Hans Jürgen; Plougmann, Nikolai

    2002-01-01

    We present two fibre Bragg gratings with reduced in-band dispersion for DWDM applications. The gratings were designed by the inverse scattering method and fabricated using the novel polarization control method for UV-writing of advanced gratings.

  5. Band structure of TiO sub 2 -doped yttria-stabilized zirconia probed by soft-x-ray spectroscopy

    CERN Document Server

    Higuchi, T; Kobayashi, K; Yamaguchi, S; Fukushima, A; Shin, S

    2003-01-01

    The electronic structure of TiO sub 2 -doped yttria-stabilized zirconia (YSZ) has been studied by soft-X-ray emission spectroscopy (SXES) and X-ray absorption spectroscopy (XAS). The valence band is mainly composed of the O 2p state. The O 1s XAS spectrum exhibits the existence of the Ti 3d unoccupied state under the Zr 4d conduction band. The intensity of the Ti 3d unoccupied state increases with increasing TiO sub 2 concentration. The energy separation between the top of the valence band and the bottom of the Ti 3d unoccupied state is in accord with the energy gap, as expected from dc-polarization and total conductivity measurements. (author)

  6. Theoretical and experimental study of multifunction C+L band hybrid fiber amplifiers

    Science.gov (United States)

    Hsu, Hai-Yin; Yu, Yi-Lin; Liaw, Shien-Kuei; Liu, Ren-Yang; Shin, Chow-Shing

    2014-03-01

    We proposed and demonstrated a 100 km hybrid C+L band fiber amplifier in the bridge-type scheme. It is composed of a C-band erbium-doped fiber amplifier (EDFA) and an L-band Raman fiber amplifier (RFA) using double-pass dispersion compensators in a loop-back scheme. Dispersion slope mismatch is compensated precisely for all C+L band channels by writing fiber Bragg gratings (FBGs) at appropriate locations. Gain variation among multiple channels can be reduced to ±0.2 dB. The pump efficiency is improved by recycling the residual pump power. The C/L band WDM coupler which at merged point rejects C band amplified spontaneous emission (ASE) using L band coupler and vice versa. Both the simulation results and experimental measurements are realized in this paper. The hybrid EDFA/RFA may find vast applications in WDM long-haul systems and optical networks.

  7. Band model for d- and f-metals

    International Nuclear Information System (INIS)

    The application of band theory to metallic systems with d- and f-orbitals in the valence and conduction bands is discussed. Because such an application pushes theory and technique to their limits, several important features are briefly recapitulated. Within the transition metal systems, the elemental systems are used to discuss the fundamental formalism being applied and the newer directions into more complex systems are mentioned. Here we focus more on anisotropic properties and Fermi surface properties. Within the f-orbital systems, the focus is more on Ce and its compounds because of current interest with a relatively brief discussion of the actinides. the point of view advanced, however, has its origins in actinide research

  8. Modelos para dispersão Raman em polímeros conjugados Raman dispersion models in conjugated polymers

    OpenAIRE

    Millen, Ricardo P.; Faria, Dalva Lu?cia A.; Temperini, Marcia L. A.

    2005-01-01

    Raman dispersion refers to the dependence of the position of Raman bands on the energy of the exciting radiation. In this work, the three main models currently used to explain this phenomenon (Conjugated Length Model, Amplitude Mode Model and Effective Conjugation Coordinate Model) are discussed. Raman dispersion is a consequence of pi electron delocalization, but each model describes in a different way how pi electron delocalization affects the position of Raman bands. Here the features, qua...

  9. A theoretical and (e,2e) experimental investigation into the complete valence electronic structure of (1.1.1) propellane

    International Nuclear Information System (INIS)

    The first comprehensive electronic structural study of the complete valence shell of [1.1.1] propellane is reported. Binding energy spectra were measured in the energy regime 3.5-46.5 eV over a range of different target electron momentum so that individual orbital momentum profiles could also be determined. These binding energy spectra were collected using an energy dispersive multichannel electron momentum spectrometer at a total energy of 1000 eV, with a coincidence energy resolution of 1.38 eV and a momentum resolution of about 0.1 a.u. The experimental orbital electron momentum profiles are compared with those calculated in the plane wave impulse approximation (PWIA) using both a triple zeta plus polarisation level SCF wavefunction and a further 13 basis sets as calculated using Density Functional Theory (DFT). A critical comparison between the experimental an theoretical momentum distributions (MDs) allows to determine the optimum wavefunction for [1.1.1]propellane. In general, the level of agreement between the experimental and theoretical MDs for the optimum wavefunction for all of the respective valence orbitals was very good. The determination of this wavefunction then allowed to derive the chemically interesting molecular properties of [1.1.1]propellane. These include infrared spectra, bond lengths, bond orders, electron densities and many others. A summary of these results and a comparison of them with the previous results of other workers is presented with the level of agreement typically being good. In particular, the existence of the C1-C3 bridging bond with a bond order of 0.70 was confirmed. 59 refs., 4 tabs., 11 figs

  10. A theoretical and (e,2e) experimental investigation into the complete valence electronic structure of (1.1.1) propellane

    Energy Technology Data Exchange (ETDEWEB)

    Adcock, W.; Clark, C.I. [Flinders Univ. of South Australia, Bedford Park, SA (Australia); Brunger, M.J.; McCarthy, I.E. [Flinders Univ. of South Australia, Bedford Park, SA (Australia). School of Physical Sciences; Michalewicz, M.T. [CSIRO, Carlton, VIC (Australia). Division of Information Technology; Von Niessen, W. [Technische Univ., Braunschweig (Germany). Institute fur Physikalische and Theoretische Chemie; Weigold, E. [Australian National Univ., Canberra, ACT (Australia). Inst. of Advanced Studies; Winkler, D.A. [Commonwealth Scientific and Industrial Research Organisation (CSIRO), Clayton, VIC (Australia). Div. of Chemical Physics

    1996-08-01

    The first comprehensive electronic structural study of the complete valence shell of [1.1.1] propellane is reported. Binding energy spectra were measured in the energy regime 3.5-46.5 eV over a range of different target electron momentum so that individual orbital momentum profiles could also be determined. These binding energy spectra were collected using an energy dispersive multichannel electron momentum spectrometer at a total energy of 1000 eV, with a coincidence energy resolution of 1.38 eV and a momentum resolution of about 0.1 a.u. The experimental orbital electron momentum profiles are compared with those calculated in the plane wave impulse approximation (PWIA) using both a triple zeta plus polarisation level SCF wavefunction and a further 13 basis sets as calculated using Density Functional Theory (DFT). A critical comparison between the experimental an theoretical momentum distributions (MDs) allows to determine the optimum wavefunction for [1.1.1]propellane. In general, the level of agreement between the experimental and theoretical MDs for the optimum wavefunction for all of the respective valence orbitals was very good. The determination of this wavefunction then allowed to derive the chemically interesting molecular properties of [1.1.1]propellane. These include infrared spectra, bond lengths, bond orders, electron densities and many others. A summary of these results and a comparison of them with the previous results of other workers is presented with the level of agreement typically being good. In particular, the existence of the C1-C3 bridging bond with a bond order of 0.70 was confirmed. 59 refs., 4 tabs., 11 figs.

  11. Core-Valence Auger Spectra of the Simple Metals.

    Science.gov (United States)

    Davis, Linda Rae

    A comprehensive study of the core-valence-valence (CVV) Auger line shapes for the simple metals, Li, Be, Na, Mg, and Al, is presented. Calculations of these line shapes are performed with a static many-body model which treats the (static) screening of a core hole by conduction electrons with a phenomenological potential. Our model is applicable only to the simple metals, because free-electron theory is used to describe the conduction electrons. The model is implemented with a finite-particle, determinantal approach, and many-body Auger matrix elements are calculated explicitly using a local approximation. The many-body effects which arise from the core-conduction interaction are treated exactly within the model. The dependence of the model line shapes (i) on parameters specifying the metal and core level, (ii) on approximation of the model, and (iii) on the many-body effects produced by the core -conduction interaction are examined in detail. Also, model calculations of the simple-metal CVV spectra for which data exist are presented. Empirical fits of the model calculations to reported data are achieved for the Li(KVV), Be(KVV), Mg(L(,2,3)VV), and Al(L(,2,3)VV) spectra. In all of these cases, the screening of the core hole by conduction electrons is found to have both s-like and p-like character. One -electron and static many-body calculations have also been performed by other authors for some of the simple-metal spectra. Our model and results are compared to those from the other calculations. Although one-electron theory has reproduced several of the reported simple-metal line shapes, our calculations are the only many-body calculations to produce line shapes in agreement with data. Model calculations for the final reported spectrum, the Mg(KVV), are not presented, because the Mg K core hole is not sufficiently long-lived for our model to be valid. Our expectations concerning the unreported Na(L(,2,3)VV) spectrum are discussed. From our empirical fits and model study, we conclude that the many-body effects which are introduced by the core-conduction interaction, although weak, significantly influence the CVV line shapes of the simple metals. This conclusion is suggestive of the inadequacy of the one-electron theory of CVV line shapes, even in cases of simple-metal spectra.

  12. Strain sensitivity of band gaps of Sn-containing semiconductors

    DEFF Research Database (Denmark)

    Li, Hong; Castelli, Ivano Eligio

    2015-01-01

    Tuning of band gaps of semiconductors is a way to optimize materials for applications within photovoltaics or as photocatalysts. One way to achieve this is through applying strain to the materials. We investigate the effect of strain on a range of Sn-containing semiconductors using density functional theory and many-body perturbation theory calculations. We find that the band gaps of bulk Sn oxides with SnO6 octahedra are highly sensitive to volumetric strain. By applying a small isotropic strain of 2% (-2%), a decrease (increase) of band gaps as large as 0.8 to 1.0 eV are obtained. We attribute the ultrahigh strain sensitivity to the pure Sn s-state character of the conduction-band edges. Other Sn-containing compounds may show both increasing and decreasing gaps under tensile strain and we show that the behavior can be understood by analyzing the role of the Sn s states in both the valence and the conduction bands.

  13. Policy with Dispersed Information

    OpenAIRE

    Angeletos, George-Marios; Pavan, Alessandro

    2009-01-01

    Information regarding economic fundamentals is widely dispersed in society, is only imperfectly aggregated through prices or other indicators of aggregate activity, and cannot be centralized by the government or any other institution. In this paper we seek to identify policies that can improve the decentralized use of such dispersed information without requiring the government to observe this information. We show that this can be achieved by appropriately designing the contingency of taxation...

  14. Tunable band gaps in silicene-MoS2 heterobilayers.

    Science.gov (United States)

    Gao, N; Li, J C; Jiang, Q

    2014-06-21

    The geometric and electronic properties of silicene paired with a MoS2 substrate are studied systematically by using density functional theory with van der Waals corrections. It is found that the nearly linear band dispersions can be preserved in the heterobilayers due to the weak interface interactions. Meanwhile, the band gap is opened because of the sublattice symmetry broken by the intrinsic interface dipole. Moreover, the band gap values could be effectively modulated under an external electric field. Therefore, a way is paved for silicene-MoS2 heterobilayers to be candidate materials for logic circuits and photonic devices. PMID:24809774

  15. Valence bond phases in S = 1/2 Kane–Mele–Heisenberg model

    Science.gov (United States)

    Zare, Mohammad H.; Mosadeq, Hamid; Shahbazi, Farhad; Jafari, S. A.

    2014-11-01

    The phase diagram of the Kane–Mele–Heisenberg model in a classical limit [47] contains disordered regions in the coupling space, as the result of competition between different terms in the Hamiltonian, leading to frustration in finding a unique ground state. In this work we explore the nature of these phases in the quantum limit, for a S = 1/2. Employing exact diagonalization in Sz and nearest neighbour valence bond bases, and bond and plaquette valence bond mean field theories, we show that the disordered regions are divided into ordered quantum states in the form of plaquette valence bond crystals and staggered dimerized phases.

  16. Breakdown of ionic character of molecular alkali bromides in inner-valence photoionization

    International Nuclear Information System (INIS)

    The inner-valence region of alkali bromide XBr (X=Li, Na, K, Rb) vapours has been studied experimentally by means of synchrotron radiation excited photoelectron spectroscopy. Experimental spectra were analyzed by comparing them with available theoretical results and previous experiments. Ionic character of alkali bromides is seen to change in the inner-valence region with increasing atomic number of the alkali atom. A mechanism involving mixing between Br 4s and Rb 4p orbitals has been suggested to account for the fine structure observed in inner-valence ionization region of RbBr

  17. Valence bond phases in S = 1/2 Kane-Mele-Heisenberg model.

    Science.gov (United States)

    Zare, Mohammad H; Mosadeq, Hamid; Shahbazi, Farhad; Jafari, S A

    2014-11-12

    The phase diagram of the Kane-Mele-Heisenberg model in a classical limit [47] contains disordered regions in the coupling space, as the result of competition between different terms in the Hamiltonian, leading to frustration in finding a unique ground state. In this work we explore the nature of these phases in the quantum limit, for a S = 1/2. Employing exact diagonalization in Sz and nearest neighbour valence bond bases, and bond and plaquette valence bond mean field theories, we show that the disordered regions are divided into ordered quantum states in the form of plaquette valence bond crystals and staggered dimerized phases. PMID:25336537

  18. Photoion mass spectroscopy and valence photoionization of hypoxanthine, xanthine and caffeine

    Energy Technology Data Exchange (ETDEWEB)

    Feyer, Vitaliy, E-mail: vitaliy.feyer@elettra.trieste.it [Sincrotrone Trieste, in Area Science Park, I-34012 Basovizza (Trieste) (Italy); Plekan, Oksana [Sincrotrone Trieste, in Area Science Park, I-34012 Basovizza (Trieste) (Italy)] [Institute of Electron Physics, 21 Universitetska St., 88017 Uzhgorod (Ukraine); Richter, Robert [Sincrotrone Trieste, in Area Science Park, I-34012 Basovizza (Trieste) (Italy); Coreno, Marcello [CNR-IMIP, Area della Ricerca di Roma 1, CP10, I-00016 Monterotondo Scalo (Italy)] [CNR-Laboratorio Nazionale TASC-INFM, I-34012 Basovizza (Trieste) (Italy); Prince, Kevin C. [Sincrotrone Trieste, in Area Science Park, I-34012 Basovizza (Trieste) (Italy)] [CNR-Laboratorio Nazionale TASC-INFM, I-34012 Basovizza (Trieste) (Italy)

    2009-03-30

    Photoionization mass spectra of hypoxanthine, xanthine and caffeine were measured using the photoelectron-photoion coincidence technique and noble gas resonance radiation at energies from 8.4 to 21.2 eV for ionization. The fragmentation patterns for these compounds show that hydrogen cyanide is the main neutral loss species at higher photon energies, while photoionization below 16.67 eV led predominantly to the parent ion. The valence photoelectron spectra of this family of molecules were measured over an extended energy range, including the inner C, N and O 2s valence orbitals. The observed ion fragments were related to ionization of the valence orbitals.

  19. Pressure and temperature dependence of the magnetic susceptibility intermediate valence Ce and Yb compounds

    International Nuclear Information System (INIS)

    The magnetic susceptibility of 13 intermediate valence Ce and Yb compounds was studied at room temperature as a function of pressure. Low temperature measurements showed a pressure induced shift of the susceptibility maximum for YbInAu2 and Ce(Rhsub(0.7) Ptsub(0.3))2. A general relationship between the pressure dependent activation energy and the fluctuation temperature is supposed for Yb compounds. The relative pressure dependence of the susceptibility has a maximum at the intermediate valence 2.5 and is decreasing toward integer valences. (TW)

  20. Valency state changes in lanthanide-contained systems under high pressure

    International Nuclear Information System (INIS)

    Changes in valency state induced by pressure in samarium sulphide SmS remind one of alchemy, as the mat black initial substance shines golden after the electron transition. The alchemist's dream is of course not realized, however the compound does exhibit an unusually interesting behaviour in the new state. The valency state of samarium as newly appeared fluctuated very rapidly between two electron configurations. Manipulation of the valency state by pressure or chemical substitution can basically change the physical properties of systems containing lanthanides. The phenomena are described and discussed in the following survey. (orig.)

  1. Photoion mass spectroscopy and valence photoionization of hypoxanthine, xanthine and caffeine

    Science.gov (United States)

    Feyer, Vitaliy; Plekan, Oksana; Richter, Robert; Coreno, Marcello; Prince, Kevin C.

    2009-03-01

    Photoionization mass spectra of hypoxanthine, xanthine and caffeine were measured using the photoelectron-photoion coincidence technique and noble gas resonance radiation at energies from 8.4 to 21.2 eV for ionization. The fragmentation patterns for these compounds show that hydrogen cyanide is the main neutral loss species at higher photon energies, while photoionization below 16.67 eV led predominantly to the parent ion. The valence photoelectron spectra of this family of molecules were measured over an extended energy range, including the inner C, N and O 2s valence orbitals. The observed ion fragments were related to ionization of the valence orbitals.

  2. The use of bulk states to accelerate the band edge state calculation of a semiconductor quantum dot

    International Nuclear Information System (INIS)

    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

  3. The polarised valence quark distribution from semi-inclusive DIS

    International Nuclear Information System (INIS)

    The semi-inclusive difference asymmetry Ah+-h- for hadrons of opposite charge has been measured by the COMPASS experiment at CERN. The data were collected in the years 2002-2004 using a 160 GeV polarised muon beam scattered off a large polarised 6LiD target in the kinematic range 0.00622. In leading order QCD (LO) the deuteron asymmetry Ah+-h- measures the valence quark polarisation and provides an evaluation of the first moment of ?uv+?dv which is found to be equal to 0.40±0.07(stat.)±0.06(syst.) over the measured range of x at Q2=10 (GeV/c)2. When combined with the first moment of g1d previously measured on the same data, this result favours a non-symmetric polarisation of light quarks ?u-bar = -?d-bar at a confidence level of two standard deviations, in contrast to the often assumed symmetric scenario ?u-bar = ?d-bar = ?s-bar =?s

  4. Valence atom with bohmian quantum potential: the golden ratio approach

    Directory of Open Access Journals (Sweden)

    Putz Mihai V

    2012-11-01

    Full Text Available 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 reactivity charge with the aim of clarifying their features with respect to the so-called DFT ground state and critical charge, respectively. Results The results, based on the so-called double variational algorithm for chemical spaces of reactivity, are fundamental and, among other issues regarding chemical bonding, solve the existing paradox of using a cubic parabola to describe a quadratic charge dependency. Conclusions Overall, the paper provides a qualitative-quantitative explanation of chemical reactivity based on more than half of an electronic pair in bonding, and provide new, more realistic values for the so-called “universal” electronegativity and chemical hardness of atomic systems engaged in reactivity (analogous to the atoms-in-molecules framework.

  5. Valence bond solid (AKLT) state from t2 g electrons

    Science.gov (United States)

    Koch-Janusz, Maciej; Khomskii, Daniel; Sela, Eran

    2015-03-01

    The models constructed by Affleck, Kennedy, Lieb, and Tasaki (AKLT) describe gapped quantum spin liquids with fractionalized boundary spin excitations. The AKLT spin-spin interactions consist of projection operators onto the maximal possible spin formed between nearest neighbours, which involves a linear combination of powers of the Heisenberg coupling (S-->i .S-->j) n, making these states difficult to realize. Indeed, except for the one dimensional spin-1 case, simple antiferromagnetic Heisenberg interactions which are typically found in magnetic insulators, do not stabilize these spin liquid states, but rather generate conventional antiferromagnetically ordered states. We show that this type of interactions can be generated by orbital physics in multiorbital Mott insulators. Motivated by microscopic modeling of spin-orbit entangled Mott insulators such as the layered hexagonal Iridates, we focus on t2 g electrons on the honeycomb lattice and propose a physical realization of the spin- 3 / 2 AKLT state. Interestingly enough, the valence bond solid (AKLT) state found for the noninteracting electrons survives the increase of the on-site (Hubbard) repulsion, but it changes to the antiferromagnetic Neel state with increase of the Hund's rule coupling.

  6. Valence-skipping compounds as positive-U electronic systems

    Science.gov (United States)

    Harrison, Walter A.

    2006-12-01

    We find that arguments favoring negative-U behavior of intra-atomic origin, based upon valence skipping for compounds of column III, IV, and V metals, do not stand up to closer examination. It is suggested that real negative-U behavior (disproportionation in compounds such as TlBr2 , Pb2O3 , and BaBiO3 ) can, and does, only arise through relaxation of neighbors associated with changes in bond populations. Even then, very high dielectric constants are required to reduce the positive-U contribution, and disproportionation is not expected with lighter metals. Analogous displacements of water molecules may produce disproportionation in aqueous solutions of TlBr2 . We find that Tl impurities in PbTe also disproportionate, through atomic displacements with transfer of electrons between bonds, which could explain, as well as would an atomic-electronic origin, an apparent “charge-Kondo effect” behavior, and enhanced superconductivity, found by Matsushita, Blume, Geballe, and Fisher.

  7. Ab initio effective interactions for sd-shell valence nucleons

    CERN Document Server

    Dikmen, E; Barrett, B R; Maris, P; Shirokov, A M; Vary, J P

    2015-01-01

    We perform \\textit{ab initio} no core shell model calculations for $A=18$ and $19$ nuclei in a $4\\hbar\\Omega$, or $N_{\\rm max}=4$, model space using the effective JISP16 and chiral N3LO nucleon-nucleon potentials and transform the many-body effective Hamiltonians into the $0\\hbar\\Omega$ model space to construct the $A$-body effective Hamiltonians in the $sd$-shell. We separate the $A$-body effective Hamiltonians with $A=18$ and $A=19$ into inert core, one- and two-body components. Then, we use these core, one- and two-body components to perform standard shell model calculations for the $A=18$ and $A=19$ systems with valence nucleons restricted to the $sd$-shell. Finally, we compare the standard shell model results in the $0\\hbar\\Omega$ model space with the exact no core shell model results in the $4\\hbar\\Omega$ model space for the $A=18$ and $A=19$ systems and find good agreement.

  8. Valence Topological Charge-Transfer Indices for Dipole Moments

    Directory of Open Access Journals (Sweden)

    Francisco Torrens

    2003-01-01

    Full Text Available New valence topological charge-transfer indices are applied to the calculation of dipole moments. The algebraic and vector semisum charge-transfer indices are defined. The combination of the charge-transfer indices allows the estimation of the dipole moments. The model is generalized for molecules with heteroatoms. The ability of the indices for the description of the molecular charge distribution is established by comparing them with the dipole moments of a homologous series of phenyl alcohols. Linear and non-linear correlation models are obtained. The new charge-transfer indices improve the multivariable non-linear regression equations for the dipole moment. When comparing with previous results, the variance decreases 92%. No superposition of the corresponding Gk–Jk and GkV – JkV pairs is observed. This diminishes the risk of co-linearity. Inclusion of the oxygen atom in the p-electron system is beneficial for the description of the dipole moment, owing to either the role of the additional p orbitals provided by the heteroatom or the role of steric factors in the p-electron conjugation. Linear and non-linear correlations between the fractal dimension and various descriptors point not only to a homogeneous molecular structure but also to the ability to predict and tailor drug properties.

  9. Magnetic properties of mixed-valence iron phosphate glasses

    Science.gov (United States)

    Akamatsu, Hirofumi; Oku, Satoshi; Fujita, Koji; Murai, Shunsuke; Tanaka, Katsuhisa

    2009-10-01

    Magnetic properties of mixed-valence iron phosphate glasses, where there coexist Fe2+ and Fe3+ ions, have been investigated. The molar fraction of Fe3+ with respect to the total iron ion, [Fe3+]/[Fetotal] , can be controlled by melting the glass at varied temperatures. Experiments of magnetic aging and memory effects as well as dynamic and static scaling analyses of relaxation time and nonlinear magnetic susceptibility have been performed to get insight into the nature of low-temperature magnetic phase of the glass system. The experimental results reveal that the iron phosphate glasses undergo paramagnet-spin-glass transitions at low temperatures. Temperature dependence of magnetic specific heat suggests that as the temperature is lowered, the magnetic moments start to be frozen at a temperature significantly higher than the spin-glass transition temperature accompanied by a deviation in magnetic susceptibility from Curie-Weiss law. The ratio of the absolute value of Weiss temperature to spin-glass transition temperature increases as the ratio [Fe3+]/[Fetotal] becomes larger. This behavior is explainable in terms of the difference in single-ion anisotropy between Fe3+ and Fe2+ ions.

  10. Electrochemical uranium valence control in centrifugal solvent extraction contactors

    International Nuclear Information System (INIS)

    In the Purex process for the reprocessing of spent nuclear fuel, the partitioning of uranium and plutonium generally requires a reducing agent for the valence change of Pu(IV) to Pu(III). Modified mixer-settlers and pulsed columns with internal electrodes have been developed for the simultaneous electroreduction and solvent extraction, and the utility of this partitioning method has been demonstrated for the reprocessing of light water reactor and fast breeder reactor (FBR) fuels. Short-residence solvent extraction contractors are needed for the reprocessing of high-burnup fuels to reduce the radiation damage to the organic solvent. Centrifugal contactors, the currently preferred machines, have inherent spatial limitations for the incorporation of electrodes. External electrolytic reduction cells could be used, provided the chemical stability of the reduced species [U(IV) and Pu(III)] can be assured. The feasibility of in-tandem operation of a multistage centrifugal contactor and an electrolytic reduction cell was investigated, and the applicability of this method to the reprocessing of FBR fuel was tested by means of computer models developed from experimental results

  11. The Polarised Valence Quark Distribution from semi-inclusive DIS

    CERN Document Server

    Alekseev, M.; Alexandrov, Yu.; Alexeev, G.D.; Amoroso, A.; Arbuzov, A.; Badelek, B.; Balestra, F.; Ball, J.; Barth, J.; Baum, G.; Bedfer, Y.; Bernet, C.; Bertini, R.; Bettinelli, M.; Birsa, R.; Bisplinghoff, J.; Bordalo, P.; Bradamante, F.; Bravar, A.; Bressan, A.; Brona, G.; Burtin, E.; Bussa, M.P.; Chapiro, A.; Chiosso, M.; Cicuttin, A.; Colantoni, M.; Costa, S.; Crespo, M.L.; Dalla Torre, S.; Dafni, T.; Das, S.; Dasgupta, S.S.; De Masi, R.; Dedek, N.; Denisov, O.Yu.; Dhara, L.; Diaz, V.; Dinkelbach, A.M.; Donskov, S.V.; Dorofeev, V.A.; Doshita, N.; Duic, V.; Dunnweber, W.; Eversheim, P.D.; Eyrich, W.; Faessler, M.; Falaleev, V.; Ferrero, A.; Ferrero, L.; Finger, M.; Finger, M., Jr.; Fischer, H.; Franco, C.; Franz, J.; Friedrich, J.M.; Frolov, V.; Garfagnini, R.; Gautheron, F.; Gavrichtchouk, O.P.; Gazda, R.; Gerassimov, S.; Geyer, R.; Giorgi, M.; Gobbo, B.; Goertz, S.; Gorin, A.M.; Grabmuller, S.; Grajek, O.A.; Grasso, A.; Grube, B.; Gushterski, R.; Guskov, A.; Haas, F.; Hannappel, J.; von Harrach, D.; Hasegawa, T.; Heckmann, J.; Hedicke, S.; Heinsius, F.H.; Hermann, R.; Hess, C.; Hinterberger, F.; von Hodenberg, M.; Horikawa, N.; Horikawa, S.; d'Hose, N.; Ilgner, C.; Ioukaev, A.I.; Ishimoto, S.; Ivanov, O.; Ivanshin, Yu.; Iwata, T.; Jahn, R.; Janata, A.; Jasinski, P.; Joosten, R.; Jouravlev, N.I.; Kabuss, E.; Kang, D.; Ketzer, B.; Khaustov, G.V.; Khokhlov, Yu.A.; Kisselev, Yu.; Klein, F.; Klimaszewski, K.; Koblitz, S.; Koivuniemi, J.H.; Kolosov, V.N.; Komissarov, E.V.; Kondo, K.; Konigsmann, K.; Konorov, I.; Konstantinov, V.F.; Korentchenko, A.S.; Korzenev, A.; Kotzinian, A.M.; Koutchinski, N.A.; Kouznetsov, O.; Kral, A.; Kravchuk, N.P.; Kroumchtein, Z.V.; Kuhn, R.; Kunne, F.; Kurek, K.; Ladygin, M.E.; Lamanna, M.; Le Goff, J.M.; Lednev, A.A.; Lehmann, A.; Levorato, S.; Lichtenstadt, J.; Liska, T.; Ludwig, I.; Maggiora, A.; Maggiora, M.; Magnon, A.; Mallot, G.K.; Mann, A.; Marchand, C.; Marroncle, J.; Martin, A.; Marzec, J.; Massmann, F.; Matsuda, T.; Maximov, A.N.; Meyer, W.; Mielech, A.; Mikhailov, Yu.V.; Moinester, M.A.; Mutter, A.; Nagaytsev, A.; Nagel, T.; Nahle, O.; Nassalski, J.; Neliba, S.; Nerling, F.; Neubert, S.; Neyret, D.P.; Nikolaenko, V.I.; Nikolaev, K.; Olshevsky, A.G.; Ostrick, M.; Padee, A.; Pagano, P.; Panebianco, S.; Panknin, R.; Panzieri, D.; Paul, S.; Pawlukiewicz-Kaminska, B.; Peshekhonov, D.V.; Peshekhonov, V.D.; Piragino, G.; Platchkov, S.; Pochodzalla, J.; Polak, J.; Polyakov, V.A.; Pretz, J.; Procureur, S.; Quintans, C.; Rajotte, J.F.; Ramos, S.; Rapatsky, V.; Reicherz, G.; Reggiani, D.; Richter, A.; Robinet, F.; Rocco, E.; Rondio, E.; Rozhdestvensky, A.M.; Ryabchikov, D.I.; Samoylenko, V.D.; Sandacz, A.; Santos, H.; Sapozhnikov, M.G.; Sarkar, S.; Savin, I.A.; Schiavon, P.; Schill, C.; Schmitt, L.; Schonmeier, P.; Schroder, W.; Shevchenko, O.Yu.; Siebert, H.W.; Silva, L.; Sinha, L.; Sissakian, A.N.; Slunecka, M.; Smirnov, G.I.; Sosio, S.; Sozzi, F.; Srnka, A.; Stinzing, F.; Stolarski, M.; Sugonyaev, V.P.; Sulc, M.; Sulej, R.; Tchalishev, V.V.; Tessaro, S.; Tessarotto, F.; Teufel, A.; Tkatchev, L.G.; Venugopal, G.; Virius, M.; Vlassov, N.V.; Vossen, A.; Webb, R.; Weise, E.; Weitzel, Q.; Windmolders, R.; Wirth, S.; Wislicki, W.; Wollny, H.; Zaremba, K.; Zavertyaev, M.; Zemlyanichkina, E.; Zhao, J.; Ziegler, R.; Zvyagin, A.

    2008-01-01

    The semi-inclusive difference asymmetry A^{h+ - h-} for hadrons of opposite charge has been measured by the COMPASS experiment at CERN. The data were collected in the years 2002-2004 using a 160 GeV polarised muon beam scattered off a large polarised 6-LiD target and cover the range 0.006 < x < 0.7 and 1 < Q^2 < 100 (GeV/c)^2. In leading order QCD (LO) the asymmetry A_d^{h+ - h-} measures the valence quark polarisation and provides an evaluation of the first moment of Delta u_v + Delta d_v which is found to be equal to 0.40 +- 0.07 (stat.) +- 0.05 (syst.) over the measured range of x at Q^2 = 10 (GeV/c)^2. When combined with the first moment of g_1^d previously measured on the same data, this result favours a non-symmetric polarisation of light quarks Delta u-bar = -Delta d-bar at a confidence level of two standard deviations, in contrast to the often assumed symmetric scenario Delta u-bar = Delta d-bar = Delta s-bar = Delta s.

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

    OpenAIRE

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

    2009-01-01

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

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

    Science.gov (United States)

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

    2014-10-01

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

  14. Externally Dispersed Interferometry for Planetary Studies

    Energy Technology Data Exchange (ETDEWEB)

    Erskine, D J; Edelstein, J; Harbeck, D; Lloyd, J

    2005-07-06

    We describe a plan to study the radial velocity of low mass stars and brown dwarfs using a combination of interferometry and multichannel dispersive spectroscopy, Externally Dispersed Interferometry (EDI). The EDI technology allows implementation of precision velocimetry and spectroscopy on existing moderate-resolution echelle or linear grating spectrograph over their full and simultaneous bandwidth. We intend to add EDI to the new Cornell TripleSpec infrared simultaneous JHK-band spectrograph at the Palomar Observatory 200'' telescope for a science-demonstration program that will allow a unique Doppler-search for planets orbiting low mass faint M, L and T type stars. The throughput advantage of EDI with a moderate resolution spectrograph is critical to achieving the requisite sensitivity for the low luminosity late L and T dwarfs.

  15. Density-Functional Theory Study of the Effects of Atomic Impurity on the Band Edges of Monoclinic WO3

    Energy Technology Data Exchange (ETDEWEB)

    Huda, M. N.; Yan, Y.; Moon, C. Y.; Wei, S. H.; Al-Jassim, M. M.

    2008-01-01

    The effects of impurities in room-temperature monoclinic WO3 were studied by using the local density approximation to density-functional theory. Our main focus is on nitrogen impurity in WO{sub 3}, where both substitutional and interstitial cases were considered. We have also considered transition-metal atom impurities and some codoping approaches in WO{sub 3}. We find that, in general, band gap reduction was a common result due to the formation of impurity bands in the band gap. Also, the changes of band-edge positions, valence-band maxima and conduction-band minima, were found to depend on the electronic properties of the foreign atom and their concentration. Our results therefore provide guidance for making WO3 a suitable candidate for photoelectrodes for hydrogen generation by water splitting.

  16. Development of shear bands in amorphous-crystalline metallic alloys

    International Nuclear Information System (INIS)

    A theoretical study is made into conditions of shear band evolution in amorphous-crystalline alloys with various morphological types of structural constituents. The condition of shear band evolution in thin amorphous alloys in the interior of the crystalline matrix is obtained. It is shown that a scale effect exists which manifests itself in suppression of the process of localized plastic flow with amorphous alloy thickness decreasing down to the limit. The analysis of the condition for shear band evolution in an amorphous alloy with nanocrystalline inclusions is accomplished. The relationship of a critical stress of shear band evolution to a volume fraction of disperse crystal inclusions is obtained. A consideration is also given to the evolution of shear bands in the material containing amorphous and crystalline areas of micro meter size. For the alloy with the structure of this type conditions for propagation of localized flows by a relay race type mechanism are determined

  17. High birefringence, low loss terahertz photonic crystal fibres with zero dispersion at 0.3 THz

    International Nuclear Information System (INIS)

    A terahertz photonic crystal fibre (THz-PCF) is designed for terahertz wave propagation. The dispersion property and model birefringence are studied by employing the finite element method. The simulation result reveals the changing patten of dispersion parameter versus the geometry. The influence of the large frequency band of terahertz on birefringence is also discussed. The design of low loss, high birefringence THz-PCFs with zero dispersion frequency at 0.3 THz is presented. (general)

  18. Transport phenomena in zonal centrifuge rotors. XII. Dispersion in reorienting self-generating density gradients

    International Nuclear Information System (INIS)

    Dispersion in reorienting self-generating gradient systems for zonal centrifugations was investigated. Dispersions in experimental runs for K-III and J-I rotors were analyzed and compared with previously published analytical results. Various factors that contributed to a sample band broadening due to dispersion are discussed and evaluated. It is concluded that a control of rotor acceleration and deceleration may not be important. 2 figures, 2 tables

  19. Adolescents' responses to the gender valence of cigarette advertising imagery: the role of affect and the self-concept.

    Science.gov (United States)

    Shadel, William G; Niaura, Raymond; Abrams, David B

    2004-12-01

    The studies presented in this manuscript evaluated the role that affect and the self-concept play in adolescent never smokers' reactions to the gender valence of cigarette advertising imagery. Study 1 (n=29; 59% female) revealed that adolescent females have more positive affective reactions to female-valenced cigarette advertising imagery compared to male-valenced cigarette advertising imagery. Study 2 (n=101; 56% female) revealed that adolescent females viewed female-valenced cigarette advertising imagery as more relevant to their self-concepts compared to male-valenced cigarette advertising imagery. Across both studies, male adolescents did not respond differently as a function of the gender valence of cigarette advertising imagery. Thus, female-valenced cigarette advertising imagery may have specific effects on never smoking female adolescents by enhancing positive affect and suggesting that women who smoke hold the same characteristics as do the young women themselves. PMID:15530718

  20. Natal and breeding dispersal of northern spotted owls

    Science.gov (United States)

    Forsman, E.D.; Anthony, R.G.; Reid, J.A.; Loschl, P.J.; Sovern, S.G.; Taylor, M.; Biswell, B.L.; Ellingson, A.; Meslow, E.C.; Miller, G.S.; Swindle, K.A.; Thrailkill, J.A.; Wagner, F.F.; Seaman, D.E.

    2002-01-01

    We studied the dispersal behavior of 1,475 northern spotted owls (Strix occidentalis caurina) during banding and radio-telemetry studies in Oregon and Washington in 1985-1996. The sample included 324 radio-marked juveniles and 1,151 banded individuals (711 juveniles, 440 non-juveniles) that were recaptured or resighted after dispersing from the initial banding location. Juveniles typically left the nest during the last week in May and the first two weeks in June (x?? ?? SE = 8 June ?? 0.53 days, n = 320, range = 15 May-1 July), and spent an average of 103.7 days in the natal territory after leaving the nest (SE = 0.986 days, n = 137, range = 76-147 days). The estimated mean date that juveniles began to disperse was 19 September in Oregon (95% CI = 17-21 September) and 30 September in Washington (95% CI = 25 September-4 October). Mean dispersal dates did not differ between males and females or among years. Siblings dispersed independently. Dispersal was typically initiated with a series of rapid movements away from the natal site during the first few days or weeks of dispersal. Thereafter, most juveniles settled into temporary home ranges in late October or November and remained there for several months. In February-April there was a second pulse of dispersal activity, with many owls moving considerable distances before settling again in their second summer. Subsequent dispersal patterns were highly variable, with some individuals settling permanently in their second summer and others occupying a series of temporary home ranges before eventually settling on territories when they were 2-5 years old. Final dispersal distances ranged from 0.6-111.2 km for banded juveniles and 1.8-103.5 km for radio-marked juveniles. The distribution of dispersal distances was strongly skewed towards shorter distances, with only 8.7% of individuals dispersing more than 50 km. Median natal dispersal distances were 14.6 km for banded males, 13.5 km for radio-marked males, 24.5 km for banded females, and 22.9 km for radio-marked females. On average, banded males and females settled within 4.2 and 7.0 territory widths of their natal sites, respectively. Maximum and final dispersal distances were largely independent of the number of days that juveniles were tracked. Although statistical tests of dispersal direction based on all owls indicated that direction of natal dispersal was non-random, the mean angular deviations and 95% CI's associated with the samples were large, and r-values (vector length) were small. This lead us to conclude that significant test results were the result of large sample size and were not biologically meaningful. Our samples were not large enough to test whether dispersal direction from individual territories was random. In the sample of radio-marked owls, 22% of males and 44% of females were paired at 1 year of age, but only 1.5% of males and 1.6% of females were actually breeding at 1 year of age. At 2 years of age, 68% of males and 77% of females were paired, but only 5.4% of males and 2.6% of females were breeding. In contrast to the radio-marked owls, most juveniles that were banded and relocated at 1 or 2 years of age were paired, although few were breeding. Although recruitment into the territorial population typically occurred when owls were 1-5 years old, 9% of banded juveniles were not recaptured until they were > 5 years old. We suspect that our estimates of age at recruitment of banded owls are biased high because of the likelihood that some individuals were not recaptured in the first year that they entered the territorial population. A minimum of 6% of the banded, non-juvenile owls on our demographic study areas changed territories each year (breeding dispersal). The likelihood of breeding dispersal was higher for females, young owls, owls that did not have a mate in the previous year, and owls that lost their mate from the previous year through death or divorce. Mean and median distances dispersed by adults were