WorldWideScience

Sample records for valence band density

  1. Simultaneous Conduction and Valence Band Quantization in Ultrashallow High-Density Doping Profiles in Semiconductors

    Science.gov (United States)

    Mazzola, F.; Wells, J. W.; Pakpour-Tabrizi, A. C.; Jackman, R. B.; Thiagarajan, B.; Hofmann, Ph.; Miwa, J. A.

    2018-01-01

    We demonstrate simultaneous quantization of conduction band (CB) and valence band (VB) states in silicon using ultrashallow, high-density, phosphorus doping profiles (so-called Si:P δ layers). We show that, in addition to the well-known quantization of CB states within the dopant plane, the confinement of VB-derived states between the subsurface P dopant layer and the Si surface gives rise to a simultaneous quantization of VB states in this narrow region. We also show that the VB quantization can be explained using a simple particle-in-a-box model, and that the number and energy separation of the quantized VB states depend on the depth of the P dopant layer beneath the Si surface. Since the quantized CB states do not show a strong dependence on the dopant depth (but rather on the dopant density), it is straightforward to exhibit control over the properties of the quantized CB and VB states independently of each other by choosing the dopant density and depth accordingly, thus offering new possibilities for engineering quantum matter.

  2. Polarization Dependent Bulk-sensitive Valence Band Photoemission Spectroscopy and Density Functional Theory Calculations: Part I. 3d Transition Metals

    Science.gov (United States)

    Ueda, Shigenori; Hamada, Ikutaro

    2017-12-01

    The X-ray polarization dependent valence band HAXPES spectra of 3d transition metals (TMs) of Ti-Zn were measured to investigate the orbital resolved electronic structures by utilizing that the fact the photoionization cross-section of the atomic orbitals strongly depends on the experimental geometry. We have calculated the HAXPES spectra, which correspond to the cross-section weighted densities of states (CSW-DOSs), where the DOSs were obtained by the density functional theory calculations, and we have determined the relative photoionization cross-sections of the 4s and 4p orbitals to the 3d orbital in the 3d TMs. The experimentally obtained bulk-sensitive 3d and 4s DOSs were good agreement with the calculated DOSs in Ti, V, Cr, and Cu. In contrast, the deviations between the experimental and calculated 3d DOSs for Mn, Fe, Co, Ni were found, suggesting that the electron correlation plays an important role in the electronic structures for these materials.

  3. Valence band energy spectrum of HgTe quantum wells with an inverted band structure

    Science.gov (United States)

    Minkov, G. M.; Aleshkin, V. Ya.; Rut, O. E.; Sherstobitov, A. A.; Germanenko, A. V.; Dvoretski, S. A.; Mikhailov, N. N.

    2017-07-01

    The energy spectrum of the valence band in HgTe /CdxHg1 -xTe quantum wells of a width (8 -20 ) nm has been studied experimentally by magnetotransport effects and theoretically in the framework of a four-band k P method. Comparison of the Hall density with the density found from a period of the Shubnikov-de Haas (SdH) oscillations clearly shows that the degeneracy of states of the top of the valence band is equal to 2 at the hole density p SdH oscillations shows that mh is equal to (0.25 ±0.02 ) m0 and weakly increases with the hole density. Such a value of mh and its dependence on the hole density are in a good agreement with the calculated effective mass.

  4. Valence band effective Hamiltonians in nitride semiconductors

    Science.gov (United States)

    Punya, Atchara; Schwertfager, Nucharee; Lambrecht, Walter

    2012-02-01

    Valence band effective Hamiltonians are useful to determine the electronic states of shallow impurities, quantum wells, quantum wires and quantum dots within the effective mass approximation. Although significant experimental and theoretical work has been performed, basic parameters such as the Rashba Sheka Pikus (RSP) Hamiltonian parameters are still uncertain. In this work, the electronic band structures of AlN, GaN and InN, all in the wurtzite crystal structure, as well as the RSP Hamiltonian parameters are determined by using the QSGW approximation in a FP-LMTO implementation. The corrections offered by this approach beyond the LDA are important to obtain the splittings and effective masses accurately. The present GW implementation, which allows for a real space representation of the self-energy, enables us to interpolate exactly to a fine k-mesh and hence to obtain accurate effective masses. We find the crystal field splitting in GaN (12 meV) in much closer agreement with experiment than previous work and obtain a negative SO coupling for InN. Moreover, we have generalized the method of invariants to crystals with orthorombic symmetry, such as ZnSiN2 ZnGeN2, ZnSnN2 and CdGeN2 and determined the corresponding Hamiltonian parameters.

  5. Strain effects on valence bands of wurtzite ZnO

    Science.gov (United States)

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

    2013-09-01

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

  6. 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 Xα-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.

  7. Valence band electronic structure of Pd based ternary chalcogenide superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Lohani, H. [Institute of Physics, Sachivalaya Marg, Bhubaneswar 751005 (India); Homi Bhabha National Institute, Training School Complex, Anushakti Nagar, Mumbai 400085 (India); Mishra, P. [Institute of Physics, Sachivalaya Marg, Bhubaneswar 751005 (India); Goyal, R.; Awana, V.P.S. [National Physical Laboratory(CSIR), Dr. K. S. Krishnan Road, New Delhi 110012 (India); Sekhar, B.R., E-mail: sekhar@iopb.res.in [Institute of Physics, Sachivalaya Marg, Bhubaneswar 751005 (India); Homi Bhabha National Institute, Training School Complex, Anushakti Nagar, Mumbai 400085 (India)

    2016-12-15

    Highlights: • VB Photoemission study and DFT calculations on Pd based ternary superconductors are presented. • Nb{sub 2}Pd{sub 0.95}S{sub 5} shows a temperature dependent pseudogap. • VB spectral features of ternary superconductors are correlated to their structural geometry. - Abstract: We present a comparative study of the valence band electronic structure of Pd based ternary chalcogenide superconductors Nb{sub 2}Pd{sub 0.95}S{sub 5}, Ta{sub 2}Pd{sub 0.97}S{sub 6} and Ta{sub 2}Pd{sub 0.97}Te{sub 6} using experimental photoemission spectroscopy and density functional based theoretical calculations. We observe a qualitatively similarity between valence band (VB) spectra of Nb{sub 2}Pd{sub 0.95}S{sub 5} and Ta{sub 2}Pd{sub 0.97}S{sub 6}. Further, we find a pseudogap feature in Nb{sub 2}Pd{sub 0.95}S{sub 5} at low temperature, unlike other two compounds. We have correlated the structural geometry with the differences in VB spectra of these compounds. The different atomic packing in these compounds could vary the strength of inter-orbital hybridization among various atoms which leads to difference in their electronic structure as clearly observed in our DOS calculations.

  8. Electron density of states at the edge of the valence band of Cd{sub 0.88}Fe{sub 0.12}Se-A photoemission yield study

    Energy Technology Data Exchange (ETDEWEB)

    Sarem, Ammar [Department of Physics, Faculty of Science, Tishreen University, Aleppo Street, Latakia (Syrian Arab Republic)], E-mail: samers@scs-net.org; Kowalski, Bogdan J. [Institute of Physics, Polish Academy of Sciences, Aleja Lotnikow 32/46, PL 02-668 Warsaw (Poland); Nehme, Elias Al-Khoury [Department of Physics, Faculty of Science, Tishreen University, Aleppo Street, Latakia (Syrian Arab Republic)

    2007-08-15

    The electronic structures of Cd{sub 0.88}Fe{sub 0.12}Se and CdSe have been investigated by photoemission yield spectroscopy (PYS) in the photon energy range from 5 to 12 eV. The (112-bar0) surfaces were obtained by cleavage under ultrahigh vacuum (UHV) conditions. An Fe-related emission appeared at 0.58 eV above the valence band edge. The freshly cleaved surface of Cd{sub 0.88}Fe{sub 0.12}Se interacted with ambient atmosphere more strongly than CdSe crystal. Leaving the sample in an UHV chamber at room temperature enabled us to identify surface related features and to observe decrease of the ionization energy E{sub i}, energy threshold E{sub d} and the crystal affinity {chi} due to change of the surface conditions. Effective density of states, derived from the experimental spectra of Cd{sub 0.88}Fe{sub 0.12}Se exhibits, in contrast with CdSe, a surface-related feature degenerated with the bulk valence band.

  9. Atomic contributions to the valence band photoelectron spectra of metal-free, iron and manganese phthalocyanines

    Energy Technology Data Exchange (ETDEWEB)

    Bidermane, I., E-mail: ieva.bidermane@physics.uu.se [Department of Physics and Astronomy, Uppsala University, Box-516, 75120 Uppsala (Sweden); Institut des Nanosciences de Paris, UPMC Univ. Paris 06, CNRS UMR 7588, F-75005 Paris (France); Brumboiu, I.E. [Department of Physics and Astronomy, Uppsala University, Box-516, 75120 Uppsala (Sweden); Totani, R. [Department of Physical and Chemical Sciences, University of L’Aquila, Via Vetoio, Coppito, I-67010 L’Aquila (Italy); Grazioli, C. [CNR-IOM, Laboratorio TASC, ss. 14 km. 163.5, Basovizza, 34149 Trieste (Italy); Departement of Chemical and Pharmaceutical Sciences, University of Trieste (Italy); Shariati-Nilsson, M.N.; Herper, H.C.; Eriksson, O.; Sanyal, B. [Department of Physics and Astronomy, Uppsala University, Box-516, 75120 Uppsala (Sweden); Ressel, B. [University of Nova Gorica, Vipavska Cesta 11c, 5270 Ajdovščina (Slovenia); Simone, M. de [CNR-IOM, Laboratorio TASC, ss. 14 km. 163.5, Basovizza, 34149 Trieste (Italy); Lozzi, L. [Department of Physical and Chemical Sciences, University of L’Aquila, Via Vetoio, Coppito, I-67010 L’Aquila (Italy); Brena, B.; Puglia, C. [Department of Physics and Astronomy, Uppsala University, Box-516, 75120 Uppsala (Sweden)

    2015-11-15

    Highlights: • In detail comparison between the valence band structure of H{sub 2}Pc, FePc and MnPc. • Comparison between the gas phase samples and thin evaporated films on Au (1 1 1). • Detailed analysis of the atomic orbital contributions to the valence band features. • DFT/HSE06 study of the valence band electronic structure of H{sub 2}Pc, FePc and MnPc. - Abstract: The present work reports a photoelectron spectroscopy study of the low-energy region of the valence band of metal-free phthalocyanine (H{sub 2}Pc) compared with those of iron phthalocyanine (FePc) and manganese phthalocyanine (MnPc). We have analysed in detail the atomic orbital composition of the valence band both experimentally, by making use of the variation in photoionization cross-sections with photon energy, and theoretically, by means of density functional theory. The atomic character of the Highest Occupied Molecular Orbital (HOMO), reflected on the outermost valence band binding energy region, is different for MnPc as compared to the other two molecules. The peaks related to the C 2p contributions, result in the HOMO for H{sub 2}Pc and FePc and in the HOMO-1 for MnPc as described by the theoretical predictions, in very good agreement with the experimental results. The DFT simulations, discerning the atomic contribution to the density of states, indicate how the central metal atom interacts with the C and N atoms of the molecule, giving rise to different partial and total density of states for these three Pc molecules.

  10. Electron momentum spectroscopy study of amantadine: binding energy spectra and valence orbital electron density distributions

    Science.gov (United States)

    Litvinyuk, I. V.; Zheng, Y.; Brion, C. E.

    2000-11-01

    The electron binding energy spectrum and valence orbital electron momentum density distributions of amantadine (1-aminoadamantane), an important anti-viral and anti-Parkinsonian drug, have been measured by electron momentum spectroscopy. Theoretical momentum distributions, calculated at the 6-311++G** and AUG-CC-PVTZ levels within the target Hartree-Fock and also the target Kohn-Sham density functional theory approximations, show good agreement with the experimental results. The results for amantadine are also compared with those for the parent molecule, adamantane, reported earlier (Chem. Phys. 253 (2000) 41). Based on the comparison tentative assignments of the valence region ionization bands of amantadine have been made.

  11. 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.

  12. All-electron exact exchange treatment of semiconductors: effect of core-valence interaction on band-gap and d-band position.

    Science.gov (United States)

    Sharma, S; Dewhurst, J K; Ambrosch-Draxl, C

    2005-09-23

    We present the first all-electron full-potential exact exchange (EXX) Kohn-Sham density functional calculations on a range of semiconductors and insulators (Ge, GaAs, CdS, Si, ZnS, C, BN, Ne, Ar, Kr, and Xe). We remove one of the main computational obstacles of such calculations by the use of a highly efficient basis for inversion of the response function. We find that the band gaps are not as close to experiment as those obtained from previous pseudopotential EXX calculations. The locations of d bands, determined using the full-potential EXX method, are in excellent agreement with experiment, irrespective of whether these are core, semicore, or valence states. We conclude that the inclusion of the core-valence interaction is necessary for accurate determination of EXX Kohn-Sham band structures and that EXX alone is not a complete answer to the band-gap problem in semiconductors.

  13. Valence-band spectra and electronic structure of CuFeO2

    Science.gov (United States)

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

    1997-08-01

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

  14. Determination of conduction and valence band electronic structure ...

    Indian Academy of Sciences (India)

    Electronic structures of rutile and anatase polymorph of TiO2 were determined by resonant inelastic X-ray scattering measurements and FEFF9.0 calculations. Difference between crystalline structures led to shifts in the rutile Ti -band to lower energy with respect to anatase, i.e., decrease in band gap. Anatase possesses ...

  15. Determining binding energies of valence-band electrons in insulators and semiconductors via lanthanide spectroscopy

    NARCIS (Netherlands)

    Dorenbos, P.

    2013-01-01

    Models and methods to determine the absolute binding energy of 4f-shell electrons in lanthanide dopants will be combined with data on the energy of electron transfer from the valence band to a lanthanide dopant. This work will show that it provides a powerful tool to determine the absolute binding

  16. 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.

  17. Valence Band Structure of InAs1-xBix and InSb1-xBix Alloy Semiconductors Calculated Using Valence Band Anticrossing Model

    Directory of Open Access Journals (Sweden)

    D. P. Samajdar

    2014-01-01

    Full Text Available The valence band anticrossing model has been used to calculate the heavy/light hole and spin-orbit split-off energies in InAs1-xBix and InSb1-xBix alloy systems. It is found that both the heavy/light hole, and spin-orbit split E+ levels move upwards in energy with an increase in Bi content in the alloy, whereas the split E− energy for the holes shows a reverse trend. The model is also used to calculate the reduction of band gap energy with an increase in Bi mole fraction. The calculated values of band gap variation agree well with the available experimental data.

  18. Systematic study on intermolecular valence-band dispersion in molecular crystalline films

    Energy Technology Data Exchange (ETDEWEB)

    Yamane, Hiroyuki, E-mail: yamane@ims.ac.jp [Institute for Molecular Science, Myodaiji, Okazaki 444-8585 (Japan); SOKENDAI (The Graduate University for Advanced Studies), Myodaiji, Okazaki 444-8585 (Japan); Kosugi, Nobuhiro [Institute for Molecular Science, Myodaiji, Okazaki 444-8585 (Japan); SOKENDAI (The Graduate University for Advanced Studies), Myodaiji, Okazaki 444-8585 (Japan)

    2015-10-01

    Highlights: • Intermolecular valence-band dispersion of crystalline films of phthalocyanines. • Intermolecular transfer integral versus lattice constant. • Site-specific intermolecular interaction and resultant valence-band dispersion. • Band narrowing effect induced by elevated temperature. - Abstract: Functionalities of organic semiconductors are governed not only by individual properties of constituent molecules but also by solid-state electronic states near the Fermi level such as frontier molecular orbitals, depending on weak intermolecular interactions in various conformations. The individual molecular property has been widely investigated in detail; on the other hand, the weak intermolecular interaction is difficult to investigate precisely due to the presence of the structural and thermal energy broadenings in organic solids. Here we show quite small but essential intermolecular valence band dispersions and their temperature dependence of sub-0.1-eV scale in crystalline films of metal phthalocyanines (H{sub 2}Pc, ZnPc, CoPc, MnPc, and F{sub 16}ZnPc) by using angle-resolved photoemission spectroscopy (ARPES) with synchrotron radiation. The observed bands show intermolecular and site dependent dispersion widths, phases, and periodicities, for different chemical substitution of terminal groups and central metals in the phthalocyanine molecule. The precise and systematic band-dispersion measurement would be a credible approach toward the comprehensive understanding of intermolecular interactions and resultant charge transport properties as well as their tuning by substituents in organic molecular systems.

  19. Electronic structure of γ-FeSi 2: angle resolved valence band photoemission and Si 2p photoemission

    Science.gov (United States)

    O'Brien, W. L.; Tonner, B. P.

    1994-06-01

    We have investigated the electronic properties of γ-FeSi 2 thin films using angle resolved valence band photoemission and Si2p core level photoemission. We find two features in the valence band data which are not present in the calculated density of states (DOS). One of these has a constant final state energy and we identify it as being due to a final state effect. Another feature, found near —1.8 eV binding energy, is located in an energy gap of the bulk DOS and is identified as a surface state. We have measured the energy dispersion of this surface state and of two bulk-like states. The surface state has a total energy shift of 0.4 eV and exhibits band extrema near positions of the (2×2) reconstructed surface Brillouin zone boundaries. High resolution Si 2p photoemission spectra on samples of varying thickness show that the Si 2p binding energy is higher in the suicide than in bulk silicon by 0.49 eV. We find no evidence of silicon adatoms in our Si 2p photoemission results.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2011-04-06

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

  1. Core Levels, Band Alignments, and Valence-Band States in CuSbS 2 for Solar Cell Applications

    Energy Technology Data Exchange (ETDEWEB)

    Whittles, Thomas J. [Stephenson; Veal, Tim D. [Stephenson; Savory, Christopher N. [Department; Thomas; Welch, Adam W. [Material; de Souza Lucas, Francisco Willian [Material; Gibbon, James T. [Stephenson; Birkett, Max [Stephenson; Potter, Richard J. [Department; Scanlon, David O. [Department; Thomas; Diamond Light Source Ltd., Diamond; Zakutayev, Andriy [Material; Dhanak, Vinod R. [Stephenson

    2017-11-17

    The earth-abundant material CuSbS2 (CAS) has shown good optical properties as a photovoltaic solar absorber material, but has seen relatively poor solar cell performance. To investigate the reason for this anomaly, the core levels of the constituent elements, surface contaminants, ionization potential, and valence-band spectra are studied by X-ray photoemission spectroscopy. The ionization potential and electron affinity for this material (4.98 and 3.43 eV) are lower than those for other common absorbers, including CuInxGa(1-x)Se2 (CIGS). Experimentally corroborated density functional theory (DFT) calculations show that the valence band maximum is raised by the lone pair electrons from the antimony cations contributing additional states when compared with indium or gallium cations in CIGS. The resulting conduction band misalignment with CdS is a reason for the poor performance of cells incorporating a CAS/CdS heterojunction, supporting the idea that using a cell design analogous to CIGS is unhelpful. These findings underline the critical importance of considering the electronic structure when selecting cell architectures that optimize open-circuit voltages and cell efficiencies.

  2. Comment on ``Heterojunction valence-band-discontinuity dependence on face orientation''

    Science.gov (United States)

    van de Walle, Chris G.; Martin, Richard M.

    1988-03-01

    In a recent Rapid Communication [Phys. Rev. B 35, 6468 (1987)], Mun~oz, Sánchez-Dehesa, and Flores presented a self-consistent tight-binding analysis of valence-band offsets in GaAs/AlAs and CdTe/HgTe, and found a sizable dependence upon interface orientation for the latter system. This result differs from that obtained by the present authors for CdTe/HgTe heterojunctions. A more general study, building upon our previous heterojunction calculations, indicates in fact that independence of interface orientation is a general characteristic of a wide class of nonpolar interfaces.

  3. Determining binding energies of valence-band electrons in insulators and semiconductors via lanthanide spectroscopy

    Science.gov (United States)

    Dorenbos, Pieter

    2013-01-01

    Models and methods to determine the absolute binding energy of 4f-shell electrons in lanthanide dopants will be combined with data on the energy of electron transfer from the valence band to a lanthanide dopant. This work will show that it provides a powerful tool to determine the absolute binding energy of valence band electrons throughout the entire family of insulator and semiconductor compounds. The tool will be applied to 28 fluoride, oxide, and nitride compounds providing the work function and electron affinity together with the location of the energy levels of all divalent and all trivalent lanthanide dopants with an accuracy that surpasses that of traditional methods like photoelectron spectroscopy. The 28 compounds were selected to demonstrate how work function and electron affinity change with composition and structure, and how electronic structure affects the optical properties of the lanthanide dopants. Data covering more than 1000 different halide (F, Cl, Br, I), chalcogenide (O, S, Se), and nitride compounds are available in the archival literature enabling us to routinely establish work function and electron affinity for this much wider collection of compounds.

  4. Valence and conduction band offsets of β-Ga2O3/AlN heterojunction

    KAUST Repository

    Sun, Haiding

    2017-10-16

    Both β-Ga2O3 and wurtzite AlN have wide bandgaps of 4.5–4.9 and 6.1 eV, respectively. We calculated the in-plane lattice mismatch between the (−201) plane of β-Ga2O3 and the (0002) plane of AlN, which was found to be 2.4%. This is the smallest mismatch between β-Ga2O3 and binary III-nitrides which is beneficial for the formation of a high quality β-Ga2O3/AlN heterojunction. However, the valence and conduction band offsets (VBO and CBO) at the β-Ga2O3/AlN heterojunction have not yet been identified. In this study, a very thin (less than 2 nm) β-Ga2O3 layer was deposited on an AlN/sapphire template to form the heterojunction by pulsed laser deposition. High-resolution X-ray photoelectron spectroscopy revealed the core-level (CL) binding energies of Ga 3d and Al 2p with respect to the valence band maximum in individual β-Ga2O3 and AlN layers, respectively. The separation between Ga 3d and Al 2p CLs at the β-Ga2O3/AlN interface was also measured. Eventually, the VBO was found to be −0.55 ± 0.05 eV. Consequently, a staggered-gap (type II) heterojunction with a CBO of −1.75 ± 0.05 eV was determined. The identification of the band alignment of the β-Ga2O3/AlN heterojunction could facilitate the design of optical and electronic devices based on these and related alloys.

  5. Spin-dependent electron-phonon coupling in the valence band of single-layer WS2

    DEFF Research Database (Denmark)

    Hinsche, Nicki Frank; Ngankeu, Arlette S.; Guilloy, Kevin

    2017-01-01

    The absence of inversion symmetry leads to a strong spin-orbit splitting of the upper valence band of semiconducting single-layer transition-metal dichalchogenides such as MoS2 or WS2. This permits a direct comparison of the electron-phonon coupling strength in states that only differ by their spin....... Here, the electron-phonon coupling in the valence band maximum of single-layer WS2 is studied by first-principles calculations and angle-resolved photoemission. The coupling strength is found to be drastically different for the two spin-split branches, with calculated values of λK=0.0021 and 0.......40 for the upper and lower spin-split valence band of the freestanding layer, respectively. This difference is somewhat reduced when including scattering processes involving the Au(111) substrate present in the experiment but it remains significant, in good agreement with the experimental results....

  6. Valence and conduction band edges of selenide and sulfide-based kesterites—a study by x-ray based spectroscopy and ab initio theory

    Science.gov (United States)

    Olar, Tetiana; Manoharan, Archana; Draxl, Claudia; Calvet, Wolfram; Ümsur, Bünyamin; Parvan, Vladimir; Chacko, Binoy; Xie, Haibing; Saucedo, Edgardo; Valle-Rios, Laura Elisa; Neldner, Kai; Schorr, Susan; Lux-Steiner, Martha Ch; Lauermann, Iver

    2017-10-01

    Thin film solar cells based on the kesterite material with the general composition Cu2ZnSn(Se,S)4 can be a substitute for the more common chalcopyrites (Cu(In,Ga)(Se,S)2) with a similar band gap range. When replacing the anion sulfide with selenide, the optical band gap of kesterite changes from 1.5 to 1 eV. Here we report on a study of the valence band maximum and conduction band minimum energies of kesterites with either S or Se as the anion. Knowing these positions is crucial for the design of solar cells in order to match the bands of the absorber material with those of the subsequent functional layers like buffer or window layer. Their relative positions were studied using photoelectron spectroscopy of the valence band edge and x-ray absorption spectroscopy of the cations Cu, Zn, and Sn, respectively. The experimental results are interpreted and confirmed in terms of calculations based on density-functional theory and the GW approach of the many-body theory.

  7. 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, ρ, 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,ρ-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.

  8. Interaction of Cr(3+) with valence and conduction bands in the long persistent phosphor ZnGa2O4:Cr(3+), studied by ENDOR spectroscopy.

    Science.gov (United States)

    Binet, Laurent; Sharma, Suchinder K; Gourier, Didier

    2016-09-28

    Cr(3+)-doped zinc gallate ZnGa2O4 is a red-near infrared (IR) long persistent phosphor that can be excited by orange-red light, in the transparency window of living tissues. With this property, persistent luminescence nanoparticles were recently used for in vivo optical imaging of tumors in mice. In order to understand the origin of the excitability of persistent luminescence by visible light in this material, a Q-band ENDOR investigation of (71/69)Ga and (53)Cr nuclei was performed in ZnGa2O4:Cr(3+) to get information on the interaction of Cr(3+) with valence and conduction bands. The positive electron spin density at Ga nuclei revealed a dominant interaction of the (4)A2 ground state of Cr(3+) with the valence band, and a weaker interaction with the conduction band. The latter may occur only in the excited (2)E and (4)T2 states of Cr(3+). It is proposed that when these two interactions are present, pairs of electrons and holes can be generated from excited Cr(3+) in distorted sites undergoing local electric field produced by neighboring defects with opposite charges.

  9. Interaction of Cr3+ with valence and conduction bands in the long persistent phosphor ZnGa2O4:Cr3+, studied by ENDOR spectroscopy

    Science.gov (United States)

    Binet, Laurent; Sharma, Suchinder K.; Gourier, Didier

    2016-09-01

    Cr3+-doped zinc gallate ZnGa2O4 is a red-near infrared (IR) long persistent phosphor that can be excited by orange-red light, in the transparency window of living tissues. With this property, persistent luminescence nanoparticles were recently used for in vivo optical imaging of tumors in mice. In order to understand the origin of the excitability of persistent luminescence by visible light in this material, a Q-band ENDOR investigation of 71/69Ga and 53Cr nuclei was performed in ZnGa2O4:Cr3+ to get information on the interaction of Cr3+ with valence and conduction bands. The positive electron spin density at Ga nuclei revealed a dominant interaction of the 4A2 ground state of Cr3+ with the valence band, and a weaker interaction with the conduction band. The latter may occur only in the excited 2E and 4T2 states of Cr3+. It is proposed that when these two interactions are present, pairs of electrons and holes can be generated from excited Cr3+ in distorted sites undergoing local electric field produced by neighboring defects with opposite charges.

  10. Redistribution of valence and conduction band states depending on the method of modification of SiO2 structure.

    Science.gov (United States)

    Konashuk, A S; Filatova, E O

    2017-10-04

    The effect of introducing porosity and the insertion of methyl groups in SiO4 tetrahedra on the distribution of valence and conduction band states of SiO2 was studied using high-resolution near edge X-ray absorption fine structure spectroscopy (NEXAFS) and soft X-ray photoelectron spectroscopy (XPS). Alignment of NEXAFS spectra and valence band XPS spectra in a common energy scale was performed using binding energies of the initial levels obtained by XPS. It was established that the insertion of methyl groups into SiO4 tetrahedra leads to a significant shift of the top of the valence band EV to smaller binding energies due to the reduction of the electronegativity of the nearest surrounding neighbors of the Si atoms, while introducing porosity changes the position of EV only slightly. The position of the bottom of the conduction band is affected by neither the introduction of porosity nor the insertion of methyl groups. The formation of the π*C[double bond, length as m-dash]C state near the Fermi level, caused by the presence of porogen residues in the structure of organosilicate glass (OSG) and responsible for the leakage currents, was revealed. It was found that high level porosity in OSG films induces a significant variation of Si-O-Si valence angles. A number of Si-O dangling bonds were found in the surface layers of por-SiO2, while methyl groups effectively passivated these dangling bonds in OSG films. The obtained results are important for understanding the regularities of electronic structure formation in SiO2-based low-k dielectrics, which is necessary for the reduction of energy dissipated in semiconductor integrated circuits (ICs).

  11. The effects of ligand valency and density on the targeting ability of multivalent nanoparticles based on negatively charged chitosan nanoparticles.

    Science.gov (United States)

    Cao, Jing; Zhang, Yahui; Wu, Yukun; Wu, Jing; Wang, Wei; Wu, Qiang; Yuan, Zhi

    2018-01-01

    It has been shown that multivalent ligands could significantly enhance the binding avidity compared with the monovalent ones; therefore, once incorporated into nanoparticles, they promote superior targeting ability without increasing the ligand density. Although ligand valency and density play a key role on the targeting ability of corresponding nanoparticles, these facotrs remain largely unexplored and detailed studies are lacking. Herein, a series of multivalent ligands with certain valencies (FAn, n indicates the valency of ligand: n=3, 5, 7) has been conveniently synthesized by conjugating different copies of folate ligands with poly(acrylic acid) (PAA). Negatively charged chitosan nanoparticles (CTS-SA NPs) have been utilized as proper multivalent platforms because they can strongly suppress non-specific protein adsorption and cellular uptake without interfering with the targeting ability of multivalent ligands. Subsequently, the structure of CTS-SA NPs has been modified using different amounts of FAn to form multivalent nanoparticles (FAn-CTS-SA NPs) with various valencies and densities. A series of specific investigations of them suggested that the cellular uptake of multivalent nanoparticles has largely varied with the ligand valency variation even at similar ligand densities; and also largely varied with ligand density variation even at the same ligand valencies. The intermediate valency and density values determined in the current study (ie., 5 and 2.4wt%, respectively) have provided the best cellular uptake, facilitating superior targeting ability at relatively low ligand valency and density. Unexpectedly, no conspicuous difference has been observed during endocytotic inhibition assays with single inhibitors, which may be attributed to the synergetic endocytotic mechanism with multiple pathways of multivalent nanoparticles. The optimal multivalent nanoparticles have also exhibited excellent biocompatibility, long-term stability in vitro and enhanced

  12. Characterization of MBE-grown InAlN/GaN heterostructure valence band offsets with varying In composition

    Energy Technology Data Exchange (ETDEWEB)

    Jiao, Wenyuan, E-mail: wyjiaonju@gmail.com; Kong, Wei; Li, Jincheng; Kim, Tong-Ho; Brown, April S. [Department of Electrical and Computer Engineering, Duke University, Durham, NC, 27708 (United States); Collar, Kristen [Department of Physics, Duke University, Durham, NC, 27708 (United States); Losurdo, Maria [CNR-NANOTEC, Istituto di Nanotecnologia, via Orabona, 4-70126 Bari (Italy)

    2016-03-15

    Angle-resolved X-ray photoelectron spectroscopy (XPS) is used in this work to experimentally determine the valence band offsets of molecular beam epitaxy (MBE)-grown InAlN/GaN heterostructures with varying indium composition. We find that the internal electric field resulting from polarization must be taken into account when analyzing the XPS data. Valence band offsets of 0.12 eV for In{sub 0.18}Al{sub 0.82}N, 0.15 eV for In{sub 0.17}Al{sub 0.83}N, and 0.23 eV for In{sub 0.098}Al{sub 0.902}N with GaN are obtained. The results show that a compositional-depended bowing parameter is needed in order to estimate the valence band energies of InAlN as a function of composition in relation to those of the binary endpoints, AlN and InN.

  13. Probability of Two-Step Photoexcitation of Electron from Valence Band to Conduction Band through Doping Level in TiO2.

    Science.gov (United States)

    Nishikawa, Masami; Shiroishi, Wataru; Honghao, Hou; Suizu, Hiroshi; Nagai, Hideyuki; Saito, Nobuo

    2017-08-17

    For an Ir-doped TiO 2 (Ir:TiO 2 ) photocatalyst, we examined the most dominant electron-transfer path for the visible-light-driven photocatalytic performance. The Ir:TiO 2 photocatalyst showed a much higher photocatalytic activity under visible-light irradiation than nondoped TiO 2 after grafting with the cocatalyst of Fe 3+ . For the Ir:TiO 2 photocatalyst, the two-step photoexcitation of an electron from the valence band to the conduction band through the Ir doping level occurred upon visible-light irradiation, as observed by electron spin resonance spectroscopy. The two-step photoexcitation through the doping level was found to be a more stable process with a lower recombination rate of hole-electron pairs than the two-step photoexcitation process through an oxygen vacancy. Once electrons are photoexcited to the conduction band by the two-step excitation, the electrons can easily transfer to the surface because the conduction band is a continuous electron path, whereas the electrons photoexcited at only the doping level could not easily transfer to the surface because of the discontinuity of this path. The observed two-step photoexcitation from the valence band to the conduction band through the doping level significantly contributes to the enhancement of the photocatalytic performance.

  14. Valence band structure of PDMS surface and a blend with MWCNTs: A UPS and MIES study of an insulating polymer

    Energy Technology Data Exchange (ETDEWEB)

    Schmerl, Natalya M.; Khodakov, Dmitriy A.; Stapleton, Andrew J.; Ellis, Amanda V.; Andersson, Gunther G., E-mail: gunther.andersson@flinders.edu.au

    2015-10-30

    Graphical abstract: - Highlights: • Valence electron spectroscopy was performed on an insulating polymer using different charge compensation methods. • MWCNT were embedded in PDMS and found to be the most effective method for reducing the charging of the insulating polymer. • The valence band spectrum of PDMS was obtained via MIES and UPS. • Ion scattering spectroscopy was used to determine the concentration depth profile of the PDMS in the sample. - Abstract: The use of polydimethylsiloxane (PDMS) is increasing with new technologies working toward compact, flexible and transparent devices for use in medical and microfluidic systems. Electronic characterization of PDMS and other insulating materials is difficult due to charging, yet necessary for many applications where the interfacial structure is vital to device function or further modification. The outermost layer in particular is of importance as this is the area where chemical reactions such as surface functionalization will occur. Here, we investigate the valence band structure of the outermost layer and near surface area of PDMS through the use of metastable induced photoelectron spectroscopy (MIES) paired with ultraviolet photoelectron spectroscopy (UPS). The chemical composition of the samples under investigation were measured via X-ray photoelectron spectroscopy (XPS), and the vertical distribution of the polymer was shown with neutral impact collision ion scattering spectroscopy (NICISS). Three separate methods for charge compensation are used for the samples, and their effectiveness is compared.

  15. Influence of leaching on surface composition, microstructure, and valence band of single grain icosahedral Al-Cu-Fe quasicrystal

    Science.gov (United States)

    Lowe, M.; Yadav, T. P.; Fournée, V.; Ledieu, J.; McGrath, R.; Sharma, H. R.

    2015-03-01

    The use of quasicrystals as precursors to catalysts for the steam reforming of methanol is potentially one of the most important applications of these new materials. To develop application as a technology requires a detailed understanding of the microscopic behavior of the catalyst. Here, we report the effect of leaching treatments on the surface microstructure, chemical composition, and valence band of the icosahedral (i-) Al-Cu-Fe quasicrystal in an attempt to prepare a model catalyst. The high symmetry fivefold surface of a single grain i-Al-Cu-Fe quasicrystal was leached with NaOH solution for varying times, and the resulting surface was characterized by x-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The leaching treatments preferentially remove Al producing a capping layer consisting of Fe and Cu oxides. The subsurface layer contains elemental Fe and Cu in addition to the oxides. The quasicrystalline bulk structure beneath remains unchanged. The subsurface gradually becomes Fe3O4 rich with increasing leaching time. The surface after leaching exhibits micron sized dodecahedral cavities due to preferential leaching along the fivefold axis. Nanoparticles of the transition metals and their oxides are precipitated on the surface after leaching. The size of the nanoparticles is estimated by high resolution transmission microscopy to be 5-20 nm, which is in agreement with the AFM results. Selected area electron diffraction (SAED) confirms the crystalline nature of the nanoparticles. SAED further reveals the formation of an interface between the high atomic density lattice planes of nanoparticles and the quasicrystal. These results provide an important insight into the preparation of model catalysts of nanoparticles for steam reforming of methanol.

  16. Spectroscopic evidence for temperature-dependent convergence of light- and heavy-hole valence bands of PbQ (Q = Te, Se, S)

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, J.; Malliakas, C. D.; Wijayaratne, K.; Karlapati, V.; Appathurai, N.; Chung, D. Y.; Rosenkranz, S.; Kanatzidis, M. G.; Chatterjee, U.

    2017-01-01

    We have conducted a temperature- dependent angle-resolved photoemission spectroscopy (ARPES) study of the electronic structures of PbTe, PbSe and PbS. Our ARPES data provide direct evidence for the light-hole upper valence bands (UVBs) and hitherto undetected heavy-hole lower valence bands (LVBs) in these materials. An unusual temperature-dependent relative movement between these bands leads to a monotonic decrease in the energy separation between their maxima with increasing temperature, which is known as band convergence and has long been believed to be the driving factor behind extraordinary thermoelectric performances of these compounds at elevated temperatures.

  17. A low-temperature study of manganese-induced ferromagnetism and valence band convergence in tin telluride

    Energy Technology Data Exchange (ETDEWEB)

    Chi, Hang, E-mail: chihang@bnl.gov [Department of Physics, University of Michigan, Ann Arbor, Michigan 48109 (United States); Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973 (United States); Tan, Gangjian; Kanatzidis, Mercouri G. [Department of Chemistry, Northwestern University, Evanston, Illinois 60208 (United States); Li, Qiang [Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973 (United States); Uher, Ctirad [Department of Physics, University of Michigan, Ann Arbor, Michigan 48109 (United States)

    2016-05-02

    SnTe is renowned for its promise in advancing energy-related technologies based on thermoelectricity and for its topological crystalline insulator character. Here, we demonstrate that each Mn atom introduces ∼4 μ{sub B} (Bohr magneton) of magnetic moment to Sn{sub 1−x}Mn{sub x}Te. The Curie temperature T{sub C} reaches ∼14 K for x = 0.12, as observed in the field dependent hysteresis of magnetization and the anomalous Hall effect. In accordance with a modified two-band electronic Kane model, the light L-valence-band and the heavy Σ-valence-band gradually converge in energy with increasing Mn concentration, leading to a decreasing ordinary Hall coefficient R{sub H} and a favorably enhanced Seebeck coefficient S at the same time. With the thermal conductivity κ lowered chiefly via point defects associated with the incorporation of Mn, the strategy of Mn doping also bodes well for efficient thermoelectric applications at elevated temperatures.

  18. Interpretation of monoclinic hafnia valence electron energy-loss spectra by time-dependent density functional theory

    Science.gov (United States)

    Hung, L.; Guedj, C.; Bernier, N.; Blaise, P.; Olevano, V.; Sottile, F.

    2016-04-01

    We present the valence electron energy-loss spectrum and the dielectric function of monoclinic hafnia (m -HfO2) obtained from time-dependent density-functional theory (TDDFT) predictions and compared to energy-filtered spectroscopic imaging measurements in a high-resolution transmission-electron microscope. Fermi's golden rule density-functional theory (DFT) calculations can capture the qualitative features of the energy-loss spectrum, but we find that TDDFT, which accounts for local-field effects, provides nearly quantitative agreement with experiment. Using the DFT density of states and TDDFT dielectric functions, we characterize the excitations that result in the m -HfO2 energy-loss spectrum. The sole plasmon occurs between 13 and 16 eV, although the peaks ˜28 and above 40 eV are also due to collective excitations. We furthermore elaborate on the first-principles techniques used, their accuracy, and remaining discrepancies among spectra. More specifically, we assess the influence of Hf semicore electrons (5 p and 4 f ) on the energy-loss spectrum, and find that the inclusion of transitions from the 4 f band damps the energy-loss intensity in the region above 13 eV. We study the impact of many-body effects in a DFT framework using the adiabatic local-density approximation (ALDA) exchange-correlation kernel, as well as from a many-body perspective using "scissors operators" matched to an ab initio G W calculation to account for self-energy corrections. These results demonstrate some cancellation of errors between self-energy and excitonic effects, even for excitations from the Hf 4 f shell. We also simulate the dispersion with increasing momentum transfer for plasmon and collective excitation peaks.

  19. Effects of surface condition on the work function and valence-band position of ZnSnN2

    Science.gov (United States)

    Shing, Amanda M.; Tolstova, Yulia; Lewis, Nathan S.; Atwater, Harry A.

    2017-12-01

    ZnSnN2 is an emerging wide band gap earth-abundant semiconductor with potential applications in photonic devices such as solar cells, LEDs, and optical sensors. We report the characterization by ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy of reactively radio-frequency sputtered II-IV-nitride ZnSnN2 thin films. For samples transferred in high vacuum, the ZnSnN2 surface work function was 4.0 ± 0.1 eV below the vacuum level, with a valence-band onset of 1.2 ± 0.1 eV below the Fermi level. The resulting band diagram indicates that the degenerate bulk Fermi level position in ZnSnN2 shifts to mid-gap at the surface due to band bending that results from equilibration with delocalized surface states within the gap. Brief (semiconductor against standard redox potentials indicated that ZnSnN2 has an appropriate energy band alignment for use as a photoanode to effect the oxygen-evolution reaction.

  20. Resonating valence bond and sigma-charge density wave phases in a benzannulated phenalenyl radical.

    Science.gov (United States)

    Bag, Pradip; Itkis, Mikhail E; Pal, Sushanta K; Donnadieu, Bruno; Tham, Fook S; Park, Hyunsoo; Schlueter, John A; Siegrist, Theo; Haddon, Robert C

    2010-03-03

    We report the preparation of the first benzannulated phenalenyl neutral radical conductor (18), and we show that the compound displays unprecedented solid state behavior: the structure is dominated by two sets of intermolecular interactions: (1) a pi-chain structure with superimposed pi-overlap of the benzannulated phenalenyls along [0 0 1], and (2) an interchain overlap involving a pair of carbon atoms (C4) along [0 1 0]. The pi-chain-type stacking motif is reminiscent of previously reported phenalenyl radicals and the room temperature structure (space group P2/c) together with the conductivity of sigma(RT) = 0.03 S/cm and the Pauli-like magnetic susceptibility are best described by the resonating valence bond (RVB) model. The interchain interaction is unstable with respect to the formation of a sigma-charge density wave (sigma-CDW) involving pairs of C4 carbon atoms between adjacent radicals and this phase is characterized by the P2(1)/c space group which involves a doubling of the unit cell along the [0 1 0] direction. The RVB and CDW phases compete for structural occupancy throughout the whole temperature range (15-293 K) with the RVB phase predominating at 15 and 293 K and the sigma-CDW phase achieving a maximum structural occupancy of about 60% at 150 K where it produces clearly discernible effects on the magnetism and conductivity.

  1. 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.

  2. Quantifying van der Waals Interactions in Layered Transition Metal Dichalcogenides from Pressure-Enhanced Valence Band Splitting.

    Science.gov (United States)

    Ci, Penghong; Chen, Yabin; Kang, Jun; Suzuki, Ryuji; Choe, Hwan Sung; Suh, Joonki; Ko, Changhyun; Park, Taegyun; Shen, Ke; Iwasa, Yoshihiro; Tongay, Sefaattin; Ager, Joel W; Wang, Lin-Wang; Wu, Junqiao

    2017-08-09

    van der Waals (vdW) forces, despite being relatively weak, hold the layers together in transition metal dichalcogenides (TMDs) and play a key role in their band structure evolution, hence profoundly affecting their physical properties. In this work, we experimentally probe the vdW interactions in MoS 2 and other TMDs by measuring the valence band maximum (VBM) splitting (Δ) at K point as a function of pressure in a diamond anvil cell. As high pressure increases interlayer wave function coupling, the VBM splitting is enhanced in 2H-stacked MoS 2 multilayers but, due to its specific geometry, not in 3R-stacked multilayers, hence allowing the interlayer contribution to be separated out of the total VBM splitting, as well as predicting a negative pressure (2.4 GPa) where the interlayer contribution vanishes. This negative pressure represents the threshold vdW interaction beyond which neighboring layers are electronically decoupled. This approach is compared to first-principles calculations and found to be widely applicable to other group-VI TMDs.

  3. Valence band electronic structure and band alignment of LaAlO{sub 3}/SrTiO{sub 3}(111) heterointerfaces

    Energy Technology Data Exchange (ETDEWEB)

    Gabel, J.; Scheiderer, P.; Zapf, M.; Schuetz, P.; Sing, M.; Claessen, R. [Physikalisches Institut and Roentgen Center for Complex Material Systems (RCCM), Universitaet Wuerzburg (Germany); Schlueter, C.; Lee, T.L. [Diamond Light Source, Didcot (United Kingdom)

    2015-07-01

    As in the famous LaAlO{sub 3}(LAO)/SrTiO{sub 3}(STO) (001) a two-dimensional electron system (2DES) also forms at the interface between LAO and STO in (111) orientation. A distinct feature of the (111) interface is its peculiar real space topology. Each bilayer represents a buckled honeycomb lattice similar to graphene which is known theoretically to host various topologically non-trivial states. Bilayer STO in proximity to the interface can be regarded as a three-orbital generalization of graphene with enhanced electron correlations making it a promising candidate for the realization of strongly correlated topological phases. We have investigated the electronic structure of the LAO/STO (111) heterostructure in relation to the oxygen vacancy concentration which we can control by synchrotron light irradiation and oxygen dosing. With hard X-ray photoemission we study the core levels, whereas resonant soft X-ray photoemission is used to probe the interfacial valence band (VB) states. Two VB features are found: a peak at the Fermi level associated with the 2DES and in-gap states at higher binding energies attributed to oxygen vacancies. By varying the oxygen vacancy contribution we can tune the emergence of the VB states and engineer the interfacial band alignment.

  4. The effect of density-of-state tails on band-to-band tunneling: Theory and application to tunnel field effect transistors

    Science.gov (United States)

    Sant, S.; Schenk, A.

    2017-10-01

    It is demonstrated how band tail states in the semiconductor influence the performance of a Tunnel Field Effect Transistor (TFET). As a consequence of the smoothened density of states (DOS) around the band edges, the energetic overlap of conduction and valence band states occurs gradually at the onset of band-to-band tunneling (BTBT), thus degrading the sub-threshold swing (SS) of the TFET. The effect of the band tail states on the current-voltage characteristics is modelled quantum-mechanically based on the idea of zero-phonon trap-assisted tunneling between band and tail states. The latter are assumed to arise from a 3-dimensional pseudo-delta potential proposed by Vinogradov [1]. This model potential allows the derivation of analytical expressions for the generation rate covering the whole range from very strong to very weak localization of the tail states. Comparison with direct BTBT in the one-band effective mass approximation reveals the essential features of tail-to-band tunneling. Furthermore, an analytical solution for the problem of tunneling from continuum states of the disturbed DOS to states in the opposite band is found, and the differences to direct BTBT are worked out. Based on the analytical expressions, a semi-classical model is implemented in a commercial device simulator which involves numerical integration along the tunnel paths. The impact of the tail states on the device performance is analyzed for a nanowire Gate-All-Around TFET. The simulations show that tail states notably impact the transfer characteristics of a TFET. It is found that exponentially decaying band tails result in a stronger degradation of the SS than tail states with a Gaussian decay of their density. The developed model allows more realistic simulations of TFETs including their non-idealities.

  5. Topology of electron charge density for chemical bonds from valence bond theory: a probe of bonding types.

    Science.gov (United States)

    Zhang, Lixian; Ying, Fuming; Wu, Wei; Hiberty, Philippe C; Shaik, Sason

    2009-01-01

    To characterize the nature of bonding we derive the topological properties of the electron charge density of a variety of bonds based on ab initio valence bond methods. The electron density and its associated Laplacian are partitioned into covalent, ionic, and resonance components in the valence bond spirit. The analysis provides a density-based signature of bonding types and reveals, along with the classical covalent and ionic bonds, the existence of two-electron bonds in which most of the bonding arises from the covalent-ionic resonance energy, so-called charge-shift bonds. As expected, the covalent component of the Laplacian at the bond critical point is found to be largely negative for classical covalent bonds. In contrast, for charge-shift bonds, the covalent part of the Laplacian is small or positive, in agreement with the weakly attractive or repulsive character of the covalent interaction in these bonds. On the other hand, the resonance component of the Laplacian is always negative or nearly zero, and it increases in absolute value with the charge-shift character of the bond, in agreement with the decrease of kinetic energy associated with covalent-ionic mixing. A new interpretation of the topology of the total density at the bond critical point is proposed to characterize covalent, ionic, and charge-shift bonding from the density point of view.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2009-05-01

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

  7. First determination of the valence band dispersion of CH3NH3PbI3 hybrid organic-inorganic perovskite

    Science.gov (United States)

    Lee, Min-I.; Barragán, Ana; Nair, Maya N.; Jacques, Vincent L. R.; Le Bolloc'h, David; Fertey, Pierre; Jemli, Khaoula; Lédée, Ferdinand; Trippé-Allard, Gaëlle; Deleporte, Emmanuelle; Taleb-Ibrahimi, Amina; Tejeda, Antonio

    2017-07-01

    The family of hybrid organic-inorganic halide perovskites is in the limelight because of their recently discovered high photovoltaic efficiency. These materials combine photovoltaic energy conversion efficiencies exceeding 22% and low-temperature and low-cost processing in solution; a breakthrough in the panorama of renewable energy. Solar cell operation relies on the excitation of the valence band electrons to the conduction band by solar photons. One factor strongly impacting the absorption efficiency is the band dispersion. The band dispersion has been extensively studied theoretically, but no experimental information was available. Herein, we present the first experimental determination of the valence band dispersion of methylammonium lead halide in the tetragonal phase. Our results pave the way for contrasting the electronic hopping or the electron effective masses in different theories by comparing to our experimental bands. We also show a significant broadening of the electronic states, promoting relaxed conditions for photon absorption, and demonstrate that the tetragonal structure associated to the octahedra network distortion below 50 °C induces only a minor modification of the electronic bands, with respect to the cubic phase at high temperature, thus minimizing the impact of the cubic-tetragonal transition on solar cell efficiencies.

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

    Science.gov (United States)

    Zieliński, M

    2013-11-20

    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.

  9. 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 [μ∼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.

  10. Modulation of valence band maximum edge and photocatalytic activity of BiOX by incorporation of halides.

    Science.gov (United States)

    Lv, Jiaxin; Hu, Qingsong; Cao, Chengjin; Zhao, Yaping

    2018-01-01

    To better know the photocatalytic performance of bismuth oxyhalides (BiOX, X = Cl, Br, I) regulated by incorporation of halides within nanostructures, BiOX nanosheets were synthesized through morphology controllable solvothermal method and characterized systematically. The organic structural property greatly influences the photocatalytic activity of BiOX: 1) as for neutral molecular phenol, BiOX shows photocatalytic activity in the order of BiOCl > BiOBr > BiOI under simulated sun light irradiation, and the photo-oxidation kinetics follow Eley-Rideal mechanism; and 2) for adsorbed anionic orange II (OII) and cationic methylene blue (MB), BiOX shows photocatalytic activity in the order of BiOCl > BiOBr > BiOI, and the photo-oxidation kinetics follow Langmuir-Hinshelwood mechanism. The crystal structure of the catalyst also greatly influences the photocatalytic activity of BiOX: 1) The relative photo-oxidation power of O 2 •- radicals or HO radicals involved in this study were different which were quantitatively detected using typical radical trapping agent, separately; 2) The relative oxidation power of photogenerated holes (h + ) in this study were in the order of BiOCl > BiOBr > BiOI, which may be ascribed to lowering the valence band maximum edge of BiOX through incorporation of halides as the atomic number of halides decreased. This study provides novel explanation for fabricating BiOX heterojunctions with tunable photocatalytic reactivity via regulating the halides ratio. Copyright © 2017 Elsevier Ltd. All rights reserved.

  11. Band offsets of CuInSe2/CdS and CuInSe2/ZnS (110) interfaces: A hybrid density functional theory study

    Science.gov (United States)

    Hinuma, Yoyo; Oba, Fumiyasu; Kumagai, Yu; Tanaka, Isao

    2013-07-01

    The valence band offsets of the CuInSe2/CdS and CuInSe2/ZnS (110) interfaces are obtained based on various definitions using first-principles calculations in the framework of hybrid density functional theory. Both the strained band offset and the unstrained, or natural, band offset are investigated, where the two phases share and do not share in-plane lattice parameters perpendicular to the stacking direction, respectively. The valence band offset is determined by first obtaining the difference between the reference levels of two phases in the regions far from the interface and then adding the difference between the valence band maximum and the reference levels of bulk for the two phases. The nonfaceted (110) interface and a number of (112)/(112¯) faceted interfaces, some containing ordered point defects in the CuInSe2 (CIS) region, are considered. The excess energies of CIS/CdS and CIS/ZnS interfaces are lower when there are no ordered point defects, in contrast to the CIS surfaces that stabilize with ordered defect formation. The valence band offset is not significantly dependent on the atomic configurations at the interface as long as there are no charged layers. Surface calculations suggest that the reference level, which is determined by the average electrostatic potential at the atomic site, is not strongly dependent on lattice strain. A definition of the natural valence band offset that assumes a strain-invariant difference in the reference levels of the two phases provides values almost independent of the in-plane lattice parameters used in the interface calculation, which are about -1.2 and -1.3 eV with respect to CIS for the CIS/CdS and CIS/ZnS interfaces that contain no charged layers, respectively. The ionization potential difference can differ from the natural valence band offset by up to 0.3 eV without any consistent tendency to overestimate or underestimate, showing that the ionization potential difference is not necessarily a reasonable measure of

  12. Electronic structure of SnF{sub 3}: An example of valence skipper which forms charge density wave

    Energy Technology Data Exchange (ETDEWEB)

    Hase, I., E-mail: i.hase@aist.go.jp [National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8568 (Japan); Yanagisawa, T. [National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8568 (Japan); Kawashima, K. [IMRA Material R& D Co., LTD., Kariya, Aichi 448-0032 (Japan)

    2016-11-15

    Highlights: • We calculated the electronic structure of SnF{sub 3} and BaBiO{sub 3} from first principles. • As for SnF{sub 3}, charge-density-wave (CDW) is found, which agrees with the experiment. • As for BaBiO{sub 3}, CDW is not found, contrary to the experiment. • We conclude that the CDW is hard in SnF{sub 3} and is soft in BaBiO{sub 3}. - Abstract: In the present study we calculated the electronic structure of the valence skipping compound SnF{sub 3} and BaBiO{sub 3} from first-principles. We confirmed that the charge-density-wave (CDW) is formed in SnF{sub 3}, and the Sn atoms in two crystallographic different sites take the valence Sn{sup 2+} and Sn{sup 4+}. Structure optimization study reveals that this CDW is stable, though the atomic position is slightly different from the experimental data. This behavior is in contrast with the case of BaBiO{sub 3}, where the structure optimization leads to the uniform state, which means that two Bi sites are equivalent. The CDW state is hard in SnF{sub 3}, which means that the CDW gap is large enough and it is difficult to melt this CDW order.

  13. Relating the defect band gap and the density functional band gap

    Science.gov (United States)

    Schultz, Peter; Edwards, Arthur

    2014-03-01

    Density functional theory (DFT) is an important tool to probe the physics of materials. The Kohn-Sham (KS) gap in DFT is typically (much) smaller than the observed band gap for materials in nature, the infamous ``band gap problem.'' Accurate prediction of defect energy levels is often claimed to be a casualty--the band gap defines the energy scale for defect levels. By applying rigorous control of boundary conditions in size-converged supercell calculations, however, we compute defect levels in Si and GaAs with accuracies of ~0.1 eV, across the full gap, unhampered by a band gap problem. Using GaAs as a theoretical laboratory, we show that the defect band gap--the span of computed defect levels--is insensitive to variations in the KS gap (with functional and pseudopotential), these KS gaps ranging from 0.1 to 1.1 eV. The defect gap matches the experimental 1.52 eV gap. The computed defect gaps for several other III-V, II-VI, I-VII, and other compounds also agree with the experimental gap, and show no correlation with the KS gap. Where, then, is the band gap problem? This talk presents these results, discusses why the defect gap and the KS gap are distinct, implying that current understanding of what the ``band gap problem'' means--and how to ``fix'' it--need to be rethought. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the U.S. Department of Energy's NNSA under contract DE-AC04-94AL85000.

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

    Science.gov (United States)

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

    2013-07-01

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

  15. 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; Şahin, 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

    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.

  16. Sulfurization Growth of SnS Thin Films and Experimental Determination of Valence Band Discontinuity for SnS-Related Solar Cells

    Science.gov (United States)

    Sugiyama, Mutsumi; Murata, Yoshitsuna; Shimizu, Tsubasa; Ramya, Kottadi; Venkataiah, Chinna; Sato, Tomoaki; Ramakrishna Reddy, K. T.

    2011-05-01

    Tin sulphide is considered to be a potential candidate for the development of low cost polycrystalline thin film solar cells. The advantages of using sulfurization process to grow SnS films were demonstrated. Polycrystalline p-type SnS films were obtained by a simple dry process at 300 °C for 90 min. The sulfurization condition depends on the deposition method of the Sn precursor. Using single-phase SnS films, band discontinuities at SnS/CdS and SnO2/SnS heterointerfaces were measured by X-ray photoelectron spectroscopy. The valence band offsets were determined to be approximately 1.5 eV for SnS/CdS and 3.5 eV for SnO2/SnS interfaces. Using these values and the energy band gaps of the corresponding layers, the energy band diagram was developed. It indicated that the SnS/CdS heterojunction is of TYPE-II form of heterostructure. This result indicated that SnS-related solar cells with CdS as window layer do not have an ideal band structure that could give high conversion efficiency.

  17. The observation of valence band change on resistive switching of epitaxial Pr0.7Ca0.3MnO3 film using removable liquid electrode

    Science.gov (United States)

    Lee, Hong-Sub; Park, Hyung-Ho

    2015-12-01

    The resistive switching (RS) phenomenon in transition metal oxides (TMOs) has received a great deal of attention for non-volatile memory applications. Various RS mechanisms have been suggested as to explain the observed RS characteristics. Many reports suggest that changes of interface and the role of oxygen vacancies originate in RS phenomena; therefore, in this study, we use a liquid drop of mercury as the top electrode (TE), epitaxial Pr0.7Ca0.3MnO3 (PCMO) (110) film of the perovskite manganite family for RS material, and an Nb-doped (0.7 at. %) SrTiO3 (100) single crystal as the substrate to observe changes in the interface between the TE and TMOs. The use of removable liquid electrode Hg drop as TE not only enables observation of the RS characteristic as a bipolar RS curve (counterclockwise) but also facilitates analysis of the valence band of the PCMO surface after resistive switching via photoelectron spectroscopy. The observed I-V behaviors of the low and high resistance states (HRS) are explained with an electrochemical migration model in PCMO film where accumulated oxygen vacancies at the interface between the Hg TE and PCMO (110) surface induce the HRS. The interpreted RS mechanism is directly confirmed via valence band spectrum analysis.

  18. Surface, final state, and spin effects in the valence-band photoemission spectra of LaCoO3(001)

    Science.gov (United States)

    Halilov, S.; Gorelov, E.; Izquierdo, M.; Yaroslavtsev, A.; Aristov, V.; Moras, P.; Sheverdyaeva, P. M.; Mahatha, S. K.; Roth, F.; Lichtenstein, A.; Molodtsov, S. L.

    2017-11-01

    The electronic structure of a LaCoO3(001) perovskite is analyzed using simulated and measured angle-resolved valence-band photoemission spectroscopy data with emphasis on the effects of the surface truncation, the final state effects, and the spin degeneracy removal. Supercell simulations reveal instability towards the formation of nonuniform spin polarization in the Co-containing layers under tensile stress. Lattice expansion reduces antiferrodistortive octahedron tilting and tips the ratio between the crystal field parameter and the exchange energy in favor of local magnetization. While the magnitude of the local moment scales with lateral strain, the Curie temperature saturates for straight Co-O-Co chains below 75 K. The comparison of simulated photoemission spectra with experiments suggests Co-O2 to be the most stable surface stoichiometry, as proposed from transport and catalytic studies.

  19. Anomalous temperature dependence in valence band spectra: A resonant photoemission study of layered perovskite Sr{sub 2}CoO{sub 4}

    Energy Technology Data Exchange (ETDEWEB)

    Pandey, Pankaj K.; Choudhary, R. J., E-mail: ram@csr.res.in; Phase, D. M. [UGC DAE Consortium for Scientific Research, University Campus, Indore 452001 (India)

    2014-05-05

    Valence band spectra (VBS) and its modification across Curie temperature (T{sub C}) of Sr{sub 2}CoO{sub 4} thin film are studied using resonant photoemission spectroscopy. It is found that VBS mainly consists of hybridized states of Co-3d t{sub 2g}e{sub g} and O-2p; however, Co-3d e{sub g} states show its prominence only in the ferromagnetic temperature regime. Below T{sub C}, spectral weight transfer takes place anomalously from high binding energy (B.E.) region to low B.E. region, signifying the enhanced intermediate or low spin state Co{sup 4+} ions. It is suggested that spin-lattice coupling and many-body effects in Sr{sub 2}CoO{sub 4} derived from the strong electron correlations lead to such temperature dependence of VBS.

  20. One-hundred-three compound band-structure benchmark of post-self-consistent spin-orbit coupling treatments in density functional theory

    Science.gov (United States)

    Huhn, William P.; Blum, Volker

    2017-08-01

    We quantify the accuracy of different non-self-consistent and self-consistent spin-orbit coupling (SOC) treatments in Kohn-Sham and hybrid density functional theory by providing a band-structure benchmark set for the valence and low-lying conduction energy bands of 103 inorganic compounds, covering chemical elements up to polonium. Reference energy band structures for the PBE density functional are obtained using the full-potential (linearized) augmented plane wave code wien2k, employing its self-consistent treatment of SOC including Dirac-type p1 /2 orbitals in the basis set. We use this benchmark set to benchmark a computationally simpler, non-self-consistent all-electron treatment of SOC based on scalar-relativistic orbitals and numeric atom-centered orbital basis functions. For elements up to Z ≈50 , both treatments agree virtually exactly. For the heaviest elements considered (Tl, Pb, Bi, Po), the band-structure changes due to SOC are captured with a relative deviation of 11% or less. For different density functionals (PBE versus the hybrid HSE06), we show that the effect of spin-orbit coupling is usually similar but can be dissimilar if the qualitative features of the predicted underlying scalar-relativistic band structures do not agree. All band structures considered in this work are available online via the NOMAD repository to aid in future benchmark studies and methods development.

  1. Measurement of valence-band offset at native oxide/BaSi{sub 2} interfaces by hard x-ray photoelectron spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Takabe, Ryota; Du, Weijie; Takeuchi, Hiroki; Toko, Kaoru [Institute of Applied Physics, University of Tsukuba, Tsukuba, Ibaraki 305-8573 (Japan); Ito, Keita [Institute of Applied Physics, University of Tsukuba, Tsukuba, Ibaraki 305-8573 (Japan); Japan Society for the Promotion of Science (JSPS), Chiyoda, Tokyo 102-0083 (Japan); Department of Electronic Engineering, Graduate School of Engineering, Tohoku University, Sendai 980-8579 (Japan); Ueda, Shigenori [Synchrotron X-ray Station at SPring-8, National Institute for Materials Science (NIMS), Hyogo 679-5148 (Japan); Quantum Beam Unit, NIMS, Tsukuba, Ibaraki 305-0047 (Japan); Kimura, Akio [Graduate School of Science, Hiroshima University, Higashi-hiroshima 739-8526 (Japan); Suemasu, Takashi [Institute of Applied Physics, University of Tsukuba, Tsukuba, Ibaraki 305-8573 (Japan); Japan Science and Technology Agency, CREST, Tokyo 102-0075 (Japan)

    2016-01-14

    Undoped n-type BaSi{sub 2} films were grown on Si(111) by molecular beam epitaxy, and the valence band (VB) offset at the interface between the BaSi{sub 2} and its native oxide was measured by hard x-ray photoelectron spectroscopy (HAXPES) at room temperature. HAXPES enabled us to investigate the electronic states of the buried BaSi{sub 2} layer non-destructively thanks to its large analysis depth. We performed the depth-analysis by varying the take-off angle (TOA) of photoelectrons as 15°, 30°, and 90° with respect to the sample surface and succeeded to obtain the VB spectra of the BaSi{sub 2} and the native oxide separately. The VB maximum was located at −1.0 eV from the Fermi energy for the BaSi{sub 2} and −4.9 eV for the native oxide. We found that the band bending did not occur near the native oxide/BaSi{sub 2} interface. This result was clarified by the fact that the core-level emission peaks did not shift regardless of TOA (i.e., analysis depth). Thus, the barrier height of the native oxide for the minority-carriers in the undoped n-BaSi{sub 2} (holes) was determined to be 3.9 eV. No band bending in the BaSi{sub 2} close to the interface also suggests that the large minority-carrier lifetime in undoped n-BaSi{sub 2} films capped with native oxide is attributed not to the band bending in the BaSi{sub 2}, which pushes away photogenerated minority carriers from the defective surface region, but to the decrease of defective states by the native oxide.

  2. Two-stage pressure-induced Yb valence change in the hexagonal Laves phase YbAg2: Investigation by time differential perturbed angular γ -γ correlation spectroscopy method and density functional calculations

    Science.gov (United States)

    Tsvyashchenko, A. V.; Nikolaev, A. V.; Salamatin, D. A.; Velichkov, A.; Salamatin, A. V.; Novikov, A. P.; Fomicheva, L. N.; El'kin, F. S.; Bibikov, A. V.; Kozin, M. G.; Budzynski, M.

    2017-12-01

    We have studied the C14 hexagonal Laves phase of YbAg2 at normal conditions and under external pressure up to 19 GPa by the time-differential perturbed angular γ -γ correlation spectroscopy (TDPAC) using 111Cd probe nuclei. Under pressure the valence of Yb undergoes a two-stage transition from 2.8 to 3. The two-stage scenario is characterized by two distinct quadrupole frequencies of 111Cd probes in a silver sublattice, monotonically increasing with pressure and saturating at 8 and 16 GPa. Our experimental data are compared with the density functional studies of the electron band structure of YbAg2, whose results are used for discussion and interpretation of these experiments. We have found that there are two different electric field gradients at inequivalent silver sites and that 4 d states of silver participate in metal bonding, allowing for the formation of the hexagonal Laves phase.

  3. Non-Abelian ν =1/2 quantum Hall state in Γ8 valence band hole liquid

    Science.gov (United States)

    Simion, George; Lyanda-Geller, Yuli

    2017-04-01

    In the search for states with non-Abelian statistics, we explore the fractional quantum Hall effect in a system of two-dimensional (2D) charge carrier holes. We propose a method of mapping states of holes confined to a finite width quantum well in a perpendicular magnetic field to states in a spherical shell geometry. We take into account strong coupling between the spin and motion of charge parallel and perpendicular to the 2D layer. This method gives the single-particle hole states used in the exact diagonalization of systems with a small number of holes in the presence of Coulomb interactions, density matrix renormalization group, and topological entanglement entropy calculations. The hole quantum Hall state at half filling of the ground state in a magnetic field near the crossing of single-hole states is likely the Moore-Read Pfaffian state.

  4. Investigation on the valence-band structure of ferromagnetic-semiconductor GaMnAs using spin-dependent resonant tunneling spectroscopy

    Science.gov (United States)

    Ohya, Shinobu; Muneta, Iriya; Hai, Pham Nam; Tanaka, Masaaki

    2010-03-01

    We investigate the valence-band (VB) structure of ferromagnetic-semiconductor GaMnAs by analyzing the resonant tunneling levels of a GaMnAs quantum well (QW) in double-barrier heterostructures. The resonant level from the heavy-hole first state (HH1) is clearly observed in the metallic GaMnAs QW with the Curie temperature of 60 K, which indicates that no holes reside in the VB of GaMnAs in the equilibrium condition. Clear enhancement of tunnel magnetoresistance induced by resonant tunneling is demonstrated. We find that the resonant levels formed in the GaMnAs QW are well explained by using the transfer matrix method with the 6x6 Luttinger-Kohn kp Hamiltonian, p-d exchange Hamiltonian, and Bir-Pikus strain Hamiltonian. The VB structure of GaMnAs is well reproduced by that of GaAs with a small exchange splitting energy of 3-5 meV and with the Fermi level lying at ˜30 meV higher than HH1 in the bandgap. This work was partly supported by Grant-in-Aids for Scientific Research, the Special Coordination Programs for Promoting Science and Technology, R&D for Next-generation Information Technology by MEXT, and PRESTO of JST.

  5. Density changes in shear bands of a metallic glass determined by correlative analytical transmission electron microscopy

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-07-01

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

  6. Dissepiments, density bands and signatures of thermal stress in Porites skeletons

    Science.gov (United States)

    DeCarlo, Thomas M.; Cohen, Anne L.

    2017-09-01

    The skeletons of many reef-building corals are accreted with rhythmic structural patterns that serve as valuable sclerochronometers. Annual high- and low-density band couplets, visible in X-radiographs or computed tomography scans, are used to construct age models for paleoclimate reconstructions and to track variability in coral growth over time. In some corals, discrete, anomalously high-density bands, called "stress bands," preserve information about coral bleaching. However, the mechanisms underlying the formation of coral skeletal density banding remain unclear. Dissepiments—thin, horizontal sheets of calcium carbonate accreted by the coral to support the living polyp—play a key role in the upward growth of the colony. Here, we first conducted a vital staining experiment to test whether dissepiments were accreted with lunar periodicity in Porites coral skeleton, as previously hypothesized. Over 6, 15, and 21 months, dissepiments consistently formed in a 1:1 ratio to the number of full moons elapsed over each study period. We measured dissepiment spacing to reconstruct multiple years of monthly skeletal extension rates in two Porites colonies from Palmyra Atoll and in another from Palau that bleached in 1998 under anomalously high sea temperatures. Spacing between successive dissepiments exhibited strong seasonality in corals containing annual density bands, with narrow (wide) spacing associated with high (low) density, respectively. A high-density "stress band" accreted during the 1998 bleaching event was associated with anomalously low dissepiment spacing and missed dissepiments, implying that thermal stress disrupts skeletal extension. Further, uranium/calcium ratios increased within stress bands, indicating a reduction in the carbonate ion concentration of the coral's calcifying fluid under stress. Our study verifies the lunar periodicity of dissepiments, provides a mechanistic basis for the formation of annual density bands in Porites, and reveals the

  7. Valence band electronic structure of Nb{sub 2}Pd{sub 1.2}Se{sub 5} and Nb{sub 2}Pd{sub 0.95}S{sub 5} superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Lohani, H. [Institute of Physics, Sachivalaya Marg, Bhubaneswar 751005 (India); Homi Bhabha National Institute, Training School Complex, Anushakti Nagar, Mumbai 400085 (India); Mishra, P. [Institute of Physics, Sachivalaya Marg, Bhubaneswar 751005 (India); Goyal, R.; Awana, V.P.S. [National Physical Laboratory(CSIR), Dr. K. S. Krishnan Road, New Delhi 110012 (India); Sekhar, B.R., E-mail: sekhar@iopb.res.in [Institute of Physics, Sachivalaya Marg, Bhubaneswar 751005 (India); Homi Bhabha National Institute, Training School Complex, Anushakti Nagar, Mumbai 400085 (India)

    2017-03-15

    We present a comparative study of our valence band photoemission results on Nb{sub 2}Pd{sub 1.2}Se{sub 5} and Nb{sub 2}Pd{sub 0.95}S{sub 5} superconductors which are supported by our DFT based electronic structure calculations. We observe that the VB spectra of both the compounds are qualitatively similar, except for some slight differences in the binding energy positions of all the features. This could be due to the unequal electronegativities of Se and S atom. The calculated density of states (DOS) reveals that the VB features are mainly composed of Pd-Se/S hybridized states. The nature of DOS originating from the distinctly coordinated Pd atoms is different. Further, various Pd-4d and Nb-4d states crossing the Fermi level (E{sub f}) signifies the multiband character of these compounds. In addition, we find a temperature dependent pseudogap in Nb{sub 2}Pd{sub 0.95}S{sub 5} which is absent in Nb{sub 2}Pd{sub 1.2}Se{sub 5}.

  8. Calculating joint confidence bands for impulse response functions using highest density regions

    OpenAIRE

    Lütkepohl, Helmut; Staszewska-Bystrova, Anna; Winker, Peter

    2016-01-01

    This paper proposes a new non-parametric method of constructing joint confidence bands for impulse response functions of vector autoregressive models. The estimation uncertainty is captured by means of bootstrapping and the highest density region (HDR) approach is used to construct the bands. A Monte Carlo comparison of the HDR bands with existing alternatives shows that the former are competitive with the bootstrap-based Bonferroni and Wald confidence regions. The relative tightness of the H...

  9. Calculating Joint Bands for Impulse Response Functions using Highest Density Regions

    OpenAIRE

    Winker, Peter; Lütkepohl, Helmut; Staszewska-Bystrova, Anna

    2016-01-01

    This paper proposes a new non-parametric method of constructing joint confidence bands for impulse response functions of vector autoregressive models. The estimation uncertainty is captured by means of bootstrapping and the highest density region (HDR) approach is used to construct the bands. A Monte Carlo comparison of the HDR bands with existing alternatives shows that the former are competitive with the bootstrap-based Bonferroni and Wald confidence regions. The relative tightness of the H...

  10. Calculation of semiconductor band gaps with the M06-L density functional.

    Science.gov (United States)

    Zhao, Yan; Truhlar, Donald G

    2009-02-21

    The performance of the M06-L density functional has been tested for band gaps in seven semiconductors plus diamond and MgO. Comparison with the local spin density approximation (LSDA), Becke-Lee-Yang-Parr (BLYP), Perdew-Burke-Eernzerhof (PBE), Tao-Perdew-Staroverov-Scuseria (TPSS), and Heyd-Scuseria-Ernzerhof (HSE) functionals shows that M06-L has improved performance for calculating band gaps as compared to other local functionals, but it is less accurate than the screened hybrid HSE functional for band gaps.

  11. Atomic valence in molecular systems

    Science.gov (United States)

    Bochicchio, R. C.; Lain, L.; Torre, A.

    2003-06-01

    Atomic valence in molecular systems is described as a partitioning of the hole distribution, the complementary part of the particle distribution. In this scheme, valence splits into three contributions, related to electron spin density, nonuniform occupancy of orbitals (nonpairing terms) and exchange density (pairing terms), respectively, and whose importance depends on the nature of the state of the system. Calculations carried out for correlated CI and Hartree-Fock state functions in both Mulliken and topological AIM type partitionings as well as theoretical results show the suitability of this formulation for describing valence concepts.

  12. Band gap engineering in silicene: A theoretical study of density functional tight-binding theory

    Science.gov (United States)

    Zaminpayma, Esmaeil; Nayebi, Payman

    2016-10-01

    In this work, we performed first principles calculations based on self-consistent charge density functional tight-binding to investigate different mechanisms of band gap tuning of silicene. We optimized structures of silicene sheet, functionalized silicene with H, CH3 and F groups and nanoribbons with the edge of zigzag and armchair. Then we calculated electronic properties of silicene, functionalized silicene under uniaxial elastic strain, silicene nanoribbons and silicene under external electrical fields. It is found that the bond length and buckling value for relaxed silicene is agreeable with experimental and other theoretical values. Our results show that the band gap opens by functionalization of silicene. Also, we found that the direct band gap at K point for silicene changed to the direct band gap at the gamma point. Also, the functionalized silicene band gap decrease with increasing of the strain. For all sizes of the zigzag silicene nanoribbons, the band gap is near zero, while an oscillating decay occurs for the band gap of the armchair nanoribbons with increasing the nanoribbons width. At finally, it can be seen that the external electric field can open the band gap of silicene. We found that by increasing the electric field magnitude the band gap increases.

  13. A study of the valence shell electronic states of s-triazine by photoabsorption spectroscopy and ab initio calculations

    DEFF Research Database (Denmark)

    Holland, D.M.P.; Shaw, D.A.; Stener, Mauro

    2016-01-01

    absorption bands due to excitation from the 1e00 or 6e0 orbitals. The interpretation of the experimental spectrum has been guided by transition energies and oscillator strengths, for Rydberg and valence states, calculated with the time-dependent version of density functional theory and with the coupled...... cluster linear response approach. The theoretical studies indicate that Rydberg/Rydberg and Rydberg/valence mixing is important....

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

    OpenAIRE

    Courrol, Lilia Coronato; Monteiro, A.M.; SILVA, F.R.O.; L. Gomes; VIEIRA, N.D.; Gidlund, Magnus; Figueiredo Neto, A.M.

    2007-01-01

    We report here the observation of the enhancement of Europium-tetracycline complex emission in Low Density Lipoprotein (LDL) solutions. Europium emission band of tetracycline solution containing Europium (III) chloride hexahydrate was tested to obtain effective enhancement in the presence of native LDL and oxidized LDL. Europium emission lifetime in the presence of lipoproteins was measured, resulting in a simple method to measure the lipoproteins quantity in an aqueous solution at physiologi...

  15. Chemical bonding and charge redistribution - Valence band and core level correlations for the Ni/Si, Pd/Si, and Pt/Si systems

    Science.gov (United States)

    Grunthaner, P. J.; Grunthaner, F. J.; Madhukar, A.

    1982-01-01

    Via a systematic study of the correlation between the core and valence level X-ray photoemission spectra, the nature of the chemical bonding and charge redistribution for bulk transition metal silicides has been examined. Particular emphasis is placed on Pt2Si and PtSi. It is observed that the strength of the metal (d)-silicon (p) interaction increases in the order Ni2Si, Pd2Si, Pt2Si. It is also observed that both the metal and silicon core lines shift to higher binding energy as the silicides are formed. The notion of charge redistribution for metallic bonds is invoked to explain these data.

  16. Quasiparticle approximation electronic structure of the Ge/Si heterojunction to correct the local-density approximation band alignments

    Science.gov (United States)

    Ribeiro, Mauro

    2017-11-01

    The core of the LDA-½ quasiparticle approximation methodology are electrostatic self-energy corrections through precise determinations of the cutoff radius which, once determined, truncates the long-ranged self-energy function originated by the procedure of removing the spurious self-energy of electrons (or holes), responsible for most of excited-states pathologies in pure LDA. Depending on the dimensionality of the system in question, one issue regarding heterostructures electronic structure calculations is how the confinement factor, which is related to the amount of self-energy to be considered in calculations, affects the band alignments. This work presents theoretical results for the Ge/Si(100) interface band offsets, and final results for valence and conduction band offsets of 0.71 eV and 0.45 eV, respectively, which are in excellent agreement with experiments.

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

    Science.gov (United States)

    Balla, Robert J.; Everhart, Joel L.

    2012-01-01

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

  18. Analysis of EEG variables to measure the affective dimensions of arousal and valence related to the vision of emotional pictures.

    Science.gov (United States)

    Gaeta, G; Susac, A; Supek, S; Babiloni, F; Vecchiato, G

    2015-01-01

    The present work aims to investigate the electroencephalographic (EEG) activity elicited by the observation of emotional pictures selected from the International Affective Picture System (IAPS) database. We analyzed the evoked activity within time intervals of increasing duration taking into account the related ratings of Valence and Arousal. The scalp statistical maps of Power Spectral Density (PSD), related to pictures with high valence, revealed an enhanced activity across frontal areas in the theta band and the involvement of fronto-parietal circuits in the alpha band. Difference in the processing of low and high arousing pictures, however, seems to be highly dependent on the valence dimension: for low valenced pictures, the difference in arousal was processed immediately after the observation of the picture, while for the high-valenced ones the processing took part in the second part of the observation. These results appear to be congruent with the literature, while the novelty of the current study is represented by the comparison of the activity elicited in different time windows by both the Arousal and Valence dimensions. It is possible, in this way, to observe how the processing of one variable influences the other, creating a dynamic description of the Valence-Arousal space.

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

    Directory of Open Access Journals (Sweden)

    Yu Wang

    2002-01-01

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

  20. Levels of valence

    Directory of Open Access Journals (Sweden)

    Vera eShuman

    2013-05-01

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

  1. Luminescence and density banding patterns in massive Porites corals around the Thai-Malay Peninsula, Southeast Asia

    NARCIS (Netherlands)

    Tanzil, J.T.I.; Lee, J.N.; Brown, B.E.; Quax, R.; Kaandorp, J.A.; Lough, J.M.; Todd, P.A.

    2016-01-01

    We characterized the annual luminescent and skeletal density banding patterns in 51 massive Porites corals from 15 reefs from six locations around the Thai-Malay Peninsula in Southeast Asia, and explored the seasonal environmental cues/drivers of band formation. Location-specific recurrent annual

  2. Trap density of states in n-channel organic transistors: variable temperature characteristics and band transport

    Directory of Open Access Journals (Sweden)

    Joung-min Cho

    2013-10-01

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

  3. Fermi integral and density-of-states functions in a parabolic band semiconductor degenerately doped with impurities forming a band tail

    Science.gov (United States)

    Chaudhuri, B. K.; Mondal, B. N.; Chakraborty, P. K.

    2018-02-01

    We provide the energy spectrum of an electron in a degenerately doped semiconductor of parabolic band. Knowing the energy spectrum, the density-of-states (DOS) functions are obtained, considering the Gaussian distribution of the potential energy of the impurity states, showing a band tail in them e.g., energy spectrum and density-of-states. Therefore, Fermi integrals (FIs) of DOS functions, having band tail, are developed by the exact theoretical calculations of the same. It is noticed that with heavy dopings in semiconductors, the total FI demonstrates complex functions, containing both real and imaginary terms of different FI functions. Their moduli possess an oscillatory function of η (reduced Fermi energy = Ef/kBT, kB is the Boltzmann constant and T is the absolute temperature) and η e (impurity screening potential), having a series solutions of confluent hypergeometric functions, Φ (a, b; z), superimposed with natural cosine functions of angle θ . The variation of θ with respect to η indicated a resonance at η =1.5. The oscillatory behaviour of FIs show the existence of `band-gaps', both in the real as well as in the forbidden bands as new band gaps in the semiconductor.

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

    Science.gov (United States)

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

    2008-12-01

    densities were measured in vertical cross-sections of each whole corallum using standard X-ray techniques utilizing a calibrated step wedge to portray banding and overall density. The combination of the stereoscope and X-ray analyses across spatial and temporal gradients provide insight into how coral reef carbonate depositional facies are affected by changes in key environmental parameters, such as increased pollution, or changing photosynthetic activity with depth or sea surface temperature fluctuations.

  5. Simulating Ru L 3 -Edge X-ray Absorption Spectroscopy with Time-Dependent Density Functional Theory: Model Complexes and Electron Localization in Mixed-Valence Metal Dimers

    Energy Technology Data Exchange (ETDEWEB)

    Van Kuiken, Benjamin E.; Valiev, Marat; Daifuku, Stephanie L.; Bannan, Caitlin; Strader, Matthew L.; Cho, Hana; Huse, Nils; Schoenlein, Robert W.; Govind, Niranjan; Khalil, Munira

    2013-05-30

    Ruthenium L3-edge X-ray absorption (XA) spectroscopy probes unoccupied 4d orbitals of the metal atom and is increasingly being used to investigate the local electronic structure in ground and excited electronic states of Ru complexes. The simultaneous development of computational tools for simulating Ru L3-edge spectra is crucial for interpreting the spectral features at a molecular level. This study demonstrates that time-dependent density functional theory (TDDFT) is a viable and predictive tool for simulating ruthenium L3-edge XA spectroscopy. We systematically investigate the effects of exchange correlation functional and implicit and explicit solvent interactions on a series of RuII and RuIII complexes in their ground and electronic excited states. The TDDFT simulations reproduce all of the experimentally observed features in Ru L3-edge XA spectra within the experimental resolution (0.4 eV). Our simulations identify ligand-specific charge transfer features in complicated Ru L3-edge spectra of [Ru(CN)6]4- and RuII polypyridyl complexes illustrating the advantage of using TDDFT in complex systems. We conclude that the B3LYP functional most accurately predicts the transition energies of charge transfer features in these systems. We use our TDDFT approach to simulate experimental Ru L3-edge XA spectra of transition metal mixed-valence dimers of the form [(NC)5MII-CN-RuIII(NH3)5] (where M = Fe or Ru) dissolved in water. Our study determines the spectral signatures of electron delocalization in Ru L3-edge XA spectra. We find that the inclusion of explicit solvent molecules is necessary for reproducing the spectral features and the experimentally determined valencies in these mixed-valence complexes. This study validates the use of TDDFT for simulating Ru 2p excitations using popular quantum chemistry codes and providing a powerful interpretive tool for equilibrium and ultrafast Ru L3-edge XA spectroscopy.

  6. Electronic band structure of beryllium oxide

    CERN Document Server

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

    2003-01-01

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

  7. Density functional investigations of the properties and thermochemistry of UF6 and UF5 using valence-electron and all-electron approaches.

    Science.gov (United States)

    Batista, Enrique R; Martin, Richard L; Hay, P Jeffrey; Peralta, Juan E; Scuseria, Gustavo E

    2004-08-01

    The structural properties and thermochemistry of UF6 and UF5 have been investigated using both Hartree-Fock and density functional theory (DFT) approximations. Within the latter approach, the local spin-density approximation, the generalized gradient approximation, and hybrid density functionals were considered. To describe the uranium atom we employed small-core (60 electrons) and large-core (78 electrons) relativistic effective core potentials (RECPs), as well as the all-electron approximation based on the two-component third-order Douglas-Kroll-Hess Hamiltonian. For structural properties, we obtained very good agreement with experiment with DFT and both large and small-core RECPs. The best match with experiment is given by the hybrid functionals with the small-core RECP. The bond dissociation energy (BDE) was obtained from the relative energies of the fragments [UF6 --> UF5 + F], corrected for zero-point energy and spin-orbit interaction. Very good agreement was found between the BDE obtained from all-electron calculations and those calculated with the small-core RECP, while those from the large-core RECP are off by more than 50%. In order to obtain good agreement with experiment in the BDE it is imperative to work with hybrid density functionals and a small-core RECP. (c) 2004 American Institute of Physics.

  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. Yrast band of 109Ag described by tilted axis cranking covariant density functional theory with a separable pairing force

    Science.gov (United States)

    Wang, Y. K.

    2017-11-01

    A separable form of the Gogny pairing force is implemented in tilted axis cranking covariant density functional theory for the description of rotational bands in open shell nuclei. The developed method is used to investigate the yrast sequence of 109Ag for an example. The experimental energy spectrum, angular momenta, and electromagnetic transition probabilities are well reproduced by taking into account pairing correlations with the separable pairing force. An abrupt transition of the rotational axis from the long-intermediate plane to the long-short one is obtained and discussed in detail.

  10. Band gaps induced by vacuum photons in closed semiconductor cavities

    OpenAIRE

    Kibis, O. V.; Arnardottir, K. B.; Shelykh, I. A.

    2014-01-01

    We consider theoretically a closed (zero-dimensional) semiconductor microcavity where confined vacuum photonic mode is coupled to electrons in valence band of the semiconductor. It is shown that vacuum-induced virtual electron transitions between valence and conduction bands result in renormalization of electron energy spectrum. As a consequence, vacuum-induced band gaps appear within the valence band. Calculated values of the band gaps are of sub-meV scale, that makes this QED effect to be m...

  11. An atomic orbital based real-time time-dependent density functional theory for computing electronic circular dichroism band spectra.

    Science.gov (United States)

    Goings, Joshua J; Li, Xiaosong

    2016-06-21

    One of the challenges of interpreting electronic circular dichroism (ECD) band spectra is that different states may have different rotatory strength signs, determined by their absolute configuration. If the states are closely spaced and opposite in sign, observed transitions may be washed out by nearby states, unlike absorption spectra where transitions are always positive additive. To accurately compute ECD bands, it is necessary to compute a large number of excited states, which may be prohibitively costly if one uses the linear-response time-dependent density functional theory (TDDFT) framework. Here we implement a real-time, atomic-orbital based TDDFT method for computing the entire ECD spectrum simultaneously. The method is advantageous for large systems with a high density of states. In contrast to previous implementations based on real-space grids, the method is variational, independent of nuclear orientation, and does not rely on pseudopotential approximations, making it suitable for computation of chiroptical properties well into the X-ray regime.

  12. Synchronous changes in coral chromatophore tissue density and skeletal banding as an adaptive response to environmental change

    Science.gov (United States)

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

    2013-12-01

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

  13. Electronic structure and thermoelectric properties of half-Heusler compounds with eight electron valence count—KScX (X = C and Ge)

    Energy Technology Data Exchange (ETDEWEB)

    Ciftci, Yasemin O. [Department of Physics, Gazi University, Teknikokullar, Ankara 06500 (Turkey); Mahanti, Subhendra D. [Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824 (United States)

    2016-04-14

    Electronic band structure and structural properties of two representative half-Heusler (HH) compounds with 8 electron valence count (VC), KScC and KScGe, have been studied using first principles methods within density functional theory and generalized gradient approximation. These systems differ from the well studied class of HH compounds like ZrNiSn and ZrCoSb which have VC = 18 because of the absence of d electrons of the transition metal atoms Ni and Co. Electronic transport properties such as Seebeck coefficient (S), electrical conductivity (σ), electronic thermal conductivity (κ{sub e}) (the latter two scaled by electronic relaxation time), and the power factor (S{sup 2}σ) have been calculated using semi-classical Boltzmann transport theory within constant relaxation time approximation. Both the compounds are direct band gap semiconductors with band extrema at the X point. Their electronic structures show a mixture of heavy and light bands near the valance band maximum and highly anisotropic conduction and valence bands near the band extrema, desirable features of good thermoelectric. Optimal p- or n-type doping concentrations have been estimated based on thermopower and maximum power factors. The optimum room temperature values of S are ∼1.5 times larger than that of the best room temperature thermoelectric Bi{sub 2}Te{sub 3}. We also discuss the impact of the band structure on deviations from Weidemann-Franz law as one tunes the chemical potential across the band gap.

  14. Equilibrium gels of limited valence colloids

    OpenAIRE

    Sciortino, Francesco; Zaccarelli, Emanuela

    2017-01-01

    Gels are low-packing arrested states of matter which are able to support stress. On cooling, limited valence colloidal particles form open networks stabilized by the progressive increase of the interparticle bond lifetime. These gels, named equilibrium gels, are the focus of this review article. Differently from other types of colloidal gels, equilibrium gels do not require an underlying phase separation to form. Oppositely, they form in a region of densities deprived of thermodynamic instabi...

  15. Valence excitation energies of alkenes, carbonyl compounds, and azabenzenes by time-dependent density functional theory: Linear response of the ground state compared to collinear and noncollinear spin-flip TDDFT with the Tamm-Dancoff approximation

    Science.gov (United States)

    Isegawa, Miho; Truhlar, Donald G.

    2013-04-01

    Time-dependent density functional theory (TDDFT) holds great promise for studying photochemistry because of its affordable cost for large systems and for repeated calculations as required for direct dynamics. The chief obstacle is uncertain accuracy. There have been many validation studies, but there are also many formulations, and there have been few studies where several formulations were applied systematically to the same problems. Another issue, when TDDFT is applied with only a single exchange-correlation functional, is that errors in the functional may mask successes or failures of the formulation. Here, to try to sort out some of the issues, we apply eight formulations of adiabatic TDDFT to the first valence excitations of ten molecules with 18 density functionals of diverse types. The formulations examined are linear response from the ground state (LR-TDDFT), linear response from the ground state with the Tamm-Dancoff approximation (TDDFT-TDA), the original collinear spin-flip approximation with the Tamm-Dancoff (TD) approximation (SF1-TDDFT-TDA), the original noncollinear spin-flip approximation with the TDA approximation (SF1-NC-TDDFT-TDA), combined self-consistent-field (SCF) and collinear spin-flip calculations in the original spin-projected form (SF2-TDDFT-TDA) or non-spin-projected (NSF2-TDDFT-TDA), and combined SCF and noncollinear spin-flip calculations (SF2-NC-TDDFT-TDA and NSF2-NC-TDDFT-TDA). Comparing LR-TDDFT to TDDFT-TDA, we observed that the excitation energy is raised by the TDA; this brings the excitation energies underestimated by full linear response closer to experiment, but sometimes it makes the results worse. For ethylene and butadiene, the excitation energies are underestimated by LR-TDDFT, and the error becomes smaller making the TDA. Neither SF1-TDDFT-TDA nor SF2-TDDFT-TDA provides a lower mean unsigned error than LR-TDDFT or TDDFT-TDA. The comparison between collinear and noncollinear kernels shows that the noncollinear kernel

  16. Determination of band alignment in the single-layer MoS2/WSe2 heterojunction

    KAUST Repository

    Chiu, Ming-Hui

    2015-07-16

    The emergence of two-dimensional electronic materials has stimulated proposals of novel electronic and photonic devices based on the heterostructures of transition metal dichalcogenides. Here we report the determination of band offsets in the heterostructures of transition metal dichalcogenides by using microbeam X-ray photoelectron spectroscopy and scanning tunnelling microscopy/spectroscopy. We determine a type-II alignment between MoS2 and WSe2 with a valence band offset value of 0.83 eV and a conduction band offset of 0.76 eV. First-principles calculations show that in this heterostructure with dissimilar chalcogen atoms, the electronic structures of WSe2 and MoS2 are well retained in their respective layers due to a weak interlayer coupling. Moreover, a valence band offset of 0.94 eV is obtained from density functional theory, consistent with the experimental determination.

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

    Directory of Open Access Journals (Sweden)

    Yano Akira

    2012-11-01

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

  18. Compton profiles and band structure calculations of IV-VI layered compounds GeS and GeSe

    Science.gov (United States)

    Rathor, A.; Sharma, V.; Heda, N. L.; Sharma, Y.; Ahuja, B. L.

    2008-04-01

    First ever isotropic experimental Compton profiles of GeS and GeSe are presented. Moreover, we present Compton profiles, energy bands and density of states (DOS) using Hartree-Fock, density functional and pseudopotential schemes. It is seen that the Hartree-Fock and density functional theories show a reasonable agreement with the experiment. The equal-valence-electron-density profiles show that GeS is more ionic than GeSe. We have also reported energy bands and DOS using full potential linearized augmented plane-wave method.

  19. Linear Low Density Polyethylene (LLDPE) as Flexible Substrate for Wrist and Arm Antennas in C-Band

    Science.gov (United States)

    Gogoi, Pragyan Jyoti; Bhattacharyya, Satyajib; Bhattacharyya, Nidhi S.

    2015-04-01

    This paper focuses on the development and study of linear low density polyethylene as a flexible substrate for conformal antennas for body-worn applications. Thermal stability, tensile strength and elongation at break of the substrate were studied. The permittivity of the substrate was 2.2 and tan δ was found to be 0.0003 at 6 GHz. Since the antenna is being developed for wrist and arm wearing in C-band, the performance of the antenna, such as the S 11 parameter and radiation pattern, were studied with different bending axes and with bending curvature approximating that of the arm and wrist. The performance of a 6 GHz rectangular patch antenna with bending was found to be consistent with the flat profile antenna at the same frequency. A maximum shift in the resonant frequency of ˜20 MHz was observed. The -10 dB bandwidth and directivity of the antenna did not change much with bending. The maximum bending radius in the present study is 10 mm, and S 11 was found to be -17.53 dB at 5.94 GHz and -14.02 dB at 6.06 GHz for a bending axis parallel to the radiating and non-radiating edge, respectively.

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

    Directory of Open Access Journals (Sweden)

    Xu-Dong Chen

    2014-08-01

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

  1. Nanoscale Studies of Energy Band Gaps and Band Offsets in Compound Semiconductor Heterostructures

    Science.gov (United States)

    Chang, Alexander S.

    The identification of the precise band offsets at semiconductor interfaces is crucially important for the successful development of electronic and optoelectronic devices. However, issues at the interfaces, such as strain or defects, needs to be investigated for precise band tuning of semiconductor heterostructures. In this dissertation, the nanometer-scale structural and electronic properties of InGaAs(Sb)N/GaAs interfaces, InGaN/GaN QDs, and GaSb/GaAs QDs are investigated using a combination of XSTM and STS. The influence of Sb incorporation on the InGaAs(Sb)N/GaAs band alignment is investigated. At the InGaAsN/GaAs (InGaAsSbN/GaAs) interfaces, type II (type I) band offsets are observed, due to strain-induced splitting of the valence band and the incorporation of Sb. Band tuning of both conduction and valence band edges with the incorporation of Sb can be used to engineer the band structure with strong confinement of electrons and holes in the InGaAsSbN quantum well layer, which is promising for light emitting applications. The influence of the growth substrate on InGaN/GaN QD formation and properties is examined. The QD density, dimension, and band gaps are compared for different InGaN QDs on free-standing GaN or GaN/AlN/sapphire substrates. We present different sources using nucleation on different substrates, and discuss their influences on the electronic band structure. Our work suggests that a wide variety of InGaN QD dimension, density, and band structure can be achieved by using different starting substrate and number of layers of InGaN QD stacks. Furthermore, the influence of strain and dislocation on the GaSb/GaAs QD band alignment is investigated using both experimental and computational tools. A combination of cross-sectional transmission electron microscopy (XTEM), XSTM, and STS reveals the formation of misfit dislocations and both coherent and semi-coherent clustered QDs, independent of Sb- vs. As-termination of the GaAs surface. Furthermore, finite

  2. Energy band alignment of antiferroelectric (Pb,La)(Zr,Sn,Ti)O{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Klein, Andreas, E-mail: aklein@surface.tu-darmstadt.de [Technische Universität Darmstadt, Institute of Materials Science, Surface Science Division, Jovanka-Bontschits-Straße 2, 64287 Darmstadt (Germany); Lohaus, Christian [Technische Universität Darmstadt, Institute of Materials Science, Surface Science Division, Jovanka-Bontschits-Straße 2, 64287 Darmstadt (Germany); Reiser, Patrick [Technische Universität Darmstadt, Institute of Materials Science, Surface Science Division, Jovanka-Bontschits-Straße 2, 64287 Darmstadt (Germany); InnovationLab GmbH, Speyerer Straße 4, 69115 Heidelberg (Germany); Dimesso, Lucangelo [Technische Universität Darmstadt, Institute of Materials Science, Surface Science Division, Jovanka-Bontschits-Straße 2, 64287 Darmstadt (Germany); Wang, Xiucai; Yang, Tongqing [Tongji University, Key Laboratory of Advanced Civil Engineering Materials (Ministry of Education), Functional Materials Research Laboratory, College of Materials Science and Engineering, Cao’an Road 4800, Shanghai 201804 (China)

    2017-06-15

    Highlights: • Energy band alignment of antiferroelectric PLZST studied by XPS. • A deconvolution procedure is applied to study band alignment of insulating materials. • Contribution of Pb 6s orbitals leads to higher valence band maximum. • Ferroelectric polarization does not contribute to valence band maximum energy. • The variation of Schottky barrier heights indicates no Fermi level pinning in PLZST. - Abstract: The energy band alignment of antiferroelectric (Pb,La)(Zr,Sn,Ti)O{sub 3} is studied with photoelectron spectroscopy using interfaces with high work function RuO{sub 2} and low work function Sn-doped In{sub 2}O{sub 3} (ITO). It is demonstrated how spectral deconvolution can be used to determine absolute Schottky barrier heights for insulating materials with a high accuracy. Using this approach it is found that the valence band maximum energy of (Pb,La)(Zr,Sn,Ti)O{sub 3} is found to be comparable to that of Pb- and Bi-containing ferroelectric materials, which is ∼1 eV higher than that of BaTiO{sub 3}. The results provide additional evidence for the occupation of the 6s orbitals as origin of the higher valence band maximum, which is directly related to the electrical properties of such compounds. The results also verify that the energy band alignment determined by photoelectron spectroscopy of as-deposited electrodes is not influenced by polarisation. The electronic structure of (Pb,La)(Zr,Sn,Ti)O{sub 3} should enable doping of the material without strongly modifying its insulating properties, which is crucial for high energy density capacitors. Moreover, the position of the energy bands should result in a great freedom of selecting electrode materials in terms of avoiding charge injection.

  3. Elastic and inelastic scattering in core and valence emission from solids: Some new directions

    Science.gov (United States)

    Fadley, Charles S.

    1990-12-01

    We review recent work from several groups that has led to some interesting new directions in the study of elastic and inelastic scattering of electrons in both core and valence x-ray photoemission (XPS) and core-initiated Auger emission from solids. The elastic diffraction of core photoelectrons as measured with high angular resolutions of approximately ±1° has been found for the example of c(2×2)S on Ni(001) to provide greater sensitivity to surface atomic structures, including interplanar relaxation in the Ni substrate. Both photoelectron diffraction and Auger electron diffraction have also recently been shown to have the potential for more direct structural determinations via holographic inversions of the data; so far, theoretical simulations have been carried out for c(2×2)S on Ni(001) and inversions of experimental data for Cu(001) and Cu(111) have also yielded encouraging results. The diffraction of inelastically scattered electrons has been found in recent work on Al(001), Ge(111), and W(110) to exhibit similar patterns to those of elastic electrons, but with significant reductions in intensity along low-index directions that can be explained by enhanced multiple scattering effects. The angular dependence of energy-integrated valence-band XPS spectra for Al(001) has furthermore been shown to provide further evidence for hole localization in the final state. This use of such spectra appears to depend on averaging over the entire Brillouin zone due to the effects of phonon-induced non-direct transitions and the analyzer angular acceptance. Finally, such zone-averaged valence spectra for AuCu3(001) have suggested a new method for estimating the atomic orbital makeup or partial densities of states of the initial valence states.

  4. Band structure, density of states, and crystal chemistry of ZrGa{sub 2} and ZrGa{sub 3} single crystals

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-04-15

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

  5. Particle-Size-Induced Valence Changes in Samarium Clusters

    Energy Technology Data Exchange (ETDEWEB)

    Mason, M. G.; Lee, S. -T.; Apai, G.; Davis, R. F.; Shirley, D. A.; Franciosi, A.; Weaver, J. H.

    1981-09-01

    Samarium clusters exhibit mixed-valence behavior which is sensitive to particle size. XPS and UPS data show samarium to be primarily divalent (4f{sup 6} ) at small particle size. The trivalent state (4f{sup 5} ) becomes progressively more abundant with increasing s1ze, becoming the dominant state for the bulk metal. These results are interpreted using a model in which band narrowing, due to reduced surface coordination, is more dominant than surface tension effects in establishing the valence of small samarium clusters.

  6. Applying a rigid band model to the XYB14 crystal family

    Science.gov (United States)

    Wan, Liwen F.; Beckman, Scott P.

    2011-10-01

    The compounds AlMgB14, AlLiB14 and MgMgB14 belong to the same space group, Imma, and share similar structural properties. It is predicted that the rigid band model accurately describes the electronic states of these orthorhombic borides. The position of the Fermi level within the states depends on the metal site constituency. In this work the electronic properties of each compound are studied in detail by ab initio methods. Löwdin population analysis is conducted to examine the local charge distribution, and the projected density of states is calculated. It is found that the valence band edge is strongly dominated by the "Binter" and "Bconnector" atoms. This indicates that moving the Fermi level into the valence band will result in changes to the local bonding between the icosahedra and the inter-icosahedra B atoms.

  7. In-medium pion valence distributions in a light-front model

    Energy Technology Data Exchange (ETDEWEB)

    Melo, J.P.B.C. de, E-mail: joao.mello@cruzeirodosul.edu.br [Laboratório de Física Teórica e Computacional – LFTC, Universidade Cruzeiro do Sul, 01506-000 São Paulo (Brazil); Tsushima, K. [Laboratório de Física Teórica e Computacional – LFTC, Universidade Cruzeiro do Sul, 01506-000 São Paulo (Brazil); Ahmed, I. [Laboratório de Física Teórica e Computacional – LFTC, Universidade Cruzeiro do Sul, 01506-000 São Paulo (Brazil); National Center for Physics, Quaidi-i-Azam University Campus, Islamabad 45320 (Pakistan)

    2017-03-10

    Pion valence distributions in nuclear medium and vacuum are studied in a light-front constituent quark model. The in-medium input for studying the pion properties is calculated by the quark-meson coupling model. We find that the in-medium pion valence distribution, as well as the in-medium pion valence wave function, are substantially modified at normal nuclear matter density, due to the reduction in the pion decay constant.

  8. Observation of a novel stapler band in 75As

    Directory of Open Access Journals (Sweden)

    C.G. Li

    2017-03-01

    Full Text Available The heavy ion fusion–evaporation reaction study for the high-spin spectroscopy of 75As has been performed via the reaction channel 70Zn(9Be, 1p3n75As at a beam energy of 42 MeV. The collective structure especially a dipole band in 75As is established for the first time. The properties of this dipole band are investigated in terms of the self-consistent tilted axis cranking covariant density functional theory. Based on the theoretical description and the examination of the angular momentum components, this dipole band can be interpreted as a novel stapler band, where the valence neutrons in (1g9/2 orbital rather than the collective core are responsible for the closing of the stapler of angular momentum.

  9. Ab initio study of valence and Rydberg states of CH3Br

    Science.gov (United States)

    Escure, Christelle; Leininger, Thierry; Lepetit, Bruno

    2009-06-01

    We performed configuration interaction ab initio calculations on the valence and 5s, 5pa1, and 5pe Rydberg bands of the CH3Br molecule as a function of the methyl-bromide distance for frozen C3v geometries. The valence state potential energy curves are repulsive, the Rydberg state ones are similar to the one of the CH3Br+ ion with a minimum at short distance. One state emerging from the 5pe band has valence and ion-pair characters as distance increases and the corresponding potential curve has a second minimum at large distance. This state has a very strong parallel electric dipole transition moment with the ground state and plays a central role in UV photon absorption spectra. It is also responsible for the parallel character of the anisotropy parameters measured in ion-pair production experiments. In each band, there is a single state, which has a non-negligible transition moment with the ground state, corresponding to a transition perpendicular to the molecular axis of symmetry, except for the 5pe band where it is parallel. The perpendicular transition moments between ground and valence states increase sharply as methyl-bromide distance decreases due to a mixing between valence and 5s Rydberg band at short distance. In each band, spin orbit interaction produces a pair of states, which have significant transition moments with the ground one. In the valence band, the mixing between singlet and triplet states is weak and the perpendicular transition to the Q11 state is dominant. In each Rydberg band, however, spin-orbit interaction is larger than the exchange interaction and the two significant transition moments with the ground state have comparable strengths. The valence band has an additional state (Q10) with significant parallel transition moment induced by spin-orbit interaction with the ground state at large distance.

  10. Wavelet-based study of valence-arousal model of emotions on EEG signals with LabVIEW.

    Science.gov (United States)

    Guzel Aydin, Seda; Kaya, Turgay; Guler, Hasan

    2016-06-01

    This paper illustrates the wavelet-based feature extraction for emotion assessment using electroencephalogram (EEG) signal through graphical coding design. Two-dimensional (valence-arousal) emotion model was studied. Different emotions (happy, joy, melancholy, and disgust) were studied for assessment. These emotions were stimulated by video clips. EEG signals obtained from four subjects were decomposed into five frequency bands (gamma, beta, alpha, theta, and delta) using "db5" wavelet function. Relative features were calculated to obtain further information. Impact of the emotions according to valence value was observed to be optimal on power spectral density of gamma band. The main objective of this work is not only to investigate the influence of the emotions on different frequency bands but also to overcome the difficulties in the text-based program. This work offers an alternative approach for emotion evaluation through EEG processing. There are a number of methods for emotion recognition such as wavelet transform-based, Fourier transform-based, and Hilbert-Huang transform-based methods. However, the majority of these methods have been applied with the text-based programming languages. In this study, we proposed and implemented an experimental feature extraction with graphics-based language, which provides great convenience in bioelectrical signal processing.

  11. The valence of small fullerenes

    Science.gov (United States)

    Milani, C.; Giambelli, C.; Roman, H. E.; Alasia, F.; Benedek, G.; Broglia, R. A.; Sanguinetti, S.; Yabana, K.

    1996-08-01

    The production and isolation of small fullerenes and of their stable compounds and the knowledge of their chemistry should pave the way to the syntesis of novel carbon-based cluster-assembled materials like carbon clathrates, hollow diamonds and diamond-like thin films. In this quest, the knowledge of the valence of the small fullerenes is essential. We report here that the small fullerenes C n (20 ≤ n ≤ 32), aside from the well known values associated with the local one electron picture of dangling bonds, display hidden valences connected with the free electron picture of the shell structure of π-electrons.

  12. Quasi-Low-Dimensional Electron Gas with One Populated Band as a Testing Ground for Time-Dependent Density-Functional Theory of Mesoscopic Systems

    Science.gov (United States)

    Nazarov, Vladimir U.

    2017-06-01

    We find an exact analytical solution to the exchange-only time-dependent density-functional theory (TDDFT) problem for a significant class of quasi-low-dimensional (QLD) materials: QLD electron gas with only one band filled in the direction perpendicular to the layer or wire. The theory yields the TD exchange potential as an explicit nonlocal operator of the TD spin density. The dressed interband (image states) excitation spectra of quasi-two-dimensional electron gas are obtained, while the comparison with the Kohn-Sham transitions provides insights into the qualitative and quantitative role of the many-body interactions. Important cancellations between the Hartree fH and the exchange fx kernels of TDDFT are found in the low-density regime, elucidating the interrelations between the Kohn-Sham and the many-body dynamics in mesoscopic systems.

  13. The accurate calculation of the band gap of liquid water by means of GW corrections applied to plane-wave density functional theory molecular dynamics simulations.

    Science.gov (United States)

    Fang, Changming; Li, Wun-Fan; Koster, Rik S; Klimeš, Jiří; van Blaaderen, Alfons; van Huis, Marijn A

    2015-01-07

    Knowledge about the intrinsic electronic properties of water is imperative for understanding the behaviour of aqueous solutions that are used throughout biology, chemistry, physics, and industry. The calculation of the electronic band gap of liquids is challenging, because the most accurate ab initio approaches can be applied only to small numbers of atoms, while large numbers of atoms are required for having configurations that are representative of a liquid. Here we show that a high-accuracy value for the electronic band gap of water can be obtained by combining beyond-DFT methods and statistical time-averaging. Liquid water is simulated at 300 K using a plane-wave density functional theory molecular dynamics (PW-DFT-MD) simulation and a van der Waals density functional (optB88-vdW). After applying a self-consistent GW correction the band gap of liquid water at 300 K is calculated as 7.3 eV, in good agreement with recent experimental observations in the literature (6.9 eV). For simulations of phase transformations and chemical reactions in water or aqueous solutions whereby an accurate description of the electronic structure is required, we suggest to use these advanced GW corrections in combination with the statistical analysis of quantum mechanical MD simulations.

  14. Madelung and Hubbard interactions in polaron band model of doped organic semiconductors.

    Science.gov (United States)

    Png, Rui-Qi; Ang, Mervin C Y; Teo, Meng-How; Choo, Kim-Kian; Tang, Cindy Guanyu; Belaineh, Dagmawi; Chua, Lay-Lay; Ho, Peter K H

    2016-09-01

    The standard polaron band model of doped organic semiconductors predicts that density-of-states shift into the π-π* gap to give a partially filled polaron band that pins the Fermi level. This picture neglects both Madelung and Hubbard interactions. Here we show using ultrahigh workfunction hole-doped model triarylamine-fluorene copolymers that Hubbard interaction strongly splits the singly-occupied molecular orbital from its empty counterpart, while Madelung (Coulomb) interactions with counter-anions and other carriers markedly shift energies of the frontier orbitals. These interactions lower the singly-occupied molecular orbital band below the valence band edge and give rise to an empty low-lying counterpart band. The Fermi level, and hence workfunction, is determined by conjunction of the bottom edge of this empty band and the top edge of the valence band. Calculations are consistent with the observed Fermi-level downshift with counter-anion size and the observed dependence of workfunction on doping level in the strongly doped regime.

  15. C3H2 : A wide-band-gap semiconductor with strong optical absorption

    Science.gov (United States)

    Lu, Hong-Yan; Cuamba, Armindo S.; Geng, Lei; Hao, Lei; Qi, Yu-Min; Ting, C. S.

    2017-10-01

    Using first-principles calculations, we predict a new type of partially hydrogenated graphene system, C3H2 , which turns out to be a semiconductor with a band gap of 3.56 eV. The bands are rather flat at the band edges and thus lead to a large density of states, which further results in strong optical absorption between the valence band and the conduction band. Particularly, it shows strong optical absorption at about 4.5 eV for the light polarized along the lines connecting the nearest unhydrogenated carbon atoms. Thus, the predicted C3H2 system may have potential applications for a polarizer as well as other high-efficiency optical devices in the near ultraviolet region.

  16. The Influence of Finasteride on Mean and Relative Spectral Density of EEG Bands in Rat Model of Thioacetamide-Induced Hepatic Encephalopathy.

    Science.gov (United States)

    Mladenović, D; Hrnčić, D; Rašić-Marković, A; Macut, Dj; Stanojlović, O

    2016-08-01

    Liver failure is associated with a neuropsychiatric syndrome, known as hepatic encephalopathy (HE). Finasteride, inhibitor of neurosteroid synthesis, may improve the course of HE. The aim of our study was to investigate the influence of finasteride on mean and relative power density of EEG bands, determined by spectral analysis, in rat model of thioacetamide-induced HE. Male Wistar rats were divided into groups: (1) control; (2) thioacetamide-treated group, TAA (900 mg/kg); (3) finasteride-treated group, FIN (150 mg/kg); and (4) group treated with finasteride (150 mg/kg) and thioacetamide (900 mg/kg), FIN + TAA. Daily doses of FIN (50 mg/kg) and TAA (300 mg/kg) were administered during 3 subsequent days, and in FIN + TAA group FIN was administered 2 h before every dose of TAA. EEG was recorded 22-24 h after treatment and analyzed by fast Fourier transformation. While TAA did not induce significant changes in the beta band, mean and relative power in this band were significantly higher in FIN + TAA versus control group (p EEG changes that correspond to mild TAA-induced HE.

  17. THE VALENCE OF CORPUSCULAR PROTEINS.

    Science.gov (United States)

    Gorin, M H; Mover, L S

    1942-07-20

    BY THE USE OF TWO EXTREME MODELS: a hydrated sphere and an unhydrated rod the valence (net charge) of corpuscular proteins can be successfully calculated from electric mobility data by the Debye-Hückel theory (modified to include the effect of the ions in the ion atmosphere) in conjunction with the electrophoretic theory of Henry. As pointed out by Abramson, this permits a comparison with values for the valence from titration data. Electrometric titration measurements of serum albumin B (Kekwick) have been determined at several ionic strengths. These results, together with the available data in the literature for serum albumin B, egg albumin, and beta-lactoglobulin have been used to compare values for the valence calculated from measurements of titration, electrophoresis, and membrane potentials. The results indicate that the usual interpretation of titration curves is open to serious question. By extrapolation of the titration data to zero ionic strength and protein concentration, there results an "intrinsic" net charge curve describing the binding of H(+) (OH(-)) ion alone. This curve agrees closely, in each case, with values of the valence calculated from mobility data (which in turn are in close accord with those estimated from membrane potential measurements). The experimental titration curves in the presence of appreciable quantities of ions and protein deviate widely from the ideal curve. It is suggested that, under these conditions, binding of undissociated acid (base) leads to erroneous values for the net charge. This binding would not affect the electrophoretic mobility. Values of the net charge obtained by the two extreme models from electrophoretic data are in agreement within 15 to 20 per cent. The agreement between the cylindrical model and the titration data is somewhat better in each case than with the sphere; i.e., this comparison enables a choice to be made between asymmetry and hydration in the interpretation of results from sedimentation and

  18. Determination of conduction and valence band electronic structure ...

    Indian Academy of Sciences (India)

    insufficient to study in-depth unoccupied states of investigated materials because it overlooks the shallow traps. Keywords. Photo-catalysis; high-resolution RIXS; electronic structure. 1. Introduction. Photocatalysis is an emerging field that offers poten- tial to address some of the energy and waste manage- ment challenges.

  19. The Initial Configuration of Young Stellar Clusters: A K-Band Number Counts Analysis of the Surface Density of Stars

    Science.gov (United States)

    Gutermuth, Robert A.; Megeath, S. Thomas; Pipher, Judith L.; Williams, Jonathan P.; Allen, Lori E.; Myers, Philip C.; Raines, S. Nicholas

    2005-10-01

    We present an analysis of stellar distributions for the young stellar clusters GGD 12-15, IRAS 20050+2720, and NGC 7129, which range in far-IR luminosity from 227 to 5.68×103 Lsolar and are all still associated with their natal molecular clouds. The data used for this analysis include near-IR data obtained with FLAMINGOS on the MMT and newly obtained wide-field 850 μm emission maps from SCUBA on the JCMT. Cluster size and azimuthal asymmetry are measured via azimuthal and radial averaging methods, respectively. To quantify the deviation of the distribution of stars from circular symmetry, we define an azimuthal asymmetry parameter, and we investigate the statistical properties of this parameter through Monte Carlo simulations. The distribution of young stars is compared to the morphology of the molecular gas using stellar surface density maps and the 850 μm maps. We find that two of the clusters are not azimuthally symmetric and show a high degree of structure. The GGD 12-15 cluster is elongated and is aligned with newly detected filamentary structure at 850 μm. IRAS 20050+2720 is composed of a chain of three subclusters, in agreement with Chen and coworkers, although our results show that two of the subclusters appear to overlap. Significant 850 μm emission is detected toward two of the subclusters but is not detected toward the central subcluster, suggesting that the dense gas may already be cleared there. In contrast to these two highly embedded subclusters, we find an anticorrelation of the stars and dust in NGC 7129, indicating that much of the parental gas and dust has been dispersed. The NGC 7129 cluster exhibits a higher degree of azimuthal symmetry, a lower stellar surface density, and a larger size than the other two clusters, suggesting that the cluster may be dynamically expanding following the recent dispersal of natal molecular gas. These analyses are further evidence that embedded, forming clusters are often not spherically symmetric structures

  20. Band calculation of lonsdaleite Ge

    Science.gov (United States)

    Chen, Pin-Shiang; Fan, Sheng-Ting; Lan, Huang-Siang; Liu, Chee Wee

    2017-01-01

    The band structure of Ge in the lonsdaleite phase is calculated using first principles. Lonsdaleite Ge has a direct band gap at the Γ point. For the conduction band, the Γ valley is anisotropic with the low transverse effective mass on the hexagonal plane and the large longitudinal effective mass along the c axis. For the valence band, both heavy-hole and light-hole effective masses are anisotropic at the Γ point. The in-plane electron effective mass also becomes anisotropic under uniaxial tensile strain. The strain response of the heavy-hole mass is opposite to the light hole.

  1. A 380 V High Efficiency and High Power Density Switched-Capacitor Power Converter using Wide Band Gap Semiconductors

    DEFF Research Database (Denmark)

    Fan, Lin; Knott, Arnold; Jørgensen, Ivan Harald Holger

    2018-01-01

    to compose the proposed power stage. Their switching and loss characteristics are analyzed with transient waveforms and thermal images. Different isolated driving circuits are compared and a compact isolated halfbridge driving circuit is proposed. The full-load efficiencies of 98.3% and 97.6% are achieved......State-of-the-art switched-capacitor DC-DC power converters mainly focus on low voltage and/or high power applications. However, at high voltage and low power levels, new designs are anticipated to emerge and a power converter that has both high efficiency and high power density is highly desirable....... This paper presents such a high voltage low power switched-capacitor DC-DC converter with an input voltage upto 380 V (compatible with rectified European mains) and an output power experimentally validated up to 21.3 W. The wideband gap semiconductor devices of GaN switches and SiC diodes are combined...

  2. Compositional bowing of band energies and their deformation potentials in strained InGaAs ternary alloys: A first-principles study

    Energy Technology Data Exchange (ETDEWEB)

    Khomyakov, Petr A.; Luisier, Mathieu; Schenk, Andreas [Integrated Systems Laboratory, Department of Information Technology and Electrical Engineering, ETH Zurich, Gloriastrasse 35, 8092 Zurich (Switzerland)

    2015-08-10

    Using first-principles calculations, we show that the conduction and valence band energies and their deformation potentials exhibit a non-negligible compositional bowing in strained ternary semiconductor alloys such as InGaAs. The electronic structure of these compounds has been calculated within the framework of local density approximation and hybrid functional approach for large cubic supercells and special quasi-random structures, which represent two kinds of model structures for random alloys. We find that the predicted bowing effect for the band energy deformation potentials is rather insensitive to the choice of the functional and alloy structural model. The direction of bowing is determined by In cations that give a stronger contribution to the formation of the In{sub x}Ga{sub 1−x}As valence band states with x ≳ 0.5, compared to Ga cations.

  3. Telecommunication Wavelength-Band Single-Photon Emission from Single Large InAs Quantum Dots Nucleated on Low-Density Seed Quantum Dots.

    Science.gov (United States)

    Chen, Ze-Sheng; Ma, Ben; Shang, Xiang-Jun; He, Yu; Zhang, Li-Chun; Ni, Hai-Qiao; Wang, Jin-Liang; Niu, Zhi-Chuan

    2016-12-01

    Single-photon emission in the telecommunication wavelength band is realized with self-assembled strain-coupled bilayer InAs quantum dots (QDs) embedded in a planar microcavity on GaAs substrate. Low-density large QDs in the upper layer active for ~1.3 μm emission are fabricated by precisely controlling the indium deposition amount and applying a gradient indium flux in both QD layers. Time-resolved photoluminescence (PL) intensity suggested that the radiative lifetime of their exciton emission is 1.5~1.6 ns. The second-order correlation function of g (2)(0) < 0.5 which demonstrates a pure single-photon emission.

  4. Effect of standard deviation, strength of magnetic field and electron density on the photonic band gap of an extrinsic disorder plasma photonic structure

    Science.gov (United States)

    Nayak, Chittaranjan; Aghajamali, Alireza; Scotognella, Francesco; Saha, Ardhendu

    2017-10-01

    Transmission properties of electromagnetic waves within microwave region of the one-dimensional random extrinsic plasma photonic crystals were computed using the transfer matrix method. The layers thicknesses of the extrinsic random photonic structure follow a Gaussian distribution. Compared with the periodic extrinsic photonic crystal, wider photonic band gaps (PBGs) were found in case of random extrinsic plasma photonic crystals with few resonant peaks. The PBGs are much wider while the randomness was increased and the number and the strength of resonant peaks were enhanced. The above observations were confirmed through analysis of histogram of normalized average transmissions for four different values of standard deviation with one thousand random samples for each group. The normalized average transmission was controlled by changing the strength of external magnetic field and the electron density of magnetized cold plasma. These features of disordered extrinsic plasma photonic structures would have potential applications such as omnidirectional reflectors and random multichannel filters with lower and higher rate of disorder.

  5. Temperature dependence of band gaps and conformational disorder in PEDOT and its selenium and tellurium derivatives: Density functional calculations

    Science.gov (United States)

    Mirsakiyeva, Amina; Hugosson, Hâkan W.; Linares, Mathieu; Delin, Anna

    2017-10-01

    The conducting polymer poly(3,4-ethylenedioxythiophene), or PEDOT, is an attractive material for flexible electronics. We present combined molecular dynamics and quantum chemical calculations, based on density functional theory, of EDOT oligomers and isoelectronic selenium and tellurium derivatives (EDOS and EDOTe) to address the effect of temperature on the geometrical and electronic properties of these systems. With finite size scaling, we also extrapolate our results to the infinite polymers, i.e., PEDOT, PEDOS, and PEDOTe. Our computations indicate that the most favourable oligomer conformations at finite temperature are conformations around the flat trans-conformation and a non-flat conformation around 45° from the cis-conformation. Also, the dihedral stiffness increases with the atomic number of the heteroatom. We find excellent agreement with experimentally measured gaps for PEDOT and PEDOS. For PEDOT, the gap does not increase with temperature, whereas this is the case for its derivatives. The conformational disorder and the choice of the basis set both significantly affect the calculated gaps.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2010-02-15

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

  7. The electronic properties of mixed valence hydrated europium chloride thin film.

    Science.gov (United States)

    Silly, M G; Charra, F; Lux, F; Lemercier, G; Sirotti, F

    2015-07-28

    We investigate the electronic properties of a model mixed-valence hydrated chloride europium salt by means of high resolution photoemission spectroscopy (HRPES) and resonant photoemission spectroscopy (RESPES) at the Eu 3d → 4f and 4d → 4f transitions. From the HRPES spectra, we have determined that the two europium oxidation states are homogeneously distributed in the bulk and that the hydrated salt film is exempt from surface mixed valence transition. From the RESPES spectra, the well separated resonant contributions characteristic of divalent and trivalent europium species (4f(6) and 4f(7) final states, respectively) are accurately extracted and quantitatively determined from the resonant features measured at the two edges. The partial absorption yield spectra, obtained by integrating the photoemission intensity in the valence-band region, can be well reproduced by atomic multiplet calculation at the M(4,5) (3d-4f) absorption edge and by an asymmetric Fano-like shape profile at the N(4,5) (4d-4f) absorption edge. The ratio of Eu(2+) and Eu(3+) species measured at the two absorption edges matches with the composition of the mixed valence europium salt as determined chemically. We have demonstrated that the observed spectroscopic features of the mixed valence salt are attributed to the mixed-valence ground state rather than surface valence transition. HRPES and RESPES spectra provide reference spectra for the study of europium salts and their derivatives.

  8. Experimental determination of excitonic band structures of single-walled carbon nanotubes using circular dichroism spectra.

    Science.gov (United States)

    Wei, Xiaojun; Tanaka, Takeshi; Yomogida, Yohei; Sato, Naomichi; Saito, Riichiro; Kataura, Hiromichi

    2016-10-05

    Experimental band structure analyses of single-walled carbon nanotubes have not yet been reported, to the best of our knowledge, except for a limited number of reports using scanning tunnelling spectroscopy. Here we demonstrate the experimental determination of the excitonic band structures of single-chirality single-walled carbon nanotubes using their circular dichroism spectra. In this analysis, we use gel column chromatography combining overloading selective adsorption with stepwise elution to separate 12 different single-chirality enantiomers. Our samples show higher circular dichroism intensities than the highest values reported in previous works, indicating their high enantiomeric purity. Excitonic band structure analysis is performed by assigning all observed Eii and Eij optical transitions in the circular dichroism spectra. The results reproduce the asymmetric structures of the valence and conduction bands predicted by density functional theory. Finally, we demonstrate that an extended empirical formula can estimate Eij optical transition energies for any (n,m) species.

  9. TiO2 Band Restructuring by B and P Dopants.

    Directory of Open Access Journals (Sweden)

    Lei Li

    Full Text Available An examination of the effect of B- and P-doping and codoping on the electronic structure of anatase TiO2 by performing density functional theory calculations revealed the following: (i B- or P-doping effects are similar to atomic undercoordination effects on local bond relaxation and core electron entrapment; (ii the locally entrapped charge adds impurity levels within the band gap that could enhance the utilization of TiO2 to absorb visible light and prolong the carrier lifetime; (iii the core electron entrapment polarizes nonbonding electrons in the upper edges of the valence and conduction bands, which reduces not only the work function but also the band gap; and (iv work function reduction enhances the reactivity of the carriers and band gap reduction promotes visible-light absorption. These observations may shed light on effective catalyst design and synthesis.

  10. Materials with intermediate valence ; a comparison with transition metals

    Science.gov (United States)

    Mott, N. F.

    A discussion of metallic intermediate valence materials is given, particularly of hybridisation between the 4f and the conduction band δ. If n, 1 - n are the numbers of ions in each of two charge states, the variation of n with temperature is described. Resistivity is ascribed to scattering of the conduction electrons into the 4f band. The mechanism is compared with that in transition metals and their alloys, particularly Pd1-xAg x. The resistivity can be very large, of order of the Ioffe-Regel value 1/3 e2/ħa. It is argued that both here and in metallic alloys, this can only occur with a two-band model. At high temperatures there is some evidence that s-f scattering does not occur. On discute des matériaux métalliques à valence intermédiaire, en particulier de l'hybridation entre la bande 4f et la bande de conduction. Notant n et 1 - n les nombres d'ions dans chacun des deux états de charge, on décrit la variation de n avec la température. Le mécanisme est comparé avec celui des métaux de transition et de leurs alliages, particulièrement Pd1-xAg x. La résistivité peut être très grande, de l'ordre de la valeur de Ioffe-Regel 1/3 e2/ħa. On donne des arguments tendant à prouver que ceci ne peut se produire que dans le cadre d'un modèle à 2 bandes. Il y a des évidences qu'à haute température la diffusion s-f n'a pas lieu.

  11. Microscopic mechanism of the tunable band gap in potassium-doped few-layer black phosphorus

    Science.gov (United States)

    Kim, Sun-Woo; Jung, Hyun; Kim, Hyun-Jung; Choi, Jin-Ho; Wei, Su-Huai; Cho, Jun-Hyung

    2017-08-01

    Tuning band gaps in two-dimensional (2D) materials is of great interest for the fundamental and practical aspects of contemporary material sciences. Recently, black phosphorus (BP) consisting of stacked layers of phosphorene was experimentally observed to show a widely tunable band gap by means of the deposition of potassium (K) atoms on the surface, thereby allowing great flexibility in the design and optimization of electronic and optoelectronic devices. Here, based on density-functional theory calculations, we demonstrates that the donated electrons from K dopants are mostly localized in the topmost BP layer and this surface charging efficiently screens the K ion potential. It is found that, as the K doping increases, the extreme surface charging and its screening of K atoms shift the conduction bands down in energy, i.e., towards a higher binding energy, because they have more charge near the surface, while it has little influence on the valence bands having more charge in the deeper layers. This result provides a different explanation for the observed tunable band gap compared to the previously proposed giant Stark effect where a vertical electric field from the positively ionized K overlayer to the negatively charged BP layers shifts the conduction band minimum Γ1 c (valence band minimum Γ8 v) downwards (upwards). The present prediction of Γ1 c and Γ8 v as a function of the K doping reproduces well the widely tunable band gap, anisotropic Dirac semimetal state, and band-inverted semimetal state, as observed in an angle-resolved photoemission spectroscopy experiment. Our findings shed new light on a route for tunable band gap engineering of 2D materials through the surface doping of alkali metals.

  12. Electronic band structure, optical, dynamical and thermodynamic properties of cesium chloride (CsCl from first-principles

    Directory of Open Access Journals (Sweden)

    Bingol Suat

    2015-01-01

    Full Text Available The geometric structural optimization, electronic band structure, total density of states for valence electrons, density of states for phonons, optical, dynamical, and thermodynamical features of cesium chloride have been investigated by linearized augmented plane wave method using the density functional theory under the generalized gradient approximation. Ground state properties of cesium chloride are studied. The calculated ground state properties are consistent with experimental results. Calculated band structure indicates that the cesium chloride structure has an indirect band gap value of 5.46 eV and is an insulator. From the obtained phonon spectra, the cesium chloride structure is dynamically stable along the various directions in the Brillouin zone. Temperature dependent thermodynamic properties are studied using the harmonic approximation model.

  13. Measurements of spectrally integrated atmospheric transmittance in the O2 Schumann-Runge bands and derived oxygen column densities - 76-102 km

    Science.gov (United States)

    Longmire, M. S.; Bartoe, J.-D. F.; Brown, C. M.; Brueckner, G. E.; Tousey, R.

    1979-01-01

    Atmospheric transmittances integrated over wavelength intervals corresponding approximately to the (15-0) through (4-0) Schumann-Runge bands of O2 have been determined from EUV solar spectra (wavelengths between 1768 and 1948 A) photographed at seven altitudes between 102 and 76 km with a rocket-borne spectrograph having a resolution of 0.07 A. The observed transmittances are compared with atmospheric transmittances predicted from three models of the O2 absorption cross section. The predicted transmittances have also been used to derive column densities of atmospheric O2 from the observations. The results are compared with values calculated from the U.S. Standard Atmosphere (1976) and with oxygen column densities determined by Prinz and Brueckner (1977) from EUV solar spectra of the Schumann-Runge continuum (wavelength below 1750 A) and of the H-Lyman alpha line (1216 A) recorded on the same films used in the present research. The comparisons test the utility of the models for studies of atmospheric photochemistry, suggest which models may be best for this purpose, and indicate how the models can be improved.

  14. Detection of novel genomic aberrations in anaplastic astrocytomas by GTG-banding, SKY, locus-specific FISH, and high density SNP-array.

    Science.gov (United States)

    Holland, Heidrun; Ahnert, Peter; Koschny, Ronald; Kirsten, Holger; Bauer, Manfred; Schober, Ralf; Meixensberger, Jürgen; Fritzsch, Dominik; Krupp, Wolfgang

    2012-06-15

    Astrocytomas represent the largest and most common subgroup of brain tumors. Anaplastic astrocytoma (WHO grade III) may arise from low-grade diffuse astrocytoma (WHO grade II) or as primary tumors without any precursor lesion. Comprehensive analyses of anaplastic astrocytomas combining both cytogenetic and molecular cytogenetic techniques are rare. Therefore, we analyzed genomic alterations of five anaplastic astrocytomas using high-density single nucleotide polymorphism arrays combined with GTG-banding and FISH-techniques. By cytogenetics, we found 169 structural chromosomal aberrations most frequently involving chromosomes 1, 2, 3, 4, 10, and 12, including two not previously described alterations, a nonreciprocal translocation t(3;11)(p12;q13), and one interstitial chromosomal deletion del(2)(q21q31). Additionally, we detected previously not documented loss of heterozygosity (LOH) without copy number changes in 4/5 anaplastic astrocytomas on chromosome regions 5q11.2, 5q22.1, 6q21, 7q21.11, 7q31.33, 8q11.22, 14q21.1, 17q21.31, and 17q22, suggesting segmental uniparental disomy (UPD), applying high-density single nucleotide polymorphism arrays. UPDs are currently considered to play an important role in the initiation and progression of different malignancies. The significance of previously not described genetic alterations in anaplastic astrocytomas presented here needs to be confirmed in a larger series. Copyright © 2012 Elsevier GmbH. All rights reserved.

  15. Quantum confinement induced shift in energy band edges and band gap of a spherical quantum dot

    Science.gov (United States)

    Borah, P.; Siboh, D.; Kalita, P. K.; Sarma, J. K.; Nath, N. M.

    2018-02-01

    We have proposed and validated an ansatz as effective potential for confining electron/hole within a spherical quantum dot in order to understand quantum confinement and its consequences associated with energy states and band gap of Spherical Quantum Dots. Within effective mass approximation formalism, we have considered an ansatz incorporating a conjoined harmonic oscillator and Coulomb interaction as the effective potential for confining an electron or a hole within a spherical quantum dot and by employing appropriate boundary conditions, we have calculated the shifts in energy of minimum of conduction band (CBM) and maximum of valence band (VBM) with respect to size of spherical quantum dots. We have also determined the quantum confinement induced shift in band gap energy of spherical quantum dots. In order to verify our theoretical predictions as well as to validate our ansatz, we have performed phenomenological analysis in comparison with available experimental results for quantum dots made of CdSe and observe a very good agreement in this regard. Our experimentally consistent theoretical results also help in mapping the probability density of electron and hole inside a spherical quantum dot. The consistency of our results with available experimental data signifies the capability as well as applicability of the ansatz for the effective confining potential to have reasonable information in the study of real nano-structured spherical systems.

  16. Uniaxial strain effects on the band structure and effective masses of wurtzite GaAs

    Science.gov (United States)

    Cheiwchanchamnangij, Tawinan; Lambrecht, Walter

    2010-03-01

    While GaAs in bulk form has the zincblende structure, recent interest in the wurtzite form of GaAs arises in the context of nanowires. The band structure of wurtzite GaAs is calculated using the full-potential (FP) linearized muffin-tin orbital (LMTO) method within the local density approximation. The relativistic and spin-orbit coupling effects are included when obtaining the conduction and valence band effective mass tensors and related Rashba-Sheka-Pikus Hamiltonian parameters. The effects of c-axis uniaxial strain on the band structure is investigated and used to determine the relevant strain deformation potentials. It is found that under increasing uniaxial strain, a crossing of the γ5 and γ1 valence band levels occurs first, followed at higher strain by an additional crossing of the γ3 and γ1 conduction bands.. The latter is related to a corresponding direct to indirect (γ-L) crossing under uniaxial strain in zinblende.

  17. Valence-Bond Theory and Chemical Structure.

    Science.gov (United States)

    Klein, Douglas J.; Trinajstic, Nenad

    1990-01-01

    Discussed is the importance of valence bond theory on the quantum-mechanical theory of chemical structure and the nature of the chemical bond. Described briefly are early VB theory, development of VB theory, modern versions, solid-state applications, models, treatment in textbooks, and flaws in criticisms of valence bond theory. (KR)

  18. Determination of the surface band bending in InxGa1−xN films by hard x-ray photoemission spectroscopy

    Directory of Open Access Journals (Sweden)

    Mickael Lozac'h, Shigenori Ueda, Shitao Liu, Hideki Yoshikawa, Sang Liwen, Xinqiang Wang, Bo Shen, Kazuaki Sakoda, Keisuke Kobayashi and Masatomo Sumiya

    2013-01-01

    Full Text Available Core-level and valence band spectra of InxGa1−xN films were measured using hard x-ray photoemission spectroscopy (HX-PES. Fine structure, caused by the coupling of the localized Ga 3d and In 4d with N 2s states, was experimentally observed in the films. Because of the large detection depth of HX-PES (~20 nm, the spectra contain both surface and bulk information due to the surface band bending. The InxGa1−xN films (x = 0–0.21 exhibited upward surface band bending, and the valence band maximum was shifted to lower binding energy when the mole fraction of InN was increased. On the other hand, downward surface band bending was confirmed for an InN film with low carrier density despite its n-type conduction. Although the Fermi level (EF near the surface of the InN film was detected inside the conduction band as reported previously, it can be concluded that EF in the bulk of the film must be located in the band gap below the conduction band minimum.

  19. ARPES study of the evolution of band structure and charge density wave properties in RTe3 ( R=Y , La, Ce, Sm, Gd, Tb, and Dy)

    Energy Technology Data Exchange (ETDEWEB)

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

    2008-01-16

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

  20. A combined theoretical and experimental study of the valence and Rydberg states of iodopentafluorobenzene

    Science.gov (United States)

    Palmer, Michael H.; Hoffmann, Søren Vrønning; Jones, Nykola C.; Coreno, Marcello; de Simone, Monica; Grazioli, Cesare; Peterson, Kirk A.; Baiardi, Alberto; Zhang, Teng; Biczysko, Malgorzata

    2017-05-01

    A new ultraviolet (UV) and vacuum ultraviolet (VUV) spectrum for iodopentafluorobenzene (C6F5I) using synchrotron radiation is reported. The measurements have been combined with those from a recent high-resolution photoelectron spectroscopic study. A major theoretical study, which includes both Franck-Condon (FC) and Herzberg-Teller (HT) analyses, leads to conclusions, which are compatible with both experimental studies. Our observation that the VUV multiplet at 7.926 eV in the VUV spectrum is a Rydberg state rather than a valence state leads to a fundamental reassignment of the VUV Rydberg spectrum over previous studies and removes an anomaly where some previously assigned Rydberg states were to optically forbidden states. Adiabatic excitation energies (AEEs) were determined from equations-of-motion coupled cluster with singles and doubles excitation; these were combined with time dependent density functional theoretical methods. Frequencies from these two methods are very similar, and this enabled the evaluation of both FC and HT contributions in the lower valence states. Multi-reference multi-root configuration interaction gave a satisfactory account of the principal UV+VUV spectral profile of C6F5I, with vertical band positions and intensities. The UV spectral onset consists of two very weak transitions assigned to 11B1 (πσ*) and 11B2 (σσ*) symmetries. The lowest unoccupied molecular orbital of a σ*(a1) symmetry has a significant C-I* antibonding character. This results in considerable lengthening of the C-I bond for both these excited states. The vibrational intensity of the lowest 11B1 state is dominated by HT contributions; the 11B2 state contains both HT and FC contributions; the third band, which contains three states, two ππ*(11A1, 21B2) and one πσ*(21B1), is dominated by FC contributions in the 1A1 state. In this 1A1 state, and the spectrally dominant bands near 6.7 (1A1) and 7.3 eV (1A1 + 1B2), the C-I bond length is in the normal range, and FC

  1. Anticipatory attentional suppression of visual features indexed by oscillatory alpha-band power increases: a high-density electrical mapping study.

    Science.gov (United States)

    Snyder, Adam C; Foxe, John J

    2010-03-17

    Retinotopically specific increases in alpha-band ( approximately 10 Hz) oscillatory power have been strongly implicated in the suppression of processing for irrelevant parts of the visual field during the deployment of visuospatial attention. Here, we asked whether this alpha suppression mechanism also plays a role in the nonspatial anticipatory biasing of feature-based attention. Visual word cues informed subjects what the task-relevant feature of an upcoming visual stimulus (S2) was, while high-density electroencephalographic recordings were acquired. We examined anticipatory oscillatory activity in the Cue-to-S2 interval ( approximately 2 s). Subjects were cued on a trial-by-trial basis to attend to either the color or direction of motion of an upcoming dot field array, and to respond when they detected that a subset of the dots differed from the majority along the target feature dimension. We used the features of color and motion, expressly because they have well known, spatially separated cortical processing areas, to distinguish shifts in alpha power over areas processing each feature. Alpha power from dorsal regions increased when motion was the irrelevant feature (i.e., color was cued), and alpha power from ventral regions increased when color was irrelevant. Thus, alpha-suppression mechanisms appear to operate during feature-based selection in much the same manner as has been shown for space-based attention.

  2. Valence evaluation with approaching or withdrawing cues: directly testing valence-arousal conflict theory.

    Science.gov (United States)

    Wang, Yan Mei; Li, Ting; Li, Lin

    2017-07-19

    The valence-arousal conflict theory assumes that both valence and arousal will trigger approaching or withdrawing tendencies. It also predicts that the speed of processing emotional stimuli will depend on whether valence and arousal trigger conflicting or congruent motivational tendencies. However, most previous studies have provided evidence of the interaction between valence and arousal only, and have not provided direct proof of the interactive links between valence, arousal and motivational tendencies. The present study provides direct evidence for the relationship between approach-withdrawal tendencies and the valence-arousal conflict. In an empirical test, participants were instructed to judge the valence of emotional words after visual-spatial cues that appeared to be either approaching or withdrawing from participants. A three-way interaction (valence, arousal, and approach-withdrawal tendency) was observed such that the response time was shorter if participants responded to a negative high-arousal stimulus after a withdrawing cue, or to a positive low-arousal stimulus after an approaching cue. These findings suggest that the approach-withdrawal tendency indeed plays a crucial role in valence-arousal conflict, and that the effect depends on the congruency of valence, arousal and tendency at an early stage of processing.

  3. On triangle meshes with valence dominant vertices

    KAUST Repository

    Morvan, Jean-Marie

    2018-02-16

    We study triangulations $\\\\cal T$ defined on a closed disc $X$ satisfying the following condition: In the interior of $X$, the valence of all vertices of $\\\\cal T$ except one of them (the irregular vertex) is $6$. By using a flat singular Riemannian metric adapted to $\\\\cal T$, we prove a uniqueness theorem when the valence of the irregular vertex is not a multiple of $6$. Moreover, for a given integer $k >1$, we exhibit non isomorphic triangulations on $X$ with the same boundary, and with a unique irregular vertex whose valence is $6k$.

  4. 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

  5. Valence and core-level binding energy shifts in realgar (As 4S 4) and pararealgar (As 4S 4) arsenic sulfides

    Science.gov (United States)

    Bullen, Heather A.; Dorko, Michael J.; Oman, Jason K.; Garrett, Simon J.

    2003-06-01

    The core level and valence band X-ray photoelectron spectra (XP spectra) of two arsenic sulfides, As 4S 4 (α-realgar) and As 4S 4 (pararealgar), are reported. Pararealgar is a polymorph of realgar created by irradiation of realgar with visible light. The core level spectra of the materials can be distinguished by small differences in core level binding energies (BEs). For example, the As 3d 5/2 and S 2p 3/2 peaks are at 43.1 and 162.8 eV BE, respectively, in realgar and 43.2 and 162.7 eV BE, respectively, in pararealgar. Density functional theory (DFT) calculations at the B3LYP/cc-pVDZ level were performed on single As 4S 4 clusters to determine the ground state orbital energies for realgar and pararealgar and electrostatic potential-derived atomic charges. The shifts in the core level BEs are qualitatively reproduced in the orbital energies and can be rationalized based on an increased average charge in pararealgar (S=-0.21, As=+0.21) versus realgar (S=-0.19, As=+0.19). A large variation in calculated charge between inequivalent As sites in pararealgar (from +0.09 to +0.31) broadens the observed arsenic XP spectra features. In addition, the four main features in the valence bands of these materials have been identified based on the DFT calculations.

  6. Band structure engineering and vacancy induced metallicity at the GaAs-AlAs interface

    KAUST Repository

    Upadhyay Kahaly, M.

    2011-09-20

    We study the epitaxial GaAs-AlAs interface of wide gap materials by full-potential density functional theory. AlAsthin films on a GaAs substrate and GaAsthin films on an AlAs substrate show different trends for the electronic band gap with increasing film thickness. In both cases, we find an insulating state at the interface and a negligible charge transfer even after relaxation. Differences in the valence and conduction band edges suggest that the energy band discontinuities depend on the growth sequence. Introduction of As vacancies near the interface induces metallicity, which opens great potential for GaAs-AlAs heterostructures in modern electronics.

  7. Multicolor emission from intermediate band semiconductor ZnO1-xSex

    Science.gov (United States)

    Welna, M.; Baranowski, M.; Linhart, W. M.; Kudrawiec, R.; Yu, K. M.; Mayer, M.; Walukiewicz, W.

    2017-03-01

    Photoluminescence and photomodulated reflectivity measurements of ZnOSe alloys are used to demonstrate a splitting of the valence band due to the band anticrossing interaction between localized Se states and the extended valence band states of the host ZnO matrix. A strong multiband emission associated with optical transitions from the conduction band to lower E- and upper E+ valence subbands has been observed at room temperature. The composition dependence of the optical transition energies is well explained by the electronic band structure calculated using the kp method combined with the band anticrossing model. The observation of the multiband emission is possible because of relatively long recombination lifetimes. Longer than 1 ns lifetimes for holes photoexcited to the lower valence subband offer a potential of using the alloy as an intermediate band semiconductor for solar power conversion applications.

  8. Perception of emotional valence in horse whinnies.

    Science.gov (United States)

    Briefer, Elodie F; Mandel, Roi; Maigrot, Anne-Laure; Briefer Freymond, Sabrina; Bachmann, Iris; Hillmann, Edna

    2017-01-01

    Non-human animals often produce different types of vocalisations in negative and positive contexts (i.e. different valence), similar to humans, in which crying is associated with negative emotions and laughter is associated with positive ones. However, some types of vocalisations (e.g. contact calls, human speech) can be produced in both negative and positive contexts, and changes in valence are only accompanied by slight structural differences. Although such acoustically graded signals associated with opposite valence have been highlighted in some species, it is not known if conspecifics discriminate them, and if contagion of emotional valence occurs as a result. We tested whether domestic horses perceive, and are affected by, the emotional valence of whinnies produced by both familiar and unfamiliar conspecifics. We measured physiological and behavioural reactions to whinnies recorded during emotionally negative (social separation) and positive (social reunion) situations. We show that horses perceive acoustic cues to both valence and familiarity present in whinnies. They reacted differently (respiration rate, head movements, height of the head and latency to respond) to separation and reunion whinnies when produced by familiar, but not unfamiliar individuals. They were also more emotionally aroused (shorter inter-pulse intervals and higher locomotion) when hearing unfamiliar compared to familiar whinnies. In addition, the acoustic parameters of separation and reunion whinnies affected the physiology and behaviour of conspecifics in a continuous way. However, we did not find clear evidence for contagion of emotional valence. Horses are thus able to perceive changes linked to emotional valence within a given vocalisation type, similar to perception of affective prosody in humans. Whinnies produced in either separation or reunion situations seem to constitute acoustically graded variants with distinct functions, enabling horses to increase their apparent vocal

  9. GROUND-BASED Paα NARROW-BAND IMAGING OF LOCAL LUMINOUS INFRARED GALAXIES. I. STAR FORMATION RATES AND SURFACE DENSITIES

    Energy Technology Data Exchange (ETDEWEB)

    Tateuchi, Ken; Konishi, Masahiro; Motohara, Kentaro; Takahashi, Hidenori; Kato, Natsuko Mitani; Kitagawa, Yutaro; Todo, Soya; Toshikawa, Koji; Sako, Shigeyuki; Uchimoto, Yuka K.; Ohsawa, Ryou; Asano, Kentaro; Kamizuka, Takafumi; Nakamura, Tomohiko; Okada, Kazushi [Institute of Astronomy, Graduate School of Science, The University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015 (Japan); Ita, Yoshifusa [Astronomical Institute, Tohoku University, 6-3 Aoba, Aramaki, Aoba-ku, Sendai, Miyagi 980-8578 (Japan); Komugi, Shinya [Division of Liberal Arts, Kogakuin University, 2665-1, Hachioji, Tokyo 192-0015 (Japan); Koshida, Shintaro [Subaru Telescope, National Astronomical Observatory of Japan, Hilo, HI 96720 (United States); Manabe, Sho [Department of Earth and Planetary Sciences, Kobe University, Kobe 657-8501 (Japan); Nakashima, Asami, E-mail: tateuchi@ioa.s.u-tokyo.ac.jp [Department of Astronomy, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan); and others

    2015-03-15

    Luminous infrared galaxies (LIRGs) are enshrouded by a large amount of dust produced by their active star formation, and it is difficult to measure their activity in optical wavelengths. We have carried out Paα narrow-band imaging observations of 38 nearby star forming galaxies including 33 LIRGs listed in the IRAS Revised Bright Galaxy Sample catalog with the Atacama Near InfraRed camera on the University of Tokyo Atacama Observatory (TAO) 1.0 m telescope (miniTAO). Star formation rates (SFRs) estimated from the Paα fluxes, corrected for dust extinction using the Balmer decrement method (typically A{sub V} ∼ 4.3 mag), show a good correlation with those from the bolometric infrared luminosity of the IRAS data within a scatter of 0.27 dex. This suggests that the correction of dust extinction for the Paα flux is sufficient in our sample. We measure the physical sizes and surface densities of infrared luminosities (Σ{sub L(IR)}) and the SFR (Σ{sub SFR}) of star forming regions for individual galaxies, and we find that most of the galaxies follow a sequence of local ultra-luminous or luminous infrared galaxies (U/LIRGs) on the L(IR)-Σ{sub L(IR)} and SFR-Σ{sub SFR} plane. We confirm that a transition of the sequence from normal galaxies to U/LIRGs is seen at L(IR) = 8 × 10{sup 10} L {sub ☉}. Also, we find that there is a large scatter in physical size, different from normal galaxies or ULIRGs. Considering the fact that most U/LIRGs are merging or interacting galaxies, this scatter may be caused by strong external factors or differences in their merging stages.

  10. Interplay of magnetism and valence instabilities in lanthanide systems

    Directory of Open Access Journals (Sweden)

    José Luiz Ferreira

    2016-06-01

    Full Text Available The valence instability in lanthanide systems is described within an extended periodic Anderson Hamiltonian (EPAM which includes Coulomb repulsion between f- and conduction- electrons, allowing to describe both discontinuous and continuous valence variations. We investigate the connection between valence and magnetism in this model and show that it can be applied to several lanthanide compounds showing both magnetic and valence instabilities.

  11. Direct observation of heterogeneous valence state in Yb-based quasicrystalline approximants

    Science.gov (United States)

    Matsunami, M.; Oura, M.; Tamasaku, K.; Ishikawa, T.; Ideta, S.; Tanaka, K.; Takeuchi, T.; Yamada, T.; Tsai, A. P.; Imura, K.; Deguchi, K.; Sato, N. K.; Ishimasa, T.

    2017-12-01

    We study the electronic structure of Tsai-type cluster-based quasicrystalline approximants, Au64Ge22Yb14 (AGY-I), Au63.5Ge20.5Yb16 (AGY-II), and Zn85.4Yb14.6 (Zn-Yb), by means of photoemission spectroscopy. In the valence band hard x-ray photoemission spectra of AGY-II and Zn-Yb, we separately observe a fully occupied Yb 4 f state and a valence fluctuation derived Kondo resonance peak, reflecting two inequivalent Yb sites, a single Yb atom in the cluster center and its surrounding Yb icosahedron, respectively. The fully occupied 4 f signal is absent in AGY-I containing no Yb atom in the cluster center. The results provide direct evidence for a heterogeneous valence state in AGY-II and Zn-Yb.

  12. Band structure, band offsets, substitutional doping, and Schottky barriers of bulk and monolayer InSe

    Science.gov (United States)

    Guo, Yuzheng; Robertson, John

    2017-09-01

    We present a detailed study of the electronic structure of the layered semiconductor InSe. We calculate the band structure of the monolayer and bulk material using density functional theory, hybrid functionals, and G W . The band gap of the monolayer InSe is calculated to be 2.4 eV in screened exchange hybrid functional, close to the experimental photoluminescence gap. The electron affinities and band offsets are calculated for vertical stacked-layer heterostructures, and are found to be suitable for tunnel field effect transistors (TFETs) in combination with WS e2 or similar. The valence-band edge of InSe is calculated to lie 5.2 eV below the vacuum level, similar to that for the closed shell systems HfS e2 or SnS e2 . Hence InSe would be suitable to act as a p -type drain in the TFET. The intrinsic defects are calculated. For Se-rich layers, the Se adatom (interstitial) is found to be the most stable defect, whereas for In-rich layers, the Se vacancy is the most stable for the neutral state. Antisites tend to have energies just above those of vacancies. The Se antisite distorts towards a bond-breaking distortion as in the EL2 center of GaAs. Both substitutional donors and acceptors are calculated to be shallow, and effective dopants. They do not reconstruct to form nondoping configurations as occurs in black phosphorus. Finally, the Schottky barriers of metals on InSe are found to be strongly pinned by metal induced gap states (MIGS) at ˜0.5 eV above the valence-band edge. Any interfacial defects would lead to a stronger pinning at a similar energy. Overall, InSe is an effective semiconductor combining the good features of 2D (lack of dangling bonds, etc.) with the good features of 3D (effective doping), which few others achieve.

  13. Origin of Dirac Cones in SiC Silagraphene: A Combined Density Functional and Tight-Binding Study.

    Science.gov (United States)

    Qin, Xuming; Liu, Yi; Li, Xiaowu; Xu, Jingcheng; Chi, Baoqian; Zhai, Dong; Zhao, Xinluo

    2015-04-16

    The formation of Dirac cones in electronic band structures via isomorphous transformation is demonstrated in 2D planar SiC sheets. Our combined density functional and tight-binding calculations show that 2D SiC featuring C-C and Si-Si atom pairs possesses Dirac cones (DCs), whereas an alternative arrangement of C and Si leads to a finite band gap. The origin of Dirac points is attributed to bare interactions between Si-Si bonding states (valence bands, VBs) and C-C antibonding states (conduction bands, CBs), while the VB-CB coupling opens up band gaps elsewhere. A mechanism of atom pair coupling is proposed, and the conditions required for DC formation are discussed, enabling one to design a class of 2D binary Dirac fermion systems on the basis of DF calculations solely for pure and alternative binary structures.

  14. Generation of Kekule valence structures and the corresponding valence bond wave function

    NARCIS (Netherlands)

    Rashid, Z.; van Lenthe, J.H.

    2010-01-01

    A new scheme, called “list of nonredundant bonds”, is presented to record the number of bonds and their positions for the atoms involved in Kekulé valence structures of (poly)cyclic conjugated systems. Based on this scheme, a recursive algorithm for generating Kekulé valence structures has been

  15. A General Valence Asymmetry in Similarity: Good Is More Alike than Bad

    Science.gov (United States)

    Koch, Alex; Alves, Hans; Krüger, Tobias; Unkelbach, Christian

    2016-01-01

    The density hypothesis (Unkelbach, Fiedler, Bayer, Stegmüller, & Danner, 2008) claims a general higher similarity of positive information to other positive information compared with the similarity of negative information to other negative information. This similarity asymmetry might explain valence asymmetries on all levels of cognitive…

  16. Self-trapped exciton and core-valence luminescence in BaF{sub 2} nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Vistovskyy, V. V., E-mail: vistvv@gmail.com; Zhyshkovych, A. V.; Chornodolskyy, Ya. M.; Voloshinovskii, A. S. [Ivan Franko National University of Lviv, 8 Kyryla i Mefodiya, 79005 Lviv (Ukraine); Myagkota, O. S. [Lviv Polytechnic National University, 12S. Bandera, 79013 Lviv (Ukraine); Gloskovskii, A. [Deutsches Elektronen-Synchrotron DESY, 22607 Hamburg (Germany); Gektin, A. V. [Institute for Scintillation Materials, NAS of Ukraine 60 Lenina Ave, 61001 Kharkiv (Ukraine); Vasil' ev, A. N. [Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, 119991 Moscow (Russian Federation); Rodnyi, P. A. [Saint-Petersburg State Polytechnical University, 29, Polytekhnicheskaya, 195251 Saint-Petersburg (Russian Federation)

    2013-11-21

    The influence of the BaF{sub 2} 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 (hν ≤ E{sub g}) 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.

  17. Band structure and optical functions of K{sub 2}ZnCl{sub 4} crystals in ferroelectric phase

    Energy Technology Data Exchange (ETDEWEB)

    Andriyevsky, B., E-mail: bohdan.andriyevskyy@tu.koszalin.pl [Faculty of Electronics and Computer Sciences, Koszalin University of Technology, 2 Sniadeckich Str., PL-75-453, Koszalin (Poland); Stadnyk, V. [Ivan Franko National University of Lviv, 8 Kyrylo-and-Mefodii Str., UA-79005 Lviv (Ukraine); Kohut, Z. [Lviv Polytechnic National University, 12 St. Bandera Str., UA-79013 Lviv (Ukraine); Romanyuk, M. [The Ivan Franko National University of Lviv, 8 Kyrylo-and-Mefodii Str., UA-79005 Lviv (Ukraine); Jaskolski, M. [Faculty of Electronics and Computer Sciences, Koszalin University of Technology, 2 Sniadeckich Str., PL-75-453, Koszalin (Poland)

    2010-11-01

    Band electronic structure (BS), density of states (DOS), and optical functions of K{sub 2}ZnCl{sub 4} crystal for the orthorhombic space group of symmetry Pna2{sub 1} corresponding to the ferroelectric phase (12 formula units in the crystallographic unit cell) have been calculated for the first time using the density functional theory based code VASP (Vienna Ab-initio Simulation Program). The valence-to-conduction band gap E{sub g} of the crystal is found to be direct in the {Gamma}-point of Brillouin zone. The effective masses m* have been calculated for the top valence and bottom conduction bands for different points and directions of Brillouin zone of the crystal and the results obtained have been analyzed. Peculiarities of the photon energy dependences n(E) and k(E) of refractive (n) and absorption (k) indices obtained in the range 0-28 eV have been identified on the basis of BS and DOS of the crystal. Calculated optical functions agree satisfactorily with the experimental data n(E) in the range of crystal's transparency, E < 5 eV.

  18. High-Resolution Conversion Electron Spectroscopy of Valence Electron Configurations (CESVEC) in Solids

    CERN Multimedia

    2002-01-01

    First measurements with the Zurich $\\beta$-spectrometer on sources from ISOLDE have demonstrated that high resolution spectroscopy of conversion electrons from valence shells is feasible.\\\\ \\\\ This makes possible a novel type of electron spectroscopy (CESVEC) on valence-electron configurations of tracer elements in solids. Thus the density of occupied electron states of impurities in solids has been measured for the first time. Such data constitute a stringent test of state-of-the-art calculations of impurity properties. Based on these results, we are conducting a systematic investigation of impurities in group IV and III-V semiconductors.

  19. Affective Priming with Associatively Acquired Valence

    Science.gov (United States)

    Aguado, Luis; Pierna, Manuel; Saugar, Cristina

    2005-01-01

    Three experiments explored the effect of affectively congruent or incongruent primes on evaluation responses to positive or negative valenced targets (the "affective priming" effect). Experiment 1 replicated the basic affective priming effect with Spanish nouns: reaction time for evaluative responses (pleasant/unpleasant) were slower on…

  20. Cesium's Off-the-Map Valence Orbital

    NARCIS (Netherlands)

    Goesten, Maarten G.; Rahm, Martin; Bickelhaupt, F. Matthias; Hensen, Emiel J.M.

    2017-01-01

    The Td-symmetric [CsO4]+ ion, featuring Cs in an oxidation state of 9, is computed to be a minimum. Cs uses outer core 5s and 5p orbitals to bind the oxygen atoms. The valence Cs 6s orbital lies too high to be involved in bonding, and contributes to Rydberg levels only. From a molecular orbital

  1. Band alignment and p -type doping of ZnSnN2

    Science.gov (United States)

    Wang, Tianshi; Ni, Chaoying; Janotti, Anderson

    2017-05-01

    Composed of earth-abundant elements, ZnSnN2 is a promising semiconductor for photovoltaic and photoelectrochemical applications. However, basic properties such as the precise value of the band gap and the band alignment to other semiconductors are still unresolved. For instance, reported values for the band gap vary from 1.4 to 2.0 eV. In addition, doping in ZnSnN2 remains largely unexplored. Using density functional theory with the Heyd-Scuseria-Ernzerhof hybrid functional, we investigate the electronic structure of ZnSnN2, its band alignment to GaN and ZnO, and the possibility of p -type doping. We find that the position of the valence-band maximum of ZnSnN2 is 0.39 eV higher than that in GaN, yet the conduction-band minimum is close to that in ZnO, which suggests that achieving p -type conductivity is likely as in GaN, yet it may be difficult to control unintentional n -type conductivity as in ZnO. Among possible p -type dopants, we explore Li, Na, and K substituting on the Zn site. We show that while LiZn is a shallow acceptor, NaZn and KZn are deep acceptors, which we trace back to large local relaxations around the Na and K impurities due to the atomic size mismatches.

  2. Reducing the negative valence of stressful memories through emotionally valenced, modality-specific tasks

    NARCIS (Netherlands)

    Tadmor, Avia; McNally, Richard J; Engelhard, Iris M

    2016-01-01

    BACKGROUND AND OBJECTIVES: People who perform a cognitively demanding secondary task while recalling a distressing memory often experience the memory as less emotional, vivid, or accurate during subsequent recollections. In this experiment, we tested whether the emotional valence (positive versus

  3. Density functional theory calculations for the band gap and formation energy of Pr4-xCaxSi12O3+xN18-x; a highly disordered compound with low symmetry and a large cell size.

    Science.gov (United States)

    Hong, Sung Un; Singh, Satendra Pal; Pyo, Myoungho; Park, Woon Bae; Sohn, Kee-Sun

    2017-06-28

    A novel oxynitride compound, Pr4-xCaxSi12O3+xN18-x, synthesized using a solid-state route has been characterized as a monoclinic structure in the C2 space group using Rietveld refinement on synchrotron powder X-ray diffraction data. The crystal structure of this compound was disordered due to the random distribution of Ca/Pr and N/O ions at various Wyckoff sites. A pragmatic approach for an ab initio calculation based on density function theory (DFT) for this disordered compound has been implemented to calculate an acceptable value of the band gap and formation energy. In general, for the DFT calculation of a disordered compound, a sufficiently large super cell and infinite variety of ensemble configurations is adopted to simulate the random distribution of ions; however, such an approach is time consuming and cost ineffective. Even a single unit cell model gave rise to 43 008 independent configurations as an input model for the DFT calculations. Since it was nearly impossible to calculate the formation energy and the band gap energy for all 43 008 configurations, an elitist non-dominated sorting genetic algorithm (NSGA-II) was employed to find the plausible configurations. In the NSGA-II, all 43 008 configurations were mathematically treated as genomes and the calculated band gap and the formation energy as the objective (fitness) function. Generalized gradient approximation (GGA) was first employed in the preliminary screening using NSGA-II, and thereafter a hybrid functional calculation (HSE06) was executed only for the most plausible GGA-relaxed configurations with lower formation and higher band gap energies. The final band gap energy (3.62 eV) obtained after averaging over the selected configurations, resembles closely the experimental band gap value (4.11 eV).

  4. Analysis of valence XPS and AES of (PP, P4VP, PVME, PPS, PTFE) polymers by DFT calculations using the model molecules

    Science.gov (United States)

    Endo, Kazunaka; Shimada, Shingo; Kato, Nobuhiko; Ida, Tomonori

    2016-10-01

    We simulated valence X-ray photoelectron spectra (VXPS) of five [(CH2CH(CH3))n {poly(propyrene) PP}, ((CH2CH(C5NH4))n {poly(4-vinyl-pyridine) P4VP}, (CH2CHO(CH3))n {poly(vinyl methyl ether) PVME}, (C6H4S)n {poly(phenylene) sulphide PPS}, (CF2CF2)n {poly(tetrafluoroethylene) PTFE}] polymers by density-functional theory (DFT) calculations using the model oligomers. The spectra reflect the differences in the chemical structures between each polymer, since the peak intensities of valence band spectra are seen to be due to photo-ionization cross-section of (C, N, O, S, F) atoms by considering the orbital energies and cross-section values of the polymer models, individually. In the Auger electron spectra (AES) simulations, theoretical kinetic energies of the AES are obtained with our modified calculation method. The modified kinetic energies correspond to two final-state holes at the ground state and at the transition-state in DFT calculations, respectively. Experimental peaks of (C, N, O)- KVV, and S L2,3VV AES for each polymer are discussed in detail by our modified calculation method.

  5. Distinct cerebellar lobules process arousal, valence and their interaction in parallel following a temporal hierarchy.

    Science.gov (United States)

    Styliadis, Charis; Ioannides, Andreas A; Bamidis, Panagiotis D; Papadelis, Christos

    2015-04-15

    The cerebellum participates in emotion-related neural circuits formed by different cortical and subcortical areas, which sub-serve arousal and valence. Recent neuroimaging studies have shown a functional specificity of cerebellar lobules in the processing of emotional stimuli. However, little is known about the temporal component of this process. The goal of the current study is to assess the spatiotemporal profile of neural responses within the cerebellum during the processing of arousal and valence. We hypothesized that the excitation and timing of distinct cerebellar lobules is influenced by the emotional content of the stimuli. By using magnetoencephalography, we recorded magnetic fields from twelve healthy human individuals while passively viewing affective pictures rated along arousal and valence. By using a beamformer, we localized gamma-band activity in the cerebellum across time and we related the foci of activity to the anatomical organization of the cerebellum. Successive cerebellar activations were observed within distinct lobules starting ~160ms after the stimuli onset. Arousal was processed within both vermal (VI and VIIIa) and hemispheric (left Crus II) lobules. Valence (left VI) and its interaction (left V and left Crus I) with arousal were processed only within hemispheric lobules. Arousal processing was identified first at early latencies (160ms) and was long-lived (until 980ms). In contrast, the processing of valence and its interaction to arousal was short lived at later stages (420-530ms and 570-640ms respectively). Our findings provide for the first time evidence that distinct cerebellar lobules process arousal, valence, and their interaction in a parallel yet temporally hierarchical manner determined by the emotional content of the stimuli. Copyright © 2015 Elsevier Inc. All rights reserved.

  6. UV-Vis spectroscopy and density functional study of solvent effect on the charge transfer band of the n → σ* complexes of 2-Methylpyridine and 2-Chloropyridine with molecular iodine

    Science.gov (United States)

    Gogoi, Pallavi; Mohan, Uttam; Borpuzari, Manash Protim; Boruah, Abhijit; Baruah, Surjya Kumar

    2017-03-01

    UV-Vis spectroscopy has established that Pyridine substitutes form n→σ* charge transfer (CT) complexes with molecular Iodine. This study is a combined approach of purely experimental UV-Vis spectroscopy, Multiple linear regression theory and Computational chemistry to analyze the effect of solvent upon the charge transfer band of 2-Methylpyridine-I2 and 2-Chloropyridine-I2 complexes. Regression analysis verifies the dependence of the CT band upon different solvent parameters. Dielectric constant and refractive index are considered among the bulk solvent parameters and Hansen, Kamlet and Catalan parameters are taken into consideration at the molecular level. Density Functional Theory results explain well the blue shift of the CT bands in polar medium as an outcome of stronger donor acceptor interaction. A logarithmic relation between the bond length of the bridging atoms of the donor and the acceptor with the dielectric constant of the medium is established. Tauc plot and TDDFT study indicates a non-vertical electronic transition in the complexes. Buckingham and Lippert Mataga equations are applied to check the Polarizability effect on the CT band.

  7. Valence-Dependent Belief Updating: Computational Validation

    Directory of Open Access Journals (Sweden)

    Bojana Kuzmanovic

    2017-06-01

    Full Text Available People tend to update beliefs about their future outcomes in a valence-dependent way: they are likely to incorporate good news and to neglect bad news. However, belief formation is a complex process which depends not only on motivational factors such as the desire for favorable conclusions, but also on multiple cognitive variables such as prior beliefs, knowledge about personal vulnerabilities and resources, and the size of the probabilities and estimation errors. Thus, we applied computational modeling in order to test for valence-induced biases in updating while formally controlling for relevant cognitive factors. We compared biased and unbiased Bayesian models of belief updating, and specified alternative models based on reinforcement learning. The experiment consisted of 80 trials with 80 different adverse future life events. In each trial, participants estimated the base rate of one of these events and estimated their own risk of experiencing the event before and after being confronted with the actual base rate. Belief updates corresponded to the difference between the two self-risk estimates. Valence-dependent updating was assessed by comparing trials with good news (better-than-expected base rates with trials with bad news (worse-than-expected base rates. After receiving bad relative to good news, participants' updates were smaller and deviated more strongly from rational Bayesian predictions, indicating a valence-induced bias. Model comparison revealed that the biased (i.e., optimistic Bayesian model of belief updating better accounted for data than the unbiased (i.e., rational Bayesian model, confirming that the valence of the new information influenced the amount of updating. Moreover, alternative computational modeling based on reinforcement learning demonstrated higher learning rates for good than for bad news, as well as a moderating role of personal knowledge. Finally, in this specific experimental context, the approach based on

  8. Vacancy formation in MoO3: hybrid density functional theory and photoemission experiments

    KAUST Repository

    Salawu, Omotayo Akande

    2016-09-29

    Molybdenum oxide (MoO3) is an important material that is being considered for numerous technological applications, including catalysis and electrochromism. In the present study, we apply hybrid density functional theory to investigate O and Mo vacancies in the orthorhombic phase. We determine the vacancy formation energies of different defect sites as functions of the electron chemical potential, addressing different charge states. In addition, we investigate the consequences of defects for the material properties. Ultraviolet photoemission spectroscopy is employed to study the valence band of stoichiometric and O defective MoO3. We show that O vacancies result in occupied in-gap states.

  9. Janus Nematic Colloids with Designable Valence

    Directory of Open Access Journals (Sweden)

    Simon Čopar

    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.

  10. Evaluative conditioning induces changes in sound valence

    Directory of Open Access Journals (Sweden)

    Anna C. 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.

  11. Human Amygdala Represents the Complete Spectrum of Subjective Valence

    Science.gov (United States)

    Jin, Jingwen; Zelano, Christina; Gottfried, Jay A.

    2015-01-01

    Although the amygdala is a major locus for hedonic processing, how it encodes valence information is poorly understood. Given the hedonic potency of odor stimuli and the amygdala's anatomical proximity to the peripheral olfactory system, we combined high-resolution fMRI with pattern-based multivariate techniques to examine how valence information is encoded in the amygdala. Ten human subjects underwent fMRI scanning while smelling 9 odorants that systematically varied in perceived valence. Representational similarity analyses showed that amygdala codes the entire dimension of valence, ranging from pleasantness to unpleasantness. This unidimensional representation significantly correlated with self-reported valence ratings but not with intensity ratings. Furthermore, within-trial valence representations evolved over time, prioritizing earlier differentiation of unpleasant stimuli. Together, these findings underscore the idea that both spatial and temporal features uniquely encode pleasant and unpleasant odor valence in the amygdala. The availability of a unidimensional valence code in the amygdala, distributed in both space and time, would create greater flexibility in determining the pleasantness or unpleasantness of stimuli, providing a mechanism by which expectation, context, attention, and learning could influence affective boundaries for guiding behavior. SIGNIFICANCE STATEMENT Our findings elucidate the mechanisms of affective processing in the amygdala by demonstrating that this brain region represents the entire valence dimension from pleasant to unpleasant. An important implication of this unidimensional valence code is that pleasant and unpleasant valence cannot coexist in the amygdale because overlap of fMRI ensemble patterns for these two valence extremes obscures their unique content. This functional architecture, whereby subjective valence maps onto a pattern continuum between pleasant and unpleasant poles, offers a robust mechanism by which context

  12. Investigation of structural, electronic and anisotropic elastic properties of Ru-doped WB{sub 2} compound by increased valence electron concentration

    Energy Technology Data Exchange (ETDEWEB)

    Surucu, Gokhan, E-mail: g_surucu@yahoo.com [Ahi Evran University, Department of Electric and Energy, 40100, Kirsehir (Turkey); Gazi University, Photonics Application and Research Center, 06500, Ankara (Turkey); Kaderoglu, Cagil [Ankara University, Department of Engineering Physics, 06100, Ankara (Turkey); Deligoz, Engin; Ozisik, Haci [Aksaray University, Department of Physics, 68100, Aksaray (Turkey)

    2017-03-01

    First principles density functional theory (DFT) calculations have been used to investigate the structural, anisotropic elastic and electronic properties of ruthenium doped tungsten-diboride ternary compounds (W{sub 1−x}Ru{sub x}B{sub 2}) for an increasing molar fraction of Ru atom from 0.1 to 0.9 by 0.1. Among the nine different compositions, W{sub 0.3}Ru{sub 0.7}B{sub 2} has been found as the most stable one due to the formation energy and band filling theory calculations. Moreover, the band structures and partial density of states (PDOS) have been computed for each x composition. After obtaining the elastic constants for all x compositions, the secondary results such as Bulk modulus, Young’s modulus, Poisson’s ratio, Shear modulus, and Vickers Hardness of polycrystalline aggregates have been derived and the relevant mechanical properties have been discussed. In addition, the elastic anisotropy has been visualized in detail by plotting the directional dependence of compressibility, Poisson ratio, Young’s and Shear moduli. - Highlights: • Effects of Ru substitution in WB{sub 2} using increased valence electron concentration. • Structural, electronic, mechanic and elastic properties for increasing Ru content. • Considered alloys are incompressible, brittle, stiffer and high hard materials.

  13. Electric field control of valence tautomeric interconversion in cobalt dioxolene.

    Science.gov (United States)

    Droghetti, A; Sanvito, S

    2011-07-22

    We demonstrate that the critical temperature for valence tautomeric interconversion in cobalt dioxolene complexes can be significantly changed when a static electric field is applied to the molecule. This is achieved by effectively manipulating the redox potential of the metallic acceptor forming the molecule. Importantly, our accurate density functional theory calculations demonstrate that already a field of 0.1  V/nm, achievable in Stark spectroscopy experiments, can produce a change in the critical temperature for the interconversion of 20 K. Our results indicate a new way for switching on and off the magnetism in a magnetic molecule. This offers the unique chance of controlling magnetism at the atomic scale by electrical means.

  14. Electric Crosstalk Effect in Valence Change Resistive Random Access Memory

    Science.gov (United States)

    Sun, Jing; Wang, Hong; Wu, Shiwei; Song, Fang; Wang, Zhan; Gao, Haixia; Ma, Xiaohua

    2017-08-01

    Electric crosstalk phenomenon in valence change resistive switching memory (VCM) is systematically investigated. When a voltage is applied on the VCM device, an electric field is formed in the isolated region between the devices, which causes the oxygen vacancies in conductive filaments (CFs) to drift apart, leading to a consequent resistance degradation of the neighboring devices. The effects of distance between memory cells, electrodes widths and physical dimensions of CFs on the memory performance are investigated in this work. Furthermore, the strategies to mitigate electric crosstalk effects are developed. According to the simulation results, the crosstalk phenomenon can become more severe as the distance between memory cells or the electrode width decreases. In order to optimize the device performance, it is helpful to control the location of the break points of CFs in the device close to the top electrode. Alternatively, taking the integration density into account, switching materials with a small field accelerated parameter can also contribute to obtaining a stable performance.

  15. 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...

  16. Theoretical investigation of the phonon-assisted tunneling in TFET with an indirect band gap semiconductor

    Science.gov (United States)

    Chen, J.; Gong, J.

    2017-11-01

    There are intense recent interests in quantum tunneling transistor as a way to go beyond the metal-oxide-semiconductor transistors. Phonon-assisted tunneling (PAT) plays the dominating role in tunneling field effect transistors with an indirect band gap semiconductor. In this work, we provide a convenient expression based on Fermi gold rule to study the electron tunneling assisted by phonon from the valence band top to the conduction band bottom. Through the comparison with different phonon modes, the transverse acoustic phonon mode provides the largest contribution to PAT. The results of the transfer matrix model predict slightly higher tunneling current compared to the Wentzel-Kramers-Brillouin approximation which ignores the effect of the reflection wave. However, the current density calculated by using our method shows that there is about an order of the magnitude lager than Kane's model. Additionally, the temperature enhances the phonon-assisted Zener tunneling current densities. Our results shed some light on understanding the PAT in indirect band gap semiconductors.

  17. Implementation of density functional theory method on object-oriented programming (C++) to calculate energy band structure using the projector augmented wave (PAW)

    Science.gov (United States)

    Alfianto, E.; Rusydi, F.; Aisyah, N. D.; Fadilla, R. N.; Dipojono, H. K.; Martoprawiro, M. A.

    2017-05-01

    This study implemented DFT method into the C++ programming language with object-oriented programming rules (expressive software). The use of expressive software results in getting a simple programming structure, which is similar to mathematical formula. This will facilitate the scientific community to develop the software. We validate our software by calculating the energy band structure of Silica, Carbon, and Germanium with FCC structure using the Projector Augmented Wave (PAW) method then compare the results to Quantum Espresso calculation’s results. This study shows that the accuracy of the software is 85% compared to Quantum Espresso.

  18. A model for the direct-to-indirect band-gap transition in monolayer ...

    Indian Academy of Sciences (India)

    Abstract. A monolayer of MoSe2 is found to be a direct band-gap semiconductor. We show, within ab-initio electronic structure calculations, that a modest biaxial tensile strain of 3% can drive it into an indirect band-gap semiconductor with the valence band maximum (VBM) shifting from K point to point. An analysis of the ...

  19. Nudged elastic band method and density functional theory calculation for finding a local minimum energy pathway of p-benzoquinone and phenol fragmentation in mass spectrometry.

    Science.gov (United States)

    Sugimura, Natsuhiko; Igarashi, Yoko; Aoyama, Reiko; Shibue, Toshimichi

    2017-02-01

    Analysis of the fragmentation pathways of molecules in mass spectrometry gives a fundamental insight into gas-phase ion chemistry. However, the conventional intrinsic reaction coordinates method requires knowledge of the transition states of ion structures in the fragmentation pathways. Herein, we use the nudged elastic band method, using only the initial and final state ion structures in the fragmentation pathways, and report the advantages and limitations of the method. We found a minimum energy path of p-benzoquinone ion fragmentation with two saddle points and one intermediate structure. The primary energy barrier, which corresponded to the cleavage of the C-C bond adjacent to the CO group, was calculated to be 1.50 eV. An additional energy barrier, which corresponded to the cleavage of the CO group, was calculated to be 0.68 eV. We also found an energy barrier of 3.00 eV, which was the rate determining step of the keto-enol tautomerization in CO elimination from the molecular ion of phenol. The nudged elastic band method allowed the determination of a minimum energy path using only the initial and final state ion structures in the fragmentation pathways, and it provided faster than the conventional intrinsic reaction coordinates method. In addition, this method was found to be effective in the analysis of the charge structures of the molecules during the fragmentation in mass spectrometry.

  20. Band gap engineering via electrostatic chemical strain in cation ordered LaSrAlO4

    Science.gov (United States)

    Balachandran, Prasanna V.; Rondinelli, James M.

    2014-03-01

    In this work, we employ density functional theory to examine a novel design route that employs A-site cation ordering to engineer the band gaps of (A,A')BO4 Ruddlesden-Popper (RP) oxides. Using LaSrAlO4 as a model material, we show that the band gap is highly sensitive to the A-site cation ordering ranging from 3-4.5 eV. When the [AlO2]-1 layers are interleaved between two chemically equivalent [LaO]1+ or [SrO]0+ layers, we obtain the smallest band gap with a reduction of ~1 eV determined from the Heyd, Scuseria, and Ernzerhof (HSE) hybrid exchange-correlation functional. We relate the observed band gap reduction to the local bond distortions arising from electrostatic chemical strain induced changes to the O 2 p and La 5 d states in the valence and conduction bands, respectively. The project was supported by The Defense Advanced Research Projects Agency (grant no. N66001-12-4224). The views, opinions, and/or findings reported here are solely those of the authors and do not represent official views of DARPA or DOD.

  1. Probing Transient Valence Orbital Changes with Picosecond Valence-to-Core X-ray Emission Spectroscopy

    DEFF Research Database (Denmark)

    March, Anne Marie; Assefa, Tadesse A.; Boemer, Christina

    2017-01-01

    valence orbitals to the nascent core-hole. Vtc-XES offers particular insight into the molecular orbitals directly involved in the light-driven dynamics; a change in the metal ligand orbital overlap results in an intensity reduction and a blue energy shift in agreement with our theoretical calculations......We probe the dynamics of valence electrons in photoexcited [Fe(terpy)2]2+ in solution to gain deeper insight into the Fe ligand bond changes. We use hard X-ray emission spectroscopy (XES), which combines element specificity and high penetration with sensitivity to orbital structure, making...... it a powerful technique for molecular studies in a wide variety of environments. A picosecond-time-resolved measurement of the complete Is X-ray emission spectrum captures the transient photoinduced changes and includes the weak valence-to-core (vtc) emission lines that correspond to transitions from occupied...

  2. Entanglement in valence-bond-solid states and quantum search

    Science.gov (United States)

    Xu, Ying

    The present dissertation covers two independent subjects: (i) The quantum entanglement in Valence-Bond-Solid states, and (ii) quantum database search algorithms. Both subjects are presented in a self-contained and pedagogical way. (i) The first chapter is a through introduction to the subject of quantum entanglement in Valence-Bond-Solid (VBS) states defined on a lattice or graph. The VBS state was first introduced as the ground state of the celebrated Affleck-Kennedy-Lieb-Tasaki (AKLT) spin chain model in statistical mechanics. Then it became essential in condensed matter physics, quantum information and measurement-based quantum computation. Recent studies elucidated important entanglement properties of the VBS state. We start with the definition of a general AKLT model and the construction of VBS ground states. A subsystem is introduced and described by the density matrix. Exact spectrum properties of the density matrix are proved and discussed. Density matrices of 1-dimensional models are diagonalized and the entanglement entropies (the von Neumann entropy and Renyi entropy) are calculated. The entropies take saturated value and the density matrix is proportional to a projector in the large subsystem limit. (ii) The second chapter is a detailed introduction to the subject of quantum database search algorithms. The problem of searching a large database (a Hilbert space) for a target item is performed by the famous Grover algorithm which locates the target item with probability 1 and a quadratic speed up compared with the corresponding classical algorithm. If the database is partitioned into blocks and one is searching for the block containing the target item instead of the target item itself, then the problem is referred to as partial search. Partial search trades accuracy for speed and the most efficient version is the Grover-Radhakrishnan-Korepin (GRK) algorithm. The target block can be further partitioned into subblocks so that GRK can be performed in a

  3. Theoretical and Experimental Study of the Crystal Structures, Lattice Vibrations, and Band Structures of Monazite-Type PbCrO4, PbSeO4, SrCrO4, and SrSeO4.

    Science.gov (United States)

    Errandonea, Daniel; Muñoz, Alfonso; Rodríguez-Hernández, Placida; Proctor, John E; Sapiña, Fernando; Bettinelli, Marco

    2015-08-03

    The crystal structures, lattice vibrations, and electronic band structures of PbCrO4, PbSeO4, SrCrO4, and SrSeO4 were studied by ab initio calculations, Raman spectroscopy, X-ray diffraction, and optical-absorption measurements. Calculations properly describe the crystal structures of the four compounds, which are isomorphic to the monazite structure and were confirmed by X-ray diffraction. Information is also obtained on the Raman- and IR-active phonons, with all of the vibrational modes assigned. In addition, the band structures and electronic densities of states of the four compounds were determined. All are indirect-gap semiconductors. In particular, chromates are found to have band gaps smaller than 2.5 eV and selenates higher than 4.3 eV. In the chromates (selenates), the upper part of the valence band is dominated by O 2p states and the lower part of the conduction band is composed primarily of electronic states associated with the Cr 3d and O 2p (Se 4s and O 2p) states. Calculations also show that the band gap of PbCrO4 (PbSeO4) is smaller than the band gap of SrCrO4 (SrSeO4). This phenomenon is caused by Pb states, which, to some extent, also contribute to the top of the valence band and the bottom of the conduction band. The agreement between experiments and calculations is quite good; however, the band gaps are underestimated by calculations, with the exception of the bang gap of SrCrO4, for which theory and calculations agree. Calculations also provide predictions of the bulk modulus of the studied compounds.

  4. Impact of d -band filling on the dislocation properties of bcc transition metals: The case of tantalum-tungsten alloys investigated by density-functional theory

    Science.gov (United States)

    Li, Hong; Draxl, Claudia; Wurster, Stefan; Pippan, Reinhard; Romaner, Lorenz

    2017-03-01

    We address the impact of tantalum alloying on dislocation properties of tungsten. To that aim, we calculate elastic constants, atomic-row displacement energy, dislocation core energy, and Peierls stress for different degrees of alloying within the framework of density-functional theory. We show that the elastic shear constants decrease monotonously with Ta content. Conversely, atomic-row displacement energy and, consequently, core energy and Peierls stress show a nonmonotonous behavior. These quantities peak at 25 at% Ta, indicating a tendency for embrittlement of W at such alloying concentrations. Our findings are in agreement with the experimental literature.

  5. The stabilities and electron structures of Al-Mg clusters with 18 and 20 valence electrons

    Science.gov (United States)

    Yang, Huihui; Chen, Hongshan

    2017-07-01

    The spherical jellium model predicts that metal clusters having 18 and 20 valence electrons correspond to the magic numbers and will show specific stabilities. We explore in detail the geometric structures, stabilities and electronic structures of Al-Mg clusters containing 18 and 20 valence electrons by using genetic algorithm combined with density functional theories. The stabilities of the clusters are governed by the electronic configurations and Mg/Al ratios. The clusters with lower Mg/Al ratios are more stable. The molecular orbitals accord with the shell structures predicted by the jellium model but the 2S level interweaves with the 1D levels and the 2S and 1D orbitals form a subgroup. The clusters having 20 valence electrons form closed 1S21P61D102S2 shells and show enhanced stability. The Al-Mg clusters with a valence electron count of 18 do not form closed shells because one 1D orbital is unoccupied. The ionization potential and electron affinity are closely related to the electronic configurations; their values are determined by the subgroups the HOMO or LUMO belong to. Supplementary material in the form of one pdf file available from the Journal web page at http://https://doi.org/10.1140/epjd/e2017-80042-9

  6. Electronic structure of InTe, SnAs and PbSb: Valence-skip compound or not?

    Energy Technology Data Exchange (ETDEWEB)

    Hase, Izumi, E-mail: i.hase@aist.go.jp [National Institute of Advanced Industrial Science and Technology, Tsukuba Central 2, 1-1-1 Umezono, Tsukuba 305-8568 (Japan); Yasutomi, Kouki [Graduate School of Pure and Applied Science, Univ. of Tsukuba, Tsukuba, 305-8571 (Japan); Yanagisawa, Takashi; Odagiri, Kousuke [National Institute of Advanced Industrial Science and Technology, Tsukuba Central 2, 1-1-1 Umezono, Tsukuba 305-8568 (Japan); Nishio, Taichiro [Department of Physics, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku, Tokyo 162-8601 (Japan)

    2016-08-15

    Highlights: • We calculated the electronic structure of InTe, SnAs and PbSb from first principles. • Obtained tight-binding parameters of InTe are close to those of BaBiO3, which suggests that their electronic properties are also alike. • InTe is favorable to emerge valence skip, while PbSb is not favorable for it. SnAs is between the two. • Our findings well agree with the experimental results. - Abstract: InTe, SnAs and PbSb formally have unusual valence states, In{sup 2+}, Sn{sup 3+} and Pb{sup 3+}. All of them have B1 crystal structure at some pressure range. They are candidates of the valence-skip compound, which may have negative effective Coulomb interaction U{sub eff} < 0. Negative-U Hubbard model is known to show charge-density wave or superconductivity in some parameter region. In fact, SnAs becomes superconducting at ambient pressure. InTe has a kind of charge-density wave at ambient pressure, and it becomes superconducting at high pressure. We investigated their electronic structures by ab-initio calculations, and calculated the number of s-electrons at the cation site. We found that InTe is favorable to emerge valence skip, while PbSb is not favorable for valence skip. SnAs is between these two. These findings well agree with the experimental results.

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

    CERN Document Server

    Delin, A

    2002-01-01

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

  8. Strong valence fluctuation in the quantum critical heavy fermion superconductor β-YbAlB4: a hard x-ray photoemission study.

    Science.gov (United States)

    Okawa, M; Matsunami, M; Ishizaka, K; Eguchi, R; Taguchi, M; Chainani, A; Takata, Y; Yabashi, M; Tamasaku, K; Nishino, Y; Ishikawa, T; Kuga, K; Horie, N; Nakatsuji, S; Shin, S

    2010-06-18

    Electronic structures of the quantum critical superconductor β-YbAlB4 and its polymorph α-YbAlB4 are investigated by using bulk-sensitive hard x-ray photoemission spectroscopy. From the Yb 3d core level spectra, the values of the Yb valence are estimated to be ∼2.73 and ∼2.75 for α- and β-YbAlB4, respectively, thus providing clear evidence for valence fluctuations. The valence band spectra of these compounds also show Yb2+ peaks at the Fermi level. These observations establish an unambiguous case of a strong mixed valence at quantum criticality for the first time among heavy fermion systems, calling for a novel scheme for a quantum critical model beyond the conventional Doniach picture in β-YbAlB4.

  9. Positive valence music restores executive control over sustained attention.

    Science.gov (United States)

    Baldwin, Carryl L; Lewis, Bridget A

    2017-01-01

    Music sometimes improves performance in sustained attention tasks. But the type of music employed in previous investigations has varied considerably, which can account for equivocal results. Progress has been hampered by lack of a systematic database of music varying in key characteristics like tempo and valence. The aims of this study were to establish a database of popular music varying along the dimensions of tempo and valence and to examine the impact of music varying along these dimensions on restoring attentional resources following performance of a sustained attention to response task (SART) vigil. Sixty-nine participants rated popular musical selections that varied in valence and tempo to establish a database of four musical types: fast tempo positive valence, fast tempo negative valence, slow tempo positive valence, and slow tempo negative valence. A second group of 89 participants performed two blocks of the SART task interspersed with either no break or a rest break consisting of 1 of the 4 types of music or silence. Presenting positive valence music (particularly of slow tempo) during an intermission between two successive blocks of the SART significantly decreased miss rates relative to negative valence music or silence. Results support an attentional restoration theory of the impact of music on sustained attention, rather than arousal theory and demonstrate a means of restoring sustained attention. Further, the results establish the validity of a music database that will facilitate further investigations of the impact of music on performance.

  10. Dissociable effects of valence and arousal in adaptive executive control

    National Research Council Canada - National Science Library

    Kuhbandner, Christof; Zehetleitner, Michael

    2011-01-01

    Based on introspectionist, semantic, and psychophysiological experimental frameworks, it has long been assumed that all affective states derive from two independent basic dimensions, valence and arousal...

  11. Band Alignment and Charge Transfer in Complex Oxide Interfaces

    Directory of Open Access Journals (Sweden)

    Zhicheng Zhong

    2017-03-01

    Full Text Available The synthesis of transition metal heterostructures is currently one of the most vivid fields in the design of novel functional materials. In this paper, we propose a simple scheme to predict band alignment and charge transfer in complex oxide interfaces. For semiconductor heterostructures, band-alignment rules like the well-known Anderson or Schottky-Mott rule are based on comparison of the work function or electron affinity of the bulk components. This scheme breaks down for oxides because of the invalidity of a single work-function approximation as recently shown in [Phys. Rev. B 93, 235116 (2016PRBMDO2469-995010.1103/PhysRevB.93.235116; Adv. Funct. Mater. 26, 5471 (2016AFMDC61616-301X10.1002/adfm.201600243]. Here, we propose a new scheme that is built on a continuity condition of valence states originating in the compounds’ shared network of oxygen. It allows for the prediction of sign and relative amplitude of the intrinsic charge transfer, taking as input only information about the bulk properties of the components. We support our claims by numerical density functional theory simulations as well as (where available experimental evidence. Specific applications include (i controlled doping of SrTiO_{3} layers with the use of 4d and 5d transition metal oxides and (ii the control of magnetic ordering in manganites through tuned charge transfer.

  12. Predicted roles of defects on band offsets and energetics at CIGS (Cu(In,Ga)Se₂/CdS) solar cell interfaces and implications for improving performance.

    Science.gov (United States)

    Xiao, Hai; Goddard, William A

    2014-09-07

    The laboratory performance of CIGS (Cu(In,Ga)Se2) based solar cells (20.8% efficiency) makes them promising candidate photovoltaic devices. However, there remains little understanding of how defects at the CIGS/CdS interface affect the band offsets and interfacial energies, and hence the performance of manufactured devices. To determine these relationships, we use density functional theory with the B3PW91 hybrid functional that we validate to provide very accurate descriptions of the band gaps and band offsets. This confirms the weak dependence of band offsets on surface orientation observed experimentally. We predict that the conduction band offset (CBO) of perfect CuInSe2/CdS interface is large, 0.79 eV, which would dramatically degrade performance. Moreover we show that band gap widening induced by Ga adjusts only the valence band offset, and we find that Cd impurities do not significantly affect the CBO. Thus we show that Cu vacancies at the interface play the key role in enabling the tunability of CBO. We predict that Na further improves the CBO through electrostatically elevating the valence levels to decrease the CBO, explaining the observed essential role of Na for high performance. Moreover we find that K leads to a dramatic decrease in the CBO to 0.05 eV, much better than Na. We suggest that the efficiency of CIGS devices might be improved substantially by tuning the ratio of Na to K, with the improved phase stability of Na balancing phase instability from K. All these defects reduce interfacial stability slightly, but not significantly.

  13. Hetero-gate-dielectric double gate junctionless transistor (HGJLT) with reduced band-to-band tunnelling effects in subthreshold regime

    Science.gov (United States)

    Ghosh, Bahniman; Mondal, Partha; Akram, M. W.; Bal, Punyasloka; Salimath, Akshay Kumar

    2014-06-01

    We propose a hetero-gate-dielectric double gate junctionless transistor (HGJLT), taking high-k gate insulator at source side and low-k gate insulator at drain side, which reduces the effects of band-to-band tunnelling (BTBT) in the sub-threshold region. A junctionless transistor (JLT) is turned off by the depletion of carriers in the highly doped thin channel (device layer) which results in a significant band overlap between the valence band of the channel region and the conduction band of the drain region, due to off-state drain bias, that triggers electrons to tunnel from the valence band of the channel region to the conduction band of the drain region leaving behind holes in the channel. These effects of band-to-band tunnelling increase the sub-threshold leakage current, and the accumulation of holes in the channel forms a parasitic bipolar junction transistor (n-p-n BJT for channel JLT) in the lateral direction by the source (emitter), channel (base) and drain (collector) regions in JLT structure in off-state. The proposed HGJLT reduces the subthreshold leakage current and suppresses the parasitic BJT action in off-state by reducing the band-to-band tunnelling probability.

  14. 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.

  15. Band-gap engineering of La1-x Nd x AlO3 (x = 0, 0.25, 0.50, 0.75, 1) perovskite using density functional theory: A modified Becke Johnson potential study

    Science.gov (United States)

    Sandeep; D, P. Rai; A, Shankar; M, P. Ghimire; Anup Pradhan, Sakhya; T, P. Sinha; R, Khenata; S, Bin Omran; R, K. Thapa

    2016-06-01

    The structural, electronic, and magnetic properties of the Nd-doped Rare earth aluminate, La1-x Nd x AlO3 (x = 0% to 100%) alloys are studied using the full potential linearized augmented plane wave (FP-LAPW) method within the density functional theory. The effects of the Nd substitution in LaAlO3 are studied using the supercell calculations. The computed electronic structure with the modified Becke-Johnson (mBJ) potential based approximation indicates that the La1-x Nd x AlO3 alloys may possess half-metallic (HM) behaviors when doped with Nd of a finite density of states at the Fermi level (E F). The direct and indirect band gaps are studied each as a function of x which is the concentration of Nd-doped LaAlO3. The calculated magnetic moments in the La1-x Nd x AlO3 alloys are found to arise mainly from the Nd-4f state. A probable half-metallic nature is suggested for each of these systems with supportive integral magnetic moments and highly spin-polarized electronic structures in these doped systems at E F. The observed decrease of the band gap with the increase in the concentration of Nd doping in LaAlO3 is a suitable technique for harnessing useful spintronic and magnetic devices. Project supported by the DST-SERB, Dy (Grant No. SERB/3586/2013-14), the UGCBSR, FRPS (Grant No. F.30-52/2014), the UGC (New Delhi, India) Inspire Fellowship DST (India), and the Deanship of Scientific Research at King Saud University (Grant No. RPG-VPP-088). M P Ghimire thanks the Alexander von Humboldt Foundation, Germany for the financial support.

  16. Prediction of composition for stable half-Heusler phases from electronic-band-structure analyses

    Energy Technology Data Exchange (ETDEWEB)

    Offernes, L. [Department of Chemistry, University of Oslo, P.O. Box 1033, Blindern, N-0315 Oslo (Norway)], E-mail: Laila.offernes@kjemi.uio.no; Ravindran, P.; Seim, C.W.; Kjekshus, A. [Department of Chemistry, University of Oslo, P.O. Box 1033, Blindern, N-0315 Oslo (Norway)

    2008-06-30

    This report describes a procedure to predict the frequently occurring non-stoichiometry of the half-Heusler XYZ alloys (viz. deviations from the equiatomic 1:1:1 composition and the usually accompanied narrow homogeneity regions) from ab initio calculated electronic-band-structure characteristics. The essential feature of this approach is to utilize the valence electron content (VEC) and the calculated electronic band structure to expose factors that according to rigid-band considerations should determine the possible deviations from 1:1:1 stoichiometry and direction of the stable solid-solution regions. These means have been used to predict the direction of equilibrium solid-solution regions for a number of ternary phase diagrams that comprise half-Heusler phases and the predictions have been tested with experimental data from literature and presently synthesized and microprobe analysed samples of NiTiSn, PtTiSn, CoTiSb, PtMnSb, NiMnSb, and CoMnSb. The predictions are made based on maximum band filling of bonding states identified through the crystal-orbital-Hamilton population (COHP) analysis and density-of-states (DOS) integration.

  17. A generation/recombination model assisted with two trap centers in wide band-gap semiconductors

    Science.gov (United States)

    Yamaguchi, Ken; Kuwabara, Takuhito; Uda, Tsuyoshi

    2013-03-01

    A generation/recombination (GR) model assisted with two trap centers has been proposed for studying reverse current on pn junctions in wide band-gap semiconductors. A level (Et1) has been assumed to be located near the bottom of the conduction band and the other (Et2) to be near the top of the valence band. The GR model has been developed by assuming (1) a high-electric field; F, (2) a short distance; d, between trap centers, (3) reduction in an energy-difference; Δeff = |Et1 - Et2| - eFd, and (4) hopping or tunneling conductions between trap centers with the same energy-level (Δeff ≈ 0). The GR rate has been modeled by trap levels, capture cross-sections, trap densities, and transition rate between trap centers. The GR rate, about 1010 greater than that estimated from the single-level model, has been predicted on pn junctions in a material with band-gap of 3.1 eV. Device simulations using the proposed GR model have been demonstrated for SiC diodes with and without a guard ring. A reasonable range for reverse current at room temperature has been simulated and stable convergence has been obtained in a numerical scheme for analyzing diodes with an electrically floating region.

  18. Raman study of band-bending at ZnSe/GaAs(001) interfaces

    Energy Technology Data Exchange (ETDEWEB)

    Bass, Utz; Frey, Alex; Mahapatra, Suddhasatta; Schumacher, Claus; Brunner, Karl; Geurts, Jean [Universitaet Wuerzburg, Physikalisches Institut, Experimentelle Physik III, Am Hubland, 97074 Wuerzburg (Germany)

    2011-07-01

    At heterovalent interfaces thermodynamically induced intermixing of the constituent materials with different numbers of valence electrons usually causes large variations in band offsets and local doping density, depending on the spatial arrangement of atoms at the interface. We varied the interface stoichiometry of n-doped ZnSe / GaAs (001) heterostructures by the predeposition of different amounts of Zn or Se on n-GaAs prior to n-ZnSe layer growth by MBE. The induced changes in band bending were optically analysed by Raman spectroscopy from coupled plasmon-LO-phonon modes and by Far-Infrared reflectance spectroscopy for calibration. We detect a depletion layer of about 50 nm at the heterointerface, which partially shifts from the GaAs into the ZnSe with Se predeposition. Together with data from electrical transport across the interface and capacitance-voltage profiling, our results are explained consistently by a 550 mV potential barrier in the conduction band at a Zn-rich n-ZnSe / n-GaAs interface, which is tuned down to about 70 mV by increasing Se predeposition. In addition, PL signatures for excitation above and below the ZnSe band gap are presented.

  19. Seniority Number in Valence Bond Theory.

    Science.gov (United States)

    Chen, Zhenhua; Zhou, Chen; Wu, Wei

    2015-09-08

    In this work, a hierarchy of valence bond (VB) methods based on the concept of seniority number, defined as the number of singly occupied orbitals in a determinant or an orbital configuration, is proposed and applied to the studies of the potential energy curves (PECs) of H8, N2, and C2 molecules. It is found that the seniority-based VB expansion converges more rapidly toward the full configuration interaction (FCI) or complete active space self-consistent field (CASSCF) limit and produces more accurate PECs with smaller nonparallelity errors than its molecular orbital (MO) theory-based analogue. Test results reveal that the nonorthogonal orbital-based VB theory provides a reverse but more efficient way to truncate the complete active Hilbert space by seniority numbers.

  20. Prediction of valence and arousal from music features

    NARCIS (Netherlands)

    Den Brinker, A.C.; Van Dinther, C.H.B.A.; Skowronek, J.

    2011-01-01

    Mood is an important attribute of music and knowledge on mood can beused as a basic ingredient in music recommender and retrieval systems. Moods are assumed to be dominantly determined by two dimensions:valence and arousal. An experiment was conducted to attain data forsong-based ratings of valence

  1. Intervalence charge transfer transition in mixed valence complexes ...

    Indian Academy of Sciences (India)

    Permanent link: http://www.ias.ac.in/article/fulltext/jcsc/114/04/0431-0442. Keywords. Mixed valence complexes; intervalence charge transfer; rotaxane; inclusion complex; optical electron transfer; cyclodextrin. Abstract. Intervalence charge transfer properties were studied for a set of mixed valence complexes incorporating ...

  2. Teaching Valence Shell Electron Pair Repulsion (VSEPR) Theory

    Science.gov (United States)

    Talbot, Christopher; Neo, Choo Tong

    2013-01-01

    This "Science Note" looks at the way that the shapes of simple molecules can be explained in terms of the number of electron pairs in the valence shell of the central atom. This theory is formally known as valence shell electron pair repulsion (VSEPR) theory. The article explains the preferred shape of chlorine trifluoride (ClF3),…

  3. Wavelet-based study of valence?arousal model of emotions on EEG signals with LabVIEW

    OpenAIRE

    Guzel Aydin, Seda; Kaya, Turgay; Guler, Hasan

    2016-01-01

    This paper illustrates the wavelet-based feature extraction for emotion assessment using electroencephalogram (EEG) signal through graphical coding design. Two-dimensional (valence?arousal) emotion model was studied. Different emotions (happy, joy, melancholy, and disgust) were studied for assessment. These emotions were stimulated by video clips. EEG signals obtained from four subjects were decomposed into five frequency bands (gamma, beta, alpha, theta, and delta) using ?db5? wavelet functi...

  4. Electronic and optical properties of the SiB{sub 2}O{sub 4} (B=Mg, Zn, and Cd) spinel oxides: An ab initio study with the Tran–Blaha-modified Becke–Johnson density functional

    Energy Technology Data Exchange (ETDEWEB)

    Allali, D. [Laboratory for Developing New Materials and their Characterization, University of Setif 1, 19000 Setif (Algeria); Bouhemadou, A., E-mail: a_bouhemadou@yahoo.fr [Laboratory for Developing New Materials and their Characterization, University of Setif 1, 19000 Setif (Algeria); Safi, E. Muhammad Abud Al [Department of Physics and Astronomy, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia); Bin-Omran, S. [Department of Physics and Astronomy, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia); Department of Physics, Faculty of Science and Humanitarian Studies, Salman Bin Abdalaziz University, Alkharj 11942 (Saudi Arabia); Chegaar, M. [Department of Physics, Faculty of Science, University of Setif 1, 19000 Setif (Algeria); Khenata, R. [Laboratoire de Physique Quantique et de Modélisation Mathématique (LPQ3M), Département de Technologie, Université de Mascara, 29000 Mascara (Algeria); Reshak, A.H. [New Technologies-Research Center, University of West Bohemia, Univerzitni 8, 306 14 Pilson (Czech Republic); Center of Excellence Geopolymer and Green Technology, School of Material Engineering, University Malaysia Perlis, 01007 Kangar, Perlis (Malaysia)

    2014-06-15

    We report ab initio density functional theory calculations of the structural, electronic and optical properties of the spinel oxides SiMg{sub 2}O{sub 4}, SiZng{sub 2}O{sub 4}, and SiCd{sub 2}O{sub 4} using the full-potential linearized augmented plane-wave method. The structural parameters calculated using both the local density and generalized gradient approximations to the exchange-correlation potential are consistent with the literature data. To calculate the electronic properties, the exchange-correlation potential is treated with various functionals, and we find that the newly developed Tran–Blaha-modified Becke–Johnson functional significantly improves the band gap. We predict a direct band gap in all of the considered SiB{sub 2}O{sub 4} compounds, and the band gaps continuously decrease as the atomic size of the B element increases. The decrease in the fundamental direct band gap (Γ–Γ) from SiMg{sub 2}O{sub 4} to SiZn{sub 2}O{sub 4} to SiCd{sub 2}O{sub 4} can be attributed to p–d mixing in the upper valence bands of SiZn{sub 2}O{sub 4} and SiCd{sub 2}O{sub 4}. The lowest conduction band is well dispersive, similar to that found for transparent conducting oxides such as ZnO. This band is mainly defined by the s and p electrons of the Si and B (B=Mg, Zn, Cd) atoms. The topmost valence band is considerably less dispersive and is defined by O-2p and B–d electrons. The charge-carrier effective masses are evaluated at the topmost valence band and at the bottommost conduction band that were calculated. The frequency-dependent complex dielectric function, absorption coefficient, refractive index, extinction coefficient, reflectivity and electron energy loss function were estimated. We find that the value of the zero-frequency limit of the dielectric function ε(0) increases as the band gap decreases. The origins of the peaks and structures in the optical spectra are determined in terms of the calculated energy band structures.

  5. Valence XPS structure and chemical bond in Cs2UO2Cl4

    Directory of Open Access Journals (Sweden)

    Teterin Yury A.

    2016-01-01

    Full Text Available Quantitative analysis was done of the valence electrons X-ray photoelectron spectra structure in the binding energy (BE range of 0 eV to ~35 eV for crystalline dicaesium tetrachloro-dioxouranium (VI (Cs2UO2Cl4. This compound contains the uranyl group UO2. The BE and structure of the core electronic shells (~35 eV-1250 eV, as well as the relativistic discrete variation calculation results for the UO2Cl4(D4h cluster reflecting U close environment in Cs2UO2Cl4 were taken into account. The experimental data show that many-body effects due to the presence of cesium and chlorine contribute to the outer valence (0-~15 eV BE spectral structure much less than to the inner valence (~15 eV-~35 eV BE one. The filled U5f electronic states were theoretically calculated and experimentally confirmed to be present in the valence band of Cs2UO2Cl4. It corroborates the suggestion on the direct participation of the U5f electrons in the chemical bond. Electrons of the U6p atomic orbitals participate in formation of both the inner (IVMO and the outer (OVMO valence molecular orbitals (bands. The filled U6p and the O2s, Cl3s electronic shells were found to make the largest contributions to the IVMO formation. The molecular orbitals composition and the sequence order in the binding energy range 0 eV-~35 eV in the UO2Cl4 cluster were established. The experimental and theoretical data allowed a quantitative molecular orbitals scheme for the UO2Cl4 cluster in the BE range 0-~35 eV, which is fundamental for both understanding the chemical bond nature in Cs2UO2Cl4 and the interpretation of other X-ray spectra of Cs2UO2Cl4. The contributions to the chemical binding for the UO2Cl4 cluster were evaluated to be: the OVMO contribution - 76%, and the IVMO contribution - 24 %.

  6. Valence instabilities as a possible source of actinide system inconsistencies

    Energy Technology Data Exchange (ETDEWEB)

    Sandenaw, T.A.

    1979-08-01

    The presence of a mixed-valence state in light actinides appears evident from the crystal structures of certain U, Np, and Pu phases. As supporting evidence, the physical property response of these actinide elements (and some of their alloys) is compared with that of rare-earth metallic compounds known to have an unstable valence. Impurities may stabilize an intermediate (different) valence state locally in rare-earth compounds in the presence of the valence state of the bulk phase. Impurity elements from different periodic table groupings may likewise stabilize different intermediate valence states in light actinide elements, thus contributing to inconsistencies in results reported by different experimentalists. Any model (theory) advanced for explaining the physical property behavior of U, Np, and Pu may also require consideration of a configurational limit. A phenomenological connection could exist between a martensitic transformation and the fluctuation temperature in both rare earth and actinide systems.

  7. High-density InAs/GaAs{sub 1−x}Sb{sub x} quantum-dot structures grown by molecular beam epitaxy for use in intermediate band solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Debnath, M. C., E-mail: mdebnath@cnsi.ucla.edu [Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, Norman, Oklahoma 73019 (United States); California NanoSystems Institute and Electrical Engineering Department, University of California-Los Angeles (UCLA), Los Angeles, California 90095 (United States); Mishima, T. D.; Santos, M. B.; Cheng, Y.; Whiteside, V. R.; Sellers, I. R. [Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, Norman, Oklahoma 73019 (United States); Hossain, K. [Amethyst Research, Inc., 123 Case Circle, Ardmore, Oklahoma 73401 (United States); Laghumavarapu, R. B.; Liang, B. L.; Huffaker, D. L. [California NanoSystems Institute and Electrical Engineering Department, University of California-Los Angeles (UCLA), Los Angeles, California 90095 (United States)

    2016-03-21

    InAs quantum-dot structures were grown using a GaAs{sub 1−x}Sb{sub x} matrix on a GaAs(001) substrate. The use of GaAs{sub 1−x}Sb{sub x} for the buffer and cap layers effectively suppressed coalescence between dots and significantly increased the dot density. The highest density (∼3.5 × 10{sup 11}/cm{sup 2}) was obtained for a nominal 3.0 monolayer deposition of InAs with an Sb composition of x = 13–14% in the GaAs{sub 1−x}Sb{sub x} matrix. When the Sb composition was increased to 18%, the resulting large photoluminescent red shift (∼90 meV) indicated the release of compressive strain inside the quantum dots. For x > 13%, we observed a significant decrease in photoluminescence intensity and an increase in the carrier lifetime (≥4.0 ns). This is attributed to the type-II band alignment between the quantum dots and matrix material.

  8. Derivation of 12- and 14-band $\\textbf{k}\\cdot\\textbf{p}$ Hamiltonians for dilute bismide and bismide-nitride semiconductors

    OpenAIRE

    Broderick, Christopher A.; Usman, Muhammad; O'Reilly, Eoin P.

    2013-01-01

    Using an $sp^{3}s^{*}$ tight-binding model we demonstrate how the observed strong bowing of the band gap and spin-orbit-splitting with increasing Bi composition in the dilute bismide alloy GaBi$_{x}$As$_{1-x}$ can be described in terms of a band-anticrossing interaction between the extended states of the GaAs valence band edge and highly localised Bi-related resonant states lying below the GaAs valence band edge. We derive a 12-band $\\textbf{k}\\cdot\\textbf{p}$ Hamiltonian to describe the band...

  9. Brønsted acidity of protic ionic liquids: a modern ab initio valence bond theory perspective.

    Science.gov (United States)

    Patil, Amol Baliram; Mahadeo Bhanage, Bhalchandra

    2016-09-21

    Room temperature ionic liquids (ILs), especially protic ionic liquids (PILs), are used in many areas of the chemical sciences. Ionicity, the extent of proton transfer, is a key parameter which determines many physicochemical properties and in turn the suitability of PILs for various applications. The spectrum of computational chemistry techniques applied to investigate ionic liquids includes classical molecular dynamics, Monte Carlo simulations, ab initio molecular dynamics, Density Functional Theory (DFT), CCSD(t) etc. At the other end of the spectrum is another computational approach: modern ab initio Valence Bond Theory (VBT). VBT differs from molecular orbital theory based methods in the expression of the molecular wave function. The molecular wave function in the valence bond ansatz is expressed as a linear combination of valence bond structures. These structures include covalent and ionic structures explicitly. Modern ab initio valence bond theory calculations of representative primary and tertiary ammonium protic ionic liquids indicate that modern ab initio valence bond theory can be employed to assess the acidity and ionicity of protic ionic liquids a priori.

  10. VALENCY AND SYNTACTICAL RELATION IN BIMANESS

    Directory of Open Access Journals (Sweden)

    Made Sri Satyawati

    2012-11-01

    Full Text Available This study presents the findings and descriptions of the replies to severalproblems that have not been completely and deeply discussed in the researchespreviously conducted on Bimanese. The problems are related to micro-linguistic factors,namely valency and syntactical relation in Bimanese. Both deductive and inductiveapproaches were applied to obtain satisfactory results. The main theory employed in thisstudy is Role and Reference Grammar Theory (RRG by Van Valin and J. Lapolla. It wasemployed to completely analyze the collected data in accordance with the problemsproposed in this research, and the inductive approach was employed to analyze the datain order to get novelties.In this study, clause structure is given the first priority to discuss, followed by thediscussion on operator, voice markers, nominalizers, and definiteness. Based on thepredicate category, the clause in Bimanese can be constructed with the constituents thatare under the categories of verb, noun, adjective, number, and adverb (prepositionalphrase. Based on the clause analysis, it has been found that in Bimanese there are severaloperators, each of which has different functional boundary in marking the clausemeaning. One operator may only sign nucleus, core (nucleus and argument, or core andperiphery. Bimanese has also been identified to have four linguistic states expressed byverbs that are made to make sense based on state (Aktisontrat, achievement, andaccomplishment. RRG classifies verbs into ten instead of four. However, in this study, tomake the analysis easier, verbs are classified into four. The predicate in Bimanese can beboth serial verbs and secondary verbs. It has also been found that the mechanism ofchange in valency is marked by the attachment of markers to the verbs resulting incausativity, applicativity, and resultivity. From those syntactical constructions, thesyntactical relation in Bimanese can be clearly identified. The discussion on syntacticalrelation

  11. Eu valence and Fermi-surface development in EuX{sub 2}Si{sub 2} (X = Co, Rh, Ir) systems

    Energy Technology Data Exchange (ETDEWEB)

    Goetze, K. [Hochfeld-Magnetlabor Dresden, Helmholtz-Zentrum Dresden-Rossendorf (Germany); TU Dresden, Institut fuer Festkoerperphysik (Germany); Seiro, S.; Geibel, C.; Rosner, H.; Petzold, V. [MPI for Chemical Physics of Solids (Germany); Polyakov, A.; Wosnitza, J. [Hochfeld-Magnetlabor Dresden, Helmholtz-Zentrum Dresden-Rossendorf (Germany); Sheikin, I. [LNCMI-Grenoble (France); Suslov, A. [National High Magnetic Field Laboratory, Tallahassee (United States)

    2013-07-01

    The valence-fluctuating Eu systems EuX{sub 2}Si{sub 2}, with X being the transition metal Co, Ir, or Rh, show different types of ground states, strongly depending on X. The instability of the Eu 4f shell underlies this phenomenon and leads among other effects to different valence states ranging from Eu{sup 2+} over mixed valence and intermediate valence behavior to Eu{sup 3+}. Investigations on the structure and the magnetic behavior of EuCo{sub 2}Si{sub 2}, EuIr{sub 2}Si{sub 2}, and EuRh{sub 2}Si{sub 2} have revealed their Eu valence. Further experiments on specific heat and resistivity gave insights to magnetic ordering, electronic correlations, and possible valence fluctuations. We report about a systematic de Haas-van Alphen study on the Fermi-surface development of the EuX{sub 2}Si{sub 2} compounds in magnetic fields up to 35 T. High-quality single crystals were available for the first time. We focus on the Fermi-surface topology obtained by angle dependent measurements and discuss a comparison to band-structure calculations.

  12. Metaheuristics-Assisted Combinatorial Screening of Eu2+-Doped Ca-Sr-Ba-Li-Mg-Al-Si-Ge-N Compositional Space in Search of a Narrow-Band Green Emitting Phosphor and Density Functional Theory Calculations.

    Science.gov (United States)

    Lee, Jin-Woong; Singh, Satendra Pal; Kim, Minseuk; Hong, Sung Un; Park, Woon Bae; Sohn, Kee-Sun

    2017-08-21

    A metaheuristics-based design would be of great help in relieving the enormous experimental burdens faced during the combinatorial screening of a huge, multidimensional search space, while providing the same effect as total enumeration. In order to tackle the high-throughput powder processing complications and to secure practical phosphors, metaheuristics, an elitism-reinforced nondominated sorting genetic algorithm (NSGA-II), was employed in this study. The NSGA-II iteration targeted two objective functions. The first was to search for a higher emission efficacy. The second was to search for narrow-band green color emissions. The NSGA-II iteration finally converged on BaLi2Al2Si2N6:Eu2+ phosphors in the Eu2+-doped Ca-Sr-Ba-Li-Mg-Al-Si-Ge-N compositional search space. The BaLi2Al2Si2N6:Eu2+ phosphor, which was synthesized with no human intervention via the assistance of NSGA-II, was a clear single phase and gave an acceptable luminescence. The BaLi2Al2Si2N6:Eu2+ phosphor as well as all other phosphors that appeared during the NSGA-II iterations were examined in detail by employing powder X-ray diffraction-based Rietveld refinement, X-ray absorption near edge structure, density functional theory calculation, and time-resolved photoluminescence. The thermodynamic stability and the band structure plausibility were confirmed, and more importantly a novel approach to the energy transfer analysis was also introduced for BaLi2Al2Si2N6:Eu2+ phosphors.

  13. First-principles energy band calculation for CaBi{sub 2}O{sub 4} with monoclinic structure

    Energy Technology Data Exchange (ETDEWEB)

    Nakamura, Hiroyuki; Ishii, Shin' ichirou [Integrated Arts and Science, Kitakyushu National College of Technology, 5-20-1 Shii, Kokuraminami-ku, Kitakyushu 802-0985 (Japan); Yamada, Kenji [Department of Materials Science and Chemical Engineering, Kitakyushu National College of Technology, 5-20-1 Shii, Kokuraminami-ku, Kitakyushu 802-0985 (Japan); Matsushima, Shigenori, E-mail: smatsu@kct.ac.jp [Department of Materials Science and Chemical Engineering, Kitakyushu National College of Technology, 5-20-1 Shii, Kokuraminami-ku, Kitakyushu 802-0985 (Japan); Arai, Masao [Computational Materials Science Center (CMSC), National Institute of Materials Science (NIMS), 1-1 Namiki, Tsukuba 305-0044 (Japan); Kobayashi, Kenkichiro [Department of Materials Science, Shizuoka University, 3-5-1 Johoku, Hamamatsu 432-8011 (Japan)

    2010-05-15

    The electronic structure of CaBi{sub 2}O{sub 4} is calculated by a GGA approach. The valence band maximum is approximately located at the {Gamma}-point or the Y-point and the conduction band minimum at the V-point. This means that CaBi{sub 2}O{sub 4} is an indirect energy gap material. The conduction band is composed of Bi 6p-O 2p interaction. On the other hand, the valence band can be divided into two energy regions ranging from -9.92 to -7.40 eV (lower valence band) and -4.69 to 0 eV (upper valence band). The former is mainly constructed from Bi 6s states interacting slightly with O 2s and 2p states, and the latter consists of O 2p states hybridizing with Bi 6s and 6p states. The states near the valence band maximum are strongly localized and the mobility of holes generated by band gap excitation is predicted to be fairly low.

  14. Emotion and language: Valence and arousal affect word recognition

    Science.gov (United States)

    Brysbaert, Marc; Warriner, Amy Beth

    2014-01-01

    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. The present study 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

  15. Quantitative first-principles calculations of valence and core excitation spectra of solid C60

    Science.gov (United States)

    Fossard, F.; Hug, G.; Gilmore, K.; Kas, J. J.; Rehr, J. J.; Vila, F. D.; Shirley, E. L.

    2017-03-01

    We present calculated valence and C 1 s near-edge excitation spectra of solid C60 and experimental results measured with high-resolution electron energy-loss spectroscopy. The near-edge calculations are carried out using three different methods: solution of the Bethe-Salpeter equation (BSE) as implemented in the ocean suite (Obtaining Core Excitations with Ab Initio methods and the NIST BSE solver), the excited-electron core-hole approach, and the constrained-occupancy method using the Stockholm-Berlin core excitation code, StoBe. The three methods give similar results and are in good agreement with experiment, though the BSE results are the most accurate. The BSE formalism is also used to carry out valence level calculations using the NIST BSE solver. Theoretical results include self-energy corrections to the band gap and bandwidths, lifetime-damping effects, and Debye-Waller effects in the core excitation case. A comparison of spectral features to those observed experimentally illustrates the sensitivity of certain features to computational details, such as self-energy corrections to the band structure and core-hole screening.

  16. 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 ...

  17. Taboo, emotionally valenced, and emotionally neutral word norms

    National Research Council Canada - National Science Library

    Janschewitz, Kristin

    2008-01-01

    Although taboo words are used to study emotional memory and attention, no easily accessible normative data are available that compare taboo, emotionally valenced, and emotionally neutral words on the same scales...

  18. Isolated olecranon fractures in children affected by osteogenesis imperfecta type I treated with single screw or tension band wiring system: Outcomes and pitfalls in relation to bone mineral density.

    Science.gov (United States)

    Persiani, Pietro; Ranaldi, Filippo M; Graci, Jole; De Cristo, Claudia; Zambrano, Anna; D'Eufemia, Patrizia; Martini, Lorena; Villani, Ciro

    2017-05-01

    The purpose of this study is to compare the results of 2 techniques, tension band wiring (TBW) and fixation with screws, in olecranon fractures in children affected with osteogenesis imperfecta (OI) type I. Between 2010 and 2014, 21 olecranon fractures in 18 children with OI (average age: 12 years old) were treated surgically. Ten patients were treated with the screw fixation and 11 with TBW. A total of 65% of olecranon fractures occurred as a result of a spontaneous avulsion of the olecranon during the contraction of the triceps muscle. The average follow-up was 36 months. Among the children treated with 1 screw, 5 patients needed a surgical revision with TBW due to a mobilization of the screw. In this group, the satisfactory results were 50%. In patients treated with TBW, the satisfactory results were 100% of the cases. The average Z-score, the last one recorded in the patients before the trauma, was -2.53 in patients treated with screw fixation and -2.04 in those treated with TBW. TBW represents the safest surgical treatment for patients suffering from OI type I, as it helps to prevent the rigidity of the elbow through an earlier recovery of the range of motion, and there was no loosening of the implant. In analyzing the average Z-score before any fracture, the fixation with screws has an increased risk of failure in combination with low bone mineral density.

  19. Density functional investigation of structural, electronic and optical properties of Ge-doped ZnO

    Science.gov (United States)

    Lv, Ying-bo; Dai, Ying; Yang, Kesong; Zhang, Zhenkui; Wei, Wei; Guo, Meng; Huang, Baibiao

    2011-10-01

    Recent experiments reported fascinating phenomenon of photoluminescence (PL) blueshift in Ge-doped ZnO. To understand it, we examined the structural, electronic and optical properties of Ge-doped ZnO (ZnO:Ge) systematically by means of density functional theory calculations. Our results show that Ge atoms tend to cluster in heavily doped ZnO. Ge clusters can limit the conductivity of doped ZnO but reinforce the near-band-edge emission. The substitutional Ge for Zn leads to Fermi level pinning in the conduction band, which indicates Ge-doped ZnO is of n-type conductivity character. It is found that the delocalized Ge 4s states hybridize with conduction band bottom, and is dominant in the region near the Fermi level, suggesting that Ge-4s states provides major free carriers in ZnO:Ge crystal. The observed blueshift of PL in Ge-doped ZnO originates from the electron transition energy from the valence band to the empty levels above Fermi level larger than the gap of undoped ZnO. The electron transition between the gap states induced by oxygen vacancy and conduction band minimum may be the origin of the new PL peak at 590 nm.

  20. Conduction Mechanism of Valence Change Resistive Switching Memory: A Survey

    OpenAIRE

    Ee Wah Lim; Razali Ismail

    2015-01-01

    Resistive switching effect in transition metal oxide (TMO) based material is often associated with the valence change mechanism (VCM). Typical modeling of valence change resistive switching memory consists of three closely related phenomena, i.e., conductive filament (CF) geometry evolution, conduction mechanism and temperature dynamic evolution. It is widely agreed that the electrochemical reduction-oxidation (redox) process and oxygen vacancies migration plays an essential role in the CF fo...

  1. Effect of valence nucleons on nuclear binding energy

    Energy Technology Data Exchange (ETDEWEB)

    Angeli, I. (Kossuth Lajos Tudomanyegyetem, Debrecen (HU))

    1991-10-01

    The nucleonic promiscuity factor P = N{sub p}N{sub n}/(N{sub p} + N{sub n}), where N{sub p}(N{sub n}) is the number of valence protons (neutrons) or holes, is shown to be a useful parameter in the description of the mass number dependence of nuclear binding energies. This means that most of the deviation from a smooth mass number dependence is caused by the isoscalar interaction between valence protons and neutrons.

  2. Emotional Valence and the Free-Energy Principle

    Science.gov (United States)

    Joffily, Mateus; Coricelli, Giorgio

    2013-01-01

    The free-energy principle has recently been proposed as a unified Bayesian account of perception, learning and action. Despite the inextricable link between emotion and cognition, emotion has not yet been formulated under this framework. A core concept that permeates many perspectives on emotion is valence, which broadly refers to the positive and negative character of emotion or some of its aspects. In the present paper, we propose a definition of emotional valence in terms of the negative rate of change of free-energy over time. If the second time-derivative of free-energy is taken into account, the dynamics of basic forms of emotion such as happiness, unhappiness, hope, fear, disappointment and relief can be explained. In this formulation, an important function of emotional valence turns out to regulate the learning rate of the causes of sensory inputs. When sensations increasingly violate the agent's expectations, valence is negative and increases the learning rate. Conversely, when sensations increasingly fulfil the agent's expectations, valence is positive and decreases the learning rate. This dynamic interaction between emotional valence and learning rate highlights the crucial role played by emotions in biological agents' adaptation to unexpected changes in their world. PMID:23785269

  3. Spontaneous polarization of the neutral interface for valence asymmetric coulombic systems.

    Science.gov (United States)

    di Caprio, D; Holovko, M

    2009-02-19

    In this paper, we discuss the phenomenon of a spontaneous polarization of a neutral hard planar interface for valence asymmetric Coulombic systems. Within a field theoretical description, we account for the existence of nontrivial charge density and electric potential profiles. The analysis of the phenomenon shows that the effect is related to combinatorics in relation with the existence of the two independent species cations and anions. This simple and basic feature is related to the quantum mechanical properties of the system. The theoretical results are compared with numerical simulations data and are shown to be in very good agreement, which a fortiori justifies our physical interpretation.

  4. Optical excitation and electron relaxation dynamics at semiconductor surfaces: a combined approach of density functional and density matrix theory applied to the silicon (001) surface

    Energy Technology Data Exchange (ETDEWEB)

    Buecking, N.

    2007-11-05

    In this work a new theoretical formalism is introduced in order to simulate the phononinduced relaxation of a non-equilibrium distribution to equilibrium at a semiconductor surface numerically. The non-equilibrium distribution is effected by an optical excitation. The approach in this thesis is to link two conventional, but approved methods to a new, more global description: while semiconductor surfaces can be investigated accurately by density-functional theory, the dynamical processes in semiconductor heterostructures are successfully described by density matrix theory. In this work, the parameters for density-matrix theory are determined from the results of density-functional calculations. This work is organized in two parts. In Part I, the general fundamentals of the theory are elaborated, covering the fundamentals of canonical quantizations as well as the theory of density-functional and density-matrix theory in 2{sup nd} order Born approximation. While the formalism of density functional theory for structure investigation has been established for a long time and many different codes exist, the requirements for density matrix formalism concerning the geometry and the number of implemented bands exceed the usual possibilities of the existing code in this field. A special attention is therefore attributed to the development of extensions to existing formulations of this theory, where geometrical and fundamental symmetries of the structure and the equations are used. In Part II, the newly developed formalism is applied to a silicon (001)surface in a 2 x 1 reconstruction. As first step, density-functional calculations using the LDA functional are completed, from which the Kohn-Sham-wave functions and eigenvalues are used to calculate interaction matrix elements for the electron-phonon-coupling an the optical excitation. These matrix elements are determined for the optical transitions from valence to conduction bands and for electron-phonon processes inside the

  5. Modified band alignment effect in ZnO/Cu2O heterojunction solar cells via Cs2O buffer insertion

    Science.gov (United States)

    Eom, Kiryung; Lee, Dongyoon; Kim, Seunghwan; Seo, Hyungtak

    2018-02-01

    The effects of a complex buffer layer of cesium oxide (Cs2O) on the photocurrent response in oxide heterojunction solar cells (HSCs) were investigated. A p-n junction oxide HSC was fabricated using p-type copper (I) oxide (Cu2O) and n-type zinc oxide (ZnO); the buffer layer was inserted between the Cu2O and fluorine-doped tin oxide (FTO). Ultraviolet–visible (UV–vis) and x-ray and ultraviolet photoelectron spectroscopy analyses were performed to characterize the electronic band structures of cells, both with and without this buffer layer. In conjunction with the measured band electronic structures, the significantly improved visible-range photocurrent spectra of the buffer-inserted HSC were analyzed in-depth. As a result, the 1 sun power conversion efficiency was increased by about three times by the insertion of buffer layer. The physicochemical origin of the photocurrent enhancement was mainly ascribed to the increased photocarrier density in the buffer layer and modified valence band offset to promote the effective hole transfer at the interface to FTO on the band-alignment model.

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

    Energy Technology Data Exchange (ETDEWEB)

    Dey, Anup, E-mail: a-dey2002@yahoo.com [Electronics and Communication Engineering Department, Kalyani Government Engineering College, Kalyani 741235 (India); Maiti, Biswajit [Physics Department, Kalyani Government Engineering College, Kalyani 741235 (India); Chanda, Debasree [Department of Engineering and Technological Studies, Kalyani University, Kalyani 741235 (India)

    2014-04-14

    A generalized theory is developed to study inter-band optical absorption coefficient (IOAC) and material gain (MG) in quantum dot structures of narrow gap III-V compound semiconductor considering the wave-vector (k{sup →}) dependence of the optical transition matrix element. The band structures of these low band gap semiconducting materials with sufficiently separated split-off valance band are frequently described by the three energy band model of Kane. This has been adopted for analysis of the IOAC and MG taking InAs, InSb, Hg{sub 1−x}Cd{sub x}Te, and In{sub 1−x}Ga{sub x}As{sub y}P{sub 1−y} lattice matched to InP, as example of III–V compound semiconductors, having varied split-off energy band compared to their bulk band gap energy. It has been found that magnitude of the IOAC for quantum dots increases with increasing incident photon energy and the lines of absorption are more closely spaced in the three band model of Kane than those with parabolic energy band approximations reflecting the direct the influence of energy band parameters. The results show a significant deviation to the MG spectrum of narrow-gap materials having band nonparabolicity compared to the parabolic band model approximations. The results reflect the important role of valence band split-off energies in these narrow gap semiconductors.

  7. All-Optical Reconstruction of Crystal Band Structure.

    Science.gov (United States)

    Vampa, G; Hammond, T J; Thiré, N; Schmidt, B E; Légaré, F; McDonald, C R; Brabec, T; Klug, D D; Corkum, P B

    2015-11-06

    The band structure of matter determines its properties. In solids, it is typically mapped with angle-resolved photoemission spectroscopy, in which the momentum and the energy of incoherent electrons are independently measured. Sometimes, however, photoelectrons are difficult or impossible to detect. Here we demonstrate an all-optical technique to reconstruct momentum-dependent band gaps by exploiting the coherent motion of electron-hole pairs driven by intense midinfrared femtosecond laser pulses. Applying the method to experimental data for a semiconductor ZnO crystal, we identify the split-off valence band as making the greatest contribution to tunneling to the conduction band. Our new band structure measurement technique is intrinsically bulk sensitive, does not require a vacuum, and has high temporal resolution, making it suitable to study reactions at ambient conditions, matter under extreme pressures, and ultrafast transient modifications to band structures.

  8. Band alignments of graphene-like III-nitride semiconductors

    Science.gov (United States)

    Ota, Yuichi

    2018-02-01

    Band alignment in graphene-like III-nitride semiconductors was investigated using first principles calculations and an empirical formula. We estimated the band edge positions using two simple approaches based on the energy of the band gap center (BGC) and electron affinity rules. The energy positions relative to the vacuum level were determined from the BGC and Mulliken electronegativities. These methods provided similar trends in the band lineup. The valence band and conduction band offsets determined by the first principles calculations agreed with the empirical results to within 0.5 eV. The findings suggest that the first principles and empirical methods provide a useful guide for high-throughput device design.

  9. Band Gap Transition Studies of U:ThO2 Using Cathodoluminescence

    Science.gov (United States)

    2014-03-27

    electron beam) EC energy (conduction band) ED energy (donor level ) Eg energy (band gap) Ei energy (ionization) EV energy (valence band) permittivity ...research. Furthermore, the search for non-fossil fuel energy sources is a principal goal for world leaders. The naturally occurring thorium-232...fissionable uranium under the pretence of energy research. Although the Th fuel cycle needs a lot more study to be made efficient, Th has many attractive

  10. Character Disposition and Behavior Type: Influences of Valence on Preschool Children's Social Judgments

    Science.gov (United States)

    Jones, Elaine F.; Tobias, Marvin; Pauley, Danielle; Thomson, Nicole Renick; Johnson, Shawana Lewis

    2009-01-01

    The authors studied the influences of valence information on preschool children's (n = 47) moral (good or bad), liking (liked or disliked by a friend), and consequence-of-behavior (reward or punishment) judgments. The authors presented 8 scenarios describing the behavior valence, positive valence (help, share), negative valence (verbal insult,…

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

    Science.gov (United States)

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

    2013-09-25

    A frustrated, effective ½-filled band Hubbard-Heisenberg model has been proposed for describing the strongly dimerized charge-transfer solid families κ-(ET)2X and Z[Pd(dmit)2]2. In addition to showing unconventional superconductivity, these materials also exhibit antiferromagnetism, candidate spin-liquid phases, and, in the case of Z=EtMe3P, a spin-gapped phase that has sometimes been referred to as a valence bond solid. We show that neither superconductivity nor the valence bond order phase occurs within the Hubbard-Heisenberg model. We suggest that a description based on ¼-filling, that is reached when the carrier concentration per molecule instead of per dimer is considered, thus may be appropriate.

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

    Science.gov (United States)

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

    2013-09-01

    A frustrated, effective \\frac{1}{2}-filled band Hubbard-Heisenberg model has been proposed for describing the strongly dimerized charge-transfer solid families κ-(ET)2X and Z[Pd(dmit)2]2. In addition to showing unconventional superconductivity, these materials also exhibit antiferromagnetism, candidate spin-liquid phases, and, in the case of Z=EtMe3P, a spin-gapped phase that has sometimes been referred to as a valence bond solid. We show that neither superconductivity nor the valence bond order phase occurs within the Hubbard-Heisenberg model. We suggest that a description based on \\frac{1}{4}-filling, that is reached when the carrier concentration per molecule instead of per dimer is considered, thus may be appropriate.

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

    Energy Technology Data Exchange (ETDEWEB)

    Saini, Hardev S.; Singh, Mukhtiyar [Department of Physics, Kurukshetra University, Kurukshetra 136119 (Haryana) (India); Reshak, Ali H. [School of Complex Systems, FFWP - South Bohemia University, Nove Hrady 37333 (Czech Republic); School of Material Engineering, Malaysia University of Perlis, P.O. Box 77, d/a Pejabat Pos Besar, 01007 Kangar, Perlis (Malaysia); Kashyap, Manish K., E-mail: manishdft@gmail.com [Department of Physics, Kurukshetra University, Kurukshetra 136119 (Haryana) (India)

    2012-03-25

    Highlights: Black-Right-Pointing-Pointer These compounds are characterized as narrow band gap semiconductors with a maximum gap (1.27 eV) for ZnGeAs{sub 2}. Black-Right-Pointing-Pointer A good agreement of band gaps with experiments is obtained within mBJLDA formalism. Black-Right-Pointing-Pointer The band gap decreases with the substitution of either one or both cations in reference compound, ZnGeAs{sub 2}. Black-Right-Pointing-Pointer The ionic/covalent character for A-As/B-As bond has been described on the basis of electro-negativity difference of the atoms. Black-Right-Pointing-Pointer The d-states of transition metal, Zn are localized deeper in valence band (E < 5 eV), showing no effective role to decide the magnitude of semiconducting band gap. - Abstract: The electronic properties of ABAs{sub 2} (A = Zn, Cd; B = Ge, Sn) compounds have been investigated using WIEN2k implementation of full potential linearized augmented plane wave (FPLAPW) method with an aim to study the effect of changing local environment by substituting cation(s) with corresponding next group element in reference compound (ZnGeAs{sub 2}) on these properties. The exchange and correlation (XC) effects are taken into account by an orbital independent modified Becke-Johnson (mBJ) potential as coupled with Local Density Approximation (LDA) for these calculations. We predict a direct band gap in all these compounds and observe that the band gap decreases with the change of either one or both cations. The calculated band gaps are in better agreement with corresponding experimental ones as compared to other calculations. The electronic band structure is analyzed in terms of contributions from various electrons and the covalency of two bonds, Zn-As and Ge-As has been discussed with respect to substitutions.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1997-04-01

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

  15. Taboo, emotionally valenced, and emotionally neutral word norms.

    Science.gov (United States)

    Janschewitz, Kristin

    2008-11-01

    Although taboo words are used to study emotional memory and attention, no easily accessible normative data are available that compare taboo, emotionally valenced, and emotionally neutral words on the same scales. Frequency, inappropriateness, valence, arousal, and imageability ratings for taboo, emotionally valenced, and emotionally neutral words were made by 78 native-English-speaking college students from a large metropolitan university. The valenced set comprised both positive and negative words, and the emotionally neutral set comprised category-related and category-unrelated words. To account for influences of demand characteristics and personality factors on the ratings, frequency and inappropriateness measures were decomposed into raters' personal reactions to the words versus raters' perceptions of societal reactions to the words (personal use vs. familiarity and offensiveness vs. tabooness, respectively). Although all word sets were rated higher in familiarity and tabooness than in personal use and offensiveness, these differences were most pronounced for the taboo set. In terms of valence, the taboo set was most similar to the negative set, although it yielded higher arousal ratings than did either valenced set. Imageability for the taboo set was comparable to that of both valenced sets. The ratings of each word are presented for all participants as well as for single-sex groups. The inadequacies of the application of normative data to research that uses emotional words and the conceptualization of taboo words as a coherent category are discussed. Materials associated with this article may be accessed at the Psychonomic Society's Archive of Norms, Stimuli, and Data, www.psychonomic.org/archive.

  16. Optical oscillator strengths for valence-shell and Br-3d inner-shell excitations of HCl and HBr.

    Science.gov (United States)

    Li, Wen-Bin; Zhu, Lin-Fan; Yuan, Zhen-Sheng; Liu, Xiao-Jing; Xu, Ke-Zun

    2006-10-21

    Absolute optical oscillator strength density spectra for valence-shell excitations of HCl and HBr, as well as for Br-3d inner-shell excitations of HBr, have been determined by high-resolution electron-energy-loss-spectroscopy method in the dipole limit. Absolute optical oscillator strengths for the discrete transitions of HCl and HBr are reported and compared with the previous results determined by the photoabsorption method.

  17. Observation of the c-f hybridization effect in valence-transition system EuPtP

    Energy Technology Data Exchange (ETDEWEB)

    Anzai, Hiroaki; Ichiki, Katsuya [Graduate School of Engineering, Osaka Prefecture University, Sakai (Japan); Schwier, Eike F.; Iwasawa, Hideaki; Arita, Masashi; Sato, Hitoshi; Shimada, Kenya; Namatame, Hirofumi; Taniguchi, Masaki [Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima (Japan); Mitsuda, Akihiro; Wada, Hirofumi [Graduate School of Science, Kyushu University, Fukuoka (Japan); Mimura, Kojiro [Graduate School of Engineering, Osaka Prefecture University, Sakai (Japan); Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima (Japan)

    2017-06-15

    We study the electronic structure of EuPtP, which exhibits two first-order valence transitions at T{sub 1} = 247 K and T{sub 2} = 201 K, using angle-resolved photoemission spectroscopy. Below T{sub 2}, we observe an energy gap at the crossing point of the bulk Eu 4f and conduction bands. The shape of band dispersions is described by a hybridization-band picture based on the periodic Anderson model. Our results demonstrate the c-f hybridization effect in the low-temperature phase of EuPtP. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  18. Social learning modulates the lateralization of emotional valence.

    Science.gov (United States)

    Shamay-Tsoory, Simone G; Lavidor, Michal; Aharon-Peretz, Judith

    2008-08-01

    Although neuropsychological studies of lateralization of emotion have emphasized valence (positive vs. negative) or type (basic vs. complex) dimensions, the interaction between the two dimensions has yet to be elucidated. The purpose of the current study was to test the hypothesis that recognition of basic emotions is processed preferentially by the right prefrontal cortex (PFC), whereas recognition of complex social emotions is processed preferentially by the left PFC. Experiment 1 assessed the ability of healthy controls and patients with right and left PFC lesions to recognize basic and complex emotions. Experiment 2 modeled the patient's data of Experiment 1 on healthy participants under lateralized displays of the emotional stimuli. Both experiments support the Type as well as the Valence Hypotheses. However, our findings indicate that the Valence Hypothesis holds for basic but less so for complex emotions. It is suggested that, since social learning overrules the basic preference of valence in the hemispheres, the processing of complex emotions in the hemispheres is less affected by valence.

  19. Space-valence priming with subliminal and supraliminal words.

    Science.gov (United States)

    Ansorge, Ulrich; Khalid, Shah; König, Peter

    2013-01-01

    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. Space-Valence Priming with Subliminal and Supraliminal Words

    Directory of Open Access Journals (Sweden)

    Ulrich eAnsorge

    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.

  1. Influence of the band bending on the photoconductivity of Li-doped ZnO microwires

    Science.gov (United States)

    Ferreyra, J. M.; Bridoux, G.; Villafuerte, M.; Straube, B.; Zamora, J.; Figueroa, C. A.; Heluani, S. P.

    2017-05-01

    Combining photoconductivity and photoluminescence measurements we have studied the band bending behavior with the Li-doping content in ZnO microwires. Our results reveal the presence of in-gap acceptor levels with energies ranging from 100 meV to 600 meV above valence band maximum. We have found that the band bending plays an important role in the photoconductivity modifying the life time of the photocarriers and enhancing the near band edge peak of photoluminescence in Li-doped samples. Using a simple model we have evaluated the influence of the band-bending on the relaxation time for the photoconductivity.

  2. Conduction Mechanism of Valence Change Resistive Switching Memory: A Survey

    Directory of Open Access Journals (Sweden)

    Ee Wah Lim

    2015-09-01

    Full Text Available Resistive switching effect in transition metal oxide (TMO based material is often associated with the valence change mechanism (VCM. Typical modeling of valence change resistive switching memory consists of three closely related phenomena, i.e., conductive filament (CF geometry evolution, conduction mechanism and temperature dynamic evolution. It is widely agreed that the electrochemical reduction-oxidation (redox process and oxygen vacancies migration plays an essential role in the CF forming and rupture process. However, the conduction mechanism of resistive switching memory varies considerably depending on the material used in the dielectric layer and selection of electrodes. Among the popular observations are the Poole-Frenkel emission, Schottky emission, space-charge-limited conduction (SCLC, trap-assisted tunneling (TAT and hopping conduction. In this article, we will conduct a survey on several published valence change resistive switching memories with a particular interest in the I-V characteristic and the corresponding conduction mechanism.

  3. Processing emotional pictures and words: effects of valence and arousal.

    Science.gov (United States)

    Kensinger, Elizabeth A; Schacter, Daniel L

    2006-06-01

    There is considerable debate regarding the extent to which limbic regions respond differentially to items with different valences (positive or negative) or to different stimulus types (pictures or words). In the present event-related fMRI study, 21 participants viewed words and pictures that were neutral, negative, or positive. Negative and positive items were equated on arousal. The participants rated each item for whether it depicted or described something animate or inanimate or something common or uncommon. For both pictures and words, the amygdala, dorsomedial prefrontal cortex (PFC), and ventromedial PFC responded equally to all high-arousal items, regardless of valence. Laterality effects in the amygdala were based on the stimulus type (word = left, picture = bilateral). Valence effects were most apparent when the individuals processed pictures, and the results revealed a lateral/medial distinction within the PFC: The lateral PFC responded differentially to negative items, whereas the medial PFC was more engaged during the processing of positive pictures.

  4. Valence-to-core-detected X-ray absorption spectroscopy

    DEFF Research Database (Denmark)

    Hall, Eleanor R.; Pollock, Christopher J.; Bendix, Jesper

    2014-01-01

    X-ray absorption spectroscopy (XAS) can provide detailed insight into the electronic and geometric structures of transition-metal active sites in metalloproteins and chemical catalysts. However, standard XAS spectra inherently represent an average contribution from the entire coordination...... environment with limited ligand selectivity. To address this limitation, we have investigated the enhancement of XAS features using valence-to-core (VtC)-detected XAS, whereby XAS spectra are measured by monitoring fluorescence from valence-to-core X-ray emission (VtC XES) events. VtC emission corresponds...... to transitions from filled ligand orbitals to the metal 1s core hole, with distinct energetic shifts for ligands of differing ionization potentials. VtC-detected XAS data were obtained from multiple valence emission features for a series of well-characterized Mn model compounds; taken together, these data...

  5. Density functional calculations of the properties of silicon-substituted hydroxyapatite.

    Science.gov (United States)

    Chappell, H F; Bristowe, P D

    2007-05-01

    Ab initio density functional plane-wave calculations are performed on silicon-substituted hydroxyapatite (SiHA). Formation energies are obtained for the substitution of a phosphorus atom by a silicon atom in each of the six phosphate groups of the unit cell in turn. It is found that the co-removal of a hydroxyl group to maintain charge neutrality is energetically favourable and the calculated unit cell volumes for the single silicon substitutions agree extremely well with experimental observation. The substitution of a second silicon atom in the unit cell is found to be almost as energetically favourable as the first (and on one site more favourable) and there can be an attractive interaction between the two Si substituents when they are closely separated. However, experimental observation suggests that for this concentration of silicon a phase transformation to a different structure occurs which, because of the imposed boundary conditions, could not be accessed in the calculations. The density of states of the SiHA indicates that new states are introduced deep into the valence band and the band gap decreases by 1.6 eV compared to phase-pure HA. No new states are introduced into the band gap indicating that the Si incorporation does not make the material inherently electrically active. Furthermore a population analysis shows that the Si impurity has only a small effect on the neighbouring ionic charge.

  6. Valence electron energy-loss spectroscopy in monochromated scanning transmission electron microscopy.

    Science.gov (United States)

    Erni, Rolf; Browning, Nigel D

    2005-10-01

    With the development of monochromators for (scanning) transmission electron microscopes, valence electron energy-loss spectroscopy (VEELS) is developing into a unique technique to study the band structure and optical properties of nanoscale materials. This article discusses practical aspects of spatially resolved VEELS performed in scanning transmission mode and the alignments necessary to achieve the current optimum performance of approximately 0.15 eV energy resolution with an electron probe size of approximately 1 nm. In particular, a collection of basic concepts concerning the acquisition process, the optimization of the energy resolution, the spatial resolution and the data processing are provided. A brief study of planar defects in a Y(1)Ba(2)Cu(3)O(7-)(delta) high-temperature superconductor illustrates these concepts and shows what kind of information can be accessed by VEELS.

  7. A hybrid density functional view of native vacancies in gallium nitride.

    Science.gov (United States)

    Gillen, Roland; Robertson, John

    2013-10-09

    We investigated the transition energy levels of the vacancy defects in gallium nitride by means of a hybrid density functional theory approach (DFT). We show that, in contrast to predictions from a recent study on the level of purely local DFT, the inclusion of screened exchange stabilizes the triply positive charge state of the nitrogen vacancy for Fermi energies close to the valence band. On the other hand, the defect levels associated with the negative charge states of the nitrogen vacancy hybridize with the conduction band and turn out to be energetically unfavorable, except for high n-doping. For the gallium vacancy, the increased magnetic splitting between up-spin and down-spin bands due to stronger exchange interactions in sX-LDA pushes the defect levels deeper into the band gap and significantly increases the associated charge transition levels. Based on these results, we propose the ϵ(0| - 1) transition level as an alternative candidate for the yellow luminescence in GaN.

  8. Representations of modality-general valence for videos and music derived from fMRI data.

    Science.gov (United States)

    Kim, Jongwan; Shinkareva, Svetlana V; Wedell, Douglas H

    2017-03-01

    This study tested for neural representations of valence that are shared across visual and auditory modalities referred to as modality-general representations. On a given trial participants made either affective or semantic judgments of short silent videos or music samples. For each modality valence was manipulated at three levels, positive, neutral, and negative, while controlling for the level of arousal. Whole-brain crossmodal identification of affect indicated the presence of modality-general valence representations that distinguished 1) positive from negative trials (signed valence) and 2) valenced from non-valenced trials (unsigned valence). These results generalized across the two tasks. Brain regions that were sensitive to valence states in the same way for both modalities were identified by searchlight analysis of fMRI data by comparing the correlation of voxel responses to the same and different valence conditions across the two modalities. These analyses identified seven clusters that distinguished signed valence, unsigned valence or both. Signed valence was represented in the precuneus, unsigned valence in the bilateral medial prefrontal cortex, superior temporal sulcus (STS)/postcentral, and middle frontal gyrus (MFG) and both types were represented in the STS/MFG and thalamus. These results support the idea that modality general valence is represented in a network of several locations throughout the brain. Copyright © 2017 Elsevier Inc. All rights reserved.

  9. Extraordinary Supercapacitor Performance of a Multicomponent and Mixed-Valence Oxyhydroxide.

    Science.gov (United States)

    Kang, Jianli; Hirata, Akihiko; Chen, Luyang; Zhu, Shengli; Fujita, Takeshi; Chen, Mingwei

    2015-07-06

    We report a novel multicomponent mixed-valence oxyhydroxide-based electrode synthesized by electrochemical polarization of a de-alloyed nanoporous NiCuMn alloy. The multicomponent oxyhydroxide has a high specific capacitance larger than 627 F cm(-3) (1097±95 F g(-1) ) at a current density of 0.25 A cm(-3) , originating from multiple redox reactions. More importantly, the oxyhydroxide electrode possesses an extraordinarily wide working-potential window of 1.8 V in an aqueous electrolyte, which far exceeds the theoretically stable window of water. The realization of both high specific capacitance and high working-potential windows gives rise to a high energy density, 51 mWh cm(-3) , of the multicomponent oxyhydroxide-based supercapacitor for high-energy and high-power applications. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. Energy-band structure in strained silicon: A 20-band kṡp and Bir-Pikus Hamiltonian model

    Science.gov (United States)

    Richard, Soline; Aniel, Frédéric; Fishman, Guy; Cavassilas, Nicolas

    2003-08-01

    A strain Bir-Pikus Hamiltonian Hst, associated with a 20-band sp3s* kṡp Hamiltonian Hkp, is used to describe the valence band and the first two conduction bands all over the Brillouin zone. Because the local (in k space) deformation potentials Ⅺu and Ⅺd used in pseudopotential method are unusable in kṡp theory, we show that taking into account the Bir-Pikus parameters (a, b) of the Brillouin zone center in the Hst Hamiltonian allows one to describe the dispersion relation in the whole Brillouin zone. The method is applied to strained Si on a relaxed Si1-xGex alloy. The values of the energy band gap, and of the Δ2-4 conduction band splitting between the four equivalent in-plane valleys Δ4 and the two valleys along the growth direction Δ2 are in very good agreement with those reported in other publications. The small value of the spin-orbit splitting in silicon is taken explicitly into account. We show that the valence band splitting is consequently not proportional to the stress.

  11. Gradient and vorticity banding

    NARCIS (Netherlands)

    Dhont, Jan K.G.; Briels, Willem J.

    2008-01-01

    "Banded structures" of macroscopic dimensions can be induced by simple shear flow in many different types of soft matter systems. Depending on whether these bands extend along the gradient or vorticity direction, the banding transition is referred to as "gradient banding" or "vorticity banding,"

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

    CERN Document Server

    Shields, P A

    2001-01-01

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

  13. Large spin splitting in the conduction band of transition metal dichalcogenide monolayers

    Science.gov (United States)

    Kośmider, K.; González, J. W.; Fernández-Rossier, J.

    2013-12-01

    We study the conduction band spin splitting that arises in transition metal dichalcogenide (TMD) semiconductor monolayers such as MoS2,MoSe2, WS2, and WSe2 due to the combination of spin-orbit coupling and lack of inversion symmetry. Two types of calculation are done. First, density functional theory (DFT) calculations based on plane waves that yield large splittings, between 3 and 30 meV. Second, we derive a tight-binding model that permits to address the atomic origin of the splitting. The basis set of the model is provided by the maximally localized Wannier orbitals, obtained from the DFT calculation, and formed by 11 atomiclike orbitals corresponding to d and p orbitals of the transition metal (W, Mo) and chalcogenide (S, Se) atoms respectively. In the resulting Hamiltonian, we can independently change the atomic spin-orbit coupling constant of the two atomic species at the unit cell, which permits to analyze their contribution to the spin splitting at the high symmetry points. We find that—in contrast to the valence band—both atoms give comparable contributions to the conduction band splittings. Given that these materials are most often n-doped, our findings are important for developments in TMD spintronics.

  14. Analysis Of Chemical Bonding Using Ab Initio Valence Bond Theory

    NARCIS (Netherlands)

    Engelberts, J.J.

    2017-01-01

    In this thesis, theoretical chemical research is presented in which the Valence Bond (VB) Theory plays a central role. For the last three chapters, the VB method is used, in combination with Magnetically Induced Ring Currents, to analyze the aromaticity of several conjugated molecules. The

  15. Language Civility, Immediacy and Peace Valence among Nigerian ...

    African Journals Online (AJOL)

    In addition, since interactions in the university, as in all human societies, are language driven, the language-based negotiation in the university can produce either harmony or discord. This study, thus, examined students' perception of university lecturers' immediacy and civility as they relate to peace valence of lecturers ...

  16. Emotional Valence and Arousal Effects on Memory and Hemispheric Asymmetries

    Science.gov (United States)

    Mneimne, Malek; Powers, Alice S.; Walton, Kate E.; Kosson, David S.; Fonda, Samantha; Simonetti, Jessica

    2010-01-01

    This study examined predictions based upon the right hemisphere (RH) model, the valence-arousal model, and a recently proposed integrated model (Killgore & Yurgelun-Todd, 2007) of emotion processing by testing immediate recall and recognition memory for positive, negative, and neutral verbal stimuli among 35 right-handed women. Building upon…

  17. "Plug-and-go" strategy to manipulate streptavidin valencies.

    Science.gov (United States)

    Sun, Xun; Montiel, Daniel; Li, Hao; Yang, Haw

    2014-08-20

    The streptavidin-biotin set is one of the most widely utilized conjugation pairs in biotechnological applications. The tetravalent nature of streptavidin and its homologues, however, tends to result in such undesirable complications as cross-linking or ill-defined stoichiometry. Here, we describe a mutagenesis-free strategy to manipulate the valencies of wild-type streptavidin that only requires commercially available reagents. The basic idea is simple: one obtains the desired streptavidin valency by blocking off unwanted binding sites using ancillary biotin ("plug"); this way, the extraordinary fM-biotin-binding affinity is fully retained for the remaining sites in streptavidin. In the present implementation, the ancillary biotin is attached to an auxiliary separation handle, negatively charged DNA or His-tagged protein, via a photochemically or enzymatically cleavable linker. Mixing streptavidin with the ancillary biotin construct produces a distribution of streptavidin valencies. The subsequent chromatographic separation readily isolates the construct of desired streptavidin valency, and the auxiliary handles are easily removed afterward ("go"). We demonstrate how this "plug-and-go" strategy allows a precise control for the compositions of streptavidin-biotin conjugates at the single-molecule level. This low-entry-barrier protocol could further expand the application scope of the streptavidin technology.

  18. Are valence and arousal separable in emotional experience?

    Science.gov (United States)

    Kron, Assaf; Pilkiw, Maryna; Banaei, Jasmin; Goldstein, Ariel; Anderson, Adam Keith

    2015-02-01

    The bipolar valence-arousal model of conscious experience of emotions is prominent in emotion research. In this work, we examine the validity of this model in the context of feelings elicited by visual stimuli. In particular, we examine whether arousal has a unique contribution over bivariate valence (separate measures for pleasure and displeasure) in explaining physiological arousal (electrodermal activity, EDA) and self-reported feelings at the level of item-specific responses across and within individuals. Our results suggest that self-reports of arousal have neither an advantage in predicting EDA nor make a unique contribution when valence is present in the model. Acceptance of the null hypothesis was confirmed with the use of the Bayesian information criterion. Arousal also showed no advantage over valence in predicting global feelings, but demonstrated a small unique component (1.5% to 4% of variance explained). These results have practical implications for both experimental design in the study of emotions and the underlying bases of their conscious experience. PsycINFO Database Record (c) 2015 APA, all rights reserved.

  19. Mn valence state and electrode performance of perovskite-type ...

    Indian Academy of Sciences (India)

    increase in the oxidation state of Mn ions was due to the formation of Mn4+ ions and oxygen vacancies. The addition of Cu ions to LSM systems could lead to enhanced electrode performance for oxygen reduction reactions originating from the change in valence of Mn ions. Keywords. Cu-doped LSM; electrical conductivity; ...

  20. Language Civility, Immediacy and Peace Valence among Nigerian ...

    African Journals Online (AJOL)

    Language Civility, Immediacy and Peace Valence among Nigerian University Academics. Alexander Essien Timothy, Vincent Ugah Uguma. Abstract. The Sustainable Development Goal (SDG) 16 seeks, in part, to “promote peaceful and inclusive societies for sustainable development ….” Since the university is a vital ...

  1. Effective valence as the control parameter of the superconducting ...

    African Journals Online (AJOL)

    In this paper, we have demonstrated that the effective valence of iron can be used as the control parameter to tune the Tc of this family of superconducting materials. This is achieved by postulating that our model of spin fluctuation which has been used to successfully account for the superconductivity in the cuprates in Ref.

  2. 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.

  3. Voice and Valency in San Luis Potosi Huasteco

    Science.gov (United States)

    Munoz Ledo Yanez, Veronica

    2014-01-01

    This thesis presents an analysis of the system of transitivity, voice and valency alternations in Huasteco of San Luis Potosi (Mayan) within a functional-typological framework. The study is based on spoken discourse and elicited data collected in the municipalities of Aquismon and Tancanhuitz de Santos in the state of San Luis Potosi, Mexico. The…

  4. verbal extensions: valency decreasing extensions in the basà ...

    African Journals Online (AJOL)

    Finance

    of the Basà language, data collected for this work include discourse ... Keywords: Basà language, reciprocal, reflexive, valency decreasing verbal .... a body part.” This definition may be associated with some inadequacies with regards to what reflexive actually means. For example, A may perform an action on B which may.

  5. Resonance and Aromaticity : An Ab Initio Valence Bond Approach

    NARCIS (Netherlands)

    Rashid, Zahid; van Lenthe, Joop H.; Havenith, Remco W. A.

    2012-01-01

    Resonance energy is one of the criteria to measure aromaticity. The effect of the use of different orbital models is investigated in the calculated resonance energies of cyclic conjugated hydrocarbons within the framework of the ab initio Valence Bond Self-Consistent Field (VBSCF) method. The VB

  6. Experimental evidence of photoinduced valence change of Fe 3 in ...

    Indian Academy of Sciences (India)

    Keywords. Photorefraction; electron paramagnetic resonance of Fe3+; BaTiO3; photo-electron paramagnetic resonance. Abstract. With a view to understanding the role of photo-induced valence changes of impurities in BaTiO3 in the phenomena of photorefraction, EPR experiments were conducted under in situ HeNe laser ...

  7. The effects of strong correlations on the band structure of Ag_8SnSe_6 argyrodite

    Directory of Open Access Journals (Sweden)

    S.V. Syrotyuk

    2016-12-01

    Full Text Available The electronic energy band spectra, as well as partial and total density of electronic states of the crystal argyrodite Ag_8SnSe_6 have been evaluated within the projector augmented waves (PAW approach by means of the ABINIT code. The one-electron energies have been evaluated using two functionals for exchange-correlation energy. The first one is the generalized gradient approximation (GGA approach. The second one is the hybrid functional PBE0 composed of the semilocal GGA part and Hartree-Fock exact exchange non-local energy for strongly correlated 4d electrons of Ag atom. The second approach eliminates the Coulomb self-interaction of the Ag 4d electrons. This leads to a significant restructuring of the energy bands in the filled valence part and to an improved location of the Ag 4d-states on the energy scale, and the resulting value of the band gap is well compared with experiment. The effects of strong correlation on the electronic structure of the crystal argyrodite are considered here for the first time.

  8. Determination of band offsets at strained NiO and MgO heterojunction for MgO as an interlayer in heterojunction light emitting diode applications

    Energy Technology Data Exchange (ETDEWEB)

    Singh, S.D., E-mail: devsh@rrcat.gov.in [Raja Ramanna Centre for Advanced Technology, Indore, Madhya Pradesh 452013 (India); Nand, Mangla [Bhabha Atomic Research Centre, Mumbai, Maharashtra 400085 (India); Ajimsha, R.S.; Upadhyay, Anuj; Kamparath, Rajiv; Mukherjee, C.; Misra, P.; Sinha, A.K. [Raja Ramanna Centre for Advanced Technology, Indore, Madhya Pradesh 452013 (India); Jha, S.N. [Bhabha Atomic Research Centre, Mumbai, Maharashtra 400085 (India); Ganguli, Tapas [Raja Ramanna Centre for Advanced Technology, Indore, Madhya Pradesh 452013 (India)

    2016-12-15

    Highlights: • Valence band offset at NiO/MgO heterojunction is experimentally determined. • Experimentally determined value of 2.3 ± 0.4 eV is significantly larger than the predicted from theoretical calculations. • The value of valence band offset is in corroboration with that estimated from the band transitivity model. • Our result can be used to predict accurately carrier transport and electroluminescence mechanisms for heterojunction LEDs. - Abstract: Valence band offset of 2.3 ± 0.4 eV at strained NiO/MgO heterojunction is determined from photoelectron spectroscopy (PES) measurements. The determined value of valence band offset is larger than that is predicted from first principle calculations, but is in corroboration with that obtained from band transitivity rule. Our PES result indicates a larger value of the valence band offset at strained NiO/MgO heterojunction and can be used to predict accurately carrier transport and electroluminescence mechanisms for n-ZnO/MgO/p-NiO and p-NiO/MgO/n-GaN heterojunction light emitting diodes.

  9. Electronic structure and positron annihilation in alkali metals: isolation of ionic core contribution and valence high-momentum components

    Energy Technology Data Exchange (ETDEWEB)

    Sob, M. (Ceskoslovenska Akademie Ved, Brno. Ustav Fyzikalni Metalurgie)

    1985-01-01

    Momentum densities of annihilation pairs from valence as well as from ionic core electrons in alkali metals are calculated ab initio and compared with the experimental results. It is shown that the valence high-momentum components constitute a great deal (23-34% in Na-Cs and probably even more in Li) of the Gaussian part of the angular correlation curves. The average core enhancement factor ..gamma..sub(c) ranges from 1.5 (Li) to 7.1 (Cs) and may be well expressed by a logarithmic function of ionic core polarizability. The presented values of ..gamma..sub(c) are much higher than the core enhancement factors in the high-momentum (> approx. 15 mrad) region which, according to the recent theory of Bonderup, Andersen and Lowy, should not be very different from unity.

  10. Band structure and thermoelectric properties of half-Heusler semiconductors from many-body perturbation theory

    Science.gov (United States)

    Zahedifar, Maedeh; Kratzer, Peter

    2018-01-01

    Various ab initio approaches to the band structure of A NiSn and A CoSb half-Heusler compounds (A = Ti, Zr, Hf) are compared and their consequences for the prediction of thermoelectric properties are explored. Density functional theory with the generalized-gradient approximation (GGA), as well as the hybrid density functional HSE06 and ab initio many-body perturbation theory in the form of the G W0 approach, are employed. The G W0 calculations confirm the trend of a smaller band gap (0.75 to 1.05 eV) in A NiSn compared to the A CoSb compounds (1.13 to 1.44 eV) already expected from the GGA calculations. While in A NiSn materials the G W0 band gap is 20% to 50% larger than in HSE06, the fundamental gap of A CoSb materials is smaller in G W0 compared to HSE06. This is because G W0 , similar to PBE, locates the valence band maximum at the L point of the Brillouin zone, whereas it is at the Γ point in the HSE06 calculations. The differences are attributed to the observation that the relative positions of the d levels of the transition metal atoms vary among the different methods. Using the calculated band structures and scattering rates taking into account the band effective masses at the extrema, the Seebeck coefficients, thermoelectric power factors, and figures of merit Z T are predicted for all six half-Heusler compounds. Comparable performance is predicted for the n -type A NiSn materials, whereas clear differences are found for the p -type A CoSb materials. Using the most reliable G W0 electronic structure, ZrCoSb is predicted to be the most efficient material with a power factor of up to 0.07 W/(K2 m) at a temperature of 600 K. We find strong variations among the different ab initio methods not only in the prediction of the maximum power factor and Z T value of a given material, but also in comparing different materials to each other, in particular in the p -type thermoelectric materials. Thus we conclude that the most elaborate, but also most costly G W0

  11. Diet after gastric banding

    Science.gov (United States)

    Gastric banding surgery - your diet; Obesity - diet after banding; Weight loss - diet after banding ... about any problems you are having with your diet, or about other issues related to your surgery ...

  12. Correlation between valence state of tin and elastic modulus of Sn-doped Li2O-B2O3-SiO2 glasses

    Science.gov (United States)

    Masai, Hirokazu; Matsumoto, Syuji; Ueda, Yuki; Koreeda, Akitoshi

    2016-05-01

    The correlation between the longitudinal elastic modulus c11 and tin valence state in Li2O-B2O3-SiO2 ternary glasses is investigated. Substitution of B2O3 for SiO2 increases the glass-transition temperature and c11 but decreases the melting temperature. 119Sn Mössbauer spectra show that the valence state of tin increased with increasing molten temperature, Tmolten, in air, and that it also affects the c11 value even though the 1.0 mol. % addition. The c11 values, whose error bars are governed by those of density, suggest that the addition of SnO2 increases c11 whereas SnO decreases. The relationship between Tmolten and the amount of Sn2+ suggests that the main factor affecting the tin valence state is oxygen, whose reactivity may correlate with the glass melt viscosity.

  13. Band structure of wurtzite quantum dots with cylindrical symmetry

    Science.gov (United States)

    Voon, Lok Lew Yan; Galeriu, Calin; Lassen, Benny

    2005-03-01

    A six-band k .p theory for wurtzite semiconductor nanostructures with cylindrical symmetry will be presented. Our work extends the formulation of Vahala and Sercel [Phys. Rev. Lett. 65, 239 (1990)] to the Rashba-Sheka-Pikus Hamiltonian for wurtzite semiconductors, without the need for the axial approximation. Results comparing this new formulation for studying the electronic structure of wurzite GaN and CdS cylindrical quantum dots with the conventional formulation will be shown; our formulation is computationally superior. An application to the search for level crossing in the valence band of cylindrical quantum rods as a function of aspect ratio will be given. Supported by NSF CAREER award.

  14. Band Structure Analysis of La0.7Sr0.3MnO3 Perovskite Manganite Using a Synchrotron

    Directory of Open Access Journals (Sweden)

    Hong-Sub Lee

    2015-01-01

    Full Text Available Oxide semiconductors and their application in next-generation devices have received a great deal of attention due to their various optical, electric, and magnetic properties. For various applications, an understanding of these properties and their mechanisms is also very important. Various characteristics of these oxides originate from the band structure. In this study, we introduce a band structure analysis technique using a soft X-ray energy source to study a La0.7Sr0.3MnO3 (LSMO oxide semiconductor. The band structure is formed by a valence band, conduction band, band gap, work function, and electron affinity. These can be determined from secondary electron cut-off, valence band spectrum, O 1s core electron, and O K-edge measurements using synchrotron radiation. A detailed analysis of the band structure of the LSMO perovskite manganite oxide semiconductor thin film was established using these techniques.

  15. High saturation intensity in InAs/GaAs quantum dot solar cells and impact on the realization of the intermediate band concept at room-temperature

    Science.gov (United States)

    Li, Tian; Dagenais, Mario

    2017-02-01

    High optical saturation intensity at room temperature is reported for an ensemble of undoped quantum dots. The non-linearity of the light-generated-current under resonant excitation from the valence band to the intermediate band is shown to be made up of two components: a background two-photon absorption term and a resonant optical saturation term. It is argued that the solar intensity is much lower than the saturation intensities involved for the first and second transitions in the intermediate band solar cell under 1-sun illumination and therefore prevents exciting an appreciable amount of population in the terminal level that can be ionized to the continuum and generate an appreciable additional current. This additional current is required for enhancing the energy conversion efficiency of a solar cell based on the intermediate band concept. Operating at cryogenic temperatures leads to a reduction in the saturation intensity but it might not be sufficient for increasing the energy conversion efficiency, unless concentrated sun light, and/or high density of quantum dots, and/or quantum dots with a lifetime more comparable to the radiative lifetime are used. The conclusions of this paper are also expected to apply to other quantum dot systems.

  16. Band structure and photocatalytic activities for H{sub 2} production of ABi{sub 2}Nb{sub 2}O{sub 9} (A = Ca, Sr, Ba)

    Energy Technology Data Exchange (ETDEWEB)

    Li, Yingxuan; Chen, Gang; Zhang, Hongjie; Lv, Zushun [Department of Applied Chemistry, Harbin Institute of Technology, Harbin 150001 (China)

    2010-04-15

    A new series of layered perovskite photocatalysts, ABi{sub 2}Nb{sub 2}O{sub 9} (A = Ca, Sr, Ba), were synthesized by the conventional solid-state reaction method and characterized by X-ray diffraction (XRD) and UV-visible spectrometer. The results showed that the structure of ABi{sub 2}Nb{sub 2}O{sub 9} (A = Ca, Sr) is orthorhombic, while that of BaBi{sub 2}Nb{sub 2}O{sub 9} is tetragonal. The band gaps of CaBi{sub 2}Nb{sub 2}O{sub 9}, SrBi{sub 2}Nb{sub 2}O{sub 9}, and BaBi{sub 2}Nb{sub 2}O{sub 9} were estimated to be 3.46, 3.43, and 3.30 eV, respectively. It was found from the electronic band structure study, using the density functional theory (DFT) with planewave basis, that the conduction bands of these photocatalysts mainly consist of Nb 4d + Bi 6p + O 2p orbitals and the valence bands are composed of hybridization with O 2p + Nb 4d + Bi 6s orbitals. The photocatalytic activities for water splitting were investigated under UV-light irradiation and indicated that these photocatalysts showed photocatalytic activity for H{sub 2} and O{sub 2} evolution from aqueous solutions containing sacrificial reagents (methanol and Ag{sup +}). (author)

  17. Electronic properties and charge density of BexZn1− xTe alloys

    Indian Academy of Sciences (India)

    Electronic band structure calculations are performed for the BeZn1−Te (0 ≤ ≤ 1 in steps of 0.2) alloys following the empirical pseudopotential method. The alloying effects are modelled through the modified virtual crystal approximation. Throughout the composition, valence band maximum resides at the point.

  18. Z2 gauge theory for valence bond solids on the kagome lattice

    Science.gov (United States)

    Hwang, Kyusung; Huh, Yejin; Kim, Yong Baek

    We present an effective Z2 gauge theory that captures various competing phases in spin-1/2 kagome lattice antiferromagnets: the topological Z2 spin liquid (SL) phase, and the 12-site and 36- site valence bond solid (VBS) phases. Our effective theory is a generalization of the recent Z2 gauge theory proposed for SL phases by Wan and Tchernyshyov. In particular, we investigate possible VBS phases that arise from vison condensations in the SL. In addition to the 12-site and 36-site VBS phases, there exists 6-site VBS that is closely related to the symmetry-breaking valence bond modulation patterns observed in the recent density matrix renormalization group simulations. We find that our results have remarkable consistency with a previous study using a different Z2 gauge theory. Motivated by the lattice geometry in the recently reported vanadium oxyfluoride kagome antiferromagnet, our gauge theory is extended to incorporate lowered symmetry by inequivalent up- and down-triangles. We investigate effects of this anisotropy on the 12-site, 36-site, and 6-site VBS phases. Particularly, interesting dimer melting effects are found in the 36-site VBS. We discuss the implications of our findings and also compare the results with a different type of Z2 gauge theory used in previous studies.

  19. Influence of band offset, nanostructuring, and applied electric field on the optoelectronic properties of vertically stacked MoS2/WS2 materials

    Science.gov (United States)

    Mlinar, Vladan

    2017-12-01

    We theoretically investigate the electronic and optical properties of multilayer vertically stacked MoS2/WS2 heterostructures, focusing on the role of the MoS2-WS2 band offset, number of monolayers in the heterostructure, effects of an applied electric field, and size reduction in lateral direction, leading to MoS2/WS2 -based nanowires and nanoplatelets. Given that different values of the MoS2-WS2 band offset have been reported, we show that the band offset determines the ordering of the energy levels in the valence band and spin projections at the K point of the Brillouin zone. These variations as function of the value of the band offset are suppressed in an external electric field. For multilayer MoS2/WS2 -based nanostructures, our calculations reveal nanowires and nanoplatelets with S-atom edges exhibit a metallic character, but nanowires with one S-atom and other Mo/W edge show the band gap with electrons located in MoS2 and holes in WS2 layer. The band gap can be controlled by the size of the nanowire in lateral direction and number of layers. The calculated real part of optical conductivity show that the lowest optical transitions originate from the optical transitions in MoS2 layers. The electronic structure is obtained from a parametrized tight-binding model that includes nonorthogonal sp 3d5 orbitals and spin orbit coupling. Our results are gauged with respect to those extracted from density functional theory and G W methods to ensure the high quality of our predictions.

  20. Valenced Cues and Contexts Have Different Effects on Event-Based Prospective Memory

    OpenAIRE

    Peter Graf; Martin Yu

    2015-01-01

    This study examined the separate influence and joint influences on event-based prospective memory task performance due to the valence of cues and the valence of contexts. We manipulated the valence of cues and contexts with pictures from the International Affective Picture System. The participants, undergraduate students, showed higher performance when neutral compared to valenced pictures were used for cueing prospective memory. In addition, neutral pictures were more effective as cues when ...

  1. Approach and withdrawal tendencies during written word processing: effects of task, emotional valence and emotional arousal

    OpenAIRE

    Citron, Francesca M. M.; Abugaber, David; Herbert, Cornelia

    2016-01-01

    The affective dimensions of emotional valence and emotional arousal affect processing of verbal and pictorial stimuli. Traditional emotional theories assume a linear relationship between these dimensions, with valence determining the direction of a behaviour (approach vs. withdrawal) and arousal its intensity or strength. In contrast, according to the valence-arousal conflict theory, both dimensions are interactively related: positive valence and low arousal (PL) are associated with an implic...

  2. Tuning of electronic band gaps and optoelectronic properties of binary strontium chalcogenides by means of doping of magnesium atom(s)- a first principles based theoretical initiative with mBJ, B3LYP and WC-GGA functionals

    Science.gov (United States)

    Debnath, Bimal; Sarkar, Utpal; Debbarma, Manish; Bhattacharjee, Rahul; Chattopadhyaya, Surya

    2018-02-01

    First principle based theoretical initiative is taken to tune the optoelectronic properties of binary strontium chalcogenide semiconductors by doping magnesium atom(s) into their rock-salt unit cells at specific concentrations x = 0.0, 0.25, 0.50, 0.75 and 1.0 and such tuning is established by studying structural, electronic and optical properties of designed binary compounds and ternary alloys employing WC-GGA, B3LYP and mBJ exchange-correlation functionals. Band structure of each compound is constructed and respective band gaps under all the potential schemes are measured. The band gap bowing and its microscopic origin are calculated using quadratic fit and Zunger's approach, respectively. The atomic and orbital origins of electronic states in the band structure of any compound are explored from its density of states. The nature of chemical bonds between the constituent atoms in each compound is explored from the valence electron density contour plots. Optical properties of any specimen are explored from the computed spectra of its dielectric function, refractive index, extinction coefficient, normal incidence reflectivity, optical conductivity optical absorption and energy loss function. Several calculated results are compared with available experimental and earlier theoretical data.

  3. Mapping of valence energy losses via energy-filtered annular dark-field scanning transmission electron microscopy.

    Science.gov (United States)

    Gu, Lin; Sigle, Wilfried; Koch, Christoph T; Nelayah, Jaysen; Srot, Vesna; van Aken, Peter A

    2009-08-01

    The advent of electron monochromators has opened new perspectives on electron energy-loss spectroscopy at low energy losses, including phenomena such as surface plasmon resonances or electron transitions from the valence to the conduction band. In this paper, we report first results making use of the combination of an energy filter and a post-filter annular dark-field detector. This instrumental design allows us to obtain energy-filtered (i.e. inelastic) annular dark-field images in scanning transmission electron microscopy of the 2-dimensional semiconductor band-gap distribution of a GaN/Al(45)Ga(55)N structure and of surface plasmon resonances of silver nanoprisms. In comparison to other approaches, the technique is less prone to inelastic delocalization and relativistic artefacts. The mixed contribution of elastic and inelastic contrast is discussed.

  4. Work Valence as a Predictor of Academic Achievement in the Family Context

    Science.gov (United States)

    Porfeli, Erik; Ferrari, Lea; Nota, Laura

    2013-01-01

    This study asserts a theoretical model of academic and work socialization within the family setting. The presumed associations between parents' work valences, children's work valences and valence perceptions, and children's academic interest and achievement are tested. The results suggest that children's perceptions of parents mediate the…

  5. 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…

  6. Distinct Brain Systems Underlie the Processing of Valence and Arousal of Affective Pictures

    Science.gov (United States)

    Nielen, M. M. A.; Heslenfeld, D. J.; Heinen, K.; Van Strien, J. W.; Witter, M. P.; Jonker, C.; Veltman, D. J.

    2009-01-01

    Valence and arousal are thought to be the primary dimensions of human emotion. However, the degree to which valence and arousal interact in determining brain responses to emotional pictures is still elusive. This functional MRI study aimed to delineate neural systems responding to valence and arousal, and their interaction. We measured neural…

  7. Magnetic-field-induced valence transition in rare-earth systems

    Indian Academy of Sciences (India)

    loys are induced by pressure, temperature or chemical alloying. The change in the valence state of rare-earth ion is found to be either continuous or discontinuous. One of the com- mon features of all the systems which show valence instabilities is that, in the intermediate valence phase, the system fluctuates between a ...

  8. 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…

  9. Distinct brain systems underlie the processing of valence and arousal of affective pictures

    NARCIS (Netherlands)

    Nielen, M. M. A.; Heslenfeld, D. J.; Heinen, K.; van Strien, J. W.; Witter, M. P.; Jonker, C.; Veltman, D. J.

    2009-01-01

    Valence and arousal are thought to be the primary dimensions of human emotion. However, the degree to which valence and arousal interact in determining brain responses to emotional pictures is still elusive. This functional MRI study aimed to delineate neural systems responding to valence and

  10. Electronic energy band parameters of CsCl evaluated on core Bloch states and plane waves

    Energy Technology Data Exchange (ETDEWEB)

    Syrotyuk, S.V. [Semiconductor Electronics Department, National University ' Lviv Polytechnic' , S. Bandera str. 12, Lviv 79013 (Ukraine); Chornodolskyy, Ya.M. [Physics Department, Ivan Franko National University of Lviv, Kyryla i Mefodiya str. 8, Lviv 79005 (Ukraine)], E-mail: chornodolsky@ukr.net; Stryganyuk, G.B. [HASYLAB at DESY, Notkestr. 85, Hamburg 22607 (Germany); Voloshinovskii, A.S. [Physics Department, Ivan Franko National University of Lviv, Kyryla i Mefodiya str. 8, Lviv 79005 (Ukraine); Rodnyi, P.A. [St. Petersburg State Polytechnical University, Polytekhnicheskaya 29, St. Petersburg 195251 (Russian Federation)

    2007-04-15

    Electronic energy bands of CsCl crystal have been calculated within the mixed basis approach with using the core Bloch states and plane waves. The calculated energy parameters of the crystal are in the satisfactory agreement with the experimental data obtained from the analysis of the core-valence luminescence spectra. The obtained results form a base for calculation of CVL spectra parameters.

  11. Unoccupied band structure of wurtzite GaN(0001)

    Energy Technology Data Exchange (ETDEWEB)

    Valla, T.; Johnson, P.D. [Department of Physics, Brookhaven National Laboratory, Upton, New York 11973 (United States); Dhesi, S.S.; Smith, K.E. [Department of Physics, Boston University, Boston, Massachusetts 02215 (United States); Doppalapudi, D.; Moustakas, T.D. [Department of Electrical and Computer Engineering, Boston University, Boston, Massachusetts 02215 (United States); Shirley, E.L. [NIST, PHY B208, Gaithersburg, Maryland 20899 (United States)

    1999-02-01

    We report an inverse photoemission study of the unoccupied states of thin-film {ital n}-type wurtzite GaN. For incident electron energies below 30 eV, free-electron bands do not provide a good description of the initial state. However, using a calculated quasiparticle band structure for the initial state, we can obtain good agreement between our measurements and the calculated low-lying conduction bands. No evidence of unoccupied surface states is observed in the probed part of the Brillouin zone, confirming earlier angle resolved photoemission studies, which identified the surface states on GaN(0001) as occupied dangling bond states, resonant with the valence band. {copyright} {ital 1999} {ital The American Physical Society}

  12. Dirac Cones, Topological Edge States, and Nontrivial Flat Bands in Two-Dimensional Semiconductors with a Honeycomb Nanogeometry

    Directory of Open Access Journals (Sweden)

    E. Kalesaki

    2014-01-01

    Full Text Available We study theoretically two-dimensional single-crystalline sheets of semiconductors that form a honeycomb lattice with a period below 10 nm. These systems could combine the usual semiconductor properties with Dirac bands. Using atomistic tight-binding calculations, we show that both the atomic lattice and the overall geometry influence the band structure, revealing materials with unusual electronic properties. In rocksalt Pb chalcogenides, the expected Dirac-type features are clouded by a complex band structure. However, in the case of zinc-blende Cd-chalcogenide semiconductors, the honeycomb nanogeometry leads to rich band structures, including, in the conduction band, Dirac cones at two distinct energies and nontrivial flat bands and, in the valence band, topological edge states. These edge states are present in several electronic gaps opened in the valence band by the spin-orbit coupling and the quantum confinement in the honeycomb geometry. The lowest Dirac conduction band has S-orbital character and is equivalent to the π-π^{⋆} band of graphene but with renormalized couplings. The conduction bands higher in energy have no counterpart in graphene; they combine a Dirac cone and flat bands because of their P-orbital character. We show that the width of the Dirac bands varies between tens and hundreds of meV. These systems emerge as remarkable platforms for studying complex electronic phases starting from conventional semiconductors. Recent advancements in colloidal chemistry indicate that these materials can be synthesized from semiconductor nanocrystals.

  13. The chemical bond in inorganic chemistry the bond valence model

    CERN Document Server

    Brown, I David

    2016-01-01

    The bond valence model is a version of the ionic model in which the chemical constraints are expressed in terms of localized chemical bonds formed by the valence charge of the atoms. Theorems derived from the properties of the electrostatic flux predict the rules obeyed by both ionic and covalent bonds. They make quantitative predictions of coordination number, crystal structure, bond lengths and bond angles. Bond stability depends on the matching of the bonding strengths of the atoms, while the conflicting requirements of chemistry and space lead to the structural instabilities responsible for the unusual physical properties displayed by some materials. The model has applications in many fields ranging from mineralogy to molecular biology.

  14. Emotional valence and arousal interact in attentional control.

    Science.gov (United States)

    Jefferies, Lisa N; Smilek, Daniel; Eich, Eric; Enns, James T

    2008-03-01

    A recent study demonstrated that observers' ability to identify targets in a rapid visual sequence was enhanced when they simultaneously listened to happy music. In the study reported here, we examined how the emotion-attention relationship is influenced by changes in both mood valence (negative vs. positive) and arousal (low vs. high). We used a standard induction procedure to generate calm, happy, sad, and anxious moods in participants. Results for an attentional blink task showed no differences in first-target accuracy, but second-target accuracy was highest for participants with low arousal and negative affect (sad), lowest for those with strong arousal and negative affect (anxious), and intermediate for those with positive affect regardless of their arousal (calm, happy). We discuss implications of this valence-arousal interaction for the control of visual attention.

  15. Nitric acid oxidation of Si to form ultrathin silicon dioxide layers with a low leakage current density

    Science.gov (United States)

    Kobayashi Asuha, Hikaru; Maida, Osamu; Takahashi, Masao; Iwasa, Hitoo

    2003-12-01

    Ultrathin silicon dioxide (SiO2) layers with excellent electrical characteristics can be formed using the nitric acid oxidation of Si (NAOS) method, i.e., by immersion of Si in nitric acid (HNO3) solutions. The SiO2 layer formed with 61 wt % HNO3 at its boiling temperature of 113 °C has a 1.3 nm thickness with a considerably high density leakage current. When the SiO2 layer is formed in 68 wt % HNO3 (i.e., azeotropic mixture with water), on the other hand, the leakage current density (e.g., 1.5 A/cm2 at the forward gate bias, VG, of 1 V) becomes as low as that of thermally grown SiO2 layers, in spite of the nearly identical SiO2 thickness of 1.4 nm. Due to the relatively low leakage current density of the NAOS oxide layer, capacitance-voltage (C-V) curves can be measured in spite of the ultrathin oxide thickness. However, a hump is present in the C-V curve, indicating the presence of high-density interface states. Fourier transformed infrared absorption measurements show that the atomic density of the SiO2 layers increases by 7% with an increase in the HNO3 concentration from 61 to 68 wt %. Measurements of valence band spectra clarify that this concentration increase causes the enhancement of the valence band discontinuity at the Si/SiO2 interface from 4.1 to 4.3 eV. When postmetallization annealing (PMA) treatment is performed at 400 °C in hydrogen on chemical SiO2/Si(100)> metal-oxide-semiconductor diodes, the leakage current density markedly increases, and this increase is attributed to a reaction between the Al electrode and the chemical SiO2 layer, resulting in a decrease in the SiO2 thickness. With PMA at 200 °C in hydrogen, on the other hand, the SiO2 thickness decreases only slightly to 1.3 nm. In this case, the leakage current density greatly decreases (e.g., 0.4 A/cm2 at VG=1 V and 5×10-3 A/cm2 at VG=-1 V), and consequently it becomes 1/3-1/10 of those for thermally grown SiO2 layers with the same thickness. The hump in the C-V curves disappears after

  16. Human Amygdala Tracks a Feature-Based Valence Signal Embedded within the Facial Expression of Surprise.

    Science.gov (United States)

    Kim, M Justin; Mattek, Alison M; Bennett, Randi H; Solomon, Kimberly M; Shin, Jin; Whalen, Paul J

    2017-09-27

    Human amygdala function has been traditionally associated with processing the affective valence (negative vs positive) of an emotionally charged event, especially those that signal fear or threat. However, this account of human amygdala function can be explained by alternative views, which posit that the amygdala might be tuned to either (1) general emotional arousal (activation vs deactivation) or (2) specific emotion categories (fear vs happy). Delineating the pure effects of valence independent of arousal or emotion category is a challenging task, given that these variables naturally covary under many circumstances. To circumvent this issue and test the sensitivity of the human amygdala to valence values specifically, we measured the dimension of valence within the single facial expression category of surprise. Given the inherent valence ambiguity of this category, we show that surprised expression exemplars are attributed valence and arousal values that are uniquely and naturally uncorrelated. We then present fMRI data from both sexes, showing that the amygdala tracks these consensus valence values. Finally, we provide evidence that these valence values are linked to specific visual features of the mouth region, isolating the signal by which the amygdala detects this valence information. SIGNIFICANCE STATEMENT There is an open question as to whether human amygdala function tracks the valence value of cues in the environment, as opposed to either a more general emotional arousal value or a more specific emotion category distinction. Here, we demonstrate the utility of surprised facial expressions because exemplars within this emotion category take on valence values spanning the dimension of bipolar valence (positive to negative) at a consistent level of emotional arousal. Functional neuroimaging data showed that amygdala responses tracked the valence of surprised facial expressions, unconfounded by arousal. Furthermore, a machine learning classifier identified

  17. Continuum-limit scaling of overlap fermions as valence quarks

    Energy Technology Data Exchange (ETDEWEB)

    Cichy, Krzysztof [Adam Mickiewicz Univ., Poznan (Poland). Faculty of Physics; Herdoiza, Gregorio; Jansen, Karl [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany). John von Neumann-Inst. fuer Computing NIC

    2009-10-15

    We present the results of a mixed action approach, employing dynamical twisted mass fermions in the sea sector and overlap valence fermions, with the aim of testing the continuum limit scaling behaviour of physical quantities, taking the pion decay constant as an example. To render the computations practical, we impose for this purpose a fixed finite volume with lattice size L{approx}1.3 fm. We also briefly review the techniques we have used to deal with overlap fermions. (orig.)

  18. Quantum Phase Transitions around the Staggered Valence Bond Solid

    OpenAIRE

    Xu, Cenke; Balents, Leon

    2011-01-01

    Motivated by recent numerical results, we study the quantum phase transitions between Z_2 spin liquid, Neel ordered, and various valence bond solid (VBS) states on the honeycomb and square lattices, with emphasis on the staggered VBS. In contrast to the well-understood columnar VBS order, the staggered VBS is not described by an XY order parameter with Z_N anisotropy close to these quantum phase transitions. Instead, we demonstrate that on the honeycomb lattice, the staggered VBS is more appr...

  19. 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...

  20. Feedback Valence Affects Auditory Perceptual Learning Independently of Feedback Probability

    Science.gov (United States)

    Amitay, Sygal; Moore, David R.; Molloy, Katharine; Halliday, Lorna F.

    2015-01-01

    Previous studies have suggested that negative feedback is more effective in driving learning than positive feedback. We investigated the effect on learning of providing varying amounts of negative and positive feedback while listeners attempted to discriminate between three identical tones; an impossible task that nevertheless produces robust learning. Four feedback conditions were compared during training: 90% positive feedback or 10% negative feedback informed the participants that they were doing equally well, while 10% positive or 90% negative feedback informed them they were doing equally badly. In all conditions the feedback was random in relation to the listeners’ responses (because the task was to discriminate three identical tones), yet both the valence (negative vs. positive) and the probability of feedback (10% vs. 90%) affected learning. Feedback that informed listeners they were doing badly resulted in better post-training performance than feedback that informed them they were doing well, independent of valence. In addition, positive feedback during training resulted in better post-training performance than negative feedback, but only positive feedback indicating listeners were doing badly on the task resulted in learning. As we have previously speculated, feedback that better reflected the difficulty of the task was more effective in driving learning than feedback that suggested performance was better than it should have been given perceived task difficulty. But contrary to expectations, positive feedback was more effective than negative feedback in driving learning. Feedback thus had two separable effects on learning: feedback valence affected motivation on a subjectively difficult task, and learning occurred only when feedback probability reflected the subjective difficulty. To optimize learning, training programs need to take into consideration both feedback valence and probability. PMID:25946173

  1. Tunable Se vacancy defects and the unconventional charge density wave in 1 T -TiSe2 -δ

    Science.gov (United States)

    Huang, S. H.; Shu, G. J.; Pai, Woei Wu; Liu, H. L.; Chou, F. C.

    2017-01-01

    A systematic study of polycrystalline 1 T -TiSe2 -δ with controlled Se loss indicates that the unconventional charge density wave (CDW) phase is found to be most pronounced in samples with δ ˜0.12 , instead of being Se vacancy free. The level of Se vacancy defects and temperature determines whether 1 T -TiSe2 -δ should be categorized as a semiconductor, a semimetal, or an excitonic insulator. An interpretation using a general band picture of p -type doped narrow-band-gap semiconductor with an impurity band (IB) in proximity to the valence band (VB) is proposed to explain the evolution of electronic structures for 1 T -TiSe2 -δ , from the intermediate doping of δ ˜0.08 , to the critical doping of δ ˜0.12 showing an anomalous resistivity peak between ˜100 -200 K , and to the heavily doped of δ ˜0.17 as an n -type degenerate semiconductor. Integrated chemical analysis and physical property characterization, including electron probe microanalysis (EPMA), synchrotron x-ray diffraction, resistivity, and Seebeck coefficient measurement results are provided for the polycrystalline samples prepared via vacuum-sealed high temperature annealing route.

  2. 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, Hπv(x,ξ,t. Our analysis focuses primarily on ξ=0, although we also capitalise on the symmetry-preserving nature of the RL truncation by connecting Hπv(x,ξ=±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 Hπv(x,0,t, expressed as the Radon transform of a single amplitude. Therewith we obtain results for Hπv(x,0,t and the associated impact-parameter dependent distribution, qπv(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 ζ=2 GeV, so as to facilitate comparisons in future with results from experiment or other nonperturbative methods.

  3. 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, qπ(x; namely, at a characteristic hadronic scale, qπ(x∼(1−x2 for x≳0.85; and the valence-quarks carry approximately two-thirds of the pion's light-front momentum.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1996-01-01

    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.

  5. Modeling direct band-to-band tunneling: From bulk to quantum-confined semiconductor devices

    Energy Technology Data Exchange (ETDEWEB)

    Carrillo-Nuñez, H.; Ziegler, A.; Luisier, M.; Schenk, A. [Integrated Systems Laboratory ETH Zürich, Gloriastrasse 35, 8092 Zürich (Switzerland)

    2015-06-21

    A rigorous framework to study direct band-to-band tunneling (BTBT) in homo- and hetero-junction semiconductor nanodevices is introduced. An interaction Hamiltonian coupling conduction and valence bands (CVBs) is derived using a multiband envelope method. A general form of the BTBT probability is then obtained from the linear response to the “CVBs interaction” that drives the system out of equilibrium. Simple expressions in terms of the one-electron spectral function are developed to compute the BTBT current in two- and three-dimensional semiconductor structures. Additionally, a two-band envelope equation based on the Flietner model of imaginary dispersion is proposed for the same purpose. In order to characterize their accuracy and differences, both approaches are compared with full-band, atomistic quantum transport simulations of Ge, InAs, and InAs-Si Esaki diodes. As another numerical application, the BTBT current in InAs-Si nanowire tunnel field-effect transistors is computed. It is found that both approaches agree with high accuracy. The first one is considerably easier to conceive and could be implemented straightforwardly in existing quantum transport tools based on the effective mass approximation to account for BTBT in nanodevices.

  6. Valenced cues and contexts have different effects on event-based prospective memory.

    Science.gov (United States)

    Graf, Peter; Yu, Martin

    2015-01-01

    This study examined the separate influence and joint influences on event-based prospective memory task performance due to the valence of cues and the valence of contexts. We manipulated the valence of cues and contexts with pictures from the International Affective Picture System. The participants, undergraduate students, showed higher performance when neutral compared to valenced pictures were used for cueing prospective memory. In addition, neutral pictures were more effective as cues when they occurred in a valenced context than in the context of neutral pictures, but the effectiveness of valenced cues did not vary across contexts that differed in valence. The finding of an interaction between cue and context valence indicates that their respective influence on event-based prospective memory task performance cannot be understood in isolation from each other. Our findings are not consistent with by the prevailing view which holds that the scope of attention is broadened and narrowed, respectively, by positively and negatively valenced stimuli. Instead, our findings are more supportive of the recent proposal that the scope of attention is determined by the motivational intensity associated with valenced stimuli. Consistent with this proposal, we speculate that the motivational intensity associated with different retrieval cues determines the scope of attention, that contexts with different valence values determine participants' task engagement, and that prospective memory task performance is determined jointly by attention scope and task engagement.

  7. Valenced cues and contexts have different effects on event-based prospective memory.

    Directory of Open Access Journals (Sweden)

    Peter Graf

    Full Text Available This study examined the separate influence and joint influences on event-based prospective memory task performance due to the valence of cues and the valence of contexts. We manipulated the valence of cues and contexts with pictures from the International Affective Picture System. The participants, undergraduate students, showed higher performance when neutral compared to valenced pictures were used for cueing prospective memory. In addition, neutral pictures were more effective as cues when they occurred in a valenced context than in the context of neutral pictures, but the effectiveness of valenced cues did not vary across contexts that differed in valence. The finding of an interaction between cue and context valence indicates that their respective influence on event-based prospective memory task performance cannot be understood in isolation from each other. Our findings are not consistent with by the prevailing view which holds that the scope of attention is broadened and narrowed, respectively, by positively and negatively valenced stimuli. Instead, our findings are more supportive of the recent proposal that the scope of attention is determined by the motivational intensity associated with valenced stimuli. Consistent with this proposal, we speculate that the motivational intensity associated with different retrieval cues determines the scope of attention, that contexts with different valence values determine participants' task engagement, and that prospective memory task performance is determined jointly by attention scope and task engagement.

  8. Estimating valence from the sound of a word: Computational, experimental, and cross-linguistic evidence.

    Science.gov (United States)

    Louwerse, Max; Qu, Zhan

    2017-06-01

    It is assumed linguistic symbols must be grounded in perceptual information to attain meaning, because the sound of a word in a language has an arbitrary relation with its referent. This paper demonstrates that a strong arbitrariness claim should be reconsidered. In a computational study, we showed that one phonological feature (nasals in the beginning of a word) predicted negative valence in three European languages (English, Dutch, and German) and positive valence in Chinese. In three experiments, we tested whether participants used this feature in estimating the valence of a word. In Experiment 1, Chinese and Dutch participants rated the valence of written valence-neutral words, with Chinese participants rating the nasal-first neutral-valence words more positive and the Dutch participants rating nasal-first neutral-valence words more negative. In Experiment 2, Chinese (and Dutch) participants rated the valence of Dutch (and Chinese) written valence-neutral words without being able to understand the meaning of these words. The patterns replicated the valence patterns from Experiment 1. When the written words from Experiment 2 were transformed into spoken words, results in Experiment 3 again showed that participants estimated the valence of words on the basis of the sound of the word. The computational study and psycholinguistic experiments indicated that language users can bootstrap meaning from the sound of a word.

  9. Role of valence fluctuations in the superconductivity of Ce122 compounds.

    Science.gov (United States)

    Yamaoka, H; Ikeda, Y; Jarrige, I; Tsujii, N; Zekko, Y; Yamamoto, Y; Mizuki, J; Lin, J-F; Hiraoka, N; Ishii, H; Tsuei, K-D; Kobayashi, T C; Honda, F; Onuki, Y

    2014-08-22

    Pressure dependence of the Ce valence in CeCu(2)Ge(2) has been measured up to 24 GPa at 300 K and to 17 GPa at 18-20 K using x-ray absorption spectroscopy in the partial fluorescence yield. A smooth increase of the Ce valence with pressure is observed across the two superconducting (SC) regions without any noticeable irregularity. The chemical pressure dependence of the Ce valence was also measured in Ce(Cu(1-x)Ni(x))(2)Si(2) at 20 K. A very weak, monotonic increase of the valence with x was observed, without any significant change in the two SC regions. Within experimental uncertainties, our results show no evidence for the valence transition with an abrupt change in the valence state near the SC II region, challenging the valence-fluctuation mediated superconductivity model in these compounds at high pressure and low temperature.

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

    DEFF Research Database (Denmark)

    Gorczyca, I.; Suski, T.; Christensen, Niels Egede

    2012-01-01

    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....

  11. Interactions between incentive valence and action information in a cued approach-avoidance task.

    Science.gov (United States)

    Hoofs, Vincent; Carsten, Thomas; Boehler, C Nico; Krebs, Ruth M

    2018-01-10

    Environmental stimuli can provoke specific response tendencies depending on their incentive valence. While some studies report positive-approach and negative-avoidance biases, others find no such mappings. To further illuminate the relationship between incentive valence and action requirement, we combined a cued monetary incentive paradigm with an approach/avoidance joystick task. Incentive type was manipulated between groups: The reward group won money, while the punishment group avoided losing money for correct and fast responses to targets following incentive cues. Depending on their orientations, targets had to be 'approached' or 'avoided'. Importantly, incentive valence (signaled by cue color) was orthogonal to action requirement (target orientation). Moreover, targets could carry valence-associated information or not (target color), which was, however, task-irrelevant. First, we observed that both valence cues (reward/punishment) improved performance compared to neutral cues, independent of the required action (approach/avoid), suggesting that advance valence cues do not necessarily produce specific action biases. Second, task-irrelevant valence associations with targets promoted action biases, with valence-associated targets facilitating approach and impairing avoid responses. Importantly, this approach bias for valence-associated targets was observed in both groups and hence occurred independently of absolute valence ('unsigned'). This rather unexpected finding might be related to the absence of a direct contrast between positive valence and negative valence within groups and the common goal to respond fast and accurately in all incentive trials. Together, our results seem to challenge the notion that monetary incentives trigger 'hard-wired' valence-action biases in that specific design choices seem to modulate the presence and/or direction of valence-action biases.

  12. Band structure of semiconductors

    CERN Document Server

    Tsidilkovski, I M

    2013-01-01

    Band Structure of Semiconductors provides a review of the theoretical and experimental methods of investigating band structure and an analysis of the results of the developments in this field. The book presents the problems, methods, and applications in the study of band structure. Topics on the computational methods of band structure; band structures of important semiconducting materials; behavior of an electron in a perturbed periodic field; effective masses and g-factors for the most commonly encountered band structures; and the treatment of cyclotron resonance, Shubnikov-de Haas oscillatio

  13. Valence photoemission spectra of aqueous Fe(2+/3+) and [Fe(CN)6](4-/3-) and their interpretation by DFT calculations.

    Science.gov (United States)

    Seidel, Robert; Thürmer, Stephan; Moens, Jan; Geerlings, Paul; Blumberger, Jochen; Winter, Bernd

    2011-10-13

    Aqueous solutions of ferrous and ferric iron (Fe(2+/3+)) and of the iron-hexacyano complexes [Fe(CN)(6)](4-/3-) are studied by photoelectron spectroscopy using a liquid microjet in conjunction with synchrotron soft X-rays for ionization. For Fe(2+)(aq) we observe two well-resolved peaks at 7.09 and 9.16 eV electron binding energy (BE) that can be assigned to the iron-hexaaquo complex. For Fe(3+)(aq) we observe only one peak above the highest valence band of liquid water, at 10.08 eV BE. Interpreting the spectra in terms of the one-electron levels of Kohn-Sham density functional theory, we find that the two peaks for Fe(2+)(aq) originate from the energy splitting between the highest occupied β (= minority) spin level (Fe d(t(2g))) and the five highest occupied α (= majority) spin levels (Fe d(t(2g)) and d(e(g))). The peak for Fe(3+)(aq) arises from d-levels that are strongly mixed with the solvent. The spectra of the aqueous hexacyano complexes show a single strong peak at 6.11 and 7.52 eV BE for [Fe(CN)(6)](4-) and [Fe(CN)(6)](3-), respectively, originating from the highest occupied Fe d(t(2g)) levels, and two further peaks at higher BE originating from the cyano ligands. The PE spectra of the reduced aquo and cyano ions are then used to obtain-solely on experimental grounds-values for the reorganization free energy of the oxidized ions. DFT/continuum calculations of this important parameter in the Marcus theory of oxidation reactions are in fairly good agreement with experiment.

  14. Two symmetric n-type interfaces SrTiO{sub 3}/LaAlO{sub 3} in perovskite: Electronic properties from density functional theory

    Energy Technology Data Exchange (ETDEWEB)

    Reshak, A. H., E-mail: maalidph@yahoo.co.uk, E-mail: mabujafar@najah.edu [New Technologies—Research Centre, 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); Abu-Jafar, M. S., E-mail: maalidph@yahoo.co.uk, E-mail: mabujafar@najah.edu [Department of Physics, An-Najah N. University, P. O. Box 7, Nablus, Palestine (Country Unknown); Al-Douri, Y. [Institute of Nano Electronic Engineering, University Malaysia Perlis, 01000 Kangar, Perlis (Malaysia); Physics Department, Faculty of Science, University of Sidi-Bel-Abbes, 22000 Sidi-Bel-Abbes (Algeria)

    2016-06-28

    The first principles study of the (001) two symmetric n-type interfaces between two insulating perovskites, the nonpolar SrTiO{sub 3} (STO), and the polar LaAlO{sub 3} (LAO) was performed. We have analyzed the formation of metallic interface states between the STO and LAO heterointerfaces by using the all-electron full-potential linearized augmented plane-wave approach based on the density functional theory, within the local density approximation, the Perdew-Burke-Ernzerhof generalized gradient approximation (PBE-GGA), and the Engel-Vosko GGA (EVGGA) formalism. It has been found that some bands cross the Fermi energy level (E{sub F}), forming a metallic nature of two symmetric n-type 6.5STO/1.5LAO interfaces with density of states at E{sub F}, N(E{sub F}) of about 3.56 (state/eV/unit cell), and bare electronic specific heat coefficient (γ) of about 0.62 mJ/(mol cell K{sup 2}). The electronic band stature and the partial density of states in the vicinity of E{sub F} are mainly originated from Ti1,2,3,4-3dxy orbitals. These bands are responsible for the metallic behavior and the forming of the Fermi surface of the two symmetric n-type 6.5STO/1.5LAO interfaces. To obtain a clear map of the valence band electronic charge density distribution of the two symmetric n-type 6.5STO/1.5LAO interfaces, we have investigated the bond's nature and the interactions between the atoms. It reveals that the charge is attracted towards O atoms as it is clear that the O atoms are surrounded by uniform blue spheres which indicate the maximum charge accumulation.

  15. Band parameters of phosphorene

    DEFF Research Database (Denmark)

    Lew Yan Voon, L. C.; Wang, J.; Zhang, Y.

    2015-01-01

    Phosphorene is a two-dimensional nanomaterial with a direct band-gap at the Brillouin zone center. In this paper, we present a recently derived effective-mass theory of the band structure in the presence of strain and electric field, based upon group theory. Band parameters for this theory...

  16. 1D valence bond solids in a magnetic field

    Science.gov (United States)

    Iaizzi, Adam; Sandvik, Anders W.

    2015-09-01

    A Valence bond solid (VBS) is a nonmagnetic, long-range ordered state of a quantum spin system where local spin singlets are formed in some regular pattern. We here study the competition between VBS order and a fully polarized ferromagnetic state as function of an external magnetic field in a one-dimensional extended Heisenberg model—the J-Q2 model— using stochastic series expansion (SSE) quantum Monte Carlo simulations with directed loop updates. We discuss the ground state phase diagram.

  17. The determination of the interface state density distribution of the Al/methyl red/p-Si Schottky barrier diode by using a capacitance method

    Energy Technology Data Exchange (ETDEWEB)

    Kilicoglu, T. [Department of Physics, Faculty of Science and Art, University of Dicle, Diyarbakir 21280 (Turkey)]. E-mail: tahsin@dicle.edu.tr; Aydin, M.E. [Department of Physics, Faculty of Science and Art, University of Dicle, Diyarbakir 21280 (Turkey); Ocak, Y.S. [Department of Physics, Faculty of Science and Art, University of Dicle, Diyarbakir 21280 (Turkey)

    2007-01-15

    Al/methyl red/p-Si Schottky barrier diodes (SBD) have been fabricated by adding a solution of the non-polymeric organic compound methyl red in chloroform on top of p-Si substrates, and then evaporating the solvent. The electronic and interface state density distribution properties were obtained from the current-voltage (I-V) and the capacitance-voltage (C-V) characteristics (high and low frequency) of Al/methyl red/p-Si SBD at room temperature. The energy distribution of the interface state density located in the inorganic semiconductor band gap at the organic compound/inorganic semiconductor interface in the energy range from (0.675-E{sub v})eV to (0.783-E{sub v})eV has been determined. In addition, the interface state density N{sub ss} range from 6.12x10{sup 13}cm{sup -2}eV{sup -1} in (0.675-E{sub v})eV to 4.31x10{sup 12}cm{sup -2}eV{sup -1} in (0.783-E{sub v})eV. The interface state density has an exponential rise with bias from the mid-gap towards the top of the valence band.

  18. Features of chemical bonds based on the overlap polarizabilities: diatomic and solid-state systems with the frozen-density embedding approach.

    Science.gov (United States)

    Moura, Renaldo T; Duarte, Gian C S; da Silva, Thiago E; Malta, Oscar L; Longo, Ricardo L

    2015-03-28

    The chemical bond overlap properties were obtained for alkali halides NaY (Y = F, Cl, Br), alkaline-earth chalcogenides MX (M = Ca, Mg and X = O, S, Se) and alkali and alkali-earth metals (Li, Na, and Mg) in diatomic and solid-state systems using an embedding approach based on the frozen density functional theory to simulate the crystalline effects. The computational protocol established provides errors for bond distances smaller than 1%. The results indicate that larger chemical bond covalency leads to larger absorption or scattering by the overlap region. The ionic specific valence and overlap polarizability are closely related to the valence orbital compactness measured by the sum of Mulliken electronegativities. The embedding approach used in this work makes it possible to quantify the effects of the crystalline environment on the chemical bond overlap properties. In the solid-state, the bond overlap charges are less polarizable, in cases of well-known ionic systems (provided by electronegativity differences), leading to smaller chemical bond covalency in solids than in diatomics. The spectroscopic properties of the polarizability of the electron density in the overlap region of a chemical bond could be measured in the 1-20 eV spectral region and could be used to characterize some bands in several spectra whose assignments are ambiguous or not available.

  19. Electronic states of thiophene/phenylene co-oligomers: Extreme-ultra violet excited photoelectron spectroscopy observations and density functional theory calculations

    Energy Technology Data Exchange (ETDEWEB)

    Kawaguchi, Yoshizo [Research Institute for Innovation in Sustainable Chemistry, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8565 (Japan); Electronics and Photonics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568 (Japan); Sasaki, Fumio; Mochizuki, Hiroyuki [Electronics and Photonics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568 (Japan); Ishitsuka, Tomoaki; Tomie, Toshihisa [Research Institute of Instrumentation Frontier, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568 (Japan); Ootsuka, Teruhisa [Nanoelectronics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568 (Japan); Watanabe, Shuji [Graduate School of Science and Engineering, Yamagata University, 1-4-12, Kojirakawa, Yamagata 990-8560 (Japan); Nanosystem Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568 (Japan); Shimoi, Yukihiro [Nanosystem Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568 (Japan); Yamao, Takeshi; Hotta, Shu [Department of Macromolecular Science and Engineering, Graduate School of Science and Technology, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto 606-8585 (Japan)

    2013-02-28

    We have investigated electronic states in the valence electron bands for the thin films of three thiophene/phenylene co-oligomer (TPCO) compounds, 2,5-bis(4-biphenylyl)thiophene (BP1T), 1,4-bis(5-phenylthiophen-2-yl)benzene (AC5), and 1,4-bis{l_brace}5-[4-(trifluoromethyl)phenyl]thiophen-2-yl{r_brace}benzene (AC5-CF{sub 3}), by using extreme-UV excited photoelectron spectroscopy (EUPS). By comparing both EUPS spectra and secondary electron spectra between AC5 and AC5-CF{sub 3}, we confirm that CF{sub 3} substitution to AC5 deepens valence states by 2 eV, and increases the ionization energy by 3 eV. From the cut-off positions of secondary electron spectra, the work functions of AC5, AC5-CF{sub 3}, and BP1T are evaluated to be 3.8 eV, 4.8 eV, and 4.0 eV, respectively. We calculate molecular orbital (MO) energy levels by the density functional theory and compare results of calculations with those of experiments. Densities of states obtained by broadening MO levels well explain the overall features of experimental EUPS spectra of three TPCOs.

  20. X-ray Emission Spectroscopy to Study Ligand Valence Orbitals in Mn Coordination Complexes

    Energy Technology Data Exchange (ETDEWEB)

    Smolentsev, Grigory; Soldatov, Alexander V; Messinger, Johannes; Merz, Kathrin; Weyhermuller, Thomas; Bergmann, Uwe; Pushkar, Yulia; Yano, Junko; Yachandra, Vittal K.; Glatzel, Pieter

    2009-03-02

    We discuss a spectroscopic method to determine the character of chemical bonding and for the identification of metal ligands in coordination and bioinorganic chemistry. It is based on the analysis of satellite lines in X-ray emission spectra that arise from transitions between valence orbitals and the metal ion 1s level (valence-to-core XES). The spectra, in connection with calculations based on density functional theory (DFT), provide information that is complementary to other spectroscopic techniques, in particular X-ray absorption (XANES and EXAFS). The spectral shape is sensitive to protonation of ligands and allows ligands, which differ only slightly in atomic number (e.g., C, N, O...), to be distinguished. A theoretical discussion of the main spectral features is presented in terms of molecular orbitals for a series of Mn model systems: [Mn(H2O)6]2+, [Mn(H2O)5OH]+, [Mn(H2O)5NH2]+, and [Mn(H2O)5NH3]2+. An application of the method, with comparison between theory and experiment, is presented for the solvated Mn2+ ion in water and three Mn coordination complexes, namely [LMn(acac)N3]BPh4, [LMn(B2O3Ph2)(ClO4)], and [LMn(acac)N]BPh4, where L represents 1,4,7-trimethyl-1,4,7-triazacyclononane, acac stands for the 2,4-pentanedionate anion, and B2O3Ph2 represents the 1,3-diphenyl-1,3-dibora-2-oxapropane-1,3-diolato dianion.

  1. Band-to-band tunneling distance analysis in the heterogate electron–hole bilayer tunnel field-effect transistor

    Energy Technology Data Exchange (ETDEWEB)

    Padilla, J. L., E-mail: jose.padilladelatorre@epfl.ch [Nanoelectronic Devices Laboratory, École Polytechnique Fédérale de Lausanne, Lausanne CH-1015 (Switzerland); Departamento de Electrónica y Tecnología de los Computadores, Universidad de Granada, Avda. Fuentenueva s/n, 18071 Granada (Spain); Palomares, A. [Departamento de Matemática Aplicada, Universidad de Granada, Avda. Fuentenueva s/n, 18071 Granada (Spain); Alper, C.; Ionescu, A. M. [Nanoelectronic Devices Laboratory, École Polytechnique Fédérale de Lausanne, Lausanne CH-1015 (Switzerland); Gámiz, F. [Departamento de Electrónica y Tecnología de los Computadores, Universidad de Granada, Avda. Fuentenueva s/n, 18071 Granada (Spain)

    2016-01-28

    In this work, we analyze the behavior of the band-to-band tunneling distance between electron and hole subbands resulting from field-induced quantum confinement in the heterogate electron–hole bilayer tunnel field-effect transistor. We show that, analogously to the explicit formula for the tunneling distance that can be easily obtained in the semiclassical framework where the conduction and valence band edges are allowed states, an equivalent analytical expression can be derived in the presence of field-induced quantum confinement for describing the dependence of the tunneling distance on the body thickness and material properties of the channel. This explicit expression accounting for quantum confinement holds valid provided that the potential wells for electrons and holes at the top and bottom of the channel can be approximated by triangular profiles. Analytical predictions are compared to simulation results showing very accurate agreement.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2006-05-10

    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. Terahertz emission from CdHgTe/HgTe quantum wells with an inverted band structure

    Energy Technology Data Exchange (ETDEWEB)

    Vasilyev, Yu. B., E-mail: Yu.Vasilyev@mail.ioffe.ru [Russian Academy of Sciences, Ioffe Physical–Technical Institute (Russian Federation); Mikhailov, N. N. [Russian Academy of Sciences, Rzhanov Institute of Semiconductor Physics, Siberian Branch (Russian Federation); Vasilyeva, G. Yu.; Ivánov, Yu. L.; Zakhar’in, A. O.; Andrianov, A. V. [Russian Academy of Sciences, Ioffe Physical–Technical Institute (Russian Federation); Vorobiev, L. E.; Firsov, D. A. [Peter the Great Saint-Petersburg Polytechnic University (Russian Federation); Grigoriev, M. N. [Ustinov Baltic State Technical University “VOENMEKh” (Russian Federation); Antonov, A. V.; Ikonnikov, A. V.; Gavrilenko, V. I. [Russian Academy of Sciences, Institute for Physics of Microstructures (Russian Federation)

    2016-07-15

    The terahertz electroluminescence from Cd{sub 0.7}Hg{sub 0.3}Te/HgTe quantum wells with an inverted band structure in lateral electric fields is experimentally detected and studied. The emission-spectrum maximum for wells 6.5 and 7 nm wide is near 6 meV which corresponds to interband optical transitions. The emission is explained by state depletion in the valence band and conduction band filling due to Zener tunneling, which is confirmed by power-law current–voltage characteristics.

  4. Expertise in video game playing is associated with reduced valence-concordant emotional expressivity.

    Science.gov (United States)

    Weinreich, André; Strobach, Tilo; Schubert, Torsten

    2015-01-01

    In carefully selected groups of video game playing (VGP) experts and nonexperts, we examined valence-concordant emotional expressivity. We measured electromyographic (EMG) activity over the corrugator supercilii muscle while participants viewed pleasant, neutral, and unpleasant pictures. Potential group differences concerning valence-concordant expressivity may arise from differences concerning the participants' emotional reactivity. To control for such differences, we concomitantly measured skin conductance response (SCR) and, in a separate affect misattribution procedure (AMP), valence transfer from the same set of stimuli. Importantly, we found attenuated valence-concordant EMG activity over the corrugator supercilii muscle in VGP experts compared to nonexperts, but no differences were evident concerning SCR or valence transfer in the AMP. The findings suggest that expertise in VGP is particularly associated with reduced valence-concordant emotional expressivity. Copyright © 2014 Society for Psychophysiological Research.

  5. Virtual Distance and Soundstage, and their Impacts on Experienced Emotional Valence

    DEFF Research Database (Denmark)

    Christensen, Justin

    2015-01-01

    Research from animal ethology and affective neuroscience suggest that a listener’s perceived distance from a signal source can alter their experienced emotional valence of the music. Furthermore, appraisal theories of emotion suggest that emotionally valenced responses will diverge according...... to the type of emotion presented. For these exploratory investigations, subjects listen to selected musical excerpts on speakers in combination with a tactile transducer attached to their chair. The listening sessions are recorded on EEG supported by subject feedback responses. My hypothesis is that musical...... stimuli should cause stronger valenced responses in the nearfield than at a distance. Thus, music experienced as being negatively valenced at a distance should be more negatively valenced in nearfield, and music that is experienced as having a positive valence at a distance should be more positively...

  6. An ecological valence theory of human color preference.

    Science.gov (United States)

    Palmer, Stephen E; Schloss, Karen B

    2010-05-11

    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 responses to color-associated objects. An empirical test provides strong support for this theory: People like colors strongly associated with objects they like (e.g., blues with clear skies and clean water) and dislike colors strongly associated with objects they dislike (e.g., browns with feces and rotten food). Relative to alternative theories, the ecological valence theory both fits the data better (even with fewer free parameters) and provides a more plausible, comprehensive causal explanation of color preferences.

  7. Valence-bond quantum Monte Carlo algorithms defined on trees.

    Science.gov (United States)

    Deschner, Andreas; Sørensen, Erik S

    2014-09-01

    We present a class of algorithms for performing valence-bond quantum Monte Carlo of quantum spin models. Valence-bond quantum Monte Carlo is a projective T=0 Monte Carlo method based on sampling of a set of operator strings that can be viewed as forming a treelike structure. The algorithms presented here utilize the notion of a worm that moves up and down this tree and changes the associated operator string. In quite general terms, we derive a set of equations whose solutions correspond to a whole class of algorithms. As specific examples of this class of algorithms, we focus on two cases. The bouncing worm algorithm, for which updates are always accepted by allowing the worm to bounce up and down the tree, and the driven worm algorithm, where a single parameter controls how far up the tree the worm reaches before turning around. The latter algorithm involves only a single bounce where the worm turns from going up the tree to going down. The presence of the control parameter necessitates the introduction of an acceptance probability for the update.

  8. The effects of colour and valence on news evaluation.

    Science.gov (United States)

    Kaspar, Kai; Grümmer, Melanie; Kießler, Antje; Neuß, Celina; Schröter, Franziska

    2017-12-01

    Research across different fields of psychology has reported effects of colour cues on a variety of cognitive processes. Especially, the colour red has been shown to have striking influences. In the context of media reception, however, colour effects have been widely neglected so far. This study made a first step in this direction by investigating the effects of the colour red (compared with blue and grey) on the way news articles are evaluated. Two types of news were framed by a coloured border while the valence of the news content additionally varied. Based on 369 participants who read and evaluated the news articles online, we observed effects for colour cues and news valence in the absence of an interaction effect, indicating that the colour red induced approach motivation. However, only the contrast between red and grey reached statistical significance, indicating that chromatic and achromatic colours may differ in their perceived visual saliency. Overall, these results provide an important complement to previous studies and have practical implications for media researchers and producers. © 2015 International Union of Psychological Science.

  9. Emotional valence contributes to music-induced analgesia.

    Science.gov (United States)

    Roy, Mathieu; Peretz, Isabelle; Rainville, Pierre

    2008-01-01

    The capacity of music to soothe pain has been used in many traditional forms of medicine. Yet, the mechanisms underlying these effects have not been demonstrated. Here, we examine the possibility that the modulatory effect of music on pain is mediated by the valence (pleasant-unpleasant dimension) of the emotions induced. We report the effects of listening to pleasant and unpleasant music on thermal pain in healthy human volunteers. Eighteen participants evaluated the warmth or pain induced by 40.0, 45.5, 47.0 and 48.5 degrees C thermal stimulations applied to the skin of their forearm while listening to pleasant and unpleasant musical excerpts matched for their high level of arousal (relaxing-stimulating dimension). Compared to a silent control condition, only the pleasant excerpts produced highly significant reductions in both pain intensity and unpleasantness, demonstrating the effect of positive emotions induced by music on pain (Pairwise contrasts with silence: p'semotional valence contributes to music-induced analgesia. These findings call for the integration of music to current methods of pain control.

  10. Visuospatial Asymmetries and Emotional Valence Influence Mental Time Travel.

    Science.gov (United States)

    Thomas, Nicole A; Takarangi, Melanie K T

    2017-11-27

    Spatial information is tightly intertwined with temporal and valence-based information. Namely, "past" is represented on the left, and "future" on the right, along a horizontal mental timeline. Similarly, right is associated with positive, whereas left is negative. We developed a novel task to examine the effects of emotional valence and temporal distance on mental representations of time. We compared positivity biases, where positive events are positioned closer to now, and right hemisphere emotion biases, where negative events are positioned to the left. When the entire life span was used, a positivity bias emerged; positive events were closer to now. When timeline length was reduced, positivity and right hemisphere emotion biases were consistent for past events. In contrast, positive and negative events were equidistant from now in the future condition, suggesting positivity and right hemisphere emotion biases opposed one another, leading events to be positioned at a similar distance. We then reversed the timeline by moving past to the right and future to the left. Positivity biases in the past condition were eliminated, and negative events were placed slightly closer to now in the future condition. We conclude that an underlying left-to-right mental representation of time is necessary for positivity biases to emerge for past events; however, our mental representations of future events are inconsistent with positivity biases. These findings point to an important difference in the way in which we represent the past and the future on our mental timeline. (PsycINFO Database Record (c) 2017 APA, all rights reserved).

  11. An ecological valence theory of human color preference

    Science.gov (United States)

    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 responses to color-associated objects. An empirical test provides strong support for this theory: People like colors strongly associated with objects they like (e.g., blues with clear skies and clean water) and dislike colors strongly associated with objects they dislike (e.g., browns with feces and rotten food). Relative to alternative theories, the ecological valence theory both fits the data better (even with fewer free parameters) and provides a more plausible, comprehensive causal explanation of color preferences. PMID:20421475

  12. Band offsets for biaxially and uniaxially stressed silicon-germanium layers with arbitrary substrate and channel orientations

    Energy Technology Data Exchange (ETDEWEB)

    Eneman, Geert; Roussel, Philippe; Brunco, David Paul; Collaert, Nadine; Mocuta, Anda; Thean, Aaron [Imec, Kapeldreef 75, 3001 Heverlee (Belgium)

    2016-08-07

    The conduction and valence band offsets between a strained silicon-germanium layer and a silicon-germanium substrate are reported for arbitrary substrate and channel crystal orientations. The offsets are calculated both for the case of biaxial stress, corresponding approximately to the stress state of a thin strained channel in a planar field-effect transistor (FET), and for uniaxial stress, which is the approximate stress state for strained channels in a FinFET configuration. Significant orientation dependence is found for the conduction band offset, overall leading to the strongest electron quantum confinement in biaxial-tensile stressed channels on {100}-oriented substrates, and uniaxial-tensile stressed channels in the 〈100〉 and 〈110〉 directions. For biaxially stressed layers on {111} substrates, the conduction band offset is significantly smaller than for {100} or {110} directions. For the valence band offset, the dependence on crystal orientation is found to be small.

  13. Electronic Band Structure of Transition Metal Dichalcogenides from Ab Initio and Slater–Koster Tight-Binding Model

    Directory of Open Access Journals (Sweden)

    Jose Ángel Silva-Guillén

    2016-10-01

    Full Text Available Semiconducting transition metal dichalcogenides present a complex electronic band structure with a rich orbital contribution to their valence and conduction bands. The possibility to consider the electronic states from a tight-binding model is highly useful for the calculation of many physical properties, for which first principle calculations are more demanding in computational terms when having a large number of atoms. Here, we present a set of Slater–Koster parameters for a tight-binding model that accurately reproduce the structure and the orbital character of the valence and conduction bands of single layer MX 2 , where M = Mo, W and X = S, Se. The fit of the analytical tight-binding Hamiltonian is done based on band structure from ab initio calculations. The model is used to calculate the optical conductivity of the different compounds from the Kubo formula.

  14. Band offsets of La2O3 on (0001) GaN grown by reactive molecular-beam epitaxy

    Science.gov (United States)

    Ihlefeld, Jon F.; Brumbach, Michael; Atcitty, Stanley

    2013-04-01

    La2O3 films were prepared on (0001)-oriented GaN substrates via reactive molecular-beam epitaxy. Film orientation and phase were assessed using reflection high-energy electron and X-ray diffraction. Films were observed to grow as predominantly hexagonal La2O3 for thicknesses less than 10 nm while film thickness greater than 10 nm favored mixed cubic and hexagonal symmetries. Band offsets were characterized by X-ray photoelectron spectroscopy on hexagonally symmetric films and valence band offsets of 0.63 ± 0.04 eV at the La2O3/GaN interface were measured. A conduction band offset of approximately 1.5 eV could be inferred from the measured valence band offset.

  15. Temperature dependence of band gaps in semiconductors: electron-phonon interaction

    Energy Technology Data Exchange (ETDEWEB)

    Kremer, Reinhard K.; Cardona, M.; Lauck, R. [MPI for Solid State Research, Stuttgart (Germany); Bhosale, J.; Ramdas, A.K. [Physics Dept., Purdue University, West Lafayette, IN (United States); Burger, A. [Fisk University, Dept. of Life and Physical Sciences, Nashville, TN (United States); Munoz, A. [MALTA Consolider Team, Dept. de Fisica Fundamental II, Universidad de La Laguna, Tenerife (Spain); Instituto de Materiales y Nanotecnologia, Universidad de La Laguna, Tenerife (Spain); Romero, A.H. [CINVESTAV, Dept. de Materiales, Unidad Queretaro, Mexico (Mexico); MPI fuer Mikrostrukturphysik, Halle an der Saale (Germany)

    2013-07-01

    We investigate the temperature dependence of the energy gap of several semiconductors with chalcopyrite structure and re-examine literature data and analyze own high-resolution reflectivity spectra in view of our new ab initio calculations of their phonon properties. This analysis leads us to distinguish between materials with d-electrons in the valence band (e.g. CuGaS{sub 2}, AgGaS{sub 2}) and those without d-electrons (e.g. ZnSnAs{sub 2}). The former exhibit a rather peculiar non-monotonic temperature dependence of the energy gap which, so far, has resisted cogent theoretical description. We demonstrate it can well be fitted by including two Bose-Einstein oscillators with weights of opposite sign leading to an increase at low-T and a decrease at higher T's. We find that the energy of the former correlates well with characteristic peaks in the phonon density of states associated with low-energy vibrations of the d-electron constituents.

  16. Band offsets in ITO/Ga2O3 heterostructures

    Science.gov (United States)

    Carey, Patrick H.; Ren, F.; Hays, David C.; Gila, B. P.; Pearton, S. J.; Jang, Soohwan; Kuramata, Akito

    2017-11-01

    The valence band offsets in rf-sputtered Indium Tin Oxide (ITO)/single crystal β-Ga2O3 (ITO/Ga2O3) heterostructures were measured with X-Ray Photoelectron Spectroscopy using the Kraut method. The bandgaps of the component materials in the heterostructure were determined by Reflection Electron Energy Loss Spectroscopy as 4.6 eV for Ga2O3 and 3.5 eV for ITO. The valence band offset was determined to be -0.78 ± 0.30 eV, while the conduction band offset was determined to be -0.32 ± 0.13 eV. The ITO/Ga2O3 system has a nested gap (type I) alignment. The use of a thin layer of ITO between a metal and the Ga2O3 is an attractive approach for reducing contact resistance on Ga2O3-based power electronic devices and solar-blind photodetectors.

  17. Electron momentum density and the momentum density of positron annihilation pairs in alkali metals: high-momentum components

    Energy Technology Data Exchange (ETDEWEB)

    Sob, M.

    1985-08-01

    The valence electron momentum density (EMD) and the momentum density of positron annihilation pairs (MDAP) are calculated ab initio for alkali metals from Li to Cs. It is shown that the proportion of valence electrons having their momenta within the central Fermi surface ranges from 75% (Cs) to 93% (Na); the momenta of the remaining valence electrons lie in the Umklapp Fermi surfaces centred at the surrounding reciprocal lattice points. In the calculation of the MDAP, various enhancement factors describing the effect of the many-body electron-positron interaction are examined; it seems that the recent model of enhancement of Umklapp terms presented by Sormann et al is not fully adequate. A relation between the EMD and MDAP is briefly discussed and the connection between the occupation of the central Fermi surface and other parameters of the electronic structure is pointed out.

  18. 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.)

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

    Energy Technology Data Exchange (ETDEWEB)

    Allen, J. W.

    2003-05-13

    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.

  20. Band Structure and Optical Properties of Ordered AuCu3

    DEFF Research Database (Denmark)

    Skriver, Hans Lomholt; Lengkeek, H. P.

    1979-01-01

    initio band structure obtained by the relativistic linear muffin-tin orbitals method. The band calculation reveals that ordered AuCu3 has distinct copper and gold d bands positioned in and hybridizing with an s band common to copper and gold. The calculated state density is found to be in good agreement...

  1. Signatures of rare-earth elements in banded corals of Kalpeni atoll-Lakshadweep archipelago in response to monsoonal variations

    Digital Repository Service at National Institute of Oceanography (India)

    Naqvi, S.A.S.; Nath, B.N.; Balaram, V.

    occurred with REE and the light rare-earths (LREE) enriched in the high density (representing monsoon season) bands. In contrast, the heavy rare-earths (HREE) are enriched in the low density bands. LREE enrichment in the high density bands is attributed...

  2. 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.

  3. 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.

  4. Time flies with music whatever its emotional valence.

    Science.gov (United States)

    Droit-Volet, Sylvie; Bigand, Emmanuel; Ramos, Danilo; Bueno, José Lino Oliveira

    2010-10-01

    The present study used a temporal bisection task to investigate whether music affects time estimation differently from a matched auditory neutral stimulus, and whether the emotional valence of the musical stimuli (i.e., sad vs. happy music) modulates this effect. The results showed that, compared to sine wave control music, music presented in a major (happy) or a minor (sad) key shifted the bisection function toward the right, thus increasing the bisection point value (point of subjective equality). This indicates that the duration of a melody is judged shorter than that of a non-melodic control stimulus, thus confirming that "time flies" when we listen to music. Nevertheless, sensitivity to time was similar for all the auditory stimuli. Furthermore, the temporal bisection functions did not differ as a function of musical mode. Copyright © 2010 Elsevier B.V. All rights reserved.

  5. Mechanisms of valence selectivity in biological ion channels.

    Science.gov (United States)

    Corry, B; Chung, S-H

    2006-02-01

    Transmembrane ion channels play a crucial role in the existence of all living organisms. They partition the exterior from the interior of the cell, maintain the proper ionic gradient across the cell membrane and facilitate signaling between cells. To perform these functions, ion channels must be highly selective, allowing some types of ions to pass while blocking the passage of others. Here we review a number of studies that have helped to elucidate the mechanisms by which ion channels discriminate between ions of differing charge, focusing on four channel families as examples: gramicidin, ClC chloride, voltage-gated calcium and potassium channels. The recent availability of high-resolution structural data has meant that the specific inter-atomic interactions responsible for valence selectivity can be pinpointed. Not surprisingly, electrostatic considerations have been shown to play an important role in ion specificity, although many details of the origins of this discrimination remain to be determined.

  6. Aging and long-term memory for emotionally valenced events.

    Science.gov (United States)

    Breslin, Carolyn W; Safer, Martin A

    2013-06-01

    In 2008, 1103 ardent Boston Red Sox fans answered questions about their team's 2003 loss and 2004 win in baseball championship games with archrival New York Yankees. Contrary to predictions based on socioemotional selectivity theory, there were no significant interactions of age and event valence for accuracy in remembering event details, or for self-reported subjective vividness and rehearsal of the memories. Fans 65 years and older tended to remember feeling only sad about the 2003 loss, whereas fans 25 years and under tended to remember feeling both sad and angry. Individuals may remember emotional feelings based on remembered goals about an event. PsycINFO Database Record (c) 2013 APA, all rights reserved.

  7. A density functional theory investigation of the electronic structure and spin moments of magnetite

    KAUST Repository

    Noh, Junghyun

    2014-08-01

    We present the results of density functional theory (DFT) calculations on magnetite, Fe3O4, which has been recently considered as electrode in the emerging field of organic spintronics. Given the nature of the potential applications, we evaluated the magnetite room-temperature cubic phase in terms of structural, electronic, and magnetic properties. We considered GGA (PBE), GGA + U (PBE + U), and range-separated hybrid (HSE06 and HSE(15%)) functionals. Calculations using HSE06 and HSE(15%) functionals underline the impact that inclusion of exact exchange has on the electronic structure. While the modulation of the band gap with exact exchange has been seen in numerous situations, the dramatic change in the valence band nature and states near the Fermi level has major implications for even a qualitative interpretation of the DFT results. We find that HSE06 leads to highly localized states below the Fermi level while HSE(15%) and PBE + U result in delocalized states around the Fermi level. The significant differences in local magnetic moments and atomic charges indicate that describing room-temperature bulk materials, surfaces and interfaces may require different functionals than their low-temperature counterparts.

  8. Study of PrBa2Cu3O7 singularity by density functional theory

    Directory of Open Access Journals (Sweden)

    V Ghanbarian

    2006-09-01

    Full Text Available   In order to study some theories about nonsuperconductivity of PrBa2Cu3O7, based on the density functional theory and with APW+lo/LAPW method some calculations for PrBa2Cu3O7 (Pr123 and YBa2Cu3O7 (Y123 were performed. The LSDA+U approximation was used for Pr(4f orbitals and the effect of changing UPr on the band structure, Pr(4f-DOS, distribution of electrons on the planes and chains, and Pr valence were investigated. Comparison of computational results with some experiments shows that a suitable region for UPr is a number larger than 0.4 Ry. With this selection the band structures of Pr123 and Y123 near Fermi energy are coincident completely. Therefore, the theories that present the reason for nonsuperconductivity of Pr123 corresponds to the difference of holes number or character of holes in Pr123 and Y123 were found to be incorrect.

  9. Radio Band Observations of Blazar Variability

    Indian Academy of Sciences (India)

    2016-01-27

    Jan 27, 2016 ... Outbursts in total flux density and linear polarization in the optical-to-radio bands are attributed to shocks propagating within the jet spine, in part, based on limited modelling invoking transverse shocks; new radiative transfer simulations allowing for shocks at arbitrary angle to the flow direction confirm this ...

  10. Ultrafast carotenoid band shifts: Experiment and theory

    NARCIS (Netherlands)

    Herek, J.L.; Wendling, M.; He, Z.; Polivka, T.; Garcia-Asua, G.; Cogdell, R.J.; Hunter, C.N.; van Grondelle, R.; Sundstrom, V.; Pullerits, T.

    2004-01-01

    The ultrafast carotenoid band shift upon excitation of nearby bacteriochlorophyll molecules was studied in three different light harvesting complexes from purple bacteria. The results were analyzed in terms of changes in local electric field of the carotenoids. Time dependent density functional

  11. Unifying Exchange Sensitivity in Transition-Metal Spin-State Ordering and Catalysis through Bond Valence Metrics.

    Science.gov (United States)

    Gani, Terry Z H; Kulik, Heather J

    2017-11-14

    Accurate predictions of spin-state ordering, reaction energetics, and barrier heights are critical for the computational discovery of open-shell transition-metal (TM) catalysts. Semilocal approximations in density functional theory, such as the generalized gradient approximation (GGA), suffer from delocalization error that causes them to overstabilize strongly bonded states. Descriptions of energetics and bonding are often improved by introducing a fraction of exact exchange (e.g., erroneous low-spin GGA ground states are instead correctly predicted as high-spin with a hybrid functional). The degree of spin-splitting sensitivity to exchange can be understood based on the chemical composition of the complex, but the effect of exchange on reaction energetics within a single spin state is less well-established. Across a number of model iron complexes, we observe strong exchange sensitivities of reaction barriers and energies that are of the same magnitude as those for spin splitting energies. We rationalize trends in both reaction and spin energetics by introducing a measure of delocalization, the bond valence of the metal-ligand bonds in each complex. The bond valence thus represents a simple-to-compute property that unifies understanding of exchange sensitivity for catalytic properties and spin-state ordering in TM complexes. Close agreement of the resulting per-metal-organic-bond sensitivity estimates, together with failure of alternative descriptors demonstrates the utility of the bond valence as a robust descriptor of how differences in metal-ligand delocalization produce differing relative energetics with exchange tuning. Our unified description explains the overall effect of exact exchange tuning on the paradigmatic two-state FeO + /CH 4 reaction that combines challenges of spin-state and reactivity predictions. This new descriptor-sensitivity relationship provides a path to quantifying how predictions in transition-metal complex screening are sensitive to the

  12. Band-type microelectrodes for amperometric immunoassays

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Ga-Yeon; Chang, Young Wook; Ko, Hyuk [Department of Materials Science and Engineering, Yonsei University, 134 Shinchon-dong, Seodaemun-gu, Seoul, 120-749 (Korea, Republic of); Kang, Min-Jung [Korea Institute of Science and Technology (KIST), Seoul (Korea, Republic of); Pyun, Jae-Chul, E-mail: jcpyun@yonsei.ac.kr [Department of Materials Science and Engineering, Yonsei University, 134 Shinchon-dong, Seodaemun-gu, Seoul, 120-749 (Korea, Republic of)

    2016-07-20

    A band-type microelectrode was made using a parylene-N film as a passivation layer. A circular-type, mm-scale electrode with the same diameter as the band-type microelectrode was also made with an electrode area that was 5000 times larger than the band-type microelectrode. By comparing the amperometric signals of 3,5,3′,5′-tetramethylbenzidine (TMB) samples at different optical density (OD) values, the band-type microelectrode was determined to be 9 times more sensitive than the circular-type electrode. The properties of the circular-type and the band-type electrodes (e.g., the shape of their cyclic voltammograms, the type of diffusion layer used, and the diffusion layer thickness per unit electrode area) were characterized according to their electrode area using the COMSOL Multiphysics software. From these simulations, the band-type electrode was estimated to have the conventional microelectrode properties, even when the electrode area was 100 times larger than a conventional circular-type electrode. These results show that both the geometry and the area of an electrode can influence the properties of the electrode. Finally, amperometric analysis based on a band-type electrode was applied to commercial ELISA kits to analyze human hepatitis B surface antigen (hHBsAg) and human immunodeficiency virus (HIV) antibodies. - Highlights: • A band-type microelectrode was made using a parylene-N film as a passivation layer. • The band-type microelectrode was 14-times more sensitive than circular-type electrode. • The influence of geometry on microelectrode properties was simulated using COMSOL. • The band-type electrode was applied to ELISA kits for hHBsAg and hHIV-antibodies.

  13. Valence-Bond Concepts in Coordination Chemistry and the Nature of Metal-Metal Bonds.

    Science.gov (United States)

    Pauling, Linus; Herman, Zelek S.

    1984-01-01

    Discusses the valence-bond method, applying it to some coordination compounds of metals, especially those involving metal-metal bonds. Suggests that transition metals can form as many as nine covalent bonds, permitting valence-theory to be extended to transition metal compounds in a more effective way than has been possible before. (JN)

  14. 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

  15. Atoms in Valence Bond – AiVB : synopsis and test results

    NARCIS (Netherlands)

    Zielinski, M.L.; van Lenthe, J.H.

    2010-01-01

    The Atoms in Valence Bond (AiVB) method, a new approach in the Valence Bond, is introduced. This approach combines the ideas behind the early Atoms in Molecules (AIM) developments, e.g. by Moffit [21], to understand a molecular wave function in terms of proper atomic wave functions, with the

  16. Application of circular dichroism spectroscopy in the study of mixed-valence asymmetric ruthenium polypyridyl complexes

    NARCIS (Netherlands)

    Ahmed, Hamid M. Y.; Coburn, Nadia; Dini, Danilo; de Jong, Jaap J. D.; Villani, Claudio; Browne, Wesley R.; Vos, Johannes G.

    2011-01-01

    Circular dichroism (CD) spectroelectrochemistry is used to determine the extent of singly occupied molecular orbital delocalization in mixed-valence multinuclear complexes, specifically the mixed-valence (RuRuIII)-Ru-II states of the four diastereoisomers of [(Ru(bpy)(2))(2)(bpt)](3+) [1; bpy =

  17. 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…

  18. Does emotional valence affect performance in non-emotional categorization tasks?

    NARCIS (Netherlands)

    Rinck, M.; Becker, E.S.

    2009-01-01

    In five experiments, a categorization task was used to test whether threatening emotional valence would automatically affect reactions, even when valence is task-irrelevant. Financial threat words (e.g., debts) required the same response as either anxiety words or pleasant words. In the first three

  19. The Effect of Stimulus Valence on Lexical Retrieval in Younger and Older Adults

    Science.gov (United States)

    Blackett, Deena Schwen; Harnish, Stacy M.; Lundine, Jennifer P.; Zezinka, Alexandra; Healy, Eric W.

    2017-01-01

    Purpose: Although there is evidence that emotional valence of stimuli impacts lexical processes, there is limited work investigating its specific impact on lexical retrieval. The current study aimed to determine the degree to which emotional valence of pictured stimuli impacts naming latencies in healthy younger and older adults. Method: Eighteen…

  20. SPIN POLARIZATION AND MAGNETIC DICHROISM IN PHOTOEMISSION FROM CORE AND VALENCE STATES IN LOCALIZED MAGNETIC SYSTEMS

    NARCIS (Netherlands)

    THOLE, BT; VANDERLAAN, G

    1991-01-01

    Using group theory we derive a general model for spin polarization and magnetic dichroism in photo-emission in the presence of atomic interactions between the hole created and the valence holes. We predict strong effects in the photoemission from core levels and localized valence levels of

  1. Dissociable modulation of overt visual attention in valence and arousal revealed by topology of scan path.

    Directory of Open Access Journals (Sweden)

    Jianguang Ni

    Full Text Available 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.

  2. 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…

  3. Singing with the Band

    Science.gov (United States)

    Altman, Timothy Meyer; Wright, Gary K.

    2012-01-01

    Usually band, orchestra, and choir directors work independently. However, the authors--one a choral director, the other a band director--have learned that making music together makes friends. Not only can ensemble directors get along, but joint concerts may be just the way to help students see how music can reach the heart. Combined instrumental…

  4. ZEBRAFISH CHROMOSOME-BANDING

    NARCIS (Netherlands)

    PIJNACKER, LP; FERWERDA, MA

    1995-01-01

    Banding techniques were carried out on metaphase chromosomes of zebrafish (Danio rerio) embryos. The karyotypes with the longest chromosomes consist of 12 metacentrics, 26 submetacentrics, and 12 subtelocentrics (2n = 50). All centromeres are C-band positive. Eight chromosomes have a pericentric

  5. Influence of emotional valence and arousal on the spread of activation in memory.

    Science.gov (United States)

    Jhean-Larose, Sandra; Leveau, Nicolas; Denhière, Guy

    2014-11-01

    Controversy still persists on whether emotional valence and arousal influence cognitive activities. Our study sought to compare how these two factors foster the spread of activation within the semantic network. In a lexical decision task, prime words were varied depending on the valence (pleasant or unpleasant) or on the level of emotional arousal (high or low). Target words were carefully selected to avoid semantic priming effects, as well as to avoid arousing specific emotions (neutral). Three SOA durations (220, 420 and 720 ms) were applied across three independent groups. Results indicate that at 220 ms, the effect of arousal is significantly higher than the effect of valence in facilitating spreading activation while at 420 ms, the effect of valence is significantly higher than the effect of arousal in facilitating spreading activation. These findings suggest that affect is a sequential process involving the successive intervention of arousal and valence.

  6. Pressure-induced anomalous valence crossover in cubic YbCu5-based compounds.

    Science.gov (United States)

    Yamaoka, Hitoshi; Tsujii, Naohito; Suzuki, Michi-To; Yamamoto, Yoshiya; Jarrige, Ignace; Sato, Hitoshi; Lin, Jung-Fu; Mito, Takeshi; Mizuki, Jun'ichiro; Sakurai, Hiroya; Sakai, Osamu; Hiraoka, Nozomu; Ishii, Hirofumi; Tsuei, Ku-Ding; Giovannini, Mauro; Bauer, Ernst

    2017-07-19

    A pressure-induced anomalous valence crossover without structural phase transition is observed in archetypal cubic YbCu5 based heavy Fermion systems. The Yb valence is found to decrease with increasing pressure, indicating a pressure-induced crossover from a localized 4f 13 state to the valence fluctuation regime, which is not expected for Yb systems with conventional c-f hybridization. This result further highlights the remarkable singularity of the valence behavior in compressed YbCu5-based compounds. The intermetallics Yb2Pd2Sn, which shows two quantum critical points (QCP) under pressure and has been proposed as a potential candidate for a reentrant Yb2+ state at high pressure, was also studied for comparison. In this compound, the Yb valence monotonically increases with pressure, disproving a scenario of a reentrant non-magnetic Yb2+ state at the second QCP.

  7. Band structure parameters of wurtzite and zinc-blende GaAs under strain in the GW approximation

    Science.gov (United States)

    Cheiwchanchamnangij, Tawinan; Lambrecht, Walter R. L.

    2011-07-01

    Quasiparticle self-consistent GW calculations are used to study the band structure in wurtzite and zinc-blende GaAs. The band-gap change between wurtzite and zinc blende is found to be sensitive to lattice constant and k-point convergence of the GW self-energy. Furthermore, the conduction-band minimum can switch between Γ1 and Γ3 character as a function of strain and the valence-band maximum can cross over from Γ5 to Γ1 under compressive uniaxial strain. The Kohn-Luttinger and Rashba-Sheka-Pikus effective Hamiltonian band structure parameters of zinc-blende and wurtzite GaAs, respectively, are determined from these first-principles band structure calculations. The uniaxial and homogeneous strain dependence of the band structure are studied and summarized in the appropriate strain deformation potential parameters.

  8. Screened coulomb hybrid DFT investigation of band gap and optical absorption predictions of CuVO3, CuNbO3 and Cu 5Ta11O30 materials

    KAUST Repository

    Harb, Moussab

    2014-01-01

    We present a joint theoretical and experimental investigation of the optoelectronic properties of CuVO3, CuNbO3 and Cu 5Ta11O30 materials for potential photocatalytic and solar cell applications. In addition to the experimental results obtained by powder X-ray diffraction and UV-Vis spectroscopy of the materials synthesized under flowing N2 gas at atmospheric pressure via solid-state reactions, the electronic structure and the UV-Vis optical absorption coefficient of these compounds are predicted with high accuracy using advanced first-principles quantum methods based on DFT (including the perturbation theory approach DFPT) within the screened coulomb hybrid HSE06 exchange-correlation formalism. The calculated density of states are found to be in agreement with the UV-Vis diffuse reflectance spectra, predicting a small indirect band gap of 1.4 eV for CuVO3, a direct band gap of 2.6 eV for CuNbO3, and an indirect (direct) band gap of 2.1 (2.6) eV for Cu5Ta 11O30. It is confirmed that the Cu(i)-based multi-metal oxides possess a strong contribution of filled Cu(i) states in the valence band and of empty d0 metal states in the conduction band. Interestingly, CuVO3 with its predicted small indirect band gap of 1.4 eV shows the highest absorption coefficient in the visible range with a broad absorption edge extending to 886 nm. This novel result offers a great opportunity for this material to be an excellent candidate for solar cell applications. © the Partner Organisations 2014.

  9. Enhanced Energy-Storage Density and High Efficiency of Lead-Free CaTiO3-BiScO3 Linear Dielectric Ceramics.

    Science.gov (United States)

    Luo, Bingcheng; Wang, Xiaohui; Tian, Enke; Song, Hongzhou; Wang, Hongxian; Li, Longtu

    2017-06-14

    A novel lead-free (1 - x)CaTiO3-xBiScO3 linear dielectric ceramic with enhanced energy-storage density was fabricated. With the composition of BiScO3 increasing, the dielectric constant of (1 - x)CaTiO3-xBiScO3 ceramics first increased and then decreased after the composition x > 0.1, while the dielectric loss decreased first and increased. For the composition x = 0.1, the polarization was increased into 12.36 μC/cm2, 4.6 times higher than that of the pure CaTiO3. The energy density of 0.9CaTiO3-0.1BiScO3 ceramic was 1.55 J/cm3 with the energy-storage efficiency of 90.4% at the breakdown strength of 270 kV/cm, and the power density was 1.79 MW/cm3. Comparison with other lead-free dielectric ceramics confirmed the superior potential of CaTiO3-BiScO3 ceramics for the design of ceramics capacitors for energy-storage applications. First-principles calculations revealed that Sc subsitution of Ti-site induced the atomic displacement of Ti ions in the whole crystal lattice, and lattice expansion was caused by variation of the bond angles and lenghths. Strong hybridization between O 2p and Ti 3d was observed in both valence band and conduction band; the hybridization between O 2p and Sc 3d at high conduction band was found to enlarge the band gap, and the static dielectric tensors were increased, which was the essential for the enhancement of polarization and dielectric properties.

  10. Electron Band Alignment at Interfaces of Semiconductors with Insulating Oxides: An Internal Photoemission Study

    Directory of Open Access Journals (Sweden)

    Valeri V. Afanas'ev

    2014-01-01

    Full Text Available Evolution of the electron energy band alignment at interfaces between different semiconductors and wide-gap oxide insulators is examined using the internal photoemission spectroscopy, which is based on observations of optically-induced electron (or hole transitions across the semiconductor/insulator barrier. Interfaces of various semiconductors ranging from the conventional silicon to the high-mobility Ge-based (Ge, Si1-xGex, Ge1-xSnx and AIIIBV group (GaAs, InxGa1-xAs, InAs, GaP, InP, GaSb, InSb materials were studied revealing several general trends in the evolution of band offsets. It is found that in the oxides of metals with cation radii larger than ≈0.7 Å, the oxide valence band top remains nearly at the same energy (±0.2 eV irrespective of the cation sort. Using this result, it becomes possible to predict the interface band alignment between oxides and semiconductors as well as between dissimilar insulating oxides on the basis of the oxide bandgap width which are also affected by crystallization. By contrast, oxides of light elements, for example, Be, Mg, Al, Si, and Sc exhibit significant shifts of the valence band top. General trends in band lineup variations caused by a change in the composition of semiconductor photoemission material are also revealed.

  11. Infrared diffuse interstellar bands

    Science.gov (United States)

    Galazutdinov, G. A.; Lee, Jae-Joon; Han, Inwoo; Lee, Byeong-Cheol; Valyavin, G.; Krełowski, J.

    2017-05-01

    We present high-resolution (R ˜ 45 000) profiles of 14 diffuse interstellar bands in the ˜1.45 to ˜2.45 μm range based on spectra obtained with the Immersion Grating INfrared Spectrograph at the McDonald Observatory. The revised list of diffuse bands with accurately estimated rest wavelengths includes six new features. The diffuse band at 15 268.2 Å demonstrates a very symmetric profile shape and thus can serve as a reference for finding the 'interstellar correction' to the rest wavelength frame in the H range, which suffers from a lack of known atomic/molecular lines.

  12. Resonating Valence Bonds and Mean-Field d-Wave Superconductivity in Graphite

    Energy Technology Data Exchange (ETDEWEB)

    Black-Schaffer, Annica M.

    2010-04-27

    We investigate the possibility of inducing superconductivity in a graphite layer by electronic correlation effects. We use a phenomenological microscopic Hamiltonian which includes nearest neighbor hopping and an interaction term which explicitly favors nearest neighbor spin-singlets through the well-known resonance valence bond (RVB) character of planar organic molecules. Treating this Hamiltonian in mean-field theory, allowing for bond-dependent variation of the RVB order parameter, we show that both s- and d-wave superconducting states are possible. The d-wave solution belongs to a two-dimensional representation and breaks time reversal symmetry. At zero doping there exists a quantum critical point at the dimensionless coupling J/t = 1.91 and the s- and d-wave solutions are degenerate for low temperatures. At finite doping the d-wave solution has a significantly higher T{sub c} than the s-wave solution. By using density functional theory we show that the doping induced from sulfur absorption on a graphite layer is enough to cause an electronically driven d-wave superconductivity at graphite-sulfur interfaces. We also discuss applying our results to the case of the intercalated graphites as well as the validity of a mean-field approach.

  13. Effect of Oxidation Degree on Valence Change and Distribution of Octahedral Fe Element in Biotite

    Directory of Open Access Journals (Sweden)

    Li Ziqian

    2017-01-01

    Full Text Available In this paper, the valence change and distribution of iron elements in octahedral vacancies of biotite were studied in the oxidation process. The biotite and saturated barium nitrate solution were mixed in dilute hydrochloric acid under hydrothermal reaction conditions, the solid after reaction was used as the test sample. Firstly, the remainder potassium and iron content were measured by atomic absorption spectrometry(AAS. Secondly, the state of iron along with oxidation degree increased was analyzed, in addition, the phase composition and the change of layer spacing in samples was detected by X-ray diffraction(XRD. Thirdly, The variation mode of Si-O bond were characterized by Fourier transform infrared spectroscopy(FT-IR.This research was adopted hydrogen ions in diluted hydrochloric acid and nitrate ions in barium nitrate to provide oxidation environment for reaction, and the oxidation degree was controlled by adjusted the amount of hydrogen ion introduced. We found out that the amount of hydrogen ion is positively correlated with oxidation degree in biotite, and the deeper oxidation degree in biotite, the lower electronegativity of singer layer. Potassium and iron element would be release out of micaceous structure during the biotite oxidation. The higher the oxidation degree is, the greater the releasing happen. The charge density combining Fe oxidation and releasing firstly increased then decreased with the oxidation degree turned greater. During the oxidation, the Si-O vibrated would change from parallel layer vibration model to vertical vibration model.

  14. Road density

    Data.gov (United States)

    U.S. Environmental Protection Agency — Road density is generally highly correlated with amount of developed land cover. High road densities usually indicate high levels of ecological disturbance. More...

  15. Band structure engineered layered metals for low-loss plasmonics

    DEFF Research Database (Denmark)

    Gjerding, Morten Niklas; Pandey, Mohnish; Thygesen, Kristian Sommer

    2017-01-01

    dichalcogenide TaS2, due to an extraordinarily small density of states for scattering in the near-IR originating from their special electronic band structure. On the basis of this observation, we propose a new class of band structure engineered van der Waals layered metals composed of hexagonal transition metal...

  16. Determination of band offsets in strained-Si heterolayers

    Energy Technology Data Exchange (ETDEWEB)

    Maiti, C.K.; Samanta, S.K.; Chatterjee, S.; Dalapati, G.K.; Bhattacharya, S.; Armstrong, B.M.; Gamble, H.S.; McCarthy, J.; Perova, T.S.; Moore, R.A

    2004-09-01

    Strained-Si/SiGe/Si structures are of increasing importance for microelectronic applications. A fully relaxed-SiGe buffer layer is required for growing strained-Si for applications towards high performance field effect transistors (FETs) having strained-Si as the channel. Preparation of epitaxial strained-Si layers on relaxed-SiGe (001) heterostructures using low pressure chemical vapor deposition (LPCVD) is reported. Gas source molecular beam epitaxy (GSMBE) grown strained-Si films are used to compare with LPCVD strained-Si films. Characterization of the strained-Si layers has been performed using AFM, TEM and Raman spectroscopy. Conduction and valence band offsets of strained-Si on relaxed-SiGe heterostructures have been extracted from measured capacitance-voltage (C-V) profiling of MOS capacitors fabricated on strained-Si using SiO{sub 2} as the dielectric. Extracted experimental values of the valence and conduction band offsets are in good agreement with theoretical predictions.

  17. 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)

  18. Laparoscopic gastric banding - discharge

    Science.gov (United States)

    ... heart disease Gastric bypass surgery Laparoscopic gastric banding Obesity Obstructive sleep apnea - adults Type 2 diabetes Patient Instructions Weight-loss surgery - after - what to ask your doctor Weight- ...

  19. Valence Scaling of Dynamic Facial Expressions Is Altered in High-Functioning Subjects with Autism Spectrum Disorders: An FMRI Study

    Science.gov (United States)

    Rahko, Jukka S.; Paakki, Jyri-Johan; Starck, Tuomo H.; Nikkinen, Juha; Pauls, David L.; Katsyri, Jari V.; Jansson-Verkasalo, Eira M.; Carter, Alice S.; Hurtig, Tuula M.; Mattila, Marja-Leena; Jussila, Katja K.; Remes, Jukka J.; Kuusikko-Gauffin, Sanna A.; Sams, Mikko E.; Bolte, Sven; Ebeling, Hanna E.; Moilanen, Irma K.; Tervonen, Osmo; Kiviniemi, Vesa

    2012-01-01

    FMRI was performed with the dynamic facial expressions fear and happiness. This was done to detect differences in valence processing between 25 subjects with autism spectrum disorders (ASDs) and 27 typically developing controls. Valence scaling was abnormal in ASDs. Positive valence induces lower deactivation and abnormally strong activity in ASD…

  20. First-principles energy band calculation of Ruddlesden-Popper compound Sr3Sn2O7 using modified Becke-Johnson exchange potential

    Science.gov (United States)

    Kamimura, Sunao; Obukuro, Yuki; Matsushima, Shigenori; Nakamura, Hiroyuki; Arai, Masao; Xu, Chao-Nan

    2015-12-01

    The electronic structure of Sr3Sn2O7 is evaluated by the scalar-relativistic full potential linearized augmented plane wave (FLAPW+lo) method using the modified Becke-Johnson potential (Tran-Blaha potential) combined with the local density approximation correlation (MBJ-LDA). The fundamental gap between the valence band (VB) and conduction band (CB) is estimated to be 3.96 eV, which is close to the experimental value. Sn 5s states and Sr 4d states are predominant in the lower and upper CB, respectively. On the other hand, the lower VB is mainly composed of Sn 5s, 5p, and O 2p states, while the upper VB mainly consists of O 2p states. These features of the DOS are well reflected by the optical transition between the upper VB and lower CB, as seen in the energy dependence of the dielectric function. Furthermore, the absorption coefficient estimated from the MBJ-LDA is similar to the experimental result.

  1. Lying about the valence of affective pictures: an fMRI study.

    Directory of Open Access Journals (Sweden)

    Tatia M C Lee

    Full Text Available The neural correlates of lying about affective information were studied using a functional magnetic resonance imaging (fMRI methodology. Specifically, 13 healthy right-handed Chinese men were instructed to lie about the valence, positive or negative, of pictures selected from the International Affective Picture System (IAPS while their brain activity was scanned by a 3T Philip Achieva scanner. The key finding is that the neural activity associated with deception is valence-related. Comparing to telling the truth, deception about the valence of the affectively positive pictures was associated with activity in the inferior frontal, cingulate, inferior parietal, precuneus, and middle temporal regions. Lying about the valence of the affectively negative pictures, on the other hand, was associated with activity in the orbital and medial frontal regions. While a clear valence-related effect on deception was observed, common neural regions were also recruited for the process of deception about the valence of the affective pictures. These regions included the lateral prefrontal and inferior parietal regions. Activity in these regions has been widely reported in fMRI studies on deception using affectively-neutral stimuli. The findings of this study reveal the effect of valence on the neural activity associated with deception. Furthermore, the data also help to illustrate the complexity of the neural mechanisms underlying deception.

  2. Vivid: How valence and arousal influence word processing under different task demands

    Science.gov (United States)

    Delaney-Busch, Nathaniel; Wilkie, Gianna; Kuperberg, Gina

    2016-01-01

    In this study, we used event-related potentials (ERPs) to examine how dimensions of emotion – valence and arousal – influence different stages of word processing under different task demands. In two experiments, two groups of participants viewed the same single emotional and neutral words while carrying out different tasks. In both experiments, valence (pleasant, unpleasant, and neutral) was fully crossed with arousal (high and low). We found that task made a substantial contribution to how valence and arousal modulated the Late Positive Complex (LPC), which is thought to reflect sustained evaluative processing (particularly of emotional stimuli). When participants performed a semantic categorization task in which emotion was not directly relevant to task performance, the LPC showed a larger amplitude for high-arousal words than low-arousal words, but no effect of valence. In contrast, when participants performed an overt valence categorization task, the LPC showed a large effect of valence (with unpleasant words eliciting the largest positivity), but no effect of arousal. These data show not only that valence and arousal act independently to influence word processing, but that their relative contributions to prolonged evaluative neural processes are strongly influenced by situational demands (and individual differences, as revealed in a subsequent analysis of subjective judgments). PMID:26833048

  3. From Semantics to Feelings: How Do Individuals with Schizophrenia Rate the Emotional Valence of Words?

    Directory of Open Access Journals (Sweden)

    Ana P. Pinheiro

    2012-01-01

    Full Text Available Schizophrenia is characterized by both emotional and language abnormalities. However, in spite of reports of preserved evaluation of valence of affective stimuli, such as pictures, it is less clear how individuals with schizophrenia assess verbal material with emotional valence, for example, the overall unpleasantness/displeasure relative to pleasantness/attraction of a word. This study aimed to investigate how schizophrenic individuals rate the emotional valence of adjectives, when compared with a group of healthy controls. One hundred and eighty-four adjectives differing in valence were presented. These adjectives were previously categorized as “neutral,” “positive” (pleasant, or “negative” (unpleasant by five judges not participating in the current experiment. Adjectives from the three categories were matched on word length, frequency, and familiarity. Sixteen individuals with schizophrenia diagnosis and seventeen healthy controls were asked to rate the valence of each word, by using a computerized version of the Self-Assessment Manikin (Bradley and Lang, 1994. Results demonstrated similar ratings of emotional valence of words, suggesting a similar representation of affective knowledge in schizophrenia, at least in terms of the valence dimension.

  4. Kondo interactions from band reconstruction in YbInCu(4).

    Science.gov (United States)

    Jarrige, I; Kotani, A; Yamaoka, H; Tsujii, N; Ishii, K; Upton, M; Casa, D; Kim, J; Gog, T; Hancock, J N

    2015-03-27

    We combine resonant inelastic x-ray scattering and model calculations in the Kondo lattice compound YbInCu_{4}, a system characterized by a dramatic increase in Kondo temperature and associated valence fluctuations below a first-order valence transition at T≃42  K. The bulk-sensitive, element-specific, and valence-projected charge excitation spectra reveal an unusual quasigap in the Yb-derived state density which drives an instability of the electronic structure and renormalizes the low-energy effective Hamiltonian at the transition. Our results provide long-sought experimental evidence for a link between temperature-driven changes in the low-energy Kondo scale and the higher-energy electronic structure of this system.

  5. Intriguing electronic properties of two-dimensional MoS2/TM2CO2 (TM = Ti, Zr, or Hf) hetero-bilayers: type-II semiconductors with tunable band gaps.

    Science.gov (United States)

    Li, Xinru; Dai, Ying; Ma, Yandong; Liu, Qunqun; Huang, Baibiao

    2015-03-27

    Two-dimensional (2D) transition metal compound (TMC) monolayers, as well as their van der Waals heterostructures with unique properties, are fundamentally and technologically intriguing. Here, heterostructures consisting of a MoS2 monolayer and TM2CO2 (TM = Ti, Zr or Hf) monolayers are systematically researched by means of the density functional theory (DFT). Different from semiconductor/metal contacts, MoS2 and TM2CO2 monolayers are all semiconductors with band gaps ranging from 0.25-1.67 eV. According to rigorous screening of stacking patterns, MoS2/Zr2CO2 is shown to be an indirect type-II semiconductor with the maximum valence and minimum conduction bands spatially separated on opposite monolayers. Simultaneously, the interface charges transfer from Zr2CO2 to MoS2 results in a built-in field that separates the electrons and holes efficiently. Also, the smaller effective masses of electrons and the holes of band edges indicate the higher carrier mobility. Moreover, strain regulation can make the hetero-bilayer's character a semiconductor-semimetal-metal transition. The physical insights pave the way for the good performance of MoS2/TM2CO2 in next-generation electronic devices and photocatalysts.

  6. Translation-Invariant Parent Hamiltonians of Valence Bond Crystals

    Science.gov (United States)

    Huerga, Daniel; Greco, Andrés; Gazza, Claudio; Muramatsu, Alejandro

    2017-04-01

    We present a general method to construct translation-invariant and SU(2) symmetric antiferromagnetic parent Hamiltonians of valence bond crystals (VBCs). The method is based on a canonical mapping transforming S =1 /2 spin operators into a bilinear form of a new set of dimer fermion operators. We construct parent Hamiltonians of the columnar and the staggered VBCs on the square lattice, for which the VBC is an eigenstate in all regimes and the exact ground state in some region of the phase diagram. We study the departure from the exact VBC regime upon tuning the anisotropy by means of the hierarchical mean field theory and exact diagonalization on finite clusters. In both Hamiltonians, the VBC phase extends over the exact regime and transits to a columnar antiferromagnet (CAFM) through a window of intermediate phases, revealing an intriguing competition of correlation lengths at the VBC-CAFM transition. The method can be readily applied to construct other VBC parent Hamiltonians in different lattices and dimensions.

  7. The genetics of anxiety-related negative valence system traits.

    Science.gov (United States)

    Savage, Jeanne E; Sawyers, Chelsea; Roberson-Nay, Roxann; Hettema, John M

    2017-03-01

    NIMH's Research Domain Criteria (RDoC) domain of negative valence systems (NVS) captures constructs of negative affect such as fear and distress traditionally subsumed under the various internalizing disorders. Through its aims to capture dimensional measures that cut across diagnostic categories and are linked to underlying neurobiological systems, a large number of phenotypic constructs have been proposed as potential research targets. Since "genes" represent a central "unit of analysis" in the RDoC matrix, it is important for studies going forward to apply what is known about the genetics of these phenotypes as well as fill in the gaps of existing knowledge. This article reviews the extant genetic epidemiological data (twin studies, heritability) and molecular genetic association findings for a broad range of putative NVS phenotypic measures. We find that scant genetic epidemiological data is available for experimentally derived measures such as attentional bias, peripheral physiology, or brain-based measures of threat response. The molecular genetic basis of NVS phenotypes is in its infancy, since most studies have focused on a small number of candidate genes selected for putative association to anxiety disorders (ADs). Thus, more research is required to provide a firm understanding of the genetic aspects of anxiety-related NVS constructs. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

  8. Effects of Emotional Valence on Hemispheric Asymmetries in Response Inhibition

    Directory of Open Access Journals (Sweden)

    Sebastian Ocklenburg

    2017-08-01

    Full Text Available Hemispheric asymmetries are a major organizational principle in human emotion processing, but their interaction with prefrontal control processes is not well understood. To this end, we determined whether hemispheric differences in response inhibition depend on the emotional valence of the stimulus being inhibited. Participants completed a lateralised Go/Nogo task, in which Nogo stimuli were neutral or emotional (either positive or negative images, while Go stimuli were scrambled versions of the same pictures. We recorded the N2 and P3 event-related potential (ERP components, two common electrophysiological measures of response inhibition processes. Behaviourally, participants were more accurate in withholding responses to emotional than to neutral stimuli. Electrophysiologically, Nogo-P3 responses were greater for emotional than for neutral stimuli, an effect driven primarily by an enhanced response to positive images. Hemispheric asymmetries were also observed, with greater Nogo-P3 following left versus right visual field stimuli. However, the visual field effect did not interact with emotion. We therefore find no evidence that emotion-related asymmetries affect response inhibition processes.

  9. 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.

  10. Aging and distraction by irrelevant speech: does emotional valence matter?

    Science.gov (United States)

    Van Gerven, Pascal W M; Murphy, Dana R

    2010-11-01

    From prior studies, we know that older adults are rarely more distracted by irrelevant speech than younger adults, which is remarkable in light of the inhibitory deficit view of aging. We tested the hypothesis that older adults are more distracted by emotional irrelevant speech during a visual cognitive task than younger adults. Forty-eight younger (mean age = 21.9 years) and 48 older individuals (mean age = 68.1 years) performed a visual counting task while being exposed to irrelevant speech consisting of random numbers intermixed with neutral, positive, or negative words. Performance in these conditions was compared with that in a silence condition. Irrelevant speech increased counting time and decreased accuracy similarly for younger and older adults. Furthermore, the emotional conditions did not elicit a stronger effect than the neutral condition. Finally, we found implicit memory for irrelevant speech, but its level was independent of emotional valence and age. We conclude that emotional irrelevant speech has no disproportionate impact on cognitive performance in older adults. This can be regarded as a challenge to the inhibitory deficit hypothesis.

  11. Positively valenced stimuli facilitate creative novel metaphoric processes by enhancing medial prefrontal cortical activation.

    Science.gov (United States)

    Subramaniam, Karuna; Beeman, Mark; Faust, Miriam; Mashal, Nira

    2013-01-01

    A metaphor is a figure of speech in which a subject is symbolic of another unrelated object. In the present study, we examined neural patterns associated with both novel unfamiliar and conventional familiar metaphoric processing, and how these patterns are modulated by affective valence. Prior to fMRI scanning, participants received a list of word pairs (novel unfamiliar metaphors as well as conventional familiar metaphors) and were asked to denote the valence (positive, negative, or neutral) of each word pair. During scanning, participants had to decide whether the word pairs formed meaningful or meaningless expressions. Results indicate that participants were faster and more accurate at deciding that positively valenced metaphors were meaningful compared to neutral metaphors. These behavioral findings were accompanied by increased activation in the medial prefrontal cortex (mPFC), posterior cingulate cortex (PCC), and the right inferior parietal lobe (RIPL). Specifically, positively valenced novel unfamiliar metaphors elicited activation in these brain regions in addition to the left superior temporal gyrus when compared to neutral novel metaphors. We also found that the mPFC and PCC mediated the processing of positively valenced metaphors when compared to negatively valenced metaphors. Positively valenced conventional metaphors, however, elicited different neural signatures when contrasted with either neutral or negatively valenced conventional metaphors. Together, our results indicate that positively valenced stimuli facilitate creative metaphoric processes (specifically novel metaphoric processes) by mediating attention and cognitive control processes required for the access, integration, and selection of semantic associations via modulation of the mPFC. The present study is important for the development of neural accounts of emotion-cognition interactions required for creativity, language, and successful social functioning in general.

  12. Polarons and soliton pairs (bipolarons) in halogen-doped quasi-one-dimensional mixed-valence platinum complexes

    Science.gov (United States)

    Haruki, M.; Kurita, S.

    1989-03-01

    The first experimental studies on halogen doping in quasi-one-dimensional, halogen-bridged, mixed-valence platinum complexes (HMPC) are presented. The electrical conductivity of the iodine compound increases over 7 orders of magnitude with iodine doping. The absorbance of the two optical-absorption bands near the midgap and the ESR intensity in dilute doped HMPC increase with the dopant concentration. In the dilute regime, halogen doping yields the same effects on optical absorption and ESR as does photoexcitation at an energy greater than or equal to the energy of the charge-transfer absorption band. The doping-induced states are located on single chains and have charge and spin. These results strongly suggest polaron formation by halogen doping. At high doping levels, a new doping-induced absorption appears at an energy of 1.55 eV at 77 K, and the ESR decreases in intensity as the doping proceeds. It appears that upon halogen doping, singly charged polarons are produced and the formation of confined charged soliton pairs (bipolarons) via the process P++P+-->S++S+ (or B2+) is favored.

  13. Band theory of metals the elements

    CERN Document Server

    Altmann, Simon L

    1970-01-01

    Band Theory of Metals: The Elements focuses on the band theory of solids. The book first discusses revision of quantum mechanics. Topics include Heisenberg's uncertainty principle, normalization, stationary states, wave and group velocities, mean values, and variational method. The text takes a look at the free-electron theory of metals, including heat capacities, density of states, Fermi energy, core and metal electrons, and eigenfunctions in three dimensions. The book also reviews the effects of crystal fields in one dimension. The eigenfunctions of the translations; symmetry operations of t

  14. Pulsed laser deposition of HfO{sub 2} thin films on indium zinc oxide: Band offsets measurements

    Energy Technology Data Exchange (ETDEWEB)

    Craciun, D.; Craciun, V., E-mail: valentin.craciun@inflpr.ro

    2017-04-01

    Highlights: • High quality amorphous IZO and HfO{sub 2} films were obtained by PLD technique. • XPS measurements were used to obtain the valence band alignment in HfO{sub 2}/IZO heterostructure. • A valence band offset (ΔE{sub V}) of 1.75 eV was obtained for the HfO{sub 2}/IZO heterostructure. • A conduction band offset (ΔE{sub C}) of 0.65 eV was estimated for the HfO{sub 2}/IZO heterostructure. - Abstract: One of the most used dielectric films for amorphous indium zinc oxide (IZO) based thin films transistor is HfO{sub 2}. The estimation of the valence band discontinuity (ΔE{sub V}) of HfO{sub 2}/IZO heterostructure grown using the pulsed laser deposition technique, with In/(In + Zn) = 0.79, was obtained from X-ray photoelectron spectroscopy (XPS) measurements. The binding energies of Hf 4d5, Zn 2p3 and In 3d5 core levels and valence band maxima were measured for thick pure films and for a very thin HfO{sub 2} film deposited on a thick IZO film. A value of ΔE{sub V} = 1.75 ± 0.05 eV was estimated for the heterostructure. Taking into account the measured HfO{sub 2} and IZO optical bandgap values of 5.50 eV and 3.10 eV, respectively, a conduction band offset ΔE{sub C} = 0.65 ± 0.05 eV in HfO{sub 2}/IZO heterostructure was then obtained.

  15. Experiencing activation: energetic arousal and tense arousal are not mixtures of valence and activation.

    Science.gov (United States)

    Schimmack, Ulrich; Reisenzein, Rainer

    2002-12-01

    R. E. Thayer (1989) proposed 2 types of activation: energetic arousal (awake-tired) and tense arousal (tense-calm). This view has been challenged by claims that energetic arousal and tense arousal are mixtures of valence and a single activation dimension. The authors present a direct test of this hypothesis by computing the correlation between the residuals of energetic arousal and tense arousal after removing the shared variance with valence. Whereas the valence activation hypothesis predicts a strong positive correlation between the 2 residuals, the authors found that it was not significantly different from 0. This finding reaffirms the view of energetic arousal and tense arousal as 2 distinct types of activation.

  16. Multielectron coincidence spectroscopy for core-valence doubly ionized states of CO.

    Science.gov (United States)

    Hikosaka, Y; Kaneyasu, T; Shigemasa, E; Lablanquie, P; Penent, F; Ito, K

    2007-07-28

    Double photoionization into states which have holes in one core and one valence orbitals has been observed in CO using a state-of-the-art multielectron coincidence method. The core-valence CO2+ structures exhibited on the electron coincidence spectra are assigned by comparison with the available calculation [H. Schulte et al., J. Chem. Phys. 105, 11108 (1996)]. Features of the spectrum confirm that the properties of the CO2+ states are characterized by the interaction between the localized valence holes and the core holes.

  17. 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.

  18. Single-band negative differential resistance in metallic armchair MoS2 nanoribbons

    Science.gov (United States)

    Chen, Cheng; Wang, Xue-Feng; Li, Yao-Sheng; Cheng, Xue-Mei; Yao, A.-Long

    2017-11-01

    Semiconductor armchair MoS2 nanoribbons can be converted into conductors by edge functionalization of H atoms or OH groups. Those metallic nanoribbons exhibit I–V characteristics of a single half-filled band with strong negative differential resistance (NDR) under a voltage bias less than 1 V. This originates from the spatial separation between electrons in the conduction and valence bands. The NDR becomes spin dependent if the H atoms or OH groups are not uniformly adsorbed on the edge. Furthermore, the spin polarization can be greatly enhanced in heterojunctions of H- and OH-passivated nanoribbons.

  19. Effect of band gap engineering in anionic-doped TiO{sub 2} photocatalyst

    Energy Technology Data Exchange (ETDEWEB)

    Samsudin, Emy Marlina; Abd Hamid, Sharifah Bee, E-mail: sharifahbee@um.edu.my

    2017-01-01

    Highlights: • Band gap engineering using anion dopants. • Mid band energy level. • Ti{sup 3+} and oxygen vacancies as impurities states. • Valence band tail extension due to doping. • Wider solar light absorption. - Abstract: A simple yet promising strategy to modify TiO{sub 2} band gap was achieved via dopants incorporation which influences the photo-responsiveness of the photocatalyst. The mesoporous TiO{sub 2} was successfully mono-doped and co-doped with nitrogen and fluorine dopants. The results indicate that band gap engineering does not necessarily requires oxygen substitution with nitrogen or/and fluorine, but from the formation of additional mid band and Ti{sup 3+} impurities states. The formation of oxygen vacancies as a result of modified color centres and Ti{sup 3+} ions facilitates solar light absorption and influences the transfer, migration and trapping of the photo-excited charge carriers. The synergy of dopants in co-doped TiO{sub 2} shows better optical properties relative to single N and F doped TiO{sub 2} with c.a 0.95 eV band gap reduction. Evidenced from XPS, the synergy between N and F in the co-doped TiO{sub 2} uplifts the valence band towards the conduction band. However, the photoluminescence data reveals poorer electrons and holes separation as compared to F-doped TiO{sub 2}. This observation suggests that efficient solar light harvesting was achievable via N and F co-doping, but excessive defects could act as charge carriers trapping sites.

  20. The Breathing Orbital Valence Bond Method in Diffusion Monte Carlo: C-H Bond Dissociation ofAcetylene

    Energy Technology Data Exchange (ETDEWEB)

    Domin, D.; Braida, Benoit; Lester Jr., William A.

    2008-05-30

    This study explores the use of breathing orbital valence bond (BOVB) trial wave functions for diffusion Monte Carlo (DMC). The approach is applied to the computation of the carbon-hydrogen (C-H) bond dissociation energy (BDE) of acetylene. DMC with BOVB trial wave functions yields a C-H BDE of 132.4 {+-} 0.9 kcal/mol, which is in excellent accord with the recommended experimental value of 132.8 {+-} 0.7 kcal/mol. These values are to be compared with DMC results obtained with single determinant trial wave functions, using Hartree-Fock orbitals (137.5 {+-} 0.5 kcal/mol) and local spin density (LDA) Kohn-Sham orbitals (135.6 {+-} 0.5 kcal/mol).

  1. Short-range resonating-valence-bond state of even-spin ladders: A recurrent variational approach

    Science.gov (United States)

    Sierra, Germán; Martín-Delgado, Miguel A.

    1997-10-01

    Using a recursive method we construct dimer and nondimer variational ansatzs of the ground state for the two-legged ladder, and compute the number of dimer coverings, the energy density, and the spin-correlation functions. The number of dimer coverings are given by the Fibonacci numbers for the dimer-resonating-valence-bond state and their generalization for the nondimer states. Our method relies on the recurrent relations satisfied by the overlaps of the states with different lengths, which can be solved using generating functions. The recurrent-relation method is applicable to other short-range systems. Based on our results we make a conjecture about the bond amplitudes of the two-legged ladder.

  2. Visible light photoreactivity from hybridization states between carbon nitride bandgap states and valence states in Nb and Ti oxides

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Hosik, E-mail: hosiklee@gmail.com [School of Mechanical and Advanced Materials Engineering, Ulsan National Institute of Science and Technology (UNIST), Unist-gil 100 Eonyang-eup, Ulsan 689-798 (Korea, Republic of); Ohno, Takahisa, E-mail: OHNO.Takahisa@nims.go.jp [Global Research Center for Environment and Energy based on Nanomaterials Science (GREEN), National Institute for Material Science, 1-2-1 Sengen, Tsukuba (Japan); Computational Materials Science Unit (CMSU), National Institute for Materials Science (NIMS), Tsukuba, Ibaraki 305-0047 (Japan)

    2013-03-29

    Highlights: ► Origin of bandgap reduction for visible photoreactivity is suggested. ► Carbon nitride adsorption in interlayer space can induce the bandgap reduction. ► The electronic structures are studied by density functional theory calculations. - Abstract: For better efficiency as photocatalysts, N-doping for visible light reactivity has been intensively studied in Lamellar niobic and titanic solid acids (HNb{sub 3}O{sub 8}, H{sub 2}Ti{sub 4}O{sub 9}), and its microscopic structures have been debated in this decade. We calculate the layered solid acids’ structures and bandgaps. Bandgap reduction by carbon nitride adsorption in interlayer space is observed computationally. It originates from localized nitrogen states which form delocalized top-valence states by hybridizing with the host oxygen states and can contribute to photo-current.

  3. The role of TM’s (M’s d valence electrons in TM@X12 and M@X12 clusters

    Directory of Open Access Journals (Sweden)

    Zhiyun Tan

    2016-12-01

    Full Text Available Using the density functional theory method, the icosahedral TM@X12 (M@X12 clusters (TM=Mn, Tc, Re; M=Zn, Cd, Hg; and X=Sn, Ge, which are composed of Sn12 (Ge12 shell covering a single TM (M atom, have been systematically examined to explore the role of TM’s (M’s d valence electrons playing in the clusters. The results show that the magnetism originate from the contribution of TM’s d valence electrons to TM@X12 clusters, where TM’s (M’s d valence electrons are not included in the superatomic electronic states to TM@X12 (M@X12 clusters. Taking into account the structural stability (imaginary frequency, binding energy, embedding energy, and core-shell interaction as well as the chemical stability (HOMO-LUMO gap after, we proposed that TM@X12 and M@X12 clusters can be assigned as the protyle superatoms. Furthermore, the results suggest that M@C60 clusters can not be superatoms, because their negative embedding energies and the distance from the center atom (M to C atom is larger than the sum of their Van Waals radii. Interestingly enough, we may obtain a simple judging method: for a magnetic superatom, the smaller the energy gap between the highest occupied magnetic state (HOMS and Fermi level or HOMO (MOgap, or MFgap, the easier on the change of its spin magnetic moment.

  4. Lung density

    DEFF Research Database (Denmark)

    Garnett, E S; Webber, C E; Coates, G

    1977-01-01

    The density of a defined volume of the human lung can be measured in vivo by a new noninvasive technique. A beam of gamma-rays is directed at the lung and, by measuring the scattered gamma-rays, lung density is calculated. The density in the lower lobe of the right lung in normal man during quiet...... breathing in the sitting position ranged from 0.25 to 0.37 g.cm-3. Subnormal values were found in patients with emphsema. In patients with pulmonary congestion and edema, lung density values ranged from 0.33 to 0.93 g.cm-3. The lung density measurement correlated well with the findings in chest radiographs...... but the lung density values were more sensitive indices. This was particularly evident in serial observations of individual patients....

  5. 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.

  6. Restrictive techniques: gastric banding

    Directory of Open Access Journals (Sweden)

    Katia Cristina da Cunha

    2006-03-01

    Full Text Available Surgery for the treatment of severe obesity has a definite role onthe therapeutic armamentarium all over the world. Initiated 40years ago, bariatric surgery has already a long way thanks tohundred of surgeons, who had constantly searched for the besttechnique for the adequate control of severe obesity. Among theimportant breakthroughs in obesity surgery there is theadjustable gastric band. It is a sylastic band, inflatable andadjustable, which is placed on the top of the stomach in order tocreate a 15-20 cc pouch, with an outlet of 1.3cm. The adjustablegastric band has also a subcutaneous reservoir through whichadjustments can be made, according to the patient evolution.The main feature of the adjustable gastric band is the fact thatis minimal invasive, reversible, adjustable and placedlaparoscopically. Then greatly diminishing the surgical traumato the severe obese patient. Belachew and Favretti’s techniqueof laparoscopic application of the adjustable gastric band isdescribed and the evolution of the technique during this years,as we has been practiced since 1998. The perioperative care ofthe patient is also described, as well as the follow-up and shortand long term controls.

  7. Band offsets of La{sub 2}O{sub 3} on (0001) GaN grown by reactive molecular-beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Ihlefeld, Jon F.; Brumbach, Michael; Atcitty, Stanley [Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States)

    2013-04-22

    La{sub 2}O{sub 3} films were prepared on (0001)-oriented GaN substrates via reactive molecular-beam epitaxy. Film orientation and phase were assessed using reflection high-energy electron and X-ray diffraction. Films were observed to grow as predominantly hexagonal La{sub 2}O{sub 3} for thicknesses less than 10 nm while film thickness greater than 10 nm favored mixed cubic and hexagonal symmetries. Band offsets were characterized by X-ray photoelectron spectroscopy on hexagonally symmetric films and valence band offsets of 0.63 {+-} 0.04 eV at the La{sub 2}O{sub 3}/GaN interface were measured. A conduction band offset of approximately 1.5 eV could be inferred from the measured valence band offset.

  8. Valence Bond Theory Reveals Hidden Delocalized Diradical Character of Polyenes.

    Science.gov (United States)

    Gu, Junjing; Wu, Wei; Danovich, David; Hoffmann, Roald; Tsuji, Yuta; Shaik, Sason

    2017-07-12

    The nature of the electronic-structure of polyenes, their delocalization features, and potential diradicaloid characters constitute a fundamental problem in chemistry. To address this problem, we used valence bond self-consistent field (VBSCF) calculations and modeling of polyenes, C2nH2n+2 (n = 2-10). The theoretical treatment shows that starting with n = 5, the polyene's wave function is mainly a shifting 1,4-diradicaloid, a character that increases as the chain length increases, while the contribution of the fundamental Lewis structure with alternating double and single bonds (1) decays quite fast and becomes minor relative to the diradicaloid pack. We show how, nevertheless, it is this wave function that predicts that polyenes will still exhibit alternating short/long CC bonds like the fundamental structure 1. Furthermore, despite the decay of the VB contribution of 1, it remains the single structure with the largest weight among all the individual structures. The mixing of all the 1,4-diradicaloid structures into 1 follows perturbation theory rules, with the result that the delocalization energy due to this mixing is additive and behaves as a linear function of the number of the double bonds, ΔEdel = -6.9 × n (kcal mol(-1)). The VB modeling shows that while the conjugation stabilizes structure 1, this stabilization energy is energetically overridden by the Pauli repulsion between two adjacent double bonds. Nevertheless, unsubstituted polyenes remain planar; this observation is addressed. Potential manifestations of the diradicaloid nature of polyenes are discussed, and it is concluded that the diradicaloid character is clearly not a well-defined physical property as in real diradicals. Thus, we went full circle to realize that our philosophical question may not be strictly resolved. The localized/delocalized properties of polyenes seem to define a "chemical duality principle". This duality of molecular wave functions is a ubiquitous beguiling phenomenon.

  9. Chemical Bonding: The Orthogonal Valence-Bond View

    Directory of Open Access Journals (Sweden)

    Alexander F. Sax

    2015-04-01

    Full Text Available Chemical bonding is the stabilization of a molecular system by charge- and spin-reorganization processes in chemical reactions. These processes are said to be local, because the number of atoms involved is very small. With multi-configurational self-consistent field (MCSCF wave functions, these processes can be calculated, but the local information is hidden by the delocalized molecular orbitals (MO used to construct the wave functions. The transformation of such wave functions into valence bond (VB wave functions, which are based on localized orbitals, reveals the hidden information; this transformation is called a VB reading of MCSCF wave functions. The two-electron VB wave functions describing the Lewis electron pair that connects two atoms are frequently called covalent or neutral, suggesting that these wave functions describe an electronic situation where two electrons are never located at the same atom; such electronic situations and the wave functions describing them are called ionic. When the distance between two atoms decreases, however, every covalent VB wave function composed of non-orthogonal atomic orbitals changes its character from neutral to ionic. However, this change in the character of conventional VB wave functions is hidden by its mathematical form. Orthogonal VB wave functions composed of orthonormalized orbitals never change their character. When localized fragment orbitals are used instead of atomic orbitals, one can decide which local information is revealed and which remains hidden. In this paper, we analyze four chemical reactions by transforming the MCSCF wave functions into orthogonal VB wave functions; we show how the reactions are influenced by changing the atoms involved or by changing their local symmetry. Using orthogonal instead of non-orthogonal orbitals is not just a technical issue; it also changes the interpretation, revealing the properties of wave functions that remain otherwise undetected.

  10. Valence, arousal, and task effects in emotional prosody processing

    Directory of Open Access Journals (Sweden)

    Silke ePaulmann

    2013-06-01

    Full Text Available Previous research suggests that emotional prosody processing is a highly rapid and complex process. In particular, it has been shown that different basic emotions can be differentiated in an early event-related brain potential (ERP component, the P200. Often, the P200 is followed by later long lasting ERPs such as the late positive complex (LPC. The current experiment set out to explore in how far emotionality and arousal can modulate these previously reported ERP components. In addition, we also investigated the influence of task demands (implicit vs. explicit evaluation of stimuli. Participants listened to pseudo-sentences (sentences with no lexical content spoken in six different emotions or in a neutral tone of voice while they either rated the arousal level of the speaker or their own arousal level. Results confirm that different emotional intonations can first be differentiated in the P200 component, reflecting a first emotional encoding of the stimulus possibly including a valence tagging process. A marginal significant arousal effect was also found in this time-window with high arousing stimuli eliciting a stronger P200 than low arousing stimuli. The P200 component was followed by a long lasting positive ERP between 400 and 750 ms. In this late time-window, both emotion and arousal effects were found. No effects of task were observed in either time-window. Taken together, results suggest that emotion relevant details are robustly decoded during early processing and late processing stages while arousal information is only reliably taken into consideration at a later stage of processing.

  11. Natural Intermediate Band in I 2 -II-IV-VI4 Quaternary Chalcogenide Semiconductors.

    Science.gov (United States)

    Liu, Qiheng; Cai, Zenghua; Han, Dan; Chen, Shiyou

    2018-01-25

    An intermediate band in the band gap of semiconductors is fundamental to the development of the intermediate band solar cells, but it is usually produced artificially, which imposes technical challenges on the experimental realization. Here we found that there are natural intermediate bands in the band gaps of the I2-II-IV-VI4 quaternary chalcogenide semiconductors such as Cu2ZnSnS4 and Ag2ZnSnSe4, which had been proposed as promising light-absorber semiconductors in thin film solar cells. By first-principles calculations, we found the lowest conduction band of these I2-II-IV-VI4 semiconductors in the kesterite structure is isolated (a lone band, resulting from the energy separation between Sn 5s and 5p states), which can be viewed as a natural intermediate band. The gap between the intermediate band and higher-energy conduction band can be increased through changing the crystal structure from the zincblende-derived kesterite structure to the wurtzite-derived wurtzite-kesterite structure. In contrast, the intermediate-conduction band gap shrinks when the component element Sn is replaced by Ge (Cu2ZnGeS4), and the gap even disappears (intermediate band disappear) when Sn is replaced by Si (Cu2ZnSiS4). Through tuning the intermediate-conduction and intermediate-valence band gaps, we show that the wurtzite-kesterite structured Ag2ZnSnSe4 may be a potential light-absorber semiconductor in intermediate band solar cells.

  12. Determination of the bulk cobalt valence state of co-perovskites containing surface-adsorbed impurities.

    Science.gov (United States)

    Haas, O; Ludwig, Chr; Wokaun, A

    2006-10-15

    We used thermogravimetric hydrogen reduction and iodometric titration to determine the bulk valence state of cobalt in Co-perovskites containing surface carbonate hydroxide or hydroxyl groups. It could be shown that thermogravimetric hydrogen reduction experiments are very sensitive to volatile surface groups, but due to their volatility, they can be specified and the bulk valence state of cobalt can still be deduced from these experiments. The iodometric titration is less sensitive to small volatile surface impurities, but precaution has to be taken that oxygen or iodine does not escape from the solution during dissolution of the sample. Best results were obtained if the sample was titrated during dissolution in a closed argon floated titration apparatus. We tested the two methods using LaCoO3 perovskite as a sample with a known valence state. Both methods delivered satisfactory results, and the valence state could be determined with an accuracy of better than 1%.

  13. Two Routes to Emotional Memory: Distinct Neural Processes for Valence and Arousal

    National Research Council Canada - National Science Library

    Elizabeth A. Kensinger; Suzanne Corkin; Marcus E. Raichle

    2004-01-01

    ... attributable to arousal. By using functional MRI and behavioral studies, we found that distinct cognitive and neural processes contribute to emotional memory enhancement for arousing information versus valenced, nonarousing information...

  14. Overlap valence quarks on a twisted mass sea. A case study for mixed action lattice QCD

    Energy Technology Data Exchange (ETDEWEB)

    Cichy, Krzysztof [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany). John von Neumann-Inst. fuer Computing NIC; Poznan Univ. (Poland). Faculty of Physics; Drach, Vincent; Jansen, Karl [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany). John von Neumann-Inst. fuer Computing NIC; Garcia-Ramos, Elena [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany). John von Neumann-Inst. fuer Computing NIC; Humboldt-Universitaet, Berlin (Germany); Herdoiza, Gregorio [UAM/CSIC Univ. Autonoma de Madrid (Spain). Dept. de Fisica Teorica; UAM/CSIC Univ. Autonoma de Madrid (Spain). Inst. de Fisica Teorica; Collaboration: European Twisted Mass Collaboration

    2012-11-15

    We discuss a Lattice QCD mixed action investigation employing Wilson maximally twisted mass sea and overlap valence fermions. Using four values of the lattice spacing, we demonstrate that the overlap Dirac operator assumes a point-like locality in the continuum limit. We also show that by adopting suitable matching conditions for the sea and valence theories a consistent continuum limit for the pion decay constant and light baryon masses can be obtained. Finally, we confront results for sea-valence mixed meson masses and the valence scalar correlator with corresponding expressions of chiral perturbation theory. This allows us to extract low energy constants of mixed action chiral perturbation which characterize the strength of unitarity violations in our mixed action setup.

  15. A continuous mapping between space and valence with left- and right-handers

    National Research Council Canada - National Science Library

    Freddi, Sébastien; Brouillet, Thibaut; Cretenet, Joël; Heurley, Loïc P; Dru, Vincent

    2016-01-01

    In this research, we examined whether emotional valence could correspond to a continuous lateral bias in space, according to a mental metaphor that establishes the mapping between a concrete domain (space...

  16. Hubbard-U band-structure methods

    DEFF Research Database (Denmark)

    Albers, R.C.; Christensen, Niels Egede; Svane, Axel

    2009-01-01

    The last decade has seen a large increase in the number of electronic-structure calculations that involve adding a Hubbard term to the local-density approximation band-structure Hamiltonian. The Hubbard term is then determined either at the mean-field level or with sophisticated many-body techniq......-structure theory. Alternatively, it may also be considered that they are just based on a Hubbard model that is more complex than the simple one- or few-band models traditionally used in many-body theories of solids....... are inconsistent with what the calculations actually do. Although many of these calculations are often treated as essentially first-principles calculations, in fact, we argue that they should be viewed from an entirely different point of view, namely, as based on phenomenological many-body corrections to band...

  17. Life changes and depressive symptoms: the effects of valence and amount of change

    OpenAIRE

    Bennik, Elise C.; Ormel, Johan; Oldehinkel, Albertine J

    2013-01-01

    Background Only few studies have focused on the effects of positive life changes on depression, and the ones that did demonstrated inconsistent findings. The aim of the present study was to obtain a better understanding of the influence of positive life changes on depressive symptoms by decomposing life changes into a valence and an amount of change component. Methods Using hierarchical multiple regression, we examined the unique effects of valence (pleasantness/unpleasantness) and amount of ...

  18. The New Resonating Valence Bond Method for Ab-Initio Electronic Simulations

    OpenAIRE

    Sorella, Sandro; Zen, Andrea

    2013-01-01

    The Resonating Valence Bond theory of the chemical bond was introduced soon after the discovery of quantum mechanics and has contributed to explain the role of electron correlation within a particularly simple and intuitive approach where the chemical bond between two nearby atoms is described by one or more singlet electron pairs. In this chapter Pauling's resonating valence bond theory of the chemical bond is revisited within a new formulation, introduced by P.W. Anderson after the discover...

  19. Time-resolved imaging of purely valence-electron dynamics during a chemical reaction

    DEFF Research Database (Denmark)

    Hockett, Paul; Bisgaard, Christer Z.; Clarkin, Owen J.

    2011-01-01

    the non-adiabatic photodissociation of carbon disulphide demonstrate how the purely electronic rearrangements of the valence electrons can be projected from inherently coupled electronic-vibrational dynamics. Combined with ongoing efforts in molecular frame alignment(20) and orientation(21,22), TRMFPADs...... offer the promise of directly imaging valence-electron dynamics during molecular processes without involving the use of strong, highly perturbing laser fields(23)....

  20. Modulating the band gap of a boron nitride bilayer with an external electric field for photocatalyst

    Energy Technology Data Exchange (ETDEWEB)

    Tang, Y. R.; Cao, J. X., E-mail: jxcao@xtu.edu.cn [Department of Physics, Xiangtan University, Xiangtan, Hunan 411105 (China); Zhang, Y. [Department of Physics and Information Technology, Baoji University of Arts and Sciences, Baoji 721016 (China)

    2016-05-21

    By virtue of first principle calculations, we propose an approach to reduce the band gap of layered semiconductors through the application of external electric fields for photocatalysis. As a typical example, the band gap of a boron nitride (BN) bilayer was reduced in the range from 4.45 eV to 0.3 eV by varying the external electric field strength. More interestingly, it is found that the uppermost valence band and the lowest conduction band are dominated by the N-p{sub z} and B-p{sub z} from different layers of the BN sheet, which suggests a wonderful photoexcited electron and hole separation system for photocatalysis. Our results imply that the strong external electric field can present an abrupt polarized surface.

  1. Impact of Band Nonparabolicity on Threshold Voltage of Nanoscale SOI MOSFET

    Directory of Open Access Journals (Sweden)

    Yasuhisa Omura

    2016-01-01

    Full Text Available This paper reconsiders the mathematical formulation of the conventional nonparabolic band model and proposes a model of the effective mass of conduction band electrons including the nonparabolicity of the conduction band. It is demonstrated that this model produces realistic results for a sub-10-nm-thick Si layer surrounded by an SiO2 layer. The major part of the discussion is focused on the low-dimensional electron system confined with insulator barriers. To examine the feasibility of our consideration, the model is applied to the threshold voltage of nanoscale SOI FinFETs and compared to prior experimental results. This paper also addresses a model of the effective mass of valence band holes assuming the nonparabolic condition.

  2. The scaling of the effective band gaps in indium-arsenide quantum dots and wires.

    Science.gov (United States)

    Wang, Fudong; Yu, Heng; Jeong, Sohee; Pietryga, Jeffrey M; Hollingsworth, Jennifer A; Gibbons, Patrick C; Buhro, William E

    2008-09-23

    Colloidal InAs quantum wires having diameters in the range of 5-57 nm and narrow diameter distributions are grown from Bi nanoparticles by the solution-liquid-solid (SLS) mechanism. The diameter dependence of the effective band gaps (DeltaE(g)s) in the wires is determined from photoluminescence spectra and compared to the experimental results for InAs quantum dots and rods and to the predictions of various theoretical models. The DeltaE(g) values for InAs quantum dots and wires are found to scale linearly with inverse diameter (d(-1)), whereas the simplest confinement models predict that DeltaE(g) should scale with inverse-square diameter (d(-2)). The difference in the observed and predicted scaling dimension is attributed to conduction-band nonparabolicity induced by strong valence-band-conduction-band coupling in the narrow-gap InAs semiconductor.

  3. Ultra wide band antennas

    CERN Document Server

    Begaud, Xavier

    2013-01-01

    Ultra Wide Band Technology (UWB) has reached a level of maturity that allows us to offer wireless links with either high or low data rates. These wireless links are frequently associated with a location capability for which ultimate accuracy varies with the inverse of the frequency bandwidth. Using time or frequency domain waveforms, they are currently the subject of international standards facilitating their commercial implementation. Drawing up a complete state of the art, Ultra Wide Band Antennas is aimed at students, engineers and researchers and presents a summary of internationally recog

  4. The power of emotional valence – From cognitive to affective processes in reading

    Directory of Open Access Journals (Sweden)

    Ulrike eAltmann

    2012-06-01

    Full Text Available The comprehension of stories requires the reader to imagine the cognitive and affective states of the characters. The content of many stories is unpleasant, as they often deal with conflict, disturbance or crisis. Nevertheless, unpleasant stories can be liked and enjoyed. In this fMRI study, we used a parametric approach to examine (1 the capacity of increasing negative valence of story contents to activate the mentalizing network (cognitive and affective theory of mind, ToM, and (2 the neural substrate of liking negatively valenced narratives. A set of 80 short narratives was compiled, ranging from neutral to negative emotional valence. For each story mean rating values on valence and liking were obtained from a group of 32 participants in a prestudy, and later included as parametric regressors in the fMRI analysis. Another group of 24 participants passively read the narratives in a 3 Tesla MRI scanner. Results revealed a stronger engagement of affective ToM-related brain areas with increasingly negative story valence. Stories that were unpleasant, but simulatiously liked, selectively engaged the medial prefrontal cortex (mPFC, which might reflect the moral exploration of the story content. Further analysis showed that the more the mPFC becomes engaged during the reading of negatively valenced stories, the more coactivation can be observed in other brain areas related to the neural processing of affective ToM and empathy.

  5. Distracted by pleasure: Effects of positive versus negative valence on emotional capture under load.

    Science.gov (United States)

    Gupta, Rashmi; Hur, Young-Jin; Lavie, Nilli

    2016-04-01

    We report 3 experiments examining the effects of positive versus negative valence and perceptual load in determining attention capture by irrelevant emotional distractors. Participants performed a letter search task searching for 1 of 2 target letters (X or N) in conditions of either low perceptual load (circular nontarget letters) or high perceptual load (angular nontarget letters that are similar to the target letters). On 25% of the trials an irrelevant emotional distractor was presented at the display center and participants were instructed to ignore it. The distractor stimulus was either positive or negative and was selected from 3 different classes: IAPS pictures of erotica or mutilated bodies (Experiment 1), happy or angry faces (Experiment 2), and faces associated with gain or loss in a prior value-learning phase involving a betting game (Experiment 3). The results showed a consistent pattern of interaction of load and valence across the 3 experiments. Irrelevant emotional distractors produced interference effects on search reaction time (RT) in conditions of low load, with no difference between negative and positive valence. High perceptual load, however, consistently reduced interference from the negative-valence distractors, but had no effect on the positive-valence distractors. As these results were consistently found across 3 different categories of emotional distractors, they suggest the general conclusion that attentional capture by irrelevant emotional distractors depends on both their valence and the level of perceptual load in the task and highlight the special status of distractors associated with pleasure. (c) 2016 APA, all rights reserved).

  6. Valence, arousal, and cognitive control: a voluntary task-switching study.

    Science.gov (United States)

    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 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.

  7. Effect of off-cut angle of hydrogen-terminated diamond(111) substrate on the quality of AlN towards high-density AlN/diamond(111) interface hole channel

    Science.gov (United States)

    Imura, Masataka; Banal, Ryan G.; Liao, Meiyong; Liu, Jiangwei; Aizawa, Takashi; Tanaka, Akihiro; Iwai, Hideo; Mano, Takaaki; Koide, Yasuo

    2017-01-01

    Single-crystal AlN/diamond heterojunction with high-density interface hole channel is successfully obtained by metal-organic vapor phase epitaxy. The AlN layer is epitaxially grown on hydrogen-terminated (H-)diamond(111) substrate. The thermal treatment of diamond substrate just before AlN growth under hydrogen and ammonia mixture environment at 1250 °C leads to surface sheet hole density as high as ˜1.0 × 1014 cm-2 without structural reconstruction of diamond surface. In addition, the use of smaller off-cut angle (0.20 ± 0.25°) H-diamond(111) substrate combined with this treatment enables to obtain single-crystal epitaxial AlN layer, which simultaneously acts as passivation of the surface hole channel with such a high density. The AlN/H-diamond(111) heterojunction reveals type-II staggered energy band configuration with valence band offset of ˜2.0 eV, which is suitable for the fabrication of p-channel field-effect transistor using AlN-gate-insulator/diamond heterojunction. These results are promising for the development of AlN/diamond hybrid power electronic devices.

  8. Band structure of W and Mo by empirical pseudopotential method

    Science.gov (United States)

    Sridhar, C. G.; Whiting, E. E.

    1977-01-01

    The empirical pseudopotential method (EPM) is used to calculate the band structure of tungsten and molybdenum. Agreement between the calculated reflectivity, density of states, density of states at the Fermi surface and location of the Fermi surface from this study and experimental measurements and previous calculations is good. Also the charge distribution shows the proper topological distribution of charge for a bcc crystal.

  9. Sr{sub 2}SmNbO{sub 6} perovskite: Synthesis, characterization and density functional theory calculations

    Energy Technology Data Exchange (ETDEWEB)

    Dutta, Alo, E-mail: alo_dutta@yahoo.com [Department of Condensed Matter Physics and Material Sciences, S. N. Bose National Centre for Basic Sciences, Block-JD, Sector III, Salt Lake, Kolkata, 700106 (India); Mukhopadhyay, P.K. [Department of Condensed Matter Physics and Material Sciences, S. N. Bose National Centre for Basic Sciences, Block-JD, Sector III, Salt Lake, Kolkata, 700106 (India); Sinha, T.P. [Department of Physics, Bose Institute, 93/1 Acharya Prafulla Chandra Road, Kolkata, 700 009 (India); Shannigrahi, Santiranjan [Institute of Materials Research and Engineering, Agency for Science Technology and Research, 3 Research Link, Singapore, 117602 (Singapore); Himanshu, A.K.; Sen, Pintu; Bandyopadhyay, S.K. [Variable Energy Cyclotron Centre, 1/AF Bidhannagar, Kolkata, 700064 (India)

    2016-08-15

    The density functional theory (DFT) under the generalized gradient approximation (GGA) has been used to investigate the electronic structure of double perovskite oxide Sr{sub 2}SmNbO{sub 6} synthesized by the solid-state reaction technique. The Rietveld refinement of the X-ray diffraction pattern of the sample shows the monoclinic P2{sub 1}/n phase at room temperature. The X-ray photoemission spectrum (XPS) of the material is collected in the energy window of 0–1200 eV. The chemical shift of the constituent elements calculated from the core level XPS spectra is used to analyze the covalency between the O anion and Sm/Nb cations. The valence band (VB) XPS spectrum is compared with the calculated VB spectrum using partial density of states in a standard way. The Raman spectrum is employed to investigate the phonon modes of the material in the monoclinic phase. Lorentzian lines are used to fit the experimental Raman spectrum, which present 24 phonon modes corresponding to the stretching and banding of NbO{sub 6}/SmO{sub 6} octahedra and translational motion of Sr along the Sr−O bond. The discrepancy between the measured and calculated band gap values has been removed by applying modified Becke-Johnson (mBJ) potential in the DFT calculations. The experimental optical band gap obtained from the UV–visible reflectance spectrum is found to be 3.42 eV, which is well matched with the DFT calculated value of 3.2 eV, and suggests the semiconducting nature of the material. The real (ε′) and imaginary (ε″) parts of the optical dielectric constant as a function of energy along the x-, y- and z-polarization directions using mBJ potential are calculated. The collective vibrational modes of the atoms, the Born effective charge of the ions and their effect on the static dielectric constant of the material are studied using DFT. The calculated value of static dielectric constant for SSN is found to be 41.3. - Highlights: • Electronic structure and dynamical

  10. Amniotic band syndrome.

    Science.gov (United States)

    Shetty, Prathvi; Menezes, Leo Theobald; Tauro, Leo Francis; Diddigi, Kumar Arun

    2013-10-01

    Amniotic band syndrome is an uncommon congenital disorder without any genetic or hereditary disposition. It involves fetal entrapment in strands of amniotic tissue and causes an array of deletions and deformations. Primary treatment is plastic and reconstructive surgery after birth with in utero fetal surgery also coming in vogue.

  11. Amniotic Band Syndrome

    OpenAIRE

    Shetty, Prathvi; Menezes, Leo Theobald; Tauro, Leo Francis; Diddigi, Kumar Arun

    2012-01-01

    Amniotic band syndrome is an uncommon congenital disorder without any genetic or hereditary disposition. It involves fetal entrapment in strands of amniotic tissue and causes an array of deletions and deformations. Primary treatment is plastic and reconstructive surgery after birth with in utero fetal surgery also coming in vogue.

  12. Colloquium: Topological band theory

    Science.gov (United States)

    Bansil, A.; Lin, Hsin; Das, Tanmoy

    2016-04-01

    The first-principles band theory paradigm has been a key player not only in the process of discovering new classes of topologically interesting materials, but also for identifying salient characteristics of topological states, enabling direct and sharpened confrontation between theory and experiment. This review begins by discussing underpinnings of the topological band theory, which involve a layer of analysis and interpretation for assessing topological properties of band structures beyond the standard band theory construct. Methods for evaluating topological invariants are delineated, including crystals without inversion symmetry and interacting systems. The extent to which theoretically predicted properties and protections of topological states have been verified experimentally is discussed, including work on topological crystalline insulators, disorder and interaction driven topological insulators (TIs), topological superconductors, Weyl semimetal phases, and topological phase transitions. Successful strategies for new materials discovery process are outlined. A comprehensive survey of currently predicted 2D and 3D topological materials is provided. This includes binary, ternary, and quaternary compounds, transition metal and f -electron materials, Weyl and 3D Dirac semimetals, complex oxides, organometallics, skutterudites, and antiperovskites. Also included is the emerging area of 2D atomically thin films beyond graphene of various elements and their alloys, functional thin films, multilayer systems, and ultrathin films of 3D TIs, all of which hold exciting promise of wide-ranging applications. This Colloquium concludes by giving a perspective on research directions where further work will broadly benefit the topological materials field.

  13. Moessbauer spectroscopic study on valence-detrapping and trapping of mixed-valence trinuclear iron(III, III, II) fluorine-substituted benzoate complexes

    Energy Technology Data Exchange (ETDEWEB)

    Sakai, Yoichi, E-mail: yocsakai@daido-it.ac.jp; Onaka, Satoru [Daido University (Japan); Takahashi, Masashi [Toho University (Japan); Ogiso, Ryo; Takayama, Tsutomu [Daido University (Japan); Nakamoto, Tadahiro [Toray Research Center (Japan)

    2012-03-15

    Four mixed-valence trinuclear iron(III, III, II) fluorine-substituted benzoate complexes were synthesized; Fe{sub 3}O(C{sub 6}F{sub 5}COO){sub 6}(C{sub 5}H{sub 5}N){sub 3}{center_dot}CH{sub 2}Cl{sub 2} (1), Fe{sub 3}O(C{sub 6}F{sub 5}COO){sub 6}(C{sub 5}H{sub 5}N){sub 3} (2), Fe{sub 3}O(2H-C{sub 6}F{sub 4}COO){sub 6}(C{sub 5}H{sub 5}N){sub 3} (3), and Fe{sub 3}O(4H-C{sub 6}F{sub 4}COO){sub 6}(C{sub 5}H{sub 5}N){sub 3} (4), in which valence-detrapping and trapping phenomena have been investigated by {sup 57}Fe- Moessbauer spectroscopy. The valence state of the three iron ions is trapped at lower temperatures while it is fully detrapped at higher temperatures for 1. Valence detrapping is not observed for 2, 3, and 4 even at room temperature, although Moessbauer spectra for 3 and 4 show complicated temperature dependence.

  14. Quasiparticle and hybrid density functional methods in defect studies: An application to the nitrogen vacancy in GaN

    Science.gov (United States)

    Lewis, D. K.; Matsubara, M.; Bellotti, E.; Sharifzadeh, S.

    2017-12-01

    Defects in semiconductors can play a vital role in the performance of electronic devices, with native defects often dominating the electronic properties of the semiconductor. Understanding the relationship between structural defects and electronic function will be central to the design of new high-performance materials. In particular, it is necessary to quantitatively understand the energy and lifetime of electronic states associated with the defect. Here, we apply first-principles density functional theory (DFT) and many-body perturbation theory within the GW approximation to understand the nature and energy of the defect states associated with a charged nitrogen vacancy on the electronic properties of gallium nitride (GaN), as a model of a well-studied and important wide gap semiconductor grown with defects. We systematically investigate the sources of error associated with the GW approximation and the role of the underlying atomic structure on the predicted defect state energies. Additionally, analysis of the computed electronic density of states (DOS) reveals that there is one occupied defect state 0.2 eV below the valence band maximum and three unoccupied defect states at energy of 0.2-0.4 eV above the conduction band minimum, suggesting that this defect in the +1 charge state will not behave as a carrier trap. Furthermore, we compare the character and energy of the defect state obtained from GW and DFT using the HSE approximate density functional and find excellent agreement. This systematic study provides a more complete understanding of how to obtain quantitative defect energy states in bulk semiconductors.

  15. Approach and Withdrawal Tendencies during Written Word Processing: Effects of Task, Emotional Valence, and Emotional Arousal.

    Science.gov (United States)

    Citron, Francesca M M; Abugaber, David; Herbert, Cornelia

    2015-01-01

    The affective dimensions of emotional valence and emotional arousal affect processing of verbal and pictorial stimuli. Traditional emotional theories assume a linear relationship between these dimensions, with valence determining the direction of a behavior (approach vs. withdrawal) and arousal its intensity or strength. In contrast, according to the valence-arousal conflict theory, both dimensions are interactively related: positive valence and low arousal (PL) are associated with an implicit tendency to approach a stimulus, whereas negative valence and high arousal (NH) are associated with withdrawal. Hence, positive, high-arousal (PH) and negative, low-arousal (NL) stimuli elicit conflicting action tendencies. By extending previous research that used several tasks and methods, the present study investigated whether and how emotional valence and arousal affect subjective approach vs. withdrawal tendencies toward emotional words during two novel tasks. In Study 1, participants had to decide whether they would approach or withdraw from concepts expressed by written words. In Studies 2 and 3 participants had to respond to each word by pressing one of two keys labeled with an arrow pointing upward or downward. Across experiments, positive and negative words, high or low in arousal, were presented. In Study 1 (explicit task), in line with the valence-arousal conflict theory, PH and NL words were responded to more slowly than PL and NH words. In addition, participants decided to approach positive words more often than negative words. In Studies 2 and 3, participants responded faster to positive than negative words, irrespective of their level of arousal. Furthermore, positive words were significantly more often associated with "up" responses than negative words, thus supporting the existence of implicit associations between stimulus valence and response coding (positive is up and negative is down). Hence, in contexts in which participants' spontaneous responses are

  16. Low Bone Density

    Science.gov (United States)

    ... Density Exam/Testing › Low Bone Density Low Bone Density Low bone density is when your bone density ... people with normal bone density. Detecting Low Bone Density A bone density test will determine whether you ...

  17. Bidirectional switch of the valence associated with a hippocampal contextual memory engram.

    Science.gov (United States)

    Redondo, Roger L; Kim, Joshua; Arons, Autumn L; Ramirez, Steve; Liu, Xu; Tonegawa, Susumu

    2014-09-18

    The valence of memories is malleable because of their intrinsic reconstructive property. This property of memory has been used clinically to treat maladaptive behaviours. However, the neuronal mechanisms and brain circuits that enable the switching of the valence of memories remain largely unknown. Here we investigated these mechanisms by applying the recently developed memory engram cell- manipulation technique. We labelled with channelrhodopsin-2 (ChR2) a population of cells in either the dorsal dentate gyrus (DG) of the hippocampus or the basolateral complex of the amygdala (BLA) that were specifically activated during contextual fear or reward conditioning. Both groups of fear-conditioned mice displayed aversive light-dependent responses in an optogenetic place avoidance test, whereas both DG- and BLA-labelled mice that underwent reward conditioning exhibited an appetitive response in an optogenetic place preference test. Next, in an attempt to reverse the valence of memory within a subject, mice whose DG or BLA engram had initially been labelled by contextual fear or reward conditioning were subjected to a second conditioning of the opposite valence while their original DG or BLA engram was reactivated by blue light. Subsequent optogenetic place avoidance and preference tests revealed that although the DG-engram group displayed a response indicating a switch of the memory valence, the BLA-engram group did not. This switch was also evident at the cellular level by a change in functional connectivity between DG engram-bearing cells and BLA engram-bearing cells. Thus, we found that in the DG, the neurons carrying the memory engram of a given neutral context have plasticity such that the valence of a conditioned response evoked by their reactivation can be reversed by re-associating this contextual memory engram with a new unconditioned stimulus of an opposite valence. Our present work provides new insight into the functional neural circuits underlying the

  18. Memory effects of sleep, emotional valence, arousal and novelty in children.

    Science.gov (United States)

    Vermeulen, Marije C M; van der Heijden, Kristiaan B; Benjamins, Jeroen S; Swaab, Hanna; van Someren, Eus J W

    2017-06-01

    Effectiveness of memory consolidation is determined by multiple factors, including sleep after learning, emotional valence, arousal and novelty. Few studies investigated how the effect of sleep compares with (and interacts with) these other factors, of which virtually none are in children. The present study did so by repeated assessment of declarative memory in 386 children (45% boys) aged 9-11 years through an online word-pair task. Children were randomly assigned to either a morning or evening learning session of 30 unrelated word-pairs with positive, neutral or negative valenced cues and neutral targets. After immediately assessing baseline recognition, delayed recognition was recorded either 12 or 24 h later, resulting in four different assessment schedules. One week later, the procedure was repeated with exactly the same word-pairs to evaluate whether effects differed for relearning versus original novel learning. Mixed-effect logistic regression models were used to evaluate how the probability of correct recognition was affected by sleep, valence, arousal, novelty and their interactions. Both immediate and delayed recognition were worse for pairs with negatively valenced or less arousing cue words. Relearning improved immediate and delayed word-pair recognition. In contrast to these effects, sleep did not affect recognition, nor did sleep moderate the effects of arousal, valence and novelty. The findings suggest a robust inclination of children to specifically forget the pairing of words to negatively valenced cue words. In agreement with a recent meta-analysis, children seem to depend less on sleep for the consolidation of information than has been reported for adults, irrespective of the emotional valence, arousal and novelty of word-pairs. © 2017 European Sleep Research Society.

  19. Bidirectional switch of the valence associated with a hippocampal contextual memory engram

    Science.gov (United States)

    Redondo, Roger L; Kim, Joshua; Arons, Autumn L; Ramirez, Steve; Liu, Xu; Tonegawa, Susumu

    2014-01-01

    The valence of memories is malleable because of their intrinsic reconstructive property1. This property of memory has been used clinically to treat maladaptive behaviours2. However, the neuronal mechanisms and brain circuits that enable the switching of the valence of memories remain largely unknown. Here, we investigated these mechanisms by applying the recently developed memory engram cell-labelling and -manipulation technique 3,4. We labelled, with Channelrhodopsin-2 (ChR2), a population of cells in either the dorsal dentate gyrus (DG) of the hippocampus or the basolateral complex of the amygdala (BLA) that were specifically activated during contextual fear or reward conditioning. Both groups of fear-conditioned mice displayed aversive light-dependent responses in an optogenetic place avoidance test, whereas both DG- and BLA-labelled mice that underwent reward conditioning exhibited an appetitive response in an optogenetic place preference test. Next, in an attempt to reverse the valence of memory within a subject, mice whose DG or BLA engram had initially been labelled by contextual fear or reward conditioning were subjected to a second conditioning of the opposite valence while their original DG or BLA engram was reactivated by blue light. Subsequent optogenetic place avoidance and preference tests revealed that while the DG-engram group displayed a response indicating a switch of the memory valence, the BLA-engram group did not. This switch was also evident at the cellular level by a change in functional connectivity between DG engram-bearing cells and BLA engram-bearing cells. Thus, we found that in the DG, the neurons carrying the memory engram of a given neutral context have plasticity such that the valence of a conditioned response evoked by their reactivation can be reversed by re-associating this contextual memory engram with a new US of an opposite valence. Our present work provides new insight into the functional neural circuit underlying the

  20. On possible existence of pseudobinary mixed valence fluorides of Ag(I)/Ag(II): a DFT study.

    Science.gov (United States)

    Grochala, Wojciech

    2011-09-01

    The DFT calculations performed within local density approximation disclose conceivable existence of two novel mixed-valence Ag(I)/Ag(II) fluorides, Ag(2)F(3), i.e., Ag(I)Ag(II)F(3) and Ag(3)F(4), i.e., Ag(I)(2)Ag(II)F(4). Ag(2)F(3) is predicted to crystallize in three equally stable NaCuF(3)-, KAgF(3)-, or CuTeO(3)-type structures, while Ag(3)F(4) should be isostructural to Na(2)CuF(4). The calculated vibration-corrected energies of formation at 0 K of Ag(2)F(3) and Ag(3)F(4) (in their most stable polytypes) from binary fluorides are negative but small (respectively, -0.09 eV and -0.21 eV per formula unit). Formation of Ag(3)F(5) (which, in fact, is a mixed valence Ag(I)/Ag(III) salt) from binary fluorides is much less likely, since the energy of formation is quite positive of about a quarter eV. The predicted volumes per formula unit for all forms of Ag(2)F(3) are larger and that for K(2)CuF(4)-type Ag(3)F(4) is smaller than the sum of volumes of the corresponding binary fluorides; Ag(2)F(3) should not form at high pressure conditions due to a decomposition to the binary constituents. Ag(2)F(3) and Ag(3)F(4) should exhibit genuine mixed- and not intermediate-valence with quite different coordination spheres of Ag(I) and Ag(II). Nevertheless, they should not be electric insulators. Ag(2)F(3) is predicted to be a metallic ferrimagnet with a magnetic superexchange coupling constant, J, of -2 meV while Ag(3)F(4) should be a metallic ferromagnet with J of +52 meV. Since Ag(2)F(3) and Ag(3)F(4) are at the verge of thermodynamic stability, a handful of exothermic reactions have been proposed which could yield these as yet unknown compounds.

  1. Non-classical behaviour of higher valence dopants in chromium (III) oxide by a Cr vacancy compensation mechanism

    Science.gov (United States)

    Carey, John J.; Nolan, Michael

    2017-10-01

    Modification of metal oxides with dopants that have a stable oxidation in their parent oxides which is higher than the host system is expected to introduce extra electrons into the material to improve carrier mobility. This is essential for applications in catalysis, SOFCs and solar energy materials. Density functional theory calculations are used to investigate the change in electronic and geometric structure of chromium (III) oxide by higher valence dopants, namely; Ce, Ti, V and Zr. For single metal doping, we find that the dopants with variable oxidation states, Ce, Ti and V, adopt a valence state of  +3, while Zr dopant has a  +4 oxidation state and reduces a neighbouring Cr cation. Chromium vacancy formation is greatly enhanced for all dopants, and favoured over oxygen vacancy formation. The Cr vacancies generate holes which oxidise Ce, Ti and V from  +3 to  +4, while also oxidising lattice oxygen sites. For Zr doping, the generated holes oxidise the reduced Cr2+ cation back to Cr3+ and also two lattice oxygen atoms. Three metal atoms in the bulk lattice facilitate spontaneous Cr vacancy from charge compensation. A non-classical compensation mechanism is observed for Ce, Ti and V; all three metals are oxidised from  +3 to  +4, which explains experimental observations that these metals have a  +4 oxidation state in Cr2O3. Charge compensation of the three Zr metals proceeds by a classical higher valence doping mechanism; the three dopants reduce three Cr cations, which are subsequently charge compensated by a Cr vacancy oxidising three Cr2+ to Cr3+. The compensated structures are the correct ground state electronic structure for these doped systems, and used as a platform to investigate cation/anion vacancy formation. Unlike the single metal doped bulks, preference is now given for oxygen vacancy formation over Cr vacancy formation, indicating that the dopants increase the reducibility of Cr2O3 with Ce doping showing the strongest

  2. Investigation of carrier density and mobility in microcrystalline silicon alloys using Hall effect and thermopower measurements; Untersuchung der Ladungstraegerkonzentration und -beweglichkeit in mikrokristallinen Siliziumlegierungen mit Hall-Effekt und Thermokraft

    Energy Technology Data Exchange (ETDEWEB)

    Sellmer, Christian

    2012-08-31

    The electronic properties of amorphous and microcrystalline silicon layers in thin-film solar cells significantly affect the efficiency of solar cells. An important property of the individual layer is the electronic transport, which is described by the variables conductivity, photoconductivity, mobility, and carrier concentration. In the past, individual characterization methods were typically used to determine the electronic properties. Using the combination of Hall effect, conductivity, and thermoelectric power measurements additional variables can be derived, such as the effective density of states at the valence and conduction band edge, making a more detailed description of the material possible. To systematically study the electronic properties - in particular carrier mobility and carrier concentration - various series of silicon films are prepared for this work including microcrystalline silicon layers of different doping and crystallinity and a series of silicon films where the Fermi level is moved by irradiation with high energy electrons on one and the same sample. The results show that the transition from amorphous to microcrystalline transport is relatively abrupt. If the electron transport takes place in only amorphous regions, it is marked by the sign anomaly of the Hall effect. If a continuous crystalline path exists, the electronic properties are dominated by the crystalline volume fraction. The results of the measurements of silicon layers are compared with those of microcrystalline silicon carbide samples. Silicon carbide is especially interesting for future applications in thin-film solar cells due to high transparency and high conductivity. It is shown that the effective density of states at the valence and conduction band edge as a function of temperature in p- and n-type microcrystalline silicon and silicon carbide samples largely coincide with those of crystalline silicon or silicon carbide. A square root shaped profile of the density of

  3. The hierarchically organized splitting of chromosome bands into sub-bands analyzed by multicolor banding (MCB).

    Science.gov (United States)

    Lehrer, H; Weise, A; Michel, S; Starke, H; Mrasek, K; Heller, A; Kuechler, A; Claussen, U; Liehr, T

    2004-01-01

    To clarify the nature of chromosome sub-bands in more detail, the multicolor banding (MCB) probe-set for chromosome 5 was hybridized to normal metaphase spreads of GTG band levels at approximately 850, approximately 550, approximately 400 and approximately 300. It could be observed that as the chromosomes became shorter, more of the initial 39 MCB pseudo-colors disappeared, ending with 18 MCB pseudo-colored bands at the approximately 300-band level. The hierarchically organized splitting of bands into sub-bands was analyzed by comparing the disappearance or appearance of pseudo-color bands of the four different band levels. The regions to split first are telomere-near, centromere-near and in 5q23-->q31, followed by 5p15, 5p14, and all GTG dark bands in 5q apart from 5q12 and 5q32 and finalized by sub-band building in 5p15.2, 5q21.2-->q21.3, 5q23.1 and 5q34. The direction of band splitting towards the centromere or the telomere could be assigned to each band separately. Pseudo-colors assigned to GTG-light bands were resistant to band splitting. These observations are in concordance with the recently proposed concept of chromosome region-specific protein swelling. Copyright 2003 S. Karger AG, Basel

  4. AMNIOTIC BAND SYNDROME

    Directory of Open Access Journals (Sweden)

    Jovana Đorđević

    2009-04-01

    Full Text Available Amniotic band syndrome (ABS is a set of congenital malformations attributed to amniotic bands that entangle fetal parts during intrauterine life, which results in a broad spectrum of anatomic disturbances - ranging from minor constriction rings and lymphedema of the digits to complex, bizarre multiple congenital anomalies incompatible with life. ABS is not very often, but should be considered in every newborn with congenital anomalies, especially defects of extremities and/or body walls. ABS can be diagnosed prenatally by ultrasound; otherwise, the defects are seen after birth. Child's karyotyping is of great importance, in order to avoid misdiagnosis and incorrect information of recurrence risk. A team of specialists should be included in the treatment and follow-up of children with ABS, according to individual needs of every single patient.The aim of this paper is to point out diagnostic and therapeutic approaches in newborns with ABS trough the report of two cases.

  5. Seasonal variation in an annually-banded coral Porites: A scanning electron microscopy investigation

    Digital Repository Service at National Institute of Oceanography (India)

    Naqvi, S.A.S.

    in high density bands and their absence in low density bands. It is proposed that during the monsoon season, run-off from the island may bring detrital material that subsequently gets incorporated in coral skeleton. By contrast, calm and dry conditions...

  6. Quantifying the importance of orbital over spin correlations in delta-Pu within density-functional theory

    Energy Technology Data Exchange (ETDEWEB)

    Soderlind, P; Wolfer, W

    2007-07-27

    Spin and orbital and electron correlations are known to be important when treating the high-temperature {delta} phase of plutonium within the framework of density-functional theory (DFT). One of the more successful attempts to model {delta}-Pu within this approach has included condensed-matter generalizations of Hund's three rules for atoms, i.e., spin polarization, orbital polarization, and spin-orbit coupling. Here they perform a quantitative analysis of these interactions relative rank for the bonding and electronic structure in {delta}-Pu within the DFT model. The result is somewhat surprising in that spin-orbit coupling and orbital polarization are far more important than spin polarization for a realistic description of {delta}-Pu. They show that these orbital correlations on their own, without any formation of magnetic spin moments, can account for the low atomic density of the {delta} phase with a reasonable equation-of-state. In addition, this unambiguously non-magnetic (NM) treatment produces a one-electron spectra with resonances close to the Fermi level consistent with experimental valence band photoemission spectra.

  7. Intervalence-resonant Raman spectroscopy of strongly coupled mixed-valence cluster dimers of ruthenium.

    Science.gov (United States)

    Rocha, Reginaldo C; Brown, Mac G; Londergan, Casey H; Salsman, J Catherine; Kubiak, Clifford P; Shreve, Andrew P

    2005-10-13

    Resonance Raman spectroelectrochemistry (RR-SEC) at -20 degrees C has been performed on the pyrazine-bridged dimer of mu-oxo-centered trinuclear ruthenium-acetate "clusters"--[(dmap)(CO)(mu-OAc)6(mu3-O)Ru3(mu-L(b))Ru3(mu3-O)(mu-OAc)6(CO)(dmap)]n (where dmap = 4-(dimethylamino)pyridine and L(b) = pyrazine-h4 and pyrazine-d4)-in three oxidation states: n = 0, -1, and -2. In the one-electron reduced, "mixed-valent" state (overall -1 charge and a single odd electron; formal oxidation states [II, II, III]-[III, III, II] on the metal centers), the Raman excitation at 800 nm is resonant with a cluster-to-cluster intervalence charge-transfer (IVCT) band. Under these conditions, scattering enhancement is observed for all four totally symmetric vibrational modes of the bridging pyrazine ligand (nu8a, nu9a, nu1, and nu6a) in the investigated spectral range (100-2000 cm(-1)), and there is no evidence of activity in non-totally symmetric vibrations. Resonantly enhanced Raman peaks related to peripheral pyridyl (dmap) ligand modes and low-frequency features arising from the trigonal Ru3O cluster core and the cluster[Ru]-[N]ligand vibrations were also observed in the spectra of the intermediate-valence (n = -1) cluster dimer. The vibrational assignments and interpretations proposed in this work were reinforced by observation of characteristic isotopic frequency shifts accompanying deuteration of the bridging pyrazine. The results reveal that the fully symmetric (A(g)) vibrational motions of the organic bridge are coupled to the nominally metal cluster-to-metal cluster fast intramolecular electron transfer (ET) and provide validation of the near-delocalized description according to a predicted three-site/three-state (e.g., metal-bridge-metal) vibronic coupling model, in which the important role of the bridging ligand in mediating electronic communication and delocalization between charge centers is explicitly considered. Further compelling evidence supporting an extended five

  8. Effect of hydrogenation on the band gap of graphene nano-flakes

    Energy Technology Data Exchange (ETDEWEB)

    Tachikawa, Hiroto, E-mail: hiroto@eng.hokudai.ac.jp; Iyama, Tetsuji; Kawabata, Hiroshi

    2014-03-03

    The effects of hydrogenation on the band gap of graphene have been investigated by means of density functional theory method. It is generally considered that the band gap increases with increasing coverage of hydrogen atom on the graphene. However, the present study shows that the band gap decreases first with increasing hydrogen coverage and reaches the lowest value at finite coverage (γ = 0.3). Next, the band gap increases to that of insulator with coverage from 0.3 to 1.0. This specific feature of the band gap is reasonably explained by broken symmetry model and the decrease of pi-conjugation. The electronic states of hydrogenated graphene are discussed. - Highlights: • Density functional theory calculations were carried out for hydrogen on graphene • Effects of hydrogenation on the band gap of graphene were examined. • The band gap showed a minimum at a finite coverage. • Mechanism of specific band gap feature was discussed.

  9. Experimental Constraints on the Partitioning and Valence of V and Cr in Garnet and Coexisting Glass

    Science.gov (United States)

    Righter, K.; Sutton, S.; Berthet, S.; Newville, M.

    2008-01-01

    A series of experiments with garnet and coexisting melt have been carried out across a range of oxygen fugacities (near hematite-magnetite (HM) to below the iron-wustite (IW) buffers) at 1.7 GPa to study the partitioning and valence of Cr and V in both phases. Experiments were carried out in a non end loaded piston cylinder apparatus, and the run products were analyzed with electron microprobe and xray absorption near edge structure (XANES) analysis at beamline 13-ID at the Advanced Photon Source of Argonne National Lab. The valence of vanadium and chromium were determined using the position and intensity of the Ka pre-edge peaks, calibrated on a series of Cr and Vbearing standard glasses. This technique has been applied to V and Cr in glasses and V in spinels previously, and in these isotropic phases there are no orientational effects on the XANES spectra (Righter et al., 2006, Amer. Mineral. 91, 1643-1656). We also now demonstrate this to be true for V and Cr in garnet. Also, previous work has shown that V has a higher valence in the glass (or melt) than in the coexisting spinel. This is also true for V in garnet-glass pairs in this study. Vanadium valence in garnets varies from 2.7 below the IW buffer to 3.7 near HM, and for coexisting glass it varies from 3.2 to 4.3. Vanadium valence measured in some natural garnets from mantle localities indicates V in the more reduced range at 2.5. Comparisons will be made between fO2 estimated from V valence and other methods for garnet-bearing mantle samples. In contrast, Cr valence measured in garnet and coexisting glass for all experimental and natural samples is 2.9- 3.0, suggesting that the valence of Cr does not vary within either phase across a large fO2 range. These results demonstrate that while V varies from 2+ to 3+ to 4+ in garnet-melt systems, Cr does not, and this will ultimately affect the partitioning behavior of these two elements in natural systems. Garnet/melt D(Cr) are between 12 and 17 across this range

  10. Mixed valence nanostructured Mn3O4 for supercapacitor applications

    Indian Academy of Sciences (India)

    Specific capacitance value of 665.08 F g−1 was obtained for symmetric supercapacitor with Mn3O4 active material at slow scan rate. Reasonably high power and energy density values, viz., 4.27 kW kg−1 and 4.36 × 10−2 Wh kg−1, respectively, were obtained for charge–discharge cycles at a constant current of 12.74 mA ...

  11. Role of correlated hopping in mixed valence phenomena

    Indian Academy of Sciences (India)

    There are totally 120 basis states and the eigenvectors of H are represented as a lin- ear combination of vectors (4). f-electron density (nf i ) = (1/N). ∑ iσ f. † iσfiσ where N is the number of lattice sites; f–d intersite correlation function cfd = (f† iσdjσ). Low- temperature specific heat is calculated using the relation. C = kBβ. 2 ∂.

  12. The influence of valence and arousal on reasoning: Affective priming in the semantic verification task

    Directory of Open Access Journals (Sweden)

    Orlić Ana

    2014-01-01

    Full Text Available The aim of the present study was to examine the effects of affective valence and arousal on the reasoning process. Reasoning was measured using a semantic verification task and the influence of valence and arousal was tracked using the affective priming paradigm. Primes were photographs varied on two dimensions - emotional valence (positive, neutral, negative and arousal (high, low. Forty-nine psychology students participated in the experiment. Results showed that reaction time needed for semantic verification was significantly faster for positive-high arousing in comparison to positive-low arousing condition and for neutral high arousing in comparison to neutral-low arousing condition, but there were no significant differences in negative low and high arousing conditions. Also, significant differences were found among all three valences in high arousing conditions and there were no such differences in low arousing conditions. These results reveal the importance of both arousal and valence in the research on the influence of emotions on the reasoning process. [Projekat Ministarstva nauke Republike Srbije, br. 179033

  13. Music, emotion, and time perception: the influence of subjective emotional valence and arousal?

    Science.gov (United States)

    Droit-Volet, Sylvie; Ramos, Danilo; Bueno, José L O; Bigand, Emmanuel

    2013-01-01

    The present study used a temporal bisection task with short (2 s) stimulus durations to investigate the effect on time estimation of several musical parameters associated with emotional changes in affective valence and arousal. In order to manipulate the positive and negative valence of music, Experiments 1 and 2 contrasted the effect of musical structure with pieces played normally and backwards, which were judged to be pleasant and unpleasant, respectively. This effect of valence was combined with a subjective arousal effect by changing the tempo of the musical pieces (fast vs. slow) (Experiment 1) or their instrumentation (orchestral vs. piano pieces). The musical pieces were indeed judged more arousing with a fast than with a slow tempo and with an orchestral than with a piano timbre. In Experiment 3, affective valence was also tested by contrasting the effect of tonal (pleasant) vs. atonal (unpleasant) versions of the same musical pieces. The results showed that the effect of tempo in music, associated with a subjective arousal effect, was the major factor that produced time distortions with time being judged longer for fast than for slow tempi. When the tempo was held constant, no significant effect of timbre on the time judgment was found although the orchestral music was judged to be more arousing than the piano music. Nevertheless, emotional valence did modulate the tempo effect on time perception, the pleasant music being judged shorter than the unpleasant music.

  14. Music, Emotion and Time Perception: The influence of subjective emotional valence and arousal?

    Directory of Open Access Journals (Sweden)

    SYLVIE eDROIT-VOLET

    2013-07-01

    Full Text Available The present study used a temporal bisection task with short (< 2 s and long (> 2 s stimulus durations to investigate the effect on time estimation of several musical parameters associated with emotional changes in affective valence and arousal. In order to manipulate the positive and negative valence of music, Experiments 1 and 2 contrasted the effect of musical structure with pieces played normally and backwards, which were judged to be pleasant and unpleasant, respectively. This effect of valence was combined with a subjective arousal effect by changing the tempo of the musical pieces (fast vs. slow (Experiment 1 or their instrumentation (orchestral vs. piano pieces. The musical pieces were indeed judged more arousing with a fast than with a slow tempo and with an orchestral than with a piano timbre. In Experiment 3, affective valence was also tested by contrasting the effect of tonal (pleasant versus atonal (unpleasant versions of the same musical pieces. The results showed that the effect of tempo in music, associated with a subjective arousal effect, was the major factor that produced time distortions with time being judged longer for fast than for slow tempi. When the tempo was held constant, no significant effect of timbre on the time judgment was found although the orchestral music was judged to be more arousing than the piano music. Nevertheless, emotional valence did modulate the tempo effect on time perception, the pleasant music being judged shorter than the unpleasant music.

  15. Differential Activation of Amygdala Arc Expression By Positive and Negatively Valenced Emotional Learning Conditions

    Directory of Open Access Journals (Sweden)

    Erica eYoung

    2013-12-01

    Full Text Available Norepinephrine is released in the amygdala following negatively arousing learning conditions. This event initiates a cascade of changes including the transcription of activity-regulated cytoskeleton-associated protein (Arc expression, an early-immediate gene associated with memory encoding. Recent evidence suggests that the valence of emotionally laden encounters may generate lateralized, as opposed to symmetric release of this transmitter in the right or left amygdala. It is currently not clear if valence-induced patterns of selective norepinephrine output across hemispheres are also reproduced in downstream pathways of cellular signaling necessary for memory formation. This question was addressed by determining if Arc expression is differentially distributed across the right and left amygdala following exposure to positively or negatively valenced learning conditions respectively. Male Sprague Dawley rats were randomly assigned to groups exposed to the Homecage only, 5 auditory tones only, or 5 auditory tones paired with footshock (0.35mA during Pavlovian fear conditioning. Western blot analysis revealed that Arc expression in the right amygdala was elevated significantly above that observed in the left amygdala 60 and 90 minutes following fear conditioning. Similarly, subjects exposed to a a negatively valenced outcome consisting of an unexpected reduction in food rewards showed a greater level of Arc expression in only the right, but not left basolateral amygdala. Presenting a positively valenced event involving an unexpected increase in food reward magnitude following bar pressing, resulted in significantly greater Arc expression in the left, but not right basolateral amygdala (p

  16. Segregation of information about emotional arousal and valence in horse whinnies.

    Science.gov (United States)

    Briefer, Elodie F; Maigrot, Anne-Laure; Mandel, Roi; Freymond, Sabrina Briefer; Bachmann, Iris; Hillmann, Edna

    2015-04-21

    Studying vocal correlates of emotions is important to provide a better understanding of the evolution of emotion expression through cross-species comparisons. Emotions are composed of two main dimensions: emotional arousal (calm versus excited) and valence (negative versus positive). These two dimensions could be encoded in different vocal parameters (segregation of information) or in the same parameters, inducing a trade-off between cues indicating emotional arousal and valence. We investigated these two hypotheses in horses. We placed horses in five situations eliciting several arousal levels and positive as well as negative valence. Physiological and behavioral measures collected during the tests suggested the presence of different underlying emotions. First, using detailed vocal analyses, we discovered that all whinnies contained two fundamental frequencies ("F0" and "G0"), which were not harmonically related, suggesting biphonation. Second, we found that F0 and the energy spectrum encoded arousal, while G0 and whinny duration encoded valence. Our results show that cues to emotional arousal and valence are segregated in different, relatively independent parameters of horse whinnies. Most of the emotion-related changes to vocalizations that we observed are similar to those observed in humans and other species, suggesting that vocal expression of emotions has been conserved throughout evolution.

  17. Neural systems subserving valence and arousal during the experience of induced emotions.

    Science.gov (United States)

    Colibazzi, Tiziano; Posner, Jonathan; Wang, Zhishun; Gorman, Daniel; Gerber, Andrew; Yu, Shan; Zhu, Hongtu; Kangarlu, Alayar; Duan, Yunsuo; Russell, James A; Peterson, Bradley S

    2010-06-01

    The circumplex model of affect construes all emotions as linear combinations of 2 independent neurophysiological dimensions, valence and arousal. We used functional magnetic resonance imaging to identify the neural networks subserving valence and arousal, and we assessed, in 10 participants, the associations of the BOLD (blood oxygen level-dependent) response, an indirect index of neural activity, with ratings of valence and arousal during the emotional experiences induced by the presentation of evocative sentences. Unpleasant emotional experience was associated with increased BOLD signal intensities in the supplementary motor, anterior midcingulate, right dorsolateral prefrontal, occipito-temporal, inferior parietal, and cerebellar cortices. Highly arousing emotions were associated with increased BOLD signal intensities in the left thalamus, globus pallidus, caudate, parahippocampal gyrus, amygdala, premotor cortex, and cerebellar vermis. Separate analyses using a finite impulse response model confirmed these results and revealed that pleasant emotions engaged an additional network that included the midbrain, ventral striatum, and caudate nucleus, all portions of a reward circuit. These findings suggest the existence of distinct networks subserving the valence and arousal dimensions of emotions, with midline and medial temporal lobe structures mediating arousal and dorsal cortical areas and mesolimbic pathways mediating valence.

  18. Emotional reactivity to valence-loaded stimuli are related to treatment response of neurocognitive therapy.

    Science.gov (United States)

    Vanderhasselt, Marie-Anne; De Raedt, Rudi; Namur, Victoria; Valiengo, Leandro C L; Lotufo, Paulo A; Bensenor, Isabela M; Baeken, Chris; Boggio, Paulo S; Brunoni, Andre R

    2016-01-15

    Emotional Context Insensitivity (ECI) is a psychological feature observed in depressed patients characterized by a decreased emotional reactivity when presented to positive- and negative valence-loaded stimuli. Given that fronto-cingulate-limbic circuits are implicated in abnormal reactivity to valence-loaded stimuli, neurocognitive treatments engaging the prefrontal cortex may be able to modulate this emotional blunting observed in MDD. Therefore, our goal was to evaluate emotional reactivity in depressed patients before and after a combination of neurocognitive interventions that engage the prefrontal cortex (cognitive control training and/or transcranial direct current stimulation). In line with the premises of the ECI framework, before the start of the antidepressant intervention, patients showed blunted emotional reactivity after exposure to negative valence-loaded stimuli. This emotional reactivity pattern changed after 9 sessions of the intervention: positive affect decreased and negative affect increased after watching a series of negative valence-loaded stimuli (i.e. images). Interestingly, higher emotional reactivity (as indexed by a larger increase in negative affect after watching the valence-loaded stimuli) at baseline predicted reductions in depression symptoms after the intervention. On the other hand, higher emotional reactivity (as indexed by a decrease in positive affect) after the intervention was marginally associated with reductions in depression symptoms. To conclude, emotional reactivity increased after the neurocognitive antidepressant intervention and it was directly associated to the degree of depression improvement. Copyright © 2015 Elsevier B.V. All rights reserved.

  19. Music, emotion, and time perception: the influence of subjective emotional valence and arousal?

    Science.gov (United States)

    Droit-Volet, Sylvie; Ramos, Danilo; Bueno, José L. O.; Bigand, Emmanuel

    2013-01-01

    The present study used a temporal bisection task with short (2 s) stimulus durations to investigate the effect on time estimation of several musical parameters associated with emotional changes in affective valence and arousal. In order to manipulate the positive and negative valence of music, Experiments 1 and 2 contrasted the effect of musical structure with pieces played normally and backwards, which were judged to be pleasant and unpleasant, respectively. This effect of valence was combined with a subjective arousal effect by changing the tempo of the musical pieces (fast vs. slow) (Experiment 1) or their instrumentation (orchestral vs. piano pieces). The musical pieces were indeed judged more arousing with a fast than with a slow tempo and with an orchestral than with a piano timbre. In Experiment 3, affective valence was also tested by contrasting the effect of tonal (pleasant) vs. atonal (unpleasant) versions of the same musical pieces. The results showed that the effect of tempo in music, associated with a subjective arousal effect, was the major factor that produced time distortions with time being judged longer for fast than for slow tempi. When the tempo was held constant, no significant effect of timbre on the time judgment was found although the orchestral music was judged to be more arousing than the piano music. Nevertheless, emotional valence did modulate the tempo effect on time perception, the pleasant music being judged shorter than the unpleasant music. PMID:23882233

  20. Interconsistent band structure of narrow-gap Hg1-xCdxTe alloys obtained with consideration of far-band influence

    Science.gov (United States)

    Bogoboyashchiy, V. V.

    1997-08-01

    Faraday rotation, absorption spectra, and the intrinsic carrier concentration temperature dependencies were investigated in order to determine the interconsistent system of values of the narrow-gap Hg1-xCdxTe band parameters. The undoped and doped with indium or copper crystals with x constant of valence band deformation potential E1 equals 12.5 eV have been determined. It has been found that doping of the material with indium, causes the appearance of donor states in the conduction band about 0.1 eV above the bottom of the band. The band structure of Hg1-xCdxTe (MCT) is studied for a long time, and its peculiarities are well known. The light carriers spectrum is believed to be described in framework of the 3-band Kane's model, and the parabolic approximation for heavy hole subband is thought to be sufficient as a rule. The influence of far bands is taken into account rather seldom. But at the same time, the values of band parameters obtained by different authors are not in a good agreement often. In result, it was impossible to agree with an acceptable accuracy the measured and the calculated values of some physical characteristics of MCT by using the known values of band parameters. In order to achieve perfect conformity between the theory and the experiment, another approach must be used. It is necessary that the complex experiment be carried out with a high accuracy of not only the measuring, but of the mathematical models of studied effects and the calculations too. All the main sources of systematic error should be revealed and removed, and the values of band parameters should be determined over again. Such a study was carried out, and its results are reported in this paper.

  1. Silicene Nano-Ribbons: Strong Resistance Towards Oxidation due to sp2 Hybridization of the Si Valence Orbitals

    Science.gov (United States)

    Le Lay, Guy; de Padova, Paola; Quaresima, Claudio; Olivieri, Bruno; Perfetti, Paolo

    2011-03-01

    We have synthesized for the first time silicene, that is, a new silicon allotrope analogous to graphene recently theoretically predicted, in the form of a massively parallel array of quantized zigzag nano-ribbons with a common ``magic'' width of 1.6 nm. They display characteristic linear band dispersions similar to the Dirac cones of graphene, in correspondence with their hexagonal arrangement seen in STM imaging. Here we show, through the angle-dependence of REEL spectra taken at the Si L2 , 3 edge, the typical signatures of 2p --> π * and 2p --> σ * transitions associated with sp 2 hybridization of the Si valence orbitals. We further show through high-resolution synchrotron radiation Si 2p core-level spectroscopy measurements that the afore mentioned silicene grating is very resistant toward oxidation. Typically, the oxygen uptake starts at about 104 higher doses than on the clean Si(111)7x7 surface. Indeed, this striking behavior is directly related to the sp 2 bonding, an additional confirmation of the silicene (i.e., graphene-like) nature of the nano-ribbons.

  2. Comparison of electron bands of hexagonal and cubic diamond

    Science.gov (United States)

    Salehpour, M. R.; Satpathy, S.

    1990-02-01

    Using the local-density-theory and the linear-muffin-tin-orbitals method, we calculate the electron band structures of hexagonal (lonsdaleite) and cubic diamond. Even though the arrangement of atoms is very similar between the two crystal structures, we find significant differences in the electron bands, especially in the conduction bands. In particular, including estimated corrections on top of the local-density results, we find the lowest theoretical gap of hexagonal diamond to be 4.5 eV, i.e., a remarkable 1.1-eV drop as compared to that of cubic diamond. The lowest gap in the hexagonal structure is still indirect as in the cubic structure, but the gap is now from Γ to K. The reduction of the band gap should be observable in optical-absorption or reflectivity experiments.

  3. Noise exposure in marching bands

    Science.gov (United States)

    Keefe, Joseph

    2005-09-01

    Previous studies involving orchestras have shown that music ensembles can produce hazardous noise levels. There are no similar data for marching bands and pep bands. In order to evaluate the noise levels produced by marching and pep bands, 1/3-octave-band sound-pressure levels were measured while these groups rehearsed and performed. Data were collected while marching with the bands to ensure a realistic environment. Comparing these data to OSHA and NIOSH criteria, marching and pep band exposures often exceed safe values. For typical exposures, OSHA doses range from 11% to 295%, while NIOSH doses range from 35% to 3055%. Exposures that would be considered hazardous in the workplace are common in marching and pep bands; students and band directors should take steps to recognize the risk posed by various instruments and various locations, and should implement hearing conservation efforts.

  4. Role of radiative decay of valence plasmons in transmission spectra of Si, SiNx and PET membranes

    Science.gov (United States)

    Yadav, P. K.; Gupta, R. K.; Modi, M. H.; Kumar, Shailendra

    2013-03-01

    Membranes of Si, SiNx and polyethylene terephthalate (PET) were investigated via vacuum ultraviolet (VUV) transmission measurements. The transmission spectra show maxima at energies equal to energies of valence plasmons (VPs) which are interpreted as signatures of radiative decay of VPs. Resonant generation and radiative decay mechanism of valence plasmons and their effects on transmission spectra are discussed. Furthermore, the energy of VPs in SiNx was also confirmed by photo electron spectroscopy (PES) measurements on SiNx thin film. The presented results demonstrate the light induced resonant generation and radiative decay of both, valence bulk and valence surface plasmons.

  5. Differences between problem and nonproblem gamblers in subjective arousal and affective valence amongst electronic gaming machine players.

    Science.gov (United States)

    Brown, Stephen L; Rodda, Simone; Phillips, James G

    2004-12-01

    Arousal-based theories of gambling suggest that excitement gained from gambling reinforces further gambling behavior. However, recent theories of emotion conceptualize mood as comprising both arousal and valence dimensions. Thus, excitement comprises arousal with positive valence. We examined self-reported changes in arousal and affective valence in 27 problem and 40 nonproblem gamblers playing electronic gaming machines (EGMs). Problem gamblers reported greater arousal increases after gambling and increases in negative valence if they lost. This accords poorly with an excitement-based explanation of problem gambling.

  6. Fuzzy Case-Based Reasoning in Product Style Acquisition Incorporating Valence-Arousal-Based Emotional Cellular Model

    Directory of Open Access Journals (Sweden)

    Fuqian Shi

    2012-01-01

    Full Text Available Emotional cellular (EC, proposed in our previous works, is a kind of semantic cell that contains kernel and shell and the kernel is formalized by a triple- L = , where P denotes a typical set of positive examples relative to word-L, d is a pseudodistance measure on emotional two-dimensional space: valence-arousal, and δ is a probability density function on positive real number field. The basic idea of EC model is to assume that the neighborhood radius of each semantic concept is uncertain, and this uncertainty will be measured by one-dimensional density function δ. In this paper, product form features were evaluated by using ECs and to establish the product style database, fuzzy case based reasoning (FCBR model under a defined similarity measurement based on fuzzy nearest neighbors (FNN incorporating EC was applied to extract product styles. A mathematical formalized inference system for product style was also proposed, and it also includes uncertainty measurement tool emotional cellular. A case study of style acquisition of mobile phones illustrated the effectiveness of the proposed methodology.

  7. Band offsets of non-polar A-plane GaN/AlN and AlN/GaN heterostructures measured by X-ray photoemission spectroscopy.

    Science.gov (United States)

    Sang, Ling; Zhu, Qin Sheng; Yang, Shao Yan; Liu, Gui Peng; Li, Hui Jie; Wei, Hong Yuan; Jiao, Chun Mei; Liu, Shu Man; Wang, Zhan Guo; Zhou, Xiao Wei; Mao, Wei; Hao, Yue; Shen, Bo

    2014-01-01

    The band offsets of non-polar A-plane GaN/AlN and AlN/GaN heterojunctions are measured by X-ray photoemission spectroscopy. A large forward-backward asymmetry is observed in the non-polar GaN/AlN and AlN/GaN heterojunctions. The valence-band offsets in the non-polar A-plane GaN/AlN and AlN/GaN heterojunctions are determined to be 1.33 ± 0.16 and 0.73 ± 0.16 eV, respectively. The large valence-band offset difference of 0.6 eV between the non-polar GaN/AlN and AlN/GaN heterojunctions is considered to be due to piezoelectric strain effect in the non-polar heterojunction overlayers.

  8. Emotional Valence, Arousal, and Threat Ratings of 160 Chinese Words among Adolescents.

    Science.gov (United States)

    Ho, Samuel M Y; Mak, Christine W Y; Yeung, Dannii; Duan, Wenjie; Tang, Sandy; Yeung, June C; Ching, Rita

    2015-01-01

    This study was conducted to provide ratings of valence/pleasantness, arousal/excitement, and threat/potential harm for 160 Chinese words. The emotional valence classification (positive, negative, or neutral) of all of the words corresponded to that of the equivalent English language words. More than 90% of the participants, junior high school students aged between 12 and 17 years, understood the words. The participants were from both mainland China and Hong Kong, thus the words can be applied to adolescents familiar with either simplified (e.g. in mainland China) or traditional Chinese (e.g. in Hong Kong) with a junior secondary school education or higher. We also established eight words with negative valence, high threat, and high arousal ratings to facilitate future research, especially on attentional and memory biases among individuals prone to anxiety. Thus, the new emotional word list provides a useful source of information for affective research in the Chinese language.

  9. Reactivity of seventeen- and nineteen-valence electron complexes in organometallic chemistry

    Science.gov (United States)

    Stiegman, Albert E.; Tyler, David R.

    1986-01-01

    A guideline to the reactivity of 17- and 19-valence electron species in organometallic chemistry is proposed which the authors believe will supersede all others. The thesis holds that the reactions of 17-electron metal radicals are associatively activated with reactions proceeding through a 19-valence electron species. The disparate reaction chemistry of the 17-electron metal radicals are unified in terms of this associative reaction pathway, and the intermediacy of 19-valence electron complexes in producing the observed products is discussed. It is suggested that related associatively activated pathways need to be considered in some reactions that are thought to occur by more conventional routes involving 16- and 18-electron intermediates. The basic reaction chemistry and electronic structures of these species are briefly discussed.

  10. Name-valence and physical attractiveness in Facebook: their compensatory effects on friendship acceptance.

    Science.gov (United States)

    Greitemeyer, Tobias; Kunz, Irene

    2013-01-01

    Name-valence and physical attractiveness have been shown to be associated with how people respond toward others, in that people judge and behave more positively toward individuals with positive names and individuals who are physically attractive. The present research examined whether Facebook users are more likely to accept friendship requests from other Facebook users with positive (relative to negative) names and who are physically attractive (relative to being moderately attractive). In fact, both name-valence and physical attractiveness affected friendship acceptance. Moreover, results revealed that name-valence can be compensated by physical attractiveness (and vice versa). Acceptance rates of requests from users with positive names who are moderately attractive, as well as requests from users with negative names who are attractive did not significantly differ from those with positive names who are attractive.

  11. fK /f{pi} in Full QCD with Domain Wall Valence Quarks

    Energy Technology Data Exchange (ETDEWEB)

    Silas Beane; Paulo Bedaque; Konstantinos Orginos; Martin Savage

    2007-05-01

    We compute the ratio of pseudoscalar decay constants f{sub K}/f{sub {pi}} using domain-wall valence quarks and rooted improved Kogut-Susskind sea quarks. By employing continuum chiral perturbation theory, we extract the Gasser-Leutwyler low-energy constant L{sub 5}, and extrapolate f{sub K}/f{sub {pi}} to the physical point. We find: f{sub K}/f{sub {pi}} = 1.218 {+-} 0.002{sub -0.024}{sup +0.011} where the first error is statistical and the second error is an estimate of the systematic due to chiral extrapolation and fitting procedures. This value agrees within the uncertainties with the determination by the MILC collaboration, calculated using Kogut-Susskind valence quarks, indicating that systematic errors arising from the choice of lattice valence quark are small.

  12. The role of valence focus and appraisal overlap in emotion differentiation.

    Science.gov (United States)

    Erbas, Yasemin; Ceulemans, Eva; Koval, Peter; Kuppens, Peter

    2015-06-01

    Emotion differentiation refers to the level of specificity with which people distinguish between their emotional states and is considered to play an important role for psychological well-being. Yet, not much is known about what characterizes people high or low in emotion differentiation and what underlies these differences. In 2 studies involving experience sampling (Studies 1-2) and lab based (Study 2) methods, we investigated how emotion differentiation is related to individual differences in valence focus and the overlap in appraisal patterns between emotions. In line with expectations, results showed that high levels of both positive and negative emotion differentiation are related to lower levels of valence focus and lower levels of appraisal overlap between emotions. These findings suggest that individuals who are low in emotion differentiation mainly emphasize the valence aspect of emotions while individuals who are high in emotion differentiation make stronger distinctions between emotions in terms of their underlying appraisal profiles. (c) 2015 APA, all rights reserved).

  13. The use of symmetrized valence and relative motion coordinates for crystal potentials

    DEFF Research Database (Denmark)

    McMurry, H. L.; Hansen, Flemming Yssing

    1980-01-01

    Symmetrized valence coordinates are linear combinations of conventional valence coordinates which display the symmetry of a set of atoms bound by the valence bonds. Relative motion coordinates are relative translations, or relative rotations, of two or more strongly bonded groups of atoms among...... which relatively weak forces act. They are useful for expressing interactions between molecules in molecular crystals and should be chosen, also, to reflect the symmetry of the interacting groups. Since coordinates defined by these procedures possess elements of symmetry in common with the bonding...... electron distributions, the force constants in the potential should be more amenable to calculation in terms of energy changes in the electronic ground state which accompany displacements of the atoms from equilibrium. It is easier to determine force constants for fitting experimental data because...

  14. Investigation of the electronic, magnetic and optical properties of {\\sf Co}_{\\sf 2}{\\sf CrZ} (Z = Si, Ge) under pressure—a density functional theory study

    Science.gov (United States)

    Seema, K.; Kumar, Ranjan

    2014-01-01

    The structural, electronic, magnetic and optical properties of Co-based Heusler compounds, Co2CrZ (Z = Si, Ge), are studied using first-principle density functional theory. The calculations are performed within the generalized gradient approximation. Our calculated structural parameters at 0 GPa agree well with previous available results. The calculated magnetic moment agrees well with the Slater-Pauling (SP) rule. We have studied the effect of pressure on the electronic and magnetic properties of Co2CrSi and Co2CrGe. With an increase in applied pressure, a decrease in cell volume is observed. Under application of external pressure, the valence band and conduction band are shifted downward which leads to a modification of electronic structure. There exists an indirect band gap along Γ-X for both the alloys. Co2CrSi and Co2CrGe retain 100% spin polarization up to 60 and 50 GPa, respectively. The local magnetic moments of the Co and Si (Ge) atoms increase with an increase in pressure whereas the local magnetic moment of the Cr atom decreases. In addition, the optical properties such as dielectric function, absorption spectra, optical conductivity and energy loss function of these alloys have also been investigated. To our knowledge this is the first theoretical prediction of the pressure dependence of the structural, electronic, magnetic and optical properties of Co2CrSi and Co2CrGe.

  15. Gate-induced band ferromagnetism in an organic polymer

    OpenAIRE

    Arita, Ryotaro; Suwa, Yuji; Kuroki, Kazuhiko; Aoki, Hideo

    2001-01-01

    We propose that a chain of five-membered rings (polyaminotriazole) should be ferromagnetic with an appropriate doping that is envisaged to be feasible with an FET structure. The ferromagnetism is confirmed by a spin density functional calculation, which also shows that ferromagnetism survives the Peierls instability. We explain the magnetism in terms of Mielke and Tasaki's flat-band ferromagnetism with the Hubbard model. This opens a new possibility of band ferromagnetism in purely organic po...

  16. Microstrip microwave band gap structures

    Indian Academy of Sciences (India)

    Microwave band gap structures exhibit certain stop band characteristics based on the periodicity, impedance contrast and effective refractive index contrast. These structures though formed in one-, two- and three-dimensional periodicity, are huge in size. In this paper, microstrip-based microwave band gap structures are ...

  17. Semiconductors bonds and bands

    CERN Document Server

    Ferry, David K

    2013-01-01

    As we settle into this second decade of the twenty-first century, it is evident that the advances in micro-electronics have truly revolutionized our day-to-day lifestyle. The technology is built upon semiconductors, materials in which the band gap has been engineered for special values suitable to the particular application. This book, written specifically for a one semester course for graduate students, provides a thorough understanding of the key solid state physics of semiconductors. It describes how quantum mechanics gives semiconductors unique properties that enabled the micro-electronics revolution, and sustain the ever-growing importance of this revolution.

  18. Statistical study of auroral omega bands

    Science.gov (United States)

    Partamies, Noora; Weygand, James M.; Juusola, Liisa

    2017-09-01

    The presence of very few statistical studies on auroral omega bands motivated us to test-use a semi-automatic method for identifying large-scale undulations of the diffuse aurora boundary and to investigate their occurrence. Five identical all-sky cameras with overlapping fields of view provided data for 438 auroral omega-like structures over Fennoscandian Lapland from 1996 to 2007. The results from this set of omega band events agree remarkably well with previous observations of omega band occurrence in magnetic local time (MLT), lifetime, location between the region 1 and 2 field-aligned currents, as well as current density estimates. The average peak emission height of omega forms corresponds to the estimated precipitation energies of a few keV, which experienced no significant change during the events. Analysis of both local and global magnetic indices demonstrates that omega bands are observed during substorm expansion and recovery phases that are more intense than average substorm expansion and recovery phases in the same region. The omega occurrence with respect to the substorm expansion and recovery phases is in a very good agreement with an earlier observed distribution of fast earthward flows in the plasma sheet during expansion and recovery phases. These findings support the theory that omegas are produced by fast earthward flows and auroral streamers, despite the rarity of good conjugate observations.

  19. Statistical study of auroral omega bands

    Directory of Open Access Journals (Sweden)

    N. Partamies

    2017-09-01

    Full Text Available The presence of very few statistical studies on auroral omega bands motivated us to test-use a semi-automatic method for identifying large-scale undulations of the diffuse aurora boundary and to investigate their occurrence. Five identical all-sky cameras with overlapping fields of view provided data for 438 auroral omega-like structures over Fennoscandian Lapland from 1996 to 2007. The results from this set of omega band events agree remarkably well with previous observations of omega band occurrence in magnetic local time (MLT, lifetime, location between the region 1 and 2 field-aligned currents, as well as current density estimates. The average peak emission height of omega forms corresponds to the estimated precipitation energies of a few keV, which experienced no significant change during the events. Analysis of both local and global magnetic indices demonstrates that omega bands are observed during substorm expansion and recovery phases that are more intense than average substorm expansion and recovery phases in the same region. The omega occurrence with respect to the substorm expansion and recovery phases is in a very good agreement with an earlier observed distribution of fast earthward flows in the plasma sheet during expansion and recovery phases. These findings support the theory that omegas are produced by fast earthward flows and auroral streamers, despite the rarity of good conjugate observations.

  20. Tunable band structures in digital oxides with layered crystal habits

    Science.gov (United States)

    Shin, Yongjin; Rondinelli, James M.

    2017-11-01

    We use density functional calculations to show that heterovalent cation-order sequences enable control over band-gap variations up to several eV and band-gap closure in the bulk band insulator LaSrAlO4. The band-gap control originates from the internal electric fields induced by the digital chemical order, which induces picoscale band bending; the electric-field magnitude is mainly governed by the inequivalent charged monoxide layers afforded by the layered crystal habit. Charge transfer and ionic relaxations across these layers play secondary roles. This understanding is used to construct and validate a descriptor that captures the layer-charge variation and to predict changes in the electronic gap in layered oxides exhibiting antisite defects and in other chemistries.

  1. A Density Functional Theory Study of the Adsorption of Benzene on Hematite (α-Fe2O3 Surfaces

    Directory of Open Access Journals (Sweden)

    Nelson Y. Dzade

    2014-02-01

    Full Text Available The reactivity of mineral surfaces in the fundamental processes of adsorption, dissolution or growth, and electron transfer is directly tied to their atomic structure. However, unraveling the relationship between the atomic surface structure and other physical and chemical properties of complex metal oxides is challenging due to the mixed ionic and covalent bonding that can occur in these minerals. Nonetheless, with the rapid increase in computer processing speed and memory, computer simulations using different theoretical techniques can now probe the nature of matter at both the atomic and sub-atomic levels and are rapidly becoming an effective and quantitatively accurate method for successfully predicting structures, properties and processes occurring at mineral surfaces. In this study, we have used Density Functional Theory calculations to study the adsorption of benzene on hematite (α-Fe2O3 surfaces. The strong electron correlation effects of the Fe 3d-electrons in α-Fe2O3 were described by a Hubbard-type on-site Coulomb repulsion (the DFT+U approach, which was found to provide an accurate description of the electronic and magnetic properties of hematite. For the adsorption of benzene on the hematite surfaces, we show that the adsorption geometries parallel to the surface are energetically more stable than the vertical ones. The benzene molecule interacts with the hematite surfaces through π-bonding in the parallel adsorption geometries and through weak hydrogen bonds in the vertical geometries. Van der Waals interactions are found to play a significant role in stabilizing the absorbed benzene molecule. Analyses of the electronic structures reveal that upon benzene adsorption, the conduction band edge of the surface atoms is shifted towards the valence bands, thereby considerably reducing the band gap and the magnetic moments of the surface Fe atoms.

  2. Acoustic correlates of emotional dimensions in laughter: arousal, dominance, and valence.

    Science.gov (United States)

    Szameitat, Diana P; Darwin, Chris J; Wildgruber, Dirk; Alter, Kai; Szameitat, Andre J

    2011-06-01

    Although laughter plays an essential part in emotional vocal communication, little is known about the acoustical correlates that encode different emotional dimensions. In this study we examined the acoustical structure of laughter sounds differing along four emotional dimensions: arousal, dominance, sender's valence, and receiver-directed valence. Correlation of 43 acoustic parameters with individual emotional dimensions revealed that each emotional dimension was associated with a number of vocal cues. Common patterns of cues were found with emotional expression in speech, supporting the hypothesis of a common underlying mechanism for the vocal expression of emotions.

  3. Inducing changes in arousal and valence: comparison of two mood induction procedures.

    Science.gov (United States)

    Jallais, Christophe; Gilet, Anne-Laure

    2010-02-01

    This research examined the relative effectiveness of two mood induction procedures (MIPs) for inducing four specific moods varying along the dimensions of both valence and arousal. Participants were randomly assigned either to an autobiographical recall or to a music and guided imagery MIP and underwent a happiness, serenity, anger, or sadness mood induction. The findings confirmed the effectiveness of the two MIPs in producing changes on both the valence and arousal dimensions of mood. The results also revealed an unexpected greater efficiency of the autobiographical recall than of the combined procedure.

  4. Valence photoelectron spectra of alkali bromides calculated within the propagator theory

    DEFF Research Database (Denmark)

    Karpenko, Alexander; Iablonskyi, Denys; Aksela, Helena

    2013-01-01

    The valence ionization spectra covering the binding energy range 0-45 eV of alkali bromide XBr (X = Li, Na, K, Rb) vapors are studied within the framework of the propagator theory. Relativistic Algebraic Diagrammatic Construction calculations have been carried out in order to investigate photoion......The valence ionization spectra covering the binding energy range 0-45 eV of alkali bromide XBr (X = Li, Na, K, Rb) vapors are studied within the framework of the propagator theory. Relativistic Algebraic Diagrammatic Construction calculations have been carried out in order to investigate...... photoionization processes and to describe molecular electronic structure. Theoretical results are compared with available experimental data....

  5. Experimental core electron density of cubic boron nitride

    DEFF Research Database (Denmark)

    Wahlberg, Nanna; Bindzus, Niels; Bjerg, Lasse

    candidate because of its many similarities with diamond: bonding pattern in the extended network structure, hardness, and the quality of the crystallites.3 However, some degree ionic interaction is a part of the bonding in boron nitride, which is not present in diamond. By investigating the core density...... beyond multipolar modeling of the valence density. As was recently shown in a benchmark study of diamond by Bindzus et al.1 The next step is to investigate more complicated chemical bonding motives, to determine the effect of bonding on the core density. Cubic boron nitride2 lends itself as a perfect...... in boron nitride we may obtain a deeper understanding of the effect of bonding on the total density. We report here a thorough investigation of the charge density of cubic boron nitride with a detailed modelling of the inner atom charge density. By combining high resolution powder X-ray diffraction data...

  6. Evidence of ion intercalation mediated band structure modification and opto-ionic coupling in lithium niobite

    Energy Technology Data Exchange (ETDEWEB)

    Shank, Joshua C.; Tellekamp, M. Brooks; Doolittle, W. Alan, E-mail: alan.doolittle@ece.gatech.edu [Department of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332 (United States)

    2015-01-21

    The theoretically suggested band structure of the novel p-type semiconductor lithium niobite (LiNbO{sub 2}), the direct coupling of photons to ion motion, and optically induced band structure modifications are investigated by temperature dependent photoluminescence. LiNbO{sub 2} has previously been used as a memristor material but is shown here to be useful as a sensor owing to the electrical, optical, and chemical ease of lithium removal and insertion. Despite the high concentration of vacancies present in lithium niobite due to the intentional removal of lithium atoms, strong photoluminescence spectra are observed even at room temperature that experimentally confirm the suggested band structure implying transitions from a flat conduction band to a degenerate valence band. Removal of small amounts of lithium significantly modifies the photoluminescence spectra including additional larger than stoichiometric-band gap features. Sufficient removal of lithium results in the elimination of the photoluminescence response supporting the predicted transition from a direct to indirect band gap semiconductor. In addition, non-thermal coupling between the incident laser and lithium ions is observed and results in modulation of the electrical impedance.

  7. Entanglement spectra of the two-dimensional Affleck-Kennedy-Lieb-Tasaki model: Correspondence between the valence-bond-solid state and conformal field theory

    Science.gov (United States)

    Lou, Jie; Tanaka, Shu; Katsura, Hosho; Kawashima, Naoki

    2011-12-01

    We investigate the entanglement properties of the valence-bond-solid (VBS) state defined on two-dimensional lattices, which is the exact ground state of the Affleck-Kennedy-Lieb-Tasaki model. It is shown that the entanglement entropy obeys an area law and the nonuniversal prefactor of the leading term is strictly less than ln2. The analysis of entanglement spectra for various lattices reveals that the reduced density matrix associated with the VBS state is closely related to a thermal density matrix of a holographic spin chain, the spectrum of which is reminiscent of that of the spin-1/2 Heisenberg chain. This correspondence is further supported by comparing the entanglement entropy in the holographic spin chain with conformal field theory predictions.

  8. Sub-band-gap laser micromachining of lithium niobate

    DEFF Research Database (Denmark)

    Christensen, F. K.; Müllenborn, Matthias

    1995-01-01

    method is reported which enables us to do laser processing of lithium niobate using sub-band-gap photons. Using high scan speeds, moderate power densities, and sub-band-gap photon energies results in volume removal rates in excess of 106µm3/s. This enables fast micromachining of small piezoelectric......Laser processing of insulators and semiconductors is usually realized using photon energies exceeding the band-gap energy. This makes laser processing of insulators difficult since high photon energies typically require either a pulsed laser or a frequency-doubled continuous-wave laser. A new...

  9. L-asparagine crystals with wide gap semiconductor features: Optical absorption measurements and density functional theory computations

    Energy Technology Data Exchange (ETDEWEB)

    Zanatta, G.; Gottfried, C. [Departamento de Bioquímica, Universidade Federal do Rio Grande do Sul, 90035-003 Porto Alegre-RS (Brazil); Silva, A. M. [Universidade Estadual do Piauí, 64260-000 Piripiri-Pi (Brazil); Caetano, E. W. S., E-mail: ewcaetano@gmail.com [Instituto de Educação, Ciência e Tecnologia do Ceará, 60040-531 Fortaleza-CE (Brazil); Sales, F. A. M.; Freire, V. N. [Departamento de Física, Universidade Federal do Ceará, Caixa Postal 6030, 60455-760 Fortaleza-CE (Brazil)

    2014-03-28

    Results of optical absorption measurements are presented together with calculated structural, electronic, and optical properties for the anhydrous monoclinic L-asparagine crystal. Density functional theory (DFT) within the generalized gradient approximation (GGA) including dispersion effects (TS, Grimme) was employed to perform the calculations. The optical absorption measurements revealed that the anhydrous monoclinic L-asparagine crystal is a wide band gap material with 4.95 eV main gap energy. DFT-GGA+TS simulations, on the other hand, produced structural parameters in very good agreement with X-ray data. The lattice parameter differences Δa, Δb, Δc between theory and experiment were as small as 0.020, 0.051, and 0.022 Å, respectively. The calculated band gap energy is smaller than the experimental data by about 15%, with a 4.23 eV indirect band gap corresponding to Z → Γ and Z → β transitions. Three other indirect band gaps of 4.30 eV, 4.32 eV, and 4.36 eV are assigned to α3 → Γ, α1 → Γ, and α2 → Γ transitions, respectively. Δ-sol computations, on the other hand, predict a main band gap of 5.00 eV, just 50 meV above the experimental value. Electronic wavefunctions mainly originating from O 2p–carboxyl, C 2p–side chain, and C 2p–carboxyl orbitals contribute most significantly to the highest valence and lowest conduction energy bands, respectively. By varying the lattice parameters from their converged equilibrium values, we show that the unit cell is less stiff along the b direction than for the a and c directions. Effective mass calculations suggest that hole transport behavior is more anisotropic than electron transport, but the mass values allow for some charge mobility except along a direction perpendicular to the molecular layers of L-asparagine which form the crystal, so anhydrous monoclinic L-asparagine crystals could behave as wide gap semiconductors. Finally, the calculations point to a high degree of optical

  10. L-Asparagine crystals with wide gap semiconductor features: optical absorption measurements and density functional theory computations.

    Science.gov (United States)

    Zanatta, G; Gottfried, C; Silva, A M; Caetano, E W S; Sales, F A M; Freire, V N

    2014-03-28

    Results of optical absorption measurements are presented together with calculated structural, electronic, and optical properties for the anhydrous monoclinic L-asparagine crystal. Density functional theory (DFT) within the generalized gradient approximation (GGA) including dispersion effects (TS, Grimme) was employed to perform the calculations. The optical absorption measurements revealed that the anhydrous monoclinic L-asparagine crystal is a wide band gap material with 4.95 eV main gap energy. DFT-GGA+TS simulations, on the other hand, produced structural parameters in very good agreement with X-ray data. The lattice parameter differences Δa, Δb, Δc between theory and experiment were as small as 0.020, 0.051, and 0.022 Å, respectively. The calculated band gap energy is smaller than the experimental data by about 15%, with a 4.23 eV indirect band gap corresponding to Z → Γ and Z → β transitions. Three other indirect band gaps of 4.30 eV, 4.32 eV, and 4.36 eV are assigned to α3 → Γ, α1 → Γ, and α2 → Γ transitions, respectively. Δ-sol computations, on the other hand, predict a main band gap of 5.00 eV, just 50 meV above the experimental value. Electronic wavefunctions mainly originating from O 2p-carboxyl, C 2p-side chain, and C 2p-carboxyl orbitals contribute most significantly to the highest valence and lowest conduction energy bands, respectively. By varying the lattice parameters from their converged equilibrium values, we show that the unit cell is less stiff along the b direction than for the a and c directions. Effective mass calculations suggest that hole transport behavior is more anisotropic than electron transport, but the mass values allow for some charge mobility except along a direction perpendicular to the molecular layers of L-asparagine which form the crystal, so anhydrous monoclinic L-asparagine crystals could behave as wide gap semiconductors. Finally, the calculations point to a high degree of optical

  11. Modeling space-charge-limited currents in organic semiconductors: Extracting trap density and mobility

    KAUST Repository

    Dacuña, Javier

    2011-11-28

    We have developed and have applied a mobility edge model that takes drift and diffusion currents to characterize the space-charge-limited current in organic semiconductors into account. The numerical solution of the drift-diffusion equation allows the utilization of asymmetric contacts to describe the built-in potential within the device. The model has been applied to extract information of the distribution of traps from experimental current-voltage measurements of a rubrene single crystal from Krellner showing excellent agreement across several orders of magnitude in the current. Although the two contacts are made of the same metal, an energy offset of 580 meV between them, ascribed to differences in the deposition techniques (lamination vs evaporation) was essential to correctly interpret the shape of the current-voltage characteristics at low voltage. A band mobility of 0.13cm 2V-1s-1 for holes is estimated, which is consistent with transport along the long axis of the orthorhombic unit cell. The total density of traps deeper than 0.1 eV was 2.2×1016cm -3. The sensitivity analysis and error estimation in the obtained parameters show that it is not possible to accurately resolve the shape of the trap distribution for energies deeper than 0.3 eV or shallower than 0.1 eV above the valence-band edge. The total number of traps deeper than 0.3 eV, however, can be estimated. Contact asymmetry and the diffusion component of the current play an important role in the description of the device at low bias and are required to obtain reliable information about the distribution of deep traps. © 2011 American Physical Society.

  12. Morphologies of omega band auroras

    Science.gov (United States)

    Sato, Natsuo; Yukimatu, Akira Sessai; Tanaka, Yoshimasa; Hori, Tomoaki

    2017-08-01

    We examined the morphological signatures of 315 omega band aurora events observed using the Time History of Events and Macroscale Interactions during Substorm ground-based all-sky imager network over a period of 8 years. We find that omega bands can be classified into the following three subtypes: (1) classical (O-type) omega bands, (2) torch or tongue (T-type) omega bands, and (3) combinations of classical and torch or tongue (O/T-type) omega bands. The statistical results show that T-type bands occur the most frequently (45%), followed by O/T-type bands (35%) and O-type bands (18%). We also examined the morphologies of the omega bands during their formation, from the growth period to the declining period through the maximum period. Interestingly, the omega bands are not stable, but rather exhibit dynamic changes in shape, intensity, and motion. They grow from small-scale bumps (seeds) at the poleward boundary of preexisting east-west-aligned auroras, rather than via the rotation or shear motion of preexisting east-west-aligned auroras, and do not exhibit any shear motion during the periods of auroral activity growth. Furthermore, the auroral luminosity is observed to increase during the declining period, and the total time from the start of the growth period to the end of the declining period is found to be about 20 min. Such dynamical signatures may be important in determining the mechanism responsible for omega band formation.

  13. Analysis of Signal Attenuation in UHF Band

    Directory of Open Access Journals (Sweden)

    Libor Michalek

    2015-01-01

    Full Text Available This paper deals with signal attenuation in ultra-high-frequency bands caused by rain. We focus mainly on the effect of the rain on the radio waves propagation in the frequency band 2.1 GHz. Two exact approaches for investigating this dependency are used. In the first approach, we use the fitting probability density function for determination Rician distribution K-factor. In the second approach, we want to find more concrete rain-rate dependency with using linear regression. The results achieved in our long-term investigation clearly indicate that the strong impact of rain itself is a minor. So-called secondary rain impacts such as scattering of reflections from wet surfaces cause the main attenuation contribution.

  14. Bulk band structure of Bi2Te3

    DEFF Research Database (Denmark)

    Michiardi, Matteo; Aguilera, Irene; Bianchi, Marco

    2014-01-01

    The bulk band structure of Bi2Te3 has been determined by angle-resolved photoemission spectroscopy and compared to first-principles calculations. We have performed calculations using the local density approximation (LDA) of density functional theory and the one-shot GW approximation within the all......-electron full-potential linearized augmented-plane-wave (FLAPW) formalism, fully taking into account spin-orbit coupling. Quasiparticle effects produce significant changes in the band structure of Bi2Te3 when compared to LDA. Experimental and calculated results are compared in the spectral regions where...

  15. Precipitation estimation using L-band and C-band soil moisture retrievals

    Science.gov (United States)

    Koster, Randal D.; Brocca, Luca; Crow, Wade T.; Burgin, Mariko S.; De Lannoy, Gabrielle J. M.

    2016-09-01

    An established methodology for estimating precipitation amounts from satellite-based soil moisture retrievals is applied to L-band products from the Soil Moisture Active Passive (SMAP) and Soil Moisture and Ocean Salinity (SMOS) satellite missions and to a C-band product from the Advanced Scatterometer (ASCAT) mission. The precipitation estimates so obtained are evaluated against in situ (gauge-based) precipitation observations from across the globe. The precipitation estimation skill achieved using the L-band SMAP and SMOS data sets is higher than that obtained with the C-band product, as might be expected given that L-band is sensitive to a thicker layer of soil and thereby provides more information on the response of soil moisture to precipitation. The square of the correlation coefficient between the SMAP-based precipitation estimates and the observations (for aggregations to ˜100 km and 5 days) is on average about 0.6 in areas of high rain gauge density. Satellite missions specifically designed to monitor soil moisture thus do provide significant information on precipitation variability, information that could contribute to efforts in global precipitation estimation.

  16. Spectroscopic evidence for bulk-band inversion and three-dimensional massive Dirac fermions in ZrTe5.

    Science.gov (United States)

    Chen, Zhi-Guo; Chen, R Y; Zhong, R D; Schneeloch, John; Zhang, C; Huang, Y; Qu, Fanming; Yu, Rui; Li, Q; Gu, G D; Wang, N L

    2017-01-31

    Three-dimensional topological insulators (3D TIs) represent states of quantum matters in which surface states are protected by time-reversal symmetry and an inversion occurs between bulk conduction and valence bands. However, the bulk-band inversion, which is intimately tied to the topologically nontrivial nature of 3D Tis, has rarely been investigated by experiments. Besides, 3D massive Dirac fermions with nearly linear band dispersions were seldom observed in TIs. Recently, a van der Waals crystal, ZrTe5, was theoretically predicted to be a TI. Here, we report an infrared transmission study of a high-mobility [∼33,000 cm2/(V ⋅ s)] multilayer ZrTe5 flake at magnetic fields (B) up to 35 T. Our observation of a linear relationship between the zero-magnetic-field optical absorption and the photon energy, a bandgap of ∼10 meV and a [Formula: see text] dependence of the Landau level (LL) transition energies at low magnetic fields demonstrates 3D massive Dirac fermions with nearly linear band dispersions in this system. More importantly, the reemergence of the intra-LL transitions at magnetic fields higher than 17 T reveals the energy cross between the two zeroth LLs, which reflects the inversion between the bulk conduction and valence bands. Our results not only provide spectroscopic evidence for the TI state in ZrTe5 but also open up a new avenue for fundamental studies of Dirac fermions in van der Waals materials.

  17. Wide Band Artificial Pulsar

    Science.gov (United States)

    Parsons, Zackary

    2017-01-01

    The Wide Band Artificial Pulsar (WBAP) is an instrument verification device designed and built by the National Radio Astronomy Observatory (NRAO) in Green Bank, West Virgina. The site currently operates the Green Bank Ultimate Pulsar Processing Instrument (GUPPI) and the Versatile Green Bank Astronomical Spectrometer (VEGAS) digital backends for their radio telescopes. The commissioning and continued support for these sophisticated backends has demonstrated a need for a device capable of producing an accurate artificial pulsar signal. The WBAP is designed to provide a very close approximation to an actual pulsar signal. This presentation is intended to provide an overview of the current hardware and software implementations and to also share the current results from testing using the WBAP.

  18. Hybrid-DFT  +  V w method for band structure calculation of semiconducting transition metal compounds: the case of cerium dioxide

    Science.gov (United States)

    Ivády, Viktor; Gali, Adam; Abrikosov, Igor A.

    2017-11-01

    Hybrid functionals’ non-local exchange-correlation potential contains a derivative discontinuity that improves on standard semi-local density functional theory (DFT) band gaps. Moreover, by careful parameterization, hybrid functionals can provide self-interaction reduced description of selected states. On the other hand, the uniform description of all the electronic states of a given system is a known drawback of these functionals that causes varying accuracy in the description of states with different degrees of localization. This limitation can be remedied by the orbital dependent exact exchange extension of hybrid functionals; the hybrid-DFT  +  V w method (Ivády et al 2014 Phys. Rev. B 90 035146). Based on the analogy of quasi-particle equations and hybrid-DFT single particle equations, here we demonstrate that parameters of hybrid-DFT  +  V w functional can be determined from approximate theoretical quasi-particle spectra without any fitting to experiment. The proposed method is illustrated on the charge self-consistent electronic structure calculation for cerium dioxide where itinerant valence states interact with well-localized 4f atomic like states, making this system challenging for conventional methods, either hybrid-DFT or LDA  +  U, and therefore allowing for a demonstration of the advantages of the proposed scheme.

  19. Dark Bands on Europa

    Science.gov (United States)

    1996-01-01

    Dark crisscrossing bands on Jupiter's moon Europa represent widespread disruption from fracturing and the possible eruption of gases and rocky material from the moon's interior in this four-frame mosaic of images from NASA's Galileo spacecraft. These and other features suggest that soft ice or liquid water was present below the ice crust at the time of disruption. The data do not rule out the possibility that such conditions exist on Europa today. The pictures were taken from a distance of 156,000 kilometers (about 96,300 miles) on June 27, 1996. Many of the dark bands are more than 1,600 kilometers (1,000 miles) long, exceeding the length of the San Andreas fault of California. Some of the features seen on the mosaic resulted from meteoritic impact, including a 30- kilometer (18.5 mile) diameter crater visible as a bright scar in the lower third of the picture. In addition, dozens of shallow craters seen in some terrains along the sunset terminator zone (upper right shadowed area of the image) are probably impact craters. Other areas along the terminator lack craters, indicating relatively youthful surfaces, suggestive of recent eruptions of icy slush from the interior. The lower quarter of the mosaic includes highly fractured terrain where the icy crust has been broken into slabs as large as 30 kilometers (18.5 miles) across. The mosaic covers a large part of the northern hemisphere and includes the north pole at the top of the image. The sun illuminates the surface from the left. The area shown is centered on 20 degrees north latitude and 220 degrees west longitude and is about as wide as the United States west of the Mississippi River. The Galileo mission is managed by NASA's Jet Propulsion Laboratory.

  20. Stronger Association Between Valence- and Arousal Ratings of Affective Pictures with Older Age: Evidence for Variation Across Emotion Categories

    DEFF Research Database (Denmark)

    Mikkelsen, Mai Bjørnskov; Mehlsen, Mimi Yung; Lyby, Marlene Skovgaard

    A sample of older and younger adults rated affective pictures according to valence, arousal and emotion category (happiness, sadness and disgust). Results indicate that older age is associated with a stronger linear association between ratings of arousal and valence. Further, the strength...