WorldWideScience

Sample records for valence band dispersion

  1. Valence holes observed in nanodiamonds dispersed in water.

    Science.gov (United States)

    Petit, Tristan; Pflüger, Mika; Tolksdorf, Daniel; Xiao, Jie; Aziz, Emad F

    2015-02-21

    Colloidal dispersion is essential for most nanodiamond applications, but its influence on nanodiamond electronic properties remains unknown. Here we have probed the electronic structure of oxidized detonation nanodiamonds dispersed in water by using soft X-ray absorption and emission spectroscopies at the carbon and oxygen K edges. Upon dispersion in water, the ?* transitions from sp(2)-hybridized carbon disappear, and holes in the valence band are observed. PMID:25597533

  2. XPS valence bands of Ti, Zr, Nb, Mo and Hf

    Science.gov (United States)

    Höchst, H.; Steiner, P.; Reiter, G.; Hüfner, S.

    1981-09-01

    The XPS valence band spectra of polycrystalline Ti, Zr, Nb, Mo and Hf have been measured with a resolution of 0.6 eV. The spectra were compared with theoretical densities of states. Good agreement is achieved if the partial densities of states are considered and a many body line shape function and life time broadening are taken into account. The sigularity index ? determined at various core lines as well as the experimentally determined relative valence band cross sections are reported.

  3. Photoelectron diffraction and band structure effects in ARXPS from the valence bands of GeS

    International Nuclear Information System (INIS)

    X-ray photoelectron spectra of the valence band region of GeS are measured in dependence on polar and azimuthal angle. The anisotropy of the valence band structures is due to both, influences of initial state wave function and photoelectron diffraction. By these means in addition to the symmetry character of initial states the atomic nature of different valence band peaks can also be explained. (author)

  4. Evolution of the Impurity Band to Diamond-Like Valence Bands in Boron Doped Diamond

    Science.gov (United States)

    Inushima, Takashi; Ota, Yuichi; Shiomi, Hiromu

    2014-02-01

    We present the absorption coefficient and the refractive index of boron doped diamond having an impurity band at 0.07 eV above the valence band maximum and compare them with those obtained by first principles calculation using a C63B supercell model containing 1.57% boron. These optical constants are in good accordance with each other, indicating that the impurity band that forms at 2p excited states of impurity boron becomes top of the valence bands in metallic condition. Based on this result we present a model of the evolution of boron atoms from isolated impurity to constituent atoms in the boron doped diamond, where the valence electrons of boron become to have k dependence and form the top of the valence bands of the C63B supercell diamond.

  5. Valence band photoemission studies of clean metals

    International Nuclear Information System (INIS)

    The application of Angle-Resolved Photoelectron Spectroscopy (ARPES) to crystalline solids and the utilization of such studies to illuminate several questions concerning the detailed electronic structure of such materials, are discussed. Specifically, by construction of a Direct Transition (DT) model and the utilization of energy-dependent angle-resolved normal photoemission in the photon energy range 32 eV < or = h? < or = 200 eV, the bulk band structure of copper is experimentally mapped out along three different directions in the Brillouin Zone; GAMMA to K, GAMMA to L, and GAMMA to X. In addition, various effects which influence the obtainable resolution in vector k-space, namely, thermal disorder, momentum broadening, and band mixing, are discussed and are shown to place severe limitations on the applicability of the DT model. Finally, a model for Angle-Resolved X-ray Photoelectron Spectroscopy (ARXPS) based on the symmetry of the initial-state wavefunctions is presented and compared to experimental results obtained from copper single crystals

  6. Conduction and Valence Band Offsets in WSe2 -Graphene Heterostructures

    Science.gov (United States)

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

    2015-03-01

    We investigate the electron transport in graphene-WSe2 heterostructures realized using a layer-by-layer transfer. Lateral electron transport shows ambipolar behavior characteristic of graphene, with a marked saturation at high positive (negative) gate bias, associated with the population of the conduction (valence) band in WSe2. The graphene carrier density dependence on gate bias was extracted from magneto-transport measurements. Using WSe2 as a top dielectric in dual-gate graphene field-effect transistors, we determine the WSe2 dielectric constant along the c-axis. By combining the graphene density dependence on gate bias in back-gated graphene-WSe2 heterostructures with the WSe2 dielectric constant, we determine the offset between the graphene charge neutrality point and the WSe2 conduction and valence bands. This work was supported by NRI, NSF and Intel.

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

    Science.gov (United States)

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

    2013-04-01

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

  8. Application of Koopmans' theorem for density functional theory to full valence-band photoemission spectroscopy modeling.

    Science.gov (United States)

    Li, Tsung-Lung; Lu, Wen-Cai

    2015-10-01

    In this work, Koopmans' theorem for Kohn-Sham density functional theory (KS-DFT) is applied to the photoemission spectra (PES) modeling over the entire valence-band. To examine the validity of this application, a PES modeling scheme is developed to facilitate a full valence-band comparison of theoretical PES spectra with experiments. The PES model incorporates the variations of electron ionization cross-sections over atomic orbitals and a linear dispersion of spectral broadening widths. KS-DFT simulations of pristine rubrene (5,6,11,12-tetraphenyltetracene) and potassium-rubrene complex are performed, and the simulation results are used as the input to the PES models. Two conclusions are reached. First, decompositions of the theoretical total spectra show that the dissociated electron of the potassium mainly remains on the backbone and has little effect on the electronic structures of phenyl side groups. This and other electronic-structure results deduced from the spectral decompositions have been qualitatively obtained with the anionic approximation to potassium-rubrene complexes. The qualitative validity of the anionic approximation is thus verified. Second, comparison of the theoretical PES with the experiments shows that the full-scale simulations combined with the PES modeling methods greatly enhance the agreement on spectral shapes over the anionic approximation. This agreement of the theoretical PES spectra with the experiments over the full valence-band can be regarded, to some extent, as a collective validation of the application of Koopmans' theorem for KS-DFT to valence-band PES, at least, for this hydrocarbon and its alkali-adsorbed complex. PMID:25974677

  9. Different symmetry of the magnetization-direction dependence between the impurity band and valence band in GaMnAs

    Science.gov (United States)

    Muneta, Iriya; Kanaki, Toshiki; Ohya, Shinobu; Tanaka, Masaaki

    2015-03-01

    In semiconductors with heavily doped with nonmagnetic shallow acceptors, an impurity band (IB) is formed around the valence band (VB) top and merged with VB. As a result, the parabolic VB top is strongly deformed in a non-parabolic dispersion. In GaMnAs, however, the VB top keeps the parabolic dispersion though there is energy overlap between VB and IB, which is completely different from the conventional nonmagnetic semiconductors. Here, we measure tunneling anisotropic magnetoresistance on GaMnAs tunnel devices in a spectroscopic way, analyze the magnetization-direction and energy dependence of the density of states (DOS), and investigate the different symmetry between VB and IB to clarify the mysterious overlap between the two bands. We find that the magnetization-direction dependence of VB DOS is mainly four-fold symmetry along [100] which is the same as the crystal symmetry, while that of IB DOS is mainly two-fold symmetry along [110] unlike the crystal symmetry. These results reveal the unique band structures of Mn-doped III-V ferromagnetic semiconductors. This work was partly supported by Grant-in-Aids for Scientific Research including Specially Promoted Research, I.M. thanks the JSPS research Fellowship Program for Young Scientists.

  10. Electronic and thermoelectric properties of van der Waals materials with ring-shaped valence bands

    Science.gov (United States)

    Wickramaratne, Darshana; Zahid, Ferdows; Lake, Roger K.

    2015-08-01

    The valence band of a variety of few-layer, two-dimensional materials consist of a ring of states in the Brillouin zone. The energy-momentum relation has the form of a "Mexican hat" or a Rashba dispersion. The two-dimensional density of states is singular at or near the band edge, and the band-edge density of modes turns on nearly abruptly as a step function. The large band-edge density of modes enhances the Seebeck coefficient, the power factor, and the thermoelectric figure of merit ZT. Electronic and thermoelectric properties are determined from ab initio calculations for few-layer III-VI materials GaS, GaSe, InS, InSe, for Bi2Se3, for monolayer Bi, and for bilayer graphene as a function of vertical field. The effect of interlayer coupling on these properties in few-layer III-VI materials and Bi2Se3 is described. Analytical models provide insight into the layer dependent trends that are relatively consistent for all of these few-layer materials. Vertically biased bilayer graphene could serve as an experimental test-bed for measuring these effects.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-09-21

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

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

    International Nuclear Information System (INIS)

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

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

    OpenAIRE

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

    2014-01-01

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

  14. Determination of the valence band structure of an alkali phosphorus oxynitride glass: A synchrotron XPS study on LiPON

    Energy Technology Data Exchange (ETDEWEB)

    Schwöbel, André, E-mail: aschwoebel@surface.tu-darmstadt.de [Technische Universität Darmstadt, Materials Science Department, Surface Science Division, Jovanka-Bontschits-Str. 2, 64287 Darmstadt (Germany); Precht, Ruben; Motzko, Markus; Carrillo Solano, Mercedes A. [Technische Universität Darmstadt, Materials Science Department, Surface Science Division, Jovanka-Bontschits-Str. 2, 64287 Darmstadt (Germany); Calvet, Wolfram [Helmholzzentrum Berlin GmbH, Solar Energy Research, Heterogeneous Materials Systems, Albert Einstein Straße 15, 12489 Berlin (Germany); Hausbrand, René; Jaegermann, Wolfram [Technische Universität Darmstadt, Materials Science Department, Surface Science Division, Jovanka-Bontschits-Str. 2, 64287 Darmstadt (Germany)

    2014-12-01

    Highlights: • In situ photoemission of LiPON solid Li-ion electrolyte. • We find that the valence band is similar to the known phosphates. • We find evidence for a resonance at the O1s edge shown by a Fano profile. • We find that the top of the valence band is due to N2p states. - Abstract: Lithium phosphorus oxynitride (LiPON) is a solid state electrolyte commonly used in thin film batteries (TFBs). Advanced TFBs face the issue of detrimental electrode–electrolyte interlayer formation, related to the electronic structure of the interface. In this contribution, we study the valence band structure of LiPON using resonant photoemission and synchrotron photoemission with variable excitation energies. The identification of different valence band features is done according to the known valence band features of meta- and orthophosphates. Additionally we compare our results with partial density of states simulations from literature. We find that the valence band structure is similar to the known metaphosphates with an additional contribution of nitrogen states at the top of the valence band. From the results we conclude that synchrotron X-ray photoemission (XPS) is a useful tool to study the valence band structure of nitridated alkali phosphate glasses.

  15. Determination of the valence band structure of an alkali phosphorus oxynitride glass: A synchrotron XPS study on LiPON

    International Nuclear Information System (INIS)

    Highlights: • In situ photoemission of LiPON solid Li-ion electrolyte. • We find that the valence band is similar to the known phosphates. • We find evidence for a resonance at the O1s edge shown by a Fano profile. • We find that the top of the valence band is due to N2p states. - Abstract: Lithium phosphorus oxynitride (LiPON) is a solid state electrolyte commonly used in thin film batteries (TFBs). Advanced TFBs face the issue of detrimental electrode–electrolyte interlayer formation, related to the electronic structure of the interface. In this contribution, we study the valence band structure of LiPON using resonant photoemission and synchrotron photoemission with variable excitation energies. The identification of different valence band features is done according to the known valence band features of meta- and orthophosphates. Additionally we compare our results with partial density of states simulations from literature. We find that the valence band structure is similar to the known metaphosphates with an additional contribution of nitrogen states at the top of the valence band. From the results we conclude that synchrotron X-ray photoemission (XPS) is a useful tool to study the valence band structure of nitridated alkali phosphate glasses

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

    International Nuclear Information System (INIS)

    For nuclei with mass A ? 120, the spin available in open-quotes normal deformation configurationsclose 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 117,118Xe

  17. 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.

  18. UV and x-ray photoelectron spectra of valence band of LaB6

    International Nuclear Information System (INIS)

    The total density of occupied states in the electronic structure of lanthanum hexaboride has been measured by use of high-resolution photoelectron spectroscopy combining far UV (Ne and He resonance lines) and x-ray excitation (monochromatized Al K ? radiation). The investigation was performed with clean and stoichiometric surfaces from poly-crystalline bulk samples and thin films, both prepared in situ. The data give new insights into bonding, band structure and thermal stability of LaB6. The valence band (approximately 12eV wide) is characterized by three main bands located at about 2 eV, 5 eV and 10 eV with additional subsidiary structures. The data are compared with published results of soft x-ray studies and the energy, position and width of the experimental bands compared and interpreted with available band-structure calculations. (author)

  19. Periodic ice banding in freezing colloidal dispersions.

    Science.gov (United States)

    Anderson, Anthony M; Worster, M Grae

    2012-12-01

    Concentrated colloidal alumina dispersions were frozen in a directional solidification apparatus that provides independent control of the freezing rate and temperature gradient. Two distinct steady-state modes of periodic ice banding were observed in the range of freezing rates examined. For each mode, the wavelength between successive bands of segregated ice decreases with increasing freezing rate. At low freezing rates (0.25-3 ?m s(-1)), the ice segregates from the suspension into ice lenses, which are cracklike in appearance, and there is visible structure in the layer of rejected particles in the unfrozen region ahead of the ice lenses. In this regime, we argue that compressive cryosuction forces lead to the irreversible aggregation of the rejected particles into a close-packed cohesive layer. The temperature in the aggregated layer is depressed below the bulk freezing point by more than 2 °C before the ice lenses are encountered; moreover, this undercooled region appears as a light-colored layer. The magnitude of the undercooling and the color change in this region both suggest the presence of pore ice and the formation of a frozen fringe. The possibility of a frozen fringe is supported by a quantitative model of the freezing behavior. At intermediate freezing rates, around 4 ?m s(-1), the pattern of ice segregation is disordered, coinciding with the disappearance of the dark- and light-colored layers. Finally, at high freezing rates (5-10 ?m s(-1)), there is a new mode of periodic ice banding that is no longer cracklike and is absent of any visible structure in the suspension ahead of the ice bands. We discuss the implications of our experimental findings for theories of ice lensing. PMID:23110707

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

    Science.gov (United States)

    Koloren?, Jind?ich; Kozub, Agnieszka L.; Shick, Alexander B.

    2015-03-01

    The correlated-band theory implemented as a combination of the local-density approximation with the dynamical mean-field theory is applied to PuO2. An insulating electronic structure, consistent with the experimental valence-band photoemission spectra, is obtained. The calculations yield a nonmagnetic ground state that is characterized by a noninteger filling of the plutonium 5f shell. The noninteger filling as well as the satellites appearing in the 4f core-level photoemission spectra originate in a sizable hybridization of the 5f shell with the 2p states of oxygen.

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

    International Nuclear Information System (INIS)

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

  2. Study of the structure of the valence band edge in bismuth-antimony telluride films

    International Nuclear Information System (INIS)

    The behaviour of kinetic coefficients in Bi2-xSbxTe3 films with high hole concentrations is studied. The temperature dependences of the coefficients of heat conduction, Hall coefficient and thermal e.m.f. of films with different hole concentrations are given. The effect of the heavy hole zone on the transfer phenomenon is studied. The obtained results explicitly reveals the two-band pattern of the Bi2-xSexTe3 valence band. The effective mass of the state density in the second subband is estimated

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-09-15

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

  4. 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.

  5. Valence-skipping and negative-U in the d-band from repulsive local Coulomb interaction

    Science.gov (United States)

    Strand, Hugo U. R.

    2014-10-01

    We show that repulsive local Coulomb interaction alone can drive valence-skipping charge disproportionation in the degenerate d-band, resulting in effective negative-U. This effect is shown to originate from anisotropic orbital-multipole scattering, and it occurs only for d1,d4,d6, and d9 fillings (and their immediate surroundings). Explicit boundaries for valence-skipping are derived, and the paramagnetic phase diagram for d4 and d6 is calculated. We also establish that the valence-skipping metal is very different, in terms of its local valence distribution, compared to the atomiclike Hund's metal. These findings explain why transition-metal compounds with the aforementioned d-band fillings are more prone to valence-skipping charge order and anomalous superconductivity.

  6. Core level and valence band investigation of WO3 thin films with synchrotron radiation

    International Nuclear Information System (INIS)

    In this work, the electronic properties of the surface of WO3 films with thickness of 150 nm, thermally evaporated in high vacuum onto Si(100) substrates and pre-treated in air by a 24-h-long annealing at 300 deg. C and 500 deg. C (obtaining polycrystalline monoclinic samples) have been studied by surface and bulk sensitive core level (W 4f) and angle integrated valence band photoemission using synchrotron radiation (ELETTRA Synchrotron). The photon energy ranged from 50 eV to 200 eV. The line shape analysis of W 4f core level spectra has shown that the surface presents a sub-stoichiometric WO3 component assigned to oxygen vacancies ultimately responsible for the gas sensitivity of this material. Correspondingly, valence band spectra show well-defined metallic states W 5d in the gap and near the Fermi level. The variations of surface chemical composition caused by Ultra High Vacuum annealing, and prolonged exposure to UV beam has been monitored by changes in spectral line shape. A general consequence of annealing in vacuum is the segregation of oxygen from the bulk toward the surface as confirmed by independent scanning tunnelling spectroscopy measurements

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

    International Nuclear Information System (INIS)

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

  8. The valence band structure of Ag{sub x}Rh{sub 1–x} alloy nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Anli [Synchrotron X-ray Station at SPring-8, National Institute for Materials Science (NIMS), 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148 (Japan); Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency (JST), 7 Goban-cho, Chiyoda-ku, Tokyo 102-0076 (Japan); Sakata, Osami, E-mail: SAKATA.Osami@nims.go.jp [Synchrotron X-ray Station at SPring-8, National Institute for Materials Science (NIMS), 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148 (Japan); Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency (JST), 7 Goban-cho, Chiyoda-ku, Tokyo 102-0076 (Japan); Synchrotron X-ray Group, Quantum Beam Unit, NIMS, 1-1-1 Kouto, Sayo-cho, Hyogo 679-5148 (Japan); Kusada, Kohei; Kobayashi, Hirokazu [Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency (JST), 7 Goban-cho, Chiyoda-ku, Tokyo 102-0076 (Japan); Division of Chemistry, Graduate School of Science, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto 606-8502 (Japan); Yayama, Tomoe; Ishimoto, Takayoshi [Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency (JST), 7 Goban-cho, Chiyoda-ku, Tokyo 102-0076 (Japan); INAMORI Frontier Research Center, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395 (Japan); Yoshikawa, Hideki [Surface Chemical Analysis Group, Nano Characterization Unit, NIMS, 1-2-1 Sengen, Tsukuba 305-0047 (Japan); Koyama, Michihisa [Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency (JST), 7 Goban-cho, Chiyoda-ku, Tokyo 102-0076 (Japan); INAMORI Frontier Research Center, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395 (Japan); International Institute for Carbon-Neutral Energy Research, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395 (Japan); and others

    2014-10-13

    The valence band (VB) structures of face-centered-cubic Ag-Rh alloy nanoparticles (NPs), which are known to have excellent hydrogen-storage properties, were investigated using bulk-sensitive hard x-ray photoelectron spectroscopy. The observed VB spectra profiles of the Ag-Rh alloy NPs do not resemble simple linear combinations of the VB spectra of Ag and Rh NPs. The observed VB hybridization was qualitatively reproduced via a first-principles calculation. The electronic structure of the Ag{sub 0.5}Rh{sub 0.5} alloy NPs near the Fermi edge was strikingly similar to that of Pd NPs, whose superior hydrogen-storage properties are well known.

  9. The valence band structure of AgxRh1–x alloy nanoparticles

    International Nuclear Information System (INIS)

    The valence band (VB) structures of face-centered-cubic Ag-Rh alloy nanoparticles (NPs), which are known to have excellent hydrogen-storage properties, were investigated using bulk-sensitive hard x-ray photoelectron spectroscopy. The observed VB spectra profiles of the Ag-Rh alloy NPs do not resemble simple linear combinations of the VB spectra of Ag and Rh NPs. The observed VB hybridization was qualitatively reproduced via a first-principles calculation. The electronic structure of the Ag0.5Rh0.5 alloy NPs near the Fermi edge was strikingly similar to that of Pd NPs, whose superior hydrogen-storage properties are well known.

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

    Science.gov (United States)

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

    2015-03-01

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

  11. Decay of Wannier-Mott excitons interacting with acoustic phonon in semiconductors with a degenerate valence band

    International Nuclear Information System (INIS)

    Decay probabilities of light and heavy excitons interacting with acoustic phonons in cubic semiconductors with a degenerate valence band are calculated. The numerical results for GaAs showed that the decay probability of the light exciton is much greater than that of the heavy one. (author). 10 refs, 1 fig

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

    International Nuclear Information System (INIS)

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

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

    International Nuclear Information System (INIS)

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

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

    International Nuclear Information System (INIS)

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-05-16

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

  16. Holes in the valence band of superconducting boron-doped diamond film studied by soft X-ray absorption and emission spectroscopy

    CERN Document Server

    Nakamura, J; Yamada, N; Kuroki, K; Okada, K; Takano, Y; Nagao, M; Sakaguchi, I; Kawarada, H; Perera, R C C; Ederer, D L; Nakamura, Jin; Oguchi, Tamio; Yamada, Nobuyoshi; Kuroki, Kazuhiko; Okada, Kozo; Takano, Yoshihiko; Nagao, Masanori; Sakaguchi, Isao; Kawarada, Hiroshi; Perera, Rupert C.C.; Ederer, David L.

    2004-01-01

    Partial densities of states of C-2p and B-2p states of superconducting and non-superconducting boron-doped diamond samples are measured using soft X-ray emission and absorption spectroscopy on C-K and B-K edges. For the superconducting sample, a large electronic density of hole states is observed in the valence band in addition to the states in the impurity band. The hole states in the valence band located at about 1.3 eV below the valence band maximum cannot be interpreted within a simple rigid band model, but may be explained by a local lattice distortion. Present results suggest that superconductivity is to be attributed to the holes in the valence band.

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

    Directory of Open Access Journals (Sweden)

    ?ukari? Nemanja A.

    2010-01-01

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

  18. Valence Band Modification and High Thermoelectric Performance in SnTe Heavily Alloyed with MnTe.

    Science.gov (United States)

    Tan, Gangjian; Shi, Fengyuan; Hao, Shiqiang; Chi, Hang; Bailey, Trevor P; Zhao, Li-Dong; Uher, Ctirad; Wolverton, Chris; Dravid, Vinayak P; Kanatzidis, Mercouri G

    2015-09-01

    We demonstrate a high solubility limit of >9 mol% for MnTe alloying in SnTe. The electrical conductivity of SnTe decreases gradually while the Seebeck coefficient increases remarkably with increasing MnTe content, leading to enhanced power factors. The room-temperature Seebeck coefficients of Mn-doped SnTe are significantly higher than those predicted by theoretical Pisarenko plots for pure SnTe, indicating a modified band structure. The high-temperature Hall data of Sn1-xMnxTe show strong temperature dependence, suggestive of a two-valence-band conduction behavior. Moreover, the peak temperature of the Hall plot of Sn1-xMnxTe shifts toward lower temperature as MnTe content is increased, which is clear evidence of decreased energy separation (band convergence) between the two valence bands. The first-principles electronic structure calculations based on density functional theory also support this point. The higher doping fraction (>9%) of Mn in comparison with ?3% for Cd and Hg in SnTe gives rise to a much better valence band convergence that is responsible for the observed highest Seebeck coefficient of ?230 ?V/K at 900 K. The high doping fraction of Mn in SnTe also creates stronger point defect scattering, which when combined with ubiquitous endotaxial MnTe nanostructures when the solubility of Mn is exceeded scatters a wide spectrum of phonons for a low lattice thermal conductivity of 0.9 W m(-1) K(-1) at 800 K. The synergistic role that Mn plays in regulating the electron and phonon transport of SnTe yields a high thermoelectric figure of merit of 1.3 at 900 K. PMID:26308902

  19. 5f band dispersion in epitaxial films of UO2

    Energy Technology Data Exchange (ETDEWEB)

    Durakiewicz, Tomasz [Los Alamos National Laboratory; Jia, Quanxi [Los Alamos National Laboratory; Roy, Lindsay E [Los Alamos National Laboratory; Martin, Richard L [Los Alamos National Laboratory; Joyce, John J [Los Alamos National Laboratory

    2009-01-01

    Polymer-assisted deposition of epitaxial films utilizes lattice pinning to produce films of very high stability and properties identical with bulk crystal. Dispersion of the 5f band is shown for the first time in a actinide Mott insulator system, which suggestes hybridization as a leading process in establishing the electronic structure. Hybrid density functional is succesfully employed to calculate the electronic structure of UO{sub 2} in agreement with experiments. UO{sub 2} continues to be a mysterious and elusive compound in terms of understanding the physical properties of a material. Most actinide oxides, including UO{sub 2} are predicted to be metallic. However, UO{sub 2} is an antiferromagnetic insulator with a relatively large gap of about 2eV. The f orbital charater of the excitations across the gap places UO{sub 2} in a Mott insulator category, but no states at the gap center have ever been measured directly, in spite of intensive efforts. In this work we present the first results of the electronic structure investigation of a epitaxial film of UO{sub 2}, where we find even more unexpected properties, like the dispersive nature of 5f bands. We also demonstrate the unexpected, very high stability of the epitaxial film of UO{sub 2}. In the lattice-pinning scheme, the crystalline nature of the film is preserved all the way up to the topmost layers even after prolonged exposure to atmospheric conditions. Hybridized, dispersive bands are common in the itinerant uranium compounds. One usually finds hybridization of f-orbitals with conduction band to be quite common in f-electron systems at low temperatures. Such bands may reside in the vicinity of the Fermi level and participate in the construction of the Fermi surface. However, in the insulator like UO{sub 2}, one expects a more atomic band nature, where f-bands are relatively flat and shifted away from the Fermi level by the gap energy scale. Precise location of UO{sub 2} on the localization-delocalization axis could be pinned down by measurements of band dispersion.

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

    OpenAIRE

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

    2013-01-01

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

  1. Dispersion law and lifetime of holes with negative effactive masses in GITAsub(1v)-band of crystals with diamond structure

    International Nuclear Information System (INIS)

    It is shown that in the low valence GITAsub(1v)-band of diamond structure crystals the holes are described by a standard dispersion law with a negative effective mass. The interaction of such holes with phonons is considered. The lifetime of the holes dependent on this interaction is estimated. It can be as high as 10-9 s in Ge at 20K

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

    OpenAIRE

    ISMAILOV, T. G.

    2000-01-01

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

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

    Science.gov (United States)

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

    2002-02-01

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

  4. Determination of conduction and valence band electronic structure of anatase and rutile TiO2

    Indian Academy of Sciences (India)

    Jakub Szlachetko; Katarzyna Michalow-Mauke; Maarten Nachtegaal; Jacinto Sá

    2014-03-01

    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 localized states located in the band gap where electrons can be trapped, which are almost absent in the rutile structure. This could well explain the reported longer lifetimes in anatase. It was revealed that HR-XAS is insufficient to study in-depth unoccupied states of investigated materials because it overlooks the shallow traps.

  5. Impact of cation-based localized electronic states on the conduction and valence band structure of Al{sub 1?x}In{sub x}N alloys

    Energy Technology Data Exchange (ETDEWEB)

    Schulz, S., E-mail: stefan.schulz@tyndall.ie [Photonics Theory Group, Tyndall National Institute, Dyke Parade, Cork (Ireland); Caro, M. A.; O' Reilly, E. P. [Photonics Theory Group, Tyndall National Institute, Dyke Parade, Cork (Ireland); Department of Physics, University College Cork, Cork (Ireland)

    2014-04-28

    We demonstrate that cation-related localized states strongly perturb the band structure of Al{sub 1?x}In{sub x}N leading to a strong band gap bowing at low In content. Our first-principles calculations show that In-related localized states are formed both in the conduction and the valence band in Al{sub 1?x}In{sub x}N for low In composition, x, and that these localized states dominate the evolution of the band structure with increasing x. Therefore, the commonly used assumption of a single composition-independent bowing parameter breaks down when describing the evolution both of the conduction and of the valence band edge in Al{sub 1?x}In{sub x}N.

  6. 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.

  7. Experimental Observation and Theoretical Description of the Pure Fano Effect in the Valence-Band Photoemission of Ferromagnets

    International Nuclear Information System (INIS)

    The pure Fano effect in angle-integrated valence-band photoemission of ferromagnets has been observed for the first time. A contribution of the intrinsic spin polarization to the spin polarization of the photoelectrons has been avoided by an appropriate choice of the experimental parameters. The theoretical description of the resulting spectra reveals a complete analogy to the Fano effect observed before for paramagnetic transition metals. While the theoretical photocurrent and spin-difference spectra are found in good quantitative agreement with experiment in the case of Fe and Co, only a qualitative agreement could be achieved in the case of Ni by calculations on the basis of plain local spin-density approximation. Agreement with experimental data could be improved in this case in a very substantial way by a treatment of correlation effects on the basis of dynamical mean field theory

  8. Valence and conduction band offsets at low-k a-SiOxCy:H/a-SiCxNy:H interfaces

    International Nuclear Information System (INIS)

    In order to understand the fundamental electrical leakage and reliability failure mechanisms in nano-electronic low-k dielectric/metal interconnect structures, we have utilized x-ray photoelectron spectroscopy and reflection electron energy loss spectroscopy to determine the valence and conduction band offsets present at interfaces between non-porous and porous low-k a-SiOxCy:H interlayer dielectrics and a-SiCxNy:H metal capping layers. The valence band offset for such interfaces was determined to be 2.7?±?0.2?eV and weakly dependent on the a-SiOC:H porosity. The corresponding conduction band offset was determined to be 2.1?±?0.2?eV. The large band offsets indicate that intra metal layer leakage is likely dominated by defects and trap states in the a-SiOC:H and a-SiCN:H dielectrics.

  9. Spin exchange energy for a pair of valence band holes in artificial molecules

    International Nuclear Information System (INIS)

    We study the exchange energy for two interacting holes in vertically stacked InGaAs quantum dots using the configuration interaction method and an axially symmetric 4-band Kohn-Luttinger Hamiltonian that introduces heavy-hole and light-hole subbands mixing due to the spin–orbit interaction. We demonstrate that, as a consequence of the band mixing, a singlet–triplet degeneracy appears for a single specific value of the interdot barrier, for which the bonding and antibonding heavy hole have identical energy. We explain this degeneracy using a simple model matrix Hamiltonian as due to the interaction effects for a degenerate ground state of the hole. We demonstrate that, in conditions of the singlet–triplet degeneracy due to hybridization of the bonding and antibonding energy levels, the spin exchange energy becomes insensitive to external electric fields. (paper)

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

    CERN Document Server

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

    2012-01-01

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

  11. Electronic structure in valence band of Nd-substituted Bi4Ti3O12 single crystal probed by soft-x-ray emission spectroscopy

    International Nuclear Information System (INIS)

    The electronic structure of Nd3+-substituted Bi4Ti3O12 single crystals was studied by soft-X-ray emission spectroscopy. The valence band is in good accordance with the band calculation. The valence band is mainly composed of the O 2p state hybridized with Ti 3d and Bi 6s states. The hybridization effect between the Ti 3d and O 2p states increases with Nd3+ substitution, indicating a change in Ti-O bond length in the a-b plane. The hybridization effect between the Bi 6s and O 2p states decreases with Nd3+ substitution. The Bi-O hybridization effect is considered to be closely related to the ferroelectric behavior. (author)

  12. Angle-resolved photoemission study of the valence-band structure of VN/sub 0.89/(100)

    International Nuclear Information System (INIS)

    The electronic structure of a VN/sub 0.89/(100) single crystal has been studied using angle-resolved photoemission spectroscopy and synchrotron radiation. Recorded normal-emission spectra are compared with theoretical photoemission spectra calculated for stoichiometric composition. A good overall agreement between recorded and calculated spectra is found for photon energies below about 35 eV. A mapping of the band structure is made and compared with a theoretical bulk-band structure. The experimentally determined dispersions of the energy bands are found to be smaller than those theoretically predicted and the location of the bands deviates, in some cases considerably. A vacancy-induced structure is identified at 2.8 eV below the Fermi energy in spectra recorded at photon energies above 31 eV. The character of the vacancy-induced states and of states located close to the Fermi energy is discussed based on observed intensity enhancements above the V 3p absorption threshold

  13. Electronic structures and valence band XPS spectra of BeO and SiC calculated by X? cluster method

    International Nuclear Information System (INIS)

    The DV-X? cluster method has been applied for calculations of the electronic structures and for analysis of valence band XPS spectra of BeO, ?-SiC (Wurutzite type) and ?-SiC (Zinc-blende type). Clusters studied are [Be4O4] for BeO, and [Si4C4] and [Si5C4]sup(0.75+) for ?-SiC and ?-SiC, respectively. The calculation for BeO has yielded the electronic level structure characteristic of an insulating material. For ?-SiC and ?-SiC the level structures can be related well with their semiconducting behavior. The calculated XPS spectrum of ?-SiC is very similler to that of ?-SiC and is in good agreement with the observed one. However, the effective charge on Si atom in ?-SiC obtained is about twice that in ?-SiC (?-SiC : +1.56, ?-SiC : +0.75). The marked difference indicates that ?-SiC is a material more ionic than ?-SiC. (author)

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

    Energy Technology Data Exchange (ETDEWEB)

    Deleuze, Michael S. [Theoretische Chemie, Departement SBG, Universiteit Hasselt, Agoralaan, Gebouw D, B-3590 Diepenbeek (Belgium)], E-mail: michael.deleuze@uhasselt.be

    2006-10-26

    A comprehensive study of the He (I) ultra-violet photoelectron spectra of the 1.2,3.4; 1.2,5.6 and 1.2,7.8 isomers of dibenzanthracene up to the double ionisation threshold at {approx}18 eV is presented with the aid of one-particle Green's Function calculations performed using the outer-valence Green's Function (OVGF) approach and the third-order algebraic diagrammatic construction [ADC(3)] scheme, along with basis sets of improving quality. Suited extrapolations of the ADC(3) results for the one-electron energies characterising the {pi}-band system ({epsilon} {sub b} < 10 eV) to Dunning's correlation consistent basis set of triple zeta quality (cc-pVTZ) enable theoretical insights into HeI measurements which approach chemical accuracy (1 kcal/mol or 43.4 meV). In contrast, a confrontation of simulated spectral envelopes with high-resolution He I photoelectron spectra indicates that polycyclic aromatic molecules with sterically overcrowded bay regions are more susceptible to undergo vibronic coupling complications at the {sigma}-ionisation onset. OVGF/cc-pVDZ or OVGF/cc-pVTZ pole strengths smaller than 0.85 systematically corroborate a breakdown of the orbital (or one-electron) picture of ionisation at the ADC(3)/6-31G levels. The extent of shake-up bands is correspondingly related to topological, structural and magnetic criteria of aromaticity. Comparison is made with calculations of the lowest doublet-doublet excitation energies of the related radical cations, by means of time-dependent density functional theory (TDDFT)

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

    International Nuclear Information System (INIS)

    A comprehensive study of the He (I) ultra-violet photoelectron spectra of the 1.2,3.4; 1.2,5.6 and 1.2,7.8 isomers of dibenzanthracene up to the double ionisation threshold at ?18 eV is presented with the aid of one-particle Green's Function calculations performed using the outer-valence Green's Function (OVGF) approach and the third-order algebraic diagrammatic construction [ADC(3)] scheme, along with basis sets of improving quality. Suited extrapolations of the ADC(3) results for the one-electron energies characterising the ?-band system (? b < 10 eV) to Dunning's correlation consistent basis set of triple zeta quality (cc-pVTZ) enable theoretical insights into HeI measurements which approach chemical accuracy (1 kcal/mol or 43.4 meV). In contrast, a confrontation of simulated spectral envelopes with high-resolution He I photoelectron spectra indicates that polycyclic aromatic molecules with sterically overcrowded bay regions are more susceptible to undergo vibronic coupling complications at the ?-ionisation onset. OVGF/cc-pVDZ or OVGF/cc-pVTZ pole strengths smaller than 0.85 systematically corroborate a breakdown of the orbital (or one-electron) picture of ionisation at the ADC(3)/6-31G levels. The extent of shake-up bands is correspondingly related to topological, structural and magnetic criteria of aromaticity. Comparison is made with calculations of the lowest doublet-doublet excitation energies of the related radical cations, by means of time-dependent density functional theory (TDDFT)

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

    International Nuclear Information System (INIS)

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

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

    International Nuclear Information System (INIS)

    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

  18. VALENCE BAND DISCONTINUITIES IN THE Hg1-xCdxTe-Hg1-yCdyTe(111)B SYSTEM - XPS STUDY

    OpenAIRE

    Hsu, C; Duc, Tran; Faurie, J.

    1987-01-01

    XPS investigations on the Hg1-xCdxTe(111)B alloys show a small change in the binding energy difference between the two cations Cd and Hg for the whole range of alloy compositions. This confirms that the charge transfer between the two cations is very small in Hg1-xCdxTe-Hg1-yCdyTe(111)B heterojunctions. From this study it is concluded that the value of the nutural band discontinuity in HgTe-CdTe heterojunction (0.35eV) is identical to the value of the valence band discontinuity measured in th...

  19. Tailoring the Valence Band Offset of Al2O3 on Epitaxial GaAs1-ySby with Tunable Antimony Composition.

    Science.gov (United States)

    Liu, Jheng-Sin; Clavel, Michael; Hudait, Mantu K

    2015-12-30

    Mixed-anion, GaAs1-ySby metamorphic materials with tunable antimony (Sb) compositions extending from 0 to 100%, grown by solid source molecular beam epitaxy (MBE), were used to investigate the evolution of interfacial chemistry under different passivation conditions. X-ray photoelectron spectroscopy (XPS) was used to determine the change in chemical state progression as a function of surface preclean and passivation, as well as the valence band offsets, conduction band offsets, energy band parameters, and bandgap of atomic layer deposited Al2O3 on GaAs1-ySby for the first time, which is further corroborated by X-ray analysis and cross-sectional transmission electron microscopy. Detailed XPS analysis revealed that the near midpoint composition, GaAs0.45Sb0.55, passivation scheme exhibits a GaAs-like surface, and that precleaning by HCl and (NH4)2S passivation are mandatory to remove native oxides from the surface of GaAsSb. The valence band offsets, ?Ev, were determined from the difference in the core level to the valence band maximum binding energy of GaAs1-ySby. A valence band offset of >2 eV for all Sb compositions was found, indicating the potential of utilizing Al2O3 on GaAs1-ySby (0 ? y ? 1) for p-type metal-oxide-semiconductor (MOS) applications. Moreover, Al2O3 showed conduction band offset of ?2 eV on GaAs1-ySby (0 ? y ? 1), suggesting Al2O3 dielectric can also be used for n-type MOS applications. The surface passivation of GaAs0.45Sb0.55 materials and the detailed band alignment analysis of Al2O3 high-? dielectrics on tunable Sb composition, GaAs1-ySby materials, provides a pathway to utilize GaAsSb materials in future microelectronic and optoelectronic applications. PMID:26642121

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

    International Nuclear Information System (INIS)

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

  1. Formation of dispersive hybrid bands at an organic-metal interface

    OpenAIRE

    González-Lakunza, N.; Fernández-Torrente, I.; Franke, K. J.; Lorente, N.; Arnau, Andrés; Pascual, J. I.

    2008-01-01

    An electronic band with quasi-one dimensional dispersion is found at the interface between a monolayer of a charge-transfer complex (TTF-TCNQ) and a Au(111) surface. Combined local spectroscopy and numerical calculations show that the band results from a complex mixing of metal and molecular states. The molecular layer folds the underlying metal states and mixes with them selectively, through the TTF component, giving rise to anisotropic hybrid bands. Our results suggest tha...

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

    Scientific Electronic Library Online (English)

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

    2013-12-01

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

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

    International Nuclear Information System (INIS)

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

  4. 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.

  5. Polarization dependent hard X-ray photoemission experiments for solids: Efficiency and limits for unraveling the orbital character of the valence band

    Energy Technology Data Exchange (ETDEWEB)

    Weinen, J., E-mail: Jonas.Weinen@cpfs.mpg.de [Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden (Germany); Koethe, T.C. [II. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, 50937 Köln (Germany); Chang, C.F.; Agrestini, S.; Kasinathan, D. [Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden (Germany); Liao, Y.F. [National Synchrotron Radiation Research Center, 101 Hsin-Ann Road, Hsinchu Science-Park, Hsinchu 30077, Taiwan (China); Fujiwara, H.; Schüßler-Langeheine, C.; Strigari, F.; Haupricht, T. [II. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, 50937 Köln (Germany); Panaccione, G. [TASC Laboratory, IOM-CNR, Area Science Park, S.S.14, Km 163.5, I-34149 Trieste (Italy); Offi, F. [CNISM and Dipartimento di Scienze, Università Roma Tre, Via della Vasca Navale 84, I-00146 Rome (Italy); Monaco, G.; Huotari, S. [European Synchrotron Radiation Facility, BP220, 38043 Grenoble (France); Tsuei, K.-D. [National Synchrotron Radiation Research Center, 101 Hsin-Ann Road, Hsinchu Science-Park, Hsinchu 30077, Taiwan (China); Tjeng, L.H. [Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden (Germany); II. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, 50937 Köln (Germany)

    2015-01-15

    Highlights: • Efficiency and limits of polarization dependent HAXPES for solid state systems. • The polarization dependence is less than expected from atomic cross-sections. • Still high contrast (?20–25) for s orbitals. • Quantitative determination of contributions to the valence band. - Abstract: We have investigated the efficiency and limits of polarization dependent hard X-ray photoelectron spectroscopy (HAXPES) in order to establish how well this method can be used to unravel quantitatively the contributions of the orbitals forming the valence band of solids. By rotating the energy analyzer rather than the polarization vector of the light using a phase retarder, we obtained the advantage that the full polarization of the light is available for the investigation. Using NiO, ZnO, and Cu{sub 2}O as examples for solid state materials, we established that the polarization dependence is much larger than in photoemission experiments utilizing ultra-violet or soft X-ray light. Yet we also have discovered that the polarization dependence is less than complete on the basis of atomic calculations, strongly suggesting that the trajectories of the outgoing electrons are affected by appreciable side-scattering processes even at these high kinetic energies. We have found in our experiment that these can be effectively described as a directional spread of ±18° of the photoelectrons. This knowledge allows us to identify, for example, reliably the Ni 3d spectral weight of the NiO valence band and at the same time to demonstrate the importance of the Ni 4s for the chemical stability of the compound.

  6. Polarization dependent hard X-ray photoemission experiments for solids: Efficiency and limits for unraveling the orbital character of the valence band

    International Nuclear Information System (INIS)

    Highlights: • Efficiency and limits of polarization dependent HAXPES for solid state systems. • The polarization dependence is less than expected from atomic cross-sections. • Still high contrast (?20–25) for s orbitals. • Quantitative determination of contributions to the valence band. - Abstract: We have investigated the efficiency and limits of polarization dependent hard X-ray photoelectron spectroscopy (HAXPES) in order to establish how well this method can be used to unravel quantitatively the contributions of the orbitals forming the valence band of solids. By rotating the energy analyzer rather than the polarization vector of the light using a phase retarder, we obtained the advantage that the full polarization of the light is available for the investigation. Using NiO, ZnO, and Cu2O as examples for solid state materials, we established that the polarization dependence is much larger than in photoemission experiments utilizing ultra-violet or soft X-ray light. Yet we also have discovered that the polarization dependence is less than complete on the basis of atomic calculations, strongly suggesting that the trajectories of the outgoing electrons are affected by appreciable side-scattering processes even at these high kinetic energies. We have found in our experiment that these can be effectively described as a directional spread of ±18° of the photoelectrons. This knowledge allows us to identify, for example, reliably the Ni 3d spectral weight of the NiO valence band and at the same time to demonstrate the importance of the Ni 4s for the chemical stability of the compound

  7. High-resolution X-ray emission and absorption study of the B 2p valence band electronic structure of MgB2

    International Nuclear Information System (INIS)

    The occupied and unoccupied valence band states of MgB2 have been studied using high-resolution soft X-ray emission and soft X-ray absorption spectroscopies. In particular, the B 2p partial density of states was measured near the Fermi level. The states at the Fermi edge are identified by comparison to calculation as being of B 2pxy origin. Resonant inelastic X-ray scattering indicates the existence of low-energy excitations at the B 1 s-edge absorption threshold. (orig.)

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

    CERN Document Server

    Darbandi, A

    2012-01-01

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

  9. Non-Fermi-liquid scattering rates and anomalous band dispersion in ferropnictides

    Science.gov (United States)

    Fink, J.; Charnukha, A.; Rienks, E. D. L.; Liu, Z. H.; Thirupathaiah, S.; Avigo, I.; Roth, F.; Jeevan, H. S.; Gegenwart, P.; Roslova, M.; Morozov, I.; Wurmehl, S.; Bovensiepen, U.; Borisenko, S.; Vojta, M.; Büchner, B.

    2015-11-01

    Angle-resolved photoemission spectroscopy is used to study the band dispersion and the quasiparticle scattering rates in two ferropnictide systems. We find the scattering rate for any given band to depend linearly on energy but to be independent of the control parameter. We demonstrate that the linear energy dependence gives rise to a weakly dispersing band with a strong mass enhancement when the band maximum crosses the chemical potential. The resulting small effective Fermi energy favors a BCS [J. Bardeen et al., Phys. Rev. 108, 1175 (1957), 10.1103/PhysRev.108.1175] -Bose-Einstein [S. N. Bose, Z. Phys. 26, 178 (1924), 10.1007/BF01327326] crossover state in the superconducting phase.

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

    CERN Document Server

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

    2010-01-01

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

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

    International Nuclear Information System (INIS)

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

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

    CERN Document Server

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

    2003-01-01

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

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

    Science.gov (United States)

    Yanagisawa, Susumu; Morikawa, Yoshitada; Schindlmayr, Arno

    2013-09-01

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

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

    Science.gov (United States)

    Chen, Tie-Xin; Cao, Liang; Zhang, Wang; Han, Yu-Yan; Zheng, Zhi-Yuan; Xu, Fa-Qiang; Ibrahim, Kurash; Qian, Hai-Jie; Wang, Jia-Ou

    2013-02-01

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

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

    International Nuclear Information System (INIS)

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

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

    Energy Technology Data Exchange (ETDEWEB)

    King, Sean W., E-mail: sean.king@intel.com [Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695 (United States); Logic Technology Development, Intel Corporation, Hillsboro, Oregon 97124 (United States); Nemanich, Robert J. [Department of Physics, North Carolina State University, Raleigh, North Carolina 27695 (United States); Department of Physics, Arizona State University, Tempe, Arizona 85281 (United States); Davis, Robert F. [Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695 (United States); Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213 (United States)

    2014-08-25

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

  17. Quasi one-dimensional band dispersion and surface metallization in long-range ordered polymeric wires.

    Science.gov (United States)

    Vasseur, Guillaume; Fagot-Revurat, Yannick; Sicot, Muriel; Kierren, Bertrand; Moreau, Luc; Malterre, Daniel; Cardenas, Luis; Galeotti, Gianluca; Lipton-Duffin, Josh; Rosei, Federico; Di Giovannantonio, Marco; Contini, Giorgio; Le Fèvre, Patrick; Bertran, François; Liang, Liangbo; Meunier, Vincent; Perepichka, Dmitrii F

    2016-01-01

    On-surface covalent self-assembly of organic molecules is a very promising bottom-up approach for producing atomically controlled nanostructures. Due to their highly tuneable properties, these structures may be used as building blocks in electronic carbon-based molecular devices. Following this idea, here we report on the electronic structure of an ordered array of poly(para-phenylene) nanowires produced by surface-catalysed dehalogenative reaction. By scanning tunnelling spectroscopy we follow the quantization of unoccupied molecular states as a function of oligomer length, with Fermi level crossing observed for long chains. Angle-resolved photoelectron spectroscopy reveals a quasi-1D valence band as well as a direct gap of 1.15?eV, as the conduction band is partially filled through adsorption on the surface. Tight-binding modelling and ab initio density functional theory calculations lead to a full description of the band structure, including the gap size and charge transfer mechanisms, highlighting a strong substrate-molecule interaction that drives the system into a metallic behaviour. PMID:26725974

  18. Calculation and analysis of complex band structure in dispersive and dissipative two-dimensional photonic crystals

    CERN Document Server

    Brûlé, Yoann; Gralak, Boris

    2015-01-01

    Numerical calculation of modes in dispersive and absorptive systems is performed using the finite element method. The dispersion is tackled in the frame of an extension of Maxwell's equations where auxiliary fields are added to the electromagnetic field. This method is applied to multi-domain cavities and photonic crystals including Drude and Drude-Lorentz metals. Numerical results are compared to analytical solutions for simple cavities and to previous results of the literature for photonic crystals, showing excellent agreement. The advantages of the developed method lie on the versatility of the finite element method regarding geometries, and in sparing the use of tedious complex poles research algorithm. Hence the complex spectrum of resonances of non-hermitian operators and dissipative systems, like two-dimensional photonic crystal made of absorbing Drude metal, can be investigated in detail. The method is used to reveal unexpected features of their complex band structures.

  19. First principles electronic band structure and phonon dispersion curves for zinc blend beryllium chalcogenide

    International Nuclear Information System (INIS)

    A detailed theoretical study of structural, electronic and Vibrational properties of BeX compound is presented by performing ab-initio calculations based on density-functional theory using the Espresso package. The calculated value of lattice constant and bulk modulus are compared with the available experimental and other theoretical data and agree reasonably well. BeX (X = S,Se,Te) compounds in the ZB phase are indirect wide band gap semiconductors with an ionic contribution. The phonon dispersion curves are represented which shows that these compounds are dynamically stable in ZB phase

  20. First principles electronic band structure and phonon dispersion curves for zinc blend beryllium chalcogenide

    Energy Technology Data Exchange (ETDEWEB)

    Dabhi, Shweta, E-mail: venu.mankad@gmail.com; Mankad, Venu, E-mail: venu.mankad@gmail.com; Jha, Prafulla K., E-mail: venu.mankad@gmail.com [Department of Physics, Maharaja Krishnakumasinhji Bhavnagar University, Bhavnagar-364001 (India)

    2014-04-24

    A detailed theoretical study of structural, electronic and Vibrational properties of BeX compound is presented by performing ab-initio calculations based on density-functional theory using the Espresso package. The calculated value of lattice constant and bulk modulus are compared with the available experimental and other theoretical data and agree reasonably well. BeX (X = S,Se,Te) compounds in the ZB phase are indirect wide band gap semiconductors with an ionic contribution. The phonon dispersion curves are represented which shows that these compounds are dynamically stable in ZB phase.

  1. Band structure effects on the Be(0001) acoustic surface plasmon energy dispersion

    International Nuclear Information System (INIS)

    We report first-principles calculations of acoustic surface plasmons on the (0001) surface of Be, as obtained in the random-phase approximation of many-body theory. The energy dispersion of these collective excitations has been obtained along two symmetry directions. Our results show a considerable anisotropy of acoustic surface plasmons, and underline the capability of experimental measurements of these plasmons to map the electron-hole excitation spectrum of the quasi two-dimensional Shockley surface state band that is present on the Be(0001) surface. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  2. Magnetic response of split-ring resonator metamaterials: From effective medium dispersion to photonic band gaps

    Indian Academy of Sciences (India)

    Sangeeta Chakrabarti; S Anantha Ramakrishna

    2012-03-01

    On systematically investigating the electromagnetic response of periodic split-ring resonator (SRR) metamaterials as a function of the size-to-wavelength ($a/\\lambda$) ratio, we ?nd that the stop bands due to the geometric resonances of the SRR weaken with increasing ($a/\\lambda$) ratio, and are eventually replaced by stop bands due to Bragg scattering. Our study traces the behaviour of SRR-based metamaterials as the resonance frequency increases and the wavelength of the radiation ?nally becomes comparable to the size of the unit cell of the metamaterial. In the intermediate stages, the dispersion of the SRR metamaterial can still be described as due to a localized magnetic resonances while Bragg scattering ?nally becomes the dominant phenomenon as $a/\\lambda \\sim 1/2$.

  3. Valence band electronic structure of Nd1?xYxMnO3 using X-ray absorption, photoemission and GGA + U calculations

    International Nuclear Information System (INIS)

    Highlights: •Decrease in the occupancy of Mn 3d orbitals with doping. •Greater splitting of the eg orbitals due to the increased Jahn–Teller distortion with doping. •Decrease in O 2p–Mn 3d charge transfer character with doping. •Increase in charge transfer energy and band gap with doping. •Calculations hint a subtle change from a charge transfer to Mott–Hubbard type insulator with doping. -- Abstract: The electronic structures of Nd1?xYxMnO3 (x = 0–0.5) were studied using X-ray absorption near-edge structure (XANES) at the Mn L3,2- and O K-edge along with valence-band photoemission spectroscopy (VB-PES). The systematic increase in white-line intensity of the Mn L3,2-edge with doping, suggests a decrease in the occupancy of Mn 3d orbitals. The O K-edge XANES shows a depletion of unoccupied states above the Fermi energy. The changes in the O K-edge spectra due to doping reflects an increase in the Jahn–Teller distortion. The VB-PES shows broadening of the features associated with Mn 3d and O 2p hybridized states and the shift of these features to a slightly higher binding energy in agreement with our GGA + U calculations. The system shows a net shift of the occupied and unoccupied states away from the Fermi energy with doping. The shift in theoretical site-projected density of states of x = 0.5 composition with respect to x = 0 suggest a subtle change from a charge transfer to Mott Hubbard type insulator

  4. First-principle studies of the electronic band structure and the phonon dispersion properties of wurtzite BN

    Science.gov (United States)

    Lei, X.; Liang, X. X.; Zhao, G. J.; Song, T. L.

    2014-03-01

    The electronic band structure and phonon dispersion of wurtzite BN are studied by the first principle calculations. The local density approximation (LDA) and the generalized gradient approximation (GGA) exchange-correlation potentials are applied in the calculations and compared. The computational results for the band structure and density of states with indirect band gaps as well as the phonon dispersive curves and density of states are obtained. The corresponding dielectric and thermodynamic properties are discussed. The conclusions are consistent with other theoretical results and experimental data.

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

    OpenAIRE

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

    2014-01-01

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

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

    DEFF Research Database (Denmark)

    Habib, Selim; Khandker, Emran

    2015-01-01

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

  7. Angle-resolved photoemission study of dispersive and narrow-band 5f states in UAsSe

    Science.gov (United States)

    Guziewicz, E.; Durakiewicz, T.; Oppeneer, P. M.; Joyce, J. J.; Thompson, J. D.; Olson, C. G.; Butterfield, M. T.; Wojakowski, A.; Moore, D. P.; Arko, A. J.

    2006-04-01

    Single crystals of ferromagnetic UAsSe have been investigated by angle-resolved photoemission spectroscopy (ARPES) in the photon energy range between 20eV and 110eV . Electron kinetic energy intensities are collected as a function of angle and mapped onto the materials reciprocal space. Energy-band mapping has been carried out both for a several-eV-wide energy interval as well as for a narrow energy interval of less than 1eV from the Fermi energy. The main features of the deduced energy bands can be explained by band-structure calculations. In the interval close to the Fermi energy, the very high energy and momentum resolution allows the observation of a narrow, yet dispersive photoemission peak mainly of 5f character situated within 50meV of the Fermi energy. The Lorentzian linewidth was found to be about 35meV with a dispersion of 30meV along the ? to Z direction and 40meV dispersion along the ? to X direction in the Brillouin zone. We have also found broader (linewidth about 70meV ), hybridized f -character bands with a conventional dispersion of about 1eV along the ? to X and the Z to R directions in the Brillouin zone. An intriguing electronic structure emerges for UAsSe in which both relatively dispersive and narrow 5f bands are present. The occurrence of 5f -band dispersions stipulates that the electronic structure of UAsSe requires lattice periodicity to be taken into account.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2008-08-13

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

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

    DEFF Research Database (Denmark)

    Sorokin, Vladislav; Thomsen, Jon Juel

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

  10. Deduction of the chemical state and the electronic structure of Nd{sub 2}Fe{sub 14}B compound from X-ray photoelectron spectroscopy core-level and valence-band spectra

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Jing; Liang, Le [School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240 (China); Zhang, Lanting, E-mail: lantingzh@sjtu.edu.cn, E-mail: lmsun@sjtu.edu.cn [School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240 (China); Hirano Institute for Materials Innovation, Shanghai Jiao Tong University, Shanghai 200240 (China); Sun, Limin, E-mail: lantingzh@sjtu.edu.cn, E-mail: lmsun@sjtu.edu.cn [Instrumental Analysis Center, Shanghai Jiao Tong University, Shanghai 200240 (China); Hirano, Shinichi [Hirano Institute for Materials Innovation, Shanghai Jiao Tong University, Shanghai 200240 (China)

    2014-10-28

    Characterization of chemical state and electronic structure of the technologically important Nd{sub 2}Fe{sub 14}B compound is attractive for understanding the physical nature of its excellent magnetic properties. X-ray photoelectron spectroscopy (XPS) study of such rare-earth compound is important and also challenging due to the easy oxidation of surface and small photoelectron cross-sections of rare-earth 4f electrons and B 2p electrons, etc. Here, we reported an investigation based on XPS spectra of Nd{sub 2}Fe{sub 14}B compound as a function of Ar ion sputtering time. The chemical state of Fe and that of B in Nd{sub 2}Fe{sub 14}B compound can be clearly determined to be 0 and ?3, respectively. The Nd in Nd{sub 2}Fe{sub 14}B compound is found to have the chemical state of close to +3 instead of +3 as compared with the Nd in Nd{sub 2}O{sub 3}. In addition, by comparing the valence-band spectrum of Nd{sub 2}Fe{sub 14}B compound to that of the pure Fe, the contributions from Nd, Fe, and B to the valence-band structure of Nd{sub 2}Fe{sub 14}B compound is made more clear. The B 2p states and B 2s states are identified to be at ?11.2 eV and ?24.6 eV, respectively, which is reported for the first time. The contribution from Nd 4f states can be identified both in XPS core-level spectrum and XPS valence-band spectrum. Although Nd 4f states partially hybridize with Fe 3d states, Nd 4f states are mainly localized in Nd{sub 2}Fe{sub 14}B compound.

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

    Directory of Open Access Journals (Sweden)

    S. Myagkota

    2003-06-01

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

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

    CERN Document Server

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

    2007-01-01

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

  13. Levels of valence

    Directory of Open Access Journals (Sweden)

    VeraShuman

    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.

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

    International Nuclear Information System (INIS)

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

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

    Scientific Electronic Library Online (English)

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

    2000-06-01

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

  16. Control of valence band offset at CdS/Cu(In,Ga)Se2 interface by inserting wide-bandgap materials for suppression of interfacial recombination in Cu(In,Ga)Se2 solar cells

    Science.gov (United States)

    Nishimura, Takahito; Hirai, Yoshiaki; Kurokawa, Yasuyoshi; Yamada, Akira

    2015-08-01

    We inserted Cu(In,Ga)3Se5 into the CdS/Cu(In,Ga)Se2 interface of Cu(In,Ga)Se2 solar cells with a flat band profile and energy bandgaps (Eg) of 1.2 and 1.4 eV in order to investigate the repelling of holes by the effect of valence band offset (?Ev). We found that open circuit voltage (VOC) was clearly improved from 0.66 to 0.75 V with Eg of 1.4 eV, although VOC was only increased from 0.63 to 0.64 V with Eg of 1.2 eV. For high efficiency, we fabricated Cu(In,Ga)Se2 solar cells with a single-graded band profile and an average Eg of 1.4 eV. Eventually, a conversion efficiency of 14.4% was obtained when Cu(In,Ga)3Se5 with a thickness of 30 nm was inserted, although the conversion efficiency was 10.5% without Cu(In,Ga)3Se5. These results suggest the importance of ?Ev in the suppression of interfacial recombination by repelling holes and possibility that the highest efficiency of Cu(In,Ga)Se2 solar cells with an average Eg of 1.4 eV could be achieved.

  17. The quasiparticle band gap in the topological insulator Bi2Te3

    OpenAIRE

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

    2013-01-01

    We present a theoretical study of dispersion of states which form the bulk band-gap edges in the three-dimensional topological insulator Bi2Te3. Within density functional theory, we analyze the effect of atomic positions varying within the error range of the available experimental data and approximation chosen for the exchange-correlation functional on the bulk band gap and k-space location of valence- and conduction-band extrema. For each set of the positions with different...

  18. Dispersal of G-band bright points at different longitudinal magnetic field strengths

    CERN Document Server

    Yunfei, Yang; Song, Feng; Hui, Deng; Feng, Wang; Jiaben, Lin

    2015-01-01

    G-band bright points (GBPs) are thought to be the foot-points of magnetic flux tubes. The aim of this paper is to investigate the relation between the diffusion regimes of GBPs and the associated longitudinal magnetic field strengths. Two high resolution observations of different magnetized environments were acquired with the Hinode/Solar Optical Telescope. Each observation was recorded simultaneously with G-band filtergrams and Narrow-band Filter Imager (NFI) Stokes I and V images. GBPs are identified and tracked automatically, and then categorized into several groups by their longitudinal magnetic field strengths, which are extracted from the calibrated NFI magnetograms using a point-by-point method. The Lagrangian approach and the distribution of diffusion indices approach are adopted separately to explore the diffusion regime of GBPs for each group. It is found that the values of diffusion index and diffusion coefficient both decrease exponentially with the increasing longitudinal magnetic field strengths...

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

    International Nuclear Information System (INIS)

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

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

    Science.gov (United States)

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

    2013-03-01

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

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

    OpenAIRE

    Otto Blehr

    1997-01-01

    The behaviour of single, and small bands of caribou (Rangifer tarandus groenlandicus) when confronted by humans was compared with the energy—saving behaviour zoologists have ascribed to caribou in encounters with non-hunting wolves (Canis lupus). When confronted by me, or upon getting my scent, caribou ran away on all occasions. Their flight was occasionally interrupted by short stops to look back in my direction, but would continue on all occasions until they were out of sight. Thi...

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

    Czech Academy of Sciences Publication Activity Database

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

    2010-01-01

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

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

    Directory of Open Access Journals (Sweden)

    Otto Blehr

    1997-04-01

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

  4. Depolarisation of light scattered by disperse systems of low-dimensional potassium polytitanate nanoparticles in the fundamental absorption band

    Energy Technology Data Exchange (ETDEWEB)

    Zimnyakov, D A; Yuvchenko, S A [Yu A Gagarin Saratov State Technical University, Saratov (Russian Federation); Pravdin, A B; Kochubey, V I [N.G. Chernyshevsky Saratov State University, Saratov (Russian Federation); Gorokhovsky, A V; Tretyachenko, E V; Kunitsky, A I

    2014-07-31

    The results of experimental studies of depolarising properties of disperse systems on the basis of potassium polytitanate nanoplatelets and nanoribbons in the visible and near-UV spectral regions are presented. It is shown that in the fundamental absorption band of the nanoparticle material the increase in the depolarisation factor takes place for the radiation scattered perpendicularly to the direction of the probing beam. For nanoribbons a pronounced peak of depolarisation is observed, which is caused by the essential anisotropy of the particles shape and the peculiarities of the behaviour of the material dielectric function. The empirical data are compared with the theoretical results for 'nanodiscs' and 'nanoneedles' with the model dielectric function, corresponding to that obtained from optical constants of the titanium dioxide dielectric function. (laser biophotonics)

  5. Depolarisation of light scattered by disperse systems of low-dimensional potassium polytitanate nanoparticles in the fundamental absorption band

    International Nuclear Information System (INIS)

    The results of experimental studies of depolarising properties of disperse systems on the basis of potassium polytitanate nanoplatelets and nanoribbons in the visible and near-UV spectral regions are presented. It is shown that in the fundamental absorption band of the nanoparticle material the increase in the depolarisation factor takes place for the radiation scattered perpendicularly to the direction of the probing beam. For nanoribbons a pronounced peak of depolarisation is observed, which is caused by the essential anisotropy of the particles shape and the peculiarities of the behaviour of the material dielectric function. The empirical data are compared with the theoretical results for 'nanodiscs' and 'nanoneedles' with the model dielectric function, corresponding to that obtained from optical constants of the titanium dioxide dielectric function. (laser biophotonics)

  6. Valence Bond Entanglement Entropy

    CERN Document Server

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

    2007-01-01

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

  7. Energy bands in graphene: Comparison between the tight-binding model and ab initio calculations

    Science.gov (United States)

    Kogan, E.; Nazarov, V. U.; Silkin, V. M.; Kaveh, M.

    2014-04-01

    We compare the classification of the electron bands in graphene, obtained by group theory algebra in the framework of a tight-binding model (TBM), with that calculated in a density-functional-theory (DFT) framework. Identification in the DFT band structure of all eight energy bands (four valence and four conduction bands) corresponding to the TBM-derived energy bands is performed and the corresponding analysis is presented. The four occupied (three ?-like and one ?-like) and three unoccupied (two ?-like and one ?-like) bands given by the DFT closely correspond to those predicted by the TBM, both by their symmetry and their dispersion law. However, the two lowest lying at the ?-point unoccupied bands (one of them of a ?-like type and the other of a ?-like one), are not of the TBM type. According to both their symmetry and the electron density these bands are plane waves orthogonal to the TBM valence bands; dispersion of these states can be determined unambiguously up to the Brillouin zone borders. On the other hand, the fourth unoccupied band given by the TBM can be identified among those given by the DFT band calculations; it is situated rather high with respect to energy. The interaction of this band with the free-electron states is so strong that it exists only in part of the k space.

  8. Valence bands, oxygen in planes and chains, and surface changes for single crystals of M2CuO4 and MBa2Cu3O/sub x/ (M = Pr,Nd,Eu,Gd)

    International Nuclear Information System (INIS)

    X-ray photoemission results for single crystals of M2CuO4 (M = Pr,Eu,Gd), MBa2Cu3O/sub x/ (M = Nd,Gd), and CuO are sintered La/sub 1.85/Sr/sub 0.15/CuO4 and YBa2Cu3O/sub 6.9/ show valence-band spectra within 10 eV of the Fermi energy that are remarkably similar in appearance, with contributions that reflect Cu-O hybrid states and the rare-earth 4f states. For Pr2CuO4 and NdBa2Cu3O/sub x/, there are two distinct 4f features due to ligand screening in the photoemission final state. The rare-earth 5p core-level emission overlaps the O 2s emission and reveals complex 5p-4f multiplet interactions. All O 1s spectra show a dominant peak at /similarreverse arrowto/528 eV that can be resolved into features separated by /similarreverse arrowto/0.7 eV. These reflect inequivalent oxygen bonding configurations in the lattice and are associated with the planes and chains for the 1:2:3 compounds and the planes and off-planes for the 2:1:4 compounds. The lower-binding-energy feature is associated with the Cu-O chains of the 1:2:3 compounds and the Cu-O planes of the 2:1:4 compounds. In addition to the O 1s main line for the Cu-O planes there is also a weak satellite. Time dependent studies of the Cu 2p and O 1s emission indicate surface modification, dependent upon the quality of the cleave. The effects of surface changes and the presence of imperfections are discussed in the context of surface studies and surface superconductivity

  9. 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

  10. Resonating valence bonds

    International Nuclear Information System (INIS)

    In this paper the authors briefly review the recent efforts to understand the novel resonating valence bond (RVB) state for the S=1/2 antiferromagnetic (AFM) Heisenberg model. The authors propose a pair hopping mechanism which generates a new form of AFM superexchange, and argue that the RVB wavefunction is successful because it takes full advantage of this pair hopping. Finally the authors argue that the high Tc copper oxides represent a new fixed point of mixed valence systems, in which the low energy charge transfer process is governed by pair hopping between copper and oxygen orbitals

  11. Electronic band structure of magnetic bilayer graphene superlattices

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-09-28

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

  12. RBM band shift-evidenced dispersion mechanism of single-wall carbon nanotube bundles with NaDDBS.

    Science.gov (United States)

    Utsumi, Shigenori; Kanamaru, Mamiko; Honda, Hiroaki; Kanoh, Hirofumi; Tanaka, Hideki; Ohkubo, Takahiro; Sakai, Hideki; Abe, Masahiko; Kaneko, Katsumi

    2007-04-01

    The dispersion process of single-wall carbon nanotube (SWNT) by using sodium dodecylbenzene sulfonate (NaDDBS) was studied by means of surface tension measurements, ultraviolet-visible (UV-Vis) spectroscopy, scanning electron microscopy (SEM), and transmission electron spectroscopy (TEM). The critical micelle concentration (CMC) and the concentration where the surface tension begins to drop increase by the presence of SWNT. The isotherm of NaDDBS amount adsorbed on SWNT shows the plateau region at 0.2-6 mM and the saturated region above 40 mM. The external surface of SWNT bundle is fully covered with adsorbed NaDDBS at the plateau region, showing that SWNTs can be dispersed with the bundle form. On the other hand, SWNTs are dispersed in individual tubes at the saturated region, where the adsorption amount corresponds to coating of individual tube surfaces with NaDDBS. This dispersion state was confirmed by SEM and TEM observations. The effect of the dispersion state of SWNTs on radial breathing mode in Raman spectrum gave inherent peak shifts, being the in situ evidences on the step-wise dispersion mechanism of the SWNT bundle to the individual tubes. PMID:17204278

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-05-01

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

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

    International Nuclear Information System (INIS)

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

  15. Fermi surface and band dispersions of MxCoO2 (M: Na, K, and Rb) studied by angle-resolved photoemission spectroscopy

    International Nuclear Information System (INIS)

    We have performed angle-resolved photoemission spectroscopy (ARPES) on MxCoO2 (M: Na, K, and Rb) with both soft X-ray and ultraviolet light to clarify the electronic structure intrinsic to the bulk CoO2 plane. We observed a large holelike a1g Fermi surface centered at the ?(A) point with no signatures for a theoretically predicted small e'g hole pocket around the K(H) point, irrespective of the species of alkali metal and its content (x). We also found that the band dispersion near the Fermi level shows a kink structure indicative of the band hybridization and/or the strong mass renormalization due to electron-phonon coupling. (author)

  16. Experimental demonstration of low-complexity fiber chromatic dispersion mitigation for reduced guard-interval OFDM coherent optical communication systems based on digital spectrum sub-band multiplexing.

    Science.gov (United States)

    Malekiha, Mahdi; Tselniker, Igor; Nazarathy, Moshe; Tolmachev, Alex; Plant, David V

    2015-10-01

    We experimentally demonstrate a novel digital signal processing (DSP) structure for reduced guard-interval (RGI) OFDM coherent optical systems. The proposed concept is based on digitally slicing optical channel bandwidth into multiple spectrally disjoint sub-bands which are then processed in parallel. Each low bandwidth sub-band has a smaller delay-spread compared to a full-band signal. This enables compensation of both chromatic dispersion (CD) and polarization mode dispersion using a simple timing and one-tap-per-symbol frequency domain equalizer with a small cyclic prefix overhead. In terms of the DSP architecture, this allows for a highly efficient parallelization of DSP tasks performed over the received signal samples by deploying multiple processors running at a lower clock rate. It should be noted that this parallelization is performed in the frequency domain and it allows for flexible optical transceiver schemes. In addition, the resulting optical receiver is simplified due to the removal of the CD compensation equalizer compared to conventional RGI-OFDM systems. In this paper we experimentally demonstrate digital sub-banding of optical bandwidth. We test the system performance for different modulation formats (QPSK, 16QAM and 32QAM) over various transmission distances and optical launch powers using a 1.5% CP overhead in all scenarios. We also compare the proposed RGI-OFDM architecture performance against common single carrier modulation formats. At the same total data rate and signal bandwidth both systems have similar performance and transmission reach whereas the proposed method allows for a significant reduction of computational complexity due to removal of CD pre/post compensation equalizer. PMID:26480077

  17. Dynamics of few-valence nucleon systems

    International Nuclear Information System (INIS)

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

  18. Valence force field and phonon spectrum of ZnS

    International Nuclear Information System (INIS)

    Valence force fields have been extensively used in the study of the vibrational analysis of spectra of molecules. The application of the valence force field to the study of the lattice vibration of solids is limited. The study of the lattice vibration of the solid with the application of valence force model involves the transformation of the valence coordinates into atomic displacement coordinates. This transformation is performed to set up the secular equation of the ZnS lattice using Urey Bradley Valence Force field. The elements of the dynamical matrix of the lattice were obtained in terms of the valence force parameters. The parameters have been evaluated with the help of experimental phonon frequencies and measured values of elastic constants. The parameters have been used to calculate phonon dispersion curves along(100), (111) and (110) directions. The agreement between the theory and experiment is found to be satisfactory. This reflects the applicability of valence force field to the study of dynamical behaviour of ZnS crystal lattice. (author)

  19. Dielectric dispersion and energy band gap of Bi1.5?xSmxZn0.92Nb1.5O6.92 solid solution

    International Nuclear Information System (INIS)

    The optical transmittance and reflectance spectra of samarium doped bismuth–zinc–niobium-oxide (BZN) pyrochlore ceramics are investigated in the wavelength range of 200–1050 nm (200–1500 THz). The Sm content in the Bi1.5?xSmxZn0.92Nb1.5O6.92 solid solution significantly alters the optical properties. Therefore, increasing the Sm doping ratio from x=0.10 to x=0.13 decreased the indirect forbidden energy band gap from 3.60 to 3.05 eV. In addition, above 350 THz, increasing the Sm content decreases the dielectric constant values and alters the dielectric dispersion parameters. The dielectric spectra which were evaluated in the frequency range of 200–1500 THz reflected a sharp decrease in the dielectric constant with increasing frequency down to 358 THz. The spectra reflected a resonance peak at this frequency. Such resonance spectrum is promising for technological applications as it is close to the illumination of 870 nm IR lasers that are used in optical communications. The calculated oscillator (Eo) and dispersion (Ed) energies near that critical range (375–425 THz) reflected an increase in both Eo and Ed with increasing Sm content.

  20. Racah materials: role of atomic multiplets in intermediate valence systems.

    Science.gov (United States)

    Shick, A B; Havela, L; Lichtenstein, A I; Katsnelson, M I

    2015-01-01

    We address the long-standing mystery of the nonmagnetic insulating state of the intermediate valence compound SmB6. Within a combination of the local density approximation (LDA) and an exact diagonalization (ED) of an effective discrete Anderson impurity model, the intermediate valence ground state with the f-shell occupation ?n4f??=?5.6 is found for the Sm atom in SmB6. This ground state is a singlet, and the first excited triplet state ~3?meV higher in the energy. SmB6 is a narrow band insulator already in LDA, with the direct band gap of ~10?meV. The electron correlations increase the band gap which now becomes indirect. Thus, the many-body effects are relevant to form the indirect band gap, crucial for the idea of "topological Kondo insulator" in SmB6. Also, an actinide analog PuB6 is considered, and the intermediate valence singlet ground state is found for the Pu atom. We propose that [Sm, Pu]B6 belong to a new class of the intermediate valence materials with the multi-orbital "Kondo-like" singlet ground-state. Crucial role of complex spin-orbital f(??n)-f?(?n+1) multiplet structure differently hybridized with ligand states in such Racah materials is discussed. PMID:26490021

  1. ??????????? ? ??????????(Valency and isomorphism

    Directory of Open Access Journals (Sweden)

    Lennart Lönngren

    2008-01-01

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

  2. The band structure of BeTe a combined experimental and theoretical study

    CERN Document Server

    Nagelstrasser, M; Fischer, F; Litz, T; Waag, A; Fleszar, A; Hanke, W; Steinrück, H P; Landwehr, Gottfried

    1998-01-01

    Using angle-resolved synchrotron-radiation photoemission spectroscopy we have determined the dispersion of the valence bands of BeTe(100) along $\\Gamma X$, i.e. the [100] direction. The measurements are analyzed with the aid of a first-principles calculation of the BeTe bulk band structure as well as of the photoemission peaks as given by the momentum conserving bulk transitions. Taking the calculated unoccupied bands as final states of the photoemission process, we obtain an excellent agreement between experimental and calculated spectra and a clear interpretation of almost all measured bands. In contrast, the free electron approximation for the final states fails to describe the BeTe bulk band structure along $\\Gamma X$ properly.

  3. Pressure Induced Valence Transitions in f-Electron Systems

    CERN Document Server

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

    2006-01-01

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

  4. A Multidimensional Measure of Work Valences

    Science.gov (United States)

    Porfeli, Erik J.; Lee, Bora; Weigold, Ingrid K.

    2012-01-01

    Work valence is derived from expectancy-valence theory and the literature on children's vocational development and is presumed to be a general appraisal of work that emerges during the childhood period. Work valence serves to promote and inhibit the motivation and tasks associated with vocational development. A measure of work valence, composed of…

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

    Energy Technology Data Exchange (ETDEWEB)

    Holland, D M P [Daresbury Laboratory, Daresbury, Warrington, Cheshire WA4 4AD (United Kingdom); Potts, A W [Department of Physics, King' s College, Strand, London WC2R 2LS (United Kingdom); Karlsson, L [Department of Physics, Uppsala University, Box 530, SE-751 21 Uppsala (Sweden); Novak, I [Department of Chemistry, National University of Singapore, Singapore 0511 (Singapore); Zaytseva, I L; Trofimov, A B; Gromov, E V [Laboratory of Quantum Chemistry, Irkutsk State University, 664003 Irkutsk (Russian Federation); Schirmer, J, E-mail: david.holland@stfc.ac.u [Theoretische Chemie, Physikalisch-Chemisches Institut, Universitaet Heidelberg, Im Neuenheimer Feld 229, D-69120 Heidelberg (Germany)

    2010-07-14

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

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

    International Nuclear Information System (INIS)

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

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

    Science.gov (United States)

    Sidiek, Erkin; Balasubramanian, Kunjithapatham

    2007-01-01

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

  8. Choice of compounds with fast core-valence transitions

    International Nuclear Information System (INIS)

    It is now well established that in a number of wide gap ionic crystals a specific intrinsic luminescence can be observed due to radiative hole transitions between the upper core band and valence band. The progress in knowledge about core-valence (CV) transitions is considered in papers. The CV transitions were first observed and interpreted in BaF2 crystals. The intrinsic luminescence due to CV transitions has a short decay time (?1ns), a high thermal stability in all its parameters, and a relatively high yield. Because of these luminescence properties, crystals with radiative CV transitions are promising scintillators. Such scintillators are particularly important in devices with a high counting rate, for instance in emission tomography. The presence of a filled valence band above the core band in which the hole is created presents the possibility of population inversion at high excitation densities. This aspect creates new possibilities for producing optical amplification and generation. This work examines different approaches to the problem of CV transitions. A class of ionic crystals, in which the radiative transitions are most efficient, is identified. It is shown how to obtain the necessary spectral width of emission, and the possibility of controlling the decay time of the emission is discussed

  9. Valence instabilities as a source of actinide system inconsistencies

    International Nuclear Information System (INIS)

    Light actinide elements alone, and in some of their alloys, may exist as a static or dynamic mixture of two configurations. Such a state can explain both a resistivity maximum and lack of magnetic order observed in so many actinide materials, and still be compatible with the existence of f-electrons in narrow bands. Impurity elements may stabilize slightly different intermediate valence states in U, Np, and Pu, thus contributing to inconsistencies in published results. The physical property behavior of mixed-valence, rare-earth compounds is very much like that observed in development of antiphase (martensitic) structures. Martensitic transformations in U, Np, and Pu, from high-temperature b. c. c. to alpha phase, may be a way of ordering an alloy-like metal of mixed or intermediate valence. The relative stability of each phase structure may depend upon its electron-valence ratio. A Hubbard model for electron correlations in a narrow energy band has been invoked in most recent theories for explaining light actinide behavior. Such a model may also be applicable to crystal symmetry changes in martensitic transformations in actinides

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

    International Nuclear Information System (INIS)

    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

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

    CERN Document Server

    Tototzintle-Huitle, H

    2005-01-01

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

  12. Valency Configuration of Transition Metal Impurities in ZnO

    CERN Document Server

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

    2006-01-01

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

  13. Band structure of ABC-trilayer graphene superlattice

    International Nuclear Information System (INIS)

    We investigate the effect of one-dimensional periodic potentials on the low energy band structure of ABC trilayer graphene first by assuming that all the three layers have the same potential. Extra Dirac points having the same electron hole crossing energy as that of the original Dirac point are generated by superlattice potentials with equal well and barrier widths. When the potential height is increased, the numbers of extra Dirac points are increased. The dispersions around the Dirac points are not isotropic. It is noted that the dispersion along the ky direction for kx?=?0 oscillates between a non-linear dispersion and a linear dispersion when the potential height is increased. When the well and barrier widths are not identical, the symmetry of the conduction and valence bands is broken. The extra Dirac points are shifted either upward or downward depending on the barrier and well widths from the zero energy, while the position of the central Dirac point oscillates with the superlattice potential height. By considering different potentials for different layers, extra Dirac points are generated not from the original Dirac points but from the valleys formed in the energy spectrum. Two extra Dirac points appear from each pair of touched valleys, so four Dirac points appeared in the spectrum at particular barrier height. By increasing the barrier height of superlattice potential two Dirac points merge into the original Dirac point. This emerging and merging of extra Dirac points is different from the equal potential case

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

    OpenAIRE

    Gabuda, S. P.; Kozlova, S. G.; Erenburg, S. B.; Bausk, N. V.

    2003-01-01

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

  15. Evidence for topological band inversion of the phase change material Ge2Sb2Te5

    OpenAIRE

    Pauly, Christian; Liebmann, Marcus; Giussani, Alessandro; Kellner, Jens; Just, Sven; Sánchez-Barriga, Jaime; Rienks, Emile; Rader, Oliver; Calarco, Raffaella; Bihlmayer, Gustav; Morgenstern, Markus

    2013-01-01

    We present an angle-resolved photoemission study of a ternary phase change material, namely Ge2Sb2Te5, epitaxially grown on Si(111) in the metastable cubic phase. The observed upper bulk valence band shows a minimum at Gamma-bar being 0.3 eV below the Fermi level E_F and a circular Fermi contour around Gamma-bar with a dispersing diameter of 0.27-0.36 Anstroms^-1. This is in agreement with density functional theory calculations of the Petrov stacking sequence in the cubic ph...

  16. Competition between initial- and final-state effects in valence- and core-level x-ray photoemission of Sb-doped SnO2

    OpenAIRE

    Egdell, Russell G; Rebane, J; Walker, T. J.; Law, D. S. L.

    1999-01-01

    High resolution valence- and core-level photoemission spectra of undoped and 3% Sb-doped SnO2 are presented. Conduction-band occupation due to Sb doping in SnO2 leads to a shift of valence-band features to high binding energy. However, the shift is less than the width of the occupied part of the conduction band. This is attributed to a shrinkage of the bulk band gap with doping, arising from an attractive dopant electron interaction and screening of the Coulomb repulsion between valence and c...

  17. Ohmic Losses in Valence-band Photoemission Experiments

    CERN Document Server

    Haslinger, R; Haslinger, Robert; Joynt, Robert

    2000-01-01

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

  18. An Intracranial EEG Study of the Neural Dynamics of Musical Valence Processing.

    Science.gov (United States)

    Omigie, Diana; Dellacherie, Delphine; Hasboun, Dominique; George, Nathalie; Clement, Sylvain; Baulac, Michel; Adam, Claude; Samson, Severine

    2015-11-01

    The processing of valence is known to recruit the amygdala, orbitofrontal cortex, and relevant sensory areas. However, how these regions interact remains unclear. We recorded cortical electrical activity from 7 epileptic patients implanted with depth electrodes for presurgical evaluation while they listened to positively and negatively valenced musical chords. Time-frequency analysis suggested a specific role of the orbitofrontal cortex in the processing of positively valenced stimuli while, most importantly, Granger causality analysis revealed that the amygdala tends to drive both the orbitofrontal cortex and the auditory cortex in theta and alpha frequency bands, during the processing of valenced stimuli. Results from the current study show the amygdala to be a critical hub in the emotion processing network: specifically one that influences not only the higher order areas involved in the evaluation of a stimulus's emotional value but also the sensory cortical areas involved in the processing of its low-level acoustic features. PMID:24904066

  19. Mixed valence model for superconductivity

    Scientific Electronic Library Online (English)

    Sven, Larsson.

    2003-12-01

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

  20. Valence holes as Luttinger spinor based qubits in quantum dots

    OpenAIRE

    Hsieh, Chang-Yu; Cheriton, Ross; Korkusinski, Marek; Hawrylak, Pawel

    2009-01-01

    We present a theory of valence holes as Luttinger spinor based qubits in p-doped self-assembled quantum dots within the 4-band $k\\cdot p$ formalism. The two qubit levels are identified with the two chiralities of the doubly degenerate ground state. We show that single qubit operations can be implemented with static magnetic field applied along the $z$ and $x$ directions, acting analogously to the $\\hat{\\sigma}_z$ and $\\hat{\\sigma}_x$ operators in the qubit subspace respectiv...

  1. Avoided valence transition in a plutonium superconductor.

    Science.gov (United States)

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

    2015-03-17

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

  2. Surface mixed valence in Sm and SmB6

    International Nuclear Information System (INIS)

    Surface-sensitive photoelectron measurements reveal bulk-to-surface shifts of the Sm 4f6 level which imply inhomogeneous valence mixing on the surface of Sm and SmB6. The surface valence fraction is estimated to be the same for both materials. The measurements take advantage of a large resonant enhancement of 4f electron emission due to 4d ? 4f photon absorption, and detailed spectra showing this phenomena are presented. It is shown that the 4d hole in the 4d ? 4f absorption process stabilizes the 4f state by approx. 4 --7 eV. Exposure of Sm films to oxygen is found to eliminate, rather than increase, the emission from the surface 4f6 state, showing that the 4f6 state does not arise from oxygen contamination. Observed variations in Sm film spectra are described, including the finding in some films of an unexplained photoemission peak 2.4 eV below the Fermi level. SmB6 also displays a broad band of Auger emission when a boron 1s core hole is created, and this is ascribed to electrons in the boron 2p bonding band. Various trends in 4d and 4f binding energies for Sm and SmB6 are pointed out and discussed

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

    International Nuclear Information System (INIS)

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

  4. Indirect-direct band gap transition through electric tuning in bilayer MoS{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Z. Y.; Si, M. S., E-mail: sims@lzu.edu.cn; Wang, Y. H.; Gao, X. P. [Key laboratory for Magnetism and Magnetic Materials of the Ministry of Education, School of Physical Science and Technology, Lanzhou University, Lanzhou 730 000 (China); Sung, Dongchul; Hong, Suklyun [Graphene Research Institute, Sejong University, Seoul 143 747 (Korea, Republic of); He, Junjie [Department of Physics, Xiangtan University, Hunan 411 105 (China)

    2014-05-07

    We investigate the electronic properties of bilayer MoS{sub 2} exposed to an external electric field by using first-principles calculations. It is found that a larger interlayer distance, referring to that by standard density functional theory (DFT) with respect to that by DFT with empirical dispersion corrections, makes indirect-direct band gap transition possible by electric control. We show that external electric field effectively manipulates the valence band contrast between the K- and ?-valleys by forming built-in electric dipole fields, which realizes an indirect-direct transition before a semiconductor-metal transition happens. Our results provide a novel efficient access to tune the electronic properties of two-dimensional layered materials.

  5. Valence instabilities in cerium intermetallics

    International Nuclear Information System (INIS)

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

  6. 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

  7. Device for the optimal coupling of light to an intermediate band solar cell made from auantum dots

    OpenAIRE

    Luque López, Antonio; Martí Vega, Antonio; Briones Fernández-Pola, Fernando; Postigo, Pablo Aitor

    2008-01-01

    The invention relates to a device for coupling light to an intermediate band solar cell (8) made from quantum dots, which also concentrates the light. The energy of the light emitting the luminescent material (2) is selected such as to produce transitions between the valence band and the conduction band of the cell. The pigments of the luminescent material (6) are selected such that the emitted photons produce transitions from the valence band to the intermediate band and from the intermediat...

  8. Valence fluctuation in CeMo2Si2C

    International Nuclear Information System (INIS)

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

  9. Valency of Yb in PbS and PbTe determined by XPS

    International Nuclear Information System (INIS)

    X-ray photoelectron spectroscopy experiments on PbTe:Yb, PbS:Yb, PbTe, and PbS crystals have been performed using the monochromatized Al K? radiation. The valence band spectrum of PbTe:Yb exhibits one set of peaks associated with divalent Yb initial states, but two sets associated with divalent and trivalent Yb are observed for PbS:Yb. The valency of Yb in PbTe:Yb is 2 (within an accuracy of the experiment) but in PbS:Yb the mixed valency of Yb is seen. These conclusions are confirmed by an analysis of Yb 4d spectra in PbTe:Yb and PbS:Yb. (author)

  10. Silicon nanowire band gap modification.

    Science.gov (United States)

    Nolan, Michael; O'Callaghan, Sean; Fagas, Giorgos; Greer, James C; Frauenheim, Thomas

    2007-01-01

    Band gap modification for small-diameter (approximately 1 nm) silicon nanowires resulting from the use of different species for surface termination is investigated by density functional theory calculations. Because of quantum confinement, small-diameter wires exhibit a direct band gap that increases as the wire diameter narrows, irrespective of surface termination. This effect has been observed in previous experimental and theoretical studies for hydrogenated wires. For a fixed cross-section, the functional group used to saturate the silicon surface significantly modifies the band gap, resulting in relative energy shifts of up to an electronvolt. The band gap shifts are traced to details of the hybridization between the silicon valence band and the frontier orbitals of the terminating group, which is in competition with quantum confinement. PMID:17212436

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

    International Nuclear Information System (INIS)

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

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

    Directory of Open Access Journals (Sweden)

    Michael Snodgrass

    2012-10-01

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

  13. Valence space electron momentum spectroscopy of diborane

    Energy Technology Data Exchange (ETDEWEB)

    Wang Feng [Centre for Molecular Simulation, Swinburne University of Technology, P.O. Box 218, Hawthorn, Melbourne, Vic. 3122 (Australia)]. E-mail: fwang@swin.edu.au; Pang Wenning [Department of Physics, Polarization Physics Laboratory, Tsinghua University, Beijing 100084 (China); Huang Ming [Department of Physics, Polarization Physics Laboratory, Tsinghua University, Beijing 100084 (China)

    2006-05-15

    A non-classical mechanism of binding in diborane (B{sub 2} H{sub 6}) is derived quantum-mechanically (B3LYP/6-311++G**) using a dual-space analysis. High-resolution binding-energy spectra of diborane, generated using an outer-valence Green's-function and density-functional theory with a statistical average of model orbital potentials (SAOP), agree satisfactorily with experiment. Electron-correlation energies of diborane produce orbital-based variations in ionization energy in the valence space, but with negligible impact on the shape of only a{sub g} symmetry orbitals as indicated in momentum space. The present work indicates quantitatively that (a) the pair of three-centre banana-shaped B-H{sub b}-B bonds are more accurately described as one diamond-shaped bond with B-H{sub b}-B-H{sub b}, (b) all bonds in diborane are electron-deficient including the four equivalent B-H{sub t} bonds, (c) there is no pure B?B bond but contributions from all valence orbitals form an unconventional electron-deficient B-B bond, and (d) only two innermost valence orbitals - 2a{sub g} and 2b{sub 1u} - are sp{sup 2}-hybridized and no evidence indicates other valence orbitals of diborane to be hybridized.

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

    OpenAIRE

    Brenig, Wolfram; Grzeschik, Matthias

    2003-01-01

    Using a series expansion based on the flow-equation method we study the ground state energy and the elementary triplet excitations of a generalized model of crossed spin-1/2 chains starting from the limit of decoupled quadrumers. The triplet dispersion is shown to be very sensitive to the inter-quadrumer frustration, exhibiting a line of almost complete localization as well as lines of quantum phase transitions limiting the stability of the valence-bond solid phase. In the v...

  15. Electronic properties of the narrow-band material ?-RuCl3

    Science.gov (United States)

    Pollini, I.

    1996-05-01

    X-ray angle-integrated and ultraviolet angle-resolved photoemission spectra of the low-spin compound t52g ?-RuCl3 show that Ru 4d and Cl 3p states contribute to the valence-band structure of this magnetic material. The energy distribution curves measured along the azimuthal directions ?-M'-? and ?-K-M using He I radiation indicate an uppermost nearly dispersionless structure of Ru 4d origin, and two dispersive features obtained from Cl 3p-derived bands. The photoemission results, together with the optical and magnetic properties described by ligand-field theory, support the view of localized 4d states forming a very narrow Ru 4d band in the vicinity of the Fermi energy. The main 4d emission structure has been thus assigned to 4d4 unscreened hole states, where the band gap corresponds to intersite d-d transitions, and ?-RuCl3 can be classified as a Mott-Hubbard compound in consideration of its electronic and magnetic characteristics. The inconsistency between the photoemission results and the transport properties, describing this material as a conventional band-gap semiconductor, is finally discussed.

  16. Molybdenum Valence in Basaltic Silicate Melts

    Science.gov (United States)

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

    2010-01-01

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

  17. Emotions and false memories: valence or arousal?

    Science.gov (United States)

    Corson, Yves; Verrier, Nadège

    2007-03-01

    The effects of mood on false memories have not been studied systematically until recently. Some results seem to indicate that negative mood may reduce false recall and thus suggest an influence of emotional valence on false memory. The present research tested the effects of both valence and arousal on recall and recognition and indicates that the effect is actually due to arousal. In fact, whether participants' mood is positive, negative, or neutral, false memories are significantly more frequent under conditions of high arousal than under conditions of low arousal. PMID:17444912

  18. Band-structure analysis from photoreflectance spectroscopy in (Ga,Mn)As

    Energy Technology Data Exchange (ETDEWEB)

    Yastrubchak, Oksana; Gluba, Lukasz; Zuk, Jerzy [Institute of Physics, Maria Curie-Sklodowska University, 20-031 Lublin (Poland); Wosinski, Tadeusz; Andrearczyk, Tomasz; Domagala, Jaroslaw Z. [Institute of Physics, Polish Academy of Sciences, 02-668 Warsaw (Poland); Sadowski, Janusz [Institute of Physics, Polish Academy of Sciences, 02-668 Warsaw, Poland and MAX-Lab, Lund University, 22100 Lund (Sweden)

    2013-12-04

    Modulation photoreflectance spectroscopy has been applied to study the band-structure evolution in (Ga,Mn)As epitaxial layers with increasing Mn content. Structural and magnetic properties of the layers were characterized with high-resolution X-ray diffractometry and SQUID magnetometery, respectively. The revealed results of decrease in the band-gap-transition energy in the (Ga,Mn)As layers with increasing Mn content are interpreted in terms of a disordered valence band, extended within the band gap, formed, in highly Mn-doped (Ga,Mn)As, as a result of merging the Mn-related impurity band with the host GaAs valence band.

  19. Electronic band structure of zinc blende CdSe and rock salt PbSe semiconductors with silicene-type honeycomb geometry

    Science.gov (United States)

    Delerue, Christophe; Vanmaekelbergh, D.

    2015-09-01

    We report on the electronic band structure of 2D CdSe and PbSe semiconductors that have a silicene-type honeycomb geometry. Atomistic tight-binding calculations are performed on several model systems that bear a strong resemblance to the silicene-type honeycomb structures that were recently obtained by nanocrystal self-assembly. The calculated band structures are compared both to those of 2D quantum wells and graphene-type honeycomb structures. It is found that in silicene type CdSe honeycomb structures, the lowest electron conduction bands (derived from S-type nanocrystal wave functions) form a Dirac-type dispersion, very similar as in graphene. The P-type bands are usually more complex. However, when the hybridization between S- and P-type bands increases, a second Dirac cone and a genuine non-trivial flat band is observed, similar as in the case of graphene-type honeycomb structures of CdSe. There is a strong non-trivial gap between the first and second valence band, hosting the quantum spin Hall effect. Silicene-type PbSe structures show Dirac features in their bands, which however can be clouded due to the multi-valley character of PbSe.

  20. Photoionization cross-sections of ground and excited valence levels of actinides

    Directory of Open Access Journals (Sweden)

    Yarzhemsky Victor G.

    2012-01-01

    Full Text Available The photoionization cross-sections of ground and excited atomic states of actinide atoms were calculated by the Dirac-Fock-Slater method for two excitation energies of X-ray radiation (1253.6 eV and 1486.6 eV. These data are required for calculations of intensities of X-ray photoelectron spectra of actinide compound valence bands and interpretation of experimental spectra.

  1. Photoionization cross-sections of ground and excited valence levels of actinides

    OpenAIRE

    Yarzhemsky Victor G.; Teterin Anton Yu.; Teterin Yury A.; Trzhaskovskaya Malvina B.

    2012-01-01

    The photoionization cross-sections of ground and excited atomic states of actinide atoms were calculated by the Dirac-Fock-Slater method for two excitation energies of X-ray radiation (1253.6 eV and 1486.6 eV). These data are required for calculations of intensities of X-ray photoelectron spectra of actinide compound valence bands and interpretation of experimental spectra.

  2. Band offset studies in pulse laser deposited Zn1-xCdxO/ZnO hetero-junctions

    Science.gov (United States)

    Devi, Vanita; Kumar, Manish; Choudhary, R. J.; Phase, D. M.; Kumar, Ravindra; Joshi, B. C.

    2015-06-01

    The valence and conduction band offsets of Zn1-xCdxO/ZnO hetero-junctions deposited by pulsed laser deposition technique were estimated by X-ray photoelectron, valence band, and UV-visible spectroscopy. Type-II band alignment (staggered gap) with ratios of conduction band to valence band offsets (?EC/?EV) was found to be 0.77 and 0.59 for Zn0.95Cd0.05O/ZnO and Zn0.90Cd0.10O/ZnO hetero-structures, respectively, which can be used in longer wavelength regime optoelectronic devices. The higher value of valence band offset as compared to conduction band offset suggests that the transport at interface is mainly due to electrons.

  3. Band offset studies in pulse laser deposited Zn1?xCdxO/ZnO hetero-junctions

    International Nuclear Information System (INIS)

    The valence and conduction band offsets of Zn1?xCdxO/ZnO hetero-junctions deposited by pulsed laser deposition technique were estimated by X-ray photoelectron, valence band, and UV-visible spectroscopy. Type-II band alignment (staggered gap) with ratios of conduction band to valence band offsets (?EC/?EV) was found to be 0.77 and 0.59 for Zn0.95Cd0.05O/ZnO and Zn0.90Cd0.10O/ZnO hetero-structures, respectively, which can be used in longer wavelength regime optoelectronic devices. The higher value of valence band offset as compared to conduction band offset suggests that the transport at interface is mainly due to electrons

  4. A study of the valence shell photoionisation dynamics of pyrimidine and pyrazine

    Energy Technology Data Exchange (ETDEWEB)

    Holland, D.M.P., E-mail: david.holland@stfc.ac.uk [Daresbury Laboratory, Daresbury, Warrington, Cheshire WA4 4AD (United Kingdom); Potts, A.W. [Department of Physics, King' s College, Strand, London WC2R 2LS (United Kingdom); Karlsson, L. [Department of Physics, Uppsala University, Box 530, SE-751 21 Uppsala (Sweden); Stener, M.; Decleva, P. [Dipartimento di Scienze Chimiche, Universita di Trieste, Via L. Giorgieri, I-34127 Trieste (Italy); Consorzio Interuniversitario Nazionale per la Scienze e Tecnologia dei Materiali, INSTM, Unita' di Trieste, Via L. Giorgieri, I-34127 Trieste (Italy); CNR-IOM, Area Science Park - Basovizza, Strada Statale 14 km 163,5, I-34149 Trieste (Italy)

    2011-11-18

    Graphical abstract: The complete valence shell photoelectron spectra of pyrimidine and pyrazine have been recorded with synchrotron radiation and interpreted with the aid of vertical ionisation energies and relative spectral intensities calculated using time-dependent density functional theory. Highlights: Black-Right-Pointing-Pointer Valence shell photoelectron spectra of pyrimidine and pyrazine have been recorded. Black-Right-Pointing-Pointer Many-body effects are important. Black-Right-Pointing-Pointer Photoionisation dynamics are affected by shape resonances. Black-Right-Pointing-Pointer Theoretical predictions for single-hole ionic states are satisfactory. - Abstract: The complete valence shell photoelectron spectra of pyrimidine and pyrazine have been recorded with synchrotron radiation and the observed structure has been interpreted with the aid of vertical ionisation energies and relative spectral intensities calculated using time-dependent density functional theory. The theoretical predictions for the single-hole ionic states due to outer valence shell ionisation agree satisfactorily with the experimental results. Ionisation from the inner valence orbitals is strongly influenced by many-body effects and the intensity associated with a particular orbital is spread amongst numerous satellites. Photoelectron angular distributions and partial cross sections have been determined both experimentally and theoretically, and demonstrate that shape resonances affect the valence shell photoionisation dynamics. In addition to shape resonances occurring a few eV above the ionisation threshold, the calculations indicate that many of the orbitals are influenced by shape resonant processes at much higher energies. Some of these higher energy resonances have been confirmed through a comparison between the relevant theoretical and experimental photoelectron asymmetry parameters. The spectral behaviour of asymmetry parameters associated with {pi}-orbitals has been shown to differ from that of asymmetry parameters associated with {sigma}-orbitals. These differences provide a means of distinguishing between the two types of orbitals even in heavily congested regions of the photoelectron spectrum suffering from band overlap.

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

    OpenAIRE

    JelleDemanet; BaptistLiefooghe; FrederickVerbruggen

    2011-01-01

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

  6. Surface states and band-to-band non-radiative transitions in silicon single crystal investigated by piezoelectric photothermal spectroscopy

    International Nuclear Information System (INIS)

    The effectiveness of piezoelectric photothermal spectroscopy (PPTS) to investigate surface states and bulk properties of single crystal silicon was demonstrated. PPTS measurements were conducted on p- and n-type, single crystal silicon. A broad peaked signal around 1.18±0.01 eV at room temperature showed the characteristics of slow states present on silicon surface. Another signal bearing a peak around 1.07±0.005 eV at room temperature was due to bulk effect. In the indirect band gap of silicon, the excitation of electrons from valence band to conduction band (so called band-to-band excitation) is not possible without phonon assistance. The PPTS measurements conducted at various temperatures revealed band-to-band and valence band-to-excitons states transition with phonon assistance. The measurements at 4.2 and 110 K resolved four types of phonon participation. A good agreement between theoretical expressions and experimental data substantiated the phonon participation in band-to-band and valence band-to-excitons states transitions

  7. Surface states and band-to-band non-radiative transitions in silicon single crystal investigated by piezoelectric photothermal spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Memon, Aftab A.; Fukuyama, Atsuhiko; Sato, Syoichiro; Ikari, Tetsuo

    2003-09-15

    The effectiveness of piezoelectric photothermal spectroscopy (PPTS) to investigate surface states and bulk properties of single crystal silicon was demonstrated. PPTS measurements were conducted on p- and n-type, single crystal silicon. A broad peaked signal around 1.18{+-}0.01 eV at room temperature showed the characteristics of slow states present on silicon surface. Another signal bearing a peak around 1.07{+-}0.005 eV at room temperature was due to bulk effect. In the indirect band gap of silicon, the excitation of electrons from valence band to conduction band (so called band-to-band excitation) is not possible without phonon assistance. The PPTS measurements conducted at various temperatures revealed band-to-band and valence band-to-excitons states transition with phonon assistance. The measurements at 4.2 and 110 K resolved four types of phonon participation. A good agreement between theoretical expressions and experimental data substantiated the phonon participation in band-to-band and valence band-to-excitons states transitions.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-08-01

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

  9. Band structures of ZnTe:O alloys with isolated oxygen and with clustered oxygen impurities

    Energy Technology Data Exchange (ETDEWEB)

    Ling, Chen, E-mail: chen.ling@tema.toyota.com; Zhou, Li Qin; Banerjee, Debasish; Jia, Hongfei

    2014-01-25

    Highlights: • Band structures of ZnTe:O alloy highly depends on the status of oxygen. • Clustered oxygen lowers the bandgap while isolated oxygen increases the bandgap. • The solar adsorption efficiency of ZnTe:O can be improved by oxygen clustering. -- Abstract: First-principles calculations reveal that band structures of ZnTe:O alloys highly depend on the configuration of oxygen in the alloy. For alloys with isolated oxygen, the calculated band structure shows the formation of intermediate states between valence and conduction band and the shift of conduction band to higher energy level. It expands the gap between valence and conduction band. For alloys with clustered oxygen, the formation of intermediate band is still observed, while the gap between valence and conduction band is decreased. For alloys with oxygen impurities adjacent to Zn vacancy, the band structure only shows the decrease of the gap between valence and conduction band without the formation of any intermediate band. These results suggest the critical role of Zn–O bonding in determining the energy level of the impurity states. On the basis of our results, a possible band engineering approach is suggested in order to improve the performance of ZnTe:O alloy as intermediate band solar adsorbent.

  10. Intramolecular electron transfer on the vibrational timescale in mixed valence ruthenium clusters

    International Nuclear Information System (INIS)

    The thermodynamic stability of the mixed valence (one electron reduced) state between linked Ru3 units was studied by means of electrochemical methods for the series of the ligand-bridged triruthenium cluster dimer, [Ru3(?3-O)(?-CH3CO2)6(CO)(L)(?-BL)Ru3(?3-O)(?-CH3CO2)6(CO)(L)] (BL = 1,4 pyrazine: L = 4-dimethylaminopyridine (dmap) (1a), pyridine (py) (1b), 4-cyanopyridine (cpy) (1c), 1-azabicyclo[2.2.2]octane (1d); BL = 4,4'-bipyridine: L= dmap (2a), py(2b), cpy (2c); BL 2,7-diazapyrene; L = dmap (3a); BL = 1,4-diazabicyclo[2.2.2]octane: L = dmap (4a), py(4b), cpy (4c). The mixed valence states undergoing rapid intermolecular electron transfers were observed by IR spectro-electrochemistry. By simulating dynamical effects on the observed ?(CO) absorption band shapes, the rate constants ke for electron transfer in the mixed valence states of 1a, 1b, 1c and 1d were estimated to be 9x1011 s-1 (at room temperature (rt)), 5x1011 s-1 (at rt), ca. 1x1011 s-1 (at rt), and 1x1012 s-1 (at -18 oC), respectively. Possible applications of this approach to asymmetric mixed valence systems were discussed. (author)

  11. Pion valence-quark parton distribution function

    Science.gov (United States)

    Chang, Lei; Thomas, Anthony W.

    2015-10-01

    Within the Dyson-Schwinger equation formulation of QCD, a rainbow ladder truncation is used to calculate the pion valence-quark distribution function (PDF). The gap equation is renormalized at a typical hadronic scale, of order 0.5 GeV, which is also set as the default initial scale for the pion PDF. We implement a corrected leading-order expression for the PDF which ensures that the valence-quarks carry all of the pion's light-front momentum at the initial scale. The scaling behavior of the pion PDF at a typical partonic scale of order 5.2 GeV is found to be (1 - x) ?, with ? ? 1.6, as x approaches one.

  12. Janus Nematic Colloids with Designable Valence

    Directory of Open Access Journals (Sweden)

    Simon ?opar

    2014-05-01

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

  13. Evaluative conditioning induces changes in sound valence

    Directory of Open Access Journals (Sweden)

    AnnaC.Bolders

    2012-04-01

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

  14. Avoided Valence Transition in a Plutonium Superconductor

    OpenAIRE

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

    2014-01-01

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

  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. New materials for intermediate band photovoltaic cells. A theoretical and experimental approach

    OpenAIRE

    Wahnón Benarroch, Perla; Palacios Clemente, Pablo; Aguilera Bonet, Irene; Seminóvski Pérez, Yohanna; Conesa, Jose Carlos; Lucena, Raquel

    2010-01-01

    Density functional theory calculations of certain transition-metal doped semiconductors show a partially occupied relatively narrow band located between valence band and conduction band. These novel systems, containing the metallic band, are called intermediate-band materials. They have enhanced optoelectronic properties which allow an increase in solar energy conversion efficiency of conventional solar cells. We previously proposed III-V, chalcopyrite and sulfide derived compounds show...

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

    International Nuclear Information System (INIS)

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

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

    CERN Document Server

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

    1999-01-01

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

  19. Reply to Isgur's comments on valence QCD

    International Nuclear Information System (INIS)

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

  20. The variational subspace valence bond method.

    Science.gov (United States)

    Fletcher, Graham D

    2015-04-01

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

  1. The variational subspace valence bond method

    Science.gov (United States)

    Fletcher, Graham D.

    2015-04-01

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

  2. The variational subspace valence bond method

    International Nuclear Information System (INIS)

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

  3. A study of the valence shell electronic structure and photoionisation dynamics of para-dichlorobenzene and para-bromochlorobenzene

    International Nuclear Information System (INIS)

    Highlights: ? Electronic structure and photoionisation dynamics of pDCB and pBCB have been studied. ? Dynamics affected by halogen atom Cooper minimum. ? Many-body effects influence inner valence shell ionisation. - Abstract: The valence shell electronic structure and photoionisation dynamics of para-dichlorobenzene and para-bromochlorobenzene have been investigated both experimentally and theoretically. High resolution photoelectron spectra of the outer valence orbitals have been recorded with HeI radiation and the observed structure has been interpreted using calculated ionisation energies and spectral intensities. The theoretical predictions for the single-hole ionic states due to outer valence ionisation agree satisfactorily with the experimental results. Ionisation from the inner valence orbitals is strongly influenced by many-body effects and the with a particular orbital is spread amongst numerous satellites. Some of the photoelectron bands exhibit vibrational progressions and tentative assignments have been proposed. The photoionisation dynamics of the outer valence orbitals of para-dichlorobenzene have been investigated theoretically by using the continuum multiple scattering approach to calculate photoionisation partial cross-sections and photoelectron anisotropy parameters. The results show that ionisation from some of the orbitals is affected by the Cooper minimum associated with the chlorine atom. Synchrotron radiation has been used to record angle resolved photoelectron spectra of the entire valence shell, for photon energies between threshold and ?100 eV, and these have allowed the corresponding experimental data to be derived. A comparison between the predicted and measured anisotropy parameters confirms the influence of the Cooper minimum in those orbitals related to the chlorine lone-pairs

  4. A study of the valence shell electronic structure and photoionisation dynamics of para-dichlorobenzene and para-bromochlorobenzene

    Energy Technology Data Exchange (ETDEWEB)

    Powis, I. [School of Chemistry, University of Nottingham, Nottingham NG7 2RD (United Kingdom); Trofimov, A.B. [Laboratory of Quantum Chemistry, Irkutsk State University, 664003 Irkutsk (Russian Federation); A.E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, 664033 Irkutsk (Russian Federation); Bodzuk, I.L. [Laboratory of Quantum Chemistry, Irkutsk State University, 664003 Irkutsk (Russian Federation); Holland, D.M.P., E-mail: david.holland@stfc.ac.uk [Daresbury Laboratory, Daresbury, Warrington, Cheshire, WA4 4AD (United Kingdom); Potts, A.W. [Department of Physics, King’s College, Strand, London WC2R 2LS (United Kingdom); Karlsson, L. [Department of Physics, Uppsala University, Box 530, SE-751 21 Uppsala (Sweden)

    2013-03-29

    Highlights: ? Electronic structure and photoionisation dynamics of pDCB and pBCB have been studied. ? Dynamics affected by halogen atom Cooper minimum. ? Many-body effects influence inner valence shell ionisation. - Abstract: The valence shell electronic structure and photoionisation dynamics of para-dichlorobenzene and para-bromochlorobenzene have been investigated both experimentally and theoretically. High resolution photoelectron spectra of the outer valence orbitals have been recorded with HeI radiation and the observed structure has been interpreted using calculated ionisation energies and spectral intensities. The theoretical predictions for the single-hole ionic states due to outer valence ionisation agree satisfactorily with the experimental results. Ionisation from the inner valence orbitals is strongly influenced by many-body effects and the with a particular orbital is spread amongst numerous satellites. Some of the photoelectron bands exhibit vibrational progressions and tentative assignments have been proposed. The photoionisation dynamics of the outer valence orbitals of para-dichlorobenzene have been investigated theoretically by using the continuum multiple scattering approach to calculate photoionisation partial cross-sections and photoelectron anisotropy parameters. The results show that ionisation from some of the orbitals is affected by the Cooper minimum associated with the chlorine atom. Synchrotron radiation has been used to record angle resolved photoelectron spectra of the entire valence shell, for photon energies between threshold and ?100 eV, and these have allowed the corresponding experimental data to be derived. A comparison between the predicted and measured anisotropy parameters confirms the influence of the Cooper minimum in those orbitals related to the chlorine lone-pairs.

  5. Superconductivity emerging near quantum critical point of valence transition

    CERN Document Server

    Watanabe, S; Miyake, K; Watanabe, Shinji; Imada, Masatoshi; Miyake, Kazumasa

    2006-01-01

    The nature of the quantum valence transition is studied in the one-dimensional periodic Anderson model with Coulomb repulsion between f and conduction electrons by the density-matrix renormalization group method. It is found that the first-order valence transition emerges with the quantum critical point and the crossover from the Kondo to the mixed-valence states is strongly stabilized by quantum fluctuation and electron correlation. It is found that the superconducting correlation is developed in the Kondo regime near the sharp valence increase. The origin of the superconductivity is ascribed to the development of the coherent motion of electrons with enhanced valence fluctuation, which results in the enhancement of the charge velocity, but not of the charge compressibility. Statements on the valence transition in connection with Ce metal and Ce compounds are given.

  6. Ultraviolet bands of potassium dimer

    International Nuclear Information System (INIS)

    The ultraviolet band spectra of potassium dimer have been investigated. The studies were performed in absorption in the second order of a 3.4 m Ebert spectrograph with a reciprocal dispersion of 2.6 A/mm. A number of new bands in the electronic states G and H not previously reported have been observed. The vibrational analysis is performed and molecular constants are evaluated. (author)

  7. Neutron scattering on intermediate valence systems

    International Nuclear Information System (INIS)

    The temperature dependence of the magnetic relaxation line widths (quasielastic (QE) line widths) and the crystal field excitations of some novel intermediate valent systems were measured by means of inelastic neutron scattering. Some striking new features of the alloys YbBe13, YbPd and Yb3Pd4 appoint them to belong to a new type of intermediate valent systems. YbAl3 shows several inelastic lines, but no QE-line was measurable. The heavy fermion systems CeCu6 and URu2Si2 show a strongly temperature dependent QE-line width, in course of which CeCu6 tends towards a nonvanishing residual value for T->0, which matches with theoretical predictions. For the first time valence instabilities of Pr (PrPd) and Sm (Smsub(0.51)Ysub(0.49)Al2) could be prooved by neutron scattering. In addition to these experiments, in YbCu2Si2 and TmTe the shifts in valency, caused by external hydrostatic pressure, were studied with a pressure cell for neutron scattering, especially designed and constructed for these special purposes. The corresponding observed changes of the QE-line widths coincide with the expected values, both in sign and absolute value. (orig.)

  8. Precision calculations of atoms with few valence electrons

    OpenAIRE

    M. G. Kozlov

    2003-01-01

    We discuss the possibility of using pair-equations for the construction of the effective Hamiltonian $H_{\\rm eff}$ for valence electrons of an atom. The low-energy part of atomic spectrum is found by solving the eigenvalue problem for $H_{\\rm eff}$. In this way it is possible to account efficiently for the valence-valence and core-valence correlations. We tested this method on a toy model of a four-electron atom with the core $1s^2$. The spectrum obtained with $H_{\\rm eff}$ ...

  9. Electronic band structure of ZnO-rich highly mismatched ZnO1?xTex alloys

    International Nuclear Information System (INIS)

    We synthesized ZnO1?xTex alloys with Te composition x?band gap obtained in this work is 1.8?eV for x?=?0.23. The optical properties of the alloys are explained by the modification of the valence band of ZnO, due to the anticrossing interactions of the localized Te states with the ZnO valence band extended states. Hence, the observed large band gap reduction is primarily originating from the upward shift of the valence band edge. We show that the optical data can be explained by the band anticrossing model with the localized level of Te located at 0.95?eV above the ZnO valence band and the band anticrossing coupling constant of 1.35?eV. These parameters allow the prediction of the compositional dependence of the band gap as well as the conduction and the valence band offsets in the full composition range of ZnO1?xTex alloys

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

    International Nuclear Information System (INIS)

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

  11. SOLVENT EFFECT ON THE VALENCE TAUTOMERISM OF BENZENE OXIDE/OXEPIN MOLECULAR SYSTEM

    OpenAIRE

    J.GUILLERMO CONTRERAS; Sandra T. Madariaga

    2001-01-01

    Thermodynamic parameters for the benzene oxide oxepin system have been calculated at MP4(SDQ)/6-31+G**//HF/6-31G** level of theory. The calculated enthalpy for this valence tautomeric equilibrium differs from that reported by Vogel et al in 1967, but agree well with the value calculated by Kollman using the MINDO/3 method. Large deviations in the experimental tautomerization entropies lead to unreliable delta Gº values. The differences in delta Hº and delta Sº can be due to the lack of band ...

  12. Structure and Properties of CeRhSn - a Valence Fluctuating System

    International Nuclear Information System (INIS)

    X ray diffraction studies have been performed on a CeRhSn single crystal and its anomalous unit-cell volume was confirmed. This, together with temperature dependence of magnetic susceptibility indicate valence-fluctuating behaviour of Ce ions. Band structure calculations support such a behaviour. Anomalous value of the quadrupole interaction constant derived from 119Sn Moessbauer spectroscopy is observed. Ac and dc magnetic susceptibility investigations as well as preliminary resistivity measurements evidence that this compound does not order magnetically down to 2 K, but one of our samples is superconducting with a transition temperature of 6.5 K. (author)

  13. Mixed valence europium nitridosilicate Eu2SiN3.

    Science.gov (United States)

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

    2009-08-12

    The mixed valence europium nitridosilicate Eu(2)SiN(3) has been synthesized at 900 degrees C in welded tantalum ampules starting from europium and silicon diimide Si(NH)(2) in a lithium flux. The structure of the black material has been determined by single-crystal X-ray diffraction analysis (Cmca (no. 64), a = 542.3(11) pm, b = 1061.0(2) pm, c = 1162.9(2) pm, Z = 8, 767 independent reflections, 37 parameters, R1 = 0.017, wR2 = 0.032). Eu(2)SiN(3) is a chain-type silicate comprising one-dimensional infinite nonbranched zweier chains of corner-sharing SiN(4) tetrahedra running parallel [100] with a maximum stretching factor f(s) = 1.0. The compound is isostructural with Ca(2)PN(3) and Rb(2)TiO(3), and it represents the first example of a nonbranched chain silicate in the class of nitridosilicates. There are two crystallographically distinct europium sites (at two different Wyckoff positions 8f) being occupied with Eu(2+) and Eu(3+), respectively. (151)Eu Mössbauer spectroscopy of Eu(2)SiN(3) differentiates unequivocally these two europium atoms and confirms their equiatomic multiplicity, showing static mixed valence with a constant ratio of the Eu(2+) and Eu(3+) signals over the whole temperature range. The Eu(2+) site shows magnetic hyperfine field splitting at 4.2 K. Magnetic susceptibility measurements exhibit Curie-Weiss behavior above 24 K with an effective magnetic moment of 7.5 mu(B)/f.u. and a small contribution of Eu(3+), in accordance with Eu(2+) and Eu(3+) in equiatomic ratio. Ferromagnetic ordering at unusually high temperature is detected at T(C) = 24 K. DFT calculations of Eu(2)SiN(3) reveal a band gap of approximately 0.2 eV, which is in agreement with the black color of the compound. Both DFT calculations and lattice energetic calculations (MAPLE) corroborate the assignment of two crystallographically independent Eu sites to Eu(2+) and Eu(3+). PMID:19610643

  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. Valence and sea quarks in the nucleon

    International Nuclear Information System (INIS)

    The constituent quark model (CQM) describes the nucleon as a system of three constituent, or valence, quarks. Despite the successes of the CQM (e.g. masses, electromagnetic coupling, magnetic moments), there is compelling evidence for the presence of sea quarks from the measurement of the flavor asymmetry of the proton and the so called proton spin crisis. In this contribution, we present the unquenched quark model which is an extension of the CQM that includes the effects of sea quarks via a 3P0 quark-antiquark pair-creation mechanism. As an application, we review the results for baryon magnetic moments and the flavor and spin content of baryons, as well as the strange magnetic moment and the strangeness radius of the proton

  16. BCS theory on a flat band lattice

    International Nuclear Information System (INIS)

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

  17. 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),…

  18. On the Relationship between Value Orientation, Valences, and Academic Achievement

    Science.gov (United States)

    Fries, Stefan; Schmid, Sebastian; Hofer, Manfred

    2007-01-01

    Value orientations are believed to influence learning in school. We assume that this influence is mediated by the valences attached to specific school subjects. In a questionnaire study (704 students from 36 classes) achievement and well-being value orientations were measured. Students also rated valence scales for the school subjects German and…

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

    Science.gov (United States)

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

    2015-04-28

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

  20. Gastric Banding

    Science.gov (United States)

    ... gastric banding before deciding to have the procedure. Advertisements for a device or procedure may not include ... demonstrated benefits for people who have not been successful using non-surgical weight loss methods. This surgical ...

  1. Thermal evolution of the band edges of 6H-SiC: X-ray methods compared to the optical band gap

    Energy Technology Data Exchange (ETDEWEB)

    Miedema, P.S., E-mail: piter.miedema@helmholtz-berlin.de [Institute for Methods and Instrumentation in Synchrotron Radiation Research G-ISRR, Helmholtz-Zentrum für Materialien und Energie GmbH, Albert-Einstein-Strasse 15, 12489 Berlin (Germany); Beye, M.; Könnecke, R.; Schiwietz, G. [Institute for Methods and Instrumentation in Synchrotron Radiation Research G-ISRR, Helmholtz-Zentrum für Materialien und Energie GmbH, Albert-Einstein-Strasse 15, 12489 Berlin (Germany); Föhlisch, A. [Institute for Methods and Instrumentation in Synchrotron Radiation Research G-ISRR, Helmholtz-Zentrum für Materialien und Energie GmbH, Albert-Einstein-Strasse 15, 12489 Berlin (Germany); Fakultät für Physik und Astronomie, Universität Potsdam, Karl-Liebknecht-Strasse 24-25, 14476 Potsdam (Germany)

    2014-12-15

    Highlights: • Conduction band minima (CBM) of 6H-SiC are estimated with Si 2p XAS. • Valence band maxima (VBM) of 6H-SiC are estimated with non-resonant Si 2p XES. • Temperature-dependent VBM and CBM of 6H-SiC show asymmetric band gap closing. • XAS, XES and RIXS band gap estimates are compared with the optical band gap. • XAS + XES versus optical band gap provides core-excitonic screening energies. - Abstract: The band gap of semiconductors like silicon and silicon carbide (SiC) is the key for their device properties. In this research, the band gap of 6H-SiC and its temperature dependence were analyzed with silicon 2p X-ray absorption spectroscopy (XAS), X-ray emission spectroscopy (XES) and resonant inelastic X-ray scattering (RIXS) allowing for a separate analysis of the conduction-band minimum (CBM) and valence-band maximum (VBM) components of the band gap. The temperature-dependent asymmetric band gap shrinking of 6H-SiC was determined with a valence-band slope of +2.45 × 10{sup ?4} eV/K and a conduction-band slope of ?1.334 × 10{sup ?4} eV/K. The apparent asymmetry, e.g., that two thirds of the band-gap shrinking with increasing temperature is due to the VBM evolution in 6H-SiC, is similar to the asymmetry obtained for pure silicon before. The overall band gap temperature-dependence determined with XAS and non-resonant XES is compared to temperature-dependent optical studies. The core-excitonic binding energy appearing in the Si 2p XAS is extracted as the main difference. In addition, the energy loss of the onset of the first band in RIXS yields to values similar to the optical band gap over the tested temperature range.

  2. Thermal evolution of the band edges of 6H-SiC: X-ray methods compared to the optical band gap

    International Nuclear Information System (INIS)

    Highlights: • Conduction band minima (CBM) of 6H-SiC are estimated with Si 2p XAS. • Valence band maxima (VBM) of 6H-SiC are estimated with non-resonant Si 2p XES. • Temperature-dependent VBM and CBM of 6H-SiC show asymmetric band gap closing. • XAS, XES and RIXS band gap estimates are compared with the optical band gap. • XAS + XES versus optical band gap provides core-excitonic screening energies. - Abstract: The band gap of semiconductors like silicon and silicon carbide (SiC) is the key for their device properties. In this research, the band gap of 6H-SiC and its temperature dependence were analyzed with silicon 2p X-ray absorption spectroscopy (XAS), X-ray emission spectroscopy (XES) and resonant inelastic X-ray scattering (RIXS) allowing for a separate analysis of the conduction-band minimum (CBM) and valence-band maximum (VBM) components of the band gap. The temperature-dependent asymmetric band gap shrinking of 6H-SiC was determined with a valence-band slope of +2.45 × 10?4 eV/K and a conduction-band slope of ?1.334 × 10?4 eV/K. The apparent asymmetry, e.g., that two thirds of the band-gap shrinking with increasing temperature is due to the VBM evolution in 6H-SiC, is similar to the asymmetry obtained for pure silicon before. The overall band gap temperature-dependence determined with XAS and non-resonant XES is compared to temperature-dependent optical studies. The core-excitonic binding energy appearing in the Si 2p XAS is extracted as the main difference. In addition, the energy loss of the onset of the first band in RIXS yields to values similar to the optical band gap over the tested temperature range

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

    Energy Technology Data Exchange (ETDEWEB)

    Potts, A.W. [Department of Physics, King’s College, Strand, London WC2R 2LS (United Kingdom); Holland, D.M.P., E-mail: david.holland@stfc.ac.uk [Daresbury Laboratory, Daresbury, Warrington, Cheshire WA4 4AD (United Kingdom); Powis, I. [School of Chemistry, University of Nottingham, Nottingham NG7 2RD (United Kingdom); Karlsson, L. [Department of Physics, Uppsala University, Box 530, SE-751 21 Uppsala (Sweden); Trofimov, A.B. [Laboratory of Quantum Chemistry, Irkutsk State University, 664003 Irkutsk (Russian Federation); A.E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, 664033 Irkutsk (Russian Federation); Bodzuk, I.L. [Laboratory of Quantum Chemistry, Irkutsk State University, 664003 Irkutsk (Russian Federation)

    2013-03-29

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

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

    International Nuclear Information System (INIS)

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

  5. Band-tail absorption in hydrogenated amorphous silicon

    International Nuclear Information System (INIS)

    Measurements of the primary and secondary photocurrent for photon energies above 0.58 eV in a-SI:H solar-cell structures determine the absorption coefficient and give information about the density of valence-band-tail states as well as show that holes are mobile deep in the bandgap

  6. Infrared spectroscopy of electronic bands in bilayer graphene

    OpenAIRE

    Kuzmenko, Alexey; van Heumen, Erik; Marel, Dirk van der,; Lerch, P.; Blake, P; Novoselov, K. S.; Geim, A. K.

    2008-01-01

    We present infrared spectra (0.1-1 eV) of electrostatically gated bilayer graphene as a function of doping and compare it with tight binding calculations. All major spectral features corresponding to the expected interband transitions are identified in the spectra: a strong peak due to transitions between parallel split-off bands and two onset-like features due to transitions between valence and conduction bands. A strong gate voltage dependence of these structures and a sig...

  7. Study on the energy band structure and photoelectrochemical performances of spinel Li4Ti5O12

    International Nuclear Information System (INIS)

    Highlights: • Spinel Li4Ti5O12 possesses more positive potential of valence band and wider band gap than TiO2. • Spinel Li4Ti5O12 displays typical n-type semiconductor characteristic and excellent UV-excitateded photocatalysis activity. • Our preliminary study will open new perspectives in investigation of other lithium-based compounds for new photocatalysts. - Abstract: Energy band structure, photoelectrochemical performances and photocatalysis activity of spinel Li4Ti5O12 are investigated for the first time in this paper. Li4Ti5O12 possesses more positive valence band potential and wider band gap than TiO2 due to its valence band consisting of Li1s and Ti3d orbitals mixed with O2p. Li4Ti5O12 shows typical photocatalysis material characteristics and excellent photocatlytic activity under UV irradiation

  8. A density explanation of valence asymmetries in recognition memory.

    Science.gov (United States)

    Alves, Hans; Unkelbach, Christian; Burghardt, Juliane; Koch, Alex S; Krüger, Tobias; Becker, Vaughn D

    2015-08-01

    The density hypothesis states that positive information is more similar than negative information, resulting in higher density of positive information in mental representations. The present research applies the density hypothesis to recognition memory to explain apparent valence asymmetries in recognition memory, namely, a recognition advantage for negative information. Previous research explained this negativity advantage on the basis of valence-induced affect. We predicted that positive information's higher density impairs recognition performance. Two old-new word recognition experiments tested whether differential density between positive and negative stimuli creates a negativity advantage in recognition memory, over and above valence-induced affect. In Experiment 1, participants better discriminated negative word stimuli (i.e., less false alarms) and showed a response bias towards positive words. Regression analyses showed the asymmetry to be function of density and not of valence. Experiment 2 varied stimulus density orthogonal to valence. Again, discriminability and response bias were a function of density and not of valence. We conclude that the higher density of positive information causes an apparent valence asymmetry in recognition memory. PMID:25772462

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

    Science.gov (United States)

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

    2014-06-01

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

  10. Valence and core electron spectra of Mg in MgO in evaporated thin films

    International Nuclear Information System (INIS)

    X-ray photoelectron spectra (XPS) are obtained for Mg in MgO using high quality (purity 99.999%) Mg films prepared and oxidized under pressures of 10-6 to 10-8 torr and measured on an ESCA-36 spectrometer at a pressure of 10-8 torr. AlK? line source was used for excitation, and the minimum of Au valence band at 5.0 eV was chosen for calibration. With incr eased oxidation the valence band shifts about 1.0 eV towards the Fermi level, but with extreme contamination it disappears completely. Accurate measurements of binding energies have been made of Mg in pure Mg, and Mg in MgO. The average shift resulting from oxidation is 1.1 eV for Mg(2s) and 1.5 eV for Mg(2p) core levels. It is also observed that the contamination effect due to oxygen decreases with increasing film thickness. The present results are compared with the previous results, and a new interpretation is offered by postulating the formation of two kinds of oxides, stoichiometric and chemisorbed layers in Mg on oxidation. (orig.)

  11. Valence modulates source memory for faces.

    Science.gov (United States)

    Bell, Raoul; Buchner, Axel

    2010-01-01

    Previous studies in which the effects of emotional valence on old-new discrimination and source memory have been examined have yielded highly inconsistent results. Here, we present two experiments showing that old-new face discrimination was not affected by whether a face was associated with disgusting, pleasant, or neutral behavior. In contrast, source memory for faces associated with disgusting behavior (i.e., memory for the disgusting context in which the face was encountered) was consistently better than source memory for other types of faces. This data pattern replicates the findings of studies in which descriptions of cheating, neutral, and trustworthy behavior were used, which findings were previously ascribed to a highly specific cheater detection module. The present results suggest that the enhanced source memory for faces of cheaters is due to a more general source memory advantage for faces associated with negative or threatening contexts that may be instrumental in avoiding the negative consequences of encounters with persons associated with negative or threatening behaviors. PMID:19966236

  12. 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 ...

  13. Equalized Electronegativity Based on the Valence Electrons and Its Application

    Science.gov (United States)

    Wu, Ya-xin; Cao, Chen-zhong; Yuan, Hua

    2011-02-01

    We take the contribution of all valence electrons into consideration and propose a new valence electrons equilibration method to calculate the equalized electronegativity including molecular electronegativity, group electronegativity, and atomic charge. The ionization potential of alkanes and mono-substituted alkanes, the chemical shift of 1H NMR, and the gas phase proton affinity of aliphatic amines, alcohols, and ethers were estimated. All the expressions have good correlations. Moreover, the Sanderson method and Bratsch method were modified on the basis of the valence electrons equilibration theory. The modified Sanderson method and modified Bratsch method are more effective than their original methods to estimate these properties.

  14. Valence bond model potential energy surface for H4

    International Nuclear Information System (INIS)

    Potential energy surfaces for the H4 system are derived using the valence bond procedure. An ab initio evaluation of the valence bond energy expression is described and some of its numerical properties are given. Next, four semiempirical evaluations of the valence bond energy are defined and parametrized to yield reasonable agreement with various ab initio calculations of H4 energies. Characteristics of these four H4 surfaces are described by means of tabulated energy minima and equipotential contour maps for selected geometrical arrangements of the four nuclei

  15. Quasirelativistic band structure of bismuth telluride

    International Nuclear Information System (INIS)

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

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

    International Nuclear Information System (INIS)

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

  17. Dispersement apparatus

    International Nuclear Information System (INIS)

    Disclosed is a dispersement apparatus for an enlarged mass of fissionable material which causes the liquid fissionable material to move by gravity into a first passage means, the first passage means being connected to a plurality of second passages with the fissionable material separating into the second passages, each second passage being connected to a plurality of third passages which results in the liquid fissionable material being further separated. Each of the passages will contain adjacent the junction thereof with the previous passage a quantity of low melting point material, such as lead or tin. The heat of reaction of the fissionable material will readily melt this meltable material prior to entering the passage. The free end of the third passage may extend within a sand base with explosive means being located therewith to further and ultimately very finely disperse the fissionable material

  18. Band Together!

    Science.gov (United States)

    Olson, Cathy Applefeld

    2011-01-01

    After nearly a decade as band director at St. James High School in St. James, Missouri, Derek Limback knows that the key to building a successful program is putting the program itself above everything else. Limback strives to augment not only his students' musical prowess, but also their leadership skills. Key to his philosophy is instilling a…

  19. Spatial Representation of Odorant Valence in an Insect Brain

    Directory of Open Access Journals (Sweden)

    Markus Knaden

    2012-04-01

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

  20. Some formal results for the valence bond basis

    International Nuclear Information System (INIS)

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

  1. A Valence Isomer Trapping Procedure for Introductory Organic Laboratory.

    Science.gov (United States)

    Kurtz, David W.; Johnson, Richard P.

    1989-01-01

    Described is an experiment which illustrates valence isomerization, the trapping of a reactive intermediate and retrosynthetic analysis applied to the Diels-Alder reaction. Included is a background discussion, experimental procedures, and a discussion of the analysis. (CW)

  2. Quantum Monte Carlo with Jastrow-Valence-Bond wave functions

    CERN Document Server

    Braïda, Benoît; Caffarel, Michel; Umrigar, C J

    2011-01-01

    We consider the use in quantum Monte Carlo (QMC) of two types of valence bond wave functions based on strictly localized active orbitals, namely valence-bond self-consistent-field (VBSCF) and breathing-orbital valence-bond (BOVB) wave functions. Complemented by a Jastrow factor, these Jastrow-Valence-Bond wave functions are tested on the four diatomic molecules C2, N2, O2, and F2 in both variational Monte Carlo (VMC) and diffusion Monte Carlo (DMC). We show that it is possible to design compact wave functions based on chemical grounds that are capable of adequately describing both static and dynamic electron correlation, and which yield accurate equilibrium well depths in DMC.

  3. Stimulus affective valence reverses spatial compatibility effect

    Scientific Electronic Library Online (English)

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

    2011-06-01

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

  4. Stimulus affective valence reverses spatial compatibility effect

    Directory of Open Access Journals (Sweden)

    rick Francisco Quintas Conde

    2011-01-01

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

  5. Phenomenology of dihadron FF: Collinear extraction of the valence transversities

    International Nuclear Information System (INIS)

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

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

    International Nuclear Information System (INIS)

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

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

    Science.gov (United States)

    Abdel-Raouf, Mohamed Assad

    1990-01-01

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

  8. Valence photoionization and photoelectron–photoion coincidence (PEPICO) study of molecular LiCl and Li2Cl2

    International Nuclear Information System (INIS)

    Highlights: ? The valence photoelectron spectra of LiCl and Li2Cl2 are recorded and re-interpreted. ? Fragmentation following ionization is explored by electron–ion coincidence. ? Ab initio calculations are used to decide which fragmentation channels are accessible. ? Formulae are provided for Franck–Condon factors pertaining to transition states. -- Abstract: Molecular LiCl and Li2Cl2 have been studied in the vapor phase with valence photoelectron and photoelectron–photoion coincidence spectroscopies. These two techniques determine the binding energies in fundamentally different ways. Binding energies obtained from photoelectron spectra are usually taken as the vertical ionization energies of the corresponding electronic states. In cases with several overlapping bands, corresponding to different electronic states, the coincidence measurement can separate the bands if the respective final states fragment differently. This applies well to the monomer case. To facilitate the determination of state-specific ionization energies in the dimeric molecule, a theoretical Franck–Condon analysis has been carried out. Moreover, ab initio coupled-cluster and density-functional-theory calculations have been used to analyze the fragmentation pattern based on asymptotic dissociation energies. The fragmentation pattern is largely common to all the accessible valence-ionized states of the dimer, consistent with rapid conversion to the ionic ground state before fragmentation. However, the highest-lying state of Li2Cl2+, 2Ag, shows enhanced propensity for Li+ as dissociation product.

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

    Directory of Open Access Journals (Sweden)

    JelleDemanet

    2011-11-01

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

  10. Charge distribution in arylhydrazine-centered mixed valence compounds with smaller bridges (five to nine bonds between closest nitrogens).

    Science.gov (United States)

    Nelsen, Stephen F; Schultz, Kevin P

    2009-05-01

    Charge distribution in six aromatic-bridged, aryldialkylhydrazine-centered mixed valence radical cations is discussed through consideration of their optical spectra. The compounds considered have two 2-phenyl-2,3-diazabicyclo-[2.2.2]octane-3-yl (HyPh) charge-bearing units linked by a 1,4-phenylene bridge and its p-methoxyphenyl (HyAn) analogue, as well as the (HyPh)(2)-substituted 1,4-naphthalene, 2,6-naphthalene, 9,10-anthracene, and 4,4'-biphenyl compounds in methylene chloride and acetonitrile. Consideration of band shape and position leads us to assign the 1,4-phenylene- and 2,6-naphthalene-bridged compounds as charge-delocalized (class III) in both solvents, but the 1,4-naphthalene-bridged one lies closer to the borderline, and appears to be charge-localized (class II) in acetonitrile. The 4,4'-biphenyl-bridged compound is clearly class II in acetonitrile, and possibly also in methylene chloride. The lowest energy absorption band for the 9,10-anthracene-bridged compound is assigned as a bridge-to-HyPh band, and its charge distribution is not clear. Problems with the often-used relationship that the electronic coupling is half the transition energy for the lowest energy band of class III mixed valence compounds are discussed, as is interpretation of the vertical reorganization energy near the class II, class III borderline. PMID:19354243

  11. 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,…

  12. Photonic band structure and omnidirectional band gap in anisotropic superlattice

    Energy Technology Data Exchange (ETDEWEB)

    Ouchani, N.; Bria, D.; Nougaoui, A. [Laboratoire de Dynamique et d' Optique des Materiaux, Departement de Physique, Faculte des Sciences, Universite Mohamed I, B.P. 524, 60000 Oujda (Morocco); Djafari-Rouhani, B. [Laboratoire de Dynamique et Structure des Materiaux Moleculaires, UMR CNRS 8024, UFR de Physique, Universite de Lille 1, 59655 Villeneuve d' Ascq (France)

    2006-06-15

    We investigate theoretically the photonic band structure of one-dimensional superlattices (SL) composed of alternating anisotropic layers with their principal axes oriented at arbitrary directions. The dispersion relation of second order is calculated analytically by using the 4 x 4 matrix method which is based on the boundary conditions of the electric and magnetic fields at each interface. It is shown that such structures can exhibit coupled electromagnetic modes between transverse magnetic TM and transverse electric TE modes, and dispersion curves that do not exist in superlattices composed only of isotropic layers. For a given value of the wave vector k {sub ?} (parallel to the layers), the dispersion curves (frequency ?) versus k {sub B} (where k {sub B} is the Bloch wave vector of the periodic system along the axis of the superlattice) are illustrated. Specific applications of these results are given for the case of the biaxial superlattice. We show that with an appropriate choice of the superlattice parameters an absolute (or omnidirectional) band gap for these coupled electromagnetic waves can be obtained. The band gap width depends on the anisotropic parameters of the media forming the SL. (author)

  13. Band touching from real space topology in frustrated hopping models

    OpenAIRE

    Bergman, Doron L.; Wu, Congjun; Balents, Leon

    2008-01-01

    We study ``frustrated'' hopping models, in which at least one energy band, at the maximum or minimum of the spectrum, is dispersionless. The states of the flat band(s) can be represented in a basis which is fully localized, having support on a vanishing fraction of the system in the thermodynamic limit. In the majority of examples, a dispersive band touches the flat band(s) at a number of discrete points in momentum space. We demonstrate that this band touching is related to...

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

    Scientific Electronic Library Online (English)

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

    2014-12-01

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

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

    OpenAIRE

    Cánovas Díaz, Enrique; Martí Vega, Antonio; López Martínez, Nair; Antolín Fernández, Elisa; García-Linares Fontes, Pablo; Farmer, C.D.; Stanley, Colin; Luque López, Antonio

    2008-01-01

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

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

    International Nuclear Information System (INIS)

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

  17. 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

    2015-11-01

    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. PMID:26588381

  18. Systematic Study of Electronic Phases, Band Gaps and Band Overlaps of Bismuth Antimony Nanowires

    OpenAIRE

    Tang, Shuang; Dresselhaus, Mildred

    2013-01-01

    We have developed an iterative one dimensional model to study the narrow band-gap and the associated non-parabolic dispersion relations for bismuth antimony nanowires. An analytical approximation has also been developed. Based on the general model, we have developed, we have calculated and analyzed the electronic phase diagrams and the band-gap/band-overlap map for bismuth antimony nanowires, as a function of stoichiometry, growth orientation, and wire width.

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

    International Nuclear Information System (INIS)

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

  20. Band Alignment and Optical Properties of (ZrO2)0.66(HfO2)0.34 Gate Dielectrics Thin Films on p-Si (100)

    OpenAIRE

    Dahlang Tahir; Hee Jae Kang; Sven Tougaard

    2011-01-01

    (ZrO2)0.66(HfO2)0.34 dielectric films on p-Si (100) were grown by atomic layer deposition method, for which the conduction band offsets, valence band offsets and band gaps were obtained by using X-ray photoelectron spectroscopy and reflection electron energy loss spectroscopy. The band gap, valence and conduction band offset values for (ZrO2)0.66(HfO2)0.34 dielectric thin film, grown on Si substrate were about 5.34, 2.35 and 1.87 eV respectively. This band alignment was similar to that of ZrO...

  1. Band offset measurements in Zn1-x Sb x O/ZnO hetero-junctions

    Science.gov (United States)

    Devi, Vanita; Kumar, Manish; Kumar, Ravindra; Singh, Amanpal; Joshi, B. C.

    2015-08-01

    Accurate knowledge of the alignment of conduction and valence bands of layers at the heterojunction and warrant knowledge of the band offsets at the interface is essential for Zn1-x Sb x O/ZnO based quantum well device designing and modeling. Under this scenario, valence band offsets of Zn1-x Sb x O/ZnO heterostructures grown by the pulsed laser deposition technique was measured by photoelectron spectroscopy and consequently, the conduction band offset was calculated by UV-visible spectroscopy. The change in band alignment has been observed with the dopant (Sb) concentration. Ratios of conduction band offset to valence band offset were estimated to be 1.67 and 0.04 for x = 0.03 and 0.06, respectively, for Sb doped films. A Type-II band alignment was observed at the Zn0.97Sb0.03O/ZnO interface, whereas the Type-I band alignment took place at the Zn0.94Sb0.06O/ZnO interface.

  2. Space-Valence Priming with Subliminal and Supraliminal Words

    Directory of Open Access Journals (Sweden)

    UlrichAnsorge

    2013-02-01

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

  3. Valence QCD Connecting QCD to the Quark Model

    CERN Document Server

    Liu Ke Feng; Draper, T; Leinweber, D; Sloan, J; Wilcox, W R; Woloshyn, R M

    1999-01-01

    A valence QCD theory is developed to study the valence quark properties of hadrons. To keep only the valence degrees of freedom, the pair creation through the Z graphs is deleted in the connected insertions; whereas, the sea quarks are eliminated in the disconnected insertions. This is achieved with a new ``valence QCD'' lagrangian where the action in the time direction is modified so that the particle and antiparticle decouple. The theory has the vector and axial $U(2N_F)$ symmetry in the particle-antiparticle space. Through lattice simulation, it appears that this is dynamically broken down to $U_q(N_F) \\times U_{\\bar{q}}(N_F)$. Furthermore, the lattice simulation reveals spin degeneracy in the hadron masses and SU(6) relations in the ratios of $F_A/D_A, F_S/D_S$, and $\\mu^n/\\mu^p$. This leads to an approximate $U_q(2N_F) \\times U_{\\bar{q}}(2N_F)$ symmetry which is the basis for the valence quark model. We find that the masses of N, $\\Delta, \\rho, \\pi, a_1$, and $a_0$ all drop precipitously compared to thei...

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

    International Nuclear Information System (INIS)

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

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

    International Nuclear Information System (INIS)

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

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

    International Nuclear Information System (INIS)

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Tobin, J.G.

    1983-07-01

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

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

    Czech Academy of Sciences Publication Activity Database

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

    2012-01-01

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

  9. Exploring scaling laws of valence neutron distributions for medium nuclei

    International Nuclear Information System (INIS)

    The root-mean-square radii of the valence neutron distributions for many nuclei in He-Mo mass range are calculated in the framework of the single-particle potential model. The scaling laws of valence neutron distributions are obtained by analyzing the relations between the radii and the binding energies of the valence neutrons. Based on these scaling laws, the necessary conditions for the occurrence of neuron halos in 2s1/2, 1p3/2, 1p1/2, 2p3/2, 2p1/2, 1d5/2 and 1d3/2 states are deduced, respectively. The derived quantitative conditions for halo occurrence can provide reference for the searching of neutron halos up to medium nuclei. (authors)

  10. 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.

  11. Affective and restorative valences for three environmental categories.

    Science.gov (United States)

    Martínez-Soto, Joel; Gonzales-Santos, Leopoldo; Barrios, Fernando A; Lena, Maria E Montero-López

    2014-12-01

    The present study evaluated images of environments in three categories with different affective and restorative valences through two computerized assessments. A non-verbal computerized response scale and the Mexican Scale of Environmental Restoration Perception were employed. 104 students assessed the affective qualities of 117 images (47 natural, 37 urban with nature, and 33 built-up without nature) according to pleasure and activation dimensions. Then 96 students assessed 54 images with high and low valence for their restorative quality. Natural images were found to generate positive affective reactions of liking and activation and high restorative quality. Affective responses to urban with nature environments tended to be positive with moderate restorative quality. Built-up without nature environments were perceived as less pleasant and had low restorative quality. However, among built-up without nature environments, some settings with striking architectural qualities evoked positive affective valences. PMID:25402210

  12. Pressure-driven valence change in ternary Eu pnictides

    Energy Technology Data Exchange (ETDEWEB)

    Huhnt, C.; Michels, G.; Schlabitz, W. [II. Physikalisches Institut, Universitaet zu Koeln, Zuelpicher Strasse 77, 50937 Koeln (Germany); Johrendt, D.; Mewis, A. [Institut fuer Anorganische Chemie und Strukturchemie der Heinrich-Heine-Universitaet, Universitaetsstrasse 1, 40225 Duesseldorf (Germany)

    1997-11-10

    We observed a structural phase transition with extremely anisotropic changes of the lattice parameters as a function of pressure at 2.6 GPa in EuPdP, which crystallizes in the hexagonal layered Ni{sub 2}In structure type. On the basis of the results of pressure-dependent x-ray diffraction experiments on the isostructural series APdP and APdAs (A=Sr or a trivalent rare-earth element) we show that the phase transition in EuPdP is accompanied by a valence change of the Eu. Strong but continuous changes of the lattice parameters with increasing pressure, which are due to increase of the Eu valence, were observed in EuNiP, EuPtP and EuPdAs, too. An estimation of the average Eu valence in these compounds leads to preferred values of the order of 2 n/6. (author)

  13. Pressure-driven valence change in ternary Eu pnictides

    International Nuclear Information System (INIS)

    We observed a structural phase transition with extremely anisotropic changes of the lattice parameters as a function of pressure at 2.6 GPa in EuPdP, which crystallizes in the hexagonal layered Ni2In structure type. On the basis of the results of pressure-dependent x-ray diffraction experiments on the isostructural series APdP and APdAs (A=Sr or a trivalent rare-earth element) we show that the phase transition in EuPdP is accompanied by a valence change of the Eu. Strong but continuous changes of the lattice parameters with increasing pressure, which are due to increase of the Eu valence, were observed in EuNiP, EuPtP and EuPdAs, too. An estimation of the average Eu valence in these compounds leads to preferred values of the order of 2 n/6. (author)

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

    Science.gov (United States)

    Nelsen, Stephen F; Schultz, Kevin P

    2009-05-14

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

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

    CERN Document Server

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

    2011-01-01

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

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

    International Nuclear Information System (INIS)

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2010-05-15

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

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

    International Nuclear Information System (INIS)

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

  19. Nature of adiabatic crossing of degenerate doublet bands in 106Ag

    International Nuclear Information System (INIS)

    In the last decade, a number of nearly degenerate pairs of rotational bands with same parity have been reported in nuclei of mass A?130 and A?100 regions. These bands are known to be strongly connected to each other. It has been proposed that a possible reason for the occurrence of these doublet bands is spontaneous breaking of chiral symmetry in triaxial nuclei due to the presence of three orthogonal angular momenta of the valence protons, valence neutrons and the core. However, for the two bands to be chiral partners, the near degeneracy in level energy and spin is a necessary but not a sufficient condition. In addition, these bands should exhibit nearly similar moment of inertia, quasiparticle alignment, signature staggering behaviour and more importantly, the transition probabilities

  20. Spin Dynamics and Magnetic Ordering in Mixed Valence Systems

    DEFF Research Database (Denmark)

    Shapiro, S. M.; Bjerrum Møller, Hans; Axe, J. D.; Birgeneau, R. J.; Bucher, E.

    1978-01-01

    Neutron scattering measurements are reported on the mixed valence compounds Ce//1// minus //xTh//x and TmSe. The chi double prime (Q, omega ) as derived from the inelastic spectra of Ce//0//. //7//4Th//0//. //2//6 shows a peak in the gamma phase near 20. 0 meV and shifts abruptly to greater than 70. 0 meV at the transition to the alpha phase. The temperature independence of the susceptibility within the gamma phase cannot be simply reconciled with the temperature dependence of the valence within...

  1. Momentum distributions for the valence orbitals of hydrogen fluoride

    International Nuclear Information System (INIS)

    The binding energy spectra and momentum distributions for the three valence orbitals of hydrogen fluoride have been obtained using the binary (e,2e) method at a total energy of 400 eV. The experimental shapes of the momentum distributions are compared with results of calculations using the wave functions of Snyder and Basch. Agreement is quite good for the 2sigma inner valence orbital. However, significant differences between theory and experiment are found for the 1? and 3sigma orbitals. In particular the 1? orbital is more spatially extended than the calculated wave function suggests

  2. Evidence for valence fluctuations in CeAs

    International Nuclear Information System (INIS)

    Anomalous temperature and pressure dependences for the 75As Knight shift in CeAs are interpreted within the framework of Hirst's model for fluctuating valence. A 30-K-wide peak in the density of states, located 85 K below E/sub F/, is inferred from the analysis. The area under the peak represents 1% of the Ce3+ valence, but due to the nature of the hyperfine interaction this is less than the actual number of electrons which would be involved in the fluctuation from Ce3+ to Ce4+

  3. pi-Acid/pi-base carbonyloxo, carbonylsulfido, and mixed-valence complexes of tungsten.

    Science.gov (United States)

    Thomas, Simon; Tiekink, Edward R T; Young, Charles G

    2006-01-01

    Carbonyloxotungsten(IV) complexes, TpWOX(CO), are produced in the reactions of dioxygen (for X = Cl, Br, I) or pyridine N-oxide [for X = S(2)P(OPr(i))(2), S(2)PPh(2)] with TpWX(CO)(2) [Tp = hydrotris(3,5-dimethylpyrazol-1-yl)borate]. Analogous carbonylsulfidotungsten(IV) species, TpWSX(CO), result from the reactions of TpWX(kappa(2)-MeCN)(CO) with propylene sulfide. The carbonyloxo complexes exhibit nu(CO) and nu(W=O) IR bands in the 1995-1965 and 957-951 cm(-1) regions, respectively; the nu(CO) and nu(W=S) bands of the carbonylsulfido species appear at 1970-1937 and 512-502 cm(-1), respectively. The complexes possess C(1) symmetry and display carbonyl (13)C NMR resonances at delta 272-287, with J(WC) 160-196 Hz. The crystal structures of TpWO(S(2)PPh(2))(CO) and TpWS(S(2)PPh(2))(CO).0.5CHCl(3) reveal distorted octahedral tungsten centers coordinated by a fac tridentate Tp ligand and mutually cis, monodentate chalcogenido [d(W=O) = 1.698(4) A; d(W=S) = 2.135(4) Angstroms], carbonyl, and dithiophosphinato ligands. In refluxing toluene, TpWOI(CO) converts into purple, mixed-valence TpW(III)I(CO)(mu-O)W(V)OITp. The dinuclear complex contains a nearly linear [173.1(6) degrees] mu-oxo bridge connecting disparate distorted octahedral tungsten centers. The metrical parameters and spectroscopic properties are consistent with the presence of a W(III)/W(V) mixed-valence species, possessing a filled, delocalized three-center (W-O-W) pi bond and a localized (on W(III)), filled d(pi) orbital that back-bonds to the carbonyl ligand. PMID:16390076

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

    International Nuclear Information System (INIS)

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

  5. BAND ALIGNMENT OF ULTRATHIN GIZO/SiO2/Si HETEROSTRUCTURE DETERMINED BY ELECTRON SPECTROSCOPY

    Directory of Open Access Journals (Sweden)

    Hee Jae Kang2

    2011-11-01

    Full Text Available Amorphous GaInZnO (GIZO thin films are grown on SiO2/Si substrate by the RF magnetron sputtering method. By thecombination of measured band gaps from reflection energy loss spectroscopy (REELS spectra and valence band fromX-ray photo-electron spectroscopy (XPS spectra, we have demonstrated the energy band alignment of GIZO thin films.The band gap values are 3.2 eV, 3.2 eV, 3.4eV and 3.6eV for the concentration ratios of Ga: In: Zn in GIZO thin filmsare 1:1:1, 2:2:1, 3:2:1 and 4:2:1, respectively. These are attributed to the larger band gap energy of Ga2O3 comparedwith In2O3 and ZnO. The valence band offsets (?Ev decrease from 2.18 to 1.68 eV with increasing amount of Ga inGIZO thin films for GIZO1 to GIZO4, respectively. These experimental values of band gap and valence band offsetwill provide the further understanding in the fundamental properties of GIZO/SiO2/Si heterostructure, which will beuseful in the design, modeling and analysis of the performance devices applications.

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

    International Nuclear Information System (INIS)

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

  7. Ultrafast dynamics. Attosecond band-gap dynamics in silicon.

    Science.gov (United States)

    Schultze, Martin; Ramasesha, Krupa; Pemmaraju, C D; Sato, S A; Whitmore, D; Gandman, A; Prell, James S; Borja, L J; Prendergast, D; Yabana, K; Neumark, Daniel M; Leone, Stephen R

    2014-12-12

    Electron transfer from valence to conduction band states in semiconductors is the basis of modern electronics. Here, attosecond extreme ultraviolet (XUV) spectroscopy is used to resolve this process in silicon in real time. Electrons injected into the conduction band by few-cycle laser pulses alter the silicon XUV absorption spectrum in sharp steps synchronized with the laser electric field oscillations. The observed ~450-attosecond step rise time provides an upper limit for the carrier-induced band-gap reduction and the electron-electron scattering time in the conduction band. This electronic response is separated from the subsequent band-gap modifications due to lattice motion, which occurs on a time scale of 60 ± 10 femtoseconds, characteristic of the fastest optical phonon. Quantum dynamical simulations interpret the carrier injection step as light-field-induced electron tunneling. PMID:25504716

  8. On the O2 Schumann-Runge band system in sunspots

    International Nuclear Information System (INIS)

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

  9. Band Magnetism

    International Nuclear Information System (INIS)

    Introduction. 1. Experimental properties of transitional metals. 1.1. Magnetic properties. 1.2. Other properties. 2. The band model. 3. Hartree-Fock Stoner theory. 3.1. Non-magnetic Hartree-Fock solution at T = 0. 3.2. Magnetic solutions. 3.3. Applications. 4. Spin waves in the random phase approximation. 5. Susceptibilities - equivalence between the RPA and the time-dependent Hartree-Fock approximation. 5.1. Definition and properties of the susceptibilities. 5.2. Susceptibilities in the RPA. Time-dependent Hartree-Fock approximation. 6. Spin density waves. 6.1. Appearance of spin density waves at Tc. 6.2. Spin density waves below Tc. 6.3. Application to-chiomium. 7. Influence of correlation. 7.1. The Landau theory of Fermi liquids. 7.2. Approximate treatment of correlation. 7.3. Applications. 8. Nearly ferromagnetic metals. 8.1. Mass enhancement due to phonons. 8.2. Mass enhancement due to paramagnons. 8.3. Applications. Conclusion. (author)

  10. Band-Gap and Band-Edge Engineering of Multicomponent Garnet Scintillators from First Principles

    Science.gov (United States)

    Yadav, Satyesh K.; Uberuaga, Blas P.; Nikl, Martin; Jiang, Chao; Stanek, Christopher R.

    2015-11-01

    Complex doping schemes in R3 Al5 O12 (where R is the rare-earth element) garnet compounds have recently led to pronounced improvements in scintillator performance. Specifically, by admixing lutetium and yttrium aluminate garnets with gallium and gadolinium, the band gap is altered in a manner that facilitates the removal of deleterious electron trapping associated with cation antisite defects. Here, we expand upon this initial work to systematically investigate the effect of substitutional admixing on the energy levels of band edges. Density-functional theory and hybrid density-functional theory (HDFT) are used to survey potential admixing candidates that modify either the conduction-band minimum (CBM) or valence-band maximum (VBM). We consider two sets of compositions based on Lu3 B5O12 where B is Al, Ga, In, As, and Sb, and R3Al5 O12 , where R is Lu, Gd, Dy, and Er. We find that admixing with various R cations does not appreciably affect the band gap or band edges. In contrast, substituting Al with cations of dissimilar ionic radii has a profound impact on the band structure. We further show that certain dopants can be used to selectively modify only the CBM or the VBM. Specifically, Ga and In decrease the band gap by lowering the CBM, while As and Sb decrease the band gap by raising the VBM, the relative change in band gap is quantitatively validated by HDFT. These results demonstrate a powerful approach to quickly screen the impact of dopants on the electronic structure of scintillator compounds, identifying those dopants which alter the band edges in very specific ways to eliminate both electron and hole traps responsible for performance limitations. This approach should be broadly applicable for the optimization of electronic and optical performance for a wide range of compounds by tuning the VBM and CBM.

  11. Photonic band structure and omnidirectional band gap in anisotropic superlattice

    International Nuclear Information System (INIS)

    We investigate theoretically the photonic band structure of one-dimensional superlattice (SL) composed of alternating anisotropic layers with their principal axis oriented at arbitrary directions. The dispersion relation of order two is calculated analytically by using the 4 x 4 matrix method which is based on boundary conditions of the electric and magnetic fields at each interface. It is shown that such structures can exhibit coupled electromagnetic modes between transverse magnetic TM and transverse electric TE modes, and dispersion curves that do not exist in superlattices composed only of isotropic layers. For a given value of the wave vector kparallel (parallel to the layers), the dispersion curves (frequency ?) versus kB (where kB is the Bloch wave vector of the periodic system along the axis of the superlattice) is illustrated. Specific applications of these results are given for the case of biaxial superlattice. With an appropriate choice of the superlattice parameters, we show that it is possible to realise, for these coupled electromagnetic waves, an absolute (or omnidirectional) band gap of width depending on the anisotropic parameters of the media forming the SL. (author)

  12. CORE PHOTOELECTRON-SPECTRA OF NARROW-BAND METALLIC MATERIALS

    OpenAIRE

    BEATHAM, N; Cox, P.; EGDELL, R; ORCHARD, A

    1980-01-01

    Complex core level structure is encountered in the photoelectron spectra of a wide range of narrow-band metallic oxides. The examples cited include cases where the metal atom is in an integral, formal oxidation state. The observations lend support to the view that multi-peak structure in the core photoelectron spectra of the cubic tungsten bronzes should be interpreted in terms of final-state effects rather than valence localisation in the neutral system. © 1980.

  13. "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. PMID:25082796

  14. Valence electron momentum spectroscopy of inert gas atoms

    International Nuclear Information System (INIS)

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

  15. Real-time observation of valence electron motion.

    Science.gov (United States)

    Goulielmakis, Eleftherios; Loh, Zhi-Heng; Wirth, Adrian; Santra, Robin; Rohringer, Nina; Yakovlev, Vladislav S; Zherebtsov, Sergey; Pfeifer, Thomas; Azzeer, Abdallah M; Kling, Matthias F; Leone, Stephen R; Krausz, Ferenc

    2010-08-01

    The superposition of quantum states drives motion on the atomic and subatomic scales, with the energy spacing of the states dictating the speed of the motion. In the case of electrons residing in the outer (valence) shells of atoms and molecules which are separated by electronvolt energies, this means that valence electron motion occurs on a subfemtosecond to few-femtosecond timescale (1 fs = 10(-15) s). In the absence of complete measurements, the motion can be characterized in terms of a complex quantity, the density matrix. Here we report an attosecond pump-probe measurement of the density matrix of valence electrons in atomic krypton ions. We generate the ions with a controlled few-cycle laser field and then probe them through the spectrally resolved absorption of an attosecond extreme-ultraviolet pulse, which allows us to observe in real time the subfemtosecond motion of valence electrons over a multifemtosecond time span. We are able to completely characterize the quantum mechanical electron motion and determine its degree of coherence in the specimen of the ensemble. Although the present study uses a simple, prototypical open system, attosecond transient absorption spectroscopy should be applicable to molecules and solid-state materials to reveal the elementary electron motions that control physical, chemical and biological properties and processes. PMID:20686571

  16. Mobile Linkers on DNA-Coated Colloids: Valency without Patches

    Science.gov (United States)

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

    2014-09-01

    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.

  17. Valence mixing in YbCuAl: a case study

    International Nuclear Information System (INIS)

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

  18. Mixed-valence copper oxides: stoichiometry-Superconductivity relationships

    International Nuclear Information System (INIS)

    Among the mixed-valence copper oxides whose structure is related to the perovskite, only those with a bidimensional structure are superconductors. Relations between superconductivity and oxygen stoichiometry are described and studied for La2Cu04, YBa2Cu3O6.9 and YBa2Cu3O6.25 compounds

  19. Real-time observation of valence electron motion.

    Energy Technology Data Exchange (ETDEWEB)

    Goulielmakis, E.; Loh, Z.-H.; Wirth, A.; Santra, R.; Rohringer, N.; Yakovlev, V. S.; Zherebtsov, S.; Pfeifer, T.; Azzeer, A. M.; Kling, M. F.; Leone, S. R.; Krausz, F.; Chemical Sciences and Engineering Division; Max-Planck-Insti. fur Quantenoptik; Univ. of California at Berkeley; LBNL; Univ. of Chicago; LLNL; Ludwig-Maximilians-Univ.; King Saud Univ.

    2010-08-05

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

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

    OpenAIRE

    Yuming Zhang; Barry Spielman

    2010-01-01

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

  1. A study of the valence shell electronic states of pyridazine by photoabsorption spectroscopy and time-dependent density functional theory calculations

    International Nuclear Information System (INIS)

    The valence shell electronic states of pyridazine have been studied experimentally, by recording the photoabsorption spectrum, and theoretically, by calculating oscillator strengths and excitation energies. The absolute photoabsorption cross section has been measured between 4 and 40 eV, using synchrotron radiation, and is dominated by prominent bands associated with intravalence transitions. In contrast, structure due to Rydberg excitations is weak. One Rydberg state, belonging to a series converging onto the X-tilde 2B2 state limit has been observed and assigned. The accompanying vibrational structure has been characterized by analogy with that in the corresponding photoelectron band. Vibrational progressions associated with Rydberg states belonging to one or more series converging onto the A-bar 2A2 state limit have also been observed. The absorption structure associated with these series is complex and only tentative assignments have been proposed for the Rydberg states. The time-dependent version of density functional theory has been used to calculate oscillator strengths and excitation energies for the optically allowed singlet–singlet valence transitions and also to obtain the excitation energies for electric-dipole-forbidden and/or spin-forbidden transitions. The valence shell photoionization dynamics have been investigated theoretically by calculating photoelectron angular distributions and photoionization partial cross sections of the four outermost orbitals. In addition, the ground state outer valence electronic configuration has been obtained at the complete active space self-consistent field and the N-electron valence state perturbation theory to second-order levels of theory. (paper)

  2. Automatic Dispersion Measurements of Helical Slow- Wave Structure

    Directory of Open Access Journals (Sweden)

    S. J. Rao

    2000-01-01

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

  3. Energy-band diagram configuration of Al2O3/oxygen-terminated p-diamond metal-oxide-semiconductor

    Science.gov (United States)

    Maréchal, A.; Aoukar, M.; Vallée, C.; Rivière, C.; Eon, D.; Pernot, J.; Gheeraert, E.

    2015-10-01

    Diamond metal-oxide-semiconductor capacitors were prepared using atomic layer deposition at 250 °C of Al2O3 on oxygen-terminated boron doped (001) diamond. Their electrical properties were investigated in terms of capacitance and current versus voltage measurements. Performing X-ray photoelectron spectroscopy based on the measured core level energies and valence band maxima, the interfacial energy band diagram configuration of the Al2O3/O-diamond is established. The band diagram alignment is concluded to be of type I with valence band offset ? E v of 1.34 ± 0.2 eV and conduction band offset ? E c of 0.56 ± 0.2 eV considering an Al2O3 energy band gap of 7.4 eV. The agreement with electrical measurement and the ability to perform a MOS transistor are discussed.

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

    OpenAIRE

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

    2002-01-01

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

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

    OpenAIRE

    Demanet, Jelle; Liefooghe, Baptist; Verbruggen, Frederick

    2011-01-01

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

  6. An ab initio study of core-valence correlation. [in atoms

    Science.gov (United States)

    Partridge, H.; Bauschlicher, C. W., Jr.; Walch, S. P.; Liu, B.

    1983-01-01

    Especially in the cases of the first two columns of the periodic table, the inclusion of core-valence correlation in ab initio CI calculations yields a contraction of the atomic valence shell and improves both calculated atomic ionization potentials and atomic energy separations. For the alkali dimers Na2, K2, and Rb2, the presently calculated bond lengths are in excellent agreement with experiments when core-valence is included. In addition, the valence dissociation energies are accurate.

  7. 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…

  8. 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…

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

    International Nuclear Information System (INIS)

    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/Al45Ga55N 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.

  10. Identification of the 0.95 eV luminescence band in n-type GaAs:Si

    International Nuclear Information System (INIS)

    The luminescence band at 0.95 eV has been identified as originating from the transition within (SiGaVGaSiGa) complexes by comparing cathodoluminescence and positron annihilation spectra. The upper and lower energy levels of the molecule-like defect complexes are suggested to lie at 22 meV below the conduction band and at about 0.5 eV above the valence band, respectively

  11. Dispersion in optical fibers and timing for particle identification

    OpenAIRE

    Paleari, Fabio

    2002-01-01

    In the framework of the TOF Wall laser calibration system of the HARP experiment, a study of time dispersion properties of mono-mode and multi-mode optical fibers in the green band (532 nm) has been carried out. Dispersion less than 4 ps/m has been obtained with $\\approx$10 $\\mu$m core diameter fibers.

  12. Systematic study of nuclear softness of superdeformed bands with NPNn scheme in A=190 mass region

    International Nuclear Information System (INIS)

    A simple pattern appeared whenever nuclear data concerning nuclear deformation was plotted against the product NpNn between the valence proton number Np and the valence neutron number Nn . In the present work a 4-parameter formula based on the prescription of Bohr and Mottelson to obtain the nuclear softness parameter ? for SD bands in A = 190 mass region has been used to study the softness parameter with NpNn for SD nuclei. The nuclear softness parameter with NpNn for the SD bands in A=190 mass region has been studied. A 4-parameter formula based on the prescription of Bohr and Mottelson to obtain the nuclear softness parameter for SD bands in A=190 mass region has been used. The systematics of the softness parameter of the SD bands in A=190 has been presented

  13. 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.

  14. Unfolding the band structure of non-crystalline photonic band gap materials

    Science.gov (United States)

    Tsitrin, Samuel; Williamson, Eric Paul; Amoah, Timothy; Nahal, Geev; Chan, Ho Leung; Florescu, Marian; Man, Weining

    2015-08-01

    Non-crystalline photonic band gap (PBG) materials have received increasing attention, and sizeable PBGs have been reported in quasi-crystalline structures and, more recently, in disordered structures. Band structure calculations for periodic structures produce accurate dispersion relations, which determine group velocities, dispersion, density of states and iso-frequency surfaces, and are used to predict a wide-range of optical phenomena including light propagation, excited-state decay rates, temporal broadening or compression of ultrashort pulses and complex refraction phenomena. However, band calculations for non-periodic structures employ large super-cells of hundreds to thousands building blocks, and provide little useful information other than the PBG central frequency and width. Using stereolithography, we construct cm-scale disordered PBG materials and perform microwave transmission measurements, as well as finite-difference time-domain (FDTD) simulations. The photonic dispersion relations are reconstructed from the measured and simulated phase data. Our results demonstrate the existence of sizeable PBGs in these disordered structures and provide detailed information of the effective band diagrams, dispersion relation, iso-frequency contours, and their angular dependence. Slow light phenomena are also observed in these structures near gap frequencies. This study introduces a powerful tool to investigate photonic properties of non-crystalline structures and provides important effective dispersion information, otherwise difficult to obtain.

  15. Spectroscopic investigation of the Dergaon meteorite with reference to 10 m and 20 m bands

    Indian Academy of Sciences (India)

    A Gohain Barua; B R Boruah; S Bhattacharyya; G D Baruah

    2003-01-01

    Analysis of a part of the meteorite which fell at Dergaon (India) on March 2, 16.40 local time (2001) is presented with the help of FTIR, absorption and atomic spectra. The FTIR spectrum exhibits prominent absorption bands in the region 800–1100 cm-1, originating from the valence vibration of SiO4, a basic component of the silicate lattice.

  16. Features of the band structure for semiconducting iron, ruthenium, and osmium monosilicides

    International Nuclear Information System (INIS)

    The pseudopotential method has been used to optimize the crystal lattice and calculate the energy band spectra for iron, ruthenium and, osmium monosilicides. It is found that all these compounds are indirect-gap semiconductors with band gaps of 0.17, 0.22, and 0.50 eV (FeSi, RuSi, and OsSi, respectively). A distinctive feature of their band structure is the 'loop of extrema' both in the valence and conduction bands near the center of the cubic Brillouin zone.

  17. Plasmon bands in metallic nanostructures

    CERN Document Server

    Inglesfield, J E; Kemp, R

    2004-01-01

    The photonic band structure of a three-dimensional lattice of metal spheres is calculated using an embedding technique, in the frequency range of the Mie plasmons. For a small filling factor of the spheres, Maxwell-Garnett theory gives an almost exact description of the dipole modes, and the multipole modes are fairly dispersionless. For a larger filling factor, crystal field effects modify the multipole frequencies, which show dispersion. These multipole bands are enclosed between the dipole modes. For touching spheres, there is a wide continuum of plasmon modes between zero frequency and the bulk metal plasmon frequency, which yield strong absorption of incident light. These plasmon modes are responsible for the blackness of colloidal silver.

  18. Universality class of non-Fermi-liquid behavior in mixed-valence systems

    International Nuclear Information System (INIS)

    A generalized Anderson single-impurity model with off-site Coulomb interactions is derived from the extended three-band Hubbard model, originally proposed to describe the physics of the copper oxides. Using the Abelian bosonization technique and canonical transformations, an effective Hamiltonian is derived in the strong-coupling limit, which is essentially analogous to the Toulouse limit of the ordinary Kondo problem. In this limit, the effective Hamiltonian can be exactly solved, with a mixed-valence quantum critical point separating two different Fermi-liquid phases, i.e., the Kondo phase and the empty orbital phase. In the mixed-valence quantum critical regime, the local moment is only partially quenched and x-ray edge singularities are generated. Around the quantum critical point, a type of non-Fermi-liquid behavior is predicted with an extra specific heat Cimp?T1/4 and a singular spin susceptibility ?imp?T-3/4. At the same time, the effective Hamiltonian under single occupancy is transformed into a resonant-level model, from which the correct Kondo physical properties (specific heat, spin susceptibility, and an enhanced Wilson ratio) are easily rederived. Finally, a brief discussion is given to relate these theoretical results to observations in UPdxCu5-x (x=1,1.5) alloys, which show single-impurity critical behavior consistent with our predictions. copyright 1996 The American Physical Societght 1996 The American Physical SocietyA generalized Anderson single-impurity model with off-site Coulomb interactions is derived from the extended three-band Hubbard model, originally proposed to describe the physics of the copper oxides. Using the Abelian bosonization technique and canonical transformations, an effective Hamiltonian is derived in the strong-coupling limit, which is essentially analogous to the Toulouse limit of the ordinary Kondo problem. In this limit, the effective Hamiltonian can be exactly solved, with a mixed-valence quantum critical point separating two different Fermi-liquid phases, i.e., the Kondo phase and the empty orbital phase. In the mixed-valence quantum critical regime, the local moment is only partially quenched and x-ray edge singularities are generated. Around the quantum critical point, a type of non-Fermi-liquid behavior is predicted with an extra specific heat Cimp?T1/4 and a singular spin susceptibility ?imp?T-3/4. At the same time, the effective Hamiltonian under single occupancy is transformed into a resonant-level model, from which the correct Kondo physical properties (specific heat, spin susceptibility, and an enhanced Wilson ratio) are easily rederived. Finally, a brief discussion is given to relate these theoretical results to observations in UPdxCu5-x (x=1,1.5) alloys, which show single-impurity critical behavior consistent with our predictions. copyright 1996 The American Physical Socie

  19. Realistic estimate of valence transversity from dihadron production

    CERN Document Server

    Radici, Marco

    2015-01-01

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

  20. On the valence shell binding energy spectrum of carbonyl sulphide

    International Nuclear Information System (INIS)

    The valence shell binding energy spectrum of carbonyl sulphide (10-45 eV) has been measured using both binary (e,2e) and dipole (e,2e) electron impact spectroscopy and calculated by the 2ph-TDA many body Green's function technique. The spectrum shows extensive structure above 20 eV, indicating a major breakdown of the quasi-particle picture for ionization of COS. The calculation is in good agreement with the present experimental and literature ESCA binding energy spectra. Binary (e,2e) spectra at two azimuthal angles support the theoretical prediciton that this extensive final ion state structure arises primarily from ionization of the COS 6sigma and 7sigma inner valence electrons. (orig.)

  1. Bond charge approximation for valence electron density in elemental semiconductors

    International Nuclear Information System (INIS)

    The spatial valence electron distribution in silicon and diamond is calculated in adiabatic bond charge approximation at zero temperature when bond charges have the Gaussian shape and their tensor character is taken into account. An agreement between theory and experiment has been achieved. For this purpose Xia's ionic pseudopotentials and Schulze-Unger's dielectric function are used. By two additional parameters Asub(B) and Zsub(B)sup(') we describe the spatial extent of the bond charge and local-field corrections, respectively. The parameter Zsub(B)sup(') accounts for the ratio between the Coulomb and exchange correlation interactions of the valence electrons and its silicon and diamond values have different signs. (author)

  2. The olfactory tubercle encodes odor valence in behaving mice.

    Science.gov (United States)

    Gadziola, Marie A; Tylicki, Kate A; Christian, Diana L; Wesson, Daniel W

    2015-03-18

    Sensory information acquires meaning to adaptively guide behaviors. Despite odors mediating a number of vital behaviors, the components of the olfactory system responsible for assigning meaning to odors remain unclear. The olfactory tubercle (OT), a ventral striatum structure that receives monosynaptic input from the olfactory bulb, is uniquely positioned to transform odor information into behaviorally relevant neural codes. No information is available, however, on the coding of odors among OT neurons in behaving animals. In recordings from mice engaged in an odor discrimination task, we report that the firing rate of OT neurons robustly and flexibly encodes the valence of conditioned odors over identity, with rewarded odors evoking greater firing rates. This coding of rewarded odors occurs before behavioral decisions and represents subsequent behavioral responses. We predict that the OT is an essential region whereby odor valence is encoded in the mammalian brain to guide goal-directed behaviors. PMID:25788670

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-01-05

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

  4. Temperley-Lieb Words as Valence-Bond Ground States

    OpenAIRE

    Arndt, Peter F; Heinzel, Thomas; Yung, C. M.

    1994-01-01

    Based on the Temperley--Lieb algebra we define a class of one-dimensional Hamiltonians with nearest and next-nearest neighbour interactions. Using the regular representation we give ground states of this model as words of the algebra. Two point correlation functions can be computed employing the Temperley--Lieb relations. Choosing a spin-1/2 representation of the algebra we obtain a generalization of the (q-deformed) Majumdar--Ghosh model. The ground states become valence-bo...

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

    CERN Document Server

    Cichy, Krzysztof; Jansen, Karl

    2009-01-01

    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 $L\\approx1.3$ fm. We also briefly review the techniques we have used to deal with overlap fermions.

  6. 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.)

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

    DEFF Research Database (Denmark)

    Hall, Eleanor R.; Pollock, Christopher J.; Bendix, Jesper; Collins, Terrence J.; Glatzel, Pieter; Debeer, Serena

    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 monito...

  8. Shell structure, emerging collectivity, and valence p-n interactions

    OpenAIRE

    Cakirli R.B.

    2014-01-01

    The structure of atomic nuclei depends on the interactions of its constituents, protons and neutrons. These interactions play a key role in the development of configuration mixing and in the onset of collectivity and deformation, in changes to the single particle energies and magic numbers, and in the microscopic origins of phase transitional behavior. Particularly important are the valence proton-neutron interactions which can be studied experimentally using double differences of binding ene...

  9. 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...

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

    OpenAIRE

    Kuperman, Victor; Estes, Zachary; 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. Th...

  11. Mixed-Valence Tetranuclear Manganese Single-Molecule Magnets

    OpenAIRE

    Yoo, Jae; Yamaguchi, Akira; Nakano, Motohiro; Krzystek, J.; Streib, William E.; Brunel, Louis-Claude; Ishimoto, Hidehiko; Christou, George; Hendrickson, David N

    2001-01-01

    The preparations, X-ray structures, and detailed physical characterizations are presented for two new mixed-valence tetranuclear manganese complexes that function as single-molecule magnets (SMM's): [Mn4(hmp)6Br2(H2O)2]Br2.4H2O and [Mn4(6-me-hmp)6Cl4].4H2O, where hmp- is the anion of 2-hydroxymethylpyridine and 6-me-hmp- is the anion of 6-methyl-2-hydroxymethylpyridine.

  12. Few-valence-particle excitations around doubly magic 132Sn

    International Nuclear Information System (INIS)

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

  13. A valence-fluctuation theory of cuprate superconductivity

    Energy Technology Data Exchange (ETDEWEB)

    Brandow, B.H. (Center for Nonlinear Studies, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States))

    1994-04-01

    The concepts and formalism of valence-fluctuation theory are applied to an Anderson lattice model of the CuO[sub 2] plane. Using a self-consistent variational treatment at the (1/N)[sup 1] level, for a finite-U lattice, we find adequate pairing attraction for realistic Hamiltonian parameters. Several unconventional features of the cuprate phenomenology are explained, including the extremely short coherence length, large resistivity, and strong gap anisotropy. ((orig.))

  14. Nuclear ?-and ?- collective bands in the SUq(2) rotator model

    International Nuclear Information System (INIS)

    The SUq(2) rotator model is used for describing the ?1- and ?1- bands of even-even rare earth and actinide collective nuclei. Good results are obtained in nuclei with valence pair number N>10. It is shown that in the excited bands the violations of the exact SU(2) symmetry is generally stronger than in the ground state bands, indicating the presence of a nonadiabatic perturbation caused by the excited vibrational degrees of freedom. The physical content of the parameter q is discussed. Predictions of the SUq(2) model for B(E2) intraband transitions in excited bands are presented and the need for specific experimental data is pointed out. (authors)

  15. Massive band gap variation in layered oxides through cation ordering

    Science.gov (United States)

    Balachandran, Prasanna V.; Rondinelli, James M.

    2015-01-01

    The electronic band gap is a fundamental material parameter requiring control for light harvesting, conversion and transport technologies, including photovoltaics, lasers and sensors. Although traditional methods to tune band gaps rely on chemical alloying, quantum size effects, lattice mismatch or superlattice formation, the spectral variation is often limited to <1?eV, unless marked changes to composition or structure occur. Here we report large band gap changes of up to 200% or ~2?eV without modifying chemical composition or use of epitaxial strain in the LaSrAlO4 Ruddlesden-Popper oxide. First-principles calculations show that ordering electrically charged [LaO]1+ and neutral [SrO]0 monoxide planes imposes internal electric fields in the layered oxides. These fields drive local atomic displacements and bond distortions that control the energy levels at the valence and conduction band edges, providing a path towards electronic structure engineering in complex oxides.

  16. Spin Dynamics and Magnetic Ordering in Mixed Valence Systems

    DEFF Research Database (Denmark)

    Shapiro, S. M.; Bjerrum MØller, Hans

    1978-01-01

    Neutron scattering measurements are reported on the mixed valence compounds Ce//1// minus //xTh//x and TmSe. The chi double prime (Q, omega ) as derived from the inelastic spectra of Ce//0//. //7//4Th//0//. //2//6 shows a peak in the gamma phase near 20. 0 meV and shifts abruptly to greater than 70. 0 meV at the transition to the alpha phase. The temperature independence of the susceptibility within the gamma phase cannot be simply reconciled with the temperature dependence of the valence within the gamma phase. TmSe is shown to order in a type I antiferromagnetic structure below T//N similar 3. 2 K. The magnetic phase diagram is understood as a successive domain reorientation and a metamagnetic phase transition for T less than 3 K with increasing field. The mixed valence nature manifests itself in a reduced moment and a markedly altered crystal field. Another sample of TmSe with a lattice parameter implying 100% Tm**3** plus exhibits spin correlations characteristic of a type II structure but never achieves long range order.

  17. Valence bond entanglement and fluctuations in random singlet phases

    Science.gov (United States)

    Tran, Huan; Bonesteel, N. E.

    2011-10-01

    The ground state of the uniform antiferromagnetic spin-1/2 Heisenberg chain can be viewed as a strongly fluctuating liquid of valence bonds, while in disordered chains these bonds lock into random singlet states on long-length scales. We show that this phenomenon can be studied numerically, even in the case of weak disorder, by calculating the mean value of the number of valence bonds leaving a block of L contiguous spins (the valence-bond entanglement entropy) as well as the fluctuations in this number. These fluctuations show a clear crossover from a small L regime, in which they behave similar to those of the uniform model, to a large L regime, in which they saturate in a way consistent with the formation of a random singlet state on long-length scales. A scaling analysis of these fluctuations is used to study the dependence on disorder strength of the length scale characterizing the crossover between these two regimes. Results are obtained for a class of models that include, in addition to the spin-1/2 Heisenberg chain, the uniform and disordered critical 1D transverse-field Ising model and chains of interacting non-Abelian anyons.

  18. Shell structure, emerging collectivity, and valence p-n interactions

    Directory of Open Access Journals (Sweden)

    Cakirli R.B.

    2014-03-01

    Full Text Available The structure of atomic nuclei depends on the interactions of its constituents, protons and neutrons. These interactions play a key role in the development of configuration mixing and in the onset of collectivity and deformation, in changes to the single particle energies and magic numbers, and in the microscopic origins of phase transitional behavior. Particularly important are the valence proton-neutron interactions which can be studied experimentally using double differences of binding energies extracted from high-precision mass measurements. The resulting quantities, called ?Vpn, are average interaction strengths between the last two protons and the last two neutrons. Focusing on the Z=50-82, N=82-126 shells, we have considered a number of aspects of these interactions, ranging from their relation to the underlying orbits, their behaviour near close shells and throughout major shells, their relation to the onset of collectivity and deformation, and the appearance of unexpected spikes in ?Vpn values for a special set of heavy nuclei with nearly equal numbers of valence protons and neutrons. We have calculated spatial overlaps between proton and neutron Nilsson orbits and compared these with the experimental results. Finally we also address the relation between masses (separation energies, changes in structure and valence nucleon number.

  19. Shell structure, emerging collectivity, and valence p-n interactions

    Science.gov (United States)

    Cakirli, R. B.

    2014-03-01

    The structure of atomic nuclei depends on the interactions of its constituents, protons and neutrons. These interactions play a key role in the development of configuration mixing and in the onset of collectivity and deformation, in changes to the single particle energies and magic numbers, and in the microscopic origins of phase transitional behavior. Particularly important are the valence proton-neutron interactions which can be studied experimentally using double differences of binding energies extracted from high-precision mass measurements. The resulting quantities, called ?Vpn, are average interaction strengths between the last two protons and the last two neutrons. Focusing on the Z=50-82, N=82-126 shells, we have considered a number of aspects of these interactions, ranging from their relation to the underlying orbits, their behaviour near close shells and throughout major shells, their relation to the onset of collectivity and deformation, and the appearance of unexpected spikes in ?Vpn values for a special set of heavy nuclei with nearly equal numbers of valence protons and neutrons. We have calculated spatial overlaps between proton and neutron Nilsson orbits and compared these with the experimental results. Finally we also address the relation between masses (separation energies), changes in structure and valence nucleon number.

  20. Chromium valences in ureilite olivine and implications for ureilite petrogenesis

    Science.gov (United States)

    Goodrich, C. A.; Sutton, S. R.; Wirick, S.; Jercinovic, M. J.

    2013-12-01

    Ureilites are a group of ultramafic achondrites commonly thought to be residues of partial melting on a carbon-rich asteroid. They show a large variation in FeO content (olivine Fo values ranging from ?74 to 95) that cannot be due to igneous fractionation and suggests instead variation in oxidation state. The presence of chromite in only a few of the most ferroan (Fo 75-76) samples appears to support such a model. MicroXANES analyses were used in this study to determine the valence states of Cr (previously unknown) in olivine cores of 11 main group ureilites. The goal of this work was to use a method that is independent of Fo to determine the oxidation conditions under which ureilites formed, in order to evaluate whether the ureilite FeO-variation is correlated with oxidation state, and whether it is nebular or planetary in origin. Two of the analyzed samples, LEW 88774 (Fo 74.2) and NWA 766 (Fo 76.7) contain primary chromite; two others, LAP 03587 (Fo 74.4) and CMS 04048 (Fo 76.2) contain sub-micrometer-sized exsolutions of chromite + Ca-rich pyroxene in olivine; and one, EET 96328 (Fo 85.2) contains an unusual chromite grain of uncertain origin. No chromite has been observed in the remaining six samples (Fo 77.4-92.3). Chromium in olivine in all eleven samples was found to be dominated by the divalent species, with valences ranging from 2.10 ± 0.02 (1?) to 2.46 ± 0.04. The non-chromite-bearing ureilites have the most reduced Cr, with a weighted mean valence of 2.12 ± 0.01, i.e., Cr2+/Cr3+ = 7.33. All low-Fo chromite-bearing ureilites have more oxidized Cr, with valences ranging from 2.22 ± 0.03 to 2.46 ± 0.04. EET 96328, whose chromite grain we interpret as a late-crystallizing phase, yielded a reduced Cr valence of 2.15 ± 0.07, similar to the non-chromite-bearing samples. Based on the measured Cr valences, magmatic (1200-1300 °C) oxygen fugacities (fO2) of the non-chromite-bearing samples were estimated to be in the range IW-1.9 to IW-2.8 (assuming basaltic melt composition), consistent with fO2 values obtained by assuming olivine-silica-iron metal (OSI) equilibrium. For the primary chromite-bearing-ureilites, the corresponding fO2 were estimated (again, assuming basaltic melt composition) to be ?IW to IW+1.0, i.e., several orders of magnitude more oxidizing than the conditions estimated for the chromite-free ureilites. In terms of Fo and Cr valence properties, ureilites appear to form two groups rather than a single “Cr-valence (or fO2) vs. Fo” trend. The chromite-bearing ureilites show little variation in Fo (?74-76) but significant variation in Cr valence, while the non-chromite-bearing ureilites show significant variation in Fo (?77-95) and little variation in Cr valence. These groups are unrelated to petrologic type (i.e., olivine-pigeonite, olivine-orthopyroxene, or augite-bearing). The chromite-bearing ureilites also have lower contents of Cr in olivine than most non-chromite-bearing ureilites, consistent with predictions based on Cr olivine/melt partitioning in spinel saturated vs. non-spinel-saturated systems. Under the assumption that at magmatic temperatures graphite-gas equilibria controlled fO2 at all depths on the ureilite parent body, we conclude: (1) that ureilite precursor materials having the Fo and Cr valence properties now observed in ureilites are unlikely to have been preserved during planetary processing; and (2) that the Fo and Cr valence properties now observed in ureilites are consistent with having been established by high-temperature carbon redox control over a range of depths on a plausible-sized ureilite parent body. The apparent limit on ureilite Fo values around 74-76 suggests that the precursor material(s) had bulk mg# ? that of LL chondrites.

  1. Predicting the Valence of a Scene from Observers’ Eye Movements

    Science.gov (United States)

    R.-Tavakoli, Hamed; Atyabi, Adham; Rantanen, Antti; Laukka, Seppo J.; Nefti-Meziani, Samia; Heikkilä, Janne

    2015-01-01

    Multimedia analysis benefits from understanding the emotional content of a scene in a variety of tasks such as video genre classification and content-based image retrieval. Recently, there has been an increasing interest in applying human bio-signals, particularly eye movements, to recognize the emotional gist of a scene such as its valence. In order to determine the emotional category of images using eye movements, the existing methods often learn a classifier using several features that are extracted from eye movements. Although it has been shown that eye movement is potentially useful for recognition of scene valence, the contribution of each feature is not well-studied. To address the issue, we study the contribution of features extracted from eye movements in the classification of images into pleasant, neutral, and unpleasant categories. We assess ten features and their fusion. The features are histogram of saccade orientation, histogram of saccade slope, histogram of saccade length, histogram of saccade duration, histogram of saccade velocity, histogram of fixation duration, fixation histogram, top-ten salient coordinates, and saliency map. We utilize machine learning approach to analyze the performance of features by learning a support vector machine and exploiting various feature fusion schemes. The experiments reveal that ‘saliency map’, ‘fixation histogram’, ‘histogram of fixation duration’, and ‘histogram of saccade slope’ are the most contributing features. The selected features signify the influence of fixation information and angular behavior of eye movements in the recognition of the valence of images. PMID:26407322

  2. Interchannel coupling effects in the valence photoionization of SF6

    International Nuclear Information System (INIS)

    The complex Kohn and polyatomic Schwinger variational techniques have been employed to illustrate the interchannel coupling correlation effects in the valence photoionization dynamics of SF6. Partial photoionization cross sections and asymmetry parameters of six valence subshells (1t1g, 5t1u, 1t2u, 3eg, 1t2g, 4t1u) are discussed in the framework of several theoretical and experimental studies. The complex Kohn results are in rather good agreement with experimental results, indicative of the fact that the interchannel coupling effects alter the photoionization dynamics significantly. We find that the dominant effect of interchannel coupling is to reduce the magnitude of shape resonant cross sections near the threshold and to induce resonant features in other channels to which resonances are coupled. The long-standing issue concerning ordering of the valence orbitals is addressed and confirmed 4t1u61t2g63eg4(5t1u6+1t2u6) 1t1g6 as the most likely ordering

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

    CERN Document Server

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

    2014-01-01

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

  4. Relaxation of femtosecond photoexcited electrons in a polar indirect band-gap semiconductor nanoparticle

    Indian Academy of Sciences (India)

    Navinder Singh

    2005-01-01

    A model calculation is given for the energy relaxation of a non-equilibrium distribution of hot electrons (holes) prepared in the conduction (valence) band of a polar indirect band-gap semiconductor, which has been subjected to homogeneous photoexcitation by a femtosecond laser pulse. The model assumes that the pulsed photoexcitation creates two distinct but spatially interpenetrating electron and hole non-equilibrium subsystems that initially relax non-radiatively through the electron (hole)–phonon processes towards the conduction (valence) band minimum (maximum), and finally radiatively through the phonon-assisted electron–hole recombination across the band-gap, which is a relatively slow process. This leads to an accumulation of electrons (holes) at the conduction (valence) band minimum (maximum). The resulting peaking of the carrier density and the entire evolution of the hot electron (hole) distribution has been calculated. The latter may be time resolved by a pump-probe study. The model is particularly applicable to a divided (nanometric) polar indirect band-gap semiconductor with a low carrier concentration and strong electron–phonon coupling, where the usual two-temperature model $[1–4]$ may not be appropriate.

  5. Field-induced valence transition of Eu(Pd1-xPtx)2Si2

    International Nuclear Information System (INIS)

    The magnetic susceptibility and high-field magnetization have been measured for the intermediate valence system Eu(Pd1-xPtx)2Si2 with 0?x?0.15. A first-order valence transition is observed for all the compounds under high field of 100 T at low temperatures. This valence transition is of first order accompanied with a large hysteresis, which is in contrast to a continuous valence change against temperature. Based on the interconfigurational fluctuation (ICF) model, the temperature- and field-induced valence transitions are discussed. It is found that a first-order valence transition can be induced by magnetic field, even if the system shows a continuous valence transition against temperature. Metamagnetic behavior at finite temperatures is also understood qualitatively by the ICF model. copyright 1997 The American Physical Society

  6. 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, reinforcement sensitivity theory suggests that emotionally valenced responses will diverge according to the type of emotion presented. For these 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 valenced in nearfield. The results are largely consistent with this hypothesis, but can also be found to be impacted by the original soundstage of the musical excerpts presented.

  7. Gold atomic clusters extracting the valence electrons to shield the carbon monoxide passivation on near-monolayer core-shell nanocatalysts in methanol oxidation reactions.

    Science.gov (United States)

    Chen, Tsan-Yao; Li, Hong Dao; Lee, Guo-Wei; Huang, Po-Chun; Yang, Po-Wei; Liu, Yu-Ting; Liao, Yen-Fa; Jeng, Horng-Tay; Lin, Deng-Sung; Lin, Tsang-Lang

    2015-06-21

    Atomic-scale gold clusters were intercalated at the inter-facet corner sites of Pt-shell Ru-core nanocatalysts with near-monolayer shell thickness. We demonstrated that these unique clusters could serve as a drain of valence electrons in the kink region of the core-shell heterojunction. As jointly revealed by density functional theory calculations and valence band spectra, these Au clusters extract core-level electrons to the valence band. They prevent corrosion due to protonation and enhance the tolerance of CO by increasing the electronegativity at the outermost surface of the NCs during the methanol oxidation reaction (MOR). In these circumstances, the retained current density of Pt-shell Ru-core NCs is doubled in a long-term (2 hours) MOR at a fixed voltage (0.5 V vs. SCE) by intercalating these sub-nanometer gold clusters. Such novel structural confinement provides a possible strategy for developing direct-methanol fuel cell (DMFC) modules with high power and stability. PMID:25991582

  8. Heterojunction band offsets and dipole formation at BaTiO3/SrTiO3 interfaces

    International Nuclear Information System (INIS)

    We used a complement of photoemission and cathodoluminescence techniques to measure formation of the BaTiO3 (BTO) on SrTiO3 (STO) heterojunction band offset grown monolayer by monolayer by molecular beam epitaxy. X-ray photoemission spectroscopy (XPS) provided core level and valence band edge energies to monitor the valence band offset in-situ as the first few crystalline BTO monolayers formed on the STO substrate. Ultraviolet photoemission spectroscopy (UPS) measured Fermi level positions within the band gap, work functions, and ionization potentials of the growing BTO film. Depth-resolved cathodoluminescence spectroscopy measured energies and densities of interface states at the buried heterojunction. Kraut-based XPS heterojunction band offsets provided evidence for STO/BTO heterojunction linearity, i.e., commutativity and transitivity. In contrast, UPS and XPS revealed a large dipole associated either with local charge transfer or strain-induced polarization within the BTO epilayer

  9. Comparative studies on photonic band structures of diamond and hexagonal diamond using the multiple scattering method

    International Nuclear Information System (INIS)

    Photonic band structures are investigated for both diamond and hexagonal diamond crystals composed of dielectric spheres, and absolute photonic band gaps (PBGs) are found in both cases. In agreement with both Karathanos and Moroz's calculations, a large PBG occurs between the eighth and ninth bands in diamond crystal, but a PBG in hexagonal diamond crystal is found to occur between the sixteenth and seventeenth bands because of the doubling of dielectric spheres in the primitive cell. To explore the physical mechanism of how the photonic band gap might be broadened, we have compared the electric field distributions (|E|2) of the 'valence' and 'conduction' band edges. Results show that the field intensity for the 'conduction' band locates in the inner core of the sphere while that of the 'valence' band concentrates in the outer shell. With this motivation, double-layer spheres are designed to enhance the corresponding photonic band gaps; the PBG is increased by 35% for the diamond structure, and 14% for the hexagonal diamond structure

  10. Come Join the Band

    Science.gov (United States)

    Olson, Cathy Applefeld

    2011-01-01

    A growing number of students in Blue Springs, Missouri, are joining the band, drawn by a band director who emphasizes caring and inclusiveness. In the four years since Melissia Goff arrived at Blue Springs High School, the school's extensive band program has swelled. The marching band alone has gone from 100 to 185 participants. Also under Goff's…

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

    Energy Technology Data Exchange (ETDEWEB)

    Ermler, Walter V.; Tilson, Jeffrey L.

    2012-12-15

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

  12. Investigation of the Band Gap in Co3O4

    Science.gov (United States)

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

    2015-03-01

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

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

    International Nuclear Information System (INIS)

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

  14. Dispersing powders in liquids

    CERN Document Server

    Nelson, R D

    1988-01-01

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

  15. Dispersion y dinamica poblacional

    Science.gov (United States)

    Dispersal behavior of fruit flies is appetitive. Measures of dispersion involve two different parameter: the maximum distance and the standard distance. Standard distance is a parameter that describes the probalility of dispersion and is mathematically equivalent to the standard deviation around ...

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

    Directory of Open Access Journals (Sweden)

    Erick E. Reyes-Vera

    2013-11-01

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

  17. Neural correlates of valence generalization in an affective conditioning paradigm.

    Science.gov (United States)

    Schick, Anita; Adam, Ruth; Vollmayr, Barbara; Kuehner, Christine; Kanske, Philipp; Wessa, Michèle

    2015-10-01

    In case of uncertainty, predictions that are based on prior, similar experiences guide our decision by processes of generalization. Over-generalization of negative information has been identified as an important feature of several psychopathologies, including anxiety disorders and depression, and might underlie biased interpretation of ambiguous information. Here, we investigated the neural correlates of valence generalization to ambiguous stimuli using a translational affective conditioning task during fMRI. Twenty-five healthy individuals participated in a conditioning procedure with (1) an initial acquisition phase, where participants learned the positive and negative valence of two different tones (reference tones) through their responses and subsequent feedback and (2) a test phase, where participants were presented with the previously learned reference tones and three additional tones with intermediate frequency to the learned reference tones. By recording the responses to these intermediate stimuli we were able to assess the participant? interpretation of ambiguous tones as either positive or negative. Behavioral results revealed a graded response pattern to the three intermediate tones, which was mirrored on the neural level. More specifically, parametric analyses OF BOLD responses to all five tones revealed a linear effect in bilateral anterior insula and SMA with lowest activation to the negative reference tone and highest activation to the positive negative tone. In addition, a cluster in the SMA showed a reverse-quadratic response, i.e., the strongest response for the most ambiguous tone. These findings suggest overlapping regions in the salience network that mediate valence generalization and decision-making under ambiguity, potentially underlying biased ambiguous cue interpretation. PMID:26057359

  18. Observation of localized flat-band modes in a one-dimensional photonic rhombic lattice

    CERN Document Server

    Mukherjee, Sebabrata

    2015-01-01

    We experimentally demonstrate the photonic realization of a dispersionless flat-band in a one-dimensional photonic rhombic lattice fabricated by ultrafast laser inscription. In the nearest neighbor tight binding approximation the lattice supports two dispersive and a non-dispersive (flat) band. We experimentally excite a superposition of flat-band eigen modes at the input of the photonic lattice and show the diffractionless propagation of the input modes due to their infinite effective mass.

  19. Valence-electron distribution of cesium crown-ether electrides

    Science.gov (United States)

    Kaplan, T. A.; Rencsok, R.; Harrison, J. F.

    1994-09-01

    Dye has argued that in the electride Cs(18-crown-6)2 the valence electrons are localized in interstitial regions, or traps, which are far from the cesium nuclei (forming a lattice of F centers). Golden and Tuttle (GT) have argued that this picture is incorrect, the electron distribution being located instead in the immediate vicinity of the Cs nucleus. Here we refute GT's arguments. We also give arguments based on ab initio calculations for an electride-type molecule, which supports a picture like Dye's versus one where the electron probability is mainly near the cesiums.

  20. Formal Valence, $d$ Occupation, and Charge-Order Transitions

    OpenAIRE

    Quan, Yundi; Pardo, Victor; Pickett, Warren E.

    2012-01-01

    While the formal valence and charge state concepts have been tremendously important in materials physics and chemistry, their very loose connection to actual charge leads to uncertainties in modeling behavior and interpreting data. We point out, taking several transition metal oxides (La$_2$VCuO$_6$, YNiO$_3$, CaFeO$_3$, AgNiO$_2$, V$_4$O$_7$) as examples, that while dividing the crystal charge into atomic contributions is an ill-posed activity, the 3d occupation of a cation...

  1. A role of valence particles number equal to 20

    International Nuclear Information System (INIS)

    The importance of the NpNn parametrization was first demonstrated by Casten in connection with the role of the proton-neutron interaction in the growth of deformation away from shell closures, and there have subsequently been many developments in this theme. The symbols Np and Nn are number of valence particles/holes of protons and neutrons, respectively (where nucleons are counted as holes beyond the middle of a major shell). The observables which reflect collective structure in the deformed mass region for even-even nuclei such as E(2+), R4/2 ? E(4+)/E(2+) and B(E2) have behaved smoothly with NpNn

  2. 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.

  3. Mixed Valence Europium Nitridosilicate Eu2SiN3

    OpenAIRE

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

    2009-01-01

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

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

    International Nuclear Information System (INIS)

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Dixit, V. K.; Kumar, Shailendra; Singh, S. D.; Khamari, S. K.; Kumar, R.; Tiwari, Pragya; Sharma, T. K.; Oak, S. M. [Raja Ramanna Centre for Advanced Technology, Indore, Madhya Pradesh 452013 (India); Phase, D. M. [UGC-DAE Consortium for Scientific Research, Khandwa Road, Indore, Madhya Pradesh 452001 (India)

    2014-03-03

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

  6. The paired-electron crystal in the two-dimensional frustrated quarter-filled band

    International Nuclear Information System (INIS)

    The competition between antiferromagnetic and spin-singlet ground states within quantum spin models and the 1/2 -filled band Hubbard model has received intense scrutiny. Here we demonstrate a frustration-induced transition from Neel antiferromagnetism to a spin-singlet state in the interacting 1/4 -filled band on an anisotropic triangular lattice. While the antiferromagnetic state has equal charge densities, 0.5, on all sites, the spin-singlet state is a paired-electron crystal, with pairs of charge-rich sites separated by pairs of charge-poor sites. The paired-electron crystal provides a natural description of the spin-gapped state proximate to superconductivity in many organic charge transfer solids. Pressure-induced superconductivity in these correlated-electron systems is likely a result of a transition from the 1/4 -filled band valence bond solid to a valence bond liquid. (fast track communication)

  7. Simulation of Band Diagram for Chemical-Vapor-Deposition Diamond Surface Conductivity

    Science.gov (United States)

    Kono, Shozo; Koide, Yasuo

    2005-12-01

    One-dimensional energy band simulation has been performed in order to understand chemical-vapor-deposition (CVD) diamond surface conductivity. It was found that the presence of shallow-level acceptors in the subsurface region and defect states at the surface causes a steep rise in the valence band toward the Fermi level, which causes accumulation of holes in the valence band in the subsurface and near-surface regions. An artificial negative charge accumulation (NCA) layer is introduced in the simulation to examine the effect of possible negatively charged adsorbates on surface conductivity. By adjusting the thickness of NCA layers, we have reproduced quantitatively both the surface conductivity change and Fermi-level change found in previous experiments [Kono et al.: Diamond Relat. Mater. 14 (2005) 459; Riedel et al.: ibid. 13 (2004) 746].

  8. Experimental and theoretical studies of band gap alignment in GaAs1?xBix/GaAs quantum wells

    International Nuclear Information System (INIS)

    Band gap alignment in GaAs1?xBix/GaAs quantum wells (QWs) was studied experimentally by photoreflectance (PR) and theoretically, ab initio, within the density functional theory in which the supercell based calculations are combined with the alchemical mixing approximation applied to a single atom in a supercell. In PR spectra, the optical transitions related to the excited states in the QW (i.e., the transition between the second heavy-hole and the second electron subband) were clearly observed in addition to the ground state QW transition and the GaAs barrier transition. This observation is clear experimental evidence that this is a type I QW with a deep quantum confinement in the conduction and valence bands. From the comparison of PR data with calculations of optical transitions in GaAs1?xBix/GaAs QW performed for various band gap alignments, the best agreement between experimental data and theoretical calculations has been found for the valence band offset of 52?±?5%. A very similar valence band offset was obtained from ab initio calculations. These calculations show that the incorporation of Bi atoms into GaAs host modifies both the conduction and the valence band. For GaAs1?xBix with 0?band shifts lineary at a rate of ?33?meV per % Bi, which only slightly decreases with Bi concentration. Whereas the valance band shift is clearly non-linear. Reducing initially at a rate of ?51?meV per % Bi for low concentrations of Bi and then at a significantly reduced rate of ?20?meV per % Bi near the end of the studied composition range. The overall reduction rate of the band gap is parabolic and the reduction rates change from ?84 to ?53?meV per % Bi for lower and higher Bi concentrations, respectively. The calculated shifts of valence and conduction bands give the variation of valence (conduction) band offset between GaAs1?xBix and GaAs in the range of ?60%–40% (?40%–60%), which is in good agreement with our conclusion derived from PR measurements

  9. Theoretical Magnon Dispersion Curves for Gd

    DEFF Research Database (Denmark)

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

    1975-01-01

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

  10. Detangling Flat Bands into Fano Lattices

    CERN Document Server

    Flach, Sergej; Bodyfelt, Joshua D; Matthies, P; Desyatnikov, Anton S

    2013-01-01

    Macroscopically degenerate flat bands (FB) in periodic lattices host compact localized states which appear due to destructive interference and local symmetry. Interference provides a deep connection between the existence of flat band states (FBS) and the appearance of Fano resonances for wave propagation. We introduce generic transformations detangling FBS and dispersive states into lattices of Fano defects. Inverting the transformation, we generate a continuum of FB models. Our procedure allows us to systematically treat perturbations such as disorder and explain the emergence of energy-dependent localization length scaling in terms of Fano resonances.

  11. 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

  12. Band-engineered SrTiO{sub 3} nanowires for visible light photocatalysis

    Energy Technology Data Exchange (ETDEWEB)

    Fu, Q.; He, T.; Li, J. L.; Yang, G. W. [State Key Laboratory of Optoelectronic Materials and Technologies, Institute of Optoelectronic and Functional Composite Materials, Nanotechnology Research Center, School of Physics and Engineering, Sun Yat-sen University, Guangzhou 510275, Guangdong (China)

    2012-11-15

    We have theoretically investigated the structural, electronic, and optical properties of perovskite SrTiO{sub 3} nanowires for use in visible light photocatalytic applications using pseudopotential density-functional theory calculations. The electronic structure calculations show that the band gap is modified in the SrTiO{sub 3} nanowires compared with that of the bulk. For TiO{sub 2}-terminated nanowires, the mid-band states induced by the combination of oxygen and strontium atoms on the surface lead to a shift in the valence band toward the conduction band without interference from the edge of the conduction band, which reduces the band gap. On the contrary, the electronic states induced by the combination of oxygen and strontium atoms on the surface of SrO-terminated nanowires lead to a shift in the conduction band toward the valence band. The calculated optical results indicate that the absorption edge of the nanowires shift towards the red-light region. These theoretical results suggest that perovskite SrTiO{sub 3} nanowires are promising candidates for use in visible light photocatalytic processes such as solar-assisted water splitting reactions.

  13. Colloidal Nanoparticles for Intermediate Band Solar Cells

    Science.gov (United States)

    Voros, Marton; Galli, Giulia; Zimanyi, Gergely

    2015-03-01

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

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

    OpenAIRE

    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 be manipulated factorially. False memories increased with age for unpresented semantic associates of word lists, and net accuracy (the ratio of true...

  15. A Time-Based Account of the Perception of Odor Objects and Valences

    OpenAIRE

    Olofsson, Jonas K.; Bowman, Nicholas E.; Khatibi, Katherine; Gottfried, Jay A.

    2012-01-01

    Is human odor perception guided by memory or emotion? Object-centered accounts predict that recognition of unique odor qualities precedes valence decoding. Valence-centered accounts predict the opposite: that stimulus-driven valence responses precede and guide identification. In a speeded response time study, participants smelled paired odors, presented sequentially, and indicated whether the second odor in each pair belonged to the same category as the first (object evaluation task) or wheth...

  16. Competition between phase separation and "classical" intermediate valence in an exactly solved model

    OpenAIRE

    Chung, Woonki; Freericks, J. K.

    1999-01-01

    The exact solution of the spin-1/2 Falicov-Kimball model on an infinite-coordination Bethe lattice is analyzed in the regime of ``classical'' intermediate valence. We find (i) either phase separation or a direct metal-insulator transition preclude intermediate valence over a large portion of the phase diagram and (ii) within the intermediate valence phase, only continuous transitions are found as functions of the localized f-electron energy or temperature.

  17. Effect of low-temperature annealing on the electronic- and band-structures of (Ga,Mn)As epitaxial layers

    International Nuclear Information System (INIS)

    The effect of outdiffusion of Mn interstitials from (Ga,Mn)As epitaxial layers, caused by post-growth low-temperature annealing, on their electronic- and band-structure properties has been investigated by modulation photoreflectance (PR) spectroscopy. The annealing-induced changes in structural and magnetic properties of the layers were examined with high-resolution X-ray diffractometry and superconducting quantum interference device magnetometry, respectively. They confirmed an outdiffusion of Mn interstitials from the layers and an enhancement in their hole concentration, which were more efficient for the layer covered with a Sb cap acting as a sink for diffusing Mn interstitials. The PR results demonstrating a decrease in the band-gap-transition energy in the as-grown (Ga,Mn)As layers, with respect to that in the reference GaAs one, are interpreted by assuming a merging of the Mn-related impurity band with the GaAs valence band. Whereas an increase in the band-gap-transition energy caused by the annealing treatment of the (Ga,Mn)As layers is interpreted as a result of annealing-induced enhancement of the free-hole concentration and the Fermi level location within the valence band. The experimental results are consistent with the valence-band origin of itinerant holes mediating ferromagnetic ordering in (Ga,Mn)As, in agreement with the Zener model for ferromagnetic semiconductors

  18. Autonomic responding to aversive words without conscious valence discrimination.

    Science.gov (United States)

    Silvert, Laetitia; Delplanque, Sylvain; Bouwalerh, Hammou; Verpoort, Charlotte; Sequeira, Henrique

    2004-07-01

    A growing body of data suggests that the emotional dimension of a stimulus can be processed without conscious identification of the stimulus. The arousal system could be activated by unrecognised biologically significant stimuli through simple physical stimulus features related to threat, without any evaluation of the meaning of the stimulus. However, unconscious processing of emotionally laden words cannot rely only on perceptual features but must include some analysis of symbolic meaning. The first aim of the present study was to assess whether masked (unrecognised) aversive words can elicit enhanced skin conductance responses (SCRs), a major autonomic index of emotional arousal, in normal participants. Our second aim was to determine whether any autonomic activation related to affective value of words is independent from access of this value to consciousness. Thus, the presentation duration of masked aversive and neutral words was determined, for each participant, in such a way that (1) identification was precluded, (2) valence discrimination was at chance, as indicated by performance in a forced-choice two-alternative task and by confidence ratings of the responses, and (3) emotional and neutral words were not detected differentially. SCRs were recorded during masked and unmasked presentations of both types of word. SCRs elicited by unmasked words, and also by masked words, were of greater magnitude when the words were emotional than when they were neutral. Consequently, in normal participants, autonomic activation can be a discriminative marker of the affective dimension of unrecognised verbal material in the absence of conscious valence identification. PMID:15210291

  19. Intracranial markers of emotional valence processing and judgments in music.

    Science.gov (United States)

    Omigie, Diana; Dellacherie, Delphine; Hasboun, Dominique; Clément, Sylvain; Baulac, Michel; Adam, Claude; Samson, Séverine

    2015-01-01

    The involvement of the amygdala and orbitofrontal cortex in the processing of valenced stimuli is well established. However, less is known about the extent to which activity in these regions reflects a stimulus' physical properties, the individual subjective experience it evokes, or both. We recorded cortical electrical activity from five epileptic patients implanted with depth electrodes for presurgical evaluation while they rated "consonant" and "dissonant" musical chords using a "pleasantness" scale. We compared the pattern of responses in the amygdala and orbitofrontal cortex when trials were sorted by pleasantness judgments relative to when they were sorted by the acoustic properties known to influence emotional reactions to musical chords. This revealed earlier differential activity in the amygdala in the physical properties-based, relative to in the judgment-based, analyses. Thus, our results demonstrate that the amygdala has, first and foremost, a high initial sensitivity to the physical properties of valenced stimuli. The finding that differentiations in the amygdala based on pleasantness ratings had a longer latency suggests that in this structure, mediation of emotional judgment follows accumulation of sensory information. This is in contrast to the orbitofrontal cortex where sensitivity to sensory information did not precede differentiation based on affective judgments. PMID:25496511

  20. Valence orbital method of calculating harmonic emission from diatomic molecule

    International Nuclear Information System (INIS)

    We present a valence orbital method of calculating high-order harmonic generation from a diatomic molecule with arbitrary orientation by using a space rotation operator. We evaluate the effects of each valence orbital on harmonic emissions from N2 and O2 molecules in detail separately. The calculation results confirm the different properties of harmonic yields from N2 and O2 molecules which are well consistent with available experimental data. We observe that due to the orientation dependence of ? and ? orbitals, the bonding orbital (?2pz)2 of N2 determines the maximum of harmonic emission when the molecular axis of N2 is aligned parallel to the laser vector, and the magnitude of the high harmonic signal gradually weakens with the orientation angle of molecular axis increasing. But for O2 molecule the antibonding orbitals (?*2py)1 and (?*2pz)1 contribute to the maximum of harmonic yield when O2 is aligned at 45° and bonding orbitals (?*2py)2 and (?*2pz)2 slightly influence the orientation angle of maximum of harmonic radiation not exactly at 45°. (atomic and molecular physics)

  1. Valency states of radioactive antimony in hydrochloric acid solutions

    International Nuclear Information System (INIS)

    Variations of 125Sb valency states in HCl solutions were investi.o.ated by the use of the N-benzoyl-N-phenyl-hydroxylamine (BPHA) extraction method. In hydrochloric acid solutions valency states of 125Sb are converted between trivalent and pentavalent states by the effects of their own radiations (extremely promoted by irradiation with the natural light) and chloride ions. For the preparation of 125Sb(III) from 125Sb(V) a refluxing method was found to be simple and easy. The 125Sb(III) thus obtained can be safely stored in a brown bottle as a 6M HCl solution. For the preparation of 125Sb(V) from 125Sb(III) the UV irradiation method was found to be useful. The more simple method, which is to expose rather the high activity sample to light, might be more easy and useful. The 125Sb(V) thus obtained can safely be stored in a brown bottle as a 6M HCl solution. (T.G.)

  2. Optical properties of chalcopyrite-type intermediate transition metal band materials from first principles

    OpenAIRE

    Aguilera Bonet, Irene; Palacios Clemente, Pablo; Wahnón Benarroch, Perla

    2008-01-01

    The optical properties of a novel potential high-efficiency photovoltaic material have been studied. This material is based on a chalcopyrite-type semiconductor (CuGaS2) with some Ga atom substituted by Ti and is characterized by the formation of an isolated transition-metal band between the valence band and the conduction band. We present a study in which ab-initio density functional theory calculations within the generalized gradient approximation are carried out to determine the optical re...

  3. Valence-electronic effect on low-temperature phase stability of the omega phase

    International Nuclear Information System (INIS)

    Low-temperature phase stability of the omega phase of BCC binary Ti alloys and Zr alloys has been expected qualitatively by first-principles population analysis of the molecular orbitals. The analysis was performed using the cluster models with 3d or 4d transition elements for binary-alloying. The results show that the positive overlap population in the valence band tends to shift downward along the energy axis as the e/a ratio is increased. This tendency implies no electronic contribution to the stability of the Zr-Ti system, having the minimum ratio, 4. To confirm this expectation, electron diffraction was carried out on single-crystal Zr-50 at.% Ti, and also Ti-24 mass% V used as the reference. The superlattice reflections of the omega phase, given by the BCC reduced wavevector q (2/3+?,2/3+?,2/3+?), were observed at ?100 K and room temperature. The results indicate that temperature dependence of the intensity distribution of the Zr alloy is much less significant than that of the Ti alloy. The x-ray diffraction measurements were also done on single-crystal Zr-30 at.% Ti, -35 at.% Ti, -50 at.% Ti to double check the temperature dependence. The results provide a feature which is quite similar to that obtained by the electron diffraction. All experimental results are found consistent with those of the population analysis

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2008-05-15

    Combining old and new de Haas-van Alphen (dHvA) and magnetoresistance data, we arrive at a detailed picture of the Fermi surface of the heavy fermion superconductor UPt{sub 3}. Our work was partially motivated by a new proposal that two 5f valence electrons per formula unit in UPt{sub 3} are localized by correlation effects-agreement with previous dHvA measurements of the Fermi surface was invoked in its support. Comprehensive comparison with our new observations shows that this 'partially localized' model fails to predict the existence of a major sheet of the Fermi surface, and is therefore less compatible with experiment than the originally proposed 'fully itinerant' model of the electronic structure of UPt{sub 3}. In support of this conclusion, we offer a more complete analysis of the fully itinerant band structure calculation, where we find a number of previously unrecognized extremal orbits on the Fermi surface.

  5. Photonic band gap materials

    International Nuclear Information System (INIS)

    An overview of the theoretical and experimental efforts in obtaining a photonic band gap, a frequency band in three-dimensional dielectric structures in which electromagnetic waves are forbidden, is presented

  6. High resolution electron momentum spectroscopy of the valence orbitals of water

    International Nuclear Information System (INIS)

    The development of a third-generation electron momentum spectrometer with significantly improved energy and momentum resolutions at Tsinghua University (?E = 0.45-0.68 eV, ?? = ±0.53o and ?? = ±0.84o) has enabled a reinvestigation of the valence orbital electron momentum distributions of H2O with improved statistical accuracy. The measurements have been conducted at impact energies of 1200 eV and 2400 eV in order to check the validity of the plane wave impulse approximation. The obtained ionization spectra and electron momentum distributions have been compared with the results of computations carried out with Hartree Fock [HF] theory, density functional theory in conjunction with the standard B3LYP functional, one-particle Green's function [1p-GF] theory along with the third-order algebraic diagrammatic construction scheme [ADC(3)], symmetry adapted cluster configuration interaction [SAC-CI] theory, and a variety of multi-reference [MR-SDCI, MR-RSPT2, MR-RSPT3] theories. The influence of the basis set on the computed momentum distributions has been investigated further, using a variety of basis sets ranging from 6-31G to the almost complete d-aug-cc-pV6Z basis set. A main issue in the present work pertains to a shake-up band of very weak intensity at 27.1 eV, of which the related momentum distribution was analyzed for the first time. The experimental evidences and the most thorough theoretical calculations demonstrate that this band borrows its ionization intensity from the 2a1 orbital

  7. High resolution electron momentum spectroscopy of the valence orbitals of water

    Energy Technology Data Exchange (ETDEWEB)

    Ning, C.G. [Department of Physics and Key Laboratory of Atomic and Molecular NanoSciences of MOE, Tsinghua University, Beijing 100084 (China); Hajgato, B. [Research Group of Theoretical Chemistry, Department SBG, Hasselt University, Agoralaan Gebouw D, B-3590 Diepenbeek (Belgium); Huang, Y.R. [Department of Physics and Key Laboratory of Atomic and Molecular NanoSciences of MOE, Tsinghua University, Beijing 100084 (China); Research Group of Theoretical Chemistry, Department SBG, Hasselt University, Agoralaan Gebouw D, B-3590 Diepenbeek (Belgium); Zhang, S.F.; Liu, K.; Luo, Z.H. [Department of Physics and Key Laboratory of Atomic and Molecular NanoSciences of MOE, Tsinghua University, Beijing 100084 (China); Knippenberg, S. [Research Group of Theoretical Chemistry, Department SBG, Hasselt University, Agoralaan Gebouw D, B-3590 Diepenbeek (Belgium); Deng, J.K. [Department of Physics and Key Laboratory of Atomic and Molecular NanoSciences of MOE, Tsinghua University, Beijing 100084 (China)], E-mail: djk-dmp@tsinghua.edu.cn; Deleuze, M.S. [Research Group of Theoretical Chemistry, Department SBG, Hasselt University, Agoralaan Gebouw D, B-3590 Diepenbeek (Belgium)], E-mail: michael.deleuze@uhasselt.be

    2008-01-22

    The development of a third-generation electron momentum spectrometer with significantly improved energy and momentum resolutions at Tsinghua University ({delta}E = 0.45-0.68 eV, {delta}{theta} = {+-}0.53{sup o} and {delta}{phi} = {+-}0.84{sup o}) has enabled a reinvestigation of the valence orbital electron momentum distributions of H{sub 2}O with improved statistical accuracy. The measurements have been conducted at impact energies of 1200 eV and 2400 eV in order to check the validity of the plane wave impulse approximation. The obtained ionization spectra and electron momentum distributions have been compared with the results of computations carried out with Hartree Fock [HF] theory, density functional theory in conjunction with the standard B3LYP functional, one-particle Green's function [1p-GF] theory along with the third-order algebraic diagrammatic construction scheme [ADC(3)], symmetry adapted cluster configuration interaction [SAC-CI] theory, and a variety of multi-reference [MR-SDCI, MR-RSPT2, MR-RSPT3] theories. The influence of the basis set on the computed momentum distributions has been investigated further, using a variety of basis sets ranging from 6-31G to the almost complete d-aug-cc-pV6Z basis set. A main issue in the present work pertains to a shake-up band of very weak intensity at 27.1 eV, of which the related momentum distribution was analyzed for the first time. The experimental evidences and the most thorough theoretical calculations demonstrate that this band borrows its ionization intensity from the 2a{sub 1} orbital.

  8. Interfacial chemical bonding state and band alignment of CaF2/hydrogen-terminated diamond heterojunction

    International Nuclear Information System (INIS)

    CaF2 films are deposited on hydrogen-terminated diamond (H-diamond) by a radio-frequency sputter-deposition technique at room temperature. Interfacial chemical bonding state and band alignment of CaF2/H-diamond heterojunction are investigated by X-ray photoelectron spectroscopy. It is confirmed that there are only C-Ca bonds at the CaF2/H-diamond heterointerface. Valence and conductance band offsets of the CaF2/H-diamond heterojunciton are determined to be 3.7 ± 0.2 and 0.3 ± 0.2 eV, respectively. It shows a type I straddling band configuration. The large valence band offset suggests advantage of the CaF2/H-diamond heterojunciton for the development of high power and high frequency field effect transistors.

  9. Single layer lead iodide: computational exploration of structural, electronic and optical properties, strain induced band modulation and the role of spin-orbital-coupling

    Science.gov (United States)

    Zhou, Mei; Duan, Wenhui; Chen, Ying; Du, Aijun

    2015-09-01

    Graphitic like layered materials exhibit intriguing electronic structures and thus the search for new types of two-dimensional (2D) monolayer materials is of great interest for developing novel nano-devices. By using density functional theory (DFT) method, here we for the first time investigate the structure, stability, electronic and optical properties of monolayer lead iodide (PbI2). The stability of PbI2 monolayer is first confirmed by phonon dispersion calculation. Compared to the calculation using generalized gradient approximation, screened hybrid functional and spin-orbit coupling effects can not only predicts an accurate bandgap (2.63 eV), but also the correct position of valence and conduction band edges. The biaxial strain can tune its bandgap size in a wide range from 1 eV to 3 eV, which can be understood by the strain induced uniformly change of electric field between Pb and I atomic layer. The calculated imaginary part of the dielectric function of 2D graphene/PbI2 van der Waals type hetero-structure shows significant red shift of absorption edge compared to that of a pure monolayer PbI2. Our findings highlight a new interesting 2D material with potential applications in nanoelectronics and optoelectronics.Graphitic like layered materials exhibit intriguing electronic structures and thus the search for new types of two-dimensional (2D) monolayer materials is of great interest for developing novel nano-devices. By using density functional theory (DFT) method, here we for the first time investigate the structure, stability, electronic and optical properties of monolayer lead iodide (PbI2). The stability of PbI2 monolayer is first confirmed by phonon dispersion calculation. Compared to the calculation using generalized gradient approximation, screened hybrid functional and spin-orbit coupling effects can not only predicts an accurate bandgap (2.63 eV), but also the correct position of valence and conduction band edges. The biaxial strain can tune its bandgap size in a wide range from 1 eV to 3 eV, which can be understood by the strain induced uniformly change of electric field between Pb and I atomic layer. The calculated imaginary part of the dielectric function of 2D graphene/PbI2 van der Waals type hetero-structure shows significant red shift of absorption edge compared to that of a pure monolayer PbI2. Our findings highlight a new interesting 2D material with potential applications in nanoelectronics and optoelectronics. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr04431f

  10. Electron Hopping through Double-Exchange Coupling in a Mixed-Valence Diiminobenzoquinone-Bridged Fe2 Complex.

    Science.gov (United States)

    Gaudette, Alexandra I; Jeon, Ie-Rang; Anderson, John S; Grandjean, Fernande; Long, Gary J; Harris, T David

    2015-10-01

    The ability of a benzoquinonoid bridging ligand to mediate double-exchange coupling in a mixed-valence Fe2 complex is demonstrated. Metalation of the bridging ligand 2,5-di(2,6-dimethylanilino)-3,6-dibromo-1,4-benzoquinone (LH2) with Fe(II) in the presence of the capping ligand tris((6-methyl-2-pyridyl)methyl)amine (Me3TPyA) affords the dinuclear complex [(Me3TPyA)2Fe(II)2(L)](2+). The dc magnetic measurements, in conjunction with X-ray diffraction and Mössbauer spectroscopy, reveal the presence of weak ferromagnetic superexchange coupling between Fe(II) centers through the diamagnetic bridging ligand to give an S = 4 ground state. The ac magnetic susceptibility measurements, collected in a small dc field, show this complex to behave as a single-molecule magnet with a relaxation barrier of Ueff = 14(1) cm(-1). The slow magnetic relaxation in the Fe(II)2 complex can be switched off through one-electron oxidation to the mixed-valence congener [(Me3TPyA)2Fe2(L)](3+), where X-ray diffraction and Mössbauer spectroscopy indicate a metal-centered oxidation. The dc magnetic measurements show an S = (9)/2 ground state for the mixed-valence complex, stemming from strong ferromagnetic exchange coupling that is best described considering electron hopping through a double-exchange coupling mechanism, with a double-exchange parameter of B = 69(4) cm(-1). In accordance with double-exchange, an intense feature is observed in the near-infrared region and is assigned as an intervalence charge-transfer band. The rate of intervalence electron hopping is comparable to that of the Mössbauer time scale, such that variable-temperature Mössbauer spectra reveal a thermally activated transition from a valence-trapped to detrapped state and provide an activation energy for electron hopping of 63(8) cm(-1). These results demonstrate the ability of quinonoid ligands to mediate electron hopping between high-spin metal centers, by providing the first example of an Fe complex that exhibits double-exchange through an organic bridging ligand and the largest metal-metal separation yet observed in any metal complex with double-exchange coupling. PMID:26375161

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

    International Nuclear Information System (INIS)

    This report summarizes a 12-year program of various kinds of synchrotron spectroscopies directed at the electronic structures of narrow band and low-dimensional materials that display correlated electron behaviors such as metal-insulator transitions, mixed valence, superconductivity, Kondo moment quenching, heavy Fermions, and non-Fermi liquid properties

  12. 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.)

  13. Dispersion relations in heavily-doped nanostructures

    CERN Document Server

    Ghatak, Kamakhya Prasad

    2016-01-01

    This book presents the dispersion relation in heavily doped nano-structures. The materials considered are III-V, II-VI, IV-VI, GaP, Ge, Platinum Antimonide, stressed, GaSb, Te, II-V, HgTe/CdTe superlattices and Bismuth Telluride semiconductors. The dispersion relation is discussed under magnetic quantization and on the basis of carrier energy spectra. The influences of magnetic field, magneto inversion, and magneto nipi structures on nano-structures is analyzed. The band structure of optoelectronic materials changes with photo-excitation in a fundamental way according to newly formulated electron dispersion laws. They control the quantum effect in optoelectronic devices in the presence of light. The measurement of band gaps in optoelectronic materials in the presence of external photo-excitation is displayed. The influences of magnetic quantization, crossed electric and quantizing fields, intense electric fields on the on the dispersion relation in heavily doped semiconductors and super-lattices are also disc...

  14. A model for the direct-to-indirect band-gap transition in monolayer MoSe2 under strain

    Indian Academy of Sciences (India)

    Ruma Das; Priya Mahadevan

    2015-06-01

    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 point to point. An analysis of the charge density reveals that while Mo–Mo interactions contribute to the VBM at 0% strain, Mo–Se interactions contribute to the highest occupied band at point. A scaling of the hopping interaction strengths within an appropriate tight binding model can capture the transition.

  15. Electronic properties of ZnWO{sub 4} based on ab initio FP-LAPW band-structure calculations and X-ray spectroscopy data

    Energy Technology Data Exchange (ETDEWEB)

    Khyzhun, O.Y., E-mail: khyzhun@ipms.kiev.ua [Frantsevych Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, 3 Krzhyzhanivsky Street, Kyiv UA-03142 (Ukraine); Bekenev, V.L. [Frantsevych Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, 3 Krzhyzhanivsky Street, Kyiv UA-03142 (Ukraine); Atuchin, V.V. [Laboratory of Optical Materials and Structures, Institute of Semiconductor Physics, SB RAS, Novosibirsk 630090 (Russian Federation); Galashov, E.N.; Shlegel, V.N. [Nikolaev Institute of Inorganic Chemistry, SB RAS, Novosibirsk 630090 (Russian Federation)

    2013-07-15

    Total and partial densities of states of the atoms constituting zinc tungstate, ZnWO{sub 4}, have been calculated using the ab initio full potential linearized augmented plane wave (FP-LAPW) method. The theoretical data reveal that main contributors in the valence band of ZnWO{sub 4} are the Zn 3d-, W 5d- and O 2p-like states: the Zn 3d- and W 5d-like states contribute mainly at the bottom, whilst the O 2p-like states at the top of the valence band, with also significant portions of contributions of the above states throughout the whole valence-band region of the tungstate under study. In addition, data of our band-structure FP-LAPW calculations indicate that the conduction band of ZnWO{sub 4} is dominated by contributions of the W 5d-like states. To verify the theoretical findings, high-quality inclusion-free ZnWO{sub 4} single crystals were specially grown along the [010] direction for the present experimental studies employing the low thermal gradient Czochralski technique. It has been established that, comparison on a common energy scale of the X-ray photoelectron valence-band spectrum and the X-ray emission bands representing the energy distribution of mainly the Zn 3d-, W 5d- and O 2p-like states of ZnWO{sub 4} confirm experimentally the present FP-LAPW theoretical data regarding the occupations of the valence band of zinc tungstate. - Graphical abstract: Display Omitted - Highlights: • Total and partial densities of states of the atoms constituting ZnWO{sub 4} are calculated. • Zn 3d and W 5d states are dominant contributors at the bottom of the valence band. • Contributions of O 2p states dominate at the top of the valence band. • Bottom of the conduction band is dominated by contributions of W 5d* states. • The theoretical results are confirmed experimentally by X-ray spectroscopy data.

  16. Trivial and inverted Dirac bands, and emergence of quantum spin Hall states in graphene on transition-metal dichalcogenides

    OpenAIRE

    Gmitra, Martin; Kochan, Denis; Högl, Petra; Fabian, Jaroslav

    2015-01-01

    Proximity orbital and spin-orbital effects of graphene on monolayer transition-metal dichalcogenides (TMDCs) are investigated from first-principles. The Dirac band structure of graphene is found to lie within the semiconducting gap of TMDCs for sulfides and selenides, while it merges with the valence band for tellurides. In the former case the proximity-induced staggered potential gaps and spin-orbit couplings (all on the meV scale) of the Dirac electrons are established by ...

  17. Direct measurement of band offset at the interface between CdS and Cu2ZnSnS4 using hard X-ray photoelectron spectroscopy

    International Nuclear Information System (INIS)

    We directly and non-destructively measured the valence band offset at the interface between CdS and Cu2ZnSnS4 (CZTS) using hard X-ray photoelectron spectroscopy (HAXPES), which can measure the electron state of the buried interface because of its large analysis depth. These measurements were made using the following real devices; CZTS(t = 700 nm), CdS(t = 100 nm)/CZTS(t = 700 nm), and CdS(t = 5 nm)/CZTS(t = 700 nm) films formed on Mo coated glass. The valence band spectra were measured by HAXPES using an X-ray photon energy of 8 keV. The value of the valence band offset at the interface between CdS and CZTS was estimated as 1.0 eV by fitting the spectra. The conduction band offset could be deduced as 0.0 eV from the obtained valence band offset and the band gap energies of CdS and CZTS

  18. Variation of rotational content in E(21+) with valence nucleon pairs and correlation with B(E2)? and E(0?+)

    Science.gov (United States)

    Gupta, J. B.; Kavathekar, A. K.

    1997-12-01

    Treating the energy of the 21+ state in even Z- even N nuclei as a sum of rotational energy (ROTE) and vibrational energy (VIBE), the evolution of the shape transition with the increase in the valence nucleon pairs product (Np Nn) is studied via the variation of ROTE/E(21+). The correspondence of relative ROTE, B(E2)? and (?def/?s.p.) values vs. the Np Nn product is illustrated. A correlation of the Rotation-Vibration interaction constant in the ground band levels with the 0?+ energy is also derived. Comparison is made with variable moment of inertia model expressions.

  19. Dispersant field monitoring procedures

    International Nuclear Information System (INIS)

    Alyeska Pipeline Service Company's (APSC) dispersant response capability in the Port of Valdez, Prince William Sound, and in the Gulf of Alaska was described. APSC provides dispersal equipment, aerial spray delivery systems, helibucket delivery systems, vessel delivery systems, along with a minimum of 600,000 gallon stockpile of the dispersant Corexit 9527. Effectiveness and effects are monitored by visual observation. In addition, fluorometer and water sample analysis are also used to provide field analytical data indicative of the environmental effects of dispersant applications. The field monitoring plan was field tested in December 1996. Details of the monitoring procedures are outlined in this paper. 18 refs., 5 tabs

  20. Valence fluctuations and electric reconstruction in the extended Anderson model on the two-dimensional Penrose lattice

    Science.gov (United States)

    Takemura, Shinichi; Takemori, Nayuta; Koga, Akihisa

    2015-04-01

    We study the extended Anderson model on the two-dimensional Penrose lattice, combining the real-space dynamical mean-field theory with the noncrossing approximation. It is found that the Coulomb repulsion between localized and conduction electrons does not induce a valence transition, but the crossover between the Kondo and mixed valence states is in contrast to the conventional periodic system. In the mixed-valence region close to the crossover, nontrivial valence distributions appear, characteristic of the Penrose lattice, demonstrating that the mixed-valence state coexists with local Kondo states in certain sites. The electric reconstruction in the mixed valence region is also addressed.

  1. The valence-fluctuating ground state of plutonium

    Science.gov (United States)

    Janoschek, Marc; Das, Pinaki; Chakrabarti, Bismayan; Abernathy, Douglas L.; Lumsden, Mark D.; Lawrence, John M.; Thompson, Joe D.; Lander, Gerard H.; Mitchell, Jeremy N.; Richmond, Scott; Ramos, Mike; Trouw, Frans; Zhu, Jian-Xin; Haule, Kristjan; Kotliar, Gabriel; Bauer, Eric D.

    2015-01-01

    A central issue in material science is to obtain understanding of the electronic correlations that control complex materials. Such electronic correlations frequently arise because of the competition of localized and itinerant electronic degrees of freedom. Although the respective limits of well-localized or entirely itinerant ground states are well understood, the intermediate regime that controls the functional properties of complex materials continues to challenge theoretical understanding. We have used neutron spectroscopy to investigate plutonium, which is a prototypical material at the brink between bonding and nonbonding configurations. Our study reveals that the ground state of plutonium is governed by valence fluctuations, that is, a quantum mechanical superposition of localized and itinerant electronic configurations as recently predicted by dynamical mean field theory. Our results not only resolve the long-standing controversy between experiment and theory on plutonium’s magnetism but also suggest an improved understanding of the effects of such electronic dichotomy in complex materials.

  2. Valence framing of political preferences and resistance to persuasion

    Directory of Open Access Journals (Sweden)

    Žeželj Iris

    2007-01-01

    Full Text Available This study tested the "valence framing effect": an assumption that negatively conceptualized attitudes (as opposing the non-preferred alternative are more resistant to later persuasion attempts. In the experiment we created choice between two political candidates and experimental subjects were led to conceptualize their political preferences in one of two possible ways: either as supporting the preferred candidate or as opposing the non-preferred candidate. The data indicate that negative preferences show less overall change when exposed to counterarguments. This finding can be incorporated in two theoretical frameworks: dual process theories of attitude change (Elaboration likelihood model and descriptive decision making theories (Prospect theory. Results are discussed for their implications for the efficacy of political communication. .

  3. Entanglement in resonating valence bond states: ladder versus isotropic lattices

    Energy Technology Data Exchange (ETDEWEB)

    Dhar, Himadri Shekhar; Sen, Aditi, E-mail: aditi@hri.res.in [School of Physical Sciences, Jawaharlal Nehru University, New Delhi 110067 (India)

    2011-11-18

    We study the behavior of bipartite, as well as genuine multipartite, entanglement of a resonating valence bond state on a ladder. Although there is negligible bipartite entanglement (BE) present in the rails, as is the case for isotropic lattices in two and higher dimensions, we show that the system possesses significant amounts of BE in the steps of the ladder. However, we find that the genuine multipartite entanglement in the system is substantially low. Therefore, both the properties of bipartite as well as multipartite entanglement in the ladder are contrary to the behavior of entanglement in isotropic lattices, indicating that the geometry of the lattice can play a significant role in quantum information processing tasks. Our results also indicate that numerical and analytical investigations obtained on ladders cannot infer the same on two-dimensional lattices. (paper)

  4. Exploring covalently bonded diamondoid particles with valence photoelectron spectroscopy

    CERN Document Server

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

    2013-01-01

    We investigated the electronic structures of diamondoid particles in the gas phase, utilizing valence photoelectron spectroscopy. The samples were singly or doubly covalently bonded dimers or trimers of the lower diamondoids. Both bond type and the combination of the bonding partners affect the overall electronic structures. For singly bonded particles we observe a small impact of the bond type on the electronic structure, whereas for doubly bonded particles the connecting bond is the deciding factor, determining the electronic structure of the uppermost occupied orbitals. In the singly bonded particles a superposition of the bonding partner orbitals determines the overall electronic structure. The strength of quantum confinement effects, i.e., the localization of electrons, depends on the bonding partner orbital energy difference. The experimental findings correspond well to density functional theory computations.

  5. Time delay in valence shell photoionization of noble gas atoms

    CERN Document Server

    Kheifets, A S

    2013-01-01

    We use the non-relativistic random phase approximation with exchange to perform calculations of valence shell photoionization of Ne, Ar, Kr and Xe from their respective thresholds to photon energy of 200 eV. The energy derivative of the complex phase of the photoionization matrix elements is converted to the photoelectron group delay that can be measured in attosecond streaking or two-photon transitions interference experiments. Comparison with reported time delay measurements in Ne and Ar at a few selected photon energies is made. Systematic mapping of time delay across a wide range of photon energies in several atomic targets allows to highlight important aspects of fundamental atomic physics that can be probed by attosecond time delay measurements.

  6. Valence-shell photoionization of chlorine-like Ar$^{+}$ ions

    CERN Document Server

    Covington, A M; Covington, I R; Hinojosa, G; Shirley, C A; Álvarez, I; Cisneros, C; Dominguez-Lopez, I; Sant'Anna, M M; Schlachter, A S; Ballance, C P; McLaughlin, B M

    2012-01-01

    Absolute cross-section measurements for valence-shell photoionization of Ar$^{+}$ ions are reported for photon energies ranging from 27.4 eV to 60.0 eV. The data, taken by merging beams of ions and synchrotron radiation at a photon energy resolution of 10 meV, indicate that the primary ion beam was a statistically weighted mixture of the $^2P^o_{3/2}$ ground state and the $^2P^o_{1/2}$ metastable state of Ar$^{+}$. Photoionization of this C$\\ell$-like ion is characterized by multiple Rydberg series of autoionizing resonances superimposed on a direct photoionization continuum. Observed resonance lineshapes indicate interference between indirect and direct photoionization channels. Resonance features are spectroscopically assigned and their energies and quantum defects are tabulated. The measurements are satisfactorily reproduced by theoretical calculations based on an intermediate coupling semi-relativistic Breit-Pauli approximation.

  7. 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.

  8. Error estimate for the valence approximation to lattice QCD

    International Nuclear Information System (INIS)

    A Monte Carlo algorithm is used to calculate msub(N)/msub(rho), msub(?)/msub(rho), msub(q)msub(rho)/msub(?)2, fsub(?)/msub(rho), fsub(rho)/msub(rho) and #betta#sub(mo) for lattice QCD with the number of flavors Nsub(f) of quarks contributing virtual loops given by zero, the valence approximation, and with Nsub(f) chosen, in effect to be -2. The difference between corresponding pairs of quantities with Nsub(f) of zero and Nsub(f) of -2 we take to be an estimate of the difference between the value for a realistic theory with Nsub(f) of +2 and for the approximate theory with Nsub(f) of zero. The changes in mass ratios and #betta#sub(mo) are consistent with zero and typically (20 +- 20)% while decay constant ratios change by as much as (88 +- 24)%. (orig.)

  9. Isotopic exchange in mixed valence compounds in the solid state

    International Nuclear Information System (INIS)

    This work aims at the determination of isotopic exchange kinetics and mechanism in two mixed valence compounds: Cs10(Sbsup(V)Cl6) (Sbsup(III)Cl6)3 and Tl3sup(I)(Tlsup(III)Cl6). The synthesis of the first compound is very difficult because in most of the cases mixtures of chloroantimoniates are obtained. Exchange in Tl4Cl6 labelled on Tlsup(III) is studied in detail by radiochemical analysis and physical techniques: ionic conductivity and positon annihilation. Cation vacancies are easily created in the lattice with formation enthalpy of 0.35 eV and migration enthalpy of 0.52 eV. Isochronic and isothermal exchange curves are described by a kinetic based on species diffusion. Models are given. Exchange is increased by grinding probably because extrinseque defects are introduced

  10. Adsorption mechanism and valency of catechol-functionalized hyperbranched polyglycerols.

    Science.gov (United States)

    Krysiak, Stefanie; Wei, Qiang; Rischka, Klaus; Hartwig, Andreas; Haag, Rainer; Hugel, Thorsten

    2015-01-01

    Nature often serves as a model system for developing new adhesives. In aqueous environments, mussel-inspired adhesives are promising candidates. Understanding the mechanism of the extraordinarily strong adhesive bonds of the catechol group will likely aid in the development of adhesives. With this aim, we study the adhesion of catechol-based adhesives to metal oxides on the molecular level using atomic force microscopy (AFM). The comparison of single catechols (dopamine) with multiple catechols on hyperbranched polyglycerols (hPG) at various pH and dwell times allowed us to further increase our understanding. In particular, we were able to elucidate how to achieve strong bonds of different valency. It was concluded that hyperbranched polyglycerols with added catechol end groups are promising candidates for durable surface coatings. PMID:26150898

  11. Resonating Valence Bond states for low dimensional S=1 antiferromagnets

    Science.gov (United States)

    Liu, Zheng-Xin; Zhou, Yi; Ng, Tai-Kai

    2014-03-01

    We study S = 1 spin liquid states in low dimensions. We show that the resonating-valence-bond (RVB) picture of S = 1 / 2 spin liquid state can be generalized to S = 1 case. For S = 1 system, a many-body singlet (with even site number) can be decomposed into superposition of products of two-body singlets. In other words, the product states of two-body singlets, called the singlet pair states (SPSs), are over complete to span the Hilbert space of many-body singlets. Furthermore, we generalized fermionic representation and the corresponding mean field theory and Gutzwiller projected stats to S = 1 models. We applied our theory to study 1D anti-ferromagnetic bilinear-biquadratic model and show that both the ground states (including the phase transition point) and the excited states can be understood excellently well within the framework. Our method can be applied to 2D S = 1 antiferromagnets.

  12. 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.

  13. Emotion Perception is Valence-Dependent during Binocular Rivalry.

    Science.gov (United States)

    Malek, Nour; Gao, Andy; Messinger, Daniel; Joober, Ridha; Tabbane, Karim; Martinez-Trujillo, Julio

    2015-09-01

    The perceptual strength of a facial expression is widely shaped by context. Binocular rivalry (BR) has proven to be a promising tool in studying face perception. It involves the alternation between two stimuli that are simultaneously, but monocularly, presented. BR is postulated to occur due to inhibitory interactions between neuronal populations tuned for the presented stimuli. Therefore, BR provides a reflection of perceptual strength, whereby shorter stimulus perception (dominance duration) signifies greater inhibition and weaker tuning. We previously demonstrated that, while there may be an interaction between the identity and emotion portrayed by face stimuli during BR, emotion has a stronger influence and thus holds greater perceptual strength. Moreover, positive emotions tend to dominate over negative ones. To assess whether perceptual strength is also dependent on the intensity of an emotion (valence), 3D natural-looking face identities of similar skin tone and gender were created in FaceGen Modeller to express five emotions (very happy, happy, neutral, sad, and very sad) and were set to rival as 29 human subjects reported which stimulus they perceived throughout a trial. Prior BR studies that investigated valence-dependence were confounded by stimuli discrepancies that highlight certain local facial features over others. Here, extreme emotions were portrayed through the use of Duchenne eye constrictions, which permitted control over feature-salience across stimuli. Subjects reported that extreme emotions were perceived for significantly greater dominance durations than basic ones (p 0.11, KS). This verifies that the observed significance using Duchenne characteristics was not driven by the local feature-eye wrinkles, but rather by the global emotion portrayed. Overall, the more intense an emotion, the greater its perceptual strength and possibly the higher its processing priority during BR. Meeting abstract presented at VSS 2015. PMID:26326735

  14. A density functional for core-valence correlation energy.

    Science.gov (United States)

    Ranasinghe, Duminda S; Frisch, Michael J; Petersson, George A

    2015-12-01

    A density functional, ?CV-DFT(?c, ?v), describing the core-valence correlation energy has been constructed as a linear combination of ?LY P (corr)(?c), ?V WN5 (corr)(?c, ?v), ?PBE (corr)(?c, ?v), ?Slater (ex)(?c, ?v), ?HCTH (ex)(?c, ?v), ?HF (ex)(?c, ?v), and FCV-DFTNi,Zi, a function of the nuclear charges. This functional, with 6 adjustable parameters, reproduces (±0.27 kcal/mol rms error) a benchmark set of 194 chemical energy changes including 9 electron affinities, 18 ionization potentials, and 167 total atomization energies covering the first- and second-rows of the periodic table. This is almost twice the rms error (±0.16 kcal/mol) obtained with CCSD(T)/MTsmall calculations, but less than half the rms error (±0.65 kcal/mol) obtained with MP2/GTlargeXP calculations, and somewhat smaller than the rms error (±0.39 kcal/mol) obtained with CCSD/MTsmall calculations. The largest positive and negative errors from ?CV-DFT(?c, ?v) were 0.88 and -0.75 kcal/mol with the set of 194 core-valence energy changes ranging from +3.76 kcal/mol for the total atomization energy of propyne to -9.05 kcal/mol for the double ionization of Mg. Evaluation of the ?CV-DFT(?c, ?v) functional requires less time than a single SCF iteration, and the accuracy is adequate for any model chemistry based on the CCSD(T) level of theory. PMID:26646873

  15. Nanostructured high valence silver oxide produced by pulsed laser deposition

    Energy Technology Data Exchange (ETDEWEB)

    Dellasega, D.; Facibeni, A.; Di Fonzo, F.; Russo, V. [Politecnico di Milano, Dipartimento di Chimica, Materiali e Ingegneria Chimica ' G. Natta' , NEMAS - Center for NanoEngineered MAterials and Surfaces, and IIT-Italian Institute of Technology, Piazza Leonardo da Vinci 32, 20133 Milano (Italy); Conti, C. [ICVBC-CNR, Via Cozzi 54, 20125 Milano (Italy); Ducati, C. [University of Cambridge, Department of Materials Science and Metallurgy, Pembroke Street, Cambridge CB2 3QZ (United Kingdom); Casari, C.S. [Politecnico di Milano, Dipartimento di Chimica, Materiali e Ingegneria Chimica ' G. Natta' , NEMAS - Center for NanoEngineered MAterials and Surfaces, and IIT-Italian Institute of Technology, Piazza Leonardo da Vinci 32, 20133 Milano (Italy); Li Bassi, A. [Politecnico di Milano, Dipartimento di Chimica, Materiali e Ingegneria Chimica ' G. Natta' , NEMAS - Center for NanoEngineered MAterials and Surfaces, and IIT-Italian Institute of Technology, Piazza Leonardo da Vinci 32, 20133 Milano (Italy)], E-mail: andrea.libassi@polimi.it; Bottani, C.E. [Politecnico di Milano, Dipartimento di Chimica, Materiali e Ingegneria Chimica ' G. Natta' , NEMAS - Center for NanoEngineered MAterials and Surfaces, and IIT-Italian Institute of Technology, Piazza Leonardo da Vinci 32, 20133 Milano (Italy)

    2009-03-01

    Among silver oxides, Ag{sub 4}O{sub 4}, i.e. high valence Ag(I)Ag(III) oxide, is interesting for applications in high energy batteries and for the development of antimicrobial coatings. We here show that ns UV pulsed laser deposition (PLD) in an oxygen containing atmosphere allows the synthesis of pure Ag{sub 4}O{sub 4} nanocrystalline thin films, permitting at the same time to control the morphology of the material at the sub-micrometer scale. Ag{sub 4}O{sub 4} films with a crystalline domain size of the order of tens of nm can be deposited provided the deposition pressure is above a threshold (roughly 4 Pa pure O{sub 2} or 20 Pa synthetic air). The formation of this particular high valence silver oxide is explained in terms of the reactions occurring during the expansion of the ablated species in the reactive atmosphere. In particular, expansion of the PLD plasma plume is accompanied by formation of low stability Ag-O dimers and atomic oxygen, providing reactive species at the substrate where the film grows. Evidence of reactive collisions in the expanding ablation plume is obtained by analysis of the plume visible shape in inert and reactive atmospheres. In addition, we show how the dimensionless deposition parameter L, relating the target-to-substrate distance to the ablation plume maximum expansion length, can be used to classify different growth regimes. It is thus possible to vary the stoichiometry and the morphology of the films, from compact and columnar to foam-like, by controlling both the gas pressure and the target-to-substrate distance.

  16. First-principle natural band alignment of GaN / dilute-As GaNAs alloy

    Directory of Open Access Journals (Sweden)

    Chee-Keong Tan

    2015-01-01

    Full Text Available Density functional theory (DFT calculations with the local density approximation (LDA functional are employed to investigate the band alignment of dilute-As GaNAs alloys with respect to the GaN alloy. Conduction and valence band positions of dilute-As GaNAs alloy with respect to the GaN alloy on an absolute energy scale are determined from the combination of bulk and surface DFT calculations. The resulting GaN / GaNAs conduction to valence band offset ratio is found as approximately 5:95. Our theoretical finding is in good agreement with experimental observation, indicating the upward movements of valence band at low-As content dilute-As GaNAs are mainly responsible for the drastic reduction of the GaN energy band gap. In addition, type-I band alignment of GaN / GaNAs is suggested as a reasonable approach for future device implementation with dilute-As GaNAs quantum well, and possible type-II quantum well active region can be formed by using InGaN / dilute-As GaNAs heterostructure.

  17. First-principle natural band alignment of GaN / dilute-As GaNAs alloy

    Science.gov (United States)

    Tan, Chee-Keong; Tansu, Nelson

    2015-01-01

    Density functional theory (DFT) calculations with the local density approximation (LDA) functional are employed to investigate the band alignment of dilute-As GaNAs alloys with respect to the GaN alloy. Conduction and valence band positions of dilute-As GaNAs alloy with respect to the GaN alloy on an absolute energy scale are determined from the combination of bulk and surface DFT calculations. The resulting GaN / GaNAs conduction to valence band offset ratio is found as approximately 5:95. Our theoretical finding is in good agreement with experimental observation, indicating the upward movements of valence band at low-As content dilute-As GaNAs are mainly responsible for the drastic reduction of the GaN energy band gap. In addition, type-I band alignment of GaN / GaNAs is suggested as a reasonable approach for future device implementation with dilute-As GaNAs quantum well, and possible type-II quantum well active region can be formed by using InGaN / dilute-As GaNAs heterostructure.

  18. 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…

  19. On ytterbium valence in intermetallic compounds with group 3 sp-elements

    International Nuclear Information System (INIS)

    Ytterbium compounds (YbAl2, YbGa2, YbIn2) with group 3 sp-elements; ore synthesized, ytterbium valency is determined using method of X-ray absorption L3-spectroscopy. It is stated that in YM2 binary phases, where M is group 3 element, ytterbium valency is near 2.30 value

  20. Pressure and irradiation effects on transport properties of samarium compounds with instable valence

    International Nuclear Information System (INIS)

    Electron transport properties in samarium compounds with instable valence are studied in this thesis: from SmS in its integer valence phases at common pressure to SmB6 compound IV at common pressure through SmSsub(1-x)Psub(x) (x6 is presented

  1. Influence of band interaction on superdeformed rotational bands

    International Nuclear Information System (INIS)

    With the first discovery of high spin superdeformed (SD) band in 152Dy, more than 250 SD bands have been observed in A ? 190, 150, 130, 80 mass regions. Except for a few SD bands, the spins of most of them have not been established experimentally. The influence of band interaction on SD bands is investigated in detail. The results based on an analysis of the band-mixing of two bands for such bands will be presented

  2. Band structure and hole scattering in p-PbTe

    International Nuclear Information System (INIS)

    Mobility (u), thermoemf (?), and temperature dependences of the Hall constant (R) in p-PbTe were calculated. While calculating considered has been the effect of the free electron mass contribution to the density mass of states at the band bottom and to the effective width of the forbidden band in the framework of the Cane type model, which leads to the absence of a ''mirror property'' of conductivity and valency bands. It is shown that, while taking into account the temperature dependence of the Hall factor, the appearance of maximum on R(T) curves may be explained only with due account of the contribution from interband scattering. Taking account of acoustic and optical mechanisms of scattering, it becomes possible to explain satisfactorily the temperature and concentration dependences of u, the temperature dependences of R and concentration dependences of ? up to concentrations of about 1020 cm-3 at heavy band parameters of msub(h)=1msub(e), ?0.18 eV. Qualitative considerations of the shape of isoenergetic surfaces of a heavy band were undertaken to explain the concentration dependences of b=usub(h)/usub(l) and causes of deviation of experimental and calculated values of ?. It is shown that the above surfaces have a complicated structure, and the heavy band may be substantially nonparabolic

  3. Valence bond supersolid in a bilayer extended Bose-Hubbard model

    Science.gov (United States)

    Ng, Kwai-Kong

    2015-02-01

    The hardcore extended Bose Hubbard model on a bilayer square lattice with attractive (repulsive) interplane (intraplane) interactions has been investigated numerically. Focusing on the strong interplane hopping parameter regime, triplet valence bonds of dimers are stabilized to form valence bond checkerboard solid at quarter filling. Increasing the particle number we confirm the presence of the exotic valence bond supersolid phase, where the valence bond solid ordering and the boson superfluidity coexist. Rising further the particle number will lead to a checkerboard solid of dimer pair at half filling for strong intraplane repulsion, or a valence bond Mott insulator for weak repulsive interactions. We analyze the rich ground state phase diagrams of this model, which can be experimentally realized in optical lattices of cold atoms.

  4. The dominant contributions of the inner valence electrons to the positron annihilation process in methanol

    International Nuclear Information System (INIS)

    The positron–electron annihilation gamma-ray spectra of methanol have been studied in the present work. The contributions of the bound electrons to the Doppler-shift of gamma-ray spectra have been analysed as well. These bound electrons are divided into three groups: core, inner valence and outer valence rather than the conventional two groups: core and valence in the positron annihilation process in the present work. The results obtained show a dominance of the inner valence electrons of methanol rather than the electrons occupied in the highest occupied molecular orbital (HOMO) in the positron–electron annihilation process. These inner valence electrons occupied in 3a? and 4a? orbitals consist of over 80% outermost atomic 2s electrons in oxygen and carbon atoms. That the positron prefers to annihilate with these outermost s electrons in atoms is suggested.

  5. A scalable synthesis of highly stable and water dispersible Ag 44(SR)30 nanoclusters

    KAUST Repository

    AbdulHalim, Lina G.

    2013-01-01

    We report the synthesis of atomically monodisperse thiol-protected silver nanoclusters [Ag44(SR)30] m, (SR = 5-mercapto-2-nitrobenzoic acid) in which the product nanocluster is highly stable in contrast to previous preparation methods. The method is one-pot, scalable, and produces nanoclusters that are stable in aqueous solution for at least 9 months at room temperature under ambient conditions, with very little degradation to their unique UV-Vis optical absorption spectrum. The composition, size, and monodispersity were determined by electrospray ionization mass spectrometry and analytical ultracentrifugation. The produced nanoclusters are likely to be in a superatom charge-state of m = 4-, due to the fact that their optical absorption spectrum shares most of the unique features of the intense and broadly absorbing nanoparticles identified as [Ag44(SR) 30]4- by Harkness et al. (Nanoscale, 2012, 4, 4269). A protocol to transfer the nanoclusters to organic solvents is also described. Using the disperse nanoclusters in organic media, we fabricated solid-state films of [Ag44(SR)30]m that retained all the distinct features of the optical absorption spectrum of the nanoclusters in solution. The films were studied by X-ray diffraction and photoelectron spectroscopy in order to investigate their crystallinity, atomic composition and valence band structure. The stability, scalability, and the film fabrication method demonstrated in this work pave the way towards the crystallization of [Ag44(SR)30]m and its full structural determination by single crystal X-ray diffraction. Moreover, due to their unique and attractive optical properties with multiple optical transitions, we anticipate these clusters to find practical applications in light-harvesting, such as photovoltaics and photocatalysis, which have been hindered so far by the instability of previous generations of the cluster. © 2013 The Royal Society of Chemistry.

  6. Perfect Dispersive Medium

    CERN Document Server

    Gupta, Shulabh

    2015-01-01

    Dispersion is at the heart of all ultrafast real-time signal processing systems across the entire electromagnetic spectrum ranging from radio-frequencies to optics. However, following Kramer-Kronig relations, these signal processing systems have been plagued with the parasitic amplitude distortions due to frequency dependent, and non-flat amplitude transmission of naturally dispersive media. This issue puts a serious limitation on the applicability and performance of these signal processing systems. To solve the above mentioned issue, a perfect dispersive medium is proposed in this work, which artificially violates the Kramer-Kronig relations, while satisfying all causality requirements. The proposed dispersive metamaterial is based on loss-gain metasurface pairs and exhibit a perfectly flat transmission response along with arbitrary dispersion in a broad bandwidth, thereby solving a seemingly unavoidable issue in all ultrafast signal processing systems. Such a metamaterial is further shown using sub-waveleng...

  7. Flat Chern Band in a Two-Dimensional Organometallic Framework

    Science.gov (United States)

    Liu, Zheng; Wang, Zheng-Fei; Mei, Jia-Wei; Wu, Yong-Shi; Liu, Feng

    2013-03-01

    By combining exotic band dispersion with nontrivial band topology, an interesting type of band structure, namely, the flat Chern band, has recently been proposed to spawn high-temperature fractional quantum Hall states. Despite the proposal of several theoretical lattice models, however, it remains doubtful whether such a “romance of flatland” could exist in a real material. Here, we present a first-principles design of a two-dimensional indium-phenylene organometallic framework that realizes a nearly flat Chern band right around the Fermi level by combining lattice geometry, spin-orbit coupling, and ferromagnetism. An effective four-band model is constructed to reproduce the first-principles results. Our design, in addition, provides a general strategy to synthesize topologically nontrivial materials by virtue of organic chemistry and nanotechnology.

  8. Modeling the effects of flow dispersion in arterial spin labeling.

    OpenAIRE

    Kazan, SM; Chappell, MA; Payne, SJ

    2009-01-01

    Recent experimental results have shown that effects such as dispersion and cardiac pulsation have a significant effect on the arterial spin labeling (ASL) signal. These have not been incorporated into the existing ASL models potentially leading to inaccuracies in flow calculation. In this study, we develop a new model, based on physical principles, to model the transit of the ASL signal from the tagging band to the imaging band using the mass transport equation. We relax the assumption of a u...

  9. Time-Delay Estimation in Dispersed Spectrum Cognitive Radio Systems

    OpenAIRE

    H. Vincent Poor; Huseyin Arslan; Qaraqe, Khalid A.; Hasari Celebi; Sinan Gezici; Fatih Kocak

    2010-01-01

    Time-delay estimation is studied for cognitive radio systems, which facilitate opportunistic use of spectral resources. A two-step approach is proposed to obtain accurate time-delay estimates of signals that occupy multiple dispersed bands simultaneously, with significantly lower computational complexity than the optimal maximum likelihood (ML) estimator. In the first step of the proposed approach, an ML estimator is used for each band of the signal in order to estimate the unknown parameter...

  10. QUANTITATIVE ANALYSIS OF BANDED STRUCTURES IN DUAL-PHASE STEELS

    OpenAIRE

    Benoit Krebs; Alain Hazotte; Lionel Germain; Mohamed Gouné

    2011-01-01

    Dual-Phase (DP) steels are composed of martensite islands dispersed in a ductile ferrite matrix, which provides a good balance between strength and ductility. Current processing conditions (continuous casting followed by hot and cold rolling) generate 'banded structures' i.e., irregular, parallel and alternating bands of ferrite and martensite, which are detrimental to mechanical properties and especially for in-use properties. We present an original and simple method to quantify the intensit...

  11. First-principles study of Cu2ZnSnS4 and the related band offsets for photovoltaic applications.

    Science.gov (United States)

    Nagoya, A; Asahi, R; Kresse, G

    2011-10-12

    First-principles calculations of the band offsets between Cu(2)ZnSnS(4) (CZTS) and XS (X = Cd, Zn) are performed. While the interface dipole contribution for the band offsets is calculated using the Perdew-Burke-Ernzerhof functional, the Heyd-Scuseria-Ernzerhof hybrid functional is employed to introduce the quasiparticle corrections to the band offsets. The calculated conduction band offset between CZTS and CdS is 0.2 eV, validating CdS for the buffer layer of the CZTS solar cell. The small conduction band offset stems from the band gap narrowing of CdS under the interface strain caused by the lattice misfit with CZTS. A large valence band offset over 0.9 eV between CZTS and ZnS indicates that precipitated ZnS is regarded as an inactive insulator phase in CZTS absorbers. PMID:21931185

  12. First-principles study of Cu2ZnSnS4 and the related band offsets for photovoltaic applications

    International Nuclear Information System (INIS)

    First-principles calculations of the band offsets between Cu2ZnSnS4 (CZTS) and XS (X = Cd, Zn) are performed. While the interface dipole contribution for the band offsets is calculated using the Perdew-Burke-Ernzerhof functional, the Heyd-Scuseria-Ernzerhof hybrid functional is employed to introduce the quasiparticle corrections to the band offsets. The calculated conduction band offset between CZTS and CdS is 0.2 eV, validating CdS for the buffer layer of the CZTS solar cell. The small conduction band offset stems from the band gap narrowing of CdS under the interface strain caused by the lattice misfit with CZTS. A large valence band offset over 0.9 eV between CZTS and ZnS indicates that precipitated ZnS is regarded as an inactive insulator phase in CZTS absorbers.

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

    DEFF Research Database (Denmark)

    Gorczyca, I.; Suski, T.

    2012-01-01

    InN/GaN superlattices offer an important way of band gap engineering in the blue-green range of the spectrum. This approach represents a more controlled method than the band gap tuning in quantum well systems by application of InGaN alloys. The electronic structures of short-period wurtzite InN/GaN(0001) superlattices are investigated, and the variation of the band gap with the thicknesses of the well and the barrier is discussed. Superlattices of the form mInN/nGaN with n ? m are simulated using band structure calculations in the Local Density Approximation with a semiempirical correction for the gap error. The calculated band gap shows a strong decrease with the thickness (m) of the InN well. In superlattices containing a single layer of InN (m = 1) the band gap increases weakly with the GaN barrier thickness n, reaching a saturation value around 2 eV. In superlattices with n = m and n > 5 the band gap closes and the systems become “metallic”. These effects are related to the existence of the built-in electric fields that strongly influence valence- and conduction-band profiles and thus determine effective band gap and emission energies of the superlattices. Varying the widths of the quantum wells and barriers one may tune band gaps over a wide spectral range, which provides flexibility in band gap engineering.

  14. Multi-band theory of magnetoexcitons in ZnO/ZnMnO quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Bardyszewski, Witold [CEA - CNRS, Nanophysique et Semiconducteurs, Institut Neel, CNRS and Universite Joseph Fourier, 25 avenue des Martyrs, 38042 Grenoble (France)

    2010-06-15

    We present a multiband magnetoexciton absorption model in ZnO/ZnMnO quantum wells which takes into account the details of the valence band structure. In our model we incorporate the k.p as well as the Coulomb coupling between valence sub-bands. The s,p-d interaction between the carriers and the magnetic ions in the barrier is taken into account within the mean field approximation. The effect of the electric field is accounted for using proper potential profile of the quantum well. As a result we obtain electric and magnetic field dependent excitonic absorption spectra from which the exciton binding energies and life-times as well as the overlap with the magnetic barrier material may be deduced (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  15. Valence Fluctuations and Electric Reconstruction in the Extended Anderson Model on the Two-Dimensional Penrose Lattice

    OpenAIRE

    Takemura, Shinichi; Takemori, Nayuta; Koga, Akihisa

    2015-01-01

    We study the extended Anderson model on the two-dimensional Penrose lattice, combining the real-space dynamical mean-field theory with the non-crossing approximation. It is found that the Coulomb repulsion between localized and conduction electrons does not induce a valence transition, but the crossover between the Kondo and mixed valence states in contrast to the conventional periodic system. In the mixed-valence region close to the crossover, nontrivial valence distributio...

  16. Optical properties of chalcopyrite-type intermediate transition metal band materials from first principles

    International Nuclear Information System (INIS)

    The optical properties of a novel potential high-efficiency photovoltaic material have been studied. This material is based on a chalcopyrite-type semiconductor (CuGaS2) with some Ga atom substituted by Ti and is characterized by the formation of an isolated transition-metal band between the valence band and the conduction band. We present a study in which ab-initio density functional theory calculations within the generalized gradient approximation are carried out to determine the optical reflectivity and absorption coefficient of the materials of interest. Calculations for the host semiconductor are in good agreement with experimental results within the limitations of the approach. We find, as desired, that because of the intermediate band, the new Ti-substituted material would be able to absorb photons of energy lower than the band-gap of the host chalcopyrite. We also analyze the partial contributions to the main peaks of its spectrum

  17. Two-band tight-binding model for push-pull polyenes

    Science.gov (United States)

    Suzuki, Yasuo Y.; Beljonne, D.; Brédas, J. L.

    1996-05-01

    We propose a two-band model for the description of the electronic structure of push-pull polyenes in order to analyze in simple ways their potentially useful electronic and optical features. The polyene part is described by two (valence and conduction) bands, which are coupled with two tight-binding frontier orbitals representing the donor and acceptor end groups. In this model, the ground state consists of the one-electron states of the (?) valence band hybridized with the donor orbitals, while the charge-transfer excited state is described as an excitation from the highest occupied molecular orbital to the lowest unoccupied molecular orbital, the latter being a hybridized one-electron state between the (?*) conduction band and the acceptor orbital. It is shown, by the Green's function method, that the electron localizations (the partial density of states) at the end groups are determined by three factors; (1) the unperturbed energy levels of the frontier orbitals, (2) the density of states of the unperturbed polyene bands, and (3) the coupling constants between the ? (?*) band and the donor (acceptor) orbital. Based on the results, a simple description is provided for the characteristic nonlinear optical responses and the intramolecular adiabatic charge-transfer mechanism of push-pull polyenes. In order to estimate the magnitude of the coupling constants, we compare the analytical results from the model with numerical calculations based on an established semiempirical method. This kind of modeling provides guidance for the design of functional push-pull polyenes.

  18. Oxide Defect Engineering Methods for Valence Change (VCM) Resistive Random Access Memories

    Science.gov (United States)

    Capulong, Jihan O.

    Electrical switching requirements for resistive random access memory (ReRAM) devices are multifaceted, based on device application. Thus, it is important to obtain an understanding of these switching properties and how they relate to the oxygen vacancy concentration and oxygen vacancy defects. Oxygen vacancy defects in the switching oxide of valence-change-based ReRAM (VCM ReRAM) play a significant role in device switching properties. Oxygen vacancies facilitate resistive switching as they form the conductive filament that changes the resistance state of the device. This dissertation will present two methods of modulating the defect concentration in VCM ReRAM composed of Pt/HfOx/Ti stack: 1) rapid thermal annealing (RTA) in Ar using different temperatures, and 2) doping using ion implantation under different dose levels. Metrology techniques such as x-ray diffractometry (XRD), x-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectroscopy were utilized to characterize the HfOx switching oxide, which provided insight on the material properties and oxygen vacancy concentration in the oxide that was used to explain the changes in the electrical properties of the ReRAM devices. The resulting impact on the resistive switching characteristics of the devices, such as the forming voltage, set and reset threshold voltages, ON and OFF resistances, resistance ratio, and switching dispersion or uniformity were explored and summarized. Annealing in Ar showed significant impact on the forming voltage, with as much as 45% (from 22V to 12 V) of improvement, as the annealing temperature was increased. However, drawbacks of a higher oxide leakage and worse switching uniformity were seen with increasing annealing temperature. Meanwhile, doping the oxide by ion implantation showed significant effects on the resistive switching characteristics. Ta doping modulated the following switching properties with increasing dose: a) the reduction of the forming voltage, and Vset and Vreset threshold voltages; b) the increase of resistance ratio, and c) the improvement of resistance dispersion. More studies are needed on ion implantation of B, as the energy that was used in this research was too much for the B to become dopants in HfOx. To further enable ReRAM integration with IC devices, behavioral models were developed using empirical data taken from real ReRAM devices.

  19. The role of valence electron concentration in the cohesive properties of YBxN1-x, YCxN1-x and YNxO1-x compounds

    International Nuclear Information System (INIS)

    The mechanical properties are not yet understood at basic levels. Previous works shows that the greatest hardness for rock-salt structures (such as TiCxN1-x) is attained for a valence electron concentration (VEC) of 4.2 electrons per atom. The present work is aimed to explore this concept for yttrium-based compounds. By means of first principles calculations we did a systematical investigation where nitrogen in YN (VEC = 4) was supplanted by either of B, C or O to reduce or increase its VEC, forming YBxN1-x, YCxN1-x and YN1-xOx ternary compounds. We have calculated the cohesive energy (EO), cell volume (VO), bulk modulus (BO) and density of states (DoS) as a function of VEC. The Fermi level (Ef,) is shifted toward the valence band by substituting B or C in YN, and toward the conduction band by means of O. It is concluded that the optimal position for Ef (maximum BO) is linked to the saturation of electronic states with eg-symmetry. At this point the excess of electrons provided by O starts filling antibonding states with t2g-symmetry. That is, BO increases monotonically as a function of VEC until VEC ? 4.1, after that point BO decrease

  20. 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…

  1. Stretch Band Exercise Program

    Science.gov (United States)

    Skirka, Nicholas; Hume, Donald

    2007-01-01

    This article discusses how to use stretch bands for improving total body fitness and quality of life. A stretch band exercise program offers a versatile and inexpensive option to motivate participants to exercise. The authors suggest practical exercises that can be used in physical education to improve or maintain muscular strength and endurance,…

  2. Valence trapping of mixed-valence [Fe3O(O2CCH3)6(py)3]·S (S = solvent) complexes at high pressure

    International Nuclear Information System (INIS)

    The transformation from valence detrapped to valence trapped for two oxo-centered trinuclear iron acetate complexes is studied at pressures up to 95 kbar with the use of a diamond anvil cell. Variable-pressure 57Fe Mossbauer spectra are presented for 57Fe-enriched [Fe3O(O2CCH3)6(py)3]xpy (1) and [Fe3O(O2CCH3)6(py)3]xCHCl3 (2), where py is pyridine. At 298 K and applied pressures less than ?20 kbar, each of the complexes gives a spectrum with a single quadrupole-split doublet, which indicates that complexes 1 and 2 are interconverting faster than the Mossbauer time scale under these conditions. Application of pressure in excess of ?80 kbar leads to both complexes becoming valence trapped, as indicated by two doublets in the Mossbauer spectrum with an area ratio of ?2:1 (FeIII:FeII). At intermediate pressures, each of these complexes gives a Mossbauer spectrum that can be fit as a superposition of a valence detrapped doublet and a valence trapped four-line pattern. The nature of the pressure-induced transformations observed in complexes 1 and 2 is discussed with reference to the phase diagram derived from a spin-Hamiltonian theoretical approach that parameterizes intermolecular interactions in terms of the molecular field approximation. 11 refs., 4 figs., 2 tabs

  3. A theoretical and (e,2e) experimental investigation into the complete valence electronic structure of (1.1.1) propellane

    International Nuclear Information System (INIS)

    The first comprehensive electronic structural study of the complete valence shell of [1.1.1] propellane is reported. Binding energy spectra were measured in the energy regime 3.5-46.5 eV over a range of different target electron momentum so that individual orbital momentum profiles could also be determined. These binding energy spectra were collected using an energy dispersive multichannel electron momentum spectrometer at a total energy of 1000 eV, with a coincidence energy resolution of 1.38 eV and a momentum resolution of about 0.1 a.u. The experimental orbital electron momentum profiles are compared with those calculated in the plane wave impulse approximation (PWIA) using both a triple zeta plus polarisation level SCF wavefunction and a further 13 basis sets as calculated using Density Functional Theory (DFT). A critical comparison between the experimental an theoretical momentum distributions (MDs) allows to determine the optimum wavefunction for [1.1.1]propellane. In general, the level of agreement between the experimental and theoretical MDs for the optimum wavefunction for all of the respective valence orbitals was very good. The determination of this wavefunction then allowed to derive the chemically interesting molecular properties of [1.1.1]propellane. These include infrared spectra, bond lengths, bond orders, electron densities and many others. A summary of these results and a comparison of them with the previous results of other workers is presented with the level of agreement typically being good. In particular, the existence of the C1-C3 bridging bond with a bond order of 0.70 was confirmed. 59 refs., 4 tabs., 11 figs

  4. Band model for d- and f-metals

    Energy Technology Data Exchange (ETDEWEB)

    Koelling, D.D.

    1982-01-01

    The application of band theory to metallic systems with d- and f-orbitals in the valence and conduction bands is discussed. Because such an application pushes theory and technique to their limits, several important features are briefly recapitulated. Within the transition metal systems, the elemental systems are used to discuss the fundamental formalism being applied and the newer directions into more complex systems are mentioned. Here we focus more on anisotropic properties and Fermi surface properties. Within the f-orbital systems, the focus is more on Ce and its compounds because of current interest with a relatively brief discussion of the actinides. the point of view advanced, however, has its origins in actinide research.

  5. Band structure of TiO sub 2 -doped yttria-stabilized zirconia probed by soft-x-ray spectroscopy

    CERN Document Server

    Higuchi, T; Kobayashi, K; Yamaguchi, S; Fukushima, A; Shin, S

    2003-01-01

    The electronic structure of TiO sub 2 -doped yttria-stabilized zirconia (YSZ) has been studied by soft-X-ray emission spectroscopy (SXES) and X-ray absorption spectroscopy (XAS). The valence band is mainly composed of the O 2p state. The O 1s XAS spectrum exhibits the existence of the Ti 3d unoccupied state under the Zr 4d conduction band. The intensity of the Ti 3d unoccupied state increases with increasing TiO sub 2 concentration. The energy separation between the top of the valence band and the bottom of the Ti 3d unoccupied state is in accord with the energy gap, as expected from dc-polarization and total conductivity measurements. (author)

  6. Direct observation of the band gap shrinkage in amorphous In2O3-ZnO thin films

    Science.gov (United States)

    Jia, Junjun; Oka, Nobuto; Shigesato, Yuzo

    2013-04-01

    We investigated the dependence of valence- and core-level photoemission spectra of amorphous In2O3-ZnO (a-IZO) films on carrier density by using hard x-ray photoemission spectroscopy (h? =8000 eV). The valence band edge distinctly shifts toward high binding energy with the increase in carrier density from 0.80 to 3.96 × 1020 cm-3, and an abrupt jump for the shift of the valence band edge from high to low binding energy occurs at a carrier density of 4.76×1020 cm-3. After considering the effect of nonparabolic bandstructure, the shifts are still less than the width of the occupied conduction band, providing direct evidence for the band gap shrinkage. Our calculation results indicate that the contribution of the band gap shrinkage increases as the carrier density increases, which accords with the observations in doped conducting crystal materials, such as Sn doped In2O3. Moreover, it is found that the conduction electrons of a-IZO films are strongly perturbed by the ionization of core levels, which leads to obvious plasmon satellites in core photoemission spectra lines.

  7. Mixed valency in quadruple hydrogen-bonded dimers of bis(biimidazolate)dirhodium complexes.

    Science.gov (United States)

    Jin-Long; Matsuda, Yuki; Uemura, Kazuhiro; Ebihara, Masahiro

    2015-03-01

    Dirhodium complexes with biimidazole (H2bim) ligands [Rh2(O2CR)2(H2bim)2Cl2] (R = Bu ([1Cl2]), Pr ([2Cl2])), [Rh2(O2CBu)2(H2bim)2](PF6)2 ([1](PF6)2), [Rh2(O2CBu)2(H2bim)2(PPh3)2](PF6)2 ([1(PPh3)2](PF6)2), and [Rh2(O2CPr)2(H2bim)2(PPh3)2]Cl2 ([2(PPh3)2]Cl2) have been synthesized. Deprotonation of the biimidazole complexes afforded the quadruply hydrogen-bonded dimers of the biimidazolate complexes [Rh2(O2CR)2(Hbim)2(PPh3)2]2 (R = Bu ([1'(PPh3)2]2) and Pr ([2'(PPh3)2]2)). Complementary hydrogen bonds between the Hbim(-) ligands are not coplanar because the Hbim(-) ions in one dirhodium complex are not parallel (the dihedral angle between them is ca. 15°). A cyclic voltammogram of [1'(PPh3)2]2 shows two sets of two consecutive oxidation waves in CH2Cl2. The one-electron-oxidized species of [1'(PPh3)2]2 showed no intervalence charge-transfer band in the electronic spectrum and an axially symmetrical ESR spectrum with hyperfine structure because of two phosphorus atoms. These observations show that the odd electron is localized in a ?(Rh-Rh) orbital on one dirhodium unit. Theoretical calculations indicate that an oxidized complex [Rh2(O2CMe)2(bim)2(PMe3)2](-) hydrogen bonded with a biimidazole complex [Rh2(O2CMe)2(H2bim)2(PMe3)2](2+) was a stable mixed-valence complex. PMID:25692759

  8. Coping with power dispersion?

    DEFF Research Database (Denmark)

    2014-01-01

    The last decades have witnessed a significant shift in policy competences away from central governments in Europe. The reallocation of competences spans over three dimensions: upwards; sideways; and downwards. This collection takes the dispersion of powers as a starting point and seeks to assess how the actors involved cope with the new configurations. In this introduction, we discuss the conceptualization of power dispersion and highlight the ways in which the contributions add to this research...

  9. Dispersion in oscillatory flows

    OpenAIRE

    Stairmand, J. W.; Bellhouse, Brian J.; Sobey, I. J. (Ian John); Dr. I.J. Sobey; Dr. B.J. Bellhouse

    1983-01-01

    ?The enhanced axial mixing which is caused by dispersion in oscillatory flows in some mass transfer devices may limit the reactor performance. This effect has provided the motivation for the present study in which oscillatory flow dispersion in a flat channel of large aspect ratio is investigated. The rate of spreading of a uniform slug of some passive tracer has been predicted using numerical and analytical techniques and the results have been verified experimentally. ...

  10. The Polarised Valence Quark Distribution from semi-inclusive DIS

    CERN Document Server

    Alekseev, M.; Alexandrov, Yu.; Alexeev, G.D.; Amoroso, A.; Arbuzov, A.; Badelek, B.; Balestra, F.; Ball, J.; Barth, J.; Baum, G.; Bedfer, Y.; Bernet, C.; Bertini, R.; Bettinelli, M.; Birsa, R.; Bisplinghoff, J.; Bordalo, P.; Bradamante, F.; Bravar, A.; Bressan, A.; Brona, G.; Burtin, E.; Bussa, M.P.; Chapiro, A.; Chiosso, M.; Cicuttin, A.; Colantoni, M.; Costa, S.; Crespo, M.L.; Dalla Torre, S.; Dafni, T.; Das, S.; Dasgupta, S.S.; De Masi, R.; Dedek, N.; Denisov, O.Yu.; Dhara, L.; Diaz, V.; Dinkelbach, A.M.; Donskov, S.V.; Dorofeev, V.A.; Doshita, N.; Duic, V.; Dunnweber, W.; Eversheim, P.D.; Eyrich, W.; Faessler, M.; Falaleev, V.; Ferrero, A.; Ferrero, L.; Finger, M.; Finger, M., Jr.; Fischer, H.; Franco, C.; Franz, J.; Friedrich, J.M.; Frolov, V.; Garfagnini, R.; Gautheron, F.; Gavrichtchouk, O.P.; Gazda, R.; Gerassimov, S.; Geyer, R.; Giorgi, M.; Gobbo, B.; Goertz, S.; Gorin, A.M.; Grabmuller, S.; Grajek, O.A.; Grasso, A.; Grube, B.; Gushterski, R.; Guskov, A.; Haas, F.; Hannappel, J.; von Harrach, D.; Hasegawa, T.; Heckmann, J.; Hedicke, S.; Heinsius, F.H.; Hermann, R.; Hess, C.; Hinterberger, F.; von Hodenberg, M.; Horikawa, N.; Horikawa, S.; d'Hose, N.; Ilgner, C.; Ioukaev, A.I.; Ishimoto, S.; Ivanov, O.; Ivanshin, Yu.; Iwata, T.; Jahn, R.; Janata, A.; Jasinski, P.; Joosten, R.; Jouravlev, N.I.; Kabuss, E.; Kang, D.; Ketzer, B.; Khaustov, G.V.; Khokhlov, Yu.A.; Kisselev, Yu.; Klein, F.; Klimaszewski, K.; Koblitz, S.; Koivuniemi, J.H.; Kolosov, V.N.; Komissarov, E.V.; Kondo, K.; Konigsmann, K.; Konorov, I.; Konstantinov, V.F.; Korentchenko, A.S.; Korzenev, A.; Kotzinian, A.M.; Koutchinski, N.A.; Kouznetsov, O.; Kral, A.; Kravchuk, N.P.; Kroumchtein, Z.V.; Kuhn, R.; Kunne, F.; Kurek, K.; Ladygin, M.E.; Lamanna, M.; Le Goff, J.M.; Lednev, A.A.; Lehmann, A.; Levorato, S.; Lichtenstadt, J.; Liska, T.; Ludwig, I.; Maggiora, A.; Maggiora, M.; Magnon, A.; Mallot, G.K.; Mann, A.; Marchand, C.; Marroncle, J.; Martin, A.; Marzec, J.; Massmann, F.; Matsuda, T.; Maximov, A.N.; Meyer, W.; Mielech, A.; Mikhailov, Yu.V.; Moinester, M.A.; Mutter, A.; Nagaytsev, A.; Nagel, T.; Nahle, O.; Nassalski, J.; Neliba, S.; Nerling, F.; Neubert, S.; Neyret, D.P.; Nikolaenko, V.I.; Nikolaev, K.; Olshevsky, A.G.; Ostrick, M.; Padee, A.; Pagano, P.; Panebianco, S.; Panknin, R.; Panzieri, D.; Paul, S.; Pawlukiewicz-Kaminska, B.; Peshekhonov, D.V.; Peshekhonov, V.D.; Piragino, G.; Platchkov, S.; Pochodzalla, J.; Polak, J.; Polyakov, V.A.; Pretz, J.; Procureur, S.; Quintans, C.; Rajotte, J.F.; Ramos, S.; Rapatsky, V.; Reicherz, G.; Reggiani, D.; Richter, A.; Robinet, F.; Rocco, E.; Rondio, E.; Rozhdestvensky, A.M.; Ryabchikov, D.I.; Samoylenko, V.D.; Sandacz, A.; Santos, H.; Sapozhnikov, M.G.; Sarkar, S.; Savin, I.A.; Schiavon, P.; Schill, C.; Schmitt, L.; Schonmeier, P.; Schroder, W.; Shevchenko, O.Yu.; Siebert, H.W.; Silva, L.; Sinha, L.; Sissakian, A.N.; Slunecka, M.; Smirnov, G.I.; Sosio, S.; Sozzi, F.; Srnka, A.; Stinzing, F.; Stolarski, M.; Sugonyaev, V.P.; Sulc, M.; Sulej, R.; Tchalishev, V.V.; Tessaro, S.; Tessarotto, F.; Teufel, A.; Tkatchev, L.G.; Venugopal, G.; Virius, M.; Vlassov, N.V.; Vossen, A.; Webb, R.; Weise, E.; Weitzel, Q.; Windmolders, R.; Wirth, S.; Wislicki, W.; Wollny, H.; Zaremba, K.; Zavertyaev, M.; Zemlyanichkina, E.; Zhao, J.; Ziegler, R.; Zvyagin, A.

    2008-01-01

    The semi-inclusive difference asymmetry A^{h+ - h-} for hadrons of opposite charge has been measured by the COMPASS experiment at CERN. The data were collected in the years 2002-2004 using a 160 GeV polarised muon beam scattered off a large polarised 6-LiD target and cover the range 0.006 < x < 0.7 and 1 < Q^2 < 100 (GeV/c)^2. In leading order QCD (LO) the asymmetry A_d^{h+ - h-} measures the valence quark polarisation and provides an evaluation of the first moment of Delta u_v + Delta d_v which is found to be equal to 0.40 +- 0.07 (stat.) +- 0.05 (syst.) over the measured range of x at Q^2 = 10 (GeV/c)^2. When combined with the first moment of g_1^d previously measured on the same data, this result favours a non-symmetric polarisation of light quarks Delta u-bar = -Delta d-bar at a confidence level of two standard deviations, in contrast to the often assumed symmetric scenario Delta u-bar = Delta d-bar = Delta s-bar = Delta s.

  11. The polarised valence quark distribution from semi-inclusive DIS

    Energy Technology Data Exchange (ETDEWEB)

    Alekseev, M. [University of Eastern Piedmont, 1500 Alessandria, and Torino Section of INFN, 10125 Turin (Italy); Alexakhin, V.Yu. [Joint Institute for Nuclear Research, 141980 Dubna, Moscow region (Russian Federation); Alexandrov, Yu. [Lebedev Physical Institute, 119991 Moscow (Russian Federation); Alexeev, G.D. [Joint Institute for Nuclear Research, 141980 Dubna, Moscow region (Russian Federation); Amoroso, A. [University of Turin, Department of Physics and Torino Section of INFN, 10125 Turin (Italy); Arbuzov, A. [Joint Institute for Nuclear Research, 141980 Dubna, Moscow region (Russian Federation); Badelek, B. [Soltan Institute for Nuclear Studies and Warsaw University, 00-681 Warsaw (Poland); Balestra, F. [University of Turin, Department of Physics and Torino Section of INFN, 10125 Turin (Italy); Ball, J. [CEA DAPNIA/SPhN Saclay, 91191 Gif-sur-Yvette (France); Barth, J. [Universitaet Bonn, Physikalisches Institut, 53115 Bonn (Germany); Baum, G. [Universitaet Bielefeld, Fakultaet fuer Physik, 33501 Bielefeld (Germany); Bedfer, Y.; Bernet, C. [CEA DAPNIA/SPhN Saclay, 91191 Gif-sur-Yvette (France); Bertini, R. [University of Turin, Department of Physics and Torino Section of INFN, 10125 Turin (Italy); Bettinelli, M. [Ludwig-Maximilians-Universitaet Muenchen, Department fuer Physik, 80799 Munich (Germany); Birsa, R. [Trieste Section of INFN, 34127 Trieste (Italy); Bisplinghoff, J. [Universitaet Bonn, Helmholtz-Institut fuer Strahlen- und Kernphysik, 53115 Bonn (Germany); Bordalo, P. [LIP, 1000-149 Lisbon (Portugal); Bradamante, F. [University of Trieste, Department of Physics and Trieste Section of INFN, 34127 Trieste (Italy); Bravar, A. [Universitaet Mainz, Institut fuer Kernphysik, 55099 Mainz (Germany); Trieste Section of INFN, 34127 Trieste (Italy)] (and others)

    2008-03-06

    The semi-inclusive difference asymmetry A{sup h{sup +}-h{sup -}} for hadrons of opposite charge has been measured by the COMPASS experiment at CERN. The data were collected in the years 2002-2004 using a 160 GeV polarised muon beam scattered off a large polarised {sup 6}LiD target in the kinematic range 0.006valence quark polarisation and provides an evaluation of the first moment of {delta}u{sub v}+{delta}d{sub v} which is found to be equal to 0.40{+-}0.07(stat.){+-}0.06(syst.) over the measured range of x at Q{sup 2}=10 (GeV/c){sup 2}. When combined with the first moment of g{sub 1}{sup d} previously measured on the same data, this result favours a non-symmetric polarisation of light quarks {delta}u-bar = -{delta}d-bar at a confidence level of two standard deviations, in contrast to the often assumed symmetric scenario {delta}u-bar = {delta}d-bar = {delta}s-bar ={delta}s.

  12. 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.

  13. Valence Auger decay following 3 s photoionization in potassium

    Science.gov (United States)

    Palaudoux, J.; Sheinerman, S.; Soronen, J.; Huttula, S.-M.; Huttula, M.; Jänkälä, K.; Andric, L.; Ito, K.; Lablanquie, P.; Penent, F.; Bizau, J.-M.; Guilbaud, S.; Cubaynes, D.

    2015-07-01

    We have studied photoionization in the inner valence 3 s subshell of K and the spectroscopic properties of the two 3 s-1(1S) and (3S) resulting states. Similar to the Rb and Cs cases, the lifetime widths of the (1S) and (3S) states are found to be markedly different, due to the electron correlation effects. The main part of the study deals with the subsequent Auger decay of the 3 s-1 states, which have the particularity to involve low energy (˜5 eV ) Auger electrons. A magnetic bottle spectrometer with a multicoincidence technique has been used to observe and filter the Auger spectra with respect to the K2 + final state. The evolution of these Auger spectra has been investigated near the ionization threshold. They show strong post-collision interaction (PCI) effects, which are well reproduced by semiclassical and eikonal models. They reveal the importance of the photoelectron-Auger-electron interaction associated with these low energy Auger electrons.

  14. Valence bond solid (AKLT) state from t2 g electrons

    Science.gov (United States)

    Koch-Janusz, Maciej; Khomskii, Daniel; Sela, Eran

    2015-03-01

    The models constructed by Affleck, Kennedy, Lieb, and Tasaki (AKLT) describe gapped quantum spin liquids with fractionalized boundary spin excitations. The AKLT spin-spin interactions consist of projection operators onto the maximal possible spin formed between nearest neighbours, which involves a linear combination of powers of the Heisenberg coupling (S-->i .S-->j) n, making these states difficult to realize. Indeed, except for the one dimensional spin-1 case, simple antiferromagnetic Heisenberg interactions which are typically found in magnetic insulators, do not stabilize these spin liquid states, but rather generate conventional antiferromagnetically ordered states. We show that this type of interactions can be generated by orbital physics in multiorbital Mott insulators. Motivated by microscopic modeling of spin-orbit entangled Mott insulators such as the layered hexagonal Iridates, we focus on t2 g electrons on the honeycomb lattice and propose a physical realization of the spin- 3 / 2 AKLT state. Interestingly enough, the valence bond solid (AKLT) state found for the noninteracting electrons survives the increase of the on-site (Hubbard) repulsion, but it changes to the antiferromagnetic Neel state with increase of the Hund's rule coupling.

  15. Ab initio effective interactions for sd-shell valence nucleons

    CERN Document Server

    Dikmen, E; Barrett, B R; Maris, P; Shirokov, A M; Vary, J P

    2015-01-01

    We perform \\textit{ab initio} no core shell model calculations for $A=18$ and $19$ nuclei in a $4\\hbar\\Omega$, or $N_{\\rm max}=4$, model space using the effective JISP16 and chiral N3LO nucleon-nucleon potentials and transform the many-body effective Hamiltonians into the $0\\hbar\\Omega$ model space to construct the $A$-body effective Hamiltonians in the $sd$-shell. We separate the $A$-body effective Hamiltonians with $A=18$ and $A=19$ into inert core, one- and two-body components. Then, we use these core, one- and two-body components to perform standard shell model calculations for the $A=18$ and $A=19$ systems with valence nucleons restricted to the $sd$-shell. Finally, we compare the standard shell model results in the $0\\hbar\\Omega$ model space with the exact no core shell model results in the $4\\hbar\\Omega$ model space for the $A=18$ and $A=19$ systems and find good agreement.

  16. Optically induced valence tautomeric interconversion in cobalt dioxolene complexes

    Scientific Electronic Library Online (English)

    Alessandra, Beni; Chiara, Carbonera; Andrea, Dei; Jean-François, Létard; Roberto, Righini; Claudio, Sangregorio; Lorenzo, Sorace.

    2006-12-01

    Full Text Available A descoberta de que vários complexos de cobalto-dioxoleno exibem bi-estabilidade magnética foto induzida foi descrita recentemente. Este fenômeno encontra-se sempre associado a processos de interconversão de tautômeros de valência entre espécies de cobalto(III) baixo spin e de cobalto(II) alto spin. [...] Enfatiza-se, nesta revisão, a forte correlação formal existente entre estes processos e o efeito LIESST (Light-Induced Excited Spin State Trapping) exibido por vários complexos de ferro(II) que sofrem interconversão de spin. A dinâmica da relaxação da espécie meta-estável fotoinduzida para o estado fundamental é discutida em termos de processos adiabáticos no âmbito da teoria de Jortner da relaxação multifônica sem radiação. Abstract in english The discovery that a number of cobalt-dioxolene complexes undergo photoswitchable behavior was reported in the recent past. This phenomenon is always associated with valence tautomeric interconversion processes involving low-spin cobalt(III) and high-spin cobalt(II) species. Herein is stressed the s [...] trong formal correlation existing between these processes and the LIESST (Light-Induced Excited Spin State Trapping) effect shown by several iron(II) complexes undergoing spin crossover interconversion. The dynamics of the relaxation of the photoinduced metastable species to the ground state is discussed in terms of non-adiabatic processes within the Jortner theory of radiationless multiphonon relaxation.

  17. Valence shell photoionization of SF6 and high harmonic generation

    Science.gov (United States)

    Jobin, Jobin; Fulfer, K.; Wilson, B.; Poliakoff, E.; Trallero, C.; Mondal, S.; Le, A.-T.; Lin, C.-D.; Lucchese, Robert

    2013-05-01

    When an atom or molecule is exposed to highly intense laser fields, the target can emit coherent radiation at photon energies which are multiples of incident laser energy. This process is known as High-order harmonic generation (HHG). There has been experimental and theoretical investigation of HHG for atoms and simple linear molecules. However, there have been few such studies for non-linear polyatomic molecules. In the current work, we investigate HHG for SF6 experimentally and theoretically. We employ quantitative rescattering theory (QRS) which makes use of the magnitude and phase of the dipole transition matrix elements for photoionization. For calculating dipole transition matrix elements we employ the ePolyscat static-exchange method. The features seen in the computed results will be compared to corresponding features in the measured HHG spectrum. The calculation is repeated for different polarization of incident laser and different intensities. The analysis allows us to reproduce then understand experimentally measured HHG spectra from SF6. Additionally, the valence shell photoionization parameters are also compared with several other theoretical and experimental results.

  18. Black Phosphorus Transistors with Near Band Edge Contact Schottky Barrier

    Science.gov (United States)

    Ling, Zhi-Peng; Sakar, Soumya; Mathew, Sinu; Zhu, Jun-Tao; Gopinadhan, K.; Venkatesan, T.; Ang, Kah-Wee

    2015-01-01

    Black phosphorus (BP) is a new class of 2D material which holds promise for next generation transistor applications owing to its intrinsically superior carrier mobility properties. Among other issues, achieving good ohmic contacts with low source-drain parasitic resistance in BP field-effect transistors (FET) remains a challenge. For the first time, we report a new contact technology that employs the use of high work function nickel (Ni) and thermal anneal to produce a metal alloy that effectively reduces the contact Schottky barrier height (?B) in a BP FET. When annealed at 300?°C, the Ni electrode was found to react with the underlying BP crystal and resulted in the formation of nickel-phosphide (Ni2P) alloy. This serves to de-pin the metal Fermi level close to the valence band edge and realizes a record low hole ?B of merely ~12?meV. The ?B at the valence band has also been shown to be thickness-dependent, wherein increasing BP multi-layers results in a smaller ?B due to bandgap energy shrinkage. The integration of hafnium-dioxide high-k gate dielectric additionally enables a significantly improved subthreshold swing (SS?~?200?mV/dec), surpassing previously reported BP FETs with conventional SiO2 gate dielectric (SS?>?1?V/dec). PMID:26667402

  19. Determination of band offsets in strained-Si heterolayers

    International Nuclear Information System (INIS)

    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 SiO2 as the dielectric. Extracted experimental values of the valence and conduction band offsets are in good agreement with theoretical predictions

  20. Photoion mass spectroscopy and valence photoionization of hypoxanthine, xanthine and caffeine

    Energy Technology Data Exchange (ETDEWEB)

    Feyer, Vitaliy, E-mail: vitaliy.feyer@elettra.trieste.it [Sincrotrone Trieste, in Area Science Park, I-34012 Basovizza (Trieste) (Italy); Plekan, Oksana [Sincrotrone Trieste, in Area Science Park, I-34012 Basovizza (Trieste) (Italy)] [Institute of Electron Physics, 21 Universitetska St., 88017 Uzhgorod (Ukraine); Richter, Robert [Sincrotrone Trieste, in Area Science Park, I-34012 Basovizza (Trieste) (Italy); Coreno, Marcello [CNR-IMIP, Area della Ricerca di Roma 1, CP10, I-00016 Monterotondo Scalo (Italy)] [CNR-Laboratorio Nazionale TASC-INFM, I-34012 Basovizza (Trieste) (Italy); Prince, Kevin C. [Sincrotrone Trieste, in Area Science Park, I-34012 Basovizza (Trieste) (Italy)] [CNR-Laboratorio Nazionale TASC-INFM, I-34012 Basovizza (Trieste) (Italy)

    2009-03-30

    Photoionization mass spectra of hypoxanthine, xanthine and caffeine were measured using the photoelectron-photoion coincidence technique and noble gas resonance radiation at energies from 8.4 to 21.2 eV for ionization. The fragmentation patterns for these compounds show that hydrogen cyanide is the main neutral loss species at higher photon energies, while photoionization below 16.67 eV led predominantly to the parent ion. The valence photoelectron spectra of this family of molecules were measured over an extended energy range, including the inner C, N and O 2s valence orbitals. The observed ion fragments were related to ionization of the valence orbitals.

  1. Pressure and temperature dependence of the magnetic susceptibility intermediate valence Ce and Yb compounds

    International Nuclear Information System (INIS)

    The magnetic susceptibility of 13 intermediate valence Ce and Yb compounds was studied at room temperature as a function of pressure. Low temperature measurements showed a pressure induced shift of the susceptibility maximum for YbInAu2 and Ce(Rhsub(0.7) Ptsub(0.3))2. A general relationship between the pressure dependent activation energy and the fluctuation temperature is supposed for Yb compounds. The relative pressure dependence of the susceptibility has a maximum at the intermediate valence 2.5 and is decreasing toward integer valences. (TW)

  2. Effect of magnetic field on the two valence transitions in EuPtP

    Energy Technology Data Exchange (ETDEWEB)

    Mitsuda, Akihiro; Okuma, Toshiya; Wada, Hirofumi [Department of Physics, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581 (Japan); Sato, Keisuke; Kindo, Koichi, E-mail: 3da@phys.kyushu-u.ac.j [Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581 (Japan)

    2010-01-15

    The hexagonal layered compound EuPtP exhibits two valence transitions at T{sub 1} = 240 K and T{sub 2} = 198 K. We present field-induced shift of temperature of the two valence transitions and magnetic field versus temperature phase diagram in EuPtP. Magnetic field dependence of the valence transition temperatures, T{sub 1} and T{sub 2}, is similar to that reported in Eu(Pd{sub 1-x}Pt{sub x}){sub 2}Si{sub 2} and YbIn{sub 1-x}Ag{sub x}Cu{sub 4}.

  3. Altered Ru, Sr atomic environments in strontium ruthenates: XAFS evidence for valence and magnetism

    International Nuclear Information System (INIS)

    We have investigated Ru, Sr atoms in strontium ruthenates: SrRuO3, Sr2RuO4 and Sr3Ru2O7 with X-ray absorption fine structure (XAFS) spectroscopy. These three strontium ruthenates have remarkable different properties. We reported that valences of ruthenium ion in these strontium ruthenates exhibit the same number of four. And the valence of strontium ion in these also indicates the same number of two. Therefore, the different magnetic properties of these strontium ruthenates do not come from atomic valences but come from these crystal structures, inter atomic distance and strains

  4. Fickian dispersion is anomalous

    Science.gov (United States)

    Cushman, John H.; O'Malley, Dan

    2015-12-01

    The thesis put forward here is that the occurrence of Fickian dispersion in geophysical settings is a rare event and consequently should be labeled as anomalous. What people classically call anomalous is really the norm. In a Lagrangian setting, a process with mean square displacement which is proportional to time is generally labeled as Fickian dispersion. With a number of counter examples we show why this definition is fraught with difficulty. In a related discussion, we show an infinite second moment does not necessarily imply the process is super dispersive. By employing a rigorous mathematical definition of Fickian dispersion we illustrate why it is so hard to find a Fickian process. We go on to employ a number of renormalization group approaches to classify non-Fickian dispersive behavior. Scaling laws for the probability density function for a dispersive process, the distribution for the first passage times, the mean first passage time, and the finite-size Lyapunov exponent are presented for fixed points of both deterministic and stochastic renormalization group operators. The fixed points of the renormalization group operators are p-self-similar processes. A generalized renormalization group operator is introduced whose fixed points form a set of generalized self-similar processes. Power-law clocks are introduced to examine multi-scaling behavior. Several examples of these ideas are presented and discussed.

  5. Strain sensitivity of band gaps of Sn-containing semiconductors

    DEFF Research Database (Denmark)

    Li, Hong; Castelli, Ivano Eligio

    2015-01-01

    Tuning of band gaps of semiconductors is a way to optimize materials for applications within photovoltaics or as photocatalysts. One way to achieve this is through applying strain to the materials. We investigate the effect of strain on a range of Sn-containing semiconductors using density functional theory and many-body perturbation theory calculations. We find that the band gaps of bulk Sn oxides with SnO6 octahedra are highly sensitive to volumetric strain. By applying a small isotropic strain of 2% (-2%), a decrease (increase) of band gaps as large as 0.8 to 1.0 eV are obtained. We attribute the ultrahigh strain sensitivity to the pure Sn s-state character of the conduction-band edges. Other Sn-containing compounds may show both increasing and decreasing gaps under tensile strain and we show that the behavior can be understood by analyzing the role of the Sn s states in both the valence and the conduction bands.

  6. Influence of the sequence on the ab initio band structures of single and double stranded DNA models

    Science.gov (United States)

    Bogár, Ferenc; Bende, Attila; Ladik, János

    2014-06-01

    The solid state physical approach is widely used for the characterization of electronic properties of DNA. In the simplest case the helical symmetry is explicitly utilized with a repeat unit containing only a single nucleotide or nucleotide pair. This model provides a band structure that is easily interpretable and reflects the main characteristic features of the single nucleotide or a nucleotide pair chain, respectively. The chemical variability of the different DNA chains is, however, almost completely neglected in this way. In the present work we have investigated the effect of the different sequences on the band structure of periodic DNA models. For this purpose we have applied the Hartree-Fock crystal orbital method for single and double stranded DNA chains with two different subsequent nucleotides in the repeat unit of former and two different nucleotide pairs in the latter case, respectively. These results are compared to simple helical models with uniform sequences. The valence and conduction bands related to the stacked nucleotide bases of single stranded DNA built up only from guanidine as well as of double stranded DNA built up only from guanidine-cytidine pairs showed special properties different from the other cases. Namely, they had higher conduction and lower valence band positions and this way larger band gaps and smaller widths of these bands. With the introduction of non-uniform guanidine containing sequences band structures became more similar to each other and to the band structures of other sequences without guanidine. The maximal bandwidths of the non-uniform sequences are considerably smaller than in the case of uniform sequences implying smaller charge carrier mobilities both in the conduction and valence bands.

  7. Multi bunch dynamics in detuned x-band structures

    International Nuclear Information System (INIS)

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

  8. Observing Abnormally Large Group Velocity at the Plasmonic Band Edge via a Universal Eigenvalue Analysis

    OpenAIRE

    Sha, Wei E. I.; Meng, Ling Ling; Choy, Wallace C. H.; Chew, Weng Cho

    2015-01-01

    We developed a novel universal eigenvalue analysis for 2D arbitrary nanostructures comprising dispersive and lossy materials. The complex dispersion relation (or complex Bloch band structure) of a metallic grating is rigorously calculated by the proposed algorithm with the finite-difference implementation. The abnormally large group velocity is observed at a plasmonic band edge with a large attenuation constant. Interestingly, we found the abnormal group velocity is caused b...

  9. Band structure investigations of GaN films using modulation spectroscopy

    International Nuclear Information System (INIS)

    The paper presents investigation results concerning band structure of gallium nitride and position of intrinsic and associate defect levels. Main optical characteristics (transmission, reflection and luminescence) were measured in both ordinary and ?-modulation mode for epitaxy-grown GaN films, allowing to determine valence band splitting caused by spin-orbital interaction (48meV) and crystalline field (10meV). Analysis of photoluminescence spectra made it possible to identify main recombination mechanisms involving donor and acceptor levels formed by intrinsic point defects VN?,V'Ga, and their associates

  10. Band parameters of phosphorene

    Science.gov (United States)

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

    2015-09-01

    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 are computed using a first-principles theory based upon the generalized-gradient approximation to the density-functional theory. These parameters and Hamiltonian will be useful for modeling physical properties of phosphorene.

  11. Band parameters of phosphorene

    DEFF Research Database (Denmark)

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

    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 are computed using a first-principles theory based upon the generalized-gradient approximation to the density-functional theory. These parameters and Hamiltonian will be useful for modeling physical properties of phosphorene.

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

    International Nuclear Information System (INIS)

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Kolek, Andrzej, E-mail: akoleknd@prz.edu.pl [Department of Electronics Fundamentals, Rzeszów University of Technology, Al. Powsta?ców Warszawy 12, 35-959 Rzeszów (Poland)

    2015-05-04

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

  14. The use of bulk states to accelerate the band edge state calculation of a semiconductor quantum dot

    International Nuclear Information System (INIS)

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

  15. Externally Dispersed Interferometry for Planetary Studies

    Energy Technology Data Exchange (ETDEWEB)

    Erskine, D J; Edelstein, J; Harbeck, D; Lloyd, J

    2005-07-06

    We describe a plan to study the radial velocity of low mass stars and brown dwarfs using a combination of interferometry and multichannel dispersive spectroscopy, Externally Dispersed Interferometry (EDI). The EDI technology allows implementation of precision velocimetry and spectroscopy on existing moderate-resolution echelle or linear grating spectrograph over their full and simultaneous bandwidth. We intend to add EDI to the new Cornell TripleSpec infrared simultaneous JHK-band spectrograph at the Palomar Observatory 200'' telescope for a science-demonstration program that will allow a unique Doppler-search for planets orbiting low mass faint M, L and T type stars. The throughput advantage of EDI with a moderate resolution spectrograph is critical to achieving the requisite sensitivity for the low luminosity late L and T dwarfs.

  16. Overlap valence quarks on a twisted mass sea: a case study for mixed action Lattice QCD

    CERN Document Server

    Cichy, Krzysztof; Garcia-Ramos, Elena; Herdoiza, Gregorio; Jansen, Karl

    2012-01-01

    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.

  17. 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.

  18. Subjective Reality: The Influence of Perceived and Objective Conversational Valence on Binge Drinking Determinants.

    Science.gov (United States)

    Hendriks, Hanneke; Putte, Bas van den; de Bruijn, Gert-Jan

    2015-01-01

    Previous studies have shown that interpersonal communication, and particularly perceived conversational valence (i.e., the perceived negativity or positivity of conversations) about health topics, influences health determinants. On the basis of 43 dyads (N = 86) discussing the topic of alcohol consumption, this study is the first to show that whereas perceived and objective conversational valence are positively related, only perceived conversational valence is a significant predictor of binge drinking attitudes and intentions. Thus, subjective reality matters more than objective reality. Furthermore, only the perceived valence of the participants' own contributions-and not of their conversation partners--influences binge drinking intentions, indicating that self-persuasion is more influential than persuasion by others. Thus, conversations in which discussants themselves express negative opinions about unhealthy behaviors can enhance public health. PMID:25848964

  19. Changing the conversation: the influence of emotions on conversational valence and alcohol consumption.

    Science.gov (United States)

    Hendriks, Hanneke; van den Putte, Bas; de Bruijn, Gert-Jan

    2014-10-01

    Health campaign effects may be improved by taking interpersonal communication processes into account. The current study, which employed an experimental, pretest-posttest, randomized exposure design (N?=?208), investigated whether the emotions induced by anti-alcohol messages influence conversational valence about alcohol and subsequent persuasion outcomes. The study produced three main findings. First, an increase in the emotion fear induced a negative conversational valence about alcohol. Second, fear was most strongly induced by a disgusting message, whereas a humorous appeal induced the least fear. Third, a negative conversational valence elicited healthier binge drinking attitudes, subjective norms, perceived behavioral control, intentions, and behaviors. Thus, health campaign planners and health researchers should pay special attention to the emotional characteristics of health messages and should focus on inducing a healthy conversational valence. PMID:23812888

  20. Of two minds: forming and changing valence-inconsistent implicit and explicit attitudes.

    Science.gov (United States)

    Rydell, Robert J; McConnell, Allen R; Mackie, Diane M; Strain, Laura M

    2006-11-01

    Because different processes underlie implicit and explicit attitudes, we hypothesized that they are differentially sensitive to different kinds of information. We measured implicit and explicit attitudes over time, as different types of attitude-relevant information about a single attitude object were presented. As expected, explicit attitudes formed and changed in response to the valence of consciously accessible, verbally presented behavioral information about the target. In contrast, implicit attitudes formed and changed in response to the valence of subliminally presented primes, reflecting the progressive accretion of attitude object-evaluation pairings. As a consequence, when subliminal primes and behavioral information were of opposite valence, people formed implicit and explicit attitudes of conflicting valence. PMID:17176426

  1. Pion form factor using domain wall valence and asqtad sea quarks

    OpenAIRE

    LHP Collaboration; Fleming, George T.; Bonnet, Frederic D. R.; Edwards, Robert G.; Lewis, Randy; Richards, David G.

    2004-01-01

    We compute the pion electromagnetic form factor in a hybrid calculation with domain wall valence quarks and improved staggered (asqtad) sea quarks. This method can easily be extended to rho-to-gamma-pi transition form factors.

  2. Of Caucasians, Asians, and Giraffes: The Influence of Categorization and Target Valence on Social Projection.

    Science.gov (United States)

    Machunsky, Maya; Walther, Eva

    2015-09-01

    Past research has indicated that social projection is moderated by categorization, with more projection onto ingroups than onto outgroups. However, a few studies have reported elevated levels of projection even onto outgroups. In line with recent evidence, we hypothesized that positive target valence is the key feature of conditions that elicit projection onto outgroups. The present research extends previous findings by testing whether the effect of valence occurs independent of categorization, with increased levels of projection onto positive ingroup and non-ingroup targets alike. We designed two experiments in which target valence was manipulated by means of evaluative conditioning. Category membership was varied by using faces of Caucasians, Asians, and giraffes. The results supported our valence hypothesis. Counter-intuitively, we also found higher levels of projection onto giraffes than onto humans. These findings suggest that current cognition-based models of projection are not sufficient to account for the whole range of projection phenomena. PMID:26160332

  3. Topological Flat Band Models and Fractional Chern Insulators

    CERN Document Server

    Bergholtz, Emil J

    2013-01-01

    Topological insulators are accompanied by exotic edge states that are protected by a bulk single-particle band gap once the filled bands are characterized by non-trivial topological invariants. Interactions can have profound effects and lead to entirely new insulating phases, with an altogether much richer and less explored phenomenology, as is particularly clear in the case of partial filling of weakly dispersive bands. Most saliently, lattice generalizations of fractional quantum Hall states, dubbed fractional Chern insulators, have recently been predicted to be stabilized by interactions within nearly dispersionless bands with non-zero Chern number, $C$. Contrary to their continuum analogues, these states do not require an external magnetic field and may potentially persist at high temperatures, which make these systems very interesting in the context of applications such as topological quantum computation. This review recapitulates the basics of tight-binding models hosting nearly flat bands with non-triv...

  4. Nodal Quasiparticle Dispersion in Strongly Correlated d-wave Superconductors

    CERN Document Server

    Randeria, M; Trivedi, N; Randeria, Mohit; Paramekanti, Arun; Trivedi, Nandini

    2003-01-01

    We analyze the effects of a momentum-dependent self-energy on the photoemission momentum distribution curve (MDC) lineshape, dispersion and linewidth. We illustrate this general analysis by a detailed examination of nodal quasiparticles in high Tc cuprates. We use variational results for the nodal quasiparticle weight Z (which varies rapidly with hole doping x) and the low energy Fermi velocity $v_F^{low}$ (which is independent of x), to show that the high energy MDC dispersion $v_{high} = v_F^{low}/Z$, so that it is much larger than the bare (band structure) velocity and also increases strongly with underdoping. We also present arguments for why the low energy Fermi velocity and the high energy dispersion are independent of the bare band structure at small x. All of these results are in good agreement with earlier and recent photoemission data [Zhou et al, Nature 423, 398 (2003)].

  5. Chemical bonding: the orthogonal valence-bond view.

    Science.gov (United States)

    Sax, Alexander F

    2015-01-01

    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. PMID:25906476

  6. 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.

  7. Valence, arousal, and task effects in emotional prosody processing

    Directory of Open Access Journals (Sweden)

    SilkePaulmann

    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.

  8. Positively Valenced Stimuli Facilitate Creative Novel Metaphoric Processes by Enhancing Medial Prefrontal Cortical Activation

    OpenAIRE

    KarunaSubramaniam; MarkBeeman; MiriamFaust

    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 neutra...

  9. Incremental Validity of Positive and Negative Valence in Predicting Personality Disorder

    OpenAIRE

    Simms, Leonard J.; Yufik, Tom; GROS, DANIEL F.

    2010-01-01

    The Big Seven model of personality includes five dimensions similar to the Big Five model as well as two evaluative dimensions—Positive Valence (PV) and Negative Valence (NV)—which reflect extremely positive and negative person descriptors, respectively. Recent theory and research have suggested that PV and NV predict significant variance in personality disorder (PD) above that predicted by the Big Five, but firm conclusions have not been possible because previous studies have been limited to...

  10. Time-resolved imaging of purely valence-electron dynamics during a chemical reaction

    DEFF Research Database (Denmark)

    Hockett, Paul; Bisgaard, Christer Z.; Clarkin, Owen J.; Stolow, Albert

    2011-01-01

    Chemical reactions are manifestations of the dynamics of molecular valence electrons and their couplings to atomic motions. Emerging methods in attosecond science can probe purely electronic dynamics in atomic and molecular systems(1-6). By contrast, time-resolved structural-dynamics methods such as electron(7-10) or X-ray diffraction(11) and X-ray absorption(12) yield complementary information about the atomic motions. Time-resolved methods that are directly sensitive to both valence-electron d...

  11. Towards a typology of valency : ein Beitrag zu den Techniken Valenz und Orientierung

    OpenAIRE

    Mosel, Ulrike; Drossard, Werner

    1984-01-01

    Grammatical relations, particularly the notions of transitivity, case marking, ergativity, passive and antipassive have been a favourite subject of typological research during the last decade, but surprisingly, the notion of valency has been of marginal interest in cross-linguistic studies, though the syntactic and semantic status of participants is, to a great extent, determined by the relational properties of the verb. Valency is the property of the verb which determines the obligatory and ...

  12. X-ray emission spectroscopy to study ligand valence orbitals in Mn coordination complexes

    OpenAIRE

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

    2009-01-01

    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 ...

  13. Taking a deeper look at online reviews: The asymmetric effect of valence intensity on shopping behaviour

    OpenAIRE

    Floh, A; Koller, Monika,; Zauner, Alexander,

    2013-01-01

    This study tests the asymmetric effect of user-generated, open-ended online reviews on online shopping behaviour (intention-to-buy, intention-to-recommend, and willingness-to-pay). Three online experiments involving manipulating the valence intensity of online reviews for hotels, books, and running shoes (overall customer sample of n=818) provide empirical support for the proposed relationship. The valence intensity of online reviews moderates the effect of online reviews on purchase intentio...

  14. Music, emotion, and time perception: the influence of subjective emotional valence and arousal?

    OpenAIRE

    EmmanuelBigand; SYLVIEDROIT-VOLET; LinoJoseBueno; daniloRamos

    2013-01-01

    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 eff...

  15. Theoretical study of valence orbital response to guanine tautomerization in coordinate and momentum spaces

    Science.gov (United States)

    Yang, Zejin; Duffy, Patrick; Zhu, Quan; Takahashi, Masahiko; Wang, Feng

    2015-10-01

    The binding energy spectra and electron momentum spectra of eight stable guanine tautomers are calculated in the complete valence space. The present results show that the canonical keto (C=O) guanine N(9)H tautomer (GU1) possesses the largest dipole moment, molecular electronic spatial extent, molecular hardness value, and the minimum first vertical ionization potential (VIP). Valence orbital profile investigations find that several orbitals remain almost unchanged during tautomerization, such as frontier highest occupied molecular orbital 39a and 18a. Several orbitals with interchanged order and inverse direction in charge spatial orientations are also detected. Outer valence orbitals (with smaller VIPs) show more complex orbital shapes in the momentum space than those of inner ones (larger VIPs) due mainly to the relatively strong inter-orbital interaction and delocalized electronic distributions. Proton rotation along C-O(H) and C-N(H) axes within hexagonal ring causes smaller influence to orbital profiles than those of proton migration within pentagonal and/or hexagonal rings. Orbital variation trends between enol (GU3-GU5) and keto (GU1, GU2, GU6-GU8) tautomers are observed, including the signature orbitals of enol form, the variation tendency of total orbital intensity, and the variation order of the maximum orbital intensity. In the outer valence momentum space (outside 26a), orbital composed by pz electrons show single peak with a gradual increasing peak site from 0.5 a.u. of inner valence orbital to 1.0 a.u. of outer valence orbital, whereas orbitals composed by px,y electrons form double peaks with respective sites at about 0.5 and 1.5 a.u., only three px,y-orbitals present single peaks (33a,34a,36a). The general variation trends in the complete valence space for all the valence orbitals on their intensities, peak sites, and orbital components are concluded.

  16. Reference Valence Effects of Affective S–R Compatibility: Are Visual and Auditory Results Consistent?

    OpenAIRE

    Xiaojun, Zhao; Xuqun, You; Changxiu, Shi; Shuoqiu, Gan; Chaoyi, Hu

    2014-01-01

    Humans may be faster to avoid negative words than to approach negative words, and faster to approach positive words than to avoid positive words. That is an example of affective stimulus–response (S–R) compatibility. The present study identified the reference valence effects of affective stimulus–response (S–R) compatibility when auditory stimulus materials are used. The researchers explored the reference valence effects of affective S–R compatibility using a mixed-design experiment based on ...

  17. Bidirectional switch of the valence associated with a hippocampal contextual memory engram

    OpenAIRE

    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 o...

  18. Emotion investigated with music of variable valence : neurophysiology and cultural influence

    OpenAIRE

    Fritz, Thomas

    2008-01-01

    Music is a powerful and reliable means to stimulate the percept of both intense pleasantness and unpleasantness in the perceiver. However, everyone’s social experiences with music suggest that the same music piece may elicit a very different valence percept in different individuals. A comparison of music from different historical periods suggests that enculturation modulates the valence percept of intervals and harmonies, and thus possibly also of relatively basic feature extraction processes...

  19. Mixed-valence states and crystal structure of biferrocene derivatives with long alkyl chains

    International Nuclear Information System (INIS)

    Mixed-valence states have been investigated for a series of binuclear ferrocenium salts with long alkyl chains. In the triiodide salts with layered structures, an interesting even-odd character in the number of carbon atoms of the alkyl chain is observed in the relationship between the inter-layer distance and the mixed-valence state. 1', 1'''-didodecylbiferrocenium triiodide is found to be most interesting because this salt has a large potential for application to molecular-based devices. (orig.)

  20. Two routes to emotional memory: Distinct neural processes for valence and arousal

    OpenAIRE

    Kensinger, Elizabeth A.; CORKIN, SUZANNE

    2004-01-01

    Prior investigations have demonstrated that emotional information is often better remembered than neutral information, but they have not directly contrasted effects attributable to valence and those 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. The former depended on an amygdalar-hippocampal network, wher...

  1. Heavy-Light Decay Constants with Dynamical Gauge Configurations and Wilson or Improved Valence Quark Action

    CERN Document Server

    Bernard, C W; DeTar, C E; Gottlieb, S; Heller, U M; Hetrick, J E; McNeile, C; Orginos, K; Sugar, R L; Toussaint, D; Bernard, Claude; DeGrand, T; DeTar, C; Gottlieb, S; Heller, Urs M.; Hetrick, James E.; Neile, Craig Mc; Orginos, Kostas; Sugar, Robert L.; Toussaint, Douglas

    2000-01-01

    We describe a calculation of heavy-light decay constants including virtual quark loop effects. We have generated dynamical gauge configurations at three masses. These are analyzed with a Wilson valence quark action. Preliminary results based on a ``fat-link'' clover valence quark action are also reported. Results from the two methods differ by 30 to 50 MeV, which is presumably due to significant - but as yet unobserved - lattice spacing dependence in one or both of the approaches.

  2. The effects of valence and arousal on the neural activity leading to subsequent memory

    OpenAIRE

    Mickley Steinmetz, Katherine R.; Kensinger, Elizabeth A.

    2009-01-01

    This study examined how valence and arousal affect the processes linked to subsequent memory for emotional information. While undergoing an fMRI scan, participants viewed neutral pictures and emotional pictures varying by valence and arousal. After the scan, participants performed a recognition test. Subsequent memory for negative or high arousal information was associated with occipital and temporal activity, while memory for positive or low arousal information was associated with frontal ac...

  3. Ultrawide Band Electromagnetic Pulses

    International Science & Technology Center (ISTC)

    Development of New Calculation-Theoretical and Metrologic Approaches in Technology of Ultrawide Band Electromagnetic Pulses, Elaboration and Investigation of Standard Field-Forming Systems of Subnanosecond Pulse Field

  4. Electron and hole photoemission detection for band offset determination of tunnel field-effect transistor heterojunctions

    International Nuclear Information System (INIS)

    We report experimental methods to ascertain a complete energy band alignment of a broken-gap tunnel field-effect transistor based on an InAs/GaSb hetero-junction. By using graphene as an optically transparent electrode, both the electron and hole barrier heights at the InAs/GaSb interface can be quantified. For a Al2O3/InAs/GaSb layer structure, the barrier height from the top of the InAs and GaSb valence bands to the bottom of the Al2O3 conduction band is inferred from electron emission whereas hole emissions reveal the barrier height from the top of the Al2O3 valence band to the bottom of the InAs and GaSb conduction bands. Subsequently, the offset parameter at the broken gap InAs/GaSb interface is extracted and thus can be used to facilitate the development of predicted models of electron quantum tunneling efficiency and transistor performance

  5. Electron and hole photoemission detection for band offset determination of tunnel field-effect transistor heterojunctions

    Energy Technology Data Exchange (ETDEWEB)

    Li, Wei [National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States); Key Laboratory for the Physics and Chemistry of Nanodevices and Department of Electronics, Peking University, Beijing 100871 (China); Zhang, Qin; Kirillov, Oleg A.; Levin, Igor; Richter, Curt A.; Gundlach, David J.; Nguyen, N. V., E-mail: Nhan.Nguyen@nist.gov, E-mail: liangxl@pku.edu.cn [National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States); Bijesh, R.; Datta, S. [Department of Electrical Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802 (United States); Liang, Yiran; Peng, Lian-Mao; Liang, Xuelei, E-mail: Nhan.Nguyen@nist.gov, E-mail: liangxl@pku.edu.cn [Key Laboratory for the Physics and Chemistry of Nanodevices and Department of Electronics, Peking University, Beijing 100871 (China)

    2014-11-24

    We report experimental methods to ascertain a complete energy band alignment of a broken-gap tunnel field-effect transistor based on an InAs/GaSb hetero-junction. By using graphene as an optically transparent electrode, both the electron and hole barrier heights at the InAs/GaSb interface can be quantified. For a Al{sub 2}O{sub 3}/InAs/GaSb layer structure, the barrier height from the top of the InAs and GaSb valence bands to the bottom of the Al{sub 2}O{sub 3} conduction band is inferred from electron emission whereas hole emissions reveal the barrier height from the top of the Al{sub 2}O{sub 3} valence band to the bottom of the InAs and GaSb conduction bands. Subsequently, the offset parameter at the broken gap InAs/GaSb interface is extracted and thus can be used to facilitate the development of predicted models of electron quantum tunneling efficiency and transistor performance.

  6. Male dispersal in the noctule bat (Nyctalus noctula): where are the limits?

    OpenAIRE

    Petit, E; Mayer, F.

    1999-01-01

    Studying the dispersal behaviour of small, volant, and nocturnal animals such as microchiropterans with direct methods (banding--recapture, telemetry) is a very difficult task. The development of easily scorable and highly variable genetic markers nowadays allows us to study some aspects of dispersal indirectly, using population genetics. Here, we applied these indirect methods to characterize male dispersal behaviour in a European bat species. The eight microsatellite loci analysed were high...

  7. High birefringence, low loss terahertz photonic crystal fibres with zero dispersion at 0.3 THz

    International Nuclear Information System (INIS)

    A terahertz photonic crystal fibre (THz-PCF) is designed for terahertz wave propagation. The dispersion property and model birefringence are studied by employing the finite element method. The simulation result reveals the changing patten of dispersion parameter versus the geometry. The influence of the large frequency band of terahertz on birefringence is also discussed. The design of low loss, high birefringence THz-PCFs with zero dispersion frequency at 0.3 THz is presented. (general)

  8. Distribution Free Prediction Bands

    OpenAIRE

    Lei, Jing; Wasserman, Larry

    2012-01-01

    We study distribution free, nonparametric prediction bands with a special focus on their finite sample behavior. First we investigate and develop different notions of finite sample coverage guarantees. Then we give a new prediction band estimator by combining the idea of "conformal prediction" (Vovk et al. 2009) with nonparametric conditional density estimation. The proposed estimator, called COPS (Conformal Optimized Prediction Set), always has finite sample guarantee in a ...

  9. Supersymmetry and Identical Bands

    OpenAIRE

    Von Brentano, P.

    2003-01-01

    Supersymmetry as applied to identical bands is discussed. A review of the work of the Koeln-Dubna group on this topic is given and examples in 171,172Yb, 173,174Hf, and 195,194Pt are discussed. The role of pseudo-spin in the supersymmetry is investigated. A recent precision lifetime measurement for identical bands in 171,172Yb is discussed.

  10. 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. PMID:22131982

  11. Observation of a blue shift in the optical response at the fundamental band gap in Ga1-xMnxAs.

    Czech Academy of Sciences Publication Activity Database

    de Boer, T.; Gamouras, A.; March, S.; Novák, Vít; Hall, K.C.

    2012-01-01

    Ro?. 85, ?. 3 (2012), "033202-1"-"033202-5". ISSN 1098-0121 R&D Projects: GA AV ?R KAN400100652; GA MŠk LC510 Institutional research plan: CEZ:AV0Z10100521 Keywords : differential reflectivity * GaMnAs * valence- band model * ferromagnetism Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.767, year: 2012

  12. Experimental Investigation of the N-Pbs/P-Si Heterojunction Band Lineup with I-V and C-V Measurements

    OpenAIRE

    Ismail, Raid A. [???? ????????? ????????

    2005-01-01

    In this paper we present experimental investigation of band lineup of near ideal PbS/Si heterojunction diode using I-V and C-V measurements. The C-V measurements show that the fabricated diodes were abrupt type, and the built-in potential Vui wds determined from C-2-V plot. The band offsets of A,Ec: 0.15 eV and A,Ev:0.55 eV were calculated at 300 K for conduction and valence bands, respectively. The energy band diagram of n-PbS/p-Si heterojunction was constructed. I-V measurements of differen...

  13. Direct measurement of band offset at the interface between CdS and Cu{sub 2}ZnSnS{sub 4} using hard X-ray photoelectron spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Tajima, Shin; Kataoka, Keita; Takahashi, Naoko; Kimoto, Yasuji; Fukano, Tatsuo; Hasegawa, Masaki; Hazama, Hirofumi [Toyota Central Research and Development Laboratories, Inc., Nagakute, Aichi 480-1192 (Japan)

    2013-12-09

    We directly and non-destructively measured the valence band offset at the interface between CdS and Cu{sub 2}ZnSnS{sub 4} (CZTS) using hard X-ray photoelectron spectroscopy (HAXPES), which can measure the electron state of the buried interface because of its large analysis depth. These measurements were made using the following real devices; CZTS(t = 700 nm), CdS(t = 100 nm)/CZTS(t = 700 nm), and CdS(t = 5 nm)/CZTS(t = 700 nm) films formed on Mo coated glass. The valence band spectra were measured by HAXPES using an X-ray photon energy of 8 keV. The value of the valence band offset at the interface between CdS and CZTS was estimated as 1.0 eV by fitting the spectra. The conduction band offset could be deduced as 0.0 eV from the obtained valence band offset and the band gap energies of CdS and CZTS.

  14. Dispersion Models for Extremes

    CERN Document Server

    Jørgensen, Bent; Martínez, José Raúl

    2007-01-01

    We propose extreme value analogues of natural exponential families and exponential dispersion models, and introduce the slope function as an analogue of the variance function. The set of quadratic and power slope functions characterize well-known families such as the Rayleigh, Gumbel, power, Pareto, logistic, negative exponential, Weibull and Fr\\'echet. We show a convergence theorem for slope functions, by which we may express the classical extreme value convergence results in terms of asymptotics for extreme dispersion models. The main idea is to explore the parallels between location families and natural exponential families, and between the convolution and minimum operations.

  15. Band-gap narrowing of TiO2 films induced by N-doping

    International Nuclear Information System (INIS)

    N-doped TiO2 films were deposited on n + -GaN/Al2O3 substrates by reactive magnetron sputtering and subsequently crystallized by annealing at 550 oC in flowing N2 gas. The N-doping concentration was ?8.8%, as determined from X-ray photoelectron spectroscopy measurements. Deep-level optical spectroscopy measurements revealed two characteristic deep levels located at 1.18 and 2.48 eV below the conduction band. The 1.18 eV level is probably attributable to the O vacancy state and can be active as an efficient generation-recombination center. Additionally, the 2.48 eV band is newly introduced by the N-doping and contributes to band-gap narrowing by mixing with the O 2p valence band

  16. Band Gap Narrowing and Widening of ZnO Nanostructures and Doped Materials.

    Science.gov (United States)

    Kamarulzaman, Norlida; Kasim, Muhd Firdaus; Rusdi, Roshidah

    2015-12-01

    Band gap change in doped ZnO is an observed phenomenon that is very interesting from the fundamental point of view. This work is focused on the preparation of pure and single phase nanostructured ZnO and Cu as well as Mn-doped ZnO for the purpose of understanding the mechanisms of band gap narrowing in the materials. ZnO, Zn0.99Cu0.01O and Zn0.99Mn0.01O materials were prepared using a wet chemistry method, and X-ray diffraction (XRD) results showed that all samples were pure and single phase. UV-visible spectroscopy showed that materials in the nanostructured state exhibit band gap widening with respect to their micron state while for the doped compounds exhibited band gap narrowing both in the nano and micron states with respect to the pure ZnO materials. The degree of band gap change was dependent on the doped elements and crystallite size. X-ray photoelectron spectroscopy (XPS) revealed that there were shifts in the valence bands. From both UV-visible and XPS spectroscopy, it was found that the mechanism for band gap narrowing was due to the shifting of the valance band maximum and conduction band minimum of the materials. The mechanisms were different for different samples depending on the type of dopant and dimensional length scales of the crystallites. PMID:26319225

  17. Band Gap Narrowing and Widening of ZnO Nanostructures and Doped Materials

    Science.gov (United States)

    Kamarulzaman, Norlida; Kasim, Muhd Firdaus; Rusdi, Roshidah

    2015-08-01

    Band gap change in doped ZnO is an observed phenomenon that is very interesting from the fundamental point of view. This work is focused on the preparation of pure and single phase nanostructured ZnO and Cu as well as Mn-doped ZnO for the purpose of understanding the mechanisms of band gap narrowing in the materials. ZnO, Zn0.99Cu0.01O and Zn0.99Mn0.01O materials were prepared using a wet chemistry method, and X-ray diffraction (XRD) results showed that all samples were pure and single phase. UV-visible spectroscopy showed that materials in the nanostructured state exhibit band gap widening with respect to their micron state while for the doped compounds exhibited band gap narrowing both in the nano and micron states with respect to the pure ZnO materials. The degree of band gap change was dependent on the doped elements and crystallite size. X-ray photoelectron spectroscopy (XPS) revealed that there were shifts in the valence bands. From both UV-visible and XPS spectroscopy, it was found that the mechanism for band gap narrowing was due to the shifting of the valance band maximum and conduction band minimum of the materials. The mechanisms were different for different samples depending on the type of dopant and dimensional length scales of the crystallites.

  18. Band alignment of epitaxial ZnS/Zn{sub 3}P{sub 2} heterojunctions

    Energy Technology Data Exchange (ETDEWEB)

    Bosco, Jeffrey P.; Demers, Steven B.; Kimball, Gregory M.; Lewis, Nathan S.; Atwater, Harry A. [Watson Laboratory and Noyes Laboratory, Beckman Institute and Kavli Nanoscience Institute, California Institute of Technology, 1200 E. California Blvd., Pasadena, California 91125 (United States)

    2012-11-01

    The energy-band alignment of epitaxial zb-ZnS(001)/{alpha}-Zn{sub 3}P{sub 2}(001) heterojunctions has been determined by measurement of shifts in the phosphorus 2p and sulfur 2p core-level binding energies for various thicknesses (0.6-2.2 nm) of ZnS grown by molecular beam epitaxy on Zn{sub 3}P{sub 2}. In addition, the position of the valence-band maximum for bulk ZnS and Zn{sub 3}P{sub 2} films was estimated using density functional theory calculations of the valence-band density-of-states. The heterojunction was observed to be type I, with a valence-band offset, {Delta}E{sub V,} of -1.19 {+-} 0.07 eV, which is significantly different from the type II alignment based on electron affinities that is predicted by Anderson theory. n{sup +}-ZnS/p-Zn{sub 3}P{sub 2} heterojunctions demonstrated open-circuit voltages of >750 mV, indicating passivation of the Zn{sub 3}P{sub 2} surface due to the introduction of the ZnS overlayer. Carrier transport across the heterojunction devices was inhibited by the large conduction-band offset, which resulted in short-circuit current densities of <0.1 mA cm{sup -2} under 1 Sun simulated illumination. Hence, constraints on the current density will likely limit the direct application of the ZnS/Zn{sub 3}P{sub 2} heterojunction to photovoltaics, whereas metal-insulator-semiconductor structures that utilize an intrinsic ZnS insulating layer appear promising.

  19. Photonic band structures in one-dimensional photonic crystals containing Dirac materials

    Science.gov (United States)

    Wang, Lin; Wang, Li-Gang

    2015-09-01

    We have investigated the band structures of one-dimensional photonic crystals (1DPCs) composed of Dirac materials and ordinary dielectric media. It is found that there exist an omnidirectional passing band and a kind of special band, which result from the interaction of the evanescent and propagating waves. Due to the interface effect and strong dispersion, the electromagnetic fields inside the special bands are strongly enhanced. It is also shown that the properties of these bands are invariant upon the lattice constant but sensitive to the resonant conditions.

  20. Effects of Aspect Ratio on the Shear Band Arrangements of Zr-Based Metallic Glasses

    Science.gov (United States)

    Feng, Shidong; Li, Gong; Yu, Pengfei; Zhang, Shiliang; Ma, Mingzhen; Qi, Li; Liu, Riping

    2015-03-01

    Effects of aspect ratios of Zr-based metallic glasses on the shear band arrangements are investigated through molecular dynamics simulations and experiments. It is found that as the aspect ratio decreases, the dense multiple shear bands form, effectively depressing the formation of the penetrating shear bands, which improves plasticity and strength of metallic glass. Simulation reproduces the images of the evolution of the shear bands in metallic glass, explaining the experimental observation. It is found that as the aspect ratio decreases, shear transformation zones disperse evenly in the entire model, restraining connecting into penetrating shear bands.