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Sample records for valence band dispersion

  1. Site-specific intermolecular valence-band dispersion in ?-phase crystalline films of cobalt phthalocyanine studied by angle-resolved photoemission spectroscopy

    International Nuclear Information System (INIS)

    The valence band structure of ?-phase crystalline films of cobalt phthalocyanine (CoPc) grown on Au(111) is investigated by using angle-resolved photoemission spectroscopy (ARPES) with synchrotron radiation. The photo-induced change in the ARPES peaks is noticed in shape and energy of the highest occupied molecular orbital (HOMO, C 2p) and HOMO-1 (Co 3d) of CoPc, and is misleading the interpretation of the electronic properties of CoPc films. From the damage-free normal-emission ARPES measurement, the clear valence-band dispersion has been first observed, showing that orbital-specific behaviors are attributable to the interplay of the intermolecular ?-? and ?-d interactions. The HOMO band dispersion of 0.1 eV gives the lower limit of the hole mobility for ?-CoPc of 28.9 cm2 V?1 s?1 at 15 K. The non-dispersive character of the split HOMO-1 bands indicates that the localization of the spin state is a possible origin of the antiferromagnetism

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

    International Nuclear Information System (INIS)

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

  3. 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.

  4. 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)

  5. Valence band photoemission studies of clean metals

    Energy Technology Data Exchange (ETDEWEB)

    Wehner, P.S.

    1978-04-01

    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..nu.. < 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. 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

  7. 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.

  8. Instanton contributions to the valence band of the double sine-Gordon potential

    International Nuclear Information System (INIS)

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

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

    International Nuclear Information System (INIS)

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

  10. 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.

  11. 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

  12. Valence and conduction band structure of the quasi-two-dimensional semiconductor Sn S2

    Science.gov (United States)

    Racke, David A.; Neupane, Mahesh R.; Monti, Oliver L. A.

    2016-02-01

    We present the momentum-resolved photoemission spectroscopy of both the valence and the conduction band region in the quasi-two-dimensional van der Waals-layered indirect band gap semiconductor Sn S2 . Using a combination of angle-resolved ultraviolet photoemission and angle-resolved two-photon photoemission (AR-2PPE) spectroscopy, we characterize the band structure of bulk Sn S2 . Comparison with density functional theory calculations shows excellent quantitative agreement in the valence band region and reveals several localized bands that likely originate from defects such as sulfur vacancies. Evidence for a moderate density of defects is also observed by AR-2PPE in the conduction band region, leading to localized bands not present in the computational results. The energetic structure and dispersion of the conduction bands is captured well by the computational treatment, with some quantitative discrepancies remaining. Our results provide a broader understanding of the electronic structure of Sn S2 in particular and van der Waals-layered semiconductors in general.

  13. Valence band electronic structure characterization of the rutile TiO? (110)-(1 × 2) reconstructed surface

    OpenAIRE

    Sánchez-Sánchez, C.; Garnier, M. G.; Aebi, Philipp; Blanco-Rey, M.; de andres, P. L.; Martín-Gago, J. A.; López, M. F.

    2012-01-01

    The electronic structure of the TiO? (110)-(1 × 2) surface has been studied by means of angular resolved ultraviolet photoemission spectroscopy (ARUPS). The valence band dispersion along the high symmetry surface directions, [001] and [1–10], has been recorded. The experimental data show no dispersion of the band-gap Ti 3d states. However, the existence of dispersive bands along the [001] direction located at about 7 eV below the Fermi level is reported. The existence of two different contrib...

  14. 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

  15. 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.

  16. 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.

  17. XPS valence band spectra and theoretical calculations for investigations on thiogermanate and thiosilicate glasses

    International Nuclear Information System (INIS)

    This paper reports on investigations of thiogermanate and thiosilicate crystals and glasses by means of XPS valence band spectra and theoretical calculations (FLAPW method). The calculations were achieved on three crystallized phases GeS2, Na2GeS3 and SiS2 and valence band spectra (visualization of the occupied electronic density of states) were precisely interpreted through modulated density of states and charge density maps. This information was used to go further in the structural investigations of some thiogermanate and thiosilicate glasses. In sodium thiogermanates, an increase in Ge-Ge bonds was revealed as the modifier content (Na2S) increases. In thiosilicates, the evolution of the valence spectra according to the nature of the alkaline atoms (Li, Na) has been interpreted as changes in the local connectivity of units (edge or corner sharing tetrahedra). This study exhibits the potentialities of valence band spectra to provide information on glassy systems

  18. Valence band excitations in $V_{2}O_{5}$

    CERN Document Server

    Atzkern, S; Knupfer, M; Golden, M S; Fink, J; Yaresko, A N; Antonov, V N; Klemm, M; Horn, S

    1999-01-01

    We present a joint theoretical and experimental investigation of the electronic and optical properties of vanadium pentoxide. Electron energy-loss spectroscopy in transmission was employed to measure the momentum-dependent loss function. This in turn was used to derive the optical conductivity, which is compared to the results of band structure calculations. A good qualitative and quantitative agreement between the theoretical and the experimental optical conductivity was observed. The experimentally observed anisotropy of the optical properties of V_2O_5 could be understood in the light of an analysis of the theoretical data involving the decomposition of the calculated optical conductivity into contributions from transitions into selected energy regions of the conduction band. In addition, based upon a tight binding fit to the band structure, values are given for the effective V3d_xy-O2p hopping terms and are compared to the corresponding values for alpha'-NaV_2O_5.

  19. Observation of valence band electron emission from n-type silicon field emitter arrays

    Science.gov (United States)

    Ding, Meng; Kim, Han; Akinwande, Akintunde I.

    1999-08-01

    Electron emission from the valence band of n-type Si field emitter arrays is reported. High electrostatic field at the surface of Si was achieved by reducing the radius of the emitter tip. Using oxidation sharpening, 1 ?m aperture polycrystalline Si gate, n-type Si field emitter arrays with small tip radius (˜10 nm) were fabricated. Three distinct emission regions were observed: conduction band emission at low gate voltages, saturated current emission from the conduction band at intermediate voltages, and valence band plus conduction band emission at high gate voltages. Emission currents at low and high voltages obey the Fowler-Nordheim theory. The ratio of the slopes of the corresponding Fowler-Nordheim fits for these two regions is 1.495 which is in close agreement with the theoretical value of 1.445.

  20. 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.

  1. 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.

  2. 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

  3. 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.

  4. 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.

  5. 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

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

    Science.gov (United States)

    Schief, H.; Toennies, J. P.

    1994-09-01

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

  7. Valence band structure and optical properties of ZnO1?xSx ternary alloys

    International Nuclear Information System (INIS)

    The k.p method and the effective mass theory are applied to compute valence-band electronic structure and optical properties of ZnO1?xSx ternary alloys under biaxial strain. A significant modification of the band structure with increasing sulfur content is revealed. Features of wave-functions and matrix elements in the transverse electrical (TE) and transverse magnetic (TM) regimes for three valence subbands are studied and discussed. The results of calculations of interband transition energy and spontaneous emission spectra are in agreement with experimental data for ZnO1?xSx films grown by radiofrequency magnetron sputtering technique. - Highlights: • The band structure and matrix elements of ZnO1?xSx alloys are calculated. • Sulfur content effect on matrix elements and emission spectra is studied. • Physical nature of the interband transitions in ZnO1?xSx alloys is explained. • A good qualitative agreement between theory and experiment is observed

  8. Evolution of the Mlct Band Following Changes in Oxidation State for Highly Coupled Mixed Valence Complexes

    Science.gov (United States)

    Lear, Benjamin J.; Chisholm, Malcolm H.

    2009-06-01

    The MLCT band for a series of dimers composed of pairs of quadruply bonded metal-metal units ([MM(CH_3CO_2)_3]_2-?_2-oxalate; where M=Mo or W) is examined in both the neutral and +1 (mixed valence) states. The MLCT band for the neutral state of these complexes exhibits clear vibronic features that are greatly reduced in intensity upon generation of the mixed valence state. Utilizing the time dependent theory of spectroscopy as developed by Eric Heller, these results (together with Raman spectra and TD-DFT calculations) are used in order to draw conclusions concerning the potential energy surfaces involved in the MLCT transition for these complexes. In particular, we are concerned with changes to the offset of the ground and excited state potential energy surfaces that occur along the coordinates involved in the vibronic coupling and which accompany changes in oxidation state. The insight thus gained is used in order to understand the degree of electronic coupling present in mixed valence species and to comment on the classification of mixed valence complexes.

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

    International Nuclear Information System (INIS)

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

  10. 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

  11. 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)

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

    Energy Technology Data Exchange (ETDEWEB)

    Minar, J. [Department Chemie und Biochemie, Physikalische Chemie, Universitaet Muenchen, Butenandtstr. 5-13, D-81377 Munich (Germany)]. E-mail: jan.minar@cup.uni-muenchen.de; Chadov, S. [Department Chemie und Biochemie, Physikalische Chemie, Universitaet Muenchen, Butenandtstr. 5-13, D-81377 Munich (Germany); Ebert, H. [Department Chemie und Biochemie, Physikalische Chemie, Universitaet Muenchen, Butenandtstr. 5-13, D-81377 Munich (Germany); Chioncel, L. [Institut fuer Theoretische Physik - Computational Physics, Technische Universitaet Graz, A-8010 Graz (Austria); Lichtenstein, A. [Institut fuer theoretische Physik, Universitaet Hamburg, 20355 Hamburg (Germany); De Nadai, C. [European Synchrotron Radiation Facility, BoIte Postale 220, 38043 Grenoble Cedex (France); Brookes, N.B. [European Synchrotron Radiation Facility, BoIte Postale 220, 38043 Grenoble Cedex (France)

    2005-07-21

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

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

    International Nuclear Information System (INIS)

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

  14. 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

  15. 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

  16. 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)

  17. Convergence of valence bands for high thermoelectric performance for p-type InN

    Science.gov (United States)

    Li, Hai-Zhu; Li, Ruo-Ping; Liu, Jun-Hui; Huang, Ming-Ju

    2015-12-01

    Band engineering to converge the bands to achieve high valley degeneracy is one of effective approaches for designing ideal thermoelectric materials. Convergence of many valleys in the valence band may lead to a high Seebeck coefficient, and induce promising thermoelectric performance of p-type InN. In the current work, we have systematically investigated the electronic structure and thermoelectric performance of wurtzite InN by using the density functional theory combined with semiclassical Boltzmann transport theory. Form the results, it can be found that intrinsic InN has a large Seebeck coefficient (254 ?V/K) and the largest value of ZeT is 0.77. The transport properties of p-type InN are better than that of n-type one at the optimum carrier concentration, which mainly due to the large Seebeck coefficient for p-type InN, although the electrical conductivity of n-type InN is larger than that of p-type one. We found that the larger Seebeck coefficient for p-type InN may originate from the large valley degeneracy in the valence band. Moreover, the low minimum lattice thermal conductivity for InN is one key factor to become a good thermoelectric material. Therefore, p-type InN could be a potential material for further applications in the thermoelectric area.

  18. 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.

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

    International Nuclear Information System (INIS)

    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

  20. The role of valence-band excitation in laser ablation of KCl

    Science.gov (United States)

    Haglund, Richard F., Jr.; Tang, Kai; Bunton, Patrick H.; Wang, Ling-Jun

    1991-01-01

    We present recent measurements of excited-atom and ion emission from KCl surfaces illuminated by vacuum-ultraviolet synchrotron radiation (h-nu = 8-28 eV) and ultraviolet laser light (h-nu = 4 eV). At low intensities characteristic of the synchrotron experiments, excited atoms are desorbed by simple valence-band excitation process involving the metallization of the KCl surface. At the higher intensities typical of laser desorption and ablation, we observe a strong decrease in K emission as a function of the number of laser shots, but an essentially constant yield of Cl. K(+) and Cl(-) emission at high intensities show similar behavior. The energetics of these desorption phenomena can be treated in a bond-orbital model which shows that creation of a single valence hole is sufficient to excite an ion to an anti-bonding state.

  1. 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.

  2. Spin splitting of the valence band Landau levels in GaAs quantum wells

    Science.gov (United States)

    Khan, I.; Ali, T.; Yasar, M.; Petrou, A.; Hanbicki, A.; Kioseoglou, G.; Li, C.; Jonker, B.

    2009-03-01

    We have studied as function of magnetic field the electroluminescence spectra from an n-i-p LED that incorporates three GaAs quantum wells in the intrinsic region. This device has excess n-type doping and as a result, the quantum wells are populated by a two-dimensional electron gas. The broad zero field emission band evolves into a series of discrete features in the presence of a magnetic field. These are identified as interband transitions between the l = 0, 1, and 2 Landau levels associated with the e1 and h1 subbands, with the selection rule ?l = 0. The EL spectra were analyzed in their ?+(LCP) and ?- (RCP) components. An energy splitting between the two polarized components is observed for each Landau level transition, which is equal to the sum of the conduction and valence band spin splittings. Since the electron g-factor value is known (g = - 0.44) we were able to determine the valence band spin splittings. Our experimental values are compared to calculated values (1) and were found to be in reasonable agreement. Work at SUNY was supported by ONR and NSF 1. H.A. Nickel et al., Phys. Rev. B, 62, 2773, (2000)

  3. UV photoemission study on the valence band of Mo (110) during argon ion bombardment

    International Nuclear Information System (INIS)

    The electronic structure change in the valence band of molybdenum (110) during argon ion bombardment is studied. The UPS measurements using synchrotron radiation show that argon ion bombardment induces a reduction in intensity of the peak at 4.10 eV below Fermi energy and a decrease in the work function. This peak reduction is explained in terms of substitution of a vacancy for a molybdenum atom. The decrease in the work function also suggests that vacancies are being created in the surface region due to argon ion bombardment. (author)

  4. Near valence-band electronic properties of semiconducting ? -Ga2O3 (100) single crystals

    Science.gov (United States)

    Navarro-Quezada, A.; Alamé, S.; Esser, N.; Furthmüller, J.; Bechstedt, F.; Galazka, Z.; Skuridina, D.; Vogt, P.

    2015-11-01

    ? -Ga2O3 is a transparent wide-band-gap semiconductor that has attracted considerable interest in recent years due to its suitable electrical conductivity and transparency in the ultraviolet spectral region. In this work we investigate the electronic properties of the near valence-band-edge region for semiconducting ? -Ga2O3 (100) bulk single crystals using core-level photoelectron spectroscopy and ab initio theory within the framework of density functional theory and the GW approach. We find good agreement between the experimental results and the theoretical calculations. This is explained by the hybridization of the Ga 3 d and O 2 s states, similar as for In2O3 .

  5. 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

  6. Optical investigation on the valence band structure of AlGaN with low Al content

    Energy Technology Data Exchange (ETDEWEB)

    Meisch, Tobias; Neuschl, Benjamin; Thonke, Klaus [Institut of Quantum Matter, Ulm University, 89069 Ulm (Germany); Lipski, Frank; Forghani, Kamran; Scholz, Ferdinand [Institut of Optoelectronics, Ulm University, 89069 Ulm (Germany); Feneberg, Martin [Institut fuer Experimentelle Physik, Abt. Materialphysik, Otto-von-Guericke-Universitaet Magdeburg, Universitaetsplatz 2, 39106 Magdeburg (Germany)

    2011-07-01

    For the binary semiconductors GaN and AlN, the crystal field splitting determining the valence band structure changes from {approx}+20 meV (GaN) to {approx}-200 meV (AlN), whereas the spin orbit splitting should remain constant at {approx} 20 meV. Therefore, for unstrained AlGaN ternary layers an interchange of the character of the topmost valence band from {gamma}{sub 9} to {gamma}{sub 7} is theoretically expected for an Al content in the range of 5-10%, manifesting itself mainly in a change of polarization of optical transitions. Strain in epitaxial layers alters the situation and shifts this crossing point. Literature reports experimental values ranging from 20% to 75% Al for the crossover. We present results of temperature dependent photoluminescence and reflectivity experiments on AlGaN layers with Al content ranging from 0 to 30%, and find different contributions from free and bound excitons. The Al content and strain were determined from multiple HRXRD reflections, and entered in a 6 x 6 k.p model calculation. We discuss our experimental spectra on the basis of this calculation.

  7. Experimental determination of conduction and valence bands of semiconductor nanoparticles using Kelvin probe force microscopy

    International Nuclear Information System (INIS)

    The ability to determine a semiconductor’s band edge positions is important for the design of new photocatalyst materials. In this paper, we introduced an experimental method based on Kelvin probe force microscopy to determine the conduction and valence band edge energies of semiconductor nanomaterials, which has rarely been demonstrated. We tested the method on six semiconductor nanoparticles (?-Fe2O3, CeO2, Al2O3, CuO, TiO2, and ZnO) with known electronic structures. The experimentally determined band edge positions for ?-Fe2O3, Al2O3, and CuO well matched the literature values with no statistical difference. Except CeO2, all other metal oxides had a consistent upward bias in the experimental measurements of band edge positions because of the shielding effect of the adsorbed surface water layer. This experimental approach may outstand as a unique alternative way of probing the band edge energy positions of semiconductor materials to complement the current computational methods, which often find limitations in new synthetic or complex materials. Ultimately, this work provides scientific foundation for developing experimental tools to probe nanoscale electronic properties of photocatalytic materials, which will drive breakthroughs in the design of novel photocatalytic systems and advance the fundamental understanding of material properties.

  8. 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

  9. 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.

  10. 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.

  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

    Energy Technology Data Exchange (ETDEWEB)

    King, Sean W., E-mail: sean.king@intel.com; Brockman, Justin; Bielefeld, Jeff; French, Marc; Kuhn, Markus [Logic Technology Development, Intel Corporation, Hillsboro, Oregon 97124 (United States); Paquette, Michelle M.; Otto, Joseph W.; Caruso, A. N. [Department of Physics and Astronomy, University of Missouri-Kansas City, Kansas City, Missouri 64110 (United States); French, Benjamin [Ocotillo Materials Laboratory, Intel Corporation, Chandler, Arizona 85248 (United States)

    2014-03-10

    To facilitate the design of heterostructure devices employing hexagonal/sp{sup 2} 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 sp{sup 2} 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-SiO{sub 2} and low-k a-SiOC:H materials (E{sub g}???8.2?8.8?eV), a type I band alignment was observed where the a-BN:H band gap (E{sub g}?=?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 (E{sub g}?=?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 (E{sub g}?=?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-SiO{sub 2} interfaces with Si (100)

  13. 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)

  14. Direct determination of the band offset in atomic layer deposited ZnO/hydrogenated amorphous silicon heterojunctions from X-ray photoelectron spectroscopy valence band spectra

    International Nuclear Information System (INIS)

    The chemical composition and band alignment at the heterointerface between atomic layer deposition-grown zinc oxide (ZnO) and hydrogenated amorphous silicon (a-Si:H) is investigated using monochromatized X-ray photoelectron spectroscopy. A new approach for obtaining the valence band offset ?EV is developed, which consists in fitting the valence band (VB) spectrum obtained for a-Si:H with a thin ZnO overlayer as the sum of experimentally obtained VB spectra of a bulk a-Si:H film and a thick ZnO film. This approach allows obtaining ?EV?=?2.71?±?0.15?eV with a minimum of assumptions, and also yields information on the change in band bending of both substrate and ZnO film. The band offset results are compared to values obtained using the usual approach of comparing valence band edge-to-core level energy differences, ?EB,CL ???EB,VB. Furthermore, a theoretical value for the VB offset is calculated from the concept of charge neutrality level line-up, using literature data for the charge neutrality levels and the experimentally determined ZnO/a-Si:H interface dipole. The thus obtained value of ?EVCNL?=?2.65?±?0.3?eV agrees well with the experimental ?EV.

  15. 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.

  16. 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)

  17. 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)

  18. Determination of the valence band offset at selected oxide/InN interfaces

    International Nuclear Information System (INIS)

    The valence band offsets (VBO) at different oxide/InN(0001) interfaces are investigated for TiO2, HfO2, Al2O3 and In2O3 using X-ray photoelectron spectroscopy. These oxide materials might be potential candidates for the use as barrier material in InN based transistors. The precise knowledge of the band alignment at the oxide/InN interface is relevant to understand the carrier transport characteristics in electronic devices. InN films with a thickness of 1 ?m were grown by PAMBE on GaN(0001)/Al2O3 templates. Thin oxide films were grown on top of these InN layers, within a series of varying thickness (1-5 nm). TiO2 and HfO2 were deposited by plasma-assisted e-beam evaporation, while for Al2O3 a remote plasma ALD process was used and In2O3 was grown by MOCVD. Thickness dependent changes of the barrier could only be found for TiO2 which exhibited the strongest degree of process-induced InN interface oxidation. The VBO values, which were determined by linear extrapolation of the thickness dependence, are 1.8 eV, 1.2 eV, 2.65 eV and 1.5 eV for the TiO2/InN, HfO2/InN, Al2O3/InN and In2O3/InN heterointerface, respectively.

  19. X-ray photoemission spectroscopy determination of the InN/yttria stabilized cubic-zirconia valence band offset

    International Nuclear Information System (INIS)

    The valence band offset of wurtzite InN(0001)/yttria stabilized cubic-zirconia (YSZ)(111) heterojunctions is determined by x-ray photoemission spectroscopy to be 1.19±0.17 eV giving a conduction band offset of 3.06±0.20 eV. Consequently, a type-I heterojunction forms between InN and YSZ in the straddling arrangement. The low lattice mismatch and high band offsets suggest potential for use of YSZ as a gate dielectric in high-frequency InN-based electronic devices

  20. 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.

  1. 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.

  2. Valence band gaps and plasma energies for galena, sphalerite, and chalcopyrite natural minerals using differential optical reflectance spectroscopy

    Science.gov (United States)

    Todoran, R.; Todoran, D.; Szakacs, Zs.

    2015-12-01

    The paper presents the determinations of the valence band gaps and plasma energies of the galena, sphalerite and chalcopyrite natural minerals. The work was carried out using differential optical reflectance spectroscopy of the clean mineral surfaces. The determination of the optical properties such as refractive index, real part of the complex dielectric constant and the location of certain van Hove singularities, was carried out using the Kramers-Kronig formalism.

  3. 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.

  4. 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

  5. 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

  6. 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.

  7. 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

  8. 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.

  9. The quasiparticle band dispersion in epitaxial multilayer silicene

    International Nuclear Information System (INIS)

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

  10. LDA+DMFT calculations of X-ray absorption and x-ray circular dichroism spectra: Role of valence-band correlations

    Energy Technology Data Exchange (ETDEWEB)

    Sipr, Ondrej; Simunek, Antonin [Institute of Physics AS CR, Cukrovarnicka 10, Prague (Czech Republic); Minar, Jan; Ebert, Hubert [Universitaet Muenchen (Germany)

    2010-07-01

    L{sub 2,3}-edge XAS and XMCD spectra of 3d elements are calculated via a self-consistent LDA+DMFT method (including thus valence-band correlations). It is found that the asymmetry of the calculated XAS white lines increases upon inclusion of the correlations for Fe and Co but not for Ni. The change in the height of the L{sub 3} and L{sub 2} peaks in the XMCD spectra is in a good agreement with the change of the orbital magnetic moment caused by adding the valence-band correlations. As a whole, adding valence-band correlations improves the agreement between the theory and experiment but visible differences still remain. Therefore, a core hole is additionally accounted for via the final state approximation and the impact of such a procedure is assessed.

  11. 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

  12. 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.

  13. Observation and theoretical description of the pure Fano-effect in the valence-band photo-emission of ferromagnets

    CERN Document Server

    Minar, J; De Nadai, C; Brookes, N B; Venturini, F; Ghiringhelli, G; Chioncel, L; Katsnelson, M I; Lichtenstein, A I

    2005-01-01

    The pure Fano-effect in angle-integrated valence-band photo-emission of ferromagnets has been observed for the first time. A contribution of the intrinsic spin polarization to the spin polarization of the photo-electrons 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 photo-current 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 (LSDA). 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 (DMFT).

  14. Fano effect in the angle-integrated valence band photoemission of the noble metals Cu, Ag, and Au

    International Nuclear Information System (INIS)

    Results of a combined experimental and theoretical investigation on the Fano-effect in the angle-integrated valence band photoemission of the noble metals are presented. In line with the fact that the Fano-effect is caused by the spin-orbit-coupling, the observed spin polarization of the photocurrent was found to be the more pronounced the higher the atomic number of the element investigated. The ratio of the normalized spin difference curves, however, agreed only for Cu and Ag with the ratio of the corresponding spin-orbit coupling strength parameters. The deviation from this expected behavior in the case of Au could be explained by the properties of individual d-p- and d-f-contributions to the total spin difference curves, that were found to be quite different for Au compared to Cu and Ag

  15. Anomalous temperature dependence in valence band spectra: A resonant photoemission study of layered perovskite Sr2CoO4

    International Nuclear Information System (INIS)

    Valence band spectra (VBS) and its modification across Curie temperature (TC) of Sr2CoO4 thin film are studied using resonant photoemission spectroscopy. It is found that VBS mainly consists of hybridized states of Co-3d t2geg and O-2p; however, Co-3d eg states show its prominence only in the ferromagnetic temperature regime. Below TC, spectral weight transfer takes place anomalously from high binding energy (B.E.) region to low B.E. region, signifying the enhanced intermediate or low spin state Co4+ ions. It is suggested that spin-lattice coupling and many-body effects in Sr2CoO4 derived from the strong electron correlations lead to such temperature dependence of VBS

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

    International Nuclear Information System (INIS)

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

  17. 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.

  18. 16O + 16O + valence neutrons in molecular orbitals structures of positive- and negative-parity superdeformed bands in 34S

    International Nuclear Information System (INIS)

    The structures of superdeformed (SD) states in 34S are investigated using the antisymmetrized molecular dynamics and generator coordinate method (GCM). The GCM basis wave functions are calculated via energy variation with a constraint on the quadrupole deformation parameter β. By applying the GCM after parity and angular momentum projections, the coexistence of two positive- and one negative-parity SD bands are predicted, and low-lying states and other deformed bands are obtained. The SD bands have structures of 16O + 16O + two valence neutrons in molecular orbitals around the two 16O cores in a cluster picture. The configurations of the two valence neutrons are δ2 and π2 for the positive-parity SD bands and π1δ1 for the negative-parity SD band

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

    Energy Technology Data Exchange (ETDEWEB)

    Eliyahu, I., E-mail: ilan.eliyahu@gmail.com [Ben Gurion University of the Negev, Beersheva 84105 (Israel); Soreq Nuclear Research Center, Yavne 81800 (Israel); Horowitz, Y.S. [Ben Gurion University of the Negev, Beersheva 84105 (Israel); Oster, L. [Sami Shamoon College of Engineering, Beersheva 84100 (Israel)

    2012-12-15

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

  20. 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)

  1. 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.

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

    CERN Document Server

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

    2006-01-01

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

  3. 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.

  4. 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

  5. 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)

  6. 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)

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

    Science.gov (United States)

    Urbanek, Janus; Vöhringer, Peter

    2013-07-25

    We recently reported first femtosecond pump–probe experiments on the geminate recombination dynamics of solvated electrons in fluid ammonia (Urbanek et al., J. Phys. Chem. B 2012, 116, 2223–2233). The electrons were generated through a vertical two-photon ionization at a total energy of 9.3 eV. Here, we present a full Monte Carlo analysis of the time-resolved data to determine the solvated electron’s thermalization distance from the ionization hole, NH(3)(+). The simulations are compared with the experiment over wide thermodynamic conditions to obtain insight into the dependence of the vertical ionization mechanism on the electronic properties of the solvent network. The simulations reveal that the average thermalization distance, , decreases strongly with both increasing temperature, T, and decreasing density, ?, from 3.2 nm in the cryogenic fluid down to roughly 0.5 nm in the dilute supercritical phase with almost gas-like densities. We combine our results with the current understanding of the T,?-dependence of the electronic structure of the liquid phase and discuss in detail the role of thermally induced energy level shifts for the valence-to-conduction band gap. The observed changes of the thermalization distance can be well attributed to a gradual decrease of the excess energy initially imparted on the ejected electron as gas-like conditions are progressively approached. PMID:23815751

  8. 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)

  9. 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)

  10. 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

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

    Science.gov (United States)

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

    2015-03-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Lowe, M.; McGrath, R.; Sharma, H. R. [Surface Science Research Centre and The Department of Physics, The University of Liverpool, Liverpool L69 3BX (United Kingdom); Yadav, T. P. [Hydrogen Energy Centre, Department of Physics, Banaras Hindu University, Varanasi 221005 (India); Fournée, V.; Ledieu, J. [Institut Jean Lamour (UMR7198 CNRS-Université de Lorraine), Parc de Saurupt, 54011 Nancy Cedex (France)

    2015-03-07

    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 Fe{sub 3}O{sub 4} 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.

  13. 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)

  14. Valence-band offsets at the AlxGa0.5-xIn0.5P-ZnSe(001) lattice-matched interface

    International Nuclear Information System (INIS)

    The difficulty in making good Ohmic contact at the interfaces with p-doped ZnSe is an important problem hindering the realization of blue-light-emitting diode lasers based on the II-VI semiconductor technology. So far no metal or semiconductor material has been found to have a low enough barrier at the (001) interface with ZnSe. A possible solution to this problem is the insertion of a so-called barrier-reduction layer at the interface with ZnSe. We have investigated the interface formation energies and valence-band offsets at the (001) interface between AlxGa0.5-xIn0.5P and ZnSe. The results of our calculations show the existence of a strong interdependence between the valence-band offset and the interface geometric structure. The interface is found to have structural and electronic similarities to the GaAs-ZnSe(001) system. The very low values obtained for the valence-band offset confirm the possibility of using this material as a major constituent of the barrier-reduction layer. copyright 1997 The American Physical Society

  15. Valence-band offsets at the AlxGa0.5-xIn0.5P-ZnSe(001) lattice-matched interface

    Science.gov (United States)

    Bernardini, F.; Nieminen, R. M.

    1997-01-01

    The difficulty in making good Ohmic contact at the interfaces with p-doped ZnSe is an important problem hindering the realization of blue-light-emitting diode lasers based on the II-VI semiconductor technology. So far no metal or semiconductor material has been found to have a low enough barrier at the (001) interface with ZnSe. A possible solution to this problem is the insertion of a so-called barrier-reduction layer at the interface with ZnSe. We have investigated the interface formation energies and valence-band offsets at the (001) interface between AlxGa0.5-xIn0.5P and ZnSe. The results of our calculations show the existence of a strong interdependence between the valence-band offset and the interface geometric structure. The interface is found to have structural and electronic similarities to the GaAs-ZnSe(001) system. The very low values obtained for the valence-band offset confirm the possibility of using this material as a major constituent of the barrier-reduction layer.

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

    International Nuclear Information System (INIS)

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

  17. 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...

  18. 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

  19. Photonic Band Structure of Dispersive Metamaterials Formulated as a Hermitian Eigenvalue Problem

    KAUST Repository

    Raman, Aaswath

    2010-02-26

    We formulate the photonic band structure calculation of any lossless dispersive photonic crystal and optical metamaterial as a Hermitian eigenvalue problem. We further show that the eigenmodes of such lossless systems provide an orthonormal basis, which can be used to rigorously describe the behavior of lossy dispersive systems in general. © 2010 The American Physical Society.

  20. Band dispersion and electronic lifetimes in crystalline organic semiconductors

    OpenAIRE

    Fratini, Simone; Ciuchi, S.

    2011-01-01

    The consequences of several microscopic interactions on the photoemission spectra of crystalline organic semiconductors are studied theoretically. It is argued that their relative roles can be disentangled by analyzing both their temperature and their momentum-energy dependence. Our analysis shows that the polaronic thermal band narrowing, which is the foundation of most theories of electrical transport in organic semiconductors, is inconsistent in the range of microscopic parameters appropri...

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-08-15

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

  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. Development of wavelength-dispersive soft X-ray emission spectrometers for transmission electron microscopes--an introduction of valence electron spectroscopy for transmission electron microscopy.

    Science.gov (United States)

    Terauchi, Masami; Koike, Masato; Fukushima, Kurio; Kimura, Atsushi

    2010-01-01

    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 Cu(1-x)Zn(x) alloys and Pt M-emission spectra were presented. The FWHM value of 12 eV was obtained for the Pt Malpha-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 pi- and sigma-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. PMID:20371492

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

    International Nuclear Information System (INIS)

    Carbon- and boron-2p states of superconducting and non-superconducting boron-doped diamond (BDD) samples are measured using soft X-ray emission and absorption spectroscopy (XES and XAS) near C- and B-K edges. The electronic structure of B 2p does not show a marked boron-doping dependence, except that a considerable amount of in-gap state in empty states is observed. In C-K XAS spectra, two peaks H and I are observed around the Fermi level. The H peak is attributed to 2p state of carbon first-nearest neighboring to the dopant boron atoms (INN-C), and the I peak to 2p state of carbon further than 1NN- C from an impurity boron. Incoherent (normal-excitation) XES spectra do not show a large chemical shift by B-doping, but its intensity just below the valence band maximum (VBM) decreases with B-doping. It cannot be interpreted within a simple rigid band model. An elastic peak of I-excited C-K XES spectrum and the width of I-peak of C-K XAS spectrum suggest that impurity state is localized in non-superconducting BDD but is not in superconducting BDD. Namely impurity state of superconducting BDD is merged with the valence band, and holes in the merged state play an important role in the occurrence of superconductivity of BDD. (author)

  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. Type-II quantum wells with tensile-strained GaAsSb layers for interband cascade lasers with tailored valence band mixing

    Science.gov (United States)

    Motyka, M.; Dyksik, M.; Ryczko, K.; Weih, R.; Dallner, M.; Höfling, S.; Kamp, M.; Sek, G.; Misiewicz, J.

    2016-03-01

    Optical properties of modified type II W-shaped quantum wells have been investigated with the aim to be utilized in interband cascade lasers. The results show that introducing a tensely strained GaAsSb layer, instead of a commonly used compressively strained GaInSb, allows employing the active transition involving valence band states with a significant admixture of the light holes. Theoretical predictions of multiband k.p theory have been experimentally verified by using photoluminescence and polarization dependent photoreflectance measurements. These results open a pathway for practical realization of mid-infrared lasing devices with uncommon polarization properties including, for instance, polarization-independent midinfrared light emitters.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. Electron density of states at the edge of the valence band of Cd0.88Fe0.12Se-A photoemission yield study

    International Nuclear Information System (INIS)

    The electronic structures of Cd0.88Fe0.12Se and CdSe have been investigated by photoemission yield spectroscopy (PYS) in the photon energy range from 5 to 12 eV. The (112-bar0) surfaces were obtained by cleavage under ultrahigh vacuum (UHV) conditions. An Fe-related emission appeared at 0.58 eV above the valence band edge. The freshly cleaved surface of Cd0.88Fe0.12Se interacted with ambient atmosphere more strongly than CdSe crystal. Leaving the sample in an UHV chamber at room temperature enabled us to identify surface related features and to observe decrease of the ionization energy Ei, energy threshold Ed and the crystal affinity ? due to change of the surface conditions. Effective density of states, derived from the experimental spectra of Cd0.88Fe0.12Se exhibits, in contrast with CdSe, a surface-related feature degenerated with the bulk valence band

  14. 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.

  15. 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.

  16. 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.

  17. 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)

  18. Valence band offset in heterojunctions between crystalline silicon and amorphous silicon (sub)oxides (a-SiO{sub x}:H, 0 < x < 2)

    Energy Technology Data Exchange (ETDEWEB)

    Liebhaber, M.; Mews, M.; Schulze, T. F.; Korte, L., E-mail: korte@helmholtz-berlin.de; Rech, B.; Lips, K. [Institute Silicon Photovoltaics, Helmholtz-Zentrum Berlin für Materialien und Energie, Kekuléstr. 5, D-12489 Berlin (Germany)

    2015-01-19

    The heterojunction between amorphous silicon (sub)oxides (a-SiO{sub x}:H, 0?valence band offset ?E{sub V} and the interface defect density, being technologically important junction parameters. ?E{sub V} increases from ?0.3?eV for the a-Si:H/c-Si interface to >4?eV for the a-SiO{sub 2}/c-Si interface, while the electronic quality of the heterointerface deteriorates. High-bandgap a-SiO{sub x}:H is therefore unsuitable for the hole contact in heterojunction solar cells, due to electronic transport hindrance resulting from the large ?E{sub V}. Our method is readily applicable to other heterojunctions.

  19. Valence band resonant photoemission spectroscopy on Ce compounds at Ce 3d-4f and 4d-4f thresholds: surface vs. bulk electronic structure

    International Nuclear Information System (INIS)

    Electron correlation in 4f orbitals strongly influences the low energy properties of Ce and its inter-metallic compounds. By exploiting the different surface sensitivity of valence band resonant photoemission (VBRP) at Ce 3d-4f and Ce 4d-4f thresholds, a lowering of the 4f hybridization has been recently observed on going from the bulk to the surface layers. We report an extensive VBRP work at both the thresholds (3d and 4d) on three Ce compounds (Ce7Rh3, CeRh2, and CeCo2). In addition to surface effects, we found different resonance behaviours for f0 and f1 configurations. These differences should not be disregarded when extracting the 4f bulk and surface contributions from the photoemission spectra. ((orig.))

  20. Chemical state analysis of heat-treated 6, 13-bis(triisopropylsilylethynyl) pentacene investigated by XPS valence band spectra, XANES spectra and first-principles calculation

    International Nuclear Information System (INIS)

    X-ray photoelectron spectroscopy (XPS) valence band spectra reflect the chemical bonding states. To take this advantage, we tried to interpret experimental spectra by the occupied density of states (DOS) based on first principles calculation. In this work, we discussed XPS and X-ray Absorption Near Edge Structure (XANES) spectra of 6, 13-bis(triisopropylsilylethynyl) pentacene (TIPS-Pen), which is well known as an organic semiconductor. We studied chemical structure change of TIPS-Pen caused by heat-treatment at 300degC under nitrogen and under the air. It has been suggested that the structural change of pentacene skeleton by Diels-Alder type reaction occurs in both cases. In addition, the sample heat-treated under the air showed desorption of the isopropyl group and increase of oxygen concentration. (author)

  1. 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.

  2. 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.

  3. 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

  4. Valence-band offset and forward-backward charge transfer in manganite/NiO and manganite/LaNiO3 heterostructures.

    Science.gov (United States)

    Ning, X K; Wang, Z J; Chen, Y N; Zhang, Z D

    2015-12-28

    The valence-band offset (VBO) of the La0.67Sr0.33MnO3/NiO (LSMO/NiO), LaMnO3/NiO (LMO/NiO), LSMO/LaNiO3 (LSMO/LNO) and LMO/LaNiO3 (LSMO/LNO) heterostructures has been investigated using X-ray photoemission spectroscopy. The VBO values are calculated to be -0.72, -0.05, +1.43 and +1.51 eV for the LSMO/NiO, LSMO/LNO, LMO/LNO and LMO/NiO heterostructures, respectively. Hence, when compared with NiO and LNO, the valence band of LSMO is shifted to a lower binding energy, whereas that of LMO is shifted to a higher binding energy. In addition, the charge transfer at the interfaces has been depicted as Mn(3.3+) + 0.7e? Mn(2.6+), Mn(3.3+) + 0.1e? Mn(3.2+), Mn(3.0+)- 0.4e? Mn(3.4+) and Mn(3.0+)- 0.5e? Mn(3.5+) for the LSMO/NiO, LSMO/LNO, LMO/LNO and LMO/NiO heterostructures, respectively. Thus, the charge transfer procedure can be described as electron hopping from NiO and LNO to LSMO in the LSMO/NiO and LSMO/LNO heterostructures, and electron hopping from LMO to NiO and LNO in the LMO/NiO and LSMO/LNO heterostructures. Therefore, the charge transfer is dependent on the VBO, and the charge transfer direction can be determined from the negative or positive values of the VBO. PMID:26597855

  5. Study of valence-band intersublevel transitions in InAs/GaAs quantum dots-in-well infrared photodetectors

    Energy Technology Data Exchange (ETDEWEB)

    Lao, Yan-Feng; Wolde, Seyoum; Unil Perera, A. G., E-mail: uperera@gsu.edu [Department of Physics and Astronomy, Georgia State University, Atlanta, Georgia 30303 (United States); Zhang, Y. H.; Wang, T. M. [Key Laboratory of Artificial Structures and Quantum Control, Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Kim, J. O.; Schuler-Sandy, Ted; Tian, Zhao-Bing; Krishna, S. S. [Center for High Technology Materials, Department of Electrical and Computer Engineering, University of New Mexico, Albuquerque, New Mexico 87106 (United States)

    2014-04-28

    The n-type quantum dot (QD) and dots-in-well (DWELL) infrared photodetectors, in general, display bias-dependent multiple-band response as a result of optical transitions between different quantum levels. Here, we present a unique characteristic of the p-type hole response, a well-preserved spectral profile, due to the much reduced tunneling probability of holes compared to electrons. This feature remains in a DWELL detector, with the dominant transition contributing to the response occurring between the QD ground state and the quantum-well states. The bias-independent response will benefit applications where single-color detection is desired and also allows achieving optimum performance by optimizing the bias.

  6. 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.

  7. A novel dispersion monitoring technique in w-band radio-over-fiber signals using clustering on asynchronous histograms

    OpenAIRE

    Granada Torres, Jhon James; Cárdenas Soto, Ana María; Guerrero González, Neil

    2014-01-01

    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 becomes 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 ...

  8. Effects of weak nonlinearity on dispersion relations and frequency band-gaps of periodic structures

    DEFF Research Database (Denmark)

    Sorokin, Vladislav; Thomsen, Jon Juel

    2015-01-01

    accounted for. The present work deals with analytically predicting dynamic responses for nonlinear continuous elastic periodic structures. Specifically, the effects of weak nonlinearity on the dispersion re-lation and frequency band-gaps of a periodic Bernoulli-Euler beam performing bending os......-cillations are analyzed. Modulation of the beam structural properties is not required to be small or piecewise constant. Various sources of nonlinearity are analyzed, namely, nonlinear (true) curvature, nonlinear inertia due to longitudinal motions of the beam, nonlinear materi-al, and also nonlinearity...

  9. 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

  10. 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.

  11. 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.)

  12. Coherent and incoherent d band dispersions in SrVO3

    Science.gov (United States)

    Takizawa, M.; Minohara, M.; Kumigashira, H.; Toyota, D.; Oshima, M.; Wadati, H.; Yoshida, T.; Fujimori, A.; Lippmaa, M.; Kawasaki, M.; Koinuma, H.; Sordi, G.; Rozenberg, M.

    2009-12-01

    We have performed an angle-resolved photoemission spectroscopy study of SrVO3 thin films. Utilizing thin films prepared in situ, with well-defined and atomically flat surfaces, contributions from surface states centered at ˜-1.5eV were dramatically reduced, enabling us to study the bulklike V3d states, including the incoherent part. A clear band dispersion is observed not only in the coherent part but also in the incoherent part and the spectral weight of the incoherent part is larger within the Fermi volume. These findings are particularly significant since the description of the so-called incoherent Hubbard band in SrVO3 needs to include the nonlocal interaction between the atoms. These trends are well reproduced by dynamical mean-field theory calculations.

  13. 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 $a/\\lambda \\sim 1/2$.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2010-07-01

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

  15. 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.

  16. 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

  17. The graphite core valence valence Auger spectrum

    Science.gov (United States)

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

    2002-04-01

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

  18. 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.

  19. 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.

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

    DEFF Research Database (Denmark)

    Sorokin, Vladislav; Thomsen, Jon Juel

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

  1. Effects of weak nonlinearity on the dispersion relation and frequency band-gaps of a periodic Bernoulli–Euler beam

    DEFF Research Database (Denmark)

    Sorokin, Vladislav S.; Thomsen, Jon Juel

    2016-01-01

    The paper deals with analytically predicting the effects of weak nonlinearity on the dispersion relation and frequency band-gaps of a periodic Bernoulli– Euler beam performing bending oscillations. Two cases are considered: (i) large transverse deflections, where nonlinear (true) curvature...

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

    International Nuclear Information System (INIS)

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

  3. 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.

  4. 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.

  5. 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.

  6. Analysis of band structure, transmission properties, and dispersion behavior of THz wave in one-dimensional parabolic plasma photonic crystal

    Science.gov (United States)

    Askari, Nasim; Mirzaie, Reza; Eslami, Esmaeil

    2015-11-01

    The photonic band gap of obliquely incident terahertz electromagnetic waves in a one-dimensional plasma photonic crystal is studied. The periodic structure consists of lossless dielectric and inhomogeneous plasma with a parabolic density profile. The dispersion relation and the THz wave transmittance are analyzed based on the electromagnetic equations and transfer matrix method. The dependence of effective plasma frequency and photonic band gap characteristics on dielectric and plasma thickness, plasma density, and incident angle are discussed in detail. A theoretical calculation for effective plasma frequency is presented and compared with numerical results. Results of these two methods are in good agreement.

  7. Chromatic dispersion mitigation in long-haul fiber-optic communication networks by sub-band partitioning.

    Science.gov (United States)

    Malekiha, Mahdi; Tselniker, Igor; Plant, David V

    2015-12-14

    We propose and experimentally demonstrate a novel sub-band multiplexed data architecture for chromatic dispersion (CD) mitigation. We have demonstrated 32 GBaud multi-sub-band (MSB) dual-polarization (DP) 16QAM transmission over 2400 km. Using this approach, the transmitted signal bandwidth is divided into multiple narrow-bandwidth sub-bands, each operating at a lower baud rate. Within each sub-band bandwidth, the CD frequency response can be approximated as a linear-phase band-pass filter, which can be considered as an analog delay that does not require compensation. Therefore, the resulting receiver digital signal processing (DSP) is simplified due to the removal of the CD compensation equalizer. In addition, this leads to efficient parallelization of DSP tasks by deploying multiple independent sub-band processors running at a lower clock rate. The proposed system reduces receiver computational complexity and offers 1 dB higher Kerr-nonlinearity tolerance and 2% extended transmission reach in comparison to the conventional single carrier systems. PMID:26699054

  8. The structure of the valence band of Cs2PuO2Cl4 single crystal by the XPS data and relativistic calculation results

    International Nuclear Information System (INIS)

    In this work for the first time the XPS spectra of the valency and core electrons of Cs2PuO2Cl4 single crystal containing the PuO22+ group were measured and analyzed in order to establish a correlation of the fine spectral structure with the plutonium ion oxidation state, the structure of its close environment and the nature of the chemical bond. Also the relativistic SCF X? DV calculation of the PuO2Cl42- (D4d) cluster at RPu-O=0.171nm and RPu-Cl=0.262 nm was done. For comparison the spectra of Cs2UO2ClO4 were studied. (author)

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

    CERN Document Server

    Mathar, R J

    2006-01-01

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

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

    Scientific Electronic Library Online (English)

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

    2000-06-01

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

  11. 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.

  12. 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...

  13. 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...

  14. 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.

  15. 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.

  16. 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.

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

    DEFF Research Database (Denmark)

    Sorokin, Vladislav; Thomsen, Jon Juel

    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...

  19. Effects of chemical pressure on the Fermi surface and band dispersion of the electron-doped high- Tc superconductors

    Science.gov (United States)

    Ikeda, M.; Yoshida, T.; Fujimori, A.; Kubota, M.; Ono, K.; Das, Hena; Saha-Dasgupta, T.; Unozawa, K.; Kaga, Y.; Sasagawa, T.; Takagi, H.

    2009-07-01

    We have performed angle-resolved photoemission spectroscopy measurements and first-principles electronic-structure calculations on the electron-doped high- Tc superconductors (HTSCs) Ln1.85Ce0.15CuO4 ( Ln=Nd , Sm, and Eu). The observed Fermi surface and band dispersion show such changes that with decreasing ionic size of Ln3+ (increasing chemical pressure), the curvature of the Fermi surface or -t'/t decreases, where t and t' are transfer integrals between the nearest-neighbor and next-nearest-neighbor Cu sites, respectively, explaining the apparently inconsistent behavior seen in the hole-doped HTSC La2-xSrxCuO4 under epitaxial strain. Around the node, the antiferromagnetic gap is opened with increasing chemical pressure. We propose that the nodal gap opening is possibly due to the decrease in -t'/t through the improved nesting, leading to the decrease in Tc .

  20. 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)

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

    Science.gov (United States)

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

    2011-01-01

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

  2. Change in the conversion rate for the E3-isomer sup(235m)U (76,8 eV; 1/2+ ? 7/2-) at variation of configurations of the valence band of the atomic shell

    International Nuclear Information System (INIS)

    In the framework of the relativistic Hartree-Fock-Slater method, a change of the conversion rate lambda for the E3 isomer (at the transition energy of h/2??=77 eV) with respect to the rate lambda for the normal configuration of uranium atom, (7ssup(1/2)sup(2)(6dsup(3/2))sup(1)(5fsup(5/2))sup(3), is calcUlated for 14 configurations of the valence band of the atomic shell, including considerable variations of the occupation numbers in 6d, 7s, and 5f orbits. A very strong change ?lambda/lambda1 is found to be due to variation of the occupation number for the 5f orbit (?N(5f) not equal to 0); the change amounts to about 8% per ?N(5f)=+-1, that is an order of magnitude higher than ?lambda/lambda1 due to variations of the occupation numbers for other orbits in the cases where N(5f)=const. Though the direct contribution from the 5f electrons to the conversion is very small (1 for ?N(5f) not equal to 0. A rigid correlation between the partial conversion rate and the r. m. s. radius of the orbit is obtained for 6p orbits

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

    International Nuclear Information System (INIS)

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

  4. 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.

  5. Band Structures of Plasmonic Polarons

    Science.gov (United States)

    Caruso, Fabio; Lambert, Henry; Giustino, Feliciano

    2015-03-01

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

  6. 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

  7. Mixed Valence Niobium

    Science.gov (United States)

    Keating, Steven James

    1992-01-01

    The structural, crystal-chemical, and electrical properties of perovskites are reviewed, with respect to metallic phases similar to tungsten bronze. Phase diagrams are presented for the SrO-NbO-NbO_{2.5 } and SrNbO_3-KNbO _3-rm Sr_{0.5}NbO _3 ternaries, and for the SrNbO_3 -rm Sr_{0.5}NbO_3 binary. The influence of oxygen partial pressure, temperature, melting, and solid solutions affecting the perovskite phase rm Sr_{x}NbO _3 (0.75 oxidation of Nb^{4+} to Nb^{5+}) results in a lattice parameter decrease, even though it has an ionic radius similar to Ba^{2+} . A unique relationship between unit cell volume and valence is established, suggesting that the oxidation state of the NbO_6 network dictates the lattice parameters and stability of the perovskite. The resistivity variation for rm Sr_{x}NbO_3, (Ba,Sr)NbO _3, (K,Sr)NbO_3, and (rm K_{0.5}Sr_ {0.5})NbO_3 indicates metallic behavior between 298K and 77K. Resistivity increased as the Nb was oxidized from Nb^{4+} to Nb^{5+}, but metallic properties persisted to at least Nb^ {5+}/(Nb^{5+} + Nb^{4+}) = 0.5. The influence of the exchanges Sr^{2+} = Ba^{2+} and V_{rm A} + Sr ^{2+} = 2K^+ on the electrical resistivity of the perovskite suggests ordering or band structure effects which are orders of magnitude stronger than those observed in metal alloys. Magnetic susceptibility measurements indicate Pauli-paramagnetism. At low temperature (oxide superconductor was found in the Sr-Nb-O system.

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

    Energy Technology Data Exchange (ETDEWEB)

    Meevasana, Warawat

    2010-05-26

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

  9. 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.

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

    International Nuclear Information System (INIS)

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

  11. 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

  12. 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

  13. Valence instabilities and inhomogeneous mixed valence in some ternary europium compounds

    International Nuclear Information System (INIS)

    Photoemission spectra and TB-LMTO-ASA band structure calculations of some mixed valency europium compounds have been studied. The band structures are compared with the band structures of the isostructural lanthanum and strontium compounds. Surprisingly a 4f density of states in the vicinity of the Fermi level is observed in inhomogeneous mixed valency EuPd3B, Eu3S4, and EuPdP. Indeed a van Hove singularity (vHS) derived from the d states of La and Pd or p states of boron or phosphorous are found in La3S4, LaPd3B and SrPdP. The valence instability in the Eu compounds is thus not necessarily due to Eu 4f states. The results also provide some ground for the assumption that inhomogeneous mixed valency is an indicator for a vHS in the conduction band. The europium compounds order anti-ferromagnetically at low temperatures, whereas La3S4 becomes superconducting at 8 K. In La3S4, the vHS coincides with the Fermi level, whereas the singularity lies below the Fermi level in SrPdP and LaPd3B. According to the van Hove scenario it must be possible to induce superconductivity via hole doping in SrPdP and LaPd3B. (orig.)

  14. 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

  15. Photoemission bands in systems of strongly correlated electrons

    Energy Technology Data Exchange (ETDEWEB)

    Haas, S. [ETH-Hoenggerberg, Zurich (Switzerland). Theor. Phys.

    1997-12-31

    Recent photoemission experiments on cuprate superconductors in their normal state are analyzed in the context of models of strongly correlated electrons. The phenomenon of antiferromagnetically induced bands close to half-filling is discussed. Also, flat regions in the dispersion of the valence band related to van Hove singularities in the electronic density of states are shown to be present. The possibility of having small, pocket-like Fermi surfaces in the vicinity of half-filling is mentioned. Finally, some analogies are presented between two-dimensional cuprates and related one-dimensional materials. (orig.) 33 refs.

  16. 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.

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

    International Nuclear Information System (INIS)

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

  18. 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.

  19. 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

  20. Precise band structure and Fermi-surface calculation for YBa2Cu3O7: Importance of three-dimensional dispersion

    International Nuclear Information System (INIS)

    With the appearance of angle-resolved photoemission data allowing the identification and measurement of the Fermi surface of the high-Tc cuprate superconductors, it is important to have precise local-density calculations with which to compare. We present well-converged local-density predictions of the band structure and Fermi surface of YBa2Cu3O7, giving special attention to the position of the flat Cu-O chain-derived bands and the effect of the buckling of the Cu-O chain that is predicted by total-energy calculations and that has been inferred by an x-ray-scattering study. We emphasize the c-axis dispersion that will lead to apparent broadening of the Fermi surface in experiments interpreted in terms of a two-dimensional electronic structure

  1. 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)

  2. 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

  3. Valence et relations grammaticales

    Directory of Open Access Journals (Sweden)

    Michael Herslund

    2015-09-01

    Full Text Available Dans la théorie de la valence, telle qu'elle a d'abord été conçue par Tesnière (1959, le verbe constitue le centre organisateur de la phrase. Les specifications lexicales d'un verbe donné sont traduites par ses possibilités combinatoires, c'est-à-dire par les membres nominaux et/ou prépositionnels avec lesquels il se combine: toute comprehénsion d'un verbe tel que envoyer, par exemple, prend son point de départ dans le fait que ce verbe dénote une situation comportant trois participants qui sont dénotés par les trois membres de phrase avec lesquels se combine ce verbe. De ce fait, la notion de valence n'offre pas seulement une façon simple de classifier les verbes d'une langue donnée, mais aussi une hypothèse sur la structure des phrases de la langue: si c'est le verbe qui détermine la structure de la phrase, la théorie de la valence doit être construite de telle sorte qu'elle permette l'élaboration d'une typologie de phrases en même temps qu'une analyse et une classification des verbes. Ce qu'il faut exiger d'une théorie de la valence, c'est done qu'elle formule une hypothèse sur la structure des phrases - les schémas canoniques - c'est-à-dire qu'elle prédise quels types de phrase existent et quels types sont exclus par principe. On n' atteint pas ce but si on se contente de l'inventaire flou et aléatoire des fonctions syntaxiques de la grammaire traditionnelle pour en faire un principe de classification des verbes: avec un tel point de départ, on formulera en réalité l'hypothese qu'il existe des phrases comportant jusqu'a sept ou huit actants, et on se trouvera devant des lacunes distributionnelles inexplicables comme par exemple l'absence d'une fonction "attribut de l'objet indirect", lacune d'autant plus mystérieuse qu'on dit le plus souvent que l'objet indirect n'est qu'une variante prépositionnelle de l'objet direct, qui, lui, a son attribut.

  4. 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

  5. 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)

  6. Energy band gap and dispersive optical parameters in Bi1.5Zn0.92Nb1.5O6.92 pyrochlore ceramics

    International Nuclear Information System (INIS)

    The compositional and optical properties of Bi1.5Zn0.92Nb1.5O6.92 pyrochlore ceramics have been investigated by means of scanning electron microscopy (SEM) and UV-vis spectroscopy, respectively. The SEM spectroscopy revealed that the pyrochlore exhibits a very dense microstructure with single-phase appearance. The absorption spectral analysis in the sharp absorption region revealed an indirect forbidden transitions band gap of 3.30 eV. The room temperature refractive index, which was calculated from the reflectance and transmittance data, allowed the identification of the dispersion and oscillator energies, static and lattice dielectric constants and static refractive index as 26.69 and 3.37 eV, 8.92 and 15.95 and 2.98, respectively.

  7. 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.

  8. 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

  9. ??????????? ? ??????????(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.

  10. From mixed valence to the Kondo lattice regime

    International Nuclear Information System (INIS)

    Many heavy fermion materials are known to cross over from the Kondo lattice regime to the mixed valence regime or vice versa as a function of pressure or doping. We study this crossover theoretically by employing the periodic Anderson model within the framework of the dynamical mean field theory. Changes occurring in the dynamics and transport across this crossover are highlighted. As the valence is decreased (increased) relative to the Kondo lattice regime, the Kondo resonance broadens significantly, while the lower (upper) Hubbard band moves closer to the Fermi level. The resistivity develops a two peak structure in the mixed valence regime: a low temperature coherence peak and a high temperature ‘Hubbard band’ peak. These two peaks merge, yielding a broad shallow maximum upon decreasing the valence further. The optical conductivity likewise exhibits an unusual absorption feature (shoulder) in the deep mid-infrared region, which grows in intensity with decreasing valence. The involvement of the Hubbard bands in dc transport and of the effective f-level in the optical conductivity are shown to be responsible for the anomalous transport properties. A two-band hybridization-gap model, which neglects incoherent effects due to many-body scattering, commonly employed to understand the optical response in these materials is shown to be inadequate, especially in the mixed valence regime. Comparison of theory with experiment carried out for (a) dc resistivities of CeRhIn5, Ce2Ni3Si5, CeFeGe3 and YbIr2Si2, (b) pressure dependent resistivity of YbInAu2 and CeCu6, and (c) optical conductivity measurements in YbIr2Si2 yields excellent agreement. (paper)

  11. 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.

  12. 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.

  13. 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…

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

    International Nuclear Information System (INIS)

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

  15. 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.

  16. The valence of Ce in CeRu 2 and CeIr 3 thru superconductivity

    Science.gov (United States)

    Hakimi, M.; Huber, J. G.

    1985-12-01

    A scheme is presented whereby valences for Ceof 3.9 inCeRu2 and 3.6 inCeIr3 are assigned thru superconductivity. Isostructural superconductors XRu2 and XIr3 ( X = La, CeandTh) are required. The superconducting transition temperatures ( Tc) of pseudo-binary compounds have been measured. The compositional variation of Tc going directly from the La (trivalent) to the Th (tetravalent) compound is matched by that going from the La to the Ce to the Th compound when an intermediate valence is assigned to Ce. It is argued that Ru 4d-bands and Ir 5d-bands are responsible for the superconductivity, and that valence electrons supplied by the X ions toward filling those bands determine Tc. Constant Ce valences are assumed, and account is taken for Ce 4f resonant state depression of Tcin ( X, Ce) Ir3 pseudo-binary compounds.

  17. 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.

  18. 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

  19. Forming Beliefs: Why Valence Matters.

    Science.gov (United States)

    Sharot, Tali; Garrett, Neil

    2016-01-01

    One of the most salient attributes of information is valence: whether a piece of news is good or bad. Contrary to classic learning theories, which implicitly assume beliefs are adjusted similarly regardless of valence, we review evidence suggesting that different rules and mechanisms underlie learning from desirable and undesirable information. For self-relevant beliefs this asymmetry generates a positive bias, with significant implications for individuals and society. We discuss the boundaries of this asymmetry, characterize the neural system supporting it, and describe how changes in this circuit are related to individual differences in behavior. PMID:26704856

  20. 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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-06-21

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

  2. 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

  3. 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.

  4. SmB$_6$: Topological insulator or semiconductor with valence-fluctuation induced hopping transport?

    OpenAIRE

    Batko, I.; Batkova, M.

    2007-01-01

    We advert to the fact that presence of valence fluctuations (VFs) in semiconductors with in-gap impurity bands unconditionally leads to dynamical changes (fluctuations) of energies of localized impurity states. We provide arguments that in the impurity subnetwork consisting of centers having energy levels fluctuating around the Fermi energy there exist favorable conditions for hops from occupied states to empty states of less energy. Consequently, we propose original valence-fluctuation induc...

  5. 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...

  6. 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

  7. 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.

  8. 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...

  9. 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...

  10. 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.

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

    Science.gov (United States)

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

    2012-05-01

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

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

    International Nuclear Information System (INIS)

    This thesis has applied magneto-optical techniques to enable a better understanding of the band structure of gallium nitride, particularly the complex behaviour expected as a result of strong valence band mixing. Effective hole masses are deduced from free excitonic-like transitions observed in magneto-reflectivity, to give a heavy A hole mass of 1.3 mo and the first experimental suggestion of a light B band mass. From the Landau-level-like transitions, once the phonon correction to the electron dispersion is considered, the deduced A valence band dispersion confirms the heavy mass, but also shows a large non-parabolicity. The effect of strain on the valence band is seen through different hole contributions to the g factor in the donor-bound exciton luminescence from heteroepitaxial compared with homoepitaxial material. Not only are the g-factors sensitive to strain, but they also are sensitive to the state of binding, being very different for the B 1s and 2s excitonic states. Despite this, in lower dimensional structures the observation of an enhanced g-factor suggests a re-ordered valence band in GaN/AlxGa1-xN quantum wells with respect to GaN epilayers, caused by a reversal of the states in the strained AlxGa1-xN barriers. The role of spontaneous and piezoelectric polarisation was found to be important in both quantitatively understanding the increased exciton binding energy with the reduction of the dimensionality in the wells, and observing a resonant phenomenon from an undoped GaN/AlxGa1-xN single heterojunction. The oscillating peak intensity was understood in terms of the changing screening efficiency of the two-dimensional electron gas. Finally, many-body effects within an electron-hole plasma in lnxAlyGa1-x-yAs quantum wells have been explored to study the effects of mass renormalisation at carrier densities typically present in laser devices. A peak in the mass renormalisation confirms the importance of excitonic correlations in the excited plasma. (author)

  13. 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

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

    International Nuclear Information System (INIS)

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

  15. Electronic polaron effects in mixed valence and heavy fermion materials

    International Nuclear Information System (INIS)

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

  16. 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...

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

    Science.gov (United States)

    Reshak, A. H.; Azam, Sikander

    2014-08-01

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

  18. 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.)

  19. 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

  20. Energy band gap and dispersive optical parameters in Bi{sub 1.5}Zn{sub 0.92}Nb{sub 1.5}O{sub 6.92} pyrochlore ceramics

    Energy Technology Data Exchange (ETDEWEB)

    Qasrawi, A.F., E-mail: atef_qasrawi@atilim.edu.t [Group of Physics, Faculty of Engineering, Atilim University, 06836 Ankara (Turkey); Department of Physics, Arab-American University, Jenin, West Bank (Palestinian Territory, Occupied); Mergen, A. [Metallurgical and Materials Engineering Dept., Marmara University, 34722 Istanbul (Turkey)

    2010-04-30

    The compositional and optical properties of Bi{sub 1.5}Zn{sub 0.92}Nb{sub 1.5}O{sub 6.92} pyrochlore ceramics have been investigated by means of scanning electron microscopy (SEM) and UV-vis spectroscopy, respectively. The SEM spectroscopy revealed that the pyrochlore exhibits a very dense microstructure with single-phase appearance. The absorption spectral analysis in the sharp absorption region revealed an indirect forbidden transitions band gap of 3.30 eV. The room temperature refractive index, which was calculated from the reflectance and transmittance data, allowed the identification of the dispersion and oscillator energies, static and lattice dielectric constants and static refractive index as 26.69 and 3.37 eV, 8.92 and 15.95 and 2.98, respectively.

  1. 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

  2. Gastric Banding

    Science.gov (United States)

    ... Radiation-Emitting Products Vaccines, Blood & Biologics Animal & Veterinary Cosmetics Tobacco ... Banding Benefits of Gastric Banding Lifestyle Changes after Gastric Banding Surgery Gastric banding is a weight loss option for ...

  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. 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.

  6. 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...

  7. 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

  8. 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.

  9. Neuroanatomical correlates of categorizing emotional valence.

    Science.gov (United States)

    Beatty, Erin L; Vartanian, Oshin; Muller-Gass, Alexandra; Robertson, John A; Mandel, David R; Stergiopoulos, Stergios

    2014-06-11

    Categorization is fundamental to cognition, and evidence suggests that categorizing emotional stimuli holds a privileged position in human information processing. According to theories on embodied emotion, the subjective emotional feeling elicited by a stimulus plays a causal role in its categorization. Using functional MRI, we tested the hypothesis that categorizing emotional stimuli in terms of valence would activate structures involved in valence-specific experience of emotion. On each trial, two pictures from the International Affective Picture System were presented successively. Upon viewing the second picture, participants categorized it as belonging to the same valence category as or a different valence category from the first picture. Categorization activated an exclusively left-lateralized set of regions implicated in taxonomic categorization (i.e. judging whether two items are of the same kind) including the middle temporal gyrus and precuneus, as well as the posterior cingulate cortex. Critically, for negative pictures categorization activated structures that underlie the experience of negative emotions (anterior insula, left orbitofrontal cortex), whereas for positive pictures categorization activated structures that underlie the experience of positive emotions (dorsomedial and ventromedial prefrontal cortex). Consistent with predictions derived from theories on embodied emotion, these results suggest that experience of emotion contributes to categorizing emotional valence. PMID:24922349

  10. 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.

  11. 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

  12. The band structures of superlattices (Ge2)1/(GaAs)m(110) with m=1-20

    International Nuclear Information System (INIS)

    The electronic band structures of superlattices (Ge2)1/(GaAs)m(110) with m=1-20 were calculated by using the renormalization technique in a tight-binding frame. The results show that the valence band top and the conduction band bottom of the superlattices (Ge2)1/(GaAs)m(110) are not at the same point in the Brillouin zone and the electronic states at the bottom of the conduction band display distinct 2-dimensional character. For the monolayer superlattice (Ge2)1/(GaAs)1 both the indirect and direct forbidden bands are very small. As the number of the GaAs layers increases the electronic states at the bottom of the conduction bands transit from 3-dimensional character to 2-dimensional character gradually and the degrees of the transitions are different for each point in the Brillouin zone. The transverse energy dispersion of the lowest conduction band remains unchanged when the number of GaAs layers m increases beyond 10. (author). 9 refs, 8 figs, 4 tabs

  13. 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.

  14. Flat Bands Under Correlated Perturbations

    OpenAIRE

    Bodyfelt, Joshua D.; Leykam, Daniel; Danieli, Carlo; Yu, Xiaoquan; Flach, Sergej

    2014-01-01

    Flat band networks are characterized by coexistence of dispersive and flat bands. Flat bands (FB) are generated by compact localized eigenstates (CLS) with local network symmetries, based on destructive interference. Correlated disorder and quasiperiodic potentials hybridize CLS without additional renormalization, yet with surprising consequencies: (i) states are expelled from the FB energy $E_{FB}$, (ii) the localization length of eigenstates vanishes as $\\xi \\sim 1 / \\ln (E- E_{FB})$, (iii)...

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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

  1. 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.

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

    International Nuclear Information System (INIS)

    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: ? Valence shell photoelectron spectra of pyrimidine and pyrazine have been recorded. ? Many-body effects are important. ? Photoionisation dynamics are affected by shape resonances. ? 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 ?-orbitals has been shown to differ from that of asymmetry parameters associated with ?-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.

  3. Optoelectronic properties of InAlN/GaN distributed bragg reflector heterostructure examined by valence electron energy loss spectroscopy.

    Science.gov (United States)

    Eljarrat, A; Estradé, S; Ga?evi?, Z; Fernández-Garrido, S; Calleja, E; Magén, C; Peiró, F

    2012-10-01

    High-resolution monochromated electron energy loss spectroscopy (EELS) at subnanometric spatial resolution and Kronig analysis of the Valence-EELS data, allowing band gap energy to be measured and an insight on the polytypism of the GaN layers. PMID:23058502

  4. 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...

  5. 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

  6. 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.

  7. Intermediate valence behaviour under pressure: how precisely can we probe it by means of resonant inelastic x-ray emission?

    International Nuclear Information System (INIS)

    Rare earths and their compounds show many interesting physical phenomena caused by the complex electronic structure related to f electrons. External pressure can affect the hybridization between 5d band electrons and the more atomic-like 4f ones, giving rise to intermediate valence behaviour. Resonant x-ray emission spectroscopy (RXES) has been shown to be a very effective tool for probing the mixed valence ground state under pressure. A RXES experiment detects the x-ray emission that follows decay into a resonantly created core hole. Being a photon-in-photon-out spectroscopic technique, it is not hindered by the presence of the pressure cell. In the case of rare earths we chose to detect the 3d-2p x-ray emission following a 2p-5d resonant excitation process. The divalent and trivalent components of the ground state are separately enhanced because they resonate at different incident photon energies. Very good precision in the determination of even small changes of valence is reached. We will present experimental results on ytterbium compounds (Y bAl2 and YbS), as well as recent data on the valence state of SmS in the gold phase, that have allowed us to unveil the progressive valence change towards the completion of trivalency. The spectral changes and the way to extract the valence from measured spectra will be discussed

  8. Janus Nematic Colloids with Designable Valence

    Directory of Open Access Journals (Sweden)

    Simon Čopar

    2014-05-01

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

  9. 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.

  10. 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.

  11. Electron attachment to valence-excited CO

    OpenAIRE

    Kumar, Sanjay; D. Mathur

    1998-01-01

    The possibility of electron attachment to the valence $^{3}\\Pi$ state of CO is examined using an {\\it ab initio} bound-state multireference configuration interaction approach. The resulting resonance has $^{4}\\Sigma^{-}$ symmetry; the higher vibrational levels of this resonance state coincide with, or are nearly coincident with, levels of the parent $a^{3}\\Pi$ state. Collisional relaxation to the lowest vibrational levels in hot plasma situations might yield the possibility of a long-lived CO...

  12. 5th International Conference on Valence Fluctuations

    CERN Document Server

    Malik, S

    1987-01-01

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

  13. Valence fluctuations between two magnetic configurations

    International Nuclear Information System (INIS)

    The subject of this work is the study of a microscopic model which describes TmSe through its most important feature, i.e.: the valence fluctuations between two magnetic configurations. Chapter I is a general review of the most important physical properties of rare-earth systems with intermediate valence (I.V.) and a general description of experimental results and theoretical models on Tm compounds. In Chapter II the Hamiltonian model is discussed and the loss of rotational invariance is also analyzed. Chapter III is devoted to the study of non-stoichiometric Tsub(x)Se compounds. It is shown that these compounds can be considered as a mixture of TmSe (I.V. system) and Tm3+0.87Se. Chapter IV is devoted to the calculation of spin-and charge susceptibilities. The results obtained permit to explain the essential features of the neutron scattering spectrum in TmSe. In Chapter V, an exactly solvable periodic Hamiltonian is presented. From the experimental results, some fundamental features are deduced to describe TmSe as an intermediate valence system whose two accessible ionic configurations are magnetic (degenerated fundamental state). (M.E.L)

  14. Intermediate Band to Conduction Band optical absorption in ZnTe:O

    OpenAIRE

    Antolín Fernández, Elisa; Chen, C.; Ramiro Gonzalez, Iñigo; Foley, James; López Estrada, Esther; Artacho Huertas, Irene; Hwang, J.; Teran, A.; Hernández Martín, Estela; Tablero Crespo, César; Martí Vega, Antonio; J. D. Phillips; Luque López, Antonio

    2012-01-01

    ZnTe doped with high concentrations of oxygen has been proposed in previous works as intermediate band (IB) material for photovoltaic applications. The existence of extra optical transitions related to the presence of an IB has already been demonstrated in this material and it has been possible to measure the absorption coefficient of the transitions from the valence band (VB) to the IB. In this work we present the first measurement of the absorption coefficient associated to transitions from...

  15. Intermediate band to conduction band optical absorption in ZnTeO

    OpenAIRE

    Antolín Fernández, Elisa; Chen, C.; Ramiro Gonzalez, Iñigo; Foley, James; López Estrada, Esther; Artacho Huertas, Irene; Hwang, J.; Teran, A.; Hernández Martín, Estela; Tablero Crespo, César; Martí Vega, Antonio; J. D. Phillips; Luque López, Antonio

    2014-01-01

    ZnTe doped with high concentrations of oxygen has been proposed in previous works as an intermediate band (IB) material for photovoltaic applications. The existence of extra optical transitions related to the presence of an IB has already been demonstrated in this material and it has been possible to measure the absorption coefficient of the transitions from the valence band (VB) to the IB. In this study, we present the first measurement of the absorption coefficient associated with transitio...

  16. 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)

  17. 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.

  18. Interface termination and band alignment of epitaxially grown alumina films on Cu-Al alloy

    Science.gov (United States)

    Yoshitake, Michiko; Song, Weijie; Libra, Ji?í; Mašek, Karel; Šutara, František; Matolín, Vladimír; Prince, Kevin C.

    2008-02-01

    Epitaxial ultrathin alumina films were grown on a Cu-9 at. % Al(111) substrate by selective oxidation of Al in the alloy in ultrahigh vacuum. The photoelectron spectra of Al 2p and valence band were measured in situ during oxidation. By analyzing multiple peaks of Al 2p, the interface atomic structure was discussed. The energy difference between the Fermi level of the substrate and the valence band maximum of alumina (band offset) was obtained. The relation between the interface atomic structure and the band offset was compared with the reported first-principles calculations. A novel method for controlling the band offset was proposed.

  19. Strongly nonparabolic variation of the band gap in In x Al1?x N with low indium content

    Science.gov (United States)

    Zubialevich, Vitaly Z.; Dinh, Duc V.; Alam, Shahab N.; Schulz, Stefan; O’Reilly, Eoin P.; Parbrook, Peter J.

    2016-02-01

    80–120 nm thick In x Al1?x N epitaxial layers with 0 x x x = 0.05, confirming previous theoretical work that used a band-anticrossing model to describe the strongly x-dependent bowing parameter, which in this case exceeds 25 eV in the x ? 0 limit. A double absorption edge observed for InAlN with x < 0.01 was attributed to crystal-field splitting of the highest valence band states. Our results indicate also that the ordering of the valence bands is changed at much lower In contents than one would expect from linear interpolation of the valence band parameters. These findings on band gap bowing and valence band ordering are of direct relevance for the design of InAlN-containing optoelectronic devices.

  20. Dynamical correlations in a Hubbard chain with resonating-valence-bond ground state

    CERN Document Server

    Giesekus, A

    1995-01-01

    Dynamical correlation functions for temperature T=0 are calculated for a Hubbard chain with infinite on-site repulsion. This chain contains three sites per unit cell and has a known resonating-valence-bond ground state for a filling of 2 particles per unit cell. A finite system of 24 sites is studied numerically. The recursion method is applied and results for spectral densities are compared to variationally calculated excited-state eigenvalues. Charge and spin degrees of freedom located at the backbone sites are considered. The spectral densities show dispersionless excitations. The energy spectrum displays a gap indicating an insulating ground state. Spectral functions for the propagation of a single hole in a resonating-valence-bond background are provided and indicate delocalized dispersive hole excitations.

  1. Valence skipping driven superconductivity and charge Kondo effect

    Energy Technology Data Exchange (ETDEWEB)

    Yanagisawa, Takashi, E-mail: t-yanagisawa@aist.go.jp; Hase, Izumi

    2013-11-15

    Highlights: •Valence skipping in metallic compounds can give rise to an unconventional superconductivity. •Several elements in the periodic table show valence skipping (or valence missing), for example, Bi forms the compounds in valence states +3 and +5. •The doping of valence skipping elements will induce superconductivity and this will lead to a possibility of high temperature superconductivity. •We consider the Wolf model with negative-U impurities, and show a phase diagram including superconducting phase. •There is a high temperature region near the boundary. -- Abstract: Valence skipping in metallic compounds can give rise to an unconventional superconductivity. Several elements in the periodic table show valence skipping (or valence missing), for example, Bi forms the compounds in valence states +3 and +5. The doping of valence skipping elements will induce superconductivity and this will lead to a possibility of high temperature superconductivity. We consider the Wolf model with negative-U impurities, and show a phase diagram including superconducting phase. The superconducting state is changed into a metallic state with a local singlet as the attractive interaction |U| increases. There is a high temperature region near the boundary.

  2. Valence skipping driven superconductivity and charge Kondo effect

    International Nuclear Information System (INIS)

    Highlights: •Valence skipping in metallic compounds can give rise to an unconventional superconductivity. •Several elements in the periodic table show valence skipping (or valence missing), for example, Bi forms the compounds in valence states +3 and +5. •The doping of valence skipping elements will induce superconductivity and this will lead to a possibility of high temperature superconductivity. •We consider the Wolf model with negative-U impurities, and show a phase diagram including superconducting phase. •There is a high temperature region near the boundary. -- Abstract: Valence skipping in metallic compounds can give rise to an unconventional superconductivity. Several elements in the periodic table show valence skipping (or valence missing), for example, Bi forms the compounds in valence states +3 and +5. The doping of valence skipping elements will induce superconductivity and this will lead to a possibility of high temperature superconductivity. We consider the Wolf model with negative-U impurities, and show a phase diagram including superconducting phase. The superconducting state is changed into a metallic state with a local singlet as the attractive interaction |U| increases. There is a high temperature region near the boundary

  3. 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

  4. 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

  5. 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.

  6. 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

  7. 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

  8. 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.

  9. 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...

  10. Energy bands in graphene: Comparison between the tight-binding model and {\\it ab initio} calculations

    OpenAIRE

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

    2013-01-01

    We compare the classification of the electron bands in graphene, obtained by group theory algebra in the framework of tight-binding model (TBM), with that calculated in the 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 corresponding analysis is presented. The four occupied (three $\\sigma$- and one $\\pi$-like) and three unoccupi...

  11. 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.

  12. 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.)

  13. 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

  14. 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.

  15. 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 $H_{\\rm eff}$ ...

  16. Dispersion Forces

    CERN Document Server

    Buhmann, Stefan Yoshi

    2012-01-01

    In this book, a modern unified theory of dispersion forces on atoms and bodies is presented which covers a broad range of advanced aspects and scenarios. Macroscopic quantum electrodynamics is shown to provide a powerful framework for dispersion forces which allows for discussing general properties like their non-additivity and the relation between microscopic and macroscopic interactions. It is demonstrated how the general results can be used to obtain dispersion forces on atoms in the presence of bodies of various shapes and materials. Starting with a brief recapitulation of volume I, this volume II deals especially with bodies of irregular shapes, universal scaling laws, dynamical forces on excited atoms, enhanced forces in cavity quantum electrodynamics, non-equilibrium forces in thermal environments and quantum friction. The book gives both the specialist and those new to the field a thorough overview over recent results in the field. It provides a toolbox for studying dispersion forces in various contex...

  17. 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

  18. 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

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

    Science.gov (United States)

    Svensson, S.; Karlsson, L.

    1992-01-01

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

  20. 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

  1. 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 ...

  2. 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

  3. 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)

  4. 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),…

  5. New Kronig-Penney Equation Emphasizing the Band Edge Conditions

    Science.gov (United States)

    Szmulowicz, Frank

    2008-01-01

    The Kronig-Penney problem is a textbook example for discussing band dispersions and band gap formation in periodic layered media. For example, in photonic crystals, the behaviour of bands next to the band edges is important for further discussions of such effects as inhibited light emission, slow light and negative index of refraction. However,…

  6. Hole Doping Evolution of the Quasiparticle Band in Models of Strongly Correlated Electrons for the High-T$_c$ Cuprates

    CERN Document Server

    Duffy, D; Haas, S W; Moreo, A; Riera, J A; Dagotto, E; Duffy, Daniel; Nazarenko, Alexander; Haas, Stephan; Moreo, Adriana; Riera, Jose; Dagotto, Elbio

    1997-01-01

    Quantum Monte Carlo (QMC) and Maximum Entropy (ME) techniques are used to study the spectral function $A({\\bf p},\\omega)$ of the one band Hubbard model in strong coupling including a next-nearest-neighbor electronic hopping with amplitude $t'/t= -0.35$. These values of parameters are chosen to improve the comparison of the Hubbard model with angle-resolved photoemission (ARPES) data for high-$T_c$ cuprates in the antiferromagnetic insulating regime. A quasiparticle (q.p.) band is clearly observed in the QMC analysis at the temperature of the simulation $T=t/3$, both at and away from half-filling. At a small hole density the quasiparticle dispersion resembles the result in the non-interacting limit $U/t=0$, although with reduced effective hopping amplitudes. Such narrow q.p. band produces a large accumulation of weight in the density of states at the top of the valence band. As the electronic density $$ decreases further away from half-filling, the chemical potential travels through this energy window with a l...

  7. 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.

  8. 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

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

    Science.gov (United States)

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

    2015-04-01

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

  10. 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…

  11. VALENCY AND SYNTACTICAL RELATION IN BIMANESS

    Directory of Open Access Journals (Sweden)

    Made Sri Satyawati

    2012-11-01

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

  12. Study of band terminating in the A ? 100 by EUROGAM

    International Nuclear Information System (INIS)

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

  13. 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...

  14. 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

  15. 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.

  16. 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.

  17. 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

  18. EDP dispersives

    OpenAIRE

    Benzoni-Gavage, Sylvie

    2009-01-01

    L'objectif de ce cours est de présenter un panorama de propriétés analytiques et algébriques de quelques équations aux dérivées partielles (EDP) modélisant des phénomènes de propagation d'ondes dispersives. Les domaines d'applications des EDP étudiées sont variés: vibrations, vagues, transitions de phase, mécanique quantique, etc.

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

    International Nuclear Information System (INIS)

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

  20. 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

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

    Science.gov (United States)

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

    2014-06-01

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

  2. 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

  3. 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 ...

  4. 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

  5. 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

  6. 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.

  7. Evidence for atomic processes in molecular valence double ionization

    International Nuclear Information System (INIS)

    Complete molecular valence-electron spectra were measured for CO. Unexpectedly, discrete lines at low kinetic energies were found, superimposed on a continuous energy spectrum representing direct double-ionization processes. The appearance of these lines is discussed in the context of the formation of the C++O+ ion pair near its associated threshold at 38.4 eV. It is ascribed to valence-excited repulsive (CO+)* states, which dissociate to a large part rapidly into atomic fragments before electronic relaxation takes place. From our spectra, partial cross sections for the different processes leading to dissociative valence double ionization are derived

  8. 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)

  9. 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.)

  10. Valence density of states of group IVA transition-metal dichalcogenides

    International Nuclear Information System (INIS)

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

  11. 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

  12. Bosonic condensation in a flat energy band

    CERN Document Server

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

    2015-01-01

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

  13. 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

  14. Inelastic neutron scattering in valence fluctuation compounds

    Energy Technology Data Exchange (ETDEWEB)

    Jon M Lawrence

    2011-02-15

    The valence fluctuation compounds are rare earth intermetallics where hybridization of the nearly-localized 4f electrons with the conduction electrons leads to incorporation of the 4f's into the itinerant states. This hybridization slows down the conduction electrons and hence gives them a heavy effective mass, justifying application of the term 'heavy Fermion' (HF) to these materials. During the project period, we grew large single crystals of several such compounds and measured their properties using both standard thermodynamic probes and state-of-the-art inelastic neutron scattering. We obtained three main results. For the intermediate valence compounds CePd{sub 3} and YbAl{sub 3}, we showed that the scattering of neutrons by the fluctuations of the 4f magnetic moment does not have the momentum dependence expected for the itinerant heavy mass state; rather, the scattering is more typical of a localized spin fluctuation. We believe that incoherent scattering localizes the excitation. For the heavy Fermion compound Ce(Ni{sub 0.935}Pd{sub 0.065}){sub 2}Ge{sub 2}, which sits at a T = 0 critical point for transformation into an antiferromagnetic (AF) phase, we showed that the scattering from the AF fluctuations does not exhibit any of the divergences that are expected at a phase transition. We speculate that alloy disorder profoundly suppresses the growth of the fluctuating AF regions, leading to short range clusters rather than regions of infinite size. Finally, we explored the applicability of key concepts used to describe the behavior of rare earth heavy Fermions to uranium based HF compounds where the 5f electrons are itinerant as opposed to localized. We found that scaling laws relating the spin fluctuation energy measured in neutron scattering to the low temperature specific heat and susceptibility are valid for the uranium compounds, once corrections are made for AF fluctuations; however, the degeneracy of the high temperature moment is smaller than expected for rare-earth-like Hund's rule behavior, essentially because the orbital moment is suppressed for itinerant 5f electrons. We also found that the standard local-moment-based theory of the temperature dependence of the specific heat, susceptibility and neutron scattering fails badly for URu{sub 2}Zn{sub 20} and UCo{sub 2}Zn{sub 20}, even though the theory is phenomenally successful for the closely related rare earth compound YbFe{sub 2}Zn{sub 20}. Both these results highlight the distinction between the itineracy of the 5f's and the localization of the 4f's. It is our hope that these results are sufficiently significant as to stimulate deeper investigation of these compounds.

  15. 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.

  16. 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.

  17. 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.

  18. Effect of valence on the electromigration in silver

    International Nuclear Information System (INIS)

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

  19. 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.

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

    CERN Document Server

    Grebenshchikov, Sergy Yu

    2013-01-01

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

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

    OpenAIRE

    Nakata, Kouki; Totsuka, Keisuke

    2011-01-01

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

  2. 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.

  3. 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

  4. 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.

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

    Science.gov (United States)

    Kaur, Avneet; Bakhshi, A. K.

    2010-04-01

    The interest in copolymers stems from the fact that they present interesting electronic and optical properties leading to a variety of technological applications. In order to get a suitable copolymer for a specific application, genetic algorithm (GA) along with negative factor counting (NFC) method has recently been used. In this paper, we study the effect of change in the ratio of conduction band discontinuity to valence band discontinuity (? Ec/? Ev) on the optimum solution obtained from GA for model binary copolymers. The effect of varying bandwidths on the optimum GA solution is also investigated. The obtained results show that the optimum solution changes with varying parameters like band discontinuity and band width of constituent homopolymers. As the ratio ? Ec/? Ev increases, band gap of optimum solution decreases. With increasing band widths of constituent homopolymers, the optimum solution tends to be dependent on the component with higher band gap.

  6. 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.

  7. Research on valence state and leaching rate of uranium in ores from Shihongtan uranium deposit and it's geological significance

    International Nuclear Information System (INIS)

    10 uranium ore samples, collected from exploration sections No.31 and No.39, Shihongtan uranium deposit, were tested for uranium content and valence states. The wide range of U4+/U6+ (0.82-1.8) indicates the variation of valence states and complexity of existing states of uranium at the ore deposit. The lixivial rates change regularly corresponding to different concentrations of lixiviant and lixiviating time. When the equilibrium is basically established, the lixivial rates of sample K01 and K02 are of stable values, which indicates the content of mobile uranium if no H2O2 is added, and the content of dissoluble uranium if H2O2 is added. Based on the geologic setting of the deposit and the characteristics of ores, the experiment results show that, the uranium in ores mainly exists in the form of dispersive adsorption, and can be leached during in-situ leach mining

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

    Science.gov (United States)

    Yuan, Jian-Min

    2001-10-01

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

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

    Science.gov (United States)

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

    2009-01-01

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

  11. Valence-band splitting in Mg/W(110) : Neither spin-orbit nor parity effect

    Science.gov (United States)

    Shikin, A. M.; Rader, O.

    2007-08-01

    Spin-orbit coupling, e.g., in the form of the Rashba effect, is of high interest due to its role in novel spintronic devices. In connection with the question whether spin-orbit splittings can be induced in a thin film by a buried interface, there is a current controversy as to the origin of measured energy splittings in Mg quantum-well films on W(110) [C. Koitzsch , Phys. Rev. Lett. 95, 126401 (2005); F. Schiller , ibid. 95, 126402 (2005)]. This problem is resolved by comparing Mg/W(110) with Mg/Mo(110) data. At variance with both previous reports, strong interaction of Mg states with surface states of the substrate is identified as the origin of the observations in question.

  12. 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

  13. Valence-band photoemission of the H-plasma annealed (100) textured CVD diamond surface

    Science.gov (United States)

    Francz, G.; Kania, P.; Oelhafen, P.; Schedel-Niedrig, T.; Schlögl, R.; Locher, R.

    1996-10-01

    A (100) textured chemical vapor deposited (CVD) diamond thin film was exposed to a hydrogen plasma at 850°C as a cleaning procedure and was subsequently investigated by X-ray absorption spectroscopy (XAS) and ultraviolet photoelectron spectroscopy (UPS) with synchrotron radiation in the range 30 eV < hv < 150 eV. The dominant feature of the UPS spectra between 30 and 60 eV excitation energy is the presence of a distinct peak at around 1.8 eV below the Fermi level. This feature can be identified as a surface state of the reconstructed diamond (100) surface. In analogy to reported UPS measurements of reconstructed natural diamonds of (100) orientation reported earlier, the results are discussed in terms of a surface reconstruction of the (100) textured CVD diamond film. The electronic properties of the (100) textured CVD diamond thin film are compared to the ones of annealed or H-plasma exposed natural diamond (100). The UPS measurements of a hydrogen-plasma exposed, reconstructed (100) textured CVD diamond surface discussed here are, to our knowledge, the first reported.

  14. Modifications in the Si valence band after ion-beam-induced oxidation

    OpenAIRE

    Alay, Josep Lluís; Vandervorst, Wilfried

    1994-01-01

    The changes undergone by the Si surface after oxygen bombardment have special interest for acquiring a good understanding of the Si+-ion emission during secondary ion mass spectrometry (SIMS) analysis. For this reason a detailed investigation on the stoichiometry of the builtup surface oxides has been carried out using in situ x-ray photoemission spectroscopy (XPS). The XPS analysis of the Si 2p core level indicates a strong presence of suboxide chemical states when bombarding at angles of in...

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

    International Nuclear Information System (INIS)

    The present thesis deals with the one-valence-particle nuclei 147Tb and 151Er. The main purpose of the study was, to study characteristic properties of the particle-phonon excitations of these nuclei. In the one-valence-proton nucleus 147Tb from the πh11/2x3- septet only the 15/2+ and 17/2+ Yrast states were known, which underly a strong diagonal exchange interaction. At mass separators in β decay experiments of the 1/2+ and the 11/2-147Dy activities and in in-beam experiments layed out on excitation of states above the Yrast line with 6Li beams the nucleus 147Tb was spectroscoped. The combination of these three data sets made the nearly complete covering of the spin range from 1/2 to 27/2 of the low-lying states in 147Tb possible. At the whole in this nucleus more than 100 hitherto unknown states could be placed and farly characterized. The unusually manifold data allowed to identify beside the complete πh11/2x3- septet also very much further particlexphonon states. Furthermore in the excitation range between 2.5 and 4 MeV numerous three-quasiparticle excitations were observed and in very sufficient way described by parameter-free shell-model calculations. A further important result is the manifestation of a neutron-one-particle-one-hole state with I=27/2, which lies with 3.7 MeV excitation close to the Yrast line. (orig./HSI)

  16. 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.

  17. 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 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. PMID:25635516

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

    International Nuclear Information System (INIS)

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

  19. 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.

  20. 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

  1. 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...

  2. 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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-04-14

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

  4. 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.

  5. 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

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

    Science.gov (United States)

    Kolek, Andrzej

    2015-05-01

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

  7. Contextual valence modulates the neural dynamics of risk processing.

    Science.gov (United States)

    Zheng, Ya; Li, Qi; Wang, Kai; Wu, Haiyan; Liu, Xun

    2015-07-01

    A well-known bias in risky decision making is that most people tend to be risk averse when gains are salient but risk seeking when losses are salient. The present study addressed the neural dynamics of this process by recording ERPs during a gambling task in a gain and a loss context. Behaviorally, participants were found to be risk averse in the gain context but risk neutral in the loss context. During the anticipation stage, an increased stimulus-preceding negativity was elicited by high- versus low-risk choices in the gain but not the loss context. During the outcome-appraisal stage, the feedback-related negativity was larger after high- versus low-risk choices in the gain instead of the loss context. For the P300, an outcome valence effect (a larger P300 for gain vs. loss outcomes) emerged following the high- versus low-risk decisions in the gain but not the loss context. Our findings suggest that risk processing can be modulated by the context of valence during the anticipation stage and by both the contextual valence and the outcome valence during the outcome-appraisal stage, which may be driven by the motivational salience imposed by the context of valence. PMID:25664392

  8. The relation between valence and arousal in subjective experience.

    Science.gov (United States)

    Kuppens, Peter; Tuerlinckx, Francis; Russell, James A; Barrett, Lisa Feldman

    2013-07-01

    Affect is basic to many if not all psychological phenomena. This article examines 2 of the most fundamental properties of affective experience--valence and arousal--asking how they are related to each other on a moment to moment basis. Over the past century, 6 distinct types of relations have been suggested or implicitly presupposed in the literature. We critically review the available evidence for each proposal and argue that the evidence does not provide a conclusive answer. Next, we use statistical modeling to verify the different proposals in 8 data sets (with Ns ranging from 80 to 1,417) where participants reported their affective experiences in response to experimental stimuli in laboratory settings or as momentary or remembered in natural settings. We formulate 3 key conclusions about the relation between valence and arousal: (a) on average, there is a weak but consistent V-shaped relation of arousal as a function of valence, but (b) there is large variation at the individual level, so that (c) valence and arousal can in principle show a variety of relations depending on person or circumstances. This casts doubt on the existence of a static, lawful relation between valence and arousal. The meaningfulness of the observed individual differences is supported by their personality and cultural correlates. The malleability and individual differences found in the structure of affect must be taken into account when studying affect and its role in other psychological phenomena. PMID:23231533

  9. 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...

  10. Theory of Valence Transition in BiNiO_{3}.

    Science.gov (United States)

    Naka, Makoto; Seo, Hitoshi; Motome, Yukitoshi

    2016-02-01

    Motivated by the colossal negative thermal expansion recently found in BiNiO_{3}, the valence transition accompanied by the charge transfer between the Bi and Ni sites is theoretically studied. We introduce an effective model for Bi-6s and Ni-3d orbitals taking into account the valence skipping of Bi cations, and investigate the ground-state and finite-temperature phase diagrams within the mean-field approximation. We find that the valence transition is caused by commensurate locking of the electron filling in each orbital associated with charge and magnetic orderings, and the critical temperature and the nature of the transitions are strongly affected by the relative energy between the Bi and Ni levels and the effective electron-electron interaction in the Bi sites. The obtained phase diagram well explains the temperature- and pressure-driven valence transitions in BiNiO_{3} and the systematic variation of valence states for a series of Bi and Pb perovskite oxides. PMID:26894723

  11. 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.

  12. 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...

  13. Dispersion-Enhanced Laser Gyroscope

    Science.gov (United States)

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

    2008-01-01

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

  14. 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.

  15. 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 χimp ∼ 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

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

    International Nuclear Information System (INIS)

    In the present work, we describe several types of photoelectron spectroscopy experiments for elucidating certain valence photoionization mechanisms and the spectroscopy of residual ions in the case of two linear triatomic molecules CO2 and CS2. Using synchrotron radiation, we have measured the partial cross section (σ) and angular distribution (β) associated to the ejection of an electron from the 4σg orbital of CO2. These measurements continuously performed between 25 and 55 eV photon energy have shown some evidence of the σu 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 β and σ variations have allowed to determine the symmetry of some of excited-ionized states of the ion. A comparison between the experimental and calculated spectra of CO2 and CS2 within a configuration interaction method (CIPSI) shows an excellent agreement and demonstrates the important role of 3 hole-two electrons configurations. In the CS2 case we also show the relationship between the double ionization continua and the structures observed at high binding energy. (author)

  17. 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

  18. Quantum-mechanical model for valence-electron emission from metal surfaces

    International Nuclear Information System (INIS)

    Electron emission from the conduction band of metal surfaces is studied under grazing scattering conditions. We investigate this process making use of the quantum-mechanical (QM) model to represent the electronic interactions within the binary collisional formalism. The QM approach is based on the use of the model potential and allows us to describe the main features of the metal surface. It provides a precise description of both one-electron states and surface induced potential. In this work, the approximation is employed to evaluate electron distributions for 100 keV protons impinging grazingly on the Al(111) surface. We have found that the realistic representation of the surface included in the QM model introduces substantial changes in the valence emission at low electron energies and intermediate ejection angles. The influence of the surface wake potential on the valence emission probability is also addressed. In order to compare with experiments, we add the contribution coming from atomic inner shells calculated with the field-distorted-wave approximation. Total theoretical results obtained with the QM model are in fairly good agreement with the available experimental data

  19. 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)

  20. Extended quantum dimer model and novel valence-bond phases

    International Nuclear Information System (INIS)

    We extend the quantum dimer model (QDM) introduced by Rokhsar and Kivelson so as to construct a concrete example of the model which exhibits the first-order phase transition between different valence-bond solids suggested recently by Batista and Trugman and look for the possibility of other exotic dimer states. We show that our model contains three exotic valence-bond phases (herringbone, checkerboard and dimer smectic) in the ground-state phase diagram and that it realizes the phase transition from the staggered valence-bond solid to the herringbone. The checkerboard phase has four-fold rotational symmetry, while the dimer smectic, in the absence of quantum fluctuations, has massive degeneracy originating from partial ordering only in one of the two spatial directions. A resonance process involving three dimers resolves this massive degeneracy and the dimer smectic becomes ordered (order from disorder)

  1. 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)

  2. 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)

  3. 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

  4. 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.

  5. Hydrodynamic dispersion

    International Nuclear Information System (INIS)

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

  6. Phonon anomalies at the valence transition of SmS : An inelasticX-ray scattering study under pressure

    OpenAIRE

    Raymond, S.; Rueff, J. P.; D'Astuto, M.; Braithwaite, D.; Krisch, M.; Flouquet, J.

    2002-01-01

    The phonon dispersion curve of SmS under pressure was studied by inelastic x-ray scattering around the pressure-induced valence transition. A significant softening of the longitudinal acoustic modes propagating along the [111] direction was observed spanning a wide $q$ region from ($\\frac{2\\pi}{3a},\\frac{2\\pi}{3a},\\frac{2\\pi}{3a}$) up to the zone boundary as SmS becomes metallic. The largest softening occurs at the zone boundary and stays stable up to the highest measured pressure of 80 kbar ...

  7. 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...

  8. Valence structure effects in the stopping of swift ions

    Science.gov (United States)

    Sigmund, P.; Sharma, A.; Schinner, A.; Fettouhi, A.

    2005-04-01

    The valence structure of a material may affect the stopping of swift charged particles primarily via Z2 structure, atom-molecule differences, gas-solid differences and metal-insulator differences. These material effects have a common physical origin and can therefore be considered from a unified point of view. Theoretical arguments focus on the effect of binding and orbital motion of the target electrons as well as projectile screening and Barkas-Andersen effect. Generally, valence effects depend on the atomic number, charge state and velocity of the projectile. Reference is made to recent calculations on the basis of binary stopping theory as well as experimental findings.

  9. Lattice anomalies in CeNi unstable valence compound

    International Nuclear Information System (INIS)

    Neutron diffraction and X-ray absorption measurements have been performed to study the changes in the structure and the Ce valence between 10 K and 295 K. No evidence for a phase transition was obtained, but some nearest-neighbour distances have clear peculiarities in the temperature range of 100 K to 150 K. The valence of Ce increases continuously with decreasing temperature, which can explain neither the lattice anomalies nor the previously observed temperature dependence of the phonon frequencies. A correlation between the gap-like magnetic excitation spectrum formed at low temperatures and observed lattice anomalies is discussed. (orig.)

  10. 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...

  11. 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

  12. Valence-differential spectroscopy of Co-Fe cyanide films

    Science.gov (United States)

    Moritomo, Y.; Nakada, F.; Kurihara, Y.

    2009-03-01

    Electrochromism is extensively investigated for practical application of display and memory devices. To develop the material, reliable information on the optical and electronic properties of the solid film is indispensable. Here, we propose valence-differential spectroscopy that can selectively extract the spectral components related to the oxidized/reduced metal site. We applied the spectroscopy to Co2+-Fe2+? and Co2+?-Fe2+ cyanide films with finely control of averaged valence (?) of the transition metal by external electric pulses. The spectroscopy revealed transition energy E, width ?, and oscillator strength f of the spectral components related to the transition metal.

  13. Superconductivity mechanism in metal oxides with variable valency

    International Nuclear Information System (INIS)

    In the present paper it is shown, that the metals with the mixed valency can have the subsystem of the local electron pairs. The local pairs may appreciably change the optical elastic modulus and the lattice parameters. The additions to the elastic modulus and the lattice parameters depend on concentration of the local pairs and temperature. The peculiarity of these dependences is the extrema. The concentration and temperature dependences of the additions are determined by intercentre correlations and pair delocalisation (pair transfer) in the subsystem of the local pairs. These results were used for the construction of the high-temperature superconductivity mechanism for the metals with the mixed valency

  14. Properties of ternary rare earth REXY compounds with 18 valence electrons

    International Nuclear Information System (INIS)

    Ternary rare earth compounds REXY, where RE is a lanthanide element, Y a transition element and Z is an sp element, offer a large variety of structure types. Our research focuses on compounds LiGaGe and MgAgAs (C1b) structure which all have 18 valence electrons. Magnetic and resistivity measurements were used to examine some of these compounds. Most of the compounds order antiferromagnetic at low temperatures. While compounds with LiGaGe structure are metallic, many of the compounds with MgAgAs structure are semiconducting. Additionally for some of these compounds a metal-insulator transition was found. The metal-insulator transition temperature depends strongly on the preparation conditions. Both the magnetic ground states and the resistance behavior are in good agreement with electronic band structure calculations

  15. 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

  16. 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.

  17. 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.

  18. 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

  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. Detangling Flat Bands into Fano Lattices

    OpenAIRE

    Flach, Sergej; Leykam, Daniel; 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 all...

  1. Application of sum rule to the dispersion model of hydrogenated amorphous silicon

    International Nuclear Information System (INIS)

    Optical data obtained for a-Si:H films by ellipsometry and spectrophotometry in the wide photon energy range 0.046–8.9 eV are fitted using the analytical dispersion models based on the application of the sum rule. The models include all absorption processes ranging from phonon absorption in IR region to core electron excitations in X-ray region. They take into account the existence of extended and localized states of valence electrons and distinguish transitions to conduction band and higher energy electron states. It is demonstrated that a combination of optical measurements over the wide range, combined with reasonable assumptions about the optical response in regions where no experimental data are available can lead to dispersion models enabling to determine the mass density of the film. Comparing the density of states determined by tight-binding method with that obtained from optical data, it is shown that an excitonic effect is significant in a-Si:H and causes a redistribution of transition probability from higher energies to the broad peak centered at 3.5 eV. Moreover, it is suggested how to apply the sum rule in the commercial ellipsometric software implementing the Tauc–Lorentz model. - Highlights: • An approach based on sum rule is used to construct dispersion model of amorphous Si. • The model is expressed fully analytically and it is computationally efficient. • It covers spectral range from phonon absorption to core electron excitations. • Material parameters such as mass density are determined using optical measurements. • It is shown that excitonic effects play an important role in interband transitions

  2. 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.

  3. 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.

  4. 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.

  5. 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

  6. Nuclear masses and the number of valence nucleons

    International Nuclear Information System (INIS)

    An improved version of the liquid drop model is presented. The addition of two terms, linear and quadratic in the total number of valence nucleons (particles or holes), improves the description of atomic masses, which can be fitted with an r.m.s. error of 1.2 MeV. Predictions are analysed an compared with those of established models

  7. 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

  8. Social Learning Modulates the Lateralization of Emotional Valence

    Science.gov (United States)

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

    2008-01-01

    Although neuropsychological studies of lateralization of emotion have emphasized valence (positive vs. negative) or type (basic vs. complex) dimensions, the interaction between the two dimensions has yet to be elucidated. The purpose of the current study was to test the hypothesis that recognition of basic emotions is processed preferentially by…

  9. Border Crossing in "Multicultural Australia": A Study of Cultural Valence.

    Science.gov (United States)

    Smolicz, J. J.; Hudson, D. M.; Secombe, M. J.

    1998-01-01

    Discusses "border crossing" by individuals who augment their cultural valence through acquiring competence in and positive attitudes toward other cultures. Reports on two studies carried out according to the principles of humanistic sociology and based on memoirs written by university graduates. (Author/VWL)

  10. Valence orbital momentum distributions in s-triazine

    International Nuclear Information System (INIS)

    Valence orbital momentum distributions, rho(q), are obtained for s-triazine, C3H3N3, from (e,2e) spectroscopy and split valence SCFMO calculations. The separation energy spectrum simulated using the calculated rho(q) and ionization energies from Green's function calculations is in good agreement with experiment from 9--20 eV, but at higher energy the simulated spectrum has higher intensity than experiment, indicating that the Green's function calculation underestimates the complexity of the inner valence region. The calculated momentum distributions have their maxima at higher values than observed experimentally for the outermost valence orbitals, but the difference in momentum distributions between the antisymmetric 4e' N2p lone pair orbital of s-triazine and the N2p lone pair orbital of ammonia is reproduced well by the calculations. Similarly, calculated and experimental differences of Fourier transformed rho(q) for the 4e' and 3a/sup prime/1 N2p lone pair orbitals of triazine are in agreement and can be interpreted using plots of 4e' and 3a/sup /1 orbital averages and differences from the SCFMO calculations. The Fourier transformed momentum distribution of the 4e' orbital clearly shows the presence of both nearest-neighbor C and second-nearest-neighbor N interactions

  11. 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.

  12. 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

  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 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.)

  15. 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.

  16. 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.)

  17. Electronic Structure of b-Axis Oriented VO2 Thin Film with Mixed-Valence States Probed by Soft-X-ray Spectroscopy

    Science.gov (United States)

    Suetsugu, Takaaki; Shimazu, Yuichi; Tsuchiya, Takashi; Kobayashi, Masaki; Sakai, Enju; Kumigashira, Hiroshi; Higuchi, Tohru

    2015-06-01

    The electronic structure of b-axis oriented VO2 thin films in monoclinic phase with various thicknesses has been studied by soft-X-ray spectroscopy. The VO2 thin films show the mixed-valence V3+/V4+ state, which is created by oxygen vacancies. The V3+ state and oxygen vacancies increase with increasing film thickness. The thinnest film of 56 nm exhibits a metal-insulator transition (MIT) at ˜340 K, although thicker films of 126 and 155 nm do not exhibit MIT. The valence band structure around the Fermi level consists of V 3d eg? , a1g, and eg? bands. The bandwidths and spectral weights of the a1g and eg? bands are smaller in the thinnest film, which corresponds to the insulating phase at 300 K. The above results indicate that the mixed-valence states with oxygen vacancies are closely related to the MIT in the monoclinic phase of VO2 thin films.

  18. Congenital Constriction Band Syndrome

    Directory of Open Access Journals (Sweden)

    Rajesh Gupta, Fareed Malik, Rishabh Gupta, M.A.Basit, Dara Singh

    2008-04-01

    Full Text Available Congenital constriction bands are anomalous bands that encircle a digit or an extremity. Congenitalconstriction band syndrome is rare condition and is mostly associated with other musculoskeletaldisorders.We report such a rare experience.

  19. 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...

  20. 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 theory is derived t...

  1. 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.

  2. 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)

  3. 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...

  4. Tunable Band Alignment with Unperturbed Carrier Mobility of On-Surface Synthesized Organic Semiconducting Wires

    Science.gov (United States)

    2016-01-01

    The tunable properties of molecular materials place them among the favorites for a variety of future generation devices. In addition, to maintain the current trend of miniaturization of those devices, a departure from the present top-down production methods may soon be required and self-assembly appears among the most promising alternatives. On-surface synthesis unites the promises of molecular materials and of self-assembly, with the sturdiness of covalently bonded structures: an ideal scenario for future applications. Following this idea, we report the synthesis of functional extended nanowires by self-assembly. In particular, the products correspond to one-dimensional organic semiconductors. The uniaxial alignment provided by our substrate templates allows us to access with exquisite detail their electronic properties, including the full valence band dispersion, by combining local probes with spatial averaging techniques. We show how, by selectively doping the molecular precursors, the product’s energy level alignment can be tuned without compromising the charge carrier’s mobility. PMID:26841052

  5. Tunable Band Alignment with Unperturbed Carrier Mobility of On-Surface Synthesized Organic Semiconducting Wires.

    Science.gov (United States)

    Basagni, Andrea; Vasseur, Guillaume; Pignedoli, Carlo A; Vilas-Varela, Manuel; Peña, Diego; Nicolas, Louis; Vitali, Lucia; Lobo-Checa, Jorge; de Oteyza, Dimas G; Sedona, Francesco; Casarin, Maurizio; Ortega, J Enrique; Sambi, Mauro

    2016-02-23

    The tunable properties of molecular materials place them among the favorites for a variety of future generation devices. In addition, to maintain the current trend of miniaturization of those devices, a departure from the present top-down production methods may soon be required and self-assembly appears among the most promising alternatives. On-surface synthesis unites the promises of molecular materials and of self-assembly, with the sturdiness of covalently bonded structures: an ideal scenario for future applications. Following this idea, we report the synthesis of functional extended nanowires by self-assembly. In particular, the products correspond to one-dimensional organic semiconductors. The uniaxial alignment provided by our substrate templates allows us to access with exquisite detail their electronic properties, including the full valence band dispersion, by combining local probes with spatial averaging techniques. We show how, by selectively doping the molecular precursors, the product's energy level alignment can be tuned without compromising the charge carrier's mobility. PMID:26841052

  6. 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…

  7. 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…

  8. 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.

  9. 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.

  10. 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.

  11. Tachyonic Dispersion in Coherent Networks

    CERN Document Server

    Chong, Y D

    2015-01-01

    We propose a technique to realize a tachyonic band structure in a coherent network, such as an array of coupled ring resonators. This is achieved by adding "PT symmetric" spatially-balanced gain and loss to each node of the network. In a square-lattice network, the quasi-energy bandstructure exhibits a tachyonic dispersion relation, centered at either the center or corner of the Brillouin zone. There is one tachyonic hyperboloid in each gap, unlike in PT-symmetric tight-binding honeycomb lattices where the hyperboloids occur in pairs. The dispersion relation can be probed by measuring the peaks in transmission across a finite network as the gain/loss parameter is varied.

  12. Tachyonic dispersion in coherent networks

    Science.gov (United States)

    Chong, Y. D.; Rechtsman, M. C.

    2016-01-01

    We propose a technique to realize a tachyonic band structure in a coherent network, such as an array of coupled ring resonators. This is achieved by adding ‘PT symmetric’ spatially balanced gain and loss to each node of the network. In a square-lattice network, the quasi-energy bandstructure exhibits a tachyonic dispersion relation, centered at either the center or corner of the Brillouin zone. There is one tachyonic hyperboloid in each gap, unlike in PT-symmetric tight-binding honeycomb lattices where the hyperboloids occur in pairs. The dispersion relation can be probed by measuring the peaks in transmission across a finite network as the gain/loss parameter is varied.

  13. 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)

  14. 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.)

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

    CERN Document Server

    Radici, Marco; Bacchetta, Alessandro; Guagnelli, Marco

    2015-01-01

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

  16. 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.

  17. Improved extraction of valence transversity distributions from inclusive dihadron production

    Science.gov (United States)

    Radici, Marco; Courtoy, A.; Bacchetta, Alessandro; Guagnelli, Marco

    2015-05-01

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

  18. Theoretical calculations of valence states in Fe-Mo compounds

    International Nuclear Information System (INIS)

    The half-metallic ferromagnetic double perovskite compound Sr2FeMoO6 is considered as an important material for spintronic applications. It appears to be fundamental to understand the role of electronic parameters controlling the half-metallic ground state. Fe-Mo double perovskites usually present some degree of Fe/Mo disorder which generally increases with doping. In this work, we study the valence states of Fe-Mo cations in the off-stoichiometric system Sr2Fe1+xMo1?xO6 (?1 ? x ? 1/3) with disorder. Our results for Fe and Mo valence states are obtained using the Green functions and the renormalization perturbation expansion method. The model is based on a correlated electron picture with localized Fe-spins and conduction Mo-electrons interacting with the local spins via a double-exchange-type mechanism

  19. 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

  20. 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.

  1. Detangling Flat Bands via Fano Structures

    Science.gov (United States)

    Bodyfelt, Joshua; Flach, Sergej; Leykam, Daniel; Desyatnikov, Anton; Matthies, Peter

    2014-03-01

    Translationally invariant lattices with flat bands (FB) in the band structure possess irreducible compact localized flat band states (FBS). The number of unit cells involved in one irreducible FBS defines the FB class of the model. For class 1, we transform and detangle the FBS and dispersive states into a Fano lattice. Inverting the scheme, we end up with a continuum of FB models for any FB class. In the case of an on-site disorder potential, the symmetric part lifts the FB degeneracy, keeping compact localization of FBS. The antisymmetric part yields Fano-induced Cauchy tails for the potential felt by the dispersive states. As a result, weak disorder enforces different energy dependent localization length scales, and highly nontrivial mode profiles at the FB energy. Scattering by perturbed FBS can then be understood as Fano resonance.

  2. 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.

  3. Incautiously Optimistic: Positively-Valenced Cognitive Avoidance in Adult ADHD

    OpenAIRE

    Knouse, Laura E; Mitchell, John T.

    2015-01-01

    Clinicians who conduct cognitive-behavioral therapy (CBT) targeting attention-deficit/hyperactivity disorder (ADHD) in adulthood have noted that their patients sometimes verbalize overly positive automatic thoughts and set overly optimistic goals. These cognitions are frequently related to failure to engage in compensatory behavioral strategies emphasized in CBT. In this paper, we offer a functional analysis of this problematic pattern, positively-valenced cognitive avoidance, and suggest met...

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

    OpenAIRE

    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...

  5. 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...

  6. Nuclear effects on valence quark distributions and sea quark distributions

    International Nuclear Information System (INIS)

    A method is presented to get nuclear effect functions RvA(xt) and Rsa(xt) on valence quark distributions and sea quark distributions from the data of 1-A DIS process and nuclear Drell-Yan process. Both the functions may be used to test the theoretical models explaining the nuclear effects. As a example, RvFe(xt) and RsFe(xt) of the iron nucleus were obtained by this method

  7. 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...

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

    International Nuclear Information System (INIS)

    Prompt γ-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

  9. 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...

  10. 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.

  11. 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...

  12. 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.))

  13. Valence transition and superconductivity in the extended periodic Anderson model

    OpenAIRE

    Phan, Van Nham

    2009-01-01

    In this thesis, an extended periodic Anderson model with an additional local Coulomb repulsion U f c between localized f electrons and conduction electrons is investigated by use of the projector-based renormalization method (PRM). First, it is shown that the model in one dimension shows a valence transition, which becomes sharper, when the energy of the f level approaches the Fermi level. The transition becomes also enhanced, when the hybridization V between the localized and conduction elec...

  14. Valence state change and defect centers induced by infrared femtosecond laser in Yb:YAG crystals

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Xinshun, E-mail: xinshunwang@hitwh.edu.cn; Liu, Yang; Zhao, Panjuan; Guo, Zhongyi; Li, Yan; Qu, Shiliang [School of Science, Harbin Institute of Technology at Weihai, Weihai 264209 (China)

    2015-04-21

    The broad band upconversion luminescence in Yb{sup 3+}:YAG crystal has been observed in experiments under the irradiation of focused infrared femtosecond laser. The dependence of the fluorescence intensity on the pump power shows that the upconversion luminescence is due to simultaneous two-photon absorption process, which indicates that the broad emission bands at 365 and 463?nm could be assigned to the 5d ? 4f transitions of Yb{sup 2+} ions and the one at 692?nm could be attributed to the electron-hole recombination process on (Yb{sup 2+}-F{sup +}) centers. The absorption spectra of the Yb:YAG crystal samples before and after femtosecond laser irradiation, and after further annealing reveal that permanent valence state change of Yb ions from Yb{sup 3+} to Yb{sup 2+} and (Yb{sup 2+}-F{sup +}) centers have been induced by infrared femtosecond laser irradiation in Yb{sup 3+}:YAG crystal.

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

    International Nuclear Information System (INIS)

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

  16. Influence of the sequence on the ab initio band structures of single and double stranded DNA models

    Energy Technology Data Exchange (ETDEWEB)

    Bogár, Ferenc, E-mail: bogar@sol.cc.u-szeged.hu [MTA-SZTE, Supramolecular and Nanostructured Materials Research Group of the Hungarian Academy of Sciences, University of Szeged, Dóm tér 8, 6720 Szeged (Hungary); Chair for Theoretical Chemistry and Laboratory of the National Foundation for Cancer Research, Friedrich–Alexander-University Erlangen–Nürnberg, Egerlandstr. 3, 91058 Erlangen (Germany); Bende, Attila, E-mail: bende@itim-cj.ro [Molecular and Biomolecular Physics Department, National Institute for Research and Development of Isotopic and Molecular Technologies, Str. Donath 65-103, C.P. 700, Cluj Napoca RO-400293 (Romania); Chair for Theoretical Chemistry and Laboratory of the National Foundation for Cancer Research, Friedrich–Alexander-University Erlangen–Nürnberg, Egerlandstr. 3, 91058 Erlangen (Germany); Ladik, János, E-mail: Janos.Ladik@chemie.uni-erlangen.de [Chair for Theoretical Chemistry and Laboratory of the National Foundation for Cancer Research, Friedrich–Alexander-University Erlangen–Nürnberg, Egerlandstr. 3, 91058 Erlangen (Germany)

    2014-06-13

    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. - Highlights: • HF Energy bands in DNA. • The role of aperiodicity in the DNA band structure. • Hole mobilities in quasi-periodic DNA with broader valence bands.

  17. 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

  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. 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

  1. 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.

  2. 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...

  3. 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

  4. 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.

  5. 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)

  6. 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.

  7. 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.

  8. 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…

  9. Mixed-valence copper oxides: stoichiometry-Superconductivity relationships. Les oxydes de cuivre a valence mixte: relations stoechiometrie - supraconductivite

    Energy Technology Data Exchange (ETDEWEB)

    Raveau, B.; Michel, C. (Institut des Sciences de la Matiere du Rayonnement (ISMRA), 14 - Caen (FR))

    1989-01-01

    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 La{sub 2}Cu0{sub 4}, YBa{sub 2}Cu{sub 3}O{sub 6.9} and YBa{sub 2}Cu{sub 3}O{sub 6.25} compounds.

  10. 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.

  11. 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

  12. 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.

  13. 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.

  14. 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

  15. 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.

  16. 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.

  17. 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

  18. 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

  19. 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

  20. Dispersive waves and caustics

    Directory of Open Access Journals (Sweden)

    Arthur D. Gorman

    1985-03-01

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

  1. 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

  2. Nucleon and pion distribution functions in the valence region

    International Nuclear Information System (INIS)

    An experimental and theoretical perspective is provided on the behavior of unpolarized distribution functions for the nucleon and pion on the valence-quark domain, namely, Bjorken x(greater-or-similar sign)0.4. This domain is a key to much of hadron physics; e.g., a hadron is defined by its flavor content and that is a valence-quark property. Furthermore, its accurate parametrization is crucial to the provision of reliable input for large collider experiments. The focus is on experimental extractions of distribution functions via electron and muon inelastic scattering, and from Drell-Yan interactions; and on theoretical treatments that emphasize an explanation of the distribution functions, providing an overview of major contemporary approaches and issues. Valence-quark physics is a compelling subject, which probes at the heart of our understanding of the standard model. There are numerous outstanding and unresolved challenges, which experiment and theory must confront. In connection with experiment, an explanation that an upgraded Jefferson Laboratory facility is well suited to provide new data on the nucleon is provided, while a future electron-ion collider could provide essential new data for the mesons. There is also great potential in using Drell-Yan interactions, at FNAL, CERN, J-PARC, and GSI, to push into the large-x domain for both mesons and nucleons. Furthermore, it is argued that explanation, in contrast to modeling and parametrization, requires a widespread acceptance of the need to adapt theory: to the lessons learnt already from the methods of nonperturbative quantum-field theory and a fuller exploitation of those methods.

  3. Dispersing powders in liquids

    CERN Document Server

    Nelson, RD

    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

  4. 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

    transitions from filled ligand orbitals to the metal 1s core hole, with distinct energetic shifts for ligands of differing ionization potentials. VtC-detected XAS data were obtained from multiple valence emission features for a series of well-characterized Mn model compounds; taken together, these data...... XAS, nonresonant XES, and VtC RXES data were all modeled within a density functional theory approach. While the TFY XAS and nonresonant XES data are readily interpreted by theory, the VtC RXES cannot be reproduced within such a simplified model. Nonetheless, dramatic changes in the experimental...

  5. 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.

  6. 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

  7. 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...

  8. Crystal growth of mixed-valence ammonium vanadates

    International Nuclear Information System (INIS)

    A new method has been developed for the synthesis of mixed-valence ammonium vanadate crystals. Single crystals of (NH4)2V3O8 were synthesized on a large scale by hydrothermal reduction of NH4VO3 in ethanol-H2O solutions in the presence of triblock copolymer Pluronic P123. The crystals are shining thin plates with (001) cleavage planes. Calcination of the (NH4)2V3O8 crystals at 300 C or above resulted in pure phases of V2O5. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  9. 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

  10. 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

  11. Band parameters of phosphorene

    DEFF Research Database (Denmark)

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

    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...

  12. 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.

  13. Detangling flat bands into Fano lattices

    Science.gov (United States)

    Flach, Sergej; Leykam, Daniel; Bodyfelt, Joshua D.; Matthies, Peter; Desyatnikov, Anton S.

    2014-02-01

    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.

  14. 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

  15. 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].

  16. 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)

  17. 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.

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

    DEFF Research Database (Denmark)

    Christensen, Justin

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

  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. Tunable topological valence in nematic shells on spherocylindrical colloidal particles.

    Science.gov (United States)

    de Oliveira, E J L; de Oliveira, I N; Lyra, M L; Mirantsev, L V

    2016-01-01

    We perform molecular dynamics simulations of the orientational ordering on nematic shells delimited by spherocylindrical nanoscopic colloidal particles. We show that under conditions of degenerate planar anchoring, the equilibrium director field structure in these shells exhibits pairs of +1/2 topological defects at the poles of spherical cups in the absence of an external electric field. In addition, a certain number of pairs of ±1/2 defects occurs on the spherical cups far from the poles, thus resulting in a total of eight valence spots. A strong field applied along the main spherocylindrical axis removes the ±1/2 defect pairs while it coalesces the polar ones into a single +1 topological defect. A strong transverse field destroys all defects on the spherical cups but generates four +1/2 defects in the cylindrical part. Therefore, an external field can be used to control the number of valence centers in spherocylindrical nematic shells, thus unveiling their capability of acting as multivalent building blocks for nanophotonic devices. PMID:26871131

  1. 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

  2. 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.)

  3. 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)

  4. Electronic band structure of ZnO-rich highly mismatched ZnO{sub 1?x}Te{sub x} alloys

    Energy Technology Data Exchange (ETDEWEB)

    Ting, M.; Jaquez, M. [Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Mechanical Engineering Department, University of California, Berkeley, California 94720 (United States); Reis, R. dos [National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Dubon, O. D. [Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Materials Science and Engineering Department, University of California, Berkeley, California 94720 (United States); Mao, S. S. [Mechanical Engineering Department, University of California, Berkeley, California 94720 (United States); Yu, K. M. [Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Department of Physics and Materials Science, City University of Hong Kong, Kowloon (Hong Kong); Walukiewicz, W. [Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

    2015-03-02

    We synthesized ZnO{sub 1?x}Te{sub x} 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 ZnO{sub 1?x}Te{sub x} alloys.

  5. Effective Lagrangian and equations for valence quark and gluon Green's functions

    International Nuclear Information System (INIS)

    Starting from the QCD Lagrangian and separating background and valence degrees of freedom, one arrives at the effective Lagrangian for valence quarks and gluons. Each term in the Lagrangian contains a product of valence quark and gluon operators acting at the end of the fundamental or adjoint string, made of background field. Simple procedure is described how to obtain from the Lagrangian self-coupled equations for quark and gluon Green's function

  6. 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...

  7. 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...

  8. 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.

  9. 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.

  10. Wide band systems

    Science.gov (United States)

    Baier, Paul Walter; Kleinhempel, Werner

    Most radio communication systems being presently introduced are digital systems. Depending on the transmission bandwidth relative to the information rate, such systems can be divided into the class of narrow band systems and wide band systems. The advantages that wide band systems offer under adverse propagation conditions are studied. After introducing digital information transmission, digital wide band systems are defined on the basis of the used transmission signal forms and are compared with narrow band systems. The need for the application of wide band systems is pointed out referring to information theory, with the resistance against noise and interference as well as the capabilities of multiple access and selective addressing being addressed. Different types of wide band systems including spread spectrum are presented. The quantitative treatment of propagation problems in narrow band and wide band systems due to time variant multipath propagation is tackled and the potential of wide band systems in combatting propagation effects is shown. It is explained that properly designed spread spectrum systems are less affected by multipath reception than narrow band systems.

  11. 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...

  12. 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

  13. Design of Broadband Dispersion Compensating Photonic Crystal Fiber

    Directory of Open Access Journals (Sweden)

    Md. Selim Habib

    2012-08-01

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

  14. 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

  15. 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.

  16. Band gap engineering via doping: A predictive approach

    Energy Technology Data Exchange (ETDEWEB)

    Andriotis, Antonis N., E-mail: andriot@iesl.forth.gr [Institute of Electronic Structure and Laser, FORTH, P.O. Box 1527, 71110 Heraklio, Crete (Greece); Menon, Madhu, E-mail: super250@uky.edu [Department of Physics and Astronomy and Center for Computational Sciences, University of Kentucky, Lexington, Kentucky 40506 (United States)

    2015-03-28

    We employ an extension of Harrison's theory at the tight binding level of approximation to develop a predictive approach for band gap engineering involving isovalent doping of wide band gap semiconductors. Our results indicate that reasonably accurate predictions can be achieved at qualitative as well as quantitative levels. The predictive results were checked against ab initio ones obtained at the level of DFT/SGGA?+?U approximation. The minor disagreements between predicted and ab initio results can be attributed to the electronic processes not incorporated in Harrison's theory. These include processes such as the conduction band anticrossing [Shan et al., Phys. Rev. Lett. 82, 1221 (1999); Walukiewicz et al., Phys. Rev. Lett. 85, 1552 (2000)] and valence band anticrossing [Alberi et al., Phys. Rev. B 77, 073202 (2008); Appl. Phys. Lett. 92, 162105 (2008); Appl. Phys. Lett. 91, 051909 (2007); Phys. Rev. B 75, 045203 (2007)], as well as the multiorbital rehybridization. Another cause of disagreement between the results of our predictive approach and the ab initio ones is shown to be the result of the shift of Fermi energy within the impurity band formed at the edge of the valence band maximum due to rehybridization. The validity of our approach is demonstrated with example applications for the systems GaN{sub 1?x}Sb{sub x}, GaP{sub 1?x}Sb{sub x}, AlSb{sub 1?x}P{sub x}, AlP{sub 1?x}Sb{sub x}, and InP{sub 1?x}Sb{sub x}.

  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. The impact of surface and retardation losses on valence electron energy-loss spectroscopy

    International Nuclear Information System (INIS)

    The inelastic scattering of fast electrons transmitting thin foils of silicon (Si), silicon nitride (Si3N4), gallium arsenide (GaAs), gallium nitride (GaN) and cadmium selenide (CdSe) was analyzed using dielectric theory. In particular, the impact of surface and bulk retardation losses on valence electron energy-loss spectroscopy (VEELS) was studied as a function of the foil thickness. It is shown that for the materials analyzed, surface and retardation losses can cause a systematic, thickness-dependent modulation of the dielectric volume losses, which can hamper the determination of the bulk dielectric data as well as the identification of band-gap and interband transition energies by VEELS. For Si and GaAs, where the dielectric function is strongly peaked with high absolute values, retardation losses lead to additional intensity maxima in the spectrum. For thin films of these materials (below ?100 nm), the additional intensity maxima are related to retardation effects due to the finite size of the sample leading to the excitation of guided light modes. For thicker films, exceeding about 200 nm, the intensity maxima are caused by bulk retardation losses, i.e., Cerenkov losses. Although thickness-dependent modulations were observed for Si3N4, GaN and CdSe, the form of the dielectric functions and their lower maxima, means that for TEM samples <100 nm thick, the band-gap energies of these materials can be accurately identified by VEELS. Guidelines are given that allow for forecasting the impact of surface and retardation losses on VEELS

  19. 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

  20. 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.