WorldWideScience
 
 
1

Angle-resolved photoemission from oriented thin films of long alkyl molecules: valence band dispersion  

Science.gov (United States)

Angle-resolved photoemission spectra were measured using synchrotron radiation for oriented thin films of hexatriacontane, CH3(CH2)34CH3, and pentatriacontan-18-one, CH3(CH2)16CO(CH2)16CH3, with their long axes perpendicular to the substrate surface. The valence band dispersion was observed along the long molecular axis over the whole Brillouin zone for both compounds. The results demonstrate that the chemical disorder caused by the C=O group in the CH2 chain does not affect the band structure so much and both compounds show valence band dispersion similar to the dispersion in an ideal polyethylene chain. Further, we observed a band which was not observed in our previous work. It determines the top of the valence band at the ? point. Comparison with theoretical results indicates that it corresponds to a band of B1 (B2g at ?) symmetry which consists of only C2p atomic orbitals directed along the carbon chain.

Ueno, Nobuo; Fujimoto, Hitoshi; Sato, Naoki; Seki, Kazuhiko; Inokuchi, Hiroo

1990-01-01

2

Hole energy and momentum distributions in valence bands  

International Nuclear Information System (INIS)

In order to understand the electrical and magnetic properties of solids, the knowledge of the density of states and the dispersion relation of the valence bands is indispensable. This thesis offers some alternative methods to obtain information about the nature of the valence band. Part A deals with the energy distribution of the photoelectrons. A simple model, which explains the core hole satellite structure in compounds with large correlation effects between the valence band holes and the created photo-hole, is outlined. CuCl, CuX2 (X = F Cl and Br) are studied, by photoemission and Auger electron spectroscopies in determining the valence band properties. Part B deals with the simultaneous measurement of the energy and the wave vector of the emitted electrons. A practical example is given for the determination of the dispersion relation in copper. The measurements of a surface resonance band and the distribution of the secondary electrons are also reported. (Auth.)

1982-01-01

3

Investigation of the XPS valence band structure from Sn chalcogenides  

International Nuclear Information System (INIS)

XPS valence band spectra reflect the electronic density of states weighted with cross-sections. The spectra will give additional information about the symmetry of the electron wave function, if they are measured in dependence on the electron emission angles. Valence band spectra of SnS, SnSe, SnTe, and SnS_2 are measured partly in dependence on the polar angle THETA. These measurements allow an identification of the symmetry of valence orbitals from intensity variations of the valence band maxima. (author)

1981-12-01

4

Valence band anticrossing in GaBixAs1-x  

Energy Technology Data Exchange (ETDEWEB)

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

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

2007-07-11

5

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)

1985-11-01

6

Measured energy-momentum densities of the valence band of aluminium  

International Nuclear Information System (INIS)

The energy-resolved momentum densities of the valence band of a thin polycrystalline aluminium film have been measured using electron momentum spectroscopy (EMS). The spectrometer used for these measurements has estimated energy and momentum resolutions of 0.9 eV and 0.10 atomic units respectively. The valence band of aluminium was clearly resolved, resembling very closely that of a free-election parabola. The measurement has been compared to linear muffin-tin orbital (LMTO) calculations for spherically averaged crystalline aluminium. Comparison has also been made between the experiment and Monte-Carlo simulations which take into account additional elastic and inelastic scattering events not considered in the LMTO calculations. The final agreement obtained between the measurement and theory for the dispersion and relative intensities of the aluminium valence band is excellent when lifetime broadening of the band is allowed for. 21 refs., 11 figs

1996-01-01

7

Core level and valence band photoemission from UAs  

International Nuclear Information System (INIS)

Ultraviolet and X-ray photoemission spectroscopy is used to study the valence band and core levels of UAs. The valence band consists of a 1.5 eV wide 'f-d' band at Esub(F) = 0. At - 0.5 eV a structure is observed which has mainly d character. The p valence band is centered at - 2.8 eV and consists of 'p-f' and 'p-s' mixing states. The 4f core levels are highly asymmetric and have a satellite 7.8 eV below the main line. The spectra of UAs are compared to the corresponding spectra of ?-U and polycrystalline As obtained under identical experimental conditions. (orig.)

1980-01-01

8

Luminescence due to radiative transitions between valence band and upper core band in ionic crystals (crossluminescence)  

International Nuclear Information System (INIS)

In some wide band gap halides of heavy alkali and alkaline-earth metals (BaF2, CsCl, RbF etc.) the energy separation between the valence band involving mainly the halogen electronic states and the upper cation core band is smaller than the band gap. Under the excitation generating holes in the core band radiative electronic transitions from the valence band to the core band take place giving rise to a specific kind of intrinsic emission which is proposed to call crossluminescence. Its decay time is about 1 ns and the thermal quenching starts at temperatures well above room temperature. The width of the emission spectrum practically coincides with the width of the valence band deduced from ultraviolet photoelectron spectroscopy and the shape of the spectrum depicts the electronic structure of the valence band. (author)

1987-12-01

9

Valence-band states of ion-bombarded polystyrene  

International Nuclear Information System (INIS)

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

1991-08-01

10

Valence bands offset between depleted semiconductors measured by photoelectron spectroscopy  

International Nuclear Information System (INIS)

A modified method to measure the valence bands offset by photoelectron spectroscopy (PES) between low doped and depleted semiconductors have been used. The surface photovoltage (SPV) and the charging effects modify the PES spectra of depleted semiconductors. The valence bands offset at the heterojunction of depleted ZnSe film and doped GaAs substrate have been measured. These samples were prepared by the laser ablation technique. The shift of PES spectra of ZnSe by about 6 eV has been observed due to the charging and SPV effects. The charging and SPV effects on PES spectra, have been reduced to negligible values in the presence of excess plasma (due to absorption from a secondary white light source) density of the order of 1018 cm-3. The effect of the charging and SPV is very small on the value of the valence bands offset measured in the presence of the excess plasma. This method to measure the valence bands offset is useful for samples prepared in ex situ conditions and with film thickness of the order of 100 nm

2004-05-15

11

Valence bands offset between depleted semiconductors measured by photoelectron spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

A modified method to measure the valence bands offset by photoelectron spectroscopy (PES) between low doped and depleted semiconductors have been used. The surface photovoltage (SPV) and the charging effects modify the PES spectra of depleted semiconductors. The valence bands offset at the heterojunction of depleted ZnSe film and doped GaAs substrate have been measured. These samples were prepared by the laser ablation technique. The shift of PES spectra of ZnSe by about 6 eV has been observed due to the charging and SPV effects. The charging and SPV effects on PES spectra, have been reduced to negligible values in the presence of excess plasma (due to absorption from a secondary white light source) density of the order of 10{sup 18} cm{sup -3}. The effect of the charging and SPV is very small on the value of the valence bands offset measured in the presence of the excess plasma. This method to measure the valence bands offset is useful for samples prepared in ex situ conditions and with film thickness of the order of 100 nm.

Kumar, Shailendra; Jha, S.N.; Jagannath,; Ganguli, Tapas; Bhaskara Rao, S.V.N.; Das, N.C

2004-05-15

12

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

1978-01-01

13

Valence band photoemission studies of clean metals  

Energy Technology Data Exchange (ETDEWEB)

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.

Wehner, P.S.

1978-04-01

14

Measurement of valence band structure in arbitrary dielectric films  

International Nuclear Information System (INIS)

A new way of measuring the band structure of various dielectric materials using the secondary electron emission from Auger neutralization of ions is introduced. The first example of this measurement scheme is the magnesium oxide (MgO) films with respect to the application of the films in the display industries. The density of state in the valence bands of MgO film and MgO film with a functional layer (FL) deposited over a dielectric surface reveals that the density peak of film with a FL is considerably less than that of film, thereby indicating a better performance of MgO film with functional layer in display devices. The second example of the measurement is the boron-zinc oxide (BZO) films with respect to the application of the films to the development of solar cells. The measurement of density of state in BZO film suggests that a high concentration of boron impurity in BZO films may enhance the transition of electrons and holes through the band gap from the valence to the conduction band in zinc oxide crystals; thereby improving the conductivity of the film. Secondary electron emission by the Auger neutralization of ions is highly instrumental for the determination of the density of states in the valence band of dielectric materials.

2012-10-01

15

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

We analyze microscopically the valence and impurity band models of ferromagnetic (Ga,Mn)As. We find that the tight-binding Anderson approach with conventional parameterization and the full potential LDA+U calculations give a very similar picture of states near the Fermi energy which reside in an exchange-split sp-d hybridized valence band with dominant orbital character of the host semiconductor; this microscopic spectral character is consistent with the physical premise of ...

Masek, J.; Maca, F.; Kudrnovsky, J.; Makarovsky, O.; Eaves, L.; Campion, R. P.; Edmonds, K. W.; Rushforth, A. W.; Foxon, C. T.; Gallagher, B. L.; Novak, V.; Sinova, Jairo; Jungwirth, T.

2010-01-01

16

Valence band study of Mg2Si by Auger spectroscopy  

International Nuclear Information System (INIS)

Previous XPS measurements of Mg2Si revealed three valence bands which were all assigned to the Si 3s and 3p states based on a completely ionic model of the bonding in Mg2Si that assumed no occupied Mg 3s or 3p states. Auger spectroscopy is element specific so that the local density of states of Mg and Si can be measured separately. The L1L23V and the L23VV Auger spectra of Mg in Mg2Si were measured from a single crystal of Mg2Si cleaved in UHV. The L23VV spectrum showed the involvement of the Mg 3p state in the upper two valence bands in agreement with recent calculations. More surprisingly the L1L23V spectrum gave evidence of the presence of the Mg 3s state in the lowest energy valence band that had not been predicted. The Auger results gave evidence of covalency in the bonding of Mg2Si

1983-01-01

17

Valence-band of cubic semiconductors: Clifford algebra approach II  

International Nuclear Information System (INIS)

Application of Clifford algebra in the analysis of valence-band spin properties in semiconductors is considered. In the first part (Dargys A 2009 Phys. Scr. 80 065701), for this purpose the isomorphism between multivectors and their matrix representations was used to transform the problem to Clifford algebra. Here equivalence rules are established between the spinors of Hilbert space and basis elements of the five-dimensional Clifford algebra Cl4,1. Then, the rules are applied to the total angular momentum components and the two-band hole Hamiltonian. The resulting biquaternionic Schroedinger equation for hole spin is solved as an example.

2010-07-01

18

Valence-band of cubic semiconductors: Clifford algebra approach II  

Science.gov (United States)

Application of Clifford algebra in the analysis of valence-band spin properties in semiconductors is considered. In the first part (Dargys A 2009 Phys. Scr. 80 065701), for this purpose the isomorphism between multivectors and their matrix representations was used to transform the problem to Clifford algebra. Here equivalence rules are established between the spinors of Hilbert space and basis elements of the five-dimensional Clifford algebra Cl4, 1. Then, the rules are applied to the total angular momentum components and the two-band hole Hamiltonian. The resulting biquaternionic Schrödinger equation for hole spin is solved as an example.

Dargys, A.

2010-07-01

19

Valence-band of cubic semiconductors: Clifford algebra approach II  

Energy Technology Data Exchange (ETDEWEB)

Application of Clifford algebra in the analysis of valence-band spin properties in semiconductors is considered. In the first part (Dargys A 2009 Phys. Scr. 80 065701), for this purpose the isomorphism between multivectors and their matrix representations was used to transform the problem to Clifford algebra. Here equivalence rules are established between the spinors of Hilbert space and basis elements of the five-dimensional Clifford algebra Cl{sub 4,1}. Then, the rules are applied to the total angular momentum components and the two-band hole Hamiltonian. The resulting biquaternionic Schroedinger equation for hole spin is solved as an example.

Dargys, A, E-mail: dargys@pfi.l [Semiconductor Physics Institute, A. Gostauto 11, LT-01108 Vilnius (Lithuania)

2010-07-15

20

Relaxation and cross section effects in valence band photoemission spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

Various problems relating to the interpretation of valence band x-ray photoemission (XPS) spectra of solids are discussed. The experiments and calculations reported herein deal with the following questions: (1) To what extent do many-body effects manifest themselves in an XPS valence band spectrum, and thus invalidate a direct comparison between the photoemission energy distribution, I(E), and the density of states, N(E), calculated on the basis of ground-state one-electron theory. (2) The effect of the binding-energy-dependent photoemission cross section on I(E) at XPS energies. (3) In favorable cases indicated by (1) and (2) we examine the effect of the interaction of the crystal field with the apparent spin-orbit splittings of core levels observed in XPS spectra. (4) The use of tight binding band structure calculations to parameterize the electronic band structure from XPS and other data is described. (5) The use of high energy angle-resolved photoemission on oriented single crystals to gain orbital symmetry information is discussed. (6) The evolution of the shape of the photoemission energy distribution (of polycrystalline Cu) as a function of photon energy from 50 less than or equal h ..omega.. less than or equal 175 is discussed.

McFeely, F.R.

1976-09-01

 
 
 
 
21

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

International Nuclear Information System (INIS)

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

1995-05-15

22

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

Directory of Open Access Journals (Sweden)

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

Sergey A. Burikov

2008-01-01

23

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

2008-01-01

24

Non-trivial surface-band dispersion on Bi(111)  

International Nuclear Information System (INIS)

We performed angle-resolved photoelectron spectroscopy of the Bi(111) surface to demonstrate that this surface supports edge states of non-trivial topology. Along the ?-bar M-bar -direction of the surface Brillouin zone, a surface-state band disperses from the projected bulk valence bands at ?-bar to the conduction bands at M-bar continuously, indicating the non-trivial topological order of three-dimensional Bi bands. We ascribe this finding to the absence of band inversion at the L point of the bulk Bi Brillouin zone. According to our analysis, a modification of tight-binding parameters can account for the non-trivial band structure of Bi without any other significant change in other physical properties. (paper)

2013-03-01

25

Electric fields and valence band offsets at strained [111] heterojunctions  

CERN Document Server

[111] ordered common atom strained layer superlattices (in particular the common anion GaSb/InSb system and the common cation InAs/InSb system) are investigated using the ab initio full potential linearized augmented plane wave (FLAPW) method. We have focused our attention on the potential line-up at the two sides of the homopolar isovalent heterojunctions considered, and in particular on its dependence on the strain conditions and on the strain induced electric fields. We propose a procedure to locate the interface plane where the band alignment could be evaluated; furthermore, we suggest that the polarization charges, due to piezoelectric effects, are approximately confined to a narrow region close to the interface and do not affect the potential discontinuity. We find that the interface contribution to the valence band offset is substantially unaffected by strain conditions, whereas the total band line-up is highly tunable, as a function of the strain conditions. Finally, we compare our results with those ...

Picozzi, S; Freeman, A J

1997-01-01

26

The absolute energy positions of conduction and valence bands of selected semiconducting minerals  

Energy Technology Data Exchange (ETDEWEB)

The absolute energy positions of conduction and valence band edges were compiled for about 50 each semiconducting metal oxide and metal sulfide minerals. The relationships between energy levels at mineral semiconductor-electrolyte interfaces and the activities of these minerals as a catalyst or photocatalyst in aqueous redox reactions are reviewed. The compilation of band edge energies is based on experimental flatband potential data and complementary empirical calculations from electronegativities of constituent elements. Whereas most metal oxide semiconductors have valence band edges 1 to 3 eV below the H{sub 2}O oxidation potential (relative to absolute vacuum scale), energies for conduction band edges are close to, or lower than, the H{sub 2}O reduction potential. These oxide minerals are strong photo-oxidation catalysts in aqueous solutions, but are limited in their reducing power. Non-transition metal sulfides generally have higher conduction and valence band edge energies than metal oxides; therefore, valence band holes in non-transition metal sulfides are less oxidizing, but conduction band electrons are exceedingly reducing. Most transition-metal sulfides, however, are characterized by small band gaps (<1 eV) and band edges situated within or close to the H{sub 2}O stability potentials. Hence, both the oxidizing power of the valence band holes and the reducing power of the conduction band electrons are lower than those of non-transition metal sulfides.

Xu, Y.; Schoonen, M.A.A.

2000-04-01

27

Energy band dispersion in photoemission spectra of argon clusters  

International Nuclear Information System (INIS)

Using photoemission we have investigated free argon clusters from a supersonic nozzle expansion in the photon energy range from threshold up to 28 eV. Measurements were performed both at high resolution with a hemispherical electrostatic energy analyser and at lower resolution with a magnetic bottle device. The latter experiments were performed for various mean cluster sizes. In addition to the ?1.5 eV broad 3p-derived valence band seen in previous work, there is a sharper feature at ?15 eV binding energy. Surprisingly for non-oriented clusters, this peak shifts smoothly in binding energy over the narrow photon energy range 15.5-17.7 eV, indicating energy band dispersion. The onset of this bulk band-like behaviour could be determined from the cluster size dependence.

2011-04-01

28

Energy band dispersion in photoemission spectra of argon clusters  

Energy Technology Data Exchange (ETDEWEB)

Using photoemission we have investigated free argon clusters from a supersonic nozzle expansion in the photon energy range from threshold up to 28 eV. Measurements were performed both at high resolution with a hemispherical electrostatic energy analyser and at lower resolution with a magnetic bottle device. The latter experiments were performed for various mean cluster sizes. In addition to the {approx}1.5 eV broad 3p-derived valence band seen in previous work, there is a sharper feature at {approx}15 eV binding energy. Surprisingly for non-oriented clusters, this peak shifts smoothly in binding energy over the narrow photon energy range 15.5-17.7 eV, indicating energy band dispersion. The onset of this bulk band-like behaviour could be determined from the cluster size dependence.

Foerstel, Marko, E-mail: marko.foerstel@ipp.mpg.de [Max-Planck-Institut fuer Plasmaphysik (IPP), EURATOM Association, Boltzmannstr. 2, 85748 Garching (Germany); Max-Planck-Institut fuer Kernphysik, Saupfercheckweg 1, 69117 Heidelberg (Germany); Mucke, Melanie; Arion, Tiberiu; Lischke, Toralf; Barth, Silko; Ulrich, Volker [Max-Planck-Institut fuer Plasmaphysik (IPP), EURATOM Association, Boltzmannstr. 2, 85748 Garching (Germany); Ohrwall, Gunnar; Bjoerneholm, Olle [Division of Molecular and Condensed Matter Physics, Department of Physics and Astronomy, Uppsala University, Box 516, SE-75120 Uppsala (Sweden); Hergenhahn, Uwe, E-mail: uwe.hergenhahn@ipp.mpg.de [Max-Planck-Institut fuer Plasmaphysik (IPP), EURATOM Association, Boltzmannstr. 2, 85748 Garching (Germany); Bradshaw, Alex M. [Max-Planck-Institut fuer Plasmaphysik (IPP), EURATOM Association, Boltzmannstr. 2, 85748 Garching (Germany); Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin (Germany)

2011-04-15

29

A k · p analytical model for valence band of biaxial strained Ge on (001) Si1?xGex  

International Nuclear Information System (INIS)

In this paper, the dispersion relationship is derived by using the k · p method with the help of the perturbation theory, and we obtain the analytical expression in connection with the deformation potential. The calculation of the valence band of the biaxial strained Ge/(001)Si1?xGex is then performed. The results show that the first valence band edge moves up as Ge fraction x decreases, while the second valence band edge moves down. The band structures in the strained Ge/ (001)Si0.4Ge0.6 exhibit significant changes with x decreasing in the relaxed Ge along the [0, 0, k] and the [k, 0, 0] directions. Furthermore, we employ a pseudo-potential total energy package (CASTEP) approach to calculate the band structure with the Ge fraction ranging from x = 0.6 to 1. Our analytical results of the splitting energy accord with the CASTEP-extracted results. The quantitative results obtained in this work can provide some theoretical references to the understanding of the strained Ge materials and the conduction channel design related to stress and orientation in the strained Ge pMOSFET. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

2012-05-01

30

Electron energy loss studies of the valence band density of states of scandium  

International Nuclear Information System (INIS)

Electron energy loss spectroscopy of the scandium (0001) surface has indicated both core level and valence band excitation loss structure. Comparison to theoretically calculated bulk densities of states for scandium shows good agreement with the experimental results. (author)

1981-02-01

31

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

International Nuclear Information System (INIS)

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

1987-01-01

32

Rare earth 4f hybridization with the GaN valence band  

Science.gov (United States)

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

Wang, Lu; Mei, Wai-Ning; McHale, S. R.; McClory, J. W.; Petrosky, J. C.; Wu, J.; Palai, R.; Losovyj, Y. B.; Dowben, P. A.

2012-11-01

33

The rare earth 4f hybridization with the GaN valence band  

Science.gov (United States)

The placement of the Gd, Er, and Yb 4f states within the GaN valence band has been explored by both experiment and theory. The 4d -- 4f photoemission resonances for various rare earth doped GaN thin films (RE = Gd, Er, Yb) provide an accurate depiction of the occupied 4f state placement within the GaN. The resonant photoemission show that the major Er and Gd rare earth 4f weight is at about 5-6 eV below the valence band maximum, similar to the 4f weights in the valence band of many other rare earth doped semiconductors. For Yb, there is very little resonant enhancement of the valence band of Yb doped GaN, consistent with a largely 4f^14-? occupancy. The placement of the rare earth 4f levels is in qualitative agreement with theoretical expectations.

Wang, Lu; Mei, Wai-Ning; McHale, Steve; McClory, John; Petrosky, James; Wu, J.; Palai, Ratnakar; Losovyj, Yaroslav; Dowben, Peter

2013-03-01

34

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

International Nuclear Information System (INIS)

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

1985-01-01

35

Valence band electronic structure of Pr1-xSrxMnO3 from photoemission studies  

International Nuclear Information System (INIS)

We have studied the charge carrier doping dependent changes in the valence band electronic structure of the Pr1-xSrxMnO3 system across the orbital ordered compositions using ultraviolet photoelectron spectroscopy. The dx2-y2 orbital ordering is found to be causing an enhancement of the Mn 3d-O 2p hybridization strength and thereby the Mn 3d contribution to the subbands in the valence region. Our photoemission studies using different photon energies help in elucidating the nature and composition of the valence band features

2005-05-18

36

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

2006-04-21

37

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

International Nuclear Information System (INIS)

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

1987-06-15

38

Valence band offset of GaN/diamond heterojunction measured by X-ray photoelectron spectroscopy  

International Nuclear Information System (INIS)

XPS was used to measure the energy discontinuity in the GaN/diamond heterostructure. The valence band offset (VBO) was determined to be 0.38 ± 0.15 eV and a type-II heterojunction with a conduction band offset (CBO) of 2.43 ± 0.15 eV was obtained.

2011-07-01

39

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

International Nuclear Information System (INIS)

Photoemission, LEED, and AES measurements were made on the mechanically polished (111) surface of a type IIa diamond. No emission from filled states in the fundamental gap was found over the photon energy range 13.3 eV< or =h?< or =200 eV. This result, coupled with the sharp 1 x 1 LEED patterns which were obtained and the relative cleanliness (of elements which can be detected by AES) of the diamond (< or approx. =1 at.% oxygen, <0.5 at.% Si) suggests hydrogen termination of the lattice. Photoelectric yield measurements demonstrate the photoelectric threshold to be at band gap energy radiation. Investigation of the photoemission electron distribution curves (EDC's) shows that, while the electron affinity at the surface is always positive, band bending is sufficient to result in an effective negative electron affinity under certain conditions. A variable surface dipole on the atomic scale, possibly due to the adsorption--desorption of a background gas, is reported. A study of the relative cross section of the upper (p-like) versus the lower (s-like) portion of the diamond valence band indicates comparable cross sections at a photon energy h?=160 eV

1980-01-01

40

Magnetic field dependent coupling of valence band states in asymmetric double quantum wells  

Energy Technology Data Exchange (ETDEWEB)

We discuss a theoretical model for the Zeeman splitting in dimension reduced structures consisting semimagnetic semiconducting materials. The interplay of the magnetic field in different orientations with the confinement and strain induced symmetry reduction in quantum well structures is discussed. The coupling of valence band states of magnetic and nonmagnetic wells in asymmetric double quantum well structures is studied. (author) 9 refs, 2 figs

Suisky, D.; Neugebauer, F. [Institut fuer Physik, Humboldt-Universitaet zu Berlin, Berlin (Germany); Enders, P. [Max-Born Institut fuer Nichtlineare Optik und Kurzzeitspektroskopie, Berlin (Germany)

1996-12-31

 
 
 
 
41

Rotational bands terminating at maximal spin in the valence space  

Energy Technology Data Exchange (ETDEWEB)

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

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

1996-12-31

42

Optical determinations of energy-band dispersion curves in novel compound semiconductor materials  

Energy Technology Data Exchange (ETDEWEB)

We present magnetoluminescence data which provides a quantitative measure of the energy-band dispersion curves of novel compound semiconductor optoelectronic materials. Data for a n-type strained-layer InGaAs/GaAs (quantum-well width {approximately} 8 nm) and a n-type 4.5-nm-wide GaAs/AlGaAs lattice-matched single-quantum well are presented. We find that the -conduction-bands are almost parabolic, with a mass of about 0.068m{sub 0} for InGaAs/GaAs and 0.085m{sub 0} for the GaAs/AlGaAs structure. The valence-bands are nonparabolic with wave vector dependent in-plane valence-band masses varying from about 0.1 m{sub 0} at zone center to about 0.3 m{sub 0} for 20 meV energies.

Jones, E.D.

1995-02-01

43

Crossover and valence band K? X-rays of chromium oxides  

International Nuclear Information System (INIS)

K? X-ray spectra of chromium metal and selected chromium oxides were measured twice using medium resolution flat crystal spectrometer and high resolution spectrometer employing Johansson geometry after excitation with 2 MeV proton beams. The positions and intensities of crossover (K?'') and valence (K?2,5) band X-rays relative to the primary K? X-ray components were extracted in a consistent way. The results were compared with the existing data obtained by proton and photon induced ionization mechanisms and theoretical predictions. The obtained results in peak relative positions and intensities were analyzed in order to study dependence on the chromium oxidation states and chromium-oxygen bond lengths in selected chromium oxides. Our results obtained by both spectrometers confirm that the linear trend observed for the valence peak relative energy shift as a function of chromium oxidation number does not depend on the experimental resolution. Experimental results for normalized intensities (i.e. relative intensities divided with the number of chromium-oxygen pairs) of crossover and valence band X-rays obtained by both spectrometers are in very good agreement, and follow exponential relationship with the average Cr-O bond lengths in corresponding chromium oxides. The observed trends in crossover and valence X-rays normalized intensities could be used to measure the average chromium-oxygen bond length in various chromium oxides, with the sum of both crossover and valence X-ray normalized intensities being the most sensitive measure.

2011-06-01

44

Hole Transport in Impurity Band and Valence Bands Studied in Moderately Doped GaAs:Mn Single Crystals  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We report on simple experiment on temperature-dependent Hall effect measurements in GaMnAs single crystalline samples with Mn composition estimated at 0.05-0.3 at.% which is slightly below the onset of ferromagnetism. Impurity band transport is visible for Mn compositions of ~0.3 at.% as a clear metallic behaviour. The results show interesting situation that the Metal-Insulator transition in GaAs:Mn occurs within the impurity band which is separated from the valence bands fo...

Slupinski, T.; Caban, J.; Moskalik, K.

2007-01-01

45

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

Energy Technology Data Exchange (ETDEWEB)

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 GeS{sub 2}, Na{sub 2}GeS{sub 3} and SiS{sub 2} 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 (Na{sub 2}S) 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.

Foix, D. [Laboratoire de Chimie Theorique et Physicochimie Moleculaire, CNRS UMR 5624, LPCM/Helioparc PAU Pyrenees, 2 Avenue du President Angot, 64053 PAU Cedex 9 (France); Martinez, H. [Laboratoire de Chimie Theorique et Physicochimie Moleculaire, CNRS UMR 5624, LPCM/Helioparc PAU Pyrenees, 2 Avenue du President Angot, 64053 PAU Cedex 9 (France)], E-mail: herve.martinez@univ-pau.fr; Pradel, A. [Laboratoire de Physicochimie de la Matiere Condensee, UMR 5617, CC 3 Universite Montpellier II, 34095 Montpellier Cedex 5 (France); Ribes, M. [Laboratoire de Physicochimie de la Matiere Condensee, UMR 5617, CC 3 Universite Montpellier II, 34095 Montpellier Cedex 5 (France); Gonbeau, D. [Laboratoire de Chimie Theorique et Physicochimie Moleculaire, CNRS UMR 5624, LPCM/Helioparc PAU Pyrenees, 2 Avenue du President Angot, 64053 PAU Cedex 9 (France)], E-mail: danielle.gonbeau@univ-pau.fr

2006-04-21

46

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

International Nuclear Information System (INIS)

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

1996-06-06

47

Measurement of valence band structure in boron-zinc-oxide films by making use of ion beams  

International Nuclear Information System (INIS)

Measurement of valence band structure in the boron-zinc oxide (BZO) films was developed using the secondary electron emission due to the Auger neutralization of ions. The energy distribution profile of the electrons emitted from boron-zinc-oxide films was measured and rescaled so that Auger self-convolution arose; thus, revealing the detailed structure of the valence band and suggesting that a high concentration of boron impurity in BZO films may enhance the transition of electrons and holes through the band gap from the valence to the conduction band in zinc oxide crystals; thereby improving the conductivity of the film.

2011-12-26

48

Electronic structure of alkane chains. Complete one-dimensional band structures of the valence states  

Science.gov (United States)

Several ultrathin films of oriented alkane chains were studied by ultraviolet photoelectron spectroscopy using UV photons in the energy range of 20-200 eV. From the experimental data the full valence band structure has been determined for self-assembled films of long-chain n-alkanethiols, Langmuir-Blodgett films of Cd-arachidate and thin films of hexatriacontane. Significant deviations from band structures obtained by ab initio calculations of Karpfen are found at the boundary of the one-dimensional Brillouin zone. Furthermore it is demonstrated that a mapping of the one-dimensional band structure can be used for precisely determining tilt angles of alkane chains.

Zubrägel, Ch.; Schneider, F.; Neumann, M.; Hähner, G.; Wöll, Ch.; Grunze, M.

1994-03-01

49

Influence of ionization energy change on valence band offset in organic p-n junction  

Science.gov (United States)

Valence band offsets at [6,6]-phenyl-C61-butyric acid methyl ester (PCBM)/metallophthalocyanine (MPc, M=Cu and Zn) interfaces have been investigated with ultraviolet photoelectron spectroscopy, which are organic p-n junctions in organic photovoltaics. The highest occupied molecular orbitals of MPcs rise toward the interface, while that of PCBM lowers. This behavior implies that the different energy band offsets from inorganic p-n junction are realized in organic p-n junction. The depletion layers were not observed at the interfaces. Such anomalous energy band offsets are attributed to the interfacial dipole and also ionization energy changes of MPcs and PCBM at the interface.

Akaike, Kouki; Kanai, Kaname; Ouchi, Yukio; Seki, Kazuhiko

2009-09-01

50

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

International Nuclear Information System (INIS)

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

2011-10-01

51

Valence band and core level X-ray photoelectron spectroscopy of lead sulfide nanoparticle polymer composites  

Science.gov (United States)

Valence band and core level X-ray photoelectron spectroscopy (XPS) were used to probe lead sulfide (PbS) nanoparticle -polymer nanocomposites. Composite materials were prepared by trapping commercially available monodisperse 3 and 10 nm PbS nanoparticles in two polymers, the non-conducting polymer, polystyrene, and the conjugated polymer, poly(2-methoxy-5-(2'-ethyl-hexyloxy)- p-phenylene vinylene (referred to below as MEH-PPV). The nanocomposites prepared from commercial nanoparticles underwent oxidation, mainly to form lead sulfate. However, the narrow size distributions of the commercial nanoparticles allowed observation of distinct changes in the valence band from the 3 to 10 nm nanoparticles. Nanocomposites of 2-5 and 4-7 nm PbS nanoparticles were synthesized by growing the particles in poly(vinyl alcohol) (referred to below as PVA) and MEH-PPV, respectively. These composites both indicated the formation of lead sulfide nanoparticles. Furthermore, the XP spectra for the PVA/PbS composite displayed bonding between the PbS nanoparticles and the polymer while MEH-PPV showed no PbS -polymer bonding. The nanoparticles synthesized in MEH-PPV did not undergo oxidation. The particle size distributions of the synthesized nanoparticles were too broad to display size-dependent changes in the valence band.

Asunskis, Daniel J.; Hanley, Luke

2007-10-01

52

Crossover and valence band K{beta} X-rays of chromium oxides  

Energy Technology Data Exchange (ETDEWEB)

K{beta} X-ray spectra of chromium metal and selected chromium oxides were measured twice using medium resolution flat crystal spectrometer and high resolution spectrometer employing Johansson geometry after excitation with 2 MeV proton beams. The positions and intensities of crossover (K{beta}'') and valence (K{beta}{sub 2,5}) band X-rays relative to the primary K{beta} X-ray components were extracted in a consistent way. The results were compared with the existing data obtained by proton and photon induced ionization mechanisms and theoretical predictions. The obtained results in peak relative positions and intensities were analyzed in order to study dependence on the chromium oxidation states and chromium-oxygen bond lengths in selected chromium oxides. Our results obtained by both spectrometers confirm that the linear trend observed for the valence peak relative energy shift as a function of chromium oxidation number does not depend on the experimental resolution. Experimental results for normalized intensities (i.e. relative intensities divided with the number of chromium-oxygen pairs) of crossover and valence band X-rays obtained by both spectrometers are in very good agreement, and follow exponential relationship with the average Cr-O bond lengths in corresponding chromium oxides. The observed trends in crossover and valence X-rays normalized intensities could be used to measure the average chromium-oxygen bond length in various chromium oxides, with the sum of both crossover and valence X-ray normalized intensities being the most sensitive measure.

Fazinic, Stjepko, E-mail: sfazinic@irb.hr [Rudjer Boskovic Institute, Bijenicka cesta 54, HR-10000 Zagreb (Croatia); Mandic, Luka [Physics Department, University of Rijeka, Omladinska 14, HR-51000 Rijeka (Croatia); Kavcic, Matjaz [Jozef Stefan Institute, Jamova 39, SI-1000 Ljubljana (Slovenia); Bozicevic, Iva [Rudjer Boskovic Institute, Bijenicka cesta 54, HR-10000 Zagreb (Croatia)

2011-06-15

53

The valence band of some light rare-earth metals studied by photoemission spectroscopy  

International Nuclear Information System (INIS)

The valence bands of La, Ce, Pr, and Nd have been studied by ultraviolet photoelectron spectroscopy (UPS) (He II, h? = 40.8 eV) and compared to results from X-ray photoelectron spectroscopy (XPS) (Mg K?sub(1,2)). The energy positions of the 4f levels are in good agreement with earlier XPS results and calculations based on estimates from optical and thermodynamic data. The widths of the sd bands and the 4f levels and the relative emission intensities are discussed. (author)

1981-01-01

54

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 Bi_2_-_xSb_xTe_3 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 Bi_2_-_xSe_xTe_3 valence band. The effective mass of the state density in the second subband is estimated

1987-01-01

55

Substituent-Induced Intermolecular Interaction in Organic Crystals Revealed by Precise Band-Dispersion Measurements  

Science.gov (United States)

We reveal quite small but different intermolecular valence band dispersions of sub-100-meV scale in crystalline films of Zn and Mn phthalocyanine (ZnPc and MnPc) and fluorinated ZnPc (F16ZnPc). The intermolecular transfer integrals are found to be reasonably dependent on the intermolecular distance with the 75±5meV/Å relation. Furthermore, the angle-resolved photoemission spectra show anomalous dispersive behaviors such as phase flips and local-dimerization-derived periodicities, which originate from the site-specific intermolecular interaction induced by substituents.

Yamane, Hiroyuki; Kosugi, Nobuhiro

2013-08-01

56

Measurement of GaN/Ge(001) Heterojunction Valence Band Offset by X-Ray Photoelectron Spectroscopy  

International Nuclear Information System (INIS)

X-ray photoelectron spectroscopy has been used to measure the valence band offset (VBO) at the GaN/Ge heterostructure interface. The VBO is directly determined to be 1.13 ± 0.19 eV, according to the relationship between the conduction band offset ?EC and the valence band offset ?EV: ?EC = E9Gan – E9Ge – ?EV, and taking the room-temperature band-gaps as 3.4 and 0.67 eV for GaN and Ge, respectively. The conduction band offset is deduced to be 1.6 ± 0.19 eV, which indicates a type-I band alignment for GaN/Ge. Accurate determination of the valence and conduction band offsets is important for the use of GaN/Ge based devices. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

2010-06-01

57

Optical signatures of valence-band mixing in positive trion recombination spectra of double quantum dots  

Science.gov (United States)

We consider optical signatures of valence band mixing in positive trion and exciton complexes in vertically stacked InGaAs quantum dots. We use the configuration interaction method and an axially symmetric four-band Luttinger-Kohn Hamiltonian (KL) that allows for heavy-hole and light-hole band mixing due to spin-orbit interaction. A scalar effective hole mass model is also included for comparison. We found essential differences (i.e., different recombination patterns) between the KL and separated-bands model spectra. In the weak-coupling regime for KL model, we obtained a good agreement with experimentally observed X patterns in contrast to the scalar effective mass model.

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

2014-06-01

58

Valence band offset of wurtzite InN/SrTiO3 heterojunction measured by x-ray photoelectron spectroscopy  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract The valence band offset (VBO of wurtzite indium nitride/strontium titanate (InN/SrTiO3 heterojunction has been directly measured by x-ray photoelectron spectroscopy. The VBO is determined to be 1.26 ± 0.23 eV and the conduction band offset is deduced to be 1.30 ± 0.23 eV, indicating the heterojunction has a type-I band alignment. The accurate determination of the valence and conduction band offsets paves a way to the applications of integrating InN with the functional oxide SrTiO3.

Li Zhiwei

2011-01-01

59

Valence band offset of InN/BaTiO3 heterojunction measured by X-ray photoelectron spectroscopy  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract X-ray photoelectron spectroscopy has been used to measure the valence band offset of the InN/BaTiO3 heterojunction. It is found that a type-I band alignment forms at the interface. The valence band offset (VBO and conduction band offset (CBO are determined to be 2.25 ± 0.09 and 0.15 ± 0.09 eV, respectively. The experimental VBO data is well consistent with the value that comes from transitivity rule. The accurate determination of VBO and CBO is important for use of semiconductor/ferrroelectric heterojunction multifunctional devices.

Zhang Weifeng

2011-01-01

60

Wavefunctions in the valence band of InAs quantum dots  

Energy Technology Data Exchange (ETDEWEB)

Magneto-capacitance spectroscopy of InAs self-assembled quantum dots allows the momentum space wavefunctions mapping of conduction and valence band states. To do this, a magnetic field is varied (strength and direction) in the base plane of the quantum dots. The perpendicular magnetic field would also influence the wavefunctions, therefore capacitance-voltage spectroscopy in a tilted field should reveal this effect. We present the result of such experiments performed on self-assembled InAs/GaAs quantum dots embedded in a Schottky diode with a carbon doped p-type back contact. The results cannot be explained by a simple model and possible consequences are discussed.

Roescu, Razvan; Reuter, Dirk; Wieck, Andreas D. [Lehrstuhl fuer Angewandte Festkoerperphysik, Ruhr-Universitaet Bochum (Germany); Zeitler, Ulrich; Maan, Jan C. [High Field Magnet Laboratory, Radboud University Nijmegen (Netherlands)

2009-07-01

 
 
 
 
61

Wavefunctions in the valence band of InAs quantum dots  

International Nuclear Information System (INIS)

Magneto-capacitance spectroscopy of InAs self-assembled quantum dots allows the momentum space wavefunctions mapping of conduction and valence band states. To do this, a magnetic field is varied (strength and direction) in the base plane of the quantum dots. The perpendicular magnetic field would also influence the wavefunctions, therefore capacitance-voltage spectroscopy in a tilted field should reveal this effect. We present the result of such experiments performed on self-assembled InAs/GaAs quantum dots embedded in a Schottky diode with a carbon doped p-type back contact. The results cannot be explained by a simple model and possible consequences are discussed.

2009-03-22

62

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

The Bethe surface of a material is an essential element in the study of inelastic scattering at low impact energies where the optical approximation fails. In this work we examine various semi-empirical models for the dielectric response function of condensed water towards an improved description of the energy-loss function over the whole energy–momentum plane (i.e. Bethe surface). The experimental “optical” data (i.e. at zero momentum transfer) for the valence bands of liquid and solid ...

Emfietzoglou, Dimitris; Abril Sa?nchez, Isabel; Garci?a Molina, Rafael; Petsalakis, I. D.; Nikjoo, Hooshang; Kyriakou, Ioanna; Pathak, A.

2007-01-01

63

Valence band satellites in the 4f-photoemission spectra of Eu- and Yb-metal  

International Nuclear Information System (INIS)

Photoemission spectra of the valence bands of Eu and Yb metal, taken at VUV (20 eV <= h#betta# <= 100 eV) and X-ray energies (AlKsub(?) and MgKsub(?) exhibit characteristic satellite structures at higher binding energies. In contrast to a previous suggestion these structures could not be identified as two-hole final states in the 4f shells. The experimental observations strongly support an interpretation of these satellites in terms of collective conduction electron excitations, i.e. bulk and surface plasmon losses. (Auth.)

1982-01-01

64

Electronic structure and valence-band spectra of FeBO3  

Science.gov (United States)

Based on ab initio electronic-structure calculations by the linear muffin-tin orbital method and the combined analysis of x-ray photoelectron and x-ray B K?, O K?, and Fe L? emission spectra in a common energy scale, the aspects of hybridization within the valence band of FeBO3 are discussed in detail. X-ray photoelectron spectra of B2O3 and H3BO3 have also been obtained and are discussed in comparison with that of FeBO3.

Postnikov, A. V.; Bartkowski, St.; Neumann, M.; Rupp, R. A.; Kurmaev, E. Z.; Shamin, S. N.; Fedorenko, V. V.

1994-11-01

65

Partial cross sections and density of states effects in the valence band photoemission from solid nitrogen  

International Nuclear Information System (INIS)

Photoelectron energy distribution curves from solid nitrogen have been measured for excitation energies ranging from threshold (14.2 eV) to 40 eV using Synchrotron Radiation. The partial cross sections for the emission from the 3sigmasub(g), 1?sub(u) and 2sigmasub(u) derived valence bands show pronounced maxima 3.4 eV, 2.9 eV and 3.0 eV above the vacuum level respectively which we interpret as being due to a high density of conduction band final states. These states are closely related to the ?sub(g)* negative-ion shape resonance for molecular nitrogen. (orig.)

1982-01-01

66

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

Energy Technology Data Exchange (ETDEWEB)

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.

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

67

Study of the 4f and valence band density of states in rare-earth metals  

International Nuclear Information System (INIS)

The 4f and valence states of all metallic rare earths have been studied using x-ray photoelectron spectroscopy (XPS) for the occupied part and bremsstrahlung isochromat spectroscopy (BIS) for the unoccupied part. It is found that the bandwidth increases from Gd to Lu, and that the valence band spectra are in fair agreement with APW calculations. The intensities of the 4f final-state multiplets are well described in terms of the coefficients of fractional parentage. There is a symmetry between the fsup(n) XPS and fsup(14-n) BIS spectra. The observed energies of the 4f excitations correspond to transitions to completely screened final states. These values enable one to predict the elements which are liable to interconfiguration fluctuation when their 4f levels are shifted to Esub(F) by the chemical environment or by compression. The large Coulomb correlation energies, U which prevent the formation of 4f bands in these elements, are directly obtained from the spectra observed and are found to be in good agreement with recent calculations. The linewidths and singularity indices of the XPS and BIS 4f lines are determined and discussed. (author)

1981-01-01

68

Valence-band splitting and shear deformation potential of dilute GaAs1-xNx alloys  

International Nuclear Information System (INIS)

The valence-band splitting in thin GaAs1-xNx (0.011?x?0.033) epilayers strained coherently by the GaAs substrate is observed in electroreflectance. This study reveals that the valence-band deformation potential does not follow the linear interpolation of those for GaAs and GaN, but shows a rather strong composition dependence with a surprising bowing in a small composition region of the alloy. These results contradict the currently held view that the conduction band is greatly altered but that the valence band is only weakly perturbed by dilute nitrogen doping of GaAs. (c) 2000 The American Physical Society

2000-02-15

69

Studies of Valence Band Alignment Between Nitrided GaPN/GaP (111) Interface Using X-ray Photoelectron Spectroscopy  

Science.gov (United States)

The analysis of core levels positions of Ga3d, N1s and P2p at different etching depth from the plasma nitrided GaP (111) surface shows that the nitrogen ions interact with both Gallium and Phosphorous ions with nearly equal probability. The analysis of valance band spectra shows the type-II band alignment between GaPN0.22/GaP and the valence band offset is ~2.2+/-0.1 eV.

Khamari, Shailesh K.; Dixit, V. K.; Sinha, A. K.; Banik, S.; Barman, S. R.; Oak, S. M.

2011-07-01

70

Effects of second valence band and resonant states on transport in undoped Pbsub(1-x)Snsub(x)Te  

International Nuclear Information System (INIS)

The temperature dependence of the Hall coefficient of n- and p-type Pbsub(1-x)Snsub(x)Te samples (x = 0.2) is analysed taking into account the temperature dependent effective masses and nonparabolicity. It is shown that the energetic separation between the edges of conduction and second valence band, respectively, is ?2 = 0.34 eV as in PbTe. From the analysis of p-type samples the existence of resonant states, which are degenerated with the upper valence band, is deduced. The concentration of these states is of the same order as the hole concentration. (author)

1980-10-16

71

Valence band offset of ?-Ga2O3/wurtzite GaN heterostructure measured by X-ray photoelectron spectroscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A sample of the ?-Ga2O3/wurtzite GaN heterostructure has been grown by dry thermal oxidation of GaN on a sapphire substrate. X-ray diffraction measurements show that the ?-Ga2O3 layer was formed epitaxially on GaN. The valence band offset of the ?-Ga2O3/wurtzite GaN heterostructure is measured by X-ray photoelectron spectroscopy. It is demonstrated that the valence band of the ?-Ga2O3/GaN structure is 1.40?±?0.08 eV.

2012-01-01

72

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

International Nuclear Information System (INIS)

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

1990-05-15

73

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

Energy Technology Data Exchange (ETDEWEB)

Codeposition of Ag and Pd on the Ru(0 0 0 1) surface has been studied by photoelectron spectroscopy (PES) by recording of valence band (VB) and 3d{sub 5/2} core electron energy distribution curves (EDCs). Two- and three-dimensional total film coverages in the temperature range 300-765 K have been characterized. At submonolayer total coverage, a flat, monolayer (ML) thick film with some degree of mixing is formed. A stable surface alloy, with Ag-Pd hybridization states {approx}2.5 eV binding energy (BE), is found when Pd is deposited after Ag. A 1 nm thick Ag{sub 52}Pd{sub 48} film formed by deposition of Pd on a Ag-precovered surface at room temperature exhibits a substantial interdiffusion of Pd and Ag. A stable concentration profile is reached between 550 and 660 K.

Bech, L. [Department of Physics and Nanotechnology, Aalborg University, DK-9220 Aalborg East (Denmark); Li, Z. [Institute of Storage Ring Facilities, University of Aarhus, DK-8000 Aarhus C (Denmark); Onsgaard, J. [Department of Physics and Nanotechnology, Aalborg University, DK-9220 Aalborg East (Denmark)], E-mail: jenson@physics.aau.dk

2007-05-15

74

Revisiting the Valence-Band and Core-Level Photoemission Spectra of NiO  

Science.gov (United States)

We have reexamined the valence-band (VB) and core-level electronic structure of NiO by means of hard and soft x-ray photoemission spectroscopies. The spectral weight of the lowest energy state was found to be enhanced in the bulk sensitive Ni 2p core-level spectrum. A configuration-interaction model including a bound state screening has shown agreement with the core-level spectrum and off- and on-resonance VB spectra. These results identify the lowest energy states in the core-level and VB spectra as the Zhang-Rice (ZR) doublet bound states, consistent with the spin-fermion model and recent ab initio calculations within dynamical mean-field theory. The results indicate that the ZR character first ionization (the lowest hole-addition) states are responsible for transport properties in NiO and doped NiO.

Taguchi, M.; Matsunami, M.; Ishida, Y.; Eguchi, R.; Chainani, A.; Takata, Y.; Yabashi, M.; Tamasaku, K.; Nishino, Y.; Ishikawa, T.; Senba, Y.; Ohashi, H.; Shin, S.

2008-05-01

75

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

International Nuclear Information System (INIS)

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

2008-09-30

76

Comparison of site-specific valence band densities of states determined from Auger spectra and XPS-determined valence band spectra in GeS (001) and GeSe (001)  

International Nuclear Information System (INIS)

Auger lineshapes of the Ge M_1M_4sub(,)_5V and M_3M_4sub(,)_5V and Se M_1M_4sub(,)_5V transitions in GeS (001) and GeSe (001) are measured and compared to XPS valence band spectra. Distortions in both types of spectra due to inelastic scattering, analyzer and source broadening, and core level lifetime broadening are removed by deconvolution techniques. The valence band consists of three main peaks at - 2eV, - 8eV, and - 13eV. There is excellent agreement of peak positions in AES and XPS spectra. The Auger lineshapes can be interpreted in terms of site-specific densities of states. They indicate that the states at approx. - 8 eV and at approx. - 13 eV are associated with the cation and anion sites respectively. The bonding p-like states at the top of the valence band have both cation and anion character. The Auger lineshapes indicate that the states closest to the valence band maximum are preferentially associated with Ge. (orig.)

1980-01-01

77

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

International Nuclear Information System (INIS)

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

2010-09-15

78

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

1987-01-01

79

Ab-initio calculation of the valence-band offset at strained GaAs/InAs (001) heterojunction.  

Science.gov (United States)

We present a self consistent pseudopotential calculation of the valence band offset (VBO) at GaAs/InAs (001) strained heterojunction, which is chosen as an example of the isovalent polar with common-anion lattice mismatched heterojunctions. The effects of...

N. Tit M. Peressi S. Baroni

1993-01-01

80

Experimental determination of valence band offset at PbTe/Ge(1 0 0) interface by synchrotron radiation photoelectron spectroscopy  

International Nuclear Information System (INIS)

The band offset at the interface of PbTe/Ge (1 0 0) heterojunction was studied by the synchrotron radiation photoelectron spectroscopy. A valence band offset of ?EV = 0.07 ± 0.05 eV, and a conduction band offset of ?EC = 0.27 ± 0.05 eV are concluded. The experimental determination of the band offset for the PbTe/Ge interface should be beneficial for the heterojunction to be applied in new optoelectronic and electronic devices.

2010-08-01

 
 
 
 
81

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

Science.gov (United States)

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.

King, Sean W.; French, Marc; Xu, Guanghai; French, Benjamin; Jaehnig, Milt; Bielefeld, Jeff; Brockman, Justin; Kuhn, Markus

2013-11-01

82

Valence-band electron-tunneling measurement of the gate work function: Application to the high-?/polycrystalline-silicon interface  

Science.gov (United States)

A technique is demonstrated to measure the band alignment between the silicon substrate and the gate electrode using the valence-band electron tunneling (VBET). When an n-channel metal-oxide-semiconductor field-effect transistor is biased in inversion the valence-band electron from the Si substrate can tunnel into the gate [A. Shanware, J. Shiely, H. Massoud, E. Vogel, K. Henson, A. Srivastava, C. Osburn, J. Hauser, and J. Wortman, Tech. Dig.-Int. Electron Devices Meet.1999, 815], depending on the overlapping of the density of states in the Si valence band and the gate. This technique is suitable to measure the band alignment between the silicon substrate and the gate electrode with any given gate dielectric, provided that both the gate and substrate leakages are dominated by direct tunneling. This technique has been applied to study the SiO2/polycrystalline-silicon (poly-Si) interface behavior in the presence of submonolayer traces of HfO2. The general applicability of VBET to arbitrary gate stacks is finally demonstrated with the HfSiON/poly-Si case.

Pantisano, Luigi; Afanas'ev, Valeri; Pourtois, Geoffrey; Chen, P. J.

2005-09-01

83

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

International Nuclear Information System (INIS)

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

1981-07-15

84

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2007-01-01

85

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

Science.gov (United States)

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

Popescu, F.; ?en, C.; Dagotto, E.; Moreo, A.

2007-08-01

86

Scanning tunneling microscopy on unpinned GaN(11¯00) surfaces: Invisibility of valence-band states  

Science.gov (United States)

We investigated the origins of the tunnel current in scanning tunneling microscopy (STM) and spectroscopy experiments on GaN(11¯00) surfaces. By calculating the tunnel currents in the presence of a tip-induced band bending for unpinned n -type GaN(11¯00) surfaces, we demonstrate that only conduction-band states are observed at positive and negative voltage polarities independent of the doping concentration. Valence-band states remain undetectable because tunneling out of the electron-accumulation zone in conduction-band states dominates by four orders of magnitude. As a result band-gap sizes cannot be determined by STM on unpinned GaN(11¯00) surfaces. Appropriate band-edge positions and gap sizes can be determined on pinned surfaces.

Ebert, Ph.; Ivanova, L.; Eisele, H.

2009-08-01

87

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

Directory of Open Access Journals (Sweden)

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

?ukari? Nemanja A.

2010-01-01

88

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

CERN Document Server

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

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

2003-01-01

89

Correlation of conductivity and angle integrated valence band photoemission characteristics in single crystal iron perovskites for 300 K  

International Nuclear Information System (INIS)

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

2010-07-01

90

Polarization-dependent ARPES measurement for valence band of anatase TiO2  

Science.gov (United States)

Angle-resolved photoelectron spectroscopy utilizing linearly polarized synchrotron radiation was conducted to examine the electronic structure of an anatase TiO2(001) thin film fabricated on LaAlO3(100) by pulsed laser deposition. Polarization-dependent measurements by changing the incidence angle of the light were performed to identify the orbital symmetry. Energy-momentum dispersion curves along the [001] direction are mapped and resolved into four components: O 2p-derived P? non-bonding, O 2p-Ti 3d ? bonding, and two ? bonding states. The intensities of the ? bonding states are obviously different between both polarizations while the intensities of the peaks due to P? and ? are almost equivalent. Two different ? states with polarization dependence were attributed to Ti t1u? orbital. The result implies that the distortion of TiO6 octahedra resolves degeneracy of T1u bands and/or breaking T2g symmetry.

Emori, Masato; Sakino, Akiko; Ozawa, Kenichi; Sakama, Hiroshi

2014-06-01

91

Intra-valence-band mixing in strain-compensated SiGe quantum wells  

CERN Document Server

We explore the midinfrared absorption of strain-compensated p-Si0.2Ge0.8/Si quantum wells for various well thicknesses and temperatures. Owing to the large band offset due to the large bi-axial strain contrast between the wells and barriers, the intersubband transitions energies from the ground state to the excited heavy hole (hh), light hole (lh) and split-off hole (so) states are resolved to ~0.5 eV. When hh2 is within ~30 meV of lh1 or so1 a partial transfer of the hh1-hh2 oscillator strength to the hh1-lh1 or hh1-so1 transitions is observed, which is otherwise forbidden for light polarized perpendicular to the plane of the wells. This is a clear sign of mixing between the hh and lh or so-states. A large temperature induced broadening of hh2 peak is observed for narrow wells indicating a non-parabolic dispersion of the hh2 states due to the mixing with the lh/so continuum. We found that the 6-band k.p theory gives a quantitative account of the observations. A possible role of many-body effects in the tempe...

Tsujino, S; Falub, C; Fromherz, T; Diehl, L; Sigg, H; Grützmacher, D

2005-01-01

92

Inhomogeneous effect of particle size on core-level and valence-band electrons: Size-dependent electronic structure of Cu3N nanoparticles  

Science.gov (United States)

The present study reports a clear evidence and physical significance of an inhomogeneous effect of particle size on electrons originating from various electronic levels of copper nitride nanoparticles. X-ray photoelectron and optical absorption spectroscopy studies reveal that a direct modification of the valence band due to size effects explained by the more appropriate surface bond contraction model results in a strong increase in the binding energy of valence-band electrons as compared to core-level electrons.

Balamurugan, B.; Maruyama, Toshiro

2006-07-01

93

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

Science.gov (United States)

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

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

2014-01-01

94

Relation between the topology of the elementary energy bands in the valence band of the Hg{sub 3}TeCl{sub 4} crystal and its anisotropy  

Energy Technology Data Exchange (ETDEWEB)

A mechanism of the Davydov-like splitting formation in the Brillouin zone of the Hg{sub 3}TeCl{sub 4} crystal (Pbca, D{sub 2h}{sup 15}) with two double translationally nonequivalent layers in the unit cell was analyzed. The topology of the 8-branch elementary energy bands creating the valence band of Hg{sub 3}TeCl{sub 4} was explained. Energetic distances between states of the elementary energy bands at the Brillouin zone edges were estimated by means of the localized function method. The topology of the elementary energy bands was related with the ratio of the interaction strength between the double layers in the unit cell and the interaction strength between single layers creating the double layer. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Sznajder, M. [Institute of Physics, University of Rzeszow (Poland)

2009-01-15

95

Relation between the topology of the elementary energy bands in the valence band of the Hg3TeCl4 crystal and its anisotropy  

International Nuclear Information System (INIS)

A mechanism of the Davydov-like splitting formation in the Brillouin zone of the Hg3TeCl4 crystal (Pbca, D2h15) with two double translationally nonequivalent layers in the unit cell was analyzed. The topology of the 8-branch elementary energy bands creating the valence band of Hg3TeCl4 was explained. Energetic distances between states of the elementary energy bands at the Brillouin zone edges were estimated by means of the localized function method. The topology of the elementary energy bands was related with the ratio of the interaction strength between the double layers in the unit cell and the interaction strength between single layers creating the double layer. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

2009-01-01

96

Evidence in the XPS valence band of the fold structure at the surface of polyethylene lamellae  

Science.gov (United States)

For the purpose of identifying surface conformations, the valence XPS spectra of mats of polyethylene single crystals as prepared from the solution and after annealing are reported and compared with the spectrum of a pressed pellet of hexatriacontane. The relative intensity of the two "C?C peaks" in the inner-valence region exhibit significant variations that are related to the chain folds occuring at the surface of the lamellae, on the one hand, and to planar zig-zag segments for the annealed and pellet samples, on the other hand.

Delhalle, J.; Riga, J.; Denis, J. P.; Deleuze, M.; Dosière, M.

1993-07-01

97

Features of valence band structure of Laves phase hydrides with advanced hydrogen storage ability  

International Nuclear Information System (INIS)

Changes in the electronic structure of intermetallic compounds (IMC) ZrVCu, ZrVFe, ZrVCo, ZrVCr as a result of their hydridation are studied. It is shown, that in all the IMC studied the hydride formation results in an increase in a relative number of Zr valence d-electrons. A correlation between the thermal stability of a hydride and the relative charge of Zr valence d-electrons is observed: the greater its change as a result of hydride formation, the more stable the hydride. Characteristics of emission Lsub(?)-spectra of zirconium in metallic Zr, IMC and their hydrides are presented

1985-01-01

98

Electronic density of states and the x-ray photoelectron spectra of the valence band of Cu-Pd alloys  

International Nuclear Information System (INIS)

We present self-consistent-field Korringa-Kohn-Rostoker coherent-potential-approximation calculations of the electronic density of states of random Cu/sub c/Pd/sub 1-c/ alloys. We find strong hybridization of the palladium d bands with the copper d bands over the entire concentration range. We do not obtain a palladium virtual bound state for the copper-rich alloys and therefore contradict the interpretation generally placed on valence-band x-ray photoelectron spectroscopy (XPS) spectra for Cu-Pd. Nevertheless, our first-principles calculations of the XPS spectra are in excellent agreement with recent measurements, and we discuss why this is so. Furthermore, we compare our density of states at the Fermi energy with specific-heat measurements

1986-02-15

99

Bulk electronic structure studied by hard X-ray photoelectron spectroscopy of the valence band: The case of intermetallic compounds  

Energy Technology Data Exchange (ETDEWEB)

Highlights: •Bulk sensitivity of HAXPES was used to explore the electronic structure of several Heusler compounds in form of bulk materials and thin films. •Strong changes of the electronic structure Heusler shape memory Mn{sub 2}NiGa appear at the phase transition. •HAXPES of C1{sub b} Heusler compounds with narrow band gap showed the existence of in gap states close to the Fermi energy. •Linear dichroism in hard X-ray photoelectron spectroscopy (LDAD-HAXPES) was used to study the angular asymmetry in photoemission from the valence states of three kinds of Heusler compounds. -- Abstract: Photoelectron spectroscopy (PES) has evolved into the most relevant, powerful, and nondestructive method for investigating atoms, molecules, and solids. In particular, hard X-ray photoelectron spectroscopy (HAXPES) has emerged as a powerful tool for investigating the bulk electronic structure of materials in a variety of applied fields such as chemistry, physics, and materials science. In addition, PES was used for investigating the symmetries of various materials’ electronic structures. However, thus far, such studies have been restricted to atoms, molecules, adsorbates, and surfaces because low-energy (<1 keV) electrons have limited probing depths. This is disadvantageous because three-dimensional (3D) bulk states cannot be studied. The present work demonstrates that this drawback can be eliminated by using hard X-rays with variable polarization for excitation. In the current study, this issue was investigated using several Heusler compounds, which have been attracting increasing levels of interest. There are more than 2000 Heusler compounds in total. Owing to their tunable electronic structures, Heusler compounds exhibit multifarious properties useful for spintronic, optoelectronic, shape memory, and thermoelectric applications. Herein, we report the results of bulk-sensitive, high energy photoelectron spectroscopy of the valence bands of several Heusler compounds for various applications. It is shown that the measured valence band spectra are clearly resolved and are in good agreement with the first-principles calculations of the compounds’ electronic structures.

Ouardi, Siham; Fecher, Gerhard H., E-mail: fecher@cpfs.mpg.de; Felser, Claudia

2013-10-15

100

Independence of Fermi-level position and valence-band edge discontinuity at GaAs-Ge(100) interfaces  

Energy Technology Data Exchange (ETDEWEB)

The valence-band discontinuity, ..delta..E/sub v/, and the Fermi-level position, E/sub F/, at GaAs-Ge(100) heterojunctions are investigated by synchrotron radiation photoemission for variations in GaAs surface As and ambient As/sub 4/ during molecular-beam epitaxial growth. E/sub F/ can be varied by 0.35 eV at the interface, and its position is uncorrelated with the constant 0.46 +- 0.05 eV measured for ..delta..E/sub v/. These results are not consistent with a defect model for heterojunction barrier heights.

Chiaradia, P.; Katnani, A.D.; Sang, H.W. Jr.; Bauer, R.S.

1984-04-02

 
 
 
 
101

Independence of Fermi-level position and valence-band edge discontinuity at GaAs-Ge(100) interfaces  

International Nuclear Information System (INIS)

The valence-band discontinuity, ?E/sub v/, and the Fermi-level position, E/sub F/, at GaAs-Ge(100) heterojunctions are investigated by synchrotron radiation photoemission for variations in GaAs surface As and ambient As4 during molecular-beam epitaxial growth. E/sub F/ can be varied by 0.35 eV at the interface, and its position is uncorrelated with the constant 0.46 +- 0.05 eV measured for ?E/sub v/. These results are not consistent with a defect model for heterojunction barrier heights

1984-04-02

102

Spectroscopy of neutron-rich Dy168,170: Yrast band evolution close to the NpNn valence maximum  

Science.gov (United States)

The yrast sequence of the neutron-rich dysprosium isotope Dy168 has been studied using multinucleon transfer reactions following collisions between a 460-MeV Se82 beam and an Er170 target. The reaction products were identified using the PRISMA magnetic spectrometer and the ? rays detected using the CLARA HPGe-detector array. The 2+ and 4+ members of the previously measured ground-state rotational band of Dy168 have been confirmed and the yrast band extended up to 10+. A tentative candidate for the 4+?2+ transition in Dy170 was also identified. The data on these nuclei and on the lighter even-even dysprosium isotopes are interpreted in terms of total Routhian surface calculations and the evolution of collectivity in the vicinity of the proton-neutron valence product maximum is discussed.

Söderström, P.-A.; Nyberg, J.; 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.; M?rginean, N.; Mason, P.; Menegazzo, R.; Mengoni, D.; Montagnoli, G.; Napoli, D.; Ollier, J.; Pietri, S.; Podolyák, Zs.; 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.

2010-03-01

103

Temperature impact on the Lorentzian noise induced by electron valence-band tunneling in partially depleted SOI p-MOSFETs  

Science.gov (United States)

In partially depleted (PD) silicon-on-insulator (SOI) MOSFETs with thin gate oxides, a particular effect named linear kink effect (LKE) occurs, which is due to the fact that the body potential is strongly affected by majority carriers injected in the body by the electron valence-band (EVB) tunneling through the ultra-thin gate oxide. This unexpected phenomenon induces a second peak in the transconductance gm curve and an excess Lorentzian noise in the low-frequency noise spectrum. A model based on RC filtered shot noise due to the EVB tunneling current and the forward current of the source-body junction was recently proposed at room temperature. In this work, the focus is on the temperature impact on the Lorentzian noise induced by valence-band electron tunneling in partially depleted SOI p-MOSFETs. For the first time, a Lorentzian noise filtered by the same RC network as the shot noise of the EVB tunneling current has been observed in the LKE operation at low temperature. It seems that the EVB tunneling current can also accompany an excess Lorentzian noise due to traps localized at the Si/gate oxide interface. A simple extension of the model developed by Lukyanchikova et al. is proposed and validated by experimental results from room temperature down to 80 K.

Guo, W.; Cretu, B.; Routoure, J.-M.; Carin, R.; Simoen, E.; Claeys, C.

2007-09-01

104

In situ core-level and valence-band photoelectron spectroscopy of reactively sputtered titanium aluminum nitride films  

International Nuclear Information System (INIS)

Titanium aluminum nitride (Ti-Al-N) films were deposited by reactive magnetron cosputtering. Core-level photoelectron spectroscopy and valence-band photoelectron spectroscopy served to characterize these films. Samples can consist of one single nanocrystalline phase, the substitutional solid solution (Ti, Al)N. There exist also ranges of compositions where a nanocomposite material is formed. This inhomogeneous film structure is indicated by shifts of the Fermi edge, which can be explained by a one-electron charging effect of nanometer-sized metallic clusters being embedded in an electrically insulating matrix. The multitude of possible chemical bonding situations within the ternary system are reflected by the core-level spectra. Complex Ti 2p line shapes may also be due to the screening properties of the conduction electrons. Valence-band spectra reveal electronic properties from metallic to dielectric character, depending on the elemental composition. In the case of nitrogen-saturated films the spectral intensity close to the Fermi edge is correlated with the Ti content

2001-03-15

105

Impact of [110]/(001) uniaxial stress on valence band structure and hole effective mass of silicon  

International Nuclear Information System (INIS)

The valence band structure and hole effective mass of silicon under a uniaxial stress in (001) surface along the [110] direction were detailedly investigated in the framework of the k · p theory. The results demonstrated that the splitting energy between the top band and the second band for uniaxial compressive stress is bigger than that of the tensile one at the same stress magnitude, and of all common used crystallographic direction, such as [110], [001], [1-bar10] and [100], the effective mass for the top band along [110] crystallographic direction is lower under uniaxial compressive stress compared with other stresses and crystallographic directions configurations. In view of suppressing the scattering and reducing the effective mass, the [110] crystallographic direction is most favorable to be used as transport direction of the charge carrier to enhancement mobility when a uniaxial compressive stress along [110] direction is applied. The obtained results can provide a theory reference for the design and the selective of optimum stress and crystallorgraphic direction configuration of uniaxial strained silicon devices. (semiconductor physics)

2011-02-01

106

Valence bands of oriented finite linear chain molecular solids as model compounds of polyethylene studied by angle-resolved photoemission  

Science.gov (United States)

Angle-resolved photoemission spectra were measured using synchrotron radiation of two kinds of oriented model compounds of polyethylene with their molecular axes perpendicular to the substrate surface, i.e. evaporated films of hexatriacontane CH 3(CH 2) 34CH 3 and Langmuir-Blodgett films of Cd arachidate (CH 3(CH 2) 17COO) 2Cd. Both films show similar photoelectron energy distribution curves determined by the long-alkyl chain. The intramolecular energy-band dispersion of polyethylene was determined from the photon-energy dependence of the normal-emission spectra. This is the first direct observation of an energy-band dispersion in organic solids. The upper bands formed by C 2p and H 1s electrons extend from 8.8 to 15.5 eV below the vacuum level, and the deeper-lying bands originating from C 2s electrons lie from 17.5 to 24.7 eV. The band structure obtained is compared to results from XPS and ESR studies. Furthermore, the experimentally determined band structure is discussed in detail in view of theoretical calculations for polyethylene. Ab initio and extended Hückel calculations give a good description of the experimental results.

Seki, Kazuhiko; Ueno, Nobuo; Karlsson, Ulf O.; Engelhardt, Rainer; Koch, Ernst-Eckhard

1986-06-01

107

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

Science.gov (United States)

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

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

2013-10-01

108

Doping-induced changes in the valence band edge structure of homoepitaxial B-doped diamond films below Mott's critical density  

International Nuclear Information System (INIS)

Heavily boron-doped p-type diamond is a key material for developing diamond-based applications in various fields. We obtain information about changes in the valence band edge of homoepitaxial boron-doped diamond films around and below Mott's critical density for a metal-non-metal transition. For a boron concentration of about 2-3 x 1020 cm-3, where this transition is expected to occur, a metal-like behaviour is observed at room temperature (RT) with the Fermi-level lying 0.1 eV above the valence band edge. For a boron concentration about 4 x 1019 cm-3, which is well below the critical density, the valence band edge is quite different from that of lightly doped samples. It is proposed as an explanation for these experimental differences that the excited-states of acceptors overlap. (Abstract Copyright [2009], Wiley Periodicals, Inc.)

2009-09-01

109

Polariton stark effect in dispersive and photonic band gap materials  

International Nuclear Information System (INIS)

The polariton stark effect has been studied in dispersive and photonic band gap materials doped with a two-level atom in the presence of a monochromatic driving laser field. The driven atom gets excited to the higher state and the system spontaneously decays to the ground state by emitting polaritons. The power spectrum of polaritons emitted by the atom is calculated by using the master equation for the density matrix in the presence of the damping. It is found that when the excitation frequency of the atom lies outside the energy gap and the Rabi frequency associated with the driving field becomes comparable to or larger than the atomic line width, the polaritons spontaneous decay spectrum splits into three peaks. We call this phenomena the stark effect. The central peak has a line width smaller than that of the two side peaks. Numerical calculations are performed for GaAs and SiC semiconductors

2003-09-01

110

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)

2013-09-25

111

XPS core level and valence band spectra of LaH_3  

International Nuclear Information System (INIS)

XPS analysis of LaH_3 shows that the conduction band of the La metal disappears and that a new hydrogen induced band is formed 5.8 eV below Esub(F). The La 3d core levels of LaH_3 are split into two peaks with about 1/3 of the intensity being in the low binding energy peak. It is proposed to describe the observed 3d structure by the screening of the 3d hole by means of a charge transfer from the new hydrogen band to the empty 4f level, the latter being pulled down below th hydrogen band. This would be a shake down process as in La metal. (author)

1982-01-01

112

Temperature-dependent valence-band photoemission spectra of La1-xSrxMnO3  

International Nuclear Information System (INIS)

We have studied the temperature dependence of the photoemission spectra of La1-xSrxMnO3 (x=0.0, 0.2, and 0.4) and found that the spectral line shape dramatically changes in the entire valence-band region, particularly for x=0.2 and 0.4. By contrast, the spectra of La0.6Sr0.4CoO3 show no significant temperature dependence. From comparison between the temperature- and composition-(x) dependent spectral changes and the temperature-composition phase diagram of La1-xSrxMnO3, we suggest that the changes are related to the degree of hole localization on oxygen p orbitals, which is influenced by electron-lattice coupling and magnetic correlations. copyright 1997 The American Physical Society

1997-10-01

113

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

Science.gov (United States)

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

Schulz, S.; Caro, M. A.; O'Reilly, E. P.

2014-04-01

114

Selenium treated (110) surfaces of GaAs and InP: valence band and geometric structure  

Science.gov (United States)

The molecular beam deposition of selenium onto ultra-high-vacuum cleaved (110) surfaces of GaAs and InP and subsequent annealing leads to the formation of a thin, stable, Se rich reacted layer with distinct structural and electronic properties. The Se treated surfaces were investigated using both angle resolved core level and valence band soft X-ray photoemission spectroscopies at the TGM2 beamline of the BESSY storage ring in order to determine the Se induced surface band structure and the geometric arrangement within the Se modified layer. The surface bands were determined along the overline?- overlineXand theoverline?- overlineX' directions of the substrate. The comparison between clean cleaved and Se treated surfaces reveals strong modifications due to the Se incorporation. An ordered arrangement of the Se atoms gives rise to diffraction effects in the photoemission signals. The diffraction patterns were calculated for different Se adsorption models using the multiple scattering cluster approximation with spherical wave corrections (MSCA-SWC).

Schröter, T.; Chassé, A.; Eckardt, I.; Tiedtke, K.; Wagner, N.; Zahn, D. R. T.; Nowak, C.; Hempelmann, A.; Richter, W.

1994-04-01

115

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

Science.gov (United States)

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

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

2013-09-01

116

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)

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.

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

117

Exciton binding energies and the valence-band offset in mixed type-I--type-II strained-layer superlattices  

International Nuclear Information System (INIS)

Strained CdTe-Cd1-xZnxTe superlattices are of mixed type: electrons and heavy holes are confined to the CdTe layers (type I) while light holes are confined to the Cd1-xZnxTe layers (type II). In this paper we calculate the exciton binding energy (EBE) as a function of superlattice period for both type-I (spatially direct) and type-II (spatially indirect) excitons. For the heavy-hole (type-I) exciton the binding energy is larger than the bulk value, and varies only slowly with the period down to small periods, where the exciton acquires a three-dimensional character and our calculation breaks down. For the light-hole (type-II) exciton the binding energy at large period is much smaller, due to the spatial separation of electron and hole. As the period decreases, the binding energy increases steadily to reach its bulk value for vanishingly small period. Given the EBE's, we can fit the already published data on the exciton transition energies with a single adjustable parameter, the ''average valence-band offset'' (averaged over the heavy and light holes). This is the algebraic sum of the chemical-offset and the hydrostatic-strain contribution, and is found to be (2±4)% of the difference in band gap between the barrier and well. This value lies in the range predicted theoretically

1992-07-15

118

Investigation of the valence band structure of thermoelectric (Bi1-xSbx)2Te3 single crystals  

International Nuclear Information System (INIS)

Using combined optical-spectroscopic and transport investigations it is succeeded for the first time to determine all relevant valence band data for the whole series of mixed crystals (Bi1-xSbx)2Te3 (0 ? x ? 1). The reflectivity of polarized infrared light including its anisotropy is measured in the wave number range of 300 to 4000 cm-1. In addition to the spectra the Hall coefficients ?123 and ?312, the electrical conductivity ? perpendicular c, and the Seebeck coefficient S perpendicular c are also given. In terms of a six-valley band model and scattering by acoustical phonons all experimental data are consistently described. The main axis masses miiH, the ellipsoid tilt angle ?, the effective density-of-states mass md, and the susceptibility masses mperpendicular(?),parallel c are calculated in dependence on composition, also the Fermi level EF, the carrier density p, the mobility ?perpendicular c, the high frequency dielectric constant ??perpendicular,parallel c and the relaxation time ?opt. For the first time the structure factors in the Hall coefficients are given. In the plot m(x) the distinct maxima of m22H and md near x = 0.8 are evident and important for the application of these substances. (author)

1988-11-01

119

Valence-band orbital character of CdO: A synchrotron-radiation photoelectron spectroscopy and density functional theory study  

Science.gov (United States)

N-type CdO is a transparent conducting oxide (TCO) which has promise in a number of areas including solar cell applications. In order to realize this potential a detailed knowledge of the electronic structure of the material is essential. In particular, standard density functional theory (DFT) methods struggle to accurately predict fundamental material properties such as the band gap. This is largely due to the underestimation of the Cd 4d binding energy, which results in a strong hybridization with the valence-band (VB) states. In order to test theoretical approaches, comparisons to experiment need to be made. Here, synchrotron-radiation photoelectron spectroscopy (SR-PES) measurements are presented, and comparison with three theoretical approaches are made. In particular the position of the Cd 4d state is measured with hard x-ray PES, and the orbital character of the VB is probed by photon energy dependent measurements. It is found that LDA + U using a theoretical U value of 2.34 eV is very successful in predicting the position of the Cd 4d state. The VB photon energy dependence reveals the O 2p photoionization cross section is underestimated at higher photon energies, and that an orbital contribution from Cd 5p is underestimated by all the DFT approaches.

Mudd, J. J.; Lee, Tien-Lin; Muñoz-Sanjosé, V.; Zúñiga-Pérez, J.; Payne, D. J.; Egdell, R. G.; McConville, C. F.

2014-04-01

120

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 st...

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

2006-01-01

 
 
 
 
121

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

CERN Document Server

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

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

2006-01-01

122

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

?ukari? Nemanja A.; Z?, Tadic? Milan

2010-01-01

123

Valence band structure of (Bisub(1-x)Sbsub(x))_2Te_3 single crystals  

International Nuclear Information System (INIS)

For the first time the anisotropy of reflectivity of polarized infrared light of p-(Bisub(1-x)Sbsub(x))_2Te_3 single crystals (0.5 <= x <= 1) is given in the wave number range of 300 to 4000 cm"-"1. In addition to the excitation of free carriers in the reflection spectra of the mixed crystals also interband excitations are observed. For the mixed crystals the optical results are consistently described in terms of a six-valley band model and scattering on acoustical phonons together with the data for the dc conductivity, the Hall coefficients, and the thermopower. The main axis masses msub(ii), the ellipsoid tilt angle theta, the effective density of states mass msub(d)sup(tot), the cyclotron mass msub(Bparallelc)sup((c)), and the susceptibility masses msub(perpendicular, parallelc)sup((CHI)) are given in dependence on composition, also the Fermi level Esub(F), the carrier density p, the mobility usub(perpendicularc), the high frequency dielectric constant epsilon'sub(infinity), and the relaxation time tau. The interband influence is interpreted by a simple band model and the energy gap Esub(g) calculated. (author)

1981-04-01

124

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

CERN Document Server

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

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

2012-01-01

125

Valence-band splitting and optical anisotropy of AlN  

Energy Technology Data Exchange (ETDEWEB)

The dielectric function (DF) of hexagonal AlN on Si(111) is determined in the range between 1 and 9.8 eV by spectroscopic ellipsometry (SE). Due to its large negative crystal-field splitting wurtzite AlN features large dichroism. Showing that SE is sensitive to both components of the DF around the absorption edge, a uniaxial model is applied which yields transition energies for the free excitonic state. The in-plane tensile stress leads to a red-shift of these transitions and to an enlarged splitting. The experimental data are compared to the results of band-structure calculations demonstrating excellent overall agreement. In addition, two high-energy critical points in the ordinary DF were determined at energies of about 7.75 and 8.85 eV. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

Rossbach, G.; Schley, P.; Gobsch, G. [Institut fuer Physik, Technische Universitaet Ilmenau (Germany); Roeppischer, M.; Werner, C.; Cobet, C.; Esser, N. [Institute for Analytical Sciences (ISAS), Berlin (Germany); Dadgar, A.; Wieneke, M.; Krost, A. [Institut fuer Experimentelle Physik, Otto-von-Guericke Universitaet Magdeburg (Germany); Goldhahn, R. [Institut fuer Physik, Technische Universitaet Ilmenau (Germany); Institut fuer Experimentelle Physik, Otto-von-Guericke Universitaet Magdeburg (Germany)

2010-07-15

126

Detection of the valence band in buried Co2MnSi-MgO tunnel junctions by means of photoemission spectroscopy  

Science.gov (United States)

This work reports on the detection of the valence band of buried Heusler compounds by means of hard x-ray photoemission spectroscopy. The measurements have been performed on the so-called ``half'' tunnel junctions that are thin films of Co2MnSi underneath MgO. Starting from the substrate, the structure of the samples is MgO(buffer)-Co2MnSi-MgO(tMgO)-AlOx with a thickness tMgO of the upper MgO layer of 2 and 20 nm. The valence band x-ray photoemission spectra have been excited by hard x rays of about 6 keV energy. The valence band spectra have been used to estimate the mean free path of the electrons through the MgO layer to be 17 nm at kinetic energies of about 6 keV. In particular, it is shown that the buried Co2MnSi films exhibit the same valence density of states as in bulk samples.

Fecher, Gerhard H.; Balke, Benjamin; Gloskowskii, Andrei; Ouardi, Siham; Felser, Claudia; Ishikawa, Takayuki; Yamamoto, Masafumi; Yamashita, Yoshiyuki; Yoshikawa, Hideki; Ueda, Shigenori; Kobayashi, Keisuke

2008-05-01

127

Capacitance-voltage spectroscopy on InAs quantum dot valence band states in tilted magnetic fields  

Energy Technology Data Exchange (ETDEWEB)

We have performed capacitance-voltage (C-V) spectroscopy on the valence band states of InAs quantum dots (QDs) in magnetic fields tilted with respect to the sample plane. We observe an unexpected behaviour for the height of the capacitance signal as function of the in-plane magnetic field, when varying the perpendicular field component, for the first two charging peaks corresponding both to an s-like ground state. With increasing perpendicular field component, the signal height for the first peak decreases strongly and for the second peak the maximum signal height is observed at finite in-plane field values. These observations are not in agreement with the usual assumption that the height-vs.-in-plane-field traces reflect the in-plane k-space probability distribution of the charged QD level because an s-like state should not vary its general shape with perpendicular field. The qualitatively different behaviour of the two peaks is attributed tentatively to correlation effects when the second electron is charged.

Reuter, D; Roescu, R; Wieck, A D [Lehrstuhl fuer Angewandte Festkoerperphysik, Ruhr-Universitaet Bochum, Universitaetsstrasse 150, D-44801 Bochum (Germany); Zeitler, U; Maan, J C, E-mail: dirk.reuter@rub.d [High Field Magnet Laboratory, Institute for Molecules and Materials, Radboud University Nijmegen, Toernooiveld 7, 6525 ED Nijmegen (Netherlands)

2010-09-01

128

UV Photoelectron Spectroscopy at Near Ambient Pressures: Mapping Valence Band Electronic Structure Changes from Cu to CuO.  

Science.gov (United States)

Valence band (VB) changes and hence electronic structure evolution was directly observed with low kinetic energy (KE) electrons at near ambient pressure (NAP) conditions with He I photon source in a custom built laboratory ambient pressure photoelectron spectrometer (Lab-APPES). Polycrystalline Cu surfaces were gradually oxidized in O2 to Cu2O, to a mixture of Cu2O + CuO, and finally to CuO between 300 and 625 K and at NAP. Typical VB features for Cu, Cu2O, and CuO were observed, and the results corroborate well with core level and Auger spectral changes. High mean free path associated with low KE electrons, very low or no inelastic scattering, and effective pumping and the design of electrostatic lens regime help to minimize the electron attenuation at NAP conditions. The present results extend the capabilities of the APPES tool to explore the in situ evolution of electronic structure of materials at NAP and high temperatures. PMID:24601627

Roy, Kanak; Gopinath, Chinnakonda S

2014-04-15

129

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

Science.gov (United States)

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

Urbanek, Janus; Vöhringer, Peter

2013-07-25

130

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

International Nuclear Information System (INIS)

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

2013-11-20

131

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

Science.gov (United States)

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

>M Zieli?ski,

2013-11-01

132

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

International Nuclear Information System (INIS)

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

2012-05-31

133

Valence Band Density of States of Cu3Si Studied by Soft X-Ray Emission Spectroscopy and a First-Principle Molecular Orbital Calculation  

Science.gov (United States)

A systematic study of the valence band structure of Cu3Si has been performed by soft X-ray emission spectroscopy and a first-principle molecular orbital calculation using the discrete-variational (DV)-X? cluster model. The existence of Cu 4s, 4p states in the valence band and their important contributions to the valence band as that of Cu 3d are indicated together with previously reported ones. The high-binding energy peak in the Si L2,3 emission spectrum is considered to originate mainly from the Si-Si 3s bonding state but also have a certain contribution of Si 3s bonding state with Cu 4s, 4p. On the other hand, the low-binding energy peaks in the Si L2,3 emission band are attributed to both the antibonding states of Si 3s and the bonding states of Si 3d with Cu 4s, 4p and Cu 3d. The bonding states of Si 3s with Cu 4s, 4p and Cu 3d are expected to exist in the lower part of the valence band for ?\\prime-Cu3Si on the basis of the theoretical calculations. As for Si p states, the high-binding energy peak and the low-binding energy peak in the Si K? emission spectrum should be attributed to the Si 3p bonding state and antibonding state with Cu 3d and Cu 4s, 4p, respectively, according to the theoretical calculations. A comparison is made between experimental spectra and theoretical density of states.

An, Zhenlian; Kamezawa, Chihiro; Hirai, Masaaki; Kusaka, Masahiko; Iwami, Motohiro

2002-12-01

134

Valence-Band Offset of m-Plane GaN(1\\bar{1}00) Films Grown on LiAlO2(100) Substrates  

Science.gov (United States)

We present first-principles calculations on the heterojunction between a wurtzite GaN(1\\bar{1}00) film and a tetragonal LiAlO2(100) substrate. The relative barrier heights of different models of the GaN(1\\bar{100)}\\parallel LiAlO2(100) interface are examined as a function of the valence-band offset. The most favorable interface consists of fourfold-coordinated N and Ga, which has the lowest valence-band offset of 0.534 eV. This interface structure indicates that the nitrided LiAlO2(100) surface stabilizes the GaN/LiAlO2 heteroepitaxial structures. Our findings explain a variety of experiments and may prove useful for improving the internal quantum efficiency of nonpolar GaN-based optoelectronic devices.

Liu, Po-Liang; Chou, Yen-Ting; Hong, Jia-Yang

2013-07-01

135

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

International Nuclear Information System (INIS)

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

2012-09-17

136

Relationship between thermoelectric power and electron density of states in valence band measured with XPS for Fe-Cr binary alloys and Fe-Cr-Ni ternary alloys  

International Nuclear Information System (INIS)

In order to clarify the mechanism behind the change in thermoelectric power (TEP) of Fe-Cr binary alloys and Fe-Cr-Ni ternary alloys due to Cr concentration, using these alloys with various Cr concentrations, dependence of TEP on Cr concentration was investigated. According to the Mott-Jones theory, TEP is largely related to electron density of states at the Fermi level. The electron density of states for the alloys in valence band was measured with X-ray photoelectron spectroscopy (XPS), and theoretically calculated TEP from the XPS spectrum was compared with experimentally measured TEP. Electron density of states in valence band of the both alloys changed due to Cr concentration, and the theoretically calculated TEP from XPS spectrum and the experimentally measured TEP similarly changed with Cr concentration. We think that the change in TEP with Cr concentration is due to the change in electron density of states with Cr concentration. (author)

2003-06-01

137

Measurement of the valence band-offset in a PbSe/ZnO heterojunction by x-ray photoelectron spectroscopy  

International Nuclear Information System (INIS)

A heterojunction of PbSe/ZnO has been grown by molecular beam epitaxy. X-ray photoelectron spectroscopy was used to directly measure the valence-band offset (VBO) of the heterojunction. The VBO, ?EV, was determined as 2.51 ± 0.05 eV using the Pb 4p3/2 and Zn 2p3/2 core levels as a reference. The conduction-band offset, ?EC, was, therefore, determined to be 0.59 ± 0.05 eV based on the above ?EV value. This analysis indicates that the PbSe/ZnO heterojunction forms a type I (Straddling Gap) heterostructure.

2012-12-24

138

Microstructure of reorientation bands in niobium alloys with ultra disperse particles of nonmetallic phase  

International Nuclear Information System (INIS)

Crystal lattice reorientation bands at initial stages of plastic flow of high-strength niobium alloys with ultra disperse particles of nonmetallic phase are detected by transmission electron microscopy. Fine structure of these bands is studied. Mechanism of their formation and the role of a high-strength state in deformation rotation mode development are discussed

1987-03-01

139

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

International Nuclear Information System (INIS)

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

2013-05-20

140

Interfacial chemistry and valence band offset between GaN and Al{sub 2}O{sub 3} studied by X-ray photoelectron spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

The interface region between Ga-face n-type GaN and Al{sub 2}O{sub 3} dielectric (achieved via atomic-layer deposition or ALD) is investigated by X-ray photoelectron spectroscopy (XPS). An increase in the Ga-O to Ga-N bond intensity ratio following Al{sub 2}O{sub 3} deposition implies that the growth of an interfacial gallium sub-oxide (GaO{sub x}) layer occurred during the ALD process. This finding may be ascribed to GaN oxidation, which may still happen following the reduction of a thin native GaO{sub x} by trimethylaluminum (TMA) in the initial TMA-only cycles. The valence band offset between GaN and Al{sub 2}O{sub 3}, obtained using both core-level and valence band spectra, is found to vary with the thickness of the deposited Al{sub 2}O{sub 3}. This observation may be explained by an upward energy band bending at the GaN surface (due to the spontaneous polarization induced negative bound charge on the Ga-face GaN) and the intrinsic limitation of the XPS method for band offset determination.

Duan, T. L.; Ang, D. S. [School of Electrical and Electronic Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 639798 (Singapore); Pan, J. S. [Institute of Materials Research and Engineering, A-STAR (Agency for Science, Technology and Research), 3 Research Link, Singapore 117602 (Singapore)

2013-05-20

 
 
 
 
141

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)

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

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

2010-01-01

142

Superconductivity of thallium-doped lead telluride. Density of states in the valence band of thallium-doped and sodium-doped PbTe  

International Nuclear Information System (INIS)

Measurements of the low-temperature specific heat and Hall coefficient of p-type PbTe doped with the acceptor impurities thallium and sodium were used to find the density of states g in the valence band as a function of the Hall density of holes p77 measured at T = 77 0K. In the range p77>4 x 1019 cm-3 a considerable difference in g(p77) was discovered between PbTe:Tl and PbTe:Na. The experimental results are interpreted in terms of the idea that the dominant perturbation of the band spectrum of PbTe by Na impurities (as distinct from Tl) is a considerable increase in the energy separation of the split-off ''heavy'' extremum in the valence band. The model under discussion gives a qualitative explanation of the reasons for the existence of bulk superconductivity in PbTe:Tl, as recently found by the present authors, and for its absence in PbTe:Na. Consequences of the present experimental results are examined and they are found to be relevant to the study of the properties of heavily doped semiconductors in both normal and superconducting states

1981-01-01

143

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

Science.gov (United States)

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

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

2013-07-01

144

Interface strain and the valence band offset at the lattice matched In0.53Ga0.47As/InP (001) interface  

International Nuclear Information System (INIS)

Total energy minimization calculations show that the interface bonds are strained in nominally lattice matched In0.53Ga0.47As/InP (001) heterostructures, in agreement with recent X-ray measurements. Anion intermixing relieves the interface strain. The calculated valence band offset varies with the interface bond lengths so the minimum energy structure must be used for a given composition. Then the calculated offset is independent of composition and is in good agreement with experiment. A simple model exhibits the qualitative features revealed by these calculations

1989-12-02

145

Synchrotron-based photoluminescence excitation spectroscopy applied to investigate the valence band splittings in AlN and Al0.94Ga0.06N  

Science.gov (United States)

We demonstrate that synchrotron-based photoluminescence excitation (PLE) spectroscopy is a versatile tool for determining valence band splittings of AlN and high aluminum content AlGaN. PLE results are independently confirmed by synchrotron-based spectroscopic ellipsometry. The splittings between the ordinary and the extraordinary absorption edges are found to be -240 meV and -170 meV for AlN and Al0.94Ga0.06N, respectively. These values differ from the crystal field energy due to residual strain.

Feneberg, Martin; Röppischer, Marcus; Esser, Norbert; Cobet, Christoph; Neuschl, Benjamin; Meisch, Tobias; Thonke, Klaus; Goldhahn, Rüdiger

2011-07-01

146

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Hassall, T. E.; Stappers, B. W.; Hessels, J. W. T.; Kramer, M.; Alexov, A.; Anderson, K.; Coenen, T.; Karastergiou, A.; Keane, E. F.; Kondratiev, V. I.; Lazaridis, K.; Leeuwen, J.; Noutsos, A.; Serylak, M.; Sobey, C.

2012-01-01

147

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

CERN Document Server

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.

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

148

Strong valence-band offset bowing of ZnO1-xSx enhances p-type nitrogen doping of ZnO-like alloys.  

Science.gov (United States)

Photoelectron spectroscopy, optical characterization, and density functional calculations of ZnO1-xSx reveal that the valence-band (VB) offset E(v)(x) increases strongly for small S content, whereas the conduction-band edge E(c)(x) increases only weakly. This is explained as the formation of local ZnS-like bonds in the ZnO host, which mainly affects the VB edge and thereby narrows the energy gap: E(g)(x=0.28) approximately E(g)(ZnO)-0.6 eV. The low-energy absorption tail is a direct Gamma(v)-->Gamma(c) transition from ZnS-like VB. The VB bowing can be utilized to enhance p-type N(O) doping with lower formation energy DeltaH(f) and shallower acceptor state in the ZnO-like alloys. PMID:17155274

Persson, Clas; Platzer-Björkman, Charlotte; Malmström, Jonas; Törndahl, Tobias; Edoff, Marika

2006-10-01

149

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

International Nuclear Information System (INIS)

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

2003-04-02

150

Exporting superconductivity across the gap: Proximity effect for semiconductor valence-band states due to contact with a simple-metal superconductor  

Science.gov (United States)

The proximity effect refers to the phenomenon whereby superconducting properties are induced in a normal conductor that is in contact with an intrinsically superconducting material. In particular, the combination of nanostructured semiconductors with bulk superconductors is of interest because these systems can host unconventional electronic excitations such as Majorana fermions when the semiconductor's charge carriers are subject to a large spin-orbit coupling. The latter requirement generally favors the use of hole-doped semiconductors. On the other hand, basic symmetry considerations imply that states from typical simple-metal superconductors will predominantly couple to a semiconductor's conduction-band states and, therefore, in the first instance generate a proximity effect for band electrons rather than holes. In this article, we show how the superconducting correlations in the conduction band are transferred also to hole states in the valence band by virtue of interband coupling. A general theory of the superconducting proximity effect for bulk and low-dimensional hole systems is presented. The interplay of interband coupling and quantum confinement is found to result in unusual wave-vector dependencies of the induced superconducting gap parameters. One particularly appealing consequence is the density tunability of the proximity effect in hole quantum wells and nanowires, which creates new possibilities for manipulating the transition to nontrivial topological phases in these systems.

Moghaddam, A. G.; Kernreiter, T.; Governale, M.; Zülicke, U.

2014-05-01

151

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

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english 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.

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

152

Emission band shape probes of the mixed-valence excited state properties of polypyridyl-bridged bis-ruthenium(II) complexes  

International Nuclear Information System (INIS)

The absorption spectra and emission spectral band shapes of several polypyridine-ligand (PP) bridged bis-ruthenium(II) complexes imply that the Ru(II)/Ru(III) electronic coupling is weak in their lowest energy metal to ligand charge transfer (MLCT) excited states. Many of these PP-bridging ligands contain pyrazine moieties and the weak electronic coupling of the excited states contrasts to the strong electronic coupling inferred for the correlated mixed-valence ground states. Although the bimetallic complexes emit at significantly lower energy than their monometallic analogs, the vibronic contributions to their 77 K emission spectra are much stronger than expected based on comparison to the monometallic analogs (around twofold in some complexes) and this feature is characteristic of bimetallic complexes in which the mixed-valence excited states are electronically localized. The weaker excited state than ground state donor/acceptor electronic coupling in this class of complexes is attributed to PP-mediated super-exchange coupling in which the mediating orbital of the bridging ligand (PP-LUMO) is partly occupied in the MLCT excited states, but is unoccupied in the ground states; therefore, the vertical Ru(III)-PP- (MLCT) energy is larger and the mixing coefficient smaller in these excited states than is found for Ru(II)-PP in the corresponding ground states

2006-07-11

153

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

CERN Multimedia

We report quasiparticle-energy calculations of the electronic bandstructure as measured by valence-band photoemission for selected II-VI compounds and group-III-nitrides. By applying GW as perturbation to the ground state of the fictitious, non-interacting Kohn-Sham electrons of density-functional theory (DFT) we systematically study the electronic structure of zinc-blende GaN, ZnO, ZnS and CdS. Special emphasis is put on analysing the role played by the cation semicore d-electrons that are explicitly included as valence electrons in our pseudopotential approach. Unlike in the majority of previous GW studies, which are almost exlusively based on ground state calculations in the local-density approximation (LDA), we combine GW with exact-exchange DFT calculations in the optimised-effective potential approach (OEPx). This is a much more elaborate and computationally expensive approach. However, we show that applying the OEPx approach leads to an improved description of the d-electron hybridisation compared to t...

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

2005-01-01

154

Recovery distances of nestling Bald Eagles banded in Florida and implications for natal dispersal and philopatry  

Science.gov (United States)

I used band recovery data to examine distances between banding and recovery locations for 154 nestling Florida Bald Eagles and discuss the implications for understanding natal dispersal and philopatry in this species. Band recoveries occurred in 23 U.S. states and five Canadian provinces between 1931-2005. Recovery distance from the natal nest averaged longer for the youngest age classes (ANOVA: F = 3.59; df = 5,153;P = 0.005), for individuals banded in earlier decades (F= 1.94; df = 5,153;P = 0.093), and for the months of May through October (F= 3.10; df = 12,153; P< 0.001). Of 35 individuals classed as mature (???3.9 yr old when recovered; range 3.9-36.5 yr), 31 were located within Florida, which suggested a strong degree of philopatry to the natal state. Among 21 mature eagles of known sex with known banding and recovery locations in Florida, females, particularly younger birds, had longer recovery distances (N = 9, mean = 93 km, SE = 22.4) than did males (N = 12, mean = 31 km, SE = 5.3; t = 2.67, df = 19, P = 0.026). The records examined here suggest a high degree of philopatry and relatively short natal dispersal distances, particularly in male Bald Eagles. ?? 2009 The Raptor Research Foundation, Inc.

Wood, P. B.

2009-01-01

155

Verification of ?7 symmetry assignment for the top valence band of ZnO by magneto-optical studies of the free A exciton state  

International Nuclear Information System (INIS)

Circularly-polarized and angular-resolved magneto-photoluminescence spectroscopy was carried out to study the free A exciton 1S state in wurtzite ZnO at 5 K. The ? 7 symmetry of the top valence band symmetry is confirmed according to the unique selection rules of Zeeman splitting lines. The out-of-plane component B? of the magnetic field, which is parallel to ZnO's c-axis, leads to linear Zeeman splitting of both the dipole-allowed ? 5 exciton state and the weakly allowed ? 1 /? 2 exciton states. The in-plane field B?, which is perpendicular to the c-axis, increases the oscillator strength of the weak ? 1 /? 2 states by forming a mixed exciton state. For the ? 7 symmetry, the lower energy Zeeman splitting peak of the weak ? 1 /? 2 can only be ?+ polarization. (paper)

2013-03-01

156

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

International Nuclear Information System (INIS)

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

2008-03-03

157

On the absence of resonance in the valence band photoemission at L2 resonance edge and the delayed onset of the normal Auger-decay  

Science.gov (United States)

No clear resonance is present in the resonant valence band photoemission spectrum of a Mn6 (S = 4) single molecule magnet grafted on Au (1 1 1) for photon energy at the L2 resonance edge. This is due to the L2-hole's dominant decay by the L2-L3V Coster-Kronig (CK) decay. The excess energy of the photon at which the Mn resonant Raman scattering regime transits to the normal Mn Auger-decay regime in MnO depends on the Mn Auger-decay channels. This is because of the localization and delocalization of two holes in the Auger final states. The Mn resonant Auger-electron spectroscopy spectra of MnO are analyzed.

Ohno, Masahide

2012-06-01

158

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.))

1995-02-01

159

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

International Nuclear Information System (INIS)

The thermopower and the relative electrical resistance of rhombohedral ?-GeTe and orthorhombic #betta#-GeTe polycrystalline samples with hole density between 3.9 x 10_2_0 and 2 x 10_2_1 cm"-_3 are measured under hydrostatic pressure up to 8.5 GPa at room temperature. The phase transition of ?-GeTe to the cubic rocksalt structure (#betta#-GeTe) reported earlier at 3.5 GPa under nonhydrostatic pressure is not observed up to 8.5 GPa. Orthorhombic #betta#-GeTe also exhibits no phase transition. The pressure dependences of the thermopower provide support for the multiple valence-band model of GeTe. (author)

1983-03-01

160

Order N photonic band structures for metals and other dispersive materials  

CERN Multimedia

We show, for the first time, how to calculate photonic band structures for metals and other dispersive systems using an efficient Order N scheme. The method is applied to two simple periodic metallic systems where it gives results in close agreement with calculations made with other techniques. Further, the approach demonstrates excellent numerical stablity within the limits we give. Our new method opens the way for efficient calculations on complex structures containing a whole new class of material.

Arriaga, J; Pendry, J B

1998-01-01

 
 
 
 
161

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

CERN Document Server

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

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

2012-01-01

162

Effect of temperature on the valency bands of HDO in water in the liquid and solid states. Effects on the analysis of heavy water using infra-red absorption  

International Nuclear Information System (INIS)

After, a description of the technique used, a qualitative examination is made of the influence of the temperature on the ?OH(3,400 cm-1) and ?OD (2,500 cm-1) valence bands of HDO in the liquid state and then during the passage to the solid state. Quantitative examination with two cells of different thickness makes it possible to define the influence of temperature on the residual absorption of the pure liquid (D2O or H2O and on the valency bands (?OH and ?OD respectively). It is found that a similar change occurs in the two bands but that the changes in the background are very different. During the passage from the liquid to the solid state the shape of the bands varies considerably but little change occurs in the total intensity. It has been possible to express these results in a simple form which is directly applicable to analytical problems. (authors)

1964-01-01

163

Thomas-Fermi-Dirac calculations of valence band states in two p-type delta-doped ZnSe quantum wells  

Energy Technology Data Exchange (ETDEWEB)

We present the hole sub-band structure study in two p-type {delta}-doped ZnSe QW's. An analytical expression for the Hartree-Fock potential is obtained following the lines of the Thomas-Fermi-Dirac (TFD) approximation. We have analyzed the dependence of the hole energy levels to the impurity density and the interlayer distance between wells. The exchange effects are also included in the present survey. We find that many body effects cannot be ignored because these are really important in the calculation at least in the low concentration regime. We have obtained an energy difference between the top of the valence band and the ground energy of the heavy hole ladder of meV in good agreement with the experimental reports (eV) available. We calculate the mobility ratio between double {delta}-doped QW's and simple {delta}-doped QW based on a phenomenological formula. We find the optimum interlayer distance between wells for maximum mobility for three impurity concentrations, which can be of great importance for technological applications. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Rodriguez-Vargas, I.; Gaggero-Sager, L.M.; Martinez-Orozco, J.C. [Facultad de Ciencias, Universidad Autonoma del Estado de Morelos, Av. Universidad 1001, Col. Chamilpa 62210 Cuernavaca, Morelos (Mexico)

2005-04-01

164

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

Science.gov (United States)

Quantum Hall measurement of two-dimensional high-mobility [? ˜2×106 cm2/(V·s)] hole systems confined in a 20 nm wide (100)-GaAs quantum well have been performed for charge densities between 4 and 5 × 1010 cm-2 in a temperature range of 10-160 mK. The Fourier analysis of the Shubnikov-de Haas (SdH) oscillations of the magnetoresistance vs. the inverse of the magnetic field 1/B reveals a single peak, indicating a degenerate heavy hole (HH) band. The hole density p =(e/h)·f agrees with the Hall measurement result within 3%. The HH band degeneracy is understood through the diminishing spin-orbit interaction due to the low charge density and the nearly symmetric confinement. SdH oscillations fitted for 0.08 T ? B ? 0.24 T to the Dingle parameters yield an effective mass between 0.30 and 0.50 me in good agreement with previous cyclotron resonance results.

Tarquini, Vinicio; Knighton, Talbot; Wu, Zhe; Huang, Jian; Pfeiffer, Loren; West, Ken

2014-03-01

165

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

Science.gov (United States)

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.

Lao, Yan-Feng; Wolde, Seyoum; Unil Perera, A. G.; Zhang, Y. H.; Wang, T. M.; Kim, J. O.; Schuler-Sandy, Ted; Tian, Zhao-Bing; Krishna, S. S.

2014-04-01

166

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

Science.gov (United States)

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

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

2013-03-01

167

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

Science.gov (United States)

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

Jones, R. M.; Dolgashev, V. A.; Miller, R. H.; Adolphsen, C.; Wang, J. W.

168

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

CERN Document Server

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

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

2003-01-01

169

Valence band offset at GaN/{beta}-Si{sub 3}N{sub 4} and {beta}-Si{sub 3}N{sub 4}/Si(111) heterojunctions formed by plasma-assisted molecular beam epitaxy  

Energy Technology Data Exchange (ETDEWEB)

Ultra thin films of pure {beta}-Si{sub 3}N{sub 4} (0001) were grown on Si (111) surface by exposing the surface to radio- frequency nitrogen plasma with a high content of nitrogen atoms. Using {beta}-Si{sub 3}N{sub 4} layer as a buffer layer, GaN epilayers were grown on Si (111) substrate by plasma-assisted molecular beam epitaxy. The valence band offset (VBO) of GaN/{beta}-Si{sub 3}N{sub 4}/Si heterojunctions is determined by X-ray photoemission spectroscopy. The VBO at the {beta}-Si3N4 / Si interface was determined by valence-band photoelectron spectra to be 1.84 eV. The valence band of GaN is found to be 0.41 {+-} 0.05 eV below that of {beta}-Si{sub 3}N{sub 4} and a type-II heterojunction. The conduction band offset was deduced to be {approx} 2.36 eV, and a change of the interface dipole of 1.29 eV was observed for GaN/{beta}-Si{sub 3}N{sub 4} interface formation.

Kumar, Mahesh; Roul, Basanta [Materials Research Centre, Indian Institute of Science, Bangalore- 560012 (India); Central Research Laboratory, Bharat Electronics, Bangalore-560013 (India); Bhat, Thirumaleshwara N.; Rajpalke, Mohana K. [Materials Research Centre, Indian Institute of Science, Bangalore- 560012 (India); Kalghatgi, A.T. [Central Research Laboratory, Bharat Electronics, Bangalore-560013 (India); Krupanidhi, S.B., E-mail: sbk@mrc.iisc.ernet.in [Materials Research Centre, Indian Institute of Science, Bangalore- 560012 (India)

2012-05-31

170

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

CERN Document Server

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

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

2009-01-01

171

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

CERN Document Server

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

Scheuer, Jacob

2009-01-01

172

Evidence for Incomplete Charge Transfer and La-Derived States in the Valence Bands of Endohedrally Doped La{at}C{sub 82}  

Energy Technology Data Exchange (ETDEWEB)

Photoelectron spectra from sublimed layers of chromatographically separated La{at}C{sub 82} are presented. Using photon energies corresponding to the La 3d to 4f transition, a resonant enhancement of the La-derived valence states is observed. From the calculated resonant intensities of La 5d and 5p states in a La atom we estimate that about (1)/(3) of an electron charge is left in the La-valence orbitals for La@C{sub 82} . In contrast to previous interpretations of La core-level photoemission studies our results demonstrate that the La valence electrons are not completely delocalized on the fullerene cage. {copyright} {ital 1997} {ital The American Physical Society}

Kessler, B.; Bringer, A.; Cramm, S.; Schlebusch, C.; Eberhardt, W. [Forschungszentrum Juelich, IFF, D-52425 Juelich (Germany); Suzuki, S.; Achiba, Y. [Department of Chemistry, Tokyo Metropolitan University, Hachioji, Tokyo 192-03 (Japan); Esch, F.; Barnaba, M.; Cocco, D. [Sincrotrone Trieste, Padriciano 99, Trieste (Italy)

1997-09-01

173

Evidence for Incomplete Charge Transfer and La-Derived States in the Valence Bands of Endohedrally Doped La at sign C82  

International Nuclear Information System (INIS)

Photoelectron spectra from sublimed layers of chromatographically separated La at sign C82 are presented. Using photon energies corresponding to the La 3d to 4f transition, a resonant enhancement of the La-derived valence states is observed. From the calculated resonant intensities of La 5d and 5p states in a La atom we estimate that about (1)/(3) of an electron charge is left in the La-valence orbitals for La at sign C82 . In contrast to previous interpretations of La core-level photoemission studies our results demonstrate that the La valence electrons are not completely delocalized on the fullerene cage. copyright 1997 The American Physical Society

1997-09-01

174

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

International Nuclear Information System (INIS)

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

1992-01-01

175

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

Science.gov (United States)

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

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

2012-11-28

176

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

Science.gov (United States)

Angle-resolved photoemission spectroscopy (ARPES) and ab initio band structure calculations have been used to study the detailed valence band structure of molybdenite, MoS2 and MoSe2. The experimental band structure obtained from ARPES has been found to be in good agreement with the theoretical calculations performed using the linear augmented plane wave (LAPW) method. In going from MoS2 to MoSe2, the dispersion of the valence bands decreases along both k? and k?, revealing the increased two-dimensional character which is attributed to the increasing interlayer distance or c/a ratio in these compounds. The width of the valence band and the band gap are also found to decrease, whereas the valence band maxima shift towards the higher binding energy from MoS2 to MoSe2.

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

2012-11-01

177

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

CERN Multimedia

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

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

2007-01-01

178

Band structure of boron doped carbon nanotubes  

CERN Document Server

We present {\\it ab initio} and self-consistent tight-binding calculations on the band structure of single wall semiconducting carbon nanotubes with high degrees (up to 25 %) of boron substitution. Besides a lowering of the Fermi energy into the valence band, a regular, periodic distribution of the p-dopants leads to the formation of a dispersive ``acceptor''-like band in the band gap of the undoped tube. This comes from the superposition of acceptor levels at the boron atoms with the delocalized carbon $\\pi$-orbitals. Irregular (random) boron-doping leads to a high concentration of hybrids of acceptor and unoccupied carbon states above the Fermi edge.

Wirtz, L; Wirtz, Ludger; Rubio, Angel

2003-01-01

179

Understanding Core-Valence-Valence Auger Lineshapes.  

Science.gov (United States)

As a result of recent advances in understanding, core-valence-valence (CVV) Auger spectroscopy is now being used as a local valence probe of molecular, chemisorbed and solid state species. Analysis of Auger data has led to the discovery of localized multi...

D. R. Jennison

1981-01-01

180

Energy-level density in doped d-band and inelastic scattering of electrons on the system of iron ions with mixed valence in HgSe:Fe crystals  

International Nuclear Information System (INIS)

The experimental studies on the specific resistance and Hall coefficients on the HgSe:Fe crystals with the different iron content in the temperature range 1.3?T?300 K and in the magnetic fields up to 60 kOe are presented. The temperature dependences of the concentration and mobility of conductivity electrons in the studied crystals are determined. The effect of the charges spatial ordering in the iron ions system with the mixed valence on the admixture states in the HgSe:Fe crystals is considered. The theoretical analysis of the states density in the doped d-band and also of the electrons inelastic scattering, connected with the recharging of the iron bivalent and trivalent ions in the scattering event, is presented. It is shown that the experimentally identified peculiarities of the electrons concentration behaviour and their mobility by the change in the iron admixture content and temperature may be explained by the effect of the Coulomb correlations in the iron ions system with the mixed valence on the doped d-band

2003-10-01

 
 
 
 
181

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

Science.gov (United States)

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

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

1982-01-01

182

Quadratic operators used in deducing exact ground states for correlated systems: ferromagnetism at half-filling provided by a dispersive band  

Energy Technology Data Exchange (ETDEWEB)

Quadratic operators are used in transforming the model Hamiltonian H-circumflex of one correlated and dispersive band in a unique positive semidefinite form coopting both the kinetic and interacting parts of the H-circumflex. The expression is used in deducing exact ground states which are minimum energy eigenstates only of the full Hamiltonian. It is shown in this framework that at half-filling, dispersive bands can also provide ferromagnetism in exact terms through correlation effects.

Chalupa, Istvan; Gulacsi, Zsolt [Department of Theoretical Physics, University of Debrecen, H-4010 Debrecen (Hungary)

2007-09-26

183

Pressure induced conduction and valence band shifts in InP and GaAs from measurements at semiconductor--electrolyte interfaces  

International Nuclear Information System (INIS)

The effect of pressure on the band gap and flatband potential of n- and p-type InP and GaAs was studied to 10 kbar at 300 K. For both InP and GaAs it was determined that the increase of the energy gap of the direct transition is to first order due to an increase in energy of the conduction band edge

1983-01-01

184

Levels of valence  

Directory of Open Access Journals (Sweden)

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.

VeraShuman

2013-05-01

185

Levels of valence.  

Science.gov (United States)

The distinction between the positive and the negative is fundamental in our emotional life. In appraisal theories, in particular in the component process model of emotion (Scherer, 1984, 2010), qualitatively different types of valence are proposed based on appraisals of (un)pleasantness, goal obstructiveness/conduciveness, low or high power, self-(in)congruence, and moral badness/goodness. This multifaceted conceptualization of valence is highly compatible with the frequent observation of mixed feelings in real life. However, it seems to contradict the one-dimensional conceptualization of valence often encountered in psychological theories, and the notion of valence as a common currency used to explain choice behavior. Here, we propose a framework to integrate the seemingly disparate conceptualizations of multifaceted valence and one-dimensional valence by suggesting that valence should be conceived at different levels, micro and macro. Micro-valences correspond to qualitatively different types of evaluations, potentially resulting in mixed feelings, whereas one-dimensional macro-valence corresponds to an integrative "common currency" to compare alternatives for choices. We propose that conceptualizing levels of valence may focus research attention on the mechanisms that relate valence at one level (micro) to valence at another level (macro), leading to new hypotheses, and addressing various concerns that have been raised about the valence concept, such as the valence-emotion relation. PMID:23717292

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

2013-01-01

186

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

Science.gov (United States)

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

Šim?nek, A.; Pol?ík, M.; Wiech, G.

1995-10-01

187

Pressure induced valence change in ytterbium monoxide  

International Nuclear Information System (INIS)

The pressure-volume relationship in YbO was investigated to 35 GPa using a diamond anvil cell and the energy dispersive X-ray diffraction technique. The anomalous compressibility exhibited by YbO above 8 GPa strongly suggests a valence change in Yb from divalent towards the trivalent state at higher pressures. The valence change appears to be continuous. The change in color from black to yellow in reflected light supports the valence change. The initial bulk modulus of YbO is B0=130+-10GPa. (author)

1981-01-01

188

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Otto Blehr

1997-01-01

189

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

Directory of Open Access Journals (Sweden)

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

Otto Blehr

1997-04-01

190

Evidence for topological band inversion of the phase change material Ge2Sb2Te5  

Science.gov (United States)

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 ?¯ being 0.3 eV below the Fermi level EF and a circular Fermi contour around ?¯ with a dispersing diameter of 0.27-0.36 Å-1. This is in agreement with density functional theory calculations of the Petrov stacking sequence in the cubic phase which exhibits a topological surface state. The topologically trivial cubic Kooi-De Hosson stacking shows a valence band maximum at ? in line with all previous calculations of the hexagonal stable phase exhibiting the valence band maximum at ? for a trivial Z2 topological invariant ?0 and away from ? for non-trivial ?0. Scanning tunneling spectroscopy exhibits a band gap of 0.4 eV around EF.

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

2013-12-01

191

Valence band discontinuity at the ZnTe/CdTe interface: Making ohmic contact to [ital P]-type CdTe  

Energy Technology Data Exchange (ETDEWEB)

We studied the growth and electronic structure of the ZnTe/CdTe(100) interface with angle-resolved synchrotron radiation photoemission (ARPES) and reflection high energy electron diffraction (RHEED). RHEED patterns during the growth of ZnTe layers on the CdTe(100) substrate showed that the initial [similar to]16 A grows in registry. After this pseudomorphic 16 A layer, the next 120 A grows with defects to relieve the 6.6% strain between ZnTe and CdTe. After [similar to]140 A, the ZnTe layers are relaxed. ARPES taken near the Brillouin zone center gave a valance band offset [Delta][ital E][sub [ital v

Niles, D.W. (National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, Colorado 80401 (United States)); Hoechst, H.; Rioux, D. (Synchrotron Radiation Center, 3731 Schneider Drive, Stoughton, Wisconsin 53589 (United States))

1992-12-01

192

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

Science.gov (United States)

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

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

2011-01-01

193

SFI++ I: A New I-band Tully-Fisher Template, the Cluster Peculiar Velocity Dispersion and H0  

CERN Multimedia

The SFI++ consists of ~5000 spiral galaxies which have measurements suitable for the application of the I-band Tully-Fisher (TF) relation. This sample builds on the SCI and SFI samples published in the 1990s but includes significant amounts of new data as well as improved methods for parameter determination. We derive a new I-band TF relation from a subset of this sample which consists of 807 galaxies in the fields of 31 nearby clusters and groups. This sample constitutes the largest ever available for the calibration of the TF template and extends the range of line-widths over which the template is reliably measured. Careful accounting is made of observational and sample biases such as incompleteness, finite cluster size, galaxy morphology and environment. We find evidence for a type-dependent TF slope which is shallower for early type than for late type spirals. The line-of-sight cluster peculiar velocity dispersion is measured for the sample of 31 clusters. This value is directly related to the spectrum of...

Masters, K L; Haynes, M P; Giovanelli, R; Masters, Karen L.; Springob, Christopher M.; Haynes, Martha P.; Giovanelli, Riccardo

2006-01-01

194

Enhanced optical conductance in graphene superlattice due to anisotropic band dispersion  

International Nuclear Information System (INIS)

The optical response of a Kronig-Penney type graphene superlattice is investigated. When an external field is applied along the periodicity of the superlattice, the total optical response of the graphene superlattice is enhanced due to the formation of anisotropic Dirac fermions. Such anisotropy tunes up the total optical spectra while maintaining the same critical electric field regardless of the degree of anisotropy. The optical conductance of anisotropic Dirac fermions exhibits two contrasting behaviours: (i) inversely proportional to the anisotropy and (ii) directly proportional to the anisotropy, depending on the direction of the external field. Interestingly, the anisotropy-induced optical conductance enhancement also occurs in gapped graphene with band structure anisotropy. This suggests that the enhanced electron-photon couplings in the presence of anisotropy is a general feature of the relativistic nature of the Dirac fermions in both massless and massive form. It is also revealed that the strong optical nonlinearity is a consequence of the relativistic nature of the Dirac fermions and the Dirac cone isotropy is not required.

2012-10-03

195

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

International Nuclear Information System (INIS)

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

1994-01-01

196

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1994-08-01

197

Valence band electronic structure of Nd{sub 1?x}Y{sub x}MnO{sub 3} using X-ray absorption, photoemission and GGA + U calculations  

Energy Technology Data Exchange (ETDEWEB)

Highlights: •Decrease in the occupancy of Mn 3d orbitals with doping. •Greater splitting of the e{sub g} orbitals due to the increased Jahn–Teller distortion with doping. •Decrease in O 2p–Mn 3d charge transfer character with doping. •Increase in charge transfer energy and band gap with doping. •Calculations hint a subtle change from a charge transfer to Mott–Hubbard type insulator with doping. -- Abstract: The electronic structures of Nd{sub 1?x}Y{sub x}MnO{sub 3} (x = 0–0.5) were studied using X-ray absorption near-edge structure (XANES) at the Mn L{sub 3,2}- and O K-edge along with valence-band photoemission spectroscopy (VB-PES). The systematic increase in white-line intensity of the Mn L{sub 3,2}-edge with doping, suggests a decrease in the occupancy of Mn 3d orbitals. The O K-edge XANES shows a depletion of unoccupied states above the Fermi energy. The changes in the O K-edge spectra due to doping reflects an increase in the Jahn–Teller distortion. The VB-PES shows broadening of the features associated with Mn 3d and O 2p hybridized states and the shift of these features to a slightly higher binding energy in agreement with our GGA + U calculations. The system shows a net shift of the occupied and unoccupied states away from the Fermi energy with doping. The shift in theoretical site-projected density of states of x = 0.5 composition with respect to x = 0 suggest a subtle change from a charge transfer to Mott–Hubbard type insulator.

Balasubramanian, Padmanabhan, E-mail: padmanabhan@iopb.res.in [Department of Physics, Tamkang University, Tamsui 251, Taiwan (China); Institute of Physics, Bhubaneshwar 751005 (India); Nair, Harikrishnan S. [J?lich Center for Neutron Sciences, Forschungszentrum J?lich, Outstation at FRM II, LichtenberGstr. 1, Garching 85747 (Germany); Tsai, H.M. [Department of Physics, Tamkang University, Tamsui 251, Taiwan (China); National Synchrotron Radiation Research Center, Hsinchu 300, Taiwan (China); Bhattacharjee, S. [Department of Physics and Astronomy, Uppsala University, Box 516, 75120 Uppsala (Sweden); Liu, M.T. [Department of Physics, Tamkang University, Tamsui 251, Taiwan (China); Yadav, Ruchika [Department of Physics, Indian Institute of Science, C.V. Raman Avenue, Bangalore 560012 (India); Chiou, J.W. [Department of Applied Physics, National University of Kaohsiung, Kaohsiung 811, Taiwan (China); Lin, H.J.; Pi, T.W. [National Synchrotron Radiation Research Center, Hsinchu 300, Taiwan (China); Tsai, M.H. [Department of Physics, National Sun Yat-Sen University, Kaohsiung 804, Taiwan (China); Elizabeth, Suja [Department of Physics, Indian Institute of Science, C.V. Raman Avenue, Bangalore 560012 (India); Pao, C.W.; Wang, B.Y.; Chuang, C.H.; Pong, W.F. [Department of Physics, Tamkang University, Tamsui 251, Taiwan (China)

2013-08-15

198

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

Science.gov (United States)

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

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

2013-05-01

199

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

Science.gov (United States)

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.

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

2014-04-01

200

Valence fluctuation phenomena  

International Nuclear Information System (INIS)

Valence fluctuation phenomena occur in rare-earth compounds in which the proximity of the 4f level to the Fermi energy leads to instabilities of the charge configuration (valence) and/or of the magnetic moment. The experimental results observed in the subset of such systems for which the 4f ions form a lattice with identical valence on each site are reviewed. The discussion includes key thermodynamic experiments, such as susceptibility and lattice constant, and spectroscopic experiments such as XPS and neutron scattering. This is followed by a review of existing theoretical work concerning both the ground states and the isomorphic phase transitions which occur in such compounds; the emphasis is on those aspects which make valence fluctuation phenomena such a challenging many-body problem. 391 references. (author)

1981-01-01

 
 
 
 
201

Levels of Valence  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The distinction between the positive and the negative is fundamental in our emotional life. In appraisal theories, in particular in the component process model of emotion (Scherer, 1984, 2010), qualitatively different types of valence are proposed based on appraisals of (un)pleasantness, goal obstructiveness/conduciveness, low or high power, self-(in)congruence, and moral badness/goodness. This multifaceted conceptualization of valence is highly compatible with the frequent observation of mix...

2013-01-01

202

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)

1972-01-01

203

The aggregation effect on the absorption band shift of disperse red-13 attached on the surface of silica spheres  

Science.gov (United States)

Optical properties of disperse red-13 (DR-13) attached on the surface of the silica spheres have been investigated. Two step synthetic processes have been used to attach the DR-13 on the surface of the silica spheres. The first step is a urethane bond formation between a DR-13 (OH) and a 3-isocyanatopropyl triethoxysilane (ICPTES, NCO) in pyridine at 50 °C. The second step is the hydrolysis and condensation reactions between the resulting compound of the first step reaction (ICPDR) and the silica spheres (ICPDRSS). The absence of a characteristic absorption peak at 2270 cm-1 representing the NCO asymmetric stretching vibration and the existence of a new absorption peat at 1700 cm-1 corresponding the CO stretching vibration indicate the urethane bond formation. The absorption intensity of the DR-13 in methanol, ethanol and 2-propanol linearly increased with the increase of the amount of the DR-13. The ICPDRSS has weak brownish color when it is dried. The field emission scanning electron microscope shows the aggregated ICPDR on the surface of the silica spheres. The average diameter of the spheres is approximately 380 nm. The color of the ICPDRSS changed to intense red when it was wetted in methanol, ethanol and 2-propanol. The absorption peak of the dried ICPDRSS film is at 475 nm. The stopband appears at 788 nm and disappears when the methanol is filled between the spheres due to the low refractive index contrast. New absorption band appears at 718 nm when the methanol is absorbed due to the large aggregation of the ICPDR on the surface of the spheres.

Kang, Kwang-Sun

2013-12-01

204

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

Energy Technology Data Exchange (ETDEWEB)

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

Meevasana, Warawat

2010-05-26

205

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

CERN Document Server

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

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

2001-01-01

206

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

International Nuclear Information System (INIS)

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

2011-03-23

207

VALENCE STATES OF SULFUR IN POLLUTION SAMPLES BY X-RAY ANALYSIS  

Science.gov (United States)

A flat single crystal spectrometer was configured to measure the valence band x-ray spectra of various forms of sulfur in air pollutants. While most different valence states showed differences in the structure of the K sub beta band, particular emphasis was placed on distinguishi...

208

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

1990-11-01

209

Micro-Valences: Affective valence in “neutral” everyday objects  

Directory of Open Access Journals (Sweden)

Full Text Available Affective valence influences both our cognition and our perception of the world. Indeed, the speed and quality with which we recognize objects in a visual scene can vary dramatically depending on its affective content. However, affective processing of visual objects has been typically studied using only stimuli with strong affective valences (e.g., guns or roses. Here we explore whether affective valence must be strong or obvious to exert an effect on our perception. We conclude that the majority of objects carry some affective valence (“micro-valences” and, thus, nominally “neutral” objects are not really neutral. Functionally, the perception of valence in everyday objects facilitates perceptually-driven choice behavior, decision-making, and affective responses.

MichaelJTarr

2012-04-01

210

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.

2010-04-30

211

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

Science.gov (United States)

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.

Qasrawi, A. F.; Mergen, A.

2014-05-01

212

Ferromagnetism in the t-t' Hubbard model: interplay of lattice, band dispersion, and interaction effects studied within a Goldstone-mode preserving scheme  

CERN Document Server

Ferromagnetism in the Hubbard model is investigated on sc, bcc, and fcc lattices using a systematic inverse-degeneracy ($1/{\\cal N}$) expansion which incorporates self-energy and vertex corrections such that spin-rotation symmetry and the Goldstone mode are explicitly preserved. First-order quantum corrections to magnon energies are evaluated for several cases, providing a comprehensive picture of the interplay of lattice, band dispersion, and interaction effects on the stability of the ferromagnetic state with respect to both long- and short-wavelength fluctuations. Our results support the belief that ferromagnetism is a generic feature of the Hubbard model at intermediate and strong coupling provided the DOS is sufficiently asymmetric and strongly peaked near band edge, as for fcc lattice with finite $t'$. For short-wavelength modes, behavior of a characteristic energy scale $\\omega^* \\sim T_c$ (magnon-DOS-peak energy) is in excellent agreement with the $T_c$ vs. $n$ behavior within DMFT, both with respect ...

Pandey, S; Pandey, Sudhakar; Singh, Avinash

2006-01-01

213

Similarities of the band structure of In4Se3 and InSe under pressure and peculiarities of the creation of the band gap  

International Nuclear Information System (INIS)

The existence of the physical elementary energy bands describing the Davydov splitting was demonstrated in the energy spectra of the layered orthorhombic In4Se3 crystal. It was confirmed that the physical elementary energy bands are related to the exactly determined Wyckoff position in the unit cell, where the maximum of the valence electron density is localized. By means of ab initio calculations, the dispersion laws with the low-energy non-parabolicity were obtained for electrons and holes of the In4Se3 crystal. The reasons for such a dispersion law to occur in In4Se3 are discussed as well as its similarity to the dispersion law for holes in the ? -InSe crystal under pressure. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

2006-03-01

214

Inorganic electron transfer: sharpening a fuzzy border in mixed valency and extending mixed valency across supramolecular systems.  

Science.gov (United States)

This article describes research from our laboratory on the chemistry and spectroscopic properties of inorganic mixed-valence complexes. After a brief review of the seminal work of Taube, Creutz, Day, Robin, Hush, and others in the 1960s and the confounding efforts to identify the borderline between class II and III mixed-valence systems in the 1990s and early 2000s, we describe our first experiments to observe and analyze the coalescence of ?(CO) band shapes in the 1D IR spectra of mixed-valence complexes of the type {[Ru3O(OAc)6(CO)(L)]2-BL}(-), where L = a pyridyl ligand and BL = pyrazine or 4,4'-bipyridine, to estimate rate constants of intramolecular electron transfer (ET). The strong involvement of the bridging ligands in mixed-valence complexes of this type was first identified in the appearance of totally symmetric vibrational modes of pyrazine bridging ligands in the IR because of strong vibronic coupling within a three-state metal cluster-bridge-metal cluster model. Application of the Brunschwig-Creutz-Sutin semiclassical three-state model of mixed valency accounts well for the appearance of two intervalence charge-transfer bands that are observed in the near-IR region of the electronic absorption spectra of these mixed-valence ions. The direct spectroscopic observation of "mixed-valence isomers", the two alternate charge distributions of a mixed-valence ion, are described. The equilibrium constants of mixed-valence isomers provide quantitative thermodynamic estimates of the electronic coupling, H(ab). The extent of delocalization in many of the mixed-valent bridged dimers of triruthenium clusters produces unusual behavior, especially rate constants for ET that are independent of normal solvent reorganization energies but do depend on solvent dynamical dipolar reorientation times. The strong dependence of rates on solvent dynamics is also found to produce a non-Arrhenius dependence of ET rate constants on temperature, faster rates in frozen solutions compared to fluid solutions. The studies of these mixed-valence systems have provided generalized guidelines for establishing where a particular mixed-valence system lies along the class II/III delocalization transition, and they have increased our understanding of the ET dynamics at the delocalization threshold. PMID:23320756

Kubiak, Clifford P

2013-05-20

215

Valence electron shake-up in photoelectron spectra  

International Nuclear Information System (INIS)

Valence electron shake-up phenomena are important in ultraviolet photoelectron spectroscopy because extra bands are formed which may complicate the interpretation, and because the primary bands are displaced in energy which may invalidate comparisons with calculated ionization energies. It would be of value during experimental work to have access to simple methods for an approximate estimation of these effects. Such methods are presented here together with applications to the photoelectron spectra of ethylene and benzene. (orig.)

1980-01-01

216

Plasmon dispersion in semimetallic armchair graphene nanoribbons  

Science.gov (United States)

The dispersion relations for plasmons in intrinsic and extrinsic semimetallic armchair graphene nanoribbons (acGNR) are calculated in the random phase approximation using the orthogonal pz-orbital tight-binding method. Our model predicts new plasmons for acGNR of odd atomic widths, N=5,11,17,... Our model further predicts plasmons in acGNR of even atomic widths, N=2,8,14,..., related to those found using a Dirac continuum model but with different quantitative dispersion characteristics. We find that the dispersion of all plasmons in semimetallic acGNR depends strongly on the localization of the pz electronic wavefunctions. We also find that overlap integrals for acGNR behave in a more complex way than predicted by the Dirac continuum model, suggesting that these plasmons will experience a small damping for all q?0. Plasmons in extrinsic semimetallic acGNR with the chemical potential in the lowest (highest) conduction (valence) band are found to have dispersion characteristics nearly identical to their intrinsic counterparts, with negligible differences in dispersion arising from the slight differences in overlap integrals for the interband and intraband transitions.

Andersen, David R.; Raza, Hassan

2012-02-01

217

Micro-Valences: Perceiving Affective Valence in Everyday Objects  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Perceiving the affective valence of objects influences how we think about and react to the world around us. Conversely, the speed and quality with which we visually recognize objects in a visual scene can vary dramatically depending on that scene’s affective content. Although typical visual scenes contain mostly “everyday” objects, the affect perception in visual objects has been studied using somewhat atypical stimuli with strong affective valences (e.g., guns or roses). Here we explor...

Lebrecht, Sophie; Barrett, Lisa Feldman; Tarr, Michael J.; Bar, Moshe

2012-01-01

218

Pressure Induced Valence Transitions in f-Electron Systems  

CERN Multimedia

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

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

2006-01-01

219

PARTICLE-SIZE-INDUCED VALENCE CHANGES IN SAMARIUM CLUSTERS  

Energy Technology Data Exchange (ETDEWEB)

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

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

1981-05-01

220

Towards a typology of valency  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Grammatical relations, particularly the notions of transitivity, case marking, ergativity, passive and antipassive have been a favourite subject of typological research during the last decade, but surprisingly, the notion of valency has been of marginal interest in cross-linguistic studies, though the syntactic and semantic status of participants is, to a great extent, determined by the relational properties of the verb. Valency is the property of the verb which determines the obligatory and ...

Mosel, Ulrike; Drossard, Werner

1984-01-01

 
 
 
 
221

Nonlinear hopping induced valence fluctuations  

International Nuclear Information System (INIS)

A model is introduced to describe intermediate valence states: any f-electron hopping process influences the hopping probability for other f-electrons. This nonlinear coupling may result from higher order interaction terms between f-electrons and conduction electrons or from a strong coupling to the lattice and its dynamics. As a function of coupling parameters and temperature several phase transitions are possible characterized by nonintegral valence changes. A possible relation to the ?-? phase transition in cerium is discussed. (orig.)

1987-01-01

222

Ocular dispersion  

Science.gov (United States)

Spectrally resolved white-light interferometry was used to measure the wavelength dependence of refractive index (i.e., dispersion) for various ocular components. The accuracy of the technique was assessed by measurement of fused silica and water, the refractive indices of which have been measured at several different wavelengths. The dispersion of bovine and rabbit aqueous and vitreous humor was measured from 400 to 1100 nm. Also, the dispersion was measured from 400 to 700 nm for aqueous and vitreous humor extracted from goat and rhesus monkey eyes. For the humors, the dispersion did not deviate significantly from water. In an additional experiment, the dispersion of aqueous and vitreous humor that had aged up to a month was compared to freshly harvested material. No difference was found between the fresh and aged media. An unsuccessful attempt was also made to use the technique for dispersion measurement of bovine cornea and lens. Future refinement may allow measurement of the dispersion of cornea and lens across the entire visible and near-infrared wavelength band. The principles of white- light interferometry including image analysis, measurement accuracy, and limitations of the technique, are discussed. In addition, alternate techniques and previous measurements of ocular dispersion are reviewed.

Hammer, Daniel X.; Noojin, Gary D.; Thomas, Robert J.; Stolarski, David J.; Rockwell, Benjamin A.; Welch, Ashley J.

1999-06-01

223

Fermi surface and electron dispersion of PbTe doped with resonant Tl impurity from KKR-CPA calculations  

Science.gov (United States)

We present results of a detailed study on the electron dispersions and Fermi surface of lead telluride doped with 2% of thallium, which is a resonant impurity in PbTe. Using the Korringa-Kohn-Rostoker method with the coherent potential approximation (KKR-CPA), Bloch spectral functions (BSFs), which replace the dispersion relations in alloys, are calculated, and BSF intensity maps over the Brillouin zone (alloy Fermi surface cross sections) are presented. It is shown that, close to the valence band edge, Tl does not create an isolated impurity band, but due to its resonant character, strongly disturbs the host electronic bands, leading to the disappearance of sharp and well-defined electronic energy bands. The consequences of this effect on the transport properties are discussed and a qualitative explanation for the improvement in the thermoelectric properties of PbTe:Tl is suggested.

Wiendlocha, Bartlomiej

2013-11-01

224

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)

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.

Sidiek, Erkin; Balasubramanian, Kunjithapatham

2007-01-01

225

A Multidimensional Measure of Work Valences  

Science.gov (United States)

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…

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

2012-01-01

226

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

Energy Technology Data Exchange (ETDEWEB)

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.

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

227

Mixed valence interactions in di-?-oxo bridged manganese complexes  

International Nuclear Information System (INIS)

The complexes [(L)2MnO2Mn(L)2]3+ where L = 2,2'-bipyridine or 1,10-phenanthroline, have been examined, in addition to the corresponding (IV, IV) complex of phenanthroline. The crystal structure of the mixed valence (III, IV) compound with L = 2,2'-bipyridine demonstrated that this complex has deeply trapped valences, corresponding to class II in the classification of Robin and Day since the bond lengths differ considerably about the manganese ions. We have examined the electronic spectrum of the (III, IV) complexes and observed broad bands in the near infrared which we have assigned to the mixed valence band expected for a class II system. No comparable band is observed for the phenanthroline (IV, IV) complex. Lowering the pH of (III, IV) dimer solutions reversibly cleaves the antiferromagnetically coupled (III, IV) dimers as determined by the increase in solution magnetic susceptibility; loss of the near infrared band occurs with dimer cleavage, although the remainder of the visible spectrum is substantially unaltered. Both absorbance and solution magnetic susceptibility changes with pH are reversible. The solvent dependence of the near infrared band is small but apparently opposite to that predicted by Hush's theory. However, the bandwidths agree well with those predicted from Hush's treatment (e.g., 0.53 ?m-1 predicted, 0.46 ?m-1 observed). A band at 688 cm-1 in the infrared spectrum of the bipyridyl (III, IV) dimer is shifted by isotopic substitution with 18O, and has been assigned to one of the stretching modes of the Mn2O2 bridge; analogous bands are found for the phenanthroline (III, IV) and -(IV, IV) complexes. Pertinent aspects of the electrochemistry are also discussed

1977-09-28

228

Similarities of the band structure of In{sub 4}Se{sub 3} and InSe under pressure and peculiarities of the creation of the band gap  

Energy Technology Data Exchange (ETDEWEB)

The existence of the physical elementary energy bands describing the Davydov splitting was demonstrated in the energy spectra of the layered orthorhombic In{sub 4}Se{sub 3} crystal. It was confirmed that the physical elementary energy bands are related to the exactly determined Wyckoff position in the unit cell, where the maximum of the valence electron density is localized. By means of ab initio calculations, the dispersion laws with the low-energy non-parabolicity were obtained for electrons and holes of the In{sub 4}Se{sub 3} crystal. The reasons for such a dispersion law to occur in In{sub 4}Se{sub 3} are discussed as well as its similarity to the dispersion law for holes in the {beta} -InSe crystal under pressure. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

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

2006-03-01

229

Valence Bond Theory and Superconductivity.  

Science.gov (United States)

Two necessary criteria for a theory of superconductivity are a phase coherence of the wave function and an attractive electron-electron interaction. We review how the BCS theory achieves these criteria and then show how a valence bond wave function can al...

R. P. Messmer R. B. Murphy

1987-01-01

230

Valency Configuration of Transition Metal Impurities in ZnO  

CERN Multimedia

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

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

2006-01-01

231

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

CERN Multimedia

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

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

2003-01-01

232

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

We present both theoretical ab-initio results within the Hedin's GW approximation and experimental angle-resolved photoemission and scanning tunneling spectroscopy measurements on TiSe?. 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 k?...

Cazzaniga, M.; Cercellier, H.; Holzmann, M.; Monney, Claude; Aebi, Philipp; Onida, Giovanni; Olevano, V.

2012-01-01

233

XPS band emission and density of states of CoAl  

International Nuclear Information System (INIS)

An investigation of the electronic structure of an ordered equimolar CoAl alloy is discussed on the basis of a recently calculated self-consistent band structure and a measured XPS valence band spectrum. The valence band and core lines of CoAl by XPS are reported for the first time. Experimental and calculated values of the spectra have been compared

1981-11-01

234

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

Science.gov (United States)

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

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

2012-05-01

235

The method of thermodynamic perturbation in the intermediate valence problem  

International Nuclear Information System (INIS)

The effect of hybridization on the free energy and the magnetic susceptibility X of intermediate valence compounds is studied employing the method of thermodynamic perturbation in second order. This method is applied to a lattice with a variable concentration c of impurities that are described by the Anderson model. A non-divergent logarithmic correction appears when the chemical potential ? sub(e) is not in the middle of the rectangular conduction band, and it is shown by a different method that this correction is also present in the exactly soluble case of independent electrons with hybridization. When c=1 the logarithmic term is cancelled by a term proportional to (?_2? sub(e)/?H_2). By thermodynamic arguments it is shown that this concentration dependent contribution coincides with a different expression that was recently obtained by another approach. The contribution of the third state of charge to X is discussed; this state is usually neglected in intermediate valence models. (Author)

1982-01-01

236

Model valence-fluctuation systems  

International Nuclear Information System (INIS)

Variational ground-state wavefunctions are presented and optimized for two model valence-fluctuation systems, based on Anderson lattice Hamiltonians in the U ? infinite limit. Although these wavefunctions are approximate, they are treated in an essentially exact manner. The (f0, f1; n = 1) system has an intuitively reasonable ground-state susceptibility, while the (f1, f2; n = 2) system is found to exhibit an insulating gap. Due to their different crystal symmetries, this gap should be realized in SmB6 but not in SmS. (orig.)

1980-01-01

237

Band structure of UO/sub 2/: an angle resolved and resonant photoemission study  

Energy Technology Data Exchange (ETDEWEB)

A detailed study of angle resolved photoemission of UO/sub 2/ <100> in the normal emission configuration is presented. The results are compared to a semirelativistic LAPW band calculation with the actual calculated empty bands used in the data reduction. Excellent agreement is found with calculations both for filled states as well as critical points in the empty states with no adjustment of bands. f-p hybridization is found at the leading edge of the valence band and not at the bottom of the valence band. p-d hybridization is found throughout the valence bands.

Arko, A.J.; Koelling, D.D.; Boring, A.M.; Ellis, W.P.; Cox, L.E.

1985-10-01

238

Mixed valence model for superconductivity  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english Superconductivity often occurs in crystals with one active electron per site with charge density wave (CDW) or spin density wave (SDW) as 'mother state'. It is proposed that superconductivity is possible when the differences in equilibrium geometry and energy between the diabatic CDW and SDW states [...] are so small that there is interaction between them via the zero point vibrations. Electron pairing in real space is directly related to oxidation states being different in two 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.

Sven, Larsson.

239

Intermediate band solar cells  

Science.gov (United States)

Intermediate band (IB)solar cells aim to exploit the energy of below bandgap energy photons in solar cells. They are based in a material that, in addition to the conventional conduction and valence bands, have an electronic band (named intermediate band) located inside the bandgap and separated from the conduction and valence band by a null density of states. The theoretical limiting efficiency of these cells is equivalent to that of a triple junction solar cell (63.2% at maximum concentration) but requiring a single material instead. Several approaches are being followed worldwide to take to practice this concept. They can be classified into ``bulk'' or ``quantum dot'' approaches. In the ``bulk'' approach, the IB emerges from the insertion of impurities that can be incorporated inside the semiconductor at high densities (beyond the Mott's transition) without forming clusters and that typically would produce deep centers at low densities. Examples experimentally pursued worldwide under this approach are the following material systems: Si:Ti, InGaN:Mn, ZnTe:O and Cu(InGa)S2:Ti. In the ``quantum dot'' approach, the IB arises from the quantum confinement of the electrons usually in the conduction band. This system has allowed in the past to demonstrate some of the principles of operation of the IB solar cells on the basis mainly of the InAs/GaAs system. This system, however, is not optimum for IB solar cell operation and the challenge is now to find a feasible combination of materials that allow both to introduce the confined energy level at the appropriate position as well as to do it at the time the number of additional energy levels introduced between the intermediate band and the conduction band is minimized.

Marti, Antonio

2010-03-01

240

A rapid, one-step, variable-valence metal ion assisted reduction method for graphene oxide  

Energy Technology Data Exchange (ETDEWEB)

A process characterized by variable-valence metal (Mn, Co, Ni, etc) ion assisted reduction of graphene oxide with NaBH{sub 4} heated at 90 deg. C for a short period of 1 h was developed to produce reduced graphene oxide (RGO), and the RGO sheets exhibited a homogeneous and stable dispersibility in water.

Chen Caifeng; Chen Tingting; Wang Hongling; Sun Genban; Yang Xiaojing, E-mail: yang.xiaojing@bnu.edu.cn [College of Chemistry, Beijing Normal University, Beijing 100875 (China)

2011-10-07

 
 
 
 
241

Band structure of superlattice with ?-like potential  

International Nuclear Information System (INIS)

Band structure of superlattice with ?-like potential has been calculated taking into account interaction of carriers of different kinds. Superlattices of semiconductors with degenerated valence band and zero-gap semiconductors have been considered. For the latter semimetal-semiconductor transition has been obtained. (author). 8 refs, 1 fig

1993-01-01

242

Electronic polaron effects in mixed valence and heavy fermion materials  

International Nuclear Information System (INIS)

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

1992-07-20

243

Valence Bond States: Link models  

CERN Document Server

An isotropic anti-ferromagnetic quantum state on a square lattice is characterized by symmetry arguments only. By construction, this quantum state is the result of an underlying valence bond structure without breaking any symmetry in the lattice or spin spaces. A detailed analysis of the correlations of the quantum state is given (using a mapping to a 2D classical statistical model and to the non-linear sigma model) as well as the results of numerical treatments (regarding exact diagonalization and variational methods). Finally, the physical relevance of the model is motivated. A comparison of the model to known anti-ferromagnetic Mott-Hubbard insulators is given by means of the two-point equal-time correlation function obtained i) numerically from the suggested state and ii) experimentally from neutron scattering on cuprates in the anti-ferromagnetic insulator phase.

Rico, E; Montangero, S; Moran, N; Pirvu, B; Vala, J; Briegel, H J

2008-01-01

244

Biaxial strain effects on the electronic band structure of wurtzite InxGa1-xN alloys using first-principles calculations  

Science.gov (United States)

Numerical simulation based on first-principles calculations is applied to study the energy band structural characteristics and the band-gap properties of wurtzite InGaN. The results show that the direct band gap, the band gap bowing parameter, the width of valence band, and the width of top valence band increase with compressive strain and decrease with tensile strain. The biaxial strain effect on the indirect band gap is little. In general, there is a larger band gap bowing parameter and larger strain-induced band gap bowing variation in Ga-rich alloys. In addition, the direct band gap, the indirect band gap, the width of valence band, and the width of top valence band decrease with increase of indium composition. Wurtzite InGaN remains the characteristic of a direct band gap material under biaxial stress.

Liou, Bo-Ting; Wu, Bang-Yenn; Kuo, Yen-Kuang

2012-02-01

245

DERIVATION AND SIGNIFICANCE OF VALENCE MOLECULAR CONNECTIVITY  

Science.gov (United States)

The physical basis for valence molecular connectivity was studied. The sigma sup upsilon and sigma values are cardinal numbers describing the electronic structure of atoms in their valence states. The value (sigma sup upsilon) + (sigma) describes the volume of a bonding atom whil...

246

Attosecond Time-Resolved Photoelectron Dispersion and Photoemission Time Delays  

Science.gov (United States)

We compute spectrograms and relative time delays for laser-assisted photoemission by single attosecond extreme ultraviolet pulses from valence band (VB) and 2p core levels (CLs) of a Mg(0001) surface within a quantum-mechanical model. Comparing the time-dependent dispersion of photoelectron (PE) wave packets for VB and CL emission, we find striking differences in their dependence on the (i) electron mean free path (MFP) in the solid, (ii) screening of the streaking laser field, and (iii) chirp of the attosecond pulse. The relative photoemission delay between VB and 2p PEs is shown to be sensitive to the electron MFP and screening of the streaking laser field inside the solid. Our model is able to reproduce a recent attosecond-streaking experiment [S. Neppl et al., Phys. Rev. Lett. 109, 087401 (2012)], which reveals no relative streaking time delay between VB and 2p PEs.

Liao, Q.; Thumm, U.

2014-01-01

247

Band structure of CdTe-ZnTe superlattice  

International Nuclear Information System (INIS)

We perform an empirical tight-binding band structure calculation for the superlattice CdTe-ZnTe. We examine the effect of strain and valence band offset on it. We find that the 6% lattice mismatch causes strain to play an important role. The trend of the superlattice band gap for all widths considered is to decrease as the valence band offset increases. We have found two interface states not reported before. This is our main result. They lie in energy about 100 meV above the valence band edge. Since this energy is about equal to the difference between our calculated superlattice band gap and the value reported experimentally, we claim that optical absorption is measuring the transitions from these interface states to the conduction band. New more detailed experiments could settle this interesting problem. (author). 8 refs, 2 figs, 2 tabs

1988-01-01

248

Band offsets in III-nitride heterostructures  

International Nuclear Information System (INIS)

We present a theoretical investigation of band offsets in GaN-based group III-nitride ternary/binary heterostructures with zinc blende structure. The band offsets in InGaN/GaN and AlGaN/GaN heterostructures were studied using the recently proposed extended sp3 tight binding model (Uenlue H 2001 Phys. Status Solidi. b 223 195). Simulations show a small valence band offset in AlGaN/GaN heterostructure and large valence band offset in the InGaN/GaN heterostructure. Furthermore, the tensile strain in AlGaN leads to positive bowing of the conduction band offsets in AlGaN/GaN heterostructure, and the compressive strain in InGaN leads to negative bowing of conduction band offsets in InGaN/GaN heterostructure as a function of composition. Good agreement is found between predictions and experiment. (author)

2002-04-07

249

Intensity redistribution of bending and stretching Raman scattering bands in water upon degassing and crystallisation  

International Nuclear Information System (INIS)

It is established for the first time that the intensities of deformation and valence Raman scattering (RS) bands in water vary oppositely in the processes of degassing and crystallising. Water degassing shifts the centre of a valence OH band to higher frequencies by approximately 2 cm-1, which points to a reduced contribution of structural complexes to the RS spectrum. (letters)

2011-01-24

250

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

Science.gov (United States)

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.

Zhang, Z. Y.; Si, M. S.; Wang, Y. H.; Gao, X. P.; Sung, Dongchul; Hong, Suklyun; He, Junjie

2014-05-01

251

Modified sf model for mixed-valence Eu chalcogenides  

International Nuclear Information System (INIS)

EuO exhibits at room temperature a pressure-induced metal-insulator transition of first order into a mixed-valence phase (psub(c) approximately equal to 300 kbar), which is followed by a structural NaCl-CsCl transition at about 400 kbar. For EuS and EuSe only the structural transitions are observed. A modified sf model is proposed for describing the mixed valency in the ferromagnetic semiconductors EuO, EuS and EuSe. It turns out that the temperature-dependent shift of the conduction band edge, occurring below Tsub(C) due to the sf exchange interaction, drives the metal-insulator transition point to substantially lower pressure values. As a consequence of the dynamic interplay between the red shift of the band edge and the 'dilution' of the Heisenberg magnet, caused by f electron fluctuations, the electronic phase transitions change from first to second order with decreasing temperature. At T = O the following critical regions are found. EuO, 200-260 kbar; EuS, 130-160 kbar; EuSe, 125-150 kbar. For EuS the electronic collapse happens in the low-temperature region clearly before the NaCl-CsCl transition and should therefore be observable as in EuO. (author)

1982-02-10

252

Valence-fluctuation mechanism for cuprate superconductivity  

International Nuclear Information System (INIS)

The authors explore the concept that the above-Tc state is a normal Fermi liquid with strong correlations of the type found in valence-fluctuation and heavy-fermion materials. Experimental evidence and theoretical arguments for this phase are presented. Using an Anderson lattice model Hamiltonian, and a variational many-body formalism, the finite-U mechanism for s-like pairing is examined in detail. At the mean field or (1/N)0 level of approximation, the pairing tendency is strongly opposed by a magnetic tendency arising from a Gutzwiller version of hybridization renormalization. Pairing does not seem possible for realistic Hamiltonian parameters. This finite-U treatment has, however, now been extended to the (1/N)1 level of approximation. The lattice aspect is found to play a major and unexpected role here, leading to strong suppression of the magnetic tendency. This refined treatment is now found to provide adequate pairing attraction, for reasonable Hamiltonian parameters. Superconductivity is found only when the charge transfer energy ?CT is quite large, ?CT approx-gt U, but there is evidence that ?CT is indeed of this magnitude in the cuprate materials. Adequate band narrowing and a very short coherence length are also obtained, in reasonable agreement with experiment. The quasiparticle interaction at the Fermi surface is strongly repulsive. This provides a reasonable source for the large and linear resistivity, as well as for other aspects of marginal-Fermi-liquid phenomenology. Evidence is found for a strong reduction of Tc due to pair-breaking by the quasiparticle scattering

1994-08-30

253

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.)

1982-01-01

254

Valence fluctuation : experimental investigations using nuclear techniques  

International Nuclear Information System (INIS)

In the recent years a great deal of research has been carried out on the properties of rare earth systems with particular reference to SmS and certain solid solutions of SmS which exhibit mixed valence states. Three types of nuclear based investigations viz. X-ray induced electron emission spectroscopy, Moessbauer spectroscopy and positron annihilation spectroscopy are carried out on the valence fluctuations and some results obtained on the above mentioned rare earth systems are reported. The approach to connect the positron experiments with the physics of mixed valence systems is outlined. Some basic unresolved questions that arise in this regard are discussed. (A.K.)

1978-12-31

255

Efficient hole transport model in warped bands for use in the simulation of Si/SiGe MOSFETs  

Digital Repository Infrastructure Vision for European Research (DRIVER)

An analytical geometric model for the valence band in strained and relaxed Si1-xGex is presented, which shows good agreement with a 6-band k·p analysis of the valence band. The geometric model allows us to define an effective mass tensor for the warped valence band structure. The model also has applications in the study of III-V semiconductors, and could aid in the interpretation of cyclotron resonance experiments in these bands. A warped three-band Monte Carlo simulation has been developed ...

Watling, J. R.; Asenov, A.; Barker, J. R.

1998-01-01

256

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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...

Luque Lo?pez, Antonio; Marti? Vega, Antonio; Briones Ferna?ndez-pola, Fernando; Postigo, Pablo Aitor

2008-01-01

257

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

CERN Document Server

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

Makkonen, I; Puska, M J

2004-01-01

258

Action versus valence in decision making.  

Science.gov (United States)

The selection of actions, and the vigor with which they are executed, are influenced by the affective valence of predicted outcomes. This interaction between action and valence significantly influences appropriate and inappropriate choices and is implicated in the expression of psychiatric and neurological abnormalities, including impulsivity and addiction. We review a series of recent human behavioral, neuroimaging, and pharmacological studies whose key design feature is an orthogonal manipulation of action and valence. These studies find that the interaction between the two is subject to the critical influence of dopamine. They also challenge existing views that neural representations in the striatum focus on valence, showing instead a dominance of the anticipation of action. PMID:24581556

Guitart-Masip, Marc; Duzel, Emrah; Dolan, Ray; Dayan, Peter

2014-04-01

259

Elastic properties of intermediate valence, Kondo and stable valence RAl_2 compounds  

International Nuclear Information System (INIS)

Measurements of ultrasonic velocities and pressure volume behavior show that, compared to integral valence rare earth dialuminides, the intermediate valence compound, YbAl_2, is mechanically soft and the Kondo compound, CeAl_2, is much less so. These results show that in the case of intermediate valence the degenerate electronic configurations strongly effect the elastic properties while for the Kondo case, where the electronic configurations are nondegenerate, there is little effect. (author)

1982-01-01

260

Elastic properties of intermediate valence, Kondo and stable valence RAl/sub 2/ compounds  

Energy Technology Data Exchange (ETDEWEB)

Measurements of ultrasonic velocities and pressure volume behavior show that, compared to integral valence rare earth dialuminides, the intermediate valence compound, YbAl/sub 2/, is mechanically soft and the Kondo compound, CeAl/sub 2/, is much less so. These results show that in the case of intermediate valence the degenerate electronic configurations strongly effect the elastic properties while for the Kondo case, where the electronic configurations are nondegenerate, there is little effect.

Penney, T.; Barbara, B.; Plaskett, T.S.; King, H.E. Jr.; LaPlaca, S.J. (IBM Watson Research Center, Yorktown Heights, NY (USA))

1982-11-01

 
 
 
 
261

Hofstadter butterflies for flat bands  

CERN Document Server

Hofstadter's diagram, or the energy spectrum against the magnetic field in tight-binding systems, is obtained for the models having flat (dispersionless) one-electron band(s) that have originally been proposed for itinerant spin ferromagnetism. Magnetic fields preserve those flat bands that arise from a topological reason, while dispersions emerge in a singular manner for the flat bands arising from interference, implying an anomalous orbital magnetism.

Aoki, H; Matsumura, H; Aoki, Hideo; Ando, Masato; Matsumura, Hajime

1996-01-01

262

Superdeformed band in 130Ce  

International Nuclear Information System (INIS)

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

1997-01-01

263

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

Science.gov (United States)

Electronic, magnetic, and transport properties of the filled platinum-germanium skutterudite CePt?Ge?? are investigated. High resolution x-ray absorption spectroscopy measurements at the cerium L(III) edge demonstrate that CePt?Ge?? in this compound has a temperature-independent valence close to three. However, magnetic susceptibility, thermopower, Hall effect, and electronic specific heat reveal a broad maximum at Tmax D 65-80 K, suggesting the presence of valence fluctuations. The Sommerfeld coefficient ? = 105 mJ mol?¹ K?², deduced from specific heat, indicates moderately enhanced band masses for CePt?Ge??. We discuss these findings and conclude that CePt?Ge?? represents a system at the border between intermediate valence (IV) and Kondo lattice behavior. In addition, the lattice specific heat and the thermal conductivity are discussed with respect to the vibrational dynamics of Ce in the [Pt?Ge??] framework. PMID:22056917

Gumeniuk, R; Kvashnina, K O; Schnelle, W; Nicklas, M; Borrmann, H; Rosner, H; Skourski, Y; Tsirlin, A A; Leithe-Jasper, A; Grin, Yu

2011-11-23

264

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

1990-01-01

265

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

Directory of Open Access Journals (Sweden)

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

Michael Snodgrass

2012-10-01

266

Valence mixing in rare earth compounds  

International Nuclear Information System (INIS)

The concepts of ''fast'' and ''slow'' time scale valence measurements are emphasized by a comparison of L/sub III/ absorption and Mossbauer effect measurements on the temperature induced valence change in EuPd/sub 2/Si/sub 2/. Further the authors show how synchrotron radiation based L/sub III/ measurements of the Ce-valence state can be used to demonstrate electronic structure trends under wide changes in chemical environment. The purpose of this paper is to provide an introduction to researchers in the People's Republic of China to the field of mixed valent rate earth compounds. They hope to illustrate some of the basic concepts in this field, how the field is contributing to the overall insight into the chemical physics of solids and finally how synchrotron radiation measurements in particular are playing a key role in this field

1985-01-01

267

Valence-quark distributions in the pion  

CERN Document Server

We calculate the pion's valence-quark momentum-fraction probability distribution using a Dyson-Schwinger equation model. Valence-quarks with an active mass of 0.35 GeV carry 70% of the pion's momentum at a resolving scale q0 = 0.57 GeV=1/(0.35 fm). The shape of the calculated distribution is characteristic of a strongly bound system and, evolved to q=2 GeV, it yields moments in agreement with lattice and phenomenological estimates, and valence-quarks carrying 49% of the pion's momentum. However, pointwise there is a discrepancy between our calculated distribution and that hitherto inferred from parametrisations of extant pion-nucleon Drell-Yan data.

Hecht, M B; Schmidt, S M

2001-01-01

268

Molybdenum Valence in Basaltic Silicate Melts  

Science.gov (United States)

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.

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

2010-01-01

269

Band Structure and Effective Masses of ZnMgO  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We analyze the influence of the Mg concentration on several important properties of the band structure of ZnMgO alloys in wurtzite structure using ab initio calculations. For this purpose, the band structure for finite concentrations is defined in terms of the Bloch spectral density, which can be calculated within the coherent potential approximation. We investigate the concentration dependence of the band gap and the crystal-field splitting of the valence bands. The effecti...

Franz, Christian; Giar, Marcel; Heinemann, Markus; Czerner, Michael; Heiliger, Christian

2013-01-01

270

Topological crystalline Kondo insulator in mixed valence ytterbium borides.  

Science.gov (United States)

The electronic structures of two mixed valence insulators YbB6 and YbB12 are studied by using the local density approximation supplemented with the Gutzwiller method and dynamic mean field theory. YbB6 is found to be a moderately correlated Z2 topological insulator, similar to SmB6 but having much larger bulk band gap. Notably, YbB12 is revealed to be in a new novel quantum state, strongly correlated topological crystalline Kondo insulator, which is characterized by its nonzero mirror Chern number. The surface calculations find an odd (three) and an even (four) number of Dirac cones for YbB6 and YbB12, respectively. PMID:24483913

Weng, Hongming; Zhao, Jianzhou; Wang, Zhijun; Fang, Zhong; Dai, Xi

2014-01-10

271

Topological Crystalline Kondo Insulator in Mixed Valence Ytterbium Borides  

Science.gov (United States)

The electronic structures of two mixed valence insulators YbB6 and YbB12 are studied by using the local density approximation supplemented with the Gutzwiller method and dynamic mean field theory. YbB6 is found to be a moderately correlated Z2 topological insulator, similar to SmB6 but having much larger bulk band gap. Notably, YbB12 is revealed to be in a new novel quantum state, strongly correlated topological crystalline Kondo insulator, which is characterized by its nonzero mirror Chern number. The surface calculations find an odd (three) and an even (four) number of Dirac cones for YbB6 and YbB12, respectively.

Weng, Hongming; Zhao, Jianzhou; Wang, Zhijun; Fang, Zhong; Dai, Xi

2014-01-01

272

Towards wireless emotional valence detection from EEG.  

Science.gov (United States)

Intelligent affective computers can have many medical and non-medical applications. However today's affective computers are limited in scope by their transferability to other application environments or that they monitor only one aspect of physiological emotion expression. Here, the use of a wireless EEG system, which can be implemented in a body area network, is used to investigate the potential of monitoring emotional valence in EEG, for application in real-life situations. The results show 82% accuracy for automatic classification of positive, negative and neutral valence based on film clip viewing, using features containing information on both the frequency content of the EEG and how this changes over time. PMID:22254773

Brown, Lindsay; Grundlehner, Bernard; Penders, Julien

2011-01-01

273

Valence states of actinides in synthetic monazites  

International Nuclear Information System (INIS)

The valence states of various actinides doped into the lanthanide orthophosphates (LnPO4) have been investigated. Actinide-doped LnPO4 single crystals were grown by means of a flux technique and the actinide valence states were determined by optical absorption spectrophotometry. Radiation damage effects were also studied in these systems. The lanthanide orthophosphates are found in nature in the form of the mineral monazite and synthetic analogs of this substance represent a promising primary containment medium for the isolation of high-level nuclear wastes

1980-11-20

274

Mixed valence quasiparticles in CuO{sub 2} planes  

Energy Technology Data Exchange (ETDEWEB)

The motion of a single hole doped to a CuO{sub 2} plane of a high temperature superconductor is described by a spin-fermion model which treats explicitly the hybridization with the upper Hubbard band. One finds that sectors of Zhang-Rice bound states coexist with reasonably damped oxygen and copper-like quasiparticles, with a considerable transfer of the spectral weight to the upper Hubbard band. The oxygen states have small dispersions and can be identified in the angle-resolved photoemission experiments for Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8}. (author) 12 refs, 2 figs

Bala, J.; Oles, A.M. [Institute of Physics, Jagiellonian University, Cracow (Poland)

1997-12-31

275

Continuity chords of bands and band structure of semiconducting compounds with TlSe-type structure  

International Nuclear Information System (INIS)

All the simple band representations of the space group D/sub 4h//sup 18/ are constructed. Using the concept of band representation and continuity chord, developed by Zak, it is shown that for semiconducting compounds with TlSe-type structure it is possible to extract some useful information about the character of localization of basic functions, belonging to the same band, i.e. in fact about the nature of the chemical bond responsible for the observed band structure. In particular, from the comparison with a calculated band structure of the ternary semiconducting compounds with TlSe-type structure, it is shown that the lower four valence bands correspond to s-states of chalcogen atoms. Two following valence bands correspond to s-states of three-valent cations. Then, a large group of ten valence bands is produced by p/sub z/-states of chalcogen atoms and p/sub x/-, p/sub y/-, p/sub z/-states of three-valent cations. (author)

1985-09-01

276

Unstable valence rare earths ion implanted into transition metals: Valence variation studies  

International Nuclear Information System (INIS)

The technique of ion implantation is applied to study the problem of valence instabilities of Ce and Eu in transition-metal hosts. L3 x-ray absorption spectroscopy measurements are used to probe the rare-earth valence state in these materials. Typical extreme valence variations are illustrated with Y, Ti, and Pd hosts. The important question of identifying extrinsic oxidation of the rare-earth implant is addressed in detail. The signatures of rare earth oxidation in the x-ray spectra of both bulk compound and implanted materials are discussed using specific examples

1988-04-15

277

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

Directory of Open Access Journals (Sweden)

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.

Yarzhemsky Victor G.

2012-01-01

278

Gossamer Superconductor, Mott Insulator, and Resonating Valence Bond State in Correlated Electron Systems  

CERN Document Server

Gutzwiller variational method is applied to an effective two-dimensional Hubbard model to examine the recently proposed gossamer superconductor by Laughlin. The ground state at half filled electron density is a gossamer superconductor for smaller intra-site Coulomb repulsion U and a Mott insulator for larger U. The gossamer superconducting state is similar to the resonant valence bond superconducting state, except that the chemical potential is approximately pinned at the mid of the two Hubbard bands away from the half filled.

Zhang, F C

2002-01-01

279

Optoelectronic Properties of InAlN/GaN Distributed Bragg Reflector Heterostructure Examined by Valence  

Digital Repository Infrastructure Vision for European Research (DRIVER)

High-resolution monochromated electron energy loss spectroscopy (EELS) at subnanometric spatial resolution and <200 meV energy resolution has been used to assess the valence band properties of a distributed Bragg reflector multilayer heterostructure composed of InAlN lattice matched to GaN. This work thoroughly presents the collection of methods and computational tools put together for this task. Among these are zero-loss-peak subtraction and nonlinear fitting tools, and theoretical model...

2012-01-01

280

Valence electronic state density in thorium dioxide  

Directory of Open Access Journals (Sweden)

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

Teterin Anton Yu.

2008-01-01

 
 
 
 
281

River Valency at Boscastle County Bridge  

River Valency at Boscastle County Bridge Last updated 15:00 on 07/04/2014 Summary The river level at Boscastle County Bridge is 0.44 metres. This measurement was recorded at 15:00 on 07/04/2014. The typical river level range for this location is between 0.10 metres and 1.00 metres. The highest river…

282

Improved Error Estimate for the Valence Approximation  

CERN Document Server

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

Lee, W

1998-01-01

283

Radial wave functions of valence nucleons  

International Nuclear Information System (INIS)

The potential for radial-shape determination of the atomic nucleus by the investigation of valence-nucleon wave functions using elastic electron scattering from the high-order multipole distribution of the nuclear magnetization density is examined. (U.K.)

1980-01-01

284

The band energy structure of RbKSO4 crystals  

Directory of Open Access Journals (Sweden)

Full Text Available The energy band structure of mechanically free and compressed RbKSO4 single crystals is investigated. It is established that the top of the valence band is located at the D point of the Brillouin zone [k = (0.5, 0.5, 0], the bottom of the conduction band lies at the ? point, and the minimum direct band gap Eg is equal to 5.80 eV. The bottom of the conduction band is predominantly formed by the K s, Li p, Rb s, and Rb p states hybridized with the S p and O p antibonding states. The pressure coefficients of the energy position of the valence and conduction band states and the band gap Eg are determined.

O.V.Bovgyra

2007-01-01

285

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

Science.gov (United States)

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

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

2011-08-19

286

Bond valence analysis of tetragonal zirconias  

Energy Technology Data Exchange (ETDEWEB)

In tetragonal zirconia, the cation is coordinated by two interpenetrating tetrahedra of oxygen ions, implying two different cation-oxygen bond lengths. On substituting the different tetravalent ions Ge, Ti, Sn, and Ce into tetragonal ZrO{sub 2}-2 mol% Y{sub 2}O{sub 3}, the mean value of the shorter cation-anion bond length varies linearly with the concentration of the substituent ion where the bond length increases or decreases depending on whether the substituted ion is larger or smaller than the zirconium ion it replaces. It is argued in this paper that the length of the longer bond is determined by the requirement that the bond valence sum remains constant. In each case the length of the longer bond is determined by the requirement that the bond valence sum remains constant. In each case the length of the longer bond calculated on this basis is in good agreement with the measured bond length (from neutron diffraction), and following small adjustments of the bond valence constants, excellent agreement is obtained. The requirement for the bond valence sum evidently accounts for the physics of the situation, and at the same time the available bond length data allow very precise determination of the bond valence constants of the different ions in the tetragonal zirconia environment. It is shown how these bond length considerations provide an explanation for the variation with composition of oxygen position and lattice parameters in all of the materials considered. Among the interesting features accounted for by this analysis are the increase in cell volume occurring when Zr is replaced by the smaller Sn ion, and slight departures from Vegard`s law observed in the substitution of Zr by Ti.

Hunter, B.A.; Howard, C.J. [Australian Nuclear Science and Technology Organisation, Menai, New South Wales (Australia); Kim, D.J. [Korea Inst. of Science and Technology, Seoul (Korea, Republic of). Ceramics Div.

1999-09-01

287

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

Energy Technology Data Exchange (ETDEWEB)

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.

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

288

The mixed valence phenomenon in compounds of f-electron  

International Nuclear Information System (INIS)

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

1980-01-01

289

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

Science.gov (United States)

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

Li, Keyan; Li, Yanju; Xue, Dongfeng

2012-06-01

290

Electronic band structure of the layered dichalcogenide MoTe2  

International Nuclear Information System (INIS)

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

2007-03-26

291

Theory of Intermediate-Valence States in Sm Compounds  

Science.gov (United States)

The intermediate-valence states of SmB6 and SmSare described in terms of the periodic Anderson model comprised ofthe localized 4f multiplet states 6H5/2 and 7F0 oftwo adjacent configurations 4f5 and 4f6,the wide conduction band states represented by the plane wave functions,and the hybridizations between the 4f and the conduction states.We take hole picture and introduce fermi operators representingthe states of 6H5/2 and a bose operator for the 7F0 singlet for each Sm site.At low temperatures, the bosons form a condensate,and consequently the fermion states hybridize with the conduction-band statesto become itinerant, accompanied with an anisotropic gap structure. The susceptibility is dominated by the Van Vleck contribution fromthe excited 7F1 level of 4f6, while the 6H5/2 states of 4f5gives a small Pauli-type contribution,in good agreement with experimental results.

Hanzawa, Katsurou

1998-09-01

292

Unusual valency and magnetic order in silver nickelates  

Science.gov (United States)

Ag2NiO2 forms as a triangular based layered nickelate, with a structure identical to the well-studied alkali nickelates LiNiO2 or NaNiO2, but with a double layer of Ag between the oxide planes. The metallic intercalant ions give rise to highly unusual valence state for silver: Ag^1/2+. We show that the reason for the underoxidation is that the two silver ions form extremely strong bonding-antibonding bands, pushing the lowest Ag-s derived band beneath the (filled) O p complex. This additionally preserves metallicity down to the lowest measured temperatures and gives rise to complex, competing magnetic interactions. The resulting spin fluctuations may explain the large discrepancy (too large for phonon renormalization) between calculated and measured linear specific heat coefficients. Our calculations do not support a controversial cooperative Jahn-Teller distortion, but a comparison with calculations and experiments for single-layer AgNiO2 suggests that magnetically driven charge disproportionation may instead explain the observed structural transition.

Streltsov, Sergey; Johannes, M. D.; Mazin, I. I.; Khomskii, D. I.

2007-03-01

293

Band structure of FeBO3: Implications for tailoring the band gap of nanoparticles  

Science.gov (United States)

The energy band structure of a transparent, green, room-temperature ferromagnetic FeBO3 has been calculated using density functional theory within the generalized gradient approximation (GGA) and the GGA+U approach. The electronic structure of FeBO3 is predicted to be antiferromagnetic and insulating, both in perfect agreement with available experiments. The predicted band structure, in particular, the shapes of the valence and conduction band edges, provides great insights into tailoring the optical band gap of FeBO3 nanoparticles: for the particle size close to 3 nm, the visible spectral region extends from green up to blue due to quantum confinement.

Shang, Shunli; Wang, Yi; Liu, Zi-Kui; Yang, Chia-En; Yin, Shizhuo

2007-12-01

294

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

Energy Technology Data Exchange (ETDEWEB)

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.

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

2014-01-25

295

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

International Nuclear Information System (INIS)

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

2014-01-25

296

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

Science.gov (United States)

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

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

2012-02-01

297

Theoretical investigations on valence vibronic transitions  

Scientific Electronic Library Online (English)

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

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

298

Evaluative conditioning induces changes in sound valence  

Directory of Open Access Journals (Sweden)

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.

AnnaC.Bolders

2012-04-01

299

Janus Nematic Colloids with Designable Valence  

Directory of Open Access Journals (Sweden)

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.

Simon ?opar

2014-05-01

300

Intermediate Band to Conduction Band optical absorption in ZnTe:O  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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...

Antoli?n Ferna?ndez, Elisa; Chen, C.; Ramiro Gonzalez, In?igo; Foley, James; Lo?pez Estrada, Esther; Artacho Huertas, Irene; Hwang, J.; Teran, A.; Herna?ndez Marti?n, Estela; Tablero Crespo, Ce?sar; Marti? Vega, Antonio; Phillips, J. D.; Luque Lo?pez, Antonio

2012-01-01

 
 
 
 
301

Correlated Topological Insulators with Mixed Valence  

Science.gov (United States)

We propose the local density approximation+Gutzwiller method incorporating a Green’s function scheme to study the topological physics of correlated materials from the first principles. Applying this method to typical mixed valence materials SmB6, we find its nontrivial Z2 topology, indicating that SmB6 is a strongly correlated topological insulator. The unique feature of this compound is that its surface states contain three Dirac cones in contrast to most known topological insulators.

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

2013-03-01

302

Valence electronic structure of Y1Ba2Cu3O7  

International Nuclear Information System (INIS)

The occupied and unoccupied valence-band structure of Y1Ba2Cu3O7 is probed with photoemission, inverse photoemission, and near-edge x-ray absorption. The Cu 3d and O 2p states nearly coincide, thereby maximizing their interaction. The occupied states are shifted down by 2 eV relative to ground-state band calculations, indicating localization and a Coulomb interaction U>2 eV. The band width is 10 eV with the top of the band at E/sub F/+2.5 eV. Cu is found in the 2+ oxidation state. O has 2p holes which are assigned to specific oxygen atoms

1987-09-01

303

Strong electron correlations in cobalt valence tautomers  

CERN Multimedia

We have examined cobalt based valence tautomer molecules such as Co(SQ)$_2$(phen) using density functional theory (DFT) and variational configuration interaction (VCI) approaches based upon a model Hamiltonian. Our DFT results extend earlier work by finding a reduced total energy gap (order 0.6 eV) between high temperature and low temperature states when we fully relax the coordinates (relative to experimental ones). Futhermore we demonstrate that the charge transfer picture based upon formal valence arguments succeeds qualitatively while failing quantitatively due to strong covalency between the Co 3$d$ orbitals and ligand $p$ orbitals. With the VCI approach, we argue that the high temperature, high spin phase is strongly mixed valent, with about 30 % admixture of Co(III) into the predominantly Co(II) ground state. We confirm this mixed valence through a fit to the XANES spectra. Moreover, the strong electron correlations of the mixed valent phase provide an energy lowering of about 0.2-0.3 eV of the high te...

La Bute-Montiago X; Endres, R G; Cox, D L

2001-01-01

304

Physics of Resonating Valence Bond Spin Liquids  

Science.gov (United States)

This thesis will investigate various aspects of the physics of resonating valence bond spin liquids. After giving an introduction to the world that lies beyond Landau's priciple of symmetry breaking, e.g. giving an overview of exotic magnetic phases and how they can be described and (possibly) found, we will study a spin-rotationally invariant model system with a known parent Hamiltonian, and argue its ground state to lie within a highly sought after exotic phase, namely the Z2 quantum spin liquid phase. A newly developed numerical procedure --Pfaffian Monte Carlo-- will be introduced to amass evidence that our model Hamiltonian indeed exhibits a Z2 quantum spin liquid phase. Subsequently, we will prove a useful mathematical property of the resonating valence bond states: these states are shown to be linearly independent. Various lattices are investigated concerning this property, and its applications and usefullness are discussed. Eventually, we present a simplified model system describing the interplay of the well known Heisenberg interaction and the Dzyaloshinskii-Moriya (DM) interaction term acting on a sawtooth chain. The effect of the interplay between the two interaction couplings on the phase diagram is investigated. To do so, we employ modern techniques such as the density matrix renormalization group (DMRG) scheme. We find that for weak DM interaction the system exhibits valence bond order. However, a strong enough DM coupling destroys this order.

Wildeboer, Julia Saskia

305

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)

1982-01-01

306

Electromagnetically induced transparency due to intervalence band coherence in a GaAs quantum well.  

Science.gov (United States)

We demonstrate electromagnetically induced transparency in the transient optical response in a GaAs quantum well by using the nonradiative coherence between the heavy-hole and the light-hole valence bands. PMID:12779161

Phillips, Mark; Wang, Hailin

2003-05-15

307

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

CERN Multimedia

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

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

2013-01-01

308

Multidimensional x-ray spectroscopy of valence and core excitations in cysteine  

Science.gov (United States)

Several nonlinear spectroscopy experiments which employ broadband x-ray pulses to probe the coupling between localized core and delocalized valence excitation are simulated for the amino acid cysteine at the K-edges of oxygen and nitrogen and the K- and L-edges of sulfur. We focus on two-dimensional (2D) and 3D signals generated by two- and three-pulse stimulated x-ray Raman spectroscopy (SXRS) with frequency-dispersed probe. We show how the four-pulse x-ray signals kI=-k1+k2+k3 and kII=k1-k2+k3 can give new 3D insight into the SXRS signals. The coupling between valence- and core-excited states can be visualized in three-dimensional plots, revealing the origin of the polarizability that controls the simpler pump-probe SXRS signals.

Biggs, Jason D.; Zhang, Yu; Healion, Daniel; Mukamel, Shaul

2013-04-01

309

Superdeformed band in "1"5"4Dy  

International Nuclear Information System (INIS)

A superdeformed band has been found in the "1"5"4Dy (N=88) nucleus. The dynamic moment of inertia is identical to that of the yrast superdeformed band of "1"5"2Dy and the transition energies are similar to those of an excited superdeformed band in "1"5"3Dy. It is proposed that the two valence neutrons above the N=86 shell gap occupy the deformation-driving [514]9/2 orbital

1995-03-01

310

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

International Nuclear Information System (INIS)

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

1981-06-01

311

Effects of valence and intermediate valence on the compressibility of the rare-earth hexaborides  

International Nuclear Information System (INIS)

The room temperature compressibilities of the rare-earth hexaborides LaB6, SmB6, EuB6, and GdB6 have been measured by single-crystal X-ray diffraction techniques under hydrostatic pressure conditions of 0-6 GPa. The bulk-moduli of the integral-valent MB6's have both valence dependent and independent contributions. The intermediate valence SmB6 is approximately 20 percent softer than the others and shows more curvature in the P-V data. This behavior indicates that as the Sm ion collapses under pressure its valence increases, but this process becomes increasingly difficult as the trivalent state is approached. (Auth.)

1981-01-30

312

Actinides, the narrowwest bands  

International Nuclear Information System (INIS)

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

1984-08-27

313

Verb Valencies and Croatian as a Foreign and Second Language  

Directory of Open Access Journals (Sweden)

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

Marica ?ilaš-Mikuli?

2011-11-01

314

Mixed-valence behaviour of impurities as a mechanism for superconductivity in IV-VI compounds  

International Nuclear Information System (INIS)

The properties of PbTe and SnTe doped with elements (indium and thallium), which create localized levels in an allowed band, are discussed from a point of view based on ideas from the theory of mixed-valence systems in the presence of the electron-lattice interaction. The qualitatively different properties of In and Tl in PbTe are attributed to different orders of the valence transition. It is shown that the electron-electron interaction induced by the virtual shift of the position of the localized level can explain the high superconducting transition temperature of PbTe doped with Tl and SnTe doped with In. (author)

1987-01-01

315

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

CERN Multimedia

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

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

1999-01-01

316

Ferromagnetic ordering of iron impurities in the mixed-valence semiconductor SmB6  

Science.gov (United States)

Electron spin resonance (ESR) was studied in the mixed-valence (MV) semiconductor SmB6 doped with 1at.% of Fe. The ESR measurements were performed on a single crystal of SmB6 in the temperature range 1.6 300K . A number of resonance lines were found with g factors indicating the presence of iron in Fe0 , Fe+ , Fe2+ , and Fe3+ states. Ferromagnetic ordering of iron ions is observed below the Curie point at 100K , which can be attributed to indirect exchange of impurity ions via polarization of the matrix (a mechanism similar to that found in PdFe alloys). However, the estimate of the intensity of this indirect exchange demonstrates a large enhancement compared to its value in PdFe, caused by the extraordinarily high density of states in a narrow f band, characteristic of a material with fluctuating valence.

Altshuler, T. S.; Goryunov, Yu. V.; Bresler, M. S.

2006-06-01

317

Gutzwiller-type approach of the size-dependent valence change in small Pr aggregates  

International Nuclear Information System (INIS)

We give a theoretical approach to the valence change in small Prn aggregates [transition: 4f3(5d6s)2?4f2(5d6s)3], our study limited to n?4. The quantum-mechanics problem (Anderson Hamiltonian) exhibits various difficulties: f-valence mixing and strong intra-atomic f correlations. For dealing with this problem we use an extension to the mixed-band systems of the Gutzwiller method. The extension is detailed and controlled by an application to the Hubbard s chain, for which the exact solution is known. As the number of f electrons and sites of our Prn system is relatively small, we take into account the full f degeneracy. We find the transition for n=3, which is close to the experimental result, n=5. A physical explanation of the phenomenon is proposed

1990-03-01

318

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

Energy Technology Data Exchange (ETDEWEB)

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 {sigma}- and {pi}-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.

Holland, D.M.P. [Daresbury Laboratory, Daresbury, Warrington, Cheshire WA4 4AD (United Kingdom)], E-mail: d.m.p.holland@dl.ac.uk; 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); Zaytseva, I.L.; Trofimov, A.B. [Laboratory of Quantum Chemistry, Irkutsk State University, Karl-Marx Street 1, 664003 Irkutsk (Russian Federation); Schirmer, J. [Theoretische Chemie, Physikalisch-Chemisches Institut, Universitaet Heidelberg, Im Neuenheimer Feld 229, D-69120 Heidelberg (Germany)

2008-11-03

319

Formation of an unconventional Ag valence state in Ag2NiO2  

Science.gov (United States)

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

Johannes, M. D.; Streltsov, S.; Mazin, I. I.; Khomskii, D. I.

2007-05-01

320

Physical properties and valence state of cerium in the filled skutterudite CePt4Ge12  

International Nuclear Information System (INIS)

Electronic, magnetic, and transport properties of the filled platinum-germanium skutterudite CePt4Ge12 are investigated. High resolution x-ray absorption spectroscopy measurements at the cerium LIII edge demonstrate that Ce in this compound has a temperature-independent valence close to three. However, magnetic susceptibility, thermopower, Hall effect, and electronic specific heat reveal a broad maximum at Tmax = 65-80 K, suggesting the presence of valence fluctuations. The Sommerfeld coefficient ? = 105 mJ mol-1 K-2, deduced from specific heat, indicates moderately enhanced band masses for CePt4Ge12. We discuss these findings and conclude that CePt4Ge12 represents a system at the border between intermediate valence (IV) and Kondo lattice behavior. In addition, the lattice specific heat and the thermal conductivity are discussed with respect to the vibrational dynamics of Ce in the [Pt4Ge12] framework. (paper)

2011-11-23

 
 
 
 
321

Electronic process of Cu(Ag, V, Rh)(0 0 1) surface oxidation: atomic valence evolution and bonding kinetics  

International Nuclear Information System (INIS)

The electronic processes of Cu(Ag, V, Rh)(0 0 1) surface oxidation are comparatively analyzed based on the recent 'chemical bond-valence band-potential barrier' (BBB) correlation mechanism [C.Q. Sun, Prog. Mater. Sci. 48, 521-685 (2003)], which allows reaction formulae for all the observed phases with identification of individual atomic valence and the binding kinetics at the surfaces with the same geometry. It is consistently understood that the forming kinetics of the primary oxide tetrahedron and its derivative on the valence density-of-states (DOS) are intrinsically common for all these analyzed systems, though the patterns of observation in terms of morphology and crystallography vary from situation to situation. However, the lattice size and electronegativity of the host surfaces determine extrinsically the site selectivity of the oxygen, the order of bond formation and the orientation of the oxide tetrahedron

2005-06-15

322

Entanglement in doped Resonating Valence Bond states  

CERN Document Server

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

Ramanathan, Ravishankar; Wiesniak, Marcin; Vedral, Vlatko

2008-01-01

323

Valence electron momentum distributions in cadmium  

International Nuclear Information System (INIS)

The valence 5s and 4d electron momentum distributions in cadmium have been measured using noncoplanar symmetric (e, 2e) electron coincidence spectroscopy at a total energy of 1200eV. They are in close agreement with Hartree-Fock momentum distributions both in shape and relative magnitudes. Some satellite lines of very low intensity have been detected. A CI calculation of the Cd ground state and several Cd"+ ion states has been carried out to predict cross reactions for the ground state and various satellite transitions. The predictions are in agreement with the data

1982-01-01

324

Collective structures and smooth band termination in 109Sn  

International Nuclear Information System (INIS)

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

1996-12-01

325

Valence Instability and Superconductivity in Heavy Fermion Systems  

CERN Document Server

Many cerium-based heavy fermion (HF) compounds have pressure-temperature phase diagrams in which a superconducting region extends far from a magnetic quantum critical point. In at least two compounds, CeCu2Si2 and CeCu2Ge2, an enhancement of the superconducting transition temperature was found to coincide with an abrupt valence change, with strong circumstantial evidence for pairing mediated by critical valence, or charge transfer, fluctuations. This pairing mechanism, and the valence instability, is a consequence of a f-c Coulomb repulsion term U_fc in the hamiltonian. While some non-superconducting Ce compounds show a clear first order valence instability, analogous to the Ce alpha-gamma transition, we argue that a weakly first order valence transition may be a general feature of Ce-based HF systems, and both magnetic and critical valence fluctuations may be responsible for the superconductivity in these systems.

Holmes, A T; Miyake, K; Holmes, Alexander T.; Jaccard, Didier; Miyake, Kazumasa

2006-01-01

326

Electron hopping in the Mössbauer spectrum of mixed valence freudenbergite  

Science.gov (United States)

Samples of pure ferric, ferrous and mixed valence freudenbergite were prepared by different techniques. The 57Fe Mössbauer spectra of the single valence samples showed poorly resolved quadrupole splittings for the ferric sample, two well-resolved quadrupole splittings for the ferrous sample and electron hopping at, and above, room temperature for the mixed valence sample, which disappeared on lowering the temperature to 50 K.

Cashion, J. D.; Lashtabeg, A.; Vance, E. R.; Ryan, D. H.

2014-04-01

327

Neural Correlates of Processing Valence and Arousal in Affective Words  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Psychological frameworks conceptualize emotion along 2 dimensions, “valence” and “arousal.” Arousal invokes a single axis of intensity increasing from neutral to maximally arousing. Valence can be described variously as a bipolar continuum, as independent positive and negative dimensions, or as hedonic value (distance from neutral). In this study, we used functional magnetic resonance imaging to characterize neural activity correlating with arousal and with distinct models of valence ...

2007-01-01

328

Valence and salience contribute to nucleus accumbens activation  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Different accounts of nucleus accumbens (NAcc) function have emphasized its role in representing either valence or salience during incentive anticipation. In an event-related FMRI experiment, we independently manipulated valence and salience by cuing participants to anticipate certain and uncertain monetary gains and losses. NAcc activation correlated with both valence and salience. On trials with certain outcomes, NAcc activation increased for anticipated gains and decreased for anticipated ...

2008-01-01

329

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

Several nonlinear spectroscopy experiments which employ broadband x-ray pulses to probe the coupling between localized core and delocalized valence excitation are simulated for the amino acid cysteine at the K-edges of oxygen and nitrogen and the K and L-edges of sulfur. We focus on two dimensional (2D) and 3D signals generated by two- and three-pulse stimulated x-ray Raman spectroscopy (SXRS) with frequency-dispersed probe. We show how the four-pulse x-ray signals $\\bold...

Biggs, Jason D.; Zhang, Yu; Healion, Daniel; Mukamel, Shaul

2013-01-01

330

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

International Nuclear Information System (INIS)

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

2008-04-01

331

Bulk band gaps in divalent hexaborides  

Energy Technology Data Exchange (ETDEWEB)

Complementary angle-resolved photoemission and bulk-sensitive k-resolved resonant inelastic x-ray scattering of divalent hexaborides reveal a >1 eV X-point gap between the valence and conduction bands, in contradiction to the band overlap assumed in several models of their novel ferromagnetism. This semiconducting gap implies that carriers detected in transport measurements arise from defects, and the measured location of the bulk Fermi level at the bottom of the conduction band implicates boron vacancies as the origin of the excess electrons. The measured band structure and X-point gap in CaB6 additionally provide a stringent test case for proper inclusion of many-body effects in quasi-particle band calculations.

Denlinger, Jonathan; Clack, Jules A.; Allen, James W.; Gweon, Gey-Hong; Poirier, Derek M.; Olson, Cliff G.; Sarrao, John L.; Bianchi, Andrea D.; Fisk, Zachary

2002-08-01

332

Packing density and valence of lithium and sodium under pressure  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The volume changes of lithium and sodium under pressure are discussed with respect to the packing density of the atoms and their valence. In densely packed Li I (bcc), Li II (fcc), and Li III (alpha-Hg ype), valence increases from 1 at ~ 5 GPa to ~ 2.5 at 40 GPa. The maximum valence 3 is attained in Li IV (body-centered cubic, 16 atoms per cell, packing density q = 0.965) at 47 GPa. In densely packed Na I (bcc) a linear increase of valence from 1 at ~ 10 GPa to 2.9 at 65 GPa is found which co...

2006-01-01

333

Temperature effects in the valence fluctuation of europium intermetallic compounds  

International Nuclear Information System (INIS)

A previously reported model for valence fluctuations in europium compound in order to account for thermal occupation effect. Experimental results are critically discussed and new experiments are suggested

1978-01-01

334

High spin band structure in 200Tl  

International Nuclear Information System (INIS)

The nuclei of mass 200 region with a few particles and holes configuration near the 208Pb doubly magic shell closure has drawn considerable experimental and theoretical attention in the past few decades. In this context, band structure of Thallium isotopes (Z=81) with one proton hole to Z=82 shell closure are interesting to investigate as a function of angular momentum to understand the various angular momentum coupling of the valence particles or holes with the underlying core

2013-12-01

335

Dispersion Forces  

CERN Document Server

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...

Buhmann, Stefan Yoshi

2012-01-01

336

Price dispersion  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We model firm pricing given consumers follow simple reservation price rules. Such reservation rules are rational when consumers are sufficiently impatient. The equilibrium exhibits price dispersion in pure strategies, with lower price firms earning higher profits. The range of price dispersion increases with the number of firms: the highest price is the monopoly one, while the lowest price tends to marginal cost. The average transaction price remains substantially above marginal cost even in ...

2003-01-01

337

An Ag3PO4/nitridized Sr2Nb2O7 composite photocatalyst with adjustable band structures for efficient elimination of gaseous organic pollutants under visible light irradiation.  

Science.gov (United States)

A new Ag3PO4/nitridized Sr2Nb2O7 (N: 0-6.18 wt%) heterojunction was designed to eliminate gaseous pollutants under visible light irradiation. The phase compositions, optical properties, and morphologies of the heterojunction photocatalysts were systematically investigated via powder X-ray diffraction, UV-visible absorption spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and transmission electron microscopy. Calculations of the electronic structure indicated that the top of the valance band of Sr2Nb2O7 could be raised by nitrogen doping. Therefore, the electronic structure of the Ag3PO4/nitridized Sr2Nb2O7 composite photocatalysts could be continually changed by controlling the amount of nitrogen in nitridized Sr2Nb2O7. Photocatalytic degradation of isopropyl alcohol (IPA) was carried out to test the photocatalytic activity of the heterojunction. The highest activity (CO2 evolution rate, 10.32 ppm h(-1)) was observed over the Ag3PO4/nitridized Sr2Nb2O7 heterojunction prepared by nitridation of Sr2Nb2O7 (SNO) at 1023 K. The CO2 evolution rate over the heterojunction was about 40 times higher than that over pure Ag3PO4 (CO2 evolution rate, 0.26 ppm h(-1)) under visible light irradiation. An investigation of the energy-band structure via valence band X-ray photoelectron spectroscopy indicated that the conduction band (CB) and valence band (VB) of Ag3PO4 are both more positive than those of nitridized Sr2Nb2O7, which facilitates the separation and transfer of photogenerated electrons and holes between the two photocatalysts. By continually adjusting the electronic structures, an optimal band gap for the nitridized Sr2Nb2O7 of 2.15 eV was obtained, and the potential of the valance band was +1.88 eV. PMID:24847986

Guo, Jianjun; Zhou, Han; Ouyang, Shuxin; Kako, Tetsuya; Ye, Jinhua

2014-06-12

338

An Ag3PO4/nitridized Sr2Nb2O7 composite photocatalyst with adjustable band structures for efficient elimination of gaseous organic pollutants under visible light irradiation  

Science.gov (United States)

A new Ag3PO4/nitridized Sr2Nb2O7 (N: 0-6.18 wt%) heterojunction was designed to eliminate gaseous pollutants under visible light irradiation. The phase compositions, optical properties, and morphologies of the heterojunction photocatalysts were systematically investigated via powder X-ray diffraction, UV-visible absorption spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and transmission electron microscopy. Calculations of the electronic structure indicated that the top of the valance band of Sr2Nb2O7 could be raised by nitrogen doping. Therefore, the electronic structure of the Ag3PO4/nitridized Sr2Nb2O7 composite photocatalysts could be continually changed by controlling the amount of nitrogen in nitridized Sr2Nb2O7. Photocatalytic degradation of isopropyl alcohol (IPA) was carried out to test the photocatalytic activity of the heterojunction. The highest activity (CO2 evolution rate, 10.32 ppm h-1) was observed over the Ag3PO4/nitridized Sr2Nb2O7 heterojunction prepared by nitridation of Sr2Nb2O7 (SNO) at 1023 K. The CO2 evolution rate over the heterojunction was about 40 times higher than that over pure Ag3PO4 (CO2 evolution rate, 0.26 ppm h-1) under visible light irradiation. An investigation of the energy-band structure via valence band X-ray photoelectron spectroscopy indicated that the conduction band (CB) and valence band (VB) of Ag3PO4 are both more positive than those of nitridized Sr2Nb2O7, which facilitates the separation and transfer of photogenerated electrons and holes between the two photocatalysts. By continually adjusting the electronic structures, an optimal band gap for the nitridized Sr2Nb2O7 of 2.15 eV was obtained, and the potential of the valance band was +1.88 eV.

Guo, Jianjun; Zhou, Han; Ouyang, Shuxin; Kako, Tetsuya; Ye, Jinhua

2014-06-01

339

Relationship Between Iron Valence States of Serpentine in CM Chondrites and Their Aqueous Alteration Degrees  

Science.gov (United States)

The 0.6-0.7 micron absorption band observed for C-type asteroids is caused by the presence of Fe(3+) in phyllosilicates . Because Fe-bearing phyllosilicates, especially serpentine, are the most dominant product of aqueous alteration in the most abundant carbonaceous chondrites, CM chondrites, it is important to understand the crystal chemistry of serpentine in CM chondrites to better understand spectral features of C-type asteroids. CM chondrites show variable degrees of aqueous alteration, which should be related to iron valences in serpentine. It is predicted that the Fe(3+)/Sum of (Fe) ratios of serpentine in CM chondrites decrease as alteration proceeds by Si and Fe(3+) substitutions from end-member cronstedtite to serpentine, which should be apparent in the absorption intensity of the 0.6-0.7 micron band from C-type asteroids. In fact, the JAXA Hayabusa 2 target (C-type asteroid: 1993 JU3) exhibits heterogeneous spectral features (0.7 micron absorption band disappears by rotation). From these points of view, we have analyzed iron valences of matrix serpentine in several CM chondrites which span the entire observed range of aqueous alteration using Synchrotron Radiation X-ray Absorption Near-Edge Structure (SR-XANES). In this abstract we discuss the relationship between obtained Fe(3+)/Sum of (Fe) ratios and alteration degrees by adding new data to our previous studies

Mikouchi, T.; Zolensky, M.; Satake, W.; Le, L.

2012-01-01

340

New Kronig-Penney Equation Emphasizing the Band Edge Conditions  

Science.gov (United States)

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,…

Szmulowicz, Frank

2008-01-01

 
 
 
 
341

BCS theory on a flat band lattice  

International Nuclear Information System (INIS)

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

2007-09-01

342

XANES study of rare-earth valency in LRu4P12 (L = Ce and Pr)  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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-insu...

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

2000-01-01

343

Awaking of ferromagnetism in GaMnN through control of Mn valence  

CERN Document Server

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

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

2006-01-01

344

Gossamer superconductor, Mott insulator, and resonating valence bond state in correlated electron systems.  

Science.gov (United States)

Gutzwiller variational method is applied to an effective two-dimensional Hubbard model to examine the recently proposed gossamer superconductor by Laughlin (LANL cond-mat/0209269). The ground state at half filled electron density is a gossamer superconductor for smaller intrasite Coulomb repulsion U and a Mott insulator for larger U. The gossamer superconducting state is similar to the resonating valence bond superconducting state, except that the chemical potential is approximately pinned at the mid of the two Hubbard bands away from the half filled. PMID:12785916

Zhang, F C

2003-05-23

345

Valence states and electronic structures of Co and Mn substituted spin gapless semiconductor PbPdO2  

Science.gov (United States)

Electronic structures of Pb(Pd0.9T0.1)O2 (T = Mn, Co) spin gapless semiconductors have been investigated by employing soft X-ray absorption spectroscopy (XAS) and photoemission spectroscopy (PES). The valence states of Co and Mn ions are found to be mixed-valent (˜2.7) and tetravalent, respectively. The measured valence-band PES and O 1s XAS spectra show that both PbPdO2 and PbPd0.9Co0.1O2 are small-gap semiconductors. This finding is supported by the calculated band structures, obtained in the density functional theory with the modified Becke-Johnson potential (mBJ) scheme. This work also shows evidence for the existence of the phase separation in Mn-substituted PbPd0.9Mn0.1O2.

Kim, D. H.; Hwang, Jihoon; Lee, Eunsook; Lee, K. J.; Choo, S. M.; Jung, M. H.; Baik, J.; Shin, H. J.; Kim, Bongjae; Kim, Kyoo; Min, B. I.; Kang, J.-S.

2014-01-01

346

Modulus of unbounded valence subdivision rules  

CERN Multimedia

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

Rushton, Brian

2011-01-01

347

Physical properties and Ce-valence of the filled skutterudite CePt4Ge12  

Science.gov (United States)

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

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

2012-02-01

348

Confounding valence and arousal: What really underlies political orientation?  

Science.gov (United States)

The negative valence model of political orientation proposed by Hibbing et al. is comprehensive and thought-provoking. We agree that there is compelling research linking threat to conservative political beliefs. However, we propose that further research is needed before it can be concluded that negative valence, rather than arousal more generally, underlies the psychological motivations to endorse conservative political belief. PMID:24970452

Tritt, Shona M; Inzlicht, Michael; Peterson, Jordan B

2014-06-01

349

Valence bond distribution and correlation in bipartite Heisenberg antiferromagnets  

Science.gov (United States)

Every singlet state of a quantum spin-1/2 system can be decomposed into a linear combination of valence bond basis states. The range of valence bonds within this linear combination as well as the correlations between them can reveal the nature of the singlet state and are key ingredients in variational calculations. In this work, we study the bipartite valence bond distributions and their correlations within the ground state of the Heisenberg antiferromagnet on bipartite lattices. In terms of field theory, this problem can be mapped to correlation functions near a boundary. In dimension d ?2, a nonlinear ? model analysis reveals that at long distances the probability distribution P (r) of valence bond lengths decays as |r|-d-1 and that valence bonds are uncorrelated. By a bosonization analysis, we also obtain P(r )?|r|-d-1 in d =1 despite the different mechanism. On the other hand, we find that correlations between valence bonds are important even at large distances in d =1, in stark contrast to d ?2. The analytical results are confirmed by high-precision quantum Monte Carlo simulations in d =1, 2, and 3. We develop a single-projection loop variant of the valence bond projection algorithm, which is well designed to compute valence bond probabilities and for which we provide algorithmic details.

Schwandt, David; Alet, Fabien; Oshikawa, Masaki

2014-03-01

350

Teaching Valence Shell Electron Pair Repulsion (VSEPR) Theory  

Science.gov (United States)

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),…

Talbot, Christopher; Neo, Choo Tong

2013-01-01

351

Angular- and light-polarization-dependent valence UV photoelectron spectra of the hexatriacontane ( n-C 36H 74) crystal  

Science.gov (United States)

Valence-band angle-resolved photoelectron spectra of oriented polycrystalline films of hexatriacontane ( n-C 36H 74) were measured by He II (40.8 cV) light. Significant dependence of the spectra on photoemissive angle and light-incidence angle was observed. The advantages and problems of angle-resolved UV photoelectron spectroscopy to the study of electronic structures of organic crystals are discussed.

Seki, Kazuluko; Inokuchi, Hiroo

1982-06-01

352

Charge Fluctuations and the Valence Transition in Yb under Pressure  

Energy Technology Data Exchange (ETDEWEB)

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

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

2009-04-21

353

Role of valence electrons for formation of glassy alloys  

Energy Technology Data Exchange (ETDEWEB)

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

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

2009-08-26

354

Valence tautomerism in co-dioxolene complexes: static and time-resolved infrared spectroscopy study.  

Science.gov (United States)

In this work, we studied the valence tautomerism process on two different Co-dioxolene complexes by means of transient infrared spectroscopy (TRIR). The molecules investigated are ls-Co(III)(Cat-N-BQ)(Cat-N-SQ) (DQ2) and [ls-Co(III)(tpy)(Cat-N-SQ)]PF6 (tpy), where Cat-NBQ = 2-(2-hydroxy-3,5-ditert-butylphenyl-imino)-4,6-ditert-butylcyclohexa-3,5-dienone, Cat-N-SQ is the dianionic radical analogue, and tpy = 2,2'-6-2?-terpyridine. DFT calculations of the harmonic frequencies for the two complexes allow us to pinpoint the normal modes to be used as markers of the semiquinonate and benzoquinonate isomers. The photoinduced one-electron charge transfer process from the radical semiquinonate ligand to the metal center leads to a ls-Co(II)(x)(Cat-N-BQ) electronic state (where x is the other ligand). Following this first step, an ultrafast ISC process (? LMCT) band at ?520 nm and in the semiquinonate band at ?1000 nm induces the valence tautomerism (VT) in both samples. From the time evolution of the TRIR spectra, we determine the time constants of the vibrational cooling in the tautomeric state (7-14 ps) and the ground state recovery times (?350 ps for tpy and ?450 ps for DQ2). In contrast, when the pump frequency is set at 712 nm, on resonance with the benzoquinonate absorption band of the second active ligand of the DQ2, no electron transfer takes place: the TRIR spectra basically show only ground state bleaching bands and no marker band of the tautomeric conversion shows up. PMID:23888870

Azzaroli, Nicolò; Lapini, Andrea; Di Donato, Mariangela; Dei, Andrea; Righini, Roberto

2013-12-12

355

Valence and magnetic ordering in intermediate valence compounds: TmSe versus SmB6  

Science.gov (United States)

The intermediate valence systems TmSe and SmB6 have been investigated up to 16 and 18 GPa by ac microcalorimetry with a pressure (p) tuning realized in situ at low temperature. For TmSe, the transition from an antiferromagnetic insulator for p3 GPa), TN is found to increase linearly with p. A similar linear p increase of TN is observed for the quasitrivalent compound TmS, which is at ambient pressure equivalent to TmSe at p~7 GPa. In the case of SmB6 long range magnetism has been detected above p~8 GPa, i.e. at a pressure slightly higher than the pressure of the insulator to metal transition. However a homogeneous magnetic phase occurs only above 10 GPa. The magnetic and electronic properties are related to the renormalization of the 4f wavefunction either to the divalent or the trivalent configurations. As observed in SmS, long range magnetism in SmB6 occurs already far below the pressure where a trivalent Sm3+ state will be reached. It seems possible to describe roughly the physical properties of the intermediate valence equilibrium by assuming formulae for the Kondo lattice temperature depending on the valence configuration. Comparison is also made with the appearance of long range magnetism in cerium and ytterbium heavy fermion compounds.

Derr, J.; Knebel, G.; Lapertot, G.; Salce, B.; Méasson, M.-A.; Flouquet, J.

2006-02-01

356

Lone conduction band in Cu2ZnSnSe4  

Science.gov (United States)

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

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

2012-03-01

357

The surface band structure of W(112)  

International Nuclear Information System (INIS)

Both the experimental and theoretical band structure of the W(112) surface are presented, with the theoretical band structure calculated by the film-LAPW (linearized augmented plane waves) method. The results permit one to compare the W(112) and Mo(112) band structures and illuminate the similarities. It is found that for the W(112) surface the main photoemission features combine contributions from both the surface and bulk, as has been previously noted for Mo(112). The main differences between the electronic structures of the furrowed W(112) and Mo(112) surfaces are seen in the width of occupied bands. The differences are attributed to the extent of localization of valence 4d and 5s electrons in Mo and 5d and 6s electrons in W. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

2004-03-01

358

Band alignment of SnS/Zn(O,S) heterojunctions in SnS thin film solar cells  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Band alignment is critical to the performance of heterojunction thin film solar cells. In this letter, we report band alignment studies of SnS/Zn(O,S) heterojunctions with various compositions of Zn(O,S). Valence band offsets (VBOs) are measured by femtosecond laser pump/probe ultraviolet photoelectron spectroscopy (fs-UPS) from which conduction band offsets (CBOs) are calculated by combining with band gaps obtained by optical transmission/reflection measurements. The SnS/Zn(O,S) heterojuncti...

Sun, Leizhi; Haight, Richard; Sinsermsuksakul, Prasert; Bok Kim, Sang; Park, Helen Hejin; Gordon, Roy Gerald

2013-01-01

359

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2004-01-01

360

The influence of electron correlation and relativistic effects on the valence shell photoelectron spectrum of iodothiophene  

Energy Technology Data Exchange (ETDEWEB)

The valence shell photoelectron spectrum of 2-iodothiophene (2-I-Th) has been studied experimentally and calculations have been carried out to characterize the main bands due to single-hole ionized states for both 2- and 3-iodothiophene. The importance of electron correlation in the formation of satellite states has also been assessed. The vertical ionization energies and spectral intensities of the entire valence shell photoelectron spectrum have been computed using the third-order algebraic-diagrammatic construction approximation for the one-particle Green function. These theoretical predictions have allowed assignments to be proposed for all the prominent structure observed in the experimental spectra, and have highlighted the breakdown of the molecular orbital model of ionization for the {pi}{sub 1}-orbital. By comparing the present theoretical and experimental results for iodothiophene with similar data for chloro-and bromothiophene, it has been found that the binding energies and intensities of the satellites associated with the {pi}{sub 1}-orbital form a pattern which is common to all three monohalothiophenes. Relativistic Hartree-Fock calculations have been carried out to investigate the importance of such effects on the valence shell ionization of iodothiophene. Synchrotron radiation has been used to measure photoelectron angular distributions and branching ratios of 2-I-Th. The spectral behaviour of the asymmetry parameters has provided an experimental means of distinguishing photoelectron bands due to {sigma}-orbitals from those associated with {pi}-orbitals. A high-resolution photoelectron spectrum of the outer valence shell of 2-I-Th has been recorded using HeI radiation, and vibrational structure has been observed and analysed in the ()()} {sup 2}A'', A-tilde {sup 2}A'', B-tilde {sup 2}A' and ()()} {sup 2}A'' state bands.

Trofimov, A B [Laboratory of Quantum Chemistry, Computer Centre, Irkutsk State University, 664003 Irkutsk (Russian Federation); Schirmer, J [Theoretische Chemie Physikalisch-Chemisches Institut, Universitaet Heidelberg, Im Neuenheimer Feld 253, D-69120 Heidelberg (Germany); Holland, D M P [Daresbury Laboratory, Daresbury, Warrington, Cheshire (United Kingdom); Potts, A W [Department of Physics, King' s College, Strand, London (United Kingdom); Karlsson, L [Department of Physics, Uppsala University, Box 530, SE-75121 Uppsala (Sweden); Maripuu, R [ESCA-LASER Laboratory, Institute of Material Science, Box 534, Regementsvaegen 1, SE-75121 Uppsala (Sweden); Siegbahn, K [ESCA-LASER Laboratory, Institute of Material Science, Box 534, Regementsvaegen 1, SE-75121 Uppsala (Sweden)

2002-12-28

 
 
 
 
361

Electronic band structure of Cu2O by spin density functional theory  

International Nuclear Information System (INIS)

The band structure of Cu2O is calculated using density functional theory in the generalized gradient approximation. By taking spin-orbit coupling into account the split between the ?7+ and the ?8+ valence band states is obtained as 128 meV. The highest valence band shows a noticeable nonparabolicity close to the ? point. This is important for the quantitative description of excitons in this material, which is considered to be the best candidate for the confirmation that Bose-Einstein condensation also occurs in excitonic systems.

2009-01-07

362

Band Together!  

Science.gov (United States)

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…

Olson, Cathy Applefeld

2011-01-01

363

Band alignment and interfacial structure of ZnO/Ge heterojunction investigated by photoelectron spectroscopy  

Science.gov (United States)

Studies on band-offset and band-alignment of heterojunction of highly c-axis oriented ZnO thin films grown on n-Ge (1 1 1) by pulsed laser deposition show a type-II band alignment with the valence band offset (?EV) of 3.1 +/- 0.2 eV. The valence band spectra of this heterojunction show band onsets corresponding to Ge, interfacial GeOx, and ZnO layers. This observation also enabled us to determine ?EV of ZnO/GeOx heterojunction to be 1.4 +/- 0.2 eV. These studies provide further insight into the band alignment of ZnO/GeOx/Ge system wherein the observed large value of ?EV of ZnO/Ge can be used for heterojunction based optoelectronic devices.

Singh, S. D.; Ajimsha, R. S.; Sahu, Vikas; Kumar, Ravi; Misra, P.; Phase, D. M.; Oak, S. M.; Kukreja, L. M.; Ganguli, Tapas; Deb, S. K.

2012-11-01

364

Surface mixed valence in Sm and SmB/sub 6/  

Energy Technology Data Exchange (ETDEWEB)

Surface-sensitive photoelectron measurements reveal bulk-to-surface shifts of the Sm 4f/sup 6/ level which imply inhomogeneous valence mixing on the surface of Sm and SmB/sub 6/. 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 4f/sup 6/ state, showing that the 4f/sup 6/ 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. SmB/sub 6/ 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 SmB/sub 6/ are pointed out and discussed.

Allen, J.W.; Johansson, L.I.; Lindau, I.; Hagstroem, S.B.

1980-02-15

365

Entanglement in Valence-Bond-Solid States  

CERN Document Server

This article reviews the quantum entanglement in Valence-Bond-Solid (VBS) states defined on a lattice or a graph. The subject is presented in a self-contained and pedagogical way. The VBS state was first introduced in the celebrated paper by I. Affleck, T. Kennedy, E. H. Lieb and H. Tasaki (abbreviation AKLT is widely used). It became essential in condensed matter physics and quantum information (measurement-based quantum computation). Many publications have been devoted to the subject. Recently entanglement was studied in the VBS state. In this review we start with the definition of a general AKLT spin chain and the construction of VBS ground state. In order to study entanglement, a block subsystem is introduced and described by the density matrix. Density matrices of 1-dimensional models are diagonalized and the entanglement entropies (the von Neumann entropy and Renyi entropy) are calculated. In the large block limit, the entropies also approach finite limits. Study of the spectrum of the density matrix le...

Korepin, Vladimir E

2009-01-01

366

Valence Bond Crystal on the Hyperkagome Antiferromagnet  

Science.gov (United States)

We describe our recent work that indicates that the ground state of the antiferromagnetic spin-1/2 Heisenberg model on the highly frustrated, three-dimensional, hyper-kagome lattice is a valence bond crystal (VBC). Performing a series expansion around an arbitrary dimer covering on the hyper-kagome we find that a ground state with a huge (72 site) unit cell is selected by the quantum fluctuations. The regularity and favorable energetics of our series expansion establishes the VBC as a serious contender to the earlier spin liquid proposals. We find that the ground state supports many, very low lying, excitations in the singlet sector and that the low energy spinful excitations (spinons and triplons) are effectively confined to various emergent lower-dimensional structures. If applicable to the recently studied sodium iridate compound, Na4Ir3O8, this scenario has interesting observable implications, such as spatially anisotropic neutron scattering spectra and possibly multiple finite temperature signatures in the magnetic specific heat due to a multi-step breaking of discrete symmetries. Most saliently, here---as for several proposed states for analogous kagome and pyrochlore magnets---one might expect a clearly resolved Ising transition at relatively high temperature. [4pt] Ref: E.J. Bergholtz, A.M. L"auchli and R. Moessner, Phys. Rev. Lett., in press (2010) [arXiv:1010.1345

Bergholtz, Emil; Lauchli, Andreas; Moessner, Roderich

2011-03-01

367

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

1985-09-01

368

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

1980-04-01

369

Equalized Electronegativity Based on the Valence Electrons and Its Application  

Science.gov (United States)

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.

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

2011-02-01

370

Band gap states of Cr in the lower part of the SiC band gap  

Energy Technology Data Exchange (ETDEWEB)

Bandgap states of Cr in p-type 4H-SiC (silicon carbide) were investigated by radiotracer-DLTS (deep level transient spectroscopy). Doping with the radioactive isotope {sup 51}Cr was done by recoil implantation followed by annealing (4h, 1600 K). Repeated DLTS measurements during the elemental transmutation of the isotope to {sup 51}V, reveal the corresponding concentration changes of bandgap states. In the lower part of the band gap accessible by these experiments, we find two Cr-related levels at 0.53 eV and 0.63 eV above the valence band edge, and no level of Vanadium. (orig.)

Pasold, G.; Grillenberger, J.; Witthuhn, W. [Jena Univ. (Germany). Inst. fuer Festkoerperphysik; Achtziger, N. [Fraunhofer-Arbeitsgruppe fuer Integrierte Schaltungen (AIS), Erlangen (Germany)

2001-07-01

371

Comment on: “Valence ionization of L-proline amino acid: Experimental and theoretical study” by F. Fathi, H. Farrokhpour, Chem. Phys. Lett. 565 (2013) 102  

Science.gov (United States)

In the cited work, the authors presented mass spectra, valence photoelectron spectra and calculations of the electronic structure of proline. They claim that several previous photoelectron spectra are invalid because they were influenced by thermal decomposition of the sample. We present photoionization mass spectra of proline as a function of temperature and show that thermal decomposition does not occur in the apparatus and at the temperatures used in our previous work. These spectra are consistent with other published spectra. The conformer populations calculated by these authors, far from contradicting previous interpretations of valence band spectra, are surprisingly consistent with them.

Plekan, Oksana; Feyer, Vitaliy; Richter, Robert; Coreno, Marcello; de Simone, Monica; Prince, Kevin C.; Carravetta, Vincenzo

2014-05-01

372

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

Science.gov (United States)

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

Majumdar, Kausik

2014-05-01

373

Valence state of Ti in conductive nanowires in sapphire  

International Nuclear Information System (INIS)

In order to reveal the valence state of Ti in conductive nanowires in sapphire, near-edge x-ray-absorption fine structures (NEXAFS) were observed. From experimental and theoretical studies on NEXAFS of reference compounds including rutile, anatase, and Ti2O3, it was found that the valence state of Ti can be identified by regarding the positions of the spectral onset and the shoulder in the main peak of Ti-K NEXAFS. The valence states of Ti doped Al2O3 polycrystalline specimens which were annealed at oxidized and reduced atmospheres were determined to be +4 and +3, respectively. The solubility limit of Ti in Al2O3 polycrystal was found to be between 1000 ppm to 1.0% at the both atmospheres. The spectrum from Ti nanowires in sapphire has a lot of similarities to the reduced specimen, the valence state was therefore concluded to be +3

2004-10-15

374

Quantum Monte Carlo with Jastrow-Valence-Bond wave functions  

CERN Multimedia

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.

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

2011-01-01

375

Some formal results for the valence bond basis  

CERN Document Server

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

Beach, K S D

2006-01-01

376

Correlated Small Polaron Transport in Mixed Valence Oxides  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The electrical transport properties of mixed ferrites, oxidic superconductors and GMR compounds having ions in mixed valence state are shown to originate from the correlated motion of polarons and scattering by the spin disorder.

1997-01-01

377

On the valence and lattice parameter in cerium intermetallic compounds  

International Nuclear Information System (INIS)

Experimental data concerning valence and lattice parameter in cerium intermetallic compounds are discussed using the concepts of electronic charge screening and charge transfer between the rare earth and the transition element. (author)

1981-01-01

378

Valence fluctuation in CeMo{sub 2}Si{sub 2}C  

Energy Technology Data Exchange (ETDEWEB)

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

Paramanik, U.B.; Anupam [Department of Physics, Indian Institute of Technology, Kanpur 208 016 (India); Burkhardt, U. [Max-Planck Institute for Chemical Physics of Solids, 01187 Dresden (Germany); Prasad, R. [Department of Physics, Indian Institute of Technology, Kanpur 208 016 (India); Geibel, C. [Max-Planck Institute for Chemical Physics of Solids, 01187 Dresden (Germany); Hossain, Z., E-mail: zakir@iitk.ac.in [Department of Physics, Indian Institute of Technology, Kanpur 208 016 (India)

2013-12-15

379

Stimulus affective valence reverses spatial compatibility effect  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english In spatial compatibility tasks, the Reaction Time to right-side stimuli is shorter for right key responses (compatible condition) than for left key responses (incompatible condition) and vice-versa for left-side stimuli. Similar results have been found when the stimulus location is not relevant for [...] response selection, such as in the Simon task. The Simon effect is the difference between the reaction times for non-corresponding and corresponding conditions. The Simon 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.

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

380

Underwater communication using weakly dispersive modal pulses  

Science.gov (United States)

In the modal description of sound propagation, signal distortion is caused primarily by dispersion, which is largely controlled by the product I( m; f)?( m; f). Here m is mode number, f is acoustic frequency, I is the action and ? is the waveguide invariant. A modal pulse with fixed m and variable f that satisfies I? ? 0 over the entire frequency band is referred to in this letter as a weakly dispersive modal pulse. The manner by which weakly dispersive modal pulses can be exploited in underwater communications applications is described and illustrated. The connection between weakly dispersive modal pulses and weakly divergent beams is discussed.

Brown, Michael G.; Udovydchenkov, Ilya A.

2013-09-01

 
 
 
 
381

Mixed-Valence Porphyrin ?-Cation Radical Derivatives: Electrochemical Investigations  

Science.gov (United States)

The electrochemistry of [Cu(OEP)] and [Ni(OEP)] are compared with the mixed-valence ?-cations [Cu(OEP•/2)]2+and[Ni(OEP•/2)]2+. These electrochemical studies, carried out with cyclic voltametry and hydrodynamic voltametry, show that the mixed valence ?-cations have distinct electrochemical properties, although the differences between the [M(OEP)]+/0 and [M(OEP•/2)]2+/0 processes are subtle.

Scheidt, W. Robert; Buentello, Kristin E.; Ehlinger, Noelle; Cinquantini, Arnaldo; Fontani, Marco; Laschi, Franco

2008-01-01

382

Mixed-Valence Porphyrin ?-Cation Radical Derivatives: Electrochemical Investigations.  

Science.gov (United States)

The electrochemistry of [Cu(OEP)] and [Ni(OEP)] are compared with the mixed-valence ?-cations [Cu(OEP•/2)]2+and[Ni(OEP•/2)]2+. These electrochemical studies, carried out with cyclic voltametry and hydrodynamic voltametry, show that the mixed valence ?-cations have distinct electrochemical properties, although the differences between the [M(OEP)](+/0) and [M(OEP•/2)]2+/0 processes are subtle. PMID:19421310

Scheidt, W Robert; Buentello, Kristin E; Ehlinger, Noelle; Cinquantini, Arnaldo; Fontani, Marco; Laschi, Franco

2008-05-01

383

Space-Valence Priming with Subliminal and Supraliminal Words  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 sup...

Ansorge, Ulrich; Khalid, Shah; Ko?nig, Peter

2013-01-01

384

Neural correlates of processing valence and arousal in affective words  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Psychological frameworks conceptualize emotion along 2 dimensions, "valence" and "arousal." Arousal invokes a single axis of intensity increasing from neutral to maximally arousing. Valence can be described variously as a bipolar continuum, as independent positive and negative dimensions, or as hedonic value (distance from neutral). In this study, we used functional magnetic resonance imaging to characterize neural activity correlating with arousal and with distinct models of ...

2007-01-01

385

The role of fluctuations in mixed valence compounds  

International Nuclear Information System (INIS)

Previous renormalization group results for a simple spinless mixed valence model yielded large intersite f-electron correlations if extended coherent hybridization mixed valence states are assumed. These correlations are simulated by an f-level energy distribution and its consequences are analysed. It is seen that a relatively small distribution width already smears the coherent hybridization gap leading to a lattice of essentially independent resonant levels. (author)

1980-01-01

386

Emotional Valence and the Free-Energy Principle  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The free-energy principle has recently been proposed as a unified Bayesian account of perception, learning and action. Despite the inextricable link between emotion and cognition, emotion has not yet been formulated under this framework. A core concept that permeates many perspectives on emotion is valence, which broadly refers to the positive and negative character of emotion or some of its aspects. In the present paper, we propose a definition of emotional valence in terms of the negative r...

2013-01-01

387

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

Directory of Open Access Journals (Sweden)

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.

JelleDemanet

2011-11-01

388

Valence resolution of facial expressions using an emotional oddball task  

Science.gov (United States)

Previous research suggests that neural and behavioral responses to surprised faces are modulated by explicit contexts (e.g., “He just found $500”). Here, we examined the effect of implicit contexts (i.e., valence of other frequently presented faces) on both valence ratings and ability to detect surprised faces (i.e., the infrequent target). In Experiment 1, we demonstrate that participants interpret surprised faces more positively when they are presented within a context of happy faces, as compared to a context of angry faces. In Experiments 2 and 3, we used the oddball paradigm to evaluate the effects of clearly valenced facial expressions (i.e., happy and angry) on default valence interpretations of surprised faces. We offer evidence that the default interpretation of surprise is negative, as participants were faster to detect surprised faces when presented within a happy context (Exp. 2). Finally, we kept the valence of the contexts constant (i.e., surprised faces) and showed that participants were faster to detect happy than angry faces (Exp. 3). Together, these experiments demonstrate the utility of the oddball paradigm to serve as an implicit context to resolve the valence ambiguity of surprised facial expressions, but that this implicit context does not completely override the default negativity.

Neta, Maital; Davis, F. Caroline; Whalen, Paul J.

2012-01-01

389

Electronic band structure of transparent conductor. Nb-doped anatase TiO2  

International Nuclear Information System (INIS)

We have investigated electronic band structure of a transparent conducting oxide, Nb-doped anatase TiO2 (TNO), by means of first-principles band calculations and photoemission measurements. The band calculations revealed that Nb 4d orbitals are strongly hybridized with Ti 3d ones to form a d-nature condition band, without impurity states in the in-gap region, resulting in high carrier density exceeding 1021 cm-3 and excellent optical transparency in the visible region. Furthermore, we confirmed that the results of valence band and core-level photoemission measurements are consistent with prediction by the present band calculations. (author)

2008-11-01

390

Mapping band alignment across complex oxide heterointerfaces.  

Science.gov (United States)

In this study, direct observation of the evolution of electronic structures across complex oxide interfaces has been revealed in the LaAlO(3)/SrTiO(3) model system using cross-sectional scanning tunneling microscopy and spectroscopy. The conduction and valence band structures across the LaAlO(3)/SrTiO(3) interface are spatially resolved at the atomic level by measuring the local density of states. This study directly maps out the electronic reconstructions and a built-in electric field in the polar LaAlO(3) layer. Results also clearly reveal the band bending and the notched band structure in the SrTiO(3) adjacent to the interface. PMID:23368366

Huang, Bo-Chao; Chiu, Ya-Ping; Huang, Po-Cheng; Wang, Wen-Ching; Tra, Vu Thanh; Yang, Jan-Chi; He, Qing; Lin, Jiunn-Yuan; Chang, Chia-Seng; Chu, Ying-Hao

2012-12-14

391

Sequential and Prosodic Design of English and Greek Non-Valenced News Receipts  

Science.gov (United States)

Results arising from a prosodic and interactional study of the organization of everyday talk in English suggest that news receipts can be grouped into two categories: valenced (e.g., "oh good") and non-valenced (e.g., "oh really"). In-depth investigation of both valenced and non-valenced news receipts shows that differences in their prosodic…

Kaimaki, Marianna

2012-01-01

392

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

Science.gov (United States)

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,…

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

2009-01-01

393

Valence shell photoelectron spectroscopy of pyrene and fluorene: photon energy dependence in the far-ultraviolet region.  

Science.gov (United States)

Inner and outer valence photoelectron spectra (PES) of pyrene and fluorene, two members of the polycyclic aromatic hydrocarbon (PAH) family, were recorded with a high-resolution synchrotron photoelectron spectrometer. Relative photoelectron emission cross sections were measured at photon energies between 15 and 40 eV. Several bands observed in the experimental PES were assigned with the help of OVGF/cc-pVDZ calculations. The first ionization potentials were estimated to be 7.436 ± 0.015 and 7.944 ± 0.055 eV for pyrene and fluorene, respectively. Photoelectron emission cross sections show a clear difference in trend for inner (?-dominated) and outer (?-dominated) bands. Contrary to the expectation from the trend observed in benzene, the inner bands significantly dominate in the photon energy region from 15 to 27 eV and then are found to contribute uniformly. A pronounced peak in the cross sections is observed at a photon energy of approximately 17 eV for both molecules (irrespective of the difference in symmetry and structure), particularly for the inner valence bands. The feature is observed to be independent of the details of the molecular orbital associated with the outgoing electron. These observations are correlated to a collective excitation in the far-ultraviolet region. PMID:24708028

Mishra, Preeti Manjari; Avaldi, Lorenzo; Bolognesi, Paola; Prince, Kevin C; Richter, Robert; Kadhane, Umesh R

2014-05-01

394

Constraints to the flat band potential of hematite photo-electrodes.  

Science.gov (United States)

We revisit the fundamental constraints that apply to flat band potential values at semiconductor photo-electrodes. On the physical scale, the Fermi level energy of a non-degenerate semiconductor at the flat band condition, EF(FB), is constrained to a position between the conduction band, EC, and the valence band, EV,: |EC| valence band must be computed on both scales a priori, where possible. This is accomplished with the aid of an analytical reconstruction of the semiconductor|electrolyte interface in question. To illustrate this approach, we provide a case study based on synthetic hematite, ?-Fe2O3. The analysis of this particular semiconductor is motivated by the large variance in the flat band potential values reported in the literature. PMID:24968087

Hankin, A; Alexander, J C; Kelsall, G H

2014-07-01

395

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

International Nuclear Information System (INIS)

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

1987-01-01

396

Valence effects on adsorption: a preliminary assessment of the effects on valence state control on sorption measurements  

International Nuclear Information System (INIS)

Electrochemical arguments are advanced to illustrate that what is usually measured in practice is a mixed potential determined by the kinetics of the electrode processes occurring at the indicator electrode. Valence states can be altered electrochemically or by use of added chemical reagents, including redox couples which can hold the potential to relatively specific potentials. The disadvantage of added chemical reagents is that they may alter the characteristics of the sorption reactions by interaction with the sorbent. Electrochemical methods are versatile and do not add reagents, but in some caes the nuclide can adsorb on the electrode itself. A description is given of the application of the electrochemical method of valence control to determination of sorption of Np(V) on alumina. Valence state control and analysis can be used to study possible redox reactions on materials which might be used as backfill materials. A description is given of survey experiments with a number of sulfides and iron-containing materials. Valence state analysis is used on the initial solutions and leachate from acid leaches of the sorbent after the sorption experiment to help determine whether valence state change is occurring. The preliminary results indicate that on the sulfides tested, sorption occurs both with and without valence state change

1983-01-01

397

Specific intermediate-valence state of insulating 4f compounds detected by L3 x-ray absorption  

International Nuclear Information System (INIS)

The intermediate valence of formally tetravalent compounds has been detected by L3 x-ray-absorption near-edge structure (XANES) in CeO2 and in PrO2 but not in UO2, which have the same CaF2 structure and large f and ligand mixing. The intermediate valence has been found both in CeO2 and in Ce(SO4)2x4H2O, which have similar local structure but different crystal structure. We show that L3 XANES final states are a direct probe of configuration interaction between 4f/sup n/ and 4f/sup n//sup +1/L configurations in the ground state and that the weight of the 4f/sup n//sup +1/L in the ground state can be deduced. The many-body final states arise from the characteristic properties of these materials: (i) the presence of localized 4f level above the oxygen 2p band separated by a gap ?epsilon-c with relevant correlation energy U/sub f//sub f/ (U/sub f//sub f/??epsilon-c) and (ii) mixing of 4f localized states with ligand valence orbitals such that the hybridization energy V is of the same order of magnitude as the energy separation ?E between the many-body configuration 4f/sup n/ and 4f/sup n//sup +1/L (V??E). These insulating materials, which cannot be classified as standard mixed-valence systems, are called here interatomic intermediate-valence systems

1987-01-15

398

Experimental studies of narrow band effects in the actinides  

International Nuclear Information System (INIS)

In many actinide metallic systems the f-electrons exhibit band behavior. This is a consequence of direct f-f wave function overlap or hybridization of f-electrons with s-, p-, and d-electrons. The f-bands can be responsible for large electronic densities of states at the Fermi level which may lead to band magnetism of various types. Although the concept of valence instabilities must be approached cautiously especially in the light actinides, it would not be surprising to observe them in the future, especially in Am compounds

1976-11-12

399

XANES study of rare-earth valency in LRu4P12 (L=Ce and Pr)  

Science.gov (United States)

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 K<=T<=300 K. We find that the metal-insulator (MI) transition at TMI=60 K in PrRu4P12 does not originate from Pr valence fluctuation.

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

1999-11-01

400

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

Science.gov (United States)

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

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

2013-01-01

 
 
 
 
401

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

International Nuclear Information System (INIS)

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

1982-01-01

402

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

1996-01-01

403

Modified Cr valence in symmetric oxygen ion conducting half cells with ion flow  

Science.gov (United States)

The degradation mechanisms in ion conducting materials, including solid oxide fuel cells (SOFC), are still of high interest in current energy research, especially with regards to material and interface stability, fuel impurities and impurities originating from sealing or interconnect materials. A common practice is the use of symmetric half-cells (e.g. cathode/electrolyte/cathode) to determine interface stability via cross section Energy Dispersive x-ray Spectroscopy line scans and overpotential magnitude and degradation via AC-impedance spectroscopy. Using these electrically driven half-cells, we have developed a new method to directly measure degradation due to oxygen ion flow through ion conducting materials and their associated interface structures. By using X-ray absorption spectroscopy of cells before and after oxygen ion flow (800 C for 100 hours), we determined that the valence state of Cr that migrated from a metallic interconnect into the porous cathode changes in valence from +3 (Cr2O3) to +6 (CrO3), depending on the direction of the oxygen ion flow. This observation is strong evidence of the influence of the oxygen ion flux on the degradation mechanisms of ion conducting materials.

Finsterbusch, Martin; Lussier, Alexandre; Negusse, Ezana; Idzerda, Yves

2010-03-01

404

Dispersion-Enhanced Laser Gyroscope  

Science.gov (United States)

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.

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

2008-01-01

405

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

Directory of Open Access Journals (Sweden)

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

P.Yakibchuk

2007-01-01

406

Magnetic field induced valence band mixing in [111] grown semiconductor quantum dots  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We present a microscopic theory of the magnetic field induced mixing of heavy-hole states +/- 3/2 in GaAs droplet dots grown on (111)A substrates. The proposed theoretical model takes into account the striking dot shape with trigonal symmetry revealed in atomic force microscopy. Our calculations of the hole states are carried out within the Luttinger Hamiltonian formalism, supplemented with allowance for the triangularity of the confining potential. They are in quantitative ...

Durnev, M. V.; Glazov, M. M.; Ivchenko, E. L.; Jo, M.; Mano, T.; Kuroda, T.; Sakoda, K.; Kunz, S.; Sallen, G.; Bouet, L.; Marie, X.; Lagarde, D.; Amand, T.; Urbaszek, B.

2012-01-01

407

Valence band spectra of acetylenic moieties on zinc oxide: Acetylide versus propargyl formation  

Energy Technology Data Exchange (ETDEWEB)

Acetylene adsorbs dissociatively on the ZnO(0001) surface, as on other metal oxides, to form acetylide intermediates, CCH. Propyne also dissociates via surface acid-base reactions; however, potential adsorbates include methylacetylide (CH{sub 3}CC) and propargyl (CH{sub 2}CCH) species. Ultraviolet photoelectron spectra (UPS) of the adsorbed intermediates formed from propyne and allene on the ZnO(0001) surface demonstrate that both react to form propargyl intermediates. UPS also provide useful fingerprints of {sigma}-bonded acetylides on both metal and metal oxide surfaces.

Vohs, J.M.; Barteau, M.A. (Univ. of Delaware, Newark (USA))

1990-01-25

408

Electrical Conductivity during XPS of Heated PMMA: Detection of Core Line and Valence Band Tacticity Effects.  

Science.gov (United States)

Electrical conductivity during the XPS of approximately 100 nm thick films of PMMA on silicon was induced by heating to above 100 degrees C. Rapid x-ray induced depolymerization set in at about the same temperature. The electrical conductivity allowed acq...

G. Beamson D. T. Clark D. S. L. Law

1998-01-01

409

Study of the 4f and valence band density of states in rare-earth metals  

International Nuclear Information System (INIS)

The partially filled 4f shell in rare earths gives rise to complex multiplet structure in both photoelectron spectroscopy (PES) and bremsstrahlung isochromat spectroscopy (BIS). The fractional parentage theory previously applied to PES is extended to BIS, and a similarity is predicted between the PES of a 4fsup(n) element and the BIS of a 4fsup(14-n) element. Fractional parentage arguments are also applied to the linewidths of the 4f multiplet levels as observed in electron spectroscopy. (author)

1981-01-01

410

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

International Nuclear Information System (INIS)

In this study, the valence states of uranium in synthetic and natural brannerite samples were studied using a combination of transmission electron microscopy-electron energy loss spectroscopy (TEM-EELS), scanning electron microscopy-energy dispersive x-ray analysis (SEM-EDX) and x-ray photoelectron spectroscopy (XPS) techniques. We used a set of five (UO2, CaUO4, SrCa2UO6, UTi2O6, Y0.5U0.5Ti2O6) U standard samples, including two synthetic brannerites, to calibrate the EELS branching ratio, M5/(M4 +M5), against the number of f electrons. The EELS data were collected at liquid nitrogen temperature in order to minimize the effects of electron beam reduction of U(VI) and U(V)

2005-01-01

411

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

Science.gov (United States)

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

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

2002-04-01

412

Quantum Criticality and Deconfinement in Phase Transitions Between Valence Bond Solids  

CERN Document Server

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

Vishwanath, A; Senthil, T; Vishwanath, Ashvin

2003-01-01

413

f-band narrowing in uranium intermetallics  

International Nuclear Information System (INIS)

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

1987-01-05

414

XPS valence state determination of Np and Pu in multicomponent borosilicate glass and application to leached 76-68 waste glass surfaces  

International Nuclear Information System (INIS)

The present study involves the use of x-ray photoemission spectroscopy (XPS) to examine the behavior of actinides at the surface of glasses. XPS is an inherently surface sensitive technique, probing the outermost 20 to 30A of a sample. The technique is routinely used to provide quantitative compositional information by monitoring the intensity of photoemitted electrons from core levels characteristic of specific elements as a sample is illuminated with monochromatic x-rays. In some cases, small changes in the binding energies of these core levels (chemical shifts) can be used to get specific information on the environments and chemical states of ions in a solid. The results of the study show that chemical shifts in actinide 4f core levels can be related to valence state. In 76 to 101 glass, neptunium is present primarily in a single valence stated while plutonium is present in two distinct valence states (probably +3 and +4). The Ti 2p/sub 3/2/ core line seems to be a good internal reference for 4f chemical shift (and consequently valence state) determination. The valence band photoemission spectrum of the neptunium glass shows a quite narrow Np5f peak indicating a f_3 ? f_2 transition resulting from the presence of Np"+_4. 4 figures

1981-11-19

415

Valence fluctuation studies in EuCu2Si2  

International Nuclear Information System (INIS)

The phenomenon of valence fluctuation of Eu between the 2+ and 3+ valence states in EuCu2Si2 has been studied through its effect on the EFG (electron field gradient) acting on 111Cd introduced as a very dilute impurity probe. Carrier-free 111In activity was diffused in the sample and the QI (quadrupole interaction) was studied by the TDPAC technique as a function of sample temperature. The QI frequencies observed were #betta#sub(Q)(80 K)=23.0(2)x106 rad/sec, #betta#sub(Q)(300 K) = 22.6(2)x106 rad/sec and #betta#sub(Q)(596 K) = 21.8(2)x106 rad/sec with the asymmetry parameter eta = 0.5 for the EFG. The valence fluctuation as a function of temperature was confirmed for the sample both before and after the diffusion of the activity, by Moessbauer studies of 151Eu where the isomer shift was found to change from 1.53 to 4.35 mm/sec as temperature was varied from 90 K to 300 K. However, the quadrupole interaction does not show any marked variation with temperature. This could be interpreted as : (1) Eu atoms in the vicinity of 111Cd probe nuclei do not undergo valence fluctuations or (2) the valence fluctuations of Eu do not affect the EFG at the impurity site. (author)

1980-08-01

416

The acoustic correlates of valence depend on emotion family.  

Science.gov (United States)

The voice expresses a wide range of emotions through modulations of acoustic parameters such as frequency and amplitude. Although the acoustics of individual emotions are well understood, attempts to describe the acoustic correlates of broad emotional categories such as valence have yielded mixed results. In the present study, we analyzed the acoustics of emotional valence for different families of emotion. We divided emotional vocalizations into "motivational," "moral," and "aesthetic" families as defined by the OCC (Ortony, Clore, and Collins) model of emotion. Subjects viewed emotional scenarios and were cued to vocalize congruent exclamations in response to them, for example, "Yay!" and "Damn!". Positive valence was weakly associated with high-pitched and loud vocalizations. However, valence interacted with emotion family for both pitch and amplitude. A general acoustic code for valence does not hold across families of emotion, whereas family-specific codes provide a more accurate description of vocal emotions. These findings are consolidated into a set of "rules of expression" relating vocal dimensions to emotion dimensions. PMID:24495430

Belyk, Michel; Brown, Steven

2014-07-01

417

Space-Valence Priming with Subliminal and Supraliminal Words  

Directory of Open Access Journals (Sweden)

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.

UlrichAnsorge

2013-02-01

418

Flat bands in topological media  

CERN Document Server

Topological media are systems whose properties are protected by topology and thus are robust to deformations of the system. In topological insulators and superconductors the bulk-surface and bulk-vortex correspondence gives rise to the gapless Dirac or Majorana fermions on the surface of the system and/or inside the vortex core. In gapless topological media, the bulk-surface and bulk-vortex correspondence is more effective: it produces topologically protected gapless fermions without dispersion - the flat band. Fermion zero modes forming the flat band are localized on the surface of the three-dimensional topological media with protected nodal lines and in the vortex core in the systems with topologically protected Dirac points. Flat band has an extremely singular density of states, which may give rise in particular to surface superconductivity with an unusually high transition temperature.

Heikkila, T T; Volovik, G E

2010-01-01

419

Magnetic frustration in mixed valence manganites  

International Nuclear Information System (INIS)

Investigation of structural and magnetotransport properties of L2/3A1/3MnO3 (A=Ca,Sr) oxides reveals a gradual increase of the magnetic frustration with bending of the Mn-O-Mn bonds. The relative strength of competing magnetic interactions is controlled not only by R0 [R0 is the mean radius of the ions at the (L, A) site] but also by the electronegativity of the divalent cation. The magnetoresistance of these oxides results mainly from spin disorder and the narrowing of the ?(eg) band has only a minor effect. We have observed that the curve TC(R0) is not universal but it is sensitive to the alkaline ions. copyright 1997 The American Physical Society

1997-01-01

420

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

International Nuclear Information System (INIS)

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

1996-01-01

 
 
 
 
421

Valence determination in high temperature superconductors using synchrotron radiation  

International Nuclear Information System (INIS)

The common feature that drives most of the insulating oxides into metallic and in some cases into superconducting state is the phenomenon of mixed valency. The newly discovered cuprate and bismutate superconductors also follow this trend. They contain elements like Cu, Bi, Tl, Pb, and rare-earths which are known to be susceptible to mixed-valency. The authors have used x-ray absorption near edge structure (XANES) spectroscopy technique to determine valence of these elements in oxide superconductors. The authors have developed a quantitative charge scale to measure effective charge on Cu, and its variation as a result of chemical doping. The authors presented the recent experimental results and some new directions to take advantage of polarized nature of synchrotron radiation

1990-06-01

422

RKKY interaction in mixed valence system and heavy fermion superconductivity  

International Nuclear Information System (INIS)

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

1985-01-01

423

States with intermediate valence in rare earth metals and semiconductors  

Energy Technology Data Exchange (ETDEWEB)

Compounds of rare earth metals manifesting phase transitions with the change of valence and states with intermediate valence are considered. Peculiarities of the substances which are demonstrated in electronic and lattice characteristics (heat capacity, magnetic susceptibility, resistance, compressibility etc.) are discussed. It is shown that anomalies in behaviour of physical values are conditioned by peculiarities of electron energy spectrum: as to the energy states with different number of f-electrons on the centre, of the type 4fsup(n) and (4fsup(n-1) + conductivity electron) proved to be similar. Main theoretical approaches, used to describe properties of the compounds and factors, determining the character of phase transitions in them are briefly outlined. Discussion of physical nature and character of the main state of systems with intermediate valence is made.

Kocharyan, A.N.; Khomskij, D.I.

1981-01-01

424

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

2010-10-01

425

States with intermediate valence in rare earth metals and semiconductors  

International Nuclear Information System (INIS)

Compounds of rare earth metals manifesting phase transitions with the change of valence and states with intermediate valence are considered. Peculiarities of the substances which are demonstrated in electronic and lattice characteristics (heat capacity, magnetic susceptibility, resistance, compressibility etc.) are discussed. It is shown that anomalies in behaviour of physical values are conditioned by peculiarities of electron energy spectrum: as to the energy states with different number of f-electrons on the centre, of the type 4fsup(n) and (4fsup(n-1) + conductivity electron) proved to be similar. Main theoretical approaches, used to describe properties of the compounds and factors, determining the character of phase transitions in them are briefly outlined. Discussion of physical nature and character of the main state of systems with intermediate valence is made

1981-01-01

426

Internal conversion coefficient for valence electrons of metals  

International Nuclear Information System (INIS)

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

1990-06-01

427

Dispersed Indeterminacy  

CERN Document Server

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

Fayngold, Moses

2013-01-01

428

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

1985-09-01

429

Role of self-trapping in luminescence and p-type conductivity of wide-band-gap oxides  

Science.gov (United States)

Using hybrid functional calculations, we investigate the behavior of holes in the valence band of a range of wide-band-gap oxides including ZnO, MgO, In2O3, Ga2O3, Al2O3, SnO2, SiO2, and TiO2. We find that, due to the orbital composition of the valence band, holes tend to form localized small polarons with characteristic lattice distortions, even in the absence of defects or impurities. These self-trapped holes (STHs) are energetically more favorable than delocalized, free holes in the valence band in all materials but ZnO and SiO2. Based on calculated optical absorption and emission energies we show that STHs provide an explanation for the luminescence peaks that have been observed in many of these oxides. Additionally, we demonstrate that polaron formation prohibits p-type conductivity in this class of materials.

Varley, Joel; Janotti, Anderson; Franchini, Cesare; van de Walle, Chris

2013-03-01

430

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2012-02-06

431

Core-valence luminescence in ABX_3 crystals  

International Nuclear Information System (INIS)

The investigation of the new type of intrinsic emission caused by recombination of core holes and valence electrons, i.e., the core valence luminescence (CVL), is made for perovskite-like ABX_3 crystals (A = Li, K, Rb, Cs; B = Mg, Ca, Sr, Ba; X = F, Cl, Br). For this crystals the spectra of CVL cover 9 - 2 eV region, time decay constants change in 1 - 3 ns and bound, emission intensity in some crystals exceeds the intensity in AHC in several times. The possibility of growing ABX_3 crystals with different lattice parameters allows us to control spectral and kinetics parameters as well as CVL light yield

1994-02-01

432

Resonating-valence-bond approaches to high-temperature superconductivity  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This thesis is devoted to a theoretical study of high-temperature superconductivity from the viewpoint of a doped Mott insulator. To this end, the square-lattice t-J model is analyzed by variational and mean-field approaches. The thesis focuses on the construction of excitations and on spectral properties in the framework of Anderson's concept of resonating-valence-bond wavefunctions. The quantum dimer model as a toy model for the resonating-valence-bond phase of Mott insulators is also explo...

Bieri, Samuel

2008-01-01

433

Problem of the valence of neptunium in chalogenides  

Energy Technology Data Exchange (ETDEWEB)

The chalcogenides of the actinides, as a rule, possess high electric conductivity; the determination of P/sub f/, the p