WorldWideScience
1

Free carrier effects in gallium nitride epilayers the valence band dispersion  

CERN Document Server

The dispersion of the A-valence-band in GaN has been deduced from the observation of high-index magneto-excitonic states in polarised interband magneto-reflectivity and is found to be strongly non-parabolic with a mass in the range 1.2-1.8 m_{e}. It matches the theory of Kim et al. [Phys. Rev. B 56, 7363 (1997)] extremely well, which also gives a strong k-dependent A-valence-band mass. A strong phonon coupling leads to quenching of the observed transitions at an LO-phonon energy above the band gap and a strong non-parabolicity. The valence band was deduced from subtracting from the reduced dispersion the electron contribution with a model that includes a full treatment of the electron-phonon interaction.

Shields, P A; Peeters, F M; Beaumont, B; Gibart, P

2001-01-01

2

Hole transport and valence-band dispersion law in a HgTe quantum well with a normal energy spectrum  

Science.gov (United States)

The results of an experimental study of the energy spectrum of a valence band in a HgTe quantum well of width d splitting are reported. The analysis of the temperature, magnetic field, and gate voltage dependences of the Shubnikov-de Haas oscillations allows us to restore the energy spectrum of the two valence-band branches, which are split by the spin-orbit interaction. Comparison with a theoretical calculation shows that a six-band kP theory well describes all the experimental data in the vicinity of the top of the valence band.

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

2014-04-01

3

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

Science.gov (United States)

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

Yamane, Hiroyuki; Kosugi, Nobuhiro

2014-12-01

4

Valence holes observed in nanodiamonds dispersed in water.  

Science.gov (United States)

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

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

2015-02-01

5

Photon energy dependence of graphite valence band photoelectron intensity  

Energy Technology Data Exchange (ETDEWEB)

We have measured two-dimensional photoelectron spectra of graphite with various photon energies. We investigated the photon energy dependence of the valence band dispersions of graphite at vicinity of Fermi level which appear at Brillouin zone (BZ) corners. We found that the photoelectron intensities of the Fermi surfaces were, however, very different even when the photon energies are selected to see the same symmetry planes of BZ. This intensity difference of the Fermi surfaces is well reproduced by considering the 'photoemission structure factor' for three-dimensional nature of graphite.

Takizawa, Masaru, E-mail: m-tkzw@fc.ritsumei.ac.j [Research Organization of Science and Engineering, Ritsumeikan University, 1-1-1 Noji-Higashi, Kusatsu, Shiga 525-8577 (Japan); Namba, Hidetoshi [Department of Physical Sciences, Faculty of Science and Engineering, Ritsumeikan University, 1-1-1 Noji-Higashi, Kusatsu, Shiga 525-8577 (Japan); Matsui, Fumihiko [Graduate School of Materials Science, Nara Institute of Science and Technology (NAIST), Ikoma, Nara 630-0192 (Japan); Daimon, Hiroshi [Department of Physical Sciences, Faculty of Science and Engineering, Ritsumeikan University, 1-1-1 Noji-Higashi, Kusatsu, Shiga 525-8577 (Japan); Graduate School of Materials Science, Nara Institute of Science and Technology (NAIST), Ikoma, Nara 630-0192 (Japan)

2010-08-15

6

Electronic structure of the valence band of the II--VI wide band gap binary/ternary alloy interfaces  

OpenAIRE

We present an electronic structure calculation of the valence band for some II--VI binary/ternary alloy interfaces. We use the empirical tight-binding method and the surface Green's function matching method. For the ternary alloys we use our previously set Hamiltonians they describe well the band gap change with composition obtained experimentally. At the interface domain, we find three non-dispersive and two interface states besides the known bulk bands. The non-dispersive ...

Olguin, D.; Baquero, R.

1996-01-01

7

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

8

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.)

9

Valence band structure of AlN probed by photoluminescence  

Science.gov (United States)

Deep ultraviolet photoluminescence (PL) was employed to probe the valence band structure of AlN epilayers grown by metal organic chemical vapor deposition on c-plane sapphire substrates. At 10K, in addition to the dominant emission peak at 6.050eV polarized in the E ?c direction, we observed two additional emission peaks at 6.249 and 6.262eV polarized in the E ?c direction. These two emission lines are assigned to the recombination of free excitons related to the B and C valence bands. A more comprehensive picture of the valence band structure of AlN is thus directly obtained from the PL measurements.

Sedhain, A.; Lin, J. Y.; Jiang, H. X.

2008-01-01

10

Interlayer Exchange Coupling Mediated by Valence Band Electrons  

OpenAIRE

The interlayer exchange coupling mediated by valence band electrons in all-semiconductor IV-VI magnetic/nonmagnetic superlattices is studied theoretically. A 3D tight-binding model, accounting for the band and magnetic structure of the constituent superlattice components is used to calculate the spin-dependent part of the total electronic energy. The antiferromagnetic coupling between ferromagnetic layers in EuS/PbS superlattices is obtained, in agreement with the experiment...

Blinowski, J.; Kacman, P.

2000-01-01

11

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.

12

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

13

Resonant fluorescence emission from the Ge and Cu valence band  

Science.gov (United States)

Working out the calculation of the double differential scattering cross section for resonantly excited X-ray emission from valence bands, one ends up [7] with a law of momentum conservation, combining Bloch-k-vectors of the envolved electrons and the incoming and outgoing photon. This leads to a rich structure of the fluorescence line that reveals properties of the underlying electronic band structure. First experiments in the hard X-ray region on Ge and Cu are presented, showing, that momentum conservation in the resonant absorption-emission process holds.

Kaprolat, A.; Schülke, W.

14

Inter-Valence-Subband/Conduction-Band-Transport IR Detectors  

Science.gov (United States)

Infrared (IR) detectors characterized by a combination of (1) high-quantum-efficiency photoexcitation of inter-valence-subband transitions of charge carriers and (2) high-mobility conduction- band transport of the thus-excited charge carriers have been proposed in an effort to develop focal-plane arrays of such devices for infrared imaging. Like many prior quantum-well infrared photodetectors (QWIPs), the proposed devices would be made from semiconductor heterostructures. In order to obtain the combination of characteristics mentioned above, the proposed devices would be designed and fabricated in novel InAs/GaSb superlattice configurations that would exploit a phenomenon known in the semiconductor art as type-II broken-gap band offset.

Ting, David; Gunapala, Sarath; Bandara, Sumith

2004-01-01

15

The vibronic optical bands of mixed valence dimeric clusters  

International Nuclear Information System (INIS)

The review of vibronic optical bands of mixed valence (MV) cluster is given. The MV dimeric clusters consist of two metal ions Me+n and Me+(n+1) in different oxidation states. The metal ions are exchange coupled. The 'extra' electron migration (double exchange) results in the series of exchange-resonance multiplets. The pairs of exchange-resonance states possessing the same total spin and different parities are coupled by the pseudo-Jahn-Teller vibronic interaction. The band shapes of allowed (?S=0) transitions are observed. The effective spin-dependent dipole moment operator for spin-forbidden transition is constructed. It is shown that the spin-allowed transitions bands have the ?-polarization (along the cluster axis). In the framework of the semiclassical approach the vibronic band-shape theory is developed for both cases of all allowed and forbidden transitions. The detected peculiarities of the band-shapes for these transitions closely connected with the key parameters of MV cluster, i.e. pseudo-Jahn-Teller coupling parameter, Heisenberg-type and double exchange parameters. For the solid coordination MV compounds vibronic coupling with the crystal lattice vibrations (optic and acoustic) is taken into account. IN the case under consideration the expressions for vibronic reduction factors for exchange and tunnel parameters are deduced. The interaction of each centre with crystal lattice vibrations lead to the addition coupling between electr to the addition coupling between electronic shells. (author)

16

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

OpenAIRE

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.

Burikov, Sergey A.; Dolenko, Tatiana A.; Fadeev, Victor V.

2008-01-01

17

Band terminations in the valence space of {sup 86}Zr  

Energy Technology Data Exchange (ETDEWEB)

High-spin states in {sup 86}Zr up to 30{sup +} and 27{sup -} were observed via the {sup 58}Ni({sup 32}S,4p) reaction at 135 MeV beam energy using the combined GAMMASPHERE and MICROBALL systems. Calculations performed with the configuration-dependent shell-correction approach show that these states are built from six g{sub 9/2} neutrons and at most four protons excited from the p{sub 1/2},p{sub 3/2},f{sub 5/2} subshells to the g{sub 9/2} subshell at small deformation. The highest observed states at 27{sup -} and 30{sup +} are interpreted as band-terminating states with the latter having the highest spin available in the valence space for {sup 86}Zr. (c) 2000 The American Physical Society.

Doering, J. [Department of Physics, Florida State University, Tallahassee, Florida 32306 (United States); Gesellschaft fuer Schwerionenforschung mbH, D-64291 Darmstadt, (Germany); Akovali, Y. A. [Physics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Baktash, C. [Physics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Durham, F. E. [Department of Physics, Tulane University, New Orleans, Louisiana 70118 (United States); Gross, C. J. [UNISOR, Oak Ridge Institute of Science and Education, Oak Ridge, Tennessee 37831 (United States); Hua, P. F. [Chemistry Department, Washington University, St. Louis, Missouri 63130 (United States); Johns, G. D. [Department of Physics, Florida State University, Tallahassee, Florida 32306 (United States); Korolija, M. [Chemistry Department, Washington University, St. Louis, Missouri 63130 (United States); LaFosse, D. R. [Chemistry Department, Washington University, St. Louis, Missouri 63130 (United States); Lee, I. Y. [Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)] (and others)

2000-03-01

18

Band terminations in the valence space of 86Zr  

International Nuclear Information System (INIS)

High-spin states in 86Zr up to 30+ and 27- were observed via the 58Ni(32S,4p) reaction at 135 MeV beam energy using the combined GAMMASPHERE and MICROBALL systems. Calculations performed with the configuration-dependent shell-correction approach show that these states are built from six g9/2 neutrons and at most four protons excited from the p1/2,p3/2,f5/2 subshells to the g9/2 subshell at small deformation. The highest observed states at 27- and 30+ are interpreted as band-terminating states with the latter having the highest spin available in the valence space for 86Zr. (c) 2000 The American Physical Society

19

Internal-strain effect on the valence band of strained silicon and its correlation with the bond angles  

International Nuclear Information System (INIS)

By means of the first-principles density-functional theory, we investigate the effect of relative atom displacement in the crystal unit cell, namely, internal strain on the valence-band dispersion of strained silicon, and find close correlation of this effect with variation in the specific bond angles due to internal strain. We consider the [111] ([110]) band dispersion for (111) ((110)) biaxial tensility and [111] ([110]) uniaxial compression, because remarkably small values of hole effective mass m* can be obtained in this dispersion. Under the practical condition of no normal stress, biaxial tensility (uniaxial compression) involves additional normal compression (tensility) and internal strain. With an increase in the internal-strain parameter, the energy separation between the highest and second-highest valence bands becomes strikingly larger, and the highest band with conspicuously small m* extends remarkably down to a lower energy region, until it intersects or becomes admixed with the second band. This is closely correlated with the change in the specific bond angles, and this change can reasonably explain the above enlargement of the band separation

20

Electronic Structure and Valence Band Spectra of Bi4Ti3O12  

OpenAIRE

The x-ray photoelectron valence band spectrum and x-ray emission valence-band spectra (Ti K _beta_5, Ti L_alpha, O K_alpha) of Bi4Ti3O12 are presented (analyzed in the common energy scale) and interpreted on the basis of a band-structure calculation for an idealized I4/mmm structure of this material.

Postnikov, A. V.; Bartkowski, St; Mersch, F.; Neumann, M.; Kurmaev, E. Z.; Cherkashenko, V. M.; Nemnonov, S. N.; Galakhov, V. R.

1995-01-01

21

Valence band structure of binary chalcogenide vitreous semiconductors by high-resolution XPS  

Energy Technology Data Exchange (ETDEWEB)

High-resolution X-ray photoelectron spectroscopy (XPS) is used to study regularities in the formation of valence band electronic structure in binary As{sub x}Se{sub 100-x}, As{sub x}S{sub 100-x}, Ge{sub x}Se{sub 100-x} and Ge{sub x}S{sub 100-x} chalcogenide vitreous semiconductors. It is shown that the highest occupied energetic states in the valence band of these materials are formed by lone pair electrons of chalcogen atoms, which play dominant role in the formation of valence band electronic structure of chalcogen-rich glasses. A well-expressed contribution from chalcogen bonding p electrons and more deep s orbitals are also recorded in the experimental valence band XPS spectra. Compositional dependences of the observed bands are qualitatively analyzed from structural and compositional points of view.

Kozyukhin, S., E-mail: sergkoz@igic.ras.ru [Russian Academy of Science, Institute of General and Inorganic Chemistry (Russian Federation); Golovchak, R. [Lviv Scientific Research Institute of Materials of SRC ' Carat' (Ukraine); Kovalskiy, A. [Lehigh University, Department of Materials Science and Engineering (United States); Shpotyuk, O. [Lviv Scientific Research Institute of Materials of SRC ' Carat' (Ukraine); Jain, H. [Lehigh University, Department of Materials Science and Engineering (United States)

2011-04-15

22

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)

23

Correlation effects in the valence bands of ferromagnetic semiconductor EuS  

CERN Document Server

We present a many body analysis of the multi-band Kondo lattice model. The study is then combined with the first principles TB-LMTO band structure calculations, in order to investigate the temperature dependent correlation effects in the 3$\\textit{p}$ valence bands of the ferromagnetic semiconductor EuS. Some of the physical properties of interest like the quasi-particle density of states (Q-DOS), spectral density (SD) and quasi-particle band structure (Q-BS) are calculated and discussed. Therewith, we propose a spin resolved ARPES of the valence bands of EuS to be performed.

Sharma, A

2005-01-01

24

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)

25

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

26

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

International Nuclear Information System (INIS)

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

27

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

Science.gov (United States)

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

Schwöbel, André; Precht, Ruben; Motzko, Markus; Carrillo Solano, Mercedes A.; Calvet, Wolfram; Hausbrand, René; Jaegermann, Wolfram

2014-12-01

28

Conformation effects in the XPS valence band spectra of aliphatic polyesters  

International Nuclear Information System (INIS)

XPS valence band spectra are reported for seven aliphatic polyesters. By comparison of the spectra with that of PMMA a qualitative understanding of the spectral features is achieved. By comparing valence band spectra of semi-crystalline solid and polymer melt samples, chain conformation effects are identified for five of the polyesters. For four of these the effects may be attributed to changes in methylenic hyperconjugation interactions on melting but the fifth contains (CH2)n segments that are too short for methylenic hyperconjugation to occur. Only one of the polyesters showed a significant conformation effect in the C 1s spectrum

29

Conformation effects in the XPS valence band spectra of aliphatic polyesters  

Energy Technology Data Exchange (ETDEWEB)

XPS valence band spectra are reported for seven aliphatic polyesters. By comparison of the spectra with that of PMMA a qualitative understanding of the spectral features is achieved. By comparing valence band spectra of semi-crystalline solid and polymer melt samples, chain conformation effects are identified for five of the polyesters. For four of these the effects may be attributed to changes in methylenic hyperconjugation interactions on melting but the fifth contains (CH{sub 2}){sub n} segments that are too short for methylenic hyperconjugation to occur. Only one of the polyesters showed a significant conformation effect in the C 1s spectrum.

Beamson, G. [National Centre for Electron Spectroscopy and Surface Analysis, CCLRC Daresbury Laboratory, Warrington, Cheshire WA4 4AD (United Kingdom)], E-mail: g.beamson@dl.ac.uk

2007-02-15

30

Electronic valence band structure of V2O5  

International Nuclear Information System (INIS)

We present high-resolution ARPES measurements of V2O5 single crystals carried out with synchrotron radiation and He I resonance lamp. The obtained experimentally band structure in k parallel is compared with calculations, e.g. The aging behavior of different bands with time is studied. The degradation of the surface due to the high reactivity is discussed referring to the previous reported experimental work.

31

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-09-21

32

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

International Nuclear Information System (INIS)

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

33

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

Science.gov (United States)

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

Neuschl, B.; Helbing, J.; Knab, M.; Lauer, H.; Madel, M.; Thonke, K.; Meisch, T.; Forghani, K.; Scholz, F.; Feneberg, M.

2014-09-01

34

Valence band variation in Si (110) nanowire induced by a covered insulator  

International Nuclear Information System (INIS)

In this work, we investigate strain effects induced by the deposition of gate dielectrics on the valence band structures in Si (110) nanowire via the simulation of strain distribution and the calculation of a generalized 6×6k·p strained valence band. The nanowire is surrounded by the gate dielectric. Our simulation indicates that the strain of the amorphous SiO2 insulator is negligible without considering temperature factors. On the other hand, the thermal residual strain in a nanowire with amorphous SiO2 insulator which has negligible lattice misfit strain pushes the valence subbands upwards by chemical vapour deposition and downwards by thermal oxidation treatment. In contrast with the strain of the amorphous SiO2 insulator, the strain of the HfO2 gate insulator in Si (110) nanowire pushes the valence subbands upwards remarkably. The thermal residual strain by HfO2 insulator contributes to the up-shifting tendency. Our simulation results for valence band shifting and warping in Si nanowires can provide useful guidance for further nanowire device design. (classical areas of phenomenology)

35

Valence Band Onset and Valence Plasmons of SnO2 and In2-xSnx O3 Thin Films  

OpenAIRE

Valence band onset (Ev), valence band tail (VBT) and valence plasmons (VPs) have been studied as a function of sputtering of SnO2 and In2-xSnxO3 (ITO) thin films, using ultraviolet photoemission spectroscopy (UPS). Decrease in Ev with respect to the Fermi level and increase in the density of energy levels of VBT have been observed after 5 minutes of sputtering using Ar+ ions (500V). Bulk and surface components of VPs of Sn, SnO and SnO2 in sputtered SnO2 thin films have been...

Kumar, Shailendra; Mukherjee, C.; Phase, D. M.

2014-01-01

36

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

37

Photoemission from solid rare gases: electron energy distributions from the valence bands  

International Nuclear Information System (INIS)

Photoelectron energy distributions for solid Ne, Ar, Kr and Xe have been measured for 8 eV <= h?/2? <= 30 eV by use of synchrotron radiation. From these one obtained the total width and structure of the valence bands. The data demonstrate that almost all available band structure calculations fail to predict quantitatively other features than the spin orbit splitting. Photoelectron energy distributions for Xe in Ar and Xe in Ne support this viewpoint. (orig.)

38

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

39

Energy spectrum of second valence band in PbSnTe solid solutions  

International Nuclear Information System (INIS)

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

40

Valence correlation bands of model oligomers of polyethylene: A Green's function study by the band-Lanczos approach  

Science.gov (United States)

The innermost valence electron levels of large molecular chains are subject to a strong breakdown of the orbital picture of ionization into particularly dense sets of shake-up lines with exceedingly small intensities, which give rise to correlation bands in the ionization spectrum. A suitable algorithm is required for a size-consistent investigation of such sets. In this work, we report the inclusion of the band-Lanczos approach in the final diagonalization step of a one-electron Green's function calculation in the algebraic diagrammatic construction scheme. From a first application to a series of oligomers CnH2n+2 (n=2-9) converging to polyethylene, the C2s correlation bands of large saturated hydrocarbons are shown to extend beyond 60 eV, and to represent, regardless of cross section effects, at least 20% of the total valence ionization intensity, and about 60% of the intensity found in the inner valence region [?b=18-70 eV]. With the band-Lanczos approach, the distribution of spectral intensity is nearly entirely recovered, with the exception of a tiny violation (2% for the n-nonane compound).

Golod, A.; Deleuze, M. S.; Cederbaum, L. S.

1999-03-01

41

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

International Nuclear Information System (INIS)

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 valence band spectra shows the type-II band alignment between GaPN0.22/GaP and the valence band offset is ?2.2±0.1 eV.

42

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.

43

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

International Nuclear Information System (INIS)

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

44

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 crossoum oxides, with the sum of both crossover and valence X-ray normalized intensities being the most sensitive measure.

45

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-09-15

46

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

47

Valence band offset of ZnO/BaTiO{sub 3} heterojunction measured by X-ray photoelectron spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

X-ray photoelectron spectroscopy has been used to measure the valence band offset of the ZnO/BaTiO{sub 3} heterojunction grown by metal-organic chemical vapor deposition. The valence band offset (VBO) is determined to be 0.48{+-}0.09 eV, and the conduction band offset (CBO) is deduced to be about 0.75 eV using the band gap of 3.1 eV for bulk BaTiO{sub 3}. It indicates that a type-II band alignment forms at the interface, in which the valence and conduction bands of ZnO are concomitantly higher than those of BaTiO{sub 3}. The accurate determination of VBO and CBO is important for use of semiconductor/ferroelectric heterojunction multifunctional devices. (orig.)

Jia, C.H.; Chen, Y.H.; Zhou, X.L.; Yang, A.L.; Zheng, G.L.; Liu, X.L.; Yang, S.Y.; Wang, Z.G. [Chinese Academy of Science, Key Laboratory of Semiconductor Material Science, Institute of Semiconductors, Beijing (China)

2010-05-15

48

Band Symmetries of Mixed-Valence Topological Insulator: SmB6  

Science.gov (United States)

We have investigated the band structure and the band symmetry of mixed-valence insulator SmB6 systematically within the density functional theory (DFT). To describe the strong correlation effect of 4f-electrons in SmB6 effectively within the DFT level, we have devised a scheme to adjust the spin-orbit coupling (SOC) strength of Sm 4f electron artificially, which is verified to be a valid approximation by comparison with the band structure from the dynamical mean-field theory (DMFT). We have analyzed the symmetries and characters of Sm 4f and 5d bands near the Fermi level (EF) in terms of the non-relativistic real cubic bases as well as the relativistic complex bases incorporating the SOC and the cubic crystal field. Based on the full band symmetry analysis, the ground state of SmB6 is found to be in the ?7 multiplet state, and Sm 5d band that hybridizes with Sm 4f band near EF has the eg symmetry. Further, we have found that the semi-core band located at ˜15 eV below EF has the mixed parity and thereby affects the parity eigenvalues of the special k-points considerably. We have discussed the possible surface states and topological class of SmB6, based on the bulk parity tables.

Kang, Chang-Jong; Kim, Junwon; Kim, Kyoo; Kang, Jeongsoo; Denlinger, Jonathan D.; Min, Byung Il

2015-02-01

49

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

Energy Technology Data Exchange (ETDEWEB)

The band width may be considered the single most important parameter characterizing the electronic structure of a solid. The ratio of band width and Coulomb repulsion determines how correlated or delocalized an electron system is. Some of the most interesting solids straddle the boundary between localized and delocalized, e.g. the high-temperature superconductors. The bulk of the band calculations available today is based on local density functional (DF) theory. Even though the Kohn-Sham eigenvalues from that theory do not represent the outcome of a band-mapping experiment, they are remarkably similar to the bands mapped via photoemission. Strictly speaking, one should use an excited state calculation that takes the solid`s many-body screening response to the hole created in photoemission into account. Diamond is a useful prototype semiconductor because of its low atomic number and large band width, which has made it a long-time favorite for testing band theory. Yet, the two experimental values of the band width of diamond have error bars of {+-}1 eV and differ by 3.2 eV. To obtain an accurate valence band width for diamond, the authors use a band-mapping method that collects momentum distributions instead of the usual energy distributions. This method has undergone extensive experimental and theoretical tests in determining the band width of lithium fluoride. An efficient, imaging photoelectron spectrometer is coupled with a state-of-the-art undulator beam line at the Advanced Light Source to allow collection of a large number of data sets. Since it takes only a few seconds to take a picture of the photoelectrons emitted into a 84{degrees} cone, the authors can use photon energies as high as 350 eV where the cross section for photoemission from the valence band is already quite low, but the emitted photoelectrons behave free-electron-like. This make its much easier to locate the origin of the inter-band transitions in momentum space.

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

1997-04-01

50

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

International Nuclear Information System (INIS)

The band width may be considered the single most important parameter characterizing the electronic structure of a solid. The ratio of band width and Coulomb repulsion determines how correlated or delocalized an electron system is. Some of the most interesting solids straddle the boundary between localized and delocalized, e.g. the high-temperature superconductors. The bulk of the band calculations available today is based on local density functional (DF) theory. Even though the Kohn-Sham eigenvalues from that theory do not represent the outcome of a band-mapping experiment, they are remarkably similar to the bands mapped via photoemission. Strictly speaking, one should use an excited state calculation that takes the solid's many-body screening response to the hole created in photoemission into account. Diamond is a useful prototype semiconductor because of its low atomic number and large band width, which has made it a long-time favorite for testing band theory. Yet, the two experimental values of the band width of diamond have error bars of ±1 eV and differ by 3.2 eV. To obtain an accurate valence band width for diamond, the authors use a band-mapping method that collects momentum distributions instead of the usual energy distributions. This method has undergone extensive experimental and theoretical tests in determining the band width of lithium fluoride. An efficient, imaging photoelectron spectrometer is coupled with a state-of-the-art undulator beam line at the Advanced Light Source to allow collection of a large number of data sets. Since it takes only a few seconds to take a picture of the photoelectrons emitted into a 84 degrees cone, the authors can use photon energies as high as 350 eV where the cross section for photoemission from the valence band is already quite low, but the emitted photoelectrons behave free-electron-like. This make its much easier to locate the origin of the inter-band transitions in momentum space

51

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

Science.gov (United States)

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

Strand, Hugo U. R.

2014-10-01

52

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

Science.gov (United States)

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

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

1991-01-01

53

Pressure variation of the valence band width in Ge: A self-consistent GW study  

DEFF Research Database (Denmark)

Analyzing x-ray emission spectra XES of germanium under pressure Struzhkin et al. [Phys. Rev. Lett. 96, 137402 (2006)] found that the valence band width of diamond Ge does not vary with pressure. This contradicts the usual experience and also what is predicted by density-functional calculations. In the present work we report results of quasiparticle self-consistent GW  (QSGW) band calculations for diamond- as well as ?-tin-type Ge under pressure. For both phases we find that the band width increases with pressure. For ?-tin Ge this agrees with experiment and density-functional theory, but for diamond Ge neither the local density approximation nor the QSGW calculations agree with the conclusions drawn from the XES data.

Modak, Paritosh; Svane, Axel

2009-01-01

54

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

Science.gov (United States)

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 structures of semiconductors is proposed. The HgTe-CdTe system is used as an example in which it is found that the valence-band maximum of HgTe lies 0.35 + or - 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 on the heterojunction band lineup and the electronic structures of semiconductor alloys, are discussed.

Shih, C. K.; Spicer, W. E.

1987-01-01

55

Highly dispersive photonic band-gap-edge optofluidic biosensors  

CERN Document Server

Highly dispersive photonic band-gap-edge optofluidic biosensors are studied theoretically. We demonstrate that these structures are strongly sensitive to the refractive index of the liquid, which is used to tune dispersion of the photonic crystal. The upper frequency band-gap edge shifts about 1.8 nm for dn=0.002, which is quite sensitive. Results from transmission spectra agree well with those obtained from the band structure theory.

Xiao, S; Xiao, Sanshui; Mortensen, Niels Asger

2006-01-01

56

Experimental study of the valence band of Bi2Se3  

Science.gov (United States)

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

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

2014-09-01

57

The Synthesis of NiO/TiO2 Heterostructures and Their Valence Band Offset Determination  

OpenAIRE

In this work, a heterojunction based on p-type NiO/n-type TiO2 nanostructures has been prepared on the fluorine doped tin oxide (FTO) glass substrate by hydrothermal method. Scanning electron microscopy (SEM) and X-Ray diffraction techniques were used for the morphological and crystalline arrays characterization. The X-ray photoelectron spectroscopy was employed to determine the valence-band offset (VBO) of the NiO/TiO2 heterojunction prepared on FTO glass substrate. The core levels of Ni 2p ...

Ibupoto, Z. H.; Abbasi, M. A.; Liu, X.; Alsalhi, M. S.; Willander, M.

2014-01-01

58

Investigation of the valence-band structure of graphite and the interaction of graphite with nickel  

International Nuclear Information System (INIS)

The valence-band structure of graphite was investigated by UPS and XPS, and the result was compared with the theoretical result of Painter et al. Due to the interaction of C-atom with Ni-atom, Ni3C was observed after vapor deposition of Ni on graphite surface. The C 2px,y orbital is raised up to 5 eV below the Fermi level, while the C 2pz orbital is approaching the Fermi level closely after formation of Ni3C

59

Electronic structure of the valence band of II--VI wide band gap semiconductor interfaces  

OpenAIRE

In this work we present the electronic band structure for (001)--CdTe interfaces with some other II--VI zinc blende semiconductors. We assume ideal interfaces. We use tight binding Hamiltonians with an orthogonal basis ($s p^3 s^*$). We make use of the well--known Surface Green's Function Matching method to calculate the interface band structure. In our calculation the dominion of the interface is constituted by four atomic layers. We consider here anion--anion interfaces on...

Olguin, D.; Baquero, R.

1996-01-01

60

Possible resolution of the valence-band offset controversy in HgTe/CdTe superlattices  

International Nuclear Information System (INIS)

The valence-band offset controversy in HgTe/CdTe superlattices can be simply resolved by showing, as we do here, that a large offset value (?>300 meV) is indeed consistent with the magneto-optical data of Berroir et al. [Phys. Rev. B 34, 891 (1986)]. The superlattice (100 A HgTe/36 A CdTe) becomes semimetallic (SM) when ? is increased from small values, but reverts to semiconducting (SC) behavior for ?>300 meV. The band gap in this new regime occurs at the superlattice Brillouin zone face. The sensitivity to layer thicknesses of such SC?SM?SC transitions is discussed and experiments suggested

61

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)

62

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

63

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

OpenAIRE

We show that repulsive local Coulomb interaction alone can drive valence-skipping charge disproportionation in the degenerate d-band, resulting in effective negative-U. This effect is shown to originate from anisotropic orbital-multipole scattering, and occurs only for $d^1$, $d^4$, $d^6$ and $d^9$ fillings (and their immediate surroundings). Explicit boundaries for valence-skipping are derived and the paramagnetic phase diagram for $d^4$ and $d^6$ is calculated. We also est...

Strand, Hugo U. R.

2014-01-01

64

Electronic band dispersion of graphene nanoribbons via Fourier-transformed scanning tunneling spectroscopy  

Science.gov (United States)

The electronic structure of atomically precise armchair graphene nanoribbons of width N =7 (7-AGNRs) are investigated by scanning tunneling spectroscopy (STS) on Au(111). We record the standing waves in the local density of states of finite ribbons as a function of sample bias and extract the dispersion relation of frontier electronic states by Fourier transformation. The wave-vector-dependent contributions from these states agree with density functional theory calculations, thus enabling the unambiguous assignment of the states to the valence band, the conduction band, and the next empty band with effective masses of 0.41 ±0.08 me ,0.40 ±0.18 me , and 0.20 ±0.03 me , respectively. By comparing the extracted dispersion relation for the conduction band to corresponding height-dependent tunneling spectra, we find that the conduction band edge can be resolved only at small tip-sample separations and has not been observed before. As a result, we report a band gap of 2.37 ±0.06 eV for 7-AGNRs adsorbed on Au(111).

Söde, Hajo; Talirz, Leopold; Gröning, Oliver; Pignedoli, Carlo Antonio; Berger, Reinhard; Feng, Xinliang; Müllen, Klaus; Fasel, Roman; Ruffieux, Pascal

2015-01-01

65

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

Science.gov (United States)

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

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

2015-04-01

66

Magneto-photoluminescence of GaN/AlGaN quantum wells: valence band reordering and excitonic binding energies  

OpenAIRE

A re-ordered valence band in GaN/AlGaN quantum wells with respect to GaN epilayers has been found as a result of the observation of an enhanced g-factor in magneto-luminescence spectra in fields up to 55 T. This has been caused by a reversal of the states in the strained AlGaN barriers thus giving different barrier heights for the different quantum well hole states. From k.p calculations in the quasi-cubic approximation, a change in the valence-band ordering will account for...

Shields, P. A.; Nicholas, R. J.; Grandjean, N.; Massies, J.

2001-01-01

67

Valence band XPS and UPS studies of non-stoichiometric superconducting NbB2+x  

International Nuclear Information System (INIS)

The electronic structure of non-stoichiometric superconducting NbB2+x has been investigated by x-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). The analysis of the valence band using XPS and UPS reveals that the boron doping induces a systematic decrease in the density of states at Fermi level N(EF) similar to that observed in the Nb1?xB2 system. In particular, N(EF) is lower for the superconducting samples than for the non-superconducting ones. In the superconducting samples, we confirm that the Tc is inversely proportional to N(EF). Therefore, the presence of superconductivity in these samples cannot be explained only as a function of the N(EF). Thus, the presence of superconductivity in our samples might be explained by increases in the number of holes in-plane conduction, due to an increase in the number of niobium vacancies as boron content is increased.

68

Thermodynamics of intermediate-valence two-band ferromagnets: magnetic properties  

Energy Technology Data Exchange (ETDEWEB)

We present the influence of the finite bandwidth of the 4f (5f) band and finite intrasite Coulomb repulsion on the magnetic properties of the generalized s-f model. The calculation of the Curie temperature T{sub C} shows that the increase of the 4f (5f) bandwidth suppress the magnetic phase and can completely destroy it. The increase in the Coulomb intrasite repulsion acts in the opposite direction. The mechanism of indirect exchange interaction is discussed in detail to explain the shapes of the T{sub C} dependence on different model parameters. The calculated T{sub C} dependence on the average occupation number or on the position of the 4f (5f) level shows great similarities to the experimentally measured T{sub C} curves versus applied pressure or dopant concentration in many intermediate-valence rare-earth or actinide compounds and alloys. (orig.).

Matlak, M. [Uniwersytet Slaski, Katowice (Poland). Inst. Fizyki; Pietruszka, M. [Faculty of Biology, Silesian University, 28 Jagiellonska, PL-40-032 Katowice (Poland)

1996-02-01

69

Thermodynamics of intermediate-valence two-band ferromagnets: magnetic properties  

International Nuclear Information System (INIS)

We present the influence of the finite bandwidth of the 4f (5f) band and finite intrasite Coulomb repulsion on the magnetic properties of the generalized s-f model. The calculation of the Curie temperature TC shows that the increase of the 4f (5f) bandwidth suppress the magnetic phase and can completely destroy it. The increase in the Coulomb intrasite repulsion acts in the opposite direction. The mechanism of indirect exchange interaction is discussed in detail to explain the shapes of the TC dependence on different model parameters. The calculated TC dependence on the average occupation number or on the position of the 4f (5f) level shows great similarities to the experimentally measured TC curves versus applied pressure or dopant concentration in many intermediate-valence rare-earth or actinide compounds and alloys. (orig.)

70

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

Science.gov (United States)

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

Nasu, T.; Hosokawa, S.; Nakatake, M.; Sato, H.; Zhang, W.; Inoue, A.

2009-01-01

71

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

International Nuclear Information System (INIS)

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

72

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

International Nuclear Information System (INIS)

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

73

The role of beryllium in the band structure of MgZnO: Lifting the valence band maximum  

Science.gov (United States)

We investigate the effect of Be on the valence band maximum (VBM) of MgZnO by measuring the band offsets of MgxZn1-xO/BexMgyZn1-x-yO heterojunctions using X-ray photoelectron spectroscopy measurements. MgxZn1-xO and BexMgyZn1-x-yO films have been grown on c-plane sapphire substrates by plasma-assisted molecular beam epitaxy. The valence band offset ( ? E V) of Mg0.15Zn0.85O ( E g = 3.62 eV)/Be0.005Mg0.19Zn0.805O ( E g = 3.73 eV) heterojunction is 0.01 eV and Be0.005Mg0.19Zn0.805O has a lower VBM. The increased Mg composition is the main factor for the reduction of VBM. The VBM of MgxZn1-xO is lower by 0.03 eV with the enlargement of E g from 3.62 eV to 3.73 eV by increasing Mg composition. Considering the effect of increased Mg composition, it is concluded that the little amount of Be makes the VBM go up by 0.02 eV when the E g of the alloy is 3.73 eV. The ? E V of Mg0.11Zn0.89O ( E g = 3.56 eV)/Be0.007Mg0.12Zn0.873O ( E g = 3.56 eV) heterojunction is calculated to be 0.03 eV and Be0.007Mg0.12Zn0.873O has a higher VBM than Mg0.11Zn0.89O, which means that a little amount Be lifts the VBM by 0.03 eV when the E g of the alloy is 3.56 eV. The experimental measurements have offered a strong support for the theoretical research that alloying Be in MgxZn1-xO alloys is hopeful to form a higher VBM and to enhance the p-type dopability of MgZnO.

Chen, S. S.; Pan, X. H.; Chen, W.; Zhang, H. H.; Dai, W.; Ding, P.; Huang, J. Y.; Lu, B.; Ye, Z. Z.

2014-09-01

74

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 M1M4sub(,)5V and M3M4sub(,)5V and Se M1M4sub(,)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.)

75

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.

76

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

International Nuclear Information System (INIS)

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

77

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

Science.gov (United States)

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

King, Sean W.; Paquette, Michelle M.; Otto, Joseph W.; Caruso, A. N.; Brockman, Justin; Bielefeld, Jeff; French, Marc; Kuhn, Markus; French, Benjamin

2014-03-01

78

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

Energy Technology Data Exchange (ETDEWEB)

To facilitate the design of heterostructure devices employing hexagonal/sp{sup 2} boron nitride, x-ray photoelectron spectroscopy has been utilized in conjunction with prior reflection electron energy loss spectroscopy measurements to determine the valence and conduction band offsets (VBOs and CBOs) present at interfaces formed between amorphous hydrogenated sp{sup 2} boron nitride (a-BN:H) and various low- and high-dielectric-constant (k) amorphous hydrogenated silicon network dielectric materials (a-SiX:H, X?=?O, N, C). For a-BN:H interfaces formed with wide-band-gap a-SiO{sub 2} and low-k a-SiOC:H materials (E{sub g}???8.2?8.8?eV), a type I band alignment was observed where the a-BN:H band gap (E{sub g}?=?5.5?±?0.2?eV) was bracketed by a relatively large VBO and CBO of ?1.9 and 1.2?eV, respectively. Similarly, a type I alignment was observed between a-BN:H and high-k a-SiC:H where the a-SiC:H band gap (E{sub g}?=?2.6?±?0.2?eV) was bracketed by a-BN:H with VBO and CBO of 1.0?±?0.1 and 1.9?±?0.2?eV, respectively. The addition of O or N to a-SiC:H was observed to decrease the VBO and increase the CBO with a-BN:H. For high-k a-SiN:H (E{sub g}?=?3.3?±?0.2?eV) interfaces with a-BN:H, a slightly staggered type II band alignment was observed with VBO and CBO of 0.1?±?0.1 and ?2.3?±?0.2?eV, respectively. The measured a-BN:H VBOs were found to be consistent with those deduced via application of the commutative and transitive rules to VBOs reported for a-BN:H, a-SiC:H, a-SiN:H, and a-SiO{sub 2} interfaces with Si (100)

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

2014-03-10

79

Origin of the band dispersion in a metal phthalocyanine crystal  

Science.gov (United States)

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

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

2014-12-01

80

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

Science.gov (United States)

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

Korte, L.; Rößler, R.; Pettenkofer, C.

2014-05-01

81

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

International Nuclear Information System (INIS)

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

82

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

Energy Technology Data Exchange (ETDEWEB)

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

Korte, L., E-mail: korte@helmholtz-berlin.de; Rößler, R.; Pettenkofer, C. [Helmholtz-Zentrum Berlin, Institute for Silicon Photovoltaics, Kekuléstrasse 5, 12489 Berlin (Germany)

2014-05-28

83

Density of valence electrons and dispersion energy in annealed dc glow discharge a-Si:H  

International Nuclear Information System (INIS)

Films of amorphous silicon films are prepared by the deposition of SiH/sub 4 in a dc plasma glow discharge reactor and at a substrate temperature of 140 degrees C. The optical energy gap and refractive index are measured at different annealing temperatures of up to 600 degrees C, in an ambient of nitrogen. The refractive index is found to be between 2.05 and 4.01 while the optical gap ranges from 1.93 and 2.16 eV. Using the model of Freeman and Paul, the density of valence electrons in the a-Si:H is estimated to be less than 5 x 10/sup 22 cm/sup -3. The dispersion energy is calculated and it is found that its value changes irregularly within 4.58 to 20.66 eV with the annealing temperature. These observations are correlated to the mechanisms involved during annealing like the out diffusion-effusion of hydrogen, re-ordering process involving microvoids and strained bonds, and finally the amorphous network undergoing recrystallization. (authors)

84

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

International Nuclear Information System (INIS)

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

85

Valence-band mixing induced by sp-d exchange interaction in CdMnTe quantum wires  

Science.gov (United States)

Anisotropic magneto-optical effects have been studied theoretically by using multi-band effective mass method. We focus on a model of an ideal CdMnTe quantum wire surrounded by infinite potential barriers. The mixing of heavy- and light-hole bands is caused by both the one-dimensional quantum confinement and the sp-d exchange interaction. As a result of the valence-band mixing characteristic to the one-dimensional diluted magnetic semiconductor, the Zeeman splitting in the magnetic field parallel to the wire direction becomes smaller than that in the perpendicular magnetic field.

Harada, Y.; Kita, T.; Wada, O.; Marsal, L.; Mariette, H.; Ando, H.

2006-03-01

86

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

87

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

International Nuclear Information System (INIS)

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

88

Analysis of high-temperature thermoelectric properties of p-type CoSb3 within a two-valence-band and two-conduction-band model  

Science.gov (United States)

Experimental data on the thermoelectric properties of p-type CoSb3 reported by Caillat et al. [J. Appl. Phys. 80, 4442 (1996)] have been analyzed, assuming not only a pair of the first valence (v1) and the first conduction (c1) bands but also the second valence (v2) and the second conduction (c2) bands. By taking into account the excitation of carriers into the v2 and the c2 bands, the behavior of the Hall coefficient as well as that of the Seebeck coefficient at high temperatures is well explained. By taking into account the nonparabolicity of the v1 band, the temperature dependence of mobility is well explained with assuming scattering due to acoustic phonons, nonpolar and polar optical phonons, and ionized impurities. Furthermore, various material parameters of CoSb3, such as the band-gap energy, effective masses, and deformation potentials, have been deduced from fitting the calculation to the experimental data on the temperature dependences of the Hall coefficient, the mobility, and the Seebeck coefficient. Among them, the band-gap energy and the effective mass of the v1 band have been corrected from the original values estimated by Caillat et al. In addition, it is shown that the experimental data on the hole-concentration dependences of both the room-temperature Seebeck coefficient and the cyclotron mass are well reproduced by the theoretical calculation using the deduced values for the nonparabolic v1 band.

Kajikawa, Y.

2014-05-01

89

Comparison of the background corrected valence band XPS spectra of Fe and Co aluminides and silicides with their electronic structures  

International Nuclear Information System (INIS)

The background corrected valence band XPS spectra and the electronic structures of FeAl, FeSi, CoAl and CoSi were studied. Clean surfaces of the polycrystalline samples were obtained by in situ fracturing of the samples in an XPS spectrometer. The energy loss parts of the Fe 2p, Co 2p and valence band spectra were removed by the deconvolution method using Al 2s or Si 2s spectra as response functions. CoAl exhibited a satellite peak in the Co 2p region, but the other compounds had no clear satellite peaks in the Co 2p and Fe 2p regions. The experimentally background corrected valence band spectra were compared with the calculated spectra using the first-principle band calculation. There were large discrepancies between the spectra above the binding energy of 5 eV. These indicated that the experimental spectra could not be explained by the electronic structures of the ground states alone

90

Valence band and catalytic activity of Au nanoparticles in Fe2O3/SiO2/Si(100) environment  

International Nuclear Information System (INIS)

A 10-nm-thick gold film was evaporated onto a SiO2/Si(100) substrate and was implanted by Ar+ ions at 40 keV and 1015 at/cm2 dose creating island like Au nanoparticles. An 80-nm-thick gold film was also deposited the onto same substrate and considered as reference. Fe2O3 film was deposited onto the gold nanoparticles and the gold/oxide interface was modeled. The valence band and the structure were measured by means of photoelectron spectroscopy (XPS) and by transmission electron microscopy (TEM), respectively. The catalytic activity was detected by CO oxidation, which was higher after the deposition of Fe2O3 layer onto Au nanoparticles than that on a continuous Au film. This observation was correlated to the nanosize and the redistributed valence band density of states of gold in the Au/Fe2O3 interface

91

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

92

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

International Nuclear Information System (INIS)

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

93

On the photoemission spectra of CoO: crystal-field analyses of the valence band structure  

International Nuclear Information System (INIS)

The valence band structure of CoO deduced from x-ray and ultraviolet photoemission spectroscopy is described in the framework of crystal-field theory. The energy of the transitions from the ground state of CO2+ to all states of CO3+ as well as the corresponding relative intensities are determined by taking, for the first time, strong-field configuration interaction into account

94

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

95

Valence band and core-level analysis of highly luminescent ZnO nanocrystals for designing ultrafast optical sensors  

OpenAIRE

Highly luminescent ZnO:Na nanocrystals of size ~2 nm were synthesized using a improved sol-lyophilization process. The surface analysis such as survey scan, core-level and valence band spectra of ZnO:Na nanocrystals were studied using x-ray photoelectron spectroscopy (XPS) to establish the presence of Na+ ions. The observed increase in band gap from 3.30 (bulk) to 4.16 eV (nano), is attributed to the quantum confinement of the motion of electron and holes in all three direct...

Joshi, Amish G.; Sahai, Sonal; Gandhi, Namita; Krishna, Y. G. Radha; Haranath, D.

2010-01-01

96

Dispersive Elastodynamics of 1D Banded Materials and Structures: Design  

CERN Document Server

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

Hussein, M I; Scott, R A

2006-01-01

97

Dispersive Elastodynamics of 1D Banded Materials and Structures: Design  

OpenAIRE

Within periodic materials and structures, wave scattering and dispersion occur across constituent material interfaces leading to a banded frequency response. In an earlier paper, the elastodynamics of one-dimensional periodic materials and finite structures comprising these materials were examined with an emphasis on their frequency-dependent characteristics. In this work, a novel design paradigm is presented whereby periodic unit cells are designed for desired frequency ban...

Hussein, M. I.; Hulbert, G. M.; Scott, R. A.

2006-01-01

98

Valence-band mixing induced by sp-d exchange interaction in CdMnTe quantum wires  

Energy Technology Data Exchange (ETDEWEB)

Anisotropic magneto-optical effects have been studied theoretically by using multi-band effective mass method. We focus on a model of an ideal CdMnTe quantum wire surrounded by infinite potential barriers. The mixing of heavy- and light-hole bands is caused by both the one-dimensional quantum confinement and the sp-d exchange interaction. As a result of the valence-band mixing characteristic to the one-dimensional diluted magnetic semiconductor, the Zeeman splitting in the magnetic field parallel to the wire direction becomes smaller than that in the perpendicular magnetic field. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Harada, Y.; Kita, T.; Wada, O. [Department of Electrical and Electronics Engineering, Faculty of Engineering, Kobe University, Rokkodai 1-1, Nada, 657-8501, Kobe (Japan); Marsal, L.; Mariette, H. [Laboratoire de Spectrometrie Physique, Universite J. Fourier, Grenoble I, CNRS (UMR 5588), Boite Postal 87, 38402 Saint Martin d' Heres Cedex (France); Ando, H. [Department of Physics, Faculty of Science and Engineering, Konan University, Okamoto 8-9-1, Higashi-Nada, 658-8501, Kobe (Japan)

2006-03-15

99

Valence-band mixing induced by sp-d exchange interaction in CdMnTe quantum wires  

International Nuclear Information System (INIS)

Anisotropic magneto-optical effects have been studied theoretically by using multi-band effective mass method. We focus on a model of an ideal CdMnTe quantum wire surrounded by infinite potential barriers. The mixing of heavy- and light-hole bands is caused by both the one-dimensional quantum confinement and the sp-d exchange interaction. As a result of the valence-band mixing characteristic to the one-dimensional diluted magnetic semiconductor, the Zeeman splitting in the magnetic field parallel to the wire direction becomes smaller than that in the perpendicular magnetic field. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

100

Transition from parabolic to ring-shaped valence band maximum in few-layer GaS, GaSe, and InSe  

Science.gov (United States)

By performing first-principles electronic structure calculations in frames of density functional theory we study the dependence of the valence band shape on the thickness of few-layer III-VI crystals (GaS, GaSe, and InSe). We estimate the critical thickness of transition from the bulklike parabolic to the ring-shaped valence band. Direct supercell calculations show that the ring-shaped extremum of the valence band appears in ? -GaS and ? -GaSe at a thickness below 6 tetralayers (˜4.6 nm ) and 8 tetralayers (˜6.4 nm ), respectively. Zone-folding calculations estimate the ? -InSe critical thickness to be equal to 28 tetralayers (˜24.0 nm ). The origin of the ring-shaped valence band maximum can be understood in terms of k.p theory, which provides a link between the curvature of the energy bands and the distance between them. We explain the dependence of the band shape on the thickness, as well as the transition between two types of extremes, by the k -dependent orbital composition of the topmost valence band. We show that in the vicinity of critical thickness the effective mass of holes in III-VI compounds depends strongly on the number of tetralayers.

Rybkovskiy, Dmitry V.; Osadchy, Alexander V.; Obraztsova, Elena D.

2014-12-01

101

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

102

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

International Nuclear Information System (INIS)

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 Mn2NiGa appear at the phase transition. •HAXPES of C1b 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

103

Oscillations in the valence band photoemission spectrum of the heterofullerene C59N: a photoelectron interference phenomenon  

OpenAIRE

The intensities of the two strongest low-binding energy features in the valence-band photoemission spectra of C59N have been observed to oscillate as the photon energy of the exciting radiation is varied. The maxima in the intensity ratio of the two peaks occur at the same photon energies as the maxima in the intensity ratios of the highest occupied molecular orbitals to next highest occupied molecular orbitals (NHOMO) peaks of C60. The amplitude of modulation of the ratio is remarkably simil...

Jones, F. H.; Butcher, M. J.; Cotier, B. N.; Moriarty, P.; Beton, P. H.; Dhanak, V. R.; Prassides, K.; Kordatos, K.; Tagmatarchis, N.; Wudl, F.

1999-01-01

104

Hard X-ray valence-band and core-level photoelectron spectroscopy of strongly correlated electron systems  

International Nuclear Information System (INIS)

Valence-band and core-level photoelectron spectroscopy (PES) has been successfully used to study strongly correlated electron systems such as CeRhAs, YbInCu4, and YbB12 at photon energies of h??6keV with high-energy resolution, ?E?160-270meV. Due to the long penetration depth of electrons with high kinetic energy, the photoelectron spectra obtained reflect the bulk electronic properties. The merits of utilizing both hard X-ray PES and VUV-SX PES to investigate the electronic states of strongly correlated electron systems in the bulk are presented

105

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

International Nuclear Information System (INIS)

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

106

Magneto-photoluminescence of GaN\\/AlGaN quantum wells valence band reordering and excitonic binding energies  

CERN Document Server

A re-ordered valence band in GaN/AlGaN quantum wells with respect to GaN epilayers has been found as a result of the observation of an enhanced g-factor in magneto-luminescence spectra in fields up to 55 T. This has been caused by a reversal of the states in the strained AlGaN barriers thus giving different barrier heights for the different quantum well hole states. From k.p calculations in the quasi-cubic approximation, a change in the valence-band ordering will account for the observed values for the g-factors. We have also observed the well-width dependence of the in-plane extent of the excitonic wavefunction from which we infer an increase in the exciton binding energy with the reduction of the well width in general agreement with theoretical calculations of Bigenwald et al (phys. stat. sol. (b) 216, 371 (1999)) that uses a variational approach in the envelope function formalism that includes the effect of the electric field in the wells.

Shields, P A; Grandjean, N; Massies, J

2001-01-01

107

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-04-28

108

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

International Nuclear Information System (INIS)

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

109

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

International Nuclear Information System (INIS)

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

110

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

International Nuclear Information System (INIS)

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

111

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

112

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

Science.gov (United States)

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

2012-12-01

113

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

International Nuclear Information System (INIS)

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.

114

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

Science.gov (United States)

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

King, Sean W.; Brockman, Justin; French, Marc; Jaehnig, Milt; Kuhn, Markus; French, Benjamin

2014-09-01

115

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

International Nuclear Information System (INIS)

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

116

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

Energy Technology Data Exchange (ETDEWEB)

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

Mascaraque, Arantzazu [Departamento Fisica de Materiales, Universidad Complutense de Madrid, Madrid 28040 (Spain); Onur Mentes, T; Locatelli, Andrea [Sincrotrone Trieste S.C.p.A, Basovizza, Trieste 34149 (Italy); McCarty, Kevin F [Sandia National Laboratories, Livermore, CA 94550 (United States); Marco, Jose F; De la Figuera, Juan [Instituto de Quimica-Fisica Rocasolano, CSIC, Madrid 28006 (Spain); Schmid, Andreas K [Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States)

2011-08-03

117

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

118

DISPERSIVE HYBRIDIZATION CORRELATION AND MAGNETISM IN A TWO - BAND MODEL  

OpenAIRE

We study a two-band Hamiltonian for hybridized and correlated bands of sc and bcc symmetry, the latter case approximating a two-dimensional band. Magnetic phase diagrams are obtained, showing in the bcc case a region of rapid phase change with filling which is absent in the sc case.

Acquarone, M.; Ray, D.

1988-01-01

119

Characterisation of MoSe/sub x/Te/sub 2-x/ (0 <= x <= 2) electrodes in terms of energetic location of valence and conduction bands  

International Nuclear Information System (INIS)

The layer type MoSe/sub x/Te/sub 2-x/ (0 <= x <= 2) has been grown by chemical vapour transport technique. The photoelectrochemical solar cells have been fabricated using the grown crystals as photoelectrodes and platinum grid as counter electrode in aqueous iodine/iodide solution. The optical band gap determination has been done from the study of the spectral response of the cells. The location of valence and conduction band edges and flat band potentials have been evaluated using Mott-Schottky plots. (author)

120

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

International Nuclear Information System (INIS)

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

121

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2006-10-26

122

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

International Nuclear Information System (INIS)

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

123

Theoretical study of influencing factors on the dispersion of bulk band-gap edges and the surface states in topological insulators Bi2Te3 and Bi2Se3  

Science.gov (United States)

The dispersion of the band-gap edge states in bulk topological insulators Bi2Te3 and Bi2Se3 is considered within density functional theory. The dependences of this dispersion both on the approximation used for an exchange-correlation functional at fixed unit cell parameters and atomic positions and on these parameters and positions that are obtained upon structural relaxation performed using a certain approximated functional are analyzed. The relative position of the Dirac point of topologically protected surface states and the valence band maximum in the surface electronic structure of the topological insulators is discussed.

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

2013-06-01

124

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.

125

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)

126

Spin orbit and tetragonal crystalline field interaction in the valence band of CuInSe2-related ordered vacancy compound CuIn7Se12  

International Nuclear Information System (INIS)

Thin films of the off-tie-line ordered vacancy compound CuIn7Se12 were deposited on optically flat glass substrates by multi-source co-evaporation method. The preliminary structural, compositional and morphological characterizations were done using X-ray diffraction, energy dispersive X-ray analysis and atomic force microscopy. The X-ray diffraction data were further analysed applying the Nelson-Riley method and CTB plus ?=? experiment rule, respectively, for lattice constants (a=5.746 A and c=11.78 A) and bond length estimations (RCu-Se=2.465 A and RIn-Se=2.554 A). A detailed analysis of the optical absorption spectra of the compound, which exhibited a three-fold optical absorption structure in the fundamental gap region, yielded three characteristic direct energy gaps at 1.37, 1.48(7) and 1.72(8) eV indicative of valence band splitting, which were evaluated using Hopfield's quasi-cubic model. The 0.04 eV increase in spin-orbit splitting parameter of the compound (0.27 eV) compared to that of CuInSe2 (0.23 eV) is found to be suggestive of the smaller contribution of Cu d orbitals to hybridization (determined by the linear hybridization model) in this Cu-deficient compound. Spectral response spectra exhibit, in addition to a maximum around 1.34±0.03 eV, two other defect transition peaks near 1.07 and 0.85 eV. The binding energies of Cu, In and Se in the compound were determined using X-ray photoelectron spectromined using X-ray photoelectron spectroscopy. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

127

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.

128

The energy bands and the dispersion relations of the spin waves in a ferromagnetic bilayer system  

Science.gov (United States)

The eigenproblems of spin waves in a ferromagnetic bilayer system with periodic boundary conditions are solved by using the interface-rescaling approach. The energy bands and the dispersion relations of the system are investigated. In addition, the effect of the uniaxial bulk anisotropy field of easy-axis type on the energy bands and the dispersion relations is also discussed. Furthermore, we conjecture that there may be the resonant-confined spin waves in the system.

Zhou, Wen Ping; Yun, Guo Hong

2004-03-01

129

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

International Nuclear Information System (INIS)

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

130

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

Science.gov (United States)

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

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

2015-03-01

131

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

Science.gov (United States)

The use of quasicrystals as precursors to catalysts for the steam reforming of methanol is potentially one of the most important applications of these new materials. To develop application as a technology requires a detailed understanding of the microscopic behavior of the catalyst. Here, we report the effect of leaching treatments on the surface microstructure, chemical composition, and valence band of the icosahedral (i-) Al-Cu-Fe quasicrystal in an attempt to prepare a model catalyst. The high symmetry fivefold surface of a single grain i-Al-Cu-Fe quasicrystal was leached with NaOH solution for varying times, and the resulting surface was characterized by x-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The leaching treatments preferentially remove Al producing a capping layer consisting of Fe and Cu oxides. The subsurface layer contains elemental Fe and Cu in addition to the oxides. The quasicrystalline bulk structure beneath remains unchanged. The subsurface gradually becomes Fe3O4 rich with increasing leaching time. The surface after leaching exhibits micron sized dodecahedral cavities due to preferential leaching along the fivefold axis. Nanoparticles of the transition metals and their oxides are precipitated on the surface after leaching. The size of the nanoparticles is estimated by high resolution transmission microscopy to be 5-20 nm, which is in agreement with the AFM results. Selected area electron diffraction (SAED) confirms the crystalline nature of the nanoparticles. SAED further reveals the formation of an interface between the high atomic density lattice planes of nanoparticles and the quasicrystal. These results provide an important insight into the preparation of model catalysts of nanoparticles for steam reforming of methanol. PMID:25747095

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

2015-03-01

132

Dispersion characteristics of a slow wave structure with metal photonic band gap cells  

International Nuclear Information System (INIS)

A slow wave structure consisting of metallic photonic band gap cells for a Ka-band Cherenkov device is proposed in this paper. Attributing to the mode selectivity of the photonic band gap, only the TM01-like mode among the TM0n-like modes exists in such a slow wave structure. The dispersion characteristics of the slow wave structure are investigated by simulation and experiment. It is shown that the dispersion curve obtained from the experiment is in agreement with that from simulation

133

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

Science.gov (United States)

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

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

2001-10-01

134

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

International Nuclear Information System (INIS)

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

135

Spin orbit splitting in the valence bands of ZrSxSe2?x: Angle resolved photoemission and density functional theory  

International Nuclear Information System (INIS)

Highlights: ? We performed high resolution ARPES on 1T–ZrSxSe2?x. ? A characteristic splitting of the chalcogen p-derived VB along high symmetry directions was observed. ? The splitting size at the A point of the BZ is found to increase from 0.06 to 0.31 eV from ZrS2 towards ZrSe2. ? Electronic structure calculations based on the DFT were performed using the model of TB–MBJ. ? The calculations show that the splitting is due to SO coupling of the valence bands. -- Abstract: Angle-resolved photoelectron spectroscopy using synchrotron radiation has been performed on 1T–ZrSxSe2?x, where x varies from 0 to 2, in order to study the influence of the spin-orbit interaction in the valence bands. The crystals were grown by chemical vapour transport technique using Iodine as transport agent. A characteristic splitting of the chalcogen p-derived valence bands along high symmetry directions has been observed experimentally. The size of the splitting increases with the increase of the atomic number of the chalcogenide, e.g. at the A point of the Brillouin zone from 0.06 eV to 0.31 eV with an almost linear dependence with x, as progressing from ZrS2 towards ZrSe2, respectively. Electronic structure calculations based on the density functional theory have been performed using the model of Tran–Blaha [1] and the modified version of the exchange potential proposed by Becke and Johnson [2] (TB–MBJ) both with and without spin-orbit (SO) coupling. The calculations show that the splitting is mainly due to spin-orbit coupling and the degeneracy of the valance bands is lifted

136

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2013-08-15

137

Dyadic Green's function study of band structures of dispersive photonic crystals  

International Nuclear Information System (INIS)

We present here in terms of a dyadic Green's function (DGF) a general description of optical phenomena in photonic crystal (PC) structures, described particularly by frequency-dependent components, assuming that PC structures are decomposed into their relatively simple constituent parts via conductivity tensors. We demonstrate this approach by explicitly calculating the DGFs for electromagnetic waves propagating in the one- and two-dimensional dispersive PCs consisting of a periodic array of identical metallic quantum wells and a periodic square array of identical metallic quantum wires, each embedded in a three-dimensional dispersive medium. By means of the explicit analytic dispersion relations, which result from the frequency poles of the corresponding DGFs, we also calculate the band structures of these dispersive PCs by simple numerical means. Our analysis shows that the band structures calculated from our DGF approach conform well with those calculated from the traditional computational methods.

138

Single-carrier impact ionization favored by a limited band dispersion  

CERN Document Server

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

Darbandi, A

2012-01-01

139

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

140

Bulk band dispersion in Ti2O3 and V2O3  

International Nuclear Information System (INIS)

We report here a comprehensive study of the bulk electronic structure of single-crystal Ti2O3 and V2O3 using both angle-integrated and angle-resolved photoemission and synchrotron radiation. The electronic structure of these materials is of particular interest because of the metal-insulator transitions which they undergo. Slight (2O3 and V2O3 as the photon energy is swept through the cation 3p?3d optical-absorption edge. A valence-band satellite is resolved in the angle-integrated photoemission spectra from V2O3; resolving this feature shows that the actual width of the O 2p band in V2O3 is almost 2.5 eV narrower than previous studies indicated

141

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

International Nuclear Information System (INIS)

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

142

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-03-28

143

Novel excitonic states in quantum Hall systems Bound states of spin waves and a valence band hole  

CERN Document Server

If the Zeeman energy is small, the lowest energy excitations of a two dimensional electron gas at filling factor nu=1 are spin waves (spin flip excitations). At nu slightly larger (smaller) than unity, reversed spin electrons (spin holes) can form bound states with K spin waves that are known as skyrmions, S_K^- (antiskyrmions, S_K^+). It is suggested in this work that a valence hole can also bind K spin waves to form an excitonic complex X_K^+, analogous to the S_K^+. One spin hole of the S_K^+ is simply replaced by the valence hole. At nu=1, the (S_K^-)-(X_K^+) attraction can potentially lead to different behavior.

Quinn, J J; Quinn, John J.; Wojs, Arkadiusz

2002-01-01

144

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

CERN Document Server

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

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

2003-01-01

145

Dispersive properties of finite, one-dimensional photonic band gap structures: applications to nonlinear quadratic interactions.  

Science.gov (United States)

We discuss the linear dispersive properties of finite one-dimensional photonic band-gap structures. We introduce the concept of a complex effective index for structures of finite length, derived from a generalized dispersion equation that identically satisfies the Kramers-Kronig relations. We then address the conditions necessary for optimal, phase-matched, resonant second harmonic generation. The combination of enhanced density of modes, field localization, and exact phase matching near the band edge conspire to yield conversion efficiencies orders of magnitude higher than quasi-phase-matched structures of similar lengths. We also discuss an unusual and interesting effect: counterpropagating waves can simultaneously travel with different phase velocities, pointing to the existence of two dispersion relations for structures of finite length. PMID:11970354

Centini, M; Sibilia, C; Scalora, M; D'Aguanno, G; Bertolotti, M; Bloemer, M J; Bowden, C M; Nefedov, I

1999-10-01

146

Novel excitonic states in quantum Hall systems: Bound states of spin waves and a valence band hole  

OpenAIRE

If the Zeeman energy is small, the lowest energy excitations of a two dimensional electron gas at filling factor nu=1 are spin waves (spin flip excitations). At nu slightly larger (smaller) than unity, reversed spin electrons (spin holes) can form bound states with K spin waves that are known as skyrmions, S_K^- (antiskyrmions, S_K^+). It is suggested in this work that a valence hole can also bind K spin waves to form an excitonic complex X_K^+, analogous to the S_K^+. One s...

Quinn, John J.; Wojs, Arkadiusz

2002-01-01

147

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

International Nuclear Information System (INIS)

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

148

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

149

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.

2013-12-01

150

Understanding the role and interplay of heavy-hole and light-hole valence bands in the thermoelectric properties of PbSe  

Science.gov (United States)

The thermoelectric properties of PbSe have significantly improved in recent years reaching figures of merit Z T ˜1.6 . The transport properties of the hole-doped high temperature thermoelectric material PbSe are particularly interesting and play a key role in this. Here, they were analyzed over wide temperature and hole concentration ranges. The special features observed in the variation of the experimental Seebeck coefficient and Hall coefficient can be accounted for within the framework of a two-band model. Two valence bands separated by a temperature dependent energy offset are considered. The extremum of the light-hole band has a density of states mass ˜0.27 mo at room temperature. It is nonparabolic and anisotropic and can be described by the Kane model. The extremum of the heavy-hole band is isotropic and parabolic with a much larger density of states mass ˜2.5 mo . We find that for heavily doped compositions, the high mass band contributes the Seebeck coefficient, even at room temperature. With rising temperature, holes are transferred from the light-hole to the heavy-hole branch, giving rise to the anomalous temperature dependent Hall coefficient, which is found peaked near ˜650 K . For Na-doped samples P b1 -xN axSe for 0.01 ?x ?0.03 , the high thermopower values of 200 -300 ? V /K at 900 K arise from the heavy-hole band, which are responsible for the excellent thermoelectric performance of PbSe.

Chasapis, Thomas C.; Lee, Yeseul; Hatzikraniotis, Euripides; Paraskevopoulos, Konstantinos M.; Chi, Hang; Uher, Ctirad; Kanatzidis, Mercouri G.

2015-02-01

151

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

152

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

CERN Document Server

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

153

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

International Nuclear Information System (INIS)

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

154

Band structure of boron doped carbon nanotubes  

OpenAIRE

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...

Wirtz, Ludger; Rubio Secades, A?ngel

2003-01-01

155

Excitonic properties related to valence band levels split by spin-orbit interaction in layered oxychalcogenide LaCuOCh(Ch=S,Se)  

International Nuclear Information System (INIS)

The energy splitting of valence band in oxychalcogenides LaCuOCh (Ch=S, Se) was studied through degenerative four-wave mixing (DFWM) signals excited by femtosecond laser pulses and high-resolution absorption spectra at 4 K. The DFWM signals for LaCuOS exhibited a beat structure with a period of 480 fs just at the exciton peak energy, indicating that the lowest exciton states were split by 9 meV, while the corresponding splitting in LaCuOSe was 125 meV. The spin-orbit interaction of Ch ion accompanied by the hybridization of Cu 3d orbital causes the splitting of the exciton levels

156

Valence-band mixing effects in the upper-excited-state magneto-optical responses of colloidal Mn2+-doped CdSe quantum dots.  

Science.gov (United States)

We present an experimental study of the magneto-optical activity of multiple excited excitonic states of manganese-doped CdSe quantum dots chemically prepared by the diffusion doping method. Giant excitonic Zeeman splittings of each of these excited states can be extracted for a series of quantum dot sizes and are found to depend on the radial quantum number of the hole envelope function involved in each transition. As seven out of eight transitions involve the same electron energy state, 1Se, the dominant hole character of each excitonic transition can be identified, making use of the fact that the g-factor of the pure heavy-hole component has a different sign compared to pure light hole or split-off components. Because the magnetic exchange interactions are sensitive to hole state mixing, the giant Zeeman splittings reported here provide clear experimental evidence of quantum-size-induced mixing among valence-band states in nanocrystals. PMID:25438717

Fainblat, Rachel; Muckel, Franziska; Barrows, Charles J; Vlaskin, Vladimir A; Gamelin, Daniel R; Bacher, Gerd

2014-12-23

157

Soft X-Ray Spectroscopic studies of Intrinsic Quantum Well States, Shallow Core Level Hybridization, and Valence Band Structure in CdO and InN  

Science.gov (United States)

InN and CdO are post-transition metal compounds that display significant metal-ligand shallow core level hybridization [1], and have recently been discovered to posses intrinsic quantum well states in electron accumulation layers near their surfaces [2]. We report here new synchrotron-based soft x-ray spectroscopic measurements of the electronic structure of CdO and InN single crystal thin films. Resonant x-ray emission spectroscopy has been employed to study the detailed valence band and shallow core level electronic structure, while high resolution angle-resolved photoemission spectroscopy was used to measure quantized electron subbands at the near-surface of both InN and CdO. [1]. L .F. J. Piper et al., Phys. Rev. B (2007) in press; [2]. L. Colakerol et al., Phys. Rev. Lett. 97, 237601, (2006)

Piper, L. F. J.; Colakerol, L.; Demasi, A.; Moustakas, T. D.; Smith, K. E.; Zuniga-Pérez, J.; Munoz-Sanjosé, V.; Fedorov, Alexei; Veal, T.; McConville, C.

2008-03-01

158

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-05-05

159

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

International Nuclear Information System (INIS)

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

160

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-08-25

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)

163

Proposal for highly residual dispersion compensating defected core decagonal photonic crystal fiber over S+C+L+U wavelength bands  

Science.gov (United States)

A defected core decagonal photonic crystal fiber is designed and numerically optimized to obtain its residual chromatic dispersion compensation in the wavelength range of 1460 to 1675 nm i.e., over S+C+L+U wavelength bands having an average dispersion of about -390 ps/(nm km) with a dispersion variation of 7 ps/(nm km). The designed fiber, with a flattened dispersion profile, has four rings of holes in the cladding region, which results in low confinement loss and small effective mode area at wavelength 1550 nm. For residual chromatic dispersion compensation, the proposed fiber can be used in wavelength division multiplexing optical fiber data communication systems.

Islam, Md. Aminul; Ahmad, Redwan; Ali, Md. Sharafat; Nasim, K. M.

2014-07-01

164

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

Science.gov (United States)

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

Dabhi, Shweta; Mankad, Venu; Jha, Prafulla K.

2014-04-01

165

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-04-24

166

Observation of magnonic band gaps in magnonic crystals with nonreciprocal dispersion relation  

Science.gov (United States)

An effect of metallization of a magnonic crystal surface on band-gap formation in the spectra of a surface spin wave (SSW) is studied both theoretically and experimentally. The structures under consideration are one-dimensional magnonic crystals based on yttrium iron garnet with an array of etched grooves, with and without a metal screen on the top of the corrugated surface. Due to nonreciprocity of propagation of the SSW, the shift of the band gap to higher frequency and from the border of the Brillouin zone in the presence of a conducting overlayer was measured in a transmission line experiment. Results of numerical calculations and model analysis are in agreement with experimental data and give further insight into the origin of the band gap and properties of the nonreciprocal SSW in metalized magnonic crystals. This gives a positive answer to the outstanding question about the possibility of detection of magnonic band gaps in the spectra of spin waves with nonreciprocal dispersion in magnonic crystals, and creates the potential for new applications and improvements of already existing prototype magnonic devices.

Mruczkiewicz, M.; Pavlov, E. S.; Vysotsky, S. L.; Krawczyk, M.; Filimonov, Yu. A.; Nikitov, S. A.

2014-11-01

167

Band structure peculiarities of three-valence REM monosulphides (CeS, NdS, CdS)  

International Nuclear Information System (INIS)

Complex investigation into peculiarities of a zone structure of trivalent REM monosulfides (CeS, NdS, GdS) was conducted on the basis of comparing data of calculation by the quasiband crystal field method with results of X-ray spectrum investigation. When constructing crystalline potentials for the calculation the following REM atom configurations were used: [Xe]+4fsup(0.9)5ssup(2)5psup(6)5dsup(1.1) for Ce, [Xe]+4fsup(2.75)5ssup(2)5psup(6)5dsup(1.25) for Nd and [Xe]+4fsup(6.5)5ssup(2)5psup(6)5dsup(1.5) for Gd([Xe]-xenon shell). Schemes of energy bands of GdS, NdS and CeS are presented and interpretation of peculiarities obtained for zone structures is given

168

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

International Nuclear Information System (INIS)

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

169

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

Energy Technology Data Exchange (ETDEWEB)

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

2014-04-28

170

Three-dimensional bulk band dispersion in polar BiTeI with giant Rashba-type spin splitting  

OpenAIRE

In layered polar semiconductor BiTeI, giant Rashba-type spin-split band dispersions show up due to the crystal structure asymmetry and the strong spin-orbit interaction. Here we investigate the 3-dimensional (3D) bulk band structures of BiTeI using the bulk-sensitive $h\

Sakano, M.; Miyawaki, J.; Chainani, A.; Takata, Y.; Sonobe, T.; Shimojima, T.; Oura, M.; Shin, S.; Bahramy, M. S.; Arita, R.; Nagaosa, N.; Murakawa, H.; Kaneko, Y.; Tokura, Y.; Ishizaka, K.

2012-01-01

171

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

172

Resonant inelastic soft-x-ray scattering from valence-band excitations in 3d0 compounds  

International Nuclear Information System (INIS)

Ti and Mn L?,? x-ray fluorescence spectra of FeTiO3 and KMnO4 were measured with monochromatic photon excitation on selected energies across the L2,3 absorption edges. The resulting inelastic x-ray-scattering structures and their changes with varying excitation energies are interpreted within the framework of a localized, many-body approach based on the Anderson impurity model, where the radiative process is characterized by transitions to low-energy interionic-charge-transfer excited states. Sweeping the excitation energy through the metal 2p threshold enhances the fluorescence transitions to the antibonding states pushed out of the band of continuous states due to strong metal 3d endash ligand 2p hybridization and matching the low-photon-energy satellites in the spectra. Based on the energy position of these charge-transfer satellites with respect to the recombination peak the effective metal 3d endash ligand 2p hybridization strength in the ground state of the system can be estimated directly from the experiment. copyright 1997 The American Physical Society

173

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

International Nuclear Information System (INIS)

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

174

Valence band offset at Al{sub 2}O{sub 3}/In{sub 0.17}Al{sub 0.83}N interface formed by atomic layer deposition  

Energy Technology Data Exchange (ETDEWEB)

The valence band offset, {Delta}E{sub V}, at an Al{sub 2}O{sub 3}/In{sub 0.17}Al{sub 0.83}N interface formed by atomic layer deposition was measured by x-ray photoelectron spectroscopy. The conventional method of using the core level separation, {Delta}E{sub CL}, between O 1s and In 4d resulted in {Delta}E{sub V} = 1.3 eV, which was apparently consistent with the direct observation of the valence band edge varying the photoelectron exit angle, {theta}. However, {Delta}E{sub CL} and full width at half maximum of core-level spectra were dependent on {theta}, which indicated significant potential gradients in Al{sub 2}O{sub 3} and InAlN layers. An actual {Delta}E{sub V} of 1.2 eV was obtained considering the potential gradients.

Akazawa, M.; Nakano, T. [Research Center for Integrated Quantum Electronics, Hokkaido University, Sapporo 060-8628 (Japan)

2012-09-17

175

Core-level and valence band photoemission study of La1-xSrxMnO3 perovskite oxide powders synthesized by mechanically and thermally activated solid-state reaction  

International Nuclear Information System (INIS)

High-resolution core-level and valence band x-ray photoemission spectroscopy measurements were performed on La1-xSrxMnO3 perovskite oxide powders synthesized for applications in solid-oxide fuel cells by high-temperature solid-state reaction (x = 0.3 and 0.19) and by room-temperature mechanical activation of the precursors (x = 0.3). A structure in the valence band at about 1 eV below the Fermi level was clearly observed and assigned to the emission from the Mn 3d-derived eg1? states, thereby allowing the extraction of information about correlation effects in this type of material. Both the core-level and valence band spectral features were found to be independent of the choice of synthesis route. This finding indicates that mechanical activation, due to its lower synthesis temperature, can represent a valid alternative method of synthesis allowing a better control of the microstructure. (author)

176

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

International Nuclear Information System (INIS)

We determine the one-particle spectral function and the corresponding derived quantities for the conducting chain lattice with finite inter-chain hopping tperpendicular and three-dimensional long-range Coulomb electron-electron interaction. The standard G0W0 approximation is used. It is shown that, due to the optical character of the anisotropic plasmon dispersion caused by the finite tperpendicular, a low energy quasi-particle ?-peak appears in the spectral function in addition to the hump present at energies of the order of the plasmon energy. Particular attention is devoted to the continuous crossover from the non-Fermi liquid regime to the Fermi liquid regime with increasing tperpendicular. It is shown that the spectral weight of the hump transfers to the quasi-particle as the optical gap in the plasmon dispersion increases together with tperpendicular, with the quasi-particle residuum Z behaving like -ln tperpendicular)-1 in the limit tperpendicular ?0. Our approach is appropriate for the wide range of energy scales given by the plasmon energy and the width of the conduction band, and is complementary to the Luttinger liquid techniques that are limited to the low energy regime close to the Fermi surface

177

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2008-08-13

178

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

OpenAIRE

Adaptive optics will almost completely remove the effects of atmospheric turbulence at 10 microns on the Extremely Large Telescope (ELT) generation of telescopes. In this paper, we observationally confirm that the next most important limitation to image quality is atmospheric dispersion, rather than telescope diffraction. By using the 6.5 meter MMT with its unique mid-IR adaptive optics system, we measure atmospheric dispersion in the N-band with the newly commissioned spect...

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

2009-01-01

179

Valence and conduction band offsets at low-k a-SiO{sub x}C{sub y}:H/a-SiC{sub x}N{sub y}:H interfaces  

Energy Technology Data Exchange (ETDEWEB)

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

King, Sean W., E-mail: sean.king@intel.com; Brockman, Justin; French, Marc; Jaehnig, Milt; Kuhn, Markus [Logic Technology Development, Intel Corporation, Hillsboro, Oregon 97124 (United States); French, Benjamin [Ocotillo Materials Laboratory, Intel Corporation, Chandler, Arizona 85248 (United States)

2014-09-21

180

Design and analysis of a broadband dispersion compensating photonic crystal fiber Raman amplifier operating in S-band.  

Science.gov (United States)

This paper presents an optimized design of a dispersion compensating photonic crystal fiber (PCF) to achieve gain-flattened Raman performances over S-band using a single pump. Genetic algorithm interfaced with an efficient full-vectorial finite element modal solver based on curvilinear edge/nodal elements is used as an optimization tool for an accurate determination of PCF design parameters. The designed PCF shows high negative dispersion coefficient (-264 ps/nm/km to -1410 ps/nm/km) and negative dispersion slope, providing coarse dispersion compensation over the entire S-band. The module comprised of 1.45-km long optimized PCF exhibits +/-0.46 dB gain ripples over 50 nm wide bandwidth and shows a very low double Rayleigh backscattering value (-59.8 dB). The proposed module can compensate for the dispersion accumulated in one span (80-km) of standard single mode fiber with a residual dispersion of +/-700 ps/nm, ensuring its applicability for 10 Gb/s WDM networks. Additionally, the designed PCF remains single mode over the range of operating wavelengths. PMID:19516499

Varshney, Shailendra K; Fujisawa, Takeshi; Saitoh, Kunimasa; Koshiba, Masanori

2006-04-17

181

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-10-28

182

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

International Nuclear Information System (INIS)

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

183

Development and Validation of Weight, Height and Age Bands to Guide the Prescription of Fixed-Dose Dispersible Tablet Formulations  

Science.gov (United States)

OBJECTIVES: Conversion of pediatric essential drugs from syrup to dispersible tablet formulations would require fixed dose options guided by the weight band in which a child falls or a proxy for weight, such as height or age. The purpose of this study was to determine whether weight, height, or age bands can be created that would lead to greater than 95% of children receiving a therapeutic dose of 6 commonly prescribed essential drugs, including paracetamol, iron sulfate, amoxicillin, co-trimoxazole (i.e., trimethoprim/sulfamethoxazole), ciprofloxacin, and co-artemether (i.e., artemether/lumefantrine). METHODS: Using World Health Organization growth standards, we created 4 weight bands and then matched them to height and age 50th percentile growth curves. The resulting weight, height, and age bands were then applied to Ugandan and Bangladeshi anthropometric data sets, and the percentage of children who would have received a correct therapeutic dose based upon weight, height, or age was determined. This percentage was interpreted as acceptable if >95%, marginal if 90% to 95% and unacceptable if determined by weight bands would deliver an acceptable therapeutic dose greater than 95% of the time. Substituting weight for age or height bands would result in unacceptable levels of under- or overdosing.

Sauvé, Laura; Senkungu, Jude Kimbowa; Arifeen, Shams El; Brant, Rollin

2015-01-01

184

Intermolecular band dispersion in a self-assembled phthalocyanine derivative film: The case of tetrakis(thiadiazole)porhyrazine  

Science.gov (United States)

The electronic band structure of a tetrakis(thiadiazole)porhyrazine (H2TTDPz) thin film prepared on SiO2 , which is a system close to a real device one, was studied by photoelectron spectroscopy (PES). Although the film was grown on a bumpy surface, clear electronic band dispersion was observed along the surface-normal direction. The bandwidth of the highest occupied molecular orbital (HOMO) band was approximately 180 meV. By analyzing the PES result using the tight-binding method, the transfer integral for the ?-? interaction, the effective mass of the HOMO hole, and the hole mobility were estimated to be approximately 45±10meV , 1/mh?=(0.14±0.03)/m0 , and ?h=8.2±1.8cm2/Vs , respectively, at 100 K.

Tanaka, Yusuke; Takahashi, Kouji; Kuzumaki, Takuya; Yamamoto, Yuta; Hotta, Kunihiro; Harasawa, Ayumi; Miyoshi, Yasuhito; Yoshikawa, Hirofumi; Ouchi, Yukio; Ueno, Nobuo; Seki, Kazuhiko; Awaga, Kunio; Sakamoto, Kazuyuki

2010-08-01

185

DISPERSAL AND MORTALITY OF RED-SHOULDERED HAWKS BANDED IN OHIO  

Science.gov (United States)

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

186

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

Science.gov (United States)

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

Ohtomo, Manabu; Shimada, Toshihiro; Hasegawa, Tetsuya

2010-03-01

187

The quasiparticle band gap in the topological insulator Bi2Te3  

OpenAIRE

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

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

2013-01-01

188

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

189

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

International Nuclear Information System (INIS)

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

190

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

Energy Technology Data Exchange (ETDEWEB)

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

Zhang HaiFeng [College of Electronic and Information Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China); Nanjing Artillery Academy, Nanjing 211132 (China); Liu Shaobin; Yang Huan [College of Electronic and Information Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China); Kong Xiangkun [College of Electronic and Information Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China); Jiangsu Key Laboratory of Meteorological Observation and Information Processing, Nanjing University of Information Science and Technology, Nanjing 210044 (China)

2013-03-15

191

Modulation instability of narrow-band nanosecond pulses propagating in anomalous-dispersion fibre  

International Nuclear Information System (INIS)

We demonstrate that, in the presence of noise, propagation of narrow-band 100-ns pulses through a 6-km long optical fibre sharply reduces their amplitude when a threshold power (?0.2 W) is exceeded. The effect is due to the development of modulation instability and is sensitive to the noise level in the spectral region ?100 GHz in width around the central frequency. (fiber and integrated optics)

192

Surface and bulk Fermiology and band dispersion in non-centrosymmetric BiTeI  

OpenAIRE

BiTeI has a layered and non-centrosymmetric structure where strong spin-orbit interaction leads to a giant spin splitting in the bulk bands. Here we present high-resolution angle-resolved photoemission (ARPES) data in the UV and soft x-ray regime that clearly disentangle the surface from the bulk electronic structure. Spin-resolved UV-ARPES measurements on opposite, non-equivalent surfaces show identical spin structures, thus clarifying the surface state character. Soft x-ra...

Landolt, Gabriel; Eremeev, Sergey V.; Koroteev, Yury M.; Slomski, Bartosz; Muff, Stefan; Kobayashi, Masaki; Strocov, Vladimir N.; Schmitt, Thorsten; Aliev, Ziya S.; Babanly, Mahammad B.; Amiraslanov, Imamaddin R.; Chulkov, Evgueni V.; Osterwalder, Jurg; Dil, J. Hugo

2012-01-01

193

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

194

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

Science.gov (United States)

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

Yan, Zhifeng; Hilpert, Markus

2014-10-01

195

Fermi energy band dispersion and orbital symmetry of Bi2Sr2CaCu2Oy studied by non-polarized-light two-dimensional photoelectron spectroscopy  

International Nuclear Information System (INIS)

To study the two-dimensional Fermi energy band dispersion of Bi2Sr2CaCu2Oy in the vicinity of the Fermi level, photoelectron intensity angular distributions (PIADs) was measured at room temperature using non-polarized He I excitation light (21.2 eV) in normal incidence geometry. Strong photoelectron peaks appeared at the M-bar points in the PIAD at the Fermi level. They are attributed to the Fermi energy band which disperses toward both the ? and Z points at higher binding energies, however, only the dispersion from the M-bar toward the Z points with increasing binding energy was observed. The disappearance of photoelectron peaks of Fermi energy band in the first Brillouin zone was explained by the transition matrix element from dx2-y2 atomic orbital to p and f final states for the case of non-polarized light at normal incidence

196

Effects of CeO2 on the XPS valence band spectra of coal under the combustion initialization stage at 400°C  

Science.gov (United States)

In order to get the catalytic mechanism of CeO2 on graphite and coal at 400°C, the morphologies of coal, graphite, and CeO2 before and after combustion were analyzed through X-ray photoelectron spectroscopy (XPS). It is found that the particle size of coal is mostly between 11.727 and 64.79 ?m, while the particle size of CeO2 is between 1.937 and 11.79 ?m. The agglomeration of coal and CeO2 can be seen by scanning electron microscopy (SEM) after reaction. XPS results show that with the addition of CeO2, the intensity of binding energy gets stronger, but there is no energy peak transition. Comparing the character of coal with and without the addition of CeO2, it can be seen that the C-C bond fractures first at 400°C, while the C-H energy-band takes electrons at the same time to be far away from the Fermi level, and the O 2s, O 2p, and C sp hybrid orbitals are all excited. Adding CeO2 can enhance the activity of the whole coal. In addition, through XPS analysis, combined with the oxygen transfer theory and the electron transfer theory, the catalytic mechanism of CeO2 for pulverized coal combustion could be obtained.

Qi, Cheng-lin; Zhang, Jian-liang; Ma, Chao; Feng, Gen-sheng; Song, Zhong-ping

2013-04-01

197

Valence Bond Entanglement Entropy  

OpenAIRE

We introduce for SU(2) quantum spin systems the Valence Bond Entanglement Entropy as a counting of valence bond spin singlets shared by two subsystems. For a large class of antiferromagnetic systems, it can be calculated in all dimensions with Quantum Monte Carlo simulations in the valence bond basis. We show numerically that this quantity displays all features of the von Neumann entanglement entropy for several one-dimensional systems. For two-dimensional Heisenberg models,...

Alet, Fabien; Capponi, Sylvain; Laflorencie, Nicolas; Mambrini, Matthieu

2007-01-01

198

Change of the conversion rate of the E 3 isomer /sup 235m/U (76.8 eV; (1)/(2) +? (7)/(2) -) upon variation of the configuration of the valence band of the atomic shell  

International Nuclear Information System (INIS)

The relativistic Hartree-Fock-Slater method is used to calculate the change of the conversion rate lambda for the E3 isomer (at the transition energy h? = 77 eV) relative to the value lambda1 for the normal atomic configuration (7s (1)/(2) )2(6d (3)/(2) )1(5f (5)/(2) )3 for 14 configurations of the valence band of the atomic shell of uranium including significant variations of the occupation numbers of the 6d, 7s, and 5f orbits. A very strong change ?lambda/lambda1 is found to occur upon variation of the occupation number of the 5f orbit [?N(5f)not =0], namely, approx.8% for ?N(5f) = +- 1, which is an order of magnitude greater than the value of ?lambda/lambda1 due to the variation of the occupation numbers of other orbits with N(5f) = const. In spite of the fact that the direct contribution of 5f electrons to the conversion is very small (1 for ?N(5f)not =0. A rigid correlation between the partial conversion rate and the rms radius of the orbit is established for 6p orbits

199

Electronic band structure of beryllium oxide  

CERN Document Server

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

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

2003-01-01

200

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

201

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

202

Levels of Valence  

OpenAIRE

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 m...

VeraShuman; DavidSander

2013-01-01

203

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

204

Electronic band structure of magnetic bilayer graphene superlattices  

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-09-28

205

Optical and reduced band gap in n- and p-type GaN and AlN  

Science.gov (United States)

We present a full band calculation of the doping-induced energy shifts of the conduction-band minimum and the valence-band maximum for n- and p-type GaN and AlN. Both wurtzite and zinc-blende structures have been considered. The resulting optical and reduced band-gap energies are presented as functions of the ionized impurity concentration in the heavily doped regime. The computational method is based on a zero-temperature Green's function formalism within the random phase approximation and with the local-field correction of Hubbard. The calculation goes beyond the spherical approximation of the energy bands by using energy dispersions and overlap integrals from a first-principle, full-potential band-structure calculation. Inclusion of the spin-orbit interaction is crucial for describing the uppermost valence bands properly, and we show that the nonparabolicity of the valence bands influences the energy shifts strongly, especially the shift of the optical band gap. With the full band structure, we can explain the results of photoluminescence measurements by Yoshikawa [et al.] [J. Appl. Phys. 86, 4400 (1999)].

Persson, C.; Sernelius, Bo E.; Ferreira da Silva, A.; Araujo, C. Moyses; Ahuja, R.; Johansson, B.

2002-09-01

206

Valency and molecular structure  

CERN Document Server

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

Cartmell, E

1977-01-01

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

Corrugated flat band as an origin of large thermopower in hole doped PtSb2  

Directory of Open Access Journals (Sweden)

Full Text Available The origin of the recently discovered large thermopower in hole-doped PtSb2 is theoretically analyzed based on a model constructed from first principles band calculation. It is found that the valence band dispersion has an overall flatness combined with some local ups and downs, which gives small Fermi surfaces scattered over the entire Brillouin zone. The Seebeck coefficient is calculated using this model, which gives good agreement with the experiment. We conclude that the good thermoelectric property originates from this “corrugated flat band”, where the coexistence of large Seebeck coefficient and large electric conductivity is generally expected.

Kouta Mori

2012-12-01

209

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

International Nuclear Information System (INIS)

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

210

Valence-band offset of n-Zn0.8Mg0.2O/ p-Ni0.8Mg0.2O heterojunction with tunable bandgaps of both sides measured by X-ray photoelectron spectroscopy  

Science.gov (United States)

The valence-band offset (VBO) of n-Zn0.8Mg0.2O/ p-Ni0.8Mg0.2O heterojunction grown by pulsed laser deposition was investigated by X-ray photoelectron spectroscopy. Core levels of Zn 2 p and Ni 2 p were used to align the VBO of n-Zn0.8Mg0.2O/ p-Ni0.8Mg0.2O heterojunction. It was found that n-Zn0.8Mg0.2O/ p-Ni0.8Mg0.2O heterojunction has a type-II band alignment and its VBO is determined to be 1.88 ± 0.05 eV, and conduction-band offset is deduced to be -1.91 ± 0.05 eV. Alloying with Mg can tune the positions of valence-band maximum (VBM), conduction-band minimum (CBM) and bandgaps of both Zn1- x Mg x O and Ni1- x Mg x O thin films, according to which we can design various heterojunction devices with desired CBM and VBM values of both sides by tuning appropriate Mg composition. Also, there is blue shift of absorption edges of the integral Zn0.8Mg0.2O/Ni0.8Mg0.2O heterojunction, which has a significant impact on the design and application of deep-ultraviolet optoelectronic devices, such as solar-blind UV detectors with high photoresponse performance.

Guo, Yan-Min; Zhu, Li-Ping; Niu, Wen-Zhe; Zhang, Xiang-Yu; Ye, Zhi-Zhen

2015-01-01

211

Micro-valences: perceiving affective valence in everyday objects.  

Science.gov (United States)

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 explore whether affective valence must be strong or overt to exert an effect on our visual perception. We conclude that everyday objects carry subtle affective valences - "micro-valences" - which are intrinsic to their perceptual representation. PMID:22529828

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

2012-01-01

212

Theory of the first-order isostructural valence phase transitions in mixed valence compounds YbIn_{x}Ag_{1-x}Cu_{4}  

OpenAIRE

For describing the first-order isostructural valence phase transition in mixed valence compounds we develop a new approach based on the lattice Anderson model. We take into account the Coulomb interaction between localized f and conduction band electrons and two mechanisms of electron-lattice coupling. One is related to the volume dependence of the hybridization. The other is related to local deformations produced by f- shell size fluctuations accompanying valence fluctuatio...

Goltsev, A. V.; Bruls, G.

2000-01-01

213

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

214

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

OpenAIRE

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 maj...

MichaelJTarr; SophieLebrecht; MosheBar; LisaFBarrett

2012-01-01

215

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

OpenAIRE

CsPbCl3 nanocrystals are obtained in perovskite-like CsBCl3 (B=Sr, Ca, Mg) matrices doped with Pb ions (CPb=0.05 and 1 mol.%). The luminescent-kinetic parameters of the CsPbCl3 nanocrystals dispersed in CsBCl3 (B=Sr, Ca, Mg) matrices are studied under the pulsed UV and X-ray excitation. The conclusion about the formation of CsPbCl3 nanocrystals is confirmed with the data of their luminescence decay kinetics and a short-wavelength shift of the exciton luminescence maximum, when compared to tha...

Myagkota, S.

2003-01-01

216

Recoil effects for valence and core photoelectrons in V3 Si  

Science.gov (United States)

Hard and soft x-ray photoelectron spectroscopy was performed for core and valence electrons in V3Si. The recoil effects on the photoelectron emission were observed not only in the case of the Si 2p core level, but also for the valence band, although such effects were not observed for the V 2p and V 3p core levels. The valence-band results are compared with the results of the theoretical model calculation based on the tight-binding cluster approximation and harmonic approximation for lattice vibrations. The Si 2p core-level results interpreted as due to the single nucleus recoil effects are consistent with the interpretation of those of the valence electrons calculated on these approximations. From the EB dependence of the valence-band recoil shifts, useful information is obtained on the Si 3p partial density of states near the Fermi level.

Suga, S.; Itoda, S.; Sekiyama, A.; Fujiwara, H.; Komori, S.; Imada, S.; Yabashi, M.; Tamasaku, K.; Higashiya, A.; Ishikawa, T.; Shang, M.; Fujikawa, T.

2012-07-01

217

Dispersive optical constants and temperature-dependent band gap of cadmium-doped indium selenide thin films  

Science.gov (United States)

Polycrystalline cadmium-doped indium selenide thin films were obtained by the thermal co-evaporation of ?-In2Se3 crystals and Cd onto glass substrates kept at a temperature of 200 °C. The temperature dependence of the optical band gap in the temperature region of 300-450 K and the room temperature refractive index, n(?), of these films have been investigated. The absorption edge shifts to lower energy as temperature increases. The fundamental absorption edge corresponds to a direct energy gap that exhibits a temperature coefficient of -6.14 × 10-4 eV K-1. The room temperature n(?) which was calculated from the transmittance data allowed the identification of the oscillator strength and energy, static and lattice dielectric constants and static refractive index as 20.06 and 3.07 eV, 7.43 and 10.52 and 2.74, respectively.

Qasrawi, A. F.

2005-08-01

218

Optical properties of mixed-valence platinum halides  

Science.gov (United States)

Temperature dependent absorption spectra are reported for PtX 2-4 -PtX 2-6 doped in Cs 2ZrX 6 (X = Cl, Br). Intense, broad bands have been assigned as mixed-valence (MV) transitions. Vibronic structure has been observed for the MV bromide system. Our results are discussed in terms of a model proposed by Hush.

Albin, Michael; Patterson, Howard H.

1980-08-01

219

Scaling laws of band gaps of phosphorene nanoribbons: A tight-binding calculation  

Science.gov (United States)

In this study, we analyze the band structure, the state characterization, and electronic transport of monolayer black phosphorus (phosphorene) zigzag nanoribbons (zPNRs) and armchair nanoribbons (aPNRs), using five-parameter tight-binding (TB) approximation. In zPNRs, the ratio of the two dominant hopping parameters indicates the possibility of a relativistic dispersion relation and the existence of a pair of separate quasiflat bands at the Fermi level. Moreover, the corresponding states are edge localized if their bands are well separated from the valence and conduction bands. We also investigated the scaling laws of the band gaps versus ribbon widths for the armchair and zigzag phosphorene nanoribbons. In aPNRs, the transverse electric field along the ribbon width enhances the band gap closure by shifting the energy of the valence and conduction band edge states. For zPNRs, a gap occurs at the middle of the relatively degenerate quasiflat bands; thus, these ribbons are a promising candidate for future field-effect transistors.

Taghizadeh Sisakht, Esmaeil; Zare, Mohammad H.; Fazileh, Farhad

2015-02-01

220

Band structure, density of states, and optical susceptibilities of a novel lithium indium orthoborate Li3InB2O6.  

Science.gov (United States)

By use of the structural parameters of the single crystal lithium indium orthoborate obtained by Penin et al. (Solid State Sci. 2001, 3, 461-468), from X- ray diffraction data, we present a first-principle study of the electronic structure and the linear optical properties for the novel lithium indium orthoborate Li3InB2O6. A full-potential linear augmented plane wave method within density functional theory with the Engel-Vosko exchange correlation was used. This compound has a wide direct energy band gap of about 3.8 eV with both the valence band maximum and conduction band minimum located at the center of the Brillouin zone. Our calculations of the partial density of states shows that the upper valence band originates predominantly from the O-p, B- p, and In-p states, and the lower conduction band is dominated by the O-s/p, In-p, and B-p states. Thus the O-p states in the upper valence band and lower conduction band has a significant effect on the energy band gap dispersion. The uniaxial anisotropy [deltaepsilon=(epsilon0zz-epsilon0xx)/epsilon0tot] is about -0.041. PMID:19642661

Reshak, Ali Hussain; Auluck, S; Kityk, I V

2009-08-27

221

Ductility Enhancement of Molybdenum Phase by Nano-sizedd Oxide Dispersions  

Energy Technology Data Exchange (ETDEWEB)

The present research is focused on ductility enhancement of molybdenum (Mo) alloys by adding nano-sized oxide particles to the alloy system. The research approach includes: (1) determination of microscopic mechanisms responsible for the macroscopic ductility enhancement effects through atomistic modeling of the metal-ceramic interface; (2) subsequent computer simulation-aided optimization of composition and nanoparticle size of the dispersion for improved performance; (3) synthesis and characterization of nanoparticle dispersion following the guidance from atomistic computational modeling analyses (e.g., by processing a small sample of Mo alloy for evaluation); and (4) experimental testing of the mechanical properties to determine optimal ductility enhancement.Through atomistic modeling and electronic structure analysis using full-potential linearized muffin-tin orbital (FP-LMTO) techniques, research to date has been performed on a number of selected chromium (Cr) systems containing nitrogen (N) and/or magnesium oxide (MgO) impurities. The emphasis has been on determining the properties of the valence electrons and the characteristics of the chemical bonds they formed. It was found that the brittle/ductile behavior of this transitional metal system is controlled by the relative population of valence charges: bonds formed by s valence electrons yield metallic, ductile behavior, whereas bonds formed by d valence electrons lead to covalent, brittle behavior. The presence of valence bands from impurities also affects the metal bonding, thereby explaining the detrimental and beneficial effects induced by the inclusion of N impurities and MgO dispersions. These understandings are useful for optimizing ductility enhancement effects on the dispersion materials.

Bruce Kang

2008-07-31

222

Micro-Valences: Perceiving Affective Valence in Everyday Objects  

OpenAIRE

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

223

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

224

Valence transversities: the collinear extraction  

OpenAIRE

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

Courtoy, Aurore; Bacchetta, Alessandro; Radici, Marco

2013-01-01

225

Choice of compounds with fast core-valence transitions  

International Nuclear Information System (INIS)

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

226

Valence effects of sorption: laboratory control of valence state  

International Nuclear Information System (INIS)

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

227

Valence instabilities as a source of actinide system inconsistencies  

International Nuclear Information System (INIS)

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

228

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

CERN Document Server

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

Tototzintle-Huitle, H

2005-01-01

229

The electronic band structure of Li2O: testing theoretical predictions using electron momentum spectroscopy  

International Nuclear Information System (INIS)

Using the technique of electron momentum spectroscopy (EMS) we have measured the oxygen 2p- and 2s-derived valence bands and lithium 1s-derived core level in lithium oxide. All three sets of bands have been measured in a single experiment allowing the energy gap between the bands to be determined. At the ? point the O(2p)-O(2s) band gap is measured to be 16.1±0.2 eV, and the O(2s)-Li(1s) band gap is 34.3±0.2 eV. We can also determine bandwidths since EMS measures the full band structure directly, resolved both in energy and momentum. As expected, the O(2s) and Li(1s) bands are essentially non-dispersing, while the O(2p) has an observed width of 1.6±0.2 eV. The experiment is compared with calculations using the linear combination of atomic orbitals approach. At the Hartree-Fock (HF) level these calculations overestimate the gap between the valence bands and the width of the O(2p) band. The three density functional methods used give a reduced intervalence band gap and bandwidth. The hybrid gradient corrected method, PBE0 (where PBE stands for 'Perdew-Burke-Ernzerhof'), gives the closest agreement for the band gap at 16.7 eV, while the gradient corrected method, PBE, gives the best value for the bandwidth at 2.0 eV. At all levels the O(2s)-Li(1s) gap is underestimated; HF gives the closest agreement at 31.8 eV. (author)

230

Core-valence luminescence in scintillators  

International Nuclear Information System (INIS)

The state of the art of core-valence luminescence (CVL) in a number of halides (BaF2, CsCl, LiBaF3, etc.) is analysed. The following items are discussed: common properties of CVL, a suppression of slow emission component in BaF2, an effect of secondary excitation density on intensity and decay profile of the emission, a neutron-gamma discrimination, spectrum simulations, impurity-associated CVL, an origin of slow- and long-wavelength CVL components, a lattice relaxation, vibrations of lattice environment and phonon broadening of the emission bands. Experimental results on impurity-associated CVL of Rb1-xCsxBr (x<0.2) are presented and discussed. It is shown that the impurity-associated luminescence gives us a convenient way for the improvement of light output and variation of the emission wavelength of the scintillators

231

Anomalies in the Fermi surface and band dispersion of quasi-one-dimensional CuO chains in the high-temperature superconductor YBa2Cu4O8  

OpenAIRE

We have investigated the electronic states in quasi-one-dimensional CuO chains by microprobe angle resolved photoemission spectroscopy. We find that the quasiparticle Fermi surface consists of six disconnected segments, consistent with recent theoretical calculations that predict the formation of narrow, elongated Fermi surface pockets for coupled CuO chains. In addition, we find a strong renormalization effect with a significant kink structure in the band dispersion. The properties of this l...

Kondo, T.; Khasanov, R.; Karpinski, J.; Kazakov, S.; Zhigadlo, N.; Bukowski, Z.; Shi, M.; Bendounan, A.; Sassa, Y.; Chang, J.; Pailhe?s, S.; Mesot, J.; Schmalian, J.; Keller, H.; Kaminski, A.

2010-01-01

232

Band structure and optical electron spectra of (TrMA)CoCl3.2H2O crystal  

International Nuclear Information System (INIS)

DFT calculations of the band structure, density of states and optical spectra of trimethylammonium cobalt chloride dihydrate [(CH3)3NH]CoCl3.2H2O single crystal have been performed for the first time within a framework of the density functional theory using the CASTEP code (Cambridge serial total energy package). The valence band energy dispersion E(k) was found to be flat, although the bottom of the conduction band reveals noticeable dispersion along the lines [000]-[0012] and [-12012]-[-1200]-[-12120]. The calculations performed in the generalized gradient spin approximation (GGS) predict nonzero magnetic moment for the TrMA-CoCl3 crystal. The optical spectra calculated agree qualitatively with the experimental absorption spectra of the crystal in the range of Co ions excitation, 1.50-2.75eV

233

Superdeformed band in 154Dy  

International Nuclear Information System (INIS)

A superdeformed band has been found in the 154Dy (N=88) nucleus. The dynamic moment of inertia is identical to that of the yrast superdeformed band of 152Dy and the transition energies are similar to those of an excited superdeformed band in 153Dy. It is proposed that the two valence neutrons above the N=86 shell gap occupy the deformation-driving [514]9/2 orbital

234

Valency Configuration of Transition Metal Impurities in ZnO  

CERN Document Server

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

235

VALENCE TRANSITION INDUCED BY ALLOYING  

OpenAIRE

We present a study of valence change in Sm1-xBxS alloys within the coherent-potential approximation including renormalisation effects on the Sm-f level and on the d levels , the origin of which being the d-f coulombic interaction and the lattice constant change.

Spronken, G.; Avignon, M.; Smirnov, I.

1980-01-01

236

GaN m -plane: Atomic structure, surface bands, and optical response  

Science.gov (United States)

Density-functional-theory calculations are combined with many-body perturbation theory in order to elucidate the geometry, electronic, and optical properties of the w z -GaN (1 1 ¯00 ) surface, i.e., the so-called m -plane. The optical absorption and reflection anisotropy related to electronic transitions between surface states are identified by comparison with measured data covering transition energies from 2.4 up to 5.4 eV. Our results show a surface relaxation mechanism consistent with the electron counting rule that causes a moderate buckling of the GaN surface dimers and gives rise to two distinct surface states: The doubly occupied N dangling bonds form a surface band that is resonant with the GaN valence-band edge at the center of the Brillouin zone, whereas the empty Ga dangling bonds occur within the GaN band gap closely following the dispersion of the conduction-band edge. These two states contribute strongly to the formation of surface excitons that redshift the optical absorption with respect to the bulk optical response. The surface optical absorption i.e., the excitonic onset below the bulk band gap followed by a broad absorption band at higher energies related to the dispersion of the surface band structure, is calculated in agreement with the experimental data.

Landmann, M.; Rauls, E.; Schmidt, W. Â. G.; Neumann, M. Â. D.; Speiser, E.; Esser, N.

2015-01-01

237

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

OpenAIRE

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

238

Valence Quarks Polarization from COMPASS  

OpenAIRE

A first evaluation of the polarized valence quark distribution $\\Delta u_v(x)+\\Delta d_v(x)$ from the COMPASS experiment (CERN/SPS) is presented. The data were collected by COMPASS in the years 2002--2004 using a 160 GeV polarized muon beam scattered off a large polarized $^6$LiD target and cover the range $1< Q^2 < 100$ GeV$^2$ and $0.006

Korzenev, A.

2007-01-01

239

Molecular invariants: atomic group valence  

International Nuclear Information System (INIS)

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

240

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

241

New bond-valence parameters for lanthanides.  

Science.gov (United States)

The bond-valence method, especially the valence-sum rule, is very useful for checking if the structures formed by trivalent lanthanides are correct. In this work bond-valence parameters (Rij), which connect bond valences and bond lengths, have been computed for a large number of bonds taken from the Cambridge Structural Database, Version 5.24 (2002) [Allen (2002). Acta Cryst. B58, 380-388]. The calculated values of bond-valence parameters for metal-organic compounds decrease with an increase in lanthanide atomic number; the Rij values are also smaller than bond-valence parameters calculated for inorganic compounds. A summary of bond-valence sums calculated for Rij given in this work and reported in the literature, and a functional correlation between lanthanide-oxygen distances and coordination number are presented. PMID:15017089

Trzesowska, Agata; Kruszynski, Rafal; Bartczak, Tadeusz J

2004-04-01

242

Influence of intermediate layers at the interface on the band discontinuities of semiconductor heterostructures  

Science.gov (United States)

Semiconductor structures fabricated by means of molecular beam epitaxy are addressed. Valence band discontinuities are determined 'in situ,' by photoelectron spectroscopy, using synchrotron radiation. It is shown that the valence band offset can be modified in a range of 0.3 eV, using extremely thin intermediate layers of antimony, bismuth, and aluminum. An antimony intermediate layer allows impedance of interface reactions. The commutativity, the independency of valence band offset from the growth sequence of involved semiconductor materials, is demonstrated. The experimentally determined valence band discontinuities are successfully compared to the currently significant theoretical models.

Maierhofer, Christiane

243

Resonant L?,? X-ray emission and L3,2 X-ray absorption spectra of 3d metals in Co2MnZ (Z=Al, Ga, Sn, Sb) Heusler alloys as an element-selective probe of spin character of valence band  

International Nuclear Information System (INIS)

The 3d metal L?,? resonant X-ray emission spectra (RXES) and L3,2 X-ray absorption spectra (XAS) of the Co2MnZ (Z=Al, Ga, Sn, Sb) alloys were measured using linearly polarized soft X-rays. The Mn L? and Co L? spectra are compared with results of spin-polarized calculations of Mn 3d and Co 3d partial densities of states performed for each alloy. It is found that a satellite observed at the high-energy side of Mn L? spectra is due to the localized Mn 3d states located above the Fermi energy. It is shown that the presence of the same satellite structure indicates a higher degree of spin-polarization of Mn 3d states than Co 3d states. Both the intensity of the satellite structure in Mn L? spectra and the L?/L?, peak ratio are increased and follow the atomic number of Z element. The effect is especially strong when excitating slightly above the L3 and L2 threshold energies as well as at resonance. We observe a correlation between these spectral parameters and the magnitude of local magnetic moment. The changes occurring in the Mn L?,? RXES are in good agreement with a predicted decrease in p-d hybridization (between the atoms of Z element and Mn atoms). The calculated local density of Mn 3d states at the Fermi energy follows the same trend as the hybridization. This suggests that L?,? RXES of 3d metals can be used to monf 3d metals can be used to monitor the degree of spin-polarization of the valence band states and the local density of states at the Fermi level. Note that neither the Mn L2,3 absorption nor the Co L2,3 and Co L?,? emission spectra of the alloys are affected by the different composition (different Z elements)

244

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

OpenAIRE

[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 p...

Picozzi, S.; Continenza, A.; Freeman, A. J.

1997-01-01

245

Origins of phase transitions in valence fluctuating YbPd  

International Nuclear Information System (INIS)

The cubic YbPd compound undergoes two first-order phase transitions at T1=125 K and T2=105 K. We report the experimental results of the X-ray diffraction (XRD) and electron diffraction of single crystals of YbPd at low temperatures. Below T1, the (h00) Bragg peaks (h: an integer) are split into two subpeaks. Below T2, the superlattice reflections of (n/2,0,0) (n: an odd number) in the XRD patterns and the superlattice spots of (1/2,0,0), (0,1/2,0), and (1/2,1/2,0) in the electron diffraction profile appear, which suggests the valence order of YbPd. We discuss two possible structures, assuming a tetragonal symmetry below T1. The origins of the transitions at T1 and T2 are probably the band Jahn-Teller effect and the valence order, respectively. (author)

246

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

Science.gov (United States)

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

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

2014-06-01

247

Valence configurations in 214Rn  

International Nuclear Information System (INIS)

Excited states of 214Rn, up to spins of ? 24 ? have been studied using ?-ray and electron spectroscopy following the 208Pb(9Be,3n)214Rn reaction. The level scheme (which differs substantially from earlier work) is compared with the results of a semi-empirical shell model calculation. The availability of high-spin orbitals for the four valence protons and two valence neutrons, and the effect of the attractive proton-neutron interaction, leads to the prediction of high-spin states at an unusually low excitation energy. Experimentally, the high level density leads to difficulties in the level scheme assignments at high spin. Nevertheless, configuration assignments, supported by transition strengths deduced from the measured lifetimes (in the nanosecond region) are suggested for the main yrast states. The decay properties also suggest that configuration mixing is important. The possibility of a gradual transition to octupole deformation, implied by the decay properties of the 11- and 10+ yrast states is also discussed. (orig.)

248

Valence configurations in 214Rn  

International Nuclear Information System (INIS)

Excited states of 214Rn, up to spins of ? 24 ? have been studied using ?-ray and electron spectroscopy following the 208Pb(9Be,3n) 214Rn reaction. The level scheme (which differs substantially from earlier work) is compared with the results of a semi-empirical shell model calculation. The availability of high spin orbitals for the four valence protons and two valence neutrons, and the effect of the attractive proton-neutron interaction, leads to the prediction of high-spin states at an unusually low excitation energy. Experimentally, the high level density leads to difficulties in the level scheme assignments at high spin. Nevertheless, configuration assignments, supported by transition strengths deduced from the measured lifetimes (in the nanosecond region) are suggested for the main yrast states. The decay properties also suggest that configuration mixing is important. The possibility of a gradual transition to octupole deformation, implied by the decay properties of the 11- and 10+ yrast states is also discussed

249

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.

2003-12-01

250

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...

251

Core-valence partitioning and quasiparticle pseudopotentials  

International Nuclear Information System (INIS)

Recent advances in quantum Monte Carlo and quasiparticle methods have made accurate many-body calculations for valence electrons possible. Current work is limited by the way core electrons are treated. We present a many-body core-valence partitioning scheme, based upon quasiparticle methods, which can be used in either frozen-core or pseudopotential calculations

252

Many-body core-valence partitioning  

International Nuclear Information System (INIS)

We discuss the physics related to partitioning core and valence electrons, a common approach taken so that one need deal only with valence electrons in subsequent work. We present an approach to core-valence partitioning which explicitly includes many-body correlations, unlike traditional single-body approaches (such as Hartree Fock or the local-density approximation). Effects of intracore and core-valence correlations are incorporated in a parametrized core-polarization potential (CPP) derived from quasiparticle calculations in atoms presented in the preceding paper. Numerical parameters for CPP's for most elements with atomic number 3?Z?40 are tabulated. Specifically, the CPP's correct a Hartree-Fock treatment of core-valence interactions. The CPP's may be used in full-atomic, rigid-core applications or may be incorporated into pseudopotentials. We present explicit tests of the CPP's on atomic systems, and we cite molecular and solid-state tests also done using ths CPP approach

253

Theory of XAS and XMCD for the field-controlled valence mixed state in RE compounds  

International Nuclear Information System (INIS)

A valence fluctuating phenomenon, which is one of the most interesting subjects in strongly correlated electron systems, has been studied theoretically in EuNi2(Si0.18Ge0.82)2, in which the field-induced valence transition from a nonmagnetic Eu3+ state (4f6) to a magnetic Eu2+ state (4f7c1) was observed at around 40 Tesla by means of X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) at Eu L-edges. Here, c denotes a hole in a conduction band. Both XAS and XMCD in fields exhibit two peaks corresponding to the two valence states, although one of them is nonmagnetic. In this paper, we propose a model to explain the field-induced valence transition, in which the hybridization between the 4f6 state and the 4f7c1 state plays an essential role. Comparing XAS and XMCD calculated with experimental data, we find that XAS and XMCD provide us with detailed microscopic information on the mixed valence state through the polarized 5d electrons. Finally, we demonstrate how effective XAS and XMCD are for studying such mixed valence phenomena.

254

Superdeformed band in [sup 154]Dy  

Energy Technology Data Exchange (ETDEWEB)

A superdeformed band has been found in the [sup 154]Dy ([ital N]=88) nucleus. The dynamic moment of inertia is identical to that of the yrast superdeformed band of [sup 152]Dy and the transition energies are similar to those of an excited superdeformed band in [sup 153]Dy. It is proposed that the two valence neutrons above the [ital N]=86 shell gap occupy the deformation-driving [514]9/2 orbital.

Nisius, D.; Janssens, R.V.F.; Khoo, T.L.; Ahmad, I.; Blumenthal, D.; Carpenter, M.P.; Crowell, B.; Gassmann, D.; Lauritsen, T. (Argonne National Laboratory, Argonne, Illinois 60439 (United States)); Ma, W.C. (Mississippi State University, Mississippi State, Mississippi 39762 (United States) Vanderbilt University, Nashville, Tennessee 37235 (United States)); Hamilton, J.H.; Ramayya, A.V. (Vanderbilt University, Nashville, Tennessee 37235 (United States)); Bhattacharyya, P.; Zhang, C.T.; Daly, P.J.; Grabowski, Z.W.; Mayer, R.H. (Purdue University, West Lafayette, Indiana 47907 (United States))

1995-03-01

255

Electronic band structure of CdF2  

International Nuclear Information System (INIS)

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

256

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2010-04-30

257

Avoided valence transition in a plutonium superconductor.  

Science.gov (United States)

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

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

2015-03-17

258

Plasmon excitation in valence shell photoelectron spectroscopy for PAHs  

Science.gov (United States)

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

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

2015-01-01

259

Ab initio valence calculations in chemistry  

CERN Document Server

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

Cook, D B

1974-01-01

260

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.)

261

Quasiparticle band gap in the topological insulator Bi2Te3  

Science.gov (United States)

We present a theoretical study of dispersion of states that form the bulk band-gap edges in the three-dimensional topological insulator Bi2Te3. Within density functional theory, we analyze the effect of atomic positions varied within the error range of the available experimental data and approximation chosen for the exchange-correlation functional on the bulk band gap and k-space location of valence- and conduction-band extrema. For each set of the positions with different exchange-correlation functionals, we show how many-body corrections calculated within a one-shot GW approach affect the mentioned characteristics of electronic structure of Bi2Te3. We thus also illustrate to what degree the one-shot GW results are sensitive to the reference one-particle band structure in the case of bismuth telluride. We found that for this topological insulator the GW corrections enlarge the fundamental band gap and for certain atomic positions and reference band structure bring its value in close agreement with experiment.

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

2013-10-01

262

Mixed valency in cerium oxide crystallographic phases: Determination of valence of the different cerium sites by the bond valence method  

OpenAIRE

We have applied the bond valence method to cerium oxides to determine the oxidation states of the Ce ion at the various site symmetries of the crystals. The crystals studied include cerium dioxide and the two sesquioxides along with some selected intermediate phases which are crystallographically well characterized. Our results indicate that cerium dioxide has a mixed-valence ground state with an f-electron population on the Ce site of 0.27 while both the A- and C-sesquioxid...

Shoko, E.; Smith, M. F.; Mckenzie, Ross H.

2008-01-01

263

Valency of selected rare-earth ions in SnTe matrix  

International Nuclear Information System (INIS)

X-ray photoelectron spectroscopy experiments on SnTe crystals doped by Sm, Eu, and Yb were performed to determine the valency of these ions in the SnTe matrix. The analysis of the x-ray photoelectron spectroscopy valence-band spectra revealed that Eu and Yb are divalent while sm is trivalent in SnTe. These conclusions were confirmed by studies of the binding energies of core levels (4d-levels of Yb and 3d-levels of Sm and Eu), which are not presented here. (author)

264

Hofstadter butterflies for flat bands  

OpenAIRE

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, Hideo; Ando, Masato; Matsumura, Hajime

1996-01-01

265

Ba2Ir3O9: a new 5d mixed-valence metallic oxide with KSbO3-type structure  

International Nuclear Information System (INIS)

Crystal structure, magnetic and transport properties of new ternary mixed-valence iridium oxide Ba2Ir3O9 are reported. A hydrothermal reaction of IrO2 and BaO2 under a pressure of 150 MPa at 650 deg. C yields small black crystals with cubic shape. Energy dispersive X-ray analysis on an as-grown crystal gives the atomic ratio Ba:Ir = 2:3. X-ray powder diffraction shows a pattern of cubic lattice with a cell parameter a = 9.42 A and further Rietveld analysis reveals the KSbO3-related structure. Although the structure of Ba2Ir3O9 is almost identical to Ba0.5IrO3 [Mat. Res. Bull. 9 (1974) 1777], there is a significant difference in the composition between them. Because the crystallographic site for Ir is unique, Ba2Ir3O9 is classified into class III mixed-valence compound where the average valence of Ir is +4.67. The magnetic susceptibility shows almost temperature independent Pauli paramagnetism of 2.9 x 10-4 emu/mol Ir at room temperature. The resistivity for a pellet sample is measured to be 1.5 x 10-1 ? cm at room temperature and shows metallic temperature dependence. At low temperature, the temperature dependent component of the resistivity is almost proportional to T2. This indicates that Ba2Ir3O9 is a bad metal because of strong electron-electron stal because of strong electron-electron scattering. The narrow 5d-band feature characteristic of the KSbO3-type structure is related to the strong electron correlation

266

Valence fluctuation in CeMo2Si2C  

International Nuclear Information System (INIS)

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

267

Symmetry of valence states of Heusler compounds explored by linear dichroism in hard-x-ray photoelectron spectroscopy.  

Science.gov (United States)

This study reports on the linear dichroism in angular-resolved photoemission from the valence band of the Heusler compounds NiTi0.9Sc0.1Sn and NiMnSb. High-resolution photoelectron spectroscopy was performed with an excitation energy of h? = 7.938??keV. The linear polarization of the photons was changed using an in-vacuum diamond phase retarder. The valence band spectra exhibit the typical structure expected from first-principles calculations of the electronic structure of these compounds. Noticeable linear dichroism is found in the valence band of both materials, and this allows for a symmetry analysis of the contributing states. The differences in the spectra are found to be caused by symmetry-dependent angular asymmetry parameters, and these occur even in polycrystalline samples without preferential crystallographic orientation. PMID:21838382

Ouardi, Siham; Fecher, Gerhard H; Kozina, Xeniya; Stryganyuk, Gregory; Balke, Benjamin; Felser, Claudia; Ikenaga, Eiji; Sugiyama, Takeharu; Kawamura, Naomi; Suzuki, Motohiro; Kobayashi, Keisuke

2011-07-15

268

Valence resonance states of N2/-/  

Science.gov (United States)

Resonant scattering observed in the transmission of electrons between 9 and 11 eV in collision with N2 has been attributed to the attachment of the scattered electron to an excited valence state. Resonance valence excited states of N2(-) are calculated that could support this hypothesis. Although calculated and observed resonance energies are in close agreement, the calculations do not reflect the observed complex angular behavior of the scattered electron.

Krauss, M.; Neumann, D.

1973-01-01

269

Coupling of THz radiation with intervalence band transitions in microcavities.  

Science.gov (United States)

The strong coupling of THz radiation and material excitations can improve the quantum efficiency of THz emitters. In this paper, we investigate THz polaritons and antipolaritons based on valence band transitions, which allow TE coupling in a simple configuration. The approach can improve the quantum efficiency of THz based devices based on TE mode in the strong coupling regime of THz radiations and intervalence bands transitions in a GaAs/AlGaAs quantum wells. A Nonequilibrium Many Body Approach for the optical response beyond the Hartree-Fock approximation is used as input to the effective dielectric function formalism for the polariton/antipolariton problem. The energy dispersion relations in the THz range are obtained by adjusting the full numerical solutions to simple analytical expressions, which can be used for non specialists in a wide number of new structures and material systems. The combination of manybody and nonparabolicity at high densities leads to dramatic changes in the polariton spectra in a nonequilibrium configuration, which is only possible for intervalence band transitions. PMID:24663634

Pereira, M F; Faragai, I A

2014-02-10

270

Surface band structure of GaN(0001)-2 x 2  

Energy Technology Data Exchange (ETDEWEB)

The results of an in-situ angle-resolved ultraviolet photoelectron spectroscopy investigation of 2 x 2 reconstructed GaN(0001) surfaces prepared by plasma assisted molecular beam epitaxy are presented. The valence band dispersion was measured by variation of the detection angle with respect to the surface normal along the [1 anti 100] (anti {gamma}- anti K) and the [11 anti 20](anti {gamma}- anti M) direction using He I (h{nu}=21.2 eV) and He II (h{nu}=40.8 eV) radiation. In addition to the bulk states which exhibit strong dispersion, two non-dispersive surface states at 2 eV and 3 eV below the Fermi level are detected in both directions. In order to identify the origin of these states and to validate the experimentally determined k-dependence of the surface and bulk electron states we performed ab-initio calculations within the density functional theory and we calculated the band structures of different 2 x 2 surface reconstructions. Based on these calculations we could identify that the aforementioned states arise from a 2 x 2 N adatom surface reconstruction.

Lorenz, Pierre; Himmerlich, Marcel; Schaefer, Juergen A.; Krischok, Stefan [Institut fuer Physik and Institut fuer Mikro- und Nanotechnologien, TU Ilmenau (Germany); Lymperakis, Liverios; Neugebauer, Joerg [Max-Planck-Institut fuer Eisenforschung GmbH, Duesseldorf (Germany); Gutt, Richard [Fraunhofer-Institut fuer Angewandte Festkoerperphysik, Freiburg (Germany)

2010-07-01

271

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

272

Observation of phonon anomalies in the intermediate-valence compound CePd3  

International Nuclear Information System (INIS)

We report measurements of the phonon dispersion relation in intermediate-valence CePd3. The longitudinal-acoustic modes show a distinct softening above 100 K and a temperature-dependent broadening and splitting at higher temperatures. Especially in the direction the longitudinal modes differ from those of other Cu3Au structures. A good fit of the room-temperature dispersion curves is given by a 16-parameter Born--von Karman model with a breathing force as an additional degree of freedom

273

Valence-quark distributions in the pion  

OpenAIRE

We calculate the pion's valence-quark momentum-fraction probability distribution using a Dyson-Schwinger equation model. Valence-quarks with an active mass of 0.30 GeV carry 71% of the pion's momentum at a resolving scale q_0=0.54 GeV = 1/(0.37 fm). The shape of the calculated distribution is characteristic of a strongly bound system and, evolved from q_0 to q=2 GeV, it yields first, second and third moments in agreement with lattice and phenomenological estimates, and valen...

Hecht, M. B.; Roberts, C. D.; Schmidt, S. M.

2000-01-01

274

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

International Nuclear Information System (INIS)

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

275

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

International Nuclear Information System (INIS)

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

276

Mixed-valence states of polynuclear iron complexes  

International Nuclear Information System (INIS)

The valence-delocalization in mixed-valence binuclear ferrocene derivatives is investigated by using several physicochemical results. It is demonstrated that the mixed-valence state is controlled by the environment in the solid state. The mechanism of the valence-delocalization in 1',1'''-diethylbiferrocenium triiodide is discussed. The difference between the valence-delocalization accompanied by the symmetry change of the counter anion and the valence-delocalization without connection with the symmetry of the counter anion is discussed. The results are compared with those of oxo-centered trinuclear iron carboxylates. (orig.)

277

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

278

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

279

Valence Bond Mapping of Antiferromagnetic Spin Chains  

OpenAIRE

Boson mapping techniques are developed to describe valence bond correlations in quantum spin chains. Applying the method to the alternating bond hamiltonian for a generic spin chain, we derive an analytic expression for the transition points which gives perfect agreement with existing Density Matrix Renormalization Group (DMRG) and Quantum Monte Carlo (QMC) calculations.

Dukelsky, Jorge; Pittel, Stuart

1997-01-01

280

On Valence Gluons in Heavy Quarkonia  

OpenAIRE

To include the explicit valence gluon degrees of freedom into spectroscopy of the lowest states of heavy quarkonia, we consider, within an adiabatic model, the properties of the lowest hybrid $\\bar{Q}Qg$-mesons and estimate the effects of their mixing with low-lying vector $\\bar{c}c$-charmonia. The perspectives of compatibility of the resulting picture with data are discussed.

Gerasimov, S. B.

1998-01-01

281

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

282

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

283

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

Science.gov (United States)

The cerebellum participates in emotion-related neural circuits formed by different cortical and subcortical areas, which sub-serve arousal and valence. Recent neuroimaging studies have shown a functional specificity of cerebellar lobules in the processing of emotional stimuli. However, little is known about the temporal component of this process. The goal of the current study is to assess the spatiotemporal profile of neural responses within the cerebellum during the processing of arousal and valence. We hypothesized that the excitation and timing of distinct cerebellar lobules is influenced by the emotional content of the stimuli. By using magnetoencephalography, we recorded magnetic fields from twelve healthy human individuals while passively viewing affective pictures rated along arousal and valence. By using a beamformer, we localized gamma-band activity in the cerebellum across time and we related the foci of activity to the anatomical organization of the cerebellum. Successive cerebellar activations were observed within distinct lobules starting ~160ms after the stimuli onset. Arousal was processed within both vermal (VI and VIIIa) and hemispheric (left Crus II) lobules. Valence (left VI) and its interaction (left V and left Crus I) with arousal were processed only within hemispheric lobules. Arousal processing was identified first at early latencies (160ms) and was long-lived (until 980ms). In contrast, the processing of valence and its interaction to arousal was short lived at later stages (420-530ms and 570-640ms respectively). Our findings provide for the first time evidence that distinct cerebellar lobules process arousal, valence, and their interaction in a parallel yet temporally hierarchical manner determined by the emotional content of the stimuli. PMID:25665964

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

2015-04-15

284

Flat Bands in Slightly Twisted Bilayer Graphene  

OpenAIRE

The bands of graphite are extremely sensitive to topological defects which modify the electronic structure. In this paper we found non-dispersive flat bands no farther than 10 meV of the Fermi energy in slightly twisted bilayer graphene as a signature of a transition from a parabolic dispersion of bilayer graphene to the characteristic linear dispersion of graphene. This transition occurs for relative rotation angles of layers around $1.5^o$ and is related to a process of la...

Morell, E. Sua?rez; Correa, J. D.; Vargas, P.; Pacheco, M.; Barticevic, Z.

2010-01-01

285

Generation of Kekulé valence structures and the corresponding valence bond wave function  

OpenAIRE

A new scheme, called “list of nonredundant bonds”, is presented to record the number of bonds and their positions for the atoms involved in Kekulé valence structures of (poly)cyclic conjugated systems. Based on this scheme, a recursive algorithm for generating Kekulé valence structures has been developed and implemented. The method is general and applicable for all kinds of (poly)cyclic conjugated systems including fullerenes. The application of the algorithm in generating V...

Rashid, Z.; Lenthe, J. H.

2010-01-01

286

Eu valence and Fermi-surface development in EuX2Si2 (X = Co, Rh, Ir) systems  

International Nuclear Information System (INIS)

The valence-fluctuating Eu systems EuX2Si2, with X being the transition metal Co, Ir, or Rh, show different types of ground states, strongly depending on X. The instability of the Eu 4f shell underlies this phenomenon and leads among other effects to different valence states ranging from Eu2+ over mixed valence and intermediate valence behavior to Eu3+. Investigations on the structure and the magnetic behavior of EuCo2Si2, EuIr2Si2, and EuRh2Si2 have revealed their Eu valence. Further experiments on specific heat and resistivity gave insights to magnetic ordering, electronic correlations, and possible valence fluctuations. We report about a systematic de Haas-van Alphen study on the Fermi-surface development of the EuX2Si2 compounds in magnetic fields up to 35 T. High-quality single crystals were available for the first time. We focus on the Fermi-surface topology obtained by angle dependent measurements and discuss a comparison to band-structure calculations.

287

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

Science.gov (United States)

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

Powis, I.; Trofimov, A. B.; Bodzuk, I. L.; Holland, D. M. P.; Potts, A. W.; Karlsson, L.

2013-03-01

288

Valence QCD: Connecting QCD to the Quark Model  

OpenAIRE

A valence QCD theory is developed to study the valence quark properties of hadrons. To keep only the valence degrees of freedom, the pair creation through the Z graphs is deleted in the connected insertions; whereas, the sea quarks are eliminated in the disconnected insertions. This is achieved with a new ``valence QCD'' lagrangian where the action in the time direction is modified so that the particle and antiparticle decouple. The theory has the vector and axial $U(2N_F)$ ...

Liu, K. F.; Dong, S. J.; Draper, T.; Leinweber, D.; Sloan, J.; Wilcox, W.; Woloshyn, R. M.

1998-01-01

289

Quantum Monte Carlo with Jastrow-valence-bond wave functions  

OpenAIRE

We consider the use in quantum Monte Carlo calculations 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 by computing the equilibrium well depths of the four diatomic molecules C$_2$, N$_2$, O$_2$, and F$_2$ in both variational Monte Carlo (VMC...

Brai?da, Benoi?t; Toulouse, Julien; Caffarel, Michel; Umrigar, C. J.

2011-01-01

290

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)

291

Determination of the uranium valence state in the brannerite structure using EELS, XPS, and EDX  

Science.gov (United States)

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, 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, and 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 minimise the effects of electron beam reduction of U6+ and U5+. Test samples consisted of three additional synthetic brannerites (Th0.7U0.3Ti2O6, Ca0.2U0.8Ti2O6, and Th0.55U0.3Ca0.15Ti2O6) and three natural brannerites from different localities. The natural brannerite samples are all completely amorphous, due to cumulative alpha decay events over geological time periods (24 508 Ma). Our U valence calibration results are in reasonable agreement with previous work, suggesting possibly a non-linear relationship between the branching ratio and the number of f electrons (and hence the average valence state) of U in solids. We found excellent agreement between the nominal valence states of U and the average valence states determined directly by EELS and estimated by EDX analysis (with assumptions regarding stoichiometry) in two of the three synthetic brannerite test samples. The average U oxidation states of the five synthetic brannerite samples, as derived from XPS analyses, are also in good agreement with those determined by other techniques. The average valence states of U in three amorphous (metamict) natural brannerite samples with alpha decay doses ranging from 3.6×1016 to 6.9×1017 ?/mg were found to be 4.4, 4.7, and 4.8, consistent with the presence of U5+ and/or U6+ as well as U4+ in these samples. These results are in general agreement with previous wet chemical analyses of natural brannerite. However, the average valence states inferred by SEM-EDX for two of the natural brannerite samples do not show satisfactory agreement with the EELS determined valence. This may be due to the occurrence of OH- groups, cation vacancies, anion vacancies, or excess oxygen in the radiation-damaged structure of natural brannerite.

Colella, M.; Lumpkin, G. R.; Zhang, Z.; Buck, E. C.; Smith, K. L.

2005-05-01

292

Band Structure of AlSb Nanoclusters  

Directory of Open Access Journals (Sweden)

Full Text Available Ab initio restricted Hartree-Fock method within the framework of large unit cell formalism is used to investigate the band structure of AlSb nanoclusters. Large unit cells of 8, 16, 54, 64 and 128 atoms are used to analyze the cohesive energy, energy gap, valence bandwidth, and the density of states of the energy levels for AlSb nanoclusters. The results of the present work revealed that the band structure of AlSb nanoclusters differs significantly from that of the bulk AlSb crystal. Also, it is found that the valence band width and the cohesive energy (absolute value increase as the AlSb crystal size increases, and they tend to stabilize for nanoclusters of more than 50 atoms.

Haider I. Isa

2012-08-01

293

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

International Nuclear Information System (INIS)

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 ?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 ?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 parameters has provided an experimental means of distinguishing photoelectron bands due to ?-orbitals from those associated with ?-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 ##tildeX SRC=http://ej.iop.org/icons/Entities/tildeX.gif ALT=tilde X ALIGN=BOTTOM/>## 2A'', A-tilde 2A'', B-tilde 2A' and ##tildeC SRC=http://ej.iop.org/icons/Entities/tildeC.gif ALT=tilde C ALIGN=MIDDLE/>## 2A'' state bands

294

Atomic-scale depth profiling of composition, chemical structure and electronic band structure of La2O3/Si(1 0 0) interfacial transition layer  

International Nuclear Information System (INIS)

The composition and chemical structures of lanthanum oxide films were determined by combining angle-resolved photoelectron spectroscopy and high resolution Rutherford backscattering studies. Conduction and valence band discontinuity at La2O3/Si(1 0 0) interface was also determined by measuring the O 1s photoelectron energy loss and valence band spectra

295

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.

2005-12-01

296

Neutron inelastic scattering from mixed valence materials  

International Nuclear Information System (INIS)

Paramagnetic scattering from mixed valence materials is reviewed. Some of the early measurements identified a broad quasielastic spectral distribution (e.g. a Lorentzian centered on zero energy with large, practically Q-independent widths (half-width approx.5-30 MeV) which remain finite as T ? OK. More recent measurements using high energy neutrons on several mixed valance systems reveal inelastic peaks superposed on the broad quasielastic spectrum at low temperatures. These inelastic peaks progressively melt away with increasing temperature, accompanied possibly by some softening, and disappear almost completely around the temperature of the maximum in the susceptibility. Several possible mechanisms could semi-qualitatively account for the observed spectral response, a deeper insight into whose origin would aid in understanding the mixed valence phenomena

297

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

298

Charge Fluctuations and the Valence Transition in Yb under Pressure  

Science.gov (United States)

We present a dynamical mean-field theory study of the valence transition (f14?f13) 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 advanced 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 with the intermediate valence behavior seen in the early trivalent lanthanides Ce, Pr, and Nd.

Ylvisaker, E. R.; Kuneš, J.; McMahan, A. K.; Pickett, W. E.

2009-06-01

299

Charge fluctuations and the valence transition in Yb under pressure  

International Nuclear Information System (INIS)

Materials, whose atomic state cannot be approximated by a single Slater determinant, are said to have fluctuating or intermediate valence. Using dynamical mean-field theory we investigate the physics of elemental Yb, which exhibits a valence transition under pressure accompanied by a crossover from the fluctuating to the intermediate valence behavior. By comparison to other rare-earth materials (Ce,Nd,Pr) we show that fluctuating and intermediate valence regimes can be distinguished by the charge susceptibility. A large charge susceptibility can explain the softness of Yb in the valence transition region.

300

Seed Dispersal  

Science.gov (United States)

In this outdoor activity and bingo-like game, learners explore why and how seeds spread far from the plants that produce them. To understand natural adaptions that let seeds and fruit be dispersed, learners make modifications to dried beans and peas so they could be dispersed by natural forces like water, air, or an animal moving from one place to another. In the "Seed-Go" Game, learners match ways that seeds are dispersed, to fill rows on the game board.

2012-06-26

301

Valence bond solid states with symplectic symmetry  

OpenAIRE

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

Schuricht, Dirk; Rachel, Stephan

2008-01-01

302

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

303

Delocalization in valence bond-hyperconjugation  

OpenAIRE

We consider delocalization in small molecules. The valence bond technology allows an arbitrary division of the 1-electron space in strictly separate, but nonorthogonal, spaces. Allowing or obstructing orbital mixing between subspaces during the SCF procedure is associated with incorporating or eliminating the hyperconjugation effect. We show an example for tert-butyl and trimethylsilyl cations and radicals. For H2, for which really extensive basis sets are feasible, we extend the basis so far...

Havenith, R. W. A.; Lenthe, J. H.

2009-01-01

304

Proton spin structure and valence quarks  

OpenAIRE

The spin structure of the system of quasifree fermions having total angular momentum $J=1/2$ is studied in a consistently covariant approach. Within this model the relations between the spin functions are obtained. Their particular cases are the sum rules Wanzura - Wilczek, Efremov - Leader - Teryaev, Burkhardt - Cottingham and also the expression for the Wanzura - Wilczek twist 2 term $g_{2}^{WW}$. With the use of the proton valence quark distributions as an input, the corr...

Zavada, Petr

2002-01-01

305

5th International Conference on Valence Fluctuations  

CERN Document Server

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

Malik, S

1987-01-01

306

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

CERN Document Server

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

307

Ba{sub 2}Ir{sub 3}O{sub 9}: a new 5d mixed-valence metallic oxide with KSbO{sub 3}-type structure  

Energy Technology Data Exchange (ETDEWEB)

Crystal structure, magnetic and transport properties of new ternary mixed-valence iridium oxide Ba{sub 2}Ir{sub 3}O{sub 9} are reported. A hydrothermal reaction of IrO{sub 2} and BaO{sub 2} under a pressure of 150 MPa at 650 deg. C yields small black crystals with cubic shape. Energy dispersive X-ray analysis on an as-grown crystal gives the atomic ratio Ba:Ir = 2:3. X-ray powder diffraction shows a pattern of cubic lattice with a cell parameter a = 9.42 A and further Rietveld analysis reveals the KSbO{sub 3}-related structure. Although the structure of Ba{sub 2}Ir{sub 3}O{sub 9} is almost identical to Ba{sub 0.5}IrO{sub 3} [Mat. Res. Bull. 9 (1974) 1777], there is a significant difference in the composition between them. Because the crystallographic site for Ir is unique, Ba{sub 2}Ir{sub 3}O{sub 9} is classified into class III mixed-valence compound where the average valence of Ir is +4.67. The magnetic susceptibility shows almost temperature independent Pauli paramagnetism of 2.9 x 10{sup -4} emu/mol Ir at room temperature. The resistivity for a pellet sample is measured to be 1.5 x 10{sup -1} {omega} cm at room temperature and shows metallic temperature dependence. At low temperature, the temperature dependent component of the resistivity is almost proportional to T{sup 2}. This indicates that Ba{sub 2}Ir{sub 3}O{sub 9} is a bad metal because of strong electron-electron scattering. The narrow 5d-band feature characteristic of the KSbO{sub 3}-type structure is related to the strong electron correlation.

Kawamura, Yoichi; Sato, Hirohiko

2004-11-30

308

Full-Band Monte Carlo Simulation of HgCdTe APDs  

Science.gov (United States)

A full-band Monte Carlo model has been developed for understanding the carrier multiplication process in HgCdTe infrared avalanche photodiodes. The proposed model is based on a realistic electronic structure obtained by pseudopotential calculations and a phonon dispersion relation determined by ab initio techniques. The calculated carrier-phonon scattering rates are consistent with the electronic structure and the phonon dispersion relation, thus removing adjustable parameters such as deformation potential coefficients. The computation of the impact ionization transition rate is based on the calculated electronic structure and the corresponding wavevector-dependent dielectric function. The Monte Carlo model is applied to investigate key performance figures of long-wavelength infrared (LWIR) and mid-wavelength infrared (MWIR) HgCdTe avalanche photodetectors such as carrier multiplication and noise properties. Good agreement is achieved between simulations and experimental results. The multiplication process in LWIR ( ? c = 9.0 ?m at 80 K) and MWIR ( ? c = 5.1 ?m at 80 K) devices is found to be initiated only by electrons, as expected from excess noise measurements. This single-carrier multiplication behavior can be traced back to the details of the computed valence-band structure and phonon scattering rates.

Bertazzi, Francesco; Moresco, Michele; Penna, Michele; Goano, Michele; Bellotti, Enrico

2010-07-01

309

Determinative Role of the Jahn-Teller Disorder in the Raman Scattering of Mixed-Valence Manganites  

CERN Document Server

The mixed-valence perovskitelike manganites are characterized by unique interrelation of Jahn-Teller distortions, electric and magnetic properties. The Jahn-Teller distortion follows the Mn(3+)->Mn(4+) charge transfer with some delay. Its development depends on the lifetime of Mn in (3+) state, governed by the Mn(4+)/Mn(3+) ratio and magnetic correlation. The non-coherence of Jahn-Teller distortions in orthorhombic mixed-valence manganites and rhombohedral RMnO3 (R = rare earth) results in oxygen disorder. We demonstrate that the Raman spectra in this case are dominated by disorder-induced bands reflecting the oxygen partial phonon density of states (PDOS). The PDOS origin of the main Raman bands in insulating phases of such compounds is evidenced by the similar lineshape of experimental spectra and calculated smeared PDOS and disappearance of the PDOS bands in ordered ferromagnetic metallic phase.

Iliev, M N; Popov, V N; Hadjiev, V G

2003-01-01

310

Determinative Role of the Jahn-Teller Disorder in the Raman Scattering of Mixed-Valence Manganites  

Science.gov (United States)

The mixed-valence perovskitelike manganites are characterized by unique interrelation of Jahn-Teller distortions, electric and magnetic properties. The Jahn-Teller distortion follows the Mn^3+ arrow Mn^4+ charge transfer with some delay. Its development depends on the lifetime of Mn in 3+ state, governed by the Mn^4+/Mn^3+ ratio and magnetic correlations. The non-coherence of Jahn-Teller distortions in orthorhombic mixed-valence manganites and rhombohedral RMnO3 (R = rare earth) results in oxygen disorder. We demonstrate that the Raman spectra in this case are dominated by disorder-induced bands reflecting the oxygen partial phonon density of states (PDOS). The PDOS origin of the main Raman bands in insulating phases of such compounds is evidenced by the similar lineshape of experimental spectra and calculated smeared PDOS and disappearance of the PDOS bands in ordered ferromagnetic metallic phase.

Iliev, M. N.; Hadjiev, V. G.; Abrashev, M. V.; Popov, V. N.

2003-03-01

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.)

312

Valency and type conversion in CuInSe2 with H2 plasma exposure: A photoemission investigation  

International Nuclear Information System (INIS)

The effect of H2 plasma exposure on CuInSe2 was studied by synchrotron radiation soft-x-ray photoemission spectroscopy. The low-power H2 plasma was generated with a commercial electron cyclotron resonance plasma source using pure H2 with the plasma exposure being performed at 200 degree C. In situ photoemission measurements were acquired after each plasma exposure in order to observe changes in the valence-band electronic structure as well as changes in the In 4d and Se 3d core lines. The results were correlated in order to relate changes in surface chemistry to the electronic structure. These measurements indicate that the H2 plasma exposure type converts the CuInSe2 surface to an n-type surface as well as converting the In+3 valency state to an In+1 valency state

313

Nernst effect of the intermediate valence compound YbAl3: revisiting the thermoelectric properties  

Science.gov (United States)

The Nernst effect and thermopower of the prototypical Yb-based intermediate valence compound YbAl3 were investigated. Different to the thermopower whose absolute values are enhanced with increasing temperature and assume a broad maximum at 175 K, the Nernst coefficient of YbAl3 is enhanced only below T ? 75 K. While the two quantities in the heavy-fermion compound CeCu2Si2 were recently found to be related by the anomalous Hall mobility due to the local asymmetric Kondo scattering, this theorem fails when being applied to YbAl3. Rather, the thermopower of YbAl3 is well described by a simple narrow-band model. We discuss the reason for this in terms of the intermediate valence nature of YbAl3 that is conceptually different from the local Kondo physics.

Wei, Beipei; Zhang, Jiahao; Sun, Peijie; Wang, Wenquan; Wang, Nanlin; Steglich, Frank

2015-03-01

314

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

International Nuclear Information System (INIS)

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

315

Formation of an unconventional Ag valence state in Ag2NiO2  

CERN Document Server

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 which 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, gamma, is likely due to strong spin fluctuations that stem from nearly complete compensation of the ferro- (metallic double exchange and the 90 degree superexchange) and antiferromagnetic (conventional superexchange via Ni-O-Ag-O-Ni path) interactions.

Johannes, M D; Mazin, I I; Khomskii, D I

2006-01-01

316

Valence skipping driven superconductivity and charge Kondo effect  

International Nuclear Information System (INIS)

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

317

Band gap engineering of TiO2 through hydrogenation  

Science.gov (United States)

The band gap of rutile TiO2 is reduced remarkably through high-temperature annealing in hydrogen atmosphere, and the absorption of visible light of the hydrogenated-TiO2 can be enhanced. These modifications of hydrogenated-TiO2 become more evident with the increase in annealing hydrogen pressure. A defect band arises near the valence band upon hydrogenation while the conduction band remains almost unchanged, which helps for meeting the requirements for hydrogen production through water splitting. This method could be also indicative for the band gap adjustment of other oxide semiconductors.

Mo, Li-Bin; Bai, Yang; Xiang, Qing-Yun; Li, Qun; Wang, Jia-Ou; Ibrahim, Kurash; Cao, Jiang-Li

2014-11-01

318

Ultraviolet bands of potassium dimer  

International Nuclear Information System (INIS)

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

319

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

International Nuclear Information System (INIS)

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

320

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2013-03-29

321

Delocalization in valence bond-Hyperconjugation  

Science.gov (United States)

We consider delocalization in small molecules. The valence bond technology allows an arbitrary division of the 1-electron space in strictly separate, but nonorthogonal, spaces. Allowing or obstructing orbital mixing between subspaces during the SCF procedure is associated with incorporating or eliminating the hyperconjugation effect. We show an example for tert-butyl and trimethylsilyl cations and radicals. For H2, for which really extensive basis sets are feasible, we extend the basis so far that the delocalization or hyperconjugation effect has nearly disappeared.

Havenith, R. W. A.; van Lenthe, J. H.

322

X-ray photoemission and magnetometric studies of valence changes in Ce(Cu1-xNix)4Ga  

International Nuclear Information System (INIS)

The compounds Ce(Cu1-xNix)4Ga crystallize in the hexagonal CaCu5-type structure for the whole doping range 0?x?1. The border compounds CeCu4Ga and CeNi4Ga represent a heavy fermion and fluctuating valence systems, respectively. We report on the studies of the valence evolution in Ce(Cu1-xNix)4Ga employing the X-ray photoemission spectroscopy (XPS) and magnetic susceptibility measurements. The photoemission of the Ce 3d peaks shows a gradual decrease of the occupation of the f states with Ni content. Simultaneously, the hybridization strength and the low temperature magnetic susceptibility are reduced. Within the valence band spectrum a transition from the dominance of the Cu 3d to the dominance of the Ni 3d states is well visible with the traces of the Ce 4f1 states for up to x=0.5. - Research highlights: ? Ni substitution for Cu in CeCu4Ga leads to the loss of Ce 4f states localization. ? Valence fluctuations visible in the XPS of Ce 3d states. ? Magnetic susceptibility measured and the valence resolved up to 1000 K. ? Importance of the temperature independent susceptibility

323

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

Science.gov (United States)

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

Potts, A. W.; Holland, D. M. P.; Powis, I.; Karlsson, L.; Trofimov, A. B.; Bodzuk, I. L.

2013-03-01

324

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

325

Correlation between Kekule valence structures and conjugated circuits  

Energy Technology Data Exchange (ETDEWEB)

The recently introduced concept of conjugated circuits is re-examined and some graph theoretical properties of conjugated circuits analyzed. Particularly, enumeration of conjugated circuits is extended to include disjoint conjugated circuits. It is shown that the total number of so derived conjugated circuits is always K - 1, where K is the number of Kekule valence structures for the molecule, for energy Kekule valence structure. This establishes a reciprocal relation between Kekule valence structures and conjugated circuits. An interesting corollary to the theorem on the number of conjugated circuits is that one can solely from an examination of a single (any) Kikule valence structure of a molecule determine the number of Kekule valence forms and even determine the form for the remaining valence structures. Polynomials which enumerate the conjugated circuits are given for selected benzenoid hydrocargons.

Gutman, I. (Univ. of Kragujevac, Yugoslavia); Randic, M.

1979-01-01

326

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

327

Attosecond band-gap dynamics in silicon  

Science.gov (United States)

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

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

2014-12-01

328

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

329

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

2014-07-01

330

Neural Correlates of Processing Valence and Arousal in Affective Words  

OpenAIRE

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 during p...

Lewis, P. A.; Critchley, H. D.; Rotshtein, P.; Dolan, R. J.

2006-01-01

331

Valence bond distribution and correlation in bipartite Heisenberg antiferromagnets  

OpenAIRE

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 la...

Schwandt, David; Alet, Fabien; Oshikawa, Masaki

2013-01-01

332

VALENCE CHANGE IN THE Pd-Ce SYSTEM  

OpenAIRE

We report X-Ray Absorption and X-Ray Photoemission measurements on crystalline and amorphous Pd1-xCex alloys. In this system, cerium presents a concentration-induced valence change. A correlation between cerium electronic configuration and density of occupied states have been shown.Valence anomalies appear to be due to the high palladium 4d density of states near the Fermi level. The effect of structural disorder on the cerium valence instability in amorphous alloys is also discussed.

Malterre, D.; Krill, G.; Durand, J.; Marchal, G.

1987-01-01

333

Rational subsets of polycyclic monoids and valence automata  

OpenAIRE

We study the classes of languages defined by valence automata with rational target sets (or equivalently, regular valence grammars with rational target sets), where the valence monoid is drawn from the important class of polycyclic monoids. We show that for polycyclic monoids of rank 2 or more, such automata accept exactly the context-free languages. For the polycyclic monoid of rank 1 (that is, the bicyclic monoid), they accept a class of languages strictly including the pa...

Render, Elaine; Kambites, Mark

2007-01-01

334

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 (? absorption bands of the two samples. Excitation in the ligand-to-metal charge transfer (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

335

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

Science.gov (United States)

We synthesized ZnO1-xTex alloys with Te composition x ZnO optical absorption edge by more than 1 eV. The minimum band gap obtained in this work is 1.8 eV for x = 0.23. The optical properties of the alloys are explained by the modification of the valence band of ZnO, due to the anticrossing interactions of the localized Te states with the ZnO valence band extended states. Hence, the observed large band gap reduction is primarily originating from the upward shift of the valence band edge. We show that the optical data can be explained by the band anticrossing model with the localized level of Te located at 0.95 eV above the ZnO valence band and the band anticrossing coupling constant of 1.35 eV. These parameters allow the prediction of the compositional dependence of the band gap as well as the conduction and the valence band offsets in the full composition range of ZnO1-xTex alloys.

Ting, M.; dos Reis, R.; Jaquez, M.; Dubon, O. D.; Mao, S. S.; Yu, K. M.; Walukiewicz, W.

2015-03-01

336

Neutron scattering on intermediate valence systems  

International Nuclear Information System (INIS)

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

337

Valence modulations in CeRuSn  

Science.gov (United States)

CeRuSn exhibits an extraordinary room temperature structure at 300 K with the coexistence of two types of Ce ions, namely trivalent Ce 3+ and intermediate-valent Ce(4-? )+, in a metallic environment. The ordered arrangement of these two Ce types on specific crystallographic sites results in a doubling of the unit cell along the c axis with respect to the basic monoclinic CeCoAl-type structure. Below room temperature, structural modulation transitions with very broad hysteresis have been reported from measurements of various bulk properties. X-ray diffraction revealed that at low temperatures the doubling of the CeCoAl-type structure is replaced by a different modulated ground state, approximating a near tripling of the basic CeCoAl cell. The transition is accompanied by a significant contraction of the c axis. We present new x-ray absorption near-edge spectroscopy data at the Ce L3 absorption edge, measured on a freshly cleaved surface of a CeRuSn single crystal. In contrast to our previous report, the new data exhibit small but significant variations as a function of temperature that are consistent with a transition of a fraction of Ce3+ ions to the intermediate valence state, analogous to the ? ?? transition in elemental cerium, when cooling through the structural transitions of CeRuSn. Such results in a valence-modulated state.

Feyerherm, R.; Dudzik, E.; Prokeš, K.; Mydosh, J. A.; Huang, Y.-K.; Pöttgen, R.

2014-07-01

338

Valence quark distributions of the proton from maximum entropy approach  

CERN Document Server

We present an attempt of maximum entropy principle to determine valence quark distributions in the proton at very low resolution scale $Q_0^2$. The initial three valence quark distributions are obtained with limited dynamical information from quark model and QCD theory. Valence quark distributions from this method are compared to the lepton deep inelastic scattering data, and the widely used CT10 and MSTW08 data sets. The obtained valence quark distributions are consistent with experimental observations and the latest global fits of PDFs. Maximum entropy method is expected to be particularly useful in the case where relatively little information from QCD calculation is given.

Wang, Rong

2014-01-01

339

Valence quark distributions of the proton from maximum entropy approach  

Science.gov (United States)

We present an attempt using the maximum entropy principle to determine valence quark distributions in the proton at a very low resolution scale Q02. The initial three valence quark distributions are obtained with limited dynamical information from quark model and QCD theory. Valence quark distributions from this method are compared to the lepton deep inelastic scattering data, and the widely used CT10 and MSTW08 data sets. The obtained valence quark distributions are consistent with experimental observations and the latest global fits of parton distribution functions. The maximum entropy method is expected to be particularly useful in cases where relatively little information from QCD theory is given.

Wang, Rong; Chen, Xurong

2015-03-01

340

Band alignment at a ZnO/GaN (0001) heterointerface  

Science.gov (United States)

We report the experimental results of the valence band offset at a ZnO/GaN (0001) heterointerface. The ZnO/GaN (0001) heterointerface is prepared by growing a ZnO layer on (0001) GaN/Al2O3, in which the ZnO layer is epitaxially deposited by plasma-assisted molecular-beam epitaxy, while the GaN template is prepared by metalorganic chemical-vapor deposition. Ex situ ultraviolet and x-ray photoelectron spectroscopy have been used to measure the valence band offset ?EV. The photoelectron spectroscopy measurements are done before and after Ar+ ion cleaning of the surfaces. Type-II band alignments with band offsets of ?EV=1.0 eV (before cleaning) and 0.8 eV (after cleaning) with the valence band maximum of GaN being placed above that of ZnO are obtained.

Hong, Soon-Ku; Hanada, Takashi; Makino, Hisao; Chen, Yefan; Ko, Hang-Ju; Yao, Takafumi; Tanaka, Akinori; Sasaki, Hiroyuki; Sato, Shigeru

2001-05-01

341

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

342

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

Directory of Open Access Journals (Sweden)

Full Text Available In a recent X-ray absorption study in boron doped diamond, Nakamura et al. have seen a well isolated narrow boron impurity band in non-superconducting samples and an additional narrow band at the chemical potential in a superconducting sample. We interpret the beautiful spectra as evidence for upper Hubbard band of a Mott insulating impurity band and an additional metallic 'mid-gap band' of a conducting 'self-doped' Mott insulator. This supports the basic framework of a recent theory of the present author of strongly correlated impurity band superconductivity (impurity band resonating valence bond, IBRVB theory in a template of a wide-gap insulator, with no direct involvement of valence band states.

G. Baskaran

2006-01-01

343

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

International Nuclear Information System (INIS)

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

344

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

International Nuclear Information System (INIS)

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

345

Attosecond time-resolved photoemission from core and valence states of magnesium.  

Science.gov (United States)

We report on laser-assisted attosecond photoemission from single-crystalline magnesium. In strong contrast to the previously investigated transition metal tungsten, photoelectron wave packets originating from the localized core level and delocalized valence-band states are launched simultaneously from the solid within the experimental uncertainty of 20 as. This phenomenon is shown to be compatible with a heuristic model based on free-particle-like propagation of the electron wave packets generated inside the crystal by the attosecond excitation pulse and their subsequent interaction with the assisting laser field at the metal-vacuum interface. PMID:23002773

Neppl, S; Ernstorfer, R; Bothschafter, E M; Cavalieri, A L; Menzel, D; Barth, J V; Krausz, F; Kienberger, R; Feulner, P

2012-08-24

346

Calculation of vibrational structure in the core and valence ESCA spectra of CO and N2  

International Nuclear Information System (INIS)

The vibrational excitations in the core and valence ESCA bands of CO and N2 have been investigated by means of Franck-Condon (FC) analysis. FC factors obtained from optimized geometries and from the force constants of the neutral ground and ionized states are compared with those obtained from calculated ionized-state energy gradients. Geometries, force constants, and energy gradients are calculated both from frozen-orbital energies and from OS RHF wavefunctions. The differences between the results of the methods employed are discussed in the light of experimental data. (orig.)

347

Tetranuclear ruthenium(II) complex with a dinucleating ligand forming multi-mixed-valence states.  

Science.gov (United States)

A square-shaped tetranuclear ruthenium(II) complex, [Ru(II)4Cl5(bpmpm)2](3+) [1; bpmpm = 4,6-bis[[N,N-bis(2'-pyridylmethyl)amino]methyl]pyrimidine], exhibited four reversible and stepwise one-electron-oxidation processes: chemical oxidation of 1 formed three different mixed-valence states, in one of which the charge is partially delocalized on the two Ru centers, to be evidenced by observation of an intervalence charge-transfer absorption band, categorized into the Robin-Day class II. PMID:25412477

Ohzu, Shingo; Ishizuka, Tomoya; Kotani, Hiroaki; Shiota, Yoshihito; Yoshizawa, Kazunari; Kojima, Takahiko

2014-12-15

348

Dispersion surfaces  

International Nuclear Information System (INIS)

The dispersion relation of linear waves in a non-relativistic, collisionless and homogeneous magnetized plasma is solved by numerical methods. Both electrostatic and electromagnetic waves with frequencies from below the ion gyrofrequency to above the electron gyrofrequency are studied for all angles of propagation. Modes occurring in a cold plasma as well as waves dependent on thermal effects are included. Dispersion surfaces, that is plots of frequency versus wave vector components, are presented for some plasma models. This presentation shows all interesting waves clearly and reveals how different modes are related. The dispersion surfaces can be used as an aid, for example, when comparing wave observations and theory, and they may also help to avoid confusing nomenclature. (author)

349

Anomalous Eu valence state and superconductivity in undoped Eu3Bi2S4F4.  

Science.gov (United States)

We have synthesized a novel europium bismuth sulfofluoride, Eu3Bi2S4F4, by solid-state reactions in sealed evacuated quartz ampules. The compound crystallizes in a tetragonal lattice (space group I4/mmm, a = 4.0771(1) Å, c = 32.4330(6) Å, and Z = 2), in which CaF2-type Eu3F4 layers and NaCl-like BiS2 bilayers stack alternately along the crystallographic c axis. There are two crystallographically distinct Eu sites, Eu(1) and Eu(2) at the Wyckoff positions 4e and 2a, respectively. Our bond valence sum calculation, based on the refined structural data, indicates that Eu(1) is essentially divalent, while Eu(2) has an average valence of ??+2.64(5). This anomalous Eu valence state is further confirmed and supported, respectively, by Mössbauer and magnetization measurements. The Eu(3+) components donate electrons into the conduction bands that are mainly composed of Bi 6px and 6py states. Consequently, the material itself shows metallic conduction and superconducts at 1.5 K without extrinsic chemical doping. PMID:25314008

Zhai, Hui-Fei; Zhang, Pan; Wu, Si-Qi; He, Chao-Yang; Tang, Zhang-Tu; Jiang, Hao; Sun, Yun-Lei; Bao, Jin-Ke; Nowik, Israel; Felner, Israel; Zeng, Yue-Wu; Li, Yu-Ke; Xu, Xiao-Feng; Tao, Qian; Xu, Zhu-An; Cao, Guang-Han

2014-10-29

350

Spectroscopic and Redox Studies of Valence-Delocalized [Fe2S2](+) Centers in Thioredoxin-like Ferredoxins.  

Science.gov (United States)

Reduced forms of the C56S and C60S variants of the thioredoxin-like Clostridium pasteurianum [Fe2S2] ferredoxin (CpFd) provide the only known examples of valence-delocalized [Fe2S2](+) clusters, which constitute a fundamental building block of all higher nuclearity Fe-S clusters. In this work, we have revisited earlier work on the CpFd variants and carried out redox and spectroscopic studies on the [Fe2S2](2+,+) centers in wild-type and equivalent variants of the highly homologous and structurally characterized Aquifex aeolicus ferredoxin 4 (AaeFd4) using EPR, UV-visible-NIR absorption, CD and variable-temperature MCD, and protein-film electrochemistry. The results indicate that the [Fe2S2](+) centers in the equivalent AaeFd4 and CpFd variants reversibly interconvert between similar valence-localized S = 1/2 and valence-delocalized S = 9/2 forms as a function of pH, with pKa values in the range 8.3-9.0, because of protonation of the coordinated serinate residue. However, freezing high-pH samples results in partial or full conversion from valence-delocalized S = 9/2 to valence-localized S = 1/2 [Fe2S2](+) clusters. MCD saturation magnetization data for valence-delocalized S = 9/2 [Fe2S2](+) centers facilitated determination of transition polarizations and thereby assignments of low-energy MCD bands associated with the Fe-Fe interaction. The assignments provide experimental assessment of the double exchange parameter, B, for valence-delocalized [Fe2S2](+) centers and demonstrate that variable-temperature MCD spectroscopy provides a means of detecting and investigating the properties of valence-delocalized S = 9/2 [Fe2S2](+) fragments in higher nuclearity Fe-S clusters. The origin of valence delocalization in thioredoxin-like ferredoxin Cys-to-Ser variants and Fe-S clusters in general is discussed in light of these results. PMID:25790339

Subramanian, Sowmya; Duin, Evert C; Fawcett, Sarah E J; Armstrong, Fraser A; Meyer, Jacques; Johnson, Michael K

2015-04-01

351

Electronic band structure of La 4Sb 3 and La 4Bi 3  

Science.gov (United States)

The self-consistent APW band calculations for La 4Sb 3 and La 4Bi 3 have been done. A narrow gap appears between the conduction bands derived dominantly from the La d states and the valence bands derived mostly from the p states of pnictogens mixed with the La d states. In Sm 4Bi 3 the 4f level is expected to be in this gap, but closes to the bottom of conduction band.

Takegahara, Katsuhiko; Harima, Hisatomo; Kasuya, Tadao

1985-10-01

352

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

Science.gov (United States)

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

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

2015-04-01

353

Colloids with valence and specific directional bonding.  

Science.gov (United States)

The ability to design and assemble three-dimensional structures from colloidal particles is limited by the absence of specific directional bonds. As a result, complex or low-coordination structures, common in atomic and molecular systems, are rare in the colloidal domain. Here we demonstrate a general method for creating the colloidal analogues of atoms with valence: colloidal particles with chemically distinct surface patches that imitate hybridized atomic orbitals, including sp, sp(2), sp(3), sp(3)d, sp(3)d(2) and sp(3)d(3). Functionalized with DNA with single-stranded sticky ends, patches on different particles can form highly directional bonds through programmable, specific and reversible DNA hybridization. These features allow the particles to self-assemble into 'colloidal molecules' with triangular, tetrahedral and other bonding symmetries, and should also give access to a rich variety of new microstructured colloidal materials. PMID:23128225

Wang, Yufeng; Wang, Yu; Breed, Dana R; Manoharan, Vinothan N; Feng, Lang; Hollingsworth, Andrew D; Weck, Marcus; Pine, David J

2012-11-01

354

Modulation of DNA condensation by cation valence  

Science.gov (United States)

Aggrecan is a negatively charged bottlebrush-shaped proteoglycan in the extracellular matrix, with unique polyelectrolyte properties. Aggrecan-hyaluronic acid aggregates are responsible for the compressive resilience of articular cartilage. Unlike linear polyelectrolytes such as DNA, aggrecan is insensitive to the presence of multivalent counterions (e.g., calcium ions) and self-assembles into micro-gels in near-physiological salt solutions. These features are preserved by aggrecan adsorbed on mica surfaces. To probe both the nature of aggrecan assemblies in solution and their surface interactions, we image the aggrecan assemblies adsorbed on mica surface using Atomic Force Microscopy The effect of counterion valence on the hydration-dehydration properties of the aggrecan assemblies will be discussed.

Chandran, Preethi; Dimitriadis, Emilios; Silva, Candida; Basser, Peter; Horkay, Ferenc

2011-03-01

355

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

356

Studies of valence-quark shadowing at HERA  

OpenAIRE

We propose to measure valence-quark shadowing by observing charged pion productions in electron-nucleus scattering at HERA. Studies of shadowing phenomena in the valence-quark distribution could be useful in discriminating among various models, which produce similar results in the $F_2$ shadowing.

Kumano, S.

1995-01-01

357

Core Polarization with Variable Oscillator Length Parameters for Valence Particles  

OpenAIRE

We study quadrupole and monopole core polarization using harmonic oscillator wave functions but with different length parameters for the valence particle as compared to the core. We use perturbation theory with a delta interaction. The results also hold for a density dependent delta interaction [1]. We study how the amount of core polarization varies with the distance of the valence particle from the core

Zamick, Larry

2010-01-01

358

Core Polarization with Variable Length Parameters for Valence Particles  

OpenAIRE

We study quadrupole and monopole core polarization using harmonic oscillator wave funtions but with different length parameters for the valence particle as compared to the core. We use perturbation theory with a delta interaction. The results also hold for a density dependent delta interaction [1]. We study how the amount of core polarization varies with the distance of the valence particle from the core.

Zamick, Larry

2010-01-01

359

Study of band terminating in the A ? 100 by EUROGAM  

International Nuclear Information System (INIS)

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

360

Qualitative feature of the low-lying spectrum of intrashell states of 4-valence-electron atoms derived from symmetry consideration  

OpenAIRE

Inherent nodal surfaces existing in the wavefunctions of intrashell states of 4-valence-electron atoms have been investigated. The decisive effect of these surfaces has been demonstrated, the ordering of low-lying levels has been predicted, a primary classification scheme has been proposed, the existence of three rotation bands has been suggested.

Bao, C. G.

1998-01-01

361

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

362

Role of valence electrons for formation of glassy alloys  

International Nuclear Information System (INIS)

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 Tg of 121 kinds of glassy alloys can be expressed as a linear function of VEC: Tg = 131VEC + 65 (2.3 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.

363

Ab initio Green's function formalism for band structures  

OpenAIRE

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

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

2004-01-01

364

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

OpenAIRE

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

365

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2013-03-29

366

XMCD spectroscopy on valence fluctuating and heavy fermion compounds in very high magnetic fields up to 40 T  

Energy Technology Data Exchange (ETDEWEB)

L-edge X-ray magnetic circular dichroism (XMCD) and X-ray absorption spectra (XAS) in several rare-earth elements have been studied in high magnetic fields up to 40 T using a pulsed magnet. XMCD spectrum of Eu in a typical valence fluctuating compound, EuNi{sub 2}(Si{sub 0.18}Ge{sub 0.82}){sub 2}, shows a characteristic two peak structure, reflecting the valence fluctuation. However, in another valence fluctuating compound, YbInCu{sub 4}, it is found that the XMCD spectrum of Yb shows only a single peak. In contrast to XMCD, two absorption bands in XAS are observed in both EuNi{sub 2}(Si{sub 0.18}Ge{sub 0.82}){sub 2} and YbInCu{sub 4}. The intensity ratio between the two absorption bands changes significantly with increasing magnetic field in these materials, suggesting the field-induced valence change. The high magnetic field XMCD and XAS measurements have also been conducted in an antiferromagnetic heavy fermion compound CeRh{sub 2}Si{sub 2}. The Ce valence is found to be nearly trivalent and insensitive to magnetic field. The XMCD at Ce L{sub 2}-edge increases rapidly around 26 T corresponding to the metamagnetic transition. The XMCD spectra in CeRh{sub 2}Si{sub 2} at high magnetic fields show only a single peak as was reported in a heavy fermion ferromagnetic compound CeRu{sub 2}Ge{sub 2} [1].

Matsuda, Y H; Her, J L [ISSP, University of Tokyo, 5-1-5 Kashiwanoha, Kahiswa, Chiba 277-8581 (Japan); Inami, T; Ohwada, K [Synchrotron Radiation Research Unit, Japan Atomic Energy Agency, Hyogo 679-5148 (Japan); Ouyang, Z W [Depertment of Physics, Huazhong University of Science and Technology, Wuhan 430074 (China); Okada, K; Nojiri, H [IMR, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan); Mitsuda, A; Wada, H [Department of Physics, Kyushu University, Fukuoka 812-8581 (Japan); Yoshimura, K [Department of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502 (Japan); Amitsuka, H [Graduate School of Science, Hokkaido University, Sapporo 060-0810 (Japan); Kawamura, N; Suzuki, M [JASRI/SPring-8, 1-1-1 Kouto, Sayo, Hyogo 679-5198 (Japan); Kotani, A, E-mail: ymatsuda@issp.u-tokyo.ac.j [KEK-PF, Oho 1-1, Tsukuba, Ibaraki, 305-0801 (Japan)

2009-11-15

367

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2013-07-01

368

Photoinduced mixed valency in zinc porphyrin dimer of triruthenium cluster dyads.  

Science.gov (United States)

The preparation, electrochemistry, and spectroscopic characterization of three new species, (ZnTPPpy)Ru3O(OAc)6(CO)-pz-Ru3O(OAc)6(CO)L, where ZnTPPpy = zinc(II) 5-(4-pyridyl)-10,15,20-triphenylporphyin, L = pyridyl ligand, and pz = pyrazine, are reported. These porphyrin-coordinated Ru3O–BL–Ru3O (BL = bridging ligand) dyads are capable of undergoing intramolecular electron transfer from the photoexcited Zn porphyrin to Ru3O donor–bridge–acceptor dimer systems. Seven reversible redox processes are observed in the cyclic voltammograms of the newly synthesized dyads, showing no significant electrochemical interaction between the redox active porphyrin and the pyrazine-bridged ruthenium dimer of Ru3O trimers. From the electrochemical behavior of the dyads, large comproportionation constants (Kc = 6.0 × 10(7) for L = dmap) were calculated from the reduction potentials of the Ru(III)Ru(III)Ru(II) clusters, indicating a stable mixed-valence state. Electronic absorption spectra of the singly reduced mixed-valence species show two intervalence charge transfer (IVCT) bands assigned within the Brunschwig–Creutz–Sutin semiclassical three-state model as metal-to-bridge and metal-to-metal in character. The progression from most to least delocalized mixed-valence dimer ions, as determined by the divergence of the IVCT bands and in agreement with electrochemical data, follows the order of L = 4-dimethylaminopyridine (dmap) > pyridine (py) > 4-cyanopyridine (cpy). These systems show dynamic coalescence of the infrared spectra in the ?(CO) region of the singly reduced state. This sets the time scale of electron exchange at electron transfer from the S1 excited state of the coordinated porphyrin to the dimer is predicted to be thermodynamically favorable, with ?GFET(0) ranging from ?0.54 eV for L = dmap to ?0.62 eV for L = cpy. Observation of IVCT band growth under continual photolysis (?exc = 568 nm) confirms a phototriggered intramolecular electron transfer process resulting in a strongly coupled singly reduced mixed-valence species. PMID:25260187

Henderson, Jane; Kubiak, Clifford P

2014-10-20

369

Band offsets and band bending at heterovalent semiconductor interfaces  

Science.gov (United States)

We present a comprehensive study of band offsets and band bending at heterovalent semiconductor heterointerfaces. A perfectly abrupt heterovalent interface is usually thermodynamically unstable, and atomic intermixing of materials with different numbers of valence electrons causes large variations in band offsets and local doping density, depending on the spatial arrangement of atoms at the interface. The studied prototypical II-VI/III-V semiconductor interfaces are n -doped ZnSe/GaAs (001) heterostructures with varied composition profiles close to the interface, which were realized by molecular-beam epitaxy with different amounts of Zn or Se predeposited on n -GaAs prior to n -ZnSe layer growth. The samples are characterized by temperature-dependent electrical transport across the interface, electrochemical capacitance-voltage profiling, Raman spectroscopy, and high-resolution x-ray diffraction. We find that the potential barrier in the conduction band at a Zn-rich n -ZnSe/ n -GaAs interface is as high as 550 meV and it gradually decreases with Se predeposition down to about 70 meV. A large depletion region at the heterointerface, about 50 nm wide, is assigned to significant intermixing of acceptor-type atoms, resulting in an effective electron deficit of 1.5×1013cm-2 . The depletion width and the acceptor density around the interface are nearly independent from the growth start procedure. Se predeposition, however, partially shifts the depletion region at the heterointerface from GaAs into ZnSe, compared to Zn predeposition. The results are discussed on the basis of a band-bending model accounting for variable band offsets, interface state density and atomic interdiffusion profiles depending on growth start.

Frey, A.; Bass, U.; Mahapatra, S.; Schumacher, C.; Geurts, J.; Brunner, K.

2010-11-01

370

Characterization of Novel Semiconductor Alloys for Band Gap Engineering  

Science.gov (United States)

The novel semiconductor alloys, In1-xAlx N, GaN1-xAsx, and ZnSe1-xOx, are promising materials for low-cost and high-efficiency solar cells and efficient solid-state lighting. The band gap of all of the alloys can be controlled through the visible electromagnetic energy spectrum by varying x. In-rich InAlN tends to be degenerately n-type due to the high electron affinity of InN and the conduction band and light hole band are non-parabolic due to the narrow band gap and the interaction of the conduction band and valence bands. The absorption spectra can be blue shifted due to the Burstein-Moss Shift. GaNAs and ZnSeO are highly mismatched alloys, where the alloying involves elements that are very dissimilar in terms of electronegativity and size. The band anticrossing model, which treats the interaction of a localized defect level with the extended states of the conduction and valence bands, quantitatively describes the properties of highly mismatched alloys. The band gap bowing parameter, which quantifies the band gap dependence on composition, of InAlN is determined while accounting for the effects of degenerate electron concentrations and non-parabolic bands on the absorption spectra. The composition is independently determined by two complimentary methods. The band gap and temperature dependence of the band gap of ZnSe 1-xOx are determined by optical spectroscopy and can be understood in terms of the band anticrossing model. The exciton kinetics is quantified through time-resolved photoluminescence and is found to cause a low temperature enhancement of the photoluminescence. The band gaps of GaNAs are determined for the full composition range for both crystalline and amorphous phases. The composition dependence of the band gap can be quantified by the band anticrossing model across the full composition range through a linear interpolation of the conduction band and valence band anticrossing models.

Broesler, Robert Joseph, Jr.

371

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

International Nuclear Information System (INIS)

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

372

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

373

Valence density of states of group IVA transition-metal dichalcogenides  

International Nuclear Information System (INIS)

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

374

Resonating-Valence-Bond Liquid in Low Dimensions  

Science.gov (United States)

The Hubbard model in D dimensions, with the on-site repulsion U and the transfer integral between nearest neighbors - t/sqrt{D} , is studied on the basis of the Kondo-lattice theory. If U/|t| ? 1, |n ? 1| ? |t|/(DU), where n is the number of electrons per unit cell, and D is so small that |J|/D ? kBTc, where J = ?4t2/U and Tc is 0 K for D = 1 and is the highest critical temperature among possible ones for D ? 2, a low-T phase where Tc electron liquid. Since the liquid is stabilized by the Kondo effect in conjunction with the resonating-valence-bond (RVB) mechanism, it is simply the RVB electron liquid; in one dimension, it is also the Tomonaga–Luttinger liquid. The Kondo energy of the RVB liquid is kBTK = O(|J|/D); its effective Fermi energy is O(kBTK). A midband appears on the chemical potential between the upper and lower Hubbard bands; the Hubbard gap is a pseudogap. As regards the density of states per unit cell of the midband, its bandwidth is O(kBTK) or O(|J|/D), its peak height is O(1/U), and its spectral weight is O[t2/(DU2)]. Since the midband almost disappears in the Heisenberg limit, the RVB electron liquid in the Heisenberg limit is simply the RVB spin liquid. The RVB electron and spin liquids adiabatically continue to each other. Since local moments form in a high-T phase where T ? TK, the high-T phase is simply the Mott insulator.

Ohkawa, Fusayoshi J.

2014-12-01

375

Plate wave stop-bands in periodically poled lithium niobate.  

Science.gov (United States)

The dispersion curves of four lowest plate acoustic waves (PAWs) in the ZX cut of a periodically poled lithium niobate (PPLN) wafer are computed numerically and investigated experimentally. Experiment is in agreement with simulated dispersion curves. Calculations and measurements reveal the stop-bands in the dispersion curves of the PAW modes in PPLN despite a wafer that has uniform mechanical properties. At a specific wave number, within the frequencies of the stop-bands, the acoustic modes do not propagate. PMID:19354350

Ostrovskii, I V; Klymko, V A; Nadtochiy, A B

2009-04-01

376

Charge ordering in the intermediate valence magnet YbPd  

OpenAIRE

An x-ray diffraction study reveals the charge ordering structure in an intermediate valence magnet YbPd with a CsCl-structure. The valence of the Yb ions forms an incommensurate structure, characterized by the wavevector (+-0.07 +-0.07 1/2) below 130 K. At 105 K, the incommensurate structure turns into a commensurate structure, characterized by the wavevector (0 0 1/2). Based on the resonant x-ray diffraction spectra of the superlattice reflections, the valences of the Yb io...

Takahashi, Ryo; Honda, Takashi; Miyake, Atsushi; Kagayama, Tomoko; Shimizu, Katsuya; Ebihara, Takao; Kimura, Tsuyoshi; Wakabayashi, Yusuke

2013-01-01

377

Atoms in Valence Bond. Method, implementation and application  

OpenAIRE

The Atoms in Valence Bond (AiVB) approach is presented. The main goal was to develop a new and innovative approach, within the existing Valence Bond framework, to build and analyze the molecular VB wave function in terms of atoms and their atomic states, in a very user-friendly environment. The necessary theoretical tools, detailed implementation in TURTLE, an ab initio VB/VBSCF program and application are described. The procedure to build the molecular Atoms in ValenceBond (AiVB) wave fu...

Zielinski, M. L.

2012-01-01

378

Valence fluctuation driven quantum phase transition  

Science.gov (United States)

In recent years quantum critical phenomenon have acquired a great interest in the condensed matter community. Many rare earth intermetallic compounds, which are also heavy fermions can be tuned easily to quantum critical point by application of external perturbations like magnetic field and pressure. YbRh2Si2 and CeCu2Si2 are a few examples. The periodic Anderson model (PAM) is a paradigm for studying these kind of systems. We investigate the extended periodic anderson model (EPAM), which includes Coulomb interaction of conduction and localised electrons using local moment approach (LMA) within dynamical mean field theory (DMFT) with the objective of developing an understanding of quantum phase transitions due to valence fluctuations. We show that tuning c-f interaction and on-site energy of localised electron (which can be achieved by varying external perturbation like pressure) leads to some exotic phenomena like vanishing of Fermi liquid scale. We study transport properties near quantum critical point and highlight the anomalies due to the proximity of QCP.

Kumar, Pramod; Vidhyadhiraja, N. S.

2012-02-01

379

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

Science.gov (United States)

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

Kaur, Avneet; Bakhshi, A. K.

2010-04-01

380

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

Energy Technology Data Exchange (ETDEWEB)

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, E-mail: kausik.majumdar@sematech.org [SEMATECH, 257 Fuller Road, STE 2200, Albany, New York 12203 (United States)

2014-05-07

381

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

382

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

International Nuclear Information System (INIS)

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

383

Pressure-induced valence change in YbAl3: a combined high pressure inelastic x-ray scattering and theoretical investigation  

Energy Technology Data Exchange (ETDEWEB)

High resolution x-ray absorption (XAS) experiments in the partial fluorescence yield mode (PFY) and resonant inelastic x-ray emission (RXES) measurements under pressure were performed on the intermediate valence compound YbAl{sub 3} up to 38 GPa. The results of the Yb L{sub 3} PFY-XAS and RXES studies show a smooth valence increase in YbAl{sub 3} from 2.75 to 2.93 at ambient to 38 GPa. In-situ angle dispersive synchrotron high pressure x-ray diffraction experiments carried out using a diamond cell at room temperature to study the equation of state showed the ambient cubic phase stable up to 40 GPa. The results obtained from self-interaction corrected local spin density functional calculations to understand the pressure effect on the Yb valence and compressibility are in good agreement with the experimental results.

Bauer, E D [Los Alamos National Laboratory; Kumar, R S [UNIV OF NV; Svane, A [UNIV OF AARHUS; Vaitheeswaran, G [ROYAL INST. OF TECHNOLOGY; Nicol, M F [UNIV OF NV; Kanchana, V [ROYAL INST OF TECHNOLOGY; Hu, M [HPCAT; Cornelius, A L [UNIV OF NV

2008-01-01

384

Pressure-induced valence change in YbAl3: a combined high pressure inelastic x-ray scattering and theoretical investigation  

International Nuclear Information System (INIS)

High resolution x-ray absorption (XAS) experiments in the partial fluorescence yield mode (PFY) and resonant inelastic x-ray emission (RXES) measurements under pressure were performed on the intermediate valence compound YbAl3 up to 38 GPa. The results of the Yb L3 PFY-XAS and RXES studies show a smooth valence increase in YbAl3 from 2.75 to 2.93 at ambient to 38 GPa. In-situ angle dispersive synchrotron high pressure x-ray diffraction experiments carried out using a diamond cell at room temperature to study the equation of state showed the ambient cubic phase stable up to 40 GPa. The results obtained from self-interaction corrected local spin density functional calculations to understand the pressure effect on the Yb valence and compressibility are in good agreement with the experimental results

385

4H-SiC band structure investigated by surface photovoltage spectroscopy  

International Nuclear Information System (INIS)

The conduction and valence band structure of high-purity 4H-SiC epilayers have been studied by surface photovoltage spectroscopy (SPS). A comparison between defect-free and single-layer stacking fault affected areas is reported. Electronic transitions, determined by SPS, are in good agreement with ab initio calculations. Electronic transitions and changes in band occupation have been observed in stacking fault rich areas below the band gap. Moreover, stacking faults induce the presence of a split-off band below the conduction band and a modification of the electron density of states in the conduction band always at the M point.

386

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

OpenAIRE

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

Nhat, Hoang Nam

2003-01-01

387

Band structure and chemical bond in alkali metal carbonates  

Science.gov (United States)

The band structure, state density, optical functions, and distribution of valence and difference density in alkali-metal carbonates are calculated within the local electron-density functional theory using the method of pseudopotential in the basis of numerical pseudoorbitals. When passing from a lithium cation to a potassium one, the character of hybridization between the crystal sublattices changes to result in an increase in the valence-band width, a decrease in the forbidden-band width, a complication of the structure of state-density spectrum, and a shift of the maxima of optical functions to the low-energy range. It is found that the electron overflow between the ?-and ?-orbitals of crystallographically nonequivalent oxygen atoms can occur in different ways, hence their interaction force with the surrounding atoms is different. The role of cations in stabilization of anion chains resulting from the electron-cloud overlapping in lithium and sodium carbonates is shown.

Fedorov, I. A.; Zhuravlev, Yu. N.; Korabel'Nikov, D. V.

2006-10-01

388

Quantum Monte Carlo with Jastrow-Valence-Bond wave functions  

CERN Document Server

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

389

Correlated Small Polaron Transport in Mixed Valence Oxides  

OpenAIRE

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.

Srivastava, C.

1997-01-01

390

Testing valence proton symmetry for Te and Cd  

Science.gov (United States)

To aid in the study of nuclei far from stability, various valence correlation schemes have been used to infer unknown properties of nuclei from known ones. One such valence correlation scheme is valence proton symmetry, which has been successfully tested for Xe and Pd pairs around the Z = 50 proton shell closure (Dewald 2008). To test the robustness of valence proton symmetry around mid-shell for the Te-Cd pairs, which is one proton pair closer to Z = 50, we measured the lifetimes of the 2^+1 level in ^116Te and ^118Te using the Recoil Distance Doppler Shift method. The results of this experiment will be presented. [4pt] A. Dewald et al. Phys. Rev. C 78, 051302 (2008)

Ahn, Tan; Bettermann, Linus; Casperson, Robert; Chevrier, Raphael; Heinz, Andreas; Ilie, Gabriela; McCarthy, David; Radeck, Desiree; Smith, Mallory; Werner, Volker; Williams, Elizabeth

2010-11-01

391

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

International Nuclear Information System (INIS)

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

392

Charge Fluctuations and the Valence Transition in Yb under Pressure  

OpenAIRE

We present a dynamical mean field theory study of the valence transition ($f^{14} \\to f^{13}$) 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 ...

Ylvisaker, E. R.; Kunes?, J.; Mcmahan, A. K.; Pickett, W. E.

2009-01-01

393

Inelastic collisions of positrons with one-valence-electron targets  

Science.gov (United States)

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

Abdel-Raouf, Mohamed Assad

1990-01-01

394

First extraction of valence transversities in a collinear framework  

OpenAIRE

We present an extraction of the valence transversity parton distributions based on an analysis of pion-pair production in deep-inelastic scattering off transversely polarized targets. Recently released data for proton and deuteron targets at HERMES and COMPASS permit a flavor separation of valence transversities. The present extraction is performed in the framework of collinear factorization, where dihadron fragmentation functions are involved. The latter are taken from a pr...

Bacchetta, Alessandro; Courtoy, Aurore; Radici, Marco

2012-01-01

395

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

OpenAIRE

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

396

Valence photoionization of the LiCl monomer and dimer  

International Nuclear Information System (INIS)

This paper reports a study of valence photoionization of the LiCl monomer and dimer. The behavior of the photoionization partial cross section for molecular valence orbitals was measured as a function of photon energy between 15 and 35 eV. A square-integrable-function method was used to model the ionization partial cross section in both the LiCl monomer and dimer.

397

Exploring covalently bonded diamondoid particles with valence photoelectron spectroscopy  

OpenAIRE

We investigated the valence electronic structure of diamondoid particles in the gas phase, utilizing valence photoelectron spectroscopy. The samples were singly or doubly covalently bonded dimers or trimers of the lower diamondoids. Both the bond type and the combination of bonding partners are shown to affect the overall electronic structure. For singly bonded particles, we observe a small impact of the bond on the electronic structure, whereas for doubly bonded particles, ...

Zimmermann, Tobias; Richter, Robert; Knecht, Andre; Fokin, Andrey A.; Koso, Tetyana V.; Chernish, Lesya V.; Gunchenko, Pavel A.; Schreiner, Peter R.; Mo?ller, Thomas; Rander, Torbjo?rn

2013-01-01

398

Stimulus affective valence reverses spatial compatibility effect  

Directory of Open Access Journals (Sweden)

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

rick Francisco Quintas Conde

2011-01-01

399

Stimulus affective valence reverses spatial compatibility effect  

Scientific Electronic Library Online (English)

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

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

2011-06-01

400

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

International Nuclear Information System (INIS)

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

401

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

402

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

403

Optically induced coherent intra-band dynamics in disordered semiconductors  

OpenAIRE

On the basis of a tight-binding model for a strongly disordered semiconductor with correlated conduction- and valence band disorder a new coherent dynamical intra-band effect is analyzed. For systems that are excited by two, specially designed ultrashort light-pulse sequences delayed by tau relatively to each other echo-like phenomena are predicted to occur. In addition to the inter-band photon echo which shows up at exactly t=2*tau relative to the first pulse, the system re...

Schlichenmaier, C.; Varga, I.; Meier, T.; Thomas, P.; Koch, S. W.

2001-01-01

404

Reaching degeneracy in two-quasiparticle chiral bands  

International Nuclear Information System (INIS)

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

405

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

International Nuclear Information System (INIS)

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

406

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

Science.gov (United States)

A frustrated, effective ½-filled band Hubbard-Heisenberg model has been proposed for describing the strongly dimerized charge-transfer solid families ?-(ET)2X and Z[Pd(dmit)2]2. In addition to showing unconventional superconductivity, these materials also exhibit antiferromagnetism, candidate spin-liquid phases, and, in the case of Z=EtMe3P, a spin-gapped phase that has sometimes been referred to as a valence bond solid. We show that neither superconductivity nor the valence bond order phase occurs within the Hubbard-Heisenberg model. We suggest that a description based on ¼-filling, that is reached when the carrier concentration per molecule instead of per dimer is considered, thus may be appropriate. PMID:23995074

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

2013-09-25

407

Origin of valence and core excitations in LiFePO4 and FePO4  

International Nuclear Information System (INIS)

Electronic structures of LiFePO4 and FePO4 have been investigated using valence and core electron energy loss spectroscopy (EELS) supported by ab initio calculations. Valence electron energy loss spectra of FePO4 are characterized by interband transitions found between 0 and 20 eV, which are not observed in LiFePO4. Spectra are fully analysed using band structure calculations and calculated dielectric functions. In particular, we show that interband transitions observed in FePO4 spectra originate from the states at the top of the valence band, which have mainly oxygen p character. From core-loss EELS, it is observed that the O-K edge in FePO4 has a pre-edge peak below the threshold of the main O-K edge. This pre-edge peak is not observed in the O-K spectra of LiFePO4. The position of the pre-edge peak is determined by a charge transfer process, which shifts the position of the iron 3d bands with respect to the conduction band. The intensity of the pre-edge peak is also determined by the changes in the hybridization of iron 3d and oxygen states as a result of extraction of lithium ions from the LiFePO4 lattice. We show that the extraction of lithium ions from LiFePO4 results in large changes in the electronic structure, such that FePO4 can be considered to be a charge transfer insulator while LiFePO4 is a typical Mott-Hubbard insulator.ical Mott-Hubbard insulator.

408

Origin of valence and core excitations in LiFePO(4) and FePO(4).  

Science.gov (United States)

Electronic structures of LiFePO(4) and FePO(4) have been investigated using valence and core electron energy loss spectroscopy (EELS) supported by ab initio calculations. Valence electron energy loss spectra of FePO(4) are characterized by interband transitions found between 0 and 20 eV, which are not observed in LiFePO(4). Spectra are fully analysed using band structure calculations and calculated dielectric functions. In particular, we show that interband transitions observed in FePO(4) spectra originate from the states at the top of the valence band, which have mainly oxygen p character. From core-loss EELS, it is observed that the O-K edge in FePO(4) has a pre-edge peak below the threshold of the main O-K edge. This pre-edge peak is not observed in the O-K spectra of LiFePO(4). The position of the pre-edge peak is determined by a charge transfer process, which shifts the position of the iron 3d bands with respect to the conduction band. The intensity of the pre-edge peak is also determined by the changes in the hybridization of iron 3d and oxygen states as a result of extraction of lithium ions from the LiFePO(4) lattice. We show that the extraction of lithium ions from LiFePO(4) results in large changes in the electronic structure, such that FePO(4) can be considered to be a charge transfer insulator while LiFePO(4) is a typical Mott-Hubbard insulator. PMID:21399256

Kinyanjui, M K; Axmann, P; Wohlfahrt-Mehrens, M; Moreau, P; Boucher, F; Kaiser, U

2010-07-14

409

Secondary seed dispersal and its role in landscape organization  

Science.gov (United States)

Mathematical models of banded vegetation patterns predict rapid upslope migration of vegetated patches not realized in field observations, a key point of disagreement between theory and observation. It is shown that the disagreement between model results and field observations can arise from seed dispersal dynamics. Two representations of biomass movement are used to test the hypothesis that secondary seed dispersal in overland flow inhibits band migration. The first is based on coupling down-slope water transport and seed advection. The second uses a kernel-based representation of seed transport where an anisotropic dispersal kernel combines the effects of isotropic primary and downslope secondary seed dispersal, and ensures that conclusions about secondary dispersal are independent of diffusive representations of biomass movement. The analysis demonstrates that secondary seed dispersal can retard upward movement of banded vegetation irrespective of the precise representation of biomass movement as long as the anisotropic effects are accounted for.

Thompson, Sally; Katul, Gabriel

2009-01-01

410

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-04-14

411

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

412

Scanning confocal electron energy-loss microscopy using valence-loss signals.  

Science.gov (United States)

Finding a faster alternative to tilt-series electron tomography is critical for rapidly evolving fields such as the semiconductor industry, where failure analysis could greatly benefit from higher throughput. We present a theoretical and experimental evaluation of scanning confocal electron energy-loss microscopy (SCEELM) using valence-loss signals, which is a promising technique for the reliable reconstruction of materials with sub-10-nm resolution. Such a confocal geometry transfers information from the focused portion of the electron beam and enables rapid three-dimensional (3D) reconstruction by depth sectioning. SCEELM can minimize or eliminate the missing-information cone and the elongation problem that are associated with other depth-sectioning image techniques in a transmission electron microscope. Valence-loss SCEELM data acquisition is an order of magnitude faster and requires little postprocessing compared with tilt-series electron tomography. With postspecimen chromatic aberration (C c) correction, SCEELM signals can be acquired in parallel in the direction of energy dispersion with the aid of a physical pinhole. This increases the efficiency by 10×-100×, and can provide 3D resolved chemical information for multiple core-loss signals simultaneously. PMID:23692691

Xin, Huolin L; Dwyer, Christian; Muller, David A; Zheng, Haimei; Ercius, Peter

2013-08-01

413

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 f3 ? f2 transition resulting from the presence of Np+4. 4 figures

414

Non-linear phase dispersion spectroscopy  

OpenAIRE

Non-linear phase dispersion spectroscopy (NLDS) is introduced as a means to retrieve wide-band, high spectral resolution profiles of the wavelength-dependent, real part of the refractive index. The method is based on detecting dispersion effects imparted to a light field with low coherence transmitted through a thin sample and detected interferometrically in the spectral domain. The same sampled signal is also processed to yield quantitative phase maps and spectral information regarding the t...

Robles, Francisco E.; Satterwhite, Lisa L.; Wax, Adam

2011-01-01

415

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

416

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

International Nuclear Information System (INIS)

The present thesis deals with the one-valence-particle nuclei 147Tb and 151Er. The main purpose of the study was, to study characteristic properties of the particle-phonon excitations of these nuclei. In the one-valence-proton nucleus 147Tb from the ?h11/2x3- septet only the 15/2+ and 17/2+ Yrast states were known, which underly a strong diagonal exchange interaction. At mass separators in ? decay experiments of the 1/2+ and the 11/2-147Dy activities and in in-beam experiments layed out on excitation of states above the Yrast line with 6Li beams the nucleus 147Tb was spectroscoped. The combination of these three data sets made the nearly complete covering of the spin range from 1/2 to 27/2 of the low-lying states in 147Tb possible. At the whole in this nucleus more than 100 hitherto unknown states could be placed and farly characterized. The unusually manifold data allowed to identify beside the complete ?h11/2x3- septet also very much further particlexphonon states. Furthermore in the excitation range between 2.5 and 4 MeV numerous three-quasiparticle excitations were observed and in very sufficient way described by parameter-free shell-model calculations. A further important result is the manifestation of a neutron-one-particle-one-hole state with I=27/2, which lies with 3.7 MeV excitation close to the Yrast line. (orig./HSI)

417

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

418

Valence QCD Connecting QCD to the Quark Model  

CERN Document Server

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

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

1999-01-01

419

Optical study of archetypical valence-fluctuating Eu systems  

International Nuclear Information System (INIS)

We have investigated the optical conductivity of the prominent valence-fluctuating compounds EuIr2Si2 and EuNi2P2 in the infrared energy range to get new insights into the electronic properties of valence-fluctuating systems. For both compounds, we observe upon cooling the formation of a renormalized Drude response, a partial suppression of the optical conductivity below 100 meV and the appearance of a midinfrared peak at 0.15 eV for EuIr2Si2 and at 0.13 eV for EuNi2P2. Most remarkably, our results show a strong similarity with the optical spectra reported for many Ce- or Yb-based heavy-fermion metals and intermediate valence systems, although the phase diagrams and the temperature dependence of the valence differ strongly between Eu- and Ce-/Yb-systems. This suggests that the hybridization between 4f- and conduction electrons, which is responsible for the properties of Ce- and Yb-systems, plays an important role in valence-fluctuating Eu systems.

420

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

421

Static corrections versus dynamic correlation effects in the valence band Compton profile spectra of Ni  

Science.gov (United States)

We compute the Compton profile of Ni using the local density approximation of density functional theory supplemented with electronic correlations treated at different levels. The total/magnetic Compton profiles show not only quantitative but also qualitative significant differences depending on whether Hubbard corrections are treated at a mean field +U or in a more sophisticated dynamic way. Our aim is to discuss the range and capability of electronic correlations to modify the kinetic energy along specific spatial directions. The second and the fourth order moments of the difference in the Compton profiles are discussed as a function of the strength of local Coulomb interaction U .

Chioncel, L.; Benea, D.; Mankovsky, S.; Ebert, H.; Minár, J.

2014-11-01

422

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)

423

The latest developments in undulator beamlines for valence band spectroscopy at SRC  

International Nuclear Information System (INIS)

A stigmatic plane grating monochromator (PGM) and a 4-meter normal incidence monochromator (NIM) were recently installed on undulator sources at the Synchrotron Radiation Center (SRC). Details of their design, installation, and performance will be reported. A new pure permanent magnet (PPM) undulator will be installed next year. The design criteria for spectroscopy beamlines utilizing this source as well as two possible monochromator designs, a modified Wadsworth and a varied line spacing (VLS) monochromator, will be discussed

424

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

OpenAIRE

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.

Yakibchuk, P.; Volkov, O.; Vakarchuk, S.

2007-01-01

425

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

426

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

International Nuclear Information System (INIS)

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

427

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

International Nuclear Information System (INIS)

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

428

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

International Nuclear Information System (INIS)

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

429

Flat Chern Band in a Two-Dimensional Organometallic Framework  

OpenAIRE

By combining exotic band dispersion with nontrivial band topology, an interesting type of band structure, namely the flat chern band (FCB), has recently been proposed to spawn high-temperature fractional quantum hall states. Despite the proposal of several theoretical lattice models, however, it remains a doubt whether such a "romance of flatland" could exist in a real material. Here, we present a first-principles design of a two-dimensional (2D) Indium-Phenylene Organometal...

Liu, Zheng; Wang, Zheng-fei; Mei, Jia-wei; Wu, Yong-shi; Liu, Feng

2012-01-01

430

The CuInSe2-CuIn3Se5 defect compound interface: Electronic structure and band alignment  

Science.gov (United States)

The interface formation between stoichiometric chalcopyrite CuInSe2 and the copper-deficient defect phase CuIn3Se5 is investigated by in situ photoelectron spectroscopy. The use of epitaxial samples allows for the preparation of highly defined surfaces and accurate analysis of the electronic structure. Valence band structures measured with synchrotron-based photoelectron spectroscopy are in agreement with density functional theory. We observe a lowering of the top valence band of CuIn3Se5 of 0.29 eV with respect to CuInSe2. The increased optical gap for copper-deficient material leads to aligned conduction bands.

Hofmann, A.; Pettenkofer, C.

2012-08-01

431

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

432

Anomalous shifts of blue and yellow luminescence bands in MBE-grown ZnO films  

International Nuclear Information System (INIS)

We observed strong shifts of the blue and yellow luminescence bands with variation of excitation intensity in ZnO films grown on sapphire by MBE using hydrogen peroxide as a source of reactive oxygen. The blue band, having a maximum in the range from 2.85 to 3.15 eV in different samples and different excitation intensities at 10 K, is attributed to diagonal transitions from the conduction band (or shallow donors) to the valence band in realm of potential fluctuations caused by random distribution of charged point defects in a compensated semiconductor. The yellow band is related to an unidentified deep acceptor

433

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

Science.gov (United States)

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

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

2015-04-01

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