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Sample records for 2p core-level photoemission

  1. Theory of photoemission from the Ni 2p core level

    Photoemission spectra are calculated for the Ni 2p core level within a small-cluster many-body scheme. The interplay between Coulomb, exchange, and spin-orbit interactions is discussed, as well as the role of extra-atomic screening. The spin-dependent transfer of spectral weight, both within and across the levels, is considered. Effects due to circular, linear, and unpolarized excitation are also examined. Local final-state configurations are reported, and a physical interpretation of the various spectral features is given. copyright 1997 The American Physical Society

  2. Detection of subsurface core-level shifts in Si 2p core-level photoemission from Si(111)-(1x1):As

    Paggel, J.J. [Philipps-Universitaet Marburg (Germany); Hasselblatt, M.; Horn, K. [Fritz-Haber Institut der Max-Planck-Gesellschraft, Berlin (Germany)] [and others

    1997-04-01

    The (7 x 7) reconstruction of the Si(111) surface arises from a lowering energy through the reduction of the number of dangling bonds. This reconstruction can be removed by the adsorption of atoms such as hydrogen which saturate the dangling bonds, or by the incorporation of atoms, such as arsenic which, because of the additional electron it possesses, can form three bonds and a nonreactive lone pair orbital from the remaining two electrons. Core and valence level photoemission and ion scattering data have shown that the As atoms replace the top silicon atoms. Previous core level spectra were interpreted in terms of a bulk and a single surface doublet. The authors present results demonstrate that the core level spectrum contains two more lines. The authors assign these to subsurface silicon layers which also experience changes in the charge distribution when a silicon atom is replaced by an arsenic atom. Subsurface core level shifts are not unexpected since the modifications of the electronic structure and/or of photohole screening are likely to decay into the bulk and not just to affect the top-most substrate atoms. The detection of subsurface components suggests that the adsorption of arsenic leads to charge flow also in the second double layer of the Si(111) surface. In view of the difference in atomic radius between As and Si, it was suggested that the (1 x 1): As surface is strained. The presence of charge rearrangement up to the second double layer implies that the atomic coordinates also exhibit deviations from their ideal Si(111) counterparts, which might be detected through a LEED I/V or photoelectron diffraction analysis.

  3. Hidden relationship between the electrical conductivity and the Mn 2p core-level photoemission spectra in La{sub 1-x}Sr{sub x}MnO{sub 3}

    Hishida, T.; Ohbayashi, K. [NGK SPARK PLUG CO., LTD., 2808 Iwasaki, Komaki, Aichi 485-8510 (Japan); Saitoh, T. [Department of Applied Physics, Tokyo University of Science, Shinjuku, Tokyo 162-8601 (Japan)

    2013-01-28

    Core-level electronic structure of La{sub 1-x}Sr{sub x}MnO{sub 3} has been studied by x-ray photoemission spectroscopy (XPS). We first report, by the conventional XPS, the well-screened shoulder structure in Mn 2p{sub 3/2} peak, which had been observed only by hard x-ray photoemission spectroscopy so far. Multiple-peak analysis revealed that the Mn{sup 4+} spectral weight was not proportional to the nominal hole concentration x, indicating that a simple Mn{sup 3+}/Mn{sup 4+} intensity ratio analysis may result in a wrong quantitative elemental analysis. Considerable weight of the shoulder at x = 0.0 and the fact that the shoulder weight was even slightly going down from x = 0.2 to 0.4 were not compatible with the idea that this weight simply represents the metallic behavior. Further analysis found that the whole Mn 2p{sub 3/2} peak can be decomposed into four portions, the Mn{sup 4+}, the (nominal) Mn{sup 3+}, the shoulder, and the other spectral weight located almost at the Mn{sup 3+} location. We concluded that this weight represents the well-screened final state at Mn{sup 4+} sites, whereas the shoulder is known as that of the Mn{sup 3+} states. We found that the sum of these two spectral weight has an empirical relationship to the conductivity evolution with x.

  4. Spin polarization and magnetic dichroism in core-level photoemission from ferromagnets

    Menchero, J G [Univ. of California, Berkeley, CA (United States). Dept. of Physics

    1997-05-01

    In this thesis we present a theoretical investigation of angle- and spin-resolved core-level photoemission from ferromagnetic Fe and Ni. We also consider magneto-dichroic effects due to reversal of the photon helicity or reversal of the sample magnetization direction. In chapter 1, we provide a brief outline of the history of photoemission, and show how it has played an important role in the development of modern physics. We then review the basic elements of the theory of core-level photoemission, and discuss the validity of the some of the commonly-used approximations. In chapter 2, we present a one-electron theory to calculate spin- and angle-resolved photoemission spectra for an arbitrary photon polarization. The Hamiltonian includes both spin-orbit and exchange interactions. As test cases for the theory, we calculate the spin polarization and magnetic dichroism for the Fe 2p core level, and find that agreement with experiment is very good.

  5. Alkaline Earth Core Level Photoemission Spectroscopy of High-Temperature Superconductors

    Vasquez, R.

    1993-01-01

    This paper examines photoemission measurements of the alkaline Earth core levels of high-temperature superconductors and related materials, models that seek to explain the large negative shifts observed relative to the corresponding alkaline Earth metals, and the effect of lattice site disorder on the core level spectra and the presence or absence of intrinsic surface peaks.

  6. Quantification of plasmon excitations in core-level photoemission

    Calculation of photoelectron spectra (PES) based on our previous dielectric response model [A. C. Simonsen et al. Phys. Rev. B 56, 1612 (1997)] for electronic excitations in PES are compared with recently reported experimental data. It is found that the dielectric description of electron energy losses in photoemission reproduces quantitatively the angular dependence of the surface and bulk electron losses observed experimentally for the Al2s photoemission spectra of Al(111), excited with MgKα radiation. The model also allows to calculate the separate intrinsic and extrinsic effects in photoemission. Thus, the extrinsic losses account for more than 95% of the total surface excitations. Regarding the bulk excitations, both extrinsic and intrinsic contributions vary significantly with emission angle. The intrinsic contribution represents ∼35% of the intensity at the bulk plasmon position at normal emission while only 18% at 80 deg. glancing emission. The calculations presented here can easily be used to interpret PES spectra of other materials in terms of intrinsic and extrinsic effects, if their dielectric properties are known

  7. Core-level and valence-band photoemission study of granular platinum films

    Photoemission and resistivity measurements have been made on Pt clusters imbedded in an amorphous silicon dioxide matrix. No significant changes in the Pt 4f/sub 7/2/ or 5d/sub 5/2/ core-level shifts or in the density of states per Pt atom at the Fermi level are seen at the percolation threshold. Most of the Pt 4f/sub 7/2/ core-level shift can be explained as a Coulomb effect due to finite cluster size. We speculate that because of the unusually large core-level shifts there may also be charge transfer from the Pt clusters to the silica matrix

  8. Evidence of the nature of core-level photoemission satellites using angle-resolved photoemission extended fine structure

    Moler, E.J.; Kellar, S.A.; Huff, W.R.A. [Lawrence Berkeley National Lab., CA (United States)] [and others

    1997-04-01

    The authors present a unique method of experimentally determining the angular momentum and intrinsic/extrinsic origin of core-level photoemission satellites by examining the satellite diffraction pattern in the Angle Resolved Photoemission Extended Fine Structure (ARPEFS) mode. They show for the first time that satellite peaks not associated with chemically differentiated atomic species display an ARPEFS intensity oscillation. They present ARPEFS data for the carbon 1s from ({radical}3x{radical}3)R30 CO/Cu(111) and p2mg(2xl)CO/Ni(110), nitrogen 1s from c(2x2) N{sub 2}/Ni(100), cobalt 1s from p(1x1)Co/Cu(100), and nickel 3p from clean nickel (111). The satellite peaks and tails of the Doniach-Sunjic line shapes in all cases exhibit ARPEFS curves which indicate an angular momentum identical to the main peak and are of an intrinsic nature.

  9. Direct evidence for the nature of core-level photoemission satellites using angle-resolved photoemission extended fine structure

    Photoemission satellites from several systems have been found to exhibit exactly the same angle-resolved photoemission extended fine structure (ARPEFS) as found in the main peaks, when referred to the equivalent photoelectron wave number k for their own photoelectrons. This provides a direct and powerful method for experimentally determining the angular momentum parameters and the intrinsic/extrinsic nature of core-level photoemission satellites. We present ARPEFS satellite data for nitrogen 1s line in c(2x2)N2/Ni(100), the nickel 3p line in clean nickel (111), the carbon 1s lines in (√(3)x√(3))R30 CO/Cu(111) and p2mg(2x1)CO/Ni(110), and the cobalt 1s line in p(1x1) Co/Cu(100). For the last two cases the open-quotes satelliteclose quotes structure is actually the low-energy tail of a Doniach-Sunjic line shape. The satellite peaks and the tails of the Doniach-Sunjic line shapes exhibit ARPEFS curves that in all cases except one indicate angular-momentum parameters identical to the main peak and an intrinsic nature. copyright 1997 The American Physical Society

  10. Young's double-slit experiment using two-center core-level photoemission: Photoelectron recoil effects

    Core-level photoemission from N2 can be considered an analogue of Young's double-slit experiment (YDSE) in which the double-slit is replaced by a pair of N 1s orbitals. The measured ratio between the 1σg and 1σu photoionization cross-sections oscillates as a function of photoelectron momentum, due to two-center YDSE interference, exhibiting a remarkable dependence on the vibrational sub-levels of the core ionized state. We theoretically demonstrate that the recoil of the photoelectron given to the ionized N atom strongly influences this interference pattern. The reason for this is that the momentum transfer affects the phases of the photoionization amplitudes

  11. Can circular dichroism in core-level photoemission provide a spectral fingerprint of adsorbed chiral molecules?

    Allegretti, F [Physics Department, University of Warwick, Coventry CV4 7AL (United Kingdom); Polcik, M [Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D 14195 Berlin (Germany); Sayago, D I [Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D 14195 Berlin (Germany); Demirors, F [Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D 14195 Berlin (Germany); O' Brien, S [Physics Department, University of Warwick, Coventry CV4 7AL (United Kingdom); Nisbet, G [Centre for Applied Catalysis, Department of Chemical and Biological Sciences, University of Huddersfield, Queensgate, Huddersfield HD1 3DH (United Kingdom); Lamont, C L A [Centre for Applied Catalysis, Department of Chemical and Biological Sciences, University of Huddersfield, Queensgate, Huddersfield HD1 3DH (United Kingdom); Woodruff, D P [Physics Department, University of Warwick, Coventry CV4 7AL (United Kingdom)

    2005-04-01

    The results of experimental measurements and theoretical simulations of circular dichroism in the angular distribution (CDAD) of photoemission from atomic core levels of each of the enantiomers of a chiral molecule, alanine, adsorbed on Cu(1 1 0) are presented. Measurements in, and out of, substrate mirror planes allow one to distinguish the CDAD due to the chirality of the sample from that due to a chiral experimental geometry. For these studies of oriented chiral molecules, the CDAD is seen not only in photoemission from the molecular chiral centre, but also from other atoms which have chiral geometries as a result of the adsorption. The magnitude of the CDAD due to the sample chirality differs for different adsorption phases of alanine, and for different emission angles and energies, but is generally small compared with CDAD out of the substrate mirror planes which is largely unrelated to the molecular chirality. While similar measurements of other molecules may reveal larger CDAD due to molecular chirality, the fact that the results for one chiral molecule show weak effects means that such CDAD is unlikely to provide a simple and routine general spectral fingerprint of adsorbed molecular chirality.

  12. Magnetism and electronic properties of Mn:Ge(111) interfaces probed by core level photoemission spectroscopy

    The electronic and magnetic properties of Mn:Ge(111) interfaces have been investigated by photoelectron spectroscopy and SQUID magnetometry. An ordered, metallic and ferromagnetic, Mn:Ge(111) interface and a disordered, semiconducting and paramagnetic, MnxGe1-x surface alloy have been considered. An analysis of the Mn 2p X-ray photoemission core line shows that the former interface can be described by a single-configuration Mn 3d6 initial state, while the latter presents satellite features typical of Mn-based diluted magnetic semiconductors, characterized by relevant ligand-to-metal charge transfer effects.

  13. Structural origin of Si-2p core-level shifts from Si(100)-c[4x2] surface: A spectral x-ray photoelectron diffraction study

    Chen, X.; Tonner, B.P. [Univ. of Wisconsin, Milwaukee, WI (United States); Denlinger, J. [Univ. of Wisconsin, Milwaukee, WI (United States)][Ernest Orlando Lawrence Berkeley National Lab., CA (United States)] [and others

    1997-04-01

    The authors have performed angle-resolved x-ray photoelectron diffraction (XPD) from a Si(100)-c(4x2) surface to study the structural origin of Si-2p core-level shifts. In the experiment, the highly resolved surface Si-2p core-level spectra were measured as a fine grid of hemisphere and photon energies, using the SpectroMicroscopy Facility {open_quotes}ultraESCA{close_quotes} instrument. By carefully decomposing the spectra into several surface peaks, the authors are able to obtain surface-atom resolved XPD patterns. Using a multiple scattering analysis, they derived a detailed atomic model for the Si(100)-c(4x2) surface. In this model, the asymmetric dimers were found tilted by 11.5 plus/minus 2.0 degrees with bond length of 2.32 plus/minus 0.05{angstrom}. By matching model XPD patterns to experiment, the authors can identify which atoms in the reconstructed surface are responsible for specific photoemission lines in the 2p spectrum.

  14. Photoemission with high-order harmonics: A tool for time-resolved core-level spectroscopy

    Christensen, Bjarke Holl; Raarup, Merete Krog; Balling, Peter

    2010-01-01

    A setup for femtosecond time-resolved photoelectron spectroscopy of solid surfaces is presented. The photon energies for core-level spectroscopy experiments are created by high-order harmonic generation from infrared 120-femtosecond laser pulses focused in a Ne gas jet. The present experimental r...... from the sample are collected by a large-solid-angle time-of-flight electron spectrometer based on a parabolic-grid reflector. Results from experiments probing the Bi 5d core-levels are presented, and the results of preliminary pump-probe experiments are described....

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

    Kolorenč, Jindřich; Kozub, Agnieszka L.; Shick, Alexander

    Bristol: IOP Publishing Ltd,, 2015, 012054. ISSN 1742-6588. [International Conference on Strongly Correlated Electron Systems 2014 (SCES2014). Grenoble (FR), 07.07.2014-14.07.2014] R&D Projects: GA ČR(CZ) GAP204/10/0330 Institutional support: RVO:68378271 Keywords : electronic-structure calculations * dynamical mean-field theory * Mott insulators * actinides * oxides * photoemission Subject RIV: BM - Solid Matter Physics ; Magnetism

  16. Graphene on Au-coated SiOx substrate: Its visibility and intrinsic core-level photoemission

    Wu, Chung-Lin; Chen, Jhih-Wei; Wang, Chiang-Lun; Chen, Chia-Hao; Chen, Yi-Chun

    2012-02-01

    With the motivation of precisely and intrinsically characterizing a exfoliate graphene using photoelectron spectroscopy, a conducting substrate having high optical contrast is greatly desired. Here, we demonstrate that exfoliated graphene can be optically visible on a thin 9-nm Au-coated SiOx substrate, and can be easily conducted into scanning photoelectron microscopy/spectroscopy (SPEM/S) studies. Because of the elimination of charging effect, precisely core-level characterization of exfoliated graphene is presented with different numbers of layers. Consequently, the usage of Au-coated SiOx substrate serves a simple but effective method to study pristine graphene by photoelectron spectroscopy and other electron-detection techniques.

  17. Angle-resolved and core-level photoemission study of interfacing the topological insulator Bi1.5Sb0.5Te1.7Se1.3 with Ag, Nb, and Fe

    N. de Jong; E. Frantzeskakis; B. Zwartsenberg; Y.K. Huang; D. Wu; P. Hlawenka; J. Sanchez-Barriga; A. Varykhalov; E. van Heumen; M.S. Golden

    2015-01-01

    Interfaces between a bulk-insulating topological insulator (TI) and metallic adatoms have been studied using high-resolution, angle-resolved, and core-level photoemission. Fe, Nb, and Ag were evaporated onto Bi1.5Sb0.5Te1.7Se1.3 (BSTS) surfaces both at room temperature and 38 K. The coverage and tem

  18. A study of angle-resolved photoemission extended fine structure as applied to the Ni 3p, Cu 3s, and Cu 3p core levels of the respective clean (111) surfaces

    Huff, W.R.A.; Moler, E.J.; Kellar, S.A. [Lawrence Berkeley National Lab., CA (United States)] [and others

    1997-04-01

    The first non-s initial state angle-resolved photoemission extended fine structure (ARPEFS) study of clean surfaces for the purpose of further understanding the technique is reported. The surface structure sensitivity of ARPEFS applied to clean surfaces and to arbitrary initial states is studied using normal photoemission data taken from the Ni 3p core levels of a Ni(111) single crystal and the Cu 3s and the Cu 3p core-levels of a Cu(111) single crystal. The Fourier transforms of these clean surface data are dominated by backscattering. Unlike the s initial state data, the p initial state data show a peak in the Fourier transform corresponding to in-plane scattering from the six nearest-neighbors to the emitter. Evidence was seen for single-scattering events from in the same plane as the emitters and double-scattering events. Using a newly developed, multiple-scattering calculation program, ARPEFS data from clean surfaces and from p initial states can be modeled to high precision. Although there are many layers of emitters when measuring photoemission from a clean surface, test calculations show that the ARPEFS signal is dominated by photoemission from atoms in the first two crystal layers. Thus, ARPEFS applied to clean surfaces is sensitive to surface reconstruction. The known contraction of the first two Cu(111) layers is confirmed. The best-fit calculation for clean Ni(111) indicates an expansion of the first two layers. To better understand the ARPEFS technique, the authors studied s and non-s initial state photoemission from clean metal surfaces.

  19. A study of angle-resolved photoemission extended fine structure as applied to the Ni 3p, Cu 3s, and Cu 3p core levels of the respective clean (111) surfaces

    The first non-s initial state angle-resolved photoemission extended fine structure (ARPEFS) study of clean surfaces for the purpose of further understanding the technique is reported. The surface structure sensitivity of ARPEFS applied to clean surfaces and to arbitrary initial states is studied using normal photoemission data taken from the Ni 3p core levels of a Ni(111) single crystal and the Cu 3s and the Cu 3p core-levels of a Cu(111) single crystal. The Fourier transforms of these clean surface data are dominated by backscattering. Unlike the s initial state data, the p initial state data show a peak in the Fourier transform corresponding to in-plane scattering from the six nearest-neighbors to the emitter. Evidence was seen for single-scattering events from in the same plane as the emitters and double-scattering events. Using a newly developed, multiple-scattering calculation program, ARPEFS data from clean surfaces and from p initial states can be modeled to high precision. Although there are many layers of emitters when measuring photoemission from a clean surface, test calculations show that the ARPEFS signal is dominated by photoemission from atoms in the first two crystal layers. Thus, ARPEFS applied to clean surfaces is sensitive to surface reconstruction. The known contraction of the first two Cu(111) layers is confirmed. The best-fit calculation for clean Ni(111) indicates an expansion of the first two layers. To better understand the ARPEFS technique, the authors studied s and non-s initial state photoemission from clean metal surfaces

  20. Photoelectron spectroscopy at a free-electron laser. Investigation of space-charge effects in angle-resolved and core-level spectroscopy and realizaton of a time-resolved core-level photoemission experiment

    Marczynski-Buehlow, Martin

    2012-01-30

    The free-electron laser (FEL) in Hamburg (FLASH) is a very interesting light source with which to perform photoelectron spectroscopy (PES) experiments. Its special characteristics include highly intense photon pulses (up to 100 J/pulse), a photon energy range of 30 eV to 1500 eV, transverse coherence as well as pulse durations of some ten femtoseconds. Especially in terms of time-resolved PES (TRPES), the deeper lying core levels can be reached with photon energies up to 1500 eV with acceptable intensity now and, therefore, element-specific, time-resolved core-level PES (XPS) is feasible at FLASH. During the work of this thesis various experimental setups were constructed in order to realize angle-resolved (ARPES), core-level (XPS) as well as time-resolved PES experiments at the plane grating monochromator beamline PG2 at FLASH. Existing as well as newly developed systems for online monitoring of FEL pulse intensities and generating spatial and temporal overlap of FEL and optical laser pulses for time-resolved experiments are successfully integrated into the experimental setup for PES. In order to understand space-charge effects (SCEs) in PES and, therefore, being able to handle those effects in future experiments using highly intense and pulsed photon sources, the origin of energetic broadenings and shifts in photoelectron spectra are studied by means of a molecular dynamic N-body simulation using a modified Treecode Algorithm for sufficiently fast and accurate calculations. It turned out that the most influencing parameter is the ''linear electron density'' - the ratio of the number of photoelectrons to the diameter of the illuminated spot on the sample. Furthermore, the simulations could reproduce the observations described in the literature fairly well. Some rules of thumb for XPS and ARPES measurements could be deduced from the simulations. Experimentally, SCEs are investigated by means of ARPES as well as XPS measurements as a function of

  1. Photoelectron spectroscopy at a free-electron laser. Investigation of space-charge effects in angle-resolved and core-level spectroscopy and realizaton of a time-resolved core-level photoemission experiment

    The free-electron laser (FEL) in Hamburg (FLASH) is a very interesting light source with which to perform photoelectron spectroscopy (PES) experiments. Its special characteristics include highly intense photon pulses (up to 100 J/pulse), a photon energy range of 30 eV to 1500 eV, transverse coherence as well as pulse durations of some ten femtoseconds. Especially in terms of time-resolved PES (TRPES), the deeper lying core levels can be reached with photon energies up to 1500 eV with acceptable intensity now and, therefore, element-specific, time-resolved core-level PES (XPS) is feasible at FLASH. During the work of this thesis various experimental setups were constructed in order to realize angle-resolved (ARPES), core-level (XPS) as well as time-resolved PES experiments at the plane grating monochromator beamline PG2 at FLASH. Existing as well as newly developed systems for online monitoring of FEL pulse intensities and generating spatial and temporal overlap of FEL and optical laser pulses for time-resolved experiments are successfully integrated into the experimental setup for PES. In order to understand space-charge effects (SCEs) in PES and, therefore, being able to handle those effects in future experiments using highly intense and pulsed photon sources, the origin of energetic broadenings and shifts in photoelectron spectra are studied by means of a molecular dynamic N-body simulation using a modified Treecode Algorithm for sufficiently fast and accurate calculations. It turned out that the most influencing parameter is the ''linear electron density'' - the ratio of the number of photoelectrons to the diameter of the illuminated spot on the sample. Furthermore, the simulations could reproduce the observations described in the literature fairly well. Some rules of thumb for XPS and ARPES measurements could be deduced from the simulations. Experimentally, SCEs are investigated by means of ARPES as well as XPS measurements as a function of FEL pulse

  2. High temperature thermal stability of the HfO2/Ge (100) interface as a function of surface preparation studied by synchrotron radiation core level photoemission

    High resolution soft x-ray photoemission spectroscopy (SXPS) have been used to study the high temperature thermal stability of ultra-thin atomic layer deposited (ALD) HfO2 layers (∼1 nm) on sulphur passivated and hydrofluoric acid (HF) treated germanium surfaces. The interfacial oxides which are detected for both surface preparations following HfO2 deposition can be effectively removed by annealing upto 700 °C without any evidence of chemical interaction at the HfO2/Ge interface. The estimated valence and conduction band offsets for the HfO2/Ge abrupt interface indicated that effective barriers exist to inhibit carrier injection.

  3. Core level photoemission spectroscopy and chemical bonding in Sr2Ta2O7

    Atuchin, V. V.; Grivel, Jean-Claude; Zhang, Z. M.

    2009-01-01

    -O bonds was characterized by the binding energy differences between the O 1s and cation core levels, Delta(O-Sr) = BE(O 1s) - BE(Sr 3d(5/2)) and Delta(O-Ta) = BE(O 1s) - BE(Ta 4f(7/2)). The chemical bonding effects were considered on the basis of our XPS results for Sr2Ta2O7 and earlier published...... structural and XPS data for other Sr- and Ta-containing oxide compounds. The new data point for Sr2Ta2O7 is consistent with the previously derived relationship for a set of Sr-bearing oxides. The binding energy difference Delta(O-Sr) was found to decrease with increasing bond distance L(Sr-O)....

  4. Line shape and composition of the In 3d5/2 core-level photoemission for the interface analysis of In-containing III–V semiconductors

    Highlights: • Photoelectron study of the controversial In 3d line shape of III–V semiconductors. • The spectral envelope is found to be fit well by a combination of symmetric peaks. • The energy band gap has no effect on the spectral features of In 3d peak. • In 3d emissions are described well with reconstruction-induced core-level shifts. • The results are important to photoelectron studies of the III–V device materials. - Abstract: The In 3d5/2 photoelectron spectroscopy peak has been widely used to determine the interface structures of In-containing III–V device materials (e.g., oxidation states). However, an unclear parameter affecting the determination of the energy shifts and number of the core-level components, and therefore, the interpreted interface structure and composition, is still the intrinsic In 3d5/2 peak line shape. It is undecided whether the line shape is naturally symmetric or asymmetric for pure In-containing III–V compounds. By using high-resolution photoelectron spectroscopy, we show that the In 3d5/2 asymmetry arising from the emission at high binding-energy tail is not an intrinsic property of InAs, InP, InSb and InGaAs. Furthermore, it is shown that asymmetry of In 3d5/2 peaks of pure III–V's originates from the natural surface reconstructions which cause the coexistence of slightly shifted In 3d5/2 components with the symmetric peak shape and dominant Lorentzian broadening

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

    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)

  6. Young's double-slit experiment using core-level photoemission from N2: revisiting Cohen-Fano's two-centre interference phenomenon

    The core-level photoelectron spectra of N2 molecules are observed at high energy resolution, resolving the 1σg and 1σu components as well as the vibrational components in the extended energy region from the threshold up to 1 keV. The σg/σu cross section ratios display modulation as a function of photoelectron momentum due to the two-centre interference, analogous to the classical Young's double-slit experiment, as predicted by Cohen and Fano a long time ago. The Cohen-Fano interference modulations display different phases depending on the vibrational excitations in the core-ionized state. Extensive ab initio calculations have been performed within the Hartree-Fock and random phase approximations in prolate spheroidal coordinates. The dependence of photoionization amplitudes on the vibrational states was taken into account using the Born-Oppenheimer approximation. The ab initio results are in reasonable agreement with the experimental data. The theoretical analysis allows the modulation to be connected with the onset of transitions to the states of increasing orbital angular momentum which occurs at increasing photon energies. Deviation from the Cohen-Fano formula is found for both the experimental and the ab initio results and is attributed to electron scattering by the neighbouring atom. A new formula for the interference modulation is derived within the framework of the multiple scattering technique. It differs from the classical Cohen-Fano formula by the addition of twice the scattering phase of the photoelectron by the neighbouring atom. We demonstrate that one can measure directly the scattering phase by fitting our formula to the experimental results

  7. Inverse photoemission and photoemission spectroscopic studies on sputter-annealed Ni–Mn–Sn and Ni–Mn–In surfaces

    Maniraj, M., E-mail: mr.maniraj@gmail.com [UGC-DAE Consortium for Scientific Research, Khandwa Road, Indore 452001, Madhya Pradesh (India); D' Souza, S.W. [UGC-DAE Consortium for Scientific Research, Khandwa Road, Indore 452001, Madhya Pradesh (India); Singh, Sandeep; Biswas, C. [Department of Condensed Matter Physics and Materials Science, SN Bose National Centre for Basic Sciences, Block JD, Sector III, Salt Lake, Kolkata 700098, West Bengal (India); Majumdar, S. [Indian Association for the Cultivation of Science, Raja S.C. Mullick Road, Jadavpur, Kolkata 700032, West Bengal (India); Barman, S.R. [UGC-DAE Consortium for Scientific Research, Khandwa Road, Indore 452001, Madhya Pradesh (India)

    2014-12-15

    Highlights: • Inverse photoemission spectra dominated by Mn 3d-like states. • Photoemission spectra show change in Ni 3d-Mn 3d hybridization with composition. • Rigid band shift is observed between Ni{sub 2}MnIn and Ni{sub 2}MnSn. • Mn 2p and 3s core-level spectra exhibit existence of exchange splitting. - Abstract: The electronic structure of nearly stoichiometric Ni–Mn–Sn and Ni–Mn–In surface is investigated by inverse photoemission and photoemission spectroscopy. Comparison of the experimental and calculated inverse photoemission spectra shows that the dominant feature is related to Mn 3d-like states. The overall shape and peak position of the theoretically obtained spectra show good agreement with the experimental ultraviolet photoemission valence band spectra. The changes in the composition dependent ultraviolet photoemission spectra reveal the change in degree of Ni 3d and Mn 3d band hybridization. Both inverse photoemission and ultraviolet photoemission study show a rigid band shift between Ni{sub 2}MnIn and Ni{sub 2}MnSn because of band filling, due to increase in the number of 5p electrons from In to Sn. Mn 2p and 3s core-level reveal unambiguous existence of exchange splitting in both the materials.

  8. Observation of the two-hole satellite in Cr and Fe metal by resonant photoemission at the 2p absorption energy

    Valence-band spectra of Cr and Fe metal were measured with photon energies around their respective 2p energies. An Auger signal is found to be superimposed on the valence-band photoemission signal for photon energies at and above the 2p absorption energy, but also for excitation energies down to ∼4 eV below the 2p absorption energy. This is the radiationless resonance Raman (resonant Raman Auger) regime and gives rise to a signal that is equivalent, in terms of the final state, to the 6 eV satellite in Ni with energies at 3.5 eV below EF in Cr and 3.2 eV below EF in Fe. (c) 2000 The American Physical Society

  9. Theory of spin-state selective nonlocal screening in Co 2p X-ray photoemission spectrum of LaCoO3

    The Co 2p X-ray photoemission spectrum (XPS) of LaCoO3 is investigated using a dp model simulating Co 3d and O 2p orbitals by means of a dynamical mean-field approach under the perovskite crystal structure. Across the spin-state transition from the low-spin to the high-spin state, the Co 2p3/2 main-line structure is substantially changed beyond expectation of a CoO6 cluster model calculation. In addition to the Coulombic multiplet effect, the origin of the spectral change is attributed to the nonlocal screening (NLS) from the correlated 3d band located on the top of the valence band to the core-excited Co site in the final state, where the NLS is practically active only for the high-spin state. The spin-state selectivity of the NLS is closely related to not only the spin state of the core-excited Co ion but also the spin and orbital character of the occupied Co 3d band in crystals. We emphasize that the Co 2p XPS can be an informative probe to investigate the spin state of Co ions in Co oxides, such as LaCoO3. (author)

  10. Photoemission Electronic States and Correlation Energies of Magnetite Based Compounds

    The photoemission spectra (XPS/UPS) for iron oxides, stoichiometric magnetite and for selected Ti and Zn doped magnetite single crystals are presented. From the Fe-3s split lines the exchange energies for FeO, Fe2O3 and magnetite based samples were estimated. It was shown that Ti and Zn ions are of 4+ and 2+ valency, respectively. The correlation energies were estimated from the Fe2p3/2 core-level spectra and from the L3- M4,5, M4,5 Auger lines. The type of insulating gap in these compounds was discussed. (author)

  11. Soft X-ray Absorption and Photoemission Studies of Ferromagnetic Mn-Implanted 3$C$-SiC

    Song, Gyong Sok; Kataoka, Takashi; Kobayashi, Masaki; Hwang, Jong Il; Takizawa, Masaru; Fujimori, Atsushi; Ohkochi, Takuo; Takeda, Yukiharu; Okane, Tetsuo; Saitoh, Yuji; Yamagami, Hiroshi; Takano, Fumiyoshi; Akinaga, Hiro

    2008-01-01

    We have performed x-ray photoemission spectroscopy (XPS), x-ray absorption spectroscopy (XAS), and resonant photoemission spectroscopy (RPES) measurements of Mn-implanted 3$C$-SiC (3$C$-SiC:Mn) and carbon-incorporated Mn$_{5}$Si$_{2}$ (Mn$_{5}$Si$_{2}$:C). The Mn 2$p$ core-level XPS and XAS spectra of 3$C$-SiC:Mn and Mn$_{5}$Si$_{2}$:C were similar to each other and showed "intermediate" behaviors between the localized and itinerant Mn 3$d$ states. The intensity at the Fermi level was found t...

  12. Determination of shallow core level spectra in selected compound semiconductors

    Core level spectra of the M shells of Ga, Ge, As, and Se and of the L shell of S have been obtained from X-ray photoemission measurements on GaAs, GeSe, and GeS. Broadening contributions from the achromatic source, the analyzer momentum window, and the extrinsic losses experienced by the photoemitted electrons in traversing the solid, as well as satellite lines due to Kα3sub(,)4 emission, are removed by deconvolution of the data with a measured electron backscatter spectrum convoluted with a source function. The results are compared with theory where available. (orig.)

  13. Angle-integrated photoemission studies of ruthocuprate Eu_2-xCe_xRuSr_2Cu_2O_10, Gd_2RuSr_2Cu_2O_10 and Eu_1.5Nb_1-xRu_xCu_2O_10 systems

    Frazer, B.; Hirai, Y.; Rast, Simon; Felner, I.; Asaf, U.; Onellion, M.

    2000-03-01

    We report on both resonant photoemission and fixed photon energy studies of the conduction band and core levels for several ruthocuprate systems. The pure Ru-containing compounds exhibit ferromagnetic order, with metallic behavior and superconductivity depending on the rare earth and oxygen content. We report on as-prepared, hydrogen loaded, and oxygen-annealed polycrystalline samples. The Nb-Ru series changes from purely superconducting to both ferromagnetic and superconducting (Ru). The resonant photoemission measurements of the conduction band across the Ru4p, Cu3p, and Eu4d core levels allow us to determine the location and contribution of Ru, Cu and rare earth related states in the conduction band. The O1s, Cu2p, Ru3p, Ce4d, and Gd4d and several Nb core levels allow us to determine the valence of Ru and Nb, and the metallicity of the Ru/Nb, rare earth, and CuO2 planes.

  14. Surface core-level shifts for Ge(100)-(2 x 1)

    Miller, T.; Rosenwinkel, E.; Chiang, T.C.

    1983-01-01

    Using surface-sensitive photoemission techniques, Ge 3d core-level binding energies for surface atoms of Ge(100)-(2 x 1) are found to be smaller than the bulk values by 0.41 eV. The surface atoms with shifted core-level binding energies correspond to one full (100) atomic layer. A surface core-exciton resonance is observed in the partial-yield measurements. The empty surface state involved in this excitonic transition, without binding-energy correction, is located at the valence-band maximum. 14 references, 2 figures, 1 table.

  15. Surface core-level shifts for Ge(100)-(2 x 1)

    Miller, T.; Rosenwinkel, E.; Chiang, T.C.

    1983-01-01

    Using surface-sensitive photoemission techniques, Ge 3d core-level binding energies for surface atoms of Ge(100)-(2 x 1) are found to be smaller than the bulk values by 0.41 eV. The surface atoms with shifted core-level binding energies correspond to one full (100) atomic layer. A surface core-exciton resonance is observed in the partial-yield measurements. The empty surface state involved in this excitonic transition, without binding-energy correction, is located at the valence-band maximum.

  16. An implementation of core level spectroscopies in a real space Projector Augmented Wave density functional theory code

    Ljungberg, M.P.; Mortensen, Jens Jørgen; Pettersson, L.G.M.

    2011-01-01

    We describe the implementation of K-shell core level spectroscopies (X-ray absorption (XAS), X-ray emission (XES), and X-ray photoemission (XPS)) in the real-space-grid-based Projector Augmented Wave (PAW) GPAW code. The implementation for XAS is based on the Haydock recursion method avoiding...

  17. Inverse photoemission and resonant photoemission characterization of semimagnetic semiconductors

    The new magnetotransport and magneto-optical properties of the semimagnetic Cd/sub 1-//sub x/Mn/sub x/Te semiconductor alloy series depend critically on the nature of the Mn-derived d states. We examine here the electronic structure of these alloys with a combination of inverse photoemission spectroscopy, core-level photoemission line-shape analysis, valence-band resonant photoemission, and local density pseudofunction theory. The spectroscopic data reflect the local Mn--Te coordination and are in remarkable agreement with our one-electron calculations. We see no evidence of Mn-derived d states in the gap, and observe an experimental dup-arrow--darrow-down exchange splitting of 8.4 +- 0.4 eV, i.e., almost twice as large as expected from earlier theoretical estimates. The ground-state configuration of Mn in the solid is primarily (dup-arrow)(sup-arrow)(pup-arrow), and the super-exchange interaction has an important role in determining the stability of such a configuration relative to (dup-arrow)5s2

  18. Angle-resolved photoemission extended fine structure: Multiple layers of emitters and multiple initial states

    Huff, W.R.A.; Kellar, S.A.; Moler, E.J. [Lawrence Berkeley Lab., CA (US)]|[California Univ., Berkeley, CA (US). Dept. of Chemistry; Chen, Y.; Wu, H.; Shirley, D.A. [Pennsylvania State Univ., University Park, PA (US). Dept. of Chemistry and Physics; Hussain, Z. [California Univ., Berkeley, CA (US). Dept. of Chemistry

    1995-08-01

    Recently, angle-resolved photoemission extended fine structure (ARPEFS) has been applied to experimental systems involving multiple layers of emitters and non-s core-level photoemission in an effort to broaden the utility of the technique. Most of the previous systems have been comprised of atomic or molecular overlayers adsorbed onto a single-crystal, metal surface and the photoemission data were taken from an s atomic core-level in the overlayer. For such a system, the acquired ARPEFS data is dominated by the p{sub o} final state wave backscattering from the substrate atoms and is well understood. In this study, we investigate ARPEFS as a surface-region structure determination technique when applied to experimental systems comprised of multiple layers of photoemitters and arbitrary initial state core-level photoemission. Understanding the data acquired from multiple layers of photoemitters is useful for studying multilayer interfaces, ''buried'' surfaces, and clean crystals in ultra- high vacuum. The ability to apply ARPEFS to arbitrary initial state core-level photoemission obviously opens up many systems to analysis. Efforts have been ongoing to understand such data in depth. We present clean Cu(111) 3s, 3p, and 3d core-level, normal photoemission data taken on a high resolution soft x-ray beamline 9.3.2 at the Advanced Light Source in Berkeley, California and clean Ni(111) 3p normal photoemission data taken at the National Synchrotron Light Source in Upton, New York, USA.

  19. Angle-resolved photoemission extended fine structure: Multiple layers of emitters and multiple initial states

    Recently, angle-resolved photoemission extended fine structure (ARPEFS) has been applied to experimental systems involving multiple layers of emitters and non-s core-level photoemission in an effort to broaden the utility of the technique. Most of the previous systems have been comprised of atomic or molecular overlayers adsorbed onto a single-crystal, metal surface and the photoemission data were taken from an s atomic core-level in the overlayer. For such a system, the acquired ARPEFS data is dominated by the po final state wave backscattering from the substrate atoms and is well understood. In this study, we investigate ARPEFS as a surface-region structure determination technique when applied to experimental systems comprised of multiple layers of photoemitters and arbitrary initial state core-level photoemission. Understanding the data acquired from multiple layers of photoemitters is useful for studying multilayer interfaces, ''buried'' surfaces, and clean crystals in ultra- high vacuum. The ability to apply ARPEFS to arbitrary initial state core-level photoemission obviously opens up many systems to analysis. Efforts have been ongoing to understand such data in depth. We present clean Cu(111) 3s, 3p, and 3d core-level, normal photoemission data taken on a high resolution soft x-ray beamline 9.3.2 at the Advanced Light Source in Berkeley, California and clean Ni(111) 3p normal photoemission data taken at the National Synchrotron Light Source in Upton, New York, USA

  20. Photoemission spectroscopy of composition and doping of high-temperature superconductors

    The authors present a systematic study of compositional and doping effects in Bi2Sr2CaCu2Oy high-Tc superconductors performed with photoemission spectroscopy. The study has been extended to Y-doping and I-intercalation of Bi-2212 high quality single crystals. The main results is that each type of dopant affects the crystal composition in its own way. Yttrium affects the Ca and Sr planes, producing a charge transfer into the CuO planes. For I-doping, they find that the main effect is a change in the interplanar distance, but X-ray Photoemission Spectroscopy (XPS) allows to see that the decrease of the critical temperature is not caused only by a structure parameter, but by a over-doping of copper planes (hole doping). They performed also a comparative study by Angle Resolved Ultraviolet Photoemission Spectroscopy [ARUPS] between this sample and an oxygen annealed specimen. XPS Cu2p core level data establish that the hole concentration in the CuO2 planes is essentially the same for these two kinds of samples. ARUPS measurements show that electronic structure of the normal states near the Fermi level has been strongly affected by iodine intercalation

  1. Core level spectroscopy in YBa2Cu3O7-δ

    The characterization of the surface electronic structure as a function of the oxygen content by means of photoemission is presented for sintered powders, films and single crystals of YBa2Cu3O7-δ. Core levels lineshapes of O, Ba and Cu are strongly influenced by the oxygen stoichiometry that is varied by heating cycles in vacuo and in O2 atmosphere. The evolution of the core levels following oxygen in- and out-diffusion was followed by X-ray diffraction measurements. The results included in this paper indicate that the observed spectral changes are related to the oxygen deficiency in the chains more than to extrinsic contamination of the surface and point to the importance of charge redistribution and oxygen ordering in the basal plane

  2. X-ray photoelectron spectrometry and binding energies of Be 1s and O 1s core levels in clinobarylite, BaBe2Si2O7, from Khibiny massif, Kola peninsula

    The electronic structure of BaBe2Si2O7, clinobarylite, has been investigated by means of X-ray photoelectron spectroscopy (XPS). The valence band of the crystal is mainly formed by Ba 5p, Ba 3s and O 2s states. At higher binding energies the emission lines related to the Si 2p, Be 1s, Si 2s, O 1s and numerous Ba-related states were analyzed in the photoemission spectrum. The Si KLL Auger line has been measured under excitation by the bremsstrahlung X-rays from the Al anode. Chemical bonding effects for Be 1s core level have been considered by comparison with electronic parameters measured for other beryllium containing oxides

  3. Coherent and incoherent processes in resonant photoemission

    Magnuson, M.; Karis, O.; Weinelt, M. [Uppsala Univ. (Sweden)] [and others

    1997-04-01

    In this contribution the authors present the distinction between coherent and incoherent processes in resonant photoemission. As a first step they determine whether an autoionization process is photoemission-like or Auger-like. The discussion is based on measurements for a weakly bonded adsorption system, Ar/Pt(111). This type of system is well adapted to investigate these effects since it yields distinctly shifted spectral features depending on the nature of the process. After this, the question of resonance photoemission in metallic systems is addressed. This is done in connection with measurements at the 2p edges for Ni metal. Ni has been one of the prototype systems for resonant photoemission. The resonances have been discussed in connection with the strong correlation and d-band localization effects in this system. Based on the results some general comments about the appearance of resonant effects in metallic systems are made.

  4. Ba 4d core-level spectroscopy in the YBa2Cu3O6.9 high-Tc superconductor: Existence of a surface-shifted component

    Two sets of spin-orbit split Ba 4d core-level photoemission peaks were observed in a crystal of YBa2Cu3O6.9. From constant final-state measurements taken as a function of kinetic energy, the low-binding-energy doublet is identified as a surface component. Possible origins of the surface shift are discussed

  5. Angle-resolved photoemission extended fine structure

    Measurements of the Angle-Resolved Photoemission Extended Fine Structure (ARPEFS) from the S(1s) core level of a c(2 x 2)S/Ni(001) are analyzed to determine the spacing between the S overlayer and the first and second Ni layers. ARPEFS is a type of photoelectron diffraction measurement in which the photoelectron kinetic energy is swept typically from 100 to 600 eV. By using this wide range of intermediate energies we add high precision and theoretical simplification to the advantages of the photoelectron diffraction technique for determining surface structures. We report developments in the theory of photoelectron scattering in the intermediate energy range, measurement of the experimental photoemission spectra, their reduction to ARPEFS, and the surface structure determination from the ARPEFS by combined Fourier and multiple-scattering analyses. 202 refs., 67 figs., 2 tabs

  6. In-situ X-ray Photoemission Spectroscopy Study of Atomic Layer Deposition of TiO2 on Silicon Substrate

    Youb Lee, Seung; Jeon, Cheolho; Kim, Seok Hwan; Kim, Yooseok; Jung, Woosung; An, Ki-Seok; Park, Chong-Yun

    2012-03-01

    In-situ X-ray photoemission spectroscopy (XPS) has been used to investigate the initial stages of TiO2 growth on a Si(001) substrate by atomic layer deposition (ALD). The core level spectra of Si 2p, C 1s, O 1s, and Ti 2p were measured at every half reaction in the titanium tetra-isopropoxide (TTIP)-H2O ALD process. The ligand exchange reactions were verified using the periodic oscillation of the C 1s concentration, as well as changes in the hydroxyl concentration. XPS analysis revealed that Ti2O3 and Si oxide were formed at the initial stages of TiO2 growth. A stoichiometric TiO2 layer was dominantly formed after two cycles and was chemically saturated after four cycles.

  7. Quanty for core level spectroscopy - excitons, resonances and band excitations in time and frequency domain

    Haverkort, Maurits W.

    2016-05-01

    Depending on the material and edge under consideration, core level spectra manifest themselves as local excitons with multiplets, edge singularities, resonances, or the local projected density of states. Both extremes, i.e., local excitons and non-interacting delocalized excitations are theoretically well under control. Describing the intermediate regime, where local many body interactions and band-formation are equally important is a challenge. Here we discuss how Quanty, a versatile quantum many body script language, can be used to calculate a variety of different core level spectroscopy types on solids and molecules, both in the frequency as well as the time domain. The flexible nature of Quanty allows one to choose different approximations for different edges and materials. For example, using a newly developed method merging ideas from density renormalization group and quantum chemistry [1-3], Quanty can calculate excitons, resonances and band-excitations in x-ray absorption, photoemission, x-ray emission, fluorescence yield, non-resonant inelastic x-ray scattering, resonant inelastic x-ray scattering and many more spectroscopy types. Quanty can be obtained from: http://www.quanty.org.

  8. Gas-phase photoemission with soft x-rays: cross sections and angular distributions

    Shirley, D.A.; Kobrin, P.H.; Truesdale, C.M.; Lindle, D.W.; Ferrett, T.A.; Heimann, P.A.; Becker, U.; Kerkhoff, H.G.; Southworth, S.H.

    1983-09-01

    A summary is presented of typical gas-phase photoemission studies based on synchrotron radiation in the 50-5000 eV range, using beam lines at the Stanford Synchrotron Radiation Laboratory. Three topics are addressed: atomic inner-shell photoelectron cross sections and asymmetries, correlation peaks in rare gases, and core-level shape resonances in molecules.

  9. Photoemission and ferromagnetism

    Photoemission is a well established technique for the study of the electronic structure of atoms and solids. In particular, angle-resolved photoemission has been used extensively to map the band structure of clean and adsorbate covered surfaces, both metal and semiconductor. Extending the technique by measuring the spin of the photoemitted electrons allows the possibility of examining the exchange split band structures characterizing ferromagnetic systems. Here the technique becomes particularly useful in the study of the magnetic properties of surfaces, thin films and associated interfaces

  10. Fourier transform photoemission spectroscopy

    Meinders, M.B J; Drabe, K.E.; Jonkman, H.T.; Sawatzky, G.A

    1996-01-01

    It is shown that photoemission spectra can be obtained by exciting the electrons with two phase-correlated wave trains. The phase-correlated wave trains are obtained by sending broad-band ultra-violet light, coming from a deuterium lamp, through a Michelson interferometer. It is possible to stabiliz

  11. Core level excitations—A fingerprint of structural and electronic properties of epitaxial silicene

    Friedlein, R., E-mail: friedl@jaist.ac.jp; Fleurence, A.; Aoyagi, K.; Yamada-Takamura, Y. [School of Materials Science, Japan Advanced Institute of Science and Technology (JAIST), 1-1, Asahidai, Nomi, Ishikawa 923-1292 (Japan); Jong, M. P. de; Van Bui, H.; Wiggers, F. B. [MESA Institute for Nanotechnology, University of Twente, 7500 AE Enschede (Netherlands); Yoshimoto, S.; Koitaya, T.; Shimizu, S.; Noritake, H.; Mukai, K.; Yoshinobu, J. [The Institute for Solid State Physics, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581 (Japan)

    2014-05-14

    From the analysis of high-resolution Si 2p photoelectron and near-edge x-ray absorption fine structure (NEXAFS) spectra, we show that core level excitations of epitaxial silicene on ZrB{sub 2}(0001) thin films are characteristically different from those of sp{sup 3}-hybridized silicon. In particular, it is revealed that the lower Si 2p binding energies and the low onset in the NEXAFS spectra as well as the occurrence of satellite features in the core level spectra are attributed to the screening by low-energy valence electrons and interband transitions between π bands, respectively. The analysis of observed Si 2p intensities related to chemically distinct Si atoms indicates the presence of at least one previously unidentified component. The presence of this component suggests that the observation of stress-related stripe domains in scanning tunnelling microscopy images is intrinsically linked to the relaxation of Si atoms away from energetically unfavourable positions.

  12. Photoemission, Correlation and Superconductivity:

    Abrecht, M.; Ariosa, D.; Cloëtta, D.; Pavuna, D.; Perfetti, L.; Grioni, M.; Margaritondo, G.

    We review some of the problems still affecting photoemission as a probe of high-temperature superconductivity, as well as important recent results concerning their solution. We show, in particular, some of the first important results on thin epitaxial films grown by laser ablation, which break the monopoly of cleaved BCSCO in this type of experiments. Such results, obtained on thin LSCO, may have general implications on the theory of high-temperature superconductivity.

  13. Angle-resolved photoemission spectroscopy observation of anomalous electronic states in EuFe2As2−xPx

    We used angle-resolved photoemission spectroscopy to investigate the electronic structure and the Fermi surface of EuFe2As2, EuFe2As1.4P0.6 and EuFe2P2. We observed doubled core level peaks associated with the pnictide atoms. Using K atoms evaporated at the surface to affect the surface quality, we show that one component of these doubled peaks is related to a surface state. Nevertheless, strong electronic dispersion along the c-axis, especially pronounced in EuFe2P2, is observed for at least one band, thus indicating that the Fe states, albeit probably affected at the surface, do not form pure two-dimensional surface states. We determine the evolution of the Fermi surface as a function of the P content and reveal that the hole Fermi surface pockets enlarge with increasing P content. We also show that the spectral weight near the Fermi level of EuFe2P2 is reduced as compared to that of EuFe2As2 and EuFe2As1.4P0.6. Finally, we identify the electronic states associated with the Eu2+ f states and show an anomalous jump in EuFe2P2. (paper)

  14. Core-level XPS spectra of fullerene, highly oriented pyrolitic graphite, and glassy carbon

    Leiro, J A; Laiho, T; Batirev, I G

    2003-01-01

    The C 1s spectra of fullerene C sub 6 sub 0 , highly oriented pyrolitic graphite (HOPG) and amorphous carbon (a-C) have been measured using X-ray photoemission. The assumed background due to the inelastic scattering of electrons of these spectra has been subtracted by the Tougaard's method. The relative intensities and the energy positions for the core-level satellites have been determined. For C sub 6 sub 0 , a comparison of the low energy pi type shake-up satellites gives good agreement between theory and experiment. Also, the energies of these features for fullerene and glassy carbon are very similar, whereas the corresponding energies for HOPG are somewhat larger, presumably, because of the higher density of the latter. Moreover, the atomic force microscopy (AFM) study indicates that the C sub 6 sub 0 samples consist of a thick layer of large clusters on the Si(111) surface, which is in line with the molecular character of the XPS spectrum. Furthermore, the broad high energy satellite does not consist of ...

  15. Surface core-level shifts for simple metals

    Aldén, Magnus; Skriver, Hans Lomholt; Johansson, Börje

    1994-01-01

    We have performed an ab initio study of the surface core-level binding energy shift (SCLS) for 11 of the simple metals by means of a Green’s-function technique within the tight-binding linear-muffin-tin-orbitals method. Initial- and final-state effects are included within the concept of complete...... screening, whereby a SCLS becomes equivalent to the surface segregation energy of a core-ionized atom, a quantity we obtain by separate bulk and surface impurity calculations. The results are in good agreement with experiment in most of those cases where the data originates from single-crystal measurements....... We discuss the surface shifts of the electrostatic potentials and the band centers in order to trace the microscopic origin of the SCLS in the simple metals and find that the anomalous subsurface core-level shifts in beryllium are caused by charge dipoles, which persist several layers into the bulk...

  16. Titanium core-level spectra in titanium tetrahalide molecules

    Molecular-orbital calculations of TiF4, TiCl4, TiBr4, and TiI4 molecules have been made with use of self-consistent local-density theory with the discrete variational (DV-Xα) method. Core-level excitation energies corresponding to x-ray photoelectron spectroscopy (XPS) measurements are calculated. Spectral peaks associated with metastable final states of the core ionized atom that include relaxation and charge transfer processes are calculated. XPS spectra of Ti core levels in these compounds show that binding energies of both main lines and satellites clearly depend on the ligated anion. The observed systematic behavior of ionization potentials and satellite separation energies for the halide series is calculated with reasonable accuracy. With use of the single-determinant formalism, contributions to the intensity of the main line and satellites are examined

  17. Measurement of the background in Auger-photoemission coincidence spectra (APECS) associated with inelastic or multi-electron valence band photoemission processes

    Satyal, S.; Joglekar, P. V.; Shastry, K.; Kalaskar, S.; Dong, Q.; Hulbert, S. L.; Bartynksi, R. A.; Weiss, A. H.

    2014-01-01

    Auger Photoelectron Coincidence Spectroscopy (APECS), in which the Auger spectra is measured in coincidence with the core level photoelectron, is capable of pulling difficult to observe low energy Auger peaks out of a large background due mostly to inelastically scattered valence band (VB) photoelectrons. However the APECS method alone cannot eliminate the background due to valence band photoemission processes in which the initial photon energy is shared by two or more electrons and one of th...

  18. Photoemission study of the IBr graphite intercalation compound using the synchrotron radiation light source

    Negishi, Saiko; Negishi, H.; Nakatake, Masashi; Yamazaki, K; Sato, Hitoshi; Shimada, Kenya; Namatame, Hirofumi; Taniguchi, Masaki; Kobayashi, K.; Sugihara, K; Oshima, H

    2006-01-01

    We measured the photoemission spectra of the IBr graphite intercalation compounds (IBr-GIC) with stage-2 and stage-4 structures at 16 K with incident photon energies hν=40-200 eV. The peak positions of the I 4d and Br 3d core-levels are unchanged for the stage-2 and stage-4 IBr-GICs. Partial density-of-states of the I 5p and Br 4p states in the valence bands have been evaluated by resonant photoemission spectroscopy. These spectra indicate a significant hybridization between the host and the ...

  19. High-resolution core-level photoemission measurements on the pentacene single crystal surface assisted by photoconduction.

    Nakayama, Yasuo; Uragami, Yuki; Yamamoto, Masayuki; Yonezawa, Keiichirou; Mase, Kazuhiko; Kera, Satoshi; Ishii, Hisao; Ueno, Nobuo

    2016-03-01

    Upon charge carrier transport behaviors of high-mobility organic field effect transistors of pentacene single crystal, effects of ambient gases and resultant probable 'impurities' at the crystal surface have been controversial. Definite knowledge on the surface stoichiometry and chemical composites is indispensable to solve this question. In the present study, high-resolution x-ray photoelectron spectroscopy (XPS) measurements on the pentacene single crystal samples successfully demonstrated a presence of a few atomic-percent of (photo-)oxidized species at the first molecular layer of the crystal surface through accurate analyses of the excitation energy (i.e. probing depth) dependence of the C1s peak profiles. Particular methodologies to conduct XPS on organic single crystal samples, without any charging nor damage of the sample in spite of its electric insulating character and fragility against x-ray irradiation, is also described in detail. PMID:26871646

  20. Origin of metallic surface core-level shifts

    Aldén, Magnus; Skriver, Hans Lomholt; Abrikosov, I. A.;

    1995-01-01

    The unique property of the open 4f energy shell in the lanthanide metals is used to show that the initial-state energy shift gives an insufficient description of surface core-level shifts. Instead a treatment, which fully includes the final-state screening, account for the experimentally observed...... surface shifts of the occupied as well as the unoccupied 4f states. The surface energy shift of the initial state corresponds approximately to the average of the shifts for the occupied and unoccupied 4f levels....

  1. Plasmon Enhanced Photoemission

    Polyakov, Aleksandr [Univ. of California, Berkeley, CA (United States)

    2012-05-08

    Next generation ultrabright light sources will operate at megahertz repetition rates with temporal resolution in the attosecond regime. For an X-Ray Free Electron Laser (FEL) to operate at such repetition rate requires a high quantum efficiency (QE) cathode to produce electron bunches of 300 pC per 1.5 μJ incident laser pulse. Semiconductor photocathodes have sufficient QE in the ultraviolet (UV) and the visible spectrum, however, they produce picosecond electron pulses due to the electron-phonon scattering. On the other hand, metals have two orders of magnitude less QE, but can produce femtosecond pulses, that are required to form the optimum electron distribution for high efficiency FEL operation. In this work, a novel metallic photocathode design is presented, where a set of nano-cavities is introduced on the metal surface to increase its QE to meet the FEL requirements, while maintaining the fast time response. Photoemission can be broken up into three steps: (1) photon absorption, (2) electron transport to the surface, and (3) crossing the metal-vacuum barrier. The first two steps can be improved by making the metal completely absorbing and by localizing the fields closer to the metal surface, thereby reducing the electron travel distance. Both of these effects can be achieved by coupling the incident light to an electron density wave on the metal surface, represented by a quasi-particle, the Surface Plasmon Polariton (SPP). The photoemission then becomes a process where the photon energy is transferred to an SPP and then to an electron. The dispersion relation for the SPP defines the region of energies where such process can occur. For example, for gold, the maximum SPP energy is 2.4 eV, however, the work function is 5.6 eV, therefore, only a fourth order photoemission process is possible. In such process, four photons excite four plasmons that together excite only one electron. The yield of such non-linear process depends strongly on the light intensity. In

  2. A medium-energy photoemission and ab-initio investigation of cubic yttria-stabilised zirconia

    Experimental and theoretical investigations into the electronic properties and structure of cubic yttria-stabilized zirconia are presented. Medium-energy x-ray photoemission spectroscopy measurements have been carried out for material with a concentration of 8-9 mol. % yttria. Resonant photoemission spectra are obtained for a range of photon energies that traverse the L2 absorption edge for both zirconium and yttrium. Through correlation with results from density-functional theory (DFT) calculations, based on structural models proposed in the literature, we assign photoemission peaks appearing in the spectra to core lines and Auger transitions. An analysis of the core level features enables the identification of shifts in the core level energies due to different local chemical environments of the constituent atoms. In general, each core line feature can be decomposed into three contributions, with associated energy shifts. Their identification with results of DFT calculations carried out for proposed atomic structures, lends support to these structural models. The experimental results indicate a multi-atom resonant photoemission effect between nearest-neighbour oxygen and yttrium atoms. Near-edge x-ray absorption fine structure spectra for zirconium and yttrium are also presented, which correlate well with calculated Zr- and Y-4d electron partial density-of-states and with Auger electron peak area versus photon energy curve

  3. A medium-energy photoemission and ab-initio investigation of cubic yttria-stabilised zirconia

    Cousland, G. P. [School of Physics, The University of Sydney, New South Wales 2006 (Australia); Australian Nuclear Science and Technology Organisation, Lucas Heights, New South Wales 2234 (Australia); Cui, X. Y. [School of Physics, The University of Sydney, New South Wales 2006 (Australia); Australian Centre for Microscopy and Microanalysis, The University of Sydney, New South Wales 2006 (Australia); Smith, A. E. [School of Physics, Monash University, Clayton, Victoria 3800 (Australia); Stampfl, C. M. [School of Physics, The University of Sydney, New South Wales 2006 (Australia); School of Materials Science and Engineering, Yonsei University, Seoul 120-749 (Korea, Republic of); Wong, L.; Tayebjee, M.; Yu, D.; Triani, G.; Evans, P. J. [Australian Nuclear Science and Technology Organisation, Lucas Heights, New South Wales 2234 (Australia); Ruppender, H.-J. [OmniVac GmbH, Espensteigstrasse 16, 67661 Kaiserslautern (Germany); Jang, L.-Y. [National Synchrotron Radiation Research Center, Hsinchu Science Park, Hsinchu 30076, Taiwan (China); Stampfl, A. P. J. [Australian Nuclear Science and Technology Organisation, Lucas Heights, New South Wales 2234 (Australia); School of Chemistry, The University of Sydney, New South Wales 2006 (Australia)

    2014-04-14

    Experimental and theoretical investigations into the electronic properties and structure of cubic yttria-stabilized zirconia are presented. Medium-energy x-ray photoemission spectroscopy measurements have been carried out for material with a concentration of 8-9 mol. % yttria. Resonant photoemission spectra are obtained for a range of photon energies that traverse the L2 absorption edge for both zirconium and yttrium. Through correlation with results from density-functional theory (DFT) calculations, based on structural models proposed in the literature, we assign photoemission peaks appearing in the spectra to core lines and Auger transitions. An analysis of the core level features enables the identification of shifts in the core level energies due to different local chemical environments of the constituent atoms. In general, each core line feature can be decomposed into three contributions, with associated energy shifts. Their identification with results of DFT calculations carried out for proposed atomic structures, lends support to these structural models. The experimental results indicate a multi-atom resonant photoemission effect between nearest-neighbour oxygen and yttrium atoms. Near-edge x-ray absorption fine structure spectra for zirconium and yttrium are also presented, which correlate well with calculated Zr- and Y-4d electron partial density-of-states and with Auger electron peak area versus photon energy curve.

  4. Photoemission study of Ca-intercalated graphite superconductor CaC6

    In this work, we have performed resonant photoemission studies of Ca-intercalated graphite superconductor CaC6. Using photon energy of the Ca 2p-3d threshold, the photoemission intensity of the peak at Fermi energy (EF) is resonantly enhanced. This result provides spectroscopic evidence for the existence of Ca 3d states at EF, and strongly supports that Ca 3d state plays a crucial role for the superconductivity of this material with relatively high Tc.

  5. Development of a high-resolution soft x-ray (30--1500 eV) beamline at the Advanced Light Source and its use for the study of angle-resolved photoemission extended fine structure

    ALS Bending magnet beamline 9.3.2 is for high resolution spectroscopy, with circularly polarized light. Fixed included-angle SGM uses three gratings for 30--1500 eV photons; circular polarization is produced by an aperture for selecting the beam above or below the horizontal plane. Photocurrent from upper and lower jaws of entrance slit sets a piezoelectric drive feedback loop on the vertically deflecting mirror for stable beam. End station has a movable platform. With photomeission data from Stanford, structure of c(2x2)P/Fe(100) was determined using angle-resolved photoemission extended fine structure (ARPEFS). Multiple-scattering spherical-wave (MSSW) calculations indicate that P atoms adsorb in fourfold hollow sites 1.02A above the first Fe layer. Self-consistent-field Xα scattered wave calculation confirm that the Fe1-Fe2 space is contracted for S/Fe but not for P/Fe; comparison is made to atomic N and O on Fe(100). Final-state effects on ARPEFS curves used literature data from the S 1s and 2p core levels of c(2x2)S/Ni(001); a generalized Ramsauer-Townsend splitting is present in the 1s but not 2p data. An approximate method for analyzing ARPEFS data from a non-s initial state using only the higher-ell partial wave was tested successfully. ARPEFS data from clean surfaces were collected normal to Ni(111) (3p core levels) and 5 degree off-normal from Cu(111)(3s, 3p). Fourier transforms (FT) resemble adsorbate systems, showing backscattering signals from atoms up to 4 layers below emitters. 3p FTs show scattering from 6 nearest neighbors in the same crystal layer as the emitters. MSSW calulation indicate that Cu 3p photoemission is mostly d-wave. FTs also indicate double-scattering and single-scattering from laterally distant atoms; calculations indicate that the signal is dominated by photoemission from the first 2 crystal layers

  6. P2P financovanie

    Dobiasová, Dana

    2015-01-01

    The aim of this bachelors thesis is to determine the effect of P2P lending on the economic indicators and the status of small and medium enterprises in the United States, specifically for the period form 2011 to 2015. To better understand the practical part, two first chapters will be focused on defining the concept of P2P lending and analysing the current situation in the United States. Besides that, it is also an emphasis on regulatory requirements which are newly starting to appear. This k...

  7. Saperi P2P

    Salvatore Iaconesi

    2009-10-01

    Full Text Available Il paper presenta l'architettura filosofica e logica di un progetto ongoing per la creazione di un'infrastruttura peer to peer per la diffusione dei saperi. Tale infrastruttura p2p vuole essere la base per costruire un framework aperto e orizzontale, che ospiti pratiche innovative di creazione, condivisione e disseminazione di informazioni e conoscenza.

  8. Lattice charge models and core level shifts in disordered alloys

    Underwood, T. L.; Cole, R. J.

    2013-10-01

    Differences in core level binding energies between atoms belonging to the same chemical species can be related to differences in their intra- and extra-atomic charge distributions, and differences in how their core holes are screened. With this in mind, we consider the charge-excess functional model (CEFM) for net atomic charges in alloys (Bruno et al 2003 Phys. Rev. Lett. 91 166401). We begin by deriving the CEFM energy function in order to elucidate the approximations which underpin this model. We thereafter consider the particular case of the CEFM in which the strengths of the ‘local interactions’ within all atoms are the same. We show that for binary alloys the ground state charges of this model can be expressed in terms of charge transfer between all pairs of unlike atoms analogously to the linear charge model (Magri et al 1990 Phys. Rev. B 42 11388). Hence, the model considered is a generalization of the linear charge model for alloys containing more than two chemical species. We then determine the model’s unknown ‘geometric factors’ over a wide range of parameter space. These quantities are linked to the nature of charge screening in the model, and we illustrate that the screening becomes increasingly universal as the strength of the local interactions is increased. We then use the model to derive analytical expressions for various physical quantities, including the Madelung energy and the disorder broadening in the core level binding energies. These expressions are applied to ternary random alloys, for which it is shown that the Madelung energy and magnitude of disorder broadening are maximized at the composition at which the two species with the largest ‘electronegativity difference’ are equal, while the remaining species have a vanishing concentration. This result is somewhat counterintuitive with regards to the disorder broadening since it does not correspond to the composition with the highest entropy. Finally, the model is applied to Cu

  9. Probing core-electron orbitals by scanning transmission electron microscopy and measuring the delocalization of core-level excitations

    Jeong, Jong Seok; Odlyzko, Michael L.; Xu, Peng; Jalan, Bharat; Mkhoyan, K. Andre

    2016-04-01

    By recording low-noise energy-dispersive x-ray spectroscopy maps from crystalline specimens using aberration-corrected scanning transmission electron microscopy, it is possible to probe core-level electron orbitals in real space. Both the 1 s and 2 p orbitals of Sr and Ti atoms in SrTi O3 are probed, and their projected excitation potentials are determined. This paper also demonstrates experimental measurement of the electronic excitation impact parameter and the delocalization of an excitation due to Coulombic beam-orbital interaction.

  10. Observation of core-level binding energy shifts between (100) surface and bulk atoms of epitaxial CuInSe2

    Core-level and valence band photoemission from semiconductors has been shown to exhibit binding energy differences between surface atoms and bulk atoms, thus allowing one to unambiguously distinguish between the two atomic positions. Quite clearly, surface atoms experience a potential different from the bulk due to the lower coordination number - a characteristic feature of any surface is the incomplete atomic coordination. Theoretical accounts of this phenomena are well documented in the literature for III-V and II-VI semiconductors. However, surface state energies corresponding to the equilibrium geometry of (100) and (111) surfaces of Cu-based ternary chalcopyrite semiconductors have not been calculated or experimental determined. These compounds are generating great interest for optoelectronic and photovoltaic applications, and are an isoelectronic analog of the II-VI binary compound semiconductors. Surface core-level binding energy shifts depend on the surface cohesive energies, and surface cohesive energies are related to surface structure. For ternary compound semiconductor surfaces, such as CuInSe2, one has the possibility of variations in surface stoichiometry. Applying standard thermodynamical calculations which consider the number of individual surface atoms and their respective chemical potentials should allow one to qualitatively determine the magnitude of surface core-level shifts and, consequently, surface state energies

  11. Observation of core-level binding energy shifts between (100) surface and bulk atoms of epitaxial CuInSe{sub 2}

    Nelson, A.J. [Colorado School of Mines, Golden, CO (United States); Berry, G.; Rockett, A. [Univ. of Illinois, Urbana-Champaign, IL (United States)] [and others

    1997-04-01

    Core-level and valence band photoemission from semiconductors has been shown to exhibit binding energy differences between surface atoms and bulk atoms, thus allowing one to unambiguously distinguish between the two atomic positions. Quite clearly, surface atoms experience a potential different from the bulk due to the lower coordination number - a characteristic feature of any surface is the incomplete atomic coordination. Theoretical accounts of this phenomena are well documented in the literature for III-V and II-VI semiconductors. However, surface state energies corresponding to the equilibrium geometry of (100) and (111) surfaces of Cu-based ternary chalcopyrite semiconductors have not been calculated or experimental determined. These compounds are generating great interest for optoelectronic and photovoltaic applications, and are an isoelectronic analog of the II-VI binary compound semiconductors. Surface core-level binding energy shifts depend on the surface cohesive energies, and surface cohesive energies are related to surface structure. For ternary compound semiconductor surfaces, such as CuInSe{sub 2}, one has the possibility of variations in surface stoichiometry. Applying standard thermodynamical calculations which consider the number of individual surface atoms and their respective chemical potentials should allow one to qualitatively determine the magnitude of surface core-level shifts and, consequently, surface state energies.

  12. Pulsed laser deposition for in-situ photoemission studies on YBa2Cu3O7-δ and related oxide films

    Schmauder, T.; Frazer, B.; Gatt, R.; Xi, Xiaoxing; Onellion, Marshall; Ariosa, Daniel; Grioni, M.; Margaritondo, Giorgio; Pavuna, Davor

    1998-12-01

    We describe a new pled laser deposition (PLD) system that is linked to an angle-resolved photoemission (ARPES) chamber at the Synchrotron Radiation Center (SRC) in Wisconsin, USA. We also discuss our first results on epitaxially grown YBa2Cu3O7-(delta ) (YBCO) films. The core level photoemission data indicate that a Ba-oxide layer is the dominant surface layer. We were not able to reproducibly detect a sharp fermi edge in the photoemission spectra and thus conclude that the surface layer is non-metallic, probably due to oxygen loss at the surface. The absence of screening of the Y and Ba core levels is a further argument for this conclusion. Further experiments with ozone treated film surfaces are currently under way.

  13. X-ray photoemission spectroscopy study of zirconium hydride

    X-ray photoemission spectroscopy (XPS) measurements are reported for ZrH/sub 1.65/ and Zr metal. The valence-band measurements are compared with available band-theory density-of-states calculations for the metal and hydride. The hydride spectrum differs significantly from the metal spectrum. Most important, a strong peak associated with hydrogen s electrons appears approximately 7 eV below the Fermi level. XPS measurements of Zr 4p core levels show a binding-energy shift of 1 eV between Zr metal and ZrH/sub 1.65/. It is argued that this shift results from charge readjustment in the vicinity of the Zr site. With the addition of hydrogen, net charge must be transferred from the Zr site to the hydrogen site. A charge-density analysis based on simplified cluster calculations is presented

  14. X-ray photoemission study of MgB2

    A c-axis oriented thin film and a high-density sintered pellet of MgB2 have been studied by x-ray photoemission spectroscopy, and compared to measurements from MgO and MgF2 single crystals. The as-grown surface has a layer which is Mg-rich and oxidized, which is effectively removed by a nonaqueous etchant. The subsurface region of the pellet is Mg deficient. This nonideal near-surface region may explain varied scanning tunneling spectroscopy results. The MgB2 core level and Auger signals are similar to measurements from metallic Mg and transition-metal diborides, and the measured valence band is consistent with the calculated density of states

  15. ANTARES, a scanning photoemission microscopy beamline at SOLEIL

    Avila, Jose; Lorcy, Stehane; Lagarde, Bruno; Giorgetta, Jean-Luc; Polack, François; Asensio, Maria C

    2013-01-01

    As one of the latest beamline built at the SOLEIL synchrotron source, ANTARES beamline offers a spectroscopic non-destructive nano-probe to study advanced materials. This innovative scanning photoemission microscopy combines linear and angle sweeps to perform precise electronic band structure determination by Nano Angle Resolved Photoelectron Spectroscopy (nanoARPES) and chemical imaging by core level detection. The beamline integrates effectively insertion devices and a high transmission beamline optics. This photon source has been combined with an advanced microscope, which has precise sample handling abilities. Moreover, it is fully compatible with a high resolution R4000 Scienta hemispherical analyzer and a set of Fresnel Zone Plates (FZP) able to focalize the beam spot up to a few tenths of nanometers, depending on the spatial resolution of the selected FZP. We present here the main conceptual design of the beamline and endstation, together with some of the firsts commissioning results.

  16. Ultrathin Pb film growth on Cu(111) studied by photoemission

    M.C.Xu; H.J.Qian; F.Q.Liu; K.Ibrahim; W.Y.Lai; S.C.Wu

    2001-01-01

    The valence bands and the Pb 5d,Cu 3p core levels of Pb films evaporated on Cu(111) were measured by synchrotron radiation photoemission and characterized by low-energy electron diffraction(LEED) and Auger electron spectroscopy(AES).The variation of the surafce state at the center of the surface Brillouin zone (SBZ) of Cu(111) with Pb coverage shows that the submonolayer Pb grows on Cu(111) at room temperature(RT) as two-dimensional(2D) islands.With the Pb coverage increasing,the Pb 5d5/2 core level shifts to higher binding energy monotonically.While the Cu 3p3/2 core level is shifted toward higher binding energy by about 120 meV due to the deposition of 1.0ML Pb.At low Ph coverage,subsequent annealing at 200℃ gives rise to Pb-Cu surface alloy formation in the first layer of Cu(111).The Pb 5d core level is shifted toward Fermi level by 20-30 meV due to the surface alloying.An assumption about electron charge transfer from Cu to Pb was adopted to interpret the observed cored level shifts.2001 Published by Elsevier Science Ltd.

  17. Electronic properties of atomic layer deposition films, anatase and rutile TiO2 studied by resonant photoemission spectroscopy

    Das, C.; Richter, M.; Tallarida, M.; Schmeisser, D.

    2016-07-01

    The TiO2 films are prepared by atomic layer deposition (ALD) method using titanium isopropoxide precursors at 250 °C and analyzed using resonant photoemission spectroscopy (resPES). We report on the Ti2p and O1s core levels, on the valence band (VB) spectra and x-ray absorption spectroscopy (XAS) data, and on the resonant photoelectron spectroscopy (resPES) profiles at the O1s and the Ti3p absorption edges. We determine the elemental abundance, the position of the VB maxima, the partial density of states (PDOS) in the VB and in the conduction band (CB) and collect these data in a band scheme. In addition, we analyze the band-gap states as well as the intrinsic states due to polarons and charge-transfer excitations. These states are found to cause multiple Auger decay processes upon resonant excitation. We identify several of these processes and determine their relative contribution to the Auger signal quantitatively. As our resPES data allow a quantitative analysis of these defect states, we determine the relative abundance of the PDOS in the VB and in CB and also the charge neutrality level. The anatase and rutile polymorphs of TiO2 are analyzed in the same way as the TiO2 ALD layer. The electronic properties of the TiO2 ALD layer are compared with the anatase and rutile polymorphs of TiO2. In our comparative study, we find that ALD has its own characteristic electronic structure that is distinct from that of anatase and rutile. However, many details of the electronic structure are comparable and we benefit from our spectroscopic data and our careful analysis to find these differences. These can be attributed to a stronger hybridization of the O2p and Ti3d4s states for the ALD films when compared to the anatase and rutile polymorphs.

  18. Evaluation of the fluorinated antisticking layer by using photoemission and NEXAFS spectroscopies

    Haruyama, Yuichi; Nakai, Yasuki; Matsui, Shinji [University of Hyogo, Graduate School of Science, Laboratory of Advanced Science and Technology for Industry, Ako, Hyogo (Japan)

    2015-11-15

    The electronic structures of four kinds of fluorinated self-assembled monolayers (F-SAMs) with different chain length, which were used for an antisticking layer, were investigated by the photoemission and the near-edge X-ray absorption fine structure (NEXAFS) spectroscopies. From the photoemission spectra in the wide and in the C 1s core-level regions, chemical compositions and components of the F-SAMs with different chain length were evaluated. By using the curve fitting analysis of the photoemission spectra in C 1s core-level region, it was found that the CF{sub 3} site is located at the top of the surface in the C sites of the F-SAM. From the C K-edge NEXAFS spectra of the F-SAMs as a function of the incidence angle of the excitation photon, it was shown that the σ*(C-F) and σ*(C-C) orbitals in the F-SAMs are parallel and perpendicular to the surface, respectively. This indicates that the C-C chain in (CF{sub 2}){sub n} part of the F-SAMs is perpendicular to the surface. Based on these results, the electronic structures of the F-SAMs are discussed. (orig.)

  19. Doping and dimensionality effects on the core-level spectra of layered ruthenates

    Guo, Haizhong; Li, Yi; Urbina, Darwin; Hu, Biao; Jin, Rongying; Liu, Tijiang; Fobes, David; Mao, Zhiqiang; Plummer, E. W.; Zhang, Jiandi

    2010-01-01

    Core-level spectra of the Mn-doped Sr3Ru2O7 and Srn+1RunO3n+1 (n = 1, 2 and 3) crystals are investigated with X-ray photoelectron spectroscopy. Doping of Mn to Sr3Ru2O7 considerably affects the distribution of core-level spectral weight. The satellite of Ru 3d core levels exhibits a substantial change with doping, indicating an enhanced electron localization across the doping- induced metal-insulator transition. However, the Ru 3p core levels remain identical with Mn-doping, thus showing no s...

  20. First principle calculations of core-level binding energy and Auger kinetic energy shifts in metallic solids

    Olovsson, Weine, E-mail: weine.olovsson@gmail.co [Department of Materials Science and Engineering, Kyoto University, Yoshida Honmachi, Sakyo-ku, Kyoto 606-8501 (Japan); Marten, Tobias [Department of Physics, Chemistry and Biology (IFM), Linkoeping University, SE-581 83 Linkoeping (Sweden); Holmstroem, Erik [Instituto de Fisica, Universidad Austral de Chile, Valdivia (Chile); Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Johansson, Boerje [Department of Physics and Materials Science, Uppsala University, P.O. Box 530, SE-751 21 Uppsala (Sweden); Applied Materials Physics, Department of Materials and Engineering, Royal Institute of Technology (KTH), SE-100 44 Stockholm (Sweden); Abrikosov, Igor A. [Department of Physics, Chemistry and Biology (IFM), Linkoeping University, SE-581 83 Linkoeping (Sweden)

    2010-05-15

    We present a brief overview of recent theoretical studies of the core-level binding energy shift (CLS) in solid metallic materials. The focus is on first principles calculations using the complete screening picture, which incorporates the initial (ground state) and final (core-ionized) state contributions of the electron photoemission process in X-ray photoelectron spectroscopy (XPS), all within density functional theory (DFT). Considering substitutionally disordered binary alloys, we demonstrate that on the one hand CLS depend on average conditions, such as volume and overall composition, while on the other hand they are sensitive to the specific local atomic environment. The possibility of employing layer resolved shifts as a tool for characterizing interface quality in fully embedded thin films is also discussed, with examples for CuNi systems. An extension of the complete screening picture to core-core-core Auger transitions is given, and new results for the influence of local environment effects on Auger kinetic energy shifts in fcc AgPd are presented.

  1. Photoemission Spectroscopy Characterization of Attempts to Deposit MoO2 Thin Film

    Irfan

    2011-01-01

    Full Text Available Attempts to deposit molybdenum dioxide (MoO2 thin films have been described. Electronic structure of films, deposited by thermal evaporation of MoO2 powder, had been investigated with ultraviolet photoemission and X-ray photoemission spectroscopy (UPS and XPS. The thermally evaporated films were found to be similar to the thermally evaporated MoO3 films at the early deposition stage. XPS analysis of MoO2 powder reveals presence of +5 and +6 oxidation states in Mo 3d core level along with +4 state. The residue of MoO2 powder indicates substantial reduction in higher oxidation states while keeping +4 oxidation state almost intact. Interface formation between chloroaluminum phthalocyanine (AlPc-Cl and the thermally evaporated film was also investigated.

  2. Electronic Structures of Purple Bronze KMo6O17 Studied by X-Ray Photoemission Spectra

    Qin, Xiaokui; Wei, Junyin; Shi, Jing; Tian, Mingliang; Chen, Hong; Tian, Decheng

    X-ray photoemission spectroscopy study has been performed for the purple bronze KMo6O17. The structures of conduction band and valence band are analogous to the results of ultraviolet photoemission spectra and are also consistent with the model of Travaglini et al., but the gap between conduction and valence band is insignificant. The shape of asymmetric and broadening line of O-1s is due to unresolved contributions from the many inequivalent oxygen sites in this crystal structure. Mo 3d core-level spectrum reveals that there are two kinds of valence states of Molybdenum (Mo+5 and Mo+6). The calculated average valence state is about +5.6, which is consistent with the expectation value from the composition of this material. The tail of Mo-3d spectrum toward higher binding energy is the consequence of the excitation of electron-hole pairs with singularity index of 0.21.

  3. Photocathode device that replenishes photoemissive coating

    Moody, Nathan A.; Lizon, David C.

    2016-06-14

    A photocathode device may replenish its photoemissive coating to replace coating material that desorbs/evaporates during photoemission. A linear actuator system may regulate the release of a replenishment material vapor, such as an alkali metal, from a chamber inside the photocathode device to a porous cathode substrate. The replenishment material deposits on the inner surface of a porous membrane and effuses through the membrane to the outer surface, where it replenishes the photoemissive coating. The rate of replenishment of the photoemissive coating may be adjusted using the linear actuator system to regulate performance of the photocathode device during photoemission. Alternatively, the linear actuator system may adjust a plasma discharge gap between a cartridge containing replenishment material and a metal grid. A potential is applied between the cartridge and the grid, resulting in ejection of metal ions from the cartridge that similarly replenish the photoemissive coating.

  4. Multi-atom resonant photoemission and the development of next-generation software and high-speed detectors for electron spectroscopy

    Kay, Alexander William

    2000-09-01

    This dissertation has involved the exploration of a new effect in photoelectron emission, multi-atom resonant photoemission (MARPE), as well as the development of new software, data analysis techniques, and detectors of general use in such research. We present experimental and theoretical results related to MARPE, in which the photoelectron intensity from a core level on one atom is influenced by a core-level absorption resonance on another. We point out that some of our and others prior experimental data has been strongly influenced by detector non-linearity and that the effects seen in new corrected data are smaller and of different form. Corrected data for the MnO(001) system with resonance between the O 1s and Mn 2p energy levels are found to be well described by an extension of well-known intraatomic resonant photoemission theory to the interatomic case, provided that interactions beyond the usual second-order Kramers-Heisenberg treatment are included. This theory is also found to simplify under certain conditions so as to yield results equivalent to a classical x-ray optical approach, with the latter providing an accurate and alternative, although less detailed and general, physical picture of these effects. Possible future applications of MARPE as a new probe of near-neighbor identities and bonding and its relationship to other known effects are also discussed. We also consider in detail specially written data acquisition software that has been used for most of the measurements reported here. This software has been used with an existing experimental system to develop the method of detector characterization and then data correction required for the work described above. The development of a next generation one-dimensional, high-speed, electron detector is also discussed. Our goal has been to design, build and test a prototype high-performance, one-dimensional pulse-counting detector that represents a significant advancement in detector technology and is well

  5. Multi-atom resonant photoemission and the development of next-generation software and high-speed detectors for electron spectroscopy

    This dissertation has involved the exploration of a new effect in photoelectron emission, multi-atom resonant photoemission (MARPE), as well as the development of new software, data analysis techniques, and detectors of general use in such research. We present experimental and theoretical results related to MARPE, in which the photoelectron intensity from a core level on one atom is influenced by a core-level absorption resonance on another. We point out that some of our and others prior experimental data has been strongly influenced by detector non-linearity and that the effects seen in new corrected data are smaller and of different form. Corrected data for the MnO(001) system with resonance between the O 1s and Mn 2p energy levels are found to be well described by an extension of well-known intraatomic resonant photoemission theory to the interatomic case, provided that interactions beyond the usual second-order Kramers-Heisenberg treatment are included. This theory is also found to simplify under certain conditions so as to yield results equivalent to a classical x-ray optical approach, with the latter providing an accurate and alternative, although less detailed and general, physical picture of these effects. Possible future applications of MARPE as a new probe of near-neighbor identities and bonding and its relationship to other known effects are also discussed. We also consider in detail specially written data acquisition software that has been used for most of the measurements reported here. This software has been used with an existing experimental system to develop the method of detector characterization and then data correction required for the work described above. The development of a next generation one-dimensional, high-speed, electron detector is also discussed. Our goal has been to design, build and test a prototype high-performance, one-dimensional pulse-counting detector that represents a significant advancement in detector technology and is well

  6. Chemical potential landscape in band filling and bandwidth-control of manganites: Photoemission spectroscopy measurements

    Ebata, K.; Takizawa, M.; A. Fujimori; Kuwahara, H; Tomioka, Y.; Y. Tokura

    2008-01-01

    We have studied the effects of band filling and bandwidth control on the chemical potential in perovskite manganites $R_{1-x}A_x$MnO$_3$ ($R$ : rare earth, $A$ : alkaline earth) by measurements of core-level photoemission spectra. A suppression of the doping-dependent chemical potential shift was observed in and around the CE-type charge-ordered composition range, indicating that there is charge self-organization such as stripe formation or its fluctuations. As a function of bandwidth, we obs...

  7. Hot Electron Photoemission from Plasmonic Nanostructures: The Role of Surface Photoemission and Transition Absorption

    Babicheva, Viktoriia; Zhukovsky, Sergei; Ikhsanov, Renat Sh;

    2015-01-01

    enhancement of photoemission in the surface scenario. We calculate the ratio of photoemission cross-section for a gold nanosphere embedded in different materials such as silicon, zinc oxide, and titanium dioxide. For the calculations, we include both surface and bulk mechanisms of photoemission, using quantum...

  8. Resonant photoemission and magnetic x-ray circular dichroism in the M shell of ultrathin films of Fe

    Using magnetic ultra thin films (2--4 ml) of Fe on Cu(001) and bulk-like Fe, the Fe3p and Fe3s core states have been investigated with resonant photoemission and core-level photoemission, including, magnetic x-ray circular dichroism (MXCD) experiments. The resonant photoemission experiment has been done in fine steps over a wide photon energy range (hν = 695 eV - 715 eV), to probe the parentage of various spectral structures. The onset of secondary channels at the L3(hν = 707 eV) and L2(hν = 72O eV) edges will be analyzed in light of results from bulk Ni. The MXCD photoelectron spectroscopy of the Fe3p exhibits a 0.2 eV shift with circular polarization variation. The previously observed split peak structure in the Fe3s will be discussed with regard to the new resonant photoemission results. The resonant photoemission results will also be put into the context of our MXCD absorption results for monolayer and multilayers of Fe

  9. Theory on photoemission and inverse photoemission spectra in VO2

    The photoemission (PES) and inverse photoemission (IPES) spectra in VO2 at temperatures above and below the metal-insulator transition (MIT) are discussed with a two-band Hubbard model. An abrupt change in the valence top character of the theoretical PES spectra at the MIT caused by a switching in the t2g orbital occupation in the ground state is found. In the insulating phase, the structure of the valence top is well described within a single-band Hubbard model, where only the d|| band participates. Since the ratio t/U∼0.2 is small, the structure of the spectrum extends to ∼1.5eV below the Fermi level. On the other hand, in the metallic phase, both the dparallel and π* bands are involved and the spectral weight is concentrated in the vicinity of the Fermi level within a range ∼0.5eV. Such a large spectral weight transfer is consistent with experiments. For the IPES spectra, a structure corresponding to the upper Hubbard band of the single-band Hubbard model is appeared at ∼1.5eV above the Fermi level in the insulating phase. However the structure is absent in the metallic phase

  10. Non linear photoemission from silicon

    Bensoussan, M.; Moison, J. M.

    1983-03-01

    Two well-defined photoemission regimes are observed from clean (111) Si surfaces under various laser irradiation conditions and photon energies. At low fluences and at photon energies above half the work function two and three quantum process are the outstanding emission mechanisms. Density of state effects of initial and intermediate states appear as the dominant spectral features. At higher fluences or at low photon energies the prevailing emission is thermoemission characterized by a Maxwellian distribution revailing a temperature quite different from the lattice one during the excitation pulse.

  11. A first-principles core-level XPS study on the boron impurities in germanium crystal

    Yamauchi, Jun [Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Yokohama 223-8522 (Japan); Yoshimoto, Yoshihide [Department of Applied Mathematics and Physics, Graduate School of Engineering, Tottori University, 4-101 Koyama-Minami, Tottori, 680-8552 (Japan); Suwa, Yuji [Central Research Laboratory, Hitachi, Ltd., Hatoyama, Saitama 350-0395 (Japan)

    2013-12-04

    We systematically investigated the x-ray photoelectron spectroscopy (XPS) core-level shifts and formation energies of boron defects in germanium crystals and compared the results to those in silicon crystals. Both for XPS core-level shifts and formation energies, relationship between defects in Si and Ge is roughly linear. From the similarity in the formation energy, it is expected that the exotic clusters like icosahedral B12 exist in Ge as well as in Si.

  12. High resolution photoemission spectroscopy: Evidence for strong chemical interaction between Mg and 3,4,9,10-perylene-tetracarboxylic dianhydride

    The interface formation between Mg and 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA) was investigated by high resolution soft x-ray photoemission spectroscopy. The interface chemistry was obtained after fitting the core level spectra as a function of Mg thickness. At the initial stage of deposition, a strong chemical interaction between Mg and the single bonded oxygen atoms of PTCDA is observed leading to the formation of MgO and a modified organic molecule. Based on the experimental evidence, the molecular structure of the modified molecule is proposed. Moreover, the changes observed in the measured C1s core level spectra are supported by density functional theory calculations

  13. Instrument developments for inverse photoemission

    Experimental developments principally concerning electron sources for inverse photoemission are presented. The specifications of the electron beam are derived from experiment requirements, taking into account the limitations encountered (space charge divergence). For a wave vector resolution of 0.2 A-1, the maximum current is 25 microA at 20 eV. The design of a gun providing such a beam in the range 5 to 50 eV is presented. Angle-resolved inverse photoemission experiments show angular effects at 30 eV. For an energy of 10 eV, angular effects should be stronger, but the low efficiency of the spectrometer in this range makes the experiments difficult. The total energy resolution of 0.3 eV is the result mainly of electron energy spread, as expected. The electron sources are based on field effect electron emission from a cathode consisting of a large number of microtips. The emission arises from a few atomic cells for each tip. The ultimate theoretical energy spread is 0.1 eV. This value is not attained because of an interface resistance problem. A partial solution of this problem allows measurement of an energy spread of 0.9 eV for a current of 100 microA emitted at 60 eV. These cathodes have a further advantage in that emission can occur at a low temperature

  14. In-adlayers on non-polar and polar InN surfaces: Ion scattering and photoemission studies

    The surface structure of In-polarity c-plane InN has been investigated by low energy ion scattering spectroscopy. Comparison of ion scattering spectra recorded along the [1 0 0 0] azimuth with model calculations indicates that the clean In-polarity c-plane InN surface is terminated by In-adlayers with a laterally contracted topmost In layer. This is consistent with previous X-ray photoemission and electron diffraction results. Additionally, the surface properties of a-plane InN have been investigated using core-level and valence band X-ray photoemission spectroscopy (XPS). From the ratio of the In and N core-level XPS signal intensities, the clean a-plane InN surface has also been found to be terminated by In-adlayers. Photoemission measurements of the valence band maximum to surface Fermi level separation for a-plane InN indicate the existence of an electron accumulation layer at the surface. This observation of electron accumulation at non-polar InN surfaces in the presence of In-adlayers is in agreement with the predictions of previous first-principles calculations

  15. Photoemission Study of the Rare Earth Intermetallic Compounds: RNi2Ge2 (R=Eu, Gd)

    EuNi2Ge2 and GdNi2Ge2 are two members of the RT2X2 (R = rare earth, T = transition metal and X = Si, Ge) family of intermetallic compounds, which has been studied since the early 1980s. These ternary rare-earth intermetallic compounds with the tetragonal ThCr2Si2 structure are known for their wide variety of magnetic properties, Extensive studies of the RT2X2 series can be found in Refs [ 1,2,3]. The magnetic properties of the rare-earth nickel germanides RNi2Ge2 were recently studied in more detail [4]. The purpose of this dissertation is to investigate the electronic structure (both valence band and shallow core levels) of single crystals of EuNi2Ge2 and GdNi2Ge2 and to check the assumptions that the f electrons are non-interacting and, consequently, the rigid-band model for these crystals would work [11], using synchrotron radiation because, to the best of our knowledge, no photoemission measurements on those have been reported. Photoemission spectroscopy has been widely used to study the detailed electronic structure of metals and alloys, and especially angle-resolved photoemission spectroscopy (ARPES) has proven to be a powerful technique for investigating Fermi surfaces (FSs) of single-crystal compounds

  16. On sulfur core level binding energies in thiol self-assembly and alternative adsorption sites: An experimental and theoretical study

    Characteristic core level binding energies (CLBEs) are regularly used to infer the modes of molecular adsorption: orientation, organization, and dissociation processes. Here, we focus on a largely debated situation regarding CLBEs in the case of chalcogen atom bearing molecules. For a thiol, this concerns the case when the CLBE of a thiolate sulfur at an adsorption site can be interpreted alternatively as due to atomic adsorption of a S atom, resulting from dissociation. Results of an investigation of the characteristics of thiol self-assembled monolayers (SAMs) obtained by vacuum evaporative adsorption are presented along with core level binding energy calculations. Thiol ended SAMs of 1,4-benzenedimethanethiol (BDMT) obtained by evaporation on Au display an unconventional CLBE structure at about 161.25 eV, which is close to a known CLBE of a S atom on Au. Adsorption and CLBE calculations for sulfur atoms and BDMT molecules are reported and allow delineating trends as a function of chemisorption on hollow, bridge, and atop sites and including the presence of adatoms. These calculations suggest that the 161.25 eV peak is due to an alternative adsorption site, which could be associated to an atop configuration. Therefore, this may be an alternative interpretation, different from the one involving the adsorption of atomic sulfur resulting from the dissociation process of the S–C bond. Calculated differences in S(2p) CLBEs for free BDMT molecules, SH group sulfur on top of the SAM, and disulfide are also reported to clarify possible errors in assignments

  17. On sulfur core level binding energies in thiol self-assembly and alternative adsorption sites: An experimental and theoretical study

    Jia, Juanjuan [Institut des Sciences Moléculaires d’Orsay, Université-Paris Sud, 91405 Orsay (France); CNRS, UMR 8214, Institut des Sciences Moléculaires d’Orsay, Orsay ISMO, Bâtiment 351, Université Paris Sud, 91405 Orsay (France); Kara, Abdelkader, E-mail: abdelkader.kara@ucf.edu, E-mail: vladimir.esaulov@u-psud.fr [Department of Physics, University of Central Florida, Orlando, Florida 32816 (United States); Pasquali, Luca [Dipartimento di Ingegneria “E. Ferrari,” Università di Modena e Reggio Emilia, Via Vignolese 905, 41125 Modena (Italy); IOM-CNR, s.s. 14, Km. 163.5 in AREA Science Park, 34149 Basovizza, Trieste (Italy); Department of Physics, University of Johannesburg, P.O. Box 524, Auckland Park 2006 (South Africa); Bendounan, Azzedine; Sirotti, Fausto [Synchrotron SOLEIL, L’Orme des Merisiers, Saint-Aubin, BP 48, F-91192 Gif-sur-Yvette Cedex (France); Esaulov, Vladimir A., E-mail: abdelkader.kara@ucf.edu, E-mail: vladimir.esaulov@u-psud.fr [Institut des Sciences Moléculaires d’Orsay, Université-Paris Sud, 91405 Orsay (France); CNRS, UMR 8214, Institut des Sciences Moléculaires d’Orsay, Orsay ISMO, Bâtiment 351, Université Paris Sud, 91405 Orsay (France); IOM-CNR, s.s. 14, Km. 163.5 in AREA Science Park, 34149 Basovizza, Trieste (Italy)

    2015-09-14

    Characteristic core level binding energies (CLBEs) are regularly used to infer the modes of molecular adsorption: orientation, organization, and dissociation processes. Here, we focus on a largely debated situation regarding CLBEs in the case of chalcogen atom bearing molecules. For a thiol, this concerns the case when the CLBE of a thiolate sulfur at an adsorption site can be interpreted alternatively as due to atomic adsorption of a S atom, resulting from dissociation. Results of an investigation of the characteristics of thiol self-assembled monolayers (SAMs) obtained by vacuum evaporative adsorption are presented along with core level binding energy calculations. Thiol ended SAMs of 1,4-benzenedimethanethiol (BDMT) obtained by evaporation on Au display an unconventional CLBE structure at about 161.25 eV, which is close to a known CLBE of a S atom on Au. Adsorption and CLBE calculations for sulfur atoms and BDMT molecules are reported and allow delineating trends as a function of chemisorption on hollow, bridge, and atop sites and including the presence of adatoms. These calculations suggest that the 161.25 eV peak is due to an alternative adsorption site, which could be associated to an atop configuration. Therefore, this may be an alternative interpretation, different from the one involving the adsorption of atomic sulfur resulting from the dissociation process of the S–C bond. Calculated differences in S(2p) CLBEs for free BDMT molecules, SH group sulfur on top of the SAM, and disulfide are also reported to clarify possible errors in assignments.

  18. Femtomagnetism in graphene induced by core level excitation of organic adsorbates

    Ravikumar, Abhilash; Baby, Anu; Lin, He; Brivio, Gian Paolo; Fratesi, Guido

    2016-01-01

    We predict the induction or suppression of magnetism in the valence shell of physisorbed and chemisorbed organic molecules on graphene occurring on the femtosecond time scale as a result of core level excitations. For physisorbed molecules, where the interaction with graphene is dominated by van der Waals forces and the system is non-magnetic in the ground state, numerical simulations based on density functional theory show that the valence electrons relax towards a spin polarized configuration upon excitation of a core-level electron. The magnetism depends on efficient electron transfer from graphene on the femtosecond time scale. On the other hand, when graphene is covalently functionalized, the system is magnetic in the ground state showing two spin dependent mid gap states localized around the adsorption site. At variance with the physisorbed case upon core-level excitation, the LUMO of the molecule and the mid gap states of graphene hybridize and the relaxed valence shell is not magnetic anymore. PMID:27089847

  19. High resolution core level spectroscopy of hydrogen-terminated (1 0 0) diamond.

    Schenk, A K; Rietwyk, K J; Tadich, A; Stacey, A; Ley, L; Pakes, C I

    2016-08-01

    Synchrotron-based photoelectron spectroscopy experiments are presented that address a long standing inconsistency in the treatment of the C1s core level of hydrogen terminated (1 0 0) diamond. Through a comparison of surface and bulk sensitive measurements we show that there is a surface related core level component to lower binding energy of the bulk diamond component; this component has a chemical shift of [Formula: see text] eV which has been attributed to carbon atoms which are part of the hydrogen termination. Additionally, our results indicate that the asymmetry of the hydrogen terminated (1 0 0) diamond C1s core level is an intrinsic aspect of the bulk diamond peak which we have attributed to sub-surface carbon layers. PMID:27299369

  20. Photoemission studies of mixed valent systems

    Photoemission spectroscopy has been used to study a number of aspects of the mixed valent state (corresponding to non-integral 4f occupation) in rare earth systems. Deep core photoemission (e.g., from 3d or 4d levels) allows the measurement of the 4f occupancy and surface valence shifts, and, as well, the indirect measurement of the effect of solid state environment on the energy of hybridization between 4f electrons and conduction electrons. 4f-Derived photoemission has been used to study surface valance and chemical shifts and to infer the nature of the mixed valent ground state. A combination of 4f-derived photoemission and add-electron spectroscopy provides a measurement of the rf Coulomb correlation energy, an important parameter in the mixed valent problem. A review of these approaches will be presented, with emphasis on Ce-based systems, whose behavior falls outside the usual description of 4f-unstable systems

  1. Nondipole Photoemission from Chiral Enantiomers of Camphor

    Bowen, K. P.; Stolte, W. C.; Young, J. A.; Demchenko, I. N.; Guillemin, R.; Hemmers, O.; Piancastelli, M. N.; Lindle, D. W.

    2010-03-01

    K-shell photoemission from the carbonyl carbon in the chiral molecule camphor has been studied in the region just above the core-shell ionization threshold. Differences between angular distributions of emitted photoelectrons from the two enantiomers are attributed to the influence of chirality combined with nondipole effects in the photoemission process, despite the fact the measurements were taken using linearly polarized x-rays. The results suggest the possibility of a new form of linear dichroism.

  2. Core-resonant double photoemission from palladium films

    Kostanovskiy, I.; Schumann, F. O.; Aliaev, Y.; Wei, Z.; Kirschner, J.

    2016-01-01

    We studied the core-resonant double photoemission process from palladium films with linearly polarized synchrotron radiation. We excited either the 3d or 4p core level and focused on the Auger transitions which leave two holes in the valence band. We find that the two-dimensional energy distributions are markedly different for the 3d and 4p decay. The 3d decay can be understood by a sequential emission of the two electrons while the 4p decay proceeds in a single step. Despite the large differences in the two-dimensional energy spectra we find the shape of the energy sum spectra rather similar. For the description of the 4p decay we propose a model which uses available single electron spectra, but suggest an alternative interpretation of these data. With this we are able to explain the range over which the available energy is shared. Key assumptions of the model are verified by our experiments on the 3d decay.

  3. Direct surface magnetometry with photoemission magnetic x-ray dichroism

    Tobin, J.G.; Goodman, K.W. [Lawrence Berkeley National Lab., CA (United States); Schumann, F.O. [Pennsylvania State Univ., University Park, PA (United States)] [and others

    1997-04-01

    Element specific surface magnetometry remains a central goal of synchrotron radiation based studies of nanomagnetic structures. One appealing possibility is the combination of x-ray absorption dichroism measurements and the theoretical framework provided by the {open_quotes}sum rules.{close_quotes} Unfortunately, sum rule analysis are hampered by several limitations including delocalization of the final state, multi-electronic phenomena and the presence of surface dipoles. An alternative experiment, Magnetic X-Ray Dichroism in Photoelectron Spectroscopy, holds out promise based upon its elemental specificity, surface sensitivity and high resolution. Computational simulations by Tamura et al. demonstrated the relationship between exchange and spin orbit splittings and experimental data of linear and circular dichroisms. Now the authors have developed an analytical framework which allows for the direct extraction of core level exchange splittings from circular and linear dichroic photoemission data. By extending a model initially proposed by Venus, it is possible to show a linear relation between normalized dichroism peaks in the experimental data and the underlying exchange splitting. Since it is reasonable to expect that exchange splittings and magnetic moments track together, this measurement thus becomes a powerful new tool for direct surface magnetometry, without recourse to time consuming and difficult spectral simulations. The theoretical derivation will be supported by high resolution linear and circular dichroism data collected at the Spectromicroscopy Facility of the Advanced Light Source.

  4. Core-resonant double photoemission from palladium films

    We studied the core-resonant double photoemission process from palladium films with linearly polarized synchrotron radiation. We excited either the 3d or 4p core level and focused on the Auger transitions which leave two holes in the valence band. We find that the two-dimensional energy distributions are markedly different for the 3d and 4p decay. The 3d decay can be understood by a sequential emission of the two electrons while the 4p decay proceeds in a single step. Despite the large differences in the two-dimensional energy spectra we find the shape of the energy sum spectra rather similar. For the description of the 4p decay we propose a model which uses available single electron spectra, but suggest an alternative interpretation of these data. With this we are able to explain the range over which the available energy is shared. Key assumptions of the model are verified by our experiments on the 3d decay. (paper)

  5. Photoemission studies of f-electron systems: Many-body effects: Final report, March 1, 1985--March 31, 1988

    Both initial and final state effects contribute to many-body features in photoemission on solids. The former reflect the ground state properties of the system, while the latter are due to the reaction of the solid state environment to the creation of a photoelectron hole. In f-electron systems both effects are expected to contribute to the photoemission spectra and one objective of this project was to separate final state effects from ground state properties. Final state effects provide valuable information about the interaction of f electrons with conduction electrons. The degree of f-electron localization and the strength of f-conduction electron hybridization for Ce- and U-based systems can be extracted from these measurements. The energy dependence of the photoemission cross section, which shows pronounced maxima in rare earth and uranium systems, also proved to be sensitive to the exact electronic state of the Ce ion. Core level photoemission spectroscopy was used as a species-specific probe to determine the electronic state of the f-shell ions and their ligands in scientific interesting systems. Application to high temperature superconducting compounds helped to determine the electronic properties necessary for superconductivity

  6. Ab initio surface core-level shifts and surface segregation energies

    Aldén, Magnus; Skriver, Hans Lomholt; Johansson, Börje

    1993-01-01

    We have calculated the surface core-level energy shifts of the 4d and 5d transition metals by means of local-density theory and a Green’s-function technique based on the linear muffin-tin orbitals method. Final-state effects are included by treating the core-ionized atom as an impurity located in...

  7. Deep layer-resolved core-level shifts in the beryllium surface

    Aldén, Magnus; Skriver, Hans Lomholt; Johansson, Börje

    1993-01-01

    Core-level energy shifts for the beryllium surface region are calculated by means of a Green’s function technique within the tight-binding linear muffin-tin orbitals method. Both initial- and final-state effects in the core-ionization process are fully accounted for. Anomalously large energy shifts...

  8. Core level shifts in Cu-Pd alloys as a function of bulk composition and structure

    Boes, Jacob R.; Kondratyuk, Peter; Yin, Chunrong; Miller, James B.; Gellman, Andrew J.; Kitchin, John R.

    2015-10-01

    CuPd alloys are important materials in hydrogen purification, where they are used as dense Pd-based separation membranes. Cu is added to impart sulfur tolerance and improved mechanical properties. At intermediate compositions and T < 873 K, a BCC alloy (B2) phase occurs, which has superior separation characteristics to those of the FCC phases that form at high Cu and high Pd compositions. Identifying the composition and temperature window where the B2 phase forms is a critical need to enable the design of improved alloys. A composition spread alloy film of Cu and Pd was synthesized. The film was characterized by electron back scatter diffraction and X-ray photoelectron spectroscopy, providing the core level shifts as a function of bulk composition and bulk structure. An anomalous deviation in the Cu core level shift was observed in the composition range 0.33 < xPd < 0.55 over which the B2 phase occurs. Density functional theory calculations were used to simulate core level shifts in the FCC and B2 alloy structures. They suggest that the anomalous deviation in core level shift is due to formation of the ordered B2 phase in this composition range.

  9. Modeling Shallow Core-Level Transitions in the Reflectance Spectra of Gallium-Containing Semiconductors

    Stoute, Nicholas; Aspnes, David

    2012-02-01

    The electronic structure of covalent materials is typically approached by band theory. However, shallow core level transitions may be better modeled by an atomic-scale approach. We investigate shallow d-core level reflectance spectra in terms of a local atomic-multiplet theory, a novel application of a theory typically used for higher-energy transitions on more ionic type material systems. We examine specifically structure in reflectance spectra of GaP, GaAs, GaSb, GaSe, and GaAs1-xPx due to transitions that originate from Ga3d core levels and occur in the 20 to 25 eV range. We model these spectra as a Ga^+3 closed-shell ion whose transitions are influenced by perturbations on 3d hole-4p electron final states. These are specifically spin-orbit effects on the hole and electron, and a crystal-field effect on the hole, attributed to surrounding bond charges and positive ligand anions. Empirical radial-strength parameters were obtained by least-squares fitting. General trends with respect to anion electronegativity are consistent with expectations. In addition to the spin-orbit interaction, crystal-field effects play a significant role in breaking the degeneracy of the d levels, and consequently are necessary to understand shallow 3d core level spectra.

  10. Vacuum space charge effects in sub-picosecond soft X-ray photoemission on a molecular adsorbate layer

    Vacuum space charge-induced kinetic energy shifts of O 1s and Ru 3d core levels in femtosecond soft X-ray photoemission spectra (PES) have been studied at a free electron laser (FEL) for an oxygen layer on Ru(0001). We fully reproduced the measurements by simulating the in-vacuum expansion of the photoelectrons and demonstrate the space charge contribution of the high-order harmonics in the FEL beam. Employing the same analysis for 400 nm pump-X-ray probe PES, we can disentangle the delay dependent Ru 3d energy shifts into effects induced by space charge and by lattice heating from the femtosecond pump pulse

  11. Angle-dependent hard X-ray photoemission study of Nb hydride formation in high-pressure supercritical water

    Soda, Kazuo, E-mail: j45880a@cc.nagoya-u.ac.jp [Department of Quantum Engineering, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan); Kondo, Hiroki; Yamaguchi, Kanta; Kato, Masahiko [Department of Quantum Engineering, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan); Shiraki, Tatsuhito; Niwa, Ken; Kusaba, Keiji; Hasegawa, Masashi [Department of Crystalline Materials Science, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan); Xeniya, Kozina; Ikenaga, Eiji [Japan Synchrotron Radiation Research Institute, 1-1-1, Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198 (Japan)

    2015-09-15

    Highlights: • Nb hydrides in 10-GPa supercritical water are studied by photoelectron spectroscopy. • The hydride components of the Nb 3d core-level spectra are increased with the depth. • The bulk valence-band spectrum shows a split band due to the Nb–H bond formation. • The hydrides are formed in the bulk and their surfaces are covered with Nb oxides. - Abstract: Nb hydrides formation in 10-GPa supercritical water has been investigated by angle-dependent micro-beam hard X-ray photoemission spectroscopy. In the Nb 3d core-level spectra, Nb hydride components are found in the slightly high binding energy side of the metallic components, and the oxide ones are observed even though little oxides are recognized in X-ray diffraction patterns. Obtained emission-angle dependence of the Nb 3d core-level spectra of Nb hydride specimens shows that the Nb hydride components increase with the emission angle decreased i.e. the sampling depth increased, while the oxide ones decrease. The bulk valence-band spectrum is obtained by decomposing the measured valence-band spectra into a bulk and surface components with use of the emission-angle dependence of the core-level and valence-band spectra; it consists of two bands. This implies the Nb–H chemical bond formation and Nb in an oxidation state, consistent with reported band structure calculations and the observed core-level chemical shifts. Thus it is confirmed by valence-band and core-level photoelectron spectroscopy that the Nb hydrides are formed inside the specimen, irrespective to the well-known high oxidation ability of supercritical water.

  12. A revisit to ultrathin NiO(0 0 1) film: LEED and valence band photoemission studies

    Das, Jayanta, E-mail: jayanta.sinp@gmail.com; Menon, Krishnakumar S.R.

    2015-08-15

    LEED and photoemission measurements have been performed on ultrathin NiO films to reinvestigate its surface quality and valence electronic structures, respectively. On Ag(0 0 1) substrate, the best epitaxial order was observed for high temperature deposition with sufficient oxygen flux associated with a post-deposition oxygen annealing. The effect of the substrate vicinity on valence band electronic structure, in case of interfacial NiO layers, has been explained. The variation of Ni 3d to O 2p photoemission cross-section with photon energy (hν) has been demonstrated in this work.

  13. A revisit to ultrathin NiO(0 0 1) film: LEED and valence band photoemission studies

    LEED and photoemission measurements have been performed on ultrathin NiO films to reinvestigate its surface quality and valence electronic structures, respectively. On Ag(0 0 1) substrate, the best epitaxial order was observed for high temperature deposition with sufficient oxygen flux associated with a post-deposition oxygen annealing. The effect of the substrate vicinity on valence band electronic structure, in case of interfacial NiO layers, has been explained. The variation of Ni 3d to O 2p photoemission cross-section with photon energy (hν) has been demonstrated in this work

  14. Photoemission spectroscopy study of the hole-doped Haldane chain Y2-xSrxBaNiO5

    In this paper, we present photoemission experiments on the hole-doped Haldane chain compound Y2-xSrxBaNiO5. By using the photon energy dependence of the photoemission cross section, we identified the symmetry of the first ionisation states (d type). Hole doping in this system leads to a significant increase in the spectral weight at the top of the valence band without any change in the vicinity of the Fermi energy. This behavior, never observed in other charge transfer oxides, could result from the Ni3d-O2p hybridization enhancement due to the shortening of the relevant Ni-O distance with doping

  15. A core level spectroscopic study on RNi2B2C (R=Y,Er) borocarbides

    Polycrystalline samples of YNi2B2C and magnetic ErNi2B2C were prepared by arc-melting technique with a Tc ∼ 15 K. Core level spectroscopic studies have been performed in order to see the valence of Y, Er and Ni. The results show that Ni and Er exists in 2+ valence state and Y exists in 3+ valence state. (author)

  16. New determination of the core-level life-time broadenings in mercury

    Highlights: • We report core-level life-time widths for mercury in the gas phase. • Photoelectron spectra for the 4p, 4d, 4f and 5p levels are analyzed. • A Coster–Kronig like CI effect is observed for the 4d3/2 level. - Abstract: Previously recorded and published photoelectron spectroscopic data for mercury in the gas phase has been reanalyzed. The life-time broadenings have been determined for a large number of core levels. It is then seen that a recent detailed derivation of core-level line-widths based on X-ray emission spectroscopy give life-time widths that are generally too large. The 4d3/24d5/2nd Coster–Kronig (CK) transition is also discussed. We find that the additional broadening of the 4d3/2 level for mercury metal is indeed due to a CK decay, in contrast to recent claims. In atomic mercury, however, the CK process in energetically forbidden. In spite of this we find that the 4d3/2 level is broadened also in this case. We propose that this is due to a mixing between the 4d3/2 hole state and discrete 4d5/2nd states

  17. New determination of the core-level life-time broadenings in mercury

    Martensson, Nils, E-mail: nils.martensson@fysik.uu.se; Svensson, Svante

    2015-07-15

    Highlights: • We report core-level life-time widths for mercury in the gas phase. • Photoelectron spectra for the 4p, 4d, 4f and 5p levels are analyzed. • A Coster–Kronig like CI effect is observed for the 4d{sub 3/2} level. - Abstract: Previously recorded and published photoelectron spectroscopic data for mercury in the gas phase has been reanalyzed. The life-time broadenings have been determined for a large number of core levels. It is then seen that a recent detailed derivation of core-level line-widths based on X-ray emission spectroscopy give life-time widths that are generally too large. The 4d{sub 3/2}4d{sub 5/2}nd Coster–Kronig (CK) transition is also discussed. We find that the additional broadening of the 4d{sub 3/2} level for mercury metal is indeed due to a CK decay, in contrast to recent claims. In atomic mercury, however, the CK process in energetically forbidden. In spite of this we find that the 4d{sub 3/2} level is broadened also in this case. We propose that this is due to a mixing between the 4d{sub 3/2} hole state and discrete 4d{sub 5/2}nd states.

  18. Gas-Phase Photoemission With Soft X-Rays: Cross Sections And Angular Distributions

    Shirley, D. A.; Kobrin, P. H.; Truesdale, C. M.; Lindle, D. W.; F errett, T. A.; Heimann, P. A.; Becker, U.; Kerkhoff, H. G.; Southworth, S. H.

    1984-03-01

    A summary is presented of typical gas-phase photoemission studies based on synchrotron radiation in the 50-5000 eV range, using beam lines at the Stanford Synchrotron Radiation Laboratory. Three topics are addressed: atomic inner-shell photoelectron cross sections and asymmetries, correlation peaks in rare gases, and core-level shape resonances in molecules. Photoelectron cross-section a(nZ) and asymmetry-parameter a(n0 studies in mercury vapor at photon energies up to 270 eV (up to 600 eV for a4f) extend coverage of these parameters to nSF6 and OCS) through C is in CO, CO2 and CF4, N ls in N2 and NO, and 0 is in CO and CO2 to 2490 eV (S ls in SF6). Several conclusions can be drawn about the photoelectron and Auger cross sections and asymmetry parameters.

  19. Magnetic x-ray linear dichroism in resonant and non-resonant Gd 4f photoemission

    Mishra, S.; Gammon, W.J.; Pappas, D.P. [Virginia Commonwealth Univ., Richmond, VA (United States)] [and others

    1997-04-01

    The enhancement of the magnetic linear dichroism in resonant 4f photoemission (MLDRPE) is studied from a 50 monolayer film of Gd/Y(0001). The ALS at beamline 7.0.1 provided the source of linearly polarized x-rays used in this study. The polarized light was incident at an angle of 30 degrees relative to the film plane, and the sample magnetization was perpendicular to the photon polarization. The linear dichroism of the 4f core levels is measured as the photon energy is tuned through the 4d-4f resonance. The authors find that the MLDRPE asymmetry is strongest at the resonance. Near the threshold the asymmetry has several features which are out of phase with the fine structure of the total yield.

  20. Na and Cs intercalation of 2H-TaSe2 studied by photoemission

    The electronic structure of the layered compound 2H-TaSe2 has been studied using angle-resolved photoemission before and after in situ intercalation with Na and Cs. Core level spectra verified that Na and Cs both intercalate easily at room temperature, with only small amounts remaining on the surface. Valence band spectra revealed changes in the electronic band structure which were much more extensive than predicted by the rigid band model, but which were in reasonable agreement with theoretical bands calculated by the LAPW method. Some discrepancies between the experimental and calculated results are probably due to intercalation induced changes in the stacking of host layers. A general similarity with results from transition metal dichalcogenides with 1T structure indicates that the intercalation properties are not critically dependent on the internal structure of the host layers. (author)

  1. A New Spin on Photoemission Spectroscopy

    Jozwiak, Chris [Univ. of California, Berkeley, CA (United States)

    2008-12-01

    The electronic spin degree of freedom is of general fundamental importance to all matter. Understanding its complex roles and behavior in the solid state, particularly in highly correlated and magnetic materials, has grown increasingly desirable as technology demands advanced devices and materials based on ever stricter comprehension and control of the electron spin. However, direct and efficient spin dependent probes of electronic structure are currently lacking. Angle Resolved Photoemission Spectroscopy (ARPES) has become one of the most successful experimental tools for elucidating solid state electronic structures, bolstered by-continual breakthroughs in efficient instrumentation. In contrast, spin-resolved photoemission spectroscopy has lagged behind due to a lack of similar instrumental advances. The power of photoemission spectroscopy and the pertinence of electronic spin in the current research climate combine to make breakthroughs in Spin and Angle Resolved Photoemission Spectroscopy (SARPES) a high priority . This thesis details the development of a unique instrument for efficient SARPES and represents a radical departure from conventional methods. A custom designed spin polarimeter based on low energy exchange scattering is developed, with projected efficiency gains of two orders of magnitude over current state-of-the-art polarimeters. For energy analysis, the popular hemispherical analyzer is eschewed for a custom Time-of-Flight (TOF) analyzer offering an additional order of magnitude gain in efficiency. The combined instrument signifies the breakthrough needed to perform the high resolution SARPES experiments necessary for untangling the complex spin-dependent electronic structures central to today's condensed matter physics.

  2. Photoemission from optoelectronic materials and their nanostructures

    Ghatak, Kamakhya Prasad; Bhattacharya, Sitangshu

    2009-01-01

    This monograph investigates photoemission from optoelectronic materials and their nanostructures. It contains open-ended research problems which form an integral part of the text and are useful for graduate courses as well as aspiring Ph.D.'s and researchers..

  3. Inverse photoemission in strongly correlated electron systems

    Eder, R; Ohta, Y.

    1996-01-01

    Based on exact results for small clusters of t-J models, we point out the existence of several distinct channels in the inverse photoemission (IPSE) spectrum. Holelike quasiparticles can either be annihilated completely or leave behind a variable number of spin excitations, which formed the dressing

  4. On the core level shifts in semiconductors: A study of the electrostatic model

    A different electrostatic model is proposed for core level shift calculation in semiconductors on the basis of a critical analysis of so-called bond charge model by Bechstedt et al. The population of valence charge on anion and on cation is no longer a linear function of Phillips' ionicity, fsub(i), and a set of additive covalent radii is used instead of a non-additive one. A phenomenological expression is given for bond charge which decreases as ionicity, fsub(i), increases. The results are in agreement with experiments, and the reasons for errors are explained. (author)

  5. Surface and bulk 4f-photoemission spectra of CeIn3 and CeSn3

    Resonant photoemission spectroscopy was performed on CeIn3 and CeSn3 at the 4d-4f and 3d-4f core thresholds. Using the different surface sensitivity between the two photon energies, surface and bulk 4f-photoemission spectra were derived for both compounds. With the noncrossing approximation of the Anderson impurity model, the 4d-4f resonant spectra together with the surface and bulk spectra were self-consistently analyzed to obtain the microscopic parameters such as the 4f-electron energy and the hybridization strength with conduction electrons. The result shows a substantial difference in these parameters between the surface and the bulk, indicating that it is important to take into account the surface effect in analyzing photoemission spectra of Ce compounds. It is also found that the 4f surface core-level shift is different between CeIn3 and CeSn3. copyright 1997 The American Physical Society

  6. Raman scattering and photoemission from Bi clusters

    This paper reports on Raman scattering measurements of Bi clusters which formed on disordered C films at 110K exhibit a phase transformation from nanocrystalline rhombohedral structure to a suggested disordered phase. XPS measurements on this phase indicate core level shifts attributed to intrinsic, initial state effects on cluster electronic states

  7. Raising Photoemission Efficiency with Surface Acoustic Waves

    A. Afanasev, F. Hassani, C.E. Korman, V.G. Dudnikov, R.P. Johnson, M. Poelker, K.E.L. Surles-Law

    2012-07-01

    We are developing a novel technique that may help increase the efficiency and reduce costs of photoelectron sources used at electron accelerators. The technique is based on the use of Surface Acoustic Waves (SAW) in piezoelectric materials, such as GaAs, that are commonly used as photocathodes. Piezoelectric fields produced by the traveling SAW spatially separate electrons and holes, reducing their probability of recombination, thereby enhancing the photoemission quantum efficiency of the photocathode. Additional advantages could be increased polarization provided by the enhanced mobility of charge carriers that can be controlled by the SAW and the ionization of optically-generated excitons resulting in the creation of additional electron-hole pairs. It is expected that these novel features will reduce the cost of accelerator operation. A theoretical model for photoemission in the presence of SAW has been developed, and experimental tests of the technique are underway.

  8. UNITS IN $F_2D_{2p}$

    Kaur, Kuldeep; Khan, Manju

    2012-01-01

    Let $p$ be an odd prime, $D_{2p}$ be the dihedral group of order 2p, and $F_{2}$ be the finite field with two elements. If * denotes the canonical involution of the group algebra $F_2D_{2p}$, then bicyclic units are unitary units. In this note, we investigate the structure of the group $\\mathcal{B}(F_2D_{2p})$, generated by the bicyclic units of the group algebra $F_2D_{2p}$. Further, we obtain the structure of the unit group $\\mathcal{U}(F_2D_{2p})$ and the unitary subgroup $\\mathcal{U}_*(F_...

  9. Dimensionality of the electronic states in Nd0.45Sr0.55MnO3 studied by soft X-ray photoemission

    The electronic states of Nd0.45Sr0.55MnO3 in the two-dimensional metal phase have been revealed by the high-resolution Mn 2p-3d resonant photoemission. The vanishingly weak intensity at EF indicates an anomalous metal due to the two-dimensionality of the electronic states

  10. Soft X-ray photoemission spectroscopy

    The main motivation behind this thesis has been to determine both the advantages and the disadvantages of the soft X-ray application of angle-resolved photoemission spectroscopy. The investigation of a well known system, Ag(001), enables us to discuss several questions such as the role of the photon momentum, the applicability of the free-electron-like final state approximation and the role of phonons. The polarisation of the incoming light has also been exploited. The choice of such a system also comes from our desire to compare the results with calculations of angle-resolved photoemission spectra in this energy range. The anomalous low temperature properties of Ce-based compounds are generally related to the Kondo effect. Original results have been obtained by investigating the valence band of three iso-structural single crystalline Ce compounds, CeCu2Ge2, CeNi2Ge2 and CeCo2Ge2. The location of the Ce M5 absorption edge within the soft X-ray energy range is exploited in order to isolate the 4f contribution to the spectra. Added to this, the use of relatively high incoming photon energies allows minimising the surface contribution. Temperature dependent, resonant, angle-resolved and angle-integrated photoemission measurements have been performed. The former are in qualitative agreement with the single impurity Anderson model, whereas the latter suggest the importance of taking the lattice into account. (author)

  11. Surface atoms core-level shifts in single crystal GaAs surfaces: Interactions with trimethylaluminum and water prepared by atomic layer deposition

    The surface As/Ga atoms 3d core-level spectra of the atomically clean GaAs(1 1 1)A-2 × 2, GaAs(0 0 1)-2 × 4, and GaAs(0 0 1)-4 × 6 surfaces were firstly presented using high-resolution synchrotron radiation photoemission as a probe. The technique clearly explicates behaviors of the As atoms in different surface reconstruction. For GaAs(1 1 1)A-2 × 2, the surface As sits in the same plane as the Ga atoms. As to the GaAs(0 0 1)-2 × 4 surface, the As–As dimers dominate the surface layer, while for GaAs(001)-4 × 6, the As existed in two forms, the As in the As–Ga dimer and the 3-fold coordinated As. Next, we present a microscopic view of in situ atomic layer deposition (ALD) of Al2O3 on GaAs taking the two (0 0 1) surfaces as examples. The precursors were trimethylaluminum (TMA) and water. TMA could exist in either a chemisorbed or physisorbed form, depending on the charge environment of the associated surface atoms. The subsequent water purge resulted in both adsorbed forms being etched off or transformed the physisorbed TMA into the As-O-Al(CH3)2 configuration. We found that the ALD process rendered the precursors partially and selectively in forming bonds with the surface atoms without disturbing the atoms in the subsurface layer. Upon annealing, the interfacial bonding was dominated with the As-Al as well as Ga-O bonds.

  12. Solvothermal synthesis and magnetic properties of β-Co2P nanorods

    Li Tian; Liao Jun Peng; Wang Ying Feng

    2015-01-01

    Hexagonal high temperature phase β-Co2P nanorods with a diameter of around 50 nm were synthesized via a mild solvothermal route. The reaction was carried out at 180 °C using cobalt chloride hexahydrate (CoCl2 · 6H2O) as Co source and yellow phosphorous as P source. The composition, structure as well as morphology were characterized by X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS) and transmission electron microscopy (TEM). The magnetic susceptibility curve indicates that the...

  13. Optimized surface-slab excited-state muffin-tin potential and surface core level shifts

    An optimized muffin-tin (MT) potential for surface slabs with preassigned surface core-level shifts (SCLS's) is presented. By using the MT radii as adjustable parameters the model is able to conserve the definition of the SCLS with respect to the bulk and concurrently to generate a potential that is continuous at the MT radii. The model is conceived for elastic electron scattering in a surface slab with exchange-correlation interaction described by the local density approximation. The model employs two data bases for the self-energy of the signal electron (after Hedin and Lundqvist or Sernelius). The potential model is discussed in detail with two surface structures Be(101-bar0), for which SCLS's are available, and Cu(111)p(2x2)Cs, in which the close-packed radii of the atoms are extremely different. It is considered plausible that tensor LEED based on an optimized MT potential can be used for determining SCLS's

  14. Towards P2P XML Database Technology

    Zhang, Y.

    2007-01-01

    To ease the development of data-intensive P2P applications, we envision a P2P XML Database Management System (P2P XDBMS) that acts as a database middle-ware, providing a uniform database abstraction on top of a dynamic set of distributed data sources. In this PhD work, we research which features suc

  15. Bulk electronic structure of FeRh undergoing metamagnetic transition via hard x-ray photoemission

    Gray, Alexander; Cooke, David; Kruger, Peter; Bordel, Catherine; Fullerton, Eric; Ueda, Shigenori; Kobayashi, Keisuke; Hellman, Frances; Fadley, Charles

    2012-02-01

    In this study changes in the electronic structure accompanying a temperature-induced metamagnetic transition from anti-ferromagnetic to ferromagnetic order are investigated in strained epitaxial FeRh thin films via valence-band and core-level hard x-ray photoelectron spectroscopy with a photon energy of 6 keV. At such high photon energy, the resulting inelastic mean-free paths of the photoemitted electrons and therefore the average probing depths are on the order of 60 å, corresponding to about 20 unit cells and ensuring truly bulk-sensitive measurement. Clear differences between the AFM and FM states are observed across the entire valence-band spectrum and these are well reproduced using density functional theory. Changes in the Fe 2p core-levels of Fe are also observed and interpreted using Anderson impurity model calculations. These results suggest that significant electronic structure changes are involved in this AFM-FM transition.

  16. Highly resolved spatial and temporal photoemission analysis of integrated circuits

    We develop an optical system for highly resolved photoemission analysis of integrated circuits. Photons emitted by switching transistors allow the operation of an integrated circuit to be observed by recording the individual photoemission acts. The ongoing feature size reduction makes the space–time-resolved detection of these extremely weak photoemissions challenging. We combine different optical and photonic solutions to achieve both a high spatial and temporal resolution in a compact analysis system. Imaging and detection modules capture photons through the substrate during normal chip operation and perform highly resolved optical analysis. We demonstrate the system capability by photoemission records of a real-world IC device. (paper)

  17. Photoemission on Co and Cu quantum wires

    The coverage dependent electronic structure of Cu and Co on vicinal W(110) surfaces has been investigated with angle resolved photoelectron spectroscopy. To prepare the quasi-one-dimensional Cu and Co systems the method of step edge decoration of the vicinal W(110) surfaces has been used. The vicinal surfaces with step edges in (110), (100) and (111) direction has been investigated using LEED. From the characteristic spot splitting a terrace width of 11 atom rows was determined. The band structures of the flat and the vicinal surfaces have indicated that the step edges have no bearing on the bulk band structure at k parallel =0. But the surface band structure shows a different dispersion and different energy positions of surface states. An analysis of the W 4fτ/2 core level spectra has resulted in an additional contribution of the step edges in the spectra of the vicinal surfaces with a surface core level shift between 120 and 150 meV. A Cu and Co coverage dependent investigation of the core levels shows that there is no Co induced surface reconstruction and up to 0.15 monolayer no Cu induced surface reconstruction. In the range of 0.15 and 0.3 monolayer Cu the surface peak shifts to higher binding energies. This is probably a result of a surface reconstruction of the W substrate In the core level spectra with Co coverage the intensity of the surface peak decreases linear with Co coverage and the intensity of a new contribution, the interface structure, increases with Co coverage. With Co respectively Cu coverage the contribution of the step edge shifts to lower respectively higher binding energies. This can be attributed to a charge transfer between the adsorbat and the substrate in different directions. (orig.)

  18. Photoemission Fingerprints for Structural Identification of Titanium Dioxide Surfaces.

    Borghetti, Patrizia; Meriggio, Elisa; Rousse, Gwenaëlle; Cabailh, Gregory; Lazzari, Rémi; Jupille, Jacques

    2016-08-18

    The wealth of properties of titanium dioxide relies on its various polymorphs and on their mixtures coupled with a sensitivity to crystallographic orientations. It is therefore pivotal to set out methods that allow surface structural identification. We demonstrate herein the ability of photoemission spectroscopy to provide Ti LMV (V = valence) Auger templates to quantitatively analyze TiO2 polymorphs. The Ti LMV decay reflects Ti 4sp-O 2p hybridizations that are intrinsic properties of TiO2 phases and orientations. Ti LMV templates collected on rutile (110), anatase (101), and (100) single crystals allow for the quantitative analysis of mixed nanosized powders, which bridges the gap between surfaces of reference and complex materials. As a test bed, the anatase/rutile P25 is studied both as received and during the anatase-to-rutile transformation upon annealing. The agreement with X-ray diffraction measurements proves the reliability of the Auger analysis and highlights its ability to detect surface orientations. PMID:27453254

  19. Electronic structure and photoemission in plutonium chalcogenides

    Shick, Alexander; Havela, L.; Gouder, T.

    Warrendale, PA : Materials Research Society, 2008 - (Shuh, D.; Chung, B.; Albrecht-Schmitt, T.; Gouder, T.; Thompson, J.), s. 53-58 ISBN 978-1-60511-074-5. - (Materials Research Society Symposium Proceedings. NN. 1104). [Actinides 2008-Basic Science, Applications, and Technology. San Francisco (US), 24.03.2008-28.03.2008] R&D Projects: GA MŠk OC 144; GA ČR GA202/07/0644 Institutional research plan: CEZ:AV0Z10100520 Keywords : electronic sructure * photoemission * magnetism * strong electron correlations Subject RIV: BM - Solid Matter Physics ; Magnetism

  20. Towards P2P XML Database Technology

    Ying ZHANG

    2007-01-01

    To ease the development of data-intensive P2P applications, we envision a P2P XML Database Management System (P2P XDBMS) that acts as a database middle-ware, providing a uniform database abstraction on top of a dynamic set of distributed data sources. In this PhD work, we research which features such a database abstraction should offer and how it can be realised efficiently by extending and combining existing XML databases with P2P technologies. The first step in this research is a distribute...

  1. Core-Level Modeling and Frequency Prediction for DSP Applications on FPGAs

    Gongyu Wang

    2015-01-01

    Full Text Available Field-programmable gate arrays (FPGAs provide a promising technology that can improve performance of many high-performance computing and embedded applications. However, unlike software design tools, the relatively immature state of FPGA tools significantly limits productivity and consequently prevents widespread adoption of the technology. For example, the lengthy design-translate-execute (DTE process often must be iterated to meet the application requirements. Previous works have enabled model-based, design-space exploration to reduce DTE iterations but are limited by a lack of accurate model-based prediction of key design parameters, the most important of which is clock frequency. In this paper, we present a core-level modeling and design (CMD methodology that enables modeling of FPGA applications at an abstract level and yet produces accurate predictions of parameters such as clock frequency, resource utilization (i.e., area, and latency. We evaluate CMD’s prediction methods using several high-performance DSP applications on various families of FPGAs and show an average clock-frequency prediction error of 3.6%, with a worst-case error of 20.4%, compared to the best of existing high-level prediction methods, 13.9% average error with 48.2% worst-case error. We also demonstrate how such prediction enables accurate design-space exploration without coding in a hardware-description language (HDL, significantly reducing the total design time.

  2. Electronic structure and core-level spectra of light actinide dioxides in the dynamical mean-field theory

    Kolorenč, Jindřich; Shick, Alexander; Lichtenstein, A.I.

    2015-01-01

    Roč. 92, č. 8 (2015), "085125-1"-"085125-10". ISSN 1098-0121 R&D Projects: GA ČR GC15-05872J Institutional support: RVO:68378271 Keywords : electronic-structure calculations * dynamical mean-field theory * Mott insulators * actinides * oxides * photoemission Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.736, year: 2014

  3. Li induced effects in the core level and π-band electronic structure of graphene grown on C-face SiC

    Johansson, Leif I., E-mail: lij@ifm.liu.se; Xia, Chao; Virojanadara, Chariya [Department of Physics, Chemistry and Biology, Linköping University, SE-58183 Linköping (Sweden)

    2015-11-15

    Studies of the effects induced in the electronic structure after Li deposition, and subsequent heating, on graphene samples prepared on C-face SiC are reported. The as prepared graphene samples are essentially undoped, but after Li deposition, the Dirac point shifts down to 1.2 eV below the Fermi level due to electron doping. The shape of the C 1s level also indicates a doping concentration of around 10{sup 14 }cm{sup −2} after Li deposition, when compared with recent calculated results of core level spectra of graphene. The C 1s, Si 2p, and Li 1s core level results show little intercalation directly after deposition but that most of the Li has intercalated after heating at 280 °C. Heating at higher temperatures leads to desorption of Li from the sample, and at 1030 °C, Li can no longer be detected on the sample. The single π-band observable from multilayer C-face graphene samples in conventional angle resolved photoelectron spectroscopy is reasonably sharp both on the initially prepared sample and after Li deposition. After heating at 280 °C, the π-band appears more diffuse and possibly split. The Dirac point becomes located at 0.4 eV below the Fermi level, which indicates occurrence of a significant reduction in the electron doping concentration. Constant energy photoelectron distribution patterns extracted from the as prepared graphene C-face sample and also after Li deposition and heating at 280 °C look very similar to earlier calculated distribution patterns for monolayer graphene.

  4. Li induced effects in the core level and π-band electronic structure of graphene grown on C-face SiC

    Studies of the effects induced in the electronic structure after Li deposition, and subsequent heating, on graphene samples prepared on C-face SiC are reported. The as prepared graphene samples are essentially undoped, but after Li deposition, the Dirac point shifts down to 1.2 eV below the Fermi level due to electron doping. The shape of the C 1s level also indicates a doping concentration of around 1014 cm−2 after Li deposition, when compared with recent calculated results of core level spectra of graphene. The C 1s, Si 2p, and Li 1s core level results show little intercalation directly after deposition but that most of the Li has intercalated after heating at 280 °C. Heating at higher temperatures leads to desorption of Li from the sample, and at 1030 °C, Li can no longer be detected on the sample. The single π-band observable from multilayer C-face graphene samples in conventional angle resolved photoelectron spectroscopy is reasonably sharp both on the initially prepared sample and after Li deposition. After heating at 280 °C, the π-band appears more diffuse and possibly split. The Dirac point becomes located at 0.4 eV below the Fermi level, which indicates occurrence of a significant reduction in the electron doping concentration. Constant energy photoelectron distribution patterns extracted from the as prepared graphene C-face sample and also after Li deposition and heating at 280 °C look very similar to earlier calculated distribution patterns for monolayer graphene

  5. Photoemission from glass dust grains: First measurements

    Nouzak, Libor; Pechal, Radim; Pavlu, Jiri; Safrankova, Jana; Nemecek, Zdenek

    2014-05-01

    Dust grains are present in the interstellar space and also on surfaces of space objects like the Moon. The grains are charged by photoemission caused by solar UV radiation and by charged particles from the ambient plasma (solar wind, planetary magnetospheres). A balance of different charging processes on both sunlit and night sides of the Moon causes interesting phenomena as dust horizon glow, dust fountains, and dust levitation. To contribute to a better understanding of these processes, we present laboratory investigations that use a single SiO2 grain of micron size (an archetype of the lunar dust) caught in the electrodynamic trap. We irradiate it by HeI (21.2 eV) photons and electrons and discuss a contribution of these two processes to the grain charge. The grain specific charge is evaluated by an analysis of its motion and position in the trap. We compare equilibrium charge-to-mass ratios given by the electron emissions induced by electrons and by the UV photons from the HeI lamp. First measurements indicate that the resulting charge is about twice larger for photoemission than that caused by an electron impact.

  6. Interaction between adsorbed hydrogen and potassium on a carbon nanocone containing material as studied by photoemission

    Yu, Xiaofeng [Nesna University College, 8700 Nesna (Norway); Raaen, Steinar, E-mail: sraaen@ntnu.no [Physics Department, Norwegian University of Science and Technology, 7491 Trondheim (Norway)

    2015-09-14

    Hydrogen adsorption on a potassium doped carbon nanocone containing material was studied by photoelectron spectroscopy and work function measurement. The valence band spectra indicate that there is charge transfer from potassium to carbon. Upon deposition on carbon potassium is in its ionic state for lower doping and shows both ionic and metallic behavior at higher doping. Adsorption of hydrogen facilitates diffusion of potassium on the carbon material as seen by changes in the K{sub 2p} core level spectrum. Variations in the measured sample work function indicate that hydrogen initially adsorb on the K dopants and subsequently adsorb on the carbon cone containing material.

  7. Interaction between adsorbed hydrogen and potassium on a carbon nanocone containing material as studied by photoemission

    Hydrogen adsorption on a potassium doped carbon nanocone containing material was studied by photoelectron spectroscopy and work function measurement. The valence band spectra indicate that there is charge transfer from potassium to carbon. Upon deposition on carbon potassium is in its ionic state for lower doping and shows both ionic and metallic behavior at higher doping. Adsorption of hydrogen facilitates diffusion of potassium on the carbon material as seen by changes in the K2p core level spectrum. Variations in the measured sample work function indicate that hydrogen initially adsorb on the K dopants and subsequently adsorb on the carbon cone containing material

  8. Vacuum space charge effects in sub-picosecond soft X-ray photoemission on a molecular adsorbate layer

    M. Dell'Angela

    2015-03-01

    Full Text Available Vacuum space charge induced kinetic energy shifts of O 1s and Ru 3d core levels in femtosecond soft X-ray photoemission spectra (PES have been studied at a free electron laser (FEL for an oxygen layer on Ru(0001. We fully reproduced the measurements by simulating the in-vacuum expansion of the photoelectrons and demonstrate the space charge contribution of the high-order harmonics in the FEL beam. Employing the same analysis for 400 nm pump-X-ray probe PES, we can disentangle the delay dependent Ru 3d energy shifts into effects induced by space charge and by lattice heating from the femtosecond pump pulse.

  9. X-ray photoemission spectrum, electronic structure, and magnetism of UCu{sub x}Sb{sub 2}

    Samsel-Czekała, M., E-mail: M.Samsel@int.pan.wroc.pl [W. Trzebiatowski Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box 1410, 50-950 Wrocław 2 (Poland); Talik, E. [A. Chełkowski Institute of Physics, University of Silesia, Uniwersytecka 4, 40-007 Katowice (Poland); Winiarski, M.J.; Troć, R. [W. Trzebiatowski Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box 1410, 50-950 Wrocław 2 (Poland)

    2015-07-25

    Highlights: • Electronic structure of UCu{sub x}Sb{sub 2} probed by X-ray photoemission (XPS) and ab initio. • Good agreement between experimental and calculated (x = 0.75) XPS valence spectra. • Good accord between experimental and calculated ferromagnetic moments on U atoms. • Complex experimental core-level XPS spectrum with three: 1-, 3- and 7-eV satellites. • Concluded dual and mixed-valence configuration of U 5f states in UCu{sub 0.83}Sb{sub 2}. - Abstract: The room temperature valence and core-level X-ray photoemission spectra of an UCu{sub 0.83}Sb{sub 2} single crystal were measured using the Al Kα source. The related theoretical valence spectra were determined from densities of states for UCu{sub x}Sb{sub 2} systems obtained from our band structure calculations using the FLAPW method in the LDA + U approximation, as implemented in the Wien2k code, and the supercell approach to simulate a deficit of the Cu atoms. The calculated spectrum of the Cu-deficit UCu{sub 0.75}Sb{sub 2} is in good accord with the experimental one, revealing a complete localization of the Cu 3d electrons and a dual (both localized and itinerant) behavior as well as unusual spin-up polarization of the U 5f states near the Fermi level. Our calculated total magnetic moments on the uranium atom are in reasonable agreement with the experimental value of magnetization. Some localization and valence-mixing of the 5f-electrons are reflected by the triple-satellite (sats. 1-eV, 3-eV and 7-eV) structure, visible in the spectrum of the U 4f core-lines. Also the calculated Fermi surface of the stoichiometric system is complex, containing five spin-polarized sheets of different dimensionality with some nesting features.

  10. Photoemission resonance study of sintered and single-crystal Bi4Ca3Sr3Cu4O16+x

    Tang, Ming; Chang, Y.; Zanoni, R.; Onellion, M.; Joynt, Robert; Huber, D. L.; Margaritondo, G.; Morris, P. A.; Bonner, W. A.; Tarascon, J. M.; Stoffel, N. G.

    1989-02-01

    We present soft x-ray photoemission spectra that probe the valence and core electronic structure of the high-Tc superconductor Bi4Ca3Sr3Cu4O16+x. The identification of spectral features was helped by the observation of the resonant behavior of a Cu-related satellite feature. The resonance occurs at photon energies near the Cu3p optical absorption edge, and affects a peak 12.5 eV below the Fermi edge. We identified this feature as a correlation satellite characteristic of Cu in the 2+ valence state. Other features observed in the spectra more than 7 eV below the Fermi edge are due to several different core levels. In particular, we observed a strong Bi5d doublet. Other core level peaks are due to the Sr4p and Ca3p orbitals, and to Bi, Sr and Ca s-orbitals. Within 7 eV of the Fermi edge, the spectra are dominated by valence states. The most important feature is the Bi4Ca3Sr3Cu4O16+x Fermi edge itself, which we observed for the first time on this, and whose existence was subsequently confirmed by several other groups. On the contrary, no edge was observed in the photoemission spectra of materials in the YBa2Cu3O7-x family. The observation of the Fermi edge has important implications for the theoretical interpretation of high-Tc superconductivity. Furthermore, it enabled us to see near-edge changes associated with the superconducting transition.

  11. Angle-resolved photoemission studies of lattice polaron formation in the cuprate Ca2CuO2Cl2

    Shen, K.M.

    2010-05-03

    To elucidate the nature of the single-particle excitations in the undoped parent cuprates, we have performed a detailed study of Ca{sub 2}CuO{sub 2}Cl{sub 2} using photoemission spectroscopy. The photoemission lineshapes of the lower Hubbard band are found to be well-described by a polaron model. By comparing the lineshape and temperature dependence of the lower Hubbard band with additional O 2p and Ca 3p states, we conclude that the dominant broadening mechanism arises from the interaction between the photohole and the lattice. The strength of this interaction was observed to be strongly anisotropic and may have important implications for the momentum dependence of the first doped hole states.

  12. Propiedad Intelectual y Redes P2P

    ALCAINE SÁNCHEZ, JUAN FRANCISCO

    2015-01-01

    La meta de este documento no es otra que la de presentar al lector información acerca de la legislación sobre propiedad intelectual y distintos protocolos y software P2P. Primero se mostrará información sobre las principales leyes españolas en materia de propiedad intelectual. Posteriormente se presentará información acerca de los principales protocolos P2P sus clientes a lo largo de la historia de las redes P2P. Por último, se mostrarán las alternativas de pago a la descarga no lega...

  13. Resonant photoemission from SmS(100)

    A strong, sharp resonance enhancement of 4f photoemission has been observed on SmS(100) surfaces for photon energies in the region of the 4d-4f transitions at about 126 eV. The discrete final state reached via the excitation hν + 4d104f6 → 4d94f7 autoionizes primarily via a super Coster-Kronig transition of the type 4d94f7 → 4d104f5 + unbound electron. Other decay channels, e.g. Sm 5p emission, as well as a surface induce binding energy shift in the Sm3+ final state are identified and discussed. (author)

  14. Short pulse photoemission from a dispenser cathode

    Bergeret, H.; Boussoukaya, M.; Chehab, R.; Leblond, B.; Le Duff, J.

    1991-03-01

    Pulsed photoemission in the picosecond regime has been obtained from a standard thermionic dispenser cathode (WBaCa) at temperatures below the measurable thermoemission threshold. A picosecond Nd : YAG mode locked laser has been used at both green and UV light. Micropulse charges up to 0.5 nC have been measured on a wideband coaxial pickup located behind the anode. They correspond to an electron saturation limit from an approximately 20 mm 2 illuminated cathode area with a surface field of 3 MV/m. The effective cathode efficiency at small laser energies, defined as the number of electrons impinging on the coaxial pickup divided by the number of photons impinging on the cathode, is about 2 × 10 -5.

  15. Time-resolved photoemission using attosecond streaking

    Nagele, Stefan; Wais, Michael; Wachter, Georg; Burgdörfer, Joachim

    2014-01-01

    We theoretically study time-resolved photoemission in atoms as probed by attosecond streaking. We review recent advances in the study of the photoelectric effect in the time domain and show that the experimentally accessible time shifts can be decomposed into distinct contributions that stem from the field-free photoionization process itself and from probe-field induced corrections. We perform accurate quantum-mechanical as well as classical simulations of attosecond streaking for effective one-electron systems and determine all relevant contributions to the time delay with attosecond precision. In particular, we investigate the properties and limitations of attosecond streaking for the transition from short-ranged potentials (photodetachment) to long-ranged Coulomb potentials (photoionization). As an example for a more complex system, we study time-resolved photoionization for endohedral fullerenes $A$@$\\text{C}_{60}$ and discuss how streaking time shifts are modified due to the interaction of the $\\text{C}_...

  16. Efficient photoemission from robust ferroelectric ceramics

    Boscolo, I. [Milan Univ., Milan (Italy); Istituto Nazionale di Fisica Nucleare, Milan, (Italy); Castellano, M.; Catani, L.; Ferrario, M.; Tazzioli, F. [Istituto Nazionale di Fisica Nucleare, Frascati, RM (Italy); Giannessi, L. [ENEA, Frascati, Rome (Italy). Centro Ricerche Elettronica

    1999-07-01

    Experimental results on photoemission by ferroelectric ceramic disks, with a possible interpretation, are presented. Two types of lead zirconate titanate lanthanum doped, PLZT, ceramics have been used for tests. 25 ps light pulses of 532 and 355 nm were used for excitation. The intensity ranged within the interval 0.1-3 GW/cm{sup 2}. The upper limit of the intensity was established by the damage threshold tested by the onset of ion emission. At low value of the intensity the yield was comparable at the two wavelengths. At the highest intensity of green light the emitted charge was 1 nC per 10 mm{sup 2}, but it was limited by the space charge effect. In fact, the applied field was only 20 kV/cm, allowed both by the mechanical design of the apparatus and the poor vacuum, 10{sup -4} mbar. No surface processing was required. The measurement of the electron pulse length under way.

  17. Time delays in correlated photoemission processes

    Pazourek, R.; Nagele, S.; Burgdörfer, J.

    2015-09-01

    We theoretically study time-resolved two-photon double ionization (TPDI) of helium as probed by attosecond streaking. We review recent advances in the understanding of the photoelectric effect in the time domain and discuss the differences between one- and two-photon ionization, as well as one- and two-electron emission. We perform exact ab-initio simulations for attosecond streaking experiments in the sequential TPDI regime and compare the results to the two-electron Eisenbud-Wigner-Smith delay for the process. Our calculations directly show that the timing of the emission process sensitively depends on the energy sharing between the two outgoing electrons. In particular, we identify Fano-like interferences in the relative time delay of the two emitted electrons when the sequential ionization channel occurs via intermediate excited ionic (shake-up) states. Furthermore, we find that the photoemission time delays are only weakly dependent on the relative emission angle of the ejected electrons.

  18. Short pulse photoemission from a dispenser cathode

    Pulsed photoemission in picosecond regime has been obtained from a standard thermionic dispenser cathode (W - Ba - Ca) at temperatures below measurable thermoemission threshold. A picosecond Nd: YAG mode locked laser has been used at both green and U.V. light. Micro-pulse charges up to 0.5 nC have been measured on a wideband coaxial pick up located behind the anode. They correspond to an electron saturation limit from an approximately 20 mm2 illuminated cathode area with a surface field of 3 MV/m. The effective cathode efficiency at small laser energies, defined as the number of electron impinging the coaxial pick up divided by the number of photons impinging the cathode, is about 2.10-5

  19. Signature of quantum criticality in photoemission spectroscopy.

    Klein, M; Nuber, A; Reinert, F; Kroha, J; Stockert, O; van Löhneysen, H

    2008-12-31

    A quantum phase transition in a heavy-fermion compound may destroy the Fermi-liquid ground state. However, the conditions for this breakdown have remained obscure. We report the first direct investigation of heavy quasiparticle formation and breakdown in the canonical system CeCu(6-x)Au(x) by ultraviolet photoemission spectroscopy at elevated temperatures without the complications of lattice coherence. Surprisingly, the single-ion Kondo energy scale T(K) exhibits an abrupt step near the quantum critical Au concentration of x(c) = 0.1. We show theoretically that this step is expected from a highly nonlinear renormalization of the local spin coupling at each Ce site, induced by spin fluctuations on neighboring sites. It provides a general high-temperature indicator for heavy-fermion quasiparticle breakdown at a quantum phase transition. PMID:19437657

  20. High- Tc superconductivity: new issues from photoemission data

    Margaritondo, G.; Grioni, M.; Vobornik, I.; Pavuna, D.

    2001-11-01

    Recent high-resolution photoemission results on high- Tc superconductors and other low-dimensional systems solve some critical issues but also open new fundamental questions. A recent breakthrough enabled us to clarify the interplay of conflicting periodicities in photoemission data, thus legitimizing the photoemission analysis of crystals with super-periodicities. On the other hand, results on the role of doping and of intentional disorder in Bi 2Sr 2CaCu 2O 8+ x single crystals raise questions about the origin of the pseudogap.

  1. Surface Optimization of RBa2Cu3O7-δ (R=Y, Nd) Epitaxial High Tc Films for In Situ Photoemission Studies

    Abrecht, M.; Schmauder, T.; Ariosa, D.; Touzelet, O.; Rast, S.; Onellion, M.; Pavuna, D.

    One of the intrinsic difficulties for in situ photoemission studies of high Tc oxide films is the surface volatility, especially the oxygen loss. In order to solve this problem, we have constructed a dedicated system for high Tc film surface studies, in particular for ARPES measurements. Here we briefly describe our pulsed laser deposition (PLD) system that is linked to the photoemission chamber at the Synchrotron Radiation Center (SRC) in Wisconsin, and discuss crystallographic and electronic properties measured on epitaxial YBa2Cu3O7-δ (YBCO) and NdBa2Cu3O7-δ (NBCO) films. Resistivity and XRD studies show that the best c axis epitaxial films, with Tc (onset)=92 K (Tc0=90.5 K), are monophase and single crystalline with crystal coherence up to almost 1 µm. Initial core level photoemission study indicates that, for YBCO on SrTiO3 (without any buffer layer), the Ba oxide layer tends to be the dominant surface layer. Further experiments are underway to reproducibly detect sharp Fermi edge and perform ARPES study on optimally doped film surfaces.

  2. Photoemission and inverse photoemission study of the electronic structure of C60 fullerenes encapsulated in single-walled carbon nanotubes

    Shiozawa, Hidetsugu; Ishii, Hiroyoshi; Kihara, Hideo; Sasaki, Naoya; Nakamura, Satoshi; Yoshida, Tetsuo; Takayama, Yasuhiro; Miyahara, Tsuneaki; Suzuki, Shinzo; Achiba, Yohji; Kodama, Takeshi; Higashiguchi, Mitsuharu; Chi, Xiaoyu; Nakatake, Masashi; Shimada, Kenya

    2006-01-01

    We have measured the valence-band photoemission and inverse photoemission spectra of single-walled carbon nanotubes (SWNTs) with mean radii of 0.7 and 0.64 nm encapsulating C60 fullerenes (peas), so-called "peapods." The photoemission spectrum of the C60 peas in the SWNTs is obtained by subtracting the spectrum of empty SWNTs from the spectrum of the peapod. The structures in the C60 pea spectra correspond well to those in the spectrum of a C60 face-centered-cubic solid. No structure is obser...

  3. Photoemission measurements for low energy x-ray detector applications

    Photoemission has been studied for nearly 100 years as both a means of investigating quantum physics, and as a practical technique for transducing optical/x-ray photons into electrical currents. Numerous x-ray detection schemes, such as streak cameras and x-ray sensitive diodes, exploit this process because of its simplicity, adaptability, and speed. Recent emphasis on diagnostics for low temperature, high density, and short-lived, plasmas for inertial confinement fusion has stimulated interest in x-ray photoemission in the sub-kilovolt regime. In this paper, a review of x-ray photoemission measurements in the 50 eV to 10 keV x-ray region is given and the experimental techniques are reviewed. A semiempirical model of x-ray photoemission is discussed and compared to experimental measurements. Finally, examples of absolutely calibrated instruments are shown

  4. Effects of non-local exchange on core level shifts for gas-phase and adsorbed molecules

    Density functional theory calculations are often used to interpret experimental shifts in core level binding energies. Calculations based on gradient-corrected (GC) exchange-correlation functionals are known to reproduce measured core level shifts (CLS) of isolated molecules and metal surfaces with reasonable accuracy. In the present study, we discuss a series of examples where the shifts calculated within a GC-functional significantly deviate from the experimental values, namely the CLS of C 1s in ethyl trifluoroacetate, Pd 3d in PdO and the O 1s shift for CO adsorbed on PdO(101). The deviations are traced to effects of the electronic self-interaction error with GC-functionals and substantially better agreements between calculated and measured CLS are obtained when a fraction of exact exchange is used in the exchange-correlation functional

  5. Uncertainties of the neutronic calculations at core level determined by the KARATE code system and the KIKO3D code

    In this paper the uncertainties of the neutronic calculations at core level - originating from the uncertainties of the basic nuclear data - are presented. The investigations have been made for a VVER-1000 core (Kozloduy-6) defined in the frame of the OECD NEA UAM benchmark. In the first part of the paper, the uncertainties of the effective multiplication factor, the assembly-wise radial power distribution, the axial power distribution and the rod worth are shown. After that the preliminary evaluation of the uncertainties of the neutron kinetic calculations are presented for a rod movement transient at HZP (Hot Zero Power) state, where the uncertainties of the time dependent core and assembly powers and the dynamic reactivity were evaluated. In both cases, we will see that the most important quantities - at core level and at HZP state - have a considerable uncertainty which is originating from the uncertainties of the basic cross section library in these investigations. (orig.)

  6. Theoretical predictions of the impact of nuclear dynamics and environment on core-level spectra of organic molecules

    Prendergast, David; Schwartz, Craig; Uejio, Janel; Saykally, Richard

    2009-03-01

    Core-level spectroscopy provides an element-specific probe of local electronic structure and bonding, but linking details of atomic structure to measured spectra relies heavily on accurate theoretical interpretation. We present first principles simulations of the x-ray absorption of a range of organic molecules both in isolation and aqueous solvation, highlighting the spectral impact of internal nuclear motion as well as solvent interactions. Our approach uses density functional theory with explicit inclusion of the core-level excited state within a plane-wave supercell framework. Nuclear degrees of freedom are sampled using various molecular dynamics techniques. We indicate specific cases for molecules in their vibrational ground state at experimental conditions, where nuclear quantum effects must be included. Prepared by LBNL under Contract DE-AC02-05CH11231.

  7. Uncertainties of the neutronic calculations at core level determined by the KARATE code system and the KIKO3D code

    Panka, Istvan; Kereszturi, Andras [Hungarian Academy of Sciences, Budapest (Hungary). Reactor Analysis Dept.

    2013-09-15

    In this paper the uncertainties of the neutronic calculations at core level - originating from the uncertainties of the basic nuclear data - are presented. The investigations have been made for a VVER-1000 core (Kozloduy-6) defined in the frame of the OECD NEA UAM benchmark. In the first part of the paper, the uncertainties of the effective multiplication factor, the assembly-wise radial power distribution, the axial power distribution and the rod worth are shown. After that the preliminary evaluation of the uncertainties of the neutron kinetic calculations are presented for a rod movement transient at HZP (Hot Zero Power) state, where the uncertainties of the time dependent core and assembly powers and the dynamic reactivity were evaluated. In both cases, we will see that the most important quantities - at core level and at HZP state - have a considerable uncertainty which is originating from the uncertainties of the basic cross section library in these investigations. (orig.)

  8. P2P Techniques for Decentralized Applications

    Pacitti, Esther

    2012-01-01

    As an alternative to traditional client-server systems, Peer-to-Peer (P2P) systems provide major advantages in terms of scalability, autonomy and dynamic behavior of peers, and decentralization of control. Thus, they are well suited for large-scale data sharing in distributed environments. Most of the existing P2P approaches for data sharing rely on either structured networks (e.g., DHTs) for efficient indexing, or unstructured networks for ease of deployment, or some combination. However, these approaches have some limitations, such as lack of freedom for data placement in DHTs, and high late

  9. P2P Live Video Streaming

    Chatzidrossos, Ilias

    2010-01-01

    The ever increasing demand for video content directed the focus of researchfrom traditional server-based schemes to peer-to-peer systems for videodelivery. In such systems, video data is delivered to the users by utilizing theresources of the users themselves, leading to a potentially scalable solution.Users connect to each other, forming a p2p overlay network on top of theInternet and exchange the video segments among themselves. The performanceof a p2p system is characterized by its capabil...

  10. Internal Photoemission Spectroscopy of 2-D Materials

    Nguyen, Nhan; Li, Mingda; Vishwanath, Suresh; Yan, Rusen; Xiao, Shudong; Xing, Huili; Cheng, Guangjun; Hight Walker, Angela; Zhang, Qin

    Recent research has shown the great benefits of using 2-D materials in the tunnel field-effect transistor (TFET), which is considered a promising candidate for the beyond-CMOS technology. The on-state current of TFET can be enhanced by engineering the band alignment of different 2D-2D or 2D-3D heterostructures. Here we present the internal photoemission spectroscopy (IPE) approach to determine the band alignments of various 2-D materials, in particular SnSe2 and WSe2, which have been proposed for new TFET designs. The metal-oxide-2-D semiconductor test structures are fabricated and characterized by IPE, where the band offsets from the 2-D semiconductor to the oxide conduction band minimum are determined by the threshold of the cube root of IPE yields as a function of photon energy. In particular, we find that SnSe2 has a larger electron affinity than most semiconductors and can be combined with other semiconductors to form near broken-gap heterojunctions with low barrier heights which can produce a higher on-state current. The details of data analysis of IPE and the results from Raman spectroscopy and spectroscopic ellipsometry measurements will also be presented and discussed.

  11. Recoil and related effects in molecular photoemission

    Highlights: ► We present a overview of recoil-related effects for general audience of experimentalists working in the field of photoelectron spectroscopy. ► Photoelectron recoil is shown to alter vibrational structure. ► Photoelectron rotational recoil is shown to induce line shifts and broadenings. ► Interference and scattering of the outgoing photoelectron wave(s) are shown to introduce oscillations of branching ratios in molecular photoelectron spectra. -- Abstract: Photoemission from free molecules in the gas phase results in a complex spectral structure of electronic, vibrational and rotational transitions. In this review, the effects that can alter this structure and particularly the branching ratios in photoelectron spectra at the kinetic energies well above the ionization thresholds are considered. Simplified models that have nevertheless been found to describe the observations well are presented for photoelectron vibrational and rotational recoil, rotational Doppler broadening, photoelectron scattering and Cohen–Fano type interference phenomena. Experimental examples are shown together with the models. Some future developments and applications of the recoil-related phenomena are briefly considered.

  12. Recoil and related effects in molecular photoemission

    Kukk, E., E-mail: edwin.kukk@utu.fi [Dept. of Physics and Astronomy, University of Turku, FIN-20014 Turku (Finland); Ueda, K. [Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577 (Japan); Miron, C. [Synchrotron SOLEIL, L' Orme des Merisiers, Saint-Aubin, BP 48, FR-91192 Gif-sur-Yvette Cedex (France)

    2012-09-15

    Highlights: Black-Right-Pointing-Pointer We present a overview of recoil-related effects for general audience of experimentalists working in the field of photoelectron spectroscopy. Black-Right-Pointing-Pointer Photoelectron recoil is shown to alter vibrational structure. Black-Right-Pointing-Pointer Photoelectron rotational recoil is shown to induce line shifts and broadenings. Black-Right-Pointing-Pointer Interference and scattering of the outgoing photoelectron wave(s) are shown to introduce oscillations of branching ratios in molecular photoelectron spectra. -- Abstract: Photoemission from free molecules in the gas phase results in a complex spectral structure of electronic, vibrational and rotational transitions. In this review, the effects that can alter this structure and particularly the branching ratios in photoelectron spectra at the kinetic energies well above the ionization thresholds are considered. Simplified models that have nevertheless been found to describe the observations well are presented for photoelectron vibrational and rotational recoil, rotational Doppler broadening, photoelectron scattering and Cohen-Fano type interference phenomena. Experimental examples are shown together with the models. Some future developments and applications of the recoil-related phenomena are briefly considered.

  13. 5-Pentadecyl-2-((p-tolyliminomethylphenol

    Amorn Petsom

    2013-07-01

    Full Text Available 5-Pentadecyl-2-((p-tolyliminomethylphenol has been synthesized by reaction of 2-hydroxy-4-pentadecylbenzaldehyde with 4-amino-1-methyl-aniline in 1,4-dioxane under reflux. The structure of the synthesized compound was assigned on the basis of elemental analysis, UV, IR, 1H-NMR, 13C-NMR and mass spectral data.

  14. Electronic Structure Changes across the Metamagnetic Transition in FeRh via Hard X-Ray Photoemission

    Gray, A. X.; Cooke, D. W.; Krüger, P.; Bordel, C.; Kaiser, A. M.; Moyerman, S.; Fullerton, E. E.; Ueda, S.; Yamashita, Y.; Gloskovskii, A.; Schneider, C. M.; Drube, W.; Kobayashi, K.; Hellman, F.; Fadley, C. S.

    2012-06-01

    Stoichiometric FeRh undergoes a temperature-induced antiferromagnetic (AFM) to ferromagnetic (FM) transition at ˜350K. In this Letter, changes in the electronic structure accompanying this transition are investigated in epitaxial FeRh thin films via bulk-sensitive valence-band and core-level hard x-ray photoelectron spectroscopy with a photon energy of 5.95 keV. Clear differences between the AFM and FM states are observed across the entire valence-band spectrum and these are well reproduced using density-functional theory. Changes in the 2p core levels of Fe are also observed and interpreted using Anderson impurity model calculations. These results indicate that significant electronic structure changes over the entire valence-band region are involved in this AFM-FM transition.

  15. Superconductivity and x-ray photoemission study of MgB2 thin films

    王淑芳; 周岳亮; 朱亚彬; 张芹; 谢侃; 陈正豪; 吕惠宾; 杨国桢

    2002-01-01

    Highly c-axis oriented MgB2 thin films with Tconset of 39.6K were fabricated by magnesium diffusing into pulsed-laser-deposited boron precursors. The estimation of critical current density Jc, using hysteresis loops and the Bean model, has given the value of 107A/cm2 (15K, 0T), which is one of the highest values ever reported. The x-ray photoemission study of the MgB2 thin films has revealed that the binding energies of Mg 2p and B 1s are at 49.4eV and 186.9eV, which are close to those of metallic Mg and transition-metal diborides, respectively.

  16. Mobile P2P Fast Similarity Search

    Bocek, T; Hecht, F. V.; Hausheer, D; Hunt, E; Stiller, B.

    2009-01-01

    In informal data sharing environments, misspellings cause problems for data indexing and retrieval. This is even more pronounced in mobile environments, in which devices with limited input devices are used. In a mobile environment, similarity search algorithms for finding misspelled data need to account for limited CPU and bandwidth. This demo shows P2P fast similarity search (P2PFastSS) running on mobile phones and laptops that is tailored to uncertain data entry and use...

  17. Spectroscopic imaging, diffraction, and holography with x-ray photoemission

    X-ray probes are capable of determining the spatial structure of an atom in a specific chemical state, over length scales from about a micron all the way down to atomic resolution. Examples of these probes include photoemission microscopy, energy-dependent photoemission diffraction, photoelectron holography, and X-ray absorption microspectroscopy. Although the method of image formation, chemical-state sensitivity, and length scales can be very different, these X-ray techniques share a common goal of combining a capability for structure determination with chemical-state specificity. This workshop will address recent advances in holographic, diffraction, and direct imaging techniques using X-ray photoemission on both theoretical and experimental fronts. A particular emphasis will be on novel structure determinations with atomic resolution using photoelectrons

  18. Phonon effects on X-ray absorption and X-ray photoemission spectra

    Highlights: • Some important phonon effects observed in X-ray absorption and X-ray photoemission spectra are discussed on the basis of nonequilibrium Green's function theory. • For the pre-edge structures, the intensity associated with forbidden electric dipole transition is sensitive to temperature compared with allowed electric quadrupole transition. • We also discuss the FC and their interference, which have negligible contribution to pre-edge intensity and energy shift. • The quasi-particle energy is also influenced by the core displacement which can be responsible for the peak shift of the pre-edges. • We also discuss the photoelectron angular distribution caused by the thermal atomic vibration. - Abstract: Some important phonon effects observed in X-ray absorption and X-ray photoemission spectra are discussed on the basis of nonequilibrium Green's function theory. This theoretical framework allows us to incorporate phonon effects, such as Debye–Waller (DW) factors, Franck–Condon (FC) factors and electron–phonon interactions in a natural way. In the case of core level excitations, we can take into account the core–hole effects in lesser Green's function g< and photoelectron propagation in greater Green's function g>. For the core–hole propagation we derive some formulas to describe the thermally displaced core functions: we have p components even for deep core s orbital due to the thermal motion. We should notice that the thermal fluctuation is quite small but it is already in the order of the spread of the core functions. Applying Mermin's theorem, we can calculate the thermal average of the hole propagator g<: here an important ingredient is the Debye–Waller factor used in X-ray and neutron diffraction. For the pre-edge structures, the intensity associated with forbidden electric dipole transition is sensitive to the temperature compared with allowed electric quadrupole transition. We also discuss the FC and

  19. Continuous-time core-level photon-stimulated desorption spectroscopy for monitoring soft x-ray-induced reactions of molecules adsorbed on a single-crystal surface

    Continuous-time core-level photon-stimulated desorption (PSD) spectroscopy was proposed for monitoring the soft x-ray-induced reactions of molecules adsorbed on a single-crystal surface. Monochromatic synchrotron radiation was used as a soft x-ray light source in the photon-induced reactions of CF3Cl adsorbed on a Si(111)-7x7 surface at 30 K and also as a probe for studying the produced fluorination states of the bonding surface Si atom in the positive-ion PSD spectroscopy. The F+ PSD spectrum was obtained by monitoring the F+ signal as a function of incident photon energy near the Si(2p) edge (98-110 eV). Sequential F+ PSD spectra were measured as a function of photon exposure at four adsorbate coverages (the first dose=0.3x1015 molecules/cm2, the second dose=0.8x1015 molecules/cm2, the third dose=2.2x1015 molecules/cm2, and the fourth dose=3.2x1015 molecules/cm2). For the first and second CF3Cl-dosed surfaces, the sequential F+ PSD spectra show the variation of their shapes with photon exposure and indicate the formation of surface SiF species. The sequential F+ PSD spectra for the third and fourth CF3Cl-dosed surfaces also show the variation of their shapes with photon exposure and depict the production of surface SiF and SiF3 species

  20. MINERVA: Collaborative P2P Search (Demo)

    Bender, Matthias; Michel, Sebastian; Triantafillou, Peter; Weikum, Gerhard; Zimmer, Christian; Böhm, Klemens; Jensen, Christian S.; Haas, Laura M.; Kersten, Martin L.; Larson, Per-Ake; Ooi, Beng Chin

    2005-01-01

    This paper proposes the live demonstration of a prototype of MINERVA, a novel P2P Web search engine. The search engine is layered on top of a DHT-based overlay network that connects an a-priori unlimited number of peers, each of which maintains a personal local database and a local search facility. Each peer posts a small amount of metadata to a physically distributed directory that is used to efficiently select promising peers from across the peer population that ca...

  1. Fullerene photoemission time delay explores molecular cavity in attoseconds

    Magrakvelidze, Maia; Dixit, Gopal; Madjet, Mohamed El-Amine; Chakraborty, Himadri S

    2014-01-01

    Time-resolved photoelectron spectroscopy can probe interference oscillations in C60 valence emissions that produce series of minima whose energy separation depends on the molecular size. We show that the quantum phase associated with these minima exhibits rapid variations due to electron correlations, causing rich structures in the photoemission time delay. These findings provide a way to utilize temporal information to access the fullerene cavity size, that is making the time to "see" the space, and can be generalized to photoemissions from clusters and nanostructures.

  2. Electronic band structure and photoemission: A review and projection

    A brief review of electronic-structure calculations in solids, as a means of interpreting photoemission spectra, is presented. The calculations are, in general, of three types: ordinary one-electron-like band structures, which apply to bulk solids and are the basis of all other calculations; surface modified calculations, which take into account, self-consistently if at all possible, the presence of a vacuum-solid interface and of the electronic modifications caused thereby; and many-body calculations, which go beyond average-field approximations and consider dynamic rearrangement effects caused by electron-electron correlations during the photoemission process. 44 refs

  3. Einstein's Photoemission from Quantum Confined Superlattices.

    Debbarma, S; Ghatak, K P

    2016-01-01

    This paper is dedicated to the 83th Birthday of Late Professor B. R. Nag, D.Sc., formerly Head of the Departments of Radio Physics and Electronics and Electronic Science of the University of Calcutta, a firm believer of the concept of theoretical minimum of Landau and an internationally well known semiconductor physicist, to whom the second author remains ever grateful as a student and research worker from 1974-2004. In this paper, an attempt is made to study, the Einstein's photoemission (EP) from III-V, II-VI, IV-VI, HgTe/CdTe and strained layer quantum well heavily doped superlattices (QWHDSLs) with graded interfaces in the presence of quantizing magnetic field on the basis of newly formulated electron dispersion relations within the frame work of k · p formalism. The EP from III-V, II-VI, IV-VI, HgTe/CdTe and strained layer quantum wells of heavily doped effective mass superlattices respectively has been presented under magnetic quantization. Besides the said emissions, from the quantum dots of the aforementioned heavily doped SLs have further investigated for the purpose of comparison and complete investigation in the context of EP from quantum confined superlattices. Using appropriate SLs, it appears that the EP increases with increasing surface electron concentration and decreasing film thickness in spiky manners, which are the characteristic features of such quantized hetero structures. Under magnetic quantization, the EP oscillates with inverse quantizing magnetic field due to Shuvnikov-de Haas effect. The EP increases with increasing photo energy in a step-like manner and the numerical values of EP with all the physical variables are totally band structure dependent for all the cases. The most striking features are that the presence of poles in the dispersion relation of the materials in the absence of band tails create the complex energy spectra in the corresponding HD constituent materials of such quantum confined superlattices and effective electron

  4. Electronic states of BP, BP +, BP -, B 2P 2, B2P2- and B2P2+

    Linguerri, Roberto; Komiha, Najia; Oswald, Rainer; Mitrushchenkov, Alexander; Rosmus, Pavel

    2008-05-01

    Using augmented sextuple zeta basis sets and internally contracted multireference configuration interaction (MRCI) wavefunctions, potential energy, electric dipole and transition moments have been computed for the X 3Π, a 1Σ +, b 1Π and A 3Σ - states of BP, X 2Σ + and A 2Π states of BP - and X 4Σ - and A 4Π states of BP +. From these data spectroscopic constants, radiative transition probabilities and photoelectron spectra of BP - and BP have been evaluated. The non-vanishing spin-orbit coupling elements between the four low lying triplet and singlet states of the neutral BP have also been calculated from MRCI wavefunctions. The treatment of the corresponding perturbations in the manifold of dense rovibrational states in the three lowest states would require a precise knowledge of the electronic excitation energies. Our best singlet-triplet separations (X-a) are calculated to be 2412 cm -1 (MRCI) and 2482 cm -1 (restricted coupled cluster with perturbative triples (RCCSD(T))) with an estimated error bound of about ±200 cm -1. All three states have long radiative lifetimes with cascading among the rovibrational levels of different states. The ionization energy IE e of BP is calculated to be 9.22 eV (MRCI) and 9.48 eV (RCCSD(T)), the electron affinity EA e 2.51 eV (MRCI) and 2.74 eV (RCCSD(T)). The photoelectron spectra of BP and BP - have been obtained from the Franck-Condon factors of the MRCI potentials. For the UV spectroscopy the dipole allowed radiative transition probabilities are given for A 3Σ - ↔ X 3Π, b 1Π ↔ a 1Σ + of BP, A 2Π ↔ X 2Σ + of BP - and A 4Π ↔ X 4Σ - of BP +. The ionization energy IE e of B 2P 2 of 8.71 eV and the electron affinity EA e of 2.34 eV have been calculated by the RCCSD(T)/aVQZ approach. Also the harmonic vibrational wavenumbers for the electronic ground states of the ions B2P2+ and B2P2- are given.

  5. Exploring the Electronic Structure and Chemical Homogeneity of Individual Bi2Te3 Nanowires by Nano-Angle-Resolved Photoemission Spectroscopy.

    Krieg, Janina; Chen, Chaoyu; Avila, José; Zhang, Zeying; Sigle, Wilfried; Zhang, Hongbin; Trautmann, Christina; Asensio, Maria Carmen; Toimil-Molares, Maria Eugenia

    2016-07-13

    Due to their high surface-to-volume ratio, cylindrical Bi2Te3 nanowires are employed as model systems to investigate the chemistry and the unique conductive surface states of topological insulator nanomaterials. We report on nanoangle-resolved photoemission spectroscopy (nano-ARPES) characterization of individual cylindrical Bi2Te3 nanowires with a diameter of 100 nm. The nanowires are synthesized by electrochemical deposition inside channels of ion-track etched polymer membranes. Core level spectra recorded with submicron resolution indicate a homogeneous chemical composition along individual nanowires, while nano-ARPES intensity maps reveal the valence band structure at the single nanowire level. First-principles electronic structure calculations for chosen crystallographic orientations are in good agreement with those revealed by nano-ARPES. The successful application of nano-ARPES on single one-dimensional nanostructures constitutes a new avenue to achieve a better understanding of the electronic structure of topological insulator nanomaterials. PMID:27311702

  6. Electronic structure of elemental curium studied by photoemission

    Gouder, T.; van der Laan, G.; Shick, Alexander; Haire, R.G.; Caciuffo, R.

    2011-01-01

    Roč. 83, č. 12 (2011), "125111-1"-"125111-6". ISSN 1098-0121 R&D Projects: GA ČR(CZ) GAP204/10/0330 Institutional research plan: CEZ:AV0Z10100520 Keywords : photoemission * actinides Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.691, year: 2011

  7. Relativistic calculations of angular dependent photoemission time delay

    Kheifets, A S; Deshmukh, P C; Dolmatov, V K; Manson, S T

    2016-01-01

    Angular dependence of photoemission time delay for the valence $np_{3/2}$ and $np_{1/2}$ subshells of Ar, Kr and Xe is studied in the dipole relativistic random phase approximation. Strong angular anisotropy of the time delay is reproduced near respective Cooper minima while the spin-orbit splitting affects the time delay near threshold.

  8. Practical Photoemission Characterization Of Molecular Films And Related Interfaces

    Even though the term ‘organic electronics’ evokes rather organic devices, a significant part of its scope deals with physical properties of ‘active elements’ such as organic films and interfaces. Examination of the film growth and the evolution of the interface formation are particularly needful for the understanding a mechanism controlling their final properties. Performing such experiments in an ultra-high vacuum allows both to ‘stretch’ the time scale for pseudo real-time observations and to control properties of the probed systems on the atomic level. Photoemission technique probes directly electronic and chemical structure and it has thereby established among major tools employed in the field.This review primarily focuses to electronic properties of oligomeric molecular films and their interfaces examined by photoemission. Yet, it does not aspire after a complete overview on the topic; it rather aims to otherwise standard issues encountered at the photoemission characterization and analysis of the organic materials, though requiring to consider particularities of molecular films in terms of the growth, electronic properties, and their characterization and analysis. In particular, the fundamental electronic parameters of molecular films such as the work function, the ionization energy, and the interfacial energy level alignment, and their interplay, will be pursued with considering often neglected influence of the molecular orientation. Further, the implication on the band bending in molecular films based on photoemission characterization, and a model on the driving mechanism for the interfacial energy level alignment will be addressed. (author)

  9. Investigating crystalline-polarity-dependent electronic structures of GaN by hard x-ray photoemission and ab-initio calculations

    Ohsawa, Takeo; Ueda, Shigenori; Suzuki, Motohiro; Tateyama, Yoshitaka; Williams, Jesse R.; Ohashi, Naoki

    2015-10-01

    Crystalline-polarity-dependent electronic structures of gallium nitride (GaN) were studied by photoemission spectroscopy (PES) using soft and hard x-rays with different linear polarizations. A peak located near the valence band (VB) maximum was enhanced for a (0001) surface compared with that for a ( 000 1 ¯ ) surface regardless of photon energy. Comparison of the VB density of states obtained by ab-initio calculations with the observed VB-PES spectra indicates that the crystalline-polarity dependence is associated with the Ga 4p and N 2p states. The most plausible origin of the crystalline-polarity-dependent VB feature is based on the photoemission phenomena of electrons in the pz-orbitals due to spontaneous electric polarization along the c-axis of GaN.

  10. Real-time TDDFT simulations of time-resolved core-level spectroscopies in solid state systems

    Pemmaraju, Sri Chaitanya Das; Prendergast, David; Theory of Nanostructured Materials Facility Team

    The advent of sub-femtosecond time-resolved core-level spectroscopies based on high harmonic generated XUV pulses has enabled the study of electron dyanamics on characteristic femtosecond time-scales. Unambiguous interpretation of these powerful yet complex spectroscopies however requires the development of theoretical algorithms capable of modeling light-matter interaction across a wide energy range spanning both valence and core orbitals. In this context we present a recent implementation of the velocity-gauge formalism of real-time TDDFT within a linear combination of atomic orbital (LCAO) framework, which facilitates efficient numerical treatment of localized semi-core orbitals. Dynamics and spectra obtained from LCAO based simulations are compared to those from a real-space grid implementation. Potential applications are also illustrated by applying the method towards interpreting recent atto-second time-resolved IR-pump XUV-probe spectroscopies investigating sub-cycle excitation dynamics in bulk silicon.

  11. Magnetic dichroism in angle-resolved hard x-ray photoemission from buried layers

    Kozina, Xeniya; Fecher, Gerhard H.; Stryganyuk, Gregory; Ouardi, Siham; Balke, Benjamin; Felser, Claudia; Schönhense, Gerd; Ikenaga, Eiji; Sugiyama, Takeharu; Kawamura, Naomi; Suzuki, Motohiro; Taira, Tomoyuki; Uemura, Tetsuya; Yamamoto, Masafumi; Sukegawa, Hiroaki; Wang, Wenhong; Inomata, Koichiro; Kobayashi, Keisuke

    2011-08-01

    This work reports the measurement of magnetic dichroism in angular-resolved photoemission from in-plane magnetized buried thin films. The high bulk sensitivity of hard x-ray photoelectron spectroscopy (HAXPES) in combination with circularly polarized radiation enables the investigation of the magnetic properties of buried layers. HAXPES experiments with an excitation energy of 8 keV were performed on exchange-biased magnetic layers covered by thin oxide films. Two types of structures were investigated with the IrMn exchange-biasing layer either above or below the ferromagnetic layer: one with a CoFe layer on top and another with a Co2FeAl layer buried beneath the IrMn layer. A pronounced magnetic dichroism is found in the Co and Fe 2p states of both materials. The localization of the magnetic moments at the Fe site conditioning the peculiar characteristics of the Co2FeAl Heusler compound, predicted to be a half-metallic ferromagnet, is revealed from the magnetic dichroism detected in the Fe 2p states.

  12. STM of photoemission studies of Au and Pd on TiO2

    This thesis presents the first scanning tunnelling microscopy (STM) images of metals dispersed on metal oxide supports recorded at high temperatures. Thermal deposition in ultra-high vacuum (UHV) of a sub-monolayer quantity of metal onto single crystal rutile titanium dioxide produces metal nanoparticles on the surface, which are known to be an effective laboratory model of metal/TiO2 powdered commercial catalysts. By acquiring real space nanoscale images of the surface in real time at elevated temperature, we gain direct insight into the mechanism of thermal sintering of these catalysts. Chapter 1 introduces the necessary background to this work, whilst the principles and implementations of the experimental techniques are discussed in the second chapter. In chapter 3 we describe experiments where valence level and shallow core states of gold nanoclusters on TiO2(110) have been studied by synchrotron excited photoemission. The shift to high binding energy and broadening of the Au 4f peaks with decreasing Au surface coverage can be understood in terms of decreasing cluster size and the associated effects of charge on the cluster in the final state. Shifts in the photoemission onset are much more pronounced than the core level shifts and show a strong dependence on the degree of reduction of the TiO2(110) substrate. These observations suggest that the photoemission onset is influenced by an initial state effect involving charge transfer from defect states into cluster states. In chapter 4 STM is used to demonstrate that deposition of Au on TiO2(110) at room temperature leads to nucleation of Au nanoparticles whose initial mean diameter varies between about 20A and 50A depending on the surface coverage. Studying the behaviour of these clusters at elevated temperatures with STM, it is found that at 750K there is growth of the larger clusters, but above 873K evaporation of gold from the surface competes with this ripening process. At 750K the Au coverage remains

  13. Investigation of the potassium fluoride post deposition treatment on the CIGSe/CdS interface using hard X-ray photoemission spectroscopy - a comparative study.

    Ümsür, Bünyamin; Calvet, Wolfram; Steigert, Alexander; Lauermann, Iver; Gorgoi, Mihaela; Prietzel, Karsten; Greiner, Dieter; Kaufmann, Christian A; Unold, Thomas; Lux-Steiner, Martha Ch

    2016-05-18

    The impact of the potassium fluoride post deposition treatment on CIGSe chalcopyrite absorbers is investigated by means of depth resolved hard X-ray photoemission spectroscopy of the near surface region. Two similar, slightly Cu-poor CIGSe absorbers were used with one being treated by potassium fluoride prior to the chemical bath deposition of an ultrathin CdS layer. The thickness of the CdS layer was chosen to be in the range of about 10 nm in order to allow the investigation of the CIGSe/CdS interface by the application of hard X-rays, increasing the information depth up to 30 nm. Besides strong intermixing on both samples, an increased Cu depletion of the KF treated absorber was observed in combination with an increased accumulation of Cd and S. In addition, a general shift of about 0.15 eV to higher binding energies of the CIGSe valence band at the absorber surface as well as the CIGSe and CdS related core levels was measured on the KF treated sample. This phenomenon is attributed to the impact of additional cadmium which acts as donor and releases further electrons into the conduction band of the absorber. Finally, the electrons accumulate at the CdS surface after having passed the interface region. This additional surface charge leads to a pronounced shift in the photoemission spectra as observed on the KF treated CIGSe absorber compared to the non-treated absorber. PMID:27160389

  14. Photoemission study of copper phthalocyanine growth on hydrogen-terminated surface: Si(100)2 × 1–H

    Ben Hamada, B.; Souissi, A.; Menzli, S.; Arbi, I.; Akremi, A.; Chefi, C. [Université de Carthage, Laboratoire de Physique des Matériaux, Unité de Service Commun Spectromètre de Surfaces, Faculté des Sciences de Bizerte, 7021 Jarzouna, Bizerte (Tunisia); Derivaz, M. [Institut de Science des Matériaux de Mulhouse (IS2M), UMR 7361 CNRS–UHA, Université de Haute Alsace, 3bis rue Alfred Werner, 68093 Mulhouse (France)

    2014-09-30

    Copper phthalocyanine molecules have grown at room temperature under ultra high vacuum on hydrogen-terminated surface Si(100)2 × 1–H. Chemical and electronic properties of the interface were investigated by ultraviolet and X-ray photoemission spectroscopy (UPS, XPS). Results: Results indicated the existence of an interfacial dipole of 0.36 ± 0.05 eV and a band bending of 0.40 ± 0.05 eV. These were evidenced by shifts of XPS core levels and change of the vacuum level position. During the growth, the work function was found to decrease from 4.5 eV for the substrate to 3.74 eV for the highest coverage (40 monolayers). This band bending was also due to the shift of the highest occupied molecular orbital. The interfacial dipole was correlated to a rearrangement of molecules on the surface. An energy level diagram of the interface was deduced from a combination of the XPS and UPS results. - Highlights: • Ultra thin films of cooper phthalocyanine were grown on Si(100)2 × 1–H surface. • Investigation was in situ by UPS, XPS and LEED. • Results indicated the existence of an interfacial dipole and a band bending. • The interfacial dipole was correlated to a rearrangement of molecules on the surface. • An energy level diagram of the interface was deduced.

  15. Orbital tomography: Deconvoluting photoemission spectra of organic molecules

    Puschnig, Peter; Reinisch, Eva-Maria; Ules, Thomas; Koller, Georg; Soubatch, Sergey; Ostler, Markus; Romaner, Lorenz; Tautz, F. Stefan; Ambrosch-Draxl, Claudia; Ramsey, Michael G.

    2012-02-01

    We study the interface of an organic monolayer with a metallic surface, i. e., PTCDA (3,4,9,10-perylene-tetracarboxylic-dianhydride) on Ag(110), by means of angle-resolved photoemission spectroscopy (ARPES) and ab initio electronic structure calculations. We present a tomographic method which uses the energy and momentum dependence of ARPES data to deconvolute spectra into individual orbital contributions beyond the limits of energy resolution. This provides an orbital-by-orbital characterization of large adsorbate systems without the need to invoke sophisticated theory of photoemission, allowing us to directly estimate the effects of bonding on individual orbitals. Moreover, this experimental data serves as a most stringent test necessary for the further development of ab initio electronic structure theory.

  16. Generalized Franck-Condon principle for resonant photoemission

    Sałek, Paweł; Gel'mukhanov, Faris; Ågren, Hans; Björneholm, Olle; Svensson, Svante

    1999-10-01

    A generalized Franck-Condon (GFC) principle for resonant x-ray Raman scattering and for resonant photoemission in particular is derived and numerically investigated. The GFC amplitudes differ from ordinary FC amplitudes by the presence of photon and photoelectron phase factors which describe the coupling-or interference-of the x-ray photons or Auger electrons with the nuclear motion. With the GFC amplitudes, a Kramers-Heisenberg relation is obtained for vibronic transitions that corrects the so-called lifetime-vibrational interference formula. For resonant photoemission in the soft-x-ray region involving typical bound potential surfaces, the generalization gives a contribution to the FC factors that can amount to 20%. For core excitation above the dissociation threshold, the GFC principle relates to Doppler effects on the ejected photoelectron both for the so-called ``molecular'' and ``atomic'' bands. The role of the GFC principle in direct photoionization is briefly discussed.

  17. Thermal and Field Enhanced Photoemission Comparison of Theory to Experiment

    Lynn-Jensen, Kevin

    2004-01-01

    Photocathodes are a critical component of high-gain FEL’s and the analysis of their emission is complex. Relating their performance under laboratory conditions to conditions of an rf photoinjector is difficult. Useful models must account for cathode surface conditions and material properties, as well as drive laser parameters. We have developed a time-dependent model accounting for the effects of laser heating and thermal propagation on photoemission. It accounts for surface conditions (coating, field enhancement, reflectivity), laser parameters (duration, intensity, wavelength), and material characteristics (reflectivity, laser penetration depth, scattering rates) to predict current distribution and quantum efficiency. The applicatIon will focus on photoemission from metals and, in particular, dispenser photocathodes: the later introduces complications such as coverage non-uniformity and field enhancement. The performance of experimentally characterized photocathodes will be extrapolated to 0.1 - 1 nC bunch...

  18. P2P IPTV Measurement: A Comparison Study

    Silverston, Thomas; Fourmaux, Olivier

    2006-01-01

    With the success of P2P file sharing, new emerging P2P applications arise on the Internet for streaming content like voice (VoIP) or live video (IPTV). Nowadays, there are lots of works measuring P2P file sharing or P2P telephony systems, but there is still no comprehensive study about P2P IPTV, whereas it should be massively used in the future. During the last FIFA world cup, we measured network traffic generated by P2P IPTV applications like PPlive, PPstream, TVants and Sopcast. In this pap...

  19. Analysis on photoemission spectrum of superconducting FeSe

    In this paper, we present the result of soft X-ray photoemission spectroscopy and its comparison with the density functional calculation. Although local density approximation seems to be a good starting point for describing the electronic structure of FeSe, the simulated spectrum poorly reproduced the structure around EB=2eV. This result suggests the necessity of theoretical treatment beyond local density approximation.

  20. THE ORGANIC LED SURFACE: A SYNCHROTRON RADIATION PHOTOEMISSION STUDY

    TUN-WEN PI; T. C. YU

    2007-01-01

    Tris(8-hydroxyquinolato) aluminum (Alq3), a prototypical molecule for organic light-emitting devices, has been studied via synchrotron radiation photoemission to investigate (1) the surface electronic structure of the molecules at room temperature and at elevated temperatures, (2) adsorption onto the inorganic Si(001)-2×1 surface, and (3) doping with the alkaline metal Mg. For case (1), three chemical environments of carbon are resolved. Moreover, the shake-up satellite structures are detecte...

  1. O- and H-induced surface core level shifts on Ru(0001): prevalence of the additivity rule

    In previous work on adsorbate-induced surface core level shifts (SCLSs), the effects caused by O atom adsorption on Rh(111) and Ru(0001) were found to be additive: the measured shifts for first-layer Ru atoms depended linearly on the number of directly coordinated O atoms. Density-functional theory calculations quantitatively reproduced this effect, allowed separation of initial- and final-state contributions, and provided an explanation in terms of a roughly constant charge transfer per O atom. We have now conducted similar measurements and calculations for three well-defined adsorbate and coadsorbate layers containing O and H atoms: (1 x 1)-H, (2 x 2)-(O+H) and (2 x 2)-(O+3H) on Ru(0001). As H is stabilized in fcc sites in the prior two structures and in hcp sites in the latter, this enables us to not only study coverage and coadsorption effects on the adsorbate-induced SCLSs, but also the sensitivity to similar adsorption sites. Remarkably good agreement is obtained between experiment and calculations for the energies and geometries of the layers, as well as for all aspects of the SCLS values. The additivity of the next-neighbor adsorbate-induced SCLSs is found to prevail even for the coadsorbate structures. While this confirms the suggested use of SCLSs as fingerprints of the adsorbate configuration, their sensitivity is further demonstrated by the slightly different shifts unambiguously determined for H adsorption in either fcc or hcp hollow sites.

  2. Core-level photoelectron study of Si(1 1 1) sq root 7x sq root 3-(Pb, Sn) surface

    Soda, K; Takada, T; Yoshimoto, O; Kato, M; Yagi, S; Morita, K; Kamada, M

    2003-01-01

    The Sn 4d and Pb 5d core-level photoelectron spectra have been studied in order to clarify their bonding properties and atomic arrangement on a Si(1 1 1) sq root 7x sq root 3-(Pb, Sn) surface, which is formed by the coadsorption of 0.4 ML Pb and 0.4 ML Sn and shows two kinds of bright spots in the scanning tunneling microscopic (STM) images: (A) those aligned zigzag on the T sub 1 site and (B) those on the T sub 1 and H sub 3 sites along the [1 1 -2] direction. The Pb 5d spectrum shows a single spin-orbit-split feature with weak tailing towards the high binding energy side, while the Sn 4d spectrum exhibits shoulder structures at the high binding energy side of the main peaks. This definitely indicates at least two different Sn-Si bonds or inequivalent Sn adsorbing sites and single bond or site for Pb. Thus the spots A at the T sub 1 site and those B at the T sub 1 and H sub 3 sites in the STM images are ascribed to Pb and Sn adatoms, respectively. The formation process of this surface will be also discussed ...

  3. Main: 1M2P [RPSD[Archive

    Full Text Available 1M2P トウモロコシ Corn Zea mays L. Casein Kinase Ii, Alpha Chain Name=Ack2; Zea Mays Mole...LVGRHSRKPWLKFMNADNQHLVSPEAIDFLDKLLRYDHQERLTALEAMTHPYFQQVRAAENSRTRA corn_1M2P.jpg ...

  4. Multiconfiguration Hartree-Fock Breit-Pauli results for the 2p 2P/sub 1/2/ - 2p 2P/sub 3/2/ E2 and M1 transitions

    Some forbidden transitions become possible through the fine structure splitting of an LS term into a series of J levels. Examples are the E2 and M1 transition between the 2p 2P/sub 1/2/ and 2p 2P/sub 3/2/ levels in the boron sequence. In the non-relativistic approximation, these levels are degenerate and there is a strong interaction between the 2s22p and 2p32P configurations, indicating important correlation efforts. Thus the theoretical determination of the fine structure splitting provides a sensitive test for a computational method. The MCHF method has been extended to include the relativistic corrections in the Breit-Pauli approximation. An MCHF-BP calculation proceeds in two stages. In the first, a non-relativistic MCHF calculation is performed to determine an orbital basis, whereas in the second the Breit-Pauli interaction matrix is diagonalized. At present the orbit-orbit interactions are neglected. Calculations have been performed with this method for 2p 2P/sub 1/2/ - 2p 2P/sub 3/2/ E2 and M1 transitions of the boron sequence. In order to study the effect of correlation outside the n = 2 complex, two sets of calculations were performed. In the first, the radial orbitals were determined for an MCHF calculation for (2s22p, 2p3) 2P and the Breit-Pauli diagonalization was over the set of four configuration states, (2s22p, 2p32P, 2p32D and 2p34S). In the second, the MCHF calculation was for [2s22p, 2p3, 2p2(1S)3p, 2s24p, 2s2p(1,3P) 3d, 2s3s(3S) 2p] 2P and the Breit-Pauli diagonalization included twenty 2P configuration states, as well as 2p32D and 2p34S, for a total of twenty-two configuration states

  5. Electronic structure of C and N co-doped TiO2: A combined hard x-ray photoemission spectroscopy and density functional theory study

    We have studied the electronic structure of C and N co-doped TiO2 using hard x-ray photoelectron spectroscopy and first-principles density functional theory calculations. Our results reveal overlap of the 2p states of O, N, and C in the system which shifts the valence band maximum towards the Fermi level. Combined with optical data we show that co-doping is an effective route for band gap reduction in TiO2. Comparison of the measured valence band with theoretical photoemission density of states reveals the possibility of C on Ti and N on O site

  6. Structure of Tl2Mo2P2O11

    Dimolybdenum dithallium diphosphate, Tl2Mo2P2O11, is isotypic with K2Mo2P2O11. Its framework is built from the original Mo2P2O15 unit, formed by one Mo2O11 group sharing four of its corners with two PO4 tetrahedra, leading to [Mo2P2O13]∞ chains running along c. The [Mo2P2O11]∞ framework forms two different intersecting tunnels running along c and left angle 110 right angle , where the TI+ ions are located. (orig.)

  7. Optimization of Extreme Ultraviolet Light Source from High Harmonic Generation for Condensed-Phase Core-Level Spectroscopy

    Lin, Ming-Fu; Verkamp, Max A.; Ryland, Elizabeth S.; Benke, Kristin; Zhang, Kaili; Carlson, Michaela; Vura-Weis, Josh

    2015-06-01

    Extreme ultraviolet (XUV) light source from high-order harmonic generation has been shown to be a powerful tool for core-level spectroscopy. In addition, this light source provides very high temporal resolution (10-18 s to 10-15 s) for time-resolved transient absorption spectroscopy. Most applications of the light source have been limited to the studies of atomic and molecular systems, with technique development focused on optimizing for shorter pulses (i.e. tens of attoseconds) or higher XUV energy (i.e. ~keV range). For the application to general molecular systems in solid and liquid forms, however, the XUV photon flux and stability are highly demanded due to the strong absorption by substrates and solvents. In this case, the main limitation is due to the stability of the high order generation process and the limited bandwidth of the XUV source that gives only discrete even/odd order peaks. Consequently, this results in harmonic artifact noise that overlaps with the resonant signal. In our current study, we utilize a semi-infinite cell for high harmonic generation from two quantum trajectories (i.e. short and long) at over-driven NIR power. This condition, produces broad XUV spectrum without using complicated optics (e.g. hollow-core fibers and double optical gating). This light source allows us to measure the static absorption spectrum of the iron M-edge from a Fe(acac)3 molecular solid film, which shows a resonant feature of 0.01 OD (~2.3% absorption). Moreover, we also investigate how sample roughness affects the static absorption spectrum. We are able to make smooth solar cell precursor materials (i.e. PbI2 and PbBr2) by spin casting and observe iodine (50 eV) and bromine (70 eV) absorption edges in the order of 0.05 OD with minimal harmonic artifact noise.

  8. Time-resolved photoemission by attosecond streaking: extraction of time information

    Nagele, Stefan; Feist, Johannes; Doblhoff-Dier, Katharina; Lemell, Christoph; T\\Hokési, Karoly; Burgdörfer, Joachim

    2011-01-01

    Attosecond streaking of atomic photoemission holds the promise to provide unprecedented information on the release time of the photoelectron. We show that attosecond streaking phase shifts indeed contain timing (or spectral phase) information associated with the Eisenbud-Wigner-Smith time delay matrix of quantum scattering. However, this is only accessible if the influence of the streaking infrared (IR) field on the emission process is properly accounted for. The IR probe field can strongly modify the observed streaking phase shift. We show that the part of the phase shift ("time shift") due to the interaction between the outgoing electron and the combined Coulomb and IR laser fields can be described classically. By contrast, the strong initial-state dependence of the streaking phase shift is only revealed through the solution of the time-dependent Schr\\"odinger equation in its full dimensionality. We find a time delay between the hydrogenic 2s and 2p initial states in He+ exceeding 20as for a wide range of I...

  9. Time-resolved photoemission by attosecond streaking: extraction of time information

    Attosecond streaking of atomic photoemission holds the promise to provide unprecedented information on the release time of the photoelectron. We show that attosecond streaking phase shifts indeed contain timing (or spectral phase) information associated with the Eisenbud-Wigner-Smith time delay matrix of quantum scattering. However, this is only accessible if the influence of the streaking infrared (IR) field on the emission process is properly accounted for. The IR probe field can strongly modify the observed streaking phase shift. We show that the part of the phase shift ('time shift') due to the interaction between the outgoing electron and the combined Coulomb and IR laser fields can be described classically. By contrast, the strong initial-state dependence of the streaking phase shift is only revealed through the solution of the time-dependent Schroedinger equation in its full dimensionality. We find a time delay between the hydrogenic 2s and 2p initial states in He+ exceeding 20 as for a wide range of IR intensities and XUV energies. (fast track communication)

  10. Time-resolved photoemission by attosecond streaking: extraction of time information

    Nagele, S; Pazourek, R; Doblhoff-Dier, K; Lemell, C; Burgdoerfer, J [Institute for Theoretical Physics, Vienna University of Technology, 1040 Vienna (Austria); Feist, J [ITAMP, Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Tokesi, K, E-mail: stefan.nagele@tuwien.ac.at, E-mail: renate.pazourek@tuwien.ac.at [Institute of Nuclear Research of the Hungarian Academy of Sciences (ATOMKI), 4001 Debrecen (Hungary)

    2011-04-28

    Attosecond streaking of atomic photoemission holds the promise to provide unprecedented information on the release time of the photoelectron. We show that attosecond streaking phase shifts indeed contain timing (or spectral phase) information associated with the Eisenbud-Wigner-Smith time delay matrix of quantum scattering. However, this is only accessible if the influence of the streaking infrared (IR) field on the emission process is properly accounted for. The IR probe field can strongly modify the observed streaking phase shift. We show that the part of the phase shift ('time shift') due to the interaction between the outgoing electron and the combined Coulomb and IR laser fields can be described classically. By contrast, the strong initial-state dependence of the streaking phase shift is only revealed through the solution of the time-dependent Schroedinger equation in its full dimensionality. We find a time delay between the hydrogenic 2s and 2p initial states in He{sup +} exceeding 20 as for a wide range of IR intensities and XUV energies. (fast track communication)

  11. X-ray-photoemission-spectroscopy evidence for anomalous oxidation states of silicon after exposure of hydrogen-terminated single-crystalline (100) silicon to a diluted N2:N2O atmosphere

    The early oxidation stages of hydrogen-terminated single-crystalline (100) silicon exposed to a diluted N2 : N2O atmosphere at 8500C for different durations have been studied by x-ray photoemission spectroscopy, following the evolution of the Si 2p signal. Evidence is given that the usual analysis, in terms of five pairs of peaks attributed to silicon in the oxidation states from 0 to +4, does not account for the observed Si 2p signal. An explanation for silicon in unusual oxidation states is proposed. (author)

  12. Operating experience with a GaAs photoemission electron source

    Tang, F.C.; Lubell, M.S.; Rubin, K.; Vasilakis, A.; Eminyan, M.; Slevin, J.

    1986-12-01

    We report on the development of several operating procedures that promise to make GaAs photoemission electron sources easier to construct, more reliable to operate, and more amenable to use in dynamic vacuum systems. We describe in particular a method for ''ohmically'' heating a <100> crystal of GaAs under vacuum to approximately 600 /sup 0/C. We also discuss our observations of the role of oxygen in the activation of the crystal surface, the use of continuous cesiation, and of the performance of the crystal under varying vacuum conditions.

  13. Operating experience with a GaAs photoemission electron source

    We report on the development of several operating procedures that promise to make GaAs photoemission electron sources easier to construct, more reliable to operate, and more amenable to use in dynamic vacuum systems. We describe in particular a method for ''ohmically'' heating a crystal of GaAs under vacuum to approximately 600 0C. We also discuss our observations of the role of oxygen in the activation of the crystal surface, the use of continuous cesiation, and of the performance of the crystal under varying vacuum conditions

  14. Measurements of relative photoemission time delays in noble gas atoms

    We determine relative photoemission time delays between valence electrons in different noble gas atoms (Ar, Ne and He) in an energy range between 31 and 37 eV. The atoms are ionized by an attosecond pulse train synchronized with an infrared laser field and the delays are measured using an interferometric technique. We compare our results with calculations using the random phase approximation with exchange and multi-configurational Hartree–Fock. We also investigate the influence of the different ionization angular channels. (paper)

  15. Polarized resonance photoemission for Nd2CuO4

    We present calculations of resonance photoemission spectra for Nd2CuO4. The calculations use a model Hamiltonian for which all parameters for the valence electrons are obtained from ab initio calculations or atomic data. Most features of the calculated sp agree well with experiment where comparison is possible. A substantial dependence on the polarization of the light is predicted for the occurrence of resonance behavior, and for the off-resonance intensity of the local singlet and one of the satellites

  16. Photoemission study of TiO2/VO2 interfaces

    Maekawa, K; Takizawa, M.; Wadati, H.; Yoshida, T.; Fujimori, A.; Kumigashira, H.; Oshima, M.; Muraoka, Y.; Nagao, Y.; Hiroi, Z.

    2006-01-01

    We have measured photoemission spectra of two kinds of TiO$_2$-capped VO$_2$ thin films, namely, that with rutile-type TiO$_2$ (r-TiO$_2$/VO$_2$) and that with amorphous TiO$_2$ (a-TiO$_2$/VO$_2$) capping layers. Below the Metal-insulator transition temperature of the VO$_2$ thin films, $\\sim 300$ K, metallic states were not observed for the interfaces with TiO$_2$, in contrast with the interfaces between the band insulator SrTiO$_3$ and the Mott insulator LaTiO$_3$ in spite of the fact that ...

  17. Understanding photoemission spectra in uranium based heavy fermion systems

    In 4f compounds, there is a two-peaked structure associated with 4f photoemission spectroscopy, while most 5f compounds yield a single broad triangular-shaped 5f intensity. Evidence is presented from measurements on ternary alloys that show that at least part of the extra-5f intensity is due to the hitherto missing main peak (or d-screened f-hole peak) just as in the 4f systems. The remaining intensity is consistent with a band structure DOS. (The compounds used were URh3B/sub x/, UPd/sub x/Rh/sub 3-x/, ThBe13, UIr3, and UBe13.)

  18. Modeling Load Balancing in Heterogeneous Unstructured P2P Systems

    Zhi J. Li

    2005-01-01

    Full Text Available Load balancing is a generally concerned problem in peer-to-peer (P2P systems. Many researches on load balancing in the structured P2P systems have been launched currently, such as Chord or other DHTs. Although the researches on load balancing in unstructured P2P systems are emerged nowadays, the simple mechanisms achieved can only perform effectively in uniform environment. In this study, the influence on load balancing of the heterogeneity existed universally in unstructured P2P systems are analyzed, the unstructured P2P systems and their load balancing and the heterogeneity are modeled. Based on the formal model, the load balancing is analyzed quantitatively under static and dynamic environment and the typical load balancing algorithms are also analyzed. Some important conclusions are drawn which can be used in new models of load balancing in unstructured P2P systems.

  19. Research and Development of P2P Worms

    Li You; Zhi-Guang Qin

    2011-01-01

    With the development and the application of many popular peer-to-peer (P2P) systems such as eMule and BitTorrent,worms probably employ the features of these P2P networks to put them at risk.Some features,such as the local routing table and the application routing mechanism,are helpful to quickly distribute the P2P worms into the networks.This paper aims to give a comprehensive survey of P2P worms.The definition and the classification of P2P worms are discussed firstly.Then,the research and development of P2P worms, including experimental analysis,propagation modeling,and defensive approaches,are addressed and analyzed in detail.

  20. Supporting Collaboration and Creativity Through Mobile P2P Computing

    Wierzbicki, Adam; Datta, Anwitaman; Żaczek, Łukasz; Rzadca, Krzysztof

    Among many potential applications of mobile P2P systems, collaboration applications are among the most prominent. Examples of applications such as Groove (although not intended for mobile networks), collaboration tools for disaster recovery (the WORKPAD project), and Skype's collaboration extensions, all demonstrate the potential of P2P collaborative applications. Yet, the development of such applications for mobile P2P systems is still difficult because of the lack of middleware.

  1. Valence-band dispersion in angle-resolved resonant photoemission from LaSb

    Angle-resolved photoemission spectra taken on single crystals of LaSb at the La 4d→4f resonance show dispersion of resonantly emitted valence-band electrons. This is the first direct demonstration that the Bloch component of valence states participates in resonant photoemission. copyright 1996 The American Physical Society

  2. Deletion of GOLGA2P3Y but not GOLGA2P2Y is a risk factor for oligozoospermia.

    Sen, Sanjukta; Agarwal, Rupesh; Ambulkar, Prafulla; Hinduja, Indira; Zaveri, Kusum; Gokral, Jyotsna; Pal, Asoke; Modi, Deepak

    2016-02-01

    The AZFc locus on the human Y chromosome harbours several multicopy genes, some of which are required for spermatogenesis. It is believed that deletion of one or more copies of these genes is a cause of infertility in some men. GOLGA2LY is one of the genes in the AZFc locus and it exists in two copies, GOLGA2P2Y and GOLGA2P3Y. The involvement of GOLGA2LY gene copy deletions in male infertility, however, is unknown. This study aimed to investigate the association of deletions of GOLGA2P2Y and GOLGA2P3Y gene copies with male infertility and with sperm concentration and motility. The frequency of GOLGA2P3Y deletion was significantly higher in oligozoospermic men compared with normozoospermic men (7.7% versus 1.2%; P = 0.0001), whereas the frequency of GOLGA2P2Y deletion was comparable between oligozoospermic and normozoospermic men (10.3% versus 11.3%). The deletion of GOLGA2P3Y but not GOLGA2P2Y was significantly higher (P = 0.03) in men with gr/gr rearrangements, indicating that GOLGA2P3Y deletions increase the susceptibility of men with gr/gr rearrangements to oligozoospermia. Furthermore, men with GOLGA2P3Y deletion had reduced sperm concentration and motility compared with men without deletion or with deletion of GOLGA2P2Y. These findings indicate GOLGA2P3Y gene copy may be candidate AZFc gene for male infertility. PMID:26655651

  3. Transition probabilities for NII 2p4f-2p3d and 2s2p23d-2s2p23p obtained by a semiclassical method

    2007-01-01

    Based on NII spectra, some transition probabilities for 2p4f-2p3d and 2s2p23d-2s2p23p are obtained by a semiclassical method. The results are in good agreement with other measurements and the data reported by the National Institute of Standards and Technology. The transition probability for a line of 424.18nm is reported for the first time. Meanwhile, a feasible method of calculating transition parameters related to special excited configurations or highly excited states is provided.

  4. Characterization of P2P IPTV Traffic: Scaling Analysis

    Silverston, Thomas; Fourmaux, Olivier; Salamatian, Kave

    2007-01-01

    P2P IPTV applications arise on the Internet and will be massively used in the future. It is expected that P2P IPTV will contribute to increase the overall Internet traffic. In this context, it is important to measure the impact of P2P IPTV on the networks and to characterize this traffic. Dur- ing the 2006 FIFA World Cup, we performed an extensive measurement campaign. We measured network traffic generated by broadcasting soc- cer games by the most popular P2P IPTV applications, namely PPLive...

  5. Search by shortcuts in P2P scientific collaboration system

    2005-01-01

    A P2P scientific collaboration is a P2P network whose members can share documents, co-compile papers and codes, and communicate with each other instantly. From the simulation experiment we found that P2P collaboration system is a power-law network with a tail between -2 and -3.We utilized the algorithm that searches by high-degree shortcuts to improve the scalability of p2p collaboration system. The experimental result shows that the algorithm works better than random walk algorithm.

  6. Aberration Corrected Photoemission Electron Microscopy with Photonics Applications

    Fitzgerald, Joseph P. S.

    Photoemission electron microscopy (PEEM) uses photoelectrons excited from material surfaces by incident photons to probe the interaction of light with surfaces with nanometer-scale resolution. The point resolution of PEEM images is strongly limited by spherical and chromatic aberration. Image aberrations primarily originate from the acceleration of photoelectrons and imaging with the objective lens and vary strongly in magnitude with specimen emission characteristics. Spherical and chromatic aberration can be corrected with an electrostatic mirror, and here I develop a triode mirror with hyperbolic geometry that has two adjacent, field-adjustable regions. I present analytic and numerical models of the mirror and show that the optical properties agree to within a few percent. When this mirror is coupled with an electron lens, it can provide a large dynamic range of correction and the coefficients of spherical and chromatic aberration can be varied independently. I report on efforts to realize a triode mirror corrector, including design, characterization, and alignment in our microscope at Portland State University (PSU). PEEM may be used to investigate optically active nanostructures, and we show that photoelectron emission yields can be identified with diffraction, surface plasmons, and dielectric waveguiding. Furthermore, we find that photoelectron micrographs of nanostructured metal and dielectric structures correlate with electromagnetic field calculations. We conclude that photoemission is highly spatially sensitive to the electromagnetic field intensity, allowing the direct visualization of the interaction of light with material surfaces at nanometer scales and over a wide range of incident light frequencies.

  7. Photoemission from stepped W(110): Umklapp or superlattice effect?

    Full text: Vicinal W(110) is an important substrate for the growth of metallic and magnetic nanostructures. In order to explore its potential to support nanostructures that lead to quantization of electronic states, the behavior of electrons on the pure stepped W(110) is studied. Using angle-resolved photoemission, we compare the electronic structure of the (110)-oriented terraces of stepped W(331) and W(551). We discover a surface-localized state which leads in [110]-terrace-normal emission to a large energy shift (∼0.8 eV) between W(110) and W(331). Away from normal emission it develops in the direction perpendicular to the steps into a repeated band dispersion. The measured periodicity agrees well with the step widths of W(331) and W(551), respectively, and is, principally, in agreement with both an initial-state superlattice effect and a final-state umklapp process. We discuss the role of the W bulk band gap and use the energy dependence in angle-resolved photoemission and low-energy electron diffraction to show that the observed behavior is due to a final-state umklapp effect at the step superlattice, as has recently been observed for carbon nanostripes on stepped Ni(771)[3] and independently on vicinal Au(111)

  8. ZrCu2P2 and HfCu2P2 phosphides and their crystal structure

    Isostructural ZrCu2P2 and HfCu2P2 compounds are prepared for the first time. X-ray diffraction analysis (of powder, DRON-2.0 diffractometer, FeKsub(α) radiation) was used to study crystal structure of HfCu2P2 phosphide belonging to the CaAl2Si2 structural type (sp. group P anti 3 m 1, R=0.095). Lattice parameters the compounds are as follows: for ZrCu2P2 a=0.3810(1), c=0.6184(5); for HfCu2P2 a=0.3799(1), c=0.6160(2) (nm). Atomic parameters in the HfCu2P2 structure and interatomic distances are determined

  9. Binding energy shift in photoemission spectroscopy study of Ni clusters deposited on rutile TiO2 surfaces

    Cluster-size-dependent binding energy (BE) shifts of Ni 2p3/2 spectra in Ni clusters with respect to bulk Ni metal have been studied as a function of Ni coverage on clean rutile TiO2(0 0 1) surfaces at room temperature. Auger parameter (AP) analysis of photoelectron spectra has been employed and revealed an obvious initial state contribution at the coverage of 0.5 monolayers (ML). The initial state effect was demonstrated to be strongly affected by the substrate and was assigned to a combination of eigenvalue shift in surface core-level shift (SCLS) and charge transfer between the metal clusters and substrates. The TiO2(0 0 1) surface stoichiometry was found to introduce different charge transfer behaviors. Our results experimentally present that the Ni clusters are charged positively on stoichiomtric TiO2 surface and less positively or even negatively on various reduced surfaces.

  10. High-kinetic-energy photoemission spectroscopy of Ni at 1s : 6-eV satellite at 4 eV

    Karis, O.; Svensson, S.; Rusz, J.; Oppeneer, P. M.; Gorgoi, M.; Schäfers, F.; Braun, W.; Eberhardt, W.; Mårtensson, N.

    2008-12-01

    Electron correlations are responsible for many profound phenomena in solid-state physics. A classical example is the 6-eV satellite in the photoelectron spectrum of Ni. Until now the satellite structure has only been investigated at the L shell and more shallow levels. Here we report a high-kinetic-energy photoemission spectroscopy (HIKE) investigation of Ni metal. We present 1s and 2p photoelectron spectra, obtained using excitation energies up to 12.6 keV. Our investigation demonstrates that the energy position of the satellite relative to the main line is different for the 1s and the 2p levels. In combination with electronic structure calculations, we show that this energy shift is attributed to unique differences in the core-valence coupling for the K and L2,3 shells in 3d transition metals, resulting in different screening of the core holes.

  11. Comparison of the electronic structure of anatase and rutile TiO2 single-crystal surfaces using resonant photoemission and x-ray absorption spectroscopy

    Thomas, A. G.; Flavell, W. R.; Mallick, A. K.; Kumarasinghe, A. R.; Tsoutsou, D.; Khan, N.; Chatwin, C.; Rayner, S.; Smith, G. C.; Stockbauer, R. L.; Warren, S.; Johal, T. K.; Patel, S.; Holland, D.; Taleb, A.; Wiame, F.

    2007-01-01

    A comparison of the electronic structure of rutile (110), anatase (101), and anatase (001) single-crystal surfaces has been made using resonant photoemission and x-ray absorption spectroscopy. Under identical preparative conditions, the anatase (101) surface shows the lowest Ti3d and 4sp hybridization in the states close to the valence-band maximum of the three surfaces. It also shows the highest concentration of surface-oxygen vacancies. The effect on the electronic structure of modifying the surface preparative route and thus the concentration of surface-oxygen vacancies is examined. The σ -antibonding Ti3deg/O2p hybridization (probed by XAS) is reduced by the removal of surface-oxygen. Photoemission shows that as the number of surface-defects is increased, the O2p-Ti3dt2gπ -bonding interaction is disrupted. For the anatase (101) surface it is found that as the number of surface-oxygen vacancies is increased, the Ti3d and 4sp contributions at the valence-band maximum are reduced. We discuss the correlation between electronic structure and photocatalytic activity of the different polymorphs of TiO2 .

  12. Research of P2P SIP technology%P2P SIP技术的研究

    隋晋光; 鲁士文

    2007-01-01

    在阐述P2P和SIP技术的基础上,引出了一种二者融合的新技术--P2P SIP,提出了采用P2P SIP技术系统的体系结构、工作方式,并且对P2P SIP技术的安全性问题进行了分析.

  13. Isotope shifts of the 2$p_{3/2}$-2$p_{1/2}$ transition in B-like ions

    Zubova, N A; Tupitsyn, I I; Shabaev, V M; Kozhedub, Y S; Plunien, G; Brandau, C; Stohlker, Th

    2016-01-01

    Isotope shifts of the 2$p_{3/2}$-2$p_{1/2}$ transition in B-like ions are evaluated for a wide range of the nuclear charge number: Z=8-92. The calculations of the relativistic nuclear recoil and nuclear size effects are performed using a large scale configuration-interaction Dirac-Fock-Sturm method. The corresponding QED corrections are also taken into account. The results of the calculations are compared with the theoretical values obtained with other methods. The accuracy of the isotope shifts of the 2$p_{3/2}$-2$p_{1/2}$ transition in B-like ions is significantly improved.

  14. Isotope shifts of the 2 p3 /2-2 p1 /2 transition in B-like ions

    Zubova, N. A.; Malyshev, A. V.; Tupitsyn, I. I.; Shabaev, V. M.; Kozhedub, Y. S.; Plunien, G.; Brandau, C.; Stöhlker, Th.

    2016-05-01

    Isotope shifts of the 2 p3 /2-2 p1 /2 transition in B-like ions are evaluated for a wide range of the nuclear charge number: Z =8 -92 . The calculations of the relativistic nuclear recoil and nuclear size effects are performed using a large-scale configuration-interaction Dirac-Fock-Sturm method. The corresponding QED corrections are also taken into account. The results of the calculations are compared with the theoretical values obtained with other methods. The accuracy of the isotope shifts of the 2 p3 /2-2 p1 /2 transition in B-like ions is significantly improved.

  15. AlvisP2P: Scalable Peer-to-Peer Text Retrieval in a Structured P2P Network

    Luu, Toan; Skobeltsyn, Gleb; Klemm, Fabius; Puh, Maroje; Podnar Zarko, Ivana; Rajman, Martin; Aberer, Karl

    2008-01-01

    In this paper we present the AlvisP2P IR engine, which enables efficient retrieval with multi-keyword queries from a global document collection available in a P2P network. In such a network, each peer publishes its local index and invests a part of its local computing resources (storage, CPU, bandwidth) to maintain a fraction of a global P2P index. This investment is rewarded by the network-wide accessibility of the local documents via the global search facility. The AlvisP2P engine uses an o...

  16. Observation of strontium segregation in LaAlO3/SrTiO3 and NdGaO3/SrTiO3 oxide heterostructures by X-ray photoemission spectroscopy

    LaAlO3 and NdGaO3 thin films of different thicknesses have been grown by pulsed laser deposition on TiO2-terminated SrTiO3 single crystals and investigated by soft X-ray photoemission spectroscopy. The surface sensitivity of the measurements has been tuned by varying photon energy hν and emission angle Θ. In contrast to the core levels of the other elements, the Sr 3d line shows an unexpected splitting for higher surface sensitivity, signaling the presence of a second strontium component. From our quantitative analysis we conclude that during the growth process Sr atoms diffuse away from the substrate and segregate at the surface of the heterostructure, possibly forming strontium oxide

  17. Observation of strontium segregation in LaAlO{sub 3}/SrTiO{sub 3} and NdGaO{sub 3}/SrTiO{sub 3} oxide heterostructures by X-ray photoemission spectroscopy

    Treske, Uwe; Heming, Nadine; Knupfer, Martin; Büchner, Bernd; Koitzsch, Andreas, E-mail: a.koitzsch@ifw-dresden.de [Institute for Solid State Research, IFW-Dresden, P.O. Box 270116, DE-01171 Dresden (Germany); Di Gennaro, Emiliano; Scotti di Uccio, Umberto; Miletto Granozio, Fabio [CNR-SPIN and Dipartimento di Fisica, Complesso Universitario di Monte S. Angelo, Via Cintia, 80126 Naples (Italy); Krause, Stefan [Helmholtz-Zentrum Berlin, BESSY, Albert-Einstein-Str. 15, 12489 Berlin (Germany)

    2014-01-01

    LaAlO{sub 3} and NdGaO{sub 3} thin films of different thicknesses have been grown by pulsed laser deposition on TiO{sub 2}-terminated SrTiO{sub 3} single crystals and investigated by soft X-ray photoemission spectroscopy. The surface sensitivity of the measurements has been tuned by varying photon energy hν and emission angle Θ. In contrast to the core levels of the other elements, the Sr 3d line shows an unexpected splitting for higher surface sensitivity, signaling the presence of a second strontium component. From our quantitative analysis we conclude that during the growth process Sr atoms diffuse away from the substrate and segregate at the surface of the heterostructure, possibly forming strontium oxide.

  18. Observation of strontium segregation in LaAlO3/SrTiO3 and NdGaO3/SrTiO3 oxide heterostructures by X-ray photoemission spectroscopy

    Treske, Uwe; Heming, Nadine; Knupfer, Martin; Büchner, Bernd; Koitzsch, Andreas; Di Gennaro, Emiliano; Scotti di Uccio, Umberto; Miletto Granozio, Fabio; Krause, Stefan

    2014-01-01

    LaAlO3 and NdGaO3 thin films of different thicknesses have been grown by pulsed laser deposition on TiO2-terminated SrTiO3 single crystals and investigated by soft X-ray photoemission spectroscopy. The surface sensitivity of the measurements has been tuned by varying photon energy hν and emission angle Θ. In contrast to the core levels of the other elements, the Sr 3d line shows an unexpected splitting for higher surface sensitivity, signaling the presence of a second strontium component. From our quantitative analysis we conclude that during the growth process Sr atoms diffuse away from the substrate and segregate at the surface of the heterostructure, possibly forming strontium oxide.

  19. Observation of strontium segregation in LaAlO3/SrTiO3 and NdGaO3/SrTiO3 oxide heterostructures by X-ray photoemission spectroscopy

    Uwe Treske

    2014-01-01

    Full Text Available LaAlO3 and NdGaO3 thin films of different thicknesses have been grown by pulsed laser deposition on TiO2-terminated SrTiO3 single crystals and investigated by soft X-ray photoemission spectroscopy. The surface sensitivity of the measurements has been tuned by varying photon energy hν and emission angle Θ. In contrast to the core levels of the other elements, the Sr 3d line shows an unexpected splitting for higher surface sensitivity, signaling the presence of a second strontium component. From our quantitative analysis we conclude that during the growth process Sr atoms diffuse away from the substrate and segregate at the surface of the heterostructure, possibly forming strontium oxide.

  20. Revisiting Photoemission and Inverse Photoemission Spectra of Nickel Oxide from First Principles: Implications for Solar Energy Conversion

    Alidoust, Nima; Toroker, Maytal; Carter, Emily A.

    2014-07-17

    We use two different ab initio quantum mechanics methods, complete active space self-consistent field theory applied to electrostatically embedded clusters and periodic many-body G₀W₀ calculations, to reanalyze the states formed in nickel(II) oxide upon electron addition and ionization. In agreement with interpretations of earlier measurements, we find that the valence and conduction band edges consist of oxygen and nickel states, respectively. However, contrary to conventional wisdom, we find that the oxygen states of the valence band edge are localized whereas the nickel states at the conduction band edge are delocalized. We argue that these characteristics may lead to low electron-hole recombination and relatively efficient electron transport, which, coupled with band gap engineering, could produce higher solar energy conversion efficiency compared to that of other transition-metal oxides. Both methods find a photoemission/inverse-photoemission gap of 3.6-3.9 eV, in good agreement with the experimental range, lending credence to our analysis of the electronic structure of NiO.

  1. Crystal structure and X-ray photoemission spectroscopic study of A{sub 2}LaMO{sub 6} [A=Ba, Ca; M=Nb, Ta

    Dutta, Alo, E-mail: alo_dutta@yahoo.com [Department of Condensed Matter Physics and Material Sciences, S. N. Bose National Centre for Basic Sciences, Block-JD, Sector-III, Salt Lake, Kolkata 700098 (India); Saha, Sujoy [Department of Physics, Bose Institute, 93/1 Acharya Prafulla Chandra Road, Kolkata 700009 (India); Kumari, Premlata [Department of Chemistry, Government P.G. College, Lansdowne, Pauri-Garhwal 246139 (India); Sinha, T.P. [Department of Physics, Bose Institute, 93/1 Acharya Prafulla Chandra Road, Kolkata 700009 (India); Shannigrahi, Santiranjan [Institute of Materials Research and Engineering, Agency for Science Technology and Research, 3 Research Link, Singapore 117602 (Singapore)

    2015-09-15

    The X-ray photoemission spectroscopic (XPS) study of the double perovskite oxides A{sub 2}LaMO{sub 6} [A=Ba, Ca; M=Nb, Ta] synthesized by the solid-state reaction technique has been carried out to investigate the nature of the chemical state of the constituent ions and the bonding between them. The Rietveld refinement of the X-ray diffraction patterns suggests the monoclinic crystal structure of all the materials at room temperature. The negative and positive chemical shifts of the core level XPS spectrum of O-1s and Nb-3d{sub 3/2}/Ta-4f{sub 5/2} respectively suggest the covalent bonding between Nb/Ta cations and O ion. The change of the bonding strength between the anion and the cations from one material to another has been analyzed. The vibrational property of the materials is investigated using the room temperature Raman spectra. A large covalency of Ta-based compound than Nb compound is confirmed from the relative shifting of the Raman modes of the materials. - Graphical abstract: Crystal structure of two perovskite oxides CLN and CLT is investigated. XPS study confirms the two different co-ordination environments of Ca and covalent bonding between B-site cations and O-ion. - Highlights: • Ordered perovskite structure obtained by Rietveld refinement of XRD patterns. • Study of nature of chemical bonding by X-ray photoemission spectroscopy. • Opposite chemical shift of d-states of Nb/Ta with respect to O. • Covalent bonding between d-states of Nb/Ta and O. • Relative Raman shifts of CLN and CLT substantiate the more covalent character of Ta than Nb.

  2. Crystal structure and X-ray photoemission spectroscopic study of A2LaMO6 [A=Ba, Ca; M=Nb, Ta

    The X-ray photoemission spectroscopic (XPS) study of the double perovskite oxides A2LaMO6 [A=Ba, Ca; M=Nb, Ta] synthesized by the solid-state reaction technique has been carried out to investigate the nature of the chemical state of the constituent ions and the bonding between them. The Rietveld refinement of the X-ray diffraction patterns suggests the monoclinic crystal structure of all the materials at room temperature. The negative and positive chemical shifts of the core level XPS spectrum of O-1s and Nb-3d3/2/Ta-4f5/2 respectively suggest the covalent bonding between Nb/Ta cations and O ion. The change of the bonding strength between the anion and the cations from one material to another has been analyzed. The vibrational property of the materials is investigated using the room temperature Raman spectra. A large covalency of Ta-based compound than Nb compound is confirmed from the relative shifting of the Raman modes of the materials. - Graphical abstract: Crystal structure of two perovskite oxides CLN and CLT is investigated. XPS study confirms the two different co-ordination environments of Ca and covalent bonding between B-site cations and O-ion. - Highlights: • Ordered perovskite structure obtained by Rietveld refinement of XRD patterns. • Study of nature of chemical bonding by X-ray photoemission spectroscopy. • Opposite chemical shift of d-states of Nb/Ta with respect to O. • Covalent bonding between d-states of Nb/Ta and O. • Relative Raman shifts of CLN and CLT substantiate the more covalent character of Ta than Nb

  3. Evidence for replicate 5p core levels in photoelectron spectra of Eu metal due to nonconstant kinetic-energy resonant Auger decay

    Satellites on the low-binding-energy side of core-level photoelectron emission due to extra 4f screening are a well-known feature in the x-ray photoelectron spectra of valence fluctuation materials and rare-earth metals. A notable exception is Eu metal, where up to now no low-binding-energy satellite has been observed. In this paper we show that in Eu metal the 4d-4f resonance can decay via a resonant Auger decay, which is not a constant kinetic-energy feature due to a rapid change of the strength of 4f screening with excitation energy, establishing a low-binding-energy replica of the 5p core-level photoelectron emission. (c) 1999 The American Physical Society

  4. Surface Carrier Dynamics on Semiconductor Studied with Femtosecond Core-Level Photoelectron Spectroscopy Using Extreme Ultraviolet High-Order Harmonic Source

    Sogawa T.

    2013-03-01

    Full Text Available We have used a femtosecond time-resolved core-level surface PES system based on the 92-eV harmonic source to study the surface carrier dynamics that induces the transient SPV on semiconductor surfaces. We clarified the temporal evolution of the transient SPV characterized by the time of the photo-generated carrier separation and recombination. This result demonstrates the potential of this technique for clarifying the initial stage of the surface carrier dynamics after photoexcitation.

  5. Surface Carrier Dynamics on Semiconductor Studied with Femtosecond Core-Level Photoelectron Spectroscopy Using Extreme Ultraviolet High-Order Harmonic Source

    Oguri, K.; Tsunoi, T.; Kato, K.; Nakano, H.; Nishikawa, T.; Gotoh, H.; Tateno, K.; Sogawa, T.

    2013-03-01

    We have used a femtosecond time-resolved core-level surface PES system based on the 92-eV harmonic source to study the surface carrier dynamics that induces the transient SPV on semiconductor surfaces. We clarified the temporal evolution of the transient SPV characterized by the time of the photo-generated carrier separation and recombination. This result demonstrates the potential of this technique for clarifying the initial stage of the surface carrier dynamics after photoexcitation.

  6. Time dependence of FEL-induced surface photovoltage on semiconductor interfaces measured with synchroton radiation photoemission spectroscopy

    During the last year, the first surface science experiments simultaneously using a Free Electron Laser (FEL) and Synchrotron Radiation (SR) have been performed on SuperACO at LURE (Orsay, France). These open-quotes two colorclose quotes experiments studied the surface photovoltage (SPV) induced on semiconductor surfaces and interfaces by the SuperACO FEL, a storage ring FEL delivering 350 nm photons which am naturally synchronized with the SR; the SPV was measured by synchrotron radiation core-level photoemission spectroscopy on the high-resolution SU3 undulator beamline. We will describe the experimental setup, which allowed us to convey the FEL light onto the samples sitting in the SU3 experimental station by means of a series of mirrors, and show the results we obtained for prototypical systems such as Ag/GaAs(110) and Si(111) 2 x 1. The dependence of the SPV was studied in function of various parameters, changing sample doping and photon flux; but our efforts were mainly devoted to studying its dependence on the time delay between the FEL pump and the SR probe. On SuperACO, such delay can be varied between 1 and 120 ns, the limits being given by the time duration of a SR pulse and by the interval between two consecutive positron bunches, respectively. The results show a clear temporal dependence of the amount of SPV on cleaved Si surfaces, where as the Ag/GaAs(110) does not show any difference on the ns time scale. We will discuss these results in terms of the role of surface recombination in the dynamics of the photoinduced electron-hole pairs. These studies follow the evolution of the density of electrostatic charge at surfaces and interfaces on a nanosecond time scale, and might pave the way for a new series of experiments: for example, one might explore what are the physical mechanisms limiting the time response of Schottky diodes

  7. Thermodynamics, core-level spectroscopy, morphology, and work function study of different TiCl{sub 3} crystalline phases: A theoretical approach

    Guo, Lei [School of Chemistry and Chemical Engineering, Chongqing University, Chongqing 400044 (China); Li, Wenpo, E-mail: cqliwp@163.com [School of Chemistry and Chemical Engineering, Chongqing University, Chongqing 400044 (China); Feng, Wenjiang [College of Physics Science and Technology, Shenyang Normal University, Shenyang 110034 (China); Zhang, Zhipeng [School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024 (China); Zhang, Shengtao [School of Chemistry and Chemical Engineering, Chongqing University, Chongqing 400044 (China)

    2014-07-25

    Highlights: • Three TiCl{sub 3} polymorphs materials were systematically investigated. • Structural results agree well with experimental and available theoretical data. • Morphological and thermodynamic properties were computed and analyzed. • Core-level spectroscopy and work function were obtained. - Abstract: Computer simulation has been widely applied in many research fields owing to its superiority in revealing an insight understanding of the phenomena. In this work, the thermodynamics, core-level spectroscopy, morphology, and work function of TiCl{sub 3} with three different crystalline phases (α, β, and γ) have been comprehensively computed employing the Materials Studio package. Our computational DFT-D approach gives a structural description of the TiCl{sub 3} phases in good agreement with experiment. The core-level spectroscopy confirmed that α, β, and γ modifications for TiCl{sub 3} have lightly affected on the valences of the constitutional elements. A series of possible growth faces (h k l) were deduced using the classic Bravais–Friedel–Donnay–Harker (BFDH) model. We conclude that the sequence of work function for (0 0 1) surface was α > β ≈ γ.

  8. Thermodynamics, core-level spectroscopy, morphology, and work function study of different TiCl3 crystalline phases: A theoretical approach

    Highlights: • Three TiCl3 polymorphs materials were systematically investigated. • Structural results agree well with experimental and available theoretical data. • Morphological and thermodynamic properties were computed and analyzed. • Core-level spectroscopy and work function were obtained. - Abstract: Computer simulation has been widely applied in many research fields owing to its superiority in revealing an insight understanding of the phenomena. In this work, the thermodynamics, core-level spectroscopy, morphology, and work function of TiCl3 with three different crystalline phases (α, β, and γ) have been comprehensively computed employing the Materials Studio package. Our computational DFT-D approach gives a structural description of the TiCl3 phases in good agreement with experiment. The core-level spectroscopy confirmed that α, β, and γ modifications for TiCl3 have lightly affected on the valences of the constitutional elements. A series of possible growth faces (h k l) were deduced using the classic Bravais–Friedel–Donnay–Harker (BFDH) model. We conclude that the sequence of work function for (0 0 1) surface was α > β ≈ γ

  9. Queries mining for efficient routing in P2P communities

    Ismail, Anis; Durand, Nicolas; Nachouki, Gilles; Hajjar, Mohammad

    2011-01-01

    Peer-to-peer (P2P) computing is currently attracting enormous attention. In P2P systems a very large number of autonomous computing nodes (the peers) pool together their resources and rely on each other for data and services. Peer-to-peer (P2P) Data-sharing systems now generate a significant portion of Internet traffic. Examples include P2P systems for network storage, web caching, searching and indexing of relevant documents and distributed network-threat analysis. Requirements for widely distributed information systems supporting virtual organizations have given rise to a new category of P2P systems called schema-based. In such systems each peer exposes its own schema and the main objective is the efficient search across the P2P network by processing each incoming query without overly consuming bandwidth. The usability of these systems depends on effective techniques to find and retrieve data; however, efficient and effective routing of content-based queries is a challenging problem in P2P networks. This wo...

  10. Angle-resolved photoemission spectroscopy for VO2 thin films grown on TiO2 (0 0 1) substrates

    We present the results of angle-resolved photoemission spectroscopy (ARPES) measurements of metallic VO2 thin films. The VO2 thin films have been grown on TiO2 (0 0 1) single crystal substrates using pulsed laser deposition. The films exhibit a first-order metal-insulator transition (MIT) at 305 K. In the ARPES spectra of the metallic phase for the films, the O 2p band shows highly dispersive feature in the binding energy range of 3-8 eV along the Γ-Z direction. The periodicity of the dispersive band is found to be 2.2 A-1 which is almost identical with the periodicity expected from the c-axis length of the VO2 thin films. The overall feature of the experimental band structure is similar to the band structure calculations, supporting that we have succeeded in observing the dispersive band of the O 2p state in the metallic VO2 thin film. The present work indicates that the ARPES measurements using epitaxial thin films are promising for determining the band structure of VO2.

  11. Measurement and Analysis of P2P IPTV Program Resource

    Wenxian Wang; Xingshu Chen; Haizhou Wang; Qi Zhang; Cheng Wang

    2014-01-01

    With the rapid development of P2P technology, P2P IPTV applications have received more and more attention. And program resource distribution is very important to P2P IPTV applications. In order to collect IPTV program resources, a distributed multi-protocol crawler is proposed. And the crawler has collected more than 13 million pieces of information of IPTV programs from 2009 to 2012. In addition, the distribution of IPTV programs is independent and incompact, resulting in chaos of program na...

  12. Comparing Pedophile Activity in Different P2P Systems

    Raphaël Fournier; Thibault Cholez; Matthieu Latapy; Isabelle Chrisment; Clémence Magnien; Olivier Festor; Ivan Daniloff

    2014-01-01

    International audience Peer-to-peer (P2P) systems are widely used to exchange content over the Internet. Knowledge of pedophile activity in such networks remains limited, despite having important social consequences. Moreover, though there are different P2P systems in use, previous academic works on this topic focused on one system at a time and their results are not directly comparable. We design a methodology for comparing KAD and eDonkey, two P2P systems among the most prominent ones an...

  13. Code wars 10 years of P2P software litigation

    Giblin, Rebecca

    2011-01-01

    Code Wars recounts the legal and technological history of the first decade of the P2P file sharing era, focusing on the innovative and anarchic ways in which P2P technologies evolved in response to decisions reached by courts with regard to their predecessors. With reference to US, UK, Canadian and Australian secondary liability regimes, this insightful book develops a compelling new theory to explain why a decade of ostensibly successful litigation failed to reduce the number, variety or availability of P2P file sharing applications - and highlights ways the law might need to change if it is

  14. Microlens Array Laser Transverse Shaping Technique for Photoemission Electron Source

    Halavanau, A; Qiang, G; Gai, W; Power, J; Piot, P; Wisniewski, E; Edstrom, D; Ruan, J; Santucci, J

    2016-01-01

    A common issue encountered in photoemission electron sources used in electron accelerators is distortion of the laser spot due to non ideal conditions at all stages of the amplification. Such a laser spot at the cathode may produce asymmetric charged beams that will result in degradation of the beam quality due to space charge at early stages of acceleration and fail to optimally utilize the cathode surface. In this note we study the possibility of using microlens arrays to dramatically improve the transverse uniformity of the drive laser pulse on UV photocathodes at both Fermilab Accelerator Science \\& Technology (FAST) facility and Argonne Wakefield Accelerator (AWA). In particular, we discuss the experimental characterization of the homogeneity and periodic patterned formation at the photocathode. Finally, we compare the experimental results with the paraxial analysis, ray tracing and wavefront propagation software.

  15. X-ray photoemission spectroscopy study of hexavalent uranium compounds

    The electronic structure of the outer occupied levels of a series of hexavalent uranium (predominately uranyl) compounds was studied using x-ray photoemission spectroscopy (XPS). The changes in the spectral features of the outer occupied levels with the variation of the uranium-oxygen bond lengths (1.7--2.1 A) are systematically investigated. Previously unexplained spectral structure has been found to result from ligand-field splitting of the occupied U 6p3/2 levels. The XPS results are compared with predictions of a relativistic molecular-cluster calculation and with the results of a simple point-charge crystal-field model. When the crystalline electric fields generated by both the primary and secondary ligands are taken into consideration, excellent quantitative agreement is obtained between the XPS data and the molecular-cluster results with no parameter adjustment

  16. Photoemission from Coated Surfaces A Comparison of Theory to Experiment

    Jensen, K

    2005-01-01

    Photocathodes for FELs and accelerators will benefit from rugged and self-rejuvenating photocathodes with high QE at the longest possible wavelength. The needs of a high power FEL are not met at present by existing photocathode-drive laser combinations: requirements generally necessitate barrier-lowering coatings which are degraded by operation. We seek to develop a controlled porosity dispenser cathode, and shall report on our coordinated experimental and theoretical studies. Our models account for field, thermal, and surface effects of cesium monolayers on photoemission, and compare well with concurrent experiments examining the QE, patchiness, and evolution of the coatings. Field enhancement, thermal variation of specific heat and electron relaxation rates and their relation to high laser intensity and/or short pulse-to-pulse separation, variations in work function effects due to coating non-uniformity, and the dependence on the wavelength of the incident light are included. The status of methods by which ...

  17. Electric field stimulation setup for photoemission electron microscopes

    Manipulating magnetisation by the application of an electric field in magnetoelectric multiferroics represents a timely issue due to the potential applications in low power electronics and the novel physics involved. Thanks to its element sensitivity and high spatial resolution, X-ray photoemission electron microscopy is a uniquely suited technique for the investigation of magnetoelectric coupling in multiferroic materials. In this work, we present a setup that allows for the application of in situ electric and magnetic fields while the sample is analysed in the microscope. As an example of the performances of the setup, we present measurements on Ni/Pb(Mg0.66Nb0.33)O3-PbTiO3 and La0.7Sr0.3MnO3/PMN-PT artificial multiferroic nanostructures

  18. Electric field stimulation setup for photoemission electron microscopes

    Buzzi, M.; Vaz, C. A. F.; Raabe, J.; Nolting, F., E-mail: frithjof.nolting@psi.ch [Paul Scherrer Institut, 5232 Villigen PSI (Switzerland)

    2015-08-15

    Manipulating magnetisation by the application of an electric field in magnetoelectric multiferroics represents a timely issue due to the potential applications in low power electronics and the novel physics involved. Thanks to its element sensitivity and high spatial resolution, X-ray photoemission electron microscopy is a uniquely suited technique for the investigation of magnetoelectric coupling in multiferroic materials. In this work, we present a setup that allows for the application of in situ electric and magnetic fields while the sample is analysed in the microscope. As an example of the performances of the setup, we present measurements on Ni/Pb(Mg{sub 0.66}Nb{sub 0.33})O{sub 3}-PbTiO{sub 3} and La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/PMN-PT artificial multiferroic nanostructures.

  19. Electric field stimulation setup for photoemission electron microscopes

    Buzzi, M.; Vaz, C. A. F.; Raabe, J.; Nolting, F.

    2015-08-01

    Manipulating magnetisation by the application of an electric field in magnetoelectric multiferroics represents a timely issue due to the potential applications in low power electronics and the novel physics involved. Thanks to its element sensitivity and high spatial resolution, X-ray photoemission electron microscopy is a uniquely suited technique for the investigation of magnetoelectric coupling in multiferroic materials. In this work, we present a setup that allows for the application of in situ electric and magnetic fields while the sample is analysed in the microscope. As an example of the performances of the setup, we present measurements on Ni/Pb(Mg0.66Nb0.33)O3-PbTiO3 and La0.7Sr0.3MnO3/PMN-PT artificial multiferroic nanostructures.

  20. Measurement and analysis of thermal photoemission from a dispenser cathode

    Jensen, Kevin L.; Feldman, Donald W.; Virgo, Matt; O'Shea, Patrick G.

    2003-08-01

    Photocathodes for free electron lasers (FELs) are required to produce nano-Coulomb pulses in picosecond time scales with demonstrable reliability, lifetime, and efficiency. Dispenser cathodes, traditionally a rugged and long-lived thermionic source, are under investigation to determine their utility as a photocathode and have shown promise. The present study describes theoretical models under development to analyze experimental data from dispenser cathodes and to create predictive time-dependent models to predict their performance as an FEL source. Here, a steady-state model of a dispenser cathode with partial coverage of a low work function coating and surface nonuniformity is developed. Quantitative agreement is found for experimental data, especially with regard to temperature, field, laser intensity, and quantum efficiency versus laser wavelength dependence. In particular, for long wavelength incident lasers of sufficient intensity, the majority of the absorbed energy heats the electron gas and background lattice, and photoemission from the heated electron distribution constitutes the emitted current.

  1. Widespread spin polarization effects in photoemission from topological insulators

    Jozwiak, C.; Chen, Y. L.; Fedorov, A. V.; Analytis, J. G.; Rotundu, C. R.; Schmid, A. K.; Denlinger, J. D.; Chuang, Y.-D.; Lee, D.-H.; Fisher, I. R.; Birgeneau, R. J.; Shen, Z.-X.; Hussain, Z.; Lanzara, A.

    2011-06-22

    High-resolution spin- and angle-resolved photoemission spectroscopy (spin-ARPES) was performed on the three-dimensional topological insulator Bi{sub 2}Se{sub 3} using a recently developed high-efficiency spectrometer. The topological surface state's helical spin structure is observed, in agreement with theoretical prediction. Spin textures of both chiralities, at energies above and below the Dirac point, are observed, and the spin structure is found to persist at room temperature. The measurements reveal additional unexpected spin polarization effects, which also originate from the spin-orbit interaction, but are well differentiated from topological physics by contrasting momentum and photon energy and polarization dependencies. These observations demonstrate significant deviations of photoelectron and quasiparticle spin polarizations. Our findings illustrate the inherent complexity of spin-resolved ARPES and demonstrate key considerations for interpreting experimental results.

  2. X-ray Photoemission Spectroscopy Studies of Cesium Antimonide Photocathodes for Photoinjector Applications

    Martini, Irene; Chevallay, Eric; Fedosseev, Valentin; Hessler, Christoph; Neupert, Holger; Nistor, Valentin; Taborelli, Mauro

    Within the CLIC (Compact Linear Collider) project, feasibility studies of a photoinjector option for the drive beam as an alternative to its baseline design using a thermionic electron gun (Geschonke et al. [1]) are on-going. This R&D program covers both the laser and the photocathode side. Cesium antimonide cathodes were produced at CERN by co-deposition onto copper substrates and characterized by photoemission and by XPS (X-ray Photoemission Spectroscopy) analysis. A systematic study on newly produced and used photocathodes was conducted in order to correlate the surface composition to the photoemissive properties.

  3. SW-R2P: A Trusted Small World Overlay P2P Network with Zero Knowledge Identification

    Yingjie Xia

    2008-10-01

    Full Text Available In order to implement both the efficiency and security in the Peer-to-Peer (P2P network, we design a trusted small world overlay P2P network with the role based and reputation based access control policies, denoted as SW-R2P. The SW-R2P system integrates the small world topology with zero knowledge identification and Bayesian trust model. The zero knowledge identification is utilized to securely cluster all the peers into several groups without transferring any related information. The peer groups are then linked together to construct a trusted small world network based on the probabilities calculated by the Bayesian trust model. The simulation experiments demonstrate that the SW-R2P system achieves the performance with increased success rate in the resources lookup, strengthened robustness under the overwhelming traffic loadings, reduced reputation errors caused by the malicious peers and enhanced peer satisfaction rate for different trust metrics. In conclusion, the SW-R2P system collectively exploits the advantages of small world, zero knowledge identification and Bayesian trust model, therefore implementing a scalable, secure and efficient P2P network.

  4. Trisomy 2p: Analysis of unusual phenotypic findings

    Lurie, I.W.; Ilyina, H.G.; Gurevich, D.B. [Belorussian Research Institute of Hereditary Disease, Minsk (Russian Federation)] [and others

    1995-01-16

    We present three probands with partial trisomies 2p21-23 due to ins(4;2)(q21;p21p23) pat, 2p23-pter due to t(2;4)(p23;q35)mat, and 2p21-pter due to t(2;11)(p21;q23.3)mat. More than 50 cases of partial trisomy 2p have been reviewed and some abnormalities, unusual for most other types of structural autosomal imbalance, have been found in patients with inherited forms of 2p trisomy and in their non-karyotyped sibs. Neural tube defects (anencephaly, occipital encephalocele, and spina bifida) were found in five probands and 4/6 affected non-karyotyped sibs. The only triplicated segment common to all was 2p24. Different forms of {open_quotes}broncho-pulmonary a/hypoplasia{close_quotes} (including two cases of lung agenesis) were described in four patients (overlapping triplicated segment was 2p21-p25). Three patients (with overlapping triplicated segment 2p23-p25) had diaphragmatic hernia. Abnormal rotation of the heart or L-transposition of large vessels (with or without visceral heterotaxia) was found in two infants (overlapping triplicated segment 2p23-p24). In two patients with common triplicated segment 2p22.3-p25, neuroblastoma has been described. The occurrence of all these defects may be explained either by the action of the same gene(s) mapped to 2p24 or by action of some independent factors located in different segments of the short arm. Although the latter hypothesis is much less probable, it can not be rejected at the present time. We propose the existence of a genetic system controlling surveillance of an abnormal embryo to explain the phenotypic differences between patients with the same imbalance within a family. In some {open_quotes}restrictive{close_quotes} combinations the abnormal embryos will die, although in {open_quotes}permissive{close_quotes} combinations they can survive. 47 refs., 2 figs., 3 tabs.

  5. P2P Concept Search: Some Preliminary Results

    Giunchiglia, Fausto; Kharkevich, Uladzimir; Noori, S.R.H

    2009-01-01

    Concept Search extends syntactic search, i.e., search based on the computation of string similarity between words, with semantic search, i.e., search based on the computation of semantic relations between complex concepts. It allows us to deal with ambiguity of natural language. P2P Concept Search extends Concept Search by allowing distributed semantic search over structured P2P network. The key idea is to exploit distributed, rather than centralized, background knowledge and indices.

  6. Chimpanzee chromosome 13 is homologous to human chromosome 2p

    Sun, N. C.; Sun, C. R.Y.; Ho, T.

    1977-01-01

    Similarities between human and chimpanzee chromosomes are shown by chromosome banding techniques and somatic cell hybridization techniques. Cell hybrids were obtained from the chimpanzee lymphocyte LE-7, and the Chinese hamster mutant cell, Gal-2. Experiments showed that the ACPL, MDHs, and Gal-Act genes could be assigned to chimpanzee chromosome 13, and since these genes have been assigned to human chromosme 2p, it is suggested that chimpanzee chromosome 13 is homologous to human chromosome 2p. (HLW)

  7. Mobile P2P Web Services Using SIP

    Guido Gehlen; Fahad Aijaz; Yi Zhu; Bernhard Walke

    2007-01-01

    Telecommunication networks and the Internet are growing together. Peer-to-Peer (P2P) services which are originally offered by network providers, like telephony and messaging, are provided through VoIP and Instant Messaging (IM) by Internet service providers, too. The IP Multimedia Subsystem (IMS) is the answer of the telecommunication industry to this trend and aims at providing Internet P2P and multimedia services controlled by the network operators. The IMS provides mobility and session man...

  8. Survey on Scheduling Technologies of P2P Media Streaming

    Guangxue Yue; Nanqing Wei; Jiansheng Liu; Xiaofeng Xiong; Linquan Xie

    2011-01-01

    P2P streaming media applications grows rapidly. Scheduling technologies are the key of streaming research. After review the history of distribution systems. We studied the main data distribution topology and P2P streaming scheduling technologies. Compared current scheduling algorithms. Finally made a conclusion and forecasted scheduling in the mesh-tree distribution structure, heterogeous network, alone with security in scheduling will be the hotspots in the near future.

  9. Characterization of P2P IPTV Traffic: Scaling Analysis

    Silverston, Thomas; Salamatian, Kave

    2007-01-01

    P2P IPTV applications arise on the Internet and will be massively used in the future. It is expected that P2P IPTV will contribute to increase the overall Internet traffic. In this context, it is important to measure the impact of P2P IPTV on the networks and to characterize this traffic. During the 2006 FIFA World Cup, we performed an extensive measurement campaign. We measured network traffic generated by broadcasting soccer games by the most popular P2P IPTV applications, namely PPLive, PPStream, SOPCast and TVAnts. From the collected data, we characterized the P2P IPTV traffic structure at different time scales. To the best of our knowledge, this is the first work, which presents a complete multiscale analysis of the P2P IPTV traffic. Our observations show that the network traffic has not the same scale behavior whether the applications use TCP or UDP. For all the applications, the download traffic is different from the upload traffic and the signaling traffic has an impact on the download traffic.

  10. Improving P2P live-content delivery using SVC

    Schierl, T.; Sánchez, Y.; Hellge, C.; Wiegand, T.

    2010-07-01

    P2P content delivery techniques for video transmission have become of high interest in the last years. With the involvement of client into the delivery process, P2P approaches can significantly reduce the load and cost on servers, especially for popular services. However, previous studies have already pointed out the unreliability of P2P-based live streaming approaches due to peer churn, where peers may ungracefully leave the P2P infrastructure, typically an overlay networks. Peers ungracefully leaving the system cause connection losses in the overlay, which require repair operations. During such repair operations, which typically take a few roundtrip times, no data is received from the lost connection. While taking low delay for fast-channel tune-in into account as a key feature for broadcast-like streaming applications, the P2P live streaming approach can only rely on a certain media pre-buffer during such repair operations. In this paper, multi-tree based Application Layer Multicast as a P2P overlay technique for live streaming is considered. The use of Flow Forwarding (FF), a.k.a. Retransmission, or Forward Error Correction (FEC) in combination with Scalable video Coding (SVC) for concealment during overlay repair operations is shown. Furthermore the benefits of using SVC over the use of AVC single layer transmission are presented.

  11. Network Awareness in P2P-TV Applications

    Traverso, Stefano; Leonardi, Emilio; Mellia, Marco; Meo, Michela

    The increasing popularity of applications for video-streaming based on P2P paradigm (P2P-TV) is raising the interest of both broadcasters and network operators. The former see a promising technology to reduce the cost of streaming content over the Internet, while offering a world-wide service. The latter instead fear that the traffic offered by these applications can grow without control, affecting other services, and possibly causing network congestion and collapse. The “Network-Aware P2P-TV Application over Wise Networks” FP7 project aims at studying and developing a novel P2P-TV application offering the chance to broadcast high definition video to broadcasters and to carefully manage the traffic offered by peers to the network, therefore avoiding worries to Internet providers about network overload. In such context, we design a simulator to evaluate performance of different P2P-TV solutions, to compare them both considering end-users’ and network providers’ perspectives, such as quality of service perceived by subscribers and link utilization. In this paper, we provide some results that show how effective can be a network aware P2P-TV system.

  12. P2P Data Management in Mobile Wireless Sensor Network

    Nida Sahar Sayeda

    2013-04-01

    Full Text Available The rapid growth in wireless technologies has made wireless communication an important source for transporting data across different domains. In the same way, there are possibilities of many potential applications that can be deployed using WSNs (Wireless Sensor Networks. However, very limited applications are deployed in real life due to the uncertainty and dynamics of the environment and scare resources. This makes data management in WSN a challenging area to find an approach that suits its characteristics. Currently, the trend is to find efficient data management schemes using evolving technologies, i.e. P2P (Peer-to-Peer systems. Many P2P approaches have been applied in WSNs to carry out the data management due to similarities between WSN and P2P. With the similarities, there are differences too that makes P2P protocols inefficient in WSNs. Furthermore, to increase the efficiency and to exploit the delay tolerant nature of WSNs, where ever possible, the mobile WSNs are gaining importance. Thus, creating a three dimensional problem space to consider, i.e. mobility, WSNs and P2P. In this paper, an efficient algorithm is proposed for data management using P2P techniques for mobile WSNs. The real world implementation and deployment of proposed algorithm is also presented

  13. Theatrical distribution and P2P movie piracy: a survey of P2P networks in Hungary using transactional data

    Bodó, B.; Lakatos, Z.

    2012-01-01

    This article examines what appears to be the most important factor shaping file sharing: the failure of traditional cultural markets to efficiently supply the demand in the online environment. Its findings are based on tracking the traffic of movies on three Hungarian P2P networks. This dataset is then matched with cinematic distribution data of the films tracked in P2P transactions. Central to our analysis is the assessment of two piracy paradigms: substitution and shortage, that is, whether...

  14. Characterization of Catechins in Water by Photoemission Yield Spectroscopy in Air.

    Yamashita, Daisuke; Ishizaki, Atsushi

    2016-01-01

    Photoemission yield spectroscopy in air (PYSA) was applied for the characterization of catechins in water in ambient conditions. According to the results of measurements on aqueous solutions of epigallocatechin gallate (EGCg) of various concentrations, the photoemission yield is almost proportional to the concentration of EGCg. Contrarily, the threshold energy of photoemission, EPET, is almost constant at 5.46 ± 0.02 eV. Moreover, we measured aqueous solutions of epicatechin (EC), epigallocatechin (EGC), and epicatechin gallate (ECg). The values of EPET of EC, EGC, ECg were estimated to be 5.72 ± 0.02, 5.68 ± 0.01, and 5.45 ± 0.02 eV, respectively, and a dependence on the molecular structure was found. Furthermore, changes in the photoemission yield spectra of heated EGCg were well explained by molecular orbital calculations on the basis of an assumption of epimerization. PMID:27169659

  15. First-principles photoemission spectroscopy of DNA and RNA nucleobases from Koopmans-compliant functionals

    Nguyen, Ngoc Linh; Ferretti, Andrea; Marzari, Nicola

    2016-01-01

    The need to interpret ultraviolet photoemission data strongly motivates the refinement of first-principles techniques able to accurately predict spectral properties. In this work we employ Koopmans-compliant functionals, constructed to enforce piecewise linearity in approximate density functionals, to calculate the structural and electronic properties of DNA and RNA nucleobases. Our results show that not only ionization potentials and electron affinities are accurately predicted with mean absolute errors < 0.1 eV, but also that calculated photoemission spectra are in excellent agreement with experimental ultraviolet photoemission spectra. In particular, the role and contribution of different tautomers to the photoemission spectra are highlighted and discussed in detail. The structural properties of nucleobases are also investigated, showing an improved description with respect to local and semilocal density-functional theory. Methodologically, our results further consolidate the role of Koopmans-compliant ...

  16. Scanning internal photoemission microscopy for the identification of hot carrier transport mechanisms

    Differt, D.; Pfeiffer, W.; Diesing, D.

    2012-09-01

    Linear and nonlinear internal photoemission in a thin-film metal-insulator-metal heterosystem, i.e., a Ta-TaOx-Ag junction, together with surface reflectivity are mapped with a lateral resolution of better than 5 μm. The spatial correlation of the different signals and time-resolved internal photoemission spectroscopy reveal excitation mechanisms and ballistic hot carrier injection. The internal photoemission yield variation with Ag layer thickness is quantitatively explained by above-barrier injection. The hot-spot-like behavior of the two-photon induced internal photoemission observed for short pulse excitation is attributed to local field enhancements because of Ag-film thickness reduction and plasmonic effects at structural defects.

  17. Low-Temperature and High-Energy-Resolution Laser Photoemission Spectroscopy

    Shimojima, Takahiro; Okazaki, Kozo; Shin, Shik

    2015-07-01

    We present a review on the developments in the photoemission spectrometer with a vacuum ultraviolet laser at Institute for Solid State Physics at the University of Tokyo. The advantages of high energy resolution, high cooling ability, and bulk sensitivity enable applications with a wide range of materials. We introduce some examples of fine electronic structures detected by laser photoemission spectroscopy and discuss the prospects of research on low-transition-temperature superconductors exhibiting unconventional superconductivity.

  18. Angle resolved photoemission from organic semiconductors: orbital imaging beyond the molecular orbital interpretation

    Dauth, M.; Wiessner, M.; Feyer, V.; Schöll, A.; Puschnig, P.; Reinert, F.; Kümmel, S.

    2015-01-01

    Fascinating pictures that can be interpreted as showing molecular orbitals have been obtained with various imaging techniques. Among these, angle resolved photoemission spectroscopy (ARPES) has emerged as a particularly powerful method. Orbital images have been used to underline the physical credibility of the molecular orbital concept. However, from the theory of the photoemission process it is evident that imaging experiments do not show molecular orbitals, but Dyson orbitals. The latter ar...

  19. Low-Temperature and High-Energy-Resolution Laser Photoemission Spectroscopy

    Shimojima, Takahiro; Okazaki, Kozo; Shin, Shik

    2016-01-01

    We present a review on the developments in the photoemission spectrometer with a vacuum ultraviolet laser at Institute for Solid State Physics at the University of Tokyo. The advantages of high energy resolution, high cooling ability, and bulk sensitivity enable applications with a wide range of materials. We introduce some examples of fine electronic structures detected by laser photoemission spectroscopy and discuss the prospects of research on low-transition-temperature superconductors exh...

  20. Final-state interference effects in valence band photoemission of (C59N)2

    Hunt, Michael R.C.; Pichler, Thomas; Šiller, Lidija; Brühwiler, Paul A.; Golden, Mark S.; Tagmatarchis, Nikos; Prassides, Kosmas; Rudolf, Petra

    2002-01-01

    Oscillatory behavior of photoemission intensity with incident photon energy has been observed for several fullerenes and fullerene derivatives. However, until now it has been unclear if these effects arise from interference associated with the spatial distribution of the initial state within the molecule or are due to scattering of the outgoing photoelectron. In order to resolve this issue we performed synchrotron radiation excited valence band photoemission measurements on multilayer (C59N)2...

  1. High-harmonic XUV source for time- and angle-resolved photoemission spectroscopy

    Dakovski, Georgi L [Los Alamos National Laboratory; Li, Yinwan [Los Alamos National Laboratory; Durakiewicz, Tomasz [Los Alamos National Laboratory; Rodriguez, George [Los Alamos National Laboratory

    2009-01-01

    We present a laser-based apparatus for visible pump/XUV probe time- and angle-resolved photoemission spectroscopy (TRARPES) utilizing high-harmonic generation from a noble gas. Femtosecond temporal resolution for each selected harmonic is achieved by using a time-delay-compensated monochromator (TCM). The source has been used to obtain photoemission spectra from insulators (UO{sub 2}) and ultrafast pump/probe processes in semiconductors (GaAs).

  2. 5f-band width and resonant photoemission of uranium intermetallic compounds

    New experimental results and theoretical arguments are used in conjunction with previously published data to demonstrate that resonant photoemission (RPS) does not provide a reliable measure of the occupied 5f density of states in uranium intermetallic compounds. We implicate a resonant Auger process in this phenomenon and argue that RPS measurements (in conjunction with x-ray photoemission spectroscopy data) in this context are more useful as a qualitative guide to U 5f--ligand hybridization

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

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

    2013-01-01

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

  4. Adsorption site and structure determination of c(2x2) N{sub 2}/Ni(100) using angle-resolved photoemission extended fine structure

    Moler, E.J.; Kellar, S.A.; Huff, W.R.A. [Lawrence Berkeley National Lab., CA (United States)] [and others

    1997-04-01

    The authors have determined the atomic spatial structure of c(2x2) N2Ni(100) with Angle-Resolved Photoemission Extended Fine Structure (ARPEFS) from the nitrogen 1s core level using monochromatized x-rays from beamline 6.1 at SSRL and beamline 9.3.2 at the ALS. The chemically shifted N 1s peak intensities were summed together to obtain ARPEFS curves for both nitrogen atoms in the molecule. They used a new, highly-optimized program based on the Rehr-Albers scattering matrix formalism to find the adsorption site and to quantitatively determine the bond-lengths. The nitrogen molecule stands upright at an atop site, with a N-Ni bond length of 2.25(1) {angstrom}, a N-N bond length of 1.10(7) {angstrom}, and a first layer Ni-Ni spacing of 1.76(4) {angstrom}. The shake-up peak shows an identical ARPEFS diffraction pattern, confirming its intrinsic nature and supporting a previous use of this feature to decompose the peak into contributions from the chemically inequivalent nitrogen atoms. Comparison to a previously published theoretical treatment of N-N-Ni and experimental structures of analogous adsorbate systems demonstrates the importance of adsorbate-adsorbate interactions in weakly chemisorbed systems.

  5. Design of an ultrahigh vacuum transfer mechanism to interconnect an oxide molecular beam epitaxy growth chamber and an x-ray photoemission spectroscopy analysis system

    We designed a mechanism and the accompanying sample holders to transfer between a VEECO 930 oxide molecular beam epitaxy (MBE) and a PHI Versa Probe X-ray photoemission spectroscopy (XPS) chamber within a multiple station growth, processing, and analysis system through ultrahigh vacuum (UHV). The mechanism consists of four parts: (1) a platen compatible with the MBE growth stage, (2) a platen compatible with the XPS analysis stage, (3) a sample coupon that is transferred between the two platens, and (4) the accompanying UHV transfer line. The mechanism offers a robust design that enables transfer back and forth between the growth chamber and the analysis chamber, and yet is flexible enough to allow transfer between standard sample holders for thin film growth and masked sample holders for making electrical contacts and Schottky junctions, all without breaking vacuum. We used this mechanism to transfer a barium strontium titanate thin film into the XPS analysis chamber and performed XPS measurements before and after exposing the sample to the air. After air exposure, a thin overlayer of carbon was found to form and a significant shift (∼1 eV) in the core level binding energies was observed.

  6. High temperature thermal stability investigations of ammonium sulphide passivated InGaAs and interface formation with Al2O3 studied by synchrotron radiation based photoemission

    Highlights: • Sulphur passivation is effective at removing the native oxides from InGaAs surface. • A 700°C anneal of the sulphur passivated surface at leads to the loss of indium. • A 1 nm Al2O3 layer improves the thermal stability of the sulphur passivated InGaAs. - Abstract: High resolution synchrotron radiation core level photoemission measurements have been used to undertake a comparative study of the high temperature thermal stability of the ammonium sulphide passivated InGaAs surface and the same surface following the atomic layer deposition (ALD) of an ultrathin (∼1 nm) Al2O3 layer. The solution based ex situ sulphur passivation was found to be effective at removing a significant amount of the native oxides and protecting the surface against re-oxidation upon air exposure. The residual interfacial oxides which form between sulphur passivated InGaAs and the ultrathin Al2O3 layer can be substantially removed at high temperature (up to 700°C) without impacting on the InGaAs stoichiometry while significant loss of indium was recorded at this temperature on the uncovered sulphur passivated InGaAs surface

  7. P2P Simulator for Queries Routing Using Data Mining

    Anis ISMAIL

    2011-09-01

    Full Text Available Data mining is used to extract hidden information from large databases. In Peer-to-Peer context, achallenging problem is how to find the appropriate Peer to deal with a given query without overlyconsuming bandwidth. Different methods proposed routing strategies of queries taking into account theP2P network at hand. An unstructured P2P system based on an organization of Peers around Super-Peersthat are connected to Super-Super-Peer according to their semantic domains is considered. This paperintegrates Decision Trees in P2P architectures for predicting Query-Suitable Super-Peers representing acommunity of Peers, where one among them is able to answer the given query. In fact, by analyzing thequeries’ log file, a predictive model that avoids flooding queries in the P2P networks constructed bypredicting the appropriate Super-Peer, and hence the Peer to answer the query. The proposed architectureis based on a Decision Tree (Base-Knowledge - BK. The efficiency of these architectures is discussedconsidering architecture without knowledge (Baseline using only the flooding queries method to answerqueries. The advantage of this knowledge based model is the robustness in Queries routing mechanism andscalability in P2P Network.

  8. A Framework For Concept Drifting P2P Traffic Identification

    Guanghui Yan

    2013-08-01

    Full Text Available Identification of network traffic using port-based or payload-based analysis is becoming increasing difficult with many Peer-to-Peer (P2P application using dynamic ports, masquerading techniques, and encryption to avoid detection. To overcome this problem, several machine learning technique were proposed to classify P2P traffics. But in the real P2P network environment, new communities of peers often attend and old communities of peers often leave. It requires the identification methods to be capable of coping with concept drift, and updating the model incrementally. In this paper, we present a concept-adapting algorithm CluMC which is based on streaming data mining techniques to identify P2P applications in Internet traffic. The CluMC use micro-cluster structures which contain potential micro-cluster structures and outlier micro-cluster structures to classify the P2P traffic and discover the concept drift with limited memory. Our performance study over a number of real data sets that we captured at a main gateway router demonstrates the effectiveness and efficiency of our method.

  9. Behavioural Correlation for Detecting P2P Bots

    Al-Hammadi, Yousof

    2010-01-01

    In the past few years, IRC bots, malicious programs which are remotely controlled by the attacker through IRC servers, have become a major threat to the Internet and users. These bots can be used in different malicious ways such as issuing distributed denial of services attacks to shutdown other networks and services, keystrokes logging, spamming, traffic sniffing cause serious disruption on networks and users. New bots use peer to peer (P2P) protocols start to appear as the upcoming threat to Internet security due to the fact that P2P bots do not have a centralized point to shutdown or traceback, thus making the detection of P2P bots is a real challenge. In response to these threats, we present an algorithm to detect an individual P2P bot running on a system by correlating its activities. Our evaluation shows that correlating different activities generated by P2P bots within a specified time period can detect these kind of bots.

  10. Self-consistent Green’s-function technique for bulk and surface impurity calculations: Surface core-level shifts by complete screening

    Aldén, M.; Abrikosov, I. A.; Johansson, B.;

    1994-01-01

    We have implemented an efficient self-consistent Green's-function technique, based on the tight-binding linear-muffin-tin-orbitals method, for calculating the electronic structure and total energy of a substitutional impurity located either in the bulk or at the surface. The technique makes use of...... shift obtained from a polycrystalline surface. Comparison is made with independent theoretical data for the surface core-level eigenvalue shift, and the much debated role of the so-called initial-and final-state contributions to the SCLS is discussed....

  11. High-energy photoemission studies of oxide interfaces

    Claessen, Ralph

    2015-03-01

    The interfaces of complex oxide heterostructures can host novel quantum phases not existing in the bulk of the constituents, with the high-mobility 2D electron system (2DES) in LaAlO3/SrTiO3 (LAO/STO) representing a prominent example. Despite extensive research the origin of the 2DES and its unusual properties - including the supposed coexistence of superconductivity and ferromagnetism - are still a matter of intense debate. Photoelectron spectroscopy, recently extended into the soft (SX-ARPES) and hard (HAXPES) X-ray regime, is a powerful method to provide detailed insight into the electronic structure of these heterostructures and, in particular, of the buried interface. This includes the identification of the orbital character of the 2DES as well as the determination of vital band structure information, such as band alignment, band bending, and even k-resolved band dispersions and Fermi surface topology. Moreover, resonant photoemission at the Ti L-edge reveals the existence of two different species of Ti 3d states, localized and itinerant, which can be distinguished and identified by their different resonance behavior. The role of oxygen vacancies is studied by controlled in-situ oxidation, which allows us to vary the composition from fully stoichiometric to strongly O-deficient. By comparison to free STO surfaces we can thus demonstrate that the metallicity of the heteointerfaces is intrinsic, i . e . it persists even in the absence of O defects. I will discuss our photoemission results on LAO/STO heterostructures in both (100) and (111) orientation as well as on the related system γ-Al2O3/STO(100), which also hosts a 2DES with an even higher mobility. Work in collaboration with J. Mannhart (MPI-FKF, Stuttgart), N. Pryds (TU Denmark), G. Rijnders (U Twente), S. Suga (U Osaka), M. Giorgoi (BESSY, HZB), W. Drube (DESY Photon Science), V.N. Strocov (Swiss Light Source), J. Denlinger (Advanced Light Source, LBNL), and T.-L. Lee (Diamond Light Source). Support by

  12. Compromising Tor Anonymity Exploiting P2P Information Leakage

    Manils, Pere; Blond, Stevens Le; Kaafar, Mohamed Ali; Castelluccia, Claude; Legout, Arnaud; Dabbous, Walid

    2010-01-01

    Privacy of users in P2P networks goes far beyond their current usage and is a fundamental requirement to the adoption of P2P protocols for legal usage. In a climate of cold war between these users and anti-piracy groups, more and more users are moving to anonymizing networks in an attempt to hide their identity. However, when not designed to protect users information, a P2P protocol would leak information that may compromise the identity of its users. In this paper, we first present three attacks targeting BitTorrent users on top of Tor that reveal their real IP addresses. In a second step, we analyze the Tor usage by BitTorrent users and compare it to its usage outside of Tor. Finally, we depict the risks induced by this de-anonymization and show that users' privacy violation goes beyond BitTorrent traffic and contaminates other protocols such as HTTP.

  13. Model of Controlling the Hubs in P2P Networks

    Yuhua Liu

    2009-06-01

    Full Text Available Research into the hubs in Peer-to-Peer (P2P networks, and present a new method to avoid generating the hubs in the networks by controlling the logical topology structure of P2P networks. We firstly introduce the controlling ideas about hierarchizing the hubs. Then, we disclose and interpret the controlling model, and give out the concrete method to carry it out. Finally, we validate our controlling model via simulations and the simulation results demonstrate that our work is effective to control the hubs in P2P networks. Thus, this model can improve the network competence to defend against coordinated attacks, promote the network robustness, and ensure the network would develop continually and healthily.

  14. N(2P) in the dayglow - Measurement and theory

    Torr, Marsha R.; Torr, Douglas G.; Richards, P. G.

    1993-01-01

    During the ATLAS-1 mission, the first dayglow altitude profiles were obtained of the N(2P) emission at 3466 A. These observations were made in the sunlit thermosphere using the Imaging Spectrometric Observatory. As all previous work on this emission has been done under auroral conditions, this study represents the first examination of the photochemical sources and sinks of N(2P) in the normal daytime thermospheric, with comparison with measurements. We find that the observations are explained by a model in which the major source is photodissociation of N2, and quenching by O is the principal low-altitude loss process, with radiative decay to N(2D) dominating above 200 km. As the dominant loss processes are likely to result in the production of N(2D), N(2P) could be a moderate source of N(2D) and may be a factor to be taken into consideration in modeling NO.

  15. P2P STREAMING MEDIA INDUSTRY IN CHINA

    Dai, Steffi (Wenjing)

    2009-01-01

    The peer-to-peer (P2P) streaming media industry opened up a new era for the cyber age, has had a significant effect on many people?s leisure time, and has changed the way many people use entertainment. Over the past few years, this industry has developed dramatically in China, and it is thriving. In terms of the current situation, the P2P streaming media industry holds typical Chinese features that both enrich the audience?s cultural life, and have some impact on other kinds of mass media. Th...

  16. Coverage dependent organic-metal interaction studied by high-resolution core level spectroscopy: SnPc (sub)monolayers on Ag(1 1 1)

    Haeming, M.; Scheuermann, C. [Experimentelle Physik II, Universitaet Wuerzburg, D-97074 Wuerzburg (Germany); Schoell, A. [Experimentelle Physik II, Universitaet Wuerzburg, D-97074 Wuerzburg (Germany); Forschungszentrum Karlsruhe, Gemeinschaftslabor fuer Nanoanalytik, D-76021 Karlsruhe (Germany)], E-mail: achim.schoell@physik.uni-wuerzburg.de; Reinert, F. [Experimentelle Physik II, Universitaet Wuerzburg, D-97074 Wuerzburg (Germany); Forschungszentrum Karlsruhe, Gemeinschaftslabor fuer Nanoanalytik, D-76021 Karlsruhe (Germany); Umbach, E. [Experimentelle Physik II, Universitaet Wuerzburg, D-97074 Wuerzburg (Germany); Forschungszentrum Karlsruhe and Karlsruhe Institute of Technology, Weberstrasse 5, D-76021 Karlsruhe (Germany)

    2009-08-15

    We study the electronic structure of tin-phthalocyanine (SnPc) molecules adsorbed on a Ag(1 1 1) surface by high-resolution photoelectron spectroscopy. We particularly address the effect of different SnPc coverages on the interaction and charge transfer at the interface. The results give evidence for a covalent molecule-substrate interaction, which is temperature and coverage dependent. The valence and core level spectra as well as the work function measurements allow us monitoring subtle differences in the strength of the interface interaction, thus demonstrating the sensitivity of the methods. The results consistently show the effect of charge exchange between substrate and molecules which obviously leads to a net charge transfer into the SnPc molecules, and which is increased with decreasing coverage. Surprisingly, the Sn3d core levels are neither effected by variations of charge transfer and interaction strength, nor by a possible 'Sn-up' or 'Sn-down' orientation, which have been observed for sub-monolayers.

  17. Photoemission and magnetic response in the bipolaronic superconductor

    Dent, C

    2001-01-01

    in the cuprates is extended to explain the crossing point in the curves of induced magnetization divided by the square root of field against temperature in the less anisotropic cuprates. This model has already been shown to provide a parameter-free expression for T sub c in a wide range of cuprates. We compare our results with experiment in YBa sub 2 Cu sub 3 O sub 7 sub - subdelta. A theory of angle-resolved photoemission (ARPES) in doped charge-transfer Mott insulators is developed taking into account the realistic band structure, (bi)polaron formation due to the strong electron-phonon interaction, and a random field potential. We derive the coherent part of the ARPES spectra with the oxygen hole spectral function calculated in the non-crossing (ladder) approximation and with the exact spectral function of a one-dimensional hole in a random potential. On the basis of this theory, explanations are proposed for several features of the ARPES spectra taken from the cuprate superconductors. These include the pol...

  18. Photoemission electron microscopy using extreme ultraviolet attosecond pulse trains

    We report the first experiments carried out on a new imaging setup, which combines the high spatial resolution of a photoemission electron microscope (PEEM) with the temporal resolution of extreme ultraviolet (XUV) attosecond pulse trains. The very short pulses were provided by high-harmonic generation and used to illuminate lithographic structures and Au nanoparticles, which, in turn, were imaged with a PEEM resolving features below 300 nm. We argue that the spatial resolution is limited by the lack of electron energy filtering in this particular demonstration experiment. Problems with extensive space charge effects, which can occur due to the low probe pulse repetition rate and extremely short duration, are solved by reducing peak intensity while maintaining a sufficient average intensity to allow imaging. Finally, a powerful femtosecond infrared (IR) beam was combined with the XUV beam in a pump-probe setup where delays could be varied from subfemtoseconds to picoseconds. The IR pump beam could induce multiphoton electron emission in resonant features on the surface. The interaction between the electrons emitted by the pump and probe pulses could be observed.

  19. Investigation of slider surfaces after wear using photoemission electron microscopy

    The tribo-chemical interactions between the slider and the hard disk surface strongly influence the performance properties of a disk drive. To study these interactions, uncoated and carbon coated sliders were subjected to various wear tests using different disks. After the wear, the test slider surfaces were studied by photoemission electron microscopy (PEEM) using tunable x rays produced by a synchrotron. Using PEEM, one can identify the elemental and chemical state of the surfaces with a high spatial resolution. It was found that wear reduces the thickness of the carbon coating in some local areas of the slider surface. In particular, the coating was removed on elevated areas and in scratches. Scratches were found on the rails of the carbon coated and uncoated sliders after wear that showed the accumulation of a degraded (oxidized) lubricant which was transferred to the slider from the disk. It was also possible to analyze the chemical composition of the debris found on the slider surface. In the present case, the debris had the same chemical composition as the carbon coating of the slider. copyright 1999 American Vacuum Society

  20. Einstein's photoemission emission from heavily-doped quantized structures

    Ghatak, Kamakhya Prasad

    2015-01-01

    This monograph solely investigates the Einstein's Photoemission(EP) from Heavily Doped(HD) Quantized Structures on the basis of newly formulated electron dispersion laws. The materials considered are quantized structures of HD non-linear optical, III-V, II-VI, Ge, Te, Platinum Antimonide, stressed materials, GaP, Gallium Antimonide, II-V, Bismuth Telluride together with various types of HD superlattices and their Quantized counterparts respectively. The EP in HD opto-electronic materials and their nanostructures is studied in the presence of strong light waves and intense electric fields  that control the studies of such quantum effect devices. The suggestions for the experimental determinations of different important physical quantities in HD 2D and 3D materials  and the importance of measurement of band gap in HD optoelectronic materials under intense built-in electric field in nano devices and strong external photo excitation (for measuring   physical properties in the presence of intense light waves w...

  1. Photoemission experiments of a large area scandate dispenser cathode

    Zhang Huang, E-mail: bamboobbu@hotmail.co [Institute of Fluid Physics, CAEP, P.O. Box 919-106, Mianyang 621900 (China); Liu Xingguang; Chen Yi; Chen Debiao; Jiang Xiaoguo; Yang Anmin; Xia Liansheng; Zhang Kaizhi; Shi Jinshui; Zhang Linwen [Institute of Fluid Physics, CAEP, P.O. Box 919-106, Mianyang 621900 (China)

    2010-09-21

    A 100-mm-diameter scandate dispenser cathode was tested as a photocathode with a 10 ns Nd:YAG laser (266 nm) on an injector test stand for linear induction accelerators. This thermionic dispenser cathode worked at temperatures ranging from room temperature to 930 {sup o}C (below or near the thermionic emission threshold) while the vacuum was better than 4x10{sup -7} Torr. The laser pulse was synchronized with a 120 ns diode voltage pulse stably and they were in single pulse mode. Emission currents were measured by a Faraday cup. The maximum peak current collected at the anode was about 100 A. The maximum quantum efficiency measured at low laser power was 2.4x10{sup -4}. Poisoning effect due to residual gas was obvious and uninterrupted heating was needed to keep cathode's emission capability. The cathode was exposed to air one time between experiments and recovered after being reconditioned. Photoemission uniformity of the cathode was also explored by changing the laser spot's position.

  2. Photoemission electron microscopy using extreme ultraviolet attosecond pulse trains

    Mikkelsen, A.; Schwenke, J.; Fordell, T.; Luo, G.; Kluender, K.; Hilner, E.; Anttu, N.; Lundgren, E.; Mauritsson, J.; Andersen, J. N.; Xu, H. Q.; L' Huillier, A. [Department of Physics, Lund University, Box 118, 22100 Lund (Sweden); Zakharov, A. A. [MAX-lab, Lund University, Box 118, 22100 Lund (Sweden)

    2009-12-15

    We report the first experiments carried out on a new imaging setup, which combines the high spatial resolution of a photoemission electron microscope (PEEM) with the temporal resolution of extreme ultraviolet (XUV) attosecond pulse trains. The very short pulses were provided by high-harmonic generation and used to illuminate lithographic structures and Au nanoparticles, which, in turn, were imaged with a PEEM resolving features below 300 nm. We argue that the spatial resolution is limited by the lack of electron energy filtering in this particular demonstration experiment. Problems with extensive space charge effects, which can occur due to the low probe pulse repetition rate and extremely short duration, are solved by reducing peak intensity while maintaining a sufficient average intensity to allow imaging. Finally, a powerful femtosecond infrared (IR) beam was combined with the XUV beam in a pump-probe setup where delays could be varied from subfemtoseconds to picoseconds. The IR pump beam could induce multiphoton electron emission in resonant features on the surface. The interaction between the electrons emitted by the pump and probe pulses could be observed.

  3. Photoemission experiments of a large area scandate dispenser cathode

    Zhang, Huang; Liu, Xing-guang; Chen, Yi; Chen, De-biao; Jiang, Xiao-guo; Yang, An-min; Xia, Lian-sheng; Zhang, Kai-zhi; Shi, Jin-shui; Zhang, Lin-wen

    2010-09-01

    A 100-mm-diameter scandate dispenser cathode was tested as a photocathode with a 10 ns Nd:YAG laser (266 nm) on an injector test stand for linear induction accelerators. This thermionic dispenser cathode worked at temperatures ranging from room temperature to 930 °C (below or near the thermionic emission threshold) while the vacuum was better than 4×10 -7 Torr. The laser pulse was synchronized with a 120 ns diode voltage pulse stably and they were in single pulse mode. Emission currents were measured by a Faraday cup. The maximum peak current collected at the anode was about 100 A. The maximum quantum efficiency measured at low laser power was 2.4×10 -4. Poisoning effect due to residual gas was obvious and uninterrupted heating was needed to keep cathode's emission capability. The cathode was exposed to air one time between experiments and recovered after being reconditioned. Photoemission uniformity of the cathode was also explored by changing the laser spot's position.

  4. Photoemission experiments of a large area scandate dispenser cathode

    A 100-mm-diameter scandate dispenser cathode was tested as a photocathode with a 10 ns Nd:YAG laser (266 nm) on an injector test stand for linear induction accelerators. This thermionic dispenser cathode worked at temperatures ranging from room temperature to 930 oC (below or near the thermionic emission threshold) while the vacuum was better than 4x10-7 Torr. The laser pulse was synchronized with a 120 ns diode voltage pulse stably and they were in single pulse mode. Emission currents were measured by a Faraday cup. The maximum peak current collected at the anode was about 100 A. The maximum quantum efficiency measured at low laser power was 2.4x10-4. Poisoning effect due to residual gas was obvious and uninterrupted heating was needed to keep cathode's emission capability. The cathode was exposed to air one time between experiments and recovered after being reconditioned. Photoemission uniformity of the cathode was also explored by changing the laser spot's position.

  5. Silane photoabsorption spectra near the Si 2p thresholds: the geometry of Si 2p excited SiH4

    张卫华; 许如清; 李家明

    2003-01-01

    Based on the multiple-scattering self-consistent-field method, we have studied the photoabsorption spectra near the Si 2p thresholds of silane. According to our calculations, the clear assignments of the inner-shell photoabsorption spectra are provided. In comparison with the high-resolution experimental spectra, the geometric structure of the Si 2p-excited SiH4** is recommended to be of a C2v symmetry. More specifically, the Si 2p-excited Si4** have two bond lengths of 2.50 a.u. and another two bond lengths of 2.77 a.u., and the corresponding two bond angles are 104.0° and 112.5° respectively.

  6. Measurement and analysis of P2P IPTV program resource.

    Wang, Wenxian; Chen, Xingshu; Wang, Haizhou; Zhang, Qi; Wang, Cheng

    2014-01-01

    With the rapid development of P2P technology, P2P IPTV applications have received more and more attention. And program resource distribution is very important to P2P IPTV applications. In order to collect IPTV program resources, a distributed multi-protocol crawler is proposed. And the crawler has collected more than 13 million pieces of information of IPTV programs from 2009 to 2012. In addition, the distribution of IPTV programs is independent and incompact, resulting in chaos of program names, which obstructs searching and organizing programs. Thus, we focus on characteristic analysis of program resources, including the distributions of length of program names, the entropy of the character types, and hierarchy depth of programs. These analyses reveal the disorderly naming conventions of P2P IPTV programs. The analysis results can help to purify and extract useful information from chaotic names for better retrieval and accelerate automatic sorting of program and establishment of IPTV repository. In order to represent popularity of programs and to predict user behavior and popularity of hot programs over a period, we also put forward an analytical model of hot programs. PMID:24772008

  7. Comparing Pedophile Activity in Different P2P Systems

    Raphaël Fournier

    2014-07-01

    Full Text Available Peer-to-peer (P2P systems are widely used to exchange content over the Internet. Knowledge of pedophile activity in such networks remains limited, despite having important social consequences. Moreover, though there are different P2P systems in use, previous academic works on this topic focused on one system at a time and their results are not directly comparable. We design a methodology for comparing KAD and eDonkey, two P2P systems among the most prominent ones and with different anonymity levels. We monitor two eDonkey servers and the KAD network during several days and record hundreds of thousands of keyword-based queries. We detect pedophile-related queries with a previously validated tool and we propose, for the first time, a large-scale comparison of pedophile activity in two different P2P systems. We conclude that there are significantly fewer pedophile queries in KAD than in eDonkey (approximately 0.09% vs. 0.25%.

  8. P2P Domain Classification using Decision Tree

    Ismail, Anis

    2011-01-01

    In Peer-to-Peer context, a challenging problem is how to find the appropriate peer to deal with a given query without overly consuming bandwidth? Different methods proposed routing strategies of queries taking into account the P2P network at hand. This paper considers an unstructured P2P system based on an organization of peers around Super-Peers that are connected to Super-Super- Peer according to their semantic domains; By analyzing the queries log file, a predictive model that avoids flooding queries in the P2P network is constructed after predicting the appropriate Super-Peer, and hence the peer to answer the query. A challenging problem in a schema-based Peer-to-Peer (P2P) system is how to locate peers that are relevant to a given query. In this paper, architecture, based on (Super-)Peers is proposed, focusing on query routing. The approach to be implemented, groups together (Super-)Peers that have similar interests for an efficient query routing method. In such groups, called Super-Super-Peers (SSP), Su...

  9. {2p_\\pi}-{2p_\\sigma} crossing in heavy symmetric ion-atom collisions: I. Level structure

    Morovi´c, Tihomir; Sepp, Wolf-Dieter; Fricke, Burkhard

    1982-01-01

    Ab initio self-consistent DFS calculations are performed for five different symmetric atomic systems from Ar-Ar to Pb-Pb. The level structure for the {2p_\\pi}-{2p_\\sigma} crossing as function of the united atomic charge Z_u is studied and interpreted. Manybody effects, spin-orbit splitting, direct relativistic effects as well as indirect relativistic effects are differently important for different Z_u. For the I-I system a comparison with other calculations is given.

  10. Theatrical distribution and P2P movie piracy: a survey of P2P networks in Hungary using transactional data

    B. Bodó; Z. Lakatos

    2012-01-01

    This article examines what appears to be the most important factor shaping file sharing: the failure of traditional cultural markets to efficiently supply the demand in the online environment. Its findings are based on tracking the traffic of movies on three Hungarian P2P networks. This dataset is t

  11. Electronic structure of YbNiX3 (X =Si, Ge) studied by hard X-ray photoemission spectroscopy

    lectronic structure of the Kondo lattices YbNiX3 (X =Si, Ge) has been investigated by means of hard x-ray photoemission spectroscopy (HAXPES) with hν = 5.95 keV. From the Yb 3d HAXPES spectra, the Yb valence in YbNiSi3 is estimated to be ∝ 2.92, which is almost temperature-independent. On the other hand, the valence in YbNiGe3 is estimated to be 2.48 at 300 K, showing significant valence fluctuation, and gradually decreases to 2.41 at 20 K on cooling. The Ni 2p3/2 and Yb3+ 4f peaks exhibit opposite energy shifts amounting to ∝ 0.6 eV between YbNiSi3 and YbNiGe3. We propose a simple model for the electronic structure of YbNiX3 based on the HAXPES results. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  12. Electronic structure of YbNiX{sub 3} (X =Si, Ge) studied by hard X-ray photoemission spectroscopy

    Sato, Hitoshi; Shimada, Kenya; Namatame, Hirofumi [Hiroshima Synchrotron Radiation Center, Hiroshima University, Kagamiyama 2-313, Higashi-Hiroshima 739-0046 (Japan); Utsumi, Yuki [Max-Planck Institute for Chemical Physics of Solids, 01187 Dresden (Germany); Kodama, Junichi; Nagata, Heisuke [Graduate School of Science, Hiroshima University, Kagamiyama 1-3-1, Higashi-Hiroshima 739-8526 (Japan); Avila, Marcos A.; Ribeiro, Raquel A. [Centro de Ciencias Naturais e Humanas, Universidade Federal do ABC, Santo Andre - SP, 09210-580 (Brazil); Umeo, Kazunori [Cryogenics and Instrumental Analysis Division, N-BARD, Hiroshima University, Higashi-Hiroshima 739-8526 (Japan); Takabatake, Toshiro [Department of Quantum Matter, AdSM, Hiroshima University, Higashi-Hiroshima 739-8530 (Japan); Institute for Advanced Materials Research, Hiroshima University, Higashi-Hiroshima 739-8530 (Japan); Mimura, Kojiro; Motonami, Satoru; Anzai, Hiroaki [Graduate School of Engineering, Osaka Prefecture University, Sakai 599-8531 (Japan); Ueda, Shigenori [Synchrotron X-ray Station at SPring-8, National Institute for Materials Science, Hyogo 679-5148 (Japan); Taniguchi, Masaki [Hiroshima Synchrotron Radiation Center, Hiroshima University, Kagamiyama 2-313, Higashi-Hiroshima 739-0046 (Japan); Graduate School of Science, Hiroshima University, Kagamiyama 1-3-1, Higashi-Hiroshima 739-8526 (Japan)

    2015-06-15

    lectronic structure of the Kondo lattices YbNiX{sub 3} (X =Si, Ge) has been investigated by means of hard x-ray photoemission spectroscopy (HAXPES) with hν = 5.95 keV. From the Yb 3d HAXPES spectra, the Yb valence in YbNiSi{sub 3} is estimated to be ∝ 2.92, which is almost temperature-independent. On the other hand, the valence in YbNiGe{sub 3} is estimated to be 2.48 at 300 K, showing significant valence fluctuation, and gradually decreases to 2.41 at 20 K on cooling. The Ni 2p{sub 3/2} and Yb{sup 3+} 4f peaks exhibit opposite energy shifts amounting to ∝ 0.6 eV between YbNiSi{sub 3} and YbNiGe{sub 3}. We propose a simple model for the electronic structure of YbNiX{sub 3} based on the HAXPES results. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  13. Supporting seamless mobility for P2P live streaming.

    Kim, Eunsam; Kim, Sangjin; Lee, Choonhwa

    2014-01-01

    With advent of various mobile devices with powerful networking and computing capabilities, the users' demand to enjoy live video streaming services such as IPTV with mobile devices has been increasing rapidly. However, it is challenging to get over the degradation of service quality due to data loss caused by the handover. Although many handover schemes were proposed at protocol layers below the application layer, they inherently suffer from data loss while the network is being disconnected during the handover. We therefore propose an efficient application-layer handover scheme to support seamless mobility for P2P live streaming. By simulation experiments, we show that the P2P live streaming system with our proposed handover scheme can improve the playback continuity significantly compared to that without our scheme. PMID:24977171

  14. Addressing the P2P Bootstrap Problem for Small Networks

    Wolinsky, David Isaac; Boykin, P Oscar; Figueiredo, Renato

    2010-01-01

    P2P overlays provide a framework for building distributed applications consisting of few to many resources with features including self-configuration, scalability, and resilience to node failures. Such systems have been successfully adopted in large-scale services for content delivery networks, file sharing, and data storage. In small-scale systems, they can be useful to address privacy concerns and for network applications that lack dedicated servers. The bootstrap problem, finding an existing peer in the overlay, remains a challenge to enabling these services for small-scale P2P systems. In large networks, the solution to the bootstrap problem has been the use of dedicated services, though creating and maintaining these systems requires expertise and resources, which constrain their usefulness and make them unappealing for small-scale systems. This paper surveys and summarizes requirements that allow peers potentially constrained by network connectivity to bootstrap small-scale overlays through the use of e...

  15. Valence band structure of the ZnO(1-bar 0-bar 1-bar -bar 0) surface studied by angle-resolved photoemission spectroscopy

    The electronic band structure of the ZnO(1-bar 0-bar 1-bar -bar 0) surface has been studied by angle-resolved photoemission spectroscopy utilizing synchrotron radiation. Photon-energy-dependent measurements and K- and O2-adsorption studies revealed that the O 2p dangling-bond state exists at 3.7eV below the Fermi level at the Γ-bar point. Polarization-dependent measurements show that the state has dominant contribution of the O 2px orbital (x is parallel to the (1-bar 2-bar -bar 1-bar 0) direction) at the Γ-bar point. It is found that the O 2p dangling-bond band lies within the projected bulk bands along the ΓX-bar -bar and-bar ΓX'-bar axes in the surface Brillouin zone. This result settles a controversial issue on the energetic position of the O 2p dangling-bond band, which has been in dispute among theoretical studies. The dispersion widths are found to be 0.8 and 0.5eV along the ΓX-bar -bar and-bar ΓX'-bar directions, respectively

  16. Simple theoretical analysis of the photoemission from quantum confined effective mass superlattices of optoelectronic materials

    Debashis De

    2011-07-01

    Full Text Available The photoemission from quantum wires and dots of effective mass superlattices of optoelectronic materials was investigated on the basis of newly formulated electron energy spectra, in the presence of external light waves, which controls the transport properties of ultra-small electronic devices under intense radiation. The effect of magnetic quantization on the photoemission from the aforementioned superlattices, together with quantum well superlattices under magnetic quantization, has also been investigated in this regard. It appears, taking HgTe/Hg1−xCdxTe and InxGa1−xAs/InP effective mass superlattices, that the photoemission from these quantized structures is enhanced with increasing photon energy in quantized steps and shows oscillatory dependences with the increasing carrier concentration. In addition, the photoemission decreases with increasing light intensity and wavelength as well as with increasing thickness exhibiting oscillatory spikes. The strong dependence of the photoemission on the light intensity reflects the direct signature of light waves on the carrier energy spectra. The content of this paper finds six different applications in the fields of low dimensional systems in general.

  17. Hard X-ray photoemission with angular resolution and standing-wave excitation

    Fadley, Charles S., E-mail: fadley@physics.ucdavis.edu [Department of Physics, University of California Davis, Davis, CA 95616 (United States); Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States)

    2013-10-15

    Highlights: •Hard X-ray photoemission with angle resolution and standing-waves is discussed. •Hard X-ray angle-resolved photoemission yields k{sup →}-resolved bulk electronic structure. •Hard X-ray photoelectron diffraction provides element-specific atomic structure. •Multilayer standing-wave measurements add depth-resolved composition. •Standing-wave excitation also yields element-specific densities of states. -- Abstract: Several aspects of hard X-ray photoemission that make use of angular resolution and/or standing-wave excitation are discussed. These include hard X-ray angle-resolved photoemission (HARPES) from valence levels, which has the capability of determining bulk electronic structure in a momentum-resolved way; hard X-ray photoelectron diffraction (HXPD), which shows promise for studying element-specific bulk atomic structure, including dopant site occupations; and standing wave studies of the composition and chemical states of buried layers and interfaces. Beyond this, standing wave photoemission can be used to derive element-specific densities of states. Some recent examples relevant to all of these aspects are discussed.

  18. Behavioural Correlation for Detecting P2P Bots

    Al-Hammadi, Yousof; Aickelin, Uwe

    2010-01-01

    In the past few years, IRC bots, malicious programs which are remotely controlled by the attacker through IRC servers, have become a major threat to the Internet and users. These bots can be used in different malicious ways such as issuing distributed denial of services attacks to shutdown other networks and services, keystrokes logging, spamming, traffic sniffing cause serious disruption on networks and users. New bots use peer to peer (P2P) protocols start to appear ...

  19. On Reducing Delays in P2P Live Streaming Systems

    Huang, Fei

    2010-01-01

    In the recent decade, peer-to-peer (P2P) technology has greatly enhanced the scalability of multimedia streaming on the Internet by enabling efficient cooperation among end-users. However, existing streaming applications are plagued by the problems of long playback latency and long churn-induced delays. First of all, many streaming applications, such as IPTV and video conferencing, have rigorous constraints on end-to-end delays. Moreover, churn-induced delays, including delays from channel sw...

  20. Addressing the P2P Bootstrap Problem for Small Networks

    Wolinsky, David Isaac; Juste, Pierre St.; Boykin, P. Oscar; Figueiredo, Renato

    2010-01-01

    P2P overlays provide a framework for building distributed applications consisting of few to many resources with features including self-configuration, scalability, and resilience to node failures. Such systems have been successfully adopted in large-scale services for content delivery networks, file sharing, and data storage. In small-scale systems, they can be useful to address privacy concerns and for network applications that lack dedicated servers. The bootstrap problem, finding an existi...

  1. An Efficient Secure Multicast Communication for P2P Network

    Huaiqing Lin

    2011-03-01

    Full Text Available A new algorithm for efficient key management for secure group communication in P2P network is presented. The protocol avoids the escrow problem in identity-based cryptosystem and the secure delivery of private keys. It has two rounds and requires constant pairing operation per user. The security of protocol is based on some underlying problems closely related to the Bilinear Diffie-Hellman Problem are computationally hard.  

  2. Inclusive χ(2P) production in Υ(3S) decay

    Using the CsI calorimeter of the CLEO II detector, the spin triplet χb(2P) states are observed in Υ(3S) radiative decays with much higher statistics than seen in previous experiments. The observed mass splittings are not described well by theoretical models, while the relative branching ratios agree with predictions that include relativistic corrections to the radiative transition rates

  3. Electronic properties of metal-organic and organic-organic interfaces studied by photoemission and photoabsorption spectroscopy

    Molodtsova, Olga

    2006-07-01

    In this work systematic studies of the organic semiconductor CuPc have been presented. In general the investigation can be devided in three parts. In the first one we have studied the electronic structure of clean CuPc thin film. The next two parts are devoted to organic-organic and metal-organic interface formation, where one of the interface components is CuPc thin film. The main results of this thesis are: - The electronic structure of the pristine organic semiconductor CuPc has been obtained by a combination of conventional and resonant photoemission, near-edge X-ray absorption, as well as by theoretical ab initio quantum-chemical calculations. The contributions of different atomic species as well as sites of the CuPc molecule to the electronic DOS has been established. A combined experimental and theoretical study of the unoccupied electronic density of states of CuPc was presented. - The electronic properties of the organic heterointerfaces between fullerite and pristine copper phthalocyanine were studied. Both interfaces, CuPc/C{sub 60} and C{sub 60}/CuPc, were found to be non-reactive with pronounced shifts of the vacuum level pointing to the formation of an interfacial dipole mainly at the CuPc side of the heterojunctions. The dipole values are close to the difference of the work functions of the two materials. Important interface parameters and hole-injection barriers were obtained. The sequence of deposition does not influence the electronic properties of the interfaces. - CuPc doped with potassium was studied by means of photoemission and photoabsorption spectroscopy. A detailed analysis of the core-level PE spectra allows one to propose possible lattice sites, which harbor the potassium ions. The films prepared in this thesis showed no finite electronic density of states at the Fermi level. - Two stages of the In/CuPc interface formation have been distinguished. The low-coverage stage is characterized by a strong diffusion of the In atoms into the

  4. Electron-hole correlation effects in core-level spectroscopy probed by the resonant inelastic soft x-ray scattering map of C{sub 60}

    Weinhardt, L.; Fuchs, O.; Schoell, A.; Reinert, F. [Universitaet Wuerzburg, Experimentelle Physik VII, Am Hubland, 97074 Wuerzburg (Germany); Batchelor, D.; Umbach, E. [Karlsruhe Institute of Technology, D-76021 Karlsruhe (Germany); Baer, M. [Solar Energy Research, Helmholtz-Zentrum Berlin fuer Materialien und Energie GmbH (HZB), 14109 Berlin (Germany); Department of Chemistry, University of Nevada, Las Vegas, Nevada 89154-4003 (United States); Blum, M. [Universitaet Wuerzburg, Experimentelle Physik VII, Am Hubland, 97074 Wuerzburg (Germany); Department of Chemistry, University of Nevada, Las Vegas, Nevada 89154-4003 (United States); Denlinger, J. D.; Yang, W. [Advanced Light Source, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720 (United States); Heske, C. [Department of Chemistry, University of Nevada, Las Vegas, Nevada 89154-4003 (United States)

    2011-09-14

    We have employed a unique spectroscopic approach, a resonant inelastic soft x-ray scattering (RIXS) map, to identify and separate electron-hole correlation effects in core-level spectroscopy. With this approach, we are able to derive a comprehensive picture of the electronic structure, separating ground state properties (such as the HOMO-LUMO separation) from excited state properties (such as the C 1s core-exciton binding energy of C{sub 60}). In particular, our approach allows us to determine the difference between core- and valence exciton binding energies in C{sub 60}[0.5 ({+-}0.2) eV]. Furthermore, the RIXS map gives detailed insight into the symmetries of the intermediate and final states of the RIXS process.

  5. LWR Thorium-Based Equilibrium-TRU (TRU-sustainable) Fuel Cycle: From 2D Fuel Lattice Model to the Full 3D Core Level Model

    A study was performed in the BNL to investigate LWR thorium-based equilibrium-TRU (TRU-sustainable) fuel cycle. In such a self-sustainable fuel cycle, only TRU lost by the fuel separation activities passes to the repository. The equilibrium transuranics inventory is recycled into each subsequent reload. Results of the study demonstrate the neutronic feasibility of a fuel cycle with ''zero-TRU'' discharge. A limitation of this study is the fact that a 2D fuel lattice model was used, specifically, the linear reactivity model, applied to the results of assembly calculations, assumes a single fuel type for all three batches. Thus, the end result of this work is a confirmation of the possibility of establishing equilibrium TRU fuel cycle via the full 3D core level calculational model

  6. A P2P streaming service architecture with distributed caching

    GUO Pan-hong; YANG Yang; LI Xin-you

    2007-01-01

    Multimedia streaming served through peer-to-peer (P2P) networks is booming nowadays. However, the end-to-end streaming quality is generally unstable due to the variability of the state of serve-peers. On the other hand, proxy caching is a bandwidth-efficient scheme for streaming over the Internet, whereas it is a substantially expensive method needing dedicated powerful proxy servers. In this paper, we present a P2P cooperative streaming architecture combined with the advantages of both P2P networks and multimedia proxy caching techniques to improve the streaming quality of participating clients. In this framework, a client will simultaneously retrieve contents from the server and other peers that have viewed and cached the same title before. In the meantime, the client will also selectively cache the aggregated video content so as to serve still future clients. The associate protocol to facilitate the multi-path streaming and a distributed utility-based partial caching scheme are detailedly discussed. We demonstrate the effectiveness of this proposed architecture through extensive simulation experiments on large, Internet-like topologies.

  7. DNA Compaction by Yeast Mitochondrial Protein ABF2p

    Friddle, R W; Klare, J E; Noy, A; Corzett, M; Balhorn, R; Baskin, R J; Martin, S S; Baldwin, E P

    2003-05-09

    We used high resolution Atomic Force Microscopy (AFM) to image compaction of linear and circular DNA by the yeast mitochondrial protein ABF2p , which plays a major role in maintaining mitochondrial DNA. AFM images show that protein binding induces drastic bends in the DNA backbone for both linear and circular DNA. At high concentration of ABF2p DNA collapses into a tight globular structure. We quantified the compaction of linear DNA by measuring the end-to-end distance of the DNA molecule at increasing concentrations of ABF2p. We also derived a polymer statistical mechanics model that gives quantitative description of compaction observed in our experiments. This model shows that a number of sharp bends in the DNA backbone is often sufficient to cause DNA compaction. Comparison of our model with the experimental data showed excellent quantitative correlation and allowed us to determine binding characteristics for ABF2. Our studies indicate that ABF2 compacts DNA through a novel mechanism that involves bending of DNA backbone. We discuss the implications of such a mechanism for mitochondrial DNA maintenance.

  8. Time-resolved photoemission by attosecond streaking. Extraction of time information

    Complete text of publication follows. Attosecond streaking is one of the most spectacular applications within the emerging field of attoscience. Streaking is based on a variant of a pump-probe setting with an extreme ultraviolet (XUV) pulse of a few hundred attoseconds serving as a pump and a phase controlled few-cycle infrared (IR) pulse as a probe. Electrons emitted in the presence of an IR field are accelerated to different final momenta and energies depending on the value of the vector potential at the release time. Thus, time information is mapped onto the energy axis in analogy to conventional streaking. Attosecond streaking of atomic photoemission holds the promise to provide unprecedented information on the release time of the photoelectron. We have shown that attosecond streaking phase shifts indeed contain timing (or spectral phase) information associated with the Eisenbud - Wigner - Smith (EWS) time delay matrix of quantum scattering. We have identified on the one-electron (or independent particle) level considerable state dependent time shifts that can be observed in attosecond streaking and which are of quantum mechanical origin. We found a time delay between the hydrogenic 2s and 2p initial states in He+ exceeding 20 as for a wide range of IR intensities and XUV energies (see Fig. 1). In addition, we have identified large time shifts which result from the coupling between the IR streaking field and the Coulomb field which depend on the final energy of the free electron and can be accounted for classically. The EWS time shift (or energy variation of the scattering phase) is found to be accessible by streaking only if both initial-state-dependent entrance channel and final-state exit channel distortions are properly accounted for. For such a scenario we have shown that time delays on the single-digit attosecond scale due to short-ranged potentials are in reach. Acknowledgements This work was supported by the FWF-Austria, grant nos SFB016 and P21141-N16

  9. Work function measurements of olivine: Implication to photoemission charging properties in planetary environments

    Gan, Hong; Li, Xiongyao; Wei, Guangfei; Wang, Shijie

    2015-12-01

    For understanding the ubiquitous photoemission charging of solid surface in planetary environments, it is important to characterize the photoemission charging properties of silicate minerals such as the work function. In this study, we measured the work function of olivine mineral based on the measurements of contact potential difference by using an ultrahigh vacuum Kelvin probe force microscopy. Our results showed that work function on olivine mineral surface is mainly affected by surface morphology and crystal orientation and that the variation range of work function is 7.3-8.5 eV. It implicates that photoemission of the olivine mineral occurs under the X-ray and solar ultraviolet irradiation with wavelength of instruct the dust mitigation technology and the electrostatic beneficiation in future space missions.

  10. PHOTOEMISSION METHOD OF TEMPERATURE MEASURING IN THE PROCESS OF SPARK PLASMA SINTERING POWDERS OF REFRACTORY METALS

    D. V. Minko

    2015-04-01

    Full Text Available Construction and algorithm of the photoemission pyrometer based on a photomultiplier are outlined; the calibration procedure is set out. The application of the photoemission method in a rapidly changing temperature is showed. It is proved that during spark plasma sintering the maximal temperature is 5500– 7500 °C, while the speed of temperature increase to its maximum ~108–109 °C/s, and the rate of decrease to 2000–4000 °C may be 106–107 °C/sec. It is recommended to use photoemission method when developing technological conditions, adjustment and control of technological processes using modern high-energy equipment (plasma, laser, cathode-ray tube to produce new materials, coatings and products for mechanical engineering, electronic industry and medicine.

  11. The role of space charge in spin-resolved photoemission experiments

    Spin-resolved photoemission is one of the most direct ways of measuring the magnetization of a ferromagnet. If all valence band electrons contribute, the measured average spin polarization is proportional to the magnetization. This is even the case if electronic excitations are present, and thus is of particular interest for studying the response of the magnetization to a pump laser pulse. Here, we demonstrate the feasibility of ultrafast spin-resolved photoemission using free electron laser (FEL) radiation and investigate the effect of space charge on the detected spin polarization. The sample is exposed to the radiation of the FEL FLASH in Hamburg. Surprisingly, the measured spin polarization depends on the fluence of the FEL radiation: a higher FEL fluence reduces the measured spin polarization. Space-charge simulations can explain this effect. These findings have consequences for future spin-polarized photoemission experiments using pulsed photon sources

  12. X-ray-induced photoemission yield for surface studies of solids beyond the photoelectron escape depth

    Stoupin, Stanislav; Zhernenkov, Mikhail

    2016-01-01

    X-ray-induced photoemission in materials research is commonly acknowledged as a method with a probing depth limited by the escape depth of the photoelectrons. This general statement should be complemented with exceptions arising from the distribution of the X-ray wavefield in the material. Here we show that the integral hard-X-ray-induced photoemission yield is modulated by the Fresnel reflectivity of a multilayer structure with the signal originating well below the photoelectron escape depth. A simple electric self-detection of the integral photoemission yield and Fourier data analysis permit extraction of thicknesses of individual layers. The approach does not require detection of the reflected radiation and can be considered as a framework for non-invasive evaluation of buried layers with hard X-rays under grazing incidence.

  13. Layer-resolved photoemission tomography: The p -sexiphenyl bilayer upon Cs doping

    Reinisch, E. M.; Puschnig, P.; Ules, T.; Ramsey, M. G.; Koller, G.

    2016-04-01

    The buried interface between a molecular thin film and the metal substrate is generally not accessible to the photoemission experiment. With the example of a sexiphenyl (6 P ) bilayer on Cu we show that photoemission tomography can be used to study the electronic level alignment and geometric structure, where it was possible to assign the observed orbital emissions to the individual layers. We further study the Cs doping of this bilayer. Initial Cs exposure leads to a doping of only the first interface layer, leaving the second layer unaffected except for a large energy shift. This result shows that it is in principle possible to chemically modify just the interface, which is important to issues like tuning of the energy level alignment and charge transfer to the interface layer. Upon saturating the film with Cs, photoemission tomography shows a complete doping (6 p4 - ) of the bilayer, with the molecular geometry changing such that the spectra become dominated by σ -orbital emissions.

  14. Origin of localized states in graphite: Indirect photoemission processes or impurities?

    Davila, M.E. [Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Cientificas (CSIC), C/ Sor Juana Ines de la Cruz, 3, 28049 Madrid (Spain)], E-mail: mdavila@icmm.csic.es; Valbuena, M.A.; Pantin, V. [Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Cientificas (CSIC), C/ Sor Juana Ines de la Cruz, 3, 28049 Madrid (Spain); Avila, J. [Synchrotron SOLEIL, Orme des Merisiers, Saint Aubin BP 48, 91192 Gif sur Yvette Cedex (France); Esquinazi, P. [Department of Superconductivity and Magnetism, Leipzig University (Germany); Asensio, M.C. [Synchrotron SOLEIL, Orme des Merisiers, Saint Aubin BP 48, 91192 Gif sur Yvette Cedex (France)

    2007-10-31

    The electronic band structure of different types of graphite samples have been investigated in order to identify the origin of non-dispersive density of states recently reported in the literature. A systematic series of synchrotron radiation angle resolved photoemission spectroscopy (ARPES) measurements on graphite single crystal, highly oriented graphite (HOPG) and epitaxial grown graphite single crystal on 6H-SiC(0 0 0 1) samples, have been carried out as well as compared with theoretical tight binding calculations. Our results indicate that these localized states are present in all the graphite-investigated samples showing the same non-dispersive character and at the same binding energies. The photoemission data taken at several photon energies demonstrate that these states are not surface states nor due to indirect photoemission processes. It seems that they are closely related to the level of impurities present in the studied samples.

  15. Measurement of the Electron Impact Photoemission Cross Sections of the 92.0 NM and 93.2 NM Emission Lines of Argon II for the VUV Radiometric Project.

    McPherson, Leroy Armon, Jr.

    Measurements of the electron impact photoemission cross sections for 92.0 nm and 93.2 nm radiation from Ar II have been made. The unpolarized radiation is produced by transitions from the 3s3p('6) ('2)S(,1/2) state to the 3s('2)3p('5) ('2)P(,1/2'3/2) states. The cross sections were determined at an incident electron energy of 100 eV and found to be (5.81 (+OR-) 0.48) x 10('-18) cm('2) for the 92.0 nm line (S(,1/2)(--->)P(,3/2)) and (3.00 (+OR -) 0.25) x 10('-18) cm('2) for the 93.2 nm line (S(,1/2)( --->)P(,1/2)). The Ar II photoemission cross sections will be part of an atlas of electron impact photoemission cross sections for emission lines throughout the vuv wavelength region. This atlas will form the basis of a new portable primary vuv radiometric standard. The new intensity standard consists of an electron beam used to excite gas atoms which subsequently emit characteristic line radiation. The absolute photon flux emitted in an emission line can be determined if the electron impact photoemission cross section for the emission line is known, along with the target gas density and the electron beam current. The absolute radiometric standard can be used to determine the detection efficiency of any uncalibrated spectrometer-detector system. The cross section measurements were made using a spectrometer with an optical system similar to the Seya -Namioka design. A type IV holographic grating with an aluminum surface overcoated with MgF(,2) was used. The detector was a venetian blind photomultiplier with a BeCu cathode. The detection efficiency was determined by using well parameterized synchrotron radiation from SURF-II at the National Bureau of Standards in Gaithersburg, Maryland. A large multiadjustable manipulator positioned the spectrometer to view a beam of synchrotron radiation as if it originated from points along the electron beam. The spectrometer -detector system response was determined separately for incident synchrotron radiation polarized both parallel

  16. Resonance and threshold effects in photoemission up to 3500 eV

    Shirley, D.A.; Kobrin, P.H.; Lindle, D.W.; Truesdale, C.M.; Southworth, S.H.; Becker, U.; Kerkhoff, H.G.

    1982-08-01

    Beam lines at the Stanford Synchrotron Radiation Laboratory (SSRL) now provide photon beams throughout the entire energy range 5 to 5000 eV, with a pulse structure very well-suited to time-of-flight (TOF) photoelectron spectroscopy. We have used this facility, together with a TOF spectrometer, to measure photoemission cross sections sigma(epsilon) and asymmetry parameters ..beta..(epsilon) for several interesting systems. A summary of early results is given. Metal vapors (Ba, Cd, Mn, Hg) were studied using a high-temperature oven. Resonant photoemission was observed in several cases. Both sigma(epsilon) and ..beta..(epsilon) showed resonant behavior at 21.1 eV for several lines in Cd. The 4d, 5s, and 5p sigma(epsilon) line profiles differed dramatically, illustrating the detailed information about continuum states that is available from photoemission. Correlation satellites in photoemission from rare gases have been observed over a very wide energy range, including those seen in the K-shells of He, Ne and Ar and in the L-shell of Ne. The structure and preliminary intensity variations of these satellites will be discussed. Molecular shape resonances in C(1s), N(1s), and O(1s) photoemission were observed for the first time, in the molecules CO, CO/sub 2/, OCS, CF/sub 4/, N/sub 2/ and NO. Both the ..pi.. and sigma resonances were observed in KVV Auger emission, and the sigma resonances were studied by photoemission. The asymmetry parameters were measured in all cases. The results are in fair agreement with theory, but show systematic deviations and trends. 31 references.

  17. The electronic and chemical structure of the a-B3CO0.5:Hy-to-metal interface from photoemission spectroscopy: implications for Schottky barrier heights.

    Driver, M Sky; Paquette, Michelle M; Karki, S; Nordell, B J; Caruso, A N

    2012-11-01

    The electronic and chemical structure of the metal-to-semiconductor interface was studied by photoemission spectroscopy for evaporated Cr, Ti, Al and Cu overlayers on sputter-cleaned as-deposited and thermally treated thin films of amorphous hydrogenated boron carbide (a-B(x)C:H(y)) grown by plasma-enhanced chemical vapor deposition. The films were found to contain ~10% oxygen in the bulk and to have approximate bulk stoichiometries of a-B(3)CO(0.5):H(y). Measured work functions of 4.7/4.5 eV and valence band maxima to Fermi level energy gaps of 0.80/0.66 eV for the films (as-deposited/thermally treated) led to predicted Schottky barrier heights of 1.0/0.7 eV for Cr, 1.2/0.9 eV for Ti, 1.2/0.9 eV for Al, and 0.9/0.6 eV for Cu. The Cr interface was found to contain a thick partial metal oxide layer, dominated by the wide-bandgap semiconductor Cr(2)O(3), expected to lead to an increased Schottky barrier at the junction and the formation of a space-charge region in the a-B(3)CO(0.5):H (y) layer. Analysis of the Ti interface revealed a thick layer of metal oxide, comprising metallic TiO and Ti (2)O (3), expected to decrease the barrier height. A thinner, insulating Al(2)O(3) layer was observed at the Al-to-a-B(3)CO(0.5):H(y) interface, expected to lead to tunnel junction behavior. Finally, no metal oxides or other new chemical species were evident at the Cu-to-a-B(3)CO(0.5):H(y) interface in either the core level or valence band photoemission spectra, wherein characteristic metallic Cu features were observed at very thin overlayer coverages. These results highlight the importance of thin-film bulk oxygen content on the metal-to-semiconductor junction character as well as the use of Cu as a potential Ohmic contact material for amorphous hydrogenated boron carbide semiconductor devices such as high-efficiency direct-conversion solid-state neutron detectors. PMID:22976833

  18. The electronic and chemical structure of the a-B3CO0.5:Hy-to-metal interface from photoemission spectroscopy: implications for Schottky barrier heights

    The electronic and chemical structure of the metal-to-semiconductor interface was studied by photoemission spectroscopy for evaporated Cr, Ti, Al and Cu overlayers on sputter-cleaned as-deposited and thermally treated thin films of amorphous hydrogenated boron carbide (a-BxC:Hy) grown by plasma-enhanced chemical vapor deposition. The films were found to contain ∼10% oxygen in the bulk and to have approximate bulk stoichiometries of a-B3CO0.5:Hy. Measured work functions of 4.7/4.5 eV and valence band maxima to Fermi level energy gaps of 0.80/0.66 eV for the films (as-deposited/thermally treated) led to predicted Schottky barrier heights of 1.0/0.7 eV for Cr, 1.2/0.9 eV for Ti, 1.2/0.9 eV for Al, and 0.9/0.6 eV for Cu. The Cr interface was found to contain a thick partial metal oxide layer, dominated by the wide-bandgap semiconductor Cr2O3, expected to lead to an increased Schottky barrier at the junction and the formation of a space-charge region in the a-B3CO0.5:H y layer. Analysis of the Ti interface revealed a thick layer of metal oxide, comprising metallic TiO and Ti 2O 3, expected to decrease the barrier height. A thinner, insulating Al2O3 layer was observed at the Al-to-a-B3CO0.5:Hy interface, expected to lead to tunnel junction behavior. Finally, no metal oxides or other new chemical species were evident at the Cu-to-a-B3CO0.5:Hy interface in either the core level or valence band photoemission spectra, wherein characteristic metallic Cu features were observed at very thin overlayer coverages. These results highlight the importance of thin-film bulk oxygen content on the metal-to-semiconductor junction character as well as the use of Cu as a potential Ohmic contact material for amorphous hydrogenated boron carbide semiconductor devices such as high-efficiency direct-conversion solid-state neutron detectors.

  19. Mapping of Si/SiC p-n heterojunctions using scanning internal photoemission microscopy

    Shingo, Masato; Liang, Jianbo; Shigekawa, Naoteru; Arai, Manabu; Shiojima, Kenji

    2016-04-01

    We demonstrated the two-dimensional characterization of p+-Si/n--SiC heterointerfaces by scanning internal photoemission microscopy (SIPM). In internal photoemission spectra, a linear relationship was found between the square root of photoyield (Y) and photon energy, and the threshold energy (qV th) was reasonably obtained to be 1.34 eV. From the SIPM results, Y and qV th maps were successfully obtained, and nanometer-deep gaps in the junction were sensitively visualized as a pattern. These results suggest that this method is a powerful tool for investigating the inhomogeneity of heterojunctions as well as their carrier transport properties.

  20. Commissioning Results Of Angle-Resolved Photoemission System At The Siam Photon Laboratory

    This report describes the first results obtained by the angle-resolved photoemission system at the Siam Photon Laboratory. Nickel single crystal with (111) surface was selected as the sample. Sample preparation methods as well as measurement procedures are described. The total energy resolution at photon energy of 35 eV was 370 MeV. Surface energy band structure of the nickel was obtained from angle-resolved photoemission spectra along two lines of symmetry: τto Τto Κand τto ΣtoΜ. The experimental energy band structure is qualitatively agreed with a theoretical calculation

  1. Vacuum space charge effect in laser-based solid-state photoemission spectroscopy

    Graf, J; Hellmann, S; Jozwiak, C.; Smallwood, C. L.; Hussain, Z.; Kaindl, R. A.; Kipp, L.; Rossnagel, K.; Lanzara, A.

    2010-01-01

    We report a systematic measurement of the space charge effect observed in the few-ps laser pulse regime in laser-based solid-state photoemission spectroscopy experiments. The broadening and the shift of a gold Fermi edge as a function of spot size, laser power, and emission angle are characterized for pulse lengths of 6 ps and 6 eV photon energy. The results are used as a benchmark for an $N$-body numerical simulation and are compared to different regimes used in photoemission spectroscopy. T...

  2. Vacuum space charge effect in laser-based solid-state photoemission spectroscopy

    Graf, Jeff

    2010-01-01

    We report a systematic measurement of the space charge effect observed in the few-ps laser pulse regime in laser-based solid-state photoemission spectroscopy experiments. The broadening and the shift of a gold Fermi edge as a function of spot size, laser power, and emission angle are characterized for pulse lengths of 6 ps and 6 eV photon energy. The results are used as a benchmark for an N-body numerical simulation and are compared to different regimes used in photoemission spectroscopy. The...

  3. A PHOTOEMISSIVE MONOENERGETIC ELECTRON SOURCE FOR CALIBRATING THE BETA—MAGNETIC SPECTROMETER

    陈志才; 孙汉城; 等

    1994-01-01

    A new kind of electron source,the photoemissive monoenergetic electron source has been inverted for calibrating the beta-magnetic spectrometer.It produces electrons in the form of simulating a radioactive monoenergetic electron source and can be made in any shape and size according to the demands of experiments.In this paper.the principles and basic constructions of the photoemissive monoenergetic electron source are listed.a new way for determining resolution function of experimental system in the resarch of neutrino rest mass has been posed and one of its actual applications is also given.

  4. Time-of-flight two-photon photoemission spectromicroscopy with femtosecond laser radiation

    Cinchetti, Mirko

    2004-01-01

    Time-of-flight photoemission spectromicroscopy was used to measure and compare the two-photon photoemission (2PPE) spectra of Cu and Ag nanoparticles with linear dimensions ranging between 40 nm and several 100 nm, with those of the corresponding homogeneous surfaces. 2PPE was induced employing femtosecond laser radiation from a frequency-doubled Ti:sapphire laser in the spectral range between 375 nm and 425 nm with a pulse width of 200 fs and a repetition rate of 80 MHz. The use...

  5. Two-color coherent control of femtosecond above-threshold photoemission from a tungsten nanotip

    Förster, Michael; Krüger, Michael; Lemell, Christoph; Wachter, Georg; Libisch, Florian; Madlener, Thomas; Burgdörfer, Joachim; Hommelhoff, Peter

    2016-01-01

    We demonstrate coherent control of multiphoton and above-threshold photoemission from a single solid-state nanoemitter driven by a fundamental and a weak second harmonic laser pulse. Depending on the relative phase of the two pulses, electron emission is modulated with a visibility of up to 94%. Electron spectra reveal that all observed photon orders are affected simultaneously and similarly. We confirm that photoemission takes place within 10 fs. Accompanying simulations indicate that the current modulation with its large contrast results from two interfering quantum pathways leading to electron emission.

  6. The effect of photoemission on the streamer development and propagation in short uniform gaps

    Georghiou, G. E.; Morrow, R.; Metaxas, A. C.

    2001-01-01

    Results are presented for the time evolution of photoemission in a 0.1 cm parallel-plane gap in atmospheric pressure air when a positive dc voltage is applied at one of the electrodes. The hydrodynamic set of equations is solved using the finite-element flux-corrected transport method in two dimensions. The time evolution of the electron distribution at the cathode and the variation of the spread of the electrons are examined during the avalanche, the avalanche-to-streamer transition and streamer propagation stages. Finally, the effect of the variation of the photoemission coefficient on the field distribution and the current waveform are presented.

  7. Angle-resolved photoemission spectroscopy (ARPES) studies of cuprate superconductors

    Palczewski, Ari Deibert [Iowa State Univ., Ames, IA (United States)

    2010-01-01

    This dissertation is comprised of three different angle-resolved photoemission spectroscopy (ARPES) studies on cuprate superconductors. The first study compares the band structure from two different single layer cuprates Tl2Ba2CuO6+δ (Tl2201) Tc, max ≈ 95 K and (Bi 1.35Pb0.85)(Sr1.47La0.38)CuO6+δ (Bi2201) Tc, max ≈ 35 K. The aim of the study was to provide some insight into the reasons why single layer cuprate's maximum transition temperatures are so different. The study found two major differences in the band structure. First, the Fermi surface segments close to (π,0) are more parallel in Tl2201 than in Bi2201. Second, the shadow band usually related to crystal structure is only present in Bi2201, but absent in higher Tc Tl2201. The second study looks at the different ways of doping Bi2Sr2CaCu2O8+δ (Bi2212) in-situ by only changing the post bake-out vacuum conditions and temperature. The aim of the study is to systematically look into the generally overlooked experimental conditions that change the doping of a cleaved sample in ultra high vacuum (UHV) experiments. The study found two major experimental facts. First, in inadequate UHV conditions the carrier concentration of Bi2212 increases with time, due to the absorption of oxygen from CO2/CO molecules, prime contaminants present in UHV systems. Second, in a very clean UHV system at elevated temperatures (above about 200 K), the carrier concentration decreases due to the loss of oxygen atoms from the Bi-O layer. The final study probed the particle-hole symmetry of the pseudogap phase in high temperature superconducting cuprates by looking at the thermally excited bands above the Fermi level. The data showed a particle-hole symmetric pseudogap which symmetrically closes away from the nested FS before the node. The data is

  8. Hermes, a collaborative environment at IN2P3

    Helft, Christian, E-mail: helft@lal.in2p3.f [Laboratoire de l' Accelerateur Lineaire Bat 200 91898 ORSAY Cedex (France)

    2010-04-01

    IN2P3, the institute bringing together HEP laboratories in France, opened a videoconferencing service in 2002 based on an industry standard H323 MCU (Multiple Control Unit). This service has steadily grown since then, serving other French scientific communities in addition to HEP and reaching an average of about thirty conferences a day. The relatively small amount of manpower required to deploy and maintain this facility can be explained by the very sound design and the large array of built-in capabilities offered by the equipment that replaced the original equipment purchased in 2005.

  9. Gestor de almacenamiento en redes P2P

    Olías de Lima Pancorbo, Carlos

    2009-01-01

    El objetivo del proyecto consiste en la implementación de un sistema de archivos distribuido mediante P2P, basándose en el entorno de desarrollo .NET. Para dicho desarrollo, la primera parte del proyecto consiste en la familiarización con un nuevo lenguaje de desarrollo integrado en la plataforma Visual Studio: Visual Basic.NET. En segundo lugar, una vez adquiridos los conocimientos necesarios para el desarrollo de aplicaciones en dicha plataforma, se implementará un Sistema de Archivos Distr...

  10. Random walk search in unstructured P2P

    Jia Zhaoqing; You Jinyuan; Rao Ruonan; Li Minglu

    2006-01-01

    Unstructured P2P has power-law link distribution, and the random walk in power-law networks is analyzed. The analysis results show that the probability that a random walker walks through the high degree nodes is high in the power-law network, and the information on the high degree nodes can be easily found through random walk. Random walk spread and random walk search method (RWSS) is proposed based on the analysis result. Simulation results show that RWSS achieves high success rates at low cost and is robust to high degree node failure.

  11. Acid sensitive background potassium channels K2P3.1 and K2P9.1 undergo rapid dynamin-dependent endocytosis

    Mant, Alexandra; Williams, Sarah; O'Kelly, Ita

    2013-01-01

    Acid-sensitive, two-pore domain potassium channels, K2p3.1 and K2p9.1, are implicated in cardiac and nervous tissue responses to hormones, neurotransmitters and drugs. K2p3.1 and K2p9.1 leak potassium from the cell at rest and directly impact membrane potential. Hence altering channel number on the cell surface drives changes in cellular electrical properties. The rate of K2p3.1 and K2p9.1 delivery to and recovery from the plasma membrane determines both channel number at the cell surface and...

  12. Complexes of (EtO)2P(O)CH2P(O)(OEt)2 with lanthanide nitrates

    The preparation of complexes of (EtO)2P(O)CH2P(O)(OEt)2 = L, with lanthanide nitrates is described. Stable complexes with composition LnL2(NO3)3 can be isolated for Ln = La-Eu and fully characterised. For LnGd-Lu solid compounds could not be isolated. Conductivity and 31P NMR spectroscopy indicate structural changes in solution between the lighter and heavier lanthanides and, whilst electro-spray mass spectrometry confirms a dramatic difference in behaviour with complexes of the heavier lanthanides readily decomposing via loss of EtNO3, other experiments show that this does not occur under the conditions of complex formation. The single crystal X-ray structures for Ln = La and Sm show the nitrates and OEt groups to be in close proximity. The changes in spectroscopic properties correlate well with the difficulties in isolating the complexes of heavier metals, and are possibly due to the formation of dimeric complexes rather than loss of ethyl nitrate. (authors)

  13. Content Distribution Mechanism in Mobile P2P Network

    Degui Zeng

    2014-05-01

    Full Text Available As content distribution in mobile P2P network facing architecture instability, the limited ability of a single node, low efficiency of content distribution and other problems, this paper proposes a new mobile network structure and content distribution mechanism strategy, the new mobile network structure will be divided into multiple subnets network for partition management. Each subnet manages information routing and dissemination strategies through a super-node. The transfer of information between subnets can be achieved by transitional node in cross region. Thus the information transfer is achieved in the entire network. Content distribution strategies using part of network coding mechanism for data compression, improve the efficiency of information transmission and download success rate. Finally, experimental verification, the experimental results show that: the proposed new mobile network structure and content distribution mechanisms strategies can reduce the disturbance of download success rate caused by fixed point, reduce the data transmission delay, and effectively improve the hit rate

  14. P2P Approach for Web Services Publishing and Discovery

    Islam, Mohmammad Towhidul; Akon, Mursalin; Shen, Xuemin (Sherman)

    Web service is an emerging paradigm for distributing business applications from different platforms to a wide variety of clients. The critical factor in seamlessly accessing web services is to discover the appropriate service and the related service providers. Unfortunately, current web service technologies use centralized directory to keep the service index, which is not scalable and at the same time vulnerable to single point of failure. Peer to peer system is a popular decentralized architecture which can be used for key look up service with scalability and self organization. Thus there is an opportunity to intersect the P2P framework with web services to provide the scalable solution. In this chapter, we discuss the key methods to deploy web services using the peer-to-peer technology.

  15. Absorption enhancement in metal nanoparticles for photoemission current for solar cells

    Gritti, Claudia; Novitsky, Andrey; Malureanu, Radu;

    2012-01-01

    In order to improve the photoconversion efficiency, we consider the possibility of increasing the photocurrent in solar cells exploiting the electron photoemission from small metal nanoparticles into a semiconductor. The effect is caused by the absorption of photons and generation of local surfac...

  16. Synchrotron photoemission study of (Zn,Co)O films with uniform Co distribution

    Guziewicz, E., E-mail: guzel@ifpan.edu.pl [Institute of Physics, Polish Academy of Sciences, 02-668 Warsaw (Poland); Lukasiewicz, M.I.; Wachnicki, L.; Kopalko, K. [Institute of Physics, Polish Academy of Sciences, 02-668 Warsaw (Poland); Kovacs, A.; Dunin-Borkowski, R.E. [Center for Electron Nanoscopy, Technical University of Denmark, Lyngby 2800 (Denmark); Witkowski, B.S.; Kowalski, B.J. [Institute of Physics, Polish Academy of Sciences, 02-668 Warsaw (Poland); Sadowski, J. [Institute of Physics, Polish Academy of Sciences, 02-668 Warsaw (Poland); MAX-Lab, Lund University, Box 118, SE-22100 Lund (Sweden); Sawicki, M.; Jakiela, R. [Institute of Physics, Polish Academy of Sciences, 02-668 Warsaw (Poland); Godlewski, M. [Institute of Physics, Polish Academy of Sciences, 02-668 Warsaw (Poland); Department of Mathematics and Natural Sciences, College of Science, Cardinal Wyszynski University, 01-815 Warsaw (Poland)

    2011-10-15

    We present results of a resonant photoemission study of (Zn,Co)O films with Co content between 2% and 7%. The films were grown by Atomic Layer Deposition (ALD) at low temperature of 160 deg. C, and show fully paramagnetic behavior. The Co ions are uniformly distributed in the ZnO matrix and are free of foreign phases and metal accumulations as indicated by TEM data. The electronic structure of (Zn,Co)O films was studied by Resonant Photoemission Spectroscopy across the Co3p-Co3d photoionization threshold. We have observed that the resonant enhancement of the photoemission intensity from the Co3d shell is not the same for samples with different cobalt content. We suggest that the Co3d contribution to the valence band depends on both Co and H content. - Highlights: > (Zn,Co)O films with uniform Co distribution were studied by Resonant Photoemission. > Resonant PES enhancement from the Co3d shell is not the same for samples with different Co contents. > Observed Co3d distributions depend on both cobalt and hydrogen content.

  17. High-resolution-angle resolved photoemission studies of high temperature superconductors

    This paper presents recent photoemission studies of Y 123 and Bi 2212 performed with high energy and angular resolution. They provide detailed information on the nature of the states near the Fermi level. Measurements of the superconducting gap, band dispersion, and the density of states near the Fermi level in the normal state all support a Fermi liquid description of these materials

  18. PHOTOEMISSION AS A PROBE OF THE COLLECTIVE EXCITATIONS IN CONDENSED MATTER SYSTEMS.

    JOHNSON, P.D.; VALLA, T.

    2006-08-01

    New developments in instrumentation have recently allowed photoemission measurements to be performed with very high energy and momentum resolution.[1] This has allowed detailed studies of the self-energy corrections to the lifetime and mass renormalization of excitations in the vicinity of the Fermi level. These developments come at an opportune time. Indeed the discovery of high temperature superconductivity in the cuprates and related systems is presenting a range of challenges for condensed matter physics.[2] Does the mechanism of high T{sub c} superconductivity represent new physics? Do we need to go beyond Landau's concept of the Fermi liquid?[3] What, if any, is the evidence for the presence or absence of quasiparticles in the excitation spectra of these complex oxides? The energy resolution of the new instruments is comparable to or better than the energy or temperature scale of superconductivity and the energy of many collective excitations. As such, photoemission has again become recognized as an important probe of condensed matter. Studies of the high T{sub c} superconductors and related materials are aided by the observation that they are two dimensional. To understand this, we note that the photoemission process results in both an excited photoelectron and a photohole in the final state. Thus the experimentally measured photoemission peak is broadened to a width reflecting contributions from both the finite lifetime of the photohole and the momentum broadening of the outgoing photoelectron.

  19. Electron photoemission in plasmonic nanoparticle arrays: analysis of collective resonances and embedding effects

    Zhukovsky, Sergei V.; Babicheva, Viktoriia; Uskov, Alexander;

    2014-01-01

    effects in the formation of plasmonic resonance is diminished. We also show that 5-20 times increase of photoemission can be achieved on embedding of nanoparticles without taking into account dynamics of ballistic electrons. The results obtained can be used to increase efficiency of plasmon...

  20. Three-dimensional band structure of layered TiTe2: Photoemission final-state effects

    Three-dimensional band structure of unoccupied and occupied states of the prototype layered material TiTe2 is determined focusing on the ΓA line of the Brillouin zone. Dispersions and lifetimes of the unoccupied states, acting as the final states in the photoemission process, are determined from a very-low-energy electron diffraction experiment supported by first-principles calculations based on a Bloch waves treatment of multiple scattering. The experimental unoccupied states of TiTe2 feature dramatic non-free-electron effects such as multiband composition and nonparabolic dispersions. The valence band layer-perpendicular dispersions are then determined from a photoemission experiment consistently interpreted on the basis of the experimental final states to achieve control over the three-dimensional wave vector. The experimental results demonstrate the absence of the Te 4pz* Fermi surface pocket at the Γ point and significant self-energy renormalization of the valence band dispersions. Photoemission calculations based on a Bloch waves formalism within the one-step theory reveal limitations of understanding photoemission from layered materials such as TiTe2 in terms of direct transitions

  1. Hot Electron Photoemission from Plasmonic Nanoparticles: Role of Transient Absorption in Surface Mechanism

    Uskov, Alexander V.; Protsenko, Igor E.; Ikhsanov, Renat S.; Babicheva, Viktoriia; Zhukovsky, Sergei; Lavrinenko, Andrei; P. O’Reilly, Eoin; Xu, Hongxing

    We analyze and compare surface- and vol ume-based internal photoelectric effects from spherical nanoparticles, obtaining analytical expression s for the photoemission rate in both cases. Similar to results for a flat metal surface, one can show that the surface mechanism preva ils, since it is...

  2. Shaping SHF train of optical picosecond pulses for generating a photoemission in SHF guns

    The paper analyses a technique of generating optical picosecond pulses (OPP) through laser beam deflection. The OPP generator consists of a laser, deflection system, optical system and amplifier-converter. The technique of OPP generation through laser beam deflection can be successfully used for triggering photoemission in SHF beams. 8 refs., 2 figs

  3. Valence-band photoemission in La and Pr: Connections with the Ce problem

    Energy distribution curves from La and Pr were taken from 32 to 80 eV photon energies. Above 50 eV the valence-band photoemission in La is very weak, implying that previous studies of Ce have underemphasized the 4f contributions. Pr exhibits two peaks attributable to 4f electrons, similar to the structures in Ce

  4. Synchrotron photoemission study of (Zn,Co)O films with uniform Co distribution

    Guziewicz, E.; Lukasiewicz, M. I.; Wachnicki, L.;

    2011-01-01

    We present results of a resonant photoemission study of (Zn,Co)O films with Co content between 2% and 7%. The films were grown by Atomic Layer Deposition (ALD) at low temperature of 160°C, and show fully paramagnetic behavior. The Co ions are uniformly distributed in the ZnO matrix and are free of...

  5. The electronic structure of spintronic materials as seen by spin-polarized angle-resolved photoemission

    Highlights: •Introduction of spin-dependent effects in modern angle-resolved photoemission from the point of view of potential applications in spintronics. •Review on modern spin-polarimeters, including the historical development of the field. •Several examples to illustrate the application of spin-polarized photoemission to ferromagnetic and non-ferromagnetic sample systems. -- Abstract: The key quantity in spintronic devices is the spin polarization of the current flowing through the various device components, which in turn is closely determined by the components’ electronic structure. Modern spin- and angle-resolved photoemission spectroscopy (spin-ARPES) can map the details of the spin-polarized electronic structure in many novel material systems – both magnetic and nonmagnetic. In order to separate close-lying electronic states, however, an improvement in energy and angular resolution as well as information depth is still mandatory. We review several types of modern photoemission spectrometers capable of spin analysis and discuss the application of the technique for several physical systems including ferromagnetic thin films and topological insulators

  6. Identification of lysines within membrane-anchored Mga2p120 that are targets of Rsp5p ubiquitination and mediate mobilization of tethered Mga2p90

    Bhattacharya, Sabyasachi; Shcherbik, Natalia; Vasilescu, Julian; Smith, Jeffrey C.; Figeys, Daniel; Haines, Dale S.

    2008-01-01

    Mga2p90 is an endoplasmic reticulum (ER) localized transcription factor that is released from the ER membrane by a unique ubiquitin-dependent mechanism. Mga2p90 mobilization requires poly-ubiquitination of its associating membrane-bound Mga2p120 anchor and subsequent Mga2p120-Mga2p90 complex disassembly that is mediated by ATPase Cdc48p and its heteromeric ubiquitin-binding adaptor Npl4p-Ufd1p. Although previous studies have identified the ubiquitin ligase (i.e. Rsp5p) and ligase binding site...

  7. Energetic Landscape of MDM2-p53 Interactions by Computational Mutagenesis of the MDM2-p53 Interaction.

    Thayer, Kelly M; Beyer, George A

    2016-01-01

    The ubiquitin ligase MDM2, a principle regulator of the tumor suppressor p53, plays an integral role in regulating cellular levels of p53 and thus a prominent role in current cancer research. Computational analysis used MUMBO to rotamerize the MDM2-p53 crystal structure 1YCR to obtain an exhaustive search of point mutations, resulting in the calculation of the ΔΔG comprehensive energy landscape for the p53-bound regulator. The results herein have revealed a set of residues R65-E69 on MDM2 proximal to the p53 hydrophobic binding pocket that exhibited an energetic profile deviating significantly from similar residues elsewhere in the protein. In light of the continued search for novel competitive inhibitors for MDM2, we discuss possible implications of our findings on the drug discovery field. PMID:26992014

  8. Ternary complex formation of Ino2p-Ino4p transcription factors and Apl2p adaptin beta subunit in yeast.

    Nikawa, Jun-ichi; Yata, Masako; Motomura, Miki; Miyoshi, Nobutaka; Ueda, Tsuyoshi; Hisada, Daisuke

    2006-11-01

    Yeast Ino2p-Ino4p heterodimeric complex is well known as a transcriptional activator for the genes regulated by inositol and choline, such as the INO1 gene. Apl2p is a large subunit of the yeast adaptin complex, an adaptor complex required for the clathrin coat to bind to the membrane. We found that Ino2p, Ino4p, and Apl2p form a ternary complex. This interaction was initially observed in a yeast two-hybrid study and subsequently verified by co-immunoprecipitation. Ino2p and Ino4p bind to Apl2p in the same region of Apl2p, viz., at the middle part and the C-terminal part. Ino2p and Ino4p bind to Apl2p independently, but more strongly when both are present. Furthermore, a disruption of APL2 together with INO2 or INO4 rendered yeast cells sensitive to oxidative stress. INO2-APL2 double disruptants also showed growth inability in non-fermentable carbon sources, such as glycerol. These results indicate a genetic interaction between APL2, INO2 and INO4 and uncovere novel functions of the Ino2p-Ino4p-Apl2p complex in yeast. PMID:17090927

  9. An Effective Calculation of Reputation in P2P Networks

    RVVSV Prasad

    2009-07-01

    Full Text Available With the advent of sophisticated networking technologies and the related applications, more and more computers are getting hooked to the Internet. This is mainly for utilizing several services ranging from information sharing to electronic transactions. P2P networks which allow decentralized systems, have posed problems related to trust when transactions have to be carried out. Current literature proposes several solutions for trust management and reputation computation. The solutions base their assessment of reputations on the number of successful transactions or on the similarity of the feedbacks. There are some concerns in the feedback ratings if we are not considering the issues like number of transactions, frequency of transactions with the same peer and different peers, age of transaction, how frequently a given peer attends a common vendor, and the number of common vendors between the pairs. This paper puts forward a reputation computation system addressing these concerns. It implicitly allows detection of malicious peers. It also incorporates a corrective mechanism, if the feedbacks are from more number of malicious peers. The implementations and the results that support our claims are also presented.

  10. Survey on Distributed Data Mining in P2P Networks

    T, Rekha Sunny

    2012-01-01

    The exponential increase of availability of digital data and the necessity to process it in business and scientific fields has literally forced upon us the need to analyze and mine useful knowledge from it. Traditionally data mining has used a data warehousing model of gathering all data into a central site, and then running an algorithm upon that data. Such a centralized approach is fundamentally inappropriate due to many reasons like huge amount of data, infeasibility to centralize data stored at multiple sites, bandwidth limitation and privacy concerns. To solve these problems, Distributed Data Mining (DDM) has emerged as a hot research area. Careful attention in the usage of distributed resources of data, computing, communication, and human factors in a near optimal fashion are paid by distributed data mining. DDM is gaining attention in peer-to-peer (P2P) systems which are emerging as a choice of solution for applications such as file sharing, collaborative movie and song scoring, electronic commerce, an...

  11. Photon-impenetrable, electron-permeable: the carbon nanotube forest as a medium for multiphoton thermal-photoemission.

    Vahdani Moghaddam, Mehran; Yaghoobi, Parham; Sawatzky, George A; Nojeh, Alireza

    2015-04-28

    Combining the photoelectric and thermionic mechanisms to generate free electrons has been of great interest since the early days of quantum physics as exemplified by the Fowler-DuBridge theory, and recently proposed for highly efficient solar conversion. We present experimental evidence of this combined effect over the entire range spanning room-temperature photoemission to thermionic emission. Remarkably, the optical stimulus alone is responsible for both heating and photoemission at the same time. Moreover, the current depends on optical intensity quadratically, indicating two-photon photoemission, for intensities of ca. 1-50 W/cm(2), which are orders of magnitude below the intensities required for two-photon photoemission from bulk metals. This surprising behavior appears to be enabled by the internal nanostructure of the carbon nanotube forest, which captures photons effectively, yet allows electrons to escape easily. PMID:25769341

  12. Spin-orbit-induced photoelectron spin polarization in angle-resolved photoemission from both atomic and condensed matter targets

    The existence of highly spin polarized photoelectrons emitted from non-magnetic solids as well as from unpolarized atoms and molecules has been found to be very common in many studies over the past 40 years. This so-called Fano effect is based upon the influence of the spin-orbit interaction in the photoionization or the photoemission process. In a non-angle-resolved photoemission experiment, circularly polarized radiation has to be used to create spin polarized photoelectrons, while in angle-resolved photoemission even unpolarized or linearly polarized radiation is sufficient to get a high spin polarization. In past years the Rashba effect has become very important in the angle-resolved photoemission of solid surfaces, also with an observed high photoelectron spin polarization. It is the purpose of the present topical review to cross-compare the spin polarization experimentally found in angle-resolved photoelectron emission spectroscopy of condensed matter with that of free atoms, to compare it with the Rashba effect and topological insulators to describe the influence and the importance of the spin-orbit interaction and to show and disentangle the matrix element and phase shift effects therein. The relationship between the energy dispersion of these phase shifts and the emission delay of photoelectron emission in attosecond-resolved photoemission is also discussed. Furthermore the influence of chiral structures of the photo-effect target on the spin polarization, the interferences of different spin components in coherent superpositions in photoemission and a cross-comparison of spin polarization in photoemission from non-magnetic solids with XMCD on magnetic materials are presented; these are all based upon the influence of the spin-orbit interaction in angle-resolved photoemission. (topical review)

  13. Observation by resonant angle-resolved photoemission of a critical thickness for 2-dimensional electron gas formation in SrTiO{sub 3} embedded in GdTiO{sub 3}

    Nemšák, S. [Department of Physics, University of California, 1 Shields Ave, Davis, California 95616 (United States); Materials Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Rd., Berkeley, California 94720 (United States); Peter-Grünberg-Institut PGI-6, Forschungszentrum Jülich, 52425 Jülich (Germany); Conti, G.; Palsson, G. K.; Conlon, C.; Fadley, C. S. [Department of Physics, University of California, 1 Shields Ave, Davis, California 95616 (United States); Materials Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Rd., Berkeley, California 94720 (United States); Cho, S.; Rault, J. E.; Avila, J.; Asensio, M.-C. [Synchrotron SOLEIL, L' Orme des Merisiers, Saint-Aubin, 91192 Gif sur Yvette Cedex (France); Jackson, C. A.; Moetakef, P.; Janotti, A.; Bjaalie, L.; Himmetoglu, B.; Van de Walle, C. G.; Stemmer, S. [Materials Department, University of California, Santa Barbara, California 93106-5050 (United States); Balents, L. [Department of Physics, University of California, Santa Barbara, California 93106-9530 (United States); Schneider, C. M. [Peter-Grünberg-Institut PGI-6, Forschungszentrum Jülich, 52425 Jülich (Germany)

    2015-12-07

    For certain conditions of layer thickness, the interface between GdTiO{sub 3} (GTO) and SrTiO{sub 3} (STO) in multilayer samples has been found to form a two-dimensional electron gas (2DEG) with very interesting properties including high mobilities and ferromagnetism. We have here studied two trilayer samples of the form [2 nm GTO/1.0 or 1.5 unit cells STO/10 nm GTO] as grown on (001) (LaAlO{sub 3}){sub 0.3}(Sr{sub 2}AlTaO{sub 6}){sub 0.7}, with the STO layer thicknesses being at what has been suggested is the critical thickness for 2DEG formation. We have studied these with Ti-resonant angle-resolved and angle-integrated photoemission and find that the spectral feature in the spectra associated with the 2DEG is present in the 1.5 unit cell sample, but not in the 1.0 unit cell sample. We also observe through core-level spectra additional states in Ti and Sr, with the strength of a low-binding-energy state for Sr being associated with the appearance of the 2DEG, and we suggest it to have an origin in final-state core-hole screening.

  14. Room temperature redox reaction by oxide ion migration at carbon/Gd-doped CeO2 heterointerface probed by an in situ hard x-ray photoemission and soft x-ray absorption spectroscopies

    Takashi Tsuchiya, Shogo Miyoshi, Yoshiyuki Yamashita, Hideki Yoshikawa, Kazuya Terabe, Keisuke Kobayashi and Shu Yamaguchi

    2013-01-01

    Full Text Available In situ hard x-ray photoemission spectroscopy (HX-PES and soft x-ray absorption spectroscopy (SX-XAS have been employed to investigate a local redox reaction at the carbon/Gd-doped CeO2 (GDC thin film heterointerface under applied dc bias. In HX-PES, Ce3d and O1s core levels show a parallel chemical shift as large as 3.2 eV, corresponding to the redox window where ionic conductivity is predominant. The window width is equal to the energy gap between donor and acceptor levels of the GDC electrolyte. The Ce M-edge SX-XAS spectra also show a considerable increase of Ce3+ satellite peak intensity, corresponding to electrochemical reduction by oxide ion migration. In addition to the reversible redox reaction, two distinct phenomena by the electrochemical transport of oxide ions are observed as an irreversible reduction of the entire oxide film by O2 evolution from the GDC film to the gas phase, as well as a vigorous precipitation of oxygen gas at the bottom electrode to lift off the GDC film. These in situ spectroscopic observations describe well the electrochemical polarization behavior of a metal/GDC/metal capacitor-like two-electrode cell at room temperature.

  15. Observation by resonant angle-resolved photoemission of a critical thickness for 2-dimensional electron gas formation in SrTiO3 embedded in GdTiO3

    For certain conditions of layer thickness, the interface between GdTiO3 (GTO) and SrTiO3 (STO) in multilayer samples has been found to form a two-dimensional electron gas (2DEG) with very interesting properties including high mobilities and ferromagnetism. We have here studied two trilayer samples of the form [2 nm GTO/1.0 or 1.5 unit cells STO/10 nm GTO] as grown on (001) (LaAlO3)0.3(Sr2AlTaO6)0.7, with the STO layer thicknesses being at what has been suggested is the critical thickness for 2DEG formation. We have studied these with Ti-resonant angle-resolved and angle-integrated photoemission and find that the spectral feature in the spectra associated with the 2DEG is present in the 1.5 unit cell sample, but not in the 1.0 unit cell sample. We also observe through core-level spectra additional states in Ti and Sr, with the strength of a low-binding-energy state for Sr being associated with the appearance of the 2DEG, and we suggest it to have an origin in final-state core-hole screening

  16. DC High Voltage Conditioning of Photoemission Guns at Jefferson Lab FEL

    Hernandez-Garcia, C.; Benson, S. V.; Biallas, G.; Bullard, D.; Evtushenko, P.; Jordan, K.; Klopf, M.; Sexton, D.; Tennant, C.; Walker, R.; Williams, G.

    2009-08-01

    DC high voltage photoemission electron guns with GaAs photocathodes have been used to produce polarized electron beams for nuclear physics experiments for about 3 decades with great success. In the late 1990s, Jefferson Lab adopted this gun technology for a free electron laser (FEL), but to assist with high bunch charge operation, considerably higher bias voltage is required compared to the photoguns used at the Jefferson Lab Continuous Electron Beam Accelerator Facility. The FEL gun has been conditioned above 400 kV several times, albeit encountering non-trivial challenges with ceramic insulators and field emission from electrodes. Recently, high voltage processing with krypton gas was employed to process very stubborn field emitters. This work presents a summary of the high voltage techniques used to high voltage condition the Jefferson Lab FEL photoemission gun.

  17. Study of f electron correlations in nonmagnetic Ce by means of spin resolved resonant photoemission

    Yu, S; Komesu, T; Chung, B W; Waddill, G D; Morton, S A; Tobin, J G

    2005-11-28

    We have studied the spin-spin coupling between two f electrons of nonmagnetic Ce by means of spin resolved resonant photoemission using circularly polarized synchrotron radiation. The two f electrons participating in the 3d{sub 5/2} {yields} 4f resonance process are coupled in a singlet while the coupling is veiled in the 3d{sub 3/2} {yields} 4f process due to an additional Coster-Kronig decay channel. The identical singlet coupling is observed in the 4d {yields} 4f resonance process. Based on the Ce measurements, it is argued that spin resolved resonant photoemission is a unique approach to study the correlation effects, particularly in the form of spin, in the rare-earths and the actinides.

  18. Volume and surface photoemission from tungsten. I. Calculation of band structure and emission spectra

    Christensen, N. Egede; Feuerbacher, B.

    1974-01-01

    photoemission spectra from W single crystals. The nondirect as well as the direct models for bulk photoemission processes are investigated. The emission from the three low-index surfaces (100), (110), and (111) exhibits strong dependence on direction and acceptance cone. According to the present band model...... there should essentially be no emission normal to the (110) face for photon energies between 9.4 and 10.6 eV. Experimental observation of emission in this gap, however, implies effects not included in the simple bulk models. In particular, effects arising from surface emission have been considered, i.......e., emission of those electrons which are excited in a single-step process from initial states near the surface to final states outside the crystal. The electrons that are emitted from the surface in directions perpendicular to the crystal planes carry information on the one-dimensional surface density of...

  19. Polarization dependence of plasmonic near-field enhanced photoemission from cross antennas

    Klaer, P.; Razinskas, G.; Lehr, M.; Wu, X.; Hecht, B.; Schertz, F.; Butt, H.-J.; Schönhense, G.; Elmers, H. J.

    2016-05-01

    The field enhancement of individual cross-shaped nanoantennas for normal incident light has been measured by the relative photoemission yield using a photoemission electron microscope. We not only measured the electron yield in dependence on the intensity of infrared light (800 nm, 100 fs), but also the polarization dependence. In the normal incidence geometry, the electrical field vector of the illuminating light lies in the surface plane of the sample, independent of the polarization state. Strong yield variations due to an out-of-plane field component as well as changes in the polarization state described by the Fresnel laws are avoided. The electron yield is related to the near-field enhancement as a function of the polarization state of the incident light. The polarization dependence is well explained by numerical simulations.

  20. Effect of humid air exposure on photoemissive and structural properties of KBr thin film photocathode

    Rai, R; Ghosh, N; Singh, B K

    2014-01-01

    We have investigated the influence of water molecule absorption on photoemissive and structural properties of potassium bromide (KBr) thin film photocathode under humid air exposure at relative humidity (RH) 65%. It is evident from photoemission measurement that the photoelectron yield of KBr photocathode is degraded exponentially with humid air exposed time. Structural studies of the "as-deposited" and "humid air aged" films reveal that there is no effect of RH on film's crystalline face centered cubic (fcc) structure. However, the average crystallite size of "humid air exposed film" KBr film has been increased as compared to "as-deposited". In addition, topographical properties of KBr film are also examined by means of scanning electron microscope (SEM), transmission electron microscope (TEM) and atomic force microscope (AFM) and it is observed that granular characteristic of film has been altered, even for short exposure to humid air.

  1. Rb-intercalated C{sub 60} compounds studied by photoemission spectroscopies

    Brambilla, A. [INFM - Dipartimento di Fisica, Politecnico di Milano, p.za L. da Vinci 32, I-20133 Milan (Italy)]. E-mail: alberto.brambilla@polimi.it; Giovanelli, L. [Sincrotrone Trieste S.C.p.A., Strada Statale 14, Km 163.5, I-34012 Basovizza, Trieste (Italy); Vilmercati, P. [Sincrotrone Trieste S.C.p.A., Strada Statale 14, Km 163.5, I-34012 Basovizza, Trieste (Italy); Cattoni, A. [INFM - Dipartimento di Fisica, Politecnico di Milano, p.za L. da Vinci 32, I-20133 Milan (Italy); Biagioni, P. [INFM - Dipartimento di Fisica, Politecnico di Milano, p.za L. da Vinci 32, I-20133 Milan (Italy); Goldoni, A. [Sincrotrone Trieste S.C.p.A., Strada Statale 14, Km 163.5, I-34012 Basovizza, Trieste (Italy); Finazzi, M. [INFM - Dipartimento di Fisica, Politecnico di Milano, p.za L. da Vinci 32, I-20133 Milan (Italy); Duo, L. [INFM - Dipartimento di Fisica, Politecnico di Milano, p.za L. da Vinci 32, I-20133 Milan (Italy)

    2005-06-15

    We report on a combined photoemission and inverse photoemission spectroscopy analysis on Rb{sub x}C{sub 60} compounds with different stoichiometries (0-bar x-bar 6). Apart from shifts and broadening of the spectral features associated to the different phase formed, we observe in the RbC{sub 60} phase the presence of the highest occupied molecular orbital (HOMO) shoulder and of its symmetric (with respect to the Fermi level) empty state. According to calculations, the metallicity of this phase and the presence of these electronic states may be taken as a fingerprint of the interplay between electron-electron and electron-phonon interactions in determining the electronic behavior of alkali metal fullerides.

  2. A photoemission study of cluster growth and morphology on inert substrates

    Thin metal overlayer growth on solid xenon was characterized by means of synchrotron radiation photoemission spectroscopy. We employed a simple experimental arrangement in which a closed-cycle refrigerator and in situ evaporated metal films were used as substrate for Xe condensation. A ''sandwich'' geometry, in which the overlayer metal was used as substrate for Xe condensation, simplified the isolation of metal and Xe emission features. The evolution of the Xe and metal photoemission intensity and the line shape of core and valence states, as a function of metal coverage, were used to estimate average particle size and nucleation site density. The coverage dependence of the Sm 4f binding energy, as well as a number of newly identified spectral fingerprints of particle coalescence, support the measured film morphology and particle size

  3. Dynamics of Molecular Orientation Observed Using Angle Resolved Photoemission Spectroscopy during Deposition of Pentacene on Graphite.

    Park, Sang Han; Kwon, Soonnam

    2016-04-19

    A real-time method to observe both the structural and the electronic configuration of an organic molecule during deposition is reported for the model system of pentacene on graphite. Structural phase transition of the thin films as a function of coverage is monitored by using in situ angle resolved photoemission spectroscopy (ARPES) results to observe the change of the electronic configuration at the same time. A photoemission theory that uses independent atomic center approximations is introduced to identify the molecular orientation from the ARPES technique. This study provides a practical insight into interpreting ARPES data regarding dynamic changes of molecular orientation during initial growth of molecules on a well-defined surface. PMID:26999332

  4. Two-photon Photo-emission of Ultrathin Film PTCDA Morphologies on Ag(111)

    Yang, Aram

    2008-01-01

    Morphology- and layer-dependent electronic structure and dynamics at the PTCDA/Ag(111) interface have been studied with angle-resolved two-photon photoemission. In Stranski-Krastanov growth modes, the exposed wetting layer inhibited the evolution of the vacuum level and valence band to bulk values. For layer-by-layer growth, we observed the transition of electron structure from monolayer to bulk values within eight monolayers. Effective masses and lifetimes of the conduction band and the n=1 ...

  5. X-ray photoemission investigation of excimer laser induced etching of InP

    ArF excimer laser induced etching of InP in various etch gases (HBr, HCl, Cl2) is discussed with regard to its spatial resolution capability. X-ray photoemission spectra and large-area etch rate measurements published before lead to fundamental understanding and interpretation of the characteristics of etched test structures. HBr and HCl require gas phase photodissociation. Cl2, in contrast, has the advantage to react spontaneously

  6. Time-resolved photoemission by attosecond streaking: extraction of time information

    Nagele, S; Pazourek, R; Feist, J.; Doblhoff-Dier, K; Lemell, C.; Tőkési, K; Burgdörfer, J.

    2011-01-01

    Attosecond streaking of atomic photoemission holds the promise to provide unprecedented information on the release time of the photoelectron. We show that attosecond streaking phase shifts indeed contain timing (or spectral phase) information associated with the Eisenbud-Wigner-Smith time delay matrix of quantum scattering. However, this is only accessible if the influence of the streaking infrared (IR) field on the emission process is properly accounted for. The IR probe field can strongly m...

  7. Bulk-Sensitive Photoemission Spectroscopy of TlFe2Se2

    We have investigated the electronic structures of the parent compound of an iron chalcogenide superconductor TlFe2Se2 by bulk-sensitive photoemission spectroscopy (PES). Valence-band PES demonstrates the energy gap opening at the Fermi level due to the shift of Fe 3d state to the higher binding energy side as compared to the calculated density of states, being consistent with the insulating behaviour in transport measurements.

  8. Adaptive Routing Algorithms in Unstructured Peer-to-Peer (P2P) Systems

    Achmad Nizar Hidayanto; Stephane Bressan

    2011-01-01

    There are a variety of peer-to-peer (P2P) systems for sharing documents currently available. According to their data organization, P2P systems are classified into two categories: structured andunstructured P2P systems. In structured P2P systems, peers are organized according to some mapping techniques, e.g. hashing function. Whereas in unstructured P2P system, peers are connected to each others randomly; resources are not moved to other peers but hosted on site. Unstructured P2P systems offer...

  9. Probing the exciton condensate phase in 1T-TiSe{sub 2} with photoemission

    Monney, C; Schwier, E F; Garnier, M G; Mariotti, N; Didiot, C; Beck, H; Aebi, P [Departement de Physique and Fribourg Center for Nanomaterials, Universite de Fribourg, CH-1700 Fribourg (Switzerland); Cercellier, H; Marcus, J [Institut Neel, CNRS-UJF, BP 166, 38042 Grenoble (France); Berger, H [EPFL, Institut de Physique de la Matiere Condensee, CH-1015 Lausanne (Switzerland); Titov, A N, E-mail: philipp.aebi@unifr.ch [Institute of Metal Physics UrD RAS, Ekaterinburg 620219 (Russian Federation)

    2010-12-15

    We present recent results obtained using angle-resolved photoemission spectroscopy performed on 1T-TiSe{sub 2}. Emphasis is put on the peculiarity of the bandstructure of TiSe{sub 2} compared to other transition metal dichalcogenides, which suggests that this system is an excellent candidate for the realization of the excitonic insulator phase. This exotic phase is discussed in relation to the BCS theory, and its spectroscopic signature is computed via a model adapted to the particular bandstructure of 1T-TiSe{sub 2}. A comparison between photoemission intensity maps calculated with the spectral function derived for this model and experimental results is shown, giving strong support for the exciton condensate phase as the origin of the charge density wave transition observed in 1T-TiSe{sub 2}. The temperature-dependent order parameter characterizing the exciton condensate phase is discussed, both on a theoretical and an experimental basis, as well as the chemical potential shift occurring in this system. Finally, the transport properties of 1T-TiSe{sub 2} are analyzed in the light of the photoemission results.

  10. Angle resolved photoemission from organic semiconductors: orbital imaging beyond the molecular orbital interpretation

    Fascinating pictures that can be interpreted as showing molecular orbitals have been obtained with various imaging techniques. Among these, angle resolved photoemission spectroscopy (ARPES) has emerged as a particularly powerful method. Orbital images have been used to underline the physical credibility of the molecular orbital concept. However, from the theory of the photoemission process it is evident that imaging experiments do not show molecular orbitals, but Dyson orbitals. The latter are not eigenstates of a single-particle Hamiltonian and thus do not fit into the usual simple interpretation of electronic structure in terms of molecular orbitals. In a combined theoretical and experimental study we thus check whether a Dyson-orbital and a molecular-orbital based interpretation of ARPES lead to differences that are relevant on the experimentally observable scale. We discuss a scheme that allows for approximately calculating Dyson orbitals with moderate computational effort. Electronic relaxation is taken into account explicitly. The comparison reveals that while molecular orbitals are frequently good approximations to Dyson orbitals, a detailed understanding of photoemission intensities may require one to go beyond the molecular orbital picture. In particular we clearly observe signatures of the Dyson-orbital character for an adsorbed semiconductor molecule in ARPES spectra when these are recorded over a larger momentum range than in earlier experiments. (paper)

  11. Photoemission electron microscopy of localized surface plasmons in silver nanostructures at telecommunication wavelengths

    We image the field enhancement at Ag nanostructures using femtosecond laser pulses with a center wavelength of 1.55 μm. Imaging is based on non-linear photoemission observed in a photoemission electron microscope (PEEM). The images are directly compared to ultra violet PEEM and scanning electron microscopy (SEM) imaging of the same structures. Further, we have carried out atomic scale scanning tunneling microscopy on the same type of Ag nanostructures and on the Au substrate. Measuring the photoelectron spectrum from individual Ag particles shows a larger contribution from higher order photoemission processes above the work function threshold than would be predicted by a fully perturbative model, consistent with recent results using shorter wavelengths. Investigating a wide selection of both Ag nanoparticles and nanowires, field enhancement is observed from 30% of the Ag nanoparticles and from none of the nanowires. No laser-induced damage is observed of the nanostructures neither during the PEEM experiments nor in subsequent SEM analysis. By direct comparison of SEM and PEEM images of the same nanostructures, we can conclude that the field enhancement is independent of the average nanostructure size and shape. Instead, we propose that the variations in observed field enhancement could originate from the wedge interface between the substrate and particles electrically connected to the substrate

  12. Photoemission-monitored x-ray standing wave studies of molecular adsorbate surface structure

    Lee, J J

    2002-01-01

    The influence of non-dipole photoemission terms on the accuracy of photoemission-monitored NIXSW structure determinations has been studied. An experimental survey has been made of values of the incoherent dipole-quadrupole parameter as a function of energy and atomic number for the Is states of elements between carbon and chlorine inclusive. These values are compared with recent theoretical calculations. The contribution of the coherent dipole-quadrupole interference terms, whose form has been theoretically derived recently, has been experimentally measured for Is photoemission from clean Al(111). The coherent dipole-quadrupole effect is found to be small and easily corrected for, while the previously-known incoherent effect is shown to result in tolerable errors in most cases. Adsorption of methyl thiol (CH sub 3 SH) on Pt(111), followed by annealing to approx 220 K is believed to result in the formation of methyl thiolate (-SCH sub 3). Two structural models are consistent with NIXSW data presented here: co-...

  13. Fingerprints of entangled spin and orbital physics in itinerant ferromagnets via angle-resolved resonant photoemission

    Da Pieve, F.

    2016-01-01

    A method for mapping the local spin and orbital nature of the ground state of a system via corresponding flip excitations is proposed based on angle-resolved resonant photoemission and related diffraction patterns, obtained here via an ab initio modified one-step theory of photoemission. The analysis is done on the paradigmatic weak itinerant ferromagnet bcc Fe, whose magnetism, a correlation phenomenon given by the coexistence of localized moments and itinerant electrons, and the observed non-Fermi-Liquid behavior at extreme conditions both remain unclear. The combined analysis of energy spectra and diffraction patterns offers a mapping of local pure spin-flip, entangled spin-flip-orbital-flip excitations and chiral transitions with vortexlike wave fronts of photoelectrons, depending on the valence orbital symmetry and the direction of the local magnetic moment. Such effects, mediated by the hole polarization, make resonant photoemission a promising tool to perform a full tomography of the local magnetic properties even in itinerant ferromagnets or macroscopically nonmagnetic systems.

  14. Photoemission electron microscopy of localized surface plasmons in silver nanostructures at telecommunication wavelengths

    Mårsell, Erik; Larsen, Esben W.; Arnold, Cord L.; Xu, Hongxing; Mauritsson, Johan; Mikkelsen, Anders, E-mail: anders.mikkelsen@sljus.lu.se [Department of Physics, Lund University, P.O. Box 118, 22 100 Lund (Sweden)

    2015-02-28

    We image the field enhancement at Ag nanostructures using femtosecond laser pulses with a center wavelength of 1.55 μm. Imaging is based on non-linear photoemission observed in a photoemission electron microscope (PEEM). The images are directly compared to ultra violet PEEM and scanning electron microscopy (SEM) imaging of the same structures. Further, we have carried out atomic scale scanning tunneling microscopy on the same type of Ag nanostructures and on the Au substrate. Measuring the photoelectron spectrum from individual Ag particles shows a larger contribution from higher order photoemission processes above the work function threshold than would be predicted by a fully perturbative model, consistent with recent results using shorter wavelengths. Investigating a wide selection of both Ag nanoparticles and nanowires, field enhancement is observed from 30% of the Ag nanoparticles and from none of the nanowires. No laser-induced damage is observed of the nanostructures neither during the PEEM experiments nor in subsequent SEM analysis. By direct comparison of SEM and PEEM images of the same nanostructures, we can conclude that the field enhancement is independent of the average nanostructure size and shape. Instead, we propose that the variations in observed field enhancement could originate from the wedge interface between the substrate and particles electrically connected to the substrate.

  15. Photoemission and the electronic properties of heavy fermions -- limitations of the Kondo model

    The electronic properties of Yb-based heavy fermions have been investigated by means of high resolution synchrotron radiation photoemission and compared with predictions of the Kondo model. The Yb heavy fermion photoemission spectra show massive disagreement with the Kondo model predictions (as calculated within the Gunnarsson-Schonhammer computational method). Moreover, the Yb heavy fermion photoemission spectra give very strong indications of core-like characteristics and compare favorable to purely divalent Yb metal and core-like Lu 4f levels. The heavy fermions YbCu2Si2, YbAgCu4 and YbAl3 were measured and shown to have lineshapes much broader and deeper in binding energy than predicted by the Kondo model. The lineshape of the bulk component of the 4f emission for these three heavy fermion materials was compared with that from Yb metal and the Lu 4f levels in LuAl3, the heavy fermion materials show no substantive spectroscopic differences from simple 4f levels observed in Yb metal and LuAl3. Also, the variation with temperature of the 4f fineshape was measured for Yb metal and clearly demonstrates that phonon broadening plays a major role in 4f level lineshape analysis and must be accounted for before considerations of correlated electron resonance effects are presumed to be at work

  16. Measurements of oscillator strengths of the 2p{sup 5}({sup 2}P{sub 1/2})nd J = 2, 3 autoionizing resonances in neon

    Mahmood, Shaukat; Amin, Nasir; Sami-ul-Haq; Shaikh, Nek M; Hussain, Shahid; Baig, M A [Atomic and Molecular Physics Laboratory, Department of Physics, Quaid-i-Azam University, Islamabad 45320 (Pakistan)

    2006-05-14

    Oscillator strengths of the 2p{sup 5}({sup 2}P{sub 1/2})nd J = 2, 3 autoionizing resonances in neon have been determined using a dc discharge plasma in conjunction with an Nd:YAG pumped dye laser system. The excited states are approached using two-step laser excitation via 2p{sup 5}3p'[1/2]{sub 1}, 2p{sup 5}3p'[3/2]{sub 1} and 2p{sup 5}3p'[3/2]{sub 2} intermediate states which are accessed from the 2p{sup 5}3s [1/2]{sub 2} metastable state, populated by the discharge in the hollow cathode lamp. The f-values have been determined for the nd'[3/2]{sub 2}, nd'[5/2]{sub 2} and nd'[5/2]{sub 3} series following the {delta}K = {delta}J = +{delta}l selection rule. Employing the saturation technique the photoionization cross section at the 2p{sup 5} {sup 2}P{sub 1/2} ionization threshold is determined as 5.5(6) Mb and consequently the f-values of the nd' J = 2, 3 autoionizing resonances have been extracted.

  17. Ligand field splittings in core level transitions for transition metal (TM) oxides: Tanabe-Sugano diagrams and (TM) dangling bonds in vacated O-atom defects

    Defect states in the forbidden band-gap below the conduction band edge are active as electron traps in nano-grain high-) transition metal (TM) oxides with thickness >0.3 nm, e.g., ZrO2 and HfO2. These oxides have received considerable attention as gate-dielectrics in complementary metal oxide semiconductor (CMOS) devices, and more recently are emerging as candidates for charge storage and memory devices. To provide a theoretical basis for device functionality, ab-initio many-electron theory is combined with X-ray absorption spectroscopy (XAS) to study O K edge and TM core level transitions. These studies identify ligand field splittings (ΔLF) for defect state features,. When compared with those obtained from O-atom and TM-atom core spectroscopic transitions, this provides direct information about defect state sun-nm bonding arrangements. comparisons are made for (i) elemental TiO2 and Ti2O3 with different formal ionic charges, Ti4+ and Ti3+ and for (ii) Magneli Phase alloys, TinO2n-1, n is an integer 9≥n>3, and (TiO2)x(HfO2)1−x alloys. The alloys display multi-valent behavior from (i) different ionic-charge states, (ii) local bond-strain, and (iii) metallic hopping transport. The intrinsic bonding defects in TM oxides are identified as pairs of singly occupied dangling bonds. For 6-fold coordinated Ti-oxides defect excited states in 2nd derivative O K pre-edge spectra are essentially the same as single Ti-atom d2 transitions in Tanabe-Sugano (T-S) diagrams. O-vacated site defects in 8-fold coordinated ZrO2 and HfO2 are described by d8 T-S diagrams. T-S defect state ordering and splittings are functions of the coordination and symmetry of vacated site bordering TM atoms. ΔLF values from the analysis of T-S diagrams indicate medium range order (MRO) extending to 3rd and 4th nearest-neighbor (NN) TM-atoms. Values are different for 6-fold Ti, and 8-fold ZrO2 and HfO2, and scale inversely with differences in respective formal ionic radii. O-vacated site bonding

  18. Observation of the Forbidden Magnetic Dipole Transition 6{sup 2}P{sub ½} --> 7{sup 2}P{sub ½} in Atomic Thallium

    Chu, S.

    1976-10-01

    A measurement of the 6{sup 2}P{sub ½} --> 7{sup 2}P{sub ½} forbidden magnetic dipole matrix element in atomic thallium is described. A pulsed, linearly polarized dye laser tuned to the transition frequency is used to excite the thallium vapor from the 6{sup 2}P{sub ½} ground state to the 7{sup 2}P{sub ½} excited state. Interference between the magnetic dipole M1 amplitude and a static electric field induced E1 amplitude results in an atomic polarization of the 7{sup 2}P{sub ½} state, and the subsequent circular polarization of 535 nm fluorescence. The circular polarization is seen to be proportional to / as expected, and measured for several transitions between hyperfine levels of the 6{sup 2}P{sub ½} and 7{sup 2}P{sub ½} states. The result is = -(2.11 +- 0.30) x 10{sup -5} parallel bar e parallel bar dirac constant/2mc, in agreement with theory.

  19. Plasma diagnostic potential of 2p4f in N$^+$ -- accurate wavelengths and oscillator strengths

    Shen, Xiaozhi; Li, Jiguang; Jönsson, Per; Wang, Jianguo

    2015-01-01

    Radiative emission lines from nitrogen and its ions are often observed in nebulae spectra, where the N$^{2+}$ abundance can be inferred from lines of the 2p4f configuration. In addition, intensity ratios between lines of the 2p3p -- 2p3s and 2p4f -- 2p3d transition arrays can serve as temperature diagnostics. To aid abundance determinations and plasma diagnostics, wavelengths and oscillator strengths were calculated with high-precision for electric-dipole (E1) transitions from levels in the 2...

  20. Soft X-ray photoemission spectroscopy of selected neurotransmitters in the gas phase

    Maris, Assimo; Melandri, Sonia; Evangelisti, Luca; Caminati, Walther [Dipartimento di Chimica ' G. Ciamician' dell' Universita, Via Selmi 2, I-40126 Bologna (Italy); Giuliano, Barbara M. [Departamento de Quimica da Universidade de Coimbra, 3004-535 Coimbra (Portugal); Plekan, Oksana [Sincrotrone Trieste, in Area Science Park, I-34149 Basovizza, Trieste (Italy); Feyer, Vitaliy [Sincrotrone Trieste, in Area Science Park, I-34149 Basovizza, Trieste (Italy); Electronic Properties (PGI-6), Peter Gruenberg Institute, Forschungszentrum Juelich GmbH, Leo-Brandt-Strasse, 52428 Juelich (Germany); Richter, Robert [Sincrotrone Trieste, in Area Science Park, I-34149 Basovizza, Trieste (Italy); Coreno, Marcello [CNR-IMIP, Montelibretti, I-00016 Rome (Italy); Prince, Kevin C., E-mail: kevin.prince@elettra.trieste.it [Sincrotrone Trieste, in Area Science Park, I-34149 Basovizza, Trieste (Italy); CNR-IOM, Laboratorio TASC, I-34149 Basovizza, Trieste (Italy)

    2012-09-15

    Highlights: Black-Right-Pointing-Pointer Neurotransmitter molecules. Black-Right-Pointing-Pointer Photoelectron spectroscopy. Black-Right-Pointing-Pointer Electronic structure. Black-Right-Pointing-Pointer Weak hydrogen bonding. -- Abstract: The valence molecular orbitals and core levels of tyramine, tryptamine and tryptophol in the gas phase have been studied using X-ray photoelectron spectroscopy (XPS) and theoretical methods. The energies of the outer valence region spectrum are found to be in agreement with previously reported He I spectra, while new data on the inner valence molecular orbitals are reported. The structures in the carbon, nitrogen and oxygen core level spectra of these molecules have been identified and assigned. These compounds are characterised by conformers with hydrogen bonding in which the {pi} systems of the phenol and indole groups act as hydrogen acceptors, but a spectroscopic signature of this hydrogen bond was not observed. This is in contrast with our previous spectra of amino acids, where conformers with specific hydrogen bonding showed strong effects in core level spectra. We attribute the difference to the weaker strength of the {pi}-hydrogen bonding.

  1. An agent-based incentive mechanism for P2P systems

    ZHANG Jian-feng; WANG Ru-chuan

    2006-01-01

    With the increasing uses of peer-to-peer (P2P)systems, the problems of fair information and resources sharing become serious. P2P systems are self-organizing,distributed systems with no centralized authority, such as Free-riding and Tragedy of Commons. Because of the voluntary participation and lack of motivation, the information and resources available in P2P networks are extremely variable and unpredictable. This article studied the problems existing in P2P networks and propose a different method to stimulate the peers in P2P networks to share information and resources,using agents so as to improve the performance of P2P networks.And through simulation experiments and analyzing the results,it can be concluded that this mechanism can effectively solve the problems of fair sharing in P2P systems.

  2. Endothelium-dependent relaxations in the aorta from K2p6.1 knockout mice

    Lloyd, Eric E.; Pandit, Lavannya M.; Crossland, Randy F.; Marrelli, Sean P.; Bryan, Robert M.

    2013-01-01

    K2P6.1 or TWIK-2, a two-pore domain K channel, is an important regulator of cardiovascular function. K2P6.1 is highly expressed in vascular smooth muscle and endothelium. Mice (8–12 wk) lacking functional K2P6.1 (K2P6.1−/−) are hypertensive and have enhanced vascular contractility. It is not known whether the lack of functional K2P6.1 in endothelium has a role in the vascular dysfunction in K2P6.1−/− mice. We tested the hypothesis: K2P6.1−/− mice have impaired endothelium-dependent relaxation...

  3. Automated angle-scanning photoemission end-station with molecular beam epitaxy at KEK-PF BL-1C

    Ono, K; Horiba, K; Oh, J H; Nakazono, S; Kihara, T; Nakamura, K; Mano, T; Mizuguchi, M; Oshima, M; Aiura, Y; Kakizaki, A

    2001-01-01

    In order to satisfy demands to study the electronic structure of quantum nanostructures, a VUV beamline and a high-resolution and high-throughput photoemission end-station combined with a molecular beam epitaxy (MBE) system have been constructed at the BL-1C of the Photon Factory. An angle-resolved photoemission spectrometer, having high energy- and angular-resolutions; VG Microtech ARUPS10, was installed. The total energy resolution of 31 meV at the 60 eV of photon energy is achieved. For the automated angle-scanning photoemission, the electron spectrometer mounted on a two-axis goniometer can be rotated in vacuum by the computer-controlled stepping motors. Another distinctive feature of this end-station is a connection to a MBE chamber in ultahigh vacuum (UHV). In this system, MBE-grown samples can be transferred into the photoemission chamber without breaking UHV. Photoemission spectra of MBE-grown GaAs(0 0 1) surfaces were measured with high-resolution and bulk and surface components are clearly resolved.

  4. Relativistic CI calculations of spectroscopic data for the 2p6 and 2p53l configurations in Ne-like ions between Mg III and Kr XXVII

    Energies, E1, M1, E2, M2 transition rates, oscillator strengths, and lifetimes from relativistic configuration interaction calculations are reported for the states of the 2p6, 2p53s, 2p53p, and 2p53d, configurations in all Ne-like ions between Mg III and Kr XXVII. Core–valence and core–core correlation effects are accounted for through single and double excitations to increasing sets of active orbitals. The Breit interaction and leading quantum electrodynamic effects are included as perturbations. The results are compared with experiments and other recent benchmark calculations. In Mg III, Al IV, Si V, P VI, S VII, and Ar IX, for which experimental energies are known to high accuracy, the mean error in the calculated energies is only 0.011%

  5. Influence of relaxation effects on probabilities of the 2s2p3 S2—2s2 2p2 3p1,2intercombination

    袁萍; 刘欣生; 等

    2003-01-01

    Transition probabilities of the 2s2p3 5S2-2s2 2P2 3P1,2 intercombination transitions in NII have been calculated by using a large-scale multiconfiguration Dirac-Fock method.In the calculation themost important effects of relativity,correlation,and relaxation are considered.From the calculated transition probabilities,the lifetime of the s22p3 5S2 metastable state is derived.The result is in excellent agreement agreement with the latest experimental result.In the meantime the influence of anomalously strong relaxation effects on probabilities of the 2s2p3 5S2-2s2 2p2 3P1,2 lines in NII have been found.

  6. Relativistic CI calculations of spectroscopic data for the 2p6 and 2p53l configurations in Ne-like ions between Mg III and Kr XXVII

    Energies, E1, M1, E2, M2 transition rates, oscillator strengths, and lifetimes from relativistic configuration interaction calculations are reported for the states of the 2p6, 2p53s, 2p53p, and 2p53d, configurations in all Ne-like ions between Mg III and Kr XXVII. Core-valence and core-core correlation effects are accounted for through SD-expansions to increasing sets of active orbitals. The Breit interaction and leading QED effects are included as perturbations. The results are compared with experiments and other recent benchmark calculations. In Mg III, Al IV, Si V, P VI, S VII, and Ar IX, for which experimental energies are known to high accuracy, the mean error in the calculated energies is only 0.011%. (author)

  7. Photoemission-monitored x-ray standing wave studies of molecular adsorbate surface structure

    The influence of non-dipole photoemission terms on the accuracy of photoemission-monitored NIXSW structure determinations has been studied. An experimental survey has been made of values of the incoherent dipole-quadrupole parameter as a function of energy and atomic number for the Is states of elements between carbon and chlorine inclusive. These values are compared with recent theoretical calculations. The contribution of the coherent dipole-quadrupole interference terms, whose form has been theoretically derived recently, has been experimentally measured for Is photoemission from clean Al(111). The coherent dipole-quadrupole effect is found to be small and easily corrected for, while the previously-known incoherent effect is shown to result in tolerable errors in most cases. Adsorption of methyl thiol (CH3SH) on Pt(111), followed by annealing to ∼ 220 K is believed to result in the formation of methyl thiolate (-SCH3). Two structural models are consistent with NIXSW data presented here: co-occupation of fcc and hcp sites, and a tilted atop-bonded geometry. On annealing to ∼500 K, complete dissociation occurs, and the remaining S atoms are found to lie in fcc sites, with evidence of partial occupation of a more complex phase. The adsorption of CO, NO and O on Ni(111), and the O+CO and O+NO coadsorbate systems have been investigated with NIXSW. The sites found for O, CO and NO are consistent with previous quantitative structure determinations. In the presence of a precoverage of oxygen, the conclusion of a recent photoelectron diffraction study that the preferred CO site is atop a substrate Ni atom is confirmed. In contrast, NO adsorption onto a (2 x 2)-O precovered surface is found to result in the restructuring of the oxygen layer, with NO adsorbing in the hollow sites, as in the pure-NO layer. Discrepancies in bond lengths between these NIXSW results and previous quantitative determinations are discussed. (author)

  8. Correlation effects in photoemission from adsorbates: Hydrogen on narrow-band metals

    Rubio, J.; Refolio, M. C.; López Sancho, M. P.; López Sancho, J. M.

    1988-08-01

    This paper deals with photoemission from a one-level atom adsorbed on a metal surface within the context of Anderson's Hamiltonian. The occupied part of the adsorbate density of states (DOS) is calculated by means of a many-electron approach that incorporates the following ingredients: (1) A neat separation between final-state interactions and initial (ground-state) effects. (2) The method (a Lehmann-type representation) leans heavily on the resolvent operator, R(z)=(z-H)-1, which is obtained by expressing Dyson's equation in terms of the (N-1)-electron states (configurations) that diagonalize the hopping-free part of Anderson's Hamiltonian, thereby including the atomic correlation (U) in a nonperturbative way while expanding in powers of the hopping parameter (V). (3) By using blocking methods, the matrix elements of R are grouped into equivalent 4×4 matrix blocks, with residual interactions, which are then put in correspondence with the sites of a rectangular lattice, thereby making the problem isomorphic to that of finding a noninteracting one-electron Green's function in the Wannier representation. (4) Renormalized perturbation theory, along with a series of convolution theorems due to Hugenholtz and Van Hove, allows one to develop a self-consistency equation that automatically takes into account an infinite number of configurations. The resulting DOS is compared with photoemission spectra from hydrogen adsorbed on tungsten (half-filled metal band) and nickel (almost full). Correlation effects turn out to produce peaks at the appropriate energies, so that an unusually good agreement is found despite the featureless, semielliptical DOS adopted for the metal. Only gross features of this quantity, such as width, center, and occupation of the band, seem to matter in a photoemission calculation.

  9. Plasma diagnostic potential of 2p4f in N$^+$ -- accurate wavelengths and oscillator strengths

    Shen, Xiaozhi; Jönsson, Per; Wang, Jianguo

    2015-01-01

    Radiative emission lines from nitrogen and its ions are often observed in nebulae spectra, where the N$^{2+}$ abundance can be inferred from lines of the 2p4f configuration. In addition, intensity ratios between lines of the 2p3p -- 2p3s and 2p4f -- 2p3d transition arrays can serve as temperature diagnostics. To aid abundance determinations and plasma diagnostics, wavelengths and oscillator strengths were calculated with high-precision for electric-dipole (E1) transitions from levels in the 2p4f configuration of N$^{+}$. Electron correlation and relativistic effects, including the Breit interaction, were systematically taken into account within the framework of the multiconfiguration Dirac-Hartree-Fock (MCDHF) method. Except for the 2p4f - 2p4d transitions with quite large wavelengths and the two-electron-one-photon 2p4f -2s2p$^3$ transitions, the uncertainties of the present calculations were controlled to within 3% and 5% for wavelengths and oscillator strengths, respectively. We also compared our results w...

  10. Role of ytterbium and ytterbium/cesium fluoride on the chemistry of poly(9,9-dioctylfluorene-co-benzothiadiazole) as investigated by photoemission spectroscopy

    Since ytterbium (Yb) possesses a low work function of 2.6 eV and Yb fluoride generally has a high negative free energy of formation, it is conceivable to use Yb, either directly or parasitically, with a metal fluoride, as a cathode in organic light-emitting diodes (OLEDs). In this work, the electronic structure and chemistry at the interface of Yb/poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) were investigated by ultraviolet and x-ray photoemission spectroscopy (UPS and XPS, respectively). We found that the deposition of Yb on top of F8BT foremost formed organometallic complexes with the sulfur but interacted partly with the nitrogen of F8BT, and eventually formed a Yb-C complex at higher Yb coverages. In the UPS spectra, Yb deposition increased the relative peak intensities corresponding to the σ-bonds originated from the aliphatic side chains, implying that some of the π-conjugated carbons in the polymer backbone may be destroyed. These results agree well with the disappearance of the π-to-π* transition as observed from the shake-up peaks of the carbon 1s core level in the XPS. The chemistry at the interfaces of Yb/CsF/Au and Yb/CsF/F8BT was also examined by XPS. In both cases, Cs was liberated from the CsF upon Yb deposition and the Yb reacted with the liberated F to form YbF3. In the Yb/CsF/F8BT system, the dissociated Cs did not exist in the metallic state, but reacted with the N atoms and carbon backbone in the F8BT. The low work function of Cs (2.2 eV) may further enhance the injection of electrons into the polymer layer. More importantly, the utilization of Yb/CsF as an electrode is polymer independent, and the CsF layer between the Yb and F8BT could retard Yb diffusion into the bulk polymer. The present results are supported by a calculation of the free energy needed to liberate the Cs in the metal/CsF system using a simple thermodynamic model. It is suggested that the use of Yb/CsF cathode in the polymer offers an advantage over most other

  11. An ultrafast electron microscope gun driven by two-photon photoemission from a nanotip cathode

    Bormann, Reiner; Strauch, Stefanie; Schäfer, Sascha, E-mail: schaefer@ph4.physik.uni-goettingen.de; Ropers, Claus, E-mail: cropers@gwdg.de [4th Physical Institute, Solids and Nanostructures, University of Göttingen, Göttingen 37077 (Germany)

    2015-11-07

    We experimentally and numerically investigate the performance of an advanced ultrafast electron source, based on two-photon photoemission from a tungsten needle cathode incorporated in an electron microscope gun geometry. Emission properties are characterized as a function of the electrostatic gun settings, and operating conditions leading to laser-triggered electron beams of very low emittance (below 20 nm mrad) are identified. The results highlight the excellent suitability of optically driven nano-cathodes for the further development of ultrafast transmission electron microscopy.

  12. Metal-insulator transition of naxwo3 studied by angle-resolved photoemission spectroscopy

    Raj, Satyabrata; Sato, Takafumi; Souma, Seigo; Takahashi, Takashi; Sarma, DD; Mahadevan, Priya

    2009-01-01

    The electronic structure of sodium tungsten bronzes NaxWO3 is investigated by high-resolution angle-resolved photoemission spectroscopy (ARPES). The ARPES spectra measured in both insulating and metallic phases of NaxWO3 reveals the origin of metal-insulator transition (MIT) in sodium tungsten bronze system. It is found that in insulating NaxWO3 the states near the Fermi level (E-F) are localized due to the strong disorder caused by the random distribution of Na+ ions in WO3 lattice. Due t...

  13. Gd and Sm on clean semiconductor surfaces—Resonant photoemission studies

    The paper presents photoemission studies of wide band gap semiconductors surfaces doped with gadolinium and samarium. The contribution of the Gd4f and Sm4f electrons to the electronic structure of the doped semiconductor systems (CdTe, GaN and ZnO) was evaluated based on the Fano resonance measured across the RE4d → RE4f intra-ion photoionization threshold. It was found that the RE valence and position of the RE4f shell varies significantly between the investigated semiconductor systems and depends not only on the used semiconductor matrix but also on the Fermi level position.

  14. Gd and Sm on clean semiconductor surfaces—Resonant photoemission studies

    Guziewicz, E., E-mail: guzel@ifpan.edu.pl [Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw (Poland); Orlowski, B.A.; Kowalski, B.J.; Kowalik, I.A.; Reszka, A.; Wachnicki, L.; Gieraltowska, S.; Godlewski, M. [Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw (Poland); Johnson, R.L. [Institut für Experimentalphysik, Universität Hamburg, Luruper Chausse 149, 22761 Hamburg (Germany)

    2013-10-01

    The paper presents photoemission studies of wide band gap semiconductors surfaces doped with gadolinium and samarium. The contribution of the Gd4f and Sm4f electrons to the electronic structure of the doped semiconductor systems (CdTe, GaN and ZnO) was evaluated based on the Fano resonance measured across the RE4d → RE4f intra-ion photoionization threshold. It was found that the RE valence and position of the RE4f shell varies significantly between the investigated semiconductor systems and depends not only on the used semiconductor matrix but also on the Fermi level position.

  15. Charge density waves in 1T-TaS2: an angle-resolved photoemission study

    Clerc, F. [Institut de Physique, Universite de Neuchatel, Rue A.L. Breguet 1, CH-2000 Neuchatel (Switzerland); Bovet, M. [Institut de Physique, Universite de Neuchatel, Rue A.L. Breguet 1, CH-2000 Neuchatel (Switzerland); Berger, H. [Institut de Physique Appliquee, EPFL, CH-1015 Lausanne (Switzerland); Despont, L. [Institut de Physique, Universite de Neuchatel, Rue A.L. Breguet 1, CH-2000 Neuchatel (Switzerland); Koitzsch, C. [Institut de Physique, Universite de Neuchatel, Rue A.L. Breguet 1, CH-2000 Neuchatel (Switzerland); Garnier, M.G. [Institut de Physique, Universite de Neuchatel, Rue A.L. Breguet 1, CH-2000 Neuchatel (Switzerland); Aebi, P. [Institut de Physique, Universite de Neuchatel, Rue A.L. Breguet 1, CH-2000 Neuchatel (Switzerland)]. E-mail: philipp.aebi@unine.ch

    2004-09-15

    The transition metal dichalcogenide 1T-TaS2 is a layered material exhibiting charge density waves. Based on angle-resolved photoemission experiments mapping spectral weight at the Fermi surface and density functional theory calculations we discuss possible mechanisms involved with the creation of charge density waves. At first the flat parts of the elliptically shaped Fermi surface appear to play an important role via Fermi surface nesting. A closer analysis of the charge density wave induced new Brillouin zones and the possible energy balance between elastic deformation energy and electronic energy points to a more complicated scenario.

  16. Charge density waves in 1T-TaS2: an angle-resolved photoemission study

    The transition metal dichalcogenide 1T-TaS2 is a layered material exhibiting charge density waves. Based on angle-resolved photoemission experiments mapping spectral weight at the Fermi surface and density functional theory calculations we discuss possible mechanisms involved with the creation of charge density waves. At first the flat parts of the elliptically shaped Fermi surface appear to play an important role via Fermi surface nesting. A closer analysis of the charge density wave induced new Brillouin zones and the possible energy balance between elastic deformation energy and electronic energy points to a more complicated scenario

  17. Angle-resolved photoemission study of Si electronic structure: Boron concentration dependence

    The boron concentration dependence of the Si electronic structure of Si(1 0 0)2 x 1 surfaces were investigated by angle-resolved photoemission spectroscopy (ARPES). The ARPES spectra exhibit rigid shifts toward lower binding energy as the boron concentration increases. The band dispersion was obtained from fitting procedure, and it is found that the top of the valence band does not exceed the Fermi level even with a boron concentration 35 times larger than the critical concentration of the metal-insulator transition.

  18. Vacuum ultraviolet photon detector with continuously adjustable resolution for inverse photoemission spectroscopy

    Liu, Shu-Hu; Hong, Cai-Hao; Zhao, Yi-Dong; Geng, Dong-Ping; Zheng, Lei; Zhao, Xiao-Liang; Li, Hua-Peng

    2014-01-01

    We present a vacuum ultraviolet (VUV) band-pass photon detector for inverse photoemission spectroscopy. A SrF2 window is used due to its high-energy cutoff of the optical transmission being 9.7eV, and acetone is selected as filling gas with the photoionization threshold also being 9.7eV. The structure of the detector described in detail is based on a Geiger-M\\"uller type counter with an MgF2 window and argon as amplification gas. Its energy resolution can be tuned continuously from 46meV with...

  19. Hard and soft X-ray photoemission spectroscopies of ferromagnetic Sm4As3

    We have investigated the bulk and surface electronic structures of Sm4As3 by using hard and soft X-ray photoemission spectroscopies (PESs). The valence band spectral shape changes much with photon energies (hν s) due to the variation of both photoionization cross sections and bulk sensitivity. PES with the wide range of hν s between 220 and 2450-bar eV demonstrates that the valence of the Sm ions is definitely trivalent in the bulk and divalent at the surface

  20. Laser-excited photoemission spectroscopy study of superconducting boron-doped diamond

    K. Ishizaka, R. Eguchi, S. Tsuda, T. Kiss, T. Shimojima, T. Yokoya, S. Shin, T. Togashi, S. Watanabe, C.-T. Chen, C.Q. Zhang, Y. Takano, M. Nagao, I. Sakaguchi, T. Takenouchi and H. Kawarada

    2006-01-01

    Full Text Available We have investigated the low-energy electronic state of boron-doped diamond thin film by the laser-excited photoemission spectroscopy. A clear Fermi-edge is observed for samples doped above the semiconductor–metal boundary, together with the characteristic structures at 150×n meV possibly due to the strong electron–lattice coupling effect. In addition, for the superconducting sample, we observed a shift of the leading edge below Tc indicative of a superconducting gap opening. We discuss the electron–lattice coupling and the superconductivity in doped diamond.

  1. Angle-resolved photoemission spectroscopy of band tails in lightly doped cuprates

    Alexandrov, A. S.; Reynolds, K.

    2007-01-01

    We amend ab initio strongly-correlated band structures by taking into account the band-tailing phenomenon in doped charge-transfer Mott-Hubbard insulators. We show that the photoemission from band tails accounts for sharp "quasi-particle" peaks, rapid loss of their intensities in some directions of the Brillouin zone ("Fermi-arcs") and high-energy "waterfall" anomalies as a consequence of matrix-element effects of disorder-localised states in the charge-transfer gap of doped cuprates.

  2. Whispering gallery mode photoemission from self-assembled poly-para-phenylenevinylene microspheres

    Kushida, Soh; Yamamoto, Yohei [Division of Materials Science and Tsukuba Research Center for Interdisciplinary Materials Science (TIMS), Faculty of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573 (Japan); Braam, Daniel; Lorke, Axel [Faculty of Physics and Center for Nanointegration Duisburg-Essen (CENIDE), University of Duisburg-Essen, Lotharstraße 1, Duisburg, D-47048 (Germany)

    2015-12-31

    Poly[2-methoxy-5-(3,7-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMOPPV) self-assembles to form well-defined spheres with several micrometers in diameter upon addition of a methanol vapor into a chloroform solution of MDMOPPV. The single sphere of MDMOPPV with 5.7 µm diameter exhibits whispering gallery mode (WGM) photoemission upon excitation with focused laser beam. The periodic emission lines are characterized by transverse electric and magnetic WGMs, and Q-factor reaches ∼345 at the highest.

  3. Correlation versus surface effects in photoemission of quasi-1D organic conductors

    Claessen, R.; Schwingenschlogl, U.; Sing, M.; Jacobsen, Claus Schelde; Dressel, M.

    2002-01-01

    The absence of spectral weight at the Fermi level in photoemission spectra of quasi-1D organic conductors has been interpreted as possible evidence for an unusual many-body state. We demonstrate that great care must be exercised to draw this conclusion exclusively on the basis of a pseudogap. A...... detailed surface characterization of the charge transfer salts (TMTSF)(2)PFt(6) and TTF-TCNQ shows that signatures of electronic correlations in the valence band spectra are strongly affected by surface effects and may even be completely obscured....

  4. Photoemission study of tris(8-hydroxyquinoline) aluminum/aluminum oxide/tris(8-hydroxyquinoline) aluminum interface

    The evolution of the interface electronic structure of a sandwich structure involving aluminum oxide and tris(8-hydroxyquinoline) aluminum (Alq), i.e. (Alq/AlOx/Alq), has been investigated with photoemission spectroscopy. Strong chemical reactions have been observed due to aluminum deposition onto the Alq substrate. The subsequent oxygen exposure releases some of the Alq molecules from the interaction with aluminum. Finally, the deposition of the top Alq layer leads to an asymmetry in the electronic energy level alignment with respect to the AlOx interlayer

  5. Soft X-ray synchrotron radiation photoemission study on uranium compounds

    We have carried out the angle-resolved photoemission experiments on some uranium compounds using soft X-ray synchrotron radiation. Bulk- and U 5f-sensitive band structure and Fermi surface were obtained for paramagnetic uranium compound UFeGa5. Although the agreement between the experimental band structure and the LDA calculation treating U 5f electrons as being itinerant is qualitative, the topology of the Fermi surface is well explained by the calculation, suggesting that the U 5f states can be essentially understood within the itinerant-electron model

  6. On the photoemission spectrum and optical gap in La2CuO4

    The photoemission and optical spectrum of La2CuO4 are computed for a CuO6 cluster model using the techniques of ab initio quantum chemistry. Evidence for a near degeneracy and strong electronic coupling between the configurations Cu3+O2- (1Ag) and Cu2+O1- (1Ag) is presented. This interaction leads to d8 character at the Fermi energy as well as in the 12eV satellite. 17 refs., 1 fig., 2 tabs

  7. Improvements in the contemporary photoemission spectroscopy implementation: A message to the ARPES community

    Patil, Swapnil

    2015-01-01

    In this short communication, we highlight the deficiencies within the contemporary angle resolved photoemission spectroscopy (ARPES) implementations and point out few remedies towards their resolution. These deficiencies prohibit the current version of the ARPES technique from revealing the many-body physics of solids in its entirety. It is believed that the origin of these deficiencies lie within the prevailing data acquisition methods used for registering information from the photoelectron. It is argued that a slight change in the data acquisition methods would remedy the situation.

  8. Electronic structure of Mo1-x Re x alloys studied through resonant photoemission spectroscopy.

    Sundar, Shyam; Banik, Soma; Sharath Chandra, L S; Chattopadhyay, M K; Ganguli, Tapas; Lodha, G S; Pandey, Sudhir K; Phase, D M; Roy, S B

    2016-08-10

    We studied the electronic structure of Mo-rich Mo1-x Re x alloys ([Formula: see text]) using valence band photoemission spectroscopy in the photon energy range 23-70 eV and density of states calculations. Comparison of the photoemission spectra with the density of states calculations suggests that, with respect to the Fermi level E F, the d states lie mostly in the binding energy range 0 to  -6 eV, whereas s states lie in the binding energy range  -4 to  -10 eV. We observed two resonances in the photoemission spectra of each sample, one at about 35 eV photon energy and the other at about 45 eV photon energy. Our analysis suggests that the resonance at 35 eV photon energy is related to the Mo 4p-5s transition and the resonance at 45 eV photon energy is related to the contribution from both the Mo 4p-4d transition (threshold: 42 eV) and the Re 5p-5d transition (threshold: 46 eV). In the constant initial state plot, the resonance at 35 eV incident photon energy for binding energy features in the range E F (BE  =  0) to  -5 eV becomes progressively less prominent with increasing Re concentration x and vanishes for x  >  0.2. The difference plots obtained by subtracting the valence band photoemission spectrum of Mo from that of Mo1-x Re x alloys, measured at 47 eV photon energy, reveal that the Re d-like states appear near E F when Re is alloyed with Mo. These results indicate that interband s-d interaction, which is weak in Mo, increases with increasing x and influences the nature of the superconductivity in alloys with higher x. PMID:27301550

  9. Retention Characteristics of CBTi144 Thin Films Explained by Means of X-Ray Photoemission Spectroscopy

    G. Biasotto; A.Z. Simões; C. S. Riccardi; M.A. Zaghete; E. Longo; J. A. Varela

    2010-01-01

    CaBi4Ti4O15 (CBTi144) thin films were grown on Pt/Ti/SiO2/Si substrates using a soft chemical solution and spin-coating method. Structure and morphology of the films were characterized by the X-ray Diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), Raman analysis, X-ray photoemission spectroscopy (XPS), and transmission electron microscopy (TEM). The films present a single phase of layered-structured perovskite with polar axis orient. The a/b-axis orientation of the ferroelec...

  10. Inner-shell photoemission from atoms and molecules using synchrotron radiation

    Photoelectron spectroscopy, in conjunction with synchrotron radiation, has been used to study inner-shell photoemission from atoms and molecules. The time structure of the synchrotron radiation permits the measurements of time-of-flight (TOF) spectra of Auger and photoelectrons, thereby increasing the electron collection efficiency. The double-angle TOF method yielded angle-resolved photoelectron intensities, which were used to determine photoionization cross sections and photoelectron angular distributions in several cases. Comparison to theoretical calculations has been made where possible to help explain observed phenomena in terms of the electronic structure and photoionization dynamics of the systems studied. 154 references, 23 figures, 7 tables

  11. Simple surface structure determination from Fourier transforms of angle-resolved photoemission extended fine structure

    Zheng, Y. [Pennsylvania State Univ., University Park, PA (United States)]|[Lawrence Berkeley Lab., CA (United States); Shirley, D.A. [Pennsylvania State Univ., University Park, PA (United States)

    1995-02-01

    The authors show by Fourier analyses of experimental data, with no further treatment, that the positions of all the strong peaks in Fourier transforms of angle-resolved photoemission extended fine structure (ARPEFS) from adsorbed surfaces can be explicitly predicted from a trial structure with an accuracy of about {+-} 0.3 {angstrom} based on a single-scattering cluster model together with the concept of a strong backscattering cone, and without any additional analysis. This characteristic of ARPEFS Fourier transforms can be developed as a simple method for determining the structures of adsorbed surfaces to an accuracy of about {+-} 0.1 {angstrom}.

  12. An ultrafast electron microscope gun driven by two-photon photoemission from a nanotip cathode

    We experimentally and numerically investigate the performance of an advanced ultrafast electron source, based on two-photon photoemission from a tungsten needle cathode incorporated in an electron microscope gun geometry. Emission properties are characterized as a function of the electrostatic gun settings, and operating conditions leading to laser-triggered electron beams of very low emittance (below 20 nm mrad) are identified. The results highlight the excellent suitability of optically driven nano-cathodes for the further development of ultrafast transmission electron microscopy

  13. Standing-wave excited soft x-ray photoemission microscopy: application to Co microdot magnetic arrays

    Gray, Alexander; Kronast, Florian; Papp, Christian; Yang, See-Hun; Cramm, Stefan; Krug, Ingo P.; Salmassi, Farhad; Gullikson, Eric M.; Hilken, Dawn L.; Anderson, Erik H.; Fischer, Peter; Durr, Hermann A.; Schneider, Claus M.; Fadley, Charles S.

    2010-10-29

    We demonstrate the addition of depth resolution to the usual two-dimensional images in photoelectron emission microscopy (PEEM), with application to a square array of circular magnetic Co microdots. The method is based on excitation with soft x-ray standing-waves generated by Bragg reflection from a multilayer mirror substrate. Standing wave is moved vertically through sample simply by varying the photon energy around the Bragg condition. Depth-resolved PEEM images were obtained for all of the observed elements. Photoemission intensities as functions of photon energy were compared to x-ray optical calculations in order to quantitatively derive the depth-resolved film structure of the sample.

  14. Correlation versus surface effects in photoemission of quasi-1D organic conductors

    Claessen, R.; Schwingenschlogl, U.; Sing, M.; Jacobsen, Claus Schelde; Dressel, M.

    2002-01-01

    The absence of spectral weight at the Fermi level in photoemission spectra of quasi-1D organic conductors has been interpreted as possible evidence for an unusual many-body state. We demonstrate that great care must be exercised to draw this conclusion exclusively on the basis of a pseudogap. A d...... detailed surface characterization of the charge transfer salts (TMTSF)(2)PFt(6) and TTF-TCNQ shows that signatures of electronic correlations in the valence band spectra are strongly affected by surface effects and may even be completely obscured....

  15. Angle-resolved photoemission from γ-Ce: Distinguishing band peaks from f-electron emission

    Angle-resolved photoemission spectra from single crystal γ-Ce(100) are presented and discussed. Valence-band peaks are observed for photon energies below 40 eV. These peaks disperse with electron exit angle and obey simple one-electron selection rules. For photon energies above 50 eV, two peaks, at the Fermi level and at 2-eV binding energy, dominate the spectra. These peaks do not disperse, and do not obey the one-electron selection rules. They are identified as atomiclike 4f emission

  16. High-resolution photoemission study of γ- and α-cerium

    High-resolution photoemission studies on the α and γ phases of cerium show changes in the binding energies of the two 4f-related features. The location of the two 4f-related features in the γ phase are at -0.2 and -2.0 eV, while in the α phase these features are located at the Fermi level and -2.1 eV. These results are a direct test of the theories proposed to explain the presence of the two features

  17. Angle resolved photoemission spectroscopy of Sr_2CuO_2Cl_2 - a revisit

    Duerr, C; Legner, S.; Hayn, R.; Borisenko, S. V.; Z. Hu; Theresiak, A.; Knupfer, M.; Golden, M. S.; Fink, J.; Ronning, F.; Shen, Z.-X.; Eisaki, H.; Uchida, S.; Janowitz, C.; Mueller, R.

    2000-01-01

    We have investigated the lowest binding-energy electronic structure of the model cuprate Sr_2CuO_2Cl_2 using angle resolved photoemission spectroscopy (ARPES). Our data from about 80 cleavages of Sr_2CuO_2Cl_2 single crystals give a comprehensive, self-consistent picture of the nature of the first electron-removal state in this model undoped CuO_2-plane cuprate. Firstly, we show a strong dependence on the polarization of the excitation light which is understandable in the context of the matri...

  18. Electronic structure of Mo1‑x Re x alloys studied through resonant photoemission spectroscopy

    Sundar, Shyam; Banik, Soma; Sharath Chandra, L. S.; Chattopadhyay, M. K.; Ganguli, Tapas; Lodha, G. S.; Pandey, Sudhir K.; Phase, D. M.; Roy, S. B.

    2016-08-01

    We studied the electronic structure of Mo-rich Mo1‑x Re x alloys (0≤slant x≤slant 0.4 ) using valence band photoemission spectroscopy in the photon energy range 23–70 eV and density of states calculations. Comparison of the photoemission spectra with the density of states calculations suggests that, with respect to the Fermi level E F, the d states lie mostly in the binding energy range 0 to  ‑6 eV, whereas s states lie in the binding energy range  ‑4 to  ‑10 eV. We observed two resonances in the photoemission spectra of each sample, one at about 35 eV photon energy and the other at about 45 eV photon energy. Our analysis suggests that the resonance at 35 eV photon energy is related to the Mo 4p–5s transition and the resonance at 45 eV photon energy is related to the contribution from both the Mo 4p–4d transition (threshold: 42 eV) and the Re 5p–5d transition (threshold: 46 eV). In the constant initial state plot, the resonance at 35 eV incident photon energy for binding energy features in the range E F (BE  =  0) to  ‑5 eV becomes progressively less prominent with increasing Re concentration x and vanishes for x  >  0.2. The difference plots obtained by subtracting the valence band photoemission spectrum of Mo from that of Mo1‑x Re x alloys, measured at 47 eV photon energy, reveal that the Re d-like states appear near E F when Re is alloyed with Mo. These results indicate that interband s–d interaction, which is weak in Mo, increases with increasing x and influences the nature of the superconductivity in alloys with higher x.

  19. Study of III-V semiconductor band structure by synchrotron photoemission

    Angle-resolved synchrotron photoemission studies of six III-V semiconductors have been carried out. For emission normal to the (110) plane of these materials, peaks in the experimental spectra were identified with the bands involved in the transitions, and the critical point energies X3, X5, and Σ1/sup min/, were determined. The data indicate that k perpendicular is conserved in the transitions. Comparison of the data with theoretical bands permits an evaluation of k perpendicular associated with the experimentally observed transition, and from this information the bands were plotted out

  20. An extremal problem on potentially $K_{p_{1},p_{2},...,p_{t}}$-graphic sequences

    Lai, Chunhui

    2004-01-01

    A sequence $S$ is potentially $K_{p_{1},p_{2},...,p_{t}}$ graphical if it has a realization containing a $K_{p_{1},p_{2},...,p_{t}}$ as a subgraph, where $K_{p_{1},p_{2},...,p_{t}}$ is a complete t-partite graph with partition sizes $p_{1},p_{2},...,p_{t} (p_{1}\\geq p_{2}\\geq ...\\geq p_{t} \\geq 1)$. Let $\\sigma(K_{p_{1},p_{2},...,p_{t}}, n)$ denote the smallest degree sum such that every $n$-term graphical sequence $S$ with $\\sigma(S)\\geq \\sigma(K_{p_{1},p_{2},...,p_{t}}, n)$ is potentially $...

  1. Research of using mobile agents for information discovery in P2P networks

    The technology of P2P is a new network-computing model that has great value of commerce and technology. After analyzing the current information discovery technology in P2P network, a new solution that is based on mobile agent is proposed. The mobile agent solution can reduce the need of bandwidth, be adapt to the dynamic of P2P network, and be asynchronous and be very fault tolerant. (authors)

  2. Analysis and Design of Instant Message System Based on P2P

    Shen Zhiwei; Ma Shaowu

    2008-01-01

    By analyzing current development conditions of mainstream Instant Message technologies and services, some detailed discussion about technical solution and formal operation deployment strategies of P2P Instant Message Services based on Interact is made. Several crucial problems of P2P Instant Message System about services management, interconnection with other instant message, security and profit-making mode are analyzed,, and how to develop P2P IM Services is proposed.

  3. IPTV-RM: A Resources Monitoring Architecture for P2P IPTV Systems

    Wenxian Wang; Xingshu Chen; Haizhou Wang

    2012-01-01

    Resources monitoring is an important problem of the overall efficient usage and control of P2P IPTV systems. The resources of IPTV can include all distributing servers, programs and peers. Several researches have tried to address this issue, but most of them illuminated P2P traffic characterization, identification and user behavior. The main contributions of this paper are twofold. Firstly, a resources monitoring architecture for P2P IPTV systems, IPTV-RM, was presented based on previous work...

  4. Convergence of Internet and TV: The Commercial Viability of P2P Content Delivery

    De Boever, Jorn

    2009-01-01

    The popularity of (illegal) P2P (peer-to-peer) file sharing has a disruptive impact on Internet traffic and business models of content providers. In addition, several studies have found an increasing demand for bandwidth consuming content, such as video, on the Internet. Although P2P systems have been put forward as a scalable and inexpensive model to deliver such content, there has been relatively little economic analysis of the potentials and obstacles of P2P systems as a ...

  5. In vitro phosphorylation and acetylation of the murine pocket protein Rb2/p130.

    Muhammad Saeed

    Full Text Available The retinoblastoma protein (pRb and the related proteins Rb2/p130 and 107 represent the "pocket protein" family of cell cycle regulators. A key function of these proteins is the cell cycle dependent modulation of E2F-regulated genes. The biological activity of these proteins is controlled by acetylation and phosphorylation in a cell cycle dependent manner. In this study we attempted to investigate the interdependence of acetylation and phosphorylation of Rb2/p130 in vitro. After having identified the acetyltransferase p300 among several acetyltransferases to be associated with Rb2/p130 during S-phase in NIH3T3 cells in vivo, we used this enzyme and the CDK4 protein kinase for in vitro modification of a variety of full length Rb2/p130 and truncated versions with mutations in the acetylatable lysine residues 1079, 128 and 130. Mutation of these residues results in the complete loss of Rb2/p130 acetylation. Replacement of lysines by arginines strongly inhibits phosphorylation of Rb2/p130 by CDK4; the inhibitory effect of replacement by glutamines is less pronounced. Preacetylation of Rb2/p130 strongly enhances CDK4-catalyzed phosphorylation, whereas deacetylation completely abolishes in vitro phosphorylation. In contrast, phosphorylation completely inhibits acetylation of Rb2/p130 by p300. These results suggest a mutual interdependence of modifications in a way that acetylation primes Rb2/p130 for phosphorylation and only dephosphorylated Rb2/p130 can be subject to acetylation. Human papillomavirus 16-E7 protein, which increases acetylation of Rb2/p130 by p300 strongly reduces phosphorylation of this protein by CDK4. This suggests that the balance between phosphorylation and acetylation of Rb2/p130 is essential for its biological function in cell cycle control.

  6. Building Database Coordination in p2p Systems Using Eca Rules

    Roshelova, Albena

    2004-01-01

    Recently, data integration systems and peer database management systems that attempt to model and integrate data in a peer-to-peer (p2p) environment have attracted the attention of researchers. Such systems give opportunities to the local relational database management system to exchange data with other nodes in a p2p environment. The databases systems in p2p are completely autonomous, heterogeneous and independent, each maintaining its own data. We would like to use these databases to answer...

  7. Implementing a Secure Key Issuing Scheme for Communication in P2P Networks

    Mohammed Azharuddin; Annapurna P Patil

    2012-01-01

    Key issuing scheme focuses on the confidentiality maintained in using the secret key for communicationin p2p networks. Identity based cryptography (IBC) was introduced into peer-to-peer (P2P) networks recently for identity verification and authentication purposes. However, current IBC-based solutions were not addressing the problem of secure private key issuing. In this paper we propose a novel secure key issuing scheme for P2P networks using IBC. We present an IBC infrastructure setup phase...

  8. Angle-resolved photoemission spectroscopy of the insulating NaxWO3: Anderson localization, polaron formation, and remnant Fermi surface.

    Raj, S; Hashimoto, D; Matsui, H; Souma, S; Sato, T; Takahashi, T; Sarma, D D; Mahadevan, Priya; Oishi, S

    2006-04-14

    The electronic structure of the insulating sodium tungsten bronze, Na(0.025)WO(3), is investigated by high-resolution angle-resolved photoemission spectroscopy. We find that near-E(F) states are localized due to the strong disorder arising from random distribution of Na+ ions in the WO(3) lattice, which makes the system insulating. The temperature dependence of photoemission spectra provides direct evidence for polaron formation. The remnant Fermi surface of the insulator is found to be the replica of the real Fermi surface in the metallic system. PMID:16712121

  9. Photon absorption and photocurrent in solar cells below semiconductor bandgap due to electron photoemission from plasmonic nanoantennas

    Novitsky, Andrey; Uskov, Alexander; Gritti, Claudia; Protsenko, I. E.; Kardynal, Beata; Lavrinenko, Andrei

    2014-01-01

    continuous metal films. Optimally designed metal nanoparticles can provide an effectivemechanismfor the photon absorption in the infrared range below the semiconductor bandgap, resulting in the generation of a photocurrent in addition to the photocurrent from band-to-band absorption in a semiconductor. Such......We model the electron photoemission frommetal nanoparticles into a semiconductor in a Schottky diode with a conductive oxide electrode hosting the nanoparticles. We show that plasmonic effects in the nanoparticles lead to a substantial enhancement in photoemission compared with devices with...

  10. An Optimized and Improved Network Trust Model Based on P2P

    Li Wei

    2013-10-01

    Full Text Available Because of the spring up of the P2P network application, its open, anonymous and self-organized characteristics has offered a path for the spreading of virus and junk data, and the security has aroused people’s common concern. The traditional network trust model dealt with dishonest node has certain limitation, for this, improved P2P network trust model and applied D-S evidence theory to the trusted computing of trust model. Through simulation experiment, the result showed: the improved P2P network trust model efficiently increased the successful trading rate of P2P network and improved the network environment

  11. Suppression of Zeeman Relaxation in Cold Collisions of \\(^2P_{1/2}\\) Atoms

    Tscherbul, T.V.; Buchachenko, A. A.; Dalgarno, Alexander; Lu, M.-J.; Weinstein, J. D.

    2009-01-01

    We present a combined experimental and theoretical study of angular momentum depolarization in cold collisions of \\(^2P\\) atoms in the presence of an external magnetic field. We show that collision-induced Zeeman relaxation of Ga\\(^2P_{1/2}\\) and In \\(^2P_{1/2}\\) atoms in cold \\(^4\\)He gas is dramatically suppressed compared to atoms in \\(^2P_{3/2}\\) states. Using rigorous quantum-scattering calculations based on ab initio interaction potentials, we demonstrate that Zeeman transitions in coll...

  12. Sla2p Is Associated with the Yeast Cortical Actin Cytoskeleton via Redundant Localization Signals

    Yang, Shirley; Cope, M. Jamie T.V.; Drubin, David G.

    1999-01-01

    Sla2p, also known as End4p and Mop2p, is the founding member of a widely conserved family of actin-binding proteins, a distinguishing feature of which is a C-terminal region homologous to the C terminus of talin. These proteins may function in actin cytoskeleton-mediated plasma membrane remodeling. A human homologue of Sla2p binds to huntingtin, the protein whose mutation results in Huntington’s disease. Here we establish by immunolocalization that Sla2p is a component of the yeast cortical a...

  13. What Happened to P2P Systems? A Special Focus on Content Distribution Systems

    Mohammad Fawzi, Ali

    2008-01-01

    Peer-to-Peer (P2P) technology has emerged as a new distributed computing paradigm. P2P technology attempts to "harness the powers of the edges of the Internet" by making efficient and effective use of peers (users) at the "edge" of the Internet, by direct interaction between peers of the system. P2P architecture has witnessed lots of interest and research in the latest years because of the popularity of file-sharing applications based on it. Content distribution is an essential P2P applicati...

  14. Time of flight-photoemission electron microscope for ultrahigh spatiotemporal probing of nanoplasmonic optical fields

    Nanoplasmonic excitations as generated by few-cycle laser pulses on metal nanostructures undergo ultrafast dynamics with timescales as short as a few hundred attoseconds (1 as = 10-18 s). So far, the spatiotemporal dynamics of optical fields localized on the nanoscale (nanoplasmonic field) have been hidden from direct access in the real space and time domain. An approach which combines photoelectron emission microscopy and attosecond streaking spectroscopy and which provides direct and non-invasive access to the nanoplasmonic field with nanometer-scale spatial resolution and temporal resolution of the order of 100 as has been proposed (Stockman et al 2007 Nat. Photon. 1 539). To implement this approach, a time of flight-photoemission electron microscope (TOF-PEEM) with ∼25 nm spatial and ∼50 meV energy resolution, which has the potential to detect a nanoplasmonic field with nanometer spatial and attosecond temporal resolution, has been developed and characterized using a 400 nm/60 ps pulsed diode laser. The first experimental results obtained using this newly developed TOF-PEEM in a two-photon photoemission mode with a polycrystalline Cu sample and an Ag microstructure film show that the yield and the kinetic energy of the emitted photoelectrons are strongly affected by the nanolocalized plasmonic field.

  15. Invited Article: High resolution angle resolved photoemission with tabletop 11 eV laser

    He, Yu; Vishik, Inna M.; Yi, Ming; Yang, Shuolong; Lee, James J.; Chen, Sudi; Rebec, Slavko N.; Leuenberger, Dominik; Shen, Zhi-Xun [SIMES, SLAC National Accelerator Laboratory, Menlo Park, California 94025 (United States); Department of Applied Physics, Stanford University, Stanford, California 94305 (United States); Liu, Zhongkai [SIMES, SLAC National Accelerator Laboratory, Menlo Park, California 94025 (United States); Department of Physics, Stanford University, Stanford, California 94305 (United States); Zong, Alfred [Department of Physics, Stanford University, Stanford, California 94305 (United States); Jefferson, C. Michael; Merriam, Andrew J. [Lumeras LLC, 207 McPherson St, Santa Cruz, California 95060 (United States); Moore, Robert G.; Kirchmann, Patrick S. [SIMES, SLAC National Accelerator Laboratory, Menlo Park, California 94025 (United States)

    2016-01-15

    We developed a table-top vacuum ultraviolet (VUV) laser with 113.778 nm wavelength (10.897 eV) and demonstrated its viability as a photon source for high resolution angle-resolved photoemission spectroscopy (ARPES). This sub-nanosecond pulsed VUV laser operates at a repetition rate of 10 MHz, provides a flux of 2 × 10{sup 12} photons/s, and enables photoemission with energy and momentum resolutions better than 2 meV and 0.012 Å{sup −1}, respectively. Space-charge induced energy shifts and spectral broadenings can be reduced below 2 meV. The setup reaches electron momenta up to 1.2 Å{sup −1}, granting full access to the first Brillouin zone of most materials. Control over the linear polarization, repetition rate, and photon flux of the VUV source facilitates ARPES investigations of a broad range of quantum materials, bridging the application gap between contemporary low energy laser-based ARPES and synchrotron-based ARPES. We describe the principles and operational characteristics of this source and showcase its performance for rare earth metal tritellurides, high temperature cuprate superconductors, and iron-based superconductors.

  16. Exploring three-dimensional orbital imaging with energy-dependent photoemission tomography

    Weiß, S.; Lüftner, D.; Ules, T.; Reinisch, E. M.; Kaser, H.; Gottwald, A.; Richter, M.; Soubatch, S.; Koller, G.; Ramsey, M. G.; Tautz, F. S.; Puschnig, P.

    2015-10-01

    Recently, it has been shown that experimental data from angle-resolved photoemission spectroscopy on oriented molecular films can be utilized to retrieve real-space images of molecular orbitals in two dimensions. Here, we extend this orbital tomography technique by performing photoemission initial state scans as a function of photon energy on the example of the brickwall monolayer of 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) on Ag(110). The overall dependence of the photocurrent on the photon energy can be well accounted for by assuming a plane wave for the final state. However, the experimental data, both for the highest occupied and the lowest unoccupied molecular orbital of PTCDA, exhibits an additional modulation attributed to final state scattering effects. Nevertheless, as these effects beyond a plane wave final state are comparably small, we are able, with extrapolations beyond the attainable photon energy range, to reconstruct three-dimensional images for both orbitals in agreement with calculations for the adsorbed molecule.

  17. Invited Article: High resolution angle resolved photoemission with tabletop 11 eV laser

    We developed a table-top vacuum ultraviolet (VUV) laser with 113.778 nm wavelength (10.897 eV) and demonstrated its viability as a photon source for high resolution angle-resolved photoemission spectroscopy (ARPES). This sub-nanosecond pulsed VUV laser operates at a repetition rate of 10 MHz, provides a flux of 2 × 1012 photons/s, and enables photoemission with energy and momentum resolutions better than 2 meV and 0.012 Å−1, respectively. Space-charge induced energy shifts and spectral broadenings can be reduced below 2 meV. The setup reaches electron momenta up to 1.2 Å−1, granting full access to the first Brillouin zone of most materials. Control over the linear polarization, repetition rate, and photon flux of the VUV source facilitates ARPES investigations of a broad range of quantum materials, bridging the application gap between contemporary low energy laser-based ARPES and synchrotron-based ARPES. We describe the principles and operational characteristics of this source and showcase its performance for rare earth metal tritellurides, high temperature cuprate superconductors, and iron-based superconductors

  18. On the angular dependence of the photoemission time delay in helium

    Ivanov, I A; Lindroth, E; Kheifets, A S

    2016-01-01

    We investigate an angular dependence of the photoemission time delay in helium as measured by the RABBITT (Reconstruction of Attosecond Beating By Interference of Two-photon Transitions) technique. The measured time delay $ \\tau_a=\\tau_W+\\tau_{cc} $ contains two distinct components: the Wigner time delay $\\tau_W$ and the continuum-continuum CC) correction $\\tau_{cc}$. In the case of helium with only one $1s\\to Ep$ photoemission channel, the Wigner time delay $\\tau_W$ does not depend on the photoelectron detection angle relative to the polarization vector. However, the CC correction $\\tau_{cc}$ shows a noticeable angular dependence. We illustrate these findings by performing two sets of calculations. In the first set, we solve the time-dependent Schr\\"odinger equation for the helium atom ionized by an attosecond pulse train and probed by an IR pulse. In the second approach, we employ the lowest order perturbation theory which describes absorption of the XUV and IR photons. Both calculations produce close resul...

  19. Ultrahigh-spatial-resolution chemical and magnetic imaging by laser-based photoemission electron microscopy

    We report the first experiments carried out on a new chemical and magnetic imaging system, which combines the high spatial resolution of a photoemission electron microscope (PEEM) with a continuous-wave deep-ultraviolet laser. Threshold photoemission is sensitive to the chemical and magnetic structures of the surface of materials. The spatial resolution of PEEM is limited by space charging when using pulsed photon sources as well as aberrations in the electron optics. We show that the use of a continuous-wave laser enabled us to overcome such a limit by suppressing the space-charge effect, allowing us to obtain a resolution of approximately 2.6 nm. With this system, we demonstrated the imaging of surface reconstruction domains on Si(001) by linear dichroism with normal incidence of the laser beam. We also succeeded in magnetic imaging of thin films with the use of magnetic circular dichroism near the Fermi level. The unique features of the ultraviolet laser will give us fast switching of the incident angles and polarizations of the photon source, which will be useful for the characterization of antiferromagnetic materials as well as ferromagnetic materials

  20. Vacuum ultraviolet photon detector with continuously adjustable resolution for inverse photoemission spectroscopy

    Liu, Shu-Hu; Zhao, Yi-Dong; Geng, Dong-Ping; Zhen, Lei; Zhao, Xiao-Liang; Li, Hua-Peng

    2014-01-01

    We present a vacuum ultraviolet (VUV) band-pass photon detector for inverse photoemission spectroscopy. A SrF2 window is used due to its high-energy cutoff of the optical transmission being 9.7eV, and acetone is selected as filling gas with the photoionization threshold also being 9.7eV. The structure of the detector described in detail is based on a Geiger-M\\"uller type counter with an MgF2 window and argon as amplification gas. Its energy resolution can be tuned continuously from 46meV with a normal temperature situation to 105meV at 215K. Meanwhile, the signal intensity of the detector is adjusted accordingly to find an optimal operation program for our inverse photoemission system which is being constructed. The ratio of acetone vapor and argon is varied carefully. Background signals and the response of time are analyzed. The detector is normalized by deuterium lamp in combination with a grating monochromator.

  1. High Resolution Angle Resolved Photoemission with Tabletop 11eV Laser

    He, Yu; Yi, Ming; Yang, Shuolong; Liu, Zhongkai; Lee, James; Chen, Sudi; Rebec, Slavko; Leuenberger, Dominik; Zong, Alfred; Jefferson, Michael; Moore, Robert; Kirchmann, Patrick; Merriam, Andrew; Shen, Zhixun

    2015-01-01

    We developed a table-top vacuum ultraviolet (VUV) laser with $113.778$nm wavelength (10.897eV) and demonstrated its viability as a photon source for high resolution angle-resolved photoemission spectroscopy (ARPES). This sub-nanosecond pulsed VUV laser operates at a repetition rate of 10MHz, provides a flux of 2$\\times$10$^{12}$ photons/second, and enables photoemission with energy and momentum resolutions better than 2meV and 0.012\\AA$^{-1}$, respectively. Space-charge induced energy shifts and spectral broadenings can be reduced below 2meV. The setup reaches electron momenta up to 1.2\\AA$^{-1}$, granting full access to the first Brillouin zone of most materials. Control over the linear polarization, repetition rate, and photon flux of the VUV source facilitates ARPES investigations of a broad range of quantum materials, bridging the application gap between contemporary low energy laser-based ARPES and synchrotron-based ARPES. We describe the principles and operational characteristics of this source, and sho...

  2. Molecular Frame Photoemission: Probe of the Photoionization Dynamics for Molecules in the Gas Phase

    D. Dowek; Y. J. Picard; P. Billaud; C. Elkharrat; J. C. Houver

    2009-01-01

    Molecular frame photoemission is a very sensitive probe of the photoionization (PI) dynamics of molecules. This paper reports a comparative study of non-resonant and resonant photoionization of D2 induced by VUV circularly polarized synchrotron radiation at SOLEIL at the level of the molecular frame photoelectron angular distributions (MFPADs). We use the vector correlation method which combines imaging and time-of-flight resolved electron-ion coincidence techniques, and a generalized formalism for the expression of the I(X, θe,φe)MFPADs.where X is the orientation of the molecular axis with respect to the light quantization axis and (θe,φe) the electron emission direction in the molecular frame. Selected MFPADs for a molecule aligned parallel or perpendicular to linearly polarized light, or perpendicular to the propagation axis of circularly polarizcd light, are presented for dissociative photoionization (DPI) of D2 at two photon excitation energies, hv=19 eV, where direct PI is the only channel opened, and hv=32.5 eV, i.e. in the region involving resonant excitation of Q1 and Q2 doubly excited state series. We discuss in particular the properties of the circular dichroism characterizing photoemission in the molecular frame for direct and resonant PI. In the latter case, a remarkable behavior is observed which may be attributed to the interference occurring between undistinguishable autoionization decay channels.

  3. Invited Article: High resolution angle resolved photoemission with tabletop 11 eV laser.

    He, Yu; Vishik, Inna M; Yi, Ming; Yang, Shuolong; Liu, Zhongkai; Lee, James J; Chen, Sudi; Rebec, Slavko N; Leuenberger, Dominik; Zong, Alfred; Jefferson, C Michael; Moore, Robert G; Kirchmann, Patrick S; Merriam, Andrew J; Shen, Zhi-Xun

    2016-01-01

    We developed a table-top vacuum ultraviolet (VUV) laser with 113.778 nm wavelength (10.897 eV) and demonstrated its viability as a photon source for high resolution angle-resolved photoemission spectroscopy (ARPES). This sub-nanosecond pulsed VUV laser operates at a repetition rate of 10 MHz, provides a flux of 2 × 10(12) photons/s, and enables photoemission with energy and momentum resolutions better than 2 meV and 0.012 Å(-1), respectively. Space-charge induced energy shifts and spectral broadenings can be reduced below 2 meV. The setup reaches electron momenta up to 1.2 Å(-1), granting full access to the first Brillouin zone of most materials. Control over the linear polarization, repetition rate, and photon flux of the VUV source facilitates ARPES investigations of a broad range of quantum materials, bridging the application gap between contemporary low energy laser-based ARPES and synchrotron-based ARPES. We describe the principles and operational characteristics of this source and showcase its performance for rare earth metal tritellurides, high temperature cuprate superconductors, and iron-based superconductors. PMID:26827301

  4. A photoemission model for low work function coated metal surfaces and its experimental validation

    Jensen, Kevin L.; Feldman, Donald W.; Moody, Nathan A.; O'Shea, Patrick G.

    2006-06-01

    Photocathodes are a critical component many linear accelerator based light sources. The development of a custom-engineered photocathode based on low work function coatings requires an experimentally validated photoemission model that accounts the complexity of the emission process. We have developed a time-dependent model accounting for the effects of laser heating and thermal propagation on photoemission. It accounts for surface conditions (coating, field enhancement, and reflectivity), laser parameters (duration, intensity, and wavelength), and material characteristics (reflectivity, laser penetration depth, and scattering rates) to predict current distribution and quantum efficiency (QE) as a function of wavelength. The model is validated by (i) experimental measurements of the QE of cesiated surfaces, (ii) the QE and performance of commercial dispenser cathodes (B, M, and scandate), and (iii) comparison to QE values reported in the literature for bare metals and B-type dispenser cathodes, all for various wavelengths. Of particular note is that the highest QE for a commercial (M-type) dispenser cathode found here was measured to be 0.22% at 266 nm, and is projected to be 3.5 times larger for a 5 ps pulse delivering 0.6 mJ/cm2 under a 50 MV/m field.

  5. Solar energy conversion via hot electron internal photoemission in metallic nanostructures: Efficiency estimates

    Collection of hot electrons generated by the efficient absorption of light in metallic nanostructures, in contact with semiconductor substrates can provide a basis for the construction of solar energy-conversion devices. Herein, we evaluate theoretically the energy-conversion efficiency of systems that rely on internal photoemission processes at metal-semiconductor Schottky-barrier diodes. In this theory, the current-voltage characteristics are given by the internal photoemission yield as well as by the thermionic dark current over a varied-energy barrier height. The Fowler model, in all cases, predicts solar energy-conversion efficiencies of <1% for such systems. However, relaxation of the assumptions regarding constraints on the escape cone and momentum conservation at the interface yields solar energy-conversion efficiencies as high as 1%–10%, under some assumed (albeit optimistic) operating conditions. Under these conditions, the energy-conversion efficiency is mainly limited by the thermionic dark current, the distribution of hot electron energies, and hot-electron momentum considerations

  6. Solar energy conversion via hot electron internal photoemission in metallic nanostructures: Efficiency estimates

    Leenheer, Andrew J.; Narang, Prineha; Atwater, Harry A., E-mail: haa@caltech.edu [Thomas J. Watson Laboratories of Applied Physics, California Institute of Technology, Pasadena, California 91125 (United States); Joint Center for Artificial Photosynthesis, Pasadena, California 91125 (United States); Lewis, Nathan S. [Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125 (United States); Joint Center for Artificial Photosynthesis, Pasadena, California 91125 (United States)

    2014-04-07

    Collection of hot electrons generated by the efficient absorption of light in metallic nanostructures, in contact with semiconductor substrates can provide a basis for the construction of solar energy-conversion devices. Herein, we evaluate theoretically the energy-conversion efficiency of systems that rely on internal photoemission processes at metal-semiconductor Schottky-barrier diodes. In this theory, the current-voltage characteristics are given by the internal photoemission yield as well as by the thermionic dark current over a varied-energy barrier height. The Fowler model, in all cases, predicts solar energy-conversion efficiencies of <1% for such systems. However, relaxation of the assumptions regarding constraints on the escape cone and momentum conservation at the interface yields solar energy-conversion efficiencies as high as 1%–10%, under some assumed (albeit optimistic) operating conditions. Under these conditions, the energy-conversion efficiency is mainly limited by the thermionic dark current, the distribution of hot electron energies, and hot-electron momentum considerations.

  7. Invited Article: High resolution angle resolved photoemission with tabletop 11 eV laser

    He, Yu; Vishik, Inna M.; Yi, Ming; Yang, Shuolong; Liu, Zhongkai; Lee, James J.; Chen, Sudi; Rebec, Slavko N.; Leuenberger, Dominik; Zong, Alfred; Jefferson, C. Michael; Moore, Robert G.; Kirchmann, Patrick S.; Merriam, Andrew J.; Shen, Zhi-Xun

    2016-01-01

    We developed a table-top vacuum ultraviolet (VUV) laser with 113.778 nm wavelength (10.897 eV) and demonstrated its viability as a photon source for high resolution angle-resolved photoemission spectroscopy (ARPES). This sub-nanosecond pulsed VUV laser operates at a repetition rate of 10 MHz, provides a flux of 2 × 1012 photons/s, and enables photoemission with energy and momentum resolutions better than 2 meV and 0.012 Å-1, respectively. Space-charge induced energy shifts and spectral broadenings can be reduced below 2 meV. The setup reaches electron momenta up to 1.2 Å-1, granting full access to the first Brillouin zone of most materials. Control over the linear polarization, repetition rate, and photon flux of the VUV source facilitates ARPES investigations of a broad range of quantum materials, bridging the application gap between contemporary low energy laser-based ARPES and synchrotron-based ARPES. We describe the principles and operational characteristics of this source and showcase its performance for rare earth metal tritellurides, high temperature cuprate superconductors, and iron-based superconductors.

  8. TCLM-P2P: Task Collaboration Logic Model Oriented to P2P Community%TCLM-P2P:面向P2P社区的任务协作逻辑模型

    王杨; 王汝传; 严远亭; 韩志杰; 赵保华

    2012-01-01

    P2P网络中广泛存在的“free riding”现象使其在任务协作领域的应用受到了极大制约.为了实现P2P网络环境下的有效任务协作,提出了一种具有激励机制的任务协作逻辑模型.基于Agent理论,首先给出了对等体、半对等体、P2P社区等概念;然后在合同网的框架下提出了面向P2P网络社区的任务协作逻辑模型TCLM-P2P(task collaborative logic model oriented to P2P community).相对于传统的任务协作模型,在合理的前提假设条件下,模型给出了模型公理和协作规则.该模型通过基于虚拟积分的协作算法实现了具有激励机制的P2P网络中的任务分配与协作.原型系统的实现及仿真实验结果表明TCLM-P2P模型具有可行性和有效性:不仅能够激励自利节点主动参与到任务分配与协作中;同时也能在一定程度上抑制节点的free riding行为,从而保障了P2P系统的有序工作.%Traditional P2P networks mainly are applied to file sharing and instant message fields. However, how to perform the task collaboration based on P2P community is a challenging job. The former research work indicated that the task collaboration in P2P network had been greatly restricted by free riding behaviors. To realize effective task allocating and task collaborating in P2P network environment, this paper presents a task collaboration logic model oriented to P2P community. Based on agent and multi-agent theory, the paper firstly introduces some concepts including the peer body, half-peer body and P2P community; then the TCLM-P2P is presented including some collaboration axioms and rulers. In order to enhance the incentive mechanism, virtual score becomes the main goal which each peer endeavor pursues. In addition, based on the contract net protocol, a task collaboration algorithm is presented. The proposed algorithm is composed of two phases. One is the task collaboration and the other is the task second bid when some peers fail

  9. X-ray photoemission study of MgB{sub 2} films synthesized from in-situ annealed MgB{sub 2}/Mg multilayers

    Santoni, A.; Vetrella, U.B.; Celentano, G.; Gambardella, U.; Mancini, A. [ENEA C.R. Frascati, Frascati (Italy)

    2007-03-15

    Superconducting MgB{sub 2} films were obtained by in-situ annealing of precursor multilayers deposited at low substrate temperature by sputtering from a MgB{sub 2} stoichiometric target and by thermal evaporation of pure Mg. After an in-situ annealing at 500-600 C, the films showed a zero resistance critical temperature up to 31 K. The as-obtained MgB{sub 2} films were investigated by X-ray photoelectron spectroscopy (XPS) and X-ray Auger electron spectroscopy (XAES). The electronic structure was studied by monitoring the B 1s, Mg 2p, O 1s core-levels and the Mg KL{sub 2}L{sub 3} Auger line. For comparison, the electronic structure of an MgB{sub 2} commercial superconducting sputtering target, of a not-annealed precursor film and of a sample obtained by direct sputtering from the MgB{sub 2} target have also been investigated. Electron spectroscopy showed that in the superconducting systems the Mg KL{sub 2}L{sub 3} Auger line kinetic energy position is always higher by about 0.9 eV with respect to the energy position of the same Auger line measured in the non-superconducting samples. (orig.)

  10. X-ray photoemission study of MgB2 films synthesized from in-situ annealed MgB2/Mg multilayers

    Superconducting MgB2 films were obtained by in-situ annealing of precursor multilayers deposited at low substrate temperature by sputtering from a MgB2 stoichiometric target and by thermal evaporation of pure Mg. After an in-situ annealing at 500-600 C, the films showed a zero resistance critical temperature up to 31 K. The as-obtained MgB2 films were investigated by X-ray photoelectron spectroscopy (XPS) and X-ray Auger electron spectroscopy (XAES). The electronic structure was studied by monitoring the B 1s, Mg 2p, O 1s core-levels and the Mg KL2L3 Auger line. For comparison, the electronic structure of an MgB2 commercial superconducting sputtering target, of a not-annealed precursor film and of a sample obtained by direct sputtering from the MgB2 target have also been investigated. Electron spectroscopy showed that in the superconducting systems the Mg KL2L3 Auger line kinetic energy position is always higher by about 0.9 eV with respect to the energy position of the same Auger line measured in the non-superconducting samples. (orig.)

  11. Deactivation of Ni2P/SiO2 catalyst in hydrodechlorination of chlorobenzene

    Highlights: • Ni2P/SiO2 has higher performance than Ni/SiO2 for hydrodechlorination. • Ni2P has higher resistance to HCl poison and to sintering than Ni. • Ni2P/SiO2 deactivation is mainly attributed to carbonaceous deposit. • Ni/SiO2 deactivation is mostly due to HCl poison and Ni sintering. - Abstract: The deactivation of the Ni2P/SiO2 catalyst in the hydrodechlorination of chlorobenzene was studied. To better illuminate the reasons for the deactivation, the effect of HCl on the structure and activity of Ni2P/SiO2 was investigated. For comparison, the deactivation of the Ni/SiO2 catalyst was also involved. It was found that the Ni2P particles possessed good resistance to HCl poison and to sintering, which is ascribed to the electron-deficiency of Niδ+(0 < δ < 1) site in Ni2P. Acted as the Lewis and Brönsted acid site, the Niδ+ site and the P-OH group on Ni2P/SiO2 catalyzed the formation of the carbonaceous deposit that was difficultly eliminated by hydrogenation. The carbonaceous deposit covered the active sites and might also induce a decrease in the Ni2P crystallinity, subsequently leading to the Ni2P/SiO2 deactivation. Different from Ni2P/SiO2, Ni/SiO2 was mainly deactivated by the chlorine poison and the sintering of nickel crystallites

  12. Institute of Information Network Technology%P2P-SIP融合及P2P-SIP系统设计

    吴亮

    2010-01-01

    随着现代通信技术的不断发展,P2P(对等网络)技术与SIP(会话初始化协议)之间相互融合成为当前研究的一个热点.文章首先介绍了P2P技术和SIP协议,随后研究怎样将P2P架构与SIP系统进行融合,重点讨论了P2P-SIP的实现过程,包括P2P-SIP终端如何使用SIP协议携带P2P消息实现节点的发现、加入、离开和用户注册等过程.

  13. 基于 SIP 的 P2P VoIP技术研究%Research on P2 P VoIP Technology Based on SIP

    杜经纬

    2015-01-01

    随着三网融合的推进,将会给VoIP带来广阔的发展空间。针对目前常用的VoIP系统存在的网络开销高、呼叫接通率低、信令过于复杂等问题,在对SIP协议在P2P网络环境下实现VoIP的关键技术进行认真分析的基础上,提出了基于SIP的P2P VoIP。通过给出基于SIP的P2P VoIP的基本体系结构,分析了该系统中对等点的发现、用户注册及离线、呼叫建立等功能的实现方法,最后提出了基于SIP的P2P VoIP系统还应该考虑的一些问题。%With the progress in the convergence of the telecommunication, internet and broadcasting networks, VoIP will be presented with broad space for development.However, existing VoIP systems usually suffer from high network overhead, low call completing rate, complex signaling, etc.To solve these problems, this paper, based on a thorough analysis of key technologists involved in VoIP using SIP protocol in the P2P network scenario, proposed the SIP-based P2P VoIP system.By introducing the basic architecture of the SIP-based P2P VoIP system, this paper also analyzes the implementation of functions including peer discovery, user registration and getting offline and call establishment, and points out some questions that should be considered in this system.

  14. Protein Kinase A Is Central for Forward Transport of Two-pore Domain Potassium Channels K2P3.1 and K2P9.1*

    Mant, Alexandra; Elliott, David; Eyers, Patrick A.; O'Kelly, Ita M.

    2011-01-01

    Acid-sensitive two-pore domain potassium channels (K2P3.1 and K2P9.1) play key roles in both physiological and pathophysiological mechanisms, the most fundamental of which is control of resting membrane potential of cells in which they are expressed. These background “leak” channels are constitutively active once expressed at the plasma membrane, and hence tight control of their targeting and surface expression is fundamental to the regulation of K+ flux and cell excitability. The chaperone p...

  15. Phagocytes: A Holistic Defense and Protection Against Active P2P Worms

    Chen, Ruichuan; Crowcroft, Jon; Tang, Liyong; Chen, Zhong

    2011-01-01

    Active Peer-to-Peer (P2P) worms present serious threats to the global Internet by exploiting popular P2P applications to perform rapid topological self-propagation. Active P2P worms pose more deadly threats than normal scanning worms because they do not exhibit easily detectable anomalies, thus many existing defenses are no longer effective. We propose an immunity system with Phagocytes --- a small subset of elected P2P hosts that are immune with high probability and specialized in finding and "eating" worms in the P2P overlay. The Phagocytes will monitor their managed P2P hosts' connection patterns and traffic volume in an attempt to detect active P2P worm attacks. Once detected, local isolation, alert propagation and software patching will take place for containment. The Phagocytes further provide the access control and filtering mechanisms for communication establishment between the internal P2P overlay and the external hosts. We design a novel adaptive and interaction-based computational puzzle scheme at ...

  16. A Study of Perkins 2P1 Graduation Performance Rates at Virginia Western Community College

    Archer, J. Andrew.

    2006-01-01

    "2P1" is the Carl Perkins label for an institution's graduation performance rate. Systems receiving Perkins funds, like Virginia's 23 community colleges, are expected to meet a federally approved 2P1 target rate. For the 3-year period 1999-2001 Virginia Western Community College (VWCC) was one of seven community colleges in the VCCS (Virginia…

  17. The full 2p-h TDA and other self-energy approximants

    A super-operator formulation for decoupling symmetry blocks of the full 2p-h TDA electron propagator matric is presented; accuracy is explored using the full 2p-h TDA overlap amplitudes to calculate relative ionization intensities for N2 and H2O. The effect of excluding orbitals on IPs and relative ionization cross sections is reported. (orig.)

  18. HFBP: Identifying P2P Traffic by Host Level and Flow Level Behavior Profiles

    Jinghua Yan

    2013-08-01

    Full Text Available Recently, Peer-to-peer (P2P networks have been widely applied in streaming media, instant messaging, file sharing and other fields, which have occupied more and more network bandwidth. Accurately identify P2P traffic is very important to management and control P2P traffic. In this paper, we introduce HFBP, a novel P2P identification scheme based on the host level and flow level behavior profiles of P2P traffic. HFBP consists of two stages. In the first stage, we calculate the probability that a host takes part in P2P application by matching its behavior with some host level behavior rules. In the second stage, we compute the probability that a flow belonging to P2P application by comparing the statistical features of each flow in the host with several flow feature profiles. We evaluate HFBP using real traffic traces. The identification accuracy achieves 93.1% and 95.1% in terms of flow and byte respectively. The experimental results prove that HFBP obtains satisfactory performance in identifying P2P traffic. 

  19. Pseudogene CYP4Z2P 3′UTR promotes angiogenesis in breast cancer

    Zheng, Lufeng; Li, Xiaoman; Gu, Yi; Ma, Yihua; Xi, Tao, E-mail: xitao18@hotmail.com

    2014-10-24

    Highlights: • A new critical role of pseudogene CYP4Z2P 3′UTR in breast cancer is proposed. • We examine the level of pseudogene CYP4Z2P 3′UTR in breast cancer tissues. • The functions of CYP4Z2P 3′UTR and mechanism were studied. • The mechanism provides new insights for the breast cancer progression. - Abstract: Pseudogenes have long been marked as “false” genes, which are similar with real genes but have no apparent function. The 3′UTR is well-known to regulate gene expression post-transcriptionally. Our recent evidence, however, indicates novel functional roles of pseudogene CYP4Z2P 3′UTR (Z2P-UTR). We found that ectopic expression of Z2P-UTR in breast cancer cells significantly increased the expression of VEGF-A without affecting cell proliferation in vitro. Meanwhile, conditioned medium (CM) from Z2P-UTR overexpression cells enhanced proliferation, migration and tube formation of HUVEC, and promoted angiogenesis in ex vivo models. Also, CM increased the expression of VEGFR2 in HUVEC. Our data suggest that Z2P-UTR can promote breast cancer angiogenesis partly via paracrine pathway of VEGF-A/VEGFR2.

  20. Pseudogene CYP4Z2P 3′UTR promotes angiogenesis in breast cancer

    Highlights: • A new critical role of pseudogene CYP4Z2P 3′UTR in breast cancer is proposed. • We examine the level of pseudogene CYP4Z2P 3′UTR in breast cancer tissues. • The functions of CYP4Z2P 3′UTR and mechanism were studied. • The mechanism provides new insights for the breast cancer progression. - Abstract: Pseudogenes have long been marked as “false” genes, which are similar with real genes but have no apparent function. The 3′UTR is well-known to regulate gene expression post-transcriptionally. Our recent evidence, however, indicates novel functional roles of pseudogene CYP4Z2P 3′UTR (Z2P-UTR). We found that ectopic expression of Z2P-UTR in breast cancer cells significantly increased the expression of VEGF-A without affecting cell proliferation in vitro. Meanwhile, conditioned medium (CM) from Z2P-UTR overexpression cells enhanced proliferation, migration and tube formation of HUVEC, and promoted angiogenesis in ex vivo models. Also, CM increased the expression of VEGFR2 in HUVEC. Our data suggest that Z2P-UTR can promote breast cancer angiogenesis partly via paracrine pathway of VEGF-A/VEGFR2

  1. Peer-to-Peer (P2P) Knowledge, Use, and Attitudes of Academic Librarians

    Hendrix, Dean

    2007-01-01

    To assess their knowledge, use, and attitudes regarding peer-to-peer (P2P) applications, this study surveyed academic librarians (n = 162) via a mail-in survey. Correlations between the sample characteristics (age, gender, year of MLS, type of library job) and P2P knowledge, use, and attitudes were also explored. Overall, academic librarians…

  2. SAPIR - Executing complex similarity queries over multi layer P2P search structures

    Falchi, Fabrizio; Batko, Michal

    2009-01-01

    This deliverable reports the activities conducted within Task 5.4 "Executing complex similarity queries over multi layer P2P search structures" of the SAPIR project. In particular the deliverable discusses complex similarity queries issues and the implementation of the query processing over the P2P indexing. The document is accompanied by a zip file containing the javadoc for MUFIN.

  3. PD2P : PanDA Dynamic Data Placement for ATLAS

    CERN. Geneva

    2012-01-01

    The PanDA Dynamic Data Placement (PD2P) system has been developed to cope with difficulties of data placement for ATLAS. PD2P is an intelligent subsystem of PanDA to distribute data by taking the following factors into account: popularity, locality, the usage pattern of the data, the distribution of CPU and storage resources, ...

  4. A Trust Scheme Based DRM Model for P2P System

    XIAO Shangqin; LU Zhengding; LING Hefei; ZOU Fuhao

    2006-01-01

    With the maturation of P2P technology, there are more and more challenges to the protection of digital rights.DRM for traditional Client/Server model can not satisfy the requirement of digital right protection of P2P network.With practical application of P2P network technology and new generational DRM technology, the article proposes a DRM model for P2P system based on trust degree.The proposed model shares the secret key to the trusty peers and affords necessary security ensure for digital content delivery based on P2P technology.Mathematic analyses and simulations show that, compared to the current DRM model, the proposed model is more robust toleration of transmit and security.

  5. A Free-Rider Forecasting Model Based on Gray System Theory in P2P Networks

    He Xu

    2012-11-01

    Full Text Available The aim of this study is to forecast the number of free-riders in P2P networks which can help network managers to know the status of the networks in advance and take appropriate measures to cope with free-riding behavior. Free-riding behavior is common in P2P networks, which has a negative impact on the robustness, availability and stability of the networks. Severe free-riding behavior may lead to the crash of the whole P2P application system. Based on the research of free-riding behavior in P2P networks, this paper constructs a free-rider forecasting model (GST model using Gray System Theory. Simulation experiments show that this model has high feasibility, and can carry out reasonable predictions on the number of free-riders in P2P networks.

  6. Computing and Routing for Trust in Structured P2P Network

    Biao Cai

    2009-09-01

    Full Text Available Study of trust in P2P network now is focus on how to effectively against various malicious behaviors such as providing fake or misleading feedback about other peers and the management of trust in a P2P environment. But the scotoma of portability that trust peer can join (leave a certain P2P network at anytime and anywhere is seldom discussed. In this paper, a structured topology for trusts management in portable P2P network based on DHT (discrete hash table is proposed first, in which includes trust management strategies and peer operations on certain DHT circle. After that, a novel trust-computing model for the structured P2P network and the main trust decisions in the structured network are introduced too. Effectiveness and practicality of the proposed trust management have been showed in simulation experiments at the end.

  7. SPF-A*: Searching Multimedia Data in Heterogeneous Mobile P2P Network

    Fan Ye

    2009-04-01

    Full Text Available Mobile P2P (MP2P network has been widely used in everyday life combined with the wireless technology development. However, most previous works concentrate on the assumption that the mobile peers are identical of their inner properties in compositing a MP2P network. However, in current network environment, heterogeneous devices are widely used; they may have different storage sizes, data transmission rate, processing ability and even security levels. In such kind of MP2P Network environment, how to make data transmission effectively is challenge. In this paper, we concentrate on how to effectively obtain a queried multimedia resource and generate a path for such data transmission on the overlay MP2P network, so as to make the resource more effectively transmit among the heterogeneous peers. A new path generating algorithm called SPF-A* (Super Peer First A* is devised, and simulation studies are conducted to validate our proposal.

  8. An Anti-attack Model Based on Complex Network Theory in P2P networks

    Peng, Hao; Zhao, Dandan; Zhang, Aixin; Li, Jianhua

    2011-01-01

    Complex network theory is a useful way to study many real systems. In this paper, an anti-attack model based on complex network theory is introduced. The mechanism of this model is based on dynamic compensation process and reverse percolation process in P2P networks. The main purpose of the paper is: (i) a dynamic compensation process can turn an attacked P2P network into a power-law (PL) network with exponential cutoff; (ii) a local healing process can restore the maximum degree of peers in an attacked P2P network to a normal level; (iii) a restoring process based on reverse percolation theory connects the fragmentary peers of an attacked P2P network together into a giant connected component. In this way, the model based on complex network theory can be effectively utilized for anti-attack and protection purposes in P2P networks.

  9. Convergence of Internet and TV: The Commercial Viability of P2P Content Delivery

    de Boever, Jorn

    The popularity of (illegal) P2P (peer-to-peer) file sharing has a disruptive impact on Internet traffic and business models of content providers. In addition, several studies have found an increasing demand for bandwidth consuming content, such as video, on the Internet. Although P2P systems have been put forward as a scalable and inexpensive model to deliver such content, there has been relatively little economic analysis of the potentials and obstacles of P2P systems as a legal and commercial content distribution model. Many content providers encounter uncertainties regarding the adoption or rejection of P2P networks to spread content over the Internet. The recent launch of several commercial, legal P2P content distribution platforms increases the importance of an integrated analysis of the Strengths, Weaknesses, Opportunities and Threats (SWOT).

  10. Time-resolved photoemission micro-spectrometer using higher-order harmonics of Ti:sapphire laser

    Full text: A new photoemission spectrometer is under construction for the photoemission microscopy and the time-resolved pump- probe experiment. The higher order harmonics of the Ti:sapphire laser is used as the light source of the VUV region in this system. Because the fundamental laser is focused tightly into the rare gas jet to generate the higher order harmonics, the spot size of the laser, in other words, the spot size of the VUV light source is smaller than a few tens of micrometer. This smallness of the spot size has advantage for the microscopy. In order to compensate the low flux of the laser harmonics, a multilayer-coated schwaltzshild optics was designed. The multilayers play also as the monochromatic filter. The spatial resolution of this schwaltzshild system is found to be less than 1 micrometer by the ray-tracing calculations. A main chamber of the system is equipped with a time-of-flight energy analyzer to improve the efficiency of the electron detection. The main chamber and the gas chamber are separated by a differential pumping chamber and a thin Al foil. The system is designed for the study of the clean surface. It will be capable to perform the sub-micron photoemission microscopy and the femto-second pump-probe photoemission study for the various photo-excited dynamics on clean surfaces

  11. Photoemission studies of f-electron systems: many-body effects. Progress report, October 1, 1982-October 1, 1983

    Research tasks discussed include: surface versus shakedown effects in XPS; x-ray absorption studies of rare-earth and uranium intermetallics; deep core XPS studies of the mixed valent systems Ce(Pd/sub 1-x/Ag/sub x/)3 and Ce(Pd/sub 1-y/Rh/sub y/)3; and photoemission experiments performed at NSLS

  12. On the excess photon noise in single-beam measurements with photo-emissive and photo-conductive cells

    Alkemade, C.T.J.

    1959-01-01

    In this paper the so-called excess photon noise is theoretically considered with regard to noise power measurements with a single, illumined photo-emissive or photo-conductive cell. Starting from a modification of Mandel's stochastic association of the emission of photo-electrons with wave intensity

  13. High-resolution, low-temperature, photoemission studies of heavy-fermion systems: UBe13 and UPt3

    High-resolution (0.13 eV) photoemission measurements performed at low temperatures (roughly-equal20 K) show that a sharp feature (measured width approx. =0.15 eV at full width at half maximum) exists at the Fermi edge in the electronic structures of UBe13 and UPt3. In UBe13 the feature shows some temperature dependence

  14. Resonant Auger decay of Ar 2p3/2-14s and 2p3/2-14p states excited by electron impact

    Auger spectra of resonantly excited 2p3/2-14s and 2p3/2-14p states in argon were measured by (e,2e) technique. The 99.2-eV scattered electrons were detected in coincidence with L3-M23M23 Auger electrons, and the experiment was performed at 343.6- and 344.9-eV electron impact to tune the energy loss to the energy of the dipole-allowed and the dipole-forbidden excitations, respectively. The resonant Auger spectra are obtained upon subtraction of the overlapping signal due to the outer-shell ionization, which was recorded at 340-eV electron-impact energy. The most intense groups of Auger transitions from 2p3/2-14s (J=1,2) and 2p3/2-14p (J=0,1,2,3) states are identified by comparison with the results of the two-step model, based on distorted-wave Born approximation with exchange and multiconfiguration descriptions of the relaxed states. The 4 s spectrum displays a substantially larger shake-up contribution than the one observed in photoexcitation experiments, which may be explained by the interference of the resonant decay path with the direct ionization excitation of the Ar 3p subshell. The majority of the observed 4p signal is assigned to the monopole and quadrupole excitations of the ground state.

  15. Solution structure of the ubiquitin-binding domain in Swa2p from Saccharomyces cerevisiae.

    Chim, Nicholas; Gall, Walter E; Xiao, Jing; Harris, Mark P; Graham, Todd R; Krezel, Andrzej M

    2004-03-01

    The SWA2/AUX1 gene has been proposed to encode the Saccharomyces cerevisiae ortholog of mammalian auxilin. Swa2p is required for clathrin assembly/dissassembly in vivo, thereby implicating it in intracellular protein and lipid trafficking. While investigating the 287-residue N-terminal region of Swa2p, we found a single stably folded domain between residues 140 and 180. Using binding assays and structural analysis, we established this to be a ubiquitin-associated (UBA) domain, unidentified by bioinformatics of the yeast genome. We determined the solution structure of this Swa2p domain and found a characteristic three-helix UBA fold. Comparisons of structures of known UBA folds reveal that the position of the third helix is quite variable. This helix in Swa2p UBA contains a bulkier tyrosine in place of smaller residues found in other UBAs and cannot pack as close to the second helix. The molecular surface of Swa2p UBA has a mostly negative potential, with a single hydrophobic surface patch found also in the UBA domains of human protein, HHR23A. The presence of a UBA domain implicates Swa2p in novel roles involving ubiquitin and ubiquitinated substrates. We propose that Swa2p is a multifunctional protein capable of recognizing several proteins through its protein-protein recognition domains. PMID:14997574

  16. Spin- and angle-resolved photoemission on the topological Kondo insulator candidate: SmB6

    Xu, Nan; Ding, Hong; Shi, Ming

    2016-09-01

    Topological Kondo insulators are a new class of topological insulators in which metallic surface states protected by topological invariants reside in the bulk band gap at low temperatures. Unlike other 3D topological insulators, a truly insulating bulk state, which is critical for potential applications in next-generation electronic devices, is guaranteed by many-body effects in the topological Kondo insulator. Furthermore, the system has strong electron correlations that can serve as a testbed for interacting topological theories. This topical review focuses on recent advances in the study of SmB6, the most promising candidate for a topological Kondo insulator, from the perspective of spin- and angle-resolved photoemission spectroscopy with highlights of some important transport results.

  17. Tunable VUV laser based spectrometer for Angle Resolved Photoemission Spectroscopy (ARPES)

    Jiang, Rui; Wu, Yun; Huang, Lunan; McMillen, Colin D; Kolis, Joseph; Giesber, Henry G; Egan, John J; Kaminski, Adam

    2014-01-01

    We have developed an angle-resolved photoemission spectrometer with tunable VUV laser as a photon source. The photon source is based on the fourth harmonic generation of a near IR beam from a Ti:sapphire laser pumped by a CW green laser and tunable between 5.3eV and 7eV. The most important part of the set-up is a compact, vacuum enclosed fourth harmonic generator based on KBBF crystals, grown hydrothermally in the US. This source can deliver a photon flux of over 10^14 photons/s. We demonstrate that this energy range is sufficient to measure the kz dispersion in an iron arsenic high temperature superconductor, which was previously only possible at synchrotron facilities.

  18. Tunable vacuum ultraviolet laser based spectrometer for angle resolved photoemission spectroscopy

    Jiang, Rui; Mou, Daixiang; Wu, Yun; Huang, Lunan; Kaminski, Adam [Division of Materials Science and Engineering, Ames Laboratory, Ames, Iowa 50011 (United States); Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011 (United States); McMillen, Colin D.; Kolis, Joseph [Department of Chemistry, Clemson University, Clemson, South Carolina 29634 (United States); Giesber, Henry G.; Egan, John J. [Advanced Photonic Crystals LLC, Fort Mill, South Carolina 29708 (United States)

    2014-03-15

    We have developed an angle-resolved photoemission spectrometer with tunable vacuum ultraviolet laser as a photon source. The photon source is based on the fourth harmonic generation of a near IR beam from a Ti:sapphire laser pumped by a CW green laser and tunable between 5.3 eV and 7 eV. The most important part of the set-up is a compact, vacuum enclosed fourth harmonic generator based on potassium beryllium fluoroborate crystals, grown hydrothermally in the US. This source can deliver a photon flux of over 10{sup 14} photon/s. We demonstrate that this energy range is sufficient to measure the k{sub z} dispersion in an iron arsenic high temperature superconductor, which was previously only possible at synchrotron facilities.

  19. Spin- and angle-resolved photoemission on the topological Kondo insulator candidate: SmB6.

    Xu, Nan; Ding, Hong; Shi, Ming

    2016-09-14

    Topological Kondo insulators are a new class of topological insulators in which metallic surface states protected by topological invariants reside in the bulk band gap at low temperatures. Unlike other 3D topological insulators, a truly insulating bulk state, which is critical for potential applications in next-generation electronic devices, is guaranteed by many-body effects in the topological Kondo insulator. Furthermore, the system has strong electron correlations that can serve as a testbed for interacting topological theories. This topical review focuses on recent advances in the study of SmB6, the most promising candidate for a topological Kondo insulator, from the perspective of spin- and angle-resolved photoemission spectroscopy with highlights of some important transport results. PMID:27391865

  20. Accessing Phonon Polaritons in Hyperbolic Crystals by Angle-Resolved Photoemission Spectroscopy

    Tomadin, Andrea; Principi, Alessandro; Song, Justin C. W.; Levitov, Leonid S.; Polini, Marco

    2015-08-01

    Recently studied hyperbolic materials host unique phonon-polariton (PP) modes. The ultrashort wavelengths of these modes, as well as their low damping, hold promise for extreme subdiffraction nanophotonics schemes. Polar hyperbolic materials such as hexagonal boron nitride can be used to realize long-range coupling between PP modes and extraneous charge degrees of freedom. The latter, in turn, can be used to control and probe PP modes. Here we analyze coupling between PP modes and plasmons in an adjacent graphene sheet, which opens the door to accessing PP modes by angle-resolved photoemission spectroscopy (ARPES). A rich structure in the graphene ARPES spectrum due to PP modes is predicted, providing a new probe of PP modes and their coupling to graphene plasmons.