WorldWideScience

Sample records for angle-resolved photoemission experiments

  1. Angle-resolved photoemission extended fine structure

    International Nuclear Information System (INIS)

    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

  2. Angle-resolved photoemission study of Ag(1 1 1)

    Science.gov (United States)

    Edamoto, K.; Miyazaki, E.; Shimokoshi, K.; Kato, H.

    1990-01-01

    The (1 1 1) face of Ag has been studied by angle-resolved photoemission spectroscopy utilizing synchrotron radiation as the excitation source (25 FIRO method. The peak positions thus determined are used to map the dispersion curves along the lang1 1 1rang (Γ-L) direction. The results show general agreement with calculated band structure, so far as the energy levels and symmetries are concerned. However, it is found that the density of state effect is dominant in the spectra obtained in the present photon energy region. The emission from the Ag 5s, p bands is observed to be broadened due to the indirect transition process.

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

    Energy Technology Data Exchange (ETDEWEB)

    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

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

    International Nuclear Information System (INIS)

    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)

  5. Laser-based spin- and angle-resolved photoemission spectroscopy for rapid, high-resolution measurements

    Science.gov (United States)

    Gotlieb, Kenneth; Bostwick, Aaron; Hussain, Zahid; Lanzara, Alessandra; Jozwiak, Christopher

    2014-03-01

    A unique spin-and angle-resolved photoemission spectrometer (spin-ARPES) is coupled with a 6 eV laser to achieve unprecedented measurements of near-EF physics in topological insulators and Rashba systems. The pairing of the spin-ARPES system with the laser allows for energy and angular resolutions never before seen in a spin-ARPES experiment. Most importantly, the high efficiency of the system and high photon flux of the laser make measurements very rapid, permitting exploration of a large experimental phase space.

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

    Energy Technology Data Exchange (ETDEWEB)

    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).

  7. Time and angle resolved photoemission spectroscopy using femtosecond visible and high-harmonic light

    Energy Technology Data Exchange (ETDEWEB)

    Mathias, S; Deicke, F; Ruffing, A; Aeschlimann, M [Department of Physics and Research Center OPTIMAS, University of Kaiserslautern, 67663 Kaiserslautern (Germany); Wiesenmayer, M; Bauer, M [Institut fuer experimentelle und angewandte Physik, Christian-Albrechts Universitaet zu Kiel, 24118 Kiel (Germany); Miaja-Avila, L; Murnane, M M; Kapteyn, H C, E-mail: SMathias@gmx.d [JILA, University of Colorado and National Institute of Standards and Technology, and Department of Physics, University of Colorado, Boulder, Colorado 80309-0440 (United States)

    2009-02-01

    The angle resolved photoelectron spectroscopy (ARPES) has emerged as a leading technique in identifying static key properties of complex systems such as the electronic band structure of adsorbed molecules, ultrathin quantum-well films or high temperature superconductors. We efficiently combined ARPES by using a two-dimensional analyzer for parallel energy (E) and momentum (k{sub ||}) detection with femtosecond time-resolved spectroscopies. Using time and angle resolved two photon photoemission (2PPE) with visible light pulses, the hot electron dynamics in complex electronic structures are directly accessible by means of angle resolved hot electron lifetime mapping. Furthermore, femtosecond ARPES spectra recorded with high harmonic generation (HHG) light pulses are presented, showing the potential of this technique for future investigations of surface dynamics and photo-induced phase transition processes.

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

    Energy Technology Data Exchange (ETDEWEB)

    Plucinski, L., E-mail: l.plucinski@fz-juelich.de [Peter Grünberg Institute PGI-6, Forschungszentrum Jülich, D-52425 Jülich (Germany); Fakultät f. Physik, Universität Duisburg-Essen, D-47057 Duisburg (Germany); Schneider, C.M. [Peter Grünberg Institute PGI-6, Forschungszentrum Jülich, D-52425 Jülich (Germany); Fakultät f. Physik, Universität Duisburg-Essen, D-47057 Duisburg (Germany)

    2013-08-15

    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.

  9. Angle resolved photoemission spectroscopy of Sr_2CuO_2Cl_2 - a revisit

    OpenAIRE

    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...

  10. Simple surface structure determination from Fourier transforms of angle-resolved photoemission extended fine structure

    Energy Technology Data Exchange (ETDEWEB)

    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}.

  11. Direct observation of the mass renormalization in SrVO3 by angle resolved photoemission spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Yoshida, t.

    2010-05-03

    We have performed an angle-resolved photoemission study of the three-dimensional perovskite-type SrVO{sub 3}. Observed spectral weight distribution of the coherent part in the momentum space shows cylindrical Fermi surfaces consisting of the V 3d t{sub 2g} orbitals as predicted by local-density approximation (LDA) band-structure calculation. The observed energy dispersion shows a moderately enhanced effective mass compared to the LDA results, corresponding to the effective mass enhancement seen in the thermodynamic properties. Contributions from the bulk and surface electronic structures to the observed spectra are discussed based on model calculations.

  12. Dirac cones, Floquet side bands, and theory of time-resolved angle-resolved photoemission

    Science.gov (United States)

    Farrell, Aaron; Arsenault, A.; Pereg-Barnea, T.

    2016-10-01

    Pump-probe techniques with high temporal resolution allow one to drive a system of interest out of equilibrium and at the same time probe its properties. Recent advances in these techniques open the door to studying new, nonequilibrium phenomena such as Floquet topological insulators and superconductors. These advances also necessitate the development of theoretical tools for understanding the experimental findings and predicting new ones. In the present paper, we provide a theoretical foundation to understand the nonequilibrium behavior of a Dirac system. We present detailed numerical calculations and simple analytic results for the time evolution of a Dirac system irradiated by light. These results are framed by appealing to the recently revitalized notion of side bands [A. Farrell and T. Pereg-Barnea, Phys. Rev. Lett. 115, 106403 (2015), 10.1103/PhysRevLett.115.106403; Phys. Rev. B 93, 045121 (2016), 10.1103/PhysRevB.93.045121], extended to the case of nonperiodic drive where the fast oscillations are modified by an envelope function. We apply this formalism to the case of photocurrent generated by a second probe pulse. We find that, under the application of circularly polarized light, a Dirac point only ever splits into two copies of side bands. Meanwhile, the application of linearly polarized light leaves the Dirac point intact while producing side bands. In both cases the population of the side bands are time dependent through their nonlinear dependence on the envelope of the pump pulse. Our immediate interest in this work is in connection to time- and angle-resolved photoemission experiments, where we find excellent qualitative agreement between our results and those in the literature [Wang et al., Science 342, 453 (2013), 10.1126/science.1239834]. However, our results are general and may prove useful beyond this particular application and should be relevant to other pump-probe experiments.

  13. Structural studies of molecular and metallic overlayers using angle- resolved photoemission extended fine structure

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Z.

    1992-10-01

    Angle-resolved photoemission extended fine structure (ARPEFS) was used to study molecular and metallic overlayers on metal surfaces through analysis of p2mg(2[times]1)CO/Ni(110) and the p(2[times]2)K/Ni(111) adsorption. For the dense p2mg(2[times]1)CO/Ni(110) surface layer, photoemission intensities from C 1s level were measured in three directions at photoelectron kinetic energies 60-400 eV. Using multiple-scattering spherical-wave (MSSW) modeling, it was found that CO molecules are adsorbed on short-bridge sites, with adjacent CO along the [110] direction displaced alternatively in opposite directions towards the [001] azimuths to form a zigzag chain geometry. The tilt angle is 16[plus minus]2[degree] from the surface normal for the direction linking the C atom and the center of the Ni bridge. The carbon C-Ni interatomic distance was determined to be 1.94[plus minus]0.02[Angstrom]. The first- to second-layer spacing of Ni is 1.27[plus minus]0.04[Angstrom], up from 1.10[Angstrom] for the clean Ni(110) surface, but close to the 1.25[Angstrom] Ni interlayer spacing in the bulk. The C-O bond length and tilt angle were varied within small ranges (1.10--1.20[Angstrom] and 15--23[degrees]) in our MSSW simulations. Best agreement between experiment and simulations was achieved at 1.16[Angstrom] and 19[degrees]. This yields an O-O distance of 2.95[Angstrom] for the two nearest CO molecules, (van der Waals' radius [approximately] 1.5 [Angstrom] for oxygen). Two different partial-wave phase-shifts were used in MSSW, and structural results from both are in very good agreement. For the p(2[times]2)K/Ni(111) overlayer, ARPEFS [chi](k) curves from K 1s level measured along [111] and [771] at 130K showed that the K atoms are preferentially adsorbed on the atop sites, in agreement with a LEED study of the same system.

  14. Structural studies of molecular and metallic overlayers using angle- resolved photoemission extended fine structure

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Z.

    1992-10-01

    Angle-resolved photoemission extended fine structure (ARPEFS) was used to study molecular and metallic overlayers on metal surfaces through analysis of p2mg(2{times}1)CO/Ni(110) and the p(2{times}2)K/Ni(111) adsorption. For the dense p2mg(2{times}1)CO/Ni(110) surface layer, photoemission intensities from C 1s level were measured in three directions at photoelectron kinetic energies 60-400 eV. Using multiple-scattering spherical-wave (MSSW) modeling, it was found that CO molecules are adsorbed on short-bridge sites, with adjacent CO along the [110] direction displaced alternatively in opposite directions towards the [001] azimuths to form a zigzag chain geometry. The tilt angle is 16{plus_minus}2{degree} from the surface normal for the direction linking the C atom and the center of the Ni bridge. The carbon C-Ni interatomic distance was determined to be 1.94{plus_minus}0.02{Angstrom}. The first- to second-layer spacing of Ni is 1.27{plus_minus}0.04{Angstrom}, up from 1.10{Angstrom} for the clean Ni(110) surface, but close to the 1.25{Angstrom} Ni interlayer spacing in the bulk. The C-O bond length and tilt angle were varied within small ranges (1.10--1.20{Angstrom} and 15--23{degrees}) in our MSSW simulations. Best agreement between experiment and simulations was achieved at 1.16{Angstrom} and 19{degrees}. This yields an O-O distance of 2.95{Angstrom} for the two nearest CO molecules, (van der Waals` radius {approximately} 1.5 {Angstrom} for oxygen). Two different partial-wave phase-shifts were used in MSSW, and structural results from both are in very good agreement. For the p(2{times}2)K/Ni(111) overlayer, ARPEFS {chi}(k) curves from K 1s level measured along [111] and [771] at 130K showed that the K atoms are preferentially adsorbed on the atop sites, in agreement with a LEED study of the same system.

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  16. Fingerprints of entangled spin and orbital physics in itinerant ferromagnets via angle-resolved resonant photoemission

    Science.gov (United States)

    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.

  17. Spin- and angle-resolved photoemission on the topological Kondo insulator candidate: SmB6.

    Science.gov (United States)

    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

  18. Accessing Phonon Polaritons in Hyperbolic Crystals by Angle-Resolved Photoemission Spectroscopy

    Science.gov (United States)

    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.

  19. Tunable VUV laser based spectrometer for Angle Resolved Photoemission Spectroscopy (ARPES)

    CERN Document Server

    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.

  20. Orbital Rashba effect and its detection by circular dichroism angle-resolved photoemission spectroscopy

    Science.gov (United States)

    Park, Jin-Hong; Kim, Choong H.; Rhim, Jun-Won; Han, Jung Hoon

    2012-05-01

    We show, by way of tight-binding and first-principles calculations, that a one-to-one correspondence between an electron's crystal momentum k and nonzero orbital angular momentum (OAM) is a generic feature of surface bands. The OAM forms a chiral structure in momentum space much as its spin counterpart in Rashba model does, as a consequence of the inherent inversion symmetry breaking at the surface but not of spin-orbit interaction. This is the orbital counterpart of conventional Rashba effect and may be called the “orbital Rashba effect.” The circular dichroism (CD) angle-resolved photoemission (ARPES) method is an efficient way to detect this new order, and we derive formulas explicitly relating the CD-ARPES signal to the existence of OAM in the band structure. The cases of degenerate p- and d-orbital bands are considered.

  1. Angle-resolved photoemission studies of the superconducting gap symmetry in Fe-based superconductors

    Directory of Open Access Journals (Sweden)

    Y.-B. Huang

    2012-12-01

    Full Text Available The superconducting gap is the fundamental parameter that characterizes the superconducting state, and its symmetry is a direct consequence of the mechanism responsible for Cooper pairing. Here we discuss about angle-resolved photoemission spectroscopy measurements of the superconducting gap in the Fe-based high-temperature superconductors. We show that the superconducting gap is Fermi surface dependent and nodeless with small anisotropy, or more precisely, a function of the momentum location in the Brillouin zone. We show that while this observation seems inconsistent with weak coupling approaches for superconductivity in these materials, it is well supported by strong coupling models and global superconducting gaps. We also suggest that a smaller lifetime of the superconducting Cooper pairs induced by the momentum dependent interband scattering inherent to these materials could affect the residual density of states at low energies, which is critical for a proper evaluation of the superconducting gap.

  2. Electronic structure of MgB2 from angle-resolved photoemission spectroscopy.

    Science.gov (United States)

    Uchiyama, H; Shen, K M; Lee, S; Damascelli, A; Lu, D H; Feng, D L; Shen, Z-X; Tajima, S

    2002-04-15

    The first angle-resolved photoemission spectroscopy results from MgB2 single crystals are reported. Along the GammaK and GammaM directions, we observed three distinct dispersive features approaching the Fermi energy. These can be assigned to the theoretically predicted sigma (B 2p(x,y)) and pi (B 2p(z)) bands. In addition, a small parabolic-like band is detected around the Gamma point, which can be attributed to a surface-derived state. The overall agreement between our results and the band calculations suggests that the electronic structure of MgB2 is of a conventional nature, thus implying that electron correlations are weak and may be of little importance to superconductivity in this system.

  3. Spin- and angle-resolved photoemission on the topological Kondo insulator candidate: SmB6

    Science.gov (United States)

    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.

  4. Modeling angle-resolved photoemission of graphene and black phosphorus nano structures.

    Science.gov (United States)

    Park, Sang Han; Kwon, Soonnam

    2016-05-10

    Angle-resolved photoemission spectroscopy (ARPES) data on electronic structure are difficult to interpret, because various factors such as atomic structure and experimental setup influence the quantum mechanical effects during the measurement. Therefore, we simulated ARPES of nano-sized molecules to corroborate the interpretation of experimental results. Applying the independent atomic-center approximation, we used density functional theory calculations and custom-made simulation code to compute photoelectron intensity in given experimental setups for every atomic orbital in poly-aromatic hydrocarbons of various size, and in a molecule of black phosphorus. The simulation results were validated by comparing them to experimental ARPES for highly-oriented pyrolytic graphite. This database provides the calculation method and every file used during the work flow.

  5. High Resolution Angle Resolved Photoemission with Tabletop 11eV Laser

    CERN Document Server

    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...

  6. Invited Article: High resolution angle resolved photoemission with tabletop 11 eV laser

    Energy Technology Data Exchange (ETDEWEB)

    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.

  7. Invited Article: High resolution angle resolved photoemission with tabletop 11 eV laser.

    Science.gov (United States)

    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

  8. Surface band structure of CdTe(111)-2 × 2 by angle-resolved photoemission

    Science.gov (United States)

    Janowitz, C.; Manzke, R.; Skibowski, M.; Orlowski, B. A.

    1991-05-01

    The surface band structure of non-cleavable CdTe(111)-2 × 2 reconstructed surfaces is determined by means of angle-resolved photoemission and constant-final-state (CFS) spectroscopy. The experiments were performed with He I radiation and synchrotron radiation from the DORIS II storage ring at HASYLAB. High-quality (111)-2 × 2 surfaces were prepared by sputtering and annealing controlled by electron diffraction (LEED and RHEED). In order to distinguish between surface and bulk related emissions in the spectra we utilized, besides the criteria that the k∥ dispersion of surface states should reveal the 2 × 2 periodicity of the surfac mesh, also photon energy dependent CFS series at several critical points of the surface Brillouin zone. The data on CdTe(111) will be compared with experimental and theoretical results which are available for the electronically similar GaAs(111) surface.

  9. Direct angle resolved photoemission spectroscopy and superconductivity of strained high-c films

    Indian Academy of Sciences (India)

    Davor Pavuna; Daniel Ariosa; Dominique Cloetta; Claudia Cancellieri; Mike Abrecht

    2008-02-01

    Since 1997 we systematically perform direct angle resolved photoemission spectroscopy (ARPES) on in-situ grown thin (< 30 nm) cuprate films. Specifically, we probe low-energy electronic structure and properties of high-c superconductors (HTSC) under different degrees of epitaxial (compressive vs. tensile) strain. In overdoped and underdoped in-plane compressed (the strain is induced by the choice of substrate) ≃ 15 nm thin La2-SrCuO4 (LSCO) films we almost double c to 40 K, from 20 K and 24 K, respectively. Yet the Fermi surface (FS) remains essentially two-dimensional. In contrast, ARPES data under tensile strain exhibit the dispersion that is three-dimensional, yet c drastically decreases. It seems that the in-plane compressive strain tends to push the apical oxygen far away from the CuO2 plane, enhances the two-dimensional character of the dispersion and increases c, while the tensile strain acts in the opposite direction and the resulting dispersion is three-dimensional. We have established the shape of the FS for both cases, and all our data are consistent with other ongoing studies, like EXAFS. As the actual lattice of cuprates is like a `Napoleon-cake', i.e. rigid CuO2 planes alternating with softer `reservoir', that distort differently under strain, our data rule out all oversimplified two-dimensional (rigid lattice) mean field models. The work is still in progress on optimized La-doped Bi-2201 films with enhanced c.

  10. Angle resolved photoemission spectroscopy study on the non-saturate magnetoresistance material WTe2

    Science.gov (United States)

    Jiang, Juan; Niu, Xiaohai; Xie, Binping; Zhang, Tong; Feng, Donglai

    2015-03-01

    By performing high resolution angle-resolved photoemission spectroscopy, we obtain the detailed electronic structure of WTe2, which has an extremely large non-saturated magnetoresistance. Unlike the simple one electron and one hole pocket as expected, we resolved a rather complicated Fermi surface in WTe2. There is a hole pocket around the Brillouin zone center Γ, two hole pockets and two electron pockets along the tungsten chain direction. Thus the large magnetoresistance cannot be simply attributed to the electron-hole compensation, since this is based on a two carrier assumption model, the real case in WTe2 should be more complicated. Surprisingly, the circular dichroism ARPES result shows a strong intensity inversion between the data under the right-circular polarized light and the left-circular polarized light. This, indicates a proper different orbital angular momentum along the tungsten chain direction, which might also related to the different spin angular momentum since there're coupled with each other. Therefore, we propose that to fully understand the large magnetoresistance in WTe2, spin channel should also be involved where backscattering are forbidden under zero field.

  11. Nodal Quasiparticle Meltdown in Ultra-High Resolution Pump-Probe Angle-Resolved Photoemission

    Energy Technology Data Exchange (ETDEWEB)

    Graf, Jeff; Jozwiak, Chris; Smallwood, Chris L.; Eisaki, H.; Kaindl, Robert A.; Lee, Dung-Hai; Lanzara, Alessandra

    2011-06-03

    High-T{sub c} cuprate superconductors are characterized by a strong momentum-dependent anisotropy between the low energy excitations along the Brillouin zone diagonal (nodal direction) and those along the Brillouin zone face (antinodal direction). Most obvious is the d-wave superconducting gap, with the largest magnitude found in the antinodal direction and no gap in the nodal direction. Additionally, while antin- odal quasiparticle excitations appear only below T{sub c}, superconductivity is thought to be indifferent to nodal excitations as they are regarded robust and insensitive to T{sub c}. Here we reveal an unexpected tie between nodal quasiparticles and superconductivity using high resolution time- and angle-resolved photoemission on optimally doped Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} . We observe a suppression of the nodal quasiparticle spectral weight following pump laser excitation and measure its recovery dynamics. This suppression is dramatically enhanced in the superconducting state. These results reduce the nodal-antinodal dichotomy and challenge the conventional view of nodal excitation neutrality in superconductivity. The electronic structures of high-Tc cuprates are strongly momentum-dependent. This is one reason why the momentum-resolved technique of angle-resolved photoemission spectroscopy (ARPES) has been a central tool in the field of high-temperature superconductivity. For example, coherent low energy excitations with momenta near the Brillouin zone face, or antinodal quasiparticles (QPs), are only observed below T{sub c} and have been linked to superfluid density. They have therefore been the primary focus of ARPES studies. In contrast, nodal QPs, with momenta along the Brillouin zone diagonal, have received less attention and are usually regarded as largely immune to the superconducting transition because they seem insensitive to perturbations such as disorder, doping, isotope exchange, charge ordering, and temperature. Clearly

  12. Direct angle resolved photoemission spectroscopy and superconductivity of strained high-Tc films

    Science.gov (United States)

    Pavuna, Davor; Ariosa, Daniel; Cloetta, Dominique; Cancellieri, Claudia; Abrecht, Mike

    2008-02-01

    Since 1997 we systematically perform direct angle resolved photoemission spectroscopy (ARPES) on in-situ grown thin (<30 nm) cuprate films. Specifically, we probe low-energy electronic structure and properties of high-T_{c} superconductors (HTSC) under different degrees of epitaxial ({compressive vs. tensile}) strain. In overdoped and underdoped in-plane compressed (the strain is induced by the choice of substrate) ≈15 nm thin La_{2-x}Sr_{x}CuO_{4} (LSCO) films we almost double T_{c} to 40 K, from 20 K and 24 K, respectively. Yet the Fermi surface (FS) remains essentially two-dimensional. In contrast, ARPES data under {tensile} strain exhibit the dispersion that is three-dimensional, yet T_{c} drastically decreases. It seems that the in-plane compressive strain tends to push the apical oxygen far away from the CuO_{2} plane, enhances the two-dimensional character of the dispersion and increases T_{c}, while the tensile strain acts in the opposite direction and the resulting dispersion is three-dimensional. We have established the shape of the FS for both cases, and all our data are consistent with other ongoing studies, like EXAFS. As the actual lattice of cuprates is like a `Napoleon-cake', i.e. rigid CuO_{2 } planes alternating with softer `reservoir', that distort differently under strain, our data rule out all oversimplified two-dimensional (rigid lattice) mean field models. The work is still in progress on optimized La-doped Bi-2201 films with enhanced T_{c}.

  13. Angle-Resolved Photoemission Spectroscopy on Electronic Structure and Electron-Phonon Coupling in Cuprate Superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, X.J.

    2010-04-30

    In addition to the record high superconducting transition temperature (T{sub c}), high temperature cuprate superconductors are characterized by their unusual superconducting properties below T{sub c}, and anomalous normal state properties above T{sub c}. In the superconducting state, although it has long been realized that superconductivity still involves Cooper pairs, as in the traditional BCS theory, the experimentally determined d-wave pairing is different from the usual s-wave pairing found in conventional superconductors. The identification of the pairing mechanism in cuprate superconductors remains an outstanding issue. The normal state properties, particularly in the underdoped region, have been found to be at odd with conventional metals which is usually described by Fermi liquid theory; instead, the normal state at optimal doping fits better with the marginal Fermi liquid phenomenology. Most notable is the observation of the pseudogap state in the underdoped region above T{sub c}. As in other strongly correlated electrons systems, these unusual properties stem from the interplay between electronic, magnetic, lattice and orbital degrees of freedom. Understanding the microscopic process involved in these materials and the interaction of electrons with other entities is essential to understand the mechanism of high temperature superconductivity. Since the discovery of high-T{sub c} superconductivity in cuprates, angle-resolved photoemission spectroscopy (ARPES) has provided key experimental insights in revealing the electronic structure of high temperature superconductors. These include, among others, the earliest identification of dispersion and a large Fermi surface, an anisotropic superconducting gap suggestive of a d-wave order parameter, and an observation of the pseudogap in underdoped samples. In the mean time, this technique itself has experienced a dramatic improvement in its energy and momentum resolutions, leading to a series of new discoveries not

  14. Gauge invariance in the theoretical description of time-resolved angle-resolved pump/probe photoemission spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Freericks, J. K.; Krishnamurthy, H. R.; Sentef, M. A.; Devereaux, T. P.

    2015-10-01

    Nonequilibrium calculations in the presence of an electric field are usually performed in a gauge, and need to be transformed to reveal the gauge-invariant observables. In this work, we discuss the issue of gauge invariance in the context of time-resolved angle-resolved pump/probe photoemission. If the probe is applied while the pump is still on, one must ensure that the calculations of the observed photocurrent are gauge invariant. We also discuss the requirement of the photoemission signal to be positive and the relationship of this constraint to gauge invariance. We end by discussing some technical details related to the perturbative derivation of the photoemission spectra, which involve processes where the pump pulse photoexcites electrons due to nonequilibrium effects.

  15. 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

    Energy Technology Data Exchange (ETDEWEB)

    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

  16. 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

    International Nuclear Information System (INIS)

    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

  17. Spin- and angle-resolved photoemission spectroscopy study of the Au(1 1 1) Shockley surface state

    Energy Technology Data Exchange (ETDEWEB)

    Muntwiler, Matthias E-mail: m.muntwiler@physik.unizh.ch; Hoesch, Moritz; Petrov, Vladimir N.; Hengsberger, Matthias; Patthey, Luc; Shi Ming; Falub, Mihaela; Greber, Thomas; Osterwalder, Juerg

    2004-07-01

    The spin character of the splitting of the Shockley surface state on Au(111) is directly verified by measurements of the in-plane and out-of-plane spin polarizations in angle-resolved photoemission spectra. The two parabolic sub-bands that are momentum-shifted with respect to each other, reveal a distinct, opposite spin polarization that within the errors lies in the surface plane. The measured in-plane orientation of the spin vectors is consistent with the simple spin structure expected from a nearly-free-electron model, where the polarization axis is tangential to the Fermi surface of the surface state.

  18. Experimental electronic structure and Fermi-surface instability of the correlated 3d sulphide BaVS3 : High-resolution angle-resolved photoemission spectroscopy

    Science.gov (United States)

    Mitrovic, S.; Fazekas, P.; Søndergaard, C.; Ariosa, D.; Barišić, N.; Berger, H.; Cloëtta, D.; Forró, L.; Höchst, H.; Kupčić, I.; Pavuna, D.; Margaritondo, G.

    2007-04-01

    The correlated 3d sulphide BaVS3 exhibits an interesting coexistence of one-dimensional and three-dimensional properties. Our experiments determine the electronic band structure and shed light on this puzzle. High-resolution angle-resolved photoemission measurements in a 4-eV -wide range below the Fermi energy level uncover and investigate the coexistence of a1g wide-band and eg narrow-band d electrons, which lead to the complicated electronic properties of this material. We explore the effects of strong correlations and the Fermi surface instability associated with the metal-insulator transition.

  19. Soft X-ray angle-resolved photoemission spectroscopy of heavily boron-doped superconducting diamond films

    Directory of Open Access Journals (Sweden)

    T. Yokoya, T. Nakamura, T. Matushita, T. Muro, H. Okazaki, M. Arita, K. Shimada, H. Namatame, M. Taniguchi, Y. Takano, M. Nagao, T. Takenouchi, H. Kawarada and T. Oguchi

    2006-01-01

    Full Text Available We have performed soft X-ray angle-resolved photoemission spectroscopy (SXARPES of microwave plasma-assisted chemical vapor deposition diamond films with different B concentrations in order to study the origin of the metallic behavior of superconducting diamond. SXARPES results clearly show valence band dispersions with a bandwidth of ~23 eV and with a top of the valence band at gamma point in the Brillouin zone, which are consistent with the calculated valence band dispersions of pure diamond. Boron concentration-dependent band dispersions near the Fermi level (EF exhibit a systematic shift of EF, indicating depopulation of electrons due to hole doping. These SXARPES results indicate that diamond bands retain for heavy boron doping and holes in the diamond band are responsible for the metallic states leading to superconductivity at low temperature. A high-resolution photoemission spectroscopy spectrum near EF of a heavily boron-doped diamond superconductor is also presented.

  20. Method to map one-dimensional electronic wave function by using multiple Brillouin zone angle resolved photoemission

    Directory of Open Access Journals (Sweden)

    Dong-Wook Lee

    2010-10-01

    Full Text Available Angle resolved photoemission spectroscopy (ARPES is a powerful tool to investigate electronic structures in solids and has been widely used in studying various materials. The electronic structure information by ARPES is obtained in the momentum space. However, in the case of one-dimensional system, we here show that we extract the real space information from ARPES data taken over multiple Brillouin zones (BZs. Intensities in the multiple BZs are proportional to the photoemission matrix element which contains information on the coefficient of the Bloch wave function. It is shown that the Bloch wave function coefficients can be extracted from ARPES data, which allows us to construct the real space wave function. As a test, we use ARPES data from proto-typical one-dimensional system SrCuO2 and construct the real space wave function.

  1. Angle-resolved photoemission studies of the CdTe(110) surface

    Science.gov (United States)

    Qu, H.; Kanski, J.; Nilsson, P. O.; Karlsson, U. O.

    1991-06-01

    The electronic structure of the CdTe(110) surface has been studied with angle-resolved photoelectron spectroscopy using synchrotron radiation. An empirical tight-binding linar combination of atomic orbitals band structure has been derived, based on normal-emission spectra. Several, previously unreported, surface-related states have been observed in off-normal emission, and their dispersions have been mapped along symmetry directions of the surface Brillouin zone.

  2. Angle-Resolved Photoemission of Solvated Electrons in Sodium-Doped Clusters

    CERN Document Server

    West, Adam H C; Luckhaus, David; Saak, Clara-Magdalena; Doppelbauer, Maximilian; Signorell, Ruth

    2015-01-01

    Angle-resolved photoelectron spectroscopy of the unpaired electron in sodium-doped water, methanol, ammonia, and dimethyl ether clusters is presented. The experimental observations and the complementary calculations are consistent with surface electrons for the cluster size range studied. Evidence against internally solvated electrons is provided by the photoelectron angular distribution. The trends in the ionization energies seem mainly determined by the degree of hydrogen bonding in the solvent and the solvation of the ion core. The onset ionization energies of water and methanol clusters do not level off at small cluster sizes, but decrease slightly with increasing cluster size.

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

    Science.gov (United States)

    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.

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

    International Nuclear Information System (INIS)

    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

  5. The orbital structure of {pi}-conjugated organic molecules on metal surfaces probed by angle-resolved photoemission

    Energy Technology Data Exchange (ETDEWEB)

    Ziroff, Johannes; Wiessner, Michael; Forster, Frank; Schoell, Achim [Universitaet Wuerzburg, Experimentelle Physik VII, D-97074 Wuerzburg (Germany); Puschnig, Peter [University of Leoben, Chair of Atomistic Modelling and Design of Materials, A-8700 Leoben (Austria); Reinert, Friedrich [Universitaet Wuerzburg, Experimentelle Physik VII, D-97074 Wuerzburg (Germany); FZ Karlsruhe, Gemeinschaftslabor fuer Nanoanalytik, D-76021 Karlsruhe (Germany)

    2010-07-01

    We present angle resolved photoemission spectra of monolayers of {pi}-conjugated molecules adsorbed on single-crystalline metal surfaces. Comparing the experimental k-dependant intensity distribution of the molecular states to DFT calculations for the free molecule allows to detect sophisticated modifications of the molecular orbitals at the interface. In case of the single-domain system PTCDA on Ag(110) the 2D emission pattern confirms that the now occupied interface state is mainly derived from the former LUMO-orbital. Moreover, a clear contribution of metal states is evident from additional intensity in normal emission. In the contrary, the structure of the molecular HOMO changes only slightly upon chemisorption on Ag surfaces. Additional data on other planar {pi}-conjugated organic molecules such as coronene or NTCDA demonstrates the potential of this approach in analysing the interaction at metal-organic interfaces in great detail.

  6. Valence Electronic Structure of Oxygen-Modified α-Mo2C(0001) Surface:. Angle-Resolved Photoemission Study

    Science.gov (United States)

    Kato, M.; Ozawa, K.; Sato, T.; Edamoto, K.

    Adsorption of oxygen on α-Mo2C(0001) is investigated with Auger electron spectroscopy (AES), low-energy electron diffraction (LEED) and angle-resolved photoemission spectroscopy (ARPES) utilizing synchrotron radiation. It is found that C KLL Auger peak intensity does not change during O2 exposure, indicating that the depletion of C atoms does not proceed. It is deduced from ARPES and LEED results that adsorbed oxygen atoms from a well-ordered (1 × 1) lattice on the α-Mo2C(0001) surface. The ARPES study shows that oxygen adsorption induces a peculiar state around Fermi level (EF). Off-normal-emission measurements prove that the state is a half-filled metallic state.

  7. One-dimensional electron system of Au/Ge(001) revealed by angle-resolved photoemission

    Energy Technology Data Exchange (ETDEWEB)

    Meyer, Sebastian; Schaefer, Joerg; Blumenstein, Christian; Claessen, Ralph [Experimentelle Physik 4, Universitaet Wuerzburg, 97074 Wuerzburg (Germany); Bostwick, Aaron; Rotenberg, Eli [Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley 94720, California (United States)

    2010-07-01

    Self-organized atomic nanowires of noble metals on semiconductor surfaces are characterized by strict spatial separation and a high degree of charge confinement. The ultimate width of single-atom dimension seems to be reached with gold chains on Ge(001).Thus they might offer the possibility to observe exotic properties, like a charge density wave (CDW), or, alternatively, a Luttinger liquid phase. Insight is gained by angle-resolved photoelectron spectroscopy (ARPES). We find that two shallow electron pockets disperse along the wire direction within the surface Brillouin zone, while a dispersion perpendicular to the wires is absent. This is confirmed by mapping the full Fermi surface (FS) topology, where sheets are found to be perfectly 1D without any interchain coupling. This is indicative of the virtual absence of coupling to the second dimension. Interestingly, while various nesting conditions are offered from the FS topology, no band back-folding from a CDW superstructure or energy gap opening is found, which opens a pathway for non-Fermi liquid physics. Thus the system emerges as a prototypical 1D electron system.

  8. Angle-resolved photoemission spectroscopy of band tails in lightly doped cuprates

    OpenAIRE

    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.

  9. Momentum-resolved electronic structure at a buried interface from soft X-ray standing-wave angle-resolved photoemission

    NARCIS (Netherlands)

    Gray, A.X.; Minar, J.; Plucinski, L.; Huijben, M.; Bostwick, A.; Rotenberg, E.; Yang, S.-H.; Braun, J.; Winkelmann, A.; Conti, G.; Eiteneer, D.; Rattanachata, A.; Greer, A.A.; Ciston, J.; Ophus, C.; Rijnders, A.J.H.M.; Blank, D.H.A.; Doennig, D.; Pentcheva, R.; Kortright, J.B.; Schneider, C.M.; Ebert, H.; Fadley, C.S.

    2013-01-01

    Angle-resolved photoemission spectroscopy (ARPES) is a powerful technique for the study of electronic structure, but it lacks a direct ability to study buried interfaces between two materials. We address this limitation by combining ARPES with soft X-ray standing-wave (SW) excitation (SWARPES), in w

  10. Angle-resolved inverse photoemission of the H-etched 6H-SiC(0001) surface

    Energy Technology Data Exchange (ETDEWEB)

    Aghdassi, Nabi; Ostendorf, Ralf; Zacharias, Helmut [Physikalisches Institut, Westfaelische Wilhelms-Universitaet Muenster (Germany)

    2009-07-01

    The etching of 6H-SiC(0001) substrates in molecular hydrogen at elevated temperatures leads to an ordered silicate adlayer as it is confirmed by LEED and AES. LEED patterns clearly feature a ({radical}(3) x {radical}(3))R30 periodicity while AES spectra are evidence for the presence of Si-O bonds. The generated surfaces appear to be fully passivated and therefore stable in ambient air. After cleaning the samples by heating in UHV up to temperatures around 750 C angle-resolved inverse photoemission is performed on the SiO{sub 2}/SiC interface. The IPE spectra reveal five features above the Fermi level around 0.5 eV, 1.2 eV, 2.3 eV, 3.5 eV and 5.5 eV, respectively, which show only a weak dispersion along the {gamma} - M and {gamma} - K directions of the (1 x 1) surface Brillouin zone.

  11. Depth- and momentum- resolved electronic structure at buried oxide interfaces from standing-wave angle-resolved photoemission

    Science.gov (United States)

    Fadley, Charles

    2015-03-01

    It is clear that interfaces in complex oxide heterostructures often represent emergent materials that possess surprising properties not associated with the parent oxides, such as two-dimensional electron gases (2DEGs), superconductivity, and magnetism. A detailed knowledge of the composition, atomic structure, and electronic structure through such interfaces is thus critical. Photomission (PES) and angle-resolved photoemission (ARPES) represent techniques of choice for such studies, but have certain limitations in being too surface sensitive and in not being able to focus specifically on buried interfaces or heterostructure layers. In this talk, I will discuss combining two newer elements of PES/ARPES to deal with this challenge: - the use of soft x-rays in the ca. few hundred-to-2000 eV regime, or even into the true hard x-ray regime, to probe more deeply into the structure, and - tailoring of the x-ray intensity profile into a strong standing wave (SW) through reflection from a multilayer heterostructure to provide much enhanced depth resolution. The relative advantages of soft/hard x-ray PES and ARPES and their complementarity to conventional VUV ARPES in the ca. 5-150 eV regime will be considered. As illustrative examples, by combining SW-PES and SW-ARPES, it has been possible to measure for the first time the detailed concentration profiles and momentum-resolved electronic structure at the SrTiO3/La0.67Sr0.33MnO3 interface and to directly measure the depth profile of the 2DEG at SrTiO3/GdTiO3 interfaces. Future directions for such measurements will also be discussed. Supported by US DOE Contract No. DE-AC02-05CH11231, ARO-MURI Grant W911-NF-09-1-0398, and the PALM-APTCOM Project (France).

  12. Tetragonal and collapsed-tetragonal phases of CaFe2As2 : A view from angle-resolved photoemission and dynamical mean-field theory

    Science.gov (United States)

    van Roekeghem, Ambroise; Richard, Pierre; Shi, Xun; Wu, Shangfei; Zeng, Lingkun; Saparov, Bayrammurad; Ohtsubo, Yoshiyuki; Qian, Tian; Sefat, Athena S.; Biermann, Silke; Ding, Hong

    2016-06-01

    We present a study of the tetragonal to collapsed-tetragonal transition of CaFe2As2 using angle-resolved photoemission spectroscopy and dynamical mean field theory-based electronic structure calculations. We observe that the collapsed-tetragonal phase exhibits reduced correlations and a higher coherence temperature due to the stronger Fe-As hybridization. Furthermore, a comparison of measured photoemission spectra and theoretical spectral functions shows that momentum-dependent corrections to the density functional band structure are essential for the description of low-energy quasiparticle dispersions. We introduce those using the recently proposed combined "screened exchange + dynamical mean field theory" scheme.

  13. Rapid high-resolution spin- and angle-resolved photoemission spectroscopy with pulsed laser source and time-of-flight spectrometer

    Energy Technology Data Exchange (ETDEWEB)

    Gotlieb, K. [Graduate Group in Applied Science and Technology, University of California, Berkeley, California 94720 (United States); Hussain, Z.; Bostwick, A.; Jozwiak, C. [Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Lanzara, A. [Department of Physics, University of California, Berkeley, California 94720, USA and Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

    2013-09-15

    A high-efficiency spin- and angle-resolved photoemission spectroscopy (spin-ARPES) spectrometer is coupled with a laboratory-based laser for rapid high-resolution measurements. The spectrometer combines time-of-flight (TOF) energy measurements with low-energy exchange scattering spin polarimetry for high detection efficiencies. Samples are irradiated with fourth harmonic photons generated from a cavity-dumped Ti:sapphire laser that provides high photon flux in a narrow bandwidth, with a pulse timing structure ideally matched to the needs of the TOF spectrometer. The overall efficiency of the combined system results in near-E{sub F} spin-resolved ARPES measurements with an unprecedented combination of energy resolution and acquisition speed. This allows high-resolution spin measurements with a large number of data points spanning multiple dimensions of interest (energy, momentum, photon polarization, etc.) and thus enables experiments not otherwise possible. The system is demonstrated with spin-resolved energy and momentum mapping of the L-gap Au(111) surface states, a prototypical Rashba system. The successful integration of the spectrometer with the pulsed laser system demonstrates its potential for simultaneous spin- and time-resolved ARPES with pump-probe based measurements.

  14. Rapid high-resolution spin- and angle-resolved photoemission spectroscopy with pulsed laser source and time-of-flight spectrometer

    Science.gov (United States)

    Gotlieb, K.; Hussain, Z.; Bostwick, A.; Lanzara, A.; Jozwiak, C.

    2013-09-01

    A high-efficiency spin- and angle-resolved photoemission spectroscopy (spin-ARPES) spectrometer is coupled with a laboratory-based laser for rapid high-resolution measurements. The spectrometer combines time-of-flight (TOF) energy measurements with low-energy exchange scattering spin polarimetry for high detection efficiencies. Samples are irradiated with fourth harmonic photons generated from a cavity-dumped Ti:sapphire laser that provides high photon flux in a narrow bandwidth, with a pulse timing structure ideally matched to the needs of the TOF spectrometer. The overall efficiency of the combined system results in near-EF spin-resolved ARPES measurements with an unprecedented combination of energy resolution and acquisition speed. This allows high-resolution spin measurements with a large number of data points spanning multiple dimensions of interest (energy, momentum, photon polarization, etc.) and thus enables experiments not otherwise possible. The system is demonstrated with spin-resolved energy and momentum mapping of the L-gap Au(111) surface states, a prototypical Rashba system. The successful integration of the spectrometer with the pulsed laser system demonstrates its potential for simultaneous spin- and time-resolved ARPES with pump-probe based measurements.

  15. Electronic structure studies of ferro-pnictide superconductors and their parent compounds using angle-resolved photoemission spectroscopy (ARPES)

    Energy Technology Data Exchange (ETDEWEB)

    Setti, Thirupathaiah

    2011-07-14

    The discovery of high temperature superconductivity in the iron pnictide compound LaO{sub 1-x}F{sub x}FeAs with T{sub c} = 26 K as created enormous interest in the high-T{sub c} superconductor community. So far, four prototypes of crystal structures have been found in the Fe-pnictide family. All four show a structural deformation followed or accompanied by a magnetic transition from a high temperature paramagnetic conductor to a low temperature antiferromagnetic metal whose transition temperature T{sub N} varies between the compounds. Charge carrier doping, isovalent substitution of the As atoms or the application of pressure suppresses the antiferromagnetic spin density wave (SDW) order and leads to a superconducting phase. More recently high Tc superconductivity has been also detected in iron chalchogenides with similar normal state properties. Since superconductivity is instability of the normal state, the study of normal state electronic structure in comparison with superconducting state could reveal important information on the pairing mechanism. Therefore, it is most important to study the electronic structure of these new superconductors, i.e., to determine Fermi surfaces and band dispersions near the Fermi level at the high symmetry points in order to obtain a microscopic understanding of the superconducting properties. Using the technique angle-resolved photoemission spectroscopy (ARPES) one measures the electrons ejected from a sample when photons impinge on it. In this way one can map the Fermi surface which provides useful information regarding the physics behind the Fermi surface topology of high T{sub c} superconductors. Furthermore, this technique provides information on the band dispersion, the orbital character of the bands, the effective mass, the coupling to bosonic excitations, and the superconducting gap. This emphasizes the importance of studying the electronic structure of the newly discovered Fe-pnictides using ARPES. In this work we have

  16. Probing the momentum-dependent response of the charge density wave phase in TbTe3 by ultrafast time- and angle-resolved photoemission

    International Nuclear Information System (INIS)

    Charge density wave (CDW) systems such as TbTe3 offer fascinating options for studying the correlation of electrons and the lattice. We investigate the ultrafast response of the charge density wave (CDW) phase in TbTe3 after femtosecond IR excitation using time- and angle-resolved photoemission. The time-dependent photoemission intensity at the Fermi level yields a characteristic time for the closing of the CDW bandgap. With increasing laser fluence the bandgap closes faster, pointing to an increasing slope of the excited potential energy surface. As function of electron momentum the amplitude of the response increases strongly at the position of the Fermi wave vector kF. These results vividly demonstrate that the CDW system is most susceptible to electronic excitations near kF and that these electronic perturbations drive collective excitations of the coupled electron-lattice system.

  17. Application of a time-of-flight spectrometer with delay-line detector for time- and angle-resolved two-photon photoemission

    Energy Technology Data Exchange (ETDEWEB)

    Damm, A. [Fachbereich Physik und Zentrum für Materialwissenschaften, Philipps-Universität, D-35032 Marburg (Germany); Güdde, J., E-mail: Jens.Guedde@physik.uni-marburg.de [Fachbereich Physik und Zentrum für Materialwissenschaften, Philipps-Universität, D-35032 Marburg (Germany); Feulner, P. [Physikdepartment E20, Technische Universität München, 85747 Garching (Germany); Czasch, A.; Jagutzki, O.; Schmidt-Böcking, H. [Institut für Kernphysik, Goethe-Universität, D-60438 Frankfurt am Main (Germany); RoentDek Handels GmbH, D-65779 Kelkheim (Germany); Höfer, U. [Fachbereich Physik und Zentrum für Materialwissenschaften, Philipps-Universität, D-35032 Marburg (Germany)

    2015-07-15

    Highlights: • The performance of a 2D time-of-flight electron spectrometer is demonstrated. • We discuss its application for time- and angle-resolved two-photon photoemission. • The decay dynamics of the first image-potential state on Cu(1 0 0) is investigated. • We find an azimuthal anisotropy of the decay rate with one-fold symmetry. • The anisotropy is attributed to residual steps on the nominal flat surface. - Abstract: We describe the design and operation of a time-of-flight electron spectrometer which is capable of simultaneously acquiring the energy and momentum distribution of low-energy photoelectrons in two dimensions parallel to the surface. We discuss its capabilities and limitations in particular for time- and angle-resolved two-photon photoemission (2PPE) with pulsed lasers. The performance of the spectrometer is demonstrated by presenting 2PPE data on the momentum-dependent electron dynamics of the first (n = 1) image-potential state on Cu(0 0 1). The data reveal a weak but systematic dependence of the decay dynamics on sample azimuth with one-fold symmetry which we attribute to a small residual step density on the nominal flat surface.

  18. Angle-resolved photoemission spectroscopy study of adsorption process and electronic structure of silver on ZnO(1010).

    Science.gov (United States)

    Ozawa, K; Sato, T; Kato, M; Edamoto, K; Aiura, Y

    2005-08-01

    The adsorption process and valence band structure of Ag on ZnO(1010) have been investigated by angle-resolved photoelectron spectroscopy utilizing synchrotron radiation. The coverage-dependent measurements of the Ag 4d band structure reveal that the Ag bands with a dispersing feature are formed even at low coverages and that the basic structure of the bands is essentially the same throughout the submonolayer region. These results indicate that the Ag atoms aggregate to form islands with an atomically ordered structure from the low coverages. Upon annealing the Ag-covered surface at 900 K, the Ag 4d band undergoes only a minor change, suggesting that the ordered structure within the Ag islands is persistent against mild annealing. From the dispersive feature of the Ag 4d states, we propose that the atomic structure has locally rectangular symmetry with a good lattice matching with the ZnO(1010) surface.

  19. Electronic and geometric structure of the PTCDA/Ag(110) interface probed by angle-resolved photoemission

    Science.gov (United States)

    Wießner, M.; Hauschild, D.; Schöll, A.; Reinert, F.; Feyer, V.; Winkler, K.; Krömker, B.

    2012-07-01

    The properties of molecular films are determined by the geometric structure of the first layers near the interface. These are in contact with the substrate and feel the effect of the interfacial bonding, which particularly, for metal substrates, can be substantial. For the model system 3,4,9,10-perylenetetracarboxylic dianhydride on Ag(110), the geometric structure of the first monolayer can be modified by preparation parameters. This leads to significant differences in the electronic structure of the first layer. Here, we show that, by combining angle-resolved photoelectron spectroscopy with low-energy electron diffraction, we cannot only determine the electronic structure of the interfacial layer and the unit cell of the adsorbate superstructure, but also the arrangement of the molecules in the unit cell. Moreover, in bilayer films, we can distinguish the first from the second layer and, thus, study the formation of the second layer and its influence on the buried interface.

  20. Anomalous asymmetry in the Fermi surface of the high-temperature superconductor YBa2Cu4O8 revealed by angle-resolved photoemission spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Kondo, Takeshi; Khasanov, R.; Sassa, Y.; Bendounan, A.; Paihes, S.; Chang, J.; Mesot, J.; Keller, H.; Zhigadlo, N.D.; Shi, M.; Bukowski, Z.; Karpinski, J.; Kaminski, A.

    2009-09-15

    We use microprobe angle-resolved photoemission spectroscopy to study the Fermi surface and band dispersion of the CuO{sub 2} planes in the high-temperature superconductor, YBa{sub 2}Cu{sub 4}O{sub 8}. We find a strong in-plane asymmetry of the electronic structure between directions along a and b axes. The saddle point of the antibonding band lies at a significantly higher energy in the a direction ({pi},0) than the b direction (0,{pi}), whereas the bonding band displays the opposite behavior. We demonstrate that the abnormal band shape is due to a strong asymmetry of the bilayer band splitting, likely caused by a nontrivial hybridization between the planes and chains. This asymmetry has an important implication for interpreting key properties of the Y-Ba-Cu-O family, especially the superconducting gap, transport, and results of inelastic neutron scattering.

  1. Angle-resolved photoemission spectroscopy with 9-eV photon-energy pulses generated in a gas-filled hollow-core photonic crystal fiber

    International Nuclear Information System (INIS)

    A recently developed source of ultraviolet radiation, based on optical soliton propagation in a gas-filled hollow-core photonic crystal fiber, is applied here to angle-resolved photoemission spectroscopy (ARPES). Near-infrared femtosecond pulses of only few μJ energy generate vacuum ultraviolet radiation between 5.5 and 9 eV inside the gas-filled fiber. These pulses are used to measure the band structure of the topological insulator Bi2Se3 with a signal to noise ratio comparable to that obtained with high order harmonics from a gas jet. The two-order-of-magnitude gain in efficiency promises time-resolved ARPES measurements at repetition rates of hundreds of kHz or even MHz, with photon energies that cover the first Brillouin zone of most materials

  2. Angle-resolved photoemission spectroscopy with 9-eV photon-energy pulses generated in a gas-filled hollow-core photonic crystal fiber

    CERN Document Server

    Bromberger, H; Belli, F; Liu, H; Calegari, F; Chavez-Cervantes, M; Li, M T; Lin, C T; Abdolvand, A; Russell, P St J; Cavalleri, A; Travers, J C; Gierz, I

    2015-01-01

    A recently developed source of ultraviolet radiation, based on optical soliton propagation in a gas-filled hollow-core photonic crystal fiber, is applied here to angle-resolved photoemission spectroscopy (ARPES). Near-infrared femtosecond pulses of only few {\\mu}J energy generate vacuum ultraviolet (VUV) radiation between 5.5 and 9 eV inside the gas-filled fiber. These pulses are used to measure the band structure of the topological insulator Bi2Se3 with a signal to noise ratio comparable to that obtained with high order harmonics from a gas jet. The two-order-of-magnitude gain in efficiency promises time-resolved ARPES measurements at repetition rates of hundreds of kHz or even MHz, with photon energies that cover the first Brillouin zone of most materials.

  3. Gap anisotropy in Bi2Sr2CaCu2O8+δ by ultrahigh-resolution angle-resolved photoemission

    International Nuclear Information System (INIS)

    Ultrahigh-resolution (ΔE up to 10 meV) angle-resolved photoemission spectroscopy on single crystals of Bi2Sr2CaCu2O8+δ (Bi-2212) show a highly anisotropic superconducting energy gap: the gap is minimized, with a value close to zero, along the Γ-X and Γ-Y symmetry directions, while a large gap (Δ=22 meV) is observed along the Γ-bar M (Cu-O bond) direction. However, the observation of gap anisotropy may depend on sample conditions; in a few cases the gap becomes more isotropic. A dip in the spectral weight at 65 meV below the Fermi energy is clearly observed only in samples with an anisotropic gap

  4. Low-temperature (1 K) angle-resolved photoemission investigation of the predicted topological Kondo insulator behavior of SmB6

    Science.gov (United States)

    Rader, Oliver; Hlawenka, Peter; Rienks, Emile; Siemensmeyer, Konrad; Weschke, Eugen; Varykhalov, Andrei; Shitsevalova, Natalya; Gabani, Slavomir; Flachbart, Karol

    2015-03-01

    The system SmB6 is known for its unusual resistivity which increases exponentially with decreasing temperature and saturates below 3 K. This has recently been attributed to topological-Kondo-insulator behavior where a topological surface state is created by Sm 4 f - 5 d hybridization and is responsible for the transport. Local-density-approximation + Gutzwiller calculations of the (100) surface predict the appearance of three Dirac cones in the surface Brillouin zone. We perform angle-resolved photoemission at temperatures below 1 K and reveal surface states at Γ and X . Bulk conduction band states near X appear at higher temperature. These findings will be discussed in detail vis-á-vis the theoretical and experimental literature.

  5. Angle-resolved photoemission spectroscopy with 9-eV photon-energy pulses generated in a gas-filled hollow-core photonic crystal fiber

    Energy Technology Data Exchange (ETDEWEB)

    Bromberger, H., E-mail: Hubertus.Bromberger@mpsd.mpg.de; Liu, H.; Chávez-Cervantes, M.; Gierz, I. [Max Planck Institute for the Structure and Dynamics of Matter, Luruper Chaussee 149, 22761 Hamburg (Germany); Ermolov, A.; Belli, F.; Abdolvand, A.; Russell, P. St. J.; Travers, J. C. [Max Planck Institute for the Science of Light, Günther-Scharowsky-Str. 1, 91058 Erlangen (Germany); Calegari, F. [Max Planck Institute for the Structure and Dynamics of Matter, Luruper Chaussee 149, 22761 Hamburg (Germany); Institute for Photonics and Nanotechnologies, IFN-CNR, Piazza Leonardo da Vinci 32, I-20133 Milano (Italy); Li, M. T.; Lin, C. T. [Max Planck Institute for Solid State Research, Heisenbergstr. 1, 70569 Stuttgart (Germany); Cavalleri, A. [Max Planck Institute for the Structure and Dynamics of Matter, Luruper Chaussee 149, 22761 Hamburg (Germany); Clarendon Laboratory, Department of Physics, University of Oxford, Parks Rd. Oxford OX1 3PU (United Kingdom)

    2015-08-31

    A recently developed source of ultraviolet radiation, based on optical soliton propagation in a gas-filled hollow-core photonic crystal fiber, is applied here to angle-resolved photoemission spectroscopy (ARPES). Near-infrared femtosecond pulses of only few μJ energy generate vacuum ultraviolet radiation between 5.5 and 9 eV inside the gas-filled fiber. These pulses are used to measure the band structure of the topological insulator Bi{sub 2}Se{sub 3} with a signal to noise ratio comparable to that obtained with high order harmonics from a gas jet. The two-order-of-magnitude gain in efficiency promises time-resolved ARPES measurements at repetition rates of hundreds of kHz or even MHz, with photon energies that cover the first Brillouin zone of most materials.

  6. Electronic structure, Dirac points and Fermi arc surface states in three-dimensional Dirac semimetal Na3Bi from angle-resolved photoemission spectroscopy

    Science.gov (United States)

    Aiji, Liang; Chaoyu, Chen; Zhijun, Wang; Youguo, Shi; Ya, Feng; Hemian, Yi; Zhuojin, Xie; Shaolong, He; Junfeng, He; Yingying, Peng; Yan, Liu; Defa, Liu; Cheng, Hu; Lin, Zhao; Guodong, Liu; Xiaoli, Dong; Jun, Zhang; M, Nakatake; H, Iwasawa; K, Shimada; M, Arita; H, Namatame; M, Taniguchi; Zuyan, Xu; Chuangtian, Chen; Hongming, Weng; Xi, Dai; Zhong, Fang; Xing-Jiang, Zhou

    2016-07-01

    The three-dimensional (3D) Dirac semimetals have linearly dispersive 3D Dirac nodes where the conduction band and valence band are connected. They have isolated 3D Dirac nodes in the whole Brillouin zone and can be viewed as a 3D counterpart of graphene. Recent theoretical calculations and experimental results indicate that the 3D Dirac semimetal state can be realized in a simple stoichiometric compound A 3Bi (A = Na, K, Rb). Here we report comprehensive high-resolution angle-resolved photoemission (ARPES) measurements on the two cleaved surfaces, (001) and (100), of Na3Bi. On the (001) surface, by comparison with theoretical calculations, we provide a proper assignment of the observed bands, and in particular, pinpoint the band that is responsible for the formation of the three-dimensional Dirac cones. We observe clear evidence of 3D Dirac cones in the three-dimensional momentum space by directly measuring on the k x –k y plane and by varying the photon energy to get access to different out-of-plane k z s. In addition, we reveal new features around the Brillouin zone corners that may be related with surface reconstruction. On the (100) surface, our ARPES measurements over a large momentum space raise an issue on the selection of the basic Brillouin zone in the (100) plane. We directly observe two isolated 3D Dirac nodes on the (100) surface. We observe the signature of the Fermi-arc surface states connecting the two 3D Dirac nodes that extend to a binding energy of ∼150 meV before merging into the bulk band. Our observations constitute strong evidence on the existence of the Dirac semimetal state in Na3Bi that are consistent with previous theoretical and experimental work. In addition, our results provide new information to clarify on the nature of the band that forms the 3D Dirac cones, on the possible formation of surface reconstruction of the (001) surface, and on the issue of basic Brillouin zone selection for the (100) surface. Project supported by the

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

    NARCIS (Netherlands)

    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

  8. Extracting the spectral function of the cuprates by a full two-dimensional analysis: Angle-resolved photoemission spectra of Bi2Sr2CuO6

    Energy Technology Data Exchange (ETDEWEB)

    Meevasana, W.

    2010-04-30

    Recently, angle-resolved photoemission spectroscopy (ARPES) has revealed a dispersion anomaly at high binding energy near 0.3-0.5 eV in various families of the high-temperature superconductors. For further studies of this anomaly we present a new two-dimensional fitting-scheme and apply it to high-statistics ARPES data of the strongly-overdoped Bi{sub 2}Sr{sub 2}CuO{sub 6} cuprate superconductor. The procedure allows us to extract the self-energy in an extended energy and momentum range. It is found that the spectral function of Bi{sub 2}Sr{sub 2}CuO{sub 6} can be parameterized using a small set of tight-binding parameters and a weakly-momentum-dependent self-energy up to 0.7 eV in binding energy and over the entire first Brillouin zone. Moreover the analysis gives an estimate of the momentum dependence of the matrix element, a quantity, which is often neglected in ARPES analyses.

  9. Fermi surface of MoO2 studied by angle-resolved photoemission spectroscopy, de Haas-van Alphen measurements, and electronic structure calculations

    Science.gov (United States)

    Moosburger-Will, Judith; Kündel, Jörg; Klemm, Matthias; Horn, Siegfried; Hofmann, Philip; Schwingenschlögl, Udo; Eyert, Volker

    2009-03-01

    A comprehensive study of the electronic properties of monoclinic MoO2 from both an experimental and a theoretical point of view is presented. We focus on the investigation of the Fermi body and the band structure using angle-resolved photoemission spectroscopy, de Haas-van Alphen measurements, and electronic structure calculations. For the latter, the full-potential augmented spherical wave method has been applied. Very good agreement between the experimental and theoretical results is found. In particular, all Fermi surface sheets are correctly identified by all three approaches. Previous controversies concerning additional holelike surfaces centered around the Z and B points could be resolved; these surfaces were artifacts of the atomic-sphere approximation used in the old calculations. Our results underline the importance of electronic structure calculations for the understanding of MoO2 and the neighboring rutile-type early transition-metal dioxides. This includes the low-temperature insulating phases of VO2 and NbO2 , which have crystal structures very similar to that of molybdenum dioxide and display the well-known prominent metal-insulator transitions.

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  11. Orbital character and electron correlation effects on two- and three-dimensional Fermi surfaces in KFe2As2 revealed by angle-resolved photoemission spectroscopy

    Directory of Open Access Journals (Sweden)

    Teppei eYoshida

    2014-04-01

    Full Text Available We have investigated orbital character and electron correlation effects on Fermi surfaces in the hole-overdoped iron pnictide superconductor KFe2As2, which shows a low Tc of ~4 K, by angle-resolved photoemission spectroscopy. From the polarization-dependence of the ARPES spectra, we have determined the orbital character of each Fermi surface. Electron mass renormalization of each band is quantitatively consistent with de Haas-van Alphen results. The outer beta and middle zeta Fermi surfaces show large renormalization factor of m*/mb ~6-7, while the inner Fermi surface has a smaller factor m*/mb ~2. Middle hole Fermi surface zeta has strong three-dimensionality compared to other Fermi surfaces, indicating the d3z2-r2 orbital character, which may be related to the octet-line nodes recently observed by laser ARPES. The observed orbital-dependent mass renormalization would give constraints on the pairing mechanism with line nodes of this system.

  12. Electronic structure as a function of doping in YBa2Cu3Ox(6.2≤x≤6.9) studied by angle-resolved photoemission

    International Nuclear Information System (INIS)

    We report angle-resolved photoemission studies on YBa2Cu3Ox with oxygen stoichiometry varied in the range 6.2≤x≤6.9. The distinct 1-eV peak, observed with hν=24 eV at the X(Y) point(s), shifts monotonically toward higher binding energies (as much as 0.20 eV) as oxygen stoichiometry is reduced from x=6.9 to 6.3. The direction and the magnitude of the shift are consistent with a simple rigid-band filling picture. However, another distinct peak observed at the X(Y) point(s), but with energy very close to EF, remains at nearly the same energy when the oxygen stoichiometry is varied from 6.9 to 6.4. This behavior is not consistent with a rigid-band picture. The intensities of the 1-eV peak and the peak at EF are significantly attenuated when the material becomes insulating

  13. Quantum Transport and Nano Angle-resolved Photoemission Spectroscopy on the Topological Surface States of Single Sb2Te3 Nanowires

    Science.gov (United States)

    Arango, Yulieth C.; Huang, Liubing; Chen, Chaoyu; Avila, Jose; Asensio, Maria C.; Grützmacher, Detlev; Lüth, Hans; Lu, Jia Grace; Schäpers, Thomas

    2016-09-01

    We report on low-temperature transport and electronic band structure of p-type Sb2Te3 nanowires, grown by chemical vapor deposition. Magnetoresistance measurements unravel quantum interference phenomena, which depend on the cross-sectional dimensions of the nanowires. The observation of periodic Aharonov-Bohm-type oscillations is attributed to transport in topologically protected surface states in the Sb2Te3 nanowires. The study of universal conductance fluctuations demonstrates coherent transport along the Aharonov-Bohm paths encircling the rectangular cross-section of the nanowires. We use nanoscale angle-resolved photoemission spectroscopy on single nanowires (nano-ARPES) to provide direct experimental evidence on the nontrivial topological character of those surface states. The compiled study of the bandstructure and the magnetotransport response unambiguosly points out the presence of topologically protected surface states in the nanowires and their substantial contribution to the quantum transport effects, as well as the hole doping and Fermi velocity among other key issues. The results are consistent with the theoretical description of quantum transport in intrinsically doped quasi-one-dimensional topological insulator nanowires.

  14. Si(111)-sq root 21 x sq root 21 -(Ag+Cs) surface studied by scanning tunneling microscopy and angle-resolved photoemission spectroscopy

    CERN Document Server

    Liu, C; Morikawa, H; Okino, H; Hasegawa, S; Okuda, T; Kinoshita, T

    2003-01-01

    Scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES) were used to study the atomic and electronic structures of the Si(111)-sq root 21 x sq root 21-(Ag + Cs) surface (sq root 21-Cs in short), which was induced by depositing caesium atoms on the Si(111)-sq root 3 x sq root 3-Ag surface at room temperature (RT). Compared with previously reported STM images of noble-metal induced sq root 21 x sq root 21 phases including the Si(111)-sq root 21 x sq root 21-(Ag+Ag) and Si(111)-sq root 21 x sq root 21-(Ag+Au) surfaces (sq root 21-Ag and sq root 21-Au, respectively), the sq root 21-Cs surface displayed quite different features in STM images. The ARPES data of the sq root 21-Cs surface revealed an intrinsic dispersive surface-state band, together with a non-dispersive one near the Fermi level, which was also different from those of the sq root 21-Ag and sq root 21-Au surfaces. These results strongly suggest different atomic arrangements between Cs- and noble-metal induced sq root ...

  15. Electronic structure of transition metal dichalcogenides PdTe2 and Cu0.05PdTe2 superconductors obtained by angle-resolved photoemission spectroscopy

    Science.gov (United States)

    Liu, Yan; Zhao, Jian-Zhou; Yu, Li; Lin, Cheng-Tian; Hu, Cheng; Liu, De-Fa; Peng, Ying-Ying; Xie, Zhuo-Jin; He, Jun-Feng; Chen, Chao-Yu; Feng, Ya; Yi, He-Mian; Liu, Xu; Zhao, Lin; He, Shao-Long; Liu, Guo-Dong; Dong, Xiao-Li; Zhang, Jun; Chen, Chuang-Tian; Xu, Zu-Yan; Weng, Hong-Ming; Dai, Xi; Fang, Zhong; Zhou, Xing-Jiang

    2015-06-01

    The layered transition metal chalcogenides have been a fertile land in solid state physics for many decades. Various MX2-type transition metal dichalcogenides, such as WTe2, IrTe2, and MoS2, have triggered great attention recently, either for the discovery of novel phenomena or some extreme or exotic physical properties, or for their potential applications. PdTe2 is a superconductor in the class of transition metal dichalcogenides, and superconductivity is enhanced in its Cu-intercalated form, Cu0.05PdTe2. It is important to study the electronic structures of PdTe2 and its intercalated form in order to explore for new phenomena and physical properties and understand the related superconductivity enhancement mechanism. Here we report systematic high resolution angle-resolved photoemission (ARPES) studies on PdTe2 and Cu0.05PdTe2 single crystals, combined with the band structure calculations. We present in detail for the first time the complex multi-band Fermi surface topology and densely-arranged band structure of these compounds. By carefully examining the electronic structures of the two systems, we find that Cu-intercalation in PdTe2 results in electron-doping, which causes the band structure to shift downwards by nearly 16 meV in Cu0.05PdTe2. Our results lay a foundation for further exploration and investigation on PdTe2 and related superconductors. Project supported by the National Natural Science Foundation of China (Grant No. 11190022), the National Basic Research Program of China (Grant Nos. 2011CB921703 and 2011CBA00110), and the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (Grant No. XDB07020300).

  16. Doping Dependence of the $(\\pi,\\pi)$ Shadow Band in La-Based Cuprates Studied by Angle-Resolved Photoemission Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Shen, Z. X.

    2011-08-15

    The ({pi},{pi}) shadow band (SB) in La-based cuprate family (La214) was studied by angle-resolved photoemission spectroscopy (ARPES) over a wide doping range from x = 0.01 to x = 0.25. Unlike the well-studied case of the Bi-based cuprate family, an overall strong, monotonic doping dependence of the SB intensity at the Fermi level (E{sub F}) was observed. In contrast to a previous report for the presence of the SB only close to x = 1/8, we found it exists in a wide doping range, associated with a doping-independent ({pi},{pi}) wave vector but strongly doping-dependent intensity: It is the strongest at x {approx} 0.03 and systematically diminishes as the doping increases until it becomes negligible in the overdoped regime. This SB with the observed doping dependence of intensity can in principle be caused by the antiferromagnetic fluctuations or a particular form of low-temperature orthorhombic lattice distortion known to persist up to x {approx} 0.21 in the system, with both being weakened with increasing doping. However, a detailed binding energy dependent analysis of the SB at x = 0.07 does not appear to support the former interpretation, leaving the latter as a more plausible candidate, despite a challenge in quantitatively linking the doping dependences of the SB intensity and the magnitude of the lattice distortion. Our finding highlights the necessity of a careful and global consideration of the inherent structural complications for correctly understanding the cuprate Fermiology and its microscopic implication.

  17. A flat band at the chemical potential of a Fe1.03Te0.94S0.06 superconductor observed by angle-resolved photoemission spectroscopy.

    Science.gov (United States)

    Starowicz, P; Schwab, H; Goraus, J; Zajdel, P; Forster, F; Rak, J R; Green, M A; Vobornik, I; Reinert, F

    2013-05-15

    The electronic structure of superconducting Fe1.03Te0.94S0.06 has been studied by angle-resolved photoemission spectroscopy (ARPES). Experimental band topography is compared to the calculations using the methods of Korringa-Kohn-Rostoker (KKR) with the coherent potential approximation (CPA) and the linearized augmented plane wave with local orbitals (LAPW+LO) method. The region of the Γ point exhibits two hole pockets and a quasiparticle peak close to the chemical potential (μ) with undetectable dispersion. This flat band with mainly d(z)(2) orbital character is most likely formed by the top of the outer hole pocket or is evidence of a third hole band. It may cover up to 3% of the Brillouin zone volume and should give rise to a Van Hove singularity. Studies performed for various photon energies indicate that at least one of the hole pockets has a two-dimensional character. The apparently nondispersing peak at μ is clearly visible for 40 eV and higher photon energies, due to an effect of the photoionization cross-section rather than band dimensionality. Orbital characters calculated by LAPW+LO for stoichiometric FeTe do not reveal the flat dz(2) band but are in agreement with the experiment for the other dispersions around Γ in Fe1.03Te0.94S0.06.

  18. Angle Resolved Photoemission Spectroscopy Studies of the Mott Insulator to Superconductor Evolution in Ca2-xNaxCuO2Cl2

    Energy Technology Data Exchange (ETDEWEB)

    Shen, Kyle Michael

    2005-09-02

    It is widely believed that many of the exotic physical properties of the high-T{sub c} cuprate superconductors arise from the proximity of these materials to the strongly correlated, antiferromagnetic Mott insulating state. Therefore, one of the fundamental questions in the field of high-temperature superconductivity is to understand the insulator-to-superconductor transition and precisely how the electronic structure of Mott insulator evolves as the first holes are doped into the system. This dissertation presents high-resolution, doping dependent angle-resolved photoemission (ARPES) studies of the cuprate superconductor Ca{sub 2-x}Na{sub x}CuO{sub 2}Cl{sub 2}, spanning from the undoped parent Mott insulator to a high-temperature superconductor with a T{sub c} of 22 K. A phenomenological model is proposed to explain how the spectral lineshape, the quasiparticle band dispersion, and the chemical potential all progress with doping in a logical and self-consistent framework. This model is based on Franck-Condon broadening observed in polaronic systems where strong electron-boson interactions cause the quasiparticle residue, Z, to be vanishingly small. Comparisons of the low-lying states to different electronic states in the valence band strongly suggest that the coupling of the photohole to the lattice (i.e. lattice polaron formation) is the dominant broadening mechanism for the lower Hubbard band states. Combining this polaronic framework with high-resolution ARPES measurements finally provides a resolution to the long-standing controversy over the behavior of the chemical potential in the high-T{sub c} cuprates. This scenario arises from replacing the conventional Fermi liquid quasiparticle interpretation of the features in the Mott insulator by a Franck-Condon model, allowing the reassignment of the position of the quasiparticle pole. As a function of hole doping, the chemical potential shifts smoothly into the valence band while spectral weight is transferred

  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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  20. 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

    International Nuclear Information System (INIS)

    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

  1. Metal-insulator transition and tunable Dirac-cone surface state in the topological insulator TlBi1 -xSbxTe2 studied by angle-resolved photoemission

    Science.gov (United States)

    Trang, Chi Xuan; Wang, Zhiwei; Yamada, Keiko; Souma, Seigo; Sato, Takafumi; Takahashi, Takashi; Segawa, Kouji; Ando, Yoichi

    2016-04-01

    We report a systematic angle-resolved photoemission spectroscopy on topological insulator (TI) TlBi1 -xSbxTe2 which is bulk insulating at 0.5 ≲x ≲0.9 and undergoes a metal-insulator-metal transition with the Sb content x . We found that this transition is characterized by a systematic hole doping with increasing x , which results in the Fermi-level crossings of the bulk conduction and valence bands at x ˜0 and x ˜1 , respectively. The Dirac point of the topological surface state is gradually isolated from the valence-band edge, accompanied by a sign reversal of Dirac carriers. We also found that the Dirac velocity is the largest among known solid-solution TI systems. The TlBi1 -xSbxTe2 system thus provides an excellent platform for Dirac-cone engineering and device applications of TIs.

  2. Angle-resolved photoemission analysis on electronic structures and thermoelectric properties of off-stoichiometric Fe2-xV1+xAl

    International Nuclear Information System (INIS)

    The electronic states of Heusler (L21)-type off-stoichiometric Fe2-xV1+xAl have been investigated by soft X-ray angle-resolved photoelectron spectroscopy (ARPES) in order to clarify the origin of their large thermoelectric powers, which cannot be explained in terms of the rigid band model. In off-normal and normal ARPES, Fe2.05V0.95Al shows a weakly dispersive bulk band around the binding energy of 0.3 eV in the Γ-X direction and an almost dispersion-less one around 0.3 eV in a gap of dispersive bulk bands in the Γ-L direction, which is attributed to the anti-site Fe defect. At the Γ point, the bulk band does not appear to cross the Fermi level EF, consistent with the rigid band model for the excess Fe content bringing about the increase in the valence electrons, but no band crossing EF down is found at the X point. The anti-site Fe defect states near EF might push up the band at the X point and cause the p-type thermoelectric properties, unexpected with the rigid band picture. The change in the electronic structures and thermoelectric properties are discussed on the off-stoichiometry and substitution of the forth element. (author)

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

    Science.gov (United States)

    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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-08-15

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

  5. Spatial structure determination of ({radical}3 x {radical}3)R30{degrees} and (1.5 x 1.5)R18{degrees}CO on Cu(111) using angle-resolved photoemission extended fine structure

    Energy Technology Data Exchange (ETDEWEB)

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

    1997-04-01

    The authors report a study of the spatial structure of ({radical}3 x {radical}3)R30{degrees} (low coverage) and (1.5 x 1.5)R18{degrees} (intermediate coverage) CO adsorbed on Cu(111), using the Angle-Resolved Photoemission Extended Fine Structure (ARPEFS) technique at beamline 9.3.2 at the Advanced Light Source. The CO molecule adsorbs on an atop site for both adsorption phases. Full multiple-scattering spherical-wave (MSSW) calculations were used to extract the C-Cu. bond length and the first Cu-Cu layer spacing for each adsorption phase. The authors find that the C-Cu bond length remains unchanged with increasing coverage, but the 1st Cu-Cu layer spacing contracts at the intermediate coverage. They calculate the bending mode force constant in the (1.5 x 1.5)R18{degrees} phase to be K{sub {delta}} = 2.2 (1) x 10{sup {minus}12} dyne-cm/rad from their experimentally determined bond lengths combined with previously published infra-red absorption frequencies.

  6. Observation by resonant angle-resolved photoemission of a critical thickness for 2-dimensional electron gas formation in SrTiO3 embedded in GdTiO3

    International Nuclear Information System (INIS)

    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

  7. Quasiparticle dynamics across the full Brillouin zone of Bi2Sr2CaCu2O8+δ traced with ultrafast time and angle-resolved photoemission spectroscopy

    Directory of Open Access Journals (Sweden)

    Georgi L. Dakovski

    2015-09-01

    Full Text Available A hallmark in the cuprate family of high-temperature superconductors is the nodal-antinodal dichotomy. In this regard, angle-resolved photoemission spectroscopy (ARPES has proven especially powerful, providing band structure information directly in energy-momentum space. Time-resolved ARPES (trARPES holds great promise of adding ultrafast temporal information, in an attempt to identify different interaction channels in the time domain. Previous studies of the cuprates using trARPES were handicapped by the low probing energy, which significantly limits the accessible momentum space. Using 20.15 eV, 12 fs pulses, we show for the first time the evolution of quasiparticles in the antinodal region of Bi2Sr2CaCu2O8+δ and demonstrate that non-monotonic relaxation dynamics dominates above a certain fluence threshold. The dynamics is heavily influenced by transient modification of the electron-phonon interaction and phase space restrictions, in stark contrast to the monotonic relaxation in the nodal and off-nodal regions.

  8. 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}

    Energy Technology Data Exchange (ETDEWEB)

    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.

  9. 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

    Energy Technology Data Exchange (ETDEWEB)

    Huff, W R.A. [California Univ., Berkeley, CA (United States). Dept. of Chemistry

    1996-02-01

    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(2{times}2)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 X{alpha} scattered wave calculation confirm that the Fe{sub 1}-Fe{sub 2} 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(2{times}2)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.

  10. Angle-resolved time delay in photoemission

    CERN Document Server

    Wätzel, Jonas; Pavlyukh, Yaroslav; Berakdar, Jamal

    2014-01-01

    We investigate theoretically the relative time delay of photoelectrons originating from different atomic subshells of noble gases. This quantity was measured via attosecond streaking and studied theoretically by Schultze et al. [Science 328, 1658 (2010)] for neon. A substantial discrepancy was found between the measured and the calculated values of the relative time delay. Several theoretical studies were put forward to resolve this issue, e.g., by including correlation effects. In the present paper we explore a further aspect, namely the directional dependence of time delay. In contrast to neon, for argon target a strong angular dependence of time delay is found near a Cooper minimum.

  11. Imaging electron dynamics with time- and angle-resolved photoelectron spectroscopy

    Science.gov (United States)

    Popova-Gorelova, Daria; Küpper, Jochen; Santra, Robin

    2016-07-01

    We theoretically study how time- and angle-resolved photoemission spectroscopy can be applied for imaging coherent electron dynamics in molecules. We consider a process in which a pump pulse triggers coherent electronic dynamics in a molecule by creating a valence electron hole. An ultrashort extreme ultraviolet probe pulse creates a second electron hole in the molecule. Information about the electron dynamics is accessed by analyzing angular distributions of photoemission probabilities at a fixed photoelectron energy. We demonstrate that a rigorous theoretical analysis, which takes into account the indistinguishability of transitions induced by the ultrashort, broadband probe pulse and electron hole correlation effects, is necessary for the interpretation of time- and angle-resolved photoelectron spectra. We show how a Fourier analysis of time- and angle-resolved photoelectron spectra from a molecule can be applied to follow its electron dynamics by considering photoelectron distributions from an indole molecular cation with coherent electron dynamics.

  12. Imaging electron dynamics with time- and angle-resolved photoelectron spectroscopy

    CERN Document Server

    Popova-Gorelova, Daria; Santra, Robin

    2016-01-01

    We theoretically study how time- and angle-resolved photoemission spectroscopy can be applied for imaging coherent electron dynamics in molecules. We consider a process in which a pump pulse triggers coherent electronic dynamics in a molecule by creating a valence electron hole. An ultrashort extreme ultraviolet (XUV) probe pulse creates a second electron hole in the molecule. Information about the electron dynamics is accessed by analyzing angular distributions of photoemission probabilities at a fixed photoelectron energy. We demonstrate that a rigorous theoretical analysis, which takes into account the indistinguishability of transitions induced by the ultrashort, broadband probe pulse and electron hole correlation effects, is necessary for the interpretation of time- and angle-resolved photoelectron spectra. We show how a Fourier analysis of time- and angle-resolved photoelectron spectra from a molecule can be applied to follow its electron dynamics by considering photoelectron distributions from an indol...

  13. A New Spin on Photoemission Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    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.

  14. A New Spin on Photoemission Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Advanced Light Source; Jozwiak, Chris

    2008-12-18

    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 bycontinual 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.

  15. Transmission function calibration of an angular resolved analyzer for X-ray photoemission spectroscopy: Theory vs experiment

    International Nuclear Information System (INIS)

    Highlights: • A calibration method for the transmission function of modern XPS analyser is shown. • This method can be applied to any soft X-ray photoemission setup. • Ray tracing calculations well agree with experimental results. • A fine calibration is carried out through variable photon energy XPS. • An escape depth correction must be included in the calibration process. - Abstract: In order to achieve the most accurate quantification results in an X-ray photoelectron spectroscopy (XPS) experiment, a fine calibration of the analyzer response is required. In this work an experimental characterization of a modern angle-resolved analyzer, carried out with a unfocused and a highly collimated synchrotron source, is shown. The transmission function is extrapolated from the discrepancy between experimental and theoretically predicted XPS peak areas; the influence of different sensitivity factors and of the escape depth correction on the expected values is also discussed. The analyzer response and the theoretical approach are then tested against energy dispersive XPS measurements (EDXPS). These results are finally compared with TF calculated on the basis of an high accuracy electron ray tracing code, also described in this work

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

    CERN Document Server

    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. Photoemission and ferromagnetism

    International Nuclear Information System (INIS)

    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

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  19. Spin-dependent surface electronic structure of Gd(0001) near the Fermi-level: An angle-resolved (I)PE study

    Energy Technology Data Exchange (ETDEWEB)

    Budke, Michael; Wittkowski, Alexander; Correa, Juliet; Donath, Markus [Physikalisches Institut, WWU Muenster, Wilhelm-Klemm-Str. 10, 48149 Muenster (Germany)

    2008-07-01

    A widely accepted picture for the surface electronic structure of Gd(0001) comprises a spin-split surface state (SS) with its majority part 0.2 eV below E{sub F} and its minority part 0.5 eV above E{sub F} with a finite exchange splitting of 0.4 eV at T{sub C}. The discussion about this SS remains controversially because spin-resolved inverse photoemission identified a SS with both minority and majority components above E{sub F}. The reason for these conflicting results might be found in different sample conditions since the Gd films are usually grown on W(110), a material with considerably different lattice constant than Gd. To overcome this suspicion, we performed both, spin- and angle-resolved direct (PE) and inverse photoemission (IPE) on the same sample preparation of a 30 ML Gd film grown on Y(0001). We were able to identify two SSs with their minority and majority components well separated from E{sub F}. While the occupied SS shows spin-mixing behaviour as observed in other PE experiments, the unoccupied SS exhibits an exchange splitting of 250 meV that vanishes at T{sub C}. To identify the nature of the unexpected SS, we performed angular-resolved IPE measurements that support the interpretation as d-like SS above E{sub F} and reveal a variety of additional spectral features.

  20. Operating experience with a GaAs photoemission electron source

    Energy Technology Data Exchange (ETDEWEB)

    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.

  1. Operating experience with a GaAs photoemission electron source

    International Nuclear Information System (INIS)

    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

  2. A spin- and angle-resolving photoelectron spectrometer

    International Nuclear Information System (INIS)

    A new type of hemispherical electron energy analyzer that permits angle and spin resolved photoelectron spectroscopy has been developed. The analyzer permits standard angle resolved spectra to be recorded with a two-dimensional detector in parallel with spin detection using a mini-Mott polarimeter. General design considerations as well as technical solutions are discussed and test results from the Au(111) surface state are presented.

  3. Photoemission spectra of charge density wave states in cuprates

    Science.gov (United States)

    Tu, Wei-Lin; Chen, Peng-Jen; Lee, Ting-Kuo

    Angle-resolved photoemission spectroscopy(ARPES) experiments have reported many exotic properties of cuprates, such as Fermi arc at normal state, two gaps at superconducting state and particle-hole asymmetry at the antinodal direction. On the other hand, a number of inhomogeneous states or so-called charge density waves(CDW) states have also been discovered in cuprates by many experimental groups. The relation between these CDW states and ARPES spectra is unclear. With the help of Gutzwiller projected mean-field theory, we can reproduce the quasiparticle spectra in momentum space. The spectra show strong correspondence to the experimental data with afore-mentioned exotic features in it.

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

    International Nuclear Information System (INIS)

    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

  5. Relaxation and cross section effects in valence band photoemission spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    McFeely, F.R.

    1976-09-01

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

  6. Angle-resolved effective potentials for disk-shaped molecules

    International Nuclear Information System (INIS)

    We present an approach for calculating coarse-grained angle-resolved effective pair potentials for uniaxial molecules. For integrating out the intramolecular degrees of freedom we apply umbrella sampling and steered dynamics techniques in atomistically-resolved molecular dynamics (MD) computer simulations. Throughout this study we focus on disk-like molecules such as coronene. To develop the methods we focus on integrating out the van der Waals and intramolecular interactions, while electrostatic charge contributions are neglected. The resulting coarse-grained pair potential reveals a strong temperature and angle dependence. In the next step we fit the numerical data with various Gay-Berne-like potentials to be used in more efficient simulations on larger scales. The quality of the resulting coarse-grained results is evaluated by comparing their pair and many-body structure as well as some thermodynamic quantities self-consistently to the outcome of atomistic MD simulations of many-particle systems. We find that angle-resolved potentials are essential not only to accurately describe crystal structures but also for fluid systems where simple isotropic potentials start to fail already for low to moderate packing fractions. Further, in describing these states it is crucial to take into account the pronounced temperature dependence arising in selected pair configurations due to bending fluctuations

  7. Angle-resolved effective potentials for disk-shaped molecules

    Energy Technology Data Exchange (ETDEWEB)

    Heinemann, Thomas, E-mail: thomas.heinemann@tu-berlin.de; Klapp, Sabine H. L., E-mail: klapp@physik.tu-berlin.de [Institut für Theoretische Physik, Technische Universität Berlin, Hardenbergstr. 36, 10623 Berlin (Germany); Palczynski, Karol, E-mail: karol.palczynski@helmholtz-berlin.de; Dzubiella, Joachim, E-mail: joachim.dzubiella@helmholtz-berlin.de [Institut für Physik, Humboldt Universität zu Berlin, Newtonstraße 15, 12489 Berlin (Germany); Helmholtz Zentrum Berlin (HZB), Institute of Soft Matter and Functional Materials, Hahn-Meitner Platz 1, 14109 Berlin (Germany)

    2014-12-07

    We present an approach for calculating coarse-grained angle-resolved effective pair potentials for uniaxial molecules. For integrating out the intramolecular degrees of freedom we apply umbrella sampling and steered dynamics techniques in atomistically-resolved molecular dynamics (MD) computer simulations. Throughout this study we focus on disk-like molecules such as coronene. To develop the methods we focus on integrating out the van der Waals and intramolecular interactions, while electrostatic charge contributions are neglected. The resulting coarse-grained pair potential reveals a strong temperature and angle dependence. In the next step we fit the numerical data with various Gay-Berne-like potentials to be used in more efficient simulations on larger scales. The quality of the resulting coarse-grained results is evaluated by comparing their pair and many-body structure as well as some thermodynamic quantities self-consistently to the outcome of atomistic MD simulations of many-particle systems. We find that angle-resolved potentials are essential not only to accurately describe crystal structures but also for fluid systems where simple isotropic potentials start to fail already for low to moderate packing fractions. Further, in describing these states it is crucial to take into account the pronounced temperature dependence arising in selected pair configurations due to bending fluctuations.

  8. Accessing Phonon Polaritons in Hyperbolic Crystals by Angle-Resolved Photoemission Spectroscopy

    OpenAIRE

    Tomadin, Andrea; Principi, Alessandro; Song, Justin C. W.; Levitov, Leonid S.; Polini, Marco

    2015-01-01

    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...

  9. Electronic structure of ion arsenic high temperature superconductors studied by angle resolved photoemission spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Chang [Iowa State Univ., Ames, IA (United States)

    2011-01-01

    The main purpose of the present thesis is to present our ARPES results on the iron arsenic superconductors. As revealed by a series of ARPES measurements on both the AEFe2As2 and the RFeAs(O,F) families (parent compound and carrier-doped systems), the electronic structures of the pnictides are complicated, three dimensional, and closely linked to their superconducting behavior (13; 14; 15; 16; 17; 18; 19). Parent compounds of these materials exhibit the basic hole-electron pocket dual plus an apparent Fermi surface reconstruction caused by long range antiferromagnetism (13; 15). When carriers are introduced, the chemical potential shifts in accordance with the Luttinger theorem and the rigid band shifting picture (13). Importantly, both the appearance and disappearance of the superconducting dome at low and high doping levels have intimate relation with topological changes at the Fermi surfaces, resulting in a specific Fermi topology being favored by superconductivity (15; 16). On the low doping side, superconductivity emerges in the phase diagram once the antiferromagnetic reconstruction disappears below the Fermi level, returning the Fermi surface to its paramagnetic-like appearance. On the high doping side, superconductivity disappears around a doping level at which the central hole pocket vanishes due to increasing electron concentration. Such phenomena are evidence for the governing role the electronic structure plays in their superconducting behavior.

  10. Studies of Dirac and Weyl fermions by angle resolved photoemission spectroscopy

    Science.gov (United States)

    Huang, Lunan

    This dissertation consists of three parts. First, we study magnetic domains in Nd2Fe14 B single crystals using high resolution magnetic force microscopy (MFM). In addition to the elongated, wavy nano-domains reported by a previous MFM study, we found that the micrometer size, star-shaped fractal pattern is constructed of an elongated network of nano-domains about 20 nm in width, with resolution-limited domain walls thinner than 2 nm. Second, we studied extra Dirac cones of multilayer graphene on SiC surface by ARPES and SPA-LEED. We discovered extra Dirac cones on Fermi surface due to SiC 6 x 6 and graphene 6√3 x 6√3 coincidence lattice on both single-layer and three-layer graphene sheets. We interpreted the position and intensity of the Dirac cone replicas, based on the scattering vectors from LEED patterns. We found the positions of replica Dirac cones are determined mostly by the 6 x 6 SiC superlattice even graphene layers grown thicker. Finally, we studied the electronic structure of MoTe2 by ARPES and experimentally confirmed the prediction of type II Weyl state in this material. By combining the result of Density Functional Theory calculations and Berry curvature calculations with out experimental data, we identified Fermi arcs, track states and Weyl points, all features predicted to exist in a type II Weyl semimetal. This material is an excellent playground for studies of exotic Fermions.

  11. Angle resolved electron energy loss spectroscopy on graphite

    Science.gov (United States)

    Diebold, U.; Preisinger, A.; Schattschneider, P.; Varga, P.

    We report on angle resolved electron energy loss spectroscopy (EELS) in reflection mode with low primary energy on a graphite single crystal. Measurements with primary electron energy of 175 eV have been performed in off-Bragg-reflex geometry in two different directions within the (0001) surface plane of the graphite single crystal. In addition, EELS measurements in specular reflection mode with different primary energies and angles of incidence were done in order to distinguish between surface and bulk plasmon losses. The energy losses and the transferred momenta of the losses have been analyzed. The results are compared with the loss functions for bulk and surface excitations calculated from the dielectric function ɛ(ω, q) obtained from TEELS-data (EELS in transmission mode) [Springer Tracts Mod. Phys. 54 (1970) 77].

  12. Imaging the wave functions of adsorbed molecules using angle-resolved photoemmision data

    Science.gov (United States)

    Lüftner, Daniel; Ules, Thomas; Reinisch, Eva Maria; Koller, Georg; Soubatch, Serguei; Tautz, F. Stefan; Ramsey, Michael G.; Puschnig, Peter

    2014-03-01

    The frontier electronic orbitals of molecules are the prime determinants of the respective compounds' chemical, electronic, and optical properties. Although orbitals are very powerful concepts, experimentally only the electron densities and energy levels are directly observable. As has been shown in recent publications, angle-resolved photoemission (ARPES) intensity maps of organic molecular layers are related to the absolute value of the Fourier transform of the initial state molecular orbital. However, the lost phase information impedes the back-transformation of the orbital into real space. Here, we show how molecular orbital images as well as the absent phase information can be retrieved by applying an iterative procedure which takes experimental ARPES maps as input and only assumes spatial confinement of the orbital. The method is demonstrated for several molecular orbitals of two proto-typical pi-conjugated molecules: the LUMO, HOMO, and HOMO-1 of pentacene, and the LUMO and HOMO of PTCDA. The technique is simple and robust and further emphasizes the capabilities of ARPES looking at spatial distributions of wave functions of adsorbed molecules thereby complementing data obtained from scanning probe methods.

  13. Angle-Resolved Plasmonic Properties of Single Gold Nanorod Dimers

    Institute of Scientific and Technical Information of China (English)

    Jian Wu; Xuxing Lu; Qiannan Zhu; Junwei Zhao; Qishun Shen; Li Zhan; Weihai Ni

    2014-01-01

    Through wet-chemical assembly methods, gold nanorods were placed close to each other and formed a dimer with a gap distance*1 nm, and hence degenerated plasmonic dipole modes of individual nanorods coupled together to produce hybridized bonding and antibonding resonance modes. Previous studies using a condenser for illumination result in averaged signals over all excitation angles. By exciting an individual dimer obliquely at different angles, we demonstrate that these two new resonance modes are highly tunable and sensitive to the angle between the excitation polarization and the dimer orientation, which follows cos2u dependence. Moreover, for dimer structures with various structure angles, the resonance wavelengths as well as the refractive index sensitivities were found independent of the structure angle. Cal-culated angle-resolved plasmonic properties are in good agreement with the measurements. The assembled nanostructures investigated here are important for fundamental researches as well as potential applications when they are used as building blocks in plasmon-based optical and optoelectronic devices.

  14. Precision angle-resolved autoionization resonances in Ar and Ne

    Energy Technology Data Exchange (ETDEWEB)

    Berrah, N.; Langer, B.; Gorczyca, T.W. [Western Michigan Univ., Kalamazoo, MI (United States)] [and others

    1997-04-01

    Theoretical work has shown that the electron angular distribution and the shape of the autoionization resonances are crucial to the understanding of certain types of electron-electron correlation. Autoionization resonances in Ne (Ar) result from the decay of the excited discrete state Ne{sup *} 2s2p{sup 6} np (Ar{sup *} 3s3p{sup 6} np) into the continuum state Ne{sup +} 2s{sup 2}2p{sup 5} + e{sup {minus}} (ks,kd) (Ar{sup +} 3s{sup 2}3p{sup 5} + e{sup {minus}} (ks,kd)). Since the continuum can also be reached by direct photoionization, both paths add coherently, giving rise to interferences that produce the characteristic Beutler-Fano line shape. In this work, the authors report on quantitative angle-resolved electron spectrometry studies of (a) the Ne 2s{sup 2}2p{sup 6} {r_arrow} 2s2p{sup 6} np (n=3-5) autoionizing resonances and the 2s{sup 2}2p{sup 6} {r_arrow} 2p{sup 4}3s3p doubly excited resonance, (b) the Ar 3s{sup 2}3p{sup 6} {r_arrow} 3s3p{sup 6} np (n=4-9) autoionization resonances and extended R-matrix calculations of the angular-distribution parameters for both Ne and Ar measurements. Their results are compared with previous theoretical work by Taylor.

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

    Science.gov (United States)

    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.

  16. Highly Angle-Resolved X-Ray Photoelectron Diffraction from Solid Surfaces

    Science.gov (United States)

    Tamura, K.; Shiraki, S.; Ishii, H.; Owari, M.; Nihei, Y.

    We have carried out the highly angle-resolved X-ray photoelectron diffraction (XPED) measurements by using the input-lens system for restriction of the detection angle. In the input-lens system, high angular resolution and high throughput are accomplished by placing an aperture not on the image plane but on the diffraction plane of electron optics. The aperture sizes (ϕ 4 mm, ϕ 2 mm, ϕ 0.5 mm, ϕ 0.25 mm) correspond to the angular resolutions (± 0.6°, ± 0.3°, ± 0.08°, ± 0.04°) respectively. Highly angle-resolved Ge3d XPED patterns from Ge(111) obtained by the angle-resolving system contain fine structure such as Kikuchi patterns. The fine structure was reproduced by multiple scattering cluster calculations.

  17. Angle-Resolved Auger Spectroscopy as a Sensitive Access to Vibronic Coupling

    Science.gov (United States)

    Knie, A.; Patanen, M.; Hans, A.; Petrov, I. D.; Bozek, J. D.; Ehresmann, A.; Demekhin, Ph. V.

    2016-05-01

    In the angle-averaged excitation and decay spectra of molecules, vibronic coupling may induce the usually weak dipole-forbidden transitions by the excitation intensity borrowing mechanism. The present complementary theoretical and experimental study of the resonant Auger decay of core-to-Rydberg excited CH4 and Ne demonstrates that vibronic coupling plays a decisive role in the formation of the angle-resolved spectra by additionally involving the decay rate borrowing mechanism. Thereby, we propose that the angle-resolved Auger spectroscopy can in general provide very insightful information on the strength of the vibronic coupling.

  18. The electronic structure of clean and adsorbate-covered Bi2Se3: an angle-resolved photoemission study

    DEFF Research Database (Denmark)

    Bianchi, Marco; Hatch, Richard; Guan, Dandan;

    2012-01-01

    , the Dirac point moves to higher binding energies, indicating an increasingly strong downward bending of the bands near the surface. This time-dependent band bending is related to a contamination of the surface and can be accelerated by intentionally exposing the surface to carbon monoxide and other species...

  19. Photoemission study of iron-based superconductor

    Institute of Scientific and Technical Information of China (English)

    Liu Zhong-Hao; Cai Yi-Peng; Zhao Yan-Ge; Jia Lei-Lei; Wang Shan-Cai

    2013-01-01

    The iron-based superconductivity (IBSC) is a great challenge in correlated system.Angle-resolved photoemission spectroscopy (ARPES) provides electronic structure of the IBSCs,the pairing strength,and the order parameter symmetry.Here,we briefly review the recent progress in IBSCs and focus on the results from ARPES.The ARPES study shows the electronic structure of “122”,“111”,“11”,and “122*” families of IBSCs.It has been agreed that the IBSCs are unconventional superconductors in strong coupling region.The order parameter symmetry basically follows s± form with considerable out-of-plane contribution.

  20. Angle-resolved ion TOF spectrometer with a position sensitive detector

    Energy Technology Data Exchange (ETDEWEB)

    Saito, Norio [Electrotechnical Lab., Tsukuba, Ibaraki (Japan); Heiser, F.; Wieliczec, K.; Becker, U.

    1996-07-01

    A angle-resolved ion time-of-flight mass spectrometer with a position sensitive anode has been investigated. Performance of this spectrometer has been demonstrated by measuring an angular distribution of a fragment ion pair, C{sup +} + O{sup +}, from CO at the photon energy of 287.4 eV. The obtained angular distribution is very close to the theoretically expected one. (author)

  1. Use of angle-resolved XPS to determine depth profiles based on Fick's second law of diffusion: description of method and simulation study

    International Nuclear Information System (INIS)

    An iterative algorithm is proposed to extract depth profiles based on Fick's second law of diffusion in a multi-element system from data supplied by angle-resolved X-ray photoelectron spectroscopy (ARXPS). Parameters related to the concentration profiles are obtained by fitting the experimental angle-dependent relative photoelectron intensities to predictions from the algorithm. The use of relative instead of absolute photoelectron intensities eliminates error due to changes in absolute photoelectron intensities resulting from the change of system geometries in angle-resolved experiments. Simulations using an infinite source diffusion model have been conducted to study the influence of errors in the raw data and to demonstrate the robustness of the algorithm. The algorithm is tested based on preliminary experimental ARXPS data from a chemically treated polymer film

  2. Measurement of Random Surface Parameters by Angle-Resolved In-plane Light Scattering with Constant Perpendicular Wave Vector

    Institute of Scientific and Technical Information of China (English)

    LI Hai-Xia; LIU Chun-Xiang; CHEN Xiao-Yi; ZHANG Mei-Na; CHENG Chuan-Fu

    2011-01-01

    We report the experimental method of angle-resolved in-plane light scattering for random surface parameter extraction. In the measurement of the scattered intensity profile at a certain angle of incidence, the perpendicular component of wave vector remains constant, which is realized by controlling the movement of the detector along a specified circular arc segment. We use the central δ-peak and the half-width of the diffused intensity profiles and their variations to obtain the roughness w, the lateral correlation length ξ and roughness exponent α of the rough surface sample. The measurement copes strictly with the theoretical analysis, and the inherent problem in previous in-plane light scattering experiment is overcome so that the changes of the perpendicular component of wave vector affect the half width a diffused intensity profile and the measurement accuracy.%@@ We report the experimental method of angle-resolved in-plane light scattering for random surface parameter extraction.In the measurement of the scattered intensity profile at a certain angle of incidence, the perpendicular component of wave vector remains constant, which is realized by controlling the movement of the detector along a specified circular arc segment.We use the central S-peak and the half-width of the diffused intensity profiles and their variations to obtain the roughness w, the lateral correlation length ξ and roughness exponent a of the rough surface sample.The measurement copes strictly with the theoretical analysis, and the inherent problem in previous in-plane light scattering experiment is overcome so that the changes of the perpendicular component of wave vector affect the half width a diffused intensity profile and the measurement accuracy.

  3. Energy and angle resolved ion scattering spectroscopy: new possibilities for surface analysis

    International Nuclear Information System (INIS)

    In this thesis the design and development of a novel, very sensitive and high-resolving spectrometer for surface analysis is described. This spectrometer is designed for Energy and Angle Resolved Ion Scattering Spectroscopy (EARISS). There are only a few techniques that are sensitive enough to study the outermost atomic layer of surfaces. One of these techniques, Low-Energy Ion Scattering (LEIS), is discussed in chapter 2. Since LEIS is destructive, it is important to make a very efficient use of the scattered ions. This makes it attractive to simultaneously carry out energy and angle dependent measurements (EARISS). (Auth.)

  4. Is the Separable Propagator Perturbation Approach Accurate in Calculating Angle Resolved Photoelectron Diffraction Spectra?

    Science.gov (United States)

    Ng, C. N.; Chu, T. P.; Wu, Huasheng; Tong, S. Y.; Huang, Hong

    1997-03-01

    We compare multiple scattering results of angle-resolved photoelectron diffraction spectra between the exact slab method and the separable propagator perturbation method. In the slab method,footnote C.H. Li, A.R. Lubinsky and S.Y. Tong, Phys. Rev. B17, 3128 (1978). the source wave and multiple scattering within the strong scattering atomic layers are expanded in spherical waves while interlayer scattering is expressed in plane waves. The transformation between spherical waves and plane waves is done exactly. The plane waves are then matched across the solid-vacuum interface to a single outgoing plane wave in the detector's direction. The separable propagator perturbation approach uses two approximations: (i) A separable representation of the Green's function propagator and (ii) A perturbation expansion of multiple scattering terms. Results of c(2x2) S-Ni(001) show that this approximate method fails to converge due to the very slow convergence of the separable representation for scattering angles less than 90^circ. However, this method is accurate in the backscattering regime and may be applied to XAFS calculations.(J.J. Rehr and R.C. Albers, Phys. Rev. B41, 8139 (1990).) The use of this method for angle-resolved photoelectron diffraction spectra is substantially less reliable.

  5. Angle-resolved multioctave supercontinua from mid-infrared laser filaments.

    Science.gov (United States)

    Mitrofanov, A V; Voronin, A A; Sidorov-Biryukov, D A; Mitryukovsky, S I; Rozhko, M V; Pugžlys, A; Fedotov, A B; Panchenko, V Ya; Baltuška, A; Zheltikov, A M

    2016-08-01

    Angle-resolved spectral analysis of a multioctave high-energy supercontinuum output of mid-infrared laser filaments is shown to provide a powerful tool for understanding intricate physical scenarios behind laser-induced filamentation in the mid-infrared. The ellipticity of the mid-infrared driver beam breaks the axial symmetry of filamentation dynamics, offering a probe for a truly (3+1)-dimensional spatiotemporal evolution of mid-IR pulses in the filamentation regime. With optical harmonics up to the 15th order contributing to supercontinuum generation in such filaments alongside Kerr-type and ionization-induced nonlinearities, the output supercontinuum spectra span over five octaves from the mid-ultraviolet deep into the mid-infrared. Full (3+1)-dimensional field evolution analysis is needed for an adequate understanding of this regime of laser filamentation. Supercomputer simulations implementing such analysis articulate the critical importance of angle-resolved measurements for both descriptive and predictive power of filamentation modeling. Strong enhancement of ionization-induced blueshift is shown to offer new approaches in filamentation-assisted pulse compression, enabling the generation of high-power few- and single-cycle pulses in the mid-infrared. PMID:27472598

  6. A photoemission study of the diamond and the single crystal C{sub 60}

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Jin

    1994-03-01

    This report studied the elctronic structure of diamond (100) and diamond/metal interface and C{sub 60}, using angle-resolved and core level photoemission. The C(100)-(2X1) surface electronic structure was studied using both core level and angle resolved valence band photoemission spectroscopy. The surface component of the C 1s core level spectrum agrees with theoretical existence of only symmetrical dimers. In the case of metal/diamond interfaces, core level and valence photoelectron spectroscopy and LEED studies WERE MADE OF B and Sb on diamond (100) and (111) surfaces. In the case of single-crystal C{sub 60}, photoemission spectra show sharp molecular features, indicating that the molecular orbitals are relatively undisturbed in solid C{sub 60}.

  7. Angle resolved XPS of monomolecular layer of 5-chlorobenzotriazole on oxidized metallic surface

    Science.gov (United States)

    Kazansky, L. P.; Selyaninov, I. A.; Kuznetsov, Yu. I.

    2012-10-01

    Angle resolved XPS is used to study adsorption of 5-chlorobenzotriazole (5-chloroBTAH) on surfaces of the oxidized metals: mild steel, copper and zinc from borate buffer solution (pH 7.4). It is shown that for the metals studied the 5-chloroBTA anions, when adsorbed, form a monomolecular layer whose thickness is ∼6 Å comparable with the size of BTA. As XPS evidences adsorption proceeds with deprotonation of 5-chloroBTAH and formation of the coordination bonds between the lone pair of nitrogens and cation of a metal. Measuring XPS at two different angles unequivocally points out almost vertical arrangement of the anions toward the sample surface, when chlorine atoms form outmost virtual layer.

  8. Angle-resolved spin wave band diagrams of square antidot lattices studied by Brillouin light scattering

    Energy Technology Data Exchange (ETDEWEB)

    Gubbiotti, G.; Tacchi, S. [Istituto Officina dei Materiali del Consiglio Nazionale delle Ricerche (IOM-CNR), Sede di Perugia, c/o Dipartimento di Fisica e Geologia, Via A. Pascoli, I-06123 Perugia (Italy); Montoncello, F.; Giovannini, L. [Dipartimento di Fisica e Scienze della Terra, Università di Ferrara, Via G. Saragat 1, I-44122 Ferrara (Italy); Madami, M.; Carlotti, G. [Dipartimento di Fisica e Geologia, Università di Perugia, Via A. Pascoli, I-06123 Perugia (Italy); Ding, J.; Adeyeye, A. O. [Information Storage Materials Laboratory, Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117576 (Singapore)

    2015-06-29

    The Brillouin light scattering technique has been exploited to study the angle-resolved spin wave band diagrams of squared Permalloy antidot lattice. Frequency dispersion of spin waves has been measured for a set of fixed wave vector magnitudes, while varying the wave vector in-plane orientation with respect to the applied magnetic field. The magnonic band gap between the two most dispersive modes exhibits a minimum value at an angular position, which exclusively depends on the product between the selected wave vector magnitude and the lattice constant of the array. The experimental data are in very good agreement with predictions obtained by dynamical matrix method calculations. The presented results are relevant for magnonic devices where the antidot lattice, acting as a diffraction grating, is exploited to achieve multidirectional spin wave emission.

  9. Photoemission and magnetic response in the bipolaronic superconductor

    CERN Document Server

    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...

  10. Photoemission, Correlation and Superconductivity:

    Science.gov (United States)

    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.

  11. Some future perspectives in soft- and hard- X-ray photoemission

    Energy Technology Data Exchange (ETDEWEB)

    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); Nemšák, Slavomir [Department of Physics, University of California Davis, Davis, CA 95616 (United States); Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States)

    2014-08-15

    Highlights: • Polarization-dependent differential photoelectric cross sections in valence photoemission. • Bulk electronic structure from hard X-ray angle-resolved photoemission. • Depth-resolved photoemission using standing-wave and total reflection excitation. • Standing-wave ambient-pressure photoemission as a probe of solid–liquid interfaces. • Molecular dissociation dynamics from photoelectron holography with free-electron laser excitation. - Abstract: We discuss several recent developments in photoemission, with comments on their perspectives for the future. These include an adequate allowance for differential cross section effects in core- and valence-angular distributions, as well as more accurate one-step modeling of angle-resolved photoemission (ARPES); the use of higher photon energies from the soft- to hard- X-ray regime to permit probing bulk electronic structure and buried layers and interfaces; extending ARPES into the soft- and hard- X-ray regimes; tailoring the X-ray wave field through X-ray optical effects including standing waves, total reflection, and tuning through resonances; using standing-wave excitation to provide much enhanced depth sensitivity in studying solid/gas and solid/liquid interfaces; and applying photoelectron holography to time-resolved studies of molecular reactions and dissociation. Specific application examples include a magnetic semiconductor, multilayer structures of complex metal oxides, a thin water solution on a metal oxide surface, and a halo-substituted benzene molecule.

  12. Analysis of the contrast in normal-incidence surface plasmon photoemission microscopy in a pump-probe experiment with adjustable polarization

    Science.gov (United States)

    Podbiel, Daniel; Kahl, Philip; Meyer zu Heringdorf, Frank-J.

    2016-04-01

    We investigate the fringe contrast in surface plasmon polariton-based two-photon photoemission microscopy in a normal-incidence geometry. In a pump-probe experiment with freely adjustable polarization of the probe pulse, we find a maximum contrast whenever the probe pulse polarization is parallel (or anti-parallel) to the propagation direction of the surface plasmon polariton wave packet. The experimental observation is compared to a wave simulation based on the known TM solution for surface plasmon polaritons. We estimate that at the Au/vacuum interface the in-plane component of the electric field of the surface plasmon polariton inside the metal is about five times larger than its out-of-plane component. We conclude that the locations of maximum plasmon-related nonlinear photoemission yield in a pump-probe experiment are the ones where the in-plane component of the electric field of the surface plasmon polariton is maximal.

  13. A flexible setup for angle-resolved X-ray fluorescence spectrometry with laboratory sources.

    Science.gov (United States)

    Spanier, M; Herzog, C; Grötzsch, D; Kramer, F; Mantouvalou, I; Lubeck, J; Weser, J; Streeck, C; Malzer, W; Beckhoff, B; Kanngießer, B

    2016-03-01

    X-ray fluorescence (XRF) analysis is one of the standard tools for the analysis of stratified materials and is widely applied for the investigation of electronics and coatings. The composition and thickness of the layers can be determined quantitatively and non-destructively. Recent work showed that these capabilities can be extended towards retrieving stratigraphic information like concentration depth profiles using angle-resolved XRF (ARXRF). This paper introduces an experimental sample chamber which was developed as a multi-purpose tool enabling different measurement geometries suited for transmission measurements, conventional XRF, ARXRF, etc. The chamber was specifically designed for attaching all kinds of laboratory X-ray sources for the soft and hard X-ray ranges as well as various detection systems. In detail, a setup for ARXRF using an X-ray tube with a polycapillary X-ray lens as source is presented. For such a type of setup, both the spectral and lateral characterizations of the radiation field are crucial for quantitative ARXRF measurements. The characterization is validated with the help of a stratified validation sample. PMID:27036820

  14. Angle resolved XPS of monomolecular layer of 5-chlorobenzotriazole on oxidized metallic surface

    International Nuclear Information System (INIS)

    Highlights: ► Adsorption of 5-chloroBTA on oxidized metals is studied by ARXPS. ► When adsorbed, 5-chloroBTA forms a monolayer whose thickness is close to molecule size. ► According to ARXPS, the planes of 5-chloroBTA anions are vertical to a metal oxide surface. ► Metal cations of the surface coordinate nitrogen atoms of 5-chloroBTA. ► Chlorine atoms forming outmost virtual layer. - Abstract: Angle resolved XPS is used to study adsorption of 5-chlorobenzotriazole (5-chloroBTAH) on surfaces of the oxidized metals: mild steel, copper and zinc from borate buffer solution (pH 7.4). It is shown that for the metals studied the 5-chloroBTA anions, when adsorbed, form a monomolecular layer whose thickness is ∼6 Å comparable with the size of BTA. As XPS evidences adsorption proceeds with deprotonation of 5-chloroBTAH and formation of the coordination bonds between the lone pair of nitrogens and cation of a metal. Measuring XPS at two different angles unequivocally points out almost vertical arrangement of the anions toward the sample surface, when chlorine atoms form outmost virtual layer.

  15. Fourier-domain angle-resolved low coherence interferometry for clinical detection of dysplasia

    Science.gov (United States)

    Terry, Neil G.; Zhu, Yizheng; Wax, Adam

    2010-02-01

    Improved methods for detecting dysplasia, or pre-cancerous growth are a current clinical need, particularly in the esophagus. The currently accepted method of random biopsy and histological analysis provides only a limited examination of tissue in question while being coupled with a long time delay for diagnosis. Light scattering spectroscopy, in contrast, allows for inspection of the cellular structure and organization of tissue in vivo. Fourier-domain angle-resolved low-coherence interferometry (a/LCI) is a novel light scattering spectroscopy technique that provides quantitative depth-resolved morphological measurements of the size and optical density of the examined cell nuclei, which are characteristic biomarkers of dysplasia. Previously, clinical viability of the a/LCI system was demonstrated through analysis of ex vivo human esophageal tissue in Barrett's esophagus patients using a portable a/LCI, as was the development of a clinical a/LCI system. Data indicating the feasibility of the technique in other organ sites (colon, oral cavity) will be presented. We present an adaptation of the a/LCI system that will be used to investigate the presence of dysplasia in vivo in Barrett's esophagus patients.

  16. A flexible setup for angle-resolved X-ray fluorescence spectrometry with laboratory sources

    Science.gov (United States)

    Spanier, M.; Herzog, C.; Grötzsch, D.; Kramer, F.; Mantouvalou, I.; Lubeck, J.; Weser, J.; Streeck, C.; Malzer, W.; Beckhoff, B.; Kanngießer, B.

    2016-03-01

    X-ray fluorescence (XRF) analysis is one of the standard tools for the analysis of stratified materials and is widely applied for the investigation of electronics and coatings. The composition and thickness of the layers can be determined quantitatively and non-destructively. Recent work showed that these capabilities can be extended towards retrieving stratigraphic information like concentration depth profiles using angle-resolved XRF (ARXRF). This paper introduces an experimental sample chamber which was developed as a multi-purpose tool enabling different measurement geometries suited for transmission measurements, conventional XRF, ARXRF, etc. The chamber was specifically designed for attaching all kinds of laboratory X-ray sources for the soft and hard X-ray ranges as well as various detection systems. In detail, a setup for ARXRF using an X-ray tube with a polycapillary X-ray lens as source is presented. For such a type of setup, both the spectral and lateral characterizations of the radiation field are crucial for quantitative ARXRF measurements. The characterization is validated with the help of a stratified validation sample.

  17. Theoretical Calculation for the Dip Feature in Tunnelling Experiment on Bi2212

    Institute of Scientific and Technical Information of China (English)

    谢刚; 韩汝珊

    2001-01-01

    We generalize a model, which was presented by Norman [Phys. Rev. Lett. 79 (1997) 3506], to calculate the Bi2Sr2CaCu2Os+δ (Bi2212) single-electron tunnelling conductance. In our calculation result, the dip feature appears which has been widely observed in tunnelling experiments. It is found that this dip feature in tunnelling experiments and the dip/hump feature in angle-resolved photoemission experiments have a common physics. Moreover, it is shown from our numerical calculation method that if the spectral function A(κ, ω) is known, the tunnelling conductance can be obtained.

  18. Gantry-angle resolved VMAT pretreatment verification using EPID image prediction

    Energy Technology Data Exchange (ETDEWEB)

    Woodruff, Henry C.; Rowshanfarzad, Pejman [School of Mathematical and Physical Sciences, The University of Newcastle, NSW 2308 (Australia); Fuangrod, Todsaporn [School of Electrical Engineering and Computer Science, The University of Newcastle, NSW 2308 (Australia); McCurdy, Boyd M. C. [Division of Medical Physics, CancerCare Manitoba, 675 McDermot Avenue, Winnipeg, Manitoba R3E 0V9 (Canada); Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba R3T 2N2 (Canada); Department of Radiology, University of Manitoba, Winnipeg, Manitoba R3T 2N2 (Canada); Greer, Peter B. [School of Mathematical and Physical Sciences, The University of Newcastle, NSW 2308, Australia and Department of Radiation Oncology, Calvary Mater Newcastle Hospital, Locked Bag 7, Hunter region Mail Centre, Newcastle, NSW 2310 (Australia)

    2013-08-15

    Purpose: Pretreatment verification of volumetric modulated arc therapy (VMAT) dose delivery with electronic portal imaging device (EPID) uses images integrated over the entire delivery or over large subarcs. This work aims to develop a new method for gantry-angle-resolved verification of VMAT dose delivery using EPID.Methods: An EPID dose prediction model was used to calculate EPID images as a function of gantry angle for eight prostate patient deliveries. EPID image frames at 7.5 frames per second were acquired during delivery via a frame-grabber system. The gantry angle for each image was encoded in kV frames which were synchronized to the MV frames. Gamma analysis results as a function of gantry angle were assessed by integrating the frames over 2° subarcs with an angle-to-agreement tolerance of 0.5° about the measured image angle.Results: The model agreed with EPID images integrated over the entire delivery with average Gamma pass-rates at 2%, 2 mm of 99.7% (10% threshold). The accuracy of the kV derived gantry angle for each image was found to be 0.1° (1 SD) using a phantom test. For the gantry-resolved analysis all Gamma pass-rates were greater than 90% at 3%, 3 mm criteria (with only two exceptions), and more than 90% had a 95% pass-rate, with an average of 97.3%. The measured gantry angle lagged behind the predicted angle by a mean of 0.3°± 0.3°, with a maximum lag of 1.3°.Conclusions: The method provides a comprehensive and highly efficient pretreatment verification of VMAT delivery using EPID. Dose delivery accuracy is assessed as a function of gantry angle to ensure accurate treatment.

  19. Two-photon Photo-emission of Ultrathin Film PTCDA Morphologies on Ag(111)

    OpenAIRE

    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 ...

  20. An XUV source using a femtosecond enhancement cavity for photoemission spectroscopy

    Science.gov (United States)

    Mills, Arthur K.; Zhdanovich, Sergey; Sheyerman, Alex; Levy, Giorgo; Damascelli, Andrea; Jones, David J.

    2015-05-01

    Recent development of extreme ultraviolet (XUV) sources based on high harmonic generation (HHG) in femtosecond enhancement cavities (fsEC) has enabled generation of high photon ux ( ̴ 1013-1014 photons/sec) in the XUV, at high repetition rates (> 50 MHz) and spanning the spectral region from 40 nm - 120 nm. Here we demonstrate the potential offered by this approach for angle-resolved photoemission spectroscopy by measuring the photoemission spectrum of Au using 8.3 and 25 eV photons with excellent resolution at rapid data rates.

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  2. Band structures of 4f and 5f materials studied by angle-resolved photoelectron spectroscopy

    Science.gov (United States)

    Fujimori, Shin-ichi

    2016-04-01

    Recent remarkable progress in angle-resolved photoelectron spectroscopy (ARPES) has enabled the direct observation of the band structures of 4f and 5f materials. In particular, ARPES with various light sources such as lasers (hν ∼ 7~\\text{eV} ) or high-energy synchrotron radiations (hν ≳ 400~\\text{eV} ) has shed light on the bulk band structures of strongly correlated materials with energy scales of a few millielectronvolts to several electronvolts. The purpose of this paper is to summarize the behaviors of 4f and 5f band structures of various rare-earth and actinide materials observed by modern ARPES techniques, and understand how they can be described using various theoretical frameworks. For 4f-electron materials, ARPES studies of \\text{Ce}M\\text{I}{{\\text{n}}5} (M=\\text{Rh} , \\text{Ir} , and \\text{Co} ) and \\text{YbR}{{\\text{h}}2}\\text{S}{{\\text{i}}2} with various incident photon energies are summarized. We demonstrate that their 4f electronic structures are essentially described within the framework of the periodic Anderson model, and that the band-structure calculation based on the local density approximation cannot explain their low-energy electronic structures. Meanwhile, electronic structures of 5f materials exhibit wide varieties ranging from itinerant to localized states. For itinerant \\text{U}~5f compounds such as \\text{UFeG}{{\\text{a}}5} , their electronic structures can be well-described by the band-structure calculation assuming that all \\text{U}~5f electrons are itinerant. In contrast, the band structures of localized \\text{U}~5f compounds such as \\text{UP}{{\\text{d}}3} and \\text{U}{{\\text{O}}2} are essentially explained by the localized model that treats \\text{U}~5f electrons as localized core states. In regards to heavy fermion \\text{U} -based compounds such as the hidden-order compound \\text{UR}{{\\text{u}}2}\\text{S}{{\\text{i}}2} , their electronic structures exhibit complex behaviors. Their overall band structures

  3. Orbital tomography: Deconvoluting photoemission spectra of organic molecules

    Science.gov (United States)

    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.

  4. Pump laser-induced space-charge effects in HHG-driven time- and angle-resolved photoelectron spectroscopy

    Science.gov (United States)

    Oloff, L.-P.; Hanff, K.; Stange, A.; Rohde, G.; Diekmann, F.; Bauer, M.; Rossnagel, K.

    2016-06-01

    With the advent of ultrashort-pulsed extreme ultraviolet sources, such as free-electron lasers or high-harmonic-generation (HHG) sources, a new research field for photoelectron spectroscopy has opened up in terms of femtosecond time-resolved pump-probe experiments. The impact of the high peak brilliance of these novel sources on photoemission spectra, so-called vacuum space-charge effects caused by the Coulomb interaction among the photoemitted probe electrons, has been studied extensively. However, possible distortions of the energy and momentum distributions of the probe photoelectrons caused by the low photon energy pump pulse due to the nonlinear emission of electrons have not been studied in detail yet. Here, we systematically investigate these pump laser-induced space-charge effects in a HHG-based experiment for the test case of highly oriented pyrolytic graphite. Specifically, we determine how the key parameters of the pump pulse—the excitation density, wavelength, spot size, and emitted electron energy distribution—affect the measured time-dependent energy and momentum distributions of the probe photoelectrons. The results are well reproduced by a simple mean-field model, which could open a path for the correction of pump laser-induced space-charge effects and thus toward probing ultrafast electron dynamics in strongly excited materials.

  5. Angle-resolved photoemission study of the evolution of band structure and charge density wave properties in RTe3 (R= Y, La, Ce, Sm, Gd, Tb and Dy)

    Energy Technology Data Exchange (ETDEWEB)

    Brouet, V.; Yang, W.L.; Zhou, X.J.; Hussain, Z.; Moore, R.G.; He, R.; Lu, D.H.; Shen, Z.X.; Laverock, J.; Dugdale, S.; Ru, N.; Fisher, I.R.

    2010-02-15

    We present a detailed ARPES investigation of the RTe{sub 3} family, which sets this system as an ideal 'textbook' example for the formation of a nesting driven Charge Density Wave (CDW). This family indeed exhibits the full range of phenomena that can be associated to CDW instabilities, from the opening of large gaps on the best nested parts of Fermi Surface (FS) (up to 0.4eV), to the existence of residual metallic pockets. ARPES is the best suited technique to characterize these features, thanks to its unique ability to resolve the electronic structure in k-space. An additional advantage of RTe{sub 3} is that the band structure can be very accurately described by a simple 2D tight-binding (TB) model, which allows one to understand and easily reproduce many characteristics of the CDW. In this paper, we first establish the main features of the electronic structure, by comparing our ARPES measurements with Linear Muffin-Tin Orbital band calculations. We use this to define the validity and limits of the TB model. We then present a complete description of the CDW properties and, for the first time, of their strong evolution as a function of R. Using simple models, we are able to reproduce perfectly the evolution of gaps in k-space, the evolution of the CDW wave vector with R and the shape of the residual metallic pockets. Finally, we give an estimation of the CDW interaction parameters and find that the change in the electronic density of states n(Ef), due to lattice expansion when different R ions are inserted, has the correct order of magnitude to explain the evolution of the CDW properties.

  6. Complete Fermi Surface and Surface State in WTe2 Revealed by High-Resolution Laser-Based Angle-Resolved Photoemission Spectroscopy

    Science.gov (United States)

    Wang, Chenlu; Zhang, Yan; Liu, Guodong; Mao, Zhiqiang; He, Shaolong; Zhao, Lin; Chen, Chuangtian; Xu, Zuyan; Zhou, Xingjiang

    WTe2, an unique transition metal dichalcogenide, attracts considerable attention recently, which shows an extremely large magnetoresistance (MR) with no saturation under very high field. In this talk, we will present our high resolution laser-ARPES study on WTe2. Our distinctive ARPES system is equipped with the VUV laser and the time-of-flight (TOF) electron energy analyzer, being featured by super-high energy resolution, simultaneous data acquisition for two-dimensional momentum space and much reduced nonlinearity effect. With this advanced apparatus, the very high quality of electronic structure data are obtained for WTe2 which gives a full picture of the Fermi surface. Meanwhile, the obtained systematic temperature dependence of its electronic state leads us to a better understanding on the origin of large magnetoresistance in WTe2.

  7. Electronic Structure of Transition Metal Dichalcogenides PdTe2 and Cu0.05PdTe2 Superconductors Obtained by Angle-Resolved Photoemission Spectroscopy

    OpenAIRE

    Liu, Yan; Zhao, Jianzhou; Yu, Li; Lin, Chengtian; Hu, Cheng; Liu, Defa; Peng, Yingying; Xie, Zhuojin; He, Junfeng; Chen, Chaoyu; Feng, Ya; Yi, Hemian; Liu, Xu; Zhao, Lin; He, Shaolong

    2015-01-01

    The layered transition metal chalcogenides have been a fertile land in solid state physics for many decades. Various MX2-type transition metal dichalcogenides, such as WTe2, IrTe2, and MoS2, have triggered great attention recently, either for the discovery of novel phenomena or some extreme or exotic physical properties, or for their potential applications. PdTe2 is a superconductor in the class of transition metal dichalcogenides, and superconductivity is enhanced in its Cu-intercalated form...

  8. Temperature-dependent photoemission features for overdoped Bi2Sr2CaCu2O8 + x cuprates

    Science.gov (United States)

    Rast, S.; Frazer, B. H.; Onellion, M.; Schmauder, T.; Abrecht, M.; Touzelet, O.; Berger, H.; Margaritondo, G.; Pavuna, D.

    2000-07-01

    We report temperature-dependent angle-resolved photoemission spectra for overdoped Bi2Sr2CaCu2O8 + x single-crystal samples. The data indicate that there is a special temperature (T+) where the spectral function changes intensity, and where the energy difference between the peak and dip features changes. The data also demonstrate that immediately above the superconducting transition temperature, the system exhibits a non-Lorentzian lineshape. We discuss implications of the data.

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  10. Spectral data of specular reflectance, narrow-angle transmittance and angle-resolved surface scattering of materials for solar concentrators

    Directory of Open Access Journals (Sweden)

    Philipp Good

    2016-03-01

    Full Text Available The spectral specular reflectance of conventional and novel reflective materials for solar concentrators is measured with an acceptance angle of 17.5 mrad over the wavelength range 300−2500 nm at incidence angles 15–60° using a spectroscopic goniometry system. The same experimental setup is used to determine the spectral narrow-angle transmittance of semi-transparent materials for solar collector covers at incidence angles 0–60°. In addition, the angle-resolved surface scattering of reflective materials is recorded by an area-scan CCD detector over the spectral range 350–1050 nm. A comprehensive summary, discussion, and interpretation of the results are included in the associated research article “Spectral reflectance, transmittance, and angular scattering of materials for solar concentrators” in Solar Energy Materials and Solar Cells.

  11. Angle-resolved light scattering of individual rod-shaped bacteria based on Fourier transform light scattering

    Science.gov (United States)

    Jo, Youngju; Jung, Jaehwang; Lee, Jee Woong; Shin, Della; Park, Hyunjoo; Nam, Ki Tae; Park, Ji-Ho; Park, Yongkeun

    2014-05-01

    Two-dimensional angle-resolved light scattering maps of individual rod-shaped bacteria are measured at the single-cell level. Using quantitative phase imaging and Fourier transform light scattering techniques, the light scattering patterns of individual bacteria in four rod-shaped species (Bacillus subtilis, Lactobacillus casei, Synechococcus elongatus, and Escherichia coli) are measured with unprecedented sensitivity in a broad angular range from -70° to 70°. The measured light scattering patterns are analyzed along the two principal axes of rod-shaped bacteria in order to systematically investigate the species-specific characteristics of anisotropic light scattering. In addition, the cellular dry mass of individual bacteria is calculated and used to demonstrate that the cell-to-cell variations in light scattering within bacterial species is related to the cellular dry mass and growth.

  12. Sidewall passivation layer thickness and composition profiles of etched silicon patterns from angle resolved x-ray photoelectron spectroscopy analysis

    Energy Technology Data Exchange (ETDEWEB)

    Haass, Moritz; Darnon, Maxime; Joubert, Olivier [CNRS/UJF-Grenoble1/CEA LTM, 17 avenue des Martyrs, 38054 Grenoble cedex 9 (France)

    2012-06-15

    In this study, we present a technique to analyze side wall passivation layers formed on silicon sidewalls after plasma processing. The thickness and chemical composition are derived from angle resolved x-ray photoelectron spectroscopy analyses. It is a non-destructive, quasi in situ method to determine profiles of the thickness and the chemical composition of passivation layers in trenches up to an aspect ratio of about 3. The performance of this technique to quantify the passivation layer thickness is compared to a standard technique using secondary electron microscopy images with respect to two different samples and is found to be at least equivalent. The possible uncertainties and limitations of this technique are discussed as well.

  13. Symmetric and anti-symmetric magnetic resonances in double-triangle nanoparticle arrays fabricated via angle-resolved nanosphere lithography

    Directory of Open Access Journals (Sweden)

    Jian Pan

    2011-12-01

    Full Text Available We report experimentally that for a particular high-symmetry planar periodic arrangement of metal double-triangle nanoparticle arrays fabricated via angle resolved nanosphere lithography, both anti-symmetric and symmetric magnetic resonances can be explicitly excited at off-normal incidence. Further, we demonstrate that the underlying mechanism for the formation of these two modes is a result of direct interactions with the incident electric and magnetic fields, respectively. As a consequence, with increasing the incident angle there is a relatively small blue-shift in the transmission for the electric-field induced anti-symmetric mode, while a remarkable red-shift is observed for the magnetic-field induced symmetric mode.

  14. Spectral data of specular reflectance, narrow-angle transmittance and angle-resolved surface scattering of materials for solar concentrators.

    Science.gov (United States)

    Good, Philipp; Cooper, Thomas; Querci, Marco; Wiik, Nicolay; Ambrosetti, Gianluca; Steinfeld, Aldo

    2016-03-01

    The spectral specular reflectance of conventional and novel reflective materials for solar concentrators is measured with an acceptance angle of 17.5 mrad over the wavelength range 300-2500 nm at incidence angles 15-60° using a spectroscopic goniometry system. The same experimental setup is used to determine the spectral narrow-angle transmittance of semi-transparent materials for solar collector covers at incidence angles 0-60°. In addition, the angle-resolved surface scattering of reflective materials is recorded by an area-scan CCD detector over the spectral range 350-1050 nm. A comprehensive summary, discussion, and interpretation of the results are included in the associated research article "Spectral reflectance, transmittance, and angular scattering of materials for solar concentrators" in Solar Energy Materials and Solar Cells.

  15. Widespread spin polarization effects in photoemission from topological insulators

    Energy Technology Data Exchange (ETDEWEB)

    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.

  16. Photoemission studies of Mg and Rb layers on Zn(0 0 0 1)

    Energy Technology Data Exchange (ETDEWEB)

    Suchodolskis, A. E-mail: suchy@uj.pfi.lt; Karpus, V.; Kanski, J.; Ilver, L.; Goethelid, M.; Karlsson, U.O

    2004-07-01

    The electronic structure of the clean Zn(0 0 0 1) surface is studied by angle resolved photoemission. An earlier detected surface state at the surface Brillouin zone centre is confirmed and a new surface state is found at the surface Brilluoin zone boundary. The surface electronic structure of Zn is found to be similar to the that of Cd. Evaporation of thin films of Mg and Rb onto the Zn(0 0 0 1) surface quenches the emission from both surface states and reduces the intensity of the bulk related structures.

  17. Inner-shell photoemission from atoms and molecules using synchrotron radiation

    International Nuclear Information System (INIS)

    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

  18. Improvements in the contemporary photoemission spectroscopy implementation: A message to the ARPES community

    CERN Document Server

    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.

  19. High-resolution three-dimensional spin- and angle-resolved photoelectron spectrometer using vacuum ultraviolet laser light

    Science.gov (United States)

    Yaji, Koichiro; Harasawa, Ayumi; Kuroda, Kenta; Toyohisa, Sogen; Nakayama, Mitsuhiro; Ishida, Yukiaki; Fukushima, Akiko; Watanabe, Shuntaro; Chen, Chuangtian; Komori, Fumio; Shin, Shik

    2016-05-01

    We describe a spin- and angle-resolved photoelectron spectroscopy (SARPES) apparatus with a vacuum-ultraviolet (VUV) laser (hν = 6.994 eV) developed at the Laser and Synchrotron Research Center at the Institute for Solid State Physics, The University of Tokyo. The spectrometer consists of a hemispherical photoelectron analyzer equipped with an electron deflector function and twin very-low-energy-electron-diffraction-type spin detectors, which allows us to analyze the spin vector of a photoelectron three-dimensionally with both high energy and angular resolutions. The combination of the high-performance spectrometer and the high-photon-flux VUV laser can achieve an energy resolution of 1.7 meV for SARPES. We demonstrate that the present laser-SARPES machine realizes a quick SARPES on the spin-split band structure of a Bi(111) film even with 7 meV energy and 0.7∘ angular resolutions along the entrance-slit direction. This laser-SARPES machine is applicable to the investigation of spin-dependent electronic states on an energy scale of a few meV.

  20. SmB6 electron-phonon coupling constant from time- and angle-resolved photoelectron spectroscopy

    Science.gov (United States)

    Sterzi, A.; Crepaldi, A.; Cilento, F.; Manzoni, G.; Frantzeskakis, E.; Zacchigna, M.; van Heumen, E.; Huang, Y. K.; Golden, M. S.; Parmigiani, F.

    2016-08-01

    SmB6 is a mixed valence Kondo system resulting from the hybridization between localized f electrons and delocalized d electrons. We have investigated its out-of-equilibrium electron dynamics by means of time- and angle-resolved photoelectron spectroscopy. The transient electronic population above the Fermi level can be described by a time-dependent Fermi-Dirac distribution. By solving a two-temperature model that well reproduces the relaxation dynamics of the effective electronic temperature, we estimate the electron-phonon coupling constant λ to range from 0.13 ±0.03 to 0.04 ±0.01 . These extremes are obtained assuming a coupling of the electrons with either a phonon mode at 10 or 19 meV. A realistic value of the average phonon energy will give an actual value of λ within this range. Our results provide an experimental report on the material electron-phonon coupling, contributing to both the electronic transport and the macroscopic thermodynamic properties of SmB6.

  1. A model-based approach for the calibration and traceability of the angle resolved scattering light sensor

    Science.gov (United States)

    Seewig, Jörg; Eifler, Matthias; Schneider, Frank; Kirsch, Benjamin; Aurich, Jan C.

    2016-06-01

    Within the field of geometric product specification there is a growing need for the application of inline measurement systems. The use of inline measurement requires robust and fast measurement principles. A very robust optical measurement principle is the angle resolved scattering light (ARS) sensor. The ARS sensor provides high precision and high resolution measurement data of technical surfaces because the surface angles are measured as an intensity distribution on a detector instead of measuring a series of discrete height values. However, until now, there were no specific measurement standards for the calibration of the ARS sensor and no traceability was ensured. In this paper, new strategies for the calibration of an ARS sensor are proposed. A new mathematical model for the ARS sensor is introduced. Based on this, two new measurement standards for the calibration of the sensor parameters are derived. These standards are designed with a model-based approach and can calibrate sensor-specific properties of the ARS sensor. The manufacturing of the standards is described and measurement results are provided.

  2. Dual analyzer system for surface analysis dedicated for angle-resolved photoelectron spectroscopy at liquid surfaces and interfaces

    Science.gov (United States)

    Niedermaier, Inga; Kolbeck, Claudia; Steinrück, Hans-Peter; Maier, Florian

    2016-04-01

    The investigation of liquid surfaces and interfaces with the powerful toolbox of ultra-high vacuum (UHV)-based surface science techniques generally has to overcome the issue of liquid evaporation within the vacuum system. In the last decade, however, new classes of liquids with negligible vapor pressure at room temperature—in particular, ionic liquids (ILs)—have emerged for surface science studies. It has been demonstrated that particularly angle-resolved X-ray Photoelectron Spectroscopy (ARXPS) allows for investigating phenomena that occur at gas-liquid and liquid-solid interfaces on the molecular level. The results are not only relevant for IL systems but also for liquids in general. In all of these previous ARXPS studies, the sample holder had to be tilted in order to change the polar detection angle of emitted photoelectrons, which restricted the liquid systems to very thin viscous IL films coating a flat solid support. We now report on the concept and realization of a new and unique laboratory "Dual Analyzer System for Surface Analysis (DASSA)" which enables fast ARXPS, UV photoelectron spectroscopy, imaging XPS, and low-energy ion scattering at the horizontal surface plane of macroscopically thick non-volatile liquid samples. It comprises a UHV chamber equipped with two electron analyzers mounted for simultaneous measurements in 0° and 80° emission relative to the surface normal. The performance of DASSA on a first macroscopic liquid system will be demonstrated.

  3. Anisotropy of chemical bonding in semifluorinated graphite C2F revealed with angle-resolved X-ray absorption spectroscopy.

    Science.gov (United States)

    Okotrub, Alexander V; Yudanov, Nikolay F; Asanov, Igor P; Vyalikh, Denis V; Bulusheva, Lyubov G

    2013-01-22

    Highly oriented pyrolytic graphite characterized by a low misorientation of crystallites is fluorinated using a gaseous mixture of BrF(3) with Br(2) at room temperature. The golden-colored product, easily delaminating into micrometer-size transparent flakes, is an intercalation compound where Br(2) molecules are hosted between fluorinated graphene layers of approximate C(2)F composition. To unravel the chemical bonding in semifluorinated graphite, we apply angle-resolved near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and quantum-chemical modeling. The strong angular dependence of the CK and FK edge NEXAFS spectra on the incident radiation indicates that room-temperature-produced graphite fluoride is a highly anisotropic material, where half of the carbon atoms are covalently bonded with fluorine, while the rest of the carbon atoms preserve π electrons. Comparison of the experimental CK edge spectrum with theoretical spectra plotted for C(2)F models reveals that fluorine atoms are more likely to form chains. This conclusion agrees with the atomic force microscopy observation of a chain-like pattern on the surface of graphite fluoride layers. PMID:23214423

  4. Quantitative angle-resolved small-spot reflectance measurements on plasmonic perfect absorbers: impedance matching and disorder effects.

    Science.gov (United States)

    Tittl, Andreas; Harats, Moshe G; Walter, Ramon; Yin, Xinghui; Schäferling, Martin; Liu, Na; Rapaport, Ronen; Giessen, Harald

    2014-10-28

    Plasmonic devices with absorbance close to unity have emerged as essential building blocks for a multitude of technological applications ranging from trace gas detection to infrared imaging. A crucial requirement for such elements is the angle independence of the absorptive performance. In this work, we develop theoretically and verify experimentally a quantitative model for the angular behavior of plasmonic perfect absorber structures based on an optical impedance matching picture. To achieve this, we utilize a simple and elegant k-space measurement technique to record quantitative angle-resolved reflectance measurements on various perfect absorber structures. Particularly, this method allows quantitative reflectance measurements on samples where only small areas have been nanostructured, for example, by electron-beam lithography. Combining these results with extensive numerical modeling, we find that matching of both the real and imaginary parts of the optical impedance is crucial to obtain perfect absorption over a large angular range. Furthermore, we successfully apply our model to the angular dispersion of perfect absorber geometries with disordered plasmonic elements as a favorable alternative to current array-based designs. PMID:25251075

  5. Automated classification of single airborne particles from two-dimensional angle-resolved optical scattering (TAOS) patterns by non-linear filtering

    Science.gov (United States)

    Crosta, Giovanni Franco; Pan, Yong-Le; Aptowicz, Kevin B.; Casati, Caterina; Pinnick, Ronald G.; Chang, Richard K.; Videen, Gorden W.

    2013-12-01

    Measurement of two-dimensional angle-resolved optical scattering (TAOS) patterns is an attractive technique for detecting and characterizing micron-sized airborne particles. In general, the interpretation of these patterns and the retrieval of the particle refractive index, shape or size alone, are difficult problems. By reformulating the problem in statistical learning terms, a solution is proposed herewith: rather than identifying airborne particles from their scattering patterns, TAOS patterns themselves are classified through a learning machine, where feature extraction interacts with multivariate statistical analysis. Feature extraction relies on spectrum enhancement, which includes the discrete cosine FOURIER transform and non-linear operations. Multivariate statistical analysis includes computation of the principal components and supervised training, based on the maximization of a suitable figure of merit. All algorithms have been combined together to analyze TAOS patterns, organize feature vectors, design classification experiments, carry out supervised training, assign unknown patterns to classes, and fuse information from different training and recognition experiments. The algorithms have been tested on a data set with more than 3000 TAOS patterns. The parameters that control the algorithms at different stages have been allowed to vary within suitable bounds and are optimized to some extent. Classification has been targeted at discriminating aerosolized Bacillus subtilis particles, a simulant of anthrax, from atmospheric aerosol particles and interfering particles, like diesel soot. By assuming that all training and recognition patterns come from the respective reference materials only, the most satisfactory classification result corresponds to 20% false negatives from B. subtilis particles and <11% false positives from all other aerosol particles. The most effective operations have consisted of thresholding TAOS patterns in order to reject defective ones

  6. A high-efficiency spin-resolved photoemission spectrometer combining time-of-flight spectroscopy with exchange-scattering polarimetry

    Energy Technology Data Exchange (ETDEWEB)

    Jozwiak, Chris M.; Graff, Jeff; Lebedev, Gennadi; Andresen, Nord; Schmid, Andreas; Fedorov, Alexei; El Gabaly, Farid; Wan, Weishi; Lanzara, Alessandra; Hussain, Zahid

    2010-04-13

    We describe a spin-resolved electron spectrometer capable of uniquely efficient and high energy resolution measurements. Spin analysis is obtained through polarimetry based on low-energy exchange scattering from a ferromagnetic thin-film target. This approach can achieve a similar analyzing power (Sherman function) as state-of-the-art Mott scattering polarimeters, but with as much as 100 times improved efficiency due to increased reflectivity. Performance is further enhanced by integrating the polarimeter into a time-of-flight (TOF) based energy analysis scheme with a precise and flexible electrostatic lens system. The parallel acquisition of a range of electron kinetic energies afforded by the TOF approach results in an order of magnitude (or more) increase in efficiency compared to hemispherical analyzers. The lens system additionally features a 90 degrees bandpass filter, which by removing unwanted parts of the photoelectron distribution allows the TOF technique to be performed at low electron drift energy and high energy resolution within a wide range of experimental parameters. The spectrometer is ideally suited for high-resolution spin- and angle-resolved photoemission spectroscopy (spin-ARPES), and initial results are shown. The TOF approach makes the spectrometer especially ideal for time-resolved spin-ARPES experiments.

  7. Fourier transform photoemission spectroscopy

    NARCIS (Netherlands)

    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

  8. Angle resolved x-ray photoelectron spectroscopy (ARXPS) analysis of lanthanum oxide for micro-flexography printing

    Energy Technology Data Exchange (ETDEWEB)

    Hassan, S., E-mail: suhaimihas@uthm.edu.my; Yusof, M. S., E-mail: mdsalleh@uthm.edu.my; Maksud, M. I., E-mail: midris1973@gmail.com [Faculty of Mechanical and Manufacturing Engineering, Universiti Tun Hussein Onn Malaysia, 86400 Batu Pahat, Johor (Malaysia); Embong, Z., E-mail: zaidi@uthm.edu.my [Faculty of Science, Technology and Human Development, Universiti Tun Hussein Onn Malaysia, 86400 Batu Pahat, Johor (Malaysia)

    2016-01-22

    Micro-flexography printing was developed in patterning technique from micron to nano scale range to be used for graphic, electronic and bio-medical device on variable substrates. In this work, lanthanum oxide (La{sub 2}O{sub 3}) has been used as a rare earth metal candidate as depositing agent. This metal deposit was embedded on Carbon (C) and Silica (Si) wafer substrate using Magnetron Sputtering technique. The choose of Lanthanum as a target is due to its wide application in producing electronic devices such as thin film battery and printed circuit board. The La{sub 2}O{sub 3} deposited on the surface of Si wafer substrate was then analyzed using Angle Resolve X-Ray Photoelectron Spectroscopy (ARXPS). The position for each synthetic component in the narrow scan of Lanthanum (La) 3d and O 1s are referred to the electron binding energy (eV). The La 3d narrow scan revealed that the oxide species of this particular metal is mainly contributed by La{sub 2}O{sub 3} and La(OH){sub 3}. The information of oxygen species, O{sup 2-} component from O 1s narrow scan indicated that there are four types of species which are contributed from the bulk (O{sup 2−}), two chemisorb component (La{sub 2}O{sub 3}) and La(OH){sub 3} and physisorp component (OH). Here, it is proposed that from the adhesive and surface chemical properties of La, it is suitable as an alternative medium for micro-flexography printing technique in printing multiple fine solid lines at nano scale. Hence, this paper will describe the capability of this particular metal as rare earth metal for use in of micro-flexography printing practice. The review of other parameters contributing to print fine lines will also be described later.

  9. Angle resolved x-ray photoelectron spectroscopy (ARXPS) analysis of lanthanum oxide for micro-flexography printing

    Science.gov (United States)

    Hassan, S.; Yusof, M. S.; Embong, Z.; Maksud, M. I.

    2016-01-01

    Micro-flexography printing was developed in patterning technique from micron to nano scale range to be used for graphic, electronic and bio-medical device on variable substrates. In this work, lanthanum oxide (La2O3) has been used as a rare earth metal candidate as depositing agent. This metal deposit was embedded on Carbon (C) and Silica (Si) wafer substrate using Magnetron Sputtering technique. The choose of Lanthanum as a target is due to its wide application in producing electronic devices such as thin film battery and printed circuit board. The La2O3 deposited on the surface of Si wafer substrate was then analyzed using Angle Resolve X-Ray Photoelectron Spectroscopy (ARXPS). The position for each synthetic component in the narrow scan of Lanthanum (La) 3d and O 1s are referred to the electron binding energy (eV). The La 3d narrow scan revealed that the oxide species of this particular metal is mainly contributed by La2O3 and La(OH)3. The information of oxygen species, O2- component from O 1s narrow scan indicated that there are four types of species which are contributed from the bulk (O2-), two chemisorb component (La2O3) and La(OH)3 and physisorp component (OH). Here, it is proposed that from the adhesive and surface chemical properties of La, it is suitable as an alternative medium for micro-flexography printing technique in printing multiple fine solid lines at nano scale. Hence, this paper will describe the capability of this particular metal as rare earth metal for use in of micro-flexography printing practice. The review of other parameters contributing to print fine lines will also be described later.

  10. Angle resolved x-ray photoelectron spectroscopy (ARXPS) analysis of lanthanum oxide for micro-flexography printing

    International Nuclear Information System (INIS)

    Micro-flexography printing was developed in patterning technique from micron to nano scale range to be used for graphic, electronic and bio-medical device on variable substrates. In this work, lanthanum oxide (La2O3) has been used as a rare earth metal candidate as depositing agent. This metal deposit was embedded on Carbon (C) and Silica (Si) wafer substrate using Magnetron Sputtering technique. The choose of Lanthanum as a target is due to its wide application in producing electronic devices such as thin film battery and printed circuit board. The La2O3 deposited on the surface of Si wafer substrate was then analyzed using Angle Resolve X-Ray Photoelectron Spectroscopy (ARXPS). The position for each synthetic component in the narrow scan of Lanthanum (La) 3d and O 1s are referred to the electron binding energy (eV). The La 3d narrow scan revealed that the oxide species of this particular metal is mainly contributed by La2O3 and La(OH)3. The information of oxygen species, O2- component from O 1s narrow scan indicated that there are four types of species which are contributed from the bulk (O2−), two chemisorb component (La2O3) and La(OH)3 and physisorp component (OH). Here, it is proposed that from the adhesive and surface chemical properties of La, it is suitable as an alternative medium for micro-flexography printing technique in printing multiple fine solid lines at nano scale. Hence, this paper will describe the capability of this particular metal as rare earth metal for use in of micro-flexography printing practice. The review of other parameters contributing to print fine lines will also be described later

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-01-15

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

  12. Theory on photoemission and inverse photoemission spectra in VO2

    International Nuclear Information System (INIS)

    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

  13. Angle-resolved soft X-ray magnetic circular dichroism in a monatomic Fe layer facing an MgO(0 0 1) tunnel barrier

    Energy Technology Data Exchange (ETDEWEB)

    Mamiya, K. [Photon Factory, Institute of Materials Structure Science (IMSS), High Energy Accelerator Research Organization, 1-1 Oho, Tsukuba, Ibaraki 305-0801 (Japan); Koide, T. [Photon Factory, Institute of Materials Structure Science (IMSS), High Energy Accelerator Research Organization, 1-1 Oho, Tsukuba, Ibaraki 305-0801 (Japan)]. E-mail: tsuneharu.koide@kek.jp; Ishida, Y. [Department of Complexity Science and Engineering, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561 (Japan); Osafune, Y. [Department of Complexity Science and Engineering, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561 (Japan); Fujimori, A. [Department of Complexity Science and Engineering, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561 (Japan); Suzuki, Y. [Graduate School of Engineering Science, Osaka University, 1-3 Toyonaka, Osaka 560-8531 (Japan); NanoElectronics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568 (Japan); Katayama, T. [NanoElectronics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568 (Japan); Yuasa, S. [NanoElectronics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568 (Japan)

    2006-11-15

    The electronic and magnetic states of a monatomic Fe(0 0 1) layer directly facing an MgO(0 0 1) tunnel barrier were studied by angle-resolved X-ray magnetic circular dichroism (XMCD) at the Fe L {sub 2,3} edges in the longitudinal (L) and transverse (T) arrangements. A strong XMCD reveals no oxidation of the 1-ML Fe, showing its crucial role in giant tunnel magnetoresistance effects in Fe/MgO/Fe magnetic tunnel junctions. Sum-rule analyses of the angle-resolved XMCD give values of a spin moment, in-plane and out-of-plane orbital and magnetic dipole moments. Argument is given on their physical implication.

  14. Electronic Structure of Magnetic 3D Metals: Ground State, Fermi Surface and Photoemission Properties

    Energy Technology Data Exchange (ETDEWEB)

    Eastman, D. E.; Janak, J. F.; Williams, A. R.; Coleman, R. V.; Wendin, G.

    1979-01-01

    Various electronic and magnetic properties of the ferromagnetic 3d metals Ni, Co and Fe and related metals are described, including ground-state properties, Fermi surfaces and both one-electron and many-electron aspects of photoemission and optical absorption processes. Experimental de Haas-van Alphen results for the spin-polarized Fermi surfaces and angle-resolved photoemission results for the exchange-split energy-band dispersions for Ni, Co and Fe are summarized. Single-particle energy-band descriptions of these Fermi surfaces and band dispersions, as well as various ground-state properties (lattice constant, cohesive energy, bulk modulus, magnetic moment, hyperfine field, etc.) are given in terms of the density-functional theory of Hohenberg, Kohn and Sham. In general, these properties can be understood quite well within the single-particle picture. Also discussed are troublesome questions concerning the exchange splitting, band dispersions and satellite structure of Ni. Various optical and photoemission processes for Co, Fe, Ni and Cu exhibiting many-electron phenomena are discussed, including four-level absorption edges, resonances, photoemission relaxation effects, shake-up processes and Auger processes.

  15. Automated angle-scanning photoemission end-station with molecular beam epitaxy at KEK-PF BL-1C

    CERN Document Server

    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.

  16. Structural and electronic properties of V2O3 ultrathin film on Ag(001): LEED and photoemission study

    Science.gov (United States)

    Kundu, Asish K.; Menon, Krishnakumar S. R.

    2016-05-01

    V2O3 ultrathin films were grown on Ag(001) substrate by reactive evaporation of vanadium (V) metal in presence of oxygen and their structural and electronic properties were studied by Low Energy Electron Diffraction (LEED), X-ray Photo Electron Spectroscopy (XPS) and Angle Resolved Photoemission Spectroscopic (ARPES) techniques, respectively. On top of square symmetry substrate Ag(001), hexagonal surface of V2O3 (0001) is stabilized in the form of two domain structure, rotated by 30°(or 90°)to each other, has been observed by LEED. Rather than epitaxial flat monolayer, formation of well-ordered V2O3 (0001) island has been confirmed from the LEED and the Photoemission Spectroscopic (PES) study. Stoichiometry of the grown film was confirmed by the XPS study. Evolution of valance band electronic structure of V2O3 (0001) surface has been studied as a function of film thickness by ARPES.

  17. Analyzing spatial correlations in tissue using angle-resolved low coherence interferometry measurements guided by co-located optical coherence tomography.

    Science.gov (United States)

    Kim, Sanghoon; Heflin, Stephanie; Kresty, Laura A; Halling, Meredith; Perez, Laura N; Ho, Derek; Crose, Michael; Brown, William; Farsiu, Sina; Arshavsky, Vadim; Wax, Adam

    2016-04-01

    Angle-resolved low coherence interferometry (a/LCI) is an optical technique used to measure nuclear morphology in situ. However, a/LCI is not an imaging modality and can produce ambiguous results when the measurements are not properly oriented to the tissue architecture. Here we present a 2D a/LCI system which incorporates optical coherence tomography imaging to guide the measurements. System design and characterization are presented, along with example cases which demonstrate the utility of the combined measurements. In addition, future development and applications of this dual modality approach are discussed. PMID:27446664

  18. The Use of XPS and Angle Resolved XPS for the Characterization of Self Assembled Monolayer Grown on Substrate Surfaces for Specific Biological Applications

    International Nuclear Information System (INIS)

    The techniques of X-Ray Photoelectron Spectroscopy (XPS) and angle resolved XPS have been utilised to characterise the chemistry and structure of SAMs grown on gold surfaces for biological applications. A study of a series of alkane thiol SAMs on gold showed that the film thickness is proportional to alkane chain length and that changes in the sulphur chemistry indicate different bonding modes at low and high overlayer coverage. It is determined that a well ordered matrix thiol has a SAM film thickness confirming that the molecules are aligned at a 27 degree tilt angle to the surface normal and bond to the gold surface via the sulphur group. (author)

  19. High-resolution soft-X-ray beamline ADRESS at Swiss Light Source for resonant inelastic X-ray scattering and angle-resolved photoelectron spectroscopies

    OpenAIRE

    Strocov, V. N.; Schmitt, T; U. Flechsig; Schmidt, T.; Imhof, A; Q. Chen; J. Raabe; Betemps, R.; Zimoch, D.; Krempasky, J.; A. Piazzalunga; X Wang; Grioni, M.; Patthey, L.

    2009-01-01

    We describe the concepts and technical realization of the high-resolution soft-X-ray beamline ADRESS operating in the energy range from 300 to 1600 eV and intended for Resonant Inelastic X-ray Scattering (RIXS) and Angle-Resolved Photoelectron Spectroscopy (ARPES). The photon source is an undulator of novel fixed-gap design where longitudinal movement of permanent magnetic arrays controls not only the light polarization (including circular and 0-180 deg rotatable linear polarizations) but als...

  20. High-resolution soft X-ray beamline ADRESS at the Swiss Light Source for resonant inelastic X-ray scattering and angle-resolved photoelectron spectroscopies

    OpenAIRE

    Strocov, V. N.; Schmitt, T; U. Flechsig; Schmidt, T.; Imhof, A; Q. Chen; J. Raabe; Betemps, R.; Zimoch, D.; Krempasky, J.; X Wang; Grioni, M.; A. Piazzalunga; Patthey, L.

    2010-01-01

    The concepts and technical realisation of the high-resolution soft X-ray beamline ADRESS operating in the energy range from 300 to 1600 eV and intended for resonant inelastic X-ray scattering (RIXS) and angle-resolved photoelectron spectroscopy (ARPES) are described. The photon source is an undulator of novel fixed-gap design where longitudinal movement of permanent magnetic arrays controls not only the light polarization (including circular and 0–180° rotatable linear polarizations) but also...

  1. Plasmon Enhanced Photoemission

    Energy Technology Data Exchange (ETDEWEB)

    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. Emergence of anisotropic heavy fermions in antiferromagnetic Kondo lattice CeIn3 revealed by photoemission

    Science.gov (United States)

    Zhang, Yun; Lu, Haiyan; Zhu, Xiegang; Tan, Shiyong; Chen, Qiuyun; Feng, Wei; Xie, Donghua; Luo, Lizhu; Zhang, Wen; Lai, Xinchun; Donglai Feng Team; Huiqiu Yuan Team

    One basic concept in heavy fermions systems is the entanglement of localized spin state and itinerant electron state. It can be tuned by two competitive intrinsic mechanisms, Kondo effect and Ruderman-Kittel-Kasuya-Yosida interaction, with external disturbances. The key issue regarding heavy fermions properties is how the two mechanisms work in the same phase region. To investigate the relation of the two mechanisms, the cubic antiferromagnetic heavy fermions compound CeIn3 was investigated by soft x-ray angle resolved photoemission spectroscopy. The hybridization between f electrons and conduction bands in the paramagnetic state was observed directly, providing compelling evidence for Kondo screening scenario and coexistence of two mechanisms. The hybridization strength shows slight and regular anisotropy in K space, implying that the two mechanisms are competitive and anisotropic. This work illuminates the concomitant and competitive relation between the two mechanisms and supplies some evidences for the anisotropic superconductivity of CeIn3

  3. Rashba splitting in an image potential state investigated by circular dichroism two-photon photoemission spectroscopy

    Science.gov (United States)

    Nakazawa, T.; Takagi, N.; Kawai, Maki; Ishida, H.; Arafune, R.

    2016-09-01

    We have explored the band splitting and spin texture of the image potential state (IPS) on Au(001) derived from the Rashba-type spin-orbit interaction (SOI) by using angle-resolved bichromatic two-photon photoemission (2PPE) spectroscopy in combination with circular dichroism (CD). The Rashba parameter for the first (n =1 ) IPS is determined to be 48-20+8meV Å , which is consistent with the spin-polarized band structure calculated from the embedded Green's function technique for semi-infinite crystals. The present results demonstrate that bichromatic CD-2PPE spectroscopy is powerful for mapping the spin-polarized unoccupied band structures originating from SOIs in various classes of condensed matter.

  4. Temperature-dependent photoemission features for overdoped Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+x} cuprates

    Energy Technology Data Exchange (ETDEWEB)

    Rast, S.; Frazer, B.H.; Onellion, M. [Wisconsin Univ., Madison, WI (United States). Dept. of Physics; Schmauder, T.; Abrecht, M.; Touzelet, O.; Berger, H.; Margaritondo, G.; Pavuna, D. [Ecole Polytechnique Federale, Lausanne (Switzerland). Inst. de Physique Appliquee

    2000-07-01

    We report temperature-dependent angle-resolved photoemission spectra for overdoped Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+x} single-crystal samples. The data indicate that there is a special temperature (T{sup +}) where the spectral function changes intensity, and where the energy difference between the peak and dip features changes. The data also demonstrate that immediately above the superconducting transition temperature, the system exhibits a non-Lorentzian lineshape. We discuss implications of the data. (orig.)

  5. Band dispersions of the π-bonded-chain reconstruction of Si(111)3x1-Li: A critical evaluation of theory and experiment

    International Nuclear Information System (INIS)

    The surface-state band-structure of the three-domain Si(111)3x1-Li reconstruction has been determined using angle-resolved photoemission. Experimental band dispersions are compared to theoretical calculations for the extended Pandey model and the Seiwatz model. Even though the extended Pandey model is favored on the basis of scanning tunneling microscopy and total-energy considerations, the calculated surface states are inconsistent with experiment. The calculated states for the Seiwatz model are consistent with the experimental dispersion along the main symmetry direction (bar Γ bar A) but serious discrepancies exist in other parts of the Brillouin zone. The disparity between the density-functional-theory calculations and experiment indicate that exchange and correlation in π-bonded Si chains may need to be analyzed beyond the mean-field band-structure approach. copyright 1996 The American Physical Society

  6. Pseudogap in cuprates driven by d-wave flux-phase order proximity effects: a theoretical analysis from Raman and ARPES experiments

    Science.gov (United States)

    Greco, Andrés; Bejas, Matías

    2014-12-01

    One of the puzzling characteristics of the pseudogap phase of high-Tc cuprates is the nodal-antinodal dichotomy. While the nodal quasiparticles have a Fermi liquid behaviour, the antinodal ones show non-Fermi liquid features and an associated pseudogap. Angle-resolved photoemission spectroscopy and electronic Raman scattering are two valuable tools which have shown universal features which are rather material-independent, and presumably intrinsic to the pseudogap phase. The doping and temperature dependence of the Fermi arcs and the pseudogap observed by photoemission near the antinode correlates with the non-Fermi liquid behaviour observed by Raman for the B1g mode. In contrast, and similar to the nodal quasiparticles detected by photoemission, the Raman B2g mode shows Fermi liquid features. We show that these two experiments can be analysed, in the context of the t-J model, by self-energy effects in the proximity to a d-wave flux-phase order instability. This approach supports a crossover origin for the pseudogap, and a scenario of two competing phases. The B2g mode shows, in an underdoped case, a depletion at intermediate energy which has attracted renewed interest. We study this depletion and discuss its origin and relation with the pseudogap.

  7. Ultrafast demagnetization dynamics of thin Fe/W(110) films: comparison of time and spin-resolved photoemission with time resolved magneto-optic experiments

    International Nuclear Information System (INIS)

    We use two complementary experimental approaches to probe ultrafast magnetization dynamics. Using a 1.55 eV pump laser pulse we demagnetize 7 monolayer (ML) thin Fe films epitaxially grown on W(110). We probe the temporal evolution of the magnetization using time-resolved magneto-optical Kerr effect (TR-MOKE) at a probe photon energy of 3.1 eV. In addition we use time- and spin- resolved photoemission (TR-SPES) to probe the evolution of the spin polarization of the film (probe photon energy 5.9 eV). With TR-MOKE for all the observed quenching the demagnetization times have the same value (within the error bars) equal to the expected cross-correlation of the pump and probe pulses (about 250 fs). However TR-SPES measurements show demagnetization times limited by the cross-correlation (about 320 fs) only for quenching below 33%. Indeed, for greater quenching we find a significant increase in the demagnetization times to about 500 fs. We explain this behavior as a clear indication of the bandstructure importance in the demagnetization process.

  8. Observation by resonant angle-resolved photoemission of a critical thickness for 2-dimensional electron gas formation in SrTiO$_3$ embedded in GdTiO$_3$

    OpenAIRE

    Nemšák, S.; CONTI, G; Pálsson, G. K.; Conlon, C.; Cho, S.; Rault, J.; Avila, J.; Asensio, M. -C.; Jackson, C; Moetakef, P.; Janotti, A.; Bjaalie, L.; Himmetoglu, B.; Van de Walle, C. G.; Balents, L.

    2015-01-01

    For certain conditions of layer thickness, the interface between GdTiO$_3$ (GTO) and SrTiO$_3$ (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$_3$)$_{0.3}$(Sr$_2$AlTaO$_6$)$_{0.7}$ (LSAT), with the STO layer thicknesses being at what has been suggeste...

  9. Common Electronic Features and Electronic Nematicity in Parent Compounds of Iron-Based Superconductors and FeSe/SrTiO3 Films Revealed by Angle-Resolved Photoemission Spectroscopy

    Science.gov (United States)

    De-Fa, Liu; Lin, Zhao; Shao-Long, He; Yong, Hu; Bing, Shen; Jian-Wei, Huang; Ai-Ji, Liang; Yu, Xu; Xu, Liu; Jun-Feng, He; Dai-Xiang, Mou; Shan-Yu, Liu; Hai-Yun, Liu; Guo-Dong, Liu; Wen-Hao, Zhang; Fang-Sen, Li; Xu-Cun, Ma; Qi-Kun, Xue; Xian-Hui, Chen; Gen-Fu, Chen; Li, Yu; Jun, Zhang; Zu-Yan, Xu; Chuang-Tian, Chen; Xing-Jiang, Zhou

    2016-07-01

    Not Available Supported by the National Natural Science Foundation of China under Grant Nos 11190022, 11334010 and 11534007, the National Basic Research Program of China under Grant No 2015CB921000, and the Strategic Priority Research Program (B) of Chinese Academy of Sciences under Grant No XDB07020300.

  10. Angle-resolved cathodoluminescence nanoscopy

    NARCIS (Netherlands)

    T. Coenen

    2014-01-01

    The field of microscopy is an important cornerstone of physical and biological sciences. The development of high-resolution microscopy/nanoscopy techniques has enabled a revolution in science and technology, greatly improving our understanding of the microscopic world around us, and forming the basi

  11. Exploring three-dimensional orbital imaging with energy-dependent photoemission tomography

    Science.gov (United States)

    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.

  12. Design and validation of an angle-resolved low-coherence interferometry fiber probe for in vivo clinical measurements of depth-resolved nuclear morphology

    Science.gov (United States)

    Zhu, Yizheng; Terry, Neil G.; Woosley, John T.; Shaheen, Nicholas J.; Wax, Adam

    2011-01-01

    We present a novel Fourier-domain angle-resolved low-coherence interferometry (a /LCI) fiber probe designed for in vivo clinical application in gastrointestinal endoscopy. The a/LCI technique measures the depth-resolved angular scattering distribution to determine the size distribution and optical density of cell nuclei for assessing the health of epithelial tissues. Clinical application is enabled by an endoscopic fiber-optic probe that employs a 2.3-m-long coherent fiber bundle and is compatible with the standard 2.8-mm-diam biopsy channel of a gastroscope. The probe allows for real-time data acquisition by collecting the scattering from multiple angles in parallel, enabled by the Fourier domain approach. The performance of the probe is characterized through measurement of critical parameters. The depth-resolved sizing capability of the system is demonstrated using single- and double-layer microsphere phantoms with subwavelength sizing precision and accuracy achieved. Initial results from a clinical feasibility test are also presented to show in vivo application in the human esophagus.

  13. Omnidirectional Measurements of Angle-Resolved Heat Capacity for Complete Detection of Superconducting Gap Structure in the Heavy-Fermion Antiferromagnet UPd_{2}Al_{3}.

    Science.gov (United States)

    Shimizu, Yusei; Kittaka, Shunichiro; Sakakibara, Toshiro; Tsutsumi, Yasumasa; Nomoto, Takuya; Ikeda, Hiroaki; Machida, Kazushige; Homma, Yoshiya; Aoki, Dai

    2016-07-15

    Quasiparticle excitations in UPd_{2}Al_{3} were studied by means of heat-capacity (C) measurements under rotating magnetic fields using a high-quality single crystal. The field dependence shows C(H)∝H^{1/2}-like behavior at low temperatures for both two hexagonal crystal axes, i.e., H∥[0001] (c axis) and H∥[112[over ¯]0] (a axis), suggesting the presence of nodal quasiparticle excitations from heavy bands. At low temperatures, the polar-angle (θ) dependence of C exhibits a maximum along H∥[0001] with a twofold symmetric oscillation below 0.5 T, and an unusual shoulder or hump anomaly has been found around 30°-60° from the c axis in C(θ) at intermediate fields (1≲μ_{0}H≲2  T). These behaviors in UPd_{2}Al_{3} purely come from the superconducting nodal quasiparticle excitations, and can be successfully reproduced by theoretical calculations assuming the gap symmetry with a horizontal linear line node. We demonstrate the whole angle-resolved heat-capacity measurements done here as a novel spectroscopic method for nodal gap determination, which can be applied to other exotic superconductors. PMID:27472129

  14. High-resolution soft-X-ray beamline ADRESS at Swiss Light Source for resonant inelastic X-ray scattering and angle-resolved photoelectron spectroscopies

    CERN Document Server

    Strocov, V N; Flechsig, U; Schmidt, T; Imhof, A; Chen, Q; Raabe, J; Betemps, R; Zimoch, D; Krempasky, J; Piazzalunga, A; Wang, X; Grioni, M; Patthey, L

    2009-01-01

    We describe the concepts and technical realization of the high-resolution soft-X-ray beamline ADRESS operating in the energy range from 300 to 1600 eV and intended for Resonant Inelastic X-ray Scattering (RIXS) and Angle-Resolved Photoelectron Spectroscopy (ARPES). The photon source is an undulator of novel fixed-gap design where longitudinal movement of permanent magnetic arrays controls not only the light polarization (including circular and 0-180 deg rotatable linear polarizations) but also the energy without changing the gap. The beamline optics is based on the well-established scheme of plane grating monochromator (PGM) operating in collimated light. The ultimate resolving power E/dE is above 33000 at 1 keV photon energy. The choice of blazed vs lamellar gratings and optimization of their profile parameters is described. Due to glancing angles on the mirrors as well as optimized groove densities and profiles of the gratings, high photon flux is achieved up to 1.0e13 photons/s/0.01%BW at 1 keV. Ellipsoida...

  15. Three-dimensional bulk electronic structure of the Kondo lattice CeIn3 revealed by photoemission

    Science.gov (United States)

    Zhang, Yun; Lu, Haiyan; Zhu, Xiegang; Tan, Shiyong; Liu, Qin; Chen, Qiuyun; Feng, Wei; Xie, Donghua; Luo, Lizhu; Liu, Yu; Song, Haifeng; Zhang, Zhengjun; Lai, Xinchun

    2016-09-01

    We show the three-dimensional electronic structure of the Kondo lattice CeIn3 using soft x-ray angle resolved photoemission spectroscopy in the paramagnetic state. For the first time, we have directly observed the three-dimensional topology of the Fermi surface of CeIn3 by photoemission. The Fermi surface has a complicated hole pocket centred at the Γ-Z line and an elliptical electron pocket centred at the R point of the Brillouin zone. Polarization and photon-energy dependent photoemission results both indicate the nearly localized nature of the 4f electrons in CeIn3, consistent with the theoretical prediction by means of the combination of density functional theory and single-site dynamical mean-field theory. Those results illustrate that the f electrons of CeIn3, which is the parent material of CeMIn5 compounds, are closer to the localized description than the layered CeMIn5 compounds.

  16. Inverse photoemission and resonant photoemission characterization of semimagnetic semiconductors

    International Nuclear Information System (INIS)

    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

  17. Model simulations of momentum-resolved photoemission from quasicrystals

    CERN Document Server

    Rotenberg, E; Horn, K

    2002-01-01

    Recent experiments have demonstrated that valence band dispersion may be observed on suitably prepared surfaces of quasicrystals. We present model calculations for optical transitions for one-dimensional a periodic lattices, and show that these calculations are consistent with the experimental photoemission results. We estimate the total number of bands which can be observed in such an experiment is reduced from infinite, to just two to three bands in a typical experiment.

  18. Angle-resolved photoelectron spectroscopy studies of the many-body effects in the electronic structure of high-T{sub c} cuprates

    Energy Technology Data Exchange (ETDEWEB)

    Inosov, Dmytro S.

    2008-06-18

    In the present work some steps are done towards understanding the anomalous effects observed in the single-particle excitation spectra of cuprates. First, the electronic properties of BSCCO are considered. The main result of this part of the work is a model of the Green's function that is later used for calculating the two-particle excitation spectrum. Then, the matrix element effects in the photoemission spectra of cuprates are discussed. After a general introduction to the problem, the thesis focuses on the recently discovered anomalous behavior of the ARPES spectra that partially originates from the momentum-dependent photoemission matrix element. The momentum- and excitation energy dependence of the anomalous high-energy dispersion, termed ''waterfalls'', is covered in full detail. Understanding the role of the matrix element effects in this phenomenon proves crucial, as they obstruct the view of the underlying excitation spectrum that is of indisputable interest. For the optimally doped bilayer Bi-based cuprate, the renormalized two-particle correlation function in the superconducting state is calculated from ARPES data within an itinerant model based on the random phase approximation (RPA). (orig.)

  19. High-resolution soft X-ray beamline ADRESS at the Swiss Light Source for resonant inelastic X-ray scattering and angle-resolved photoelectron spectroscopies.

    Science.gov (United States)

    Strocov, V N; Schmitt, T; Flechsig, U; Schmidt, T; Imhof, A; Chen, Q; Raabe, J; Betemps, R; Zimoch, D; Krempasky, J; Wang, X; Grioni, M; Piazzalunga, A; Patthey, L

    2010-09-01

    The concepts and technical realisation of the high-resolution soft X-ray beamline ADRESS operating in the energy range from 300 to 1600 eV and intended for resonant inelastic X-ray scattering (RIXS) and angle-resolved photoelectron spectroscopy (ARPES) are described. The photon source is an undulator of novel fixed-gap design where longitudinal movement of permanent magnetic arrays controls not only the light polarization (including circular and 0-180 degrees rotatable linear polarizations) but also the energy without changing the gap. The beamline optics is based on the well established scheme of plane-grating monochromator operating in collimated light. The ultimate resolving power E/DeltaE is above 33000 at 1 keV photon energy. The choice of blazed versus lamellar gratings and optimization of their profile parameters is described. Owing to glancing angles on the mirrors as well as optimized groove densities and profiles of the gratings, the beamline is capable of delivering high photon flux up to 1 x 10(13) photons s(-1) (0.01% BW)(-1) at 1 keV. Ellipsoidal refocusing optics used for the RIXS endstation demagnifies the vertical spot size down to 4 microm, which allows slitless operation and thus maximal transmission of the high-resolution RIXS spectrometer delivering E/DeltaE > 11000 at 1 keV photon energy. Apart from the beamline optics, an overview of the control system is given, the diagnostics and software tools are described, and strategies used for the optical alignment are discussed. An introduction to the concepts and instrumental realisation of the ARPES and RIXS endstations is given. PMID:20724785

  20. Photocathode device that replenishes photoemissive coating

    Energy Technology Data Exchange (ETDEWEB)

    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.

  1. Time delays in correlated photoemission processes

    Science.gov (United States)

    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.

  2. Nonlinear Photoemission Electron Micrographs of Plasmonic Nanoholes in Gold Thin Films

    Energy Technology Data Exchange (ETDEWEB)

    Gong, Yu; Joly, Alan G.; El-Khoury, Patrick Z.; Hess, Wayne P.

    2014-11-06

    Nonlinear photoemission electron microscopy of isolated nanoholes in gold thin films map propagating surface plasmon polaritons (SPPs) launched from the lithographically patterned plasmonic structures. A damped sinusoidal elongated ring-like photoemission beat pattern is observed from the nanoholes, following low angle of incidence irradiation of these structures with sub-15 fs 780 nm laser pulses. A notable agreement between finite difference time domain simulations and experiment corroborates our assignment of the observed photoemission patterns to SPPs launched from isolated nanoholes and probed through nonlinear photoemission. We also demonstrate how the efficiency of coupling light waves into isolated plasmonic holes can be tuned by varying hole diameter. In this regard, a simple intuitive geometrical model, which accounts for the observed and simulated diameter dependent plasmonic response, is proposed. Overall, this study paves the way for designing nanohole assemblies where optical coupling and subsequent plasmon propagation can be rationally controlled through 2D SPP interferometry

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

    International Nuclear Information System (INIS)

    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

  4. ARPES experiment in fermiology of quasi-2D metals (Review Article)

    OpenAIRE

    Kordyuk, A. A.

    2014-01-01

    Angle resolved photoemission spectroscopy (ARPES) enables direct observation of the Fermi surface and underlying electronic structure of crystals---the basic concepts to describe all the electronic properties of solids and to understand the key electronic interactions involved. The method is the most effective to study quasi-2D metals, to which the subjects of almost all hot problems in modern condensed matter physics have happened to belong. This has forced incredibly the development of the ...

  5. Coherent and incoherent processes in resonant photoemission

    Energy Technology Data Exchange (ETDEWEB)

    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.

  6. Nondipole Photoemission from Chiral Enantiomers of Camphor

    Science.gov (United States)

    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.

  7. Growth and photoemission spectroscopic studies of ultrathin noble metal films on graphite

    Indian Academy of Sciences (India)

    S K Mahatha; Krishnakumar S R Menon

    2015-06-01

    Growth of Cu, Ag and Au thin films on graphite(0 0 0 1)surface and possible formation of quantum well (QW) states originating due to the confinement of thin film sp electrons within the band gap of graphite along M symmetry direction are investigated using low-energy electron diffraction (LEED) and angle-resolved photoemission spectroscopy (ARPES). Higher surface diffusivity and surface energy of Cu on graphite surface led to cluster growth and does not reveal any quantum size effect, while Ag and Au films grow epitaxially in spite of large lattice mismatch. However, better surface ordering has been achieved by growing Ag and Au at low temperature (LT), followed by room-temperature (RT) annealing which are evident from LEED and the presence of sharp Shockley-type surface state (SS) at Fermi level (F). ARPES study of Ag films on graphite does not show any QW states, whereas Au films demonstrate a very sharp SS, Au bulk bands and well-resolved QW states or resonances. The observed low in-plane dispersions of these Au QW states or resonances are compared with the dispersions obtained in the previous Au QW state studies as well as for free-standing Au films.

  8. New ambient pressure photoemission endstation at Advanced Light Source beamline 9.3.2

    KAUST Repository

    Grass, Michael E.

    2010-01-01

    During the past decade, the application of ambient pressure photoemission spectroscopy (APPES) has been recognized as an important in situ tool to study environmental and materials science, energy related science, and many other fields. Several APPES endstations are currently under planning or development at the USA and international light sources, which will lead to a rapid expansion of this technique. The present work describes the design and performance of a new APPES instrument at the Advanced Light Source beamline 9.3.2 at Lawrence Berkeley National Laboratory. This new instrument, Scienta R4000 HiPP, is a result of collaboration between Advanced Light Source and its industrial partner VG-Scienta. The R4000 HiPP provides superior electron transmission as well as spectromicroscopy modes with 16 μm spatial resolution in one dimension and angle-resolved modes with simulated 0.5° angular resolution at 24° acceptance. Under maximum transmission mode, the electron detection efficiency is more than an order of magnitude better than the previous endstation at beamline 9.3.2. Herein we describe the design and performance of the system, which has been utilized to record spectra above 2 mbar. © 2010 American Institute of Physics.

  9. A fermi liquid electric structure and the nature of the carriers in high-T/sub c/ cuprates: A photoemission study

    Energy Technology Data Exchange (ETDEWEB)

    Arko, A.J.; List, R.S.; Bartlett, R.J.; Cheong, S.W.; Fisk, Z.; Thompson, J.D.; Olson, C.G.; Yang, A.B.; Liu, R.; Gu, C.; Veal, B.W.; Liu, J.Z.; Paulikas, A.P.; Vandervoort, K.; Claus, H.; Campuzano, J.C.; Schirber, J.E.; Shinn, N.D.

    1989-01-01

    We have performed angle-integrated and angle-resolved photoemission measurements at 20 K on well-characterized single crystals of high-T/sub c/ cuprates (both 1:2:3-type and 2:2:1:2-type) cleaved in situ, and find a relatively large, resolution limited Fermi edge which shows large amplitude variations with photon energy, indicative of band structure final state effects. The lineshapes of the spectra of the 1:2:3 materials as a function of photon energy are well reproduced by band structure predictions, indicating a correct mix of 2p and 3d orbitals on the calculations, while the energy positions of the peaks agree with calculated bands only to within /approx/0.5 eV. This may yet prove to reflect the effects of Coulomb correlation. We nevertheless conclude that a Fermi liquid approach to conductivity is appropriate. Angle-resolved data, while still incomplete, suggest agreement with the Fermi surface predicted by the LDA calculations. A BCS-like energy gap is observed in the 2:2:1:2 materials, whose magnitude is twice the weak coupling BCS value (i.e., 2/Delta/ = 7 KT/sub c/). 49 refs., 11 figs.

  10. Polarized resonance photoemission for Nd2CuO4

    International Nuclear Information System (INIS)

    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

  11. Photoemission from Au{111} and {110}. Temperature effects

    DEFF Research Database (Denmark)

    Christensen, Niels Egede

    1979-01-01

    Full zone band structures of gold have been calculated for three lattice constants by means of the relativistic augmented-plane-wave method. The results are used in an analysis of recent high-resolution symmetry-oriented normal photoemission data (Heiman and Neddermeyer). For those elements...... of structure which can be interpreted as bulk direct contributions we find temperature shifts in the spectral positions in agreement with the experiment. Comparison of absolute spectral positions suggests that the d-band complex in the calculation should be down-shifted by 0.38 eV relative to the Fermi level...

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

    DEFF Research Database (Denmark)

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

    2015-01-01

    photoemission rate and transition absorption for nanoparticles surrounded by various media with a broad range of permittivities and show that photoemission rate and transition absorption follow the same dependence on the permittivity. Thus, we conclude that transition absorption is responsible...... calculations for the former one and a three-step phenomenological approach for the latter one. By comparison of both mechanisms, we show that the role of surface mechanism in the total photoemission cannot be neglected, as it dominates in the near-infrared wavelength range. We also show that in order...

  13. Momentum-Dependent Charge Transfer Excitations in Sr{sub {bold 2}}CuO {sub {bold 2}}Cl{sub {bold 2}} Angle-Resolved Electron Energy Loss Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Y.Y.; Zhang, F.C.; Dravid, V.P.; Ng, K.K.; Klein, M.V.; Schnatterly, S.E.; Miller, L.L. [Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208 (United States)]|[Science and Technology Center for Superconductivity, Northwestern University, Evanston, Illinois 60208 (United States)]|[Department of Physics, University of Cincinnati, Cincinnati, Ohio 45221 (United States)]|[Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon (Hong Kong)]|[Department of Physics, Science and Technology Center for Superconductivity, University of Illinois, Urbana, Illinois 61801 (United States)]|[Department of Physics, University of Virginia, Charlottesville, Virginia 22901 (United States)]|[Ames Laboratory, Iowa State University, Ames, Iowa 50011 (United States)

    1996-08-01

    Electron-hole pair excitations in the insulating cuprates Sr{sub 2}CuO{sub 2}Cl{sub 2} were investigated by angle-resolved electron energy loss spectroscopy. The optically allowed and optically forbidden transitions were observed to be strongly anisotropic in Cu-O{sub 2} plane. The former show a large energy dispersion {approximately}1.5 eV along [110], and the latter appear at a higher energy position ({approximately}4.5 eV) only along [100], but not along [110]. We interpret these results as transitions involving excitons. A small exciton model is examined to explain both the observed features. {copyright} {ital 1996 The American Physical Society.}

  14. Angle-resolved X-ray photoelectron spectroscopy of topmost surface for LaNiO 3 thin film grown on SrTiO 3 substrate by laser molecular beam epitaxy

    Science.gov (United States)

    Chen, P.; Xu, S. Y.; Lin, J.; Ong, C. K.; Cui, D. F.

    1999-01-01

    The LaNiO 3 thin film was grown on SrTiO 3 (001) substrate by computer-controlled laser molecular beam epitaxy (laser MBE). In situ monitoring of the growing film surface was performed with a reflection high energy electron diffraction (RHEED). Angle-resolved X-ray photoelectron spectroscopy (ARXPS) indicated that the terminating plane of the LaNiO 3 film was the LaO atomic plane, and the SrTiO 3 (001) surfaces of as-supplied substrate as well as HF-pretreated substrate were predominantly terminated with TiO atomic plane. The structural conversion of the topmost atomic layer from NiO to LaO occurred during the LaNiO 3 epitaxial growth process.

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

    Science.gov (United States)

    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.

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

    OpenAIRE

    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...

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

    OpenAIRE

    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...

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

    Institute of Scientific and Technical Information of China (English)

    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.

  19. Inverse photoemission in strongly correlated electron systems

    NARCIS (Netherlands)

    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

  20. Universal features in the photoemission spectroscopy of high-temperature superconductors

    Science.gov (United States)

    Zhao, Junjing; Chatterjee, Utpal; Ai, Dingfei; Hinks, David G.; Zheng, Hong; Gu, G. D.; Castellan, John-Paul; Rosenkranz, Stephan; Claus, Helmut; Norman, Michael R.; Randeria, Mohit; Campuzano, Juan Carlos

    2013-01-01

    The energy gap for electronic excitations is one of the most important characteristics of the superconducting state, as it directly reflects the pairing of electrons. In the copper–oxide high-temperature superconductors (HTSCs), a strongly anisotropic energy gap, which vanishes along high-symmetry directions, is a clear manifestation of the d-wave symmetry of the pairing. There is, however, a dramatic change in the form of the gap anisotropy with reduced carrier concentration (underdoping). Although the vanishing of the gap along the diagonal to the square Cu–O bond directions is robust, the doping dependence of the large gap along the Cu–O directions suggests that its origin might be different from pairing. It is thus tempting to associate the large gap with a second-order parameter distinct from superconductivity. We use angle-resolved photoemission spectroscopy to show that the two-gap behavior and the destruction of well-defined electronic excitations are not universal features of HTSCs, and depend sensitively on how the underdoped materials are prepared. Depending on cation substitution, underdoped samples either show two-gap behavior or not. In contrast, many other characteristics of HTSCs, such as the dome-like dependence of on doping, long-lived excitations along the diagonals to the Cu–O bonds, and an energy gap at the Brillouin zone boundary that decreases monotonically with doping while persisting above (the pseudogap), are present in all samples, irrespective of whether they exhibit two-gap behavior or not. Our results imply that universal aspects of high- superconductivity are relatively insensitive to differences in the electronic states along the Cu–O bond directions. PMID:24101464

  1. Raising Photoemission Efficiency with Surface Acoustic Waves

    Energy Technology Data Exchange (ETDEWEB)

    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.

  2. Occupied and unoccupied band structure of Ag(100) determined by photoemission from Ag quantum wells and bulk samples

    International Nuclear Information System (INIS)

    Angle-resolved photoemission spectra taken from atomically uniform films of Ag on Fe(100) show layer-resolved quantum-well peaks. The measured peak positions as a function of film thickness permit a unique determination of the initial band dispersion via the Bohr-Sommerfeld quantization rule. This information, combined with normal-emission data taken from a single crystal Ag(100), leads to a unique determination of the final band dispersion. In this study, we employ a two-band model with four adjustable parameters for a simultaneous fit to these experimental results. The initial and final band dispersions deduced from the fit are accurate to better than 0.03 eV at any wave vector k within the range of measurement. The analytic formula for the band dispersions and the parameters for the best fit are given for future reference. The Fermi wave vector along [100], normalized to the Brillouin-zone size, is determined to be kF/kΓX=0.828±0.001, which is more accurate than the de Haas-van Alphen result. The corresponding Fermi velocity is νF=1.06 in units of the free-electron value. The combined reflection phase for the electron wave at the two boundaries is also deduced and compared with a semiempirical formula. This comparison allows us to deduce the edges of the hybridization gap in the Fe substrate. (c) 2000 The American Physical Society

  3. Angle-resolved cathodoluminescence imaging polarimetry

    CERN Document Server

    Osorio, Clara I; Brenny, Benjamin; Polman, Albert; Koenderink, A Femius

    2015-01-01

    Cathodoluminescence spectroscopy (CL) allows characterizing light emission in bulk and nanostructured materials and is a key tool in fields ranging from materials science to nanophotonics. Previously, CL measurements focused on the spectral content and angular distribution of emission, while the polarization was not fully determined. Here we demonstrate a technique to access the full polarization state of the cathodoluminescence emission, that is the Stokes parameters as a function of the emission angle. Using this technique, we measure the emission of metallic bullseye nanostructures and show that the handedness of the structure as well as nanoscale changes in excitation position induce large changes in polarization ellipticity and helicity. Furthermore, by exploiting the ability of polarimetry to distinguish polarized from unpolarized light, we quantify the contributions of different types of coherent and incoherent radiation to the emission of a gold surface, silicon and gallium arsenide bulk semiconductor...

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  5. UNCONTROLLED PHOTOMULTIPLIER CURRENT IN PHOTOEMISSION ANALYSIS

    Directory of Open Access Journals (Sweden)

    K. A. Viazava

    2016-01-01

    Full Text Available The dependence of photon energy from energy of photoelectron is base of photoemission radiation analysis. In such photoemission measurements except current of photocathode is always exist a reverse current from the collector of electrons to the photocathode in two-electrode sensors. There are various ways of reverse and uncontrolled current eliminating or reducing their influence. The constructive method is based on creating an electron-optical system of photoelectronic device, which would be a photoelectron energy analyzer. The second method – technological. However, it requires the manufacture of the photocathode and the dynode system in different vacuum chamber with subsequent connection to a single device in vacuum environment without exposure to the atmosphere. The purpose of this article is to determinate the effect of photoemission from photocathode chamber and the first dynode of photomultiplier on energy distribution of the photoelectrons from photocathode. To solve this problem authors obtained calibration curves for measuring pyrometer module ПИФ 4/2 with ФЭУ-114 as a sensor at supply voltage 1350 V and different decelerating voltages. The effect of illumination on the value of modulation coefficient on temperature k(T and wavelength k(λ is shown. In temperature measurements, this effect is evident in fact that at temperatures below 1400 K linear dependence ln k – T-1 is broken. Still this linear dependence is a necessary consequence of the fact that the measured temperature is color temperature. However, this calibration curve can be used to measure low temperature if the target measurements condition and calibration conditions are identical. In wavelength calibration, curve k(λ at λ > 760 nm is two-valued, that doesn’t allow to identify monochromatic radiation by this method and bring in errors in temperature measurements. 

  6. Surface and subsurface oxidation of Mo2C/Mo(100): low-energy ion-scattering, auger electron, angle-resolved X-ray photoelectron, and mass spectroscopy studies.

    Science.gov (United States)

    Ovári, László; Kiss, János; Farkas, Arnold P; Solymosi, Frigyes

    2005-03-17

    The interaction of oxygen with a carburized Mo(100) surface was investigated at different temperatures (300-1000 K). The different information depths of low-energy ion-scattering (LEIS) spectroscopy, with topmost layer sensitivity, Auger electron spectroscopy (AES), and angle-resolved X-ray photoelectron spectroscopy (ARXPS) allowed us to discriminate between reactions on the topmost layer and subsurface transformations. According to ARXPS measurements, a carbide overlayer was prepared by the high-temperature decomposition of C(2)H(4) on Mo(100), and the carbon distribution proved to be homogeneous with a Mo(2)C stoichiometry down to the information depth of XPS. O(2) adsorbs dissociatively on the carbide layer at room temperature. One part of the chemisorbed oxygen is bound to both C and Mo sites, indicated by LEIS. Another fraction of oxygen atoms probably resides in the hollow sites not occupied by C. The removal of C from the outermost layer by O(2), in the form of CO, detected by mass spectroscopy (MS), was observed at 500-600 K. The carbon-depleted first layer is able to adsorb more oxygen compared to the Mo(2)C/Mo(100) surface. Applying higher doses of O(2) at 800 K results in the inward diffusion of O and the partial oxidation of Mo atoms. This process, however, is not accompanied by the removal of C from subsurface sites. The depletion of C from the bulk starts only at 900 K (as shown by MS, AES, and XPS), very probably by the diffusion of C to the surface followed by its reaction with oxygen. At T(ads) = 1000 K, the carbon content of the sample, down to the information depth of XPS, decreased further, accompanied by the attenuation of the C concentration gradient and a substantially decreased amount of oxygen.

  7. Photoemission from glass dust grains: First measurements

    Science.gov (United States)

    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.

  8. Time-resolved photoemission using attosecond streaking

    CERN Document Server

    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}_...

  9. Resonant photoemission from SmS(100)

    International Nuclear Information System (INIS)

    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)

  10. Signature of quantum criticality in photoemission spectroscopy.

    Science.gov (United States)

    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

  11. Efficient photoemission from robust ferroelectric ceramics

    Energy Technology Data Exchange (ETDEWEB)

    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.

  12. Photoemission studies of f-electron systems: many-body effects. Progress report, October 1, 1982-October 1, 1983

    International Nuclear Information System (INIS)

    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

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

    Science.gov (United States)

    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.

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

    International Nuclear Information System (INIS)

    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

  15. Polarized hard X-ray photoemission system with micro-positioning technique for probing ground-state symmetry of strongly correlated materials.

    Science.gov (United States)

    Fujiwara, Hidenori; Naimen, Sho; Higashiya, Atsushi; Kanai, Yuina; Yomosa, Hiroshi; Yamagami, Kohei; Kiss, Takayuki; Kadono, Toshiharu; Imada, Shin; Yamasaki, Atsushi; Takase, Kouichi; Otsuka, Shintaro; Shimizu, Tomohiro; Shingubara, Shoso; Suga, Shigemasa; Yabashi, Makina; Tamasaku, Kenji; Ishikawa, Tetsuya; Sekiyama, Akira

    2016-05-01

    An angle-resolved linearly polarized hard X-ray photoemission spectroscopy (HAXPES) system has been developed to study the ground-state symmetry of strongly correlated materials. The linear polarization of the incoming X-ray beam is switched by a transmission-type phase retarder composed of two diamond (100) crystals. The best value of the degree of linear polarization was found to be -0.96, containing a vertical polarization component of 98%. A newly developed low-temperature two-axis manipulator enables easy polar and azimuthal rotations to select the detection direction of photoelectrons. The lowest temperature achieved was 9 K, offering the chance to access the ground state even for strongly correlated electron systems in cubic symmetry. A co-axial sample monitoring system with long-working-distance microscope enables the same region on the sample surface to be measured before and after rotation. Combining this sample monitoring system with a micro-focused X-ray beam by means of an ellipsoidal Kirkpatrick-Baez mirror (25 µm × 25 µm FWHM), polarized valence-band HAXPES has been performed on NiO for voltage application as resistive random access memory to demonstrate the micro-positioning technique and polarization switching.

  16. Photoemission electron microscopy of localized surface plasmons in silver nanostructures at telecommunication wavelengths

    International Nuclear Information System (INIS)

    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

  17. Photoemission electron microscopy of localized surface plasmons in silver nanostructures at telecommunication wavelengths

    Energy Technology Data Exchange (ETDEWEB)

    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.

  18. Recoil and related effects in molecular photoemission

    Energy Technology Data Exchange (ETDEWEB)

    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.

  19. Internal Photoemission Spectroscopy of 2-D Materials

    Science.gov (United States)

    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.

  20. Recoil and related effects in molecular photoemission

    International Nuclear Information System (INIS)

    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.

  1. Photoemission electron microscopy and scanning electron microscopy of Magnetospirillum magnetotacticum's magnetosome chains.

    Science.gov (United States)

    Keutner, Christoph; von Bohlen, Alex; Berges, Ulf; Espeter, Philipp; Schneider, Claus M; Westphal, Carsten

    2014-10-01

    Magnetotactic bacteria are of great interdisciplinary interest, since a vast field of applications from magnetic recording media to medical nanorobots is conceivable. A key feature for a further understanding is the detailed knowledge about the magnetosome chain within the bacteria. We report on two preparation procedures suitable for UHV experiments in reflective geometry. Further, we present the results of scanning electron microscopy, as well as the first photoemission electron microscopy experiments, both accessing the magnetosomes within intact magnetotactic bacteria and compare these to scanning electron microscopy data from the literature. From the images, we can clearly identify individual magnetosomes within their chains.

  2. Core-resonant double photoemission from palladium films

    International Nuclear Information System (INIS)

    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)

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

    Energy Technology Data Exchange (ETDEWEB)

    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. Time-resolved photoemission micro-spectrometer using higher-order harmonics of Ti:sapphire laser

    International Nuclear Information System (INIS)

    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

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

    Energy Technology Data Exchange (ETDEWEB)

    1992-02-01

    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.

  6. Einstein's Photoemission from Quantum Confined Superlattices.

    Science.gov (United States)

    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

  7. Fullerene photoemission time delay explores molecular cavity in attoseconds

    CERN Document Server

    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.

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

    International Nuclear Information System (INIS)

    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

  9. Nanofocusing, shadowing, and electron mean free path in the photoemission from aerosol droplets

    CERN Document Server

    Signorell, Ruth; Yoder, Bruce L; Bodi, Andras; Chasovskikh, Egor; Lang, Lukas; Luckhaus, David

    2016-01-01

    Angle-resolved photoelectron spectroscopy of aerosol droplets is a promising method for the determination of electron mean free paths in liquids. It is particularly attractive for volatile liquids, such as water. Here we report the first angle-resolved photoelectron images of droplets with defined sizes, viz. of water, glycerol, and dioctyl phthalate droplets. We present an approach that allows one to gradually vary the conditions from dominant shadowing to dominant nanofocusing to optimize the information content contained in the photoelectron images. Example simulations of water droplet photoelectron images and preliminary data for electron mean free paths for liquid water at low kinetic energy (<3eV) are provided.

  10. Nanofocusing, shadowing, and electron mean free path in the photoemission from aerosol droplets

    Science.gov (United States)

    Signorell, Ruth; Goldmann, Maximilian; Yoder, Bruce L.; Bodi, Andras; Chasovskikh, Egor; Lang, Lukas; Luckhaus, David

    2016-08-01

    Angle-resolved photoelectron spectroscopy of aerosol droplets is a promising method for the determination of electron mean free paths in liquids. It is particularly attractive for volatile liquids, such as water. Here we report the first angle-resolved photoelectron images of droplets with defined sizes, viz. of water, glycerol, and dioctyl phthalate droplets. Simulations of water droplet photoelectron images and data for electron mean free paths for liquid water at low kinetic energy (<3 eV) are provided. We present an approach that allows one to gradually vary the conditions from shadowing to nanofocusing to optimize the information content contained in the photoelectron images.

  11. A state-of-the-art photoemission spectroscopy

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    @@ Photoelectric effect refers to a phenomenon that electrons are ejected when a material is irradiated by light. Photoemission spectroscopy is widely used as an experimental method to directly measure the electronic structure of materials. Based on this technique, cutting-edge research is conducted on various issues in such fields as semiconductors,superconductors, magnetic materials.

  12. Directional uv photoemission from (100) and (110) molybdenum surfaces

    DEFF Research Database (Denmark)

    Cinti, R. C.; Khoury, E. Al; Chakraverty, B. K.;

    1976-01-01

    A study of the (100) and (110) molybdenum surfaces by directional photoemission spectroscopy is presented. Energy distribution spectra formed by photoelectrons emitted normal to the surfaces have been measured for photon energies between 10.2 and 21.2 eV. The results are discussed in terms of cal...

  13. Relativistic calculations of angular dependent photoemission time delay

    CERN Document Server

    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.

  14. Relativistic calculations of angle-dependent photoemission time delay

    Science.gov (United States)

    Kheifets, Anatoli; Mandal, Ankur; Deshmukh, Pranawa C.; Dolmatov, Valeriy K.; Keating, David A.; Manson, Steven T.

    2016-07-01

    Angular dependence of photoemission time delay for the valence n p3 /2 and n p1 /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.

  15. Watching Electrons Transfer from Metals to Insulators using Two Photon Photoemission

    Energy Technology Data Exchange (ETDEWEB)

    Johns, James E. [Univ. of California, Berkeley, CA (United States)

    2010-05-01

    Ultrafast angle-resolved two photon photoemission was used to study the dynamics and interfacial band structure of ultrathin films adsorbed onto Ag(111). Studies focused on the image potential state (IPS) in each system as a probe for measuring changes in electronic behavior in differing environments. The energetics and dynamics of the IPS at the toluene/Ag(111) interface are strongly dependent upon coverage. For a single monolayer, the first IPS is bound by 0.81 eV below the vacuum level and has a lifetime of 50 femtoseconds (fs). Further adsorption of toluene creates islands of toluene with an exposed wetting layer underneath. The IPS is then split into two peaks, one corresponding to the islands and one corresponding to the monolayer. The wetting layer IPS shows the same dynamics as the monolayer, while the lifetime of the islands increases exponentially with increasing thickness. Furthermore, the island IPS transitions from delocalized to localized within 500 fs, and electrons with larger parallel momenta decay much faster. Attempts were made using a stochastic model to extract the rates of localization and intraband cooling at differing momenta. In sexithiophene (6T) and dihexyl-sexithiophene (DH6T), the IPS was used as a probe to see if the nuclear motion of spectating side chains can interfere with molecular conduction. The energy and band mass of the IPS was measured for 6T and two geometries of DH6T on Ag(111). Electrons injected into the thicker coverages of DH6T grew exponentially heavier until they were completely localized by 230 fs, while those injected into 6T remained nearly free electron like. Based off of lifetime arguments and the density of defects, the most likely cause for the mass enhancement of the IPS in this system is small polaron formation caused by coupling of the electron to vibrations of the alkyl substituents. The energetic relaxation of the molecular adsorbate was also measured to be 20 meV/100 fs for the DH6T, and 0 meV/100 fs for

  16. Ultrahigh-spatial-resolution chemical and magnetic imaging by laser-based photoemission electron microscopy

    International Nuclear Information System (INIS)

    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

  17. Generalized Franck-Condon principle for resonant photoemission

    Science.gov (United States)

    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.

  18. orbital selective correlation reduce in collapse tetragonal phase of CaFe2(As0.935P0.065)2 and electronic structure reconstruction studied by angel resolved photoemission spectroscopy

    Science.gov (United States)

    Zeng, Lingkun

    We performed an angle-resolved photoemission spectroscopy (ARPES) study of the CaFe2(As0.935P0.065)2 in the collapse tetragonal(CT) phase and uncollapse tetragonal(UCT) phase. We find in the CT phase the electronic correlation dramatically reduces respective to UCT phase. Meanwhile, the reduction of correlation in CT phase show an orbital selective effect: correlation in dxy reduces the most, and then dxz/yz, while the one in dz2-r2 almost keeps the same. In CT phase, almost all bands sink downwards to higher binding energy, leading to the hole like bands around Brillouin zone(BZ) center sink below EF compared with UCT phase. However, the electron pocket around Brillouin Zone(BZ) corner(M) in UCT phase, forms a hole pocket around BZ center(Z point) in CT phase. Moreover, the dxy exhibits larger movement down to higher binding energy, resulting in farther away from dyz/xz and closer to dxy.We propose the electron filling ,namely high spin state in UCT phase to low spin state in CT phase(due to competing between crystal structure field and Hund's coupling), other than the Fermi surface nesting might be responsible for the absent of magnetic ordering.

  19. Photoemission electron microscopy and scanning electron microscopy of Magnetospirillum magnetotacticum’s magnetosome chains

    Energy Technology Data Exchange (ETDEWEB)

    Keutner, Christoph [Technische Univ. Dortmund, Dortmung (Germany); von Bohlen, Alex [Leibniz-Institut fur Analytische Wissenschaften, Dortmund (Germany); Berges, Ulf [Technische Univ. Dortmund, Dortmung (Germany); Espeter, Philipp [Technische Univ. Dortmund, Dortmung (Germany); Schneider, Claus M. [Peter Grunberg Institut, Julich (Germany); Westphal, Carsten [Technische Univ. Dortmund, Dortmung (Germany)

    2014-10-07

    Magnetotactic bacteria are of great interdisciplinary interest, since a vast field of applications from magnetic recording media to medical nanorobots is conceivable. A key feature for a further understanding is the detailed knowledge about the magnetosome chain within the bacteria. We report on two preparation procedures suitable for UHV experiments in reflective geometry. Further, we present the results of scanning electron microscopy, as well as the first photoemission electron microscopy experiments, both accessing the magnetosomes within intact magnetotactic bacteria and compare these to scanning electron microscopy data from the literature. From the images, we can clearly identify individual magnetosomes within their chains.

  20. Laser-induced electron emission from a tungsten nanotip: identifying above threshold photoemission using energy-resolved laser power dependencies

    CERN Document Server

    Bionta, M R; Champeaux, J P; Faure, S; Masseboeuf, A; Moretto-Capelle, P; Chatel, B

    2013-01-01

    We present an experiment studying the interaction of a strongly focused 25 fs laser pulse with a tungsten nanotip, investigating the different regimes of laser-induced electron emission. We study the dependence of the electron yield with respect to the static electric field applied to the tip. Photoelectron spectra are recorded using a retarding field spectrometer and peaks separated by the photon energy are observed with a 45 % contrast. They are a clear signature of above threshold photoemission (ATP), and are confirmed by extensive spectrally resolved studies of the laser power dependence. Understanding these mechanisms opens the route to control experiment in the strong-field regime on nanoscale objects.

  1. Electronic structure investigation of atomic layer deposition ruthenium(oxide) thin films using photoemission spectroscopy

    Science.gov (United States)

    Schaefer, Michael; Schlaf, Rudy

    2015-08-01

    Analyzing and manipulating the electronic band line-up of interfaces in novel micro- and nanoelectronic devices is important to achieve further advancement in this field. Such band alignment modifications can be achieved by introducing thin conformal interfacial dipole layers. Atomic layer deposition (ALD), enabling angstrom-precise control over thin film thickness, is an ideal technique for this challenge. Ruthenium (Ru0) and its oxide (RuO2) have gained interest in the past decade as interfacial dipole layers because of their favorable properties like metal-equivalent work functions, conductivity, etc. In this study, initial results of the electronic structure investigation of ALD Ru0 and RuO2 films via photoemission spectroscopy are presented. These experiments give insight into the band alignment, growth behavior, surface structure termination, and dipole formation. The experiments were performed in an integrated vacuum system attached to a home-built, stop-flow type ALD reactor without exposing the samples to the ambient in between deposition and analysis. Bis(ethylcyclopentadienyl)ruthenium(II) was used as precursor and oxygen as reactant. The analysis chamber was outfitted with X-ray photoemission spectroscopy (LIXPS, XPS). The determined growth modes are consistent with a strong growth inhibition situation with a maximum average growth rate of 0.21 Å/cycle for RuO2 and 0.04 Å/cycle for Ru.0 An interface dipole of up to -0.93 eV was observed, supporting the assumption of a strongly physisorbed interface. A separate experiment where the surface of a RuO film was sputtered suggests that the surface is terminated by an intermediate, stable, non-stoichiometric RuO2/OH compound whose surface is saturated with hydroxyl groups.

  2. Electronic structure investigation of atomic layer deposition ruthenium(oxide) thin films using photoemission spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Schaefer, Michael, E-mail: mvschaefer@mail.usf.edu, E-mail: schlaf@mail.usf.edu [Department of Physics, University of South Florida, Tampa, Florida 33620 (United States); Schlaf, Rudy, E-mail: mvschaefer@mail.usf.edu, E-mail: schlaf@mail.usf.edu [Department of Electrical Engineering, University of South Florida, Tampa, Florida 33620 (United States)

    2015-08-14

    Analyzing and manipulating the electronic band line-up of interfaces in novel micro- and nanoelectronic devices is important to achieve further advancement in this field. Such band alignment modifications can be achieved by introducing thin conformal interfacial dipole layers. Atomic layer deposition (ALD), enabling angstrom-precise control over thin film thickness, is an ideal technique for this challenge. Ruthenium (Ru{sup 0}) and its oxide (RuO{sub 2}) have gained interest in the past decade as interfacial dipole layers because of their favorable properties like metal-equivalent work functions, conductivity, etc. In this study, initial results of the electronic structure investigation of ALD Ru{sup 0} and RuO{sub 2} films via photoemission spectroscopy are presented. These experiments give insight into the band alignment, growth behavior, surface structure termination, and dipole formation. The experiments were performed in an integrated vacuum system attached to a home-built, stop-flow type ALD reactor without exposing the samples to the ambient in between deposition and analysis. Bis(ethylcyclopentadienyl)ruthenium(II) was used as precursor and oxygen as reactant. The analysis chamber was outfitted with X-ray photoemission spectroscopy (LIXPS, XPS). The determined growth modes are consistent with a strong growth inhibition situation with a maximum average growth rate of 0.21 Å/cycle for RuO{sub 2} and 0.04 Å/cycle for Ru.{sup 0} An interface dipole of up to −0.93 eV was observed, supporting the assumption of a strongly physisorbed interface. A separate experiment where the surface of a RuO film was sputtered suggests that the surface is terminated by an intermediate, stable, non-stoichiometric RuO{sub 2}/OH compound whose surface is saturated with hydroxyl groups.

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

    DEFF Research Database (Denmark)

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

    2014-01-01

    We theoretically study the characteristics of photoelectron emission in plasmonic nanoparticle arrays. Nanoparticles are partially embedded in a semiconductor, forming Schottky barriers at metal/semiconductor interfaces through which photoelectrons can tunnel from the nanoparticle into the semico......-based photodetectors and photovoltaic devices. The results may provide clues to designing an experiment where the contributions of surface and volume photoelectric effects to the overall photocurrent would be defined.......-induced Rayleigh anomalies can overlap the wavelength of the localized surface plasmon resonance of the individual particles, bringing about collective effects from the nanoparticle array. Using full-wave numerical simulations, we analyze the effects of lattice constant, embedding depth, and refractive index step...... 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...

  4. Design of a high-bunch-charge 112-MHz superconducting RF photoemission electron source

    Science.gov (United States)

    Xin, T.; Brutus, J. C.; Belomestnykh, Sergey A.; Ben-Zvi, I.; Boulware, C. H.; Grimm, T. L.; Hayes, T.; Litvinenko, Vladimir N.; Mernick, K.; Narayan, G.; Orfin, P.; Pinayev, I.; Rao, T.; Severino, F.; Skaritka, J.; Smith, K.; Than, R.; Tuozzolo, J.; Wang, E.; Xiao, B.; Xie, H.; Zaltsman, A.

    2016-09-01

    High-bunch-charge photoemission electron-sources operating in a continuous wave (CW) mode are required for many advanced applications of particle accelerators, such as electron coolers for hadron beams, electron-ion colliders, and free-electron lasers. Superconducting RF (SRF) has several advantages over other electron-gun technologies in CW mode as it offers higher acceleration rate and potentially can generate higher bunch charges and average beam currents. A 112 MHz SRF electron photoinjector (gun) was developed at Brookhaven National Laboratory to produce high-brightness and high-bunch-charge bunches for the coherent electron cooling proof-of-principle experiment. The gun utilizes a quarter-wave resonator geometry for assuring beam dynamics and uses high quantum efficiency multi-alkali photocathodes for generating electrons.

  5. Design of a High-bunch-charge 112-MHz Superconducting RF Photoemission Electron Source

    CERN Document Server

    Xin, T; Belomestnykh, Sergey A; Ben-Zvi, I; Boulware, C H; Grimm, T L; Hayes, T; Litvinenko, Vladimir N; Mernick, K; Narayan, G; Orfin, P; Pinayev, I; Rao, T; Severino, F; Skaritka, J; Smith, K; Than, R; Tuozzolo, J; Wang, E; Xiao, B; Xie, H; Zaltsman, A

    2016-01-01

    High-bunch-charge photoemission electron-sources operating in a continuous wave (CW) mode are required for many advanced applications of particle accelerators, such as electron coolers for hadron beams, electron-ion colliders, and free-electron lasers (FELs). Superconducting RF (SRF) has several advantages over other electron-gun technologies in CW mode as it offers higher acceleration rate and potentially can generate higher bunch charges and average beam currents. A 112 MHz SRF electron photoinjector (gun) was developed at Brookhaven National Laboratory (BNL) to produce high-brightness and high-bunch-charge bunches for the Coherent electron Cooling Proof-of-Principle (CeC PoP) experiment. The gun utilizes a quarter-wave resonator (QWR) geometry for assuring beam dynamics, and uses high quantum efficiency (QE) multi-alkali photocathodes for generating electrons.

  6. Strong-field photoemission from silicon field emitter arrays

    Energy Technology Data Exchange (ETDEWEB)

    Keathley, Phillip D.; Putnam, William P. [Department of Electrical Engineering and Computer Science and Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA (United States); Sell, Alexander; Kaertner, Franz X. [Department of Electrical Engineering and Computer Science and Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA (United States); Center for Free-Electron Laser Science, DESY, Hamburg (Germany); Dept. of Physics, Hamburg Univ. (Germany); Guerrera, Stephen; Velasquez-Garcia, Luis [Microsystems Technology Laboratories, Massachusetts Institute of Technology, Cambridge, MA (United States)

    2013-02-15

    Strong-field photoemission from silicon field emitter arrays is investigated experimentally and results are explained using a ''simple-man'' optical-field emission model. Spectra are collected throughout an in-situ laser annealing process, leading to a red-shift in emitted electron energy along with an increase in electron yield. After the annealing process, a high energy plateau is formed which is explained through optical-field emission along with electron re-scattering with the tip surface. (copyright 2012 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

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

    International Nuclear Information System (INIS)

    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)

  8. SUM-RULES FOR MAGNETIC DICHROISM IN RARE-EARTH 4F-PHOTOEMISSION

    NARCIS (Netherlands)

    THOLE, BT; VANDERLAAN, G

    1993-01-01

    We present new sum rules for magnetic dichroism in spin polarized photoemission from partly filled shells which give the expectation values of the orbital and spin magnetic moments and their correlations in the ground state. We apply this to the 4f photoemission of rare earths, where the polarizatio

  9. Enhanced photoemission from laser-excited plasmonic nano-objects in periodic arrays.

    Science.gov (United States)

    Fedorov, N; Geoffroy, G; Duchateau, G; Štolcová, L; Proška, J; Novotný, F; Domonkos, M; Jouin, H; Martin, P; Raynaud, M

    2016-08-10

    The process of photoelectron emission from gold surfaces covered with nano-objects that are organized in the form of a periodic array is addressed in the short laser pulse regime ([Formula: see text] fs) at moderate intensities [Formula: see text] W cm(-2) and for various laser wavelengths. The emission spectrum from a gold single crystal measured under the same conditions is used for reference. The comparison of the photo-emission yield and the energy of the ejected electrons with their counterparts from the (more simple) reference system shows that the periodic conditions imposed on the target surface drastically enhance both quantities. In addition to the standard mechanism of Coulomb explosion, a second mechanism comes into play, driven by surface plasmon excitation. This can be clearly demonstrated by varying the laser wavelength. This interpretation of the experimental data is supported by predictions from model calculations that account both for the primary quantum electron emission and for the subsequent surface-plasmon-driven acceleration in the vacuum. Despite the fact that the incident laser intensity is as low as [Formula: see text] W cm(-2), such a structured target permits generating electrons with energies as high as 300 eV. Experiments with two incident laser beams of different wavelengths with an adjustable delay, have also been carried out. The results show that there exist various channels for the decay of the photo-emission signal, depending on the target type. These observations are shedding light on the various relaxation mechanisms that take place on different timescales. PMID:27299999

  10. Enhanced photoemission from laser-excited plasmonic nano-objects in periodic arrays

    Science.gov (United States)

    Fedorov, N.; Geoffroy, G.; Duchateau, G.; Štolcová, L.; Proška, J.; Novotný, F.; Domonkos, M.; Jouin, H.; Martin, P.; Raynaud, M.

    2016-08-01

    The process of photoelectron emission from gold surfaces covered with nano-objects that are organized in the form of a periodic array is addressed in the short laser pulse regime (≤slant 50 fs) at moderate intensities ∼ {{10}10} W cm‑2 and for various laser wavelengths. The emission spectrum from a gold single crystal measured under the same conditions is used for reference. The comparison of the photo-emission yield and the energy of the ejected electrons with their counterparts from the (more simple) reference system shows that the periodic conditions imposed on the target surface drastically enhance both quantities. In addition to the standard mechanism of Coulomb explosion, a second mechanism comes into play, driven by surface plasmon excitation. This can be clearly demonstrated by varying the laser wavelength. This interpretation of the experimental data is supported by predictions from model calculations that account both for the primary quantum electron emission and for the subsequent surface-plasmon-driven acceleration in the vacuum. Despite the fact that the incident laser intensity is as low as ∼ 5× {{10}10} W cm‑2, such a structured target permits generating electrons with energies as high as 300 eV. Experiments with two incident laser beams of different wavelengths with an adjustable delay, have also been carried out. The results show that there exist various channels for the decay of the photo-emission signal, depending on the target type. These observations are shedding light on the various relaxation mechanisms that take place on different timescales.

  11. Angle-resolved heat capacity of heavy fermion superconductors.

    Science.gov (United States)

    Sakakibara, Toshiro; Kittaka, Shunichiro; Machida, Kazushige

    2016-09-01

    Owing to a strong Coulomb repulsion, heavy electron superconductors mostly have anisotropic gap functions which have nodes for certain directions in the momentum space. Since the nodal structure is closely related to the pairing mechanism, its experimental determination is of primary importance. This article discusses the experimental methods of the gap determination by bulk heat capacity measurements in a rotating magnetic field. The basic idea is based on the fact that the quasiparticle density of states in the vortex state of nodal superconductors is field and direction dependent. We present our recent experimental results of the field-orientation dependence of the heat capacity in heavy fermion superconductors CeTIn5 (T  =  Co, Ir), UPt3, CeCu2Si2, and UBe13 and discuss their gap structures. PMID:27482621

  12. Attosecond double-slit experiment.

    Science.gov (United States)

    Lindner, F; Schätzel, M G; Walther, H; Baltuska, A; Goulielmakis, E; Krausz, F; Milosević, D B; Bauer, D; Becker, W; Paulus, G G

    2005-07-22

    A new scheme for a double-slit experiment in the time domain is presented. Phase-stabilized few-cycle laser pulses open one to two windows (slits) of attosecond duration for photoionization. Fringes in the angle-resolved energy spectrum of varying visibility depending on the degree of which-way information are measured. A situation in which one and the same electron encounters a single and a double slit at the same time is observed. The investigation of the fringes makes possible interferometry on the attosecond time scale. From the number of visible fringes, for example, one derives that the slits are extended over about 500 as.

  13. 48-Channel electron detector for photoemission spectroscopy and microscopy

    Science.gov (United States)

    Gregoratti, L.; Barinov, A.; Benfatto, E.; Cautero, G.; Fava, C.; Lacovig, P.; Lonza, D.; Kiskinova, M.; Tommasini, R.; Mähl, S.; Heichler, W.

    2004-01-01

    We show that it is possible to use a multichannel electron detector in a zone plate based photoemission spectromicroscopy in a snap shot mode to reduce the total acquisition time for a given counting time by 50% relative to the standard scanning mode while preserving the feature of the spectra. We describe the result of tests performed at Elettra using its microbeam (150 nm) together with a 48-channel detector designed for the PHOIBOS 100 analyzer optimized for extremely small x-ray sources. We also give a short summary of the technical features of the detector and describe one possible calibration procedure for its use in the snap shot mode. We show initial results from using this device to perform chemical maps of surfaces at a resolution of 150 nm.

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

    CERN Document Server

    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. Electric field stimulation setup for photoemission electron microscopes

    Energy Technology Data Exchange (ETDEWEB)

    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.

  16. Electric field stimulation setup for photoemission electron microscopes

    Science.gov (United States)

    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.

  17. X-ray photoemission spectroscopy study of zirconium hydride

    International Nuclear Information System (INIS)

    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

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

    International Nuclear Information System (INIS)

    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

  19. High-resolution photoemission study of MgB2.

    Science.gov (United States)

    Takahashi, T; Sato, T; Souma, S; Muranaka, T; Akimitsu, J

    2001-05-21

    We have performed high-resolution photoemission spectroscopy on MgB2 and observed opening of a superconducting gap with a narrow coherent peak. We found that the superconducting gap is s like with the gap value ( Delta) of 4.5+/-0.3 meV at 15 K. The temperature dependence (15-40 K) of the gap value follows well the BCS form, suggesting that 2Delta/k(B)T(c) at T = 0 is about 3. No pseudogap behavior is observed in the normal state. The present results strongly suggest that MgB2 is categorized into a phonon-mediated BCS superconductor in the weak-coupling regime.

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

    Science.gov (United States)

    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

  1. Observation of Kondo resonance in rare-earth hexaborides using high resolution photoemission spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Maiti, Kalobaran; Patil, Swapnil; Adhikary, Ganesh [Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400005 (India); Balakrishnan, Geetha, E-mail: kbmaiti@tifr.res.in [Department of Physics, University of Warwick, Coventry, CV4 7AL (United Kingdom)

    2011-01-01

    We studied the electronic structure of rare earth hexaborides, CeB{sub 6}, PrB{sub 6} and NdB{sub 6} using state-of-the-art high resolution photoemission spectroscopy. CeB{sub 6} is a dense Kondo system. PrB{sub 6} and NdB{sub 6} are antiferromagnetic (Neel temperature {approx}7 K), known to be stable moment systems and do not exhibit Kondo effect. Photoemission spectra exhibit distinct signature of surface and bulk electronic structures of these compounds. The energy position of the surface feature is not influenced by the 4f density of states. High resolution spectra of CeB{sub 6} reveal multiple Kondo resonance features in the bulk spectra due to various photoemission final states. Interestingly, high resolution photoemission spectra of antiferromagnetic PrB{sub 6} also exhibit a sharp feature at the Fermi level that shows temperature dependence similar to the Kondo resonance features.

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

    CERN Document Server

    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 ...

  3. Photoemission spectra of aqueous solutions of salts from many-body perturbation theory

    Science.gov (United States)

    Gaiduk, Alex P.; Skone, Jonathan H.; Govoni, Marco; Galli, Giulia

    The computational design of electrode materials for energy conversion and storage processes requires an accurate description of the energy levels of the electrolyte and of electrolyte/electrode interfaces. Conventional density-functional approximations are in general not well suited for this task as they yield inaccurate orbital energies. Many-body perturbation theory (MBPT) predicts vertical ionization potentials and energy gaps in better agreement with experiments, providing the possibility for an accurate description of the electronic properties of electrolytes. We coupled ab initio molecular dynamics with MBPT calculations to investigate the photoemission spectra of a 1 M aqueous solution of NaCl. For the first time we were able to determine the absolute positions of the spectra peaks, with excellent agreement with experiments for both the solute and solvent peak positions. The best results were obtained using wavefunctions obtained from dielectric-dependent hybrid calculations as a starting point for MBPT. Work supported by DOE BES DE-SC0008938. Computer time provided by the Argonne Leadership Computing Facility through the INCITE program.

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

    Science.gov (United States)

    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.

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

    International Nuclear Information System (INIS)

    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

  6. High-energy photoemission studies of oxide interfaces

    Science.gov (United States)

    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

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

    Science.gov (United States)

    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.

  8. Comparison of the photoemission behaviour between negative electron affinity GaAs and GaN photocathodes

    International Nuclear Information System (INIS)

    In view of the important application of GaAs and GaN photocathodes in electron sources, differences in photoemission behaviour, namely the activation process and quantum yield decay, between the two typical types of III—V compound photocathodes have been investigated using a multi-information measurement system. The activation experiment shows that a surface negative electron affinity state for the GaAs photocathode can be achieved by the necessary Cs—O two-step activation and by Cs activation alone for the GaN photocathode. In addition, a quantum yield decay experiment shows that the GaN photocathode exhibits better stability and a longer lifetime in a demountable vacuum system than the GaAs photocathode. The results mean that GaN photocathodes are more promising candidates for electron source emitter use in comparison with GaAs photocathodes. (interdisciplinary physics and related areas of science and technology)

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

    CERN Document Server

    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...

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

    Science.gov (United States)

    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

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

    Science.gov (United States)

    Li, Tsung-Lung; Lu, Wen-Cai

    2015-10-01

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

  12. Photoemission and magnetic circular dichroism studies of magnetic semiconductors

    Science.gov (United States)

    Fujimori, Atsushi

    2005-03-01

    Recently, a series of novel ferromagnetic semiconductors have been synthesized using MBE and related techniques and have attracted much attention because of unknown mechanisms of carrier-induced ferromagnetism and potential applications as "spin electronics" devices. Some new materials show ferromagnetism even well above room temperature. Photoemission spectroscopy has been used to study the d orbitals of the dilute transition-metal atoms, mostly Mn, and their hybridization with the host band states [1]. Soft x-ray absorption spectroscopy (XAS) and magnetic circular dichroism (MCD) at the transition-metal 2p-3d absorption edges are useful techniques to study the valence and spin states of the transition-metal atoms. Furthermore, since MCD has different sensitivities to the ferromagnetic and paramagnetic components at different temperatures and magnetic fileds, if the sample is a mixture of ferromagnetic and non-ferromagnetic transition- metal atoms, it can be used to separate the two components and to study their electronic structures. In this talk, results are presented for the prototypical diluted ferromagnetic semiconductor Ga1-xMnxAs [2] and the room-temperature ferromagnets Zn1-xCoxO and Ti1-xCoxO2.I acknowledge collaboration with Y. Ishida, J.-I. Hwang, M. Kobayashi, Y. Takeda, Y. Saitoh, J. Okamoto, T. Okane, Y. Muramatsu, K. Mamiya, T. Koide, A. Tanaka, M. Tanaka, Hayashi, S. Ohya, T. Kondo, H. Munekata, H. Saeki, H. Tabata, T. Kawai, Y. Matsumoto, H. Koinuma, T. Fukumura and M. Kawasaki. This work was supported by a Grant-in-Aid for Scientific Research in Priority Area "Semiconductor nano-spintronics" (14076209) from MEXT, Japan.1. J. Okabayashi et al., Phys. Rev. B 64, 125304 (2001).2. A. Fujimori et al., J. Electron Spectrosc. Relat. Phenom., in press.

  13. Time-dependent many-body treatment of electron-boson dynamics: Application to plasmon-accompanied photoemission

    Science.gov (United States)

    Schüler, M.; Berakdar, J.; Pavlyukh, Y.

    2016-02-01

    Recent experiments access the time-resolved photoelectron signal originating from plasmon satellites in correlated materials and address their buildup and decay in real time. Motivated by these developments, we present the Kadanoff-Baym formalism for the nonequilibrium time evolution of interacting fermions and bosons. In contrast to the fermionic case, the bosons are described by second-order differential equations. Solution of the bosonic Kadanoff-Baym equations—which is the central ingredient of this work—requires substantial modification of the usual two-times electronic propagation scheme. The solution is quite general and can be applied to a number of problems, such as the interaction of electrons with quantized photons, phonons, and other bosonic excitations. Here the formalism is applied to the photoemission from a deep core hole accompanied by plasmon excitation. We compute the time-resolved photoelectron spectra and discuss the effects of intrinsic and extrinsic electron energy losses and their interference.

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

    Directory of Open Access Journals (Sweden)

    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.

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

    Science.gov (United States)

    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.

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

    Directory of Open Access Journals (Sweden)

    D. V. Minko

    2012-01-01

    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.

  17. Simple theoretical analysis of the Einstein’s photoemission from quantum confined superlattices

    Science.gov (United States)

    Pahari, S.; Bhattacharya, S.; Roy, S.; Saha, A.; De, D.; Ghatak, K. P.

    2009-11-01

    In this paper, we study the Einstein's photoemission from III-V, II-VI, IV-VI and HgTe/CdTe quantum well superlattices (QWSLs) with graded interfaces and quantum well effective mass superlattices in the presence of a quantizing magnetic field on the basis of newly formulated dispersion relations in the respective cases. Besides, the same has been studied from the afore-mentioned quantum dot superlattices and it appears that the photoemission oscillates with increasing carrier degeneracy and quantizing magnetic field in different manners. In addition, the photoemission oscillates with film thickness and increasing photon energy in quantum steps together with the fact that the solution of the Boltzmann transport equation will introduce new physical ideas and new experimental findings under different external conditions. The influence of band structure is apparent from all the figures and we have suggested three applications of the analyses of this paper in the fields of superlattices and microstructures.

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

    CERN Document Server

    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.

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

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

    CERN Document Server

    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.

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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.

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

    DEFF Research Database (Denmark)

    Uskov, Alexander V.; Protsenko, Igor E.; Ikhsanov, Renat S.;

    2014-01-01

    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...

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

    International Nuclear Information System (INIS)

    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

  5. X-ray photoemission spectroscopy study on the effects of functionalization in fulleropyrrolidine and pyrrolidine derivatives

    NARCIS (Netherlands)

    Benne, Darja; Maccallini, Enrico; Rudolf, Petra; Sooambar, Chloe; Prato, Maurizio

    2006-01-01

    Fulleropyrrolidine and pyrrolidine derivatives were studied using X-ray photoemission spectroscopy in order to determine the effects of the C(60)-cage on the pyrrolidine nitrogen, as well as the influence of further derivatisation. Charge transfer from the carbon pyrrolidine ring to the C(60)-cages

  6. MULTIPLET FINE-STRUCTURE IN THE PHOTOEMISSION OF THE GADOLINIUM AND TERBIUM 5P LEVELS

    NARCIS (Netherlands)

    THOLE, BT; WANG, XD; HARMON, BN; LI, DQ; DOWBEN, PA

    1993-01-01

    Fine structure is observed in the photoemission of the gadolinium and terbium 5p levels. The 5p levels are split into multiplets due to spin-orbit splitting and to Coulomb and exchange interactions with the f shell. The calculated theoretical spectra are in good agreement with the experimental resul

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

    DEFF Research Database (Denmark)

    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...

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

    Science.gov (United States)

    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.

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  10. Two-photon photoemission from a copper cathode in an X -band photoinjector

    Science.gov (United States)

    Li, H.; Limborg-Deprey, C.; Adolphsen, C.; McCormick, D.; Dunning, M.; Jobe, K.; Raubenheimer, T.; Vrielink, A.; Vecchione, T.; Wang, F.; Weathersby, S.

    2016-02-01

    This paper presents two-photon photoemission from a copper cathode in an X -band photoinjector. We experimentally verified that the electron bunch charge from photoemission out of a copper cathode scales with laser intensity (I) square for 400 nm wavelength photons. We compare this two-photon photoemission process with the single photon process at 266 nm. Despite the high reflectivity (R ) of the copper surface for 400 nm photons (R =0.48 ) and higher thermal energy of photoelectrons (two-photon at 200 nm) compared to 266 nm photoelectrons, the quantum efficiency of the two-photon photoemission process (400 nm) exceeds the single-photon process (266 nm) when the incident laser intensity is above 300 GW /cm2 . At the same laser pulse energy (E ) and other experimental conditions, emitted charge scales inversely with the laser pulse duration. A thermal emittance of 2.7 mm-mrad per mm root mean square (rms) was measured on our cathode which exceeds by sixty percent larger compared to the theoretical predictions, but this discrepancy is similar to previous experimental thermal emittance on copper cathodes with 266 nm photons. The damage of the cathode surface of our first-generation X -band gun from both rf breakdowns and laser impacts mostly explains this result. Using a 400 nm laser can substantially simplify the photoinjector system, and make it an alternative solution for compact pulsed electron sources.

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

    DEFF Research Database (Denmark)

    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...

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

    International Nuclear Information System (INIS)

    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

  13. Significant relaxation of residual negative carrier in polar Alq3 film directly detected by high-sensitivity photoemission

    Science.gov (United States)

    Kinjo, Hiroumi; Lim, Hyunsoo; Sato, Tomoya; Noguchi, Yutaka; Nakayama, Yasuo; Ishii, Hisao

    2016-02-01

    Tris(8-hydroxyquinoline)aluminum (Alq3) has been widely applied as a good electron-injecting layer (EIL) in organic light-emitting diodes. High-sensitivity photoemission measurement revealed a clear photoemission by visible light, although its ionization energy is 5.7 eV. This unusual photoemission is ascribed to Alq3 anions captured by positive polarization charges. The observed electron detachment energy of the anion was about 1 eV larger than the electron affinity reported by inverse photoemission. This difference suggests that the injected electron in the Alq3 layer is energetically relaxed, leading to the reduction in injection barrier. This nature is one of the reasons why Alq3 worked well as the EIL.

  14. Positron studies of defected metals, metallic surfaces

    International Nuclear Information System (INIS)

    Specific problems proposed under this project included the treatment of electronic structure and momentum density in various disordered and defected systems. Since 1987, when the new high-temperature superconductors were discovered, the project focused extensively on questions concerning the electronic structure and Fermiology of high-Tc superconductors, in particular, (i) momentum density and positron experiments, (ii) angle-resolved photoemission intensities, (iii) effects of disorder and substitutions in the high-Tc's

  15. Surface states and bulk electronic structure in the candidate type-II Weyl semimetal WTe2

    OpenAIRE

    Bruno, F. Y.; Tamai, A.; Wu, Q. S.; Cucchi, I.; Barreteau, C.; A. de la Torre; Walker, S. McKeown; Riccò, S; Wang, Z.; Kim, T K; Hoesch, M.; Shi, M. (Mimi); Plumb, N. C.; Giannini, E; Soluyanov, A. A.

    2016-01-01

    We report angle-resolved photoemission experiments identifying an arc-like surface state connecting the bulk electron and hole pockets of the candidate type-II Weyl semimetal WTe2. This surface state can be isolated clearly on one of two distinct surface terminations observed experimentally, which we associate with the in-equivalent top and bottom surfaces of the non-centrosymmetric crystal structure. We further use the identification of the two different surfaces to clarify the number of bul...

  16. Photoemission and core-level magnetic circular dichroism studies of diluted magnetic semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Fujimori, A. [Department of Complexity Science and Engineering, Universtiy of Tokyo, 1-5-1 Kashiwanoha, Kashiwa, Chiba 277-8561 (Japan) and Synchrotron Radiation Research Center, Japan Atomic Energy Research Institute, SPring-8, Mikazuki, Hyogo 679-5148 (Japan)]. E-mail: fujimori@phys.s.u-tokyo.ac.jp; Okabayashi, J. [Department of Applied Chemistry, University of Tokyo, 7-3-1 Hongo, Bunkyou-ku, Tokyo 113-8656 (Japan); Takeda, Y. [Synchrotron Radiation Research Center, Japan Atomic Energy Research Institute, SPring-8, Mikazuki, Hyogo 679-5148 (Japan); Mizokawa, T. [Department of Complexity Science and Engineering, Universtiy of Tokyo, 1-5-1 Kashiwanoha, Kashiwa, Chiba 277-8561 (Japan); Okamoto, J. [Synchrotron Radiation Research Center, Japan Atomic Energy Research Institute, SPring-8, Mikazuki, Hyogo 679-5148 (Japan); Mamiya, K. [Photon Factory, IMSS, High Energy Accelerator Research Organization, Tsukuba, Ibaraki 305 (Japan); Saitoh, Y. [Synchrotron Radiation Research Center, Japan Atomic Energy Research Institute, SPring-8, Mikazuki, Hyogo 679-5148 (Japan); Muramatsu, Y. [Synchrotron Radiation Research Center, Japan Atomic Energy Research Institute, SPring-8, Mikazuki, Hyogo 679-5148 (Japan); Oshima, M. [Department of Applied Chemistry, University of Tokyo, 7-3-1 Hongo, Bunkyou-ku, Tokyo 113-8656 (Japan); Ohya, S. [Department of Electronic Engineering, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Tanaka, M. [Department of Electronic Engineering, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan)

    2005-06-15

    An overview is given on the photoemission studies of the electronic structure of diluted magnetic semiconductors (DMS's), in particular of the prototypical ferromagnetic DMS Ga{sub 1-x}Mn{sub x}As. Configuration-interaction cluster-model analyses of the photoemission data allow us to estimate the p-d exchange coupling constant and hence to predict how to increase the Curie temperature in new materials. Spectra near the Fermi level combined with the transport and optical properties suggest a highly incoherent metallic state for the ferromagnetic metallic phase. It is shown that new insight into the chemically and magnetically inhomogeneous states of DMS's can be gained by the temperature and magnetic field dependence of core-level magnetic circular dichroism signals.

  17. Study of f electron correlations in nonmagnetic Ce by means of spin resolved resonant photoemission

    Energy Technology Data Exchange (ETDEWEB)

    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. Rb-intercalated C{sub 60} compounds studied by photoemission spectroscopies

    Energy Technology Data Exchange (ETDEWEB)

    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.

  19. Communication: Induced photoemission from nonadiabatic dynamics assisted by dynamical Stark effect.

    Science.gov (United States)

    Arasaki, Yasuki; Scheit, Simona; Takatsuka, Kazuo

    2013-04-28

    Through nonadiabatic interaction due to electron transfer as that in alkali halides, vibrational dynamics on the ionic potential energy surface (large dipole moment) is coupled to that on the covalent surface (small dipole moment). Thus, population transfer between the states should cause long-range electron jump between two remote sites, which thereby leads to a sudden change of the large molecular dipole moment. Therefore, by making repeated use of the dynamical Stark effect, one may expect emission of photons from it. We show with coupled quantum wavepacket dynamics calculation that such photoemission can indeed occur and can be controlled by an external field. The present photoemission can offer an alternative scheme to study femtosecond and subfemtosecond vibrational and electronic dynamics and may serve as a unique optical source. PMID:23635103

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

    Directory of Open Access Journals (Sweden)

    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.

  1. Volume and surface photoemission from tungsten. I. Calculation of band structure and emission spectra

    DEFF Research Database (Denmark)

    Christensen, N. Egede; Feuerbacher, B.

    1974-01-01

    The electronic energy-band structure of tungsten has been calculated by means of the relativistic-augmented-plane-wave method. A series of mutually related potentials are constructed by varying the electronic configuration and the amount of Slater exchange included. The best band structure...... of 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.......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...

  2. Effect of humid air exposure on photoemissive and structural properties of KBr thin film photocathode

    CERN Document Server

    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.

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

    Energy Technology Data Exchange (ETDEWEB)

    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.)

  4. Photoemission-monitored x-ray standing wave studies of molecular adsorbate surface structure

    CERN Document Server

    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-...

  5. Photoemission from real iron surfaces and its relationship to light penetration of the overlayer

    Science.gov (United States)

    Momose, Yoshihiro; Suzuki, Daisuke; Sakurai, Takao; Nakayama, Keiji

    2015-02-01

    We report the photoemission from real iron surfaces at elevated temperatures, called thermally assisted photoemission (TAPE), and its relationship to the X-ray photoelectron spectroscopy (XPS) results. TAPE measurements were carried out using a Geiger counter under a gaseous atmosphere of He containing 1 % isobutane vapor at normal atmospheric pressure. A sample was initially heated to temperatures ranging from 25 to 353 °C under light irradiation at a certain wavelength of 200, 210, 220, and 230 nm, and then, wavelength was scanned from 300 to 170 nm at the final temperature. The values of a constant related to electron photoemission probability, αA, where A is identical with the Richardson constant, and photothreshold (photoelectric work function), ϕ, were obtained from a plot of the square root of the electron photoemission intensity against the photon energy; the αA values increased with temperature, and the ϕ values also increased with temperature. From the Arrhenius plot, the αA was found to have an activation energy Δ E αA = 0.096 eV. The activation energies of the surface oxygen component ratio Z = O2-/(OH + O2-) and the surface elemental composition ratio X = Fe/(O + N + C + Fe) obtained from the XPS data were also determined from their Arrhenius plots: Δ E Z = 0.113 eV and Δ E X = 0.039 eV, respectively. From a close resemblance between the latter activation energies and those of the Δ E αA and the Δ E a = 0.112-0.040 eV for the quantum yields (Momose et al. in Appl Phys A. doi: 10.1007/s00339-014-8589-7, 2014), it was found that the increase in the intensity of the TAPE with temperature was strongly associated with the increase in the values of Z and X with temperature. It was therefore concluded that the ability of the surface overlayer to pass the incident light became a rate-determining step to start the photoemission, which was decisively controlled by the temperature-dependent surface oxygen components and surface compositions. The

  6. Photoemission from Graphene on Copper and Cesium Antimonide: Theory and Experiment

    Science.gov (United States)

    Finkenstadt, Daniel; Jensen, Kevin L.; Lambrakos, Samuel G.; Shabaev, Andrew; Moody, Nathan A.

    The work function is calculated using DFT for a substrate of flat copper on which a single layer of graphene is deposited. These calculations show a reduced work function, compared to bare copper, when graphene is deposited on a cathode. Based on our DFT-calculated results, a simple model using the transfer matrix approach gives the transmission probability near and above the barrier maximum. An important element of our model is the DFT-calculated, macroscopically-averaged electrostatic potential. Using this potential, graphene behaves as a resonant well for electrons transmitted between the substrate and vacuum regions. Another system to be discussed is graphene atop cesium antimonide, which has very low work function making it technologically useful, in particular for the development of an x-ray free electron laser. On cesium antimonide, we examine whether graphene may allow for the retention of an underlying cesium layer that is often damaged in high-field applications. A discussion of these results in light of recent experimental characterization at LANL will be given. Funding and support provide by ONR and DOE.

  7. A combined droplet train and ambient pressure photoemission spectrometer for the investigation of liquid/vapor interfaces

    Energy Technology Data Exchange (ETDEWEB)

    Starr, David E.; Wong, Ed K.; Worsnop, Douglas R.; Wilson, Kevin R.; Bluhm, Hendrik

    2008-05-01

    We describe a combined ambient pressure photoelectron spectroscopy/droplet train apparatus for investigating the nature and heterogeneous chemistry of liquid/vapor interfaces. In this instrument a liquid droplet train with typical droplet diameters from 50...150 {micro}m is produced by a vibrating orifice aerosol generator (VOAG). The droplets are irradiated by soft X-rays (100...1500 eV) in front of the entrance aperture of a differentially pumped electrostatic lens system that transfers the emitted electrons into a conventional hemispherical electron analyzer. The photoemission experiments are performed at background pressures of up to several Torr, which allows the study of environmentally important liquid/vapor interfaces, in particular aqueous solutions, under equilibrium conditions. The exposure time of the droplet surface to the background gases prior to the XPS measurement can be varied, which will allow future kinetic measurements of gas uptake on liquid surfaces. As an example, a measurement of the surface composition of a {chi} = 0.21 aqueous methanol solution is presented. The concentration of methanol at the vapor/liquid interface is enhanced by a factor of about 3 over the bulk value, while the expected bulk value is recovered at depths larger than about 1.5 nm.

  8. Photoemission surface characterization of (0 0 1) In{sub 2}O{sub 3} thin film through the interactions with oxygen, water and carbon monoxide: Comparison with (1 1 1) orientation

    Energy Technology Data Exchange (ETDEWEB)

    Brinzari, V., E-mail: vbrinzari@mail.ru [State University of Moldova, str. Mateevich 60A, MD-2009 Chisinau, Republic of Moldova (Moldova, Republic of); Cho, B.K. [Gwangju Institute of Science and Technology, Gwangju (Korea, Republic of); Kamei, M. [National Institute for Material Science, Namiki, Tsukuba, Ibaraki (Japan); Korotcenkov, G., E-mail: ghkoro@yahoo.com [Gwangju Institute of Science and Technology, Gwangju (Korea, Republic of)

    2015-01-01

    Highlights: • SRPES of In{sub 2}O{sub 3}(0 0 1) thin film under heating activated gas exposures of O{sub 2}, H{sub 2}O, CO. • Changes in surface band bending and composition vs. these treatments. • Models of (0 0 1) surface terminations, compositions and zone diagrams. • Changes in VB spectra radically differ from the same ones for (1 1 1) film. • Adsorbed water species do not donate electrons into conduction band. - Abstract: Synchrotron radiation ultraviolet photoemission experiments at photon energies of 150 and 49 eV have been performed on (0 0 1) In{sub 2}O{sub 3} epitaxial layer with thickness of 120 nm grown by electron beam evaporation method. Valence band (VB) photoemission spectra have been monitored under separate oxygen, water and carbon monoxide exposures (100 L) at different sample temperatures within the range utilized for chemoresistive gas sensors operation (20–450 °C). Large changes in photoemission response within the whole VB were observed for all gases. Surface potential changes were identified as a shift of the valence band edge relative to the Fermi energy. It was found that the initial state of the In{sub 2}O{sub 3} surface after standard preparation procedure corresponded to highly reduced surface, close to “metallic” surface. Treatments in oxygen resulted in oxidation of the surface and regular upward band bending have been changing up to 0.27 eV. These two extreme states of the In{sub 2}O{sub 3} surface corresponded to the surface zone diagrams with accumulation layer and flat bands, respectively. Surface potential changes under water and carbon monoxide treatment have been irregular vs. temperature and small enough (<0.05 eV). However, the magnitudes of photoemission deviations under these treatments were large and comparable with intensity of an initial photoemission itself before the treatment (ΔI{sub ph} ∼ 10–40%). The obtained results have been compared with the ones previously received for (1 1 1) surface and

  9. Correlation effects in photoemission from adsorbates: Hydrogen on narrow-band metals

    Science.gov (United States)

    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.

  10. Interfacial electronic structure of Na deposited on rubrene thin film studied by synchrotron radiation photoemission

    Science.gov (United States)

    Wei, Ching-Hsuan; Cheng, Chiu-Ping; Lin, Hong-Cheu; Pi, Tun-Wen

    2015-12-01

    The electronic structure of rubrene doped with various concentrations of Na was studied by synchrotron-radiation photoemission. Three stages of development were found with increasing Na concentration; Na penetrating deep into the organic film, followed by development of gap states, and ended with a metallic Na film. The charge transfer from Na to rubrene resulted in a vacuum-level shift. By doping Na into rubrene, we could control the IP of the organic molecule, which is favorable for application in organic semiconductor devices.

  11. An ultrafast electron microscope gun driven by two-photon photoemission from a nanotip cathode

    International Nuclear Information System (INIS)

    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. Whispering gallery mode photoemission from self-assembled poly-para-phenylenevinylene microspheres

    Energy Technology Data Exchange (ETDEWEB)

    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.

  13. Electron attachment rate constant measurement by photoemission electron attachment ion mobility spectrometry (PE-EA-IMS)

    Science.gov (United States)

    Su, Desheng; Niu, Wenqi; Liu, Sheng; Shen, Chengyin; Huang, Chaoqun; Wang, Hongmei; Jiang, Haihe; Chu, Yannan

    2012-12-01

    Photoemission electron attachment ion mobility spectrometry (PE-EA-IMS), with a source of photoelectrons induced by vacuum ultraviolet radiation on a metal surface, has been developed to study electron attachment reaction at atmospheric pressure using nitrogen as the buffer gas. Based on the negative ion mobility spectra, the rate constants for electron attachment to tetrachloromethane and chloroform were measured at ambient temperature as a function of the average electron energy in the range from 0.29 to 0.96 eV. The experimental results are in good agreement with the data reported in the literature.

  14. Electronic structure of Mo1‑x Re x alloys studied through resonant photoemission spectroscopy

    Science.gov (United States)

    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.

  15. Electronic structure of Mo1-x Re x alloys studied through resonant photoemission spectroscopy.

    Science.gov (United States)

    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

  16. Gd and Sm on clean semiconductor surfaces—Resonant photoemission studies

    Energy Technology Data Exchange (ETDEWEB)

    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.

  17. Vacuum ultraviolet photon detector with continuously adjustable resolution for inverse photoemission spectroscopy

    OpenAIRE

    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...

  18. Doppler effect in resonant photoemission from SF6: correlation between Doppler profile and Auger emission anisotropy.

    Science.gov (United States)

    Kitajima, M; Ueda, K; De Fanis, A; Furuta, T; Shindo, H; Tanaka, H; Okada, K; Feifel, R; Sorensen, S L; Gel'mukhanov, F; Baev, A; Agren, H

    2003-11-21

    Fragmentation of the SF6 molecule upon F 1s excitation has been studied by resonant photoemission. The F atomiclike Auger line exhibits the characteristic Doppler profile that depends on the direction of the photoelectron momentum relative to the polarization vector of the radiation as well as on the photon energy. The measured Doppler profiles are analyzed by the model simulation that takes account of the anisotropy of the Auger emission in the molecular frame. The Auger anisotropy extracted from the data decreases with an increase in the F-SF5 internuclear distance.

  19. On the photoemission spectrum and optical gap in La2CuO4

    International Nuclear Information System (INIS)

    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

  20. Standing-wave excited soft x-ray photoemission microscopy: application to Co microdot magnetic arrays

    Energy Technology Data Exchange (ETDEWEB)

    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.

  1. Retention Characteristics of CBTi144 Thin Films Explained by Means of X-Ray Photoemission Spectroscopy

    OpenAIRE

    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...

  2. Interference of spin states in photoemission from Sb/Ag(111) surface alloys

    Energy Technology Data Exchange (ETDEWEB)

    Meier, Fabian; Osterwalder, Juerg; Hugo Dil, J [Physik-Institut, Universitaet Zuerich, Winterthurerstrasse 190, CH-8057 Zuerich (Switzerland); Petrov, Vladimir [St Petersburg Polytechnical University, 29 Polytechnicheskaya Street, 195251 St Petersburg (Russian Federation); Mirhosseini, Hossein; Henk, Juergen [Max-Planck-Institut fuer Mikrostrukturphysik, D-06120 Halle (Saale) (Germany); Patthey, Luc, E-mail: jan-hugo.dil@psi.ch [Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen (Switzerland)

    2011-02-23

    Using a three-dimensional spin polarimeter we have gathered evidence for the interference of spin states in photoemission from the surface alloy Sb/Ag(111). This system features a small Rashba-type spin splitting of a size comparable to the momentum broadening of the quasiparticles, thus causing an intrinsic overlap between states with orthogonal spinors. Besides a small spin polarization caused by the spin splitting, we observe a large spin polarization component in the plane normal to the quantization axis of the Rashba effect. Strongly suggestive of coherent spin rotation, this effect is largely independent of the photon energy and photon polarization. (fast track communication)

  3. An ultrafast electron microscope gun driven by two-photon photoemission from a nanotip cathode

    Energy Technology Data Exchange (ETDEWEB)

    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.

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

    OpenAIRE

    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...

  5. Spin-Orbit Effects in Spin-Resolved L2,3 Core Level Photoemission of 3d Ferromagnetic Thin Films

    Energy Technology Data Exchange (ETDEWEB)

    Komesu, T; Waddill, G D; Yu, S W; Butterfield, M; Tobin, J G

    2007-10-02

    We present spin-resolved 2p core level photoemission for the 3d transition metal films of Fe and Co grown on Cu(100). We observe clear spin asymmetry in the main 2p core level photoemission peaks of Fe and Co films consistent with trends in the bulk magnetic moments. The spin polarization can be strongly enhanced, by variation of the experimental geometry, when the photoemission is undertaken with circularly polarized light, indicating that spin-orbit interaction can have a profound in spin polarized photoemission. Further spin polarized photoemission studies using variable circularly polarized light at high photon energies, high flux are indicated, underscoring the value of synchrotron measurements at facilities with increased beam stability.

  6. Interaction of light and surface plasmon polaritons in Ag Islands studied by nonlinear photoemission microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Buckanie, N.M.; Kirschbaum, P.; Sindermann, S.; Heringdorf, F.-J. Meyer zu, E-mail: meyerzh@uni-due.de

    2013-07-15

    Two photon photoemission microscopy was used to study the interaction of femtosecond laser pulses with Ag islands prepared using different strategies on Si(111) and SiO{sub 2}. The femtosecond laser pulses initiate surface plasmon polariton (SPP) waves at the edges of the island. The superposition of the electrical fields of the femtosecond laser pulses with the electrical fields of the SPP results in a moiré pattern that is comparable despite the rather different methods of preparation and that gives access to the wavelength and direction of the SPP waves. If the SPPs reach edges of the Ag islands, they can be converted back into light waves. The incident and refracted light waves result in an interference pattern that can again be described with a moiré pattern, demonstrating that Ag islands can be used as plasmonic beam deflectors for light. - Highlights: • Surface plasmon polaritons were studied on Ag islands in two photon photoemission microscopy. • Ag islands were prepared using self-assembly, electron beam lithography, and a focused ion beam. • The SPP pattern on Ag islands can be described with a simple moiré concept. • SPP output coupling results in a pattern that can again be described by the moiré effect.

  7. Photoemission study of CdS heterojunction formation with binary selenide semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Nelson, A.J. [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States)

    1995-11-01

    Synchrotron radiation soft x-ray photoemission spectroscopy was used to investigate the development of the electronic structure at the CdS/Cu{sub 2{minus}{ital x}}Se and CdS/In{sub 6}Se{sub 7} heterojunction interfaces. Cu{sub 2{minus}{ital x}}Se and In{sub 6}Se{sub 7} layers were deposited on GaAs (100) by physical vapor deposition from Cu{sub 2}Se and In{sub 2}Se{sub 3} sources. CdS overlayers were then deposited {ital in} {ital situ}, at room temperature, in steps on these layers. Photoemission measurements were acquired after each growth to observe changes in the valence-band electronic structure and changes in the In4{ital d} and Cd4{ital d} core lines. The results were used to correlate the interfacial chemistry with the electronic structure and to directly determine the CdS/Cu{sub 2{minus}{ital x}}Se and CdS/In{sub 6}Se{sub 7} heterojunction valence-band discontinuities and the consequent heterojunction band diagrams. These results are compared to the valence-band offset ({Delta}{ital E}{sub {ital v}}) for the CdS/CuInSe{sub 2} heterojunction interface.

  8. Synchrotron-radiation photoemission study of CdS/CuInSe sub 2 heterojunction formation

    Energy Technology Data Exchange (ETDEWEB)

    Nelson, A.J.; Gebhard, S. (Solar Energy Research Institute, 1617 Cole Boulevard, Golden, CO (USA)); Rockett, A. (Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL (USA)); Colavita, E. (Department of Physics, University of Calabria, I-87036 Arcavacata di Rende, Cosenza (Italy)); Engelhardt, M.; Hoechst, H. (Synchrotron Radiation Center, University of Wisconsin-Madison, Stoughton, WI (USA))

    1990-10-15

    Synchrotron-radiation soft-x-ray photoemission spectroscopy was used to investigate the development of the electronic structure at the CdS/CuInSe{sub 2} heterojunction interface. CdS overlayers were deposited in steps on single-crystal {ital p}- and {ital n}-type CuInSe{sub 2} at 250 {degree}C. Results indicate that the CdS grows in registry with the substrate, initially in a two-dimensional growth mode followed by three-dimensional island growth as is corroborated by reflection high-energy electron-diffraction analysis. Photoemission measurements were acquired after each growth in order to observe changes in the valence-band electronic structure as well as changes in the In 4{ital d}, Se 3{ital d}, Cd 4{ital d}, and S 2{ital p} core lines. The results were used to correlate the interface chemistry with the electronic structure at these interfaces and to directly determine the CdS/CuInSe{sub 2} heterojunction valence-band discontinuity and the consequent heterojunction band diagram. These results show that the Katnani-Margaritondo method is unreliable in determining offsets for heterojunctions where significant Fermi-level pinning may occur and where the local structure and chemistry of the interface depends strongly on the specific heterojunction.

  9. Vacuum ultraviolet photon detector with continuously adjustable resolution for inverse photoemission spectroscopy

    CERN Document Server

    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.

  10. Solar energy conversion via hot electron internal photoemission in metallic nanostructures: Efficiency estimates

    International Nuclear Information System (INIS)

    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

  11. Molecular Frame Photoemission: Probe of the Photoionization Dynamics for Molecules in the Gas Phase

    Institute of Scientific and Technical Information of China (English)

    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.

  12. On the angular dependence of the photoemission time delay in helium

    CERN Document Server

    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...

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  14. Internal photoemission study on charge trapping behavior in rapid thermal oxides on strained-Si/SiGe heterolayers

    Energy Technology Data Exchange (ETDEWEB)

    Bera, M.K. [Department of Electronic Engineering, City University of Hong Kong, 83-Tat Chee Avenue, Kowloon (Hong Kong); Department of Electronics and ECE, Indian Institute of Technology Kharagpur, 721302 (India)], E-mail: mkbera@cityu.edu.hk; Mahata, C. [Department of Electronics and ECE, Indian Institute of Technology Kharagpur, 721302 (India); Bhattacharya, S. [School of Electrical and Electronic Engineering, The Queen' s University of Belfast, BT7 INN (United Kingdom); Chakraborty, A.K. [Department of Chemistry, University of Durham, Durham, DH1 3LE (United Kingdom); Armstrong, B.M.; Gamble, H.S. [School of Electrical and Electronic Engineering, The Queen' s University of Belfast, BT7 INN (United Kingdom); Maiti, C.K. [Department of Electronics and ECE, Indian Institute of Technology Kharagpur, 721302 (India)

    2008-12-30

    A comparative study on the nature of defects and their relationship to charge trapping with enhanced photosensitivity has been investigated through magnetic resonance and internal photoemission (IPE) experiments for rapid thermal grown oxides (RTO) on strained-Si/Si{sub 0.8}Ge{sub 0.2} and on co-processed bulk-Si (1 0 0) substrates. Both the band and defect-related electronic states were characterized through EPR, IPE, C-V and I-V measurements under UV-illumination. Surface chemical characterization of as-grown ultrathin oxides (5-7 nm) has been performed using high-resolution XPS. Enhancement in Ge-segregation with increasing oxidation temperature is reported. Comparative studies on interface properties and leakage current behavior of rapid thermal oxides have also been studied through fabricating metal-oxide-semiconductor capacitor structures. A degraded electrical property with increasing oxidation temperature is reported. Constant voltage stressing (CVS) in the range of 5.5-7 V was used to study the breakdown characteristics of different samples. We observe a distinguishably different time-to-breakdown (t{sub bd}) phenomenon for bulk-Si and strained-Si/SiGe samples. Whereas the oxide on bulk-Si shows a typical breakdown behavior, the RTO grown oxide on strained-Si/SiGe samples showed a quasi-or soft-breakdown with lower t{sub bd} value. It may be pointed out that quasi-breakdown may be a stronger reliability limiting factor for strained-Si/SiGe devices in the oxide thickness range studied.

  15. A photoemission study of interfaces between organic semiconductors and Co as well as Al2O3/Co contacts

    NARCIS (Netherlands)

    Grobosch, M.; Schmidt, C.; Naber, W.J.M.; Wiel, van der W.G.; Knupfer, M.

    2010-01-01

    We have studied the energy-level alignment of ex situ, acetone cleaned Co and Al2O3/Co contacts to the organic semiconductors pentacene and rubrene by combined X-ray and ultraviolet photoemission spectroscopy. Our results demonstrate that the work function under these conditions is smaller than in t

  16. On the excess photon noise in single-beam measurements with photo-emissive and photo-conductive cells

    NARCIS (Netherlands)

    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

  17. CHARGE-TRANSFER SATELLITES AND MULTIPLET SPLITTING IN X-RAY PHOTOEMISSION SPECTRA OF LATE TRANSITION-METAL HALIDES

    NARCIS (Netherlands)

    OKADA, K; KOTANI, A; THOLE, BT

    1992-01-01

    Core-level X-ray photoemission spectra (XPS) are calculated for Ni and Co dihalides with an MX6 cluster model (M = Ni, Co; X = F, Cl, Br), where intra-atomic multiplet coupling as well as covalency mixing is taken into account. The effects of the intra-atomic configuration interaction between (3s)1(

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

    International Nuclear Information System (INIS)

    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

  19. Interaction of light and surface plasmon polaritons in Ag islands studied by nonlinear photoemission microscopy.

    Science.gov (United States)

    Buckanie, N M; Kirschbaum, P; Sindermann, S; Meyer zu Heringdorf, F-J

    2013-07-01

    Two photon photoemission microscopy was used to study the interaction of femtosecond laser pulses with Ag islands prepared using different strategies on Si(111) and SiO₂. The femtosecond laser pulses initiate surface plasmon polariton (SPP) waves at the edges of the island. The superposition of the electrical fields of the femtosecond laser pulses with the electrical fields of the SPP results in a moiré pattern that is comparable despite the rather different methods of preparation and that gives access to the wavelength and direction of the SPP waves. If the SPPs reach edges of the Ag islands, they can be converted back into light waves. The incident and refracted light waves result in an interference pattern that can again be described with a moiré pattern, demonstrating that Ag islands can be used as plasmonic beam deflectors for light.

  20. Temperature dependence of high-resolution resonant photoemission spectra of CeSi

    International Nuclear Information System (INIS)

    High-resolution Ce 4d-4f resonant photoemission spectra near the Fermi level of CeSi with the Neel temperature of 5.9K have been measured at temperatures from 5.6 to 200K, in order to investigate the competition between the Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction and the Kondo effect. As temperature is decreasing down to 30K, the intensity due to the Ce 4f5/21 final state increases because of the evolution of the heavy Fermion behaviour caused by the Kondo effect. The intensity, however, decreases gradually from 30 to 5.6K. This indicates that the heavy Fermion behaviour is strongly suppressed by the anti-ferromagnetic ordering due to the RKKY interaction

  1. Retention Characteristics of CBTi144 Thin Films Explained by Means of X-Ray Photoemission Spectroscopy

    Directory of Open Access Journals (Sweden)

    G. Biasotto

    2010-01-01

    Full Text Available 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 ferroelectric film is considered to be associated with the preferred orientation of the Pt bottom electrode. XPS measurements were employed to understand the nature of defects on the retention behavior of CBTi144 films. We have observed that the main source of retention-free characteristic of the capacitors is the oxygen environment in the CBTi144 lattice.

  2. Dynamic screening of a localized hole during photoemission from a metal cluster

    CERN Document Server

    Koval, N E; Borisov, A G; Muiño, R Díez

    2012-01-01

    Recent advances in attosecond spectroscopy techniques have fueled the interest in the theoretical description of electronic processes taking place in the subfemtosecond time scale. We here study the coupled dynamic screening of a localized hole and a photoelectron emitted from a metal cluster using a semi-classical model. Electron density dynamics in the cluster is calculated with Time Dependent Density Functional Theory and the motion of the photoemitted electron is described classically. We show that the dynamic screening of the hole by the cluster electrons affects the motion of the photoemitted electron. At the very beginning of the photoemission process, the emitted electron is accelerated by the cluster electrons that pile up to screen the hole. This is a velocity dependent effect that needs to be accounted for when calculating the energy lost by the electron due to inelastic processes.

  3. Synchrotron-Radiation Photoemission Study of Electronic Structures of a Cs-Doped Rubrene Surface

    Science.gov (United States)

    Cheng, Chiu-Ping; Lu, Meng-Han; Chu, Yu-Ya; Pi, Tun-Wen

    Using synchrotron-radiation photoemission spectroscopy, we have studied the electronic structure of a cesium-doped rubrene thin film. The addition of cesium atoms causes the movement of the valence-band spectra and the change in line shapes at different concentration that can be separated into four different stages. In the first stage, the cesium atoms continuously diffuse into the substrate, and the Fermi level moves in the energy gap as a result of an electron transferred from the cesium to the rubrene. The second stage, in which the shifts of the spectra are interrupted, is characterized by the introduction of two in-gap states. When increasing doping of cesium into the third stage, the spectra move again; whereas, the line shapes maintain at the stoichiometric ratio of one. In the fourth stage, new in-gap states appear, which are the highest occupied molecular orbital (HOMO) and HOMO+1 states of (rubrene)2- anion.

  4. Photoemission spectroscopy studies of SrTiO{sub 3} and its interface to gold

    Energy Technology Data Exchange (ETDEWEB)

    Wintz, Susi; Grobosch, Mandy; Knupfer, Martin [IFW Dresden, P.O. Box 270116, 01171 Dresden (Germany); Seibt, Juliane; Hanzig, Florian; Stoecker, Hartmut; Meyer, Dirk C. [Institut fuer Experimentelle Physik, TU Bergakademie Freiberg, Leipziger Str. 23, 09596 Freiberg (Germany)

    2011-07-01

    Motivated by applications of strontium titanate (SrTiO{sub 3}, STO) in non-volatile memory devices we studied the surface of STO by means of x-ray and ultra violet photoemission spectroscopy. The focus of the analysis was purity, doping and the annealing time. It could be demonstrated that a surface contamination layer consisting of carbonates and hydroxides exists on surfaces prepared under ambient conditions. In addition, the interface between STO and gold was investigated. We show that there is a weak interaction of these materials, however a Schottky-type Au/SrTiO{sub 3} junction is formed. Finally the work function of all STO samples was determined. The work function depends on the modification of the STO surface. This fact should considered for the formation of such a Schottky-type junction.

  5. Strong screening in photoemission at interfaces between organic semiconductors and gold: polarization effects versus charge transfer

    Energy Technology Data Exchange (ETDEWEB)

    Kolacyak, Daniel; Peisert, Heiko; Chasse, Thomas [Universitaet Tuebingen, Institut fuer Physikalische Chemie (Germany); Petershans, Andre [Forschungszentrum Karlsruhe, Institut fuer Technische Chemie (Germany)

    2008-07-01

    We studied electronic polarization effects at organic/metal interfaces using combined photoemission spectroscopy (PES) and X-ray excited Auger electron spectroscopy (XAES) as a function of the organic layer thickness. As a model system, sandwich structures of metall-phthalocyanines (e.g consisting of PcMg and PcZn) were deposited on gold. It was found, that the screening of the photohole is remarkably increased for molecules directly at the interface whereas further layers are affected weakly. This may be caused by a fast charge transfer across the interface as a result of the photoionization due to the overlap organic/metal wave functions. Furthermore, differences in the screening were found for buried molecules and molecules on the surface of the organic film ascribed to different polarization energies. The influence of the morphology and orientation was studied by comparing different substrates: polycrystalline gold foil and single crystalline Au(100).

  6. Improvement of photoemission performance of a gradient-doping transmission-mode GaAs photocathode

    Institute of Scientific and Technical Information of China (English)

    Zhang Yi-Jun; Niu Jun; Zhao Jing; Xiong Ya-Juan; Ren Ling; Chang Ben-Kang; Qian Yun-Sheng

    2011-01-01

    Two types of transmission-mode GaAs photocathodes grown by molecular beam epitaxy are compared in terms of activation process and spectral response,one has a gradient-doping structure and the other has a uniform-doping structure.The experimental results show that the gradient-doping photocathode can obtain a higher photoemission capability than the uniform-doping one. As a result of the downward graded band-bending structure,the cathode performance parameters,such as the electron average diffusion length and the surface electron escape probability obtained by fitting quantum yield curves,are greater for the gradient-doping photocathode.The electron diffusion length is within a range of from 2.0 to 5.4 μm for doping concentration varying from 1019 to 1018 cm-3 and the electron average diffusion length of the gradient-doping photocathode achieves 3.2 μm.

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

    Institute of Scientific and Technical Information of China (English)

    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.

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

    Science.gov (United States)

    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.

  9. Simulation study of the field emission and photoemission on metallic photocathodes. Emitted beam dynamics

    International Nuclear Information System (INIS)

    After a bibliographic research on field emission, photoemission and photo-field emission, the principle of the field equations (Poisson and Maxwell's) resolution by the finite element method is developed. The PRIAM program is shown to be efficient (adaptive mesh and refinement in the selected area). Several possibilities exist to reduce the effect of space charge such as the decrease of the laser pulse duration, the increase of the electric field and the application of a magnetic field. Calculations of the transverse emittance for a metallic plan photocathode have been made at different moments of the emission: transverse emittance is small at the beginning and at the end of the emission. It passes by a maximum which can be the origin of the electronic beam explosion for strong field. If a small emittance is wanted, one must illuminate the photocathode by a short pulsed laser

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  11. Electron-vibration coupling induced renormalization in the photoemission spectrum of diamondoids

    Science.gov (United States)

    Gali, Adam; Demján, Tamás; Vörös, Márton; Thiering, Gergő; Cannuccia, Elena; Marini, Andrea

    2016-04-01

    The development of theories and methods devoted to the accurate calculation of the electronic quasi-particle states and levels of molecules, clusters and solids is of prime importance to interpret the experimental data. These quantum systems are often modelled by using the Born-Oppenheimer approximation where the coupling between the electrons and vibrational modes is not fully taken into account, and the electrons are treated as pure quasi-particles. Here, we show that in small diamond cages, called diamondoids, the electron-vibration coupling leads to the breakdown of the electron quasi-particle picture. More importantly, we demonstrate that the strong electron-vibration coupling is essential to properly describe the overall lineshape of the experimental photoemission spectrum. This cannot be obtained by methods within Born-Oppenheimer approximation. Moreover, we deduce a link between the vibronic states found by our many-body perturbation theory approach and the well-known Jahn-Teller effect.

  12. Electron–vibration coupling induced renormalization in the photoemission spectrum of diamondoids

    Science.gov (United States)

    Gali, Adam; Demján, Tamás; Vörös, Márton; Thiering, Gergő; Cannuccia, Elena; Marini, Andrea

    2016-01-01

    The development of theories and methods devoted to the accurate calculation of the electronic quasi-particle states and levels of molecules, clusters and solids is of prime importance to interpret the experimental data. These quantum systems are often modelled by using the Born–Oppenheimer approximation where the coupling between the electrons and vibrational modes is not fully taken into account, and the electrons are treated as pure quasi-particles. Here, we show that in small diamond cages, called diamondoids, the electron–vibration coupling leads to the breakdown of the electron quasi-particle picture. More importantly, we demonstrate that the strong electron–vibration coupling is essential to properly describe the overall lineshape of the experimental photoemission spectrum. This cannot be obtained by methods within Born–Oppenheimer approximation. Moreover, we deduce a link between the vibronic states found by our many-body perturbation theory approach and the well-known Jahn–Teller effect. PMID:27103340

  13. Angular distribution and atomic effects in condensed phase photoelectron spectroscopy

    International Nuclear Information System (INIS)

    A general concept of condensed phase photoelectron spectroscopy is that angular distribution and atomic effects in the photoemission intensity are determined by different mechanisms, the former being determined largely by ordering phenomena such as crystal momentum conservation and photoelectron diffraction while the latter are manifested in the total (angle-integrated) cross section. In this work, the physics of the photoemission process is investigated in several very different experiments to elucidate the mechanisms of, and correlation between, atomic and angular distribution effects. Theoretical models are discussed and the connection betweeen the two effects is clearly established. The remainder of this thesis, which describes experiments utilizing both angle-resolved and angle-integrated photoemission in conjunction with synchrotron radiation in the energy range 6 eV less than or equal to h ν less than or equal to 360 eV and laboratory sources, is divided into three parts

  14. Introductory Lecture. Probing wavepacket dynamics with femtosecond energy- and angle-resolved photoelectron spectroscopy

    OpenAIRE

    Takatsuka, Kazuo; Arasaki, Yasuki; Wang, Kwanghsi; McKoy, Vincent

    2000-01-01

    Several recent studies have demonstrated how well-suited femtosecond time-resolved photoelectron spectra are for mapping wavepacket dynamics in molecular systems. Theoretical studies of femtosecond photoelectron spectra which incorporate a robust description of the underlying photoionization dynamics should enhance the utility of such spectra as a probe of wavepackets and of the evolution of electronic structure. This should be particularly true in regions of avoided crossings where the photo...

  15. Attosecond electronic and nuclear quantum photodynamics of ozone monitored with time and angle resolved photoelectron spectra

    CERN Document Server

    Decleva, P; Perveaux, A; Lauvergnat, D; Gatti, F; Lasorne, B; Halász, G J; Vibók, Á

    2016-01-01

    Recently we reported a series of numerical simulations proving that it is possible in principle to create an electronic wave packet and subsequent electronic motion in a neutral molecule photoexcited by a UV pump pulse within a few femtoseconds. We considered the ozone molecule: for this system the electronic wave packet leads to a dissociation process. In the present work, we investigate more specifically the time-resolved photoelectron angular distribution of the ozone molecule that provides a much more detailed description of the evolution of the electronic wave packet. We thus show that this experimental technique should be able to give access to observing in real time the creation of an electronic wave packet in a neutral molecule and its impact on a chemical process.

  16. Angle-resolved 2D imaging of electron emission processes in atoms and molecules

    International Nuclear Information System (INIS)

    A variety of electron emission processes have been studied in detail for both atomic and molecular systems, using a highly efficient experimental system comprising two time-of-flight (TOF) rotatable electron energy analyzers and a 3rd generation synchrotron light source. Two examples are used here to illustrate the obtained results. Firstly, electron emissions in the HCL molecule have been mapped over a 14 eV wide photon energy range over the Cl 2p ionization threshold. Particular attention is paid to the dissociative core-excited states, for which the Auger electron emission shows photon energy dependent features. Also, the evolution of resonant Auger to the normal Auger decay distorted by post-collision interaction has been observed and the resonating behavior of the valence photoelectron lines studied. Secondly, an atomic system, neon, in which excitation of doubly excited states and their subsequent decay to various accessible ionic states has been studied. Since these processes only occurs via inter-electron correlations, the many body dynamics of an atom can be probed, revealing relativistic effects, surprising in such a light atom. Angular distribution of the decay of the resonances to the parity unfavored continuum exhibits significant deviation from the LS coupling predictions

  17. Electronic Properties of Layered Oxides:. Pulsed Laser Deposition of YBCO Films for In-Situ Studies by Photoemission Spectroscopy

    Science.gov (United States)

    Pavuna, D.; Ariosa, D.; Berger, H.; Christensen, S.; Frazer, B.; Gatt, R.; Grioni, M.; Margaritondo, G.; Misra, S.; Onellion, M.; Schmauder, T.; Vobornik, I.; Xi, X.; Zacchigna, M.; Zwick, F.

    Due to imperfect surfaces of most cuprate samples, almost all Photoemission studies in the past decade were performed on Bi2Sr2CaCu2O8+x, even though a large fraction of other studies and electronic applications was reported for YBa2Cu3O7-δ (YBCO) family of superconducting compounds. In order to systematically study the gap parameter and the Fermi surface variation in high symmetry directions of YBCO and related oxide films we have constructed a new facility at the Wisconsin Synchrotron Radiation Center. We use the pulsed laser ablation (PLD) system that is directly linked to the photoemission chamber. In our unique approach, the samples never leave the controlled ambient and we oxidize our films, either by molecular oxygen or by ozone. In this paper, we, summarize some of the most relevant recent results on electronic properties of layered oxides and describe our new facility for the study of YBCO and related oxide films.

  18. Interface characterization of metal-HfO2-InAs gate stacks using hard x-ray photoemission spectroscopy

    Directory of Open Access Journals (Sweden)

    O. Persson

    2013-07-01

    Full Text Available MOS devices based on III-V semiconductors and thin high-k dielectric layers offer possibilities for improved transport properties. Here, we have studied the interface structure and chemical composition of realistic MOS gate stacks, consisting of a W or Pd metal film and a 6- or 12-nm-thick HfO2 layer deposited on InAs, with Hard X-ray Photoemission Spectroscopy. In and As signals from InAs buried more than 18 nm below the surface are clearly detected. The HfO2 layers are found to be homogeneous, and no influence of the top metal on the sharp InAs-HfO2 interface is observed. These results bridge the gap between conventional photoemission spectroscopy studies on various metal-free model samples with very thin dielectric layers and realistic MOS gate stacks.

  19. Electronic states of solids probed by bulk-sensitive high-resolution soft X-ray photoemission spectroscopy

    CERN Document Server

    Sekiyama, A

    2003-01-01

    High-energy and high-resolution soft x-ray photoemission studies have been performed on strongly correlated Ce compounds and vanadium oxides at BL25SU of SPring-8. The bulk spectra of CeRu sub 2 are explained by a band-structure calculation (itinerant model) whereas the other Ce 4f spectra are well reproduced by calculations based on the single impurity Anderson model (model from a localized limit). In a strong contrast to so far reported results, the bulk spectral functions are revealed to be insensitive to x for Sr sub 1 sub - sub x Ca sub x VO sub 3. Our study has demonstrated the importance of high-energy and high-resolution photoemission spectroscopy for revealing detailed bulk electronic states of strongly correlated systems. (author)

  20. Electronic properties of layered oxides: Pulsed laser deposition of YBCO films for in-situ studies by photoemission spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Pavuna, D.; Ariosa, D. (Ecole Polytechnique, Lausanne (Switzerland)); Berger, H. (and others)

    1998-12-20

    Due to imperfect surfaces of most cuprate samples, almost all photoemission studies in the past decade were performed on Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub 8+x], even though a large fraction of other studies and electronic applications was reported for YBa[sub 2]Cu[sub 3]O[sub 7[minus][delta

  1. Benchmarking of 3D space charge codes using direct phase space measurements from photoemission high voltage DC gun

    OpenAIRE

    Bazarov, Ivan V.; Dunham, Bruce M.; Gulliford, Colwyn; Li, Yulin; Liu, Xianghong; Sinclair, Charles K.; Soong, Ken; Hannon, Fay

    2008-01-01

    We present a comparison between space charge calculations and direct measurements of the transverse phase space for space charge dominated electron bunches after a high voltage photoemission DC gun followed by an emittance compensation solenoid magnet. The measurements were performed using a double-slit setup for a set of parameters such as charge per bunch and the solenoid current. The data is compared with detailed simulations using 3D space charge codes GPT and Parmela3D with initial parti...

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

    International Nuclear Information System (INIS)

    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

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

    International Nuclear Information System (INIS)

    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

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

    International Nuclear Information System (INIS)

    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

    Energy Technology Data Exchange (ETDEWEB)

    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

  6. Electronic structure of Co-Ni-Ga Heusler alloys studied by resonant photoemission

    Energy Technology Data Exchange (ETDEWEB)

    Baral, Madhusmita, E-mail: madhusmita@rrcat.gov.in; Banik, Soma, E-mail: madhusmita@rrcat.gov.in; Ganguli, Tapas, E-mail: madhusmita@rrcat.gov.in; Chakrabarti, Aparna, E-mail: madhusmita@rrcat.gov.in; Deb, S. K. [Indus Synchrotrons Utilization Division, Raja Ramanna Centre for Advanced Technology, Indore-452013 (India); Thamizhavel, A. [Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400005 (India); Wadikar, Avinash; Phase, D. M. [UGC-DAE Consortium for Scientific Research, University Campus, Khandwa Road, Indore-452017 (India)

    2014-04-24

    The electronic structures of Co{sub 2.01}Ni{sub 1.05}Ga{sub 0.94} and Co{sub 1.76}Ni{sub 1.46}Ga{sub 0.78} Heusler alloys have been investigated by resonant photoemission spectroscopy across the 3p-3d transition of Co and Ni. For the Ni excess composition Co{sub 1.76}Ni{sub 1.46}Ga{sub 0.78}, the valence band peak shows a shift of 0.25 eV as compared to the near stoichiometric composition Co{sub 2.01}N1{sub 1.05}Ga{sub 0.94}. Also an enhancement is observed in the Ni related satellite features in the valence band for the Ni excess composition. Due to hybridization of Co and Ni 3d states in these systems, the Co and Ni 3p-3d resonance energies are found to be higher as compared to Co and Ni metals. Theoretical first principle calculation is performed to understand the features in the valence band and the shape of the resonance profile.

  7. Band alignments in Fe/graphene/Si(001) junctions studied by x-ray photoemission spectroscopy

    Science.gov (United States)

    Le Breton, J.-C.; Tricot, S.; Delhaye, G.; Lépine, B.; Turban, P.; Schieffer, P.

    2016-08-01

    The control of tunnel contact resistance is of primary importance for semiconductor-based spintronic devices. This control is hardly achieved with conventional oxide-based tunnel barriers due to deposition-induced interface states. Manipulation of single 2D atomic crystals (such as graphene sheets) weakly interacting with their substrate might represent an alternative and efficient way to design new heterostructures for a variety of different purposes including spin injection into semiconductors. In the present paper, we study by x-ray photoemission spectroscopy the band alignments and interface chemistry of iron-graphene-hydrogenated passivated silicon (001) surfaces for a low and a high n-doping concentration. We find that the hydrogen passivation of the Si(001) surface remains efficient even with a graphene sheet on the Si(001) surface. For both doping concentrations, the semiconductor is close to flat-band conditions which indicates that the Fermi level is unpinned on the semiconductor side of the Graphene/Si(001):H interface. When iron is deposited on the graphene/Si(001):H structures, the Schottky barrier height remains mainly unaffected by the metallic overlayer with a very low barrier height for electrons, a sought-after property in semiconductor based spintronic devices. Finally, we demonstrate that the graphene layer intercalated between the metal and semiconductor also serves as a protection against iron-silicide formation even at elevated temperatures preventing from the formation of a Si-based magnetic dead layer.

  8. Estimation of diffusion coefficient by photoemission electron microscopy in ion-implanted nanostructures

    International Nuclear Information System (INIS)

    We have fabricated parallel stripes of nanostructures in an n-type Si substrate by implanting 30 keV Ga+ ions from a focused ion beam (FIB) source. Two sets of implantation were carried out. In one case, during implantation the substrate was held at room temperature and in the other case at 400 deg. C. Photoemission electron microscopy (PEEM) was carried out on these samples. The implanted parallel stripes, each with a nominal dimension of 4000 nm x 100 nm, appear as bright regions in the PEEM image. Line scans of the intensities from the PEEM image were recorded along and across these stripes. The intensity profile at the edges of a line scan is broader for the implantation carried out at 400 deg. C compared to room temperature. From the analysis of this intensity profile, the lateral diffusion coefficient of Ga in silicon was estimated assuming that the PEEM intensity is proportional to Ga concentration. The diffusion coefficient at 400 deg. C has been estimated to be ∼1.3 x 10-15 m2/s. Across the stripes an asymmetric diffusion profile has been observed, which has been related to the sequence of implantation of these stripes and the associated defect distribution due to lateral straggling of the implanted ions.

  9. Resonant inverse photoemission study of late transition metals at 3p absorption edge

    International Nuclear Information System (INIS)

    Full text: Resonant inverse photoemission spectra (RIPES) of late transition metals (TM) were observed near TM 3p absorption edge. The RIPES spectra of polycrystalline Co, Ni and Cu, as well as single crystal Ni, were observed. Figure 1 shows resonant IPES spectra of polycrystalline Co, Ni and Cu, which were prepared by evaporation. These spectra ware excited by energy above 3p absorption edge (off-resonance). Since a core hole is created by these energies, TM 3d → 3p fluorescence peak is observed in each spectrum at high energy, which is indicated by vertical bars. The main peak just above EF is TM 3d structure, while TM 4sp is observed at 10 ∼ 15 eV. In resonant spectra, the 3d structure changes its intensity, while the 4sp structure does not. In case of Ni metal, satellite structures are also observed at about 2 and 4 eV. From a calculation by Tanaka and Jo, which is based on the Anderson impurity model, the observation of satellite structures suggests the 10 ∼ 20 % 3d8 in ground state The RIPES spectra in this study give us a direct evidence of 3d8 component in Ni metal

  10. CHEMISTRY OF SO{sub 2} ON MODEL METAL AND OXIDE CATALYSTS: PHOTOEMISSION AND XANES STUDIES

    Energy Technology Data Exchange (ETDEWEB)

    RODRIGUEZ,J.A.; JIRSAK,T.; CHATURVEDI,S.; HRBEK,J.; FREITAG,A.; LARESE,J.Z.

    2000-07-09

    High-resolution synchrotron based photoemission and x-ray absorption spectroscopy have been used to study the interaction of SO{sub 2} with a series of metals and oxides. The chemistry of SO{sub 2} on metal surfaces is rich. At low coverages, the molecule fully decomposes into atomic S and O. At large coverages, the formation of SO{sub 3} and SO{sub 4} takes place. The following sequence was found for the reactivity of the metals towards SO{sub 2}: Pt {approx} Rh < Ru < Mo << Zn, Sn, Cs. Alloying can be useful for reducing the chemical affinity of a metal for SO{sub 2} and controlling S poisoning. Pd atoms bonded to Rh and Pt atoms bonded to Sn interact weakly with SO{sub 2}. In general, SO{sub 2} mainly reacts with the O centers of metal oxides. SO{sub 4} is formed on CeO{sub 2} and SO{sub 3} on ZnO. On these systems there is no decomposition of SO{sub 2}. Dissociation of the molecule is observed after introducing a large amount of Ce{sup 3+} sites in ceria, or after depositing Cu or alkali metals on the oxide surfaces. These promote the catalytic activity of the oxides during the destruction of SO{sub 2}.

  11. Study of neutralization kinetics in charged polymer-metal nanocomposite systems by photoemission spectroscopy

    International Nuclear Information System (INIS)

    In case of photoelectron spectroscopy of an insulating material the data obtained from the charged surface are often distorted due to differentially charged surface domains. Recently we have developed a controlled surface neutralization technique to study the kinetics of the surface charging. Here we demonstrate the application of the technique to study the neutralization kinetics of both thick and thin films of charged polymer-metal nanocomposite material using photoemission. Neutralization kinetics of grounded and floated pure polymer thin films was also studied. It was observed that for the thick sample the transition of positively charged domains to overcompensated ones occurs through percolation. In case of grounded thin films the growth of overcompensated domains exhibit a linear behavior followed by saturation. When electrons appear at both surfaces of a floated thin film, the neutralization kinetics show a completely different behavior. Present investigation indicates that for thin films of insulating materials appearing to be neutral in presence of an electron source, controlled neutralization technique may be an important tool to distinguish between presence of multiple chemical species and differential charging.

  12. Study of the P3HT/PCBM interface using photoemission yield spectroscopy

    Science.gov (United States)

    Grzibovskis, Raitis; Vembris, Aivars

    2016-04-01

    Photogeneration efficiency and charge carrier extraction from active layer are the parameters that determine the efficiency of organic photovoltaics (OPVs). Devices made of organic materials often consist of thin (up to 100nm) layers. At this thickness different interface effects become more pronounced. The electron affinity and ionization energy shift can affect the charge carrier transport across metal-organic interface which can affect the performance of the entire device. In the case of multilayer OPVs, energy level compatibility at the organic-organic interface is as important. Photoemission yield spectroscopy was used for organic-organic interface study by ionization energy measurements. In this work we studied "sandwich" type samples of two well-known organic photovoltaic materials- poly(3- hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM). Ionization energy changes at the P3HT/PCBM interface depending on PCBM layer thickness were studied. P3HT layer was obtained by spin-coating while PCBM was deposited on the P3HT by thermal evaporation in vacuum. No ionization energy shift of P3HT was observed. On the contrary, PCBM at the interface with P3HT created additional 0.40eV barrier for hole transport from PCBM to P3HT.

  13. High-resolution photoemission study of II-VI semiconductor nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Graber, T.; Niederdraenk, F.; Kumpf, C.; Schoell, A.; Umbach, E. [Univ. Wuerzburg, Experimentelle Physik II (Germany)

    2007-07-01

    Semiconductor nanoparticles are of rapidly increasing interest due to their various actual and potential applications, such as, e.g., active components in LEDs or solar cells. Very small (1-5 nm) particles are also of particular interest in fundamental research since they represent a size scale which is in between the well-established descriptions of solid state and molecular physics. We report on high resolution X-ray photoemission data of ZnO, CdSe and CdSe/ZnS core-shell nanoparticles in the range of 1-5 nm diameter. The particles were produced by a wet-chemical preparation method with organic stabilizers and drop-deposited on H-passivated silicon and polycrystalline Au substrates. A detailed analysis was performed to identify the various contributions from the core, shell, interface, and surface to the total signal in order to understand the influences of different synthesis routes on the particle composition. Influences of different solvents as well as beam damage and aging processes are discussed. (orig.)

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

    Institute of Scientific and Technical Information of China (English)

    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.

  15. Optical communication with two-photon coherent states. II - Photoemissive detection and structured receiver performance

    Science.gov (United States)

    Shapiro, J. H.; Yuen, H. P.; Machado Mata, J. A.

    1979-01-01

    In a previous paper (1978), the authors developed a method of analyzing the performance of two-photon coherent state (TCS) systems for free-space optical communications. General theorems permitting application of classical point process results to detection and estimation of signals in arbitrary quantum states were derived. The present paper examines the general problem of photoemissive detection statistics. On the basis of the photocounting theory of Kelley and Kleiner (1964) it is shown that for arbitrary pure state illumination, the resulting photocurrent is in general a self-exciting point process. The photocount statistics for first-order coherent fields reduce to those of a special class of Markov birth processes, which the authors term single-mode birth processes. These general results are applied to the structure of TCS radiation, and it is shown that the use of TCS radiation with direct or heterodyne detection results in minimal performance increments over comparable coherent-state systems. However, significant performance advantages are offered by use of TCS radiation with homodyne detection. The abstract quantum descriptions of homodyne and heterodyne detection are derived and a synthesis procedure for obtaining quantum measurements described by arbitrary TCS is given.

  16. Synchrotron radiation photoemission study of metal overlayers on hydrogenated amorphous silicon at room temperature

    Energy Technology Data Exchange (ETDEWEB)

    Pi, J.

    1990-09-21

    In this dissertation, metals deposited on a hydrogenated amorphous silicon (a-Si:H) film at room temperature are studied. The purpose of this work is mainly understanding the electronic properties of the interface, using high-resolution synchrotron radiation photoemission techniques as a probe. Atomic hydrogen plays an important role in passivating dangling bonds of a-Si:H films, thus reducing the gap-state distribution. In addition, singly bonded hydrogen also reduces states at the top of the valence band which are now replaced by deeper Si-H bonding states. The interface is formed by evaporating metal on an a-Si:H film in successive accumulations at room temperature. Au, Ag, and Cr were chosen as the deposited metals. Undoped films were used as substrates. Since some unique features can be found in a-Si:H, such as surface enrichment of hydrogen diffused from the bulk and instability of the free surface, we do not expect the metals/a-Si:H interface to behave exactly as its crystalline counterpart. Metal deposits, at low coverages, are found to gather preferentially around regions deficient in hydrogen. As the thickness is increased, some Si atoms in those regions are likely to leave their sites to intermix with metal overlayers like Au and Cr. 129 refs., 30 figs.

  17. Halide-Substituted Electronic Properties of Organometal Halide Perovskite Films: Direct and Inverse Photoemission Studies.

    Science.gov (United States)

    Li, Chi; Wei, Jian; Sato, Mikio; Koike, Harunobu; Xie, Zhong-Zhi; Li, Yan-Qing; Kanai, Kaname; Kera, Satoshi; Ueno, Nobuo; Tang, Jian-Xin

    2016-05-11

    Solution-processed perovskite solar cells are attracting increasing interest due to their potential in next-generation hybrid photovoltaic devices. Despite the morphological control over the perovskite films, quantitative information on electronic structures and interface energetics is of paramount importance to the optimal photovoltaic performance. Here, direct and inverse photoemission spectroscopies are used to determine the electronic structures and chemical compositions of various methylammonium lead halide perovskite films (MAPbX3, X = Cl, Br, and I), revealing the strong influence of halide substitution on the electronic properties of perovskite films. Precise control over halide compositions in MAPbX3 films causes the manipulation of the electronic properties, with a qualitatively blue shift along the I → Br → Cl series and showing the increase in ionization potentials from 5.96 to 7.04 eV and the change of transport band gaps in the range from 1.70 to 3.09 eV. The resulting light absorption of MAPbX3 films can cover the entire visible region from 420 to 800 nm. The results presented here provide a quantitative guide for the analysis of perovskite-based solar cell performance and the selection of optimal carrier-extraction materials for photogenerated electrons and holes. PMID:27101940

  18. Photo-induced charge-orbital switching in transition-metal compounds probed by photoemission spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Takubo, K; Mizokawa, T [Department of Physics and Department of Complexity Science and Engineering, University of Tokyo, Kashiwa, Chiba 277-8561 (Japan); Takubo, N; Miyano, K [Research Center for Advanced Science and Technology (RCAST), University of Tokyo, Tokyo 153-8904 (Japan); Matsumoto, N; Nagata, S, E-mail: takubo@sces.k.u-tokyo.ac.j [Department of Materials Science and Engineering, Muroran Institute of Technology, 27-1 Mizumoto-cho, Muroran, Hokkaido, 050-8585 Japan (Japan)

    2009-02-01

    Transition-metal compounds with spin, charge, and orbital degrees of freedom tend to have frustrated electronic states coupled with local lattice distortions and to show drastic response to external stimuli such as photo-excitation. We have studied the charge-orbital states in perovskite-type Pr{sub 0.55}(Ca{sub 1-y}Sr{sub y}){sub 0.45}MnO{sub 3} thin films (PCSMO) and spinel-type CuIr{sub 2}S{sub 4} using photoemission spectroscopy combined with additional laser illumination. PCSMO and CuIr{sub 2}S{sub 4} are clear-cut examples of transition-metal compounds showing photo-induced metallic conductivities but the charge-orbital states in the two systems show contrasting responses to the photo-excitation. The charge-orbital states in PCSMO are stabilized by Jahn-Teller or Breathing-type lattice distortions and can be destroyed by photo-excitation. On the other hand, the charge-orbital states in CuIr{sub 2}S{sub 4} are stabilized by dimer formation and tend to be robust against photo-excitation.

  19. The study of transition metal surfaces and thin films with inverse photoemission and scanning tunnelling microscopy

    CERN Document Server

    Wilson, L K

    1997-01-01

    clean Cr(001) and the thick films. This suggests that hybridisation between the substrate bands and the film bands and interface induced states are significant. The spectra taken from sub-monolayer coverages of Fe show marked intensity increase at the Fermi energy, this is a feature of LDOS calculations on Fe atoms at the Fe/Cr interface. Fe growth on surfaces of Cu(100) precovered with c(2x2)N has been studied with scanning tunnelling microscopy. The images show that the Fe does not grow on areas covered with nitrogen. Two different c(2x2)N templates have been used and the shape and size of the Fe islands is seen to be altered. The unoccupied electronic states at the surface of Cr(001) have been observed using k-resolved inverse photoemission. Normal incidence IPE spectra have been taken over a range of incident electron energies (14-24 eV). The spectra show only small variation with incident energy, this is attributed to densities of states effects due to the absence of symmetry allowed initial states at th...

  20. Building blocks of an artificial kagome spin ice: Photoemission electron microscopy of arrays of ferromagnetic islands

    Science.gov (United States)

    Mengotti, E.; Heyderman, L. J.; Fraile Rodríguez, A.; Bisig, A.; Le Guyader, L.; Nolting, F.; Braun, H. B.

    2008-10-01

    Arrays of dipolar coupled ferromagnetic islands arranged in specific geometries provide ideal systems to directly study frustration. We have examined with photoemission electron microscopy the magnetic configurations in three basic building blocks of an artificial kagome spin ice consisting of one, two, and three rings. The kagome spin ice arrangement is particularly interesting because it is highly frustrated and the three interactions at a vertex are equivalent. Employing dipolar energy calculations, we are able to make a full characterization of the magnetic states and therefore identify the lowest energy states. Experimentally we find that the ice rule is always obeyed even at low dipolar coupling strengths. However, as the number of rings increases there is a drastic decrease in the ability to achieve the low-energy states via demagnetization, a behavior also identified in the magnetization reversal. This carries the implication that the ground state will never be achieved in the infinite system. Finally, we show that at low coupling, the applied field direction governs the resulting states. This work opens the door to a novel class of systems for future spintronic applications.

  1. Two-photon photoemission investigation of electronic and dynamical properties of alkali atoms adsorbed on noble metal surfaces

    Science.gov (United States)

    Sametoglu, Vahit

    We present a systematic time-resolved two-photon photoemission study of the electronic and dynamical properties of Li through Cs adsorbed on Cu(111) and Ag(111) surfaces. A fundamental problem in surface science is how to describe the electronic structure of a chemisorption interface based on the intrinsic properties of the interacting materials. Because of their simple s-electron structure, elements of the alkali atom group comprise paradigmatic adsorbates in many theories of chemisorption, whereas the complementary experimental studies are sparse and incomplete. Through a combination of spectroscopic and femtosecond time-resolved surface measurements, we are able to probe systematically the binding energies, symmetries, and electron and nuclear relaxation dynamics of the initially unoccupied alkali atom resonances. As a prelude, we study the two-photon photoemission process occurring at the bare Ag(111) surface. We develop a quantitative model for two-photon photoemission process, where the nonresonant and k-dependent two-photon absorption between the lower and upper sp-bands is modeled by the optical Bloch equations, and the angle-dependent intensities are described by the Fresnel equations. Our two-photon photoemission spectra of Li through Cs chemisorbed Cu(111) and Ag(111) surfaces reveal two resonances with the m = 0 and m = +/-1 symmetry ('m' is the projection of the orbital angular momentum 'l' onto the surface plane). For the m = 0 resonance, which is derived from the hybridization of the ns and npz orbitals of alkali atoms, we find a binding energy of 1.84--1.99 eV below the vacuum level, which is independent of the alkali atom period, and tunes with coverage in a universal manner. At 0.3--0.7 eV higher energy, we discover and identify the m = +/-1 resonance by its characteristic angular intensity distribution, which derives from the antisymmetry of the npx and npy orbitals. We implement a quantitative model for the alkali atom chemisorption based on the

  2. Realisation of a ultra-high vacuum system and technique development of microscopical emitters preparation in silicium. First measurements of field emission current and field photoemission

    International Nuclear Information System (INIS)

    The development of research in the domain of photocathode (electron sources) illuminated by laser light to produce intense multiple bunches of electrons in short time is needed by many applications as linear collider e+e-, free electron laser, lasertron, etc... In this way, after a study of field emission, of photoemission and of photofield emission, we prepared microscopical emitters in silicium heavy and weakly doped a boron using a technique of microlithography. Then, we realized a system of ultra-high vacuum of studying property of emission from photocathodes realized. The experiment results obtained in field emission and photofield emission have shown that a behaviour unexpected for P-silicium tips array compared to P+-silicon tips array. With P-type silicon, a quantum yield of 21 percent has been measured for laser power of 140 mW and for applied field of 1.125 x 107 V/m and an instantaneous response to laser light beam has been observed. It has been noted that presence of oxyde at the surface of photocathode limits extensively the emission current. The fluctuations of emission current are due to quality of vacuum

  3. X-ray excited optical luminescence, photoluminescence, photostimulated luminescence and x-ray photoemission spectroscopy studies on BaFBr:Eu

    CERN Document Server

    Subramanian, N; Govinda-Rajan, K; Mohammad-Yousuf; Santanu-Bera; Narasimhan, S V

    1997-01-01

    The results of x-ray excited optical luminescence (XEOL), photoluminescence (PL), photostimulated luminescence (PSL) and x-ray photoemission spectroscopy (XPS) studies on the x-ray storage phosphor BaFBr:Eu are presented in this paper. Analyses of XEOL, PL and PSL spectra reveal features corresponding to the transitions from 4f sup 6 td sup 1 to 4f sup 7 configurations in different site symmetries of Eu sup 2 sup +. Increasing x-ray dose is seen to lead to a red shift in the maximum of the PL excitation spectrum for the 391 nm emission. The XEOL and XPS spectra do not show any signature of Eu sup 3 sup + in the samples studied by us, directly raising doubts about the model of Takahashi et al in which Eu sup 2 sup + is expected to ionize to Eu sup 3 sup + upon x-ray irradiation and remain stable until photostimulation. XEOL and PSL experiments with simultaneous x-ray irradiation and He - Ne laser excitation as well as those with sequential x-ray irradiation and laser stimulation bring out the competition betwe...

  4. Realisation and experimental testing of silicon-point cathodes for field emission and field photoemission in a continuous and pulsed regime

    International Nuclear Information System (INIS)

    Acceleration technique and free electron laser improvements require the production of intense, bunched electron beams with small emittance. Photocathodes with arrays of tips have been prepared using microlithographic technique. Si(P) and Si(N) with (100) and (111) crystallographic orientation are used. Current emission due to field effect has been measured. Study of band bending at the surface with strong applied electric field is outline. Its interest is proved in field photoemission. Fowler-Nordheim' theory is used to determine the field reinforcement and emissive area. Experience in high vacuum chamber (pressure of few 10-10 torr) yields satisfactory results from low P type silicon, instantaneous photocurrent is observed during a short exposure of light. Photocurrent of about a hundred times dark-current, at the threshold of field emission, from heavy density of tips is measured. An acousto-optic cell allows producing, with a continuous Argon laser, some pulsed beams of light. Optical excitation and photocurrent pulses follow with the same time. Quantum efficiency around 1% has been measured with low energy pulsed laser of a few nJ during few tens of ns at frequency of few MHz. (orig.)

  5. Adsorption energy and geometry of adsorbed organic molecules on Au(111) probed by surface-state photoemission

    Energy Technology Data Exchange (ETDEWEB)

    Ziroff, Johannes; Forster, Frank [Universitaet Wuerzburg, Experimentelle Physik II, D-97074 Wuerzburg (Germany); Reinert, Friedrich [Universitaet Wuerzburg, Experimentelle Physik II, D-97074 Wuerzburg (Germany); Forschungszentrum Karlsruhe, Gemeinschaftslabor fuer Nanoanalytik, D-76021 Karlsruhe (Germany)

    2009-07-01

    The modification of the Au(111) surface states by an adsorbed monolayer of large {pi}-conjugated molecules (PTCDA, NTCDA, CuPc) was investigated by high-resolution angle-resolved photoelectron spectroscopy. We determined binding energy, band mass, and Rashba-splitting and discuss the results in the context of rare-gas adsorption on noble metals. This comparison allows the determination of the bonding strength of the adsorbates, found to be physisorptive with derived binding energies per molecule of 2.0 eV for PTCDA and 1.5 eV for NTCDA. We will also present a superstructure model for the NTCDA/Au(111) system, deduced from low energy electron diffraction images in combination with band-backfolding of the Tamm and Shockley states. The coverage dependent evolution of the surface states was also investigated for the three molecules, giving evidence for a dilute-phase growth of the CuPc molecule on the Au(111) surface.

  6. The slope-background for the near-peak regimen of photoemission spectra

    Energy Technology Data Exchange (ETDEWEB)

    Herrera-Gomez, A., E-mail: aherrera@qro.cinvestav.mx [CINVESTAV-Unidad Queretaro, Queretaro 76230 (Mexico); Bravo-Sanchez, M. [CINVESTAV-Unidad Queretaro, Queretaro 76230 (Mexico); Aguirre-Tostado, F.S. [Centro de Investigación en Materiales Avanzados, Chihuahua, Chihuahua 31109 (Mexico); Vazquez-Lepe, M.O. [Departamento de Ingeniería de Proyectos, Universidad de Guadalajara, Jalisco 44430 (Mexico)

    2013-08-15

    Highlights: •We propose a method that accounts for the change in the background slope of XPS data. •The slope-background can be derived from Tougaard–Sigmund's transport theory. •The total background is composed by Shirley–Sherwood and Tougaard type backgrounds. •The slope-background employs one parameter that can be related to REELS spectra. •The slope, in conjunction with the Shirley–Sherwood background, provides better fits. -- Abstract: Photoemission data typically exhibits a change on the intensity of the background between the two sides of the peaks. This step is usually very well reproduced by the Shirley–Sherwood background. Yet, the change on the slope of the background in the near-peak regime, although usually present, is not always as obvious to the eye. However, the intensity of the background signal associated with the evolution of its slope can be appreciable. The slope-background is designed to empirically reproduce the change on the slope. Resembling the non-iterative Shirley method, the proposed functional form relates the slope of the background to the integrated signal at higher electron kinetic energies. This form can be predicted under Tougaard–Sigmund's electron transport theory in the near-peak regime. To reproduce both the step and slope changes on the background, it is necessary to employ the slope-background in conjunction with the Shirley–Sherwood background under the active-background method. As it is shown for a series of materials, the application of the slope-background provides excellent fits, is transparent to the operator, and is much more independent of the fitting range than other background methods. The total area assessed through the combination of the slope and the Shirley–Sherwood backgrounds is larger than when only the Shirley–Sherwood background is employed, and smaller than when the Tougaard background is employed.

  7. Internal photoemission from plasmonic nanoparticles: comparison between surface and volume photoelectric effects.

    Science.gov (United States)

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

    2014-05-01

    We study the emission of photoelectrons from plasmonic nanoparticles into a surrounding matrix. We consider two mechanisms of electron emission from the nanoparticles--surface and volume ones--and use models for these two mechanisms which allow us to obtain analytical results for the photoelectron emission rate from a nanoparticle. Calculations have been carried out for a step potential at the surface of a spherical nanoparticle, and a simple model for the hot electron cooling has been used. We highlight the effect of the discontinuity of the dielectric permittivity at the nanoparticle boundary in the surface mechanism, which leads to a substantial (by ∼5 times) increase of the internal photoelectron emission rate from a nanoparticle compared to the case when such a discontinuity is absent. For a plasmonic nanoparticle, a comparison of the two photoeffect mechanisms was undertaken for the first time which showed that the surface photoeffect can in the general case be larger than the volume one, which agrees with the results obtained for a flat metal surface first formulated by Tamm and Schubin in their pioneering development of a quantum-mechanical theory of photoeffect in 1931. In accordance with our calculations, this possible predominance of the surface effect is based on two factors: (i) effective cooling of hot carriers during their propagation from the volume of the nanoparticle to its surface in the scenario of the volume mechanism and (ii) strengthening of the surface mechanism through the effect of the discontinuity of the dielectric permittivity at the nanoparticle boundary. The latter is stronger at relatively lower photon energies and correspondingly is more substantial for internal photoemission than for an external one. We show that in the general case, it is essential to take both mechanisms into account in the development of devices based on the photoelectric effect and when considering hot electron emission from a plasmonic nanoantenna.

  8. Test of theoretical models for ultrafast heterogeneous electron transfer with femtosecond two-photon photoemission data

    Indian Academy of Sciences (India)

    Lars Gundlach; Tobias Letzig; Frank Willig

    2009-09-01

    The energy distribution of electrons injected into acceptor states on the surface of TiO2 was measured with femtosecond two-photon photoemission. Shape and relative energetic position of these distribution curves with respect to the corresponding donor states, i.e. of perylene chromophores in the first excited singlet state attached via different bridge-anchor groups to the TiO2 surface, were compared with the predictions of different theoretical models for light-induced ultrafast heterogeneous electron transfer (HET). Gerischer’s early scenario for light-induced HET was considered and two recent explicit calculations, i.e. a fully quantum mechanical analytical model and a time-dependent density functional theory model based on molecular dynamics simulations for the vibrational modes were also considered. Based on the known vibrational structure in the photoionization spectrum of perylene in the gas phase and that measured in the linear absorption spectra of the perylene chromophores anchored on the TiO2 surface the energy distribution curves for the injected electrons were fitted assuming the excitation of the dominant 0.17 eV vibrational mode in the ionized perylene chromophore leading to a corresponding Franck-Condon dictated progression in the energy distribution curves. Each individual peak was fitted with a Voigt profile where the Lorentzian contribution was taken from the time-resolved HET data and the Gaussian contribution attributed to inhomogeneous broadening. The measured room temperature energy distribution curves for the injected electrons are explained with the fully quantum mechanical model for light-induced HET with the high energy, 0.17 eV, skeletal stretching mode excited in the ionized perylene chromophore. The corresponding energy distribution of the injected electrons is fully accommodated in acceptor states on the TiO2 surface fulfilling the wide band limit.

  9. Ultrafast Multiphoton Pump-probe Photoemission Excitation Pathways in Rutile TiO2(110)

    Energy Technology Data Exchange (ETDEWEB)

    Argondizzo, Adam; Cui, Xuefeng; Wang, Cong; Sun, Huijuan; Shang, Honghui; Zhao, Jin; Petek, Hrvoje

    2015-04-27

    We investigate the spectroscopy and photoinduced electron dynamics within the conduction band of reduced rutile TiO2(110) surface by multiphoton photoemission (mPP) spectroscopy with wavelength tunable ultrafast (!20 fs) laser pulse excitation. Tuning the mPP photon excitation energy between 2.9 and 4.6 eV reveals a nearly degenerate pair of new unoccupied states located at 2.73 ± 0.05 and 2.85 ± 0.05 eV above the Fermi level, which can be analyzed through the polarization and sample azimuthal orientation dependence of the mPP spectra. Based on the calculated electronic structure and optical transition moments, as well as related spectroscopic evidence, we assign these resonances to transitions between Ti 3d bands of nominally t2g and eg symmetry, which are split by crystal field. The initial states for the optical transition are the reduced Ti3+ states of t2g symmetry populated by formation oxygen vacancy defects, which exist within the band gap of TiO2. Furthermore,we studied the electron dynamics within the conduction band of TiO2 by three-dimensional time-resolved pump-probe interferometric mPP measurements. The spectroscopic and time-resolved studies reveal competition between 2PP and 3PP processes where the t2g-eg transitions in the 2PP process saturate, and are overtaken by the 3PP process initiated by the band-gap excitation from the valence band of TiO2.

  10. Two-photon Photoemission of Organic Semiconductor Molecules on Ag(111)

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Aram [Univ. of California, Berkeley, CA (United States)

    2008-05-01

    Angle- and time-resolved two-photon photoemission (2PPE) was used to study systems of organic semiconductors on Ag(111). The 2PPE studies focused on electronic behavior specific to interfaces and ultrathin films. Electron time dynamics and band dispersions were characterized for ultrathin films of a prototypical n-type planar aromatic hydrocarbon, PTCDA, and representatives from a family of p-type oligothiophenes.In PTCDA, electronic behavior was correlated with film morphology and growth modes. Within a fewmonolayers of the interface, image potential states and a LUMO+1 state were detected. The degree to which the LUMO+1 state exhibited a band mass less than a free electron mass depended on the crystallinity of the layer. Similarly, image potential states were measured to have free electron-like effective masses on ordered surfaces, and the effective masses increased with disorder within the thin film. Electron lifetimes were correlated with film growth modes, such that the lifetimes of electrons excited into systems created by layer-by-layer, amorphous film growth increased by orders of magnitude by only a few monolayers from the surface. Conversely, the decay dynamics of electrons in Stranski-Krastanov systems were limited by interaction with the exposed wetting layer, which limited the barrier to decay back into the metal.Oligothiophenes including monothiophene, quaterthiophene, and sexithiophene were deposited on Ag(111), and their electronic energy levels and effective masses were studied as a function of oligothiophene length. The energy gap between HOMO and LUMO decreased with increasing chain length, but effective mass was found to depend on domains from high- or low-temperature growth conditions rather than chain length. In addition, the geometry of the molecule on the surface, e.g., tilted or planar, substantially affected the electronic structure.

  11. CdS and Cd-Free Buffer Layers on Solution Phase Grown Cu2ZnSn(SxSe1- x)4 :Band Alignments and Electronic Structure Determined with Femtosecond Ultraviolet Photoemission Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Haight, Richard; Barkhouse, Aaron; Wang, Wei; Yu, Luo; Shao, Xiaoyan; Mitzi, David; Hiroi, Homare; Sugimoto, Hiroki

    2013-12-02

    The heterojunctions formed between solution phase grown Cu2ZnSn(SxSe1- x)4(CZTS,Se) and a number of important buffer materials including CdS, ZnS, ZnO, and In2S3, were studied using femtosecond ultraviolet photoemission spectroscopy (fs-UPS) and photovoltage spectroscopy. With this approach we extract the magnitude and direction of the CZTS,Se band bending, locate the Fermi level within the band gaps of absorber and buffer and measure the absorber/buffer band offsets under flatband conditions. We will also discuss two-color pump/probe experiments in which the band bending in the buffer layer can be independently determined. Finally, studies of the bare CZTS,Se surface will be discussed including our observation of mid-gap Fermi level pinning and its relation to Voc limitations and bulk defects.

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

    OpenAIRE

    M. Dell'Angela; Anniyev, T.; Beye, M; Coffee, R.; Föhlisch, A.; Gladh, J.; Kaya, S.; Katayama, T.; Krupin, O.; Nilsson, A; Nordlund, D.; Schlotter, W. F.; Sellberg, J. A.; Sorgenfrei, F.; J. J. Turner

    2015-01-01

    Vacuum space charge effects in sub-picosecond soft X-ray photoemission on a molecular adsorbate layer M. Dell'Angela, T. Anniyev, M. Beye, R. Coffee, A. Föhlisch, J. Gladh, S. Kaya, T. Katayama, O. Krupin, A. Nilsson, D. Nordlund, W. F. Schlotter, J. A. Sellberg, F. Sorgenfrei, J. J. Turner, H. Öström, H. Ogasawara, M. Wolf, and W. Wurth Citation: Structural Dynamics 2, 025101 (2015); doi: 10.1063/1.4914892 View online: http://dx.doi.org/10.1063/1.4914892 View Table of Co...

  13. X-Ray Photoemission Measurements of La(1-x)Ca(x)CoO3(x = 0, 0.5)

    Science.gov (United States)

    Vasquez, R. P.

    1996-01-01

    X-ray photoemission measurements of the core levels and valence electronic structure of LaCoO3 and La(0.5)Ca(0.5)CoO3 high quality epitaxial films are presented. Shifts of the core levels and main valence band features are consistent with a doping-induced change in the chemical potential. Oxygen states are found to significantly contribute to a peak in the valence band at 1 eV binding energy, verifying earlier results of cluster calculations. A Fermi level crossing of this same band upon doping is observed, yielding a high Fermi level density of states.

  14. Mn-induced modifications of Ga 3d photoemission from (Ga, Mn)As: evidence for long range effects.

    Science.gov (United States)

    Kanski, J; Ulfat, I; Ilver, L; Leandersson, M; Sadowski, J; Karlsson, K; Pal, P

    2012-10-31

    Using synchrotron based photoemission, we have investigated the Mn-induced changes in Ga 3d core level spectra from as-grown Ga(1-x)Mn(x)As. Although Mn is located in Ga substitutional sites, and therefore does not have any Ga nearest neighbors, the impact of Mn on the Ga core level spectra is pronounced even at Mn concentrations in the region of 0.5%. The analysis shows that each Mn atom affects a volume corresponding to a sphere with around 1.4 nm diameter.

  15. Generation of a 500-keV electron beam with milliampere current from a photoemission DC gun

    International Nuclear Information System (INIS)

    A high-brightness, high-current electron gun for energy recovery linac light sources and high repetition rate X-ray FEL requires an exit beam energy of ≥ 500 keV to reduce space-charge induced emittance growth in the drift space from the gun exit to the following accelerator entrance. We have developed a DC photoemission gun employing a segmented insulator to mitigate the field emission problem, which is a major obstacle for operation of DC guns at ≥ 500 kV. The first demonstration of generating a 500-keV electron beam with currents up to 1.8 mA is presented. (author)

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

    International Nuclear Information System (INIS)

    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

  17. Pseudogap and Superconducting Gap in SmFeAs(O1-xFx) Superconductor from Photoemission Spectroscopy

    Institute of Scientific and Technical Information of China (English)

    LIU Hai-Yun; CHEN Xian-Hui; REN Zhi-An; YI Wei; CHE Guang-Can; CHEN Gen-Fu; WANG Nan-Lin; WANG Gui-Ling; ZHOU Yong; ZHU Yong; WANG Xiao-Yang; JIA Xiao-Wen; ZHAO Zhong-Xian; XU Zu-Yan; CHEN Chuang-Tian; ZHOU Xing-Jiang; ZHANG Wen-Tao; ZHAO Lin; MENG Jian-Qiao; LIU Guo-Dong; DONG Xiao-Li; WU Gang; LIU Rong-Hua

    2008-01-01

    High resolution photoemission measurements are carried out on non-superconducting SmOFeAs parent compound and superconducting SmFeAs(O1-xFx) (x=0.12, and 0.15) compounds. The momentum-integrated spectra exhibit a clear Fermi cutoff that shows little leading-edge shift in the superconducting state. A robust feature at 13 meV is identified in all these samples. Spectral weight suppression near EF with decreasing temperature is observed in both undoped and doped samples that points to a possible existence of a pseudogap in these Fe-based compounds.

  18. Photoelectron yield spectroscopy and inverse photoemission spectroscopy evaluations of p-type amorphous silicon carbide films prepared using liquid materials

    Directory of Open Access Journals (Sweden)

    Tatsuya Murakami

    2016-05-01

    Full Text Available Phosphorus-doped amorphous silicon carbide films were prepared using a polymeric precursor solution. Unlike conventional polymeric precursors, this polymer requires neither catalysts nor oxidation for its synthesis and cross-linkage, providing semiconducting properties in the films. The valence and conduction states of resultant films were determined directly through the combination of inverse photoemission spectroscopy and photoelectron yield spectroscopy. The incorporated carbon widened energy gap and optical gap comparably in the films with lower carbon concentrations. In contrast, a large deviation between the energy gap and the optical gap was observed at higher carbon contents because of exponential widening of the band tail.

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

    International Nuclear Information System (INIS)

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

  20. A search for spin-polarized photoemission from GaAs using light with orbital angular momentum

    Energy Technology Data Exchange (ETDEWEB)

    Nathan Clayburn, James McCarter, Joan Dreiling, Bernard Poelker, Dominic Ryan, Timothy Gay

    2013-01-01

    Laser light with photon energy near the bandgap of GaAs and with different amounts of orbital angular momentum was used to produce photoemission from unstrained GaAs. The degree of electron spin polarization was measured using a micro-Mott polarimeter and found to be consistent with zero with an upper limit of ~3% for light with up to ±5{bar h} of orbital angular momentum. In contrast, the degree of spin polarization was 32.32 ± 1.35% using circularly-polarized laser light at the same wavelength, which is typical of bulk GaAs.

  1. Angle Integrated Photoemission Study of SmO0.85F0.15FeAs

    Institute of Scientific and Technical Information of China (English)

    OU Hong-Wei; WU Tao; CHEN Xian-Hui; CHEN Yan; FENG Dong-Lai; ZHAO Jia-Feng; ZHANG Yan; SHEN Da-Wei; ZHOU Bo; YANG Le-Xian; HE Cheng; CHEN Fei; XU Min

    2008-01-01

    The electronic structure of the new superconductor SmO1-xFxFeAs (x = 0.15) is studied by angle-integrated photoemission spectroscopy. Our data show a sharp feature very close to the Fermi energy, and a relative fiat distribution of the density of states between 0.SeV and 3eV binding energy, which agrees well with the band structure calculations considering an antiferromagnetic ground state. No noticeable gap opening is observed at 12 K below the superconducting transition temperature, indicating the existence of large ungapped regions in the Brillouin zone.

  2. Direct observation of Higgs mode oscillations in the pump-probe photoemission spectra of electron-phonon mediated superconductors

    Science.gov (United States)

    Kemper, A. F.; Sentef, M. A.; Moritz, B.; Freericks, J. K.; Devereaux, T. P.

    2015-12-01

    Using the nonequilibrium Keldysh formalism, we solve the equations of motion for electron-phonon superconductivity, including an ultrafast pump field. We present results for time-dependent photoemission spectra out of equilibrium which probe the dynamics of the superconducting gap edge. The partial melting of the order by the pump field leads to oscillations at twice the melted gap frequency, a hallmark of the Higgs or amplitude mode. Thus the Higgs mode can be directly excited through the nonlinear effects of an electromagnetic field and detected without requiring any additional symmetry breaking.

  3. Domain imaging on multiferroic BiFeO{sub 3}(001) by linear and circular dichroism in threshold photoemission

    Energy Technology Data Exchange (ETDEWEB)

    Sander, Anke; Christl, Maik [Institute of Physics, Martin-Luther-Universität Halle-Wittenberg, Von-Danckelmann-Platz 3, 06120 Halle(Saale) (Germany); Chiang, Cheng-Tien [Max Planck Institute of Microstructure Physics, Weinberg 2, 06120 Halle(Saale) (Germany); Institute of Physics, Martin-Luther-Universität Halle-Wittenberg, Von-Danckelmann-Platz 3, 06120 Halle(Saale) (Germany); Alexe, Marin [Department of Physics, University of Warwick, Coventry CV4 7AL (United Kingdom); Widdra, Wolf, E-mail: wolf.widdra@physik.uni-halle.de [Institute of Physics, Martin-Luther-Universität Halle-Wittenberg, Von-Danckelmann-Platz 3, 06120 Halle(Saale) (Germany); Max Planck Institute of Microstructure Physics, Weinberg 2, 06120 Halle(Saale) (Germany)

    2015-12-14

    We demonstrate ferroelectric domain imaging at BiFeO{sub 3}(001) single crystal surfaces with laser-based threshold photoemission electron microscopy (PEEM). Work function differences and linear dichroism allow for the identification of the eight independent ferroelectric domain configurations in the PEEM images. There, the determined domain structure is consistent with piezoresponse force microscopy of the sample surface and can also be related to the circular dichroic PEEM images. Our results provide a method for efficient mapping of complex ferroelectric domains with laser-excited PEEM and may allow lab-based time-resolved studies of the domain dynamics in the future.

  4. Stoner vs. spin-mixing behavior in the bulk magnetism of Gd: A spin-resolved photoemission study

    Indian Academy of Sciences (India)

    K Maiti; M C Malagoli; A Dallmeyer; C Carbone

    2002-05-01

    The temperature dependence of the rare-earth 2-bulk band has been regarded as an exemplary case which realizes the simple Stoner behavior. We examined the evolution of Gd2 bulk bands with temperature in the range 0.5 ≤ /C ≤ 1 with spin-resolved, photoemission spectroscopy. The direct observation of the spin-dependent spectral line shapes reveals a complex temperature dependence and manifests a clear inadequacy of the Stoner model to the description of the magnetism in rare earths.

  5. Comparison between laser-induced photoemissions and phototransmission of hard tissues using fibre-coupled Nd:YAG and Er(3+)-doped fibre lasers.

    Science.gov (United States)

    El-Sherif, Ashraf Fathy

    2012-07-01

    During pulsed laser irradiation of dental enamel, laser-induced photoemissions result from the laser-tissue interaction through mechanisms including fluorescence and plasma formation. Fluorescence induced by non-ablative laser light interaction has been used in tissue diagnosis, but the photoemission signal accompanying higher power ablative processes may also be used to provide real-time monitoring of the laser-tissue interaction. The spectral characteristics of the photoemission signals from normal and carious tooth enamel induced by two different pulsed lasers were examined. The radiation sources compared were a high-power extra-long Q-switched Nd:YAG laser operating at a wavelength of 1,066 nm giving pulses (with pulse durations in the range 200-250 μs) in the near infrared and a free-running Er(3+)-doped ZBLAN fibre laser operating at a wavelength near 3 μm with similar pulse durations in the mid-infrared region. The photoemission spectra produced during pulsed laser irradiation of enamel samples were recorded using a high-resolution spectrometer with a CCD array detector that enabled an optical resolution as high as 0.02 nm (FWHM). The spectral and time-dependence of the laser-induced photoemission due to thermal emission and plasma formation were detected during pulsed laser irradiation of hard tissues and were used to distinguish between normal and carious teeth. The use of these effects to distinguish between hard and soft biological tissues during photothermal ablation with a pulsed Nd:YAG laser or an Er fibre laser appears feasible. The real-time spectrally resolved phototransmission spectrum produced during pulsed Nd:YAG laser irradiation of human tooth enamel samples was recorded, with a (normalized) relative transmission coefficient of 1 (100%) for normal teeth and 0.6 (60%) for the carious teeth. The photoemission signal accompanying ablative events may also be used to provide real-time monitoring of the laser-tissue interaction.

  6. Band structure of Heusler compounds studied by photoemission and tunneling spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Arbelo Jorge, Elena

    2011-07-01

    Heusler compounds are key materials for spintronic applications. They have attracted a lot of interest due to their half-metallic properties predicted by band structure calculations. The aim of this work is to evaluate experimentally the validity of the predictions of half metallicity by band structure calculations for two specific Heusler compounds, Co{sub 2}FeAl{sub 0.3}Si{sub 0.7} and Co{sub 2}MnGa. Two different spectroscopy methods for the analysis of the electronic properties were used: Angular Resolved Ultraviolet Photoemission Spectroscopy (ARUPS) and Tunneling Spectroscopy. Heusler compounds are prepared as thin films by RF-sputtering in an ultra high vacuum system. For the characterization of the samples, bulk and surface crystallographic and magnetic properties of Co{sub 2}FeAl{sub 0.3}Si{sub 0.7} and Co{sub 2}MnGa are studied. X-ray and electron diffraction reveal a bulk and surface crossover between two different types of sublattice order (from B2 to L2{sub 1}) with increasing annealing temperature. X-ray magnetic circular dichroism results show that the magnetic properties in the surface and bulk are identical, although the magnetic moments obtained are 5 % below from the theoretically predicted. By ARUPS evidence for the validity of the predicted total bulk density of states (DOS) was demonstrated for both Heusler compounds. Additional ARUPS intensity contributions close to the Fermi energy indicates the presence of a specific surface DOS. Moreover, it is demonstrated that the crystallographic order, controlled by annealing, plays an important role on broadening effects of DOS features. Improving order resulted in better defined ARUPS features. Tunneling magnetoresistance measurements of Co{sub 2}FeAl{sub 0.3}Si{sub 0.7} and Co{sub 2}MnGa based MTJ's result in a Co{sub 2}FeAl{sub 0.3}Si{sub 0.7} spin polarization of 44 %, which is the highest experimentally obtained value for this compound, although it is lower than the 100 % predicted. For Co

  7. Electron-phonon interaction in high temperature superconductors

    Directory of Open Access Journals (Sweden)

    H. Khosroabadi

    2006-09-01

    Full Text Available   We explore the important role of the strong electron-phonon interaction in high temperature superconductivity through the study of the results of some important experiments, such as inelastic neutron and X-ray scattering, angle resolved photoemission spectroscopy, and isotope effects. We also present our computational results of the eigenvalues and eigenvectors of the Ag Raman modes, and the ionic displacement dependence of the electronic band structure by density functional theory. It is clearly evident that the role of phonons in the mechanism behind the high-temperature superconducting state should be seriously considered.

  8. Features in Quasi-particle Excitations and Tunnelling Spectra due to Coupling to Spin Fluctuations in High-Tc Cuprates

    Institute of Scientific and Technical Information of China (English)

    赵力; 李建新; 龚昌德; 赵柏儒

    2002-01-01

    In a self-consistent mean-field treatment of the two-dimensional t - t' - J model, we theoretically examine thecoupling of in-plane quasi-particles to the antiferromagnetic spin fluctuations in high-Tc superconductors, whichrenormalizes the fermionic self-energy. We reproduce the characteristic peak,lip-hump structure observed notonly in angle-resolved photoemission spectroscopy, but also in superconductor-insulator-normal metal junctionsand scanning tunnelling microscopy experiments. We consider the evolution of this structure with doping. Itis shown that this kind of coupling can account for many anomalous properties of high-Tc superconductors insuperconducting states.

  9. Realisation and experimental testing of silicon-point cathodes for field emission and field photoemission in a continuous and pulsed regime; Realisation et etude experimentale des cathodes a reseaux de pointes en silicium pour emission de champ et photoemission de champ en regime continu et pulse

    Energy Technology Data Exchange (ETDEWEB)

    Aboubacar, A.

    1993-03-26

    Acceleration technique and free electron laser improvements require the production of intense, bunched electron beams with small emittance. Photocathodes with arrays of tips have been prepared using microlithographic technique. Si(P) and Si(N) with (100) and (111) crystallographic orientation are used. Current emission due to field effect has been measured. Study of band bending at the surface with strong applied electric field is outline. Its interest is proved in field photoemission. Fowler-Nordheim` theory is used to determine the field reinforcement and emissive area. Experience in high vacuum chamber (pressure of few 10{sup -10} torr) yields satisfactory results from low P type silicon, instantaneous photocurrent is observed during a short exposure of light. Photocurrent of about a hundred times dark-current, at the threshold of field emission, from heavy density of tips is measured. An acousto-optic cell allows producing, with a continuous Argon laser, some pulsed beams of light. Optical excitation and photocurrent pulses follow with the same time. Quantum efficiency around 1% has been measured with low energy pulsed laser of a few nJ during few tens of ns at frequency of few MHz. (orig.).

  10. The effect of In doping in CdS/CuInSe[sub 2] heterojunction formation: A photoemission investigation

    Energy Technology Data Exchange (ETDEWEB)

    Nelson, A.J.; Niles, D.W. (National Renewable Energy Laboratory, 1617 Cole Blvd., Golden, Colorado 80401 (United States)); Rioux, D.; Patel, R.; Hoechst, H. (Synchrotron Radiation Center, 3731 Schneider Drive, Stoughton, Wicsonsin 53589 (United States))

    1992-12-01

    Synchrotron radiation soft x-ray photoemission spectroscopy was used to investigate the development of the electronic structure at the CdS(In)/CuInSe[sub 2] heterojunction interface. In-doped CdS overlayers were deposited in steps on single-crystal [ital n]-type CuInSe[sub 2] at 250 [degree]C. Results indicate that the CdS(In) grows in registry with the substrate, initially in a two dimensional growth mode followed by three dimensional island growth as is corroborated by RHEED analysis. Photoemission measurements were acquired after each growth in order to observe changes in the valence band electronic structure as well as changes in the In4d, Se3d, Cd4d, and S2p core lines. The results were used to correlate the interface chemistry with the electronic structure at these interfaces and to directly determine the CdS(In)/CuInSe[sub 2] heterojunction valence band discontinuity and the consequent heterojunction band diagram as a function of In dopant concentration. We measured a valence band offset [Delta]E[sub v]=0.3 eV, independent of In doping.

  11. Probing the energy levels of perovskite solar cells via Kelvin probe and UV ambient pressure photoemission spectroscopy.

    Science.gov (United States)

    Harwell, J R; Baikie, T K; Baikie, I D; Payne, J L; Ni, C; Irvine, J T S; Turnbull, G A; Samuel, I D W

    2016-07-20

    The field of organo-lead halide perovskite solar cells has been rapidly growing since their discovery in 2009. State of the art devices are now achieving efficiencies comparable to much older technologies like silicon, while utilising simple manufacturing processes and starting materials. A key parameter to consider when optimising solar cell devices or when designing new materials is the position and effects of the energy levels in the materials. We present here a comprehensive study of the energy levels present in a common structure of perovskite solar cell using an advanced macroscopic Kelvin probe and UV air photoemission setup. By constructing a detailed map of the energy levels in the system we are able to predict the importance of each layer to the open circuit voltage of the solar cell, which we then back up through measurements of the surface photovoltage of the cell under white illumination. Our results demonstrate the effectiveness of air photoemission and Kelvin probe contact potential difference measurements as a method of identifying the factors contributing to the open circuit voltage in a solar cell, as well as being an excellent way of probing the physics of new materials.

  12. Measurements of Schottky barrier at the low-k SiOC:H/Cu interface using vacuum ultraviolet photoemission spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Guo, X.; Pei, D.; Zheng, H.; Shohet, J. L. [Plasma Processing and Technology Laboratory and Department of Electrical and Computer Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States); King, S. W. [Logic Technology Development, Intel Corporation, Hillsboro, Oregon 97124 (United States); Lin, Y.-H.; Fung, H.-S.; Chen, C.-C. [National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan (China); Nishi, Y. [Department of Electrical Engineering, Stanford University, Stanford, California 94305 (United States)

    2015-12-07

    The band alignment between copper interconnects and their low-k interlayer dielectrics is critical to understanding the fundamental mechanisms involved in electrical leakage in low-k/Cu interconnects. In this work, vacuum-ultraviolet (VUV) photoemission spectroscopy is utilized to determine the potential of the Schottky barrier present at low-k a-SiOC:H/Cu interfaces. By examining the photoemission spectra before and after VUV exposure of a low-k a-SiOC:H (k = 3.3) thin film fabricated by plasma-enhanced chemical-vapor deposition on a polished Cu substrate, it was found that photons with energies of 4.9 eV or greater can deplete accumulated charge in a-SiOC:H films, while VUV photons with energies of 4.7 eV or less, did not have this effect. These critical values were identified to relate the electric potential of the interface barrier between the a-SiOC:H and the Cu layers. Using this method, the Schottky barrier at the low-k a-SiOC:H (k = 3.3)/Cu interface was determined to be 4.8 ± 0.1 eV.

  13. Probing the energy levels of perovskite solar cells via Kelvin probe and UV ambient pressure photoemission spectroscopy.

    Science.gov (United States)

    Harwell, J R; Baikie, T K; Baikie, I D; Payne, J L; Ni, C; Irvine, J T S; Turnbull, G A; Samuel, I D W

    2016-07-20

    The field of organo-lead halide perovskite solar cells has been rapidly growing since their discovery in 2009. State of the art devices are now achieving efficiencies comparable to much older technologies like silicon, while utilising simple manufacturing processes and starting materials. A key parameter to consider when optimising solar cell devices or when designing new materials is the position and effects of the energy levels in the materials. We present here a comprehensive study of the energy levels present in a common structure of perovskite solar cell using an advanced macroscopic Kelvin probe and UV air photoemission setup. By constructing a detailed map of the energy levels in the system we are able to predict the importance of each layer to the open circuit voltage of the solar cell, which we then back up through measurements of the surface photovoltage of the cell under white illumination. Our results demonstrate the effectiveness of air photoemission and Kelvin probe contact potential difference measurements as a method of identifying the factors contributing to the open circuit voltage in a solar cell, as well as being an excellent way of probing the physics of new materials. PMID:27384817

  14. Reversible switching in self-assembled monolayers of azobenzene thiolates on Au (111) probed by threshold photoemission

    International Nuclear Information System (INIS)

    Highlights: ► Photoelectron spectroscopy of liquid phase prepared SAMs of azobenzene derivative. ► Photo-induced reversible switching in densely packed SAM is monitored. ► Maximum density of switched molecules in SAM is derived from photoemission data. ► Switching reaction only enabled at defects sites within the molecular layer. - Abstract: The reversible photo- and thermally activated isomerization of the molecular switch 3-(4-(4-Hexyl-phenylazo)-phenoxy)-propane-1-thiol (ABT, short for AzoBenzeneThiol) deposited by self-assembly from solution on Au (111) was studied using laser-based photoelectron spectroscopy. Differences in the molecular dipole moment characteristic for the trans and the cis isomer of ABT were monitored via changes in the sample work function, accessible by detection of the threshold energy for photoemission. A quantitative analysis of our data shows that the fraction of molecules within the densely packed monolayer that undergoes a switching process is of the order of 1%. This result indicates the relevance of substrate and film defects required to overcome the steric or electronic hindrance of the isomerization reaction in a densely packed monolayer.

  15. Photoemission and photo-field-emission from photocathodes with arrays of silicon tips under continuous and pulsed lasers action

    International Nuclear Information System (INIS)

    The electron machines's development and improvement go through the discovery of new electron sources of high brightness. After reminding the interests in studying silicon cathodes with array of tips as electron sources, I describe, in the three steps model, the main phenomenological features related to photoemission and photoemission and photo-field-emission from a semi-conductor. the experimental set-ups used for the measurements reported in chapter four, five and six are described in chapter three. In chapter three. In chapter four several aspects of photo-field-emission in continuous and nanosecond regimes, studied on the Clermont-Ferrand's test bench are tackled. We have measured quantum efficacies of 0.4 percent in the red (1.96 eV). Temporal responses in the nanoseconds range (10 ns) were observed with the Nd: YLF laser. With the laser impinging at an oblique angle we obtained ratios of photocurrent to dark current of the order of twenty. The issue of the high energy extracted photocurrent saturation is addressed and I give a preliminary explanation. In collaboration with the L.A.L. (Laboratoire de l'Accelerateur Lineaire) some tests with shortened pulsed laser beam (Nd: YAG laser 35 ps) were performed. Satisfactory response times have been obtained within the limitation of the scope (400 ps). (authors). 101 refs. 93 figs., 27 tabs., 3 photos., 1 append

  16. Photoemission and photo-field-emission from photocathodes with arrays of silicon tips under continuous and pulsed lasers action; Photoemission et photoemission de champ a partir de photocathodes a reseaux de pointes de silicium sous l`action de lasers continus et pulses

    Energy Technology Data Exchange (ETDEWEB)

    Laguna, M.

    1995-11-01

    The electron machines`s development and improvement go through the discovery of new electron sources of high brightness. After reminding the interests in studying silicon cathodes with array of tips as electron sources, I describe, in the three steps model, the main phenomenological features related to photoemission and photoemission and photo-field-emission from a semi-conductor. the experimental set-ups used for the measurements reported in chapter four, five and six are described in chapter three. In chapter three. In chapter four several aspects of photo-field-emission in continuous and nanosecond regimes, studied on the Clermont-Ferrand`s test bench are tackled. We have measured quantum efficacies of 0.4 percent in the red (1.96 eV). Temporal responses in the nanoseconds range (10 ns) were observed with the Nd: YLF laser. With the laser impinging at an oblique angle we obtained ratios of photocurrent to dark current of the order of twenty. The issue of the high energy extracted photocurrent saturation is addressed and I give a preliminary explanation. In collaboration with the L.A.L. (Laboratoire de l`Accelerateur Lineaire) some tests with shortened pulsed laser beam (Nd: YAG laser 35 ps) were performed. Satisfactory response times have been obtained within the limitation of the scope (400 ps). (authors). 101 refs. 93 figs., 27 tabs., 3 photos., 1 append.

  17. X-ray photoemission, calorimetric, and electrical transport properties of CeCu{sub 4}Mn{sub y}Al{sub 1−y}

    Energy Technology Data Exchange (ETDEWEB)

    Synoradzki, K., E-mail: karol.synoradzki@ifmpan.poznan.pl [Institute of Molecular Physics, Polish Academy of Science, Smoluchowskiego 17, 60-179 Poznań (Poland); Toliński, T. [Institute of Molecular Physics, Polish Academy of Science, Smoluchowskiego 17, 60-179 Poznań (Poland); Chełkowska, G.; Bajorek, A. [Institute of Physics, Silesian University, Uniwersytecka 4, 40-007 Katowice (Poland); Zapotoková, M. [Institute of Experimental Physics, Slovak Academy of Sciences, Watsonova 47, 043 53 Košice (Slovakia); Reiffers, M. [Faculty of Humanities and Natural Sciences, Prešov University, 17. novembra 1, 081 16 Prešov (Slovakia); Hoser, A. [Helmholtz-Zentrum, Glienicker Straße 100, D-14109 Berlin (Germany)

    2014-07-15

    Highlights: • Ce 4f states well localized in the CeCu{sub 4}Mn{sub y}Al{sub 1−y} compounds. • Spin-glass contribution to specific heat has been estimated. • Magnetic phase diagram corroborated for CeCu{sub 4}Mn{sub y}Al{sub 1−y}. • Lack of a long-range magnetic order in CeCu{sub 4}Mn confirmed by neutron diffraction. - Abstract: We report the X-ray photoemission spectra (XPS) and the electrical resistivity measurements for the transition Kondo lattice – spin-glass (SG) in the series CeCu{sub 4}Mn{sub y}Al{sub 1−y}. The study includes additionally the low temperature (down to T = 400 mK) heat capacity results. The XPS measurements revealed that the Ce 4f states are well localized. Electrical resistivity studies illustrate a smooth evolution from the ∼ −ln T relation to the metallic behaviour with the increase of the Mn content. Moreover, the specific heat has been analysed considering the electronic, phonon, Schottky (Crystal Electric Field – CEF), Kondo, and SG contributions. The assumption that the CEF splitting of the energy levels is similar for all the compositions allowed us to estimate the SG and Kondo contribution to the heat capacity. Additionally, the neutron diffraction experiment on the parent CeCu{sub 4}Mn compound has confirmed that it does not show a long-range magnetic order.

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  19. Hard x-ray photoemission and density functional theory study of the internal electric field in SrTiO3/LaAlO3 oxide heterostructures

    NARCIS (Netherlands)

    E. Slooten; Z. Zhong; H.J.A. Molegraaf; P.D. Eerkes; S. de Jong; F. Massee; E. van Heumen; M.K. Kruize; S. Wenderich; J.E. Kleibeuker; M. Gorgoi; H. Hilgenkamp; A. Brinkman; M Huijben; G. Rijnders; D.H.A. Blank; G. Koster; P.J. Kelly; M. Golden

    2013-01-01

    A combined experimental and theoretical investigation of the electronic structure of the archetypal oxide heterointerface system LaAlO3 on SrTiO3 is presented. High-resolution, hard x-ray photoemission is used to uncover the occupation of Ti 3d states and the relative energetic alignment—and hence i

  20. Synthesis of diamond-like carbon films on Si substrates by photoemission-assisted plasma-enhanced chemical vapor deposition

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Meng [Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan); Ogawa, Shuichi, E-mail: ogasyu@tagen.tohoku.ac.jp [Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan); Takabayashi, Susumu; Otsuji, Taiichi [Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan); Core Research for Evolutionary Science and Technology, Japan Science and Technology Agency, K' s Gobancho Bldg., 7 Gobancho, Chiyoda-ku, Tokyo 102-0076 (Japan); Takakuwa, Yuji [Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan)

    2012-11-15

    Diamond-like carbon (DLC) films grown by photoemission-assisted plasma-enhanced chemical vapor deposition (PA-PECVD) have attracted attention as a gate insulator for graphene-channel field effect transistors (GFETs). In this study, the possibility of using PA-PECVD to grow insulating DLC films for GFETs is explored by focusing on the growth rate and uniformity of DLC films on Si substrates. Initially, the DLC films were formed at a constant rate but the growth rate decreased rapidly when the thickness reached approximately 400 nm. This is because of a decrease in photoelectron emissions from the Si substrates as they are covered by DLC films which absorb UV photons. However, the DLC films formed uniformly at thicknesses less than 16%. This result indicates that PA-PECVD is a promising method for growing DLC films as the gate dielectric layer of GFETs.

  1. Insight into the spin state at the surface of LaCoO3 revealed by photoemission electron microscopy

    Science.gov (United States)

    Yaroslavtsev, A. A.; Izquierdo, M.; Carley, R.; Dávila, M. E.; Ünal, A. A.; Kronast, F.; Lichtenstein, A.; Scherz, A.; Molodtsov, S. L.

    2016-04-01

    The evolution of the spin transition in LaCoO3 has been investigated with photoemission electron microscopy (PEEM) as a function of temperature. The investigated temperature range spanned from a predominantly low spin configuration (125 K) to the proposed percolation limit for metallization (413 K). The data show that the spin configuration exhibits an inhomogeneous spatial distribution that is very sensitive to the surface preparation method. In the region of the semiconductor-to-metal transition (300 to 450 K), the spatial contrast is continuously reduced, indicating a smooth transition without domain percolation. These observations support a new interpretation of the temperature evolution of the system that is in agreement with current theoretical understanding of the spin transition.

  2. Analysis of the injection layer of PTCDA in OLEDs using x-ray photoemission spectroscopy and atomic force microscopy

    Institute of Scientific and Technical Information of China (English)

    Ou Gu-Ping; Song Zhen; Wu You-Yu; Chen Xiao-Qiang; Zhang Fu-Jia

    2006-01-01

    Through the investigation of the sample surface and interface of 3, 4, 9, 10-perylenetetracarboxylic dianhydride(PTCDA)/indium-tin-oxide (ITO) thin films using atomic force microscopy, it has been found that the surface is complanate, the growth is uniform and the defects cover basically the surface of ITO. Furthermore, the number of pinholes is small. The analysis of the sample surface and interface further verifies this result by using x-ray photoemission spectroscopy. At the same time, PTCDA is found to have the ability of restraining the diffusion of chemical constituents from ITO to the hole transport layer, which is beneficial to the improvement of the performance and the useful lifetime of the organic light emitting diodes (OLEDs).

  3. Features in the electronic structure and photoemission spectra of organic molecular semiconductors: The molecules of metal-phthalocyanines and PTCDA

    Science.gov (United States)

    Tikhonov, E. V.; Uspenskii, Yu. A.; Khokhlov, D. R.

    2013-09-01

    The role of many-electron effects in the formation of electronic quasiparticle spectra in organic molecular semiconductors (OMS) is analyzed. Many-body perturbation theory, ab initio calculations of metal phthalocyanines and PTCDA molecules, and experimental photoemission spectra are applied to this analysis. It is shown that density functional theory (DFT) poorly reproduces the electronic spectra of OMS. The use of a hybrid functional method (HFM) provides precise reproduction of both valence and conducting bands, while the HOMO-LUMO gap remains underestimated. The correct gap width is obtained in both DFT and HFM, when it is calculated through ionization and affinity energies. It is shown that such an approach gives a formula for gap correction due to electron correlations, which is close to an expression derived from the GW approximation.

  4. A photoemission study of the interaction of Ga with CeO2(1 1 1) thin films

    International Nuclear Information System (INIS)

    The interaction of gallium with CeO2(1 1 1) layers was studied using standard and resonant photoelectron spectroscopy, by means of both a laboratory X-ray source and tunable synchrotron light. Firstly a 1.5-nm thick CeO2 film was grown on a Cu(1 1 1) substrate. Secondly Ga was deposited in six steps up to a thickness of 0.35 nm, at room temperature. The interaction of gallium with the oxide layer induced partial CeO2 reduction, and gallium oxidation. The photoemission data suggest that a mixed Ga-Ce-O oxide was established similarly to the Sn-Ce-O case for Sn deposited on cerium oxide layers. As a consequence, gallium-induced weakening of Ce-O bonds provides a higher number of active sites on the surface that play a major role in its catalytic behaviour

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

    Directory of Open Access Journals (Sweden)

    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.

  6. Benchmarking of 3D space charge codes using direct phase space measurements from photoemission high voltage DC gun

    CERN Document Server

    Bazarov, Ivan V; Gulliford, Colwyn; Li, Yulin; Liu, Xianghong; Sinclair, Charles K; Soong, Ken; Hannon, Fay

    2008-01-01

    We present a comparison between space charge calculations and direct measurements of the transverse phase space for space charge dominated electron bunches after a high voltage photoemission DC gun followed by an emittance compensation solenoid magnet. The measurements were performed using a double-slit setup for a set of parameters such as charge per bunch and the solenoid current. The data is compared with detailed simulations using 3D space charge codes GPT and Parmela3D with initial particle distributions created from the measured transverse and temporal laser profiles. Beam brightness as a function of beam fraction is calculated for the measured phase space maps and found to approach the theoretical maximum set by the thermal energy and accelerating field at the photocathode.

  7. Photoemission study of the formation of intimate In-InGaAs(100) contacts at room and cryogenic temperatures

    Science.gov (United States)

    Cammack, D. S.; McGregor, S. M.; McChesney, J. J.; Dharmadasa, I. M.; Clark, S. A.; Dunstan, P. R.; Burgess, S. R.; Wilks, S. P.; Elliott, M.

    1997-06-01

    Previous current-voltage studies of In contacts deposited on atomically clean (intimate) In53Ga47As(100) have indicated the potential to "select" barrier heights in this materials system by cryogenic processing. Soft x-ray photoemission spectroscopy was used to determine the electronic and chemical nature of these interfaces, as a function of formation temperature. Metallization at room temperature results in a predominantly three-dimensional mode of growth, accompanied by the outdiffusion of As. Low temperature metallization appears to reduce clustering and inhibit As outdiffusion. It is proposed that the distribution of surface states and the fermi level pinning position are altered by the changes that occur in the geometry and bonding of the interface at low temperature.

  8. Characterization of induced nanoplasmonic fields in time-resolved photoemission from gold nanospheres: a classical trajectory approach

    Science.gov (United States)

    Saydanzad, Erfan; Thumm, Uwe

    2016-05-01

    Attosecond time-resolved (XUV-pump, IR-probe) spectroscopy has been shown to be a powerful method for investigating the electron dynamics in atoms, and this technique is now being transferred to the investigation of electronic excitations, electron propagation, and collective electronic (plasmonic) effects in solids. Based on classical trajectory calculations, we simulated (i) the final photoelectron velocity distribution in order to provide observable velocity-map images for gold nanospheres of 10 and 100 nm diameter and (ii) streaked photoemission spectra. By analyzing our numerical results, we illustrate how spatio-temporal information about the sub-IR-cycle plasmonic and electronic dynamics is encoded in velocity-map images and streaked photoelectron spectra. Supported by the NE/KS NSF-EPSCOR program.

  9. Electronic properties of Mn-phthalocyanine–C{sub 60} bulk heterojunctions: Combining photoemission and electron energy-loss spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Roth, Friedrich [Center for Free-Electron Laser Science/DESY, Notkestraße 85, D-22607 Hamburg (Germany); Herzig, Melanie; Knupfer, Martin [FW Dresden, P.O. Box 270116, D-01171 Dresden (Germany); Lupulescu, Cosmin [Institute of Optics and Atomic Physics, TU Berlin, Straße des 17. Juni 135, D-10623 Berlin (Germany); Darlatt, Erik; Gottwald, Alexander [Physikalisch-Technische Bundesanstalt (PTB), Abbestraße 2-12, D-10587 Berlin (Germany); Eberhardt, Wolfgang [Center for Free-Electron Laser Science/DESY, Notkestraße 85, D-22607 Hamburg (Germany); Institute of Optics and Atomic Physics, TU Berlin, Straße des 17. Juni 135, D-10623 Berlin (Germany)

    2015-11-14

    The electronic properties of co-evaporated mixtures (blends) of manganese phthalocyanine and the fullerene C{sub 60} (MnPc:C{sub 60}) have been studied as a function of the concentration of the two constituents using two supplementary electron spectroscopic methods, photoemission spectroscopy (PES) and electron energy-loss spectroscopy (EELS) in transmission. Our PES measurements provide a detailed picture of the electronic structure measured with different excitation energies as well as different mixing ratios between MnPc and C{sub 60}. Besides a relative energy shift, the occupied electronic states of the two materials remain essentially unchanged. The observed energy level alignment is different compared to that of the related CuPc:C{sub 60} bulk heterojunction. Moreover, the results from our EELS investigations show that, despite the rather small interface interaction, the MnPc related electronic excitation spectrum changes significantly by admixing C{sub 60} to MnPc thin films.

  10. Photoemission study of the uranium ternary compounds U3T3X4 (T = Ni, Cu; X = Sn, Sb)

    International Nuclear Information System (INIS)

    Valence-band structures of U3Ni3Sn4, U3Ni3Sb4, U3Cu3Sn4 and U3Cu3Sb4 ranging from a semiconductor to a heavy fermion system, are studied using photemission spectroscopy with synchrotron radiation. We found that the Ni 3d band in U3Ni3Sn4 is not fully filled up, the Cu 3d states in the ferromagnet U3Cu3Sb4 are strongly hybridized with the Sb 5p states, but the 3d states localized in the heavy-fermion compound U3Cu3Sn4. However, the U 5f emission spectra obtained by the resonant photoemission technique are nearly identical for all compounds and have an asymmetric peak of 1.6 eV in width. (author)

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

    International Nuclear Information System (INIS)

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

  12. Weight of zero-loss electrons and sum rules in extrinsic processes that can influence photoemission spectra

    International Nuclear Information System (INIS)

    It was argued in a recent paper by Joynt [Science 284, 777 (1999)] that in the case of poorly conducting solids a photoemission spectrum close to the Fermi energy may be strongly influenced by extrinsic loss processes similar to those occurring in high-resolution electron-energy-loss spectroscopy, thereby obscuring information concerning the density of states or one-electron Green's function sought for. In this paper we present a number of arguments, both theoretical and experimental, that demonstrate that energy-loss processes occurring once the electron is outside the solid, contribute only weakly to the spectrum, and can in most cases be either neglected or treated as a weak structureless background

  13. Weight of zero-loss electrons and sum rules in extrinsic processes that can influence photoemission spectra

    Science.gov (United States)

    Schulte, K.; James, M. A.; Steeneken, P. G.; Sawatzky, G. A.; Suryanarayanan, R.; Dhalenne, G.; Revcolevschi, A.

    2001-04-01

    It was argued in a recent paper by Joynt [Science 284, 777 (1999)] that in the case of poorly conducting solids a photoemission spectrum close to the Fermi energy may be strongly influenced by extrinsic loss processes similar to those occurring in high-resolution electron-energy-loss spectroscopy, thereby obscuring information concerning the density of states or one-electron Green's function sought for. In this paper we present a number of arguments, both theoretical and experimental, that demonstrate that energy-loss processes occurring once the electron is outside the solid, contribute only weakly to the spectrum, and can in most cases be either neglected or treated as a weak structureless background.

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  15. Co1.5 Fe1.5 Ge and Co2 MnSi Half-Metal Magnetic behavior tested by spin-resolved photoemission and ferromagnetic resonance

    Science.gov (United States)

    Andrieu, Stéphane

    2015-03-01

    In a magnetic spin-valve or tunnel junction, a crucial parameter to get both large magnetoresistance (MR) and a good Spin Transfer Torque (STT) efficiency is the spin-polarization of the magnetic electrodes. So-called ``Half-Metallic'' Magnetic (HMM) materials are of interest for such devices due to the existence of a spin-gap at the Fermi level for minority spins. Recently, MR enhancements have been observed by different groups on Co2-xFe1 +xGe and Co2MnSi Heusler materials, suggesting HMM behavior. A second consequence of that minority spin gap is that very low magnetic damping is expected. Combining both properties in a device is a challenge for decreasing the critical current necessary to switch the magnetization using STT. Up to now, many Heusler alloys are claimed to get this HMM property, but direct demonstration using spin-resolved photoemission is often missing. Here we focus on 2 systems, (i) Co1.5Fe1.5Ge for which a significant increase of the GMR was observed in spin valves, and (ii) Co2MnSi for which very large TMR values were observed in MgO-based MTJs. The Co1.5Fe1.5Ge and Co2MnSi(001) films (noted CFG and CMS) were prepared by Molecular Beam Epitaxy coupled to the Spin-Resolved PhotoEmission (SR-PES) set-up on CASSIOPEE beamline at SOLEIL synchrotron. The L21 chemical ordering was confirmed in CFG films by using anomalous diffraction on SIXS beamline at SOLEIL. However, SR-PES experiments did not show any HMM behavior on our CFG films. Similar PES experiments performed on CMS showed that the minority spin density of states (DOS) drops down to zero at -0.4eV below EF, leading to a 100% spin polarization. However, we also observed an increase of the minority spin DOS at EF, not predicted by ab initio calculations on the bulk structure. The spin-gap is thus decreased due to the surface symmetry breaking. We will show however that this spin-gap can be enlarged when finishing the surface by 1 Mn atomic plane, or when covering with the MgO barrier

  16. INVESTIGATION ON THE VALENCE STATE OF Ce ATOM IN BULK AND NANOCRYSTAL CeO2 BY X-RAY ABSORPTION AND PHOTOEMISSION

    Institute of Scientific and Technical Information of China (English)

    K. Ibrahim; Z.Y. Wu; J. Zhang; M.I. Abbas; F.Q. Liu; H.J. Qian

    2001-01-01

    Valence band photoemission spectra (PES) for both bulk and nanocrystal CeO2 have been measured on and off resonance of Ce 4d 4f absorption edge. The PES show that the bulk and nanocrystal CeO2 of diameter ranging from 8nm to 50nm exhibit a peak near Fermi edge with binding energy of about 1.8eV. The 1.8eVpeak shows a strong dependence on excitation energy, although it looks like the contribution of Ce3+ ion following the data reported in literatures. However, according to the results of resonance photoemission and X-ray absorption spectra at O 1s edge, this electronic structure may be associated to the intermediate state charge transfer effects.

  17. Electronic study of Al substituted La{sub 0.7}Ca{sub 0.3}MnO{sub 3} using photoemission spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Phase, D. M., E-mail: dmphase@csr.res.in; Kumar, Manish, E-mail: dmphase@csr.res.in; Wadikar, A. D., E-mail: dmphase@csr.res.in; Choudhary, R. J., E-mail: dmphase@csr.res.in [UGC-DAE Consortium for Scientific Research, Khandwa Road, Indore-452001 (India)

    2014-04-24

    Polycrystalline samples of La{sub 0.7}Ca{sub 0.3}Mn{sub 1−X}Al{sub X}O{sub 3} (X=0, 0.05, 0.15) are prepared using solid state reaction route. Photoemission spectroscopy measurements were performed on these samples to investigate their electronic properties. Al shows 3+ oxidation state in both Al doped samples while no effect of Al doping is found on the core level spectrum of La 4d and Ca 2p orbitals and they were found in 3{sup +} and 2{sup +} oxidation state respectively in all the samples . Mn 2p core level photoemission measurements indicates that for 5% Al doped sample (lower doping) Al ions replaces the Mn{sup 3+} ions while they substitute Mn{sup 4+} in 15 % Al doped sample ((higher doping)

  18. Mott localization in a pure stripe antiferromagnet Rb1-δFe1.5-σS2

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Meng; Yi, Ming; Cao, Huibo; de la Cruz, C.; Mo, S. K.; Huang, Q. Z.; Bourret-Courchesne, E.; Dai, Pengcheng; Lee, D. H.; Shen, Z. X.; Birgeneau, R. J.

    2015-09-01

    A combination of neutron diffraction and angle-resolved photoemission spectroscopy measurements on a pure antiferromagnetic stripe Rb1-δFe1.5-σS2 is reported. A neutron diffraction experiment on a powder sample shows that a 98% volume fraction of the sample is in the antiferromagnetic stripe phase with rhombic iron vacancy order and a refined composition of Rb0.66Fe1.36S2, and that only 2% of the sample is in the block antiferromagnetic phase with √5×√5 iron vacancy order. Furthermore, a neutron diffraction experiment on a single crystal shows that there is only a single phase with the stripe antiferromagnetic order with the refined composition of Rb0.78Fe1.35S2, while the phase with block antiferromagnetic order is absent. Angle-resolved photoemission spectroscopy measurements on the same crystal with the pure stripe phase reveal that the electronic structure is gapped at the Fermi level with a gap larger than 0.325 eV. The data collectively demonstrate that the extra 10% iron vacancies in addition to the rhombic iron vacancy order effectively impede the formation of the block antiferromagnetic phase; the data also suggest that the stripe antiferromagnetic phase with rhombic iron vacancy order is a Mott insulator.

  19. Isolierte Moleküle und delokalisierte Zustände: Einblick in die elektronische Struktur organischer Adsorbate mittels winkelaufgelöster Photoemission

    OpenAIRE

    Wießner, Michael

    2013-01-01

    Die vorliegende Arbeit demonstriert an Hand von verschiedenen Modellsystemen wie detailliert sich die grundlegenden Eigenschaften molekularer Adsorbate mit der winkelaufgelösten Photoemission erkunden lassen. Die von Peter Puschnig et al. vorgestellte Verknüpfung zwischen Photoemissionsintensität und den Molekülorbitalen im Grundzustand mittels einer Fouriertransformation war dabei entscheidend, um die verschiedenen physikalischen Effekte einordnen und verstehen zu können. Während für Coronen...

  20. Direct characterization of the energy level alignments and molecular components in an organic hetero-junction by integrated photoemission spectroscopy and reflection electron energy loss spectroscopy analysis

    Science.gov (United States)

    Yun, Dong-Jin; Shin, Weon-Ho; Bulliard, Xavier; Park, Jong Hwan; Kim, Seyun; Chung, Jae Gwan; Kim, Yongsu; Heo, Sung; Kim, Seong Heon

    2016-08-01

    A novel, direct method for the characterization of the energy level alignments at bulk-heterojunction (BHJ)/electrode interfaces on the basis of electronic spectroscopy measurements is proposed. The home-made in situ photoemission system is used to perform x-ray/ultraviolet photoemission spectroscopy (XPS/UPS), reflection electron energy loss spectroscopy (REELS) and inverse photoemission spectroscopy of organic-semiconductors (OSCs) deposited onto a Au substrate. Through this analysis system, we are able to obtain the electronic structures of a boron subphthalocyanine chloride:fullerene (SubPC:C60) BHJ and those of the separate OSC/electrode structures (SubPC/Au and C60/Au). Morphology and chemical composition analyses confirm that the original SubPC and C60 electronic structures remain unchanged in the electrodes prepared. Using this technique, we ascertain that the position and area of the nearest peak to the Fermi energy (EF = 0 eV) in the UPS (REELS) spectra of SubPC:C60 BHJ provide information on the highest occupied molecular orbital level (optical band gap) and combination ratio of the materials, respectively. Thus, extracting the adjusted spectrum from the corresponding SubPC:C60 BHJ UPS (REELS) spectrum reveals its electronic structure, equivalent to that of the C60 materials. This novel analytical approach allows complete energy-level determination for each combination ratio by separating its electronic structure information from the BHJ spectrum.

  1. Direct characterization of the energy level alignments and molecular components in an organic hetero-junction by integrated photoemission spectroscopy and reflection electron energy loss spectroscopy analysis.

    Science.gov (United States)

    Yun, Dong-Jin; Shin, Weon-Ho; Bulliard, Xavier; Park, Jong Hwan; Kim, Seyun; Chung, Jae Gwan; Kim, Yongsu; Heo, Sung; Kim, Seong Heon

    2016-08-26

    A novel, direct method for the characterization of the energy level alignments at bulk-heterojunction (BHJ)/electrode interfaces on the basis of electronic spectroscopy measurements is proposed. The home-made in situ photoemission system is used to perform x-ray/ultraviolet photoemission spectroscopy (XPS/UPS), reflection electron energy loss spectroscopy (REELS) and inverse photoemission spectroscopy of organic-semiconductors (OSCs) deposited onto a Au substrate. Through this analysis system, we are able to obtain the electronic structures of a boron subphthalocyanine chloride:fullerene (SubPC:C60) BHJ and those of the separate OSC/electrode structures (SubPC/Au and C60/Au). Morphology and chemical composition analyses confirm that the original SubPC and C60 electronic structures remain unchanged in the electrodes prepared. Using this technique, we ascertain that the position and area of the nearest peak to the Fermi energy (EF = 0 eV) in the UPS (REELS) spectra of SubPC:C60 BHJ provide information on the highest occupied molecular orbital level (optical band gap) and combination ratio of the materials, respectively. Thus, extracting the adjusted spectrum from the corresponding SubPC:C60 BHJ UPS (REELS) spectrum reveals its electronic structure, equivalent to that of the C60 materials. This novel analytical approach allows complete energy-level determination for each combination ratio by separating its electronic structure information from the BHJ spectrum. PMID:27420635

  2. Two dimensional band structure mapping of organic single crystals using the new generation electron energy analyzer ARTOF

    Energy Technology Data Exchange (ETDEWEB)

    Vollmer, A.; Ovsyannikov, R.; Gorgoi, M.; Krause, S.; Oehzelt, M. [Helmholtz-Zentrum Berlin fuer Materialien und Energie GmbH, Elektronenspeicherring BESSY II, 12489 Berlin (Germany); Lindblad, A.; Martensson, N.; Svensson, S. [Uppsala University, Department of Materials Chemistry and Department of Physics and Astronomy, Uppsala (Sweden); Karlsson, P.; Lundvuist, M. [VG Scienta AB, Uppsala (Sweden); Schmeiler, T.; Pflaum, J. [Lehrstuhl fuer Experimentelle Physik VI, Universitaet Wuerzburg und ZAE Bayern, 97074 Wuerzburg (Germany); Koch, N., E-mail: norbert.koch@physik.hu-berlin.de [Helmholtz-Zentrum Berlin fuer Materialien und Energie GmbH, Elektronenspeicherring BESSY II, 12489 Berlin (Germany); Institut fuer Physik, Humboldt-Universitaet zu Berlin, 12489 Berlin (Germany)

    2012-04-15

    Highlights: Black-Right-Pointing-Pointer A novel type of photoemission detector is introduced: the Angle Resolved Time Of Flight electron energy analyzer (ARTOF). Black-Right-Pointing-Pointer It enables electronic band structure determination under measurement conditions that are ideal for radiation-sensitive samples. Black-Right-Pointing-Pointer The band structures of rubrene single crystal is confirmed. Black-Right-Pointing-Pointer The absence of HOMO-band dispersion for tetracene single crystals is revealed. - Abstract: We report on a novel type of photoemission detector, the Angle Resolved Time Of Flight electron energy analyzer (ARTOF 10k), which enables electronic band structure determination under measurement conditions that are ideal for radiation-sensitive samples. This is facilitated through the combination of very high electron transmission and wide accessible angular range in one geometry. These properties make the ARTOF 10k predestined to investigate specimens that strongly suffer from radiation damage during photoemission experiments under 'standard' conditions, such as organic single crystals, as extremely low fluxes can be used while not compromising spectra accumulation times and signal-to-noise ratio. Even though organic single crystals are of increasing fundamental and applied scientific interest, knowledge of their electronic properties is still largely based on theoretical calculations due to major experimental challenges in measuring photoemission. In this work we show that the band structures of rubrene and tetracene single crystals can be obtained with unprecedented quality using the ARTOF 10k detector. The dispersion of the highest occupied band in rubrene is confirmed in accordance with an earlier report and we disclose the absence of notable dispersion for the highest occupied energy level on the surface of tetracene single crystals.

  3. Electronic structure and excited state dynamics in optically excited PTCDA films investigated with two-photon photoemission

    Science.gov (United States)

    Marks, M.; Sachs, S.; Schwalb, C. H.; Schöll, A.; Höfer, U.

    2013-09-01

    We present an investigation of the electronic structure and excited state dynamics of optically excited 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA) thin films adsorbed on Ag(111) using two-photon photoemission spectroscopy (2PPE). 2PPE allows us to study both occupied and unoccupied electronic states, and we are able to identify signals from the highest occupied and the two lowest unoccupied electronic states of the PTCDA thin film in the 2PPE spectra. The energies for occupied states are identical to values from ultraviolet photoelectron spectroscopy. Compared to results from inverse photoelectron spectroscopy (IPES), the 2PPE signals from the two lowest unoccupied electronic states, LUMO and LUMO+1, are found at 0.8 eV and 1.0 eV lower energies, respectively. We attribute this deviation to the different final states probed in 2PPE and IPES and the attractive interaction of the photoexcited electron and the remaining hole. Furthermore, we present a time-resolved investigation of the excited state dynamics of the PTCDA film in the femtosecond time regime. We observe a significantly shorter inelastic excited state lifetime compared to findings from time-resolved photoluminescence spectroscopy of PTCDA single crystals which could originate from excitation quenching by the metal substrate.

  4. Solar energy conversion via internal photoemission in aluminum, copper, and silver: Band structure effects and theoretical efficiency estimates

    Science.gov (United States)

    Chang, Yin-Jung; Shih, Ko-Han

    2016-05-01

    Internal photoemission (IPE) across an n-type Schottky junction due to standard AM1.5G solar illumination is quantified with practical considerations for Cu, Ag, and Al under direct and fully nondirect transitions, all in the context of the constant matrix element approximation. Under direct transitions, photoemitted electrons from d bands dominate the photocurrent and exhibit a strong dependence on the barrier energy ΦB but are less sensitive to the change in the metal thickness. Photocurrent is shown to be nearly completely contributed by s-state electrons in the fully nondirect approximation that offers nearly identical results as in the direct transition for metals having a free-electron-like band structure. Compared with noble metals, Al-based IPE has the highest quantum yield up to about 5.4% at ΦB = 0.5 eV and a maximum power conversion efficiency of approximately 0.31% due mainly to its relatively uniform and wide Pexc energy spectral width. Metals (e.g., Ag) with a larger interband absorption edge are shown to outperform those with shallower d-bands (e.g., Cu and Au).

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

    Energy Technology Data Exchange (ETDEWEB)

    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)

  6. ARTICLES: A Surface Femtosecond Two-Photon Photoemission Spectrometer for Excited Electron Dynamics and Time-Dependent Photochemical Kinetics

    Science.gov (United States)

    Ren, Ze-feng; Zhou, Chuan-yao; Ma, Zhi-bo; Xiao, Chun-lei; Mao, Xin-chun; Dai, Dong-xu; LaRue, Jerry; Cooper, Russell; Wodtke, Alec M.; Yang, Xue-ming

    2010-06-01

    A surface femtosecond two-photon photoemission (2PPE) spectrometer devoted to the study of ultrafast excited electron dynamics and photochemical kinetics on metal and metal oxide surfaces has been constructed. Low energy photoelectrons are measured using a hemispherical electron energy analyzer with an imaging detector that allows us to detect the energy and the angular distributions of the photoelectrons simultaneously. A Mach-Zehnder interferometer was built for the time-resolved 2PPE (TR-2PPE) measurement to study ultrafast surface excited electron dynamics, which was demonstrated on the Cu(111) surface. A scheme for measuring time-dependent 2PPE (TD-2PPE) spectra has also been developed for studies of surface photochemistry. This technique has been applied to a preliminary study on the photochemical kinetics on ethanol/TiO2(110). We have also shown that the ultrafast dynamics of photoinduced surface excited resonances can be investigated in a reliable way by combining the TR-2PPE and TD-2PPE techniques.

  7. Genuine metal-insulator transition of V2O3 revealed by hard X-ray photoemission

    International Nuclear Information System (INIS)

    V2O3 is a paradigmatic example of Mott-Hubbard (MH) metal-insulator transition (MIT) materials; it displays the 1st-order transition from the paramagnetic metal (PM) to the antiferromagnetic insulator (AFI) at 150 K. In order to reveal the mechanism of the Mott-Hubbard metal-insulator transition (MH-MIT) in V2O3, we have performed the hard X-ray photoemission (HAXPES) with hν=8170 eV at BL19LXU in SPring-8. The energy resolution was set to 130 meV. The clean surface of the single crystalline sample was obtained by cleavage in situ in ultra-high vacuum. The significant spectral transfer of the V 3d states is observed through the MH-MIT. We reveal the simple Mott-Hubbard scenario does not describe the transition, and new reliable model is required to explain the MH-MIT on V2O3

  8. Dynamic High Pressure: a novel approach toward near ambient pressure photoemission spectroscopy and spectromicroscopy

    International Nuclear Information System (INIS)

    A Dynamic High Pressure (DHP) system has been developed, tested and implemented in the scanning photoelectron microscope (SPEM) operated at ESCAmicroscopy beamline at Elettra synchrotron. The system consists of a compact gas injection set up that allows experiments with local pressure near the sample several orders of magnitude higher that the allowable pressure for X-ray photoelectron spectroscopy setups. The DHP setup controls the amount of gas injected toward the sample by fine tuning the time and spatial profiles using a pulsed valve and a nozzle, respectively. The DHP functionality and effectiveness has been demonstrated by in operando oxidation experiments of Ru and Si. The obtained results confirmed that using the DHP the gas exposure onto the sample is equivalent to a static pressure between 10−3 and 10−2 mbar, about 3 orders of magnitude higher than the maximum gas pressure for the XPS machines under operation.

  9. Direct angle resolved photoelectron spectroscopy (DARPES) on high-T{sub c} films: doping, strains, Fermi surface topology and superconductivity

    Energy Technology Data Exchange (ETDEWEB)

    Pavuna, D; Ariosa, D; Cancellieri, C; Cloetta, D; Abrecht, M [Institute of Physics of Complex Matter, FSB, Ecole Polytechnique Federale de Lausanne (EPFL), CH-1015 Lausanne (Switzerland)], E-mail: davor.pavuna@epfl.ch

    2008-03-15

    Since 1997 we systematically perform Direct ARPES ( = DARPES) on in-situ grown, non-cleaved, ultra-thin (<25nm) cuprate films. Specifically, we probe low energy electronic structure and properties of high-T{sub c} films under different degree of epitaxial (compressive vs tensile) strain. In overdoped in-plane compressed La{sub 2-x}Sr{sub x}CuO{sub 4} (LSCO) thin films we double T{sub c} from 20K to 40K, yet the Fermi surface (FS) remains essentially 2-dimensional (2D). In contrast, tensile strained films show 3-dimensional (3D) dispersion, while T{sub c} is drastically reduced. It seems that the in-plane compressive strain tends to push the apical oxygen far away from the CuO{sub 2} plane, enhances the 2D character of the dispersion and increases T{sub c}, while the tensile strain seems to act exactly in the opposite direction and the resulting dispersion is 3D. We have the FS topology for both cases. As the actual lattice of cuprates is 'Napoleon-cake' -like i.e. rigid CuO{sub 2} planes alternate with softer 'reservoir' (that strains distort differently) our results tend to rule out 2D rigid lattice mean field models. Finally, we briefly discuss recent successful determination of the FS topology from the observed wavevector quantization by DARPES in cuprate films thinner than 18 units cells (<24nm). Such an approach is of broader interest as it can be extended to other similar confined (ultra-thin) functional oxide systems.

  10. Direct angle resolved photoelectron spectroscopy (DARPES) on high-Tc films: doping, strains, Fermi surface topology and superconductivity

    Science.gov (United States)

    Pavuna, D.; Ariosa, D.; Cancellieri, C.; Cloetta, D.; Abrecht, M.

    2008-03-01

    Since 1997 we systematically perform Direct ARPES ( = DARPES) on in-situ grown, non-cleaved, ultra-thin (<25nm) cuprate films. Specifically, we probe low energy electronic structure and properties of high-Tc films under different degree of epitaxial (compressive vs tensile) strain. In overdoped in-plane compressed La2-xSrxCuO4 (LSCO) thin films we double Tc from 20K to 40K, yet the Fermi surface (FS) remains essentially 2-dimensional (2D). In contrast, tensile strained films show 3-dimensional (3D) dispersion, while Tc is drastically reduced. It seems that the in-plane compressive strain tends to push the apical oxygen far away from the CuO2 plane, enhances the 2D character of the dispersion and increases Tc, while the tensile strain seems to act exactly in the opposite direction and the resulting dispersion is 3D. We have the FS topology for both cases. As the actual lattice of cuprates is 'Napoleon-cake' -like i.e. rigid CuO2 planes alternate with softer 'reservoir' (that strains distort differently) our results tend to rule out 2D rigid lattice mean field models. Finally, we briefly discuss recent successful determination of the FS topology from the observed wavevector quantization by DARPES in cuprate films thinner than 18 units cells (<24nm). Such an approach is of broader interest as it can be extended to other similar confined (ultra-thin) functional oxide systems.

  11. Level sequence and splitting identification of closely-spaced energy levels by angle-resolved analysis of the fluorescence light

    CERN Document Server

    Wu, Z W; Surzhykov, A; Dong, C Z; Fritzsche, S

    2016-01-01

    The angular distribution and linear polarization of the fluorescence light following the resonant photoexcitation is investigated within the framework of the density matrix and second-order perturbation theory. Emphasis has been placed on "signatures" for determining the level sequence and splitting of intermediate (partially) overlapping resonances, if analyzed as a function of the photon energy of the incident light. Detailed computations within the multiconfiguration Dirac-Fock method have been performed especially for the $1s^{2}2s^{2}2p^{6}3s\\;\\, J_{i}=1/2 \\,+\\, \\gamma_{1} \\:\\rightarrow\\: (1s^{2}2s2p^{6}3s)_{1}3p_{3/2}\\;\\, J=1/2, \\, 3/2 \\:\\rightarrow\\: 1s^{2}2s^{2}2p^{6}3s\\;\\, J_{f}=1/2 \\,+\\, \\gamma_{2}$ photoexcitation and subsequent fluorescence emission of atomic sodium. A remarkably strong dependence of the angular distribution and linear polarization of the $\\gamma_{2}$ fluorescence emission is found upon the level sequence and splitting of the intermediate $(1s^{2}2s2p^{6}3s)_{1}3p_{3/2}\\;\\, J=1/2,...

  12. Level sequence and splitting identification of closely spaced energy levels by angle-resolved analysis of fluorescence light

    Science.gov (United States)

    Wu, Z. W.; Volotka, A. V.; Surzhykov, A.; Dong, C. Z.; Fritzsche, S.

    2016-06-01

    The angular distribution and linear polarization of the fluorescence light following the resonant photoexcitation is investigated within the framework of density matrix and second-order perturbation theory. Emphasis has been placed on "signatures" for determining the level sequence and splitting of intermediate (partially) overlapping resonances, if analyzed as a function of photon energy of incident light. Detailed computations within the multiconfiguration Dirac-Fock method have been performed, especially for the 1 s22 s22 p63 s ,Ji=1 /2 +γ1→(1s22 s 2 p63 s ) 13 p3 /2,J =1 /2 ,3 /2 →1 s22 s22 p63 s ,Jf=1 /2 +γ2 photoexcitation and subsequent fluorescence emission of atomic sodium. A remarkably strong dependence of the angular distribution and linear polarization of the γ2 fluorescence emission is found upon the level sequence and splitting of the intermediate (1s22 s 2 p63 s ) 13 p3 /2,J =1 /2 ,3 /2 overlapping resonances owing to their finite lifetime (linewidth). We therefore suggest that accurate measurements of the angular distribution and linear polarization might help identify the sequence and small splittings of closely spaced energy levels, even if they cannot be spectroscopically resolved.

  13. Electronic structure of Pc2Lu and (PcAlF)n oriented thin films using angle resolved photoelectron spectroscopy

    Science.gov (United States)

    Fahy, M. R.; Fujimoto, H.; Dann, A. J.; Hoshi, H.; Inokuchi, H.; Maruyama, Y.; Willis, M. R.

    1990-04-01

    Ultraviolet photoelectron spectra have been measured for the radical phthalocyanine dimer, Pc2Lu, and the fluorine bridge stacked phthalocyanine polymer (PcAlF)n. Previous workers have shown that both materials can, under appropriate conditions, be prepared in a well characterised, highly oriented thin film form. Thus, samples for this work were prepared by in situ sublimation at very slow evaporation rates onto crystalline substrates to try to maximise the degree of sample orientation. The angle dependence of the spectra were measured and the sample structure subsequently examined using high resolution TEM. The TEM results show that the (PcAlF)n films have a much higher level of orientation than the Pc2Lu films and this is reflected by the angle dependences of the UPS measurements. The spectra for (PcAlF)n are very similar to measurements on most other simple phthalocyanine compounds and have a small angular dependence. The spectra for Pc2Lu show almost no angular dependence. Again the spectra are broadly similar to that of other Pc's with two significant differences, the lowest energy peak is split and the whole spectra is shifted to lower energy. This result will be discussed in terms of simple molecular orbital ideas. The effect of air on the spectra of both materials was examined and the spectra of (PcAlF)n was found to be particularly sensitive. Attempts to determine the position of the lutetium orbitals by varying the light frequency around the lutetium resonance energies was attempted but no significant variation in the spectra was observed.

  14. Electronic structure of Li{sub 1+x}[Mn{sub 0.5}Ni{sub 0.5}]{sub 1−x}O{sub 2} studied by photoemission and x-ray absorption spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Yokoyama, Y. [Department of Physics, University of Tokyo, Chiba 277-8561 (Japan); Institute for Solid State Physics, University of Tokyo, Chiba 277-8581 (Japan); Ootsuki, D. [Department of Physics, University of Tokyo, Chiba 277-8561 (Japan); Sugimoto, T. [Department of Complexity Science and Engineering, University of Tokyo, Chiba 277-8561 (Japan); Wadati, H. [Institute for Solid State Physics, University of Tokyo, Chiba 277-8581 (Japan); Okabayashi, J. [Research Center for Spectrochemistry, University of Tokyo, Tokyo 113-0033 (Japan); Yang, Xu; Du, Fei; Chen, Gang [Key Laboratory of Physics and Technology for Advanced Batteries (Ministry of Education), College of Physics, Jilin University, Changchun 130012 (China); Mizokawa, T. [Department of Applied Physics, Waseda University, Tokyo 169-8555 (Japan)

    2015-07-20

    We have studied the electronic structure of Li{sub 1+x}[Mn{sub 0.5}Ni{sub 0.5}]{sub 1−x}O{sub 2} (x = 0.00 and 0.05), one of the promising cathode materials for Li ion battery, by means of x-ray photoemission and absorption spectroscopy. The results show that the valences of Mn and Ni are basically 4+ and 2+, respectively. However, the Mn{sup 3+} component in the x = 0.00 sample gradually increases with the bulk sensitivity of the experiment, indicating that the Jahn-Teller active Mn{sup 3+} ions are introduced in the bulk due to the site exchange between Li and Ni. The Mn{sup 3+} component gets negligibly small in the x = 0.05 sample, which indicates that the excess Li suppresses the site exchange and removes the Jahn-Teller active Mn{sup 3+}.

  15. Photoemission spectra and effective masses of n- and p-type oxide semiconductors from first principles: ZnO, CdO, SnO2, MnO, and NiO

    International Nuclear Information System (INIS)

    While there is a persistent interest in oxides, e.g., for semiconductor technology or optoelectronics, it seems to be difficult to achieve n-type and p-type doping for one and the same material. At the same time, it is important to understand the electronic structure for both types of doping individually. In this work, we use modern electronic-structure calculations to compute the density of states as well as effective electron and hole masses for n-type (ZnO, CdO, SnO2) and p-type (MnO, NiO) oxide materials. We establish our ab initio electronic structures by comparison to photoemission experiments at various incident photon energies. Taking into account the photoionization cross-sections, we are able to analyze the contributions of different atomic states and to verify the results by comparison to measured data. Based on these electronic structures, we calculate free-electron and free-hole masses as well as their dependence on the concentration of free carriers in the system. For SnO2, we compare with experimental results from another article (see M. Feneberg et al., Phys. Status Solidi A, DOI 10.1002/pssa.201330147 (2013)) in this special issue. (copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

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

    DEFF Research Database (Denmark)

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

    2010-01-01

    realization allows the sample, located in an ultrahigh-vacuum chamber, to be illuminated by 106 65-eV photons per laser pulse at a 10 Hz repetition rate. The spectral width of a single harmonic is 0.77 eV (FWHM), and a few harmonics are selected by specially designed Mo/Si multi-layer mirrors. Photoelectrons......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...

  17. Optical spectroscopy and photoemission of {alpha}- and {gamma}-cerium from LDA+DMFT

    Energy Technology Data Exchange (ETDEWEB)

    Haule, Kristjan [Jozef Stefan Institute, SI-1000, Ljubljana (Slovenia)]. E-mail: kristjan.Haule@ijs.si; Kotliar, Gabriel [Department of Physics and Center for Material Theory, Rutgers University, Pscataway, NJ 08854 (United States)

    2005-04-30

    Using a novel approach to calculate optical properties of strongly correlated systems, we address the old question of the physical origin of the {alpha}->{gamma} transitions in Ce. We find that the Kondo collapse model, involving both the f and the spd electrons, describes the optical data better than a Mott transition picture involving the f electrons only. Our results compare well with existing experiments on thin films. We predict the optical spectra for both {alpha} and {gamma} phases of Ce and find the development of a hybridization pseudogap in the vicinity of the phase transition.

  18. Adaptive electron beam shaping using a photoemission gun and spatial light modulator

    Science.gov (United States)

    Maxson, Jared; Lee, Hyeri; Bartnik, Adam C.; Kiefer, Jacob; Bazarov, Ivan

    2015-02-01

    The need for precisely defined beam shapes in photoelectron sources has been well established. In this paper, we use a spatial light modulator and simple shaping algorithm to create arbitrary, detailed transverse laser shapes with high fidelity. We transmit this shaped laser to the photocathode of a high voltage dc gun. Using beam currents where space charge is negligible, and using an imaging solenoid and fluorescent viewscreen, we show that the resultant beam shape preserves these detailed features with similar fidelity. Next, instead of transmitting a shaped laser profile, we use an active feedback on the unshaped electron beam image to create equally accurate and detailed shapes. We demonstrate that this electron beam feedback has the added advantage of correcting for electron optical aberrations, yielding shapes without skew. The method may serve to provide precisely defined electron beams for low current target experiments, space-charge dominated beam commissioning, as well as for online adaptive correction of photocathode quantum efficiency degradation.

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

    Energy Technology Data Exchange (ETDEWEB)

    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

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

    Science.gov (United States)

    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.

  1. Photoemission study of the Poly(3-hexylthiophene)/TiO2 interface and the role of 4-Mercaptopyridine

    International Nuclear Information System (INIS)

    We report on a combined X-ray and UV photoemission spectroscopy study (XPS, UPS) of the interface between Poly(3-hexylthiophene) (P3HT) and mesoporous titanium dioxide (TiO2), a key element in the development of hybrid solar cells. We employed the elemental specificity of XPS to directly probe, on the complete P3HT/TiO2 heterostructure, the changes in the electronic levels alignment at the interface upon the addition of 4-Mercaptopyridine (4-MPy) molecules. We estimate an upper limit of 50 meV to the contribution of 4-MPy to the P3HT/TiO2 interfacial dipole. In addition, UPS was used to provide a quantitative estimate of the relevant parameters controlling the transfer of charge through the hybrid interface, such as the binding energy of the TiO2 valence and conduction bands and of the P3HT highest occupied/lowest unoccupied molecular orbitals. In both cases, we confirm that the alignment of P3HT energy levels to those of the substrate is not influenced by the position of the Fermi level inside the TiO2 band gap. - Highlights: • We studied the electronic structure of the Poly(3-hexylthiophene)/TiO2 interface. • 4-mercaptopyridine (4-MPy) molecules were used as interface modifiers. • The contribution of 4-MPy to the interfacial dipole is limited to 50 meV. • No pinning of Poly(3-hexylthiophene) energy levels to the Fermi level is observed

  2. Combined Photoemission Spectroscopy and Electrochemical Study of a Mixture of (Oxy)carbides as Potential Innovative Supports and Electrocatalysts.

    Science.gov (United States)

    Calvillo, Laura; Valero-Vidal, Carlos; Agnoli, Stefano; Sezen, Hikmet; Rüdiger, Celine; Kunze-Liebhäuser, Julia; Granozzi, Gaetano

    2016-08-01

    Active and stable non-noble metal materials, able to substitute Pt as catalyst or to reduce the Pt amount, are vitally important for the extended commercialization of energy conversion technologies, such as fuel cells and electrolyzers. Here, we report a fundamental study of nonstoichiometric tungsten carbide (WxC) and its interaction with titanium oxycarbide (TiOxCy) under electrochemical working conditions. In particular, the electrochemical activity and stability of the WxC/TiOxCy system toward the ethanol electrooxidation reaction (EOR) and hydrogen evolution reaction (HER) are investigated. The chemical changes caused by the applied potential are established by combining photoemission spectroscopy and electrochemistry. WxC is not active toward the ethanol electrooxidation reaction at room temperature but it is highly stable under these conditions thanks to the formation of a passive thin film on the surface, consisting mainly of WO2 and W2O5, which prevents the full oxidation of WxC. In addition, WxC is able to adsorb ethanol, forming ethoxy groups on the surface, which constitutes the first step for the ethanol oxidation. The interaction between WxC and TiOxCy plays an important role in the electrochemical stability of WxC since specific orientations of the substrate are able to stabilize WxC and prevent its corrosion. The beneficial interaction with the substrate and the specific surface chemistry makes tungsten carbide a good electrocatalyst support or cocatalyst for direct ethanol fuel cells. However, WxC is active toward the HER and chemically stable under hydrogen reduction conditions, since no changes in the chemical composition or dissolution of the film are observed. This makes tungsten carbide a good candidate as electrocatalyst support or cocatalyst for the electrochemical production of hydrogen. PMID:27399154

  3. Optical characteristics of p-type GaAs-based semiconductors towards applications in photoemission infrared detectors

    Science.gov (United States)

    Lao, Y. F.; Perera, A. G. U.; Wang, H. L.; Zhao, J. H.; Jin, Y. J.; Zhang, D. H.

    2016-03-01

    Free-carrier effects in a p-type semiconductor including the intra-valence-band and inter-valence-band optical transitions are primarily responsible for its optical characteristics in infrared. Attention has been paid to the inter-valence-band transitions for the development of internal photoemission (IPE) mid-wave infrared (MWIR) photodetectors. The hole transition from the heavy-hole (HH) band to the spin-orbit split-off (SO) band has demonstrated potential applications for 3-5 μm detection without the need of cooling. However, the forbidden SO-HH transition at the Γ point (corresponding to a transition energy Δ0, which is the split-off gap between the HH and SO bands) creates a sharp drop around 3.6 μm in the spectral response of p-type GaAs/AlGaAs detectors. Here, we report a study on the optical characteristics of p-type GaAs-based semiconductors, including compressively strained InGaAs and GaAsSb, and a dilute magnetic semiconductor, GaMnAs. A model-independent fitting algorithm was used to derive the dielectric function from experimental reflection and transmission spectra. Results show that distinct absorption dip at Δ0 is observable in p-type InGaAs and GaAsSb, while GaMnAs displays enhanced absorption without degradation around Δ0. This implies the promise of using GaMnAs to develop MWIR IPE detectors. Discussions on the optical characteristics correlating with the valence-band structure and free-hole effects are presented.

  4. Photoemission study of the Poly(3-hexylthiophene)/TiO2 interface and the role of 4-Mercaptopyridine

    Energy Technology Data Exchange (ETDEWEB)

    Calloni, A., E-mail: alberto1.calloni@mail.polimi.it [CNISM and Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo Da Vinci 32, 20133 Milano (Italy); Berti, G.; Ferrari, A.; Brambilla, A.; Bussetti, G. [CNISM and Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo Da Vinci 32, 20133 Milano (Italy); Canesi, E.V.; Petrozza, A. [Center for Nano Science and Technology @ Polimi, Istituto Italiano di Tecnologia, via Pascoli 70/3, 20133 Milano (Italy); Duò, L. [CNISM and Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo Da Vinci 32, 20133 Milano (Italy)

    2014-06-02

    We report on a combined X-ray and UV photoemission spectroscopy study (XPS, UPS) of the interface between Poly(3-hexylthiophene) (P3HT) and mesoporous titanium dioxide (TiO{sub 2}), a key element in the development of hybrid solar cells. We employed the elemental specificity of XPS to directly probe, on the complete P3HT/TiO{sub 2} heterostructure, the changes in the electronic levels alignment at the interface upon the addition of 4-Mercaptopyridine (4-MPy) molecules. We estimate an upper limit of 50 meV to the contribution of 4-MPy to the P3HT/TiO{sub 2} interfacial dipole. In addition, UPS was used to provide a quantitative estimate of the relevant parameters controlling the transfer of charge through the hybrid interface, such as the binding energy of the TiO{sub 2} valence and conduction bands and of the P3HT highest occupied/lowest unoccupied molecular orbitals. In both cases, we confirm that the alignment of P3HT energy levels to those of the substrate is not influenced by the position of the Fermi level inside the TiO{sub 2} band gap. - Highlights: • We studied the electronic structure of the Poly(3-hexylthiophene)/TiO{sub 2} interface. • 4-mercaptopyridine (4-MPy) molecules were used as interface modifiers. • The contribution of 4-MPy to the interfacial dipole is limited to 50 meV. • No pinning of Poly(3-hexylthiophene) energy levels to the Fermi level is observed.

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  6. Multichannel spin polarimeter for energy- and angle-dispersive photoemission measurements

    International Nuclear Information System (INIS)

    was already implemented for an application in the viewpoint of fundamental research: as test for the validity of bandstructure calculations for the Heusler compound Co2MnGa, where a good agreement between experiment and theory could be demonstrated. With the multichannel spin filter, a basis to a measurement procedure for electron spin polarization enhanced by orders of magnitude was established. This paves the way to experiments that are not possible with state-of-the-art single channel detectors.

  7. Charge transfer dynamics of 3,4,9,10-perylene-tetracarboxylic-dianhydride molecules on Au(111) probed by resonant photoemission spectroscopy.

    Science.gov (United States)

    Cao, Liang; Wang, Yu-Zhan; Chen, Tie-Xin; Zhang, Wen-Hua; Yu, Xiao-Jiang; Ibrahim, Kurash; Wang, Jia-Ou; Qian, Hai-Jie; Xu, Fa-Qiang; Qi, Dong-Chen; Wee, Andrew T S

    2011-11-01

    Charge transfer dynamics across the lying-down 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) organic semiconductor molecules on Au(111) interface has been investigated using the core-hole clock implementation of resonant photoemission spectroscopy. It is found that the charge transfer time scale at the PTCDA∕Au(111) interface is much larger than the C 1s core-hole lifetime of 6 fs, indicating weak electronic coupling between PTCDA and the gold substrate due to the absence of chemical reaction and∕or bonding. PMID:22070311

  8. On the X-ray induced chemical reduction of CeO2 as seen with X-ray photoemission spectroscopy

    International Nuclear Information System (INIS)

    A recent X-ray photoemission spectroscopy (XPS) study (M.V. Rama Rao and T. Shripathi, J. Electron Spectrosc. Relat. Phenom., 87 (1997) 121) on X-ray irradiated ceria stated that hydroxyl groups play a meaningful role in enhancing the chemical reduction of this oxide and that chemical damage mainly involves layers lying at depths that are larger than photoelectron attenuation lengths. We comment upon this paper, and show that the experimental evidence therein presented by the authors does not warrant these conclusions. (Copyright (c) 1998 Elsevier Science B.V., Amsterdam. All rights reserved.)

  9. Synchronization and Characterization of an Ultra-Short Laser for Photoemission and Electron-Beam Diagnostics Studies at a Radio Frequency Photoinjector

    Energy Technology Data Exchange (ETDEWEB)

    Maxwell, Timothy; Ruan, Jinhao; Piot, Philippe; Lumpkin, Alex

    2012-03-01

    A commercially-available titanium-sapphire laser system has recently been installed at the Fermilab A0 photoinjector laboratory in support of photoemission and electron beam diagnostics studies. The laser system is synchronized to both the 1.3-GHz master oscillator and a 1-Hz signal use to trigger the radiofrequency system and instrumentation acquisition. The synchronization scheme and performance are detailed. Long-term temporal and intensity drifts are identified and actively suppressed to within 1 ps and 1.5%, respectively. Measurement and optimization of the laser's temporal profile are accomplished using frequency-resolved optical gating.

  10. Interferometric two-photon photoemission correlation technique and femtosecond wet-electron dynamics at the TiO2 (110) surface

    Institute of Scientific and Technical Information of China (English)

    Bin LI; Jin ZHAO; Min FENG; Ken ONDA

    2008-01-01

    The femtosecond time-resolved two-photon pho-toemission (TR-2PP) and the ultra high vacuum (UHV) sur-face science techniques are integrated to investigate the elec-tronic structures and the interracial electron transfer dynamics at the atomically ordered adsorbate overlayers on TiO,2single-crystalline surfaces. Our research into the CH,3OH/TiO,2sys-tem exhibits complex dynamics, providing abundant informa-tion with regard to electron transport and solvation processes in the interfacial solvent structures. These represent the fundamentally physical, photochemical, and photocatalytic reactions of protic chemicals covered with metal-oxides.

  11. In situ photoemission study of interface and film formation during epitaxial growth of Er2O3 film on Si(001) substrate

    Institute of Scientific and Technical Information of China (English)

    ZHU Yanyan; FANG Zebo; LIU Yongsheng; LIAO Can; CHEN Sheng

    2008-01-01

    Synchrotron radiation photoemission spectroscopy was used to study the formation process of Er2O3/Si(001) interface and film during epitaxial growth on Si. A shift in the O core-level binding energy was found accompanied by a shift in the Er2O3 valence band maxi-mum. This shift depended on the oxide layer thickness and interfacial structure. An interfacial layer was observed at the initial growth of Er2O3 film on Si, which was supposed to be attributed to the effect of Er atom catalytic oxidation effect.

  12. Doping-driven evolution of the superconducting state from a doped Mott insulator: Cluster dynamical mean-field theory

    Science.gov (United States)

    Civelli, M.

    2009-05-01

    In this paper we investigate the zero-temperature doping-driven evolution of a superconductor toward the Mott insulator in a two-dimensional electron model, relevant for high-temperature superconductivity. To this purpose we use a cluster extension of dynamical mean-field theory. Our results show that a standard d -wave superconductor, realized at high doping, is driven into the Mott insulator via an intermediate superconducting state displaying unconventional physical properties. By restoring the translational invariance of the lattice, we give an interpretation of these findings in momentum space. In particular, we show that at a finite doping a strong momentum-space differentiation takes place: non-Fermi liquid and insulatinglike (pseudogap) characters rise in some regions (antinodes), while Fermi liquid quasiparticles survive in other regions (nodes) of momentum space. We describe the consequence of these happenings on the spectral properties, stressing in particular the behavior of the superconducting gap, which reveals two distinct nodal and antinodal energy scales as a function of doping, detected in photoemission and Raman spectroscopy experiments. We study and compare with experimental results the doping-dependent behavior of other physical quantities, such as for instance, the nodal quasiparticle velocity (extracted in angle-resolved photoemission) and the low-energy slopes of the local density of states and of the Raman scattering response. We then propose a description of the evolution of the electronic structure while approaching the Mott transition. We show that, within our formalism, a strong asymmetry naturally arises in the local density of states, measured in scanning tunneling spectroscopy. We investigate in detail the doping evolution of the electronic bands, focusing on the kinklike quasiparticle dispersion observed with angle-resolved photoemission in specific cuts of the momentum-energy space. We finally show the consequences of the

  13. Soft x-ray photoemission investigation on the effect of In doping in CdS/CuInSe sub 2 heterojunction formation

    Energy Technology Data Exchange (ETDEWEB)

    Nelson, A.J.; Niles, D.W. (National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, Colorado 80401 (United States)); Rioux, D.; Patel, R.; Hoechst, H. (Synchrotron Radiation Center, University of Wisconsin-Madison, 3731 Schneider Drive, Stoughton, Wisconsin 53589 (United States))

    1992-12-15

    Synchrotron radiation soft x-ray photoemission spectroscopy was used to investigate the development of the electronic structure at the CdS(In)/CuInSe{sub 2} heterojunction interface. In-doped CdS overlayers were deposited in steps on single-crystal {ital n}-type CuInSe{sub 2} at 250 {degree}C. Results indicate that the CdS(In) grows in registry with the substrate, initially in a two-dimensional growth mode followed by three-dimensional island growth as is corroborated by reflection high-energy electron diffraction analysis. Photoemission measurements were acquired after each growth in order to observe changes in the valence-band electronic structure. The results were used to correlate the interface chemistry with the electronic structure at these interfaces and to directly determine the CdS(In)/CuInSe{sub 2} heterojunction valence-band discontinuity and the consequent heterojunction band diagram as a function of In dopant concentration. We measured a valence-band offset {Delta}{ital E}{sub {ital v}}=0.3 eV, independent of In doping.

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

    Science.gov (United States)

    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 .

  15. Fabrication and hard X-ray photoemission analysis of photocathodes with sharp solar-blind sensitivity using AlGaN films grown on Si substrates

    International Nuclear Information System (INIS)

    Photocathode devices operating in reflection-mode, where the photoemission is detected on the same side as the light irradiation, were developed for the detection of deep ultraviolet light by using p-AlxGa1-xN films grown on Si(1 1 1) substrates. The external quantum efficiencies were as high as 20-15% at 200 nm and 280 nm, while the value was as low as 10-2% at 310 nm. The on-off ratio was more than four orders of magnitude, which represents high solar-blind sensitivity. The escape probability of AlxGa1-xN photocathode was decreased with increase of AlN mole fraction. The effective barrier potential against the photoelectron emission near the surface was reduced due to the upward shift of conduction band of AlxGa1-xN. The photoemission from the AlxGa1-xN films terminated with Cs-O adatoms will be discussed in terms of band diagrams that were evaluated by hard X-ray photoelectron spectroscopy.

  16. Studies of magnetism and exchange scattering in solids using synchrotron radiation and spin polarized photoemission. Final technical report, June 1, 1981-May 31, 1984

    International Nuclear Information System (INIS)

    Progress has been made toward developing Spin Polarized EXAFS (SPEXAFS) as a technique for studying magnetism in solids. The first observations have been made of EXAFS by means of photoemission with sufficient data to permit a traditional Fourier-transform analysis of atomic structure. Some of the advantages of photoelectron detection of EXAFS are: (1) vuv light may be used thereby extending greatly the useable range of photon energies; (2) the number of elements that may be studied for surface EXAFS is increased; (3) the possibility exists for measurements that cannot be done in other ways. In addition to its intrinsic interest, this result is crucial to the study of the spin dependence of EXAFS. These measurements were carried out on the vuv storage ring at the National Synchrotron Light Source. Data obtained on the spin dependence of EXAFS in MnF2 at room temperature tentatively show dependence of the Mn absorber atom phase shift on the exchange interaction within the absorber atom. This effect has not been discussed theoretically. Preliminary observations have been made of the Fano resonance in Mn 3d photoemission at the 3p to 3d threshold

  17. Time-resolved two-photon photoemission at the Si(001)-surface. Hot electron dynamics and two-dimensional Fano resonance; Zeitaufgeloeste Zweiphotonen-Photoemission an der Si(001)-Oberflaeche. Dynamik heisser Elektronen und zweidimensionaler Fano-Effekt

    Energy Technology Data Exchange (ETDEWEB)

    Eickhoff, Christian

    2010-10-27

    By combining ultrafast laser excitation with energy-, angle- and time-resolved twophoton photoemission (2PPE), the electronic properties of bulk silicon and the Si(001) surface are investigated in this thesis. A custom-built laser- and UHV-systemequipped with a display type 2D-CCD-detector gives new insight into the relaxation dynamics of excited carriers on a femtosecond timescale. The bandgap between occupied valence bands and unoccupied conduction bands characteristically influences the dynamics of excited electrons in the bulk, as well as in surface states and resonances. For the electron-phonon interaction this leads to the formation of a bottleneck during the relaxation of hot electrons in the conduction band, which maintains the elevated electronic temperature for several picoseconds. During relaxation, excited electrons also scatter from the conduction band into the unoccupied dangling-bond surface state D{sub down}. Depending on the excitation density this surface recombination is dominated by electron-electron- or electron-phonon scattering. The relaxation of the carriers in the D{sub down}-band is again slowed down by the formation of a bottleneck in electron-phonon coupling. Furthermore, the new laser system has allowed detection of the Rydberg-like series of image-potential resonances on the Si(001)-surface. It is shown that the lifetime of these image-potential resonances in front of the semiconducting surface exhibits the same behavior as those in front of metallic surfaces. Moreover the electron-phonon coupling in the first image-potential resonance was investigated and compared to the D{sub down}-surface state. For the first time, Fano-type lineprofiles are demonstrated and analyzed in a 2PPEprocess on a surface. Tuning the photon energy of the pump-laser across the resonance between the occupied dangling-bond state D{sub up}, and the unoccupied image-potential resonance n=1, reveals a clear intensity variation that can be successfully described

  18. Discharge amplified photo-emission from ultra-thin films applied to tuning work function of transparent electrodes in organic opto-electronic devices

    Energy Technology Data Exchange (ETDEWEB)

    Gentle, A.R. [Physics and Advanced Materials, University of Technology, Sydney, PO Box 123, Broadway, NSW 2007 Australia (Australia); Smith, G.B., E-mail: g.smith@uts.edu.au [Physics and Advanced Materials, University of Technology, Sydney, PO Box 123, Broadway, NSW 2007 Australia (Australia); Watkins, S.E. [CSIRO Materials Science and Engineering, Clayton South, Victoria 3169 (Australia)

    2013-11-15

    A novel photoemission technique utilising localised discharge amplification of photo-yield is reported. It enables fast, accurate measurement of work function and ionisation potential for ultra-thin buffer layers vacuum deposited onto single and multilayer transparent conducting electrodes for organic solar cells and OLED's. Work function in most traditional transparent electrodes has to be raised to maximise charge transfer while high transmittance and high conductance must be retained. Results are presented for a range of metal oxide buffers, which achieve this goal. This compact photo-yield spectroscopy tool with its fast turn-around has been a valuable development aid since ionisation potential can vary significantly as deposition conditions change slightly, and as ultra-thin films grow. It has also been useful in tracking the impact of different post deposition cleaning treatments along with some storage and transport protocols, which can adversely reduce ionisation potential and hence subsequent device performance.

  19. Element-specific study of epitaxial NiO/Ag/CoO/Fe films grown on vicinal Ag(001) using photoemission electron microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Meng, Y.; Li, J.; Tan, A.; Jin, E.; Son, J.; Park, J. S.; Doran, A.; Young, A. T.; Scholl, A.; Arenholz, E.; Wu, J.; Hwang, C.; Zhao, H. W.; Qiu, Z. Q.

    2011-01-10

    NiO/Ag/CoO/Fe single crystalline films are grown epitaxially on a vicinal Ag(001) substrate using molecular beam epitaxy and investigated by photoemission electron microscopy. We find that after zero-field cooling, the in-plane Fe magnetization switches from parallel to perpendicular direction of the atomic steps of the vicinal surface at thinner CoO thickness but remains in its original direction parallel to the steps at thicker CoO thickness. CoO and NiO domain imaging result shows that both CoO/Fe and NiO/CoO spins are perpendicularly coupled, suggesting that the Fe magnetization switching may be associated with the rotatable-frozen spin transition of the CoO film.

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

    Science.gov (United States)

    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.