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Sample records for core-level photoemission study

  1. 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.

  2. Core level photoemission of rotaxanes : A summary on binding energies

    NARCIS (Netherlands)

    Mendoza, S. M.; Berna, J.; Perez, E. M.; Kay, E. R.; Mateo-Alonso, A.; De Nadai, C.; Zhang, S.; Baggerman, J.; Wiering, P. G.; Leigh, D. A.; Prato, M.; Brouwer, A.M.; Rudolf, P.; Nadaï, C. De

    2008-01-01

    Several rotaxanes were studied by XPS in the form of thin films or monolayers on gold substrates. Here we report a database of photoemission spectra of the C 1s, N 1s and F 1s core levels. Binding energy ranges are summarized, classifying the core levels according to the chemical groups that form pa

  3. Core level photoemission of rotaxanes: A summary on binding energies

    Energy Technology Data Exchange (ETDEWEB)

    Mendoza, S.M. [Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen (Netherlands); Berna, J.; Perez, E.M.; Kay, E.R. [School of Chemistry, University of Edinburgh, King' s Buildings, West Mains Road, Edinburgh EH9 3JJ (United Kingdom); Mateo-Alonso, A. [Dipartimento di Scienze Farmaceutiche, Universita di Trieste, Piazzale Europa 1, 34127 Trieste (Italy); De Nadai, C. [Laboratoire Interdisciplinaire de Spectroscopie Electronique, Facultes Universitaires Notre Dame de la Paix, 61 Rue de Bruxelles, B-5000 Namur (Belgium); Zhang, S. [School of Chemistry, University of Edinburgh, King' s Buildings, West Mains Road, Edinburgh EH9 3JJ (United Kingdom); Baggerman, J.; Wiering, P.G. [Van' t Hoff Institute for Molecular Sciences, University of Amsterdam, Nieuwe Achtergracht 129, NL-1018 WS Amsterdam (Netherlands); Leigh, D.A. [School of Chemistry, University of Edinburgh, King' s Buildings, West Mains Road, Edinburgh EH9 3JJ (United Kingdom); Prato, M. [Dipartimento di Scienze Farmaceutiche, Universita di Trieste, Piazzale Europa 1, 34127 Trieste (Italy); Brouwer, A.M. [Van' t Hoff Institute for Molecular Sciences, University of Amsterdam, Nieuwe Achtergracht 129, NL-1018 WS Amsterdam (Netherlands); Rudolf, P. [Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen (Netherlands)], E-mail: P.Rudolf@rug.nl

    2008-09-15

    Several rotaxanes were studied by XPS in the form of thin films or monolayers on gold substrates. Here we report a database of photoemission spectra of the C 1s, N 1s and F 1s core levels. Binding energy ranges are summarized, classifying the core levels according to the chemical groups that form part of the rotaxanes.

  4. Electronic Charges and Electric Potential at LaAlO3/SrTiO3 Interfaces Studied by Core-Level Photoemission Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Hwang, Harold

    2011-08-19

    We studied LaAlO{sub 3}/SrTiO{sub 3} interfaces for varying LaAlO{sub 3} thickness by core-level photoemission spectroscopy. In Ti 2p spectra for conducting 'n-type' interfaces, Ti{sup 3+} signals appeared, which were absent for insulating 'p-type' interfaces. The Ti{sup 3+} signals increased with LaAlO{sub 3} thickness, but started well below the critical thickness of 4 unit cells for metallic transport. Core-level shifts with LaAlO{sub 3} thickness were much smaller than predicted by the polar catastrophe model. We attribute these observations to surface defects/adsorbates providing charges to the interface even below the critical thickness.

  5. Core-level photoemission from alkali metals on Ru(001)

    Energy Technology Data Exchange (ETDEWEB)

    Shek, M. (Department of Physics, Hunter College of The City University of New York, New York, New York 10021 (USA)); Hrbek, J. (Department of Chemistry, Brookhaven National Laboratory, Upton, New York 11973-5000 (USA)); Sham, T.K. (Department of Chemistry, University of Western Ontario, London, Ontario, Canada NA65B7 (Canada)); Xu, G. (Department of Chemistry, Brookhaven National Laboratory, Upton, New York 11973-5000 (USA))

    1990-02-15

    We report soft-x-ray photoemission results on the core-level binding energies of Li, Na, K, and Cs adsorbed on Ru(001). For all four alkali metals, the saturated alkali-metal--Ru interface core level and the second- (surface-) layer core-level binding energies differ by as much as 0.85--1.25 eV. Surface versus bulklike core-level shifts are reported for Li, K, and Cs, which are 0.55 eV for Li and {similar to}0.25 eV for the other two. For increasing coverages of Li, Na, and K in direct contact with Ru, there are significant decreases in the core-level binding energies, the total shift ranging from {similar to}{minus}1.25 eV for Li to {similar to}{minus}0.80 eV for K; the shift for Cs is small and the reasons for the deviation are discussed. A comparison between our observations and the prediction from the thermodynamic model of Johannson and Martensson is also given.

  6. Comparative study of the core level photoemission of the ZrB{sub 2} and ZrB{sub 12}

    Energy Technology Data Exchange (ETDEWEB)

    Huerta, L. [Instituto de Investigaciones en Materiales, Universidad Nacional Autonoma de Mexico, 04510 Mexico D.F. (Mexico); Duran, A. [Centro de Nanociencias y Nanotecnologia, Universidad Nacional Autonoma de Mexico, Apartado Postal 2681, Ensenada, Baja California 22800 (Mexico); Falconi, R. [Division Academica de Ciencias Basicas, Universidad Juarez Autonoma de Tabasco, Cunduacan, Tabasco, CP 86690, AP 24 (Mexico); Flores, M. [Departamento de Ingenieria de Proyectos, CUCEI, Universidad de Guadalajara, AP 307, Zapopan Jal 45101 (Mexico); Escamilla, R., E-mail: rauleg@servidor.unam.m [Instituto de Investigaciones en Materiales, Universidad Nacional Autonoma de Mexico, 04510 Mexico D.F. (Mexico)

    2010-05-01

    X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) were used to investigate the binding energies and valence band for ZrB{sub 2} and ZrB{sub 12}. The Zr 3d and B 1s core levels were identified. The Zr 3d core level shows a spin-orbit split 3d{sub 5/2} and 3d{sub 3/2} while that for B 1s core level exhibited a single symmetric peak, these being typical of zirconium and boride signals. Comparing the Zr 3d and B 1s core levels with metallic Zr, B{sub 2}O{sub 3} and ZrO{sub 2} reference materials only a negative chemical shift for Zr 3d associated to ZrB{sub 2} was observed, which suggests that the charge transfer model based on the concept of electronegativity was not applicable to explain the superconductivity in the ZrB{sub 12} sample. The measured valence band using UPS is consistent with the band-structure calculations indicating a higher density of states (DOS) at E{sub F} for ZrB{sub 12} respect to ZrB{sub 2}. Finally, we found that the weak mixed B-p and Zr-d states for ZrB{sub 12} is crucial for the superconductivity due to the state population increased the DOS at the E{sub F}.

  7. Coverage dependence of photoemission core levels of alkali-metal overlayers

    Energy Technology Data Exchange (ETDEWEB)

    Sham, T.K.; Shek, M.; Xu, G.; Hrbek, J.

    1989-05-01

    Photoemission from alkali-metal core levels (Li 1s, Na 2s, K 3p, Cs 5p, and 4d) has been studied for different alkali-metal coverages on Ru(001) using synchrotron radiation from the Vacuum Ultraviolet (VUV) ring at the National Synchrotron Light Source (NSLS). The alkali atoms interacting directly with the Ru substrate show coverage-dependent binding-energy shifts towards the Fermi level, with the largest shift for Li (1.1 eV) and the smallest ones for K and Cs. At coverages > 1 monolayer (ML), the core-level shift between the second (surface) and the first (interface) layer is observed in all alkali overlayers. At ''thin'' multilayer coverages (/similar to/3 ML), all alkali overlayers exhibit three sets of core-level photoemission bands which are assigned to the interface, the immediate ''bulk,'' and the surface in increasing binding energy. At coverages >5 ML (''thick'' multilayer) all alkali metals exhibit bulklike properties and surface--atom core-level binding-energy shifts are observed in all cases.

  8. 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.

  9. 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.

  10. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Menchero, Jose Gabriel [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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Chellappan, Rajesh Kumar, E-mail: rajesh.chellappan2@mail.dcu.ie [School of Physical Sciences, Dublin City University, Dublin 9 (Ireland); Gajula, Durga Rao; McNeill, David [School of Electronics, Electrical Engineering and Computer Science, Queen' s University Belfast (United Kingdom); Hughes, Greg [School of Physical Sciences, Dublin City University, Dublin 9 (Ireland)

    2014-02-15

    High resolution soft x-ray photoemission spectroscopy (SXPS) have been used to study the high temperature thermal stability of ultra-thin atomic layer deposited (ALD) HfO{sub 2} layers (∼1 nm) on sulphur passivated and hydrofluoric acid (HF) treated germanium surfaces. The interfacial oxides which are detected for both surface preparations following HfO{sub 2} deposition can be effectively removed by annealing upto 700 °C without any evidence of chemical interaction at the HfO{sub 2}/Ge interface. The estimated valence and conduction band offsets for the HfO{sub 2}/Ge abrupt interface indicated that effective barriers exist to inhibit carrier injection.

  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. 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.

  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. ELECTRONIC-STRUCTURE OF LA2-XSRXNIO4 STUDIED BY PHOTOEMISSION AND INVERSE-PHOTOEMISSION SPECTROSCOPY

    NARCIS (Netherlands)

    EISAKI, H; UCHIDA, S; MIZOKAWA, T; NAMATAME, H; FUJIMORI, A; VANELP, J; KUIPER, P; SAWATZKY, GA; HOSOYA, S; KATAYAMAYOSHIDA, H

    1992-01-01

    The electronic structure of La2-xSrxNiO4 is studied by use of photoemission spectroscopy, bremsstrahlung-isochromat spectroscopy (BIS), and electron-energy-loss spectroscopy. Quantitative analyses are made on the valence-band and Ni 2p core-level photoemission spectra through configuration-interacti

  17. ELECTRONIC-STRUCTURE OF LA2-XSRXNIO4 STUDIED BY PHOTOEMISSION AND INVERSE-PHOTOEMISSION SPECTROSCOPY

    NARCIS (Netherlands)

    EISAKI, H; UCHIDA, S; MIZOKAWA, T; NAMATAME, H; FUJIMORI, A; VANELP, J; KUIPER, P; SAWATZKY, GA; HOSOYA, S; KATAYAMAYOSHIDA, H

    1992-01-01

    The electronic structure of La2-xSrxNiO4 is studied by use of photoemission spectroscopy, bremsstrahlung-isochromat spectroscopy (BIS), and electron-energy-loss spectroscopy. Quantitative analyses are made on the valence-band and Ni 2p core-level photoemission spectra through

  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. Photoemission spectroscopy study of a multi-alkali photocathode

    CERN Document Server

    Ettema, A R H

    2000-01-01

    In this paper a photoemission study of the highest core levels of the elements and the electron escape barrier (work function) in a multi-alkali photocathode are presented. The core levels indicate that the alkali atoms are in an oxidized state and therefore the compound Na sub 2 KSb can be regarded as an ionic semiconductor. The measured escape barrier of the Cs sub 2 O surface layer is determined as 2.3 eV.

  20. Photoemission study of K on graphite

    NARCIS (Netherlands)

    Bennich, P.; Puglia, C.; Brühwiler, P.A.; Nilsson, A.; Sandell, A.; Mårtensson, N.; Rudolf, P.

    1999-01-01

    The physical and electronic structure of the dispersed and (2×2) phases of K/graphite have been characterized by valence and core-level photoemission. Charge transfer from K to graphite is found to occur at all coverages, and includes transfer of charge to the second graphite layer. A rigid band

  1. Core-level X-ray photoemission spectral shift through the successive phase transitions in layered TlInS{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Ishizu, Takahiko [Department of Mathematical Sciences, Graduate School of Engineering, Osaka Prefecture University, Sakai 599-8531 (Japan); Mimura, Kojiro [Department of Mathematical Sciences, Graduate School of Engineering, Osaka Prefecture University, Sakai 599-8531 (Japan)], E-mail: mimura@ms.osakafu-u.ac.jp; Shim, Yong Gu [Department of Physics and Electronics, Graduate School of Engineering, Osaka Prefecture University, Sakai 599-8531 (Japan); Wakita, Kazuki [Department of Electrical, Electronics and Computer Engineering, Chiba Institute of Technology, Narashino 275-0016 (Japan); Mamedov, Nazim [Institute of Physics, Azerbaijan National Academy of Science, Baku, AZ-1143 (Azerbaijan); Taguchi, Yukihiro; Ichikawa, Kouichi [Department of Mathematical Sciences, Graduate School of Engineering, Osaka Prefecture University, Sakai 599-8531 (Japan)

    2008-12-31

    Temperature-dependent change in core-level electronic structures of the layered semiconductor-ferroelectric TlInS{sub 2} with incommensurate phase has been investigated by means of X-ray photoemission spectroscopy. The temperature dependence of the relative peak position for each core level (Tl 4f, In 3d and S 2p) is found to differ very much in the regions bordering each other at the normal-incommensurate phase transition point of 218 K. The obtained data suggest that the charge distribution in TlInS{sub 2} dramatically changes upon passing from the normal phase (T > 218 K) to the spatially modulated incommensurate phase (T < 218 K)

  2. 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}.

  3. Photoemission studies of wurtzite zinc oxide.

    Science.gov (United States)

    Powell, R. A.; Spicer, W. E.; Mcmenamin, J. C.

    1972-01-01

    The electronic structure of wurtzite zinc oxide, investigated over the widest possible photon energy range by means of photoemission techniques, is described. Of particular interest among the results of the photoemission study are the location of the Zn 3rd core states, the width of the upper valence bands, and structure in the conduction-band and valence-band density of states.

  4. 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

  5. Photoemission studies of high-temperature superconductivity

    Energy Technology Data Exchange (ETDEWEB)

    Margaritondo, G. (Inst. de Physique Appliquee, Ecole Polytechnique Federale de Lausanne, CH-1015 Lausanne (CH))

    1990-11-01

    Photoemission spectroscopy has recently emerged as one of the leading techniques in the study of high-temperature superconductors. Relevant successes include the direct detection of the superconductivity gap, tests for departure from Fermi-liquid behavior, and many interface chemical studies with technological interest. The authors present a review of the fundamental and applied aspects of this technique.

  6. Photoemission study of the ferromagnetic Kondo system CeRh3B2

    Science.gov (United States)

    Fujimori, A.; Takahashi, T.; Okabe, A.; Kasaya, M.; Kasuya, T.

    1990-04-01

    We have studied the electronic structure of CeRh3B2, which has an anomalously high ferromagnetic ordering temperature, by photoemission and Auger-electron spectroscopy. The Ce 4f occupancy nf~=0.85 evaluated from the Ce 3d core-level photoemission spectrum indicates a moderately strong valence fluctuation in the Kondo regime. Rh d-derived valence-band photoemission spectra are found to be in good agreement with the results of band-structure calculations when a strong energy dependence of the hole lifetime is taken into account. This observation and the deviation of the Rh M4,5VV Auger spectrum from the self-convolution of the Rh d partial density of states provide evidence for electron correlation within the Rh d band of order of U=1-2 eV. We discuss a possible effect of the latter electron correlation on the ferromagnetic instability of this compound.

  7. 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.

  8. Oxidation of Mg adsorbed on Ru(001): A photoemission study

    Energy Technology Data Exchange (ETDEWEB)

    Malik, I.J.; Hrbek, J. (Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973 (United States)); Shek, M. (National Synchrotron Light Source, Brookhaven National Laboratory, Upton, New York 11973 (United States)); Bzowski, A.; Kristof, P.; Sham, T.K. (Department of Chemistry, University of Western Ontario, London, Ontario NA6 5B7 (Canada))

    1992-07-01

    We studied the interaction of oxygen with Mg overlayers adsorbed on Ru(001). Soft x-ray synchrotron radiation was used to explore photoemission from the valence band, the O 2{ital p}, O 2{ital s}, and Mg 2{ital p} levels, as well as intra- and interatomic Auger processes. The photoemission results are complemented by thermal desorption data. The O/Mg/Ru system shows photoemission features characteristic of molecular orbitals of a dioxygen species.

  9. Layer resolved spectroscopy of potassium adsorbed on a Ru(001) surface: Photoemission and thermal desorption study

    Energy Technology Data Exchange (ETDEWEB)

    Hrbek, J. (Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973 (US)); Shek, M. (Department of Physics, Hunter College of CUNY, New York, New York 10021); Sham, T.K. (Department of Chemistry, University of Western Ontario, London, Ontario N6A 5B7, Canada); Xu, G. (Chemistry Department, Brookhaven National Laboratory, Upton, New York, 11973)

    1989-11-01

    High-resolution photoemission spectroscopy and thermal desorption were used to study the coverage dependence of the K 3{ital p}{sub 3/2,1/2} core levels of K overlayers on Ru(001). Three doublets were observed to evolve sequentially and to shift to higher binding energy with increasing coverage of potassium. The doublets were assigned to photoemission from the interface (first layer), bulk'' (second layer), and surface (third layer). Spin--orbit splitting was observed for the first time in the condensed potassium phase by photoemission. The results are discussed in terms of the equivalent core approximation using a Born--Haber cycle. In the thermal desorption data three coverage regimes can be distinguished: a first layer desorbing with first-order kinetics and a strongly decreasing heat of adsorption ({ital E}{sub {ital A}} =2.80--0.87 eV); a second layer with zero-order desorption kinetics and {ital E}{sub {ital A}} =0.78 eV; a third layer and multilayers with the same kinetic order but with {ital E}{sub {ital A}} increasing from 0.78 to 0.93 eV, which is close to the heat of sublimation of potassium.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1997-04-01

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

  11. Time-resolved soft X-ray core-level photoemission spectroscopy at 880 °C using the pulsed laser and synchrotron radiation and the pulse heating current

    Science.gov (United States)

    Abukawa, T.; Yamamoto, S.; Yukawa, R.; Kanzaki, S.; Mukojima, K.; Matsuda, I.

    2017-02-01

    We developed a time-resolved photoemission spectroscopy system for tracking the temporal variation in an electronic state of a heated sample. Our pump-probe method used laser and synchrotron radiation pulses on a silicon surface that was heated by a synchronized pulse current that did not interfere with the measurements. The transient surface photovoltage effect on the Si 2p core spectra was measured from room temperature to 880 °C and was found to be consistent with the thermal carrier distributions in silicon crystals at the corresponding temperatures. This versatile technique may have applications studying molecular dynamics on high temperature surfaces such as in catalytic reactions.

  12. Inverse photoemission studies of C-60 on Au(110)

    NARCIS (Netherlands)

    Pedio, M.; Grilli, M.L.; Ottaviani, C.; Capozi, M.; Quaresima, C.; Perfetti, P.; Thiry, P.A.; Caudano, R.; Rudolf, P.

    1995-01-01

    The unoccupied states of C60 have been studied for single monolayer and multilayer coverages on Au(110) with Inverse Photoemission Spectroscopy (IPES). In agreement with previous results on C60 on gold, we find that only the first monolayer, which is chemisorbed, shows a different spectrum compared

  13. Magnetic circular dichroism study of ultrathin Ni films by threshold photoemission and angle resolved photoemission spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Nakagawa, Takeshi, E-mail: nakagawa@ims.ac.j [Institute for Molecular Science, Nishigonaka 38, Myodaiji, Okazaki (Japan); Yamamoto, Isamu; Takagi, Yasumasa [Institute for Molecular Science, Nishigonaka 38, Myodaiji, Okazaki (Japan); Yokoyama, Toshihiko, E-mail: yokoyama@ims.ac.j [Institute for Molecular Science, Nishigonaka 38, Myodaiji, Okazaki (Japan)

    2010-08-15

    Threshold photoemission magnetic circular dichroism (MCD) for 12 monolayer (ML) Ni thin films grown on Cu(0 0 1) was measured with a total electron yield method. The obtained MCD asymmetry using the total electron yield method reaches as much as 10% near the photoemission threshold. On the other hand, the MCD asymmetry in angle resolved photoemission spectra with the photon energy of 5.28 eV was also investigated for Cs/Ni(12 ML)/Cu(0 0 1) and was found to give a similar MCD asymmetry. The high MCD asymmetry in the total electron yield can be interpreted by the argument that the angle and energy selection is spontaneously achieved in the total electron yield near the photoemission threshold for low photon energy excitation.

  14. 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.

  15. 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.

  16. Photoemission study of the adsorption of benzotriazole on copper

    Energy Technology Data Exchange (ETDEWEB)

    Fang, B.S.

    1985-01-01

    A photoemission study was performed on the chemisorption of benzotriazole (BTA) on polycrystalline copper (clean and oxidized) surfaces to understand the corrosion inhibition mechanism. The energy distribution curves indicate benzotriazole bonding to copper through nitrogen lone pair orbitals. They also disagree with the models which suggest that the benzotriazole molecular plane is oriented parallel to the copper surface by showing a lack of ..pi..-d interaction. The observed chemisorption of benzotriazole on atomically clean copper surfaces at room temperature suggests that an oxide layer is not necessary for the adsorption of benzotriazole. No structural difference was observed in the photoemission studies on BTA-clean copper and BTA-cuprous oxide surface film. This result demonstrates the major role of the copper atom upon benzotriazole adsorption. A new model of the CuBTA chemisorbed structure is presented. The Cu-BTA polymer is formed by strong charge-transfer interactions between benzotriazole molecules instead of by BTA-Cu-BTA connections. It successfully interprets the experimental results from solubility and tarnish resistance tests on adsorbed films on copper surfaces. It also gives a reasonable explanation for the different inhibition coefficients among BTA-treated copper single crystal surfaces. Mechanisms are suggested for the benzotriazole inhibition mechanisms.

  17. 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.

  18. a Photoemission Study of the Adsorption of Benzotriazole on Copper.

    Science.gov (United States)

    Fang, Bo-Shung

    1985-12-01

    A photoemission study was performed on the chemisorption of benzotriazole (BTA) on polycrystalline copper (clean and oxidized) surfaces to understand the corrosion inhibition mechanism. The energy distribution curves indicate benzotriazole bonding to copper through nitrogen lone pair orbitals. They also disagree with the models which suggest that the benzotriazole molecular plane is oriented parallel to the copper surface by showing a lack of (pi)-d interaction. The observed chemisorption of benzotriazole on atomi- cally clean copper surfaces at room temperature suggests that an oxide layer is not necessary for the adsorption of benzotriazole. No structural difference was observed in the photoemission studies on BTA-clean copper and BTA-cuprous oxide surface film. This results demonstrates the major role of the copper atom upon benzotriazole adsorption. A new model of the CuBTA chemisorbed structure is presented. The Cu-BTA polymer is formed by strong charge -transfer interac- tions between benzotriazole molecules instead of by BTA-Cu-BTA connections. It successfully interprets the experimental results from solubility and tarnish resistance tests on adsorbed films on copper surfaces. It also gives a reasonable explanation for the different inhibition coefficients among BTA-treated copper single crystal surfaces. This study leads to an understanding of the benzotriazole inhi- bition mechanism: (1) All the copper atoms can be bound to BTA nitrogen atoms and the absence of active surface sites prevents attack by corrosive ions. (2) The BTA molecule stands vertically, or nearly so, to the copper surface, but still allows the formation of a compact protective surface film. (3) The strong infinite polymer. chains stabilize the protective film and strengthen its inhibition capability. ('1)DOE Report IS-T-1196. This work was performed under contract No. W-7405-Eng-82 with the U.S. Department of Energy.

  19. Photoemission Electron Microscopy as a Tool for Studying Steel Grains

    Science.gov (United States)

    Roese, Peter; Keutner, Christoph; Berges, Ulf; Espeter, Philipp; Westphal, Carsten

    2017-03-01

    Key properties of steel like stability, weldability, or ability for absorbing deformation energy are defined by their grain structure. The knowledge about their micrometer and submicrometer structure is of particular interest for tailor-cut macroscopic steel properties. We report on photoemission electron microscopy studies which in principle yield a higher magnification than comparable optical techniques. A flat surface without any topographic features was obtained by applying a non-etching preparation procedure. PEEM images showed very tiny phase islands embedded within a steel phase matrix. Furthermore, we developed an analysis procedure for PEEM images for dual-phase steels. As a result, it is possible to identify the individual work functions of different steel phases at the surface.

  20. Photoemission Electron Microscopy as a Tool for Studying Steel Grains

    Science.gov (United States)

    Roese, Peter; Keutner, Christoph; Berges, Ulf; Espeter, Philipp; Westphal, Carsten

    2017-01-01

    Key properties of steel like stability, weldability, or ability for absorbing deformation energy are defined by their grain structure. The knowledge about their micrometer and submicrometer structure is of particular interest for tailor-cut macroscopic steel properties. We report on photoemission electron microscopy studies which in principle yield a higher magnification than comparable optical techniques. A flat surface without any topographic features was obtained by applying a non-etching preparation procedure. PEEM images showed very tiny phase islands embedded within a steel phase matrix. Furthermore, we developed an analysis procedure for PEEM images for dual-phase steels. As a result, it is possible to identify the individual work functions of different steel phases at the surface.

  1. Preparation of solid-state samples of a transition metal coordination compound for synchrotron radiation photoemission studies

    CERN Document Server

    Crotti, C; Celestino, T; Fontana, S

    2003-01-01

    The aim of this research was to identify a sample preparation method suitable for the study of transition metal complexes by photoemission spectroscopy with synchrotron radiation as the X-ray source, even in the case where the compound is not evaporable. Solid-phase samples of W(CO) sub 4 (dppe) [dppe=1,2-bis(diphenylphosphino)ethane] were prepared according to different methods and their synchrotron radiation XPS spectra measured. The spectra acquired from samples prepared by spin coating show core level peaks only slightly broader than the spectrum recorded from UHV evaporated samples. Moreover, for these samples the reproducibility of the binding energy values is excellent. The dependence of the spin coating technique on parameters such as solvent and solution concentration, spinning speed and support material was studied. The same preparation method also allowed the acquisition of valence band spectra, the main peaks of which were clearly resolved. The results suggest that use of the spin coating techniqu...

  2. Core-level photoabsorption study of defects and metastable bonding configurations in boron nitride

    Energy Technology Data Exchange (ETDEWEB)

    Jimenez, I.; Jankowski, A.F.; Terminello, L.J. [Lawrence Berkeley National Lab., CA (United States)] [and others

    1997-04-01

    Boron nitride is an interesting material for technological applications and for fundamental solid state physics investigations. It is a compound isoelectronic with carbon and, like carbon can possess sp{sup 2} and sp{sup 3} bonded phases resembling graphite and diamond. BN crystallizes in the sp{sup 2}-bonded hexagonal (h-BN), rhombohedral (r-BN) and turbostratic phases, and in the sp{sup 3}-bonded cubic (c-BN) and wurtzite (w-BN) phases. A new family of materials is obtained when replacing C-C pairs in graphite with isoelectronic B-N pairs, resulting in C{sub 2}BN compounds. Regarding other boron compounds, BN is exceptional in the sense that it has standard two-center bonds with conventional coordination numbers, while other boron compounds (e.g. B{sub 4}C) are based on the boron icosahedron unit with three-center bonds and high coordination numbers. The existence of several allotropic forms and fullerene-like structures for BN suggests a rich variety of local bonding and poses the questions of how this affects the local electronic structure and how the material accommodates the stress induced in the transition regions between different phases. One would expect point defects to play a crucial role in stress accommodation, but these must also have a strong influence in the electronic structure, since the B-N bond is polar and a point defect will thus be a charged structure. The study of point defects in relationship to the electronic structure is of fundamental interest in these materials. Recently, the authors have shown that Near-Edge X-ray Absorption Fine Structure (NEXAFS) is sensitive to point defects in h-BN, and to the formation of metastable phases even in amorphous materials. This is significant since other phase identification techniques like vibrational spectroscopies or x-ray diffraction yield ambiguous results for nanocrystalline and amorphous samples. Serendipitously, NEXAFS also combines chemical selectivity with point defect sensitivity.

  3. 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.

  4. Electronic properties of the interface between p-CuI and anatase-phase n-TiO2 single crystal and nanoparticulate surfaces: a photoemission study.

    Science.gov (United States)

    Kumarasinghe, A R; Flavell, W R; Thomas, A G; Mallick, A K; Tsoutsou, D; Chatwin, C; Rayner, S; Kirkham, P; Warren, S; Patel, S; Christian, P; O'Brien, P; Grätzel, M; Hengerer, R

    2007-09-21

    We present a study of the growth of the p-type inorganic semiconductor CuI on n-type TiO2 anatase single crystal (101) surfaces and on nanoparticulate anatase surfaces using synchrotron radiation photoemission spectroscopy. Core level photoemission data obtained using synchrotron radiation reveal that both the substrate (TiO2) and the overlayer (CuI) core levels shift to a lower binding energy to different degrees following the growth of CuI on TiO2. Valence band photoemission data show that the valence band maximum of the clean substrate differs from that of the dosed surface which may be interpreted qualitatively as due to the introduction of a new density of states within the band gap of TiO2 as a result of the growth of CuI. The valence band offset for the heterojunction n-TiO2p-CuI has been measured using photoemission for both nanoparticulate and single crystal TiO2 surfaces, and the band energy alignment for these heterojunction interfaces is presented. With the information obtained here, it is suggested that the interface between p-CuI and single crystal anatase-phase n-TiO2 is a type-II heterojunction interface, with significant band bending. The measured total band bending matches the work function change at the interface, i.e., there is no interface dipole. In the case of the nanoparticulate interface, an interface dipole is found, but band bending within the anatase nanoparticles remains quite significant. We show that the corresponding depletion layer may be accommodated within the dimension of the nanoparticles. The results are discussed in the context of the functional properties of dye-sensitized solid state solar cells.

  5. 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

  6. Evidence for the photoemission nature of Gd 4f resonant photoemission

    Energy Technology Data Exchange (ETDEWEB)

    Mishra, S.R.; Gammon, W.J. [Virginia Commonwealth Univ., Richmond, VA (United States). Dept. of Physics; Cummins, T.R.; Waddill, G.D. [Univ. of Missouri, Rolla, MO (United States). Dept. of Physics; Laan, G. van der [Daresbury Lab., Warrington (United Kingdom); Goodman, K.W.; Tobin, J.G. [Lawrence Livermore National Lab., CA (United States)

    1998-12-31

    The constructive interference between direct and indirect channels above the absorption threshold of a core level leads to a massive increase in the emission cross section leading to a phenomenon called resonant photoemission. Using novel magnetic linear dichroism in angular distribution photoelectron spectroscopy experiment, the authors have tried to understand the nature of the resonant photoemission process in Gd metal. The presence of dichroism in Gd 4f photoemission intensity at a photo energy corresponding to resonant photoemission clearly demonstrates the photoemission-like nature of the resonant photoemission process.

  7. 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.

  8. 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.

  9. 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

  10. 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 (Bi1.35Pb0.85)(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 di erences 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 consistent with

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

    Science.gov (United States)

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

    2000-03-01

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

  12. Synchrotron radiation photoemission study of Pb{sub 1−x}Cd{sub x}Te crystal with local structure

    Energy Technology Data Exchange (ETDEWEB)

    Orlowski, B.A.; Szczerbakow, A.; Dziawa, P.; Gas, K.; Reszka, A.; Kowalski, B.J. [Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw (Poland); Thiess, S.; Drube, W. [Hamburger Synchrotronstrahlungslabor HASYLAB am DESY, Notkestr. 85, D-22603 Hamburg (Germany)

    2015-12-01

    The paper presents photoemission study of core level binding energy shifts caused by local crystalline structure collapse in cubic Pb{sub 1−x}Cd{sub x}Te crystal. Photoemission spectra of two kinds of semiconductor samples are compared. The first one is ternary crystal of Pb{sub 0.94}Cd{sub 0.06}Te with the frozen rock salt structure where the crystalline local structure collapse is expected due to the difference of ion radii of Cd and Pb cations. The second sample was the CdTe(22 nm)/PbTe(6 nm)/CdTe(4 μm)/GaAs(1 1 1)B nanostructure grown by molecular beam epitaxy (MBE) method, where crystalline local structure is not expected to be created. The photoemission spectra show that for the crystal with local structure the electron binding energies of cations are higher (e.g. +0.2 eV) whereas for anions they are lower (e.g. −0.08 eV) than in the multilayer structure. A model is proposed to explain obtained results by the local crystalline structure collapse in Pb{sub 0.94}Cd{sub 0.06}Te crystal.

  13. Surface structure and photoemission studies of nanocrystalline TiO{sub 2} layer/ITO coated glass interface

    Energy Technology Data Exchange (ETDEWEB)

    Taleatu, Bidini Alade, E-mail: bdntaleatu@gmail.com [Department of Physics and Engineering Physics, Obafemi Awolowo University, Ile-Ife (Nigeria); School of Chemistry and Physics, University of KwaZulu-Natal, P Bag X01, Scottsville, 3209 Pietermaritzburg (South Africa); Omotoso, Ezekiel [Department of Physics and Engineering Physics, Obafemi Awolowo University, Ile-Ife (Nigeria); Mola, Genene Tessema [School of Chemistry and Physics, University of KwaZulu-Natal, P Bag X01, Scottsville, 3209 Pietermaritzburg (South Africa)

    2016-02-15

    Highlights: • Titanium oxide thin film was grown on ITO glass substrate by electrodeposition technique. • The samples were charaterized and analysed by some surface studying facilities. • Photoemission studies were carried out befor and after annealing to understand possible interaction between the TiO{sub 2} layer and substrate as a result of postdeposition heat treatment. - Abstract: Room temperature growth of nanocrystalline TiO{sub 2} thin film was carried out by two-electrode cell. The film was characterized by surface probing techniques. Morphological studies revealed that film's grains are evenly distributed across substrate surface. Average height of grains distribution is below 64 nm. Post-deposition annealing aided film's particles’ orientation in a structure that resulted in compact layer. Average crystallite size was estimated as 19.5 nm. Quality and chemical states of film composition were observed by core level photoemission studies. From XPS studies, small shift (∼0.11 eV) observed in binding energy position of Ti 2p{sub 3/2} corroborated oxidation states of titanium species found in TiO{sub 2} structure. Peak broadening and formation of In−O−Sn linkage at oxygen valence band indicated interactions between substrate's atoms due to annealing. Apart from substrate's atoms interaction, chemical state of Ti profile remained stable implying no major chemical interaction between ITO atoms and film components. This study demonstrated TiO{sub 2} as a recipe for stable barrier layer capable of hindering charge trapping in nanostructured photonic devices.

  14. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-09-14

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

  16. Hybridization and crystal-field effects in Kondo insulators studied by means of core-level spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Strigari, Fabio

    2015-04-13

    and even for symmetries lower than tetragonal. In addition to that, HAXPES measurements on the CeM{sub 2}Al{sub 10} series are presented. A common technique for studying hybridization effects in rare earths, and their electronic structure in general, is photoelectron spectroscopy in the soft X-ray range (hv ≤ 1.5 keV). However, in this energy region surface effects are known to matter so that the picture about the hybridization interaction might be distorted with respect to the bulk. The use of hard X-rays (hν=5-10 keV) guarantees a sufficiently large probing depth for obtaining information about the actual bulk electronic structure. In a detailed quantitative analysis of HAXPES 3d core level spectra - using a combination of full multiplet calculations and a configuration interaction model (fm-CI model) - the hybridization strength can be quantified. The XAS results show that the CEF ground states of CeRu{sub 2}Al{sub 10} and CeOs{sub 2}Al are very similar, while it is clearly different for the non-ordering system CeFe{sub 2}Al{sub 10}. The CEF description nicely explains the magnetic anisotropy observed in susceptibility data and to a large extent the small ordered moments along the c axis. We provide a reliable quantitative description of the CEF ground state of the CeM{sub 2}Al{sub 10} compounds. Furthermore, the analysis of the HAXPES data in the fm-CI model allows to quantify the intermediate 4f valence and establishes that the exchange interaction increases within the series from Ru to Os to Fe. A substantial amount of Kondo screening is shown to be present even in the magnetically ordered Ru and Os compounds. The polarized XAS study on CeNiSn demonstrates that the monoclinic CEF is well described in a trigonal approximation, and the determined 4f ground-state wave function is consistent with results from inelastic neutron scattering for Cu-doped CeNiSn. Moreover, the systematic investigation of the CeRh{sub 1-x}Ir{sub x}In{sub 5} substitution series by means

  17. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Olson, C.G.; Liu, R.; Lynch, D.W. (Ames Lab. and Dept. of Physics, Iowa State Univ. (USA)); Veal, B.W.; Chang, Y.C.; Jiang, P.Z.; Liu, J.Z.; Paulikas, A.P. (Argonne National Lab., IL (USA)); Arko, A.J.; List, R.S. (Los Alamos National Lab., NM (USA))

    1989-12-01

    Recent photoemission studies of Y 123 and Bi 2212 performed with high energy and angular resolution have provided 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. (orig.).

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

    Energy Technology Data Exchange (ETDEWEB)

    Olson, C.G.; Liu, R.; Lynch, D.W.; Veal, B.W.; Chang, Y.C.; Jiang, P.Z.; Liu, J.Z.; Paulikas, A.P.; Arko, A.J.; List, R.S. (Ames Lab., IA (USA); Argonne National Lab., IL (USA); Los Alamos National Lab., NM (USA))

    1989-08-01

    Recent photoemission studies of Y 123 and Bi 2212 performed with high energy and angular resolution have provided 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 refs., 4 figs.

  20. 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...

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2011-10-15

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

  2. GaAs clean up studied with synchrotron radiation photoemission

    Science.gov (United States)

    Tallarida, Massimo; Adelmann, Christoph; Delabie, Annelies; van Elshocht, Sven; Caymax, Matty; Schmeisser, Dieter

    2012-12-01

    In this contribution we describe the chemical changes at the surface of GaAs upon adsorption of tri-methyl-aluminum (TMA). TMA is used to grow Al2O3 with atomic layer deposition (ALD) usually using H2O as oxygen source. Recently, it was pointed out that the adsorption of TMA on various III-V surfaces reduces the native oxide, allowing the growth of an abrupt III-V/High-K interface with reduced density of defects. Synchrotron radiation photoemission spectroscopy (SR-PES) is a powerful method to characterize surfaces and interfaces of many materials, as it is capable to determine their chemical composition as well as the electronic properties. We performed in-situ SR-PES measurements after exposing a GaAs surface to TMA pulses at about 250°C. Upon using the possibility of tuning the incident photon energy we compared the Ga3d spectra at 41 eV, 71 eV, 91 eV and 121 eV, as well as the As3d at 71 eV and 91 eV. Finally, we show that using SR-PES allows a further understanding of the surface composition, which is usually not accessible with other techniques.

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

    Energy Technology Data Exchange (ETDEWEB)

    Park, Jongik [Iowa State Univ., Ames, IA (United States)

    2004-01-01

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

  4. Photoemission study of the initial stage of Er/Si(100) interface formation

    CERN Document Server

    Chen Gang; Li Zhe Shen; Wang Xun

    2002-01-01

    The initial stage of Er/Si(100) interface formation has been investigated by using synchrotron radiation photoelectron spectroscopy combined with low-energy electron diffraction. Both the valence band and the core level peaks of the Si photoemission spectra shift rigidly with increasing Er coverage in the submonolayer region. Upon depositing 0.6 monolayers of Er on the Si(100) surface at room temperature, the surface Fermi level is ultimately pinned at 0.29 eV above its initial value, which is equivalent to a Schottky barrier height of 0.67 eV. No evidence is found for the formation of Er silicides at the as-deposited surfaces. Annealing of the Er-covered Si(100) surfaces at 600 deg. C results in the appearance of a new peak located 1.2 eV below the Si 2p peak, indicating the presence of some sort of Er silicide. Meanwhile, the Er 4f spectrum measured for samples upon annealing exhibits a well-resolved fine structure, implying that only monospecies of Er silicide may exist on the surface.

  5. Photoemission study of CuO and Cu sub 2 O single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Shen, Z. (Stanford Electronics Laboratory, Stanford University, Stanford, CA (USA)); List, R.S. (Los Alamos National Laboratory, Los Alamos, NM (USA)); Dessau, D.S. (Stanford Electronics Laboratory, Stanford University, Stanford, CA (USA)); Parmigiani, F. (IBM Almaden Research Center, San Jose, CA (USA)); Arko, A.J.; Bartlett, R. (Los Alamos National Laboratory, Los Alamos, NM (USA)); Wells, B.O.; Lindau, I.; Spicer, W.E. (Stanford Electronics Laboratory, Stanford University, Stanford, CA (USA))

    1990-11-01

    We present results of resonant-photoemission and high-resolution x-ray-photoemission-spectroscopy (XPS) studies on single-crystalline CuO, which confirms most of the earlier data obtained from polycrystalline samples. However, some minor differences with earlier results were also observed, which are concentrated on a mainly oxygen-related feature. The important first ionization state is much better resolved in our high-resolution XPS data, and is found to have both copper and oxygen orbital character. This is consistent (though not a proof) with the theoretical prediction that the first ionization state is a {sup 1}{ital A}{sub 1{ital g}} singlet with holes on both oxygen and copper sites. The 16-eV satellite is found to show a Cu antiresonance, and is assigned to a {sup 1}{ital A}{sub 1{ital g}} singlet with both holes on the copper sites.

  6. 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-...

  7. The surface core level shift for lithium at the surface of lithium borate

    Energy Technology Data Exchange (ETDEWEB)

    Wooten, David [Air Force Institute of Technology, 2950 Hobson Way, Wright Patterson Air Force Base, OH 45433-7765 (United States); Ketsman, I.; Xiao, Jie [Department of Physics and Astronomy and the Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, P.O. Box 880111, Lincoln, NE 68588-0111 (United States); Losovyj, Ya.B. [Department of Physics and Astronomy and the Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, P.O. Box 880111, Lincoln, NE 68588-0111 (United States); J. Bennett Johnston Sr. Center for Advanced Microstructures and Devices, Louisiana State University, 6980 Jefferson Highway, Baton Rouge, LA 70806 (United States); Petrosky, J.; McClory, J. [Air Force Institute of Technology, 2950 Hobson Way, Wright Patterson Air Force Base, OH 45433-7765 (United States); Burak, Ya.V.; Adamiv, V.T. [Institute of Physical Optics, Dragomanov 23, Lviv 79005 (Ukraine); Dowben, P.A., E-mail: pdowben@unl.ed [Department of Physics and Astronomy and the Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, P.O. Box 880111, Lincoln, NE 68588-0111 (United States)

    2010-01-01

    The shallow Li 1s core level exhibits a surface-to-bulk core level shift for the stoichiometric Li{sub 2}B{sub 4}O{sub 7}(1 1 0) surface. Angle-resolved photoemission spectroscopy was used to indentify Li 1s bulk and surface core level components at binding energies -56.5+-0.4 and -53.7+-0.5 eV, respectively. We find photoemission evidence for surface states of Li{sub 2}B{sub 4}O{sub 7}(1 1 0) that exist in the gap of the projected bulk density of states. The existence of surface states is consistent with the large surface-to-bulk core level shift for the Li 1s core.

  8. 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.

  9. 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)

  10. Photoemission Studies on N-Substituted Dithienylated Phenothiazines.

    Science.gov (United States)

    Fingerle, Mathias; Hemgesberg, Maximilian; Schmitt, Yvonne; Lach, Stefan; Gerhards, Markus; Thiel, Werner R; Ziegler, Christiane

    2015-06-22

    Dithienylated phenothiazines (DTPTs) with different functional groups attached to the central nitrogen atom are presented as a class of versatile metal-free chromophores for the design of dye-sensitized solar cells (DSSCs) and organic light-emitting diodes (OLEDs). The electronic characteristics of spin-coated thin films on polycrystalline gold were studied using photoelectron spectroscopy assisted by theoretical calculations, scanning force microscopy, and UV/Vis spectroscopy. Complementary fluorescence spectra show light emission in the blue region (465 nm). The absorption properties and good hole-transporting abilities make DTPTs feasible hole-transporting materials (HTM) and metal-free chromophores in UV-sensitive solar cell designs.

  11. Photoemission study of the adsorption of benzotriazole on copper

    Energy Technology Data Exchange (ETDEWEB)

    Fang, B.S.

    1986-01-01

    A new model of the CuBTA chemisorbed structure is presented. The Cu-BTA polymer is formed by strong charge-transfer interactions between benzotriazole molecules instead of by BTA-Cu-BTA connections. It successfully interprets the experimental results from solubility and tarnish resistance tests on adsorbed films on copper surfaces. It also gives a reasonable explanation for the different inhibition coefficients among BTA-treated copper single crystal surfaces. This study leads to an understanding of the benzotriazole inhibition mechanism: (1) All the copper atoms can be bound to BTA nitrogen atoms and the absence of active surface sites prevents attack by corrosive ions. (2) The BTA molecule stands vertically, or nearly so, to the copper surface, but still allows the formation of a compact protective surface film. (3) The strong infinite polymer chains stabilize the protective film and strengthen its inhibition capability. 92 refs., 26 figs., 10 tabs.

  12. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-09-15

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

  14. 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.

  15. Zen and the art of dichroic photoemission

    Energy Technology Data Exchange (ETDEWEB)

    Laan, Gerrit van der, E-mail: gerrit.vanderlaan@diamond.ac.uk

    2015-04-15

    Highlights: • General theory for angle and spin dependence of dichroic core-level photoemission. • Fundamental spectra give correlation between spin and orbital moments. • Interference term between emission channels results in MLDAD and CDAD. • Core-hole polarization is probed by resonant photoemission. - Abstract: The discovery of magnetic dichroism in photoemission is celebrating its 25th anniversary this year. Here a review of the underlying general theory for the angular and spin dependence of dichroic core-level photoemission is presented using both a single-particle model and a many-body approach. The established methods of angular momentum coupling offer an elegant and powerful way to analyse the magnetic dichroism and spin polarization in photoemission from core and localized valence levels. In the presence of core-valence interactions one can distinguish different fundamental spectra, which via sum rules are related to physical properties described by coupled tensor operators for spin and orbital moments. By separating the angular dependence from the physical information, different geometries can be distinguished to measure the magnetic circular dichroism (MCD), linear dichroism (LD), circular dichroism in the angular dependence (CDAD), and magnetic linear dichroism in the angular dependence (MLDAD). Various ways to probe the core-hole polarization are discussed, such as using the angular dependence, moment analysis of the spectral distribution, and resonant photoemission decay.

  16. 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

  17. Atom-Specific Identification of Adsorbed Chiral Molecules by Photoemission

    Science.gov (United States)

    Kim, J. W.; Carbone, M.; Dil, J. H.; Tallarida, M.; Flammini, R.; Casaletto, M. P.; Horn, K.; Piancastelli, M. N.

    2005-09-01

    The study of chiral adsorbed molecules is important for an analysis of enantioselectivity in heterogeneous catalysis. Here we show that such molecules can be identified through circular dichroism in core-level photoemission arising from the chiral carbon atoms in stereoisomers of 2,3-butanediol molecules adsorbed on Si(100), using circularly polarized x rays. The asymmetry in the carbon 1s intensity excited by right and left circularly polarized light is readily observed, and changes sign with the helicity of the radiation or handedness of the enantiomers; it is absent in the achiral form of the molecule. This observation demonstrates the possibility of determining molecular chirality in the adsorbed phase.

  18. Core-level binding-energy shifts due to end effects in polymers: A Hartree-Fock Green's-function study

    Science.gov (United States)

    Seel, M.; Ladik, J.

    1985-10-01

    Hartree-Fock Green's-function studies of end effects on the core-level structure of metallic and insulating quasi-one-dimensional model polymers reveal additional core peaks outside the bulk bands. In the metallic case, shifts to both lower (~-150 meV) and higher (~+50 meV) binding energies are observed, whereas in the insulating case, split-off peaks occur only at the lower-binding-energy side (~-150 meV). It is shown that a positive or negative net valence population alone does not determine the direction of the shift. The binding-energy changes are determined by a detailed balance between the energy loss due to a decrease in the electron-nuclear attraction and the energy gain due to a decrease in the electron-electron repulsion experienced by the core electrons of the end atoms. This can probably also explain why for some metal surfaces, shifts towards lower, and for others, shifts towards higher, binding energies are found. In the valence region of the investigated lithium chains, the ends do not produce localized end states.

  19. The Evolution of Ga and As Core Levels in the Formation of Fe/GaAs(001): A High Resolution Soft X-ray Photoelectron Spectroscopic Study

    Energy Technology Data Exchange (ETDEWEB)

    Thompson, J W; Neal, J R; Shen, T H; Morton, S A; Tobin, J G; Waddill, G D; Matthew, J D; Greig, D; Hopkinson, M

    2006-12-08

    A high resolution soft x-ray photoelectron spectroscopic study of Ga and As 3d core levels has been conducted for Fe/GaAs (001) as a function of Fe thickness. This work has provided unambiguous evidence of substrate disrupting chemical reactions induced by the Fe overlayer--a quantitative analysis of the acquired spectra indicates significantly differing behavior of Ga and As during Fe growth, and our observations have been compared with existing theoretical models. Our results demonstrate that the outdiffusing Ga and As remain largely confined to the interface region, forming a thin intermixed layer. Whereas at low coverages Fe has little influence on the underlying GaAs substrate, the onset of substrate disruption when the Fe thickness reaches 3.5 {angstrom} results in major changes in the energy distribution curves (EDCs) of both As and Ga 3d cores. Our quantitative analysis suggests the presence of two new As environments of metallic character; one bound to the interfacial region and another which, as confirmed by in-situ oxidation experiments, surface segregates and persists over a wide range of overlayer thickness. Analysis of the corresponding Ga 3d EDCs found not two, but three new environments--also metallic in nature. Two of the three are interface-resident whereas the third undergoes outdiffusion at low Fe coverages. Based on the variations of the integrated intensities of each component, we present a schematic of the proposed chemical make-up of the Fe/GaAs (001) system.

  20. The evolution of Ga and As core levels in the formation of Fe/GaAs (001):A high resolution soft x-ray photoelectron spectroscopic study

    Energy Technology Data Exchange (ETDEWEB)

    Thompson, Jamie; Neal, James; Shen, Tiehan; Morton, Simon; Tobin, James; Waddill, George Dan; Matthew, Jim; Greig, Denis; Hopkinson, Mark

    2008-07-14

    A high resolution soft x-ray photoelectron spectroscopic study of Ga and As 3d core levels has been conducted for Fe/GaAs (001) as a function of Fe thickness. This work has provided unambiguous evidence of substrate disrupting chemical reactions induced by the Fe overlayer--a quantitative analysis of the acquired spectra indicates significantly differing behavior of Ga and As during Fe growth, and our observations have been compared with existing theoretical models. Our results demonstrate that the outdiffusing Ga and As remain largely confined to the interface region, forming a thin intermixed layer. Whereas at low coverages Fe has little influence on the underlying GaAs substrate, the onset of substrate disruption when the Fe thickness reaches 3.5 Angstrom results in major changes in the energy distribution curves (EDCs) of both As and Ga 3d cores. Our quantitative analysis suggests the presence of two additional As environments of metallic character: one bound to the interfacial region and another which, as confirmed by in situ oxidation experiments, surface segregates and persists over a wide range of overlayer thickness. Analysis of the corresponding Ga 3d EDCs found not two, but three additional environments--also metallic in nature. Two of the three are interface resident whereas the third undergoes outdiffusion at low Fe coverages. Based on the variations of the integrated intensities of each component, we present a schematic of the proposed chemical makeup of the Fe/GaAs (001) system.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-09-14

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

  2. Study of silicon/oxides interfaces by means of Si2p resonant photoemission

    Energy Technology Data Exchange (ETDEWEB)

    Tallarida, Massimo [BTU-Cottbus, Konrad-Wachsmann-Allee 17, 03046, Cottbus (Germany)], E-mail: tallamas@tu-cottbus.de; Schmeisser, Dieter [BTU-Cottbus, Konrad-Wachsmann-Allee 17, 03046, Cottbus (Germany)

    2008-11-03

    In this paper we show results from resonant photoemission experiments where energy dispersive curves (EDC) were collected at various photon energies around the Si2p absorption edge. From the complete collection we have extracted the spectrum measured at the photon energy of 125 eV and studied the Auger feature included in the EDC. From the comparison of the Auger line of the bulk SiO{sub 2} with the expected transitions we demonstrate the occurrence of inter-atomic transitions in the bulk oxide. Comparing the Auger line from the bulk oxide with that from a native oxide we may observe the occurrence of inter-atomic transitions localized at the interface. We propose an interpretation of this result by considering the geometry at the interface.

  3. 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.

  4. Polaron dynamics in thin polythiophene films studied with time-resolved photoemission

    Science.gov (United States)

    Varene, Erwan; Tegeder, Petra

    2012-04-01

    Femtosecond time-resolved two-photon photoemission spectroscopy is employed to study the dynamics of an excited state in a thin regioregular poly(3-hexylthiophene) (RR-P3HT) film deposited on a conducting polymer poly(3,4-ethylene-dioxythiophene): poly-(styrenesulfonate) (PEDT:PSS) electrode following optical excitation at 2.1 eV. We found that the biexponential decay of this excited state has a fast component (2.6 ps) assigned to bound polaron pairs which recombine quickly or separate to be added to the slow component (7.6 ps). The latter is attributed to polarons generated via charge transfer between adjacent polymer chains.

  5. 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.

  6. Synchrotron radiation photoemission spectrum study on K3C60 film

    Institute of Scientific and Technical Information of China (English)

    李宏年; 徐亚伯; 鲍世宁; 李海洋; 何丕模; 钱海杰; 刘风琴; 奎热西·易卜拉欣

    2000-01-01

    K3C60 single crystal film was prepared on the cleaved (111) surface of C60 single crystal. Synchrotron radiation angle-resolved photoemission spectra were measured at normal emission with sample temperature at - 150K. Up to four subpeaks of LUMO-derived band were observed. These sub-peaks exhibit distinct energy dispersions which resemble in general the theoretical ones calculated for K3C60 at low temperature with the so-called one-dimensional disordered structure. But there is large deviation of experimental sub-band intervals from the theoretical values. This result is meaningful for the studies of the physical properties of alkali-doped C60 solids, e.g. the mechanism for superconductivity.

  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. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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

  13. X-ray photoemission electron microscopy for the study of semiconductor materials

    Energy Technology Data Exchange (ETDEWEB)

    Anders, S.; Stammler, T.; Padmore, H.A. [Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720 (United States); Terminello, L.J.; Jankowski, A.F. [Lawrence Livermore National Laboratory, 7000 East Ave., Livermore, California 94550 (United States); Stoehr, J. [IBM Almaden Research Center, 650 Harry Road, San Jose, California 95120 (United States); Diaz, J. [Departamento de Fisic, Facultad de Ciencias, Universidad de Oviedo, Avda. Calvo Sotelo s/n, Oviedo, 33007 (Spain); Cossy-Favre, A. [EMPA, Duebendorf, Ueberlandstrasse 129, 8600 Duebendorf (Switzerland); Singh, S. [Center for X-ray Lithography, University of Wisconsin-Madison, Stoughton, Wisconsin 53589 (United States)

    1998-11-01

    Photoemission Electron Microscopy using X-rays (X-PEEM) is a novel combination of two established materials analysis techniques{emdash}PEEM using UV light, and Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy. This combination allows the study of elemental composition and bonding structure of the sample by NEXAFS spectroscopy with a high spatial resolution given by the microscope. A simple, two lens, 10 kV operation voltage PEEM has been used at the Stanford Synchrotron Radiation Laboratory and at the Advanced Light Source (ALS) in Berkeley to study various problems including materials of interest for the semiconductor industry. In the present paper we give a short overview over the method and the instrument which was used, and describe in detail a number of applications. These applications include the study of the different phases of titanium disilicide, various phases of boron nitride, and the analysis of small particles. A brief outlook is given on possible new fields of application of the PEEM technique, and the development of new PEEM instruments. {copyright} {ital 1998 American Institute of Physics.}

  14. X-ray photoemission electron microscopy for the study of semiconductor materials

    Energy Technology Data Exchange (ETDEWEB)

    Anders, S.; Stammler, T.; Padmore, H. [Lawrence Berkeley National Lab., CA (United States). Advanced Light Source Div.; Terminello, L.J.; Jankowski, A.F. [Lawrence Livermore National Lab., CA (United States); Stohr, J. [IBM Almaden Research Center, San Jose, CA (United States); Diaz, J. [Univ. de Oviedo (Spain). Dept. de Fisica; Cossy-Gantner, A. [EMPA, Duebendorf (Germany)

    1998-03-01

    Photoemission Electron Microscopy (PEEM) using X-rays is a novel combination of two established materials analysis techniques--PEEM using UV light, and Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy. This combination allows the study of elemental composition and bonding structure of the sample by NEXAFS spectroscopy with a high spatial resolution given by the microscope. A simple, two lens, 10 kV operation voltage PEEM has been used at the Stanford Synchrotron Radiation Laboratory and at the Advanced Light Source (ALS) in Berkeley to study various problems including materials of interest for the semiconductor industry. In the present paper the authors give a short overview over the method and the instrument which was used, and describe in detail a number of applications. These applications include the study of the different phases of titanium disilicide, various phases of boron nitride, and the analysis of small particles. A brief outlook is given on possible new fields of application of the PEEM technique, and the development of new PEEM instruments.

  15. 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.

  16. Manifestation of screening effects and A-O covalency in the core level spectra of A site elements in the ABO3 structure of Ca1-xSrxRuO3

    Science.gov (United States)

    Singh, Ravi Shankar; Maiti, Kalobaran

    2007-08-01

    We investigate the evolution of Ca2p and Sr3d core level spectra in Ca1-xSrxRuO3 using photoemission spectroscopy. Core level spectra in this system exhibit multiple features and unusual evolution with the composition and temperatures. Analysis of the core level spectra in conjunction with the band structure results indicates final state effects due to different core hole screening channels. Such screening in the photoemission final states can be attributed to the large A-O covalency in these systems. Changes in the core level spectra with temperature and composition suggest significant modification in A-O (A=Ca/Sr) covalency in Ca-dominated samples, which gradually reduces with the increase in Sr content and becomes insignificant in SrRuO3 . This study thus provides a direct evidence of cation-oxygen covalency and its evolution with temperature, which may be useful in understanding the unusual ground state properties of these materials.

  17. 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.

  18. Photoemission study on the formation of Mo contacts to CuInSe2

    Science.gov (United States)

    Nelson, A. J.; Niles, D. W.; Kazmerski, L. L.; Rioux, D.; Patel, R.; Hoechst, H.

    1992-08-01

    Synchrotron radiation soft-X-ray photoemission spectroscopy was used to investigate the development of the electronic structure at the Mo/CuInSe2 interface. Mo overlayers were e-beam deposited in steps on single-crystal n-type CuInSe2 at ambient temperature. 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 4d, Se 3d, and Mo 4d core lines. Photoemission measurements on the valence-band and core lines were also obtained after annealing. The results were used to correlate the interface chemistry with the electronic structure at this interface and to directly determine the maximum possible Schottky barrier height to be not greater than 0.2 eV at the Mo/CuInSe2 junction before annealing, thus showing that this contact is essentially ohmic.

  19. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-09-30

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

  1. An x-ray photoemission electron microscope using an electron mirror aberration corrector for the study of complex materials

    Science.gov (United States)

    Feng, J.; Forest, E.; MacDowell, A. A.; Marcus, M.; Padmore, H.; Raoux, S.; Robin, D.; Scholl, A.; Schlueter, R.; Schmid, P.; Stöhr, J.; Wan, W.; Wei, D. H.; Wu, Y.

    2005-04-01

    A new ultrahigh-resolution photoemission electron microscope called PEEM3 is being developed at the advanced light source (ALS). An electron mirror combined with a sophisticated magnetic beam separator is used to provide simultaneous correction of spherical and chromatic aberrations. Installed on an elliptically polarized undulator beamline, PEEM3 will be operated with very high spatial resolution and high flux to study the composition, structure, electric and magnetic properties of complex materials.

  2. Photoemission study of ferrocenes: insights into the electronic structure of Si-based hybrid materials

    Energy Technology Data Exchange (ETDEWEB)

    Boccia, A; Marrani, A G; Stranges, S; Zanoni, R [Dipartimento di Chimica, Universita degli Studi di Roma ' La Sapienza' , piazzale Aldo Moro 5, I-00185 Rome (Italy); Alagia, M [ISMN-CNR, Sezione Romal, Piazzale Aldo Moro 5, I-00185 Roma, Italy and Laboratorio Nazionale TASC-CNR SS-14, Km 163.5, Basovizza, I-34012 Trieste (Italy); Iozzi, M F; Cossi, M [Dipartimento di Scienze dell' Ambiente e della Vita, Universita del Piemonte Orientale, via V. Bellini 25/G, I-15100 Alessandria (Italy)], E-mail: Andrea.Marrani@uniromal.it

    2008-03-15

    We present here the results of synchrotron radiation-excited UV-photoemission investigation and DFT calculations on vinylferrocene (VFC), a redox molecule suitable for applications in molecular electronics. A detailed assignment is discussed of the valence photoelectron spectra (UPS), which provides new data on the electronic structure and offers a partial re-interpretation of previous assignments on VFC based on theoretical and experimental evidences. Furthermore, the present results can allow for a meaningful comparison of photoemission results from the corresponding hybrid obtained by covalently attaching VFC to Si oriented surfaces.

  3. 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.

  4. 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...

  5. 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.

  6. 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}.

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

    DEFF Research Database (Denmark)

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

    2011-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Shen, K.M.

    2010-05-03

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

  9. Magnetic circular dichroism photoemission electron microscopy using laser and threshold photoemission

    Energy Technology Data Exchange (ETDEWEB)

    Nakagawa, Takeshi; Watanabe, Kazuya; Matsumoto, Yoshiyasu; Yokoyama, Toshihiko, E-mail: nakagawa@ims.ac.j, E-mail: yokoyama@ims.ac.j [Institute for Molecular Science, Myodaiji-cho, Okazaki, Aichi 444-8585 (Japan)

    2009-08-05

    We demonstrate that laser induced valence band photoemission can be used in the observation of magnetic domain structures with a magnetic circular dichroism photoemission electron microscope (MCD-PEEM). It has been widely considered that valence band photoemission MCD asymmetry is rather small compared to that obtained with x-rays because of its weak spin-orbit coupling. However, we show that the MCD asymmetry is high near the photoemission threshold, permitting us to perform MCD-PEEM experiments. The use of intense and pulsed lasers as excitation sources enables PEEM studies of two-photon photoemission MCD and all optical time resolved MCD.

  10. 镍金属的光电子光谱研究%Photoemission Studies of Metallic Nickel

    Institute of Scientific and Technical Information of China (English)

    江阳

    2002-01-01

    Photoemission experiments have been used to verify theoretical explanation for physical properties of many materials. For example, interesting properties of metallic nickel, i.e. seemingly contradictory nature between electrical conduction and magnetism, which is studied in this paper, could be explained by photoemission experiments. Through photoemission experiments, the 3d- 4s hybridization and very high density of 3d states can be demonstrated clearly. The hybridization results in the contribution of 3d holes to electrical conductivity and the high density of state gives rise to a very high effective mass. These findings verify theoretical explanation for poor electrical conductivity of metallic nickel. In addition, spin - polarized photoemission shows the existence of molecular field, which is the theoretical essence for ferromagnetism. The discrepancies between experimental and theoretical results are alsodiscussed in this paper.%光电子光谱实验对许多材料物理性质的理论解释给予了验证.对于镍金属的电导性与磁场性质给出了实验上的解释.通过试验,清楚的看出镍金属的3d-4s杂化及其非常高的3d态密度.由于杂化使得3d带的空穴参与了导电过程,而高的态密度使其具有极高的有效质量.这些发现都对镍金属弱导电性的理论解释做了支持.此外,从自旋-极化光电子光谱实验也显示了理论上对铁磁性本质解释一分子场(交换场)的存在.并讨论实验与理论结果的差异.

  11. SPIN POLARIZATION AND MAGNETIC DICHROISM IN PHOTOEMISSION FROM CORE AND VALENCE STATES IN LOCALIZED MAGNETIC SYSTEMS

    NARCIS (Netherlands)

    THOLE, BT; VANDERLAAN, G

    1991-01-01

    Using group theory we derive a general model for spin polarization and magnetic dichroism in photo-emission in the presence of atomic interactions between the hole created and the valence holes. We predict strong effects in the photoemission from core levels and localized valence levels of

  12. SPIN POLARIZATION AND MAGNETIC DICHROISM IN PHOTOEMISSION FROM CORE AND VALENCE STATES IN LOCALIZED MAGNETIC SYSTEMS

    NARCIS (Netherlands)

    THOLE, BT; VANDERLAAN, G

    1991-01-01

    Using group theory we derive a general model for spin polarization and magnetic dichroism in photo-emission in the presence of atomic interactions between the hole created and the valence holes. We predict strong effects in the photoemission from core levels and localized valence levels of transitio

  13. Electronic states of PrCoO{sub 3}: x-ray photoemission spectroscopy and LDA +U density of states studies

    Energy Technology Data Exchange (ETDEWEB)

    Pandey, S K [UGC-DAE Consortium for Scientific Research, University Campus, Khandwa Road, Indore 452 017 (India); Kumar, Ashwani [School of Physics, Devi Ahilya University, Khandwa Road, Indore 452 017 (India); Chaudhari, S M [UGC-DAE Consortium for Scientific Research, University Campus, Khandwa Road, Indore 452 017 (India); Pimpale, A V [UGC-DAE Consortium for Scientific Research, University Campus, Khandwa Road, Indore 452 017 (India)

    2006-02-01

    Electronic states of PrCoO{sub 3} are studied using x-ray photoemission spectroscopy. The Pr 3d{sub 5/2} core level and valence band (VB) were recorded using an Mg K {alpha} source. The core level spectrum shows that the 3d{sub 5/2} level is split into two components of multiplicity four and two, respectively, due to coupling of the spin states of the hole in 3d{sub 5/2} with the Pr 4f hole spin state. The observed splitting is 4.5 eV. The VB spectrum is interpreted using density of states (DOS) calculations under LDA and LDA +U. It is noted that LDA is not sufficient to explain the observed VB spectrum. Inclusion of on-site Coulomb correlation for Co 3d electrons in LDA +U calculations gives DOS which is useful in qualitative explanation of the ground state. However, it is necessary to include interactions between Pr 4f electrons to get better agreement with the experimental VB spectrum. It is seen that the VB consists of Pr 4f, Co 3d and O 2p states. Pr 4f, Co 3d and O 2p bands are highly mixed, indicating strong hybridization of these three states. The band near the Fermi level has about equal contributions from Pr 4f and O 2p states with somewhat smaller contribution from Co 3d states. Thus in the Zaanen, Sawatzky and Allen scheme PrCoO{sub 3} can be considered as a charge transfer insulator. The charge transfer energy {delta} can be obtained using LDA DOS calculations and the Coulomb-exchange energy U{sup '} from LDA +U. The explicit values for PrCoO{sub 3} are {delta} = 3.9 eV and U{sup '} = 5.5 eV; the crystal field splitting and 3d bandwidth of Co ions are also found to be 2.8 and 1.8 eV, respectively.

  14. Trends in adsorbate induced core level shifts

    Science.gov (United States)

    Nilsson, Viktor; Van den Bossche, Maxime; Hellman, Anders; Grönbeck, Henrik

    2015-10-01

    Photoelectron core level spectroscopy is commonly used to monitor atomic and molecular adsorption on metal surfaces. As changes in the electron binding energies are convoluted measures with different origins, calculations are often used to facilitate the decoding of experimental signatures. The interpretation could in this sense benefit from knowledge on trends in surface core level shifts for different metals and adsorbates. Here, density functional theory calculations have been used to systematically evaluate core level shifts for (111) and (100) surfaces of 3d, 4d, and 5d transition metals upon CO, H, O and S adsorption. The results reveal trends and several non-intuitive cases. Moreover, the difficulties correlating core level shifts with charging and d-band shifts are underlined.

  15. Thermal effects on Co/Mo2C multilayer mirrors studied by soft x-ray standing wave enhanced photoemission spectroscopy

    Science.gov (United States)

    Giglia, A.; Mukherjee, S.; Mahne, N.; Nannarone, S.; Jonnard, P.; Le Guen, K.; Yuan, Y.-Y.; André, J.-M.; Wang, Z.-S.; Li, H.-C.; Zhu, J.-T.

    2013-05-01

    Here is presented the spectroscopic study of the evolution of the first buried interfaces of a B4C capped Co/Mo2C multilayer mirror induced by thermal treatment up to 600°C. This kind of study is typically performed to simulate the response of multilayer optics working in extreme conditions, as for instance when irradiated by new high brilliance sources as Free Electron Lasers. In fact, the efficiency of multilayers is related to the optical contrast between the alternating high and low density layers, and then to the degree of interdiffusion and the creation or evolution of interface compounds. The analysis has been performed at the Co L23 edge with different soft x-ray spectroscopic techniques including diffuse and specular reflectivity, total electron and fluorescent yield at the BEAR beamline at Elettra (Trieste) (http://www.elettra.trieste.it/elettra-beamlines/bear.html). The presentation is focused on the spectroscopic results obtained by soft x-ray standing wave enhanced photoemission (XSW) from the Mo 3d, B 1s, C 1s, O 1s core levels by using a photon energy close to the Co L23 edge and corresponding to the first Bragg peak of the multilayer. The experimental results have been compared with simulations to obtain information both on the chemical state (e.g. oxidation state) and interface morphology in terms of profiles of distribution of elements and interdiffusion of B, oxidized B and C in the interface region. In summary, it is possible to conclude in favour of a good stability of the multilayer in the investigated temperature range, as confirmed by the good performance in terms of reflectivity. These results confirm the usefulness of XSW for this kind analysis of multilayer optics.

  16. Core-level spectra from graphene

    OpenAIRE

    Sernelius, Bo

    2014-01-01

    We calculate core-level spectra for pristine and doped free-standing graphene sheets. Instructions for how to perform the calculations are given in detail. Although pristine graphene is not metallic the core-level spectrum presents low-energy tailing which is characteristic of metallic systems. The peak shapes vary with doping level in a characteristic way. The spectra are compared to experiments and show good agreement. We compare to two different pristine samples and to one doped sample. Th...

  17. Controlled surface neutralization: A quantitative approach to study surface charging in photoemission

    Energy Technology Data Exchange (ETDEWEB)

    Mukherjee, S. [Surface Physics Division, Saha Institute of Nuclear Physics, 1/AF, Bidhannagar, Kolkata 700064 (India); Mukherjee, M. [Surface Physics Division, Saha Institute of Nuclear Physics, 1/AF, Bidhannagar, Kolkata 700064 (India)], E-mail: manabendra.mukherjee@saha.ac.in

    2007-02-15

    Photons when used to probe poorly conducting materials induce emission of secondary electrons that are inadequately compensated from the sample ground giving rise to a phenomenon commonly known as sample charging. In case of photoemission spectroscopy of an insulating material the data obtained from the charged surface are accordingly distorted. Here we have used a controlled neutralization technique to obtain photoemission data from continuously varying equilibrium charging conditions from two dissimilar insulating polymeric systems. A quantitative scheme for data analysis has been developed to demonstrate systematic behavior in the apparently distorted spectra and the charging peak shift has been described by an effective model. It is shown that the neutralization responses are non-linear for both the systems and possess intrinsic similarity. Around a critical electron flux the neutralization of the samples appears to occur through the percolation of homogeneously dispersed surface domains.

  18. Photoemission studies of the normal and high-temperature superconducting states

    Science.gov (United States)

    Margaritondo, G.; Onellion, M.

    1996-02-01

    Photoemission has become a most powerful electronic probe of high-TC superconductors. The main present emphasis is on the BCSCO-2212 gap symmetry. After much controversy, a consensus emerges: (1) no symmetric s-waves; (2) the symmetry depends on temperature and doping; (3) the optimal doping data are consistent with dx2-y2 waves; (4) for other dopings, the symmetry is consistent with mixed s and d-waves. The data, though, cannot rule out other hypotheses, specifically asymmetric s-waves. Photoemission also revealed unexpected phenomena, notably for Co-doped BCSCO-2212. By fine-tuning the doping one can replace the room temperature itinerant electronic states with localized states; Tc changes too, but there is still high-TC superconductivity. This indicates that Anderson localization and high-TC superconductivity can coexist.

  19. 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.

  20. Photoemission study on the formation of Mo contacts to CuInSe sub 2

    Energy Technology Data Exchange (ETDEWEB)

    Nelson, A.J.; Niles, D.W.; Kazmerski, L.L. (National Renewable Energy Laboratory, 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))

    1992-08-01

    Synchrotron radiation soft-x-ray photoemission spectroscopy was used to investigate the development of the electronic structure at the Mo/CuInSe{sub 2} interface. Mo overlayers were {ital e}-beam deposited in steps on single-crystal {ital n}-type CuInSe{sub 2} at ambient temperature. 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}, and Mo 4{ital d} core lines. Photoemission measurements on the valence-band and core lines were also obtained after annealing. The results were used to correlate the interface chemistry with the electronic structure at this interface and to directly determine the maximum possible Schottky barrier height {phi}{sub {ital b}} to be {le}0.2 eV at the Mo/CuInSe{sub 2} junction before annealing, thus showing that this contact is essentially ohmic.

  1. Auger and x-ray photoemission spectroscopy study on Cs2Te photocathodes

    Science.gov (United States)

    di Bona, A.; Sabary, F.; Valeri, S.; Michelato, P.; Sertore, D.; Suberlucq, G.

    1996-09-01

    Thin films of Cs2Te have been produced and analyzed by Auger depth profiling and x-ray photoemission spectroscopy (XPS). The formation of the photoemissive material passes through different phases, each of them has been characterized by XPS and by its total yield in the spectral region 3.5-5 eV. Copper and molybdenum substrates have been considered. While Mo behaves to all practical purposes like an ideal support for Cs2Te, strong diffusion from the substrate material into the photoemissive film has been observed on photocathodes fabricated on Cu. The ruggedness of the photocathodes has been tested by exposing them to a few hundred Langmuirs of different gases, namely O2, CO2, CO, N2, and CH4. The last three have no effect on the photocathode lifetime, while a substantial reduction of the quantum efficiency has been observed after the exposure to oxygen. The main reason for this is the formation of a thick cesium oxide layer at the surface of the photocathode. However, the oxygen pollution can be partially recovered by the combined effect of heating the photocathode at 230 °C and illuminating the poisoned material with the 4.9 eV radiation. No rejuvenation has been observed under the effect of the temperature or the radiation alone.

  2. Excitonic Insulator State in Ta2NiSe5 Probed by Photoemission Spectroscopy

    Science.gov (United States)

    Wakisaka, Y.; Sudayama, T.; Takubo, K.; Mizokawa, T.; Arita, M.; Namatame, H.; Taniguchi, M.; Katayama, N.; Nohara, M.; Takagi, H.

    2009-07-01

    We report on a photoemission study of Ta2NiSe5 that has a quasi-one-dimensional structure and an insulating ground state. Ni 2p core-level spectra show that the Ni 3d subshell is partially occupied and the Ni 3d states are heavily hybridized with the Se 4p states. In angle-resolved photoemission spectra, the valence-band top is found to be extremely flat, indicating that the ground state can be viewed as an excitonic insulator state between the Ni 3d-Se 4p hole and the Ta 5d electron. We argue that the high atomic polarizability of Se plays an important role to stabilize the excitonic state.

  3. 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.

  4. 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

  5. A photoemission study of benzotriazole on clean copper and cuprous oxide

    Science.gov (United States)

    Fang, Bo-Shung; Olson, Clifford G.; Lynch, David W.

    1986-11-01

    Photoemission spectra of benzotriazole (BTA) chemisorbed on clean Cu and on cuprous oxide were compared with the spectra of condensed- and gas-phase BTA. Chemisorbed BTA bonds to both Cu and Cu 2O via lone-pair orbitais on the nitrogen ring. The lack of a chemical shift for the π- orbitais indicates that BTA does not lie flat on the surface. We propose a model for the geometry and bonding of chemisorbed BTA which accounts for its corrosion inhibition on Cu, and for the corrosion inhibition, or lack of inhibition, by molecules similar to BTA.

  6. Laser-excited photoemission spectroscopy study of superconducting boron-doped diamond

    Directory of Open Access Journals (Sweden)

    K. Ishizaka, R. Eguchi, S. Tsuda, T. Kiss, T. Shimojima, T. Yokoya, S. Shin, T. Togashi, S. Watanabe, C.-T. Chen, C.Q. Zhang, Y. Takano, M. Nagao, I. Sakaguchi, T. Takenouchi and H. Kawarada

    2006-01-01

    Full Text Available We have investigated the low-energy electronic state of boron-doped diamond thin film by the laser-excited photoemission spectroscopy. A clear Fermi-edge is observed for samples doped above the semiconductor–metal boundary, together with the characteristic structures at 150×n meV possibly due to the strong electron–lattice coupling effect. In addition, for the superconducting sample, we observed a shift of the leading edge below Tc indicative of a superconducting gap opening. We discuss the electron–lattice coupling and the superconductivity in doped diamond.

  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. Electronic structure of LiCoO2 thin films: A combined photoemission spectroscopy and density functional theory study

    Science.gov (United States)

    Ensling, David; Thissen, Andreas; Laubach, Stefan; Schmidt, Peter C.; Jaegermann, Wolfram

    2010-11-01

    The electronic properties of LiCoO2 have been studied by theoretical band-structure calculations (using density functional theory) and experimental methods (photoemission). Synchrotron-induced photoelectron spectroscopy, resonant photoemission spectroscopy (ResPES), and soft x-ray absorption (XAS) have been applied to investigate the electronic structure of both occupied and unoccupied states. High-quality PES spectra were obtained from stoichiometric and highly crystalline LiCoO2 thin films deposited “in situ” by rf magnetron sputtering. An experimental approach of separating oxygen- and cobalt-derived (final) states by ResPES in the valence-band region is presented. The procedure takes advantage of an antiresonant behavior of cobalt-derived states at the 3p-3d excitation threshold. Information about the unoccupied density of states has been obtained by OK XAS. The structure of the CoL absorption edge is compared to semiempirical charge-transfer multiplet calculations. The experimental results are furthermore compared with band-structure calculations considering three different exchange potentials [generalized gradient approximation (GGA), using a nonlocal Hubbard U (GGA+U) and using a hybrid functional (Becke, three-parameter, Lee-Yang-Parr [B3LYP])]. For these different approaches total density of states and partial valence-band density of states have been investigated. The best qualitative agreement with experimental results has been obtained by using a GGA+U functional with U=2.9eV .

  10. First-principles calculation of core-level binding energy shift in surface chemical processes

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Combined with third generation synchrotron radiation light sources, X-ray photoelectron spectroscopy (XPS) with higher energy resolution, brilliance, enhanced surface sensitivity and photoemission cross section in real time found extensive applications in solid-gas interface chemistry. This paper reports the calculation of the core-level binding energy shifts (CLS) using the first-principles density functional theory. The interplay between the CLS calculations and XPS measurements to uncover the structures, adsorption sites and chemical reactions in complex surface chemical processes are highlight. Its application on clean low index (111) and vicinal transition metal surfaces, molecular adsorption in terms of sites and configuration, and reaction kinetics are domonstrated.

  11. 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.

  12. Photoemission and density functional theory study of Ir(111); energy band gap mapping.

    Science.gov (United States)

    Pletikosić, I; Kralj, M; Sokčević, D; Brako, R; Lazić, P; Pervan, P

    2010-04-07

    We have performed combined angle-resolved photoemission spectroscopy (ARPES) experiments and density functional theory (DFT) calculations of the electronic structure of the Ir(111) surface, with the focus on the existence of energy band gaps. The investigation was motivated by the experimental results suggesting Ir(111) as an ideal support for the growth of weakly bonded graphene. Therefore, our prime interest was electronic structure around the [Formula: see text] symmetry point. In accordance with DFT calculations, ARPES has shown a wide energy band gap with the shape of a parallelogram centred around the [Formula: see text] point. Within the gap three surface states were identified; one just below the Fermi level and two spin-orbit split surface states at the bottom of the gap.

  13. Band Discontinuities in Gallium Phosphide/Crystalline Silicon Heterojunctions Studied by Internal Photoemission

    Science.gov (United States)

    Sakata, Isao; Kawanami, Hitoshi

    2008-09-01

    We measured the band lineup of gallium phosphide (GaP) on crystalline silicon (c-Si) heterojunctions (HJs) by using internal photoemission (IPE), where the heterojunctions were prepared by using solid-source molecular beam epitaxy. It was found that the conduction-band and valence-band discontinuities, denoted by ΔEc and ΔEv, are 0.09+/-0.01 and 1.05+/-0.01 eV, respectively. By performing measurements on samples with different GaP layer thicknesses, we clarified that ΔEv of the present GaP-on-Si HJs is not affected by strain normal to the growth direction. The values of ΔEc and ΔEv obtained for the GaP-on-Si HJs are significantly different from those reported for thin Si-on-GaP HJs, and the implications of this discrepancy are briefly discussed.

  14. Angle-resolved photoemission study of quasi one-dimensional TlInSe{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Mimura, Kojiro [Department of Mathematical Sciences, Graduate School of Engineering, Osaka Prefecture University, Sakai 599-8531 (Japan)], E-mail: mimura@ms.osakafu-u.ac.jp; Wakita, Kazuki [Department of Physics and Electronics, Graduate School of Engineering, Osaka Prefecture University, Sakai 599-8531 (Japan); Arita, Masashi [Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima 739-0046 (Japan); Mamedov, Nazim; Orudzhev, Guseyn [Institute of Physics, Azerbaijan National Academy of Science, Baku, AZ-1143 (Azerbaijan); Taguchi, Yukihiro; Ichikawa, Kouichi [Department of Mathematical Sciences, Graduate School of Engineering, Osaka Prefecture University, Sakai 599-8531 (Japan); Namatame, Hirofumi; Taniguchi, Masaki [Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima 739-0046 (Japan)

    2007-05-15

    TlInSe{sub 2} with a quasi one-dimensional chain structure and a giant Seebeck coefficient of more than 10{sup 6} {mu}V/K below 140 {sup o}C has been investigated by means of angle-resolved photoemission spectroscopy at 50 K and 280 K. The obtained energy bands favorably agree with the calculated band structure and show quite noticeable dispersion in the direction normal to the chains. A rigid shift toward lower binding energies, a splitting and the formation of the mini-gap-like structures are clearly observed in the experimental electronic bands with the temperature reduced to 50 K. These features are indicative of an incommensurate superlattice phase emerging in TlInSe{sub 2} with temperature, and causing the record-breaking values of Seebeck coefficient.

  15. An Angle Resolved Photoemission Study of a Mott Insulator and Its Evolution to a High Temperature Superconductor

    Energy Technology Data Exchange (ETDEWEB)

    Ronning, Filip

    2002-03-19

    One of the most remarkable facts about the high temperature superconductors is their close proximity to an antiferromagnetically ordered Mott insulating phase. This fact suggests that to understand superconductivity in the cuprates we must first understand the insulating regime. Due to material properties the technique of angle resolved photoemission is ideally suited to study the electronic structure in the cuprates. Thus, a natural starting place to unlocking the secrets of high Tc would appears to be with a photoemission investigation of insulating cuprates. This dissertation presents the results of precisely such a study. In particular, we have focused on the compound Ca{sub 2-x}Na{sub x}CuO{sub 2}Cl{sub 2}. With increasing Na content this system goes from an antiferromagnetic Mott insulator with a Neel transition of 256K to a superconductor with an optimal transition temperature of 28K. At half filling we have found an asymmetry in the integrated spectral weight, which can be related to the occupation probability, n(k). This has led us to identify a d-wave-like dispersion in the insulator, which in turn implies that the high energy pseudogap as seen by photoemission is a remnant property of the insulator. These results are robust features of the insulator which we found in many different compounds and experimental conditions. By adding Na we were able to study the evolution of the electronic structure across the insulator to metal transition. We found that the chemical potential shifts as holes are doped into the system. This picture is in sharp contrast to the case of La{sub 2-x}Sr{sub x}CuO{sub 4} where the chemical potential remains fixed and states are created inside the gap. Furthermore, the low energy excitations (ie the Fermi surface) in metallic Ca{sub 1.9}Na{sub 0.1}CuO{sub 2}Cl{sub 2} is most well described as a Fermi arc, although the high binding energy features reveal the presence of shadow bands. Thus, the results in this dissertation provide a

  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...

  17. A Mechanistic Study of CO2 Reduction at the Interface of a Gallium Phosphide (GaP) Surface using Core-level Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Flynn, Kristen [SLAC National Accelerator Lab., Menlo Park, CA (United States)

    2015-08-18

    Carbon dioxide (CO2) emission into the atmosphere has increased tremendously through burning of fossil fuels, forestry, etc.. The increased concentration has made CO2 reductions very attractive though the reaction is considered uphill. Utilizing the sun as a potential energy source, CO2 has the possibility to undergo six electron and four proton transfers to produce methanol, a useable resource. This reaction has been shown to occur selectively in an aqueous pyridinium solution with a gallium phosphide (GaP) electrode. Though this reaction has a high faradaic efficiency, it was unclear as to what role the GaP surface played during the reaction. In this work, we aim to address the fundamental role of GaP during the catalytic conversion, by investigating the interaction between a clean GaP surface with the reactants, products, and intermediates of this reaction using X-ray photoelectron spectroscopy. We have determined a procedure to prepare atomically clean GaP and our initial CO2 adsorption studies have shown that there is evidence of chemisorption and reaction to form carbonate on the clean surface at LN2 temperatures (80K), in contrast to previous theoretical calculations. These findings will enable future studies on CO2 catalysis.

  18. A Mechanistic Study of CO2 Reduction at the Interface of a Gallium Phosphide (GaP) Surface using Core-level Spectroscopy - Oral Presentation

    Energy Technology Data Exchange (ETDEWEB)

    Flynn, Kristen [SLAC National Accelerator Lab., Menlo Park, CA (United States)

    2015-08-19

    Carbon dioxide (CO2) emission into the atmosphere has increased tremendously through burning of fossil fuels, forestry, etc.. The increased concentration has made CO2 reductions very attractive though the reaction is considered uphill. Utilizing the sun as a potential energy source, CO2 has the possibility to undergo six electron and four proton transfers to produce methanol, a useable resource. This reaction has been shown to occur selectively in an aqueous pyridinium solution with a gallium phosphide (GaP) electrode. Though this reaction has a high faradaic efficiency, it was unclear as to what role the GaP surface played during the reaction. In this work, we aim to address the fundamental role of GaP during the catalytic conversion, by investigating the interaction between a clean GaP surface with the reactants, products, and intermediates of this reaction using X-ray photoelectron spectroscopy. We have determined a procedure to prepare atomically clean GaP and our initial CO2 adsorption studies have shown that there is evidence of chemisorption and reaction to form carbonate on the clean surface at LN2 temperatures (80K), in contrast to previous theoretical calculations. These findings will enable future studies on CO2 catalysis.

  19. Study of spatial homogeneity and nitridation of an Al nanopattern template with spectroscopic photoemission and low energy electron microscopy

    Science.gov (United States)

    Qi, B.; Ólafsson, S.; Zakharov, A. A.; Göthelid, M.; Agnarsson, B.; Gislason, H. P.

    2013-01-01

    We report a study on the spatial homogeneity and nitridation of a nanopattern template using a spectroscopic photoemission and low energy electron microscopy. The template was composed of Al nanodots which were patterned into a SiO2/Si(1 1 1) surface using e-beam lithography and reactive ion etching. The template exhibited a global inhomogeneity in terms of the local topography, Al composition and structure of the individual nanopatterns. After nitridation, the individual nanopatterns were diminished, more corrugated and faceted. The nitridated nanopatterns were structurally ordered but differently orientated. The nitridation effectively removed the fluorine contaminants by decomposition of the fluorocarbon sidewalls, resulting in the AlN nanopatterns and partially nitridated Si substrate surface outside the nanopattern domains.

  20. 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.

  1. High temperature thermal stability investigations of ammonium sulphide passivated InGaAs and interface formation with Al{sub 2}O{sub 3} studied by synchrotron radiation based photoemission

    Energy Technology Data Exchange (ETDEWEB)

    Chauhan, Lalit, E-mail: lalit.chauhan2@mail.dcu.ie [School of Physical Sciences, Dublin City University, Glasnevin, Dublin 9 (Ireland); Gajula, Durga Rao; McNeill, David [School of Electronics, Electrical Engineering and Computer Science, Queen' s University Belfast (United Kingdom); Hughes, Greg [School of Physical Sciences, Dublin City University, Glasnevin, Dublin 9 (Ireland)

    2014-10-30

    Highlights: • Sulphur passivation is effective at removing the native oxides from InGaAs surface. • A 700°C anneal of the sulphur passivated surface at leads to the loss of indium. • A 1 nm Al2O3 layer improves the thermal stability of the sulphur passivated InGaAs. - Abstract: High resolution synchrotron radiation core level photoemission measurements have been used to undertake a comparative study of the high temperature thermal stability of the ammonium sulphide passivated InGaAs surface and the same surface following the atomic layer deposition (ALD) of an ultrathin (∼1 nm) Al{sub 2}O{sub 3} layer. The solution based ex situ sulphur passivation was found to be effective at removing a significant amount of the native oxides and protecting the surface against re-oxidation upon air exposure. The residual interfacial oxides which form between sulphur passivated InGaAs and the ultrathin Al{sub 2}O{sub 3} layer can be substantially removed at high temperature (up to 700°C) without impacting on the InGaAs stoichiometry while significant loss of indium was recorded at this temperature on the uncovered sulphur passivated InGaAs surface.

  2. 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

    We study mechanisms of photoemission of hot electrons from plasmonic nanoparticles. We analyze the contribution of "transition absorption", i.e., loss of energy of electrons passing through the boundary between different materials, to the surface mechanism of photoemission. We calculate photoemis...

  3. 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.

  4. Spin-polarized photoemission study on the temperature dependence of the exchange splitting of Ni

    Science.gov (United States)

    Raue, R.; Hopster, H.; Clauberg, R.

    1984-06-01

    Using spin-polarized photoemission with high energy- and angle resolution (Δ E=100 meV, ΔΘ=±3°) we have investigated the temperature dependence of the exchange splitting of Ni in the temperature range 0.5≦ T/T c≦0.94. At room temperature we find Δ ex=0.18 eV for the exchange splitting of the S 4 band at the X point of the Brillouin zone. With increasing temperature the total (spin-averaged) energy distribution shows a narrowing and merges into one peak. The spin-resolved energy distribution curves approach each other and are strongly broadened. A discussion of the data within current theories of itinerant electron magnetism is given. The spectra indicate that neither the pure Stoner model nor the prediction of local band theory, assuming a temperature independent exchange splitting are justified for Ni. We conclude that the exchange splitting decreases with increasing temperature and that transverse as well as longitudinal spin fluctuations are responsible for the broadening of the spin-resoived energy distribution curves.

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

    Energy Technology Data Exchange (ETDEWEB)

    Almeras, P.; Berger, H.; Margaritondo, G. [Ecole Polytechnique Federale, Lausanne (Switzerland). Dept. de Physique; Ma, J.; Onellion, M. [Univ. of Wisconsin, Madison, WI (United States). Dept. of Physics

    1994-12-31

    The authors present a systematic study of compositional and doping effects in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub y} high-{Tc} superconductors performed with photoemission spectroscopy. The study has been extended to Y-doping and I-intercalation of Bi-2212 high quality single crystals. The main results is that each type of dopant affects the crystal composition in its own way. Yttrium affects the Ca and Sr planes, producing a charge transfer into the CuO planes. For I-doping, they find that the main effect is a change in the interplanar distance, but X-ray Photoemission Spectroscopy (XPS) allows to see that the decrease of the critical temperature is not caused only by a structure parameter, but by a over-doping of copper planes (hole doping). They performed also a comparative study by Angle Resolved Ultraviolet Photoemission Spectroscopy [ARUPS] between this sample and an oxygen annealed specimen. XPS Cu2p core level data establish that the hole concentration in the CuO{sub 2} planes is essentially the same for these two kinds of samples. ARUPS measurements show that electronic structure of the normal states near the Fermi level has been strongly affected by iodine intercalation.

  6. Surface core-level shifts for simple metals

    DEFF Research Database (Denmark)

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

    1994-01-01

    . We discuss the surface shifts of the electrostatic potentials and the band centers in order to trace the microscopic origin of the SCLS in the simple metals and find that the anomalous subsurface core-level shifts in beryllium are caused by charge dipoles, which persist several layers into the bulk......We have performed an ab initio study of the surface core-level binding energy shift (SCLS) for 11 of the simple metals by means of a Green’s-function technique within the tight-binding linear-muffin-tin-orbitals method. Initial- and final-state effects are included within the concept of complete....... We furthermore conclude that the unexpected negative sign of the SCLS in beryllium is predominantly an initial-state effect and is caused by the high electron density in this metal....

  7. Uranium passivation by C+ implantation: a photoemission and secondary ion mass spectrometry study

    Energy Technology Data Exchange (ETDEWEB)

    Nelson, A J; Felter, T E; Wu, K J; Evans, C; Ferreira, J; Siekhaus, W; McLean, W

    2005-01-20

    Implantation of 33 keV C{sup +} ions into polycrystalline U{sup 238} with a dose of 4.3 x 10{sup 17} cm{sup -2} produces a physically and chemically modified surface layer that prevents further air oxidation and corrosion. X-ray photoelectron spectroscopy and secondary ion mass spectrometry were used to investigate the surface chemistry and electronic structure of this C{sup +} ion implanted polycrystalline uranium and a non-implanted region of the sample, both regions exposed to air for more than a year. In addition, scanning electron microscopy was used to examine and compare the surface morphology of the two regions. The U 4f, O 1s and C 1s core-level and valence band spectra clearly indicate carbide formation in the modified surface layer. The time-of-flight secondary ion mass spectrometry depth profiling results reveal an oxy-carbide surface layer over an approximately 200 nm thick UC layer with little or no residual oxidation at the carbide layer/U metal transitional interface.

  8. Photoemission and LEED study of the Sn/Rh(111) surface--early oxidation steps and thermal stability.

    Science.gov (United States)

    Hanyš, Petr; Píš, Igor; Mašek, Karel; Sutara, František; Matolín, Vladimír; Nehasil, Václav

    2012-01-11

    We have deposited two monolayers of Sn onto Rh(111) single crystal. After the deposition, no ordered structure was revealed by low energy electron diffraction (LEED). We oxidized the obtained system in a low-pressure oxygen atmosphere at 420 K. The oxidized sample was then gradually heated to study the thermal stability of the oxide layer. We characterized the system by synchrotron radiation stimulated photoelectron spectroscopy and LEED. Valence band and core level photoelectron spectra of rhodium, tin and oxygen were used to study the oxidation of the Sn-Rh(111) surface and its behaviour upon annealing. A low stoichiometric oxide of Sn was created on the surface. The oxidation process did not continue towards creation of SnO(2) with higher oxygen dose. The annealing at 970 K caused decomposition of the surface oxide of Sn and creation of an ordered (√3 × √3)R30° Sn-Rh(111) surface alloy.

  9. Oxidation of the Si(100) surface promoted by Sr overlayer - An X-ray photoemission study. [high temperature superconductors

    Science.gov (United States)

    Mesarwi, A.; Fan, W. C.; Ignatiev, A.

    1990-01-01

    The interaction of strontium films with the underlaying Si (100) surface and the Sr-promoted low-temperature oxidation of Si were investigated, using XPS, at three different Sr coverages (theta): theta = 0.55 monolayer (ML), theta = 1 ML, and theta = 1.85 ML. Oxygen adsorption was studied both at room temperature and at 500 C, and at oxygen exposures up to 2 x 10 to the 6th L (1 L = 10 to the -6th torr) and 2 x 10 to the 5th L, respectively. The XPS spectra of the Si2p, O1s, and Sr3d core levels were measured for the atomically clean Si, the Sr-covered Si, and for the Sr-covered Si after each oxygen exposure. Results indicate that Sr interacts with the Si(100) surface forming a strong ionic bond, and that Sr promotes the oxidation of the Si (100) surface.

  10. Core level shifts of intercalated graphene

    Science.gov (United States)

    Schröder, Ulrike A.; Petrović, Marin; Gerber, Timm; Martínez-Galera, Antonio J.; Grånäs, Elin; Arman, Mohammad A.; Herbig, Charlotte; Schnadt, Joachim; Kralj, Marko; Knudsen, Jan; Michely, Thomas

    2017-03-01

    Through intercalation of metals and gases the Dirac cone of graphene on Ir(111) can be shifted with respect to the Fermi level without becoming destroyed by strong hybridization. Here, we use x-ray photoelectron spectroscopy to measure the C 1s core level shift (CLS) of graphene in contact with a number of structurally well-defined intercalation layers (O, H, Eu, and Cs). By analysis of our own and additional literature data for decoupled graphene, the C 1s CLS is found to be a non-monotonic function of the doping level. For small doping levels the shifts are well described by a rigid band model. However, at larger doping levels, a second effect comes into play which is proportional to the transferred charge and counteracts the rigid band shift. Moreover, not only the position, but also the C 1s peak shape displays a unique evolution as a function of doping level. Our conclusions are supported by intercalation experiments with Li, with which, due to the absence of phase separation, the doping level of graphene can be continuously tuned.

  11. Many-electron interactions and first-principles studies of spectral functions: spin multiplets and plasmon satellites in photoemission spectra

    Science.gov (United States)

    Lischner, Johannes

    2013-03-01

    The photoemission spectrum of an interacting system is often simply thought to be qualitatively similar to the corresponding non-interacting system: interactions only cause a shift and a broadening of the quasiparticle peak and result in a transfer of spectral weight into an incoherent background. We discuss two cases where this simple quasiparticle picture of photoemission fails and interactions result in a more drastic, qualitative difference from the non-interacting system. For electronic systems with unfilled shells, the coupling of angular momenta results in a multiplet structure in the photoemission spectrum. We describe how accurate calculations of multiplet splittings are possible within the GW approximation and present results for several magnetic molecules and defects, such as the negatively charged nitrogen-vacancy defect (NV-) center in diamond. We also discuss plasmon satellite structures in photoemission spectra. We show for bulk silicon and doped graphene that the ab initioGW approximation overestimates the quasiparticle-satellite separation significantly and falsely predicts a plasmaron excitation. By including significant vertex corrections via the ab initioGW +cumulant approximation, we improve the description of plasmon satellites and find good agreement with experimental photoemission spectra. The work was supported by NSF grant No. DMR10-1006184 and U.S. DOE under Contract No. DE-AC02-05CH11231. Computational resources have been provided NERSC and NICS.

  12. A single centre water splitting dye complex adsorbed on rutile TiO{sub 2}(110): Photoemission, x-ray absorption, and optical spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Weston, Matthew; Britton, Andrew J.; Handrup, Karsten; O' Shea, James N. [School of Physics and Astronomy, University of Nottingham, NG7 2RD Nottingham (United Kingdom); Nottingham Nanotechnology and Nanoscience Centre (NNNC), University of Nottingham, NG7 2RD Nottingham (United Kingdom); Reade, Thomas J.; Champness, Neil R. [School of Chemistry, University of Nottingham, NG7 2RD Nottingham (United Kingdom)

    2011-09-21

    A single centre water splitting dye complex (aqua(2,2'-bipyridyl-4,4'-dicarboxylic acid)-(2,2':6',6''-terpyridine)Ruthenium(II)), along with a related complex ((2,2'-bipyridyl-4,4'-dicarboxylic acid)-(2,2':6',6''-terpyridine)chloride Ruthenium(II)), has been investigated using photoemission and compared to molecules with similar structures. Dye molecules were deposited in situ using ultra-high vacuum electrospray deposition, which allows for the deposition of thermally labile molecules, such as these dye molecules. Adsorption of the dye molecules on the rutile TiO{sub 2}(110) surface has been studied using core-level and valence photoemission. Core-level photoemission spectra reveal that each complex bonds to the surface via deprotonation of its carboxylic acid groups. A consideration of the energy level alignments reveals that both complexes are capable of charge transfer from the adsorbed molecules to the conduction band of the rutile TiO{sub 2} substrate.

  13. Anisotropic electronic band structure of intrinsic Si(110) studied by angle-resolved photoemission spectroscopy and first-principles calculations

    Science.gov (United States)

    Matsushita, Stephane Yu; Takayama, Akari; Kawamoto, Erina; Hu, Chunping; Hagiwara, Satoshi; Watanabe, Kazuyuki; Takahashi, Takashi; Suto, Shozo

    2017-09-01

    We have studied the electronic band structure of the hydrogen-terminated Si(110)-(1 ×1 ) [H:Si(110)-(1 ×1 )] surface using angle-resolved photoemission spectroscopy (ARPES) and first-principles calculations in the framework of density functional theory with local density approximation (LDA). The bulk-truncated H:Si(110)-(1 ×1 ) surface is a good template to investigate the electronic band structure of the intrinsic Si(110). In the ARPES spectra, seven bulk states and one surface state due to the H-H interaction are observed clearly. The four bulk states consisting of Si 3 px y orbitals exhibit anisotropic band dispersions along the high symmetric direction of Γ ¯-X ¯ and Γ ¯-X¯' directions, where one state shows one-dimensional character. The calculated band structures show a good agreement with the experimental results except the surface state. We discuss the exact nature of electronic band structures and the applicability of LDA. We have estimated the anisotropic effective masses of electrons and holes of Si(110) for device application.

  14. Core level binding energies of functionalized and defective graphene.

    Science.gov (United States)

    Susi, Toma; Kaukonen, Markus; Havu, Paula; Ljungberg, Mathias P; Ayala, Paola; Kauppinen, Esko I

    2014-01-01

    X-ray photoelectron spectroscopy (XPS) is a widely used tool for studying the chemical composition of materials and it is a standard technique in surface science and technology. XPS is particularly useful for characterizing nanostructures such as carbon nanomaterials due to their reduced dimensionality. In order to assign the measured binding energies to specific bonding environments, reference energy values need to be known. Experimental measurements of the core level signals of the elements present in novel materials such as graphene have often been compared to values measured for molecules, or calculated for finite clusters. Here we have calculated core level binding energies for variously functionalized or defected graphene by delta Kohn-Sham total energy differences in the real-space grid-based projector-augmented wave density functional theory code (GPAW). To accurately model extended systems, we applied periodic boundary conditions in large unit cells to avoid computational artifacts. In select cases, we compared the results to all-electron calculations using an ab initio molecular simulations (FHI-aims) code. We calculated the carbon and oxygen 1s core level binding energies for oxygen and hydrogen functionalities such as graphane-like hydrogenation, and epoxide, hydroxide and carboxylic functional groups. In all cases, we considered binding energy contributions arising from carbon atoms up to the third nearest neighbor from the functional group, and plotted C 1s line shapes by using experimentally realistic broadenings. Furthermore, we simulated the simplest atomic defects, namely single and double vacancies and the Stone-Thrower-Wales defect. Finally, we studied modifications of a reactive single vacancy with O and H functionalities, and compared the calculated values to data found in the literature.

  15. Ultrafast electron dynamics in the topological insulator Bi{sub 2}Se{sub 3} studied by time-resolved photoemission spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Sobota, J.A.; Yang, S.-L. [Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025 (United States); Geballe Laboratory for Advanced Materials, Department ofApplied Physics, Stanford University, Stanford, CA 94305 (United States); Department of Physics, Stanford University, Stanford, CA 94305 (United States); Leuenberger, D. [Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025 (United States); Geballe Laboratory for Advanced Materials, Department ofApplied Physics, Stanford University, Stanford, CA 94305 (United States); Kemper, A.F. [Lawrence Berkeley National Lab, 1 Cyclotron Road, Berkeley, CA 94720 (United States); Analytis, J.G. [Department of Physics, University of California, Berkeley, CA 94720 (United States); Fisher, I.R. [Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025 (United States); Geballe Laboratory for Advanced Materials, Department ofApplied Physics, Stanford University, Stanford, CA 94305 (United States); Kirchmann, P.S., E-mail: kirchman@stanford.edu [Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025 (United States); Devereaux, T.P. [Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025 (United States); Geballe Laboratory for Advanced Materials, Department ofApplied Physics, Stanford University, Stanford, CA 94305 (United States); and others

    2014-08-15

    We characterize the topological insulator Bi{sub 2}Se{sub 3} using time- and angle-resolved photoemission spectroscopy. By employing two-photon photoemission, a complete picture of the unoccupied electronic structure from the Fermi level up to the vacuum level is obtained. We demonstrate that the unoccupied states host a second Dirac surface state which can be resonantly excited by 1.5 eV photons. We then study the ultrafast relaxation processes following optical excitation. We find that they culminate in a persistent non-equilibrium population of the first Dirac surface state, which is maintained by a meta-stable population of the bulk conduction band. Finally, we perform a temperature-dependent study of the electron–phonon scattering processes in the conduction band, and find the unexpected result that their rates decrease with increasing sample temperature. We develop a model of phonon emission and absorption from a population of electrons, and show that this counter-intuitive trend is the natural consequence of fundamental electron–phonon scattering processes. This analysis serves as an important reminder that the decay rates extracted by time-resolved photoemission are not in general equal to single electron scattering rates, but include contributions from filling and emptying processes from a continuum of states.

  16. 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.

  17. A study of photoemission using CW and pulsed UV light sources to probe surface slip band structure evolution of single crystal aluminium

    Science.gov (United States)

    Cai, Mingdong; Langford, Stephen; Dickinson, J. Thomas

    2008-03-01

    We report measurements of photoelectron emission from high-purity single crystal aluminum during uniaxial tensile deformation. A 248 nm pulsed excimer laser was used as a light source and the generated photoemission data was compared with that using a filtered mercury lamp. Time-of-flight curves of photoelectrons generated by pulsed excimer laser irradiation were observed showing a two peaked structure. These two peaks correspond to photoelectrons of two energy levels. It was also found that real time total photoelectron charge increases linearly with strain; and the increment is heterogeneous. Photoemission using low-energy photons is sensitive to changes in surface morphology accompanying deformation, including slip line and band formation. The discontinuity in photoelectron intensity and the heterogeneous surface slip band structure prove the production of fresh surface area is not continuous, which is predicted by a recent dislocation dynamics theory based on percolation process. Except for differences in instrumentation and data analysis, the photoemission data from a filtered mercury lamp and from the excimer laser are comparable. Current studies extend the application of the excimer laser into surface dynamics analysis.

  18. 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

  19. 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

  20. 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.

  1. Comment on ‘Electronic structure of Mo(1-x)Re x alloys studied through resonant photoemission spectroscopy’

    Science.gov (United States)

    Evans, Prescott; Dowben, P. A.

    2017-03-01

    Further analysis of the resonant photoemission data, found within Sundar et al (2016 J. Phys.: Condens. Matter 28 315502), show the intensities do not follow the elemental composition in the Mo1-x Re x alloy. Similar trends are observed in the published data for Gd1-x Ni x alloy films. The analysis of the resonant photoemission intensities suggests that Mo in the Mo1-x Re x alloy and Gd in the Gd1-x Ni x alloy have nearest neighbor bonds to Re and Ni respectively. This means the A-B bond is favored over the average of the A-A bond and the B-B bond in these binary alloys, so that the short range order favors strong local ordering rather than clustering alloys.

  2. 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.

  3. Hard x-ray photoemission and density functional theory study of the internal electric field in SrTiO3/LaAlO3 oxide heterostructures

    Science.gov (United States)

    Slooten, E.; Zhong, Zhicheng; Molegraaf, H. J. A.; Eerkes, P. D.; de Jong, S.; Massee, F.; van Heumen, E.; Kruize, M. K.; Wenderich, S.; Kleibeuker, J. E.; Gorgoi, M.; Hilgenkamp, H.; Brinkman, A.; Huijben, M.; Rijnders, G.; Blank, D. H. A.; Koster, G.; Kelly, P. J.; Golden, M. S.

    2013-02-01

    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 internal electric fields—within the LaAlO3 layer. First, the Ti 2p core-level spectra clearly show occupation of Ti 3d states already for two unit cells of LaAlO3. Second, the LaAlO3 core levels were seen to shift to lower binding energy as the LaAlO3 overlayer thickness, n, was increased, agreeing with the expectations from the canonical electron transfer model for the emergence of conductivity at the interface. However, not only is the energy offset of only ˜300 meV between n=2 (insulating interface) and n=6 (metallic interface) an order of magnitude smaller than the simple expectation, but it is also clearly not the sum of a series of unit-cell-by-unit-cell shifts within the LaAlO3 block. Both of these facts argue against the simple charge-transfer picture involving a cumulative shift of the LaAlO3 valence bands above the SrTiO3 conduction bands, resulting in charge transfer only for n≥4. We discuss effects which could frustrate this elegant and simple charge-transfer model, concluding that although it cannot be ruled out, photodoping by the x-ray beam is unlikely to be the cause of the observed behavior. Turning to the theoretical data, our density functional simulations show that the presence of oxygen vacancies at the LaAlO3 surface at the 25% level reverses the direction of the internal field in the LaAlO3. Therefore, taking the experimental and theoretical results together, a consistent picture emerges for real-life samples in which nature does not wait until n=4 and already for n=2 mechanisms other than internal-electric-field-driven electron transfer from idealized LaAlO3 to near-interfacial states in the SrTiO3 substrate are active in heading off the

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

    Science.gov (United States)

    Haverkort, Maurits W.

    2016-05-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Lunan [Iowa State Univ., Ames, IA (United States)

    2016-01-01

    This dissertation consists of three parts. First, we study magnetic domains in Nd2Fe14B 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 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 6 SiC superlattice even graphene layers grown thicker. Finally, we studied the electronic structure of MoTe2 by ARPES and experimentally con rmed 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 identi ed 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.

  6. 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.

  7. Comparative study of rare earth hexaborides using high resolution angle-resolved photoemission

    Energy Technology Data Exchange (ETDEWEB)

    Ramankutty, S.V., E-mail: s.v.ramankutty@uva.nl [Van der Waals-Zeeman Institute, Institute of Physics (IoP), University of Amsterdam, Science Park 904, 1098 XH Amsterdam (Netherlands); Jong, N. de; Huang, Y.K.; Zwartsenberg, B. [Van der Waals-Zeeman Institute, Institute of Physics (IoP), University of Amsterdam, Science Park 904, 1098 XH Amsterdam (Netherlands); Massee, F. [Laboratory of Atomic and Solid State Physics, Department of Physics, Cornell University, Ithaca, NY 14853 (United States); Bay, T.V. [Van der Waals-Zeeman Institute, Institute of Physics (IoP), University of Amsterdam, Science Park 904, 1098 XH Amsterdam (Netherlands); Golden, M.S., E-mail: m.s.golden@uva.nl [Van der Waals-Zeeman Institute, Institute of Physics (IoP), University of Amsterdam, Science Park 904, 1098 XH Amsterdam (Netherlands); Frantzeskakis, E., E-mail: e.frantzeskakis@uva.nl [Van der Waals-Zeeman Institute, Institute of Physics (IoP), University of Amsterdam, Science Park 904, 1098 XH Amsterdam (Netherlands)

    2016-04-15

    Highlights: • ARPES electronic structure study of rare-earth (RE) hexaborides SmB{sub 6}, CeB{sub 6} and YbB{sub 6}. • Increasing RE valence Yb[II], Sm[II/III], Ce[III] increases d-band occupancy. • YbB{sub 6} and SmB{sub 6} posses 2D states at E{sub F}, whereas the Fermi surface of CeB{sub 6} is 3D. • ARPES, LEED and STM data prove structural relaxation of the SmB{sub 6}(001) surface. - Abstract: Strong electron correlations in rare earth hexaborides can give rise to a variety of interesting phenomena like ferromagnetism, Kondo hybridization, mixed valence, superconductivity and possibly topological characteristics. The theoretical prediction of topological properties in SmB{sub 6} and YbB{sub 6} has rekindled the scientific interest in the rare earth hexaborides, and high-resolution ARPES has been playing a major role in the debate. The electronic band structure of the hexaborides contains the key to understand the origin of the different phenomena observed, and much can be learned by comparing the experimental data from different rare earth hexaborides. We have performed high-resolution ARPES on the (001) surfaces of YbB{sub 6}, CeB{sub 6} and SmB{sub 6}. On the most basic level, the data show that the differences in the valence of the rare earth element are reflected in the experimental electronic band structure primarily as a rigid shift of the energy position of the metal 5d states with respect to the Fermi level. Although the overall shape of the d-derived Fermi surface contours remains the same, we report differences in the dimensionality of these states between the compounds studied. Moreover, the spectroscopic fingerprint of the 4f states also reveals considerable differences that are related to their coherence and the strength of the d–f hybridization. For the SmB{sub 6} case, we use ARPES in combination with STM imaging and electron diffraction to reveal time dependent changes in the structural symmetry of the highly debated SmB{sub 6

  8. First in-flight synchrotron X-ray absorption and photoemission study of carbon soot nanoparticles

    Science.gov (United States)

    Ouf, F.-X.; Parent, P.; Laffon, C.; Marhaba, I.; Ferry, D.; Marcillaud, B.; Antonsson, E.; Benkoula, S.; Liu, X.-J.; Nicolas, C.; Robert, E.; Patanen, M.; Barreda, F.-A.; Sublemontier, O.; Coppalle, A.; Yon, J.; Miserque, F.; Mostefaoui, T.; Regier, T. Z.; Mitchell, J.-B. A.; Miron, C.

    2016-11-01

    Many studies have been conducted on the environmental impacts of combustion generated aerosols. Due to their complex composition and morphology, their chemical reactivity is not well understood and new developments of analysis methods are needed. We report the first demonstration of in-flight X-ray based characterizations of freshly emitted soot particles, which is of paramount importance for understanding the role of one of the main anthropogenic particulate contributors to global climate change. Soot particles, produced by a burner for several air-to-fuel ratios, were injected through an aerodynamic lens, focusing them to a region where they interacted with synchrotron radiation. X-ray photoelectron spectroscopy and carbon K-edge near-edge X-ray absorption spectroscopy were performed and compared to those obtained for supported samples. A good agreement is found between these samples, although slight oxidation is observed for supported samples. Our experiments demonstrate that NEXAFS characterization of supported samples provides relevant information on soot composition, with limited effects of contamination or ageing under ambient storage conditions. The highly surface sensitive XPS experiments of airborne soot indicate that the oxidation is different at the surface as compared to the bulk probed by NEXAFS. We also report changes in soot’s work function obtained at different combustion conditions.

  9. Surface study of metal-containing ionic liquids by means of photoemission and absorption spectroscopies

    Science.gov (United States)

    Caporali, Stefano; Pedio, Maddalena; Chiappe, Cinzia; Pomelli, Christian S.; Acres, Robert G.; Bardi, Ugo

    2016-06-01

    The vacuum/liquid interface of different ionic liquids obtained by dissolving bistriflimide salts of Ag, Al, Cu, Ni, and Zn in 1-butyl-3-methylimidazolium bistriflimide ([bmim][Tf2N]) was investigated under vacuum using AR-XPS and NEXAFS. The XPS spectra show chemical shifts of the nitrogen of the bistriflimide anion as a function of the metal type, indicating different strength of the coordination bonds. In silver bearing ILs, silver ions were found to be only weakly coordinated. On the contrary, Ni, Cu, Zn, and especially Al exhibit large chemical shifts attributable to strong interaction with the bistriflimide ions. The outermost surface was enriched with or depleted of metal ions as a function of the nature of the metals. Nickel and zinc tend to slightly concentrate at the surface while copper, silver, and especially aluminum are depleted at the surface. We also observed that the aliphatic alkyl chains of the cations tend to protrude outside the surface in all systems studied. However, the presence of metals generally increases the amount of bistriflimide at the vacuum/liquid interface.

  10. Photoemission study of metallic iron nanoparticles surface aging in biological fluids. Influence on biomolecules adsorption

    Energy Technology Data Exchange (ETDEWEB)

    Canivet, L.; Denayer, F.O. [Université de Lille 2, Droit et Santé, 42 rue P. Duez, 59000 Lille (France); Champion, Y.; Cenedese, P. [CNRS-ICMPE, 2 rue H. Dunant, 94320 Thiais (France); Dubot, P., E-mail: pdubot@icmpe.cnrs.fr [CNRS-ICMPE, 2 rue H. Dunant, 94320 Thiais (France)

    2014-07-01

    Iron nanoparticles (nFe) prepared by vaporization and cryogenic condensation process (10–100 nm) has been exposed to Hank's balanced salt solution (HBSS) and the B-Ali cell growth fluids. These media can be used for cellular growth to study nFe penetration through cell membrane and its induced cytotoxicity. Surface chemistry of nFe exposed to such complex fluids has been characterized as the nanoparticles surface can be strongly changed by adsorption or corrosion processes before reaching intracellular medium. Particle size and surface chemistry have been characterized by scanning electron microscopy (SEM) and high-resolution X-ray photoelectron spectroscopy (HR-XPS). Exposition of nFe particles to growth and differentiation media leads to the formation of an oxy-hydroxide layer containing chlorinated species. We found that the passivated Fe{sub 2}O{sub 3} layer of the bare nFe particles is rapidly transformed into a thicker oxy-hydroxide layer that has a greater ability to adsorb molecular ions or ionic biomolecules like proteins or DNA.

  11. 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.

  12. Synchronization and Characterization of an Ultra-Short Laser for Photoemission and Electron-Beam Diagnostics Studies at a Radio Frequency Photoinjector

    CERN Document Server

    Maxwell, Timothy; Piot, Philippe; Lumpkin, Alex

    2012-01-01

    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.

  13. 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.

  14. 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.

  15. Photoemission study of 5f localization in UPd/sub 3-//sub x/(Pt,Rh)/sub x/

    Energy Technology Data Exchange (ETDEWEB)

    Arko, A.J.; Koelling, D.D.; Dunlap, B.D.; Mitchell, A.W.; Capasso, C.; del Giudice, M.

    1988-04-15

    Photoemission measurements in the two systems UPd/sub 3-//sub x/(Pt,Rh)/sub x/ show that the 5f spectra are consistent with localized 5f electrons (peak in spectral weight is below E/sub F/ for all x within the double hexagonal DO/sub 24/ phase) while at both phase transitions the 5f peaks lock in at E/sub F/ consistent with intinerancy. A satellite 5f peak which we attribute to d screening is observed in both localized and itinerant systems.

  16. Photoemission study of 5f localization in UPd/sub 3-x/(Pt,Rh)/sub x/

    Energy Technology Data Exchange (ETDEWEB)

    Arko, A.J.; Koelling, D.D.; Dunlap, B.D.; Mitchell, A.W.

    1987-10-01

    Photoemission measurements in the two systems UPd/sub 3-x/(Pt,Rh)/sub x/ show that the 5f spectra are consistent with localized 5f electrons (peak in spectral weight is below E/sub F/ for all x within the double hexagonal DO/sub 24/ phase) while at both phase transitions the 5f peaks lock in at E/sub F/ consistent with intinerancy. A satellite 5f peak representative of d-screening is observed in both localized and itinerant systems. 17 refs., 3 figs.

  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. Valence-band photoemission intensities in thorium dioxide

    Energy Technology Data Exchange (ETDEWEB)

    Ellis, W.P.; Boring, A.M.; Cox, L.E.; Cowan, R.D.; Arko, A.J. (Los Alamos National Lab., NM (USA)); Allen, J.W. (Michigan Univ., Ann Arbor, MI (USA). Dept. of Physics); Pate, B.B.; Lindau, I. (Stanford Univ., CA (USA). Synchrotron Radiation Lab.)

    1989-11-01

    Resonant photoemission spectra of the O 2p-derived valence band of insulating ThO{sub 2} are compared to linear muffin-tin orbital (LMTO) density-of-state (DOS) and XPS intensity calculations. At Th 5d core-level threshold energies (85 {le} hv {le} 120 eV), resonance is greatest at the bottom of the O 2p band where calculated p/d hybrid states are greatest; p/f hybrid content is weak by comparison. We conclude that the dominant hybridization is between O 2p states and Th 6d. (author).

  19. Bulk superconducting gap of V{sub 3}Si studied by low-energy ultrahigh-resolution photoemission spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Sato, T., E-mail: t-sato@arpes.phys.tohoku.ac.jp [Department of Physics, Tohoku University, Sendai 980-8578 (Japan); Souma, S. [WPI Research Center, Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan); Nakayama, K. [Department of Physics, Tohoku University, Sendai 980-8578 (Japan); Sugawara, K. [WPI Research Center, Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan); Toyota, N. [Department of Physics, Tohoku University, Sendai 980-8578 (Japan); Takahashi, T. [Department of Physics, Tohoku University, Sendai 980-8578 (Japan); WPI Research Center, Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan)

    2016-04-15

    Highlights: • We report ultrahigh-resolution photoemission spectroscopy of A15 compound V{sub 3}Si. • We found a sharp quasiparticle peak due to superconducting-gap opening. • The surface metallic component is negligibly small in the bulk-sensitive measurement. • We show that V{sub 3}Si is a single-gap s-wave superconductor. - Abstract: We have performed low-energy ultrahigh-resolution photoemission spectroscopy (PES) of A15 compound V{sub 3}Si with a xenon-plasma discharge lamp to elucidate the bulk superconducting gap. Below the superconducting transition temperature (T{sub c} = 15.9 K), we found a sharp quasiparticle peak at the Fermi level in the PES spectrum. The gap spectrum is well fitted by a single s-wave superconducting-gap function together with a dip structure at ∼30 meV suggestive of a strong electron-phonon coupling. The anomalous in-gap state previously observed in the PES measurement with high-energy photons is absent or negligibly small in the present bulk-sensitive measurement. The present PES result shows that V{sub 3}Si is a single-gap s-wave superconductor.

  20. 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

  1. 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.

  2. Chlorine-induced modifications in the electronic structure of Ag surfaces: a metastable deexcitation spectroscopy and photoemission comparative study

    CERN Document Server

    Pasquali, L; Canepa, M; Staicu-Casagrande, E M; Esaulov, V A

    2003-01-01

    Surface-sensitive spectroscopic techniques, namely metastable deexcitation spectroscopy (MDS) and ultraviolet photoemission (UPS), have been applied to investigate the effects of chlorine chemisorption on the electronic properties (surface density of states and charge density) of Ag(100), Ag(110) and Ag(111) surfaces. Initial stages of chemisorption, up to the formation of a saturated Cl overlayer, have been examined. In particular, MDS permitted us to observe at low Cl gas exposure a progressive depletion of the Ag (5s) charge due to transfer and bonding with Cl atoms. From both MDS and UPS it was possible to observe the development of Cl (3p) bonding and anti-bonding states, the amount of their splitting increasing with coverage. Differences between chemisorption at the three surfaces have been noticed and they have been justified in terms of the different adatom packing and possible formation of small AgCl clusters (especially for the Ag(111) surface).

  3. Future directions in standing-wave photoemission

    Energy Technology Data Exchange (ETDEWEB)

    Gray, Alexander X., E-mail: axgray@temple.edu

    2014-08-15

    Highlights: • Probing magnetic properties at the buried interface with SW-MCD. • Probing electronic structure at the buried interface with resonant SW-XPS and SW-HAXPES. • Probing momentum-resolved electronic structure at a buried interface with SWARPES. • Adding depth resolution to photoemission microscopy with standing-wave excitation. • Standing-wave localization, total reflection and waveguide effects. - Abstract: Over the past decade, standing-wave photoemission (SW-XPS) has evolved into a powerful and versatile non-destructive technique for probing element-specific electronic, magnetic, and structural properties of buried layers and interfaces with sub-nanometer depth resolution. In this article, I will discuss several promising future directions in this emergent field stemming from experimental and theoretical studies wherein SW-XPS is combined with other X-ray techniques, such as magnetic circular dichroism (MCD), hard X-ray photoemission spectroscopy (HAXPES), angle-resolved photoemission (ARPES), and photoemission microscopy (PEEM), adding extra dimensions to the measurement and thus widening the scope of scientific and technological questions accessible via the use of standing waves. I will further discuss examples of recently developed methods for X-ray standing-wave data analysis, which yield layer-resolved matrix-element-weighted densities of states at interfaces as well as Ångstrom-level changes in periodicity of synthetic superlattices. Finally, I will explore the possibility of localizing the standing waves near the surface and within a buried layer by the use of aperiodic superlattices, total reflection, and X-ray waveguide effects.

  4. Relationships Between Complex Core Level Spectra and Materials Properties

    Energy Technology Data Exchange (ETDEWEB)

    Nelin, Constance J.; Bagus, Paul S.; Ilton, Eugene S.; Chambers, Scott A.; Kuhlenbeck, Helmut; Freund, Hans-Joachim

    2010-12-01

    The XPS of many oxides are quite complex and there may be several peaks of significant intensity for each subshell. These peaks arise from many-electron effects, which normally are treated with configuration interaction (CI) wavefunctions where static correlation effects are taken into account. It is common to use semiempirical methods to determine the matrix elements of the CI Hamiltonian and there are few rigorous CI calculations where parameters are not adjusted to fit experiment. In contrast, we present, in the present work, theoretical XPS spectra obtained with rigorous CI wavefunctions for CeO2 where the XPS are especially complex; several different core levels are studied. This study uses an embedded CeO8 cluster model to represent bulk CeO2 and the relativistic CI wavefunctions are determined using four-component spinors from Dirac-Fock calculations. In particular, we examine the importance of interatomic many-body effects where there is a transfer of electrons from occupied oxygen 2p orbitals into empty cation orbitals as it is common to ascribe the complex XPS to this effect. We also contrast the importance of many-body charge-transfer effects for the isoelectronic cations of Ce4+ and La3+. The long-range goal of this work is to relate the XPS features to the nature of the chemical bonding in CeO2 and we describe our progress toward this goal.

  5. Chiral asymmetry in the angle-resolved O and C 1s-1 core photoemissions of the R enantiomer of glycidol

    Science.gov (United States)

    Powis, Ivan; Harding, Chris J.; Barth, Silko; Joshi, Sanjeev; Ulrich, Volker; Hergenhahn, Uwe

    2008-11-01

    We present measurements of a photoelectron circular dichroism in photoionization from O and C 1s core levels, of the R enantiomer of glycidol (C3H6O2) in the gas phase. This dichroism emerges from a forward-backward asymmetry in the angular distribution of electrons created on ionization with circularly polarized synchrotron radiation and is already fully present in the pure electric dipole approximation. Asymmetry factors obtained for the core levels in this study range up to a few percent, but it is likely that these values are limited by a failure to resolve photoemission from individual atomic sites. Theoretical modeling is provided to examine possible differences between these alternative atomic photoemission sites, and between different conformational structures of glycidol. The calculated chiral angular distribution parameters that support the circular dichroism display a much enhanced sensitivity to the molecular conformation compared to the conventional photoionization cross section and the β parameter. Likely conformer structures can be suggested after comparison with the experiment.

  6. Angle resolved photoemission in semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Petroff, Y.

    1983-02-01

    Bases of angular resolved photoemission: determination of the electronic band structure of solids (bulk), measurements of life-time and mean free path, determination of surfaces states (valence and core) and their relationship with surface reconstruction are described.

  7. Origin of metallic surface core-level shifts

    DEFF Research Database (Denmark)

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

    1995-01-01

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

  8. 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

  9. 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)

  10. 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.

  11. Study of photoemission and work function of large surface areas, phase 3, phase 4. [wavelength dependences of photoelectric space probe materials

    Science.gov (United States)

    1973-01-01

    The photoemission of materials which might be used in probe measurements of the exo-atmospheric electric field is considered by evaluating the wavelength dependence of their photoelectric yield for eleven elements over the range 800 to 3200 A. Yield data for zinc, copper beryllium, platinum, cadmium, graphite, carbon, gold, silver, tantalum, and tungsten show that copper-beryllium is a preferred material. Silver has one of the highest photoemissions when exposed to solar radiation.

  12. Angle resolved photoemission spectroscopy and surface states

    Science.gov (United States)

    Kar, Nikhiles

    2016-10-01

    Angle Resolved Photo Emission Spectroscopy (ARPES) has been a very effective tool to study the electronic states of solids, from simple metals to complex systems like cuprate superconductors. For photon energy in the range of 10 - 100 eV, it is a surface sensitive process as the free path of the photo emitted electrons is of the order of a few lattice parameters. However to interpret the experimental data one needs to have a theoretical foundation for the photoemission process. From the theory of photoemission it may be seen that one can get information about the state from which the electron has been excited. As the translational periodicity is broken normal to the surface, a new type of electron state in the forbidden energy gap can exist localized in the surface region. ARPES can reveal the existence and the property of such surface states. We shall also discuss briefly how the electromagnetic field of the photons are influenced by the presence of the surface and how one can try to take that into account in photoemission theory.

  13. High-energy photoemission spectroscopy for investigating bulk electronic structures of strongly correlated systems

    Energy Technology Data Exchange (ETDEWEB)

    Sekiyama, Akira, E-mail: sekiyama@mp.es.osaka-u.ac.jp [Division of Materials Physics, Graduate School of Engineering Science, Osaka University, Toyonaka 560-8531, Osaka (Japan); SPring-8/RIKEN, Sayo 679-5148, Hyogo (Japan)

    2016-04-15

    Progress of high-energy photoemission spectroscopy for investigating the bulk electronic structures of strongly correlated electron systems is reviewed. High-resolution soft X-ray photoemission has opened the door for revealing the bulk strongly correlated spectral functions overcoming the surface contributions. More bulk-sensitive hard X-ray photoemission spectroscopy (HAXPES) enables us to study the electronic structure with negligible surface contribution. The recent development of the polarization-dependent HAXPES is also described in this short review.

  14. Ba 4/ital d/ core-level spectroscopy in the YBa/sub 2/Cu/sub 3/O/sub 6. 9/ high-/ital T//sub /ital c// superconductor: Existence of a surface-shifted component

    Energy Technology Data Exchange (ETDEWEB)

    Liu, R.; Olson, C. G.; Yang, A.; Gu, C.; Lynch, D. W.; Arko, A. J.; List, R. S.; Bartlett, R. J.; Veal, B. W.; Liu, J. Z.; and others

    1989-08-01

    Two sets of spin-orbit split Ba 4/ital d/ core-level photoemission peaks were observed in a crystal of YBa/sub 2/Cu/sub 3/O/sub 6.9/. From constant final-state measurements taken as a function of kinetic energy, the low-binding-energy doublet is identified as a surface component. Possible origins of the surface shift are discussed.

  15. Two-photon photoemission study of the coverage-dependent electronic structure of chemisorbed alkali atoms on a Ag(111) surface.

    Science.gov (United States)

    Wang, Lei-Ming; Sametoglu, Vahit; Winkelmann, Aimo; Zhao, Jin; Petek, Hrvoje

    2011-09-01

    We report a systematic investigation of the electronic structure of chemisorbed alkali atoms (Li-Cs) on a Ag(111) surface by two-photon photoemission spectroscopy. Angle-resolved two-photon photoemission spectra are obtained for 0-0.1 monolayer coverage of alkali atoms. The interfacial electronic structure as a function of periodic properties and the coverage of alkali atoms is observed and interpreted assuming ionic adsorbate/substrate interaction. The energy of the alkali atom σ-resonance at the limit of zero coverage is primarily determined by the image charge interaction, whereas at finite alkali atom coverages, it follows the formation of a dipolar surface field. The coverage- and angle-dependent two-photon photoemission spectra provide information on the photoinduced charge-transfer excitation of adsorbates on metal surfaces. This work complements the previous work on alkali/Cu(111) chemisorption [Phys. Rev. B 2008, 78, 085419].

  16. HREELS and photoemission study of GaSb( 1 0 0 )-(1×3) surfaces prepared by optimal atomic hydrogen cleaning

    Science.gov (United States)

    Veal, T. D.; Lowe, M. J.; McConville, C. F.

    2002-03-01

    High-resolution electron-energy-loss spectroscopy (HREELS) and synchrotron-radiation photoemission spectroscopy (SRPES) have been used to study the Sb-stabilised GaSb(1 0 0)-(1×3) surface prepared by a two-stage low-temperature atomic hydrogen cleaning (AHC) procedure. The use of a maximum annealing temperature of 300 °C avoids the degradation of surface stoichiometry associated with higher annealing temperatures. After AHC at a sample temperature of 100 °C, SRPES results show that all Sb oxides have been removed and only a small amount of Ga oxide remains. Further AHC treatment at 300 °C results in a clean surface with a sharp (1×3) low energy electron diffraction pattern. SRPES results indicate that the surface stoichiometry is identical to that previously found for GaSb(1 0 0)-(1×3) prepared by in situ molecular beam epitaxy. Electron energy-dependent HREEL spectra exhibit a coupled plasmon-phonon mode which has been used to study the electronic structure of the near-surface region. Semi-classical dielectric theory simulations of the HREEL spectra of the clean GaSb(1 0 0)-(1×3) surface indicate no detectable electronic damage or dopant passivation results from the AHC treatment. Valence band SRPES indicates that the surface Fermi level is close to the valence band maximum, suggesting the presence of an inversion layer at the surface.

  17. 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...

  18. Electronic structure and polar catastrophe at the surface of LixCoO2 studied by angle-resolved photoemission spectroscopy

    Science.gov (United States)

    Okamoto, Y.; Matsumoto, R.; Yagihara, T.; Iwai, C.; Miyoshi, K.; Takeuchi, J.; Horiba, K.; Kobayashi, M.; Ono, K.; Kumigashira, H.; Saini, N. L.; Mizokawa, T.

    2017-09-01

    We report an angle-resolved photoemission spectroscopy (ARPES) study of LixCoO2 single crystals which have a hole-doped CoO2 triangular lattice. Similar to NaxCoO2 , the Co 3 d a1 g band crosses the Fermi level with strongly renormalized band dispersion while the Co 3 d eg' bands are fully occupied in LixCoO2 (x =0.46 and 0.71). At x =0.46 , the Fermi surface area is consistent with the bulk hole concentration indicating that the ARPES result represents the bulk electronic structure. On the other hand, at x =0.71 , the Fermi surface area is larger than the expectation which can be associated with the inhomogeneous distribution of Li reported in the previous scanning tunneling microscopy study by Iwaya et al. [Phys. Rev. Lett. 111, 126104 (2013), 10.1103/PhysRevLett.111.126104]. However, the Co 3 d peak is systematically shifted towards the Fermi level with hole doping excluding phase separation between hole rich and hole poor regions in the bulk. Therefore, the deviation of the Fermi surface area at x =0.71 can be attributed to hole redistribution at the surface avoiding polar catastrophe. The bulk Fermi surface of Co 3 d a1 g is very robust around x =0.5 even in the topmost CoO2 layer due to the absence of the polar catastrophe.

  19. High-resolution angle-resolved photoemission studies of high Tc superconductor Bi sub 2 Sr sub 2 CaCu sub 2 O sub 8

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Rong.

    1990-09-21

    An angle-resolved photoemission study of the normal and superconducting states in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} was performed. Measurements in the normal state show bands dispersing through the Fermi level from at least 350 meV below E{sub F}. The Fermi level crossings are consistant with local-density band calculation, including a point calculated to be of Bi-O character. Additional measurements were made where bands crossed the Fermi level between 100 and 250K, along with measurements on an adjacent Pt foil. The Fermi edges of both materials agree to within the noise. Below the Fermi level, the spectra show correlation effects on the form of an increased effective mass. The shape of the spectra can be explained by a lifetime-broadened photohole and secondary electrons. The effective inverse photohole lifetime is linear in energy. A superconducting gap has been measured at a number of points where there is density at the Fermi level in the normal state. By proper modeling, a gap of 24 meV was obtained for all these points, including points of Cu-O and Bi-O character respectively, according to band calculation. The lack of gap anisotropy in the basal plane suggests that pinning in this material is not d-wave pairing.

  20. Hard x-ray photoemission study of Yb1-x Zr x B12: the effects of electron doping on the Kondo insulator YbB12

    Science.gov (United States)

    Rousuli, A.; Sato, H.; Iga, F.; Hayashi, K.; Ishii, K.; Wada, T.; Nagasaki, T.; Mimura, K.; Anzai, H.; Ichiki, K.; Ueda, S.; Kondo, A.; Kindo, K.; Takabatake, T.; Shimada, K.; Namatame, H.; Taniguchi, M.

    2017-07-01

    We have carried out hard x-ray photoemission spectroscopy (HAXPES) of Yb1-x Zr x B12 (0≤slant x≤slant 0.875 ) to study the effects of electron doping on the Kondo insulator YbB12. The Yb valences of Yb1-x Zr x B12 at 300 K estimated from the Yb 3d HAXPES spectra decreased after substituting Yb with Zr from 2.93 for YbB12 to 2.83 for Yb0.125Zr0.875B12. A temperature dependent valence decrease was found upon cooling for all doping concentrations. We found peak shifts of the B 1s and Zr 3d5/2, and Yb3+ 4f spectra toward the deeper binding-energy with increasing Zr concentration, which indicates a shift of the Fermi level to the higher energy and that of the Yb 4f hole level close to the Fermi level, respectively, due to electron doping. These results qualitatively show the enhanced hybridization between the Yb 4f and conduction-band states with Zr substitution, consistent with magnetic susceptibility measurements.

  1. 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 ...

  2. Inverse photoemission studies of the empty electronic states and surface stability of La/sub 1. 85/Sr/sub 0. 15/CuO/sub 4/

    Energy Technology Data Exchange (ETDEWEB)

    Gao, Y.; Wagener, T.J.; Weaver, J.H.; Arko, A.J.; Flandermeyer, B.; Capone, D.W. II

    1987-09-01

    The energy distribution of the unoccupied electronic states of the high-T/sub c/ superconductor La/sub 1.85/Sr/sub 0.15/CuO/sub 4/ have been identified at room temperature using inverse photoemission. The density of states is very low from E/sub F/ to --3.5 eV above E/sub F/, strong emission features appear 5.8 and 8.7 eV above the Fermi level, E/sub F/, and the empty-state spectrum is unstructured thereafter until at least 25 eV. The prominent empty-state features are confined to an energy interval of --8 eV and are associated with the La 5d and 4f levels. The ratio of 4f intensity to 5d intensity showed a --5 fold increase for incident electron energies of --1500 eV compared to --30 eV. Our empty-state studies showed that the effects of high-energy electron-stimulated desorption were most pronounced --1.6 eV above E/sub F/, and the exposure of the sample to oxygen showed enhancement of these states.

  3. 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.

  4. 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.

  5. Resonant photoemission at the oxygen K edge as a tool to study the electronic properties of defects at SiO 2 /Si and SiO 2 /SiC interfaces

    Science.gov (United States)

    Tallarida, Massimo; Sohal, Rakesh; Schmeisser, Dieter

    2006-10-01

    Silicon is by far the most important material used in microelectronics, partly due to the excellent electronic properties of its native oxide (SiO 2), but substitute semiconductors are constantly the matter of research. SiC is one of the most promising candidates, also because of the formation of SiO 2 as native oxide. However, the SiO 2/SiC interface has very poor electrical properties due to a very high density of interface states which reduce its functionality in MIS devices. We have studied the electronic properties of defects in the SiO 2/Si and SiO 2/SiC interfaces by means of XAS, XPS and resonant photoemission at the O 1s and the Si 2p edges, using silicon dioxide thermally grown with thicknesses below 10 nm. Our XAS data are in perfect agreement with literature; in addition, resonant photoemission reveals the resonant contributions of the individual valence states. For the main peaks in the valence band we find accordance between the resonant behaviour and the absorption spectra, except for the peaks at -15 eV binding energy, whose resonant photoemission spectra have extra features. One of them is present in both interfaces and is due to similar defects, while another one at lower photon energy is present only for the SiO 2/SiC interface. This is related to a defect state which is not present at the SiO 2/Si interface.

  6. Hard x-ray photoemission and density functional theory study of the internal electric field in SrTiO3/LaAlO3 oxide heterostructures

    NARCIS (Netherlands)

    Slooten, E.; Zhong, Z.C.; Molegraaf, H.J.A.; Eerkes, P.D.; Jong, de S.; Massee, F.; Heumen, E.; Kruize, M.K.; Wenderich, S.; Kleibeuker, J.E.; Gorgoi, M.; Hilgenkamp, J.W.M.; Brinkman, A.; Huijben, M.; Rijnders, A.J.H.M.; Blank, D.H.A.; Koster, G.; Kelly, P.J.; Golden, M.S.

    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

  7. 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.)

  8. Hard X-ray photoemission spectroscopy of transition-metal oxide thin films and interfaces

    Energy Technology Data Exchange (ETDEWEB)

    Wadati, H., E-mail: wadati@ap.t.u-tokyo.ac.jp [Department of Applied Physics and Quantum-Phase Electronics Center (QPEC), University of Tokyo, Hongo, Tokyo 113-8656 (Japan); Fujimori, A. [Department of Physics, University of Tokyo, Bunkyo-ku, Tokyo 113-0033 (Japan)

    2013-10-15

    Highlights: •Photoemission spectroscopy is a powerful technique to study the electronic structures of transition-metal oxides. •Hard X-ray photoemission spectroscopy (HXPES) is a new type of photoemission spectroscopy which can probe bulk states. •HXPES is very suitable for studying oxide thin films such as the composition dependence and the film thickness dependence. -- Abstract: Photoemission spectroscopy is a powerful experimental technique to study the electronic structures of solids, especially of transition-metal oxides. Recently, hard X-ray photoemission spectroscopy (HXPES) has emerged as a more relevant experimental technique to obtain clear information about bulk states. Here, we describe how HXPES can be conveniently applied to study the interesting subjects on oxide thin films such as the composition dependence and the film thickness dependence of the electronic structures and the interfacial electronic structure of multilayers.

  9. Photoemission-based microelectronic devices

    Science.gov (United States)

    Forati, Ebrahim; Dill, Tyler J.; Tao, Andrea R.; Sievenpiper, Dan

    2016-11-01

    The vast majority of modern microelectronic devices rely on carriers within semiconductors due to their integrability. Therefore, the performance of these devices is limited due to natural semiconductor properties such as band gap and electron velocity. Replacing the semiconductor channel in conventional microelectronic devices with a gas or vacuum channel may scale their speed, wavelength and power beyond what is available today. However, liberating electrons into gas/vacuum in a practical microelectronic device is quite challenging. It often requires heating, applying high voltages, or using lasers with short wavelengths or high powers. Here, we show that the interaction between an engineered resonant surface and a low-power infrared laser can cause enough photoemission via electron tunnelling to implement feasible microelectronic devices such as transistors, switches and modulators. The proposed photoemission-based devices benefit from the advantages of gas-plasma/vacuum electronic devices while preserving the integrability of semiconductor-based devices.

  10. 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.

  11. Anisotropy in the thermal hysteresis of resistivity and charge density wave nature of single crystal SrFeO3-δ: X-ray absorption and photoemission studies.

    Science.gov (United States)

    Hsieh, S H; Solanki, R S; Wang, Y F; Shao, Y C; Lee, S H; Yao, C H; Du, C H; Wang, H T; Chiou, J W; Chin, Y Y; Tsai, H M; Chen, J-L; Pao, C W; Cheng, C-M; Chen, W-C; Lin, H J; Lee, J F; Chou, F C; Pong, W F

    2017-12-01

    The local electronic and atomic structures of the high-quality single crystal of SrFeO3-δ (δ~0.19) were studied using temperature-dependent x-ray absorption and valence-band photoemission spectroscopy (VB-PES) to investigate the origin of anisotropic resistivity in the ab-plane and along the c-axis close to the region of thermal hysteresis (near temperature for susceptibility maximum, Tm~78 K). All experiments herein were conducted during warming and cooling processes. The Fe L 3,2-edge X-ray linear dichroism results show that during cooling from room temperature to below the transition temperature, the unoccupied Fe 3d e g states remain in persistently out-of-plane 3d 3z(2)-r(2) orbitals. In contrast, in the warming process below the transition temperature, they change from 3d 3z(2)-r(2) to in-plane 3d x(2)-y(2) orbitals. The nearest-neighbor (NN) Fe-O bond lengths also exhibit anisotropic behavior in the ab-plane and along the c-axis below Tm. The anisotropic NN Fe-O bond lengths and Debye-Waller factors stabilize the in-plane Fe 3d x(2)-y(2) and out-of-plane 3d 3z(2)-r(2) orbitals during warming and cooling, respectively. Additionally, a VB-PES study further confirms that a relative band gap opens at low temperature in both the ab-plane and along the c-axis, providing the clear evidence of the charge-density-wave nature of SrFeO3-δ (δ~0.19) single crystal.

  12. Plasmon-exciton coupling at Ag nanocluster decorated TiO2(110) surface studied by time-resolved two-photon photoemission spectroscopy

    Science.gov (United States)

    Tan, Shijing; Argondizzo, Adam; Petek, Hrvoje

    We study the spectroscopy and electron dynamics at Ag nanocluster decorated TiO2(110) surface upon photoexcitation of plasmonic modes by two-photon photoemission spectroscopy (2PP). Depositing Ag onto a reduced rutile TiO2(110) surface at room temperature forms pancake-like Ag particles with an average diameter of 4 nm and height of 1.5 nm. Measurements of the 2PP yield from Ag/TiO2 surface with tunable femtosecond laser excitation show enhancement at plasmonic resonances. Exciting with s-polarization (S -->) the plasmonic resonance enhancement has a single peak at 3.1 eV, whereas with p-polarization (P -->) there is an additional more intense resonance at 3.8 eV. We attribute the 3.1 and 3.8 eV peaks to the in-plane and the surface-normal plasmon modes respectively. Crystal azimuth orientation dependent excitation with (S -->) shows an anisotropy in the 2PP spectra for the 3.1 eV in-plane plasmon mode when the laser electric field is aligned in the [001] vs. [ 1 1 0 ] directions. The existence of two plasmon modes and the in-plane plasmon anisotropy imply that the plasmon modes are perturbed by coherent coupling with excitons in the rutile TiO2 substrate. We speculate that plasmon-exciton resonant energy transfer could play an important role in the plasmonically enhanced photocatalysis at the Ag/TiO2 surface.

  13. Simulation and characterization of the crystal growth by photoemission; Simulation et caracterisation de la croissance cristalline par photoemission

    Energy Technology Data Exchange (ETDEWEB)

    Fazouan, N.

    1994-05-16

    In this thesis, we argue in favour of photoemission as an in-situ characterization tool for the homo-epitaxial growth of GaAs. The first part, is concerned with the interpretation of the origin of the photoemission oscillations as first observed by J.N. Eckstein and al during MBE growth of GaAs. To study this effect, two approaches have been used. These approaches are based on reaction surface and roughness observations to study the growth mode. They associate the photoemission current with the presence of uncovered gallium adatoms, i.e. those which do not have an arsenic atom above them. The first approach is based on chemical rate theory, whereas the second is based on an atomistic simulation of GaAs homo-epitaxy. This last approach introduces the notion of interlayer migration processes and uses a Monte Carlo technique to look at the temporal evolution of the configuration and hence the morphology. It is shown with these two approaches that the photoemission current has similar characteristics as to those of RHEED, c.g.the same oscillation period. The results obtained have shown the relationship between the photoemission oscillations amplitude and the growth mode which are determined by the mechanisms of absorption and diffusion of gallium atoms and arsenic atoms of molecules. Finally, the study of the effect of the surface reactions shows the importance of these in the case where arsenic is supplied in molecular form (As{sub 2}). The last part concerns the experimental measurements at the threshold photoemission current during epitaxial growth of GaAs by metal-organic vapour phase epitaxy (MOVPE). The objective of this experimental study is to test the good running of the photo-assisted MOVPE low pressure system and to study the possibilities offered by this as an in-situ diagnostic tool for MOVPE. (author). 101 refs., 80 figs., 6 tabs.

  14. 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.

  15. Valence-band electronic structure of Zn3P2 as a function of annealing as studied by synchrotron radiation photoemission

    Science.gov (United States)

    Nelson, Art J.; Kazmerski, L. L.; Engelhardt, Mike; Hochst, Hartmut

    1990-02-01

    Ultraviolet photoemission (UPS) utilizing synchrotron radiation has been used to characterize changes in the valence-band electronic structure of crystalline Zn3P2 as a function of annealing temperature. The Zn3P2 crystal was etched in bromine-methanol prior to analysis and annealing was performed in vacuum at 300 and 350 °C after sputter cleaning. The UPS spectra for the virgin material are qualitatively similar to the photoemission results for various II-VI Zn compound semiconductors and a comparison of the Zn 3d binding energies with respect to the valence band maximum is presented. The results for the virgin material and the 300 °C anneal are further compared with the theoretically predicted band structure of Zn3P2 as determined by a pseudopotential energy band calculation. Loss of phosphorus from the surface and the presence of elemental zinc on the surface after the 350 °C anneal is evident.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1997-04-01

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

  17. 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.

  18. Space-charge effects in high-energy photoemission

    Energy Technology Data Exchange (ETDEWEB)

    Verna, Adriano, E-mail: adriano.verna@uniroma3.it [Dipartimento di Scienze, Università degli Studi Roma Tre, Via della Vasca Navale 84, I-00146 Roma (Italy); CNISM Unità di Roma Tre, Via della Vasca Navale 84, I-00146 Roma (Italy); Greco, Giorgia [Dipartimento di Scienze, Università degli Studi Roma Tre, Via della Vasca Navale 84, I-00146 Roma (Italy); Lollobrigida, Valerio [Dipartimento di Scienze, Università degli Studi Roma Tre, Via della Vasca Navale 84, I-00146 Roma (Italy); Scuola Dottorale in Matematica e Fisica, Università Roma Tre, Via della Vasca Navale 84, I-00146 Roma (Italy); Offi, Francesco; Stefani, Giovanni [Dipartimento di Scienze, Università degli Studi Roma Tre, Via della Vasca Navale 84, I-00146 Roma (Italy); CNISM Unità di Roma Tre, Via della Vasca Navale 84, I-00146 Roma (Italy)

    2016-05-15

    Highlights: • N-body simulations of interacting photoelectrons in hard X-ray experiments. • Secondary electrons have a pivotal role in determining the energy broadening. • Space charge has negligible effects on the photoelectron momentum distribution. • A simple model provides the characteristic time for energy-broadening mechanism. • The feasibility of time-resolved high-energy experiments with FELs is discussed. - Abstract: Pump-and-probe photoelectron spectroscopy (PES) with femtosecond pulsed sources opens new perspectives in the investigation of the ultrafast dynamics of physical and chemical processes at the surfaces and interfaces of solids. Nevertheless, for very intense photon pulses a large number of photoelectrons are simultaneously emitted and their mutual Coulomb repulsion is sufficiently strong to significantly modify their trajectory and kinetic energy. This phenomenon, referred as space-charge effect, determines a broadening and shift in energy for the typical PES structures and a dramatic loss of energy resolution. In this article we examine the effects of space charge in PES with a particular focus on time-resolved hard X-ray (∼10 keV) experiments. The trajectory of the electrons photoemitted from pure Cu in a hard X-ray PES experiment has been reproduced through N-body simulations and the broadening of the photoemission core-level peaks has been monitored as a function of various parameters (photons per pulse, linear dimension of the photon spot, photon energy). The energy broadening results directly proportional to the number N of electrons emitted per pulse (mainly represented by secondary electrons) and inversely proportional to the linear dimension a of the photon spot on the sample surface, in agreement with the literature data about ultraviolet and soft X-ray experiments. The evolution in time of the energy broadening during the flight of the photoelectrons is also studied. Despite its detrimental consequences on the energy

  19. Wigner photoemission time delay from endohedral anions

    Science.gov (United States)

    Kumar, Ashish; Varma, Hari R.; Deshmukh, Pranawa C.; Manson, Steven T.; Dolmatov, Valeriy K.; Kheifets, Anatoli

    2016-10-01

    Characteristic features of Wigner photoemission time delay from endohedral anions A@C60q along with their dependence on the anion charge q are unraveled. Specifically, significant enhancement of the time delay in the innermost dipole photoionization channels near threshold is found, owing to the presence of the Coulomb confined resonances (CRs). Moreover, it is shown that interchannel coupling of the inner-shell Coulomb CRs with outer-shell photoionization channels results in resonantly enhanced time delay in the release of the outer-shell photoelectron well above, several hundreds eV, the outer-shell thresholds. It is also demonstrated that, and explained why, photoionization cross sections of the innermost subshells as well as outer subshells (near the inner-subshell threshold) depends only very weakly on the anion charge q , but the dependence of the corresponding time delays on q can be significant. Furthermore, Coulomb CRs are found to emerge in the innermost quadrupole photoionization channels as well, thereby causing considerable time delay in the quadrupole photoemission. These findings are illustrated in calculations of the photoionization of inner and outer subshells of the endohedral anions Ne@C60-1 and Ne@C60-5 that were chosen as case studies.

  20. A photoemission and XAS study of oxygen coadsorbed with a (2x2) layer of K on graphite

    NARCIS (Netherlands)

    Puglia, C.; Bennich, P.; Hasselström, J.; Bröhwiler, P.A.; Nilsson, A.; Mårtensson, N.; Rudolf, P.

    1997-01-01

    We have studied the coadsorption of oxygen with a (2 × 2) monolayer of K on graphite. At least three different adsorption phases for oxygen have been found. Different spectroscopic techniques have been used in order to identify the different oxygen species adsorbed on the surface. For low oxygen

  1. Photoemission study of fluorination atmospheric pressure plasma processes on EPDM: Influence of the carrier and fluorinating gas

    Energy Technology Data Exchange (ETDEWEB)

    Martinez, L., E-mail: lidia.martinez@icmm.csic.es [Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC) Cantoblanco, 28049 Madrid (Spain); Huttel, Y. [Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC) Cantoblanco, 28049 Madrid (Spain); Verheyde, B.; Vanhulsel, A. [Flemish Institute for Technological Research (VITO), Boeretang 200, 2400 Mol (Belgium); Roman, E. [Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC) Cantoblanco, 28049 Madrid (Spain)

    2010-11-15

    Fluorination plasma treatments at atmospheric pressure were used to modify the surface composition of EPDM elastomer. In this study, two different precursors (CF{sub 4} and SF{sub 6}) and two carrier gases (He and Ar) were used for the surface modification of EPDM elastomer. The surface modifications were studied by means of X-ray photoelectron spectroscopy. We have observed a strong influence of the gas selection on the extent of the surface modification induced with these treatments. In general terms, the use of CF{sub 4} generates a higher concentration of fluorine in the elastomer surface. On the other hand, the use of He as carrier gas also increases the effectiveness of the modification process. The fluorine uptake varies between 2 and 13%, although the formation of fluorine-containing functional groups was detected when the amount of fluorine on the surface exceeded 7%. After all treatments, an important oxygen uptake was observed, with amounts three or four times higher than the untreated elastomer.

  2. Exploring electronic structure of one-atom thick polycrystalline graphene films: A nano angle resolved photoemission study

    Science.gov (United States)

    Avila, José; Razado, Ivy; Lorcy, Stéphane; Fleurier, Romain; Pichonat, Emmanuelle; Vignaud, Dominique; Wallart, Xavier; Asensio, María C.

    2013-01-01

    The ability to produce large, continuous and defect free films of graphene is presently a major challenge for multiple applications. Even though the scalability of graphene films is closely associated to a manifest polycrystalline character, only a few numbers of experiments have explored so far the electronic structure down to single graphene grains. Here we report a high resolution angle and lateral resolved photoelectron spectroscopy (nano-ARPES) study of one-atom thick graphene films on thin copper foils synthesized by chemical vapor deposition. Our results show the robustness of the Dirac relativistic-like electronic spectrum as a function of the size, shape and orientation of the single-crystal pristine grains in the graphene films investigated. Moreover, by mapping grain by grain the electronic dynamics of this unique Dirac system, we show that the single-grain gap-size is 80% smaller than the multi-grain gap recently reported by classical ARPES. PMID:23942471

  3. 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...

  4. 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.

  5. Photoemission of Mn6Cr single-molecule magnets

    Science.gov (United States)

    Heinzmann, U.; Merschjohann, F.; Helmstedt, A.; Gryzia, A.; Winter, A.; Steppeler, S.; Müller, N.; Brechling, A.; Sacher, M.; Richthofen, C.-G. Freiherr v.; Glaser, T.; Voss, S.; Fonin, M.; Rüdiger, U.

    2009-11-01

    We present the status of new experimental studies of X-ray absorption spectroscopy, magnetic circular dichroism in photoemission and spin-resolved photoelectron spectroscopy of Mn6Cr single-molecule magnet systems by use of circularly-polarized synchrotron radiation of the electron storage rings in Maxlab Lund, Sweden und BESSY, Berlin, Germany.

  6. 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.

  7. Resonant Photoemission and M_{2,3}-Absorption Spectra in Nickel Dichloride

    Science.gov (United States)

    Igarashi, J.

    Ni 3p-resonant photoemission and Ni M_{2,3}-absorption spectra are calculated in detail on a cluster of (NiCl_6)^{4-} with the use of the transition matrix elements evaluated on the Herman-Skillman potential in Ni atom. Overall spectral shape agrees well with experiment, allowing a determination of the parameters which characterize Ni 3d and Cl 3p states. Resonance behavior is discussed near the Ni 3p-core level photothreshold. The resonant enhancement is found to be larger for the peak with higher binding energy in the d^7-multiplets.

  8. Energy-resolved photoemission studies of Be-containing surfaces for fusion; Energievariierte Photoemissionsstudien an berylliumhaltigen Oberflaechen fuer die Fusion

    Energy Technology Data Exchange (ETDEWEB)

    Koeppen, Martin

    2013-02-04

    . Oxygen diffusion is observed and attributed to diffusion of BeO. Further, the influence of a BeO-interlayer on the carbidisation in the system C-W is investigated. Already at RT small amounts of carbidised W are visible. At 1280 K further carbidisation of W is observed. No reaction between BeO and W is visible. Carbidisation of W shows, that BeO does not serve as a diffusion barrier for C, even at RT. Using energy-resolved XPS and the newly developed quantitative model allows detailed studies of multi-component surface reactions considering the evolution of the depth distribution.

  9. Magnetic contrast in threshold photoemission electron microscopy

    NARCIS (Netherlands)

    Veghel, Marinus Godefridus Adrianus van

    2004-01-01

    In threshold photoemission electron microscopy (threshold PEEM), photoelectrons are excited by UV photons with an energy just above the photoemission threshold. The lateral intensity distribution of these electrons is then imaged by an electrostatic lens system. In this thesis, the possibilities o

  10. Equivalent-core calculation of core-level relaxation energies in photoelectron spectroscopy: A molecular-orbital approach

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Y. [Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Zhuang, G.; Ross, P.N. [Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Van Hove, M.A.; Fadley, C.S. [Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)]|[Department of Physics, University of California at Davis, Davis, California 95616 (United States)

    1998-10-01

    The equivalent-core approximation is implemented in a novel way so as to calculate core-level relaxation energies in photoelectron spectroscopy. The method is based on self-consistent field (SCF) Hartree{endash}Fock molecular-orbital calculations via linear combinations of atomic orbitals, and involves evaluating the difference of sums of two-electron Coulomb and exchange integrals, for all electrons in an atom and in its equivalent-core ion. By thus avoiding SCF calculations with a core hole present (the true final state of photoemission), this procedure is shown to significantly save computing time in comparison with an exact SCF direct-hole calculation. Application of the method in single atoms and selected molecules shows about a 10{percent} difference with respect to direct-hole calculation results. The approximation introduces about 1{endash}6 eV errors compared to the experimental results of gas phase molecules. This method thus should be a generally useful procedure for estimating relaxation energies in core spectra. {copyright} {ital 1998 American Institute of Physics.}

  11. 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}_...

  12. Time-resolved photoemission using attosecond streaking

    Science.gov (United States)

    Nagele, S.; Pazourek, R.; Wais, M.; Wachter, G.; Burgdörfer, J.

    2014-04-01

    We theoretically study time-resolved photoemission in atoms as probed by attosecond streaking. We review recent advances in the study of the photoelectric efect in the time domain and show that the experimentally accessible time shifts can be decomposed into distinct contributions that stem from the feld-free photoionization process itself and from probe-field induced corrections. We perform accurate quantum-mechanical as well as classical simulations of attosecond streaking for efective 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@C60 and discuss how streaking time shifts are modifed due to the interaction of the C60 cage with the probing infrared streaking field.

  13. Angle - resolved - photoemission study of Bi sub 2 Sr sub 2 CaCu sub 2 O sub 8+. delta. : Metallicity of the Bi-O plane

    Energy Technology Data Exchange (ETDEWEB)

    Wells, B.O.; Shen, Z.; Dessau, D.S.; Spicer, W.E.; Olson, C.G.; Mitzi, D.B.; Kapitulnik, A.; List, R.S.; Arko, A. (Stanford Electronics Laboratories, Stanford University, Stanford, CA (USA) Ames Laboratory, Iowa State University, Ames, IA Department of Applied Physics, Stanford University, Stanford, CA (USA) Los Alamos National Laboratory, Los Alamos, NM (USA))

    1990-12-10

    We have performed high-resolution angle-resolved-photoemission experiments on Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} single crystals with different annealing histories. By depositing a small amount of Au on the surface, we were able to distinguish electronic states associated with the Bi-O surface layer. We found that the Bi-O atomic surface layer is metallic and superconducting for samples that were high-temperature annealed in oxygen but not for as-grown samples. The Cu-O plane is found to be superconducting in all samples.

  14. Valence-band electronic structure of Zn sub 3 P sub 2 as a function of annealing as studied by synchrotron radiation photoemission

    Energy Technology Data Exchange (ETDEWEB)

    Nelson, A.J.; Kazmerski, L.L. (Solar Energy Research Institute, 1617 Cole Boulevard, Golden, Colorado 80401 (US)); Engelhardt, M.; Hochst, H. (Synchrotron Radiation Center, University of Wisconsin-Madison, 3731 Schneider Drive, Stoughton, Wisconsin 53589 (US))

    1990-02-01

    Ultraviolet photoemission (UPS) utilizing synchrotron radiation has been used to characterize changes in the valence-band electronic structure of crystalline Zn{sub 3}P{sub 2} as a function of annealing temperature. The Zn{sub 3}P{sub 2} crystal was etched in bromine-methanol prior to analysis and annealing was performed in vacuum at 300 and 350 {degree}C after sputter cleaning. The UPS spectra for the virgin material are qualitatively similar to the photoemission results for various II-VI Zn compound semiconductors and a comparison of the Zn 3{ital d} binding energies with respect to the valence band maximum is presented. The results for the virgin material and the 300 {degree}C anneal are further compared with the theoretically predicted band structure of Zn{sub 3}P{sub 2} as determined by a pseudopotential energy band calculation. Loss of phosphorus from the surface and the presence of elemental zinc on the surface after the 350 {degree}C anneal is evident.

  15. 50 years anniversary of the discovery of the core level chemical shifts. The early years of photoelectron spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Mårtensson, Nils [Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala (Sweden); Sokolowski, Evelyn [Tvär-Ramsdal 1, 611 99 Tystberga (Sweden); Svensson, Svante, E-mail: Svante.Svensson@fysik.uu.se [Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala (Sweden)

    2014-03-01

    Highlights: • 50 years since the discovery of t the core level chemical shift. • The pioneering years of ESCA. • A critical review of the first core electron chemical shift results. - Abstract: The pioneering years of photoelectron spectroscopy in Uppsala are discussed, especially the work leading to the discovery of the core level chemical shifts. At a very early stage of the project, the pioneering group observed what they described as evidence for chemical shifts in the core level binding energies. However, it can now be seen that the initial observations to a large extent was due to charging of the samples. It is interesting to note that the decisive experiment was realized, not as a result of a systematic study, but was obtained with a large element of serendipity. Only when a chemical binding energy shift was observed between two S2p electron lines in the same molecule, the results were accepted internationally, and the fascinating expansion of modern core level photoelectron spectroscopy could start.

  16. 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

  17. Photoemission spectromicroscopy with MAXIMUM at Wisconsin

    Energy Technology Data Exchange (ETDEWEB)

    Ng, W.; Ray-Chaudhuri, A.K.; Cole, R.K.; Wallace, J.; Crossley, S.; Crossley, D.; Chen, G.; Green, M.; Guo, J.; Hansen, R.W.C.; Cerrina, F.; Margaritondo, G. (Dept. of Electrical Engineering, Dept. of Physics and Synchrotron Radiation Center, Univ. of Wisconsin, Madison (USA)); Underwood, J.H.; Korthright, J.; Perera, R.C.C. (Center for X-ray Optics, Accelerator and Fusion Research Div., Lawrence Berkeley Lab., CA (USA))

    1990-06-01

    We describe the development of the scanning photoemission spectromicroscope MAXIMUM at the Wisoncsin Synchrotron Radiation Center, which uses radiation from a 30-period undulator. The article includes a discussion of the first tests after the initial commissioning. (orig.).

  18. 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.

  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. Angle-resolved photoemission study of the electronic structures of AuAl{sub 2} and PtGa{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Hsu, L.S. [National Chang-Hua Univ. of Education (Taiwan, Province of China). Dept. of Physics; Denlinger, J.D.; Allen, J.W. [Univ. of Michigan, Ann Arbor, MI (United States). Randall Lab.

    1998-12-31

    Synchrotron-radiation-excited angle-resolved photoemission spectra of AuAl{sub 2} and PtGa{sub 2} are presented. Experimental dispersion relations from normal emission spectra are compared to semi-relativistic augmented-plane-wave band-structure calculations. For PtGa{sub 2}, the Pt 5d bands show good agreement within a few tenths of an eV, while for AuAl{sub 2}, the experimental Au 5d band width is {approx} 0.5 eV greater than theory. In addition, polar-angle spectra and Fermi-edge intensity mapping allow the band dispersions of weak s-p bands to be revealed, and a hole pocket centered on the L-point is observed.

  1. Electronic structure studies of YBa[sub 2]Cu[sub 3]O[sub x](6. 2 [le] x [le] 6. 9) using angle resolved photoemission

    Energy Technology Data Exchange (ETDEWEB)

    Veal, B.W.; Liu, Rong; Paulikas, A.P.; Koelling, D.D.; Downey, J.W. (Argonne National Lab., IL (United States)); Shi, Hao (Argonne National Lab., IL (United States) Missouri Univ., Kansas City, MO (United States). Dept. of Physics); Olson, C.G. (Ames Lab., IA (United States)); Arko, A.J.; Joyce, J.J.; Blythe, R. (Los Alamos National Lab., NM (United States))

    1992-11-01

    Using high resolution angle resolved photoemission, the electronic structure of YBa[sub 2]Cu[sub 3]O[sub x] is examined when oxygen stoichiometries are varied in the range 6.2 [le] [times] [le] 6.9. Detailed measurements of the Fermi surface for YBa[sub 2]Cu[sub 3]O[sub 6.9] are presented and are compared with predictions of band theory. In the metallic region of the phase diagram, changes in the Fermi surfaces are measured as a function of oxygen stoichiometry. The electronic structure is monitored as the oxide changes from a metal to a semiconductor with additional oxygen depletion. For intermediate stoichiometries, effects of oxygen vacancy ordering are considered. Unusual resonant effects observed at several photon energies are examined as oxygen content is varied.

  2. Electronic structure studies of YBa[sub 2]Cu[sub 3]O[sub x] (6. 2[<=]x[<=]6. 9) using angle-resolved photoemission

    Energy Technology Data Exchange (ETDEWEB)

    Veal, B.W.; Liu, Rong; Paulikas, A.P.; Koelling, D.D.; Shi, Hao; Downey, J.W. (Materials Science Division and Science and Technology Center for Superconductivity, Argonne National Laboratory, Argonne, IL (United States)); Olson, C.G. (Ames Laboratory and Department of Physics, Iowa State University, Ames, IA (United States)); Arko, A.J.; Joyce, J.J.; Blythe, R. (Los Alamos National Laboratory, Los Alamos, NM (United States))

    1993-12-01

    Using high-resolution angle-resolved photoemission, the electronic structure of YBa[sub 2]Cu[sub 3]O[sub x] is examined when oxygen stoichiometries are varied in the range 6.2[<=]x[<=]6.9. Detailed measurements of the Fermi surface for YBa[sub 2]Cu[sub 3]O[sub 6.9] are presented and are compared with predictions of band theory. In the metallic region of the phase diagram, changes in the Fermi surfaces are measured as a function of oxygen stoichiometry. The electronic structure is monitored as the oxide changes from a metal to a semiconductor with additional oxygen depletion. For intermediate stoichiometries, effects of oxygen-vacancy ordering are considered. Unusual resonant effects observed at several photon energies are examined as the oxygen content is varied.

  3. Fermi-surface topology of YBa sub 2 Cu sub 3 O sub x with varied oxygen stoichiometry: A photoemission study

    Energy Technology Data Exchange (ETDEWEB)

    Liu, R.; Veal, B.W.; Paulikas, A.P.; Downey, J.W.; Kostic, P.J.; Fleshler, S.; Welp, U. (Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)); Olson, C.G.; Wu, X. (Ames Laboratory and Department of Physics, Iowa State University, Ames, Iowa 50011 (United States)); Arko, A.J.; Joyce, J.J. (Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States))

    1992-11-01

    High-resolution angle-resolved photoemission measurements are reported for YBa{sub 2}Cu{sub 3}O{sub {ital x}} when oxygen stoichiometry {ital x} was varied between 6.3 and 6.9. Fermi surfaces were measured and their dependence on oxygen stoichiometry was monitored by observing the dispersing behavior of spectral features, scanning the entire first Brillouin zone. For {ital x}=6.9, measured Fermi surfaces correspond very well with the plane-related Fermi surfaces calculated from band theory. Relatively small changes in Fermi surfaces were observed when oxygen stoiochiometry was varied in the range 6.5{le}{ital x}{le}6.9, where the material is metallic. However, significant changes in the spectral behavior were observed when the material becomes insulating.

  4. X-ray absorption and photoemission study of spin state and metal-insulator transition in GdBaCo{sub 2}O{sub 5.47}

    Energy Technology Data Exchange (ETDEWEB)

    Hu, Z.; Wu Hua; Koethe, T.; Haverkort, M.W.; Burnus, T.; Gegner, J.; Zobel, C.; Lorenz, T.; Tjeng, L.H. [2. Physikalisches Inst., Univ. zu Koeln (Germany); Barilo, S.N. [Inst. of Solid State and Semiconductors Physics, National Academy of Sciences (Belarus); Lin, H.J.; Chen, C.T. [National Synchrotron Radiation Research Center, Tsinchu (China); Brookes, N.B. [European Synchrotron Radiation Facility (France)

    2007-07-01

    The fundamental physics of the magnetoresistance materials RBaCo{sub 2}O{sub 5.5} (R=Sm,Eu,Gd,Tb,Dy,Y), particularly the issue of spin-state and metal-insulator transition (MIT), is currently under intense debate. Using valence-baud photoemission spectra and X-ray absorption spectra at both the O-K and Co-L{sub 2,3} edges, we found that crossing the MIT, the band gap decreases but does not collapse across the MIT. More significantly, our spectroscopic evidence firmly rules out the widely accepted model for the low-temperate phase, namely that the Co{sup 3+} ions in the octahedral sites are mainly low spin and in the pyramidal sites intermediate spin. We rather found that the MIT in this system is very similar to the high temperature (600 K) MIT of LaCoO{sub 3}. (orig.)

  5. Core-level spectroscopy investigation of the Mo{sub 0.75}Re{sub 0.25}(100) surface

    Energy Technology Data Exchange (ETDEWEB)

    Lyman, P.F.; Zehner, D.M.

    1993-10-01

    Preferential surface segregation in the Mo{sub 0.75}(100) surface region was investigated using high-resolution core-level spectroscopy with synchrotron radiation. The magnitude and direction of the surface core-level shifts observed in this study can be qualitatively understood by comparison to W and Mo core-level shifts. Measured core-level intensities are found to be consistent with the segregation of Mo to the surface of the alloy, with an enrichment of Re in the second layer (as found in previous investigations). It is inferred that both Tc and Os will segregate to the Mo{sub 0.75}Re{sub 0.25}(100) surface.

  6. Electronic structure in the bulk and at the surface of lanthanide materials. A detailed study with X-ray emission and inverse photoemission

    CERN Document Server

    Huebinger, F

    2000-01-01

    LaTe. With measurements of the O3-XE in the Lanthanum-Chalcogenides we could demonstrate the transfer of s-like valence electrons from the Lanthanum atom to the Chalcogen atom. Furthermore, the binding energy of the state at the Lanthanum atom was determined. The surface core-level shift is smaller by 25 % in the Chalcogenides than in La-metal. We also describe a theoretical model, which qualitatively explains the observed larger shifts of the core-level binding energy in PE than in IPE from Lanthan-Chalcogenides. This dissertation is concerned with the occupied and unoccupied electronic structure of lanthanide materials. With surface sensitive electron-excited x-ray emission spectroscopy (XES) we could experimentally determine a surface and bulk partial density of states (p-DOS) for the metals Lanthanum, Lutetium and Samarium. From calculations of the O3-XE transition probability we anticipate a three times higher probability for s-like than for d-like electrons to fill the 5p3/2-hole; this was confirmed exp...

  7. Electron-phonon coupling and its evidence in the photoemission spectra of lead

    OpenAIRE

    Reinert, F.; Eltner, B.; Nicolay, G.; Ehm, D.; Schmidt, S; Huefner, S.

    2003-01-01

    We present a detailed study on the influence of strong electron-phonon coupling to the photoemission spectra of lead. Representing the strong-coupling regime of superconductivity, the spectra of lead show characteristic features that demonstrate the correspondence of physical properties in the normal and the superconducting state, as predicted by the Eliashberg theory. These features appear on an energy scale of a few meV and are accessible for photoemission only by using modern spectrometers...

  8. 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

  9. 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.

  10. Adlayer Core-Level Shifts of Random Metal Overlayers on Transition-Metal Substrates

    DEFF Research Database (Denmark)

    Ganduglia-Pirovano, M. V.; Kudrnovský, J.; Scheffler, M.

    1997-01-01

    We calculate the difference of the ionization energies of a core electron of a surface alloy, i.e., a B atom in a A(1-x)B(x) overlayer on a fee B(001) substrate, and a core electron of the clean fee B(001) surface using density-functional theory. We analyze the initial-state contributions and the...... the initial-state trends are explained in terms of the change of inter- and intra-atomic screening upon alloying. A possible role of alloying on the chemical reactivity of metal surfaces is discussed....... and the screening effects induced by the core hole, and study the influence of the alloy composition for a number of noble metal-transition metal systems. Our analysis clearly indicates the importance of final-state screening effects for the interpretation of measured core-level shifts. Calculated deviations from...

  11. Temperature-dependent hard X-ray photoemission spectra of ternary Tl compounds with high Seebeck coefficient

    Energy Technology Data Exchange (ETDEWEB)

    Mimura, Kojiro; Ishizu, Takahiko; Yamamoto, Kazuya; Takasu, Junta; Yonehira, Yuri; Taguchi, Yukihiro; Ichikawa, Kouichi [Department of Mathematical Sciences, Graduate School of Engineering, Osaka Prefecture University, Sakai (Japan); Wakita, Kazuki [Department of Electrical, Electronics and Computer Engineering, Chiba Institute of Technology, Narashino, Chiba (Japan); Mamedov, Nazim [Institute of Physics, Azerbaijan National Academy of Sciences, Baku (Azerbaijan); Yan, Ke; Ikenaga, Eiji [Japan Synchrotron Radiation Research Institute, Kouto, Sayo-cho (Japan); Kobayashi, Keisuke [National Institute for Materials Science, Kouto, Sayo-cho, Sayo-gun, Hyogo (Japan)

    2009-05-15

    The temperature dependence of the core-level and valence-band electronic structures of TlGaTe{sub 2} and TlInSe{sub 2} that exhibits high values of Seebeck coefficient has been studied by hard X-ray photoemission spectroscopy over the temperature range 40-450 K. The relative peak position and peak width for Tl 4f, Ga 2p and Te 3d in TlGaTe{sub 2} are determined. It is shown that not only chemical shift defying the peak position but also electron-phonon interaction responsible for temperature line-broadening has rather peculiar temperature behaviour that reflects incommensurate phase transition. Thermoelectric power of TlGaTe{sub 2} is evaluated and found to be very close to that of TlInSe{sub 2}. It is shown that Tl 4f spectra of both compounds also display close similarity (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  12. 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.

  13. Observation of the surface 4f state of CePd{sub 7} by means of the resonant-inverse-photoemission study at the Ce 4d absorption edge

    Energy Technology Data Exchange (ETDEWEB)

    Kanai, K.; Tezuka, Y.; Fujisawa, M.; Harada, Y.; Shin, S. [Synchrotron Radiation Laboratory, Institute for Solid State Physics, University of Tokyo, Tanashi, Tokyo 188 (Japan); Schmerber, G.; Kappler, J.P.; Parlebas, J.C. [IPCMS-GEMME (UMR 46 CNR), Universite Louis Pasteur, 23, rue du Loess, 67037 Strasbourg (France); Kotani, A. [Institute for Solid State Physics, University of Tokyo, 7-22-1 Roppongi, Minato-ku, Tokyo 106 (Japan)

    1997-01-01

    The resonant inverse photoemission study (RIPES) of CePd{sub 7}, has been carried out at the Ce 4d{r_arrow}4f absorption edge. The strong resonant enhancement of the 4f cross section enables us to distinguish two 4f components in the empty electronic state near the Fermi level. The incidence-angle dependence of the RIPES indicates a clear difference between ground-state configurations at the bulk and surface. It is found that the former shows a strongly hybridized 4f state, while the latter shows a localized 4f character. The angle dependence of the RIPES of {alpha}-Ce metal has been also carried out and similar results as those of CePd{sub 7} were obtained. The RIPES at the Ce 4d{r_arrow}4f edge is found to be a powerful method to investigate the surface 4f state. {copyright} {ital 1997} {ital The American Physical Society}

  14. Core-level magnetic circular dichroism in 3d and 4f magnetic systems (invited) (abstract)

    Science.gov (United States)

    Koide, T.

    1994-05-01

    With the recent availability of circulary polarized synchrotron radiation over a wide photon energy range from VUV to hard X rays, the magnetic circular dichroism (MCD) in core-level photoabsorption has rapidly attracted growing interest, both experimentally and theoretically. This novel technique can provide element-specific and site-selective information about the magnetic and the electronic states in various magnetic substances because the core-level MCD process involves optical transitions in which the one-electron initial states are well localized and have well-defined angular momenta. In order to get insight into the local magnetic states in 3d and 4f magnetic systems, we have studied MCD of ferrites, Fe1-xPtx alloys, and mixed-valence CeRh3B2 at the core-absorption edges in the VUV˜soft x-ray region. The experiments were performed by utilizing directly characterized, circularly polarized undulator radiation and off-plane synchrotron radiation1 in conjunction with an ultrahigh vacuum compatible superconducting magnet of special design.2 Clear MCD signals were observed for CeRh3B2 in the prethreshold region of the Ce 4d→4f (N4,5) edges. A comparison of the experimental MCD spectrum with theoretical ones3 for uniaxial crystal fields of Δc=0 and 0.2 eV shows that the experimental spectrum qualitatively agrees with the theoretical one for Δc=0 eV. Theory predicts that the MCD pattern for ΔcCeRh3B2. We will also present the MCD data in the M2,3 core-absorption region for ferrites (Fe3O4 and CoFe2O4) and Fe1-xPtx alloys, discussing the results.

  15. 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.

  16. Theoretical studies of energy photoemission spectra (XPS) of S and SO sub 2 adsorbed on Ni clusters by Hartree-Fock method

    CERN Document Server

    Martínez, E; Rincon, L

    2002-01-01

    Theoretical results of photoemission energy spectral of the atomic sulfur and of the SO sub 2 molecule, adsorbed over surfaces of Ni(110) and Ni(l l l) clusters, are reported in this work. Clusters with 11, 13, 15 and 17 atoms of Ni were used for the model. The calculations were done by Hartree-Fock method, and basis sets of type STO-NG and p-q1G (p3,6; q= 2,3; N= 3,6) were used. The ionization potentials (IP) were interpreted within the Koopmans Theorem. The results obtained for the IP of 1s, 2s and 2p orbitals are 2472.03 eV, 238.14 eV and 173.55 eV, respectively; while for the same orbitals of the sulfur in SO sub 2 these values are 2481.30 eV, 246.61 eV and 182.17 eV. The theoretical results were compared with experimental results reported in the references, and the error ranges are between 5 eV and 30 eV, in agreement with the standard for the Hartree-Fock method. (Author)

  17. Photoemission from single crystals of EuBa/sub 2/Cu/sub 3/O/sub 7-//sub x/ cleaved below 20 K: Temperature-dependent oxygen loss

    Energy Technology Data Exchange (ETDEWEB)

    List, R.S.; Arko, A.J.; Fisk, Z.; Cheong, S.W.; Conradson, S.D.; Thompson, J.D.; Pierce, C.B.; Peterson, D.E.; Bartlett, R.J.; Shinn, N.D.; and others

    1988-12-01

    The first low-temperature photoemission spectra from well-oxygenated and characterized, cleaved single crystals of the 1:2:3-type superconductors, specifically EuBa/sub 2/Cu/sub 3/O/sub 7-//sub x/, are presented. In contrast with polycrystalline or higher-temperature single-crystalline studies, a distinct and very stable density of states is found at the Fermi edge below 20 K. As the crystal is warmed even to 80 K the emission is rapidly lost from both the upper and lower portions of the Cu-O hybrids. At room temperature there is a loss of intensity at the Fermi edge with an accompanying change in the Ba 4d core-level line shape and the presence of a charging effect indicative of an insulating surface. These results imply that upon warming from 20 K there is very rapid oxygen loss from the cleaved surface with a resulting loss of superconducting behavior. This suggests that future photoemission experiments, especially those investigating detailed band structure, should be performed at low temperatures.

  18. Core levels, valence band structure and unoccupied states of clean InN surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Himmerlich, Marcel; Eisenhardt, Anja; Schaefer, Juergen A.; Krischok, Stefan [Institut fuer Physik and Institut fuer Mikro- und Nanotechnologien, TU Ilmenau (Germany)

    2008-07-01

    In this study we used a surface analytics system directly connected to a MBE growth module to study the surface properties of thin InN films. The samples were prepared by plasma assisted molecular beam epitaxy on GaN/Al{sub 2}O{sub 3}(0001) templates and exhibited a 2 x 2 reconstruction after growth. The prepared samples were analysed by photoelectron spectroscopy as well as electron energy loss spectroscopy (EELS). For the occupied states, a very good agreement to available theoretical calculations is found. Although, the valence band maximum is located at 1.6 eV, indicating strong downward band bending of {proportional_to}0.9 eV, photoemission is detected up to E{sub F}. This indicates that the Fermi level is pinned above the conduction band minimum, as recently predicted. The spin-orbit splitting of the In 4d level at 17.8 eV could be resolved using He II radiation. Furthermore, from the fine structure of the secondary electron cascade peak we extract the energy of different unoccupied states 0 eV to 9 eV above the vacuum level. These measurements enable us to identify features in the InN EELS spectra, with a loss energy larger than 16 eV, as interband transitions from the In 4d level.

  19. Surface core-level shifts for Pt single-crystal surfaces

    Science.gov (United States)

    Baetzold, R. C.; Apai, G.; Shustorovich, E.; Jaeger, R.

    1982-10-01

    The (111) and (110) surfaces of Pt, clean, oxidized, and covered by CO, have been investigated for surface 4f core-level binding-energy shifts. For the (111) face the surface Pt4f72 core level was shifted by 0.40+/-0.05 eV to lower binding energy relative to the bulk peak. On the (110)-(1×2) reconstructed surface similarly shifted peaks at 0.21+/-0.05 and 0.55+/-0.05 eV were observed. Chemisorbed carbon monoxide shifts the Pt(111) surface-related core level by 1.3 eV to higher binding energy. Formation of subsurface oxygen did not produce changes in the Pt(111)4f72 core-level binding energies. The results obtained are explained and their possible implications are discussed.

  20. Bulk sensitive hard x-ray photoemission electron microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Patt, M., E-mail: m.patt@fz-juelich.de; Wiemann, C. [Peter Grünberg Institute (PGI-6) and JARA-FIT, Research Center Jülich, D-52425 Jülich (Germany); Weber, N.; Escher, M.; Merkel, M. [Focus GmbH, Neukirchner Str. 2, D-65510 Hünstetten (Germany); Gloskovskii, A.; Drube, W. [DESY Photon Science, Deutsches Elektronen-Synchrotron, D-22603 Hamburg (Germany); Schneider, C. M. [Peter Grünberg Institute (PGI-6) and JARA-FIT, Research Center Jülich, D-52425 Jülich (Germany); Fakultät f. Physik and Center for Nanointegration Duisburg-Essen (CeNIDE), Universität Duisburg-Essen, D-47048 Duisburg (Germany)

    2014-11-15

    Hard x-ray photoelectron spectroscopy (HAXPES) has now matured into a well-established technique as a bulk sensitive probe of the electronic structure due to the larger escape depth of the highly energetic electrons. In order to enable HAXPES studies with high lateral resolution, we have set up a dedicated energy-filtered hard x-ray photoemission electron microscope (HAXPEEM) working with electron kinetic energies up to 10 keV. It is based on the NanoESCA design and also preserves the performance of the instrument in the low and medium energy range. In this way, spectromicroscopy can be performed from threshold to hard x-ray photoemission. The high potential of the HAXPEEM approach for the investigation of buried layers and structures has been shown already on a layered and structured SrTiO{sub 3} sample. Here, we present results of experiments with test structures to elaborate the imaging and spectroscopic performance of the instrument and show the capabilities of the method to image bulk properties. Additionally, we introduce a method to determine the effective attenuation length of photoelectrons in a direct photoemission experiment.

  1. Core-level excitation and fragmentation of chlorine dioxide

    Science.gov (United States)

    Flesch, R.; Plenge, J.; Rühl, E.

    2006-03-01

    Inner-shell excitation and fragmentation of chlorine dioxide (OClO) in the Cl 2p- and O 1s-excitation regime is reported. The electronic structure of the element-selectively excited radical is studied by X-ray absorption and total cation yields. A comparison of both approaches allows us to estimate the absolute photoionization cross-section and the ionization yield near the Cl 2p- and O 1s-absorption edges. The latter quantity is characteristically enhanced in core-ionization continua. We observe below both core-absorption edges intense core-to-valence-transitions. These are assigned in comparison with related work on core-excited sulfur dioxide. These results give clear evidence that the highest molecular orbital of OClO is half-filled. High-resolution spectra recorded in the Cl 2p-regime show evidence for Rydberg transitions. The extrapolation of the term values of the low-lying Rydberg states allows us to derive the Cl 2p-ionization energy of OClO. Fragmentation of core-excited OClO is reported. Photoelectron-photoion-coincidence (PEPICO) spectra are recorded, indicating that singly and doubly charged fragments are formed. Fission of the doubly and multiply charged OClO leads to singly charged fragments. These are measured by photoion-photoion-coincidence (PIPICO) spectra, where characteristic changes in intensity of the fission channels in the Cl 2p- and O 1s-continuum are observed.

  2. Theory of hot electron photoemission from graphene

    Science.gov (United States)

    Ang, Lay Kee; Liang, Shijun

    Motivated by the development of Schottky-type photodetectors, some theories have been proposed to describe how the hot carriers generated by the incident photon are transported over the Schottky barrier through the internal photoelectric effect. One of them is Fowler's law proposed as early as 1931, which studied the temperature dependence of photoelectric curves of clean metals. This law is very successful in accounting for mechanism of detecting photons of energy lower than the band gap of semiconductor based on conventional metal/semiconductor Schottky diode. With the goal of achieving better performance, graphene/silicon contact-based- graphene/WSe2 heterostructure-based photodetectors have been fabricated to demonstrate superior photodetection efficiency. However, the theory of how hot electrons is photo-excited from graphene into semiconductor remains unknown. In the current work, we first examine the photoemission process from suspended graphene and it is found that traditional Einstein photoelectric effect may break down for suspended graphene due to the unique linear band structure. Furthermore, we find that the same conclusion applies for 3D graphene analog (e.g. 3D topological Dirac semi-metal). These findings are very useful to further improve the performance of graphene-based photodetector, hot-carrier solar cell and other kinds of sensor.

  3. Spin-orbit delays in photoemission

    Science.gov (United States)

    Jordan, I.; Huppert, M.; Pabst, S.; Kheifets, A. S.; Baykusheva, D.; Wörner, H. J.

    2017-01-01

    Attosecond delays between photoelectron wave packets emitted from different electronic shells are now well established. Is there any delay between electrons originating from the same electronic shell but leaving the cation in different fine-structure states? This question is relevant for all attosecond photoemission studies involving heavy elements, be it atoms, molecules or solids. We answer this fundamental question by measuring energy-dependent delays between photoelectron wave packets associated with the 3/2 2P and 1/2 2P components of the electronic ground states of Xe+ and Kr+. We observe delays reaching up to 33 ±6 as in the case of Xe. Our results are compared with two state-of-the-art theories. Whereas both theories quantitatively agree with the results obtained for Kr, neither of them fully reproduces the experimental results in Xe. Performing delay measurements very close to the ionization thresholds, we compare the agreement of several analytical formulas for the continuum-continuum delays with experimental data. Our results show an important influence of spin-orbit coupling on attosecond photoionization delays, highlight the requirement for additional theory development, and offer a precision benchmark for such work.

  4. Electronic structure near E sub F in YBa sub 2 Cu sub 3 O sub x for 6. 35 le x le 6. 9: A photoemission study

    Energy Technology Data Exchange (ETDEWEB)

    Liu, R.; Veal, B.W.; Paulikas, A.P.; Downey, J.W.; Shi, H. (Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)); Olson, C.G.; Gu, C. (Ames Laboratory and Department of Physics, Iowa State University, Ames, Iowa 50011 (United States)); Arko, A.J.; Joyce, J.J. (Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States))

    1992-03-01

    High-resolution angle-resolved photoemission measurements are reported for YBa{sub 2}Cu{sub 3}O{sub {ital x}} when oxygen stoichiometries are in the range 6.35{le}{ital x}{le}6.9. The stoichiometry dependence of spectral features at energies close to the Fermi level was monitored along major symmetry lines in the two-dimensional Brillouin zone. Along {bar {Gamma}}-{ital {bar S}}, two bands dispersing through {ital E}{sub {ital F}} were observed in YBa{sub 2}Cu{sub 3}O{sub 6.9}. Band calculations indicate that these are plane''-related features. These two bands and the Fermi surfaces that they define are nearly independent of oxygen stoichiometry. The spectral weight near {ital E}{sub {ital F}} is relatively constant for 6.4{le}{ital x}{le}6.9. However, the spectral weight falls off significantly when {ital x}=6.35 (insulating), although the dispersive behavior that is characteristic of the higher oxygen stoichiometries persists. This abrupt intensity change might signal the onset of an electronic structure governed by strong correlation. Along {bar {Gamma}}-{ital {bar Y}}({ital {bar X}}), one band dispersing through {ital E}{sub {ital F}} was observed in YBa{sub 2}Cu{sub 3}O{sub 6.9}. As oxygen was removed, the intensity of this dispersive feature decreased systematically. Predictions of band theory indicate that this band is a chain''-related feature. In general, predictions of band theory appear to be quite reliable near {ital E}{sub {ital F}} in the oxygen stoichiometry range {ital x}{ge}6.4, where the material shows metallic behavior.

  5. Core level photoemission spectroscopy and chemical bonding in Sr2Ta2O7

    DEFF Research Database (Denmark)

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

    2009-01-01

    structural and XPS data for other Sr- and Ta-containing oxide compounds. The new data point for Sr2Ta2O7 is consistent with the previously derived relationship for a set of Sr-bearing oxides. The binding energy difference Delta(O-Sr) was found to decrease with increasing bond distance L(Sr-O)....

  6. Photoemission from optoelectronic materials and their nanostructures

    CERN Document Server

    Ghatak, Kamakhya Prasad; Bhattacharya, Sitangshu

    2009-01-01

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

  7. 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.

  8. Cathodoluminescence and Photoemission of Doped Lithium Tetraborate

    Science.gov (United States)

    2011-03-01

    41 The Photoemission Spectroscopy System .....................................................................43 Source ...Page 1. Measured and Standard Wavelengths for the non VUV system ......................................... 53 2. Mean Gaussian...explored. Neutron detection has the advantages of low natural background count, few neutron sources in normal commerce operations, and different

  9. Photoemission electron microscopy, a tool for plasmonics

    Energy Technology Data Exchange (ETDEWEB)

    Douillard, L., E-mail: ludovic.douillard@cea.fr; Charra, F.

    2013-08-15

    Highlights: •Brief review of photoemission electron microscopy PEEM as a tool for plasmonics, •PEEM gives access to (tip free) near field maps of subwavelength length resolution, •PEEM makes use of a true optical excitation scheme, exhibiting strong connections to ultrafast optical spectrometries. -- Abstract: A key challenge to plasmonics is the development of experimental tools allowing access to the spatial distribution of the optical near field at the nanometre scale. A recent approach for mapping the near optical field is the use of the photoemission electron microscopy PEEM. Indeed, photoemission can be strongly enhanced upon excitation of surface plasmons. By collecting the photoemitted electrons, two-dimensional intensity maps reflecting the actual distribution of the optical near-field are obtained. In the following a brief overview of the possibilities of the photoemission electron microscopy as a tool for plasmonics is given. Main focuses will be set on experimental results regarding the mapping of the near optical field at nanometer scale, the investigation of the spatio-temporal dynamics of plasmon-polariton waves and the manipulation at will of the near field.

  10. Comparative angle-resolved photoemission spectroscopy study of CaRuO3 and SrRuO3 thin films: Pronounced spectral weight transfer and possible precursor of lower Hubbard band

    Science.gov (United States)

    Yang, H. F.; Fan, C. C.; Liu, Z. T.; Yao, Q.; Li, M. Y.; Liu, J. S.; Jiang, M. H.; Shen, D. W.

    2016-09-01

    In the prototypical 4 d system (Sr ,Ca ) RuO3 , the degree and origin of electron correlations, and how they correlate with physical properties, still remain elusive, though extensive studies have been performed. In this work we present a comparative electronic structure study of high-quality epitaxial CaRuO3 and SrRuO3 thin films, by means of reactive molecular beam epitaxy and in situ angle-resolved photoemission spectroscopy. We found that while SrRuO3 possesses sharp features signaling the Fermi liquid state, the isostructural CaRuO3 exhibits broad features and its spectral weight is markedly transferred from the Fermi level to -1.2 eV forming a "hump" structure which resembles the Mott-Hubbard system (Sr ,Ca ) VO3 . We suggest that this hump is the precursor of the lower Hubbard band, and the U /W (U and W represent the on-site Coulomb interactions and bandwidth, respectively) of our CaRuO3 thin film is much larger than that of SrRuO3. In addition, we discuss the origin of electron correlations as well as the ferromagnetism in SrRuO3 which is absent in CaRuO3. Our findings put constraints on future studies, and also show that perovskite ruthenates are indeed an experimentally tunable system for the study of electron correlations.

  11. Photo-emission of two protons from nuclei

    Energy Technology Data Exchange (ETDEWEB)

    Anguiano, Marta [Departamento de Radiacion Electromagnetica, Instituto de Fisica Aplicada, CSIC, Serrano 144, E-28006 Madrid (Spain)]. E-mail: marta.anguiano@iec.csic.es; Co' , Giampaolo [Dipartimento di Fisica, Universita di Lecce, I-73100 Lecce (Italy); Istituto Nazionale di Fisica Nucleare sez. di Lecce, I-73100 Lecce (Italy)]. E-mail: giampaolo.co@le.infn.it; Lallena, Antonio M. [Departamento de Fisica Moderna, Universidad de Granada, E-18071 Granada (Spain)]. E-mail: lallena@ugr.es

    2004-11-15

    The photo-emission of two protons from the {sup 12}C, {sup 16}O and {sup 40}Ca nuclei is investigated. Aim of the work is the study of the possibilities offered by this probe to obtain information about the characteristics of the short-range correlations. We have also evaluated the effects of the two-body {delta}-currents which, in this processes, compete with those produced by the short-range correlations. Our results show that ({gamma},pp) processes could be more useful than (e,e'pp) for the study of the short-range correlations.

  12. Angle-resolved photoemission spectroscopy on high-temperature superconductors. Studies of Bi2212 and single-layer FeSe film grown on SrTiO{sub 3} substrate

    Energy Technology Data Exchange (ETDEWEB)

    He, Junfeng [Chinese Academy of Sciences, Beijing (China). Inst. of Physics

    2016-07-01

    This book mainly focuses on the study of the high-temperature superconductor Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+δ} (Bi2212) and single-layer FeSe film grown on SrTiO{sub 3} (STO) substrate by means of angle-resolved photoemission spectroscopy (ARPES). It provides the first electronic evidence for the origin of the anomalous high-temperature superconductivity in single-layer FeSe grown on SrTiO{sub 3} substrate. Two coexisted sharp-mode couplings have been identified in superconducting Bi2212. The first ARPES study on single-layer FeSe/STO films has provided key insights into the electronic origin of superconductivity in this system. A phase diagram and electronic indication of high T{sub c} and insulator to superconductor crossover have been established in the single-layer FeSe/STO films. Readers will find essential information on the techniques used and interesting physical phenomena observed by ARPES.

  13. Photoemission of graded-doping GaN photocathode

    Institute of Scientific and Technical Information of China (English)

    Fu Xiao-Qian; Chang Ben-Kang; Wang Xiao-Hui; Li Biao; Du Yu-Jie; Zhang Jun-Ju

    2011-01-01

    We study the photoemission process of graded-doping GaN photocathode and find that the built-in electric fields can increase the escape probability and the effective diffusion length of photo-generated electrons, which results in the enhancement of quantum efficiency. The intervalley scattering mechanism and the lattice scattering mechanism in high electric fields are also investigated. To prevent negative differential mobility from appearing, the surface doping concentration needs to be optimized, and it is calculated to be 3.19×1017 cm-3. The graded-doping GaN photocathode with higher performance can be realized by further optimizing the doping profile.

  14. 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.

  15. 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.

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

    DEFF Research Database (Denmark)

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

    1993-01-01

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

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

    Science.gov (United States)

    Stoute, Nicholas; Aspnes, David

    2012-02-01

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

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

    DEFF Research Database (Denmark)

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

    1993-01-01

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

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

    NARCIS (Netherlands)

    Friedlein, R.; Fleurence, A.; Aoyagi, K.; Jong, de M.P.; Van Bui, H.; Wiggers, F.B.; Yoshimoto, S.; Koitaya, T.; Shimizu, S.; Noritake, H.; Mukai, K.; Yoshinobu, J.; Yamada-Takamura, Y.

    2014-01-01

    From the analysis of high-resolution Si 2p photoelectron and near-edge x-ray absorption fine structure (NEXAFS) spectra, we show that core level excitations of epitaxial silicene on ZrB2(0001) thin films are characteristically different from those of sp 3-hybridized silicon. In particular, it is rev

  20. 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.

  1. Transport and magnetic behavior under pressure and high-resolution photoemission studies of Ce{sub 2}Rh{sub 0.7}Co{sub 0.3}Si{sub 3}, an alloy on the verge of quantum critical point

    Energy Technology Data Exchange (ETDEWEB)

    Mukherjee, K; Iyer, Kartik K; Patil, Swapnil; Maiti, K; Sampathkumaran, E V, E-mail: kmukherjee@tifr.res.in, E-mail: sampath@tifr.res.in [Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai-400005 (India)

    2011-01-01

    We report the influence of external pressure on the temperature dependence of magnetization and electrical resistivity as well as high-resolution photoemission studies for an alloy, Ce{sub 2}Rh{sub 0.7}Co{sub 0.3}Si{sub 3}, ordering magnetically below 3 K. It is found that external pressure has the same effect as that induced by (further) Co substitution for Rh in the series, Ce{sub 2}Rh{sub 1-x}Co{sub x}Si{sub 3}, resulting in qualitative changes in the features in the magnetic and transport data, with a suppression of magnetic ordering followed by quantum critical point effect. The high-resolution photo-emission spectra reveal signature of Kondo feature even at ambient pressure. These findings support the validity of spin-density-wave picture in this series.

  2. Photoemission of switchable mirrors and quantum wells

    OpenAIRE

    Koitzsch, Christian; Aebi, Philippe

    2005-01-01

    This thesis focuses on the electronic properties of materials, which were explored with Angle Resolved Photoemission (ARPES) and Density Functional Theory (DFT). The natural fingerprint of electronic phenomena in crystalline solids, e.g. in this thesis the hydrogen-induced metal-insulator transition and the formation of standing electron waves in quantum wells, is the k-resolved band structure or in short the E(k) relation in the solid. The experimental technique to explore the occupied band ...

  3. 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.

  4. Electron-phonon coupling and its evidence in the photoemission spectra of lead.

    Science.gov (United States)

    Reinert, F; Eltner, B; Nicolay, G; Ehm, D; Schmidt, S; Hüfner, S

    2003-10-31

    We present a detailed study of the influence of strong electron-phonon coupling on the photoemission spectra of lead. Representing the strong-coupling regime of superconductivity, the spectra of lead show characteristic features that demonstrate the correspondence of physical properties in the normal and the superconducting state, as predicted by the Eliashberg theory. These features appear on an energy scale of a few meV and are accessible for photoemission only by using modern spectrometers with high-resolution in energy and angle.

  5. Photoemission starting of induction rf-driven multicusp ion sources

    Science.gov (United States)

    Pickard, D. S.; Leung, K. N.; Perkins, L. T.; Ponce, D. M.; Young, A. T.

    1996-02-01

    It has been demonstrated that pulsed and continuous wave, rf-driven hydrogen discharges can be started with photoemission. The extracted H- current from a photoemission-started plasma has been investigated and does not differ significantly from that of a filament-started plasma. The minimum pressure for photoemissive starting was found to be higher than that of filament starting, 17 mTorr compared to 7 mTorr, respectively, in this particular configuration.

  6. Increased electron photoemission from plasmonic nanoparticles and photoemission enhanced solar cells

    DEFF Research Database (Denmark)

    Novitsky, Andrey; Uskov, Alexander; Gritti, Claudia;

    2011-01-01

    Numerical simulation shows possibility to enhance substantially (by one-two orders) the electron photoemission through surface of metal nanoparticles embedded into photovoltaic structures. This, in turn, can lead to increase of the solar cells efficiency due to efficient light-to-electricity tran......Numerical simulation shows possibility to enhance substantially (by one-two orders) the electron photoemission through surface of metal nanoparticles embedded into photovoltaic structures. This, in turn, can lead to increase of the solar cells efficiency due to efficient light......-to-electricity transformation below the solar cell semiconductor bandgap....

  7. 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

  8. Electronic Structure of the Kitaev Material α-RuCl3 Probed by Photoemission and Inverse Photoemission Spectroscopies.

    Science.gov (United States)

    Sinn, Soobin; Kim, Choong Hyun; Kim, Beom Hyun; Lee, Kyung Dong; Won, Choong Jae; Oh, Ji Seop; Han, Moonsup; Chang, Young Jun; Hur, Namjung; Sato, Hitoshi; Park, Byeong-Gyu; Kim, Changyoung; Kim, Hyeong-Do; Noh, Tae Won

    2016-12-21

    Recently, α-RuCl3 has attracted much attention as a possible material to realize the honeycomb Kitaev model of a quantum-spin-liquid state. Although the magnetic properties of α-RuCl3 have been extensively studied, its electronic structure, which is strongly related to its Kitaev physics, is poorly understood. Here, the electronic structure of α-RuCl3 was investigated by photoemission (PE) and inverse-photoemission (IPE) spectroscopies. The band gap was directly measured from the PE and IPE spectra and was found to be 1.9 eV, much larger than previously estimated values. Local density approximation (LDA) calculations showed that the on-site Coulomb interaction U could open the band gap without spin-orbit coupling (SOC). However, the SOC should also be incorporated to reproduce the proper gap size, indicating that the interplay between U and SOC plays an essential role. Several features of the PE and IPE spectra could not be explained by the results of LDA calculations. To explain such discrepancies, we performed configuration-interaction calculations for a RuCl6(3-) cluster. The experimental data and calculations demonstrated that the 4d compound α-RuCl3 is a Jeff = 1/2 Mott insulator rather than a quasimolecular-orbital insulator. Our study also provides important physical parameters required for verifying the proposed Kitaev physics in α-RuCl3.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-07-15

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

  10. Electronic structure of a narrow-gap semiconductor FeGa3 investigated by photoemission and inverse photoemission spectroscopies

    Science.gov (United States)

    Arita, M.; Shimada, K.; Utsumi, Y.; Morimoto, O.; Sato, H.; Namatame, H.; Taniguchi, M.; Hadano, Y.; Takabatake, T.

    2011-06-01

    We have performed a photoemission and inverse photoemission spectroscopic study of a narrow-gap semiconductor FeGa3, in order to characterize the occupied and unoccupied electronic states. The energy-gap size was found to be ~0.4 eV, and the valence-band maximum (VBM) was located around the A point of the Brillouin zone. We observed a dispersive Ga 4sp derived band near the Fermi level (EF), and Fe 3d narrow bands located at -0.5 and -1.1 eV away from EF. In contrast to the case of FeSi, there was no temperature-dependent peak enhancement at the VBM on cooling. The observed density of states and band dispersions were reasonably reproduced by the LDA+U calculation with the on-site effective Coulomb interaction Ueff~3 eV to the Fe 3d states. Present results indicate that, in spite of sizable Ueff/W~0.6 (W: band width), electron correlation effects are not significant in FeGa3 compared with FeSi since the VBM consists of the dispersive band with the reduced Fe 3d contribution, and the energy gap is large.

  11. Vacuum scanning capillary photoemission microscopy

    DEFF Research Database (Denmark)

    Aseyev, S.A.; Cherkun, A P; Mironov, B N

    2017-01-01

    of a gold reflecting layer on a compact disc which has been illuminated by an unfocused laser beam with a wavelength 400nm, from a femtosecond laser with a beam size of 4mm. A quartz capillary with a 2-µm aperture has been used in the experiments. The period of gold microstructure, shown to be 1.6µ...... distribution of the recorded photoelectrons consisted of periodic mountain-valley strips, resembling the surface profile of the sample. Submicron spatial resolution has been achieved. This approach paves the way to study pulsed photodesorption of large organic molecular ions with high spatial and element...

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

    Energy Technology Data Exchange (ETDEWEB)

    JOHNSON, P.D.; VALLA, T.

    2006-08-01

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

  13. Interface properties of magnetic tunnel junction La0.7Sr0.3MnO3/SrTiO3 superlattices studied by standing-wave excited photoemission spectroscopy

    NARCIS (Netherlands)

    Gray, A.X.; Papp, C.; Balke, B.; Yang, S.-H.; Huijben, M.; Rotenberg, E.; Bostwick, A.; Ueda, S.; Yamashita, Y.; Kobayashi, K.; Gullikson, E.M.; Kortright, J.B.; Groot, de F.M.F.; Rijnders, G.; Blank, D.H.A.; Ramesh, R.; Fadley, C.S.

    2010-01-01

    The chemical and electronic-structure profiles of magnetic tunnel junction (MTJ) La0.7Sr0.3MnO3/SrTiO3 (LSMO/STO) superlattices have been quantitatively determined via soft and hard x-ray standing-wave excited photoemission, x-ray absorption and x-ray reflectivity, in conjunction with x-ray optical

  14. Depth-Resolved Composition and Electronic Structure of Buried Layers and Interfaces in a LaNiO{sub 3}/SrTiO{sub 3} Superlattice from Soft- and Hard- X-ray Standing-Wave Angle-Resolved Photoemission

    Energy Technology Data Exchange (ETDEWEB)

    Eiteneer, D. [Department of Physics, University of California, Davis, California 95616 (United States); Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Pálsson, G.K., E-mail: gunnar.palsson@physics.uu.se [Department of Physics, University of California, Davis, California 95616 (United States); Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Nemšák, S. [Department of Physics, University of California, Davis, California 95616 (United States); Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Peter-Grünberg-Institut PGI-6, Forschungszentrum Julich, 52425 Julich (Germany); Gray, A.X. [Department of Physics, University of California, Davis, California 95616 (United States); Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025 (United States); Kaiser, A.M. [Department of Physics, University of California, Davis, California 95616 (United States); Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Son, J.; LeBeau, J. [Materials Department, University of California, Santa Barbara, California 93106 (United States); Conti, G. [Department of Physics, University of California, Davis, California 95616 (United States); Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); and others

    2016-08-15

    Highlights: • Depth resolved electronic structure of LaNiO{sub 3}/SrTiO{sub 3} superlattices is measured. • The structure is determined by x-ray standing wave angle-resolved photoemission. • Similarity to the electronic structure of La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/SrTiO{sub 3} is discussed. - Abstract: LaNiO{sub 3} (LNO) is an intriguing member of the rare-earth nickelates in exhibiting a metal-insulator transition for a critical film thickness of about 4 unit cells [Son et al., Appl. Phys. Lett. 96, 062114 (2010)]; however, such thin films also show a transition to a metallic state in superlattices with SrTiO{sub 3} (STO) [Son et al., Appl. Phys. Lett. 97, 202109 (2010)]. In order to better understand this transition, we have studied a strained LNO/STO superlattice with 10 repeats of [4 unit-cell LNO/3 unit-cell STO] grown on an (LaAlO{sub 3}){sub 0.3}(Sr{sub 2}AlTaO{sub 6}){sub 0.7} substrate using soft x-ray standing-wave-excited angle-resolved photoemission (SWARPES), together with soft- and hard- x-ray photoemission measurements of core levels and densities-of-states valence spectra. The experimental results are compared with state-of-the-art density functional theory (DFT) calculations of band structures and densities of states. Using core-level rocking curves and x-ray optical modeling to assess the position of the standing wave, SWARPES measurements are carried out for various incidence angles and used to determine interface-specific changes in momentum-resolved electronic structure. We further show that the momentum-resolved behavior of the Ni 3d e{sub g} and t{sub 2g} states near the Fermi level, as well as those at the bottom of the valence bands, is very similar to recently published SWARPES results for a related La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/SrTiO{sub 3} superlattice that was studied using the same technique (Gray et al., Europhysics Letters 104, 17004 (2013)), which further validates this experimental approach and our conclusions. Our

  15. Effects of vibrational motion on core-level spectra of prototype organic molecules

    Energy Technology Data Exchange (ETDEWEB)

    Uejio, Janel S.; Schwartz, Craig P.; Saykally, Richard J.; Prendergast, David

    2008-08-21

    A computational approach is presented for prediction and interpretation of core-level spectra of complex molecules. Applications are presented for several isolated organic molecules, sampling a range of chemical bonding and structural motifs. Comparison with gas phase measurements indicate that spectral lineshapes are accurately reproduced both above and below the ionization potential, without resort to ad hoc broadening. Agreement with experiment is significantly improved upon inclusion of vibrations via molecular dynamics sampling. We isolate and characterize spectral features due to particular electronic transitions enabled by vibrations, noting that even zero-point motion is sufficient in some cases.

  16. A photoemission study of BaO overlayers adsorbed on W(110) and their interaction with H 2O, CO 2, and O 2

    Science.gov (United States)

    Mueller, D. R.; Kurtz, R. L.; Stockbauer, R. L.; Madey, T. E.; Shih, Arnold

    1990-11-01

    The electronic structure of barium oxide overlayers on W(110) and their interaction with H 2O, CO 2 and O 2 has been examined using ultraviolet photo electron spectroscopy. At room temperature water vapor and carbon dioxide react with a c(5 × 1)-BaO monolayer adsorbed on W(110) to produce adsorbed OH and CO 3 species. Heating the W(110)-c(5 × 1)-BaO surface following water or carbon dioxide exposure dissociates the adsorbed hydroxide or carbonate. On the lower coverage c(7 × 1)-BaO and c(2 × 4)-BaO adlayers complete dissociation of a fraction of the adsorbed species is evident at room temperature. The interaction of oxygen with W(110) is enhanced by the presence of barium oxide on the tungsten surface. These results are compared with the findings of a previous study of barium oxide films adsorbed on W(100).

  17. A photoemission study of the effectiveness of nickel, manganese, and cobalt based corrosion barriers for silicon photo-anodes during water oxidation

    Science.gov (United States)

    O'Connor, Robert; Bogan, Justin; McCoy, Anthony; Byrne, Conor; Hughes, Greg

    2016-05-01

    Silicon is an attractive material for solar water splitting applications due to its abundance and its capacity to absorb a large fraction of incident solar radiation. However, it has not received as much attention as other materials due to its tendency to oxidize very quickly in aqueous environments, particularly when it is employed as the anode where it drives the oxygen evolution reaction. In recent years, several works have appeared in the literature examining the suitability of thin transition metal oxide films grown on top of the silicon to act as a corrosion barrier. The film should be transparent to solar radiation, allow hole transport from the silicon surface to the electrolyte, and stop the diffusion of oxygen from the electrolyte back to the silicon. In this work, we compare Mn-oxide, Co-oxide, and Ni-oxide thin films grown using physical vapor deposition in order to evaluate which material offers the best combination of photocurrent and corrosion protection. In addition to the electrochemical data, we also present a detailed before-and-after study of the surface chemistry of the films using x-ray photoelectron spectroscopy. This approach allows for a comprehensive analysis of the mechanisms by which the corrosion barriers protect the underlying silicon, and how they degrade during the water oxidation reaction.

  18. Fe/GaAs(001) and MgO/Fe/GaAs(001) epitaxial systems: A spin- and angle-resolved photoemission study

    Energy Technology Data Exchange (ETDEWEB)

    Gottlob, Daniel [Forschungszentrum Juelich GmbH (Germany); Technische Universitaet Dortmund (Germany); Plucinski, Lukasz; Schneider, Claus M. [Forschungszentrum Juelich GmbH (Germany); Westphal, Carsten [Technische Universitaet Dortmund (Germany)

    2011-07-01

    Spintronics is an important field of current Solid State Research and memory units based on Magnetic Tunnel Junctions (MTJs) are now within reach. In MTJ's the nature of the electronic structure at the interface determines the spin-selectivity of the tunneling process, and thereby the magnetorestive potential of the MTJ. Electronic interface states can influence the tunneling process in epitaxial MTJs especially for thinner tunnel barriers. The research that has been done at Beamline 5, DELTA, Dortmund in the context of a Diploma thesis focussed on the electronic structure of Fe/GaAs(001) and MgO/Fe/GaAs(001) and a surface/interface state of these systems. The samples have been prepared in situ by molecular beam epitaxy and characterized by LEED and Auger spectroscopy. The electronic structure was probed in two different regions of the Brillouin zone, which have been chosen for reference (normal emission, {gamma} point) and the expectation of the surface state (21 off normal) that has been seen on Fe/W(001) in a previous study. Measurements on the MgO capped iron sample have been conducted to confirm whether the surface state does transform into an interface state.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-05-14

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

  20. 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.

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

    Science.gov (United States)

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

    2003-08-01

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

  2. 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 ...

  3. 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.

  4. Photoemission starting of induction rf-driven multicusp ion sources

    Energy Technology Data Exchange (ETDEWEB)

    Pickard, D.S.; Leung, K.N.; Perkins, L.T.; Ponce, D.M.; Young, A.T. [Lawrence Berkeley Laboratory, University of California, Berkeley, California 94720 (United States)

    1996-02-01

    It has been demonstrated that pulsed and continuous wave, rf-driven hydrogen discharges can be started with photoemission. The extracted H{sup {minus}} current from a photoemission-started plasma has been investigated and does not differ significantly from that of a filament-started plasma. The minimum pressure for photoemissive starting was found to be higher than that of filament starting, 17 mTorr compared to 7 mTorr, respectively, in this particular configuration. {copyright} {ital 1996 American Institute of Physics.}

  5. 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.

  6. Molecular photoemission studies using synchrotron radiation

    Energy Technology Data Exchange (ETDEWEB)

    Truesdale, C.M.

    1983-04-01

    The angular distributions of photoelectrons and Auger electrons were measured by electron spectroscopy using synchrotron radiation. The experimental results are compared with theoretical calculations to interpret the electronic behavior of photoionization for molecular systems.

  7. 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.

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

    Science.gov (United States)

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

    2012-11-01

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

  9. Exploring the core level shift origin of sulfur and thiolates on Pd(111) surfaces.

    Science.gov (United States)

    Salvarezza, Roberto Carlos; Carro, Pilar

    2015-10-01

    Thiol molecules on planar metal surfaces are widely used for building sensing and electronic devices and also as capping agents to protect and to control the size and shape of nanoparticles. In the case of Pd the thiol molecules exhibit a complex behavior because C-S bond scission is possible, resulting in a significant amount of co-adsorbed S. Therefore identification of these species on Pd is a key point for many applications, a task that is usually achieved by XPS. Here we show, from DFT calculations, that the core level shift (CLS) of the S 2p binding energy (BE) of thiol and sulfur on different thiol-Pd(111) surface models strongly depends on the adsorbed or subsurface state of sulfur atoms. Our results reflect the complexity of S 2p BE behavior and contribute to understanding and reanalyzing the experimental data of thiolated Pd surfaces.

  10. Core-level electronic properties of nanostructured NiO coatings

    Energy Technology Data Exchange (ETDEWEB)

    Palacin, S. [Departamento de Fisica Aplicada, Universidad Autonoma de Madrid, Cantoblanco, 28049 Madrid (Spain); Gutierrez, A. [Departamento de Fisica Aplicada, Universidad Autonoma de Madrid, Cantoblanco, 28049 Madrid (Spain)], E-mail: a.gutierrez@uam.es; Preda, I.; Hernandez-Velez, M. [Departamento de Fisica Aplicada, Universidad Autonoma de Madrid, Cantoblanco, 28049 Madrid (Spain); Sanz, R. [Instituto de Ciencia de Materiales, CSIC, Cantoblanco, 28049 Madrid (Spain); Jimenez, J.A. [Centro Nacional de Investigaciones Metalurgicas, CSIC, Av. Gregorio del Amo 8, 28040 Madrid (Spain); Soriano, L. [Departamento de Fisica Aplicada, Universidad Autonoma de Madrid, Cantoblanco, 28049 Madrid (Spain)

    2007-10-31

    Nanostructured NiO films with different thicknesses were grown on nanoporous alumina membrane substrates by reactive evaporation of Ni in an oxygen atmosphere. The reactive deposition process was assisted by a low energy oxygen ion-beam in order to increase the NiO input into the pores. Surface morphology and structure of the films were analyzed by SEM and XPS. SEM observations reveal a well adhered film of NiO on the substrate. This film appears to be uniform and presents a rather irregular nanostructured morphology, built of NiO clusters with sizes ranging between 5 and 30 nm. The core-level electronic properties of this nanostructured NiO film result to be similar to those of an ultrathin film about one monolayer thick. This behaviour can be explained by the large surface to volume ratio of both systems.

  11. Soft x-ray photoemission of clean and sulfur-covered polar ZnO surfaces: A view of the stabilization of polar oxide surfaces

    Science.gov (United States)

    Lahiri, Jayeeta; Senanayake, Sanjaya; Batzill, Matthias

    2008-10-01

    The two polar surfaces of ZnO were investigated by soft x-ray photoemission spectroscopy. Surface components due to variation in the Madelung energy were identified in photoemission core-level spectra. Sulfur adsorption was used to passivate the surfaces in order to enable separation of the bulk from the surface components. For the ZnO(0001)-Zn surface the observed photoemission peaks were consistent with a Zn-deficient surface, exhibiting a high density of O-terminated step edges. The ZnO(000-1)-O surface is very reactive toward hydrogen adsorption and only above 650 K a hydrogen free surface was observed. For hydrogen-free and small hydrogen coverage an electrostatic shift of the Fermi-level toward the band-gap center was observed. This indicates an incomplete compensation of the internal electrostatic potential by surface oxygen vacancies or charged adsorbates. Coadsorption of sulfur lowered the desorption temperature for hydrogen indicating the possibility to tune the chemical properties of these polar surfaces by dopants.

  12. Spin polarization in photoemission from the cuprate superconductor Bi2Sr2CaCu2O8 +δ

    Science.gov (United States)

    Fanciulli, Mauro; Muff, Stefan; Weber, Andrew P.; Dil, J. Hugo

    2017-06-01

    Photoelectrons produced from the excitation of spin-degenerate states in solids can have a sizable spin polarization, which is related to the phase of interfering channels in the photoemission matrix elements. Such spin polarization can be measured by spin-resolved photoemission spectroscopy to gain information about the transitions and the Wigner time delay of the process. Incorporating strongly correlated electron systems into this paradigm could yield a novel means of extracting phase information crucial to understanding the mechanism of their emergent behavior. In this work, we present, as a case study, experimental measurements of the cuprate superconductor Bi2Sr2CaCu2O8 +δ by spin-resolved photoemission while maintaining full angular and energy resolution. A spin polarization of at least 10 % is observed, which is related to the phase of the photoelectron wave function.

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

    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.

  14. The electronic structure of La{sub 0.66}Ca{sub 0.33}MnO{sub 3} and La{sub 1.2}Sr{sub 1.8}Mn{sub 2}O{sub 7} studied by angle resolved photoemission

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Rong [Department of Physics, Michigan State University, East Lansing, Michigan 48824 (United States); Tonjes, W. C. [Department of Physics, Michigan State University, East Lansing, Michigan 48824 (United States); Olson, C. G. [Ames Laboratory, Ames, Iowa 50011 (United States); Joyce, J. J. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Arko, A. J. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Neumeier, J. J. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Mitchell, J. F. [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Zheng, H. [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)

    2000-07-15

    We report angle resolved photoemission studies of La{sub 0.66}Ca{sub 0.33}MnO{sub 3} and La{sub 1.2}Sr{sub 1.8}Mn{sub 2}O{sub 7} using single crystal samples. The Mn 3p-3d resonance photoemission data of La{sub 0.66}Ca{sub 0.33}MnO{sub 3} show that the states at 2.5 eV binding energy have predominantly Mn 3d character, qualitatively consistent with the predictions of local spin density approximation calculations except for a 1 eV shift toward higher binding energy. Band dispersions are observed in the normal emission data. The spectra of La{sub 1.2}Sr{sub 1.8}Mn{sub 2}O{sub 7} show well defined features and strong matrix element effects, indicating excellent surface quality. (c) 2000 American Institute of Physics.

  15. Angle-Resolved Resonant Photoemission as a Probe of Spatial Localization and Character of Electron States

    Science.gov (United States)

    Molodtsov, S. L.; Richter, M.; Danzenbächer, S.; Wieling, S.; Steinbeck, L.; Laubschat, C.

    1997-01-01

    Resonant photoemission (PE) in the angle-resolved mode is proposed as a method to determine the spatial localization and the angular momentum character of valence band states from on-resonance PE signals across the Brillouin zone. This technique is applied to study ordered films of La metal. The obtained experimental data agree well with the results of band-structure calculations and related eigenvector analysis.

  16. 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.

  17. Core level photoelectron spectroscopy on the lanthanide-induced hydrolysis of DNA

    Science.gov (United States)

    Shigekawa, Hidemi; Ikawa, Hiroyuki; Yoshizaki, Ryozo; Iijima, Yoshitoki; Sumaoka, Jun; Komiyama, Makoto

    1996-03-01

    The electronic structures of the complexes of diphenyl phosphate (DPP), a model compound of DNA, with lanthanide ions have been investigated to shed light on the mechanism of the cerium (IV)-induced nonenzymatic hydrolysis of DNA. Binding energies of the P 2p core level of DPP were 134.2 eV for the complexes with La(III), Eu(III), and Lu(III), and was 134.4 eV for the Ce(IV) complex, when the metal/DPP molar ratio was 1:1. When the molar ratio was increased, only Ce(IV), the most active metal ion for DNA hydrolysis, showed a chemical shift of ˜0.5 eV toward the higher binding energy region. The chemical shift of ˜0.5 eV toward the higher binding energy region. The chemical shift was due to the systematic increase in the intensity of the higher binding energy component. The observed change in the electronic structure of the DPP-Ce(IV) complex may be related to the superb ability of Ce(IV) for the hydrolysis of DNA.

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

    Directory of Open Access Journals (Sweden)

    Gongyu Wang

    2015-01-01

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

  19. Electronic structure studies of YBa{sub 2}Cu{sub 3}O{sub x}(6.2 {le} x {le} 6.9) using angle resolved photoemission

    Energy Technology Data Exchange (ETDEWEB)

    Veal, B.W.; Liu, Rong; Paulikas, A.P.; Koelling, D.D.; Downey, J.W. [Argonne National Lab., IL (United States); Shi, Hao [Argonne National Lab., IL (United States)]|[Missouri Univ., Kansas City, MO (United States). Dept. of Physics; Olson, C.G. [Ames Lab., IA (United States); Arko, A.J.; Joyce, J.J.; Blythe, R. [Los Alamos National Lab., NM (United States)

    1992-11-01

    Using high resolution angle resolved photoemission, the electronic structure of YBa{sub 2}Cu{sub 3}O{sub x} is examined when oxygen stoichiometries are varied in the range 6.2 {le} {times} {le} 6.9. Detailed measurements of the Fermi surface for YBa{sub 2}Cu{sub 3}O{sub 6.9} are presented and are compared with predictions of band theory. In the metallic region of the phase diagram, changes in the Fermi surfaces are measured as a function of oxygen stoichiometry. The electronic structure is monitored as the oxide changes from a metal to a semiconductor with additional oxygen depletion. For intermediate stoichiometries, effects of oxygen vacancy ordering are considered. Unusual resonant effects observed at several photon energies are examined as oxygen content is varied.

  20. 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.

  1. Core-Exciton Decay in Photoemission and the Nonmetal - Transition.

    Science.gov (United States)

    Zhang, Jiandi

    Ultra thin films or overlayers of materials, normally metallic in the bulk case, can exhibit nonmetallic characters. Typically, these systems undergo a nonmetal-to-metal transition with changing film density, crystalline structure, or thickness. The purpose of this thesis is to identify this electronic phase transition and to investigate the corresponding fundamental mechanisms by studying the detailed electronic structure. In particular, I attempted to look at the evolution of electronic structure in films undergoing this transition. The core -exciton decay in the resonant photoemission was probed, from both theoretical and experimental points of view, to correlate with the change of film metallicity. Resonant photoemission, combining with normal photoemission, was found to be a sensitive and successful method to identify the overlayer nonmetal-metal transition, both from static and dynamic pictures. In most of this work, we concentrate on the studies of the evolution of electronic structure of ultra thin films of divalent metals, on different crystalline surfaces. The formation of new Hg electronic states arising from the electron orbital hybridization between adjacent adatoms, the formation of quantum well states in the overlayers, and the evolution of mercury shape resonance due to 5d to epsilonf excitation, all provide indications of when mercury overlayers undergo a nonmetal to metal transition. This transition has been found to be associated the changes in adatom coordination number. On both Cu(100) and W(110), the interactions between the Hg adatoms and the substrates are very weak and the surface bonding is more like covalent bonding at low coverages. The Hg overlayers on these two surfaces resembles free-standing layers, and the metallicity of the overlayers is largely determined by the nearest neighbor interactions of Hg adatoms. Comparing Hg overlayers on Ni(111) where there exists a nonmetal to metal transition caused by the structure phase transition

  2. Chemical bonding of water to metal surfaces studied with core-level spectroscopies

    DEFF Research Database (Denmark)

    Schiros, T.; Andersson, Klas Jerker; Pettersson, L.G.M.;

    2010-01-01

    and the interaction between the water monolayer and the surface. By combining synchrotron radiation-based X-ray photoelectron spectroscopy (XPS). X-ray absorption spectroscopy (XAS) and X-ray emission spectroscopy (XES) techniques with density functional theory (DFT) computational methods we obtain element......-specific information on the partial local density of states, local atomic structure, geometrical parameters and molecular orientation, allowing general principles for water-metal interaction to be derived....

  3. X-ray photo-emission and energy dispersive spectroscopy of HA coated titanium

    Energy Technology Data Exchange (ETDEWEB)

    Drummond, J.L.; Steinberg, A.D. [Univ. of Illinois, Chicago, IL (United States); Krauss, A.R. [Argonne National Lab., IL (United States)] [and others

    1997-08-01

    The purpose of this study was to determine the chemical composition changes of hydroxyapatite (HA) coated titanium using surface analysis (x-ray photo-emission) and bulk analysis (energy dispersive spectroscopy). The specimens examined were controls, 30 minutes and 3 hours aged specimens in distilled water or 0.2M sodium phosphate buffer (pH 7.2) at room temperature. Each x-ray photo-emission cycle consisted of 3 scans followed by argon sputtering for 10 minutes for a total of usually 20 cycles, corresponding to a sampling depth of {approximately} 1500 {angstrom}. The energy dispersive spectroscopy analysis was on a 110 by 90 {mu}m area for 500 sec. Scanning electron microscopy examination showed crystal formation (3P{sub 2}O{sub 5}*2CAO*?H{sub 2}O by energy dispersive spectroscopy analysis) on the HA coating for the specimens aged in sodium phosphate buffer. The x-ray photo-emission results indicated the oxidation effect of water on the titanium (as TiO{sub 2}) and the effect of the buffer to increase the surface concentration of phosphorous. No differences in the chemical composition were observed by energy dispersive spectroscopy analysis. The crystal growth was only observed for the sodium phosphate buffer specimens and only on the HA surface.

  4. 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.

  5. 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...

  6. 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.

  7. Real-time observation of collective excitations in photoemission

    Science.gov (United States)

    Lemell, C.; Neppl, S.; Wachter, G.; Tőkési, K.; Ernstorfer, R.; Feulner, P.; Kienberger, R.; Burgdörfer, J.

    2015-06-01

    Ejection of an electron by absorption of an extreme ultraviolet (xuv) photon probes the many-electron response of a solid well beyond the single-particle picture. Photoemission spectra feature complex correlation satellite structures signifying the simultaneous excitation of single or multiple plasmons. The time delay of the plasmon satellites relative to the main line can be resolved in attosecond streaking experiments. Time-resolved photoemission thus provides the key to discriminate between intrinsic and extrinsic plasmon excitation. We demonstrate the determination of the branching ratio between intrinsic and extrinsic plasmon generation for simple metals.

  8. 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.

  9. Time-resolved two-photon photoemission from metal surfaces

    CERN Document Server

    Weinelt, M

    2002-01-01

    The Rydberg-like series of image-potential states is a prototype system for loosely bound electrons at a metal surface. The electronic structure and the femtosecond dynamics of these states is studied by high-resolution energy-and time-resolved two-photon photoemission spectroscopy. The electron trapped in the image potential moves virtually freely laterally to the surface where it is subject to inelastic and quasielastic scattering processes which cause decay of population and phase relaxation. The influence of surface corrugation on these processes has been investigated for adsorbates on Cu(001) and stepped Cu(117) and Cu(119) surfaces which are vicinal to Cu(001). The dynamics depend on both the distance of the electron in front of the surface and the parallel momentum. For CO molecules on Cu(001) inelastic scattering into bulk states and adsorbate-induced resonances determine the decay rate. For small numbers of Cu adatoms on Cu(001) and the vicinal surfaces the decay rate of image-potential states is sig...

  10. A soft X-ray study of a Li-S surface compound

    Energy Technology Data Exchange (ETDEWEB)

    Shek, M.L. (Shek (M.L.), Ridge, NY (United States)); Sham, T.K. (Univ. of Western Ontario, London, Ontario (Canada). Dept. of Chemistry); Hrbek, J.; Xu, G.Q. (Brookhaven National Lab., Upton, NY (United States). Chemistry Dept.)

    1991-01-01

    The authors have studied a Li[sub 2]S[sub x] compound (x [approx] 0.79 to 0.95) with soft X-ray excited valence and core-level photoemission and Auger electron emission. The Li 1s core level is found at a binding energy of 56.9 eV, shifted by [approximately] 1.9 eV relative to the bulk 1s level of Li metal. The LiKVV Auger transition gives two peaks at kinetic energies 44.9 and 41.2 eV with respect to the Fermi level, corresponding to final states with two valence holes on different sites or on the same site, respectively. The S 2p photoemission doublets are observed at 162.7 and [approximately] 163.7 eV, their de-excitation giving rise to the SL[sub 2,3]VV Auger peak at 149.2 eV. The authors discuss the electronic interactions in the Li[sub 2]S[sub x] surface compound, and make a comparison with those in a Li-O surface compound.

  11. Soft X-ray absorption and photoemission spectroscopy study of semiconductor oxide nanoparticles for dye-sensitized solar cell: ZnSnO3 and Zn2SnO4

    Science.gov (United States)

    Kim, Hyun Woo; Lee, Eunsook; Kim, D. H.; Seong, Seungho; Moon, Soo Yeon; Shin, Yu-Ju; Baik, J.; Shin, H. J.; Kang, J.-S.

    2016-06-01

    The electronic structures of the Zn-stannate nanoparticles of ZnSnO3 and Zn2SnO4, which are the potential nano-structured semiconductor oxides for a dye sensitized solar cell (DSSC), have been investigated by employing photoemission spectroscopy (PES) and soft X-ray absorption spectroscopy (XAS), and compared to those of reference materials. The divalent and tetravalent valence states of Zn2+ and Sn4+ ions are confirmed experimentally. The energy levels of both the valence-band and conduction-band edges are determined experimentally. The top of the valence band in PES is slightly higher in Zn2SnO4 than in ZnSnO3. The onset energies of the O 1s XAS spectra of the Zn-stannates are found to be similar to each other, but higher than that of TiO2. The O 1 s XAS spectrum of ZnSnO3 exhibits the higher unoccupied density of states near the bottom of the conduction band than those of Zn2SnO4, SnO2 and ZnO, reflecting the larger number of holes in the Zn 3 d bands of ZnSnO3. Hence, the easier electron transfer is expected from the LUMO (lowest unoccupied molecular orbital) of a dye molecule to the conduction band of ZnSnO3 nanoparticles on the transparent conductive electrode of a DSSC.

  12. SiO mass spectrometry and Si-2p photoemission spectroscopy for the study of oxidation reaction dynamics of Si(001) surface by supersonic O sub 2 molecular beams under 1000K

    CERN Document Server

    Teraoka, Y; Moritani, K

    2003-01-01

    The Si sup 1 sup 8 O desorption yield was measured in the Si(001) surface temperature region from 900K to 1300K at the sup 1 sup 8 O sub 2 incident energies of 0.7eV, 2.2eV and 3.3eV. The Si sup 1 sup 8 O desorption yield in a surface temperature region higher than 1000K increased with increasing incident energy, indicating the incident-energy-induced oxidation and the variation of angular distribution of Si sup 1 sup 8 O desorption. Inversely, the Si sup 1 sup 8 O desorption yield decreased with increasing incident energy in the region from 900K to 1000K, indicating the coexistence of the passive and the active oxidation. In order to clarify the reaction mechanisms of the later phenomenon, real-time in-situ Si-2p photoemission spectroscopy has been performed. The obtained Si-2p spectra showed the variation of the oxide-nuclei quality from the sub-oxide-rich structure to the SiO sub 2 -rich structure. The formation of the SiO sub 2 structure suppresses the SiO desorption due to the enhanced O sub 2 sticking a...

  13. 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...

  14. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-09-15

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

  16. Vacancy formation in MoO3: hybrid density functional theory and photoemission experiments

    KAUST Repository

    Salawu, Omotayo Akande

    2016-09-29

    Molybdenum oxide (MoO3) is an important material that is being considered for numerous technological applications, including catalysis and electrochromism. In the present study, we apply hybrid density functional theory to investigate O and Mo vacancies in the orthorhombic phase. We determine the vacancy formation energies of different defect sites as functions of the electron chemical potential, addressing different charge states. In addition, we investigate the consequences of defects for the material properties. Ultraviolet photoemission spectroscopy is employed to study the valence band of stoichiometric and O defective MoO3. We show that O vacancies result in occupied in-gap states.

  17. Inverse-photoemission spectroscopy of GaSe and InSe

    Science.gov (United States)

    Sporken, R.; Hafsi, R.; Coletti, F.; Debever, J. M.; Thiry, P. A.; Chevy, A.

    1994-04-01

    The lamellar semiconductors GaSe and InSe have been studied with k-resolved inverse-photoemission spectroscopy along two major symmetry directions (Γ¯ K¯ and Γ¯ M¯) of the surface Brillouin zone. Three bands with well-resolved features are observed from which the dispersion of the conduction bands can be determined with good precision. The minimum of the conduction band is found at M¯ in GaSe and at Γ¯ in InSe. These results are compared with theoretical studies using pseudopotential and tight-binding calculations.

  18. Core-level spectra and binding energies of transition metal nitrides by non-destructive x-ray photoelectron spectroscopy through capping layers

    Science.gov (United States)

    Greczynski, G.; Primetzhofer, D.; Lu, J.; Hultman, L.

    2017-02-01

    capped TMN films, thus characteristic of a native surface, show a systematic trend, which contrasts with the large BE spread of literature "reference" values. Hence, non-destructive core level XPS employing capping layers provides an opportunity to obtain high-quality spectra, characteristic of virgin in situ grown and analyzed TMN films, although with larger versatility, and allows for extracting core level BE values that are more reliable than those obtained from sputter-cleaned N-deficient surfaces. Results presented here, recorded from a consistent set of binary TMN's grown under the same conditions and analyzed in the same instrument, provide a useful reference for future XPS studies of multinary materials systems allowing for true deconvolution of complex core level spectra.

  19. An innovative Yb-based ultrafast deep ultraviolet source for time-resolved photoemission experiments.

    Science.gov (United States)

    Boschini, F; Hedayat, H; Dallera, C; Farinello, P; Manzoni, C; Magrez, A; Berger, H; Cerullo, G; Carpene, E

    2014-12-01

    Time- and angle-resolved photoemission spectroscopy is a powerful technique to study ultrafast electronic dynamics in solids. Here, an innovative optical setup based on a 100-kHz Yb laser source is presented. Exploiting non-collinear optical parametric amplification and sum-frequency generation, ultrashort pump (hν = 1.82 eV) and ultraviolet probe (hν = 6.05 eV) pulses are generated. Overall temporal and instrumental energy resolutions of, respectively, 85 fs and 50 meV are obtained. Time- and angle-resolved measurements on BiTeI semiconductor are presented to show the capabilities of the setup.

  20. An innovative Yb-based ultrafast deep ultraviolet source for time-resolved photoemission experiments

    Energy Technology Data Exchange (ETDEWEB)

    Boschini, F.; Hedayat, H.; Dallera, C.; Cerullo, G. [Dipartimento di Fisica, Politecnico di Milano, 20133 Milan (Italy); Farinello, P. [Dipartimento di Ingegneria Industriale e dell' Informazione, Università di Pavia, 27100 Pavia (Italy); Manzoni, C.; Carpene, E., E-mail: ettore.carpene@polimi.it [IFN-CNR Dipartimento di Fisica, Politecnico di Milano, 20133 Milan (Italy); Magrez, A.; Berger, H. [Institute of Condensed Matter Physics (ICMP), École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne (Switzerland)

    2014-12-15

    Time- and angle-resolved photoemission spectroscopy is a powerful technique to study ultrafast electronic dynamics in solids. Here, an innovative optical setup based on a 100-kHz Yb laser source is presented. Exploiting non-collinear optical parametric amplification and sum-frequency generation, ultrashort pump (hν = 1.82 eV) and ultraviolet probe (hν = 6.05 eV) pulses are generated. Overall temporal and instrumental energy resolutions of, respectively, 85 fs and 50 meV are obtained. Time- and angle-resolved measurements on BiTeI semiconductor are presented to show the capabilities of the setup.

  1. 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.

  2. 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.

  3. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Aram; Yang, Aram; Shipman, Steven T.; Garrett-Roe, Sean; Johns, James; Strader, Matt; Szymanski, Paul; Muller, Eric; Harris, Charles B.

    2007-11-29

    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 image potential state were measured to be larger for disordered layers. The effective mass was interpreted in the context of charge mobility measurements.

  5. Quantum Efficiency Measurements of Femtosecond Vectorial Photoemission on Cu Photocathodes

    CERN Document Server

    Banfi, F; Galimberti, P G; Giannetti, C; Pagliara, S; Parmigiani, F; Pedersoli, E

    2005-01-01

    Quantum Efficiency (QE) measurements of single photon photoemission from a Cu(111) single crystal and a Cu polycrystal photocathodes, irradiated by 150~fs-6.28~eV laser pulses, are reported over a broad range of incidence angle in both s and p polarizations. The maximum value of QE for the Cu polycrystal sample is Y~4*10(-4), obtained with p polarization at an angle of incidence theta=65°. Our data confirm the vectorial photoemission model. Issues concerning surface roughness and symmetry considerations are addressed. An explanation in terms of non local conductivity tensor is proposed. Advantages of a 6.28~eV photon as compared to the standard 4.71~eV photon in use with Cu photocathodes are discussed.

  6. Photoemission, low-dimensionality and high-temperature superconductivity

    Energy Technology Data Exchange (ETDEWEB)

    Margaritondo, G. [Ecole Polytechnique Federale, Lausanne (Switzerland). Inst. de Physique Appliquee]|[Sincrotrone Trieste SCpA (Italy)

    1996-12-31

    Several experiments by different authors have established the existence of an anomalous photoemission effect in one-dimensional systems, including one-dimensional metallic crystals and other examples of one-dimensional metals. The effect consists of the suppression of the photoemission signal at energies close to the Fermi level--whereas for metals one would expect to see a Fermi edge. Increasing evidence exists, in the authors opinion, that this phenomenon is due to the decoupling of charge and spin coordinates and to a departure from the Fermi-liquid framework. If confirmed, this conclusion would be extremely relevant to high-temperature superconductivity, since it would pave the way to the use of a similar concept for non-Fermi-liquid theories of high-temperature superconductors.

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

    CERN Document Server

    Lynn-Jensen, Kevin

    2004-01-01

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

  8. Soft X-ray photoemission spectroscopy of selected neurotransmitters in the gas phase

    Energy Technology Data Exchange (ETDEWEB)

    Maris, Assimo; Melandri, Sonia; Evangelisti, Luca; Caminati, Walther [Dipartimento di Chimica ' G. Ciamician' dell' Universita, Via Selmi 2, I-40126 Bologna (Italy); Giuliano, Barbara M. [Departamento de Quimica da Universidade de Coimbra, 3004-535 Coimbra (Portugal); Plekan, Oksana [Sincrotrone Trieste, in Area Science Park, I-34149 Basovizza, Trieste (Italy); Feyer, Vitaliy [Sincrotrone Trieste, in Area Science Park, I-34149 Basovizza, Trieste (Italy); Electronic Properties (PGI-6), Peter Gruenberg Institute, Forschungszentrum Juelich GmbH, Leo-Brandt-Strasse, 52428 Juelich (Germany); Richter, Robert [Sincrotrone Trieste, in Area Science Park, I-34149 Basovizza, Trieste (Italy); Coreno, Marcello [CNR-IMIP, Montelibretti, I-00016 Rome (Italy); Prince, Kevin C., E-mail: kevin.prince@elettra.trieste.it [Sincrotrone Trieste, in Area Science Park, I-34149 Basovizza, Trieste (Italy); CNR-IOM, Laboratorio TASC, I-34149 Basovizza, Trieste (Italy)

    2012-09-15

    Highlights: Black-Right-Pointing-Pointer Neurotransmitter molecules. Black-Right-Pointing-Pointer Photoelectron spectroscopy. Black-Right-Pointing-Pointer Electronic structure. Black-Right-Pointing-Pointer Weak hydrogen bonding. -- Abstract: The valence molecular orbitals and core levels of tyramine, tryptamine and tryptophol in the gas phase have been studied using X-ray photoelectron spectroscopy (XPS) and theoretical methods. The energies of the outer valence region spectrum are found to be in agreement with previously reported He I spectra, while new data on the inner valence molecular orbitals are reported. The structures in the carbon, nitrogen and oxygen core level spectra of these molecules have been identified and assigned. These compounds are characterised by conformers with hydrogen bonding in which the {pi} systems of the phenol and indole groups act as hydrogen acceptors, but a spectroscopic signature of this hydrogen bond was not observed. This is in contrast with our previous spectra of amino acids, where conformers with specific hydrogen bonding showed strong effects in core level spectra. We attribute the difference to the weaker strength of the {pi}-hydrogen bonding.

  9. 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.

  10. Photoemission in YbCu sub 2 Si sub 2 : Problems with the Kondo impurity model

    Energy Technology Data Exchange (ETDEWEB)

    Lawrence, J.M. (California Univ., Irvine (United States)); Arko, A.J.; Joyce, J.J.; Canfield, P.C.; Fisk, Z.; Thompson, J.D. (Los Alamos National Lab., NM (United States))

    1991-01-01

    We report valence band photoemission results for YbCu{sub 2}Si{sub 2}. The 4f{sup 13}(J=7/2) final state peak, centered 60meV below the Fermi level {epsilon}{sub F}, lacks the temperature dependence and is broader than predicted for a Kondo resonance. Together with the recent photoemission results for cerium compounds, these results raise serious doubts about the Kondo impurity explanation of heavy fermion photoemission. 7 refs., 3 figs.

  11. Photoemission in YbCu sub 2 Si sub 2 : problem with the Kondo impurity model

    Energy Technology Data Exchange (ETDEWEB)

    Lawrence, J.M.; Arko, A.J.; Joyce, J.J.; Canfield, P.C.; Fisk, Z.; Thompson, J.D.; Bartlett, R.J. (Los Alamos National Lab., NM (United States))

    1992-02-01

    We report valence band photoemission results for YbCu{sub 2}Si{sub 2}. The 4f{sup 13}(J = 7/2) final state peak, centered 60 meV below the Fermi level element of{sub F}, lacks the temperature dependence and is broader than predicted for a Kondo resonance. Together with recent photoemission results for cerium compounds, these results raise serious doubts about the Kondo impurity explanation of heavy fermion photoemission. (orig.).

  12. 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.

  13. 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.

  14. High-resolution x-ray photoemission electron microscopy at the Advanced Light Source

    Energy Technology Data Exchange (ETDEWEB)

    Stammler, T.; Anders, S.; Padmore, H.A. [Lawrence Berkeley National Lab., CA (United States); Stoehr, J. [IBM Almaden Research Center, San Jose, CA (United States); Scheinfein, M. [Arizona State Univ., Tempe, AZ (United States). Dept. of Physics and Astronomy; Ade, H. [North Carolina State Univ., Raleigh, NC (United States). Dept. of Physics

    1998-12-31

    X-ray Photoemission Electron Microscopy (X-PEEM) is a full-field imaging technique where the sample is illuminated by an x-ray beam and the photoemitted electrons are imaged on a screen by means of an electron optics. It therefore combines two well-established materials analysis techniques--photoemission electron microscopy (PEEM) and x-ray spectroscopy such as near edge x-ray absorption fine structure (NEXAFS) spectroscopy. This combination opens a wide field of new applications in materials research and has proven to be a powerful tool to investigate simultaneously topological, elemental, chemical state, and magnetic properties of surfaces, thin films, and multilayers at high spatial resolution. A new X-PEEM installed at the bend magnet beamline 7.3.1.1 at the Advanced Light Source (ALS) is designed for a spatial resolution of 20 nm and is currently under commissioning. An overview of the ongoing experimental program using X-PEEM in the field of materials research at the ALS is given by elemental and chemical bonding contrast imaging of hard disk coatings and sliders, field emission studies on diamond films as possible candidates for field-emission flat-panel displays, and the study of dewetting and decomposition phenomena of thin polymer blends and bilayers.

  15. sp2/sp3 hybridization ratio in amorphous carbon from C 1s core-level shifts: X-ray photoelectron spectroscopy and first-principles calculation

    Science.gov (United States)

    Haerle, Rainer; Riedo, Elisa; Pasquarello, Alfredo; Baldereschi, Alfonso

    2002-01-01

    Using a combined experimental and theoretical approach, we address C 1s core-level shifts in amorphous carbon. Experimental results are obtained by x-ray photoelectron spectroscopy (XPS) and electron-energy-loss spectroscopy (EELS) on thin-film samples of different atomic density, obtained by a pulsed-laser deposition growth process. The XPS spectra are deconvoluted into two contributions, which are attributed to sp2- and sp3-hybridized atoms, respectively, separated by 0.9 eV, independent of atomic density. The sp3 hybridization content extracted from XPS is consistent with the atomic density derived from the plasmon energy in the EELS spectrum. In our theoretical study, we generate several periodic model structures of amorphous carbon of different densities applying two schemes of increasing accuracy in sequence. We first use a molecular-dynamics approach, based on an environmental-dependent tight-binding Hamiltonian to quench the systems from the liquid phase. The final model structures are then obtained by further atomic relaxation using a first-principles pseudopotential plane-wave approach within density-functional theory. Within the latter framework, we also calculate carbon 1s core-level shifts for our disordered model structures. We find that the shifts associated to threefold- and fourfold- coordinated carbon atoms give rise to two distinct peaks separated by about 1.0 eV, independent of density, in close agreement with experimental observations. This provides strong support for decomposing the XPS spectra into two peaks resulting from sp2- and sp3-hybridized atoms. Core-hole relaxations effects account for about 30% of the calculated shifts.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-11-15

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

  17. 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.

  18. Angle resolved photoemission spectroscopy reveals spin charge separation in metallic MoSe2 grain boundary

    Science.gov (United States)

    Ma, Yujing; Diaz, Horacio Coy; Avila, José; Chen, Chaoyu; Kalappattil, Vijaysankar; Das, Raja; Phan, Manh-Huong; Čadež, Tilen; Carmelo, José M. P.; Asensio, Maria C.; Batzill, Matthias

    2017-02-01

    Material line defects are one-dimensional structures but the search and proof of electron behaviour consistent with the reduced dimension of such defects has been so far unsuccessful. Here we show using angle resolved photoemission spectroscopy that twin-grain boundaries in the layered semiconductor MoSe2 exhibit parabolic metallic bands. The one-dimensional nature is evident from a charge density wave transition, whose periodicity is given by kF/π, consistent with scanning tunnelling microscopy and angle resolved photoemission measurements. Most importantly, we provide evidence for spin- and charge-separation, the hallmark of one-dimensional quantum liquids. Our studies show that the spectral line splits into distinctive spinon and holon excitations whose dispersions exactly follow the energy-momentum dependence calculated by a Hubbard model with suitable finite-range interactions. Our results also imply that quantum wires and junctions can be isolated in line defects of other transition metal dichalcogenides, which may enable quantum transport measurements and devices.

  19. High-resolution x-ray photoemission spectra of silver

    DEFF Research Database (Denmark)

    Barrie, A.; Christensen, N. E.

    1976-01-01

    An electron spectrometer fitted with an x-ray monochromator for Al Kα1,2 radiation (1486.6 eV) has been used to record high-resolution x-ray photoelectron spectra for the 4d valence band as well as the 3d spin doublet in silver. The core-level spectrum has a line shape that can be described...

  20. 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.

  1. 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.

  2. 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

  3. 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

  4. A study of the Fe-based superconductor SmFeAsO{sub 1-x}F{sub x} by x-ray photoelectron spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Y; Chen, Y L; Cui, Y J; Cheng, C H; Zhao, Y [Key Laboratory of Magnetic Levitation Technologies and Maglev Trains (Ministry of Education of China), Superconductivity R and D Center (SRDC), Mail Stop 165, Southwest Jiaotong University, Chengdu, Sichuan 610031 (China); Zhang, H [Department of Physics, Peking University, Beijing 100871 (China)], E-mail: yzhao@swjtu.edu.cn

    2009-01-15

    The electronic structure of the Fe-based superconductor SmFeAsO{sub 1-x}F{sub x} (x = 0 and 0.2) is studied with x-ray photoemission spectroscopy (XPS) through comparing the band structures of the nonsuperconducting parent material SmFeAsO and the superconducting SmFeAsO{sub 0.8}F{sub 0.2} (T{sub c} = 52.5 K). A small peak centered at 0.2 eV below the Fermi level, E{sub F}, in the valence band is observed in the parent material SmFeAsO, which is due to the low-spin state of the Fe 3d electrons. With fluorine doping, the peak at 0.2 eV disappears and a broad plateau forms near the Fermi level; in the meantime, the density of states at E{sub F} is slightly suppressed. The O 1s and Sm 3d core levels shift towards high energy by {approx}0.55 eV with fluorine doping, but in a sharp comparison, the Fe 2p and As 3d core levels do not shift significantly (the binding energy shift is less than 0.01 eV). It is deduced from the core-level shifts that the Fermi level of the system moves up by 0.55 eV by fluorine doping.

  5. Threshold photoemission magnetic circular dichroism of perpendicularly magnetized Ni films on Cu(001): theory and experiment

    Energy Technology Data Exchange (ETDEWEB)

    Kronseder, Matthias; Guenther, Stefan; Woltersdorf, Georg; Back, Christian H. [Universitaet Regensburg, Regensburg (Germany)

    2011-07-01

    Threshold photoemission magnetic circular dichroism (TP-MCD) for perpendicularly magnetized Ni films on Cu(001) was measured with a total electron yield method. This dichroism was used to observe the magnetic domain structure of these samples in a photoemission electron microscope. A spin-polarized relativistic Korringa-Kohn-Rostoker Green's function calculation including a dynamical mean field theory approach within the one-step-photoemission model reproduces the measured asymmetry in the photocurrents for left and right circularly polarized light. In addition, a three-step photoemission model calculation based on the same ab-initio calculation is used to quantitatively explain the MCD effect near the photoemission threshold. Furthermore, the dependence of the MCD-asymmetry on the polarization state of the incoming photons is theoretically computed and experimentally verified.

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

    Science.gov (United States)

    2015-01-01

    We use two different ab initio quantum mechanics methods, complete active space self-consistent field theory applied to electrostatically embedded clusters and periodic many-body G0W0 calculations, to reanalyze the states formed in nickel(II) oxide upon electron addition and ionization. In agreement with interpretations of earlier measurements, we find that the valence and conduction band edges consist of oxygen and nickel states, respectively. However, contrary to conventional wisdom, we find that the oxygen states of the valence band edge are localized whereas the nickel states at the conduction band edge are delocalized. We argue that these characteristics may lead to low electron–hole recombination and relatively efficient electron transport, which, coupled with band gap engineering, could produce higher solar energy conversion efficiency compared to that of other transition-metal oxides. Both methods find a photoemission/inverse-photoemission gap of 3.6–3.9 eV, in good agreement with the experimental range, lending credence to our analysis of the electronic structure of NiO. PMID:24689856

  7. Revisiting photoemission and inverse photoemission spectra of nickel oxide from first principles: implications for solar energy conversion.

    Science.gov (United States)

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

    2014-07-17

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

  8. 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.

  9. Complete momentum and energy resolved TOF electron spectrometerfor time-resolved photoemission spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Hussain, Zahid; Lebedev, G.; Tremsin, A.; Siegmund, O.; Chen, Y.; Shen, Z.X.; Hussain, Z.

    2007-08-12

    Over the last decade, high-resolution Angle-Resolved Photoemission Spectroscopy (ARPES) has emerged as a tool of choice for studying the electronic structure of solids, in particular, strongly correlated complex materials such as cuprate superconductors. In this paper we present the design of a novel time-of-flight based electron analyzer with capability of 2D in momentum space (kx and ky) and all energies (calculated from time of flight) in the third dimension. This analyzer will utilize an improved version of a 2D delay linedetector capable of imaging with<35 mm (700x700 pixels) spatial resolution and better than 120 ps FWHM timing resolution. Electron optics concepts and optimization procedure are considered for achieving an energy resolution less than 1 meV and an angular resolution better than 0.11.

  10. Imaging and characterization of conducting ferroelectric domain walls by photoemission electron microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Schaab, J.; Meier, D., E-mail: dennis.meier@mat.ethz.ch [Department of Materials, ETH Zurich, Vladimir-Prelog-Weg 4, 8093 Zurich (Switzerland); Krug, I. P. [Institut für Optik und Atomare Physik, TU Berlin, Hardenbergstrasse 36, 10623 Berlin (Germany); Forschungszentrum Jülich Peter Grünberg Institute (PGI-6), Leo-Brandt-Strasse, 52425 Jülich (Germany); Nickel, F.; Gottlob, D. M.; Doğanay, H.; Schneider, C. M. [Forschungszentrum Jülich Peter Grünberg Institute (PGI-6), Leo-Brandt-Strasse, 52425 Jülich (Germany); Cano, A. [CNRS, Univ. Bordeaux, ICMCB, UPR 9048, F-33600 Pessac (France); Hentschel, M. [4th Physics Institute and Research Center SCoPE, University of Suttgart, Pfaffenwaldring 57, 70659 Stuttgart (Germany); Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Yan, Z.; Bourret, E. [Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Ramesh, R. [Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Department of Materials Science and Engineering, University of California, Berkeley, California 94720 (United States)

    2014-06-09

    High-resolution X-ray photoemission electron microscopy (X-PEEM) is a well-established method for imaging ferroelectric domain structures. Here, we expand the scope of application of X-PEEM and demonstrate its capability for imaging and investigating domain walls in ferroelectrics with high spatial resolution. Using ErMnO{sub 3} as test system, we show that ferroelectric domain walls can be visualized based on photo-induced charging effects and local variations in their electronic conductance can be mapped by analyzing the energy distribution of photoelectrons. Our results open the door for non-destructive, contact-free, and element-specific studies of the electronic and chemical structure at domain walls in ferroelectrics.

  11. An Aberration Corrected Photoemission Electron Microscope at the Advanced Light Source

    Science.gov (United States)

    Feng, J.; MacDowell, A. A.; Duarte, R.; Doran, A.; Forest, E.; Kelez, N.; Marcus, M.; Munson, D.; Padmore, H.; Petermann, K.; Raoux, S.; Robin, D.; Scholl, A.; Schlueter, R.; Schmid, P.; Stöhr, J.; Wan, W.; Wei, D. H.; Wu, Y.

    2004-05-01

    Design of a new aberration corrected Photoemission electron microscope PEEM3 at the Advanced Light Source is outlined. PEEM3 will be installed on an elliptically polarized undulator beamline and will be used for the study of complex materials at high spatial and spectral resolution. The critical components of PEEM3 are the electron mirror aberration corrector and aberration-free magnetic beam separator. The models to calculate the optical properties of the electron mirror are discussed. The goal of the PEEM3 project is to achieve the highest possible transmission of the system at resolutions comparable to our present PEEM2 system (50 nm) and to enable significantly higher resolution, albeit at the sacrifice of intensity. We have left open the possibility to add an energy filter at a later date, if it becomes necessary driven by scientific need to improve the resolution further.

  12. Core-level positive-ion and negative-ion fragmentation of gaseous and condensed HCCl3 using synchrotron radiation

    Science.gov (United States)

    Lu, K. T.; Chen, J. M.; Lee, J. M.; Haw, S. C.; Liang, Y. C.; Deng, M. J.

    2011-07-01

    We investigated the dissociation dynamics of positive-ion and negative-ion fragments of gaseous and condensed HCCl3 following photoexcitation of Cl 2p electrons to various resonances. Based on ab initio calculations at levels HF/cc-pVTZ and QCISD/6-311G*, the first doublet structures in Cl L-edge x-ray absorption spectrum of HCCl3 are assigned to transitions from the Cl (2P3/2,1/2) initial states to the 10a1* orbitals. The Cl 2p → 10a1* excitation of HCCl3 induces a significant enhancement of the Cl+ desorption yield in the condensed phase and a small increase in the HCCl+ yield in the gaseous phase. Based on the resonant photoemission of condensed HCCl3, excitations of Cl 2p electrons to valence orbitals decay predominantly via spectator Auger transitions. The kinetic energy distributions of Cl+ ion via the Cl 2p → 10a1* excitation are shifted to higher energy ˜0.2 eV and ˜0.1 eV relative to those via the Cl 2p → 10e* excitation and Cl 2p → shape resonance excitation, respectively. The enhancement of the yields of ionic fragments at specific core-excited resonance states is assisted by a strongly repulsive surface that is directly related to the spectator electrons localized in the antibonding orbitals. The Cl- anion is significantly reinforced in the vicinity of Cl 2p ionization threshold of gaseous HCCl3, mediated by photoelectron recapture through post-collision interaction.

  13. Ce Core-Level Spectroscopy, and Magnetic and Electrical Transport Properties of Lightly Ce-Doped YCoO3

    Science.gov (United States)

    Kobayashi, Yoshihiko; Koike, Tsuyoshi; Okawa, Mario; Takayanagi, Ryohei; Takei, Shohei; Minohara, Makoto; Kobayashi, Masaki; Horiba, Koji; Kumigashira, Hiroshi; Yasui, Akira; Ikenaga, Eiji; Saitoh, Tomohiko; Asai, Kichizo

    2016-11-01

    We have investigated the Ce and Co core level spectroscopy, and the magnetic and electrical transport properties of lightly Ce-doped YCoO3. We have successfully synthesized single-phase Y1-xCexCoO3 for 0.0 ≤ x ≤ 0.1 by the sol-gel method. Hard X-ray photoelectron and X-ray absorption spectroscopy experiments reveal that the introduced Ce ions are tetravalent, which is considered to be the first case of electron doping into bulk trivalent Co oxides with perovskite RECoO3 (RE: rare-earth element or Y) caused by RE site substitution. The magnitude of the effective magnetic moment peff obtained from the temperature dependence of magnetic susceptibility χ(T) at higher temperatures is close to that for high-spin Co2+ introduced by the Ce doping, implying that the electrons doped into the Co site induce Co2+ with a high-spin state. For x = 0.1, ferromagnetic ordering is observed below about 7 K. Electrical transport properties such as resistivity and thermoelectric power show that negative electron-like carriers are introduced by Ce substitution.

  14. 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.

  15. Theory of pump–probe ultrafast photoemission and X-ray absorption spectra

    Energy Technology Data Exchange (ETDEWEB)

    Fujikawa, Takashi, E-mail: tfujikawa@faculty.chiba-u.jp; Niki, Kaori

    2016-01-15

    Highlights: • Pump–probe ultrafast XAFS and XPS spectra are theoretically studied. • Keldysh Green's function theory is applied. • Important many-body effects are explicitly included. - Abstract: Keldysh Green's function approach is extensively used in order to derive practical formulas to analyze pump–probe ultrafast photoemission and X-ray absorption spectra. Here the pump pulse is strong enough whereas the probe X-ray pulse can be treated by use of a perturbation theory. We expand full Green's function in terms of renormalized Green's function without the interaction between electrons and probe pulse. The present theoretical formulas allow us to handle the intrinsic and extrinsic losses, and furthermore resonant effects in X-ray Absorption Fine Structures (XAFS). To understand the radiation field screening in XPS spectra, we have to use more sophisticated theoretical approach. In the ultrafast XPS and XAFS analyses the intrinsic and extrinsic loss effects can interfere as well. In the XAFS studies careful analyses are necessary to handle extrinsic losses in terms of damped photoelectron propagation. The nonequilibrium dynamics after the pump pulse irradiation is well described by use of the time-dependent Dyson orbitals. Well above the edge threshold, ultrafast photoelectron diffraction and extended X-ray absorption fine structure (EXAFS) provide us with transient structural change after the laser pump excitations. In addition to these slow processes, the rapid oscillation in time plays an important role related to pump electronic excitations. Near threshold detailed information could be obtained for the combined electronic and structural dynamics. In particular high-energy photoemission and EXAFS are not so influenced by the details of excited states by pump pulse. Random-Phase Approximation (RPA)-boson approach is introduced to derive some practical formulas for time-dependent intrinsic amplitudes.

  16. heterojunction interface investigated by X-ray photoemission spectroscopy

    Science.gov (United States)

    Lin, Lingyan; Yu, Jinling; Cheng, Shuying; Lu, Peimin; Lai, Yunfeng; Lin, Sile; Zhao, Pengyi

    2014-09-01

    The band alignment at the In2S3/Cu2ZnSnS4 heterojunction interface is investigated by X-ray photoemission spectroscopy. In2S3 is thermally evaporated onto the contamination-free polycrystalline Cu2ZnSnS4 surface prepared by magnetron sputtering. The valence band offset is measured to be 0.46 ± 0.1 eV, which matches well with the valance band offset value 0.49 eV calculated using "transitivity" method. The conduction band offset is determined to be 0.82 ± 0.1 eV, indicating a `type I' band alignment at the heterojunction interface.

  17. 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.

  18. 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.

  19. 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(Mg(0.66)Nb(0.33))O3-PbTiO3 and La(0.7)Sr(0.3)MnO3/PMN-PT artificial multiferroic nanostructures.

  20. 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.

  1. Two-photon photoemission from metals induced by picosecond laser pulses

    Science.gov (United States)

    Bechtel, J. H.; Smith, W. L.; Bloembergen, N.

    1977-01-01

    We have measured the two-photon photoemission current density from tungsten, tantalum, and molybdenum when irradiated by 532-nm wavelength radiation. This wavelength was produced by the second-harmonic radiation of single picosecond laser pulses from a mode-locked neodymium-doped yttrium-aluminum-garnet laser. The results are interpreted in terms of both a simple temperature-independent two-photon photoemission effect and a generalization of the Fowler-DuBridge theory of photoemission. The laser polarization dependence of the emitted current is also reported.

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

    Science.gov (United States)

    Kay, Alexander William

    2000-10-01

    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

  3. 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 [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

    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

  4. 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.

  5. 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 ...

  6. 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.

  7. Study of the electronic properties of Zn{sub 0.8–4x}Ho{sub x}O{sub y} (0.05 ≤ x ≤ 0.09) by X-ray absorption and photoemission spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Ekicibil, A. [Physic Department, University of Cukurova, 01330 Adana (Turkey); Ozkendir, O.M. [Tarsus Technology Faculty, Mersin University, 33400 Tarsus (Turkey); Farha, A.H. [Department of Electrical and Computer Engineering, Old Dominion University, Norfolk, VA 23529 (United States); Department of Physics, Faculty of Science, Ain Shams University, Cairo 11566 (Egypt); Ufuktepe, Y., E-mail: ufuk@cu.edu.tr [Physic Department, University of Cukurova, 01330 Adana (Turkey)

    2015-07-15

    Highlights: • The electronic structure of Ho doped ZnO was investigated by XANES and XPS. • The electronic structure was directly influenced by the Ho concentration in the ZnO. • The crystal structure showed little/no correlation to the substitution of Ho. • The substitution of Ho causes a weaker antiferromagnetic interaction. • The blue shift in band gap is observed and discussed. - Abstract: The electronic structure of Zn{sub 0.8–4x}Ho{sub x}O{sub y} (0.05 ≤ x ≤ 0.09) was investigated using X-ray absorption near edge structure (XANES) and X-ray photoelectron spectroscopy (XPS). Samples were prepared by the solid state reaction method. Using X-ray absorption spectroscopy, the investigation of M{sub 4,5} absorption edge of Ho revealed that the electronic structure was directly influenced by the Ho concentration in the Zn{sub 0.8–4x}Ho{sub x}O{sub y} sample whereas the crystal structure properties showed little/no correlation to the substitution of Ho. The electronic structure differs substantially from those of the reference ZnO. The O K-edge spectra suggest that the combination of the Ho with ZnO enhances the effective charge of the O ions. A systematic study on the composition from lower to higher value of Ho dopant showed the blue shift in band gaps and is discussed in the view of the electronic structure of the Zn{sub 0.8–4x}Ho{sub x}O{sub y} samples. The inverse susceptibility (1/χ) against temperature curves is plotted to identify the magnetic contribution. Those curves indicate that the substitution of Ho into the ZnO compound causes a weaker antiferromagnetic (AFM) interaction.

  8. X-Ray Photoemission Study of the Oxidation of Hafnium

    Directory of Open Access Journals (Sweden)

    A. R. Chourasia

    2009-01-01

    Full Text Available About 20 Å of hafnium were deposited on silicon substrates using the electron beam evaporation technique. Two types of samples were investigated. In one type, the substrate was kept at the ambient temperature. After the deposition, the substrate temperature was increased to 100, 200, and 300∘C. In the other type, the substrate temperature was held fixed at some value during the deposition. For this type, the substrate temperatures used were 100, 200, 300, 400, 500, 550, and 600∘C. The samples were characterized in situ by the technique of X-ray photoelectron spectroscopy. No trace of elemental hafnium is observed in the deposited overlayer. Also, there is no evidence of any chemical reactivity between the overlayer and the silicon substrate over the temperature range used. The hafnium overlayer shows a mixture of the dioxide and the suboxide. The ratio of the suboxide to dioxide is observed to be more in the first type of samples. The spectral data indicate that hafnium has a strong affinity for oxygen. The overlayer gets completely oxidized to form HfO2 at substrate temperature around 300∘C for the first type of samples and at substrate temperature greater than 550∘C for the second type.

  9. Copper-ceria interaction: A combined photoemission and DFT study

    Science.gov (United States)

    Szabová, Lucie; Skála, Tomáš; Matolínová, Iva; Fabris, Stefano; Farnesi Camellone, Matteo; Matolín, Vladimír

    2013-02-01

    Stoichiometric and partially reduced ceria films were deposited on preoxidized Ru(0 0 0 1) crystal by Ce evaporation in oxygen atmosphere of different pressures at 700 K. Copper-ceria interaction was investigated by deposition of metalic copper on both types of substrate. The samples were characterized by low energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS) of core states and resonant photoelectron spectroscopy (RPES) of the valence bands. Copper adsorption on stoichiometric ceria caused reduction of CeO2, while on the oxygen-defficient ceria it partially reoxidized the substrate. This is in agreement with DFT+U calculations of copper adsorption on stoichiometric and defective ceria surfaces.

  10. Photoemission studies of amorphous silicon induced by P + ion implantation

    Science.gov (United States)

    Petö, G.; Kanski, J.

    1995-12-01

    An amorphous Si layer was formed on a Si (1 0 0) surface by P + implantation at 80 keV. This layer was investigated by means of photoelectron spectroscopy. The resulting spectra are different from earlier spectra on amorphous Si prepared by e-gun evaporation or cathode sputtering. The differences consist of a decreased intensity in the spectral region corresponding to p-states, and appearace of new states at higher binding energy. Qualitativity similar results have been reported for Sb implanted amorphous Ge and the modification seems to be due to the changed short range order.

  11. 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...

  12. Internal photoemission in molecular junctions: parameters for interfacial barrier determinations.

    Science.gov (United States)

    Fereiro, Jerry A; Kondratenko, Mykola; Bergren, Adam Johan; McCreery, Richard L

    2015-01-28

    The photocurrent spectra for large-area molecular junctions are reported, where partially transparent copper top contacts permit illumination by UV-vis light. The effect of variation of the molecular structure and thickness are discussed. Internal photoemission (IPE), a process involving optical excitation of hot carriers in the contacts followed by transport across internal system barriers, is dominant when the molecular component does not absorb light. The IPE spectrum contains information regarding energy level alignment within a complete, working molecular junction, with the photocurrent sign indicating transport through either the occupied or unoccupied molecular orbitals. At photon energies where the molecular layer absorbs, a secondary phenomenon is operative in addition to IPE. In order to distinguish IPE from this secondary mechanism, we show the effect of the source intensity as well as the thickness of the molecular layer on the observed photocurrent. Our results clearly show that the IPE mechanism can be differentiated from the secondary mechanism by the effects of variation of experimental parameters. We conclude that IPE can provide valuable information regarding interfacial energetics in intact, working molecular junctions, including clear discrimination of charge transport mediated by electrons through unoccupied system orbitals from that mediated by hole transport through occupied system orbitals.

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

    Directory of Open Access Journals (Sweden)

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

    2013-01-01

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

  14. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Rutkowski, M. M.; Zeng Zhaoquan [Department of Physics, Ohio State University, Columbus, Ohio 43210 (United States); McNicholas, K. M. [Department of Electrical and Computer Engineering, Ohio State University, Columbus, Ohio 43210 (United States); Brillson, L. J. [Department of Physics, Ohio State University, Columbus, Ohio 43210 (United States); Department of Electrical and Computer Engineering, Ohio State University, Columbus, Ohio 43210 (United States)

    2013-06-15

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

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

    Science.gov (United States)

    Rutkowski, M. M.; McNicholas, K. M.; Zeng, Zhaoquan; Brillson, L. J.

    2013-06-01

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

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

    Science.gov (United States)

    Rutkowski, M M; McNicholas, K M; Zeng, Zhaoquan; Brillson, L J

    2013-06-01

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

  18. Soft X-Ray Spectroscopic Study of Dense Strontium-Doped Lanthanum Manganite Cathodes for Solid Oxide Fuel Cell Applications

    Energy Technology Data Exchange (ETDEWEB)

    L Piper; A Preston; S Cho; A DeMasi; J Laverock; K Smith; L Miara; J Davis; S Basu; et al.

    2011-12-31

    The evolution of the Mn charge state, chemical composition, and electronic structure of La{sub 0.8}Sr{sub 0.2}MnO{sub 3} (LSMO) cathodes during the catalytic activation of solid oxide fuel cell (SOFC) has been studies using X-ray spectroscopy of as-processed, exposed, and activated dense thin LSMO films. Comparison of O K-edge and Mn L{sub 3,2}-edge X-ray absorption spectra from the different stages of LSMO cathodes revealed that the largest change after the activation occurred in the Mn charge state with little change in the oxygen environment. Core-level X-ray photoemission spectroscopy and Mn L{sub 3} resonant photoemission spectroscopy studies of exposed and as-processed LSMO determined that the SOFC environment (800 C ambient pressure of O{sub 2}) alone results in La deficiency (severest near the surface with Sr doping >0.55) and a stronger Mn{sup 4+} contribution, leading to the increased insulating character of the cathode prior to activation. Meanwhile, O K-edge X-ray absorption measurements support Sr/La enrichment nearer the surface, along with the formation of mixed Sr{sub x}Mn{sub y}O{sub z} and/or passive MnO{sub x} and SrO species.

  19. Probing the momentum-dependent response of the charge density wave phase in TbTe{sub 3} by ultrafast time- and angle-resolved photoemission

    Energy Technology Data Exchange (ETDEWEB)

    Kirchmann, P.S. [Department of Applied Physics, Stanford University, Stanford, CA (United States); Fachbereich Physik, Freie Universitaet Berlin (Germany); Schmitt, F.T.; Moore, R.G.; Chu, J.H.; Ru, N.; Fisher, I.R.; Shen, Z.X. [Department of Applied Physics, Stanford University, Stanford, CA (United States); Bovensiepen, U. [Fachbereich Physik, Freie Universitaet Berlin (Germany); Universitaet Duisburg-Essen, Institut fuer Experimentelle Physik, Duisburg (Germany); Rettig, L.; Krenz, M. [Fachbereich Physik, Freie Universitaet Berlin (Germany); Perfetti, L. [Fachbereich Physik, Freie Universitaet Berlin (Germany); Ecole Polytechnique, Palaiseau (France); Wolf, M. [Fachbereich Physik, Freie Universitaet Berlin (Germany); Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin (Germany)

    2010-07-01

    Charge density wave (CDW) systems such as TbTe{sub 3} 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 TbTe{sub 3} 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 k{sub F}. These results vividly demonstrate that the CDW system is most susceptible to electronic excitations near k{sub F} and that these electronic perturbations drive collective excitations of the coupled electron-lattice system.

  20. X-ray photoemission spectra for Al(x)Ga(1-x)As

    Science.gov (United States)

    Ireland, P. J.; Kazmerski, L. L.; Fisher, R. F.

    1984-06-01

    X-ray photoelectron spectroscopy (XPS) is used in both a qualitative and quantitative fashion to study the Al(x)Ga(1-x)As alloy. Gallium and aluminum atoms are always bonded to the arsenic atom. As the concentration of Al increases, a notable shift in the As-3d level could be expected as Ga and Al both have different electronegativities. Spectra taken on molecular beam epitaxially grown samples do not show this shift in the As-3d core level. The composition of the films have been measured with an electron probe, and these results agree very well with the XPS quantitative data. Standard spectra are presented for films with x = 0.16, 0.23, 0.32, 0.46, and 0.65.

  1. Adsorption study of copper phthalocyanine on Si(111)(√3 × √3)R30°Ag surface

    Science.gov (United States)

    Menzli, S.; Ben Hamada, B.; Arbi, I.; Souissi, A.; Laribi, A.; Akremi, A.; Chefi, C.

    2016-04-01

    The adsorption of copper phthalocyanine (CuPc) molecules on Si(111)(√3 × √3)R30°Ag surface is studied at room temperature under ultra high vacuum. Crystallographic, chemical and electronic properties of the interface are investigated by low energy electron diffraction (LEED), ultraviolet and X-ray photoemission spectroscopies (UPS, XPS) and X-ray photoemission diffraction (XPD). LEED and XPD results indicate that after one monolayer deposition the molecular layer is highly ordered with a flat lying adsorption configuration. The corresponding pattern reveals the coexistence of three symmetrically equivalent orientations of molecules with respect to the substrate. XPS core level spectra of the substrate reveal that there is no discernible chemical interaction between molecules and substrate; however there is evidence of Fermi level movement. During the growth, the work function was found to decrease from 4.90 eV for the clean substrate to 4.35 eV for the highest coverage (60 monolayers). Within a thickness of two monolayer deposition an interface dipole of 0.35 eV and a band bending of 0.2 eV have been found. UPS spectra indicate the existence of a band bending of the highest occupied molecular orbital (HOMO) of 0.55 eV. The changes in the work function, in the Fermi level position and in the HOMO state have been used to determine the energy level alignment at the interface.

  2. Momentum-dependent effects in 4{ital f} photoemission spectra from strongly correlated CeBe{sub 13}

    Energy Technology Data Exchange (ETDEWEB)

    Andrews, A.B.; Joyce, J.J.; Arko, A.J.; Fisk, Z. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Riseborough, P.S. [Polytchnic Institute of New York, Brooklyn, New York 11201 (United States)

    1996-02-01

    We have studied the mixed-valent compound CeBe{sub 13} using a combination of high-resolution angle-resolved resonant photoemission and x-ray absorption. Based on the angle and temperature dependence of the intensity of the {ital f}{sup 1} peak at the Fermi level, we conclude that the 4{ital f} state is most likely a narrow band with a bandwidth of {approximately}50 meV, and may cross the Fermi level. The temperature dependence of the valence band photoemission spectroscopy can be accounted for by conventional thermal broadening effects. A mean valence of {ital v}{approximately}3.04 is extracted from {ital M}{sub 4,5} absorption spectra which agrees with {ital L}{sub III} edge measurements, however the temperature dependence is negligible. A large amplitude anisotropy is observed in the {ital f}{sup 0} peak, as well as about 0.1 eV of dispersion. Residual gas dosing in the submonolayer regime suggests that much of the {ital f}{sup 0} intensity is surface related. {copyright} {ital 1996 The American Physical Society.}

  3. 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.

  4. 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.

  5. 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.

  6. Iron 1s X-ray photoemission of Fe{sub 2}O{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Miedema, P.S., E-mail: p.s.miedema@gmail.com [Inorganic Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht (Netherlands); Borgatti, F. [CNR-ISMN, Instituto per Io Studio di Materiali Nanostrutturati, Via Gobetti 101, I-40129 Bologna (Italy); Offi, F. [Dipartimento di Scienze, Università di Roma Tre, I-00146 Rome (Italy); Panaccione, G. [Consiglio Nazionale delle Ricerche, CNR-IOM, Laboratorio TASC, Area Science Park, I-34149 Trieste (Italy); Groot, F.M.F. de [Inorganic Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht (Netherlands)

    2015-08-15

    Highlights: • Three peaks of 1s XPS of Fe{sub 2}O{sub 3} means use of three configurations. • 1s XPS vs 2p XPS: advantage of 1s XPS for charge transfer parameter analysis. • Charge transfer multiplet analysis with same parameters for 1s and 2p XPS. - Abstract: We present the 1s X-ray photoemission spectrum of α-Fe{sub 2}O{sub 3} in comparison with its 2p photoemission spectrum. We show that in case of transition metal oxides, because the 1s core hole is not affected by core hole spin-orbit coupling and almost not affected by core-valence multiplet effects, the Fe 1s spectrum and the complementary charge transfer multiplet calculations allow for an accurate determination of the charge transfer parameters. The consistency of the obtained parameters for the 1s photoemission was confirmed with 2p photoemission calculations and compared to 2p experimental photoemission spectra.

  7. Correlated electronic states of SrVO{sub 3} revealed by angle-resolved photoemission spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Yoshida, T. [Graduate School of Human and Environmental Studies, Kyoto University, Sakyo-ku, Kyoto 606-8501 (Japan); Kobayashi, M. [KEK, Photon Factory, Tsukuba 305-0801, Ibaraki (Japan); Yoshimatsu, K. [KEK, Photon Factory, Tsukuba 305-0801, Ibaraki (Japan); Department of Physics, The University of Tokyo, Tokyo 113-0033 (Japan); Kumigashira, H. [KEK, Photon Factory, Tsukuba 305-0801, Ibaraki (Japan); Fujimori, A. [Department of Physics, The University of Tokyo, Tokyo 113-0033 (Japan)

    2016-04-15

    In this article, we review recent progress in angle-resolved photoemission (ARPES) studies of the Mott-Hubbard-type correlated electron systems SrVO{sub 3}. It has the d{sup 1} electron configuration and is an ideal model compound to study electron correlation effects in normal metal. ARPES studies of bulk single-crystal SrVO{sub 3} and CaVO{sub 3} have revealed the difference in the mass renormalization of electrons between them. In-situ ARPES studies of thin films fabricated by the pulsed laser deposition method have clarified not only quasi-particle dispersions, which show a kink like high-T{sub c} cuprates, but also finite dispersions in the incoherent part. Self-energy in a wide energy range has been deduced from the ARPES spectral weight using Kramers–Kronig transformation. The obtained self-energy has several structures which yield the incoherent feature and a pseudogap-like dip similar to the high-T{sub c} cuprates. Quantum-well states in ultrathin films of SrVO{sub 3} have revealed sub-bands with correlated electrons. These findings of electron correlation effects outlined in the present article would provide a starting point not only for fundamental condensed-matter physics but also for the development of new devices with correlated electrons.

  8. Strong Linear Dichroism in Spin-Polarized Photoemission from Spin-Orbit-Coupled Surface States

    Science.gov (United States)

    Bentmann, H.; Maaß, H.; Krasovskii, E. E.; Peixoto, T. R. F.; Seibel, C.; Leandersson, M.; Balasubramanian, T.; Reinert, F.

    2017-09-01

    A comprehensive understanding of spin-polarized photoemission is crucial for accessing the electronic structure of spin-orbit coupled materials. Yet, the impact of the final state in the photoemission process on the photoelectron spin has been difficult to assess in these systems. We present experiments for the spin-orbit split states in a Bi-Ag surface alloy showing that the alteration of the final state with energy may cause a complete reversal of the photoelectron spin polarization. We explain the effect on the basis of ab initio one-step photoemission theory and describe how it originates from linear dichroism in the angular distribution of photoelectrons. Our analysis shows that the modulated photoelectron spin polarization reflects the intrinsic spin density of the surface state being sampled differently depending on the final state, and it indicates linear dichroism as a natural probe of spin-orbit coupling at surfaces.

  9. Integrated experimental setup for angle resolved photoemission spectroscopy of transuranic materials.

    Science.gov (United States)

    Graham, Kevin S; Joyce, John J; Durakiewicz, Tomasz

    2013-09-01

    We have developed the Angle Resolved Photoemission Spectroscopy (ARPES) system for transuranic materials. The ARPES transuranic system is an endstation upgrade to the Laser Plasma Light Source (LPLS) at Los Alamos National Laboratory. The LPLS is a tunable light source for photoemission with a photon energy range covering the vacuum ultraviolet (VUV) and soft x-ray regions (27-140 eV). The LPLS was designed and developed for transuranic materials. Transuranic photoemission is currently not permitted at the public synchrotrons worldwide in the VUV energy range due to sample encapsulation requirements. With the addition of the ARPES capability to the LPLS system there is an excellent opportunity to explore new details centered on the electronic structure of actinide and transuranic materials.

  10. Localized electronic states and photoemission superconducting condensate in Bi 2Sr 2CaCu 2O 8+x

    Science.gov (United States)

    Ma, Jian; Quitmann, C.; Kelley, R. J.; Margaritondo, G.; Onellion, M.

    1995-04-01

    We present the first detailed angle-resolved photoemission evidence that there are two types of carriers that contribute to the photoe-mission superconducting condensate in Bi 2Sr 2CaCu 2O 8+x. Our data indicate that both itinerant and somewhat localized normal state carriers can contribute to the formation of Cooper pairs.

  11. 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.

  12. Generating few-cycle pulses for nanoscale photoemission easily with an erbium-doped fiber laser.

    Science.gov (United States)

    Thomas, Sebastian; Holzwarth, Ronald; Hommelhoff, Peter

    2012-06-18

    We demonstrate a simple setup capable of generating four-cycle pulses at a center wavelength of 1700 nm for nanoscale photoemission. Pulses from an amplified erbium-doped fiber laser are spectrally broadened by propagation through a highly non-linear fiber. Subsequently, we exploit dispersion in two different types of glass to compress the pulses. The pulse length is estimated by measuring an interferometric autocorrelation trace and comparing it to a numerical simulation. We demonstrate highly non-linear photoemission of electrons from a nanometric tungsten tip in a hitherto unexplored pulse parameter range.

  13. Theoretical estimates of spherical and chromatic aberration in photoemission electron microscopy.

    Science.gov (United States)

    Fitzgerald, J P S; Word, R C; Könenkamp, R

    2016-01-01

    We present theoretical estimates of the mean coefficients of spherical and chromatic aberration for low energy photoemission electron microscopy (PEEM). Using simple analytic models, we find that the aberration coefficients depend primarily on the difference between the photon energy and the photoemission threshold, as expected. However, the shape of the photoelectron spectral distribution impacts the coefficients by up to 30%. These estimates should allow more precise correction of aberration in PEEM in experimental situations where the aberration coefficients and precise electron energy distribution cannot be readily measured.

  14. Characterization of the native oxide of CuInSe2 using synchrotron radiation photoemission

    Science.gov (United States)

    Nelson, Art J.; Gebhard, Steven; Kazmerski, L. L.; Colavita, Elio; Engelhardt, Mike; Höchst, Hartmut

    1990-10-01

    Synchrotron radiation soft x-ray photoemission spectroscopy was used to investigate the native oxide of n-type single-crystal CuInSe2. Photoemission measurements were acquired on the oxide surface before and after removal using sputter etching. Observed changes in the valence-band electronic structure as well as changes in the In 4d and Se 3d core lines were correlated with the interface chemistry at the oxide/CuInSe2 interface. These results show the native oxide to be composed of an In2O3 outer layer (no SeO2) with an additional Cu2Se interface layer.

  15. Preparation and Photoemission Spectra of Rb3C60 Single-Crystal Thin Films

    Institute of Scientific and Technical Information of China (English)

    李宏年; 吴太权; 陈晓; 李海洋; 鲍世宁; 徐亚伯; 钱海杰; 易卜拉欣奎热西; 刘风琴

    2002-01-01

    Rb3 C60 single-crystal thin films were prepared on the cleaved (111) surface of C60 single crystal. The photoemission spectrum line shapes of the lowest unoccupied molecular orbital (LUMO) derived band at room temperature and 150K were established by synchrotron radiation photoemission spectrum measurements. The density of states near the Fermi level was distinctly affected by temperature. No less than six sub-peaks of the LUMOband were observed even at room temperature. The existence of so many sub-peaks offered the opportunities to analyse in more detail the orientational structure and the electron-Boson interactions of the narrow-band metallic Rb3 C60 .

  16. Capability of Resonant Photoemission with Soft X-Rays in Rare-Earth Systems

    Science.gov (United States)

    Harasaki, Akiko; Tanaka, Arata; Jo, Takeo

    1993-07-01

    We theoretically discuss the capability of resonant photoemission with soft X-rays in clarifying the valence electronic state, by choosing Ce 4d core X-ray photoemission spectroscopy (4d XPS) at the Ce 3d threshold in CeRh3B2 with hexagonal crystal structure. On the basis of the Anderson model including multiplet splitting, we show that the dependence of 4d XPS on the energy and the linear polarization with respect to the hexagonal c-axis of the incident photon and the binding energy can be a powerful characteristic for probing a proposed uniaxial anisotropic distribution of 4f electrons.

  17. Two-Color Coherent Control of Femtosecond Above-Threshold Photoemission from a Tungsten Nanotip

    Science.gov (United States)

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

    2016-11-01

    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 contrast of the oscillating current signal 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.

  18. 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.

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

    Science.gov (United States)

    Zhukovsky, Sergei V.; Babicheva, Viktoriia E.; Uskov, Alexander V.; Protsenko, Igor E.; Lavrinenko, Andrei V.

    2014-09-01

    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 semiconductor; photodetection in the infrared range, where photon energies are below the semiconductor band gap (insufficient for band-to-band absorption in semiconductor), is therefore possible. The nanoparticles are arranged in a sparse rectangular lattice so that the wavelength of the lattice-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 between the semiconductor layer and an adjacent transparent conductive oxide layer. We show that the presence of refractive index mismatch between media surrounding the nanoparticles disrupts the formation of a narrow absorption peak associated with the Rayleigh anomaly, so the role of collective lattice 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-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.

  20. The band structure of VO2 measured by angle-resolved photoemission

    Science.gov (United States)

    Moreschini, Luca; Chang, Young Jun; Innocenti, Davide; Walter, Andrew L.; Kim, Young Su; Gaines, Geoffrey; Bostwick, Aaron; Denlinger, Jonathan; Rotenberg, Eli

    2011-03-01

    The origin of the 340K metal-insulator transition (MIT) in VO2 is still under debate. the main reason is that no direct experimental verifications of the electronic structure of VO2 exist up to this point. The quality of the available single crystals is not sufficient for ARPES measurements, so that photoemission is limited to angle-integrated mode. New opportunities are offered by oxide films, on which data of equal or even higher quality have been reported (Saeki et al., PRB 2009). WIth the in situ pulsed-laser-deposition (PLD) system available on beamline 7.0.1 at the Advanced Light Source we have grown VO2(001) films on a TiO2 substrate and measured the Fermi surface of the metallic phase. These results will permit a direct comparison with the existing band calculations and open the way to the study of the MIT as a function, e.g., of film thickness or electron doping with Cr. Work supported by U.S. DOE (DE-AC02-05CH11231 for ALS), the Max Planck Society, and the Swiss National Science Foundation (PBELP2-125484).

  1. High-resolution angle-resolved photoemission investigation of potassium and phosphate tungsten bronzes

    Energy Technology Data Exchange (ETDEWEB)

    Paul, Sanhita; Kumari, Spriha; Raj, Satyabrata, E-mail: raj@iiserkol.ac.in

    2016-04-15

    Highlights: • Electronic structure of potassium and phosphate tungsten bronzes. • Origin of transport anomalies in bronzes. • Flat segments of Fermi surfaces are connected by a nesting vector, q. • Nesting driven charge-density wave is responsible for the anomalies. - Abstract: We have performed high-resolution angle-resolved photoemission spectroscopy (ARPES) and density functional ab initio theoretical calculation to study the electronic structure of potassium (K{sub 0.25}WO{sub 3}) and phosphate (P{sub 4}W{sub 12}O{sub 44}) tungsten bronzes. We have experimentally determined the band dispersions and Fermi surface topology of these bronzes and compared with our theoretical calculations and a fair agreement has been seen between them. Our experimental as well as theoretical investigation elucidates the origin of transport anomalies in these bronzes. The Fermi surfaces of these bronzes consist of flat patches, which can be connected with each other by a constant nesting wave vector, q. The scattering wave vectors found from diffraction measurements match with these nesting vectors and the anomalies in the transport properties of these bronzes can be well explained by the evolution of charge-density wave with a partial nesting between the flat segments of the Fermi surfaces.

  2. 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.

  3. 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.

  4. Electronic structure of the gold/Bi sub 2 Sr sub 2 CaCu sub 2 O sub 8 and gold/EuBa sub 2 Cu sub 3 O sub 7 minus. delta. interfaces as studied by photoemission spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Dessau, D.S.; Shen, Z.; Wells, B.O.; Spicer, W.E. (Stanford Electronics Laboratories, Stanford University, Stanford, California 94305 (USA)); List, R.S.; Arko, A.J.; Bartlett, R.J.; Fisk, Z.; Cheong, S. (Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (USA)); Mitzi, D.B.; Kapitulnik, A. (Department of Applied Physics, Stanford University, Stanford, California 94305 (USA)); Schirber, J.E. (Sandia National Laboratories, Sandia, New Mexico 87185 (USA))

    1990-07-16

    High-resolution photoemission has been used to probe the electronic structure of the gold/Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} and gold/EuBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} interface formed by a low-temperature (20 K) gold evaporation on cleaved high quality single crystals. We find that the metallicity of the EuBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} substrate in the near surface region ({similar to}5 A) is essentially destroyed by the gold deposition, while the near surface region of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} remains metallic. This has potentially wide ranging consequences for the applicability of the different types of superconductors in real devices.

  5. 1S core-level spectroscopy of graphite: The effects of phonons on emission and absorption and validity of the final-state rule

    Energy Technology Data Exchange (ETDEWEB)

    Franck, C.P.; Schnatterly, S.E.; Zutavern, F.J.; Aton, T.; Cafolla, T.; Carson, R.D.

    1985-04-15

    We have used both electron-induced soft x-ray emission and fast inelastic electron scattering to observe 1S core-level emission and absorption in graphite near threshold. Linear phonon coupling with partial relaxation is found to quantitatively explain the absorption linewidth, the emission broadening, and the unusually large difference between emission and absorption threshold energies (Stokes shift). Both emission and absorption line shapes quantitatively obey the final-state rule, which asserts that the best single-particle potential describing these many electron processes is the final-state potential.

  6. Correlation versus surface effects in photoemission of quasi-1D organic conductors

    DEFF Research Database (Denmark)

    Claessen, R.; Schwingenschlogl, U.; Sing, M.;

    2002-01-01

    The absence of spectral weight at the Fermi level in photoemission spectra of quasi-1D organic conductors has been interpreted as possible evidence for an unusual many-body state. We demonstrate that great care must be exercised to draw this conclusion exclusively on the basis of a pseudogap...

  7. 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...

  8. A vacuum photoemission detector for X-ray tomography on the ITER facility

    NARCIS (Netherlands)

    Barykov, IA; Gott, YV; Stepanenko, MM

    2004-01-01

    A vacuum photoemission detector designed for plasma tornography in X rays on the ITER facility is described. Such detectors allow X rays to be detected in the presence of intense neutron and gamma-photon fluxes. The results of tests of a prototype of this detector on a Co-60 source of gamma rays, it

  9. 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...

  10. Effect of wave-function localization on the time delay in photoemission from surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, C.-H.; Thumm, U. [Department of Physics, Kansas State University, Manhattan, Kansas 66506 (United States)

    2011-12-15

    We investigate streaking time delays in the photoemission from a solid model surface as a function of the degree of localization of the initial-state wave functions. We consider a one-dimensional slab with lattice constant a{sub latt} of attractive Gaussian-shaped core potentials of width {sigma}. The parameter {sigma}/a{sub latt} thus controls the overlap between adjacent core potentials and localization of the electronic eigenfunctions on the lattice points. Small values of {sigma}/a{sub latt}<<1 yield lattice eigenfunctions that consist of localized atomic wave functions modulated by a ''Bloch-envelope'' function, while the eigenfunctions become delocalized for larger values of {sigma}/a{sub latt} > or approx 0.4. By numerically solving the time-dependent Schroedinger equation, we calculate photoemission spectra from which we deduce a characteristic bimodal shape of the band-averaged photoemission time delay: as the slab eigenfunctions become increasingly delocalized, the time delay quickly decreases near {sigma}/a{sub latt}=0.3 from relatively large values below {sigma}/a{sub latt}{approx}0.2 to much smaller delays above {sigma}/a{sub latt}{approx}0.4. This change in wave-function localization facilitates the interpretation of a recently measured apparent relative time delay between the photoemission from core and conduction-band levels of a tungsten surface.

  11. 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

  12. Photoemission search for an RVB state in novel thallium-compound high-temperature superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Hwu, Y.; Marsi, M.; Terrasi, A.; Onellion, M.; Huber, D.L.; Margaritondo, G. (University of Wisconsin-Madison, Stoughton, Wisconsin 53589-3097 (USA)); Wang, J.H.; Sheng, Z.Z.; Hermann, A.M. (Department of Physics, University of Arkansas, Fayetteville, AK (USA))

    1990-01-25

    We used photoemission spectroscopy with synchrotron radiation to search for evidence of a resonating valence bond (RVB) state in a series of thallium-containing high-temperature superconductors. As in the case of Bi compounds, no positive evidence was found, and the data imply a low upper limit for the energy of hypothetical spinons.

  13. Photoemission search for an RVB state in novel thallium-compound high-temperature superconductors

    Science.gov (United States)

    Hwu, Y.; Marsi, M.; Terrasi, A.; Onellion, M.; Huber, D. L.; Margaritondo, G.; Wang, J. H.; Sheng, Z. Z.; Hermann, A. M.

    1990-01-01

    We used photoemission spectroscopy with synchrotron radiation to search for evidence of a resonating valence bond (RVB) state in a series of thallium-containing high-temperature superconductors. As in the case of Bi compounds, no positive evidence was found, and the data imply a low upper limit for the energy of hypothetical spinons.

  14. Plasmonic silicon Schottky photodetectors: the physics behind graphene enhanced internal photoemission

    DEFF Research Database (Denmark)

    Levy, Uriel; Grajower, Meir; Gonçalves, P. A. D.

    2017-01-01

    Recent experiments have shown that the plasmonic assisted internal photoemission from a metal to silicon can be significantly enhanced by introducing a monolayer of graphene between the two media. This is despite the limited absorption in a monolayer of undoped graphene (∼πα=2.3%). Here we propos...

  15. Chemical analysis of particles and semiconductor microstructures by synchrotron radiation soft x-rays photoemission spectromicroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Gozzo, F.; Triplett, B.; Fujimoto, H. [Intel Corp., Santa Clara, CA (United States). Dept. of Components Research] [and others

    1998-12-31

    Chemical analysis on a microscopic scale was performed on a TiN particle sample on silicon and on two patterned samples using a synchrotron source scanning photoemission microscope. For all the experiments, they exploit the ability, developed in the experimental system, to reach specific locations on the wafer and analyze the local chemical state.

  16. Application of a grating coupler for surface plasmon polariton excitation in a photoemission electron microscopy experiment

    DEFF Research Database (Denmark)

    Leißner, Till; Jauernik, Stephan; Lemke, Christoph

    Surface plasmon polariton (SPP) excitation at a gold-vacuum interface via 800 nm light pulses mediated by a periodic array of gold ridges is probed at high lateral resolution by means of photoemission electron microscopy (PEEM). We directly monitor and quantify the coupling properties as a function...

  17. 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.

  18. 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

    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...

  19. Attosecond-controlled photoemission from metal nanowire tips in the few-electron regime

    KAUST Repository

    Ahn, B.

    2017-02-07

    Metal nanotip photoemitters have proven to be versatile in fundamental nanoplasmonics research and applications, including, e.g., the generation of ultrafast electron pulses, the adiabatic focusing of plasmons, and as light-triggered electron sources for microscopy. Here, we report the generation of high energy photoelectrons (up to 160 eV) in photoemission from single-crystalline nanowire tips in few-cycle, 750-nm laser fields at peak intensities of (2-7.3) × 1012 W/cm2. Recording the carrier-envelope phase (CEP)-dependent photoemission from the nanowire tips allows us to identify rescattering contributions and also permits us to determine the high-energy cutoff of the electron spectra as a function of laser intensity. So far these types of experiments from metal nanotips have been limited to an emission regime with less than one electron per pulse. We detect up to 13 e/shot and given the limited detection efficiency, we expect up to a few ten times more electrons being emitted from the nanowire. Within the investigated intensity range, we find linear scaling of cutoff energies. The nonlinear scaling of electron count rates is consistent with tunneling photoemission occurring in the absence of significant charge interaction. The high electron energy gain is attributed to field-induced rescattering in the enhanced nanolocalized fields at the wires apex, where a strong CEP-modulation is indicative of the attosecond control of photoemission.

  20. 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.

  1. Electronic properties of Mn-phthalocyanine-C60 bulk heterojunctions: Combining photoemission and electron energy-loss spectroscopy

    Science.gov (United States)

    Roth, Friedrich; Herzig, Melanie; Lupulescu, Cosmin; Darlatt, Erik; Gottwald, Alexander; Knupfer, Martin; Eberhardt, Wolfgang

    2015-11-01

    The electronic properties of co-evaporated mixtures (blends) of manganese phthalocyanine and the fullerene C60 (MnPc:C60) 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 C60. 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:C60 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 C60 to MnPc thin films.

  2. Progress on PEEM3 — An Aberration Corrected X-Ray Photoemission Electron Microscope at the ALS

    Science.gov (United States)

    MacDowell, A. A.; Feng, J.; DeMello, A.; Doran, A.; Duarte, R.; Forest, E.; Kelez, N.; Marcus, M. A.; Miller, T.; Padmore, H. A.; Raoux, S.; Robin, D.; Scholl, A.; Schlueter, R.; Schmid, P.; Stöhr, J.; Wan, W.; Wei, D. H.; Wu, Y.

    2007-01-01

    A new ultrahigh-resolution photoemission electron microscope called PEEM3 is being developed and built at the Advanced Light Source (ALS). An electron mirror combined with a much-simplified magnetic dipole separator is to be used to provide simultaneous correction of spherical and chromatic aberrations. It is installed on an elliptically polarized undulator (EPU) beamline, and will be operated with very high spatial resolution and high flux to study the composition, structure, electric and magnetic properties of complex materials. The instrument has been designed and is described. The instrumental hardware is being deployed in 2 phases. The first phase is the deployment of a standard PEEM type microscope consisting of the standard linear array of electrostatic electron lenses. The second phase will be the installation of the aberration corrected upgrade to improve resolution and throughput. This paper describes progress as the instrument enters the commissioning part of the first phase.

  3. Performance of the TPSS Functional on Predicting Core Level Binding Energies of Main Group Elements Containing Molecules: A Good Choice for Molecules Adsorbed on Metal Surfaces.

    Science.gov (United States)

    Pueyo Bellafont, Noèlia; Viñes, Francesc; Illas, Francesc

    2016-01-12

    Here we explored the performance of Hartree-Fock (HF), Perdew-Burke-Ernzerhof (PBE), and Tao-Perdew-Staroverov-Scuseria (TPSS) functionals in predicting core level 1s binding energies (BEs) and BE shifts (ΔBEs) for a large set of 68 molecules containing a wide variety of functional groups for main group elements B → F and considering up to 185 core levels. A statistical analysis comparing with X-ray photoelectron spectroscopy (XPS) experiments shows that BEs estimations are very accurate, TPSS exhibiting the best performance. Considering ΔBEs, the three methods yield very similar and excellent results, with mean absolute deviations of ∼0.25 eV. When considering relativistic effects, BEs deviations drop approaching experimental values. So, the largest mean percentage deviation is of 0.25% only. Linear trends among experimental and estimated values have been found, gaining offsets with respect to ideality. By adding relativistic effects to offsets, HF and TPSS methods underestimate experimental values by solely 0.11 and 0.05 eV, respectively, well within XPS chemical precision. TPSS is posed as an excellent choice for the characterization, by XPS, of molecules on metal solid substrates, given its suitability in describing metal substrates bonds and atomic and/or molecular orbitals.

  4. 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.

  5. Photon absorption and photocurrent in solar cells below semiconductor bandgap due to electron photoemission from plasmonic nanoantennas

    DEFF Research Database (Denmark)

    Novitsky, Andrey; Uskov, Alexander; Gritti, Claudia;

    2014-01-01

    We model the electron photoemission frommetal nanoparticles into a semiconductor in a Schottky diode with a conductive oxide electrode hosting the nanoparticles. We show that plasmonic effects in the nanoparticles lead to a substantial enhancement in photoemission compared with devices with conti....... Such structure can form the dais of the development of plasmonic photoemission enhanced solar cells....... with continuous metal films. Optimally designed metal nanoparticles can provide an effectivemechanismfor the photon absorption in the infrared range below the semiconductor bandgap, resulting in the generation of a photocurrent in addition to the photocurrent from band-to-band absorption in a semiconductor...

  6. Ligand field splittings in core level transitions for transition metal (TM) oxides: Tanabe-Sugano diagrams and (TM) dangling bonds in vacated O-atom defects

    Science.gov (United States)

    Lucovsky, Gerry; Wu, Kun; Pappas, Brian; Whitten, Jerry

    2013-04-01

    Defect states in the forbidden band-gap below the conduction band edge are active as electron traps in nano-grain high-) transition metal (TM) oxides with thickness >0.3 nm, e.g., ZrO2 and HfO2. These oxides have received considerable attention as gate-dielectrics in complementary metal oxide semiconductor (CMOS) devices, and more recently are emerging as candidates for charge storage and memory devices. To provide a theoretical basis for device functionality, ab-initio many-electron theory is combined with X-ray absorption spectroscopy (XAS) to study O K edge and TM core level transitions. These studies identify ligand field splittings (ΔLF) for defect state features,. When compared with those obtained from O-atom and TM-atom core spectroscopic transitions, this provides direct information about defect state sun-nm bonding arrangements. comparisons are made for (i) elemental TiO2 and Ti2O3 with different formal ionic charges, Ti4+ and Ti3+ and for (ii) Magneli Phase alloys, TinO2n-1, n is an integer 9>=n>3, and (TiO2)x(HfO2)1-x alloys. The alloys display multi-valent behavior from (i) different ionic-charge states, (ii} local bond-strain, and (iii) metallic hopping transport. The intrinsic bonding defects in TM oxides are identified as pairs of singly occupied dangling bonds. For 6-fold coordinated Ti-oxides defect excited states in 2nd derivative O K pre-edge spectra are essentially the same as single Ti-atom d2 transitions in Tanabe-Sugano (T-S) diagrams. O-vacated site defects in 8-fold coordinated ZrO2 and HfO2 are described by d8 T-S diagrams. T-S defect state ordering and splittings are functions of the coordination and symmetry of vacated site bordering TM atoms. ΔLF values from the analysis of T-S diagrams indicate medium range order (MRO) extending to 3rd and 4th nearest-neighbor (NN) TM-atoms. Values are different for 6-fold Ti, and 8-fold ZrO2 and HfO2, and scale inversely with differences in respective formal ionic radii. O-vacated site bonding

  7. 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.

  8. 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

  9. 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

  10. 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.

  11. 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.

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

    Science.gov (United States)

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

    2015-04-28

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

  14. 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.

  15. Plasmonic silicon Schottky photodetectors: The physics behind graphene enhanced internal photoemission

    Science.gov (United States)

    Levy, Uriel; Grajower, Meir; Gonçalves, P. A. D.; Mortensen, N. Asger; Khurgin, Jacob B.

    2017-02-01

    Recent experiments have shown that the plasmonic assisted internal photoemission from a metal to silicon can be significantly enhanced by introducing a monolayer of graphene between the two media. This is despite the limited absorption in a monolayer of undoped graphene (˜π α =2.3 % ). Here we propose a physical model where surface plasmon polaritons enhance the absorption in a single-layer graphene by enhancing the field along the interface. The relatively long relaxation time in graphene allows for multiple attempts for the carrier to overcome the Schottky barrier and penetrate into the semiconductor. Interface disorder is crucial to overcome the momentum mismatch in the internal photoemission process. Our results show that quantum efficiencies in the range of few tens of percent are obtainable under reasonable experimental assumptions. This insight may pave the way for the implementation of compact, high efficiency silicon based detectors for the telecom range and beyond.

  16. Plasmonic silicon Schottky photodetectors: The physics behind graphene enhanced internal photoemission

    Directory of Open Access Journals (Sweden)

    Uriel Levy

    2017-02-01

    Full Text Available Recent experiments have shown that the plasmonic assisted internal photoemission from a metal to silicon can be significantly enhanced by introducing a monolayer of graphene between the two media. This is despite the limited absorption in a monolayer of undoped graphene ( ∼ π α = 2.3 % . Here we propose a physical model where surface plasmon polaritons enhance the absorption in a single-layer graphene by enhancing the field along the interface. The relatively long relaxation time in graphene allows for multiple attempts for the carrier to overcome the Schottky barrier and penetrate into the semiconductor. Interface disorder is crucial to overcome the momentum mismatch in the internal photoemission process. Our results show that quantum efficiencies in the range of few tens of percent are obtainable under reasonable experimental assumptions. This insight may pave the way for the implementation of compact, high efficiency silicon based detectors for the telecom range and beyond.

  17. Strongly correlated electron systems: Photoemission and the single-impurity model

    Energy Technology Data Exchange (ETDEWEB)

    Arko, A.J.; Joyce, J.J.; Andrews, A.B.; Thompson, J.D.; Smith, J.L.; Mandrus, D.; Hundley, M.F.; Cornelius, A.L. [Los Alamos National Laboratories, Los Alamos, New Mexico 87545 (United States); Moshopoulou, E.; Fisk, Z. [NHMFL, Florida State University, Tallahassee, Florida 32306-4005 (United States); Canfield, P.C. [Iowa State University/Ames Laboratory, Ames, Iowa 50011 (United States); Menovsky, A. [Natuurkundig Laboratorium, University of Amsterdam, Amsterdam (The Netherlands)

    1997-09-01

    We present high-resolution, angle-resolved photoemission spectra for Ce-based and U-based strongly correlated electron systems. The experimental results are irreconcilable with the long-accepted single-impurity model, which predicts a narrow singlet state, in close proximity to the Fermi energy, whose linewidth and binding energy are a constant determined by a characteristic temperature T{sub K} for the material. We report that both 4f and 5f photoemission features disperse with crystal momentum at temperatures both above and below T{sub K}; these are characteristics consistent with narrow bands but not with the single-impurity model. Inclusion of the lattice must be considered at all temperatures. Variants of the periodic Anderson model are consistent with this approach. {copyright} {ital 1997} {ital The American Physical Society}

  18. TOF Electron Energy Analyzer for Spin and Angular Resolved Photoemission Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Lebedev, Gennadi; Jozwiak, Chris; Andresen, Nord; Lanzara, Alessandra; Hussain, Zahid

    2008-07-09

    Current pulsed laser and synchrotron x-ray sources provide new opportunities for Time-Of- Flight (TOF) based photoemission spectroscopy to increase photoelectron energy resolution and efficiency compared to current standard techniques. The principals of photoelectron timing front formation, temporal aberration minimization, and optimization of electron beam transmission are presented. We have developed these concepts into a high resolution Electron Optical Scheme (EOS) of a TOF Electron Energy Analyzer (TOF-EEA) for photoemission spectroscopy. The EOS of the analyzer includes an electrostatic objective lens, three columns of transport lenses and a 90 degree energy band pass filter (BPF). The analyzer has two modes of operation: Spectrometer Mode (SM) with straight passage of electrons through the EOS undeflected by the BPF, allowing the entire spectrum to be measured, and Monochromator Mode (MM) in which the BPF defines a certain energy window inside the scope of the electron energy spectrum.

  19. Photoemission Electron Microscopy as a tool for the investigation of optical near fields

    CERN Document Server

    Cinchetti, M; Nepjiko, S A; Sch"onhense, G; Rochholz, H; Kreiter, M

    2005-01-01

    Photoemission electron microscopy was used to image the electrons photoemitted from specially tailored Ag nanoparticles deposited on a Si substrate (with its native oxide SiO$_{x}$). Photoemission was induced by illumination with a Hg UV-lamp (photon energy cutoff $\\hbar\\omega_{UV}=5.0$ eV, wavelength $\\lambda_{UV}=250$ nm) and with a Ti:Sapphire femtosecond laser ($\\hbar\\omega_{l}=3.1$ eV, $\\lambda_{l}=400$ nm, pulse width below 200 fs), respectively. While homogeneous photoelectron emission from the metal is observed upon illumination at energies above the silver plasmon frequency, at lower photon energies the emission is localized at tips of the structure. This is interpreted as a signature of the local electrical field therefore providing a tool to map the optical near field with the resolution of emission electron microscopy.

  20. Photoemission from Low Work Function Coated Metal Surfaces A Comparison of Theory to Experiment

    CERN Document Server

    Jensen, Kevin; Moody, Nathan A

    2005-01-01

    The development of rugged and/or self rejuvenating photocathodes with high quantum efficiency (QE) using the longest wavelength drive laser is of paramount importance for RF photo-injectors for high power FELs and accelerators. We report on our program to develop advanced photocathodes and to develop and validate models of photoemission from coated metals to analyze experimental data,* provide emission models usable by beam simulation codes,** and project performance. The model accounts for the effects of laser heating, thermal evolution, surface conditions, laser parameters, and material characteristics, and predicts current distribution and QE. The photoemission and QE from metals and dispenser photocathodes is evaluated: the later introduces complications such as coverage non-uniformity and field enhancement. The performance of the models is compared to our experimental results for dispenser photocathodes and cesiated surfaces (e.g., tungsten, silver, etc.) in which the time-dependent models are shown to a...

  1. RESONANT PHOTOEMISSION OF BULK CeO2 AND NANO—CeO2 FILMS

    Institute of Scientific and Technical Information of China (English)

    M.I.Abbas; K.Ibrahim; Z.Y.Wu; J.Zhang; F.Q.Liu; H.J.Qian

    2001-01-01

    Photoemission behaviors of nano-CeO2 films with parlicle sizes ranging from 8nm to 50nm and bulk CeO2 in Ce 4d-4f absorption region have been investigated.Resonant enhancements of Ce 4f valance band and Ce 5p bands for nano film and bulk material have been observed.The variation of electron density of Ce 4d-4f resonace.

  2. 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.

  3. Photoemission and the electronic properties of heavy fermions -- limitations of the Kondo model

    Energy Technology Data Exchange (ETDEWEB)

    Joyce, J.J.; Arko, A.J.; Andrews, A.B. [and others

    1993-09-01

    The electronic properties of Yb-based heavy fermions have been investigated by means of high resolution synchrotron radiation photoemission and compared with predictions of the Kondo model. The Yb heavy fermion photoemission spectra show massive disagreement with the Kondo model predictions (as calculated within the Gunnarsson-Schonhammer computational method). Moreover, the Yb heavy fermion photoemission spectra give very strong indications of core-like characteristics and compare favorable to purely divalent Yb metal and core-like Lu 4f levels. The heavy fermions YbCu{sub 2}Si{sub 2}, YbAgCu{sub 4} and YbAl{sub 3} were measured and shown to have lineshapes much broader and deeper in binding energy than predicted by the Kondo model. The lineshape of the bulk component of the 4f emission for these three heavy fermion materials was compared with that from Yb metal and the Lu 4f levels in LuAl{sub 3}, the heavy fermion materials show no substantive spectroscopic differences from simple 4f levels observed in Yb metal and LuAl{sub 3}. Also, the variation with temperature of the 4f fineshape was measured for Yb metal and clearly demonstrates that phonon broadening plays a major role in 4f level lineshape analysis and must be accounted for before considerations of correlated electron resonance effects are presumed to be at work.

  4. Photoemission and the electronic properties of heavy fermions - limitations of the Kondo model

    Energy Technology Data Exchange (ETDEWEB)

    Joyce, J.J. [Los Alamos Nat. Lab., NM (United States); Arko, A.J. [Los Alamos Nat. Lab., NM (United States); Andrews, A.B. [Los Alamos Nat. Lab., NM (United States); Blyth, R.I.R. [Los Alamos Nat. Lab., NM (United States); Bartlett, R.J. [Los Alamos Nat. Lab., NM (United States); Thompson, J.D. [Los Alamos Nat. Lab., NM (United States); Fisk, Z. [Los Alamos Nat. Lab., NM (United States); Riseborough, P.S. [Polytechnic Institute of New York, Department of Physics, Brooklyn, NY 11201 (United States); Canfield, P.C. [Ames Laboratory USDOE, Ames, IA 50011 (United States); Olson, C.G. [Ames Laboratory USDOE, Ames, IA 50011 (United States); Benning, P.J. [Ames Laboratory USDOE, Ames, IA 50011 (United States)

    1995-03-01

    The electronic properties of Yb-based heavy fermions have been investigated by means of high resolution synchrotron radiation photoemission and compared with predictions of the Kondo model. The Yb heavy fermion photoemission spectra show significant disagreement with the Kondo model predictions (as calculated within the Gunnarsson-Schonhammer computational method). Moreover, the Yb heavy fermion photoemission spectra give strong indications of core-like characteristics and compare favorably to purely divalent Yb metal and core-like Lu 4f levels. The heavy fermions YbCu{sub 2}Si{sub 2}, YbAgCu{sub 4} and YbAl{sub 3} were measured and shown to have lineshapes much broader and deeper in binding energy than predicted by the Kondo model. The lineshape of the bulk component of the 4f emission for these three heavy fermion materials was compared with that from Yb metal and the Lu 4f levels in LuAl{sub 3}. The heavy fermion materials show no substantive spectroscopic differences from 4f levels observed in Yb metal and LuAl{sub 3}. Also, the variation with temperature of the 4f lineshape was measured for Yb metal and clearly demonstrates that phonon broadening plays a major role in 4f level lineshape analysis and must be accounted for before considerations of correlated electron resonance effects are presumed to be at work. ((orig.)).

  5. Room temperature redox reaction by oxide ion migration at carbon/Gd-doped CeO2 heterointerface probed by an in situ hard x-ray photoemission and soft x-ray absorption spectroscopies

    Directory of Open Access Journals (Sweden)

    Takashi Tsuchiya, Shogo Miyoshi, Yoshiyuki Yamashita, Hideki Yoshikawa, Kazuya Terabe, Keisuke Kobayashi and Shu Yamaguchi

    2013-01-01

    Full Text Available In situ hard x-ray photoemission spectroscopy (HX-PES and soft x-ray absorption spectroscopy (SX-XAS have been employed to investigate a local redox reaction at the carbon/Gd-doped CeO2 (GDC thin film heterointerface under applied dc bias. In HX-PES, Ce3d and O1s core levels show a parallel chemical shift as large as 3.2 eV, corresponding to the redox window where ionic conductivity is predominant. The window width is equal to the energy gap between donor and acceptor levels of the GDC electrolyte. The Ce M-edge SX-XAS spectra also show a considerable increase of Ce3+ satellite peak intensity, corresponding to electrochemical reduction by oxide ion migration. In addition to the reversible redox reaction, two distinct phenomena by the electrochemical transport of oxide ions are observed as an irreversible reduction of the entire oxide film by O2 evolution from the GDC film to the gas phase, as well as a vigorous precipitation of oxygen gas at the bottom electrode to lift off the GDC film. These in situ spectroscopic observations describe well the electrochemical polarization behavior of a metal/GDC/metal capacitor-like two-electrode cell at room temperature.

  6. Laser induced threshold photoemission magnetic circular dichroism and its application to photoelectron microscope

    Energy Technology Data Exchange (ETDEWEB)

    Nakagawa, Takeshi, E-mail: nakagawa@ims.ac.jp [Institute for Molecular Science, Myodaiji-cho, Okazaki, 444-8585 (Japan); The Graduate University for Advanced Studies (Sokendai), Myodaiji-cho, Okazaki, 444-8585 (Japan); Yokoyama, Toshihiko, E-mail: yokoyama@ims.ac.jp [Institute for Molecular Science, Myodaiji-cho, Okazaki, 444-8585 (Japan); The Graduate University for Advanced Studies (Sokendai), Myodaiji-cho, Okazaki, 444-8585 (Japan)

    2012-10-15

    Highlights: Black-Right-Pointing-Pointer Threshold photoemission magnetic circular dichroism results are presented. Black-Right-Pointing-Pointer The enhanced MCD contrast is used to observe magnetic domains by PEEM. Black-Right-Pointing-Pointer Magnetization axis, probing depth and angle dependence of MCD are described. Black-Right-Pointing-Pointer Laser based measurements in this method expand the possibility of PEEM. -- Abstract: This work enlightens the threshold photoemission magnetic circular dichroism (MCD) and its adaption on photoemission electron microscopy (PEEM) using lasers. MCD is a simple and efficient way to investigate magnetic properties since it does not need any spin analyzers with low efficiency, and thus the MCD related techniques have developed to observe magnetic domains. Usually, MCD in a total yield measurement in the valence band with weak spin-orbit coupling (SOC) excited by low photon energy (h{nu}{<=} 6 eV) does not compete with the X-ray magnetic circular dichroism (XMCD) with strong SOC. XMCD PEEM observation of magnetic domains has been successfully established while MCD PEEM derived from valence bands has not been. However, using angle and energy resolved photoelectron, valence band MCD provides large asymmetry similar to that by XMCD. Threshold measurement of photoelectron in a total electron yield procedure can take advantage of the measurement of photoelectrons with a limited angle and energy mode. This restriction of the photoelectron makes the threshold MCD technique an efficient way to get magnetic information and gives more than 10% asymmetry for Ni/Cu(0 0 1), which is comparable to that obtained by angle resolved photoemission. Thus the threshold MCD technique is a suitable method to observe magnetic domains by PEEM. For threshold MCD, incident angle dependence and high sensitivity to out-of-plane magnetized films compared with in-plane ones are discussed. Ultrashort pulse lasers make it feasible to measure two photon

  7. 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

  8. Electronic structure of aromatic amino acids studied by soft x-ray spectroscopy

    Science.gov (United States)

    Zhang, Wenhua; Carravetta, Vincenzo; Plekan, Oksana; Feyer, Vitaliy; Richter, Robert; Coreno, Marcello; Prince, Kevin C.

    2009-07-01

    The electronic structure of phenylalanine, tyrosine, tryptophan, and 3-methylindole in the gas phase was investigated by x-ray photoemission spectroscopy (XPS) and near edge x-ray absorption fine structure (NEXAFS) spectroscopy at the C, N, and O K-edges. The XPS spectra have been calculated for the four principal conformers of each amino acid, and the spectra weighted by the Boltzmann population ratios calculated from published free energies. Instead of the single peaks expected from the stoichiometry of the compounds, the N 1s core level spectra of phenylalanine and tryptophan show features indicating that more than one conformer is present. The calculations reproduce the experimental features. The C and O 1s spectra do not show evident effects due to conformational isomerism. The calculations predict that such effects are small for carbon, and for oxygen it appears that only broadening occurs. The carbon K-edge NEXAFS spectra of these aromatic amino acids are similar to the published data of the corresponding molecules in the solid state, but show more structure due to the higher resolution in the present study. The N K-edge spectra of tryptophan and 3-methylindole differ from phenylalanine and tyrosine, as the first two both contain a nitrogen atom located in a pyrrole ring. The nitrogen K-edge NEXAFS spectra of aromatic amino acids do not show any measurable effects due to conformational isomerism, in contrast to the photoemission results. Calculations support this result and show that variations of the vertical excitation energies of different conformers are small, and cannot be resolved in the present experiment. The O NEXAFS spectra of these three aromatic compounds are very similar to other, simpler amino acids, which have been studied previously.

  9. 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.

  10. Radiationless S 1 → S 0 phenyl deactivation pathway: an investigation of iodine-marked bi-phenyl on a silicon surface by means of time resolved core-level photoelectron spectroscopy

    Science.gov (United States)

    Michelswirth, Martin; Dachraoui, Hatem; Mattay, Jochen; Heinzmann, Ulrich

    2012-02-01

    The S 1 → S 0 radiationless deactivation of iodine terminated bi-phenyl immobilized on a silicon surface was probed by analysing the I4d signature (BE: 45.6 eV, 47.3 eV) by means of High Harmonic Generation (HHG) based photoelectron spectroscopy. Modifications of the 4d5/2,3/2 spectroscopic contents spanning about 0.2 ps after UV activation (266 nm) were verified as showing a transient molecular response character. A localization to the terminated phenyl substructure in the complex structural environment on the surface was ensured according to the core-level nature of the recorded I4d. The activation of the bi-phenyl achieved by UV irradiation, corresponding to the UV absorption band-edge, was verified as being dominated by a Bπ → Bπ* phenyl excitation. Time-Dependent Density Functional Theory (TD-DFT) modellings were therefore performed. They were matched to Configuration Interaction semi-empirical calculations (CI-MNDO) verifying the Rustagi-Ducuing relation. The simulated singlet-singlet excitation spectrum was referenced to the spectra of an iodine terminated monomer and a linear oligophenyl chain (N = 8). Thus the deactivation response studied was assigned to a conical intersection promoted ? reaction pathway.

  11. 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.

  12. 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.

  13. Characterization of heterojunctions in crystalline-silicon-based solar cells by internal photoemission

    Energy Technology Data Exchange (ETDEWEB)

    Sakata, Isao; Yamanaka, Mitsuyuki; Kawanami, Hitoshi [Research Center for Photovoltaics, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, AIST Central-2, Tsukuba, Ibaraki 305-8568 (Japan)

    2009-06-15

    Internal photoemission (IPE) has been successfully applied to evaluate band offsets of heterojunctions (HJs) in crystalline silicon (c-Si)-based solar cells. Tunneling of carriers through the potential spike at HJ and the presence of a carrier conduction path in the wide-band-gap material of HJ can affect the IPE results. In other words, IPE measures the effective band discontinuity, including effects of the carrier conduction path. This feature of IPE is suited for the characterization of solar-cell structures. Results obtained for hydrogenated amorphous silicon/c-Si HJ and gallium phosphide/c-Si HJ are presented and discussed. (author)

  14. Imaging of 5f densities of states in resonant photoemission measurements

    Energy Technology Data Exchange (ETDEWEB)

    Arko, A.J.; Koelling, D.D.; Capasso, C.; del Giudice, M.; Olson, C.G.

    1988-07-15

    Medium-resolution spectra (..delta..E = 0.25 eV) at the 5f Fano resonance in uranium intermetallics are compared to spectra above and below the resonance region to show that the 5f (and 6d) spectral weight obtained from resonant photoemission (RP) compares well to the 5f spectral weight obtained at other photon energies. In well-hybridized systems, the 5f signal from RP gives an excellent representation of the 5f density of states (DOS). In narrow-band and localized systems, a satellite may appear in addition to 5f DOS-like structure, indicative of correlation effects.

  15. RESONANT PHOTOEMISSION OF BULK CeO2 AND NANO-CeO2 FILMS

    Institute of Scientific and Technical Information of China (English)

    M.I. Abbas; K. Ibrahim; Z.Y. Wu; J. Zhang; F.Q. Liu; H.J. Qian

    2001-01-01

    Photoemission behaviors of nano-CeO2 films with particle sizes ranging from 8nm 1o50nm and bulk CeO2 in Ce 4d-4f absorption region have been investigated. Resonantenhancements of Ce 4f valance band and Ce 5p bands for nano film and bulk materialhave been observed. The variation of electron density of states in valance bands ofnano and bulk structures of CeO2 is discussed in terms of Ce 4d-4f resonance.

  16. 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}.

  17. 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.

  18. 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)

  19. The Si(100)-Sb 2{times}1 and Ge(100) 2{times}1 surfaces: A multi-technique study

    Energy Technology Data Exchange (ETDEWEB)

    Richter, M.

    1993-08-01

    The electronic and geometric structures of the clean and Sb terminated Si(100)2{times}1 and Ge(100)-2{times}1 surfaces have been investigated using a multi-technique approach. Low energy electron diffraction (LEED), scanning tunneling microscopy (STM), surface extended X-ray absorption fine structure (SEXAFS) spectroscopy and angle-integrated core-level photoemission electron spectroscopy (PES) were employed to measure the surface symmetry, defect structure, relevant bond lengths, atomic coordination and electronic structure. By employing a multi-technique approach, it is possible to correlate changes in the geometric structure to specific features of the core-level lineshape of the substrate. This allows for the assignment of components of the core-level lineshape to be assigned to specific surface and near-surface atoms.

  20. THEORETICAL DEPENDENCE OF LONG WAVELENGTH PHOTOEMISSION UPON THE SIZE OF Ag NANOPARTICLES EMBEDDED IN BaO SEMICONDUCTOR THIN FILM

    Institute of Scientific and Technical Information of China (English)

    杨海; 蔡武德; 许北雪; 吴锦雷

    2001-01-01

    The dependence of long wavelength photoemission upon the size of Ag nanoparticles embedded in a BaO semicon- ductor is predicted and discussed theoretically. The calculated results show that the increase in the diameter of the Ag nanoparticle, in the range from 1.5 to 37.0nm, leads to the emergence of a roughly Gaussian form of the photoemission spectra and the peaks become markedly narrower. The results also show that the increase in the diameter of the Agnanoparticle leads to the decrease of the long wavelength threshold. The incident light wavelength corresponding to the peak value of the photoemission gets bigger with the increase of the size of Ag nanoparticles, thus showing a redshift.

  1. 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.

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

    Science.gov (United States)

    Ohtomo, Manabu; Shimada, Toshihiro; Hasegawa, Tetsuya

    2010-03-01

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

  3. Experimental investigation of the electronic structure of Gd5Ge2Si2 by photoemission and x-ray absorption spectroscopy

    NARCIS (Netherlands)

    Bondino, F.; Brinkman, A.; Zangrando, M.; Carbone, F.; Marel, van der D.; Schlagel, D.L.; Lograsso, T.A.; Gschneider Jr., K.A.; Pecharsky, V.K.; Parmigiani, F.

    2007-01-01

    The electronic structure of the magnetic refrigerant Gd5Ge2Si2 has been experimentally investigated by photoemission and x-ray absorption spectroscopy. The resonant photoemission and x-ray absorption measurements performed across the Gd N4,5 and Gd M4,5 edges identify the position of Gd 4f multiplet

  4. 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.

  5. 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...

  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. 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...

  8. Time-resolved magnetic imaging in an aberration-corrected, energy-filtered photoemission electron microscope

    Energy Technology Data Exchange (ETDEWEB)

    Nickel, F., E-mail: fl.nickel@fz-juelich.de [Peter Grünberg Institut PGI-6 “Electronic Properties”, Research Center Jülich, 52425 Jülich (Germany); Gottlob, D.M. [Peter Grünberg Institut PGI-6 “Electronic Properties”, Research Center Jülich, 52425 Jülich (Germany); Fakultät für Physik und Center for Nanointegration Duisburg-Essen (CeNIDE), Universität Duisburg-Essen, 47048 Duisburg (Germany); Krug, I.P.; Doganay, H.; Cramm, S. [Peter Grünberg Institut PGI-6 “Electronic Properties”, Research Center Jülich, 52425 Jülich (Germany); Kaiser, A.M. [SPECS Surface Nano Analysis GmbH, Voltastraße 5, 13355 Berlin (Germany); Lin, G. [Institute for Integrative Nanosciences, IFW Dresden, Helmholtzstraße 20, 01069 Dresden (Germany); Material Systems for Nanoelectronics, Chemnitz University of Technology, Reichenhainer Strasse 70, 09107 Chemnitz (Germany); Makarov, D.; Schmidt, O.G. [Institute for Integrative Nanosciences, IFW Dresden, Helmholtzstraße 20, 01069 Dresden (Germany); and others

    2013-07-15

    We report on the implementation and usage of a synchrotron-based time-resolving operation mode in an aberration-corrected, energy-filtered photoemission electron microscope. The setup consists of a new type of sample holder, which enables fast magnetization reversal of the sample by sub-ns pulses of up to 10 mT. Within the sample holder current pulses are generated by a fast avalanche photo diode and transformed into magnetic fields by means of a microstrip line. For more efficient use of the synchrotron time structure, we developed an electrostatic deflection gating mechanism capable of beam blanking within a few nanoseconds. This allows us to operate the setup in the hybrid bunch mode of the storage ring facility, selecting one or several bright singular light pulses which are temporally well-separated from the normal high-intensity multibunch pulse pattern. - Highlights: • A new time-resolving operation mode in photoemission electron microscopy is shown. • Our setup works within an energy-filtered, aberration-corrected PEEM. • A new gating system for bunch selection using synchrotron radiation is developed. • An alternative magnetic excitation system is developed. • First tr-imaging using an energy-filtered, aberration-corrected PEEM is shown.

  9. First-principles approach to excitons in time-resolved and angle-resolved photoemission spectra

    Science.gov (United States)

    Perfetto, E.; Sangalli, D.; Marini, A.; Stefanucci, G.

    2016-12-01

    In this work we put forward a first-principles approach and propose an accurate diagrammatic approximation to calculate the time-resolved (TR) and angle-resolved photoemission spectrum of systems with excitons. We also derive an alternative formula to the TR photocurrent which involves a single time-integral of the lesser Green's function. The diagrammatic approximation applies to the relaxed regime characterized by the presence of quasistationary excitons and vanishing polarization. The nonequilibrium self-energy diagrams are evaluated using excited Green's functions; since this is not standard, the analytic derivation is presented in detail. The final result is an expression for the lesser Green's function in terms of quantities that can all be calculated in a first-principles manner. The validity of the proposed theory is illustrated in a one-dimensional model system with a direct gap. We discuss possible scenarios and highlight some universal features of the exciton peaks. Our results indicate that the exciton dispersion can be observed in TR and angle-resolved photoemission.

  10. 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

  11. Soft-x-ray fluorescence study of buried silicides in antiferromagnetically coupled Fe/Si multilayers

    Energy Technology Data Exchange (ETDEWEB)

    Carlisle, J.A.; Chaiken, A.; Michel, R.P. [Lawrence Berkeley National Lab., CA (United States)] [and others

    1997-04-01

    Multilayer films made by alternate deposition of two materials play an important role in electronic and optical devices such as quantum-well lasers and x-ray mirrors. In addition, novel phenomena like giant magnetoresistance and dimensional crossover in superconductors have emerged from studies of multilayers. While sophisticated x-ray techniques are widely used to study the morphology of multilayer films, progress in studying the electronic structure has been slower. The short mean-free path of low-energy electrons severely limits the usefulness of photoemission and related electron free path of low-energy electrons severely limit spectroscopies for multilayer studies. Soft x-ray fluorescence (SXF) is a bulk-sensitive photon-in, photon-out method to study valence band electronic states. Near-edge x-ray absorption fine-structure spectroscopy (NEXAFS) measured with partial photon yield can give complementary bulk-sensitive information about unoccupied states. Both these methods are element-specific since the incident x-ray photons excite electrons from core levels. By combining NEXAFS and SXF measurements on buried layers in multilayers and comparing these spectra to data on appropriate reference compounds, it is possible to obtain a detailed picture of the electronic structure. Results are presented for a study of a Fe/Si multilayer system.

  12. Carbon 1s photoemission line analysis of C-based adsorbate on (111)In2O3 surface: The influence of reducing and oxidizing conditions

    Science.gov (United States)

    Brinzari, V.; Cho, B. K.; Korotcenkov, G.

    2016-12-01

    Synchrotron radiation photoemission study of C 1s line of (111) In2O3 surface was carried out under HV (high vacuum) doses of oxygen, carbon monoxide and water. Gas interaction with the surface was activated by heating of In2O3 monocrystalline film at temperatures of 160 or 250 °C. The study of complex structure of C 1 s line and evolution of its fine components allowed to establish their nature and to propose possible surface adsorbed species and reactions, including a direct chemisorption and dissociation of CO molecules. Reduction or oxidation of the surface determines whether the first (chemisorption) or the second (dissociation) process takes place. The latter is responsible for additional formation of ionosorbed oxygen. Both processes have not been previously reported for In2O3 and for conductive metal oxides.

  13. Surface and sensor studies of doped titanium dioxide

    CERN Document Server

    Duncan, M

    2000-01-01

    selective toward SO sub 2 at low vanadium doping level. An attempt was made to correlate sensor response to the surface composition. In addition a preliminary analysis of the kinetics of the surface reaction between SO sub 2 and V-doped TiO sub 2 was performed. The effects of doping TiO sub 2 with V and Nb have been investigated. Doping of TiO sub 2 was achieved both by conventional solid state techniques and a diffusional technique to introduce dopants into single crystal substrates. The electronic structure of both polycrystalline and (110) and (210) oriented single crystal Ti sub 1 sub - sub x Nb sub x O sub 2 was investigated by photoelectron spectroscopy using monochromatized X-rays and synchrotron radiation to excite spectra. The chemical identity of the band gap state introduced by Nb sup 4 sup + dopants was determined both by resonant photoemission and high resolution core level spectroscopy. Comparisons are drawn with vanadium doped TiO sub 2 previously studied in this laboratory and with the parent ...

  14. SPIN POLARIZATION AND MAGNETIC DICHROISM IN PHOTOEMISSION FROM CORE AND VALENCE STATES IN LOCALIZED MAGNETIC SYSTEMS .3. ANGULAR-DISTRIBUTIONS

    NARCIS (Netherlands)

    THOLE, BT; VANDERLAAN, G

    1994-01-01

    A general analysis is presented for angle-dependent photoemission from magnetic and oriented atoms using linearly and circularly polarized x-rays. The anisotropy in the angular distribution in a localized material is due to the polarization of the photon, the polarization of the shell from which the

  15. 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

  16. Photoelectron spectroscopic studies of ultra-thin CuPc layers on a Si(111)-(√3 × √3)R30°-B surface

    Science.gov (United States)

    Menzli, S.; Laribi, A.; Mrezguia, H.; Arbi, I.; Akremi, A.; Chefi, C.; Chérioux, F.; Palmino, F.

    2016-12-01

    The adsorption of copper phthalocyanine (CuPc) molecules on Si(111)-(√3 × √3)R30°-B surface is investigated at room temperature under ultra-high vacuum. Crystallographic, chemical and electronic properties of the interface are investigated by low energy electron diffraction (LEED), ultraviolet and X-ray photoemission spectroscopies (UPS, XPS) and X-ray photoemission diffraction (XPD). LEED and XPD results shed light on the growth mechanism of CuPc on this substrate. At one monolayer coverage the growth mode was characterized by the formation of crystalline 3D nanoislands. The molecular packing deduced from this study appears very close to the one of the bulk CuPc α phase. The 3D islands are formed by molecules aligned in a standing manner. XPS core level spectra of the substrate reveal that there is no discernible chemical interaction between molecules and substrate. However there is charge transfer from molecules to the substrate. During the growth, the work function (WF) was found to decrease from 4.50 eV for the clean substrate to 3.70 eV for the highest coverage (30 monolayers). Within a thickness of two monolayers deposition, an interface dipole of 0.50 eV was found. A substrate band bending of 0.25 eV was deduced over all the range of exposure. UPS spectra indicate the existence of a band bending of the highest occupied molecular orbital (HOMO) of 0.30 eV. The changes in the work function, in the Fermi level position and in the onset of the molecular HOMO state have been used to determine the energy level alignment at the interface.

  17. 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.

  18. Watching adsorption and electron beam induced decomposition on the model system Mo(CO){sub 6}/Cu(1 1 1) by X-ray absorption and photoemission spectroscopies

    Energy Technology Data Exchange (ETDEWEB)

    Paufert, Pierre, E-mail: pierre.paufert@u-bourgogne.fr [ICB, UMR 6303 CNRS-Université de Bourgogne, BP 47870, 21078 Dijon cedex (France); Fonda, Emiliano [Synchrotron SOLEIL, BP48, St Aubin, 91192 Gif sur Yvette cedex (France); Li, Zheshen [ISA, University of Aarhus, Ny Munkegade, DK-8000 Aarhus C (Denmark); Domenichini, Bruno, E-mail: bruno.domenichini@u-bourgogne.fr [ICB, UMR 6303 CNRS-Université de Bourgogne, BP 47870, 21078 Dijon cedex (France); Bourgeois, Sylvie [ICB, UMR 6303 CNRS-Université de Bourgogne, BP 47870, 21078 Dijon cedex (France)

    2013-11-01

    An in-depth study of the first steps of electron beam assisted growth of Mo from molybdenum hexacarbonyl on Cu(1 1 1) has been carried out exploiting the complementarity of X-ray photoemission and X-ray absorption spectroscopies. Frank van der Merwe (2D) growth mode has been observed for the completion of the two first monolayers of adsorbed molecules through a simple physisorption process. Irradiation of the Mo(CO){sub 6} deposit by 1 keV electron beam induces a modification of molybdenum coordination, the average number of C-neighbors decreasing from 6 to 3. Decomposed molecules remain on the surface after annealing at 520 K and organize themselves, the molybdenum atoms moving in Cu(1 1 1) surface fcc hollow sites. After annealing at 670 K, metallic molybdenum growth begins, if the total amount of adsorbed Mo atoms exceeds 1.2 monolayers.

  19. Watching adsorption and electron beam induced decomposition on the model system Mo(CO)6/Cu(1 1 1) by X-ray absorption and photoemission spectroscopies

    Science.gov (United States)

    Paufert, Pierre; Fonda, Emiliano; Li, Zheshen; Domenichini, Bruno; Bourgeois, Sylvie

    2013-11-01

    An in-depth study of the first steps of electron beam assisted growth of Mo from molybdenum hexacarbonyl on Cu(1 1 1) has been carried out exploiting the complementarity of X-ray photoemission and X-ray absorption spectroscopies. Frank van der Merwe (2D) growth mode has been observed for the completion of the two first monolayers of adsorbed molecules through a simple physisorption process. Irradiation of the Mo(CO)6 deposit by 1 keV electron beam induces a modification of molybdenum coordination, the average number of C-neighbors decreasing from 6 to 3. Decomposed molecules remain on the surface after annealing at 520 K and organize themselves, the molybdenum atoms moving in Cu(1 1 1) surface fcc hollow sites. After annealing at 670 K, metallic molybdenum growth begins, if the total amount of adsorbed Mo atoms exceeds 1.2 monolayers.

  20. Preliminary soft x-ray studies of [beta]-SiC

    Energy Technology Data Exchange (ETDEWEB)

    Shek, M.L. (National Synchrotron Light Source Department, Brookhaven National Laboratory, Upton, New York 11973 (United States)); Miyano, K.E. (Physics Department, Tulane University, New Orleans, Louisiana 70118 (United States)); Dong, Q.; Callcott, T.A. (Physics Department, University of Tennessee, Knoxville, Tennessee 37996 (United States)); Ederer, D.L. (Physics Department, Tulane University, New Orleans, Louisiana 70118 (United States))

    1994-07-01

    We have looked at [beta]-SiC with soft x-ray emission and photoemission spectroscopy. From the Si [ital L][sub 23] and C [ital K] emissions, the Si [ital s]+[ital d]-like and C [ital p] partial density of states in the bulk valence band are identified and compared with valence band photoemission. In addition to bulk electronic structural features, photoemission from a (3[times]2) Si-rich surface shows two surface-derived valence features at [similar to][minus]2.6 and [similar to][minus]1.6 eV relative to the Fermi level. The intensities of these valence features vary as those of surface Si 2[ital p] core level components shifted by [minus]0.5 and [minus]1.4 eV from the bulklike SiC Si 2[ital p] core level. We have also used the Si [ital L][sub 23] absorption edge as a probe of the unfilled states near the conduction band minimum.